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Sample records for carboxylate promoted intramolecular

  1. Chelation-assisted Pd-catalysed ortho-selective oxidative C-H/C-H cross-coupling of aromatic carboxylic acids with arenes and intramolecular Friedel-Crafts acylation: one-pot formation of fluorenones.

    Science.gov (United States)

    Sun, Denan; Li, Bijin; Lan, Jingbo; Huang, Quan; You, Jingsong

    2016-03-01

    Pd-Catalysed ortho-selective oxidative C-H/C-H cross-coupling of aromatic carboxylic acids with arenes and subsequent intramolecular Friedel-Crafts acylation has been accomplished for the first time through a chelation-assisted C-H activation strategy. Starting from the readily available substrates, a variety of fluorenone derivatives are obtained in one pot. The direct use of naturally occurring carboxylic acid functionalities as directing groups avoids unnecessary steps for installation and removal of an extra directing group. PMID:26861768

  2. Carbon dioxide utilization via carbonate-promoted C-H carboxylation

    Science.gov (United States)

    Banerjee, Aanindeeta; Dick, Graham R.; Yoshino, Tatsuhiko; Kanan, Matthew W.

    2016-03-01

    Using carbon dioxide (CO2) as a feedstock for commodity synthesis is an attractive means of reducing greenhouse gas emissions and a possible stepping-stone towards renewable synthetic fuels. A major impediment to synthesizing compounds from CO2 is the difficulty of forming carbon-carbon (C-C) bonds efficiently: although CO2 reacts readily with carbon-centred nucleophiles, generating these intermediates requires high-energy reagents (such as highly reducing metals or strong organic bases), carbon-heteroatom bonds or relatively acidic carbon-hydrogen (C-H) bonds. These requirements negate the environmental benefit of using CO2 as a substrate and limit the chemistry to low-volume targets. Here we show that intermediate-temperature (200 to 350 degrees Celsius) molten salts containing caesium or potassium cations enable carbonate ions (CO32-) to deprotonate very weakly acidic C-H bonds (pKa > 40), generating carbon-centred nucleophiles that react with CO2 to form carboxylates. To illustrate a potential application, we use C-H carboxylation followed by protonation to convert 2-furoic acid into furan-2,5-dicarboxylic acid (FDCA)—a highly desirable bio-based feedstock with numerous applications, including the synthesis of polyethylene furandicarboxylate (PEF), which is a potential large-scale substitute for petroleum-derived polyethylene terephthalate (PET). Since 2-furoic acid can readily be made from lignocellulose, CO32--promoted C-H carboxylation thus reveals a way to transform inedible biomass and CO2 into a valuable feedstock chemical. Our results provide a new strategy for using CO2 in the synthesis of multi-carbon compounds.

  3. Phosphazene-promoted metal-free ring-opening polymerization of ethylene oxide initiated by carboxylic acid

    KAUST Repository

    Zhao, Junpeng

    2014-03-11

    The effectiveness of carboxylic acid as initiator for the anionic ring-opening polymerization of ethylene oxide was investigated with a strong phosphazene base (t-BuP4) used as promoter. Kinetic study showed an induction period, i.e., transformation of carboxylic acid to hydroxyl ester, followed by slow chain growth together with simultaneous and fast end-group transesterification, which led to poly(ethylene oxide) (PEO) consisting of monoester (monohydroxyl), diester, and dihydroxyl species. An appropriate t-BuP4/acid ratio was proven to be essential to achieve better control over the polymerization and low dispersity of PEO. This work provides important information and enriches the toolbox for macromolecular and biomolecular engineering with protic initiating sites. © 2014 American Chemical Society.

  4. Phenazine-1-Carboxylic Acid Promotes Bacterial Biofilm Development via Ferrous Iron Acquisition▿†

    OpenAIRE

    Wang, Yun; Wilks, Jessica C.; Danhorn, Thomas; Ramos, Itzel; Croal, Laura; Newman, Dianne K.

    2011-01-01

    The opportunistic pathogen Pseudomonas aeruginosa forms biofilms, which render it more resistant to antimicrobial agents. Levels of iron in excess of what is required for planktonic growth have been shown to promote biofilm formation, and therapies that interfere with ferric iron [Fe(III)] uptake combined with antibiotics may help treat P. aeruginosa infections. However, use of these therapies presumes that iron is in the Fe(III) state in the context of infection. Here we report the ability o...

  5. Synthesis, Hydrolysis, and Protonation-Promoted Intramolecular Reductive Breakdown of Potential NRTIs: Stavudine α-P-Borano-γ-P-N-l-tryptophanyltriphosphates

    Directory of Open Access Journals (Sweden)

    Zhihong Xu

    2015-10-01

    Full Text Available Phosphorus-modified prodrugs of dideoxynucleoside triphosphates (ddNTPs have shown promise as pronucleotide strategies for improving antiviral activity compared to their parent dideoxynucleosides. Borane modified NTPs offer a promising choice as nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs. However, the availability of α-P-borano-γ-P-substituted NTP analogs remains limited due to challenges with synthesis and purification. Here, we report the chemical synthesis and stability of a new potential class of NRTI prodrugs: stavudine (d4T 5′-α-P-borano-γ-P-N-L-tryptophanyltriphosphates. One-pot synthesis of these compounds was achieved via a modified cyclic trimetaphosphate approach. Pure Rp and Sp diastereomers were obtained after HPLC separation. Based on LC-MS analysis, we report degradation pathways, half-lives (5–36 days and mechanisms arising from structural differences to generate the corresponding borano tri- and di-phosphates, and H-phosphonate, via several parallel routes in buffer at physiologically relevant pH and temperature. Here, the major hydrolysis products, d4T α-P-boranotriphosphate Rp and Sp isomers, were isolated by HPLC and identified with spectral data. We first propose that one of the major degradation products, d4T H-phosphonate, was generated from the d4T pronucleotides via a protonation-promoted intramolecular reduction followed by a second step nucleophilic attack. This report could provide valuable information for pronucleotide-based drug design in terms of selective release of target nucleotides.

  6. Structure of a dinuclear cadmium complex with 2,2′-bipyridine, monodentate nitrate and 3-carboxy-6-methylpyridine-2-carboxylate ligands: intramolecular carbonyl(lone pair...π(ring and nitrate(π...π(ring interactions

    Directory of Open Access Journals (Sweden)

    Juan Granifo

    2015-08-01

    Full Text Available The centrosymmetric dinuclear complex bis(μ-3-carboxy-6-methylpyridine-2-carboxylato-κ3N,O2:O2;κ3O2:N,O2-bis[(2,2′-bipyridine-κ2N,N′(nitrato-κOcadmium] methanol monosolvate, [Cd2(C8H6NO42(NO32(C10H8N22]·CH3OH, was isolated as colourless crystals from the reaction of Cd(NO32·4H2O, 6-methylpyridine-2,3-dicarboxylic acid (mepydcH2 and 2,2′-bipyridine in methanol. The asymmetric unit consists of a CdII cation bound to a μ-κ3N,O2:O2-mepydcH− anion, an N,N′-bidentate 2,2′-bipyridine group and an O-monodentate nitrate anion, and is completed with a methanol solvent molecule at half-occupancy. The Cd complex unit is linked to its centrosymmetric image through a bridging mepydcH− carboxylate O atom to complete the dinuclear complex molecule. Despite a significant variation in the coordination angles, indicating a considerable departure from octahedral coordination geometry about the CdII atom, the Cd—O and Cd—N distances in this complex are surprisingly similar. The crystal structure consists of O—H...O hydrogen-bonded chains parallel to a, further bound by C—H...O contacts along b to form planar two-dimensional arrays parallel to (001. The juxtaposed planes form interstitial columnar voids that are filled by the methanol solvent molecules. These in turn interact with the complex molecules to further stabilize the structure. A search in the literature showed that complexes with the mepydcH− ligand are rare and complexes reported previously with this ligand do not adopt the μ-κ3 coordination mode found in the title compound.

  7. Structure of a dinuclear cadmium complex with 2,2'-bi-pyridine, monodentate nitrate and 3-carb-oxy-6-methyl-pyridine-2-carboxyl-ate ligands: intra-molecular carbon-yl(lone pair)⋯π(ring) and nitrate(π)⋯π(ring) inter-actions.

    Science.gov (United States)

    Granifo, Juan; Suarez, Sebastián; Baggio, Ricardo

    2015-08-01

    The centrosymmetric dinuclear complex bis-(μ-3-carb-oxy-6-methyl-pyridine-2-carboxyl-ato)-κ(3) N,O (2):O (2);κ(3) O (2):N,O (2)-bis-[(2,2'-bi-pyridine-κ(2) N,N')(nitrato-κO)cadmium] methanol monosolvate, [Cd2(C8H6NO4)2(NO3)2(C10H8N2)2]·CH3OH, was isolated as colourless crystals from the reaction of Cd(NO3)2·4H2O, 6-methyl-pyridine-2,3-di-carb-oxy-lic acid (mepydcH2) and 2,2'-bi-pyridine in methanol. The asymmetric unit consists of a Cd(II) cation bound to a μ-κ(3) N,O (2):O (2)-mepydcH(-) anion, an N,N'-bidentate 2,2'-bi-pyridine group and an O-mono-dentate nitrate anion, and is completed with a methanol solvent mol-ecule at half-occupancy. The Cd complex unit is linked to its centrosymmetric image through a bridging mepydcH(-) carboxyl-ate O atom to complete the dinuclear complex mol-ecule. Despite a significant variation in the coordination angles, indicating a considerable departure from octa-hedral coordination geometry about the Cd(II) atom, the Cd-O and Cd-N distances in this complex are surprisingly similar. The crystal structure consists of O-H⋯O hydrogen-bonded chains parallel to a, further bound by C-H⋯O contacts along b to form planar two-dimensional arrays parallel to (001). The juxtaposed planes form inter-stitial columnar voids that are filled by the methanol solvent mol-ecules. These in turn inter-act with the complex mol-ecules to further stabilize the structure. A search in the literature showed that complexes with the mepydcH(-) ligand are rare and complexes reported previously with this ligand do not adopt the μ-κ(3) coordination mode found in the title compound. PMID:26396748

  8. A phenazine-1-carboxylic acid producing polyextremophilic Pseudomonas chlororaphis (MCC2693) strain, isolated from mountain ecosystem, possesses biocontrol and plant growth promotion abilities.

    Science.gov (United States)

    Jain, Rahul; Pandey, Anita

    2016-09-01

    The genus Pseudomonas is known to comprise a huge diversity of species with the ability to thrive in different habitats, including those considered as extreme environments. In the present study, a psychrotolerant, wide pH tolerant and halotolerant strain of Pseudomonas chlororaphis GBPI_507 (MCC2693), isolated from the wheat rhizosphere growing in a mountain location in Indian Himalayan Region (IHR), has been investigated for its antimicrobial potential with particular reference to phenazine production and plant growth promoting traits. GBPI_507 showed phenazine production at the temperatures ranged from 14 to 25°C. The benzene extracted compound identified as phenazine-1-carboxylic acid (PCA) through GC-MS exhibited antimicrobial properties against Gram positive bacteria and actinomycetes. The inhibition of phytopathogens in diffusible biocontrol assays was recorded in an order: Alternaria alternata>Phytophthora sp.>Fusarium solani>F. oxysporum. In volatile metabolite assays, all the pathogens, except Phytophthora sp. produced distorted colonies, characterized by restricted sporulation. The isolate also possessed other growth promoting and biocontrol traits including phosphate solubilization and production of siderophores, HCN, ammonia, and lytic enzymes (lipase and protease). Molecular studies confirmed production of PCA by the bacterium GBPI_507 through presence of phzCD and phzE genes in its genome. The polyextremophilic bacterial strain possesses various important characters to consider it as a potential agent for field applications, especially in mountain ecosystem, for sustainable and eco-friendly crop production. PMID:27394000

  9. Structural analysis of the promoter of tomato 1-aminocyclopropane-1-carboxylate synthase 6 gene(Le-ACS6)

    Institute of Scientific and Technical Information of China (English)

    LIN JingYu; FAN Rong; WAN XiaoRong; CHARNG Yeeyung; WANG NingNing

    2007-01-01

    Ethylene plays an important role in the regulation of many growth and developmental processes of higher plants. In tomato, Le-ACS6, a member of the ACC synthase multigene family involved in system 1 ethylene biosynthesis during fruit ripening, is subject to negative feedback regulation by ethylene. To identify the cis-elements that are responsible for the negative feedback control, we established an in vitro transient assay system employing particle bombardment on mature-green tomato fruit pericarp to examine the expression of a luciferase (LUC) reporter gene driven by a 5'-serially deleted Le-ACS6 promoter. The results localized putative cis-elements required for negative ethylene-response between -347 and -266 upstream from the translational start site ATG. Several lines of stable transformation of the Le-ACS6 promoter and GUS reporter fusion gene containing internal deletion from -347 to -266 were generated. The expression pattern of the GUS reporter showed that removal of the nucleotides from -347 to -266 completely eliminated the response of the Le-ACS6 promoter to exogenous ethylene.

  10. Intramolecular and nonlinear dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Davis, M.J. [Argonne National Laboratory, IL (United States)

    1993-12-01

    Research in this program focuses on three interconnected areas. The first involves the study of intramolecular dynamics, particularly of highly excited systems. The second area involves the use of nonlinear dynamics as a tool for the study of molecular dynamics and complex kinetics. The third area is the study of the classical/quantum correspondence for highly excited systems, particularly systems exhibiting classical chaos.

  11. Prospective Use of 1-Aminocyclopropane-1-Carboxylate Deaminase-Producing Bacteria for Plant Growth Promotion and Defense against Biotic and Abiotic Stresses in Peat-Soil-Agriculture

    Directory of Open Access Journals (Sweden)

    EDI HUSEN

    2008-12-01

    Full Text Available The 1-aminocyclopropane-1-carboxylate (ACC deaminase (EC4.1.99.4 is an enzyme produced by some soil bacteria to degrade ACC (the immediate precursor of ethylene to reduce ethylene biosynthesis in higher plants. Increased concentrations of ethylene in plant tissues, which are triggered by various biotic and abiotic stresses, inhibits plant growth and weakens the plant defense against the stressors. Various findings on the successful use of ACC deaminase producing bacteria for plant growth under unfavorable soil conditions are inspiring their use in tropical peat-soil-agriculture, which possesses bio-physical constraints. It has been proven that inoculation of plants with ACC deaminase producing bacteria decreased ethylene inhibition generated by unfavorable environmental conditions, such as nutrient shortage, flooding, drought, high salts, and the presence of heavy metals and organic pollutants. Understanding the mechanisms by which ACC deaminase-producing bacteria act to reduce plant stress and the fitness of bacterial traits with the properties and constraints of peat-soils becomes a key to utilize these bacteria in improving crop productivity. The bacteria may ameliorate plant stress as well as promote plant growth under seasonal bio-physical changes of peat-soils that are usually encountered in the field.

  12. Conformationally gated fragmentations and rearrangements promoted by interception of the Bergman cyclization through intramolecular H-abstraction: a possible mechanism of auto-resistance to natural enediyne antibiotics?

    Science.gov (United States)

    Baroudi, Abdulkader; Mauldin, Justin; Alabugin, Igor V

    2010-01-27

    A variety of fragmentations and rearrangements can follow Bergman cyclization in enediynes equipped with acetal rings mimicking the carbohydrate moiety of natural enediyne antibiotics of the esperamicine and calchiamicine families. In the first step of all these processes, intramolecular H-atom abstraction efficiently intercepts the p-benzyne product of the Bergman cyclization through a six-membered TS and transforms the p-benzyne into a new more stable radical. Depending on the substitution pattern and reaction conditions, this radical follows four alternative paths: (a) abstraction of an external hydrogen atom, (b) O-neophyl rearrangement which transposes O- and C-atoms of the substituent, (c) fragmentation of the O-C bond in the acetal ring, or (d) fragmentation with elimination of the appended acetal moiety as a whole. Experiments with varying concentrations of external H-atom donor (1,4-cyclohexadiene) were performed to gain further insight into the competition between intermolecular H-abstraction and the fragmentations. The Thorpe-Ingold effect in gem-dimethyl substituted enediynes enhances the efficiency of fragmentation to the extent where it cannot be prevented even by a large excess of external H-atom donor. These processes provide insight into a possible mechanism of unusual fragmentation of esperamicin A(1) upon its Bergman cycloaromatization and lay foundation for a new approach for the conformational control of reactivity of these natural antitumor antibiotics. Such an approach, in conjunction with supramolecular constraints, may provide a plausible mechanism for resistance to enediyne antibiotics by the enediyne-producing microorganisms. PMID:20041688

  13. [11C]Carbon Monoxide in Palladium- / Selenium-Promoted Carbonylation Reactions : Synthesis of 11C-Imides, Hydrazides, Amides, Carboxylic Acids, Carboxylic Esters, Carbothioates, Ketones and Carbamoyl Compounds

    OpenAIRE

    Karimi, Farhad

    2002-01-01

    [11C]Carbon monoxide in low concentrations has been used in palladium- or seleniummediated carbonylation reactions such as the synthesis of 11C-imides, hydrazides, amides, carboxylic acids, esters, carbothioates, ketones and carbamoyl compounds. In these reactions aryl iodides have been used in most cases. However, less reactive aryl triflate, chloride and bromides were activated using tetrabutylammonium iodide. The reactivities of nucleophiles may have influence on the radiochemical yield of...

  14. Reações intramoleculares como modelos não miméticos de catálise enzimática Intramolecular reactions as non mimetic models of enzyme catalysis

    OpenAIRE

    José Carlos Gesser; Santiago Yunes; Rosilene M. Clementin; Faruk Nome

    1997-01-01

    This review gives a critical idea on the importance of intramolecular reactions as models for enzymatic catalysis. Intramolecular lactonizations, ester and amide hydrolysis studies result in theories which try to explain the difference between intermolecular, intramolecular and enzyme reactions and rationalize the enhancement promoted by these biological catalyst.

  15. ACC (1-Aminocyclopropane-1-Carboxylate) Deaminase Activity, a Widespread Trait in Burkholderia Species, and Its Growth-Promoting Effect on Tomato Plants▿

    OpenAIRE

    Onofre-Lemus, Janette; Hernández-Lucas, Ismael; Girard, Lourdes; Caballero-Mellado, Jesús

    2009-01-01

    The genus Burkholderia includes pathogens of plants and animals and some human opportunistic pathogens, such as the Burkholderia cepacia complex (Bcc), but most species are nonpathogenic, plant associated, and rhizospheric or endophytic. Since rhizobacteria expressing ACC (1-aminocyclopropane-1-carboxylate) deaminase may enhance plant growth by lowering plant ethylene levels, in this work we investigated the presence of ACC deaminase activity and the acdS gene in 45 strains, most of which are...

  16. Intramolecular Aminoboration of Unfunctionalized Olefins.

    Science.gov (United States)

    Yang, Chun-Hua; Zhang, Yu-Shi; Fan, Wen-Wen; Liu, Gong-Qing; Li, Yue-Ming

    2015-10-19

    A direct and catalyst-free method for the intramolecular aminoboration of unfunctionalized olefins is reported. In the presence of BCl3 (1 equiv) as the sole boron source, intramolecular aminoboration of sulfonamide derivatives of 4-penten-1-amines, 5-hexen-1-amines, and 2-allylanilines proceeded readily without the use of any catalyst. The boronic acids obtained after hydrolysis could be converted into the corresponding pinacol borates in a straightforward manner by treatment with pinacol under anhydrous conditions. PMID:26331979

  17. Special Issue: Intramolecular Hydrogen Bonding

    Directory of Open Access Journals (Sweden)

    Ronald K. Castellano

    2014-09-01

    Full Text Available Intramolecular hydrogen bonds play critical structure- and function-serving roles in biological and synthetic molecular systems. This special issue, through eight contributions, showcases the prominence of these non-covalent interactions within several scientific disciplines, and in various structural contexts and environments. Reported, for example, are the consequences of intramolecular hydrogen bonds on the structures of molecules that show biological activity, for biological mechanisms, and for the conformational switching of functional synthetic molecules. Also showcased in the contributions are the state-of-the-art experimental and theoretical methods available for the characterization of intramolecular hydrogen bonds, which critically report on their strengths, geometries, and spectroscopic signatures in the gas, solid, and solution phases.

  18. A Clean and Selective Radical Homocoupling Employing Carboxylic Acids with Titania Photoredox Catalysis

    OpenAIRE

    Manley, David W; Walton, John C

    2014-01-01

    A titania photoredox catalysis protocol was developed for the homocoupling of C-centered radicals derived from carboxylic acids. Intermolecular reactions were generally efficient and selective, furnishing the desired dimers in good yields under mild neutral conditions. Selective cross-coupling with two acids proved unsuccessful. An intramolecular adaptation enabled macrocycles to be prepared, albeit in modest yields.

  19. Palladium(II)-Catalyzed Tandem Synthesis of Acenes Using Carboxylic Acids as Traceless Directing Groups.

    Science.gov (United States)

    Kim, Kiho; Vasu, Dhananjayan; Im, Honggu; Hong, Sungwoo

    2016-07-18

    A straightforward synthetic strategy for generating useful anthracene derivatives was developed involving palladium(II)-catalyzed tandem transformation with carboxylic acids as traceless directing groups. Carboxyl-directed C-H alkenylation, carboxyl-directed secondary C-H activation and rollover, intramolecular C-C bond formation, and decarboxylative aromatization are proposed as the key steps in the tandem reaction pathway. This novel synthetic route utilizes a broad range of substrates and provides a convenient synthetic tool that allows access to acenes. PMID:27244536

  20. 2-(Carboxymethylsulfanylpyridine-3-carboxylic acid monohydrate

    Directory of Open Access Journals (Sweden)

    Xiao-Juan Wang

    2010-06-01

    Full Text Available The title compound, C8H7NO4S·H2O, was obtained by reaction of 2-mercaptopyridine-3-carboxylic acid with chloroacetic acid. In the molecular structure, the dihedral angle between the two least-squares planes defined by the pyridine ring and the carboxy group is 8.32 (9°. The carboxymethylsulfanyl group makes a torsion angle of 82.64 (12° with the pyridine ring. An intramolecular O—H...N hydrogen bond between the acidic function of the carboxymethylsulfanyl group and the pyridine N atom stabilizes the conformation, whereas intermolecular O—H...O hydrogen bonding with the uncoordinated water molecules is responsible for packing of the structure, leading to chains propagating in [001].

  1. Symmetry of intramolecular quantum dynamics

    CERN Document Server

    Burenin, Alexander V

    2012-01-01

    The main goal of this book is to give a systematic description of intramolecular quantum dynamics on the basis of only the symmetry principles. In this respect, the book has no analogs in the world literature. The obtained models lead to a simple, purely algebraic, scheme of calculation and are rigorous in the sense that their correctness is limited only to the correct choice of symmetry of the internal dynamics. The book is basically intended for scientists working in the field of molecular spectroscopy, quantum and structural chemistry.

  2. Excited state Intramolecular Proton Transfer in Anthralin

    DEFF Research Database (Denmark)

    Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens;

    1998-01-01

    Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results in an......, associated with an excited-state intramolecular proton transfer process....

  3. Intramolecular and intermolecular hydrogen bonds in aminophenols

    International Nuclear Information System (INIS)

    IR-Fourier spectroscopy methods are adopted to study intramolecular and intermolecular hydrogen bonds that form in CCl4 solutions of aminophenol derivatives and in a solid phase of these compounds pressed in KBr. If a hydroxyl group is present in the molecule in the ortho-position to an amino group, then intramolecular interactions between OH and NH groups will take place in aminophenol solutions. Intramolecular O-HO=S=O and N-H...O=S=O hydrogen bonds are found in solutions of compounds containing a sulfonamide fragment. Additional acylation of the amino group causes an intramolecular O-H...O=C hydrogen bond to form in solutions. Functional groups OH, NH, SO2, and C=O interact with one another in various ways in the solid phase to form intermolecular hydrogen bonds in aminophenols. (authors) Keywords aminophenol - IR spectrum - intramolecular hydrogen bond - intermolecular hydrogen bond

  4. Cyclization of Free Radicals at the C-7 Position of Ethyl Indole–2-carboxylate Derivatives: an Entry to a New Class of Duocarmycin Analogues

    Directory of Open Access Journals (Sweden)

    Wasim N. Abdullah

    2005-12-01

    Full Text Available Aryl free-radicals generated at the C-7 position of ethyl indole-2-carboxylates bearing N-allyl and propargylic groups triggered intramolecular cyclizations to furnish a new class of Duocarmycin analogues, formal ethyl pyrrolo[3,2,1-ij]quinoline-2- carboxylate derivatives, through the less favorable 6-endo-trig cyclization mode.

  5. Catalytic, Conjugate Reduction-Aldol Addition Reaction of β'Oxoal kyl α, β-Unsatu rated Carboxylates%Catalytic, Conjugate Reduction-Aldol Addition Reaction of β'Oxoal kyl α, β-Unsatu rated Carboxylates

    Institute of Scientific and Technical Information of China (English)

    郑爱军; 姜岚; 李争宁

    2012-01-01

    Intramolecular conjugate reduction-aldol addition reactions of β'-oxoalkyl a,fl-unsaturated carboxylates were performed in the presence of copper catalysts generated in situ from copper salts, phosphine ligands and silanes. Moderate to good yields and high diastereoselectivities were obtained in 15 min to 3 h using bis[(2-diphenyl- phosphino)phenyl] ether as the ligand.

  6. Promotion

    OpenAIRE

    Alam, Hasan B.

    2013-01-01

    This article gives an overview of the promotion process in an academic medical center. A description of different promotional tracks, tenure and endowed chairs, and the process of submitting an application is provided. Finally, some practical advice about developing skills and attributes that can help with academic growth and promotion is dispensed.

  7. Exciton Correlations in Intramolecular Singlet Fission.

    Science.gov (United States)

    Sanders, Samuel N; Kumarasamy, Elango; Pun, Andrew B; Appavoo, Kannatassen; Steigerwald, Michael L; Campos, Luis M; Sfeir, Matthew Y

    2016-06-15

    We have synthesized a series of asymmetric pentacene-tetracene heterodimers with a variable-length conjugated bridge that undergo fast and efficient intramolecular singlet fission (iSF). These compounds have distinct singlet and triplet energies, which allow us to study the spatial dynamics of excitons during the iSF process, including the significant role of exciton correlations in promoting triplet pair generation and recombination. We demonstrate that the primary photoexcitations in conjugated dimers are delocalized singlets that enable fast and efficient iSF. However, in these asymmetric dimers, the singlet becomes more localized on the lower energy unit as the length of the bridge is increased, slowing down iSF relative to analogous symmetric dimers. We resolve the recombination kinetics of the inequivalent triplets produced via iSF, and find that they primarily decay via concerted processes. By identifying different decay channels, including delayed fluorescence via triplet-triplet annihilation, we can separate transient species corresponding to both correlated triplet pairs and uncorrelated triplets. Recombination of the triplet pair proceeds rapidly despite our experimental and theoretical demonstration that individual triplets are highly localized and unable to be transported across the conjugated linker. In this class of compounds, the rate of formation and yield of uncorrelated triplets increases with bridge length. Overall, these constrained, asymmetric systems provide a unique platform to isolate and study transient species essential for singlet fission, which are otherwise difficult to observe in symmetric dimers or condensed phases. PMID:27183040

  8. Intra-molecular refrigeration in enzymes

    CERN Document Server

    Briegel, Hans J

    2009-01-01

    We present a simple mechanism for intra-molecular refrigeration, where parts of a molecule are actively cooled below the environmental temperature. We discuss the potential role and applications of such a mechanism in biology, in particular in enzymatic reactions.

  9. Intra-molecular refrigeration in enzymes

    OpenAIRE

    Briegel, H. J.; Popescu, S.

    2013-01-01

    We present a simple mechanism for intra-molecular refrigeration, where parts of a molecule are actively cooled below the environmental temperature. We discuss the potential role and applications of such a mechanism in biology, in particular in enzymatic reactions.

  10. 1-Azaniumylcyclobutane-1-carboxylate monohydrate

    Directory of Open Access Journals (Sweden)

    Ray J. Butcher

    2014-02-01

    Full Text Available In the title compound, C5H9NO2·H2O, the amino acid is in the usual zwitterionic form involving the α-carboxylate group. The cyclobutane backbone of the amino acid is disordered over two conformations, with occupancies of 0.882 (7 and 0.118 (7. In the crystal, N—H...O and O—H...O hydrogen bonds link the zwitterions [with the water molecule involved as both acceptor (with the NH3+ and donor (through a single carboxylate O from two different aminocyclobutane carboxylate moities], resulting in a two-dimensional layered structure lying parallel to (100.

  11. Intramolecular charge separation in spirobifluorene-based donor–acceptor compounds adsorbed on Au and indium tin oxide electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Heredia, Daniel; Otero, Luis [Departamento de Química, Universidad Nacional de Río Cuarto, Río Cuarto, Agencia Postal 3, X5804BYA (Argentina); Gervaldo, Miguel, E-mail: mgervaldo@exa.unrc.edu.ar [Departamento de Química, Universidad Nacional de Río Cuarto, Río Cuarto, Agencia Postal 3, X5804BYA (Argentina); Fungo, Fernando [Departamento de Química, Universidad Nacional de Río Cuarto, Río Cuarto, Agencia Postal 3, X5804BYA (Argentina); Dittrich, Thomas [Helmholtz Centre Berlin for Materials and Energy, Berlin, Hahn-Meitner-Platz 1, D-14109 (Germany); Lin, Chih-Yen; Chi, Liang-Chen; Fang, Fu-Chuan [Department of Chemistry, National Taiwan University, Taiwan, Taipei 106, Taiwan (China); Wong, Ken-Tsung, E-mail: kenwong@ntu.edu.tw [Department of Chemistry, National Taiwan University, Taiwan, Taipei 106, Taiwan (China)

    2013-01-01

    Surface photovoltage (SPV) measurements were performed with a Kelvin-probe in spirobifluorene-based donor (diphenylamine)–acceptor (dicyano or cyanoacrylic acid moieties) compounds adsorbed from highly diluted solutions onto Au and indium tin oxide electrode surfaces. Strong intramolecular charge separation (negative SPV signals up to more than 0.1 V) due to directed molecule adsorption was observed only for spirobifluorene donor–acceptor compounds with carboxylic acid moiety. SPV signals and onset energies of electronic transitions depended on ambience conditions. - Highlights: ► Fluorene donor–acceptor derivatives were adsorbed at Au and indium tin oxide. ► Surface photovoltage measurements were performed with a Kelvin-probe. ► Strong intra-molecular charge separation was observed. ► SPV signals depended on ambience conditions.

  12. Intramolecular charge separation in spirobifluorene-based donor–acceptor compounds adsorbed on Au and indium tin oxide electrodes

    International Nuclear Information System (INIS)

    Surface photovoltage (SPV) measurements were performed with a Kelvin-probe in spirobifluorene-based donor (diphenylamine)–acceptor (dicyano or cyanoacrylic acid moieties) compounds adsorbed from highly diluted solutions onto Au and indium tin oxide electrode surfaces. Strong intramolecular charge separation (negative SPV signals up to more than 0.1 V) due to directed molecule adsorption was observed only for spirobifluorene donor–acceptor compounds with carboxylic acid moiety. SPV signals and onset energies of electronic transitions depended on ambience conditions. - Highlights: ► Fluorene donor–acceptor derivatives were adsorbed at Au and indium tin oxide. ► Surface photovoltage measurements were performed with a Kelvin-probe. ► Strong intra-molecular charge separation was observed. ► SPV signals depended on ambience conditions

  13. Studies of the Intramolecular Aromatic-ring Stacking Interactions in the Ternary Platinum(Ⅱ) Complexes

    Institute of Scientific and Technical Information of China (English)

    SUN Hong-liang

    2005-01-01

    The stability constants of some ternary mixed-ligand complexes, Pt(Phen)(CA)+, where Phen=1,10-phenanthroline and CA- =carboxylate, were determined by means of potentiometric pH titration in aqueous solutions(I=0.1 mol/L, KNO3; 25 ℃), and the stability of them was compared with that of the corresponding binary complexes. It was revealed that the ternary complexes containing phenylalkane carboxylates ligands(PCA-) are much more stable than those formed with formate and acetate. The results indicate that there exist the intramolecular aromatic-ring interactions between the phenanthroline ring of Phen and the phenyl moiety of ligand PCA- in the ternary mixed-ligand Pt(Phen)(PCA)- complexes. The extent of the stacking interactions, which depends on the number of methylene groups between the phenyl moieties and the coordinated phenylalkane carboxylate groups, was calculated. The best-fitted stack was obtained for the complexes with 2-phenylacetate and 3-phenylpropionate as the ligands.

  14. Intramolecular versus intermolecular hydrogen bonding in solution

    OpenAIRE

    Vliegenthart, J. F. G.; Kroon, Jan; Kroon-Batenburg, L.M.J.; Leeflang, B.R.

    1994-01-01

    The balance between intra- and intermolecular hydrogen bonding is studied for a solution of methyl beta-cellobioside in water and dimethylsulfoxide by 1H NMR and molecular dynamics simulations. In water O(3) predominantly interacts with water molecules, whereas in dimethylsulfoxide it is intramolecularly hydrogen bonded to O(5Œ). The temperature coefficient of the chemical shift of the hydroxy groups appears to be a reliable indicator of intermolecular hydrogen-bond formation, whereas the ex...

  15. EFFECT OF CARBOXYLIC IONOPHOROUS ANTIBACTERIALS ON THE GROWTH OF SELECTED MICROALGAE

    Science.gov (United States)

    Carboxylic ionophorous antibiotics are routinely used in cattle, chicken and turkey concentrated feedlot operations as anticoccidial and growth promotant feed additives and may, through runoff and effluents, enter adjacent waterways. The effects of these compounds on the growth o...

  16. Carboxyl group reactivity in actin

    International Nuclear Information System (INIS)

    While earlier work showed that the carboxyl groups of proteins could be quantitatively coupled to amino groups at pH 4.75 in the presence of EDC and a denaturing agent, the work presented here indicates that under milder conditions the modification of sidechain carboxyls is limited and somewhat specific. Most of the incorporated glycine ethyl ester (GEE) is apparently bound to five carboxyls. The total GEE incorporated was 3 to 4 moles/mole of protein as measured by an increase in Gly upon acid hydrolysis and amino acid analysis, as well as total radioactivity. 3.55 residues were found in peptides, 2.75 bound to residues 1 to 4, and 0.8 bound to Gly-100. 9 refs., 2 figs., 2 tabs

  17. Mixed Intramolecular Hydrogen Bonding in Dihydroxythiophene-based Units and Boron and Technetium Chelation

    International Nuclear Information System (INIS)

    Three novel potential metal ion chelating units have been synthesized and characterized: 5-hexylcarbamoyl- 3,4-dihydroxythiophene-2-carboxylic acid methyl ester (5), 3-benzyloxy-4-hydroxythiophene-2,5-dicarboxylic acid bis-hexylamide (6), and 3,4-dihydroxythiophene-2,5-dicarboxylic acid bis-hexylamide (7). The crystal structure of 6 was obtained and suggests the presence of three distinct intramolecular hydrogen bonds, namely [Namide-H···O] [O-H···Oamide] and [Namide-H···S]. Boron chelation with 5, 6 and 7 through the use of BF3, B(OH)3 or B(OMe)3 was probed by 1H, 11B, and 13C NMR spectroscopy. Technetium (I) chelation with 5, 6 and 7 was also studied via HPLC elutions using [99mTc(CO)3(OH2)3]+

  18. Computational design of effective, bioinspired HOCl antioxidants: the role of intramolecular Cl+ and H+ shifts.

    Science.gov (United States)

    Karton, Amir; O'Reilly, Robert J; Pattison, David I; Davies, Michael J; Radom, Leo

    2012-11-21

    The enzyme myeloperoxidase generates significant amounts of hypochlorous acid (HOCl) at sites of inflammation to inflict oxidative damage upon invading pathogens. However, excessive production of this potent oxidant is associated with numerous inflammatory diseases. Recent kinetic measurements suggest that the endogenous antioxidant carnosine is an effective HOCl scavenger. On the basis of computational modeling, we suggest a possible mechanism for this antioxidant activity. We find that a unique structural relationship between three adjacent functional groups (imidazole, carboxylic acid, and terminal amine) enables an intramolecular chlorine transfer to occur. In particular, two sequential proton shifts are coupled with a Cl(+) shift converting the kinetically favored product (chlorinated at the imidazole nitrogen) into the thermodynamically favored product (chlorinated at the terminal amine) effectively trapping the chlorine. We proceed to design systems that share similar structural features to those of carnosine but with even greater HOCl-scavenging capabilities. PMID:23148773

  19. Secondary isotope effects in intramolecular catalysis. Mono-p-bromophenyl succinate hydrolysis

    Energy Technology Data Exchange (ETDEWEB)

    Gandour, R.D.; Stella, V.J.; Coyne, M.; Schowen, R.L.; Icaza, E.A.

    1978-04-28

    Kinetic isotope effects have been measured for the intramolecular nucleophilic carboxylate-catalyzed hydrolysis, k/sub s/, of mono-p-bromophenyl succinate and mono-p-bromophenyl succinate-d/sub 4/. The resulting isotope effect, k/sub s//sup h/sub 4///k/sub s//sup d/sub 4//, equals 1.035, a normal effect. This is contrary to what is expected for acyl transfer reactions where the transition-state structure resembles a tetrahedral intermediate. However, the direction of the isotope effect is in agreement with a transition-state structure resembling succinic anhydride. Combining this result with previous kinetic and structural studies, a detailed transition-state structure for the hydrolysis reaction is proposed. 31 references, 2 tables.

  20. On combinatorial properties of elementary intramolecular operations

    Directory of Open Access Journals (Sweden)

    Vladimir Rogojin

    2014-11-01

    Full Text Available Here we tackle a problem from biology in terms of discrete mathematics. We are interested in a complex DNA manipulation process happening in eukaryotic organisms of a subclass of ciliate species called {\\it Stichotrichia} during so-called gene assembly. This process is in particular interesting since one can interpret gene assembly in ciliates as sorting of permutations. We survey here results related to studies on sorting permutations with some specific rewriting rules that formalize elementary intramolecular gene assembly operations. The research question is ``what permutation may be sorted with our operations?"

  1. Femtosecond laser studies of ultrafast intramolecular processes

    Energy Technology Data Exchange (ETDEWEB)

    Hayden, C. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    The goal of this research is to better understand the detailed mechanisms of chemical reactions by observing, directly in time, the dynamics of fundamental chemical processes. In this work femtosecond laser pulses are used to initiate chemical processes and follow the progress of these processes in time. The authors are currently studying ultrafast internal conversion and subsequent intramolecular relaxation in unsaturated hydrocarbons. In addition, the authors are developing nonlinear optical techniques to prepare and monitor the time evolution of specific vibrational motions in ground electronic state molecules.

  2. (19)F NMR study of ligand dynamics in carboxylate-bridged diiron(II) complexes supported by a macrocyclic ligand.

    Science.gov (United States)

    Minier, Mikael A; Lippard, Stephen J

    2015-11-01

    A series of asymmetrically carboxylate-bridged diiron(ii) complexes featuring fluorine atoms as NMR spectroscopic probes, [Fe2(PIM)(Ar(4F-Ph)CO2)2] (10), [Fe2(F2PIM)(Ar(Tol)CO2)2] (11), and [Fe2(F2PIM)(Ar(4F-Ph)CO2)2] (12), were prepared and characterized by X-ray crystallography, Mössbauer spectroscopy, and VT (19)F NMR spectroscopy. These complexes are part of a rare family of syn N-donor diiron(ii) compounds, [Fe2(X2PIM)(RCO2)2], that are structurally very similar to the active site of the hydroxylase enzyme component of reduced methane monooxygenase (MMOHred). Solution characterization of these complexes demonstrates that they undergo intramolecular carboxylate rearrangements, or carboxylate shifts, a dynamic feature relevant to the reactivity of the diiron centers in bacterial multicomponent monooxygenases. PMID:26418547

  3. 19F NMR Study of Ligand Dynamics in Carboxylate-Bridged Diiron(II) Complexes Supported by a Macrocyclic Ligand

    Science.gov (United States)

    Minier, Mikael A.; Lippard, Stephen J.

    2015-01-01

    A series of asymmetrically carboxylate-bridged diiron(II) complexes featuring fluorine atoms as NMR spectroscopic probes, [Fe2(PIM)(Ar4F-PhCO2)2] (10), [Fe2(F2PIM)(ArTolCO2)2] (11), and [Fe2(F2PIM)(Ar4F-PhCO2)2] (12), were prepared and characterized by X-ray crystallography, Mössbauer spectroscopy, and VT 19F NMR spectroscopy. These complexes are part of a rare family of syn-N diiron(II) complexes, [Fe2(X2PIM)(RCO2)2], that are structurally very similar to the active site of the hydroxylase enzyme component of reduced methane monooxygenase (MMOHred). Solution characterization of these complexes demonstrates that they undergo intramolecular carboxylate rearrangements, or carboxylate shifts, a dynamic feature relevant to the reactivity of the diiron centers in bacterial multicomponent monooxygenases. PMID:26418547

  4. Synthesis and Characterization of Manganese Carboxylates

    OpenAIRE

    Maryudi; R.M. Yunus; A.H. Nour; M.H. Abidin

    2009-01-01

    The explorations of prodegradant additives for plastics from trans-metals organic salts have been being conducted. This study reports a method of synthesis of manganese carboxylates and their characterization. The new method involves reaction between molten carboxylic acid with sodium hydroxide in alcoholic solution to produce sodium carboxylate and continued by reacting sodium carboxylate with chloride salt of manganese. First reaction and second reaction were conducted at 80-85°C and under ...

  5. Rapid Synthesis of Size-controlled Gold Nanoparticles by Complex Intramolecular Photoreduction

    Institute of Scientific and Technical Information of China (English)

    DONG Shou-an; YANG Sheng-chun; TANG Chun

    2007-01-01

    A rapid synthesis of size-controlled gold nanoparticles was proposed. The method is based on the sensitive intramolecular photoreduction reaction of Fe( Ⅲ )-EDTA complex in chloroacetic acid-sodium acetate buffer solution,where Fe(Ⅱ)-EDTA complex generated by photo-promotion acts as a reductant of AuCl4- ions. Gold nanoparticles formed were stabilized by EDTA ligand or other protective agents added. As a result, well-dispersed gold nanoparticles with an average diameter range of 6.7 to 50. 9 nm were obtained. According to the characterizations by the UV spectrum and TEM, the intramolecular charge transfer of the excited states of complex Fe(Ⅲ) -EDTA and the mechanism of forming gold nanoparticles were discussed in detail.

  6. Regulation of interleukin-4 signaling by extracellular reduction of intramolecular disulfides

    International Nuclear Information System (INIS)

    Interleukin-4 (IL-4) contains three structurally important intramolecular disulfides that are required for the bioactivity of the cytokine. We show that the cell surface of HeLa cells and endotoxin-activated monocytes can reduce IL-4 intramolecular disulfides in the extracellular space and inhibit binding of IL-4 to the IL-4Rα receptor. IL-4 disulfides were in vitro reduced by thioredoxin 1 (Trx1) and protein disulfide isomerase (PDI). Reduction of IL-4 disulfides by the cell surface of HeLa cells was inhibited by auranofin, an inhibitor of thioredoxin reductase that is an electron donor to both Trx1 and PDI. Both Trx1 and PDI have been shown to be located at the cell surface and our data suggests that these enzymes are involved in catalyzing reduction of IL-4 disulfides. The pro-drug N-acetylcysteine (NAC) that promotes T-helper type 1 responses was also shown to mediate the reduction of IL-4 disulfides. Our data provides evidence for a novel redox dependent pathway for regulation of cytokine activity by extracellular reduction of intramolecular disulfides at the cell surface by members of the thioredoxin enzyme family.

  7. Four-component synthesis of 1,3,4-oxadiazole derivatives from N-isocyaniminotriphenylphosphorane, aromatic carboxylic acids, aromatic bis-aldehydes, and secondary amines

    OpenAIRE

    Ramazani, Ali; Karimi, Zahra; SOULDOZI, Ali; AHMADI, Yavar

    2012-01-01

    The 1:1 iminium intermediate generated by the addition of a secondary amine to aromatic bis-aldehydes (isophthalaldehyde and terphthalaldehyde) is trapped by the N-isocyaniminotriphenylphosphorane in the presence of a aromatic carboxylic acid derivative, which leads to the formation of corresponding iminophosphorane intermediate. Then disubstituted 1,3,4-oxadiazole derivatives are formed via intramolecular aza-Wittig reaction of the iminophosphorane intermediates. The reactions were ...

  8. Structure Property Relationships of Carboxylic Acid Isosteres.

    Science.gov (United States)

    Lassalas, Pierrik; Gay, Bryant; Lasfargeas, Caroline; James, Michael J; Tran, Van; Vijayendran, Krishna G; Brunden, Kurt R; Kozlowski, Marisa C; Thomas, Craig J; Smith, Amos B; Huryn, Donna M; Ballatore, Carlo

    2016-04-14

    The replacement of a carboxylic acid with a surrogate structure, or (bio)-isostere, is a classical strategy in medicinal chemistry. The general underlying principle is that by maintaining the features of the carboxylic acid critical for biological activity, but appropriately modifying the physicochemical properties, improved analogs may result. In this context, a systematic assessment of the physicochemical properties of carboxylic acid isosteres would be desirable to enable more informed decisions of potential replacements to be used for analog design. Herein we report the structure-property relationships (SPR) of 35 phenylpropionic acid derivatives, in which the carboxylic acid moiety is replaced with a series of known isosteres. The data set generated provides an assessment of the relative impact on the physicochemical properties that these replacements may have compared to the carboxylic acid analog. As such, this study presents a framework for how to rationally apply isosteric replacements of the carboxylic acid functional group. PMID:26967507

  9. Modeling and computations of the intramolecular electron transfer process in the two-heme protein cytochrome c4

    DEFF Research Database (Denmark)

    Natzmutdinov, Renat R.; Bronshtein, Michael D.; Zinkicheva, Tamara T.;

    2012-01-01

    performed computational modeling of the intramolecular ET process by a combination of density functional theory (DFT) and quantum mechanical charge transfer theory to disclose reasons for this difference. We first address the electronic structures of the model heme core with histidine and methionine axial...... ligands in both low- and high-spin states by structure-optimized DFT. The computations enable estimating the intramolecular reorganization energy of the ET process for different combinations of low- and high-spin heme couples. Environmental reorganization free energies, work terms (‘‘gating’’) and driving......–Fe separations. The reactivity of low- and high-spin heme groups was notably different. The ET rate is exceedingly low for the crystallographic equilibrium orientation but increases by several orders of magnitude for thermally accessible non-equilibrium configurations. Deprotonation of the propionate carboxyl...

  10. Complicated Composting: Persistent Pyridine Carboxylic Acid Herbicides

    OpenAIRE

    Reimer, Julie

    2013-01-01

    This paper reviews pyridine carboxylic acid herbicide impacts on compost. Pyridine carboxylic acid herbicides are not completely broken down during grass growth, harvest and drying of hay, in the digestive tract of livestock, or during composting. These herbicides are a popular choice for broadleaf weed control because of this persistence: they remain effective for months or years. Pyridine carboxylic acids are also more effective than the common herbicide 2, 4-dichlorophenoxyacetic acid and ...

  11. Temperature dependence of turnover in a Sc(OTf)3-catalyzed intramolecular Schmidt reaction

    Science.gov (United States)

    Fehl, Charlie; Hirt, Erin E.; Li, Sze-Wan; Aubé, Jeffrey

    2015-01-01

    The intramolecular Schmidt reaction of ketones and tethered azides is an efficient method for the generation of amides and lactams. This reaction is catalyzed by Lewis acids, which tightly bind the strongly basic amide product and result in product inhibition. We report herein conditions to achieve a catalytic Schmidt reaction using substoichiometric amounts of the heat-stable Lewis acid Sc(OTf)3. This species was shown to effectively release products of the Schmidt reaction in a temperature-dependent fashion. Thus, heat was able to promote catalyst turnover. A brief substrate scope was conducted using these conditions. PMID:26085693

  12. Synchronous intramolecular cycloadditions of the polyene macrolactam polyketide heronamide C.

    Science.gov (United States)

    Booth, Thomas J; Alt, Silke; Capon, Robert J; Wilkinson, Barrie

    2016-05-11

    A growing number of natural products appear to arise from biosynthetic pathways that involve pericyclic reactions. We show here that for the heronamides this can occur via two spontaneous pathways involving alternative thermal or photochemical intramolecular cycloadditions. PMID:27091090

  13. Intramolecular hydrogen bonds in sulfur-containing aminophenols

    Science.gov (United States)

    Belkov, M. V.; Harbachova, A. N.; Ksendzova, G. A.; Polozov, G. I.; Skornyakov, I. V.; Sorokin, V. L.; Tolstorozhev, G. B.; Shadyro, O. I.

    2010-07-01

    IR Fourier spectroscopy methods have been adopted to study intramolecular interactions that occur in CCl4 solutions of antiviral derivatives of aminophenol. Analysis of the IR spectra showed that intramolecular bonds O-H···N, O-H···O=C, N-H···O=S=O, and O-H···O=S=O can occur in these compounds depending on the substituent on the amino group. Not only the presence of intramolecular O-H···N, O-H···O=S=O, and N- H···O=S=O hydrogen bonds in 2-amino-4,6-di-tert-butylphenol derivatives containing a sulfonamide fragment but also conformational equilibrium among these types of intramolecular interactions are essential for the manifestation of high efficiency in suppressing HIV-infection in cell culture.

  14. Keto-Enol Tautomerizations Catalyzed by Water and Carboxylic Acids

    Science.gov (United States)

    da Silva, G.

    2009-12-01

    The ability of weakly-bound complexes to influence the kinetics of gas phase reactions, particularly in atmospheric chemistry, has long been speculated. This study uses quantum chemistry and statistical reaction rate theory to identify that bound water molecules can significantly reduce barriers to intramolecular hydrogen shift reactions, via a double-hydrogen-shift mechanism. The bound water molecule directly participates in the hydrogen shift reaction, exchanging a H atom with its counterpart. For the vinyl alcohol to acetaldehyde keto-enol tautomerization this mechanism cuts the reaction barrier approximately in half, reducing it by over 30 kcal mol-1. In contrast, while a non-participatory ‘bystander’ water molecule also reduces the hydrogen shift barrier, it is only by around 3 kcal/mol. When a carboxylic acid replaces water in the double-hydrogen-shift mechanism the barrier to keto-enol tautomerization is decimated, reduced to less than 6 kcal/mol (around 15 kcal/mol in the reverse direction). This results from reduced strain in the hydrogen shift transition state, and achieves enol lifetimes in the troposphere that become short on relevant timescales. Rapid enol to ketone isomerizations are currently required to explain the oxidation products of isoprene. The wider significance of rapid hydrogen shift reactions in atmospherically relevant molecules and radicals is also explored.

  15. Biogeochemistry of the stable carbon isotopes in carboxylic acids

    International Nuclear Information System (INIS)

    The carbon isotopic compositions of the carboxyl carbons of fatty acids were determined by measuring the isotopic composition of the carbon dioxide quantitatively released from the acid. A modified version of the Schmidt decarboxylation developed and tested in this work was employed. A study of the evolution of CO2 at 5 +- 20C from the Schmidt decarboxylation of octanoic acid during the developmental program revealed two kinetic phases, each characterized by different rate constants and carbon isotope effects. The first, slower reaction phase displayed overall first-order kinetics, its rate being independent of HN3 concentration. Both pre-equilibration of the HN3-CHCl3 decarboxylation reagent with H2SO4 and saturation of the catalytic H2SO4 phase with KHSO4 drastically altered the rate of evolution and isotopic composition of the product CO2. The mechanistic implications of these results were discussed. A review of the metabolism of saturated fatty acids was made in which the impact of potential isotope fractionations in the various chemical reactions comprising the biosynthetic pathways on the intramolecular carbon isotope distribution within fatty acids was discussed

  16. Online Measurement of the Intramolecular Isotopic Composition of Acetate in Natural Porewater Samples

    Science.gov (United States)

    Thomas, R. B.; Arthur, M. A.; Freeman, K. H.

    2006-12-01

    Carbon dioxide and methane are traditionally considered to be the dominant end products of anaerobic metabolism while acetate is thought to be a rapidly consumed intermediate. However, in some settings, recent evidence has grown to suggest that, at least transiently, acetate can be a major metabolic end product. In natural systems, isotopic mass balances can be used to partition the flow of carbon to methane, CO2, and acetate. However, these isotopic estimates require intramolecular measurements of acetate in addition to isotopic measurements of the gaseous species, CO2 and CH4. In practice, the intramolecular isotopic composition of acetate is rarely measured because the analysis is technically challenging and traditionally requires prior separation and offline pyrolysis of purified acetate. As a result of these technical challenges, acetate methyl carbon is usually assumed to be a few permil depleted relative to the carbon isotopic composition of bulk organic matter. In environments where acetate may be produced by autotrophic acetogens this assumption can be devastatingly false. This work describes the use of an online method for the analysis of the intramolecular carbon isotopic composition of dissolved acetate from dilute surface water samples with a detection limit of injected sample down to 500uM. Preconcentration of samples via lyophilization has resulted in detection limits as low as 30uM. In 2002, at Penn State, Dias et al. (Organic Geochemistry Vol. 33, p161-168) reported a technique to examine the intramolecular isotopic composition of acetate from oil-prone source rocks using SPME extraction with an online GC-pyrolysis-IRMS. We have adapted the Dias method to be used with direct injection of dilute natural water samples. Briefly, this procedure protonates acetate with a .1M addition of oxalic acid and vaporizes the sample in the GC inlet at low temperatures. This prevents oxalic acid decomposition and provides sufficient separation of acetate from

  17. Gallium(III)- and calcium(II)-catalyzed Meyer-Schuster rearrangements followed by intramolecular aldol condensation or endo-Michael addition.

    Science.gov (United States)

    Presset, M; Michelet, B; Guillot, R; Bour, C; Bezzenine-Lafollée, S; Gandon, V

    2015-03-28

    The first gallium- and calcium-catalyzed Meyer-Schuster rearrangements are described. Under substrate control, the incipient conjugated ketones can be trapped intramolecularly by β-keto esters or amides to yield cyclic products after aldol condensation or endo-Michael addition. An interesting additive effect that promotes the latter tandem process with calcium has been found. PMID:25503868

  18. Carboxylation and anaplerosis in neurons and glia.

    Science.gov (United States)

    Hassel, B

    2000-01-01

    Anaplerosis, or de novo formation of intermediates of the tricarboxylic acid (TCA) cycle, compensates for losses of TCA cycle intermediates, especially alpha-ketoglutarate, from brain cells. Loss of alpha-ketoglutarate occurs through release of glutamate and GABA from neurons and through export of glutamine from glia, because these amino acids are alpha-ketoglutarate derivatives. Anaplerosis in the brain may involve four different carboxylating enzymes: malic enzyme, phosphoenopyruvate carboxykinase (PEPCK), propionyl-CoA carboxylase, and pyruvate carboxylase. Anaplerotic carboxylation was for many years thought to occur only in glia through pyruvate carboxylase; therefore, loss of transmitter glutamate and GABA from neurons was thought to be compensated by uptake of glutamine from glia. Recently, however, anaplerotic pyruvate carboxylation was demonstrated in glutamatergic neurons, meaning that these neurons to some extent can maintain transmitter synthesis independently of glutamine. Malic enzyme, which may carboxylate pyruvate, was recently detected in neurons. The available data suggest that neuronal and glial pyruvate carboxylation could operate at as much as 30% and 40-60% of the TCA cycle rate, respectively. Cerebral carboxylation reactions are probably balanced by decarboxylation reactions,, because cerebral CO2 formation equals O2 consumption. The finding of pyruvate carboxylation in neurons entails a major revision of the concept of the glutamine cycle. PMID:11414279

  19. Catalytic ozonation not relying on hydroxyl radical oxidation: A selective and competitive reaction process related to metal-carboxylate complexes

    KAUST Repository

    Zhang, Tao

    2014-01-01

    Catalytic ozonation following non-hydroxyl radical pathway is an important technique not only to degrade refractory carboxylic-containing organic compounds/matter but also to avoid catalyst deactivation caused by metal-carboxylate complexation. It is unknown whether this process is effective for all carboxylates or selective to special molecule structures. In this work, the selectivity was confirmed using O3/(CuO/CeO2) and six distinct ozone-resistant probe carboxylates (i.e., acetate, citrate, malonate, oxalate, pyruvate and succinate). Among these probe compounds, pyruvate, oxalate, and citrate were readily degraded following the rate order of oxalate>citrate>pyruvate, while the degradation of acetate, malonate, and succinate was not promoted. The selectivity was independent on carboxylate group number of the probe compounds and solution pH. Competitive degradation was observed for carboxylate mixtures following the preference order of citrate, oxalate, and finally pyruvate. The competitive degradation was ascribed to competitive adsorption on the catalyst surface. It was revealed that the catalytically degradable compounds formed bidentate chelating or bridging complexes with surface copper sites of the catalyst, i.e., the active sites. The catalytically undegradable carboxylates formed monodentate complexes with surface copper sites or just electrostatically adsorbed on the catalyst surface. The selectivity, relying on the structure of surface metal-carboxylate complex, should be considered in the design of catalytic ozonation process. © 2013 Elsevier B.V.

  20. Human ceruloplasmin. Intramolecular electron transfer kinetics and equilibration

    DEFF Research Database (Denmark)

    Farver, O; Bendahl, L; Skov, L K;

    1999-01-01

    Pulse radiolytic reduction of disulfide bridges in ceruloplasmin yielding RSSR(-) radicals induces a cascade of intramolecular electron transfer (ET) processes. Based on the three-dimensional structure of ceruloplasmin identification of individual kinetically active disulfide groups and type 1 (T1...... with a rate constant of 3.9 +/- 0.8. No reoxidation of T1B Cu(I) could be resolved. It appears that the third T1 center (T1C of domain 2) is not participating in intramolecular ET, as it seems to be in a reduced state in the resting enzyme....

  1. Intramolecular vibrational dynamical barrier due to extremely irrational couplings

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The intramolecular vibrational dynamics due to extremely irrational couplings is demonstrated by contrast to the resonance couplings, for the three-mode case of H2O as an example. The extremely irrational couplings are shown to impose such strong hindrance to intramolecular vibrational relaxation (IVR) that they act as barriers. They restrict the direct action/energy transfer between the two stretching modes, though they allow the transfer between a stretching and a bending modes. In contrast, the resonance is more mediated by the bending mode and leads to chaotic IVR. It is also shown that there is a region in the dynamical space in which resonance and extremely irrational couplings coexist.

  2. Intramolecular Amide Hydrolysis in N-Methylmaleamic Acid Revisited

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The intramolecular amide hydrolysis of N-methylmaleamic acid have been revisited by use of density functional theory and inclusion of solvent effects. The results indicate that concerted reaction mechanism is favored over stepwise reaction mechanism. This is in agreement with the previous theoretical study. Sovlent effects have significant influence on the reaction barrier.

  3. Substituent effects on intramolecular hydrogen bonds in 5-nitrosopyrimidine derivates

    Czech Academy of Sciences Publication Activity Database

    Procházková, Eliška; Čechová, Lucie; Janeba, Zlatko; Dračínský, Martin

    Praha : -, 2013. s. 149-149. [ESOR 2013. European Symposium on Organic Reactivity /14./. 01.09.2013-06.09.2013, Praha] R&D Projects: GA ČR GA13-24880S Institutional support: RVO:61388963 Keywords : NMR spectroscopy * intramolecular hydrogen bonds * 5-nitrosopyrimidine derivates * DFT calculations * UV/ VIS spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry

  4. Mechanisms of intramolecular communication in a hyperthermophilic acylaminoacyl peptidase

    DEFF Research Database (Denmark)

    Papaleo, Elena; Renzetti, Giulia; Tiberti, Matteo

    2012-01-01

    Protein dynamics and the underlying networks of intramolecular interactions and communicating residues within the three-dimensional (3D) structure are known to influence protein function and stability, as well as to modulate conformational changes and allostery. Acylaminoacyl peptidase (AAP) subf...

  5. Silver-catalysed intramolecular hydroamination of alkynes with trichloroacetimidates.

    Science.gov (United States)

    Wong, Valerie H L; Hor, T S Andy; Hii, King Kuok Mimi

    2013-10-18

    Silver(I) complexes catalyse the intramolecular addition of trichloroacetimidates to alkynes. In the absence of a ligand, the selectivity of the reaction is dependent upon the nature of the counter-anion and solvent. The introduction of non-chelating nitrogeneous ligands suppresses competitive Brønsted acid catalysis, improving the yield and selectivity of the reaction. PMID:23999555

  6. EPOXY RESINS TOUGHENED WITH CARBOXYL TERMINATED POLYETHERS

    Institute of Scientific and Technical Information of China (English)

    YU Yunchao; LI Yiming

    1983-01-01

    Carboxyl terminated polyethers, the adducts of hydroxyl terminated polytetrahydrofuran and maleic anhydride, were used as toughener for epoxy resins. The morphology of the toughened resins was investigated by means of turbidity measurement, dynamic mechanical testing and scanning electron microscope observation. It turned out that the molecular weight and the carboxyl content of the polyether and the cure conditions are important factors, which affect the particle size of the polyether-rich domains and, in turn, the mechanical properties of the cured resin. Carboxyl terminated polytetrahydrofurans have a low glass transition temperature, and in appropriate amount they do not affect the thermal resistance of the resin. These advantages make them preferable as toughener for epoxy resins.

  7. Novel Polymers with Carboxylic Acid Loading

    DEFF Research Database (Denmark)

    Thomsen, Anders Daugaard; Malmström, Eva; Hvilsted, Søren

    2006-01-01

    Click chemistry has been used to prepare a range of novel polymers with pendant carboxylic acid side groups. Four azido carboxylic acids, either mono- or difunctional and aliphatic or aromatic, have been prepared and thoroughly characterized. Extensive model reactions with 1-ethyl-4-hydroxybenzene......, the simplest model for poly(4-hydroxystyrene), and the four azido carboxylic acids have been conducted to establish the proper reaction conditions and provide an analytical frame for the corresponding polymers. Poly(4-hydroxystyrene) moieties in three different polymers—poly(4-hydroxystyrene), poly(4...... the polymers in general exhibit [when poly(4-hydroxystyrene) is a substantial part] significant changes in the glass-transition temperature from the polar poly(4-hydroxystyrene) (120–130 °C) to the much less polar alkyne polymers (46–60 °C). A direct correlation between the nature of the pendant groups...

  8. Hygroscopic Characteristics of Alkylaminium Carboxylate Aerosols.

    Science.gov (United States)

    Gomez-Hernandez, Mario; McKeown, Megan; Secrest, Jeremiah; Marrero-Ortiz, Wilmarie; Lavi, Avi; Rudich, Yinon; Collins, Don R; Zhang, Renyi

    2016-03-01

    The hygroscopic growth factor (HGF) and cloud condensation nuclei (CCN) activity for a series of alkylaminium carboxylate aerosols have been measured using a hygroscopicity tandem differential mobility analyzer coupled to a condensation particle counter and a CCN counter. The particles, consisting of the mixtures of mono- (acetic, propanoic, p-toluic, and cis-pinonic acid) and dicarboxylic (oxalic, succinic, malic, adipic, and azelaic acid) acid with alkylamine (mono-, di-, and trimethylamines), represent those commonly found under diverse environmental conditions. The hygroscopicity parameter (κ) of the alkylaminium carboxylate aerosols was derived from the HGF and CCN results and theoretically calculated. The HGF at 90% RH is in the range of 1.3 to 1.8 for alkylaminium monocarboxylates and 1.1 to 2.2 for alkylaminium dicarboxylates, dependent on the molecular functionality (i.e., the carboxylic or OH functional group in organic acids and methyl substitution in alkylamines). The κ value for all alkylaminium carboxylates is in the range of 0.06-1.37 derived from the HGF measurements at 90% RH, 0.05-0.49 derived from the CCN measurements, and 0.22-0.66 theoretically calculated. The measured hygroscopicity of the alkylaminium carboxylates increases with decreasing acid to base ratio. The deliquescence point is apparent for several of the alkylaminium dicarboxylates but not for the alkylaminium monocarboxylates. Our results reveal that alkylaminium carboxylate aerosols exhibit distinct hygroscopic and deliquescent characteristics that are dependent on their molecular functionality, hence regulating their impacts on human health, air quality, and direct and indirect radiative forcing on climate. PMID:26794419

  9. Radiolytically generated cation radicals and their intramolecular transformations

    International Nuclear Information System (INIS)

    Recent theoretical and experimental results indicate that conventional cation radicals derived directly from their neutral precursors are often less stable than their nonconventional isomers with no stable counterparts. Many organic cation radicals may spontaneously isomerise, often by a single intramolecular hydrogen transfer, to more stable distonic forms characterised by spatially separated charge and radical side. Cation radicals radiolytically generated in Freon matrices were investigated using low temperature EPR spectroscopy and DFT quantum chemical calculations, which helped to assign the observed transients and to explain the underlying transformations. Different types of transformations of the cation radicals were comprehensively studied. The primary cation radicals of the 2,5-dihydrofuran (2,5-DHF) and 2,5-dihydropyrrol (2,5-DHP) are not stable and undergo irreversible transformation to 2,4-DHF.+ or 2,4-DHP.+, respectively, by intramolecular H-shift within the molecular ring to the former double bond. The 2,4-DHF.+ and 2,4-DHP.+ are stable only at a small temperature range and undergo further intramolecular rearrangements through 2→3 and 3→4 H-shifts, which can be induced by illumination with visible light. In case of lactone cation radicals intramolecular H-transfer occurs from the methylene group in α-position to the primary radical centre localized on carbonyl oxygen. The stability of the primary species depends on geometrical parameters of the lactones studied. The cation radicals of 5-membered ring lactones are most stable, due to the largest separation between the H-atom on the ring and the carbonyl oxygen and, as follows, the largest activation energy. The formation of two new cyclic species was observed in the case of the cation radical of ethyl acrylate (EA), in a reaction sequence of hydrogen transfer from the ester group to the carbonyl oxygen and subsequent intramolecular cycloaddition of the terminal radical to the vinyl double bond

  10. Mass spectrometric behaviour of carboxylated polyethylene glycols and carboxylated octylphenol ethoxylates.

    Science.gov (United States)

    Frańska, Magdalena; Zgoła, Agnieszka; Rychłowska, Joanna; Szymański, Andrzej; Łukaszewski, Zenon; Frański, Rafał

    2003-01-01

    Mass spectrometric behaviour of mono- and di-carboxylated polyethylene glycols (PEGCs and CPEGCs) and carboxylated octylphenol ethoxylates (OPECs) are discussed. The tendency for ionisation (deprotonation, protonation and cationisation by alkali metal cations) of carboxylated PEGs was compared with that of non-carboxylated correspondents by using both secondary ion mass spectrometry (SIMS) and electrospray ionisation (ESI). The fragmentation of the PEGCs and CPEGCs is discussed and also compared with their neutral correspondents, PEGs. The B/E mass spectra were recorded, using secondary ion mass spectrometry as a method for generation, for deprotonated and protonated molecules and molecules cationised by alkali metal cations. The fragmentation behaviour of PEGs is found to be different from that of CPEGCs, The presence of carboxylic groups may be confirmed not only by the determination of molecular weights of the ethoxylates studied, but also on the basis of the fragment ions formed. The metastable decomposition of the [OPEC-H](-) ions proceed through the cleavage of the bond between the octylphenol moiety and the ethoxylene chain leading to the octylphenoxy anions. It permits determination of the mass of the hydrophobic moiety of the studied carboxylated alkylphenol ethoxylate. ESI mass spectra recorded in the negative ion mode were found to be more suitable for the determination of the average molecular weight of carboxylated ethoxylates than SI mass spectra. PMID:12939494

  11. Photophysics of indole-2-carboxylic acid (I2C) and indole-5-carboxylic acid (I5C): heavy atom effect.

    Science.gov (United States)

    Kowalska-Baron, Agnieszka; Gałęcki, Krystian; Wysocki, Stanisław

    2013-12-01

    In this study the effect of carboxylic group substitution in the 2 and 5 position of indole ring on the photophysics of the parent indole chromophore has been studied. The photophysical parameters crucial in triplet state decay mechanism of aqueous indole-2-carboxylic acid (I2C) and indole-5-carboxylic acid (I5C) have been determined applying our previously proposed methodology based on the heavy atom effect and fluorescence and phosphorescence decay kinetics [Kowalska-Baron et al., 2012]. The determined time-resolved phosphorescence spectra of I2C and I5C are red-shifted as compared to that of the parent indole. This red-shift was especially evident in the case of I2C and may indicate the possibility of hydrogen bonded complex formation incorporating carbonyl CO, the NH group of I2C and, possibly, surrounding water molecules. The possibility of the excited state charge transfer process and the subsequent electronic charge redistribution in such a hydrogen bonded complex may also be postulated. The resulting stabilization of the I2C triplet state is manifested by its relatively long phosphorescence lifetime in aqueous solution (912 μs). The relatively short phosphorescence lifetime of I5C (56 μs) may be the consequence of more effective ground-state quenching of I5 C triplet state. This hypothesis may be strengthened by the significantly larger value of the determined rate constant of I5C triplet state quenching by its ground-state (4.4 × 10(8)M(-1)s(-1)) as compared to that for indole (6.8 × 10(7)M(-1)s(-1)) and I2C (2.3 × 10(7)M(-1)s(-1)). The determined bimolecular rate constant for triplet state quenching by iodide [Formula: see text] is equal to 1 × 10(4)M(-1)s(-1); 6 × 10(3)M(-1)s(-1) and 2.7 × 10(4)M(-1)s(-1) for indole, I2 C and I5 C, respectively. In order to obtain a better insight into iodide quenching of I2C and I5C triplet states in aqueous solution, the temperature dependence of the bimolecular rate constants for iodide quenching of the

  12. Carbon isotopic fractionation in the biosynthesis of bacterial fatty acids. Ozonolysis of unsaturated fatty acids as a means of determining the intramolecular distribution of carbon isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Monson, K.D.; Hayes, J.M. (Indiana Univ., Bloomington (USA). Dept. of Chemistry; Indiana Univ., Bloomington (USA). Dept. of Geology)

    1982-02-01

    Methods for the determination of /sup 13/C abundances at individual olefinic carbon positions have been developed, tested, and shown to perform accurately. (1) The double bond is oxidized with ozone; (2) silver oxide is used to cleave the resulting ozonide quantitatively to carboxylic-acid fragments; (3) a modified Schmidt decarboxylation is used to produce CO/sub 2/ quantitatively from the carboxyl groups of the separated cleavage products; and (4) the CO/sub 2/ is utilized for mass spectrometric analysis. The results of intramolecular isotopic analyses are combined with molecular-average isotopic compositions determined by total combustion in order to show that fatty acids biosynthesized by Escherichia coli grown aerobically with glucose as the sole carbon source and harvested at late log phase are depleted by approximately 3 parts per thousand in /sup 13/C relative to the glucose. This fractionation arises in the formation of acetyl-coenzyme A by pyruvate dehydrogenase and is localized at the carboxyl position in the acetyl-CoA product. The isotopic order in that two-carbon subunit is carried through the biosynthesis of fatty acids so that alternate positions in the fatty-acid chains are depleted in /sup 13/C by an amount equal to twice the molecular-average depletion. The kinetic isotope effect at C-2 for pyruvate dehydrogenase in vivo is shown to be approximately 2.3%.

  13. Carbon isotopic fractionation in the biosynthesis of bacterial fatty acids. Ozonolysis of unsaturated fatty acids as a means of determining the intramolecular distribution of carbon isotopes

    International Nuclear Information System (INIS)

    Methods for the determination of 13C abundances at individual olefinic carbon positions have been developed, tested, and shown to perform accurately. (1) The double bond is oxidized with ozone; (2) silver oxide is used to cleave the resulting ozonide quantitatively to carboxylic-acid fragments; (3) a modified Schmidt decarboxylation is used to produce CO2 quantitatively from the carboxyl groups of the separated cleavage products; and (4) the CO2 is utilized for mass spectrometric analysis. The results of intramolecular isotopic analyses are combined with molecular-average isotopic compositions determined by total combustion in order to show that fatty acids biosynthesized by Escherichia coli grown aerobically with glucose as the sole carbon source and harvested at late log phase are depleted by approximately 3 parts per thousand in 13C relative to the glucose. This fractionation arises in the formation of acetyl-coenzyme A by pyruvate dehydrogenase and is localized at the carboxyl position in the acetyl-CoA product. The isotopic order in that two-carbon subunit is carried through the biosynthesis of fatty acids so that alternate positions in the fatty-acid chains are depleted in 13C by an amount equal to twice the molecular-average depletion. The kinetic isotope effect at C-2 for pyruvate dehydrogenase in vivo is shown to be approximately 2.3%. (author)

  14. Intramolecular fluorescence correlation spectroscopy in a feedback tracking microscope

    CERN Document Server

    McHale, Kevin

    2009-01-01

    We derive the statistics of the signals generated by shape fluctuations of large molecules studied by feedback tracking microscopy. We account for the influence of intramolecular dynamics on the response of the tracking system, and derive a general expression for the fluorescence autocorrelation function that applies when those dynamics are linear. We show that tracking provides enhanced sensitivity to translational diffusion, molecular size, heterogeneity and long time-scale decays in comparison to traditional fluorescence correlation spectroscopy. We demonstrate our approach by using a three-dimensional tracking microscope to study genomic $\\lambda$-phage DNA molecules with various fluorescence label configurations. We conclude with a discussion of related techniques, including computation of the relevant statistics for camera-based intramolecular correlation measurements.

  15. Nitric Acid Dehydration Using Perfluoro Carboxylate and Mixed Sulfonate/Carboxylate Membranes

    Energy Technology Data Exchange (ETDEWEB)

    R.L. Ames

    2004-09-01

    Perfluoro ionomer membranes are tetrafluoro ethylene-based materials with microheterogeneous structures consisting of a hydrophobic polymer backbone and a hydrophilic side-chain cluster region. Due to the ionomer cluster morphology, these films exhibit unique transport properties. Recent investigations with perfluoro sulfonate and perfluoro sulfonate/carboxylate composite polymers have demonstrated their value in the dehydration of nitric acid and they show potential as an alternative to conventional, energy intensive unit operations in the concentration of acid feeds. As a result, investigations were conducted to determine the feasibility of using pure perfluoro carboxylate and mixed perfluoro sulfonate/carboxylate films for the dehydration of nitric acid because of the speculation of improved water selectivity of the carboxylate pendant chain. During the first phase of these investigations the effort was focused on generating a thin, solution cast perfluoro carboxylate ionomer film, to evaluate the general, chemical and physical characteristics of the polymer, and to assess the material's aqueous transport performance (flux and nitrate separation efficiencies) in pervaporation and high-pressure environments. Results demonstrated that generating robust solution-cast films was difficult yet a number of membranes survived high trans-membrane pressures up to 700 psig. General characterization of the solution cast product showed reduced ion exchange capacities when compared with thicker, ''as received'' perfluoro carboxylate and similar sulfonate films. Small angle x-ray scattering analysis results suggested that the solution cast carboxylate films contained a small fraction of sulfonate terminated side-chains. Aqueous transport experimentation showed that permeate fluxes for both pure water and nitric acid were approximately two orders of magnitude smaller for the carboxylate solution cast membranes when compared to their sulfonate

  16. Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

    OpenAIRE

    Andrew Tigchelaar; William Tam

    2012-01-01

    Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)]2 as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon–halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75–94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium c...

  17. Intramolecular fluorescence correlation spectroscopy in a feedback tracking microscope

    OpenAIRE

    McHale, Kevin; Mabuchi, Hideo

    2009-01-01

    We derive the statistics of the signals generated by shape fluctuations of large molecules studied by feedback tracking microscopy. We account for the influence of intramolecular dynamics on the response of the tracking system, and derive a general expression for the fluorescence autocorrelation function that applies when those dynamics are linear. We show that tracking provides enhanced sensitivity to translational diffusion, molecular size, heterogeneity and long time-scale decays in compar...

  18. Directing Group in Decarboxylative Cross-Coupling: Copper-Catalyzed Site-Selective C-N Bond Formation from Nonactivated Aliphatic Carboxylic Acids.

    Science.gov (United States)

    Liu, Zhao-Jing; Lu, Xi; Wang, Guan; Li, Lei; Jiang, Wei-Tao; Wang, Yu-Dong; Xiao, Bin; Fu, Yao

    2016-08-01

    Copper-catalyzed directed decarboxylative amination of nonactivated aliphatic carboxylic acids is described. This intramolecular C-N bond formation reaction provides efficient access to the synthesis of pyrrolidine and piperidine derivatives as well as the modification of complex natural products. Moreover, this reaction presents excellent site-selectivity in the C-N bond formation step through the use of directing group. Our work can be considered as a big step toward controllable radical decarboxylative carbon-heteroatom cross-coupling. PMID:27439145

  19. Methyl 3-(Quinolin-2-ylindolizine-1-carboxylate

    Directory of Open Access Journals (Sweden)

    Roumaissa Belguedj

    2015-12-01

    Full Text Available A novel compound, methyl 3-(quinolin-2-ylindolizine-1-carboxylate (2 has been synthesized by cycloaddition reaction of 1-(quinolin-2-ylmethylpyridinium ylide (1 with methyl propiolate in presence of sodium hydride in THF. The structure of this compound was established by IR, 1H-NMR, 13C-NMR and MS data

  20. 2-Isopropyl-5-methylcyclohexyl quinoline-2-carboxylate

    Directory of Open Access Journals (Sweden)

    E. Fazal

    2014-01-01

    Full Text Available In the title compound, C20H25NO2, the cyclohexyl ring adopts a slightly disordered chair conformation. The dihedral angle between the mean planes of the quinoline ring and the carboxylate group is 22.2 (6°. In the crystal, weak C—H...N interactions make chains along [010].

  1. Pd-Catalyzed sequential β-C(sp(3))-H arylation and intramolecular amination of δ-C(sp(2))-H bonds for synthesis of quinolinones via an N,O-bidentate directing group.

    Science.gov (United States)

    Guan, Mingyu; Pang, Yubo; Zhang, Jingyu; Zhao, Yingsheng

    2016-05-19

    The pharmacological importance of 2-quinolinone derivatives is well known. Herein, we developed an effective protocol for the synthesis of 2-quinolinone derivatives by palladium-catalyzed sequential β-C(sp(3))-H arylation and selective intramolecular C(sp(2))-H/N-H amination starting with aryl iodides and carboxylic acids. A novel directing group, glycine dimethylamide, was used in the synthesis. We synthesized various quinolinone derivatives, including 5-substituted quinolinones, which are difficult to obtain using the traditional pathway. The directing group could be easily removed and could be readily transformed into other useful functional groups. PMID:27161570

  2. Structural Studies of 2-Pentyl/Pentenyl-Substituted Methyl 4-Hydroxy-2H-1,2-Benzothiazine-3-Carboxylate-1,1-Dioxide

    Directory of Open Access Journals (Sweden)

    Muhammad Nadeem ARSHAD

    2012-12-01

    Full Text Available Crystal structures of methyl 2-pentyl-4-hydroxy-2H-1,2-benzothiazine-3-carboxylate-1,1-dioxide 1 and methyl 2-pentenyl-4-hydroxy-2H-1,2-benzothiazine-3-carboxylate-1,1-dioxide 2 have been determined after their synthesis from saccharin. 1 and 2 crystallize in a monoclinic and orthorhombic crystal system, respectively. The asymmetric unit of both contains one molecule of each compound and shows intramolecular O-H×××O interactions generating six membered ring motifs S11(6. Intermolecular hydrogen bonding interactions have been observed in the molecule with the pentyl side chain. The thiazine ring in both molecules adopts a half chair conformation with a r.m.s. deviation of 0.2049 Å and 0.2161 Å.

  3. Production of carboxylic acid and salt co-products

    Energy Technology Data Exchange (ETDEWEB)

    Hanchar, Robert J.; Kleff, Susanne; Guettler, Michael V.

    2014-09-09

    This invention provide processes for producing carboxylic acid product, along with useful salts. The carboxylic acid product that is produced according to this invention is preferably a C.sub.2-C.sub.12 carboxylic acid. Among the salts produced in the process of the invention are ammonium salts.

  4. 40 CFR 721.2950 - Carboxylic acid glycidyl esters.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Carboxylic acid glycidyl esters. 721... Substances § 721.2950 Carboxylic acid glycidyl esters. (a) Chemical substances and significant new uses subject to reporting. (1) The chemical substance identified generically as carboxylic acid glycidyl...

  5. Hydrolytic activity of -alkoxide/acetato-bridged binuclear Cu(II) complexes towards carboxylic acid ester

    Indian Academy of Sciences (India)

    Weidong Jiang; Bin Xu; Zhen Xiang; Shengtian Huang; Fuan Liu; Ying Wang

    2013-09-01

    Two -alkoxide/acetate-bridged small molecule binuclear copper(II) complexes were synthesized, and used to promote the hydrolysis of a classic carboxylic acid ester, -nitrophenyl picolinate (PNPP). Both binuclear complexes exhibited good hydrolytic reactivity, giving rise to . 15547- and 17462-fold acceleration over background value for PNPP hydrolysis at neutral conditions, respectively. For comparing, activities of the other two mononuclear analogues were evaluated, revealing that binuclear complexes show approximately 150- and 171-fold kinetic advantage over their mononuclear analogues.

  6. Borate esters as convenient reagents for direct amidation of carboxylic acids and transamidation of primary amides

    OpenAIRE

    Starkov, P.; Sheppard, T. D.

    2011-01-01

    Simple borates serve as effective promoters for amide bond formation with a variety of carboxylic acids and amines. With trimethyl or tris(2,2,2-trifluoroethyl) borate, amides are obtained in good to excellent yield and high purity after a simple work-up procedure. Tris(2,2,2-trifluoroethyl) borate can also be used for the straightforward conversion of primary amides to secondary amides via transamidation.

  7. Dynamical correlation between quantum entanglement and intramolecular energy in molecular vibrations: An algebraic approach

    International Nuclear Information System (INIS)

    The dynamical correlation between quantum entanglement and intramolecular energy in realistic molecular vibrations is explored using the Lie algebraic approach. The explicit expression of entanglement measurement can be achieved using algebraic operations. The common and different characteristics of dynamical entanglement in different molecular vibrations are also provided. The dynamical study of quantum entanglement and intramolecular energy in small molecular vibrations can be helpful for controlling the entanglement and further understanding the intramolecular dynamics. (atomic and molecular physics)

  8. Synthesis, Characterization and Weak Intramolecular Interactions of Porphyrins Bearing Nucleobases

    Institute of Scientific and Technical Information of China (English)

    阮文娟; 李瑛; 赵小菁; 王传忠; 朱志昂; 缪方明

    2003-01-01

    5,10, 15-Triphenyl-20-{2- [α- (adenine-9 ) acetylamino]} phenyl porphyrin ( 1 ), 5,10, 15-triphenyl-20-{2-[α-(cytosine-1)acetylamino]} phenyl porphyrin (2), 5, 10, 15-triphenyl-20-{4-[α-(cytosine-1)ethoxy]} phenyl porphyrin (3) and their zinc complexes Zn-1, Zn-2 and Zn-3 have been prepared and characterized by 1H NMR spectra, elemental analyses, electronic absorption spectra and mass spectra (FAB). Intramolecular π-π interactions and intramolecular metal-~ interaction for 1, 2, Zn-1,and Zn-2 have been investigated by several methods. 1H NMR studies demonstrate that the porphyrin π-system in 1 and 2 is parallel to the adenine and the cytosine aromatic ring, respectively. The electronic absorption spectral properties of free porphyrin derivatives and their zinc complexes have been compared with those of H2TPP and ZnTPP. The results show that the UV-vis spectra of 1 and 2 are the same as that of H2TPP,whereas the spectra of their zinc complexes show 7 nm red shifts of the Soret bands compared to that of ZnTPP. The emission spectra of Zn-1 and Zn-2 are independent of excitation wavelength. From combination of the evidence of absorption and emission spectra it is suggested the existence of intramolecular metal-π interaction in Zn-1 and Zn-2. The results of conformational analysis agreed quite nicely with that of experiments, thus it was further to validate the experimental conclusions.

  9. Carboxylated Polyurethanes Containing Hyperbranched Polyester Soft Segments

    Directory of Open Access Journals (Sweden)

    Žigon, M.

    2006-09-01

    Full Text Available hyperbranched polyester soft segments (HB PU with functional carboxylic groups in order to enable the preparation of stable HB PU dispersions. Carboxylated hyperbranched polyurethanes were synthesized using a hyperbranched polyester based on 2,2-bis(methylolpropionic acid of the fourth pseudo-generation (Boltorn H40 and hexamethylene (HDI or isophorone diisocyanate (IPDI. The reactivity of hyperbranched polyester with HDI was lower than expected, possibly due to the presence of less reactive hydroxyl groups in the linear repeat units. A gel was formed at mole ratios rNCO/OH = 1:2 or 1:4. The synthesis of HB PU was performed with partly esterified hyperbranched polyester with lowered hydroxyl functionality. The carboxyl groups were incorporated in the HB PU backbone by reaction of residual hydroxyl groups with cis-1,2-cyclohexanedicarboxylic anhydride. HB PU aqueous dispersions were stable at least for two months, although their films were brittle. The tensile strength and Young's modulus of blends of linear and HB PU decreased with increasing content of HB PU whereas elongation at break remained nearly constant, which was explained in terms of looser chain packing due to more open tree-like hyperbranched structures.

  10. Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide

    International Nuclear Information System (INIS)

    This paper studies the intramolecular photoinduced electron-transfer (PET) of covalent bonded azobenzene-perylene diimide (AZO-PDI) in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 1011 s−1 is found. This PET process is also consolidated by femtosecond transient absorption spectra

  11. OH stretching frequencies in systems with intramolecular hydrogen bonds

    DEFF Research Database (Denmark)

    Spanget-Larsen, Jens; Hansen, Bjarke Knud Vilster; Hansen, Poul Erik

    2011-01-01

    OH stretching wavenumbers were investigated for 30 species with intramolecularly hydrogen bonded hydroxyl groups, covering the range from 3600 to ca. 1900 cm-1. Theoretical wavenumbers were predicted with B3LYP/6-31G(d) density functional theory using the standard harmonic approximation, as well as....... This is significant in view of the fact that the full anharmonic PT2 analysis requires orders-of-magnitude more computing time than the harmonic analysis. νOH also correlates with OH chemical shifts....

  12. Intramolecular Hydrogen Bonding in (2-Hydroxybenzoyl)benzoylmethane Enol

    DEFF Research Database (Denmark)

    Hansen, Bjarke Knud Vilster; Winther, Morten; Spanget-Larsen, Jens

    2014-01-01

    dienol form of 1,3-dibenzoylacetone. But in these examples the two H-bonds are equivalent, while in the case of OHDBM they are chemically different, involving one enolic and one phenolic hydroxy group. OHDBM is thus an interesting model compound with two competing H-bonds to the same carbonyl group. In......In the stable enol tautomer of the title compound (OHDBM), one carbonyl group is flanked by two β-hydroxy groups, giving rise to bifold intramolecular H-bonding. A similar situation is found in other β,β'-dihydroxy carbonyl compounds like chrysazin, anthralin, 2,2'-dihydroxybenzophenone, and the...

  13. Recording Intramolecular Mechanics during the Manipulation of a Large Molecule

    International Nuclear Information System (INIS)

    The technique of single atom manipulation by means of the scanning tunneling microscope (STM) applies to the controlled displacement of large molecules. By a combined experimental and theoretical work, we show that in a constant height mode of manipulation the STM current intensity carries detailed information on the internal mechanics of the molecule when guided by the STM tip. Controlling and time following the intramolecular behavior of a large molecule on a surface is the first step towards the design of molecular tunnel-wired nanorobots

  14. Intramolecular Fluorescence Correlation Spectroscopy in a Feedback Tracking Microscope

    Science.gov (United States)

    McHale, Kevin; Mabuchi, Hideo

    2010-07-01

    We derive the statistics of the signals generated by shape fluctuations of large molecules studied by feedback tracking microscopy. We account for the influence of intramolecular dynamics on the response of the tracking system, and derive a general expression for the fluorescence autocorrelation function that applies when those dynamics are linear. We show that tracking provides enhanced sensitivity to translational diffusion, molecular size, heterogeneity and long time-scale decays in comparison to traditional fluorescence correlation spectroscopy. We demonstrate our approach by using a three-dimensional tracking microscope to study genomic $\\lambda$-phage DNA molecules with various fluorescence label configurations.

  15. Theoretical study on some inter- and intra-molecular interactions

    OpenAIRE

    Fan, Hongjun

    2006-01-01

    Ab-initio MP2&CI and DF calculations were used to study some chemical topics that involve inter- and intra-molecular so-called weak interactions. These topics include: i) What is the physical origin of the single bond rotational barrier, e.g. of ethane? Our answer is that the kinetic Pauli repulsion between CH bond pairs is much more important than hyperconjugative attraction of CH bond pairs through virtual CH σ* orbitals. ii) What is the physical origin of the bond length expansion...

  16. The intramolecular electron transfer between copper sites of nitrite reductase

    DEFF Research Database (Denmark)

    Farver, O; Eady, R R; Abraham, Z H;

    1998-01-01

    The intramolecular electron transfer (ET) between the type 1 Cu(I) and the type 2 Cu(II) sites of Alcaligenes xylosoxidans dissimilatory nitrite reductase (AxNiR) has been studied in order to compare it with the analogous process taking place in ascorbate oxidase (AO). This internal process is......(I) and the trinuclear copper centre in ascorbate oxidase, and the characteristics of the internal ET processes of these enzymes are compared. The data are consistent with the faster ET observed in nitrite reductase arising from a more advantageous entropy of activation when compared with ascorbate...

  17. High-pressure effects on intramolecular electron transfer compounds

    CERN Document Server

    He Li Ming; Li Hong; Zhang Bao Wen; Li Yi; Yang Guo Qiang

    2002-01-01

    We explore the effect of pressure on the fluorescence spectra of the intramolecular electron transfer compound N-(1-pyrenylmethyl), N-methyl-4-methoxyaniline (Py-Am) and its model version, with poly(methyl methacrylate) blended in, at high pressure up to 7 GPa. The emission properties of Py-Am and pyrene show distinct difference with the increase of pressure. This difference indicates the strength of the charge transfer interaction resulting from the adjusting of the conformation of Py-Am with increase of pressure. The relationship between the electronic state of the molecule and pressure is discussed.

  18. 4-Hydroxy-2-methyl-1,1-dioxo-2H-1λ6,2- benzothiazine-3-carboxylic acid hemihydrate

    Directory of Open Access Journals (Sweden)

    M. Nawaz Tahir

    2012-03-01

    Full Text Available In the title compound, C10H9NO5S·0.5H2O, two geometrically different organic molecules are present. The benzene rings and the carboxylate groups are oriented at dihedral angles of 13.44 (4 and 21.15 (18°. In both molecules, an intramolecular O—H...O hydrogen bond generates an S(6 ring. In the crystal, both moleucles form inversion dimers linked by pairs of O—H...O hydrogen bonds to generate R22(8 loops. The dimers are consolidated into chains extending along [100] by bridging O—H...O hydrogen bonds from the water molecule. A weak C—H...O hydrogen bond also occurs.

  19. Surface chemical properties of sodium salts of carboxylic acids isolated from Green River shale. [Sodium carboxylates

    Energy Technology Data Exchange (ETDEWEB)

    McKay, J.F.; Blanche, M.S.; Robertson, R.E.

    1985-12-01

    Organic material isolated from Green River shale varies substantially with the method of isolation. Short-time supercritical fluid treatment and solvent extraction of Green River shale produces large amounts of sodium carboxylates. These sodium salts were observed to form emulsions and therefore be surface active. Quantitative surface activity measurements were then determined using the shale extract. The material was found to have a limiting surface tension of about 41 dynes/cm (as expected) for carboxylates. However, the critical micelle concentration is quite high and has a measured molecular weight value of 600. This probably results from higher solubility of the lower molecular weight species. The solution did not display hysteresis. In general the carboxylic acid salts isolated from Green River shale displayed surface activity similar to those of model compounds cited in the literature.

  20. Intramolecular hydrogen-bonding studies by NMR spectroscopy

    CERN Document Server

    Cantalapiedra, N A

    2000-01-01

    o-methoxybenzamide and N-methyl-o-methylbenzamide, using the pseudo-contact shifts calculated from the sup 1 H and sup 1 sup 3 C NMR spectra. The main conformation present in solution for o-fluorobenzamide was the one held by an intramolecular N-H...F hydrogen bond. Ab-initio calculations (at the RHF/6-31G* level) have provided additional data for the geometry of the individual molecules. A conformational equilibrium study of some nipecotic acid derivatives (3-substituted piperidines: CO sub 2 H, CO sub 2 Et, CONH sub 2 , CONHMe, CONEt sub 2) and cis-1,3-disubstituted cyclohexane derivatives (NHCOMe/CO sub 2 Me, NHCOMe/CONHMe, NH sub 2 /CO sub 2 H) has been undertaken in a variety of solvents, in order to predict the intramolecular hydrogen-bonding energies involved in the systems. The conformer populations were obtained by direct integration of proton peaks corresponding to the equatorial and axial conformations at low temperature (-80 deg), and by geometrically dependent coupling constants ( sup 3 J sub H s...

  1. Intramolecular photosensitization of the pinene-ocimene rearrangement

    International Nuclear Information System (INIS)

    Bonding of nopol to the para position of acetophenone produces 5,5-dimethyl-2-(2-(p-acetylphenoxy)ethyl)bi-cyclo[3.1.1]hept-2-ene 1, which contains two chromophores: a para-alkoxyacetophenone and an α-pinene, connected by a single methylene group. UV irradiation of I in both benzene and methanol produces none of the intramolecular [2 + 2] cycloaddition that most para-(3-buten-1-oxy)acetophenones undergo. Instead, the pinene unit rearranges to a triene skeleton identical to that of ocimene, a known photoproduct of pinene. At modest conversion the diene portion of the triene is cis but gradually is converted to a 52:48 trans:cis ratio. It is concluded that intramolecular triplet energy transfer from the excited ketone chromophore forms the 1,2-biradical triplet state of the pinene moiety, which then undergoes cyclobutylcarbinyl ring opening to a 1,4-biradical that cleaves to the 1,3,6-triene structure of ocimene. This mechanism is suggested to be responsible for the earlier reported intermolecularly sensitized rearrangement of a-pinene to the ocimene isomers. (author)

  2. Synthesis of dihydrophenanthridines by a sequence of Ugi-4CR and palladium-catalyzed intramolecular C-H functionalization

    Directory of Open Access Journals (Sweden)

    2008-04-01

    Full Text Available BackgroundSmall polyfunctionalized heterocyclic compounds play important roles in the drug discovery process and in the isolation and structural identification of biological macromolecules. It is expected that ready access to diverse sets of heterocycles can not only help improving the known biological and pharmacokinetic properties of drugs, but also assist the discovery of molecules that exhibit biological effects beyond those associated with previously known macromolecules. By virtue of their inherent convergence, high productivity, their exploratory and complexity-generating power, multicomponent reactions (MCRs are undoubtedly well suited for creating molecular diversity. The combination of MCRs with an efficient post-functionalization reaction has proven to be an efficient strategy to increase the skeleton diversity.ResultsThe Ugi reaction of an o-iodobenzaldehyde (2, an aniline (3, an isocyanide (4, and a carboxylic acid (5 afforded α-acetamido-α-phenylacetamide (6 in good to excellent yields. The palladium-catalyzed intramolecular C-H functionalization of these adducts under ligandless conditions provided the functionalized dihydrophenanthridines (1.ConclusionHighly functionalized dihydrophenanthridines are synthesized in only two steps from readily accessible starting materials in good to excellent overall yields.

  3. Aspects of secondary bonding intramolecular interaction in organomercury and organochalcogen derivatives

    Indian Academy of Sciences (India)

    Sagar Sharma; Tapash Chakraborty; Kriti Srivastava; Harkesh B Singh

    2011-03-01

    Recent trends in the area of intramolecularly coordinated organomercury and organochalcogens derivatives are reviewed. Intramolecular coordination in organomercury derivatives facilitates the formation of mercurametallamacrocycle and leads to novel metal-metal interaction with closed shell ions. It also plays a key role in stabilizing telluroxanes as well as in the activation of chalcogen-carbon bonds.

  4. Direct Observation of Cascade of Photoinduced Ultrafast Intramolecular Charge Transfer Dynamics in Diphenyl Acetylene Derivatives: Via Solvation and Intramolecular Relaxation.

    Science.gov (United States)

    Karunakaran, Venugopal; Das, Suresh

    2016-07-21

    Interaction of light with electron donor-acceptor π-conjugated systems leading to intramolecular charge transfer (ICT) plays an essential role in transformation of light energy. Here the cascade of photoinduced ICT processes is directly observed by investigating the excited state relaxation dynamics of cyano and mono/di methoxy substituted diphenyl acetylene derivatives using femtosecond pump-probe spectroscopy and nanosecond laser flash photolysis. The femtosecond transient absorption spectra of the chromophores upon ultrafast excitation reveal the dynamics of intermediates involved in transition from initially populated Frank-Condon state to local excited state (LE). It also provides the dynamic details of the transition from the LE to the charge transfer state yielding the formation of the radical ions. Finally, the charge transfer state decays to the triplet state by geminate charge recombination. The latter dynamics are observed in the nanosecond transient absorption spectra. It is found that excited state relaxation pathways are controlled by different stages of solvation and intramolecular relaxation depending on the solvent polarity. The twisted ICT state is more stabilized (978 ps) in acetonitrile than cyclohexane where major components of transient absorption originate from the S1 state. PMID:27347705

  5. Carboxylic Acid Esters as Substrates of Cholinesterases

    Science.gov (United States)

    Brestkin, A. P.; Rozengart, E. V.; Abduvakhabov, A. A.; Sadykov, A. A.

    1983-10-01

    Data on the kinetics of the hydrolysis of various carboxylic acid esters by two main types of cholinesterases — acetylcholinesterase from human erythrocytes and butyrylcholinesterase from horse blood serum — are surveyed. It is shown that the rate of enzyme hydrolysis depends significantly on the structure of the acyl part of the ester molecule, the nature of the ester heteroatom, the structure of the alcohol component, and particularly the structure of the onium group. Esters based on natural products are of special interest as specific substrates of these enzymes. The role of the productive and non-productive sorption of the substrates in enzyme catalysis is demonstrated. The bibliography includes 81 references.

  6. Metal extraction by amides of carboxylic acids

    International Nuclear Information System (INIS)

    Extraction ability of various amides was studied. Data on extraction of rare earths, vanadium, molybdenum, rhenium, uranium, niobium, tantalum by N,N-dibutyl-amides of acetic, nonanic acids and fatly synthetic acids of C7-C9 fractions are presented. Effect of salting-out agents, inorganic acid concentrations on extraction process was studied. Potential ability of using amides of carboxylic acids for extractional concentration of rare earths as well as for recovery and separation of iron, rhenium, vanadium, molybdenum, uranium, niobium, and tantalum was shown

  7. Effect of solvent on proton location and dynamic behavior in short intramolecular hydrogen bonds studied by molecular dynamics simulations and NMR experiments

    Science.gov (United States)

    Mori, Yukie; Masuda, Yuichi

    2015-09-01

    Hydrogen phthalate anion has a short strong O-H-O hydrogen bond (H-bond). According to previous experimental studies, the H-bond is asymmetric and two tautomers are interconverted in aqueous solutions. In the present study, the effects of polar solvents on the H-bond in a zwitterionic hydrogen phthalate derivative 1 were investigated by quantum mechanics/molecular mechanics molecular dynamics (MD) simulations. The analyses of the trajectories for the methanol solution showed that the H-bonding proton tends to be located closer to the carboxylate group that forms fewer intermolecular H-bonds, than to the other carboxylate group and that the intramolecular proton transfer in 1 is triggered by the breakage and/or formation of an intermolecular H-bond. The enol form of dibenzoylmethane (2) also has a short H-bond, and the OH bond is reported to be rather long (>1.1 Å) in the crystal. In the present study, the effects of the solvent on the H-bond in 2 were investigated by molecular orbital (MO) calculations, MD simulations and nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) calculations for 2 in vacuum indicated that the barrier height for the intramolecular proton transfer is almost the same as the zero-point energy of the vibrational ground state, resulting in broad distribution of the proton density along the H-bond, owing to the nuclear quantum effect. The OH distances were determined in CCl4, acetonitrile, and dimethylsulfoxide solutions from the magnetic dipolar interactions between the 17O and 1H nuclei monitoring the nuclear magnetic relaxation times of 1H. The experimental results indicated that the H-bond geometry of 2 is influenced by the interactions with dimethylsulfoxide, suggesting the formation of a bifurcated H-bond, which was supported by the DFT calculations. The MD simulations for the methanol solution of 2 showed that the asymmetry of the OH distance is correlated with the asymmetry in the electrostatic field of the

  8. Carboxylation and Decarboxylation of Aluminum Oxide Nanoparticles Using Bifunctional Carboxylic Acids and Octylamine

    Directory of Open Access Journals (Sweden)

    Shirin Alexander

    2016-01-01

    Full Text Available The carboxylation of alumina nanoparticles (NPs, with bifunctional carboxylic acids, provides molecular anchors that are used for building more complexed structures via either physisorption or chemisorption. Colloidal suspensions of the NPs may be prepared by covalently bonding a series of carboxylic acids with secondary functional groups (HO2C-R-X to the surface of the NPs: lysine (X = NH2, p-hydroxybenzoic acid (X = OH, fumaric acid (X = CO2H, and 4-formylbenzoic acid (X = C(OH. Subsequent reaction with octylamine at either 25°C or 70°C was investigated. Fourier transform IR-attenuated reflectance spectroscopy (FTIR-ATR, thermogravimetric analysis (TGA, and scanning electron microscopy (SEM along with energy dispersive X-ray (EDX analysis were used to characterize the bifunctionalized monolayers and/or multilayer corona surrounding the alumina NPs and investigate the reaction mechanism of octylamine with the functional groups (X of the NPs. Except for the fumaric functionalized NPs, addition of octylamine to the functionalized NPs leads to removal of excess carboxylic acid corona from the surface via an amide formation. The extent of the multilayer is dependent on the strength of the acid⋯acid interaction.

  9. On the Catalytic Effect of Water in the Intramolecular Diels–Alder Reaction of Quinone Systems: A Theoretical Study

    Directory of Open Access Journals (Sweden)

    Jorge Soto-Delgado

    2012-11-01

    Full Text Available The mechanism of the intramolecular Diels–Alder (IMDA reaction of benzoquinone 1, in the absence and in the presence of three water molecules, 1w, has been studied by means of density functional theory (DFT methods, using the M05-2X and B3LYP functionals for exploration of the potential energy surface (PES. The energy and geometrical results obtained are complemented with a population analysis using the NBO method, and an analysis based on the global, local and group electrophilicity and nucleophilicity indices. Both implicit and explicit solvation emphasize the increase of the polarity of the reaction and the reduction of activation free energies associated with the transition states (TSs of this IMDA process. These results are reinforced by the analysis of the reactivity indices derived from the conceptual DFT, which show that the increase of the electrophilicity of the quinone framework by the hydrogen-bond formation correctly explains the high polar character of this intramolecular process. Large polarization at the TSs promoted by hydrogen-bonds and implicit solvation by water together with a high electrophilicity-nucleophilicity difference consistently explains the catalytic effects of water molecules.

  10. Estimating the energy of intramolecular hydrogen bonds in chitosan oligomers

    Science.gov (United States)

    Mikhailov, G. P.; Lazarev, V. V.

    2016-07-01

    The effect the number of chitosan monomer units CTS n ( n = 1-5), the protonation of chitosan dimers, and the interaction between CTS n ( n = 1-3) and acetate ions have on the energy of intramolecular hydrogen bonds is investigated by means of QTAIM analysis and solving the vibrational problem within the cluster-continuum model. It is established that the number of H-bonds in CTS n is 2 n - 1 and the total energy of H-bonds grows by ~20 kJ/mol. It is concluded that the hydrogen bonds between CTS and acetate ions play a major role in the stabilization of polyelectrolyte complexes in dilute acetic acid solutions of CTS.

  11. Intramolecular Charge Transfer States in the Condensed Phase

    Science.gov (United States)

    Williams, C. F.; Herbert, J. M.

    2009-06-01

    Time-Dependent Density Functional Theory (TDDFT) with long range corrected functionals can give accurate results for the energies of electronically excited states involving Intramolecular Charge Transfer (ICT) in large molecules. If this is combined with a Molecular Mechanics (MM) representation of the surrounding solvent this technique can be used to interpret the results of condensed phase UV-Vis Spectroscopy. Often the MM region is represented by a set of point charges, however this means that the solvent cannot repolarize to adapt to the new charge distribution as a result of ICT and so the excitation energies to ICT states are overestimated. To solve this problem an algorithm that interfaces TDDFT with the polarizable force-field AMOEBA is presented; the effect of solvation on charge transfer in species such as 4,4'dimethylaminobenzonitrile (DMABN) is discussed. M.A. Rohrdanz, K.M. Martins, and J.M. Herbert, J. Chem. Phys. 130 034107 (2008).

  12. Intramolecular Coaggregation Behavior in Novel Cyclotriveratrylenes with Cholic Acid Podants

    Institute of Scientific and Technical Information of China (English)

    黎占亭; 赵新; 蒋锡夔; 赵成学; 陈章; 陈云涛

    2001-01-01

    Two molecules 1a and 1b consisting of one cyclotriveratrylene (CTV) and three cholic acid podants have been designed and synthesized.Fluorescent studies water/dimetboxyethane mixtures reveal an intramolecular coaggregation between the CTV and the attached cholic acid moieties.Their fluorescent emission intensity increases and then decreases with the increase of water content, whereas under the same measuring conditions the intensity of CTV derivative 2a, which possesses no similar cholic acid moiety,increases and then reaches a maximum value.The intensity decrease in 1a and 1b has been attributed to the decrease of the microenvirommental polarity in media of increasing polarity because of the shielding effect of the hydrophobic face of the cholic acid moiety.

  13. Intramolecular electron transfer in Pseudomonas aeruginosa cd(1) nitrite reductase

    DEFF Research Database (Denmark)

    Farver, Ole; Brunori, Maurizio; Cutruzzolà, Francesca;

    2009-01-01

    The cd(1) nitrite reductases, which catalyze the reduction of nitrite to nitric oxide, are homodimers of 60 kDa subunits, each containing one heme-c and one heme-d(1). Heme-c is the electron entry site, whereas heme-d(1) constitutes the catalytic center. The 3D structure of Pseudomonas aeruginosa...... nitrite reductase has been determined in both fully oxidized and reduced states. Intramolecular electron transfer (ET), between c and d(1) hemes is an essential step in the catalytic cycle. In earlier studies of the Pseudomonas stutzeri enzyme, we observed that a marked negative cooperativity is...... controlling this internal ET step. In this study we have investigated the internal ET in the wild-type and His369Ala mutant of P. aeruginosa nitrite reductases and have observed similar cooperativity to that of the Pseudomonas stutzeri enzyme. Heme-c was initially reduced, in an essentially diffusion...

  14. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange

    Science.gov (United States)

    Yang, Woon Seok; Noh, Jun Hong; Jeon, Nam Joong; Kim, Young Chan; Ryu, Seungchan; Seo, Jangwon; Seok, Sang Il

    2015-06-01

    The band gap of formamidinium lead iodide (FAPbI3) perovskites allows broader absorption of the solar spectrum relative to conventional methylammonium lead iodide (MAPbI3). Because the optoelectronic properties of perovskite films are closely related to film quality, deposition of dense and uniform films is crucial for fabricating high-performance perovskite solar cells (PSCs). We report an approach for depositing high-quality FAPbI3 films, involving FAPbI3 crystallization by the direct intramolecular exchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidinium iodide. This process produces FAPbI3 films with (111)-preferred crystallographic orientation, large-grained dense microstructures, and flat surfaces without residual PbI2. Using films prepared by this technique, we fabricated FAPbI3-based PSCs with maximum power conversion efficiency greater than 20%.

  15. Cysteine amide adduct formation from carboxylic acid drugs via UGT-mediated bioactivation in human liver microsomes.

    Science.gov (United States)

    Harada, H; Toyoda, Y; Endo, T; Kobayashi, M

    2015-10-01

    Although chemical trapping has been widely used to evaluate cytochrome P450-mediated drug bioactivation, thus far, only a few in vitro-trapping studies have been performed on UDP-glucuronosyltransferase (UGT)-mediated drug bioactivation. In this study, we used cysteine (Cys) as trapping agent to gain new insights into the UGT-mediated bioactivation involving acyl glucuronides of carboxylic acid drugs. Diclofenac, ketoprofen and ibuprofen were incubated in human liver microsomes with UDPGA and Cys, followed by analysis using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS). The N-acyl-Cys amide adduct of diclofenac was characterized by mass analysis and was detectable even in photodiode array analysis. Our data indicated that the formation of such adducts reflects the reactivity of the corresponding acyl glucuronides. In addition, it was suggested that the adduct formation requires an N-terminal Cys moiety with both a free amine and a free thiol group, from the results using various cysteine derivatives. We propose that the S-acyl-Cys thioester adduct can form via transacylation of an acyl glucuronide and can then form to an N-acyl-Cys amide adduct through intramolecular S- to N-acyl rearrangement. This series of the reactions has important implications as a possible bioactivation mechanism for covalent binding of carboxylic acid drugs to macromolecules. PMID:26601426

  16. Carboxyl-terminated butadiene-acrylonitrile-toughened epoxy/carboxyl-modified carbon nanotube nanocomposites: Thermal and mechanical properties

    OpenAIRE

    H. F. Xie; Wang, Y. T.; Wang, C. S.; H. Y. Yin; Wang, L.L.; R. S. Cheng

    2012-01-01

    Carboxyl-modified multi-walled carbon nanotubes (MWCNT–COOHs) as nanofillers were incorporated into diglycidyl ether of bisphenol A (DGEBA) toughened with carboxyl-terminated butadiene-acrylonitrile (CTBN). The carboxyl functional carbon nanotubes were characterized by Fourier-transform infrared spectroscopy and thermogravimetric analysis. Furthermore, cure kinetics, glass transition temperature (Tg), mechanical properties, thermal stability and morphology of DGEBA/CTBN/MWCNT–COOH...

  17. Photoinduced Intramolecular Charge Transfer in Donor-acceptor Dyad and Donor-bridge-acceptor Triad

    Institute of Scientific and Technical Information of China (English)

    Yong Ding; Yuan-zuo Li; Feng-cai Ma

    2008-01-01

    The ground and excited state properties of the [60]fullerene,diphenylbenzothiadiazole-triphenylamine (PBTDP-TPA) dyad and fullerene-diphenylbenzothiadiazole-triphenylamine (fullerene-PBTDP-TPA) triad were investigated theoretically using density functional theory with B3LYP functional and 3-21G basis set and time-dependent density functional theory with B3LYP functional and STO-3G basis set as well as 2D and 3D real space analysis methods.The 2D site representation reveals the electron-hole coherence on exci- tation.The 3D transition density shows the orientation and strength of the transition dipole moment,and the 3D charge difference density gives the orientation and result of the intramolecular charge transfer.Also, photoinduced intermolecular charge transfer (ICT) in PBTDP-TPA-fullerene triad are identified with 2D and 3D representations,which reveals the mechanisms of ICT in donor-bridge-acceptor triad on excitation. Besides that we also found that the direct superexchange ICT from donor to acceptor (tunneling through the bridge) strongly promotes the ICT in the donor-bridge-acceptor triad.

  18. Ion exchange properties of carboxylate bagasse

    International Nuclear Information System (INIS)

    Bagasse fibers were chemically modified using three different reactions: esterification using monochloro acetic acid, esterification using succinic anhydride, and oxidation using sodium periodate and sodium chlorite to prepare cation exchanger bearing carboxylic groups. Bagasse was crosslinked using epichlorohydrin before chemical modification to avoid loss of its constituents during the chemical modification. The structure of the prepared derivatives was proved using Fourier transform infrared (FTIR) and chemical methods. The ability of the prepared bagasse cation exchangers to adsorb heavy metal ions (Cu+2, Ni+2, Cr+3, Fe+3), on a separate basis or in a mixture of them, at different metal ion concentration was tested. Thermal stability of the different bagasse derivative was studied using thermogravimetric analysis (TGA)

  19. Boron-containing amino carboxylic acid compounds and uses thereof

    International Nuclear Information System (INIS)

    Novel compounds which are useful for boron neutron capture therapy (BNCT) are disclosed. The compounds comprise a stable boron-containing group and an aminocycloalkane carboxylic acid group or a boronated acyclic hydrocarbon-linked amino carboxylic acid. Methods for synthesis of the compounds and for use of the compounds in BNCT are disclosed

  20. Lysine carboxylation: unveiling a spontaneous post-translational modification

    International Nuclear Information System (INIS)

    A computational method for the prediction of lysine carboxylation (KCX) in protein structures is described. The method accurately identifies misreported KCXs and predicts previously unknown KCX sites. The carboxylation of lysine residues is a post-translational modification (PTM) that plays a critical role in the catalytic mechanisms of several important enzymes. It occurs spontaneously under certain physicochemical conditions, but is difficult to detect experimentally. Its full impact is unknown. In this work, the signature microenvironment of lysine-carboxylation sites has been characterized. In addition, a computational method called Predictor of Lysine Carboxylation (PreLysCar) for the detection of lysine carboxylation in proteins with available three-dimensional structures has been developed. The likely prevalence of lysine carboxylation in the proteome was assessed through large-scale computations. The results suggest that about 1.3% of large proteins may contain a carboxylated lysine residue. This unexpected prevalence of lysine carboxylation implies an enrichment of reactions in which it may play functional roles. The results also suggest that by switching enzymes on and off under appropriate physicochemical conditions spontaneous PTMs may serve as an important and widely used efficient biological machinery for regulation

  1. Estimation of Intramolecular Hydrogen-bonding Energy via the Substitution Method

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The intramolecular hydrogen-bonding energies for eighteen molecules were calculated based on the substitution method, and compared with those predicted by the cis-trans method.The energy values obtained from two methods are close to each other with a correlation coefficient of 0.96.Furthermore, the hydrogen-bonding energies based on the substitution method are consistent with the geometrical features of intramolecular hydrogen bonds.Both of them demonstrate that the substitution method is capable of providing a good estimation of intramolecular hydrogen-bonding energy.

  2. Biodegradation of cycloalkane carboxylic acids in oil sand tailings

    International Nuclear Information System (INIS)

    The biodegradation of both an n-alkane and several carboxylated cycloalkanes was examined experimentally within tailings produced by the extraction of bitumen from the Athabasca oil sands. The carboxylated cycloalkanes examined were structurally similar to naphthenic acids that have been associated with the acute toxicity of oil sand tailings. The biodegradation potential of naphthenic acids was estimated by determining the biodegradation of both the carboxylated cycloalkanes and hexadecane in oil sand tailings. Carboxylated cycloalkanes were biodegraded within oil sands tailings, although compounds with methyl substitutions on the cycloalkane ring were more resistant to microbial degradation. Microbial activity against hexadecane and certain carboxylated cycloalkanes was found to be nitrogen and phosphorus limited. 21 refs., 3 refs., 1 tab

  3. Intramolecular interactions stabilizing compact conformations of the intrinsically disordered kinase-inhibitor domain of Sic1: a molecular dynamics investigation.

    Directory of Open Access Journals (Sweden)

    ElenaPapaleo

    2012-11-01

    The yeast CKI Sic1 is a 284-amino acid IDP that binds to Cdk1 in complex with the Clb5,6 cyclins, preventing phosphorylation of G1 substrates and, therefore, entrance to the S phase. Sic1 degradation, triggered by multiple phosphorylation events, promotes cell-cycle progression. Previous experimental studies pointed out a propensity of Sic1 and its isolated domains to populate both extended and compact conformations. The present contribution provides models of the compact conformations of the Sic1 kinase-inhibitory domain (KID by all-atom molecular-dynamics simulations in explicit solvent and in the absence of interactors. The results are integrated by spectroscopic and spectrometric data. Helical IFSUs are identified, along with networks of intramolecular interactions. The results identify a group of hub residues and electrostatic interactions which are likely to be involved in the stabilization of globular states.

  4. DFT and AIM studies of intramolecular hydrogen bonds in dicoumarols

    International Nuclear Information System (INIS)

    Density functional calculations with Becke's three parameter hybrid method using the correlation functional of Lee, Yang and Parr (B3LYP) were carried out for 3,3'-benzylidenebis(4-hydroxycoumarin) (phenyldicoumarol, PhDC), 3,3'-methylenebis(4-hydroxycoumarin) (dicoumarol, DC) and the parent compound, 4-hydroxycoumarin (4-HC). Different basis sets were tested in the course of the calculations: 6-31G*, 6-31+G** and 6-311G*. In full agreement with available X-ray data, B3LYP/6-31G* calculations of the lowest-energy conformer, PhDC showed two O-H···O asymmetrical intramolecular hydrogen bonds with O···O distances 2.638 and 2.696 A. The HB energies in PhDC were estimated of -55.46 and -52.32 kJ/mol, respectively. The values obtained correlated with the calculated and experimental O···O distances and predicted difference in the hydrogen bonding strengths in PhDC. The total HB energy in PhDC was calculated of -107.73 kJ/mol. At the same level of theory, both O···O intramolecular distances in DC were calculated identical (2.696 A) and thus two symmetrical hydrogen bondings were obtained. The single HB strength was estimated of -50.89 kJ/mol and the total one of -101.79 kJ/mol. The electron density (ρb) and Laplacian (∇2ρb) properties, estimated by AIM calculations, showed that both O···H bonds have low ρb and positive ∇2ρb values (consistent with electrostatic character of the HBs), whereas both O-H bonds have covalent character (∇2ρb-1) in comparison with that obtained for the second O-H which forms the weaker HB in PhDC (-559 cm-1)

  5. The origin of enantioselectivity in the l-threonine-derived phosphine-sulfonamide catalyzed aza-Morita-Baylis-Hillman reaction: Effects of the intramolecular hydrogen bonding

    KAUST Repository

    Lee, Richmond

    2013-01-01

    l-Threonine-derived phosphine-sulfonamide 4 was identified as the most efficient catalyst to promote enantioselective aza-Morita-Baylis-Hillman (MBH) reactions, affording the desired aza-MBH adducts with excellent enantioselectivities. Density functional theory (DFT) studies were carried out to elucidate the origin of the observed enantioselectivity. The importance of the intramolecular N-H⋯O hydrogen-bonding interaction between the sulfonamide and enolate groups was identified to be crucial in inducing a high degree of stereochemical control in both the enolate addition to imine and the subsequent proton transfer step, affording aza-MBH reactions with excellent enantioselectivity. © 2013 The Royal Society of Chemistry.

  6. Intramolecular Aldol Condensation of a - Oxo Ketene Dibenzylthioacetals: A Facile Route to Substituted Thiophenes

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A new method for the synthesis of substituted thiophenes was through intramolecular aldol condensation of α-oxo ketene dibenzylthioacetals.All products were confirmed with IR,1H NMR and elemental analysis.

  7. Aspects of organochalcogen (S, Se, Te) compounds stabilized by intramolecular coordination

    Indian Academy of Sciences (India)

    G Mugesh; Arunashree Panda; Harkesh B Singh

    2000-06-01

    The application of intramolecular coordination in the isolation of novel diaryl diselenides and their derivatives, monomeric chalcogenolato complexes of group 12 metals, glutathione peroxidase mimics, hybrid bi-, tri- and multidentate ligands and selenium-containing azamacrocycles is described.

  8. Synthesis of 2-Cyclopentenone Derivatives via Palladium-Catalyzed Intramolecular Carbonyl α-Alkenylation.

    Science.gov (United States)

    Chen, Panpan; Meng, Yinggao; Wang, Han; Han, Feipeng; Wang, Yulong; Song, Chuanjun; Chang, Junbiao

    2016-08-01

    2-Cyclopentenone derivatives have been efficiently synthesized from 5-bromo-5-hexen-2-ones via palladium-catalyzed intramolecular carbonyl α-alkenylation followed by double-bond migration under mild reaction conditions. PMID:27463262

  9. Mechanism of the Intramolecular Hexadehydro-Diels-Alder Reaction.

    Science.gov (United States)

    Marell, Daniel J; Furan, Lawrence R; Woods, Brian P; Lei, Xiangyun; Bendelsmith, Andrew J; Cramer, Christopher J; Hoye, Thomas R; Kuwata, Keith T

    2015-12-01

    Theoretical analysis of the mechanism of the intramolecular hexadehydro-Diels-Alder (HDDA) reaction, validated against prior and newly measured kinetic data for a number of different tethered yne-diynes, indicates that the reaction proceeds in a highly asynchronous fashion. The rate-determining step is bond formation at the alkyne termini nearest the tether, which involves a transition-state structure exhibiting substantial diradical character. Whether the reaction then continues to close the remaining bond in a concerted fashion or in a stepwise fashion (i.e., with an intervening intermediate) depends on the substituents at the remaining terminal alkyne positions. Computational modeling of the HDDA reaction is complicated by the significant diradical character that arises along the reaction coordinate, which leads to instabilities in both restricted singlet Kohn-Sham density functional theory (DFT) and coupled cluster theory based on a Hartree-Fock reference wave function. A consistent picture emerges, however, from comparison of broken-symmetry DFT calculations and second-order perturbation theory based on complete-active-space self-consistent-field (CASPT2) calculations. PMID:26270857

  10. Low activation barriers characterize intramolecular electron transfer in ascorbate oxidase

    DEFF Research Database (Denmark)

    Farver, O; Pecht, I

    1992-01-01

    Anaerobic reduction kinetics of the zucchini squash ascorbate oxidase (AO; L-ascorbate:oxygen oxidoreductase, EC 1.10.3.3) by pulse radiolytically produced CO2- radical ions were investigated. Changes in the absorption bands of type 1 [Cu(II)] (610 nm) and type 3 [Cu(II)] (330 nm) were monitored...... transfer to type 3 [Cu(II)]. The observed specific rates are similar to values reported for the limiting-rate constants of AO reduction by excess substrate, suggesting that internal electron transfer is the rate-determining step of AO activity. The temperature dependence of the intramolecular electron...... transfer rate constants was measured from 275 to 308 K at pH 5.5 and, from the Eyring plots, low activation enthalpies were calculated--namely, 9.1 +/- 1.1 and 6.8 +/- 1.0 kJ.mol-1 for the fastest and slowest phases, respectively. The activation entropies observed for these respective phases were -170...

  11. Theoretical Study on Intramolecular Proton Transfer of Perylenequinonoid Derivatives

    Institute of Scientific and Technical Information of China (English)

    Liang SHEN; De Zhan CHEN

    2004-01-01

    Intramolecular proton transfer of hypomycin A in the ground state S0 and singlet excited state S1 were calculated by high level quantum chemical method in this letter. It was found that the IPT barriers for I→TS1 are 38.56 kJ/mol in S0 and 8.19 kJ/mol in S1, while those for I→TS4 get approximately 17 kJ/mol higher in S0 and 28 kJ/mol higher in S1. The calculation of IPT rate constants suggests that the experiment observed process of PQD is in S1. The height of the IPT barriers correlate not only with the variance of charge for labile hydrogen, the change of H-bond's length, the change of O-H bond's length and the change of O-O distance, but also with the reactant molecular H-bond's length. Moreover, the correlations are the same for S0 and S1.

  12. Intramolecular Alkene Aminocarbonylation Using Concerted Cycloadditions of Amino-Isocyanates.

    Science.gov (United States)

    Ivanovich, Ryan A; Clavette, Christian; Vincent-Rocan, Jean-François; Roveda, Jean-Grégoire; Gorelsky, Serge I; Beauchemin, André M

    2016-06-01

    The ubiquity of nitrogen heterocycles in biologically active molecules challenges synthetic chemists to develop a variety of tools for their construction. While developing metal-free hydroamination reactions of hydrazine derivatives, it was discovered that carbazates and semicarbazides can also lead to alkene aminocarbonylation products if nitrogen-substituted isocyanates (N-isocyanates) are formed in situ as reactive intermediates. At first this reaction required high temperatures (150-200 °C), and issues included competing hydroamination and N-isocyanate dimerization pathways. Herein, improved conditions for concerted intramolecular alkene aminocarbonylation with N-isocyanates are reported. The use of βN-benzyl carbazate precursors allows the effective minimization of N-isocyanate dimerization. Diminished dimerization leads to higher yields of alkene aminocarbonylation products, to reactivity at lower temperatures, and to an improved scope for a reaction sequence involving alkene aminocarbonylation followed by 1,2-migration of the benzyl group. Furthermore, fine-tuning of the blocking (masking) group on the N-isocyanate precursor, and reaction conditions relying on base catalysis for N-isocyanate formation from simpler precursors resulted in room temperature reactivity, consequently minimizing the competing hydroamination pathway. Collectively, this work highlights that controlled reactivity of aminoisocyanates is possible, and provides a broadly applicable alkene aminocarbonylation approach to heterocycles possessing the β-aminocarbonyl motif. PMID:27112602

  13. Bridge- and Solvent-Mediated Intramolecular Electronic Communications in Ubiquinone-Based Biomolecular Wires

    OpenAIRE

    Liu, Xiao-Yuan; Ma, Wei; Zhou, Hao; Cao, Xiao-Ming; Long, Yi-Tao

    2015-01-01

    Intramolecular electronic communications of molecular wires play a crucial role for developing molecular devices. In the present work, we describe different degrees of intramolecular electronic communications in the redox processes of three ubiquinone-based biomolecular wires (Bis-CoQ0s) evaluated by electrochemistry and Density Functional Theory (DFT) methods in different solvents. We found that the bridges linkers have a significant effect on the electronic communications between the two pe...

  14. SYNTHESIS OF 8-HYDROXYQUINOLINE CHALCONES: TRANS CONFIGURATION, INTRAMOLECULAR HYDROGEN BONDS, BROMINATION, AND ANTIFUNGAL ACTIVITY

    OpenAIRE

    ALONSO J MARRUGO-GONZÁLEZ; VALERIE D ORLOV; ROBERTO FERNANDEZ-MAESTRE

    2012-01-01

    Nine (8-Hydroxyquinolin-5-yl)-arylpropenones were synthesized and their structures demonstrated by IR and NMRspectroscopy. These molecules showed transconfiguration and strong intramolecular hydrogen bonding; in the IR spectra of 5-formyl-8-hydroxyquinoline, 5-acetyl-8-hydroxyquinoline, 1-(8-hydroxyquinolin-5-yl)-3-phenylprop-2-en-1-one and 3-(8-hydroxyquinolin-5-yl)-1-phenylprop-2-en-1-one in CHCl3, besides the known intermolecular hydrogen band (~3180 cm-1), we identified the intramolecular...

  15. Dynamic Arrest in Polymer Melts: Competition between Packing and Intramolecular Barriers

    OpenAIRE

    Bernabei, Marco; Moreno, Ángel J.; Colmenero, Juan

    2008-01-01

    We present molecular dynamics simulations of a simple model for polymer melts with intramolecular barriers. We investigate structural relaxation as a function of the barrier strength. Dynamic correlators can be consistently analyzed within the framework of the mode coupling theory of the glass transition. Control parameters are tuned in order to induce a competition between general packing effects and polymer-specific intramolecular barriers as mechanisms for dynamic arrest. This competition ...

  16. Visible-Light-Induced Decarboxylative Functionalization of Carboxylic Acids and Their Derivatives.

    Science.gov (United States)

    Xuan, Jun; Zhang, Zhao-Guo; Xiao, Wen-Jing

    2015-12-21

    Visible-light-induced radical decarboxylative functionalization of carboxylic acids and their derivatives has recently received considerable attention as a novel and efficient method to create CC and CX bonds. Generally, this visible-light-promoted decarboxylation process can smoothly occur under mild reaction conditions with a broad range of substrates and an excellent functional-group tolerance. The radical species formed from the decarboxylation step can participate in not only single photocatalytic transformations, but also dual-catalytic cross-coupling reactions by combining photoredox catalysis with other catalytic processes. Recent advances in this research area are discussed herein. PMID:26509837

  17. Critical Design Features of Phenyl Carboxylate-Containing Polymer Microbicides

    OpenAIRE

    Rando, Robert F.; Obara, Sakae; Osterling, Mark C.; Mankowski, Marie; Miller, Shendra R.; Ferguson, Mary L.; Krebs, Fred C.; Wigdahl, Brian; Labib, Mohamed; Kokubo, Hiroyasu

    2006-01-01

    Recent studies of cellulose-based polymers substituted with carboxylic acids like cellulose acetate phthalate (CAP) have demonstrated the utility of using carboxylic acid groups instead of the more common sulfate or sulfonate moieties. However, the pKa of the free carboxylic acid group is very important and needs careful selection. In a polymer like CAP the pKa is approximately 5.28. This means that under the low pH conditions found in the vaginal lumen, CAP would be only minimally soluble an...

  18. Applications of Carboxylic Acid Reductases in Oleaginous Microbes

    Energy Technology Data Exchange (ETDEWEB)

    Resch, Michael G.; Linger, Jeffrey; McGeehan, John; Tyo, Keith; Beckham, Gregg

    2016-04-24

    Carboxylic acid reductases (CARs) are recently emerging reductive enzymes for the direct production of aldehydes from biologically-produced carboxylic acids. Recent work has demonstrated that these powerful enzymes are able to reduce a very broad range of volatile- to long-chain fatty acids as well as aromatic acids. Here, we express four CAR enzymes from different fungal origins to test their activity against fatty acids commonly produced in oleaginous microbes. These in vitro results will inform metabolic engineering strategies to conduct mild biological reduction of carboxylic acids in situ, which is conventionally done via hydrotreating catalysis at high temperatures and hydrogen pressures.

  19. On DABAL-Me₃ promoted formation of amides

    OpenAIRE

    Dubois, Nathalie; Glynn, Daniel; McInally, Thomas; Rhodes, Barrie; Woodward, Simon; Irvine, Derek; Dodds, Chris

    2013-01-01

    The range and utility of DABAL-Me3 couplings of methyl esters and free carboxylic acids with primary and secondary amines under a variety of conditions (reflux, sealed tube, microwave) has been compared for a significant range of coupling partners of relevance to the preparation of amides of interest in pharmaceutical chemistry. Commercial microwave reactors promote the fastest couplings and allow the use of significantly sterically hindered amines (primary and secondary) and carboxylic acids...

  20. Synthesis, spectroscopic characterization and in vitro antimicrobial, anticancer and antileishmanial activities as well interaction with Salmon sperm DNA of newly synthesized carboxylic acid derivative, 4-(4-methoxy-2-nitrophenylamino)-4-oxobutanoic acid

    Science.gov (United States)

    Sirajuddin, Muhammad; Ali, Saqib; McKee, Vickie; Ullah, Hameed

    2015-03-01

    This paper stresses on the synthesis, characterization of novel carboxylic acid derivative and its application in pharmaceutics. Carboxylic acid derivatives have a growing importance in medicine, particularly in oncology. A novel carboxylic acid, 4-(4-methoxy-2-nitrophenylamino)-4-oxobutanoic acid, was synthesized and characterized by elemental analysis, FT-IR, NMR (1H, and 13C), mass spectrometry and single crystal X-ray structural analysis. The structure of the title compound, C11H12N2O6, shows the molecules dimerised by short intramolecular Osbnd H⋯O hydrogen bonds. The compound was screened for in vitro antimicrobial, anticancer, and antileishmanial activities as well as interaction with SS-DNA. The compound was also checked for in vitro anticancer activity against BHK-21, H-157 and HCEC cell lines, and showed significant anticancer activity. The compound was almost non-toxic towards human corneal epithelial cells (HCEC) and did not show more than 7.4% antiproliferative activity when used at the 2.0 μg/mL end concentration. It was also tested for antileishmanial activity against the promastigote form of leishmania major and obtained attractive result. DNA interaction study exposes that the binding mode of the compound with SS-DNA is an intercalative as it results in hypochromism along with minor red shift. A new and efficient strategy to identify pharmacophores sites in carboxylic acid derivative for antibacterial/antifungal activity using Petra, Osiris and Molinspiration (POM) analyses was also carried out.

  1. Crystal structure of (μ-1,4-di-carb-oxy-butane-1,4-di-carboxyl-ato)bis-[bis-(tri-phenyl-phosphane)silver(I)] di-chloro-methane tris-olvate.

    Science.gov (United States)

    Frenzel, Peter; Korb, Marcus; Lang, Heinrich

    2016-02-01

    The mol-ecular structure of the tetra-kis(tri-phenyl-phosphan-yl)disilver salt of butane-1,1,4,4-tetra-carb-oxy-lic acid, [Ag2(C8H8O8)(C18H15P)4]·3CH2Cl2, crystallizes with one and a half mol-ecules of di-chloro-methane in the asymmetric unit. The coordination complex exhibits an inversion centre through the central CH2-CH2 bond. The Ag(I) atom has a distorted trigonal-planar P2O coordination environment. The packing is characterized by inter-molecular T-shaped π-π inter-actions between the phenyl rings of the PPh3 substituents in neighbouring mol-ecules, forming a ladder-type superstructure parallel to [010]. These ladders are arranged in layers parallel to (101). Intra-molecular hydrogen bonds between the OH group and one O atom of the Ag-bonded carboxyl-ate group results in an asymmetric bidendate coordination of the carboxyl-ate moiety to the Ag(I) ion. PMID:26958391

  2. Dynamics of the excited state intramolecular charge transfer

    International Nuclear Information System (INIS)

    The 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan), a derivative of 6-propanoyl- 2-dimethylaminonaphthalene (prodan), has been used as a fluorescent probe in cell imaging, especially in visualizing the lipid rafts by the generalized polarization (GP) images, where GP=(I440-I490)/(I440+I490) with I being the fluorescence intensity. The fluorescence spectrum of laurdan is sensitive to its dipolar environment due to the intramolecular charge transfer (ICT) process in S1 state, which results in a dual emission from the locally excited (LE) and the ICT states. The ICT process and the solvation of the ICT state are very sensitive to the dipolar nature of the environment. In this work, the ICT of laurdan in ethanol has been studied by femtosecond time resolved fluorescence (TRF), especially TRF spectra measurement without the conventional spectral reconstruction method. TRF probes the excited states exclusively, a unique advantage over the pump/probe transient absorption technique, although time resolution of the TRF is generally lower than transient absorption and the TRF spectra measurement was possible only though the spectral reconstruction. Over the years, critical advances in TRF technique have been made in our group to achieve <50 fs time resolution with direct full spectra measurement capability. Detailed ICT and the subsequent solvation processes can be visualized unambiguously from the TRF spectra. Fig. 1 shows the TRF spectra of laurdan in ethanol at several time delays. Surprisingly, two bands at 433 and 476 nm are clearly visible in the TRF spectra of laurdan even at T = 0 fs. As time increases, the band at 476 nm shifts to the red while its intensity increases. The band at 433 nm also shifts slightly to the red, but loses intensity as time increases. The intensity of the 476 nm band reaches maximum at around 5 ps, where it is roughly twice as intense as that at 0 fs, and stays constant until lifetime decay is noticeable. The spectra were fit by two log

  3. Novel Polymers with a High Carboxylic Acid Loading

    DEFF Research Database (Denmark)

    Thomsen, Anders Daugaard; Malmström, Eva; Hvilsted, Søren

    2006-01-01

    ABSTRACT: Click chemistry has been used to prepare a range of novel polymers with pendant carboxylic acid side groups. Four azido carboxylic acids, either mono- or difunctional and aliphatic or aromatic, have been prepared and thoroughly characterized. Extensive model reactions with 1-ethyl-4......-hydroxybenzene, the simplest model for poly(4-hydroxystyrene), and the four azido carboxylic acids have been conucted to establish the proper reaction conditions and provide an analytical frame for the corresponding polymers. Poly(4-hydroxystyrene) moieties in three different polymers—poly (4-hydroxystyrene......), poly(4-hydroxystyrene-co-methyl methacrylate), and poly(4-hydroxy- styrene-b-styrene)-----have been quantitatively transformed into oxypropynes by the use of either Williamson nr Mitsunobu strategies and subsequently reacted with the azido carboxylic acids. Detailed differential scanning calorimetry...

  4. Selective carboxyl methylation of structurally altered calmodulins in Xenopus oocytes

    International Nuclear Information System (INIS)

    The eucaryotic protein carboxyl methyltransferase specifically modifies atypical D-aspartyl and L-isoaspartyl residues which are generated spontaneously as proteins age. The selectivity of the enzyme for altered proteins in intact cells was explored by co-injecting Xenopus laevis oocytes with S-adenosyl-L-[methyl-3H]methionine and structurally altered calmodulins generated during a 14-day preincubation in vitro. Control experiments indicated that the oocyte protein carboxyl methyltransferase was not saturated with endogenous substrates, since protein carboxyl methylation rates could be stimulated up to 8-fold by increasing concentrations of injected calmodulin. The oocyte protein carboxyl methyltransferase showed strong selectivities for bovine brain and bacterially synthesized calmodulins which had been preincubated in the presence of 1 mM EDTA relative to calmodulins which had been preincubated with 1 mM CaCl2. Radioactive methyl groups were incorporated into base-stable linkages with recombinant calmodulin as well as into carboxyl methyl esters following its microinjection into oocytes. This base-stable radioactivity most likely represents the trimethylation of lysine 115, a highly conserved post-translational modification which is present in bovine and Xenopus but not in bacterially synthesized calmodulin. Endogenous oocyte calmodulin incorporates radioactivity into both carboxyl methyl esters and into base-stable linkages following microinjection of oocytes with S-adenosyl-[methyl-3H]methionine alone. The rate of oocyte calmodulin carboxyl methylation in injected oocytes is calculated to be similar to that of lysine 115 trimethylation, suggesting that the rate of calmodulin carboxyl methylation is similar to that of calmodulin synthesis. At steady state, oocyte calmodulin contains approximately 0.0002 esters/mol of protein, which turn over rapidly

  5. The essential activated carboxyl group of inorganic pyrophosphatase.

    Science.gov (United States)

    Avaeva, S M; Bakuleva, N P; Baratova, L A; Nazarova, T I; Fink, N Y

    1977-05-12

    1. A carboxyl group of high reactivity has been found in inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) from yeast. This group interacts with agents which react neither with carboxyl groups of low molecular weight compounds nor with other carboxyl groups of the protein. 2. The reaction of this activated carboxyl group with inorganic phosphate, hydroxylamine, N-methyl- and O-methylhydroxylamines, and glycine methyl ester has been studied. 3. Homoserine and homoserine lactone were found in the hydrolyzate of phosphorylated and NaBH4-reduced pyrophosphatase, indicating that an aspartyl residue is phosphorylated. 4. Hydroxylamine and other nucleophilic agents cause inactivation of pyrophosphatase as a result of interaction with a carboxyl group. Both diaminobutyric and diaminopropionic acids were seen in the acid hydrolyzate of the protein treated with hydroxylamine and subjected to rearrangement in the presence of carbodiimide. 5. The ways in which the activation of a carboxyl group in the enzyme is achieved and the presumed mechanism of action of inorganic pyrophosphatase are discussed. PMID:16652

  6. Silver colloidal effects on excited-state structure and intramolecular charge transfer of p-N, N-dimethylaminobenzoic acid in aqueous cyclodextrin solutions

    International Nuclear Information System (INIS)

    The silver colloidal effects on the excited-state structure and intramolecular charge transfer (ICT) of p-N,N-dimethylaminobenzoic acid (DMABA) in aqueous cyclodextrin (CD) solutions have been investigated by UV-VIS absorption, steady-state and time-resolved fluorescence, and transient Raman spectroscopy. As the concentration of silver colloids increases, the ratio of the ICT emission to the normal emission (Ia/Ib) of DMABA in the aqueous α-CD solutions are greatly decreased while the Ia/Ib values in the aqueous β-CD solutions are significantly enhanced. It is also noteworthy that the ICT emission maxima are red-shifted by 15-40 nm upon addition of silver colloids, implying that DMABA encapsulated in α-CD or β-CD cavity is exposed to more polar environment. The transient resonance Raman spectra of DMABA in silver colloidal solutions demonstrate that DMABA in the excited-state is desorbed from silver colloidal surfaces as demonstrated by the disappearance of vs(CO2-)(1380 cm-1) with appearance of v (C-OH)(1280 cm-1) band, respectively. Thus, in the aqueous β-CD solutions the carboxylic acid group of DMABA in the excited-state can be readily hydrogen bonded with the secondary hydroxyl group of β-CD while in aqueous and α-CD solutions the carboxylic acid group of DMABA has the hydrogen-bonding interaction with water. Consequently, in the aqueous β-CD solutions the enhancement of the Ia/Ib value arises from the intermolecular hydrogen-bonding interaction between DMABA and the secondary hydroxyl group of β-CD as well as the lower polarity of the rim of the β-CD cavity compared to bulk water. This is also supported by the increase of the association constant for DMABA/β-CD complex in the presence of silver colloids

  7. Intramolecular ex vivo Fluorescence Resonance Energy Transfer (FRET of Dihydropyridine Receptor (DHPR β1a Subunit Reveals Conformational Change Induced by RYR1 in Mouse Skeletal Myotubes.

    Directory of Open Access Journals (Sweden)

    Dipankar Bhattacharya

    Full Text Available The dihydropyridine receptor (DHPR β1a subunit is essential for skeletal muscle excitation-contraction coupling, but the structural organization of β1a as part of the macromolecular DHPR-ryanodine receptor type I (RyR1 complex is still debatable. We used fluorescence resonance energy transfer (FRET to probe proximity relationships within the β1a subunit in cultured skeletal myotubes lacking or expressing RyR1. The fluorescein biarsenical reagent FlAsH was used as the FRET acceptor, which exhibits fluorescence upon binding to specific tetracysteine motifs, and enhanced cyan fluorescent protein (CFP was used as the FRET donor. Ten β1a reporter constructs were generated by inserting the CCPGCC FlAsH binding motif into five positions probing the five domains of β1a with either carboxyl or amino terminal fused CFP. FRET efficiency was largest when CCPGCC was positioned next to CFP, and significant intramolecular FRET was observed for all constructs suggesting that in situ the β1a subunit has a relatively compact conformation in which the carboxyl and amino termini are not extended. Comparison of the FRET efficiency in wild type to that in dyspedic (lacking RyR1 myotubes revealed that in only one construct (H458 CCPGCC β1a -CFP FRET efficiency was specifically altered by the presence of RyR1. The present study reveals that the C-terminal of the β1a subunit changes conformation in the presence of RyR1 consistent with an interaction between the C-terminal of β1a and RyR1 in resting myotubes.

  8. Selective esterification of non-conjugated carboxylic acids in the presence of conjugated or aromatic carboxylic acids over active carbon supported methanesulfonic acid

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Non-conjugated carboxylic acids are selectively esterified in good yields in the presence of conjugated or aromatic carboxylic acids by stirring over active carbon supported methanesulfonic acid in di-chloromethane at room temperature.

  9. Kinetic and Thermodynamic Parameters for Uncatalyzed Esterification of Carboxylic Acid

    Directory of Open Access Journals (Sweden)

    Kehinde S. Bankole

    2014-06-01

    Full Text Available A fundamental study on uncatalyzed esterification of various biomass-derived aliphatic carboxylic acids with stoichiometric amount of ethanol has been investigated in an isothermal batch reactor, with the objective to convert carboxylic acids to corresponding ethyl esters and to determine both the kinetic and thermodynamic parameters. The effects of temperature on the conversion of carboxylic acid, kinetic and thermodynamic parameters have been investigated. Temperature was found to have significant effect on the rate of reaction and conversion of carboxylic acid. A simple second order reversible kinetic model was developed to determine the kinetic and thermodynamic parameters. The thermodynamic and kinetic parameters varied for uncatalyzed esterification reaction of both short-chain and long-chain carboxylic acids considered. The predicted data from the kinetic model were correlated with experimental data and the two sets of data agreed reasonably well for the uncatalyzed esterification systems. It was observed that the Van’t Hoff plot for uncatalyzed esterification of linoleic acid was non-linear curve, whereas for the Arrhenius and Eyring plots, they were linear. Additional experiments to assess the catalytic and corrosion effects of several metallic substances revealed Inconel 625 alloy, nickel wire and stainless steel materials were susceptible to corrosion problem with uncatalyzed esterification reaction at elevated reaction temperatures. However, tantalum and grade-5 titanium materials were corrosion resistance metals, suitable for similar reaction conditions and this can encourage the design of a flow reactor system. Although, uncatalyzed esterification of carboxylic acids at elevated reaction temperature is still at laboratory scale. It is our hope that the estimated kinetic and thermodynamic parameters would be the guiding tools for reactor scale-up, thus providing a new perspective into the conversion of biomass-derived carboxylic

  10. Reações Pericíclicas Intramoleculares na Síntese de Novos Cromenos

    OpenAIRE

    Laia, Fernanda Maria Ribeiro

    2015-01-01

    O trabalho apresentado nesta tese de doutoramento teve como objetivo a síntese de novos derivados de cromenos através de reações pericíclicas intramoleculares. A concretização deste objetivo foi conseguida através do estudo de reações de ciclo-adição 1,3-dipolar intramolecular de iletos azometinos, e de ciclo-adição 1,7- e 1,3-dipolar intramolecular de aniões metil 1-azafulvénio. Foi também explorada a síntese de derivados de cromenos via rearranjo de Claisen de éteres arílicos e pro...

  11. Mean-Field Theory of Intra-Molecular Charge Ordering in (TTM--TTP)I3

    Science.gov (United States)

    Omori, Yukiko; Tsuchiizu, Masahisa; Suzumura, Yoshikazu

    2011-02-01

    We examine an intra-molecular charge-ordered (ICO) state in the multi-orbital molecular compound (TTM--TTP)I3 on the basis of an effective two-orbital model derived from ab initio calculations. Representing the model in terms of the fragment molecular-orbital (MO) picture, the ICO state is described as the charge disproportionation on the left and right fragment MOs. By applying the mean-field theory, the phase diagram of the ground state is obtained as a function of the inter-molecular Coulomb repulsion and the intra-molecular transfer integral. The ICO state is stabilized by large inter-fragment Coulomb interactions, and the small intra-molecular transfer energy between two fragment MOs. Furthermore, we examine the finite-temperature phase diagram. The relevance to the experimental observations in the molecular compound of (TTM--TTP)I3 is also discussed.

  12. Photo-induced intramolecular electron transfer and intramolecular vibrational relaxation of rhodamine 6G in DMSO revealed by multiplex transient grating spectroscopy

    International Nuclear Information System (INIS)

    Photo-induced intramolecular electron transfer (PIET) and intramolecular vibrational relaxation (IVR) dynamics of the excited state of rhodamine 6G (Rh6G+) in DMSO are investigated by multiplex transient grating. Two major components are resolved in the dynamics of Rh6G+. The first component, with a lifetime τPIET = 140 fs–260 fs, is attributed to PIET from the phenyl ring to the xanthene plane. The IVR process occurring in the range τIVR = 3.3 ps–5.2 ps is much slower than the first component. The PIET and IVR processes occurring in the excited state of Rh6G+ are quantitatively determined, and a better understanding of the relationship between these processes is obtained. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  13. Photophysics of 2-(4'-amino-2'-hydroxyphenyl)-1H-imidazo-[4,5-c]pyridine and its analogues: intramolecular proton transfer versus intramolecular charge transfer.

    Science.gov (United States)

    Behera, Santosh Kumar; Karak, Ananda; Krishnamoorthy, G

    2015-02-12

    Photophysical characteristics of 2-(4'-amino-2'-hydroxyphenyl)-1H-imidazo-[4,5-c]pyridine (AHPIP-c) have been studied in various aprotic and protic solvents using UV-visible, steady state fluorescence and time-resolved fluorescence spectroscopic techniques. To comprehend the competition between the intramolecular charge transfer (ICT) and the excited state intramolecular proton transfer (ESIPT) processes, the photophysical properties of 2-(4'-amino-2'-methoxyphenyl)-1H-imidazo-[4,5-c]pyridine (AMPIP-c) and 2-(4'-aminophenyl)-1H-imidazo-[4,5-c]pyridine (APIP-c) were also investigated. Though APIP-c displays twisted ICT (TICT) emission in protic solvents, AHPIP-c exhibits normal and tautomer emissions in aprotic as well as in protic solvents due to ESIPT. However, the methoxy derivative, AMPIP-c, emits weak TICT fluorescence in methanol. PMID:25337987

  14. Large molecules on surfaces: deposition and intramolecular STM manipulation by directional forces

    International Nuclear Information System (INIS)

    Intramolecular manipulation of single molecules on a surface with a scanning tunnelling microscope enables the controlled modification of their structure and, consequently, their physical and chemical properties. This review presents examples of intramolecular manipulation experiments with rather large molecules, driven by directional, i.e. chemical or electrostatic, forces between tip and molecule. It is shown how various regimes of forces can be explored and characterized with one and the same manipulation of a single molecule by changing the tip-surface distance. Furthermore, different deposition techniques under ultrahigh vacuum conditions are discussed because the increasing functionality of such molecules can lead to fragmentation during the heating step, making their clean deposition difficult.

  15. Reversible Tuning of Interfacial and Intramolecular Charge Transfer in Individual MnPc Molecules.

    Science.gov (United States)

    Zhong, Jian-Qiang; Wang, Zhunzhun; Zhang, Jia Lin; Wright, Christopher A; Yuan, Kaidi; Gu, Chengding; Tadich, Anton; Qi, Dongchen; Li, He Xing; Lai, Min; Wu, Kai; Xu, Guo Qin; Hu, Wenping; Li, Zhenyu; Chen, Wei

    2015-12-01

    The reversible selective hydrogenation and dehydrogenation of individual manganese phthalocyanine (MnPc) molecules has been investigated using photoelectron spectroscopy (PES), low-temperature scanning tunneling microscopy (LT-STM), synchrotron-based near edge X-ray absorption fine structure (NEXAFS) measurements, and supported by density functional theory (DFT) calculations. It is shown conclusively that interfacial and intramolecular charge transfer arises during the hydrogenation process. The electronic energetics upon hydrogenation is identified, enabling a greater understanding of interfacial and intramolecular charge transportation in the field of single-molecule electronics. PMID:26528623

  16. Enhanced dispersion stability and mobility of carboxyl-functionalized carbon nanotubes in aqueous solutions through strong hydrogen bonds

    International Nuclear Information System (INIS)

    Dispersion of carbon nanotubes has been heavily studied due to its importance for their technical applications, toxic effects, and environmental impacts. Common electrolytes, such as sodium chloride and potassium chloride, promote agglomeration of nanoparticles in aqueous solutions. On the contrary, we discovered that acetic electrolytes enhanced the dispersion of multi-walled carbon nanotubes (MWCNTs) with carboxyl functional group through the strong hydrogen bond, which was confirmed by UV–Vis spectrometry, dispersion observations and aerosolization-quantification method. When concentrations of acetate electrolytes such as ammonium acetate (CH3CO2NH4) and sodium acetate (CH3CO2Na) were lower than 0.03 mol per liter, MWCNT suspensions showed better dispersion and had higher mobility in porous media. The effects by the acetic environment are also applicable to other nanoparticles with the carboxyl functional group, which was demonstrated with polystyrene latex particles as an example

  17. Enhanced dispersion stability and mobility of carboxyl-functionalized carbon nanotubes in aqueous solutions through strong hydrogen bonds

    Energy Technology Data Exchange (ETDEWEB)

    Bahk, Yeon Kyoung; He, Xu; Gitsis, Emmanouil; Kuo, Yu-Ying [ETH Zurich, Institute of Environmental Engineering (Switzerland); Kim, Nayoung [EMPA, Building Energy Materials and Components (Switzerland); Wang, Jing, E-mail: jing.wang@ifu.baug.ethz.ch [ETH Zurich, Institute of Environmental Engineering (Switzerland)

    2015-10-15

    Dispersion of carbon nanotubes has been heavily studied due to its importance for their technical applications, toxic effects, and environmental impacts. Common electrolytes, such as sodium chloride and potassium chloride, promote agglomeration of nanoparticles in aqueous solutions. On the contrary, we discovered that acetic electrolytes enhanced the dispersion of multi-walled carbon nanotubes (MWCNTs) with carboxyl functional group through the strong hydrogen bond, which was confirmed by UV–Vis spectrometry, dispersion observations and aerosolization-quantification method. When concentrations of acetate electrolytes such as ammonium acetate (CH{sub 3}CO{sub 2}NH{sub 4}) and sodium acetate (CH{sub 3}CO{sub 2}Na) were lower than 0.03 mol per liter, MWCNT suspensions showed better dispersion and had higher mobility in porous media. The effects by the acetic environment are also applicable to other nanoparticles with the carboxyl functional group, which was demonstrated with polystyrene latex particles as an example.

  18. Bacterial Conversion of Hydroxylamino Aromatic Compounds by both Lyase and Mutase Enzymes Involves Intramolecular Transfer of Hydroxyl Groups

    OpenAIRE

    Nadeau, Lloyd J.; He, Zhongqi; Spain, Jim C.

    2003-01-01

    Hydroxylamino aromatic compounds are converted to either the corresponding aminophenols or protocatechuate during the bacterial degradation of nitroaromatic compounds. The origin of the hydroxyl group of the products could be the substrate itself (intramolecular transfer mechanism) or the solvent water (intermolecular transfer mechanism). The conversion of hydroxylaminobenzene to 2-aminophenol catalyzed by a mutase from Pseudomonas pseudoalcaligenes JS45 proceeds by an intramolecular hydroxyl...

  19. Application of the intramolecular vinylogous Morita-Baylis-Hillman reaction toward the synthesis of the spinosyn A tricyclic nucleus.

    Science.gov (United States)

    Mergott, Dustin J; Frank, Scott A; Roush, William R

    2002-09-01

    [reaction: see text] A concise synthesis of the spinosyn A tricyclic nucleus 27 has been developed by a route featuring a one-pot tandem intramolecular Diels-Alder reaction and intramolecular vinylogous Morita-Baylis-Hillman cyclization in which five stereocenters in tricycle 10 are set with excellent selectivity. PMID:12201741

  20. (1H-1,3-Benzimidazole-5,6-dicarboxylic acid(5-carboxylato-1H-1,3-benzimidazole-6-carboxylic acidsilver(I monohydrate

    Directory of Open Access Journals (Sweden)

    Hong Zhai

    2009-11-01

    Full Text Available The title compound, [Ag(C9H5N2O4(C9H6N2O4]·H2O, contains one independent Ag atom, a neutral 1H-benzimidazole-5,6-dicarboxylic acid (bdcH, its monodeprotonated form, i.e. 5-carboxylato-1H-1,3-benzimidazole-6-carboxylic acid (bdc, and one solvent water molecule, the latter being disordered over three sites with site occupancy factors of 0.375 (× 2 and 0.25. In addition, the H atom on one carboxylic acid residue is disordered, being connected to each of the O atoms 50% of the time. The Ag atom is in a virtually linear geometry defined by two N atoms derived from the bdc and bdcH ligands. The three-dimensional supramolecular structure is stablized by extensive O—H...O and N—H...O hydrogen bonds. An intramolecular O—H...O hydrogen bond is also present.

  1. Pyrazine Carboxylic Acid Derivatives of Dichlorobis(Cyclopentadienyltitanium(IV

    Directory of Open Access Journals (Sweden)

    Satish Chandra Dixit

    2012-07-01

    Full Text Available Reactions of dichlorobis(cyclopentadienyltitanium(IV with pyrazine carboxylic acids viz. 2-pyrazine carboxylic acid (2-PzCH, 5-methyl-2-pyrazine carboxylic acid (MPzCH and 2,3-pyrazine dicarboxylic acid (2,3-PzDCH2 were carried out in different stoichiometric ratios. Complexes of the type Cp2Ti(2-PzCCl , Cp2Ti(2-PzC2 ,Cp2Ti(MPzCCl,Cp2Ti(MPzC2, Cp2Ti(2,3-PzDCHCl and Cp2Ti(2,3-PzDCH2 were obtained. These newly synthesized complexes were characterized on the basis of elemental analyses, electrical conductance, magnetic moment and spectral data.

  2. Pyrazine Carboxylic Acid Derivatives of Dichlorobis(Cyclopentadienyl)titanium(IV)

    OpenAIRE

    Satish Chandra Dixit; Rohit Kumar Singh

    2012-01-01

    Reactions of dichlorobis(cyclopentadienyl)titanium(IV) with pyrazine carboxylic acids viz. 2-pyrazine carboxylic acid (2-PzCH), 5-methyl-2-pyrazine carboxylic acid (MPzCH) and 2,3-pyrazine dicarboxylic acid (2,3-PzDCH2) were carried out in different stoichiometric ratios. Complexes of the type Cp2Ti(2-PzC)Cl , Cp2Ti(2-PzC)2 ,Cp2Ti(MPzC)Cl,Cp2Ti(MPzC)2, Cp2Ti(2,3-PzDCH)Cl and Cp2Ti(2,3-PzDCH)2 were obtained. These newly synthesized complexes were characterized on the basis of elemental analyse...

  3. Effect of solvent on proton location and dynamic behavior in short intramolecular hydrogen bonds studied by molecular dynamics simulations and NMR experiments

    Energy Technology Data Exchange (ETDEWEB)

    Mori, Yukie, E-mail: mori.yukie@ocha.ac.jp; Masuda, Yuichi

    2015-09-08

    Highlights: • MD simulations were performed to study dynamics of strong hydrogen bonds. • Nuclear magnetic relaxation times of proton were measured in solution. • The hydrogen bond of dibenzoylmethane enol is asymmetric in methanol solution. • Formation or breakage of intermolecular hydrogen bonds can trigger proton transfer. • Dimethylsulfoxide may form a bifurcated hydrogen bond with a hydrogen-bonded system. - Abstract: Hydrogen phthalate anion has a short strong O–H–O hydrogen bond (H-bond). According to previous experimental studies, the H-bond is asymmetric and two tautomers are interconverted in aqueous solutions. In the present study, the effects of polar solvents on the H-bond in a zwitterionic hydrogen phthalate derivative 1 were investigated by quantum mechanics/molecular mechanics molecular dynamics (MD) simulations. The analyses of the trajectories for the methanol solution showed that the H-bonding proton tends to be located closer to the carboxylate group that forms fewer intermolecular H-bonds, than to the other carboxylate group and that the intramolecular proton transfer in 1 is triggered by the breakage and/or formation of an intermolecular H-bond. The enol form of dibenzoylmethane (2) also has a short H-bond, and the OH bond is reported to be rather long (>1.1 Å) in the crystal. In the present study, the effects of the solvent on the H-bond in 2 were investigated by molecular orbital (MO) calculations, MD simulations and nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) calculations for 2 in vacuum indicated that the barrier height for the intramolecular proton transfer is almost the same as the zero-point energy of the vibrational ground state, resulting in broad distribution of the proton density along the H-bond, owing to the nuclear quantum effect. The OH distances were determined in CCl{sub 4}, acetonitrile, and dimethylsulfoxide solutions from the magnetic dipolar interactions between the {sup 17

  4. Effect of solvent on proton location and dynamic behavior in short intramolecular hydrogen bonds studied by molecular dynamics simulations and NMR experiments

    International Nuclear Information System (INIS)

    Highlights: • MD simulations were performed to study dynamics of strong hydrogen bonds. • Nuclear magnetic relaxation times of proton were measured in solution. • The hydrogen bond of dibenzoylmethane enol is asymmetric in methanol solution. • Formation or breakage of intermolecular hydrogen bonds can trigger proton transfer. • Dimethylsulfoxide may form a bifurcated hydrogen bond with a hydrogen-bonded system. - Abstract: Hydrogen phthalate anion has a short strong O–H–O hydrogen bond (H-bond). According to previous experimental studies, the H-bond is asymmetric and two tautomers are interconverted in aqueous solutions. In the present study, the effects of polar solvents on the H-bond in a zwitterionic hydrogen phthalate derivative 1 were investigated by quantum mechanics/molecular mechanics molecular dynamics (MD) simulations. The analyses of the trajectories for the methanol solution showed that the H-bonding proton tends to be located closer to the carboxylate group that forms fewer intermolecular H-bonds, than to the other carboxylate group and that the intramolecular proton transfer in 1 is triggered by the breakage and/or formation of an intermolecular H-bond. The enol form of dibenzoylmethane (2) also has a short H-bond, and the OH bond is reported to be rather long (>1.1 Å) in the crystal. In the present study, the effects of the solvent on the H-bond in 2 were investigated by molecular orbital (MO) calculations, MD simulations and nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) calculations for 2 in vacuum indicated that the barrier height for the intramolecular proton transfer is almost the same as the zero-point energy of the vibrational ground state, resulting in broad distribution of the proton density along the H-bond, owing to the nuclear quantum effect. The OH distances were determined in CCl4, acetonitrile, and dimethylsulfoxide solutions from the magnetic dipolar interactions between the 17O and 1H

  5. Radiolysis of carboxylic acids adsorbed in clay minerals

    International Nuclear Information System (INIS)

    This research is aimed at studying the effect of ionizing radiation in an heterogeneous system formed by a carboxylic acid adsorbed in a clay mineral. The study is focussed to discriminate if the presence of a solid surface alters the formation and distribution of radiolytic products in relation to the radiolysis of the carboxylic acid without the surface (clay). The results showed that the radiolysis of the system clay-acid goes along a defined path rather than showing various pathways of decomposition as in the case of simple aqueous solutions. The main pathway was the decarboxylation of the target compound rather than condensation/dimerization reactions

  6. Cyclodextrin derivatives with cyanohydrin and carboxylate groups as artificial glycosidases

    DEFF Research Database (Denmark)

    Bols, Mikael; Ortega-Caballero, Fernando

    2006-01-01

    Two cyclodextrin derivatives (1 and 2) were prepared in an attempt to create glycosidase mimics with a general acid catalyst and a nucleophilic carboxylate group. The catalysts 1 and 2 were found to catalyse the hydrolysis of 4-nitrophenyl beta-D-glucopyranoside at pH 8.0, but rapidly underwent...... decomposition with loss of hydrogen cyanide to convert the cyanohydrin to the corresponding aldehyde. The initial rate of the catalysis shows that the cyanohydrin group in these molecules functions as a good catalyst, but that the carboxylate has no positive effect. The decomposition product aldehydes display...

  7. Biotin Carboxyl Carrier Protein in Barley Chloroplast Membranes

    DEFF Research Database (Denmark)

    Kannangara, C. G.; Jense, C J

    1975-01-01

    Biotin localized in barley chloroplast lamellae is covalently bound to a single protein with an approximate molecular weight of 21000. It contains one mole of biotin per mole of protein and functions as a carboxyl carrier in the acetyl-CoA carboxylase reaction. The protein was obtained by...... solubilization of the lamellae in phenol/acetic acid/8 M urea. Feeding barley seedlings with [14C]-biotin revealed that the vitamin is not degraded into respiratory substrates by the plant, but is specifically incorporated into biotin carboxyl carrier protein....

  8. Coordination polymers: trapping of radionuclides and chemistry of tetravalent actinides (Th, U) carboxylates

    International Nuclear Information System (INIS)

    The use of nuclear energy obviously raises the question of the presence of radionuclides in the environment. Currently, their mitigation is a major issue associated with nuclear chemistry. This thesis focuses on both the trapping of radionuclides by porous solids called Metal-Organic Frameworks (MOF) and the crystal chemistry of the carboxylate of tetravalent actinides (AnIV). The academic knowledge of the reactivity of carboxylate of AnIV could help the understanding of actinides speciation in environment. We focused on the sequestration of iodine by aluminum based MOF. The functionalization (electron-donor group) of the MOF drastically enhances the iodine capture capacity. The removal of light actinides (Th and U) from aqueous solution was also investigated as well as the stability of (Al)-MOF under γ radiation. More than twenty coordination polymers based on tetravalent actinides have been synthesized and characterized by single crystal X-ray diffraction. The use of controlled hydrolysis promotes the formation of coordination polymers exhibiting polynuclear cluster ([U4], [Th6], [U6] and [U38]). In order to understand the formation of the largest cluster, the ex-situ study of the solvo-thermal synthesis of compound {U38} has also been investigated. (author)

  9. Usnic Acid and the Intramolecular Hydrogen Bond: A Computational Experiment for the Organic Laboratory

    Science.gov (United States)

    Green, Thomas K.; Lane, Charles A.

    2006-01-01

    A computational experiment is described for the organic chemistry laboratory that allows students to estimate the relative strengths of the intramolecular hydrogen bonds of usnic and isousnic acids, two related lichen secondary metabolites. Students first extract and purify usnic acid from common lichens and obtain [superscript 1]H NMR and IR…

  10. Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    1981-01-01

    Intramolecular electron transfer (ET) over distances up to about 10 Å between states in which the electron is localized on donor and acceptor groups by interaction with molecular or external solvent nuclear motion occurs, in particular, in two classes of systems. The excess electron in anionic ra...

  11. Coherent nuclear wave packet dynamics of laurdan launched by intramolecular charge transfer

    Directory of Open Access Journals (Sweden)

    Kim S. Y.

    2013-03-01

    Full Text Available Coherent nuclear wave packets in the product state launched by the ultrafast intramolecular charge transfer are observed by time-resolved fluorescence with 40 fs time resolution. Direct information on reaction coordinates and structural changes can be obtained.

  12. Solvent-induced reversible solid-state colour change of an intramolecular charge-transfer complex.

    Science.gov (United States)

    Li, Ping; Maier, Josef M; Hwang, Jungwun; Smith, Mark D; Krause, Jeanette A; Mullis, Brian T; Strickland, Sharon M S; Shimizu, Ken D

    2015-10-11

    A dynamic intramolecular charge-transfer (CT) complex was designed that displayed reversible colour changes in the solid-state when treated with different organic solvents. The origins of the dichromatism were shown to be due to solvent-inclusion, which induced changes in the relative orientations of the donor pyrene and acceptor naphthalenediimide units. PMID:26299357

  13. Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads

    KAUST Repository

    Whited, Matthew T.

    2012-01-01

    We report the synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage. Both molecules undergo symmetry-breaking intramolecular charge transfer in the excited state, and the directly linked dyad serves as a visible-light-absorbing analogue of 9,9′-bianthryl.

  14. Intramolecular and Lattice Melting in n-Alkane Monolayers: An Analog of Melting in Lipid Bilayers

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Herwig, K.W.; Matthies, B.;

    1999-01-01

    to 350 K above which a large thermal expansion and decrease in coherence length occurs. The MD simulations provide evidence that this behavior is due to a phase transition in the monolayer in which intramolecular and translational order are lost simultaneously. This melting transition is qualitatively...

  15. A novel stereoselective synthesis of N-heterocycles by intramolecular hydrovinylation

    DEFF Research Database (Denmark)

    Bothe, Ulrich; Rudbeck, H. C.; Tanner, David Ackland; Johannsen, Mogens

    2001-01-01

    A novel method for the synthesis of bicyclic amines has been developed. Cyclisation of 1,6-dienes by intramolecular hydrovinylation in the presence of catalytic amounts of allylpalladium chloride dimer afforded bicyclic amines in one step. Added phosphines, silver salts, as well as the nature of ...

  16. Rationalizing Ring-Size Selectivity in Intramolecular Pd-Catalyzed Allylations of Resonance-Stabilized Carbanions

    DEFF Research Database (Denmark)

    Norrby, Per-Ola; Mader, Mary M.; Vitale, Maxime; Prestat, Guillaume; Poli, Giovanni

    2003-01-01

    Computational methods were applied to the Pd-catalyzed intramolecular allylations of resonance-stabilized carbanions obtained from amide and ketone substrates, with the aim of rationalizing the endo- vs. exo-selectivity in the cyclizations. In addition, ester substrates were prepared and subjecte...

  17. New amidines from intramolecular cyclization in triflic acid of nitroketene aminals with a tethered phenyl ring

    Indian Academy of Sciences (India)

    Soro Yaya; Bamba Fanté; Siaka Sorho; Coustard Jean-Marie; Adima A Augustin

    2007-05-01

    Nitroketene aminals with a tethered phenyl group underwent an intramolecular cyclization in trifluoromethanesulfonic acid to afford the corresponding N-(3-ethyl-hydrohydroxyiminobenzocycloalkenylidene) methylamine trifluoromethanesulfonate. The yields were fair to good excepted for the starting compound 1-[N-ethyl-N-(2-phenylethyl)amino]-1-methylamino-2-nitroethene.

  18. Recent applications of intramolecular Diels-Alder reactions to natural product synthesis

    DEFF Research Database (Denmark)

    Juhl, M.; Tanner, David Ackland

    2009-01-01

    This tutorial review presents some recent examples of intramolecular Diels-Alder (IMDA) reactions as key complexity-generating steps in the total synthesis of structurally intricate natural products. The opportunities afforded by transannular (TADA) versions of the IMDA reaction in complex molecule...

  19. Synthesis, Crystal and Molecular Structure Studies and DFT Calculations of Phenyl Quinoline-2-Carboxylate and 2-Methoxyphenyl Quinoline-2-Carboxylate; Two New Quinoline-2 Carboxylic Derivatives

    Directory of Open Access Journals (Sweden)

    Edakot Fazal

    2015-02-01

    Full Text Available The crystal and molecular structures of the title compounds, phenyl quinoline-2-carboxylate and 2-methoxyphenyl quinoline-2-carboxylate, two new derivatives of quinolone-2-carboxylic acid, are reported and confirmed by single crystal X-ray diffraction and spectroscopic data. Compound (I, C16H11NO2, crystallizes in the monoclinic space group P21/c, with 8 molecules in the unit cell. The unit cell parameters are a = 14.7910(3 Å; b = 5.76446(12 Å; c = 28.4012(6 Å; β = 99.043(2°; V = 2391.45(9 Å3. Compound (II, C17H13NO5, crystallizes in the monoclinic space group P21/n with 4 molecules in the unit cell. The unit cell parameters are a = 9.6095(3 Å; b = 10.8040(3 Å; c = 13.2427(4 Å; β = 102.012(3°; V = 1344.76(7 Å3. Density functional theory (DFT geometry optimized molecular orbital calculations were performed and frontier molecular orbitals of each compound are displayed. Correlation between the calculated molecular orbital energies (eV for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound has been proposed. Additionally, similar correlations observed among six closely related compounds examining small structural differences to their frontier molecular orbital surfaces and from their DFT molecular orbital energies, provide further support for the suggested assignments of the title compounds.

  20. Synthesis of (2R,3aR,8aR)-6-Chloro-3a-hydroxy-1,2,3,3a,8,8a- hexahydropyrrolo[2,3-b]indole-2-carboxylic Acid Methyl Ester by Reductive Cyclization

    Institute of Scientific and Technical Information of China (English)

    HONG,Wen-Xu(洪文旭); YAO,Zhu-Jun(姚祝军)

    2004-01-01

    A synthesis of(2R,3aR,8aR)-6-chloro-3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid methyl ester(1)was achieved.An aldol reaction with Garner aldehyde,a hydroxyl introduction by Davis reagent,and a reductive intramolecular ring-closure reaction were served as the key steps.This piece of work provides a new way to synthesize the analogues of hexahydropyrrolo[2,3-b]indole,starting from readily available chemical substrates and inexpensive reagents.

  1. Light dependence of carboxylation capacity for C3 photosynthesis models

    Science.gov (United States)

    Photosynthesis at high light is often modelled by assuming limitation by the maximum capacity of Rubisco carboxylation at low carbon dioxide concentrations, by electron transport capacity at higher concentrations, and sometimes by triose-phosphate utilization rate at the highest concentrations. Pho...

  2. Conformation of some carboxylic acids and their derivatives

    NARCIS (Netherlands)

    Kanters, J.A.; Kroon, Jan; Peerdeman, A.F.; Schoone, J.C.

    1967-01-01

    The conformation in the crystalline state of some aliphatic carboxylic acids and their derivatives has been analysed. This analysis, based upon the results of structure determinations by means of X-ray diffraction, seems to support the concept that the conformation of a molecule is governed chiefly

  3. Acidity of carboxylic acids: a rebuttal and redefinition

    Czech Academy of Sciences Publication Activity Database

    Exner, Otto; Čársky, Petr

    2001-01-01

    Roč. 123, č. 39 (2001), s. 9564-9570. ISSN 0002-7863 R&D Projects: GA ČR GA203/99/1454 Institutional research plan: CEZ:AV0Z4055905 Keywords : carboxylic acids Subject RIV: CC - Organic Chemistry Impact factor: 6.079, year: 2001

  4. Organometallic carboxylate resists for extreme ultraviolet with high sensitivity

    Science.gov (United States)

    Passarelli, James; Murphy, Michael; Re, Ryan Del; Sortland, Miriam; Hotalen, Jodi; Dousharm, Levi; Fallica, Roberto; Ekinci, Yasin; Neisser, Mark; Freedman, Daniel A.; Brainard, Robert L.

    2015-10-01

    We have developed organometallic carboxylate compounds [RnM)] capable of acting as negative-tone extreme ultraviolet (EUV) resists. The most sensitive of these resists contain antimony, three R-groups and two carboxylate groups, and carboxylate groups with polymerizable olefins (e.g., acrylate, methacrylate, or styrenecarboxylate). Evidence suggests that high sensitivity is achieved through the polymerization of olefins in the exposed region. We have performed a systematic sensitivity study of the molecules of the type RnM) where we have studied seven R groups, four main group metals (M), and three polymerizable carboxylate groups (O2CR‧). The sensitivity of these resists was evaluated using Emax or dose to maximum resist thickness after exposure and development. We found that the greatest predictor of sensitivity of the RnSb) resists is their level of polymerizable olefins. We mathematically define the polymerizable olefin loading (POL) as the ratio of the number of olefins versus the number of nonhydrogen atoms. Linear and log plots of Emax versus POL for a variety of molecules of the type R3Sb) lend insight into the behavior of these resists.

  5. Atmospheric chemistry of carboxylic acids: microbial implication versus photochemistry

    Science.gov (United States)

    Vaïtilingom, M.; Charbouillot, T.; Deguillaume, L.; Maisonobe, R.; Parazols, M.; Amato, P.; Sancelme, M.; Delort, A.-M.

    2011-02-01

    Clouds are multiphasic atmospheric systems in which the dissolved organic compounds, dominated by carboxylic acids, are subject to multiple chemical transformations in the aqueous phase. Among them, solar radiation, by generating hydroxyl radicals (•OH), is considered as the main catalyzer of the reactivity of organic species in clouds. We investigated to which extent the active biomass existing in cloud water represents an alternative route to the chemical reactivity of carboxylic acids. Pure cultures of seventeen bacterial strains (Arthrobacter, Bacillus, Clavibacter, Frigoribacterium, Pseudomonas, Sphingomonas and Rhodococcus), previously isolated from cloud water and representative of the viable community of clouds were first individually incubated in two artificial bulk cloud water solutions at 17 °C and 5 °C. These solutions mimicked the chemical composition of cloud water from "marine" and "continental" air masses, and contained the major carboxylic acids existing in the cloud water (i.e. acetate, formate, succinate and oxalate). The concentrations of these carboxylic compounds were monitored over time and biodegradation rates were determined. In average, they ranged from 2 ×10-19 for succinate to 1 × 10-18 mol cell-1 s-1 for formate at 17 °C and from 4 × 10-20 for succinate to 6 × 10-19 mol cell-1 s-1 for formate at 5 °C, with no significant difference between "marine" and "continental" media. In parallel, irradiation experiments were also conducted in these two artificial media to compare biodegradation and photodegradation of carboxylic compounds. To complete this comparison, the photodegradation rates of carboxylic acids by •OH radicals were calculated from literature data. Inferred estimations suggested a significant participation of microbes to the transformation of carboxylic acids in cloud water, particularly for acetate and succinate (up to 90%). Furthermore, a natural cloud water sample was incubated (including its indigenous microflora

  6. Controlled clustering of carboxylated SPIONs through polyethylenimine

    International Nuclear Information System (INIS)

    Clusters of magnetite nanoparticles (MNPs) were synthesized using poly(acrylic acid-co-maleic acid) coated MNPs (PAM@MNP) and branched polyethylenimine (PEI). Materials were characterized by potentiometric titration, zeta potential and dynamic light scattering (DLS) measurements. PEI and PAM@MNP are oppositely charged as characterized by zeta potential measurements (+8, −34 mV respectively) and titration (10.30 mmol −NH3+/g PEI; 0.175 mmol −COO−/g PAM@MNP) at pH 6.5±0.2; therefore magnetic clusters are formed by electrostatic adhesion. Two different preparation methods and the effect of PEI and electrolyte (NaCl) concentration on the cluster formation was studied. Choosing an optimal concentration of PEI (charge ratio of PEI to PAM@MNP: 0.17) and electrolyte (10 mM), a concentrated (10 g MNP/L) product containing PEI–PAM@MNP nanoclusters with size of 165±10 nm was prepared. Its specific absorption rate (SAR) measured in AC magnetic field (110 kHz, 25 mT) is 12 W/g Fe. The clustered product is expected to have enhanced contrast efficiency in MRI. - Highlights: • SPION clusters of controlled size were prepared by means of electrostatic adhesion. • Nanocluster formation optimum was at 0.17 charge ratio of PEI to PAM@MNP. • Huge aggregates form at higher PEI to PAM@MNP charge ratio. • Higher ionic strength promotes the formation of clusters at lower PEI concentrations

  7. Carboxyl-terminal truncated HBx regulates a distinct microRNA transcription program in hepatocellular carcinoma development.

    Directory of Open Access Journals (Sweden)

    Wing-Kit Yip

    Full Text Available BACKGROUND: The biological pathways and functional properties by which misexpressed microRNAs (miRNAs contribute to liver carcinogenesis have been intensively investigated. However, little is known about the upstream mechanisms that deregulate miRNA expressions in this process. In hepatocellular carcinoma (HCC, hepatitis B virus (HBV X protein (HBx, a transcriptional trans-activator, is frequently expressed in truncated form without carboxyl-terminus but its role in miRNA expression and HCC development is unclear. METHODS: Human non-tumorigenic hepatocytes were infected with lentivirus-expressing full-length and carboxyl-terminal truncated HBx (Ct-HBx for cell growth assay and miRNA profiling. Chromatin immunoprecipitation microarray was performed to identify the miRNA promoters directly associated with HBx. Direct transcriptional control was verified by luciferase reporter assay. The differential miRNA expressions were further validated in a cohort of HBV-associated HCC tissues using real-time PCR. RESULTS: Hepatocytes expressing Ct-HBx grew significantly faster than the full-length HBx counterparts. Ct-HBx decreased while full-length HBx increased the expression of a set of miRNAs with growth-suppressive functions. Interestingly, Ct-HBx bound to and inhibited the transcriptional activity of some of these miRNA promoters. Notably, some of the examined repressed-miRNAs (miR-26a, -29c, -146a and -190 were also significantly down-regulated in a subset of HCC tissues with carboxyl-terminal HBx truncation compared to their matching non-tumor tissues, highlighting the clinical relevance of our data. CONCLUSION: Our results suggest that Ct-HBx directly regulates miRNA transcription and in turn promotes hepatocellular proliferation, thus revealing a viral contribution of miRNA deregulation during hepatocarcinogenesis.

  8. 40 CFR 721.4663 - Fluorinated carboxylic acid alkali metal salts.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Fluorinated carboxylic acid alkali... Specific Chemical Substances § 721.4663 Fluorinated carboxylic acid alkali metal salts. (a) Chemical... fluorinated carboxylic acid alkali metal salts (PMNs P-95-979/980/981) are subject to reporting under...

  9. 40 CFR 721.10142 - Oxabicycloalkane carboxylic acid alkanediyl ester (generic).

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Oxabicycloalkane carboxylic acid... New Uses for Specific Chemical Substances § 721.10142 Oxabicycloalkane carboxylic acid alkanediyl... substance identified generically as oxabicycloalkane carboxylic acid alkanediyl ester (PMN P-06-199)...

  10. Ligand-Binding Properties of the Carboxyl-Terminal Repeat Domain of Streptococcus mutans Glucan-Binding Protein A

    OpenAIRE

    Haas, Wolfgang; Banas, Jeffrey A.

    2000-01-01

    Streptococcus mutans glucan-binding protein A (GbpA) has sequence similarity in its carboxyl-terminal domain with glucosyltransferases (GTFs), the enzymes responsible for catalyzing the synthesis of the glucans to which GbpA and GTFs can bind and which promote S. mutans attachment to and accumulation on the tooth surface. It was predicted that this C-terminal region, comprised of what have been termed YG repeats, represents the GbpA glucan-binding domain (GBD). In an effort to test this hypot...

  11. Dynamic NMR studies of base-catalyzed intramolecular single vs. intermolecular double proton transfer of 1,3-bis(4-fluorophenyl)triazene

    International Nuclear Information System (INIS)

    In this paper, we explore the mechanisms of degenerate base-catalyzed intra- and intermolecular proton transfer using dynamic liquid state NMR. For this purpose, the model compound 1,3-bis(4-fluorophenyl)[1,3-15N2]triazene (1) was studied with and without the presence of dimethylamine (2), trimethylamine (3) and water, using tetrahydrofuran-d 8 and methylethylether-d 8 as solvents, down to 130 K. Compound 1 represents an analog of carboxylic acids and of diarylamidines forming cyclic dimers in which a fast double proton transfer takes place. By contrast, the structure of 1 was chosen in such a way that this double proton transfer is suppressed, thus revealing the base catalyzed transfer by dynamic 1H and 19F NMR. Surprisingly, both 2 and 3 can pick up the mobile proton of 1 at one nitrogen atom and carry it to the other nitrogen atom of 1, resulting in an intramolecular transfer process catalyzed each time by a different base molecule. Even more surprising is that the intramolecular transfer catalyzed by 2 is faster than the superimposed intermolecular double proton transfer. In the absence of added bases, a 1 is subject to a slow proton exchange with 2-amino-5,4'-difluoro-diphenyl-diazene (4) which is formed in small quantities from 1 in the presence of acid impurities. This process can be minimized by a proper sample preparation technique. The kinetic H/D isotope effects are small, especially in the catalysis by 2, indicating a major heavy atom rearrangement and absence of tunneling. Semi-empirical PM3 and ab initio DFT calculations indicate a reaction pathway via a hydrogen bond switch of the protonated amine representing the transition state. The Arrhenius curves of all processes exhibit strong convex curvatures. This phenomenon is explained in terms of the hydrogen bond association of 1 with the added bases, preceding the proton transfer. At low temperatures, all catalysts are in a hydrogen bonded reactive complex with 1, and the rate constants observed equal

  12. Dynamic NMR studies of base-catalyzed intramolecular single vs. intermolecular double proton transfer of 1,3-bis(4-fluorophenyl)triazene

    Science.gov (United States)

    Limbach, Hans-Heinrich; Männle, Ferdinand; Detering, Carsten; Denisov, Gleb S.

    2005-12-01

    In this paper, we explore the mechanisms of degenerate base-catalyzed intra- and intermolecular proton transfer using dynamic liquid state NMR. For this purpose, the model compound 1,3-bis(4-fluorophenyl)[1,3- 15N 2]triazene ( 1) was studied with and without the presence of dimethylamine ( 2), trimethylamine ( 3) and water, using tetrahydrofuran- d8 and methylethylether- d8 as solvents, down to 130 K. Compound 1 represents an analog of carboxylic acids and of diarylamidines forming cyclic dimers in which a fast double proton transfer takes place. By contrast, the structure of 1 was chosen in such a way that this double proton transfer is suppressed, thus revealing the base catalyzed transfer by dynamic 1H and 19F NMR. Surprisingly, both 2 and 3 can pick up the mobile proton of 1 at one nitrogen atom and carry it to the other nitrogen atom of 1, resulting in an intramolecular transfer process catalyzed each time by a different base molecule. Even more surprising is that the intramolecular transfer catalyzed by 2 is faster than the superimposed intermolecular double proton transfer. In the absence of added bases, a 1 is subject to a slow proton exchange with 2-amino-5,4'-difluoro-diphenyl-diazene ( 4) which is formed in small quantities from 1 in the presence of acid impurities. This process can be minimized by a proper sample preparation technique. The kinetic H/D isotope effects are small, especially in the catalysis by 2, indicating a major heavy atom rearrangement and absence of tunneling. Semi-empirical PM3 and ab initio DFT calculations indicate a reaction pathway via a hydrogen bond switch of the protonated amine representing the transition state. The Arrhenius curves of all processes exhibit strong convex curvatures. This phenomenon is explained in terms of the hydrogen bond association of 1 with the added bases, preceding the proton transfer. At low temperatures, all catalysts are in a hydrogen bonded reactive complex with 1, and the rate constants observed

  13. Evidence for excited-state intramolecular proton transfer in 4-chlorosalicylic acid from combined experimental and computational studies: Quantum chemical treatment of the intramolecular hydrogen bonding interaction

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Bijan Kumar [Department of Chemistry, University of Calcutta, 92 Acharya Prafulla Chandra Road, Calcutta 700009 (India); Guchhait, Nikhil, E-mail: nikhil.guchhait@rediffmail.com [Department of Chemistry, University of Calcutta, 92 Acharya Prafulla Chandra Road, Calcutta 700009 (India)

    2012-07-25

    Highlights: Black-Right-Pointing-Pointer Experimental and computational studies on the photophysics of 4-chlorosalicylic acid. Black-Right-Pointing-Pointer Spectroscopically established ESIPT reaction substantiated by theoretical calculation. Black-Right-Pointing-Pointer Quantum chemical treatment of IMHB unveils strength, nature and directional nature. Black-Right-Pointing-Pointer Superiority of quantum chemical treatment of H-bond over geometric criteria. Black-Right-Pointing-Pointer Role of H-bond as a modulator of aromaticity. -- Abstract: The photophysical study of a pharmaceutically important chlorine substituted derivative of salicylic acid viz., 4-chlorosalicylic acid (4ClSA) has been carried out by steady-state absorption, emission and time-resolved emission spectroscopy. A large Stokes shifted emission band with negligible solvent polarity dependence marks the spectroscopic signature of excited-state intramolecular proton transfer (ESIPT) reaction in 4ClSA. Theoretical calculation by ab initio and Density Functional Theory methods yields results consistent with experimental findings. Theoretical potential energy surfaces predict the occurrence of proton transfer in S{sub 1}-state. Geometrical and energetic criteria, Atoms-In-Molecule topological parameters, Natural Bond Orbital population analysis have been exploited to evaluate the intramolecular hydrogen bond (IMHB) interaction and to explore its directional nature. The inter-correlation between aromaticity and resonance assisted H-bond is also discussed in this context. Our results unveil that the quantum chemical treatment is a more accurate tool to assess hydrogen bonding interaction in comparison to geometrical criteria.

  14. Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds

    DEFF Research Database (Denmark)

    Hansen, Poul Erik

    2015-01-01

    The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between “static......” and tautomeric systems. Isotope effects on chemical shifts are particularly useful in such studies. All kinds of intramolecular hydrogen bonded systems will be treated, typical hydrogen bond donors: OH, NH, SH and NH+, typical acceptors C=O, C=N, C=S C=N−. The paper will be deal with both secondary...... and primary isotope effects on chemical shifts. These two types of isotope effects monitor the same hydrogen bond, but from different angles...

  15. Intramolecular symmetry-adapted perturbation theory with a single-determinant wavefunction

    International Nuclear Information System (INIS)

    We introduce an intramolecular energy decomposition scheme for analyzing non-covalent interactions within molecules in the spirit of symmetry-adapted perturbation theory (SAPT). The proposed intra-SAPT approach is based upon the Chemical Hamiltonian of Mayer [Int. J. Quantum Chem. 23(2), 341–363 (1983)] and the recently introduced zeroth-order wavefunction [J. F. Gonthier and C. Corminboeuf, J. Chem. Phys. 140(15), 154107 (2014)]. The scheme decomposes the interaction energy between weakly bound fragments located within the same molecule into physically meaningful components, i.e., electrostatic-exchange, induction, and dispersion. Here, we discuss the key steps of the approach and demonstrate that a single-determinant wavefunction can already deliver a detailed and insightful description of a wide range of intramolecular non-covalent phenomena such as hydrogen bonds, dihydrogen contacts, and π − π stacking interactions. Intra-SAPT is also used to shed the light on competing intra- and intermolecular interactions

  16. Intramolecular symmetry-adapted perturbation theory with a single-determinant wavefunction

    Energy Technology Data Exchange (ETDEWEB)

    Pastorczak, Ewa; Prlj, Antonio; Corminboeuf, Clémence, E-mail: clemence.corminboeuf@epfl.ch [Laboratory for Computational Molecular Design, Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland); Gonthier, Jérôme F. [Center for Computational Molecular Science and Technology, School of Chemistry and Biochemistry, School of Computational Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States)

    2015-12-14

    We introduce an intramolecular energy decomposition scheme for analyzing non-covalent interactions within molecules in the spirit of symmetry-adapted perturbation theory (SAPT). The proposed intra-SAPT approach is based upon the Chemical Hamiltonian of Mayer [Int. J. Quantum Chem. 23(2), 341–363 (1983)] and the recently introduced zeroth-order wavefunction [J. F. Gonthier and C. Corminboeuf, J. Chem. Phys. 140(15), 154107 (2014)]. The scheme decomposes the interaction energy between weakly bound fragments located within the same molecule into physically meaningful components, i.e., electrostatic-exchange, induction, and dispersion. Here, we discuss the key steps of the approach and demonstrate that a single-determinant wavefunction can already deliver a detailed and insightful description of a wide range of intramolecular non-covalent phenomena such as hydrogen bonds, dihydrogen contacts, and π − π stacking interactions. Intra-SAPT is also used to shed the light on competing intra- and intermolecular interactions.

  17. Intramolecular symmetry-adapted perturbation theory with a single-determinant wavefunction

    Science.gov (United States)

    Pastorczak, Ewa; Prlj, Antonio; Gonthier, Jérôme F.; Corminboeuf, Clémence

    2015-12-01

    We introduce an intramolecular energy decomposition scheme for analyzing non-covalent interactions within molecules in the spirit of symmetry-adapted perturbation theory (SAPT). The proposed intra-SAPT approach is based upon the Chemical Hamiltonian of Mayer [Int. J. Quantum Chem. 23(2), 341-363 (1983)] and the recently introduced zeroth-order wavefunction [J. F. Gonthier and C. Corminboeuf, J. Chem. Phys. 140(15), 154107 (2014)]. The scheme decomposes the interaction energy between weakly bound fragments located within the same molecule into physically meaningful components, i.e., electrostatic-exchange, induction, and dispersion. Here, we discuss the key steps of the approach and demonstrate that a single-determinant wavefunction can already deliver a detailed and insightful description of a wide range of intramolecular non-covalent phenomena such as hydrogen bonds, dihydrogen contacts, and π - π stacking interactions. Intra-SAPT is also used to shed the light on competing intra- and intermolecular interactions.

  18. Enantioselective Intramolecular Hydroarylation of Alkenes via Directed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Hitoshi; Thalji, Reema; Bergman, Robert; Ellman, Jonathan

    2008-05-22

    Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe){sub 2}]{sub 2} and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.

  19. Intramolecular hydrogen bonding and calixarene-like structures in p-cresol/formaldehyde resins

    Science.gov (United States)

    Opaprakasit, P.; Scaroni, A.; Painter, P.

    2001-08-01

    The nature of the strong hydrogen bonds found in p-cresol/formaldehyde (PCF) resins, compared to ordinary phenolic compounds, is studied. The evidence from FTIR spectroscopy indicates that this strong interaction is due to intramolecular hydrogen bonding from "calixarene-like" structures. The formation of this structure in PCF is enabled by its "linear" (all- ortho-linkage) structure, which is not present in branched resins. Additionally, a transition is observed at around 175 to 200°C where the intramolecular hydrogen bonded structure is lost. This structure cannot be recovered upon cooling or annealing due to restrictions on conformational rotations that are coupled to a new pattern of intermolecular hydrogen bonding. However, the structure is reformed by dissolving the resin in solution and casting new films.

  20. Intramolecular Crystal Nucleation Favored by Polymer Crystallization: Monte Carlo Simulation Evidence.

    Science.gov (United States)

    Zhang, Rong; Zha, Liyun; Hu, Wenbing

    2016-07-14

    We performed dynamic Monte Carlo simulations of half-half binary blends of symmetric (double and mutual) crystallizable polymers. We separately enhanced the driving forces for polymer-uniform and polymer-staggered crystals. Under parallel enhancements, polymer-uniform crystals exhibit faster nucleation and growth, with more chain folding and less lamellar thickening, than those in polymer-staggered crystals. We attributed the results to intramolecular crystal nucleation, ruined by enhanced polymer-staggered crystallization. Our observations provide direct molecular-level evidence to support the fact that intramolecular crystal nucleation is favored by polymer crystallization in quiescent solutions and melt, which yields chain folding for the characteristic β-sheet or lamellar morphology of macromolecular crystals. PMID:27300471

  1. Computational study of topological effects on intramolecular electron transfer in mixed-valence compounds

    Institute of Scientific and Technical Information of China (English)

    Yinxi YU; Haobin WANG

    2011-01-01

    The constrained density functional theory (CDFT) was used to investigate the topological effects on intramolecular electron transfer processes that have been reported in previous experimental work [Inorg.Chem.,1997,36 (22),pp 5037-50491.The computation mainly focused on three isomers of diferrocenylbenzenes (ortho,para,and meta) and 5-substituted derivatives of m-diferrocencylbenzenes with R =NH2,Cl,CH3,CN,NO2,N(CH3)3+3,and N+2.The influence of a third group R' (R' =NH2 and N+2) was introduced to the ortho and para isomers.The calculations were compared with the experimental results.The relation between the substituted functional groups and the effectiveness of intramolecular electron transfer was discussed on the basis of CDFT computational results.

  2. Broadband Tunable Microlasers Based on Controlled Intramolecular Charge-Transfer Process in Organic Supramolecular Microcrystals.

    Science.gov (United States)

    Dong, Haiyun; Wei, Yanhui; Zhang, Wei; Wei, Cong; Zhang, Chunhuan; Yao, Jiannian; Zhao, Yong Sheng

    2016-02-01

    Wavelength tunable micro/nanolasers are indispensable components for various photonic devices. Here, we report broadband tunable microlasers built by incorporating a highly polarized organic intramolecular charge-transfer (ICT) compound with a supramolecular host. The spatial confinement of the ICT dye generates an optimized energy level system that favors controlled population distribution between the locally excited (LE) state and the twisted intramolecular charge-transfer (TICT) state, which is beneficial for significantly broadening the tailorable gain region. As a result, we realized a wide tuning of lasing wavelength in the organic supramolecular microcrystals based on temperature-controlled population transfer from the LE to TICT state. The results will provide a useful enlightenment for the rational design of miniaturized lasers with desired performances. PMID:26756966

  3. Functionalization of carbon nanotube by carboxyl group under radial deformation

    Science.gov (United States)

    Lara, Ivi Valentini; Zanella, Ivana; Fagan, Solange Binotto

    2014-01-01

    The dependence of the structural and the electronic properties of functionalized (5, 5) single-walled carbon nanotubes (SWNT) were investigated through ab initio density functional simulations when the carboxyl group is bonded on the flatter or curved regions. Radial deformations result in diameter decrease of up to 20 per cent of the original size, which was the limit reduction that maintains the SWNT functionalized structure. Changes on the electronic structure were observed due to the symmetry break of the SWNT caused by both the carboxyl group and the C-C bond distortions resulted by the radial deformation. It is observed that the functionalization process is specially favored by the sp3 hybridization induced on the more curved region of the deformed SWNT.

  4. Enhance decarboxylation reaction of carboxylic acids in clay minerals

    International Nuclear Information System (INIS)

    Clay minerals are important constituents of the Earth's crust. These minerals catalyze reactions in several ways: by energy transfer processes, redox reactions, stabilization of intermediates and by Broensted or Lewis acidity behavior. Important set of organic reactions can be improved in the precedence of clay minerals. Besides the properties of clays to catalyze chemical reactions, it is possible to enhance some of its reactions by using ionizing radiation. The phenomenon of radiation-induced catalysis may be connected with ionizing process in the solid and with the trapped non-equilibrium charge carriers. In this paper we are reporting the decarboxylation reaction of carboxylic acids catalyzed by clay and by irradiation of the system acid-clay. We studied the behaviour of several carboxylic acids and analyzed them by gas chromatography, X-ray and infrared spectroscopy. The results showed that decarboxylation of the target compound is the dominating pathway. The reaction is enhanced by gamma radiation in several orders of magnitude. (author)

  5. 1-(5,5-Dimethoxypentyl-3-methylimidazolium-2-carboxylate

    Directory of Open Access Journals (Sweden)

    Olaf Walter

    2013-11-01

    Full Text Available The title compound, C12H20N2O4, represents one example of a zwitterionic imidazolium salt with a carboxylate group at the 2-position of the imidazolium ring. The dihedral angle between the heterocyclic ring and the carboxylate group is 31.3 (1°. The side chain linking the N atom of the ring and the methine C atom has a gauche–anti–anti conformation [torsion angles = −60.3 (2, −175.7 (2 and 178.7 (2°, respectively]. In the crystal, molecules are linked by short C—H...O hydrogen bonds involving the C—H groups in the aromatic ring to generate (001 sheets.

  6. Sensing of antipyretic carboxylates by simple chromogenic calix[4]pyrroles.

    Science.gov (United States)

    Nishiyabu, Ryuhei; Anzenbacher, Pavel

    2005-06-15

    We present a simple, two- or three-step method for the synthesis of chromogenic octamethylcalix[4]pyrrole-based (OMCP) sensors for anions. Electrophilic aromatic substitution allows for converting the pyrrole moieties of OMCP into a dye. The formation of a sensor-anion complex results in partial charge transfer and a dramatic change in color. The absorption (UV-vis) and NMR titration experiments show that the chromogenic OMCPs sense anions administered as aqueous solutions, even at high ionic strength ( approximately 0.1 M NaCl), while displaying selectivity for pyrophosphate and carboxylate anions. The experiments with polyurethane sensor films show a strong response for aqueous carboxylates, such as antipyretics naproxen approximately ibuprofen > salicylate, without being biased by bicarbonate or carboxy termini of blood plasma proteins. PMID:15941245

  7. Substrate specificity within a family of outer membrane carboxylate channels.

    Directory of Open Access Journals (Sweden)

    Elif Eren

    2012-01-01

    Full Text Available Many Gram-negative bacteria, including human pathogens such as Pseudomonas aeruginosa, do not have large-channel porins. This results in an outer membrane (OM that is highly impermeable to small polar molecules, making the bacteria intrinsically resistant towards many antibiotics. In such microorganisms, the majority of small molecules are taken up by members of the OprD outer membrane protein family. Here we show that OprD channels require a carboxyl group in the substrate for efficient transport, and based on this we have renamed the family Occ, for outer membrane carboxylate channels. We further show that Occ channels can be divided into two subfamilies, based on their very different substrate specificities. Our results rationalize how certain bacteria can efficiently take up a variety of substrates under nutrient-poor conditions without compromising membrane permeability. In addition, they explain how channel inactivation in response to antibiotics can cause resistance but does not lead to decreased fitness.

  8. Enhancing magnetoresistance in tetrathiafulvalene carboxylate modified iron oxide nanoparticle assemblies

    Science.gov (United States)

    Lv, Zhong-Peng; Luan, Zhong-Zhi; Cai, Pei-Yu; Wang, Tao; Li, Cheng-Hui; Wu, Di; Zuo, Jing-Lin; Sun, Shouheng

    2016-06-01

    We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO-) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications.We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO-) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications. Electronic supplementary information (ESI) available: Experimental details; supplementary figures and tables. See DOI: 10.1039/c6nr03311c

  9. Influences of Carboxyl Methyl Cellulose on Performances of Mortar

    Institute of Scientific and Technical Information of China (English)

    WANG Yuli; ZHOU Mingkai; SHAN Junhong; XU Fang; YANG Yuhui

    2007-01-01

    Carboxyl methyl cellulose (CMC) was mixed into mortar to improve the waterretention performance of mortar, the quality of floated coat of aerated concrete became better. The consistency and compression strength of mortar with CMC were studied. The water absorption was studied with the method of filter paper. The micro mechanism was researched with X-ray diffraction and scanning electron microscopy(SEM). The experimental results show the water-holding performance of mortar with CMC is largely improved and it is better when the mixed amount is about 1.5%; the compression strength had a descending trend with the increase of CMC; CMC reacted with calcium hydroxide(CH) into the deposition of calcium carboxyl methyl cellulose.

  10. Fluorescently tuned nitrogen-doped carbon dots from carbon source with different content of carboxyl groups

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hao; Wang, Yun; Dai, Xiao; Zou, Guifu, E-mail: kqzhang@suda.edu.cn, E-mail: zouguifu@suda.edu.cn [College of Physics, Optoelectronics and Energy and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Gao, Peng; Zhang, Ke-Qin, E-mail: kqzhang@suda.edu.cn, E-mail: zouguifu@suda.edu.cn; Du, Dezhuang [National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, Suzhou 215123 (China); Guo, Jun [Testing and Analysis Center, Soochow University, Suzhou 215123 (China)

    2015-08-01

    In this study, fluorescent nitrogen-doped carbon dots (NCDs) were tuned via varying the sources with different number of carboxyl groups. Owing to the interaction between amino and carboxyl, more amino groups conjugate the surface of the NCDs by the source with more carboxyl groups. Fluorescent NCDs were tuned via varying the sources with different content of carboxyl groups. Correspondingly, the nitrogen content, fluorescence quantum yields and lifetime of NCDs increases with the content of carboxyl groups from the source. Furthermore, cytotoxicity assay and cell imaging test indicate that the resultant NCDs possess low cytotoxicity and excellent biocompatibility.

  11. Fluorescently tuned nitrogen-doped carbon dots from carbon source with different content of carboxyl groups

    International Nuclear Information System (INIS)

    In this study, fluorescent nitrogen-doped carbon dots (NCDs) were tuned via varying the sources with different number of carboxyl groups. Owing to the interaction between amino and carboxyl, more amino groups conjugate the surface of the NCDs by the source with more carboxyl groups. Fluorescent NCDs were tuned via varying the sources with different content of carboxyl groups. Correspondingly, the nitrogen content, fluorescence quantum yields and lifetime of NCDs increases with the content of carboxyl groups from the source. Furthermore, cytotoxicity assay and cell imaging test indicate that the resultant NCDs possess low cytotoxicity and excellent biocompatibility

  12. Complex formation of Np(V) with various carboxylates

    International Nuclear Information System (INIS)

    The stability constants of Np(V) complexes with a series of aliphatic and aromatic carboxylates, including hydroxycarboxylates, hydroxydicarboxylates, dicarboxylates and pyridinecarboxylates have been obtained in 1.0 M NaClO4 by a solvent extraction method using thenoyltrifluoroacetone and 1,10- phenanthroline in isoamyl alcohol. Stabilities of these complexes are discussed in terms of their structures and ligand basicities. (orig.)

  13. Enhancing magnetoresistance in tetrathiafulvalene carboxylate modified iron oxide nanoparticle assemblies.

    Science.gov (United States)

    Lv, Zhong-Peng; Luan, Zhong-Zhi; Cai, Pei-Yu; Wang, Tao; Li, Cheng-Hui; Wu, Di; Zuo, Jing-Lin; Sun, Shouheng

    2016-06-16

    We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO(-)) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications. PMID:27271347

  14. Circulating Nonphosphorylated Carboxylated Matrix Gla Protein Predicts Survival in ESRD

    OpenAIRE

    Schlieper, Georg; Westenfeld, Ralf; Krüger, Thilo; Cranenburg, Ellen C.; Magdeleyns, Elke J.; Brandenburg, Vincent M.; Djuric, Zivka; Damjanovic, Tatjana; Ketteler, Markus; Vermeer, Cees; Dimkovic, Nada; Floege, Jürgen; Schurgers, Leon J.

    2011-01-01

    The mechanisms for vascular calcification and its associated cardiovascular mortality in patients with ESRD are not completely understood. Dialysis patients exhibit profound vitamin K deficiency, which may impair carboxylation of the calcification inhibitor matrix gla protein (MGP). Here, we tested whether distinct circulating inactive vitamin K–dependent proteins associate with all-cause or cardiovascular mortality. We observed higher levels of both desphospho-uncarboxylated MGP (dp-ucMGP) a...

  15. Crystal structure of ethyl 2,4-dichloroquinoline-3-carboxylate

    Directory of Open Access Journals (Sweden)

    Alberto Cabrera

    2015-12-01

    Full Text Available In the crystal structure of the title compound, C12H9Cl2NO2, the mean planes through the quinoline and carboxylate groups have r.m.s. deviations of 0.006 and 0.021 Å, respectively, and form a dihedral angle of 87.06 (19°. In the crystal, molecules are linked via very weak C—H...O hydrogen bonds, forming chains, which propagate along the c-axis direction.

  16. Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis*

    OpenAIRE

    Chernev, Petko; Zaharieva, Ivelina; Dau, Holger; Haumann, Michael

    2010-01-01

    Understanding the mechanisms of electron transfer (ET) in photosynthetic reaction centers (RCs) may inspire novel catalysts for sunlight-driven fuel production. The electron exit pathway of type II RCs comprises two quinone molecules working in series and in between a non-heme iron atom with a carboxyl ligand (bicarbonate in photosystem II (PSII), glutamate in bacterial RCs). For decades, the functional role of the iron has remained enigmatic. We tracked the iron site using microsecond-resolu...

  17. Block and Graft Copolymers Containing Carboxylate or Phosphonate Anions

    OpenAIRE

    Hu, Nan

    2014-01-01

    This dissertation focuses on synthesis and characterization of graft and block copolymers containing carboxylate or phosphonate anions that are potential candidates for biomedical applications such as drug delivery and dental adhesives. Ammonium bisdiethylphosphonate (meth)acrylate and acrylamide phosphonate monomers were synthesized based on aza-Michael addition reactions. Free radical copolymerizations of these monomers with an acrylate-functional poly(ethylene oxide) (PEO) macromonomer...

  18. Vibrationally highly excited molecules and intramolecular mode coupling through high-overtone spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wong, J.S.; Moore, C.B.

    1981-08-01

    High overtone spectra of organic molecules can be interpreted using the local mode model for absorptions by the inequivalent C-H bonds. The spectra can be assigned using either observed C-H bond lengths or isolated fundamental frequencies. The spectra of trihalomethanes indicate that the dominant intramolecular mode coupling for the C-H stretching overtones is Fermi resonance with combination states with one less C-H stretching quantum plus two quanta of the C-H bending vibrations.

  19. HIV-2 RNA dimerization is regulated by intramolecular interactions in vitro

    OpenAIRE

    Baig, Tayyba T.; Lanchy, Jean-Marc; Lodmell, J. Stephen

    2007-01-01

    Genomic RNA dimerization is an essential process in the retroviral replication cycle. In vitro, HIV-2 RNA dimerization is mediated at least in part by direct intermolecular interaction at stem–loop 1 (SL1) within the 5′-untranslated leader region (UTR). RNA dimerization is thought to be regulated via alternate presentation and sequestration of dimerization signals by intramolecular base-pairings. One of the proposed regulatory elements is a palindrome sequence (pal) located upstream of SL1. T...

  20. Optimized measurements of separations and angles between intra-molecular fluorescent markers

    DEFF Research Database (Denmark)

    Mortensen, Kim; Sung, Jongmin; Flyvbjerg, Henrik;

    2015-01-01

    We demonstrate a novel, yet simple tool for the study of structure and function of biomolecules by extending two-colour co-localization microscopy to fluorescent molecules with fixed orientations and in intra-molecular proximity. From each colour-separated microscope image in a time-lapse movie a......, thereby establishing short, double-labelled DNA molecules as probes of 3D orientation of anything to which one can attach them firmly....

  1. An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

    Directory of Open Access Journals (Sweden)

    Zhiyuan Ma

    2012-06-01

    Full Text Available Intramolecular inverse electron demand cycloadditions of isatin-derived 1,2,4-triazines with acetylenic dienophiles tethered by amidations or transesterifications proceed in excellent yields to produce lactam- or lactone-fused α-carbolines. Beginning with various isatins and alkynyl dienophiles, a pilot-scale library of eighty-eight α-carbolines was prepared by using this robust methodology for biological evaluation.

  2. Auger electron spectroscopy as a tool for measuring intramolecular charges of adsorbed molecules

    Science.gov (United States)

    Magkoev, T. T.

    1993-10-01

    A way for the determination of the values of intramolecular charges of adsorbed molecules of some binary dielectrics, based on Auger electron spectroscopy (AES), is proposed. These values can be obtained from the coverage dependences of the ratios of intensities of anion KL 23L 23 and KL 1L 1 Auger transitions, which are sensitive to the amount of charge at the 2p-orbitals. As an example, MgO adsorbed on Mo(110) is presented.

  3. Stable Blue Phosphorescence Iridium(III) Cyclometalated Complexes Prompted by Intramolecular Hydrogen Bond in Ancillary Ligand.

    Science.gov (United States)

    Yi, Seungjun; Kim, Jin-Hyoung; Cho, Yang-Jin; Lee, Jiwon; Choi, Tae-Sup; Cho, Dae Won; Pac, Chyongjin; Han, Won-Sik; Son, Ho-Jin; Kang, Sang Ook

    2016-04-01

    Improvement of the stability of blue phosphorescent dopant material is one of the key factors for real application of organic light-emitting diodes (OLEDs). In this study, we found that the intramolecular hydrogen bonding in an ancillary ligand from a heteroleptic Ir(III) complex can play an important role in the stability of blue phosphorescence. To rationalize the role of intramolecular hydrogen bonding, a series of Ir(III) complexes is designed and prepared: Ir(dfppy)2(pic-OH) (1a), Ir(dfppy)2(pic-OMe) (1b), Ir(ppy)2(pic-OH) (2a), and Ir(ppy)2(pic-OMe) (2b). The emission lifetime of Ir(dfppy)2(pic-OH) (1a) (τem = 3.19 μs) in dichloromethane solution was found to be significantly longer than that of Ir(dfppy)2(pic-OMe) (1b) (τem = 0.94 μs), because of a substantial difference in the nonradiative decay rate (knr = 0.28 × 10(5) s(-1) for (1a) vs 2.99 × 10(5) s(-1) for (1b)). These results were attributed to the intramolecular OH···O═C hydrogen bond of the 3-hydroxy-picolinato ligand. Finally, device lifetime was significantly improved when 1a was used as the dopant compared to FIrpic, a well-known blue dopant. Device III (1a as dopant) achieved an operational lifetime of 34.3 h for an initial luminance of 400 nits compared to that of device IV (FIrpic as dopant), a value of 20.1 h, indicating that the intramolecular hydrogen bond in ancillary ligand is playing an important role in device stability. PMID:26991672

  4. Synthesis of Coumarins and Quinolones by Intramolecular Aldol Condensation Reactions of Titanium Enediolates

    OpenAIRE

    Fürstner, A.; Jumbam, D.; Shi, N.

    1995-01-01

    Low-valent titanium prepared by the reduction of TiCl3 with zinc dust oxidatively adds to α-ketoamides or α-ketoesters with the formation of the corresponding titanium enediolates. These 1,2-difunctional nucleophiles, which have hardly been used in organic synthesis so far, undergo regioselective intramolecular aldol condensation reactions with various electrophiles such as aldehydes, ketones, nitriles, esters and amides. This methodology allows the synthesis of differently substituted coumar...

  5. Reflex: intramolecular barcoding of long-range PCR products for sequencing multiple pooled DNAs

    OpenAIRE

    Casbon, James A; Slatter, Andrew F; Musgrave-Brown, Esther; Osborne, Robert J.; Lichtenstein, Conrad P.; Brenner, Sydney

    2013-01-01

    We present an intramolecular reaction, Reflex™, to derive shorter, sequencer-ready, daughter polymerase chain reaction products from a pooled population of barcoded long-range polymerase chain reaction products, whilst still preserving the cognate DNA barcodes. Our Reflex workflow needs only a small number of primer extension steps to rapidly enable uniform sequence coverage of long contiguous sequence targets in large numbers of samples at low cost on desktop next-generation sequencers.

  6. Analyzing intramolecular vibrational energy redistribution via the overlap intensity-level velocity correlator

    OpenAIRE

    Keshavamurthy, Srihari; Cerruti, Nicholas R.; Tomsovic, Steven

    2002-01-01

    Numerous experimental and theoretical studies have established that intramolecular vibrational energy redistribution (IVR) in isolated molecules has a heirarchical tier structure. The tier structure implies strong correlations between the energy level motions of a quantum system and its intensity-weighted spectrum. A measure, which explicitly accounts for this correaltion, was first introduced by one of us as a sensitive probe of phase space localization. It correlates eigenlevel velocities w...

  7. Carboxylic acid-functionalized SBA-15 nanorods for gemcitabine delivery

    International Nuclear Information System (INIS)

    The present study deals with the functionalization of mesoporous silica nanoparticles as drug delivery systems. Mono, di, and tri amino-functionalized SBA-15 nanorods were synthesized by post-grafting method using (3-aminopropyl) triethoxysilane, N-(2-aminoethyl-)3- aminopropyltrimethoxysilane, and 3-[2-(2-aminoethylamino) ethylamino] propyl trimethoxysilane, respectively. The carboxylic acid derivatives of the amino-functionalized samples were obtained using succinic anhydride. Tminopropyltrimethoxysilanehe obtained modified materials were investigated as matrixes for the anticancer drug (gemcitabine) delivery. The prepared samples were characterized by SAXS, N2 adsorption/desorption, SEM, transmission electron microscopy, thermogravimetric analysis, and FTIR and UV spectroscopies. The adsorption and release properties of all samples were studied. It was revealed that the adsorption capacity and release behavior of gemcitabine were highly dependent on the type of the introduced functional groups. The carboxylic acid-modified samples have higher loading content, due to the strong interaction with gemcitabine. The maximum content of deposited drug in the modified SBA-15 nanorods is close to 40 wt%. It was found that the surface functionalization leads toward significant decrease of the drug release rate. The carboxylic acid-functionalized samples have slower release rate in contrast with the amino-functionalized samples

  8. Biarylalkyl Carboxylic Acid Derivatives as Novel Antischistosomal Agents.

    Science.gov (United States)

    Mäder, Patrick; Blohm, Ariane S; Quack, Thomas; Lange-Grünweller, Kerstin; Grünweller, Arnold; Hartmann, Roland K; Grevelding, Christoph G; Schlitzer, Martin

    2016-07-01

    Parasitic platyhelminths are responsible for serious infectious diseases, such as schistosomiasis, which affect humans as well as animals across vast regions of the world. The drug arsenal available for the treatment of these diseases is limited; for example, praziquantel is the only drug currently used to treat ≥240 million people each year infected with Schistosoma spp., and there is justified concern about the emergence of drug resistance. In this study, we screened biarylalkyl carboxylic acid derivatives for their antischistosomal activity against S. mansoni. These compounds showed significant influence on egg production, pairing stability, and vitality. Tegumental lesions or gut dilatation was also observed. Substitution of the terminal phenyl residue in the biaryl scaffold with a 3-hydroxy moiety and derivatization of the terminal carboxylic acid scaffold with carboxamides yielded compounds that displayed significant antischistosomal activity at concentrations as low as 10 μm with satisfying cytotoxicity values. The present study provides detailed insight into the structure-activity relationships of biarylalkyl carboxylic acid derivatives and thereby paves the way for a new drug-hit moiety for fighting schistosomiasis. PMID:27159334

  9. ELECTROANALYTICAL APPLICATIONS OF CARBOXYL-MODIFIED CARBON NANOTUBE FILM ELECTRODES

    Institute of Scientific and Technical Information of China (English)

    C.G. Hu; W.L. Wang; K.J. Liao; W. Zhu

    2003-01-01

    The electrochemical behavior of a carboxyl-modified carbon nanotube films was investigated to explore its possibility in electroanalytical applicaton. Cyclic voltammetry of quinone was conducted in 1mol/L Na2SO4, which showed a stable, quasi-reversible voltammetric response for quinone / hydroquinone, and the anodic and the cathodic peak potentials were 0.657V and -0.029V (vs. SCE) at a scan rate of 0.1V.s-1, respectively. Both anodic and cathodic peak currents depended linearly on the square root of the scan rate over the range of 0.01-0. 5 V.s-1, which suggested that the process of the electrode reactions was diffusion-controlled. Carboxyl-modified carbon nanotube electrodes made it possible to determine low level of dopamine selectively in the presence of a large excess of ascorbic acid in acidic media using derivative voltammetry.The results obtained were discussed in details. This work demonstrates the potential of carboxyl-modified carbon nanotube electrodes for electroanalytical applications.

  10. Cellular uptake and anticancer activity of carboxylated gallium corroles.

    Science.gov (United States)

    Pribisko, Melanie; Palmer, Joshua; Grubbs, Robert H; Gray, Harry B; Termini, John; Lim, Punnajit

    2016-04-19

    We report derivatives of gallium(III) tris(pentafluorophenyl)corrole, 1 [Ga(tpfc)], with either sulfonic (2) or carboxylic acids (3, 4) as macrocyclic ring substituents: the aminocaproate derivative, 3 [Ga(ACtpfc)], demonstrated high cytotoxic activity against all NCI60 cell lines derived from nine tumor types and confirmed very high toxicity against melanoma cells, specifically the LOX IMVI and SK-MEL-28 cell lines. The toxicities of 1, 2, 3, and 4 [Ga(3-ctpfc)] toward prostate (DU-145), melanoma (SK-MEL-28), breast (MDA-MB-231), and ovarian (OVCAR-3) cancer cells revealed a dependence on the ring substituent: IC50values ranged from 4.8 to >200 µM; and they correlated with the rates of uptake, extent of intracellular accumulation, and lipophilicity. Carboxylated corroles 3 and 4, which exhibited about 10-fold lower IC50values ( 3 > 2 > 1 (intracellular accumulation of gallium corroles was fastest in melanoma cells). We conclude that carboxylated gallium corroles are promising chemotherapeutics with the advantage that they also can be used for tumor imaging. PMID:27044076

  11. Carboxylic acid-functionalized SBA-15 nanorods for gemcitabine delivery

    Energy Technology Data Exchange (ETDEWEB)

    Bahrami, Zohreh; Badiei, Alireza, E-mail: abadiei@khayam.ut.ac.ir [University of Tehran, School of Chemistry, College of Science (Iran, Islamic Republic of); Ziarani, Ghodsi Mohammadi [Alzahra University, Research Laboratory of Pharmaceutical (Iran, Islamic Republic of)

    2015-03-15

    The present study deals with the functionalization of mesoporous silica nanoparticles as drug delivery systems. Mono, di, and tri amino-functionalized SBA-15 nanorods were synthesized by post-grafting method using (3-aminopropyl) triethoxysilane, N-(2-aminoethyl-)3- aminopropyltrimethoxysilane, and 3-[2-(2-aminoethylamino) ethylamino] propyl trimethoxysilane, respectively. The carboxylic acid derivatives of the amino-functionalized samples were obtained using succinic anhydride. Tminopropyltrimethoxysilanehe obtained modified materials were investigated as matrixes for the anticancer drug (gemcitabine) delivery. The prepared samples were characterized by SAXS, N{sub 2} adsorption/desorption, SEM, transmission electron microscopy, thermogravimetric analysis, and FTIR and UV spectroscopies. The adsorption and release properties of all samples were studied. It was revealed that the adsorption capacity and release behavior of gemcitabine were highly dependent on the type of the introduced functional groups. The carboxylic acid-modified samples have higher loading content, due to the strong interaction with gemcitabine. The maximum content of deposited drug in the modified SBA-15 nanorods is close to 40 wt%. It was found that the surface functionalization leads toward significant decrease of the drug release rate. The carboxylic acid-functionalized samples have slower release rate in contrast with the amino-functionalized samples.

  12. Green process for chemical functionalization of nanocellulose with carboxylic acids.

    Science.gov (United States)

    Espino-Pérez, Etzael; Domenek, Sandra; Belgacem, Naceur; Sillard, Cécile; Bras, Julien

    2014-12-01

    An environmentally friendly and simple method, named SolReact, has been developed for a solvent-free esterification of cellulose nanocrystals (CNC) surface by using two nontoxic carboxylic acids (CA), phenylacetic acid and hydrocinnamic acid. In this process, the carboxylic acids do not only act as grafting agent, but also as solvent media above their melting point. Key is the in situ solvent exchange by water evaporation driving the esterification reaction without drying the CNC. Atomic force microscopy and X-ray diffraction analyses showed no significant change in the CNC dimensions and crystallinity index after this green process. The presence of the grafted carboxylic was characterized by analysis of the "bulk" CNC with elemental analysis, infrared spectroscopy, and (13)C NMR. The ability to tune the surface properties of grafted nanocrystals (CNC-g-CA) was evaluated by X-ray photoelectron spectroscopy analysis. The hydrophobicity behavior of the functionalized CNC was studied through the water contact-angle measurements and vapor adsorption. The functionalization of these bionanoparticles may offer applications in composite manufacturing, where these nanoparticles have limited dispersibility in hydrophobic polymer matrices and as nanoadsorbers due to the presence of phenolic groups attached on the surface. PMID:25353612

  13. Bridge- and Solvent-Mediated Intramolecular Electronic Communications in Ubiquinone-Based Biomolecular Wires

    Science.gov (United States)

    Liu, Xiao-Yuan; Ma, Wei; Zhou, Hao; Cao, Xiao-Ming; Long, Yi-Tao

    2015-05-01

    Intramolecular electronic communications of molecular wires play a crucial role for developing molecular devices. In the present work, we describe different degrees of intramolecular electronic communications in the redox processes of three ubiquinone-based biomolecular wires (Bis-CoQ0s) evaluated by electrochemistry and Density Functional Theory (DFT) methods in different solvents. We found that the bridges linkers have a significant effect on the electronic communications between the two peripheral ubiquinone moieties and solvents effects are limited and mostly depend on the nature of solvents. The DFT calculations for the first time indicate the intensity of the electronic communications during the redox processes rely on the molecular orbital elements VL for electron transfer (half of the energy splitting of the LUMO and LUMO+1), which is could be affected by the bridges linkers. The DFT calculations also demonstrates the effect of solvents on the latter two-electron transfer of Bis-CoQ0s is more significant than the former two electrons transfer as the observed electrochemical behaviors of three Bis-CoQ0s. In addition, the electrochemistry and theoretical calculations reveal the intramolecular electronic communications vary in the four-electron redox processes of three Bis-CoQ0s.

  14. Unique Intramolecular Electronic Communications in Mono-ferrocenylpyrimidine Derivatives: Correlation between Redox Properties and Structural Nature

    International Nuclear Information System (INIS)

    Highlights: • Unique intramolecular electronic communications (electron withdrawing and π-bond delocalization effects) exist in the mono-ferrocenylpyrimidine derivatives. • The redox potential shift correlates the pyrimidine ring torsion angle with the extent of electron delocalization. • The correlation between redox properties and structural nature in mono-ferrocenylpyrimidine derivatives is evident. - Abstract: The correlation between redox properties and structural nature in a complete set of mono-ferrocenylpyrimidine derivatives (2-ferrocenylpyrimidine, 2-FcPy; 4-ferrocenylpyrimidine, 4-FcPy; 5-ferrocenylpyrimidine, 5-FcPy) was evaluated by investigating the intramolecular electronic communications. Both conventional electrochemical measurements in organic solvents and thin-film voltammetric studies of these compounds were carried out. It was discovered that their formal potentials are significantly different from each other, and shift negatively in the order of 4-FcPy > 5-FcPy > 2-FcPy. This result suggests that the intramolecular electronic communication is dictated by the delocalization effect of the π-bonding systems in 2-FcPy, and that the electron-withdrawing effect of the nitrogen atoms in the pyrimidine ring plays the key role in 4-FcPy and 5-FcPy. The single crystal X-ray structure analyis and Density Functional Theory (DFT) calculation provided additional evidence (e.g., different torsion angles between the cyclopentadienyl and pyrimidine rings) to support the observed correlation between the redox properties and structural nature

  15. MLL becomes functional through intra-molecular interaction not by proteolytic processing.

    Directory of Open Access Journals (Sweden)

    Akihiko Yokoyama

    Full Text Available The mixed lineage leukemia (MLL protein is an epigenetic transcriptional regulator that controls proliferative expansion of immature hematopoietic progenitors, whose aberrant activation triggers leukemogenesis. A mature MLL protein is produced by formation of an intra-molecular complex and proteolytic cleavage. However the biological significance of these two post-transcriptional events remains unclear. To address their in vivo roles, mouse mutant alleles were created that exclusively express either a variant protein incapable of intra-molecular interaction (designated de or an uncleavable mutant protein (designated uc. The de homozygous mice died during midgestation and manifested devastating failure in embryonic development and reduced numbers of hematopoietic progenitors, whereas uc homozygous mice displayed no apparent defects. Expression of MLL target genes was severely impaired in de homozygous fibroblasts but unaffected in uc homozygous fibroblasts. These results unequivocally demonstrate that intra-molecular complex formation is a crucial maturation step whereas proteolytic cleavage is dispensable for MLL-dependent gene activation and proliferation in vivo.

  16. Characterization of intramolecular hydrogen bonds by atomic charges and charge fluxes.

    Science.gov (United States)

    Baranović, Goran; Biliškov, Nikola; Vojta, Danijela

    2012-08-16

    The electronic charge redistribution and the infrared intensities of the two types of intramolecular hydrogen bonds, O-H···O and O-H···π, of o-hydroxy- and o-ethynylphenol, respectively, together with a set of related intermolecular hydrogen bond complexes are described in terms of atomic charges and charge fluxes derived from atomic polar tensors calculated at the B3LYP/cc-pVTZ level of theory. The polarizable continuum model shows that both the atomic charges and charge fluxes are strongly dependent on solvent. It is shown that their values for the OH bond in an intramolecular hydrogen bond are not much different from those for the "free" OH bond, but the changes are toward the values found for an intermolecular hydrogen bond. The intermolecular hydrogen bond is characterized not only by the decreased atomic charge but also by the enlarged charge flux term of the same sign producing thus an enormous increase in IR intensity. The overall behavior of the charges and fluxes of the hydrogen atom in OH and ≡CH bonds agree well with the observed spectroscopic characteristics of inter- and intramolecular hydrogen bonding. The main reason for the differences between the two types of the hydrogen bond lies in the molecular structure because favorable linear proton donor-acceptor arrangement is not possible to achieve within a small molecule. The calculated intensities (in vacuo and in polarizable continuum) are only in qualitative agreement with the measured data. PMID:22809455

  17. An intramolecular disulfide bond designed in myoglobin fine-tunes both protein structure and peroxidase activity.

    Science.gov (United States)

    Wu, Lei-Bin; Yuan, Hong; Zhou, Hu; Gao, Shu-Qin; Nie, Chang-Ming; Tan, Xiangshi; Wen, Ge-Bo; Lin, Ying-Wu

    2016-06-15

    Disulfide bond plays crucial roles in stabilization of protein structure and in fine-tuning protein functions. To explore an approach for rational heme protein design, we herein rationally introduced a pair of cysteines (F46C/M55C) into the scaffold of myoglobin (Mb), mimicking those in native neuroglobin. Molecular modeling suggested that it is possible for Cys46 and Cys55 to form an intramolecular disulfide bond, which was confirmed experimentally by ESI-MS analysis, DTNB reaction and CD spectrum. Moreover, it was shown that the spontaneously formed disulfide bond of Cys46-Cys55 fine-tunes not only the heme active site structure, but also the protein functions. The substitution of Phe46 with Ser46 in F46S Mb destabilizes the protein while facilitates H2O2 activation. Remarkably, the formation of an intramolecular disulfide bond of Cys46-Cys55 in F46C/M55C Mb improves the protein stability and regulates the heme site to be more favorable for substrate binding, resulting in enhanced peroxidase activity. This study provides valuable information of structure-function relationship for heme proteins regulated by an intramolecular disulfide bond, and also suggests that construction of such a covalent bond is useful for design of functional heme proteins. PMID:27117233

  18. Six new coordination polymers constructed by 3-carboxyl-5-oxycarboxymethylpyridinio-1-carboxylate: Crystal structures, topologies, photoluminescent and magnetic properties

    International Nuclear Information System (INIS)

    Six new two-dimensional (2D) coordination polymers, [ML(H2O)3]n (M=Zn (1), Cd (2), Mn (3), Co (4)), [CdL(H2O)]n (5), [CdL(4,4′-bipy)]n·nH2O (6), (H2L=3-carboxyl-5-oxycarboxymethylpyridinio-1-carboxylate, 4,4′-bipy=4,4′-bipyridine), have been hydrothermally synthesized and characterized by single crystal X-ray diffraction analyses, IR spectra, and thermogravimetric analyses. 1, 2, 3, 4 are isostructural and feature a binodal (4,6)-connected topology with left- and right-handed helical chains with a pitch of 9.9560 Å. 5 can be topologically presented as an uninodal 6-connected network if the hydrogen bonds are also considered. 6 is a binodal (3,5)-connected 2D layer network. The photoluminescent properties of 1, 2, 5, 6 and magnetic properties of 3, 4 have been studied and discussed. - Graphical abstract: The structural differences show that the ligand, the metal center, and the reaction conditions have great influence on the structure of the final assembly. - Highlights: • A new asymmetric flexible tricarboxylate ligand of 3-carboxyl-5-oxycarboxymethylpyridinio-1-carboxylate was synthesized. • Six new two-dimensional (2D) coordination polymers have been hydrothermally obtained. • 1, 2, 3, 4 are isostructural and feature a binodal (4,6)-connected topology with left- and right-handed helical chains. • The photoluminescent properties of 1, 2, 5, 6 and magnetic properties of 3, 4 have been studied

  19. Carboxyl-terminated butadiene-acrylonitrile-toughened epoxy/carboxyl-modified carbon nanotube nanocomposites: Thermal and mechanical properties

    Directory of Open Access Journals (Sweden)

    H. F. Xie

    2012-09-01

    Full Text Available Carboxyl-modified multi-walled carbon nanotubes (MWCNT–COOHs as nanofillers were incorporated into diglycidyl ether of bisphenol A (DGEBA toughened with carboxyl-terminated butadiene-acrylonitrile (CTBN. The carboxyl functional carbon nanotubes were characterized by Fourier-transform infrared spectroscopy and thermogravimetric analysis. Furthermore, cure kinetics, glass transition temperature (Tg, mechanical properties, thermal stability and morphology of DGEBA/CTBN/MWCNT–COOHs nanocomposites were investigated by differential scanning calorimetry (DSC, dynamic mechanical analysis (DMA, universal test machine, thermogravimetric analysis and scanning electron microscopy (SEM. DSC kinetic studies showed that the addition of MWCNT–COOHs accelerated the curing reaction of the rubber-toughened epoxy resin. DMA results revealed that Tg of rubber-toughened epoxy nanocomposites lowered with MWCNT–COOH contents. The tensile strength, elongation at break, flexural strength and flexural modulus of DGEBA/CTBN/MWCNT-COOHs nanocomposites were increased at lower MWCNT-COOH concentration. A homogenous dispersion of nanocomposites at lower MWCNT–COOH concentration was observed by SEM.

  20. Intramolecular stable isotope distributions detect plant metabolic responses on century time scales

    Science.gov (United States)

    Schleucher, Jürgen; Ehlers, Ina; Augusti, Angela; Betson, Tatiana

    2014-05-01

    Plants respond to environmental changes on a vast range of time scales, and plant gas exchanges constitute important feedback mechanisms in the global C cycle. Responses on time scales of decades to centuries are most important for climate models, for prediction of crop productivity, and for adaptation to climate change. Unfortunately, responses on these timescale are least understood. We argue that the knowledge gap on intermediate time scales is due to a lack of adequate methods that can bridge between short-term manipulative experiments (e.g. FACE) and paleo research. Manipulative experiments in plant ecophysiology give information on metabolism on time scales up to years. However, this information cannot be linked to results from retrospective studies in paleo research, because little metabolic information can be derived from paleo archives. Stable isotopes are prominent tools in plant ecophysiology, biogeochemistry and in paleo research, but in all applications to date, isotope ratios of whole molecules are measured. However, it is well established that stable isotope abundance varies among intramolecular groups of biochemical metabolites, that is each so-called "isotopomer" has a distinct abundance. This intramolecular variation carries information on metabolic regulation, which can even be traced to individual enzymes (Schleucher et al., Plant, Cell Environ 1999). Here, we apply intramolecular isotope distributions to study the metabolic response of plants to increasing atmospheric [CO2] during the past century. Greenhouse experiments show that the deuterium abundance among the two positions in the C6H2 group of photosynthetic glucose depends on [CO2] during growth. This is observed for all plants using C3 photosynthesis, and reflects the metabolic flux ratio between photorespiration and photosynthesis. Photorespiration is a major C flux that limits assimilation in C3 plants, which encompass the overwhelming fraction of terrestrial photosynthesis and the

  1. A Capillary Electrochromatographic Microchip Packed with Self-Assembly Colloidal Carboxylic Silica Beads

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, In Sun; Kim, Shin Seon; Park, Jong Man [Konkuk University, Seoul (Korea, Republic of)

    2012-04-15

    An electrochromatographic microchip with carboxyl-group-derivatized mono-disperse silica packing was prepared from the corresponding colloidal silica solution by utilizing capillary action and self-assembly behavior. The silica beads in water were primed by the capillary action toward the ends of cross-patterned microchannel on a cyclic olefinic copolymer (COC) substrate. Slow evaporation of water at the front of packing promoted the self-assembled packing of the beads. After thermally binding a cover plate on the chip substrate, reservoirs for sample solutions were fabricated at the ends of the microchannel. The packing at the entrances of the microchannel was silver coated to fix utilizing an electroless silver-plating technique to prevent the erosion of the packed structure caused by the sudden switching of a high voltage DC power source. The electrochromatographic behavior of the microchip was explored and compared to that of the microchip with bare silica packing in basic borate buffer. Electrophoretic migration of Rhodamine B was dominant in the microchip with the carboxyl-derivatized silica packing that resulted in a migration approximated twice as fast, while the reversible adsorption was dominant in the bare silica-packed microchip. Not only the faster migration rates of the negatively charged FITC-derivatives of amino acids but also the different migration due to the charge interaction at the packing surface were observed. The electrochromatographic characteristics were studied in detail and compared with those of the bare silica packed microchip in terms of the packing material, the separation potential, pH of the running buffer, and also the separation channel length

  2. A Capillary Electrochromatographic Microchip Packed with Self-Assembly Colloidal Carboxylic Silica Beads

    International Nuclear Information System (INIS)

    An electrochromatographic microchip with carboxyl-group-derivatized mono-disperse silica packing was prepared from the corresponding colloidal silica solution by utilizing capillary action and self-assembly behavior. The silica beads in water were primed by the capillary action toward the ends of cross-patterned microchannel on a cyclic olefinic copolymer (COC) substrate. Slow evaporation of water at the front of packing promoted the self-assembled packing of the beads. After thermally binding a cover plate on the chip substrate, reservoirs for sample solutions were fabricated at the ends of the microchannel. The packing at the entrances of the microchannel was silver coated to fix utilizing an electroless silver-plating technique to prevent the erosion of the packed structure caused by the sudden switching of a high voltage DC power source. The electrochromatographic behavior of the microchip was explored and compared to that of the microchip with bare silica packing in basic borate buffer. Electrophoretic migration of Rhodamine B was dominant in the microchip with the carboxyl-derivatized silica packing that resulted in a migration approximated twice as fast, while the reversible adsorption was dominant in the bare silica-packed microchip. Not only the faster migration rates of the negatively charged FITC-derivatives of amino acids but also the different migration due to the charge interaction at the packing surface were observed. The electrochromatographic characteristics were studied in detail and compared with those of the bare silica packed microchip in terms of the packing material, the separation potential, pH of the running buffer, and also the separation channel length

  3. Density functional study of electronic, charge density, and chemical bonding properties of 9-methyl-3-Thiophen-2-YI-Thieno [3,2-e] [1, 2, 4] Thriazolo [4,3-c] pyrimidine-8-Carboxylic acid ethyl ester crystals

    Science.gov (United States)

    Reshak, A. H.; Kamarudin, H.; Alahmed, Z. A.; Auluck, S.; Chyský, Jan

    2014-06-01

    A comprehensive theoretical density functional investigation of the electronic crystal structure, chemical bonding, and the electron charge densities of 9-Methyl-3-Thiophen-2-YI-Thieno [3, 2-e] [1, 2, 4] Thriazolo [4,3-c] Pyrimidine-8-Carboxylic Acid Ethyl Ester (C15H12N4O2S2) is performed. The density of states at Fermi level equal to 5.50 (3.45) states/Ry cell, and the calculated bare electronic specific heat coefficient is found to be 0.95 (0.59) mJ/mole-K2 for the local density approximation (Engel-Vosko generalized gradient approximation). The electronic charge density space distribution contours in (1 0 0) and (1 1 0) planes were calculated. We find that there are two independent molecules (A and B) in the asymmetric unit exhibit intramolecular C-H…O, C-H…N interactions. This intramolecular interaction is different in molecules A and B, where A molecule show C-H…O interaction while B molecule exhibit C-H…N interaction. We should emphasis that there is π-π interaction between the pyrimidine rings of the two neighbors B molecules gives extra strengths and stabilizations to the superamolecular structure. The calculated distance between the two neighbors pyrimidine rings found to be 3.345 Å, in good agreement with the measured one (3.424(1) Å).

  4. Separation and determination of some carboxylic acids by capillary electrophoresis

    Energy Technology Data Exchange (ETDEWEB)

    Sladkov, V.; Fourest, B

    2006-07-01

    Separation and determination of some organic acids, mono-carboxylic (formic and acetic), dicarboxylic (oxalic and tartaric), tricarboxylic (citric) acids and aromatic acids (phtalic, benzoic, mellitic and trimellitic), by capillary electrophoresis are reviewed. The method development parameters, such as separation and injection mode, are discussed. Special attention is paid to the comparison of different detection types (spectroscopic and electrochemical). The optimisation of the carrier electrolyte composition (choice of carrier electrolyte, effect of pH, ionic strength, electro-osmotic flow modifier) is treated. Different additives (alkali-earth and transition metal ions, cyclodextrins and alcohol), which are often used for improving organic acid separation, are also considered. (authors)

  5. (2S,4R-4-Fluoropyrrolidinium-2-carboxylate

    Directory of Open Access Journals (Sweden)

    David B. Hobart Jr

    2012-08-01

    Full Text Available The crystal structure of the title compound, C5H8FNO2, at 100 K, displays intermolecular N—H...O hydrogen bonding between the ammonium and carboxylate groups as a result of its zwitterionic nature in the solid state. The five-membered ring adopts an envelope conformation with the C atom at the 3-position as the flap. The compound is of interest with respect to the synthesis and structural properties of synthetic collagens. The absolute structure was determined by comparison with the commercially available material.

  6. Sodium borohydride reduction of aromatic carboxylic acids via methyl esters

    Indian Academy of Sciences (India)

    Aamer Saeed; Zaman Ashraf

    2006-09-01

    A number of important aromatic carboxylic acids precursors, or intermediates in the syntheses of natural products, are converted into methyl esters and reduced to the corresponding primary alcohols using a sodium borohydride-THF-methanol system. The alcohols are obtained in 70-92% yields in 2-5 hours, in a pure state. This two-step procedure not only provides a better alternative to aluminum hydride reduction of acids but also allows the selective reduction of esters in presence of acids, amides, nitriles or nitro functions which are not affected under these conditions.

  7. Synthesis and properties of scandium carboxylate metal-organic frameworks

    OpenAIRE

    Gonzalez-Santiago, Berenice

    2015-01-01

    This work investigated the synthesis, characterisation and properties of known and novel scandium carboxylate Metal-organic Frameworks (MOFs). The first part reports the performance of these Sc-MOFs as Lewis acid catalysts. The porous MOF scandium trimesate MIL-100(Sc) and the scandium terephthalates such as MIL-101(Sc), MIL-88B(Sc) and MIL-68(Sc) (prepared as the Sc-analogue for the first time), and scandium biphenyldicarboxylate MIL-88D(Sc) were prepared and tested as Lewis acid catalysts. ...

  8. Carboxylic ester hydrolases in mitochondria from rat skeletal muscle

    DEFF Research Database (Denmark)

    Kirkeby, S; Moe, D; Zelander, T

    1990-01-01

    organophosphate and organomercury. The activity of the indoxyl acetate esterases was enhanced by the non-ionic detergents Tween-40 and Lubrol. After freezing, thawing and high speed centrifugation most of the alpha-naphthyl acetate splitting enzymes were found in the supernatant, indicating that the enzymes are......A mitochondrial pellet, prepared from rat skeletal muscle, contained a number of carboxylic ester hydrolase isoenzymes. The esterases which split alpha-naphthyl acetate were organophosphate sensitive, whereas two out of three indoxyl acetate hydrolysing enzymes were resistant to both...

  9. Separation and determination of some carboxylic acids by capillary electrophoresis

    International Nuclear Information System (INIS)

    Separation and determination of some organic acids, mono-carboxylic (formic and acetic), dicarboxylic (oxalic and tartaric), tricarboxylic (citric) acids and aromatic acids (phtalic, benzoic, mellitic and trimellitic), by capillary electrophoresis are reviewed. The method development parameters, such as separation and injection mode, are discussed. Special attention is paid to the comparison of different detection types (spectroscopic and electrochemical). The optimisation of the carrier electrolyte composition (choice of carrier electrolyte, effect of pH, ionic strength, electro-osmotic flow modifier) is treated. Different additives (alkali-earth and transition metal ions, cyclodextrins and alcohol), which are often used for improving organic acid separation, are also considered. (authors)

  10. Toxicity of perfluorinated carboxylic acids for aquatic organisms.

    Science.gov (United States)

    Tichý, Miloň; Valigurová, Radka; Cabala, Radomír; Uzlová, Rut; Rucki, Marián

    2010-06-01

    Toxicity of perfluorinated carboxylic acids with carbon chain C(8) to C(12) were tested with oligochaeta Tubifex tubifex. Toxicity was evaluated as the exposure time ET(50) from onset of damage of the oligochaeta in saturated aqueous solutions. The ET(50) fluctuated between 25 and 257 minutes. No statistically significant difference was found among the C(8), C(9) and C(12) acids (ET(50) between 143 and 257 minutes with large standard deviation). The acids with carbon chain C(10) and C(11) induced the effect significantly quicker (25 to 47 minutes). No acute toxicity measured in the three-minute test was observed in any case. PMID:21217876

  11. Toxicity of perfluorinated carboxylic acids for aquatic organisms

    OpenAIRE

    Tichý, Miloň; Valigurová, Radka; Čabala, Radomír; Uzlová, Rut; Rucki, Marián

    2010-01-01

    Toxicity of perfluorinated carboxylic acids with carbon chain C8 to C12 were tested with oligochaeta Tubifex tubifex. Toxicity was evaluated as the exposure time ET50 from onset of damage of the oligochaeta in saturated aqueous solutions. The ET50 fluctuated between 25 and 257 minutes. No statistically significant difference was found among the C8, C9 and C12 acids (ET50 between 143 and 257 minutes with large standard deviation). The acids with carbon chain C10 and C11 induced the effect sign...

  12. A bis(amine-carboxylate) copper(II) coordination compound forms a two-dimensional metal-organic framework when crystallized from water and methanol.

    Science.gov (United States)

    Munro, Orde Q; Akerman, Matthew P; Gillham, Kate

    2009-09-01

    When {2,2'-[(2-methyl-2-nitropropane-1,3-diyl)diimino]diacetato}copper(II), [Cu(C(8)H(13)N(3)O(6))], (I), was crystallized from a binary mixture of methanol and water, a monoclinic two-dimensional water- and methanol-solvated metal-organic framework (MOF) structure, distinctly different from the known orthorhombic one-dimensional coordination polymer of (I), was isolated, namely catena-poly[[copper(II)-mu(3)-2,2'-[(2-methyl-2-nitropropane-1,3-diyl)diimino]diacetato] methanol 0.45-solvate 0.55-hydrate], {[Cu(C(8)H(13)N(3)O(6))].0.45CH(3)OH.0.55H(2)O}(n), (II). The monoclinic structure of (II) comprises centrosymmetric dimers stabilized by a dative covalent Cu(2)O(2) core and intramolecular N-H...O hydrogen bonds. Each dimer is linked to four neighbouring dimers via symmetry-related (opposing) pairs of bridging carboxylate O atoms to generate a ;diamondoid' net or two-dimensional coordination network. Tight voids of 166 A(3) are located between these two-dimensional MOF sheets and contain a mixture of water and methanol with fractional occupancies of 0.55 and 0.45, respectively. The two-dimensional MOF sheets have nanometre-scale spacings (11.2 A) in the crystal structure. Hydrogen-bonding between the methanol/water hydroxy groups and a Cu-bound bridging carboxylate O atom apparently negates thermal desolvation of the structure below 358 K in an uncrushed crystal of (II). PMID:19726848

  13. EFFECT OF DIFFERENT TREATMENTS ON CELLULOSE TOWARD CARBOXYLATION AND ITS APPLICATION FOR METAL ION ABSORPTION

    Directory of Open Access Journals (Sweden)

    A. M. A. Nada

    2009-02-01

    Full Text Available Carboxylation of cotton linters was investigated relative to its use in ion exchange. The effects of different treatments of cotton linters, such as alkali, acid, and activating agents, e.g. LiCl, on the molecular structure and carboxylation of cotton linters were taken in our consideration. The absence or presence of a crosslinking was considered, and the efficiency of these prepared carboxylated cotton linters toward metal ions uptake, as well as thermal analysis of treated and carboxylated cotton linters, was investigated. It was found that treatment of cotton linters with alkali and activating agent decreased the crystallinity index (band intensity at 1425/band intensity at 890 cm-1. On the other hand, the prepared carboxylated cotton linters had lower crystallinity index than uncarboxylated linters. Thermal analysis of the treated and carboxylated cotton linters allowed calculation of the activation energy of thermally treated materials. It was found that the crosslinked and acid treated cotton linters had a higher activation.

  14. Metazoan promoters

    DEFF Research Database (Denmark)

    Lenhard, Boris; Sandelin, Albin Gustav; Carninci, Piero

    2012-01-01

    Promoters are crucial for gene regulation. They vary greatly in terms of associated regulatory elements, sequence motifs, the choice of transcription start sites and other features. Several technologies that harness next-generation sequencing have enabled recent advances in identifying promoters ...

  15. Do carboximide–carboxylic acid combinations form co-crystals? The role of hydroxyl substitution on the formation of co-crystals and eutectics

    Directory of Open Access Journals (Sweden)

    Ramanpreet Kaur

    2015-05-01

    Full Text Available Carboxylic acids, amides and imides are key organic systems which provide understanding of molecular recognition and binding phenomena important in biological and pharmaceutical settings. In this context, studies of their mutual interactions and compatibility through co-crystallization may pave the way for greater understanding and new applications of their combinations. Extensive co-crystallization studies are available for carboxylic acid/amide combinations, but only a few examples of carboxylic acid/imide co-crystals are currently observed in the literature. The non-formation of co-crystals for carboxylic acid/imide combinations has previously been rationalized, based on steric and computed stability factors. In the light of the growing awareness of eutectic mixtures as an alternative outcome in co-crystallization experiments, the nature of various benzoic acid/cyclic imide combinations is established in this paper. Since an additional functional group can provide sites for new intermolecular interactions and, potentially, promote supramolecular growth into a co-crystal, benzoic acids decorated with one or more hydroxyl groups have been systematically screened for co-crystallization with one unsaturated and two saturated cyclic imides. The facile formation of an abundant number of hydroxybenzoic acid/cyclic carboximide co-crystals is reported, including polymorphic and variable stoichiometry co-crystals. In the cases where co-crystals did not form, the combinations are shown invariably to result in eutectics. The presence or absence and geometric disposition of hydroxyl functionality on benzoic acid is thus found to drive the formation of co-crystals or eutectics for the studied carboxylic acid/imide combinations.

  16. OH stretching frequencies in systems with intramolecular hydrogen bonds: Harmonic and anharmonic analyses

    International Nuclear Information System (INIS)

    Graphical abstract: Stretching wavenumbers for intramolecularly hydrogen-bonded OH groups computed with second order perturbation theoretical anharmonic procedures were found to be essentially linearly related to those obtained within the much faster harmonic analysis. Moreover, the observed OH stretching wavenumbers were found to correlate linearly with predicted harmonic wavenumbers, thereby providing an approximate empirical relationship for the prediction of OH stretching bands. Highlights: ► Stretching wavenumbers for intramolecularly hydrogen-bonded OH groups. ► Harmonic and second order perturbation theory anharmonic approximations. ► Computed harmonic and anharmonic wavenumbers linearly related. ► Linear correlations between observed and computed wavenumbers. ► Linear correlation with OH proton NMR chemical shifts. - Abstract: OH stretching wavenumbers were investigated for 30 species with intramolecularly hydrogen-bonded hydroxyl groups, covering the range from 3600 to ca. 1900 cm−1. Theoretical wavenumbers were predicted with B3LYP/6-31G(d) density functional theory using the standard harmonic approximation, as well as the second-order perturbation theoretical (PT2) anharmonic approximations available with the Gaussian software package. The wavenumbers computed with the anharmonic procedures were found to be essentially linearly related to those obtained within the harmonic analysis. The theoretical wavenumbers were compared with experimental values taken from the literature, supplemented with values estimated from infrared (IR) absorption spectra recorded for the purpose of this study. An approximately linear relationship was established between the observed wavenumbers νOH and the results of the harmonic analysis. This is significant in view of the fact that the full anharmonic PT2 analysis requires orders-of-magnitude more computing time than the harmonic analysis. νOH also correlates with OH chemical shifts.

  17. Health Promotion

    DEFF Research Database (Denmark)

    Povlsen, Lene; Borup, I.

    2015-01-01

    In 1953 when the Nordic School of Public Health was founded, the aim of public health programmes was disease prevention more than health promotion. This was not unusual, since at this time health usually was seen as the opposite of disease and illness. However, with the Ottawa Charter of 1986......, the World Health Organization made a crucial change to view health not as a goal in itself but as the means to a full life. In this way, health promotion became a first priority and fundamental action for the modern society. This insight eventually reached NHV and in 2002 - 50 years after the foundation...... - an associate professorship was established with a focus on health promotion. Nevertheless, the concept of health promotion had been integrated with or mentioned in courses run prior to the new post. Subsequently, a wide spectrum of courses in health promotion was introduced, such as Empowerment for Child...

  18. Exploring the reductive capacity of Pyrococcus furiosus. The reduction of carboxylic acids and pyridine nucleotides

    OpenAIRE

    Ban, van den, A.W.

    2001-01-01

    This Ph.D. project started in 1997 and its main goal was to obtain insight in the reductive capacity of the hyperthermophilic archaeon Pyrococcus furiosus . The research was focused on the biocatalytic reduction of carboxylic acids.Reductions of carboxylic acids are interesting reactions, since the generated products, aldehydes and alcohols, are potentially applicable in the fine-chemical industry. However, the reduction of carboxylic acids to the corresponding aldehydes is a thermodynamicall...

  19. Electrochemical deposition of a copper carboxylate layer on copper as potential corrosion inhibitor

    OpenAIRE

    Elia, Alice; De Wael, Karolien; Dowsett, Mark; Adriaens, Annemie

    2012-01-01

    Carboxylic acids and sodium carboxylates are used to protect metals against aqueous and atmospheric corrosion. In this paper we describe the application of a layer of copper carboxylate on the surface of a copper electrode by means of cyclic voltammetry technique, and tests which measure the corresponding resistance to aqueous corrosion. Unlike the soaking process, which also forms a film on the surface, the use of cyclic voltammetry allows one to follow the deposition process of the copper c...

  20. A synthetic approach to carbon-14 labeled anti-bacterial naphthyridine and quinolone carboxylic acids

    Energy Technology Data Exchange (ETDEWEB)

    Ekhato, I.V.; Huang, C.C. (Parke, Davis and Co., Ann Arbor, MI (United States))

    1993-09-01

    Labeled versions of (S)-clinafloxacin (1) and two napththyridine carboxylic acid anti-bacterial compounds 2 and 3 which are currently in development were synthesized. Preparations started from hitherto unknown bromo compounds 22 and 10, from which the corresponding [sup 14]C-labeled aromatic carboxylic acids 23 and 12 were generated by metal-halogen exchange followed by carboxylation reaction. Details of these preparations are given. (author).

  1. Identification of Two Tyrosine Residues Required for the Intramolecular Mechanism Implicated in GIT1 Activation

    OpenAIRE

    Antonio Totaro; Veronica Astro; Diletta Tonoli; Ivan de Curtis

    2014-01-01

    GIT1 is an ArfGAP and scaffolding protein regulating cell adhesion and migration. The multidomain structure of GIT1 allows the interaction with several partners. Binding of GIT1 to some of its partners requires activation of the GIT1 polypeptide. Our previous studies indicated that binding of paxillin to GIT1 is enhanced by release of an intramolecular interaction between the amino-terminal and carboxy-terminal portions that keeps the protein in a binding-incompetent state. Here we have addre...

  2. A single intermolecular contact mediates intramolecular stabilization of both RNA and protein

    OpenAIRE

    Calabro, Valerie; Daugherty, Matthew D.; Frankel, Alan D.

    2005-01-01

    An arginine-rich peptide from the Jembrana disease virus (JDV) Tat protein is a structural “chameleon” that binds bovine immunodeficiency virus (BIV) or HIV TAR RNAs in two different binding modes, with an affinity for BIV TAR even higher than the cognate BIV peptide. We determined the NMR structure of the JDV Tat–BIV TAR high-affinity complex and found that the C-terminal tyrosine in JDV Tat forms a network of inter- and intramolecular hydrogen bonding and stacking interactions that simultan...

  3. A concise, efficient synthesis of sugar-based benzothiazoles through chemoselective intramolecular C-S coupling

    KAUST Repository

    Shen, Chao

    2012-01-01

    Sugar-based benzothiazoles are a new class of molecules promising for many biological applications. Here, we have synthesized a wide range of sugar-based benzothiazoles from readily accessible glycosyl thioureas by chemoselective, palladium-catalyzed C-S coupling reactions. Corroborated by theoretical calculations, a mechanistic investigation indicates that the coordination to the palladium by a pivaloyl carbonyl group and the presence of intramolecular hydrogen bonding play important roles in the efficiency and chemoselectivity of reaction. These fluorescent glycoconjugates can be observed to readily enter mammalian tumor cells and exhibit potential in vitro antitumor activity. This journal is © The Royal Society of Chemistry 2012.

  4. Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

    OpenAIRE

    Barnes, Jonathan C.; Fahrenbach, Albert C.; Dyar, Scott M.; Frasconi, Marco; Giesener, Marc A.; Zhu, Zhixue; Liu, Zhichang; Hartlieb, Karel J.; Carmieli, Ranaan; Wasielewski, Michael R.; Stoddart, J. Fraser

    2012-01-01

    The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquat-p-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ ring encircles the DNP unit. Reduction of the CBPQT...

  5. Use of ionic model for analysis of intramolecular movement in alkali metal metaborate molecules

    International Nuclear Information System (INIS)

    To clear out the peculiarities of intramolecular movement in MBO2 (where M=Li, Na, K, Rb, Cs) molecules the energy dependence of cation electrostatic interaction with BO2 anion on the charge value of oxygen, values of the MOB valence angle and internuclear distance r(M-O) is calculated. The calculation results on the base of ionic model show that the minimum of potential energy function corresponds to angular configuration of the MBO2 molecules. Parameters of potential function of deformation oscillation connected with the change of MOB angle, are evaluated

  6. Inter- and Intramolecular Vibrational Distribution in IR Multiple Photon Excitation: CF2Cl2 Molecule

    OpenAIRE

    Doljikov, Yu. S.; Malinovsky, A. L.; Ryabov, E. A.

    1988-01-01

    Vibrational energy distribution of IR MP-excited CF2Cl2 is studied when pumping molecules through ν1 and ν8 modes. In both cases the intermolecular distribution is found to be in a state of nonequilibrium consisting of ensembles of “hot” and “cold” molecules. The structure of the “cold” ensemble is different when ν1 and ν8 modes are pumped. Statistical intramolecular energy distribution caused by stochastization of vibrational motion is found for “hot” molecules. The estimated value of stocha...

  7. Fluorescence behavior of intramolecular charge transfer state in trans-ethyl p-(dimethylamino)cinamate

    International Nuclear Information System (INIS)

    Steady-state and time-resolved emission studies have been performed to investigate the intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino)cinamate (EDAC) in various solvents. Large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the excited state compared to the ground state. The excited state properties in hydrogen-bonding solvents are markedly different from other solvents indicating the possible competition of intermolecular hydrogen bond formation with the electron donor site and ICT

  8. Excited state intramolecular charge transfer reaction in 4-(1-azetidinyl)benzonitrile: Solvent isotope effects

    Indian Academy of Sciences (India)

    Tuhin Pradhan; Piue Ghoshal; Ranjit Biswas

    2009-01-01

    Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several other properties such as quantum yield and radiative rates have been found to be insensitive to the solvent isotope substitution in all these solvents. The origin of the solvent isotope insensitivity of the reaction is discussed and correlated with the observed slowing down of the solvation dynamics upon isotope substitution.

  9. Rotational isomers, intramolecular hydrogen bond, and IR spectra of o-vinylphenol

    International Nuclear Information System (INIS)

    Absorption bands of OH stretching vibrations in IR spectra of o-vinylphenol (o-VP) in the weakly polar solvents CCl4 and n-hexane were studied. Several rotamers of the free OH group were observed for o-VP in n-hexane. The fraction of o-VP rotamers with an O–H…π intramolecular hydrogen bond (IHB) was less than 20% according to experimental estimates for CCl4 solutions and calculations in the gas phase and cyclohexane. The theoretical effective enthalpy of the o-VP IHB was estimated for rotamer A (–ΔH=0.20 kcal/mol). (authors)

  10. Synthesis and Intramolecular [4+2] Cycloaddition Reactions of 4-Pyridazinecarbonitriles with Alkyne Side Chains

    OpenAIRE

    Norbert Haider; Günther Fülep

    1998-01-01

    The preparation of a series of new 3-(alkynyl-X)-substituted 4-pyridazinecarbonitriles 2-5 (X = O, NH) is described. The compounds are shown to undergo thermally induced intramolecular Diels-Alder reactions with inverse electron demand, affording the fused benzonitriles 6-8. Incorporation of a 1,2-phenylene unit into the side chain, as in the case of compounds 10 and 13, results in a more favorable conformation of the dienophilic substructure and thus to a pronounced acceleration of the [4+2]...

  11. Biocompatibility studies of polyacrylonitrile membranes modified with carboxylated polyetherimide

    Energy Technology Data Exchange (ETDEWEB)

    Senthilkumar, S.; Rajesh, S.; Jayalakshmi, A.; Mohan, D., E-mail: mohantarun@gmail.com

    2013-10-15

    Poly (ether-imide) (PEI) was carboxylated and used as the hydrophilic modification agent for the preparation of polyacrylonitrile (PAN) membranes. Membranes were prepared with different blend compositions of PAN and CPEI by diffusion induced precipitation. The modified membranes were characterized by thermo gravimetric analysis (TGA), mechanical analysis, scanning electron microscopy (SEM) and contact angle measurement to understand the influence of CPEI on the properties of the membranes. The biocompatibility studies exhibited reduced plasma protein adsorption, platelet adhesion and thrombus formation on the modified membrane surface. The complete blood count (CBC) results of CPEI incorporated membranes showed stable CBC values and significant decrease in the complement activation were also observed. In addition to good cytocompatibility, monocytes cultured on these modified membranes exhibited improved functional profiles in 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. Thus it could be concluded that PAN/CPEI membranes with excellent biocompatibility can be useful for hemodialysis. Highlights: • Carboxylated PEI was prepared and utilized as hydrophilic modification agent. • CPEI incorporated into PAN to improved biocompatibility and cyto compatibility • Biocompatibility of membranes was correlated with morphology and hydrophilicity. • Antifouling studies of the PAN/CPEI membranes was studied by BSA as model foulant.

  12. Adsorption behavior of epirubicin hydrochloride on carboxylated carbon nanotubes.

    Science.gov (United States)

    Chen, Zhe; Pierre, Dramou; He, Hua; Tan, Shuhua; Pham-Huy, Chuong; Hong, Hao; Huang, Jilong

    2011-02-28

    The aim of this study was to understand the interaction between carboxylated carbon nanotubes (c-CNTs) and anticancer agents and evaluate the drug-loading ability of c-CNTs. We prepared carboxylated multi-walled carbon nanotubes (c-MWNTs) with nitric acid treatment, then evaluated the adsorption ability of c-MWNTs as adsorbents for loading of the anticancer drug, epirubicin hydrochloride (EPI), and investigated the adsorption behavior of EPI on c-MWNTs. Unmodified multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) were included as comparative adsorbents. The results showed that carbon nanotubes were able to form supramolecular complexes with EPI via π-π stacking and possessed favorable loading properties as drug carriers. The Freundilich adsorption model was successfully employed to describe the adsorption process. Because of the high surface area and hydrogen bonding, c-MWNTs' adsorption efficiency was the highest and the most stable and their drug-loading capacity was superior to that of MWNTs. With the increase of pH, the adsorption capacity of EPI on the c-MWNTs increased. Low-temperature facilitated the adsorption. More rapid EPI adsorption rate and higher drug-loading ability were observed from c-MWNTs with smaller diameter. Moreover, the adsorption kinetics of EPI on c-MWNTs could be well depicted by using the pseudo-second-order kinetic model. PMID:21145959

  13. Integrated process for preparing a carboxylic acid from an alkane

    Energy Technology Data Exchange (ETDEWEB)

    Benderly, Abraham (Elkins Park, PA); Chadda, Nitin (Radnor, PA); Sevon, Douglass (Fairless Hills, PA)

    2011-12-20

    The present invention relates to an integrated process for producing unsaturated carboxylic acids from the corresponding C.sub.2-C.sub.4 alkane. The process begins with performance of thermally integrated dehydrogenation reactions which convert a C.sub.2-C.sub.4 alkane to its corresponding C.sub.2-C.sub.4 alkene, and which involve exothermically converting a portion of an alkane to its corresponding alkene by oxidative dehydrogenation in an exothermic reaction zone, in the presence of oxygen and a suitable catalyst, and then feeding the products of the exothermic reaction zone to an endothermic reaction zone wherein at least a portion of the remaining unconverted alkane is endothermically dehydrogenated to form an additional quantity of the same corresponding alkene, in the presence of carbon dioxide and an other suitable catalyst. The alkene products of the thermally integrated dehydrogenation reactions are then provided to a catalytic vapor phase partial oxidation process for conversion of the alkene to the corresponding unsaturated carboxylic acid or nitrile. Unreacted alkene and carbon dioxide are recovered from the oxidation product stream and recycled back to the thermally integrated dehydrogenation reactions.

  14. On the intermediacy of carboxyphosphate in biotin-dependent carboxylations

    International Nuclear Information System (INIS)

    In the ATP-dependent carboxylation of biotin that is catalyzed by most biotin-dependent carboxylases, a fundamental mechanistic question is whether the ATP activates bicarbonate (via the formation of carboxyphosphate as an intermediate) or whether the ATP activates biotin (via the formation of O-phosphobiotin). The authors have resorted to three mechanistic tests using the biotin carboxylase subunit of acetyl-CoA carboxylase from Escherichia coli: positional isotope exchange, intermediate trapping, and 18O tracer experiments on the ATPase activity. First, no catalysis of positional isotope exchange in adenosine 5'-([α,β-18O,β,β-18O2]triphosphate) was observed when either biotin or bicarbonate was absent, nor was any exchange seen in the presence of both N-1-methylbiotin and bicarbonate. Second, the putative carboxyphosphate intermediate could not be trapped as its trimethyl ester, under conditions of incubation and analysis where the authentic triester was shown to be adequately stable. In the third test, however, they showed that the ATPase activity of biotin carboxylase that is seen in the absence of biotin, an activity that is known to parallel the normal carboxylase reaction when biotin is present, occurs with the transfer of an 18O label directly from [18O]bicarbonate into the product Pi. This result suggests that the bicarbonate-dependent biotin-independent ATPase reaction catalyzed by biotin carboxylase goes via carboxyphosphate and that the carboxylation of biotin itself may proceed analogously

  15. Complexes of carboxyl-containing polymer and monosubstituted bipyridinium salts

    Science.gov (United States)

    Merekalova, N. D.; Bondarenko, G. N.; Krylsky, D. W.; Zakirov, M. I.; Talroze, R. V.

    2013-09-01

    Semi-empirical PM3 method for the quantum calculations of molecular electronic structure based on NDDO integral approximation is used to investigate the complex formation of monosubstituted 4,4‧-bipyridinium salts BpyR (Hal) containing a halide anion interacting with the quaternary nitrogen atom and carboxylic group of the two-units construct. Significant effect of the BpyR (Hal) electronic structure is unveiled that contributes in two different structures of these salts, namely, partial charge transfer complex and ion pair structure, both having stable energy minima. We demonstrate that (i) the structure of the N-substituent modulates the energy and electronic characteristics of monosubstituted salts BpyR with chlorine and bromine anions and (ii) the coulomb interactions between quaternary N-atom, halogen anion, and the proton of carboxylic group stimulate the transformation of the charge transfer complex into the ion pair structure. Results of calculations are compared with the experimental FTIR spectra of blends of BpyR(Hal) with Eudragit copolymer.

  16. Biocompatibility studies of polyacrylonitrile membranes modified with carboxylated polyetherimide

    International Nuclear Information System (INIS)

    Poly (ether-imide) (PEI) was carboxylated and used as the hydrophilic modification agent for the preparation of polyacrylonitrile (PAN) membranes. Membranes were prepared with different blend compositions of PAN and CPEI by diffusion induced precipitation. The modified membranes were characterized by thermo gravimetric analysis (TGA), mechanical analysis, scanning electron microscopy (SEM) and contact angle measurement to understand the influence of CPEI on the properties of the membranes. The biocompatibility studies exhibited reduced plasma protein adsorption, platelet adhesion and thrombus formation on the modified membrane surface. The complete blood count (CBC) results of CPEI incorporated membranes showed stable CBC values and significant decrease in the complement activation were also observed. In addition to good cytocompatibility, monocytes cultured on these modified membranes exhibited improved functional profiles in 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. Thus it could be concluded that PAN/CPEI membranes with excellent biocompatibility can be useful for hemodialysis. Highlights: • Carboxylated PEI was prepared and utilized as hydrophilic modification agent. • CPEI incorporated into PAN to improved biocompatibility and cyto compatibility • Biocompatibility of membranes was correlated with morphology and hydrophilicity. • Antifouling studies of the PAN/CPEI membranes was studied by BSA as model foulant

  17. Substituent effects on hydrogen bonding of aromatic amide-carboxylate.

    Science.gov (United States)

    Sen, Ibrahim; Kara, Hulya; Azizoglu, Akın

    2016-10-01

    N-(p-benzoyl)-anthranilic acid (BAA) derivatives have been synthesized with different substituents (X: Br, Cl, OCH3, CH3), and their crystal structures have been analyzed in order to understand the variations in their molecular geometries with respect to the substituents by using (1)H NMR, (13)C NMR, IR and X-ray single-crystal diffraction. The carboxylic acid group forms classic OH⋯O hydrogen bonded dimers in a centrosymmetric R2(2)(8) ring motifs for BAA-Br and BAA-Cl. However, no carboxylic acid group forms classic OH⋯O hydrogen bonded dimers in BAA-OCH3 and BAA-CH3. The asymmetric unit consists of two crystallographically independent molecules in BAA-OCH3. DFT computations show that the interaction energies between monomer and dimer are in the range of 0.5-3.8kcal/mol with the B3LYP/6-31+G*, B3LYP/6-31++G*, B3LYP/6-31++G**, and B3LYP/AUG-cc-pVDZ levels of theory. The presence of different hydrogen bond patterns is also governed by the substrate. For monomeric compounds studied herein, theoretical calculations lead to two low-energy conformers; trans (a) and cis (b). Former one is more stable than latter by about 4kcal/mol. PMID:27239947

  18. [Synthesis and bronchodilator action of 4-(methoxycarbonylalkylsulfinyl)-4-pyrrol carboxylic esters].

    Science.gov (United States)

    Eiden, F; Grusdt, U

    1989-11-01

    The dihydro-dimethoxyfuran carboxylic ester 3 reacts with different mercaptoalkyl carboxylates to give the carbomethoxyalkylthio-tetrahydrofuran carboxylic esters 4. Methanol elimination of 4 yields the dihydrofuran derivatives 5. 4 and 5 can be oxidized to afford the sulfoxides 6 and the sulfones 7, respectively. 4 reacts with primary amines to give the title compounds 8. Derivatives of 8 can be cyclized to afford the thienopyrroles 11 and 12 as well as the thienopyranopyrrole 14. The mercaptopyrrole carboxylic ester 10 is obtained from 8f by elimination of propenic acid. 8e shows bronchodilatoric activity in low concentration. PMID:2624526

  19. A simple and versatile design concept for fluorophore derivatives with intramolecular photostabilization

    Science.gov (United States)

    van der Velde, Jasper H. M.; Oelerich, Jens; Huang, Jingyi; Smit, Jochem H.; Aminian Jazi, Atieh; Galiani, Silvia; Kolmakov, Kirill; Guoridis, Giorgos; Eggeling, Christian; Herrmann, Andreas; Roelfes, Gerard; Cordes, Thorben

    2016-01-01

    Intramolecular photostabilization via triple-state quenching was recently revived as a tool to impart synthetic organic fluorophores with `self-healing' properties. To date, utilization of such fluorophore derivatives is rare due to their elaborate multi-step synthesis. Here we present a general strategy to covalently link a synthetic organic fluorophore simultaneously to a photostabilizer and biomolecular target via unnatural amino acids. The modular approach uses commercially available starting materials and simple chemical transformations. The resulting photostabilizer-dye conjugates are based on rhodamines, carbopyronines and cyanines with excellent photophysical properties, that is, high photostability and minimal signal fluctuations. Their versatile use is demonstrated by single-step labelling of DNA, antibodies and proteins, as well as applications in single-molecule and super-resolution fluorescence microscopy. We are convinced that the presented scaffolding strategy and the improved characteristics of the conjugates in applications will trigger the broader use of intramolecular photostabilization and help to emerge this approach as a new gold standard.

  20. Organometallic copper I, II or III species in an intramolecular dechlorination reaction

    KAUST Repository

    Poater, Albert

    2013-03-15

    The present paper gives insight into an intramolecular dechlorination reaction involving Copper (I) and an ArCH2Cl moiety. The discussion of the presence of a CuIII organometallic intermediate becomes a challenge, and because of the lack of clear experimental detection of this proposed intermediate, and due to the computational evidence that it is less stable than other isomeric species, it can be ruled out for the complex studied here. Our calculations are completely consistent with the key hypothesis of Karlin et al. that TMPA-CuI is the substrate of intramolecular dechlorination reactions as well as the source to generate organometallic species. However the organometallic character of some intermediates has been refused because computationally these species are less stable than other isomers. Thus this study constitutes an additional piece towards the full understanding of a class of reaction of biological relevance. Further, the lack of high energy barriers and deep energy wells along the reaction pathway explains the experimental difficulties to trap other intermediates. © Springer-Verlag Berlin Heidelberg 2013.

  1. The role of intramolecular self-destruction of reactive metabolic intermediates in determining toxicity.

    Science.gov (United States)

    Svennebring, Andreas

    2016-04-01

    When reactive centers are formed in chemical conversions, intermolecular reactions tend to dominate over intramolecular alternatives whenever both alternatives are possible. Hence, when reactive metabolites are formed from xenobiotics, intramolecular quenching by moieties adjacent to a toxicophore may play an important role in reducing toxicity related to reactive intermediates. The phenomenon is likely to be particularly noticeable for toxicophores that are readily associated with a type of toxicity that is rarely caused by other structural motives. In two demonstrative investigations, it is concluded that nitrobenzenes for which the expected nitrosyl metabolite is likely to react with adjacent groups are less toxic than what is rationally expected, and that among aryl amine drugs allowing for the immediate quenching of the corresponding N-aryl hydroxylamine metabolite, the typical erythrocyte toxicity often seen with aryl amines is absent. The deliberate introduction of effective quenching groups nearby a toxicophoric moiety may present a potential strategy for reducing toxicity in the design of drugs and other man-made xenobiotics. PMID:26542997

  2. A Direct Mechanism of Ultrafast Intramolecular Singlet Fission in Pentacene Dimers.

    Science.gov (United States)

    Fuemmeler, Eric G; Sanders, Samuel N; Pun, Andrew B; Kumarasamy, Elango; Zeng, Tao; Miyata, Kiyoshi; Steigerwald, Michael L; Zhu, X-Y; Sfeir, Matthew Y; Campos, Luis M; Ananth, Nandini

    2016-05-25

    Interest in materials that undergo singlet fission (SF) has been catalyzed by the potential to exceed the Shockley-Queisser limit of solar power conversion efficiency. In conventional materials, the mechanism of SF is an intermolecular process (xSF), which is mediated by charge transfer (CT) states and depends sensitively on crystal packing or molecular collisions. In contrast, recently reported covalently coupled pentacenes yield ∼2 triplets per photon absorbed in individual molecules: the hallmark of intramolecular singlet fission (iSF). However, the mechanism of iSF is unclear. Here, using multireference electronic structure calculations and transient absorption spectroscopy, we establish that iSF can occur via a direct coupling mechanism that is independent of CT states. We show that a near-degeneracy in electronic state energies induced by vibronic coupling to intramolecular modes of the covalent dimer allows for strong mixing between the correlated triplet pair state and the local excitonic state, despite weak direct coupling. PMID:27280166

  3. Intra-molecular Triplet Energy Transfer is a General Approach to Improve Organic Fluorophore Photostability

    Science.gov (United States)

    Zheng, Qinsi; Jockusch, Steffen; Rodríguez-Calero, Gabriel G.; Zhou, Zhou; Zhao, Hong; Altman, Roger B.; Abruña, Héctor D.; Blanchard, Scott C.

    2015-01-01

    Bright, long-lasting and non-phototoxic organic fluorophores are essential to the continued advancement of biological imaging. Traditional approaches towards achieving photostability, such as the removal of molecular oxygen and the use of small-molecule additives in solution, suffer from potentially toxic side effects, particularly in the context of living cells. The direct conjugation of small-molecule triplet state quenchers, such as cyclooctatetraene (COT), to organic fluorophores has the potential to bypass these issues by restoring reactive fluorophore triplet states to the ground state through intra-molecular triplet energy transfer. Such methods have enabled marked improvement in cyanine fluorophore photostability spanning the visible spectrum. However, the generality of this strategy to chemically and structurally diverse fluorophore species has yet to be examined. Here, we show that the proximal linkage of COT increases the photon yield of a diverse range of organic fluorophores widely used in biological imaging applications, demonstrating that the intra-molecular triplet energy transfer mechanism is a potentially general approach for improving organic fluorophore performance and photostability. PMID:26700693

  4. Flow Cytometry Enables Multiplexed Measurements of Genetically Encoded Intramolecular FRET Sensors Suitable for Screening.

    Science.gov (United States)

    Doucette, Jaimee; Zhao, Ziyan; Geyer, Rory J; Barra, Melanie M; Balunas, Marcy J; Zweifach, Adam

    2016-07-01

    Genetically encoded sensors based on intramolecular FRET between CFP and YFP are used extensively in cell biology research. Flow cytometry has been shown to offer a means to measure CFP-YFP FRET; we suspected it would provide a unique way to conduct multiplexed measurements from cells expressing different FRET sensors, which is difficult to do with microscopy, and that this could be used for screening. We confirmed that flow cytometry accurately measures FRET signals using cells transiently transfected with an ERK activity reporter, comparing responses measured with imaging and cytometry. We created polyclonal long-term transfectant lines, each expressing a different intramolecular FRET sensor, and devised a way to bar-code four distinct populations of cells. We demonstrated the feasibility of multiplexed measurements and determined that robust multiplexed measurements can be conducted in plate format. To validate the suitability of the method for screening, we measured responses from a plate of bacterial extracts that in unrelated experiments we had determined contained the protein kinase C (PKC)-activating compound teleocidin A-1. The multiplexed assay correctly identifying the teleocidin A-1-containing well. We propose that multiplexed cytometric FRET measurements will be useful for analyzing cellular function and for screening compound collections. PMID:26908592

  5. A theoretical study of solvent effects on the characteristics of the intramolecular hydrogen bond in Droxidopa

    Indian Academy of Sciences (India)

    Mehdi Yoosefian; Hassan Karimi-Maleh; Afsaneh L Sanati

    2015-06-01

    The molecular structures and intramolecular hydrogen bond of Droxidopa have been investigated with density functional theory. It is found that strong hydrogen bonds (O–H…N and O…H–O) exist in the title compound. These hydrogen bonds play essential roles in determining conformational preferences and energy, which would have important effects in biological activity mechanisms that will strongly influence its characteristics in solution. A computational study of a representative number of actual and model structures was carried out in five solvents with different polarities and different types of interactions with solute molecules: water, ethanol, carbon tetrachloride, dimethyl sulfoxide, and tetrahydrofuran, utilizing the polarizable continuum model (PCM) model. The calculations were performed at the B3LYP/6-311++G(d,p) level of theory. In addition, the topological properties of the electron density distributions for O–H…N(O) intramolecular hydrogen bond were analyzed in terms of the Bader’s theory of atoms in molecules. Furthermore, the analyses of different hydrogen bonds in this molecule by quantum theory of natural bond orbital (NBO) methods support the density functional theory (DFT) results.

  6. Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

    Directory of Open Access Journals (Sweden)

    Andreas Gansäuer

    2013-08-01

    Full Text Available The intramolecular radical addition to aniline derivatives was investigated by DFT calculations. The computational methods were benchmarked by comparing the calculated values of the rate constant for the 5-exo cyclization of the hexenyl radical with the experimental values. The dispersion-corrected PW6B95-D3 functional provided very good results with deviations for the free activation barrier compared to the experimental values of only about 0.5 kcal mol−1 and was therefore employed in further calculations. Corrections for intramolecular London dispersion and solvation effects in the quantum chemical treatment are essential to obtain consistent and accurate theoretical data. For the investigated radical addition reaction it turned out that the polarity of the molecules is important and that a combination of electrophilic radicals with preferably nucleophilic arenes results in the highest rate constants. This is opposite to the Minisci reaction where the radical acts as nucleophile and the arene as electrophile. The substitution at the N-atom of the aniline is crucial. Methyl substitution leads to slower addition than phenyl substitution. Carbamates as substituents are suitable only when the radical center is not too electrophilic. No correlations between free reaction barriers and energies (ΔG‡ and ΔGR are found. Addition reactions leading to indanes or dihydrobenzofurans are too slow to be useful synthetically.

  7. Solvent viscosity influence on the chemiexcitation efficiency of inter and intramolecular chemiluminescence systems.

    Science.gov (United States)

    Khalid, Muhammad; Souza, Sergio P; Ciscato, Luiz F M L; Bartoloni, Fernando H; Baader, Wilhelm J

    2015-07-01

    The effects of the medium viscosity on the chemiexcitation quantum yields of the induced decomposition of 1,2-dioxetanes (highly efficient intramolecular CIEEL system) and the catalyzed decomposition of diphenoyl peroxide and a 1,2-dioxetanone derivative (model systems for the intermolecular CIEEL mechanism, despite their low efficiency) are compared in this work. Quantum yields of the rubrene catalyzed decomposition of diphenoyl peroxide and spiro-adamantyl-1,2-dioxetanone as well as the fluoride induced decomposition of a phenoxy-substituted 1,2-dioxetane derivative are shown to depend on the composition of the binary solvent mixture toluene/diphenyl ether, which possess similar polarity parameters but different viscosities. Correlations of the quantum yield data with the medium viscosity using the diffusional and the frictional (free-volume) models indicate that the induced 1,2-dioxetane decomposition indeed occurs by an entirely intramolecular process and the low efficiency of the intermolecular chemiluminescence systems (catalyzed decomposition of diphenoyl peroxide and 1,2-dioxetanone derivative) is not primarily due to the cage escape of radical ion species. PMID:26067192

  8. How To Reach Intense Luminescence for Compounds Capable of Excited-State Intramolecular Proton Transfer?

    Science.gov (United States)

    Skonieczny, Kamil; Yoo, Jaeduk; Larsen, Jillian M; Espinoza, Eli M; Barbasiewicz, Michał; Vullev, Valentine I; Lee, Chang-Hee; Gryko, Daniel T

    2016-05-23

    Photoinduced intramolecular direct arylation allows structurally unique compounds containing phenanthro[9',10':4,5]imidazo[1,2-f]phenanthridine and imidazo[1,2-f]phenanthridine skeletons, which mediate excited-state intramolecular proton transfer (ESIPT), to be efficiently synthesized. The developed polycyclic aromatics demonstrate that the combination of five-membered ring structures with a rigid arrangement between a proton donor and a proton acceptor provides a means for attaining large fluorescence quantum yields, exceeding 0.5, even in protic solvents. Steady-state and time-resolved UV/Vis spectroscopy reveals that, upon photoexcitation, the prepared protic heteroaromatics undergo ESIPT, converting them efficiently into their excited-state keto tautomers, which have lifetimes ranging from about 5 to 10 ns. The rigidity of their structures, which suppresses nonradiative decay pathways, is believed to be the underlying reason for the nanosecond lifetimes of these singlet excited states and the observed high fluorescence quantum yields. Hydrogen bonding with protic solvents does not interfere with the excited-state dynamics and, as a result, there is no difference between the occurrences of ESIPT processes in MeOH versus cyclohexane. Acidic media has a more dramatic effect on suppressing ESIPT by protonating the proton acceptor. As a result, in the presence of an acid, a larger proportion of the fluorescence of ESIPT-capable compounds originates from their enol excited states. PMID:27062363

  9. Hydrogen-bonded Intramolecular Charge Transfer Excited State of Dimethylaminobenzophenone using Time Dependent Density Functional Theory

    Institute of Scientific and Technical Information of China (English)

    Yu-ling Chu; Zhong Yang; Zhe-feng Pan; Jing Liu; Yue-yi Han; Yong Ding; Peng Song

    2012-01-01

    Density functional theory and time-dependent density-functional theory have been used to investigate the photophysical properties and relaxation dynamics of dimethylaminobenzophenone (DMABP) and its hydrogen-bonded DMABP-MeOH dimer.It is found that,in nonpolar aprotic solvent,the transitions from S0 to S1 and S2 states of DMABP have both n→π* and π→π* characters,with the locally excited feature mainly located on the C=O group and the partial CT one characterized by electron transfer mainly from the dimethylaminophenyl group to the C=O group.But when the intermolecular hydrogen bond C=O…H-O is formed,the highly polar intramolecular charge transfer character switches over to the first excited state of DMABP-MeOH dimer and the energy difference between the two lowlying electronically excited states increases.To gain insight into the relaxation dynamics of DMABP and DMABP-MeOH dimer in the excited state,the potential energy curves for conformational relaxation are calculated.The formation of twisted intramolecular charge transfer state via diffusive twisting motion of the dimethylamino/dimethylaminophenyl groups is found to be the major relaxation process.In addition,the decay of the S1 state of DMABP-MeOH dimer to the ground state,through nonradiative intermolecular hydrogen bond stretching vibrations,is facilitated by the formation of the hydrogen bond between DMABP and alcohols.

  10. The role of intramolecular crosslinking in the radiolysis of bulk crystallized high density polyethylene

    International Nuclear Information System (INIS)

    Intramolecular crosslinks have been suggested to occur in bulk crystallized, irradiated, high density polyethylene (HDPE) and to account for the low rates of gel formation, especially those of previously annealed samples when compared with that manifested by the same resin when previously quenched from the melt. Such crosslinks do not contribute to the development of gel and contribute to only a limited extent to the elastic properties above the crystalline melting point when compared with intermolecular crosslinks, but, if the mesh size of the intra- and inter-molecular networks are comparable, are fully reflected in the rupture elongation. The rupture elongations of a wide range of HDPE resins, for a given sol fraction or elastic modulus, are found to be at least as high as and often higher than those of low (LDPE) or linear low (LLDPE) polyethylene resins, indicating that intramolecular crosslinking of this type does not occur to a significantly greater extent in these higher crystallinity resins. Other factors more likely to account for the reduced rates of inter alia gel formation in some HDPE resins are discussed. (author)

  11. Intramolecular cyclopropanation and C-H insertion reactions with metal carbenoids generated from cyclopropenes.

    Science.gov (United States)

    Archambeau, Alexis; Miege, Frédéric; Meyer, Christophe; Cossy, Janine

    2015-04-21

    Activation of unsaturated carbon-carbon bonds by means of transition metal catalysts is an exceptionally active research field in organic synthesis. In this context, due to their high ring strain, cyclopropenes constitute an interesting class of substrates that displays a versatile reactivity in the presence of transition metal catalysts. Metal complexes of vinyl carbenes are involved as key intermediates in a wide variety of transition metal-catalyzed ring-opening reactions of cyclopropenes. Most of the reported transformations rely on intermolecular or intramolecular addition of nucleophiles to these latter reactive species. This Account focuses specifically on the reactivity of carbenoids resulting from the ring-opening of cyclopropenes in cyclopropanation and C-H insertion reactions, which are arguably two of the most representative transformations of metal complexes of carbenes. Compared with the more conventional α-diazo carbonyl compounds, the use of cyclopropenes as precursors of metal carbenoids in intramolecular cyclopropanation or C-H insertion reactions has been largely underexploited. One of the challenges is to devise appropriately substituted and readily available cyclopropenes that would not only undergo regioselective ring-opening under mild conditions but also trigger the subsequent desired transformations with a high level of chemoselectivity and stereoselectivity. These goals were met by considering several substrates derived from the readily available 3,3-dimethylcyclopropenylcarbinols or 3,3-dimethylcyclopropenylcarbinyl amines. In the case of 1,6-cyclopropene-enes, highly efficient and diastereoselective gold(I)-catalyzed ring-opening/intramolecular cyclopropanations were developed as a route to diversely substituted heterocycles and carbocycles possessing a bicyclo[4.1.0]heptane framework. The use of rhodium(II) catalysts enabled us to widen the scope of this transformation for the synthesis of medium-sized heterocyclic scaffolds

  12. Atmospheric chemistry of carboxylic acids: microbial implication versus photochemistry

    Directory of Open Access Journals (Sweden)

    M. Vaïtilingom

    2011-08-01

    Full Text Available The objective of this work was to compare experimentally the contribution of photochemistry vs. microbial activity to the degradation of carboxylic acids present in cloud water. For this, we selected 17 strains representative of the microflora existing in real clouds and worked on two distinct artificial cloud media that reproduce marine and continental cloud chemical composition. Photodegradation experiments with hydrogen peroxide (H2O2 as a source of hydroxyl radicals were performed under the same microcosm conditions using two irradiation systems. Biodegradation and photodegradation rates of acetate, formate, oxalate and succinate were measured on both media at 5 °C and 17 °C and were shown to be on the same order of magnitude (around 10−10–10−11 M s−1. The chemical composition (marine or continental origin had little influence on photodegradation and biodegradation rates while the temperature shift from 17 °C to 5 °C decreased biodegradation rates of a factor 2 to 5.

    In order to test other photochemical scenarios, theoretical photodegradation rates were calculated considering hydroxyl (OH radical concentration values in cloud water estimated by cloud chemistry modelling studies and available reaction rate constants of carboxylic compounds with both hydroxyl and nitrate radicals. Considering high OH concentration ([OH] = 1 × 10−12 M led to no significant contribution of microbial activity in the destruction of carboxylic acids. On the contrary, for lower OH concentration (at noon, [OH] = 1 × 10−14 M, microorganisms could efficiently compete with photochemistry and in similar contributions than the ones estimated by our experimental approach.

    Combining these two approaches (experimental and theoretical, our results led to the following conclusions: oxalate was only photodegraded; the photodegradation of formate was usually more

  13. Intramolecular coordination bonds O → Te and N → Te in molecules of β-tellurocyclohexenals and their nitrogen analogues

    International Nuclear Information System (INIS)

    The structure of six compounds that are derivatives of β-tellurocyclohexenal with a fixed cis-configuration and double bond containing coordinated groupings, was studied by the method of X-ray diffraction analysis. It was ascertained that all the compounds studied have Z-configuration with double bond giving rise to formation of intramolecular coordination bonds O → Te or N → Te at T-shaped configuration of tellurium atom bonds. Influence of electronegativity of substituent at tellurium atom and, accordingly, strength of intramolecular coordination bonds O → Te and N → Te was considered

  14. Computational evidence for intramolecular hydrogen bonding and nonbonding X···O interactions in 2'-haloflavonols

    Directory of Open Access Journals (Sweden)

    Tânia A. O. Fonseca

    2012-01-01

    Full Text Available The conformational isomerism and stereoelectronic interactions present in 2'-haloflavonols were computationally analyzed. On the basis of the quantum theory of atoms in molecules (QTAIM and natural bond orbital (NBO analysis, the conformer stabilities of 2'-haloflavonols were found to be dictated mainly by a C=O···H–O intramolecular hydrogen bond, but an unusual C–F···H–O hydrogen-bond and intramolecular C–X···O nonbonding interactions are also present in such compounds.

  15. Intramolecular Conjugate Ene Reaction of γ-Difluoromethyl- and γ-Trifluoromethyl-α,β-Unsaturated γ-Butyrolactones.

    Science.gov (United States)

    Srimontree, Watchara; Masusai, Chonticha; Soorukram, Darunee; Kuhakarn, Chutima; Reutrakul, Vichai; Pohmakotr, Manat

    2015-11-01

    A general synthetic strategy to cis-fused bicyclic γ-butyrolactones via the retro-Diels-Alder reaction/intramolecular conjugate ene cascade (RDA/ICE) reaction under the flash-vacuum pyrolysis of maleic anhydride adducts is developed. The reaction gave high yields of products with high stereoselectivity. The existence of the difluoromethyl or trifluoromethyl group at the γ-position of the in situ-generated homoalkenyl- or homoalkynyl-α,β-unsaturated γ-butyrolactones was found to accelerate the rate of the intramolecular conjugate ene reaction leading to γ-difluoromethylated and γ-trifluoromethylated cis-fused bicyclic γ-butyrolactones. PMID:26417837

  16. Electrochemical properties of polyethylene membrane modified with carboxylic acid group

    International Nuclear Information System (INIS)

    Two cation-exchange membranes modified with the carboxylic acid group for battery separator were prepared by radiation-induced grafting of acrylic acid (AA) and methacrylic acid (MA) onto a polyethylene (PE) film. The surface area, thickness, volume, water uptake, ion-exchange capacity, specific electric resistance, and electrolyte flux were evaluated after PE film was grafted with AA and MA. It was found that KOH diffusion flux of AA-grafted PE membrane and MA-grafted PE membrane increased with an increase in the degree of grafting. AA-grafted PE membrane had a higher diffusion flux than MA-grafted PE membrane. Electrical resistance of two cation-exchange membranes modified with AA and MA decreased rapidly with an increase in the degree of grafting. (author)

  17. γ irradiation of carboxylated styrene-butadiene rubber latex

    International Nuclear Information System (INIS)

    The crosslinking behavior of carboxylated styrene-butadiene rubber latex (CSBRL) by using gamma radiation with 2-ethyl hexyl acrylate (2-EHA) as crosslinking sensitizer has been studied in detail. In addition, the variation of the particle size and distribution of latex, chemical structure and thermal property of CSBRL with absorbed dose have been discussed. Also the radiation vulcanization mechanism of CSBRL has been suggested. The experiments showed that, the dose rate has small effect on the cross-link behavior of CSBRL, and the swelling ratio decreased rapidly with the increase of absorbed dose. Increasing the dose, the average molecular weight per crosslinked units (Mc) decreased and crosslinking density increased. When the dose is below 25 kGy, no significant changes in the particle size and distribution of latex were observed. The micro-FTIR analysis and DSC curves confirmed the existence of grafting reaction accompanying the crosslinking reaction during the gamma irradiation with 2-EHA as sensitizer

  18. Improved preparation of halopropyl bridged carboxylic ortho esters

    Directory of Open Access Journals (Sweden)

    Richard J. Petroski

    2008-10-01

    Full Text Available Bridged ortho esters of 3-halopropyl carboxylic acids were prepared by esterification of 3-methyl-3-hydroxymethyloxetane with 3-bromopropionyl chloride and pyridine in dry THF, followed by rearrangement with boron trifluoroetherate, to afford 1-(2-bromoethyl-4-methyl-2,6,7-trioxabicyclo[2,2,2]-octane. The 1-(2-iodoethyl-4-methyl-2,6,7-trioxabicyclo[2,2,2]-octane analogue could not be prepared directly by halogen exchange of 1-(2-bromoethyl-4-methyl-2,6,7-trioxabicyclo[2,2,2]-octane but could be prepared by halogen exchange of the (3-methyloxetan-3-ylmethyl 3-bromopropanoate with a mixture of sodium iodide and anhydrous sodium sulfate in acetone, followed by rearrangement with boron trifluoroetherate.

  19. Spectrofluorimetric determination of gallium with calon-carboxylic acid

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A simple and sensitive spectrofluorimetric procedure for the analysis of microquantities of gallium in alloy wasdescribed. The method is based on the formation of Ga(Ⅲ)-CCA (calon-carboxylic acid) complex. The emission of thefluorescent complex was measured at λ = 620 nm with excitation at λ = 584 nm. A good linearity was found in the galliumrange of 0.7-280 ng/mL. The precision of the method is good and the relative standard deviation is 1.9% for a gallium stan-dard solution of 70 ng/mL. The procedure was proved to be suitable in terms of accuracy and selectivity for the mi-croamount of gallium in alloy.

  20. Preparations and applications in UV curing coatings of epoxy acrylates containing carboxyl

    International Nuclear Information System (INIS)

    This paper introduces preparations of epoxy acrylates containing carboxyl through the reactions of epoxy acrylates with butanedioic anhydride, pentanedioic anhydride, cis-butenedioic anhydride, phthalic anhydride, tetrabromophthalic anhydride and -tetrahydrophthalic anhydride. These epoxy acrylates containing carboxyl have been applied to UV-curing coatings and their effects on properties of UV-curing coatings have been studied

  1. Carboxyl-modified single-walled carbon nanotubes negatively affect bacterial growth and denitrification activity

    Science.gov (United States)

    Zheng, Xiong; Su, Yinglong; Chen, Yinguang; Wan, Rui; Li, Mu; Wei, Yuanyuan; Huang, Haining

    2014-07-01

    Single-walled carbon nanotubes (SWNTs) have been used in a wide range of fields, and the surface modification via carboxyl functionalization can further improve their physicochemical properties. However, whether carboxyl-modified SWNT poses potential risks to microbial denitrification after its release into the environment remains unknown. Here we present the possible effects of carboxyl-modified SWNT on the growth and denitrification activity of Paracoccus denitrificans (a model denitrifying bacterium). It was found that carboxyl-modified SWNT were present both outside and inside the bacteria, and thus induced bacterial growth inhibition at the concentrations of 10 and 50 mg/L. After 24 h of exposure, the final nitrate concentration in the presence of 50 mg/L carboxyl-modified SWNT was 21-fold higher than that in its absence, indicating that nitrate reduction was substantially suppressed by carboxyl-modified SWNT. The transcriptional profiling revealed that carboxyl-modified SWNT led to the transcriptional activation of the genes encoding ribonucleotide reductase in response to DNA damage and also decreased the gene expressions involved in glucose metabolism and energy production, which was an important reason for bacterial growth inhibition. Moreover, carboxyl-modified SWNT caused the significant down-regulation and lower activity of nitrate reductase, which was consistent with the decreased efficiency of nitrate reduction.

  2. Exploring the reductive capacity of Pyrococcus furiosus. The reduction of carboxylic acids and pyridine nucleotides

    NARCIS (Netherlands)

    Ban, van den E.C.D.

    2001-01-01

    This Ph.D. project started in 1997 and its main goal was to obtain insight in the reductive capacity of the hyperthermophilic archaeon Pyrococcus furiosus . The research was focused on the biocatalytic reduction of carboxylic acids.Reductions of carboxylic acids are interes

  3. 40 CFR 721.2088 - Carboxylic acids, (C6-C9) branched and linear.

    Science.gov (United States)

    2010-07-01

    ... linear. 721.2088 Section 721.2088 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... Specific Chemical Substances § 721.2088 Carboxylic acids, (C6-C9) branched and linear. (a) Chemical... as carboxylic acids, (C6-C9) branched and linear (PMNs P-93-313, 314, 315, and 316) are subject...

  4. 14CO2 ratios method for detecting pyruvate carboxylation

    International Nuclear Information System (INIS)

    The pattern of oxidative metabolism of pyruvate may be assessed by comparing the steady-state 14CO2 production from four isotopes in identical samples. The assay requires measuring the ratios of steady-state 14CO2 production from two isotope pairs, [2-14C]pyruvate:[3-14C]pyruvate and [1-14C]acetate:[2-14C]acetate. These ratios are defined as the ''pyruvate 14CO2 ratio'' and the ''acetate 14CO2 ratio,'' respectively. If pyruvate is metabolized exclusively via pyruvate dehydrogenase (PDH), the two ratios will be identical. Alternatively, if any pyruvate enters the tricarboxylic acid (TCA) cycle via pyruvate carboxylation (PC), the pyruvate 14CO2 ratio will be less than the acetate 14CO2 ratio. If pyruvate enters the TCA cycle only through PC (with oxaloacetate and fumarate in equilibrium) the pyruvate 14CO2 ratio will approach a value of 1.0. An equation is presented for the quantitative evaluation of pyruvate oxidation by these two pathways. We have used this method to detect relative changes in the pattern of pyruvate metabolism in rat liver mitochondria produced by exposure to 1 mM octanoyl carnitine, a compound known to alter the PC:PDH activity ratio. The major advantages of the method are (i) that it provides a sensitive method for detecting pyruvate carboxylation at physiological pyruvate concentrations and (ii) that it provides a method for distinguishing between effects on pyruvate transport and effects on pyruvate oxidation

  5. Solvent extraction studies on uranium (VI) with high molecular weight carboxylic acids from acetate medium

    International Nuclear Information System (INIS)

    Carboxylic acids are cation exchanger type of extractant which extract metal ions from weak acidic solutions by ion exchange mechanism. They are present as dimer (H2A2) in the non polar organic diluents. High molecular weight carboxylic acids such as versatic 10 acid and naphthenic acid are used for the separation of high purity of yttrium from heavy fraction of rare earths. Extraction behavior of rare earths with different types of carboxylic acids is also reported. Literature survey revealed that the extraction behavior of uranium from aqueous solutions with carboxylic acids is scanty. An attempt has been made in the present work to examine the extraction behavior of U(VI) with three different types of high molecular weight carboxylic acids namely cekanoic acid, neoheptanoic acid and versatic 10 acid dissolved in xylene. Extraction of metal ions is very much dependent on pH of the solution

  6. Efficient Fixation of Carbon Dioxide by Electrolysis - Facile Synthesis of Useful Carboxylic Acids -

    Institute of Scientific and Technical Information of China (English)

    Masao Tokuda

    2006-01-01

    Electrochemical fixation of atmospheric pressure of carbon dioxide to organic compounds is a useful and attractive method for synthesizing of various carboxylic acids. Electrochemical fixation of carbon dioxide, electrochemical carboxylation, organic halides, organic triflates, alkenes, aromatic compounds, and carbonyl compounds can readily occur in the presence of an atmospheric pressure of carbon dioxide to form the corresponding carboxylic acids with high yields, when a sacrificial anode such as magnesium or aluminum is used in the electrolysis. The electrochemical carboxylation of vinyl bromides was successfully applied for the synthesis of the precursor of nonsteroidal anti-inflammatory agents such as ibuprofen and naproxen. On the other hand, supercritical carbon dioxide (scCO2) has significant potential as an environmentally benign solvent in organic synthesis and it could be used both as a solvent and as a reagent in these electrochemical carboxylations by using a small amount of cosolvent.

  7. Promoting Models

    Science.gov (United States)

    Li, Qin; Zhao, Yongxin; Wu, Xiaofeng; Liu, Si

    There can be multitudinous models specifying aspects of the same system. Each model has a bias towards one aspect. These models often override in specific aspects though they have different expressions. A specification written in one model can be refined by introducing additional information from other models. The paper proposes a concept of promoting models which is a methodology to obtain refinements with support from cooperating models. It refines a primary model by integrating the information from a secondary model. The promotion principle is not merely an academic point, but also a reliable and robust engineering technique which can be used to develop software and hardware systems. It can also check the consistency between two specifications from different models. A case of modeling a simple online shopping system with the cooperation of the guarded design model and CSP model illustrates the practicability of the promotion principle.

  8. The carboxyl-terminal domain of large T antigen rescues SV40 host range activity in trans independent of acetylation.

    Science.gov (United States)

    Poulin, Danielle L; DeCaprio, James A

    2006-05-25

    The host range activity of SV40 has been described as the inability of mutant viruses with deletions in the C terminal region of large T Ag to replicate in certain types of African green monkey kidney cells. We constructed new mutant viruses expressing truncated T Ag proteins and found that these mutant viruses exhibited the host range phenotype. The host range phenotype was independent of acetylation of T Ag at lysine 697. Co-expression of the C terminal domain of T Ag (aa 627-708) in trans increased both T Ag and VP1 mRNA as well as protein levels for host range mutant viruses in the restrictive cell type. In addition, the T Ag 627-708 fragment promoted the productive lytic infection of host range mutant viruses in the nonpermissive cell type. The carboxyl-terminal region of T Ag contains a biological function essential for the SV40 viral life cycle. PMID:16510165

  9. Brønsted acid cocatalysis in photocatalytic intramolecular coupling of tertiary amines: efficient synthesis of 2-arylindols.

    Science.gov (United States)

    Yuan, Xiaoqian; Wu, Xinxin; Dong, Shupeng; Wu, Guibing; Ye, Jinxing

    2016-08-21

    We report herein a highly efficient intramolecular coupling reaction of tertiary amines and ketones (α,β-unsaturated ketones) by using a Brønsted acid as a cocatalyst, affording 2-arylindols in good to excellent yields (up to 92%) under visible light irradiation at room temperature. PMID:27431277

  10. A Convergent Enantioselective Total Synthesis of (-)-Perhydrohistrionicotoxin with an Intramolecular Imino Ene-type Reaction as a Key Step

    DEFF Research Database (Denmark)

    Tanner, David Ackland; Hagberg, Lars

    1998-01-01

    A convergent enantioselective total synthesis of the neurotoxic spirocyclic alkaloid (-)-perhydrohistrionicotoxin (2) is described. A Lewis acid-mediated intramolecular imine ene-type reaction was used for the key spirocyclisation step (14 to 3, with 3 being obtained as a single diastereoisomer...

  11. On Hydrogen Bonding in the Intramolecularly Chelated Taitomers of Enolic Malondialdehyde and its Mono- and Dithio-Analogues

    DEFF Research Database (Denmark)

    Carlsen, Lars; Duus, Fritz

    The intramolecular hydrogen bondings in enolic malondialdehyde and it mono- and dithio-analogues have been evaluated by a semiempricial SCF–MO–CNDO method. The calculations predict that the hydrogen bonds play an important part in the stabilities of malondialdehyde and monothiomalondialdehyde, wh......, whereas dithiomalondialdehyde hardly exists as a hydrogen-chelated tautomeric form....

  12. Synthesis of 2-Benzylthio-5-phenyl-3,4-disubstituted Thiophenes by Intramolecular Condensation of a-Oxo Ketene Dibenzylthioacetals

    Institute of Scientific and Technical Information of China (English)

    WANG,Mang(王芒); AI,Lin(艾林); ZHANG,Ji-Yu(张继余); LIU,Qun(刘群); GAO,Lian-Xun(高连勋)

    2002-01-01

    A facile route to 2-benzylthio-5-phenyl-3,4-disubstituted thiophenes was described. Catalyzed by sodium hydroxide, the title compounds were synthesized in moderate to good yields simply from the intramolecular aidol type condensation of a-oxo ketene dibenzylthioacetals. The chemical selectivity for this annulation reaction was studied and discussed.

  13. Construction of the Core of Pseudolaric Acid A and Mechanistic Studies on Intramolecular [4+3] Cycloaddition

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This paper describes the construction of hemiacetal 2, the core of pseudolaric acid A via oxidative cleavage of acetonide 6 or 7 and enolization-hemiacetalization of aldehyde 8. A plausible general mechanism for the intramolecular [4+3] cycloaddition of sulfoxide 4 to adduct 3 is suggested.

  14. On the Importance of Electron Correlation Effects for the Intramolecular Stacking Geometry of a Bis-Thiophene Derivative

    Czech Academy of Sciences Publication Activity Database

    Pluháčková, Kristýna; Grimme, S.; Hobza, Pavel

    2008-01-01

    Roč. 112, č. 48 (2008), s. 12469-12474. ISSN 1089-5639 R&D Projects: GA MŠk LC512; GA AV ČR IAA400550510 Institutional research plan: CEZ:AV0Z40550506 Keywords : electron correlation effects * intramolecular stacking * thiophene derivative Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.871, year: 2008

  15. Palladium-catalyzed regioselective intramolecular coupling of o-carborane with aromatics via direct cage B-H activation.

    Science.gov (United States)

    Quan, Yangjian; Xie, Zuowei

    2015-03-18

    Palladium-catalyzed intramolecular coupling of o-carborane with aromatics via direct cage B-H bond activation has been achieved, leading to the synthesis of a series of o-carborane-functionalized aromatics in high yields with excellent regioselectivity. In addition, the site selectivity can also be tuned by the substituents on cage carbon atom. PMID:25747772

  16. The effect of intramolecular quantum modes on free energy relationships for electron transfer reactions

    DEFF Research Database (Denmark)

    Ulstrup, Jens; Jortner, Joshua

    1975-01-01

    -frequency intramolecular degrees of feedom on the free energy relationship for series of closely related reactions was investigated for various model systems involving displacement of potential energy surfaces, frequency shift, and anharmonicity effects. The free energy plots are generally found to pass through a maximum...... free energy relationships, predicted for low temperatures and high frequencies, and which are analogous to the vibrational structure in optical transitions. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.......A general quantum mechanical description of exothermic electron transfer reactions is formulated by treating such reactions as the nonradiative decay of a ''supermolecule'' consisting of the electron donor, the electron acceptor, and the polar solvent. In particular, the role of the high...

  17. Electronic structure of planar-quasicycled organic molecules with intramolecular hydrogen bond

    Directory of Open Access Journals (Sweden)

    ALEXEI N. PANKRATOV

    2007-03-01

    Full Text Available By means of the HF/6-311G(d,p method, the electronic structure of the series of organic molecules, among which are malonaldehyde, acetylacetone, thiomalonaldehyde,’the derivatives of aniline 2-XC6H4NH2, phenol 2-XC6H4OH, benzenethiol 2-XC6H4SH (X = CHO, COOH, COO-, NO, NO2, OH, OCH3, SH, SCH3, F, Cl, Br, 8-hydroxyquinoline, 8-mercaptoquinoline, tropolone, has been studied. The intramolecular hydrogen bond (IHB has been established to lead to a local electron redistribution in quasicycle, and primarily to the electron density transfer between the direct IHB participants – from the hydrogen atom toward the proton-aceptor atom. On forming the IHB of the S–H···O type, the electron density in general decreases on the sulphohydryl hydrogen atom and increases on the sulphur atom.

  18. Raman spectroscopy in hot compressed hydrogen and nitrogen - implications for the intramolecular potential

    Energy Technology Data Exchange (ETDEWEB)

    Goncharov, A F; Crowhurst, J C

    2005-09-19

    Raman measurements of molecular hydrogen (H{sub 2} and D{sub 2}) and nitrogen (N{sub 2}) have been made under simultaneous conditions of high temperature and high static pressure. Measurements have been made on H{sub 2} and D{sub 2} to 50 GPa and 1600 K, and on N{sub 2} to 50 GPa and 2000 K. In all three materials the familiar molecular stretching mode (vibron) is accompanied in the high-temperature Raman spectra by one or more lower-frequency peaks due to transitions from excited vibrational states. We find that the frequency differences between these bands decreases with pressure, implying that the anharmonicity of the corresponding part of the intramolecular potential also decreases. This is accompanied by an increase in the measured linewidths of the bands that is consistent with a decrease of the depth of the potential and an approaching molecular dissociation.

  19. Intramolecular Force Contrast and Dynamic Current-Distance Measurements at Room Temperature

    Science.gov (United States)

    Huber, F.; Matencio, S.; Weymouth, A. J.; Ocal, C.; Barrena, E.; Giessibl, F. J.

    2015-08-01

    Scanning probe microscopy can be used to probe the internal atomic structure of flat organic molecules. This technique requires an unreactive tip and has, until now, been demonstrated only at liquid helium and liquid nitrogen temperatures. We demonstrate intramolecular and intermolecular force contrast at room temperature on PTCDA molecules adsorbed on a Ag /Si (111 )-(√{3 }×√{3 }) surface. The oscillating force sensor allows us to dynamically measure the vertical decay constant of the tunneling current. The precision of this method is increased by quantifying the transimpedance of the current to voltage converter and accounting for the tip oscillation. This measurement yields a clear contrast between neighboring molecules, which we attribute to the different charge states.

  20. Total Synthesis of Flocoumafen via Knoevenagel Condensation and Intramolecular Ring Cyclization: General Access to Natural Products

    Directory of Open Access Journals (Sweden)

    Mankil Jung

    2012-02-01

    Full Text Available The total synthesis and structure determination of cis- and trans-flocoumafen was described. The key synthetic steps involve Knoevenagel condensation with p-methoxybenzaldehyde, in situ decarboxylation and intramolecular ring cyclization to construct the tetralone skeleton. Stereospecific reduction of the O-alkylated ketone 13 afforded good yield of precusor alcohol 5. Final coupling of alcohol 5 with 4-hydroxy-coumarin yielded flocoumafen (1. Separation and structure determination of cis- and trans-flocoumafen through 2D NMR analyses-assisted computer simulation techniques for the evaluation of anticoagulant activities are reported for the first time. This method is useful for generating the core tetralone skeleton of 4-hydroxycoumarin derivatives and provides a generalized access to various warfarin type anticoagulants.

  1. A DFT Study on Intramolecular Hydrogen Bond in Substituted Catechols and Their Radicals

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Density functional theory (DFT) at B3LYP/6-31G(d,p) level was employed to calculate intramolecular hydrogen bond enthalpies (HIHB), O-H charge differences, O-H bond lengths and bond orders for various substituted catechols and their radicals generated after H-abstraction. It was found that although the charge difference between hydrogen-bonded H and O played a role in determining HIHB, HIHB was mainly governed by the hydrogen bond length. As the oxygen-centered radical has great tendency to form a chemical bond with the H atom, hydrogen bond lengths in catecholic radicals are systematically shorter than those in catechols. Hence, the HIHB for the former are higher than those for the latter.

  2. Short Intramolecular N–H⋯C(carbonyl) Interactions in Mixed-Ligand Molybdenum Hexacarbonyl Derivatives

    OpenAIRE

    Budge, Matthew G.; Kathleen J. Muir; Geoffrey P. McQuillan; Harrison, William T. A.

    2011-01-01

    The syntheses and single-crystal structures of Mo(CO)3(phen)(dipy) (1), Mo(CO)3(biquin)(dipy) (2) and Mo(CO)3(dpme)(dipy) (3), (phen = 1,10-phenanthroline, C12H8N2; dipy = 2,2'-dipyridylamine, C10H9N3; biquin = 2,2'-biquinoline, C18H12N2; dpme = 2,2'-dipyridylmethane, C11H10N2) are described. In each case, distorted fac-MoC3N3 octahedral coordination geometries arise for the metal atoms. Short intramolecular N–H…C interactions from the dipy N–H group to a carbonyl carbon atom o...

  3. Intramolecular charge ordering in the multi molecular orbital system (TTM-TTP)I3

    Science.gov (United States)

    Bonnet, Marie-Laure; Robert, Vincent; Tsuchiizu, Masahisa; Omori, Yukiko; Suzumura, Yoshikazu

    2010-06-01

    Starting from the structure of the (TTM-TTP)I3 molecular-based material, we examine the characteristics of frontier molecular orbitals using ab initio (CASSCF/CASPT2) configurations interaction calculations. It is shown that the singly occupied and second-highest-occupied molecular orbitals are close to each other, i.e., this compound should be regarded as a two-orbital system. By dividing virtually the [TTM-TTP] molecule into three fragments, an effective model is constructed to rationalize the origin of this picture. In order to investigate the low-temperature, symmetry breaking experimentally observed in the crystal, the electronic distribution in a pair of [TTM-TTP] molecules is analyzed from CASPT2 calculations. Our inspection supports and explains the speculated intramolecular charge ordering which is likely to give rise to low-energy magnetic properties.

  4. Mechanical property of carbon nanotubes with intramolecular junctions: Molecular dynamics simulations

    International Nuclear Information System (INIS)

    Intramolecular junctions (IMJs) of carbon nanotubes hold a promise of potential applications in nano-electromechanical systems. However, their structure-property relation is still unclear. Using the revised second-generation Tersoff-Brenner potential, molecular dynamics simulations were performed to study the mechanical properties of single-walled to four-walled carbon nanotubes with IMJs under uniaxial tension. The dependence of deformation and failure behaviors of IMJs on the geometric parameters was examined. It was found that the rupture strength of a junction is close to that of its thinner carbon nanotube segment, and the rupture strain and Young's modulus show a significant dependence on its geometry. The simulations also revealed that the damage and rupture of multi-walled carbon nanotube junctions take place first in the innermost layer and then propagate consecutively to the outer layers. This study is helpful for optimal design and safety evaluation of IMJ-based nanoelectronics

  5. Origins of stereoselectivity in intramolecular aldol reactions catalyzed by cinchona amines.

    Science.gov (United States)

    Lam, Yu-Hong; Houk, K N

    2015-02-11

    The intramolecular aldol condensation of 4-substituted heptane-2,6-diones leads to chiral cyclohexenones. The origins of the enantioselectivities of this reaction, disclosed by List et al. using a cinchona alkaloid-derived primary amine (cinchona amine) organocatalyst, have been determined with dispersion-corrected density functional theory (DFT). The stereocontrol hinges on the chair preference of the substrate-enamine intermediate and the conformational preferences of a hydrogen-bonded nine-membered aldol transition state containing eight heavy atoms. The conformations of the hydrogen-bonded ring in the various stereoisomeric transition structures have been analyzed in detail and shown to closely resemble the conformers of cyclooctane. A model of stereoselectivity is proposed for the cinchona amine catalysis of this reaction. The inclusion of Grimme's dispersion corrections in the DFT calculations (B3LYP-D3(BJ)) substantially improves the agreement of the computed energetics and experiment, attesting to the importance of dispersion effects in stereoselectivity. PMID:25629689

  6. A two-state model of twisted intramolecular chargetransfer in monomethine dyes

    CERN Document Server

    Olsen, Seth

    2012-01-01

    We describe a two-state model Hamiltonian that can describes the development of twisted intramolecular charge-transfer behavior in monomethine dyes, both near and far from the cyanine limit. Monomethine dyes are useful as biological probes due to their binding-dependent fluorescence turn-on behavior. The model is a generalized Mulliken-Hush diabatic Hamiltonian wherein the diabatic energies and couplings are coupled to twisting about distinct bonds of the monomethine bridge. We parameterize the Hamiltonian against multireference perturbation theory calculations of the ground and excited states of four distinct oxonol protonation states of a green fluorescent protein chromophore model. The four chromophores illustrate different regimes of detuning from the cyanine limit. The model describes correctly the distinct relationships between twisting and charge-transfer behavior in each case. We expose a deep connection between the existence of twist-dependent polarization and the existence of twisted conical interse...

  7. Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers.

    Science.gov (United States)

    Zirzlmeier, Johannes; Casillas, Rubén; Reddy, S Rajagopala; Coto, Pedro B; Lehnherr, Dan; Chernick, Erin T; Papadopoulos, Ilias; Thoss, Michael; Tykwinski, Rik R; Guldi, Dirk M

    2016-05-21

    We show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 ± 10% and (0.7 ± 0.1) × 10(12) s(-1), respectively, in room temperature solutions. PMID:27122097

  8. Electron capture dissociation proceeds with a low degree of intramolecular migration of peptide amide hydrogens

    DEFF Research Database (Denmark)

    Rand, Kasper D; Adams, Christopher M; Zubarev, Roman A;

    2008-01-01

    scrambling) that occurs during vibrational excitation of gas-phase ions. Unlike traditional collisional ion activation, electron capture dissociation (ECD) is not associated with substantial vibrational excitation. We investigated the extent of intramolecular backbone amide hydrogen (1H/2H) migration upon...... electrospray ion source by, e.g., high declustering potentials or during precursor ion selection (via sideband excitation) in the external linear quadrupole ion trap undergo nearly complete hydrogen (1H/2H) scrambling. Similarly, collision-induced dissociation (CID) in the external linear quadrupole ion trap...... closely mimic the known solution deuteration pattern of the selectively labeled peptides. This excellent correlation between the results obtained from gas phase and solution suggests that ECD holds great promise as a general method to obtain single residue resolution in proteins from solution 1H/2H...

  9. Effects of acid concentration on intramolecular charge transfer reaction of 4-(azetidinyl) benzonitrile in solution

    Indian Academy of Sciences (India)

    Biswajit Guchhait; Tuhin Pradhan; Ranjit Biswas

    2014-01-01

    Effects of acid concentration on excited state intramolecular charge transfer reaction of 4-(azetidinyl) benzonitrile (P4C) in aprotic (acetonitrile and ethyl acetate) and protic (ethanol) solvents have been studied by means of steady state absorption and fluorescence, and time resolved fluorescence spectroscopic techniques. While absorption and fluorescence bands of P4C have been found to be shifted towards higher energy with increasing acid concentration in acetonitrile and ethyl acetate, no significant dependence has been observed in ethanolic solutions. Reaction rate becomes increasingly slower with acid concentration in acetonitrile and ethyl acetate. In contrast, acid in ethanolic solutions does not produce such an effect on reaction rate. Time-dependent density functional theory calculations have been performed to understand the observed spectroscopic results.

  10. Theoretical investigation of intramolecular vibrational energy redistribution in HFCO and DFCO induced by an external field.

    Science.gov (United States)

    Pasin, Gauthier; Iung, Christophe; Gatti, Fabien; Richter, Falk; Léonard, Céline; Meyer, Hans-Dieter

    2008-10-14

    The present paper is devoted to a full quantum mechanical study of the intramolecular vibrational energy redistribution in HFCO and DFCO. In contrast to our previous studies [Pasin et al., J. Chem. Phys. 124, 194304 (2006) and 126, 024302 (2007)], the dynamics is now performed in the presence of an external time-dependent field. This more closely reflects the experimental conditions. A six-dimensional dipole surface is computed. The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. Special emphasis is placed on the excitation of the out-of-plane bending vibration and on the dissociation of the molecule. In the case of DFCO, we predict that it is possible to excite the out-of-plane bending mode of vibration and to drive the dissociation to DF+CO with only one laser pulse with a fixed frequency and without excitation of an electronic state. PMID:19045144

  11. Uncovering Intramolecular π-Type Hydrogen Bonds in Solution by NMR Spectroscopy and DFT Calculations.

    Science.gov (United States)

    Mastrorilli, Piero; Gallo, Vito; Todisco, Stefano; Latronico, Mario; Saielli, Giacomo

    2016-06-01

    Reaction between the phosphinito bridged diplatinum species [(PHCy2 )Pt(μ-PCy2 ){κ(2) P,O-μ-P(O)Cy2 }Pt(PHCy2 )](Pt-Pt) (1), and (trimethylsilyl)acetylene at 273 K affords the σ-acetylide complex [(PHCy2 )(η(1) -Me3 SiC≡C)Pt(μ-PCy2 )Pt(PHCy2 ){κP-P(OH)Cy2 }](Pt-Pt) (2) featuring an intramolecular π-type hydrogen bond. Scalar and dipolar couplings involving the POH proton were detected by 2D NMR experiments. Relativistic DFT calculations of the geometry, relative energy, and NMR properties of model systems of 2 confirmed the structural assignment and allowed the energy of the π-type hydrogen bond to be estimated (ca. 22 kJ mol(-1) ). PMID:27097847

  12. Unusual NHC-Iridium(I) Complexes and Their Use in the Intramolecular Hydroamination of Unactivated Aminoalkenes.

    Science.gov (United States)

    Sipos, Gellért; Ou, Arnold; Skelton, Brian W; Falivene, Laura; Cavallo, Luigi; Dorta, Reto

    2016-05-10

    N-heterocyclic carbene (NHC) ligands with naphthyl side chains were employed for the synthesis of unsaturated, yet isolable [(NHC)Ir(cod)](+) (cod=1,5-cyclooctadiene) complexes. These compounds are stabilised by an interaction of the aromatic wingtip that leads to a sideways tilt of the NHC-Ir bond. Detailed studies show how the tilting of such N-heterocyclic carbenes affects the electronic shielding properties of the carbene carbon atom and how this is reflected by significant upfield shifts in the (13) C NMR signals. When employed in the intramolecular hydroamination, these [(NHC)Ir(cod)](+) species show very high catalytic activity under mild reaction conditions. An enantiopure version of the catalyst system produces pyrrolidines with excellent enantioselectivities. PMID:27059164

  13. Molecular structure and intramolecular hydrogen bonding in 2-hydroxybenzophenones: A theoretical study

    Indian Academy of Sciences (India)

    Mansoureh Zahedi-Tabrizi; Sayyed Faramarz Tayyari; Farideh Badalkhani-Khamseh; Reihaneh Ghomi; Fatemeh Afshar-Qahremani

    2014-07-01

    The intramolecular hydrogen bonding (IHB) in a series of 3-, 4- and 5-substituted 2-hydroxybenzophenone (HBP) is studied using density functional theory calculations. All calculations are performed at the B3LYP level, using 6-311++G∗∗ basis set. To understand the substitution effects on the nature of IHB and the electronic structure of the chelated ring system, the vibrational frequencies, 1H chemical shift, topological parameters, natural bond orders and natural charges over atoms involved in the chelated ring of HBP and its derivatives were calculated. TheWiberg bond indices and the natural charges over atoms involved in the chelated ring have been computed using the natural bond orbital (NBO) analysis. The computations were further complemented with an atoms-in-molecules (AIM) topological analysis to characterize the nature of the IHB in the considered molecules. Several correlations between geometrical parameters, 1H NMR chemical shift and topological parameters with the IHB strength are obtained.

  14. Performance of density functional theory methods to describe intramolecular hydrogen shifts

    Indian Academy of Sciences (India)

    Nelly González-Rivas; Andrés Cedillo

    2005-09-01

    The performance of three exchange and correlation density functionals, LDA, BLYP and B3LYP, with four basis sets is tested in three intramolecular hydrogen shift reactions. The best reaction and activation energies come from the hybrid functional B3LYP with triple- basis sets, when they are compared with high-level post-Hartree-Fock results from the literature. For a fixed molecular geometry, the electrophilic Fukui function is computed from a finite difference approximation. Fukui function shows a small dependence with both the exchange and correlation functional and the basis set. Evolution of the Fukui function along the reaction path describes important changes in the basic sites of the corresponding molecules. These results are in agreement with the chemical behavior of those species.

  15. Solution-state structure of an intramolecular G-quadruplex with propeller, diagonal and edgewise loops

    Science.gov (United States)

    Marušič, Maja; Šket, Primož; Bauer, Lubos; Viglasky, Viktor; Plavec, Janez

    2012-01-01

    We herein report on the formation and high-resolution NMR solution-state structure determination of a G-quadruplex adopted by d[G3ATG3ACACAG4ACG3] comprised of four G-tracts with the third one consisting of four guanines that are intervened with non-G streches of different lengths. A single intramolecular antiparallel (3+1) G-quadruplex exhibits three stacked G-quartets connected with propeller, diagonal and edgewise loops of different lengths. The propeller and edgewise loops are well structured, whereas the longer diagonal loop is more flexible. To the best of our knowledge, this is the first high-resolution G-quadruplex structure where all of the three main loop types are present. PMID:22532609

  16. [Role of intramolecular bonds in stability of certain enzymes of the cellulolytic complex].

    Science.gov (United States)

    Sirdova, T M; Tsiperovikh, O S

    1976-01-01

    Stability of C1- and C2-cellulases, CX-exo- and CX-endoglucanases and beta-glucosidase of Aspergillus awamori was studied as affected by monoatomic aliphatic alcohols --methanol, ethanol, propanol and isopropanol; bi- and triatomic alcohols - ethylene glycol and glycerol, urea as well as detergents of dodecyl sulphate and sodium nonilate. The mentioned enzymes are established to manifest the highest activity in 40-60% glycerol. It is also shown that their stability is changed differently under the effect of other alcohols, urea and detergents. The latter testifies to the fact that the studied enzymes are nonidentical, in particular, they differ between themselves by a ratio of intramolecular forces which stabilize their macrostructure. PMID:1258159

  17. DFT study of the intramolecular hydrogen bonds in the amino and nitro-derivatives of malonaldehyde

    International Nuclear Information System (INIS)

    The keto and enol conformations of 2-NH2-, 3-NH2-, 4-NH2-, 3-NO2-malonaldehyde, malonamide and nitromalonamide were studied at ab initio B3LYP/6-31G** level in order to determine the conformational equilibrium and the substituent effects on the strength of the various intramolecular hydrogen bonds, paying particular attention to the O-H?O bridge. The π-electron delocalization and the related resonance parameter were calculated following the procedure suggested by Grabowski, and compared with the Gilli λ-parameter. The obtained results show that the hydrogen bond strength (EHB) is mainly governed by the resonance variations inside the chelate ring induced by the substituent groups. In the nitromalonamide, where the conjugated system is enlarged by the presence of the nitro group and two additional (H)N-H?O bridges, the resonance contribution reaches 63%, but it is strongly dependent on the molecular geometry of the open conformation

  18. Monodisperse micrometer-size carboxyl-functionalized polystyrene particles obtained by radiation-induced polymerization and the research on its application

    International Nuclear Information System (INIS)

    Monodisperse carboxyl-functionalized polystyrene particles size with range of 0.6∼2.1μm were synthesized by two-stage radiation-induced dispersion polymerization of styrene in ethanol/water media using poly (vinylpyrrolidone)(PVP) as the stabilizer and itaconic acid (IA) as a functional comonomer. The resulting carboxylated polystyrene (PS) particles have a narrower size distribution compared with those obtained by one-stage dispersion polymerization. In the two-stage method, the presence of additional IA in the second reaction stage may help to prevent secondary nucleation and to promote the formation of monodisperse particles. The effects of concentration of IA, PVP and solvent polarity on the particle size and size distribution have been discussed in detail. The carboxyl group density on the surface of the copolymer particles has been determined directly by conductometric titration. In order to examine the functionality of the particles, P(St-co-IA)/Co composite microspheres are prepared by repetitious inter-face reduction reactions. (authors)

  19. Tether-directed synthesis of highly substituted oxasilacycles via an intramolecular allylation employing allylsilanes

    Directory of Open Access Journals (Sweden)

    Cox Liam R

    2007-02-01

    Full Text Available Abstract Background Using a silyl tether to unite an aldehyde electrophile and allylsilane nucleophile into a single molecule allows a subsequent Lewis-acid-mediated allylation to proceed in an intramolecular sense and therefore receive all the benefits associated with such processes. However, with the ability to cleave the tether post allylation, a product that is the result of a net intermolecular reaction can be obtained. In the present study, four diastereoisomeric β-silyloxy-α-methyl aldehydes, which contain an allylsilane tethered through the β-carbinol centre, have been prepared, in order to probe how the relative configuration of the two stereogenic centres affects the efficiency and selectivity of the intramolecular allylation. Results Syn-aldehydes, syn-4a and syn-4b, both react poorly, affording all four possible diastereoisomeric oxasilacycle products. In contrast, the anti aldehydes anti-4a and anti-4b react analogously to substrates that lack substitution at the α-site, affording only two of the four possible allylation products. Conclusion The outcome of the reaction with anti-aldehydes is in accord with reaction proceeding through a chair-like transition state (T.S.. In these systems, the sense of 1,3-stereoinduction can be rationalised by the aldehyde electrophile adopting a pseudoaxial orientation, which will minimise dipole-dipole interactions in the T.S. The 1,4-stereoinduction in these substrates is modest and seems to be modulated by the R substituent in the starting material. In the case of the syn-substrates, cyclisation through a chair T.S. is unlikely as this would require the methyl substituent α to the reacting carbonyl group to adopt an unfavourable pseudoaxial position. It is therefore proposed that these substrates react through poorly-defined T.S.s and consequently exhibit essentially no stereoselectivity.

  20. Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

    Science.gov (United States)

    Zirzlmeier, Johannes; Casillas, Rubén; Reddy, S. Rajagopala; Coto, Pedro B.; Lehnherr, Dan; Chernick, Erin T.; Papadopoulos, Ilias; Thoss, Michael; Tykwinski, Rik R.; Guldi, Dirk M.

    2016-05-01

    We show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 +/- 10% and (0.7 +/- 0.1) × 1012 s-1, respectively, in room temperature solutions.We show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 +/- 10% and (0.7 +/- 0.1) × 1012 s-1, respectively, in room temperature solutions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02493a

  1. Intramolecular Halogen Transfer via Halonium Ion Intermediates in the Gas Phase.

    Science.gov (United States)

    Chai, Yunfeng; Xiong, Xingchuang; Yue, Lei; Jiang, You; Pan, Yuanjiang; Fang, Xiang

    2016-01-01

    The fragmentation of halogen-substituted protonated amines and quaternary ammonium ions (R(1)R(2)R(3)N(+)CH2(CH2)nX, where X = F, Cl, Br, I, n = 1, 2, 3, 4) was studied by electrospray ionization tandem mass spectrometry. A characteristic fragment ion (R(1)R(2)R(3)N(+)X) resulting from halogen transfer was observed in collision-induced dissociation. A new mechanism for the intramolecular halogen transfer was proposed that involves a reactive intermediate, [amine/halonium ion]. A potential energy surface scan using DFT calculation for CH2-N bond cleavage process of protonated 2-bromo-N,N-dimethylethanamine supports the formation of this intermediate. The bromonium ion intermediate-involved halogen transfer mechanism is supported by an examination of the ion/molecule reaction between isolated ethylenebromonium ion and triethylamine, which generates the N-bromo-N,N,N-triethylammonium cation. For other halogens, Cl and I also can be involved in similar intramolecular halogen transfer, but F cannot be involved. With the elongation of the carbon chain between the halogen (bromine as a representative example) and amine, the migration ability of halogen decreases. When the carbon chain contains two or three CH2 units (n = 1, 2), formal bromine cation transfer can take place, and the transfer is easier when n = 1. When the carbon chain contains four or five CH2 units (n = 3, 4), formal bromine cation transfer does not occur, probably because the five- and six-membered cyclic bromonium ions are very stable and do not donate the bromine to the amine. PMID:26383734

  2. 40 CFR 721.4097 - 7-Oxabicyclo[4.1.0]heptane-3-carboxylic acid, methyl ester.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false 7-Oxabicyclo heptane-3-carboxylic acid... Specific Chemical Substances § 721.4097 7-Oxabicyclo heptane-3-carboxylic acid, methyl ester. (a) Chemical...-oxabicyclo heptane-3-carboxylic acid, methyl ester (PMN P-98-101) is subject to reporting under this...

  3. 40 CFR 721.984 - Amino-hydroxy sulfonaphthylazo-disubstituted phenyl azo benzene carboxylate salt (generic).

    Science.gov (United States)

    2010-07-01

    ...-disubstituted phenyl azo benzene carboxylate salt (generic). 721.984 Section 721.984 Protection of Environment...-disubstituted phenyl azo benzene carboxylate salt (generic). (a) Chemical substance and significant new uses...-disubstituted phenyl azo benzene carboxylate salt (PMN P-00-0351) is subject to reporting under this section...

  4. Exploration of zeroth-order wavefunctions and energies as a first step toward intramolecular symmetry-adapted perturbation theory

    International Nuclear Information System (INIS)

    Non-covalent interactions occur between and within all molecules and have a profound impact on structural and electronic phenomena in chemistry, biology, and material science. Understanding the nature of inter- and intramolecular interactions is essential not only for establishing the relation between structure and properties, but also for facilitating the rational design of molecules with targeted properties. These objectives have motivated the development of theoretical schemes decomposing intermolecular interactions into physically meaningful terms. Among the various existing energy decomposition schemes, Symmetry-Adapted Perturbation Theory (SAPT) is one of the most successful as it naturally decomposes the interaction energy into physical and intuitive terms. Unfortunately, analogous approaches for intramolecular energies are theoretically highly challenging and virtually nonexistent. Here, we introduce a zeroth-order wavefunction and energy, which represent the first step toward the development of an intramolecular variant of the SAPT formalism. The proposed energy expression is based on the Chemical Hamiltonian Approach (CHA), which relies upon an asymmetric interpretation of the electronic integrals. The orbitals are optimized with a non-hermitian Fock matrix based on two variants: one using orbitals strictly localized on individual fragments and the other using canonical (delocalized) orbitals. The zeroth-order wavefunction and energy expression are validated on a series of prototypical systems. The computed intramolecular interaction energies demonstrate that our approach combining the CHA with strictly localized orbitals achieves reasonable interaction energies and basis set dependence in addition to producing intuitive energy trends. Our zeroth-order wavefunction is the primary step fundamental to the derivation of any perturbation theory correction, which has the potential to truly transform our understanding and quantification of non

  5. Thermal stability of carboxylic acid functionality in coal; Sekitanchu ni sonzaisuru karubokishiruki no netsubunkai kyodo

    Energy Technology Data Exchange (ETDEWEB)

    Tsutsumi, Y.; Aida, T. [Kinki University, Osaka (Japan). Faculty of Engineering

    1996-10-28

    Carboxyl in coal was focused in discussing its pyrolytic behavior while tracking change of its absolute amount relative to the heating temperatures. A total of four kinds of coals, consisting of two kinds brown coals, sub-bituminous coal and bituminous coal were used. Change in the absolute amount of carboxyl due to heating varies with coalification degree. Decomposition starts in the bituminous coal from around 300{degree}C, and is rapidly accelerated when 400{degree}C is exceeded. Carboxyls in brown coals exist two to three times as much as those in bituminous and sub-bituminous coals, of which 40% is decomposed at a temperature as low as about 300{degree}C. Their pyrolytic behavior at temperatures higher than 400{degree}C resembles that of the bituminous coal. Carboxyls consist of those easy to decompose and difficult to decompose. Aromatic and aliphatic carboxylic acids with simple structure are stable at temperatures lower than 300{degree}C, and decompose abruptly from about 400{degree}C, hence their behavior resembles that of carboxyls in bituminous and sub-bituminous coals. Structure of low-temperature decomposing carboxyls in brown coals is not known, but it is assumed that humic acid originated from natural materials remains in the structure. 4 refs., 3 figs., 1 tab.

  6. Transition from Bioinert to Bioactive Material by Tailoring the Biological Cell Response to Carboxylated Nanocellulose.

    Science.gov (United States)

    Hua, Kai; Rocha, Igor; Zhang, Peng; Gustafsson, Simon; Ning, Yi; Strømme, Maria; Mihranyan, Albert; Ferraz, Natalia

    2016-03-14

    This work presents an insight into the relationship between cell response and physicochemical properties of Cladophora cellulose (CC) by investigating the effect of CC functional group density on the response of model cell lines. CC was carboxylated by electrochemical TEMPO-mediated oxidation. By varying the amount of charge passed through the electrolysis setup, CC materials with different degrees of oxidation were obtained. The effect of carboxyl group density on the material's physicochemical properties was investigated together with the response of human dermal fibroblasts (hDF) and human osteoblastic cells (Saos-2) to the carboxylated CC films. The introduction of carboxyl groups resulted in CC films with decreased specific surface area and smaller total pore volume compared with the unmodified CC (u-CC). While u-CC films presented a porous network of randomly oriented fibers, a compact and aligned fiber pattern was depicted for the carboxylated-CC films. The decrease in surface area and total pore volume, and the orientation and aggregation of the fibers tended to augment parallel to the increase in the carboxyl group density. hDF and Saos-2 cells presented poor cell adhesion and spreading on u-CC, which gradually increased for the carboxylated CC as the degree of oxidation increased. It was found that a threshold value in carboxyl group density needs be reached to obtain a carboxylated-CC film with cytocompatibility comparable to commercial tissue culture material. Hence, this study demonstrates that a normally bioinert nanomaterial can be rendered bioactive by carefully tuning the density of charged groups on the material surface, a finding that not only may contribute to the fundamental understanding of biointerface phenomena, but also to the development of bioinert/bioactive materials. PMID:26886265

  7. Carboxyl-terminal sequences influence the import of mitochondrial protein precursors in vivo

    International Nuclear Information System (INIS)

    The large subunit of carbamoyl phosphate synthase A from Neurospora crassa is encoded by a nuclear gene but is localized in the mitochondrial matrix. The authors have utilized N. crassa strains that produce both normal and carboxyl-terminal-truncated forms of carbamoyl phosphate synthase A to ask whether the carboxyl terminus affects import of the carbamoyl phosphate synthase A precursor. They found that carboxyl-terminal-truncated precursors were directed to mitochondria but that they were imported less efficiently than full-length proteins that were synthesized in the same cytoplasm. The results suggest that effective import of proteins into mitochondria requires appropriate combinations of targeting sequences and three-dimensional structure

  8. The investigation of the reactions of some pyrazole-3-carboxylic acids with various diamines and diols

    OpenAIRE

    Rahmi Kasımoğulları; Makbule Maden; Samet Mert

    2012-01-01

    In this study, some new derivatives were synthesized of 4-benzoyl-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid (1) and 4-(ethoxycarbonyl)-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid (2) that they were pyrazole carboxylic acid derivatives. Firstly, 1 and 2 reacted with SOCl2 to transform them into acyl chlorides (3, 4). Then various bis-carboxamide derivatives (58) were obtained from the reaction of 3 and 4 with various diamines and also a ;#946;-hydroxy ester (9) deri...

  9. The investigation of the reactions of some pyrazole-3-carboxylic acids with various diamines and diols

    OpenAIRE

    Kasımoğulları, Rahmi; Maden, Makbule; Mert, Samet

    2012-01-01

    In this study, some new derivatives were synthesized of 4-benzoyl-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid (1) and 4-(ethoxycarbonyl)-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid (2) that they were pyrazole carboxylic acid derivatives. Firstly, 1 and 2 reacted with SOCl2 to transform them into acyl chlorides (3, 4). Then various bis-carboxamide derivatives (5–8) were obtained from the reaction of 3 and 4 with various diamines and also a β-hydroxy ester (9)...

  10. A novel synthesis of carbon-labelled quinolone-3-carboxylic acid antibacterials

    Energy Technology Data Exchange (ETDEWEB)

    Carr, R.M.; Sutherland, D.R. (Glaxo Research and Development Ltd., Greenford (United Kingdom). Isotope Chemistry Group)

    1994-10-01

    3-Iodoquinolones were prepared from the corresponding quinolone-3-carboxylic acids by Hunsdiecker-type iododecarboxylation reactions with lead tetraacetate and iodine. Cyanation of the iodo compounds with mixtures of potassium [[sup 13]C]cyanide and copper (1) iodide, gave [3-[sup 13]C]cyanoquinolones which on acidic hydrolysis afforded quinolone-[3-[sup 13]C]carboxylic acids. In this way, nalidixic acid, an immediate precursor of norfloxacin, and quinolone WIN57273 were labelled with carbon-13 in the metabolically stable carboxylic acid fragment. (author).

  11. Genome Sequence of the Banana Plant Growth-Promoting Rhizobacterium Pseudomonas fluorescens PS006.

    Science.gov (United States)

    Gamez, Rocío M; Rodríguez, Fernando; Ramírez, Sandra; Gómez, Yolanda; Agarwala, Richa; Landsman, David; Mariño-Ramírez, Leonardo

    2016-01-01

    Pseudomonas fluorescens is a well-known plant growth-promoting rhizobacterium (PGPR). We report here the first whole-genome sequence of PGPR P. fluorescens evaluated in Colombian banana plants. The genome sequences contains genes involved in plant growth and defense, including bacteriocins, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, and genes that provide resistance to toxic compounds. PMID:27151797

  12. Genome Sequence of the Banana Plant Growth-Promoting Rhizobacterium Pseudomonas fluorescens PS006

    OpenAIRE

    Gamez, Rocío M.; Rodríguez, Fernando; Ramírez, Sandra; Gómez, Yolanda; Agarwala, Richa; Landsman, David; Mariño-Ramírez, Leonardo

    2016-01-01

    Pseudomonas fluorescens is a well-known plant growth-promoting rhizobacterium (PGPR). We report here the first whole-genome sequence of PGPR P. fluorescens evaluated in Colombian banana plants. The genome sequences contains genes involved in plant growth and defense, including bacteriocins, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, and genes that provide resistance to toxic compounds.

  13. Genome Sequence of the Banana Plant Growth-Promoting Rhizobacterium Pseudomonas fluorescens PS006

    Science.gov (United States)

    Gamez, Rocío M.; Rodríguez, Fernando; Ramírez, Sandra; Gómez, Yolanda; Agarwala, Richa; Landsman, David

    2016-01-01

    Pseudomonas fluorescens is a well-known plant growth-promoting rhizobacterium (PGPR). We report here the first whole-genome sequence of PGPR P. fluorescens evaluated in Colombian banana plants. The genome sequences contains genes involved in plant growth and defense, including bacteriocins, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, and genes that provide resistance to toxic compounds. PMID:27151797

  14. Structural and thermal properties of carboxylic acid functionalized polythiophenes

    Directory of Open Access Journals (Sweden)

    Ariane de França Mescoloto

    2014-01-01

    Full Text Available Polythiophenes functionalized with polar groups at the end of side-chain have emerged as an alternative method to obtain good compatibility between this class of conjugated polymers and electron acceptor compounds. The aim is to prevent phase segregation and to improve the efficiency of the polythiophene technological devices. However, homopolymers synthesized from thiophene rings with high polar groups at the end of the side-chain, such as hydroxyl and carboxylic acid groups, are poorly soluble in common volatile organic solvents. We report on a systematic preparation of copolymers of 3-hexylthiophene (HT and thiophene-3-acetic acid (TAA, using different feed ratios. The chemical structures of the copolymers were confirmed by FTIR and ¹H-NMR. The TAA content in these copolymers were 33, 38 and 54 mol %. HPSEC results did not show any remarkable correlation with TAA contents in the copolymers. In contrast, the thermal analyses showed a decrease in the thermal stability and an increase in rigidity of their backbones, for the copolymers with high amounts of TAA. The solubility and optical property of copolymers were also related to the TAA contents. Thus, the properties of these copolymers can be modulated by a simple control of feed ratio of TAA in the copolymerization.

  15. Variable Denticity in Carboxylate Binding to the Uranyl Coordination Complexes

    International Nuclear Information System (INIS)

    Tris-carboxylate complexes of the uranyl (UO2)2+ cation with acetate and benzoate were generated using electrospray ionization mass spectrometry, and then isolated in a Fourier transformion cyclotron resonance mass spectrometer. Wavelength-selective infrared multiple photon dissociation (IRMPD) of the tris-acetatouranyl anion resulted in a redox elimination of an acetate radical, which was used to generate an IR spectrum that consisted of six prominent absorption bands. These were interpreted with the aid of density functional theory calculations in terms of symmetric and antisymmetric -CO2 stretches of both the monodentate and bidentate acetate, CH3 bending and umbrella vibrations, and a uranyl O-U-O asymmetric stretch. The comparison of the calculated and measured IR spectra indicated that the tris-acetate complex contained two acetate ligands bound in a bidentate fashion, while the third acetate was monodentate. In similar fashion, the tris-benzoate uranyl anion was formed and photodissociated by loss of a benzoate radical, enabling measurement of the infrared spectrum that was in close agreement with that calculated for a structure containing one monodentate, and two bidentate benzoate ligands.

  16. Variable Denticity in Carboxylate Binding to the Uranyl Coordination Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Groenewold, G. S.; De Jong, Wibe A.; Oomens, Jos; Van Stipdonk, Michael J.

    2010-05-01

    Tris-carboxylate complexes of the uranyl [UO2]2+ cation with acetate and benzoate were generated using electrospray ionization mass spectrometry, and then isolated in a Fourier transformion cyclotron resonance mass spectrometer. Wavelength-selective infrared multiple photon dissociation (IRMPD) of the tris-acetatouranyl anion resulted in a redox elimination of an acetate radical, which was used to generate an IR spectrum that consisted of six prominent absorption bands. These were interpreted with the aid of density functional theory calculations in terms of symmetric and antisymmetric -CO2 stretches of both the monodentate and bidentate acetate, CH3 bending and umbrella vibrations, and a uranyl O-U-O asymmetric stretch. The comparison of the calculated and measured IR spectra indicated that the tris-acetate complex contained two acetate ligands bound in a bidentate fashion, while the third acetate was monodentate. In similar fashion, the tris-benzoate uranyl anion was formed and photodissociated by loss of a benzoate radical, enabling measurement of the infrared spectrum that was in close agreement with that calculated for a structure containing one monodentate, and two bidentate benzoate ligands.

  17. Z-effect reversal in carboxylic acid associates.

    Science.gov (United States)

    Medvedev, Michael G; Bushmarinov, Ivan S; Lyssenko, Konstantin A

    2016-05-01

    The carboxylic group is a common fragment in synthetic compounds and biomolecules. Its conformation is assumed to be dominantly cis due to so-called Z-effect. However, in this study, we show that the nature of the H-bond acceptor in RCOOHX directly affects the conformational preference of the resulting supermolecule. This result is evident from the statistical analysis of available crystallographic data and was quantified using accurate quantum chemical calculations. We propose the term "supramolecular stereoelectronic effect" for the observed conformational preference. The likely reason for this is the interaction of the O-HX hydrogen bond with the C[double bond, length as m-dash]O double bond in the trans conformation, which in case of anionic X is strong enough to reverse the Z-effect. Explicit consideration of trans COOHX stabilization can help crystal structure predictions and biomolecular simulations. In particular, this effect plays a key role in the transition between the T6 and R6 forms of human insulin. PMID:27109148

  18. Preorganized tridentate analogues of mixed hydroxyoxime/carboxylate nickel extractants.

    Science.gov (United States)

    Roebuck, James W; Turkington, Jennifer R; Rogers, David M; Bailey, Philip J; Griffin, Violina; Fischmann, Adam J; Nichol, Gary S; Pelser, Max; Parsons, Simon; Tasker, Peter A

    2016-03-01

    A series of 22 tridentate unsaturated mono-anionic ligands having the atom-sequence Y-C[double bond, length as m-dash]C-N=CH-C=C-Z(-1), with Y = N, O, or S and Z = O or S, has been studied to establish whether this backbone could be used to develop strong solvent extractants for nickel(II) which will preferably also show a high selectivity over iron(III) in the pH-dependent process: 2LH(org) + NiSO4 ⇌ [(L)2Ni]org + H2SO4. All are capable of forming octahedral [(L)2Ni] complexes with a mer-arrangement of the YNZ(-1) donor set. X-ray crystal structures of three salicylaldimine proligands derived from 3-bromo-5-t-butyl-2-hydroxybenzaldehyde show these to have pre-organised donor sets in which the three donors are held in an approximately orthogonal arrangement by intramolecular hydrogen bonds. The tautomers observed are dependent on the nature of the Y atom and the extent to which it is favourable for this to form a bonding interaction with the acidic hydrogen atom on the salicylaldimine unit. X-ray crystal structure determinations of seven of the [(L)2Ni] complexes show these to have significantly distorted octahedral coordination geometries which partly account for the proligands proving to be fairly weak Ni-extractants. DFT calculations show that extractant strength is dependent on a combination of the binding strength of the YNZ(-1) donor set to the nickel ion and on the ease of deprotonation of the extractant. On this basis 3-nitro-4-t-octyl-6-(quinolin-8-imino)phenol is predicted, and is found, to be the strongest Ni-extractant. The extractants have low hydrolytic stability, reverting to their aldehyde precursors when solutions in water-immiscible solvents are contacted with aqueous acid, making them poor candidates for development as reagents for nickel recovery based on pH-swing processes of the type shown above. PMID:26811997

  19. Promoting industrialisation

    International Nuclear Information System (INIS)

    When the first nuclear power programme is decided upon, automatically the country has to initiate in parallel a programme to modify or add to its current industrial structure and resources. The extent of this new industrialisation depends upon many factors which both, the Government and the Industries have to consider. The Government has a vital role which includes the setting up of the background against which the industrial promotion should take place and in many cases may have also to play an active role all along this programme. Equally, the existing industries have an important role so as to achieve the most efficient participation in the nuclear programme. Invariably the industrial promotional programme will incur a certain degree of transfer of technology, the extent depending on the policies adopted. For this technology transfer to take place efficiently, both the donor and the receiver have to recognise each other's legitimate ambitions and fears. The transfer of technology is a process having a high human content and both donor and receiver have to take this into account. This can be further complicated when there is a difference in culture between them. Technology transfer is carried out within a contractual and organisational framework which will identify the donor (licensor) and the receiver (licensee). This framework may take various forms from a simple cooperative agreement, through a joint-venture organisation right to a standard contract between two separate entities. Each arrangement has its advantages and drawbacks and requires investment of different degrees. One of the keys to a successful industrial promotion is having it carried out in a timely fashion which will be parallel with the nuclear power programme. Experience in some countries has shown the problems when the industrialisation is out of phase with the programme whilst in other cases this industrialisation was at a level and scale unjustified. (author)

  20. Plastic scintillators with high loading of one or more metal carboxylates

    Science.gov (United States)

    Cherepy, Nerine; Sanner, Robert Dean

    2016-01-12

    In one embodiment, a material includes at least one metal compound incorporated into a polymeric matrix, where the metal compound includes a metal and one or more carboxylate ligands, where at least one of the one or more carboxylate ligands includes a tertiary butyl group, and where the material is optically transparent. In another embodiment, a method includes: processing pulse traces corresponding to light pulses from a scintillator material; and outputting a result of the processing, where the scintillator material comprises at least one metal compound incorporated into a polymeric matrix, the at least one metal compound including a metal and one or more carboxylate ligands, where at least one of the one or more carboxylate ligands has a tertiary butyl group, and where the scintillator material is optically transparent and has an energy resolution at 662 keV of less than about 20%.

  1. High-level production of C-11-carboxyl-labeled amino acids

    International Nuclear Information System (INIS)

    Carbon-11-labeled amino acids have significant potential as agents for positron tomographic functional imaging. We have developed a rapid, high-temperature, high-pressure modification of the Buecherer--Strecker amino acid synthesis and found it to be quite general for the production of C-11-carboxyl-labeled neutral amino acids. Production of C-11-carboxyl-labeled DL-tryptophan requires certain modifications in the procedure. Twelve different amino acids have been produced to date by this technique. Synthesis and chromatographic purification require approximately 40 min, and C-11-carboxyl-labeled amino acids have been produced in yields of up to 425 mCi. Two C-11-carboxyl-labeled amino acids are being investigated clinically for tumor scanning and two others for pancreatic imaging. Over 120 batches of the various agents have been produced for clinical use over a three-year period

  2. Pyrazole carboxamides and carboxylic acids as protein kinase inhibitors in aberrant eukaryotic signal transduction

    DEFF Research Database (Denmark)

    Persson, Tobias; Yde, Christina W.; Rasmussen, Jakob Ewald;

    2007-01-01

    Densely functionalised pyrazole carboxamides and carboxylic acids were synthesised in an expedient manner through saponification and transamidation, respectively, of ester-functionalised pyrazoles. This synthetic protocol allowed for three diversifying steps in which appendages on the pyrazole...

  3. Thermal decomposition of freeze-dried μ-oxo-carboxylates of manganese and iron

    International Nuclear Information System (INIS)

    The decomposition of freeze-dried mixed carboxylates of manganese and iron was investigated by means of DTA, TG, mass spectroscopy and X-ray powder diffractometry. The three main steps of decomposition are characterized as release of (a) H2O, (b) carboxylic acid and CO2/CO, and (c) the corresponding carbonyl compound and CO2. In particular, the course of process (b) strongly depends on the stability of the metal-carboxylate link in the three investigated carboxylates. Well-crystallized single-phase manganese ferrites can be obtained on decomposition of formates of appropriate composition and thermal treatment of decomposition products at 600C while maintaining a p(O2) within the coexistence field of manganese ferrite. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  4. Synthesis and Anti-influenza Virus Activity of Ethyl 6-Bromo-5-hydroxyindole-3-carboxylate Derivatives

    Institute of Scientific and Technical Information of China (English)

    Yan Fang ZHAO; Jin Hua DONG; Ping GONG

    2004-01-01

    A series of ethyl 6-bromo-5-hydroxyindole-3-carboxylate derivatives were synthesized and their in vitro anti-influenza virus activity was evaluated. All the compounds were characterized by 1H NMR and MS.

  5. Efficient Debromination of Vicinal (, (-Dibromo Carboxylic Acid Derivatives with the Sm/HOAc System

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The α, β vicinal dibromo carboxylic acid and its derivatives were debrominated with Sm/HOAc system to afford the corresponding cinnamic acid and its derivatives in good yields under mild conditions.

  6. Functional properties and structural characterization of rice δ1-pyrroline-5-carboxylate reductase

    Science.gov (United States)

    Forlani, Giuseppe; Bertazzini, Michele; Zarattini, Marco; Funck, Dietmar; Ruszkowski, Milosz; Nocek, Bogusław

    2015-01-01

    The majority of plant species accumulate high intracellular levels of proline to cope with hyperosmotic stress conditions. Proline synthesis from glutamate is tightly regulated at both the transcriptional and the translational levels, yet little is known about the mechanisms for post-translational regulation of the enzymatic activities involved. The gene coding in rice (Oryza sativa L.) for δ1-pyrroline-5-carboxylate (P5C) reductase, the enzyme that catalyzes the second and final step in this pathway, was isolated and expressed in Escherichia coli. The structural and functional properties of the affinity-purified protein were characterized. As for most species, rice P5C reductase was able to use in vitro either NADH or NADPH as the electron donor. However, strikingly different effects of cations and anions were found depending on the pyridine nucleotide used, namely inhibition of NADH-dependent activity and stimulation of NADPH-dependent activity. Moreover, physiological concentrations of proline and NADP+ were strongly inhibitory for the NADH-dependent reaction, whereas the NADPH-dependent activity was mildly affected. Our results suggest that only NADPH may be used in vivo and that stress-dependent variations in ion homeostasis and NADPH/NADP+ ratio could modulate enzyme activity, being functional in promoting proline accumulation and potentially also adjusting NADPH consumption during the defense against hyperosmotic stress. The apparent molecular weight of the native protein observed in size exclusion chromatography indicated a high oligomerization state. We also report the first crystal structure of a plant P5C reductase at 3.40-Å resolution, showing a decameric quaternary assembly. Based on the structure, it was possible to identify dynamic structural differences among rice, human, and bacterial enzymes. PMID:26284087

  7. Functional properties and structural characterization of rice δ(1)-pyrroline-5-carboxylate reductase.

    Science.gov (United States)

    Forlani, Giuseppe; Bertazzini, Michele; Zarattini, Marco; Funck, Dietmar; Ruszkowski, Milosz; Nocek, Bogusław

    2015-01-01

    The majority of plant species accumulate high intracellular levels of proline to cope with hyperosmotic stress conditions. Proline synthesis from glutamate is tightly regulated at both the transcriptional and the translational levels, yet little is known about the mechanisms for post-translational regulation of the enzymatic activities involved. The gene coding in rice (Oryza sativa L.) for δ(1)-pyrroline-5-carboxylate (P5C) reductase, the enzyme that catalyzes the second and final step in this pathway, was isolated and expressed in Escherichia coli. The structural and functional properties of the affinity-purified protein were characterized. As for most species, rice P5C reductase was able to use in vitro either NADH or NADPH as the electron donor. However, strikingly different effects of cations and anions were found depending on the pyridine nucleotide used, namely inhibition of NADH-dependent activity and stimulation of NADPH-dependent activity. Moreover, physiological concentrations of proline and NADP(+) were strongly inhibitory for the NADH-dependent reaction, whereas the NADPH-dependent activity was mildly affected. Our results suggest that only NADPH may be used in vivo and that stress-dependent variations in ion homeostasis and NADPH/NADP(+) ratio could modulate enzyme activity, being functional in promoting proline accumulation and potentially also adjusting NADPH consumption during the defense against hyperosmotic stress. The apparent molecular weight of the native protein observed in size exclusion chromatography indicated a high oligomerization state. We also report the first crystal structure of a plant P5C reductase at 3.40-Å resolution, showing a decameric quaternary assembly. Based on the structure, it was possible to identify dynamic structural differences among rice, human, and bacterial enzymes. PMID:26284087

  8. Palladium-Catalyzed C–C Bond Formations via Activation of Carboxylic Acids and Their Derivatives

    OpenAIRE

    Song, Bingrui

    2013-01-01

    Applications of carboxylic acids and their derivatives in transition metal-catalyzed cross-coupling reactions regio-selectively forming Csp3-Csp2, and Csp2-Csp2 bonds were explored in this thesis. Several important organic building blocks such as aryl acetates, diaryl acetates, imines, ketones, biaryls, styrenes and polysubstituted alkenes were successfully accessed from carboxylic acids and their derivatives by the means of C–H activation and decarboxylative cross-couplings. An efficient ...

  9. A Simple Method for the Determination of Enantiomeric Excess and Identity of Chiral Carboxylic Acids

    OpenAIRE

    Joyce, Leo A.; Maynor, Marc S.; Dragna, Justin M.; da Cruz, Gabriella M.; Lynch, Vincent M.; Canary, James W.; Eric V. Anslyn

    2011-01-01

    The association between an achiral copper(II) host (1) and chiral carboxylate guests was studied using exciton-coupled circular dichroism (ECCD). Enantiomeric complexes were created upon binding of the enantiomers of the carboxylate guests to the host, and the sign of the resultant CD signal allowed for determination of the configuration of the studied guest. The difference in magnitudes and shapes of the CD signals, in conjunction with linear discriminant analysis (LDA), allowed for the iden...

  10. 2-(2-Chlorophenyl-5-methyl-1,3-dioxane-5-carboxylic acid

    Directory of Open Access Journals (Sweden)

    Guo-Kai Jia

    2012-07-01

    Full Text Available In the title compound, C12H13ClO4, the 1,3-dioxane ring adopts a chair conformation and the 2-chlorobenzene and methyl substituents occupy equatorial sites. The carboxyl group is in an axial inclination. In the crystal, carboxylic acid inversion dimers linked by pairs of O—H...O hydrogen bonds generate R22(8 loops.

  11. Probing the orthosteric binding site of GABAA receptors with heterocyclic GABA carboxylic acid bioisosteres

    DEFF Research Database (Denmark)

    Petersen, Jette G; Bergmann, Rikke; Krogsgaard-Larsen, Povl; Balle, Thomas; Frølund, Bente

    2013-01-01

    selective and potent GABAAR agonists. This review investigates the use of heterocyclic carboxylic acid bioisosteres within the GABAAR area. Several heterocycles including 3-hydroxyisoxazole, 3-hydroxyisoxazoline, 3-hydroxyisothiazole, and the 1- and 3-hydroxypyrazole rings have been employed in order to map...... the orthosteric binding site. The physicochemical properties of the heterocyclic moieties making them suitable for bioisosteric replacement of the carboxylic acid in the molecule of GABA are discussed. A variety of synthetic strategies for synthesis of the heterocyclic scaffolds are available...

  12. Redshift or adduct stabilization -- a computational study of hydrogen bonding in adducts of protonated carboxylic acids

    DEFF Research Database (Denmark)

    Olesen, Solveig Gaarn; Hammerum, Steen

    2009-01-01

    always yield consistent predictions, as illustrated by the hydrogen bonds formed by the E and Z OH groups of protonated carboxylic acids. The delta-PA and the stabilization of a series of hydrogen bonded adducts indicate that the E OH group forms the stronger hydrogen bonds, whereas the bond length...... carboxylic acids are different. The OH bond length and IR redshift afford the better measure of hydrogen bond strength....

  13. Expedited Synthesis of Benzofuran-2-Carboxylic Acids via Microwave-Assisted Perkin Rearrangement Reaction

    OpenAIRE

    Marriott, Karla-Sue C.; Bartee, Rena; Morrison, Andrew Z.; Stewart, Leonard; Wesby, Julian

    2012-01-01

    3-Halocoumarins are readily converted into benzofuran-2-carboxylic acids via a Perkin (coumarin-benzofuran ring contraction) rearrangement reaction. This rearrangement entails initial base catalyzed ring fission. The resulting phenoxide anion then attacks a vinyl halide to produce the final benzofuran moiety. We explored this reaction under microwave reaction conditions and were able to significantly reduce reaction times as well as obtain very high yields of a series of benzofuran-2-carboxyl...

  14. Gamma-aminoadamantane carboxylic acids : orientating building blocks in peptide chemistry

    OpenAIRE

    Wanka, Lukas

    2007-01-01

    The present thesis deals with gamma-aminoadamantane carboxylic acids. Allthough the simplest of these structural analogues of GABA were known for decades, no significant peptide chemistry has been disclosed. Therefore, improved syntheses of these compounds were worked out that allowed for facilitated syntheses of already known as well as new members of gamma-aminoadamantane carboxylic acids. Fmoc-/tert. butyl protective group chemistry was utilized to synthesize peptides incorporating the gam...

  15. Ozone-driven daytime formation of secondary organic aerosol containing carboxylic acid groups and alkane groups

    OpenAIRE

    Liu, S.; D. A. Day; J. E. Shields; L. M. Russell

    2011-01-01

    Carboxylic acids are present in substantial quantities in atmospheric particles, and they play an important role in the physical and chemical properties of aerosol particles. During measurements in coastal California in the summer of 2009, carboxylic acid functional groups were exclusively associated with a fossil fuel combustion factor derived from factor analysis of Fourier transform infrared spectroscopic measurements and closely correlated with oxygenated organic factors from aerosol mass...

  16. Copper-catalyzed intermolecular oxyamination of olefins using carboxylic acids and O-benzoylhydroxylamines

    Science.gov (United States)

    Hemric, Brett N

    2016-01-01

    Summary This paper reports a novel approach for the direct and facile synthesis of 1,2-oxyamino moieties via an intermolecular copper-catalyzed oxyamination of olefins. This strategy utilizes O-benzoylhydroxylamines as an electrophilic amine source and carboxylic acids as a nucleophilic oxygen source to achieve a modular difunctionalization of olefins. The reaction proceeded in a regioselective manner with moderate to good yields, exhibiting a broad scope of carboxylic acid, amine, and olefin substrates. PMID:26877805

  17. Effect of the cement type on compatibility with carboxylate superplasticisers

    Directory of Open Access Journals (Sweden)

    Bundyra-Oracz, G.

    2011-06-01

    Full Text Available An empirical study was conducted to gain a fuller understanding of the interactions taking place in cementsuperplasticiser systems. To this end, two clinkers of known chemical and phase composition were prepared in this study to gain insight into such interactions. One contained no tricalcium aluminate (C1, while the other had a 9% C3A content (C2. These clinkers were ground to approximately 340 m2/kg and blended with gypsum only or gypsum and Klein compound (3CaO·3Al2O3·CaSO4 (1, 2. Sufficient compound was added to C1 to ensure the formation of about the same amount of ettringite after 0.5 and 1 h of hydration as found in cement C2 + gypsum. The admixture used was a carboxylate superplasticiser. Rheology measurements showed that while paste yield stress was correlated to ettringite formation, no such simple relationship was observed for plastic viscosity. Plastic viscosity depended on the total hydrates formed, i.e., not only as ettringite but also as C-S-H gel. The findings revealed that in clinkers with very low sulfate and potassium contents, the rheology of carboxylate-containing cement paste is primarily controlled by ettringite formation.

    En el presente trabajo se ha realizado un estudio empírico con el objetivo de profundizar en el conocimiento de las interacciones del sistema cemento-superplastificante. Con este fin, se prepararon dos clínkeres con una composición química y de fases conocida: el primero (C1 sin aluminato tricálcico y el segundo (C2 con un contenido en C3A del 9%. Ambos se molieron hasta obtener una superficie específica aproximada de 340 m2/kg y se emplearon con dos adiciones: yeso y el compuesto de Klein (3CaO·3Al2O3·CaSO4 (1, 2. Se añadió la cantidad necesaria del compuesto de Klein a C1 para garantizar la formación, tras 0,5 y 1ª h. de hidratación, de aproximadamente la misma cantidad de etringita en dicho

  18. A theoretical study on the structure, intramolecular interactions, and detonation performance of hydrazinium dinitramide.

    Science.gov (United States)

    Zhang, Xueli; Liu, Yan; Wang, Fang; Gong, Xuedong

    2014-01-01

    The structures of hydrazinium dinitramide (HDN) in the gas phase and in aqueous solution have been studied at different levels of theory by using quantum chemistry. The intramolecular hydrogen-bond interactions in HDN were studied by employing the quantum theory of atoms in molecules (QTAIM), as well as those in ammonium dinitramide (ADN), hydrazinium nitroformate (HNF), and ammonium nitroformate (ANF) for comparison. The results showed that HDN possessed the strongest hydrogen bonds, with the largest hydrogen-bond energy (-47.95 kJ mol(-1)) and the largest total hydrogen-bond energy (-60.29 kJ mol(-1)). In addition, the charge transfer between the cation and the anion, the binding energy, the energy difference between the frontier orbitals, and the second-order perturbation energy of HDN were all the largest among the investigated compounds. These strongest intramolecular interactions accounted for the highest decomposition temperature of HDN among all four compounds. The IR spectra in the gas phase and in aqueous solution were very different and showed the significant influence of the solvent. The UV spectrum showed the strongest absorption at about 253 nm. An orbital-interaction diagram demonstrated that the transition of electrons mainly happened inside the anion of HDN. The detonation velocity (D=8.34 km s(-1)) and detonation pressure (P=30.18 GPa) of HDN were both higher than those of ADN (D=7.55 km s(-1) and P=24.83 GPa). The composite explosive HDN/CL-20 with the weight ratio wCL-20 /wHDN =0.388:0.612 showed the best performance (D=9.36 km s(-1) , P=39.82 GPa), which was close to that of CL-20 (D=9.73 km s(-1), P=45.19 GPa) and slightly better than that of the composite explosive ADN/CL-20 (wCL-20 /wADN =0.298:0.702, D=9.34 km s(-1), P=39.63 GPa). PMID:24108480

  19. Towards understanding the unbound state of drug compounds: Implications for the intramolecular reorganization energy upon binding.

    Science.gov (United States)

    Foloppe, Nicolas; Chen, I-Jen

    2016-05-15

    There has been an explosion of structural information for pharmaceutical compounds bound to biological targets, but the conformations and dynamics of compounds free in solution are poorly characterized, if at all. Yet, knowledge of the unbound state is essential to understand the fundamentals of molecular recognition, including the much debated conformational intramolecular reorganization energy of a compound upon binding (ΔEReorg). Also, dependable observation of the unbound compounds is important for ligand-based drug discovery, e.g. with pharmacophore modelling. Here, these questions are addressed with long (⩾0.5μs) state-of-the-art molecular dynamics (MD) simulations of 26 compounds (including 7 approved drugs) unbound in explicit solvent. These compounds were selected to be chemically diverse, with a range of flexibility, and good quality bioactive X-ray structures. The MD-simulated free compounds are compared to their bioactive structure and conformers generated with ad hoc sampling in vacuo or with implicit generalized Born (GB) aqueous solvation models. The GB conformational models clearly depart from those obtained in explicit solvent, and suffer from conformational collapse almost as severe as in vacuo. Thus, the global energy minima in vacuo or with GB are not suitable representations of the unbound state, which can instead be extensively sampled by MD simulations. Many, but not all, MD-simulated compounds displayed some structural similarity to their bioactive structure, supporting the notion of conformational pre-organization for binding. The ligand-protein complexes were also simulated in explicit solvent, to estimate ΔEReorg as an enthalpic difference ΔHReorg between the intramolecular energies in the bound and unbound states. This fresh approach yielded ΔHReorg values⩽6kcal/mol for 18 out of 26 compounds. For three particularly polar compounds 15⩽ΔHReorg⩽20kcal/mol, supporting the notion that ΔHReorg can be substantial. Those large

  20. Intramolecular isotope distributions reveal lower than expected increases in photosynthesis over the past 200 years

    Science.gov (United States)

    Ehlers, Ina; Augusti, Angela; Köhler, Iris; Zuidema, Pieter; Robertson, Iain; Nilsson, Mats; Schleucher, Jürgen

    2015-04-01

    The ability of the biosphere to act as CO2 sink through photosynthesis strongly influences future atmospheric CO2 concentrations and crop productivity. However, plant responses to increasing atmospheric CO2 are poorly understood, in particular on time scales of decades that are most relevant for the global carbon cycle. Most plants in the global terrestrial vegetation and most crops use the C3 photosynthetic pathway. Photorespiration is a side reaction of C3 photosynthesis that reduces CO2 assimilation in all C3 plants. By studying intramolecular isotope distributions (isotopomer abundances) in century-long archives of plant material, we reconstruct how the atmospheric CO2 increase since industrialization has changed the ratio of photorespiration to photosynthesis. For 12 tree species from five continents, we observe that the CO2 increase has reduced the photorespiration / photosynthesis ratio. However, the observed reduction is on average 50 % smaller than expected from CO2 manipulation experiments. This apparent discrepancy is explained by results from a factorial CO2 / temperature manipulation experiment, which shows that isotopomers reflect the integrated effect of CO2 and temperature on the photorespiration / photosynthesis ratio. Thus, the 50 % smaller suppression of photorespiration in trees is explained by increases in leaf temperature of 2 ° C, due to global warming and a possible contribution of reduced transpirational cooling due to stomatal closure. Previous studies of long-term effects of increasing CO2 on trees have measured 13C fractionation of leaf gas exchange (Δ13C) in tree-ring series. In several studies a discrepancy was observed: strong historic increases in photosynthesis are estimated, but increases in biomass are not observed. The temperature influence revealed by our isotopomer data resolves this discrepancy; the lower estimate of CO2 fertilization has major implications for the future role of forests as CO2 sink and for vegetation

  1. How many carboxyl groups does an average molecule of humic-like substances contain?

    Directory of Open Access Journals (Sweden)

    I. Salma

    2008-10-01

    Full Text Available The carboxyl groups of atmospheric humic-like substances (HULIS are of special interest because they influence the solubility in water, affect the water activity and surface tension of droplets in the air, and allow formation of chelates with biologically active elements. Experimentally determined abundances of the carboxyl group within HULIS by functional group analysis are consistent with our knowledge on the average molecular mass of HULIS if the number of dissociable carboxyl groups is assumed to be rather small. The best agreement between the average molecular mass derived from the existing abundance data and the average molecular mass published earlier occurs for assuming approximately one dissociable carboxyl group only. This implies that HULIS can not be regarded as polycarboxilic acid in diluted solutions. The average molecular mass of HULIS derived from our electrochemical measurements with the assumption of one dissociable carboxyl group or equivalently, one dissociable sulphate ester per molecule ranges from 250 to 310 Da. It was concluded that HULIS are a moderately strong/weak acid with a dissociation constant of about pK=3.4, which fits well into the interval represented by fulvic and humic acids. The mean number of dissociable hydrogen (i.e. of carboxyl groups and sulphate esters jointly in HULIS molecules was refined to be between 1.1 and 1.4 in acidic solutions.

  2. How many carboxyl groups does an average molecule of humic-like substances contain?

    Directory of Open Access Journals (Sweden)

    I. Salma

    2008-05-01

    Full Text Available The carboxyl groups of atmospheric humic-like substances (HULIS are of special interest because they influence the solubility in water, affect the water activity and surface tension of droplets in the air, and allow formation of chelates with biologically active elements. Experimentally determined abundances of the carboxyl group within HULIS by functional group analysis are consistent with our knowledge on the average molecular mass of HULIS if the number of dissociable carboxyl groups is assumed to be rather small. The best agreement between the average molecular mass derived from the existing abundance data and the average molecular mass published earlier occurs for assuming approximately one dissociable carboxyl group only. This implies that HULIS can not be regarded as polycarboxilic acid. The average molecular mass of HULIS derived from our electrochemical measurements with the assumption of one dissociable carboxyl group per molecule ranges from 248 to 305 Da. It was concluded that HULIS are a moderately strong/weak acid with a dissociation constant of about pK=3.4, which fits well into the interval represented by fulvic and humic acids. The mean number of dissociable carboxyl groups in HULIS molecules was refined to be between 1.1 and 1.4.

  3. Alkali base triggered intramolecular charge transfer metallogels based on symmetrical A-π-D-chiral-D-π-A type ligands.

    Science.gov (United States)

    Dixit, Manish Kumar; Pandey, Vinay Kumar; Dubey, Mrigendra

    2016-04-13

    Three l-tartaric acid based symmetrical A-π-D-chiral-D-π-A type structural isomeric nitrobenzylidenes () have been synthesized with intent to achieve isomer specific metallogels with intramolecular charge transfer properties. Alkali metal ions in these systems not only trigger charge transfer but also play a vital role in gelation. The presence of intramolecular rather than intermolecular charge transfer as well as aggregation has been well established by various kinds of experiments using UV-vis, CD, (1)H NMR, DFT and crystallography techniques. The role of alkali metal ions in triggering ICT was proved by titration with their respective crown ethers. Notably, Na(+) afforded twisted fiber morphology whilst Li(+) gave merely long range fibers. The true gel phase material was proved by detailed rheological studies. PMID:26974120

  4. Excited-state intramolecular proton transfer of 2-acetylindan-1,3-dione studied by ultrafast absorption and fluorescence spectroscopy

    Directory of Open Access Journals (Sweden)

    Pramod Kumar Verma

    2016-03-01

    Full Text Available We employ transient absorption from the deep-UV to the visible region and fluorescence upconversion to investigate the photoinduced excited-state intramolecular proton-transfer dynamics in a biologically relevant drug molecule, 2-acetylindan-1,3-dione. The molecule is a ß-diketone which in the electronic ground state exists as exocyclic enol with an intramolecular H-bond. Upon electronic excitation at 300 nm, the first excited state of the exocyclic enol is initially populated, followed by ultrafast proton transfer (≈160 fs to form the vibrationally hot endocyclic enol. Subsequently, solvent-induced vibrational relaxation takes place (≈10 ps followed by decay (≈390 ps to the corresponding ground state.

  5. Intramolecular proton transfer through the adjoining π-conjugated system in Shiff base: Application for colorimetric sensing of fluoride anion

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Xudong, E-mail: 081022009@fudan.edu.cn [College of Chemistry and Material Sciences, Hebei Normal University, Yuhua Road 113, Shijiazhuang 050024 (China); College of Science and Hebei Research Center of Pharmaceutical and Chemical Engineering, Hebei University of Science and Technology, Yuhua Road 70, Shijiazhuang 050080 (China); Zhang, Ping [College of Chemistry and Material Sciences, Hebei Normal University, Yuhua Road 113, Shijiazhuang 050024 (China); Li, Yajuan; Zhen, Xiaoli; Geng, Lijun; Wang, Yanqiu [College of Science and Hebei Research Center of Pharmaceutical and Chemical Engineering, Hebei University of Science and Technology, Yuhua Road 70, Shijiazhuang 050080 (China); Ma, Zichuan, E-mail: ma7405@hebtu.edu.cn [College of Chemistry and Material Sciences, Hebei Normal University, Yuhua Road 113, Shijiazhuang 050024 (China)

    2014-07-01

    In this paper, a new kind of phenol-based chemsensor L2 comprised of a Schiff base and azo groups was rationally designed and synthesized. It could selectively recognize fluoride anion among tested anions such as F{sup −}, AcO{sup −}, H{sub 2}PO{sub 4}{sup −}, Cl{sup −}, Br{sup −}, and I{sup −} with obvious color changes from yellow to fuchsia. The intramolecular PT (proton transfer) in L1 and L2 was responsible for the sensing ability, which was certified by the {sup 1}H NMR and Uv–vis experiments. - Highlights: • The phenol derivative L2 could selectively sense F{sup −} among test anions. • Intramolecular proton transfer happened when L2 was bonded with F{sup −}. • It is the first antipyrine-based anion receptor.

  6. Intramolecular fixation of t-butyl groups in thiolactim ethers influencing molecular conformation and the packing behavior

    Science.gov (United States)

    Hübscher, Jörg; Gruber, Thomas; Seichter, Wilhelm; Kortus, Jens; Weber, Edwin

    2015-07-01

    Derived from the result of a previous crystallographic study regarding an ethynylene bridged bispyrimidine, the presence of two intramolecular C-H⋯N hydrogen bonding contacts being responsible for a fixation of the terminal t-butylthio units to the azine nitrogens was noticed. Acting as stimulus, a series of different pyridine and pyridazine derivatives also featuring this unusual functionality has been synthesized and structurally studied. In order to support the investigations concerning this particular bonding pattern performed via X-ray structure analysis, calculations based on the density functional theory were carried out. It was found that the formation of the intramolecular hydrogen bonding motif has not only impact on the molecular stability but in some cases also predictably influences the reactivity and the packing behavior of the different heterocycles.

  7. Ligand-binding properties of the carboxyl-terminal repeat domain of Streptococcus mutans glucan-binding protein A.

    Science.gov (United States)

    Haas, W; Banas, J A

    2000-02-01

    Streptococcus mutans glucan-binding protein A (GbpA) has sequence similarity in its carboxyl-terminal domain with glucosyltransferases (GTFs), the enzymes responsible for catalyzing the synthesis of the glucans to which GbpA and GTFs can bind and which promote S. mutans attachment to and accumulation on the tooth surface. It was predicted that this C-terminal region, comprised of what have been termed YG repeats, represents the GbpA glucan-binding domain (GBD). In an effort to test this hypothesis and to quantitate the ligand-binding specificities of the GbpA GBD, several fusion proteins were generated and tested by affinity electrophoresis or by precipitation of protein-ligand complexes, allowing the determination of binding constants. It was determined that the 16 YG repeats in GbpA comprise its GBD and that GbpA has a greater affinity for dextran (a water-soluble form of glucan) than for mutan (a water-insoluble form of glucan). Placement of the GBD at the carboxyl terminus was necessary for maximum glucan binding, and deletion of as few as two YG repeats from either end of the GBD reduced the affinity for dextran by over 10-fold. Interestingly, the binding constant of GbpA for dextran was 34-fold higher than that calculated for the GBDs of two S. mutans GTFs, one of which catalyzes the synthesis of water-soluble glucan and the other of which catalyzes the synthesis of water-insoluble glucan. PMID:10633107

  8. Thermochemistry of 2,2,5,7,8-pentamethylchroman-6-ol (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox)

    International Nuclear Information System (INIS)

    Highlights: • We measured Cp,mo(cr/g), ΔfHmo(cr/g), ΔfusHmo and ΔsubHmo for 2,2,5,7,8-pentamethylchroman-6-ol (PMC). • We measured Cp,mo(cr/g), ΔfHmo(cr/g), ΔfusHmo and ΔsubHmo for 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox). • We found that, if present, an intramolecular hydrogen bond in trolox must be weak. • We found that the replacement of a CH3 group in PMC by a COOH group in trolox approximately conforms to group additivity. - Abstract: 2,2,5,7,8-Pentamethylchroman-6-ol (PMC, CAS number 950-99-2) and 6-hydroxy-2,5,7,8-tetramethyl chroman-2-carboxylic acid (trolox, CAS number 53188-07-1) are perhaps the two most widely used model compounds for α-tocoferol, the main active antioxidant form of vitamin E. Because the antioxidant activity of α-tocoferol, and of phenol derivatives (ArOH) in general (such as PMC and trolox), is intimately related to the breaking of the ArO-H bond, considerable efforts have been made to investigate how the energetics of that bond is linked to the structure and energetics of both the ArO· radical and the ArOH parent compound, which are reflected by the corresponding enthalpies of formation. In this work the standard molar enthalpies of formation of crystalline PMC (triclinic, space group P1¯ phase) and trolox (monoclinic, space group P21/c phase), at T = 298.15 K, were obtained as ΔfHmo(PMC,cr) = −(513.7 ± 3.4) kJ · mol−1 and ΔfHmo(trolox,crI) = −(892.5 ± 4.1) kJ · mol−1 by combustion calorimetry. The results of drop-sublimation Calvet microcalorimetry experiments and vapor pressure vs. temperature measurements by the Knudsen effusion method, combined with Cp,mo(cr) and Cp,mo(g) data obtained by differential scanning calorimetry and calculated at the B3LYP/6-31+G(d, p) level of theory, respectively, led to ΔsubHmo(PMC) = (107.4 ± 0.8) kJ · mol−1 and ΔsubHmo(trolox) = (136.9 ± 2.5) kJ · mol−1 at T = 298.15 K. From the obtained ΔsubHmo(cr) and ΔsubHmo values it was possible

  9. An intramolecular interaction between the FHA domain and a coiled coil negatively regulates the kinesin motor KIF1A

    OpenAIRE

    Lee, Jae-Ran; Shin, Hyewon; Choi, Jeonghoon; Ko, Jaewon; Kim, Seho; Lee, Hyun Woo; Kim, Karam; Rho, Seong-Hwan; Lee, Jun Hyuck; Song, Hye-Eun; Eom, Soo Hyun; Kim, Eunjoon

    2004-01-01

    Motor proteins not actively involved in transporting cargoes should remain inactive at sites of cargo loading to save energy and remain available for loading. KIF1A/Unc104 is a monomeric kinesin known to dimerize into a processive motor at high protein concentrations. However, the molecular mechanisms underlying monomer stabilization and monomer-to-dimer transition are not well understood. Here, we report an intramolecular interaction in KIF1A between the forkhead-associated (FHA) domain and ...

  10. Ultrafast Investigation of Intramolecular Charge Transfer and Solvation Dynamics of Tetrahydro[5]-helicene-Based Imide Derivatives

    OpenAIRE

    Huaning Zhu; Meng Li; Jiangpu Hu; Xian Wang; Jialong Jie; Qianjin Guo; Chuanfeng Chen; Andong Xia

    2016-01-01

    We report the excited-state intramolecular charge transfer (ICT) characteristics of four tetrahydro[5] helicene-based imide (THHBI) derivatives with various electron-donating substitutes in different polarity of solvents using steady-state, time-resolved transient absorption (TA) spectroscopy. It is found that, the small bathochromic-shift of the absorption spectra but large red shift of the emission spectra for all dyes with increasing solvent polarity indicates the larger dipole moment of t...

  11. A straightforward synthesis of an aminocyclitol based on an enzymatic aldol reaction and a highly stereoselective intramolecular Henry reaction

    OpenAIRE

    El Blidi, Lahssen; Crestia, Dominique; Gallienne, Estelle; Demuynck, Colette; Bolte, Jean; Lemaire, Marielle

    2004-01-01

    The reactions of 4-nitroaldehydes 9 and 10 with dihydroxyacetonephosphate (DHAP) catalyzed by fructose-1,6-diphosphate aldolase from rabbit muscle were studied. Starting from 9 or 10, only one main stereomer of nitrocyclitol 8 was isolated. A highly stereoselective intramolecular cyclization (Henry reaction or nitroaldol reaction) took place under acidic conditions during the aldolase catalyzed condensation and phytase catalyzed phosphate hydrolysis coupled step. The catalytic hydrogenation o...

  12. An intramolecular recombination mechanism for the formation of the rRNA gene palindrome of Tetrahymena thermophila.

    OpenAIRE

    Butler, D. K.; Yasuda, L E; Yao, M C

    1995-01-01

    Large palindromic DNAs are found in a wide variety of eukaryotic cells. In Tetrahymena thermophila, a large palindrome is formed from a single rRNA gene (rDNA) during nuclear differentiation. We present evidence that a key step in the formation of the rDNA palindrome of T. thermophila involves homologous intramolecular recombination. Heteroduplex micronuclear rDNA molecules were constructed in vitro and microinjected into developing macronuclei, where they formed palindromes. Analysis of the ...

  13. Simulating two-dimensional infrared-Raman and Raman spectroscopies for intermolecular and intramolecular modes of liquid water.

    Science.gov (United States)

    Ito, Hironobu; Tanimura, Yoshitaka

    2016-02-21

    Full classical molecular dynamics (MD) simulations of two-dimensional (2D) infrared-Raman and 2D Raman spectroscopies of liquid water were carried out to elucidate a mode-mode coupling mechanism using a polarizable water model for intermolecular and intramolecular vibrational spectroscopy (POLI2VS). This model is capable of describing both infrared and Raman spectra. Second-order response functions, which consist of one molecular polarizability and two molecular dipole moments for 2D IR-Raman and three molecular polarizabilities for 2D Raman spectroscopies, were calculated using an equilibrium-non-equilibrium hybrid MD approach. The obtained signals were analyzed using a multi-mode Brownian oscillator (BO) model with nonlinear system-bath interactions representing the intramolecular OH stretching, intramolecular HOH bending, hydrogen bonded (HB)-intermolecular librational motion and HB-intermolecular vibrational (translational) motion of liquid water. This model was applied through use of hierarchal Fokker-Planck equations. The qualitative features of the peak profiles in the 2D spectra obtained from the MD simulations are accurately reproduced with the BO model. This indicates that this model captures the essential features of the intermolecular and intramolecular motion. We elucidate the mechanisms governing the 2D signal profiles involving anharmonic mode-mode coupling, the nonlinearities of the polarizability and dipole moment, and the vibrational dephasing processes of liquid water even in the case that the 2D spectral peaks obtained from the MD simulation overlap or are unclear. The mode coupling peaks caused by electrical anharmonic coupling (EAHC) and mechanical anharmonic coupling (MAHC) are observed in all of the 2D spectra. We find that the strength of the MAHC between the OH-stretching and HB-intermolecular vibrational modes is comparable to that between the OH-stretching and HOH bending modes. Moreover, we find that this OH-stretching and HB

  14. The Role of Intramolecular Barriers on the Glass Transition of Polymers: Computer Simulations vs. Mode Coupling Theory

    OpenAIRE

    Bernabei, Marco; Moreno, Ángel J.; Colmenero, Juan

    2009-01-01

    We present computer simulations of a simple bead-spring model for polymer melts with intramolecular barriers. By systematically tuning the strength of the barriers, we investigate their role on the glass transition. Dynamic observables are analyzed within the framework of the Mode Coupling Theory (MCT). Critical nonergodicity parameters, critical temperatures and dynamic exponents are obtained from consistent fits of simulation data to MCT asymptotic laws. The so-obtained MCT $\\lambda$-expone...

  15. A Novel Practical Synthesis of Phenanthrenes Using Iron(Ⅲ) Chloride Involved Intramolecular Oxidative Coupling at Room Temperature

    Institute of Scientific and Technical Information of China (English)

    L(U),Mao-Yun; WANG,Kai-Liang; CAI,Fei; WANG,Hai-Ying; WANG,Qing-Min

    2008-01-01

    Iron(Ⅲ) chloride has been used to prepare the polymethoxy substituted phenanthrene derivatives via in-tramolecular oxidative coupling of (E or Z)-2,3-di(substituted phenyl)acrylate at room temperature in excellent yields. Mild reaction conditions and the use of inexpensive and nontoxic FeCI3 provide a novel practical and large-scaled viable route for the synthesis of the important phenanthrene rings.

  16. Atroposelective formation of dibenz[c,e]azepines via intramolecular direct arylation with centre-axis chirality transfer.

    Science.gov (United States)

    Cheetham, Caroline A; Massey, Richard S; Pira, Silvain L; Pritchard, Robin G; Wallace, Timothy W

    2011-03-21

    5-Substituted 6,7-dihydrodibenz[c,e]azepines, a class of secondary amine incorporating a centre-axis chirality relay, are accessible from 1-substituted N-(2-bromobenzyl)-1-phenylmethanamines via N-acylation and ring-closing intramolecular direct arylation. The ring closure proceeds with high atropodiastereoselectivity due to strain effects that are induced by trigonalisation of the nitrogen atom, as predicted using molecular mechanics calculations. PMID:21267501

  17. Single-chain crosslinked star polymers via intramolecular crosslinking of self-folding amphiphilic copolymers in water

    OpenAIRE

    Terashima, Takaya; Sugita, Takanori; Sawamoto, Mitsuo

    2015-01-01

    Single-chain crosslinked star polymers with multiple hydrophilic short arms and a hydrophobic core were created as novel microgel star polymers of single polymer chains. The synthetic process involves the intramolecular crosslinking of self-folding amphiphilic random copolymers in water. For this process, amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic olefin pendants were synthesized by ruthenium-catalyzed living radical copolymerization of PEG m...

  18. On the Possibility of Uphill Intramolecular Electron Transfer in Multicopper Oxidases: Electrochemical and Quantum Chemical Study of Bilirubin Oxidase

    Czech Academy of Sciences Publication Activity Database

    Shleev, S.; Andoralov, V.; Falk, M.; Reimann, C. T.; Ruzgas, T.; Srnec, Martin; Ryde, U.; Rulíšek, Lubomír

    2012-01-01

    Roč. 24, č. 7 (2012), s. 1524-1540. ISSN 1040-0397 Grant ostatní: 7th Framework Program(XE) NMP4-SL-2009-229255 Institutional research plan: CEZ:AV0Z40550506 Keywords : bilirubin oxidase * intramolecular electron transfer * rate-limiting catalytic step * reorganization energy * QM/MM calculations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.817, year: 2012

  19. Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach

    Science.gov (United States)

    Viana, Rommel B.; Ribeiro, Gabriela L. O.; Santos, Sinara F. F.; Quintero, David E.; Viana, Anderson B.; da Silva, Albérico B. F.; Moreno-Fuquen, Rodolfo

    2016-06-01

    The aim of this investigation was to determine the molecular properties and provide an interpretation of the vibrational mode couplings of these two paracetamol analogues: 2-bromo-2-methyl-N-(4-nitrophenyl)-propanamide and 2-bromo-2-methyl-N-p-tolyl-propanamide. E/Z isomers, keto/enol unimolecular rearrangement and prediction of the transition state structures in each mechanism were also assessed using the Density Functional Theory (DFT). The DFT estimates a high energy gap between E and Z isomers (9-11 kcal·mol- 1), with barrier heights ranging from 16 to 19 kcal·mol- 1. In contrast, the barrier energies on the keto/enol isomerization are almost 10 kcal·mol- 1 higher than those estimated for the E/Z rearrangement. The kinetic rate constant was also determined for each reaction mechanism. Natural bond orbital analysis and the quantum theory of atoms in molecules were used to interpret the intramolecular hydrogen bonds and to understand the most important interactions that govern the stabilization of each isomer. Furthermore, an analysis of the atomic charge distribution using different population methodologies was also performed.

  20. Probing the critical residues for intramolecular fructosyl transfer reaction of a levan fructotransferase.

    Science.gov (United States)

    Moon, Keum-Ok; Choi, Kyoung-Hwa; Kang, Ho-Young; Oh, Jeong-Il; Jang, Se Bok; Park, Cheon-Seok; Lee, Jong-Hoon; Cha, Jaeho

    2008-06-01

    Levan fructotransferase (LFTase) preferentially catalyzes the transfructosylation reaction in addition to levan hydrolysis, whereas other levan-degrading enzymes hydrolyze levan into a levan-oligosaccharide and fructose. Based on sequence comparisons and enzymatic properties, the fructosyl transfer activity of LFTase is proposed to have evolved from levanase. In order to probe the residues that are critical to the intramolecular fructosyl transfer reaction of the Microbacterium sp. AL-210 LFTase, an error-prone PCR mutagenesis process was carried out, and the mutants that led to a shift in activity from transfructosylation towards hydrolysis of levan were screened by the DNS method. After two rounds of mutagenesis, TLC and HPLC analyses of the reaction products by the selected mutants revealed two major products; one is a di-D-fructose- 2,6':6,2'-dianhydride (DFAIV) and the other is a levanbiose. The newly detected levanbiose corresponds to the reaction product from LFTase lacking transferring activity. Two mutants (2-F8 and 2-G9) showed a high yield of levanbiose (38-40%) compared with the wild-type enzyme, and thus behaved as levanases. Sequence analysis of the individual mutants responsible for the enhanced hydrolytic activity indicated that Asn-85 was highly involved in the transfructosylation activity of LFTase. PMID:18600048

  1. Fluorescent sensors for selective detection of thiols: expanding the intramolecular displacement based mechanism to new chromophores.

    Science.gov (United States)

    Niu, Li-Ya; Zheng, Hai-Rong; Chen, Yu-Zhe; Wu, Li-Zhu; Tung, Chen-Ho; Yang, Qing-Zheng

    2014-03-21

    Biological thiols, including cysteine (Cys), homocystein (Hcy) and glutathione (GSH), play crucial roles in maintaining the appropriate redox status of biological systems. An abnormal level of biothiols is associated with different diseases, therefore, the discrimination between them is of great importance. Herein, we present two fluorescent sensors for selective detection of biothiols based on our recently reported intramolecular displacement mechanism. We expanded this mechanism to commercially available chromophores, 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) and heptamethine cyanine dye IR-780. The sensors operate by undergoing displacement of chloride by thiolate. The amino groups of Cys/Hcy further replace the thiolate to form amino-substituted products, which exhibit dramatically different photophysical properties compared to sulfur-substituted products from the reaction with GSH. NBD-Cl is highly selective towards Cys/Hcy and exhibits significant fluorescence enhancement. IR-780 showed a variation in its fluorescence ratio towards Cys over other thiols. Both of the sensors can be used for live-cell imaging of Cys. The wide applicability of the mechanism may provide a powerful tool for developing novel fluorescent sensors for selective detection of biothiols. PMID:24466567

  2. Effect of ionophores on the rate of intramolecular cation exchange in durosemiquinone ion pairs

    Science.gov (United States)

    Eastman, M. P.; Bruno, G. V.; Mcguyer, C. A.; Gutierrez, A. R.; Shannon, J. M.

    1979-01-01

    The effects of the ionophores 15-crown-5 (15C5), 18-crown-6 (18C6), dibenzo-18-crown-6 (DBC) and cryptand 222 (C222) on intramolecular cation exchange in ion pairs of the sodium salt of the durosemiquinone anion in benzene solution are investigated. Electron paramagnetic resonance spectra of the 18C6 and 15C5 complexes with durosemiquinone reduced by contact with a sodium mirror show an alternating line width which indicates that the sodium ion is being exchanged between equivalent sites near the oxygens of the semiquinone with activation energies of 8.7 and 6.0 kcal/mole and Arrhenius preexponential factors of 9 x 10 to the 12th/sec and 10 to the 12th/sec, respectively. Spectra obtained for the DBC complexes show no evidence of exchange, while those of C222 indicate rapid exchange. It is also noted that the hyperfine splitting constants measured do not change over the 50-K temperature interval studied.

  3. Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

    Directory of Open Access Journals (Sweden)

    Ritesh Nandy

    2010-10-01

    Full Text Available Several 2-(phenylethynyltriphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different polarity. For a given derivative, solvent polarity had minimal effect on the absorption maxima. However, for a given solvent the absorption maxima red shifted with increasing conjugation of the substituent. The fluorescence emission of these derivatives was very sensitive to solvent polarity. In the presence of strongly electron withdrawing (–CN and strongly electron donating (–NMe2 substituents large Stokes shifts (up to 130 nm, 7828 cm−1 were observed in DMSO. In the presence of carbonyl substituents (–COMe and –COPh, the largest Stokes shift (140 nm, 8163 cm−1 was observed in ethanol. Linear correlation was observed for the Stokes shifts in a Lippert–Mataga plot. Linear correlation of Stokes shift was also observed with ET(30 scale for protic and aprotic solvents but with different slopes. These results indicate that the fluorescence emission arises from excited state intramolecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending upon the nature of the substituent on the phenyl ring. HOMO–LUMO energy gaps have been estimated from the electrochemical and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations.

  4. Intramolecular hydrogen bonding in 5-nitrosalicylaldehyde: IR spectrum and quantum chemical calculations

    Science.gov (United States)

    Moosavi-Tekyeh, Zainab; Taherian, Fatemeh; Tayyari, Sayyed Faramarz

    2016-05-01

    The structural parameters, and vibrational frequencies of 5-nitrosalicylaldehyde (5NSA) were studied by the FT-IR and Raman spectra and the quantum chemical calculations carried out at the B3LYP/6-311++G(d,p) level of theory in order to investigate the intramolecular hydrogen bonding (IHB) present in its structure. The strength and nature of IHB in the optimized structure of 5NSA were studied in detail by means of the atoms in molecules (AIM) and the natural bond orbital (NBO) approaches. The results obtained were then compared with the corresponding data for its parent molecule, salicylaldehyde (SA). Comparisons made between the geometrical structures for 5NSA and SA, their OH/OD stretching and out-of-plane bending modes, their enthalpies for the hydrogen bond, and their AIM parameters demonstrated a stronger H-bonding in 5NSA compared with that in SA. The calculated binding enthalpy (ΔHbind) for 5NSA was -10.92 kcal mol-1. The observed νOH and γOH appeared at about 3120 cm-1 and 786 cm-1 respectively. The stretching frequency shift of H-bond formation was 426 cm-1 which is consistent with ΔHbind and the strength of H-bond in 5NSA. The delocalization energies and electron delocalization indices derived by the NBO and AIM approaches indicate that the resonance effects were responsible for the stronger IHB in 5NSA than in SA.

  5. Thiol peroxidase-like activity of some intramolecularly coordinated diorganyl diselenides

    Indian Academy of Sciences (India)

    Sangit Kumar; Harkesh B Singh

    2005-11-01

    Several new diaryl diselenides having intramolecular coordinating groups have been synthesized by ortho-lithiation/Na2Se2 routes in good yield. Bis[2-(N-phenylferrocenecarboxamide)] diselenide (10), bis[2-(N-tert-butylferrocenecarboxamide)] diselenide (11), ()()-bis[2(--phenethylferrocenecarboxamide)] diselenide (12) were synthesized by the ortho-lithiation route. Bis[2-(N,N-dimethylaminomethylnaphthyl)] diselenide (13) was synthesized by lithium/bromide exchange reaction whereas bis(2,4-dinitrophenyl) diselenide (14) was prepared by the reaction of disodium diselenide with 2,4- dinitro-1-chlorobenzene. Thiol peroxidase-like activities of the diorganodiselenides have been evaluated by using H2O2 as substrate and PhSH as cosubstrate. Diselenides (13) and (14) with dimethylaminomethyl- or nitro-donor groups in close proximity to selenium, show much better thiol peroxidase-like activities compared to diselenides 10-12 with amide donor groups. Cyclic voltammetry study of diselenides 10-12 derived from redox-active ferrocenamide has been carried out.

  6. Lipid Regulated Intramolecular Conformational Dynamics of SNARE-Protein Ykt6

    Science.gov (United States)

    Dai, Yawei; Seeger, Markus; Weng, Jingwei; Song, Song; Wang, Wenning; Tan, Yan-Wen

    2016-08-01

    Cellular informational and metabolic processes are propagated with specific membrane fusions governed by soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNARE). SNARE protein Ykt6 is highly expressed in brain neurons and plays a critical role in the membrane-trafficking process. Studies suggested that Ykt6 undergoes a conformational change at the interface between its longin domain and the SNARE core. In this work, we study the conformational state distributions and dynamics of rat Ykt6 by means of single-molecule Förster Resonance Energy Transfer (smFRET) and Fluorescence Cross-Correlation Spectroscopy (FCCS). We observed that intramolecular conformational dynamics between longin domain and SNARE core occurred at the timescale ~200 μs. Furthermore, this dynamics can be regulated and even eliminated by the presence of lipid dodecylphoshpocholine (DPC). Our molecular dynamic (MD) simulations have shown that, the SNARE core exhibits a flexible structure while the longin domain retains relatively stable in apo state. Combining single molecule experiments and theoretical MD simulations, we are the first to provide a quantitative dynamics of Ykt6 and explain the functional conformational change from a qualitative point of view.

  7. Suppression of human immunodeficiency virus type 1 activity in vitro by oligonucleotides which form intramolecular tetrads.

    Science.gov (United States)

    Rando, R F; Ojwang, J; Elbaggari, A; Reyes, G R; Tinder, R; McGrath, M S; Hogan, M E

    1995-01-27

    An oligonucleotide (I100-15) composed of only deoxyguanosine and thymidine was able to inhibit human immunodeficiency virus type-1 (HIV-1) in culture assay systems. I100-15 did not block virus entry into cells but did reduce viral-specific transcripts. As assessed by NMR and polyacrylamide gel methods, I100-15 appears to form a structure in which two stacked guanosine tetrads are connected by three two-base long loops. Structure/activity experiments indicated that formation of intramolecular guanosine tetrads was necessary to achieve maximum antiviral activity. The single deoxyguanosine nucleotide present in each loop was found to be extremely important for the overall antiviral activity. The toxicity of I100-15 was determined to be well above the 50% effective dose (ED50) in culture which yielded a high therapeutic index (> 100). The addition of a cholesterol moiety to the 3' terminus of I100-15 (I100-23) reduced the ED50 value to less than 50 nM (from 0.12 microM for I100-15) and increased the duration of viral suppression to greater than 21 days (versus 7-10 days for I100-15) after removal of the drug from infected cell cultures. The favorable therapeutic index of such molecules coupled with the prolonged suppression of HIV-1, suggest that such compounds further warrant investigation as potential therapeutic agents. PMID:7829511

  8. Enantioselective approach to polycyclic polyprenylated acylphloroglucinols via catalytic asymmetric intramolecular cyclopropanation.

    Science.gov (United States)

    Uetake, Yuta; Uwamori, Masahiro; Nakada, Masahisa

    2015-02-01

    The formal enantioselective total synthesis of nemorosone, garsubellin A, clusianone, and hyperforin is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of an α-diazo ketone, a common synthetic intermediate for the above four polycyclic polyprenylated acylphloroglucinols previously reported by us, exhibited low enantioselectivity. However, CAIMCP of the corresponding α-diazo β-keto sulfone afforded the desired product in 79% yield with 84% ee. Investigation of the CAIMCP of the α-diazo β-keto sulfone demonstrated the formation of a rearrangement product in the presence of molecular sieves 4 Å, whereas, in the presence of H2O, the byproduct derived from ring-opening of the desired cyclopropane was observed. X-ray crystallographic analysis suggested that the above two products are derived from the same chiral intermediate. The product derived from ring-opening of the cyclopropane was successfully transformed to the respective synthetic intermediates for the total syntheses of nemorosone, garsubellin A, clusianone, and hyperforin, which had previously been reported by us. PMID:25581002

  9. Analysis of longitudinal vibration band gaps in periodic carbon nanotube intramolecular junctions using finite element method

    Science.gov (United States)

    Li, Jiaqian; Shen, Haijun

    2015-12-01

    The longitudinal vibration band gaps in periodic (n, 0)-(2n, 0) single-walled carbon nanotube(SWCNT) intramolecular junctions(IMJs) are investigated based on the finite element calculation. The frequency ranges of band gaps in frequency response functions(FRF) simulated by finite element method (FEM) show good agreement with those in band structure obtained by simple spring-mass model. Moreover, a comprehensive parametric study is also conducted to highlight the influences of the geometrical parameters such as the size of unit cell, component ratios of the IMJs and diameters of the CNT segments as well as geometric imperfections on the first band gap. The results show that the frequency ranges and the bandwidth of the gap strongly depend on the geometrical parameters. Furthermore, the influences of geometrical parameters on gaps are nuanced in IMJs with different topological defects. The existence of vibration band gaps in periodic IMJs lends a new insight into the development of CNT-based nano-devices in application of vibration isolation.

  10. Discovery of intramolecular trans-sialidases in human gut microbiota suggests novel mechanisms of mucosal adaptation

    Science.gov (United States)

    Tailford, Louise E.; Owen, C. David; Walshaw, John; Crost, Emmanuelle H.; Hardy-Goddard, Jemma; Le Gall, Gwenaelle; de Vos, Willem M.; Taylor, Garry L.; Juge, Nathalie

    2015-07-01

    The gastrointestinal mucus layer is colonized by a dense community of microbes catabolizing dietary and host carbohydrates during their expansion in the gut. Alterations in mucosal carbohydrate availability impact on the composition of microbial species. Ruminococcus gnavus is a commensal anaerobe present in the gastrointestinal tract of >90% of humans and overrepresented in inflammatory bowel diseases (IBD). Using a combination of genomics, enzymology and crystallography, we show that the mucin-degrader R. gnavus ATCC 29149 strain produces an intramolecular trans-sialidase (IT-sialidase) that cleaves off terminal α2-3-linked sialic acid from glycoproteins, releasing 2,7-anhydro-Neu5Ac instead of sialic acid. Evidence of IT-sialidases in human metagenomes indicates that this enzyme occurs in healthy subjects but is more prevalent in IBD metagenomes. Our results uncover a previously unrecognized enzymatic activity in the gut microbiota, which may contribute to the adaptation of intestinal bacteria to the mucosal environment in health and disease.

  11. On prediction of OH stretching frequencies in intramolecularly hydrogen bonded systems

    Science.gov (United States)

    Hansen, Poul Erik; Spanget-Larsen, Jens

    2012-06-01

    OH stretching frequencies are investigated for a series of non-tautomerizing systems with intramolecular hydrogen bonds. Effective OH stretching wavenumbers are predicted by the application of empirical correlation procedures based on the results of B3LYP/6-31G(d) theoretical calculations in the harmonic and PT2 anharmonic approximations, as well as on experimental NMR parameters, i.e., proton chemical shifts (δH) and two-bond deuterium isotope effects on 13C chemical shifts (2ΔCOD). The procedures are applied in a discussion of the spectra of 2,6-dihydroxy-4-methylbenzaldehyde and 8-hydroxyquinoline N-oxide. The spectrum of the former displays a broad, composite band between 3500 and 2500 cm-1 which can be assigned to overlapping monomer and dimer contributions. In the latter case, the results support a reassignment of the OH stretching band of 8-hydroxyquinoline N-oxide; the reassignment is supported by correlation with the IR spectra of a series of substituted derivatives.

  12. Regulation of activity of the yeast TATA-binding protein through intra-molecular interactions

    Indian Academy of Sciences (India)

    Perumal Vanathi; Anurag Kumar Mishra; Purnima Bhargava

    2003-06-01

    Dimerization is proposed to be a regulatory mechanism for TATA-binding protein (TBP) activity both in vitro and in vivo. The reversible dimer-monomer transition of TBP is influenced by the buffer conditions in vitro. Using in vitro chemical cross-linking, we found yeast TBP (yTBP) to be largely monomeric in the presence of the divalent cation Mg2+, even at high salt concentrations. Apparent molecular mass of yTBP at high salt with Mg2+, run through a gel filtration column, was close to that of monomeric yTBP. Lowering the monovalent ionic concentration in the absence of Mg2+, resulted in dimerization of TBP. Effect of Mg2+ was seen at two different levels: at higher TBP concentrations, it suppressed the TBP dimerization and at lower TBP levels, it helped keep TBP monomers in active conformation (competent for binding TATA box), resulting in enhanced TBP-TATA complex formation in the presence of increasing Mg2+. At both the levels, activity of the full-length TBP in the presence of Mg2+ was like that reported for the truncated C-terminal domain of TBP from which the N-terminus is removed. Therefore for full-length TBP, intra-molecular interactions can regulate its activity via a similar mechanism.

  13. Triggered Excited-State Intramolecular Proton Transfer Fluorescence for Selective Triplex DNA Recognition.

    Science.gov (United States)

    Wang, Ying; Hu, Yuehua; Wu, Tao; Zhou, Xiaoshun; Shao, Yong

    2015-12-01

    The triplex DNA has received much interest due to its various applications in gene regulation, molecular switch, and sensor development. However, realizing a highly selective recognition using a fluorescence probe specific only for the triplex topology is still a great challenge. Herein, we found that relative to the structural analogues of natural robinetin, myricetin, quercetin, kaempferol, morin, rutin, baicalin, luteolin, naringenin, genistein, chrysin, galangin, isorhamnetin, and several synthetic flavonoids, fisetin (FIS) is the brightest emitter when targeting the triplex DNA in contrast to binding with ss-DNA, ds-DNA (with or without an abasic site), i-motif, and DNA/RNA G-quadruplexes. Only the triplex association triggers the FIS green fluorescence that is relaxed from the tautomer favorable for excited-state intramolecular proton transfer (ESIPT). FIS can stabilize the triplex structure and primarily interact with the two terminals of the triplex via a 2:1 binding mode. This work demonstrates the potential of FIS as a DNA structure-selective switch-on ESIPT probe when evolving the triplex-forming oligonucleotides and developing the novel triplex-based sensors and switches. PMID:26556582

  14. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    DEFF Research Database (Denmark)

    Farver, O.; Zhang, Jingdong; Chi, Qijin;

    2001-01-01

    Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K-1 mol(-1)) and...... activation entropy difference and to compensate for the different temperature dependencies of E-0'. Thus, differences in driving force and thermal expansion appear as the most straightforward rationale for the observed isotope effect....... dependence of E-0' is also different, yielding entropy changes of -57 J K-1 mol-l in water and -84 J K-1 mol(-1) in deuterium oxide. The driving force difference of 10 mV is in keeping with the kinetic isotope effect, but the contribution to DeltaS(double dagger) from the temperature dependence of E-0' is...... positive rather than negative. Isotope effects are, however, also inherent in the nuclear reorganization Gibbs free energy and in the tunneling factor for the electron transfer process. A slightly larger thermal protein expansion in H2O than in D2O (0.001 nm K-1) is sufficient both to account for the...

  15. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    DEFF Research Database (Denmark)

    Farver, O; Zhang, J; Chi, Q;

    2001-01-01

    Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K(-1) mol(-1)) a...... account for the activation entropy difference and to compensate for the different temperature dependencies of E(0'). Thus, differences in driving force and thermal expansion appear as the most straightforward rationale for the observed isotope effect....... temperature dependence of E(0') is also different, yielding entropy changes of -57 J K(-1) mol(-1) in water and -84 J K(-1) mol(-1) in deuterium oxide. The driving force difference of 10 mV is in keeping with the kinetic isotope effect, but the contribution to DeltaS from the temperature dependence of E(0......') is positive rather than negative. Isotope effects are, however, also inherent in the nuclear reorganization Gibbs free energy and in the tunneling factor for the electron transfer process. A slightly larger thermal protein expansion in H(2)O than in D(2)O (0.001 nm K(-1)) is sufficient both to...

  16. Lipid Regulated Intramolecular Conformational Dynamics of SNARE-Protein Ykt6.

    Science.gov (United States)

    Dai, Yawei; Seeger, Markus; Weng, Jingwei; Song, Song; Wang, Wenning; Tan, Yan-Wen

    2016-01-01

    Cellular informational and metabolic processes are propagated with specific membrane fusions governed by soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNARE). SNARE protein Ykt6 is highly expressed in brain neurons and plays a critical role in the membrane-trafficking process. Studies suggested that Ykt6 undergoes a conformational change at the interface between its longin domain and the SNARE core. In this work, we study the conformational state distributions and dynamics of rat Ykt6 by means of single-molecule Förster Resonance Energy Transfer (smFRET) and Fluorescence Cross-Correlation Spectroscopy (FCCS). We observed that intramolecular conformational dynamics between longin domain and SNARE core occurred at the timescale ~200 μs. Furthermore, this dynamics can be regulated and even eliminated by the presence of lipid dodecylphoshpocholine (DPC). Our molecular dynamic (MD) simulations have shown that, the SNARE core exhibits a flexible structure while the longin domain retains relatively stable in apo state. Combining single molecule experiments and theoretical MD simulations, we are the first to provide a quantitative dynamics of Ykt6 and explain the functional conformational change from a qualitative point of view. PMID:27493064

  17. Polymer globule with fractal properties caused by intramolecular nanostructuring and spatial constrains.

    Science.gov (United States)

    Glagoleva, Anna A; Vasilevskaya, Valentina V; Khokhlov, Alexei R

    2016-06-21

    By means of computer simulation, we studied macromolecules composed of N dumbbell amphiphilic monomer units with attractive pendant groups. In poor solvents, these macromolecules form spherical globules that are dense in the case of short chains (the gyration radius RG∼N(1/3)), or hollow inside and obey the RG∼N(1/2) law when the macromolecules are sufficiently long. Due to the specific intramolecular nanostructuring, the vesicle-like globules of long amphiphilic macromolecules posses some properties of fractal globules, by which they (i) could demonstrate the same scaling statistics for the entire macromolecule and for short subchains with m monomer units and (ii) possess a specific territorial structure. Within a narrow slit, the globule loses its inner cavity, takes a disk-like shape and scales as N(1/2) for much shorter macromolecules. However, the field of end-to-end distance r(m) ∼m(1/2) dependence for subchains becomes visibly smaller. The results obtained were compared with the homopolymer case. PMID:27198966

  18. Dynamics of intramolecular spin exchange interaction of a nitronyl nitroxide diradical in solution and on surfaces

    Science.gov (United States)

    Lloveras, V.; Badetti, E.; Veciana, J.; Vidal-Gancedo, J.

    2016-02-01

    In this paper we report the study of the dynamics of a thermally modulated intramolecular spin exchange interaction of a novel diradical nitronyl nitroxide-substituted disulfide in solution and when it is grafted on a gold surface. The structure of this diradical was designed to have flexible chains leading to intramolecular collisions and hence spin exchange interaction, and with an appropriate binding group to be grafted on the gold surface to study its behavior on the surface. In solution, this diradical shows a strong spin exchange interaction between both radicals which is modulated by temperature, but also gold nanoparticles (AuNPs) functionalized with this diradical permit investigation of such a phenomenon in surface-grafted radicals. The spin-labelled AuNP synthesis was optimized to obtain high coverage of spin labels to lead to high spin exchange interaction. The obtained AuNPs were studied by Electron Paramagnetic Resonance (EPR), UV-Vis, and IR spectroscopies, HR-TEM microscopy, Cyclic Voltammetry (CV), Energy Dispersive X-ray analysis (EDX) and Thermogravimetric Analysis (TGA). This inorganic-organic hybrid material also showed dipolar interactions between its radicals which were confirmed by the appearance in the EPR spectra of an |Δms| = 2 transition at half-field. This signal gives direct evidence of the presence of a high-spin state and permitted us to study the nature of the magnetic coupling between the spins which was found to be antiferromagnetic. Self-Assembled Monolayers (SAMs) of these radicals on the Au (111) substrate were also prepared and studied by contact angle, X-Ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Cyclic Voltammetry and EPR. The magnetic as well as the electrochemical properties of the hybrid surfaces were studied and compared with the properties of this diradical in solution. Analogies between the properties of AuNPs with high coverage of radicals and those of SAM were

  19. Femtosecond Heterodyne Transient Grating Spectroscopic Studies of Intramolecular Charge Transfer Character of Peridinin and Peridinin Analogs

    Science.gov (United States)

    Bishop, Michael; Khosravi, Soroush; Obaid, Razib; Whitelock, Hope; Carroll, Ann Marie; Lafountain, Amy; Frank, Harry; Beck, Warren; Gibson, George; Berrah, Nora

    2016-05-01

    The peridinin chlorophyll-a protein is a light harvesting complex found in several species of dinoflagellates. Peridinin absorbs strongly in the mid-visible spectral region and, despite the lack of a strong permanent dipole moment in its lowest energy excited state, is able to transfer excitation energy quickly and efficiently to chlorophyll-a. It is believed that the high efficiency arises from the development of intramolecular charge-transfer (ICT) character upon photoexcitation. Recently, heterodyne transient grating spectroscopy has been used to study the ultrafast (ICT character in the case of peridinin, but up to now the work has not provided appropriate control experiments. The present experiments examine peridinin and two peridinin analogs, S1-peridinin and S2-peridinin. S1-peridinin is reported to have greatly diminished ICT character, and S2-peridinin is reported to have little-or-no ICT character. Heterodyne transient grating data will be presented and provide a more unambiguous characterization spectral and kinetic properties associated with the peridinin ICT state. Funded by the DoE-BES, Grant No. DE-SC0012376.

  20. General cell-binding activity of intramolecular G-quadruplexes with parallel structure.

    Directory of Open Access Journals (Sweden)

    Tianjun Chang

    Full Text Available G-quadruplexes (G4s are four-stranded nucleic acid structures adopted by some repetitive guanine-rich sequences. Putative G-quadruplex-forming sequences (PQSs are highly prevalent in human genome. Recently some G4s have been reported to have cancer-selective antiproliferative activity. A G4 DNA, AS1411, is currently in phase II clinical trials as an anticancer agent, which is reported to bind tumor cells by targeting surface nucleolin. AS1411 also has been extensively investigated as a target-recognition element for cancer cell specific drug delivery or cancer cell imaging. Here we show that, in addition to AS1411, intramolecular G4s with parallel structure (including PQSs in genes have general binding activity to many cell lines with different affinity. The binding of these G4s compete with each other, and their targets are certain cellular surface proteins. The tested G4s exhibit enhanced cellular uptake than non-G4 sequences. This uptake may be through the endosome/lysosome pathway, but it is independent of cellular binding of the G4s. The tested G4s also show selective antiproliferative activity that is independent of their cellular binding. Our findings provide new insight into the molecular recognition of G4s by cells; offer new clues for understanding the functions of G4s in vivo, and may extend the potential applications of G4s.

  1. Intramolecular interactions, isomerization and vibrational frequencies of two paracetamol analogues: A spectroscopic and a computational approach.

    Science.gov (United States)

    Viana, Rommel B; Ribeiro, Gabriela L O; Santos, Sinara F F; Quintero, David E; Viana, Anderson B; da Silva, Albérico B F; Moreno-Fuquen, Rodolfo

    2016-06-01

    The aim of this investigation was to determine the molecular properties and provide an interpretation of the vibrational mode couplings of these two paracetamol analogues: 2-bromo-2-methyl-N-(4-nitrophenyl)-propanamide and 2-bromo-2-methyl-N-p-tolyl-propanamide. E/Z isomers, keto/enol unimolecular rearrangement and prediction of the transition state structures in each mechanism were also assessed using the Density Functional Theory (DFT). The DFT estimates a high energy gap between E and Z isomers (9-11kcal·mol(-1)), with barrier heights ranging from 16 to 19kcal·mol(-1). In contrast, the barrier energies on the keto/enol isomerization are almost 10kcal·mol(-1) higher than those estimated for the E/Z rearrangement. The kinetic rate constant was also determined for each reaction mechanism. Natural bond orbital analysis and the quantum theory of atoms in molecules were used to interpret the intramolecular hydrogen bonds and to understand the most important interactions that govern the stabilization of each isomer. Furthermore, an analysis of the atomic charge distribution using different population methodologies was also performed. PMID:26974474

  2. Intramolecular interactions contributing for the conformational preference of bioactive diphenhydramine: Manifestation of the gauche effect

    Science.gov (United States)

    de Rezende, Fátima M. P.; Andrade, Laize A. F.; Freitas, Matheus P.

    2015-08-01

    Diphenhydramine is an antihistamine used to treat some symptoms of allergies and the common cold. It is usually marketed as the hydrochloride salt, and both the neutral and cation forms have the O-C-C-N fragment. The gauche effect is well known in fluorine-containing chains, because its main origin is hyperconjugative and the σ∗C-F is a low-lying acceptor orbital, allowing electron delocalization in the conformation where F and an adjacent electronegative substituent in an ethane fragment are in the gauche orientation. Our experimental (NMR) and theoretical findings indicate that diphenhydramine exhibits the gauche effect, since the preferential conformations have the O-C-C-N moiety in this orientation due especially to antiperiplanar σC-H → σ∗C-O and σC-H → σ∗C-N interactions. This conformational preference is strengthened in the protonated form due to an incremental electrostatic gauche effect. Because the gauche conformation matches the bioactive structure of diphenhydramine complexed with histamine methyltransferase, it is suggested that intramolecular interactions, and not only induced fit, rule its bioactive form.

  3. Analysis of longitudinal vibration band gaps in periodic carbon nanotube intramolecular junctions using finite element method

    Directory of Open Access Journals (Sweden)

    Jiaqian Li

    2015-12-01

    Full Text Available The longitudinal vibration band gaps in periodic (n, 0–(2n, 0 single-walled carbon nanotube(SWCNT intramolecular junctions(IMJs are investigated based on the finite element calculation. The frequency ranges of band gaps in frequency response functions(FRF simulated by finite element method (FEM show good agreement with those in band structure obtained by simple spring-mass model. Moreover, a comprehensive parametric study is also conducted to highlight the influences of the geometrical parameters such as the size of unit cell, component ratios of the IMJs and diameters of the CNT segments as well as geometric imperfections on the first band gap. The results show that the frequency ranges and the bandwidth of the gap strongly depend on the geometrical parameters. Furthermore, the influences of geometrical parameters on gaps are nuanced in IMJs with different topological defects. The existence of vibration band gaps in periodic IMJs lends a new insight into the development of CNT-based nano-devices in application of vibration isolation.

  4. Vibrational Spectroscopy of Intramolecular Hydrogen Bonds in the Infrared and Near-Infrared Regions

    DEFF Research Database (Denmark)

    Schrøder, Sidsel Dahl

    This PhD thesis describes the gas phase studies of four intramolecular hydrogen bonds: O-H···O (in methyl lactate), O-H···π (in methallyl carbinol and allyl carbinol), O-H···N (in methylated and triuoromethylated 2-aminoethanol) and N-H···N (in the diamines 1,2-diaminoethane, 1,3-diaminopropane and...... 1,4-diaminobutane). Experimentally, the hydrogen bonds have been studied with vibrational spectroscopy in the infrared and near-infrared regions. The focus is primarily on spectra recorded in the near-infrared regions, which in these studies are dominated by O-H and N-H stretching overtones...... spectra. The experimental characterization of hydrogen bonds have been complemented by theoretical analyzes. These analyzes are based on the electron density topology, natural bond orbital theory and visualization of the distribution of electrostatic potential energy in the molecules. In these studies...

  5. Self-consistent field/density functional study of conformational properties of polymers at interfaces: role of intramolecular interactions.

    Science.gov (United States)

    Bryk, Paweł; Macdowell, Luis G

    2008-09-14

    We study the properties of athermal polymers at hard walls using two different versions of self-consistent field theory (SCFT). We calculate the segment density profiles, center of mass profiles, bond orientation vector profiles, and end-to-end vector distributions and compare with grand canonical Monte Carlo simulations. Using the same excess free energy prescription for both theories, we investigate the role of the excluded volume intramolecular interactions on these properties, show the relation between SCFT and density functional theory, and discuss several numerical implementations of the SCFT method. The phantom chain model gives Gaussian chain statistics independent of the conditions. Including the full intramolecular potential leads to an improved description of the low density regime but it does not produce any significant improvement in the semidiluted and concentrated regimes. We show that a viable compromise is achieved by using the effective field resulting from the phantom chain model and by calculating single chain properties using the full intramolecular potential. PMID:19044937

  6. The intramolecular cyclization of bis-2,5-dimethylene-2,5-dihydrofurans and bis-2,5-dimethylene-2,5-dihydrothiophenes: An approach to macrocycles

    Energy Technology Data Exchange (ETDEWEB)

    Klumpp, D.A.

    1994-01-11

    The first two papers of this dissertation present our work with the intramolecular cyclizations of a pair of p-quinodimethanes. The p-quinodimethanes were generated by flash vacuum pyrolysis (FVP) and were linked by a bridging chain. The third paper of this dissertation presents our work in the synthetic manipulation of the products formed from the intramolecular reactions of the p-quinodimethanes.

  7. Nickel-Catalyzed Intramolecular [3 + 2 + 2] Cycloadditions of Alkylidenecyclopropanes. A Straightforward Entry to Fused 6,7,5-Tricyclic Systems

    OpenAIRE

    Saya Codesal, Lucía; Fernández, Israel; López, Fernando; Mascareñas Cid, José Luis

    2014-01-01

    A highly diastereo- and chemoselective intramolecular nickel-catalyzed cycloaddition of alkene- and alkyne-tethered alkynylidenecyclopropanes is reported. The method constitutes the first fully intramolecular [3 + 2 + 2] alkylidenecyclopropropane cycloaddition occurring via a proximal cleavage of the cyclopropane and makes it possible to build relevant 6,7,5-tricyclic frameworks in a single-pot reaction. Importantly, the reaction outcome is highly dependent on the characteristics of the nicke...

  8. Effect of substituent position on electrodeposition, morphology, and capacitance performance of polyindole bearing a carboxylic group

    International Nuclear Information System (INIS)

    Graphical abstract: The effect of carboxylic substituent position on the electrodeposition, morphology, and capacitance performance of substituted polyindole derivative nanowires were investigated for the first time. The results indicated that the position of the carboxylic substitution had remarkable impact on the diameter size and capacitance performance of these polymer nanowires. Furthermore, these polymers with high specific capacitance and excellent stability would be strong candidates as electrode material for supercapacitor. - Highlights: • Three carboxylic group substituted polyindole nanowires were synthesized. • Effect of substituent position on their morphology was firstly reported. • Effect of substituent position on their capacitance performance was reported. • The three polyindole nanowires showed excellent capacitance performance. - Abstract: In this paper, the effects of carboxylic substituent position on their electrodeposition, morphology and capacitance properties were investigated for the first time. The results indicated that three carboxylic group substituted polyindole derivatives nanowires, namely poly(indole-5-carboxylic acid) (5-PICA), poly(indole-6-carboxylic acid) (6-PICA), and poly(indole-7-carboxylic acid) (7-PICA), were successfully electrochemically synthesized in acetonitrile containing 0.1 M LiClO4, whereas poly(indole-4-carboxylic acid) (4-PICA) was difficult to be obtained. For 5-PICA, 6-PICA and 7-PICA nanowires, the diameters of nanowires demonstrated by the scanning electron microscopy were about 100 nm, 50 nm, and 30 nm, respectively. Their specific capacitances and energy densities in 1.0 M H2SO4 solution were measured to be 355 F g−1, 383 F g−1, 430 F g−1 at 2.5 A g−1 and 40.0, 43.1, 48.3 Wh kg−1 at a power density of 1125 W kg−1, respectively, and their specific capacitance retentions after 1000 charge/discharge processes reached 94.5%, 95.1%, and 96%, respectively. These results indicated that the

  9. Intramolecular Proton Transfer Boosts Water Oxidation Catalyzed by a Ru Complex.

    Science.gov (United States)

    Matheu, Roc; Ertem, Mehmed Z; Benet-Buchholz, Jordi; Coronado, Eugenio; Batista, Victor S; Sala, Xavier; Llobet, Antoni

    2015-08-26

    We introduce a new family of complexes with the general formula [Ru(n)(tda)(py)2](m+) (n = 2, m = 0, 1; n = 3, m = 1, 2(+); n = 4, m = 2, 3(2+)), with tda(2-) being [2,2':6',2″-terpyridine]-6,6″-dicarboxylate, including complex [Ru(IV)(OH)(tda-κ-N(3)O)(py)2](+), 4H(+), which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 3(2+) under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV-vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), including solid-state monocrystal X-ray diffraction analysis. In oxidation state IV, the Ru center is seven-coordinated and diamagnetic, whereas in oxidation state II, the complex has an unbonded dangling carboxylate and is six-coordinated while still diamagnetic. With oxidation state III, the coordination number is halfway between the coordination of oxidation states II and IV. Species generated in situ have also been characterized by spectroscopic, computational, and electrochemical techniques, together with the related species derived from a different degree of protonation and oxidation states. 4H(+) can be generated potentiometrically, or voltammetrically, from 3(2+), and both coexist in solution. While complex 3(2+) is not catalytically active, the catalytic performance of complex 4H(+) is characterized by the foot of the wave analysis, giving an impressive turnover frequency record of 8000 s(-1) at pH 7.0 and 50 000 s(-1) at pH 10.0. Density functional theory calculations provide a complete description of the water oxidation catalytic cycle of 4H(+), manifesting the key functional role of the dangling carboxylate in lowering the activation free energies that lead to O-O bond formation. PMID:26226390

  10. 分子内酰基化反应合成新型六环稠杂环化合物%Synthesis of Novel Hexacyclic -fused Heterocyclic Compounds via Intramolecular Friedel -Crafts Acylation

    Institute of Scientific and Technical Information of China (English)

    聂成铭; 徐良玉; 李阳; 高文涛

    2013-01-01

    The hitherto unreported benzo[h]naphtho[1′,2′,6,7]oxepino[3,4-b] quinolin-17(8H) -one (3a) was synthesized by the intramolecular Friedel -Crafts acylation reaction of 2 -(( naphthalen -2 -yloxy)methyl)benzo[h]quinoline -3-carboxylic acid 2 under the treatment of Eaton′s reagent (P2O5 -Me-SO3 ) .The precursor 2 was prepared through one -pot reaction of ethyl 2-( chloromethyl ) benzo [ h] quinoline-3-carboxylate 1 with α-naphthol or β-naphthol .The substrate 1 was obtained in good yield by a mild , effi-cient and direct reaction of α-naphthylamine with 4 -chloroacetoacetate under the treatment of Vilsmeier -Haack reagent.The structures of all the new compounds were identified by ESI -MS, IR, NMR spectra and Ele-mental analysis .%以2-氯甲基-3-苯并喹啉甲酸乙酯(1)为底物与α-萘酚、β-萘酚反应经“一锅法”合成了中间体2-(α-萘氧甲基)苯并[ h]喹啉-3-羧酸(2a)、2-(β-萘氧甲基)苯并[ H]喹啉-3-羧酸(2b)。化合物2a,2b在Eaton′s试剂作用下合成两种新型六环稠杂环化合物萘并[2′,1′,6,7]氧杂卓并[3,4-b]苯并喹啉-7(14H)-酮(3a)和萘并[1′,2′,6,7]氧杂卓并[3,4-b]苯并喹啉-15(8H)-酮(3b)。化合物2a,2b发生分子内傅一克酰基化闭环反应,所合成的新化合物2a、2b、3a、3b的结构经红外光谱、核磁共振谱、质谱及元素分析等得以确认。

  11. Density Functional Theory Study on the Interactions of Metal Ions with Long Chain Deprotonated Carboxylic Acids.

    Science.gov (United States)

    Mehandzhiyski, Aleksandar Y; Riccardi, Enrico; van Erp, Titus S; Koch, Henrik; Åstrand, Per-Olof; Trinh, Thuat T; Grimes, Brian A

    2015-10-01

    In this work, interactions between carboxylate ions and calcium or sodium ions are investigated via density functional theory (DFT). Despite the ubiquitous presence of these interactions in natural and industrial chemical processes, few DFT studies on these systems exist in the literature. Special focus has been placed on determining the influence of the multibody interactions (with up to 4 carboxylates and one metal ion) on an effective pair-interaction potential, such as those used in molecular mechanics (MM). Specifically, DFT calculations are employed to quantify an effective pair-potential that implicitly includes multibody interactions to construct potential energy curves for carboxylate-metal ion pairs. The DFT calculated potential curves are compared to a widely used molecular mechanics force field (OPLS-AA). The calculations indicate that multibody effects do influence the energetic behavior of these ionic pairs and the extent of this influence is determined by a balance between (a) charge transfer from the carboxylate to the metal ions which stabilizes the complex and (b) repulsion between carboxylates, which destabilizes the complex. Additionally, the potential curves of the complexes with 1 and 2 carboxylates and one counterion have been examined to higher separation distance (20 Å) by the use of relaxed scan optimization and constrained density functional theory (CDFT). The results from the relaxed scan optimization indicate that near the equilibrium distance, the charge transfer between the metal ion and the deprotonated carboxylic acid group is significant and leads to non-negligible differences between the DFT and MM potential curves, especially for calcium. However, at longer separation distances the MM calculated interaction potential functions converge to those calculated with CDFT, effectively indicating the approximate domain of the separation distance coordinate where charge transfer between the ions is occurring. PMID:26331433

  12. Ozone-driven photochemical formation of carboxylic acid groups from alkane groups

    Directory of Open Access Journals (Sweden)

    S. Liu

    2011-03-01

    Full Text Available Carboxylic acids are ubiquitous in atmospheric particles, and they play an important role in the physical and chemical properties of aerosol particles. During measurements in coastal California in the summer of 2009, carboxylic acid functional groups were highly associated with trajectories from an industrial region with high organic mass (OM, likely from fossil fuel combustion emissions. The concentration of carboxylic acid groups peaked during daytime, suggesting a photochemical secondary formation mechanism. This daytime increase in concentration was tightly correlated with O3 mixing ratio, indicating O3 was the likely driver in acid formation. Based on the diurnal cycles of carboxylic acid and alkane groups, the covariation of carboxylic acid groups with O3, and the composition of the Combustion factor resulted from the factor analyses, gas-phase alkane oxidation by OH radicals to form dihyfrofuran followed by further oxidation of dihydrofuran by O3 is the likely acid formation mechanism. Using the multi-day average of the daytime increase of carboxylic acid group concentrations and m/z 44-based Aged Combustion factor, we estimated the lower-bound contributions of secondary organic aerosol (SOA formed in 12-h daytime of processing in a single day to be 30% of the carboxylic acid groups and 25–45% of the Combustion factor concentration. These unique ambient observations of photochemically-driven acid formation suggest that gas-phase alkanes might be important sources of SOA formation in this coastal region.

  13. Photoelectrochemical properties of WO3 nanoparticulate thin films prepared by carboxylic acid-assisted electrodeposition

    International Nuclear Information System (INIS)

    Optimisation of particle sizes of WO3 films is important for photoelectrochemical applications. However, most of the developed size-controlled synthesis techniques involve complicated instruments or vacuum systems. The present work presents an alternative method using carboxylic acid-assisted electrodeposition where WO3 thin films were deposited from peroxotungstic acid (PTA) solution containing different carboxylic acids (formic, oxalic, citric). The effects of carboxylic acids on the electrodeposition and the resultant morphological, mineralogical, optical, and photoelectrochemical properties of the WO3 films were investigated. The analysis showed that the films consisted of equiaxed nanoparticulate monoclinic WO3. The deposition thicknesses and the average grain (individual particle and agglomerate) sizes of the films were dependent on the amount of hydronium ions and the molecular weight and associated sizes of the conjugate bases released upon the dissociation of carboxylic acids in the PTA solutions, which result in hydrogen bond formation and molecular dispersion. The photocurrent densities of the films deposited with carboxylic acids were greater than that of the film deposited from pure PTA. These differences were attributed to improvements in (1) grain size, which controls photogenerated electron-hole transport, and (2) effective grain boundary area, which controls the numbers of active reaction sites and electron-hole recombination sites. - Highlights: • Carboxylic acid-assisted electrodeposition of WO3 films from peroxotungstic acid. • The types of carboxylic acids control the deposition rates and microstructure. • WO3 grain sizes and effective grain boundary areas determine the photocurrents. • Maximal photocurrent measured in the smallest-aggregate films (∼ 83 nm)

  14. Asymmetric synthesis of crambescin A-C carboxylic acids and their inhibitory activity on voltage-gated sodium channels.

    Science.gov (United States)

    Nakazaki, Atsuo; Nakane, Yoshiki; Ishikawa, Yuki; Yotsu-Yamashita, Mari; Nishikawa, Toshio

    2016-06-21

    Synthesis of both enantiomers of crambescin B carboxylic acid is described. A cis-enyne starting material was epoxidized under the conditions of Katsuki asymmetric epoxidation to give 95% ee of the epoxide, which was transformed to crambescin B carboxylic acid via bromocation-triggered cascade cyclization as the key step. Enantiomerically pure crambescin A and C carboxylic acids were also synthesized from the product of the cascade reaction. Structure-activity relationship (SAR) studies against voltage-gated sodium channel (VGSC) inhibition using those synthetic compounds revealed that the natural enantiomer of crambescin B carboxylic acid was most active and comparable to tetrodotoxin, and the unalkylated cyclic guanidinium structure is indispensible, while the carboxylate moiety is not important. The absolute stereochemistry of crambescin A was determined by a comparison of the methyl ester derived from natural crambescin A with that derived from the stereochemically defined crambescin A carboxylic acid synthesized in this study. PMID:27215973

  15. Interaction Between the Biotin Carboxyl Carrier Domain and the Biotin Carboxylase Domain in Pyruvate Carboxylase from Rhizobium etli†

    OpenAIRE

    Lietzan, Adam D.; Menefee, Ann L.; Zeczycki, Tonya N.; Kumar, Sudhanshu; Attwood, Paul V.; Wallace, John C.; Cleland, W. Wallace; Maurice, Martin St.

    2011-01-01

    Pyruvate carboxylase (PC) catalyzes the ATP-dependent carboxylation of pyruvate to oxaloacetate, an important anaplerotic reaction in mammalian tissues. To effect catalysis, the tethered biotin of PC must gain access to active sites in both the biotin carboxylase domain and the carboxyl transferase domain. Previous studies have demonstrated that a mutation of threonine 882 to alanine in PC from Rhizobium etli renders the carboxyl transferase domain inactive and favors the positioning of bioti...

  16. Phosphorescent emissions of phosphine copper(I) complexes bearing 8-hydroxyquinoline carboxylic acid analogue ligands

    International Nuclear Information System (INIS)

    The pseudotetrahedral complexes of [Cu(PPh3)2(L)], where L=8-hydroxy-2-methylquinoline-7-carboxylic acid (1), 8-hydroxy-2,5-dimethylquinoline-7-carboxylic acid (2) or 5-chloro-8-hydroxy-2-methylquinoline-7-carboxylic acid (3) have been synthesized and structurally characterized by X-ray crystallography. Their properties have been examined through combinations of IR, NMR, electronic absorption spectroscopy and cyclic voltammetry. The complexes exhibit extraordinary photophysical properties. Complex (1) in solid state exhibits an emission quantum yield of 4.67% and an excited life time of 1.88 ms (frozen DCM solution up to 6.7 ms). When dissolved in a coordinating solvent (acetonitrile) the charge transfer emission was quenched on a microsecond scale. - Highlights: • Synthesis of copper(I) complexes with 8-hydroxyquinoline carboxylic acid ligands. • Very long lived phosphorescent copper(I) complexes. • [Cu(PPh3)2(L)] where L=8-hydroxy-2-methylquinoline-7-carboxylic acid luminesce in the solid state exhibits extremely long lifetime on millisecond scale (1.9 ms). • In frozen MeOH:EtOH solution lifetime increases to 7 ms. • Quantum efficiency equal to 4.7%

  17. Phosphorescent emissions of phosphine copper(I) complexes bearing 8-hydroxyquinoline carboxylic acid analogue ligands

    Energy Technology Data Exchange (ETDEWEB)

    Małecki, Jan G., E-mail: gmalecki@us.edu.pl [Department of Crystallography, Institute of Chemistry, University of Silesia, Szkolna 9 street, 40-006 Katowice (Poland); Łakomska, Iwona, E-mail: iwolak@chem.umk.pl [Department of Chemistry, Nicolaus Copernicus University, Toruń (Poland); Maroń, Anna [Department of Crystallography, Institute of Chemistry, University of Silesia, Szkolna 9 street, 40-006 Katowice (Poland); Szala, Marcin [Institute of Chemistry, University of Silesia, ul. Szkolna 9, 40-006 Katowice (Poland); Fandzloch, Marzena [Department of Chemistry, Nicolaus Copernicus University, Toruń (Poland); Nycz, Jacek E., E-mail: jacek.nycz@us.edu.pl [Institute of Chemistry, University of Silesia, ul. Szkolna 9, 40-006 Katowice (Poland)

    2015-05-15

    The pseudotetrahedral complexes of [Cu(PPh{sub 3}){sub 2}(L)], where L=8-hydroxy-2-methylquinoline-7-carboxylic acid (1), 8-hydroxy-2,5-dimethylquinoline-7-carboxylic acid (2) or 5-chloro-8-hydroxy-2-methylquinoline-7-carboxylic acid (3) have been synthesized and structurally characterized by X-ray crystallography. Their properties have been examined through combinations of IR, NMR, electronic absorption spectroscopy and cyclic voltammetry. The complexes exhibit extraordinary photophysical properties. Complex (1) in solid state exhibits an emission quantum yield of 4.67% and an excited life time of 1.88 ms (frozen DCM solution up to 6.7 ms). When dissolved in a coordinating solvent (acetonitrile) the charge transfer emission was quenched on a microsecond scale. - Highlights: • Synthesis of copper(I) complexes with 8-hydroxyquinoline carboxylic acid ligands. • Very long lived phosphorescent copper(I) complexes. • [Cu(PPh{sub 3}){sub 2}(L)] where L=8-hydroxy-2-methylquinoline-7-carboxylic acid luminesce in the solid state exhibits extremely long lifetime on millisecond scale (1.9 ms). • In frozen MeOH:EtOH solution lifetime increases to 7 ms. • Quantum efficiency equal to 4.7%.

  18. Synthesis, spectroscopic characterization, biological screenings, DNA binding study and POM analyses of transition metal carboxylates

    Science.gov (United States)

    Uddin, Noor; Sirajuddin, Muhammad; Uddin, Nizam; Tariq, Muhammad; Ullah, Hameed; Ali, Saqib; Tirmizi, Syed Ahmed; Khan, Abdur Rehman

    2015-04-01

    This article contains the synthesis of a novel carboxylic acid derivative, its transition metal complexes and evaluation of biological applications. Six carboxylate complexes of transition metals, Zn(II) and Hg(II), have been successfully synthesized and characterized by FT-IR and NMR (1H, 13C). The ligand, HL, (4-[(2,6-Diethylphenyl)amino]-4-oxobutanoic acid) was also characterized by single crystal X-ray analysis. The complexation occurs via oxygen atoms of the carboxylate moiety. FT-IR date show the bidentate nature of the carboxylate moiety of the ligand as the Δν value in all complexes is less than that of the free ligand. The ligand and its complexes were screened for antifungal and antileishmanial activities. The results showed that the ligand and its complexes are active with few exceptions. UV-visible spectroscopy and viscometry results reveal that the ligand and its complexes interact with the DNA via intercalative mode of interaction. A new and efficient strategy to identify the pharmacophores and anti-pharmacophores sites in carboxylate derivatives for the antibacterial/antifungal activity using Petra, Osiris and Molinspiration (POM) analyses was also carried out.

  19. Improved antifouling properties of polyamide nanofiltration membranes by reducing the density of surface carboxyl groups.

    Science.gov (United States)

    Mo, Yinghui; Tiraferri, Alberto; Yip, Ngai Yin; Adout, Atar; Huang, Xia; Elimelech, Menachem

    2012-12-18

    Carboxyls are inherent functional groups of thin-film composite polyamide nanofiltration (NF) membranes, which may play a role in membrane performance and fouling. Their surface presence is attributed to incomplete reaction of acyl chloride monomers during the membrane active layer synthesis by interfacial polymerization. In order to unravel the effect of carboxyl group density on organic fouling, NF membranes were fabricated by reacting piperazine (PIP) with either isophthaloyl chloride (IPC) or the more commonly used trimesoyl chloride (TMC). Fouling experiments were conducted with alginate as a model hydrophilic organic foulant in a solution, simulating the composition of municipal secondary effluent. Improved antifouling properties were observed for the IPC membrane, which exhibited lower flux decline (40%) and significantly greater fouling reversibility or cleaning efficiency (74%) than the TMC membrane (51% flux decline and 40% cleaning efficiency). Surface characterization revealed that there was a substantial difference in the density of surface carboxyl groups between the IPC and TMC membranes, while other surface properties were comparable. The role of carboxyl groups was elucidated by measurements of foulant-surface intermolecular forces by atomic force microscopy, which showed lower adhesion forces and rupture distances for the IPC membrane compared to TMC membranes in the presence of calcium ions in solution. Our results demonstrated that a decrease in surface carboxyl group density of polyamide membranes fabricated with IPC monomers can prevent calcium bridging with alginate and, thus, improve membrane antifouling properties. PMID:23205860

  20. Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: Temperature dependence

    International Nuclear Information System (INIS)

    Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO4) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-ΔGr) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO4 concentrations, and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (-ΔGr), the former in ethanol and ACN increases only linearly with the increase in driving force (-ΔGr). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.

  1. Intramolecular allosteric communication in dopamine D2 receptor revealed by evolutionary amino acid covariation.

    Science.gov (United States)

    Sung, Yun-Min; Wilkins, Angela D; Rodriguez, Gustavo J; Wensel, Theodore G; Lichtarge, Olivier

    2016-03-29

    The structural basis of allosteric signaling in G protein-coupled receptors (GPCRs) is important in guiding design of therapeutics and understanding phenotypic consequences of genetic variation. The Evolutionary Trace (ET) algorithm previously proved effective in redesigning receptors to mimic the ligand specificities of functionally distinct homologs. We now expand ET to consider mutual information, with validation in GPCR structure and dopamine D2 receptor (D2R) function. The new algorithm, called ET-MIp, identifies evolutionarily relevant patterns of amino acid covariations. The improved predictions of structural proximity and D2R mutagenesis demonstrate that ET-MIp predicts functional interactions between residue pairs, particularly potency and efficacy of activation by dopamine. Remarkably, although most of the residue pairs chosen for mutagenesis are neither in the binding pocket nor in contact with each other, many exhibited functional interactions, implying at-a-distance coupling. The functional interaction between the coupled pairs correlated best with the evolutionary coupling potential derived from dopamine receptor sequences rather than with broader sets of GPCR sequences. These data suggest that the allosteric communication responsible for dopamine responses is resolved by ET-MIp and best discerned within a short evolutionary distance. Most double mutants restored dopamine response to wild-type levels, also suggesting that tight regulation of the response to dopamine drove the coevolution and intramolecular communications between coupled residues. Our approach provides a general tool to identify evolutionary covariation patterns in small sets of close sequence homologs and to translate them into functional linkages between residues. PMID:26979958

  2. Intramolecular interactions in aminoacyl nucleotides: Implications regarding the origin of genetic coding and protein synthesis

    Science.gov (United States)

    Lacey, J. C., Jr.; Mullins, D. W., Jr.; Watkins, C. L.; Hall, L. M.

    1986-01-01

    Cellular organisms store information as sequences of nucleotides in double stranded DNA. This information is useless unless it can be converted into the active molecular species, protein. This is done in contemporary creatures first by transcription of one strand to give a complementary strand of mRNA. The sequence of nucleotides is then translated into a specific sequence of amino acids in a protein. Translation is made possible by a genetic coding system in which a sequence of three nucleotides codes for a specific amino acid. The origin and evolution of any chemical system can be understood through elucidation of the properties of the chemical entities which make up the system. There is an underlying logic to the coding system revealed by a correlation of the hydrophobicities of amino acids and their anticodonic nucleotides (i.e., the complement of the codon). Its importance lies in the fact that every amino acid going into protein synthesis must first be activated. This is universally accomplished with ATP. Past studies have concentrated on the chemistry of the adenylates, but more recently we have found, through the use of NMR, that we can observe intramolecular interactions even at low concentrations, between amino acid side chains and nucleotide base rings in these adenylates. The use of this type of compound thus affords a novel way of elucidating the manner in which amino acids and nucleotides interact with each other. In aqueous solution, when a hydrophobic amino acid is attached to the most hydrophobic nucleotide, AMP, a hydrophobic interaction takes place between the amino acid side chain and the adenine ring. The studies to be reported concern these hydrophobic interactions.

  3. Intramolecular electron transfer in ruthenium-modified cytochrome C: Driving force effects

    International Nuclear Information System (INIS)

    The measurement of intramolecular electron transfer rates in several cis- and trans- tetraammine(L)-ruthenium-His33-modified horse heart cytochromes c (L = isonicotinamide, pyridine, N-methylpyrazinium, and H2O/OH) is reported herein. Activation parameters have also been obtained for L = isonicotinamide and pyridine. Only modest rate increases are observed for large changes in driving force (from L = pyridine to N-methylpyrazinium). The heme-to-ruthenium electron transfer rates for L = isonicotinamide, pyridine, and N-methylpyrazinium were measured by oxidation of the fully reduced complexes by radiolytically-generated carbonate (CO3-) radical. From previously reported work and these results, it is clear that the oxidative and reductive methods do not result in production of the same electron transfer intermediate. Possible reasons for this will be discussed. It is important to consider the effects of the local protein environment on the properties of the ruthenium center. There is a general effect of moderation of reduction potentials; that is to say that protein-bound high-potential complexes have lower reduction potentials than their small molecule models. The reverse holds for the low potential complexes. This effect can be a significant source of error in driving force estimates based on model complexes. Identification of the operative electron transfer mechanism remains an unsolved problem. Efforts will be made to increase the driving force further (within the constraints of the heme-ruthenium system) to determine the applicable reorganization parameters. Interpretation will be aided by parallel investigations into the effects of protein conformation and the distance dependences of through-bond and through-space electron transfer mechanisms

  4. Absence of Vitamin K-Dependent γ-Carboxylation in Human Periostin Extracted from Fibrotic Lung or Secreted from a Cell Line Engineered to Optimize γ-Carboxylation

    Science.gov (United States)

    Annis, Douglas S.; Ma, Hanqing; Balas, Danika M.; Kumfer, Kraig T.; Sandbo, Nathan; Potts, Gregory K.; Coon, Joshua J.; Mosher, Deane F.

    2015-01-01

    Periostin (PN, gene name POSTN) is an extracellular matrix protein that is up-regulated in bronchial epithelial cells and lung fibroblasts by TH-2 cytokines. Its paralog, TGF-β-induced protein (βig-h3, gene name TGFBI), is also expressed in the lung and up-regulated in bronchial myofibroblasts by TGF-β. PN and βig-h3 contain fasciclin 1 modules that harbor putative recognition sequences for γ-glutamyl carboxylase and are annotated in UniProt as undergoing vitamin K-dependent γ-carboxylation of multiple glutamic acid residues. γ-carboxylation profoundly alters activities of other proteins subject to the modification, e.g., blood coagulation factors, and would be expected to alter the structure and function of PN and βig-h3. To analyze for the presence of γ-carboxylation, proteins extracted from fibrotic lung were reacted with monoclonal antibodies specific for PN, βig-h3, or modification with γ-carboxyglutamic acid (Gla). In Western blots of 1-dimensional gels, bands stained with anti-PN or -βig-h3 did not match those stained with anti-Gla. In 2-dimensional gels, anti-PN-positive spots had pIs of 7.0 to >8, as expected for the unmodified protein, and there was no overlap between anti-PN-positive and anti-Gla-positive spots. Recombinant PN and blood coagulation factor VII were produced in HEK293 cells that had been transfected with vitamin K 2, 3-epoxide reductase C1 to optimize γ-carboxylation. Recombinant PN secreted from these cells did not react with anti-Gla antibody and had pIs similar to that found in extracts of fibrotic lung whereas secreted factor VII reacted strongly with anti-Gla antibody. Over 67% coverage of recombinant PN was achieved by mass spectrometry, including peptides with 19 of the 24 glutamates considered targets of γ-carboxylation, but analysis revealed no modification. Over 86% sequence coverage and three modified glutamic acid residues were identified in recombinant fVII. These data indicate that PN and βig-h3 are not subject

  5. Absence of Vitamin K-Dependent γ-Carboxylation in Human Periostin Extracted from Fibrotic Lung or Secreted from a Cell Line Engineered to Optimize γ-Carboxylation.

    Directory of Open Access Journals (Sweden)

    Douglas S Annis

    Full Text Available Periostin (PN, gene name POSTN is an extracellular matrix protein that is up-regulated in bronchial epithelial cells and lung fibroblasts by TH-2 cytokines. Its paralog, TGF-β-induced protein (βig-h3, gene name TGFBI, is also expressed in the lung and up-regulated in bronchial myofibroblasts by TGF-β. PN and βig-h3 contain fasciclin 1 modules that harbor putative recognition sequences for γ-glutamyl carboxylase and are annotated in UniProt as undergoing vitamin K-dependent γ-carboxylation of multiple glutamic acid residues. γ-carboxylation profoundly alters activities of other proteins subject to the modification, e.g., blood coagulation factors, and would be expected to alter the structure and function of PN and βig-h3. To analyze for the presence of γ-carboxylation, proteins extracted from fibrotic lung were reacted with monoclonal antibodies specific for PN, βig-h3, or modification with γ-carboxyglutamic acid (Gla. In Western blots of 1-dimensional gels, bands stained with anti-PN or -βig-h3 did not match those stained with anti-Gla. In 2-dimensional gels, anti-PN-positive spots had pIs of 7.0 to >8, as expected for the unmodified protein, and there was no overlap between anti-PN-positive and anti-Gla-positive spots. Recombinant PN and blood coagulation factor VII were produced in HEK293 cells that had been transfected with vitamin K 2, 3-epoxide reductase C1 to optimize γ-carboxylation. Recombinant PN secreted from these cells did not react with anti-Gla antibody and had pIs similar to that found in extracts of fibrotic lung whereas secreted factor VII reacted strongly with anti-Gla antibody. Over 67% coverage of recombinant PN was achieved by mass spectrometry, including peptides with 19 of the 24 glutamates considered targets of γ-carboxylation, but analysis revealed no modification. Over 86% sequence coverage and three modified glutamic acid residues were identified in recombinant fVII. These data indicate that PN and

  6. Novel Regenerated Solvent Extraction Processes for the Recovery of Carboxylic Acids or Ammonia from Aqueous Solutions Part I. Regeneration of Amine-Carboxylic Acid Extracts

    Energy Technology Data Exchange (ETDEWEB)

    Poole, L.J.; King, C.J.

    1990-03-01

    Two novel regenerated solvent extraction processes are examined. The first process has the potential to reduce the energy costs inherent in the recovery of low-volatility carboxylic acids from dilute aqueous solutions. The second process has the potential for reducing the energy costs required for separate recovery of ammonia and acid gases (e.g. CO{sub 2} and H{sub 2}S) from industrial sour waters. The recovery of carboxylic acids from dilute aqueous solution can be achieved by extraction with tertiary amines. An approach for regeneration and product recovery from such extracts is to back-extract the carboxylic acid with a water-soluble, volatile tertiary amine, such as trimethylamine. The resulting trimethylammonium carboxylate solution can be concentrated and thermally decomposed, yielding the product acid and the volatile amine for recycle. Experimental work was performed with lactic acid, succinic acid, and fumaric acid. Equilibrium data show near-stoichiometric recovery of the carboxylic acids from an organic solution of Alamine 336 into aqueous solutions of trimethylamine. For fumaric and succinic acids, partial evaporation of the aqueous back extract decomposes the carboxylate and yields the acid product in crystalline form. The decomposition of aqueous solutions of trimethylammonium lactates was not carried out to completion, due to the high water solubility of lactic acid and the tendency of the acid to self-associate. The separate recovery of ammonia and acid gases from sour waters can be achieved by combining steam-stripping of the acid gases with simultaneous removal of ammonia by extraction with a liquid cation exchanger. The use of di-2,4,4-trimethylpentyl phosphinic acid as the liquid cation exchanger is explored in this work. Batch extraction experiments were carried out to measure the equilibrium distribution ratio of ammonia between an aqueous buffer solution and an organic solution of the phosphinic acid (0.2N) in Norpar 12. The concentration

  7. Ethyl 2-phenyl-5,6-dihydropyrrolo[2,1-a]isoquinoline-3-carboxylate

    Directory of Open Access Journals (Sweden)

    Zhao-Peng Yu

    2012-07-01

    Full Text Available In the title compound, C21H19NO2, the six-membered heterocycle assumes a screw-boat conformation. The phenyl ring is oriented with respect to the pyrrole ring at a dihedral angle of 64.76 (10°. An intramolecular C—H...O hydrogen bond helps to stabilize the molecular structure. There are weak C—H...π interactions between inversion-related molecules in the crystal.

  8. tert-Butyl 2-borono-1H-pyrrole-1-carboxylate

    Directory of Open Access Journals (Sweden)

    Zheng Zhong

    2009-04-01

    Full Text Available In the crystal structure of the title compound, C9H14BNO4, the boronic acid group and carbamate groups are nearly co-planar with the pyrrole ring, making dihedral angles of 0.1 (2 and 2.2 (2°, respectively. Intramolecular and intermolecular O—H...O hydrogen bonds help to stabilize the structure, the latter interaction leading to inversion dimers..

  9. CMPO-calix[4]arenes with spacer containing intramolecular hydrogen bonding: Effect of local rigidification on solvent extraction toward f-block elements

    International Nuclear Information System (INIS)

    Highlights: • Three CMPO-calix[4]arenes with spacer containing intramolecular hydrogen bonds were designed and synthesized. • The influence of local rigidification caused by intramolecular hydrogen bonds upon extraction of f-elements was investigated. • Selective extraction is realized via tuning local chelating surroundings by aid of intramolecular hydrogen bonds. -- Abstract: To understand intramolecular hydrogen bonding in effecting liquid–liquid extraction behavior of CMPO-calixarenes, three CMPO-modified calix[4]arenes (CMPO-CA) 5a–5c with hydrogen-bonded spacer were designed and synthesized. The impact of spacer rotation that is hindered by introduction of intramolecular hydrogen bonding upon extraction of La3+, Eu3+, Yb3+, Th4+, and UO22+ has been examined. The results show that 5b and 5c containing only one hydrogen bond with a less hindered rotation spacer extract La3+ more efficiently than 5a containing two hydrogen bonds with a more hindered rotation spacer, demonstrating the importance of local rigidification of spacer in the design of extractants in influencing the coordination environment. The large difference in extractability between La3+ and Yb3+ (or Eu3+) by 5b (or 5c), and the small difference by 5a, suggests intramolecular hydrogen bonding do exert pronounced influence upon selective extraction of light and heavy lanthanides. Log–log plot analysis indicates a 1:1, 2:1 and 1:1 stoichiometry (ligand/metal) for the extracted complex formed between 5b and La3+, Th4+, UO22+, respectively. Additionally, their corresponding acyclic analogs 7a–7c exhibit negligible extraction toward these metal ions. These results reveal the possibility of selective extraction via tuning local chelating surroundings of CMPO-CA by aid of intramolecular hydrogen bonding

  10. CMPO-calix[4]arenes with spacer containing intramolecular hydrogen bonding: Effect of local rigidification on solvent extraction toward f-block elements

    Energy Technology Data Exchange (ETDEWEB)

    Chu, Hongzhu; He, Lutao; Jiang, Qian; Fang, Yuyu; Jia, Yiming; Yuan, Xiangyang; Zou, Shuliang; Li, Xianghui [Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, College of Chemistry, Sichuan University, Chengdu 610064 (China); Feng, Wen, E-mail: wfeng9510@scu.edu.cn [Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, College of Chemistry, Sichuan University, Chengdu 610064 (China); Yang, Yuanyou; Liu, Ning [Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, College of Chemistry, Sichuan University, Chengdu 610064 (China); Luo, Shunzhong; Yang, Yanqiu; Yang, Liang [Institute of Nuclear Physics and Chemistry, CAEP, Mianyang 621900 (China); Yuan, Lihua, E-mail: lhyuan@scu.edu.cn [Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, College of Chemistry, Sichuan University, Chengdu 610064 (China)

    2014-01-15

    Highlights: • Three CMPO-calix[4]arenes with spacer containing intramolecular hydrogen bonds were designed and synthesized. • The influence of local rigidification caused by intramolecular hydrogen bonds upon extraction of f-elements was investigated. • Selective extraction is realized via tuning local chelating surroundings by aid of intramolecular hydrogen bonds. -- Abstract: To understand intramolecular hydrogen bonding in effecting liquid–liquid extraction behavior of CMPO-calixarenes, three CMPO-modified calix[4]arenes (CMPO-CA) 5a–5c with hydrogen-bonded spacer were designed and synthesized. The impact of spacer rotation that is hindered by introduction of intramolecular hydrogen bonding upon extraction of La{sup 3+}, Eu{sup 3+}, Yb{sup 3+}, Th{sup 4+}, and UO{sub 2}{sup 2+} has been examined. The results show that 5b and 5c containing only one hydrogen bond with a less hindered rotation spacer extract La{sup 3+} more efficiently than 5a containing two hydrogen bonds with a more hindered rotation spacer, demonstrating the importance of local rigidification of spacer in the design of extractants in influencing the coordination environment. The large difference in extractability between La{sup 3+} and Yb{sup 3+} (or Eu{sup 3+}) by 5b (or 5c), and the small difference by 5a, suggests intramolecular hydrogen bonding do exert pronounced influence upon selective extraction of light and heavy lanthanides. Log–log plot analysis indicates a 1:1, 2:1 and 1:1 stoichiometry (ligand/metal) for the extracted complex formed between 5b and La{sup 3+}, Th{sup 4+}, UO{sub 2}{sup 2+}, respectively. Additionally, their corresponding acyclic analogs 7a–7c exhibit negligible extraction toward these metal ions. These results reveal the possibility of selective extraction via tuning local chelating surroundings of CMPO-CA by aid of intramolecular hydrogen bonding.

  11. Ni- and Fe-catalyzed Carboxylation of Unsaturated Hydrocarbons with CO2.

    Science.gov (United States)

    Juliá-Hernández, Francisco; Gaydou, Morgane; Serrano, Eloisa; van Gemmeren, Manuel; Martin, Ruben

    2016-08-01

    The sustainable utilization of available feedstock materials for preparing valuable compounds holds great promise to revolutionize approaches in organic synthesis. In this regard, the implementation of abundant and inexpensive carbon dioxide (CO2) as a C1 building block has recently attracted considerable attention. Among the different alternatives in CO2 fixation, the preparation of carboxylic acids, relevant motifs in pharmaceuticals and agrochemicals, is particularly appealing, thus providing a rapid and unconventional entry to building blocks that are typically prepared via waste-producing protocols. While significant advances have been realized, the utilization of simple unsaturated hydrocarbons as coupling partners in carboxylation events is undoubtedly of utmost academic and industrial relevance, as two available feedstock materials can be combined in a catalytic fashion. This review article aims to describe the main achievements on the direct carboxylation of unsaturated hydrocarbons with CO2 by using cheap and available Ni or Fe catalytic species. PMID:27573397

  12. Isotope-Encoded Carboxyl Group Footprinting for Mass Spectrometry-Based Protein Conformational Studies

    Science.gov (United States)

    Zhang, Hao; Liu, Haijun; Blankenship, Robert E.; Gross, Michael L.

    2016-01-01

    We report an isotope-encoding method coupled with carboxyl-group footprinting to monitor protein conformational changes. The carboxyl groups of aspartic/glutamic acids and of the C-terminus of proteins can serve as reporters for protein conformational changes when labeled with glycine ethyl ester (GEE) mediated by carbodiimide. In the new development, isotope-encoded "heavy" and "light" GEE are used to label separately the two states of the orange carotenoid protein (OCP) from cyanobacteria. Two samples are mixed (1:1 ratio) and analyzed by a single LC-MS/MS experiment. The differences in labeling extent between the two states are represented by the ratio of the "heavy" and "light" peptides, providing information about protein conformational changes. Combining isotope-encoded MS quantitative analysis and carboxyl-group footprinting reduces the time of MS analysis and improves the sensitivity of GEE and other footprinting.

  13. Chiral trans-1,2-diaminocyclohexane derivatives as chiral solvating agents for carboxylic acids

    Indian Academy of Sciences (India)

    Mariappan Periasamy; Manasi Dalai; Meduri Padmaja

    2010-07-01

    Efficient use of the readily accessible chiral 2-symmetric acyclic diamines (1-2) as well as macrocyclic amines (3-5) containing trans-1,2-diaminocyclohexyl moiety as chiral solvating agents (CSA) for the determination of enantiomeric excess of representative carboxylic acids (6-7) and an amino acid derivative (8) is illustrated. The enantiomeric composition of different carboxylic acids estimated here by the 1H NMR method, based on the integration of the corresponding methine proton signals are in good correlation with that determined using HPLC method. The data are in accordance with the formation of multimolecular diastereomeric complexes in solution, which render good splitting of NMR signals for the enantiomers of representative carboxylic acids as well as for -Ts-phenylglycine (up to = 0.295 ppm, 118 Hz).

  14. The investigation of the reactions of some pyrazole-3-carboxylic acids with various diamines and diols

    Directory of Open Access Journals (Sweden)

    Rahmi Kasımoğulları

    2012-06-01

    Full Text Available In this study, some new derivatives were synthesized of 4-benzoyl-1-(3-nitrophenyl-5-phenyl-1H-pyrazole-3-carboxylic acid (1 and 4-(ethoxycarbonyl-1-(3-nitrophenyl-5-phenyl-1H-pyrazole-3-carboxylic acid (2 that they were pyrazole carboxylic acid derivatives. Firstly, 1 and 2 reacted with SOCl2 to transform them into acyl chlorides (3, 4. Then various bis-carboxamide derivatives (5–8 were obtained from the reaction of 3 and 4 with various diamines and also a ;#946;-hydroxy ester (9 derivative was obtained from the reaction of 3 with ethylene glycol. The structures of synthesized compounds were elucidated with using FT-IR, 1H NMR, 13C NMR and elemental analysis methods.

  15. Crystal Structure and Properties of the Carboxylic Acid Derivatives of Schizonpeta mulifida (L.) Briq.

    Institute of Scientific and Technical Information of China (English)

    LIU,Ju-Tao; YU,Ji-Cheng; JIANG,Hui-Ming; ZHANG,Li-Ying; ZHAO,Xiao-Jing; FAN,Sheng-Di

    2008-01-01

    The chemical constituents of the carboxylic acid derivatives from the ear of Schizonepeta were investigated,1H and 13C NMR chemical shifts of the carboxylic acid derivatives were accurately assigned.Two carboxylic acid derivative constituents were separated by a silica gel column.The structures were elucidated by the physical and chemical properties,IR,1H NMR,13C NMR,MALDI-TDF-MS and X-ray single crystal diffractometry.They were identified as 3-imino-N-(a-imidoethylamino)butyrolactam and neononane tetracid,respectively.The antitumoral activity on liver tumor ceils SMMC-7721 was determined in vitro.The experimental results showed that the former was better than the latter,and with increasing the concentration of the former the inhibitory activity was increased.

  16. Beyond ketonization: selective conversion of carboxylic acids to olefins over balanced Lewis acid–base pairs

    Energy Technology Data Exchange (ETDEWEB)

    Baylon, Rebecca A. L.; Sun, Junming; Martin, Kevin J.; Venkitasubramanian, Padmesh; Wang, Yong

    2016-01-01

    Dwindling petroleum reserves combined with increased energy demand and political factors encouraging an increase in energy independence have led to a large amount of research on sustainable alternatives. To this end, biomass conversion has been recognized as themost readily viable technology to produce biofuel concerning our reliance on liquid fuels for transportation and has the advantage of being easily integrated into our heavy use of combustion engines. The interest in biomass conversion has also resulted in reduced costs and a greater abundance of bio-oil, a mixture of hundreds of oxygenates including alcohols, aldehydes, carboxylic acids, and ketones. However, the presence of carboxylic acids in bio-oil derived from lignocellulose pyrolysis leads to low pH, instability, and corrosiveness. In addition, carboxylic acids (i.e. acetic acid) can also be produced via fermentation of sugars. This can be accomplished by a variety of homoacetogenic microorganisms that can produce acetic acid with 100% carbon yield.

  17. Communication: Physical origins of ionization potential shifts in mixed carboxylic acids and water complexes

    Science.gov (United States)

    Gu, Quanli; Tang, Zhen; Su, Peifeng; Wu, Wei; Yang, Zhijun; Trindle, Carl O.; Knee, Joseph L.

    2016-08-01

    The ionization potential (IP) of the aromatic alpha hydroxy carboxylic acid, 9-hydroxy-9-fluorene carboxylic acid (9HFCA), is shifted by complexation with hydrogen bonding ligands such as water and formic acid. Generalized Kohn-Sham energy decomposition analysis decomposes the intermolecular binding energies into a frozen energy term, polarization, correlation, and/or dispersion energy terms, as well as terms of geometric relaxation and zero point energy. We observe that in each dimer the attractive polarization always increases upon ionization, enhancing binding in the cation and shifting the IP toward the red. For 9HFCA—H2O, a substantial decrease of the repulsive frozen energy in cation further shifts the IP toward red. For 9HFCA—HCOOH, the increase of the frozen energy actually occurs in the cation and shifts the IP toward blue. Consistent with the experimental measurements, our analysis provides new, non-intuitive perspectives on multiple hydrogen bonds interactions in carboxylic acids and water complexes.

  18. Carboxylated dithiafulvenes and tetrathiafulvalene vinylogues: synthesis, electronic properties, and complexation with zinc ions

    Directory of Open Access Journals (Sweden)

    Yunfei Wang

    2015-06-01

    Full Text Available A class of carboxyl and carboxylate ester-substituted dithiafulvene (DTF derivatives and tetrathiafulvalene vinylogues (TTFVs has been synthesized and their electronic and electrochemical redox properties were characterized by UV–vis spectroscopic and cyclic voltammetric analyses. The carboxyl-TTFV was applied as a redox-active ligand to complex with Zn(II ions, forming a stable Zn-TTFV coordination polymer. The structural, electrochemical, and thermal properties of the coordination polymer were investigated by infrared spectroscopy, cyclic voltammetry, powder X-ray diffraction, and differential scanning calorimetric analyses. Furthermore, the microscopic porosity and surface area of the Zn-TTFV coordination polymer were measured by nitrogen gas adsorption analysis, showing a BET surface of 148.2 m2 g−1 and an average pore diameter of 10.2 nm.

  19. On the one pot syntheses of chromeno[4,3-b]pyridine-3-carboxylate and chromeno[3,4-c]pyridine-3-carboxylate and dihydropyridines

    Energy Technology Data Exchange (ETDEWEB)

    Navarrete-Encina, Patricio A.; Vega-Retter, Christian, E-mail: pnavarre@vtr.ne [Universidad de Chile, Santiago (Chile). Facultad de Ciencias Quimicas y Farmaceuticas. Lab. de Sintesis Organica y Fisicoquimica; Salazar, Ricardo; Perez, Karina; Squella, Juan A.; Nunez-Vergara, Luis J. [Universidad de Chile, Santiago (Chile). Fac. de Ciencias Quimicas y Farmaceuticas. Lab. de Bioelectroquimica

    2010-07-01

    Substituted chromenos, dihydropyridines and pyridines have been important in the syntheses of compounds having interesting pharmacological properties. Therefore, we found of interest to synthesize chromenopyridines and chromeno dihydropyridines (i.e., fused chromeno and dihydropyridine or pyridine rings) to further study their biological activity. Here, we propose one-pot syntheses for substituted ethyl-2,4-dimethyl-5-oxo-5H-chromeno[4,3-b]pyridine-3-carboxylates, ethyl-2,4-dimethyl-5-oxo-5H-chromeno[3,4-c]pyridine-3-carboxylates and their respective 1,4-dihydropyridines based on a modified Hantzsch pyridine synthesis using 2-hydroxyaryl aldehydes, with electron withdrawing and electron donating groups on the phenyl ring, as starting reactants. Sixteen compounds were synthesized by the described method and fully characterized. An average yield of 37% was obtained for the different derivatives. (author)

  20. Carboxylic acid derivatives via catalytic carboxylation of unsaturated hydrocarbons: whether the nature of a reductant may determine the mechanism of CO2 incorporation?

    OpenAIRE

    Kirillov, E.; Carpentier, J.-F.; Bunel, E

    2015-01-01

    International audience Application of CO2 as a renewable feedstock and C1 building block for prodn. of commodity and fine chems. is a highly challenging but obvious industry-relevant task. Of particular interest is the catalytic coupling of CO2 with inexpensive unsatd. hydrocarbons (olefins, dienes, styrenes, alkynes), providing direct access to carboxylic acids and their derivs. Although not brand new for the scientific community, it is still a complete challenge, as no truly effective ca...

  1. Crystal structure of methyl 2-(2H-1,3-benzodioxol-5-yl-7,9-dibromo-8-oxo-1-oxaspiro[4.5]deca-2,6,9-triene-3-carboxylate

    Directory of Open Access Journals (Sweden)

    Lucimara Julio Martins

    2014-12-01

    Full Text Available The title compound, C18H12Br2O6, was synthesized from Morita–Baylis–Hillman adducts. It incorporates the brominated spiro-hexadienone moiety typically exhibited by compounds of this class that exhibit biological activity. Both the brominated cyclohexadienone and the central five-membered rings are nearly planar (r.m.s. deviations of 0.044 and 0.016 Å, respectively, being almost perpendicularly oriented [interplanar angle = 89.47 (5°]. With respect to the central five-membered ring, the brominated cyclohexadienone ring, the benzodioxol ring and the carboxylate fragment make C—O—C—C, O—C—C—C and C—C—C—O dihedral angles of −122.11 (8, −27.20 (11 and −8.40 (12°, respectively. An intramolecular C—H...O hydrogen bond occurs. In the crystal, molecules are linked by non-classical C—H...O and C—H...Br hydrogen bonds resulting in a molecular packing in which the brominated rings are in a head-to-head orientation, forming well marked planes parallel to the b axis.

  2. Ethyl (2Z-2-(3-methoxybenzylidene-7-methyl-3-oxo-5-phenyl-2,3-dihydro-5H-1,3-thiazolo[3,2-a]pyrimidine-6-carboxylate

    Directory of Open Access Journals (Sweden)

    Jerry P. Jasinski

    2010-03-01

    Full Text Available In the title compound, C24H22N2O4S, the central pyrimidine ring is significantly puckered, assuming a conformation intermediate between a boat and a screw boat. The nearly planar thiazole ring (r.m.s. deviation = 0.0258 Å is fused with the pyriamidine ring, making a dihedral angle of 9.83 (7°. The carboxyl group is in an extended conformation with an anti-periplanar orientation with respect to the dihydropyrimidine ring. The benzene ring linked at the chiral C atom is perpendicular to the pyrimidine ring [dihedral angle = 85.21 (8°] whereas the phenyl ring is nearly coplanar, making a dihedral angle of 13.20 (8°. An intramolecular C—H...S hydrogen bond is observed. The crystal packing is influenced by weak intermolecular C—H...π interactions and π–π stacking between the thiazole and phenyl rings [centroid–centroid distance = 3.9656 (10 Å], which stack the molecules along the c axis.

  3. Intramolecular Lactonization of Poly(α-hydroxyacrylic acid: Kinetics and Reaction Mechanism

    Directory of Open Access Journals (Sweden)

    Heli Virkki

    2015-01-01

    Full Text Available Poly(α-hydroxyacrylic acid, PHA, is one of the few polymers with biodegradable properties used in mechanical pulp bleaching to stabilize hydrogen peroxide. A new method for the in situ follow-up of the lactone ring formation of PHA has been developed. The results have further been applied to describe the reaction kinetics of the lactonization and hydrolysis reactions through parameter estimation. In addition, the reaction mechanism is elucidated by multivariate data analysis. Satisfactory identification and semiquantitative separation of the lactone ring as well as the acyclic (carboxyl and hydroxyl groups forms have been established by 1H NMR in the pH range of 1–9. The lactonization reaction approaching equilibrium can be described by pseudo-first-order kinetics in the pH range of 1–6. The rate constants of the pseudo-first-order kinetic model have been estimated by nonlinear regression. Due to the very low rates of lactonization as well as the weak pH dependency of the reaction, an addition-elimination mechanism is proposed. Additionally, the presence of a transient reaction intermediate during lactonization reaction could be identified by subjecting the measurement data to multivariate data analysis (PCA, principal component analysis. A good correlation was found between the kinetic and the PCA models in terms of model validity.

  4. Intramolecular cyclization of aspartic acid residues assisted by three water molecules: a density functional theory study

    International Nuclear Information System (INIS)

    Aspartic acid (Asp) residues in peptides and proteins (l-Asp) are known to undergo spontaneous nonenzymatic reactions to form l-β-Asp, d-Asp, and d-β-Asp residues. The formation of these abnormal Asp residues in proteins may affect their three-dimensional structures and hence their properties and functions. Indeed, the reactions have been thought to contribute to aging and pathologies. Most of the above reactions of the l-Asp residues proceed via a cyclic succinimide intermediate. In this paper, a novel three-water-assisted mechanism is proposed for cyclization of an Asp residue (forming a gem-diol precursor of the succinimide) by the B3LYP/6-31 + G(d,p) density functional theory calculations carried out for an Asp-containing model compound (Ace−Asp−Nme, where Ace = acetyl and Nme = NHCH3). The three water molecules act as catalysts by mediating ‘long-range’ proton transfers. In the proposed mechanism, the amide group on the C-terminal side of the Asp residue is first converted to the tautomeric iminol form (iminolization). Then, reorientation of a water molecule and a conformational change occur successively, followed by the nucleophilic attack of the iminol nitrogen on the carboxyl carbon of the Asp side chain to form the gem-diol species. A satisfactory agreement was obtained between the calculated and experimental energetics.

  5. Arabidopsis ETO1 specifically interacts with and negatively regulates type 2 1-aminocyclopropane-1-carboxylate synthases

    Directory of Open Access Journals (Sweden)

    Saito Koji

    2005-08-01

    Full Text Available Abstract Background In Arabidopsis, ETO1 (ETHYLENE-OVERPRODUCER1 is a negative regulator of ethylene evolution by interacting with AtACS5, an isoform of the rate-limiting enzyme, 1-aminocyclopropane-1-carboxylate synthases (ACC synthase or ACS, in ethylene biosynthetic pathway. ETO1 directly inhibits the enzymatic activity of AtACS5. In addition, a specific interaction between ETO1 and AtCUL3, a constituent of a new type of E3 ubiquitin ligase complex, suggests the molecular mechanism in promoting AtACS5 degradation by the proteasome-dependent pathway. Because orthologous sequences to ETO1 are found in many plant species including tomato, we transformed tomato with Arabidopsis ETO1 to evaluate its ability to suppress ethylene production in tomato fruits. Results Transgenic tomato lines that overexpress Arabidopsis ETO1 (ETO1-OE did not show a significant delay of fruit ripening. So, we performed yeast two-hybrid assays to investigate potential heterologous interaction between ETO1 and three isozymes of ACC synthases from tomato. In the yeast two-hybrid system, ETO1 interacts with LE-ACS3 as well as AtACS5 but not with LE-ACS2 or LE-ACS4, two major isozymes whose gene expression is induced markedly in ripening fruits. According to the classification of ACC synthases, which is based on the C-terminal amino acid sequences, both LE-ACS3 and AtACS5 are categorized as type 2 isozymes and possess a consensus C-terminal sequence. In contrast, LE-ACS2 and LE-ACS4 are type 1 and type 3 isozymes, respectively, both of which do not possess this specific C-terminal sequence. Yeast two-hybrid analysis using chimeric constructs between LE-ACS2 and LE-ACS3 revealed that the type-2-ACS-specific C-terminal tail is required for interaction with ETO1. When treated with auxin to induce LE-ACS3, seedlings of ETO1-OE produced less ethylene than the wild type, despite comparable expression of the LE-ACS3 gene in the wild type. Conclusion These results suggest that ETO1

  6. Preparation of conjugated poly(ethyl acetylene carboxylate) as optical limiter of laser radiation

    International Nuclear Information System (INIS)

    The optical limiting action of poly (ethylacetylene carboxylate) dissolved in dichloroethane were investigated under irradiation with 8 ns laser pulses at 532 nm. The optical limiting measurements were performed at a series of concentrations. The threshold limiting fluence was observed for high concentrations at 5 J/cm2 with a transmission of about 20 %. No optical limiting action was observed at very low concentration of the prepared polymer in the dichloroethane solvent. The observed data show that poly (ethylacetylene carboxylate) has the potential for the use as optical limiting material for future applications. (author)

  7. A Concise Synthesis and the Antibacterial Activity of 5,6-Dimethoxynaphthalene-2-carboxylic Acid

    OpenAIRE

    GÖKSU, Süleyman; UĞUZ, Metin Tansu

    2005-01-01

    5,6-Dimethoxynaphthalene-2-carboxylic acid was synthesized in 7 steps and with an overall yield of 46%. Bromination of 2-naphthol, and methylation with dimethyl sulfate followed by Friedel-Crafts acylation with AcCl gave 2-acetyl-5-bromo-6-methoxynaphthalene. 2-Acetyl-5-bromo-6-methoxynaphthalene was converted to 5-bromo-6- methoxynaphthalene-2-carboxylic acid by a haloform reaction. The esterification of the acid with methanol, methoxylation with NaOCH3 in the presence of CuI and s...

  8. Photosensitization of Nanocrystalline TiO2 Electrode Modifiedwith C60 Carboxylic Acid Derivatives

    Institute of Scientific and Technical Information of China (English)

    张文; 史亚茹; 甘良兵; 黄春辉; 王艳琴; 虎民

    2001-01-01

    C60 carboxylic acid derivatives can be readily adsorbed on the surface of nanocrystalline TiO2 films act as charge-transfer sensitizer. The electron transport from TiO2 to the C60 derivatives results in the generation of the cathodic photocurrent. The short-circuit photocurrent of a C60 tetracarboxylic acid is 0.45 μA/cm2 under 464 um light illumination. The photoelectric behaviour of ITO electrodes modified by the same C60 carboxylic acids is different from that of the modified TiO2 electrodes, and shows anodic photocurrent.

  9. Facile synthesis of α-hydroxy carboxylic acids from the corresponding α-amino acids

    DEFF Research Database (Denmark)

    Stuhr-Hansen, Nicolai; Padrah, Shahrokh; Strømgaard, Kristian

    2014-01-01

    An effective and improved procedure is developed for the synthesis of α-hydroxy carboxylic acids by treatment of the corresponding protonated α-amino acid with tert-butyl nitrite in 1,4-dioxane-water. The amino moiety must be protonated and located α to a carboxylic acid function in order to...... undergo initial diazotization and successive hydroxylation, since neither β-amino acids nor acid derivatives such as esters and amides undergo hydroxylations. The method is successfully applied for the synthesis of 18 proteinogenic amino acids. © 2014 Elsevier Ltd. All rights reserved....

  10. (±)-trans-3-Benzoyl-bicyclo-[2.2.2]octane-2-carboxylic acid.

    Science.gov (United States)

    Lalancette, Roger A; Thompson, Hugh W; Brunskill, Andrew P J

    2008-01-01

    The title keto acid, C(16)H(18)O(3), displays significant twisting of all three ethyl-ene bridges in its bicyclo-[2.2.2]octane structure owing to steric inter-actions; the bridgehead-to-bridgehead torsion angles are 13.14 (12), 13.14 (13) and 9.37 (13)°. The compound crystallizes as centrosymmetric carboxyl dimers [O⋯O = 2.6513 (12) Å and O-H⋯O = 178°], which have two orientations within the cell and contain no significant carboxyl disorder. PMID:21201657

  11. (±-trans-3-Benzoylbicyclo[2.2.2]octane-2-carboxylic acid

    Directory of Open Access Journals (Sweden)

    Andrew P. J. Brunskill

    2008-09-01

    Full Text Available The title keto acid, C16H18O3, displays significant twisting of all three ethylene bridges in its bicyclo[2.2.2]octane structure owing to steric interactions; the bridgehead-to-bridgehead torsion angles are 13.14 (12, 13.14 (13 and 9.37 (13°. The compound crystallizes as centrosymmetric carboxyl dimers [O...O = 2.6513 (12 Å and O—H...O = 178°], which have two orientations within the cell and contain no significant carboxyl disorder.

  12. Determination of 13C and 18O isotopic abundances of carboxyl substances; application to amino acids

    International Nuclear Information System (INIS)

    Flash pyrolysis of organic acids or of their salts gives off carbon dioxide which can be analysed by mass spectrometry for 13C and 18O abundance. This principle has been applied to Cd13C18O3 using an induction furnace, and used to determine the 13C and 18O content of the carboxylic group of some amino acids. The technique described has many advantages over the classical pyrolysis methods using sealed tubes. It is rapid and simple and especially effective in determining the isotopic composition of hygroscopic carboxyl substances. (U.K.)

  13. Comparative structure analysis of non-polar organic ferrofluids stabilized by saturated mono-carboxylic acids.

    Science.gov (United States)

    Avdeev, M V; Bica, D; Vékás, L; Aksenov, V L; Feoktystov, A V; Marinica, O; Rosta, L; Garamus, V M; Willumeit, R

    2009-06-01

    The structure of ferrofluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that in case of saturated acid surfactants, magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids. PMID:19376524

  14. 5,6-dihydroxyindole-2-carboxylic acid (DHICA): a First Principles Density-Functional Study

    CERN Document Server

    Powell, B J

    2016-01-01

    We report first principles density functional calculations for 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and several reduced forms. DHICA and 5,6-dihydroxyindole (DHI) are believed to be the basic building blocks of the eumelanins. Our results show that carboxylation has a significant effect on the physical properties of the molecules. In particular, the relative stabilities and the HOMO-LUMO gaps (calculated with the $\\Delta$SCF method) of the various redox forms are strongly affected. We predict that, in contrast to DHI, the density of unpaired electrons, and hence the ESR signal, in DHICA is negligibly small.

  15. Activation of a Ca(2+)-dependent protein kinase involves intramolecular binding of a calmodulin-like regulatory domain

    Science.gov (United States)

    Huang, J. F.; Teyton, L.; Harper, J. F.; Evans, M. L. (Principal Investigator)

    1996-01-01

    Ca(2+)-dependent protein kinases (CDPKs) are regulated by a C-terminal calmodulin-like domain (CaM-LD). The CaM-LD is connected to the kinase by a short junction sequence which contains a pseudosubstrate autoinhibitor. To understand how the CaM-LD regulates a CDPK, a recombinant CDPK (isoform CPK-1 from Arabidopsis, accession no. L14771) was made as a fusion protein in Escherichia coli. We show here that a truncated CDPK lacking a CaM-LD (e.g. mutant delta NC-26H) can be activated by exogenous calmodulin or an isolated CaM-LD (Kact approximately 2 microM). We propose that Ca2+ activation of a CDPK normally occurs through intramolecular binding of the CaM-LD to the junction. When the junction and CaM-LD are made as two separate polypeptides, the CaM-LD can bind the junction in a Ca(2+)-dependent fashion with a dissociation constant (KD) of 6 x 10(-6) M, as determined by kinetic binding analyses. When the junction and CaM-LD are tethered in a single polypeptide (e.g. in protein JC-1), their ability to engage in bimolecular binding is suppressed (e.g. the tethered CaM-LD cannot bind a separate junction). A mutation which disrupts the putative CaM-LD binding sequence (e.g. substitution LRV-1444 to DLPG) appears to block intramolecular binding, as indicated by the restored ability of a tethered CaM-LD to engage in bimolecular binding. This mutation, in the context of a full-length enzyme (mutant KJM46H), appears to block Ca2+ activation. Thus, a disruption of intramolecular binding correlates with a disruption of the Ca2+ activation mechanism. CDPKs provide the first example of a member of the calmodulin superfamily where a target binding sequence is located within the same polypeptide.

  16. Selective determination of cysteines through precolumn double-labeling and liquid chromatography followed by detection of intramolecular FRET.

    Science.gov (United States)

    Yoshitake, Makoto; Nohta, Hitoshi; Sejima, Naoko; Todoroki, Kenichiro; Yoshida, Hideyuki; Yamaguchi, Masatoshi

    2011-02-01

    In this paper we introduce a novel approach for highly selective and sensitive analysis of cysteines (glutathione, cysteine, and homocysteine). This method is based on the detection of intramolecular fluorescence resonance energy transfer (FRET) in a liquid chromatography (LC) system after double-labeling of the amino and sulfhydryl groups of the cysteines. In this detection process, we monitored the FRET between the amine-derivatized and thiol-derivatized fluorophores. We screened 16 combinations of fluorescent reagents. As a result, FRET occurred most effectively when the sulfhydryl and amino groups of the cysteines were derivatized with 7-diethylamino-3-[{4'-(iodoacetyl)amino}phenyl]-4-methylcoumarin (DCIA, Ex/Em 390/480 nm) and 4-fluoro-7-nitrobenz-2-oxo-1,3-diazole (NBD-F, Ex/Em 480/540 nm), respectively, in this order. The double-labeled cysteines emitted NBD-F fluorescence (540 nm) through an intramolecular FRET process when they were excited at the wavelength of maximum excitation of DCIA (390 nm). The generation of FRET was confirmed by comparison with analysis of n-amylamine or tryptophan (amines without a sulfhydryl group) and 6-mercaptohexanol (thiol without an amino group) performed using LC and a three-dimensional fluorescence detection system. We were able to separate the double-labeled cysteines (DCIA and NBD-F) when performing LC on an ODS column with isocratic elution. The limits of quantification (signal-to-noise ratio = 10) and detection (signal-to-noise ratio = 3) for the cysteines, for a 20-μL injection volume, were in the range 150-670 fmol and 46-200 fmol, respectively. The sensitivity of the intramolecular FRET-forming derivatization method is higher than that of a system which takes advantage of conventional detection of the derivatives. Furthermore, this method provides sufficient selectivity and sensitivity to determine the total cysteines present in the plasma of healthy humans. PMID:21153590

  17. Conserved Intramolecular Interactions Maintain Myosin Interacting-Heads Motifs Explaining Tarantula Muscle Super-Relaxed State Structural Basis.

    Science.gov (United States)

    Alamo, Lorenzo; Qi, Dan; Wriggers, Willy; Pinto, Antonio; Zhu, Jingui; Bilbao, Aivett; Gillilan, Richard E; Hu, Songnian; Padrón, Raúl

    2016-03-27

    Tarantula striated muscle is an outstanding system for understanding the molecular organization of myosin filaments. Three-dimensional reconstruction based on cryo-electron microscopy images and single-particle image processing revealed that, in a relaxed state, myosin molecules undergo intramolecular head-head interactions, explaining why head activity switches off. The filament model obtained by rigidly docking a chicken smooth muscle myosin structure to the reconstruction was improved by flexibly fitting an atomic model built by mixing structures from different species to a tilt-corrected 2-nm three-dimensional map of frozen-hydrated tarantula thick filament. We used heavy and light chain sequences from tarantula myosin to build a single-species homology model of two heavy meromyosin interacting-heads motifs (IHMs). The flexibly fitted model includes previously missing loops and shows five intramolecular and five intermolecular interactions that keep the IHM in a compact off structure, forming four helical tracks of IHMs around the backbone. The residues involved in these interactions are oppositely charged, and their sequence conservation suggests that IHM is present across animal species. The new model, PDB 3JBH, explains the structural origin of the ATP turnover rates detected in relaxed tarantula muscle by ascribing the very slow rate to docked unphosphorylated heads, the slow rate to phosphorylated docked heads, and the fast rate to phosphorylated undocked heads. The conservation of intramolecular interactions across animal species and the presence of IHM in bilaterians suggest that a super-relaxed state should be maintained, as it plays a role in saving ATP in skeletal, cardiac, and smooth muscles. PMID:26851071

  18. Influence of end-to-end diffusion on intramolecular energy transfer as observed by frequency-domain fluorometry

    Science.gov (United States)

    Lakowicz, Joseph R.; Wiczk, Wieslaw M.; Gryczynski, Ignacy; Szmacinski, Henryk; Johnson, Michael L.

    1990-05-01

    We investigated the influence of end-to-end diffusion on intramolecular energy transfer between a naphthalene donor and dansyl acceptor linked by polymethylene chain. A range of viscosities of 0.6 - 200cP were obtained using propylene glycol at different temperatures (0-80°C) and methanol at 20°C. The intensity decays of naphthalene were measured in frequency-domain. Several theoretical models, including distance distributions were used to fit the data. The results indicate that end-to-end diffusion of flexible donor - acceptor pairs can be readily detected and quantified using frequency-domain fluorometry.

  19. Structural conversion and intramolecular electron transfer in ferrocenylanthraquinones triggered by Keggin type of heteropoly acid serving as proton source

    Institute of Scientific and Technical Information of China (English)

    LIU Shuxia; LI Dehui; SU Zhongmin; WANG Enbo

    2004-01-01

    Intramolecular electron transfer triggered by proton and the mechanism of structural conversion in a ethynylene-bridged ferrocene-anthraquinone organic electron donor(D)-acceptor(A) g-conjugated system (1-FcAq) in the presence of a Keggin type heteropoly acid as proton source are discussed. Heteropoly acids can stabilize the protonated ethynylene-bridged ferrocene-anthraquinone conjugated complex, and the stable protonated complex has been isolated in air and characterized by elemental analyses, IR,1H NMR, and CV. Upon the inducement of proton, electron transfer from ferrocene moiety (Fc) to anthraquinone moiety (Aq) causes the rearrangement of the conjugated system to create a fulvene-cumulene structuere.

  20. Evaluation of intramolecular charge transfer state of 4-, -dimethylamino cinnamaldehyde using time-dependent density functional theory

    Indian Academy of Sciences (India)

    Surajit Ghosh; K V S Girish; Subhadip Ghosh

    2013-07-01

    Intramolecular charge transfer of 4-,-dimethylamino cinnamaldehyde (DMACA) in vacuum and in five different aprotic solvents has been studied by using time-dependent density functional theory (TDDFT). Polarizable continuum model (PCM) was employed to consider solvent-solute interactions. The potential energy curves were constructed at different torsional angle of ,-dimethylamino moiety with respect to the adjacent phenyl ring. A large bathochromic shift in our calculated emission and absorption energies for polar solvents is a clear reminiscent of charge transfer nature of the excited state. Finally, the reported results are in agreement with experimental findings.

  1. Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroaniline

    DEFF Research Database (Denmark)

    Eriksen, Janus J.; Sauer, Stephan P. A.; Mikkelsen, Kurt V.; Christiansen, O.; Aa. Jensen, Hans Jørgen; Kongsted, Jacob

    We investigate the failure of Time{Dependent Density Functional Theory (TDDFT) with the CAM{B3LYP exchange{correlation (xc) functional coupled to the Polarizable Embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge{transfer excitation in para...... to benchmark results of TDDFT calculations with CAM-B3LYP for intramolecular charge{transfer excitations in molecular systems similar to pNA against higher{level ab initio wave function methods, like, e.g., CCSD, prior to their use. Using the calculated change in dipole moment upon excitation as a...

  2. Molecular eigenstate spectroscopy: Application to the intramolecular dynamics of some polyatomic molecules in the 3000 to 7000 cm-1 region

    International Nuclear Information System (INIS)

    This project uses high resolution infrared spectroscopy to probe the mechanism of intramolecular vibrational redistribution (IVR) in isolated polyatomic molecules. We have found only vibrationally anharmonic coupling in the C-H stretch region of 1-butyne but rotationally mediated coupling is evident in similar spectra of ethanol. The ''keyhole'' model of IVR was developed to account for the similarities and differences between these molecules. The concepts of the model are being implemented numerically in random matrix calculations. A second F-center laser has been purchased and is now being set up to develop an infrared double resonance technique which can be applied to this problem. 4 refs., 5 figs

  3. NMR of proteins (4Fe-4S): structural properties and intramolecular electron transfer

    International Nuclear Information System (INIS)

    NMR started to be applied to Fe-S proteins in the seventies. Its use has recently been enlarged as the problems arising from the paramagnetic polymetallic clusters ware overcome. Applications to [4Fe-4S] are presented herein. The information derived thereof deepens the understanding of the redox properties of these proteins which play a central role in the metabolism of bacterial cells. The secondary structure elements and the overall folding of Chromatium vinosum ferredoxin (Cv Fd) in solution have been established by NMR. The unique features of this sequence have been shown to fold as an α helix at the C-terminus and as a loop between two cysteines ligand of one cluster: these two parts localize in close proximity from one another. The interaction between nuclear and electronic spins is a source of additional structural information for (4Fe-AS] proteins. The conformation of the cysteine-ligands, as revealed by the Fe-(Sγ-Cβ-Hβ)Cys dihedral angles, is related to the chemical shifts of the signals associated with the protons of these residues. The longitudinal relaxation times of the protons depend on their distance to the cluster. A quantitative relationship has been established and used to show that the solution structure of the high-potential ferredoxin from Cv differs significantly from the crystal structure around Phe-48. Both parameters (chemical shifts and longitudinal relaxation times) give also insight into the electronic and magnetic properties of the [4Fe-4S] clusters. The rate of intramolecular electron transfer between the two [4FE-4S] clusters of ferredoxins has been measured by NMR. It is far slower in the case of Cv Fd than for shorter ferredoxins. The difference may be associated with changes in the magnetic and/or electronic properties of one cluster. The strong paramagnetism of the [4Fe-4S] clusters, which originally limited the applicability of NMR to proteins containing these cofactors, has been proven instrumental in affording new

  4. Long-Lived Triplet Excited States of Bent-Shaped Pentacene Dimers by Intramolecular Singlet Fission.

    Science.gov (United States)

    Sakuma, Takao; Sakai, Hayato; Araki, Yasuyuki; Mori, Tadashi; Wada, Takehiko; Tkachenko, Nikolai V; Hasobe, Taku

    2016-03-24

    Intramolecular singlet fission (ISF) is a promising photophysical process to construct more efficient light energy conversion systems as one excited singlet state converts into two excited triplet states. Herein we synthesized and evaluated bent-shaped pentacene dimers as a prototype of ISF to reveal intrinsic characters of triplet states (e.g., lifetimes of triplet excited states). In this study, meta-phenylene-bridged TIPS-pentacene dimer (PcD-3Ph) and 2,2'-bipheynyl bridged TIPS-pentacene dimer (PcD-Biph) were newly synthesized as bent-shaped dimers. In the steady-state spectroscopy, absorption and emission bands of these dimers were fully characterized, suggesting the appropriate degree of electronic coupling between pentacene moieties in these dimers. In addition, the electrochemical measurements were also performed to check the electronic interaction between two pentacene moieties. Whereas the successive two oxidation peaks owing to the delocalization were observed in a directly linked-pentacene dimer (PcD) by a single bond, the cyclic voltammograms in PcD-Biph and PcD-3Ph implied the weaker interaction compared to that of p-phenylene-bridged TIPS-pentacene dimer (PcD-4Ph) and PcD. The femtosecond and nanosecond transient absorption spectra clearly revealed the slower ISF process in bent-shaped pentacene dimers (PcD-Biph and PcD-3Ph), more notably, the slower relaxation of the excited triplet states in PcD-Biph and PcD-3Ph. Namely, the quantum yields of triplet states (ΦT) by ISF approximately remain constant (ca. 180-200%) in all dimer systems, whereas the lifetimes of the triplet excited states became much longer (up to 360 ns) in PcD-Biph as compared to PcD-4Ph (15 ns). Additionally, the lifetimes of the corresponding triplet states in PcD-Biph and PcD-3Ph were sufficiently affected by solvent viscosity. In particular, the lifetimes of PcD-Biph triplet state in THF/paraffin (1.0 μs) increased up to approximately three times as compared to that in THF

  5. Relaxation dynamics in quantum dissipative systems: The microscopic effect of intramolecular vibrational energy redistribution

    International Nuclear Information System (INIS)

    We investigate the effect of inter-mode coupling on the vibrational relaxation dynamics of molecules in weak dissipative environments. The simulations are performed within the reduced density matrix formalism in the Markovian regime, assuming a Lindblad form for the system-bath interaction. The prototypical two-dimensional model system representing two CO molecules approaching a Cu(100) surface is adapted from an ab initio potential, while the diatom-diatom vibrational coupling strength is systematically varied. In the weak system-bath coupling limit and at low temperatures, only first order non-adiabatic uni-modal coupling terms contribute to surface-mediated vibrational relaxation. Since dissipative dynamics is non-unitary, the choice of representation will affect the evolution of the reduced density matrix. Two alternative representations for computing the relaxation rates and the associated operators are thus compared: the fully coupled spectral basis, and a factorizable ansatz. The former is well-established and serves as a benchmark for the solution of Liouville-von Neumann equation. In the latter, a contracted grid basis of potential-optimized discrete variable representation is tailored to incorporate most of the inter-mode coupling, while the Lindblad operators are represented as tensor products of one-dimensional operators, for consistency. This procedure results in a marked reduction of the grid size and in a much more advantageous scaling of the computational cost with respect to the increase of the dimensionality of the system. The factorizable method is found to provide an accurate description of the dissipative quantum dynamics of the model system, specifically of the time evolution of the state populations and of the probability density distribution of the molecular wave packet. The influence of intra-molecular vibrational energy redistribution appears to be properly taken into account by the new model on the whole range of coupling strengths. It

  6. Further studies on cation clock reactions in glycosylation: observation of a configuration specific intramolecular sulfenyl transfer and isolation and characterization of a tricyclic acetal.

    Science.gov (United States)

    Huang, Min; Furukawa, Takayuki; Retailleau, Pascal; Crich, David; Bohé, Luis

    2016-06-01

    The use of the 2-O-(2-trimethylsilylmethallyl) group as intramolecular nucleophile and cation clock reaction in the glucopyranose series depends on the nature of the glycosyl donor. As previously reported, with trichloroacetimidates the anticipated intramolecular Sakurai reaction proceeds efficiently and is an effective clock, whereas with sulfoxides complications arise. The source of these complications is now shown to be an intramolecular sulfenyl transfer reaction between the tethered allylsilane and the activated sulfoxide. These results illustrate how a different unimolecular clock reaction may be required for a given cation when it is generated from different donors in order to avoid side reactions. The synthesis and cyclization of a 2-O-(3-hydroxypropyl) glucopyranosyl sulfoxide leading on activation to the formation of a trans-fused acetal is also described. The formation of this crystallographically-established trans-fused acetal is discussed in terms of the high effective concentration of the intramolecular nucleophile which leads to a high degree of a SN2 character in the displacement of the α-glucosyl triflate or at the level of the corresponding α-CIP. The possible use of such intramolecular alcohols as clock reactions and their limitations is discussed. PMID:27085740

  7. Effect of silane treatment of carboxylic-functionalized multi-walled carbon nanotubes on the thermal properties of epoxy nanocomposites

    Directory of Open Access Journals (Sweden)

    2010-04-01

    Full Text Available The effect of silane treatment of carboxylic-functionalized multi-walled carbon nanotubes (COOH-MWCNTs on the thermal properties of COOH-MWCNTs/epoxy nanocomposites was studied by comparing the research results on differential scanning calorimetry and thermogravimetric analysis data of silane treated COOH-MWCNTs/epoxy system with those of as-received COOH-MWCNTs/epoxy system. At the initial curing stage, silane treatment of COOH-MWCNTs does not change the autocatalytic cure reaction mechanism of COOH-MWCNTs/diglycidyl ether of bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole (COOH-MWCNTs/DGEBA/EMI-2,4 system, however, silane treatment of COOH-MWCNTs has catalytic effect on the curing process, which could help to shorten pre-cure time or lower pre-temperature. Then, at the later curing stage, silane treatment of COOH-MWCNTs promotes vitrification, which would help to shorten post-cure time or lower post-temperature. Therefore, overall, silane treatment of COOH-MWCNTs could bring positive effect on the processing of epoxy nanocomposites. Furthermore, it was also found that silane treatment of COOH-MWCNTs does not affect the thermal degradation pattern of COOH-MWCNTs/DGEBA/EMI-2,4 system, however, decreases the thermal stability of COOH-MWCNTs/DGEBA/EMI-2,4 nanocomposites.

  8. Characterization of multimetric variants of ubiquitin carboxyl-terminal hydrolase L1 in water by small-angle neutron scattering

    International Nuclear Information System (INIS)

    Here, we illustrated that the morphological structures of ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) variants and Parkinson's disease (PD) exhibit good pathological correlation by a small-angle neutron scattering (SANS). UCH-L1 is a neuro-specific multiple functional enzyme, deubiquitinating, ubiquityl ligase, and also involved in stabilization of mono-ubiquitin. To examine the relationship between multiple functions of UCH-L1 and the configuration of its variants [wild-type, I93M (linked to familial Parkinson's disease), and S18Y (linked to reduced risk of Parkinson's disease)], in this report, we proposed that these were all self-assembled dimers by an application of a rotating ellipsoidal model; the configurations of these dimers were quite different. The wild-type was a rotating ellipsoidal. The globular form of the monomeric component deformed by the I93M mutation. Conversely, the S18Y polymorphism promoted the globularity. Thus, the multiple functional balance is closely linked to the intermolecular interactions between the UCH-L1 monomer and the final dimeric configuration

  9. Isolation, characterization and colonization of 1-aminocyclopropane-1-carboxylate deaminase-producing bacteria XG32 and DP24.

    Science.gov (United States)

    Wang, Mei-Xia; Liu, Jia; Chen, Shuang-Lin; Yan, Shu-Zhen

    2012-03-01

    Two 1-aminocyclopropane-1-carboxylate deaminase-producing bacterial strains (DP24 and XG32) were isolated from surface-sterilized tomato roots and rizhospere soil. The strains were identified as Pseudomonas fluorescens biovar. IV (XG2) and Erwinia herbicola (DP24) by physiological and biochemical tests, and 16S rRNA gene analysis. Both strains showed positive plant growth-promoting activity when inoculated into cucumber (Cucumis sativus), tomato (Lycopersicon esculentum), pepper (Capsicum annuum) and rapeseed (Brassica napus L.). Colonization ability and behavior of these two strains were determined by treating mutant strains with rifampicin and fluorescence in situ hybridization (FISH) assay with rRNA targeted probes, respectively. Both strains were endophytic colonizers of pepper plants. The behavior of the two strains was not identical. Strain XG32 only colonized the root and reached the max level of 27.7 × 10(7) c.f.u./g (fresh weight), after 12 days postinoculation, while strain DP24 was able to colonize the roots, stems and leaves. The max level was reached at 40.87 × 10(7) c.f.u./g (fresh weight) in the roots, 17 × 10(7) c.f.u./g in the stems after 7 days postinoculation and 44.84 × 10(7) c.f.u./g in the leaves after 12 days postinoculation. PMID:22805836

  10. Significant improvement in the pore properties of SBA-15 brought about by carboxylic acids and hydrothermal treatment

    Indian Academy of Sciences (India)

    Milan Kanti Naskar; M Eswaramoorthy

    2008-01-01

    A comparative study of the pore properties of SBA-15 samples prepared under nonhydrothermal and hydrothermal conditions, in the absence and presence of carboxylic acids such as succinic, tartaric and citric acids has been carried out. In the absence of carboxylic acid, flake-like and spheroid particles were generally obtained irrespective of the preparative procedures. On the other hand, stirring of the pre-mix induces a rod-like morphology in presence of carboxylic acids. The samples prepared under non-hydrothermal conditions exhibit a higher degree of silicate condensation compared to those synthesized under hydrothermal conditions. SBA-15 samples prepared under hydrothermal conditions show higher values of the d (100) spacing independent of the presence of carboxylic acids. Presence of carboxylic acids as well as hydrothermal treatment improves the pore properties of SBA-15.

  11. Optimal activation of carboxyl-superparamagnetic iron oxide nanoparticles bioconjugated with antibody using orthogonal array design.

    Science.gov (United States)

    Liu, Lin; Zhang, Xiaoqang; Zhang, Yu; Pu, Yuepu; Yin, Lihong; Tang, Meng; Liu, Hui

    2013-12-01

    This study aims to bioconjugate anti-EMMPRIN monoclonal antibody on the surface of carboxyl-SPIO nanoparticles and to optimize the activated conditions of bioconjugation. Anti-EMMPRIN monoclonal antibody bioconjugated carboxyl-SPIO nanoparticles were performed through a coupling strategy of EDC and sulfo-NHS. The procedure was comprised of two steps by activation of carboxyl-SPIO nanoparticles and conjugation with monoclonal antibody. The optimal activated parameters of bioconjugation were evaluated by single factor design and orthogonal array design. SDS-PAGE analysis and Bradford assay was used for testing and verifying the efficiency of activated conditions obtained from orthogonal array. The results show that pH value, temperature and reaction time were important factors that influence bioconjugated efficiency. The activated parameters with pH value 6.2, temperature 25 degrees C and reaction time 30 min were obviously optimal for activation of carboxyl-SPIO nanoparticles and conjugation with monoclonal EMMPEIN antibody. This coupling strategy for anti-EMMPRIN mAb bioconjugated on SPIO nanoparticles was efficient, and may be further applied in the fields of medical or biological practices. PMID:24266206

  12. Kinetics of the esterification of active pharmaceutical ingredients containing carboxylic Acid functionality in polyethylene glycol

    DEFF Research Database (Denmark)

    Schou-Pedersen, Anne Marie V; Hansen, Steen Honoré; Moesgaard, Birthe;

    2014-01-01

    reactions. In this study, kinetics of two active pharmaceutical ingredients, cetirizine and indomethacin possessing carboxylic acid functionality, has been studied in PEG 400 and PEG 1000 at 50°C, 60°C, 70°C, and 80°C. HPLC-UV was applied for the determination of concentrations in the kinetic studies...

  13. Carboxylic Group Embedded Carbon Balls as a New Supported Catalyst for Hydrogen Economic Reactions.

    Science.gov (United States)

    Bordoloi, Ankur

    2016-03-01

    Carboxylic group functionalized carbon balls have been successfully synthesized by using a facile synthesis method and well characterized with different characterization techniques such as XPS, MAS NMR, SEM, ICP and N2 physi-sorption analysis. The synthesized material has been effectively utilized as novel support to immobilized ruthenium catalyst for hydrogen economic reactions. PMID:27455763

  14. Effects of intermediate metabolite carboxylic acids of TCA cycle on Microcystis with overproduction of phycocyanin.

    Science.gov (United States)

    Bai, Shijie; Dai, Jingcheng; Xia, Ming; Ruan, Jing; Wei, Hehong; Yu, Dianzhen; Li, Ronghui; Jing, Hongmei; Tian, Chunyuan; Song, Lirong; Qiu, Dongru

    2015-04-01

    Toxic Microcystis species are the main bloom-forming cyanobacteria in freshwaters. It is imperative to develop efficient techniques to control these notorious harmful algal blooms (HABs). Here, we present a simple, efficient, and environmentally safe algicidal way to control Microcystis blooms, by using intermediate carboxylic acids from the tricarboxylic acid (TCA) cycle. The citric acid, alpha-ketoglutaric acid, succinic acid, fumaric acid, and malic acid all exhibited strong algicidal effects, and particularly succinic acid could cause the rapid lysis of Microcystis in a few hours. It is revealed that the Microcystis-lysing activity of succinic acid and other carboxylic acids was due to their strong acidic activity. Interestingly, the acid-lysed Microcystis cells released large amounts of phycocyanin, about 27-fold higher than those of the control. On the other hand, the transcription of mcyA and mcyD of the microcystin biosynthesis operon was not upregulated by addition of alpha-ketoglutaric acid and other carboxylic acids. Consider the environmental safety of intermediate carboxylic acids. We propose that administration of TCA cycle organic acids may not only provide an algicidal method with high efficiency and environmental safety but also serve as an applicable way to produce and extract phycocyanin from cyanobacterial biomass. PMID:25342454

  15. Carboxyl terminal of rhodopsin kinase is required for the phosphorylation of photo—activated rhodopsin

    Institute of Scientific and Technical Information of China (English)

    YUQINGMING; LANMA; 等

    1998-01-01

    Human rhodopsin kinase (RK) and a carboxyl terminus-truncated mutant RK lacking the last 59 amino acids (RKC) were expressed in human embryonic kidney 293 cells to investigate the role of the carboxyl terminus of RK in recognition and phosphorylation of rhodopsin.RKC,like the wild-type RK,was detected in both plasma membranes and cytosolic fractions.The Cterminal truncated rhodopsin kinase was unable to phosphorylate photo-activated rhodopsin,but possesses kinase activity similar to the wild-type RK in phosphorylation of small peptide substrate.It suggests that the truncation did not disturb the gross structures of RK catalytic domain.Our results also show that RKC failed to translocate to photo-activated rod out segments.Taken together,our study demonstrate the carboxyl terminus of RK is required for phosphorylation of photo-activated rhodopsin and strongly indicate that carboxyl-terminus of RK may be involved in interaction with photo-activated rhodopsin.

  16. Mapping of Fab-1:VEGF Interface Using Carboxyl Group Footprinting Mass Spectrometry

    Science.gov (United States)

    Wecksler, Aaron T.; Kalo, Matt S.; Deperalta, Galahad

    2015-12-01

    A proof-of-concept study was performed to demonstrate that carboxyl group footprinting, a relatively simple, bench-top method, has utility for first-pass analysis to determine epitope regions of therapeutic mAb:antigen complexes. The binding interface of vascular endothelial growth factor (VEGF) and the Fab portion of a neutralizing antibody (Fab-1) was analyzed using carboxyl group footprinting with glycine ethyl ester (GEE) labeling. Tryptic peptides involved in the binding interface between VEGF and Fab-1 were identified by determining the specific GEE-labeled residues that exhibited a reduction in the rate of labeling after complex formation. A significant reduction in the rate of GEE labeling was observed for E93 in the VEGF tryptic peptide V5, and D28 and E57 in the Fab-1 tryptic peptides HC2 and HC4, respectively. Results from the carboxyl group footprinting were compared with the binding interface identified from a previously characterized crystal structure (PDB: 1BJ1). All of these residues are located at the Fab-1:VEGF interface according to the crystal structure, demonstrating the potential utility of carboxyl group footprinting with GEE labeling for mapping epitopes.

  17. A Combinatorial Interplay Among the 1-Aminocyclopropane-1-carboxylate Isoforms Regulates Ethylene Biosynthesis in Arabidopsis thaliana

    Science.gov (United States)

    Ethylene (C2H4) is a unique plant-signaling molecule that regulates numerous developmental processes. The key enzyme in the two-step biosynthetic pathway of ethylene is 1-aminocyclopropane-1-carboxylate synthase (ACS), which catalyzes the conversion of Sadenosyl-methionine (AdoMet) to ACC, the precu...

  18. Facilitation of peptide fibre formation by arginine-phosphate/carboxylate interactions

    Indian Academy of Sciences (India)

    K Krishna Prasad; Sandeep Verma

    2008-01-01

    This study describes peptide fibre formation in a hexapeptide, derived from the V3 loop of HIV-1, mediated by the interactions between arginine residues and phosphate/carboxylate anions. This charge neutralization approach was further confirmed when the deletion of arginine residue from the hexapeptide sequence resulted in fibre formation, which was studied by a combination of microscopic techniques.

  19. ANTI-CORROSION PROPERTIES OF CARBOXYLIC ACID IN WATER-GLYCOL SOLUTIONS

    Directory of Open Access Journals (Sweden)

    BASHKIRCEVA N.Y.

    2012-01-01

    Full Text Available Sodium salts of carboxylic acids were investigated to evaluate the corrosion properties of the water-glycol solutions. Corrosion tests were performed by methods of gravimetry and galvanostatic dissolution with metals used in cooling systems. The compositions of anticorrosion systems and their concentration that provide the most effective inhibition of metals were determined.

  20. Templating route for mesostructured calcium phosphates with carboxylic acid- and amine-type surfactants.

    Science.gov (United States)

    Ikawa, Nobuaki; Hori, Hideki; Kimura, Tatsuo; Oumi, Yasunori; Sano, Tsuneji

    2008-11-18

    Mesostructured calcium phosphates constructed by ionic frameworks were synthesized using carboxylic acid- and amine-type surfactants in mixed solvent systems of ethanol and water. A lamellar mesostructured calcium phosphate was prepared using palmitic acid as an anionic surfactant, as in the case using n-alkylamines. A wormhole-like mesostructured calcium phosphate can be obtained using dicarboxyl N-lauroyl- l-glutamic acid, whose headgroup is larger than that of palmitic acid. Similar mesostructured product was obtained using 4-dodecyldiethylenetriamine with a large headgroup containing two primary amine groups. Interactions of carboxyl and primary amino groups in the surfactant molecules with inorganic species are quite important for the formation of mesostructured calcium phosphates. The Ca/P molar ratio of mesostructured calcium phosphates was strongly affected by the molecular structure of surfactants containing carboxyl and primary amino groups. Ca-rich materials can be obtained using carboxylic acid-type surfactants (Ca/P approximately 1.7) rather than amine-type surfactants (Ca/P approximately 1.0). PMID:18947246