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Sample records for strong core-ligand covalent

  1. Covalent Organic

    DEFF Research Database (Denmark)

    Vutti, Surendra

    chemistry of silicon, InAs and GaAs materials, covalentsurface functionalization using organosilanes, liquid-phase, and vapor-phasefunctionalizations, diazo-transfer reaction, CuAAC click chemistry, different types ofbiorthogonal chemistries, SPAAC chemistry, and cellular interactions of chemically...... immobilization of D-amino acid adhesion peptideson azide functionalized silicon, GaAs and InAs materials by using CuAAC-click chemistry.The covalent immobilization of penetration peptide (TAT) on gold nanotips of InAs NWs isalso demonstrated.In chapter four, the covalent immobilization of GFP on silicon wafers......, GaAs wafers andGaAs NWs is demonstrated. Series of Fmoc-Pra-OH, NHS-PEG5-NHS and BCN-NHSfunctionalized silicon surfaces has been prepared, whereby GFP-N3 and GFP-bicyclononyneare immobilized by using CuAAC and SPAAC chemistry. The specific and covalentimmobilization of GFP-N3 on bicyclononyne...

  2. Average and extreme multi-atom Van der Waals interactions: Strong coupling of multi-atom Van der Waals interactions with covalent bonding

    Directory of Open Access Journals (Sweden)

    Finkelstein Alexei V

    2007-07-01

    Full Text Available Abstract Background The prediction of ligand binding or protein structure requires very accurate force field potentials – even small errors in force field potentials can make a 'wrong' structure (from the billions possible more stable than the single, 'correct' one. However, despite huge efforts to optimize them, currently-used all-atom force fields are still not able, in a vast majority of cases, even to keep a protein molecule in its native conformation in the course of molecular dynamics simulations or to bring an approximate, homology-based model of protein structure closer to its native conformation. Results A strict analysis shows that a specific coupling of multi-atom Van der Waals interactions with covalent bonding can, in extreme cases, increase (or decrease the interaction energy by about 20–40% at certain angles between the direction of interaction and the covalent bond. It is also shown that on average multi-body effects decrease the total Van der Waals energy in proportion to the square root of the electronic component of dielectric permittivity corresponding to dipole-dipole interactions at small distances, where Van der Waals interactions take place. Conclusion The study shows that currently-ignored multi-atom Van der Waals interactions can, in certain instances, lead to significant energy effects, comparable to those caused by the replacement of atoms (for instance, C by N in conventional pairwise Van der Waals interactions.

  3. Host-Guest Complexes of Cyclodextrins and Nanodiamonds as a Strong Non-Covalent Binding Motif for Self-Assembled Nanomaterials.

    Science.gov (United States)

    Schibilla, Frauke; Voskuhl, Jens; Fokina, Natalie A; Dahl, Jeremy E P; Schreiner, Peter R; Ravoo, Bart Jan

    2017-11-13

    We report the inclusion of carboxy- and amine-substituted molecular nanodiamonds (NDs) adamantane, diamantane, and triamantane by β-cyclodextrin and γ-cyclodextrin (β-CD and γ-CD), which have particularly well-suited hydrophobicity and symmetry for an optimal fit of the host and guest molecules. We studied the host-guest interactions in detail and generally observed 1:1 association of the NDs with the larger γ-CD cavity, but observed 1:2 association for the largest ND in the series (triamantane) with β-CD. We found higher binding affinities for carboxy-substituted NDs than for amine-substituted NDs. Additionally, cyclodextrin vesicles (CDVs) were decorated with d-mannose by using adamantane, diamantane, and triamantane as non-covalent anchors, and the resulting vesicles were compared with the lectin concanavalin A in agglutination experiments. Agglutination was directly correlated to the host-guest association: adamantane showed lower agglutination than di- or triamantane with β-CDV and almost no agglutination with γ-CDV, whereas high agglutination was observed for di- and triamantane with γ-CDV. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: Persistent magnetism with interlayer As-As bond formation in Rh-doped Ca0 .8Sr0 .2Fe2As2

    Science.gov (United States)

    Zhao, K.; Glasbrenner, J. K.; Gretarsson, H.; Schmitz, D.; Bednarcik, J.; Etter, M.; Sun, J. P.; Manna, R. S.; Al-Zein, A.; Lafuerza, S.; Scherer, W.; Cheng, J. G.; Gegenwart, P.

    2018-02-01

    A well-known feature of the CaFe2As2 -based superconductors is the pressure-induced collapsed tetragonal phase that is commonly ascribed to the formation of an interlayer As-As bond. Using detailed x-ray scattering and spectroscopy, we find that Rh-doped Ca0.8Sr0.2Fe2As2 does not undergo a first-order phase transition and that local Fe moments persist despite the formation of interlayer As-As bonds. Our density functional theory calculations reveal that the Fe-As bond geometry is critical for stabilizing magnetism and the pressure-induced drop in the c lattice parameter observed in pure CaFe2As2 is mostly due to a constriction within the FeAs planes. The collapsed tetragonal phase emerges when covalent bonding of strongly hybridized Fe 3 d and As 4 p states completely wins out over their exchange splitting. Thus the collapsed tetragonal phase is properly understood as a strong covalent phase that is fully nonmagnetic with the As-As bond forming as a by-product.

  5. Chemistry of Covalent Organic Frameworks.

    Science.gov (United States)

    Waller, Peter J; Gándara, Felipe; Yaghi, Omar M

    2015-12-15

    Linking organic molecules by covalent bonds into extended solids typically generates amorphous, disordered materials. The ability to develop strategies for obtaining crystals of such solids is of interest because it opens the way for precise control of the geometry and functionality of the extended structure, and the stereochemical orientation of its constituents. Covalent organic frameworks (COFs) are a new class of porous covalent organic structures whose backbone is composed entirely of light elements (B, C, N, O, Si) that represent a successful demonstration of how crystalline materials of covalent solids can be achieved. COFs are made by combination of organic building units covalently linked into extended structures to make crystalline materials. The attainment of crystals is done by several techniques in which a balance is struck between the thermodynamic reversibility of the linking reactions and their kinetics. This success has led to the expansion of COF materials to include organic units linked by these strong covalent bonds: B-O, C-N, B-N, and B-O-Si. Since the organic constituents of COFs, when linked, do not undergo significant change in their overall geometry, it has been possible to predict the structures of the resulting COFs, and this advantage has facilitated their characterization using powder X-ray diffraction (PXRD) techniques. It has also allowed for the synthesis of COF structures by design and for their formation with the desired composition, pore size, and aperture. In practice, the modeled PXRD pattern for a given expected COF is compared with the experimental one, and depending on the quality of the match, this is used as a starting point for solving and then refining the crystal structure of the target COF. These characteristics make COFs an attractive class of new porous materials. Accordingly, they have been used as gas storage materials for energy applications, solid supports for catalysis, and optoelectronic devices. A large and

  6. Atomic Covalent Functionalization of Graphene

    Science.gov (United States)

    Johns, James E.; Hersam, Mark C.

    2012-01-01

    -dimensional materials with fundamentally different electronic and physical properties. Specifically, we focus on recent studies of the addition of atomic hydrogen, fluorine, and oxygen to the basal plane of graphene. In each of these reactions a high energy, activating step initiates the process, breaking the local π structure and distorting the surrounding lattice. Scanning tunneling microscopy experiments reveal that substrate mediated interactions often dominate when the initial binding event occurs. We then compare these substrate effects with the results of theoretical studies that typically assume a vacuum environment. As the surface coverage increases, clusters often form around the initial distortion, and the stoichiometric composition of the saturated end product depends strongly on both the substrate and reactant species. In addition to these chemical and structural observations, we review how covalent modification can extend the range of physical properties that are achievable in two-dimensional materials. PMID:23030800

  7. Covalent and non-covalent functionalization and solubilization of ...

    Indian Academy of Sciences (India)

    Wintec

    Abstract. Double-walled carbon nanotubes (DWNTs) have been functionalized by both covalent and non-covalent means. Covalent functionalization has been carried out by attaching an aliphatic amide function to DWNTs which enable solubilization in non-polar solvents. Solubilization in non-polar sol- vents has also been ...

  8. Covalent and non-covalent functionalization and solubilization of ...

    Indian Academy of Sciences (India)

    Non-covalent functionalization of DWNTs has been carried out by using polyethylene glycol (PEG) and polyoxyethylene(40)nonylphenyl ether (IGPAL), both of which enable solubilization in aqueous media. These functionalized DWNTs have been characterized by transmission electron microscopy, IR and Raman ...

  9. Covalent magnetism and magnetic impurities.

    Science.gov (United States)

    Gruber, C; Bedolla, P O; Mohn, P

    2013-05-08

    We use the model of covalent magnetism and its application to magnetic insulators applied to the case of insulating carbon doped BaTiO3. Since the usual Stoner mechanism is not applicable we study the possibility of the formation of magnetic order based on a mechanism favoring singly occupied orbitals. On the basis of our model parameters we formulate a criterion similar to the Stoner criterion but also valid for insulators. We describe the model of covalent magnetism using a molecular orbital picture and determine the occupation numbers for spin-up and spin-down states. Our model allows a simulation of the results of our ab initio calculations for E(ℳ) which are found to be in very good agreement.

  10. Electron population uncertainty and atomic covalency

    International Nuclear Information System (INIS)

    Chesnut, D.B.

    2006-01-01

    The atoms-in-molecules (AIM) index of atomic covalency is directly related to the AIM atomic population uncertainty. The covalent bond order, delocalization index, and, therefore, the atomic covalency are maximal when electron pairs are equally shared by the atoms involved. When polarization effects are present, these measures of covalent bond character decrease. We present atomic covalences for the single- and double-heavy atom hydrides of elements of the first and second low rows of the periodic table to illustrate these effects. Some usual behavior is seen in hydrogen-bridged species due in some cases to stronger than expected multicenter bonds and in other cases to many atoms contributing to the covalency index

  11. Capillary electrophoresis of covalently functionalized single-chirality carbon nanotubes.

    Science.gov (United States)

    He, Pingli; Meany, Brendan; Wang, Chunyan; Piao, Yanmei; Kwon, Hyejin; Deng, Shunliu; Wang, YuHuang

    2017-07-01

    We demonstrate the separation of chirality-enriched single-walled carbon nanotubes (SWCNTs) by degree of surface functionalization using high-performance CE. Controlled amounts of negatively charged and positively charged functional groups were attached to the sidewall of chirality-enriched SWCNTs through covalent functionalization using 4-carboxybenzenediazonium tetrafluoroborate or 4-diazo-N,N-diethylaniline tetrafluoroborate, respectively. Surfactant- and pH-dependent studies confirmed that under conditions that minimized ionic screening effects, separation of these functionalized SWCNTs was strongly dependent on the surface charge density introduced through covalent surface chemistry. For both heterogeneous mixtures and single-chirality-enriched samples, covalently functionalized SWCNTs showed substantially increased peak width in electropherogram spectra compared to nonfunctionalized SWCNTs, which can be attributed to a distribution of surface charges along the functionalized nanotubes. Successful separation of functionalized single-chirality SWCNTs by functional density was confirmed with UV-Vis-NIR absorption and Raman scattering spectroscopies of fraction collected samples. These results suggest a high degree of structural heterogeneity in covalently functionalized SWCNTs, even for chirality-enriched samples, and show the feasibility of applying CE for high-performance separation of nanomaterials based on differences in surface functional density. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Covalently Bound Nitroxyl Radicals in an Organic Framework

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, Barbara K.; Braunecker, Wade A.; Bobela, David C.; Nanayakkara, Sanjini U.; Reid, Obadiah G.; Johnson, Justin C.

    2016-09-15

    A series of covalent organic framework (COF) structures is synthesized that possesses a tunable density of covalently bound nitroxyl radicals within the COF pores. The highest density of organic radicals produces an electron paramagnetic resonance (EPR) signal that suggests the majority of radicals strongly interact with other radicals, whereas for smaller loadings the EPR signals indicate the radicals are primarily isolated but with restricted motion. The dielectric loss as determined from microwave absorption of the framework structures compared with an amorphous control suggests that free motion of the radicals is inhibited when more than 25% of available sites are occupied. The ability to tune the mode of radical interactions and the subsequent effect on redox, electrical, and optical characteristics in a porous framework may lead to a class of structures with properties ideal for photoelectrochemistry or energy storage.

  13. Flavins as Covalent Catalysts: New Mechanisms Emerge.

    Science.gov (United States)

    Piano, Valentina; Palfey, Bruce A; Mattevi, Andrea

    2017-06-01

    With approximately 1% of proteins being flavoproteins, flavins are at the heart of a plethora of redox reactions in all areas of biology. Thanks to a series of fascinating recent discoveries, in addition to redox chemistry, covalent catalysis is now being recognized more frequently as a common strategy in flavoenzymes, with unprecedented mechanisms becoming apparent. Thus, noncanonical covalent reactions by flavins are emerging as a new pervasive concept in basic enzymology and biochemistry. These diverse enzymes are engaged in most biological processes, positioning the knowledge being gained from these new mechanisms to be translated into drugs that function through covalent mechanisms. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. Disorder phenomena in covalent semiconductors

    International Nuclear Information System (INIS)

    Popescu, M.A.

    1975-01-01

    The structure of the amorphous semiconductors has been investigated by means of X-ray diffraction and by computer simulation of random network models. Amorphous germanium contains mainly five and six-membered rings of atoms. In glassy state, the ternary compounds A 2 B 4 C 2 5 , such as CdGeAs 2 contain only even rings of atoms (six-membered and eight-membered rings). In the memory glasses of the type A 2 B 4 C 2 5 , such as GeAs 2 Te 7 , the valency state of every element is that from the crystal and important van der Waals forces are effective in the network. No Ge-Ge, Ge-As and As-As bonds are formed. The high pressure forms of the germanium have been simulated by computer. The force constants of the covalent bonds in Ge III and Ge IV differ from those in Ge I. The bond bending force constant decreases rapidly when the density of the crystal increases, a fact which has been imparted to a reduction of the sp 3 hybridization. The compressibility curve of the Ge I has been explained. The effect of the radial and uniaxial deformation on the non-crystalline networks has been studied. The compressibility of the amorphous germanium is by 1.5 per cent greater than that of crystalline germanium. The Poisson coefficient for a-Ge network is 0.233. The structure of the As 2 S 3 glass doped with different amounts of germanium (up to 40 at. per cent) and silver (up to 12 at. per cent) has been investigated. The As 2 S 3 Gesub(x) compositions are constituted from a disordered packing of structural units whose chemical composition and relative proportion in the glass essentially depends on the germanium content. (author)

  15. Covalency in Americium(III) Hexachloride.

    Science.gov (United States)

    Cross, Justin N; Su, Jing; Batista, Enrique R; Cary, Samantha K; Evans, William J; Kozimor, Stosh A; Mocko, Veronika; Scott, Brian L; Stein, Benjamin W; Windorff, Cory J; Yang, Ping

    2017-06-28

    Developing a better understanding of covalency (or orbital mixing) is of fundamental importance. Covalency occupies a central role in directing chemical and physical properties for almost any given compound or material. Hence, the concept of covalency has potential to generate broad and substantial scientific advances, ranging from biological applications to condensed matter physics. Given the importance of orbital mixing combined with the difficultly in measuring covalency, estimating or inferring covalency often leads to fiery debate. Consider the 60-year controversy sparked by Seaborg and co-workers ( Diamond, R. M.; Street, K., Jr.; Seaborg, G. T. J. Am. Chem. Soc. 1954 , 76 , 1461 ) when it was proposed that covalency from 5f-orbitals contributed to the unique behavior of americium in chloride matrixes. Herein, we describe the use of ligand K-edge X-ray absorption spectroscopy (XAS) and electronic structure calculations to quantify the extent of covalent bonding in-arguably-one of the most difficult systems to study, the Am-Cl interaction within AmCl 6 3- . We observed both 5f- and 6d-orbital mixing with the Cl-3p orbitals; however, contributions from the 6d-orbitals were more substantial. Comparisons with the isoelectronic EuCl 6 3- indicated that the amount of Cl 3p-mixing with Eu III 5d-orbitals was similar to that observed with the Am III 6d-orbitals. Meanwhile, the results confirmed Seaborg's 1954 hypothesis that Am III 5f-orbital covalency was more substantial than 4f-orbital mixing for Eu III .

  16. Covalent Surface Modifications of Carbon Nanotubes.

    Energy Technology Data Exchange (ETDEWEB)

    Pavia Sanders, Adriana [Sandia National Lab. (SNL-CA), Livermore, CA (United States); O' Bryan, Greg [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

    2017-07-01

    A report meant to document the chemistries investigated by the author for covalent surface modification of CNTs. Oxidation, cycloaddition, and radical reactions were explored to determine their success at covalently altering the CNT surface. Characterization through infrared spectroscopy, Raman spectroscopy, and thermo gravimetric analysis was performed in order to determine the success of the chemistries employed. This report is not exhaustive and was performed for CNT surface modification exploration as it pertains to the "Next Gen" project.

  17. Preparation and characterization of PEGylated multiwall carbon nanotubes as covalently conjugated and non-covalent drug carrier: A comparative study.

    Science.gov (United States)

    Habibizadeh, Mina; Rostamizadeh, Kobra; Dalali, Naser; Ramazani, Ali

    2017-05-01

    In this study, PEGylated multiwall carbon nanotubes (MWNTs)-based drug delivery system was developed. Ibuprofen as a model drug was loaded by physical and chemical method. The surface functionalization of nanotubes was carried out by enrichment of acylated groups. In order to synthesis PEGylated MWNTs, hydrophilic diamino-polyethylene glycol was covalently linked to the MWNTs surface via amidation reaction. Finally, ibuprofen was chemically and physically loaded on the PEGylated MWNTs. The resultants were characterized by FTIR, AFM, and DLS techniques. Cytotoxicity of PEGylated MWNTs were examined by MTT assay and the results revealed that PEG functionalized nanotubes did not show significant detrimental effects on the viability of L929 Cells. The percent of drug loading for chemically and physically drug payload carrier were determined to be 52.5% and 38%, respectively. The release of ibuprofen from covalently conjugated and non-covalent drug loaded PEGylated MWNTs at pH=7.4, and 5.3 were investigated, as well. From the results, it was found that chemically loaded MWNTs showed much sustained release behavior compared to the physically loaded one, especially at pH=5.3. The kinetic of drug release was also investigated. The results strongly suggest that the chemically conjugated PEGylated MWNTs could be used as controlled release system for various drugs. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Non covalent assembly of coordination superstructures

    CERN Document Server

    Khlobystov, A N

    2002-01-01

    The main topic of this work is the design of discrete and polymeric multi-component coordination structures using non-covalent interactions between organic and inorganic molecular components. All of the structures described herein are based on transition metal cations and N-donor heterocyclic bis-exodentate ligands with different geometries and various spacer functionalities. The predominant method used for the structural characterisation of the complexes was single crystal X-ray crystallography. X-ray powder diffraction, IR and NMR spectroscopies and TEM and AFM imaging were used to characterise the bulk products from the reactions. Chapter 1 is a comparative review of non-covalent interactions relevant to coordination superstructures and covers the latest developments in the area of crystal engineering and supramolecular chemistry. The nature, geometry and relative energy of the non-covalent interactions are considered in detail in order to reveal their influence on the structure and properties of complexes...

  19. Covalent bonds against magnetism in transition metal compounds.

    Science.gov (United States)

    Streltsov, Sergey V; Khomskii, Daniel I

    2016-09-20

    Magnetism in transition metal compounds is usually considered starting from a description of isolated ions, as exact as possible, and treating their (exchange) interaction at a later stage. We show that this standard approach may break down in many cases, especially in 4d and 5d compounds. We argue that there is an important intersite effect-an orbital-selective formation of covalent metal-metal bonds that leads to an "exclusion" of corresponding electrons from the magnetic subsystem, and thus strongly affects magnetic properties of the system. This effect is especially prominent for noninteger electron number, when it results in suppression of the famous double exchange, the main mechanism of ferromagnetism in transition metal compounds. We study this mechanism analytically and numerically and show that it explains magnetic properties of not only several 4d-5d materials, including Nb2O2F3 and Ba5AlIr2O11, but can also be operative in 3d transition metal oxides, e.g., in CrO2 under pressure. We also discuss the role of spin-orbit coupling on the competition between covalency and magnetism. Our results demonstrate that strong intersite coupling may invalidate the standard single-site starting point for considering magnetism, and can lead to a qualitatively new behavior.

  20. Effect of photocurrent enhancement in porphyrin–graphene covalent hybrids

    International Nuclear Information System (INIS)

    Tang, Jianguo; Niu, Lin; Liu, Jixian; Wang, Yao; Huang, Zhen; Xie, Shiqiang; Huang, Linjun; Xu, Qingsong; Wang, Yuan; Belfiore, Laurence A.

    2014-01-01

    Graphene oxide (GO) sheets were covalently functionalized with 5-p-aminophenyl-10,15,20-triphenylporphyrin (NH 2 TPP) by an amidation reaction between the amino group in NH 2 TPP and carboxyl groups in GO. The Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning and transmission electron microscopies reveal that NH 2 TPP covalent bonds form on the double surface of graphene oxide sheets, generating a unique nano-framework, i.e., NH 2 TPP-graphene-NH 2 TPP. Its UV–visible spectroscopy reveals that the absorption spectrum is not a linear superposition of the spectra of NH 2 TPP and graphene oxide, because a 59 nm red shift of the strong graphene oxide absorption is observed from 238 to 297 nm, with significant spectral broadening between 300 and 700 nm. Fluorescence emission spectroscopy indicates efficient quenching of NH 2 TPP photoluminescence in this hybrid material, suggesting that photo-induced electron transfer occurs at the interface between NH 2 TPP and GO. A reversible on/off photo-current density of 47 mA/cm 2 is observed when NH 2 TPP-graphene-NH 2 TPP hybrid sandwiches are subjected to pulsed white-light illumination. Covalently-bound porphyrins decrease the optical HOMO/LUMO band gap of graphene oxide by ≈ 1 eV, according to UV–visible spectroscopy. Cyclic voltammetry predicts a small HOMO/LUMO band gap of 0.84 eV for NH 2 TPP-graphene-NH 2 TPP hybrid sandwiches, which is consistent with efficient electron transfer and fluorescence quenching. - Highlights: • Porphyrins are covalently bound to sheets of graphene oxide via an amidation reaction. • The formed hetero-junction interface decreases the optical band gap of graphene oxide. • Cyclic voltammetry predicts a graphene oxide band gap of 0.84 eV, which is easily photo-excited. • Its on/off photo-current density of 46 μA/cm 2 is 5-fold larger than that for physically stacked hybrid

  1. Effect of photocurrent enhancement in porphyrin–graphene covalent hybrids

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Jianguo, E-mail: jianguotangde@hotmail.com [Institute of Hybrid Materials―the Growing Base for State Key Laboratory, Qingdao University, Qingdao 266071 (China); Niu, Lin; Liu, Jixian; Wang, Yao; Huang, Zhen; Xie, Shiqiang; Huang, Linjun; Xu, Qingsong; Wang, Yuan [Institute of Hybrid Materials―the Growing Base for State Key Laboratory, Qingdao University, Qingdao 266071 (China); Belfiore, Laurence A. [Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, CO 80523 (United States)

    2014-01-01

    Graphene oxide (GO) sheets were covalently functionalized with 5-p-aminophenyl-10,15,20-triphenylporphyrin (NH{sub 2}TPP) by an amidation reaction between the amino group in NH{sub 2}TPP and carboxyl groups in GO. The Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning and transmission electron microscopies reveal that NH{sub 2}TPP covalent bonds form on the double surface of graphene oxide sheets, generating a unique nano-framework, i.e., NH{sub 2}TPP-graphene-NH{sub 2}TPP. Its UV–visible spectroscopy reveals that the absorption spectrum is not a linear superposition of the spectra of NH{sub 2}TPP and graphene oxide, because a 59 nm red shift of the strong graphene oxide absorption is observed from 238 to 297 nm, with significant spectral broadening between 300 and 700 nm. Fluorescence emission spectroscopy indicates efficient quenching of NH{sub 2}TPP photoluminescence in this hybrid material, suggesting that photo-induced electron transfer occurs at the interface between NH{sub 2}TPP and GO. A reversible on/off photo-current density of 47 mA/cm{sup 2} is observed when NH{sub 2}TPP-graphene-NH{sub 2}TPP hybrid sandwiches are subjected to pulsed white-light illumination. Covalently-bound porphyrins decrease the optical HOMO/LUMO band gap of graphene oxide by ≈ 1 eV, according to UV–visible spectroscopy. Cyclic voltammetry predicts a small HOMO/LUMO band gap of 0.84 eV for NH{sub 2}TPP-graphene-NH{sub 2}TPP hybrid sandwiches, which is consistent with efficient electron transfer and fluorescence quenching. - Highlights: • Porphyrins are covalently bound to sheets of graphene oxide via an amidation reaction. • The formed hetero-junction interface decreases the optical band gap of graphene oxide. • Cyclic voltammetry predicts a graphene oxide band gap of 0.84 eV, which is easily photo-excited. • Its on/off photo-current density of 46 μA/cm{sup 2} is 5-fold larger than that for physically stacked hybrid.

  2. Identification of covalent active site inhibitors of dengue virus protease

    Directory of Open Access Journals (Sweden)

    Koh-Stenta X

    2015-12-01

    Full Text Available Xiaoying Koh-Stenta,1 Joma Joy,1 Si Fang Wang,1 Perlyn Zekui Kwek,1 John Liang Kuan Wee,1 Kah Fei Wan,2 Shovanlal Gayen,1 Angela Shuyi Chen,1 CongBao Kang,1 May Ann Lee,1 Anders Poulsen,1 Subhash G Vasudevan,3 Jeffrey Hill,1 Kassoum Nacro11Experimental Therapeutics Centre, Agency for Science, Technology and Research (A*STAR, Singapore; 2Novartis Institute for Tropical Diseases, Singapore; 3Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, SingaporeAbstract: Dengue virus (DENV protease is an attractive target for drug development; however, no compounds have reached clinical development to date. In this study, we utilized a potent West Nile virus protease inhibitor of the pyrazole ester derivative class as a chemical starting point for DENV protease drug development. Compound potency and selectivity for DENV protease were improved through structure-guided small molecule optimization, and protease-inhibitor binding interactions were validated biophysically using nuclear magnetic resonance. Our work strongly suggests that this class of compounds inhibits flavivirus protease through targeted covalent modification of active site serine, contrary to an allosteric binding mechanism as previously described.Keywords: flavivirus protease, small molecule optimization, covalent inhibitor, active site binding, pyrazole ester derivatives

  3. Dynamic signaling cascades: reversible covalent reaction-coupled molecular switches.

    Science.gov (United States)

    Ren, Yulong; You, Lei

    2015-11-11

    The research of systems chemistry exploring complex mixtures of interacting synthetic molecules has been burgeoning recently. Herein we demonstrate for the first time the coupling of molecular switches with a dynamic covalent reaction (DCR) and the modulation of created chemical cascades with a variety of inputs, thus closely mimicking a biological signaling system. A novel Michael type DCR of 10-methylacridinium perchlorate and monothiols exhibiting excellent regioselectivity and tunable affinity was discovered. A delicate balance between the unique reactivity of the reactant and the stability of the adduct leads to the generation of a strong acid in a thermodynamically controlled system. The dynamic cascade was next created via coupling of the DCR and a protonation-induced configurational switch (E/Z isomerization) through a proton relay. Detailed examination of the interdependence of the equilibrium enabled us to rationally optimize the cascade and also shed light on the possible intermediate of the switching process. Furthermore, relative independence of the coupled reactions was verified by the identification of stimuli that are able to facilitate one reaction but suppress the other. To further enhance systematic complexity, a second DCR of electrophilic aldehydes and thiols was employed for the reversible inhibition of the binary system, thus achieving the interplay of multiple equilibria. Finally, a fluorescence switch was turned on through coupling with the DCR, showcasing the versatility of our strategy. The results described herein should pave the way for the exploitation of multifunctional dynamic covalent cascades.

  4. The covalent effect on the energy levels of d2 ions in tetragonal crystal

    International Nuclear Information System (INIS)

    Li, Dong-yang; Du, Mao-lu

    2014-01-01

    In contrast to the traditional method which is unsuitable for the prediction of optical for the transition metal ion in covalence and low-symmetry crystal, this paper reports a new method to investigate the optical properties of d 2 ions in covalent and tetragonal crystals and provides a new energy matrix. By using the energy matrix, the variation of energy levels and of the energy-level splitting as the parameter ε are studied; the energy-levels calculated by energy matrix taking no account of crystal-field parameter B 00 0 and by energy matrix taking account of B 00 0 are compared. It was found that the effect of the difference of covalence factors N t and N e on the energy levels and the energy-level splitting is very important and cannot be neglected when the optical properties of d 2 ions in strong covalent crystals are investigated; B 00 0 has an important contribution to the energy levels and should not be neglected; the different covalence of t 2 and e orbitals should be considered not only in the electrostatic repulsions part of the energy matrix but also in the crystal-field potential part of the energy matrix. The complete matrix is applied to calculate the energy-levels of GaP:V 3+ semiconductor. The calculated results are in agreement with the experiment data

  5. Covalent labeling of the hepatic glucagon receptor

    International Nuclear Information System (INIS)

    Herberg, J.T.; Iyengar, R.

    1985-01-01

    The procedure for covalently labeling the hepatic glucagon receptor utilizes the light-sensitive heterobifunctional cross-linker hydroxysuccinimidyl-p-azidobenzoate (HSAB) to link the bound [ 125 I-Tyr 10 ]monoiodoglucagon ([ 125 I]MIG) to the receptor protein. The method involves first the binding of the labeled hormone to its receptor and the removal of the excess unbound label. This is followed by incubation with the cross-linker, in the dark and then under ultraviolet illumination to covalently couple the bound [ 125 I]MIG. HSAB contains an amino reactive group as well as an aryl azide which, upon light activation, is converted to an aryl nitrene that reacts in a chemically unspecific manner

  6. Covalent modification of platelet proteins by palmitate

    International Nuclear Information System (INIS)

    Muszbek, L.; Laposata, M.

    1989-01-01

    Covalent attachment of fatty acid to proteins plays an important role in association of certain proteins with hydrophobic membrane structures. In platelets, the structure of many membrane glycoproteins (GPs) has been examined in detail, but the question of fatty acid acylation of platelet proteins has not been addressed. In this study, we wished to determine (a) whether platelet proteins could be fatty acid acylated; and, if so, (b) whether these modified proteins were present in isolated platelet membranes and cytoskeletal fractions; and (c) if the pattern of fatty acid acylated proteins changed on stimulation of the platelets with the agonist thrombin. We observed that in platelets allowed to incorporate 3H-palmitate, a small percentage (1.37%) of radioactivity incorporated into the cells became covalently bound to protein. Selective cleavage of thioester, thioester plus O-ester, and amide-linked 3H-fatty acids from proteins, and their subsequent analysis by high-performance liquid chromatography (HPLC) indicated that the greatest part of 3H-fatty acid covalently bound to protein was thioester-linked 3H-palmitate. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography, at least ten major radiolabeled proteins were detected. Activation of platelets by thrombin greatly increased the quantity of 3H-palmitoylated proteins associated with the cytoskeleton. Nearly all radiolabeled proteins were recovered in the membrane fraction, indicating that these proteins are either integral or peripheral membrane proteins or proteins tightly associated to membrane constituents. Components of the GPIIb-IIIa complex were not palmitoylated. Thus, platelet proteins are significantly modified posttranslationally by 3H-palmitate, and incorporation of palmitoylated proteins into the cytoskeleton is a prominent component of the platelet response to thrombin stimulation

  7. Electrical properties of covalently functionalized graphene

    Directory of Open Access Journals (Sweden)

    Paul Plachinda

    2017-02-01

    Full Text Available We have employed first-principle calculations to study transformation of graphene’s electronic structure under functionalization by covalent bonds with di erent atomic and molecular groups - epoxies, amines, PFPA. It is shown that this functionalization leads to an opening in the graphene’s band gap on order of tens meV, but also leads to reduction of electrical conductivity. We also discuss the influence of charge exchange between the functionalizing molecule and graphene’s conjugated electrons on electron transport properties.

  8. Electrospinning covalently cross-linking biocompatible hydrogelators

    Science.gov (United States)

    Schultz, Kelly M.; Campo-Deaño, Laura; Baldwin, Aaron D.; Kiick, Kristi L.; Clasen, Christian; Furst, Eric M.

    2012-01-01

    Many hydrogel materials of interest are homogeneous on the micrometer scale. Electrospinning, the formation of sub-micrometer to micrometer diameter fibers by a jet of fluid formed under an electric field, is one process being explored to create rich microstructures. However, electrospinning a hydrogel system as it reacts requires an understanding of the gelation kinetics and corresponding rheology near the liquid-solid transition. In this study, we correlate the structure of electrospun fibers of a covalently cross-linked hydrogelator with the corresponding gelation transition and kinetics. Polyethylene oxide (PEO) is used as a carrier polymer in a chemically cross-linking poly(ethylene glycol)-high molecular weight heparin (PEG-HMWH) hydrogel. Using measurements of gelation kinetics from multiple particle tracking microrheology (MPT), we correlate the material rheology with the the formation of stable fibers. An equilibrated, cross-linked hydrogel is then spun and the PEO is dissolved. In both cases, microstructural features of the electrospun fibers are retained, confirming the covalent nature of the network. The ability to spin fibers of a cross-linking hydrogel system ultimately enables the engineering of materials and microstructural length scales suitable for biological applications. PMID:23459473

  9. Covalently functionalized carbon nanostructures and methods for their separation

    Science.gov (United States)

    Wang, YuHuang; Brozena, Alexandra H; Deng, Shunliu; Zhang, Yin

    2015-03-17

    The present invention is directed to carbon nanostructures, e.g., carbon nanotubes, methods of covalently functionalizing carbon nanostructures, and methods of separating and isolating covalently functionalized carbon. In some embodiments, carbon nanotubes are reacted with alkylating agents to provide water soluble covalently functionalized carbon nanotubes. In other embodiments, carbon nanotubes are reacted with a thermally-responsive agent and exposed to light in order to separate carbon nanotubes of a specific chirality from a mixture of carbon nanotubes.

  10. Revisiting nitrogen species in covalent triazine frameworks

    KAUST Repository

    Osadchii, Dmitrii Yu.

    2017-11-28

    Covalent triazine frameworks (CTFs) are porous organic materials promising for applications in catalysis and separation due to their high stability, adjustable porosity and intrinsic nitrogen functionalities. CTFs are prepared by ionothermal trimerization of aromatic nitriles, however, multiple side reactions also occur under synthesis conditions, and their influence on the material properties is still poorly described. Here we report the systematic characterization of nitrogen in CTFs using X-ray photoelectron spectroscopy (XPS). With the use of model compounds, we could distinguish several types of nitrogen species. By combining these data with textural properties, we unravel the influence that the reaction temperature, the catalyst and the monomer structure and composition have on the properties of the resulting CTF materials.

  11. DNA Linked To Single Wall Carbon Nanotubes: Covalent Versus Non-Covalent Approach

    Science.gov (United States)

    Chung, C.-L.; Nguyen, K.; Lyonnais, S.; Streiff, S.; Campidelli, S.; Goux-Capes, L.; Bourgoin, J.-P.; Filoramo, A.

    2008-10-01

    Nanometer-scale structures represent a novel and intriguing field, where scientists and engineers manipulate materials at the atomic and molecular scale levels to produce innovative materials. Carbon nanotubes constitute a relatively new class of materials exhibiting exceptional mechanical and electronic properties and were found to be promising candidates for molecular electronics, sensing or biomedical applications. Considering the bottom-up strategy in nanotechnology, the combination of the recognition properties of DNA with the electronic properties of single walled carbon nanotubes (SWNTs) seems to be a promising approach for the future of electronics. With the aim to assemble DNA with SWNTs, two complementary strategies have been envisioned: the covalent linkage of DNA on carboxylic groups of SWNTs under classical coupling condition and the non-covalent approach based on biotin-streptavidin molecular recognition properties. Here, we present and compare the results that we obtained with these two different methods; we want to objectively show the advantages and disadvantages of each approach.

  12. Molecular electrostatic potential analysis of non-covalent complexes

    Indian Academy of Sciences (India)

    and acceptor atoms due to complex formation) and interaction energy, Eint for a large variety of the non- covalent dimers in the categories HB, DHB, and XB. The MESP based eDA concept proposed by Mohan and. Suresh has unified the HB, DHB, and XB non-covalent complexes in a single category, the eDA complex.61.

  13. Excitation Localization/Delocalization Isomerism in a Strongly Coupled Covalent Dimer of 1,3-Diphenylisobenzofuran

    Czech Academy of Sciences Publication Activity Database

    Schrauben, J. N.; Akdag, A.; Wen, Jin; Havlas, Zdeněk; Ryerson, J. L.; Smith, M. B.; Michl, Josef; Johnson, J. C.

    2016-01-01

    Roč. 120, č. 20 (2016), s. 3473-3483 ISSN 1089-5639 R&D Projects: GA ČR GA15-19143S Institutional support: RVO:61388963 Keywords : intramolecular singlet fission * density functional theory * exciton fission Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.847, year: 2016

  14. Detection of HBV Covalently Closed Circular DNA

    Directory of Open Access Journals (Sweden)

    Xiaoling Li

    2017-06-01

    Full Text Available Chronic hepatitis B virus (HBV infection affects approximately 240 million people worldwide and remains a serious public health concern because its complete cure is impossible with current treatments. Covalently closed circular DNA (cccDNA in the nucleus of infected cells cannot be eliminated by present therapeutics and may result in persistence and relapse. Drug development targeting cccDNA formation and maintenance is hindered by the lack of efficient cccDNA models and reliable cccDNA detection methods. Southern blotting is regarded as the gold standard for quantitative cccDNA detection, but it is complicated and not suitable for high-throughput drug screening, so more sensitive and simple methods, including polymerase chain reaction (PCR-based methods, Invader assays, in situ hybridization and surrogates, have been developed for cccDNA detection. However, most methods are not reliable enough, and there are no unified standards for these approaches. This review will summarize available methods for cccDNA detection. It is hoped that more robust methods for cccDNA monitoring will be developed and that standard operation procedures for routine cccDNA detection in scientific research and clinical monitoring will be established.

  15. Design of a covalently bonded glycosphingolipid microarray

    DEFF Research Database (Denmark)

    Arigi, Emma; Blixt, Klas Ola; Buschard, Karsten

    2012-01-01

    Glycosphingolipids (GSLs) are well known ubiquitous constituents of all eukaryotic cell membranes, yet their normal biological functions are not fully understood. As with other glycoconjugates and saccharides, solid phase display on microarrays potentially provides an effective platform for in vi......Glycosphingolipids (GSLs) are well known ubiquitous constituents of all eukaryotic cell membranes, yet their normal biological functions are not fully understood. As with other glycoconjugates and saccharides, solid phase display on microarrays potentially provides an effective platform......, the major classes of plant and fungal GSLs. In this work, a prototype "universal" GSL-based covalent microarray has been designed, and preliminary evaluation of its potential utility in assaying protein-GSL binding interactions investigated. An essential step in development involved the enzymatic release......-mercaptoethylamine, was also tested. Underivatized or linker-derivatized lyso-GSL were then immobilized on N-hydroxysuccinimide- or epoxide-activated glass microarray slides and probed with carbohydrate binding proteins of known or partially known specificities (i.e., cholera toxin B-chain; peanut agglutinin...

  16. Covalently crosslinked diels-alder polymer networks.

    Energy Technology Data Exchange (ETDEWEB)

    Bowman, Christopher (University of Colorado, Boulder, CO); Adzima, Brian J. (University of Colorado, Boulder, CO); Anderson, Benjamin John

    2011-09-01

    This project examines the utility of cycloaddition reactions for the synthesis of polymer networks. Cycloaddition reactions are desirable because they produce no unwanted side reactions or small molecules, allowing for the formation of high molecular weight species and glassy crosslinked networks. Both the Diels-Alder reaction and the copper-catalyzed azide-alkyne cycloaddition (CuAAC) were studied. Accomplishments include externally triggered healing of a thermoreversible covalent network via self-limited hysteresis heating, the creation of Diels-Alder based photoresists, and the successful photochemical catalysis of CuAAC as an alternative to the use of ascorbic acid for the generation of Cu(I) in click reactions. An analysis of the results reveals that these new methods offer the promise of efficiently creating robust, high molecular weight species and delicate three dimensional structures that incorporate chemical functionality in the patterned material. This work was performed under a Strategic Partnerships LDRD during FY10 and FY11 as part of a Sandia National Laboratories/University of Colorado-Boulder Excellence in Science and Engineering Fellowship awarded to Brian J. Adzima, a graduate student at UC-Boulder. Benjamin J. Anderson (Org. 1833) was the Sandia National Laboratories point-of-contact for this fellowship.

  17. Covalent stabilization of a small molecule-RNA complex.

    Science.gov (United States)

    Peacock, Hayden; Bachu, Radhika; Beal, Peter A

    2011-09-01

    We demonstrate covalent bond formation between an RNA aptamer containing a cysteamine-tethered nucleobase and helix-threading peptides (HTPs) containing α-bromoacetamide N-termini. The reaction is high yielding and inhibited by a DNA strand Watson-Crick complementary to the aptamer sequence indicating covalent reaction is dependent on the high affinity HTP-binding site present in the folded aptamer. These results are important for future structural studies of HTP-RNA complexes and methods for the discovery of new high affinity analogs via covalent tethering strategies. Copyright © 2011 Elsevier Ltd. All rights reserved.

  18. Hydrogels Based on Dynamic Covalent and Non Covalent Bonds: A Chemistry Perspective

    Directory of Open Access Journals (Sweden)

    Francesco Picchioni

    2018-03-01

    Full Text Available Hydrogels based on reversible covalent bonds represent an attractive topic for research at both academic and industrial level. While the concept of reversible covalent bonds dates back a few decades, novel developments continue to appear in the general research area of gels and especially hydrogels. The reversible character of the bonds, when translated at the general level of the polymeric network, allows reversible interaction with substrates as well as responsiveness to variety of external stimuli (e.g., self-healing. These represent crucial characteristics in applications such as drug delivery and, more generally, in the biomedical world. Furthermore, the several possible choices that can be made in terms of reversible interactions generate an almost endless number of possibilities in terms of final product structure and properties. In the present work, we aim at reviewing the latest developments in this field (i.e., the last five years by focusing on the chemistry of the systems at hand. As such, this should allow molecular designers to develop a toolbox for the synthesis of new systems with tailored properties for a given application.

  19. On-surface covalent linking of organic building blocks on a bulk insulator.

    Science.gov (United States)

    Kittelmann, Markus; Rahe, Philipp; Nimmrich, Markus; Hauke, Christopher M; Gourdon, André; Kühnle, Angelika

    2011-10-25

    On-surface synthesis in ultrahigh vacuum provides a promising strategy for creating thermally and chemically stable molecular structures at surfaces. The two-dimensional confinement of the educts, the possibility of working at higher (or lower) temperatures in the absence of solvent, and the templating effect of the surface bear the potential of preparing compounds that cannot be obtained in solution. Moreover, covalently linked conjugated molecules allow for efficient electron transport and are, thus, particularly interesting for future molecular electronics applications. When having these applications in mind, electrically insulating substrates are mandatory to provide sufficient decoupling of the molecular structure from the substrate surface. So far, however, on-surface synthesis has been achieved only on metallic substrates. Here we demonstrate the covalent linking of organic molecules on a bulk insulator, namely, calcite. We deliberately employ the strong electrostatic interaction between the carboxylate groups of halide-substituted benzoic acids and the surface calcium cations to prevent molecular desorption and to reach homolytic cleavage temperatures. This allows for the formation of aryl radicals and intermolecular coupling. By varying the number and position of the halide substitution, we rationally design the resulting structures, revealing straight lines, zigzag structures, and dimers, thus providing clear evidence for the covalent linking. Our results constitute an important step toward exploiting on-surface synthesis for molecular electronics and optics applications, which require electrically insulating rather than metallic supporting substrates.

  20. Diazonium-derived aryl films on gold nanoparticles: evidence for a carbon-gold covalent bond.

    Science.gov (United States)

    Laurentius, Lars; Stoyanov, Stanislav R; Gusarov, Sergey; Kovalenko, Andriy; Du, Rongbing; Lopinski, Gregory P; McDermott, Mark T

    2011-05-24

    Tailoring the surface chemistry of metallic nanoparticles is generally a key step for their use in a wide range of applications. There are few examples of organic films covalently bound to metal nanoparticles. We demonstrate here that aryl films are formed on gold nanoparticles from the spontaneous reduction of diazonium salts. The structure and the bonding of the film is probed with surface-enhanced Raman scattering (SERS). Extinction spectroscopy and SERS show that a nitrobenzene film forms on gold nanoparticles from the corresponding diazonium salt. Comparison of the SERS spectrum with spectra computed from density functional theory models reveals a band characteristic of a Au-C stretch. The observation of this stretch is direct evidence of a covalent bond. A similar band is observed in high-resolution electron energy loss spectra of nitrobenzene layers on planar gold. The bonding of these types of films through a covalent interaction on gold is consistent with their enhanced stability observed in other studies. These findings provide motivation for the use of diazonium-derived films on gold and other metals in applications where high stability and/or strong adsorbate-substrate coupling are required.

  1. Competition between Dehydrogenative Organometallic Bonding and Covalent Coupling of an Unfunctionalized Porphyrin on Cu(111).

    Science.gov (United States)

    Xiang, Feifei; Gemeinhardt, Anja; Schneider, M Alexander

    2018-02-27

    We studied the formation of linked porphyrin oligomers from 5,15-diphenylporphyrin (2H-DPP) by thermal, substrate-assisted organometallic and dehydrogenation coupling on Cu(111) by scanning tunneling microscopy. In the range of 300-620 K, we find three distinct stages, at 300 K, the intact 2H-DPP molecules self-assemble into linear structures held together by van der Waals forces. Increasing the substrate temperature, self-metalation and intramolecular ring-closing reactions result in planar and isolated DPP species on the surface. By C-H cleavage, porphyrin oligomers bonded by organometallic and covalent bonds between the modified DPP are formed. The amount of covalently bonded DPP oligomers increases strongly with annealing time and temperature, and they become the dominant species at 570 K. In contrast, the number of organometallically bonded DPP oligomers increases moderately even up to 620 K, indicating that in this case the organometallic bond is no precursor of the covalent bond.

  2. Effective scheme for partitioning covalent bonds in density-functional embedding theory: From molecules to extended covalent systems.

    Science.gov (United States)

    Huang, Chen; Muñoz-García, Ana Belén; Pavone, Michele

    2016-12-28

    Density-functional embedding theory provides a general way to perform multi-physics quantum mechanics simulations of large-scale materials by dividing the total system's electron density into a cluster's density and its environment's density. It is then possible to compute the accurate local electronic structures and energetics of the embedded cluster with high-level methods, meanwhile retaining a low-level description of the environment. The prerequisite step in the density-functional embedding theory is the cluster definition. In covalent systems, cutting across the covalent bonds that connect the cluster and its environment leads to dangling bonds (unpaired electrons). These represent a major obstacle for the application of density-functional embedding theory to study extended covalent systems. In this work, we developed a simple scheme to define the cluster in covalent systems. Instead of cutting covalent bonds, we directly split the boundary atoms for maintaining the valency of the cluster. With this new covalent embedding scheme, we compute the dehydrogenation energies of several different molecules, as well as the binding energy of a cobalt atom on graphene. Well localized cluster densities are observed, which can facilitate the use of localized basis sets in high-level calculations. The results are found to converge faster with the embedding method than the other multi-physics approach ONIOM. This work paves the way to perform the density-functional embedding simulations of heterogeneous systems in which different types of chemical bonds are present.

  3. Non Covalent Interactions and Internal Dynamics in Adducts of Freons

    Science.gov (United States)

    Caminati, Walther; Gou, Qian; Evangelisti, Luca; Feng, Gang; Spada, Lorenzo; Vallejo-López, Montserrat; Lesarri, Alberto; Cocinero, Emilio J.

    2014-06-01

    The complexation of chlorofluorocarbons (CFCs) with atmospheric water and pollutants of the atmosphere affects their reactivity and it seems to accelerate, for example, the decomposition rate of freons in the atmosphere [1]. For this reason we characterized shapes, stabilities, nature of the non-covalent interactions, structures and internal dynamics of a number of complexes of CFCs with water and of their dimers or oligomers by rotational spectroscopy. It has been found that hydrogenated CFCs form adducts with other molecules through weak hydrogen bonds (WHBs). Their C-H groups can act as proton donors, enhanced by the electron withdrawing of the halogen atoms, interacting with the electron rich regions of the partner molecules [2]. Also in adducts or oligomers of hydrogenated CFCs the monomer units are held together by nets of WHBs [3]. When CFCs are perhalogenated, the positive electrostatic region ("σ-hole") can interact electrostatically with negative sites of another, or of the same molecular entity, giving rise, according to IUPAC, to the so called halogen bond (HaB). However, it has been observed that when the perhalogenated CFCs has a Π electron system, a lone pair•••Π interaction (Bürgi-Dunitz) is favoured [4]. We describe here the HaBs that CF4 and CF3Cl form with a variety of partner molecules such as water, ammonia, dimethyl ether, etc. Important spectroscopic features outline strong dynamics effects taking place in this kind of complex. References [1] V. Vaida, H. G. Kjaergaard, K. J. Feierabend, Int. Rev. Phys. Chem. 22 (2003) 203. [2] See, for example: W. Caminati, S. Melandri, A. Maris, P. Ottaviani, Angew. Chem. Int. Ed. 45 (2006) 2438. [3] G. Feng, L. Evangelisti, I. Cacelli, L. Carbonaro, G. Prampolini, W. Caminati, Chem. Commun. 50 (2014) 171. [4] Q. Gou, G. Feng, L. Evangelisti, W. Caminati, Angew. Chem. Int. Ed. 52 (2013) 52 11888.

  4. Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

    DEFF Research Database (Denmark)

    Walzer, K.; Marx, E.; Greenham, N.C.

    2003-01-01

    We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers...... and the bands in the substrate which are bent under the influence of the strong electric field between the closely separated semiconductor substrate and STM tip. The polarity of the forward bias direction is determined by the alignment of the CdSe electronic states with the semiconductor bands. (C) 2003...

  5. Covalent binding of sulfamethazine to natural and synthetic humic acids: assessing laccase catalysis and covalent bond stability.

    Science.gov (United States)

    Gulkowska, Anna; Sander, Michael; Hollender, Juliane; Krauss, Martin

    2013-07-02

    Sulfonamide antibiotics form stable covalent bonds with quinone moieties in organic matter via nucleophilic addition reactions. In this work, we combined analytical electrochemistry with trace analytics to assess the catalytic role of the oxidoreductase laccase in the binding of sulfamethazine (SMZ) to Leonardite humic acid (LHA) and to four synthetic humic acids (SHAs) polymerized from low molecular weight precursors and to determine the stability of the formed bonds. In the absence of laccase, a significant portion of the added SMZ formed covalent bonds with LHA, but only a very small fraction (<0.4%) of the total quinone moieties in LHA reacted. Increasing absolute, but decreasing relative concentrations of SMZ-LHA covalent bonds with increasing initial SMZ concentration suggested that the quinone moieties in LHA covered a wide distribution in reactivity for the nucleophilic addition of SMZ. Laccase catalyzed the formation of covalent bonds by oxidizing unreactive hydroquinone moieties in LHA to reactive, electrophilic quinone moieties, of which a large fraction (5%) reacted with SMZ. Compared to LHA, the SHA showed enhanced covalent bond formation in the absence of laccase, suggesting a higher reactivity of their quinone moieties toward nucleophilic addition. This work supports that binding to soil organic matter (SOM) is an important process governing the fate, bioactivity, and extractability of sulfonamides in soils.

  6. Construction of covalently coupled, concatameric dimers of 7TM receptors

    DEFF Research Database (Denmark)

    Terpager, Marie; Scholl, D Jason; Kubale, Valentina

    2009-01-01

    -Ala repeats flanked by flexible spacers and positively charged residues to ensure correct inside-out orientation plus an extracellular HA-tag to construct covalently coupled dimers of 7TM receptors. Such 15 TM concatameric homo- and heterodimers of the beta(2)-adrenergic and the NK(1) receptors, which...... for either of the protomers, which was not observed upon simple coexpression of the two receptors. It is concluded that covalently joined 7TM receptor dimers with surprisingly normal receptor properties can be constructed with use of an artificial transmembrane connector, which perhaps can be used to fuse...

  7. Assay of covalent intermediate of 5'-nucleotide phosphodiesterase

    International Nuclear Information System (INIS)

    Blytt, H.J.; Brotherton, J.E.; Butler, L.

    1985-01-01

    A new procedure is reported for isolating a covalent phosphoryl enzyme (diester) intermediate of bovine intestinal 5'-nucleotide phosphodiesterase. The convenience of the procedure makes it possible to determine effects of reaction conditions on the yield of covalent intermediate. Under optimum conditions, using [methyl- 3 H]deoxythymidine 5'-triphosphate as substrate, more than 50% of the enzyme is recovered as thymidylyl enzyme, a 10-fold increase in yield over the previous procedure. Yields of thymidylyl enzyme were maximal at pH 4, whereas optimum catalytic activity is observed at pH greater than 9

  8. Covalent magnetism, exchange interactions and anisotropy of the high temperature layered antiferromagnet MnB₂.

    Science.gov (United States)

    Khmelevskyi, S; Mohn, P

    2012-01-11

    The investigation of the electronic structure and magnetism for the compound MnB(2) with crystal structure type AlB(2) has been revisited to resolve contradictions between various experimental and theoretical results present in the literature. We find that MnB(2) exhibits an interesting example of a Kübler's covalent magnetism (Williams et al 1981 J. Appl. Phys. 52 2069). The covalent magnetism also appears to be the source of some disagreement between the calculated values of the magnetic moments and those given by neutron diffraction experiments. We show that this shortcoming is due to the atomic sphere approximation applied in earlier calculations. The application of the disordered local moment approach and the calculation of the inter-atomic exchange interactions within the Liechtenstein formalism reveal strong local moment antiferromagnetism with a high Néel temperature predicted from Monte Carlo simulations. A fully relativistic band structure calculation and then the application of the torque method yields a strong in-plane anisotropy of the Mn magnetic moments. The agreement of these results with neutron diffraction studies rules out any possible weak itinerant electron magnetism scenarios as proposed earlier for MnB(2).

  9. Enhancement of the performance of covalently immobilized lipase ...

    African Journals Online (AJOL)

    STORAGESEVER

    2010-06-07

    Jun 7, 2010 ... FT-IR, fourier transform infrared. the enzyme towards organic media (Xie et al., ... characterized by FT-IR spectroscopy (Zeiss, Specord M 80) using. KBr method. Covalent immobilization of lipase in the ... and kcat, interpreted from the Lineweaver-Burk plots, were shown in Table 1. The data indicate that the ...

  10. Covalent bindings in proteins following UV-C irradiation

    International Nuclear Information System (INIS)

    Diezel, W.; Meffert, H.; Soennichsen, N.; Reinicke, C.

    1980-01-01

    Following a UV-C irradiation of catalase cross-linked catalase subunits could be detected by sodium dodecylsulfate gel electrophoresis. The subunits of aldolase were not cross-linked. The origin of covalent bindings in the catalase molecule is suggested to be effected by a free radical chain reaction induced by the heme component of catalase after UV-C irradiation. (author)

  11. Factors Contributing to Students' Misconceptions in Learning Covalent Bonds

    Science.gov (United States)

    Erman, Erman

    2017-01-01

    This study aims to identify students' misconceptions regarding covalent bonds. Seventy-seven graduate students in the middle of Indonesia participated in the study. Data were collected in three stages. First, misconceptions were identified by using the Semi Open Diagnostic Test. Ten students who experienced the worst misconceptions were…

  12. Covalent microcontact printing of proteins fro cell patterning

    NARCIS (Netherlands)

    Rozkiewicz, D.I.; Kraan, Yvonne M.; Werten, Marc W.T.; de Wolf, Frits A.; Subramaniam, Vinod; Ravoo, B.J.; Reinhoudt, David

    2006-01-01

    We describe a straightforward approach to the covalent immobilization of cytophilic proteins by microcontact printing, which can be used to pattern cells on substrates. Cytophilic proteins are printed in micropatterns on reactive self-assembled monolayers by using imine chemistry. An

  13. Hybridization characteristics of biomolecular adaptors, covalent DNA streptavidin conjugates

    NARCIS (Netherlands)

    Niemeyer, CM; Burger, W; Hoedemakers, RMJ

    1998-01-01

    Semisynthetic, covalent streptavidin-DNA adducts are versatile molecular connectors for the fabrication of both nano-and microstructured protein arrays by use of DNA hybridization. In this study, the hybridization characteristics of six adduct species, each containing a different DNA sequence of 21

  14. Covalently cross-linked polyetheretherketone proton exchange membrane for DMFC

    CSIR Research Space (South Africa)

    Luo, H

    2009-05-01

    Full Text Available The proton exchange membrane was prepared by covalent cross-linking sulfonated-sulfinated polyetheretherketone. The cross-linked membrane showed high proton conductivity (0.04 S/cm) with suitable water uptake, low methanol permeability (2.21 × 10...

  15. Evidence for covalent binding of epicocconone with proteins from ...

    Indian Academy of Sciences (India)

    TECS

    Evidence for covalent binding of epicocconone with proteins from synchronous fluorescence spectra ... the interaction of epicocconone with human serum albumin is significantly different from its interaction with surfactant assemblies. .... at 620 nm is collected at right angles to the direction of the excitation beam, at magic ...

  16. Macrophage migration inhibitory factor covalently complexed with phenethyl isothiocyanate

    OpenAIRE

    Tyndall, Joel D. A.; Lue, Hongqi; Rutledge, Malcolm T.; Bernhagen, Jurgen; Hampton, Mark B.; Wilbanks, Sigurd M.

    2012-01-01

    Macrophage migration inhibitory factor undergoes a localized conformational shift in response to covalent modification by phenethyl isothiocyanate, a natural compound with anti-inflammatory and anticancer properties. The inhibitor sits within a deep hydrophobic pocket and defines a potential target for the development of improved inhibitors.

  17. Improved covalent functionalization of multi-walled carbon ...

    Indian Academy of Sciences (India)

    Abstract. Ascorbic acid has been covalently linked to multi-walled carbon nanotubes (MWCNTs). The structures of the functionalized MWCNTs were characterized with Fourier-transform infrared spectroscopy. Thermogravi- metric analysis results also demonstrated the presence of organic portions of the functionalized ...

  18. Preparation and properties of electro-conductive fabrics based on polypyrrole: covalent vs. non-covalent attachment

    Science.gov (United States)

    David, N. C.; Anavi, D.; Milanovich, M.; Popowski, Y.; Frid, L.; Amir, E.

    2017-10-01

    Electro-conductive fabrics were prepared via in situ oxidative polymerization of pyrrole (Py) in the presence of unmodified and chemically modified cotton fabrics. Chemical modification of cotton fabric was achieved by covalent attachment of a bifunctional linker molecule to the surface of the fabric, followed by incorporation of a monomer unit onto the linker. The fabrics were characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron spectroscopy, and thermal analysis. Furthermore, the effect of Py concentration on the degree of polypyrrole (PPy) grafting, surface morphology, electrical resistivity, and laundering durability were studied for both types of cotton fabrics. Reductions of several orders of magnitude in surface and volume electrical resistivities were observed for both non-covalently and covalently linked cotton-PPy systems, whereas the effect of covalent pre-treatment of the fabric was stronger at low Py concentration. On the other hand, at higher monomer concentration, the electrical properties and laundering durability of the fabrics we comparable for both unmodified and chemically pre-treated cotton fabrics, indicating that only a small fraction of PPy chains were chemically grafted onto the fabric surface with the majority of the polymer being connected to the fabric through hydrogen bonds.

  19. A covalent PIN1 inhibitor selectively targets cancer cells by a dual mechanism of action

    Science.gov (United States)

    Campaner, Elena; Rustighi, Alessandra; Zannini, Alessandro; Cristiani, Alberto; Piazza, Silvano; Ciani, Yari; Kalid, Ori; Golan, Gali; Baloglu, Erkan; Shacham, Sharon; Valsasina, Barbara; Cucchi, Ulisse; Pippione, Agnese Chiara; Lolli, Marco Lucio; Giabbai, Barbara; Storici, Paola; Carloni, Paolo; Rossetti, Giulia; Benvenuti, Federica; Bello, Ezia; D'Incalci, Maurizio; Cappuzzello, Elisa; Rosato, Antonio; Del Sal, Giannino

    2017-06-01

    The prolyl isomerase PIN1, a critical modifier of multiple signalling pathways, is overexpressed in the majority of cancers and its activity strongly contributes to tumour initiation and progression. Inactivation of PIN1 function conversely curbs tumour growth and cancer stem cell expansion, restores chemosensitivity and blocks metastatic spread, thus providing the rationale for a therapeutic strategy based on PIN1 inhibition. Notwithstanding, potent PIN1 inhibitors are still missing from the arsenal of anti-cancer drugs. By a mechanism-based screening, we have identified a novel covalent PIN1 inhibitor, KPT-6566, able to selectively inhibit PIN1 and target it for degradation. We demonstrate that KPT-6566 covalently binds to the catalytic site of PIN1. This interaction results in the release of a quinone-mimicking drug that generates reactive oxygen species and DNA damage, inducing cell death specifically in cancer cells. Accordingly, KPT-6566 treatment impairs PIN1-dependent cancer phenotypes in vitro and growth of lung metastasis in vivo.

  20. Highly Elastic and Ultratough Hybrid Ionic-Covalent Hydrogels with Tunable Structures and Mechanics.

    Science.gov (United States)

    Yang, Yanyu; Wang, Xing; Yang, Fei; Wang, Luning; Wu, Decheng

    2018-03-25

    Hybrid ionically-covalently crosslinked double-network (DN) hydrogels are attracting increasing attention on account of their self-recovery ability and fatigue resistance, but their relative low mechanical strength and tedious performance adjustment severely limit their applications. Herein, a new strategy to concurrently fabricate hybrid ionic-covalent DN hydrogels and modulate their structures and mechanics is reported, in which an in situ formed chitosan ionic network is incorporated by post-crosslinking the chitosan-based composite hydrogel using multivalent anions solutions. The obtained hybrid DN hydrogels exhibit predominant mechanical properties including superior elastic modulus, high tensile strength, and ultrahigh fracture energy because of the more efficient energy dissipation of rigid short-chain chitosan network. Notably, the swollen hydrogels still remain mechanically strong and tough even after immersion in water for 24 h. More significantly, simply changing the post-crosslinking time can vary the compactness and rigidity of the chitosan network in situ, achieving flexible and efficient modulation of the structures and mechanics of the hybrid DN hydrogels. This study opens up a new horizon in the preparation and regulation of DN hydrogels for promising applications in tissue scaffolds, actuators, and wearable devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Covalent linkage of nanodiamond-paclitaxel for drug delivery and cancer therapy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Kuang-Kai; Wang, Chi-Ching; Chao, Jui-I [Department of Biological Science and Technology, National Chiao Tung University, Hsinchu 30013, Taiwan (China); Zheng, Wen-Wei; Lo, Yu-Shiu; Chen, Chinpiao [Department of Chemistry, National Dong Hwa University, Hualien 97401, Taiwan (China); Chiu, Yu-Chung; Cheng, Chia-Liang, E-mail: clcheng@mail.ndhu.edu.tw, E-mail: chinpiao@mail.ndhu.edu.tw, E-mail: jichao@faculty.nctu.edu.tw [Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan (China)

    2010-08-06

    A nanoparticle-conjugated cancer drug provides a novel strategy for cancer therapy. In this study, we manipulated nanodiamond (ND), a carbon nanomaterial, to covalently link paclitaxel for cancer drug delivery and therapy. Paclitaxel was bound to the surface of 3-5 nm sized ND through a succession of chemical modifications. The ND-paclitaxel conjugation was measured by atomic force microscope and nuclear magnetic resonance spectroscopy, and confirmed with infrared spectroscopy by the detection of deuterated paclitaxel. Treatment with 0.1-50 {mu}g ml{sup -1} ND-paclitaxel for 48 h significantly reduced the cell viability in the A549 human lung carcinoma cells. ND-paclitaxel induced both mitotic arrest and apoptosis in A549 cells. However, ND alone or denatured ND-paclitaxel (after treatment with strong alkaline solution, 1 M NaOH) did not induce the damage effects on A549 cells. ND-paclitaxel was taken into lung cancer cells in a concentration-dependent manner using flow cytometer analysis. The ND-paclitaxel particles were located in the microtubules and cytoplasm of A549 cells observed by confocal microscopy. Furthermore, ND-paclitaxel markedly blocked the tumor growth and formation of lung cancer cells in xenograft SCID mice. Together, we provide a functional covalent conjugation of ND-paclitaxel, which can be delivered into lung carcinoma cells and preserves the anticancer activities on the induction of mitotic blockage, apoptosis and anti-tumorigenesis.

  2. Strong van der Waals attractive forces in nanotechnology

    Science.gov (United States)

    Reimers, Jeffrey

    The Dobson classification scheme for failure of London-like expressions for describing dispersion is reviewed. New ways to measure using STM data and calculate by first principles free energies of organic self-assembly processes from solution will be discussed, considering tetraalkylporphyrins on graphite. How strong van der Waals forces can compete against covalent bonding to produce new molecular isomers and reaction pathways will also be demonstrated, focusing on golds-sulfur bonds for sensors and stabilizing nanoparticles.

  3. Generation of Multicomponent Molecular Cages using Simultaneous Dynamic Covalent Reactions.

    Science.gov (United States)

    Drożdż, Wojciech; Bouillon, Camille; Kotras, Clément; Richeter, Sébastien; Barboiu, Mihail; Clément, Sébastien; Stefankiewicz, Artur R; Ulrich, Sébastien

    2017-12-19

    Cage compounds are very attractive structures for a wide range of applications and there is ongoing interest in finding effective ways to access such kinds of complex structures, particularly those possessing dynamic adaptive features. Here we report the accessible synthesis of new type of organic cage architectures, possessing two different dynamic bonds within one structure: hydrazones and disulfides. Implementation of three distinct functional groups (thiols, aldehydes and hydrazides) in the structure of two simple building blocks resulted in their spontaneous and selective self-assembly into aromatic cage-type architectures. These organic cages contain up to ten components linked together by twelve reversible covalent bonds. The advantage provided by the presented approach is that these cage structures can adaptively self-sort from a complex virtual mixture of polymers or macrocycles and that dynamic covalent chemistry enables their deliberate disassembly through controlled component exchange. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Highly selective covalent organic functionalization of epitaxial graphene

    Science.gov (United States)

    Bueno, Rebeca A.; Martínez, José I.; Luccas, Roberto F.; Del Árbol, Nerea Ruiz; Munuera, Carmen; Palacio, Irene; Palomares, Francisco J.; Lauwaet, Koen; Thakur, Sangeeta; Baranowski, Jacek M.; Strupinski, Wlodek; López, María F.; Mompean, Federico; García-Hernández, Mar; Martín-Gago, José A.

    2017-05-01

    Graphene functionalization with organics is expected to be an important step for the development of graphene-based materials with tailored electronic properties. However, its high chemical inertness makes difficult a controlled and selective covalent functionalization, and most of the works performed up to the date report electrostatic molecular adsorption or unruly functionalization. We show hereafter a mechanism for promoting highly specific covalent bonding of any amino-terminated molecule and a description of the operating processes. We show, by different experimental techniques and theoretical methods, that the excess of charge at carbon dangling-bonds formed on single-atomic vacancies at the graphene surface induces enhanced reactivity towards a selective oxidation of the amino group and subsequent integration of the nitrogen within the graphene network. Remarkably, functionalized surfaces retain the electronic properties of pristine graphene. This study opens the door for development of graphene-based interfaces, as nano-bio-hybrid composites, fabrication of dielectrics, plasmonics or spintronics.

  5. Covalency in the f-element-chalcogen bond

    Energy Technology Data Exchange (ETDEWEB)

    Ingram, Kieran I.M. [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom); Kaltsoyannis, Nikolas [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)], E-mail: n.kaltsoyannis@ucl.ac.uk; Gaunt, Andrew J.; Neu, Mary P. [Inorganic, Isotope and Actinide Chemistry (C-IIAC), Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2007-10-11

    The geometric and electronic structures of the title complexes have been studied using gradient corrected density functional theory. Excellent agreement is observed between computed r(M-E) and experimental values in analogous {sup i}Pr complexes. Natural charge analysis indicates that the M-E bond becomes less ionic in the order O>S>S> Te, and that this decrease is largest for U and smallest for La. Natural and Mulliken overlap populations suggest increasing M-E covalency as group 16 is descended, and also in the order Lacovalency down group 16 arises from increased metal d (and s) participation in the bonding, while that from La to Pu and U stems from larger 5f orbital involvement compared with 4f.

  6. Applications of reversible covalent chemistry in analytical sample preparation.

    Science.gov (United States)

    Siegel, David

    2012-12-07

    Reversible covalent chemistry (RCC) adds another dimension to commonly used sample preparation techniques like solid-phase extraction (SPE), solid-phase microextraction (SPME), molecular imprinted polymers (MIPs) or immuno-affinity cleanup (IAC): chemical selectivity. By selecting analytes according to their covalent reactivity, sample complexity can be reduced significantly, resulting in enhanced analytical performance for low-abundance target analytes. This review gives a comprehensive overview of the applications of RCC in analytical sample preparation. The major reactions covered include reversible boronic ester formation, thiol-disulfide exchange and reversible hydrazone formation, targeting analyte groups like diols (sugars, glycoproteins and glycopeptides, catechols), thiols (cysteinyl-proteins and cysteinyl-peptides) and carbonyls (carbonylated proteins, mycotoxins). Their applications range from low abundance proteomics to reversible protein/peptide labelling to antibody chromatography to quantitative and qualitative food analysis. In discussing the potential of RCC, a special focus is on the conditions and restrictions of the utilized reaction chemistry.

  7. Covalent interactions of acetaldehyde with the actin/microfilament system.

    Science.gov (United States)

    Xu, D S; Jennett, R B; Smith, S L; Sorrell, M F; Tuma, D J

    1989-01-01

    The covalent binding of [14C]acetaldehyde to purified rabbit skeletal muscle actin was characterized. As we have found for other cytoskeletal proteins, actin formed stable covalent adducts under reductive and non-reductive conditions. Under non-reductive conditions, individual and competition binding studies versus albumin both showed that the G-form of actin is more reactive toward acetaldehyde than the F-form. When proteins were compared on an 'equi-lysine' basis under non-reducing conditions, G-actin was found to preferentially compete with albumin for binding to acetaldehyde. Time-course dialysis studies indicated that acetaldehyde-actin adducts become more stable with prolonged incubation at 37 degrees C. These data raise the possibility that actin could be a preferential target for adduct formation in cellular systems and will serve as the basis for ongoing studies aimed at defining the role of acetaldehyde-protein adducts in ethanol-induced cell injury.

  8. Covalent bond symmetry breaking and protein secondary structure

    OpenAIRE

    Lundgren, Martin; Niemi, Antti J.

    2011-01-01

    Both symmetry and organized breaking of symmetry have a pivotal r\\^ole in our understanding of structure and pattern formation in physical systems, including the origin of mass in the Universe and the chiral structure of biological macromolecules. Here we report on a new symmetry breaking phenomenon that takes place in all biologically active proteins, thus this symmetry breaking relates to the inception of life. The unbroken symmetry determines the covalent bond geometry of a sp3 hybridized ...

  9. Covalent binding of aniline to humic substances. 1. Kinetic studies

    Science.gov (United States)

    Weber, E.J.; Spidle, D.L.; Thorn, K.A.

    1996-01-01

    The reaction kinetics for the covalent binding of aniline with reconstituted IHSS humic and fulvic acids, unfractionated DOM isolated from Suwannee River water, and whole samples of Suwannee River water have been investigated. The reaction kinetics in each of these systems can be adequately described by a simple second-order rate expression. The effect of varying the initial concentration of aniline on reaction kinetics suggested that approximately 10% of the covalent binding sites associated with Suwannee River fulvic acid are highly reactive sites that are quickly saturated. Based on the kinetic parameters determined for the binding of aniline with the Suwannee River fulvic and humic acid isolates, it was estimated that 50% of the aniline concentration decrease in a Suwannee River water sample could be attributed to reaction with the fulvic and humic acid components of the whole water sample. Studies with Suwannee River fulvic acid demonstrated that the rate of binding decreased with decreasing pH, which parallels the decrease in the effective concentration of the neutral form, or reactive nucleophilic species of aniline. The covalent binding of aniline with Suwannee River fulvic acid was inhibited by prior treatment of the fulvic acid with hydrogen sulfide, sodium borohydride, or hydroxylamine. These observations are consistent with a reaction pathway involving nucleophilic addition of aniline to carbonyl moieties present in the fulvic acid.

  10. Photophysics of covalently functionalized single wall carbon nanotubes with verteporfin

    Science.gov (United States)

    Staicu, Angela; Smarandache, Adriana; Pascu, Alexandru; Pascu, Mihail Lucian

    2017-09-01

    Covalently functionalized single wall carbon nanotubes (SWCNT) with the photosensitizer verteporfin (VP) were synthesized and studied. Photophysical properties of the obtained compounds like optical absorption, laser-induced fluorescence and generated singlet oxygen were investigated. In order to highlight the features of the conjugated compound, its photophysical characteristics were compared with those of the mixtures of the initial components. The optical absorption data evidenced a compound that combines features of the primary SWCNTs and VP. This is the also the case of the laser induced fluorescence of the synthesized product. Moreover, fluorescence quantum yield (Φf) of the compound (Φf = 2.4%) is smaller than for the mixture of SWCNT and VP in (Φf = 3.2%). The behavior is expected, because linked VP (carrying the fluorescent moiety) transfers easier a part of its excitation energy to the SWCNT in the covalent structure. Relative to the quantum yield of singlet oxygen generation (ΦΔ) by Methylene Blue, it was found that the ΦΔ for the conjugated VP-SWCNT is 51% while for the mixture ΦΔ is 23%. The results indicate covalently functionalized single walled carbon nanotubes with verteporfin as potential compounds of interest in targeted drug delivery and photodynamic therapy.

  11. Covalent assembly of gold nanoparticles for nonvolatile memory applications.

    Science.gov (United States)

    Gupta, Raju Kumar; Kusuma, Damar Yoga; Lee, P S; Srinivasan, M P

    2011-12-01

    This work reports a versatile approach for enhancing the stability of nonvolatile memory devices through covalent assembly of functionalized gold nanoparticles. 11-mercapto-1-undecanol functionalized gold nanoparticles (AuNPs) with a narrow size distribution and particle size of about 5 nm were synthesized. Then, the AuNPs were immobilized on a SiO(2) substrate using a functionalized polymer as a surface modifier. Microscopic and spectroscopic techniques were used to characterize the AuNPs and their morphology before and after immobilization. Finally, a metal-insulator-semiconductor (MIS) type memory device with such covalently anchored AuNPs as a charge trapping layer was fabricated. The MIS structure showed well-defined counterclockwise C-V hysteresis curves indicating a good memory effect. The flat band voltage shift was 1.64 V at a swapping voltage between ±7 V. Furthermore, the MIS structure showed a good retention characteristic up to 20,000 s. The present synthetic route to covalently immobilize gold nanoparticles system will be a step towards realization for the nanoparticle-based electronic devices and related applications. © 2011 American Chemical Society

  12. Hydrogen scrambling in non-covalent complexes of peptides.

    Science.gov (United States)

    Modzel, Maciej; Stefanowicz, Piotr; Szewczuk, Zbigniew

    2012-12-15

    Mass spectrometry analysis combined with hydrogen-deuterium exchange (HDX-MS) is arising as a tool for quick analysis of native protein conformation. However, during collision-induced dissociation (CID) the spatial distribution of deuterium is not always conserved. It is therefore important to find out how hydrogen scrambling occurs--this study concentrates on the possibility of scrambling between amino acid residues spatially close together, but not connected by covalent bonds. Peptides used in this study were synthesized by Fmoc strategy. Deuteration occurred in ammonia formate solution in D(2)O. Non-covalent complexes consisting of a deuterated and a non-deuterated peptide were analyzed by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR-MS) with quadrupole mass filter. Low-energy CID was used for complex dissociation. The complexes were isolated on a quadrupole and subjected to CID to cause dissociation. The deuterium distribution before and after the dissociation of a non-covalent complex to its components was measured. The study revealed that no significant scrambling occurred between the constituents of the complexes--the degree of scrambling did not exceed 10%. The results obtained for the complexes should be similar to those for protein parts spatially close together--hydrogen scrambling between them should be negligible. The knowledge that almost all the scrambling occurs along peptide chains gives a better insight into the mechanism of HDX inside a protein. Copyright © 2012 John Wiley & Sons, Ltd.

  13. Reactions between aromatic hydrocarbons and heterocycles: covalent and proton-bound dimer cations of benzene/pyridine.

    Science.gov (United States)

    El-Shall, M Samy; Ibrahim, Yehia M; Alsharaeh, Edreese H; Meot-Ner Mautner, Michael; Watson, Simon P

    2009-07-29

    Despite the fact that benzene (Bz) and pyridine (Py) are probably the most common and extensively studied organic molecules, the observation of a covalent adduct in the ionized benzene/pyridine system has never been reported. This Article reports the first experimental and theoretical evidence of a covalent (Bz x Py)(*+) adduct that results from the reaction of Bz(*+) with pyridine or Py(*+) with benzene. These reactions are studied using mass-selected ion mobility, chemical reactivity, collisional dissociation, and ab initio calculations. The (Bz x Py)(*+) adduct does not exchange ligands with Bz to form Bz(2)(*+) or with Py to form (Py)(2)H(+) despite the strong bonds in these homodimers. The thermochemistry then suggests that the (Bz x Py)(*+) heterodimer is bonded covalently with a bonding energy of >33 kcal/mol. Correspondingly, ab initio calculations identify covalently bonded propeller-shaped isomers of (Bz x Py)(*+) with bonding energies of 31-38 kcal/mol, containing a C-N bond. The mobility of the (Bz x Py)(*+) adduct in helium is consistent with these covalent dimers. As to noncovalent adducts, the computations identify novel distonic hydrogen-bonded complexes (C(5)H(5)NH(+) x C(6)H(5)(*)) where the charge resides on one component (PyH(+)), while the radical site resides on the other component (C(6)H(5)(*)). Collisional dissociation suggests that the covalent and distonic dimers may interconvert at high energies. The most stable distonic (C(5)H(5)NH(+) x C(6)H(5)(*)) complex contains a hydrogen bond to the phenyl radical carbon site with a calculated dissociation energy of 16.6 kcal/mol. This bond is somewhat stronger than the NH(+) x pi hydrogen bonds of PyH(+) to the pi system of the phenyl radical and of the benzene molecule. For this NH(+) x pi bond in the PyH(+) x Bz dimer, the measured binding energy is 13.4 kcal/mol, and ab initio calculations identify two T-shaped isomers with the NH(+) pointing to the center of the benzene ring or to the

  14. Stable Covalent Organic Frameworks for Exceptional Mercury Removal from Aqueous Solutions.

    Science.gov (United States)

    Huang, Ning; Zhai, Lipeng; Xu, Hong; Jiang, Donglin

    2017-02-15

    The pre-designable porous structures found in covalent organic frameworks (COFs) render them attractive as a molecular platform for addressing environmental issues such as removal of toxic heavy metal ions from water. However, a rational structural design of COFs in this aspect has not been explored. Here we report the rational design of stable COFs for Hg(II) removal through elaborate structural design and control over skeleton, pore size, and pore walls. The resulting framework is stable under strong acid and base conditions, possesses high surface area, has large mesopores, and contains dense sulfide functional termini on the pore walls. These structural features work together in removing Hg(II) from water and achieve a benchmark system that combines capacity, efficiency, effectivity, applicability, selectivity, and reusability. These results suggest that COFs offer a powerful platform for tailor-made structural design to cope with various types of pollution.

  15. β-Ketoenamine-linked covalent organic frameworks capable of pseudocapacitive energy storage.

    Science.gov (United States)

    DeBlase, Catherine R; Silberstein, Katharine E; Truong, Thanh-Tam; Abruña, Héctor D; Dichtel, William R

    2013-11-13

    Two-dimensional covalent organic frameworks (2D COFs) are candidate materials for charge storage devices because of their micro- or mesoporosity, high surface area, and ability to predictably organize redox-active groups. The limited chemical and oxidative stability of established COF linkages, such as boroxines and boronate esters, precludes these applications, and no 2D COF has demonstrated reversible redox behavior. Here we describe a β-ketoenamine-linked 2D COF that exhibits reversible electrochemical processes of its anthraquinone subunits, excellent chemical stability to a strongly acidic electrolyte, and one of the highest surface areas of the imine- or enamine-linked 2D COFs. Electrodes modified with the redox-active COF show higher capacitance than those modified with a similar non-redox-active COF, even after 5000 charge-discharge cycles. These findings demonstrate the promise of using 2D COFs for capacitive storage.

  16. Removal U(VI) from artificial seawater using facilely and covalently grafted polyacrylonitrile fibers with lysine

    Science.gov (United States)

    Li, Wenting; Liu, Qi; Liu, Jingyuan; Zhang, Hongsen; Li, Rumin; Li, Zhanshuang; Jing, Xiaoyan; Wang, Jun

    2017-05-01

    Polyacrylonitrile fibers (PANF) covalently modified with lysine (PAN-Lys) was facilely synthesized and carefully characterized. The critical factors affecting U(VI) adsorption from aqueous solution were exploited, such as initial pH, contact time, concentration and temperature. The adsorption process is strongly dependent on solution pH. With excellent adsorption capacity and high affinity toward U(VI), the process for U(VI) is extremely rapid and the equilibrium can be reached within 20 min. The thermodynamics and kinetics were strictly evaluated. In addition, the hypothetical adsorption mechanisms were proposed. Moreover, the adsorption behavior at low concentrations (3-30 μg L-1) in simulated seawater was also investigated. Therefore, PAN-Lys can be potentially utilized for the efficient removal of U(VI) from seawater.

  17. Testing strong interaction theories

    International Nuclear Information System (INIS)

    Ellis, J.

    1979-01-01

    The author discusses possible tests of the current theories of the strong interaction, in particular, quantum chromodynamics. High energy e + e - interactions should provide an excellent means of studying the strong force. (W.D.L.)

  18. Emergent property of high hardness for C-rich ruthenium carbides: partial covalent Ru-Ru bonds.

    Science.gov (United States)

    Xu, Chunhong; Yu, Hongyu; Kuo, Bao; Ma, Shuailing; Xiao, Xuehui; Li, Da; Duan, Defang; Jin, Xilian; Liu, Bingbing; Cui, Tian

    2018-02-28

    Hard materials are being investigated all the time by combining transition metals with light elements. Combining a structure search with first-principles functional calculations, we first discovered three stable stoichiometric C-rich ruthenium carbides in view of three synthesis routes, namely, the ambient phases of Ru 2 C 3 and RuC, and two high pressure phases of RuC 4 . There is a phase transition of RuC 4 from the P3[combining macron]m1 structure to the R3[combining macron]m structure above 98 GPa. The calculations of elastic constants and phonon dispersions show their mechanical and dynamical stability. The large elastic modulus, high Debye temperature and the estimated hardness values suggest that these hard ruthenium carbides have good mechanical properties. The analyses of electronic structure and chemical bonding indicate that chemical bonding, not carbon content, is the key factor for the hardness in these metallic C-rich ruthenium carbides. The partial covalent Ru-C bonds and strong covalent C-C bonds are responsible for the high hardness. Moreover, the emergence of partial covalent Ru-Ru bonds can enhance the hardness of RuC, while the ionic Ru-Ru bonds can weaken the hardness of Ru 2 C 3 .

  19. Eriocalyxin B Inhibits STAT3 Signaling by Covalently Targeting STAT3 and Blocking Phosphorylation and Activation of STAT3.

    Directory of Open Access Journals (Sweden)

    Xiaokui Yu

    Full Text Available Activated STAT3 plays an important role in oncogenesis by stimulating cell proliferation and resisting apoptosis. STAT3 therefore is an attractive target for cancer therapy. We have screened a traditional Chinese herb medicine compound library and found Eriocalyxin B (EB, a diterpenoid from Isodon eriocalyx, as a specific inhibitor of STAT3. EB selectively inhibited constitutive as well as IL-6-induced phosphorylation of STAT3 and induced apoptosis of STAT3-dependent tumor cells. EB did not affect the upstream protein tyrosine kinases or the phosphatase (PTPase of STAT3, but rather interacted directly with STAT3. The effects of EB could be abolished by DTT or GSH, suggesting a thiol-mediated covalent linkage between EB and STAT3. Site mutagenesis of cysteine in and near the SH2 domain of STAT3 identified Cys712 to be the critical amino acid for the EB-induced inactivation of STAT3. Furthermore, LC/MS/MS analyses demonstrated that an α, β-unsaturated carbonyl of EB covalently interacted with the Cys712 of STAT3. Computational modeling analyses also supported a direct interaction between EB and the Cys712 of STAT3. These data strongly suggest that EB directly targets STAT3 through a covalent linkage to inhibit the phosphorylation and activation of STAT3 and induces apoptosis of STAT3-dependent tumor cells.

  20. Rationally Designed, Multifunctional Self-Assembled Nanoparticles for Covalently Networked, Flexible and Self-Healable Superhydrophobic Composite Films.

    Science.gov (United States)

    Lee, Yujin; You, Eun-Ah; Ha, Young-Geun

    2018-03-21

    For constructing bioinspired functional films with various superhydrophobic functions, including self-cleaning, anticorrosion, antibioadhesion, and oil-water separation, hydrophobic nanomaterials have been widely used as crucial structural components. In general, hydrophobic nanomaterials, however, cannot form strong chemical bond networks in organic-inorganic hybrid composite films because of the absence of chemically compatible binding components. Herein, we report the rationally designed, multifunctional self-assembled nanoparticles with tunable functionalities of covalent cross-linking and hydrophobicity for constructing three-dimensionally interconnected superhydrophobic composite films via a facile solution-based fabrication at room temperature. The multifunctional self-assembled nanoparticles allow the systematic control of functionalities of composite films, as well as the stable formation of covalently linked superhydrophobic composite films with excellent flexibility (bending radii of 6.5 and 3.0 mm, 1000 cycles) and self-healing ability (water contact angle > 150°, ≥10 cycles). The presented strategy can be a versatile and effective route to generating other advanced functional films with covalently interconnected composite networks.

  1. Covalent DNA-protein crosslinking occurs after hyperthermia and radiation

    International Nuclear Information System (INIS)

    Cress, A.E.; Bowden, G.T.

    1983-01-01

    Covalent DNA-protein crosslinks occur in exponentially growing mouse leukemia cells (L1210) after exposure to ionizing radiation. The amount of DNA-protein crosslinks as measured by a filter binding assay is dose dependent upon X irradiation. Although hyperthermia and radiation in combination are synergistic with respect to cell lethality, the combination does not result in an increase of DNA-protein crosslinks when assayed immediately following treatments. Hyperthermia (43 degrees C/15 min) given prior to radiation does not alter the radiation dose dependency of the amount of initial crosslinking. In addition, the amount of DNA-protein crosslinking produced by heat plus radiation is independent of the length of heating the cells at 43 degrees C. The DNA-protein crosslinks produced by 50-Gy X ray alone are removed after 2 hr at 37 degrees C. However, if hyperthermia (43 degrees C/15 min) is given prior to 100-Gy X ray, the removal of DNA-protein crosslinks is delayed until 4.0 hr after radiation. Phospho-serine and phospho-threonine bonds are not produced with either radiation or the combination of hyperthermia plus radiation as judged by the resistance of the bonds to guanidine hydrochloride. However, hyperthermia plus radiation causes an increase in phosphate to nitrogen type bonding. These results show that radiation alone causes covalent DNA-protein crosslinks. Hyperthermia in combination with radiation does not increase the total amount of the crosslinks but delays the removal of the crosslinks and alters the distribution of the types of chemical bonding. These data suggest that the synergistic action on hyperthermia with radiation is more related to the rate of removal and the type of chemical bonding involved in the covalent DNA-protein crosslinks rather than the amount of DNA-protein crosslinks

  2. Reaction mechanisms for on-surface synthesis of covalent nanostructures

    International Nuclear Information System (INIS)

    Björk, J

    2016-01-01

    In recent years, on-surface synthesis has become an increasingly popular strategy to form covalent nanostructures. The approach has great prospects for facilitating the manufacture of a range of fascinating materials with atomic precision. However, the on-surface reactions are enigmatic to control, currently restricting its bright perspectives and there is a great need to explore how the reactions are governed. The objective of this topical review is to summarize theoretical work that has focused on comprehending on-surface synthesis protocols through studies of reaction mechanisms. (topical review)

  3. The Search for Covalently Ligandable Proteins in Biological Systems

    Directory of Open Access Journals (Sweden)

    Syed Lal Badshah

    2016-09-01

    Full Text Available This commentary highlights the recent article published in Nature, June 2016, titled: “Proteome-wide covalent ligand discovery in native biological systems”. They screened the whole proteome of different human cell lines and cell lysates. Around 700 druggable cysteines in the whole proteome were found to bind the electrophilic fragments in both active and inactive states of the proteins. Their experiment and computational docking results agreed with one another. The usefulness of this study in terms of bringing a change in medicinal chemistry is highlighted here.

  4. Inter- and intramolecular non-covalent interactions in 1-methylimidazole-2-carbaldehyde complexes of copper, silver, and gold

    Science.gov (United States)

    Koskinen, Laura; Jääskeläinen, Sirpa; Hirva, Pipsa; Haukka, Matti

    2014-09-01

    Three new imidazole compounds, [CuBr2(mimc)2] (1), [Ag(mimc)2][CF3SO3] (2), and [AuCl3(mimc)] (3) (mimc = 1-methylimidazole-2-carbaldehyde), have been synthesized, structurally characterized, and further analyzed using the QTAIM analysis. The compounds exhibit self-assembled 3D networks arising from intermolecular non-covalent interactions such as metallophilic interactions, metal-π contacts, halogens-halogen interactions, and hydrogen bonds. These weak interactions have a strong impact on the coordination sphere of the metal atoms and on the packing of compounds 1, 2, and 3.

  5. From covalent bonding to coalescence of metallic nanorods

    Directory of Open Access Journals (Sweden)

    Lee Soohwan

    2011-01-01

    Full Text Available Abstract Growth of metallic nanorods by physical vapor deposition is a common practice, and the origin of their dimensions is a characteristic length scale that depends on the three-dimensional Ehrlich-Schwoebel (3D ES barrier. For most metals, the 3D ES barrier is large so the characteristic length scale is on the order of 200 nm. Using density functional theory-based ab initio calculations, this paper reports that the 3D ES barrier of Al is small, making it infeasible to grow Al nanorods. By analyzing electron density distributions, this paper shows that the small barrier is the result of covalent bonding in Al. Beyond the infeasibility of growing Al nanorods by physical vapor deposition, the results of this paper suggest a new mechanism of controlling the 3D ES barrier and thereby nanorod growth. The modification of local degree of covalent bonding, for example, via the introduction of surfactants, can increase the 3D ES barrier and promote nanorod growth, or decrease the 3D ES barrier and promote thin film growth.

  6. Bifunctional avidin with covalently modifiable ligand binding site.

    Directory of Open Access Journals (Sweden)

    Jenni Leppiniemi

    Full Text Available The extensive use of avidin and streptavidin in life sciences originates from the extraordinary tight biotin-binding affinity of these tetrameric proteins. Numerous studies have been performed to modify the biotin-binding affinity of (streptavidin to improve the existing applications. Even so, (streptavidin greatly favours its natural ligand, biotin. Here we engineered the biotin-binding pocket of avidin with a single point mutation S16C and thus introduced a chemically active thiol group, which could be covalently coupled with thiol-reactive molecules. This approach was applied to the previously reported bivalent dual chain avidin by modifying one binding site while preserving the other one intact. Maleimide was then coupled to the modified binding site resulting in a decrease in biotin affinity. Furthermore, we showed that this thiol could be covalently coupled to other maleimide derivatives, for instance fluorescent labels, allowing intratetrameric FRET. The bifunctional avidins described here provide improved and novel tools for applications such as the biofunctionalization of surfaces.

  7. Solvent-free covalent functionalization of nanodiamond with amines

    International Nuclear Information System (INIS)

    Basiuk, Elena V.; Santamaría-Bonfil, Adriana; Meza-Laguna, Victor; Gromovoy, Taras Yu.; Alvares-Zauco, Edgar; Contreras-Torres, Flavio F.; Rizo, Juan; Zavala, Guadalupe; Basiuk, Vladimir A.

    2013-01-01

    Covalent functionalization of pristine nanodiamond (ND) with 1,12-diaminododecane (DAD), 1,5-diaminonaphthalene (DAN), poly(ethylene glycol) diamine (PEGDA), and polyethylenimine (PEI) was carried out by employing solvent-free methodology, which is based on thermal instead of chemical activation of carboxylic groups at ND surface. A simple solubility/dispersibility test in water and isopropanol showed an increased lipophilicity of the functionalized samples. The conversion of intrinsic carboxylic groups into the corresponding amide derivatives was characterized by means of Fourier-transform infrared spectroscopy. Thermogravimetric analysis found the highest organic content of about 18% for ND-PEI, followed by ND-DAD, for which the contribution of covalently bonded diamine was estimated to be of ca. 10%. In temperature programmed desorption measurements with mass spectrometric detection, the presence of organic functionalizing groups changed both mass spectra and thermodesorption curves of ND. The changes in morphology of primary and secondary ND aggregates were characterized by scanning and transmission electron microscopy, as well as by atomic force microscopy. The current–voltage measurements under atmospheric pressure found an increased conductivity for ND-DAN, as compared to that of pristine ND, whereas for ND-DAD, ND-PEGDA and ND-PEI a dramatic decrease in conductivity due to functionalization was observed.

  8. Solvent-free covalent functionalization of nanodiamond with amines

    Energy Technology Data Exchange (ETDEWEB)

    Basiuk, Elena V., E-mail: elenagd@unam.mx [Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, 04510 México D.F. (Mexico); Santamaría-Bonfil, Adriana; Meza-Laguna, Victor [Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, 04510 México D.F. (Mexico); Gromovoy, Taras Yu. [Institute of Surface Chemistry, National Academy of Sciences of the Ukraine, Gen. Naumova 17, 03164 Kiev (Ukraine); Alvares-Zauco, Edgar [Facultad de Ciencias, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, 04510 México D.F. (Mexico); Contreras-Torres, Flavio F.; Rizo, Juan [Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, 04510 México D.F. (Mexico); Zavala, Guadalupe [Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, 62210, Cuernavaca, Morelos (Mexico); Basiuk, Vladimir A. [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, 04510 México, D.F. (Mexico)

    2013-06-15

    Covalent functionalization of pristine nanodiamond (ND) with 1,12-diaminododecane (DAD), 1,5-diaminonaphthalene (DAN), poly(ethylene glycol) diamine (PEGDA), and polyethylenimine (PEI) was carried out by employing solvent-free methodology, which is based on thermal instead of chemical activation of carboxylic groups at ND surface. A simple solubility/dispersibility test in water and isopropanol showed an increased lipophilicity of the functionalized samples. The conversion of intrinsic carboxylic groups into the corresponding amide derivatives was characterized by means of Fourier-transform infrared spectroscopy. Thermogravimetric analysis found the highest organic content of about 18% for ND-PEI, followed by ND-DAD, for which the contribution of covalently bonded diamine was estimated to be of ca. 10%. In temperature programmed desorption measurements with mass spectrometric detection, the presence of organic functionalizing groups changed both mass spectra and thermodesorption curves of ND. The changes in morphology of primary and secondary ND aggregates were characterized by scanning and transmission electron microscopy, as well as by atomic force microscopy. The current–voltage measurements under atmospheric pressure found an increased conductivity for ND-DAN, as compared to that of pristine ND, whereas for ND-DAD, ND-PEGDA and ND-PEI a dramatic decrease in conductivity due to functionalization was observed.

  9. Covalent and density-controlled surface immobilization of E-cadherin for adhesion force spectroscopy.

    Directory of Open Access Journals (Sweden)

    Dagmar Fichtner

    Full Text Available E-cadherin is a key cell-cell adhesion molecule but the impact of receptor density and the precise contribution of individual cadherin ectodomains in promoting cell adhesion are only incompletely understood. Investigating these mechanisms would benefit from artificial adhesion substrates carrying different cadherin ectodomains at defined surface density. We therefore developed a quantitative E-cadherin surface immobilization protocol based on the SNAP-tag technique. Extracellular (EC fragments of E-cadherin fused to the SNAP-tag were covalently bound to self-assembled monolayers (SAM of thiols carrying benzylguanine (BG head groups. The adhesive functionality of the different E-cadherin surfaces was then assessed using cell spreading assays and single-cell (SCSF and single-molecule (SMSF force spectroscopy. We demonstrate that an E-cadherin construct containing only the first and second outmost EC domain (E1-2 is not sufficient for mediating cell adhesion and yields only low single cadherin-cadherin adhesion forces. In contrast, a construct containing all five EC domains (E1-5 efficiently promotes cell spreading and generates strong single cadherin and cell adhesion forces. By varying the concentration of BG head groups within the SAM we determined a lateral distance of 5-11 nm for optimal E-cadherin functionality. Integrating the results from SCMS and SMSF experiments furthermore demonstrated that the dissolution of E-cadherin adhesion contacts involves a sequential unbinding of individual cadherin receptors rather than the sudden rupture of larger cadherin receptor clusters. Our method of covalent, oriented and density-controlled E-cadherin immobilization thus provides a novel and versatile platform to study molecular mechanisms underlying cadherin-mediated cell adhesion under defined experimental conditions.

  10. Strongly Correlated Topological Insulators

    Science.gov (United States)

    2016-02-03

    Strongly Correlated Topological Insulators In the past year, the grant was used for work in the field of topological phases, with emphasis on finding...surface of topological insulators. In the past 3 years, we have started a new direction, that of fractional topological insulators. These are materials...in which a topologically nontrivial quasi-flat band is fractionally filled and then subject to strong interactions. The views, opinions and/or

  11. Strong Cosmic Censorship

    Science.gov (United States)

    Isenberg, James

    2017-01-01

    The Hawking-Penrose theorems tell us that solutions of Einstein's equations are generally singular, in the sense of the incompleteness of causal geodesics (the paths of physical observers). These singularities might be marked by the blowup of curvature and therefore crushing tidal forces, or by the breakdown of physical determinism. Penrose has conjectured (in his `Strong Cosmic Censorship Conjecture`) that it is generically unbounded curvature that causes singularities, rather than causal breakdown. The verification that ``AVTD behavior'' (marked by the domination of time derivatives over space derivatives) is generically present in a family of solutions has proven to be a useful tool for studying model versions of Strong Cosmic Censorship in that family. I discuss some of the history of Strong Cosmic Censorship, and then discuss what is known about AVTD behavior and Strong Cosmic Censorship in families of solutions defined by varying degrees of isometry, and discuss recent results which we believe will extend this knowledge and provide new support for Strong Cosmic Censorship. I also comment on some of the recent work on ``Weak Null Singularities'', and how this relates to Strong Cosmic Censorship.

  12. Covalent immobilization of Pseudomonas cepacia lipase on semiconducting materials

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez, Renny Edwin [Microelectronics and MEMS Laboratory, Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai (India)], E-mail: rennyedwin@gmail.com; Bhattacharya, Enakshi [Microelectronics and MEMS Laboratory, Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai (India)], E-mail: enakshi@ee.iitm.ac.in; Chadha, Anju [Department of Biotechnology, National Centre for Catalysis Research, Indian Institute of Technology Madras, Chennai (India)], E-mail: anjuc@iitm.ac.in

    2008-05-30

    Lipase from Pseudomonas cepacia was covalently immobilized on crystalline silicon, porous silicon and silicon nitride surfaces. The various stages of immobilization were characterized using FTIR (Fourier transform infrared) spectroscopy. The surface topography of the enzyme immobilized surfaces was investigated using scanning electron microscopy (SEM). The quantity of the immobilized active enzyme was estimated by the para-nitrophenyl palmitate (pNPP) assay. The immobilized lipase was used for triglyceride hydrolysis and the acid produced was detected by a pH sensitive silicon nitride surface as a shift in the C-V (capacitance-voltage) characteristics of an electrolyte-insulator-semiconductor capacitor (EISCAP) thus validating the immobilization method for use as a biosensor.

  13. Covalent Organic Framework Electrocatalysts for Clean Energy Conversion.

    Science.gov (United States)

    Lin, Chun-Yu; Zhang, Detao; Zhao, Zhenghang; Xia, Zhenhai

    2018-02-01

    Covalent organic frameworks (COFs) are promising for catalysis, sensing, gas storage, adsorption, optoelectricity, etc. owning to the unprecedented combination of large surface area, high crystallinity, tunable pore size, and unique molecular architecture. Although COFs are in their initial research stage, progress has been made in the design and synthesis of COF-based electrocatalysis for the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and CO 2 reduction in energy conversion and fuel generation. Design principles are also established for some of the COF materials toward rational design and rapid screening of the best electrocatalysts for a specific application. Herein, the recent advances in the design and synthesis of COF-based catalysts for clean energy conversion and storage are presented. Future research directions and perspectives are also being discussed for the development of efficient COF-based electrocatalysts. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Near universal support for covalent immobilisation of enzymes for biotechnology

    International Nuclear Information System (INIS)

    Elnashar, M.M.; Millner, P.A.; Gibson, T.D.

    2005-01-01

    Carrageenan [1], natural polymer, has been modified to be used as a universal/near universal support to immobilise enzymes, where the gel remained stable at 70 degree C for 24 h at a wide range of buffers and ph s and its mechanical strength was 400% greater than the unmodified gel. The new matrix successfully immobilised covalently eight commercially used enzymes including hydrolases, Upases, oxidoreductases, proteases and dehydrogenases. It also acted as a self buffering system in case of hydrolases and stopped enzyme's product inhibition. The apparent Km values of immobilised enzymes were found in many cases to be much less than those of the free enzymes. Another interesting correlation was observed where the great lowering of the apparent Km with immobilised enzymes was directly proportional to the substrate molecular weight. In economic terms, the new matrix is at least two orders of magnitude cheaper than supports such as Eupergit C

  15. Non-Covalent Organocatalyzed Domino Reactions Involving Oxindoles: Recent Advances

    Directory of Open Access Journals (Sweden)

    Tecla Gasperi

    2017-09-01

    Full Text Available The ubiquitous presence of spirooxindole architectures with several functionalities and stereogenic centers in bioactive molecules has been appealing for the development of novel methodologies seeking their preparation in high yields and selectivities. Expansion and refinement in the field of asymmetric organocatalysis have made possible the development of straightforward strategies that address these two requisites. In this review, we illustrate the current state-of-the-art in the field of spirooxindole synthesis through the use of non-covalent organocatalysis. We aim to provide a concise overview of very recent methods that allow to the isolation of unique, densely and diversified spirocyclic oxindole derivatives with high structural diversity via the use of cascade, tandem and domino processes.

  16. Prolonged and tunable residence time using reversible covalent kinase inhibitors.

    Science.gov (United States)

    Bradshaw, J Michael; McFarland, Jesse M; Paavilainen, Ville O; Bisconte, Angelina; Tam, Danny; Phan, Vernon T; Romanov, Sergei; Finkle, David; Shu, Jin; Patel, Vaishali; Ton, Tony; Li, Xiaoyan; Loughhead, David G; Nunn, Philip A; Karr, Dane E; Gerritsen, Mary E; Funk, Jens Oliver; Owens, Timothy D; Verner, Erik; Brameld, Ken A; Hill, Ronald J; Goldstein, David M; Taunton, Jack

    2015-07-01

    Drugs with prolonged on-target residence times often show superior efficacy, yet general strategies for optimizing drug-target residence time are lacking. Here we made progress toward this elusive goal by targeting a noncatalytic cysteine in Bruton's tyrosine kinase (BTK) with reversible covalent inhibitors. Using an inverted orientation of the cysteine-reactive cyanoacrylamide electrophile, we identified potent and selective BTK inhibitors that demonstrated biochemical residence times spanning from minutes to 7 d. An inverted cyanoacrylamide with prolonged residence time in vivo remained bound to BTK for more than 18 h after clearance from the circulation. The inverted cyanoacrylamide strategy was further used to discover fibroblast growth factor receptor (FGFR) kinase inhibitors with residence times of several days, demonstrating the generalizability of the approach. Targeting of noncatalytic cysteines with inverted cyanoacrylamides may serve as a broadly applicable platform that facilitates 'residence time by design', the ability to modulate and improve the duration of target engagement in vivo.

  17. Spin Labeling ESR Investigation of Covalently Bound Residues in Soil

    Science.gov (United States)

    Aleksandrova, Olga; Steinhoff, Heinz-Juergen; Klasmeier, Joerg; Schulz, Marcus; Matthies, Michael

    2013-04-01

    Organic xenobiotic chemicals, such as pesticides, biocides and veterinary pharmaceuticals, interact with soil, which results in the simultaneous formations of metabolites, mineralization products, and bound or non-extractable residues (NER). Substances or metabolites with reactive functional groups, such as aniline or phenol, have a tendency to give a larger proportion of NER. Despite numerous studies on NER, the majority of their chemical structures is still unknown. Reversible sequestration and irreversible formation of NER were also observed for veterinary antibiotic pharmaceuticals, after their application to soil with and without manure. For this purpose, we hypothesized a key role of specific functional groups of soil contaminants, via which contaminants are covalently bound to soil constituents, and advance a method of spin labeling ESR investigation of reaction products using a membrane method. Spin labels (SL) represent chemically stable paramagnetic molecules used as molecular labels and molecular probes for testing the covalent binding, structural properties, and molecular mobility of different physical, chemical, and biological systems. In the case of covalent binding of SL, their ESR spectra become broadened. We used stable nitroxide radicals (NR) as SL. These radicals modeled organic chemical contaminants and differed only in one functional group. The paramagnetic SL 4-Amino Tempo (4-amino-2,2,6,6-tetramethyl-1-piperidinylox) differed from Tempo (2,2,6,6-Tetramethylpiperidinooxy) in a substituent at the para-position of the piperidine ring, whereas Aniline Tempo (1-Piperidinyloxy, 2,2,6,-tetramethyl, 6-Aniline) differed from Tempo in an Aniline substituting one CH3 functional group. Before experimental analysis, we tested temporal changes in the concentration of both NR incubated with soil and found that the life-times of them in soil exceeded 3 days. We contaminated and labeled soil samples with NR, adding to soil the aqueous solution, which already

  18. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials.

    Science.gov (United States)

    Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Siegrist, Theo; Singh, David J

    2016-05-19

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionic and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. This different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.

  19. Covalent DNA-protein crosslinking occurs after hyperthermia and radiation

    International Nuclear Information System (INIS)

    Cress, A.E.; Bowden, G.T.

    1983-01-01

    Covalent DNA-protein crosslinks occur in exponentially growing mouse leukemia cells (L1210) after exposure to ionizing radiation. The amount of DNA-protein crosslinks as measured by a filter binding assay is dose dependent upon x irradiation. Although hyperthermia and radiation in combination are synergistic with respect to cell lethality, the combination does not result in an increase of DNA-protein crosslinks when assayed immediately following treatments. Hyperthermia (43 0 C/15 min) given prior to radiation dose not alter the radiation dose dependency of the amount of initial crosslinking. In addition, the amount of DNA-protein crosslinking produced by heat plus radiation is independent of the length of heating the cells at 43 0 C. The DNA-protein crosslinks produced y 50-Gy x ray alone are removed after 2 hr at 37 0 C. However, if hyperthermia (43 0 C/15 min) is given prior to 100-Gy x ray, the removal of DNA-protein crosslinks is delayed until 4.0 hr after radiation. Phospho-serine and phospho-threonine bonds are not produced with either radiation or the combination of hyperthermia plus radiation as judged by the resistance of the bonds to guanidine hydrochloride. However, hyperthermia plus radiation causes an increase in phosphate to nitrogen type bonding. These results show that radiation alone causes covalent DNA-protein crosslinks. Hyperthermia in combination with radiation does not increase the total amount of the crosslinks but delays the removal of the crosslinks and alters the distribution of the types of chemical bonding

  20. Strong Arcwise Connectedness

    OpenAIRE

    Espinoza, Benjamin; Gartside, Paul; Kovan-Bakan, Merve; Mamatelashvili, Ana

    2012-01-01

    A space is `n-strong arc connected' (n-sac) if for any n points in the space there is an arc in the space visiting them in order. A space is omega-strong arc connected (omega-sac) if it is n-sac for all n. We study these properties in finite graphs, regular continua, and rational continua. There are no 4-sac graphs, but there are 3-sac graphs and graphs which are 2-sac but not 3-sac. For every n there is an n-sac regular continuum, but no regular continuum is omega-sac. There is an omega-sac ...

  1. Abortion: Strong's counterexamples fail

    DEFF Research Database (Denmark)

    Di Nucci, Ezio

    2009-01-01

    This paper shows that the counterexamples proposed by Strong in 2008 in the Journal of Medical Ethics to Marquis's argument against abortion fail. Strong's basic idea is that there are cases--for example, terminally ill patients--where killing an adult human being is prima facie seriously morally......'s scenarios have some valuable future or admitted that killing them is not seriously morally wrong. Finally, if "valuable future" is interpreted as referring to objective standards, one ends up with implausible and unpalatable moral claims....

  2. Covalently bound conjugates of albumin and heparin: Synthesis, fractionation and characterization

    NARCIS (Netherlands)

    Hennink, Wim E.; Feijen, Jan; Ebert, Charles D.; Kim, Sung Wan

    1983-01-01

    Covalently bound conjugates of human serum albumin and heparin were prepared as compounds which could improve the blood-compatibility of polymer surfaces either by preadsorption or by covalent coupling of the conjugates onto blood contacting surfaces. The conjugates (10–16 weight % of heparin) were

  3. Covalently Immobilised Cytochrome C Imaged by In Situ Scanning Tunnelling Microscopy

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Olesen, Klaus G.; Danilov, Alexey I.

    1997-01-01

    In situ scanning tunnelling microscopy (STM) imaging of cytochrome c (cyt c) on polycrystalline Pt surfaces and on Au(lll) was achieved first by covalent immobilisation of 3-aminopropyltriethoxysilane (3-APTS) brought to react with oxide present on the Pt surfaces. Covalently bound 3-APTS forms...

  4. Covalent-ionically cross-linked polyetheretherketone proton exchange membrane for direct methanol fuel cell

    CSIR Research Space (South Africa)

    Luo, H

    2010-08-01

    Full Text Available In this paper, the proton exchange membrane prepared by covalent-ionically crosslinking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-pphenylene- oxa-p-phenylene-oxy-phenylene) (SsPEEK-WC) is reported. Compared with covalent...

  5. Application of the Covalent Bond Classification Method for the Teaching of Inorganic Chemistry

    Science.gov (United States)

    Green, Malcolm L. H.; Parkin, Gerard

    2014-01-01

    The Covalent Bond Classification (CBC) method provides a means to classify covalent molecules according to the number and types of bonds that surround an atom of interest. This approach is based on an elementary molecular orbital analysis of the bonding involving the central atom (M), with the various interactions being classified according to the…

  6. A novel fluorescence sensor based on covalent immobilization of 3-amino-9-ethylcarbazole by using silver nanoparticles as bridges and carriers.

    Science.gov (United States)

    Tan, Shu-Zhen; Hu, Yan-Jun; Gong, Fu-Chun; Cao, Zhong; Xia, Jiao-Yun; Zhang, Ling

    2009-03-23

    A novel technique of covalent immobilization of indicator dyes in the preparation of fluorescence sensors is developed. Silver nanoparticles are used as bridges and carriers for anchoring indicator dyes. 3-amino-9-ethylcarbazole (AEC) was employed as an example of indicator dyes with terminal amino groups and covalently immobilized onto the outmost surface of a quartz glass slide. First, the glass slide was functionalized by (3-mercaptopropyl) trimethoxysilane (MPS) to form a thiol-terminated self-assembled monolayer, where silver nanoparticles were strongly bound to the surface through covalent bonding. Then, 16-mercaptohexadecanoic acid (MHDA) was self-assembled to bring carboxylic groups onto the surface of silver nanoparticles. A further activation by using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) converted the carboxylic groups into succinimide esters. Finally, the active succinimide esters on the surface of silver nanoparticles were reacted with AEC. Thus, AEC was covalently bound to the glass slide and an AEC-immobilized sensor was obtained. The sensor exhibited very satisfactory reproducibility and reversibility, rapid response and no dye-leaching. Rutin can quench the fluorescence intensity of the sensor and be measured by using the sensor. The linear response of the sensor to rutin covers the range from 2.0 x 10(-6) to 1.5 x 10(-4) molL(-1) with a detection limit of 8.0 x 10(-7) molL(-1). The proposed technique may be feasible to the covalent immobilization of other dyes with primary amino groups.

  7. Towards 4th generation biomaterials: a covalent hybrid polymer-ormoglass architecture

    Science.gov (United States)

    Sachot, N.; Mateos-Timoneda, M. A.; Planell, J. A.; Velders, A. H.; Lewandowska, M.; Engel, E.; Castaño, O.

    2015-09-01

    Hybrid materials are being extensively investigated with the aim of mimicking the ECM microenvironment to develop effective solutions for bone tissue engineering. However, the common drawbacks of a hybrid material are the lack of interactions between the scaffold's constituents and the masking of its bioactive phase. Conventional hybrids often degrade in a non-homogeneous manner and the biological response is far from optimal. We have developed a novel material with strong interactions between constituents. The bioactive phase is directly exposed on its surface mimicking the structure of the ECM of bone. Here, polylactic acid electrospun fibers have been successfully and reproducibly coated with a bioactive organically modified glass (ormoglass, Si-Ca-P2 system) covalently. In comparison with the pure polymeric mats, the fibers obtained showed improved hydrophilicity and mechanical properties, bioactive ion release, exhibited a nanoroughness and enabled good cell adhesion and spreading after just one day of culture (rMSCs and rEPCs). The fibers were coated with different ormoglass compositions to tailor their surface properties (roughness, stiffness, and morphology) by modifying the experimental parameters. Knowing that cells modulate their behavior according to the exposed physical and chemical signals, the development of this instructive material is a valuable advance in the design of functional regenerative biomaterials.Hybrid materials are being extensively investigated with the aim of mimicking the ECM microenvironment to develop effective solutions for bone tissue engineering. However, the common drawbacks of a hybrid material are the lack of interactions between the scaffold's constituents and the masking of its bioactive phase. Conventional hybrids often degrade in a non-homogeneous manner and the biological response is far from optimal. We have developed a novel material with strong interactions between constituents. The bioactive phase is directly exposed

  8. Comparison of covalent and noncovalent immobilization of Malatya apricot pectinesterase (Prunus armeniaca L.).

    Science.gov (United States)

    Karakuş, Emine; Pekyardımcı, Sule

    2012-02-01

    Pectinesterase isolated from Malatya apricot pulp was noncovalently and covalently immobilized onto bentonite and glutaraldehyde-containing amino group functionalized porous glass beads surface at pH 8.0 and pH 9.0, respectively. The effect of various parameters such as pH, temperature, activation energy, heat and storage stability on immobilized enzyme were investigated. The optimum temperature of covalently and noncovalently immobilized PE was 50°C. This value was 60°C for free PE. Although optimum pH of covalently-immobilized PE was 8.0, this parameter was 9.0 for free and covalently-immobilized PE. The noncovalently immobilized enzyme exhibited better thermostability than the free and covalently immobilized PE.

  9. A strong comeback

    International Nuclear Information System (INIS)

    Marier, D.

    1992-01-01

    This article presents the results of a financial rankings survey which show a strong economic activity in the independent energy industry. The topics of the article include advisor turnover, overseas banks, and the increase in public offerings. The article identifies the top project finance investors for new projects and restructurings and rankings for lenders

  10. Strong Electroweak Symmetry Breaking

    CERN Document Server

    Grinstein, Benjamin

    2011-01-01

    Models of spontaneous breaking of electroweak symmetry by a strong interaction do not have fine tuning/hierarchy problem. They are conceptually elegant and use the only mechanism of spontaneous breaking of a gauge symmetry that is known to occur in nature. The simplest model, minimal technicolor with extended technicolor interactions, is appealing because one can calculate by scaling up from QCD. But it is ruled out on many counts: inappropriately low quark and lepton masses (or excessive FCNC), bad electroweak data fits, light scalar and vector states, etc. However, nature may not choose the minimal model and then we are stuck: except possibly through lattice simulations, we are unable to compute and test the models. In the LHC era it therefore makes sense to abandon specific models (of strong EW breaking) and concentrate on generic features that may indicate discovery. The Technicolor Straw Man is not a model but a parametrized search strategy inspired by a remarkable generic feature of walking technicolor,...

  11. Plasmons in strong superconductors

    International Nuclear Information System (INIS)

    Baldo, M.; Ducoin, C.

    2011-01-01

    We present a study of the possible plasmon excitations that can occur in systems where strong superconductivity is present. In these systems the plasmon energy is comparable to or smaller than the pairing gap. As a prototype of these systems we consider the proton component of Neutron Star matter just below the crust when electron screening is not taken into account. For the realistic case we consider in detail the different aspects of the elementary excitations when the proton, electron components are considered within the Random-Phase Approximation generalized to the superfluid case, while the influence of the neutron component is considered only at qualitative level. Electron screening plays a major role in modifying the proton spectrum and spectral function. At the same time the electron plasmon is strongly modified and damped by the indirect coupling with the superfluid proton component, even at moderately low values of the gap. The excitation spectrum shows the interplay of the different components and their relevance for each excitation modes. The results are relevant for neutrino physics and thermodynamical processes in neutron stars. If electron screening is neglected, the spectral properties of the proton component show some resemblance with the physical situation in high-T c superconductors, and we briefly discuss similarities and differences in this connection. In a general prospect, the results of the study emphasize the role of Coulomb interaction in strong superconductors.

  12. Hydrolytic Stability of Boronate Ester-Linked Covalent Organic Frameworks

    KAUST Repository

    Li, Huifang

    2018-01-30

    The stability of covalent organic frameworks (COFs) is essential to their applications. However, the common boronate ester-linked COFs are susceptible to attack by nucleophiles (such as water molecules) at the electron-deficient boron sites. To provide an understanding of the hydrolytic stability of the representative boronate ester-linked COF-5 and of the associated hydrolysis mechanisms, density functional theory (DFT) calculations were performed to characterize the hydrolysis reactions of the molecule formed by the condensation of 1,4-phenylenebis(boronic acid) (PBBA) and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) monomers; two cases were considered, one dealing with the freestanding molecule and the other with the molecule interacting with COF layers. It was found that the boronate ester (B–O) bond dissociation, which requires one H2O molecule, has a relatively high energy barrier of 22.3 kcal mol−1. However, the presence of an additional H2O molecule significantly accelerates hydrolysis by reducing the energy barrier by a factor of 3. Importantly, the hydrolysis of boronate ester bonds situated in a COF environment follows reaction pathways that are different and have increased energy barriers. These results point to an enhanced hydrolytic stability of COF-5 crystals.

  13. Electrophilicities and Protein Covalent Binding of Demethylation Metabolites of Colchicine.

    Science.gov (United States)

    Guo, Xiucai; Lin, Dongju; Li, Weiwei; Wang, Kai; Peng, Ying; Zheng, Jiang

    2016-03-21

    Colchicine, an alkaloid existing in plants of Liliaceous colchicum, has been widely used in the treatment of gout and familial Mediterranean fever. The administration of colchicine was found to cause liver injury in humans. The mechanisms of colchicine-induced liver toxicity remain unknown. The objectives of this study were to determine the electrophilicities of demethylation metabolites of colchicine and investigate the protein adductions derived from the reactive metabolites of colchicine. Four demethylated colchicine (1-, 2-, 3-, and 10-DMCs), namely, M1-M4, were detected in colchicine-fortified microsomal incubations. Four N-acetyl cysteine (NAC) conjugates (M5-M8) derived from colchicine were detected in the microsomes in the presence of NAC. M5 and M6 were derived from 10-DMC. M7 resulted from the reaction of 2-DMC or 3-DMC with NAC, and M8 originated from 10-DMC. Microsomal protein covalent binding was observed after exposure to colchicine. Two cysteine adducts (CA-1 and CA-2) derived from 10-DMC were found in proteolytically digested microsomal protein samples after incubation with colchicine. The findings allow us to define the chemical property of demethylation metabolites of colchicine and the interaction between protein and the reactive metabolites of colchicine generated in situ.

  14. Functionalization of silicone rubber for the covalent immobilization of fibronectin.

    Science.gov (United States)

    Völcker, N; Klee, D; Höcker, H; Langefeld, S

    2001-02-01

    Surface modification techniques were employed in order to provide functionalized silicone rubber with enhanced cytocompatibility. Acrylic acid (AAc), methacrylic acid (MAAc) and glycidylmethacrylate (GMA) were graft-co-polymerized onto the surface of silicone induced by an argon plasma and thermal initiation. The polymerizations were carried out in solution, in the case of acrylic acid a vapor phase graft-co-polymerization subsequent to argon plasma activation was carried out as well. Human fibronectin (hFn), which acts as a cell adhesion mediator for fibroblasts, was immobilized by making use of the generated carboxylic or epoxy groups, respectively. Surface analysis was accomplished by means of X-ray photoelectron spectroscopy (XPS), infrared spectroscopy in attenuated total reflection mode (IR-ATR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic contact angle measurements using the Wilhelmy-plate method. The amount of immobilized active hFn was semiquantified by enzyme-linked immunosorbent assay (ELISA) using a structure-specific antibody against the cell-binding domain of hFn. In vitro testing showed a remarkable difference between surfaces exposing adsorbed-only and surfaces with covalently immobilized hFn. Copyright 2001 Kluwer Academic Publishers

  15. Graphene magnetism induced by covalent adsorption of aromatic radicals.

    Science.gov (United States)

    Lin, He; Fratesi, Guido; Brivio, Gian Paolo

    2015-01-21

    We report a computational study of adsorption of aromatic radicals onto graphene, with the aim of understanding the effect of covalent molecular functionalization on the magnetic and structural properties of graphene. Our results show that the adsorption of an aromatic radical like phenyl also functionalized with donor or acceptor groups generates a band gap and two spin-dependent midgap states, one located above and the other below the Fermi energy of pristine graphene, which cause a net magnetic moment. Due to the interaction between the radical and graphene, we find that the carbon atom on the adsorption site is lifted out of the graphene plane, and its pz orbital is removed from the π band system, leaving the electrons in the other sublattice unpaired, which results in nonzero magnetism. But the band gap of the full system is insensitive to the different attached species and the midgap states are independent of the alignment of the molecular orbitals, so that the magnetic moment is the same for the various radicals studied. The net result of the radical adsorption is to have almost the same aromatic species as those in the gas phase but anchored on a surface.

  16. Anion binding in covalent and self-assembled molecular capsules.

    Science.gov (United States)

    Ballester, Pablo

    2010-10-01

    This critical review describes selected examples extracted from the extensive literature generated during the past 42 years on the topic of anion binding in molecular capsules. The goal of including anions in molecular capsules emerges from the idea of incorporating the traits exhibited by biological receptors into synthetic ones. At the outset of this research area the capsules were unimolecular. The scaffold of the receptor was designed to covalently link a series of functional groups that could converge into a cavity and to avoid its collapse. The initial examples involved the encapsulation of one monoatomic spherical anion. With time, the cavity size of the receptor was increased and encapsulation of polyatomic anions and co-encapsulation became a reality. Synthetic economy fueled the use of aggregates of self-complementary molecules rather than one large molecule as capsules. The main purpose of this review is to give a general overview of the topic which might be of interest to supramolecular or non supramolecular chemists alike (149 references).

  17. Covalently Bonded Chitosan on Graphene Oxide via Redox Reaction

    Directory of Open Access Journals (Sweden)

    Víctor M. Castaño

    2013-03-01

    Full Text Available Carbon nanostructures have played an important role in creating a new field of materials based on carbon. Chemical modification of carbon nanostructures through grafting has been a successful step to improve dispersion and compatibility in solvents, with biomolecules and polymers to form nanocomposites. In this sense carbohydrates such as chitosan are extremely valuable because their functional groups play an important role in diversifying the applications of carbon nanomaterials. This paper reports the covalent attachment of chitosan onto graphene oxide, taking advantage of this carbohydrate at the nanometric level. Grafting is an innovative route to modify properties of graphene, a two-dimensional nanometric arrangement, which is one of the most novel and promising nanostructures. Chitosan grafting was achieved by redox reaction using different temperature conditions that impact on the morphology and features of graphene oxide sheets. Transmission Electron Microscopy, Fourier Transform Infrared, Raman and Energy Dispersive spectroscopies were used to study the surface of chitosan-grafted-graphene oxide. Results show a successful modification indicated by the functional groups found in the grafted material. Dispersions of chitosan-grafted-graphene oxide samples in water and hexane revealed different behavior due to the chemical groups attached to the graphene oxide sheet.

  18. COVALENT IMMOBILIZATION OF INVERTASE ON EPOXY-ACTIVATED POLYANILINE FILMS

    Directory of Open Access Journals (Sweden)

    Loredana Vacareanu

    2013-08-01

    Full Text Available The growing interest in manufacturing and use of biosensors is their rapid and selective detection of the target analyte. The immobilization of the enzymes, onto the appropriate matrix is the key-step in the construction of biosensing devices, considerably affecting its performance. In this study, new polyaniline bearing epoxy groups was synthesized by electrochemical polymerization reactions, as adherent, green film deposited on electrode surface, and was further used as immobilization matrix for invertase enzyme. The immobilization was carried out by condensation reactions between the amino groups of the enzyme molecules and the epoxy groups of polyaniline film. The covalent attachment was achieved by simple immersing the epoxy-activated polyaniline in acetate buffer solution (10 mM, pH 6.0 containing 2mg/mL invertase, for 24 h at 4 ºC, by continuous stirring. The polyaniline films thus obtained were analyzed before and after the invertase attachment, by using FT-IR spectroscopy and SEM microscopy. The presence of the invertase was evaluated by measuring their activity, using UV-Vis spectroscopy, in the presence of a known amount of sucrose as a substrate. These tests, performed for three times under the same conditions, revealed that even after five washes of the polyaniline /invertase electrode to remove the unbounded enzyme, the enzyme remain attached on the polyaniline film, being able to hydrolyze the sucrose presented in the assay solutions.

  19. Self-Suspended Suspensions of Covalently Grafted Hairy Nanoparticles

    KAUST Repository

    Choudhury, Snehashis

    2015-03-17

    © 2015 American Chemical Society. Dispersions of small particles in liquids have been studied continuously for almost two centuries for their ability to simultaneously advance understanding of physical properties of fluids and their widespread use in applications. In both settings, the suspending (liquid) and suspended (solid) phases are normally distinct and uncoupled on long length and time scales. In this study, we report on the synthesis and physical properties of a novel family of covalently grafted nanoparticles that exist as self-suspended suspensions with high particle loadings. In such suspensions, we find that the grafted polymer chains exhibit unusual multiscale structural transitions and enhanced conformational stability on subnanometer and nanometer length scales. On mesoscopic length scales, the suspensions display exceptional homogeneity and colloidal stability. We attribute this feature to steric repulsions between grafted chains and the space-filling constraint on the tethered chains in the single-component self-suspended materials, which inhibits phase segregation. On macroscopic length scales, the suspensions exist as neat fluids that exhibit soft glassy rheology and, counterintuitively, enhanced elasticity with increasing temperature. This feature is discussed in terms of increased interpenetration of the grafted chains and jamming of the nanoparticles. (Chemical Presented).

  20. Extending density functional embedding theory for covalently bonded systems.

    Science.gov (United States)

    Yu, Kuang; Carter, Emily A

    2017-12-19

    Quantum embedding theory aims to provide an efficient solution to obtain accurate electronic energies for systems too large for full-scale, high-level quantum calculations. It adopts a hierarchical approach that divides the total system into a small embedded region and a larger environment, using different levels of theory to describe each part. Previously, we developed a density-based quantum embedding theory called density functional embedding theory (DFET), which achieved considerable success in metals and semiconductors. In this work, we extend DFET into a density-matrix-based nonlocal form, enabling DFET to study the stronger quantum couplings between covalently bonded subsystems. We name this theory density-matrix functional embedding theory (DMFET), and we demonstrate its performance in several test examples that resemble various real applications in both chemistry and biochemistry. DMFET gives excellent results in all cases tested thus far, including predicting isomerization energies, proton transfer energies, and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps for local chromophores. Here, we show that DMFET systematically improves the quality of the results compared with the widely used state-of-the-art methods, such as the simple capped cluster model or the widely used ONIOM method.

  1. Coval: improving alignment quality and variant calling accuracy for next-generation sequencing data.

    Directory of Open Access Journals (Sweden)

    Shunichi Kosugi

    Full Text Available Accurate identification of DNA polymorphisms using next-generation sequencing technology is challenging because of a high rate of sequencing error and incorrect mapping of reads to reference genomes. Currently available short read aligners and DNA variant callers suffer from these problems. We developed the Coval software to improve the quality of short read alignments. Coval is designed to minimize the incidence of spurious alignment of short reads, by filtering mismatched reads that remained in alignments after local realignment and error correction of mismatched reads. The error correction is executed based on the base quality and allele frequency at the non-reference positions for an individual or pooled sample. We demonstrated the utility of Coval by applying it to simulated genomes and experimentally obtained short-read data of rice, nematode, and mouse. Moreover, we found an unexpectedly large number of incorrectly mapped reads in 'targeted' alignments, where the whole genome sequencing reads had been aligned to a local genomic segment, and showed that Coval effectively eliminated such spurious alignments. We conclude that Coval significantly improves the quality of short-read sequence alignments, thereby increasing the calling accuracy of currently available tools for SNP and indel identification. Coval is available at http://sourceforge.net/projects/coval105/.

  2. The covalence effect of energy levels of ZnS:Mn2+

    International Nuclear Information System (INIS)

    Dong-Yang, Li; Mao-Lu, Du; Yi, Huang

    2013-01-01

    The contribution of the different covalence for t 2 and e orbitals must be considered in the investigation of the optical and magnetic properties of the transition metal ion in II–VI and III–V semiconductors. In present paper, two covalent parameters N t and N e associated with t 2 and e orbitals have been adopted to describe the covalence. The energy matrices considering the different covalence for t 2 and e orbitals have been provided for d 5 ions in crystal. These matrices show that the contribution from the Racah parameter A cannot be neglected in calculation of energy-level of d 5 ions in covalent crystal. The calculated results using the matrix show that the energy levels of 4 E and 4 A 1 states split, and the energy-level difference between 4 E and 4 A 1 states increases with increase of the different covalence between t 2 and e orbitals. These energy levels are always degenerate, when the different covalence for t 2 and e orbitals is neglected. By using the energy matrices, the energy-level of ZnS:Mn 2+ has been calculated. The calculated energy levels of ZnS:Mn 2+ are in good agreement with the experiments

  3. Reversible CO2 Capture by Conjugated Ionic Liquids through Dynamic Covalent Carbon-Oxygen Bonds.

    Science.gov (United States)

    Pan, Mingguang; Cao, Ningning; Lin, Wenjun; Luo, Xiaoyan; Chen, Kaihong; Che, Siying; Li, Haoran; Wang, Congmin

    2016-09-08

    The strong chemisorption of CO2 is always accompanied by a high absorption enthalpy, and traditional methods to reduce the absorption enthalpy lead to decreased CO2 capacities. Through the introduction of a large π-conjugated structure into the anion, a dual-tuning approach for the improvement of CO2 capture by anion-functionalized ionic liquids (ILs) resulted in a high capacity of up to 0.96 molCO2  mol-1IL and excellent reversibility. The increased capacity and improved desorption were supported by quantum chemical calculations, spectroscopic investigations, and thermogravimetric analysis. The increased capacity may be a result of the strengthened dynamic covalent bonds in these π-electron-conjugated structures through anion aggregation upon the uptake of CO2 , and the improved desorption originates from the charge dispersion of interaction sites through the large π-electron delocalization. These results provide important insights into effective strategies for CO2 capture. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. New biofuel integrating glycerol into its composition through the use of covalent immobilized pig pancreatic lipase.

    Science.gov (United States)

    Luna, Diego; Posadillo, Alejandro; Caballero, Verónica; Verdugo, Cristóbal; Bautista, Felipa M; Romero, Antonio A; Sancho, Enrique D; Luna, Carlos; Calero, Juan

    2012-01-01

    By using 1,3-specific Pig Pancreatic lipase (EC 3.1.1.3 or PPL), covalently immobilized on AlPO(4)/Sepiolite support as biocatalyst, a new second-generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol and other alcohols of low molecular weight. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a molar relation 2/1. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuel composition, has similar physicochemical properties compared to those of conventional biodiesel and also avoids the removal step of this by-product. The biocatalyst was found to be strongly fixed to the inorganic support (75%). Nevertheless, the efficiency of the immobilized enzyme was reduced to half (49.1%) compared to that of the free PPL. The immobilized enzyme showed a remarkable stability as well as a great reusability (more than 40 successive reuses) without a significant loss of its initial catalytic activity. Immobilized and free enzymes exhibited different reaction mechanisms, according to the different results in the Arrhenius parameters (Ln A and Ea). However, the use of supported PPL was found to be very suitable for the repetitive production of biofuel due to its facile recyclability from the reaction mixture.

  5. New Biofuel Integrating Glycerol into Its Composition Through the Use of Covalent Immobilized Pig Pancreatic Lipase

    Directory of Open Access Journals (Sweden)

    Carlos Luna

    2012-08-01

    Full Text Available By using 1,3-specific Pig Pancreatic lipase (EC 3.1.1.3 or PPL, covalently immobilized on AlPO4/Sepiolite support as biocatalyst, a new second-generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol and other alcohols of low molecular weight. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG blended in a molar relation 2/1. This novel product, which integrates glycerol as monoacylglycerols (MG into the biofuel composition, has similar physicochemical properties compared to those of conventional biodiesel and also avoids the removal step of this by-product. The biocatalyst was found to be strongly fixed to the inorganic support (75%. Nevertheless, the efficiency of the immobilized enzyme was reduced to half (49.1% compared to that of the free PPL. The immobilized enzyme showed a remarkable stability as well as a great reusability (more than 40 successive reuses without a significant loss of its initial catalytic activity. Immobilized and free enzymes exhibited different reaction mechanisms, according to the different results in the Arrhenius parameters (Ln A and Ea. However, the use of supported PPL was found to be very suitable for the repetitive production of biofuel due to its facile recyclability from the reaction mixture.

  6. Removal U(VI) from artificial seawater using facilely and covalently grafted polyacrylonitrile fibers with lysine

    Energy Technology Data Exchange (ETDEWEB)

    Li, Wenting; Liu, Qi; Liu, Jingyuan; Zhang, Hongsen; Li, Rumin; Li, Zhanshuang; Jing, Xiaoyan [Key Laboratory of Superlight Material and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin 150001 (China); Wang, Jun, E-mail: zhqw1888@sohu.com [Key Laboratory of Superlight Material and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin 150001 (China); Institute of Advanced Marine Materials, Harbin Engineering University, 150001 (China)

    2017-05-01

    Highlights: • Novel lysine modified fibrous adsorbents were prepared using a facile and green method. • PAN-Lys exhibited high adsorption activity and fast adsorption rate. • PAN-Lys significantly remove U(VI) from simulated seawater. - Abstract: Polyacrylonitrile fibers (PANF) covalently modified with lysine (PAN-Lys) was facilely synthesized and carefully characterized. The critical factors affecting U(VI) adsorption from aqueous solution were exploited, such as initial pH, contact time, concentration and temperature. The adsorption process is strongly dependent on solution pH. With excellent adsorption capacity and high affinity toward U(VI), the process for U(VI) is extremely rapid and the equilibrium can be reached within 20 min. The thermodynamics and kinetics were strictly evaluated. In addition, the hypothetical adsorption mechanisms were proposed. Moreover, the adsorption behavior at low concentrations (3–30 μg L{sup −1}) in simulated seawater was also investigated. Therefore, PAN-Lys can be potentially utilized for the efficient removal of U(VI) from seawater.

  7. Removal U(VI) from artificial seawater using facilely and covalently grafted polyacrylonitrile fibers with lysine

    International Nuclear Information System (INIS)

    Li, Wenting; Liu, Qi; Liu, Jingyuan; Zhang, Hongsen; Li, Rumin; Li, Zhanshuang; Jing, Xiaoyan; Wang, Jun

    2017-01-01

    Highlights: • Novel lysine modified fibrous adsorbents were prepared using a facile and green method. • PAN-Lys exhibited high adsorption activity and fast adsorption rate. • PAN-Lys significantly remove U(VI) from simulated seawater. - Abstract: Polyacrylonitrile fibers (PANF) covalently modified with lysine (PAN-Lys) was facilely synthesized and carefully characterized. The critical factors affecting U(VI) adsorption from aqueous solution were exploited, such as initial pH, contact time, concentration and temperature. The adsorption process is strongly dependent on solution pH. With excellent adsorption capacity and high affinity toward U(VI), the process for U(VI) is extremely rapid and the equilibrium can be reached within 20 min. The thermodynamics and kinetics were strictly evaluated. In addition, the hypothetical adsorption mechanisms were proposed. Moreover, the adsorption behavior at low concentrations (3–30 μg L −1 ) in simulated seawater was also investigated. Therefore, PAN-Lys can be potentially utilized for the efficient removal of U(VI) from seawater.

  8. Evidence for covalent attachment of phospholipid to the capsular polysaccharide of Haemophilus influenzae type b

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, J.S.; Doelling, V.W.; Graveline, J.F.; McCoy, D.W.

    1985-08-01

    Cells of Haemophilus influenzae type b were grown in a liquid medium containing (TH)palmitate or ( UC)ribose or both for two generations of exponential growth. Radiolabeled type-specific capsular polysaccharide, polyribosyl ribitol phosphate (PRP), was purified from the culture supernatant by Cetavlon precipitation, ethanol fractionation, and hydroxylapatite and Sepharose 4B chromatography. The doubly labeled ( (TH)palmitate and ( UC)ribose) PRP preparation was found to coelute in a single peak from a Sepharose 4B column, suggesting that both precursors were incorporated into the purified PRP. A singly labeled ( (TH)palmitate) purified PRP preparation was found to be quantitatively immune precipitated by human serum containing antibody against PRP. Only after acid, alkaline, or phospholipase A2 treatment of PRP labeled with (TH)palmitate or (TH)palmitate and ( UC)ribose followed by chloroform-methanol extraction could most of the TH-radioactivity be recovered in the organic phase. The chloroform-soluble acid-hydrolyzed or phospholipase A2-treated product was identified as palmitic acid after thin-layer chromatography. These results strongly suggest that a phospholipid moiety is covalently associated with the H. influenzae type b polysaccharide PRP.

  9. New Biofuel Integrating Glycerol into Its Composition Through the Use of Covalent Immobilized Pig Pancreatic Lipase

    Science.gov (United States)

    Luna, Diego; Posadillo, Alejandro; Caballero, Verónica; Verdugo, Cristóbal; Bautista, Felipa M.; Romero, Antonio A.; Sancho, Enrique D.; Luna, Carlos; Calero, Juan

    2012-01-01

    By using 1,3-specific Pig Pancreatic lipase (EC 3.1.1.3 or PPL), covalently immobilized on AlPO4/Sepiolite support as biocatalyst, a new second-generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol and other alcohols of low molecular weight. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a molar relation 2/1. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuel composition, has similar physicochemical properties compared to those of conventional biodiesel and also avoids the removal step of this by-product. The biocatalyst was found to be strongly fixed to the inorganic support (75%). Nevertheless, the efficiency of the immobilized enzyme was reduced to half (49.1%) compared to that of the free PPL. The immobilized enzyme showed a remarkable stability as well as a great reusability (more than 40 successive reuses) without a significant loss of its initial catalytic activity. Immobilized and free enzymes exhibited different reaction mechanisms, according to the different results in the Arrhenius parameters (Ln A and Ea). However, the use of supported PPL was found to be very suitable for the repetitive production of biofuel due to its facile recyclability from the reaction mixture. PMID:22949849

  10. Non-covalent interactions of cadmium sulphide and gold nanoparticles with DNA

    Science.gov (United States)

    Atay, Z.; Biver, T.; Corti, A.; Eltugral, N.; Lorenzini, E.; Masini, M.; Paolicchi, A.; Pucci, A.; Ruggeri, G.; Secco, F.; Venturini, M.

    2010-08-01

    Mercaptoethanol-capped CdS nanoparticles (CdSnp) and monohydroxy-(1-mercaptoundec-11-yl)tetraethylene-glycol-capped Au nanoparticles (Aunp) were synthesised, characterised and their interactions with DNA were investigated. Aunp are stable in different aqueous solvents, whereas CdSnp do precipitate in 0.1 M NaCl and form two different cluster types in 0.1 M NaNO3. As regards the CdSnp/DNA interaction, absorbance and fluorescence titrations, ethidium bromide displacement assays and gel electrophoresis experiments indicate that a non-covalent interaction between DNA and the CdSnp external surface does take place. The binding constant was evaluated to be equal to (2.2 ± 0.5) × 105 M-1. On the contrary, concerning Aunp, no direct interaction with DNA could be observed. Possible interaction with serum albumin was also checked, but no effects could be observed for either CdSnp or Aunp. Finally, short-time exposure of cultured cells to nanoparticles revealed the ability of CdSnp to enter the cells and allocate both in cytosol and nucleus, thus promoting cell proliferation at low concentration ( p resulted in a significant inhibition of cell growth, accompanied by apoptotic cell death. Aunp neither enter the cells, nor do affect cell proliferation. In conclusion, our data indicate that CdSnp can strongly interact with living cells and nucleic acid while no effects or interactions were observed for Aunp.

  11. Durable Anti-Superbug Polymers: Covalent Bonding of Ionic Liquid onto the Polymer Chains.

    Science.gov (United States)

    Guan, Jipeng; Wang, Yanyuan; Wu, Shilu; Li, Yongjin; Li, Jingye

    2017-12-11

    Here, we fabricated the ionic liquid (IL) grafted poly(vinylidene fluoride) (PVDF) (PVDF-g-IL) via electron-beam irradiation to fight common bacteria and multidrug-resistant "superbugs". Two types of ILs, 1-vinyl-3-butylimmidazolium chloride (IL (Cl)) and 1-vinyl-3-ethylimidazolium tetrafluoroborate (IL (BF 4 )), were used. It was found that the PVDF-g-IL exhibited superior antibacterial performance, with almost the same mechanical and thermal performance as unmodified PVDF. Nonwovens and films made from PVDF-g-IL materials exhibited broad-spectrum antimicrobial activity against common bacteria and "superbugs" with the strong electrostatic interactions between ILs and microbial cell membranes. With extremely low IL loading (0.05 wt %), the cell reduction of PVDF-g-IL (Cl) nonwovens improved from 0.2 to 4.4 against S. aureus. Moreover, the antibacterial activity of PVDF-g-IL nonwovens was permanent for the covalent bonds between ILs and polymer chains. The work provides a simple strategy to immobilize ionic antibacterial agents onto polymer substrates, which may have great potential applications in healthcare and household applications.

  12. Fabrication of cross-linked hydrazone covalent organic frameworks by click chemistry and application to solid phase microextraction.

    Science.gov (United States)

    Wu, Mingxue; Chen, Gang; Ma, Jiutong; Liu, Ping; Jia, Qiong

    2016-12-01

    Covalent organic frameworks (COFs) are an emerging class of porous organic frameworks with diverse promising applications. Herein, we presented the first example of cross-linked hydrazone COFs (cross-linked COFs) coating via thiol-ene click chemistry for solid phase microextraction (SPME). Strong covalent bonds and interlayer of the prepared networks ensured the adsorption capacity and durability of the novel SPME fiber. π-π conjugated structure existed because of abundant phenyl rings and -C=N groups in the cross-lined COFs. A series of characterizations indicated that the cross-linked COFs possessed large surface areas, high porosities and stabilities as well as hydrophobicities. The fiber was applied to SPME of pesticide residues coupled with gas chromatography with an electron capture detector (GC-ECD). Under the optimum experimental conditions, enhancement factors in the range of 2190-10,998 were obtained, illustrating that the cross-linked COFs possessed remarkable preconcentration ability. The low detection limits of 0.0003-0.0023ngkg -1 were achieved with relative standard deviations (RSDs) in the range of 3.4-7.6% (intra-batch) and 5.7-11.6% (inter-batch), respectively. Recovery values in the range of 78.2-107.0% were obtained when the SPME-GC method was applied to the analysis of pesticides in cucumber samples. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. Strong-coupling approximations

    International Nuclear Information System (INIS)

    Abbott, R.B.

    1984-03-01

    Standard path-integral techniques such as instanton calculations give good answers for weak-coupling problems, but become unreliable for strong-coupling. Here we consider a method of replacing the original potential by a suitably chosen harmonic oscillator potential. Physically this is motivated by the fact that potential barriers below the level of the ground-state energy of a quantum-mechanical system have little effect. Numerically, results are good, both for quantum-mechanical problems and for massive phi 4 field theory in 1 + 1 dimensions. 9 references, 6 figures

  14. Strong interaction and QFD

    International Nuclear Information System (INIS)

    Ebata, T.

    1981-01-01

    With an assumed weak multiplet structure for bosonic hadrons, which is consistent with the ΔI = 1/2 rule, it is shown that the strong interaction effective hamiltonian is compatible with the weak SU(2) x U(1) gauge transformation. Especially the rho-meson transforms as a triplet under SU(2)sub(w), and this is the origin of the rho-photon analogy. It is also shown that the existence of the non-vanishing Cabibbo angle is a necessary condition for the absence of the exotic hadrons. (orig.)

  15. Strong Coupling Holography

    CERN Document Server

    Dvali, Gia

    2009-01-01

    We show that whenever a 4-dimensional theory with N particle species emerges as a consistent low energy description of a 3-brane embedded in an asymptotically-flat (4+d)-dimensional space, the holographic scale of high-dimensional gravity sets the strong coupling scale of the 4D theory. This connection persists in the limit in which gravity can be consistently decoupled. We demonstrate this effect for orbifold planes, as well as for the solitonic branes and string theoretic D-branes. In all cases the emergence of a 4D strong coupling scale from bulk holography is a persistent phenomenon. The effect turns out to be insensitive even to such extreme deformations of the brane action that seemingly shield 4D theory from the bulk gravity effects. A well understood example of such deformation is given by large 4D Einstein term in the 3-brane action, which is known to suppress the strength of 5D gravity at short distances and change the 5D Newton's law into the four-dimensional one. Nevertheless, we observe that the ...

  16. Role of covalent defects on phonon softening in metallic carbon nanotubes.

    Science.gov (United States)

    Nguyen, Khoi T; Shim, Moonsub

    2009-05-27

    We have examined how electrical characteristics and charging dependent Raman G-band phonon softening in individual metallic carbon nanotubes are influenced by covalent defects. In addition to decreasing electrical conductance with increasing on/off current ratio eventually leading to semiconducting behavior, adding covalent defects reduces the degree of softening and broadening of longitudinal optical (LO) phonon mode of the G-band near the charge neutrality point where the bands cross. On the other hand, the transverse optical (TO) mode softening is enhanced by defects. Implications on the interpretation of Raman G-band phonon softening and on utilizing Raman spectroscopy to examine covalent functionalization are discussed.

  17. Novel covalently linked insulin dimer engineered to investigate the function of insulin dimerization

    DEFF Research Database (Denmark)

    Vinther, Tine N.; Norrman, Mathias; Strauss, Holger M.

    2012-01-01

    An ingenious system evolved to facilitate insulin binding to the insulin receptor as a monomer and at the same time ensure sufficient stability of insulin during storage. Insulin dimer is the cornerstone of this system. Insulin dimer is relatively weak, which ensures dissociation into monomers...... and insulin stability and function, we engineered a covalently linked insulin dimer in which two monomers were linked by a disulfide bond. The structure of this covalent dimer was identical to the self-association dimer of human insulin. Importantly, this covalent dimer was capable of further oligomerization...

  18. LIGO: The strong belief

    CERN Multimedia

    Antonella Del Rosso

    2016-01-01

    Twenty years of designing, building and testing a number of innovative technologies, with the strong belief that the endeavour would lead to a historic breakthrough. The Bulletin publishes an abstract of the Courier’s interview with Barry Barish, one of the founding fathers of LIGO.   The plots show the signals of gravitational waves detected by the twin LIGO observatories at Livingston, Louisiana, and Hanford, Washington. (Image: Caltech/MIT/LIGO Lab) On 11 February, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo collaborations published a historic paper in which they showed a gravitational signal emitted by the merger of two black holes. These results come after 20 years of hard work by a large collaboration of scientists operating the two LIGO observatories in the US. Barry Barish, Linde Professor of Physics, Emeritus at the California Institute of Technology and former Director of the Global Design Effort for the Internat...

  19. Covalent Crosslinking of Carbon Nanotube Materials for Improved Tensile Strength

    Science.gov (United States)

    Baker, James S.; Miller, Sandi G.; Williams, Tiffany A.; Meador, Michael A.

    2013-01-01

    Carbon nanotubes have attracted much interest in recent years due to their exceptional mechanical properties. Currently, the tensile properties of bulk carbon nanotube-based materials (yarns, sheets, etc.) fall far short of those of the individual nanotube elements. The premature failure in these materials under tensile load has been attributed to inter-tube sliding, which requires far less force than that needed to fracture individual nanotubes.1,2 In order for nanotube materials to achieve their full potential, methods are needed to restrict this tube-tube shear and increase inter-tube forces.Our group is examining covalent crosslinking between the nanotubes as a means to increase the tensile properties of carbon nanotube materials. We are working with multi-walled carbon nanotube (MWCNT) sheet and yarn materials obtained from commercial sources. Several routes to functionalize the nanotubes have been examined including nitrene, aryl diazonium, and epoxide chemistries. The functional nanotubes were crosslinked through small molecule or polymeric bridges. Additionally, electron beam irradiation induced crosslinking of the non-functional and functional nanotube materials was conducted. For example, a nanotube sheet material containing approximately 3.5 mol amine functional groups exhibited a tensile strength of 75 MPa and a tensile modulus of 1.16 GPa, compared to 49 MPa and 0.57 GPa, respectively, for the as-received material. Electron beam irradiation (2.2x 1017 ecm2) of the same amine-functional sheet material further increased the tensile strength to 120 MPa and the modulus to 2.61 GPa. This represents approximately a 150 increase in tensile strength and a 360 increase in tensile modulus over the as-received material with only a 25 increase in material mass. Once we have optimized the nanotube crosslinking methods, the performance of these materials in polymer matrix composites will be evaluated.

  20. Covalent immobilization of antimicrobial peptides (AMPs) onto biomaterial surfaces.

    Science.gov (United States)

    Costa, Fabíola; Carvalho, Isabel F; Montelaro, Ronald C; Gomes, P; Martins, M Cristina L

    2011-04-01

    Bacterial adhesion to biomaterials remains a major problem in the medical devices field. Antimicrobial peptides (AMPs) are well-known components of the innate immune system that can be applied to overcome biofilm-associated infections. Their relevance has been increasing as a practical alternative to conventional antibiotics, which are declining in effectiveness. The recent interest focused on these peptides can be explained by a group of special features, including a wide spectrum of activity, high efficacy at very low concentrations, target specificity, anti-endotoxin activity, synergistic action with classical antibiotics, and low propensity for developing resistance. Therefore, the development of an antimicrobial coating with such properties would be worthwhile. The immobilization of AMPs onto a biomaterial surface has further advantages as it also helps to circumvent AMPs' potential limitations, such as short half-life and cytotoxicity associated with higher concentrations of soluble peptides. The studies discussed in the current review report on the impact of covalent immobilization of AMPs onto surfaces through different chemical coupling strategies, length of spacers, and peptide orientation and concentration. The overall results suggest that immobilized AMPs may be effective in the prevention of biofilm formation by reduction of microorganism survival post-contact with the coated biomaterial. Minimal cytotoxicity and long-term stability profiles were obtained by optimizing immobilization parameters, indicating a promising potential for the use of immobilized AMPs in clinical applications. On the other hand, the effects of tethering on mechanisms of action of AMPs have not yet been fully elucidated. Therefore, further studies are recommended to explore the real potential of immobilized AMPs in health applications as antimicrobial coatings of medical devices. Copyright © 2010 Acta Materialia Inc. All rights reserved.

  1. Spin Labeling ESR Investigation of a Role of Humic Acids at Covalent Binding of Xenobiotics to Soil

    Science.gov (United States)

    Aleksandrova, Olga

    2014-05-01

    The environmental risk of organic xenobiotic chemicals released into soils is controlled by their sorption and binding processes. However, the molecular mechanisms of reversible and irreversible interactions of xenobiotics with soil constituents and an influence of humic substances on this interaction are only partly understood. New methods and approaches aimed at understanding of molecular mechanisms in the soil environment and a role of humic substances in the sorption and binding processes are today required to manage and keep the quality of soil used and fertilized in agricultural industry. The paper presents a new approach of using stable ESR spin labels to investigate a role of humic substances in the interactions of organic xenobiotic chemicals with constituents of natural soil via the typical functional groups of xenobiotics, such as Amines. At the experiment, the nitroxide spin labels, such as TEMPO (2,2,6,6-Tetramethylpiperidin-1-oxyl), Amino-TEMPO (4-amino-2,2,6,6-Tetramethylpiperidin-1-oxyl) and Aniline spin labels (2,5,5-Trimethyl-2-(3-aminophenyl)pyrrolidin-1-oxyl), were added to samples of different natural soils, such luvisol, cambisol and chernozem. Amino-TEMPO and Aniline spin labels include the aliphatic amino and aromatic amino functional groups, respectively. A significant broadening of the ESR spectrum of Aniline spin labels incubated in different soils indicated a stable effect of covalent binding of the spin labels to soil constituents via the aromatic amino, whereas the ESR spectra of the other two spin labels were not broadened that pointed at the absence of covalent binding of spin labels via the aliphatic amino. As shown, a part of bound spin labels via the aromatic amino increased with increasing of the concentration of humic acids in soil. The same broadened signals were also be detected with the humic acids extracted from the investigated soils. A strong covalent binding of spin labels to humic substances via the aromatic amines was

  2. Use of Functionalized Carbon Nanotubes for Covalent Attachment of Nanotubes to Silicon

    Science.gov (United States)

    Tour, James M.; Dyke, Christopher A.; Maya, Francisco; Stewart, Michael P.; Chen, Bo; Flatt, Austen K.

    2012-01-01

    The purpose of the invention is to covalently attach functionalized carbon nanotubes to silicon. This step allows for the introduction of carbon nanotubes onto all manner of silicon surfaces, and thereby introduction of carbon nano - tubes covalently into silicon-based devices, onto silicon particles, and onto silicon surfaces. Single-walled carbon nanotubes (SWNTs) dispersed as individuals in surfactant were functionalized. The nano - tube was first treated with 4-t-butylbenzenediazonium tetrafluoroborate to give increased solubility to the carbon nanotube; the second group attached to the sidewall of the nanotube has a silyl-protected terminal alkyne that is de-protected in situ. This gives a soluble carbon nanotube that has functional groups appended to the sidewall that can be attached covalently to silicon. This reaction was monitored by UV/vis/NJR to assure direct covalent functionalization.

  3. Construction and repair of highly ordered 2D covalent networks by chemical equilibrium regulation.

    Science.gov (United States)

    Guan, Cui-Zhong; Wang, Dong; Wan, Li-Jun

    2012-03-21

    The construction of well-ordered 2D covalent networks via the dehydration of di-borate aromatic molecules was successfully realized through introducing a small amount of water into a closed reaction system to regulate the chemical equilibrium.

  4. Covalent organic polymer functionalization of activated carbon surfaces through acyl chloride for environmental clean-up

    DEFF Research Database (Denmark)

    Mines, Paul D.; Thirion, Damien; Uthuppu, Basil

    2017-01-01

    Nanoporous networks of covalent organic polymers (COPs) are successfully grafted on the surfaces of activated carbons, through a series of surface modification techniques, including acyl chloride formation by thionyl chloride. Hybrid composites of activated carbon functionalized with COPs exhibit...

  5. SbcCD-Mediated Processing of Covalent Gyrase-DNA Complex in Escherichia coli

    OpenAIRE

    Aedo, Sandra; Tse-Dinh, Yuk-Ching

    2013-01-01

    Quinolones trap the covalent gyrase-DNA complex in Escherichia coli, leading to cell death. Processing activities for trapped covalent complex have not been characterized. A mutant strain lacking SbcCD nuclease activity was examined for both accumulation of gyrase-DNA complex and viability after quinolone treatment. Higher complex levels were found in ΔsbcCD cells than in wild-type cells after incubation with nalidixic acid and ciprofloxacin. However, SbcCD activity protected cells against th...

  6. The Chemistry and Biochemistry of Heme c: Functional Bases for Covalent Attachment

    OpenAIRE

    Bowman, Sarah E. J.; Bren, Kara L.

    2008-01-01

    A discussion of the literature concerning the synthesis, function, and activity of heme c-containing proteins is presented. Comparison of the properties of heme c, which is covalently bound to protein, is made to heme b, which is bound noncovalently. A question of interest is why nature uses biochemically expensive heme c in many proteins when its properties are expected to be similar to heme b. Considering the effects of covalent heme attachment on heme conformation and on the proximal histi...

  7. Covalently Bonded Three-Dimensional Carbon Nanotube Solids via Boron Induced Nanojunctions

    Science.gov (United States)

    2012-04-13

    Novel Carbon Morphologies : From Covalent Y-Junctions to Sea - Urchin -Like Structures. Adv. Func. Mater. 19, 1193–1199 (2009). 15. Sumpter, B. G. et al...between carbon nanotubes (CNTs) and the modification of their straight tubular morphology are two strategies needed to successfully synthesize...nitrogen or sulfur can also induce dramatic tubule morphology changes in CNTs, including covalent multi-junctions12–15, however never were these

  8. John Strong (1941 - 2006)

    CERN Multimedia

    Wickens, F

    Our friend and colleague John Strong was cruelly taken from us by a brain tumour on Monday 31st July, a few days before his 65th birthday John started his career working with a group from Westfield College, under the leadership of Ted Bellamy. He obtained his PhD and spent the early part of his career on experiments at Rutherford Appleton Laboratory (RAL), but after the early 1970s his research was focussed on experiments in CERN. Over the years he made a number of notable contributions to experiments in CERN: The Omega spectrometer adopted a system John had originally developed for experiments at RAL using vidicon cameras to record the sparks in the spark chambers; He contributed to the success of NA1 and NA7, where he became heavily involved in the electronic trigger systems; He was responsible for the second level trigger system for the ALEPH detector and spent five years leading a team that designed and built the system, which ran for twelve years with only minor interventions. Following ALEPH he tur...

  9. Stirring Strongly Coupled Plasma

    CERN Document Server

    Fadafan, Kazem Bitaghsir; Rajagopal, Krishna; Wiedemann, Urs Achim

    2009-01-01

    We determine the energy it takes to move a test quark along a circle of radius L with angular frequency w through the strongly coupled plasma of N=4 supersymmetric Yang-Mills (SYM) theory. We find that for most values of L and w the energy deposited by stirring the plasma in this way is governed either by the drag force acting on a test quark moving through the plasma in a straight line with speed v=Lw or by the energy radiated by a quark in circular motion in the absence of any plasma, whichever is larger. There is a continuous crossover from the drag-dominated regime to the radiation-dominated regime. In the crossover regime we find evidence for significant destructive interference between energy loss due to drag and that due to radiation as if in vacuum. The rotating quark thus serves as a model system in which the relative strength of, and interplay between, two different mechanisms of parton energy loss is accessible via a controlled classical gravity calculation. We close by speculating on the implicati...

  10. Strong-interaction nonuniversality

    International Nuclear Information System (INIS)

    Volkas, R.R.; Foot, R.; He, X.; Joshi, G.C.

    1989-01-01

    The universal QCD color theory is extended to an SU(3) 1 direct product SU(3) 2 direct product SU(3) 3 gauge theory, where quarks of the ith generation transform as triplets under SU(3)/sub i/ and singlets under the other two factors. The usual color group is then identified with the diagonal subgroup, which remains exact after symmetry breaking. The gauge bosons associated with the 16 broken generators then form two massive octets under ordinary color. The interactions between quarks and these heavy gluonlike particles are explicitly nonuniversal and thus an exploration of their physical implications allows us to shed light on the fundamental issue of strong-interaction universality. Nonuniversality and weak flavor mixing are shown to generate heavy-gluon-induced flavor-changing neutral currents. The phenomenology of these processes is studied, as they provide the major experimental constraint on the extended theory. Three symmetry-breaking scenarios are presented. The first has color breaking occurring at the weak scale, while the second and third divorce the two scales. The third model has the interesting feature of radiatively induced off-diagonal Kobayashi-Maskawa matrix elements

  11. Effective Acetylene/Ethylene Separation at Ambient Conditions by a Pigment-Based Covalent-Triazine Framework

    KAUST Repository

    Lu, Yue

    2017-10-24

    A novel covalent-triazine framework (CTF-PO71) is designed and prepared from an organic pigment molecule for high-performance gas separation. The functional sites with different electrostatic potentials on the pore surface of CTF-PO71 demonstrate a strong interaction between C2H2 and CTF-PO71 to achieve preferential adsorption of C2H2 over C2H4, thus enabling effective capture of a trace amount of C2H2 from the gas mixture. This is the first organic porous polymer that is capable of separating C2H2 and C2H4. The commercial availability and the low cost of the pigment as well as the high stability of the resultant framework endow CTF-PO71 with a significant potential for practical applications.

  12. Non-covalently functionalized carbon nanostructures for synthesizing carbon-based hybrid nanomaterials.

    Science.gov (United States)

    Li, Haiqing; Song, Sing I; Song, Ga Young; Kim, Il

    2014-02-01

    Carbon nanostructures (CNSs) such as carbon nanotubes, graphene sheets, and nanodiamonds provide an important type of substrate for constructing a variety of hybrid nanomaterials. However, their intrinsic chemistry-inert surfaces make it indispensable to pre-functionalize them prior to immobilizing additional components onto their surfaces. Currently developed strategies for functionalizing CNSs include covalent and non-covalent approaches. Conventional covalent treatments often damage the structure integrity of carbon surfaces and adversely affect their physical properties. In contrast, the non-covalent approach offers a non-destructive way to modify CNSs with desired functional surfaces, while reserving their intrinsic properties. Thus far, a number of surface modifiers including aromatic compounds, small-molecular surfactants, amphiphilic polymers, and biomacromolecules have been developed to non-covalently functionalize CNS surfaces. Mediated by these surface modifiers, various functional components such as organic species and inorganic nanoparticles were further decorated onto their surfaces, resulting in versatile carbon-based hybrid nanomaterials with broad applications in chemical engineering and biomedical areas. In this review, the recent advances in the generation of such hybrid nanostructures based on non-covalently functionalized CNSs will be reviewed.

  13. Cysteinome: The first comprehensive database for proteins with targetable cysteine and their covalent inhibitors.

    Science.gov (United States)

    Wu, Sijin; Luo Howard, Huizhe; Wang, Haina; Zhao, Weijie; Hu, Qiwan; Yang, Yongliang

    2016-09-23

    The covalent modification of intrinsically nucleophilic cysteine in proteins is crucial for diverse biochemical events. Bioinformatics approaches may prove useful in the design and discovery of covalent molecules targeting the cysteine in proteins to tune their functions and activities. Herein, we describe the Cysteinome, the first online database that provides a rich resource for the display, search and analysis of structure, function and related annotation for proteins with targetable cysteine as well as their covalent modulators. To this end, Cysteinome compiles 462 proteins with targetable cysteine from 122 different species along with 1217 covalent modulators curated from existing literatures. Proteins are annotated with a detailed description of protein families, biological process and related diseases. In addition, covalent modulators are carefully annotated with chemical name, chemical structure, binding affinity, physicochemical properties, molecule type and related diseases etc. The Cysteinome database may serve as a useful platform for the identification of crucial proteins with targetable cysteine in certain cellular context. Furthermore, it may help biologists and chemists for the design and discovery of covalent chemical probes or inhibitors homing at functional cysteine of critical protein targets implicated in various physiological or disease process. The Cysteinome database is freely available to public at http://www.cysteinome.org/. Copyright © 2016. Published by Elsevier Inc.

  14. N-Epoxypropyl poly(p-phenylene terephthalamide) covalently and non-covalently coated multi-walled carbon nanotubes for PVC reinforcement

    Science.gov (United States)

    Pan, Fangwei; Qu, Rongjun; Jia, Xinhua; Sun, Changmei; Sun, Hushan; An, Kai; Mu, Yinglei; Ji, Chunnuan; Yin, Ping; Zhang, Ying

    2017-09-01

    Poly(p-phenylene terephthalamide) (PPTA) coated multi-walled carbon nanotubes (PPTA-MWNTs) showed an enhancement effect on the yield strength and Young's modulus of PVC composite films, but no improvement in toughness. In this paper, MWNTs were covalently and non-covalently coated by N-epoxypropyl PPTA (PPTA-ECH) to prepare PPTA-ECH-MWNTs-NH2-x and PPTA-ECH-MWNTs-x, which were used as additives to reinforce PVC composite films. It was found that the maximum yield strength, Young's modulus, and toughness of PPTA-ECH-MWNTs-NH2-x/PVC composite films increased by 227.84%, 201.56%, and 589.96%, respectively, in comparison to pure PVC, while those of PPTA-ECH-MWNTs-x/PVC composite films increased by 215.08%, 153.13%, and 540.81%, respectively. The maximum yield strength, maximum Young's modulus, and maximum toughness of both PPTA-ECH-MWNTs-NH2-x/PVC and PPTA-ECH-MWNTs-x/PVC showed significant improvement as compared to PPTA-MWNTs/PVC composite film and PPTA-MWNTs-NH2/PVC. This indicates that N-epoxypropyl PPTA covalently and non-covalently coated MWNTs are promising additives for reinforcing PVC.

  15. Reversible Covalent Reaction of Levosimendan with Cardiac Troponin C in Vitro and in Situ.

    Science.gov (United States)

    Klein, Brittney A; Reiz, Béla; Robertson, Ian M; Irving, Malcolm; Li, Liang; Sun, Yin-Biao; Sykes, Brian D

    2018-04-17

    The development of calcium sensitizers for the treatment of systolic heart failure presents difficulties, including judging the optimal efficacy and the specificity to target cardiac muscle. The thin filament is an attractive target because cardiac troponin C (cTnC) is the site of calcium binding and the trigger for subsequent contraction. One widely studied calcium sensitizer is levosimendan. We have recently shown that when a covalent cTnC-levosimendan analogue is exchanged into cardiac muscle cells, they become constitutively active, demonstrating the potency of a covalent complex. We have also demonstrated that levosimendan reacts in vitro to form a reversible covalent thioimidate bond specifically with cysteine 84, unique to cTnC. In this study, we use mass spectrometry to show that the in vitro mechanism of action of levosimendan is consistent with an allosteric, reversible covalent inhibitor; to determine whether the presence of the cTnI switch peptide or changes in either Ca 2+ concentration or pH modify the reaction kinetics; and to determine whether the reaction can occur with cTnC in situ in cardiac myofibrils. Using the derived kinetic rate constants, we predict the degree of covalently modified cTnC in vivo under the conditions studied. We observe that covalent bond formation would be highest under the acidotic conditions resulting from ischemia and discuss whether the predicted level could be sufficient to have therapeutic value. Irrespective of the in vivo mechanism of action for levosimendan, our results provide a rationale and basis for the development of reversible covalent drugs to target the failing heart.

  16. Photoactive Zn(II)Porphyrin–multi-walled carbon nanotubes nanohybrids through covalent β-linkages

    Energy Technology Data Exchange (ETDEWEB)

    Lipińska, Monika E., E-mail: m.e.lipinska@gmail.com [REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto (Portugal); Rebelo, Susana L.H., E-mail: susana.rebelo@fc.up.pt [REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto (Portugal); Pereira, M. Fernando R., E-mail: fpereira@fe.up.pt [Laboratório de Catálise e Materiais (LCM), Laboratório Associado LSRE/LCM, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto (Portugal); Figueiredo, José L., E-mail: jlfig@fe.up.pt [Laboratório de Catálise e Materiais (LCM), Laboratório Associado LSRE/LCM, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto (Portugal); Freire, Cristina, E-mail: acfreire@fc.up.pt [REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto (Portugal)

    2013-12-16

    Donor–acceptor nanohybrids by a covalent linkage between the β-position of a Zn(II)Porphyrin and multi-walled carbon nanotubes are reported for the first time, in a closer analogy to the natural light harvesting systems, which are based on β-substituted porphyrinoid structures, the chlorophylls. An unique and direct connection was established through the immobilization of the Zn(II)(β-NH{sub 2}-tetraphenylporphyrin), using diazonium chemistry, in order to afford i) a short and conjugated linkage between the two aromatic systems and ii) an amide bond resulting from a three-step functionalization synthesis. Electronic and steady-state fluorescence spectroscopies confirmed high photoinduced electron communication through the β-linkage when compared to analogous meso-phenyl linkers, stating its positive effect. The procedure involving the amide linkage allowed higher chromophore loadings; however, the direct conjugated bond showed improved photoinduced activity and a different emission pattern that can be associated with intense communication within the expanded π-system MWCNT–metalloporphyrin. - Graphical abstract: Preparation and photo-induced activity of two donor–acceptor nanohybrids is reported based on different linkages through β-position of porphyrin core to MWCNT, direct conjugation and amide bond. - Highlights: • β-linked Zn(II)Porphyrin–MWCNT nanohybrids were prepared through direct or amide bond. • Efficient and mild functionalizations were achieved using diazonium chemistry. • Good nanohybrid dispersibility was obtained in low boiling point solvent. • Nanohybrids showed strong photoinduced electronic transfer. • The emission quenching was higher for the π-expanded system.

  17. The significant role of covalency in determining the ground state of cobalt phthalocyanines molecule

    Directory of Open Access Journals (Sweden)

    Jing Zhou

    2016-03-01

    Full Text Available To shed some light on the metal 3d ground state configuration of cobalt phthalocyanines system, so far in debate, we present an investigation by X-ray absorption spectroscopy (XAS at Co L2,3 edge and theoretical calculation. The density functional theory calculations reveal highly anisotropic covalent bond between central cobalt ion and nitrogen ligands, with the dominant σ donor accompanied by weak π-back acceptor interaction. Our combined experimental and theoretical study on the Co-L2,3 XAS spectra demonstrate a robust ground state of 2A1g symmetry that is built from 73% 3d7 character and 27% 3 d 8 L ¯ ( L ¯ denotes a ligand hole components, as the first excited-state with 2Eg symmetry lies about 158 meV higher in energy. The effect of anisotropic and isotropic covalency on the ground state was also calculated and the results indicate that the ground state with 2A1g symmetry is robust in a large range of anisotropic covalent strength while a transition of ground state from 2A1g to 2Eg configuration when isotropic covalent strength increases to a certain extent. Here, we address a significant anisotropic covalent effect of short Co(II-N bond on the ground state and suggest that it should be taken into account in determining the ground state of analogous cobalt complexes.

  18. The significant role of covalency in determining the ground state of cobalt phthalocyanines molecule

    Science.gov (United States)

    Zhou, Jing; Zhang, Linjuan; Hu, Zhiwei; Kuo, Changyang; Liu, Hengjie; Lin, Xiao; Wang, Yu; Pi, Tun-Wen; Wang, Jianqiang; Zhang, Shuo

    2016-03-01

    To shed some light on the metal 3d ground state configuration of cobalt phthalocyanines system, so far in debate, we present an investigation by X-ray absorption spectroscopy (XAS) at Co L2,3 edge and theoretical calculation. The density functional theory calculations reveal highly anisotropic covalent bond between central cobalt ion and nitrogen ligands, with the dominant σ donor accompanied by weak π-back acceptor interaction. Our combined experimental and theoretical study on the Co-L2,3 XAS spectra demonstrate a robust ground state of 2A1g symmetry that is built from 73% 3d7 character and 27% 3 d 8 L ¯ ( L ¯ denotes a ligand hole) components, as the first excited-state with 2Eg symmetry lies about 158 meV higher in energy. The effect of anisotropic and isotropic covalency on the ground state was also calculated and the results indicate that the ground state with 2A1g symmetry is robust in a large range of anisotropic covalent strength while a transition of ground state from 2A1g to 2Eg configuration when isotropic covalent strength increases to a certain extent. Here, we address a significant anisotropic covalent effect of short Co(II)-N bond on the ground state and suggest that it should be taken into account in determining the ground state of analogous cobalt complexes.

  19. Breaking the dogma: PCB-derived semiquinone free radicals do not form covalent adducts with DNA, GSH, and amino acids.

    Science.gov (United States)

    Wangpradit, Orarat; Rahaman, Asif; Mariappan, S V Santhana; Buettner, Garry R; Robertson, Larry W; Luthe, Gregor

    2016-02-01

    Covalent bond formations of free radical metabolites with biomolecules like DNA and proteins are thought to constitute a major mechanism of toxicity and carcinogenesis. Glutathione (GSH) is generally accepted as a radical scavenger protecting the cell. In the present study, we investigated a semiquinone radical (SQ(●-)) metabolite of the semivolatile 4-chlorobiphenyl, using electron paramagnetic resonance spectroscopy, and oxygen consumption. Proton nuclear magnetic resonance ((1)H NMR) and liquid chromatography-mass spectrometry (LC-MS) were also employed to elucidate the radical interaction with DNA, amino acids, and GSH. We found that DNA and oligonucleotides stabilized SQ(●-) by electron delocalization in the π-stacking system, resulting in persistent radical intercalated, rather than forming a covalent bond with SQ(●-). This finding was strongly supported by the semiempirical calculation of the semioccupied molecular orbital and the linear combination of the atomic orbitals, indicating 9.8 kcal mol(-1) energy gain. The insertion of SQ(●-) into the DNA strand may result in DNA strand breaks and interruption of DNA replication process or even activate radical mediated secondary reactions. The presence of amino acids resulted in a decrease of the electron paramagnetic resonance (EPR) signal of SQ(●-) and correlated with their isoelectric points. The pH shifts the equilibrium of the dianions of hydroquinone and influenced indirectly the formation of SQ(●-). Similar findings were observed with GSH and Cys. GSH and Cys functioned as indirect radical scavengers; their activities depend on their chemical equilibria with the corresponding quinones, and their further reaction via Michael addition. The generally accepted role of GSH as radical scavenger in biological systems should be reconsidered based upon these findings, questioning the generally accepted view of radical interaction of semiquinones with biologically active compounds, like DNA, amino acids

  20. Covalent Organic Frameworks and Cage Compounds: Design and Applications of Polymeric and Discrete Organic Scaffolds.

    Science.gov (United States)

    Beuerle, Florian; Gole, Bappaditya

    2017-12-05

    Porous organic materials are an emerging class of functional nanostructures with unprecedented properties. Dynamic covalent assembly of small organic building blocks under thermodynamic control is utilized for the intriguingly simple formation of complex molecular architectures in one-pot procedures. In this review, we aim to analyze the basic design principles that govern the formation of either covalent organic frameworks as crystalline porous polymers or covalent organic cage compounds as shape-persistent molecular objects. Common synthetic protocols and characterization techniques will be discussed besides more advanced strategies such as postsynthetic modification or self-sorting. When appropriate, healthy comparisons are drawn between polymeric frameworks and discrete organic cages considering their underlying properties. Furthermore, we highlight the potential of these materials for applications ranging from gas storage to catalysis or organic electronics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. How covalence breaks adsorption-energy scaling relations and solvation restores them

    DEFF Research Database (Denmark)

    Vallejo, Federico Calle; Krabbe, Alexander; García Lastra, Juan Maria

    2017-01-01

    of those adsorbates on the metal centers Cr, Mn, Fe, Co, Ni and Cu, using H, F, OH, NH2, CH3, and BH2 as ring ligands. We show that covalence systematically breaks scaling relations under vacuum by strengthening certain M-OOH bonds. However, covalence modifies adsorbate solvation in solution depending...... on the degree of covalence of the metal-adsorbate bonds. The two effects have similar magnitudes and opposite signs, such that scaling relations are restored in solution. Thus, solvation is a crucial ingredient that must be taken into account in studies aimed at breaking scaling relations in solution. Our...... findings suggest that the choice of metal and ligand determines the catalytic activity within the limits imposed by scaling relations, whereas the choice of an appropriate solvent can drive such activity beyond those limits....

  2. Data in support of covalent attachment of tyrosinase onto cyanuric chloride crosslinked magnetic nanoparticles

    Directory of Open Access Journals (Sweden)

    Kourosh Abdollahi

    2016-12-01

    Full Text Available Preparation and characterization of cross linked amine-functionalized magnetic nanoparticles as an appropriate support for covalent immobilization on tyrosinase was presented in the study "Covalent immobilization of tyrosinase onto cyanuric chloride crosslinked amine-functionalized superparamagnetic nanoparticles: synthesis and characterization of the recyclable nanobiocatalyst" (Abdollahi et al., 2016 [1]. Herein, complementary data regarding X-ray powder diffraction (XRD to characterize the synthesized magnetic nanoparticles, and transmission electron microscopy (TEM to determine the size and morphology of tyrosinase immobilized magnetic nanoparticles (tyrosinase-MNPs were reported. The purification results of the extracted tyrosinase from mushroom Agaricus bisporus were provided in a purification table. The covalent immobilization of tyrosinase onto cyanuric chloride functionalized magnetic nanoparticles was proved by performing thermo-gravimetric and energy-dispersive X-ray spectroscopy analyses. The operational stability of immobilized tyrosinase was investigated by incubating tyrosinase-MNPs at different pH and temperatures.

  3. Aromatic Polyamines Covalent Triazine Polymer as Sorbent for CO2 Adsorption

    Science.gov (United States)

    Lee, Siew-Pei; Mellon, N.; Shariff, Azmi M.; Leveque, Jean-Marc

    2017-08-01

    A novel aromatic polyamine covalent triazine-based polymer, CPDA was obtained by the polymerization of amino group (1,4-phenylenediamine) and cyanuric chloride. CPDA was characterized with Fourier Transform Infra-red spectroscopy (FTIR) and the thermal behaviour was studied with thermal gravimetric analysis (TGA) and derivative thermal analysis (DTA). A comparison study for CO2 adsorption capacity on covalent organic polymer 1 (COP-1) and CPDA was performed. By introducing the aromatic ring into the nitrogen fertile triazine based system, the thermal stability of the network is enhanced. Polymer structure containing secondary amine functionality was observed in this study. Besides, the suggested chemical pathway is another approach to synthesis of covalent organic materials using economic monomers and absence of expensive catalyst.

  4. Combination of computational methods, adsorption isotherms and selectivity tests for the conception of a mixed non-covalent-semi-covalent molecularly imprinted polymer of vanillin.

    Science.gov (United States)

    Puzio, Kinga; Delépée, Raphaël; Vidal, Richard; Agrofoglio, Luigi A

    2013-08-06

    A novel molecularly imprinted polymer (MIP) for vanillin was prepared by photo initiated polymerization in dichloromethane using a mixed semi-covalent and non-covalent imprinting strategy. Taking polymerisable syringaldehyde as "dummy" template, acrylamide was chosen as functional monomer on B3LYP/6-31+G(d,p) density functional theory computational method basis with counterpoise. The binding parameters for the recognition of vanillin on imprinted polymers were studied with three different isotherm models (Langmuir, bi-Langmuir and Langmuir-Freundlich) and compared. The results indicate an heterogeneity of binding sites. It was found and proved by DFT calculations that the specific binding of vanillin in the cavities is due to non-covalent interactions of the template with the hydroxyphenyl- and the amide-moieties. The binding geometry of vanillin in the MIP cavity was also modelled. The obtained MIP is highly specific for vanillin (with an imprinting factor of 7.4) and was successfully applied to the extraction of vanillin from vanilla pods, red wine spike with vanillin, natural and artificial vanilla sugar with a recovery of 80%. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. On the covalent character of rare gas bonding interactions: a new kind of weak interaction.

    Science.gov (United States)

    Zou, Wenli; Nori-Shargh, Davood; Boggs, James E

    2013-01-10

    At the averaged quadratic coupled-cluster (AQCC) level, a number of selected rare gas (Rg) containing systems have been studied using the quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO), and several other analysis methods. According to the criteria for a covalent bond, most of the Rg-M (Rg = He, Ne, Ar, Kr, Xe; M = Be, Cu, Ag, Au, Pt) bonds in this study are assigned to weak interactions instead of van der Walls or covalent ones. Our results indicate that the rare gas bond is a new kind of weak interaction, like the hydrogen bond for example.

  6. Covalent cross-linking of single fibers from rabbit psoas increases oscillatory power

    OpenAIRE

    Tawada, K.; Kawai, M.

    1990-01-01

    Single fibers from chemically skinned rabbit psoas muscle were treated with 1-ethyl-3-[3-dimethyl-amino)proyl]-carbodiimide (EDC) at 20 degrees C after rigor was induced. A 22-min treatment resulted in 18% covalent cross-linking between myosin heads and the thin filament as determined by stiffness measurements. This treatment also results in covalent cross-linking among rod portions of myosin molecules in the backbone of the thick filament. The fibers thus prepared are stable and do not disso...

  7. Covalency effects on momentum distributions in compounds: Positron annihilation in Fe3O4

    International Nuclear Information System (INIS)

    Chiba, T.

    1976-01-01

    A simple method based on the LCAO--MO scheme is presented for the calculation of the momentum distribution in compounds for positron annihilation or Compton scattering. The method is applied to analyze the covalency structure from the spin-density distribution in Fe 3 O 4 measured by Mijnarends and Singru. The degree of covalency is found to be f/sub sigma/ 2 =10%, f/subs/ 2 =0.3%, and f/sub pi/ 2 =4% for the antibonding orbitals of Fe 2+ and Fe 3+ in octahedral sites

  8. Dialing in the Ratio of Covalent and Coordination Cross-links in Self-healing Hydrogels

    DEFF Research Database (Denmark)

    Andersen, Amanda; Krogsgaard, Marie; Birkedal, Henrik

    Mussel-inspired hydrogels have drawn considerable attention. They can be based on either covalent crosslinking through catechol oxidation chemistry or on coordination chemistry through reversible catecholato–metal bonds, which incorporates self-healing properties.1-6 For practical applications......-healing abilities even at high pH but that can be stiffened at will by dialing in the required degree of covalent crosslinking. This dial-in method thus harnesses two aspects of catechol-type chemistries to yield double network hydrogels in a straightforward and highly controllable manner....

  9. Ionization of covalent immobilized poly(4-vinylphenol) monolayers measured by ellipsometry, QCM and SPR

    Energy Technology Data Exchange (ETDEWEB)

    Uppalapati, Suji [Department of Chemistry, University of Massachusetts Lowell, 1 University Ave., Lowell, MA 01854 (United States); Kong, Na; Norberg, Oscar [KTH-Royal Institute of Technology, Department of Chemistry, Teknikringen 30, S-10044 Stockholm (Sweden); Ramström, Olof, E-mail: ramstrom@kth.se [KTH-Royal Institute of Technology, Department of Chemistry, Teknikringen 30, S-10044 Stockholm (Sweden); Yan, Mingdi, E-mail: Mingdi_Yan@uml.edu [Department of Chemistry, University of Massachusetts Lowell, 1 University Ave., Lowell, MA 01854 (United States); KTH-Royal Institute of Technology, Department of Chemistry, Teknikringen 30, S-10044 Stockholm (Sweden)

    2015-07-15

    Covalently immobilized poly(4-vinylphenol) (PVP) monolayer films were fabricated by spin coating PVP on perfluorophenyl azide (PFPA)-functionalized surfaces followed by UV irradiation. The pH-responsive behavior of these PVP ultrathin films was evaluated by ellipsometry, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). By monitoring the responses of these films to pH in situ, the ionization constant of the monolayer thin films was obtained. The apparent pK{sub a} value of these covalently immobilized PVP monolayers, 13.4 by SPR, was 3 units higher than that of the free polymer in aqueous solution.

  10. Quantum electrodynamics of strong fields

    International Nuclear Information System (INIS)

    Greiner, W.

    1983-01-01

    Quantum Electrodynamics of Strong Fields provides a broad survey of the theoretical and experimental work accomplished, presenting papers by a group of international researchers who have made significant contributions to this developing area. Exploring the quantum theory of strong fields, the volume focuses on the phase transition to a charged vacuum in strong electric fields. The contributors also discuss such related topics as QED at short distances, precision tests of QED, nonperturbative QCD and confinement, pion condensation, and strong gravitational fields In addition, the volume features a historical paper on the roots of quantum field theory in the history of quantum physics by noted researcher Friedrich Hund

  11. Covalent functionalization of graphene oxide with polyglycerol and their use as templates for anchoring magnetic nanoparticles

    NARCIS (Netherlands)

    Pham, Tuan Anh; Kumar, Nanjundan Ashok; Jeong, Yeon Tae

    An efficient strategy for the preparation of water-dispersible hybrid material containing graphene oxide and polyglycerol for the first time is demonstrated. Pristine graphite was firstly oxidized to obtain graphene oxide with hydroxyl functional groups. Then, the covalent grafting of polyglycerol

  12. Two-Dimensional Covalent Organic Frameworks for Carbon Dioxide Capture through Channel-Wall Functionalization

    NARCIS (Netherlands)

    Huang, N.; Chen, X.; Krishna, R.; Jiang, D.

    2015-01-01

    Ordered open channels found in two-dimensional covalent organic frameworks (2D COFs) could enable them to adsorb carbon dioxide. However, the frameworks' dense layer architecture results in low porosity that has thus far restricted their potential for carbon dioxide adsorption. Here we report a

  13. Functionality of whey proteins covalently modified by allyl isothiocyanate. Part 2

    NARCIS (Netherlands)

    Keppler, Julia K.; Steffen-Heins, Anja; Berton-Carabin, Claire C.; Ropers, Marie Hélène; Schwarz, Karin

    2018-01-01

    Allyl isothiocyanate (AITC) is a small electrophilic molecule which can be found in cabbage after degradation of glucosinolates. The covalent attachment of AITC to whey protein isolate (WPI) was previously reported to increase their hydrophobicity and structural flexibility at acidic pH values. It

  14. A simple approach for immobilization of gold nanoparticles on graphene oxide sheets by covalent bonding

    NARCIS (Netherlands)

    Pham, Tuan Anh; Choi, Byung Choon; Lim, Kwon Taek; Jeong, Yeon Tae

    2011-01-01

    Amino - functionalized gold nanoparticles with a diameter of around 5 nm were immobilized onto the surface of graphene oxide sheets (GOS) by covalent bonding through a simple amidation reaction. Pristine graphite was firstly oxidized and exfoliated to obtain GOS, which further were acylated with

  15. Regio- and Stereospecific Conversion of 4-Alkylphenols by the Covalent Flavoprotein Vanillyl-Alcohol Oxidase

    NARCIS (Netherlands)

    Heuvel, Robert H.H. van den; Fraaije, Marco W.; Laane, Colja; Berkel, Willem J.H. van

    1998-01-01

    The regio- and stereospecific conversion of prochiral 4-alkylphenols by the covalent flavoprotein vanillyl-alcohol oxidase was investigated. The enzyme was active, with 4-alkylphenols bearing aliphatic side chains of up to seven carbon atoms. Optimal catalytic efficiency occurred with 4-ethylphenol

  16. Targeting of naproxen covalently linked to HSA to sinusoidal cell types of the liver

    NARCIS (Netherlands)

    Melgert, BN; Lebbe, C; Wartna, E; Molema, G; Poelstra, K; Albrecht, C; Reichen, J; Meijer, DKF; Wisse, E; Knook, DL; Balabaud, C

    1997-01-01

    We have coupled the anti-inflammatory drug naproxen (Nap) covalently to human serum albumin (HSA) to deliver this drug selectively to non parenchymal cell types of the liver during endotoxin induced hepatic inflammation. Liver endothelial cells and Kupffer cells play an important role in the

  17. Tailor-Made Pore Surface Engineering in Covalent Organic Frameworks: Systematic Functionalization for Performance Screening

    NARCIS (Netherlands)

    Huang, N.; Krishna, R.; Jiang, D.

    2015-01-01

    Imine-linked covalent organic frameworks (COFs) were synthesized to bear content-tunable, accessible, and reactive ethynyl groups on the walls of one-dimensional pores. These COFs offer an ideal platform for pore-wall surface engineering aimed at anchoring diverse functional groups ranging from

  18. Carbohydrate as covalent crosslink in human inter-alpha-trypsin inhibitor

    DEFF Research Database (Denmark)

    Jessen, T E; Faarvang, K L; Ploug, M

    1988-01-01

    The primary structure of inter-alpha-trypsin inhibitor is partially elucidated, but controversy about the construction of the polypeptide backbone still exists. We present evidence suggesting that inter-alpha-trypsin inhibitor represents a novel plasma protein structure with two separate polypept...... polypeptide chains covalently crosslinked only by carbohydrate (chondroitin sulphate)....

  19. Formation of Me–O–Si covalent bonds at the interface between polysilazane and stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Amouzou, Dodji, E-mail: adodji@gmail.com [Research Centre in Physics of Matter and Radiation (PMR), University of Namur, Rue de Bruxelles 61, 5000 Namur (Belgium); Fourdrinier, Lionel; Maseri, Fabrizio [CRM-Group, Boulevard de Colonster, B 57, 4000 Liège (Belgium); Sporken, Robert [Research Centre in Physics of Matter and Radiation (PMR), University of Namur, Rue de Bruxelles 61, 5000 Namur (Belgium)

    2014-11-30

    Highlights: • Natural metal-oxides, hydroxides are detected on the top surface of steel substrates we tested. • Polysilazane reacts with hydroxide functional groups on steel substrates to form Cr–O–Si and Fe–O–Si covalent bonds. • Covalent bonding between steel and polysilazane at the interface was probed using spectroscopic techniques. - Abstract: In earlier works, we demonstrated the potential of polysilazane (PSZ) coatings for a use as insulating layers in Cu(In,Ga)Se{sub 2} (CIGS) solar cells prepared on steels substrates and showed a good adhesion between PSZ coatings and both AISI316 and AISI430 steels. In the present paper, spectroscopic techniques are used to elucidate the reason of such adhesion. X-ray Photoelectron Spectroscopy (XPS) was used to investigate surfaces for the two steel substrates and showed the presence of metal oxides and metal hydroxides at the top surface. XPS has been also used to probe interfaces between substrates and PSZ, and metallosiloxane (Me–O–Si) covalent bonds have been detected. These results were confirmed by Infra-Red Reflection Absorption Spectroscopy (IRRAS) analyses since vibrations related to Cr–O–Si and Fe–O–Si compounds were detected. Thus, the good adhesion between steel substrates and PSZ coatings was explained by covalent bonding through chemical reactions between PSZ precursors and hydroxide functional groups present on top surface of the two types of steel. Based on these results, an adhesion mechanism between steel substrates and PSZ coatings is proposed.

  20. Methionine Sulfoxides on PrPSc: A Prion-Specific Covalent Signature

    NARCIS (Netherlands)

    Canello, T.; Engelstein, R.; Moshel, O.; Xanthopoulos, K.; Langeveld, J.P.M.; Sklaviadis, T.; Gasset, M.; Gabizon, R.

    2008-01-01

    Prion diseases are fatal neurodegenerative disorders believed to be transmitted by PrPSc, an aberrant form of the membrane protein PrPC. In the absence of an established form-specific covalent difference, the infectious properties of PrPSc were uniquely ascribed to the self-perpetuation properties

  1. Stabilization of 5A1 urease by covalent attachement to wool | Ahmed ...

    African Journals Online (AJOL)

    The investigation of five bacterial strains for urease production referred that Bacillus licheniformis 5A1 had the highest urease activity (10.3U/ml/min) after 24h. The enzyme was covalently coupled to different carriers via glutaraldehyde, and wool gave the highest immobilization yield (76.4%) and retained 85% of the original ...

  2. Covalent organic framework-coated magnetic graphene as a novel support for trypsin immobilization.

    Science.gov (United States)

    Wang, Heping; Jiao, Fenglong; Gao, Fangyuan; Zhao, Xinyuan; Zhao, Yan; Shen, Yehua; Zhang, Yangjun; Qian, Xiaohong

    2017-03-01

    Deep and efficient proteolysis is the critical premise in mass spectrometry-based bottom-up proteomics. It is difficult for traditional in-solution digestion to meet the requirement unless prolonged digestion time and enhanced enzyme dosage are employed, which makes the whole workflow time-consuming and costly. The abovementioned problems could be effectively ameliorated by anchoring many proteases on solid supports. In this work, covalent organic framework-coated magnetic graphene (MG@TpPa-1) was designed and prepared as a novel enzyme carrier for the covalent immobilization of trypsin with a high degree of loading (up to 268 μg mg -1 ). Profiting from the advantages of magnetic graphene and covalent organic frameworks, the novel trypsin bioreactor was successfully applied for the enzymatic digestion of a model protein with dramatically improved digestion efficiency, stability, and reusability. Complete digestion could be achieved in a time period as short as 2 min. For the digestion of proteins extracted from Amygdalus pedunculata, a total of 2833 protein groups were identified, which was slightly more than those obtained by 12 h of in-solution digestion (2739 protein groups). All of the results demonstrate that MG@TpPa-1-trypsin is an excellent candidate for sample preparation in a high-throughput proteomics analysis. Graphical abstract Covalent organic frameworks-coated magnetic graphene was prepared as novel carrier for highly efficient tryptic immobilization.

  3. Liquid chromatography/tandem mass spectrometry detection of covalent binding of acetaminophen to human serum albumin

    NARCIS (Netherlands)

    Damsten, Micaela C.; Commandeur, Jan N. M.; Fidder, Alex; Hulst, Albert G.; Touw, Daan; Noort, Daan; Vermeulen, Nico P. E.

    2007-01-01

    Covalent binding of reactive electrophilic intermediates to proteins is considered to play an important role in the processes leading to adverse drug reactions and idiosyncratic drug reactions. Consequently, both for the discovery and the development of new drugs, there is a great interest in

  4. Covalent binding of nitrogen mustards to the cysteine-34 residue in human serum albumin

    NARCIS (Netherlands)

    Noort, D.; Hulst, A.G.; Jansen, R.

    2002-01-01

    Covalent binding of various clinically important nitrogen mustards to the cysteine-34 residue of human serum albumin, in vitro and in vivo, is demonstrated. A rapid method for detection of these adducts is presented, based on liquid chromatography-tandem mass spectrometry analysis of the adducted

  5. Immobilization of β-glucosidase onto mesoporous silica support: Physical adsorption and covalent binding of enzyme

    Directory of Open Access Journals (Sweden)

    Ivetić Darjana Ž.

    2014-01-01

    Full Text Available This paper investigates β-glucosidase immobilization onto mesoporous silica support by physical adsorption and covalent binding. The immobilization was carried out onto micro-size silica aggregates with the average pore size of 29 nm. During physical adsorption the highest yield of immobilized β-glucosidase was obtained at initial protein concentration of 0.9 mg ml-1. Addition of NaCl increased 1.7-fold, while Triton X-100 addition decreased 6-fold yield of adsorption in comparison to the one obtained without any addition. Covalently bonded β-glucosidase, via glutaraldehyde previously bonded to silanized silica, had higher yield of immobilized enzyme as well as higher activity and substrate affinity in comparison to the one physically adsorbed. Covalent binding did not considerably changed pH and temperature stability of obtained biocatalyst in range of values that are commonly used in reactions in comparison to unbounded enzyme. Furthermore, covalent binding provided biocatalyst which retained over 70% of its activity after 10 cycles of reuse. [Projekat Ministarstva nauke Republike Srbije, br. III 45021

  6. Discovery of covalent inhibitors for MIF tautomerase via cocrystal structures with phantom hits from virtual screening

    Energy Technology Data Exchange (ETDEWEB)

    McLean, Larry R.; Zhang, Ying; Li, Hua; Li, Ziyu; Lukasczyk, Ulrike; Choi, Yong-Mi; Han, Zuoning; Prisco, Joy; Fordham, Jeremy; Tsay, Joseph T.; Reiling, Stephan; Vaz, Roy J.; Li, Yi; (Sanofi)

    2010-10-28

    Biochemical and X-ray crystallographic studies confirmed that hydroxyquinoline derivatives identified by virtual screening were actually covalent inhibitors of the MIF tautomerase. Adducts were formed by N-alkylation of the Pro-1 at the catalytic site with a loss of an amino group of the inhibitor.

  7. Improved Performance of Pseudomonas fluorescens lipase by covalent immobilization onto Amberzyme

    NARCIS (Netherlands)

    Aslan, Yakup; Handayani, Nurrahmi; Stavila, Erythrina; Loos, Katja

    2013-01-01

    Objective: In this study, the conditions of covalent immobilization of Pseudomonas fluorescens lipase onto an oxirane-activated support (Amberzyme) were optimized to obtain a high activity yield. Furthermore, the operational and storage stabilities of immobilized lipase were tested. Methods: Optimum

  8. Covalent immobilization of redox protein within the mesopores of transparent conducting electrodes

    Czech Academy of Sciences Publication Activity Database

    Müller, V.; Rathouský, Jiří; Fattakhova-Rohlfing, D.

    2014-01-01

    Roč. 116, JAN 2014 (2014), s. 1-8 ISSN 0013-4686 R&D Projects: GA ČR GA104/08/0435 Institutional support: RVO:61388955 Keywords : Covalent immobilization * Porous electrodes * Redox proteins Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.504, year: 2014

  9. Ultrafast cooling by covalently bonded graphene-carbon nanotube hybrid immersed in water

    DEFF Research Database (Denmark)

    Chen, Jie; Walther, Jens Honore; Koumoutsakos, Petros

    2016-01-01

    , we demonstrate, through transient heat-dissipation simulations, that a covalently bonded graphene-carbon nanotube (G-CNT) hybrid immersed in water is a promising solution for the ultrafast cooling of such high-temperature and high heat-flux surfaces. The G-CNT hybrid offers a unique platform...

  10. Direct covalent coupling of proteins to nanostructured plasma polymers: a route to tunable cell adhesion

    Czech Academy of Sciences Publication Activity Database

    Melnichuk, I.; Choukourov, A.; Bilek, M.; Weiss, A.; Vandrovcová, Marta; Bačáková, Lucie; Hanuš, J.; Kousal, J.; Shelemin, A.; Solař, P.; Slavínská, D.; Biederman, H.

    2015-01-01

    Roč. 351, Oct 1 (2015), s. 537-545 ISSN 0169-4332 R&D Projects: GA MZd(CZ) NT13297 Institutional support: RVO:67985823 Keywords : covalent binding * plasma polymers * MG-63 osteoblasts Subject RIV: CD - Macromolecular Chemistry Impact factor: 3.150, year: 2015

  11. Covalently Bonded Graphene-Carbon Nanotube Hybrid for High-Performance Thermal Interfaces

    DEFF Research Database (Denmark)

    Chen, Jie; Walther, Jens H.; Koumoutsakos, Petros

    2015-01-01

    their applications as effective thermal interface materials (TIMs). Here, a covalently bonded graphene–CNT (G-CNT) hybrid is presented that multiplies the axial heat transfer capability of individual CNTs through their parallel arrangement, while at the same time it provides a large contact area for efficient heat...

  12. Recent advances in covalent, site-specific protein immobilization [version 1; referees

    DEFF Research Database (Denmark)

    Meldal, Morten Peter; Schoffelen, Sanne

    2016-01-01

    The properties of biosensors, biomedical implants, and other materials based on immobilized proteins greatly depend on the method employed to couple the protein molecules to their solid support. Covalent, site-specific immobilization strategies are robust and can provide the level of control...

  13. Inorganic Materials as Supports for Covalent Enzyme Immobilization: Methods and Mechanisms

    Directory of Open Access Journals (Sweden)

    Paolo Zucca

    2014-09-01

    Full Text Available Several inorganic materials are potentially suitable for enzymatic covalent immobilization, by means of several different techniques. Such materials must meet stringent criteria to be suitable as solid matrices: complete insolubility in water, reasonable mechanical strength and chemical resistance under the operational conditions, the capability to form manageable particles with high surface area, reactivity towards derivatizing/functionalizing agents. Non-specific protein adsorption should be always considered when planning covalent immobilization on inorganic solids. A huge mass of experimental work has shown that silica, silicates, borosilicates and aluminosilicates, alumina, titania, and other oxides, are the materials of choice when attempting enzyme immobilizations on inorganic supports. More recently, some forms of elemental carbon, silicon, and certain metals have been also proposed for certain applications. With regard to the derivatization/functionalization techniques, the use of organosilanes through silanization is undoubtedly the most studied and the most applied, although inorganic bridge formation and acylation with selected acyl halides have been deeply studied. In the present article, the most common inorganic supports for covalent immobilization of the enzymes are reviewed, with particular focus on their advantages and disadvantages in terms of enzyme loadings, operational stability, undesired adsorption, and costs. Mechanisms and methods for covalent immobilization are also discussed, focusing on the most widespread activating approaches (such as glutaraldehyde, cyanogen bromide, divinylsulfone, carbodiimides, carbonyldiimidazole, sulfonyl chlorides, chlorocarbonates, N-hydroxysuccinimides.

  14. Mechanisms for Covalent Immobilization of Horseradish Peroxidase on Ion-Beam-Treated Polyethylene

    Directory of Open Access Journals (Sweden)

    Alexey V. Kondyurin

    2012-01-01

    Full Text Available The surface of polyethylene was modified by plasma immersion ion implantation. Structure changes including carbonization and oxidation were observed. High surface energy of the modified polyethylene was attributed to the presence of free radicals on the surface. The surface energy decay with storage time after treatment was explained by a decay of the free radical concentration while the concentration of oxygen-containing groups increased with storage time. Horseradish peroxidase was covalently attached onto the modified surface by the reaction with free radicals. Appropriate blocking agents can block this reaction. All aminoacid residues can take part in the covalent attachment process, providing a universal mechanism of attachment for all proteins. The native conformation of attached protein is retained due to hydrophilic interactions in the interface region. The enzymatic activity of covalently attached protein remained high. The long-term activity of the modified layer to attach protein is explained by stabilisation of unpaired electrons in sp2 carbon structures. A high concentration of free radicals can give multiple covalent bonds to the protein molecule and destroy the native conformation and with it the catalytic activity. The universal mechanism of protein attachment to free radicals could be extended to various methods of radiation damage of polymers.

  15. Crystal structure of a covalent intermediate in DNA cleavage and rejoining by Escherichia coli DNA topoisomerase I

    Science.gov (United States)

    Zhang, Zhongtao; Cheng, Bokun; Tse-Dinh, Yuk-Ching

    2011-01-01

    DNA topoisomerases control DNA topology by breaking and rejoining DNA strands via covalent complexes with cleaved DNA substrate as catalytic intermediates. Here we report the structure of Escherichia coli topoisomerase I catalytic domain (residues 2–695) in covalent complex with a cleaved single-stranded oligonucleotide substrate, refined to 2.3-Å resolution. The enzyme-substrate intermediate formed after strand cleavage was captured due to the presence of the D111N mutation. This structure of the covalent topoisomerase-DNA intermediate, previously elusive for type IA topoisomerases, shows distinct conformational changes from the structure of the enzyme without bound DNA and provides detailed understanding of the covalent catalysis required for strand cleavage to take place. The portion of cleaved DNA 5′ to the site of cleavage is anchored tightly with extensive noncovalent protein–DNA interactions as predicted by the “enzyme-bridged” model. Distortion of the scissile strand at the -4 position 5′ to the cleavage site allows specific selectivity of a cytosine base in the binding pocket. Many antibacterial and anticancer drugs initiate cell killing by trapping the covalent complexes formed by topoisomerases. We have demonstrated in previous mutagenesis studies that accumulation of the covalent complex of bacterial topoisomerase I is bactericidal. This structure of the covalent intermediate provides the basis for the design of novel antibiotics that can trap the enzyme after formation of the covalent complex. PMID:21482796

  16. Covalent attachment of antagonists to the a7 nicotinic acetylcholine receptor: synthesis and reactivity of substituted maleimides

    DEFF Research Database (Denmark)

    Ambrus, Joseph I; Halliday, Jill I; Kanizaj, Nicholas

    2012-01-01

    The 3-methylmaleimide congeners of the natural product methyllycaconitine (MLA) and an analogue covalently attach to functional cysteine mutants of the a7 nicotinic acetylcholine receptor (nAChR).......The 3-methylmaleimide congeners of the natural product methyllycaconitine (MLA) and an analogue covalently attach to functional cysteine mutants of the a7 nicotinic acetylcholine receptor (nAChR)....

  17. Covalent organic frameworks as supports for a molecular Ni based ethylene oligomerization catalyst for the synthesis of long chain olefins

    NARCIS (Netherlands)

    Rozhko, E.; Bavykina, A.V.; Osadchii, D.; Makkee, M.; Gascon Sabate, J.

    2017-01-01

    The use of two different classes of covalent organic frameworks (covalent triazine and imine linked frameworks) as supports for molecular Ni2+ catalysts is presented. For COFs, a large concentration of N heteroatoms, either in the form of quasi bipyridine or as diiminopyridine

  18. Evidence of covalent bond formation at the silane-metal interface during plasma polymerization of bis-1,2-(triethoxysilyl)ethane (BTSE) on aluminium

    Science.gov (United States)

    Batan, A.; Mine, N.; Douhard, B.; Brusciotti, F.; De Graeve, I.; Vereecken, J.; Wenkin, M.; Piens, M.; Terryn, H.; Pireaux, J. J.; Reniers, F.

    2010-06-01

    Silane and silane-like films were deposited from bis-1,2-(triethoxysilyl)ethane by vacuum and atmospheric plasma onto aluminium. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used for probing the aluminium/plasma polymer film interface. An AlOSi + fragment was identified at nominal mass m/ z = 70.9539 amu, indicating a strong chemical interaction (formation of a covalent bond) at the substrate/film interface. Until now, this strong silane-aluminium interaction has never been observed in plasma polymer BTSE films. Ageing tests in an ultrasonic water bath combined with X-ray photoelectron spectroscopy measurements allowed to indirectly confirm good adhesion, and therefore the formation of a chemical bond at the interface.

  19. Development of covalent inhibitors that can overcome resistance to first-generation FGFR kinase inhibitors

    Science.gov (United States)

    Tan, Li; Wang, Jun; Tanizaki, Junko; Huang, Zhifeng; Aref, Amir R.; Rusan, Maria; Zhu, Su-Jie; Zhang, Yiyun; Ercan, Dalia; Liao, Rachel G.; Capelletti, Marzia; Zhou, Wenjun; Hur, Wooyoung; Kim, NamDoo; Sim, Taebo; Gaudet, Suzanne; Barbie, David A.; Yeh, Jing-Ruey Joanna; Yun, Cai-Hong; Hammerman, Peter S.; Mohammadi, Moosa; Jänne, Pasi A.; Gray, Nathanael S.

    2014-01-01

    The human FGF receptors (FGFRs) play critical roles in various human cancers, and several FGFR inhibitors are currently under clinical investigation. Resistance usually results from selection for mutant kinases that are impervious to the action of the drug or from up-regulation of compensatory signaling pathways. Preclinical studies have demonstrated that resistance to FGFR inhibitors can be acquired through mutations in the FGFR gatekeeper residue, as clinically observed for FGFR4 in embryonal rhabdomyosarcoma and neuroendocrine breast carcinomas. Here we report on the use of a structure-based drug design to develop two selective, next-generation covalent FGFR inhibitors, the FGFR irreversible inhibitors 2 (FIIN-2) and 3 (FIIN-3). To our knowledge, FIIN-2 and FIIN-3 are the first inhibitors that can potently inhibit the proliferation of cells dependent upon the gatekeeper mutants of FGFR1 or FGFR2, which confer resistance to first-generation clinical FGFR inhibitors such as NVP-BGJ398 and AZD4547. Because of the conformational flexibility of the reactive acrylamide substituent, FIIN-3 has the unprecedented ability to inhibit both the EGF receptor (EGFR) and FGFR covalently by targeting two distinct cysteine residues. We report the cocrystal structure of FGFR4 with FIIN-2, which unexpectedly exhibits a “DFG-out” covalent binding mode. The structural basis for dual FGFR and EGFR targeting by FIIN3 also is illustrated by crystal structures of FIIN-3 bound with FGFR4 V550L and EGFR L858R. These results have important implications for the design of covalent FGFR inhibitors that can overcome clinical resistance and provide the first example, to our knowledge, of a kinase inhibitor that covalently targets cysteines located in different positions within the ATP-binding pocket. PMID:25349422

  20. Development of covalent inhibitors that can overcome resistance to first-generation FGFR kinase inhibitors.

    Science.gov (United States)

    Tan, Li; Wang, Jun; Tanizaki, Junko; Huang, Zhifeng; Aref, Amir R; Rusan, Maria; Zhu, Su-Jie; Zhang, Yiyun; Ercan, Dalia; Liao, Rachel G; Capelletti, Marzia; Zhou, Wenjun; Hur, Wooyoung; Kim, NamDoo; Sim, Taebo; Gaudet, Suzanne; Barbie, David A; Yeh, Jing-Ruey Joanna; Yun, Cai-Hong; Hammerman, Peter S; Mohammadi, Moosa; Jänne, Pasi A; Gray, Nathanael S

    2014-11-11

    The human FGF receptors (FGFRs) play critical roles in various human cancers, and several FGFR inhibitors are currently under clinical investigation. Resistance usually results from selection for mutant kinases that are impervious to the action of the drug or from up-regulation of compensatory signaling pathways. Preclinical studies have demonstrated that resistance to FGFR inhibitors can be acquired through mutations in the FGFR gatekeeper residue, as clinically observed for FGFR4 in embryonal rhabdomyosarcoma and neuroendocrine breast carcinomas. Here we report on the use of a structure-based drug design to develop two selective, next-generation covalent FGFR inhibitors, the FGFR irreversible inhibitors 2 (FIIN-2) and 3 (FIIN-3). To our knowledge, FIIN-2 and FIIN-3 are the first inhibitors that can potently inhibit the proliferation of cells dependent upon the gatekeeper mutants of FGFR1 or FGFR2, which confer resistance to first-generation clinical FGFR inhibitors such as NVP-BGJ398 and AZD4547. Because of the conformational flexibility of the reactive acrylamide substituent, FIIN-3 has the unprecedented ability to inhibit both the EGF receptor (EGFR) and FGFR covalently by targeting two distinct cysteine residues. We report the cocrystal structure of FGFR4 with FIIN-2, which unexpectedly exhibits a "DFG-out" covalent binding mode. The structural basis for dual FGFR and EGFR targeting by FIIN3 also is illustrated by crystal structures of FIIN-3 bound with FGFR4 V550L and EGFR L858R. These results have important implications for the design of covalent FGFR inhibitors that can overcome clinical resistance and provide the first example, to our knowledge, of a kinase inhibitor that covalently targets cysteines located in different positions within the ATP-binding pocket.

  1. Strong WW Interaction at LHC

    Energy Technology Data Exchange (ETDEWEB)

    Pelaez, Jose R

    1998-12-14

    We present a brief pedagogical introduction to the Effective Electroweak Chiral Lagrangians, which provide a model independent description of the WW interactions in the strong regime. When it is complemented with some unitarization or a dispersive approach, this formalism allows the study of the general strong scenario expected at the LHC, including resonances.

  2. Strong-back safety latch

    International Nuclear Information System (INIS)

    DeSantis, G.N.

    1995-01-01

    The calculation decides the integrity of the safety latch that will hold the strong-back to the pump during lifting. The safety latch will be welded to the strong-back and will latch to a 1.5-in. dia cantilever rod welded to the pump baseplate. The static and dynamic analysis shows that the safety latch will hold the strong-back to the pump if the friction clamps fail and the pump become free from the strong-back. Thus, the safety latch will meet the requirements of the Lifting and Rigging Manual for under the hook lifting for static loading; it can withstand shock loads from the strong-back falling 0.25 inch

  3. Strong-back safety latch

    Energy Technology Data Exchange (ETDEWEB)

    DeSantis, G.N.

    1995-03-06

    The calculation decides the integrity of the safety latch that will hold the strong-back to the pump during lifting. The safety latch will be welded to the strong-back and will latch to a 1.5-in. dia cantilever rod welded to the pump baseplate. The static and dynamic analysis shows that the safety latch will hold the strong-back to the pump if the friction clamps fail and the pump become free from the strong-back. Thus, the safety latch will meet the requirements of the Lifting and Rigging Manual for under the hook lifting for static loading; it can withstand shock loads from the strong-back falling 0.25 inch.

  4. Titanium: light, strong, and white

    Science.gov (United States)

    Woodruff, Laurel; Bedinger, George

    2013-01-01

    Titanium (Ti) is a strong silver-gray metal that is highly resistant to corrosion and is chemically inert. It is as strong as steel but 45 percent lighter, and it is twice as strong as aluminum but only 60 percent heavier. Titanium dioxide (TiO2) has a very high refractive index, which means that it has high light-scattering ability. As a result, TiO2 imparts whiteness, opacity, and brightness to many products. ...Because of the unique physical properties of titanium metal and the whiteness provided by TiO2, titanium is now used widely in modern industrial societies.

  5. Irreversible inactivation of snake venom l-amino acid oxidase by covalent modification during catalysis of l-propargylglycine☆

    Science.gov (United States)

    Mitra, Jyotirmoy; Bhattacharyya, Debasish

    2013-01-01

    Snake venom l-amino acid oxidase (SV-LAAO, a flavor-enzyme) has attracted considerable attention due to its multifunctional nature, which is manifest in diverse clinical and biological effects such as inhibition of platelet aggregation, induction of cell apoptosis and cytotoxicity against various cells. The majority of these effects are mediated by H2O2 generated during the catalytic conversion of l-amino acids. The substrate analog l-propargylglycine (LPG) irreversibly inhibited the enzyme from Crotalus adamanteus and Crotalus atrox in a dose- and time-dependent manner. Inactivation was irreversible which was significantly protected by the substrate l-phenylalanine. A Kitz–Wilson replot of the inhibition kinetics suggested formation of reversible enzyme–LPG complex, which occurred prior to modification and inactivation of the enzyme. UV–visible and fluorescence spectra of the enzyme and the cofactor strongly suggested formation of covalent adduct between LPG and an active site residue of the enzyme. A molecular modeling study revealed that the FAD-binding, substrate-binding and the helical domains are conserved in SV-LAAOs and both His223 and Arg322 are the important active site residues that are likely to get modified by LPG. Chymotrypsin digest of the LPG inactivated enzyme followed by RP-HPLC and MALDI mass analysis identified His223 as the site of modification. The findings reported here contribute towards complete inactivation of SV-LAAO as a part of snake envenomation management. PMID:23772385

  6. A perfluorinated covalent triazine-based framework for highly selective and water-tolerant CO2 capture

    KAUST Repository

    Zhao, Yunfeng

    2013-01-01

    We designed and synthesized a perfluorinated covalent triazine-based framework (FCTF-1) for selective CO2 capture. The incorporation of fluorine (F) groups played multiple roles in improving the framework\\'s CO 2 adsorption and separation capabilities. Thermodynamically, the strongly polar C-F bonds promoted CO2 adsorption via electrostatic interactions, especially at low pressures. FCTF-1\\'s CO2 uptake was 1.76 mmol g-1 at 273 K and 0.1 bar through equilibrium adsorption, exceeding the CO2 adsorption capacity of any reported porous organic polymers to date. In addition, incorporating F groups produced a significant amount of ultra-micropores (<0.5 nm), which offered not only high gas adsorption potential but also kinetic selectivity for CO2-N 2 separation. In mixed-gas breakthrough experiments, FCTF-1 exhibited an exceptional CO2-N2 selectivity of 77 under kinetic flow conditions, much higher than the selectivity (31) predicted from single-gas equilibrium adsorption data. Moreover, FCTF-1 proved to be tolerant to water and its CO2 capture performance remained excellent when there was moisture in the gas mixture, due to the hydrophobic nature of the C-F bonds. In addition, the moderate adsorbate-adsorbent interaction allowed it to be fully regenerated by pressure swing adsorption processes. These attributes make FCTF-1 a promising sorbent for CO2 capture from flue gas. © 2013 The Royal Society of Chemistry.

  7. Covalent immobilization of lipase onto aminopropyl-functionalized hydroxyapatite-encapsulated-γ-Fe2O3nanoparticles: A magnetic biocatalyst for interesterification of soybean oil.

    Science.gov (United States)

    Xie, Wenlei; Zang, Xuezhen

    2017-07-15

    Hydroxyapatite-encapsulated γ-Fe 2 O 3 nanoparticles were prepared, and lipase from Candida rugosa was then covalently bound onto the magnetic materials via covalent linkages. The magnetic carrier and immobilized lipase were characterized by enzyme activity assays, XRD, FT-IR, TEM, VSM and N 2 adsorption-desorption techniques. Results demonstrated that γ-Fe 2 O 3 nanoparticles were coated with the hydroxyapatite, and the lipase was indeed tethered to the magnetic carriers without damage to their structure. The immobilized lipase showed a strong magnetic responsiveness and displayed high catalytic activities towards the interesterification of soybean oil. The interesterified products were evaluated for their total fatty acid (FA) composition, slip melting point (SMP), iodine value, triacylglycerols (TAGs) profile and FA composition at sn-2 position in TAGs. The FA positional distributions and TAG species significantly changed after the enzymatic interesterification. Besides this, the interesterified products showed an obvious reduction in their SMP in comparison with the physical blends. Copyright © 2017 Elsevier Ltd. All rights reserved.

  8. Biofuel that Keeps Glycerol as Monoglyceride by 1,3-Selective Ethanolysis with Pig Pancreatic Lipase Covalently Immobilized on AlPO4 Support

    Directory of Open Access Journals (Sweden)

    Felipa M. Bautista

    2013-07-01

    Full Text Available By using pig pancreatic lipase (EC 3.1.1.3 or PPL as a biocatalyst, covalently immobilized on amorphous AlPO4 support, a new second generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG blended in a 2:1 molar ratio. This novel product, which integrates glycerol as monoacylglycerols (MG into the biofuels composition, has similar physicochemical properties as conventional biodiesel and also avoids the removal step of the by-product by washing of the biodiesel with water. Immobilization of PPL was achieved by covalent attachment of the ε-amino group of the lysine residues of PPL with the aldehyde groups of p-hydroxybenzaldehyde linked on a hybrid organic-inorganic functionalized AlPO4 surface. With this procedure, the PPL biocatalyst was strongly fixed to the inorganic support surface (94.3%. Nevertheless, the efficiency of the immobilized enzyme was relatively lower compared to that of the free PPL, but it showed a remarkable stability as well as a great capacity of reutilization (25 reuses without a significant loss of its initial catalytic activity. Therefore, this enzymatic method allows the production of a biodiesel which integrates the glycerol, allows a more efficient fabrication method and minimizes the waste production as compared to the conventional alkali-catalyzed process.

  9. Solvent-free covalent functionalization of multi-walled carbon nanotubes and nanodiamond with diamines: Looking for cross-linking effects

    International Nuclear Information System (INIS)

    Basiuk, Elena V.; Basiuk, Vladimir A.; Meza-Laguna, Víctor; Contreras-Torres, Flavio F.; Martínez, Melchor; Rojas-Aguilar, Aarón; Salerno, Marco

    2012-01-01

    Highlights: ► Diamines were used for one-step functionalization of nanotubes and nanodiamond. ► We found experimental evidences of cross-linking effects in these nanomaterials. ► We found a strong orientation effect in the functionalized carbon nanotubes. - Abstract: The covalent functionalization of carbon nanomaterials with diamines is a way to enhance the mechanical strength of nanocomposites due to cross-linking effects, to form complex networks for nanotube-based electronic circuits, as well as is important for a number of biomedical applications. The main goal of the present work was to covalently functionalize pristine multi-walled carbon nanotubes and nanodiamond with three aliphatic diamines (1,8-diaminooctane, 1,10-diaminodecane and 1,12-diaminododecane) and one aromatic diamine (1,5-diaminonaphthalene), by employing a simple one-step solvent-free methodology, which is based on thermal instead of chemical activation. We looked for experimental evidences of cross-linking effects in the carbon nanomaterials synthesized by using solubility/dispersibility tests, atomic force microscopy, scanning and transmission electron microscopy, as well as Fourier-transform infrared spectroscopy and thermogravimetric analysis for additional characterization.

  10. Solvent-free covalent functionalization of multi-walled carbon nanotubes and nanodiamond with diamines: Looking for cross-linking effects

    Energy Technology Data Exchange (ETDEWEB)

    Basiuk, Elena V., E-mail: elenagd@unam.mx [Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510 Mexico, D.F. (Mexico); Nanophysics Department, Italian Institute of Technology, via Morego 30, 16163 Genova, Liguria (Italy); Basiuk, Vladimir A. [Nanophysics Department, Italian Institute of Technology, via Morego 30, 16163 Genova, Liguria (Italy); Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510 Mexico, D.F. (Mexico); Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos (Mexico); Meza-Laguna, Victor; Contreras-Torres, Flavio F.; Martinez, Melchor [Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510 Mexico, D.F. (Mexico); Rojas-Aguilar, Aaron [Centro de Investigacion y de Estudios Avanzados, Instituto Politecnico Nacional, Av. Instituto Politecnico Nacional 2508, Col. San Pedro Zacatenco, 07360 Mexico, D.F. (Mexico); Salerno, Marco [Nanophysics Department, Italian Institute of Technology, via Morego 30, 16163 Genova, Liguria (Italy); and others

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer Diamines were used for one-step functionalization of nanotubes and nanodiamond. Black-Right-Pointing-Pointer We found experimental evidences of cross-linking effects in these nanomaterials. Black-Right-Pointing-Pointer We found a strong orientation effect in the functionalized carbon nanotubes. - Abstract: The covalent functionalization of carbon nanomaterials with diamines is a way to enhance the mechanical strength of nanocomposites due to cross-linking effects, to form complex networks for nanotube-based electronic circuits, as well as is important for a number of biomedical applications. The main goal of the present work was to covalently functionalize pristine multi-walled carbon nanotubes and nanodiamond with three aliphatic diamines (1,8-diaminooctane, 1,10-diaminodecane and 1,12-diaminododecane) and one aromatic diamine (1,5-diaminonaphthalene), by employing a simple one-step solvent-free methodology, which is based on thermal instead of chemical activation. We looked for experimental evidences of cross-linking effects in the carbon nanomaterials synthesized by using solubility/dispersibility tests, atomic force microscopy, scanning and transmission electron microscopy, as well as Fourier-transform infrared spectroscopy and thermogravimetric analysis for additional characterization.

  11. Preserving π-conjugation in covalently functionalized carbon nanotubes for optoelectronic applications

    Science.gov (United States)

    Setaro, Antonio; Adeli, Mohsen; Glaeske, Mareen; Przyrembel, Daniel; Bisswanger, Timo; Gordeev, Georgy; Maschietto, Federica; Faghani, Abbas; Paulus, Beate; Weinelt, Martin; Arenal, Raul; Haag, Rainer; Reich, Stephanie

    2017-01-01

    Covalent functionalization tailors carbon nanotubes for a wide range of applications in varying environments. Its strength and stability of attachment come at the price of degrading the carbon nanotubes sp2 network and destroying the tubes electronic and optoelectronic features. Here we present a non-destructive, covalent, gram-scale functionalization of single-walled carbon nanotubes by a new [2+1] cycloaddition. The reaction rebuilds the extended π-network, thereby retaining the outstanding quantum optoelectronic properties of carbon nanotubes, including bright light emission at high degree of functionalization (1 group per 25 carbon atoms). The conjugation method described here opens the way for advanced tailoring nanotubes as demonstrated for light-triggered reversible doping through photochromic molecular switches and nanoplasmonic gold-nanotube hybrids with enhanced infrared light emission.

  12. New technology for regiospecific covalent coupling of polysaccharide antigens in ELISA for serological detection

    DEFF Research Database (Denmark)

    Jauho, E.S.; Boas, Ulrik; Wiuff, Camilla

    2000-01-01

    plates and avoids cross-reactivity due to conserved domains in the lipid A. Furthermore, the covalent binding of the polysaccharide antigens are compatible with harsh assay conditions, such as extensive washing procedures and buffers with high salt concentrations with no risk of antigen leakage. Here we......In this study we demonstrate a new UV irradiation technique for covalent coupling of bacterial polysaccharides derived from lipopolysaccharides to microtiter plates and the use of such plates in an enzyme linked immunosorbent assay (ELISA). Lipopolysaccharides were cleaved by mild acid hydrolysis...... into the lipid A part and the polysaccharide part. The polysaccharide was conjugated regiospecifically to a photochemically active compound, anthraquinone, resulting in a polysaccharide-anthraquinone conjugate. Anthraquinones forms active radicals when exposed to soft UV irradiation (350 nm) permitting...

  13. Photoinduced electron transfer and fluorescence mechanisms in covalently linked polynuclear aromatic-nucleotide complexes

    Energy Technology Data Exchange (ETDEWEB)

    Geacintov, N.E.; Mao, Bing; Zhao, Rushen; Chen, Junxin; Liu, Tong Ming; Ya, Nai-Qi (New York Univ., NY (United States). Dept. of Chemistry); France, L.L.; Sutherland, J.D. (Brookhaven National Lab., Upton, NY (United States))

    1992-01-01

    The fluorescence of polycyclic aromatic hydrocarbon-nucleic acid complexes is quenched by photoinduced electron transfer mechanisms in aqueous solutions at ambient temperatures. These effects are illustrated with the biologically important compound benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE), a mutagenic and carcinogenic metabolite of the environmental pollutant benzo(a)pyrene, which forms covalent mutagenic lesions with 2{prime}-deoxyguanosine (dG) residues in DNA. The dependence of the fluroescence yeild and fluorescence decay times of the covalent model adduct (+)-trans-BPDE-N{sup 2}-dG as a function of temperature and methanol/water composition are described. Because of the sensitivity of the fluorescence of the pyrenyl residue to the polarity of the microenvironment, the magnitude of the fluorescence yield can be used to distinguish between highly hydrophobic (e.g. intercalation) and other more solvent-exposed BPDE-nucleic acid binding sites.

  14. Photoinduced electron transfer and fluorescence mechanisms in covalently linked polynuclear aromatic-nucleotide complexes

    Energy Technology Data Exchange (ETDEWEB)

    Geacintov, N.E.; Mao, Bing; Zhao, Rushen; Chen, Junxin; Liu, Tong Ming; Ya, Nai-Qi [New York Univ., NY (United States). Dept. of Chemistry; France, L.L.; Sutherland, J.D. [Brookhaven National Lab., Upton, NY (United States)

    1992-04-01

    The fluorescence of polycyclic aromatic hydrocarbon-nucleic acid complexes is quenched by photoinduced electron transfer mechanisms in aqueous solutions at ambient temperatures. These effects are illustrated with the biologically important compound benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), a mutagenic and carcinogenic metabolite of the environmental pollutant benzo[a]pyrene, which forms covalent mutagenic lesions with 2{prime}-deoxyguanosine (dG) residues in DNA. The dependence of the fluroescence yeild and fluorescence decay times of the covalent model adduct (+)-trans-BPDE-N{sup 2}-dG as a function of temperature and methanol/water composition are described. Because of the sensitivity of the fluorescence of the pyrenyl residue to the polarity of the microenvironment, the magnitude of the fluorescence yield can be used to distinguish between highly hydrophobic (e.g. intercalation) and other more solvent-exposed BPDE-nucleic acid binding sites.

  15. Synthesis and characterization of covalent diphenylalanine nanotube-folic acid conjugates

    DEFF Research Database (Denmark)

    León, John Jairo Castillo; Rindzevicius, Tomas; Wu, Kaiyu

    2014-01-01

    Herein, we describe the synthesis and characterization of a covalent nanoscale assembly formed between diphenylalanine micro/nanotubes (PNT) and folic acid (FA). The conjugate was obtained via chemical functionalization through coupling of amine groups of PNTs and carboxylic groups of FA. The sur......Herein, we describe the synthesis and characterization of a covalent nanoscale assembly formed between diphenylalanine micro/nanotubes (PNT) and folic acid (FA). The conjugate was obtained via chemical functionalization through coupling of amine groups of PNTs and carboxylic groups of FA...... performed on a large area silver-capped (diameter of 62 nm) silicon nanopillars with an approximate height of 400 nm and a width of 200 nm. The results showed that the PNT-FA synthesis procedure preserves the molecular structure of FA. The PNT-FA conjugate presented in this study is a promising candidate...

  16. Layer-by-Layer Self-Assembled Graphene Multilayer Films via Covalent Bonds for Supercapacitor Electrodes

    Directory of Open Access Journals (Sweden)

    Xianbin Liu

    2015-05-01

    Full Text Available To maximize the utilization of its single-atom thin nature, a facile scheme to fabricate graphene multilayer films via a layer-by-layer self-assembled process was presented. The structure of multilayer films was constructed by covalently bonding graphene oxide (GO using p-phenylenediamine (PPD as a covalent cross-linking agent. The assembly process was confirmed to be repeatable and the structure was stable. With the π-π conjugated structure and a large number of spaces in the framework, the graphene multi‐ layer films exhibited excellent electrochemical perform‐ ance. The uniform ultrathin electrode exhibited a capacitance of 41.71 μF/cm2 at a discharge current of 0.1 μA/cm2, and displayed excellent stability of 88.9 % after 1000 charge-discharge cycles.

  17. High-quality covalently grafting hemoglobin on gold electrodes: characterization, redox thermodynamics and bio-electrocatalysis.

    Science.gov (United States)

    Tian, Yuan; Ran, Qin; Xu, Jingjing; Xian, Yuezhong; Peng, Ru; Jin, Litong

    2009-12-07

    Herein, we report a versatile surface chemistry methodology to covalently immobilize ligands and proteins to self-assembled monolayers (SAMs) on gold electrode. The strategy is based on two steps: 1) the coupling of soluble azido-PEG-amimo ligand with an alkynyl-terminated monolayer via click reaction and 2) covalent immobilization hemoglobin (Hb) to the amine-terminated ligand via carbodiimide reaction. Surface-enhanced Raman scattering spectroscopy (SERS), atomic force microscopy (AFM), reflection absorption infrared spectroscopy (RAIR) and cyclic voltammetry are used to characterize the model interfacial reactions. We also demonstrate the excellent biocompatibility of the interface for Hb immobilization and reliable application of the proposed method for H(2)O(2) biosensing. Moreover, the redox thermodynamics of the Fe(3+)/Fe(2+) couple in Hb is also investigated.

  18. Fast and accurate covalent bond predictions using perturbation theory in chemical space

    Science.gov (United States)

    Chang, Kuang-Yu; von Lilienfeld, Anatole

    I will discuss the predictive accuracy of perturbation theory based estimates of changes in covalent bonding due to linear alchemical interpolations among systems of different chemical composition. We have investigated single, double, and triple bonds occurring in small sets of iso-valence-electronic molecular species with elements drawn from second to fourth rows in the p-block of the periodic table. Numerical evidence suggests that first order estimates of covalent bonding potentials can achieve chemical accuracy (within 1 kcal/mol) if the alchemical interpolation is vertical (fixed geometry) among chemical elements from third and fourth row of the periodic table. When applied to nonbonded systems of molecular dimers or solids such as III-V semiconductors, alanates, alkali halides, and transition metals, similar observations hold, enabling rapid predictions of van der Waals energies, defect energies, band-structures, crystal structures, and lattice constants.

  19. Modeling the role of covalent enzyme modification in Escherichia coli nitrogen metabolism

    International Nuclear Information System (INIS)

    Kidd, Philip B; Wingreen, Ned S

    2010-01-01

    In the bacterium Escherichia coli, the enzyme glutamine synthetase (GS) converts ammonium into the amino acid glutamine. GS is principally active when the cell is experiencing nitrogen limitation, and its activity is regulated by a bicyclic covalent modification cascade. The advantages of this bicyclic-cascade architecture are poorly understood. We analyze a simple model of the GS cascade in comparison to other regulatory schemes and conclude that the bicyclic cascade is suboptimal for maintaining metabolic homeostasis of the free glutamine pool. Instead, we argue that the lag inherent in the covalent modification of GS slows the response to an ammonium shock and thereby allows GS to transiently detoxify the cell, while maintaining homeostasis over longer times

  20. Self-Exfoliated Guanidinium-Based Ionic Covalent Organic Nanosheets (iCONs).

    Science.gov (United States)

    Mitra, Shouvik; Kandambeth, Sharath; Biswal, Bishnu P; Khayum M, Abdul; Choudhury, Chandan K; Mehta, Mihir; Kaur, Gagandeep; Banerjee, Subhrashis; Prabhune, Asmita; Verma, Sandeep; Roy, Sudip; Kharul, Ulhas K; Banerjee, Rahul

    2016-03-02

    Covalent organic nanosheets (CONs) have emerged as functional two-dimensional materials for versatile applications. Although π-π stacking between layers, hydrolytic instability, possible restacking prevents their exfoliation on to few thin layered CONs from crystalline porous polymers. We anticipated rational designing of a structure by intrinsic ionic linker could be the solution to produce self-exfoliated CONs without external stimuli. In an attempt to address this issue, we have synthesized three self-exfoliated guanidinium halide based ionic covalent organic nanosheets (iCONs) with antimicrobial property. Self-exfoliation phenomenon has been supported by molecular dynamics (MD) simulation as well. Intrinsic ionic guanidinium unit plays the pivotal role for both self-exfoliation and antibacterial property against both Gram-positive and Gram-negative bacteria. Using such iCONs, we have devised a mixed matrix membrane which could be useful for antimicrobial coatings with plausible medical benefits.

  1. Shape-Controlled Synthesis and Self-Sorting of Covalent Organic Cage Compounds.

    Science.gov (United States)

    Klotzbach, Stefanie; Beuerle, Florian

    2015-08-24

    The directional bonding approach is a powerful tool to rationally control both shape and stoichiometry of three-dimensional objects built from rigid building blocks under dynamic covalent conditions. Co-condensation of catechol-functionalized tribenzotriquinacene derivatives which have 90° angles between the reactive sites and diboronic acids with bite angles of 60°, 120°, and 180°, led to the efficient formation of, respectively, bipyramidal, tetrahedral, or cubic covalent organic cage compounds in a predictable manner. Investigations on the self-sorting of ternary mixtures containing two competitive boronic acids revealed either narcissistic or social self-sorting depending on the stability of the segregated cages relative to feasible three-component assemblies. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Essential motions in a fungal lipase with bound substrate, covalently attached inhibitor and product

    DEFF Research Database (Denmark)

    Peters, Günther H.J.; Bywater, R.P.

    2002-01-01

    As an aid to understanding the influence of dynamic fluctuations during esterolytic catalysis, we follow protein flexibility at three different steps along the catalytic pathway from substrate binding to product clearance via a covalently attached inhibitor, which represents a transition-state mi......As an aid to understanding the influence of dynamic fluctuations during esterolytic catalysis, we follow protein flexibility at three different steps along the catalytic pathway from substrate binding to product clearance via a covalently attached inhibitor, which represents a transition...... flexibility suggesting that these processes occur along rough energy surfaces with only a few minima. Detailed energetic analyses along the trajectories indicated that in all cases binding is dominated by van der Waals interactions. The carboxylate form of the product is stabilized by a tight hydrogen bond...

  3. Three-dimensional metal-intercalated covalent organic frameworks for near-ambient energy storage

    Science.gov (United States)

    Gao, Fei; Ding, Zijing; Meng, Sheng

    2013-01-01

    A new form of nanoporous material, metal intercalated covalent organic framework (MCOF) is proposed and its energy storage property revealed. Employing density functional and thermodynamical analysis, we find that stable, chemically active, porous materials could form by stacking covalent organic framework (COF) layers with metals as a gluing agent. Metal acts as active sites, while its aggregation is suppressed by a binding energy significantly larger than the corresponding cohesive energy of bulk metals. Two important parameters, metal binding and metal-metal separation, are tuned by selecting suitable building blocks and linkers when constructing COF layers. Systematic searches among a variety of elements and organic molecules identify Ca-intercalated COF with diphenylethyne units as optimal material for H2 storage, reaching a striking gravimetric density ~ 5 wt% at near-ambient conditions (300 K, 20 bar), in comparison to < 0.1 wt% for bare COF-1 under the same condition. PMID:23698018

  4. Systematic Tuning and Multifunctionalization of Covalent Organic Polymers for Enhanced Carbon Capture

    Energy Technology Data Exchange (ETDEWEB)

    Xiang, Zhonghua; Mercado, Rocio; Huck, Johanna M.; Wang, Hui; Guo, Zhanhu; Wang, Wenchuan; Cao, Dapeng; Haranczyk, Maciej; Smit, Berend

    2015-10-21

    Porous covalent polymers are attracting increasing interest in the fields of gas adsorption, gas separation, and catalysis due to their fertile synthetic polymer chemistry, large internal surface areas, and ultrahigh hydrothermal stabilities. While precisely manipulating the porosities of porous organic materials for targeted applications remains challenging, we show how a large degree of diversity can be achieved in covalent organic polymers by incorporating multiple functionalities into a single framework, as is done for crystalline porous materials. Here, we synthesized 17 novel porous covalent organic polymers (COPs) with finely tuned porosities, a wide range of Brunauer–Emmett–Teller (BET) specific surface areas of 430–3624 m2 g–1, and a broad range of pore volumes of 0.24–3.50 cm3 g–1, all achieved by tailoring the length and geometry of building blocks. Furthermore, we are the first to successfully incorporate more than three distinct functional groups into one phase for porous organic materials, which has been previously demonstrated in crystalline metal–organic frameworks (MOFs). COPs decorated with multiple functional groups in one phase can lead to enhanced properties that are not simply linear combinations of the pure component properties. For instance, in the dibromobenzene-lined frameworks, the bi- and multifunctionalized COPs exhibit selectivities for carbon dioxide over nitrogen twice as large as any of the singly functionalized COPs. These multifunctionalized frameworks also exhibit a lower parasitic energy cost for carbon capture at typical flue gas conditions than any of the singly functionalized frameworks. Despite the significant improvement, these frameworks do not yet outperform the current state-of-art technology for carbon capture. Nonetheless, the tuning strategy presented here opens up avenues for the design of novel catalysts, the synthesis of functional sensors from these materials, and the improvement in the performance

  5. Description of Non-Covalent Interactions in SCC-DFTB Methods

    Czech Academy of Sciences Publication Activity Database

    Miriyala, Vijay Madhav; Řezáč, Jan

    2017-01-01

    Roč. 38, č. 10 (2017), s. 688-697 ISSN 0192-8651 R&D Projects: GA ČR(CZ) GJ16-11321Y Institutional support: RVO:61388963 Keywords : density functional tight binding * DFTB3 * non-covalent interactions * dispersion correction * hydrogen bonding correction Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 3.229, year: 2016

  6. Nanomolar hydrogen peroxide detection using horseradish peroxidase covalently linked to undoped nanocrystalline diamond surfaces

    Czech Academy of Sciences Publication Activity Database

    Wang, Q.; Kromka, Alexander; Houdková, Jana; Babchenko, Oleg; Rezek, Bohuslav; Li, M.; Boukherroub, R.; Szunerits, S.

    2012-01-01

    Roč. 28, č. 1 (2012), s. 587-592 ISSN 0743-7463 R&D Projects: GA AV ČR KAN400100701; GA AV ČR(CZ) IAAX00100902 Institutional research plan: CEZ:AV0Z10100521 Keywords : intrinsic diamond * large area growth * optical biosensor * covalent * XPS Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.187, year: 2012

  7. A non-volatile memory device consisting of graphene oxide covalently functionalized with ionic liquid.

    Science.gov (United States)

    Bhunia, Prasenjit; Hwang, Eunhee; Min, Misook; Lee, Junghyun; Seo, Sohyeon; Some, Surajit; Lee, Hyoyoung

    2012-01-21

    We introduce non-volatile resistive crossbar memory based on ionic liquid covalently functionalized on a partially reduced graphene oxide (PrGO). The write-read-erase-read (WRER) cycles were very stable after several hundred cycles and the retention time of both the ON and OFF states was stable for over 1000 s, indicating that the device we developed can function as a non-volatile memory device. This journal is © The Royal Society of Chemistry 2012

  8. Template-directed self-assembly of dynamic covalent capsules with polar interiors.

    Science.gov (United States)

    Galán, Albano; Escudero-Adán, Eduardo C; Ballester, Pablo

    2017-11-01

    Chiral polyimine molecular capsules with polar interiors have been prepared through template covalent dynamic self-assembly. An aryl-extended tetraaldehyde calix[4]pyrrole scaffold was condensed with suitable diamines as linkers using templates for efficient self-assembly. The capsular complexes were characterized in solution, gas phase and the solid-state. Unprecedented transfer of asymmetry was observed from a chiral diamine linker to the resulting supramolecular capsular assembly.

  9. Photophysical properties of porphyrinoid sensitizers non-covalently bound to host molecules; models for photodynamic therapy

    Czech Academy of Sciences Publication Activity Database

    Lang, Kamil; Mosinger, Jiří; Wagnerová, Dana Marie

    2004-01-01

    Roč. 248, 3-4 (2004), s. 321-350 ISSN 0010-8545 R&D Projects: GA ČR GA203/01/0634; GA ČR GA203/02/0420; GA ČR GA203/02/1483 Institutional research plan: CEZ:AV0Z4032918 Keywords : non-covalent binding * porphyrin * excited states Subject RIV: CA - Inorganic Chemistry Impact factor: 6.446, year: 2004

  10. Covalent Functionalization of NiTi Surfaces with Bioactive Peptide Amphiphile Nanofibers

    Science.gov (United States)

    Sargeant, Timothy D.; Rao, Mukti S.; Koh, Chung-Yan

    2009-01-01

    Surface modification enables the creation of bioactive implants using traditional material substrates without altering the mechanical properties of the bulk material. For applications such as bone plates and stents, it is desirable to modify the surface of metal alloy substrates to facilitate cellular attachment, proliferation, and possibly differentiation. In this work we present a general strategy for altering the surface chemistry of nickel-titanium shape memory alloy (NiTi) in order to covalently attach self-assembled peptide amphiphile (PA) nanofibers with bioactive functions. Bioactivity in the systems studied here includes biological adhesion and proliferation of osteoblast and endothelial cell types. The optimized surface treatment creates a uniform TiO2 layer with low levels of Ni on the NiTi surface, which is subsequently covered with an aminopropylsilane coating using a novel, lower temperature vapor deposition method. This method produces an aminated surface suitable for covalent attachment of PA molecules containing terminal carboxylic acid groups. The functionalized NiTi surfaces have been characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and atomic force microscopy (AFM). These techniques offer evidence that the treated metal surfaces consist primarily of TiO2 with very little Ni, and also confirm the presence of the aminopropylsilane overlayer. Self-assembled PA nanofibers presenting the biological peptide adhesion sequence Arg-Gly-Asp-Ser are capable of covalently anchoring to the treated substrate, as demonstrated by spectrofluorimetry and AFM. Cell culture and scanning electron microscopy (SEM) demonstrate cellular adhesion, spreading, and proliferation on these functionalized metal surfaces. Furthermore, these experiments demonstrate that covalent attachment is crucial for creating robust PA nanofiber coatings, leading to confluent cell monolayers. PMID:18083225

  11. Non-covalent O⋅⋅⋅O interactions among isopolyanions using a cis ...

    Indian Academy of Sciences (India)

    WINTEC

    2008-05-09

    May 9, 2008 ... N–H⋅⋅⋅O and C–H⋅⋅⋅O hydrogen bonds, in which the protonated organic cation plays a significant role. The crystal structure also reveals an unusual cluster–cluster (non-covalent O⋅⋅⋅O) interaction using cis-. (MoO2} moieties of the isopolyanion. N–H⋅⋅⋅O hydrogen bonds, originated from ...

  12. Sequence-targeted chemical modifications of nucleic acids by complementary oligonucleotides covalently linked to porphyrins.

    OpenAIRE

    Trung Le Doan; Perrouault, L; Chassignol, M; Nguyen, T T; Hélène, C

    1987-01-01

    Oligo-heptathymidylates covalently linked to porphyrins bind to complementary sequences and can induce local damages on the target molecule. In dark reactions, iron porphyrin derivatives exhibited various chemical reactivities resulting in base oxidation, crosslinking and chain scission reactions. Reactions induced by reductants, such as ascorbic acid, dithiothreitol or mercapto-propionic acid, led to very localised reactions. A single base was the target for more than 50% of the damages. Oxi...

  13. Designing Porphyrinic Covalent Organic Frameworks for the Photodynamic Inactivation of Bacteria

    Czech Academy of Sciences Publication Activity Database

    Hynek, Jan; Zelenka, J.; Rathouský, Jiří; Kubát, Pavel; Ruml, T.; Demel, Jan; Lang, Kamil

    2018-01-01

    Roč. 10, č. 10 (2018), s. 8527-8535 ISSN 1944-8244 R&D Projects: GA ČR(CZ) GA16-15020S Institutional support: RVO:61388980 ; RVO:61388955 Keywords : antibacterial coating * biofilm * covalent organic framework * photodynamic * porphyrin * singlet oxygen Subject RIV: CA - Inorganic Chemistry; CF - Physical ; Theoretical Chemistry (UFCH-W) OBOR OECD: Inorganic and nuclear chemistry; Physical chemistry (UFCH-W) Impact factor: 7.504, year: 2016

  14. Inulin hydrolysis by inulinase immobilized covalently on magnetic nanoparticles prepared with wheat gluten hydrolysates

    OpenAIRE

    Homa Torabizadeh; Asieh Mahmoudi

    2018-01-01

    Inulinase can produce a high amount of fructose syrup from inulin in a one-step enzymatic process. Inulinase from Aspergillus niger was immobilized covalently on Fe3O4 magnetic nanoparticles functionalized with wheat gluten hydrolysates (WGHs). Wheat gluten was enzymatically hydrolyzed by two endopeptidases Alcalase and Neutrase and related nanoparticles were prepared by desolvation method. Magnetite nanoparticles were coated with WGHs nanoparticles and then inulinase was immobilized onto it ...

  15. The SNAP Strong Lens Survey

    Energy Technology Data Exchange (ETDEWEB)

    Marshall, P.

    2005-01-03

    Basic considerations of lens detection and identification indicate that a wide field survey of the types planned for weak lensing and Type Ia SNe with SNAP are close to optimal for the optical detection of strong lenses. Such a ''piggy-back'' survey might be expected even pessimistically to provide a catalogue of a few thousand new strong lenses, with the numbers dominated by systems of faint blue galaxies lensed by foreground ellipticals. After sketching out our strategy for detecting and measuring these galaxy lenses using the SNAP images, we discuss some of the scientific applications of such a large sample of gravitational lenses: in particular we comment on the partition of information between lens structure, the source population properties and cosmology. Understanding this partitioning is key to assessing strong lens cosmography's value as a cosmological probe.

  16. Strong coupling phase in QED

    International Nuclear Information System (INIS)

    Aoki, Ken-ichi

    1988-01-01

    Existence of a strong coupling phase in QED has been suggested in solutions of the Schwinger-Dyson equation and in Monte Carlo simulation of lattice QED. In this article we recapitulate the previous arguments, and formulate the problem in the modern framework of the renormalization theory, Wilsonian renormalization. This scheme of renormalization gives the best understanding of the basic structure of a field theory especially when it has a multi-phase structure. We resolve some misleading arguments in the previous literature. Then we set up a strategy to attack the strong phase, if any. We describe a trial; a coupled Schwinger-Dyson equation. Possible picture of the strong coupling phase QED is presented. (author)

  17. Nuclear matrix proteins are covalently linked to DNA after ionizing radiation

    International Nuclear Information System (INIS)

    Cress, A.E.

    1985-01-01

    The authors investigated the production of covalent DNA protein crosslinks (DPC) with ionizing radiation. A particular class of nonhistone chromosomal proteins becomes covalently bound to the DNA after 5,000 rads of X-ray. They partially purified these complexes by CsCl density gradient sedimentation. The incorporation of /sup 35/S-met and one dimensional SDS polyacrylimide gel electrophoresis reveals that the proteins involved in the DPC correspond in MW, solubility and predominance to a subset of the nuclear matrix proteins. The DPC are removed after the repair of double and single-stranded scissions is complete as judged by neutral and alkaline elutions. The removal process of the DPC is independent of RNA and protein synthesis inhibition. These data are interesting since these proteins have similar characteristics to the proposed nuclear attachment sites of DNA loops involved in the organization of the genome. The authors are presently using ''Western'' blotting and two dimensional electrophoresis to further identify the specific proteins involved in the DPC. Their current working hypothesis is that the protein involved in the DPC consists primarily of structural nuclear proteins which become covalently crosslinked after ionizing radiation

  18. Rehealable, fully recyclable, and malleable electronic skin enabled by dynamic covalent thermoset nanocomposite.

    Science.gov (United States)

    Zou, Zhanan; Zhu, Chengpu; Li, Yan; Lei, Xingfeng; Zhang, Wei; Xiao, Jianliang

    2018-02-01

    Electronic skin (e-skin) mimicking functionalities and mechanical properties of natural skin can find broad applications. We report the first dynamic covalent thermoset-based e-skin, which is connected through robust covalent bonds, rendering the resulting devices good chemical and thermal stability at service condition. By doping the dynamic covalent thermoset with conductive silver nanoparticles, we demonstrate a robust yet rehealable, fully recyclable, and malleable e-skin. Tactile, temperature, flow, and humidity sensing capabilities are realized. The e-skin can be rehealed when it is damaged and can be fully recycled at room temperature, which has rarely, if at all, been demonstrated for e-skin. After rehealing or recycling, the e-skin regains mechanical and electrical properties comparable to the original e-skin. In addition, malleability enables the e-skin to permanently conform to complex, curved surfaces without introducing excessive interfacial stresses. These properties of the e-skin yield an economical and eco-friendly technology that can find broad applications in robotics, prosthetics, health care, and human-computer interface.

  19. Kinetic Selectivity and Thermodynamic Features of Competitive Imine Formation in Dynamic Covalent Chemistry.

    Science.gov (United States)

    Kulchat, Sirinan; Chaur, Manuel N; Lehn, Jean-Marie

    2017-08-16

    The kinetic and thermodynamic selectivities of imine formation have been investigated for several dynamic covalent libraries of aldehydes and amines. Two systems were examined, involving the reaction of different types of primary amino groups (aliphatic amines, alkoxy-amines, hydrazides and hydrazines) with two types of aldehydes, sulfobenzaldehyde and pyridoxal phosphate in aqueous solution at different pD (5.0, 8.5, 11.4) on one hand, 2-pyridinecarboxaldehyde and salicylaldehyde in organic solvents on the other hand. The reactions were performed separately for given amine/aldehyde pairs as well as in competitive conditions between an aldehyde and a mixture of amines. In the latter case, the time evolution of the dynamic covalent libraries generated was followed, taking into consideration the operation of both kinetic and thermodynamic selectivities. The results showed that, in aqueous solution, the imine of the aliphatic amine was not stable, but oxime and hydrazone formed well in a pH dependent way. On the other hand, in organic solvents, the kinetic product was the imine derived from an aliphatic amine and the thermodynamic products were oxime and hydrazone. The insights gained from these experiments provide a basis for the implementation of imine formation in selective derivatization of mono-amines in mixtures as well as of polyfunctional compounds presenting different types of amino groups. They may in principle be extended to other dynamic covalent chemistry systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Stabilization of enzymes by multipoint covalent immobilization on supports activated with glyoxyl groups.

    Science.gov (United States)

    López-Gallego, Fernando; Fernandez-Lorente, Gloria; Rocha-Martin, Javier; Bolivar, Juan M; Mateo, Cesar; Guisan, Jose M

    2013-01-01

    Stabilization of enzymes via immobilization techniques is a valuable approach in order to convert a necessary protocol (immobilization) into a very interesting tool to improve key enzyme properties (stabilization). Multipoint covalent attachment of each immobilized enzyme molecule may promote a very interesting stabilizing effect. The relative distances among all enzyme residues involved in immobilization has to remain unaltered during any conformational change induced by any distorting agent. Amino groups are very interesting nucleophiles placed on protein surfaces. The immobilization of enzyme through the region having the highest amount of amino groups (Lys residues) is key for a successful stabilization. Glyoxyl groups are small aliphatic aldehydes that form very unstable Schiff's bases with amino groups and they do not seem to be useful for enzyme immobilization at neutral pH. However, under alkaline conditions, glyoxyl supports are able to immobilize enzymes via a first multipoint covalent immobilization through the region having the highest amount of Lysine groups. Activation of supports with a high surface density of glyoxyl groups and the performance of very intense enzyme-support multipoint covalent attachments are here described.

  1. Construction of a Hierarchical Architecture of Covalent Organic Frameworks via a Postsynthetic Approach.

    Science.gov (United States)

    Zhang, Gen; Tsujimoto, Masahiko; Packwood, Daniel; Duong, Nghia Tuan; Nishiyama, Yusuke; Kadota, Kentaro; Kitagawa, Susumu; Horike, Satoshi

    2018-02-21

    Covalent organic frameworks (COFs) represent an emerging class of crystalline porous materials that are constructed by the assembly of organic building blocks linked via covalent bonds. Several strategies have been developed for the construction of new COF structures; however, a facile approach to fabricate hierarchical COF architectures with controlled domain structures remains a significant challenge, and has not yet been achieved. In this study, a dynamic covalent chemistry (DCC)-based postsynthetic approach was employed at the solid-liquid interface to construct such structures. Two-dimensional imine-bonded COFs having different aromatic groups were prepared, and a homogeneously mixed-linker structure and a heterogeneously core-shell hollow structure were fabricated by controlling the reactivity of the postsynthetic reactions. Solid-state nuclear magnetic resonance (NMR) spectroscopy and transmission electron microscopy (TEM) confirmed the structures. COFs prepared by a postsynthetic approach exhibit several functional advantages compared with their parent phases. Their Brunauer-Emmett-Teller (BET) surface areas are 2-fold greater than those of their parent phases because of the higher crystallinity. In addition, the hydrophilicity of the material and the stepwise adsorption isotherms of H 2 O vapor in the hierarchical frameworks were precisely controlled, which was feasible because of the distribution of various domains of the two COFs by controlling the postsynthetic reaction. The approach opens new routes for constructing COF architectures with functionalities that are not possible in a single phase.

  2. Waterborne Polyurethane Coatings with Covalently Linked Black Dye Sudan Black B

    Directory of Open Access Journals (Sweden)

    Tao Wang

    2017-10-01

    Full Text Available Colored waterborne polyurethanes have been widely used in paintings, leathers, textiles, and coatings. Here, a series of black waterborne polyurethanes (WPUs with different ratios of black dye, Sudan Black B (SDB, were prepared by step-growth polymerization. WPU emulsions as obtained exhibit low particle sizes and remarkable storage stability at the same time. At different dye loadings, essential structural, statistical and thermal properties are characterized. FTIR (fourier transform infrared spectra indicate that SDB is covalently linked into waterborne polyurethane chains. All of the WPUs with covalently linked SDB show better color fastness and resistance of thermal migration than those with SDB mixed physically. Besides, WPUs incorporated SDB covalently with different polymeric diols, polytetramethylene ether glycol (PTMG, polypropylene glycol (PPG, poly-1, 4-butylene adipate glycol (PBA and polycaprolactone glycol (PCL, were prepared to obtain different properties to cater to a variety of practical demands. By a spraying method, the black WPUs can be directly used as metal coatings without complex dyeing process by simply mixing coating additive and other waterborne resins, which exhibit excellent coating performance.

  3. Covalent bonding of chloroanilines to humic constituents: Pathways, kinetics, and stability

    International Nuclear Information System (INIS)

    Kong, Deyang; Xia, Qing; Liu, Guoqiang; Huang, Qingguo; Lu, Junhe

    2013-01-01

    Covalent coupling to natural humic constituents comprises an important transformation pathway for anilinic pollutants in the environment. We systematically investigated the reactions of chlorine substituted anilines with catechol and syringic acid in horseradish peroxidase (HRP) catalyzed systems. It was demonstrated that although nucleophilic addition was the mechanism of covalent bonding to both catechol and syringic acid, chloroanilines coupled to the 2 humic constituents via slightly different pathways. 1,4-addition and 1,2-addition are involved to catechol and syringic acid, respectively. 1,4-addition showed empirical 2nd order kinetics and this pathway seemed to be more permanent than 1,2-addition. Stability experiments demonstrated that cross-coupling products with syringic acid could be easily released in acidic conditions. However, cross-coupling with catechol was relatively stable at similar conditions. Thus, the environmental behavior and bioavailability of the coupling products should be carefully assessed. -- Highlights: •Chloroanilines covalently coupled to humic constituents in HRP catalyzed processes, which facilitated their transformation. •MS technique was employed to analyze the coupling products and therefore elucidate the reaction pathways. •Chloroanilines couple to catechol and syringic acid via 1,4- and 1,2-nucleophilic addition pathways, respectively. •Cross-coupling products formed via 1,4-nucleophilic addition pathway were more stable than those via 1,2-addition pathway. -- Bound residues of chloroanilines formed via 1,2- and 1,4-nucleophilic addition pathways showed different stability

  4. Covalent Surface Modification of Gallium Arsenide Photocathodes for Water Splitting in Highly Acidic Electrolyte.

    Science.gov (United States)

    Garner, Logan E; Steirer, K Xerxes; Young, James L; Anderson, Nicholas C; Miller, Elisa M; Tinkham, Jonathan S; Deutsch, Todd G; Sellinger, Alan; Turner, John A; Neale, Nathan R

    2017-02-22

    Efficient water splitting using light as the only energy input requires stable semiconductor electrodes with favorable energetics for the water-oxidation and proton-reduction reactions. Strategies to tune electrode potentials using molecular dipoles adsorbed to the semiconductor surface have been pursued for decades but are often based on weak interactions and quickly react to desorb the molecule under conditions relevant to sustained photoelectrolysis. Here, we show that covalent attachment of fluorinated, aromatic molecules to p-GaAs(1 0 0) surfaces can be employed to tune the photocurrent onset potentials of p-GaAs(1 0 0) photocathodes and reduce the external energy required for water splitting. Results indicate that initial photocurrent onset potentials can be shifted by nearly 150 mV in pH -0.5 electrolyte under 1 Sun (1000 W m -2 ) illumination resulting from the covalently bound surface dipole. Though X-ray photoelectron spectroscopy analysis reveals that the covalent molecular dipole attachment is not robust under extended 50 h photoelectrolysis, the modified surface delays arsenic oxide formation that results in a p-GaAs(1 0 0) photoelectrode operating at a sustained photocurrent density of -20.5 mA cm -2 within -0.5 V of the reversible hydrogen electrode. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Achieving enhanced hydrophobicity of graphene membranes by covalent modification with polydimethylsiloxane

    Energy Technology Data Exchange (ETDEWEB)

    Lei, Wei-Wei; Li, Hang [College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065 (China); Shi, Ling-Ying, E-mail: shilingying@scu.edu.cn [College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065 (China); Diao, Yong-Fu; Zhang, Yu-Lin; Ran, Rong [College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065 (China); Ni, Wei, E-mail: niwei@iccas.ac.cn [Institute of Chemical Materials, China Academy of Engineering Physics, Chengdu 610200 (China)

    2017-05-15

    Highlights: • The graphene oxide (GO) was covalently modified by amino terminated polydimethylsiloxane (PDMS) through amidation reaction. • Through the vacuum filtration method, the GO, RGO and PDMS-modified graphene membranes were successfully prepared respectively. • The morphology of membranes had smooth surface and well-stacked structure indicated by SEM and EDS mapping results. • The contact angle of GO-g-PDMS membrane was high to be 129.5° indicating a great enhancement of hydrophobicity. - Abstract: In this study, the graphene oxide was covalently modified by amino terminated polydimethylsiloxane (PDMS) through amidation reaction. And the membranes of the graphene oxide (GO), reduced graphene oxide (RGO) and PDMS-covalently modified graphene were prepared respectively by a vacuum filtration method, and the wettability of these membranes were investigated. Infrared spectroscopy, Raman, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetry analysis combined with dispersion ability indicated that PDMS chains were successfully grafted on the surface of graphene oxide sheets. The morphology of the prepared membranes had smooth surface and well-stacked structure in the cross-section indicated by the scanning electron microscope and EDS-mapping. The contact angle measurements indicated that the PDMS-modified graphene membrane with water contact angle 129.5° showed increased hydrophobicity compared with GO and RGO membranes.

  6. Overall conformation of covalently stabilized domain-swapped dimer of human cystatin C in solution

    Science.gov (United States)

    Murawska, Magdalena; Szymańska, Aneta; Grubb, Anders; Kozak, Maciej

    2017-11-01

    Human cystatin C (HCC), a small protein, plays a crucial role in inhibition of cysteine proteases. The most common structural form of human cystatin C in crystals is a dimer, which has been evidenced both for the native protein and its mutants. In these structures, HCC dimers were formed through the mechanism of domain swapping. The structure of the monomeric form of human cystatin C was determined for V57N mutant and the mutant with the engineered disulfide bond (L47C)-(G69C) (known as stab1-HCC). On the basis of stab1-HCC, a number of covalently stabilized oligomers, including also dimers have been obtained. The aim of this study was to analyze the structure of the covalently stabilized dimer HCC in solution by the small angle X-ray scattering (SAXS) technique and synchrotron radiation. Experimental data confirmed that in solution this protein forms a dimer, which is characterized by the radius of gyration RG = 3.1 nm and maximum intramolecular distance Dmax = 10.3 nm. Using the ab initio method and program DAMMIN, we propose a low resolution structure of stabilized covalently cystatin C in solution. Stab-HCC dimer adopts in solution an elongated conformation, which is well reconstructed by the ab initio model.

  7. Strong Decomposition of Random Variables

    DEFF Research Database (Denmark)

    Hoffmann-Jørgensen, Jørgen; Kagan, Abram M.; Pitt, Loren D.

    2007-01-01

    A random variable X is stongly decomposable if X=Y+Z where Y=Φ(X) and Z=X-Φ(X) are independent non-degenerated random variables (called the components). It is shown that at least one of the components is singular, and we derive a necessary and sufficient condition for strong decomposability...

  8. Strong interaction at finite temperature

    Indian Academy of Sciences (India)

    Abstract. We review two methods discussed in the literature to determine the effective parameters of strongly interacting particles as they move through a heat bath. The first one is the general method of chiral perturbation theory, which may be readily applied to this problem. The other is the method of thermal QCD sum rules ...

  9. Strong-strong beam-beam simulation on parallel computer

    Energy Technology Data Exchange (ETDEWEB)

    Qiang, Ji

    2004-08-02

    The beam-beam interaction puts a strong limit on the luminosity of the high energy storage ring colliders. At the interaction points, the electromagnetic fields generated by one beam focus or defocus the opposite beam. This can cause beam blowup and a reduction of luminosity. An accurate simulation of the beam-beam interaction is needed to help optimize the luminosity in high energy colliders.

  10. Strong-strong beam-beam simulation on parallel computer

    International Nuclear Information System (INIS)

    Qiang, Ji

    2004-01-01

    The beam-beam interaction puts a strong limit on the luminosity of the high energy storage ring colliders. At the interaction points, the electromagnetic fields generated by one beam focus or defocus the opposite beam. This can cause beam blowup and a reduction of luminosity. An accurate simulation of the beam-beam interaction is needed to help optimize the luminosity in high energy colliders

  11. Noncovalent Interaction Energies in Covalent Complexes: TEM-1 beta-Lactamase and beta-Lactams

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaojun; Minasov, George; Shoichet, Brian K. (NWU)

    2010-03-08

    The class A {beta}-lactamase TEM-1 is a key bacterial resistance enzyme against {beta}-lactam antibiotics, but little is known about the energetic bases for complementarity between TEM-1 and its inhibitors. Most inhibitors form a covalent adduct with the catalytic Ser70, making the measurement of equilibriumconstants, and hence interaction energies, technically difficult. This study evaluates noncovalent interactions withincovalent complexes by examining the differential stability of TEM-1 and its inhibitor adducts. The thermal denaturation of TEM-1 follows a two-state, reversible model with a melting temperature (T{sub m}) of 51.6 C and a van't Hoff enthalpy of unfolding ({Delta}H{sub VH}) of 146.2 kcal/mol at pH 7.0. The stability of the enzyme changes on forming an inhibitor adduct. As expected, some inhibitors stabilize TEM-1; transition-state analogues increase the T{sub m} by up to 3.7 C(1.7 kcal/mol). Surprisingly, all {beta}-lactam covalent acyl-enzyme complexes tested destabilize TEM-1 significantly relative to the apoenzyme. For instance, the clinically used inhibitor clavulanic acid and the {beta}-lactamase-resistant {beta}-lactams moxalactam and imipenem destabilize TEM-1 by over 2.6 C (1.2 kcal/mol) in their covalent adducts. Based on the structure of the TEM-1/imipenem complex (Maveyraud et al., J Am Chem Soc 1998;120:9748-52), destabilization by moxalactam and imipenem is thought to be caused by a steric clash between the side-chain of Asn132 and the 6(7)-{alpha} group of these {beta}-lactams. To test this hypothesis, the mutant enzyme N132A was made. In contrast with wild-type, the covalent complexes between N132A and both imipenem and moxalactam stabilize the enzyme, consistent with the hypothesis. To investigate the structural bases of this dramatic change instability, the structure of N132A/imipenem was determined by X-ray crystallography. In the complex with N132A, imipenemadopts a very different conformation from that observed in the wild

  12. Covalent immobilization of oligonucleotides on p-aminophenyl-modified carbon screen-printed electrodes for viral DNA sensing.

    Science.gov (United States)

    Ruffien, Audrey; Dequaire, Murielle; Brossier, Pierre

    2003-04-07

    DNA-sensing platforms were prepared by covalently attaching oligonucleotide capture probes onto p-aminophenyl-functionalized carbon surfaces and applied to the determination of an amplified herpes virus DNA sequence in an electrochemical hybridization assay.

  13. 4fn-15d centroid shift in lanthanides and relation with anion polarizability, covalency, and cation electronegativity

    International Nuclear Information System (INIS)

    Dorenbos, P.; Andriessen, J.; Eijk, C.W.E. van

    2003-01-01

    Data collected on the centroid shift of the 5d-configuration of Ce 3+ in oxide and fluoride compounds were recently analyzed with a model involving the correlated motion between 5d-electron and ligand electrons. The correlation effects are proportional to the polarizability of the anion ligands and it leads, like covalency, to lowering of the 5d-orbital energies. By means of ab initio Hartree-Fock-LCAO calculations including configuration interaction the contribution from covalency and correlated motion to the centroid shift are determined separately for Ce 3+ in various compounds. It will be shown that in fluoride compounds, covalency provides an insignificant contribution. In oxides, polarizability appears to be of comparable importance as covalency

  14. PREFACE: Strongly correlated electron systems Strongly correlated electron systems

    Science.gov (United States)

    Saxena, Siddharth S.; Littlewood, P. B.

    2012-07-01

    This special section is dedicated to the Strongly Correlated Electron Systems Conference (SCES) 2011, which was held from 29 August-3 September 2011, in Cambridge, UK. SCES'2011 is dedicated to 100 years of superconductivity and covers a range of topics in the area of strongly correlated systems. The correlated electronic and magnetic materials featured include f-electron based heavy fermion intermetallics and d-electron based transition metal compounds. The selected papers derived from invited presentations seek to deepen our understanding of the rich physical phenomena that arise from correlation effects. The focus is on quantum phase transitions, non-Fermi liquid phenomena, quantum magnetism, unconventional superconductivity and metal-insulator transitions. Both experimental and theoretical work is presented. Based on fundamental advances in the understanding of electronic materials, much of 20th century materials physics was driven by miniaturisation and integration in the electronics industry to the current generation of nanometre scale devices. The achievements of this industry have brought unprecedented advances to society and well-being, and no doubt there is much further to go—note that this progress is founded on investments and studies in the fundamentals of condensed matter physics from more than 50 years ago. Nevertheless, the defining challenges for the 21st century will lie in the discovery in science, and deployment through engineering, of technologies that can deliver the scale needed to have an impact on the sustainability agenda. Thus the big developments in nanotechnology may lie not in the pursuit of yet smaller transistors, but in the design of new structures that can revolutionise the performance of solar cells, batteries, fuel cells, light-weight structural materials, refrigeration, water purification, etc. The science presented in the papers of this special section also highlights the underlying interest in energy-dense materials, which

  15. Covalent Linkage of HIV-1 Trimers to Synthetic Liposomes Elicits Improved B Cell and Antibody Responses.

    Science.gov (United States)

    Bale, Shridhar; Goebrecht, Geraldine; Stano, Armando; Wilson, Richard; Ota, Takayuki; Tran, Karen; Ingale, Jidnyasa; Zwick, Michael B; Wyatt, Richard T

    2017-08-15

    We have demonstrated that a liposomal array of well-ordered trimers enhances B cell activation, germinal center formation, and the elicitation of tier-2 autologous neutralizing antibodies. Previously, we coupled well-ordered cleavage-independent NFL trimers via their C-terminal polyhistidine tails to nickel lipids integrated into the lipid bilayer. Despite favorable in vivo effects, concern remained over the potentially longer-term in vivo instability of noncovalent linkage of the trimers to the liposomes. Accordingly, we tested both cobalt coupling and covalent linkage of the trimers to the liposomes by reengineering the polyhistidine tail to include a free cysteine on each protomer of model BG505 NFL trimers to allow covalent linkage. Both cobalt and cysteine coupling resulted in a high-density array of NFL trimers that was stable in both 20% mouse serum and 100 mM EDTA, whereas the nickel-conjugated trimers were not stable under these conditions. Binding analysis and calcium flux with anti-Env-specific B cells confirmed that the trimers maintained conformational integrity following coupling. Following immunization of mice, serologic analysis demonstrated that the covalently coupled trimers elicited Env-directed antibodies in a manner statistically significantly improved compared to soluble trimers and nickel-conjugated trimers. Importantly, the covalent coupling not only enhanced gp120-directed responses compared to soluble trimers, it also completely eliminated antibodies directed to the C-terminal His tag located at the "bottom" of the spike. In contrast, soluble and noncovalent formats efficiently elicited anti-His tag antibodies. These data indicate that covalent linkage of well-ordered trimers to liposomes in high-density array displays multiple advantages in vitro and in vivo IMPORTANCE Enveloped viruses typically encode a surface-bound glycoprotein that mediates viral entry into host cells and is a primary target for vaccine design. Liposomes with

  16. In vitro covalent binding of the pyrethroids cismethrin, cypermethrin and deltamethrin to rat liver homogenate and microsomes

    Energy Technology Data Exchange (ETDEWEB)

    Catinot, R.; Hoellinger, H.; Sonnier, M.; Do-Cao-Thang; Pichon, J.; Nguyen-Hoang-Nam

    1989-05-01

    Phenobarbital-induced rat liver homogenate and microsomes were used to study covalent binding of /sup 14/C-labelled (at the alcohol moiety) cismethrin, /sup 14/C-labelled (at the alcohol and acid moieties) cypermethrin, and /sup 14/C-labelled (at the alcohol and acid moieties) deltamethrin. Covalent binding was dependent on pyrethroid concentration. With liver homogenate, inhibition of esterases by tetraethylpyrophosphate and of mitochondrial respiration by rotenone or potassium cyanide only slightly altered the covalent binding level. With microsomes, inhibition of cytochrome P-450 and mixed function oxidases by carbon monoxide and piperonyl butoxide reduced the covalent binding so far as to be nearly absent. Eighty percent inhibition of epoxide hydrolase decreased the covalent binding by 50%. The comparison of data between alcohol and acid labelling of the same pyrethroid suggested that, in vitro, the whole molecule is bound to proteins and that hydrolysis can occur afterwards. The experiments stress the role of cytochrome P-450-dependent monoxygenases in the covalent binding process. (orig.).

  17. Strongly correlated systems experimental techniques

    CERN Document Server

    Mancini, Ferdinando

    2015-01-01

    The continuous evolution and development of experimental techniques is at the basis of any fundamental achievement in modern physics. Strongly correlated systems (SCS), more than any other, need to be investigated through the greatest variety of experimental techniques in order to unveil and crosscheck the numerous and puzzling anomalous behaviors characterizing them. The study of SCS fostered the improvement of many old experimental techniques, but also the advent of many new ones just invented in order to analyze the complex behaviors of these systems. Many novel materials, with functional properties emerging from macroscopic quantum behaviors at the frontier of modern research in physics, chemistry and materials science, belong to this class of systems. The volume presents a representative collection of the modern experimental techniques specifically tailored for the analysis of strongly correlated systems. Any technique is presented in great detail by its own inventor or by one of the world-wide recognize...

  18. Strongly Correlated Systems Theoretical Methods

    CERN Document Server

    Avella, Adolfo

    2012-01-01

    The volume presents, for the very first time, an exhaustive collection of those modern theoretical methods specifically tailored for the analysis of Strongly Correlated Systems. Many novel materials, with functional properties emerging from macroscopic quantum behaviors at the frontier of modern research in physics, chemistry and materials science, belong to this class of systems. Any technique is presented in great detail by its own inventor or by one of the world-wide recognized main contributors. The exposition has a clear pedagogical cut and fully reports on the most relevant case study where the specific technique showed to be very successful in describing and enlightening the puzzling physics of a particular strongly correlated system. The book is intended for advanced graduate students and post-docs in the field as textbook and/or main reference, but also for other researchers in the field who appreciates consulting a single, but comprehensive, source or wishes to get acquainted, in a as painless as po...

  19. Strongly correlated systems numerical methods

    CERN Document Server

    Mancini, Ferdinando

    2013-01-01

    This volume presents, for the very first time, an exhaustive collection of those modern numerical methods specifically tailored for the analysis of Strongly Correlated Systems. Many novel materials, with functional properties emerging from macroscopic quantum behaviors at the frontier of modern research in physics, chemistry and material science, belong to this class of systems. Any technique is presented in great detail by its own inventor or by one of the world-wide recognized main contributors. The exposition has a clear pedagogical cut and fully reports on the most relevant case study where the specific technique showed to be very successful in describing and enlightening the puzzling physics of a particular strongly correlated system. The book is intended for advanced graduate students and post-docs in the field as textbook and/or main reference, but also for other researchers in the field who appreciate consulting a single, but comprehensive, source or wishes to get acquainted, in a as painless as possi...

  20. Strongly nonlinear oscillators analytical solutions

    CERN Document Server

    Cveticanin, Livija

    2014-01-01

    This book provides the presentation of the motion of pure nonlinear oscillatory systems and various solution procedures which give the approximate solutions of the strong nonlinear oscillator equations. The book presents the original author’s method for the analytical solution procedure of the pure nonlinear oscillator system. After an introduction, the physical explanation of the pure nonlinearity and of the pure nonlinear oscillator is given. The analytical solution for free and forced vibrations of the one-degree-of-freedom strong nonlinear system with constant and time variable parameter is considered. Special attention is given to the one and two mass oscillatory systems with two-degrees-of-freedom. The criteria for the deterministic chaos in ideal and non-ideal pure nonlinear oscillators are derived analytically. The method for suppressing chaos is developed. Important problems are discussed in didactic exercises. The book is self-consistent and suitable as a textbook for students and also for profess...

  1. Flavour Democracy in Strong Unification

    CERN Document Server

    Abel, S A; Abel, Steven; King, Steven

    1998-01-01

    We show that the fermion mass spectrum may naturally be understood in terms of flavour democratic fixed points in supersymmetric theories which have a large domain of attraction in the presence of "strong unification". Our approach provides an alternative to the approximate Yukawa texture zeroes of the Froggatt-Nielsen mechanism. We discuss a particular model based on a broken gauged $SU(3)_L\\times SU(3)_R$ family symmetry which illustrates our approach.

  2. Donor-Acceptor Interaction Determines the Mechanism of Photoinduced Electron Injection from Graphene Quantum Dots into TiO2: π-Stacking Supersedes Covalent Bonding.

    Science.gov (United States)

    Long, Run; Casanova, David; Fang, Wei-Hai; Prezhdo, Oleg V

    2017-02-22

    Interfacial electron transfer (ET) constitutes the key step in conversion of solar energy into electricity and fuels. Required for fast and efficient charge separation, strong donor-acceptor interaction is typically achieved through covalent chemical bonding and leads to fast, adiabatic ET. Focusing on interfaces of pyrene, coronene, and a graphene quantum dot (GQD) with TiO 2 , we demonstrate the opposite situation: covalent bonding leads to weak coupling and nonadiabatic (NA) ET, while through-space π-electron interaction produces adiabatic ET. Using real-time time-dependent density functional theory combined with NA molecular dynamics, we simulate photoinduced ET into TiO 2 from flat and vertically placed molecules and GQD containing commonly used carboxylic acid linkers. Both arrangements can be achieved experimentally with GQDs and other two-dimensional materials, such as MoS 2 . The weak through-bond donor-acceptor coupling is attributed to the π-electron withdrawing properties of the carboxylic acid group. The calculated ET time scales are in excellent agreement with pump-probe optical experiments. The simulations show that the ET proceeds faster than energy relaxation. The electron couples to a broad spectrum of vibrational modes, ranging from 100 cm -1 large-scale motions to 1600 cm -1 C-C stretches. Compared to graphene/TiO 2 heterojunctions, the molecule/TiO 2 and GQD/TiO 2 systems exhibit energy gaps, allowing for longer-lived excited states and hot electron injection, facilitating charge separation and higher voltage. The reported state-of-the-art simulations generate a detailed time-domain, atomistic description of the interfacial charge and energy transfer and relaxation processes, and demonstrate that the fundamental principles leading to efficient charge separation in nanoscale materials depend strongly and often unexpectedly on the type of donor-acceptor interaction. Understanding these principles is critical to the development of highly

  3. Structure characterization of unexpected covalent O-sulfonation and ion-pairing on an extremely hydrophilic peptide with CE-MS and FT-ICR-MS.

    Science.gov (United States)

    Pattky, Martin; Nicolardi, Simone; Santiago-Schübel, Beatrix; Sydes, Daniel; van der Burgt, Yuri E M; Klein, Antonia N; Jiang, Nan; Mohrlüder, Jeannine; Hänel, Karen; Kutzsche, Janine; Funke, S A; Willbold, D; Willbold, S; Huhn, C

    2015-09-01

    In this study, we characterized unexpected side-products in a commercially synthesized peptide with the sequence RPRTRLHTHRNR. This so-called peptide D3 was selected by mirror phage display against low molecular weight amyloid-β-peptide (Aβ) associated with Alzheimer's disease. Capillary electrophoresis (CE) was the method of choice for structure analysis because the extreme hydrophilicity of the peptide did not allow reversed-phase liquid chromatography (RPLC) and hydrophilic interaction stationary phases (HILIC). CE-MS analysis, applying a strongly acidic background electrolyte and different statically adsorbed capillary coatings, provided fast and efficient analysis and revealed that D3 unexpectedly showed strong ion-pairing with sulfuric acid. Moreover, covalent O-sulfonation at one or two threonine residues was identified as a result of a side reaction during peptide synthesis, and deamidation was found at either the asparagine residue or at the C-terminus. In total, more than 10 different species with different m/z values were observed. Tandem-MS analysis with collision induced dissociation (CID) using a CE-quadrupole-time-of-flight (QTOF) setup predominantly resulted in sulfate losses and did not yield any further characteristic fragment ions at high collision energies. Therefore, direct infusion Fourier transform ion cyclotron resonance (FT-ICR) MS was employed to identify the covalent modification and discriminate O-sulfonation from possible O-phosphorylation by using an accurate mass analysis. Electron transfer dissociation (ETD) was used for the identification of the threonine O-sulfation sites. In this work, it is shown that the combination of CE-MS and FT-ICR-MS with ETD fragmentation was essential for the full characterization of this extremely basic peptide with labile modifications.

  4. Atoms in strong laser fields

    International Nuclear Information System (INIS)

    L'Huillier, A.

    2002-01-01

    When a high-power laser focuses into a gas of atoms, the electromagnetic field becomes of the same magnitude as the Coulomb field which binds a 1s electron in a hydrogen atom. 3 highly non-linear phenomena can happen: 1) ATI (above threshold ionization): electrons initially in the ground state absorb a large number of photons, many more than the minimum number required for ionization; 2) multiple ionization: many electrons can be emitted one at a time, in a sequential process, or simultaneously in a mechanism called direct or non-sequential; and 3) high order harmonic generation (HHG): efficient photon emission in the extreme ultraviolet range, in the form of high-order harmonics of the fundamental laser field can occur. The theoretical problem consists in solving the time dependent Schroedinger equation (TDSE) that describes the interaction of a many-electron atom with a laser field. A number of methods have been proposed to solve this problem in the case of a hydrogen atom or a single-active electron atom in a strong laser field. A large effort is presently being devoted to go beyond the single-active approximation. The understanding of the physics of the interaction between atoms and strong laser fields has been provided by a very simple model called ''simple man's theory''. A unified view of HHG, ATI, and non-sequential ionization, originating from the simple man's model and the strong field approximation, expressed in terms of electrons trajectories or quantum paths is slowly emerging. (A.C.)

  5. Strongly Interacting Light Dark Matter

    Directory of Open Access Journals (Sweden)

    Sebastian Bruggisser, Francesco Riva, Alfredo Urbano

    2017-09-01

    Full Text Available In the presence of approximate global symmetries that forbid relevant interactions, strongly coupled light Dark Matter (DM can appear weakly coupled at small energy and generate a sizable relic abundance. Fundamental principles like unitarity restrict these symmetries to a small class, where the leading interactions are captured by effective operators up to dimension-8. Chiral symmetry, spontaneously broken global symmetries and non-linearly realized supersymmetry are examples of this. Their DM candidates (composite fermions, pseudo Nambu-Goldstone Bosons and Goldstini are interesting targets for LHC missing-energy searches.

  6. Strongly interacting light dark matter

    International Nuclear Information System (INIS)

    Bruggisser, Sebastian; Riva, Francesco; Urbano, Alfredo

    2016-07-01

    In the presence of approximate global symmetries that forbid relevant interactions, strongly coupled light Dark Matter (DM) can appear weakly coupled at small-energy and generate a sizable relic abundance. Fundamental principles like unitarity restrict these symmetries to a small class, where the leading interactions are captured by effective operators up to dimension-8. Chiral symmetry, spontaneously broken global symmetries and non-linearly realized supersymmetry are examples of this. Their DM candidates (composite fermions, pseudo-Nambu-Goldstone Bosons and Goldstini) are interesting targets for LHC missing-energy searches.

  7. Rydberg atoms in strong fields

    International Nuclear Information System (INIS)

    Kleppner, D.; Tsimmerman, M.

    1985-01-01

    Experimental and theoretical achievements in studying Rydberg atoms in external fields are considered. Only static (or quasistatic) fields and ''one-electron'' atoms, i.e. atoms that are well described by one-electron states, are discussed. Mainly behaviour of alkali metal atoms in electric field is considered. The state of theoretical investigations for hydrogen atom in magnetic field is described, but experimental data for atoms of alkali metals are presented as an illustration. Results of the latest experimental and theoretical investigations into the structure of Rydberg atoms in strong fields are presented

  8. Scalar strong interaction hadron theory

    CERN Document Server

    Hoh, Fang Chao

    2015-01-01

    The scalar strong interaction hadron theory, SSI, is a first principles' and nonlocal theory at quantum mechanical level that provides an alternative to low energy QCD and Higgs related part of the standard model. The quark-quark interaction is scalar rather than color-vectorial. A set of equations of motion for mesons and another set for baryons have been constructed. This book provides an account of the present state of a theory supposedly still at its early stage of development. This work will facilitate researchers interested in entering into this field and serve as a basis for possible future development of this theory.

  9. Strong Plate, Weak Slab Dichotomy

    Science.gov (United States)

    Petersen, R. I.; Stegman, D. R.; Tackley, P.

    2015-12-01

    Models of mantle convection on Earth produce styles of convection that are not observed on Earth.Moreover non-Earth-like modes, such as two-sided downwellings, are the de facto mode of convection in such models.To recreate Earth style subduction, i.e. one-sided asymmetric recycling of the lithosphere, proper treatment of the plates and plate interface are required. Previous work has identified several model features that promote subduction. A free surface or pseudo-free surface and a layer of material with a relatively low strength material (weak crust) allow downgoing plates to bend and slide past overriding without creating undue stress at the plate interface. (Crameri, et al. 2012, GRL)A low viscosity mantle wedge, possibly a result of slab dehydration, decouples the plates in the system. (Gerya et al. 2007, Geo)Plates must be composed of material which, in the case of the overriding plate, are is strong enough to resist bending stresses imposed by the subducting plate and yet, as in the case of the subducting plate, be weak enough to bend and subduct when pulled by the already subducted slab. (Petersen et al. 2015, PEPI) Though strong surface plates are required for subduction such plates may present a problem when they encounter the lower mantle.As the subducting slab approaches the higher viscosity, lower mantle stresses are imposed on the tip.Strong slabs transmit this stress to the surface.There the stress field at the plate interface is modified and potentially modifies the style of convection. In addition to modifying the stress at the plate interface, the strength of the slab affects the morphology of the slab at the base of the upper mantle. (Stegman, et al 2010, Tectonophysics)Slabs that maintain a sufficient portion of their strength after being bent require high stresses to unbend or otherwise change their shape.On the other hand slabs that are weakened though the bending process are more amenable to changes in morphology. We present the results of

  10. Nucleation and Growth of Covalent Organic Frameworks from Solution: The Example of COF-5

    KAUST Repository

    Li, Haoyuan

    2017-10-24

    The preparation of two-dimensional covalent organic frameworks (2D COFs) with large crystalline domains and controlled morphology is necessary for realizing the full potential of their atomically precise structures and uniform, tailorable porosity. Currently 2D COF syntheses are developed empirically, and most materials are isolated as insoluble and unprocessable powders with typical crystalline domain sizes smaller than 50 nm. Little is known about their nucleation and growth processes, which involve a combination of covalent bond formation, degenerate exchange, and non-covalent stacking processes. A deeper understanding of the chemical processes that lead to COF polymerization and crystallization is key to achieving improved materials quality and control. Here, we report a kinetic Monte Carlo (KMC) model that describes the formation of a prototypical boronate-ester linked 2D COF known as COF-5 from its 2,3,6,7,10,11-hexahydroxytriphenylene and 1,4-phenylene bis(boronic acid) monomers in solution. The key rate parameters for the KMC model were derived from experimental measurements when possible and complemented with reaction pathway analyses, molecular dynamics simulations, and binding free-energy calculations. The essential features of experimentally measured COF-5 growth kinetics are reproduced well by the KMC simulations. In particular, the simulations successfully captured a nucleation process followed by a subsequent growth process. The nucleating species are found to be multi-layer structures that form through multiple pathways. During the growth of COF-5, extensions in the lateral (in-plane) and vertical (stacking) directions are both seen to be linear with respect to time and are dominated by monomer addition and oligomer association, respectively. Finally, we show that the experimental observations of increased average crystallite size with the addition of water are modeled accurately by the simulations. These results will inform the rational development

  11. Zein nanoparticles as delivery systems for covalently linked and physically entrapped folic acid

    Energy Technology Data Exchange (ETDEWEB)

    Chuacharoen, Thanida [Suan Sunandha Rajabhat University, Faculty of Science and Technology (Thailand); Sabliov, Cristina M., E-mail: CSabliov@agcenter.lsu.edu [Louisiana State University and LSU AgCenter, Department of Biological and Agricultural Engineering (United States)

    2017-02-15

    Zein nanoparticles covalently linked to folic acid were hypothesized to sustain the release of the folic acid in addition to targeting cancer cells overexpressing folate-binding receptors, whereas zein nanoparticles with physically entrapped folic acid would only be able to control the release of the bioactive without targeting of cancer cells. The two types of particles, folic acid covalently linked zein nanoparticles (ZN-FA nps) and zein nanoparticles with entrapped folic acid (ZN(FA) nps), were synthesized and the covalent link between folic acid and zein was assessed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy ({sup 1}H NMR). Their size, polydispersity index, zeta potential, morphology, and loading capacity were evaluated by dynamic light scattering (DLS), transmission electron microscopy (TEM), and spectrophotometric technique. The release studies of the folic acid preformed in phosphate-buffered saline (PBS) at 37 °C for 7 days concluded that the release of the loaded folic acid was sustained over 7 days for both systems. The cytotoxicity was investigated using a methyl thiazolyl tetrazolium (MTT) assay, and the results showed that zein nanoparticles were biocompatible to HeLa (an overexpressing folate receptor cells) and A549 (a deficient folate receptor cells) cells, which have different levels of folate receptors on surface and both folic acid nanoparticle systems were able to diminish the adverse toxic effect of folic acid to cells. The increased uptake of ZN-FA nps relative to ZN(FA) nps supported the use of ZN-FA nps as targeting nanoagents to cells overexpressing folate receptors.

  12. Structure, stability and electrochromic properties of polyaniline film covalently bonded to indium tin oxide substrate

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wenzhi, E-mail: zhangwz@xatu.edu.cn [Key Laboratory for Photoelectric Functional Materials and Devices of Shaanxi Province, School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710021 (China); Ju, Wenxing; Wu, Xinming; Wang, Yan; Wang, Qiguan; Zhou, Hongwei; Wang, Sumin [Key Laboratory for Photoelectric Functional Materials and Devices of Shaanxi Province, School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710021 (China); Hu, Chenglong [Key Laboratory of Optoelectronic Chemical Materials and Devices of Ministry of Education, School of Chemistry and Environmental Engineering, Jianghan University, Wuhan 430056 (China)

    2016-03-30

    Graphical abstract: A chemical bonding approach was proposed to prepare the PANI film covalently bonded to ITO substrate and the film exhibited high electrochemical activities and stability compared with that obtained by conventional film-forming approach. - Highlights: • The PANI film covalently bonded to ITO substrate was prepared using ABPA as modifier. • The oxidative potentials of the obtained PANI film were decreased. • The obtained PANI film exhibits high electrochemical activities and stability. - Abstract: Indium tin oxide (ITO) substrate was modified with 4-aminobenzylphosphonic acid (ABPA), and then the polyaniline (PANI) film covalently bonded to ITO substrate was prepared by the chemical oxidation polymerization. X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR-IR) spectroscopy, and atomic force microscopy (AFM) measurements demonstrated that chemical binding was formed between PANI and ABPA-modified ITO surface, and the maximum thickness of PANI layer is about 30 nm. The adhesive strength of PANI film on ITO substrate was tested by sonication. It was found that the film formed on the modified ITO exhibited a much better stability than that on bare one. Cyclic voltammetry (CV) and UV–vis spectroscopy measurements indicated that the oxidative potentials of PANI film on ABPA-modified ITO substrate were decreased and the film exhibited high electrochemical activities. Moreover, the optical contrast increased from 0.58 for PANI film (without ultrasound) to 1.06 for PANI film (after ultrasound for 60 min), which had an over 83% enhancement. The coloration time was 20.8 s, while the bleaching time was 19.5 s. The increase of electrochromic switching time was due to the lower ion diffusion coefficient of the large cation of (C{sub 4}H{sub 9}){sub 4}N{sup +} under the positive and negative potentials as comparison with the small Li{sup +} ion.

  13. Tuning the apparent formal potential of covalently attached ferrocene using SAM bearing ionizable -COOH groups

    International Nuclear Information System (INIS)

    Mukherjee, Sohini; Bandyopadhyay, Sabyasachi; Dey, Abhishek

    2013-01-01

    Highlights: • Covalent attachment of ethynylferrocene on the mixed SAM using “click” chemistry. • Control of redox potential at the plane of electron transfer by double layer effect. • Effect of pH of the medium on the redox potential of covalently attached ferrocene. • Change of redox potential of ethynylferrocene with variation of chain length of the diluent and the surface coverage. -- Abstract: A method of tuning the apparent formal potential at the interface between the electrode surface covered with carboxylate thiol self assembled monolayer (SAM) and the solution containing electrolytes is reported. Redox active ferrocene moiety has been covalently attached to the terminal azido groups in the SAM using “click” chemistry. Cyclic voltammetry experiments show that the reduction potential of this ferrocene moiety can be tuned easily from 0.345 V to 0.200 V, i.e. by 145 mV by varying the chain length of the thiol carboxylic acid diluents, changing the pH of the electrolytic solution and by changing the coverage of the surface. Using the (applying the theory of interfacial potential distribution by Smith and White and including the Stern layer effect on the potential of the redox species at the interface proposed by Fawcett) modified Nernst equation the shift of apparent formal potential of redox species at the interface has been analyzed when the chain length of the diluents, pH of the solution and coverage of the surface are changed. The data indicate that the phenomenon is governed by the ionizable polar head groups SAM, i.e. -COOH which changes the interfacial microenvironment around the redox active ferrocene centre

  14. Increased Protein Structural Resolution from Diethylpyrocarbonate-based Covalent Labeling and Mass Spectrometric Detection

    Science.gov (United States)

    Zhou, Yuping; Vachet, Richard W.

    2012-04-01

    Covalent labeling and mass spectrometry are seeing increased use together as a way to obtain insight into the 3-dimensional structure of proteins and protein complexes. Several amino acid specific (e.g., diethylpyrocarbonate) and non-specific (e.g., hydroxyl radicals) labeling reagents are available for this purpose. Diethylpyrocarbonate (DEPC) is a promising labeling reagent because it can potentially probe up to 30% of the residues in the average protein and gives only one reaction product, thereby facilitating mass spectrometric analysis. It was recently reported, though, that DEPC modifications are labile for some amino acids. Here, we show that label loss is more significant and widespread than previously thought, especially for Ser, Thr, Tyr, and His residues, when relatively long protein digestion times are used. Such label loss ultimately decreases the amount of protein structural information that is obtainable with this reagent. We find, however, that the number of DEPC modified residues and, thus, protein structural information, can be significantly increased by decreasing the time between the covalent labeling reaction and the mass spectrometric analysis. This is most effectively accomplished using short (e.g., 2 h) proteolytic digestions with enzymes such as immobilized chymotrypsin or Glu-C rather than using methods (e.g., microwave or ultrasonic irradiation) that accelerate proteolysis in other ways. Using short digestion times, we show that the percentage of solvent accessible residues that can be modified by DEPC increases from 44% to 67% for cytochrome c, 35% to 81% for myoglobin, and 76% to 95% for β-2-microglobulin. In effect, these increased numbers of modified residues improve the protein structural resolution available from this covalent labeling method. Compared with typical overnight digestion conditions, the short digestion times decrease the average distance between modified residues from 11 to 7 Å for myoglobin, 13 to 10 Å for

  15. Synthesis and non-covalent functionalization of carbon nanotubes rings: new nanomaterials with lectin affinity

    International Nuclear Information System (INIS)

    Assali, Mohyeddin; Leal, Manuel Pernía; Khiar, Noureddine; Fernández, Inmaculada

    2013-01-01

    We present a mild and practical carbon nanotubes rings (CNRs) synthesis from non-covalent functionalized and water-soluble linear single-wall carbon nanotubes. The hemi-micellar–supramolecular self-organization of lactose-based glycolipid 1 on the ring surface, followed by photo-polymerization of the diacetylenic function triggered by UV light afforded the first water-soluble and biocompatible CNRs. The obtained donut-like nanoconstructs expose a high density of lactose moieties on their surface, and are able to engage specific interactions with Arachis hypogea lectin similar to glycoconjugates on the cell membrane. (paper)

  16. Synthesis, characterisation and optical studies of new tetraethyl- rubyrin-graphene oxide covalent adducts

    Science.gov (United States)

    Garg, Kavita; Shanmugam, Ramakrishanan; Ramamurthy, Praveen C.

    2018-02-01

    Tetrathia-rubyrin and graphene oxide (GO) covalent adduct was synthesized, characterised and optical properties were studied. GO-Rubyrin adducts showed fluorescence quenching of rubyrin due to electron or energy transfer from rubyrin to graphene oxide, which also reflected in UV-vis absorbance spectroscopy. The non-linear optical responses were measured through Z scan technique in nano-second regime. The enhanced optical non-linearity was observed after attachment of GO with rubyrin, can be ascribed to the photo-induced electron or energy transfer from the electron rich rubyrin moiety to the electron deficient GO.

  17. Correlations of acute toxicity of metal ions and the covalent/ionic character of their bonds

    Energy Technology Data Exchange (ETDEWEB)

    Turner, J.E.; Williams, M.W.; Jacobson, K.B.; Hingerty, B.E.

    1984-01-01

    We have investigated correlations between physicochemical properties of 24 metal ions and their acute toxicity in mice and Drosophila. A high correlation for a softness parameter suggests that the relative covalent/ionic character of the bonds formed by the metal ions may be important in determining their toxicity. This hypothesis is reinforced by model calculations of metal binding to dinucleotides in water. Since the nature of bonds depends on ligand electronegativity, we searched for correlations involving this parameter. Although electronegativity is useful for interpreting some aspects of metal-ion behavior related to toxicity, it does not yield improved correlations. 8 refs., 3 figs., 1 tab.

  18. In situ surface enhanced resonance Raman scattering analysis of a reactive dye covalently bound to cotton.

    Science.gov (United States)

    White, P C; Munro, C H; Smith, W E

    1996-06-01

    An in situ surface enhanced resonance Raman scattering (SERRS) procedure is described for the analysis of a reactive dye covalently bound to a single strand of a cotton fibre. This procedure can be completed in 5 h, whereas an alternative enzyme digestion method takes approximately 21 h. These two fibre preparation methods give similar spectra from picogram quantities of dye present on a 2-5 mm length of fibre. The in situ nature of the analysis and the small sample size make this method particularly suitable for forensic applications.

  19. Dynamic nuclear polarization of membrane proteins: covalently bound spin-labels at protein–protein interfaces

    International Nuclear Information System (INIS)

    Wylie, Benjamin J.; Dzikovski, Boris G.; Pawsey, Shane; Caporini, Marc; Rosay, Melanie; Freed, Jack H.; McDermott, Ann E.

    2015-01-01

    We demonstrate that dynamic nuclear polarization of membrane proteins in lipid bilayers may be achieved using a novel polarizing agent: pairs of spin labels covalently bound to a protein of interest interacting at an intermolecular interaction surface. For gramicidin A, nitroxide tags attached to the N-terminal intermolecular interface region become proximal only when bimolecular channels forms in the membrane. We obtained signal enhancements of sixfold for the dimeric protein. The enhancement effect was comparable to that of a doubly tagged sample of gramicidin C, with intramolecular spin pairs. This approach could be a powerful and selective means for signal enhancement in membrane proteins, and for recognizing intermolecular interfaces

  20. Crystal structure of the covalent intermediate of amylosucrase from Neisseria polysaccharea

    DEFF Research Database (Denmark)

    Jensen, Malene H; Mirza, Osman Asghar; Albenne, Cecile

    2004-01-01

    be used for trapping the reaction intermediate for crystallographic studies. In this paper, the crystal structure of the acid/base catalyst mutant, E328Q, with a covalently bound glucopyranosyl moiety is presented. Sucrose cocrystallized crystals were soaked with alpha-D-glucopyranosyl fluoride, which...... for such intermediates. Analysis of the active site shows how oligosaccharide binding disrupts the putative nucleophilic water binding site found in the hydrolases of the GH family 13. This reveals important parts of the structural background for the shift in function from hydrolase to transglycosidase seen...

  1. Chemically Stable Covalent Organic Framework (COF)-Polybenzimidazole Hybrid Membranes: Enhanced Gas Separation through Pore Modulation.

    Science.gov (United States)

    Biswal, Bishnu P; Chaudhari, Harshal D; Banerjee, Rahul; Kharul, Ulhas K

    2016-03-24

    Highly flexible, TpPa-1@PBI-BuI and TpBD@PBI-BuI hybrid membranes based on chemically stable covalent organic frameworks (COFs) could be obtained with the polymer. The loading obtained was substantially higher (50 %) than generally observed with MOFs. These hybrid membranes show an exciting enhancement in permeability (about sevenfold) with appreciable separation factors for CO2/N2 and CO2/CH4. Further, we found that with COF pore modulation, the gas permeability can be systematically enhanced. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Covalent functionalization of carbon nanotube forests grown in situ on a metal-silicon chip

    KAUST Repository

    Johansson, Johan R.

    2012-03-12

    We report on the successful covalent functionalization of carbon nanotube (CNT) forests, in situ grown on a silicon chip with thin metal contact film as the buffer layer between the CNT forests and the substrate. The CNT forests were successfully functionalized with active amine and azide groups, which can be used for further chemical reactions. The morphology of the CNT forests was maintained after the functionalization. We thus provide a promising foundation for a miniaturized biosensor arrays system that can be easily integrated with Complementary Metal-Oxide Semiconductor (CMOS) technology.

  3. Dispersive and Covalent Interactions between Graphene and Metal Surfaces from the Random Phase Approximation

    DEFF Research Database (Denmark)

    Olsen, Thomas; Yan, Jun; Mortensen, Jens Jørgen

    2011-01-01

    We calculate the potential energy surfaces for graphene adsorbed on Cu(111), Ni(111), and Co(0001) using density functional theory and the random phase approximation (RPA). For these adsorption systems covalent and dispersive interactions are equally important and while commonly used approximations...... for exchange-correlation functionals give inadequate descriptions of either van der Waals or chemical bonds, RPA accounts accurately for both. It is found that the adsorption is a delicate competition between a weak chemisorption minimum close to the surface and a physisorption minimum further from the surface....

  4. New technology for regiospecific covalent coupling of polysaccharide antigens in ELISA for serological detection

    DEFF Research Database (Denmark)

    Jauho, E.S.; Boas, Ulrik; Wiuff, Camilla

    2000-01-01

    into the lipid A part and the polysaccharide part. The polysaccharide was conjugated regiospecifically to a photochemically active compound, anthraquinone, resulting in a polysaccharide-anthraquinone conjugate. Anthraquinones forms active radicals when exposed to soft UV irradiation (350 nm) permitting...... the formation of stable covalent bonds to polymers e.g, microtiter plates. By this technique the polysaccharides are bound through the anthraquinone part of the polysaccharide-anthraquinone conjugates to the microtiter plates. This minimizes denaturation of O-antigen epitopes during binding to the microtiter...

  5. Atomic structures and covalent-to-metallic transition of lead clusters Pbn (n=2-22)

    International Nuclear Information System (INIS)

    Wang Baolin; Zhao Jijun; Chen Xiaoshuang; Shi Daning; Wang Guanghou

    2005-01-01

    The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of Pb n (n=2-22) clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed

  6. Self-assembly of bridged silsesquioxanes: modulating structural evolution via cooperative covalent and noncovalent interactions.

    Science.gov (United States)

    Creff, Gaelle; Pichon, Benoît P; Blanc, Christophe; Maurin, David; Sauvajol, Jean-Louis; Carcel, Carole; Moreau, Joël J E; Roy, Pascale; Bartlett, John R; Man, Michel Wong Chi; Bantignies, Jean-Louis

    2013-05-07

    The self-assembly of a bis-urea phenylene-bridged silsesquioxane precursor during sol-gel synthesis has been investigated by in situ infrared spectroscopy, optical microscopy, and light scattering. In particular, the evolution of the system as a function of processing time was correlated with covalent interactions associated with increasing polycondensation and noncovalent interactions such as hydrogen bonding. A comprehensive mechanism based on the hydrolysis of the phenylene-bridged organosilane precursor prior to the crystallization of the corresponding bridged silsesquioxane via H-bonding and subsequent irreversible polycondensation is proposed.

  7. EDITORIAL: Strongly correlated electron systems Strongly correlated electron systems

    Science.gov (United States)

    Ronning, Filip; Batista, Cristian

    2011-03-01

    Strongly correlated electrons is an exciting and diverse field in condensed matter physics. This special issue aims to capture some of that excitement and recent developments in the field. Given that this issue was inspired by the 2010 International Conference on Strongly Correlated Electron Systems (SCES 2010), we briefly give some history in order to place this issue in context. The 2010 International Conference on Strongly Correlated Electron Systems was held in Santa Fe, New Mexico, a reunion of sorts from the 1989 International Conference on the Physics of Highly Correlated Electron Systems that also convened in Santa Fe. SCES 2010—co-chaired by John Sarrao and Joe Thompson—followed the tradition of earlier conferences, in this century, hosted by Buzios (2008), Houston (2007), Vienna (2005), Karlsruhe (2004), Krakow (2002) and Ann Arbor (2001). Every three years since 1997, SCES has joined the International Conference on Magnetism (ICM), held in Recife (2000), Rome (2003), Kyoto (2006) and Karlsruhe (2009). Like its predecessors, SCES 2010 topics included strongly correlated f- and d-electron systems, heavy-fermion behaviors, quantum-phase transitions, non-Fermi liquid phenomena, unconventional superconductivity, and emergent states that arise from electronic correlations. Recent developments from studies of quantum magnetism and cold atoms complemented the traditional subjects and were included in SCES 2010. 2010 celebrated the 400th anniversary of Santa Fe as well as the birth of astronomy. So what's the connection to SCES? The Dutch invention of the first practical telescope and its use by Galileo in 1610 and subsequent years overturned dogma that the sun revolved about the earth. This revolutionary, and at the time heretical, conclusion required innovative combinations of new instrumentation, observation and mathematics. These same combinations are just as important 400 years later and are the foundation of scientific discoveries that were discussed

  8. Highly Stable Porous Covalent Triazine-Piperazine Linked Nanoflower as a Feasible Adsorbent for Flue Gas CO2 Capture

    KAUST Repository

    Das, Swapan Kumar

    2016-02-11

    Here, we report a porous covalent triazine-piperazine linked polymer (CTPP) featuring 3D nanoflower morphology and enhanced capture/removal of CO2, CH4 from air (N2), essential to control greenhouse gas emission and natural gas upgrading. 13C solid-state NMR and FTIR analyses and CHN and X-ray photoelectron spectroscopy (XPS) elemental analyses confirmed the integration of triazine and piperazine components in the network. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) analyses revealed a relatively uniform particle size of approximately 400 to 500 nm with 3D nanoflower microstructure, which was formed by the self-assembly of interwoven and slight bent nanoflake components. The material exhibited outstanding chemical robustness under acidic and basic medium and high thermal stability up to 773 K. The CTPP possess high surface area (779 m2/g) and single-component gas adsorption study exhibited enhanced CO2 and CH4 uptake of 3.48 mmol/g, 1.09 mmol/g, respectively at 273 K, 1 bar; coupled with high sorption selectivities for CO2/N2 and CH4/N2 of 128 and 17, respectively. The enriched Lewis basicity of the CTPP favors the interaction with CO2, which results in an enhanced CO2 adsorption capacity and high CO2/N2 selectivity. The binary mixture breakthrough study for the flue gas composition at 298 K showed a high CO2/N2 selectivity of 82. CO2 heats of adsorption for the CTPP (34 kJ mol−1) were realized at the borderline between strong physisorption and weak chemisorption (QstCO2; 25−50 kJ mol−1) and low Qst value for N2 (22.09 kJ mol−1), providing the ultimate validation for the high selectivity of CO2 over N2.

  9. Physics of Strongly Coupled Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Kraeft, Wolf-Dietrich [Universitat Rostock (Germany)

    2007-07-15

    Strongly coupled plasmas (or non-ideal plasmas) are multi-component charged many-particle systems, in which the mean value of the potential energy of the system is of the same order as or even higher than the mean value of the kinetic energy. The constituents are electrons, ions, atoms and molecules. Dusty (or complex) plasmas contain still mesoscopic (multiply charged) particles. In such systems, the effects of strong coupling (non-ideality) lead to considerable deviations of physical properties from the corresponding properties of ideal plasmas, i.e., of plasmas in which the mean kinetic energy is essentially larger than the mean potential energy. For instance, bound state energies become density dependent and vanish at higher densities (Mott effect) due to the interaction of the pair with the surrounding particles. Non-ideal plasmas are of interest both for general scientific reasons (including, for example, astrophysical questions), and for technical applications such as inertially confined fusion. In spite of great efforts both experimentally and theoretically, satisfactory information on the physical properties of strongly coupled plasmas is not at hand for any temperature and density. For example, the theoretical description of non-ideal plasmas is possible only at low densities/high temperatures and at extremely high densities (high degeneracy). For intermediate degeneracy, however, numerical experiments have to fill the gap. Experiments are difficult in the region of 'warm dense matter'. The monograph tries to present the state of the art concerning both theoretical and experimental attempts. It mainly includes results of the work performed in famous Russian laboratories in recent decades. After outlining basic concepts (chapter 1), the generation of plasmas is considered (chapter 2, chapter 3). Questions of partial (chapter 4) and full ionization (chapter 5) are discussed including Mott transition and Wigner crystallization. Electrical and

  10. Strongly coupled dust coulomb clusters

    International Nuclear Information System (INIS)

    Juan Wentau; Lai Yingju; Chen Mingheng; I Lin

    1999-01-01

    The structures and motions of quasi-2-dimensional strongly coupled dust Coulomb clusters with particle number N from few to hundreds in a cylindrical rf plasma trap are studied and compared with the results from the molecular dynamic simulation using more ideal models. Shell structures with periodic packing in different shells and intershell rotational motion dominated excitations are observed at small N. As N increases, the boundary has less effect, the system recovers to the triangular lattice with isotropic vortex type cooperative excitations similar to an infinite N system except the outer shell region. The above generic behaviors are mainly determined by the system symmetry and agree with the simulation results. The detailed interaction form causes minor effect such as the fine structure of packing

  11. Probability densities in strong turbulence

    Science.gov (United States)

    Yakhot, Victor

    2006-03-01

    In this work we, using Mellin’s transform combined with the Gaussian large-scale boundary condition, calculate probability densities (PDFs) of velocity increments P(δu,r), velocity derivatives P(u,r) and the PDF of the fluctuating dissipation scales Q(η,Re), where Re is the large-scale Reynolds number. The resulting expressions strongly deviate from the Log-normal PDF P(δu,r) often quoted in the literature. It is shown that the probability density of the small-scale velocity fluctuations includes information about the large (integral) scale dynamics which is responsible for the deviation of P(δu,r) from P(δu,r). An expression for the function D(h) of the multifractal theory, free from spurious logarithms recently discussed in [U. Frisch, M. Martins Afonso, A. Mazzino, V. Yakhot, J. Fluid Mech. 542 (2005) 97] is also obtained.

  12. Stereodynamic tetrahydrobiisoindole “NU-BIPHEP(O”s: functionalization, rotational barriers and non-covalent interactions

    Directory of Open Access Journals (Sweden)

    Golo Storch

    2016-07-01

    Full Text Available Stereodynamic ligands offer intriguing possibilities in enantioselective catalysis. “NU-BIPHEPs” are a class of stereodynamic diphosphine ligands which are easily accessible via rhodium-catalyzed double [2 + 2 + 2] cycloadditions. This study explores the preparation of differently functionalized “NU-BIPHEP(O” compounds, the characterization of non-covalent adduct formation and the quantification of enantiomerization barriers. In order to explore the possibilities of functionalization, we studied modifications of the ligand backbone, e.g., with 3,5-dichlorobenzoyl chloride. Diastereomeric adducts with Okamoto-type cellulose derivatives and on-column deracemization were realized on the basis of non-covalent interactions. Enantioselective dynamic HPLC (DHPLC allowed for the determination of rotational barriers of ΔG‡298K = 92.2 ± 0.3 kJ mol−1 and 99.5 ± 0.1 kJ mol−1 underlining the stereodynamic properties of “NU-BIPHEPs” and “NU-BIPHEP(Os”, respectively. These results make the preparation of tailor-made functionalized stereodynamic ligands possible and give an outline for possible applications in enantioselective catalysis.

  13. Covalent docking of selected boron-based serine beta-lactamase inhibitors

    Science.gov (United States)

    Sgrignani, Jacopo; Novati, Beatrice; Colombo, Giorgio; Grazioso, Giovanni

    2015-05-01

    AmpC β-lactamase is a hydrolytic enzyme conferring resistance to β-lactam antibiotics in multiple Gram-negative bacteria. Therefore, identification of non-β-lactam compounds able to inhibit the enzyme is crucial for the development of novel antibacterial therapies. In general, AmpC inhibitors have to engage the highly solvent-exposed catalytic site of the enzyme. Therefore, understanding the implications of ligand-protein induced-fit and water-mediated interactions behind the inhibitor-enzyme recognition process is fundamental for undertaking structure-based drug design process. Here, we focus on boronic acids, a promising class of beta-lactamase covalent inhibitors. First, we optimized a docking protocol able to reproduce the experimentally determined binding mode of AmpC inhibitors bearing a boronic group. This goal was pursued (1) performing rigid and flexible docking calculations aiming to establish the role of the side chain conformations; and (2) investigating the role of specific water molecules in shaping the enzyme active site and mediating ligand protein interactions. Our calculations showed that some water molecules, conserved in the majority of the considered X-ray structures, are needed to correctly predict the binding pose of known covalent AmpC inhibitors. On this basis, we formalized our findings in a docking and scoring protocol that could be useful for the structure-based design of new boronic acid AmpC inhibitors.

  14. A Covalent Linker Allows for Membrane Targeting of An Oxylipin Biosynthetic Complex

    Energy Technology Data Exchange (ETDEWEB)

    Gilbert, N.C.; Niebuhr, M.; Tsuruta, H.; Bordelon, T.; Ridderbusch, O.; Dassey, A.; Brash, A.R.; Bartlett, S.G.; Newcomer, M.E.

    2009-05-18

    A naturally occurring bifunctional protein from Plexaura homomalla links sequential catalytic activities in an oxylipin biosynthetic pathway. The C-terminal lipoxygenase (LOX) portion of the molecule catalyzes the transformation of arachidonic acid (AA) to the corresponding 8R-hydroperoxide, and the N-terminal allene oxide synthase (AOS) domain promotes the conversion of the hydroperoxide intermediate to the product allene oxide (AO). Small-angle X-ray scattering data indicate that in the absence of a covalent linkage the two catalytic domains that transform AA to AO associate to form a complex that recapitulates the structure of the bifunctional protein. The SAXS data also support a model for LOX and AOS domain orientation in the fusion protein inferred from a low-resolution crystal structure. However, results of membrane binding experiments indicate that covalent linkage of the domains is required for Ca2+-dependent membrane targeting of the sequential activities, despite the noncovalent domain association. Furthermore, membrane targeting is accompanied by a conformational change as monitored by specific proteolysis of the linker that joins the AOS and LOX domains. Our data are consistent with a model in which Ca2+-dependent membrane binding relieves the noncovalent interactions between the AOS and LOX domains and suggests that the C2-like domain of LOX mediates both protein-protein and protein-membrane interactions.

  15. Surface modification of polypropylene nonwoven fabrics via covalent immobilization of nonionic sugar-based surfactants

    Energy Technology Data Exchange (ETDEWEB)

    Xin, Zhirong, E-mail: xinzhirong2012@126.com; Yan, Shunjie; Ding, Jiaotong; Yang, Zongfeng; Du, Binbin; Du, Shanshan

    2014-05-01

    Graphical abstract: - Highlights: • Amphiphilic N-alkyl-1-amino-1-deoxy-D-glucitol were prepared. • The pGMA-grafted membranes were obtained via photo-grafting of glycidyl methacrylate. • Amphiphilic C{sub n}AG were covalent immobilized onto the pGMA-grafted membranes. • The C{sub n}AG-grafted membranes obviously suppressed protein adsorption and platelet adhesion. - Abstract: Amphiphilic N-alkyl-1-amino-1-deoxy-D-glucitol (C{sub n}AG, n = 8, 12) were successfully prepared. Polypropylene nonwoven fabrics (PP{sub NWF}) were grafted with glycidyl methacrylate (GMA) via a technique of UV-induced graft polymerization combined with plasma pre-treatment, and then PP{sub NWF}-g-GMA was used for the covalent immobilization of C{sub n}AG. The surface graft polymerization was confirmed by ATR-FTIR and XPS, respectively. Effect of grafting parameters, e.g., acetone content, monomer concentration and UV irradiation time on the grafting density of GMA was investigated. And the hemocompatibility of the modified PP{sub NWF} was evaluated by protein adsorption and platelet adhesion. It was founded that the C{sub n}AG-modified substrates greatly suppressed protein adsorption and platelet adhesion compared with the native and pGMA-grafted PP{sub NWF}.

  16. Covalent modification of a ten-residue cationic antimicrobial peptide with levofloxacin

    Science.gov (United States)

    Rodriguez, Carlos; Papanastasiou, Emilios; Juba, Melanie; Bishop, Barney

    2014-09-01

    The rampant spread of antibiotic resistant bacteria has spurred interest in alternative strategies for developing next-generation antibacterial therapies. As such, there has been growing interest in cationic antimicrobial peptides (CAMPs) and their therapeutic applications. Modification of CAMPs via conjugation to auxiliary compounds, including small molecule drugs, is a new approach to developing effective, broad-spectrum antibacterial agents with novel physicochemical properties and versatile antibacterial mechanisms. Here, we’ve explored design parameters for engineering CAMPs conjugated to small molecules with favorable physicochemical and antibacterial properties by covalently affixing a fluoroquinolone antibiotic, levofloxacin, to the ten-residue CAMP Pep-4. Relative to the unmodified Pep-4, the conjugate was found to demonstrate substantially increased antibacterial potency under high salt concentrations. Historically, it has been observed that most CAMPs lose antibacterial effectiveness in such high ionic strength environments, a fact that has presented a challenge to their development as therapeutics. Physicochemical studies revealed that P4LC was more hydrophobic than Pep-4, while mechanistic findings indicated that the conjugate was more effective at disrupting bacterial membrane integrity. Although the inherent antibacterial effect of the incorporated levofloxacin molecules did not appear to be substantially realized in this conjugate, these findings nevertheless suggest that covalent attachment of small molecule antibiotics with favorable physicochemical properties to CAMPs could be a promising strategy for enhancing peptide performance and overall therapeutic potential. These results have broader applicability to the development of future CAMP-antibiotic conjugates for potential therapeutic applications.

  17. Formation and properties of electroactive fullerene based films with a covalently attached ferrocenyl redox probe

    International Nuclear Information System (INIS)

    Wysocka-Zolopa, Monika; Winkler, Krzysztof; Caballero, Ruben; Langa, Fernando

    2011-01-01

    Highlights: → Formation of redox active films of ferrocene derivatives of C 60 and palladium. → Fullerene moieties are covalently bonded to palladium atoms to form a polymeric network. → Electrochemical activity at both positive and negative potentials. → Charge transfer processes accompanied by transport of supporting electrolyte to and from the polymer layers. - Abstract: Redox active films have been produced via electrochemical reduction in a solution containing palladium(II) acetate and ferrocene derivatives of C 60 (Fc-C 60 and bis-Fc-C 60 ). In these films, fullerene moieties are covalently bonded to palladium atoms to form a polymeric network. Fc-C 60 /Pd and bis-Fc-C 60 /Pd films form uniform and relatively smooth layers on the electrode surface. These films are electrochemically active in both the positive and negative potential regions. At negative potentials, reduction of fullerene moiety takes place resulting in voltammetric behavior resembles typical of conducting polymers. In the positive potential range, oxidation of ferrocene is responsible for the formation of a sharp and symmetrical peak on the voltammograms. In this potential range, studied films behave as typical redox polymers. The charge associated with the oxidation process depends on the number of ferrocene units attached to the C 60 moiety. Oxidation and reduction of these redox active films are accompanied by transport of supporting electrolyte to and from the polymer layer. Films also show a higher permeability to anions than to cations.

  18. Interfacial design of carbon nanotube polymer composites: a hybrid system of noncovalent and covalent functionalizations

    Science.gov (United States)

    Liu, J. Q.; Xiao, T.; Liao, K.; Wu, P.

    2007-04-01

    Homogeneous dispersion of carbon nanotubes (CNTs) throughout the polymer matrix and their adequate interfacial bonding are critical for load transfer in CNT-polymer composites. However, both cannot be realized simultaneously by either covalent or noncovalent functionalization. A hybrid system integrating both covalent and noncovalent functionalizations is presented for interfacial design of CNT-polymer composites. To investigate the feasibility of this system, examples of the epoxidized single-walled carbon nanotube (SWNT) subsequently wrapped by poly(m-phenylenevinylene- co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) are studied by means of molecular dynamics simulations. It is shown by our results that PmPV molecules are miscible with epoxy resin and tend to wrap around the epoxidized SWNT, which could be used to weaken the interaction between SWNTs and consequently improve the dispersion of SWNTs into the matrix. The interfacial shear strength of CNT-polymer composites can be improved significantly by properly designed functionalizations, especially the hybrid system.

  19. Chemoselective small molecules that covalently modify one lysine in a non-enzyme protein in plasma

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Sungwook; Connelly, Stephen; Reixach, Natàlia; Wilson, Ian A.; Kelly, Jeffery W. (Scripps)

    2010-02-19

    A small molecule that could bind selectively to and then react chemoselectively with a non-enzyme protein in a complex biological fluid, such as blood, could have numerous practical applications. Herein, we report a family of designed stilbenes that selectively and covalently modify the prominent plasma protein transthyretin in preference to more than 4,000 other human plasma proteins. They react chemoselectively with only one of eight lysine {epsilon}-amino groups within transthyretin. The crystal structure confirms the expected binding orientation of the stilbene substructure and the anticipated conjugating amide bond. These covalent transthyretin kinetic stabilizers exhibit superior amyloid inhibition potency compared to their noncovalent counterparts, and they prevent cytotoxicity associated with amyloidogenesis. Though there are a few prodrugs that, upon metabolic activation, react with a cysteine residue inactivating a specific non-enzyme, we are unaware of designed small molecules that react with one lysine {epsilon}-amine within a specific non-enzyme protein in a complex biological fluid.

  20. Electron beam controlled covalent attachment of small organic molecules to graphene.

    Science.gov (United States)

    Markevich, Alexander; Kurasch, Simon; Lehtinen, Ossi; Reimer, Oliver; Feng, Xinliang; Müllen, Klaus; Turchanin, Andrey; Khlobystov, Andrei N; Kaiser, Ute; Besley, Elena

    2016-02-07

    The electron beam induced functionalization of graphene through the formation of covalent bonds between free radicals of polyaromatic molecules and C=C bonds of pristine graphene surface has been explored using first principles calculations and high-resolution transmission electron microscopy. We show that the energetically strongest attachment of the radicals occurs along the armchair direction in graphene to carbon atoms residing in different graphene sub-lattices. The radicals tend to assume vertical position on graphene substrate irrespective of direction of the bonding and the initial configuration. The "standing up" molecules, covalently anchored to graphene, exhibit two types of oscillatory motion--bending and twisting--caused by the presence of acoustic phonons in graphene and dispersion attraction to the substrate. The theoretically derived mechanisms are confirmed by near atomic resolution imaging of individual perchlorocoronene (C24Cl12) molecules on graphene. Our results facilitate the understanding of controlled functionalization of graphene employing electron irradiation as well as mechanisms of attachment of impurities via the processing of graphene nanoelectronic devices by electron beam lithography.

  1. Covalent Immobilization of Bacillus licheniformis γ-Glutamyl Transpeptidase on Aldehyde-Functionalized Magnetic Nanoparticles

    Directory of Open Access Journals (Sweden)

    Meng-Chun Chi

    2013-02-01

    Full Text Available This work presents the synthesis and use of surface-modified iron oxide nanoparticles for the covalent immobilization of Bacillus licheniformis γ-glutamyl transpeptidase (BlGGT. Magnetic nanoparticles were prepared by an alkaline solution of divalent and trivalent iron ions, and they were subsequently treated with 3-aminopropyltriethoxysilane (APES to obtain the aminosilane-coated nanoparticles. The functional group on the particle surface and the amino group of BlGGT was then cross-linked using glutaraldehyde as the coupling reagent. The loading capacity of the prepared nanoparticles for BlGGT was 34.2 mg/g support, corresponding to 52.4% recovery of the initial activity. Monographs of transmission electron microscopy revealed that the synthesized nanoparticles had a mean diameter of 15.1 ± 3.7 nm, and the covalent cross-linking of the enzyme did not significantly change their particle size. Fourier transform infrared spectroscopy confirmed the immobilization of BlGGT on the magnetic nanoparticles. The chemical and kinetic behaviors of immobilized BlGGT are mostly consistent with those of the free enzyme. The immobilized enzyme could be recycled ten times with 36.2% retention of the initial activity and had a comparable stability respective to free enzyme during the storage period of 30 days. Collectively, the straightforward synthesis of aldehyde-functionalized nanoparticles and the efficiency of enzyme immobilization offer wide perspectives for the practical use of surface-bound BlGGT.

  2. A new family of covalent inhibitors block nucleotide binding to the active site of pyruvate kinase.

    Science.gov (United States)

    Morgan, Hugh P; Walsh, Martin J; Blackburn, Elizabeth A; Wear, Martin A; Boxer, Matthew B; Shen, Min; Veith, Henrike; McNae, Iain W; Nowicki, Matthew W; Michels, Paul A M; Auld, Douglas S; Fothergill-Gilmore, Linda A; Walkinshaw, Malcolm D

    2012-11-15

    PYK (pyruvate kinase) plays a central role in the metabolism of many organisms and cell types, but the elucidation of the details of its function in a systems biology context has been hampered by the lack of specific high-affinity small-molecule inhibitors. High-throughput screening has been used to identify a family of saccharin derivatives which inhibit LmPYK (Leishmania mexicana PYK) activity in a time- (and dose-) dependent manner, a characteristic of irreversible inhibition. The crystal structure of DBS {4-[(1,1-dioxo-1,2-benzothiazol-3-yl)sulfanyl]benzoic acid} complexed with LmPYK shows that the saccharin moiety reacts with an active-site lysine residue (Lys335), forming a covalent bond and sterically hindering the binding of ADP/ATP. Mutation of the lysine residue to an arginine residue eliminated the effect of the inhibitor molecule, providing confirmation of the proposed inhibitor mechanism. This lysine residue is conserved in the active sites of the four human PYK isoenzymes, which were also found to be irreversibly inhibited by DBS. X-ray structures of PYK isoforms show structural differences at the DBS-binding pocket, and this covalent inhibitor of PYK provides a chemical scaffold for the design of new families of potentially isoform-specific irreversible inhibitors.

  3. Boosting lithium storage in covalent organic framework via activation of 14-electron redox chemistry.

    Science.gov (United States)

    Lei, Zhendong; Yang, Qinsi; Xu, Yi; Guo, Siyu; Sun, Weiwei; Liu, Hao; Lv, Li-Ping; Zhang, Yong; Wang, Yong

    2018-02-08

    Conjugated polymeric molecules have been heralded as promising electrode materials for the next-generation energy-storage technologies owing to their chemical flexibility at the molecular level, environmental benefit, and cost advantage. However, before any practical implementation takes place, the low capacity, poor structural stability, and sluggish ion/electron diffusion kinetics remain the obstacles that have to be overcome. Here, we report the synthesis of a few-layered two-dimensional covalent organic framework trapped by carbon nanotubes as the anode of lithium-ion batteries. Remarkably, upon activation, this organic electrode delivers a large reversible capacity of 1536 mAh g -1 and can sustain 500 cycles at 100 mA g -1 . Aided by theoretical calculations and electrochemical probing of the electrochemical behavior at different stages of cycling, the storage mechanism is revealed to be governed by 14-electron redox chemistry for a covalent organic framework monomer with one lithium ion per C=N group and six lithium ions per benzene ring. This work may pave the way to the development of high-capacity electrodes for organic rechargeable batteries.

  4. Cellulose acetate membranes functionalized with resveratrol by covalent immobilization for improved osseointegration

    Science.gov (United States)

    Pandele, A. M.; Neacsu, P.; Cimpean, A.; Staras, A. I.; Miculescu, F.; Iordache, A.; Voicu, S. I.; Thakur, V. K.; Toader, O. D.

    2018-04-01

    Covalent immobilization of resveratrol onto cellulose acetate polymeric membranes used as coating on a Mg-1Ca-0.2Mn-0.6Zr alloy is presented for potential application in the improvement of osseointegration processes. For this purpose, cellulose acetate membrane is hydrolysed in the presence of potassium hydroxide, followed by covalent immobilization of aminopropyl triethoxy silane. Resveratrol was immobilized onto membranes using glutaraldehyde as linker. The newly synthesised functional membranes were thoroughly characterized for their structural characteristics determination employing X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetric analysis (TGA/DTG) and scanning electron microscopy (SEM) techniques. Subsequently, in vitro cellular tests were performed for evaluating the cytotoxicity biocompatibility of synthesized materials and also the osseointegration potential of obtained derivatised membrane material. It was demonstrated that both polymeric membranes support viability and proliferation of the pre-osteoblastic MC3T3-E1 cells, thus providing a good protection against the potential harmful effects of the compounds released from coated alloys. Furthermore, cellulose acetate membrane functionalized with resveratrol exhibits a significant increase in alkaline phosphatase activity and extracellular matrix mineralization, suggesting its suitability to function as an implant surface coating for guided bone regeneration.

  5. Covalent Anchoring of Chloroperoxidase and Glucose Oxidase on the Mesoporous Molecular Sieve SBA-15

    Directory of Open Access Journals (Sweden)

    Martin Hartmann

    2010-02-01

    Full Text Available Functionalization of porous solids plays an important role in many areas, including heterogeneous catalysis and enzyme immobilization. In this study, large-pore ordered mesoporous SBA-15 molecular sieves were synthesized with tetraethyl orthosilicate (TEOS in the presence of the non-ionic triblock co-polymer Pluronic P123 under acidic conditions. These materials were grafted with 3 aminopropyltrimethoxysilane (ATS, 3-glycidoxypropyltrimethoxysilane (GTS and with 3 aminopropyltrimethoxysilane and glutaraldehyde (GA-ATS in order to provide covalent anchoring points for enzymes. The samples were characterized by nitrogen adsorption, powder X-ray diffraction, solid-state NMR spectroscopy, elemental analysis, diffuse reflectance fourier transform infrared spectroscopy and diffuse reflectance UV/Vis spectroscopy. The obtained grafted materials were then used for the immobilization of chloroperoxidase (CPO and glucose oxidase (GOx and the resulting biocatalysts were tested in the oxidation of indole. It is found that enzymes anchored to the mesoporous host by the organic moieties can be stored for weeks without losing their activity. Furthermore, the covalently linked enzymes are shown to be less prone to leaching than the physically adsorbed enzymes, as tested in a fixed-bed reactor under continuous operation conditions.

  6. Covalent-display of an active chimeric-recombinant tissue plasminogen activator on polyhydroxybutyrate granules surface.

    Science.gov (United States)

    Hafizi, Akram; Malboobi, Mohamad Ali; Jalali-Javaran, Mokhtar; Maliga, Pal; Alizadeh, Houshang

    2017-11-01

    To develop a deliberately engineered expression and purification system for an active chimeric-recombinant tissue plasminogen activator (crtPA) using co-expression with polyhydroxybutyrate (PHB) operon genes. Fusion of crtPA with PhaC-synthase simplified the purification steps through crtPA sedimentation with PHB particles. Moreover, the covalently immobilized crtPA was biologically active as shown in a chromogenic assay. Upon WELQut-protease activity, the released single-chain crtPA converted to the two-chain form which produced a pattern of bands with approx. MW of 32 and 11 kDa in addition to the full length crtPA. Fusion of crtPA with PhaC-synthase not only simplifies purification from the bacterial host lysate, but also co-expression of PHB operon genes creates an oxidative environment, thereby reducing the inclusion body formation possibility. The isolated crtPA-PHB granules exhibited crtPA serine protease activity. Thus, fusion with the PhaC protein could be used as a scaffold for covalent displaying of functional disulfide-rich proteins.

  7. An NMR study of the covalent and noncovalent interactions of CC-1065 and DNA

    International Nuclear Information System (INIS)

    Scahill, T.A.; Jensen, R.M.; Swenson, D.H.; Hatzenbuhler, N.T.; Petzold, G.; Wierenga, W.; Brahme, N.D.

    1990-01-01

    The binding of the antitumor drug CC-1065 has been studied with nuclear magnetic resonance (NMR) spectroscopy. This study involves two parts, the elucidation of the covalent binding site of the drug to DNA and a detailed investigation of the noncovalent interactions of CC-1065 with a DNA fragment through analysis of 2D NOE (NOESY) experiments. A CC-1065-DNA adduct was prepared, and an adenine adduct was released upon heating. NMR ( 1 H and 13 C) analysis of the adduct shows that the drug binds to N3 of adenine by reaction of its cyclopropyl group. The reaction pathway and product formed were determined by analysis of the 13 C DEPT spectra. An octamer duplex, d(CGATTAGC·GCTAATCG), was synthesized and used in the interaction study of CC-1065 and the oligomer. The duplex and the drug-octamer complex were both analyzed by 2D spectroscopy (COSY, NOESY). The relative intensity of the NOEs observed between the drug (CC-1065) and the octamer duplex shows conclusively that the drug is located in the minor groove, covalently attached to N3 of adenine 6 and positioned from the 3' → 5' end in relation to strand A [d(CGATTA 6 GC)]. A mechanism for drug binding and stabilization can be inferred from the NOE data and model-building studies

  8. New highly luminescent hybrid materials: terbium pyridine-picolinate covalently grafted on kaolinite.

    Science.gov (United States)

    de Faria, Emerson H; Nassar, Eduardo J; Ciuffi, Katia J; Vicente, Miguel A; Trujillano, Raquel; Rives, Vicente; Calefi, Paulo S

    2011-04-01

    Luminescent hybrid materials derived from kaolinite appear as promising materials for optical applications due to their specific properties. The spectroscopic behavior of terbium picolinate complexes covalently grafted on kaolinite and the influence of the secondary ligand and thermal treatment on luminescence are reported. The resulting materials were characterized by thermal analysis, element analysis, X-ray diffraction, infrared absorption spectroscopy, and photoluminescence. The thermogravimetric curves indicated an enhancement in the thermal stability up to 300 °C for the lanthanide complexes covalently grafted on kaolinite, with respect to the isolated complexes. The increase in the basal spacing observed by X-ray diffraction confirmed the insertion of the organic ligands into the basal space of kaolinite, involving the formation of a bond between Al-OH and the carboxylate groups, as evidenced by infrared spectroscopy. The luminescent hybrid material exhibited a stronger characteristic emission of Tb(3+) compared to the isolated complex. The excitation spectra displayed a broad band at 277 nm, assigned to a ligand-to-metal charge transfer, while the emission spectra presented bands related to the electronic transitions characteristic of the Tb(3+) ion from the excited state (5)D(4) to the states (7)F(J) (J=5, 4, and 3), with the 4→5 transition having high intensity with green emission. © 2011 American Chemical Society

  9. Azidobupramine, an Antidepressant-Derived Bifunctional Neurotransmitter Transporter Ligand Allowing Covalent Labeling and Attachment of Fluorophores.

    Directory of Open Access Journals (Sweden)

    Thomas Kirmeier

    Full Text Available The aim of this study was to design, synthesize and validate a multifunctional antidepressant probe that is modified at two distinct positions. The purpose of these modifications was to allow covalent linkage of the probe to interaction partners, and decoration of probe-target complexes with fluorescent reporter molecules. The strategy for the design of such a probe (i.e., azidobupramine was guided by the need for the introduction of additional functional groups, conveying the required properties while keeping the additional moieties as small as possible. This should minimize the risk of changing antidepressant-like properties of the new probe azidobupramine. To control for this, we evaluated the binding parameters of azidobupramine to known target sites such as the transporters for serotonin (SERT, norepinephrine (NET, and dopamine (DAT. The binding affinities of azidobupramine to SERT, NET, and DAT were in the range of structurally related and clinically active antidepressants. Furthermore, we successfully visualized azidobupramine-SERT complexes not only in SERT-enriched protein material but also in living cells stably overexpressing SERT. To our knowledge, azidobupramine is the first structural analogue of a tricyclic antidepressant that can be covalently linked to target structures and further attached to reporter molecules while preserving antidepressant-like properties and avoiding radioactive isotopes.

  10. Clustering of carboxylated magnetite nanoparticles through polyethylenimine: Covalent versus electrostatic approach

    Science.gov (United States)

    Tóth, Ildikó Y.; Nesztor, Dániel; Novák, Levente; Illés, Erzsébet; Szekeres, Márta; Szabó, Tamás; Tombácz, Etelka

    2017-04-01

    Carboxylated magnetite nanoparticles (MNPs) are frequently used to develop materials with enhanced properties for MRI and hyperthermia. The controlled clustering of MNPs via covalent or electrostatic approaches provides opportunity to prepare high quality materials. MNPs were prepared by co-precipitation and coated by poly(acrylic acid-co-maleic acid) (PAM@MNP). The clusters were synthesized from purified PAM@MNPs and polyethylenimine (PEI) solution via electrostatic interaction and covalent bond formation (ES-cluster and CB-cluster, respectively). The electrostatic adhesion (-NH3+ and -COO-) and the formed amide bond were confirmed by ATR-FTIR. The averaged area of CB-clusters was about twice as large as that of ES-cluster, based on TEM. The SAXS results showed that the surface of MNPs was smooth and the nanoparticles were close packed in both clusters. The pH-dependent aggregation state and zeta potential of clusters were characterized by DLS and electrophoresis measurements, the clusters were colloidally stable at pH>5. In hyperthermia experiments, the values of SAR were about two times larger for the chemically bonded cluster. The MRI studies showed exceptionally high transversion relaxivities, the r2 values are 457 mM-1 s-1 and 691 mM-1 s-1 for ES-cluster and CB-cluster, respectively. Based on these results, the chemically clustered product shows greater potential for feasible biomedical applications.

  11. Nonvolatile memory device using gold nanoparticles covalently bound to reduced graphene oxide.

    Science.gov (United States)

    Cui, Peng; Seo, Sohyeon; Lee, Junghyun; Wang, Luyang; Lee, Eunkyo; Min, Misook; Lee, Hyoyoung

    2011-09-27

    Nonvolatile memory devices using gold nanoparticles (AuNPs) and reduced graphene oxide (rGO) sheets were fabricated in both horizontal and vertical structures. The horizontal memory device, in which a singly and doubly overlayered semiconducting rGO channel was formed by simply using a spin-casting technique to connect two gold electrodes, was designed for understanding the origin of charging effects. AuNPs were chemically bound to the rGO channel through a π-conjugated molecular linker. The π-conjugated bifunctional molecular linker, 4-mercapto-benzenediazonium tetrafluoroborate (MBDT) salt, was newly synthesized and used as a molecular bridge to connect the AuNPs and rGOs. By using a self-assembly technique, the diazonium functional group of the MBDT molecular linker was spontaneously immobilized on the rGOs. Then, the monolayered AuNPs working as capacitors were covalently connected to the thiol groups of the MBDT molecules, which were attached to rGOs (AuNP-frGO). These covalent bonds were confirmed by XPS analyses. The current-voltage characteristics of both the horizontal and vertical AuNP-frGO memory devices showed noticeable nonlinear hysteresis, stable write-multiple read-erase-multiple read cycles over 1000 s, and a long retention time over 700 s. In addition, the vertical AuNP-frGO memory device showed a large current ON/OFF ratio and high stability. © 2011 American Chemical Society

  12. In vitro covalent binding of 3-[14C]methylindole metabolites in goat tissues

    International Nuclear Information System (INIS)

    Bray, T.M.; Carlson, J.R.; Nocerini, M.R.

    1984-01-01

    Covalent binding of 3-[ 14 C]methylindole (3[ 14 C]MI) in crude microsomal preparations of goat lung, liver, and kidney was measured to determine if a reactive intermediate was formed during the in vitro metabolism of 3-methylindole (3MI). The bound radioactivity was highest in lung compared to liver and kidney. The amount of bound radioactivity per nanomole of cytochrome P-450 was approximately 10 times higher in the lung compared to the liver. No detectable bound radioactivity was found when 3-[ 3 H]methyloxindole was used as the substrate. Cofactor requirements and the effects of inhibitors indicate that a mixed function oxidase (MFO) system is involved in formation of a reactive intermediate. Inhibitors and conjugating agents that are known to reduce the severity of 3MI-induced lung injury such as piperonyl butoxide (MFO inhibitor) and glutathione (conjugating agent) significantly decreased the in vitro binding of 3[ 14 C]MI. The results indicate that a reactive intermediate is produced during the metabolism of 3MI by the MFO system. The organ specificity in binding suggests that covalent binding by lung microsomes may be related to the mechanism of 3MI-induced lung injury

  13. Synthesis of Covalently Cross-Linked Colloidosomes from Peroxidized Pickering Emulsions

    Directory of Open Access Journals (Sweden)

    Nadiya Popadyuk

    2016-10-01

    Full Text Available A new approach to the formation of cross-linked colloidosomes was developed on the basis of Pickering emulsions that were stabilized exclusively by peroxidized colloidal particles. Free radical polymerization and a soft template technique were used to convert droplets of a Pickering emulsion into colloidosomes. The peroxidized latex particles were synthesized in the emulsion polymerization process using amphiphilic polyperoxide copolymers poly(2-tert-butylperoxy-2-methyl-5-hexen-3-ine-co-maleic acid (PM-1-MAc or poly[N-(tert-butylperoxymethylacrylamide]-co-maleic acid (PM-2-MAc, which were applied as both initiators and surfactants (inisurfs. The polymerization in the presence of the inisurfs results in latexes with a controllable amount of peroxide and carboxyl groups at the particle surface. Peroxidized polystyrene latex particles with a covalently grafted layer of inisurf PM-1-MAc or PM-2-MAc were used as Pickering stabilizers to form Pickering emulsions. A mixture of styrene and/or butyl acrylate with divinylbenzene and hexadecane was applied as a template for the synthesis of colloidosomes. Peroxidized latex particles located at the interface are involved in the radical reactions of colloidosomes formation. As a result, covalently cross-linked colloidosomes were obtained. It was demonstrated that the structure of the synthesized (using peroxidized latex particles colloidosomes depends on the amount of functional groups and pH during the synthesis. Therefore, the size and morphology of colloidosomes can be controlled by latex particle surface properties.

  14. Potent and Selective Covalent Quinazoline Inhibitors of KRAS G12C

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Mei; Lu, Jia; Li, Lianbo; Feru, Frederic; Quan, Chunshan; Gero, Thomas W.; Ficarro, Scott B.; Xiong, Yuan; Ambrogio, Chiara; Paranal, Raymond M.; Catalano, Marco; Shao, Jay; Wong, Kwok-Kin; Marto, Jarrod A.; Fischer, Eric S.; Jänne, Pasi A.; Scott, David A.; Westover, Kenneth D.; Gray, Nathanael S. (DFCI); (UTSMC); (Harvard-Med); (NYUSM)

    2017-08-01

    Targeted covalent small molecules have shown promise for cancers driven by KRAS G12C. Allosteric compounds that access an inducible pocket formed by movement of a dynamic structural element in KRAS, switch II, have been reported, but these compounds require further optimization to enable their advancement into clinical development. We demonstrate that covalent quinazoline-based switch II pocket (SIIP) compounds effectively suppress GTP loading of KRAS G12C, MAPK phosphorylation, and the growth of cancer cells harboring G12C. Notably we find that adding an amide substituent to the quinazoline scaffold allows additional interactions with KRAS G12C, and remarkably increases the labeling efficiency, potency, and selectivity of KRAS G12C inhibitors. Structural studies using X-ray crystallography reveal a new conformation of SIIP and key interactions made by substituents located at the quinazoline 2-, 4-, and 7-positions. Optimized lead compounds in the quinazoline series selectively inhibit KRAS G12C-dependent signaling and cancer cell growth at sub-micromolar concentrations.

  15. Local Electronic Structure of a Single-Layer Porphyrin-Containing Covalent Organic Framework

    KAUST Repository

    Chen, Chen

    2017-12-20

    We have characterized the local electronic structure of a porphyrin-containing single-layer covalent organic framework (COF) exhibiting a square lattice. The COF monolayer was obtained by the deposition of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMA) and 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) onto a Au(111) surface in ultrahigh vacuum followed by annealing to facilitate Schiff-base condensations between monomers. Scanning tunneling spectroscopy (STS) experiments conducted on isolated TAPP precursor molecules and the covalently linked COF networks yield similar transport (HOMO-LUMO) gaps of 1.85 ± 0.05 eV and 1.98 ± 0.04 eV, respectively. The COF orbital energy alignment, however, undergoes a significant downward shift compared to isolated TAPP molecules due to the electron-withdrawing nature of the imine bond formed during COF synthesis. Direct imaging of the COF local density of states (LDOS) via dI/dV mapping reveals that the COF HOMO and LUMO states are localized mainly on the porphyrin cores and that the HOMO displays reduced symmetry. DFT calculations reproduce the imine-induced negative shift in orbital energies and reveal that the origin of the reduced COF wave function symmetry is a saddle-like structure adopted by the porphyrin macrocycle due to its interactions with the Au(111) substrate.

  16. Tribromobenzene on Cu(111): Temperature-dependent formation of halogen-bonded, organometallic, and covalent nanostructures.

    Science.gov (United States)

    Fan, Qitang; Wang, Tao; Liu, Liming; Zhao, Jin; Zhu, Junfa; Gottfried, J Michael

    2015-03-14

    The temperature-controlled surface-assisted synthesis of halogen bonded, organometallic, and covalent nanostructures based on 1,3,5-tribromo-benzene (TriBB) was studied with scanning tunneling microscopy and X-ray photoemission spectroscopy in ultrahigh vacuum. Vapor deposition of TriBB onto a Cu(111) surface held at 90 K leads to the formation of large domains of a honeycomb-like organic monolayer structure stabilized by triangular nodes with Br⋯Br intermolecular bonds. Upon annealing the organic monolayer to ∼140 K, a new hexagonal close-packed structure with intact TriBB molecules connected by Cu adatoms is formed. Further warming up the sample to 300 K gives rise to the scission of C-Br bonds and formation of C-Cu-C bonds between phenyl fragments such that stable dendritic organometallic networks are formed. Larger islands of organometallic networks are obtained by maintaining the temperature of Cu(111) at 420 K during deposition of TriBB. Simultaneously, large islands of Br atoms are formed around the organometallic networks. Annealing the more extended organometallic network (prepared at 420 K) to 520 K leads to the formation of a branched covalent organic framework (COF) which comprises structural elements of porous graphene and is surrounded by Br islands. These organometallic networks and COFs appear as small dendritic and branched domains, most likely due to the steric influence exerted by the Br islands.

  17. Surface modification of polypropylene nonwoven fabrics via covalent immobilization of nonionic sugar-based surfactants

    International Nuclear Information System (INIS)

    Xin, Zhirong; Yan, Shunjie; Ding, Jiaotong; Yang, Zongfeng; Du, Binbin; Du, Shanshan

    2014-01-01

    Graphical abstract: - Highlights: • Amphiphilic N-alkyl-1-amino-1-deoxy-D-glucitol were prepared. • The pGMA-grafted membranes were obtained via photo-grafting of glycidyl methacrylate. • Amphiphilic C n AG were covalent immobilized onto the pGMA-grafted membranes. • The C n AG-grafted membranes obviously suppressed protein adsorption and platelet adhesion. - Abstract: Amphiphilic N-alkyl-1-amino-1-deoxy-D-glucitol (C n AG, n = 8, 12) were successfully prepared. Polypropylene nonwoven fabrics (PP NWF ) were grafted with glycidyl methacrylate (GMA) via a technique of UV-induced graft polymerization combined with plasma pre-treatment, and then PP NWF -g-GMA was used for the covalent immobilization of C n AG. The surface graft polymerization was confirmed by ATR-FTIR and XPS, respectively. Effect of grafting parameters, e.g., acetone content, monomer concentration and UV irradiation time on the grafting density of GMA was investigated. And the hemocompatibility of the modified PP NWF was evaluated by protein adsorption and platelet adhesion. It was founded that the C n AG-modified substrates greatly suppressed protein adsorption and platelet adhesion compared with the native and pGMA-grafted PP NWF

  18. “Stereoscopic” 2D super-microporous phosphazene-based covalent organic framework: Design, synthesis and selective sorption towards uranium at high acidic condition

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Shuang; Zhao, Xiaosheng; Li, Bo; Bai, Chiyao; Li, Yang; Wang, Lei; Wen, Rui; Zhang, Meicheng; Ma, Lijian; Li, Shoujian, E-mail: sjli000616@scu.edu.cn

    2016-08-15

    Highlights: • Phosphorus element was first introduced into covalent organic frameworks (COFs). • Monomer in C{sub 3}-like spatial configuration was first used to construct COF materials. • A new 2D super-microporous phosphazene-based sorbent (MPCOF) was synthesized. • Separation of U (VI) by MPCOF at high acidic media (up to 1M HNO{sub 3}) was achieved. • Selectivity for U (VI) separation from multi-ion solution can reach unreported 92%. - Abstract: So far, only five primary elements (C, H, O, N and B) and two types of spatial configuration (C{sub 2}–C{sub 4}, C{sub 6} and T{sub d}) are reported to build the monomers for synthesis of covalent organic frameworks (COFs), which have partially limited the route selection for accessing COFs with new topological structure and novel properties. Here, we reported the design and synthesis of a new “stereoscopic” 2D super-microporous phosphazene-based covalent organic framework (MPCOF) by using hexachorocyclotriphosphazene (a P-containing monomer in a C{sub 3}-like spatial configuration) and p-phenylenediamine (a linker). The as-synthesized MPCOF shows high crystallinity, relatively high heat and acid stability and distinctive super-microporous structure with narrow pore-size distributions ranging from 1.0–2.1 nm. The results of batch sorption experiments with a multi-ion solution containing 12 co-existing cations show that in the pH range of 1–2.5, MPCOF exhibits excellent separation efficiency for uranium with adsorption capacity more than 71 mg/g and selectivity up to record-breaking 92%, and furthermore, an unreported sorption capacity (>50 mg/g) and selectivity (>60%) were obtained under strong acidic condition (1 M HNO{sub 3}). Studies on sorption mechanism indicate that the uranium separation by MPCOF in acidic solution is realized mainly through both intra-particle diffusion and size-sieving effect.

  19. A hydrazone covalent organic polymer based micro-solid phase extraction for online analysis of trace Sudan dyes in food samples.

    Science.gov (United States)

    Zhang, Chengjiang; Li, Gongke; Zhang, Zhuomin

    2015-11-06

    Covalent organic polymers (COPs) connected by covalent bonds are a new class of porous network materials with large surface area and potential superiority in sample pretreatment. In this study, a new hydrazone linked covalent organic polymer (HL-COP) adsorbent was well-designed and synthesized based on a simple Schiff-base reaction. The condensation of 1,4-phthalaldehyde and 1,3,5-benzenetricarbohydrazide as organic building blocks led to the synthesis of HL-COP with uniform particle size and good adsorption performance. This HL-COP adsorbent with high hydrophobic property and rich stacking π electrons contained abundant phenyl rings and imine (CN) groups throughout the entire molecular framework. The adsorption mechanism was explored and discussed based on π-π affinity, hydrophobic effect, hydrogen bonding and electron-donor-acceptor (EDA) interaction, which contributed to its strong recognition affinity to target compounds. Enrichment factors were 305-757 for six Sudan dyes by HL-COP micro-solid phase extraction (μ-SPE), indicating its remarkable preconcentration ability. Furthermore, the adsorption amounts by HL-COP μ-SPE were 1.0-11.0 folds as those by three commonly used commercial adsorbents. Then, HL-COP was applied as adsorbent of online μ-SPE coupled with high performance liquid chromatography (HPLC) for enrichment and analysis of trace Sudan dyes in food samples with detection limit of 0.03-0.15μg/L. The method was successfully applied for online analysis of chilli powder and sausage samples. Sudan II and Sudan III in one positive chilli powder sample were actually found and determined with concentrations of 8.3 and 6.8μg/kg, respectively. The recoveries of chilli powder and sausage samples were in range of 75.8-108.2% and 73.8-112.6% with relative standard deviations of 1.2-8.5% and 1.9-9.4% (n=5), respectively. The proposed method was accurate, reliable and convenient for the online simultaneous analysis of trace Sudan dyes in food samples

  20. Covalent immobilization of xylanase produced from Bacillus pumilus SV-85S on electrospun polymethyl methacrylate nanofiber membrane.

    Science.gov (United States)

    Kumar, Pankaj; Gupta, Ashish; Dhakate, Sanjay R; Mathur, Rakesh B; Nagar, Sushil; Gupta, Vijay K

    2013-01-01

    Polymethyl methacrylate (PMMA) nanofiber membrane (NFM) was synthesized by an electrospinning technique. These membranes were utilized as a support for immobilization of xylanase enzyme to study its pH stability, thermal stability, and reusability. The morphology of aligned NFM was studied by optical microscopy and scanning electron microscopy. The PMMA NFM was functionalized with phenylenediamine and activated with glutaraldehyde to yield an aldehyde group on its surface for covalent immobilization of xylanase. The Fourier transform infrared analysis of the covalently immobilized xylanase confirmed that the enzyme was immobilized on PMMA NFM via amide linkages. The immobilization efficiency of covalently bound xylanase was found experimentally to be 90%. A forward shift in pH optima from 6.0-7.0 (soluble enzyme) to 7.0-9.0 (immobilized enzyme) was observed after xylanase immobilization. The pH and temperature stability of xylanase were enhanced upon its covalent immobilization. The immobilized enzyme was active on repeated use and retained ∼80% of its initial activity after 11 reaction cycles. The improved thermal and operational stability of the covalently immobilized enzyme on PMMA NFM might be advantageous for industrial applications. © 2013 International Union of Biochemistry and Molecular Biology, Inc.

  1. Strong Ideal Convergence in Probabilistic Metric Spaces

    Indian Academy of Sciences (India)

    In the present paper we introduce the concepts of strongly ideal convergent sequence and strong ideal Cauchy sequence in a probabilistic metric (PM) space endowed with the strong topology, and establish some basic facts. Next, we define the strong ideal limit points and the strong ideal cluster points of a sequence in this ...

  2. Strong ideal convergence in probabilistic metric spaces

    Indian Academy of Sciences (India)

    In the present paper we introduce the concepts of strongly ideal convergent sequence and strong ideal Cauchy sequence in a probabilistic metric (PM) space endowed with the strong topology, and establish some basic facts. Next, we define the strong ideal limit points and the strong ideal cluster points of a sequence in this ...

  3. Remnants of strong tidal interactions

    International Nuclear Information System (INIS)

    Mcglynn, T.A.

    1990-01-01

    This paper examines the properties of stellar systems that have recently undergone a strong tidal shock, i.e., a shock which removes a significant fraction of the particles in the system, and where the shocked system has a much smaller mass than the producer of the tidal field. N-body calculations of King models shocked in a variety of ways are performed, and the consequences of the shocks are investigated. The results confirm the prediction of Jaffe for shocked systems. Several models are also run where the tidal forces on the system are constant, simulating a circular orbit around a primary, and the development of tidal radii under these static conditions appears to be a mild process which does not dramatically affect material that is not stripped. The tidal radii are about twice as large as classical formulas would predict. Remnant density profiles are compared with a sample of elliptical galaxies, and the implications of the results for the development of stellar populations and galaxies are considered. 38 refs

  4. John Strong - 1941-2006

    CERN Document Server

    2006-01-01

    Our friend and colleague John Strong was cruelly taken from us by a brain tumour on 31 July, a few days before his 65th birthday. John started his career and obtained his PhD in a group from Westfield College, initially working on experiments at Rutherford Appleton Laboratory (RAL). From the early 1970s onwards, however, his research was focused on experiments in CERN, with several particularly notable contributions. The Omega spectrometer adopted a system John had originally developed for experiments at RAL using vidicon cameras (a type of television camera) to record the sparks in the spark chambers. This highly automated system allowed Omega to be used in a similar way to bubble chambers. He contributed to the success of NA1 and NA7, where he became heavily involved in the electronic trigger systems. In these experiments the Westfield group joined forces with Italian colleagues to measure the form factors of the pion and the kaon, and the lifetime of some of the newly discovered charm particles. Such h...

  5. Strong seismic ground motion propagation

    International Nuclear Information System (INIS)

    Seale, S.; Archuleta, R.; Pecker, A.; Bouchon, M.; Mohammadioun, G.; Murphy, A.; Mohammadioun, B.

    1988-10-01

    At the McGee Creek, California, site, 3-component strong-motion accelerometers are located at depths of 166 m, 35 m and 0 m. The surface material is glacial moraine, to a depth of 30.5 m, overlying homfels. Accelerations were recorded from two California earthquakes: Round Valley, M L 5.8, November 23, 1984, 18:08 UTC and Chalfant Valley, M L 6.4, July 21, 1986, 14:42 UTC. By separating out the SH components of acceleration, we were able to determine the orientations of the downhole instruments. By separating out the SV component of acceleration, we were able to determine the approximate angle of incidence of the signal at 166 m. A constant phase velocity Haskell-Thomson model was applied to generate synthetic SH seismograms at the surface using the accelerations recorded at 166 m. In the frequency band 0.0 - 10.0 Hz, we compared the filtered synthetic records to the filtered surface data. The onset of the SH pulse is clearly seen, as are the reflections from the interface at 30.5 m. The synthetic record closely matches the data in amplitude and phase. The fit between the synthetic accelerogram and the data shows that the seismic amplification at the surface is a result of the contrast of the impedances (shear stiffnesses) of the near surface materials

  6. Identification of an estrogen receptor α non covalent ubiquitin-binding surface: role in 17β-estradiol-induced transcriptional activity.

    Science.gov (United States)

    Pesiri, Valeria; La Rosa, Piergiorgio; Stano, Pasquale; Acconcia, Filippo

    2013-06-15

    Ubiquitin (Ub)-binding domains (UBDs) located in Ub receptors decode the ubiquitination signal by non-covalently engaging the Ub modification on their binding partners and transduce the Ub signalling through Ub-based molecular interactions. In this way, inducible protein ubiquitination regulates diverse biological processes. The estrogen receptor alpha (ERα) is a ligand-activated transcription factor that mediates the pleiotropic effects of the sex hormone 17β-estradiol (E2). Fine regulation of E2 pleiotropic actions depends on E2-dependent ERα association with a plethora of binding partners and/or on the E2 modulation of receptor ubiquitination. Indeed, E2-induced ERα polyubiquitination triggers receptor degradation and transcriptional activity, and E2-dependent reduction in ERα monoubiquitination is crucial for E2 signalling. Monoubiquitinated proteins often contain UBDs, but whether non-covalent Ub-ERα binding could occur and play a role in E2-ERα signalling is unknown. Here, we report an Ub-binding surface within the ERα ligand binding domain that directs in vitro the receptor interaction with both ubiquitinated proteins and recombinant Ub chains. Mutational analysis reveals that ERα residues leucine 429 and alanine 430 are involved in Ub binding. Moreover, impairment of ERα association to ubiquitinated species strongly affects E2-induced ERα transcriptional activity. Considering the importance of UBDs in the Ub-based signalling network and the central role of different ERα binding partners in the modulation of E2-dependent effects, our discoveries provide novel insights into ERα activity that could also be relevant for ERα-dependent diseases.

  7. Is there any fundamental difference between ionic, covalent, and others types of bond? A canonical perspective on the question.

    Science.gov (United States)

    Walton, Jay R; Rivera-Rivera, Luis A; Lucchese, Robert R; Bevan, John W

    2017-06-21

    The concept of chemical bonding is normally presented and simplified through two models: the covalent bond and the ionic bond. Expansion of the ideal covalent and ionic models leads chemists to the concepts of electronegativity and polarizability, and thus to the classification of polar and non-polar bonds. In addition, the intermolecular interactions are normally viewed as physical phenomena without direct correlation to the chemical bond in any simplistic model. Contrary to these traditional concepts of chemical bonding, recently developed canonical approaches demonstrate a unified perspective on the nature of binding in pairwise interatomic interactions. This new canonical model, which is a force-based approach with a basis in fundamental molecular quantum mechanics, confirms much earlier assertions that in fact there are no fundamental distinctions among covalent bonds, ionic bonds, and intermolecular interactions including the hydrogen bond, the halogen bond, and van der Waals interactions.

  8. Evaluation of the release characteristics of covalently attached or electrostatically bound biocidal polymers utilizing SERS and UV-Vis absorption

    Directory of Open Access Journals (Sweden)

    G. N. Mathioudakis

    2016-09-01

    Full Text Available In this work, biocidal polymers with antimicrobial quaternized ammonium groups introduced in the polymer biocidal chains either through covalent attachment or electrostatic interaction have been separately incorporated in a poly (methyl methacrylate polymer matrix. The objective of present study was to highlight the release characteristics of biocidal polymers, primarily in saline but also in water ethanol solutions, utilizing UV-Vis absorption and Surface Enhanced Raman Scattering (SERS. It is shown that through the combination of UV-Vis and SERS techniques, upon the release process, it is possible the discrimination of the polymeric backbone and the electrostatically bound biocidal species. Moreover, it is found that electrostatically bound and covalently attached biocidal species show different SERS patterns. The long term aim is the development of antimicrobial polymeric materials containing both ionically bound and covalently attached quaternary ammonium thus achieving a dual functionality in a single component polymeric design.

  9. Probing covalency in halogen bonds through donor K-edge X-ray absorption spectroscopy: polyhalides as coordination complexes.

    Science.gov (United States)

    Mustoe, Chantal L; Gunabalasingam, Mathusan; Yu, Darren; Patrick, Brian O; Kennepohl, Pierre

    2017-10-13

    The properties of halogen bonds (XBs) in solid-state I 2 X - and I 4 X - materials (where X = Cl, Br) are explored using donor K-edge X-ray absorption spectroscopy (XAS) to experimentally determine the degree of charge transfer in such XB interactions. The degree of covalency in these bonds is substantial, even in cases where significantly weaker secondary interactions are observed. These data, in concert with previous work in this area, suggests that certain halogen bonds have covalent contributions to bonding that are similar to, and even exceed, those observed in transition metal coordinate bonds. For this reason, we suggest that XB interactions of this type be denoted in a similar way to coordination bonds (X → Y) as opposed to using a representation that is the same as for significantly less covalent hydrogen bonds (XY).

  10. Strongly interacting photons and atoms

    International Nuclear Information System (INIS)

    Alge, W.

    1999-05-01

    This thesis contains the main results of the research topics I have pursued during the my PhD studies at the University of Innsbruck and partly in collaboration with the Institut d' Optique in Orsay, France. It is divided into three parts. The first and largest part discusses the possibility of using strong standing waves as a tool to cool and trap neutral atoms in optical cavities. This is very important in the field of nonlinear optics where several successful experiments with cold atoms in cavities have been performed recently. A discussion of the optical parametric oscillator in a regime where the nonlinearity dominates the evolution is the topic of the second part. We investigated mainly the statistical properties of the cavity output of the three interactive cavity modes. Very recently a system has been proposed which promises fantastic properties. It should exhibit a giant Kerr nonlinearity with negligible absorption thus leading to a photonic turnstile device based on cold atoms in cavity. We have shown that this model suffers from overly simplistic assumptions and developed several more comprehensive approaches to study the behavior of this system. Apart from the division into three parts of different contents the thesis is divided into publications, supplements and invisible stuff. The intention of the supplements is to reach researchers which work in related areas and provide them with more detailed information about the concepts and the numerical tools we used. It is written especially for diploma and PhD students to give them a chance to use the third part of our work which is actually the largest one. They consist of a large number of computer programs we wrote to investigate the behavior of the systems in parameter regions where no hope exists to solve the equations analytically. (author)

  11. Topics in strong Langmuir turbulence

    International Nuclear Information System (INIS)

    Skoric, M.M.

    1981-01-01

    This thesis discusses certain aspects of the turbulence of a fully ionised non-isothermal plasma dominated by the Langmuir mode. Some of the basic properties of strongly turbulent plasmas are reviewed. In particular, interest is focused on the state of Langmuir turbulence, that is the turbulence of a simple externally unmagnetized plasma. The problem of the existence and dynamics of Langmuir collapse is discussed, often met as a non-linear stage of the modulational instability in the framework of the Zakharov equations (i.e. simple time-averaged dynamical equations). Possible macroscopic consequences of such dynamical turbulent models are investigated. In order to study highly non-linear collapse dynamics in its advanced stage, a set of generalized Zakharov equations are derived. Going beyond the original approximation, the author includes the effects of higher electron non-linearities and a breakdown of slow-timescale quasi-neutrality. He investigates how these corrections may influence the collapse stabilisation. Recently, it has been realised that the modulational instability in a Langmuir plasma will be accompanied by the collisionless-generation of a slow-timescale magnetic field. Accordingly, a novel physical situation has emerged which is investigated in detail. The stability of monochromatic Langmuir waves in a self-magnetized Langmuir plasma, is discussed, and the existence of a novel magneto-modulational instability shown. The wave collapse dynamics is investigated and a physical interpretation of the basic results is given. A problem of the transient analysis of an interaction of time-dependent electromagnetic pulses with linear cold plasma media is investigated. (Auth.)

  12. Promoting Strong Written Communication Skills

    Science.gov (United States)

    Narayanan, M.

    2015-12-01

    The reason that an improvement in the quality of technical writing is still needed in the classroom is due to the fact that universities are facing challenging problems not only on the technological front but also on the socio-economic front. The universities are actively responding to the changes that are taking place in the global consumer marketplace. Obviously, there are numerous benefits of promoting strong written communication skills. They can be summarized into the following six categories. First, and perhaps the most important: The University achieves learner satisfaction. The learner has documented verbally, that the necessary knowledge has been successfully acquired. This results in learner loyalty that in turn will attract more qualified learners.Second, quality communication lowers the cost per pupil, consequently resulting in increased productivity backed by a stronger economic structure and forecast. Third, quality communications help to improve the cash flow and cash reserves of the university. Fourth, having high quality communication enables the university to justify the need for high costs of tuition and fees. Fifth, better quality in written communication skills result in attracting top-quality learners. This will lead to happier and satisfied learners, not to mention greater prosperity for the university as a whole. Sixth, quality written communication skills result in reduced complaints, thus meaning fewer hours spent on answering or correcting the situation. The University faculty and staff are thus able to devote more time on scholarly activities, meaningful research and productive community service. References Boyer, Ernest L. (1990). Scholarship reconsidered: Priorities of the Professorate.Princeton, NJ: Carnegie Foundation for the Advancement of Teaching. Hawkins, P., & Winter, J. (1997). Mastering change: Learning the lessons of the enterprise.London: Department for Education and Employment. Buzzel, Robert D., and Bradley T. Gale. (1987

  13. S-nitrosoglutathione covalently modifies cysteine residues of human carbonyl reductase 1 and affects its activity.

    Science.gov (United States)

    Hartmanová, Tereza; Tambor, Vojtěch; Lenčo, Juraj; Staab-Weijnitz, Claudia A; Maser, Edmund; Wsól, Vladimír

    2013-02-25

    Carbonyl reductase 1 (CBR1 or SDR21C1) is a ubiquitously-expressed, cytosolic, monomeric, and NADPH-dependent enzyme. CBR1 participates in apoptosis, carcinogenesis and drug resistance, and has a protective role in oxidative stress, cancer and neurodegeneration. S-Nitrosoglutathione (GSNO) represents the newest addition to its diverse substrate spectrum, which includes a wide range of xenobiotics and endogenous substances. GSNO has also been shown to covalently modify and inhibit CBR1. The aim of the present study was to quantify and characterize the resulting modifications. Of five candidate cysteines for modification by 2 mM GSNO (positions 26, 122, 150, 226, 227), the last four were analyzed using MALDI-TOF/TOF mass spectrometry and then quantified using the Selected Reaction Monitoring Approach on hyphenated HPLC with a triple quadrupole mass spectrometer. The analysis confirmed GSNO concentration-dependent S-glutathionylation of cysteines at positions 122, 150, 226, 227 which was 2-700 times higher compared to wild-type CBR1 (WT-CBR1). Moreover, a disulfide bond between neighboring Cys-226 and Cys-227 was detected. We suggest a role of these two cysteines as a redox-sensitive cysteine pair. The catalytic properties of wild-type and enzyme modified with 2 mM GSNO were also investigated by steady state kinetic experiments with various substrates. GSNO treatment of CBR1 resulted in a 2-5-fold decrease in kcat with menadione, 4-benzoylpyridine, 2,3-hexanedione, daunorubicin and 1,4-naphthoquinone. In contrast, the same treatment increased kcat for substrates containing a 1,2-diketo group in a ring structure (1,2-naphthoquinone, 9,10-phenanthrenequinone, isatin). Except for 9,10-phenanthrenequinone, all changes in kcat were at least in part compensated for by a similar change in Km, overall yielding no drastic changes in catalytic efficiency. The findings indicate that GSNO-induced covalent modification of cysteine residues affects the kinetic mechanism of CBR1

  14. Efficient protein immobilization on polyethersolfone electrospun nanofibrous membrane via covalent binding for biosensing applications

    Energy Technology Data Exchange (ETDEWEB)

    Mahmoudifard, Matin [Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Soudi, Sara [Stem Cell Biology Department, Stem Cell Technology Research Center, Tehran (Iran, Islamic Republic of); Department of Immunology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Soleimani, Masoud [Department of Hematology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Hosseinzadeh, Simzar [Nanotechnology and Tissue Engineering Department, Stem Cell Technology Research Center, Tehran (Iran, Islamic Republic of); School of Advanced Medical Technologies, Tehran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Esmaeili, Elaheh [Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Department of Hematology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Vossoughi, Manouchehr, E-mail: vosoughi@sharif.edu [Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Chemical and Petroleum Engineering Department, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

    2016-01-01

    In this paper we introduce novel strategy for antibody immobilization using high surface area electrospun nanofibrous membrane based on ethyl-3-(3-dimethylaminopropyl)-carbodiimide/N-hydroxysuccinimide (EDC/NHS) coupling chemistry. To present the high performance of proposed biosensors, anti-staphylococcus enterotoxin B (anti-SEB) was used as a model to demonstrate the utility of our proposed system. Polymer solution of polyethersolfone was used to fabricate fine nanofibrous membrane. Moreover, industrial polyvinylidene fluoride membrane and conventional microtiter plate were also used to compare the efficiency of antibody immobilization. Scanning electron microscopy images were taken to study the morphology of the membranes. The surface activation of nanofibrous membrane was done with the help of O{sub 2} plasma. PES nanofibrous membrane with carboxyl functional groups for covalent attachment of antibodies were treated by EDC/NHS coupling agent. The quantity of antibody immobilization was measured by enzyme-linked immuno sorbent assay (ELISA) method. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectroscopy was performed to confirm the covalent immobilization of antibody on membrane. Atomic force microscopy, scanning electron microscopy and invert fluorescence microscopy were used to analyze the antibody distribution pattern on solid surfaces. Results show that oxygen plasma treatment effectively increased the amount of antibody immobilization through EDC/NHS coupling chemistry. It was found that the use of nanofibrous membrane causes the improved detection signal of ELISA based biosensors in comparison to the standard assay carried out in the 96-well microtiter plate. This method has the potential to improve the ELISA-based biosensor and we believe that this technique can be used in various biosensing methods. - Highlights: • Introduction of novel strategy for antibody immobilization using high surface area electrospun

  15. Sponges with covalently tethered amines for high-efficiency carbon capture

    KAUST Repository

    Qi, Genggeng

    2014-12-12

    © 2014 Macmillan Publishers Limited. All rights reserved. Adsorption using solid amine sorbents is an attractive emerging technology for energy-efficient carbon capture. Current syntheses for solid amine sorbents mainly based on physical impregnation or grafting-to methods (for example, aminosilane-grafting) lead to limited sorbent performance in terms of stability and working capacity, respectively. Here we report a family of solid amine sorbents using a grafting-from synthesis approach and synthesized by cationic polymerization of oxazolines on mesoporous silica. The sorbent with high amount of covalently tethered amines shows fast adsorption rate, high amine efficiency and sorbent capacity well exceeding the highest value reported to date for lowerature carbon dioxide sorbents under simulated flue gas conditions. The demonstrated efficiency of the new amine-immobilization chemistry may open up new avenues in the development of advanced carbon dioxide sorbents, as well as other nitrogen-functionalized systems.

  16. Targeting transcriptional addictions in small cell lung cancer with a covalent CDK7 inhibitor.

    Science.gov (United States)

    Christensen, Camilla L; Kwiatkowski, Nicholas; Abraham, Brian J; Carretero, Julian; Al-Shahrour, Fatima; Zhang, Tinghu; Chipumuro, Edmond; Herter-Sprie, Grit S; Akbay, Esra A; Altabef, Abigail; Zhang, Jianming; Shimamura, Takeshi; Capelletti, Marzia; Reibel, Jakob B; Cavanaugh, Jillian D; Gao, Peng; Liu, Yan; Michaelsen, Signe R; Poulsen, Hans S; Aref, Amir R; Barbie, David A; Bradner, James E; George, Rani E; Gray, Nathanael S; Young, Richard A; Wong, Kwok-Kin

    2014-12-08

    Small cell lung cancer (SCLC) is an aggressive disease with high mortality, and the identification of effective pharmacological strategies to target SCLC biology represents an urgent need. Using a high-throughput cellular screen of a diverse chemical library, we observe that SCLC is sensitive to transcription-targeting drugs, in particular to THZ1, a recently identified covalent inhibitor of cyclin-dependent kinase 7. We find that expression of super-enhancer-associated transcription factor genes, including MYC family proto-oncogenes and neuroendocrine lineage-specific factors, is highly vulnerability to THZ1 treatment. We propose that downregulation of these transcription factors contributes, in part, to SCLC sensitivity to transcriptional inhibitors and that THZ1 represents a prototype drug for tailored SCLC therapy. Copyright © 2014 Elsevier Inc. All rights reserved.

  17. Covalent immobilization of lipases on monodisperse magnetic microspheres modified with PAMAM-dendrimer

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Weiwei [Lanzhou University, State Key Laboratory of Applied Organic Chemistry, Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, College of Chemistry and Chemical Engineering, Institute of Biochemical Engineering and Environmental Technology (China); Zhang, Yimei [Suzhou Research Academy of North China Electric Power University (China); Hou, Chen; Pan, Duo; He, Jianjun; Zhu, Hao, E-mail: zhuhao07@lzu.edu.cn [Lanzhou University, State Key Laboratory of Applied Organic Chemistry, Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, College of Chemistry and Chemical Engineering, Institute of Biochemical Engineering and Environmental Technology (China)

    2016-02-15

    This paper reported an immobilization of Candida rugosa lipase (CRL) onto PAMAM-dendrimer-grafted magnetic nanoparticles synthesized by a modified solvothermal reduction method. The dendritic magnetic nanoparticles were amply characterized by several instrumental measurements, and the CRL was covalently anchored on the three generation supports with glutaraldehyde as coupling reagent. The amount of immobilized enzyme was up to 150 mg/g support and the factors related with the enzyme activity were investigated. The immobilization of lipase improved their performance in wider ranges of pH and temperature. The immobilized lipase exhibited excellent thermal stability and reusability in comparison with free enzyme and can be reused 10 cycles with the enzymatic activity remained above 90 %. The properties of lipase improved obviously after being immobilized on the dendritic supports. The inactive immobilized lipase could be regenerated with glutaraldehyde and Cu{sup 2+}, respectively. This synthetic strategy was facile and eco-friendly for applications in lipase immobilization.

  18. Preparation of Immobilized Recombinant Tubulin Beta(TuBb on Chitosan Nanoparticles by Covalent Binding Method

    Directory of Open Access Journals (Sweden)

    Yan Qingfang

    2016-01-01

    Full Text Available Objective In order to screen TuBb inhibitors, this paper describes the preparation of immobilized TuBb on chitosan nanoparticles. Methods TuBb was immobilized onto chitosan nanoparticles by covalent binding method. Results The results of the univariate test indicated that the highest immobilized yield can be obtained when the optimal immobilization condition was 1 mg of TuBb, 0.5 mol/L of buffer solution with pH 6.5, immobilization 30 min and immobilization at 0-4 °C. Conclusions The authors conclude that the immobilized TuBb maintain the catalysis properties and can be used as the screening of TuBb inhibitors.

  19. Site-selective protein immobilization by covalent modification of GST fusion proteins.

    Science.gov (United States)

    Zhou, Yiqing; Guo, Tianlin; Tang, Guanghui; Wu, Hui; Wong, Nai-Kei; Pan, Zhengying

    2014-11-19

    The immobilization of functional proteins onto solid supports using affinity tags is an attractive approach in recent development of protein microarray technologies. Among the commonly used fusion protein tags, glutathione S-transferase (GST) proteins have been indispensable tools for protein-protein interaction studies and have extensive applications in recombinant protein purification and reversible protein immobilization. Here, by utilizing pyrimidine-based small-molecule probes with a sulfonyl fluoride reactive group, we report a novel and general approach for site-selective immobilization of Schistosoma japonicum GST (sjGST) fusion proteins through irreversible and specific covalent modification of the tyrosine-111 residue of the sjGST tag. As demonstrated by sjGST-tagged eGFP and sjGST-tagged kinase activity assays, this immobilization approach offers the advantages of high immobilization efficiency and excellent retention of protein structure and activity.

  20. Tailor-Made Pore Surface Engineering in Covalent Organic Frameworks: Systematic Functionalization for Performance Screening.

    Science.gov (United States)

    Huang, Ning; Krishna, Rajamani; Jiang, Donglin

    2015-06-10

    Imine-linked covalent organic frameworks (COFs) were synthesized to bear content-tunable, accessible, and reactive ethynyl groups on the walls of one-dimensional pores. These COFs offer an ideal platform for pore-wall surface engineering aimed at anchoring diverse functional groups ranging from hydrophobic to hydrophilic units and from basic to acidic moieties with controllable loading contents. This approach enables the development of various tailor-made COFs with systematically tuned porosities and functionalities while retaining the crystallinity. We demonstrate that this strategy can be used to efficiently screen for suitable pore structures for use as CO2 adsorbents. The pore-surface-engineered walls exhibit an enhanced affinity for CO2, resulting in COFs that can capture and separate CO2 with high performance.

  1. Assembly and structural analysis of a covalently closed nano-scale DNA cage

    DEFF Research Database (Denmark)

    Andersen, Félicie Faucon; Knudsen, Bjarne; Oliveira, Cristiano Luis Pinto De

    2008-01-01

     The inherent properties of DNA as a stable polymer with unique affinity for partner molecules determined by the specific Watson-Crick base pairing makes it an ideal component in self-assembling structures. This has been exploited for decades in the design of a variety of artificial substrates...... are necessary before complex DNA structures can be routinely designed for the use in basal science and/or biotechnology. Here we present the design, construction and structural analysis of a covalently closed and stable 3D DNA structure with the connectivity of an octahedron, as defined by the double...... be described as a nano-scale DNA cage, Hence, in theory it could hold proteins or other bio-molecules to enable their investigation in certain harmful environments or even allow their organization into higher order structures...

  2. Enzymatic Activity Enhancement of Non-Covalent Modified Superoxide Dismutase and Molecular Docking Analysis

    Directory of Open Access Journals (Sweden)

    Fa-Jun Song

    2012-03-01

    Full Text Available The enzyme activity of superoxide dismutase was improved in the pyrogallol autoxidation system by about 27%, after interaction between hydroxypropyl-β-cyclo- dextrin and superoxide dismutase. Fluorescence spectrometry was used to study the interaction between hydroxypropyl-β-cyclodextrin and superoxide dismutase at different temperatures. By doing this, it can be found that these interactions increase fluorescence sensitivity. In the meantime, the synchronous fluorescence intensity revealed the interaction sites to be close to the tryptophan (Trp and tyrosine (Tyr residues of superoxide dismutase. Furthermore, molecular docking was applied to explore the binding mode between the ligands and the receptor. This suggested that HP-β-CD interacted with the B ring, G ring and the O ring and revealed that the lysine (Lys residues enter the nanocavity. It was concluded that the HP-β-CD caused specific conformational changes in SOD by non-covalent modification.

  3. Improved immobilization of laccase on a glassy carbon electrode by oriented covalent attachment

    Directory of Open Access Journals (Sweden)

    Liu Xin

    2014-01-01

    Full Text Available A laccase from Thermus thermophilus HB27 was reported to be potentially useful in the design of a temperature controlled biofuel cell. For enhancing its application in different thermal conditions, we engineered a laccase-oriented immobilized electrode. A site-directed mutant N323C of the laccase was constructed. A photometric assay was employed in order to compare the catalytic properties of wild-type laccase and mutant. The mutant was attached to a glass carbon electrode by covalent cross-linking. The electrochemical properties of the immobilized laccase were investigated by cyclic voltammetry. This immobilization allowed the active electrode to function at temperatures up to 95°C. The thermal and pH dependence profiles were similar to those of the soluble enzyme investigated by spectrophotometry.

  4. Covalent Immobilization of β-Glucosidase on Magnetic Particles for Lignocellulose Hydrolysis

    DEFF Research Database (Denmark)

    Alftrén, Johan; Hobley, Timothy John

    2013-01-01

    β-Glucosidase hydrolyzes cellobiose to glucose and is an important enzyme in the consortium used for hydrolysis of cellulosic and lignocellulosic feedstocks. In the present work, β-glucosidase was covalently immobilized on non-porous magnetic particles to enable re-use of the enzyme. It was found...... that particles activated with cyanuric chloride and polyglutaraldehyde gave the highest bead-related immobilized enzyme activity when tested with p-nitrophenyl-β-D-glucopyranoside (104.7 and 82.2 U/g particles, respectively). Furthermore, the purified β-glucosidase preparation from Megazyme gave higher bead......-related enzyme activities compared to Novozym 188 (79.0 and 9.8 U/g particles, respectively). A significant improvement in thermal stability was observed for immobilized enzyme compared to free enzyme; after 5 h (at 65 °C), 36 % of activity remained for the former, while there was no activity in the latter...

  5. Characteristics of enzyme hydrolyzing natural covalent bond between RNA and protein VPg of encephalomyocarditis virus

    International Nuclear Information System (INIS)

    Drygin, Yu.F.; Siyanova, E.Yu.

    1986-01-01

    The isolation and a preliminary characterization of the enzyme specifically hydrolyzing the phosphodiester bond between protein VPg and the RNA of encephalomyocarditis virus was the goal of the present investigation. The enzyme was isolated from a salt extract of Krebs II mouse ascites carcinoma cells by ion-exchange and affinity chromatography. It was found that the enzyme actually specifically cleaves the covalent bond between the RNA and protein, however, the isolation procedure does not free the enzyme from impurities which partially inhibit it. The enzyme cleaves the RNA-protein VPg complex of polio virus at a high rate, it is completely inactivated at 55 0 C, and is partially inhibited by EDTA

  6. Extra-electron induced covalent strengthening and generalization of intrinsic ductile-to-brittle criterion

    Science.gov (United States)

    Niu, Haiyang; Chen, Xing-Qiu; Liu, Peitao; Xing, Weiwei; Cheng, Xiyue; Li, Dianzhong; Li, Yiyi

    2012-10-01

    Traditional strengthening ways, such as strain, precipitation, and solid-solution, come into effect by pinning the motion of dislocation. Here, through first-principles calculations we report on an extra-electron induced covalent strengthening mechanism, which alters chemical bonding upon the introduction of extra-valence electrons in the matrix of parent materials. It is responsible for the brittle and high-strength properties of Al12W-type compounds featured by the typical fivefold icosahedral cages, which are common for quasicrystals and bulk metallic glasses (BMGs). In combination with this mechanism, we generalize ductile-to-brittle criterion in a universal hyperbolic form by integrating the classical Pettifor's Cauchy pressure with Pugh's modulus ratio for a wide variety of materials with cubic lattices. This study provides compelling evidence to correlate Pugh's modulus ratio with hardness of materials and may have implication for understanding the intrinsic brittleness of quasicrystals and BMGs.

  7. Non-covalent functionalization of single wall carbon nanotubes and graphene by a conjugated polymer

    KAUST Repository

    Jiwuer, Jilili

    2014-07-07

    We report first-principles calculations on the binding of poly[(9,9-bis-(6-bromohexylfluorene-2,7-diyl)-co-(benzene-1,4-diyl)] to a (8,0) single wall carbon nanotube (SWCNT) and to graphene. Considering different relative orientations of the subsystems, we find for the generalized gradient approximation a non-binding state, whereas the local density approximation predicts reasonable binding energies. The results coincide after inclusion of van der Waals corrections, which demonstrates a weak interaction between the polymer and SWCNT/graphene, mostly of van der Waals type. Accordingly, the density of states shows essentially no hybridization. The physisorption mechanism explains recent experimental observations and suggests that the conjugated polymer can be used for non-covalent functionalization.

  8. Conductive Microporous Covalent Triazine-Based Framework for High-Performance Electrochemical Capacitive Energy Storage.

    Science.gov (United States)

    Li, Yajuan; Zheng, Shuanghao; Liu, Xue; Li, Pan; Sun, Lei; Yang, Ruixia; Wang, Sen; Wu, Zhong-Shuai; Bao, Xinhe; Deng, Wei-Qiao

    2017-11-14

    Nitrogen-enriched porous nanocarbon, graphene, and conductive polymers attract increasing attention for application in supercapacitors. However, electrode materials with a large specific surface area (SSA) and a high nitrogen doping concentration, which is needed for excellent supercapacitors, has not been achieved thus far. Herein, we developed a class of tetracyanoquinodimethane-derived conductive microporous covalent triazine-based frameworks (TCNQ-CTFs) with both high nitrogen content (>8 %) and large SSA (>3600 m 2  g -1 ). These CTFs exhibited excellent specific capacitances with the highest value exceeding 380 F g -1 , considerable energy density of 42.8 Wh kg -1 , and remarkable cycling stability without any capacitance degradation after 10 000 cycles. This class of CTFs should hold a great potential as high-performance electrode material for electrochemical energy-storage systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Core/Shell Conjugated Polymer/Quantum Dot Composite Nanofibers through Orthogonal Non-Covalent Interactions

    Directory of Open Access Journals (Sweden)

    Brad W. Watson

    2016-11-01

    Full Text Available Nanostructuring organic polymers and organic/inorganic hybrid materials and controlling blend morphologies at the molecular level are the prerequisites for modern electronic devices including biological sensors, light emitting diodes, memory devices and solar cells. To achieve all-around high performance, multiple organic and inorganic entities, each designed for specific functions, are commonly incorporated into a single device. Accurate arrangement of these components is a crucial goal in order to achieve the overall synergistic effects. We describe here a facile methodology of nanostructuring conjugated polymers and inorganic quantum dots into well-ordered core/shell composite nanofibers through cooperation of several orthogonal non-covalent interactions including conjugated polymer crystallization, block copolymer self-assembly and coordination interactions. Our methods provide precise control on the spatial arrangements among the various building blocks that are otherwise incompatible with one another, and should find applications in modern organic electronic devices such as solar cells.

  10. Covalent dimers of 1,3-diphenylisobenzofuran for singlet fission: synthesis and electrochemistry.

    Science.gov (United States)

    Akdag, Akin; Wahab, Abdul; Beran, Pavel; Rulíšek, Lubomír; Dron, Paul I; Ludvík, Jiří; Michl, Josef

    2015-01-02

    The synthesis of covalent dimers in which two 1,3-diphenylisobenzofuran units are connected through one phenyl substituent on each is reported. In three of the dimers, the subunits are linked directly, and in three others, they are linked via an alkane chain. A seventh new compound in which two 1,3-diphenylisobenzofuran units share a phenyl substituent is also described. These materials are needed for investigations of the singlet fission process, which promises to increase the efficiency of solar cells. The electrochemical oxidation and reduction of the monomer, two previously known dimers, and the seven new compounds have been examined, and reversible redox potentials have been compared with results obtained from density functional theory. Although the overall agreement is satisfactory, some discrepancies are noted and discussed.

  11. Rapid and Efficient Redox Processes within 2D Covalent Organic Framework Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    DeBlase, Catherine R. [Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, United States; Hernández-Burgos, Kenneth [Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, United States; Silberstein, Katharine E. [Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, United States; Rodríguez-Calero, Gabriel G. [Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, United States; Bisbey, Ryan P. [Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, United States; Abruña, Héctor D. [Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, United States; Dichtel, William R. [Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853-1301, United States

    2015-02-17

    Two-dimensional covalent organic frameworks (2D COFs) are ideally suited for organizing redox-active subunits into periodic, permanently porous polymer networks of interest for pseudocapacitive energy storage. Here we describe a method for synthesizing crystalline, oriented thin films of a redox-active 2D COF on Au working electrodes. The thickness of the COF film was controlled by varying the initial monomer concentration. A large percentage (80–99%) of the anthraquinone groups are electrochemically accessible in films thinner than 200 nm, an order of magnitude improvement over the same COF prepared as a randomly oriented microcrystalline powder. As a result, electrodes functionalized with oriented COF films exhibit a 400% increase in capacitance scaled to electrode area as compared to those functionalized with the randomly oriented COF powder. These results demonstrate the promise of redox-active COFs for electrical energy storage and highlight the importance of controlling morphology for optimal performance.

  12. Rapid and Efficient Redox Processes within 2D Covalent Organic Framework Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    DeBlase, Catherine R.; Hernández-Burgos, Kenneth; Silberstein, Katharine E.; Rodríguez-Calero, Gabriel G.; Bisbey, Ryan P.; Abruña, Héctor D.; Dichtel, William R.

    2015-03-24

    Two-dimensional covalent organic frameworks (2D COFs) are ideally suited for organizing redox-active subunits into periodic, permanently porous polymer networks of interest for pseudocapacitive energy storage. Here we describe a method for synthesizing crystalline, oriented thin films of a redox-active 2D COF on Au working electrodes. The thickness of the COF film was controlled by varying the initial monomer concentration. A large percentage (80–99%) of the anthraquinone groups are electrochemically accessible in films thinner than 200 nm, an order of magnitude improvement over the same COF prepared as a randomly oriented microcrystalline powder. As a result, electrodes functionalized with oriented COF films exhibit a 400% increase in capacitance scaled to electrode area as compared to those functionalized with the randomly oriented COF powder. These results demonstrate the promise of redox-active COFs for electrical energy storage and highlight the importance of controlling morphology for optimal performance.

  13. Tailored Ahp-cyclodepsipeptides as Potent Non-covalent Serine Protease Inhibitors.

    Science.gov (United States)

    Köcher, Steffen; Rey, Juliana; Bongard, Jens; Tiaden, André N; Meltzer, Michael; Richards, Peter J; Ehrmann, Michael; Kaiser, Markus

    2017-07-10

    The S1 serine protease family is one of the largest and most biologically important protease families. Despite their biomedical significance, generic approaches to generate potent, class-specific, bioactive non-covalent inhibitors for these enzymes are still limited. In this work, we demonstrate that Ahp-cyclodepsipeptides represent a suitable scaffold for generating target-tailored inhibitors of serine proteases. For efficient synthetic access, we developed a practical mixed solid- and solution-phase synthesis that we validated through performing the first chemical synthesis of the two natural products Tasipeptin A and B. The suitability of the Ahp-cyclodepsipeptide scaffold for tailored inhibitor synthesis is showcased by the generation of the most potent human HTRA protease inhibitors to date. We anticipate that our approach may also be applied to other serine proteases, thus opening new avenues for a systematic discovery of serine protease inhibitors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Covalently Cross-Linked Sulfone Polybenzimidazole Membranes with Poly(Vinylbenzyl Chloride) for Fuel Cell Applications

    DEFF Research Database (Denmark)

    Yang, Jingshuai; Aili, David; Li, Qingfeng

    2013-01-01

    Covalently cross-linked polymer membranes were fabricated from poly(aryl sulfone benzimidazole) (SO(2) PBI) and poly(vinylbenzyl chloride) (PVBCl) as electrolytes for high-temperature proton-exchange-membrane fuel cells. The cross-linking imparted organo insolubility and chemical stability against...... radical attack to the otherwise flexible SO(2) PBI membranes. Steady phosphoric acid doping of the cross-linked membranes was achieved at elevated temperatures with little swelling. The acid-doped membranes exhibited increased mechanical strength compared to both pristine SO(2) PBI and poly[2,2'-(m......-phenylene)-5,5'-bibenzimidazole] (mPBI). The superior characteristics of the cross-linked SO(2) PBI membranes allowed higher acid doping levels and, therefore, higher proton conductivity. Fuel-cell tests with the cross-linked membranes demonstrated a high open circuit voltage and improved power performance...

  15. Non-Covalent Binding of DNA to Carbon Nanotubes Controlled by Biological Recognition Complex

    Science.gov (United States)

    Goux-Capes, Laurence; Filoramo, Arianna; Cote, Denis; Valentin, Emmanuel; Bourgoin, Jean-Philippe; Patillon, Jean-Nöel

    2004-09-01

    Single wall carbon nanotubes (SWNTs) occupy a special place within molecular electronics. Indeed, they exist as semiconducting or metallic wires and have been used to demonstrate molecular devices like transistors, diodes or SET (single electron transistor). However, the future of this class of SWNT-based devices is strictly related to the development of a bottom-up self-assembly technique. The exceptional recognition properties of DNA molecule make it an ideal candidate for this task. Here, we describe a non-covalent method to connect carbon nanotubes to DNA strands using the streptavidin/biotin complex. Control experiments show that in absence of biotin, the DNA strand do not bind to SWNT. The binding of SWNT to DNA strand has also been carefully checked by washing experiments, showing the strength of the DNA anchorage on SWNTs. Combining this approach with molecular combing enable us to align nanotubes on substrate.

  16. [Preparation of chiral monolithic column with covalently bonded cellulose and their application to rapid enantioseparation].

    Science.gov (United States)

    Wang, Jiabin; Wang, Xiao; Li, Jianhua; Lü, Haixia; Lin, Xucong; Xie, Zenghong; Zhang, Qiqing

    2011-12-01

    A chiral monolithic capillary column for rapid enantioseparation was prepared by covalently bonding of cellulose tris(4-methylbenzoate) (CTMB) on N-acryloxysuccinimide-based monolith. The preparation and derivatization conditions of the monolithic column were optimized. The successful grafting of CTMB was confirmed on the characterizations of the infrared spectrum and the cathodic electroosmotic flow (EOF). The effects of acetic acid concentration and methanol content on the enantioseparation were studied. The solvent resistance, reproducibility and stability of the monolithic column have also been investigated. The rapid enantioseparation of the five solutes (phenylalanine, tyrosine, tryptophan, propranolol and phenylethanol) with resolution (R(s)) values up to 1.31 was achieved within 1.2 min on the prepared chiral capillary monolithic column by capillary electrochromatography.

  17. Quantitative Measurement of GPCR Endocytosis via Pulse-Chase Covalent Labeling.

    Science.gov (United States)

    Kumagai, Hidetoshi; Ikeda, Yuichi; Motozawa, Yoshihiro; Fujishiro, Mitsuhiro; Okamura, Tomohisa; Fujio, Keishi; Okazaki, Hiroaki; Nomura, Seitaro; Takeda, Norifumi; Harada, Mutsuo; Toko, Haruhiro; Takimoto, Eiki; Akazawa, Hiroshi; Morita, Hiroyuki; Suzuki, Jun-ichi; Yamazaki, Tsutomu; Yamamoto, Kazuhiko; Komuro, Issei; Yanagisawa, Masashi

    2015-01-01

    G protein-coupled receptors (GPCRs) play a critical role in many physiological systems and represent one of the largest families of signal-transducing receptors. The number of GPCRs at the cell surface regulates cellular responsiveness to their cognate ligands, and the number of GPCRs, in turn, is dynamically controlled by receptor endocytosis. Recent studies have demonstrated that GPCR endocytosis, in addition to affecting receptor desensitization and resensitization, contributes to acute G protein-mediated signaling. Thus, endocytic GPCR behavior has a significant impact on various aspects of physiology. In this study, we developed a novel GPCR internalization assay to facilitate characterization of endocytic GPCR behavior. We genetically engineered chimeric GPCRs by fusing HaloTag (a catalytically inactive derivative of a bacterial hydrolase) to the N-terminal end of the receptor (HT-GPCR). HaloTag has the ability to form a stable covalent bond with synthetic HaloTag ligands that contain fluorophores or a high-affinity handle (such as biotin) and the HaloTag reactive linker. We selectively labeled HT-GPCRs at the cell surface with a HaloTag PEG ligand, and this pulse-chase covalent labeling allowed us to directly monitor the relative number of internalized GPCRs after agonist stimulation. Because the endocytic activities of GPCR ligands are not necessarily correlated with their agonistic activities, applying this novel methodology to orphan GPCRs, or even to already characterized GPCRs, will increase the likelihood of identifying currently unknown ligands that have been missed by conventional pharmacological assays.

  18. Highly sensitive covalently functionalized light-addressable potentiometric sensor for determination of biomarker

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Jintao [School of Life and Environmental Sciences, Guilin University of Electronic Technology, Guilin, Guangxi 541004 (China); Guangxi Experiment Center of Information Sciences, Guilin University of Electronic Technology, Guilin, Guangxi 541004 (China); Guan, Mingyuan; Huang, Guoyin; Qiu, Hengming; Chen, Zhengcheng [School of Life and Environmental Sciences, Guilin University of Electronic Technology, Guilin, Guangxi 541004 (China); Li, Guiyin, E-mail: liguiyin01@163.com [School of Life and Environmental Sciences, Guilin University of Electronic Technology, Guilin, Guangxi 541004 (China); Guangxi Experiment Center of Information Sciences, Guilin University of Electronic Technology, Guilin, Guangxi 541004 (China); Huang, Yong, E-mail: huangyong503@126.com [School of Life and Environmental Sciences, Guilin University of Electronic Technology, Guilin, Guangxi 541004 (China); Guangxi Experiment Center of Information Sciences, Guilin University of Electronic Technology, Guilin, Guangxi 541004 (China)

    2016-06-01

    A biomarker is related to the biological status of a living organism and shows great promise for the early prediction of a related disease. Herein we presented a novel structured light-addressable potentiometric sensor (LAPS) for the determination of a model biomarker, human immunoglobulin G (hIgG). In this system, the goat anti-human immunoglobulin G antibody was used as recognition element and covalently immobilized on the surface of light-addressable potentiometric sensor chip to capture human immunoglobulin G. Due to the light addressable capability of light-addressable potentiometric sensor, human immunoglobulin G dissolved in the supporting electrolyte solution can be detected by monitoring the potential shifts of the sensor. In order to produce a stable photocurrent, the laser diode controlled by field-programmable gate array was used as the light emitter to drive the light-addressable potentiometric sensor. A linear correlation between the potential shift response and the concentration of human immunoglobulin G was achieved and the corresponding regression equation was ΔV (V) = 0.00714C{sub hIgG} (μg/mL)–0.0147 with a correlation coefficient of 0.9968 over a range 0–150 μg/mL. Moreover, the light-addressable potentiometric sensor system also showed acceptable stability and reproducibility. All the results demonstrated that the system was more applicable to detection of disease biomarkers with simple operation, multiple-sample format and might hold great promise in various environmental, food, and clinical applications. - Highlights: • A novel structured light-addressable potentiometric sensor (LAPS) based on covalently functionalized membrane was designed. • The composition of the surface of LAPS chip was investigated by X-ray photoelectron spectroscopy (XPS). • hIgG dissolved in the supporting electrolyte solution can be detected by monitoring the potential shifts of LAPS.

  19. Covalently bound DNA on naked iron oxide nanoparticles: Intelligent colloidal nano-vector for cell transfection.

    Science.gov (United States)

    Magro, Massimiliano; Martinello, Tiziana; Bonaiuto, Emanuela; Gomiero, Chiara; Baratella, Davide; Zoppellaro, Giorgio; Cozza, Giorgio; Patruno, Marco; Zboril, Radek; Vianello, Fabio

    2017-11-01

    Conversely to common coated iron oxide nanoparticles, novel naked surface active maghemite nanoparticles (SAMNs) can covalently bind DNA. Plasmid (pDNA) harboring the coding gene for GFP was directly chemisorbed onto SAMNs, leading to a novel DNA nanovector (SAMN@pDNA). The spontaneous internalization of SAMN@pDNA into cells was compared with an extensively studied fluorescent SAMN derivative (SAMN@RITC). Moreover, the transfection efficiency of SAMN@pDNA was evaluated and explained by computational model. SAMN@pDNA was prepared and characterized by spectroscopic and computational methods, and molecular dynamic simulation. The size and hydrodynamic properties of SAMN@pDNA and SAMN@RITC were studied by electron transmission microscopy, light scattering and zeta-potential. The two nanomaterials were tested by confocal scanning microscopy on equine peripheral blood-derived mesenchymal stem cells (ePB-MSCs) and GFP expression by SAMN@pDNA was determined. Nanomaterials characterized by similar hydrodynamic properties were successfully internalized and stored into mesenchymal stem cells. Transfection by SAMN@pDNA occurred and GFP expression was higher than lipofectamine procedure, even in the absence of an external magnetic field. A computational model clarified that transfection efficiency can be ascribed to DNA availability inside cells. Direct covalent binding of DNA on naked magnetic nanoparticles led to an extremely robust gene delivery tool. Hydrodynamic and chemical-physical properties of SAMN@pDNA were responsible of the successful uptake by cells and of the efficiency of GFP gene transfection. SAMNs are characterized by colloidal stability, excellent cell uptake, persistence in the host cells, low toxicity and are proposed as novel intelligent DNA nanovectors for efficient cell transfection. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. An interpenetrating, microstructurable and covalently attached conducting polymer hydrogel for neural interfaces.

    Science.gov (United States)

    Kleber, Carolin; Bruns, Michael; Lienkamp, Karen; Rühe, Jürgen; Asplund, Maria

    2017-08-01

    This study presents a new conducting polymer hydrogel (CPH) system, consisting of the synthetic hydrogel P(DMAA-co-5%MABP-co-2,5%SSNa) and the conducting polymer (CP) poly(3,4-ethylenedioxythiophene) (PEDOT), intended as coating material for neural interfaces. The composite material can be covalently attached to the surface electrode, can be patterned by a photolithographic process to influence selected electrode sites only and forms an interpenetrating network. The hybrid material was characterized using cyclic voltammetry (CV), impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS), which confirmed a homogeneous distribution of PEDOT throughout all CPH layers. The CPH exhibited a 2,5 times higher charge storage capacity (CSC) and a reduced impedance when compared to the bare hydrogel. Electrochemical stability was proven over at least 1000 redox cycles. Non-toxicity was confirmed using an elution toxicity test together with a neuroblastoma cell-line. The described material shows great promise for surface modification of neural probes making it possible to combine the beneficial properties of the hydrogel with the excellent electronic properties necessary for high quality neural microelectrodes. Conductive polymer hydrogels have emerged as a promising new class of materials to functionalize electrode surfaces for enhanced neural interfaces and drug delivery. Common weaknesses of such systems are delamination from the connection surface, and the lack of suitable patterning methods for confining the gel to the selected electrode site. Various studies have reported on conductive polymer hydrogels addressing one of these challenges. In this study we present a new composite material which offers, for the first time, the unique combination of properties: it can be covalently attached to the substrate, forms an interpenetrating network, shows excellent electrical properties and can be patterned via UV-irradiation through a structured mask. Copyright

  1. Catalytic mechanism and inhibition of tRNA (Uracil-5-)methyltransferase: evidence for covalent catalysis

    International Nuclear Information System (INIS)

    Santi, D.V.; Hardy, L.W.

    1987-01-01

    tRNA (Ura-5-) methyltransferase catalyzes the transfer of a methyl group from S-adenosylmethionine (AdoMet) to the 5-carbon of a specific Urd residue in tRNA. This results in stoichiometric release of tritium from [5- 3 H] Urd-labeled substrate tRNA isolated from methyltransferase-deficient Escherichia coli. The enzyme also catalyzes an AdoMet-independent exchange reaction between [5- 3 H]-Urd-labeled substrate tRNA and protons of water at a rate that is about 1% that of the normal methylation reaction, but with identical stoichiometry. S-Adenosylhomocysteine inhibits the rate of the exchange reaction by 2-3-fold, whereas an analog having the sulfur of AdoMet replaced by nitrogen accelerates the exchange reaction 9-fold. In the presence (but not absence) of AdoMet, 5-fluorouracil-substituted tRNA (FUra-tRNA) leads to the first-order inactivation of the enzyme. This is accompanied by the formation of a stable covalent complex containing the enzyme, FUra-tRNA, and the methyl group AdoMet. A mechanism for catalysis is proposed that explains both the 5-H exchange reaction and the inhibition by FUra-tRNA: the enzyme forms a covalent Michael adduct with substrate or inhibitor tRNA by attack of a nucleophilic group of the enzyme at carbon 6 of the pyrimidine residue to be modified. As a result, an anion equivalent is generated at carbon 5 that is sufficiently reactive to be methylated by AdoMet. Preliminary experiments and precedents suggest that the nucleophilic catalyst of the enzyme is a thiol group of cysteine. The potent irreversible inhibition by FUra-tRNA suggest that a mechanism for the RNA effects of FUra may also involve irreversible inhibition of RNA-modifying enzymes

  2. Step-by-step build-up of covalent poly(ethylene oxide) nanogel films.

    Science.gov (United States)

    Zahouani, S; Hurman, L; De Giorgi, M; Vigier-Carrière, C; Boulmedais, F; Senger, B; Frisch, B; Schaaf, P; Lavalle, P; Jierry, L

    2017-11-30

    Hydrogels based on poly(ethylene glycol) (PEG) are commonly used for studies related to cell fate and tissue engineering. Here we present a new covalent layer-by-layer build-up process leading to PEG coatings of nanometer size called "nanogel films". Compared to macroscopic hydrogels, such nanogels should provide a fine control over the structure and the thickness of the coating. Alternated deposition of bifunctional and tetra functional PEG molecules reacting through thiol/maleimide click chemistry is evaluated by quartz crystal microbalance. We first study parameters influencing the build-up process of such coatings and demonstrate the importance of (i) the nature of the first deposited layer, (ii) the PEG concentrations and (iii) the length of the PEG chains that appears to be the most significant parameter influencing film growth. The build-up process can be extended to a large variety of substrates like SiO 2 or polymers by using an appropriate anchoring layer. Covalent functionalization of these nanogel films by proteins or enzymes is suited by modifying the biomolecules with thiol or maleimide groups and immobilizing them during the build-up process. Activity of the embedded enzymes can be maintained. Moreover ligands like biotin can be incorporated into the film and recognition by streptavidin can be modulated by playing with the number of PEG layers covering biotin. Compared to well-known PEG hydrogels, these new coatings are promising as they allow to (i) build thin nanometric coatings, (ii) finely control the amount of deposited PEG and (iii) organize the position of the embedded biomolecules inside the film layers.

  3. Comparative methods for analysis of protein covalent modification by electrophilic quinoids formed from xenobiotics

    Science.gov (United States)

    Yu, Bolan; Qin, Zhihui; Wijewickrama, Gihani T.; Edirisinghe, Praneeth; Bolton, Judy L.; Thatcher, Gregory R. J.

    2010-01-01

    Conjugation of biotin and fluorophore tags is useful for assaying covalent protein modification. Oxidative bioactivation of selective estrogen receptor modulators (SERMs) yields reactive quinoid electrophiles that covalently modify proteins; bioactivation is associated with carcinogenic and chemopreventive effects. Identification of the protein targets of electrophilic metabolites is of general important for xenobiotics. Four methodologies, using SERM derivatives and biotin/fluorophore tags, were compared for purification and quantification: (1) covert oxidatively activated tags (COATags; SERM conjugated to biotin); (2) dansylTags (SERM conjugated to fluorophore); and azidoTags (SERM azide derivatives) in a 2-step conjugation to biotin, either using (3) Staudinger ligation; or (4) click chemistry. All synthetic derivatives retained the estrogen receptor ligand characteristics of the parent SERMs. Model proteins with bioactivation by tyrosinase in buffer or cell lysates and liver proteins with in situ bioactivation in rat primary hepatocytes were studied by immunoassay and fluorescence. Comparison showed: the azidoTag/Staudinger method was sensitive but nonspecific; the azidoTag/click methodology had low sensitivity; and, the dansylTag methodology failed to detect modified proteins in hepatocytes. The COATag methodology was adjudged superior, detecting 5 ng of modified protein in vitro and identifying protein targets in hepatocytes. In metabolism studies in rat liver microsomes, the azide group was metabolically labile, one contributing factor in not selecting an azidoTag methodology in the highly oxidative environments required for bioactivation. For study of the protein targets of electrophilic metabolites formed by in situ oxidative bioactivation, the COATag is both sensitive and specific, and does not appear to suffer from poor cell permeability. PMID:19301905

  4. Covalent Modification of Bacteriophage T4 DNA Inhibits CRISPR-Cas9.

    Science.gov (United States)

    Bryson, Alexandra L; Hwang, Young; Sherrill-Mix, Scott; Wu, Gary D; Lewis, James D; Black, Lindsay; Clark, Tyson A; Bushman, Frederic D

    2015-06-16

    The genomic DNAs of tailed bacteriophages are commonly modified by the attachment of chemical groups. Some forms of DNA modification are known to protect phage DNA from cleavage by restriction enzymes, but others are of unknown function. Recently, the CRISPR-Cas nuclease complexes were shown to mediate bacterial adaptive immunity by RNA-guided target recognition, raising the question of whether phage DNA modifications may also block attack by CRISPR-Cas9. We investigated phage T4 as a model system, where cytosine is replaced with glucosyl-hydroxymethylcytosine (glc-HMC). We first quantified the extent and distribution of covalent modifications in T4 DNA by single-molecule DNA sequencing and enzymatic probing. We then designed CRISPR spacer sequences targeting T4 and found that wild-type T4 containing glc-HMC was insensitive to attack by CRISPR-Cas9 but mutants with unmodified cytosine were sensitive. Phage with HMC showed only intermediate sensitivity. While this work was in progress, another group reported examples of heavily engineered CRISRP-Cas9 complexes that could, in fact, overcome the effects of T4 DNA modification, indicating that modifications can inhibit but do not always fully block attack. Bacteria were recently found to have a form of adaptive immunity, the CRISPR-Cas systems, which use nucleic acid pairing to recognize and cleave genomic DNA of invaders such as bacteriophage. Historic work with tailed phages has shown that phage DNA is often modified by covalent attachment of large chemical groups. Here we demonstrate that DNA modification in phage T4 inhibits attack by the CRISPR-Cas9 system. This finding provides insight into mechanisms of host-virus competition and also a new set of tools that may be useful in modulating the activity of CRISPR-Cas9 in genome engineering applications. Copyright © 2015 Bryson et al.

  5. Microsolvation and the Effects of Non-Covalent Interactions on Intramolecular Dynamics

    Science.gov (United States)

    Foguel, Lidor; Vealey, Zachary; Vaccaro, Patrick

    2017-06-01

    Physicochemical processes brought about by non-covalent interactions between neighboring molecules are undeniably of crucial importance in the world around us, being responsible for effects ranging from the subtle (yet precise) control of biomolecular recognition events to the very existence of condensed phases. Of particular interest is the differential ability of distinct non-covalent forces, such as those mediated by dispersion-dominated aryl (π-π) coupling and electrostatically-driven hydrogen bonding, to affect unimolecular transformations by altering potential surface topographies and the nature of reaction coordinates. A concerted experimental and computational investigation of "microsolvation" (solvation at the molecular level) has been undertaken to elucidate the site-specific coupling between solute and solvent degrees of freedom, as well as attendant consequences for the efficiency and pathway of intrinsic proton-transfer dynamics. Targeted species have been synthesized in situ under "cold" supersonic free-jet expansion conditions (T_{rot} ≈ 1-2K) by complexing an active (proton-transfer) substrate with various ligands (e.g., water isotopologs and benzene derivatives) for which competing interaction mechanisms can lead to unique binding motifs. A series of fluorescence-based spectroscopic measurements have been performed on binary adducts formed with the prototypical 6-hydroxy-2-formylfulvene (HFF) system, where a quasi-linear intramolecular O-H...O bond and a zero-point energy that straddles the proton-transfer barrier crest synergistically yield the largest tunneling-induced splitting ever reported for the ground electronic state of an isolated neutral molecule. Such characteristics afford a localized metric for unraveling incipient changes in unimolecular reactivity, with comparison of experimentally observed and quantum-chemical predicted rovibronic landscapes serving to discriminate complexes built upon electrostatic (hydrogen-bonding) and

  6. Clustering of carboxylated magnetite nanoparticles through polyethylenimine: Covalent versus electrostatic approach

    Energy Technology Data Exchange (ETDEWEB)

    Tóth, Ildikó Y., E-mail: Ildiko.Toth@chem.u-szeged.hu [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary); Nesztor, Dániel [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary); Novák, Levente [Department of Colloid and Environmental Chemistry, University of Debrecen, Egyetem square 1, Debrecen (Hungary); Illés, Erzsébet; Szekeres, Márta; Szabó, Tamás [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary); Tombácz, Etelka, E-mail: tombacz@chem.u-szeged.hu [Department of Physical Chemistry and Materials Science, University of Szeged, Aradi vt. square 1, Szeged (Hungary)

    2017-04-01

    Carboxylated magnetite nanoparticles (MNPs) are frequently used to develop materials with enhanced properties for MRI and hyperthermia. The controlled clustering of MNPs via covalent or electrostatic approaches provides opportunity to prepare high quality materials. MNPs were prepared by co-precipitation and coated by poly(acrylic acid-co-maleic acid) (PAM@MNP). The clusters were synthesized from purified PAM@MNPs and polyethylenimine (PEI) solution via electrostatic interaction and covalent bond formation (ES-cluster and CB-cluster, respectively). The electrostatic adhesion (–NH{sub 3}{sup +} and –COO{sup –}) and the formed amide bond were confirmed by ATR-FTIR. The averaged area of CB-clusters was about twice as large as that of ES-cluster, based on TEM. The SAXS results showed that the surface of MNPs was smooth and the nanoparticles were close packed in both clusters. The pH-dependent aggregation state and zeta potential of clusters were characterized by DLS and electrophoresis measurements, the clusters were colloidally stable at pH>5. In hyperthermia experiments, the values of SAR were about two times larger for the chemically bonded cluster. The MRI studies showed exceptionally high transversion relaxivities, the r{sub 2} values are 457 mM{sup −1} s{sup −1} and 691 mM{sup −1} s{sup −1} for ES-cluster and CB-cluster, respectively. Based on these results, the chemically clustered product shows greater potential for feasible biomedical applications. - Highlights: • Chemically bonded clusters (CB-cluster) were prepared from PEI and PAM-coated MNPs. • The electrostatically clustered units (ES-cluster) are smaller and more compact. • The electrostatic adhesion and the amide bond formation were confirmed by ATR-FTIR. • CB-cluster dispersions are colloidally stable under physiological conditions. • CB-cluster shows great potential for application in MRI and hyperthermia.

  7. Covalent immobilisation of VEGF on plasma-coated electrospun scaffolds for tissue engineering applications.

    Science.gov (United States)

    Guex, A G; Hegemann, D; Giraud, M N; Tevaearai, H T; Popa, A M; Rossi, R M; Fortunato, G

    2014-11-01

    Recent findings in the field of biomaterials and tissue engineering provide evidence that surface immobilised growth factors display enhanced stability and induce prolonged function. Cell response can be regulated by material properties and at the site of interest. To this end, we developed scaffolds with covalently bound vascular endothelial growth factor (VEGF) and evaluated their mitogenic effect on endothelial cells in vitro. Nano- (254±133 nm) or micro-fibrous (4.0±0.4 μm) poly(ɛ-caprolactone) (PCL) non-wovens were produced by electrospinning and coated in a radio frequency (RF) plasma process to induce an oxygen functional hydrocarbon layer. Implemented carboxylic acid groups were converted into amine-reactive esters and covalently coupled to VEGF by forming stable amide bonds (standard EDC/NHS chemistry). Substrates were analysed by X-ray photoelectron spectroscopy (XPS), enzyme-linked immuno-assays (ELISA) and immunohistochemistry (anti-VEGF antibody and VEGF-R2 binding). Depending on the reaction conditions, immobilised VEGF was present at 127±47 ng to 941±199 ng per substrate (6mm diameter; concentrations of 4.5 ng mm(-2) or 33.3 ng mm(-2), respectively). Immunohistochemistry provided evidence for biological integrity of immobilised VEGF. Endothelial cell number of primary endothelial cells or immortalised endothelial cells were significantly enhanced on VEGF-functionalised scaffolds compared to native PCL scaffolds. This indicates a sustained activity of immobilised VEGF over a culture period of nine days. We present a versatile method for the fabrication of growth factor-loaded scaffolds at specific concentrations. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Specificity of Protein Covalent Modification by the Electrophilic Proteasome Inhibitor Carfilzomib in Human Cells*

    Science.gov (United States)

    Federspiel, Joel D.; Codreanu, Simona G.; Goyal, Sandeep; Albertolle, Matthew E.; Lowe, Eric; Teague, Juli; Wong, Hansen; Guengerich, F. Peter; Liebler, Daniel C.

    2016-01-01

    Carfilzomib (CFZ) is a second-generation proteasome inhibitor that is Food and Drug Administration and European Commission approved for the treatment of relapsed or refractory multiple myeloma. CFZ is an epoxomicin derivative with an epoxyketone electrophilic warhead that irreversibly adducts the catalytic threonine residue of the β5 subunit of the proteasome. Although CFZ produces a highly potent, sustained inactivation of the proteasome, the electrophilic nature of the drug could potentially produce off-target protein adduction. To address this possibility, we synthesized an alkynyl analog of CFZ and investigated protein adduction by this analog in HepG2 cells. Using click chemistry coupled with streptavidin based IP and shotgun tandem mass spectrometry (MS/MS), we identified two off-target proteins, cytochrome P450 27A1 (CYP27A1) and glutathione S-transferase omega 1 (GSTO1), as targets of the alkynyl CFZ probe. We confirmed the adduction of CYP27A1 and GSTO1 by streptavidin capture and immunoblotting methodology and then site-specifically mapped the adducts with targeted MS/MS methods. Although CFZ adduction of CYP27A1 and GSTO1 in vitro decreased the activities of these enzymes, the small fraction of these proteins modified by CFZ in intact cells should limit the impact of these off-target modifications. The data support the high selectivity of CFZ for covalent modification of its therapeutic targets, despite the presence of a reactive electrophile. The approach we describe offers a generalizable method to evaluate the safety profile of covalent protein-modifying therapeutics. PMID:27503896

  9. Vanillyl alcohol oxidases produced in Komagataella phaffii contain a highly stable non-covalently bound anionic FAD semiquinone

    NARCIS (Netherlands)

    Gygli, G.A.; Berkel, van W.J.H.

    2017-01-01

    Vanillyl alcohol oxidase (VAO) from Penicillium simplicissimum is a covalent flavoprotein that has emerged as a promising biocatalyst for the production of aromatic fine chemicals such as vanillin, coniferyl alcohol and enantiopure 1-(4’-hydroxyphenyl) alcohols. The largescale production of this

  10. Convenient Preparation of Bactericidal Hydrogels by Covalent Attachment of Stabilized Antimicrobial Peptides Using Thiol-ene Click Chemistry

    NARCIS (Netherlands)

    Cleophas, Rik T. C.; Riool, Martijn; van Ufford, H. C. Quarles; Zaat, Sebastian A. J.; Kruijtzer, John A. W.; Liskamp, Rob M. J.

    2014-01-01

    This report describes the design and synthesis of a bactericidal poly(ethylene glycol)-based (PEG) hydrogel coating with covalently attached antimicrobial peptides (AMP) stabilized against proteolytic degradation. As such, mimics of the highly active AMP HHC10 (H-KRWWKWIRW-NH2) were designed for

  11. Non-covalent conjugates of single-walled carbon nanotubes and folic acid for interaction with cells overexpressing folate receptors

    DEFF Research Database (Denmark)

    Castillo, John J.; Rindzevicius, Tomas; Novoa, Leidy V.

    2013-01-01

    We here present amethod to form a noncovalent conjugate of single-walled carbon nanotubes and folic acid aimed to interact with cells over-expressing folate receptors. The bonding was obtained without covalent chemical functionalization using a simple, rapid “one pot” synthesis method. The zeta p...

  12. Non-covalent synthesis of calix[4]arene-capped porphyrins in polar solvents via ionic interactions

    NARCIS (Netherlands)

    Fiammengo, R.; Timmerman, P.; Huskens, Jurriaan; Versluis, Kees; Heck, Albert J.R.; Reinhoudt, David

    2002-01-01

    Non-covalent synthesis of calix[4]arene capped porphyrins can be achieved in polar solvents (up to 45% molar fraction of water) via ionic interaction. Thus tetracationic meso-tetrakis(N-alkylpyridinium-3-yl) porphyrins 1a–d and tetra anionic 25,26,27,28-tetrakis(2-ethoxyethoxy)-calix[4]arene

  13. Moving beyond Definitions: What Student-Generated Models Reveal about Their Understanding of Covalent Bonding and Ionic Bonding

    Science.gov (United States)

    Luxford, Cynthia J.; Bretz, Stacey Lowery

    2013-01-01

    Chemistry students encounter a variety of terms, definitions, and classification schemes that many instructors expect students to memorize and be able to use. This research investigated students' descriptions of ionic and covalent bonding beyond definitions in order to explore students' knowledge about chemical bonding. Using Johnstone's Multiple…

  14. Engineering covalent oligomers of the mechanosensitive channel of large conductance from Escherichia coli with native conductance and gating characteristics

    NARCIS (Netherlands)

    Folgering, JHA; Wolters, JC; Poolman, B

    2005-01-01

    To obtain a gene construct for making single substitutions per channel and to determine the quaternary structure of the mechanosensitive channel MscL from Escherichia coli, covalent oligomers (monomer to hexamer) were engineered by gene fusion; up to six copies of the mscL gene were fused in tandem.

  15. Towards a biocompatible artificial lung: Covalent functionalization of poly(4-methylpent-1-ene (TPX with cRGD pentapeptide

    Directory of Open Access Journals (Sweden)

    Lena Möller

    2013-02-01

    Full Text Available Covalent multistep coating of poly(methylpentene, the membrane material in lung ventilators, by using a copper-free “click” approach with a modified cyclic RGD peptide, leads to a highly biocompatible poly(methylpentene surface. The resulting modified membrane preserves the required excellent gas-flow properties while being densely seeded with lung endothelial cells.

  16. Covalent Trapping of Methyllycaconitine at the α4-α4 Interface of the α4β2 Nicotinic Acetylcholine Receptor

    DEFF Research Database (Denmark)

    Absalom, Nathan L; Quek, Gracia; Lewis, Trevor M

    2013-01-01

    containing an α4(D204C) mutation predicted by homology modeling to be within reach of the reactive probe. We demonstrate that covalent trapping results in irreversible reduction of ACh-elicited currents in the (α4)3(β2)2 stoichiometry, indicating that MLA binds to the α4-α4 interface of the (α4)3(β2...

  17. A QUANTUM MECHANICAL STUDY OF THE PROTONATION AND COVALENT HYDRATION OF QUINAZOLINE IN THE PRESENCE OF METAL CATIONS

    Science.gov (United States)

    We have investigated the protonation and reversible covalent hydration of quinazoline in the presence of Li+, Na+, and Ca2+ ions using ab initio quantum mechanical calculations at the MP2/6-31G**//HF/6-31G*level of theory. Proton affinities, enthalpies of hydration at 298.15K (DH...

  18. Assessment of covalent bond formation between coupling agents and wood by FTIR spectroscopy and pull strength tests

    DEFF Research Database (Denmark)

    Rasmussen, Jonas Stensgaard; Barsberg, Søren Talbro; Venås, Thomas Mark

    2014-01-01

    In the focus was the question whether metal alkoxide coupling agents – titanium, silane, and zirconium – form covalent bonds to wood and how they improve coating adhesion. In a previous work, a downshift of the lignin infrared (IR) band ∼1600 cm-1 was shown to be consistent with the formation of ...... importance for improved wood coating adhesion....

  19. Covalently bound phosphate residues in bovine milk xanthine oxidase and in glucose oxidase from Aspergillus niger: A reevaluation

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, J.L.; Rajagopalan, K.V. (Duke Univ. Medical Center, Durham, NC (USA)); London, R.E. (National Institute of Environmental Health Science, Research Triangle Park, NC (USA))

    1989-09-01

    The reported presence of covalently bound phosphate residues in flavoproteins has significant implications with regard to the catalytic mechanisms and structural stability of the specific enzymes themselves and in terms of general cellular metabolic regulation. These considerations have led to a reevaluation of the presence of covalently bound phosphorus in the flavoproteins xanthine oxidase and glucose oxidase. Milk xanthine oxidase purified by a procedure that includes anion-exchange chromatography is shown to contain three phosphate residues. All three are noncovalently associated with the protein, two with the FAD cofactor, and one with the molybdenum cofactor. Results of chemical analysis and {sup 31}P NMR spectroscopy indicate that enzyme purified by this method contains no phosphoserine residues. Xanthine oxidase preparations purified by chromatography on calcium phosphate gel in place of DEAE-Sephadex yielded higher phosphate-to-protein ratios, which could be reduced to the expected values by additional purification on a folate affinity column. Highly active, highly purified preparations of glucose oxidase are shown to contain only the two phosphate residues of the FAD cofactor. The covalently bound bridging phosphate reported by others may arise in aged or degraded preparations of the enzyme but appears not to be a constituent of functional glucose oxidase. These results suggest that the presence of covalent phosphate residues in other flavoproteins should be rigorously reevaluated as well.

  20. Are Orbital-Resolved Shared-Electron Distribution Indices and Cioslowski Covalent Bond Orders Useful for Molecules?

    Czech Academy of Sciences Publication Activity Database

    Cooper, D.L.; Ponec, Robert; Kohout, M.

    2015-01-01

    Roč. 113, 13-14 (2015), s. 1682-1689 ISSN 0026-8976 Institutional support: RVO:67985858 Keywords : domain averaged fermi holes * shared electron-distribution indices * Cioslowski covalent bond orders Subject RIV: CC - Organic Chemistry Impact factor: 1.837, year: 2015

  1. Covalent interactions of 1,2,3-trichloropropane with hepatic macromolecules: studies in the male F-344 rat.

    Science.gov (United States)

    Weber, G L; Sipes, I G

    1990-07-01

    Preliminary investigations into the role of biotransformation in 1,2,3-trichloropropane (TCP)-induced tumor formation have been undertaken. Male F-344 rats were administered 30 mg/kg [14C]TCP (100 microCi/kg) ip and killed 4 hr later. The extent of covalent binding to hepatic protein, DNA, and RNA was 418, 244, and 432 pmol [14C]TCP equivalents/mg, respectively. An in vivo covalent binding time course showed no significant change in [14C]TCP equivalents bound to hepatic DNA (1-48 hr), while binding to protein was maximal by 4 hr and decreased significantly by 48 hr. The binding of TCP-associated radioactivity to hepatic protein and DNA was shown to be cumulative for two and three doses when given 24 hr apart. Pretreatment of animals with phenobarbital caused a decrease while pretreatment with SKF 525-A caused an increase in covalent binding of [14C]TCP equivalents to protein and DNA. Pretreatment of rats with beta-naphthoflavone did not alter the covalent binding of [14C]TCP equivalents to protein or DNA. However, glutathione depletion with L-buthionine-(R,S)-sulfoximine increased binding to protein by 342% while it decreased binding to DNA by 56%. Intraperitoneal administration of TCP also depleted hepatic GSH by 41 and 61% 2 hr after doses of 30 and 100 mg/kg. The in vivo binding data suggest a dual role for GSH in the bioactivation of TCP. It may, in part, be that GSH is involved in the bioactivation and covalent binding of TCP to hepatic DNA. However, it also appears to detoxify a reactive intermediate(s) that binds to protein.

  2. Atoms and clusters in strong laser fields

    NARCIS (Netherlands)

    Marchenko, T.

    2008-01-01

    This thesis describes experimental and theoretical studies on the interaction of strong infrared laser fields with atoms and atomic clusters. Part I provides an overview of the main strong-field phenomena in atoms, molecules and clusters and describes the state-of-the-art in strong-field science.

  3. Strong Bisimilarity of Simple Process Algebras

    DEFF Research Database (Denmark)

    Srba, Jirí

    2003-01-01

    We study bisimilarity and regularity problems of simple process algebras. In particular, we show PSPACE-hardness of the following problems: (i) strong bisimilarity of Basic Parallel Processes (BPP), (ii) strong bisimilarity of Basic Process Algebra (BPA), (iii) strong regularity of BPP, and (iv) ...

  4. 78 FR 15710 - Strong Sensitizer Guidance

    Science.gov (United States)

    2013-03-12

    ... definition of ``strong sensitizer'' found at 16 CFR 1500.3(c)(5). The Commission is proposing to revise the supplemental definition of ``strong sensitizer'' due to advancements in the science of sensitization that have... document is intended to clarify the ``strong sensitizer'' definition, assist manufacturers in understanding...

  5. Application of strong phosphoric acid to radiochemistry

    International Nuclear Information System (INIS)

    Terada, Kikuo

    1977-01-01

    Not only inorganic and organic compounds but also natural substrances, such as accumulations in soil, are completely decomposed and distilled by heating with strong phosphoric acid for 30 to 50 minutes. As applications of strong phosphoric acid to radiochemistry, determination of uranium and boron by use of solubilization effect of this substance, titration of uranyl ion by use of sulfuric iron (II) contained in this substance, application to tracer experiment, and determination of radioactive ruthenium in environmental samples are reviewed. Strong phosphoric acid is also applied to activation analysis, for example, determination of N in pyrographite with iodate potassium-strong phosphoric acid method, separation of Os and Ru with sulfuric cerium (IV) - strong phosphoric acid method or potassium dechromate-strong phosphoric acid method, analysis of Se, As and Sb rocks and accumulations with ammonium bromide, sodium chloride and sodium bromide-strong phosphoric acid method. (Kanao, N.)

  6. Covalent functionalization of graphene oxide with biocompatible poly(ethylene glycol) for delivery of paclitaxel.

    Science.gov (United States)

    Xu, Zhiyuan; Wang, Song; Li, Yongjun; Wang, Mingwei; Shi, Ping; Huang, Xiaoyu

    2014-10-08

    Graphene oxide (GO), a novel 2D nanomaterial prepared by the oxidation of natural graphite, has been paid much attention in the area of drug delivery due to good biocompatibility and low toxicity. In the present work, 6-armed poly(ethylene glycol) was covalently introduced into the surface of GO sheets via a facile amidation process under mild conditions, making the modified GO, GO-PEG (PEG: 65 wt %, size: 50-200 nm), stable and biocompatible in physiological solution. This nanosized GO-PEG was found to be nontoxic to human lung cancer A549 and human breast cancer MCF-7 cells via cell viability assay. Furthermore, paclitaxel (PTX), a widely used cancer chemotherapy drug, was conjugated onto GO-PEG via π-π stacking and hydrophobic interactions to afford a nanocomplex of GO-PEG/PTX with a relatively high loading capacity for PTX (11.2 wt %). This complex could quickly enter into A549 and MCF-7 cells evidenced by inverted fluorescence microscopy using Fluorescein isothiocyanate as a probe, and it also showed remarkably high cytotoxicity to A549 and MCF-7 cells in a broad range of concentration of PTX and time compared to free PTX. This kind of nanoscale drug delivery system on the basis of PEGylated GO may find potential application in biomedicine.

  7. Covalent Surface Modification of Silicon Oxides with Alcohols in Polar Aprotic Solvents.

    Science.gov (United States)

    Lee, Austin W H; Gates, Byron D

    2017-09-05

    Alcohol-based monolayers were successfully formed on the surfaces of silicon oxides through reactions performed in polar aprotic solvents. Monolayers prepared from alcohol-based reagents have been previously introduced as an alternative approach to covalently modify the surfaces of silicon oxides. These reagents are readily available, widely distributed, and are minimally susceptible to side reactions with ambient moisture. A limitation of using alcohol-based compounds is that previous reactions required relatively high temperatures in neat solutions, which can degrade some alcohol compounds or could lead to other unwanted side reactions during the formation of the monolayers. To overcome these challenges, we investigate the condensation reaction of alcohols on silicon oxides carried out in polar aprotic solvents. In particular, propylene carbonate has been identified as a polar aprotic solvent that is relatively nontoxic, readily accessible, and can facilitate the formation of alcohol-based monolayers. We have successfully demonstrated this approach for tuning the surface chemistry of silicon oxide surfaces with a variety of alcohol containing compounds. The strategy introduced in this research can be utilized to create silicon oxide surfaces with hydrophobic, oleophobic, or charged functionalities.

  8. Covalently linked kanamycin - Ciprofloxacin hybrid antibiotics as a tool to fight bacterial resistance.

    Science.gov (United States)

    Shavit, Michal; Pokrovskaya, Varvara; Belakhov, Valery; Baasov, Timor

    2017-06-01

    To address the growing problem of antibiotic resistance, a set of 12 hybrid compounds that covalently link fluoroquinolone (ciprofloxacin) and aminoglycoside (kanamycin A) antibiotics were synthesized, and their activity was determined against both Gram-negative and Gram-positive bacteria, including resistant strains. The hybrids were antagonistic relative to the ciprofloxacin, but were substantially more potent than the parent kanamycin against Gram-negative bacteria, and overcame most dominant resistance mechanisms to aminoglycosides. Selected hybrids were 42-640 fold poorer inhibitors of bacterial protein synthesis than the parent kanamycin, while they displayed similar inhibitory activity to that of ciprofloxacin against DNA gyrase and topoisomerase IV enzymes. The hybrids showed significant delay of resistance development in both E. coli and B. subtilis in comparison to that of component drugs alone or their 1:1 mixture. More generally, the data suggest that an antagonistic combination of aminoglycoside-fluoroquinolone hybrids can lead to new compounds that slowdown/prevent the emergence of resistance. Copyright © 2017 Elsevier Ltd. All rights reserved.

  9. Versatile bio-ink for covalent immobilization of chimeric avidin on sol-gel substrates.

    Science.gov (United States)

    Heikkinen, Jarkko J; Kivimäki, Liisa; Määttä, Juha A E; Mäkelä, Inka; Hakalahti, Leena; Takkinen, Kristiina; Kulomaa, Markku S; Hytönen, Vesa P; Hormi, Osmo E O

    2011-10-15

    A bio-ink for covalent deposition of thermostable, high affinity biotin-binding chimeric avidin onto sol-gel substrates was developed. The bio-ink was prepared from heterobifunctional crosslinker 6-maleimidohexanoic acid N-hydroxysuccinimide which was first reacted either with 3-aminopropyltriethoxysilane or 3-aminopropyldimethylethoxysilane to form silane linkers 6-maleimide-N-(3-(triethoxysilyl)propyl)hexanamide or -(ethoxydimethylsilyl)propyl)-hexanamide. C-terminal cysteine genetically engineered to chimeric avidin was reacted with the maleimide group of silane linker in methanol/PBS solution to form a suspension, which was printed on sol-gel modified PMMA film. Different concentrations of chimeric avidin and ratios between silane linkers were tested to find the best properties for the bio-ink to enable gravure or inkjet printing. Bio-ink prepared from 3-aminopropyltriethoxysilane was found to provide the highest amount of active immobilized chimeric avidin. The developed bio-ink was shown to be valuable for automated fabrication of avidin-functionalized polymer films. Copyright © 2011 Elsevier B.V. All rights reserved.

  10. Highly optimized CO2 capture by inexpensive nanoporous covalent organic polymers and their amine composites.

    Science.gov (United States)

    Patel, Hasmukh A; Yavuz, Cafer T

    2015-01-01

    Carbon dioxide (CO2) storage and utilization requires effective capture strategies that limit energy penalties. Polyethylenimine (PEI)-impregnated covalent organic polymers (COPs) with a high CO2 adsorption capacity are successfully prepared in this study. A low cost COP with a high specific surface area is suitable for PEI loading to achieve high CO2 adsorption, and the optimal PEI loading is 36 wt%. Though the adsorbed amount of CO2 on amine impregnated COPs slightly decreased with increasing adsorption temperature, CO2/N2 selectivity is significantly improved at higher temperatures. The adsorption of CO2 on the sorbent is very fast, and a sorption equilibrium (10% wt) was achieved within 5 min at 313 K under the flow of simulated flue gas streams. The CO2 capture efficiency of this sorbent is not affected under repetitive adsorption-desorption cycles. The highest CO2 capture capacity of 75 mg g(-1) at 0.15 bar is achieved under dry CO2 capture however it is enhanced to 100 mg g(-1) in the mixed gas flow containing humid 15% CO2. Sorbents were found to be thermally stable up to at least 200 °C. TGA and FTIR studies confirmed the loading of PEIs on COPs. This sorbent with high and fast CO2 sorption exhibits a very promising application in direct CO2 capture from flue gas.

  11. In situ metalation of free base phthalocyanine covalently bonded to silicon surfaces

    Directory of Open Access Journals (Sweden)

    Fabio Lupo

    2014-11-01

    Full Text Available Free 4-undecenoxyphthalocyanine molecules were covalently bonded to Si(100 and porous silicon through thermic hydrosilylation of the terminal double bonds of the undecenyl chains. The success of the anchoring strategy on both surfaces was demonstrated by the combination of X-ray photoelectron spectroscopy with control experiments performed adopting the commercially available 2,3,9,10,16,17,23,24-octakis(octyloxy-29H,31H-phthalocyanine, which is not suited for silicon anchoring. Moreover, the study of the shape of the XPS N 1s band gave relevant information on the interactions occurring between the anchored molecules and the substrates. The spectra suggest that the phthalocyanine ring interacts significantly with the flat Si surface, whilst ring–surface interactions are less relevant on porous Si. The surface-bonded molecules were then metalated in situ with Co by using wet chemistry. The efficiency of the metalation process was evaluated by XPS measurements and, in particular, on porous silicon, the complexation of cobalt was confirmed by the disappearance in the FTIR spectra of the band at 3290 cm−1 due to –NH stretches. Finally, XPS results revealed that the different surface–phthalocyanine interactions observed for flat and porous substrates affect the efficiency of the in situ metalation process.

  12. Enantioselective Synthesis of Various Cyanohydrins Using Covalently Immobilized Preparations of Hydroxynitrile Lyase from Prunus dulcis.

    Science.gov (United States)

    Alagöz, Dilek; Tükel, S Seyhan; Yildirim, Deniz

    2015-11-01

    The carrier-based and carrier-free (cross-linked enzyme aggregate) covalent immobilizations of Prunus dulcis hydroxynitrile lyase were investigated. The immobilized preparations were tested for enantioselective carbon-carbon bond formation activity in the biphasic medium. Of the tested preparations, only cross-linked enzyme aggregate of P. dulcis hydroxynitrile lyase (PdHNL-CLEA) achieved the synthesis of (R)-mandelonitrile with 93% yield and 99% enantiopurity. PdHNL-CLEA was also used in the synthesis of various (R)-cyanohydrins from corresponding aldehydes/ketones and hydrocyanic acid. When 4-methoxybenzaldehyde, 4-methyl benzaldehyde, and 4-hydroxybenzaldehyde were used as substrates, the yield-enantiomeric excess of corresponding (R)-cyanohydrins were obtained as 95-95, 85-79, and 2-25%, respectively, after 96 h at pH 4.0 and 5 °C. For acetophenone, 4-fluoroacetophenone, 4-chloroacetophenone, 4-bromoacetophenone, and 4-iodoacetophenone, the yield-enantiomeric excess of corresponding (R)-cyanohydrins were 1-99, 20-84, 11-95, 5-99, and 3-24%, respectively at the same conditions. The results demonstrate PdHNL-CLEA can be effectively used in the synthesis of (R)-mandelonitrile.

  13. The non-covalent decoration of self-assembling protein fibers.

    Science.gov (United States)

    Mahmoud, Zahra N; Grundy, Daniel J; Channon, Kevin J; Woolfson, Derek N

    2010-10-01

    The design of self-assembling fibers presents challenges in basic science, and has potential for developing materials for applications in areas such as tissue engineering. A contemporary issue in the field is the construction of multi-component, functionalized systems. Previously, we have developed peptide-based fibers, the SAF system, that comprises two complementary peptides, which affords considerable control over assembly and morphology. Here we present a straightforward route to functionalizing the SAFs with small molecules and, subsequently, other moieties. This is achieved via non-covalent recruitment of charged peptide tags, which offers advantages such as further control, reversibility, and future prospects for developing recombinant tags. We demonstrate the concept by appending fluorescent labels and biotin (and thence gold nanoparticles) to the peptides, and visualising the resulting decorated SAFs by light and electron microscopy. The peptide tags bind in the nm-mum range, and show specificity compared with control peptides, and for the SAFs over similar alpha-helix-based peptide fibers. 2010 Elsevier Ltd. All rights reserved.

  14. Isocyanate-mediated covalent immobilization of Mucor miehei lipase onto SBA-15 for transesterification reaction.

    Science.gov (United States)

    Canilho, N; Jacoby, J; Pasc, A; Carteret, C; Dupire, F; Stébé, M J; Blin, J L

    2013-12-01

    Mucor miehei lipase (Mm-L) covalently bind on a hexagonally ordered silica SBA-15 (Santa Barbara Amorphous), previously functionalized with isocyanate moieties, was examined as biocatalyst for transesterification of colza oil with methanol. The isocyanate-mesoporous silica (NCO-SBA-15) was obtained by condensation of silanol with triethoxysilane propyl isocyanate (TPI). The efficiency of the functionalization has been evidenced by infrared, (29)Si and (13)C NMR spectroscopies. The substrate provided a moderate hydrophobic microenvironment together with reactive sites for chemical immobilization of the enzyme. The biocatalyst containing 0.28 g of Mm-L per gram of support afforded a high level of transesterification activity (yield up to 80%) while using 1:1 molar ratio of methanol/colza oil and small amount of water. The biocatalyst showed higher operational stability than the corresponding physisorbed enzyme since it can be reused 6 times against 2 consecutive runs for the physisorbed enzyme. © 2013 Elsevier B.V. All rights reserved.

  15. Bioelectrochemistry of non-covalent immobilized alcohol dehydrogenase on oxidized diamond nanoparticles.

    Science.gov (United States)

    Nicolau, Eduardo; Méndez, Jessica; Fonseca, José J; Griebenow, Kai; Cabrera, Carlos R

    2012-06-01

    Diamond nanoparticles are considered a biocompatible material mainly due to their non-cytotoxicity and remarkable cellular uptake. Model proteins such as cytochrome c and lysozyme have been physically adsorbed onto diamond nanoparticles, proving it to be a suitable surface for high protein loading. Herein, we explore the non-covalent immobilization of the redox enzyme alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae (E.C.1.1.1.1) onto oxidized diamond nanoparticles for bioelectrochemical applications. Diamond nanoparticles were first oxidized and physically characterized by X-ray diffraction (XRD), FT-IR and TEM. Langmuir isotherms were constructed to investigate the ADH adsorption onto the diamond nanoparticles as a function of pH. It was found that a higher packing density is achieved at the isoelectric point of the enzyme. Moreover, the relative activity of the immobilized enzyme on diamond nanoparticles was addressed under optimum pH conditions able to retain up to 70% of its initial activity. Thereafter, an ethanol bioelectrochemical cell was constructed by employing the immobilized alcohol dehydrogenase onto diamond nanoparticles, this being able to provide a current increment of 72% when compared to the blank solution. The results of this investigation suggest that this technology may be useful for the construction of alcohol biosensors or biofuel cells in the near future. Copyright © 2011 Elsevier B.V. All rights reserved.

  16. H-shaped supra-amphiphiles based on a dynamic covalent bond.

    Science.gov (United States)

    Wang, Guangtong; Wang, Chao; Wang, Zhiqiang; Zhang, Xi

    2012-10-16

    The imine bond, a kind of dynamic covalent bond, is used to bind two bolaform amphiphiles together with spacers, yielding H-shaped supra-amphiphiles. Micellar aggregates formed by the self-assembly of the H-shaped supra-amphiphiles are observed. When pH is tuned down from basic to slightly acidic, the benzoic imine bond can be hydrolyzed, leading to the dissociation of H-shaped supra-amphiphiles. Moreover, H-shaped supra-amphiphiles have a lower critical micelle concentration than their building blocks, which is very helpful in enhancing the stability of the benzoic imine bond being hydrolyzed by acid. The surface tension isotherms of the H-shaped supra-amphiphiles with different spacers indicate their twisty conformation at a gas-water interface. The study of H-shaped supra-amphiphiles can enrich the family of amphiphiles, and moreover, the pH-responsiveness may make them apply to controlled or targetable drug delivery in a biological environment.

  17. A 3D Covalent Organic Framework with Exceptionally High Iodine Capture Capability.

    Science.gov (United States)

    Wang, Chang; Wang, Yu; Ge, Rile; Song, Xuedan; Xing, Xueqing; Jiang, Qike; Lu, Hui; Hao, Ce; Guo, Xinwen; Gao, Yanan; Jiang, Donglin

    2018-01-12

    Using porous materials to cope with environmental issues is promising but remains a challenge especially for removing the radioactive vapor wastes in fission because of harsh adsorption conditions. Here we report a new, stable covalent organic framework (COF) as a porous platform for removing iodine vapor-a major radioactive fission waste. The three-dimensional COF consists of a diamond topology knotted by adamantane units, creates ordered one-dimensional pores and are highly porous. The COF enables the removal of iodine vapor via charge transfer complex formation with the pore walls to achieve exceptional capacity. Moreover, the 3D COF is "soft" to trigger structural fitting to iodine while retaining connectivity and enables cycle use for many times while retaining high uptake capacity. These results set a new benchmark for fission waste removal and suggest the great potential of COFs as a designable porous material for challenging world-threatening pollution issues. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Covalently attached metalloporphyrins in LBL self-assembled redox polyelectrolyte thin films

    International Nuclear Information System (INIS)

    Carballo, R.R.; Campodall' Orto, V.; Hurst, J.A.; Spiaggi, A.; Bonazzola, C.; Rezzano, I.N.

    2008-01-01

    A formylporphyrin has been covalently bound to Poly (Allylamine Hydrochloride) (PAH) and electrostatically self-assembled polyelectrolyte films, containing the attached metalloporphyrin, have been constructed. The UV-vis absorption band at 390 nm has been followed as core porphyrin marker. The reflection-absorption IR spectra of the gold films modified with layer-by-layer (LBL) polyelectrolytes were recorded after 6 and 12 layers. Characteristic infrared absorbance bands of porphyrin, PAH and PVS became more evident on increasing the number of bilayers. The absorption bands at 750, 1214 and 2960 cm -1 , attributed at ν(S-O), ν s (SO 3 - ) and ν(=NH 2 + ), respectively, showed a linear growth (R 2 > 0.99) with the number of adsorbed layers. A lower correlation coefficient was observed for the band at 1585 cm -1 attributed to Fe-protoporphyrin. In order to evaluate the electron transfer (ET) rate, the ΔE p of the [Fe(CN) 6 ] 4- /[Fe(CN) 6 ] 3- couple in solution was measured after covering the electrode. A proportional increase of the ΔE p with the number of layers is observed up to the 4th layer. After the second bilayer, the magnitude of the peak separation is highly related to the charge of the topmost layer. The method allowed controlling the film thickness via the number of deposited layers (LBL). The electrode described, resulted in a good catalyst for O 2 reduction and sulfite oxidation

  19. Improving Properties of a Novel β-Galactosidase from Lactobacillus plantarum by Covalent Immobilization.

    Science.gov (United States)

    Benavente, Rocio; Pessela, Benevides C; Curiel, Jose Antonio; de las Rivas, Blanca; Muñoz, Rosario; Guisán, Jose Manuel; Mancheño, Jose M; Cardelle-Cobas, Alejandra; Ruiz-Matute, Ana I; Corzo, Nieves

    2015-04-30

    A novel β-galactosidase from Lactobacillus plantarum (LPG) was over-expressed in E. coli and purified via a single chromatographic step by using lowly activated IMAC (immobilized metal for affinity chromatography) supports. The pure enzyme exhibited a high hydrolytic activity of 491 IU/mL towards o-nitrophenyl β-D-galactopyranoside. This value was conserved in the presence of different divalent cations and was quite resistant to the inhibition effects of different carbohydrates. The pure multimeric enzyme was stabilized by multipoint and multisubunit covalent attachment on glyoxyl-agarose. The glyoxyl-LPG immobilized preparation was over 20-fold more stable than the soluble enzyme or the one-point CNBr-LPG immobilized preparation at 50 °C. This β-galactosidase was successfully used in the hydrolysis of lactose and lactulose and formation of different oligosaccharides was detected. High production of galacto-oligosaccharides (35%) and oligosaccharides derived from lactulose (30%) was found and, for the first time, a new oligosaccharide derived from lactulose, tentatively identified as 3'-galactosyl lactulose, has been described.

  20. Postsynthetic Functionalization of Three-Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions.

    Science.gov (United States)

    Lu, Qiuyu; Ma, Yunchao; Li, Hui; Guan, Xinyu; Yusran, Yusran; Xue, Ming; Fang, Qianrong; Yan, Yushan; Qiu, Shilun; Valtchev, Valentin

    2018-02-19

    Chemical functionalization of covalent organic frameworks (COFs) is critical for tuning their properties and broadening their potential applications. However, the introduction of functional groups, especially to three-dimensional (3D) COFs, still remains largely unexplored. Reported here is a general strategy for generating a 3D carboxy-functionalized COF through postsynthetic modification of a hydroxy-functionalized COF, and for the first time exploration of the 3D carboxy-functionalized COF in the selective extraction of lanthanide ions. The obtained COF shows high crystallinity, good chemical stability, and large specific surface area. Furthermore, the carboxy-functionalized COF displays high metal loading capacities together with excellent adsorption selectivity for Nd 3+ over Sr 2+ and Fe 3+ as confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens a way to their use in environmentally related applications. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Immobilization of Candida antarctica Lipase B by Covalent Attachment to Green Coconut Fiber

    Science.gov (United States)

    Brígida, Ana I. S.; Pinheiro, Álvaro D. T.; Ferreira, Andrea L. O.; Pinto, Gustavo A. S.; Gonçalves, Luciana R. B.

    The objective of this study was to covalently immobilize Candida antarctica type B lipase (CALB) onto silanized green coconut fibers. Variables known to control the number of bonds between enzyme and support were evaluated including contact time, pH, and final reduction with sodium borohydride. Optimal conditions for lipase immobilization were found to be 2h incubation at both pH 7.0 and 10.0. Thermal stability studies at 60°C showed that the immobilized lipase prepared at pH 10.0 (CALB-10) was 363-fold more stable than the soluble enzyme and 5.4-fold more stable than the biocatalyst prepared at pH 7.0 (CALB-7). CALB-7 was found to have higher specific activity and better stability when stored at 5°C. When sodium borohydride was used as reducing agent on CALB-10 there were no improvement in storage stability and at 60°C stability was reduced for both CALB-7 and CALB-10.

  2. Improving Properties of a Novel β-Galactosidase from Lactobacillus plantarum by Covalent Immobilization

    Directory of Open Access Journals (Sweden)

    Rocio Benavente

    2015-04-01

    Full Text Available A novel β-galactosidase from Lactobacillus plantarum (LPG was over-expressed in E. coli and purified via a single chromatographic step by using lowly activated IMAC (immobilized metal for affinity chromatography supports. The pure enzyme exhibited a high hydrolytic activity of 491 IU/mL towards o-nitrophenyl β-d-galactopyranoside. This value was conserved in the presence of different divalent cations and was quite resistant to the inhibition effects of different carbohydrates. The pure multimeric enzyme was stabilized by multipoint and multisubunit covalent attachment on glyoxyl-agarose. The glyoxyl-LPG immobilized preparation was over 20-fold more stable than the soluble enzyme or the one-point CNBr-LPG immobilized preparation at 50 °C. This β-galactosidase was successfully used in the hydrolysis of lactose and lactulose and formation of different oligosaccharides was detected. High production of galacto-oligosaccharides (35% and oligosaccharides derived from lactulose (30% was found and, for the first time, a new oligosaccharide derived from lactulose, tentatively identified as 3'-galactosyl lactulose, has been described.

  3. Recent advances in covalent, site-specific protein immobilization [version 1; referees: 3 approved

    Directory of Open Access Journals (Sweden)

    Morten Meldal

    2016-09-01

    Full Text Available The properties of biosensors, biomedical implants, and other materials based on immobilized proteins greatly depend on the method employed to couple the protein molecules to their solid support. Covalent, site-specific immobilization strategies are robust and can provide the level of control that is desired in this kind of application. Recent advances include the use of enzymes, such as sortase A, to couple proteins in a site-specific manner to materials such as microbeads, glass, and hydrogels. Also, self-labeling tags such as the SNAP-tag can be employed. Last but not least, chemical approaches based on bioorthogonal reactions, like the azide–alkyne cycloaddition, have proven to be powerful tools. The lack of comparative studies and quantitative analysis of these immobilization methods hampers the selection process of the optimal strategy for a given application. However, besides immobilization efficiency, the freedom in selecting the site of conjugation and the size of the conjugation tag and the researcher’s expertise regarding molecular biology and/or chemical techniques will be determining factors in this regard.

  4. Molecular single-bond covalent radii for elements 1-118.

    Science.gov (United States)

    Pyykkö, Pekka; Atsumi, Michiko

    2009-01-01

    A self-consistent system of additive covalent radii, R(AB)=r(A) + r(B), is set up for the entire periodic table, Groups 1-18, Z=1-118. The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same fit. Both E-E, E-H, and E-CH(3) data are incorporated for most elements, E. Many E-E' data inside the same group are included. For the late main groups, the system is close to that of Pauling. For other elements it is close to the methyl-based one of Suresh and Koga [J. Phys. Chem. A 2001, 105, 5940] and its predecessors. For the diatomic alkalis MM' and halides XX', separate fits give a very high accuracy. These primary data are then absorbed with the rest. The most notable exclusion are the transition-metal halides and chalcogenides which are regarded as partial multiple bonds. Other anomalies include H(2) and F(2). The standard deviation for the 410 included data points is 2.8 pm.

  5. Site-Specific Covalent Conjugation of Modified mRNA by tRNA Guanine Transglycosylase.

    Science.gov (United States)

    Ehret, Fabian; Zhou, Cun Yu; Alexander, Seth C; Zhang, Dongyang; Devaraj, Neal K

    2018-03-05

    Modified mRNA (mod-mRNA) has recently been widely studied as the form of RNA useful for therapeutic applications due to its high stability and lowered immune response. Herein, we extend the scope of the recently established RNA-TAG (transglycosylation at guanosine) methodology, a novel approach for genetically encoded site-specific labeling of large mRNA transcripts, by employing mod-mRNA as substrate. As a proof of concept, we covalently attached a fluorescent probe to mCherry encoding mod-mRNA transcripts bearing 5-methylcytidine and/or pseudouridine substitutions with high labeling efficiencies. To provide a versatile labeling methodology with a wide range of possible applications, we employed a two-step strategy for functionalization of the mod-mRNA to highlight the therapeutic potential of this new methodology. We envision that this novel and facile labeling methodology of mod-RNA will have great potential in decorating both coding and noncoding therapeutic RNAs with a variety of diagnostic and functional moieties.

  6. Comparison of covalent immobilization of amylase on polystyrene pellets with pentaethylenehexamine and pentaethylene glycol spacers.

    Science.gov (United States)

    Wang, Feng; Gu, Zhiguo; Cui, Zhenggang; Liu, Liming

    2011-10-01

    α-Amylase from Aspergillus oryzae was covalently immobilized onto polystyrene pellets with pentaethylenehexamine (PS-PEHA-Ald) and pentaethylene glycol (PS-PG-Ald) carrying a terminal aldehyde group. Optimum immobilization occured at pH 8.0 and 25 °C, and at pH 7.0 and 35 °C for PS-PEHA-Ald and PS-PG-Ald, respectively. PS-PEHA-Ald immobilized enzyme retained approximately 75% of the initial activity over 45 days of storage, 70% of the initial activity after nine runs of recycling and displayed the better resistance to detrimental metal ions. PS-PG-Ald immobilized enzyme retained approximately 50% of the initial activity in 8h at 70 °C. The catalytic efficiencies of PS-PEHA-Ald immobilized and PS-PG-Ald immobilized amylase were 1.42 and 1.29 times higher than that of native enzyme. The activation energy of the reaction mediated by the amylase was reduced by 58.1% and 57.3% when PS-PEHA-Ald and PS-PG-Ald used as support respectively. Copyright © 2011 Elsevier Ltd. All rights reserved.

  7. Fructose Production by Inulinase Covalently Immobilized on Sepabeads in Batch and Fluidized Bed Bioreactor

    Directory of Open Access Journals (Sweden)

    Gabriele Iorio

    2010-03-01

    Full Text Available The present work is an experimental study of the performance of a recently designed immobilized enzyme: inulinase from Aspergillus sp. covalently immobilized on Sepabeads. The aim of the work is to test the new biocatalyst in conditions of industrial interest and to assess the feasibility of the process in a fluidized bed bioreactor (FBBR. The catalyst was first tested in a batch reactor at standard conditions and in various sets of conditions of interest for the process. Once the response of the catalyst to different operating conditions was tested and the operational stability assessed, one of the sets of conditions tested in batch was chosen for tests in FBBR. Prior to reaction tests, preliminary fluidization tests were realized in order to define an operating range of admissible flow rates. As a result, the FBR was run at different feed flow rates in a closed cycle configuration and its performance was compared to that of the batch system. The FBBR proved to be performing and suitable for scale up to large fructose production.

  8. Metal–organic and covalent organic frameworks as single-site catalysts

    Science.gov (United States)

    Rogge, S. M. J.; Bavykina, A.; Hajek, J.; Garcia, H.; Olivos-Suarez, A. I.; Sepúlveda-Escribano, A.; Vimont, A.; Clet, G.; Bazin, P.; Kapteijn, F.

    2017-01-01

    Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions. PMID:28338128

  9. Breast cancer photothermal therapy based on gold nanorods targeted by covalently-coupled bombesin peptide

    Science.gov (United States)

    Heidari, Zahra; Salouti, Mojtaba; Sariri, Reyhaneh

    2015-05-01

    Photothermal therapy, a minimally invasive treatment method for killing cancers cells, has generated a great deal of interest. In an effort to improve treatment efficacy and reduce side effects, better targeting of photoabsorbers to tumors has become a new concept in the battle against cancer. In this study, a bombesin (BBN) analog that can bind to all gastrin-releasing peptide (GRP) receptor subtypes was bound covalently with gold nanorods (GNRs) using Nanothinks acid as a link. The BBN analog was also coated with poly(ethylene glycol) to increase its stability and biocompatibility. The interactions were confirmed by ultraviolet-visible and Fourier transform infrared spectroscopy. A methylthiazol tetrazolium assay showed no cytotoxicity of the PEGylated GNR-BBN conjugate. The cell binding and internalization studies showed high specificity and uptake of the GNR-BBN-PEG conjugate toward breast cancer cells of the T47D cell line. The in vitro study revealed destruction of the T47D cells exposed to the new photothermal agent combined with continuous-wave near-infrared laser irradiation. The biodistribution study showed significant accumulation of the conjugate in the tumor tissue of mice with breast cancer. The in vivo photothermal therapy showed the complete disappearance of xenographted breast tumors in the mouse model.

  10. Covalently bonded disordered thin-film materials. Materials Research Society symposium proceedings Volume 498

    International Nuclear Information System (INIS)

    Siegal, M.P.; Milne, W.I.; Jaskie, J.E.

    1998-01-01

    The current and potential impact of covalently bonded disordered thin films is enormous. These materials are amorphous-to-nanocrystalline structures made from light atomic weight elements from the first row of the periodic table. Examples include amorphous tetrahedral diamond-like carbon, boron nitride, carbon nitride, boron carbide, and boron-carbon-nitride. These materials are under development for use as novel low-power, high-visibility elements in flat-panel display technologies, cold-cathode sources for microsensors and vacuum microelectronics, encapsulants for both environmental protection and microelectronics, optical coatings for laser windows, and ultra-hard tribological coatings. researchers from 17 countries and a broad range of academic institutions, national laboratories and industrial organizations come together in this volume to report on the status of key areas and recent discoveries. More specifically, the volume is organized into five sections. The first four highlight ongoing work primarily in the area of amorphous/nanocrystalline (disordered) carbon thin films; theoretical and experimental structural characterization; electrical and optical characterizations; growth methods; and cold-cathode electron emission results. The fifth section describes the growth, characterization and application of boron- and carbon-nitride thin films

  11. Covalent structure of the insect toxin of the North African scorpion Androctonus australis Hector

    Energy Technology Data Exchange (ETDEWEB)

    Darbon, H.; Kopeyan, C.; van Rietschoten, J.; Rochat, H. (I.N.S.E.R.M. U172 and S.C. 10, Laboratory of Biochemistry, Faculty of Medicine, Marseilles, France); Zlotkin, E. (Department of Zoology, Hebrew University of Jerusalem, Israel)

    1982-01-01

    The complete covalent structure of the insect toxin purified from the venom of the North-African scorpion Androctonus australis Hector was described. Its amino acid sequence was established by phenylisothiocyanate degradation of several protein derivatives and proteolytic fragments in a liquid protein sequencer using either a ''protein'' or a ''peptide'' program. The position of the four disulfide bridges were deduced by analysis of proteolytic peptides before and after performic oxidation, and by partial labeling of the half cystine residues with (/sup 14/C)-iodoacetic acid and determining the specific radioactivities of the S-(/sup 14/C)-carboxymethylated phenylthiohydantoin cysteines. The sequences of the insect and mammal toxins from scorpions can be aligned with homology with the positions of seven half-cystine residues as registers. The mammal and insect toxins have three disulfide bridges at homologous positions. The fourth bridge is different in that Cys/sup 12/ in mammal toxin II is replaced by Cys/sup 38/ in the insect toxin. It is likely that the position of the disulfide bridges is the same for all scorpion neurotoxins active on mammals. We believe that the shift of one half-cystine residue in the insect toxin may induce a conformational change in the structure of the protein, which, in turn, may partially account for the total specificity of this toxin for insect nervous system.

  12. Inulin hydrolysis by inulinase immobilized covalently on magnetic nanoparticles prepared with wheat gluten hydrolysates

    Directory of Open Access Journals (Sweden)

    Homa Torabizadeh

    2018-03-01

    Full Text Available Inulinase can produce a high amount of fructose syrup from inulin in a one-step enzymatic process. Inulinase from Aspergillus niger was immobilized covalently on Fe3O4 magnetic nanoparticles functionalized with wheat gluten hydrolysates (WGHs. Wheat gluten was enzymatically hydrolyzed by two endopeptidases Alcalase and Neutrase and related nanoparticles were prepared by desolvation method. Magnetite nanoparticles were coated with WGHs nanoparticles and then inulinase was immobilized onto it using glutaraldehyde as crosslinking agent. Parallel studies employing differential scanning calorimetry and field emmision scanning electron microscopy were carried out to observe functional and structural variations in free inulinase during immobilization. Optimum temperature of immobilized inulinase was increased, while, pH and Km values were decreased compared to free enzyme. Overall, a 12.3 folds rise was detected in enzyme half-life value after Immobilization at 75 °C and enzyme preserved 70% of its initial activity after 12 cycles of hydrolysis with 75% of enzyme loading.

  13. A theoretical study for electronic and transport properties of covalent functionalized MoS2 monolayer

    Science.gov (United States)

    Gao, Lijuan; Yang, Zhao-Di; Zhang, Guiling

    2017-06-01

    The geometries, electronic and electron transport properties of a series of functionalized MoS2 monolayers were investigated using density-functional theory (DFT) and the non-equilibrium Green's function (NEGF) methods. n-Propyl, n-trisilicyl, phenyl, p-nitrophenyl and p-methoxyphenyl are chosen as electron-donating groups. The results show covalent functionalization with electron-donating groups could make a transformation from typical semiconducting to metallic properties for appearance of midgap level across the Fermi level (Ef). The calculations of transport properties for two-probe devices indicate that conductivities of functionalized systems are obviously enhanced relative to pristine MoS2 monolayer. Grafted groups contribute to the major transport path and play an important role in enhancing conductivity. The NDR effect is found. The influence of grafted density is also studied. Larger grafted density leads to wider bandwidth of midgap level, larger current response of I-V curves and larger current difference between peak and valley.

  14. Protein attachment to silane-functionalized porous silicon: A comparison of electrostatic and covalent attachment.

    Science.gov (United States)

    Baranowska, Malgorzata; Slota, Agata J; Eravuchira, Pinkie J; Alba, Maria; Formentin, Pilar; Pallarès, Josep; Ferré-Borrull, Josep; Marsal, Lluís F

    2015-08-15

    Porous silicon (pSi) is a prosperous biomaterial, biocompatible, and biodegradable. Obtaining regularly functionalized pSi surfaces is required in many biotechnology applications. Silane-PEG-NHS (triethoxysilane-polyethylene-glycol-N-hydroxysuccinimide) is useful for single-molecule studies due to its ability to attach to only one biomolecule. We investigate the functionalization of pSi with silane-PEG-NHS and compare it with two common grafting agents: APTMS (3-aminopropylotrimethoxysilane) as electrostatic linker, and APTMS modified with glutaraldehyde as covalent spacer. We show the arrangement of two proteins (collagen and bovine serum albumin) as a function of the functionalization and of the pore size. FTIR is used to demonstrate correct functionalization while fluorescence confocal microscopy reveals that silane-PEG-NHS results in a more uniform protein distribution. Reflection interference spectroscopy (RIfS) is used to estimate the attachment of linker and proteins. The results open a way to obtain homogenous chemical modified silicon supports with a great value in biosensing, drug delivery and cell biology. Copyright © 2015 Elsevier Inc. All rights reserved.

  15. Conjugated polymer covalently modified graphene oxide quantum dots for ternary electronic memory devices.

    Science.gov (United States)

    Fan, Fei; Zhang, Bin; Cao, Yaming; Yang, Xutong; Gu, Junwei; Chen, Yu

    2017-08-03

    Zero dimensional graphene oxide (GO) quantum dots (GOQDs) have been expected to play an important role in the development of new memory materials. When the size of GO was reduced to that of GOQDs, both the electron affinity and ionization potential of GO were found to be decreased, and this was followed by the elevation of lowest energy unoccupied molecular orbital (LUMO) energy level. This implies that the electron withdrawing ability of GOQDs is weaker than that of GO. In this work, a novel arylamine-based polyazomethine covalently functionalized graphene oxide quantum dots (TPAPAM-GOQDs), which was synthesized using an amidation reaction, was for the first time used to fabricate a ternary memory device with a configuration of gold/TPAPAM-GOQDs/indium tin oxide. The current ratio of OFF : ON-1 : ON-2 was found to be 1 : 60 : 3000. Its conductive nature was also revealed using an in situ conductive atomic force microscopy technique. This memory device could potentially increase the memory capacity of the device from the conventional 2 n to 3 n when compared to binary memory devices.

  16. Covalent Organic Framework Material bearing Phloroglucinol Building Units as a Potent Anticancer Agent

    KAUST Repository

    Bhanja, Piyali

    2017-08-23

    Covalent organic frameworks (COFs) having periodicity in pores of nanoscale dimensions can be suitably designed for the organic building units bearing reactive functional groups at their surfaces. Thus, they are an attractive option as an anticancer agent to overcome the limitations of chemotherapy. Herein, we first report a new porous biodegradable nitrogen containing COF material, EDTFP-1 (ethylenedianiline-triformyl phloroglucinol), synthesized using 4,4\\'-ethylenedianiline and 2,4,6-triformylphloroglucinol via Schiff base condensation reaction. EDTFP-1 exhibited 3D-hexagonal porous structure with average pores of ca. 1.5 nm dimension. Here, we have explored the anti-cancer potentiality of EDTFP-1. Result demonstrated an enhanced cytotoxicity was observed against four cancer cells HCT 116, HepG2, A549, and MIA-Paca2 with significant lower IC50 on HCT116 cells. Additionally, EDTFP-1-induced cell death was associated with the characteristic apoptotic changes like cell membrane blebbing, nuclear DNA fragmentation, externalization of phosphatidylserine from the cell membrane followed by a loss of mitochondrial membrane potential as well as modulation of pro and anti-apoptotic proteins. Further, the result depicted a direct correlation between the generations of ROS with mitochondrial-dependant apoptosis through the involvement of p53 phosphorylation upon EDTFP-1 induction, suggesting this COF material is a novel chemotherapeutic agent for cancer treatment.

  17. Efficient production of hydrogen from formic acid using a covalent triazine framework supported molecular catalyst.

    Science.gov (United States)

    Bavykina, A V; Goesten, M G; Kapteijn, F; Makkee, M; Gascon, J

    2015-03-01

    A heterogeneous molecular catalyst based on Ir(III) Cp* (Cp*=pentamethylcyclopentadienyl) attached to a covalent triazine framework (CTF) is reported. It catalyses the production of hydrogen from formic acid with initial turnover frequencies (TOFs) up to 27,000 h(-1) and turnover numbers (TONs) of more than one million in continuous operation. The CTF support, with a Brunauer-Emmett-Teller (BET) surface area of 1800 m(2)  g(-1), was constructed from an optimal 2:1 ratio of biphenyl and pyridine carbonitrile building blocks. Biphenyl building blocks induce mesoporosity and, therefore, facilitate diffusion of reactants and products whereas free pyridinic sites activate formic acid towards β-hydride elimination at the metal, rendering unprecedented rates in hydrogen production. The catalyst is air stable, produces CO-free hydrogen, and is fully recyclable. Hydrogen production rates of more than 60 mol L(-1)  h(-1) were obtained at high catalyst loadings of 16 wt % Ir, making it attractive towards process intensification. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Study of the non-covalent interactions of ginsenosides and lysozyme using electrospray ionization mass spectrometry.

    Science.gov (United States)

    Tang, Jun; Fu, Qiang; Cui, Meng; Xing, Junpeng; Liu, Zhiqiang; Liu, Shuying

    2015-11-15

    Ginsenosides are an important class of natural products extracted from ginseng that possess various important biological activities. Studies of interactions of ginsenosides with proteins are essential for comprehensive understanding of the biological activities of ginsenosides. In this study, the interactions of ginsenosides with lysozyme were investigated by electrospray ionization mass spectrometry (ESI-MS). Both protopanaxadiol-type and protopanaxatriol-type ginsenosides were chosen to explore the interactions of ginsenosides towards lysozyme near the physiological conditions by direct ESI-MS, respectively. Comparative experiments were conducted to confirm the interactions were specific. In addition, the dissociation constants of ginsenoside-lysozyme complexes were determined by a ESI-MS titration strategy. The results showed ginsenosides bound to lysozyme at the stoichiometries of 1:1 and 2:1. The association constants of ginsenosides to lysozyme were in the order of Re>Rd>Rf>Rg2 >Rg3 . According to their structures, the binding affinities associated with the type of aglycone and the type and the number of sugar moieties linked on the aglycone. It has been demonstrated that ESI-MS is a powerful tool to probe the non-covalent interactions between lysozyme and ginsenosides. These results provide insights into the interaction of ginsenosides with lysozyme at the molecular level. The developed strategy could be applied to determine the interactions of proteins with other natural products. Copyright © 2015 John Wiley & Sons, Ltd.

  19. Gelation of covalently edge-modified laponites in aqueous media. 1. rheology and nuclear magnetic resonance.

    Science.gov (United States)

    Patil, Suhas P; Mathew, Renny; Ajithkumar, T G; Rajamohanan, P R; Mahesh, T S; Kumaraswamy, Guruswamy

    2008-04-17

    We describe the covalent modification of the edges of laponite with organic groups and the influence of this modification on gelation behavior. We compare three materials: an unmodified laponite, a laponite edge modified with a trimethyl moiety (MLap), and an octyldimethyl moiety (OLap). Gelation is investigated using rheology and NMR T1 relaxation measurements and nuclear Overhauser enhancement spectroscopy (NOESY). MLap and OLap show qualitatively different gelation. Gelation of MLap is very similar to laponite: MLap gels over the same time scale as laponite and has about the same solid modulus, and the MLap gel is almost as transparent as laponite. In contrast, OLap gels rapidly relative to laponite and forms a weak, turbid gel. We believe that gelation in laponite and MLap results from the formation of a network of well-dispersed platelets (or a few platelets), while in OLap, gelation results from a network of stacks of several platelets. NMR relaxation measurements indicate that gelation does not affect the average relaxation of water protons. However, T1 increases marginally for the protons in the organic moieties in MLap and decreases for protons in the organic moieties in OLap. Relaxation measurements, analyses of line width, and NOESY taken together suggest that, in OLap, gelation is a consequence of association of the organic moieties on the laponite edges, and that this association strengthens with time. Thus, the time-dependent changes in NMR suggest a structural origin for the time-dependent changes in the rheological behavior.

  20. Efficient Vibrational Energy Transfer through Covalent Bond in Indigo Carmine Revealed by Nonlinear IR Spectroscopy.

    Science.gov (United States)

    He, Xuemei; Yu, Pengyun; Zhao, Juan; Wang, Jianping

    2017-10-12

    Ultrafast vibrational relaxation and structural dynamics of indigo carmine in dimethyl sulfoxide were examined using femtosecond pump-probe infrared and two-dimensional infrared (2D IR) spectroscopies. Using the intramolecularly hydrogen-bonded C═O and delocalized C═C stretching modes as infrared probes, local structural and dynamical variations of this blue dye molecule were observed. Energy relaxation of the vibrationally excited C═O stretching mode was found to occur through covalent bond to the delocalized aromatic vibrational modes on the time scale of a few picoseconds or less. Vibrational quantum beating was observed in magic-angle pump-probe, anisotropy, and 2D IR cross-peak dynamics, showing an oscillation period of ca. 1010 fs, which corresponds to the energy difference between the C═O and C═C transition frequency (33 cm -1 ). This confirms a resonant vibrational energy transfer happened between the two vibrators. However, a more efficient energy-accepting mode of the excited C═O stretching was believed to be a nearby combination and/or overtone mode that is more tightly connected to the C═O species. On the structural aspect, dynamical-time-dependent 2D IR spectra reveal an insignificant inhomogeneous contribution to time-correlation relaxation for both the C═O and C═C stretching modes, which is in agreement with the generally believed structural rigidity of such conjugated molecules.

  1. Electronic, structural, and substrate effect properties of single-layer covalent organic frameworks

    International Nuclear Information System (INIS)

    Liang, Liangbo; Zhu, Pan; Meunier, Vincent

    2015-01-01

    Recently synthesized two-dimensional covalent organic frameworks (COFs) exhibit high surface area, large pore size, and unique structural architectures, making them promising materials for various energy applications. Here, a total of nine COFs structures, including two deposited on a hexagonal boron nitride substrate, are investigated using density functional theory, quasi-particle many-body theory within the GW approximation, and an image charge model. The structures considered belong to two major families (thiophene-based COF-n (T-COF-n) and tetrakis (4-aminophenyl) porphyrin-x (TAPP-x)) differing from the presence of B—O or C=N linkers. While T-COF-n structures are shown to constitute planar networks, TAPP-x systems can display non-negligible corrugation due to the out-of-plane rotation of phenyl rings. We find that the electronic properties do not differ significantly when altering the chain molecules within each family. Many-body effects are shown to lead to large band-gap increase while the presence of the substrate yields appreciable reductions of the gaps, due to substrate polarization effects

  2. Non-Covalent Photo-Patterning of Gelatin Matrices Using Caged Collagen Mimetic Peptides

    Science.gov (United States)

    Li, Yang; Hoa San, Boi; L. Kessler, Julian; Hwan Kim, Jin; Xu, Qingguo; Hanes, Justin; Yu, Seungju Michael

    2015-01-01

    Advancements in photolithography have enabled us to spatially encode biochemical cues in biocompatible platforms such as synthetic hydrogels. Conventional patterning works through photo-activated chemical reactions on inert polymer networks. However, these techniques cannot be directly applied to protein hydrogels without chemically altering the protein scaffolds. To this end, we developed a non-covalent photo-patterning strategy for gelatin (denatured collagen) hydrogels utilizing a caged collagen mimetic peptide (caged CMP) which binds to gelatin strands through UV activated, triple helix hybridization. Here we present 2D and 3D photo-patterning of gelatin hydrogels enabled by the caged CMPs as well as creation of concentration gradients of CMPs. We show that photo-patterning of PEG-conjugated caged CMPs can be used to spatially control cell adhesion on gelatin films. CMP’s specificity for binding to gelatin allows patterning of almost any synthetic or natural gelatin-containing matrix, such as zymograms, gelatin-methacrylate hydrogels, and even a corneal tissue. Since the CMP is a chemically and biologically inert peptide which is proven to be an ideal carrier for bioactive molecules, our patterning method provides a radically new tool for immobilizing drugs to natural tissues and for functionalizing scaffolds for complex tissue formation. PMID:25476588

  3. Ultrasensitive detection of clenbuterol by a covalent imprinted polymer as a biomimetic antibody.

    Science.gov (United States)

    Tang, Yiwei; Gao, Jingwen; Liu, Xiuying; Gao, Xue; Ma, Tao; Lu, Xiaonan; Li, Jianrong

    2017-08-01

    As an ideal biomimetic antibody, molecularly imprinted polymer (MIP) has shown great promise in immunoassays. Here, we developed a covalent imprinting method to prepare MIP artificial antibody towards clenbuterol on the well surface of a microtiter plate. Template molecule (clenbuterol) was splited by hydrolysis with functional monomer and removed by methanol/acetic acid solution, and then three-dimensional cavities were fabricated in the MIP, which can rebind template molecule via hydrogen bond interaction. Using this artificial antibody, we developed a novel biomimetic enzyme-linked immunosorbent assay (ELISA) with excellent sensitivity and specificity. The linear range for clenbuterol was 10 -5 to 1000μgL -1 , with a detection limit of 10 -7 μgL -1 . Cross reactivity of this MIP artificial antibody to other four structural analogs was less than 0.93%. This method was applied to determine clenbuterol in real samples with satisfactory result, suggesting a promising application of the biomimetic ELISA in food and environmental analysis. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. Mechanism of the Topotactic Formation of gamma-Zirconium Phosphate Covalently Pillared with Diphosphonate Groups.

    Science.gov (United States)

    Alberti, G.; Giontella, E.; Murcia-Mascarós, S.; Vivani, R.

    1998-09-07

    The topotactic reaction of gamma-ZrPO(4)[O(2)P(OH)(2)].2H(2)O (gamma-ZrP) with benzenediphosphonic acid was examined in water and in acetone-water mixtures. This reaction was found to take place in water only on the external surface of the microcrystals, and pillared compounds were never obtained, even after very long reaction times. On the contrary, covalently pillared compounds were quickly obtained in acetone-water mixtures. The mechanism of the latter topotactic reaction was investigated by determining the rate of the phosphate groups released and the rate of the benzenediphosphonates taken up by gamma-ZrP over a long time (50 days). These data showed that pillared derivatives of gamma-ZrP can be obtained because colloidal dispersions of exfoliated lamellae are formed in acetone-water mixtures. The diphosphonate group acts initially as a monovalent species, replacing only one dihydrogen phosphate group on the surface of the exfoliated gamma-lamellae. The colloidal and partially derivatized lamellae thus formed can interact with each other by forming polylamellar pillared systems. When the number of pillared lamellae exceeds a given value (usually 5-6), flocculation of the colloidal gamma-ZrP takes place. Topotactic reactions between packets of pillared lamellae may also continue in the flocculated system. Therefore, the average number of the pillared lamellae slowly increases over time.

  5. Adsorption of marine phycotoxin okadaic acid on a covalent organic framework.

    Science.gov (United States)

    Salonen, Laura M; Pinela, Sara R; Fernandes, Soraia P S; Louçano, João; Carbó-Argibay, Enrique; Sarriá, Marisa P; Rodríguez-Abreu, Carlos; Peixoto, João; Espiña, Begoña

    2017-11-24

    Phycotoxins, compounds produced by some marine microalgal species, can reach high concentrations in the sea when a massive proliferation occurs, the so-called harmful algal bloom. These compounds are especially dangerous to human health when concentrated in the digestive glands of seafood. In order to generate an early warning system to alert for approaching toxic outbreaks, it is very important to improve monitoring methods of phycotoxins in aquatic ecosystems. Solid-phase adsorption toxin tracking devices reported thus far based on polymeric resins have not been able to provide an efficient harmful algal bloom prediction system due to their low adsorption capabilities. In this work, a water-stable covalent organic framework (COF) was evaluated as adsorbent for the hydrophobic toxin okadaic acid, one of the most relevant marine toxins and the parental compound of the most common group of toxins responsible for the diarrhetic shellfish poisoning. Adsorption kinetics of okadaic acid onto the COF in seawater showed that equilibrium concentration was reached in only 60min, with a maximum experimental adsorption of 61mgg -1 . Desorption of okadaic acid from the COF was successful with both 70% ethanol and acetonitrile as solvent, and the COF material could be reused with minor losses in adsorption capacity for three cycles. The results demonstrate that COF materials are promising candidates for solid-phase adsorption in water monitoring devices. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Stable non-covalent labeling of layered silicate nanoparticles for biological imaging.

    Science.gov (United States)

    Mortimer, Gysell M; Jack, Kevin S; Musumeci, Anthony W; Martin, Darren J; Minchin, Rodney F

    2016-04-01

    Layered silicate nanoparticles (LSN) are widely used in industrial applications and consumer products. They also have potential benefits in biomedical applications such as implantable devices and for drug delivery. To study how nanomaterials interact with cells and tissues, techniques to track and quantify their movement through different biological compartments are essential. While radiolabels can be very sensitive, particularly for in vivo studies, fluorescent labeling has been preferred in recent years because of the array of methods available to image and quantify fluorescent nanoparticles. However, labeling can be problematic, especially if it alters the physical properties of the nanomaterial. Herein is described a novel non-covalent labeling technique for LSN using readily available fluorescent dimeric cyanine dyes without the need to use excess amounts of dye to achieve labeling, or the need for removal of unbound dye. The approach utilizes the cationic binding properties of layered silicate clays and the multiple quaternary nitrogens associated with the dyes. Preparation of YOYO-1 labeled LSN with optimal dispersion in aqueous media is presented. The utilization of the labeled particles is then demonstrated in cell binding and uptake studies using flow cytometry and confocal microscopy. The labeled LSN are highly fluorescent, stable and exhibit identical physical properties with respect to the unlabeled nanoparticles. The general approach described here is applicable to other cyanine dyes and may be utilized more widely for labeling nanoparticles that comprise a crystalline plate structure with a high binding capacity. Crown Copyright © 2016. Published by Elsevier B.V. All rights reserved.

  7. Inulin hydrolysis by inulinase immobilized covalently on magnetic nanoparticles prepared with wheat gluten hydrolysates.

    Science.gov (United States)

    Torabizadeh, Homa; Mahmoudi, Asieh

    2018-03-01

    Inulinase can produce a high amount of fructose syrup from inulin in a one-step enzymatic process. Inulinase from Aspergillus niger was immobilized covalently on Fe 3 O 4 magnetic nanoparticles functionalized with wheat gluten hydrolysates (WGHs). Wheat gluten was enzymatically hydrolyzed by two endopeptidases Alcalase and Neutrase and related nanoparticles were prepared by desolvation method. Magnetite nanoparticles were coated with WGHs nanoparticles and then inulinase was immobilized onto it using glutaraldehyde as crosslinking agent. Parallel studies employing differential scanning calorimetry and field emmision scanning electron microscopy were carried out to observe functional and structural variations in free inulinase during immobilization. Optimum temperature of immobilized inulinase was increased, while, pH and K m values were decreased compared to free enzyme. Overall, a 12.3 folds rise was detected in enzyme half-life value after Immobilization at 75 °C and enzyme preserved 70% of its initial activity after 12 cycles of hydrolysis with 75% of enzyme loading.

  8. Optimized assembly and covalent coupling of single-molecule DNA origami nanoarrays.

    Science.gov (United States)

    Gopinath, Ashwin; Rothemund, Paul W K

    2014-12-23

    Artificial DNA nanostructures, such as DNA origami, have great potential as templates for the bottom-up fabrication of both biological and nonbiological nanodevices at a resolution unachievable by conventional top-down approaches. However, because origami are synthesized in solution, origami-templated devices cannot easily be studied or integrated into larger on-chip architectures. Electrostatic self-assembly of origami onto lithographically defined binding sites on Si/SiO2 substrates has been achieved, but conditions for optimal assembly have not been characterized, and the method requires high Mg2+ concentrations at which most devices aggregate. We present a quantitative study of parameters affecting origami placement, reproducibly achieving single-origami binding at 94±4% of sites, with 90% of these origami having an orientation within ±10° of their target orientation. Further, we introduce two techniques for converting electrostatic DNA-surface bonds to covalent bonds, allowing origami arrays to be used under a wide variety of Mg2+-free solution conditions.

  9. Novel trifluoromethylated 9-amino-3,4-dihydroacridin-1(2H)-ones act as covalent poisons of human topoisomerase IIα.

    Science.gov (United States)

    Infante Lara, Lorena; Sledge, Alexis; Laradji, Amine; Okoro, Cosmas O; Osheroff, Neil

    2017-02-01

    A number of topoisomerase II-targeted anticancer drugs, including amsacrine, utilize an acridine or related aromatic core as a scaffold. Therefore, to further explore the potential of acridine-related compounds to act as topoisomerase II poisons, we synthesized a series of novel trifluoromethylated 9-amino-3,4-dihydroacridin-1(2H)-one derivatives and examined their ability to enhance DNA cleavage mediated by human topoisomerase IIα. Derivatives containing a H, Cl, F, and Br at C7 enhanced enzyme-mediated double-stranded DNA cleavage ∼5.5- to 8.5-fold over baseline, but were less potent than amsacrine. The inclusion of an amino group at C9 was critical for activity. The compounds lost their activity against topoisomerase IIα in the presence of a reducing agent, displayed no activity against the catalytic core of topoisomerase IIα, and inhibited DNA cleavage when incubated with the enzyme prior to the addition of DNA. These findings strongly suggest that the compounds act as covalent, rather than interfacial, topoisomerase II poisons. Published by Elsevier Ltd.

  10. Design Principles for Covalent Organic Frameworks as Efficient Electrocatalysts in Clean Energy Conversion and Green Oxidizer Production.

    Science.gov (United States)

    Lin, Chun-Yu; Zhang, Lipeng; Zhao, Zhenghang; Xia, Zhenhai

    2017-05-01

    Covalent organic frameworks (COFs), an emerging class of framework materials linked by covalent bonds, hold potential for various applications such as efficient electrocatalysts, photovoltaics, and sensors. To rationally design COF-based electrocatalysts for oxygen reduction and evolution reactions in fuel cells and metal-air batteries, activity descriptors, derived from orbital energy and bonding structures, are identified with the first-principle calculations for the COFs, which correlate COF structures with their catalytic activities. The calculations also predict that alkaline-earth metal-porphyrin COFs could catalyze the direct production of H 2 O 2 , a green oxidizer and an energy carrier. These predictions are supported by experimental data, and the design principles derived from the descriptors provide an approach for rational design of new electrocatalysts for both clean energy conversion and green oxidizer production. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Covalent Modification of Highly Ordered Pyrolytic Graphite with a Stable Organic Free Radical by Using Diazonium Chemistry.

    Science.gov (United States)

    Seber, Gonca; Rudnev, Alexander V; Droghetti, Andrea; Rungger, Ivan; Veciana, Jaume; Mas-Torrent, Marta; Rovira, Concepció; Crivillers, Núria

    2017-01-26

    A novel, persistent, electrochemically active perchlorinated triphenylmethyl (PTM) radical with a diazonium functionality has been covalently attached to highly ordered pyrolytic graphite (HOPG) by electrografting in a single-step process. Electrochemical scanning tunneling microscopy (EC-STM) and Raman spectroscopy measurements revealed that PTM molecules had a higher tendency to covalently react at the HOPG step edges. The cross-section profiles from EC-STM images showed that there was current enhancement at the functionalized areas, which could be explained by redox-mediated electron tunneling through surface-confined redox-active molecules. Cyclic voltammetry clearly demonstrated that the intrinsic properties of the organic radical were preserved upon grafting and DFT calculations also revealed that the magnetic character of the PTM radical was preserved. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. DFT+DMFT study on soft moment magnetism and covalent bonding in SrRu2O6

    Science.gov (United States)

    Hariki, Atsushi; Hausoel, Andreas; Sangiovanni, Giorgio; Kuneš, Jan

    2017-10-01

    The dynamical mean-field theory is used to study the three-orbital model of the d3 compound SrRu2O3 both with and without explicitly including the O-p states. Depending on the size of the Hund's coupling J , at low to intermediate temperatures we find solutions corresponding to Mott or correlated covalent insulators. The latter can explain the experimentally observed absence of Curie susceptibility in the paramagnetic phase. At high temperatures, a single phase with smoothly varying properties is observed. SrRu2O3 provides an ideal system to study the competition between the local moment physics and covalent bonding, since both effects are maximized, while SO interaction is found to play a minor role.

  13. Strongly correlating liquids and their isomorphs

    OpenAIRE

    Pedersen, Ulf R.; Gnan, Nicoletta; Bailey, Nicholas P.; Schröder, Thomas B.; Dyre, Jeppe C.

    2010-01-01

    This paper summarizes the properties of strongly correlating liquids, i.e., liquids with strong correlations between virial and potential energy equilibrium fluctuations at constant volume. We proceed to focus on the experimental predictions for strongly correlating glass-forming liquids. These predictions include i) density scaling, ii) isochronal superposition, iii) that there is a single function from which all frequency-dependent viscoelastic response functions may be calculated, iv) that...

  14. Atom collisions in a strong electromagnetic field

    International Nuclear Information System (INIS)

    Smirnov, V.S.; Chaplik, A.V.

    1976-01-01

    It is shown that the long-range part of interatomic interaction is considerably altered in a strong electromagnetic field. Instead of the van der Waals law the potential asymptote can best be described by a dipole-dipole R -3 law. Impact broadening and the line shift in a strong nonresonant field are calculated. The possibility of bound states of two atoms being formed in a strong light field is discussed

  15. Immobilization of alkaline phosphatase on magnetic particles by site-specific and covalent cross-linking catalyzed by microbial transglutaminase.

    Science.gov (United States)

    Moriyama, Kousuke; Sung, Kyunga; Goto, Masahiro; Kamiya, Noriho

    2011-06-01

    Bacterial alkaline phosphatase (BAP) was site-specifically and covalently immobilized on magnetic particles (MPs) using the enzymatic reaction of microbial transglutaminase (MTG). Immobilization efficiency was affected by the chemical surface treatment of MPs and immobilized BAP exhibited more than 90% of the initial activity after 10 rounds of recycling. Copyright © 2011 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

  16. The microwave-assisted solvothermal synthesis of a crystalline two-dimensional covalent organic framework with high CO2 capacity.

    Science.gov (United States)

    Wei, Hao; Chai, Shuangzhi; Hu, Nantao; Yang, Zhi; Wei, Liangming; Wang, Lin

    2015-08-07

    We report the synthesis of a two-dimensional enamine-linked covalent organic framework (COF) using a rapid microwave-assisted solvothermal method in significantly less time and high yield under a relatively low temperature. This COF was found to have a high crystallinity, high stability, high BET surface area, and a high CO2 capacity and adsorption selectivity of CO2/N2.

  17. Improved thermooxidation and sedimentation stability of covalently-coated carbonyl iron particles with cholesteryl groups and their influence on magnetorheology

    Czech Academy of Sciences Publication Activity Database

    Mrlík, M.; Ilčíková, M.; Pavlínek, V.; Mosnáček, J.; Peer, Petra; Filip, Petr

    2013-01-01

    Roč. 396, april (2013), s. 146-151 ISSN 0021-9797 R&D Projects: GA ČR GA202/09/1626 Grant - others:GA MŠk(CZ) ED2.1.00/03.0111 Institutional support: RVO:67985874 Keywords : covalent coating * carbonyl iron * cholesteryl chloroformate * thermooxidation * Magnetorheology Subject RIV: BK - Fluid Dynamics Impact factor: 3.552, year: 2013

  18. Covalent Hybrid of Spinel Manganese-Cobalt Oxide and Gra-phene as Advanced Oxygen Reduction Electrocatalysts

    OpenAIRE

    Liang, Yongye; Wang, Hailiang; Zhou, Jigang; Li, Yanguang; Wang, Jian; Regier, Tom; Dai, Hongjie

    2012-01-01

    Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co3O4 nanoparticles, a manganese-cobalt spinel MnCo2O4/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrid results in covalent coupl...

  19. Supramolecular catalysis. Part 1: non-covalent interactions as a tool for building and modifying homogeneous catalysts.

    Science.gov (United States)

    Raynal, Matthieu; Ballester, Pablo; Vidal-Ferran, Anton; van Leeuwen, Piet W N M

    2014-03-07

    Supramolecular catalysis is a rapidly expanding discipline which has benefited from the development of both homogeneous catalysis and supramolecular chemistry. The properties of classical metal and organic catalysts can now be carefully tailored by means of several suitable approaches and the choice of reversible interactions such as hydrogen bond, metal-ligand, electrostatic and hydrophobic interactions. The first part of these two subsequent reviews will be dedicated to catalytic systems for which non-covalent interactions between the partners of the reaction have been designed although mimicking enzyme properties has not been intended. Ligand, metal, organocatalyst, substrate, additive, and metal counterion are reaction partners that can be held together by non-covalent interactions. The resulting catalysts possess unique properties compared to analogues lacking the assembling properties. Depending on the nature of the reaction partners involved in the interactions, distinct applications have been accomplished, mainly (i) the building of bidentate ligand libraries (intra ligand-ligand), (ii) the building of di- or oligonuclear complexes (inter ligand-ligand), (iii) the alteration of the coordination spheres of a metal catalyst (ligand-ligand additive), and (iv) the control of the substrate reactivity (catalyst-substrate). More complex systems that involve the cooperative action of three reaction partners have also been disclosed. In this review, special attention will be given to supramolecular catalysts for which the observed catalytic activity and/or selectivity have been imputed to non-covalent interaction between the reaction partners. Additional features of these catalysts are the easy modulation of the catalytic performance by modifying one of their building blocks and the development of new catalytic pathways/reactions not achievable with classical covalent catalysts.

  20. Oxygen Evolution at Manganite Perovskite Ruddlesden-Popper Type Particles: Trends of Activity on Structure, Valence and Covalence

    Directory of Open Access Journals (Sweden)

    Majid Ebrahimizadeh Abrishami

    2016-11-01

    Full Text Available An improved understanding of the correlation between the electronic properties of Mn-O bonds, activity and stability of electro-catalysts for the oxygen evolution reaction (OER is of great importance for an improved catalyst design. Here, an in-depth study of the relation between lattice structure, electronic properties and catalyst performance of the perovskite Ca1−xPrxMnO3 and the first-order RP-system Ca2−xPrxMnO4 at doping levels of x = 0, 0.25 and 0.5 is presented. Lattice structure is determined by X-ray powder diffraction and Rietveld refinement. X-ray absorption spectroscopy of Mn-L and O-K edges gives access to Mn valence and covalency of the Mn-O bond. Oxygen evolution activity and stability is measured by rotating ring disc electrode studies. We demonstrate that the highest activity and stability coincidences for systems with a Mn-valence state of +3.7, though also requiring that the covalency of the Mn-O bond has a relative minimum. This observation points to an oxygen evolution mechanism with high redox activity of Mn. Covalency should be large enough for facile electron transfer from adsorbed oxygen species to the MnO6 network; however, it should not be hampered by oxidation of the lattice oxygen, which might cause a crossover to material degradation. Since valence and covalency changes are not entirely independent, the introduction of the energy position of the eg↑ pre-edge peak in the O-K spectra as a new descriptor for oxygen evolution is suggested, leading to a volcano-like representation of the OER activity.

  1. Enhancement of localization phenomena driven by covalency in the SrBiMn{sub 1.75}Ti{sub 0.25}O{sub 6} manganite

    Energy Technology Data Exchange (ETDEWEB)

    Asensio de Lucas, E.; Alvarez-Serrano, I. [Depto. Quimica Inorganica I, Facultad Ciencias Quimicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Cuello, G.J. [Institut Laue-Langevin, 6 rue Jules Horowitz, F-38042 Grenoble (France); Garcia-Hernandez, M. [Instituto de Ciencia de Materiales de Madrid, CSIC, E-28049 Cantoblanco, Madrid (Spain); Lopez, M.L., E-mail: marisal@quim.ucm.es [Depto. Quimica Inorganica I, Facultad Ciencias Quimicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Pico, C.; Veiga, M.L. [Depto. Quimica Inorganica I, Facultad Ciencias Quimicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain)

    2012-05-05

    Graphical abstract: Enhancement of localization phenomena driven by covalency in the BiSrMn{sub 1.75}Ti{sub 0.25}O{sub 6} manganite. The CO/OO phenomena and magnetic clusters (Mn{sub 4}) stabilization at temperatures up to 520 K in BiSrMn{sub 1.75}Ti{sub 0.25}O{sub 6} are connected to a structural transition. The observed enhancement of electronic localization is interpreted considering covalent effects of Ti{sup 4+} and Bi{sup 3+} cations as the main driving force. Highlights: Black-Right-Pointing-Pointer The structural, electronic and magnetic behaviour of the new SrBiMn{sub 1.75}Ti{sub 0.25}O{sub 6} manganite is reported. Black-Right-Pointing-Pointer A structural transition above 520 K takes place, coinciding with relevant changes in the transport properties. Black-Right-Pointing-Pointer The electronic behavior is interpreted in terms of a remarkably high orbital and charge ordering temperature and cluster models. Black-Right-Pointing-Pointer The observed features are explained considering a scenario in which bonds covalence is enhanced by the Bi{sup 3+} and Ti{sup 4+} cations. - Abstract: Manganites are materials that show remarkable phenomena related to charge orbital ordering (CO/OO) and it is extremely important to understand the fundamental nature of this behaviour. This paper reports on the structural, electronic and magnetic behaviour of the new SrBiMn{sub 1.75}Ti{sub 0.25}O{sub 6} manganite and the dependence of these properties with temperature. A detailed structural analysis has been carried out by electron, X-ray, neutron diffraction between 4 and 700 K. The electron diffraction patterns obtained at room temperature (RT) evidence that the average structure (a{approx}b{approx}{radical}(2)a{sub p} and c {approx} 2a{sub p}) presents a modulation that doubles the a and c lattice parameters. A very high charge ordering (CO) transition temperature of 510 K, similar to that found for the non-doped material, SrBiMn{sub 2}O{sub 6}, is observed. Above this

  2. Accurate frozen-density embedding potentials as a first step towards a subsystem description of covalent bonds.

    Science.gov (United States)

    Fux, Samuel; Jacob, Christoph R; Neugebauer, Johannes; Visscher, Lucas; Reiher, Markus

    2010-04-28

    The frozen-density embedding (FDE) scheme [Wesolowski and Warshel, J. Phys. Chem. 97, 8050 (1993)] relies on the use of approximations for the kinetic-energy component v(T)[rho(1),rho(2)] of the embedding potential. While with approximations derived from generalized-gradient approximation kinetic-energy density functional weak interactions between subsystems such as hydrogen bonds can be described rather accurately, these approximations break down for bonds with a covalent character. Thus, to be able to directly apply the FDE scheme to subsystems connected by covalent bonds, improved approximations to v(T) are needed. As a first step toward this goal, we have implemented a method for the numerical calculation of accurate references for v(T). We present accurate embedding potentials for a selected set of model systems, in which the subsystems are connected by hydrogen bonds of various strength (water dimer and F-H-F(-)), a coordination bond (ammonia borane), and a prototypical covalent bond (ethane). These accurate potentials are analyzed and compared to those obtained from popular kinetic-energy density functionals.

  3. Relativistic four-component potential energy curves for the lowest 23 covalent states of molecular bromine (Br2).

    Science.gov (United States)

    Gomes, José da Silva; Gargano, Ricardo; Martins, João B L; M de Macedo, Luiz Guilherme

    2014-08-07

    The covalent excited states and ground state of the Br2 molecule has been investigated by using four-component relativistic COSCI and MRCISD methods. These methods were performed for all covalent states in the representation Ω((±)). Calculated potential energy curves (PECs) were obtained at the four-component COSCI level, and spectroscopic constants (R(e), D(e), D0, ω(e), ω(e)x(e), ω(e)y(e), B(e), α(e), γ(e), Te, Dv) for bounded states are reported. The vertical excitations for all covalent states are reported at COSCI, MRCISD, and MRCISD+Q levels. We also present spectroscopic constants for two weakly bounded states (A':(1)2u and B':(1)0(-)u) not yet reported in the literature, as well as accurate analytical curves for all five relativistic molecular bounded sates [the ground state X:0 g(+) and the excited states A:(1)1(u), B:(1)0(u)(+), C:(2)1(u), and B':(1)0(u)(-)] found in this work.

  4. A durable and biocompatible ascorbic acid-based covalent coating method of polydimethylsiloxane for dynamic cell culture.

    Science.gov (United States)

    Leivo, Joni; Virjula, Sanni; Vanhatupa, Sari; Kartasalo, Kimmo; Kreutzer, Joose; Miettinen, Susanna; Kallio, Pasi

    2017-07-01

    Polydimethylsiloxane (PDMS) is widely used in dynamic biological microfluidic applications. As a highly hydrophobic material, native PDMS does not support cell attachment and culture, especially in dynamic conditions. Previous covalent coating methods use glutaraldehyde (GA) which, however, is cytotoxic. This paper introduces a novel and simple method for binding collagen type I covalently on PDMS using ascorbic acid (AA) as a cross-linker instead of GA. We compare the novel method against physisorption and GA cross-linker-based methods. The coatings are characterized by immunostaining, contact angle measurement, atomic force microscopy and infrared spectroscopy, and evaluated in static and stretched human adipose stem cell (hASC) cultures up to 13 days. We found that AA can replace GA as a cross-linker in the covalent coating method and that the coating is durable after sonication and after 6 days of stretching. Furthermore, we show that hASCs attach and proliferate better on AA cross-linked samples compared with physisorbed or GA-based methods. Thus, in this paper, we provide a new PDMS coating method for studying cells, such as hASCs, in static and dynamic conditions. The proposed method is an important step in the development of PDMS-based devices in cell and tissue engineering applications. © 2017 The Author(s).

  5. Non-covalent modification of granulocyte-colony stimulating factor (G-CSF) by coiled-coil technology.

    Science.gov (United States)

    Reichert, Christian; Perozzo, Remo; Borchard, Gerrit

    2016-09-10

    We present here an approach to non-covalently combine an engineered model protein with a PEGylated peptide via coiled-coil binding. To this end a fusion protein of G-CSF and the peptide sequence (JunB) was created-one sequence of JunB was expressed at the N-terminal of GCSF. JunB is able to bind to the peptide sequence cFos, which was in turn covalently linked to a chain of poly(ethylene glycol) (PEG). The selected peptide sequences are leucine zipper motives from transcription factors and are known to bind to each other specifically by formation of a super secondary structure called coiled-coil. The binding between PEGylated peptides of various molecular weights and the modified protein was assessed by isothermal calorimetry (ITC), dynamic light scattering (DLS), circular dichroism (CD), and fluorescence anisotropy. Our findings show that the attachment of 2 and 5kDa PEG does not interfere with coiled-coil formation and thus binding of peptide to fusion protein. With this work we successfully demonstrate the non-covalent binding of a model moiety (PEG) to a protein through coiled-coil interaction. Copyright © 2016 Elsevier B.V. All rights reserved.

  6. Facile route to covalently-jointed graphene/polyaniline composite and it’s enhanced electrochemical performances for supercapacitors

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Hanxun [School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093 (China); Han, Xuebin; Qiu, Feilong [School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093 (China); School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093 (China); Yang, Junhe, E-mail: hxqiu@usst.edu.cn [School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093 (China)

    2016-07-15

    Highlights: • A novel synthetic approach to graphene/polyaniline composite is developed. • Covalently bonds are introduced between graphene and polyaniline. • The composite exhibits great electrochemical property with capacitance of 489 F g{sup −1}. - Abstract: A polyaniline/graphene composite with covalently-bond is synthesized by a novel approach. In this way, graphene oxide is functionalized firstly by introducing amine groups onto the surface with the reduction of graphene oxide in the process and then served as the anchor sites for the growth of polyaniline (PANI) via in-situ polymerization. The composite material is characterized by electron microscopy, the resonant Raman spectra, X-ray diffraction, transform infrared spectroscopy and X-ray photoelectron spectroscopy. The electrochemical properties of the composite are measured by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charging/discharging. With the functionalization process, the graphene/polyaniline composite electrode exhibits remarkably enhanced electrochemical performance with specific capacitance of 489 F g{sup −1} at 0.5 A g{sup −1}, which is superior to those of its individual components. The outstanding electrochemical performance of the hybrid can be attributed to its covalently synergistic effect between graphene and polyaniline, suggesting promising potentials for supercapacitors.

  7. Highly stable ionic-covalent cross-linked sulfonated poly(ether ether ketone) for direct methanol fuel cells

    Science.gov (United States)

    Lei, Linfeng; Zhu, Xingye; Xu, Jianfeng; Qian, Huidong; Zou, Zhiqing; Yang, Hui

    2017-05-01

    A novel ionic cross-linked sulfonated poly(ether ether ketone) containing equal content of sulfonic acid and pendant tertiary amine groups (TA-SPEEK) has been initially synthesized for the application in direct methanol fuel cells (DMFCs). By adjusting the ratio of p-xylene dibromide to tertiary amine groups of TA-SPEEK, a series of ionic-covalent cross-linked membranes (C-SPEEK-x) with tunable degree of cross-linking are prepared. Compared with the pristine membrane, the ionic and ionic-covalent cross-linked proton exchange membranes (PEMs) exhibit reduced methanol permeability and improved mechanical properties, dimensional and oxidative stability. The proton conductivity and methanol selectivity of protonated TA-SPEEK and C-SPEEK-x at 25 °C is up to 0.109 S cm-1 and 3.88 × 105 S s cm-3, respectively, which are higher than that of Nafion 115. The DMFC incorporating C-SPEEK-25 exhibits a maximum power density as high as 35.3 mW cm-2 with 4 M MeOH at 25 °C (31.8 mW cm-2 for Nafion 115). Due to the highly oxidative stability of the membrane, no obvious performance degradation of the DMFC is observed after more than 400 h operation, indicating such cost-effective ionic-covalent cross-linked membranes have substantial potential as alternative PEMs for DMFC applications.

  8. Pore Environment Control and Enhanced Performance of Enzymes Infiltrated in Covalent Organic Frameworks.

    Science.gov (United States)

    Sun, Qi; Fu, Chung-Wei; Aguila, Briana; Perman, Jason; Wang, Sai; Huang, Hsi-Ya; Xiao, Feng-Shou; Ma, Shengqian

    2018-01-24

    In the drive toward green and sustainable methodologies for chemicals manufacturing, biocatalysts are predicted to have much to offer in the years to come. That being said, their practical applications are often hampered by a lack of long-term operational stability, limited operating range, and a low recyclability for the enzymes utilized. Herein, we show how covalent organic frameworks (COFs) possess all the necessary requirements needed to serve as ideal host materials for enzymes. The resultant biocomposites of this study have shown the ability boost the stability and robustness of the enzyme in question, namely lipase PS, while also displaying activities far outperforming the free enzyme and biocomposites made from other types of porous materials, such as mesoporous silica and metal-organic frameworks, exemplified in the kinetic resolution of the alcohol assays performed. The ability to easily tune the pore environment of a COF using monomers bearing specific functional groups can improve its compatibility with a given enzyme. As a result, the orientation of the enzyme active site can be modulated through designed interactions between both components, thus improving the enzymatic activity of the biocomposites. Moreover, in comparison with their amorphous analogues, the well-defined COF pore channels not only make the accommodated enzymes more accessible to the reagents but also serve as stronger shields to safeguard the enzymes from deactivation, as evidenced by superior activities and tolerance to harsh environments. The amenability of COFs, along with our increasing understanding of the design rules for stabilizing enzymes in an accessible fashion, gives great promise for providing "off the shelf" biocatalysts for synthetic transformations.

  9. Triazine-based covalent organic frameworks for photodynamic inactivation of bacteria as type-II photosensitizers.

    Science.gov (United States)

    Liu, Tingting; Hu, Xinyuan; Wang, Yanfeng; Meng, Liyang; Zhou, Yanan; Zhang, Jixiang; Chen, Min; Zhang, Xiaomei

    2017-10-01

    With the increase of antibiotic resistances in microorganisms, photodynamic inactivation (PDI) as a clinically proven antibacterial therapy is gaining increasing attention in recent years due to its high efficacy. Herein, we reported two covalent organic frameworks (COFs) materials, namely COFs-Trif-Benz and COF-SDU1, as effective type-II photosensitizers for photodynamic inactivation of bacteria. COFs-Trif-Benz and COF-SDU1 are synthesized through a facile solvothermal reaction between tri-(4-formacylphenoxy)-1,3,5-triazine (trif) and benzidine or p-phenylenediamine with high yield. Their highly ordered and porous structures were confirmed by Fourier transform infrared (FT-IR) spectra, solid state 13 C CP/MAS NMR spectrum, powder X-ray diffraction (PXRD) and Brunauer-Emmett-Teller (BET) analyses. The electronic absorption spectra and electrochemical experiments revealed that the extensive π-conjugation over COFs-Trif-Benz and COF-SDU1 greatly enhance their absorbance capability for visible light and make them have a lower band gap. The photocatalytic antibacterial assay was studied against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli O86:B7 (E. coli O86) bacteria. Two materials can kill more than 90% bacteria at concentrations of 100μgmL -1 after 60-90min of illumination. Thus, both COFs are effective photosensitizers. Mechanism investigation revealed the antibacterial characteristics of the COFs-Trif-Benz and COF-SDU1 can generate reactive oxygen species (ROS) by energy transfer to molecular oxygen ( 3 O 2 ) to produce a highly reactive singlet oxygen ( 1 O 2 ). Hence, the two materials during the photodynamic were mainly via mechanism type II. Copyright © 2017. Published by Elsevier B.V.

  10. Covalent conjugation of the equine infectious anemia virus Gag with SUMO.

    Science.gov (United States)

    Wang, Jinzhong; Wen, Shuping; Zhao, Rui; Qi, Jing; Liu, Zhao; Li, Weiwei; An, Jing; Wood, Charles; Wang, Ying

    2017-05-06

    The conjugation of small ubiquitin-like modifier (SUMO) to the target protein, namely, SUMOylation, is involved in the regulation of many important biological events including host-pathogen interaction. Some viruses have evolved to exploit the host SUMOylation machinery to modify their own protein. Retroviral Gag protein plays critical roles in the viral life cycle. The HIV-1 p6 and the Moloney murine leukemia virus CA have been reported to be conjugated with SUMO. In this study, we report for the first time, to our knowledge, the covalent conjugation of equine infectious anemia virus (EIAV) Gag with SUMO. The C-terminal p9 domain of Gag is a main target for SUMOylation and SUMO is attached to multiple sites of p9, including K30 whose mutation abolished p9 SUMOylation completely. The SUMOylation of p9, but not the p9-K30 mutant, was also detected in equine fibroblastic cells ATCC ® CCL-57™. Ubc9 and its C93 residue are indispensable for the SUMOylation of p9. Using confocal microscopy, it is found that EIAV Gag localizes primarily, if not exclusively, in the cytoplasm of the cell and the co-localization of EIAV Gag with Ubc9 was observed. Our findings that EIAV Gag is SUMOylated at p9-K30, together with previous findings on the defects of p9-K30 mutant in viral DNA translocation from cytoplasm to the nucleus, suggests that SUMOylation of Gag may be involved in such functions. Copyright © 2017 Elsevier Inc. All rights reserved.

  11. Computational prediction of methylation types of covalently modified lysine and arginine residues in proteins.

    Science.gov (United States)

    Deng, Wankun; Wang, Yongbo; Ma, Lili; Zhang, Ying; Ullah, Shahid; Xue, Yu

    2017-07-01

    Protein methylation is an essential posttranslational modification (PTM) mostly occurs at lysine and arginine residues, and regulates a variety of cellular processes. Owing to the rapid progresses in the large-scale identification of methylation sites, the available data set was dramatically expanded, and more attention has been paid on the identification of specific methylation types of modification residues. Here, we briefly summarized the current progresses in computational prediction of methylation sites, which provided an accurate, rapid and efficient approach in contrast with labor-intensive experiments. We collected 5421 methyllysines and methylarginines in 2592 proteins from the literature, and classified most of the sites into different types. Data analyses demonstrated that different types of methylated proteins were preferentially involved in different biological processes and pathways, whereas a unique sequence preference was observed for each type of methylation sites. Thus, we developed a predictor of GPS-MSP, which can predict mono-, di- and tri-methylation types for specific lysines, and mono-, symmetric di- and asymmetrical di-methylation types for specific arginines. We critically evaluated the performance of GPS-MSP, and compared it with other existing tools. The satisfying results exhibited that the classification of methylation sites into different types for training can considerably improve the prediction accuracy. Taken together, we anticipate that our study provides a new lead for future computational analysis of protein methylation, and the prediction of methylation types of covalently modified lysine and arginine residues can generate more useful information for further experimental manipulation. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  12. The Synthesis, Structures and Chemical Properties of Macrocyclic Ligands Covalently Bonded into Layered Arrays

    International Nuclear Information System (INIS)

    Clearfield, Abraham

    2003-01-01

    OAK-B135 The immobilization of crown ethers tends to limit the leveling effect of solvents making the macrocycles more selective. In addition immobilization has the added advantage of relative ease of recovery of the otherwise soluble crown. We have affixed CH2PO3H2 groups to azacrown ethers. The resultant phosphorylated macrocycles may spontaneously aggregate into crystalline supramolecular linear arrays or contacted with cations produce layered or linear polymers. In the linear polymers the metal and phosphonic acids covalently bond into a central stem with the macrocyclic rings protruding from the stem as leaves on a twig. Two types of layered compounds were obtained with group 4 metals. Monoaza-crown ethers form a bilayer where the M4+ plus phosphonic acid groups build the layer and the rings fill the interlayer space. 1, 10-diazadiphosphonic acids cross-link the metal phosphonate layers forming a three-dimensional array of crown ethers. In order to improve diffusion into these 3-D arrays they are spaced by inclusion of phosphate or phosphate groups. Two series of azamacrocylic crown ethers were prepared containing rings with 20 to 32 atoms. These larger rings can complex two cations per ring. Methylene phosphonic acid groups have been bonded to the aza ring atoms to increase the complexing ability of these ligands. Our approach is to carry out acid-base titrations in the absence and presence of cations to determine the pKa values of the protons, both those bonded to aza groups and those associated with the phosphonic acid groups. From the differences in the titration curves obtained with and without the cations present we obtain the stoichiometry of complex formation and the complex stability constants. Some of the applications we are targeting include phase transfer catalysis, separation of cations and the separation of radioisotopes for diagnostic and cancer therapeutic purposes

  13. Protein samples for NMR: expression and analysis without purification, and stabilization by covalent cyclization

    International Nuclear Information System (INIS)

    Otting, G.; Ozawa, K.; Prosselkov, P.; Williams, N.K.; Dixon, N.E.; Liepinsh, E.

    2002-01-01

    Full text: A modified cell-free in vitro expression system was established for the expression of milligram quantities of protein per mL reaction medium. Expression levels of the E coli cytoplasmic peptidyl-prolyl cis-trans isomerase, PpiB, in 0 6 mL reaction medium were sufficient for the direct recording of clean 15N-HSQC spectra without chromatographic purification or sample concentration steps, using a 600 MHz NMR spectrometer with cryoprobe. Besides providing a route to high-throughput sample preparation, in vitro expression systems are known to be highly economic in their utilization of selectively labelled ammo acids. Using dual-selective labelling with 15N- and 13C-labelled amino acids, the 15N-HSQC cross peaks of strategically selected ammo acids can readily be identified and monitored for their response to the presence of ligand molecules, again without sample purification. 2) The N-terminal domain of E coli DnaB is a protein of ca 110 residues with a structured core composed of 6 helices. Additional segments of 10 residues each at the N- and C-termini are highly mobile. Both ends are close in space and can be linked together in a covalent peptide bond using intern technology. The core structures of linear (lin-DnaB-N) and cyclized (cz-DnaB-N) protein are conserved, as evidenced by superimposable NOESY spectra and chemical shifts. The linker segment in cz-DnaB-N is mobile as shown by 1H-15N NOEs. Yet, the cyclic protein melts about 10 degrees higher than the linear version. A stabilization free energy of ca 2 kcal/mol is in agreement with predictions based on the reduced entropy in the unfolded state. Amide proton exchange rates are much slower in the cyclic protein and reveal cooperative exchange through total, global unfolding at a rate of once every 100 minutes in the linear protein

  14. Covalently attached metalloporphyrins in LBL self-assembled redox polyelectrolyte thin films

    Energy Technology Data Exchange (ETDEWEB)

    Carballo, R.R.; Campodall' Orto, V.; Hurst, J.A.; Spiaggi, A.; Rezzano, I.N. [Departmento de Quimica Analitica y Fisicoquimica, Facultad de Farmacia y Bioquimica, Universidad de Buenos Aires, Junin 956, CP 1113 Buenos Aires (Argentina); Bonazzola, C. [INQUIMAE, Departamento de Quimica Inorganica, Analitica y Quimica Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellon 2, Ciudad Universitaria, CP 1428 Buenos Aires (Argentina)

    2008-06-30

    A formylporphyrin has been covalently bound to Poly (Allylamine Hydrochloride) (PAH) and electrostatically self-assembled polyelectrolyte films, containing the attached metalloporphyrin, have been constructed. The UV-vis absorption band at 390 nm has been followed as core porphyrin marker. The reflection-absorption IR spectra of the gold films modified with layer-by-layer (LBL) polyelectrolytes were recorded after 6 and 12 layers. Characteristic infrared absorbance bands of porphyrin, PAH and PVS became more evident on increasing the number of bilayers. The absorption bands at 750, 1214 and 2960 cm{sup -1}, attributed at {nu}(S-O), {nu}{sub s}(SO{sub 3}{sup -}) and {nu}(=NH{sub 2}{sup +}), respectively, showed a linear growth (R{sup 2} > 0.99) with the number of adsorbed layers. A lower correlation coefficient was observed for the band at 1585 cm{sup -1} attributed to Fe-protoporphyrin. In order to evaluate the electron transfer (ET) rate, the {delta}E{sub p} of the [Fe(CN){sub 6}]{sup 4-}/[Fe(CN){sub 6}]{sup 3-} couple in solution was measured after covering the electrode. A proportional increase of the {delta}E{sub p} with the number of layers is observed up to the 4th layer. After the second bilayer, the magnitude of the peak separation is highly related to the charge of the topmost layer. The method allowed controlling the film thickness via the number of deposited layers (LBL). The electrode described, resulted in a good catalyst for O{sub 2} reduction and sulfite oxidation. (author)

  15. Atomic Ensemble Effects and Non-Covalent Interactions at the Electrode–Electrolyte Interface

    Directory of Open Access Journals (Sweden)

    Angel Cuesta

    2016-09-01

    Full Text Available Cyanide-modified Pt(111 electrodes have been recently employed to study atomic ensemble effects in electrocatalysis. This work, which will be briefly reviewed, reveals that the smallest site required for methanol dehydrogenation and formic acid dehydration is composed of three contiguous Pt atoms. By blocking these trigonal sites, the specific adsorption of anions, such as sulfate and phosphate, can be inhibited, thus increasing the rate of oxygen reduction reaction by one order of magnitude or more. Moreover, alkali metal cations affect hydrogen adsorption on cyanide-modified Pt(111. This effect is attributed to the non-covalent interactions at the electrical double layer between specifically adsorbed anions or dipoles and the alkali metal cations. A systematic investigation is conducted on the effect of the concentration of alkali metal cations. Accordingly, a simple model that reproduces the experimental observations accurately and enables the understanding of the trends in the strength of the interaction between M+ and CNad when moving from Li+ to Cs+, as well as the deviations from the expected trends, is developed. This simple model can also explain the occurrence of super-Nernstian shifts of the equilibrium potential of interfacial proton-coupled electron transfers. Therefore, the model can be generally applied to explain quantitatively the effect of cations on the properties of the electrical double layer. The recently reported effects of alkali metal cations on several electrocatalytic reactions must be mediated by the interaction between these cations and chemisorbed species. As these interactions seem to be adequately and quantitatively described by our model, we expect the model to also be useful to describe, explain, and potentially exploit these effects.

  16. [Covalent stretokinase-polyethylene glycol conjugates with increased stability and decreased side effects].

    Science.gov (United States)

    Aĭsina, R B; Mukhametova, L I; Tiupa, D V; Gershkovich, K B; Gulin, D A; Varfolomeev, S D

    2014-01-01

    By variation of incubation time of streptokinase (SK) with activated polyethylene glycol (M 2 and 5 kDa, PEG2 and PEG5) it was obtained covalent SK-PEG2 and SK-PEG5 conjugates with different modification degrees of amino groups of protein and their properties were studied in vitro as compared with free SK. It was shown, that maximal stable and retaining 80% fibrinolytic activity SK-PEG2 and SK-PEG5 conjugates are formed when the modification degrees of amino groups of protein are 54 and 52%, respectively. At interaction of the given conjugates with equimolar plasminogen concentration it were formed the plasmin (Pm)·SK-PEG2 and Pm·SK-PEG5 activator complexes, the maximal amidase activity of which is equal to activity of unmodified Pm·SK complex. It was found, that the catalytic efficiency of plasminogen activation (kPg/KPg) by Pm·SK-PEG2 complex is some higher (2.84 min(-1) μM(-1)) and by Pm·SK-PEG5 complex is lower (1.17 min(-1) μM(-1)), than that by unmodified Pm·SK complex (2.1 min(-1) μM(-1)). Investigation of lysis kinetics of human plasma clots and depletion of plasminogen and fibrinogen in plasma under the action of free SK and SK-PEG2 and SK-PEG5 conjugates showed, that the latter's have high thrombolytic activity (89 and 72%, respectively) and cause 3.5-4 fold lower side effects, than free SK. Obtained by us SK-PEG2 and SK-PEG5 conjugates with increased stability and decreased side effects may be used in the therapy of thrombotic disorders.

  17. Methionine sulfoxides on PrPSc: a prion-specific covalent signature.

    Science.gov (United States)

    Canello, Tamar; Engelstein, Roni; Moshel, Ofra; Xanthopoulos, Konstantinos; Juanes, María E; Langeveld, Jan; Sklaviadis, Theodoros; Gasset, Maria; Gabizon, Ruth

    2008-08-26

    Prion diseases are fatal neurodegenerative disorders believed to be transmitted by PrP (Sc), an aberrant form of the membrane protein PrP (C). In the absence of an established form-specific covalent difference, the infectious properties of PrP (Sc) were uniquely ascribed to the self-perpetuation properties of its aberrant fold. Previous sequencing of the PrP chain isolated from PrP(27-30) showed the oxidation of some methionine residues; however, at that time, these findings were ascribed to experimental limitations. Using the unique recognition properties of alphaPrP mAb IPC2, protein chemistry, and state of the art mass spectrometry, we now show that while a large fraction of the methionine residues in brain PrP (Sc) are present as methionine sulfoxides this modification could not be found on brain PrP (C) as well as on its recombinant models. In particular, the pattern of oxidation of M213 with respect to the glycosylation at N181 of PrP (Sc) differs both within and between species, adding another diversity factor to the structure of PrP (Sc) molecules. Our results pave the way for the production of prion-specific reagents in the form of antibodies against oxidized PrP chains which can serve in the development of both diagnostic and therapeutic strategies. In addition, we hypothesize that the accumulation of PrP (Sc) and thereafter the pathogenesis of prion disease may result from the poor degradation of oxidized aberrantly folded PrP.

  18. Crystal structures of Mycobacterium tuberculosis GlgE and complexes with non-covalent inhibitors

    Energy Technology Data Exchange (ETDEWEB)

    Lindenberger, Jared J.; Veleti, Sri Kumar; Wilson, Brittney N.; Sucheck, Steven J.; Ronning, Donald R. (Toledo)

    2015-08-06

    GlgE is a bacterial maltosyltransferase that catalyzes the elongation of a cytosolic, branched α-glucan. In Mycobacterium tuberculosis (M. tb), inactivation of GlgE (Mtb GlgE) results in the rapid death of the organism due to a toxic accumulation of the maltosyl donor, maltose-1-phosphate (M1P), suggesting that GlgE is an intriguing target for inhibitor design. In this study, the crystal structures of the Mtb GlgE in a binary complex with maltose and a ternary complex with maltose and a maltosyl-acceptor molecule, maltohexaose, were solved to 3.3 Å and 4.0 Å, respectively. The maltohexaose structure reveals a dominant site for α-glucan binding. To obtain more detailed interactions between first generation, non-covalent inhibitors and GlgE, a variant Streptomyces coelicolor GlgEI (Sco GlgEI-V279S) was made to better emulate the Mtb GlgE M1P binding site. The structure of Sco GlgEI-V279S complexed with α-maltose-C-phosphonate (MCP), a non-hydrolyzable substrate analogue, was solved to 1.9 Å resolution, and the structure of Sco GlgEI-V279S complexed with 2,5-dideoxy-3-O-α-D-glucopyranosyl-2,5-imino-D-mannitol (DDGIM), an oxocarbenium mimic, was solved to 2.5 Å resolution. These structures detail important interactions that contribute to the inhibitory activity of these compounds, and provide information on future designs that may be exploited to improve upon these first generation GlgE inhibitors.

  19. Resemblance of actin-binding protein/actin gels to covalently crosslinked networks

    Science.gov (United States)

    Janmey, Paul A.; Hvidt, Søren; Lamb, Jennifer; Stossel, Thomas P.

    1990-05-01

    THE maintainance of the shape of cells is often due to their surface elasticity, which arises mainly from an actin-rich cytoplasmic cortex1,2. On locomotion, phagocytosis or fission, however, these cells become partially fluid-like. The finding of proteins that can bind to actin and control the assembly of, or crosslink, actin filaments, and of intracellular messages that regulate the activities of some of these actin-binding proteins, indicates that such 'gel sol' transformations result from the rearrangement of cortical actin-rich networks3. Alternatively, on the basis of a study of the mechanical properties of mixtures of actin filaments and an Acanthamoeba actin-binding protein, α-actinin, it has been proposed that these transformations can be accounted for by rapid exchange of crosslinks between actin filaments4: the cortical network would be solid when the deformation rate is greater than the rate of crosslink exchange, but would deform or 'creep' when deformation is slow enough to permit crosslinker molecules to rearrange. Here we report, however, that mixtures of actin filaments and actin-binding protein (ABP), an actin crosslinking protein of many higher eukaryotes, form gels Theologically equivalent to covalently crosslinked networks. These gels do not creep in response to applied stress on a time scale compatible with most cell-surface movements. These findings support a more complex and controlled mechanism underlying the dynamic mechanical properties of cortical cytoplasm, and can explain why cells do not collapse under the constant shear forces that often exist in tissues.

  20. Strong ideal convergence in probabilistic metric spaces

    Indian Academy of Sciences (India)

    sequence and strong ideal Cauchy sequence in a probabilistic metric (PM) space endowed with the strong topology, and ... also important applications in nonlinear analysis [2]. The theory was brought to ..... for each t > 0 since each set on the right-hand side of the relation (3.1) belongs to I. Thus, by Definition 2.11 and the ...

  1. Large N baryons, strong coupling theory, quarks

    International Nuclear Information System (INIS)

    Sakita, B.

    1984-01-01

    It is shown that in QCD the large N limit is the same as the static strong coupling limit. By using the static strong coupling techniques some of the results of large N baryons are derived. The results are consistent with the large N SU(6) static quark model. (author)

  2. Optimization of strong and weak coordinates

    NARCIS (Netherlands)

    Swart, M.; Bickelhaupt, F.M.

    2006-01-01

    We present a new scheme for the geometry optimization of equilibrium and transition state structures that can be used for both strong and weak coordinates. We use a screening function that depends on atom-pair distances to differentiate strong coordinates from weak coordinates. This differentiation

  3. Strong decays of nucleon and delta resonances

    International Nuclear Information System (INIS)

    Bijker, R.; Leviatan, A.

    1996-01-01

    We study the strong couplings of the nucleon and delta resonances in a collective model. In the ensuing algebraic treatment we derive closed expressions for decay widths which are used to analyze the experimental data for strong decays into the pion and eta channels. (Author)

  4. Theoretical studies of strongly correlated fermions

    Energy Technology Data Exchange (ETDEWEB)

    Logan, D. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1997-04-01

    Strongly correlated fermions are investigated. An understanding of strongly correlated fermions underpins a diverse range of phenomena such as metal-insulator transitions, high-temperature superconductivity, magnetic impurity problems and the properties of heavy-fermion systems, in all of which local moments play an important role. (author).

  5. Seismic switch for strong motion measurement

    Science.gov (United States)

    Harben, P.E.; Rodgers, P.W.; Ewert, D.W.

    1995-05-30

    A seismic switching device is described that has an input signal from an existing microseismic station seismometer and a signal from a strong motion measuring instrument. The seismic switch monitors the signal level of the strong motion instrument and passes the seismometer signal to the station data telemetry and recording systems. When the strong motion instrument signal level exceeds a user set threshold level, the seismometer signal is switched out and the strong motion signal is passed to the telemetry system. The amount of time the strong motion signal is passed before switching back to the seismometer signal is user controlled between 1 and 15 seconds. If the threshold level is exceeded during a switch time period, the length of time is extended from that instant by one user set time period. 11 figs.

  6. COVALENT BINDING OF REDUCED METABOLITES OF [15N3] TNT TO SOIL ORGANIC MATTER DURING A BIOREMEDIATION PROCESS ANALYZED BY 15N NMR SPECTROSCOPY. (R826646)

    Science.gov (United States)

    Evidence is presented for the covalent binding ofbiologically reduced metabolites of 2,4,6-15N3-trinitrotoluene(TNT) to different soil fractions (humic acids, fulvicacids, and humin) using liquid 15N NMR spectroscopy. Asilylation p...

  7. Modification of ISFESTs by covalent anchoring of poly(hydroxyethyl methacrylate) hydrogel. Introduction of a thermodynamically defined semiconductor-sensing membrane interface

    NARCIS (Netherlands)

    Sudholter, Ernst; Sudhölter, Ernst J.R.; van der Wal, Peter D.; van der Wal, P.D.; Skowronska-Ptasinska, Maria; van den Berg, Albert; Bergveld, Piet; Reinhoudt, David

    1990-01-01

    Silicon dioxide ion-sensitive field effect transistors were modified by silylation with methacryloxypropyltrimethoxysilane (MPTS) and with in situ photopolymerized poly(hydroxyethyl methacrylate). Subsequently, the covalently linked methacrylate was swollen with a buffered potassium chloride

  8. Functionalization of multiwalled carbon nanotubes by microwave irradiation for lysozyme attachment: comparison of covalent and adsorption methods by kinetics of thermal inactivation

    Science.gov (United States)

    Puentes-Camacho, Daniel; Velázquez, Enrique F.; Rodríguez-Félix, Dora E.; Castillo-Ortega, Mónica; Sotelo-Mundo, Rogerio R.; del Castillo-Castro, Teresa

    2017-12-01

    Proteins suffer changes in their tertiary structure when they are immobilized, and enzymatic activity is affected due to the low biocompatibility of some supporting materials. In this work immobilization of lysozyme on carbon nanotubes previously functionalized by microwave irradiation was studied. The effectiveness of the microwave-assisted acid treatment of carbon nanotubes was evaluated by XPS, TEM, Raman and FTIR spectroscopy. The carboxylic modification of nanotube surfaces by this fast, simple and feasible method allowed the physical adsorption and covalent linking of active lysozyme onto the carbonaceous material. Thermal inactivation kinetics, thermodynamic parameters and storage stability were studied for adsorbed and covalent enzyme complexes. A major stability was found for lysozyme immobilized by the covalent method, the activation energy for inactivation of the enzyme was higher for the covalent method and it was stable after 50 d of storage at 4 °C. The current study highlights the effect of protein immobilization method on the biotechnological potential of nanostructured biocatalysts.

  9. Use of Synergistic Interactions to Fabricate Strong, Tough, and Conductive Artificial Nacre Based on Graphene Oxide and Chitosan.

    Science.gov (United States)

    Wan, Sijie; Peng, Jingsong; Li, Yuchen; Hu, Han; Jiang, Lei; Cheng, Qunfeng

    2015-10-27

    Graphene is the strongest and stiffest material, leading to the development of promising applications in many fields. However, the assembly of graphene nanosheets into macrosized nanocomposites for practical applications remains a challenge. Nacre in its natural form sets the "gold standard" for toughness and strength, which serves as a guide to the assembly of graphene nanosheets into high-performance nanocomposites. Here we show the strong, tough, conductive artificial nacre based on graphene oxide through synergistic interactions of hydrogen and covalent bonding. Tensile strength and toughness was 4 and 10 times higher, respectively, than that of natural nacre. The exceptional integrated strong and tough artificial nacre has promising applications in aerospace, artificial muscle, and tissue engineering, especially for flexible supercapacitor electrodes due to its high electrical conductivity. The use of synergistic interactions is a strategy for the development of high-performance nanocomposites.

  10. Structural and biochemical analyses reveal insights into covalent flavinylation of the Escherichia coli Complex II homolog quinol:fumarate reductase

    Energy Technology Data Exchange (ETDEWEB)

    Starbird, C.A.; Maklashina, Elena; Sharma, Pankaj; Qualls-Histed, Susan; Cecchini, Gary; Iverson, T.M. (VA); (UCSF); (Vanderbilt)

    2017-06-14

    The Escherichia coli Complex II homolog quinol:fumarate reductase (QFR, FrdABCD) catalyzes the interconversion of fumarate and succinate at a covalently attached FAD within the FrdA subunit. The SdhE assembly factor enhances covalent flavinylation of Complex II homologs, but the mechanisms underlying the covalent attachment of FAD remain to be fully elucidated. Here, we explored the mechanisms of covalent flavinylation of the E. coli QFR FrdA subunit. Using a ΔsdhE E. coli strain, we show that the requirement for the assembly factor depends on the cellular redox environment. We next identified residues important for the covalent attachment and selected the FrdAE245 residue, which contributes to proton shuttling during fumarate reduction, for detailed biophysical and structural characterization. We found that QFR complexes containing FrdAE245Q have a structure similar to that of the WT flavoprotein, but lack detectable substrate binding and turnover. In the context of the isolated FrdA subunit, the anticipated assembly intermediate during covalent flavinylation, FrdAE245 variants had stability similar to that of WT FrdA, contained noncovalent FAD, and displayed a reduced capacity to interact with SdhE. However, small-angle X-ray scattering (SAXS) analysis of WT FrdA cross-linked to SdhE suggested that the FrdAE245 residue is unlikely to contribute directly to the FrdA-SdhE protein-protein interface. We also found that no auxiliary factor is absolutely required for flavinylation, indicating that the covalent flavinylation is autocatalytic. We propose that multiple factors, including the SdhE assembly factor and bound dicarboxylates, stimulate covalent flavinylation by preorganizing the active site to stabilize the quinone-methide intermediate.

  11. 6-Ethynylthieno[3,2-d]- and 6-ethynylthieno[2,3-d]pyrimidin-4-anilines as tunable covalent modifiers of ErbB kinases.

    Science.gov (United States)

    Wood, Edgar R; Shewchuk, Lisa M; Ellis, Byron; Brignola, Perry; Brashear, Ronald L; Caferro, Thomas R; Dickerson, Scott H; Dickson, Hamilton D; Donaldson, Kelly H; Gaul, Michael; Griffin, Robert J; Hassell, Anne M; Keith, Barry; Mullin, Robert; Petrov, Kimberly G; Reno, Michael J; Rusnak, David W; Tadepalli, Sarva M; Ulrich, John C; Wagner, Craig D; Vanderwall, Dana E; Waterson, Alex G; Williams, Jon D; White, Wendy L; Uehling, David E

    2008-02-26

    Analysis of the x-ray crystal structure of mono-substituted acetylenic thienopyrimidine 6 complexed with the ErbB family enzyme ErbB-4 revealed a covalent bond between the terminal carbon of the acetylene moiety and the sulfhydryl group of Cys-803 at the solvent interface. The identification of this covalent adduct suggested that acetylenic thienopyrimidine 6 and related analogs might also be capable of forming an analogous covalent adduct with EGFR, which has a conserved cysteine (797) near the ATP binding pocket. To test this hypothesis, we treated a truncated, catalytically competent form of EGFR (678-1020) with a structurally related propargylic amine (8). An investigation of the resulting complex by mass spectrometry revealed the formation of a covalent complex of thienopyrimidine 8 with Cys-797 of EGFR. This finding enabled us to readily assess the irreversibility of various inhibitors and also facilitated a structure-activity relationship understanding of the covalent modifying potential and biological activity of a series of acetylenic thienopyrimidine compounds with potent antitumor activity. Several ErbB family enzyme and cell potent 6-ethynyl thienopyrimidine kinase inhibitors were found to form covalent adducts with EGFR.

  12. Strong and superstrong pulsed magnetic fields generation

    CERN Document Server

    Shneerson, German A; Krivosheev, Sergey I

    2014-01-01

    Strong pulsed magnetic fields are important for several fields in physics and engineering, such as power generation and accelerator facilities. Basic aspects of the generation of strong and superstrong pulsed magnetic fields technique are given, including the physics and hydrodynamics of the conductors interacting with the field as well as an account of the significant progress in generation of strong magnetic fields using the magnetic accumulation technique. Results of computer simulations as well as a survey of available field technology are completing the volume.

  13. Impurity screening in strongly coupled plasma systems

    CERN Document Server

    Kyrkos, S

    2003-01-01

    We present an overview of the problem of screening of an impurity in a strongly coupled one-component plasma within the framework of the linear response (LR) theory. We consider 3D, 2D and quasi-2D layered systems. For a strongly coupled plasma the LR can be determined by way of the known S(k) structure functions. In general, an oscillating screening potential with local overscreening and antiscreening regions emerges. In the case of the bilayer, this phenomenon becomes global, as overscreening develops in the layer of the impurity and antiscreening in the adjacent layer. We comment on the limitations of the LR theory in the strong coupling situation.

  14. The lambda sigma calculus and strong normalization

    DEFF Research Database (Denmark)

    Schack-Nielsen, Anders; Schürmann, Carsten

    Explicit substitution calculi can be classified into several dis- tinct categories depending on whether they are confluent, meta-confluent, strong normalization preserving, strongly normalizing, simulating, fully compositional, and/or local. In this paper we present a variant of the λσ-calculus......, which satisfies all seven conditions. In particular, we show how to circumvent Mellies counter-example to strong normalization by a slight restriction of the congruence rules. The calculus is implemented as the core data structure of the Celf logical framework. All meta-theoretic aspects of this work...

  15. Covalently-controlled properties by design in group IV graphane analogues.

    Science.gov (United States)

    Jiang, Shishi; Arguilla, Maxx Q; Cultrara, Nicholas D; Goldberger, Joshua E

    2015-01-20

    properties such as photoluminescence to be readily observable without the need to exfoliate down to single layers. Furthermore, these materials can be resilient to oxidation and thermal degradation, making them attractive candidates for next generation functional materials for electronic devices and beyond. This class of two-dimensional materials not only are promising building blocks for a variety of conventional semiconductor applications but also provide a pioneering platform to systematically and rationally control material properties using covalent chemistry. The stability and tunability of these versatile materials will push this system toward the forefront of two-dimensional research.

  16. Boride ceramics covalent functionalization and its effect on the thermal conductivity of epoxy composites

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Zhi-Qiang, E-mail: yuzhiqiang@fudan.edu.cn [Department of Materials Science, Fudan University, 200433 Shanghai (China); Wu, Yicheng [Department of Materials Science, Fudan University, 200433 Shanghai (China); Wei, Bin; Baier, Horst [Institute of Lightweight Structures, Technical University Munich (TUM), Boltzmannstr. 15, D-85747 Garching (Germany)

    2015-08-15

    Zirconium diboride/aluminium oxide (ZrB{sub 2}/Al{sub 2}O{sub 3}) composite particles were functionalized with epoxide functionalized γ-glycidoxypropyltrimethoxysilane by the covalent bonding approach to improve the interfacial compatibility of composite particles in epoxy matrix. The composites of epoxy resin filled with functionalized ZrB{sub 2}/Al{sub 2}O{sub 3} were prepared by in situ bulk condensation polymerization of bisphenol A and epichlorohydrin in the presence of ZrB{sub 2}/Al{sub 2}O{sub 3}. The heat-conducting properties of composites were investigated by the finite element method (FEM) and the thermal conductivity test. The finite-element program ANSYS was used for this numerical analysis, and three-dimensional spheres-in-cube lattice array models were built to simulate the microstructure of composite materials for different filler contents. The thermal conductivity of composites was determined by laser flash method (LFA447 Nanoflash), using the measured heat capacity and thermal diffusivity, with separately entered density data. The results show that the effective chemical bonds are formed between ZrB{sub 2}/Al{sub 2}O{sub 3} and γ-glycidoxypropyltrimethoxysilane after the surface functionalization. The interfacial compatibility and bonding of modified particles with the epoxy matrix are improved. The thermal conductivities of functionalized composites with 3 vol% and 5 vol% loading are increased by 8.3% and 12.5% relative to the unmodified composites, respectively. Comparison of experimental values and calculated values of the thermal conductivity, the average relative differences are under 5%. The predictive values of thermal conductivity of epoxy composites are in reasonable agreement with the experimental values. - Highlights: • The surfaces of ZrB{sub 2}/Al{sub 2}O{sub 3} were functionalized by silane coupling agents. • The thermal conductivity (TC) of modified epoxy composites is improved significantly. • The FEM values of TC are in

  17. Covalent IR820-PEG-diamine nanoconjugates for theranostic applications in cancer

    Directory of Open Access Journals (Sweden)

    Fernandez-Fernandez A

    2014-10-01

    Full Text Available Alicia Fernandez-Fernandez,1,2 Romila Manchanda,1,3 Denny Carvajal,1,4 Tingjun Lei,1,5 Supriya Srinivasan,1 Anthony J McGoron11Biomedical Engineering Department, Florida International University, Miami, FL, USA; 2Physical Therapy Department, Nova Southeastern University, Fort Lauderdale, FL, USA; 3Chemistry Department, Galgotias University, Greater Noida, UP, India; 4Mount Sinai Medical Center, 5Cirle, Miami, FL, USAAbstract: Near-infrared dyes can be used as theranostic agents in cancer management, based on their optical imaging and localized hyperthermia capabilities. However, their clinical translatability is limited by issues such as photobleaching, short circulation times, and nonspecific biodistribution. Nanoconjugate formulations of cyanine dyes, such as IR820, may be able to overcome some of these limitations. We covalently conjugated IR820 with 6 kDa polyethylene glycol (PEG-diamine to create a nanoconjugate (IRPDcov with potential for in vivo applications. The conjugation process resulted in nearly spherical, uniformly distributed nanoparticles of approximately 150 nm diameter and zeta potential -0.4±0.3 mV. The IRPDcov formulation retained the ability to fluoresce and to cause hyperthermia-mediated cell-growth inhibition, with enhanced internalization and significantly enhanced cytotoxic hyperthermia effects in cancer cells compared with free dye. Additionally, IRPDcov demonstrated a significantly longer (P<0.05 plasma half-life, elimination half-life, and area under the curve (AUC value compared with IR820, indicating larger overall exposure to the theranostic agent in mice. The IRPDcov conjugate had different organ localization than did free IR820, with potential reduced accumulation in the kidneys and significantly lower (P<0.05 accumulation in the lungs. Some potential advantages of IR820-PEG-diamine nanoconjugates may include passive targeting of tumor tissue through the enhanced permeability and retention effect, prolonged

  18. Phosphopeptide Enrichment by Covalent Chromatography after Derivatization of Protein Digests Immobilized on Reversed-Phase Supports

    Science.gov (United States)

    Nika, Heinz; Nieves, Edward; Hawke, David H.; Angeletti, Ruth Hogue

    2013-01-01

    A rugged sample-preparation method for comprehensive affinity enrichment of phosphopeptides from protein digests has been developed. The method uses a series of chemical reactions to incorporate efficiently and specifically a thiol-functionalized affinity tag into the analyte by barium hydroxide catalyzed β-elimination with Michael addition using 2-aminoethanethiol as nucleophile and subsequent thiolation of the resulting amino group with sulfosuccinimidyl-2-(biotinamido) ethyl-1,3-dithiopropionate. Gentle oxidation of cysteine residues, followed by acetylation of α- and ε-amino groups before these reactions, ensured selectivity of reversible capture of the modified phosphopeptides by covalent chromatography on activated thiol sepharose. The use of C18 reversed-phase supports as a miniaturized reaction bed facilitated optimization of the individual modification steps for throughput and completeness of derivatization. Reagents were exchanged directly on the supports, eliminating sample transfer between the reaction steps and thus, allowing the immobilized analyte to be carried through the multistep reaction scheme with minimal sample loss. The use of this sample-preparation method for phosphopeptide enrichment was demonstrated with low-level amounts of in-gel-digested protein. As applied to tryptic digests of α-S1- and β-casein, the method enabled the enrichment and detection of the phosphorylated peptides contained in the mixture, including the tetraphosphorylated species of β-casein, which has escaped chemical procedures reported previously. The isolates proved highly suitable for mapping the sites of phosphorylation by collisionally induced dissociation. β-Elimination, with consecutive Michael addition, expanded the use of the solid-phase-based enrichment strategy to phosphothreonyl peptides and to phosphoseryl/phosphothreonyl peptides derived from proline-directed kinase substrates and to their O-sulfono- and O-linked β-N-acetylglucosamine (O

  19. Ru(bpy)(3) covalently doped silica nanoparticles as multicenter tunable structures for electrochemiluminescence amplification.

    Science.gov (United States)

    Zanarini, Simone; Rampazzo, Enrico; Ciana, Leopoldo Della; Marcaccio, Massimo; Marzocchi, Ettore; Montalti, Marco; Paolucci, Francesco; Prodi, Luca

    2009-02-18

    The electrochemiluminescence (ECL) of doped silica nanoparticles (DSNPs), prepared by a reverse microemulsion method that leads to covalent incorporation of the Ru(bpy)(3)(2+), was investigated in acetonitrile and aqueous buffers. The emission was produced for the first time by cation-anion direct annihilation, and the position of ECL maxima indirectly allowed estimation of the E(1/2,IOx) and E(1/2,IRed) potentials for Ru(bpy)(3) inside DSNPs. The weak ECL emission is most likely generated by an intrananoparticle ruthenium unit annihilation rather than by the electron transfer between a reduced and oxidized DSNP due to the very low diffusivities of the nanoparticles. Thiol-terminated DSNPs were self-assembled on gold substrates, forming compact and stable monolayers which mimic probe-target assays with DSNPs as labels. The ECL intensity obtained by such functionalized substrates in aqueous media, using tripropylamine (TPrA) as coreactant, was surprisingly increased with respect to direct electrochemical oxidation because of the ability of oxidized TPrA to diffuse within the DSNPs structure and reach a higher number of emitting units with respect to direct electron tunneling. The experimental results have been explained by proposing a basic physical-chemical model which supports evaluation of the number of redox-active centers per nanoparticle. In the model the contrasting effects of increased luminescence quantum yield and decreased diffusion coefficient with respect to free (i.e., not bound within the silica structure) emitting molecules were taken into account. This allows, in principle, optimizing the ECL emission intensity as a function of DSNP size, doping material, charge, doping level, supporting electrolyte, electrode material, and solvent. Finally, it is worth noting that this study has provided a more than 1000-fold increase of the ECL signal of a chemically and electrochemically stable DSNP compared to that of a single dye, suggesting that use of this

  20. Chlorophyll a Covalently Bonded to Organo-Modified Translucent Silica Xerogels: Optimizing Fluorescence and Maximum Loading

    Directory of Open Access Journals (Sweden)

    M. A. García-Sánchez

    2016-07-01

    Full Text Available Chlorophyll is a pyrrolic pigment with important optical properties, which is the reason it has been studied for many years. Recently, interest has been rising with respect to this molecule because of its outstanding physicochemical properties, particularly applicable to the design and development of luminescent materials, hybrid sensor systems, and photodynamic therapy devices for the treatment of cancer cells and bacteria. More recently, our research group has been finding evidence for the possibility of preserving these important properties of substrates containing chlorophyll covalently incorporated within solid pore matrices, such as SiO2, TiO2 or ZrO2 synthesized through the sol-gel process. In this work, we study the optical properties of silica xerogels organo-modified on their surface with allyl and phenyl groups and containing different concentrations of chlorophyll bonded to the pore walls, in order to optimize the fluorescence that these macrocyclic species displays in solution. The intention of this investigation was to determine the maximum chlorophyll a concentration at which this molecule can be trapped inside the pores of a given xerogel and to ascertain if this pigment remains trapped as a monomer, a dimer, or aggregate. Allyl and phenyl groups were deposited on the surface of xerogels in view of their important effects on the stability of the molecule, as well as over the fluorescence emission of chlorophyll; however, these organic groups allow the trapping of either chlorophyll a monomers or dimers. The determination of the above parameters allows finding the most adequate systems for subsequent in vitro or in vivo studies. The characterization of the obtained xerogels was performed through spectroscopic absorption, emission and excitation spectra. These hybrid systems can be employed as mimics of natural systems; the entrapment of chlorophyll inside pore matrices indicates that it is possible to exploit some of the most

  1. Strong Coupling Corrections in Quantum Thermodynamics

    Science.gov (United States)

    Perarnau-Llobet, M.; Wilming, H.; Riera, A.; Gallego, R.; Eisert, J.

    2018-03-01

    Quantum systems strongly coupled to many-body systems equilibrate to the reduced state of a global thermal state, deviating from the local thermal state of the system as it occurs in the weak-coupling limit. Taking this insight as a starting point, we study the thermodynamics of systems strongly coupled to thermal baths. First, we provide strong-coupling corrections to the second law applicable to general systems in three of its different readings: As a statement of maximal extractable work, on heat dissipation, and bound to the Carnot efficiency. These corrections become relevant for small quantum systems and vanish in first order in the interaction strength. We then move to the question of power of heat engines, obtaining a bound on the power enhancement due to strong coupling. Our results are exemplified on the paradigmatic non-Markovian quantum Brownian motion.

  2. Finding quantum effects in strong classical potentials

    Science.gov (United States)

    Hegelich, B. Manuel; Labun, Lance; Labun, Ou Z.

    2017-06-01

    The long-standing challenge to describing charged particle dynamics in strong classical electromagnetic fields is how to incorporate classical radiation, classical radiation reaction and quantized photon emission into a consistent unified framework. The current, semiclassical methods to describe the dynamics of quantum particles in strong classical fields also provide the theoretical framework for fundamental questions in gravity and hadron-hadron collisions, including Hawking radiation, cosmological particle production and thermalization of particles created in heavy-ion collisions. However, as we show, these methods break down for highly relativistic particles propagating in strong fields. They must therefore be improved and adapted for the description of laser-plasma experiments that typically involve the acceleration of electrons. Theory developed from quantum electrodynamics, together with dedicated experimental efforts, offer the best controllable context to establish a robust, experimentally validated foundation for the fundamental theory of quantum effects in strong classical potentials.

  3. The Charm and Beauty of Strong Interactions

    Science.gov (United States)

    El-Bennich, Bruno

    2018-01-01

    We briefly review common features and overlapping issues in hadron and flavor physics focussing on continuum QCD approaches to heavy bound states, their mass spectrum and weak decay constants in different strong interaction models.

  4. Atomica ionization by strong coherent radiation

    International Nuclear Information System (INIS)

    Brandi, H.S.; Davidovich, L.

    1979-07-01

    The relation among the three most frequently used non-perturbative methods proposed to study the ionization of atoms by strong electromagnetic fields is established. Their range of validity is also determined. (Author) [pt

  5. Perturbation of an exact strong gravity solution

    International Nuclear Information System (INIS)

    Baran, S.A.

    1982-10-01

    Perturbations of an exact strong gravity solution are investigated. It is shown, by using the new multipole expansions previously presented, that this exact and static spherically symmetric solution is stable under odd parity perturbations. (author)

  6. Strong-force theorists scoop Noble Prize

    CERN Multimedia

    Durrani, Matin

    2004-01-01

    Three US theorists have shared the 2004 Nobel Prize in Physics "for the discovery of asymptotic freedom in the theory of the strong interaction". Their theoretical work explains why quarks behave almost as free particles at high energies (½ page)

  7. Calculating hadronic properties in strong QCD

    International Nuclear Information System (INIS)

    Pennington, M.R.

    1996-01-01

    This talk gives a brief review of the progress that has been made in calculating the properties of hadrons in strong QCD. In keeping with this meeting I will concentrate on those properties that can be studied with electromagnetic probes. Though perturbative QCD is highly successful, it only applies in a limited kinematic regime, where hard scattering occur, and the quarks move in the interaction region as if they are free, pointlike objects. However, the bulk of strong interactions are governed by the long distance regime, where the strong interaction is strong. It is this regime of length scales of the order of a Fermi, that determines the spectrum of light hadrons and their properties. The calculation of these properties requires an understanding of non-perturbative QCD, of confinement and chiral symmetry breaking. (author)

  8. How strong is it? The interpretation of force and compliance constants as bond strength descriptors.

    Science.gov (United States)

    Brandhorst, Kai; Grunenberg, Jörg

    2008-08-01

    Knowledge about individual covalent or non-covalent bond strengths is the Holy Grail of many modern molecular sciences. Recent developments of new descriptors for such interaction strengths based on potential constants are summarised in this tutorial review. Several publications for and against the use of compliance matrices (inverse force constants matrix) have appeared in the literature in the last few years. However the mathematical basis for understanding, and therefore interpreting, compliance constants is still not well developed. We therefore summarise the theoretical foundations and point to the advantages and disadvantages of the use of force constants versus compliance constants for the description of both non-covalent and covalent interactions.

  9. Building strong brands – does it matter?

    OpenAIRE

    Aure, Kristin Gaaseide; Nervik, Kristine Dybvik

    2014-01-01

    Brand equity has proven, through several decades of research, to be a primary source of competitive advantage and future earnings (Yoo & Donthu, 2001). Building strong brands has therefore become a priority for many organizations, with the presumption that building strong brands yields these advantages (Yasin et al., 2007). A quantitative survey was conducted at Sunnmøre in Norway in order to answer the two developed research questions. - Does the brand equity dimensions; brand...

  10. Algebra of strong and electroweak interactions

    International Nuclear Information System (INIS)

    Bolokhov, S.V.; Vladimirov, Yu.S.

    2004-01-01

    The algebraic approach to describing the electroweak and strong interactions is considered within the frames of the binary geometrophysics, based on the principles of the Fokker-Feynman direct interparticle interaction theories of the Kaluza-Klein multidimensional geometrical models and the physical structures theory. It is shown that in this approach the electroweak and strong elementary particles interaction through the intermediate vector bosons, are characterized by the subtypes of the algebraic classification of the complex 3 x 3-matrices [ru

  11. Manipulating light with strongly modulated photonic crystals

    International Nuclear Information System (INIS)

    Notomi, Masaya

    2010-01-01

    Recently, strongly modulated photonic crystals, fabricated by the state-of-the-art semiconductor nanofabrication process, have realized various novel optical properties. This paper describes the way in which they differ from other optical media, and clarifies what they can do. In particular, three important issues are considered: light confinement, frequency dispersion and spatial dispersion. First, I describe the latest status and impact of ultra-strong light confinement in a wavelength-cubic volume achieved in photonic crystals. Second, the extreme reduction in the speed of light is reported, which was achieved as a result of frequency dispersion management. Third, strange negative refraction in photonic crystals is introduced, which results from their unique spatial dispersion, and it is clarified how this leads to perfect imaging. The last two sections are devoted to applications of these novel properties. First, I report the fact that strong light confinement and huge light-matter interaction enhancement make strongly modulated photonic crystals promising for on-chip all-optical processing, and present several examples including all-optical switches/memories and optical logics. As a second application, it is shown that the strong light confinement and slow light in strongly modulated photonic crystals enable the adiabatic tuning of light, which leads to various novel ways of controlling light, such as adiabatic frequency conversion, efficient optomechanics systems, photon memories and photons pinning.

  12. HBV-Specific shRNA is Capable of Reducing the Formation of Hepatitis B Virus Covalently Closed Circular DNA, but has No Effect on Established Covalently Closed Circular DNA in vitro

    OpenAIRE

    Starkey, Jason L.; Chiari, Estelle F.; Isom, Harriet C.

    2009-01-01

    Hepatitis B virus (HBV) covalently closed circular DNA (CCC DNA) is the source of HBV transcripts and persistence in chronically infected patients. The novel aspect of this study was to determine the effect of RNA interference (RNAi) on HBV CCC DNA when administered prior to establishment of HBV replication or during chronic HBV infection. HBV replication was initiated in HepG2 cells by transduction with HBV baculovirus. Subculture of HBV expressing HepG2 cells at 10 days post-transduction ge...

  13. Strong Motion Earthquake Data Values of Digitized Strong-Motion Accelerograms, 1933-1994

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Strong Motion Earthquake Data Values of Digitized Strong-Motion Accelerograms is a database of over 15,000 digitized and processed accelerograph records from...

  14. The extended reciprocity: Strong belief outperforms persistence.

    Science.gov (United States)

    Kurokawa, Shun

    2017-05-21

    The existence of cooperation is a mysterious phenomenon and demands explanation, and direct reciprocity is one key potential explanation for the evolution of cooperation. Direct reciprocity allows cooperation to evolve for cooperators who switch their behavior on the basis of information about the opponent's behavior. Here, relevant to direct reciprocity is information deficiency. When the opponent's last move is unknown, how should players behave? One possibility is to choose cooperation with some default probability without using any further information. In fact, our previous paper (Kurokawa, 2016a) examined this strategy. However, there might be beneficial information other than the opponent's last move. A subsequent study of ours (Kurokawa, 2017) examined the strategy which uses the own last move when the opponent's last move is unknown, and revealed that referring to the own move and trying to imitate it when information is absent is beneficial. Is there any other beneficial information else? How about strong belief (i.e., have infinite memory and believe that the opponent's behavior is unchanged)? Here, we examine the evolution of strategies with strong belief. Analyzing the repeated prisoner's dilemma game and using evolutionarily stable strategy (ESS) analysis against an invasion by unconditional defectors, we find the strategy with strong belief is more likely to evolve than the strategy which does not use information other than the opponent player's last move and more likely to evolve than the strategy which uses not only the opponent player's last move but also the own last move. Strong belief produces the extended reciprocity and facilitates the evolution of cooperation. Additionally, we consider the two strategies game between strategies with strong belief and any strategy, and we consider the four strategies game in which unconditional cooperators, unconditional defectors, pessimistic reciprocators with strong belief, and optimistic reciprocators with

  15. Accuracy of the DLPNO-CCSD(T) method for non-covalent bond dissociation enthalpies from coinage metal cation complexes

    KAUST Repository

    Minenkov, Yury

    2015-08-27

    The performance of the domain based local pair-natural orbital coupled-cluster (DLPNO-CCSD(T)) method has been tested to reproduce the experimental gas phase ligand dissociation enthalpy in a series of Cu+, Ag+ and Au+ complexes. For 33 Cu+ - non-covalent ligand dissociation enthalpies all-electron calculations with the same method result in MUE below 2.2 kcal/mol, although a MSE of 1.4 kcal/mol indicates systematic underestimation of the experimental values. Inclusion of scalar relativistic effects for Cu either via effective core potential (ECP) or Douglass-Kroll-Hess Hamiltonian, reduces the MUE below 1.7 kcal/mol and the MSE to -1.0 kcal/mol. For 24 Ag+ - non-covalent ligand dissociation enthalpies the DLPNO-CCSD(T) method results in a mean unsigned error (MUE) below 2.1 kcal/mol and vanishing mean signed error (MSE). For 15 Au+ - non-covalent ligand dissociation enthalpies the DLPNO-CCSD(T) methods provides larger MUE and MSE, equal to 3.2 and 1.7 kcal/mol, which might be related to poor precision of the experimental measurements. Overall, for the combined dataset of 72 coinage metal ion complexes DLPNO-CCSD(T) results in a MUE below 2.2 kcal/mol and an almost vanishing MSE. As for a comparison with computationally cheaper density functional theory (DFT) methods, the routinely used M06 functional results in MUE and MSE equal to 3.6 and -1.7 kca/mol. Results converge already at CC-PVTZ quality basis set, making highly accurate DLPNO-CCSD(T) estimates to be affordable for routine calculations (single-point) on large transition metal complexes of > 100 atoms.

  16. On the Mott transition and the new metal-insulator transitions in doped covalent and polar crystals

    International Nuclear Information System (INIS)

    Dzhumanov, S.; Begimkulov, U.; Kurbanov, U.T.; Yavidov, B.Y.

    2001-10-01

    The Mott transition and new metal-insulator transitions (MIT's) and their distinctive features in doped covalent semiconductors and polar compounds are studied within the continuum model of extrinsic carrier self-trapping, the Hubbard impurity band model (with on-site Coulomb repulsion and screening effects) and the extrinsic (bi)polaronic band model (with short- and long-range carrier-impurity, impurity-phonon and carrier-phonon interactions and intercarrier correlation) using the appropriate tight-binding approximations and variational methods. We have shown the formation possibility of large-radius localized one- and two-carrier impurity (or defect) states and narrow impurity bands in the band gap and charge transfer gap of these carrier-doped systems. The extrinsic Mott-Hubbard and (bi)polaronic insulating gaps are calculated exactly. The proper criterions for Mott transition, extrinsic excitonic and (bi)polaronic MIT's are obtained. We have demonstrated that the Mott transition occurs in doped covalent semiconductors (i.e. Si and Ge) and some insulators with weak carrier-phonon coupling near the large-radius dopants. While, in doped polar compounds (e.g. oxide high-T c superconductors (HTSC) and related materials) the MIT's are new extrinsic (or intrinsic) (bi)polaronic MIT's. We have found that the anisotropy of the dielectric (or (bi)polaronic) properties of doped cuprate HTSC is responsible for smooth (or continuous) MIT's, stripe formation and suppression of high-T c superconductivity. Various experimental results on in-gap states, bands and MIT's in doped covalent semiconductors, oxide HTSC and related materials are in good agreement with the developed theory of Mott transition and new (bi)polaronic MIT's. (author)

  17. Intermolecular covalent pi-pi bonding interaction indicated by bond distances, energy bands, and magnetism in biphenalenyl biradicaloid molecular crystal.

    Science.gov (United States)

    Huang, Jingsong; Kertesz, Miklos

    2007-02-14

    Density-functional theory (DFT) calculations were performed for energy band structure and geometry optimizations on the stepped pi-chain, the isolated molecule and (di)cations of the chain, and various related molecules of a neutral biphenalenyl biradicaloid (BPBR) organic semiconductor 2. The dependence of the geometries on crystal packing provides indirect evidence for the intermolecular covalent pi-pi bonding interaction through space between neighboring pi-stacked phenalenyl units along the chain. The two phenalenyl electrons on each molecule, occupying the singly occupied molecular orbitals (SOMOs), are participating in the intermolecular covalent pi-pi bonding making them partially localized on the phenalenyl units and less available for intramolecular delocalization. The band structure shows a relatively large bandwidth and small band gap indicative of good pi-pi overlap and delocalization between neighboring pi-stacked phenalenyl units. A new interpretation is presented for the magnetism of the stepped pi-chain of 2 using an alternating Heisenberg chain model, which is consistent with DFT total energy calculations for 2 and prevails against the previous interpretation using a Bleaney-Bowers dimer model. The obtained transfer integrals and the magnetic exchange parameters fit well into the framework of a Hubbard model. All presented analyses on molecular geometries, energy bands, and magnetism provide a coherent picture for 2 pointing toward an alternating chain with significant intermolecular through-space covalent pi-pi bonding interactions in the molecular crystal. Surprisingly, both the intermolecular transfer integrals and exchange parameters are larger than the intramolecular through-bond values indicating the effectiveness of the intermolecular overlap of the phenalenyl SOMO electrons.

  18. Enhancement of Alkaline Protease Activity and Stability via Covalent Immobilization onto Hollow Core-Mesoporous Shell Silica Nanospheres.

    Science.gov (United States)

    Ibrahim, Abdelnasser Salah Shebl; Al-Salamah, Ali A; El-Toni, Ahmed M; Almaary, Khalid S; El-Tayeb, Mohamed A; Elbadawi, Yahya B; Antranikian, Garabed

    2016-01-29

    The stability and reusability of soluble enzymes are of major concerns, which limit their industrial applications. Herein, alkaline protease from Bacillus sp. NPST-AK15 was immobilized onto hollow core-mesoporous shell silica (HCMSS) nanospheres. Subsequently, the properties of immobilized proteases were evaluated. Non-, ethane- and amino-functionalized HCMSS nanospheres were synthesized and characterized. NPST-AK15 was immobilized onto the synthesized nano-supports by physical and covalent immobilization approaches. However, protease immobilization by covalent attachment onto the activated HCMSS-NH₂ nanospheres showed highest immobilization yield (75.6%) and loading capacity (88.1 μg protein/mg carrier) and was applied in the further studies. In comparison to free enzyme, the covalently immobilized protease exhibited a slight shift in the optimal pH from 10.5 to 11.0, respectively. The optimum temperature for catalytic activity of both free and immobilized enzyme was seen at 60 °C. However, while the free enzyme was completely inactivated when treated at 60 °C for 1 h the immobilized enzyme still retained 63.6% of its initial activity. The immobilized protease showed higher V(max), k(cat) and k(cat)/K(m), than soluble enzyme by 1.6-, 1.6- and 2.4-fold, respectively. In addition, the immobilized protease affinity to the substrate increased by about 1.5-fold. Furthermore, the enzyme stability in various organic solvents was significantly enhanced upon immobilization. Interestingly, the immobilized enzyme exhibited much higher stability in several commercial detergents including OMO, Tide, Ariel, Bonux and Xra by up to 5.2-fold. Finally, the immobilized protease maintained significant catalytic efficiency for twelve consecutive reaction cycles. These results suggest the effectiveness of the developed nanobiocatalyst as a candidate for detergent formulation and peptide synthesis in non-aqueous media.

  19. Dimeric DNA Aptamer Complexes for High-capacity–targeted Drug Delivery Using pH-sensitive Covalent Linkages

    Directory of Open Access Journals (Sweden)

    Olcay Boyacioglu

    2013-01-01

    Full Text Available Treatment with doxorubicin (Dox results in serious systemic toxicities that limit effectiveness for cancer treatment and cause long-term health issues for cancer patients. We identified a new DNA aptamer to prostate-specific membrane antigen (PSMA using fixed sequences to promote Dox binding and developed dimeric aptamer complexes (DACs for specific delivery of Dox to PSMA+ cancer cells. DACs are stable under physiological conditions and are internalized specifically into PSMA+ C4-2 cells with minimal uptake into PSMA-null PC3 cells. Cellular internalization of DAC was demonstrated by confocal microscopy and flow cytometry. Covalent modification of DAC with Dox (DAC-D resulted in a complex with stoichiometry ~4:1. Dox was covalently bound in DAC-D using a reversible linker that promotes covalent attachment of Dox to genomic DNA following cell internalization. Dox was released from the DAC-D under physiological conditions with a half-life of 8 hours, sufficient for in vivo targeting. DAC-D was used to selectively deliver Dox to C4-2 cells with endosomal release and nuclear localization of Dox. DAC-D was selectively cytotoxic to C4-2 cells with similar cytotoxicity as the molar equivalent of free-Dox. In contrast, DAC-D displayed minimal cytotoxicity to PC3 cells, demonstrating the complex displays a high degree of selectivity for PSMA+ cells. DAC-D displays specificity and stability features that may be useful for improved delivery of Dox selectively to malignant tissue in vivo.

  20. Hollow nanoporous covalent triazine frameworks via acid vapor-assisted solid phase synthesis for enhanced visible light photoactivity

    KAUST Repository

    Huang, Wei

    2016-04-11

    Herein, we report a novel trifluoromethanesulfonic acid vapor-assisted solid phase synthetic method to construct nanoporous covalent triazine frameworks with highly ordered hollow interconnected pores under mild reaction conditions. This unique solid state synthetic route allows not only the avoidance of undesired side reactions caused by traditional high temperature synthesis, but also the maintaining of defined and precise optical and electronic properties of the nonporous triazine frameworks. Promising photocatalytic activity of the polytriazine networks was demonstrated in the photoreduction reaction of 4-nitrophenol into 4-aminophenol under visible light irradiation.