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Sample records for intramolecular heck reaction

  1. Fast and versatile microwave-assisted intramolecular Heck reaction in peptide macrocyclization using microwave energy.

    Science.gov (United States)

    Byk, Gerardo; Cohen-Ohana, Mirit; Raichman, Daniel

    2006-01-01

    We have revisited the intramolecular Heck reaction and investigated the microwave-assisted macrocyclization on preformed peptides using a model series of ring-varying peptides acryloyl-Gly-[Gly](n)-Phe(4-I)NHR; n = 0-4. The method was applied to both solution and solid supported cyclizations. We demonstrate that the intramolecular Heck reaction can be performed in peptides both in solution and solid support using a modified domestic microwave within 1 to 30 minutes in DMF under reflux with moderate yields ranging from 15 to 25% for a scale between 2-45 mg of linear precursors. The approach was applied to the synthesis of a constrained biologically relevant peptidomimetic bearing an Arg-Gly-Asp (RGD) sequence. These results make the microwave-assisted Heck reaction an attractive renovated approach for peptidomimetics. Copyright 2006 Wiley Periodicals, Inc.

  2. An Intramolecular Heck reaction that Prefers a 5-endo- to a 6-exo-trig Cyclization Pathway

    DEFF Research Database (Denmark)

    Vital, Paulo; Norrby, Per-Ola; Tanner, David Ackland

    2006-01-01

    A regioselective aromatic Claisen rearrangement was used to prepare 17a, the precursor of triflate 17e. The intramolecular Heck reaction of 17e is promoted only by bidentate phosphine ligands, giving exclusively and in excellent yield 20, the product of a 5-endo-trig cyclization, despite the poss......A regioselective aromatic Claisen rearrangement was used to prepare 17a, the precursor of triflate 17e. The intramolecular Heck reaction of 17e is promoted only by bidentate phosphine ligands, giving exclusively and in excellent yield 20, the product of a 5-endo-trig cyclization, despite...

  3. Matsuda–Heck reaction with arenediazonium tosylates in water

    Directory of Open Access Journals (Sweden)

    Ksenia V. Kutonova

    2015-03-01

    Full Text Available An environmentally friendly Matsuda–Heck reaction with arenediazonium tosylates has been developed for the first time. A range of alkenes was arylated in good to quantitative yields in water. The reaction is significantly accelerated when carried out under microwave heating. The arylation of haloalkylacrylates with diazonium salts has been implemented for the first time.

  4. The Heck reaction in the production of fine chemicals

    NARCIS (Netherlands)

    Vries, Johannes G. de

    2001-01-01

    An overview is given of the use of the Heck reaction for the production of fine chemicals. Five commercial products have been identified that are produced on a scale in excess of 1 ton/year. The herbicide Prosulfuron™ is produced via a Matsuda reaction of 2-sulfonatobenzenediazonium on

  5. Copper-catalyzed oxidative Heck reactions between alkyltrifluoroborates and vinyl arenes.

    Science.gov (United States)

    Liwosz, Timothy W; Chemler, Sherry R

    2013-06-21

    We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification, and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented.

  6. Reactivity and Regioselectivity in the Heck Reaction - A Hammett Study of 4-Substituted Styrenes

    DEFF Research Database (Denmark)

    Fristrup, Peter; Le Quement, Sebastian; Tanner, David Ackland

    2004-01-01

    The regioselectivity in the cationic Heck reaction of 4-substituted styrenes was addressed by a Hammett study. In this branching reaction, plots based on the substrate reactivity did not give meaningful data, whereas the product distribution was variable due to differing preferences for further...

  7. Supported liquid phase catalyst coating in micro flow Mizoroki-Heck reaction

    NARCIS (Netherlands)

    Stouten, S.C.; Noël, T.; Wang, Q.; Hessel, V.

    2015-01-01

    A Supported Liquid Phase Catalyst (SLPC) coating was successfully applied for the Mizoroki–Heck reaction in micro flow. Foremost, extended on stream operation was enabled and the on stream performance stability was verified. Stable catalytic activity was achieved during two consecutive runs totaling

  8. Mild and Efficient Nickel-Catalyzed Heck Reactions with Electron-Rich Olefins

    DEFF Research Database (Denmark)

    Gøgsig, Thomas; Kleimark, Jonatan; Lill, Sten O. Nilsson

    2012-01-01

    proved compatible, and the corresponding aryl methyl ketone could be secured after hydrolysis in yields approaching quantitative. Good functional group tolerance was observed matching the characteristics of the analogous Pd-catalyzed Heck reaction. The high levels of catalytic activity were explained...

  9. Design, Testing and Kinetic Analysis of Bulky Monodentate Phosphorus Ligands in the Mizoroki-Heck Reaction

    NARCIS (Netherlands)

    Dodds, Deborah L.; Boele, Maarten D. K.; van Strijdonck, Gino P. F.; de Vries, Johannes G.; van Leeuwen, Piet W. N. M.; Kamer, Paul C. J.

    A series of new monodentate phosphane ligands 2 have been evaluated in the MizorokiHeck arylation reaction of iodobenzene and styrene and compared with our previously reported ligands, 1, 3 and 4. The concept of rational ligand design is discussed, and we describe how the performance of this new

  10. Intramolecular and Transannular Diels-Alder Reactions

    DEFF Research Database (Denmark)

    Tanner, David Ackland; Ascic, Erhad

    2014-01-01

    Few reactions can compete with the Diels-Alder (DA) [4+2] cycloaddition for the rapid and efficient generation of molecular complexity. The DA reaction is atom-economic and stereospecific, as well as diastereo- and regioselective. The intramolecular version (IMDA) of the DA cycloaddition and its...... and dienophile, methods for acceleration of IMDA reactions (such as use of high pressure) and catalysis (using oxophilic or carbophilic metal complexes, Brønsted acids, and enzymes). The use of furans as diene components (IMDAF), intramolecular hetero-DA (IMHDA) and IMDA reactions with inverse electron demand...... are also covered. Applications of IMDA to asymmetric synthesis (from substrate control through to enantioselective catalysis, including organocatalysis) are presented, along with tandem sequences involving IMDA cycloaddition. A theme pervading the whole chapter is the use of IMDA reactions for the total...

  11. Palladium-Catalyzed Heck Coupling Reaction of Aryl Bromides in Aqueous Media Using Tetrahydropyrimidinium Salts as Carbene Ligands

    Directory of Open Access Journals (Sweden)

    İsmail Özdemir

    2010-01-01

    Full Text Available An efficient and stereoselective catalytic system for the Heck cross coupling reaction using novel 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (1, LHX and Pd(OAc2 loading has been reported. The palladium complexes derived from the salts 1a-f prepared in situ exhibit good catalytic activity in the Heck coupling reaction of aryl bromides under mild conditions.

  12. Carbonylative Heck Reactions Using CO Generated ex Situ in a Two-Chamber System

    DEFF Research Database (Denmark)

    Hermange, Philippe; Gøgsig, Thomas; Lindhardt, Anders Thyboe

    2011-01-01

    A carbonylative Heck reaction of aryl iodides and styrene derivatives employing a two-chamber system using a stable, crystalline, and nontransition metal based carbon monoxide source is reported. By applying near-stoichiometric amounts of the carbon monoxide precursor, an effective exploitation o...... of the hazardous CO gas is obtained affording chalcone derivatives in good yields. Application to isotope labeling, incorporating 13CO, was further established....

  13. Aqueous Oxidative Heck Reaction as a Protein-Labeling Strategy

    NARCIS (Netherlands)

    Ourailidou, Marilena; van der Meer, Jan-Ytzen; Baas, Bert-Jan; Jeronimus-Stratingh, Catherine; Gottumukkala, Aditya L.; Poelarends, Gerrit J.; Minnaard, Adriaan J.; Dekker, Frans

    2014-01-01

    An increasing number of chemical reactions are being employed for bio-orthogonal ligation of detection labels to protein-bound functional groups. Several of these strategies, however, are limited in their application to pure proteins and are ineffective in complex biological samples such as cell

  14. : Recyclable, ligand free palladium(II) catalyst for Heck reaction

    Indian Academy of Sciences (India)

    well as heterogeneous palladium catalysts, generated from either palladium(0) compounds or palladium(II) acetate or chloride salts.6 Several ligands such as phosphines, phoshites, carbenes, thioethers have been successfully employed for this reaction.7 However, homogeneous catalysis results in problems of recovery.

  15. Single-Site Palladium(II) Catalyst for Oxidative Heck Reaction: Catalytic Performance and Kinetic Investigations

    Energy Technology Data Exchange (ETDEWEB)

    Duan, Hui; Li, Mengyang; Zhang, Guanghui; Gallagher, James R.; Huang, Zhiliang; Sun, Yu; Luo, Zhong; Chen, Hongzhong; Miller, Jeffrey T.; Zou, Ruqiang; Lei, Aiwen; Zhao, Yanli

    2015-01-01

    ABSTRACT: The development of organometallic single-site catalysts (SSCs) has inspired the designs of new heterogeneous catalysts with high efficiency. Nevertheless, the application of SSCs in certain modern organic reactions, such as C-C bond formation reactions, has still been less investigated. In this study, a single-site Pd(II) catalyst was developed, where 2,2'-bipyridine-grafted periodic mesoporous organosilica (PMO) was employed as the support of a Pd(II) complex. The overall performance of the single-site Pd(II) catalyst in the oxidative Heck reaction was then investigated. The investigation results show that the catalyst displays over 99% selectivity for the product formation with high reaction yield. Kinetic profiles further confirm its high catalytic efficiency, showing that the rate constant is nearly 40 times higher than that for the free Pd(II) salt. X-ray absorption spectroscopy reveals that the catalyst has remarkable lifetime and recyclability.

  16. Breaking the regioselectivity rule for acrylate insertion in the Mizoroki-Heck reaction.

    Science.gov (United States)

    Wucher, Philipp; Caporaso, Lucia; Roesle, Philipp; Ragone, Francesco; Cavallo, Luigi; Mecking, Stefan; Göttker-Schnetmann, Inigo

    2011-05-31

    In modern methods for the preparation of small molecules and polymers, the insertion of substrate carbon-carbon double bonds into metal-carbon bonds is a fundamental step of paramount importance. This issue is illustrated by Mizoroki-Heck coupling as the most prominent example in organic synthesis and also by catalytic insertion polymerization. For unsymmetric substrates H(2)C = CHX the regioselectivity of insertion is decisive for the nature of the product formed. Electron-deficient olefins insert selectively in a 2,1-fashion for electronic reasons. A means for controlling this regioselectivity is lacking to date. In a combined experimental and theoretical study, we now report that, by destabilizing the transition state of 2,1-insertion via steric interactions, the regioselectivity of methyl acrylate insertion into palladium-methyl and phenyl bonds can be inverted entirely to yield the opposite "regioirregular" products in stoichiometric reactions. Insights from these experiments will aid the rational design of complexes which enable a catalytic and regioirregular Mizoroki-Heck reaction of electron-deficient olefins.

  17. Diphosphinoazine Palladium(II) Complexes as Catalysts for the Heck Reaction of Bromides and an Activated Chloride

    Czech Academy of Sciences Publication Activity Database

    Včelák, Jaroslav; Storch, Jan; Czakoová, Marie; Čermák, Jan

    2004-01-01

    Roč. 222, 1-2 (2004), s. 121-126 ISSN 1381-1169 R&D Projects: GA ČR GA203/01/0554; GA AV ČR IAA4072205 Institutional research plan: CEZ:AV0Z4072921 Keywords : heck reaction * amido complex es * palladium Subject RIV: CA - Inorganic Chemistry Impact factor: 2.316, year: 2004

  18. Palladium(II-catalyzed Heck reaction of aryl halides and arylboronic acids with olefins under mild conditions

    Directory of Open Access Journals (Sweden)

    Tanveer Mahamadali Shaikh

    2013-08-01

    Full Text Available A series of general and selective Pd(II-catalyzed Heck reactions were investigated under mild reaction conditions. The first protocol has been developed employing an imidazole-based secondary phosphine oxide (SPO ligated palladium complex (6 as a precatalyst. The catalytic coupling of aryl halides and olefins led to the formation of the corresponding coupled products in excellent yields. A variety of substrates, both electron-rich and electron-poor olefins, were converted smoothly to the targeted products in high yields. Compared with the existing approaches employing SPO–Pd complexes in a Heck reaction, the current strategy features mild reaction conditions and broad substrate scope. Furthermore, we described the coupling of arylboronic acids with olefins, which were catalyzed by Pd(OAc2 and employed N-bromosuccinimide as an additive under ambient conditions. The resulted biaryls have been obtained in moderate to good yields.

  19. Intramolecular Diels-Alder Reactions in Organic Synthesis

    OpenAIRE

    Sizemore, Nicholas Blandford Luke

    2014-01-01

    Intramolecular Diels-Alder (IMDA) reactions are an important class of reactions in synthetic organic chemistry for the rapid construction of polycyclic frameworks. Three classes of IMDA reactions were investigated synthetically and computationally: 1) all-carbon type 1 IMDA reactions, 2) N-acylnitroso type 2 IMDA reactions, and 3) cyano-azadiene IMDA reactions. The first class was implemented in research toward the total synthesis of maoecrystal Z and isopalhinine A. The second class was stud...

  20. Magnetically Separable Fe3O4@DOPA-Pd: A Heterogeneous Catalyst for Aqueous Heck Reaction

    Science.gov (United States)

    Magnetically separable Fe3O4@DOPA-Pd catalyst has been synthesized via anchoring of palladium over dopamine-coated magnetite via non-covalent interaction and the catalyst is utilized for expeditious Heck coupling in aqueous media.

  1. O-Carboxymethyl Chitosan Supported Heterogeneous Palladium and Ni Catalysts for Heck Reaction

    Directory of Open Access Journals (Sweden)

    Dongjun Lv

    2017-01-01

    Full Text Available Two polymer catalysts (Pd-OCMCS and Ni-OCMCS with good reusability were synthesized by coordinating Pd and Ni onto O-carboxymethyl chitosan (OCMCS. The chemical structure and thermal stability of prepared catalysts were determined by Fourier transform infrared (FT-IR spectra, Energy Dispersive Spectrometer (EDSanalysis, X-ray diffraction (XRD, and thermogravimetric analyzer (TG-DTG, and the analysis results showed that the Pd and Ni ions coordinated onto the OCMCS and formed a ligand with the –COOH group, amino groups, and –OH group on the OCMCS, and the EDS and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES analysis results showed that the loading amounts of Pd and Ni were approximately 8.3% and 8.9%, respectively. In the Heck reaction between aryl halides and n-butyl acrylate catalyzed by the prepared catalyst, the test results showed that the product yield followed the order of aryl iodide > aryl bromide > aryl chloride. Additionally, the product yield for the aryl iodide and aryl bromide could reach up to 99% and 96%, respectively. Moreover, the electron-withdrawing and electron-donating property of the group on the aryl also affected the product yield, and the product yield for aryl halides with electron-withdrawing group p-NO2, p-CH3CO, and p-CHO was higher than that with electron-donating group p-CH3.

  2. Intramolecular inverse electron demand Diels-Alder reactions of pyrimidines

    NARCIS (Netherlands)

    Frissen, A.E.

    1990-01-01

    This thesis deals with the intramolecular inverse electron demand Diels-Alder reaction of pyrimidines. The main objective of the study was to investigate the synthetic applicability of this reaction and to get more insight in the electronic and steric effects which determine the reactivity

  3. Preparation and Characterization of Pd Modified TiO2 Nanofiber Catalyst for Carbon–Carbon Coupling Heck Reaction

    Directory of Open Access Journals (Sweden)

    Leah O. Nyangasi

    2017-01-01

    Full Text Available TiO2 fibers were prepared through electrospinning of poly methyl methacrylate (PMMA and titanium isopropoxide (TIP solution followed by calcination of fibers in air at 500°C. Cetyltrimethylammonium bromide (CTAB protected palladium nanoparticles (Pd NPs prepared through reduction method were successfully adsorbed on the TiO2 nanofibers (NF. Combined studies of X-ray diffraction (XRD, scanning electron microscope (SEM, and transmission electron microscope (TEM indicated that the synthesized Pd/TiO2 had anatase. BET indicated that the synthesized TiO2 and Pd/TiO2 had a surface area of 53.4 and 43.4 m2/g, respectively. The activity and selectivity of 1 mol% Pd/TiO2 in the Heck reaction have been investigated towards the Mizoroki-Heck carbon–carbon cross-coupling of bromobenzene (ArBr and styrene. Temperature, time, solvent, and base were optimized and catalyst was recycled thrice. 1H NMR and 13C NMR indicated that stilbene, a known compound from literature, was obtained in various Heck reactions at temperatures between 100°C and 140°C but the recyclability was limited due to some palladium leaching and catalyst poisoning which probably arose from some residual carbon from the polymer. The catalyst was found to be highly active under air atmosphere with reaction temperatures up to 140°C. Optimized reaction condition resulted in 89.7% conversions with a TON of 1993.4 and TOF value of 332.2 hr−1.

  4. Enhancement in the Catalytic Activity of Pd/USY in the Heck Reaction Induced by H2 Bubbling

    Directory of Open Access Journals (Sweden)

    Miki Niwa

    2010-12-01

    Full Text Available Pd was loaded on ultra stable Y (USY zeolites prepared by steaming NH4-Y zeolite under different conditions. Heck reactions were carried out over the prepared Pd/USY. We found that H2 bubbling was effective in improving not only the catalytic activity of Pd/USY, but also that of other supported Pd catalysts and Pd(OAc2. Moreover, the catalytic activity of Pd/USY could be optimized by choosing appropriate steaming conditions for the preparation of the USY zeolites; Pd loaded on USY prepared at 873 K with 100% H2O gave the highest activity (TOF = 61,000 h−1, which was higher than that of Pd loaded on other kinds of supports. The prepared Pd/USY catalysts were applicable to the Heck reactions using various kinds of substrates including bromo- and chloro-substituted aromatic and heteroaromatic compounds. Characterization of the acid properties of the USY zeolites revealed that the strong acid site (OHstrong generated as a result of steaming had a profound effect on the catalytic activity of Pd.

  5. Enhancement in the catalytic activity of Pd/USY in the heck reaction induced by H2 bubbling.

    Science.gov (United States)

    Okumura, Kazu; Tomiyama, Takuya; Moriyama, Sayaka; Nakamichi, Ayaka; Niwa, Miki

    2010-12-24

    Pd was loaded on ultra stable Y (USY) zeolites prepared by steaming NH(4)-Y zeolite under different conditions. Heck reactions were carried out over the prepared Pd/USY. We found that H₂ bubbling was effective in improving not only the catalytic activity of Pd/USY, but also that of other supported Pd catalysts and Pd(OAc)₂. Moreover, the catalytic activity of Pd/USY could be optimized by choosing appropriate steaming conditions for the preparation of the USY zeolites; Pd loaded on USY prepared at 873 K with 100% H₂O gave the highest activity (TOF = 61,000 h⁻¹), which was higher than that of Pd loaded on other kinds of supports. The prepared Pd/USY catalysts were applicable to the Heck reactions using various kinds of substrates including bromo- and chloro-substituted aromatic and heteroaromatic compounds. Characterization of the acid properties of the USY zeolites revealed that the strong acid site (OH(strong)) generated as a result of steaming had a profound effect on the catalytic activity of Pd.

  6. Case Report of Focal Epithelial Hyperplasia (Heck's Disease) with Polymerase Chain Reaction Detection of Human Papillomavirus 13.

    Science.gov (United States)

    Brehm, Mary A; Gordon, Katie; Firan, Miahil; Rady, Peter; Agim, Nnenna

    2016-05-01

    Focal epithelial hyperplasia (FEH), or Heck's disease, is an uncommon benign proliferation of oral mucosa caused by the human papillomavirus (HPV), particularly subtypes 13 and 32. The disease typically presents in young Native American patients and is characterized by multiple asymptomatic papules and nodules on the oral mucosa, lips, tongue, and gingiva. The factors that determine susceptibility to FEH are unknown, but the ethnic and geographic distribution of FEH suggests that genetic predisposition, particularly having the human lymphocytic antigen DR4 type, may be involved in pathogenesis. We report a case of FEH with polymerase chain reaction detection of HPV13 in a healthy 11-year-old Hispanic girl and discuss the current understanding of disease pathogenesis, susceptibility, and treatment. © 2016 Wiley Periodicals, Inc.

  7. Investigating the nature of palladium chain-walking in the enantioselective redox-relay Heck reaction of alkenyl alcohols.

    Science.gov (United States)

    Hilton, Margaret J; Xu, Li-Ping; Norrby, Per-Ola; Wu, Yun-Dong; Wiest, Olaf; Sigman, Matthew S

    2014-12-19

    The mechanism of the redox-relay Heck reaction was investigated using deuterium-labeled substrates. Results support a pathway through a low energy palladium-alkyl intermediate that immediately precedes product formation, ruling out a tautomerization mechanism. DFT calculations of the relevant transition structures at the M06/LAN2DZ+f/6-31+G* level of theory show that the former pathway is favored by 5.8 kcal/mol. Palladium chain-walking toward the alcohol, following successive β-hydride eliminations and migratory insertions, is also supported in this study. The stereochemistry of deuterium labels is determined, lending support that the catalyst remains bound to the substrate during the relay process and that both cis- and trans-alkenes form from β-hydride elimination.

  8. Encaging palladium(0 in layered double hydroxide: A sustainable catalyst for solvent-free and ligand-free Heck reaction in a ball mill

    Directory of Open Access Journals (Sweden)

    Wei Shi

    2017-08-01

    Full Text Available In this paper, the synthesis of a cheap, reusable and ligand-free Pd catalyst supported on MgAl layered double hydroxides (Pd/MgAl-LDHs by co-precipitation and reduction methods is described. The catalyst was used in Heck reactions under high-speed ball milling (HSBM conditions at room temperature. The effects of milling-ball size, milling-ball filling degree, reaction time, rotation speed and grinding auxiliary category, which would influence the yields of mechanochemical Heck reactions, were investigated in detail. The characterization results of XRD, ICP–MS and XPS suggest that Pd/MgAl-LDHs have excellent textural properties with zero-valence Pd on its layers. The reaction results indicate that the catalyst could be utilized in HSBM systems to afford a wide range of Heck coupling products in satisfactory yields. Furthermore, this catalyst could be easily recovered and reused for at least five times without significant loss of catalytic activity.

  9. Reusable Polymer-Supported Terpyridine Palladium Complex for Suzuki-Miyaura, Mizoroki-Heck, Sonogashira, and Tsuji-Trost Reaction in Water

    Directory of Open Access Journals (Sweden)

    Takuya Nagamine

    2011-03-01

    Full Text Available A novel heterogeneous transition-metal catalyst comprising a polymer-supported terpyridine palladium(II complex was prepared and found to promote the Suzuki-Miyaura, Mizoroki-Heck, Sonogashira, and Tsuji-Trost, reactions in water under aerobic conditions with a high to excellent yield. The catalyst was recovered by simple filtration and directly reused several times without loss of catalytic activity.

  10. Enantio- and Stereoselective Construction of Atisane Scaffold via Organocatalytic Intramolecular Michael Reaction and Diels-Alder Reaction.

    Science.gov (United States)

    Sekita, Hiroko; Adachi, Kyohei; Kobayashi, Ippei; Sato, Yusuke; Nakada, Masahisa

    2017-05-05

    An enantio- and stereoselective construction of the atisane scaffold via organocatalytic intramolecular Michael reaction and Diels-Alder reaction is described. The organocatalytic intramolecular Michael reaction has been found to stereoselectively generate a trans-stereodiad comprising an all-carbon quaternary and a tertiary stereogenic centers. Use of the chiral secondary amine bearing thiourea with benzoic acid as additive is the key to obtaining the desired product with excellent ee in synthetically acceptable yield. The prepared chiral building block has been successfully converted to the compound including the atisane scaffold via the highly stereoselective intramolecular Diels-Alder reaction.

  11. Metabolic alkene labeling and in vitro detection of histone acylation via the aqueous oxidative Heck reaction

    NARCIS (Netherlands)

    Ourailidou, Maria E; Dockerty, Paul; Witte, Martin; Poelarends, Gerrit J; Dekker, Frank J

    2015-01-01

    The detection of protein lysine acylations remains a challenge due to lack of specific antibodies for acylations with various chain lengths. This problem can be addressed by metabolic labeling techniques using carboxylates with reactive functionalities. Subsequent chemoselective reactions with a

  12. Pd-isatin Schiff base complex immobilized onγ-Fe2O3 as a magnetically recyclable catalyst for the Heck and Suzuki cross-coupling reactions

    Institute of Scientific and Technical Information of China (English)

    Sara Sobhani; Farzaneh Zarifi

    2015-01-01

    A Pd‐isatin Schiff base complex immobilized onγ‐Fe2O3 (Pd‐isatin Schiff base‐γ‐Fe2O3) was synthe‐sized and characterized by Fourier transform infrared, scanning electron microscopy, high resolu‐tion transmission electron microscopy, X‐ray diffraction, thermogravimetric gravimetric analysis, inductively‐coupled plasma, X‐ray photoelectron spectroscopy, and elemental analysis. It was used as a magnetically reusable Pd catalyst for the Heck and Suzuki cross‐coupling reactions.

  13. Intramolecular Diels-Alder reactions of pyrimidines, a synthetic and computational study

    NARCIS (Netherlands)

    Stolle, W.A.W.

    1992-01-01

    This thesis deals with an investigation on the ringtransformation reactions of 2and 5-(ω-alkynyl)pyrimidine derivatives, which undergo upon heating an intramolecular Diels-Alder reaction and subsequently a spontaneous retro Diels- Alder reaction. To get a better insight into the

  14. Palladium(II/Cationic 2,2’-Bipyridyl System as a Highly Efficient and Reusable Catalyst for the Mizoroki-Heck Reaction in Water

    Directory of Open Access Journals (Sweden)

    Fu-Yu Tsai

    2010-01-01

    Full Text Available A water-soluble and air-stable Pd(NH32Cl2/cationic 2,2’-bipyridyl system was found to be a highly-efficient and reusable catalyst for the coupling of aryl iodides and alkenes in neat water using Bu3N as a base. The reaction was conducted at 140 °C in a sealed tube in air with a catalyst loading as low as 0.0001 mol % for the coupling of activated aryl iodides with butyl and ethyl acrylates, providing the corresponding products in good to excellent yields with very high turnover numbers. In the case of styrene, Mizoroki-Heck coupling products were obtained in good to high yields by using a greater catalyst loading (1 mol % and TBAB as a phase-transfer agent. After extraction, the residual aqueous solution could be reused several times with only a slight decrease in its activity, making the Mizoroki-Heck reaction “greener”.

  15. Arylation of beta, gamma-unsaturated lactones by a Heck-Matsuda reaction: an unexpected route to aryldiazene butenolides and pyridazinones

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Jason G.; Correia, Carlos Roque D., E-mail: roque@iqm.unicamp.b [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Inst. de Quimica

    2010-07-01

    The palladium catalysed coupling of aryldiazonium salts with {beta}-{gamma}-unsaturated lactones under basic conditions has been investigated. Both (3H)-furanone and {alpha}-angelicalactone were evaluated as substrates in the Heck Matsuda reaction but both failed to afford the desired arylated butenolides. Under basic conditions, {beta}-{gamma}-unsaturated lactones generate highly nucleophilic enolates that preferentially undergo azo coupling reactions with arenediazonium salts to afford aryldiazene butenolides. The electronic and steric effect of the substituents on the aryldiazonium salt in the azo coupling reaction is described. Aryldiazene-lactone derivatives were obtained in good yields from a highly facile and straightforward procedure. An aminoisomaleimide was formed from (3H)-furanone and cyclized to the corresponding pyridazinones in modest yield. (author)

  16. Synthesis of novel steroid-tetrahydroquinoline hybrid molecules and D-homosteroids by intramolecular cyclization reactions.

    Science.gov (United States)

    Magyar, Angéla; Wölfling, János; Kubas, Melanie; Cuesta Seijo, Jose Antonio; Sevvana, Madhumati; Herbst-Irmer, Regine; Forgó, Péter; Schneider, Gyula

    2004-05-01

    Steroidal aryliminium salts were prepared from D-seco-pregnene aldehyde 2b, and their BF3.OEt2-catalyzed reactions were studied. The nature of the substituent R1 in the anilines 3-6 essentially influenced the chemoselectivity. Using unsubstituted 3, 4-methoxy- (4) or 4-bromoaniline (5), different tetrahydroquinoline derivatives 7a-13a via intramolecular hetero Diels-Alder reaction were formed. In the case of 4-nitroaniline (6) the N-arylamino-D-homopregnane (14a) were also obtained. We assume, that an intramolecular Prins reaction led to this type of fluoro-D-homosteroid. The main products represent a new class of tetrahydroquinolino-androstenes.

  17. 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 molecu...... comprehensive, reviews....

  18. Tetradentate N2O2 Chelated Palladium(II Complexes: Synthesis, Characterization, and Catalytic Activity towards Mizoroki-Heck Reaction of Aryl Bromides

    Directory of Open Access Journals (Sweden)

    Siti Kamilah Che Soh

    2013-01-01

    Full Text Available Four air and moisture-stable palladium(II-Schiff base complexes, N,N′-bis(α-methylsalicylidenepropane-1,3-diamine palladium(II (2a, N,N′-bis(4-methyl-α-methylsalicylidenepropane-1,3-diamine palladium(II (2b, N,N′-bis(3,5-di-tert-butylsalicylidenepropane-1,3-diamine palladium(II (2c, and N,N′-bis(4-methoxy-salicylidenepropane-1,3-diamine palladium(II (2d, have been successfully synthesised and characterised by CHN elemental analyses and conventional spectroscopic methods. These complexes were investigated as catalysts in the phosphine-free Mizoroki-Heck cross-coupling reactions of aryl bromides with methyl acrylate.

  19. A facile one-pot solvothermal method for synthesis of magnetically recoverable Pd-Fe3O4 hybrid nanocatalysts for the Mizoroki-Heck reaction

    Science.gov (United States)

    Zhen, Fangchen; Ran, Maofei; Chu, Wei; Jiang, Chengfa; Sun, Wenjing

    2018-03-01

    Pd-Fe3O4 hybrid nanostructures were prepared using a simple one-pot hydrothermal method. The prepared materials were characterized by Fourier transform-infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma, N2 adsorption-desorption, and vibrating sample magnetometry. This self-assembled nanosystem acted as an efficient magnetically recyclable noble metal-based multi-functional nanocatalyst. It showed excellent catalytic activity and stability for the Heck reaction of iodobenzene and styrene under mild conditions. The methods used to prepare the Pd-Fe3O4 catalysts were simple and low-cost, which will be useful for the large-scale development and application of a magnetically recoverable Pd catalyst.

  20. Fe(II)/Fe(III)-Catalyzed Intramolecular Didehydro-Diels-Alder Reaction of Styrene-ynes.

    Science.gov (United States)

    Mun, Hyeon Jin; Seong, Eun Young; Ahn, Kwang-Hyun; Kang, Eun Joo

    2018-02-02

    The intramolecular didehydro-Diels-Alder reaction of styrene-ynes was catalyzed by Fe(II) and Fe(III) to produce various naphthalene derivatives under microwave heating conditions. Mechanistic calculations found that the Fe(II) catalyst activates the styrenyl diene in an inverse-electron-demand Diels-Alder reaction, and the consecutive dehydrogenation reaction can be promoted by either Fe(II)-catalyzed direct dehydrogenation or an Fe(III)-catalyzed rearomatization/dehydrogenation pathway.

  1. Water-dispersable hybrid Au-Pd nanoparticles as catalysts in ethanol oxidation, aqueous phase Suzuki-Miyaura and Heck reactions

    KAUST Repository

    Song, Hyon Min

    2012-01-01

    The catalytic activities of water-dispersable Au@Pd core-shell nanoparticles (NPs) and Au-Pd alloy NPs were examined. There is growing interest in Au-Pd hybridized NPs in a supported matrix or non-supported forms as catalysts in various reactions that are not limited to conventional Pd-related reactions. Four different Au@Pd core-shell NPs in this study were prepared at room temperature with help from the emulsion phase surrounding the Au core NPs. Au-Pd alloy NPs were prepared over 90 °C, and underwent phase transfer to aqueous medium for their catalytic use. Au@Pd core-shell NPs show catalytic activity in ethanol oxidation reactions as electrocatalysts, and both core-shell and alloy NPs are good to excellent catalysts in various Suzuki-Miyaura and Heck reactions as heterogeneous catalysts. Specifically, Au@Pd core-shell NPs with sharp branched arms show the highest yield in the reactions tested in this study. A relatively small amount (0.25 mol%) was used throughout the catalytic reactions. © 2012 The Royal Society of Chemistry.

  2. Property (RD) for Hecke Pairs

    International Nuclear Information System (INIS)

    Shirbisheh, Vahid

    2012-01-01

    As the first step towards developing noncommutative geometry over Hecke C ∗ -algebras, we study property (RD) (Rapid Decay) for Hecke pairs. When the subgroup H in a Hecke pair (G, H) is finite, we show that the Hecke pair (G, H) has (RD) if and only if G has (RD). This provides us with a family of examples of Hecke pairs with property (RD). We also adapt Paul Jolissant’s works in Jolissaint (J K-Theory 2:723–735, 1989; Trans Amer Math Soc 317(1):167–196, 1990) to the setting of Hecke C ∗ -algebras and show that when a Hecke pair (G, H) has property (RD), the algebra of rapidly decreasing functions on the set of double cosets is closed under holomorphic functional calculus of the associated (reduced) Hecke C ∗ -algebra. Hence they have the same K 0 -groups.

  3. Excited state intramolecular charge transfer reaction in 4-(1 ...

    Indian Academy of Sciences (India)

    Administrator

    cal reactions to the determination of paleotempera- tures from isotopic ... ordered liquid than H2O due to stronger H-bond in- teractions in the deuterated water ... layer chromatography and monitoring the excitation wavelength dependence of ...

  4. [Development of boomerang-type intramolecular cascade reactions and application to natural product synthesis].

    Science.gov (United States)

    Takasu, K

    2001-12-01

    Intramolecular cascade reaction has received much attention as a powerful methodology to construct a polycyclic framework in organic synthesis. We have been developing "boomerang-type cascade reaction" to construct a variety of polycyclic skeletons efficiently. In the above reactions, a nucleophilic function of substrates changes the character into an electrophile after the initial reaction, and the electrophilic group acts as a nucleophile in the second reaction. That is, the reaction center stepwise moves from one functional group back to the same one via other functional groups. The stream of the electron concerning the cascade reaction is like a locus of boomerang. We show here three different boomerang-type reactions via ionic species or free radicals. 1) Diastereoselective Michael-aldol reaction based on the chiral auxiliary method and enantioselective Michael-aldol reaction by the use of external chiral sources. 2) Short and efficient total syntheses of longifolane sesquiterpenes utilizing intramolecular double Michael addition as a key step. 3) Development of boomerang-type radical cascade reaction of halopolyenes to construct terpenoid skeletons and its regioselectivity.

  5. N-heterocycle carbene (NHC)-ligated cyclopalladated N,N-dimethylbenzylamine: a highly active, practical and versatile catalyst for the Heck-Mizoroki reaction.

    Science.gov (United States)

    Peh, Guang-Rong; Kantchev, Eric Assen B; Zhang, Chi; Ying, Jackie Y

    2009-05-21

    The wide dissemination of catalytic protocols in academic and industrial laboratories is facilitated by the development of catalysts that are not only highly active but also user-friendly, stable to moisture, air and long term storage and easy to prepare on a large scale. Herein we describe a protocol for the Heck-Mizoroki reaction mediated by cyclopalladated N,N-dimethylbenzylamine (dmba) ligated with a N-heterocyclic carbene, 1,3-bis(mesityl)imidazol-2-ylidene (IMes), that fulfils these criteria. The precatalyst can be synthesized on approximately 100 g scale by a tri-component, sequential, one-pot reaction of N,N-dimethylbenzylamine, PdCl2 and IMes.HCl in refluxing acetonitrile in air in the presence of K2CO3. This single component catalyst is stable to air, moisture and long term storage and can be conveniently dispensed as a stock solution in NMP. It mediates the Heck-Mizoroki reaction of a range of aryl- and heteroaryl bromides in reagent grade NMP at the 0.1-2 mol% range without the need for rigorous anhydrous techniques or a glovebox, and is active even in air. The catalyst is capable of achieving very high levels of catalytic activity (TON of up to 5.22 x 10(5)) for the coupling of a deactivated arylbromide, p-bromoanisole, with tBu acrylate as a benchmark substrate pair. A wide range of aryl bromides, iodides and, for the first time with a NHC-Pd catalyst, a triflate was coupled with diverse acrylate derivatives (nitrile, tert-butyl ester and amides) and styrene derivatives. The use of excess (>2 equiv.) of the aryl bromide and tert-butyl acrylate leads to mixture of tert-butyl beta,beta-diarylacrylate and tert-butyl cinnamate derivatives depending on the substitution pattern of the aryl bromide. Electron rich m- and p-substituted arylbromides give the diarylated products exclusively, whereas electron-poor aryl bromides give predominantly mono-arylated products. For o-substituted aryl bromides, no doubly arylated products could be obtained under any

  6. Synthesis, Chemosensory Properties, and Self-Assembly of Terpyridine-Containing Conjugated Polycarbazole through RAFT Polymerization and Heck Coupling Reaction

    Directory of Open Access Journals (Sweden)

    Po-Chih Yang

    2017-09-01

    Full Text Available We report the responsive fluorescence chemosensory phenomena of a carbazole-functionalized crosslinked polymer (PCaT with pendent terpyridine (tpy groups as receptors of metal ions. The polymer was synthesized using Heck polymerization between 3,6-dibromide groups in a carbazole-based polymer (PC2Br and divinyl tpy monomer. The effects of the polymeric structure on the optical and chemosensory properties of the PCaT were compared with those of a carbazole-tpy alternating conjugated polymer (PCT. Photoluminescence titrations demonstrated that the PCaT and PCT had the high sensing ability toward Fe3+ ions, with Stern–Volmer constants of 8.10 × 104 and 6.68 × 104 M−1, respectively. The limit of detection (LOD toward Fe3+ of the PCaT and PCT was estimated to be 1.31 × 10−6 and 1.81 × 10−6 M, respectively, and the superior LOD of the PCaT was ascribed to its lowly crosslinked structure. The fluorescence of the solutions of these polymers that were quenched by Fe3+ ions recovered when trace CN− anions were added because of the high stability constant of the CN−–Fe3+ complex. Micellar aggregates with a mean diameter of approximately 239.5 nm were formed by dissolving the PCaT in tetrahydrofuran (THF solution. Our results suggest that the PCaT is a promising material for chemosensory applications.

  7. Effect of a weak magnetic field on the Mizoroki–Heck coupling reaction in the presence of wicker-like palladium-poly(N-vinylpyrrolidone)-iron nanocatalyst

    Energy Technology Data Exchange (ETDEWEB)

    Rafiee, Ezzat, E-mail: ezzat_rafiee@yahoo.com [Department of Inorganic Chemistry, Faculty of Chemistry, Razi University, Kermanshah 67149 (Iran, Islamic Republic of); Institute of Nano Science and Nano Technology, Razi University, Kermanshah 67149 (Iran, Islamic Republic of); Joshaghani, Mohammad [Department of Inorganic Chemistry, Faculty of Chemistry, Razi University, Kermanshah 67149 (Iran, Islamic Republic of); Institute of Nano Science and Nano Technology, Razi University, Kermanshah 67149 (Iran, Islamic Republic of); Abadi, Parvaneh Ghaderi-Shekhi [Institute of Nano Science and Nano Technology, Razi University, Kermanshah 67149 (Iran, Islamic Republic of)

    2016-06-15

    The wicker-like Pd-PVP-Fe (palladium-poly(N-vinylpyrrolidone)-iron) was synthesized by the external magnetic field (EMF). The Pd-based catalyst with nano and the face-centered cubic (fcc) structure was obtained at room temperature without using any additive. The resulting composite was characterized. The results show that EMF has a great influence on morphology, particle size, and crystalline structure of the Pd-PVP-Fe composite. The resulting composite (Pd-PVP-Fe), was found to be an effective catalyst for the Mizoroki–Heck reaction while is exposed to EMF with the intensity at 486 µT. The reused catalyst for at least five repeating cycles, shows excellent activity. - Highlights: • The wicker-like Pd-PVP-Fe nanocatalyst was synthesized via external magnetic field. • The resulting catalyst composite was characterized. • The C–C coupling reaction was carried out at magnetic field and room temperature. • Magnetic field affects on the morphology and size of the catalyst. • The catalyst could be reused without significant degradation in activity.

  8. Origin of Exo/Endo Selectivity in the Intramolecular Diels-Alder Reaction

    International Nuclear Information System (INIS)

    Yan, Shihai; Ryu, Do Hyun; Lee, Jin Yong

    2010-01-01

    The stereoselectivity of the intramolecular Diels-Alder reactions of 1 and its derivatives were investigated by ab initio calculations. The stereoselectivity mainly originates from the steric repulsion and the orbital interactions. The additional s-cis and s-trans conformations by introducing the carbonyl group at the neighbor of diene or dienophile may change the stereoselectivity, hence this kind of substitution can be utilized for stereoselective asymmetric synthesis

  9. Photoinduced intramolecular substitution reaction of aryl halide with carbonyl oxygen of amide group

    CERN Document Server

    Park, Y T; Kim, M S; Kwon, J H

    2002-01-01

    Photoreaction of N-(o-halophenyl)acetamide in basic acetonitrile produces an intramolecular substituted product, 2-methylbenzoxazole in addition to reduced product, acetanilide, whereas photoreaction of N-(o-halobenzyl)acetamide affords a reduced product, N-benzylacetamide only. On the basis of preparative reaction, kinetics, and UV/vis absorption behavior, an electrophilic aromatic substitution of aryl halide with oxygen of its amide bond are proposed.

  10. Photoinduced intramolecular substitution reaction of aryl halide with carbonyl oxygen of amide group

    Energy Technology Data Exchange (ETDEWEB)

    Park, Yong Tae; Song, Myong Geun; Kim, Moon Sub; Kwon, Jeong Hee [Kyungpook National Univ., Daegu (Korea, Republic of)

    2002-09-01

    Photoreaction of N-(o-halophenyl)acetamide in basic acetonitrile produces an intramolecular substituted product, 2-methylbenzoxazole in addition to reduced product, acetanilide, whereas photoreaction of N-(o-halobenzyl)acetamide affords a reduced product, N-benzylacetamide only. On the basis of preparative reaction, kinetics, and UV/vis absorption behavior, an electrophilic aromatic substitution of aryl halide with oxygen of its amide bond are proposed.

  11. Photoinduced intramolecular substitution reaction of aryl halide with carbonyl oxygen of amide group

    International Nuclear Information System (INIS)

    Park, Yong Tae; Song, Myong Geun; Kim, Moon Sub; Kwon, Jeong Hee

    2002-01-01

    Photoreaction of N-(o-halophenyl)acetamide in basic acetonitrile produces an intramolecular substituted product, 2-methylbenzoxazole in addition to reduced product, acetanilide, whereas photoreaction of N-(o-halobenzyl)acetamide affords a reduced product, N-benzylacetamide only. On the basis of preparative reaction, kinetics, and UV/vis absorption behavior, an electrophilic aromatic substitution of aryl halide with oxygen of its amide bond are proposed

  12. The preparation and intramolecular radical cyclisation reactions of chiral oxyme ethers

    International Nuclear Information System (INIS)

    Booth, Susan E.; Jenkins, Paul R.

    1998-01-01

    Chiral oxime ether 2 and Oxime ester 4 have been prepared by alkylation and esterification of the oxime 1. Racemic hydroxylamine 6 and chiral hydroxylamine 10 have been synthesised from N-hydroxysuccinimide and the corresponding alcohol in the presence of diethyl azo dicarboxylate, the two product were converted into the oxime ethers 7 and 11 respectively. The intramolecular radical cyclisation reactions of these oxime ethers and esters has been studied, successful reaction was observed to produce alkyl hydroxylamines 3,8 and 12. (author)

  13. The Preparation and Intramolecular Radical Cyclisation Reactions of Chiral Oxime Ethers

    Directory of Open Access Journals (Sweden)

    Booth Susan E.

    1998-01-01

    Full Text Available Chiral oxime ether 2 and Oxime ester 4 have been prepared by alkylation and esterification of the oxime 1. Racemic hydroxylamine 6 and chiral hydroxylamine 10 have been synthesised from N-hydroxysuccinimide and the corresponding alcohol in the presence of diethylazodicarboxylate, the two products were converted into the oxime ethers 7 and 11 respectively. The intramolecular radical cyclisation reactions of these oxime ethers and esters has been studied, successful reaction was observed to produce alkyl hydroxylamines 3, 8 and 12.

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

    Directory of Open Access Journals (Sweden)

    Norbert Haider

    1998-01-01

    Full Text Available 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] cycloaddition reaction.

  15. Hecke algebras with unequal parameters

    CERN Document Server

    Lusztig, G

    2003-01-01

    Hecke algebras arise in representation theory as endomorphism algebras of induced representations. One of the most important classes of Hecke algebras is related to representations of reductive algebraic groups over p-adic or finite fields. In 1979, in the simplest (equal parameter) case of such Hecke algebras, Kazhdan and Lusztig discovered a particular basis (the KL-basis) in a Hecke algebra, which is very important in studying relations between representation theory and geometry of the corresponding flag varieties. It turned out that the elements of the KL-basis also possess very interesting combinatorial properties. In the present book, the author extends the theory of the KL-basis to a more general class of Hecke algebras, the so-called algebras with unequal parameters. In particular, he formulates conjectures describing the properties of Hecke algebras with unequal parameters and presents examples verifying these conjectures in particular cases. Written in the author's precise style, the book gives rese...

  16. 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.

  17. Synthesis of hybrid interfacial silica-based nanospheres composite as a support for ultra-small palladium nanoparticle and application of PdNPs/HSN in Mizoroki-Heck reaction

    Science.gov (United States)

    Rostamnia, Sadegh; Kholdi, Saba

    2017-12-01

    The silica based hollow nanosphere (silica-HNS) containing polymer of polyaniline was synthesized and chosen as a promising support for PdNPs. Then it was applied as a green catalyst in the reaction of Heck coupling with high yield. TEM and SEM-EDX/mapping images were used to study the structure and morphology. FT-IR spectroscopy, Thermal gravimetry analysis (TGA), and BET were used to characterize and investigate the catalyst. Also, the amounts of Pd loading were characterized by ICP-AES technique. Catalyst recyclability showed 5 successful runs for the reaction.

  18. Fused-Ring Formation by an Intramolecular "Cut-and-Sew" Reaction between Cyclobutanones and Alkynes.

    Science.gov (United States)

    Deng, Lin; Jin, Likun; Dong, Guangbin

    2018-03-01

    The development of a catalytic intramolecular "cut-and-sew" transformation between cyclobutanones and alkynes to construct cyclohexenone-fused rings is described herein. The challenge arises from the need for selective coupling at the more sterically hindered proximal position, and can be addressed by using an electron-rich, but less bulky, phosphine ligand. The control experiment and 13 C-labelling study suggest that the reaction may start with cleavage of the less hindered distal C-C bond of cyclobutanones, followed by decarbonylation and CO reinsertion to enable Rh insertion at the more hindered proximal position. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Synthesis of novel room temperature chiral ionic liquids: application as reaction media for the heck arylation of aza-endocyclic acrylates

    Energy Technology Data Exchange (ETDEWEB)

    Pastre, Julio C.; Correia, Carlos R.D., E-mail: genisson@chimie.ups-tlse.f, E-mail: roque@iqm.unicamp.b [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Inst. de Quimica; Genisson, Yves [Universite Paul Sabatier, Toulouse (France). Lab. de Synthese et Physicochimie des Molecules d' Interet Biologique; Saffon, Nathalie [Universite Paul Sabatier, Toulouse (France). Structure federative toulousaine en chimie moleculaire (SFTCM); Dandurand, Jany [Universite Paul Sabatier, Toulouse (France). Lab. de Physique des Polymeres

    2010-07-01

    New achiral and chiral RTILs were prepared using novel and/or optimized synthetic routes. These new series of imidazolinium, imidazolium, pyridinium and nicotine-derived ionic liquids were fully characterized including differential scanning calorimetry (DSC) analysis. The performance of these achiral and chiral room temperature ionic liquids (RTILs) was demonstrated by means of the Heck arylation of endocyclic acrylates employing arenediazonium salts and aryl iodides. The Heck arylations performed in the presence of these ionic entities, either as a solvent or as an additive, were effective leading to complete conversion of the substrate and good to excellent yield of the Heck adduct. In spite of the good performances, no asymmetric induction was observed in any of the cases studied. Two new diastereoisomeric NHC-palladium complexes were prepared in good yields from a chiral imidazolium salt and their structure characterized by X-ray diffraction. Overall, the Heck arylations employing arenediazonium tetrafluoroborates in RTILs were more effective than the traditional protocols employing aryl iodides in terms of reactivity and yields. (author)

  20. Medium-Ring Effects on the Endo/Exo Selectivity of the Organocatalytic Intramolecular Diels-Alder Reaction.

    Science.gov (United States)

    Hooper, Joel F; James, Natalie C; Bozkurt, Esra; Aviyente, Viktorya; White, Jonathan M; Holland, Mareike C; Gilmour, Ryan; Holmes, Andrew B; Houk, K N

    2015-12-18

    The intramolecular Diels-Alder reaction has been used as a powerful method to access the tricyclic core of the eunicellin natural products from a number of 9-membered-ring precursors. The endo/exo selectivity of this reaction can be controlled through a remarkable organocatalytic approach, employing MacMillan's imidazolidinone catalysts, although the mechanistic origin of this selectivity remains unclear. We present a combined experimental and density functional theory investigation, providing insight into the effects of medium-ring constraints on the organocatalyzed intramolecular Diels-Alder reaction to form the isobenzofuran core of the eunicellins.

  1. Negative resists for i-line lithography utilizing acid-catalyzed intramolecular dehydration reaction

    Science.gov (United States)

    Ueno, Takumi; Uchino, Shou-ichi; Hattori, Keiko T.; Onozuka, Toshihiko; Shirai, Seiichiro; Moriuchi, Noboru; Hashimoto, Michiaki; Koibuchi, S.

    1994-05-01

    Chemical amplification negative resist system composed of a novolak resin, a carbinol and an acid generator is investigated for i-line phase-shift lithography. The reaction in this resist is based on an acid-catalyzed intramolecular dehydration reaction. The dehydration products act as aqueous-base dissolution inhibitors, and carbinol compounds in unexposed areas work as dissolution promoters. The resist composed of a novolak resin, 1,4-bis((alpha) -hydroxyisopropyl) benzene (DIOL-1) and 2- naphthoylmethyltetramethylenesulfonium triflate (PAG-2) gives the best lithographic performance in terms of sensitivity and resolution. Line-and-space patterns of 0.275 micrometers are obtained using an i-line stepper (NA:0.45) in conjunction with a phase shifting mask.

  2. Oxidative Heck Reaction as a Tool for Para-selective Olefination of Aniline: A DFT Supported Mechanism.

    Science.gov (United States)

    Moghaddam, Firouz Matloubi; Pourkaveh, Raheleh; Karimi, Ashkan

    2017-10-06

    This study describes the first para-selective palladium-catalyzed alkenylation of tertiary amines. This regioselective C-H activation was conducted without any chelation moieties. A series of olefins were reacted under mild reaction conditions at 60 °C, and the corresponding products were obtained in good yields with high selectivity.

  3. Reaction Coordinate, Free Energy, and Rate of Intramolecular Proton Transfer in Human Carbonic Anhydrase II.

    Science.gov (United States)

    Paul, Sanjib; Paul, Tanmoy Kumar; Taraphder, Srabani

    2018-03-22

    The role of structure and dynamics of an enzyme has been investigated at three different stages of its function including the chemical event it catalyzes. A one-pot computational method has been designed for each of these stages on the basis of classical and/or quantum mechanical-molecular mechanical molecular dynamics and transition path sampling simulations. For a pair of initial and final states A and B separated by a high free-energy barrier, using a two-stage selection process, several collective variables (CVs) are identified that can delineate A and B. However, these CVs are found to exhibit strong cross-coupling over the transition paths. A set of mutually orthogonal order parameters is then derived from these CVs and an optimal reaction coordinate, r, determined applying half-trajectory likelihood maximization along with a Bayesian information criterion. The transition paths are also used to project the multidimensional free energy surface and barrier crossing dynamics along r. The proposed scheme has been applied to the rate-determining intramolecular proton transfer reaction of the well-known enzyme human carbonic anhydrase II. The potential of mean force, F( r), in the absence of the chemical step is found to reproduce earlier results on the equilibrium population of two side-chain orientations of key residue His-64. Estimation of rate constants, k, from mean first passage times for the three different stages of catalysis shows that the rate-determining step of intramolecular proton transfer occurs with k ≃ 1.0 × 10 6 s -1 , in close agreement with known experimental results.

  4. C—C bond formation in the intramolecular Diels-Alder reaction of triene amides

    Directory of Open Access Journals (Sweden)

    Abdelilah Benallou

    2018-02-01

    Full Text Available The mechanism nature of the intramolecular Diels–Alder reaction has been performed; and thus, the changes of C—C bond forming/breaking along IRC are characterized in this study. Conceptual DFT analyses of the most favorable adduct fused/exo shows that the flux electronic will take place from diene to dienophile moiety. Moreover, ELF topological analysis based on the electron density predicts that C—C bond is formed by the coupling of two pseudoradical centers generated at the most significant atoms of the molecules. However, C2 vs C3, also C1 and C4 interaction comes mainly from the global electron density transfer which takes place along the reaction. Two- stage one-step is the proposed mechanism of this reaction, the first stage aims for the formation of C2—C3 σ bond while the second stage aims for C1—C4 σ bond formation. Interestingly, the observed asynchronicity of this IMDA reaction due principally to the asymmetric reorganization of electron density at the most attractive centers.

  5. C-C bond formation in the intramolecular Diels-Alder reaction of triene amides.

    Science.gov (United States)

    Benallou, Abdelilah; El Alaoui El Abdallaoui, Habib; Garmes, Hocine

    2018-02-01

    The mechanism nature of the intramolecular Diels-Alder reaction has been performed; and thus, the changes of C-C bond forming/breaking along IRC are characterized in this study. Conceptual DFT analyses of the most favorable adduct fused/exo shows that the flux electronic will take place from diene to dienophile moiety. Moreover, ELF topological analysis based on the electron density predicts that C-C bond is formed by the coupling of two pseudoradical centers generated at the most significant atoms of the molecules. However, C2 vs C3, also C1 and C4 interaction comes mainly from the global electron density transfer which takes place along the reaction. Two- stage one-step is the proposed mechanism of this reaction, the first stage aims for the formation of C2-C3 σ bond while the second stage aims for C1-C4 σ bond formation. Interestingly, the observed asynchronicity of this IMDA reaction due principally to the asymmetric reorganization of electron density at the most attractive centers.

  6. Intramolecular energy transfer and mode-specific effects in unimolecular reactions of 1,2-difluoroethane

    Science.gov (United States)

    Raff, Lionel M.

    1989-06-01

    The unimolecular decomposition reactions of 1,2-difluoroethane upon mode-specific excitation to a total internal energy of 7.5 eV are investigated using classical trajectory methods and a previously formulated empirical potential-energy surface. The decomposition channels for 1,2-difluoroethane are, in order of importance, four-center HF elimination, C-C bond rupture, and hydrogen-atom dissociation. This order is found to be independent of the particular vibrational mode excited. Neither fluorine-atom nor F2 elimination reactions are ever observed even though these dissociation channels are energetically open. For four-center HF elimination, the average fraction of the total energy partitioned into internal HF motion varies between 0.115-0.181 depending upon the particular vibrational mode initially excited. The internal energy of the fluoroethylene product lies in the range 0.716-0.776. Comparison of the present results with those previously obtained for a random distribution of the initial 1,2-difluoroethane internal energy [J. Phys. Chem. 92, 5111 (1988)], shows that numerous mode-specific effects are present in these reactions in spite of the fact that intramolecular energy transfer rates for this system are 5.88-25.5 times faster than any of the unimolecular reaction rates. Mode-specific excitation always leads to a total decomposition rate significantly larger than that obtained for a random distribution of the internal energy. Excitation of different 1,2-difluoroethane vibrational modes is found to produce as much as a 51% change in the total decomposition rate. Mode-specific effects are also seen in the product energy partitioning. The rate coefficients for decomposition into the various channels are very sensitive to the particular mode excited. A comparison of the calculated mode-specific effects with the previously determined mode-to-mode energy transfer rate coefficients [J. Chem. Phys. 89, 5680 (1988)] shows that, to some extent, the presence of mode

  7. 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...

  8. Synthesis of 1-indanones through the intramolecular Friedel-Crafts acylation reaction using NbCl5 as Lewis acid

    International Nuclear Information System (INIS)

    Polo, Ellen Christine; Silva-Filho, Luiz Carlos da; Silva, Gil Valdo Jose da; Constantino, Mauricio Gomes

    2008-01-01

    The intramolecular Friedel-Crafts acylation reaction of 3-arylpropanoic acids to give 1-indanones can be effected in good yields under mild conditions (room temperature) by using niobium pentachloride. Our results indicate that NbCl 5 acts both as reagent (to transform carboxylic acids into acyl chlorides) and as catalyst in the Friedel-Crafts cyclization. (author)

  9. Intramolecular anionic diels-alder reactions of 1-aryl-4-oxahepta-1,6-diyne systems in DMSO.

    Science.gov (United States)

    Kudoh, Takayuki; Mori, Tomoko; Shirahama, Mitsuhito; Yamada, Masashi; Ishikawa, Teruhiko; Saito, Seiki; Kobayashi, Hisayoshi

    2007-04-25

    Base-promoted cycloaddition reactions of 1-aryl- or 1-aryl-7-substituted-4-oxahepta-1,6-diyne systems in DMSO have proven to involve an anionic intramolecular Diels-Alder process taking place even at room temperature in spite of the reaction suffering from temporary disruption of aromaticity. Although initially formed alpha-arylallenide anion can be protonated by DMSO, it can be back to the allenide anion probably because of a small acidity difference between alpha-arylallene and DMSO. The alpha-arylallenide anion in combination with the alpha-aryl substituent can constitute an anionic diene structure that undergoes the intramolecular Diels-Alder reaction involving the C(6)-yne part, a very fast process probably because of the increased HOMO-1 level of the anionic diene, as shown by DFT calculations. Diversified substituted naphthalenes, benzofurans, phenanthrenes, and quinolines, including biaryl architectures, are available from 4-oxahepta-1,6-diynes in a highly expeditious way.

  10. Pd nanoparticles immobilized on carbon nanotubes with a polyaniline coaxial coating for the Heck reaction: coating thickness as the key factor influencing the efficiency and stability of the catalyst

    KAUST Repository

    Yu, Rui; Liu, Rui; Deng, Jie; Ran, Maofei; Wang, Ning; Chu, Wei; He, Zhiwei; Du, Zheng; Jiang, Chengfa; Sun, Wenjing

    2018-01-01

    Pd nanoparticles (NPs) supported on polyaniline (PANI)-coated carbon nanotubes (CNTs) were synthesized using a low-cost and simple method for application in the Heck reaction. The effects of the PANI/CNT coating weight ratio on the catalytic stability and recyclability of the composite were determined by using a combination of experimental and computational methods. The results show that through coordination of the N-species in PANI with the Pd NPs, the nitrogen-rich PANI@CNT provides a strong support for the Pd NPs. The thickness of the PANI layer is the key in determining the stability of the catalyst. PANI becomes protonated in the presence of CNTs, as electron transfer from the former to the latter creates strong interactions between the two. Thus, PANI becomes more stable in nanocomposites with a higher CNT content, e.g., PANI/CNT = 0.5 : 1. The catalyst with a PANI/CNT ratio of 0.5 : 1 exhibited the best recycling performance, and only a small loss of activity was observed after 10 cycles. However, upon increasing the PANI content (e.g., PANI/CNT = 4 : 1), the PANI units tend to form bulk structures that are less stable than those that wrap around the CNTs. Such a structure is unstable; therefore, the PANI layers can easily deform or break away from the CNT backbones. Hence, these catalysts deactivate during recycling. Thus, our study demonstrates that the assembly of noble-metal NPs on CNTs bearing a thin coaxial PANI coating is a powerful technique to prepare reusable catalysts for the Heck reaction. Coating thickness is also a key factor affecting the efficiency and stability of the catalyst.

  11. Pd nanoparticles immobilized on carbon nanotubes with a polyaniline coaxial coating for the Heck reaction: coating thickness as the key factor influencing the efficiency and stability of the catalyst

    KAUST Repository

    Yu, Rui

    2018-02-12

    Pd nanoparticles (NPs) supported on polyaniline (PANI)-coated carbon nanotubes (CNTs) were synthesized using a low-cost and simple method for application in the Heck reaction. The effects of the PANI/CNT coating weight ratio on the catalytic stability and recyclability of the composite were determined by using a combination of experimental and computational methods. The results show that through coordination of the N-species in PANI with the Pd NPs, the nitrogen-rich PANI@CNT provides a strong support for the Pd NPs. The thickness of the PANI layer is the key in determining the stability of the catalyst. PANI becomes protonated in the presence of CNTs, as electron transfer from the former to the latter creates strong interactions between the two. Thus, PANI becomes more stable in nanocomposites with a higher CNT content, e.g., PANI/CNT = 0.5 : 1. The catalyst with a PANI/CNT ratio of 0.5 : 1 exhibited the best recycling performance, and only a small loss of activity was observed after 10 cycles. However, upon increasing the PANI content (e.g., PANI/CNT = 4 : 1), the PANI units tend to form bulk structures that are less stable than those that wrap around the CNTs. Such a structure is unstable; therefore, the PANI layers can easily deform or break away from the CNT backbones. Hence, these catalysts deactivate during recycling. Thus, our study demonstrates that the assembly of noble-metal NPs on CNTs bearing a thin coaxial PANI coating is a powerful technique to prepare reusable catalysts for the Heck reaction. Coating thickness is also a key factor affecting the efficiency and stability of the catalyst.

  12. Intramolecular carbenoid ylide forming reactions of 2-diazo-3-keto-4-phthalimidocarboxylic esters derived from methionine and cysteine

    Directory of Open Access Journals (Sweden)

    Marc Enßle

    2012-03-01

    Full Text Available Methionine, S-benzylcysteine and S-allylcysteine were converted into 2-diazo-3-oxo-4-phthalimidocarboxylic esters 8a–c in three steps. Upon rhodium-catalysed dediazoniation, two intramolecular carbenoid reactions competed, namely the formation of a cyclic sulfonium ylide and that of a six-ring carbonyl ylide. The S-methyl and S-benzyl ylides 12a and b could be isolated, while S-allyl ylide 12c underwent a [2,3]-sigmatropic rearrangement. The short-lived carbonyl ylides derived from methionine and S-benzylcysteine formed head-to-tail dimers by a [3 + 3]-cycloaddition and could be trapped with external dipolarophiles, while the S-allyl derivative 14c yielded the pentacyclic compound 17 by an intramolecular [3 + 2]-cycloaddition reaction.

  13. Representations of affine Hecke algebras

    CERN Document Server

    Xi, Nanhua

    1994-01-01

    Kazhdan and Lusztig classified the simple modules of an affine Hecke algebra Hq (q E C*) provided that q is not a root of 1 (Invent. Math. 1987). Ginzburg had some very interesting work on affine Hecke algebras. Combining these results simple Hq-modules can be classified provided that the order of q is not too small. These Lecture Notes of N. Xi show that the classification of simple Hq-modules is essentially different from general cases when q is a root of 1 of certain orders. In addition the based rings of affine Weyl groups are shown to be of interest in understanding irreducible representations of affine Hecke algebras. Basic knowledge of abstract algebra is enough to read one third of the book. Some knowledge of K-theory, algebraic group, and Kazhdan-Lusztig cell of Cexeter group is useful for the rest

  14. Tandem cross enyne metathesis (CEYM)-intramolecular Diels-Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds.

    Science.gov (United States)

    Miró, Javier; Sánchez-Roselló, María; Sanz, Álvaro; Rabasa, Fernando; Del Pozo, Carlos; Fustero, Santos

    2015-01-01

    A new tandem cross enyne metathesis (CEYM)-intramolecular Diels-Alder reaction (IMDAR) has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM-IMDAR protocols.

  15. Synthesis of 2,5-Disubstituted Octahydroquinolin-4-ones via anIntramolecular Hetero Diels-Alder Reaction

    Directory of Open Access Journals (Sweden)

    J. Antonio Palenzuela

    2007-02-01

    Full Text Available A route for the preparation of 2,5-disubstituted octahydroquinolin-4-ones, synthetic precursors of the decahydroquinoline-type toxins, is presented. The key steps are an asymmetric epoxidation and an intramolecular hetero Diels-Alder reaction between an activated diene and an imine. The presence of an allylic stereogenic center induces some selectivity and thus only two cycloadducts are obtained in 70:30 ratio and good yield.

  16. Synthesis and characterization of para-pyridine linked NHC palladium complexes and their studies for the Heck-Mizoroki coupling reaction.

    Science.gov (United States)

    Liu, Ya-Ming; Lin, Yi-Chun; Chen, Wen-Ching; Cheng, Jen-Hao; Chen, Yi-Lin; Yap, Glenn P A; Sun, Shih-Sheng; Ong, Tiow-Gan

    2012-06-28

    This paper describes the synthesis of 1-(pyridine-4-ylmethyl) NHC and their Pd(II) and Ag(I) complexes, which are fully characterized. Interestingly, we have also synthesized a Pd complex 3a-CO(3) using a more direct treatment of K(2)CO(3) with PdCl(2). 3a-CO(3) represents the first reported solid structure of a Pd η(2)-carbonato complex stabilized by an NHC framework. 3a-CO(3) can be easily converted to a PdCl(2) derivative by treating it with chloroform. We have found these palladium complexes mediate the Heck-Mizoroki coupling with a low catalyst loading. Furthermore, we also expand such catalytic manifold toward constructing fused polyaromatic substrates, a highly useful class of compounds in optoelectronic chemistry.

  17. An abnormally slow proton transfer reaction in a simple HBO derivative due to ultrafast intramolecular-charge transfer events.

    Science.gov (United States)

    Alarcos, Noemí; Gutierrez, Mario; Liras, Marta; Sánchez, Félix; Douhal, Abderrazzak

    2015-07-07

    We report on the steady-state, picosecond and femtosecond time-resolved studies of a charge and proton transfer dye 6-amino-2-(2'-hydroxyphenyl)benzoxazole (6A-HBO) and its methylated derivative 6-amino-2-(2'-methoxyphenyl)benzoxazole (6A-MBO), in different solvents. With femtosecond resolution and comparison with the photobehaviour of 6A-MBO, we demonstrate for 6A-HBO in solution, the photoproduction of an intramolecular charge-transfer (ICT) process at S1 taking place in ∼140 fs or shorter, followed by solvent relaxation in the charge transferred species. The generated structure (syn-enol charge transfer conformer) experiences an excited-state intramolecular proton-transfer (ESIPT) reaction to produce a keto-type tautomer. This subsequent proton motion occurs in 1.2 ps (n-heptane), 14 ps (DCM) and 35 ps (MeOH). In MeOH, it is assisted by the solvent molecules and occurs through tunneling for which we got a large kinetic isotope effect (KIE) of about 13. For the 6A-DBO (deuterated sample in CD3OD) the global proton-transfer reaction takes place in 200 ps, showing a remarkable slow KIE regime. The slow ESIPT reaction in DCM (14 ps), not through tunnelling as it is not sensitive to OH/OD exchange, has however to overcome an energy barrier using intramolecular as well as solvent coordinates. The rich ESIPT dynamics of 6A-HBO in the used solutions is governed by an ICT reaction, triggered by the amino group, and it is solvent dependent. Thus, the charge injection to a 6A-HBO molecular frame makes the ICT species more stable, and the phenol group less acidic, slowing down the subsequent ESIPT reaction. Our findings bring new insights into the coupling between ICT and ESIPT reactions on the potential-energy surfaces of several barriers.

  18. Total synthesis of (+/-)-taiwaniaquinol B via a domino intramolecular friedel-crafts acylation/carbonyl alpha-tert-alkylation reaction.

    Science.gov (United States)

    Fillion, Eric; Fishlock, Dan

    2005-09-28

    The first synthesis of taiwaniaquinol B, a 6-nor-5(6-->7)abeoabietane-type diterpenoid exhibiting the uncommon fused 6-5-6 tricyclic carbon skeleton, was accomplished in 15 steps. A Lewis acid-promoted tandem intramolecular Friedel-Crafts/carbonyl alpha-tert-alkylation reaction was exploited as the core strategy for the synthesis of the sterically congested 1-indanone-containing tricyclic structure. This multiple carbon-carbon bond forming reaction exploits the unique reactivity of Meldrum's acid. The facile precursor synthesis makes this a useful methodology for the expedient modification and assembly of sterically congested 1-indanone-containing ring systems.

  19. Tandem cross enyne metathesis (CEYM–intramolecular Diels–Alder reaction (IMDAR. An easy entry to linear bicyclic scaffolds

    Directory of Open Access Journals (Sweden)

    Javier Miró

    2015-08-01

    Full Text Available A new tandem cross enyne metathesis (CEYM–intramolecular Diels–Alder reaction (IMDAR has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM–IMDAR protocols.

  20. The Intramolecular Diels–Alder Reaction of Tryptamine-Derived Zincke Aldehydes Is a Stepwise Process

    OpenAIRE

    Pham, Hung V.; Martin, David B. C.; Vanderwal, Christopher D.; Houk, K. N.

    2012-01-01

    Computational studies show that the base-mediated intramolecular Diels–Alder of tryptamine-derived Zincke aldehydes, used as a key step in the synthesis of the Strychnos alkaloids norfluorocurarine and strychnine, proceeds via a stepwise pathway. The experimentally determined importance of a potassium counterion in the base is explained by its ability to preorganize the Zincke aldehyde diene in an s-cis conformation suitable to bicyclization. Computation also supports the thermodynamic import...

  1. A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Trong-Nghia [Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Department of Physical Chemistry, Hanoi University of Science and Technology, Hanoi (Viet Nam); Putikam, Raghunath; Lin, M. C., E-mail: chemmcl@emory.edu [Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan (China)

    2015-03-28

    We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH{sub 2}OO and anti/syn-CH{sub 3}C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH{sub 2}OO and anti-CH{sub 3}C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH{sub 3}C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C–H bonds. For syn-CH{sub 3}C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH{sub 3} group by the terminal O atom producing CH{sub 2}C(H)O–OH. At 298 K, the intramolecular insertion process in CH{sub 2}OO was found to be 600 times faster than the commonly assumed ring-closing reaction.

  2. A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states

    International Nuclear Information System (INIS)

    Nguyen, Trong-Nghia; Putikam, Raghunath; Lin, M. C.

    2015-01-01

    We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH 2 OO and anti/syn-CH 3 C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH 2 OO and anti-CH 3 C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH 3 C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C–H bonds. For syn-CH 3 C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH 3 group by the terminal O atom producing CH 2 C(H)O–OH. At 298 K, the intramolecular insertion process in CH 2 OO was found to be 600 times faster than the commonly assumed ring-closing reaction

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

    Directory of Open Access Journals (Sweden)

    Renato Contreras

    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.

  4. Dynamics of excited-state intramolecular proton transfer reactions in piroxicam. Role of triplet states

    Science.gov (United States)

    Cho, Dae Won; Kim, Yong Hee; Yoon, Minjoong; Jeoung, Sae Chae; Kim, Dongho

    1994-08-01

    The picosecond time-resolved fluorescence and transient absorption behavior of piroxicam at room temperature are reported. The keto tautomer in the excited singlet state ( 1K*) formed via the fast intramolecular proton transfer (≈ 20 ps) is observed. The short-lived (7.5 ns) triplet state of keto tauomer ( 3K*) is generated from 1K * in toluene whereas it is hardly observed in ethanol. Consequently, rapid reverse proton transfer takes place from 3K * to the enol triplet state ( 3E *.

  5. Microwave-assisted intramolecular dehydrogenative Diels-Alder reactions for the synthesis of functionalized naphthalenes/solvatochromic dyes.

    Science.gov (United States)

    Kocsis, Laura S; Benedetti, Erica; Brummond, Kay M

    2013-04-01

    Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable. The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts. The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields.

  6. Catalysis in the Service of Green Chemistry: Nobel Prize-Winning Palladium-Catalysed Cross-Couplings, Run in Water at Room Temperature: Heck, Suzuki-Miyaura and Negishi reactions carried out in the absence of organic solvents, enabled by micellar catalysis.

    Science.gov (United States)

    Lipshutz, Bruce H; Taft, Benjamin R; Abela, Alexander R; Ghorai, Subir; Krasovskiy, Arkady; Duplais, Christophe

    2012-04-01

    Palladium-catalysed cross-couplings, in particular Heck, Suzuki-Miyaura and Negishi reactions developed over three decades ago, are routinely carried out in organic solvents. However, alternative media are currently of considerable interest given an increasing emphasis on making organic processes 'greener'; for example, by minimising organic waste in the form of organic solvents. Water is the obvious leading candidate in this regard. Hence, this review focuses on the application of micellar catalysis, in which a 'designer' surfactant enables these award-winning coupling reactions to be run in water at room temperature.

  7. Blocks and families for cyclotomic Hecke algebras

    CERN Document Server

    Chlouveraki, Maria

    2009-01-01

    The definition of Rouquier for the families of characters introduced by Lusztig for Weyl groups in terms of blocks of the Hecke algebras has made possible the generalization of this notion to the case of complex reflection groups. The aim of this book is to study the blocks and to determine the families of characters for all cyclotomic Hecke algebras associated to complex reflection groups. This volume offers a thorough study of symmetric algebras, covering topics such as block theory, representation theory and Clifford theory, and can also serve as an introduction to the Hecke algebras of complex reflection groups.

  8. Bicyclic Guanidine Catalyzed Asymmetric Tandem Isomerization Intramolecular-Diels-Alder Reaction: The First Catalytic Enantioselective Total Synthesis of (+)-alpha-Yohimbine.

    Science.gov (United States)

    Feng, Wei; Jiang, Danfeng; Kee, Choon-Wee; Liu, Hongjun; Tan, Choon-Hong

    2016-02-04

    Hydroisoquinoline derivatives were prepared in moderate to good enantioselectivities via a bicyclic guanidine-catalyzed tandem isomerization intramolecular-Diels-Alder (IMDA) reaction of alkynes. With this synthetic method, the first enantioselective synthesis of (+)-alpha-yohimbine was completed in 9 steps from the IMDA products. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Syntheses of the hexahydroindene cores of indanomycin and stawamycin by combinations of iridium-catalyzed asymmetric allylic alkylations and intramolecular Diels-Alder reactions.

    Science.gov (United States)

    Gärtner, Martin; Satyanarayana, Gedu; Förster, Sebastian; Helmchen, Günter

    2013-01-02

    Short and concise syntheses of the hexahydroindene cores of the antibiotics indanomycin (X-14547 A) and stawamycin are presented. Key methods used are an asymmetric iridium-catalyzed allylic alkylation, a modified Julia olefination, a Suzuki-Miyaura coupling, and an intramolecular Diels-Alder reaction. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Intramolecular kinetic isotope effect in gas-phase proton-transfer reactions

    International Nuclear Information System (INIS)

    Wellman, K.M.; Victoriano, M.E.; Isolani, P.C.; Riveros, J.M.

    1979-01-01

    The k/sub H//k/sub D/ isotope effects were determined by ICR for the reaction of substituted toluenes with several alkoxides. The results showed a definite trend for k/sub H//k/sub D/ starting as a normal isotope effect for appreciably exothermic reaction (> 3 kcal mol -1 ) and proceeding smoothly toward an inverse isotope effect as the reaction approached thermoneutrality or becomes endothermic. These observations were explained by a reaction which involved a double minima potential with a central energy barrier

  11. 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

    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-frequenc...

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

    KAUST Repository

    Poater, Albert; Cavallo, Luigi

    2013-01-01

    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

  13. Morphological effects on the selectivity of intramolecular versus intermolecular catalytic reaction on Au nanoparticles.

    Science.gov (United States)

    Wang, Dan; Sun, Yuanmiao; Sun, Yinghui; Huang, Jing; Liang, Zhiqiang; Li, Shuzhou; Jiang, Lin

    2017-06-14

    It is hard for metal nanoparticle catalysts to control the selectivity of a catalytic reaction in a simple process. In this work, we obtain active Au nanoparticle catalysts with high selectivity for the hydrogenation reaction of aromatic nitro compounds, by simply employing spine-like Au nanoparticles. The density functional theory (DFT) calculations further elucidate that the morphological effect on thermal selectivity control is an internal key parameter to modulate the nitro hydrogenation process on the surface of Au spines. These results show that controlled morphological effects may play an important role in catalysis reactions of noble metal NPs with high selectivity.

  14. Tunable differentiation of tertiary C-H bonds in intramolecular transition metal-catalyzed nitrene transfer reactions.

    Science.gov (United States)

    Corbin, Joshua R; Schomaker, Jennifer M

    2017-04-13

    Metal-catalyzed nitrene transfer reactions are an appealing and efficient strategy for accessing tetrasubstituted amines through the direct amination of tertiary C-H bonds. Traditional catalysts for these reactions rely on substrate control to achieve site-selectivity in the C-H amination event; thus, tunability is challenging when competing C-H bonds have similar steric or electronic features. One consequence of this fact is that the impact of catalyst identity on the selectivity in the competitive amination of tertiary C-H bonds has not been well-explored, despite the potential for progress towards predictable and catalyst-controlled C-N bond formation. In this communication, we report investigations into tunable and site-selective nitrene transfers between tertiary C(sp 3 )-H bonds using a combination of transition metal catalysts, including complexes based on Ag, Mn, Rh and Ru. Particularly striking was the ability to reverse the selectivity of nitrene transfer by a simple change in the identity of the N-donor ligand supporting the Ag(i) complex. The combination of our Ag(i) catalysts with known Rh 2 (ii) complexes expands the scope of successful catalyst-controlled intramolecular nitrene transfer and represents a promising springboard for the future development of intermolecular C-H N-group transfer methods.

  15. Water-dispersable hybrid Au-Pd nanoparticles as catalysts in ethanol oxidation, aqueous phase Suzuki-Miyaura and Heck reactions

    KAUST Repository

    Song, Hyon Min; Moosa, Basem; Khashab, Niveen M.

    2012-01-01

    The catalytic activities of water-dispersable Au@Pd core-shell nanoparticles (NPs) and Au-Pd alloy NPs were examined. There is growing interest in Au-Pd hybridized NPs in a supported matrix or non-supported forms as catalysts in various reactions

  16. Intramolecular didehydro-Diels-Alder reaction and its impact on the structure-function properties of environmentally sensitive fluorophores.

    Science.gov (United States)

    Brummond, Kay M; Kocsis, Laura S

    2015-08-18

    Reaction discovery plays a vital role in accessing new chemical entities and materials possessing important function.1 In this Account, we delineate our reaction discovery program regarding the [4 + 2] cycloaddition reaction of styrene-ynes. In particular, we highlight our studies that lead to the realization of the diverging reaction mechanisms of the intramolecular didehydro-Diels-Alder (IMDDA) reaction to afford dihydronaphthalene and naphthalene products. Formation of the former involves an intermolecular hydrogen atom abstraction and isomerization, whereas the latter is formed via an unexpected elimination of H2. Forming aromatic compounds by a unimolecular elimination of H2 offers an environmentally benign alternative to typical oxidation protocols. We also include in this Account ongoing work focused on expanding the scope of this reaction, mainly its application to the preparation of cyclopenta[b]naphthalenes. Finally, we showcase the synthetic utility of the IMDDA reaction by preparing novel environmentally sensitive fluorophores. The choice to follow this path was largely influenced by the impact this reaction could have on our understanding of the structure-function relationships of these molecular sensors by taking advantage of a de novo construction and functionalization of the aromatic portion of these compounds. We were also inspired by the fact that, despite the advances that have been made in the construction of small molecule fluorophores, access to rationally designed fluorescent probes or sensors possessing varied and tuned photophysical, spectral, and chemical properties are still needed. To this end, we report our studies to correlate fluorophore structure with photophysical property relationships for a series of solvatochromic PRODAN analogs and viscosity-sensitive cyanoacrylate analogs. The versatility of this de novo strategy for fluorophore synthesis was demonstrated by showing that a number of functional groups could be installed at

  17. Condensed tannins. Base-catalysed reactions of polymeric procyanidins with phloroglucinol: Intramolecular rearrangements

    Science.gov (United States)

    Peter E. Laks; Richard W. Hemingway; Anthony H. Conner

    1987-01-01

    Reactions of polymeric procyanidins with phloroglucinol at pH 12.0 and temperatures of 23 or 50°C gave epicatechin-(4β)-phloroglucinol (7), by cleavage of the interflavanoid bond between procyanidin units with subsequent addition of phloroglucinol, and (+)-catechin from the terminal unit. The phloroglucinol adduct (7) rearranged to an enolic form of 8-(3,4-...

  18. Transition Metal Donor-Peptide-Acceptor Complexes: From Intramolecular Electron Transfer Reactions to the Study of Reactive Intermediates

    Energy Technology Data Exchange (ETDEWEB)

    Isied, Stephan S.

    2003-03-11

    The trans-polyproline (PII) oligomers (Figure 1) are unusually rigid peptide structures which have been extensively studied by our group for peptide mediated intramolecular electron transfer (ET) at long distances. We have previously studied ET across a series of metal ion donor (D) acceptor (A) oligoproline peptides with different distances, driving forces and reorganizational energies. The majority of these experiments involve generating the ET intermediate using pulse radiolysis methods, although more recently photochemical methods are also used. Results of these studies showed that ET across peptides can vary by more than twelve orders of magnitude. Using ruthenium bipyridine donors, ET reaction rate constants across several proline residues (n = 4 - 9) occurred in the millisecond (ms) to {micro}s timescale, thus limiting the proline peptide conformational motions to only minor changes (far smaller than the large changes that occur on the ms to sec timescale, such as trans to cis proline isomerization). The present report describes our large data base of experimental results for D-peptide-A complexes in terms of a model where the involvement of both superexchange and hopping (hole and electron) mechanisms account for the long range ET rate constants observed. Our data shows that the change from superexchange to hopping mechanisms occurs at different distances depending on the type of D and A and their interactions with the peptides. Our model is also consistent with generalized models for superexchange and hopping which have been put forward by a number of theoretical groups to account for long range ET phenomena.

  19. Click and Release: A Chemical Strategy toward Developing Gasotransmitter Prodrugs by Using an Intramolecular Diels-Alder Reaction.

    Science.gov (United States)

    Ji, Xingyue; Zhou, Cheng; Ji, Kaili; Aghoghovbia, Robert E; Pan, Zhixiang; Chittavong, Vayou; Ke, Bowen; Wang, Binghe

    2016-12-19

    Prodrug strategies have been proven to be a very effective way of addressing delivery problems. Much of the chemistry in prodrug development relies on the ability to mask an appropriate functional group, which can be removed under appropriate conditions. However, developing organic prodrugs of gasotransmitters represent unique challenges. This is especially true with carbon monoxide, which does not have an easy "handle" for bioreversible derivatization. By taking advantage of an intramolecular Diels-Alder reaction, we have developed a prodrug strategy for preparations of organic CO prodrugs that are stable during synthesis and storage, and yet readily release CO with tunable release rates under near physiological conditions. The effectiveness of the CO prodrug system in delivering a sufficient quantity of CO for possible therapeutic applications has been studied using a cell culture anti-inflammatory assay and a colitis animal model. These studies fully demonstrate the proof of concept, and lay a strong foundation for further medicinal chemistry work in developing organic CO prodrugs. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Hecke symmetries and characteristic relations on reflection equation algebras

    International Nuclear Information System (INIS)

    Gurevich, D.I.; Pyatov, P.N.

    1996-01-01

    We discuss how properties of Hecke symmetry (i.e., Hecke type R-matrix) influence the algebraic structure of the corresponding Reflection Equation (RE) algebra. Analogues of the Newton relations and Cayley-Hamilton theorem for the matrix of generators of the RE algebra related to a finite rank even Hecke symmetry are derived. 10 refs

  1. A trace formula for the Iwahori-Hecke algebra

    NARCIS (Netherlands)

    Opdam, E.M.

    1999-01-01

    The Iwahori-Hecke algebra has a canonicaltrace $\\tau$. The trace is the evaluation at the identity element in the usual interpretation of the Iwahori-Hecke algebra as a sub-algebra of the convolution algebra of a p-adic semi-simple group. The Iwahori-Hecke algebra contains an important commutative

  2. Cascade olefin isomerization/intramolecular Diels-Alder reaction catalyzed by N-heterocyclic carbenes.

    Science.gov (United States)

    Kowalczyk, Marcin; Lupton, David W

    2014-05-19

    The addition of an N-heterocyclic carbene to the carbonyl group of an α,β,γ,δ-unsaturated enol ester affords a hemiacetal azolium intermediate that enables a cascade olefin isomerization/Diels-Alder reaction, for which mechanistic studies implicate Lewis base catalysis. Preliminary studies into the utility of the products have been undertaken with reductive and oxidative cleavage, giving materials for potential use in complex-target synthesis. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Intramolecular Redox-Mannich Reactions: Facile Access to the Tetrahydroprotoberberine Core.

    Science.gov (United States)

    Ma, Longle; Seidel, Daniel

    2015-09-07

    Cyclic amines such as pyrrolidine undergo redox-annulations with 2-formylaryl malonates. Concurrent oxidative amine α-CH bond functionalization and reductive N-alkylation render this transformation redox-neutral. This redox-Mannich process provides regioisomers of classic Reinhoudt reaction products as an entry to the tetrahydroprotoberberine core, enabling the synthesis of (±)-thalictricavine and its epimer. An unusually mild amine-promoted dealkoxycarbonylation was discovered in the course of these studies. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. On the effect of tether composition on cis/trans selectivity in intramolecular Diels-Alder reactions.

    Science.gov (United States)

    Paddon-Row, Michael N; Longshaw, Alistair I; Willis, Anthony C; Sherburn, Michael S

    2009-01-05

    Intramolecular Diels-Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6-31+G(d) and CBS-QB3 levels of theory for a series of 1,3,8-nonatrienes, H(2)C=CH-CH=CH-CH(2)-X-Z-CH=CH(2) [-X-Z- = -CH(2)-CH(2)- (1); -O-C(=O)- (2); -CH(2)-C(=O)- (3); -O-CH(2)- (4); -NH-C(=O)- (5); -S-C(=O)- (6); -O-C(=S)- (7); -NH-C(=S)- (8); -S-C(=S)- (9)]. For each system studied (1-9), cis- and trans-TS isomers, corresponding, respectively, to endo- and exo-positioning of the -C-X-Z- tether with respect to the diene, have been located and their relative energies (E(rel) (TS)) employed to predict the cis/trans IMDA product ratio. Although the E(rel) (TS) values are modest (typically NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis-TS, namely (1) unfavorable torsional (eclipsing) strain about the C4-C5 bond, that is caused by the -C-X-C(=Y)- group's strong tendency to maintain local planarity; and (2) attractive electrostatic and secondary orbital interactions between the endo-(thio)carbonyl group, C=Y, and the diene. The former interaction predominates when X is weakly electronegative (X=N, S), while the latter is dominant when X is more strongly electronegative (X=O), or a methylene group (X=CH(2)) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1, 2, 3, and 4 (published work) and 5, 6, and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans-selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14, which undergoes a more trans-selective IMDA reaction

  5. Excited state intramolecular charge transfer reaction in binary mixtures of water and tertiary butanol (TBA): alcohol mole fraction dependence.

    Science.gov (United States)

    Pradhan, Tuhin; Ghoshal, Piue; Biswas, Ranjit

    2008-02-07

    The excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) has been studied in water-tertiary butanol (TBA) mixtures at different alcohol mole fractions by using steady state and time-resolved fluorescence spectroscopy. The ratio between the areas under the locally excited (LE) and charge transferred (CT) emission bands is found to exhibit a sharp rise at alcohol mole fraction approximately 0.04, a value at which several thermodynamic properties of this mixture is known to show anomalous change due to the enhancement of H-bonding network. The radiative rate associated with the LE emission also shows a maximum at this TBA mole fraction. Although the structural transition from the water-like tetrahedral network to the alcohol-like chain is reflected in the red shift of the absorption spectrum up to TBA mole fraction approximately 0.10, the emission bands (both LE and CT) show the typical nonideal alcohol mole fraction dependence at all TBA mole fractions. Quantum yield, CT radiative rate as well as transition moments also exhibit a nonideal alcohol mole fraction dependence. The time-resolved emission decay of P4C has been found to be biexponential at all TBA mole fractions, regardless of emission collection around either the LE or the CT bands. The time constant associated with the slow component (tau(slow)) shows a minimum at TBA mole fraction approximately 0.04, whereas such a minimum for the fast time constant, tau(fast) (representing the rate of LE --> CT conversion reaction) is not observed. The nonobservation of the minimum in tau(fast) might be due to the limited time resolution employed in our experiments.

  6. α-Bromodiazoacetamides – a new class of diazo compounds for catalyst-free, ambient temperature intramolecular C–H insertion reactions

    Directory of Open Access Journals (Sweden)

    Åsmund Kaupang

    2013-07-01

    Full Text Available In this work, we introduce a new class of halodiazocarbonyl compounds, α-halodiazoacetamides, which through a metal-free, ambient-temperature thermolysis perform intramolecular C–H insertions to produce α-halo-β-lactams. When carried out with α-bromodiazoacetamides bearing cyclic side chains, the thermolysis reaction affords bicyclic α-halo-β-lactams, in some cases in excellent yields, depending on the ring size and substitution pattern of the cyclic amide side chains.

  7. TD-DFT investigation of the potential energy surface for Excited-State Intramolecular Proton Transfer (ESIPT) reaction of 10-hydroxybenzo[h]quinoline: Topological (AIM) and population (NBO) analysis of the intramolecular hydrogen bonding interaction

    International Nuclear Information System (INIS)

    Paul, Bijan Kumar; Guchhait, Nikhil

    2011-01-01

    Here, we report a Density Functional Theoretical (DFT) study on the photophysics of a potent Excited-State Intramolecular Proton Transfer (ESIPT) molecular system, viz., 10-hydroxybenzo[h]quinoline (HBQ). Particular emphasis has been rendered on the assessment of the proton transfer reaction in HBQ in the ground and excited-states through elucidation and a careful perusal of the potential energy surfaces (PES). The non-viability of Ground-State Intramolecular Proton Transfer (GSIPT) process is dictated by a high-energy barrier coupled with no energy minimum for the proton transferred (K-form) form at the ground-state (S 0 ) PES. Remarkable reduction of the barrier along with thermodynamic stability inversion between the enol (E-form) and the keto forms (K-form) of HBQ upon photoexcitation from S 0 to the S 1 -state advocate for the operation of ESIPT process. These findings have been cross-validated on the lexicon of analysis of optimized geometry parameters, Mulliken's charge distribution on the heavy atoms, and molecular orbitals (MO) of the E- and the K-forms of HBQ. Our computational results also corroborate to experimental observations. From the modulations in optimized geometry parameters in course of the PT process a critical assessment has been endeavoured to delve into the movement of the proton during the process. Additional stress has been placed on the analysis of the intramolecular hydrogen bonding (IMHB) interaction in HBQ. The IMHB interaction has been explored by calculation of electron density ρ(r) and the Laplacian ∇ 2 ρ(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) method and by calculation of interaction between σ* of OH with the lone pair of the nitrogen atom using Natural Bond Orbital (NBO) analysis. - Highlights: → Theoretical modelling of the photophysics of an ESIPT probe 10-hydroxybenzo[h]quinoline (HBQ). → Calculation of intramolecular hydrogen bond (IMHB) energy. → Role of hyperconjugative charge transfer

  8. 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.

  9. An efficient and green synthesis of 1-indanone and 1-tetralone via intramolecular Friedel-Crafts acylation reaction

    DEFF Research Database (Denmark)

    Tran, Phuong Hoang; Huynh, Vy Hieu; Hansen, Poul Erik

    2015-01-01

    Metal-triflate-catalyzed intramolecular Friedel–Crafts acylation of 3-arylpropanoic and 4-arylbutanoic acids in triflate-anion ionic liquids under monomodal microwave irradiation is reported. The environmentally benign synthetic procedure allows the formation of cyclic ketones in good yields with...

  10. The roles of polycarboxylates in Cr(VI)/sulfite reaction system: Involvement of reactive oxygen species and intramolecular electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Bo, E-mail: bjiang86upc@163.com [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong (China); School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao 266033 (China); Wang, Xianli; Liu, Yukun [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong (China); Wang, Zhaohui [College of Environmental Science and Engineering, Donghua University, Shanghai 201620 (China); Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480 (Australia); Zheng, Jingtang, E-mail: jtzheng03@163.com [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong (China); Wu, Mingbo, E-mail: wumb@upc.edu.cn [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, Shandong (China)

    2016-03-05

    Highlights: • The formations of SO{sub 4}·{sup −} and OH·, involve in Cr(VI) reduction induced by S(IV). • Affinity of polycarboxylate to Cr(VI) accelerates Cr(VI) reduction rate. • Polycarboxylates can act as electron donors for Cr(VI) reduction retrenching S(IV). • Only oxalate can enhance the formations of SO{sub 4}·{sup −} and OH· in Cr(VI)/S(IV) system. - Abstract: In this study, the effects of polycarboxylates on both Cr(VI) reduction and S(IV) consumption in Cr(VI)/S(IV) system was investigated in acidic solution. Under aerobic condition, the productions of reactive oxygen species (ROS), i.e., SO{sub 4}·{sup −} and OH·, have been confirmed in S(IV) reducing Cr(VI) process by using electron spin resonance and fluorescence spectrum techniques, leading to the excess consumption of S(IV). However, when polycarboxylates (oxalic, citric, malic and tartaric acid) were present in Cr(VI)/S(IV) system, the affinity of polycarboxylates to CrSO{sub 6}{sup 2−} can greatly promote the reduction of Cr(VI) via expanding the coordination of Cr(VI) species from tetrahedron to hexahedron. Besides, as alternatives to S(IV), these polycarboxylates can also act as electron donors for Cr(VI) reduction via intramolecular electron transfer reaction, which is dependent on the energies of the highest occupied molecular orbital of these polycarboxylates. Notably, the variant electron donating capacity of these polycarboxylates resulted in different yield of ROS and therefore the oxidation efficiencies of other pollutants, e.g., rhodamine B and As(III). Generally, this study does not only shed light on the mechanism of S(IV) reducing Cr(VI) process mediated by polycarboxylates, but also provides an escalated, cost-effective and green strategy for the remediation of Cr(VI) using sulfite as a reductant.

  11. Intramolecular Nicholas reactions in the synthesis of dibenzocycloheptanes. Synthesis of allocolchicine NSC 51046 and analogues and the formal synthesis of (-)-allocolchicine.

    Science.gov (United States)

    Djurdjevic, Sinisa; Yang, Fei; Green, James R

    2010-12-03

    The preparation of dibenzocycloheptyne-Co(2)(CO)(6) complexes by intramolecular Nicholas reactions of biaryl-2-propargyl alcohol-Co(2)(CO)(6) derivatives is described. Reductive decomplexation of the dibenzocycloheptyne-Co(2)(CO)(6) complexes affords the corresponding dibenzocycloheptenes, individual members of which have been employed in a formal total synthesis of (-)-allocolchicine, the preparation of 6,7-dihydro-3,4,9,10,11-pentamethoxy-5H-dibenzo[a,c]cyclohepten-5-one, and the enantioselective total syntheses of NSC 51046 and its 3,8,9,10-tetramethoxy regioisomer.

  12. Synthesis of Cyclohexane-Fused Isocoumarins via Cationic Palladium(II)-Catalyzed Cascade Cyclization Reaction of Alkyne-Tethered Carbonyl Compounds Initiated by Intramolecular Oxypalladation of Ester-Substituted Aryl Alkynes.

    Science.gov (United States)

    Zhang, Jianbo; Han, Xiuling; Lu, Xiyan

    2016-04-15

    A cationic Pd(II)-catalyzed cascade cyclization reaction of alkyne-tethered carbonyl compounds was developed. This reaction is initiated by intramolecular oxypalladation of alkynes with an ester group followed by 1,2-addition of the formed C-Pd(II) bond to the carbonyl group, providing a highly efficient method for the synthesis of cyclohexane-fused isocoumarins.

  13. Quasi-coherent Hecke category and Demazure descent

    DEFF Research Database (Denmark)

    Arkhipov, Sergey; Kanstrup, Tina

    2015-01-01

    Let G be a reductive algebraic group with a Borel subgroup B. We define the quasi-coherent Hecke category for the pair (G,B). For any regular Noetherian G- scheme X we construct a monoidal action of the Hecke category on the derived category of B-equivariant quasi-coherent sheaves on X. Using the...

  14. Eisenstein Hecke algebras and Iwasawa theory

    Science.gov (United States)

    Wake, Preston

    We show that if an Eisenstein component of the p-adic Hecke algebra associated to modular forms is Gorenstein, then it is necessary that the plus-part of a certain ideal class group is trivial. We also show that this condition is sufficient whenever a conjecture of Sharifi holds. We also formulate a weaker Gorenstein property, and show that this weak Gorenstein property holds if and only if a weak form of Sharifi's conjecture and a weak form of Greenberg's conjecture hold.

  15. Kneser-Hecke-operators in coding theory

    OpenAIRE

    Nebe, Gabriele

    2005-01-01

    The Kneser-Hecke-operator is a linear operator defined on the complex vector space spanned by the equivalence classes of a family of self-dual codes of fixed length. It maps a linear self-dual code $C$ over a finite field to the formal sum of the equivalence classes of those self-dual codes that intersect $C$ in a codimension 1 subspace. The eigenspaces of this self-adjoint linear operator may be described in terms of a coding-theory analogue of the Siegel $\\Phi $-operator.

  16. A molecular dynamics study of intramolecular proton transfer reaction of malonaldehyde in solution based upon a mixed quantum-classical approximation. II. Proton transfer reaction in non-polar solvent

    Science.gov (United States)

    Kojima, H.; Yamada, A.; Okazaki, S.

    2015-05-01

    The intramolecular proton transfer reaction of malonaldehyde in neon solvent has been investigated by mixed quantum-classical molecular dynamics (QCMD) calculations and fully classical molecular dynamics (FCMD) calculations. Comparing these calculated results with those for malonaldehyde in water reported in Part I [A. Yamada, H. Kojima, and S. Okazaki, J. Chem. Phys. 141, 084509 (2014)], the solvent dependence of the reaction rate, the reaction mechanism involved, and the quantum effect therein have been investigated. With FCMD, the reaction rate in weakly interacting neon is lower than that in strongly interacting water. However, with QCMD, the order of the reaction rates is reversed. To investigate the mechanisms in detail, the reactions were categorized into three mechanisms: tunneling, thermal activation, and barrier vanishing. Then, the quantum and solvent effects were analyzed from the viewpoint of the reaction mechanism focusing on the shape of potential energy curve and its fluctuations. The higher reaction rate that was found for neon in QCMD compared with that found for water solvent arises from the tunneling reactions because of the nearly symmetric double-well shape of the potential curve in neon. The thermal activation and barrier vanishing reactions were also accelerated by the zero-point energy. The number of reactions based on these two mechanisms in water was greater than that in neon in both QCMD and FCMD because these reactions are dominated by the strength of solute-solvent interactions.

  17. Synthesis of Bioactive 2-(Arylaminothiazolo[5,4-f]-quinazolin-9-ones via the Hügershoff Reaction or Cu- Catalyzed Intramolecular C-S Bond Formation

    Directory of Open Access Journals (Sweden)

    Damien Hédou

    2016-06-01

    Full Text Available A library of thirty eight novel thiazolo[5,4-f]quinazolin-9(8H-one derivatives (series 8, 10, 14 and 17 was prepared via the Hügershoff reaction and a Cu catalyzed intramolecular C-S bond formation, helped by microwave-assisted technology when required. The efficient multistep synthesis of the key 6-amino-3-cyclopropylquinazolin-4(3H-one (3 has been reinvestigated and performed on a multigram scale from the starting 5-nitroanthranilic acid. The inhibitory potency of the final products was evaluated against five kinases involved in Alzheimer’s disease and showed that some molecules of the 17 series described in this paper are particularly promising for the development of novel multi-target inhibitors of kinases.

  18. New Palladium-Catalyzed Domino Reaction with Intramolecular Ring Closure of an N-(2-Chloro-3-heteroaryl) arylamide: First Synthesis of Oxazolo[4,5-b] pyrazines

    DEFF Research Database (Denmark)

    Demmer, Charles S.; Hansen, Jacob C.; Kehler, Jan

    2014-01-01

    The synthesis of novel planar heterocycles is at the heart of basic research as such scaffolds constitute key building blocks in important diverse areas of research: drug discovery, material sciences, and pesticides. The well-known benzoxazole is often contained in drug candidates but tweaking its...... lipophilicity and target interaction points are often desired. In this respect, the oxazolo[4,5-b]pyrazine is an attractive heterocyclic scaffold as it possesses increased water solubility as well as two additional hydrogen bonding acceptors. We here report a new Pd(II)-catalyzed domino reaction comprising...... the first Pd(II)-assisted intramolecular cyclization of an N-(2-chloro-3-heteroaryl)arylamide and validate its value by application to the first synthesis of 2-substituted oxazolo[4,5-b]pyrazines. We demonstrate that a bidentate phosphorus ligand as well as the presence of an aromatic nitrogen atom...

  19. Multicomponent, flow diazotization/Mizoroki-Heck coupling protocol: dispelling myths about working with diazonium salts.

    Science.gov (United States)

    Nalivela, Kumara S; Tilley, Michael; McGuire, Michael A; Organ, Michael G

    2014-05-26

    A single pass flow diazotization/Mizoroki-Heck protocol has been developed for the production of cinnimoyl and styryl products. The factors that govern aryl diazonium salt stability have been examined in detail leading to the development of a MeOH/DMF co-solvent system in which the diazonium salts can be generated in the presence of all other reaction components and then coupled selectively to give the desired products. Finally the key role of the reaction quench for flow reactions has been demonstrated. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Unusual selectivity-determining factors in the phosphine-free Heck arylation of allyl ethers

    DEFF Research Database (Denmark)

    Ambrogio, I.; Fabrizi, G.; Cacchi, S.

    2008-01-01

    The Heck reaction of aryl iodides and bromides with allyl ethers has been investigated. Using phosphinefree Pd(OAc)(2) in DNIF at 90 degrees C in the presence of Bu4NOAc, the reaction gave cinnamyl derivatives, usually in good to high yields, with a wide range of aryl halides. The reaction...... tolerates a variety of functional groups, including ether, amide, alcohol, aldehyde, ketone, ester, cyano, carboxylic acid, and nitro groups. Ortho-substituted arylating agents afforded moderate yields in some cases, though good to high yields were obtained with o-iodotoluene, iodovanillin, and 1...

  1. Pd@HNTs-CDNS-g-C3N4: A novel heterogeneous catalyst for promoting ligand and copper-free Sonogashira and Heck coupling reactions, benefits from halloysite and cyclodextrin chemistry and g-C3N4 contribution to suppress Pd leaching.

    Science.gov (United States)

    Sadjadi, Samahe; Heravi, Majid M; Malmir, Masoumeh

    2018-04-15

    For the first time, a ternary hybrid system composed of halloysite nanotubes, HNTs, cyclodextrin nanosponges, CDNS, and g-C 3 N 4 is prepared and used for immobilization of Pd(0) nanoparticles and development of a heterogeneous catalyst, Pd@HNTs-CDNS-g-C 3 N 4 for promoting ligand and copper-free Sonogashira and Heck coupling reactions in aqueous media. HNT as a porous tubular clay with outstanding thermal, mechanical and textural properties can act as a support for immobilizing Pd nanoparticles. The role of CDNS can be explained on the base of its capability to form inclusion complexe with substrates and bringing them in the vicinity of the catalytic active sites. Regarding the role of g-C 3 N 4 in catalysis, it is proved that its presence can suppress the Pd leaching dramatically. The contribution of each component as well as synergistic effect between them results in high catalytic activity and recyclability (up to 10 reaction runs) of the catalyst. Copyright © 2018 Elsevier Ltd. All rights reserved.

  2. From affine Hecke algebras to boundary symmetries

    International Nuclear Information System (INIS)

    Doikou, Anastasia

    2005-01-01

    Motivated by earlier works we employ appropriate realizations of the affine Hecke algebra and we recover previously known non-diagonal solutions of the reflection equation for the U q (gl n -bar ) case. The corresponding N site spin chain with open boundary conditions is then constructed and boundary non-local charges associated to the non-diagonal solutions of the reflection equation are derived, as coproduct realizations of the reflection algebra. With the help of linear intertwining relations involving the aforementioned solutions of the reflection equation, the symmetry of the open spin chain with the corresponding boundary conditions is exhibited, being essentially a remnant of the U q (gl n -bar ) algebra. More specifically, we show that representations of certain boundary non-local charges commute with the generators of the affine Hecke algebra and with the local Hamiltonian of the open spin chain for a particular choice of boundary conditions. Furthermore, we are able to show that the transfer matrix of the open spin chain commutes with a certain number of boundary non-local charges, depending on the choice of boundary conditions

  3. Gold-Catalyzed Cyclization of Furan-Ynes bearing a Propargyl Carbonate Group: Intramolecular Diels-Alder Reaction with In Situ Generated Allenes.

    Science.gov (United States)

    Sun, Ning; Xie, Xin; Chen, Haoyi; Liu, Yuanhong

    2016-09-26

    Gold-catalyzed cyclization of various furan-ynes with a propargyl carbonate or ester moiety results in the formation of a series of polycyclic aromatic ring systems. The reactions can be rationalized through a tandem gold-catalyzed 3,3-rearrangement of the propargyl carboxylate moiety in furan-yne substrates to form an allenic intermediate, which is followed by an intramolecular Diels-Alder reaction of furan and subsequent ring-opening of the oxa-bridged cycloadduct. It was found that the steric and electronic properties of phosphine ligands on the gold catalyst had a significant impact on the reaction outcome. In the case of 1,5-furan-yne, the cleavage of the oxa-bridge in the cycloadduct with concomitant 1,2-migration of the R(1) group occurs to furnish anthracen-1(2H)-ones bearing a quaternary carbon center. For 1,4-furan-yne, a facile aromatization of the cycloadduct takes place to give 9-oxygenated anthracene derivatives. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Bioinspired intramolecular Diels-Alder reaction: a rapid access to the highly-strained cyclopropane-fused polycyclic skeleton.

    Science.gov (United States)

    Zhu, Shifa; Guo, Zhengjiang; Huang, Zhipeng; Jiang, Huanfeng

    2014-02-24

    A bioinsipred gold-catalyzed tandem Diels-Alder/Diels-Alder reaction of an enynal and a 1,3-diene, forming the highly-strained benzotricyclo[3.2.1.0(2,7) ]octane skeleton, was reported. In contrast, a Diels-Alder/Friedel-Crafts tandem reaction occurred instead when silver salts were used as the catalyst. Although both reactions experienced the similar Diels-Alder reaction of a pyrylium intermediate with a 1,3-diene, they have different reaction mechanisms. The former proceeded with a stepwise Diels-Alder reaction, while the latter one with a concerted one. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Scope and limitations of the Heck-Matsuda-coupling of phenol diazonium salts and styrenes: a protecting-group economic synthesis of phenolic stilbenes.

    Science.gov (United States)

    Schmidt, Bernd; Elizarov, Nelli; Berger, René; Hölter, Frank

    2013-06-14

    4-Phenol diazonium salts undergo Pd-catalyzed Heck reactions with various styrenes to 4'-hydroxy stilbenes. In almost all cases higher yields and fewer side products were observed, compared to the analogous 4-methoxy benzene diazonium salts. In contrast, the reaction fails completely with 2- and 3-phenol diazonium salts. For these substitution patterns the methoxy-substituted derivatives are superior.

  6. Enantioselective copper catalysed intramolecular C-H insertion reactions of α-diazo-β-keto sulfones, α-diazo-β-keto phosphine oxides and 2-diazo-1,3-diketones; the influence of the carbene substituent.

    Science.gov (United States)

    Shiely, Amy E; Slattery, Catherine N; Ford, Alan; Eccles, Kevin S; Lawrence, Simon E; Maguire, Anita R

    2017-03-22

    Enantioselectivities in C-H insertion reactions, employing the copper-bis(oxazoline)-NaBARF catalyst system, leading to cyclopentanones are highest with sulfonyl substituents on the carbene carbon, and furthermore, the impact is enhanced by increased steric demand on the sulfonyl substituent (up to 91%ee). Enantioselective intramolecular C-H insertion reactions of α-diazo-β-keto phosphine oxides and 2-diazo-1,3-diketones are reported for the first time.

  7. Isotopic labeling as a tool to establish intramolecular vibrational coupling: The reaction of 2-propanol on Mo(110)

    International Nuclear Information System (INIS)

    Uvdal, P.; Wiegand, B.C.; Serafin, J.G.; Friend, C.M.

    1992-01-01

    The reactions of 2-propanol on Mo(110) were investigated using temperature programmed reaction, high resolution electron energy loss, and x-ray photoelectron spectroscopies. 2-Propanol forms 2-propoxide upon adsorption at 120 K on Mo(110). The 2-propoxide intermediate deoxygenates via selective γ C--H bond scission to eliminate propene as well as C--O bond hydrogenolysis to form trace amounts of propane. The C--O bond of 2-propoxide is estimated to be nearly perpendicular to the surface. Selective isotopic labeling was used to establish the coupling between the C--O stretch and modes associated with the hydrocarbon framework. The degree of coupling was strongly affected by bonding to the surface, primarily due to weakening of the C--O bond when 2-propoxide is bound to Mo(110). Selective isotopic labeling was, therefore, essential in making vibrational assignments and in identifying key reaction steps. Only a small kinetic isotope effect was observed during reaction of (CD 3 )(CH 3 )CHOH, consistent with a substantial component of C--O bond breaking in the transition state for propene elimination. Coupling of the C--O stretch to motion of the methyl group is also suggested to be important in the transition state for propene elimination

  8. Reações de inserção intramolecular de diazo compostos polifuncionais catalisadas por ródio(II: síntese de oxetan-3-ona-2-carboxilato e outros heterociclos funcionalizados Rhodium(II-catalysed intramolecular insertion reaction of multifunctional diazo compounds: synthesis of oxetan-3-one-2-carboxilate and other heterocycles

    Directory of Open Access Journals (Sweden)

    Albert Padwa

    1999-12-01

    Full Text Available gamma-Hydroxy-alpha-diazo-beta-ketoesters are key intermediates in the chemistry of penicilin-based antibiotics and natural products. The method developed here for the synthesis of ethyl 2-diazo-4-hydroxy-3-oxo-butanoate 17 (in two steps from the diazo mercurial 2 compares very favorably with those reported in the literature for similar compounds. The Rh2(OAc4-mediated intramolecular OH-insertion reaction of the diazo hydroxy ester 17 was investigated, furnishing the oxetan-3-one-2-carboxilate 18 in good yield. When the diazo ester lacks a free hydroxyl group as in the case of the phenoxy diazo ester 11 an intramolecular CH-insertion takes place, affording the 2H-chromene 20 in almost quantitative yield. The behavior of other functionalized diazo esters towards Rh2(OAc4 was also investigated.

  9. Domino reactions initiated by intramolecular hydride transfers from tri(di)arylmethane fragments to ketenimine and carbodiimide functions.

    Science.gov (United States)

    Alajarin, Mateo; Bonillo, Baltasar; Ortin, Maria-Mar; Sanchez-Andrada, Pilar; Vidal, Angel; Orenes, Raul-Angel

    2010-10-21

    The ability of triarylmethane and diarylmethane fragments to behave as hydride donors participating in thermal [1,5]-H shift/6π-ERC tandem processes involving ketenimine and carbodiimide functions is disclosed. C-Alkyl-C-phenyl ketenimines N-substituted by a triarylmethane substructure convert into a variety of 3,3,4,4-tetrasubstituted-3,4-dihydroquinolines, as structurally related carbodiimides transform into 3,4,4-trisubstituted-3,4-dihydroquinazolines via transient ortho-azaxylylenes. The first step of these one-pot conversions, the [1,5]-H shift, is considered to be a hydride migration on the basis of the known hydricity of the tri(di)arylmethane fragment and the electrophilicity of the central heterocumulenic carbon atom, whereas the final electrocyclization involves the formation of a sterically congested C-C or C-N bond. In the cases of C,C-diphenyl substituted triarylmethane-ketenimines the usual 6π-ERC becomes prohibited by the presence of two phenyl rings at each end of the azatrienic system. This situation opens new reaction channels: (a) following the initial hydride shift, the tandem sequence continues with an alternative electrocyclization mode to give 9,10-dihydroacridines, (b) the full sequence is initiated by a rare 1,5 migration of an electron-rich aryl group, followed by a 6π-ERC which leads to 2-aryl-3,4-dihydroquinolines, or (c) a different [1,5]-H shift/6π-ERC sequence involving the initial migration of a hydrogen atom from a methyl group at the ortho position to the nitrogen atom of the ketenimine function. Diarylmethane-ketenimines bearing a methyl group at the benzylic carbon atom experience a tandem double [1,5]-H shift, the first one being the usual benzylic hydride transfer whereas the second one involves the methyl group at the initial benzylic carbon atom, the reaction products being 2-aminostyrenes. Diarylmethane-ketenimines lacking such a methyl group convert into 3,4-dihydroquinolines by the habitual tandem [1,5]-H shift/6

  10. Reactions of recoil tritium generated by the 3He(n,p)3H reaction with aromatic compounds -intramolecular tritium distribution and radiochemical yield

    International Nuclear Information System (INIS)

    Nogawa, N.; Morikawa, Naotake; Oohashi, Kunio; Matuoka, H.; Moki, T.; Moriya, T.

    1986-01-01

    Reactions of recoil tritium with benzoic acid, acetanilide and β-phenethyl alcohol were studied using the 3 He(=n,p) 3 H reaction. The tritium distribution in the aromatic ring is approximately uniform in all the irradiated compounds and the tritium activity per C-H bond in the methyl and ethylene groups is 7 to 8 relative to that of the corresponding ring as standard. These findings are substantially the same as those obtained previously by the 6 Li(n,α) 3 H reactions, suggesting the same mechanism of tritiation for both recoil reactions. The tritiated parent compounds were obtained in high radiochemical yields: 45% for benzoic acid, 30% for acetanilide, 12% for β-phenethyl alcohol. (author)

  11. Continuous-flow Heck synthesis of 4-methoxybiphenyl and methyl 4-methoxycinnamate in supercritical carbon dioxide expanded solvent solutions

    Directory of Open Access Journals (Sweden)

    Phei Li Lau

    2013-12-01

    Full Text Available The palladium metal catalysed Heck reaction of 4-iodoanisole with styrene or methyl acrylate has been studied in a continuous plug flow reactor (PFR using supercritical carbon dioxide (scCO2 as the solvent, with THF and methanol as modifiers. The catalyst was 2% palladium on silica and the base was diisopropylethylamine due to its solubility in the reaction solvent. No phosphine co-catalysts were used so the work-up procedure was simplified and the green credentials of the reaction were enhanced. The reactions were studied as a function of temperature, pressure and flow rate and in the case of the reaction with styrene compared against a standard, stirred autoclave reaction. Conversion was determined and, in the case of the reaction with styrene, the isomeric product distribution was monitored by GC. In the case of the reaction with methyl acrylate the reactor was scaled from a 1.0 mm to 3.9 mm internal diameter and the conversion and turnover frequency determined. The results show that the Heck reaction can be effectively performed in scCO2 under continuous flow conditions with a palladium metal, phosphine-free catalyst, but care must be taken when selecting the reaction temperature in order to ensure the appropriate isomer distribution is achieved. Higher reaction temperatures were found to enhance formation of the branched terminal alkene isomer as opposed to the linear trans-isomer.

  12. Synthesis and Computational Studies Demonstrate the Utility of an Intramolecular Styryl Diels-Alder Reaction and Di-t-butylhydroxytoluene Assisted [1,3]-Shift to Construct Anticancer dl-Deoxypodophyllotoxin.

    Science.gov (United States)

    Saavedra, Diana I; Rencher, Benjamin D; Kwon, Doo-Hyun; Smith, Stacey J; Ess, Daniel H; Andrus, Merritt B

    2018-02-16

    Deoxypodophyllotoxin is a secondary metabolite lignan possessing potent anticancer activity with potential as a precursor for known anticancer drugs, but its use is limited by scarcity from natural sources. We here report the total synthesis of racemic deoxypodophyllotoxin in seven steps using an intramolecular styryl Diels-Alder reaction strategy uniquely suited to assemble the deoxypodophyllotoxin core. Density functional theory was used to analyze concerted, polar, and singlet-open-shell diradical reaction pathways, which identified a low-energy concerted [4 + 2] Diels-Alder pathway followed by a faster di-t-butylhydroxytoluene assisted [1,3]-formal hydrogen shift.

  13. DFT-Based Explanation of the Effect of Simple Anionic Ligands on the Regioselectivity of the Heck Arylation of Acrolein Acetals

    DEFF Research Database (Denmark)

    Henriksen, Signe Teuber; Tanner, David Ackland; Cacchi, Sandro

    2009-01-01

    The Heck arylation of acrolein acetal has been studied computationally and compared to the corresponding reaction with allyl ethers. The reaction can be controlled to give either cinnamaldehydes or arylpropanoic esters by addition of different coordinating anions, acetate, or chloride. The comput...... reaction conditions. The difference between the two substrate classes could be rationalized in terms of relative hydride donating power of the two substrates....

  14. Reações de inserção intramolecular de diazo compostos polifuncionais catalisadas por ródio(II): síntese de oxetan-3-ona-2-carboxilato e outros heterociclos funcionalizados Rhodium(II)-catalysed intramolecular insertion reaction of multifunctional diazo compounds: synthesis of oxetan-3-one-2-carboxilate and other heterocycles

    OpenAIRE

    Albert Padwa; Marcus Mandolesi Sá

    1999-01-01

    gamma-Hydroxy-alpha-diazo-beta-ketoesters are key intermediates in the chemistry of penicilin-based antibiotics and natural products. The method developed here for the synthesis of ethyl 2-diazo-4-hydroxy-3-oxo-butanoate 17 (in two steps from the diazo mercurial 2) compares very favorably with those reported in the literature for similar compounds. The Rh2(OAc)4-mediated intramolecular OH-insertion reaction of the diazo hydroxy ester 17 was investigated, furnishing the oxetan-3-one-2-carboxil...

  15. "Aplicação da reação de heck na sintese de compostos heterociclicos"

    OpenAIRE

    Leonardo Silva Santos

    1999-01-01

    Resumo: A reação de Heck intramolecular para as lactamas 4a, 4b, 4g e 4f forneceu exclusivamente produtos de ciclização 6-exo-trig em bons rendimentos e foram acompanhadas da migração da dupla ligação exocíclica fornecendo o biciclo 5 a partir da g-Iactama 4a, uma mistura em proporção molar aproximadamente igual a 6:1 dos biciclos 7 e 8 a partir da d- lactama 4b, uma mistura dos isômeros 18 e 19 a partir da lactama 4f na proporção molar aproximadamente igual a 2:1, e apenas o produto exocícli...

  16. Metodologies d’anulació en substrats heterocíclics: Reaccions de RCM i ciclacions de Heck

    OpenAIRE

    Alonso Serrano, Sandra

    2010-01-01

    [cat] La present Tesi Doctoral es situa en el context de l’estudi d’estratègies sintètiques per a la formació d’anells en l’àrea heterocíclica. En particular, s’han avaluat les possibilitats sintètiques de la combinació de dues reaccions d’eficàcia prou reconeguda per a la formació d’enllaços carboni-carboni, la reacció de RCM i la reacció intramolecular de Heck d’halurs vinílics, per a la construcció de les estructures policíliques amb pont característiques dels alcaloides ervitsina i apari...

  17. Diastereoselective Synthesis of Novel Heterocyclic Scaffolds through Tandem Petasis 3-Component/Intramolecular Diels-Alder and ROM-RCM Reactions

    DEFF Research Database (Denmark)

    Ishøy, Mette; Petersen, Rico; Petersen, Michael Åxman

    2017-01-01

    A high-yielding, stereoselective and extraordinarily complexity generatingPetasis 3-component/intramolecular Diels-Alderreaction has been developed. In combination with ROM-RCM, rapid access to complex sp3-rich heterocyclic scaffolds amenableto subsequent functionalization and library synthesis...

  18. Markov trace on the Yokonuma-Hecke algebra

    International Nuclear Information System (INIS)

    Juyumaya, J.

    2002-11-01

    The objective of this note is to prove that there exists a Markov trace on the Yokonuma-Hecke algebra. A motivation to define a Markov trace is to get polynomial invariants for knots in the sense of Jones construction. (author)

  19. Spectroscopic studies of the intramolecular hydrogen bonding in o-hydroxy Schiff bases, derived from diaminomaleonitrile, and their deprotonation reaction products

    Science.gov (United States)

    Szady-Chełmieniecka, Anna; Kołodziej, Beata; Morawiak, Maja; Kamieński, Bohdan; Schilf, Wojciech

    2018-01-01

    The structural study of five Schiff bases derived from diaminomaleonitrile (DAMN) and 2-hydroxy carbonyl compounds was performed using 1H, 13C and 15N NMR methods in solution and in the solid state as well. ATR-FTIR and X-Ray spectroscopies were used for confirmation of the results obtained by NMR method. The imine obtained from DAMN and benzaldehyde was synthesized as a model compound which lacks intramolecular hydrogen bond. Deprotonation of all synthesized compounds was done by treating with tetramethylguanidine (TMG). NMR data revealed that salicylidene Schiff bases in DMSO solution exist as OH forms without intramolecular hydrogen bonds and independent on the substituents in aromatic ring. In the case of 2-hydroxy naphthyl derivative, the OH proton is engaged into weak intramolecular hydrogen bond. Two of imines (salDAMN and 5-BrsalDAMN) exist in DMSO solution as equilibrium mixtures of two isomers (A and B). The structures of equilibrium mixture in the solid state have been studied by NMR, ATR-FTIR and X-Ray methods. The deprotonation of three studied compounds (salDAMN, 5-BrsalDAMN, and 5-CH3salDAMN) proceeded in two different ways: deprotonation of oxygen atom (X form) or of nitrogen atom of free primary amine group of DAMN moiety (Y form). For 5-NO2salDAMN and naphDAMN only one form (X) was observed.

  20. Evidence for excited state intramolecular charge transfer reaction in donor-acceptor molecule 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester: Experimental and quantum chemical approach

    International Nuclear Information System (INIS)

    Kumar Paul, Bijan; Samanta, Anuva; Kar, Samiran; Guchhait, Nikhil

    2010-01-01

    Intramolecular charge transfer (ICT) reaction has been investigated in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) using spectroscopic techniques. The molecule DPDAME shows local emission in non-polar solvent and dual emission in polar solvents. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the charge transfer character of the excited state. Quantum chemical calculations have been performed at Hartree-Fock (HF) and density functional theoretical (DFT) levels to correlate the experimental findings. Potential energy curves (PECs) for the ICT reaction have been evaluated along the donor twist angle at DFT and time dependent density functional theory (TDDFT) levels for the ground and excited states, respectively, using B3LYP hybrid functional and 6-31G** basis set. The solvent effects on the spectral properties have been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results are found to well substantiate the solvent polarity dependent Stokes shifted emission of DPDAME. Huge enhancement of dipole moment (Δμ=16.42 D) of the molecule following photoexcitation dictates the highly polar character of the excited state. Although elucidation of PECs does not exactly predict the operation of ICT according to twisted intramolecular charge transfer (TICT) model in DPDAME, lowering of vertical transition energy as a function of the donor twist coordinate scripts the occurrence of red shifted emission as observed experimentally.

  1. Lipase-catalyzed asymmetric synthesis of naphtho[2,3-c]furan-1(3H)-one derivatives by a one-pot dynamic kinetic resolution/intramolecular Diels-Alder reaction: Total synthesis of (-)-himbacine.

    Science.gov (United States)

    Sugiyama, Koji; Kawanishi, Shinji; Oki, Yasuhiro; Kamiya, Marin; Hanada, Ryosuke; Egi, Masahiro; Akai, Shuji

    2018-04-01

    One-pot sequential reactions using the acyl moieties installed by enzymatic dynamic kinetic resolution of alcohols have been little investigated. In this work, the acryloyl moiety installed via the lipase/oxovanadium combo-catalyzed dynamic kinetic resolution of a racemic dienol [4-(cyclohex-1-en-1-yl)but-3-en-2-ol or 1-(cyclohex-1-en-1-yl)but-2-en-1-ol] with a (Z)-3-(phenylsulfonyl)acrylate underwent an intramolecular Diels-Alder reaction in a one-pot procedure to produce an optically active naphtho[2,3-c]furan-1(3H)-one derivative (98% ee). This method was successfully applied to the asymmetric total synthesis of (-)-himbacine. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Solvent-dependent reactions for the synthesis of β-keto-benzo-δ-sultone scaffolds via DBU-catalyzed O-sulfonylation/intramolecular Baylis-Hillman/1,3-H shift or dehydration tandem sequences.

    Science.gov (United States)

    Ghandi, Mehdi; Bozcheloei, Abolfazl Hasani; Nazari, Seyed Hadi; Sadeghzadeh, Masoud

    2011-12-16

    We have developed a solvent-dependent method for the synthesis of novel benzo-δ-sultone scaffolds. A variety of benzylbenzo[e][1,2]oxathiin-4(3H)-one-2,2-dioxides were obtained in high yields in DMF using a one-pot, DBU-catalyzed condensation of 2-hydroxybenzaldehydes with a number of (E)-2-phenylethenesulfonyl chlorides. On the other hand, the initially prepared 2-formylphenyl-(E)-2-phenylethenesulfonate derivatives underwent DBU-catalyzed reactions to a series of 3-[methoxy(phenyl)methyl]benzo[e][1,2]oxathiine-2,2-dioxides in moderate to good yields in MeOH. These reactions presumably proceed via DBU-catalyzed O-sulfonylation/intramolecular Baylis-Hillman/1,3-H shift or dehydration tandem sequences, respectively.

  3. Back-breeding the aurochs: the Heck brothers, National Socialism and imagined geographies for nonhuman Lebensraum

    NARCIS (Netherlands)

    Driessen, C.P.G.; Lorimer, J.

    2016-01-01

    This chapter investigates the bio-geographical imaginations behind the animal 'back-breeding' programs carried out by Lutz and Heinz Heck - two influential German zoologists who ran Berlin and Munich zoos. Partly with close connections to and patronage from the National Socialist elite, the Heck

  4. Photoinduced intramolecular charge transfer (ICT) reaction in trans-methyl p-(dimethylamino) cinnamate: A combined fluorescence measurement and quantum chemical calculations

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Amrita [Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata 700009 (India); Kar, Samiran [Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India); Guchhait, Nikhil [Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata 700009 (India)], E-mail: nikhilg@postmark.net

    2006-01-05

    The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor-acceptor system has been investigated by steady-state absorption and emission spectroscopy and quantum chemical calculations. The molecule t-MDMAC shows an emission from the locally excited state in non-polar solvents. In addition to weak local emission, a strong solvent dependent red shifted fluorescence in polar aprotic solvents is attributed to highly polar intramolecular charge transfer state. However, the formation of hydrogen-bonded clusters with polar protic solvents has been suggested from a linear correlation between the observed red shifted fluorescence band maxima with hydrogen bonding parameters ({alpha}). Calculations by ab initio and density functional theory show that the lone pair electron at nitrogen center is out of plane of the benzene ring in the global minimum ground state structure. In the gas phase, a potential energy surface along the twist coordinate at the donor (-NMe{sub 2}) and acceptor (-CH = CHCOOMe) sites shows stabilization of S{sub 1} state and destabilization S{sub 2} and S{sub 0} states. A similar potential energy calculation along the twist coordinate in acetonitrile solvent using non-equilibrium polarized continuum model also shows more stabilization of S{sub 1} state relative to other states and supports solvent dependent red shifted emission properties. In all types of calculations it is found that the nitrogen lone pair is delocalized over the benzene ring in the global minimum ground state and is localized on the nitrogen centre at the 90 deg. twisted configuration. The S{sub 1} energy state stabilization along the twist coordinate at the donor site and localized nitrogen lone pair at the perpendicular configuration support well the observed dual fluorescence in terms of proposed twisted intramolecular charge transfer (TICT) model.

  5. 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.

  6. Two-rowed Hecke algebra representations at roots of unity

    International Nuclear Information System (INIS)

    Welsh, T.A.

    1996-01-01

    The explicit construction of irreducible representations of the Hecke algebra H n (q) of type A n-1 was studied for the non-generic case where q is a root of unity. The approach is via the Specht modules of H n (q) which are irreducible in the generic case and possess a natural basis indexed by Young tableaux. The general framework in which the non-generic H n (q)-modules are to be constructed is set up and, in particular, the full set of modules corresponding to two-part partitions is described. Many examples are given. 12 refs

  7. New stereoselective intramolecular

    Science.gov (United States)

    Alajarin; Vidal; Tovar; Ramirez De Arellano MC; Cossio; Arrieta; Lecea

    2000-11-03

    Efficient 1,4-asymmetric induction has been achieved in the highly stereocontrolled intramolecular [2 + 2] cycloadditions between ketenimines and imines, leading to 1,2-dihydroazeto[2, 1-b]quinazolines. The chiral methine carbon adjacent to the iminic nitrogen controls the exclusive formation of the cycloadducts with relative trans configuration at C2 and C8. The stepwise mechanistic model, based on theoretical calculations, fully supports the stereochemical outcome of these cycloadditions.

  8. Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond

    Indian Academy of Sciences (India)

    Ultrafast Dynamics of Chemical Reactions in Condensed Phase: Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond · PowerPoint Presentation · Slide 3 · Slide 4 · Slide 5 · Slide 6 · Slide 7 · Slide 8 · Slide 9 · Slide 10 · Slide 11 · Slide 12 · Slide 13 · Slide 14 · Slide 15 · Slide 16 · Slide 17 · Slide 18 · Slide 19.

  9. Intramolecular charge transfer of 4-(dimethylamino)benzonitrile probed by time-resolved fluorescence and transient absorption: No evidence for two ICT states and a πσ* reaction intermediate

    International Nuclear Information System (INIS)

    Zachariasse, Klaas A.; Druzhinin, Sergey I.; Senyushkina, Tamara; Kovalenko, Sergey A.

    2009-01-01

    For the double exponential fluorescence decays of the locally excited (LE) and intramolecular charge transfer (ICT) states of 4-(dimethylamino)benzonitrile (DMABN) in acetonitrile (MeCN) the same times τ 1 and τ 2 are observed. This means that the reversible LE ICT reaction, starting from the initially excited LE state, can be adequately described by a two state mechanism. The most important factor responsible for the sometimes experimentally observed differences in the nanosecond decay time, with τ 1 (LE) 1 (ICT), is photoproduct formation. By employing a global analysis of the LE and ICT fluorescence response functions with a time resolution of 0.5 ps/channel in 1200 channels reliable kinetic and thermodynamic data can be obtained. The arguments presented in the literature in favor of a πσ* state with a bent CN group as an intermediate in the ICT reaction of DMABN are discussed. From the appearance of an excited state absorption (ESA) band in the spectral region between 700 and 800 nm in MeCN for N,N-dimethylanilines with CN, Br, F, CF 3 , and C(=O)OC 2 H 2 p-substituents, it is concluded that this ESA band cannot be attributed to a πσ * state, as only the C-C≡N group can undergo the required 120 deg. bending.

  10. Intramolecular Diels–Alder reaction as a key step in tandem or sequential processes: a versatile tool for the synthesis of fused and bridged bicyclic or polycyclic compounds.

    Digital Repository Service at National Institute of Oceanography (India)

    Parvatkar, P.T.; Kadam, H.K.; Tilve, S.G.

    This review summarizes the recent examples of tandem or sequential reactions used for the last 10 years for the synthesis of fused and bridged bicyclic or polycyclic compounds with IMDA cycloaddition as the key means to access these compounds...

  11. 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; Zhong, Fangrui; Zheng, Bin; Meng, Yuezhong; Lu, Yixin; Huang, Kuo-Wei

    2013-01-01

    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.

  12. On the fourth moment of Hecke Maass forms and the Random Wave Conjecture

    OpenAIRE

    Buttcane, Jack; Khan, Rizwanur

    2016-01-01

    Conditionally on the Generalized Lindel\\"of Hypothesis, we obtain an asymptotic for the fourth moment of Hecke Maass cusp forms of large Laplacian eigenvalue for the full modular group. This lends support to the Random Wave Conjecture.

  13. Combined experimental and theoretical study of the mechanism and enantioselectivity of palladium-catalyzed intermolecular Heck coupling

    DEFF Research Database (Denmark)

    Henriksen, Signe Teuber; Norrby, Per-Ola; Kaukoranta, Päivi

    2008-01-01

    . The steric interactions in this transition state fully account for the enantioselectivity observed with the ligands studied. The calculations also predict relative reactivity and nonlinear mixing effects for the investigated ligands; these predictions are fully validated by experimental testing. Finally......The asymmetric Heck reaction using P,N-ligands has been studied by a combination of theoretical and experimental methods. The reaction follows Halpern-style selectivity; that is, the major isomer is produced from the least favored form of the pre-insertion intermediate. The initially formed Ph......, the low conversion observed with some catalysts was found to be caused by inactivation due to weak binding of the ligand to Pd(0). Adding monodentate PPh3 alleviated the precipitation problem without deteriorating the enantioselectivity and led to one of the most effective catalytic systems to date....

  14. Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenylethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

    KAUST Repository

    Chua, Ming Hui; Huang, Kuo-Wei; Xu, Jianwei; Wu, Jishan

    2015-01-01

    The straightforward synthesis of 3,5-di(triphenylethylenyl) BODIPYs 1–3 from the condensation of 2-(triphenylethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of 1 resulted in a “1,2-migratory shift” of one triphenylethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry.

  15. Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenylethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

    KAUST Repository

    Chua, Ming Hui

    2015-08-17

    The straightforward synthesis of 3,5-di(triphenylethylenyl) BODIPYs 1–3 from the condensation of 2-(triphenylethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of 1 resulted in a “1,2-migratory shift” of one triphenylethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry.

  16. Regularized inner products and weakly holomorphic Hecke eigenforms

    Science.gov (United States)

    Bringmann, Kathrin; Kane, Ben

    2018-01-01

    We show that the image of repeated differentiation on weak cusp forms is precisely the subspace which is orthogonal to the space of weakly holomorphic modular forms. This gives a new interpretation of weakly holomorphic Hecke eigenforms. The research of the first author is supported by the Alfried Krupp Prize for Young University Teachers of the Krupp foundation and the research leading to these results receives funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant agreement n. 335220—AQSER. The research of the second author was supported by grants from the Research Grants Council of the Hong Kong SAR, China (project numbers HKU 27300314, 17302515, and 17316416).

  17. Spherical Hecke algebra in the Nekrasov-Shatashvili limit

    Energy Technology Data Exchange (ETDEWEB)

    Bourgine, Jean-Emile [Asia Pacific Center for Theoretical Physics (APCTP),Pohang, Gyeongbuk 790-784 (Korea, Republic of)

    2015-01-21

    The Spherical Hecke central (SHc) algebra has been shown to act on the Nekrasov instanton partition functions of N=2 gauge theories. Its presence accounts for both integrability and AGT correspondence. On the other hand, a specific limit of the Omega background, introduced by Nekrasov and Shatashvili (NS), leads to the appearance of TBA and Bethe like equations. To unify these two points of view, we study the NS limit of the SHc algebra. We provide an expression of the instanton partition function in terms of Bethe roots, and define a set of operators that generates infinitesimal variations of the roots. These operators obey the commutation relations defining the SHc algebra at first order in the equivariant parameter ϵ{sub 2}. Furthermore, their action on the bifundamental contributions reproduces the Kanno-Matsuo-Zhang transformation. We also discuss the connections with the Mayer cluster expansion approach that leads to TBA-like equations.

  18. Synthesis, molecular docking and biological evaluation as HDAC inhibitors of cyclopeptide mimetics by a tandem three-component reaction and intramolecular [3+2] cycloaddition.

    Science.gov (United States)

    Pirali, Tracey; Faccio, Valeria; Mossetti, Riccardo; Grolla, Ambra A; Di Micco, Simone; Bifulco, Giuseppe; Genazzani, Armando A; Tron, Gian Cesare

    2010-02-01

    Novel macrocyclic peptide mimetics have been synthesized by exploiting a three-component reaction and an azide-alkyne [3 + 2] cycloaddition. The prepared compounds were screened as HDAC inhibitors allowing us to identify a new compound with promising biological activity. In order to rationalize the biological results, computational studies have also been performed.

  19. Highly efficient induction of chirality in intramolecular

    Science.gov (United States)

    Cossio; Arrieta; Lecea; Alajarin; Vidal; Tovar

    2000-06-16

    Highly stereocontrolled, intramolecular [2 + 2] cycloadditions between ketenimines and imines leading to 1,2-dihydroazeto[2, 1-b]quinazolines have been achieved. The source of stereocontrol is a chiral carbon atom adjacent either to the iminic carbon or nitrogen atom. In the first case, the stereocontrol stems from the preference for the axial conformer in the first transition structure. In the second case, the origin of the stereocontrol lies on the two-electron stabilizing interaction between the C-C bond being formed and the sigma orbital corresponding to the polar C-X bond, X being an electronegative atom. These models can be extended to other related systems for predicting the stereochemical outcome in this intramolecular reaction.

  20. Group characters, symmetric functions, and the Hecke algebra

    CERN Document Server

    Goldschmidt, David M

    1993-01-01

    Directed at graduate students and mathematicians, this book covers an unusual set of interrelated topics, presenting a self-contained exposition of the algebra behind the Jones polynomial along with various excursions into related areas. The book is made up of lecture notes from a course taught by Goldschmidt at the University of California at Berkeley in 1989. The course was organized in three parts. Part I covers, among other things, Burnside's Theorem that groups of order p^aq^b are solvable, Frobenius' Theorem on the existence of Frobenius kernels, and Brauer's characterization of characters. Part II covers the classical character theory of the symmetric group and includes an algorithm for computing the character table of S^n ; a construction of the Specht modules; the "determinant form" for the irreducible characters; the hook-length formula of Frame, Robinson, and Thrall; and the Murnaghan-Nakayama formula. Part III covers the ordinary representation theory of the Hecke algebra, the construction of the ...

  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. Eigenvalues of the Laplacian and of the Hecke operators for PSL(2,Z)

    International Nuclear Information System (INIS)

    Steil, G.

    1994-03-01

    A new method is described to compute with high accuracy a large number of eigenvalues and eigenfunctions (Maass wave forms) of the Laplacian and of the Hecke operators for the modular group. It relies essentially on the theory of Hecke operators. The results of the computations confirm some important conjectures from number theory, namely Ramanujan-Petersson, Sato-Tate, and the conjecture that the discrete spectrum of the Laplacian be simple. Examples of the numerical data are included as a reference. The algorithm can be generalized to other non-cocompact but cofinite arithmetic groups, like Picard group PSL(2, Z)[i]) and Hecke triangle groups Γ(√2) and Γ(√3). (orig.)

  3. Perspectivas mecanisticas de reações organicas catalisadas por paladio : Heck, oxa-Heck e acoplamento de Buchwald-Hartwig por ESI-MS/MS

    OpenAIRE

    Boniek Gontijo Vaz

    2009-01-01

    Resumo: A espectrometria de Massas por eletronspray (ESI-MS) tornou-se um método prático para o estudo de mecanismos reacionais em solução. Neste trabalho importantes reações catalisadas por paládio: reação de Heck-Mizoroki, oxa-Heck e o acoplamento de Buchwald-Hartwig foram monitoradas por ESI-MS visando interceptar espécies que comprovam as atuais propostas mecanísticas ou que abram caminho para novas propostas para estas reações. O monitoramento das reações foi realizado no modo off-line, ...

  4. Matrix units and Schur elements for the degenerate cyclotomic Hecke algebras

    OpenAIRE

    Zhao, Deke

    2011-01-01

    The paper uses the cellular basis of the (semi-simple) degenerate cyclotomic Hecke algebras to investigate these algebras exhaustively. As a consequence, we describe explicitly the "Young's seminormal form" and a orthogonal bases for Specht modules and determine explicitly the closed formula for the natural bilinear form on Specht modules and Schur elements for the degenerate cyclotomic Hekce algebras.

  5. R-matrix arising from affine Hecke algebras and its application to Macdonald's difference operators

    International Nuclear Information System (INIS)

    Kato, Shinichi

    1994-01-01

    We shall give a certain trigonometric R-matrix associated with each root system by using affine Hecke algebras. From this R-matrix, we derive a quantum Knizhnik-Zamolodchikov equation after Cherednik, and show that the solutions of this KZ equation yield eigenfunctions of Macdonald's difference operators. (orig.)

  6. Intramolecular addition of benzylic radicals onto ketenimines. Synthesis of 2-alkylindoles.

    Science.gov (United States)

    Alajarín, Mateo; Vidal, Angel; Ortín, María-Mar

    2003-12-07

    The inter- and intramolecular addition of free radicals onto ketenimines is studied. All the attempts to add intermolecularly several silicon, oxygen or carbon centered radicals to N-(4-methylphenyl)-C,C-diphenyl ketenimine were unsuccessful. In contrast, the intramolecular addition of benzylic radicals, generated from xanthates, onto the central carbon of a ketenimine function with its N atom linked to the ortho position of the aromatic ring occurred under a variety of reaction conditions. These intramolecular cyclizations provide a novel radical-mediated synthesis of 2-alkylindoles.

  7. Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

    KAUST Repository

    Vummaleti, Sai V. C.; Alghamdi, Miasser; Poater, Albert; Falivene, Laura; Scaranto, Jessica; Beetstra, Dirk J.; Morton, Jason G.; Cavallo, Luigi

    2015-01-01

    Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

  8. Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

    KAUST Repository

    Vummaleti, Sai V. C.

    2015-11-13

    Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

  9. A Family of Finite-Dimensional Representations of Generalized Double Affine Hecke Algebras of Higher Rank

    Science.gov (United States)

    Fu, Yuchen; Shelley-Abrahamson, Seth

    2016-06-01

    We give explicit constructions of some finite-dimensional representations of generalized double affine Hecke algebras (GDAHA) of higher rank using R-matrices for U_q(sl_N). Our construction is motivated by an analogous construction of Silvia Montarani in the rational case. Using the Drinfeld-Kohno theorem for Knizhnik-Zamolodchikov differential equations, we prove that the explicit representations we produce correspond to Montarani's representations under a monodromy functor introduced by Etingof, Gan, and Oblomkov.

  10. Intramolecular Association within the SAFT Framework

    DEFF Research Database (Denmark)

    Avlund, Ane Søgaard; Kontogeorgis, Georgios; Chapman, Walter G.

    2011-01-01

    A general theory for modelling intramolecular association within the SAFT framework is proposed. Sear and Jackson [Phys. Rev. E. 50 (1), 386 (1994)] and Ghonasgi and Chapman [J. Chem. Phys. 102 (6), 2585 (1995)] have previously extended SAFT to include intramolecular association for chains with two...... the contribution to the Helmholtz free energy from association (inter- as well as intramolecularly) at equilibrium. Sear and Jackson rederived the contribution to the Helmholtz free energy from association from the theory by Wertheim [J. Stat. Phys. 42 (3–4), 459 (1986)] with inclusion of intramolecular...

  11. Symmetry of quantum intramolecular dynamics

    International Nuclear Information System (INIS)

    Burenin, Alexander V

    2002-01-01

    The paper reviews the current progress in describing quantum intramolecular dynamics using merely symmetry principles as a basis. This closed qualitative approach is of particular interest because it is the only method currently available for a broad class of topical problems in the internal dynamics of molecules. Moreover, a molecule makes a physical system whose collective internal motions are geometrically structured, so that its description by perturbation methods requires a symmetry analysis of this structure. The nature of the geometrical symmetry groups crucial for the closed formulation of the qualitative approach is discussed. In particular, the point group of a molecule is of this type. (methodological notes)

  12. 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.

  13. Intramolecular electron transfer in single-site-mutated azurins

    DEFF Research Database (Denmark)

    Farver, O; Skov, L K; Pascher, T

    1993-01-01

    . Natl. Acad. Sci. U.S.A. 86, 6968-6972]. The RSSR- radical produced in the above reaction was reoxidized in a slower intramolecular electron-transfer process (30-70 s-1 at 298 K) concomitant with a further reduction of the Cu(II) ion. The temperature dependence of the latter rates was determined......, lambda = 135 kJ mol-1 for the reorganization energy was derived. When Trp48, situated midway between the donor and the acceptor, was replaced by Leu or Met, only a small change in the rate of intramolecular electron transfer was observed, indicating that the aromatic residue in this position...... is apparently only marginally involved in electron transfer in wild-type azurin. Pathway calculations also suggest that a longer, through-backbone path is more efficient than the shorter one involving Trp48. The former pathway yields an exponential decay factor, beta, of 6.6 nm-1. Another mutation, raising...

  14. Thermal and catalytic intramolecular [4+2]-cycloaddition in 2-alkenylfurans

    International Nuclear Information System (INIS)

    Zubkov, Fedor I; Nikitina, Evgenia V; Varlamov, Alexey V

    2005-01-01

    The published data on the intramolecular Diels-Alder reaction in compounds of the 2-alkenylfuran series are generalised. The methods and conditions for the preparation of tricyclic systems are considered. The effects of the substituents in the furan and the unsaturated fragments on the cycloaddition are discussed. The application of this reaction to the synthesis of alkaloids and terpenoids is exemplified.

  15. Thermal and catalytic intramolecular [4+2]-cycloaddition in 2-alkenylfurans

    Energy Technology Data Exchange (ETDEWEB)

    Zubkov, Fedor I; Nikitina, Evgenia V; Varlamov, Alexey V [Department of Physical, Mathematical and Natural Sciences, Peoples' Friendship University of Russia (Russian Federation)

    2005-07-31

    The published data on the intramolecular Diels-Alder reaction in compounds of the 2-alkenylfuran series are generalised. The methods and conditions for the preparation of tricyclic systems are considered. The effects of the substituents in the furan and the unsaturated fragments on the cycloaddition are discussed. The application of this reaction to the synthesis of alkaloids and terpenoids is exemplified.

  16. Nekrasov and Argyres-Douglas theories in spherical Hecke algebra representation

    Science.gov (United States)

    Rim, Chaiho; Zhang, Hong

    2017-06-01

    AGT conjecture connects Nekrasov instanton partition function of 4D quiver gauge theory with 2D Liouville conformal blocks. We re-investigate this connection using the central extension of spherical Hecke algebra in q-coordinate representation, q being the instanton expansion parameter. Based on AFLT basis together with intertwiners we construct gauge conformal state and demonstrate its equivalence to the Liouville conformal state, with careful attention to the proper scaling behavior of the state. Using the colliding limit of regular states, we obtain the formal expression of irregular conformal states corresponding to Argyres-Douglas theory, which involves summation of functions over Young diagrams.

  17. Nekrasov and Argyres–Douglas theories in spherical Hecke algebra representation

    Energy Technology Data Exchange (ETDEWEB)

    Rim, Chaiho, E-mail: rimpine@sogang.ac.kr; Zhang, Hong, E-mail: kilar@itp.ac.cn

    2017-06-15

    AGT conjecture connects Nekrasov instanton partition function of 4D quiver gauge theory with 2D Liouville conformal blocks. We re-investigate this connection using the central extension of spherical Hecke algebra in q-coordinate representation, q being the instanton expansion parameter. Based on AFLT basis together with intertwiners we construct gauge conformal state and demonstrate its equivalence to the Liouville conformal state, with careful attention to the proper scaling behavior of the state. Using the colliding limit of regular states, we obtain the formal expression of irregular conformal states corresponding to Argyres–Douglas theory, which involves summation of functions over Young diagrams.

  18. Hecke algebraic properties of dynamical R-matrices. Application to related quantum matrix algebras

    International Nuclear Information System (INIS)

    Khadzhiivanov, L.K.; Todorov, I.T.; Isaev, A.P.; Pyatov, P.N.; Ogievetskij, O.V.

    1998-01-01

    The quantum dynamical Yang-Baxter (or Gervais-Neveu-Felder) equation defines an R-matrix R cap (p), where p stands for a set of mutually commuting variables. A family of SL (n)-type solutions of this equation provides a new realization of the Hecke algebra. We define quantum antisymmetrizers, introduce the notion of quantum determinant and compute the inverse quantum matrix for matrix algebras of the type R cap (p) a 1 a 2 = a 1 a 2 R cap. It is pointed out that such a quantum matrix algebra arises in the operator realization of the chiral zero modes of the WZNW model

  19. 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 unus......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......, associated with an excited-state intramolecular proton transfer process....

  20. Synthesis of 2-vinylic indoles and derivatives via a Pd-catalyzed tandem coupling reaction.

    Science.gov (United States)

    Fayol, Aude; Fang, Yuan-Qing; Lautens, Mark

    2006-09-14

    A novel one-step synthesis of valuable 2-vinylic indoles and their tricycle derivatives is described. This reaction, which utilizes a gem-dibromovinyl unit as a readily available starting material, occurs via an efficient Pd-catalyzed tandem Buchwald-Hartwig/Heck reaction.

  1. Thiocarbamate-Directed Tandem Olefination-Intramolecular Sulfuration of Two Ortho C-H Bonds: Application to Synthesis of a COX-2 Inhibitor.

    Science.gov (United States)

    Li, Wendong; Zhao, Yingwei; Mai, Shaoyu; Song, Qiuling

    2018-02-16

    A palladium-catalyzed dual ortho C-H bond activation of aryl thiocarbamates is developed. This tandem reaction initiates by thiocarbamate-directed ortho C-H palladation, which leads to favorable olefin insertion rather than reductive elimination. The oxidative Heck reaction followed by another C-H activation and sulfuration affords the dual-functionalized products. This reaction provides a concise route to the S,O,C multisubstituted benzene skeleton which could be successfully applied for the synthesis of a COX-2 inhibitor.

  2. Iwahori-Hecke algebras and Schur algebras of the symmetric group

    CERN Document Server

    Mathas, Andrew

    1999-01-01

    This volume presents a fully self-contained introduction to the modular representation theory of the Iwahori-Hecke algebras of the symmetric groups and of the q-Schur algebras. The study of these algebras was pioneered by Dipper and James in a series of landmark papers. The primary goal of the book is to classify the blocks and the simple modules of both algebras. The final chapter contains a survey of recent advances and open problems. The main results are proved by showing that the Iwahori-Hecke algebras and q-Schur algebras are cellular algebras (in the sense of Graham and Lehrer). This is proved by exhibiting natural bases of both algebras which are indexed by pairs of standard and semistandard tableaux respectively. Using the machinery of cellular algebras, which is developed in Chapter 2, this results in a clean and elegant classification of the irreducible representations of both algebras. The block theory is approached by first proving an analogue of the Jantzen sum formula for the q-Schur algebras. T...

  3. Magnetically separable Fe3O4@DOPA–Pd: a heterogeneous catalyst for aqueous Heck reaction

    Data.gov (United States)

    U.S. Environmental Protection Agency — Magnetically separable Fe3O4@DOPA–Pd catalyst has been synthesized via anchoring of palladium over dopamine-coated magnetite via co-ordinate interaction and the...

  4. Formation of benzo[f]-1-indanone frameworks by regulable intramolecular annulations of gem-dialkylthio trienynes.

    Science.gov (United States)

    Fang, Zhongxue; Liu, Ying; Barry, Badru-Deen; Liao, Peiqiu; Bi, Xihe

    2015-02-20

    An atom-economic route to benzo[f]-1-indanone frameworks has been developed starting from the readily available gem-dialkylthio trienynes by intramolecular annulations. The chemoselectivity of the intramolecular cyclizations can be regulated by both the base and the type of gas atmosphere used in the reaction, thus allowing the divergent synthesis of the corresponding functionalized benzo[f]-1-indanones in good to excellent yields.

  5. Potassium hydroxide/dimethyl sulfoxide promoted intramolecular cyclization for the synthesis of benzimidazol-2-ones.

    Science.gov (United States)

    Beyer, Astrid; Reucher, Christine M M; Bolm, Carsten

    2011-06-03

    A new protocol for intramolecular N-arylations of ureas to form benzimidazol-2-ones has been developed. The cyclization reaction occurs in the presence of KOH and DMSO at close to ambient temperature. Under these conditions the yields are high and a wide range of functional groups are tolerated.

  6. Intra-molecular selectivity of muonium towards chlorinated aromatic compounds

    International Nuclear Information System (INIS)

    Venkateswaran, K.; Stadlbauer, J.M.; Laing, M.E.; Klugkist, J.; Chong, D.P.; Porter, G.B.; Walker, D.C.

    1994-01-01

    Muon resonance studies show that muonium atoms (Mu) in ethanol add selectively to certain C-sites of aromatic compounds containing -Cl and -OH substituents. The sites chosen seem to be those carrying the lowest electron density. This helps to characterize Mu as a nucleophile in addition reactions and, in this respect, Mu differs from ordinary H-atoms. The study shows no apparent inter-molecular selectivity between a pair of aromatic solutes in an equimolar mixture, but strong intra-molecular selectivity in an ether composed of those two aromatic rings. This difference between intra- and inter-molecular selectivity is interpreted as kinetic in origin - arising from the 'caging effect' of the solvent and peculiar to reactions close to the diffusion-controlled limit. (orig.)

  7. Solvent control of intramolecular proton transfer

    DEFF Research Database (Denmark)

    Manolova, Y.; Marciniak, Heinz; Tschierlei, S.

    2017-01-01

    of molecules in the enol and zwitterionic proton transfer (PT) form exists in the ground state. However, the zwitterion is the energetically favored one in the electronically excited state. Optical excitation of the enol form results in intramolecular proton transfer and formation of the PT form within 1.4 ps...

  8. INTRAMOLECULAR ISOTOPE EFFECTS IN HYDROCARBON MASS SPECTRA

    Energy Technology Data Exchange (ETDEWEB)

    Stevenson, D. P.; Schachtschneider, J. H.

    1963-07-15

    Approximate calculations based on the quasi-equilibrium rate theory of the origin of mass spectra are shown to lead to an approximately correct magnitude for the intramolecular ( pi /sup -/) isotope effect on C--H bond dissociation probabilities of various deuterohydrocarbons. (auth)

  9. Photoswitchable Intramolecular H-Stacking of Perylenebisimide

    NARCIS (Netherlands)

    Wang, Jiaobing; Kulago, Artem; Browne, Wesley R.; Feringa, Ben L.

    2010-01-01

    Dynamic control over the formation of H- or J-type aggregates of chromophores is of fundamental importance for developing responsive organic optoelectronic materials. In this study, the first example of photoswitching between a nonstacked and an intramolecularly H-stacked arrangement of

  10. Differential calculi on quantum vector spaces with Hecke-type relations

    International Nuclear Information System (INIS)

    Baez, J.C.

    1991-01-01

    From a vector space V equipped with a Yang-Baxter operator R one may form the r-symmetric algebra S R V=TV/ , which is a quantum vector space in the sense of Manin, and the associated quantum matrix algebra M R V=T(End(V))/ -1 >. In the case when R satisfies a Hecke-type identity R 2 =(1-q)R+q, we construct a differential calculus Ω R V for S R V which agrees with that constructed by Pusz, Woronowicz, Wess, and Zumino when R is essentially the R-matrix of GL q (n). Elements of Ω R V may be regarded as differential forms on the quantum vector space S R V. We show that Ω R V is M R V-covariant in the sense that there is a coaction Φ * :Ω R V→M R VxΩ R V with Φ * d=(1xd)Φ * extending the natural coaction Φ:S R V→M R VxS R V. (orig.)

  11. Multiplicative Structure and Hecke Rings of Generator Matrices for Codes over Quotient Rings of Euclidean Domains

    Directory of Open Access Journals (Sweden)

    Hajime Matsui

    2017-12-01

    Full Text Available In this study, we consider codes over Euclidean domains modulo their ideals. In the first half of the study, we deal with arbitrary Euclidean domains. We show that the product of generator matrices of codes over the rings mod a and mod b produces generator matrices of all codes over the ring mod a b , i.e., this correspondence is onto. Moreover, we show that if a and b are coprime, then this correspondence is one-to-one, i.e., there exist unique codes over the rings mod a and mod b that produce any given code over the ring mod a b through the product of their generator matrices. In the second half of the study, we focus on the typical Euclidean domains such as the rational integer ring, one-variable polynomial rings, rings of Gaussian and Eisenstein integers, p-adic integer rings and rings of one-variable formal power series. We define the reduced generator matrices of codes over Euclidean domains modulo their ideals and show their uniqueness. Finally, we apply our theory of reduced generator matrices to the Hecke rings of matrices over these Euclidean domains.

  12. Reaction

    African Journals Online (AJOL)

    abp

    19 oct. 2017 ... Reaction to Mohamed Said Nakhli et al. concerning the article: "When the axillary block remains the only alternative in a 5 year old child". .... Bertini L1, Savoia G, De Nicola A, Ivani G, Gravino E, Albani A et al ... 2010;7(2):101-.

  13. Decomposition reactions of bifenox anion radical involving intramolecular electron transfer

    Czech Academy of Sciences Publication Activity Database

    Hromadová, Magdaléna; Mořkovská, Petra; Pospíšil, Lubomír; Giannarelli, S.

    2005-01-01

    Roč. 582, 1-2 (2005), s. 156-164 ISSN 0022-0728 R&D Projects: GA MŠk OC D15.10; GA ČR GP203/02/P082; GA ČR GA203/03/0821 Institutional research plan: CEZ:AV0Z40400503 Keywords : bifenox * nitro-group reduction * double-layer effect Subject RIV: CG - Electrochemistry Impact factor: 2.223, year: 2005

  14. Excited state intramolecular charge transfer reaction in non-aqueous ...

    Indian Academy of Sciences (India)

    polar phase and thus leading to less swelling of reverse .... ues were restricted up to the limit at which no phase separation was ..... The lower panel of figure 1 also indicates that the slopes of ... probe in its ground and excited states.55.

  15. Photoinduced intramolecular charge-transfer reactions in 4-amino-3 ...

    Indian Academy of Sciences (India)

    TECS

    cooled molecular beams. Theoretical calculations using density functional theory help to determine structure, vibrational modes, potential energy surface, transition energy and oscillator strength for correlating experimental findings.

  16. Intramolecular Wittig reaction: A new synthesis of (S)- pyrrolam A

    Digital Repository Service at National Institute of Oceanography (India)

    Majik, M.S.; Parameswaran, P.S.; Tilve, S.G.

    . R. Liddell, Nat. Prod. Rep. 2002, 19, 773; J. T. Wroble, in C28The Alkaloids: Chemistry & PharmacologyC29, Ed. A. Brossi, Academic Press, San Diego, 1985, Vol.26, Chapt.7, p.327, and references cited therein; M. Boppre´, Naturwissenschaften 1986, 73...

  17. Hiperplasia epitelial focal (doença de Heck em descendente de índios brasileiros: relato de caso Focal epithelial hyperplasia (Heck's disease in Brazilian indian descent: report of a case

    Directory of Open Access Journals (Sweden)

    Pedro Paulo de Andrade Santos

    2007-12-01

    Full Text Available A hiperplasia epitelial focal, ou doença de Heck, é uma enfermidade rara, benigna, que afeta a mucosa oral de crianças e adultos jovens de diversas regiões do mundo e em diferentes grupos étnicos, como indígenas e esquimós. Apresenta correlação com o papilomavírus humano (HPV no qual os tipos 13 e 32 têm sido consistentemente detectados nessas lesões. Este artigo relata um caso de uma paciente de 18 anos de idade, descendente de índios potiguares, que compareceu ao serviço de estomatologia da Universidade Federal do Rio Grande do Norte (UFRN, exibindo lesões bem definidas, arredondadas, planas, localizadas em cavidade oral, com tempo de evolução de aproximadamente dois anos. As lesões foram submetidas a biópsias incisionais, constatado-se no exame histopatológico alterações epiteliais, como acantose, cristas epiteliais em forma de "taco de golfe" além de células mitosóides. Esses achados histopatológicos foram compatíveis com a hipótese clínica de hiperplasia epitelial focal (doença de Heck.The focal epithelial hyperplasia or Heck's disease is a benign rare pathology, that affects children and young adults oral mucosal in many world regions, and different ethnic groups, for example Indians and Eskimos. Presents correlation with the subtypes 13 and 32 of human papillomavirus (HPV. This article report a case of an 18-year-old patient, descent of potiguar indian, attended in stomatology service of Federal University of Rio Grande do Norte (UFRN, presenting well defined lesions, round, plane, localized in oral cavity with an evolution of two years. The lesions were submitted to incisional biopsies, verifying in histopathologic exam, epithelial alterations, like acanthosis, epithelial projections in "parquet block of golf" beyond mitosoid cells. These histopathological findings were compatible with clinical hypothesis of focal epithelial hyperplasia (Heck's disease.

  18. Surprisingly Mild Enolate-Counterion-Free Pd(0)-Catalyzed Intramolecular Allylic Alkylations

    DEFF Research Database (Denmark)

    Madec, David; Prestat, Guillaume; Martini, Elisabetta

    2005-01-01

    Palladium-catalyzed intramolecular allylic alkylations of unsaturated EWG-activated amides can take place under phase-transfer conditions or in the presence of a crown ether. These new reaction conditions are milder and higher yielding than those previously reported. A rationalization for such an...... for such an unexpected result is put forth and validated by DFT-B3LYP calculations. The results suggest cyclization via a counterion-free (E)-enolate TS....

  19. 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?"

  20. Intramolecular Charge-Transfer Interaction of Donor-Acceptor-Donor Arrays Based on Anthracene Bisimide.

    Science.gov (United States)

    Iwanaga, Tetsuo; Ogawa, Marina; Yamauchi, Tomokazu; Toyota, Shinji

    2016-05-20

    We designed anthracene bisimide (ABI) derivatives having two triphenylamine (TPA) groups as donor units at the 9,10-positions to form a novel π-conjugated donor-acceptor system. These compounds and their analogues with ethynylene linkers were synthesized by Suzuki-Miyaura and Sonogashira coupling reactions, respectively. In UV-vis spectra, the linker-free derivatives showed broad absorption bands arising from intramolecular charge-transfer interactions. Introducing ethynylene linkers resulted in a considerable red shift of the absorption bands. In fluorescence spectra, the ethynylene derivatives showed intense emission bands at 600-650 nm. Their photophysical and electrochemical properties were compared with those of the corresponding mono TPA derivatives on the basis of theoretical calculations and cyclic voltammetry to evaluate the intramolecular electronic interactions between the donor and acceptor units.

  1. 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.

  2. One-pot synthesis of spiropyrroloquinoline-isoindolinone and their aza-analogs via the Ugi-4CR/metal-free intramolecular bis-annulation process.

    Science.gov (United States)

    Ghandi, Mehdi; Zarezadeh, Nahid; Abbasi, Alireza

    2015-08-14

    This presentation discloses a one-pot synthesis of a series of spiropyrroloquinoline isoindolinone and spiropyrroloquinoline aza-isoindolinone scaffolds. The reaction proceeds by the combination of a Ugi four-component reaction (4CR) and two intramolecular cyclizations under metal-free conditions. The proof of the structures relies on analytical investigation and X-ray crystallography.

  3. Application of “Boomerang” Linear Polystyrene-Stabilized Pd Nanoparticles to a Series of C-C Coupling Reactions in Water

    Directory of Open Access Journals (Sweden)

    Atsushi Ohtaka

    2015-02-01

    Full Text Available The application of a catch-and-release system for soluble Pd species between water (reaction medium and polystyrene (polymer support was examined in the Suzuki coupling reaction with 2-bromothiophene and the Heck reaction with styrene or bromobenzene. Although a slight increase in particle size was observed by TEM after re-stabilization of the Pd species on linear polystyrene, no agglomeration was observed.

  4. Intramolecular electron transfer through a bridging carboxylate group coordinated to two cobalt(III)-ions

    International Nuclear Information System (INIS)

    Wieghardt, K.

    1978-01-01

    Reduction of the binuclear μ-p-nitrobenzoato -di-μ-hydroxo -bis[triammine cobalt(III)] cation with (CH 3 ) 2 COH radicals yields a radical cation with the p-nitrobenzoato radical being coordinated to two cobalt(III) ions at the carboxylic group. The unprotonated form of this species undergoes intramolecular electron transfer producing Co(II) (k = (3.3 +- 0.3). x 10 3 s -1 ). The role of the carboxylate group in the intramolecular electron transfer process is tentatively assessed in terms of an intramolecular outer-sphere reaction because of lack of overlap of the donor orbitals (π) and the acceptor orbital (sigma). The protonated form of the radical cation (pKsub(a) = 2.5) disproportionates via a bimolecular process without production of Co(II). The effect of two coordinated Co(III) ions as compared to only one on the properties of the nitrobenzoate radical anion are discussed. (orig.) 891 HK 892 GM [de

  5. Intramolecular interactions in a new tris-dithizonatocobalt(III) complex

    International Nuclear Information System (INIS)

    Eschwege, Karel G. von; As, Lydia van; Joubert, Chris C.; Swarts, Jannie C.; Aquino, Manuel A.S.; Cameron, T. Stanley

    2013-01-01

    Graphical abstract: Electrochemically Co(HDz) 3 (5), show three main ligand-based redox processes, two reductions and one oxidation. Ligand oxidations can be resolved into three components highlighting effective intramolecular interactions between molecular fragments; a spectroelectrochemical study of (5) highlighted spectroscopic changes during the six observed redox steps. - Highlights: • Comparative CV's of dithizone (1), PhHg(HDz) and new Co(HDz) 3 (5), is discussed. • One oxidation and two reductions per ligand and a Co III/II couple for (5) are observed. • Mono- and tris-coordinated PhHg(HDz) and (5) have stable metal thioether bonds. • Crystal structure details explain good resolution between ligand redox processes. • Spectro-electrochemistry of (5) highlights spectroscopic properties of redox products. - Abstract: The reactions between dithizone (H 2 Dz (1)) or potassium dithizonate (KHDz (3)), and [Co(H 2 O) 6 ] 2+ (6), in acetone or methanol to liberate tris-dithizonatocobalt(III), Co(HDz) 3 (5), are described. The structure of (5) was confirmed by single crystal X-ray analyses and shows bidentate coordination to Co III via S and N donor atoms for all three HDz − ligands. A comparative voltammetric and spectro-electrochemical study revealed that (1) can be oxidised in two one-electron transfer steps, to generate a disulphide first and then HDz + . In contrast, upon complexation with cobalt, the free mercaptan group of (1) becomes a stable “metal thioether”, Co-S-C, which effectively prevents disulphide formation in all three ligands of (5) upon electrochemical oxidation. As a result, each ligand of Co(HDz) 3 shows just one oxidation process. Intramolecular communication between ligands is evident because the three separate ligand-based oxidations are well resolved. Two irreversible ligand reduction steps, each consisting of three unresolved components related to each of the three ligands, were also observed. The Co II /Co III couple

  6. 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.

  7. 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.

  8. Effects of acid concentration on intramolecular charge transfer ...

    Indian Academy of Sciences (India)

    rate. Time-dependent density functional theory calculations have been performed to understand the observed spectroscopic results. Keywords. Intramolecular charge transfer; absorption and fluorescence; time resolved fluorescence measurements; acid concentration dependence; time-dependent density functional theory.

  9. Intramolecularly Hydrogen-Bonded Polypyrroles as Electro-Optical Sensors

    National Research Council Canada - National Science Library

    Nicholson, Jesse

    2001-01-01

    We have developed a new class of polypyrroles bearing both hydrogen-bond acceptor and hydrogen-donor groups such that the intramolecular hydrogen bonding holds the system planar enhancing conjugation...

  10. Molecular structures and intramolecular dynamics of pentahalides

    Science.gov (United States)

    Ischenko, A. A.

    2017-03-01

    This paper reviews advances of modern gas electron diffraction (GED) method combined with high-resolution spectroscopy and quantum chemical calculations in studies of the impact of intramolecular dynamics in free molecules of pentahalides. Some recently developed approaches to the electron diffraction data interpretation, based on direct incorporation of the adiabatic potential energy surface parameters to the diffraction intensity are described. In this way, complementary data of different experimental and computational methods can be directly combined for solving problems of the molecular structure and its dynamics. The possibility to evaluate some important parameters of the adiabatic potential energy surface - barriers to pseudorotation and saddle point of intermediate configuration from diffraction intensities in solving the inverse GED problem is demonstrated on several examples. With increasing accuracy of the electron diffraction intensities and the development of the theoretical background of electron scattering and data interpretation, it has become possible to investigate complex nuclear dynamics in fluxional systems by the GED method. Results of other research groups are also included in the discussion.

  11. Palladium catalysts deposited on silica materials: Comparison of catalysts based on mesoporous and amorphous supports in Heck reaction

    Czech Academy of Sciences Publication Activity Database

    Demel, J.; Čejka, Jiří; Štěpnička, P.

    2010-01-01

    Roč. 329, 1-2 (2010), s. 13-20 ISSN 1381-1169 R&D Projects: GA ČR GA104/09/0561 Institutional research plan: CEZ:AV0Z40400503 Keywords : heterogeneous catalysts * immobolized catalysts * supported catalysts Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.872, year: 2010

  12. Synthesis and catalytic evaluation in the Heck reaction of deposited palladium catalysts immobilized via amide linkers and their molecular analogues

    Czech Academy of Sciences Publication Activity Database

    Semler, M.; Čejka, Jiří; Štěpnička, P.

    2014-01-01

    Roč. 227, MAY 2014 (2014), s. 207-214 ISSN 0920-5861 R&D Projects: GA ČR GA104/09/0561; GA ČR(CZ) GA13-08944S Institutional support: RVO:61388955 Keywords : deposited catalysts * palladium * amide linkers Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.893, year: 2014

  13. Diazo Esters as Dienophiles in Intramolecular (4 + 2) Cycloadditions: Computational Explorations of Mechanism.

    Science.gov (United States)

    Duan, Abing; Yu, Peiyuan; Liu, Fang; Qiu, Huang; Gu, Feng Long; Doyle, Michael P; Houk, K N

    2017-02-22

    The first experimental examples of Diels-Alder (DA) reactions of diazo compounds as heterodienophiles with dienes have been studied with density functional theory (DFT) using the M06-2X functional. For comparison, the reactivities of diazo esters as dienophiles or 1,3-dipoles with 1,3-dienes in intermolecular model systems have been analyzed by the distortion/interaction model. The 1,3-dipolar cycloaddition is strongly favored for the intermolecular system. The intramolecular example is unique because the tether strongly favors the (4 + 2) cycloaddition.

  14. Enantioselective Intramolecular CH-Insertions upon Cu-Catalyzed Decomposition of Phenyliodonium Ylides

    Directory of Open Access Journals (Sweden)

    Christelle Boléa

    2001-02-01

    Full Text Available The Cu-catalyzed intramolecular CH insertion of phenyliodonium ylide 5b has been investigated at 0° C in the presence of several chiral ligands. Enantioselectivities vary in the range of 38–72 %, and are higher than those resulting from reaction of the diazo compound 5c at 65° C. The results are consistent with a carbenoid mechanism for Cu-catalyzed decomposition of phenyliodonium ylides.

  15. Intramolecular transformation of thiyl radicals to α-aminoalkyl radicals: 'ab initio' calculations on homocystein

    International Nuclear Information System (INIS)

    Chhun, S.; Berges, J.; Bleton, V.; Abedinzadeh, Z.

    2000-01-01

    One-electron oxidation of thiols by oxidizing radicals leads to the formation of thiyl radical and carbon-centered radicals. It has been shown experimentally that in the absence of oxygen, the thiyl radicals derived from certain thiols of biological interest such as glutathion, cysteine and homocysteine decay rapidly by intramolecular rearrangement reactions into the carbon-centered radical. In the present work we have investigated theoretically the structure and the stability of thiyl and carbon-centered radicals of homocysteine in order to check the possibility of this rearrangement. (author)

  16. Cooperative Metal–Ligand Catalyzed Intramolecular Hydroamination and Hydroalkoxylation of Allenes Using a Stable Iron Catalyst

    KAUST Repository

    El-Sepelgy, Osama

    2018-01-18

    A new iron-catalyzed chemoselective intramolecular hydroamination and hydroalkoxylation of the readily available α-allenic amines and alcohols to valuable unsaturated 5-membered heterocycles, 2,3-dihydropyrrole and 2,3-dihydrofuran, is reported. Effective selectivity control is achieved by a metal–ligand cooperative activation of the substrates. The mild reaction conditions and the use of low amounts of an air and moisture stable iron catalyst allow for the hydrofunctionalization of a wide range of allenes bearing different functional groups in good yields in the absence of base or any sensitive additives.

  17. Cooperative Metal–Ligand Catalyzed Intramolecular Hydroamination and Hydroalkoxylation of Allenes Using a Stable Iron Catalyst

    KAUST Repository

    El-Sepelgy, Osama; Brzozowska, Aleksandra; Sklyaruk, Jan; Jang, Yoon Kyung; Zubar, Viktoriia; Rueping, Magnus

    2018-01-01

    A new iron-catalyzed chemoselective intramolecular hydroamination and hydroalkoxylation of the readily available α-allenic amines and alcohols to valuable unsaturated 5-membered heterocycles, 2,3-dihydropyrrole and 2,3-dihydrofuran, is reported. Effective selectivity control is achieved by a metal–ligand cooperative activation of the substrates. The mild reaction conditions and the use of low amounts of an air and moisture stable iron catalyst allow for the hydrofunctionalization of a wide range of allenes bearing different functional groups in good yields in the absence of base or any sensitive additives.

  18. Pulse radiolytic and electrochemical investigations of intramolecular electron transfer in carotenoporphyrins and carotenoporphyrin-quinone triads

    International Nuclear Information System (INIS)

    Land, E.J.; Lexa, D.; Bensasson, R.V.; Gust, D.; Moore, T.A.; Moore, A.L.; Liddell, P.A.; Nemeth, G.A.

    1987-01-01

    Thermodynamic and kinetic aspects of intramolecular electron-transfer reactions in carotenoporphyrin dyads and carotenoid-porphyrin-quinone triads have been studied by using pulse radiolysis and cyclic voltammetry. Rapid (<1 μs) electron transfer from carotenoid radical anions to attached porphyrins has been inferred. Carotenoid cations, on the other hand, do not readily accept electrons from attached porphyrins or pyropheophorbides. Electrochemical studies provide the thermodynamic basis for these observations and also allow estimation of the energetics of photoinitiated two-step electron transfer and two-step charge recombination in triad models for photosynthetic charge separation

  19. Tandem Cu-catalyzed ketenimine formation and intramolecular nucleophile capture: Synthesis of 1,2-dihydro-2-iminoquinolines from 1-(o-acetamidophenyl)propargyl alcohols

    Science.gov (United States)

    Kant, Ruchir

    2014-01-01

    Summary The copper-catalyzed ketenimine formation reaction of 1-(o-acetamidophenyl)propargyl alcohols with various sulfonyl azides is found to undergo a concomitant intramolecular nucleophile attack to generate 1,2-dihydro-2-iminoquinolines after aromatization (via elimination of acetyl and hydroxy groups) and tautomerization. The reaction produces 4-substituted and 3,4-unsubstituted title compounds in moderate to good yields under mild reaction conditions. PMID:24991276

  20. 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.

  1. Studies toward the synthesis of palhinine lycopodium alkaloids: a Morita-Baylis-Hillman/intramolecular Diels-Alder approach.

    Science.gov (United States)

    Sizemore, Nicholas; Rychnovsky, Scott D

    2014-02-07

    A synthetic route to the isotwistane core of palhinine lycopodium alkaloids is described. A Morita-Baylis-Hillman/intramolecular Diels-Alder (IMDA) strategy sets the vicinal all-carbon quaternary centers present in this family of natural products. The regioselectivity of the IMDA reaction is dictated by the conditions employed for silyl enol ether formation, with one set of conditions providing the core of cardionine and alternate conditions generating the desired isotwistane core of isopalhinine.

  2. Tandem Wittig-ene reaction approach to kainic acid

    Digital Repository Service at National Institute of Oceanography (India)

    Majik, M.S.; Parameswaran, P.S.; Tilve, S.G.

    The first example of a tandem Wittig-intramolecular ene reaction approach and its application toward the synthesis of kainic acid is reported. The synthetic pathway involves conversion of prenyl bromide into phosphorane 3, followed by one-pot Wittig...

  3. Photochemical Dynamics of Intramolecular Singlet Fission

    Science.gov (United States)

    Lin, Zhou; Iwasaki, Hikari; Van Voorhis, Troy

    2017-06-01

    Singlet fission (SF) converts a singlet exciton (S_1) into a pair of triplet ones (T_1) via a ``multi-exciton'' (ME) intermediate: S_1 \\longleftrightarrow ^1ME \\longleftrightarrow ^1(T_1T_1) \\longrightarrow 2T_1. In exothermic cases, e.g., crystalline pentacene or its derivatives, the quantum yield of SF can reach 200%. With SF doubling the electric current generated by an incident high-energy photon, the solar conversion efficiency in pentacene-based organic photovoltaics (OPVs) can exceed the Shockley-Queisser limit of 33.7%. The ME state is popularly considered to be a dimeric state with significant charge transfer (CT) character that is strongly coupled to both S_1 and ^1(T_1T_1), while this local model lacks strong support from full quantum dynamics studies. Intramolecular SF (ISF) occurring to covalently-bound dimers in the solution phase is an excellent model for a straightforward dynamics simulation of local excitons. In the present study, we investigate the ISF mechanisms for three covalently-bound dimers of pentacene derivatives, including ortho-, meta-, and para-bis(6,13-bis(triisopropylsilylethynyl)pentacene)benzene, in non-protic solvents. Specifically, we propagate the real-time, non-adiabatic quantum mechanical/molecular mechanical (QM/MM) dynamics on the potential energy surfaces associated with the states of S_1, ^1(T_1T_1) and CT. We explore how the energies of these ISF-relevant states and the non-adiabatic couplings between each other fluctuate with time and the instantaneous molecular configuration (e.g., intermonomer distance and orientation). We also quantitatively compare Condon and non-Condon ISF dynamics with solution-phase spectroscopic data. Our results allow us to understand the roles of CT energy levels in the ISF mechanism and propose a design strategy to maximize ISF efficiency. M. B. Smith and J. Michl, Chem. Rev. 110, 6891 (2010). W. Shockley and H. J. Queisser, J. Appl. Phys. 32, 510 (1961). T. C. Berkelbach, M. S. Hybertsen

  4. Potential Chemical Systems for Intramolecular Cycloaddition Cures

    Science.gov (United States)

    1979-05-01

    allowed electrocyclic photochemical ring closure of stilbene to dihydrophenanthrene is well known (Reference 12). The presence of an oxidant , e.g...CH (c) R 3 0 00 > 0 I I (42) The keto-diynes 36 follow a uniform reaction pathway with chlorotris- ( triphenylphosphine )rhodium[I] to yield the...Irradiation of 36b similarly gives 49. The mechanism proposed for the photochemical reaction involves an initial formation of the reactive cyclobutadiene by

  5. Intramolecular hydrogen bonding in malonaldehyde and its radical analogues.

    Science.gov (United States)

    Lin, Chen; Kumar, Manoj; Finney, Brian A; Francisco, Joseph S

    2017-09-28

    High level Brueckner doubles with triples correction method-based ab initio calculations have been used to investigate the nature of intramolecular hydrogen bonding and intramolecular hydrogen atom transfer in cis-malonaldehyde (MA) and its radical analogues. The radicals considered here are the ones that correspond to the homolytic cleavage of C-H bonds in cis-MA. The results suggest that cis-MA and its radical analogues, cis-MA RS , and cis-MA RA , both exist in planar geometry. The calculated intramolecular O-H⋯O=C bond in cis-MA is shorter than that in the radical analogues. The intramolecular hydrogen bond in cis-MA is stronger than in its radicals by at least 3.0 kcal/mol. The stability of a cis-malonaldehyde radical correlates with the extent of electron spin delocalization; cis-MA RA , in which the radical spin is more delocalized, is the most stable MA radical, whereas cis-MA RS , in which the radical spin is strongly localized, is the least stable radical. The natural bond orbital analysis indicates that the intramolecular hydrogen bonding (O⋯H⋯O) in cis-malonaldehyde radicals is stabilized by the interaction between the lone pair orbitals of donor oxygen and the σ * orbital of acceptor O-H bond (n → σ * OH ). The calculated barriers indicate that the intramolecular proton transfer in cis-MA involves 2.2 kcal/mol lower barrier than that in cis-MA RS .

  6. Iodine-Mediated Intramolecular Dehydrogenative Coupling: Synthesis of N-Alkylindolo[3,2-c]- and -[2,3-c]quinoline Iodides.

    Science.gov (United States)

    Volvoikar, Prajesh S; Tilve, Santosh G

    2016-03-04

    An I2/TBHP-mediated intramolecular dehydrogenative coupling reaction is developed for the synthesis of a library of medicinally important 5,11-dialkylindolo[3,2-c]quinoline salts and 5,7-dimethylindolo[2,3-c]quinoline salts. The annulation reaction is followed by aromatization to yield tetracycles in good yield. This protocol is also demonstrated for the synthesis of the naturally occurring isocryptolepine in salt form.

  7. Structural diversity through intramolecular cycloaddition and modulation of chemical reactivity in excited state. Synthesis and photoreactions of 3-oxa-tricyclo[5.2.2.0(1,5)]undecenones: novel stereoselective route to oxa-triquinanes and oxa-sterpuranes.

    Science.gov (United States)

    Singh, V; Alam, S Q

    2000-11-20

    Synthesis of 11-methyl-3-oxa-tricyclo[5.2.2.0(1,5)]undecenones by intramolecular Diels-Alder reaction of highly labile spiroepoxycyclohexa-2,4-dienones and its photochemical reactions upon triplet (3T) and singlet (1S) excitation leading to a stereoselective route to oxa-triquinane and oxa-sterpurane, respectively, is described.

  8. Evaluation of intramolecular charge transfer state of 4-N, N ...

    Indian Academy of Sciences (India)

    Abstract. Intramolecular charge transfer of 4-N,N-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 ...

  9. 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...

  10. Preparation of CN /Carbon Nanotube Intramolecular Junctions by ...

    African Journals Online (AJOL)

    NICO

    intramolecular junctions composed of CNx with a bamboo-like structure and empty hollow carbon nanotubes were observed, ... and excellent thermal and mechanical properties.1,2 In recent .... tion of hexane, and the other segment with a curved compart- ... by an arrow lies at the interface of the junction between 'b' and.

  11. Unfolding and Targeting Thermodynamics of a DNA Intramolecular Complex with Joined Triplex-Duplex Domains.

    Science.gov (United States)

    Johnson, Sarah E; Reiling-Steffensmeier, Calliste; Lee, Hui-Ting; Marky, Luis A

    2018-01-25

    Our laboratory is interested in developing methods that can be used for the control of gene expression. In this work, we are investigating the reaction of an intramolecular complex containing a triplex-duplex junction with partially complementary strands. We used a combination of isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), and spectroscopy techniques to determine standard thermodynamic profiles for these targeting reactions. Specifically, we have designed single strands to target one loop (CTTTC) or two loops (CTTTC and GCAA) of this complex. Both reactions yielded exothermic enthalpies of -66.3 and -82.8 kcal/mol by ITC, in excellent agreement with the reaction enthalpies of -72.7 and -88.7 kcal/mol, respectively, obtained from DSC Hess cycles. The favorable heat contributions result from the formation of base-pair stacks involving mainly the unpaired bases of the loops. This shows that each complementary strand is able to invade and disrupt the secondary structure. The simultaneous targeting of two loops yielded a more favorable reaction free energy, by approximately -8 kcal/mol, which corresponds to the formation of roughly four base-pair stacks involving the unpaired bases of the 5'-GCAA loop. The main conclusion is that the targeting of loops with a large number of unpaired bases results in a more favorable reaction free energy.

  12. Electron transfer reactions of metal complexes in solution

    International Nuclear Information System (INIS)

    Sutin, N.

    1977-01-01

    A few representative electron-transfer reactions are selected and their kinetic parameters compared with the predictions of activated complex models. Since Taube has presented an elegant treatment of intramolecular electron-transfer reactions, emphasis is on bimolecular reactions. The latter electron-transfer reactions are more complicated to treat theoretically since the geometries of their activated complexes are not as well known as for the intramolecular case. In addition in biomolecular reactions, the work required to bring the two reactants together needs to be calculated. Since both reactants generally carry charges this presents a non-trivial problem at the ionic strengths usually used to study bimolecular electron transfer

  13. A strategic approach to [6,6]-bicyclic lactones

    DEFF Research Database (Denmark)

    Jepsen, Tue Heesgaard; Glibstrup, Emil; Crestey, Francois Louis Jean

    2017-01-01

    We report an effective synthetic protocol to access [6,6]-bicyclic lactone moieties through a regio- and stereoselective intramolecular Mizoroki–Heck cross-coupling reaction followed by a 6π-electrocyclization. This method enabled the first synthesis of the elusive CD fragment of the Erythrina...

  14. Structural, photophysical, and theoretical studies of imidazole-based excited-state intramolecular proton transfer molecules

    Science.gov (United States)

    Somasundaram, Sivaraman; Kamaraj, Eswaran; Hwang, Su Jin; Park, Sanghyuk

    2018-02-01

    Imidazole-based excited state intramolecular proton transfer (ESIPT) blue fluorescent molecules, 2-(1-(4-chlorophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (BHPI-Cl) and 2-(1-(4-bromophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (BHPI-Br) were designed and synthesized by Debus-Radziszewski method through a one-pot multicomponent reaction in high yield. The synthesized compounds were fully characterized by 1H NMR, 13C NMR, FT-IR, FT-Raman, GC-Mass, and elemental analysis. The molecular structures in single crystal lattice were studied by X-ray crystallographic analysis. Because of the intramolecular hydrogen bonding, hydroxyphenyl group is planar to the central imidazole ring, while the other phenyl rings gave distorted conformations to the central heterocyclic ring. BHPI-Cl and BHPI-Br molecules showed intense ESIPT fluorescence at 480 nm, because the two twisted phenyl rings on 4- and 5-positions have reduced intermolecular interaction between adjacent molecules in each crystal through a head-to-tail packing manner. Quantum chemical calculations of energies were carried out by (TD-)DFT using B3LYP/6-31G(d, p) basis set to predict the electronic absorption spectra of the compounds, and they showed good agreement between the computational and the experimental values. The thermal analyses of the synthesized molecules were also carried out by TGA/DSC method.

  15. 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.

  16. A theoretical investigation on the regioselectivity of the intramolecular hetero Diels-Alder and 1,3-dipolar cycloaddition of 2-vinyloxybenzaldehyde derivatives

    Directory of Open Access Journals (Sweden)

    Hamzehloueian Mahshid

    2014-01-01

    Full Text Available The present study reports a systematic computational analysis of the two possible pathways, fused and bridged, for an intramolecular hetero Diels-Alder (IMHDA and an intramolecular 1,3-dipolar cycloaddition (IMDCA of 2-vinyloxybenzaldehyde derivatives. The potential energy surface analysis for both reactions is in agreement with experimental observations. The activation energies associated with the two regioisomeric channels in IMHDA reaction show that the bridged product is favored, although in IMDCA, the most stable TS results the fused product. The global electronic properties of fragments within each molecule were studied to discuss the reactivity patterns and charge transfer direction in the intramolecular processes. The asynchronicity of the bond formation and aromaticity of the optimized TSs in the Diels-Alder reaction as well as cycloaddition reaction were evaluated. Finally, 1H NMR chemical shifts of the possible regioisomers have been calculated using the GIAO method which of the most stable products are in agreement with the experimental data in the both reaction.

  17. Synthesis and intramolecular cyclizationof thiosemicarbazide morpholilacetic acid

    Directory of Open Access Journals (Sweden)

    Moldyr Dyusebaeva

    2015-12-01

    Full Text Available The paper gives details on the synthesis of four new, potentially biologically active compounds based on amorpholineheterocycle structure. By alkylation of morpholine with ethyl bromoacetate, a morfolilacetic acid ethyl ester was synthesized. Its reaction with hydrazine hydrate led to the hydrazide. We developed the method for synthesis and studied cyclization of thiosemicarbazide morfolilaceticacidin in alkaline medium with formation of bisgeterocyclic system. The possibility of the existence of this compound in two tautomeric forms: thione and thiol, i.e. a 3- (1'-morpholyl-methyl -1,2,4-triazole-5-thione and 3- (1-morpholyl-1'-methyl -5-mercapto-1,2,4-triazole was described. In neutral medium, one product was obtained. According to spectral data, it is attributed to the structure of 3-(1'-morpholil-methyl-1,2,4-triazole-5-thione. Structure of newly synthesized compounds is confirmed by IR and 1H-NMR spectra and data of elemental analysis. These compounds are potentially biologically active substances and are promising for further research.

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

    KAUST Repository

    Sipos, Gellé rt; Ou, Arnold; Skelton, Brian W.; Falivene, Laura; Cavallo, Luigi; Dorta, Reto

    2016-01-01

    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 13CNMR 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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    KAUST Repository

    Sipos, Gellért

    2016-04-10

    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 13CNMR 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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Structure and Intramolecular Proton Transfer of Alanine Radical Cations

    International Nuclear Information System (INIS)

    Lee, Gab Yong

    2012-01-01

    The structures of the four lowest alanine conformers, along with their radical cations and the effect of ionization on the intramolecular proton transfer process, are studied using the density functional theory and MP2 method. The energy order of the radical cations of alanine differs from that of the corresponding neutral conformers due to changes in the basicity of the NH 2 group upon ionization. Ionization favors the intramolecular proton transfer process, leading to a proton-transferred radical-cation structure, [NH 3 + -CHCH 3 -COO·], which contrasts with the fact that a proton-transferred zwitterionic conformer is not stable for a neutral alanine in the gas phase. The energy barrier during the proton transfer process is calculated to be about 6 kcal/mol

  1. Competing Intramolecular vs. Intermolecular Hydrogen Bonds in Solution

    Directory of Open Access Journals (Sweden)

    Peter I. Nagy

    2014-10-01

    Full Text Available A hydrogen bond for a local-minimum-energy structure can be identified according to the definition of the International Union of Pure and Applied Chemistry (IUPAC recommendation 2011 or by finding a special bond critical point on the density map of the structure in the framework of the atoms-in-molecules theory. Nonetheless, a given structural conformation may be simply favored by electrostatic interactions. The present review surveys the in-solution competition of the conformations with intramolecular vs. intermolecular hydrogen bonds for different types of small organic molecules. In their most stable gas-phase structure, an intramolecular hydrogen bond is possible. In a protic solution, the intramolecular hydrogen bond may disrupt in favor of two solute-solvent intermolecular hydrogen bonds. The balance of the increased internal energy and the stabilizing effect of the solute-solvent interactions regulates the new conformer composition in the liquid phase. The review additionally considers the solvent effects on the stability of simple dimeric systems as revealed from molecular dynamics simulations or on the basis of the calculated potential of mean force curves. Finally, studies of the solvent effects on the type of the intermolecular hydrogen bond (neutral or ionic in acid-base complexes have been surveyed.

  2. Unprecedented twofold intramolecular hydroamination in diam(m)ine-dicarboxylatodichloridoplatinum(IV) complexes - ethane-1,2-diamine vs. ammine ligands.

    Science.gov (United States)

    Reithofer, Michael R; Galanski, Markus; Arion, Vladimir B; Keppler, Bernhard K

    2008-03-07

    Reaction of (OC-6-13)-bis(2Z-3-carboxyacrylato)dichlorido(ethane-1,2-diamine)platinum(IV) and (OC-6-13)-diamminebis(2Z-3-carboxyacrylato)dichloridoplatinum(IV) with propylamine in the presence of 1,1'-carbonyl diimidazole afforded not the expected amides; instead, beside amide formation, a twofold intramolecular attack of the am(m)ine ligand at the C[double bond, length as m-dash]C bonds was observed involving either both (ethane-1,2-diamine) or only one (ammine) coordinated nitrogen atom(s).

  3. Aqueous Synthesis of 1-H-2-Substituted Benzimidazoles via Transition-Metal-Free Intramolecular Amination of Aryl Iodides

    Directory of Open Access Journals (Sweden)

    Chunxia Chen

    2012-10-01

    Full Text Available A straightforward method has been developed for the synthesis of the benzimidazole ring system through a carbon-nitrogen cross-coupling reaction. In the presence of 2.0 equiv. of K2CO3 in water at 100 °C for 30 h, the intramolecular cyclization of N-(2-iodoarylbenzamidine provides benzimidazole derivatives in moderate to high yields. Remarkably, the procedure occurs exclusively in water and doesn’t require the use of any additional reagent/catalyst, rendering the methodology highly valuable from both environmental and economical points of view.

  4. Construction of Azabicyclo[6.4.0]dodecatrienes Based on Rhodium(I)-Catalyzed Intramolecular [6+2] Cycloaddition between Azetidine, Allene, and Alkynes.

    Science.gov (United States)

    Yasuda, Shigeo; Yokosawa, Haruna; Mukai, Chisato

    2016-01-01

    Treatment of the allenylazetidine-alkynes with a catalytic amount of [RhCl(CO)dppp]2 (dppp: 1,3-bis(diphenylphosphino)propane) effected the intramolecular hetero-[6+2]-type ring-closing reaction via the C-C bond cleavage of the azetidine ring to produce azabicyclo[6.4.0]dodecatriene derivatives in good to excellent yields. The formation of the oxa analogue could also be achieved.

  5. Application of Carbohydrate-Templated Asymmetric Diels-Alder Reaction to the Syntheses of ent-Penicillones A and B.

    Science.gov (United States)

    Weng, Chia-Hao; Hsu, Day-Shin; Liao, Chun-Chen

    2016-11-18

    Total syntheses of ent-penicillones A (ent-1) and B (ent-2) from 3,5-dimethylcatechol (3) were accomplished in 10 and 9 synthetic steps, respectively. A carbohydrate-templated asymmetric intramolecular Diels-Alder reaction of a masked o-benzoquinone (MOB) 9 and an aqueous acid-catalyzed intramolecular aldol reaction are the key synthetic steps. In addition, the absolute configurations of the bicyclo[2.2.2]oct-5-en-2-one core obtained from the per-O-benzylated α-d-glucopyranosyl as a carbohydrate template in the intramolecular Diels-Alder reaction of MOBs were revised.

  6. Intramolecular ketenimine-ketenimine [2 + 2] and [4 + 2] cycloadditions.

    Science.gov (United States)

    Alajarín, Mateo; Bonillo, Baltasar; Sanchez-Andrada, Pilar; Vidal, Angel; Bautista, Delia

    2007-07-20

    Bis(ketenimines), in which the two heterocumulenic functions are placed in close proximity on a carbon skeleton to allow their mutual interaction, show a rich and not easily predictable chemistry. Intramolecular [2 + 2] or [4 + 2] cycloadditions are, respectively, observed when both ketenimine functions are supported on either ortho-benzylic or 2,2'-biphenylenic scaffolds. In addition, nitrogen-to-carbon [1,3] and [1,5] shifts of arylmethyl groups in N-arylmethyl-C,C-diphenyl ketenimines are also disclosed.

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

    International Nuclear Information System (INIS)

    Feng Wen-Ke; Wang Shu-Feng; Gong Qi-Huang; Feng Yi-Yu; Feng Wei; Yi Wen-Hui

    2010-01-01

    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 10 11 s −1 is found. This PET process is also consolidated by femtosecond transient absorption spectra

  8. Synthesis of anatoxin a via intramolecular cyclization of iminium salts

    International Nuclear Information System (INIS)

    Bates, H.A.; Rapoport, H.

    1979-01-01

    Anatoxin a (1) has been synthesized by exploiting intramolecular cyclization between an iminium salt and a nucleophilic carbon to construct the 9-azabicyclo[4.2.1]nonane ring system. Cyclization of malonate iminiumsalt 16 at alkaline pH afforded a low yield of bicyclic malonate 18 owing to an unfavorable equilibrium constant and lability of the iminium salt in base. In contrast, cyclization of ketoiminium salt 31 afforded a good yield of bicyclic ketone 34 in acidic methanol. Dihydropyrrolium salts 16 and 31 were generated quantitatively by decarbonylation of substituted N-methylprolines 15 and 30b, obtained by reduction of the corresponding pyrroles

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

    DEFF Research Database (Denmark)

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

    2014-01-01

    , and the 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 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...

  10. TDDFT study on excited state intramolecular proton transfer mechanism in 2-amino-3-(2‧-benzazolyl)-quinolines

    Science.gov (United States)

    Jia, Xueli; Li, Chaozheng; Li, Donglin; Liu, Yufang

    2018-03-01

    The intramolecular proton transfer reaction of the 2-amino-3-(2‧-benzoxazolyl)-quinoline (ABO) and 2-amino-3-(2‧-benzothiazolyl)-quinoline (ABT) molecules in both S0 and S1 states at B3LYP/6-311 ++G(d,p) level in ethanol solvent have been studied to reveal the deactivation mechanism of the tautomers of the two molecules from the S1 state to the S0 state. The results show that the tautomers of ABO and ABT molecules may return to the S0 state by emitting fluorescence. In addition, the bond lengths, angles and infrared spectra are analyzed to confirm the hydrogen bonds strengthened upon photoexcitation, which can facilitate the proton transfer process. The frontier molecular orbitals (MOs) and natural bond orbital (NBO) are also calculated to indicate the intramolecular charge transfer which can be used to explore the tendency of ESIPT reaction. The potential energy surfaces of the ABO and ABT molecules in the S0 and S1 states have been constructed. According to the energy potential barrier of 9.12 kcal/mol for ABO molecule and 5.96 kcal/mol for ABT molecule, it can be indicated that the proton transfer may occur in the S1 state.

  11. Immobilized Palladium Nanoparticles on Zirconium Carboxy-Aminophosphonates Nanosheets as an Efficient Recoverable Heterogeneous Catalyst for Suzuki–Miyaura and Heck Coupling

    Directory of Open Access Journals (Sweden)

    Vadym Kozell

    2017-06-01

    Full Text Available Zirconium phosphate glycine diphosphonate nanosheets (ZPGly have been used as support for the preparation of solid palladium nanoparticles, namely Pd@ZPGly. Thanks to the presence of carboxy-aminophosponate groups on the layer surface, ZPGly-based materials were able to stabilize a high amount of palladium (up to 22 wt % also minimizing the amount of metal leached in the final products of representative important cross-coupling processes selected for proving the catalysts’ efficiency. The catalytic systems have been fully characterized and used in low amounts (0.1 mol % in the Suzuki–Miyaura and Heck cross-couplings. Moreover, the protocols were optimized for the use of recoverable azeotropic mixtures (aq. EtOH 96% or aq. CH3CN 84%, respectively and in the flow procedure allowing one to isolate the final pure products, without any purification step, with very low residual palladium content and with a very low waste production.

  12. Aqueous microwaves assisted cross-coupling reactions applied to unprotected nucleosides.

    Directory of Open Access Journals (Sweden)

    CHRISTOPHE eLEN

    2015-02-01

    Full Text Available Nucleoside analogues have attracted much attention due to their potential biological activities. Amongst all synthetic nucleosides, C5-modified pyrimidines and C7- or C8-modified purines have mostly been prepared using palladium cross-coupling reactions and then studied as antitumoral and antiviral agents. Our objective is to focus this review on the Suzuki-Miyaura and on the Heck cross-couplings of nucleosides using microwave irradiations which are an alternative technology compatible with green chemistry and sustainable development.

  13. Heterocycles by Transition Metals Catalyzed Intramolecular Cyclization of Acetylene Compounds

    International Nuclear Information System (INIS)

    Vizer, S.A.; Yerzhanov, K.B.; Dedeshko, E.C.

    2003-01-01

    Review shows the new strategies in the synthesis of heterocycles, having nitrogen, oxygen and sulfur atoms, via transition metals catalyzed intramolecular cyclization of acetylenic compounds on the data published at the last 30 years, Unsaturated heterocyclic compounds (pyrroles and pyrroline, furans, dihydro furans and benzofurans, indoles and iso-indoles, isoquinolines and isoquinolinones, aurones, iso coumarins and oxazolinone, lactams and lactones with various substitutes in heterocycles) are formed by transition metals, those salts [PdCl 2 , Pd(OAc) 2 , HgCl 2 , Hg(OAc) 2 , Hg(OCOCF 3 ) 2 , AuCl 3 ·2H 2 O, NaAuCl 4 ·2H 2 O, CuI, CuCl], oxides (HgO) and complexes [Pd(OAc) 2 (PPh 3 )2, Pd(PPh 3 ) 4 , PdCl 2 (MeCN) 2 , Pd(OAc ) 2 /TPPTS] catalyzed intramolecular cyclization of acetylenic amines, amides, ethers, alcohols, acids, ketones and βdiketones. More complex hetero polycyclic systems typical for natural alkaloids can to obtain similar. Proposed mechanisms of pyrroles, isoquinolines, iso indoles and indoles, benzofurans and iso coumarins, thiazolopyrimidinones formation are considered. (author)

  14. Mild one-pot Horner-Wadsworth-Emmons olefination and intramolecular N-arylation for the syntheses of indoles, all regio-isomeric azaindoles, and thienopyrroles.

    Science.gov (United States)

    Choi, Ji Hye; Lim, Hwan Jung

    2015-05-14

    The syntheses of various N-protected aromatic-ring fused pyrrole-2-carboxylate derivatives have been accomplished using mild one-pot Horner-Wadsworth-Emmons olefination and Cu-catalyzed intramolecular N-arylation reactions. The optimized mild one-pot reaction conditions of various 2-bromo arylcarboxaldehydes with commercially available N-protected phosphonoglycine trimethylesters gave the desired aromatic-ring fused pyrrole-2-carboxylates, such as substituted indole-, all regio-isomeric azaindole-, and thienopyrrole-2-carboxylates, in good to excellent yields. These conditions showed broad substrate compatibility, without the loss of the protecting group.

  15. An efficient synthesis of α-amino-δ-valerolactones by the ugi five-center three-component reaction

    International Nuclear Information System (INIS)

    Kim, Young Bae; Lee, Duck Hyung; Park, Soo Jung; Keum, Gyo Chang; Jang, Min Seok; Kang, Soon Bang; Kim, You Seung

    2002-01-01

    A novel approach to α-amino-δ-valerolactones derivatives 8 by the intramolecular Ugi five-center three-component reaction (U-5C-3CR) using the multifunctional starting material, L-pentahomoserine 5 is described

  16. Vibrational spectroscopy and intramolecular energy transfer in isocyanic acid (HNCO)

    International Nuclear Information System (INIS)

    Coffey, M.J.; Berghout, H.L.; Woods, E. III; Crim, F.F.

    1999-01-01

    Room temperature photoacoustic spectra in the region of the first through the fourth overtones (2ν 1 to 5ν 1 ) and free-jet action spectra of the second through the fourth overtones (3ν 1 to 5ν 1 ) of the N - H stretching vibration permit analysis of the vibrational and rotational structure of HNCO. The analysis identifies the strong intramolecular couplings that control the early stages of intramolecular vibrational energy redistribution (IVR) and gives the interaction matrix elements between the zero-order N - H stretching states and the other zero-order states with which they interact. The experimentally determined couplings and zero-order state separations are consistent with ab initio calculations of East, Johnson, and Allen [J. Chem. Phys. 98, 1299 (1993)], and comparison with the calculation identifies the coupled states and likely interactions. The states most strongly coupled to the pure N - H stretching zero-order states are ones with a quantum of N - H stretching excitation (ν 1 ) replaced by different combinations of N - C - O asymmetric or symmetric stretching excitation (ν 2 or ν 3 ) and trans-bending excitation (ν 4 ). The two strongest couplings of the nν 1 state are to the states (n-1)ν 1 +ν 2 +ν 4 and (n-1)ν 1 +ν 3 +2ν 4 , and sequential couplings through a series of low order resonances potentially play a role. The analysis shows that if the pure N - H stretch zero-order state were excited, energy would initially flow out of that mode into the strongly coupled mode in 100 fs to 700 fs, depending on the level of initial excitation. copyright 1999 American Institute of Physics

  17. Kinetics of reactions of chromium, molybdenum and tungsten hexacarbonyls with hydroxylamine and trimethylamine oxide

    International Nuclear Information System (INIS)

    Maksakov, V.A.; Ershova, V.A.

    1994-01-01

    Mechanism of M(CO) 6 (M = Cr, Mo, W) reaction with hydroxylamine was studied. On the basis of kinetic data it was ascertained that as a result of the reaction CO oxidation to CO 2 and intramolecular transfer of amine formed to the central atom of metal occur. Mechanisms of M(CO) 6 reactions with hydroxylamine and trimethylamine oxide are compared

  18. 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.

  19. Fast intramolecular electron transfer and dual fluorescence. Configurational change of the amino nitrogen (pyramidal→planar)

    International Nuclear Information System (INIS)

    Haar, Th. von der; Hebecker, A.; Il'Ichev, Yu.; Kuehnle, W.; Zachariasse, K. A.

    1996-01-01

    The fast excited state intramolecular charge transfer (ICT) and dual fluorescence observed with several 4-aminobenzonitriles is discussed. It is shown that the magnitude of the energy gap between the two lowest excited states determines the occurrence or absence of ICT. The photophysical behavior of a series of four 4-aminobenzonitriles in which the amino nitrogen atom is part of a four- to seven-membered heterocyclic ring, P4C to P7C, is studied by using time-resolved fluorescence measurements. The ICT rate constant strongly decreases with decreasing ring size. With P4C in diethyl ether ICT does not occur. This is attributed to the increase of the amino nitrogen inversion barrier with decreasing ring size. The change of the amino nitrogen from pyramidal to planar is considered to be an important reaction coordinate. The photophysics of the 4-aminobenzonitriles is different from that of other ICT systems such as donor/acceptor-substituted stilbenes and 9,9'-bianthryl, which are governed by the charge distribution and macroscopic Coulombic interaction in their CT states

  20. Synthesis of Chromane Derivatives via Indium-mediated Intramolecular Allenylation and Allylation to Imines

    International Nuclear Information System (INIS)

    Kang, Han Young; Yu, Yeon Kwon

    2004-01-01

    The results of preparing chromans by intramolecular allylation are shown in Table 2. The results indicated that the indium-mediated allylation was not as efficient as the allenylation. About 10-20% decrease in yields was observed. As mentioned above, in each case only a single isomer was observed, and the stereochemistry of the product was determined as cis by analysis of 1 H NMR and NOE spectra. There are, however, still some limitations in these transformations. Especially, in the case of allylation mixtures of cis and trans isomers are always produced in about 2 : 1 ratio (cis/trans). The ratio was not improved under the various reaction conditions we attempted. Since the indium-mediated addition to carbonyl groups has been successful, it occurred to us that it would be worthwhile to test the addition to carbon-nitrogen double bonds, that is, imine groups. We wish to report here the results of the investigations on allylation and allenylation to C=N bond to provide the chromane structures. The whole transformations

  1. Preparation of heterogeneous catalysts supported on mesoporous molecular sieves modified with various N-groups and their use in the Heck reaction

    Czech Academy of Sciences Publication Activity Database

    Demel, Jan; Sujandi, X.; Park, S.; Y.; Čejka, Jiří; Štěpnička, P.

    2009-01-01

    Roč. 302, 1-2 (2009), s. 28-35 ISSN 1381-1169 R&D Projects: GA MŠk(CZ) LC06070; GA ČR GA104/09/0561 Institutional research plan: CEZ:AV0Z40400503 Keywords : supported catalysis * palladium * bifunctional catalysts * nanoparticles Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.135, year: 2009

  2. The used of palladium nanoparticles supported on MCM-41 mesoporous molecular sieves in Heck reaction: A comparison of basic and neutral supports

    Czech Academy of Sciences Publication Activity Database

    Demel, Jan; Čejka, Jiří; Štěpnička, P.

    2007-01-01

    Roč. 274, 1-2 (2007), s. 127-132 ISSN 1381-1169 R&D Projects: GA ČR GA104/05/0192; GA MŠk(CZ) LC06070 Institutional research plan: CEZ:AV0Z40400503 Keywords : bifunctional catalysts * supported catalysts * palladium * nanoparticles * MCM-41 Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.707, year: 2007

  3. The use of palladium nanoparticles supported with MCM-41 and basic (Al)MCM-41 mesoporous sieves in microwave-assisted Heck reaction

    Czech Academy of Sciences Publication Activity Database

    Demel, Jan; Park, S.-E.; Čejka, Jiří; Štěpnička, P.

    2008-01-01

    Roč. 132, 1-4 (2008), s. 63-67 ISSN 0920-5861 Institutional research plan: CEZ:AV0Z40400503 Keywords : bifunctional catalysts * supported catalysts * palladium * nanoparticles Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.004, year: 2008

  4. Diversity-Oriented Synthesis of Coumarin-Linked Benzimidazoles via a One-Pot, Three-Step, Intramolecular Knoevenagel Cyclization.

    Science.gov (United States)

    Yao, Po-Hsin Eric; Kumar, Sunil; Liu, Yu-Li; Fang, Chiu-Ping; Liu, Chia-Chen; Sun, Chung-Ming

    2017-04-10

    Diversity-oriented synthesis of coumarin-linked benzimidazoles from N-(2-aminophenyl)-2-cyanoacetamide was achieved via a one-pot, three-step sequential reaction in excellent yields. In situ intramolecular cyclization of the cyanoacetamide afforded benzimidazoles which subsequently underwent a Knoevenagel condensation of the 2-cyanomethylbenzimidazoles with salicylaldehydes promoted by triethylamine to reach the target compounds. An important intermediate, 2-(2-imino-2H-chromen-3-yl)-1H-benzimidazole was characterized by X-ray analysis and further hydrolyzed to 2-(coumarin-3-yl)benzimidazole in acidic condition. Among the synthesized compounds, some were found to be promising inhibitors of porcine kidney d-amino acid oxidase (pkDAO).

  5. Experimental test of a four-level kinetic model for excited-state intramolecular proton transfer dye lasers

    Energy Technology Data Exchange (ETDEWEB)

    Costela, A; Munnoz, J M; Douhal, A; Figuera, J M; Acuna, A U [Inst. de Quimica Fisica ' ' Rocasolano' ' , C.S.I.C., Madrid (Spain)

    1989-11-01

    The nanosecond pulses of a dye laser oscillator based on the excited-state intramolecular proton-transfer reaction (IPT) of salicylamide and 2'-hydroxylphenyl benzimidazole dyes have been studied as a function of several experimental parameters. To explain the operation of this laser a numerical four-level kinetic model was developed until the lasing properties of these dyes, in the presence of a variable oxygen concentration and pumped with a double pulse technique, could be reproduced. This was possible only by assuming that the efficiency of the laser is controlled by the absorption cross-section of a transient state with a lifetime in the nanosecond-picosecond range, which was tentatively identified as a ground state tautomeric species. (orig.).

  6. Enantioselective synthesis of almorexant via iridium-catalysed intramolecular allylic amidation

    NARCIS (Netherlands)

    Fananas Mastral, Martin; Teichert, Johannes F.; Fernandez-Salas, Jose Antonio; Heijnen, Dorus; Feringa, Ben L.

    2013-01-01

    An enantioselective synthesis of almorexant, a potent antagonist of human orexin receptors, is presented. The chiral tetrahydroisoquinoline core structure was prepared via iridium-catalysed asymmetric intramolecular allylic amidation. Further key catalytic steps of the synthesis include an oxidative

  7. Zinc(II) complexes with intramolecular amide oxygen coordination as models of metalloamidases.

    Science.gov (United States)

    Rivas, Juan C Mareque; Salvagni, Emiliano; Prabaharan, Ravi; de Rosales, Rafael Torres Martin; Parsons, Simon

    2004-01-07

    Polydentate ligands (6-R1-2-pyridylmethyl)-R2(R1= NHCOtBu, R2= bis(2-pyridylmethyl)amine L1, bis(2-(methylthio)ethyl)amine L2 and N(CH2CH2)2S L3) form mononuclear zinc(II) complexes with intramolecular amide oxygen coordination and a range of coordination environments. Thus, the reaction of Zn(ClO4)2.6H2O with L1-3 in acetonitrile affords [(L)Zn](ClO4)2(L=L1, 1; L2, 2) and [(L3)Zn(H2O)(NCCH3)](ClO4)2 3. The simultaneous amide/water binding in resembles the motif that has been proposed to be involved in the double substrate/nucleophile Lewis acidic activation and positioning mechanism of amide bond hydrolysis in metallopeptidases. X-ray diffraction, 1H and 13C NMR and IR data suggests that the strength of amide oxygen coordination follows the trend 1>2 >3. L1-3 and undergo cleavage of the tert-butylamide upon addition of Me4NOH.5H2O (1 equiv.) in methanol at 50(1)degrees C. The rate of amide cleavage follows the order 1> 2> 3, L1-3. The extent by which the amide cleavage reaction is accelerated in 1-3 relative to the free ligands, L1-3, is correlated with the strength of amide oxygen binding and Lewis acidity of the zinc(II) centre in deduced from the X-ray, NMR and IR studies.

  8. Tyrosine-lipid peroxide adducts from radical termination: para coupling and intramolecular Diels-Alder cyclization.

    Science.gov (United States)

    Shchepin, Roman; Möller, Matias N; Kim, Hye-young H; Hatch, Duane M; Bartesaghi, Silvina; Kalyanaraman, Balaraman; Radi, Rafael; Porter, Ned A

    2010-12-15

    Free radical co-oxidation of polyunsaturated lipids with tyrosine or phenolic analogues of tyrosine gave rise to lipid peroxide-tyrosine (phenol) adducts in both aqueous micellar and organic solutions. The novel adducts were isolated and characterized by 1D and 2D NMR spectroscopy as well as by mass spectrometry (MS). The spectral data suggest that the polyunsaturated lipid peroxyl radicals give stable peroxide coupling products exclusively at the para position of the tyrosyl (phenoxy) radicals. These adducts have characteristic (13)C chemical shifts at 185 ppm due to the cross-conjugated carbonyl of the phenol-derived cyclohexadienone. The primary peroxide adducts subsequently undergo intramolecular Diels-Alder (IMDA) cyclization, affording a number of diastereomeric tricyclic adducts that have characteristic carbonyl (13)C chemical shifts at ~198 ppm. All of the NMR HMBC and HSQC correlations support the structure assignments of the primary and Diels-Alder adducts, as does MS collision-induced dissociation data. Kinetic rate constants and activation parameters for the IMDA reaction were determined, and the primary adducts were reduced with cuprous ion to give a phenol-derived 4-hydroxycyclohexa-2,5-dienone. No products from adduction of peroxyls at the phenolic ortho position were found in either the primary or cuprous reduction product mixtures. These studies provide a framework for understanding the nature of lipid-protein adducts formed by peroxyl-tyrosyl radical-radical termination processes. Coupling of lipid peroxyl radicals with tyrosyl radicals leads to cyclohexenone and cyclohexadienone adducts, which are of interest in and of themselves since, as electrophiles, they are likely targets for protein nucleophiles. One consequence of lipid peroxyl reactions with tyrosyls may therefore be protein-protein cross-links via interprotein Michael adducts.

  9. Neutral Guests Complexation with Calix[4]arenes Preorganised by Intramolecular McMurry Reaction

    Czech Academy of Sciences Publication Activity Database

    Lhoták, P.; Zieba, R.; Hromádko, V.; Stibor, I.; Sýkora, Jan

    2003-01-01

    Roč. 44, č. 24 (2003), s. 4519-4522 ISSN 0040-4039 R&D Projects: GA ČR GA203/03/0926 Institutional research plan: CEZ:AV0Z4072921 Keywords : calixarene * inclusion Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.326, year: 2003

  10. Fluorescence correlation spectroscopy on electron transfer reactions : probing inter- and intramolecular redox processes

    NARCIS (Netherlands)

    Sen, S.

    2016-01-01

    We developed a new FRET-based technique, “Fluredox”, which allows fluorescence readout of the redox state of oxido-reductases at single molecule level. Commercially available red-absorbing fluorophore ATTO655 was selected for labeling Azurin, a small blue mononuclear copper protein. Single molecule

  11. Intramolecular Crosstalk between Catalytic Activities of Receptor Kinases

    KAUST Repository

    Kwezi, Lusisizwe

    2018-01-22

    Signal modulation is important for the growth and development of plants and this process is mediated by a number of factors including physiological growth regulators and their associated signal transduction pathways. Protein kinases play a central role in signaling, including those involving pathogen response mechanisms. We previously demonstrated an active guanylate cyclase (GC) catalytic center in the brassinosteroid insensitive receptor (AtBRI1) within an active intracellular kinase domain resulting in dual enzymatic activity. Here we propose a novel type of receptor architecture that is characterized by a functional GC catalytic center nested in the cytosolic kinase domain enabling intramolecular crosstalk. This may be through a cGMP-AtBRI1 complex forming that may induce a negative feedback mechanism leading to desensitisation of the receptor, regulated through the cGMP production pathway. We further argue that the comparatively low but highly localized cGMP generated by the GC in response to a ligand is sufficient to modulate the kinase activity. This type of receptor therefore provides a molecular switch that directly and/or indirectly affects ligand dependent phosphorylation of downstream signaling cascades and suggests that subsequent signal transduction and modulation works in conjunction with the kinase in downstream signaling.

  12. Intramolecular Crosstalk between Catalytic Activities of Receptor Kinases

    KAUST Repository

    Kwezi, Lusisizwe; Wheeler, Janet I; Marondedze, Claudius; Gehring, Christoph A; Irving, Helen R

    2018-01-01

    Signal modulation is important for the growth and development of plants and this process is mediated by a number of factors including physiological growth regulators and their associated signal transduction pathways. Protein kinases play a central role in signaling, including those involving pathogen response mechanisms. We previously demonstrated an active guanylate cyclase (GC) catalytic center in the brassinosteroid insensitive receptor (AtBRI1) within an active intracellular kinase domain resulting in dual enzymatic activity. Here we propose a novel type of receptor architecture that is characterized by a functional GC catalytic center nested in the cytosolic kinase domain enabling intramolecular crosstalk. This may be through a cGMP-AtBRI1 complex forming that may induce a negative feedback mechanism leading to desensitisation of the receptor, regulated through the cGMP production pathway. We further argue that the comparatively low but highly localized cGMP generated by the GC in response to a ligand is sufficient to modulate the kinase activity. This type of receptor therefore provides a molecular switch that directly and/or indirectly affects ligand dependent phosphorylation of downstream signaling cascades and suggests that subsequent signal transduction and modulation works in conjunction with the kinase in downstream signaling.

  13. TDDFT study on intramolecular hydrogen bond of photoexcited methyl salicylate.

    Science.gov (United States)

    Qu, Peng; Tian, Dongxu

    2014-01-01

    The equilibrium geometries, IR-spectra and transition mechanism of intramolecular hydrogen-bonded methyl salicylate in excited state were studied using DFT and TDDFT with 6-31++G (d, p) basis set. The length of hydrogen bond OH⋯OC is decreased from 1.73 Å in the ground state to 1.41 and 1.69 Å in the excited S1 and S3 states. The increase of bond length for HO and CO group also indicates that in excited state the hydrogen bond OH⋯OC is strengthened. IR spectra show HO and CO stretching bands are strongly redshifted by 1387 and 67 cm(-1) in the excited S1 and S3 states comparing to the ground state. The excitation energy and the absorption spectrum show the S3 state is the main excited state of the low-lying excited states. By analyzing the frontier molecular orbitals, the transition from the ground state to the excited S1 and S3 states was predicted to be the π→π∗ mode. Copyright © 2013 Elsevier B.V. All rights reserved.

  14. Intramolecular oxidative deselenization of acylselenoureas: a facile synthesis of benzoxazole amides and carbonic anhydrase inhibitors.

    Science.gov (United States)

    Angeli, A; Peat, T S; Bartolucci, G; Nocentini, A; Supuran, C T; Carta, F

    2016-12-28

    A mild, efficient and one pot procedure to access benzoxazoles using easily accessible acylselenoureas as starting materials has been discovered. Mechanistic studies revealed a pH dependent intramolecular oxidative deselenization, with ring closure due to an intramolecular nucleophilic attack of a phenoxide ion. All the benzoxazoles herein reported possessed a primary sulfonamide zinc binding group and showed effective inhibitory action on the enzymes, carbonic anhydrases.

  15. A New Pathway to 3-Hetaryl-2-oxo-2H-chromenes: On the Proposed Mechanisms for the Reaction of 3-Carbamoyl-2-iminochromenes with Dinucleophiles

    Directory of Open Access Journals (Sweden)

    Yaroslav V. Bilokin

    2000-10-01

    Full Text Available The present account summarizes the author's studies to elucidate the mechanisms of the recently reported rearrangements resulting from inter- and/or intramolecular reactions of 2-imino-2H-chromene-3-carboxamides with different dinucleophiles.

  16. Copper(II)-catalyzed amidations of alkynyl bromides as a general synthesis of ynamides and Z-enamides. An intramolecular amidation for the synthesis of macrocyclic ynamides.

    Science.gov (United States)

    Zhang, Xuejun; Zhang, Yanshi; Huang, Jian; Hsung, Richard P; Kurtz, Kimberly C M; Oppenheimer, Jossian; Petersen, Matthew E; Sagamanova, Irina K; Shen, Lichun; Tracey, Michael R

    2006-05-26

    A general and efficient method for the coupling of a wide range of amides with alkynyl bromides is described here. This novel amidation reaction involves a catalytic protocol using copper(II) sulfate-pentahydrate and 1,10-phenanthroline to direct the sp-C-N bond formation, leading to a structurally diverse array of ynamides including macrocyclic ynamides via an intramolecular amidation. Given the surging interest in ynamide chemistry, this atom economical synthesis of ynamides should invoke further attention from the synthetic organic community.

  17. Palladium-catalyzed aryl amination-heck cyclization cascade: A one-flask approach to 3-substituted Indoles

    DEFF Research Database (Denmark)

    Jensen, Thomas; Pedersen, Henrik; Bang-Andersen, B.

    2008-01-01

    Two for the price of one: A Pd/dppf-based catalyst provides access to the title compounds from 1,2-dihalogenated aromatic compounds and allylic amines in a single reaction flask. The initial aryl amination step occurs with excellent selectivity for the aryl iodide to ensure the formation of a sin......Two for the price of one: A Pd/dppf-based catalyst provides access to the title compounds from 1,2-dihalogenated aromatic compounds and allylic amines in a single reaction flask. The initial aryl amination step occurs with excellent selectivity for the aryl iodide to ensure the formation...

  18. Rates of the main thermonuclear reactions

    International Nuclear Information System (INIS)

    Abramovich, S.N.; Guzhovskii, B.Ya.; Dunaeva, S.A.; Fomushkin, E.F.

    1992-01-01

    The data on the cross sections of main thermonuclear reactions have been estimated with an account of the latest experimental results in a form of S-factor spline presentation. Based on this estimation, the reates of these reactions in 0.0001-1 MeV temperature range in the supposition of Maxwell distribution of relative velocities have been computed. The Maxwell-Boltzmann averaged -factors were calculated according to the table values of the reaction rates. Then the -factors were approximated with the 3 order spline-function. The necessity of the account of electron shielding and intramolecular movement at low temperatures is discussed (orig.)

  19. Dynamics of the excited state intramolecular charge transfer

    International Nuclear Information System (INIS)

    Joo, T.; Kim, C.H.

    2006-01-01

    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=(I 440 -I 490 )/(I 440 +I 490 ) 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 S 1 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

  20. New fast organic scintillators using intramolecular bromine quenching

    International Nuclear Information System (INIS)

    Berlman, I.B.; Lutz, S.S.; Flournoy, J.M.; Ashford, C.B.; Franks, L.A.

    1984-01-01

    Organic scintillator solutions with decay times as fast as 500 ps and with relatively high conversion efficiencies have been developed. The intramolecular quenching was achieved through the novel approach of adding a bromine atom to the 3- or 4-position of para-oligophenylenes, the fluorescent solutes in these binary solutions. The bromine serves to enhance singlet-to-triplet intersystem crossing in the chromophore, causing a reduction in the scintillation yield and a concomitant reduction in the decay time. The very fast value given above probably also involves some intermolecular self-quenching at high concentration. In addition, the bromine reduces the symmetry of the molecules, thereby increasing their solubility. Finally, an alkyl chain on the opposite para position further increases the solubility and also increases the immunity of the chromophore to quenching. The decay times for binary liquid solutions in toluene (at the indicated concentrations) were 0.51 ns for 4-BHTP (0.14 M), 0.75 ns for 3-BHTP (0.14 M), 0.57 ns for 3-BTP (0.14 M), and 1.3 ns for 4-BHQP (0.06 M). Binary plastics with 4-BHTP as the solute in concentrations up to 0.14 M were cast in polystyrene. The shortest decay time, 0.40 ns, was measured for the 0.14 M concentration. A plastic scintillator containing 3-BTP (0.11 M in polystyrene) had a decay time of 0.85 ns. These results compare favorably with the plastic scintillator BC-422 whose decay time is about 1.4 ns. (orig./HSI)

  1. Rh(I-catalyzed intramolecular [2 + 2 + 1] cycloaddition of allenenes: Construction of bicyclo[4.3.0]nonenones with an angular methyl group and tricyclo[6.4.0.01,5]dodecenone

    Directory of Open Access Journals (Sweden)

    Chisato Mukai

    2011-04-01

    Full Text Available The [RhCl(COdppp]2-catalyzed intramolecular carbonylative [2 + 2 + 1] cycloaddition of allenenes was developed to prepare bicyclo[4.3.0]nonenones possessing a methyl group at the ring junction, which is difficult to achieve by the Pauson–Khand reaction of the corresponding enynes. This method also provided a new procedure for the construction of the tricyclo[6.4.0.01,5]dodecenone framework in a satisfactory yield.

  2. Construction of axial chirality by rhodium-catalyzed asymmetric dehydrogenative Heck coupling of biaryl compounds with alkenes.

    Science.gov (United States)

    Zheng, Jun; You, Shu-Li

    2014-11-24

    Enantioselective construction of axially chiral biaryls by direct C-H bond functionalization reactions has been realized. Novel axially chiral biaryls were synthesized by the direct C-H bond olefination of biaryl compounds, using a chiral [Cp*Rh(III)] catalyst, in good to excellent yields and enantioselectivities. The obtained axially chiral biaryls were found as suitable ligands for rhodium-catalyzed asymmetric conjugate additions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. DIELS-ALDER REACTIONS IN AQUEOUS-SOLUTIONS - ENFORCED HYDROPHOBIC INTERACTIONS BETWEEN DIENE AND DIENOPHILE

    NARCIS (Netherlands)

    BLOKZIJL, W; BLANDAMER, MJ; ENGBERTS, JBFN

    1991-01-01

    Second-order rate constants and isobaric activation parameters for the intermolecular Diels-Alder reactions of cyclopentadiene with alkyl vinyl ketones (2a,b) and 5-substituted-1,4-naphthoquinones (3a-c) as well as for the intramolecular Diels-Alder reaction of N-furfuryl-N-methylmaleamic acid (4)

  4. Diels-Alder reactions in water : Enforced hydrophobic interaction and hydrogen bonding

    NARCIS (Netherlands)

    Engberts, Jan B.F.N.

    1995-01-01

    Second-order rate constants have been measured for the Diels-Alder (DA) reactions of cyclopentadiene with dienophiles of varying hydrophobicity and hydrogen-bond acceptor capacity in water, in a series of organic solvents and in alcohol-water mixtures. The intramolecular DA reaction of

  5. DIELS-ALDER REACTIONS IN WATER - ENFORCED HYDROPHOBIC INTERACTION AND HYDROGEN-BONDING

    NARCIS (Netherlands)

    Engberts, J.B.F.N.

    Second-order rate constants have been measured for the Diels-Alder (DA) reactions of cyclopentadiene with dienophiles of varying hydrophobicity and hydrogen-bond acceptor capacity in water, in a series of organic solvents and in alcohol-water mixtures. The intramolecular DA reaction of

  6. New Oxime Ligand with Potential for Proton-Coupled Electron-Transfer Reactions

    DEFF Research Database (Denmark)

    Deville, Claire; Sundberg, Jonas; McKenzie, Christine Joy

    Proton-coupled electron-transfer (PCET) is found in a range of oxidation-reduction reactions in biology.1 This mechanism is of interest for applications in energy conversion processes. The PCET reaction has been shown to be facilitated when the proton is transferred to an intramolecular basic sit...

  7. First examples of intramolecular addition of primary amidyl radicals to olefins

    Energy Technology Data Exchange (ETDEWEB)

    Gaudreault, P.; Drouin, C.; Lessard, J. [Sherbrooke Univ., PQ (Canada). Dept. de Chimie

    2005-07-01

    This paper presents the first examples of radical cyclization involving a primary amidyl radical and a pendant olefin. Amidyl radicals have attracted interest in terms of their structure, reactivity, and ways to generate them. The intramolecular addition of an amidyl radical on a pendant olefin appears to be a powerful synthetic tool for creating nitrogen-containing heterocycles. Although several examples of cyclization involving secondary amidyl radicals are cited in the the literature, there are no examples of a successful cyclization involving a primary amidyl radical. This is because all attempts to prepare the usual radical precursors have failed when applied to olefinic primary amides. This study reveals that N-(phenylthio) derivatives of olefinic primary amides can be easily prepared and that nitrogen heterocycles resulting from their radical cyclization can be obtained in good to very good yields. Four olefinic primary amides were chosen as models for radical cyclization of primary amidyl radicals. They were prepared from the corresponding carboxylic acids via the acid chlorides. Conversion of primary amides into suitable amidyl radical precursors was also examined. The study showed that N-(phenylthio) amides could be easily prepared by following a slightly modified protocol developed by Esker and Newcomb, by reacting the anion of the amide with phenylsulfenyl chloride. In particular, olefinic N-(phenylthio) amides were prepared and used as primary amidyl radical precursors in a reaction with a solution of 2,2'-azobis(isobutyronitrile) in catalytic quantities and tributyltin hydride in benzene. The resulting yields of cyclic products ranged from 63 to 85 per cent. The intent of the study was to demonstrate that it is no longer necessary to prepare an N-protected precursor and then remove the protecting group after cyclization. Further studies are currently underway. 10 refs., 1 tab.

  8. Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.

    Science.gov (United States)

    Santos, Fabiano da Silveira; Descalzo, Rodrigo Roceti; Gonçalves, Paulo Fernando Bruno; Benvenutti, Edilson Valmir; Rodembusch, Fabiano Severo

    2012-08-21

    Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.

  9. Heck and Heckle Seamounts, northeast Pacific Ocean: High extrusion rates of primitive and highly depleted mid-ocean ridge basalt on off-ridge seamounts

    Science.gov (United States)

    Leybourne, M. I.; van Wagoner, N. A.

    1991-09-01

    We analyzed, petrographically and chemically, basalt from eight dredge hauls from the Heck and Heckle seamounts, northeast Pacific Ocean. Major elements were determined for mineral, glass, and whole rock samples, and trace and rare earth elements were determined for glass and whole rock samples. The dredge hauls included hyaloclastites and fragments from sheet flows and pillows. The clinkery fragments are interpreted to be deformed sheet flow tops, characteristic of high effusion rates. The hyaloclastites recovered are reworked deposits, as indicated by the wide compositional range of the glass shards, abundance of clay and calcite matrix, and bedding. Most rocks are aphyric, but the analyzed plagioclase and olivine phenocrysts and microcrysts are equilibrium compositions and show minor compositional zonation (up to 7.5% An, chains have a limited range of incompatible element ratios, whereas the adjacent West Valley Segment of the Juan de Fuca Ridge is highly heterogeneous. In contrast, lavas from the East Pacific near-ridge seamounts exhibit a wider range of incompatible element ratios than do the adjacent East Pacific Rise basalts. On the West Valley Segment, magma supply is less robust associated with lower spreading rates compared to the East Pacific Rise at 10°N. In contrast, at fast spreading centers robust melting produces a mixed mantle signature in axial lavas, while suppressed melting at the seamounts reveals the heterogeneities. We suggest that at some spreading ridges, more fertile portions of the mantle are preferentially melted such that the outwelled portions of the mantle tapped by the seamounts are more depleted.

  10. Conductance and activation energy for electron transport in series and parallel intramolecular circuits.

    Science.gov (United States)

    Hsu, Liang-Yan; Wu, Ning; Rabitz, Herschel

    2016-11-30

    We investigate electron transport through series and parallel intramolecular circuits in the framework of the multi-level Redfield theory. Based on the assumption of weak monomer-bath couplings, the simulations depict the length and temperature dependence in six types of intramolecular circuits. In the tunneling regime, we find that the intramolecular circuit rule is only valid in the weak monomer coupling limit. In the thermally activated hopping regime, for circuits based on two different molecular units M a and M b with distinct activation energies E act,a > E act,b , the activation energies of M a and M b in series are nearly the same as E act,a while those in parallel are nearly the same as E act,b . This study gives a comprehensive description of electron transport through intramolecular circuits from tunneling to thermally activated hopping. We hope that this work can motivate additional studies to design intramolecular circuits based on different types of building blocks, and to explore the corresponding circuit laws and the length and temperature dependence of conductance.

  11. Sky-blue emitting bridged diiridium complexes: beneficial effects of intramolecular π-π stacking.

    Science.gov (United States)

    Congrave, Daniel G; Hsu, Yu-Ting; Batsanov, Andrei S; Beeby, Andrew; Bryce, Martin R

    2018-02-06

    The potential of intramolecular π-π interactions to influence the photophysical properties of diiridium complexes is an unexplored topic, and provides the motivation for the present study. A series of diarylhydrazide-bridged diiridium complexes functionalised with phenylpyridine (ppy)-based cyclometalating ligands is reported. It is shown by NMR studies in solution and single crystal X-ray analysis that intramolecular π-π interactions between the bridging and cyclometalating ligands rigidify the complexes leading to high luminescence quantum efficiencies in solution and in doped films. Fluorine substituents on the phenyl rings of the bridge promote the intramolecular π-π interactions. Notably, these non-covalent interactions are harnessed in the rational design and synthesis of the first examples of highly emissive sky-blue diiridium complexes featuring conjugated bridging ligands, for which they play a vital role in the structural and photophysical properties. Experimental results are supported by computational studies.

  12. Chemical origin of blue- and redshifted hydrogen bonds: intramolecular hyperconjugation and its coupling with intermolecular hyperconjugation.

    Science.gov (United States)

    Li, An Yong

    2007-04-21

    Upon formation of a H bond Y...H-XZ, intramolecular hyperconjugation n(Z)-->sigma*(X-H) of the proton donor plays a key role in red- and blueshift characters of H bonds and must be introduced in the concepts of hyperconjugation and rehybridization. Intermolecular hyperconjugation transfers electron density from Y to sigma*(X-H) and causes elongation and stretch frequency redshift of the X-H bond; intramolecular hyperconjugation couples with intermolecular hyperconjugation and can adjust electron density in sigma*(X-H); rehybridization causes contraction and stretch frequency blueshift of the X-H bond on complexation. The three factors--intra- and intermolecular hyperconjugations and rehybridization--determine commonly red- or blueshift of the formed H bond. A proton donor that has strong intramolecular hyperconjugation often forms blueshifted H bonds.

  13. Vinylcyclopropylacyl and polyeneacyl radicals. Intramolecular ketene alkyl radical additions in ring synthesis.

    Science.gov (United States)

    De Boeck, Benoit; Herbert, Nicola M A; Harrington-Frost, Nicole M; Pattenden, Gerald

    2005-01-21

    Treatment of a variety of substituted vinylcyclopropyl selenyl esters, e.g. 11, with Bu(3)SnH-AIBN in refluxing benzene leads to the corresponding acyl radical intermediates, which undergo rearrangement and intramolecular cyclisations via their ketene alkyl radical equivalents producing cyclohexenones in 50-60% yield. By contrast, treatment of conjugated triene selenyl esters, e.g. 32, with Bu(3)SnH-AIBN produces substituted 2-cyclopentenones via intramolecular cyclisations of their ketene alkyl radical intermediates. Under the same radical-initiating conditions the selenyl esters derived from o-vinylbenzoic acid and o-vinylcinnamic acid undergo intramolecular cyclisations producing 1-indanone and 5,6-dihydrobenzocyclohepten-7-one respectively in 60-70% yields. A tandem radical cyclisation from the alpha,beta,gamma,delta-diene selenyl ester 31 provides an expeditious synthesis of the diquinane 35 in 69% yield.

  14. Application of the generator coordinates method to the intra-molecular proton tunneling in the malonaldehyde molecule; Aplicacao do metodo das coordenadas geradoras ao processo de tunelamento do proton intramolecular na molecula de malonaldeido

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Andre Campos Kersten

    1995-12-31

    The effects of different vibrational modes on the isomerization process of polyatomic molecules, or solvent`s effects on reaction rates are object of up-to-date interest. In general, such many body phenomena are, in principle, multidimensional, and they first require a reduction of relevant degrees of freedom. In order to investigated, some aspects of the intra-molecular proton tunneling on a malonaldehyde molecule, we use the Generator Coordinate Method. The model used to describe such a process is the so-called System-Bath model, where the system is the reaction coordinate and the bath are the intrinsic degrees of freedom (vibrational modes of the molecule), which are described by a harmonic oscillator set linearly coupled to the system. The reduction of the multidimensional problem to the effective unidimensional one is done using a energy related variational principle on the intrinsic degrees of freedom. we obtained analytically a effective Hamiltonian where the effects of the various degrees of freedom reveal themselves in the appearance of a effective mass and in changes of the shape of the potential barrier. The analyticity of the method was crucial on identifying clearly the roles played by the different physical parameters involved. (author) 17 refs., 29 figs.

  15. Benzothiazole-Based AIEgen with Tunable Excited-State Intramolecular Proton Transfer and Restricted Intramolecular Rotation Processes for Highly Sensitive Physiological pH Sensing.

    Science.gov (United States)

    Li, Kai; Feng, Qi; Niu, Guangle; Zhang, Weijie; Li, Yuanyuan; Kang, Miaomiao; Xu, Kui; He, Juan; Hou, Hongwei; Tang, Ben Zhong

    2018-04-23

    In this work, a benzothiazole-based aggregation-induced emission luminogen (AIEgen) of 2-(5-(4-carboxyphenyl)-2-hydroxyphenyl)benzothiazole (3) was designed and synthesized, which exhibited multifluorescence emissions in different dispersed or aggregated states based on tunable excited-state intramolecular proton transfer (ESIPT) and restricted intramolecular rotation (RIR) processes. 3 was successfully used as a ratiometric fluorescent chemosensor for the detection of pH, which exhibited reversible acid/base-switched yellow/cyan emission transition. More importantly, the pH jump of 3 was very precipitous from 7.0 to 8.0 with a midpoint of 7.5, which was well matched with the physiological pH. This feature makes 3 very suitable for the highly sensitive detection of pH fluctuation in biosamples and neutral water samples. 3 was also successfully used as a ratiometric fluorescence chemosensor for the detection of acidic and basic organic vapors in test papers.

  16. Intramolecular electron transfer in ascorbate oxidase is enhanced in the presence of oxygen

    DEFF Research Database (Denmark)

    Farver, O; Wherland, S; Pecht, I

    1994-01-01

    Intramolecular electron transfer from the type 1 copper center to the type 3 copper(II) pair is induced in the multi-copper enzyme, ascorbate oxidase, following pulse radiolytic reduction of the type 1 Cu(II) ion. In the presence of a slight excess of dioxygen over ascorbate oxidase, interaction...... between the trinuclear copper center and O2 is observed even with singly reduced ascorbate oxidase molecules. Under these conditions, the rate constant for intramolecular electron transfer from type 1 Cu(I) to type 3 Cu(II) increases 5-fold to 1100 +/- 300 s-1 (20 degrees C, pH 5.8) as compared...

  17. The low-lying πσ* state and its role in the intramolecular charge transfer of aminobenzonitriles and aminobenzethyne

    International Nuclear Information System (INIS)

    Lee, Jae-Kwang; Fujiwara, Takashige; Kofron, William G.; Zgierski, Marek Z.; Lim, Edward C.

    2008-01-01

    Electronic absorption spectra of the low-lying ππ* and πσ* states of several aminobenzonitriles and 4-dimethylaminobenzethyne have been studied by time-resolved transient absorption and time-dependent density functional theory calculation. In acetonitrile, the lifetime of the πσ*-state absorption is very short (picoseconds or subpicosecond) for molecules that exhibit intramolecular charge transfer (ICT), and very long (nanoseconds) for those that do not. Where direct comparison of the temporal characteristics of the πσ*-state and the ICT-state transients could be made, the formation rate of the ICT state is identical to the decay rate of the πσ* state within the experimental uncertainty. These results are consistent with the πσ*-mediated ICT mechanism, L a (ππ*)→πσ*→ICT, in which the decay rate of the πσ* state is determined by the rate of the solvent-controlled πσ*→ICT charge-shift reaction. The ππ*→πσ* state crossing does not occur in 3-dimethylaminobenzonitrile or 2-dimethylaminobenzonitrile, as predicted by the calculation, and 4-aminobenzonitrile and 4-dimethylaminobenzethyne does not exhibit the ICT reaction, consistent with the higher energy of the ICT state relative to the πσ* state

  18. Application of the generator coordinates method to the intra-molecular proton tunneling in the malonaldehyde molecule

    International Nuclear Information System (INIS)

    Schmidt, Andre Campos Kersten

    1995-01-01

    The effects of different vibrational modes on the isomerization process of polyatomic molecules, or solvent's effects on reaction rates are object of up-to-date interest. In general, such many body phenomena are, in principle, multidimensional, and they first require a reduction of relevant degrees of freedom. In order to investigated, some aspects of the intra-molecular proton tunneling on a malonaldehyde molecule, we use the Generator Coordinate Method. The model used to describe such a process is the so-called System-Bath model, where the system is the reaction coordinate and the bath are the intrinsic degrees of freedom (vibrational modes of the molecule), which are described by a harmonic oscillator set linearly coupled to the system. The reduction of the multidimensional problem to the effective unidimensional one is done using a energy related variational principle on the intrinsic degrees of freedom. we obtained analytically a effective Hamiltonian where the effects of the various degrees of freedom reveal themselves in the appearance of a effective mass and in changes of the shape of the potential barrier. The analyticity of the method was crucial on identifying clearly the roles played by the different physical parameters involved. (author)

  19. Intramolecular Oxidative O-Demethylation of an Oxoferryl Porphyrin Complexed with a Per-O-methylated β-Cyclodextrin Dimer.

    Science.gov (United States)

    Kitagishi, Hiroaki; Kurosawa, Shun; Kano, Koji

    2016-11-22

    The intramolecular oxidation of ROCH 3 to ROCH 2 OH, where the latter compound spontaneously decomposed to ROH and HCHO, was observed during the reaction of the supramolecular complex (met-hemoCD3) with cumene hydroperoxide in aqueous solution. Met-hemoCD3 is composed of meso-tetrakis(4-sulfonatophenyl)porphinatoiron(III) (Fe III TPPS) and a per-O-methylated β-cyclodextrin dimer having an -OCH 2 PyCH 2 O- linker (Py=pyridine-3,5-diyl). The O=Fe IV TPPS complex was formed by the reaction of met-hemoCD3 with cumene hydroperoxide, and isolated by gel-filtration chromatography. Although the isolated O=Fe IV TPPS complex in the cyclodextrin cage was stable in aqueous solution at 25 °C, it was gradually converted to Fe II TPPS (t 1/2 =7.6 h). This conversion was accompanied by oxidative O-demethylation of an OCH 3 group in the cyclodextrin dimer. The results indicated that hydrogen abstraction by O=Fe IV TPPS from ROCH 3 yields HO-Fe III TPPS and ROCH 2 . . This was followed by radical coupling to afford Fe II TPPS and ROCH 2 OH. The hemiacetal (ROCH 2 OH) immediately decomposed to ROH and HCHO. This study revealed the ability of oxoferryl porphyrin to induce two-electron oxidation. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. On the intramolecular proton transfer of 3-hydroxyflavone in the first singlet excited state: A theoretical study

    International Nuclear Information System (INIS)

    Casadesus, Ricard; Vendrell, Oriol; Moreno, Miquel; Lluch, Jose M.; Morokuma, Keiji

    2006-01-01

    The intramolecular proton-transfer reaction in 3-hydroxyflavone (3HF) is theoretically studied both in the ground (S 0 ) and first singlet excited (S 1 ) electronic states. In S 0 the proton-transfer reaction is shown to be quite unfavorable at the DFT (B3LYP) level. However, the back proton transfer is found to be a feasible process with a small energy barrier, both results being in qualitative agreement with known experimental facts. Different theoretical levels are considered and compared for S 1 . The ab initio configuration interaction singles (CIS) method overestimates the energy of S 1 and give too high energy barriers for the proton-transfer reaction. The complete active space SCF (CASSCF) method gives a more reasonable value but the inclusion of the dynamical correlation through second-order perturbation theory (CASPT2) upon CASSCF geometries or the use of the time-dependent DFT (TDDFT) method upon CIS geometries gives a barrierless process. Optimization of geometries (minima and transition-state structures) at the TDDFT level leads to a small but non-negligible energy barrier for the proton-transfer reaction in S 1 and global energies that fit quite well with the known experimental (spectroscopic and femtochemistry) data. Finally the effect of a polar environment is analyzed through a continuum model, which gives only a small difference from the previous gas-phase results. This points out that the remarkable changes in the photochemistry of 3HF observed experimentally are not to be solely attributed to the polarity of the surrounding media

  1. On the intramolecular proton transfer of 3-hydroxyflavone in the first singlet excited state: A theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Casadesus, Ricard [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322 (United States); Vendrell, Oriol [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Moreno, Miquel [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain)], E-mail: mmf@klingon.uab.es; Lluch, Jose M. [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Morokuma, Keiji [Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322 (United States)

    2006-06-20

    The intramolecular proton-transfer reaction in 3-hydroxyflavone (3HF) is theoretically studied both in the ground (S{sub 0}) and first singlet excited (S{sub 1}) electronic states. In S{sub 0} the proton-transfer reaction is shown to be quite unfavorable at the DFT (B3LYP) level. However, the back proton transfer is found to be a feasible process with a small energy barrier, both results being in qualitative agreement with known experimental facts. Different theoretical levels are considered and compared for S{sub 1}. The ab initio configuration interaction singles (CIS) method overestimates the energy of S{sub 1} and give too high energy barriers for the proton-transfer reaction. The complete active space SCF (CASSCF) method gives a more reasonable value but the inclusion of the dynamical correlation through second-order perturbation theory (CASPT2) upon CASSCF geometries or the use of the time-dependent DFT (TDDFT) method upon CIS geometries gives a barrierless process. Optimization of geometries (minima and transition-state structures) at the TDDFT level leads to a small but non-negligible energy barrier for the proton-transfer reaction in S{sub 1} and global energies that fit quite well with the known experimental (spectroscopic and femtochemistry) data. Finally the effect of a polar environment is analyzed through a continuum model, which gives only a small difference from the previous gas-phase results. This points out that the remarkable changes in the photochemistry of 3HF observed experimentally are not to be solely attributed to the polarity of the surrounding media.

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

    NARCIS (Netherlands)

    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

  3. Epr, structural characteristics and intramolecular movements of some phenoxyl radicals in toluene

    OpenAIRE

    Nizameev, I.; Pudovkin, M.; Kadirov, M.

    2010-01-01

    The method of electron paramagnetic resonance (EPR) spectroscopy was used for studying magnetic and dynamic properties of phenoxyl radicals in toluene at 170-370 K. Characteristics of intramolecular motion and structure of phenoxyl radicals were determined from the temperature dependence of EPR spectra. For all the given compounds the activation energies of transitions between the conformers were calculated.

  4. 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...

  5. 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...

  6. On prediction of OH stretching frequencies in intramolecularly hydrogen bonded systems

    DEFF Research Database (Denmark)

    Hansen, Poul Erik; Spanget-Larsen, Jens

    2012-01-01

    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...

  7. Chemical synthesis of dual labeled proteins via differently protected alkynes enables intramolecular FRET analysis.

    Science.gov (United States)

    Hayashi, Gosuke; Kamo, Naoki; Okamoto, Akimitsu

    2017-05-30

    We report a novel method for multisite protein conjugation by setting differently silyl-protected alkynes as conjugation handles, which can remain intact through the whole synthetic procedure and provide sequential and orthogonal conjugation. This strategy enables efficient preparation of a dual dye-labeled protein and structural analysis via an intramolecular FRET mechanism.

  8. Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

    Directory of Open Access Journals (Sweden)

    Valentin A. Rassadin

    2017-09-01

    Full Text Available A new and efficient approach to five- and six-membered benzannelated sultams by intramolecular C-arylation of tertiary 1-(methoxycarbonylmethanesulfonamides under palladium catalysis is described. In case of the α-toluenesulfonamide derivative, an unexpected formation of a 2,3-diarylindole was observed under the same conditions.

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

    DEFF Research Database (Denmark)

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

    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 ...

  10. Intramolecular 13C analysis of tree rings provides multiple plant ecophysiology signals covering decades.

    Science.gov (United States)

    Wieloch, Thomas; Ehlers, Ina; Yu, Jun; Frank, David; Grabner, Michael; Gessler, Arthur; Schleucher, Jürgen

    2018-03-22

    Measurements of carbon isotope contents of plant organic matter provide important information in diverse fields such as plant breeding, ecophysiology, biogeochemistry and paleoclimatology. They are currently based on 13 C/ 12 C ratios of specific, whole metabolites, but we show here that intramolecular ratios provide higher resolution information. In the glucose units of tree-ring cellulose of 12 tree species, we detected large differences in 13 C/ 12 C ratios (>10‰) among carbon atoms, which provide isotopically distinct inputs to major global C pools, including wood and soil organic matter. Thus, considering position-specific differences can improve characterisation of soil-to-atmosphere carbon fluxes and soil metabolism. In a Pinus nigra tree-ring archive formed from 1961 to 1995, we found novel 13 C signals, and show that intramolecular analysis enables more comprehensive and precise signal extraction from tree rings, and thus higher resolution reconstruction of plants' responses to climate change. Moreover, we propose an ecophysiological mechanism for the introduction of a 13 C signal, which links an environmental shift to the triggered metabolic shift and its intramolecular 13 C signature. In conclusion, intramolecular 13 C analyses can provide valuable new information about long-term metabolic dynamics for numerous applications.

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

    KAUST Repository

    Whited, Matthew T.; Patel, Niral M.; Roberts, Sean T.; Allen, Kathryn; Djurovich, Peter I.; Bradforth, Stephen E.; Thompson, Mark E.

    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.

  12. Intramolecular excimer and exciplex emission of 1,4-dipyrenyl substituted cyclohexasilane

    NARCIS (Netherlands)

    van Walree, C.A.; Kaats-Richters, V.E.M.; Jenneskens, L.W.; Williams, R.M.; van Stokkum, I.H.M.

    2002-01-01

    Intramolecular excimer emission is observed for cis-1,4-di(1-pyrenyl)decamethylcyclohexasilane in nonpolar solvents. Time-resolved fluorescence spectroscopy and kinetic modelling indicate that the driving force of excimer formation is very small, and that the process is governed by the flexibility

  13. Effect of intramolecular hydrogen bonding and electron donation on substituted anthrasemiquinone characteristics

    International Nuclear Information System (INIS)

    Pal, H.; Mukherjee, T.

    1994-01-01

    The acid-base and redox characteristics of the semiquinones of a number of hydroxy and amino-substituted anthraquinones have been investigated. Results are explained on the basis of electron-donating properties and intramolecular hydrogen bond forming capabilities of the substituents. (author). 4 refs., 1 tab., 1 fig

  14. Rapid examination of the kinetic process of intramolecular lactamization of gabapentin using DSC-FTIR

    International Nuclear Information System (INIS)

    Hsu, C.-H.; Lin, S.-Y.

    2009-01-01

    The thermal stability and thermodynamics of gabapentin (GBP) in the solid state were investigated by DSC and TG techniques, and FTIR microspectroscopy. The detailed intramolecular lactamization process of GBP to form gabapentin-lactam (GBP-L) was also determined by thermal FTIR microspectroscopy. GBP exhibited a DSC endothermic peak at 169 deg. C. The weight loss in TG curve of GBP suggested that the evaporation process of water liberated via intramolecular lactamization was simultaneously combined with the evaporation process of GBP-L having a DSC endothermic peak at 91 deg. C. A thermal FTIR microspectroscopy clearly evidenced the IR spectra at 3350 cm -1 for water liberated and at 1701 cm -1 for lactam structure formed due to the lactam formation of GBP. This study indicates that the activation energy for combined processes of intramolecular lactamization of GBP and evaporation of GBP-L was about 114.3 ± 23.3 kJ/mol, but for the evaporation of GBP-L alone was 76.2 ± 1.5 kJ/mol. A powerful simultaneous DSC-FTIR combined technique was easily used to quickly examine the detailed kinetic processes of intramolecular cyclization of GPB and evaporation of GBP-L in the solid state

  15. Application of the aza-Diels-Alder reaction in the synthesis of natural products.

    Science.gov (United States)

    Cao, Min-Hui; Green, Nicholas J; Xu, Sheng-Zhen

    2017-04-11

    The Diels-Alder reaction that involves a nitrogen atom in the diene or dienophile is termed the aza-Diels-Alder reaction. As well as the powerful all-carbon Diels-Alder reaction, the aza-Diels-Alder reaction has also played an important role in the total synthesis of natural products. Herein, we review various natural products using an aza-Diels-Alder reaction as a key step to their total synthesis, and divide the syntheses into inter- and intra-molecular aza-Diels-Alder reactions and a retro-aza-Diels-Alder reaction. Inter- and intra-molecular aza-Diels-Alder reactions involve an imine as an electron deficient dienophile and an imine as an electron deficient azadiene. The significance of the aza-Diels-Alder reaction for the construction of a six-membered ring containing nitrogen is tremendous, but the development of asymmetric, in particular catalytic enantioselective intramolecular aza-Diels-Alder reaction in the total synthesis of natural products remains highly challenging, and will no doubt see enormous advances in the future.

  16. Chlorine isotope effects from isotope ratio mass spectrometry suggest intramolecular C-Cl bond competition in trichloroethene (TCE) reductive dehalogenation.

    Science.gov (United States)

    Cretnik, Stefan; Bernstein, Anat; Shouakar-Stash, Orfan; Löffler, Frank; Elsner, Martin

    2014-05-20

    Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE) dehalogenation was investigated. Selective biotransformation reactions (i) of tetrachloroethene (PCE) to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii) of TCE to cis-1,2-dichloroethene (cis-DCE) in cultures of Geobacter lovleyi strain SZ were investigated. Compound-average carbon isotope effects were -19.0‰ ± 0.9‰ (PCE) and -12.2‰ ± 1.0‰ (TCE) (95% confidence intervals). Using instrumental advances in chlorine isotope analysis by continuous flow isotope ratio mass spectrometry, compound-average chorine isotope effects were measured for PCE (-5.0‰ ± 0.1‰) and TCE (-3.6‰ ± 0.2‰). In addition, position-specific kinetic chlorine isotope effects were determined from fits of reactant and product isotope ratios. In PCE biodegradation, primary chlorine isotope effects were substantially larger (by -16.3‰ ± 1.4‰ (standard error)) than secondary. In TCE biodegradation, in contrast, the product cis-DCE reflected an average isotope effect of -2.4‰ ± 0.3‰ and the product chloride an isotope effect of -6.5‰ ± 2.5‰, in the original positions of TCE from which the products were formed (95% confidence intervals). A greater difference would be expected for a position-specific reaction (chloride would exclusively reflect a primary isotope effect). These results therefore suggest that both vicinal chlorine substituents of TCE were reactive (intramolecular competition). This finding puts new constraints on mechanistic scenarios and favours either nucleophilic addition by Co(I) or single electron transfer as reductive dehalogenation mechanisms.

  17. Chlorine Isotope Effects from Isotope Ratio Mass Spectrometry Suggest Intramolecular C-Cl Bond Competition in Trichloroethene (TCE Reductive Dehalogenation

    Directory of Open Access Journals (Sweden)

    Stefan Cretnik

    2014-05-01

    Full Text Available Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (biochemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE dehalogenation was investigated. Selective biotransformation reactions (i of tetrachloroethene (PCE to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii of TCE to cis-1,2-dichloroethene (cis-DCE in cultures of Geobacter lovleyi strain SZ were investigated. Compound-average carbon isotope effects were −19.0‰ ± 0.9‰ (PCE and −12.2‰ ± 1.0‰ (TCE (95% confidence intervals. Using instrumental advances in chlorine isotope analysis by continuous flow isotope ratio mass spectrometry, compound-average chorine isotope effects were measured for PCE (−5.0‰ ± 0.1‰ and TCE (−3.6‰ ± 0.2‰. In addition, position-specific kinetic chlorine isotope effects were determined from fits of reactant and product isotope ratios. In PCE biodegradation, primary chlorine isotope effects were substantially larger (by −16.3‰ ± 1.4‰ (standard error than secondary. In TCE biodegradation, in contrast, the product cis-DCE reflected an average isotope effect of −2.4‰ ± 0.3‰ and the product chloride an isotope effect of −6.5‰ ± 2.5‰, in the original positions of TCE from which the products were formed (95% confidence intervals. A greater difference would be expected for a position-specific reaction (chloride would exclusively reflect a primary isotope effect. These results therefore suggest that both vicinal chlorine substituents of TCE were reactive (intramolecular competition. This finding puts new constraints on mechanistic scenarios and favours either nucleophilic addition by Co(I or single electron transfer as reductive dehalogenation mechanisms.

  18. Heterocyclization reaction of 4-(2-Methylaziridin-1-yl)-3-ureidobenzotrifluorides under appel's conditions

    International Nuclear Information System (INIS)

    Cho, Hyun In; Lee, Kee Jung

    2003-01-01

    The reaction of 4-(2-Methylaziridin-1-yl)-3-ureidobenzotrifluorides 4 with triphenylphosphine, carbon tetrachloride, and triethylamine (Appel's condition) led to the corresponding carbodiimides 5, which underwent intramolecular cycloaddition reaction with aziridine under the reaction condition to give the benzimidazole-fused heterocycles, 2.3-dihydro-1H-imidazo(1,2-a)benzimidazoles 8 and 12,13-dihydro-5H-benzimidazo(2,3-b)(1,3)benzodizzepines 9

  19. Quantitative analysis of intramolecular exciplex and electron transfer in a double-linked zinc porphyrin-fullerene dyad.

    Science.gov (United States)

    Al-Subi, Ali Hanoon; Niemi, Marja; Tkachenko, Nikolai V; Lemmetyinen, Helge

    2012-10-04

    Photoinduced charge transfer in a double-linked zinc porphyrin-fullerene dyad is studied. When the dyad is excited at the absorption band of the charge-transfer complex (780 nm), an intramolecular exciplex is formed, followed by the complete charge separated (CCS) state. By analyzing the results obtained from time-resolved transient absorption and emission decay measurements in a range of solvents with different polarities, we derived a dependence between the observable lifetimes and internal parameters controlling the reaction rate constants based on the semiquantum Marcus electron-transfer theory. The critical value of the solvent polarity was found to be ε(r) ≈ 6.5: in solvents with higher dielectric constants, the energy of the CCS state is lower than that of the exciplex and the relaxation takes place via the CCS state predominantly, whereas in solvents with lower polarities the energy of the CCS state is higher and the exciplex relaxes directly to the ground state. In solvents with moderate polarities the exciplex and the CCS state are in equilibrium and cannot be separated spectroscopically. The degree of the charge shift in the exciplex relative to that in the CCS state was estimated to be 0.55 ± 0.02. The electronic coupling matrix elements for the charge recombination process and for the direct relaxation of the exciplex to the ground state were found to be 0.012 ± 0.001 and 0.245 ± 0.022 eV, respectively.

  20. Dual fluorescence of excited state intra-molecular proton transfer of HBFO: mechanistic understanding, substituent and solvent effects.

    Science.gov (United States)

    Yang, Wenjing; Chen, Xuebo

    2014-03-07

    A combined approach of the multiconfigurational perturbation theory with the Rice-Ramsperger-Kassel-Marcus methodology has been employed to calculate the minimum potential energy profiles and the rates of excited state intra-molecular proton transfer (ESIPT) for the WOLED material molecule of HBFO and its four meta- or para-substituted compounds in gas phase, acetonitrile and cyclohexane solvents. The kinetic control for these reactions is quantitatively determined and extensively studied on the basis of the accurate potential energy surfaces when the thermodynamic factor associated with the free energy change becomes negligible in the case of the existence of a significant barrier in the ESIPT process. These computational efforts contribute to a deep understanding of the ESIPT mechanism, dual emission characteristics, kinetic controlling factor, substituent and solvent effects for these material molecules. The white light emission is generated by the establishment of dynamic equilibrium between enol and keto forms in the charge transfer excited SCT((1)ππ*) state. The performance of white light emission is quantitatively demonstrated to be mainly sensitive to the molecular tailoring approach of the electronic properties of meta- or para- substituents by the modulation of the forward/backward ESIPT rate ratio. The quality of white light emission is slightly tunable through its surrounding solvent environment. These computational results will provide a useful strategy for the molecular design of OLED and WOLED materials.

  1. Chemo- and Enantioselective Intramolecular Silver-Catalyzed Aziridinations.

    Science.gov (United States)

    Ju, Minsoo; Weatherly, Cale D; Guzei, Ilia A; Schomaker, Jennifer M

    2017-08-07

    Asymmetric nitrene-transfer reactions are a powerful tool for the preparation of enantioenriched amine building blocks. Reported herein are chemo- and enantioselective silver-catalyzed aminations which transform di- and trisubstituted homoallylic carbamates into [4.1.0]-carbamate-tethered aziridines in good yields and with ee values of up to 92 %. The effects of the substrate, silver counteranion, ligand, solvent, and temperature on both the chemoselectivity and ee value were explored. Stereochemical models were proposed to rationalize the observed absolute stereochemistry of the aziridines, which undergo nucleophilic ring opening to yield enantioenriched amines with no erosion in stereochemical integrity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Reactions of ruthenium and osmium cluster carbonyls with heteroatom-substituted and functionalized alkynes

    International Nuclear Information System (INIS)

    Koridze, A.A.

    2000-01-01

    The results of studies of the reactions of ruthenium and osmium cluster carbonyls with metal (M = Re, Mn, Fe) alkynes, silylalkynes, propargyl alcohols and their derivatives, diynes, enynes, and ferrocenylacetylene are summarized. Intramolecular rearrangements in the cluster complexes including migrations of carbonyl, hydride, and hydrocarbon ligands and the metal core reorganization are considered [ru

  3. Exciplex mediated photoinduced electron transfer reactions of phthalocyanine-fullerene dyads

    NARCIS (Netherlands)

    Niemi, Marja; Tkachenko, Nikolai V.; Efimov, Alexander; Lehtivuori, Heli; Ohkubo, Kei; Fukuzumi, Shunichi; Lemmetyinen, Helge

    2008-01-01

    Evidences of an intramolecular exciplex intermediate in a photoinduced electron transfer (ET) reaction of double-linked free-base and zinc phthalocyanine-C-60 dyads were found. This was the first time for a dyad with phthalocyanine donor. Excitation of the phthalocyanine moiety of the dyads results

  4. Intramolecular Parallel [4+3] Cycloadditions of Cyclopropane 1,1-Diesters with [3]Dendralenes: Efficient Construction of [5.3.0]Decane and Corresponding Polycyclic Skeletons.

    Science.gov (United States)

    Zhang, Chi; Tian, Jun; Ren, Jun; Wang, Zhongwen

    2017-01-26

    Aiming to develop efficient and general strategies for construction of complex and diverse polycyclic skeletons, we have successfully developed [4+3]IMPC (intramolecular parallel cycloaddition) of cyclopropane 1,1-diesters with [3]dendralenes. With a combination of the [4+3]IMPC and subsequent [4+n] cycloadditions, trans-[5.3.0]decane skeleton and its corresponding structurally complex and diverse polycyclic variants could be constructed efficiently. This novel [4+3] cycloaddition reaction mode of donor-acceptor cyclopropanes proceeds as a result of the ring-strain relief of a trans-[3.3.0]octane. We strongly believe that the developed methods will demonstrate potential applications in natural products synthesis and drug discovery. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. 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.

  6. Does the Intramolecular Hydrogen Bond Affect the Spectroscopic Properties of Bicyclic Diazole Heterocycles?

    Directory of Open Access Journals (Sweden)

    Paweł Misiak

    2018-01-01

    Full Text Available The formation of an intramolecular hydrogen bond in pyrrolo[1,2-a]pyrazin-1(2H-one bicyclic diazoles was analyzed, and the influence of N-substitution on HB formation is discussed in this study. B3LYP/aug-cc-pVDZ calculations were performed for the diazole, and the quantum theory of atoms in molecules (QTAIM approach as well as the natural bond orbital (NBO method was applied to analyze the strength of this interaction. It was found that the intramolecular hydrogen bond that closes an extra ring between the C=O proton acceptor group and the CH proton donor, that is, C=O⋯H–C, influences the spectroscopic properties of pyrrolopyrazine bicyclic diazoles, particularly the carbonyl frequencies. The influence of N-substitution on the aromaticity of heterocyclic rings is also discussed in this report.

  7. Numerical simulation of dynamic quenching of dual-split fluorescence of molecules with intramolecular hydrogen bonds

    International Nuclear Information System (INIS)

    Morozov, V.A.; Chuvulkin, N.D.; Smolenskij, E.A.; Dubina, Yu.M.

    2014-01-01

    The dynamic quenching of intensity pulses of the dual-split fluorescence (DSF) has been simulated using numerical solutions of the equations for the population matrix of five states of the model fluorescent molecule (FM). The state with the highest energy is considered as resonantly excited by irradiation, and two other excited states populated by subsequent relaxation processes are taken as initial states for the FM transitions with emission of the DSF photons. The FM model parameters are selected to fit typical parameters of the molecules with intramolecular proton photo transfer. Quenching is considered as a consequence of non-radiative decay of the FM excited states due to collisions with the quencher molecules. Examples of two types of the DSF quenching of the FM are given. The first type leads to an intramolecular radiationless decay of particular excited states of the FM, and the second one results in radiationless transitions from the same states to the quencher molecule states. (authors)

  8. Modeling and computations of the intramolecular electron transfer process in the two-heme protein cytochrome em>c>4

    DEFF Research Database (Denmark)

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

    2012-01-01

    force were determined using dielectric continuum models. We then calculated the electronic transmission coefficient of the intramolecular ET rate using perturbation theory combined with the electronic wave functions determined by the DFT calculations for different heme group orientations and Fe...

  9. Hecke algebras and harmonic analysis

    NARCIS (Netherlands)

    Opdam, E.M.; Sanz-Solé, M.; Soria, J.; Varona, J.L.; Verdera, J.

    2006-01-01

    The International Congress of Mathematicians (ICM) is held every four years. It is a major scientific event, bringing together mathematicians from all over the world, and demonstrating the vital role that mathematics play in our society. In particular, the Fields Medals are awarded to recognize

  10. Mode selectivity in the intramolecular cyclization of ketenimines bearing N-acylimino units: a computational and experimental study.

    Science.gov (United States)

    Alajarín, Mateo; Sánchez-Andrada, Pilar; Vidal, Angel; Tovar, Fulgencio

    2005-02-18

    [reaction: see text] The mode selectivity in the intramolecular cyclization of a particular class of ketenimines bearing N-acylimino units has been studied by ab initio and DFT calculations. In the model compounds the carbonyl carbon atom and the keteniminic nitrogen atom are linked either by a vinylic or an o-phenylene tether. Two cyclization modes have been analyzed: the [2+2] cycloaddition furnishing compounds with an azeto[2,1-b]pyrimidinone moiety and a 6pi-electrocyclic ring closure leading to compounds enclosing a 1,3-oxazine ring. The [2+2] cycloaddition reaction takes place via a two-step process with formation of a zwitterionic intermediate, which has been characterized as a cross-conjugated mesomeric betaine. The 6pi-electrocyclic ring closure occurs via a transition state whose pseudopericyclic character has been established on the basis of its magnetic properties, geometry, and NBO analysis. The 6pi-electrocyclic ring closure is energetically favored over the [2+2] cycloaddition, although the [2+2] cycloadducts are the thermodynamically controlled products. A quantitative kinetic analysis predicts that 1,3-oxazines would be the kinetically controlled products, but they should transform rapidly and totally into the [2+2] cycloadducts at room temperature. In the experimental study, a number of N-acylimino-ketenimines, in which both reactive functions are supported on an o-phenylene scaffold, have been successfully synthesized in three steps starting from 2-azidobenzoyl chloride. These compounds rapidly convert into azeto[2,1-b]quinazolin-8-ones in moderate to good yields as a result of a formal [2+2] cycloaddition.

  11. Iron(II)-catalyzed intramolecular aminohydroxylation of olefins with functionalized hydroxylamines.

    Science.gov (United States)

    Liu, Guan-Sai; Zhang, Yong-Qiang; Yuan, Yong-An; Xu, Hao

    2013-03-06

    A diastereoselective aminohydroxylation of olefins with a functionalized hydroxylamine is catalyzed by new iron(II) complexes. This efficient intramolecular process readily affords synthetically useful amino alcohols with excellent selectivity (dr up to > 20:1). Asymmetric catalysis with chiral iron(II) complexes and preliminary mechanistic studies reveal an iron nitrenoid is a possible intermediate that can undergo either aminohydroxylation or aziridination, and the selectivity can be controlled by careful selection of counteranion/ligand combinations.

  12. Towards single-molecule detection of intramolecular exciplexes: Photophysics of a benzanthrone derivative

    Energy Technology Data Exchange (ETDEWEB)

    Hattori, Akifumi [Graduate School of Bio-Applications and Systems Engineering (BASE), Tokyo University of Agriculture and Technology, 2-24-16 Naka-machi, Koganei, Tokyo, 184-8588 (Japan); Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1-S8, Meguro-ku, Tokyo, 152-8552 (Japan); Sato, Hisaya [Graduate School of Bio-Applications and Systems Engineering (BASE), Tokyo University of Agriculture and Technology, 2-24-16 Naka-machi, Koganei, Tokyo, 184-8588 (Japan); Vacha, Martin [Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama 2-12-1-S8, Meguro-ku, Tokyo, 152-8552 (Japan)]. E-mail: vacha@op.titech.ac.jp

    2007-01-15

    We report luminescence study of intramolecular exciplexes based on an aminobenzanthrone derivative, dimethyl-amino-N-acetyl-3-aminobenzanthrone (BDA). The BDA compound shows strong dependence of the exciplex emission band intensity on the solvent dielectric function and moderate dependence on its viscosity. The exciplex emission mechanism is discussed in view of the unusual solvent polarity dependence and solvent-dependent excited state lifetimes. Preliminary results on single-molecule detection in polymer films are also presented.

  13. Towards single-molecule detection of intramolecular exciplexes: Photophysics of a benzanthrone derivative

    International Nuclear Information System (INIS)

    Hattori, Akifumi; Sato, Hisaya; Vacha, Martin

    2007-01-01

    We report luminescence study of intramolecular exciplexes based on an aminobenzanthrone derivative, dimethyl-amino-N-acetyl-3-aminobenzanthrone (BDA). The BDA compound shows strong dependence of the exciplex emission band intensity on the solvent dielectric function and moderate dependence on its viscosity. The exciplex emission mechanism is discussed in view of the unusual solvent polarity dependence and solvent-dependent excited state lifetimes. Preliminary results on single-molecule detection in polymer films are also presented

  14. Some kinetic and spectroscopic evidence on intramolecular relaxation processes in polyatomic molecules

    International Nuclear Information System (INIS)

    Quack, M.

    1983-01-01

    The description and definition of intramolecular vibrational relaxation processes is discussed within the framework of the quantum mechanical and statistical mechanical equations of motion. The evidence from quite different experimental sources is summarized under the common aspect of vibrational relaxation. Although much of the evidence remains ambiguous, there is good indication that a localized vibrational excitation relaxes typically in 0.1 to 10 picoseconds, which is long compared to many optical and reactive processes

  15. 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...... ECD using peptides with a unique selective deuterium incorporation. Our results show that only limited amide hydrogen migration occurs upon ECD, provided that vibrational excitation prior to the electron capture event is minimized. Peptide ions that are excessively vibrationally excited...

  16. Antimalarial peroxides: the first intramolecular 1,2,4,5-tetraoxane

    Directory of Open Access Journals (Sweden)

    BOGDAN A. SOLAJA

    2002-07-01

    Full Text Available An intramolecular steroidal 1,2,4,5-tetraoxane has been synthesised in six steps starting from methyl 3-oxo-7a,12a-diacetoxy-5b-cholan-24-oate. The synthesised 1,2,4,5-tetraoxane has moderate in vitro antimalarial activity against P. falciparum strains (IC50 (D6 = 0.35 mg/mL; IC50 (W2 = 0.29 mg/mL.

  17. Ductile Glass of Polyrotaxane Toughened by Stretch-Induced Intramolecular Phase Separation.

    Science.gov (United States)

    Kato, Kazuaki; Nemoto, Kaito; Mayumi, Koichi; Yokoyama, Hideaki; Ito, Kohzo

    2017-09-27

    A new class of ductile glasses is created from a thermoplastic polyrotaxane. The hard glass, which has a Young's modulus of 1 GPa, shows crazing, necking, and strain hardening with a total elongation of 330%. Stress concentration is prevented through a unique stretch-induced intramolecular phase separation of the cyclic components and the exposed backbone. In situ synchrotron X-ray scattering studies indicate that the backbone polymer chains slip through the cyclic components in the regions where the stress is concentrated.

  18. Intramolecular Azide to Alkene Cycloadditions for the Construction of Pyrrolobenzodiazepines and Azetidino-Benzodiazepines

    Directory of Open Access Journals (Sweden)

    Karl Hemming

    2014-10-01

    Full Text Available The coupling of proline- and azetidinone-substituted alkenes to 2-azidobenzoic and 2-azidobenzenesulfonic acid gives precursors that undergo intramolecular azide to alkene 1,3-dipolar cycloadditions to give imine-, triazoline- or aziridine-containing pyrrolo[1,4]benzodiazepines (PBDs, pyrrolo[1,2,5]benzothiadiazepines (PBTDs, and azetidino[1,4]benzodiazepines. The imines and aziridines are formed after loss of nitrogen from a triazoline cycloadduct. The PBDs are a potent class of antitumour antibiotics.

  19. 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.

  20. THE ROLE OF INTRAMOLECULAR TIES ENERGY IN THE PYROLYSIS PROCESS OF PET

    Directory of Open Access Journals (Sweden)

    P. Iu. Salikov

    2014-01-01

    Full Text Available Summary. Recycling plastic waste to focus on. The main type of used products made of polyethylene terephthalate (PET is a container from the various types of beverages. There was considered a possibility of waste of PET (bottles, bottles, packaging containers by pyrolysis. Most of the proposed methods are not suitable for recycling (recycling of waste consumption contamination. Purpose - to develop technological foundations and optimum modes waste PET to obtain useful secondary products, taking into account the energy of chemical intramolecular bonds. Applied scientific basis of recycling PET into useful forms of secondary products, in particular the establishment of the collapse of the intramolecular bonds, depending on the temperature of the pyrolysis method of mathematical processing - differentiation of polynomial equations change in the degree of pyrolysis temperature-dependent. The optimum modes of processing. The block diagram of apparatus for processing contaminated waste PET pyrolysis methods of control processing in accordance with the specified composition of secondary products. The possibility of controlling the amount and types of fuel components of secondary products due to measurable parameters of the pyrolysis process. The effective temperature pyrolysis of waste PET with the CCA-tures energy intramolecular bonds.

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

    International Nuclear Information System (INIS)

    Xiang, Debo; Noel, Jerome; Shao, Huibo; Dupas, Georges; Merbouh, Nabyl; Yu, Hua-Zhong

    2015-01-01

    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

  2. Light induced intramolecular electron and energy transfer events in rigidly linked borondipyrromethene: Corrole Dyad

    Energy Technology Data Exchange (ETDEWEB)

    Giribabu, Lingamallu, E-mail: giribabu@iict.res.in [Inorganic & Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500007, Telangana (India); Jain, Kanika [Department of Chemistry, School of Chemical Sciences & Pharmacy, Central University of Rajasthan, Kishangarh, Dist. Ajmer, Rajasthan 305817 (India); Sudhakar, Kolanu; Duvva, Naresh [Inorganic & Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500007, Telangana (India); Chitta, Raghu, E-mail: raghuchitta@curaj.ac.in [Department of Chemistry, School of Chemical Sciences & Pharmacy, Central University of Rajasthan, Kishangarh, Dist. Ajmer, Rajasthan 305817 (India)

    2016-09-15

    We have designed and synthesized a photo-induced energy/electron donor–acceptor conjugate comprising of corrole linked to BODIPY at the 5-position via ester linkage. The dyad was characterized by elemental analysis, MALDI-MS, UV-Visible, {sup 1}H NMR fluorescence spectroscopy (steady-state and time-resolved) as well as electrochemical methods. A comparison of the UV–visible and {sup 1}H NMR spectra of the dyad with those of the corresponding individual model compounds (i.e., BODIPY-CO{sub 2}H and BPFC-OH) reveal that there exist minimum π–π interactions between BODIPY and corrole π-planes. Quenched emission of BODIPY and corrole part of the dyad has been observed in five different solvents. Excitation spectral data provided evidence for an intramolecular excitation energy transfer (EET) from the singlet BODIPY to the corrole and an intramolecular photoinduced electron transfer (PET) from singlet state of corrole to ground state of BODIPY. Detailed analysis of the data suggests that Forster's dipole–dipole mechanism does not adequately explain this energy transfer but, an electron exchange mediated mechanism can, in principle, contribute to the intramolecular EET.

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

    International Nuclear Information System (INIS)

    Curbo, Sophie; Gaudin, Raphael; Carlsten, Mattias; Malmberg, Karl-Johan; Troye-Blomberg, Marita; Ahlborg, Niklas; Karlsson, Anna; Johansson, Magnus; Lundberg, Mathias

    2009-01-01

    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.

  4. Intramolecular Hydrogen Bonding and Conformational Preferences of Arzanol—An Antioxidant Acylphloroglucinol

    Directory of Open Access Journals (Sweden)

    Liliana Mammino

    2017-08-01

    Full Text Available Arzanol is a naturally-occurring prenylated acylphloroglucinol isolated from Helichrysum italicum and exhibiting anti-oxidant, antibiotic and antiviral activities. The molecule contains an α-pyrone moiety attached to the phloroglucinol moiety through a methylene bridge. The presence of several hydrogen bond donor or acceptor sites makes intramolecular hydrogen bonding patterns the dominant stabilising factor. Conformers with all the possible different hydrogen bonding patterns were calculated at the HF/6-31G(d,p and DFT/B3LYP/6-31+G(d,p levels with fully relaxed geometry in vacuo and in three solvents—chloroform, acetonitrile and water (these levels being chosen to enable comparisons with previous studies on acylphloroglucinols. Calculations in solution were performed with the Polarisable Continuum Model. The results show that the lowest energy conformers have the highest number of stronger intramolecular hydrogen bonds. The influence of intramolecular hydrogen bonding patterns on the other molecular properties is also analysed.

  5. Impact of undamped and damped intramolecular vibrations on the efficiency of photosynthetic exciton energy transfer

    Science.gov (United States)

    Juhász, Imre Benedek; Csurgay, Árpád I.

    2018-04-01

    In recent years, the role of molecular vibrations in exciton energy transfer taking place during the first stage of photosynthesis attracted increasing interest. Here, we present a model formulated as a Lindblad-type master equation that enables us to investigate the impact of undamped and especially damped intramolecular vibrational modes on the exciton energy transfer, particularly its efficiency. Our simulations confirm the already reported effects that the presence of an intramolecular vibrational mode can compensate the energy detuning of electronic states, thus promoting the energy transfer; and, moreover, that the damping of such a vibrational mode (in other words, vibrational relaxation) can further enhance the efficiency of the process by generating directionality in the energy flow. As a novel result, we show that this enhancement surpasses the one caused by pure dephasing, and we present its dependence on various system parameters (time constants of the environment-induced relaxation and excitation processes, detuning of the electronic energy levels, frequency of the intramolecular vibrational modes, Huang-Rhys factors, temperature) in dimer model systems. We demonstrate that vibrational-relaxation-enhanced exciton energy transfer (VREEET) is robust against the change of these characteristics of the system and occurs in wide ranges of the investigated parameters. With simulations performed on a heptamer model inspired by the Fenna-Matthews-Olson (FMO) complex, we show that this mechanism can be even more significant in larger systems at T = 300 K. Our results suggests that VREEET might be prevalent in light-harvesting complexes.

  6. Intramolecular BSSE and dispersion affect the structure of a dipeptide conformer

    Science.gov (United States)

    Hameed, Rabia; Khan, Afsar; van Mourik, Tanja

    2018-05-01

    B3LYP and MP2 calculations with the commonly-used 6-31+G(d) basis set predict qualitatively different structures for the Tyr-Gly conformer book1, which is the most stable conformer identified in a previous study. The structures differ mainly in the ψtyr Ramachandran angle (138° in the B3LYP structure and 120° in the MP2 structure). The causes for the discrepant structures are attributed to missing dispersion in the B3LYP calculations and large intramolecular BSSE in the MP2 calculations. The correct ψtyr value is estimated to be 130°. The MP2/6-31+G(d) profile identified an additional conformer, not present on the B3LYP surface, with a ψtyr value of 96° and a more folded structure. This minimum is, however, likely an artefact of large intramolecular BSSE values. We recommend the use of basis sets of at least quadruple-zeta quality in density functional theory (DFT), DFTaugmented with an empirical dispersion term (DFT-D) and second-order Møller-Plesset perturbation theory (MP2 ) calculations in cases where intramolecular BSSE is expected to be large.

  7. Synthesis research of squalene synthetase inhibitor CP-263, 114. How is skeleton construction carried out?; Sukuaren gosei koso sogaizai CP-263,114 no gosei kenkyu - ikanishite kokkaku kochiku wo okonauka?

    Energy Technology Data Exchange (ETDEWEB)

    Matsushima, Y. [Tokyo Inst. of Tech., Tokyo (Japan)

    2000-01-01

    CP-263, 114 isolated as a squalene synthetase inhibitor and the decyclization of CP-225, 917 was not only expected to be a lead chemical compound of the hypercholesterolemia medicine, but also have collected the attention of the organic synthetic chemistry researchers all over the world from the ring structure of advanced oxygen functionalization. In the CP- chemical compound, the constructive method of the bicyclo ring structure is a key of the synthesis, there are three reports to use the intramolecular Diels-Alder reaction (Fukuyama) and the siloxy-Cope rearrangement (Leighton), intramolecular Heck reaction (Danishefsky) as a result of succeeding in including the foothold to the side-chain lactol ring. Recently, Nicolaou et al. succeeded for the first time in the total synthesis racemic modification shell. They carried out the skeleton construction by the intramolecular Diels-Alder reaction, and constructed the maleic anhydride structure in taking the ketone as a foothold. (NEDO)

  8. Pulse radiolysis studies of intramolecular electron transfer in model peptides and proteins. 7. Trp -> TyrO radical transformation in hen egg-white lysozyme. Effects of pH, temperature, Trp62 oxidation and inhibitor binding

    DEFF Research Database (Denmark)

    Bobrowski, K.; Holcman, J.; Poznanski, J.

    1997-01-01

    Intramolecular long-range electron transfer (LRET) in hen egg-white lysozyme (HEWL) accompanying Trp --> TyrO radical transformation was investigated in aqueous solution by pulse radiolysis as a function of pH (5.2-7.4) and temperature (283-328K). The reaction was induced by highly selective...... below its denaturation temperature. Selective oxidation by ozone of the Trp62 indole side-chain in HEWL to N'-formylkynurenine (NFKyn62-HEWL) caused a large drop in the initial yield of Trp(.) radicals, G(Trp(.))(i). This was accompanied by a relatively small decrease in k(5) but selective oxidation...

  9. Stereoselective synthesis of organosulfur compounds incorporating N-aromatic heterocyclic motifs and quaternary carbon centers via a sulfa-Michael triggered tandem reaction.

    Science.gov (United States)

    Qin, Tianyou; Cheng, Lu; Zhang, Sean Xiao-An; Liao, Weiwei

    2015-06-14

    A novel sulfa-Michael addition (SMA)-triggered tandem reaction was developed by combining a SMA reaction with a simultaneous rearomatization process utilizing a less reactive carbonyl group as an intramolecular electrophile partner, which provided a unique synthetic route to access various organosulfur compounds incorporating an N-aromatic heterocyclic motif and quaternary carbon centers.

  10. Rh(II)-catalyzed reactions of differentially substituted bis(diazo) functionalities.

    Science.gov (United States)

    Bonderoff, Sara A; Padwa, Albert

    2013-08-16

    The chemoselective reaction of donor/acceptor (D/A) and acceptor/acceptor (A/A) diazo moieties in the same molecule was examined using 3-diazo-1-(ethyl 2-diazomalonyl)indolin-2-one under rhodium(II) catalysis. The D/A diazo group undergoes selective cyclopropanation as well as XH-insertion, leaving behind the second diazo group for a further intramolecular dipolar cycloaddition reaction.

  11. Radical-mediated annulation reactions. A versatile strategy for the preparation of a series of carbocycles.

    Science.gov (United States)

    Sibi, M P; Chen, J; Rheault, T R

    2001-11-15

    [reaction--see text] A series of novel 6-endo [4 + 2] and 7-endo [5 + 2] radical-mediated annulation reactions are described. These annulation sequences involve an intermolecular radical addition followed by intramolecular trapping with an allyltin moiety incorporated into the radical precursor fragment. This methodology allows for access to functionalized 6- and 7-membered carbocycles as well as bicyclic compounds with good to excellent levels of stereocontrol.

  12. Specific optical signalling of anions via intramolecular charge transfer pathway based on acridinedione fluorophore

    International Nuclear Information System (INIS)

    Thiagarajan, Viruthachalam; Ramamurthy, Perumal

    2007-01-01

    We present a simple but highly specific acridinedione fluorophore (ADD-1) that acts both as a fluorescent and colorimetric sensor for anions in acetonitrile. The specific optical signalling of ADD-1 is due to the formation of new distinct intramolecular charge transfer (ICT) emitting states in the presence of AcO - (490 nm), H 2 PO 4 - (440 nm), and F - (510 nm) over other anions. Presence of F - shows a colour change that is perceptible to the naked eye, from colourless to an intense fluorescent green due to the deprotonation of acridinedione ring amino hydrogen

  13. Size measuring techniques as tool to monitor pea proteins intramolecular crosslinking by transglutaminase treatment.

    Science.gov (United States)

    Djoullah, Attaf; Krechiche, Ghali; Husson, Florence; Saurel, Rémi

    2016-01-01

    In this work, techniques for monitoring the intramolecular transglutaminase cross-links of pea proteins, based on protein size determination, were developed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of transglutaminase-treated low concentration (0.01% w/w) pea albumin samples, compared to the untreated one (control), showed a higher electrophoretic migration of the major albumin fraction band (26 kDa), reflecting a decrease in protein size. This protein size decrease was confirmed, after DEAE column purification, by dynamic light scattering (DLS) where the hydrodynamic radius of treated samples appears to be reduced compared to the control one. Copyright © 2015 Elsevier Ltd. All rights reserved.

  14. Influence of intramolecular hydrogen bonds on the binding potential of methylated β-cyclodextrin derivatives

    Directory of Open Access Journals (Sweden)

    Gerhard Wenz

    2012-11-01

    Full Text Available Various heptasubstituted derivatives of β-cyclodextrin (β-CD bearing 1, 2 and 3 methyl substituents per glucose unit were synthesized by regioselective methods. Binding free energies and binding enthalpies of these hosts towards 4-tert-butylbenzoate and adamantane-1-carboxylate were determined by isothermal titration microcalorimetry (ITC. It was found that methyl substituents at the secondary positions of β-CD lead to a tremendous reduction of the binding potential, while methylation at the primary positions significantly improved binding. Stabilizing intramolecular hydrogen bonds between the glucose units were made responsible for the high binding potentials of those β-CD derivatives that possess secondary hydroxy groups.

  15. 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

    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 activation......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...

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

    International Nuclear Information System (INIS)

    Ezhov, Yu.S.; Vinogradov, V.S.

    1978-01-01

    To clear out the peculiarities of intramolecular movement in MBO 2 (where M=Li, Na, K, Rb, Cs) molecules the energy dependence of cation electrostatic interaction with BO 2 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 MBO 2 molecules. Parameters of potential function of deformation oscillation connected with the change of MOB angle, are evaluated

  17. A new reactivity mode for the diazo group: diastereoselective 1,3-aminoalkylation reaction of β-amino-α-diazoesters to give triazolines.

    Science.gov (United States)

    Kuznetsov, Alexey; Gulevich, Anton V; Wink, Donald J; Gevorgyan, Vladimir

    2014-08-18

    A novel mode of reactivity for the diazo group, the 1,3-addition of a nucleophile and an electrophile to the diazo group, has been realized in the intramolecular aminoalkylation of β-amino-α-diazoesters to form tetrasubstituted 1,2,3-triazolines. The reaction exhibited a broad scope, good functional group tolerance, and excellent diastereoselectivity. In addition, a new Au-catalyzed intramolecular transannulation reaction of the obtained propargyl triazolines to give pyrroles has been discovered. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Kinetic evidence for the formation of discrete 1,4-dehydrobenzene intermediates. Trapping by inter- and intramolecular hydrogen atom transfer and observation of high-temperature CIDNP

    Energy Technology Data Exchange (ETDEWEB)

    Lockhart, Thomas P. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); California Inst. of Technology (CalTech), Pasadena, CA (United States); Comita, Paul B. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); California Inst. of Technology (CalTech), Pasadena, CA (United States); Bergman, Robert G. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); California Inst. of Technology (CalTech), Pasadena, CA (United States)

    1981-07-01

    Upon heating, alkyl-substituted cis-1,2-diethynyl olefins undergo cyclization to yield reactive 1,4-dehydrobenzenes; the products isolated may be derived from either unimolecular or bimolecular reactions of the intermediate. (Z)-4,5-Diethynyl-4-octene (4) undergoes rearrangement to yield 2,3-di-n-propyl-1,4-dehydrobenzene (17). Solution pyrolysis of 4 in inert aromatic solvents produces three unimolecular products, (Z)-dodeca-4,8-diyn-6-ene (7), benzocyclooctene (9), and o-allyl-n-propylbenzene (10), in high yield. When 1,4-cyclohexadiene is added to the pyrolysis solution as a trapping agent, high yields of the reduced product o-di-n-propylbenzene (12) are obtained. The kinetics of solution pyrolysis of 4 in the presence and absence of trapping agent establish that 2,3-di-n-propyl-1,4-dehydrobenzene is a discrete intermediate on the pathway leading to products. When the reaction was run in the heated probe of an NMR spectrometer, CIDNP was observed in 10. This observation, along with kinetic and chemical trapping evidence, indicates the presence of two additional intermediates, formed from 17 by sequential intramolecular [1,5] hydrogen transfer, on the pathway to products. The observation of CIDNP, coupled with the reactivity exhibited by 17 and the other two intermediates, implicate a biradical description of these molecules. Biradical 17 has been estimated to have a lifetime of about 10-9 s at 200°C and to lie in a well of about 5 kcal/mol with respect to the lowest energy unimolecular pathway ([1,5] hydrogen transfer). Ring opening (expected to be the lowest energy process for 1,4-dehydrobenzenes in which intramolecular hydrogen transfer is unlikely) to the isomeric diethynyl olefin 7 appears to have an activation enthalpy of about 10 kcal/moL Upon thermal reaction in the gas phase (400°C) or in solution in inert solvents (Z)-hexa-2,3-diethyl-1,5-diyn-3-ene (5) rearranges in good yield to the isomeric diethynyl olefin (Z)-deca-3,7-diyn-5-ene (8

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

    International Nuclear Information System (INIS)

    Lyons, B.J.

    1986-01-01

    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)

  20. EVAPORATION: a new vapour pressure estimation methodfor organic molecules including non-additivity and intramolecular interactions

    Directory of Open Access Journals (Sweden)

    S. Compernolle

    2011-09-01

    Full Text Available We present EVAPORATION (Estimation of VApour Pressure of ORganics, Accounting for Temperature, Intramolecular, and Non-additivity effects, a method to predict (subcooled liquid pure compound vapour pressure p0 of organic molecules that requires only molecular structure as input. The method is applicable to zero-, mono- and polyfunctional molecules. A simple formula to describe log10p0(T is employed, that takes into account both a wide temperature dependence and the non-additivity of functional groups. In order to match the recent data on functionalised diacids an empirical modification to the method was introduced. Contributions due to carbon skeleton, functional groups, and intramolecular interaction between groups are included. Molecules typically originating from oxidation of biogenic molecules are within the scope of this method: aldehydes, ketones, alcohols, ethers, esters, nitrates, acids, peroxides, hydroperoxides, peroxy acyl nitrates and peracids. Therefore the method is especially suited to describe compounds forming secondary organic aerosol (SOA.

  1. Molecular Dynamics Simulation of Barnase: Contribution of Noncovalent Intramolecular Interaction to Thermostability

    Directory of Open Access Journals (Sweden)

    Zhiguo Chen

    2013-01-01

    Full Text Available Bacillus amyloliquefaciens ribonuclease Barnase (RNase Ba is a 12 kD (kilodalton small extracellular ribonuclease. It has broad application prospects in agriculture, clinical medicine, pharmaceutical, and so forth. In this work, the thermal stability of Barnase has been studied using molecular dynamics simulation at different temperatures. The present study focuses on the contribution of noncovalent intramolecular interaction to protein stability and how they affect the thermal stability of the enzyme. Profiles of root mean square deviation and root mean square fluctuation identify thermostable and thermosensitive regions of Barnase. Analyses of trajectories in terms of secondary structure content, intramolecular hydrogen bonds and salt bridge interactions indicate distinct differences in different temperature simulations. In the simulations, Four three-member salt bridge networks (Asp8-Arg110-Asp12, Arg83-Asp75-Arg87, Lys66-Asp93-Arg69, and Asp54-Lys27-Glu73 have been identified as critical salt bridges for thermostability which are maintained stably at higher temperature enhancing stability of three hydrophobic cores. The study may help enlighten our knowledge of protein structural properties, noncovalent interactions which can stabilize secondary peptide structures or promote folding, and also help understand their actions better. Such an understanding is required for designing efficient enzymes with characteristics for particular applications at desired working temperatures.

  2. An excited-state intramolecular photon transfer fluorescence probe for localizable live cell imaging of cysteine

    Science.gov (United States)

    Liu, Wei; Chen, Wen; Liu, Si-Jia; Jiang, Jian-Hui

    2017-03-01

    Small molecule probes suitable for selective and specific fluorescence imaging of some important but low-concentration intracellular reactive sulfur species such as cysteine (Cys) pose a challenge in chemical biology. We present a readily available, fast-response fluorescence probe CHCQ-Ac, with 2-(5‧-chloro-2-hydroxyl-phenyl)-6-chloro-4(3 H)-quinazolinone (CHCQ) as the fluorophore and acrylate group as the functional moiety, that enables high-selectivity and high-sensitivity for detecting Cys in both solution and biological system. After specifically reacted with Cys, the probe undergoes a seven-membered intramolecular cyclization and released the fluorophore CHCQ with excited-state intramolecular photon transfer effect. A highly fluorescent, insoluble aggregate was then formed to facilitate high-sensitivity and high-resolution imaging. The results showed that probe CHCQ-Ac affords a remarkably large Stokes shift and can detect Cys under physiological pH condition with no interference from other analytes. Moreover, this probe was proved to have excellent chemical stability, low cytotoxicity and good cell permeability. Our design of this probe provides a novel potential tool to visualize and localize cysteine in bioimaging of live cells that would greatly help to explore various Cys-related physiological and pathological cellular processes in cell biology and diagnostics.

  3. 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. © 2016 Society for Laboratory Automation and Screening.

  4. Discovery of intramolecular signal transduction network based on a new protein dynamics model of energy dissipation.

    Directory of Open Access Journals (Sweden)

    Cheng-Wei Ma

    Full Text Available A novel approach to reveal intramolecular signal transduction network is proposed in this work. To this end, a new algorithm of network construction is developed, which is based on a new protein dynamics model of energy dissipation. A key feature of this approach is that direction information is specified after inferring protein residue-residue interaction network involved in the process of signal transduction. This enables fundamental analysis of the regulation hierarchy and identification of regulation hubs of the signaling network. A well-studied allosteric enzyme, E. coli aspartokinase III, is used as a model system to demonstrate the new method. Comparison with experimental results shows that the new approach is able to predict all the sites that have been experimentally proved to desensitize allosteric regulation of the enzyme. In addition, the signal transduction network shows a clear preference for specific structural regions, secondary structural types and residue conservation. Occurrence of super-hubs in the network indicates that allosteric regulation tends to gather residues with high connection ability to collectively facilitate the signaling process. Furthermore, a new parameter of propagation coefficient is defined to determine the propagation capability of residues within a signal transduction network. In conclusion, the new approach is useful for fundamental understanding of the process of intramolecular signal transduction and thus has significant impact on rational design of novel allosteric proteins.

  5. Effect of Hartree-Fock exact exchange on intramolecular magnetic coupling constants of organic diradicals

    Science.gov (United States)

    Cho, Daeheum; Ko, Kyoung Chul; Ikabata, Yasuhiro; Wakayama, Kazufumi; Yoshikawa, Takeshi; Nakai, Hiromi; Lee, Jin Yong

    2015-01-01

    The intramolecular magnetic coupling constant (J) of diradical systems linked with five- or six-membered aromatic rings was calculated to obtain the scaling factor (experimental J/calculated J ratio) for various density functional theory (DFT) functionals. Scaling factors of group A (PBE, TPSSh, B3LYP, B97-1, X3LYP, PBE0, and BH&HLYP) and B (M06-L, M06, M06-2X, and M06-HF) were shown to decrease as the amount of Hartree-Fock exact exchange (HFx) increases, in other words, overestimation of calculated J becomes more severe as the HFx increases. We further investigated the effect of HFx fraction of DFT functional on J value, spin contamination, and spin density distributions by comparing the B3LYP analogues containing different amount of HFx. It was revealed that spin contamination and spin densities at each atom increases as the HFx increases. Above all, newly developed BLYP-5 functional, which has 5% of HFx, was found to have the scaling factor of 1.029, indicating that calculated J values are very close to that of experimental values without scaling. BLYP-5 has potential to be utilized for accurate evaluation of intramolecular magnetic coupling constant (J) of diradicals linked by five- or six-membered aromatic ring couplers.

  6. Effect of Hartree-Fock exact exchange on intramolecular magnetic coupling constants of organic diradicals

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Daeheum; Ko, Kyoung Chul; Lee, Jin Yong, E-mail: jinylee@skku.edu [Department of Chemistry, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Ikabata, Yasuhiro; Wakayama, Kazufumi; Yoshikawa, Takeshi [Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555 (Japan); Nakai, Hiromi, E-mail: nakai@waseda.jp [Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555 (Japan); Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555 (Japan); CREST, Japan Science and Technology Agency, Tokyo 102-0075 (Japan); Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520 (Japan)

    2015-01-14

    The intramolecular magnetic coupling constant (J) of diradical systems linked with five- or six-membered aromatic rings was calculated to obtain the scaling factor (experimental J/calculated J ratio) for various density functional theory (DFT) functionals. Scaling factors of group A (PBE, TPSSh, B3LYP, B97-1, X3LYP, PBE0, and BH and HLYP) and B (M06-L, M06, M06-2X, and M06-HF) were shown to decrease as the amount of Hartree-Fock exact exchange (HFx) increases, in other words, overestimation of calculated J becomes more severe as the HFx increases. We further investigated the effect of HFx fraction of DFT functional on J value, spin contamination, and spin density distributions by comparing the B3LYP analogues containing different amount of HFx. It was revealed that spin contamination and spin densities at each atom increases as the HFx increases. Above all, newly developed BLYP-5 functional, which has 5% of HFx, was found to have the scaling factor of 1.029, indicating that calculated J values are very close to that of experimental values without scaling. BLYP-5 has potential to be utilized for accurate evaluation of intramolecular magnetic coupling constant (J) of diradicals linked by five- or six-membered aromatic ring couplers.

  7. Vibrational Spectroscopy of Intramolecular Hydrogen Bonds in the Infrared and Near-Infrared Regions

    DEFF Research Database (Denmark)

    Schrøder, Sidsel Dahl

    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....... Overtone spectra have been recorded with intracavity laser photoacoustic laser spectroscopy and conventional long path absorption spectroscopy. Theoretically, a combination of electronic structure calculations and local mode models have been employed to guide the assignment of bands in the vibrational......,4-diaminobutane, no sign of intramolecular N-H···N hydrogen bonds were identified in the overtone spectra. However, theoretical analyzes indicate that intramolecular N-H···N hydrogen bonds are present in all three diamines if two hydrogen atoms on one of the methylene groups are substituted with triuoromethyl...

  8. On the nature of intramolecular vibrational energy transfer in dense molecular environments

    Energy Technology Data Exchange (ETDEWEB)

    Benten, Rebekka S. von [Institut fuer Physikalische Chemie der Universitaet Goettingen, Tammannstrasse 6, D-37077 Goettingen (Germany); Abel, Bernd, E-mail: Bernd.Abel@uni-lepzig.de [Wilhelm-Ostwald-Institut fuer Physikalische und Theoretische Chemie, Universitaet Leipzig, Linne-Strasse 2, D-04103 Leipzig (Germany)

    2010-12-09

    Graphical abstract: Mechanisms of IVR in multi-tiers of intramolecular energy levels in different molecular environments are investigated. - Abstract: Transient femtosecond-IR-pump-UV-absorption probe-spectroscopy has been employed to shed light on the nature of intramolecular vibrational energy transfer (IVR) in dense molecular environments ranging from the diluted gas phase to the liquid. A general feature in our experiments and those of others is that IVR proceeds via multiple timescales if overtones or combination vibrations of high frequency modes are excited. It has been found that collisions enhance IVR if its (slower) timescales can compete with collisions. This enhancement is, however, much more weaker and rather inefficient as opposed to the effect of collisions on intermolecular energy transfer which is well known. In a series of experiments we found that IVR depends not significantly on the average energy transferred in a collision but rather on the number of collisions. The collisions are much less efficient in affecting IVR than VET. We conclude that collision induced broadening of vibrational energy levels reduces the energy gaps and enhances existing couplings between tiers. The present results are an important step forward to rationalize and understand apparently different and not consistent results from different groups on different molecular systems between gas and liquid phases.

  9. Understanding perovskite formation through the intramolecular exchange method in ambient conditions

    Science.gov (United States)

    Szostak, Rodrigo; Castro, Jhon A. P.; Marques, Adriano S.; Nogueira, Ana F.

    2017-04-01

    Among the methods to prepare hybrid organic-inorganic perovskite films, the intramolecular exchange method was the first one that made possible to prepare perovskite solar cells with efficiencies higher than 20%. However, perovskite formation by this method is not completely understood, especially in ambient conditions. In this work, perovskite films were prepared by the intramolecular exchange method in ambient conditions. The spin coating speed and the frequency of the MAI solution dripping onto PbI2(DMSO) were varied during the deposition steps. With the combination of these two parameters, a rigid control of the solvent drying was possible. Thus, depending on the chosen conditions, the intermediate MAPb3I8·2DMSO was formed with residual PbI2. Otherwise, direct formation of perovskite film was attained. A mechanism for the direct formation of bulk perovskite was proposed. We also investigated how the posterior thermal annealing affects the crystallinity and defects in perovskite films. With prolonged thermal annealing, the excess of MAI can be avoided, increasing the efficiency and decreasing the hysteresis of the solar cells. The best perovskite solar cell achieved a stabilized power output of 12.9%. The findings of this work pave the way for realizing the fabrication of efficient perovskite solar cells in ambient atmosphere, a very desirable condition for cost-efficient large scale manufacturing of this technology.

  10. Instantaneous normal mode analysis for intermolecular and intramolecular vibrations of water from atomic point of view.

    Science.gov (United States)

    Chen, Yu-Chun; Tang, Ping-Han; Wu, Ten-Ming

    2013-11-28

    By exploiting the instantaneous normal mode (INM) analysis for models of flexible molecules, we investigate intermolecular and intramolecular vibrations of water from the atomic point of view. With two flexible SPC/E models, our investigations include three aspects about their INM spectra, which are separated into the unstable, intermolecular, bending, and stretching bands. First, the O- and H-atom contributions in the four INM bands are calculated and their stable INM spectra are compared with the power spectra of the atomic velocity autocorrelation functions. The unstable and intermolecular bands of the flexible models are also compared with those of the SPC/E model of rigid molecules. Second, we formulate the inverse participation ratio (IPR) of the INMs, respectively, for the O- and H-atom and molecule. With the IPRs, the numbers of the three species participated in the INMs are estimated so that the localization characters of the INMs in each band are studied. Further, by the ratio of the IPR of the H atom to that of the O atom, we explore the number of involved OH bond per molecule participated in the INMs. Third, by classifying simulated molecules into subensembles according to the geometry of their local environments or their H-bond configurations, we examine the local-structure effects on the bending and stretching INM bands. All of our results are verified to be insensible to the definition of H-bond. Our conclusions about the intermolecular and intramolecular vibrations in water are given.

  11. Pericyclic reactions in an aqueous molecular flask.

    Science.gov (United States)

    Murase, Takashi; Fujita, Makoto

    2010-10-01

    A self-assembled molecular flask with a nanometer-sized restricted cavity offers a new reaction environment that is quite different from the bulk solution. The self-assembled cage accommodates a pair of hydrophobic molecules to perform unusual Diels-Alder reactions and [2+2] photoadditions of otherwise unreactive aromatic molecules. In this cage, for example, the Diels-Alder reaction of naphthalene proceeds smoothly under mild conditions, and aceanthrylene shows reactivity for both [2+2] and [2+4] cycloadditions via the identical ternary host-guest complex. The observed greatly enhanced reactivity stems from the increased local concentration and pre-organization of the substrate pair within the cage, which reduces the entropic cost and switches the reaction profile from a bimolecular to a pseudo-intramolecular reaction pathway. The reinforced orientation and arrangement of substrate pairs specify regio- and stereo-selectivities of the subsequent reactions in the cavity. Chiral auxiliaries outside the cage create the inner chiral environment and induce asymmetric reactions inside the cage (up to 50% ee). © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

  12. Correlation among Singlet-Oxygen Quenching, Free-Radical Scavenging, and Excited-State Intramolecular-Proton-Transfer Activities in Hydroxyflavones, Anthocyanidins, and 1-Hydroxyanthraquinones.

    Science.gov (United States)

    Nagaoka, Shin-Ichi; Bandoh, Yuki; Nagashima, Umpei; Ohara, Keishi

    2017-10-26

    Singlet-oxygen ( 1 O 2 ) quenching, free-radical scavenging, and excited-state intramolecular proton-transfer (ESIPT) activities of hydroxyflavones, anthocyanidins, and 1-hydroxyanthraquinones were studied by means of laser, stopped-flow, and steady-state spectroscopies. In hydroxyflavones and anthocyanidins, the 1 O 2 quenching activity positively correlates to the free-radical scavenging activity. The reason for this correlation can be understood by considering that an early step of each reaction involves electron transfer from the unfused phenyl ring (B-ring), which is singly bonded to the bicyclic chromen or chromenylium moiety (A- and C-rings). Substitution of an electron-donating OH group at B-ring enhances the electron transfer leading to activation of the 1 O 2 quenching and free-radical scavenging. In 3-hydroxyflavones, the OH substitution at B-ring reduces the activity of ESIPT within C-ring, which can be explained in terms of the nodal-plane model. As a result, the 1 O 2 quenching and free-radical scavenging activities negatively correlate to the ESIPT activity. A catechol structure at B-ring is another factor that enhances the free-radical scavenging in hydroxyflavones. In contrast to these hydroxyflavones, 1-hydroxyanthraquinones having an electron-donating OH substituent adjacent to the O-H---O═C moiety susceptible to ESIPT do not show a simple correlation between their 1 O 2 quenching and ESIPT activities, because the OH substitution modulates these reactions.

  13. A highly selective turn-on fluorescent probe for hypochlorous acid based on hypochlorous acid-induced oxidative intramolecular cyclization of boron dipyrromethene-hydrazone

    International Nuclear Information System (INIS)

    Chen, Wei-Chieh; Venkatesan, Parthiban; Wu, Shu-Pao

    2015-01-01

    Highlights: • A BODIPY-based fluorescent probe for sensing HOCl was developed. • The probe utilizes the HOCl-promoted cyclization in response to the amount of HOCl. • The probe might have application in the investigation of HOCl in biological systems. - Abstract: A BODIPY-based fluorescent probe, HBP, was developed for the detection of hypochlorous acid based on the specific hypochlorous acid-promoted oxidative intramolecular cyclization of heterocyclic hydrazone in response to the amount of HOCl. The reaction is accompanied by a 41-fold increase in the fluorescent quantum yield (from 0.004 to 0.164). The fluorescence intensity of the reaction between HOCl and HBP is linear in the HOCl concentration range of 1–8 μM with a detection limit of 2.4 nM (S/N = 3). Confocal fluorescence microscopy imaging using RAW264.7 cells showed that the new probe HBP could be used as an effective fluorescent probe for detecting HOCl in living cells

  14. A highly selective turn-on fluorescent probe for hypochlorous acid based on hypochlorous acid-induced oxidative intramolecular cyclization of boron dipyrromethene-hydrazone

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wei-Chieh; Venkatesan, Parthiban; Wu, Shu-Pao, E-mail: spwu@mail.nctu.edu.tw

    2015-07-02

    Highlights: • A BODIPY-based fluorescent probe for sensing HOCl was developed. • The probe utilizes the HOCl-promoted cyclization in response to the amount of HOCl. • The probe might have application in the investigation of HOCl in biological systems. - Abstract: A BODIPY-based fluorescent probe, HBP, was developed for the detection of hypochlorous acid based on the specific hypochlorous acid-promoted oxidative intramolecular cyclization of heterocyclic hydrazone in response to the amount of HOCl. The reaction is accompanied by a 41-fold increase in the fluorescent quantum yield (from 0.004 to 0.164). The fluorescence intensity of the reaction between HOCl and HBP is linear in the HOCl concentration range of 1–8 μM with a detection limit of 2.4 nM (S/N = 3). Confocal fluorescence microscopy imaging using RAW264.7 cells showed that the new probe HBP could be used as an effective fluorescent probe for detecting HOCl in living cells.

  15. Rhodium(II-Catalysed Intramolecular O-H Insertion of a-Diazo-g-Azido-d-Hydroxy-b-Ketoesters: Evidence for a Novel Sigmatropic Rearrangement of an Allylic Azide Intermediate

    Directory of Open Access Journals (Sweden)

    Padwa Albert

    1999-01-01

    Full Text Available The Rh2(OAc4 catalyzed intramolecular O-H insertion reaction of delta-hydroxy-alpha-diazoesters affords 3(2H-furanone-2-carboxylates in good yield but with moderate selectivity (d.e. ca 60%. The initially formed 2,5-substituted cis-furanones were found to epimerize to the corresponding 2,5-trans isomers when subjected to silica gel chromatography. The Rh2(OAc4 catalyzed decomposition of gamma-azido-delta-hydroxy-alpha-diazoesters also furnished 3(2H-furanone-2-carboxylates. These compounds are derived by a sequential O-H insertion reaction followed by a concerted [3,3]-sigmatropic shift of the allylic azide intermediate.

  16. Unprecedented intramolecular [3 + 2] cycloadditions of azido-ketenimines and azido-carbodiimides. Synthesis of indolo[1,2-a]quinazolines and tetrazolo[5,1-b]quinazolines.

    Science.gov (United States)

    Alajarin, Mateo; Bonillo, Baltasar; Ortin, Maria-Mar; Orenes, Raul-Angel; Vidal, Angel

    2011-10-07

    N-(2-azidomethyl)phenyl ketenimines and N-(2-azidomethyl)phenyl-N'-alkyl(aryl) carbodiimides undergo, under mild thermal conditions, intramolecular [3 + 2] cycloaddition reactions between the azido group and either the C=C or the distal C=N double bonds of the ketenimine and carbodiimide functions respectively. The reaction products are indolo[1,2-a]quinazolines and/or indolo[2,1-b]quinazolines in the case of azido-ketenimines, and tetrazolo[5,1-b]quinazolines in the case of azido-carbodiimides. The formation of the two classes of indoloquinazolines implies the ulterior dinitrogen extrusion from the non-isolated, putative [3 + 2] cycloadducts between the azide and ketenimine functions, whereas in the case of azido-carbodiimides the initial cycloadducts, tetrazoloquinazolines, were cleanly isolated and further converted into 2-aminoquinazolines by thermally induced dinitrogen extrusion.

  17. Laccase-catalyzed oxidation and intramolecular cyclization of dopamine: A new method for selective determination of dopamine with laccase/carbon nanotube-based electrochemical biosensors

    International Nuclear Information System (INIS)

    Xiang, Ling; Lin, Yuqing; Yu, Ping; Su, Lei; Mao, Lanqun

    2007-01-01

    This study demonstrates a new electrochemical method for the selective determination of dopamine (DA) with the coexistence of ascorbic acid (AA) and 3,4-dihydroxyphenylacetic acid (DOPAC) with laccase/multi-walled carbon nanotube (MWNT)-based biosensors prepared by cross-linking laccase into MWNT layer confined onto glassy carbon electrodes. The method described here is essentially based on the chemical reaction properties of DA including oxidation, intramolecular cyclization and disproportionation reactions to finally give 5,6-dihydroxyindoline quinone and on the uses of the two-electron and two-proton reduction of the formed 5,6-dihydroxyindoline quinone to constitute a method for the selective determination of DA at a negative potential that is totally separated from those for the redox processes of AA and DOPAC. Instead of the ECE reactions of DA with the first oxidation of DA being driven electrochemically, laccase is used here as the biocatalyst to drive the first oxidation of DA into its quinone form and thus initialize the sequential reactions of DA finally into 5,6-dihydroxyindoline quinone. In addition, laccase also catalyzes the oxidation of AA and DOPAC into electroinactive species with the concomitant reduction of O 2 . As a consequence, a combinational exploitation of the chemical properties inherent in DA and the multifunctional catalytic properties of laccase as well as the excellent electrochemical properties of carbon nanotubes substantially enables the prepared laccase/MWNT-based biosensors to be well competent for the selective determination of DA with the coexistence of physiological levels of AA and DOPAC. This demonstration offers a new method for the selective determination of DA, which could be potentially employed for the determination of DA in biological systems

  18. Nuclear reactions

    International Nuclear Information System (INIS)

    Lane, A.M.

    1980-01-01

    In reviewing work at Harwell over the past 25 years on nuclear reactions it is stated that a balance has to be struck in both experiment and theory between work on cross-sections of direct practical relevance to reactors and on those relevant to an overall understanding of reaction processes. The compound nucleus and direct process reactions are described. Having listed the contributions from AERE, Harwell to developments in nuclear reaction research in the period, work on the optical model, neutron capture theory, reactions at doorway states with fine structure, and sum-rules for spectroscopic factors are considered in more detail. (UK)

  19. Structural effects on the electronic characteristics of intramolecularly intercalated alkali-rubrene complexes

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tsung-Lung, E-mail: quantum@mail.ncyu.edu.tw [Department of Electrophysics, National Chia-Yi University, 300 Hsueh-Fu Road, Chiayi, 60004, Taiwan, ROC (China); Lu, Wen-Cai, E-mail: wencailu@jlu.edu.cn [Laboratory of Fiber Materials and Modern Textile, Growing Base for State Key Laboratory, College of Physics, Qingdao University, Qingdao, Shandong 266071 (China); State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun, Jilin 130021 (China)

    2016-11-01

    The geometric and electronic structures of neutral monolithium- and monosodium-rubrene (Li{sub 1} Rub and Na{sub 1} Rub) isomers are investigated and compared with monopotassium-rubrene (K{sub 1} Rub). Based on the alkali binding site, all isomers of these alkali-rubrene complexes can be subdivided into two types: intramolecularly intercalated and extramolecularly adsorbed. The minimum-energy Li{sub 1} Rub and Na{sub 1} Rub are intercalated structures, whereas the minimum-energy K{sub 1} Rub is adsorbed. The fact that the intercalated Li{sub 1} Rub and Na{sub 1} Rub structures are energetically favorable over the adsorbed ones can be explained by two energy rules. First, “double” proximity of the intercalating alkali element to a pair of phenyl side groups enormously reduces the total energy. Second, accommodation of a minuscule intercalant does not significantly deform the carbon frame and, thus, increases the energy only by a small amount. Additionally, the peculiar effects of intramolecular intercalation on the electronic structures of molecules are also studied in this simulation of monoalkali intercalation. In the monoalkali-intercalated rubrene complex, only one of the two pairs of phenyl groups of rubrene is intercalated, intentionally leaving another pair pristine, which facilitates the comparison of electronic structures between the intercalated and pristine pairs of phenyl side groups in a single molecule. The uniformity of chemical environments of the phenyl groups of the intercalated Li{sub 1} Rub/Na{sub 1} Rub is deteriorated by the incorporation of the intercalant, and leads to their spectral characteristics in contrast to K{sub 1} Rub. In particular, the introduction of the intercalant promotes the carbon 2p orbitals of the intercalated phenyl pair to take part in the electronic structures of the HOMO and LUMO peaks of Li{sub 1} Rub/Na{sub 1} Rub. The unpaired electron in the HOMO is delocalized over the backbone with higher probability of

  20. Structural effects on the electronic characteristics of intramolecularly intercalated alkali-rubrene complexes

    International Nuclear Information System (INIS)

    Li, Tsung-Lung; Lu, Wen-Cai

    2016-01-01

    The geometric and electronic structures of neutral monolithium- and monosodium-rubrene (Li 1 Rub and Na 1 Rub) isomers are investigated and compared with monopotassium-rubrene (K 1 Rub). Based on the alkali binding site, all isomers of these alkali-rubrene complexes can be subdivided into two types: intramolecularly intercalated and extramolecularly adsorbed. The minimum-energy Li 1 Rub and Na 1 Rub are intercalated structures, whereas the minimum-energy K 1 Rub is adsorbed. The fact that the intercalated Li 1 Rub and Na 1 Rub structures are energetically favorable over the adsorbed ones can be explained by two energy rules. First, “double” proximity of the intercalating alkali element to a pair of phenyl side groups enormously reduces the total energy. Second, accommodation of a minuscule intercalant does not significantly deform the carbon frame and, thus, increases the energy only by a small amount. Additionally, the peculiar effects of intramolecular intercalation on the electronic structures of molecules are also studied in this simulation of monoalkali intercalation. In the monoalkali-intercalated rubrene complex, only one of the two pairs of phenyl groups of rubrene is intercalated, intentionally leaving another pair pristine, which facilitates the comparison of electronic structures between the intercalated and pristine pairs of phenyl side groups in a single molecule. The uniformity of chemical environments of the phenyl groups of the intercalated Li 1 Rub/Na 1 Rub is deteriorated by the incorporation of the intercalant, and leads to their spectral characteristics in contrast to K 1 Rub. In particular, the introduction of the intercalant promotes the carbon 2p orbitals of the intercalated phenyl pair to take part in the electronic structures of the HOMO and LUMO peaks of Li 1 Rub/Na 1 Rub. The unpaired electron in the HOMO is delocalized over the backbone with higher probability of distributing over the central two fused rings than over the outer two

  1. Hydrosilylation induced by N→Si intramolecular coordination: spontaneous transformation of organosilanes into 1-aza-silole-type molecules in the absence of a catalyst.

    Science.gov (United States)

    Novák, Miroslav; Dostál, Libor; Alonso, Mercedes; De Proft, Frank; Růžička, Aleš; Lyčka, Antonín; Jambor, Roman

    2014-02-24

    Our attempts to synthesize the N→Si intramolecularly coordinated organosilanes Ph2 L(1) SiH (1 a), PhL(1) SiH2 (2 a), Ph2 L(2) SiH (3 a), and PhL(2) SiH2 (4 a) containing a CH=N imine group (in which L(1) is the C,N-chelating ligand {2-[CH=N(C6 H3 -2,6-iPr2)]C6 H4}(-) and L(2) is {2-[CH=N(tBu)]C6 H4}(-)) yielded 1-[2,6-bis(diisopropyl)phenyl]-2,2-diphenyl-1-aza-silole (1), 1-[2,6-bis(diisopropyl)phenyl]-2-phenyl-2-hydrido-1-aza-silole (2), 1-tert-butyl-2,2-diphenyl-1-aza-silole (3), and 1-tert-butyl-2-phenyl-2-hydrido-1-aza-silole (4), respectively. Isolated organosilicon amides 1-4 are an outcome of the spontaneous hydrosilylation of the CH=N imine moiety induced by N→Si intramolecular coordination. Compounds 1-4 were characterized by NMR spectroscopy and X-ray diffraction analysis. The geometries of organosilanes 1 a-4 a and their corresponding hydrosilylated products 1-4 were optimized and fully characterized at the B3LYP/6-31++G(d,p) level of theory. The molecular structure determination of 1-3 suggested the presence of a Si-N double bond. Natural bond orbital (NBO) analysis, however, shows a very strong donor-acceptor interaction between the lone pair of the nitrogen atom and the formal empty p orbital on the silicon and therefore, the calculations show that the Si-N bond is highly polarized pointing to a predominantly zwitterionic Si(+) N(-) bond in 1-4. Since compounds 1-4 are hydrosilylated products of 1 a-4 a, the free energies (ΔG298), enthalpies (ΔH298), and entropies (ΔH298) were computed for the hydrosilylation reaction of 1 a-4 a with both B3LYP and B3LYP-D methods. On the basis of the very negative ΔG298 values, the hydrosilylation reaction is highly exergonic and compounds 1 a-4 a are spontaneously transformed into 1-4 in the absence of a catalyst. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. A Facial Protocol for the Synthesis of Benzofuran Derivatives by the Reaction of o-Hydroxy Aryl Ketone, Amine and Chloroacetyl Chloride

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Shuai; Wang, Xiuhua; Liu, Jiqiang; Liu, Chang; Chen, Jianbin; Zuo, Hua [Southwest Univ., Chongqing (China); Xie, Yongsheng; Dong, Wenliang; Shin, Dongsoo [Changwon National Univ., Changwon (Korea, Republic of)

    2014-06-15

    A facile and effective method has been developed for the synthesis of a novel series of benzofuran derivatives via N-acylation, O-alkylation and intramolecular condensation reactions, starting from readily available substituted o-hydroxy aryl ketone, and chloroacetyl arylamides. This metal-free transition process is characterized by mild reaction conditions, atom economy, short reaction time and a high yield with a decreased amount of by-products.

  3. Intramolecular Valence and Spin Interaction in meso and rac Diastereomers of a p-Quinonoid-Bridged Diruthenium Complex

    Czech Academy of Sciences Publication Activity Database

    Kumbhakar, D.; Sarkar, B.; Maji, S.; Mobin, S. M.; Fiedler, Jan; Urbanos, F. A.; Jimenez-Aparicio, R.; Kaim, W.; Lahiri, G. K.

    2008-01-01

    Roč. 130, č. 51 (2008), s. 17575-17583 ISSN 0002-7863 R&D Projects: GA MŠk OC 139; GA MŠk LC510 Institutional research plan: CEZ:AV0Z40400503 Keywords : intramolecular valence * spin interaction * diruthenium complex Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 8.091, year: 2008

  4. Environment-sensitive quinolone demonstrating long-lived fluorescence and unusually slow excited-state intramolecular proton transfer kinetics

    Czech Academy of Sciences Publication Activity Database

    Zamotaiev, O. M.; Shvadchak, Volodymyr; Sych, T. P.; Melnychuk, N. A.; Yushchenko, Dmytro A.; Mely, Y.; Pivovarenko, V. G.

    2016-01-01

    Roč. 4, č. 3 (2016), č. článku 034004. ISSN 2050-6120 Institutional support: RVO:61388963 Keywords : quinolone * fluorescent probes * local polarity * hydration * excited-state intramolecular proton transfer * kinetics Subject RIV: CC - Organic Chemistry Impact factor: 2.656, year: 2016

  5. An intramolecular [2 + 2] cycloaddition of ketenimines via palladium-catalyzed rearrangements of N-allyl-ynamides.

    Science.gov (United States)

    DeKorver, Kyle A; Hsung, Richard P; Song, Wang-Ze; Wang, Xiao-Na; Walton, Mary C

    2012-06-15

    A cascade of Pd-catalyzed N-to-C allyl transfer-intramolecular ketenimine-[2 + 2] cycloadditions of N-allyl ynamides is described. This tandem sequence is highly stereoselective and the [2 + 2] cycloaddition could be rendered in a crossed or fused manner depending on alkene substitutions, leading to bridged and fused bicycloimines.

  6. 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

    1980-01-01

    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...

  7. Approach to Interfacial and Intramolecular Electron Transfer of the Diheme Protein Cytochrome c(4) Assembled on Au(111) Surfaces

    DEFF Research Database (Denmark)

    Chi, Qijin; Zhang, Jingdong; Taner, Arslan

    2010-01-01

    in homogeneous solution for which kinetic analysis clearly testifies to electrostatic cooperative effects but no intramolecular, interheme ET higher than 0.1-10 s(-1). This difference suggests a strong gating feature of the process. On the basis of the three-dimensional structure of P. stutzeri cyt c(4), gating...

  8. Intramolecular synergistic effect of glutamic acid, cysteine and glycine against copper corrosion in hydrochloric acid solution

    International Nuclear Information System (INIS)

    Zhang Daquan; Xie Bin; Gao Lixin; Cai Qirui; Joo, Hyung Goun; Lee, Kang Yong

    2011-01-01

    The corrosion protection of copper by glutamic acid, cysteine, glycine and their derivative (glutathione) in 0.5 M hydrochloric acid solution has been studied by the electrochemical impedance spectroscopy and cyclic voltammetry. The inhibition efficiency of the organic inhibitors on copper corrosion increases in the order: glutathione > cysteine > cysteine + glutamic acid + glycine > glutamic acid > glycine. Maximum inhibition efficiency for cysteine reaches about 92.9% at 15 mM concentration level. The glutathione can give 96.4% inhibition efficiency at a concentration of 10 mM. The molecular structure parameters were obtained by PM3 (Parametric Method 3) semi-empirical calculation. The intramolecular synergistic effect of glutamic acid, cysteine and glycine moieties in glutathione is attributed to the lower energy of the lowest unoccupied molecular orbital (E LUMO ) level and to the excess hetero-atom adsorption centers and the bigger coverage on the copper surface.

  9. Theoretical study of γ-aminobutyric acid conformers: Intramolecular interactions and ionization energies

    Science.gov (United States)

    Wang, Ke-Dong; Wang, Mei-Ting; Meng, Ju

    2014-10-01

    Allowing for all combinations of internal single-bond rotamers, 1,296 unique trial structures of γ-Aminobutyric acid (GABA) are obtained. All of these structures are optimized at the M06-2X level of theory and a total of 68 local minimal conformers are found. The nine low-lying conformers are used for further studies. According to the calculated relative Gibbs free energies at M06-2X level of theory, we find that the dispersion is important for the relative energy of GABA. The intramolecular hydrogen bonds and hyperconjugative interaction and their effects on the conformational stability are studied. The results show that both of them have great influence on the conformers. The vertical ionization energies (VIE) are calculated and match the experimental data well. The results show that the neutral GABA in the gas phase is a multi-conformer system and at least four conformations exist.

  10. Phase transition and intramolecular hydrogen bonding in nitro derivatives of ortho-hydroxy acetophenones

    Science.gov (United States)

    Filarowski, A.; Kochel, A.; Koll, A.; Bator, G.; Mukherjee, S.

    2006-03-01

    The crystal structures of two ortho-hydroxy aryl ketones (5-chloro-3-nitro-2-hydroxyacetophenone, 5-methyl-3-nitro-2-hydroxyacetophenone and the complex 5-chloro-3-nitro-2-hydroxyacetophenone with 2-aminobenzoic acid (anthranilic acid)) were determined by X-ray diffraction. The existence of an intramolecular hydrogen bond of enol character between the hydroxyl and acetyl groups was found by the X-ray method. The enol character was also confirmed by DFT (B3LYP/6-31+G(d,p)) calculations. A phase transition was found at 138 K in 5-chloro-3-nitro-2-hydroxyacetophenone. This phase transition was investigated by differential scanning calorimetry (DSC), dilatometry, and the dielectric method. A study of the nitro-group dynamics in the ortho-hydroxy acetophenones was carried out with DFT (B3LYP/6-31+G(d,p)) calculations.

  11. Controlling Long-Lived Triplet Generation from Intramolecular Singlet Fission in the Solid State

    KAUST Repository

    Pace, Natalie A.

    2017-11-30

    The conjugated polymer poly(benzothiophene dioxide) (PBTDO1) has recently been shown to exhibit efficient intramolecular singlet fission in solution. In this paper, we investigate the role of intermolecular interactions in triplet separation dynamics after singlet fission. We use transient absorption spectroscopy to determine the singlet fission rate and triplet yield in two polymers differing only by side chain motif in both solution and the solid state. Whereas solid-state films show singlet fission rates identical to those measured in solution, the average lifetime of the triplet population increases dramatically, and is strongly dependent on side-chain identity. These results show that it may be necessary to carefully engineer the solid-state microstructure of these “singlet fission polymers” in order to produce the long-lived triplets needed to realize efficient photovoltaic devices.

  12. Voltage Losses in Organic Solar Cells: Understanding the Contributions of Intramolecular Vibrations to Nonradiative Recombinations

    KAUST Repository

    Chen, Xiankai

    2017-12-18

    The large voltage losses usually encountered in organic solar cells significantly limit the power conversion efficiencies (PCEs) of these devices, with the result that the current highest PCE values in single-junction organic photovoltaic remain smaller than for other solar cell technologies, such as crystalline silicon or perovskite solar cells. In particular, the nonradiative recombinations to the electronic ground state from the lowest-energy charge-transfer (CT) states at the donor-acceptor interfaces in the active layer of organic devices, are responsible for a significant part of the voltage losses. Here, to better comprehend the nonradiative voltage loss mechanisms, a fully quantum-mechanical rate formula is employed within the framework of time-dependent perturbation theory, combined with density functional theory. The objective is to uncover the specific contributions of intramolecular vibrations to the CT-state nonradiative recombinations in several model systems, which include small-molecule and polymer donors as well as fullerene and nonfullerene acceptors.

  13. Rotational Isomers, Intramolecular Hydrogen Bond, and IR Spectra of o-Vinylphenol Homologs

    Science.gov (United States)

    Glazunov, V. P.; Berdyshev, D. V.; Balaneva, N. N.; Radchenko, O. S.; Novikov, V. L.

    2018-03-01

    The ν(OH) stretching-mode bands in solution IR spectra of five o-vinylphenol (o-VPh) homologs in the slightly polar solvents CCl4 and n-hexane were studied. Several rotamers with free OH groups were found in solutions of o-VPh and its methyl-substituted derivatives in n-hexane. The proportion of rotamers in o-VPh homologs with intramolecular hydrogen bonds (IHBs) O-H...π varied from 22 to 97% in the gas and cyclohexane according to B3LYP/cc-pVTZ calculations. The theoretically estimated effective enthalpies -ΔH of their IHBs varied in the range 0.20-2.24 kcal/mol.

  14. Controlling Long-Lived Triplet Generation from Intramolecular Singlet Fission in the Solid State

    KAUST Repository

    Pace, Natalie A.; Zhang, Weimin; Arias, Dylan H.; McCulloch, Iain; Rumbles, Garry; Johnson, Justin C.

    2017-01-01

    The conjugated polymer poly(benzothiophene dioxide) (PBTDO1) has recently been shown to exhibit efficient intramolecular singlet fission in solution. In this paper, we investigate the role of intermolecular interactions in triplet separation dynamics after singlet fission. We use transient absorption spectroscopy to determine the singlet fission rate and triplet yield in two polymers differing only by side chain motif in both solution and the solid state. Whereas solid-state films show singlet fission rates identical to those measured in solution, the average lifetime of the triplet population increases dramatically, and is strongly dependent on side-chain identity. These results show that it may be necessary to carefully engineer the solid-state microstructure of these “singlet fission polymers” in order to produce the long-lived triplets needed to realize efficient photovoltaic devices.

  15. Intramolecular migration of amide hydrogens in protonated peptides upon collisional activation

    DEFF Research Database (Denmark)

    Jørgensen, Thomas J. D.; Gårdsvoll, H.; Ploug, M.

    2005-01-01

    Presently different opinions exist as to the degree of scrambling of amide hydrogens in gaseous protonated peptides and proteins upon collisional activation in tandem mass spectrometry experiments. This unsettled controversy is not trivial, since only a very low degree of scrambling is tolerable...... if collision-induced dissociation (CID) should provide reliable site-specific information from (1)H/(2)H exchange experiments. We have explored a series of unique, regioselectively deuterium-labeled peptides as model systems to probe for intramolecular amide hydrogen migration under low-energy collisional...... are protected against exchange with the solvent, while the amide hydrogens of the nonbinding sequences exchange rapidly with the solvent. We have utilized such long-lived complexes to generate peptides labeled with deuterium in either the binding or nonbinding region, and the expected regioselectivity...

  16. Functional analysis of propeptide as an intramolecular chaperone for in vivo folding of subtilisin nattokinase.

    Science.gov (United States)

    Jia, Yan; Liu, Hui; Bao, Wei; Weng, Meizhi; Chen, Wei; Cai, Yongjun; Zheng, Zhongliang; Zou, Guolin

    2010-12-01

    Here, we show that during in vivo folding of the precursor, the propeptide of subtilisin nattokinase functions as an intramolecular chaperone (IMC) that organises the in vivo folding of the subtilisin domain. Two residues belonging to β-strands formed by conserved regions of the IMC are crucial for the folding of the subtilisin domain through direct interactions. An identical protease can fold into different conformations in vivo due to the action of a mutated IMC, resulting in different kinetic parameters. Some interfacial changes involving conserved regions, even those induced by the subtilisin domain, blocked subtilisin folding and altered its conformation. Insight into the interaction between the subtilisin and IMC domains is provided by a three-dimensional structural model. Copyright © 2010 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  17. Spectroscopy and intramolecular relaxation of methyl salicylate in its first excited singlet state

    Science.gov (United States)

    Kuper, Jerry W.; Perry, David S.

    1984-05-01

    High resolution fluorescence excitation experiments are reported for the blue emitting rotamer of methyl salicylate in its first excited singlet state. These experiments employ moderate expansions of methyl salicylate seeded in argon ( P0D=5-8 Torr cm) to achieve rotational and vibrational cooling in a pulsed supersonic jet. The rotational contour of the electronic origin at 30 055.3 cm-1 is shown to be consistent with a geometrically distorted π-π* excited state, partially polarized along the A axis and with a rotational temperature of 5-7 K. A noticeable broadening of the spectral features beyond the rotational contour begins at 500 cm-1 above the origin and then increases rapidly above 900 cm-1 reaching a width of 12 cm-1 near 1200 cm-1. The constancy of fluorescence decay lifetimes in this region indicate that intramolecular vibrational relaxation in the S1 manifold is the broadening mechanism.

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

    Science.gov (United States)

    Gonthier, Jérôme F.; Corminboeuf, Clémence

    2014-04-01

    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

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

    International Nuclear Information System (INIS)

    Gonthier, Jérôme F.; Corminboeuf, Clémence

    2014-01-01

    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

  20. Ultrafast intramolecular charge transfer with N-(4-cyanophenyl)carbazole. Evidence for a LE precursor and dual LE + ICT fluorescence.

    Science.gov (United States)

    Galievsky, Victor A; Druzhinin, Sergey I; Demeter, Attila; Mayer, Peter; Kovalenko, Sergey A; Senyushkina, Tamara A; Zachariasse, Klaas A

    2010-12-09

    The photophysics of N-(4-cyanophenyl)carbazole (NP4CN) was investigated by using absorption and fluorescence spectra, picosecond fluorescence decays, and femtosecond transient absorption. In the nonpolar n-hexane as well as in the polar solvent acetonitrile (MeCN), a locally excited (LE) state is detected, as a precursor for the intramolecular charge transfer (ICT) state. A LE → ICT reaction time τ(2) at 22 °C of 0.95 ps in ethyl cyanide (EtCN) and 0.32 ps in MeCN is determined from the decay of the LE excited state absorption (ESA) maximum around 620 nm. In the ESA spectrum of NP4CN in n-hexane at a pump-probe delay time of 100 ps, an important contribution of the LE band remains alongside the ICT band, in contrast to what is observed in EtCN and MeCN. This shows that a LE ⇄ ICT equilibrium is established in this solvent and the ICT reaction time of 0.5 ps is equal to the reciprocal of the sum of the forward and backward ICT rate constants 1/(k(a) + k(d)). In the photostationary S(0) → S(n) absorption spectrum of NP4CN in n-hexane and MeCN, an additional CT absorption band appears, absent in the sum of the spectra of its electron donor (D) and acceptor (A) subgroups carbazole and benzonitrile. This CT band is located at an energy of ∼4000 cm(-1) lower than for N-phenylcarbazole (NPC), due to the larger electron affinity of the benzonitrile moiety of NP4CN than the phenyl subunit of NPC. The fluorescence spectrum of NP4CN in n-hexane at 25 °C mainly consists of a structured LE emission, with a small ICT admixture, indicating that a LE → ICT reaction just starts to occur under these conditions. In di-n-pentyl ether (DPeE) and di-n-butyl ether (DBE), a LE emission is found upon cooling at the high-energy edge of the ICT fluorescence band, caused by the onset of dielectric solvent relaxation. This is not the case in more polar solvents, such as diethyl ether (DEE) and MeCN, in which a structureless ICT emission band fully overlaps the strongly quenched LE

  1. Petasis/Diels-Alder/Cyclization Cascade Reactions for the Generation of Scaffolds with Multiple Stereogenic Centers and Orthogonal Handles for Library Production

    DEFF Research Database (Denmark)

    Flagstad, Thomas; Azevedo, Carlos M. G.; Min, Geanna

    2018-01-01

    A new effective strategy for the synthesis of sp3‐rich small molecules for library production is presented. The key steps to generate complexity highlight Petasis 3‐component reaction followed by an intramolecular Diels‐Alder and cyclization to generate a densely enriched tricyclic or tetracyclic...

  2. N-Iodosuccinimide-Promoted Hofmann-Löffler Reactions of Sulfonimides under Visible Light.

    Science.gov (United States)

    O'Broin, Calvin Q; Fernández, Patricia; Martínez, Claudio; Muñiz, Kilian

    2016-02-05

    Conditions for an attractive and productive protocol for the position-selective intramolecular C-H amination of aliphatic groups (Hofmann-Löffler reaction) are reported employing sulfonimides as nitrogen sources. N-Iodosuccinimide is the only required promoter for this transformation, which is conveniently initiated by visible light. The overall transformation provides pyrrolidines under mild and selective conditions as demonstrated for 17 different substrates.

  3. A Thermal Dehydrogenative Diels–Alder Reaction of Styrenes for the Concise Synthesis of Functionalized Naphthalenes

    Science.gov (United States)

    Kocsis, Laura S.; Benedetti, Erica

    2012-01-01

    Functionalized naphthalenes are valuable building blocks in many important areas. A microwave-assisted, intramolecular dehydrogenative Diels-Alder reaction of styrenyl derivatives to provide cyclopenta[b]naphthalene substructures not previously accessible using existing synthetic methods is described. The synthetic utility of these uniquely functionalized naphthalenes was demonstrated by a single-step conversion of one of these cycloadducts to a fluorophore bearing a structural resemblance to Prodan. PMID:22913473

  4. A thermal dehydrogenative Diels-Alder reaction of styrenes for the concise synthesis of functionalized naphthalenes.

    Science.gov (United States)

    Kocsis, Laura S; Benedetti, Erica; Brummond, Kay M

    2012-09-07

    Functionalized naphthalenes are valuable building blocks in many important areas. A microwave-assisted, intramolecular dehydrogenative Diels-Alder reaction of styrenyl derivatives to provide cyclopenta[b]naphthalene substructures not previously accessible using existing synthetic methods is described. The synthetic utility of these uniquely functionalized naphthalenes was demonstrated by a single-step conversion of one of these cycloadducts to a fluorophore bearing a structural resemblance to Prodan.

  5. Selectivity control in pd-catalyzed c-h functionalization reactions

    OpenAIRE

    Flores Gaspar, Areli

    2013-01-01

    Benzocyclobutenones are an intriguing four-membered ring ketone. In the present thesis, we have developed a new protocol for selectively preparing benzocyclobutenones through intramolecular acylation of aryl bromides via palladium catalyzed C-H bond functionalization reactions based on rac-BINAP ligand. We also found that a subtle modification on the ligand backbone lead to a new catalytic manifold for preparing configurationally-pure styrene derivatives, when using dcpp (bis-dicyclohexylphos...

  6. Pd(II) catalyzed transformation of Schiff bases in complexes of the type trans-[PdCl2(NH2Ar-X)(2)] (X = H, CH3, Cl): Reactivity with aldehydes and Heck coupling reaction

    Czech Academy of Sciences Publication Activity Database

    Kumari, N.; Yadav, V. K.; Záliš, Stanislav; Mishra, L.

    2012-01-01

    Roč. 51, č. 4 (2012), s. 554-563 ISSN 0376-4710 Institutional support: RVO:61388955 Keywords : Schiff base * Palladium * crystal structure Subject RIV: CG - Electrochemistry Impact factor: 0.787, year: 2012

  7. A general strategy for synthesis of cyclophane-braced peptide macrocycles via palladium-catalysed intramolecular sp3 C-H arylation

    Science.gov (United States)

    Zhang, Xuekai; Lu, Gang; Sun, Meng; Mahankali, Madhu; Ma, Yanfei; Zhang, Mingming; Hua, Wangde; Hu, Yuting; Wang, Qingbing; Chen, Jinghuo; He, Gang; Qi, Xiangbing; Shen, Weijun; Liu, Peng; Chen, Gong

    2018-05-01

    New methods capable of effecting cyclization, and forming novel three-dimensional structures while maintaining favourable physicochemical properties are needed to facilitate the development of cyclic peptide-based drugs that can engage challenging biological targets, such as protein-protein interactions. Here, we report a highly efficient and generally applicable strategy for constructing new types of peptide macrocycles using palladium-catalysed intramolecular C(sp3)-H arylation reactions. Easily accessible linear peptide precursors of simple and versatile design can be selectively cyclized at the side chains of either aromatic or modified non-aromatic amino acid units to form various cyclophane-braced peptide cycles. This strategy provides a powerful tool to address the long-standing challenge of size- and composition-dependence in peptide macrocyclization, and generates novel peptide macrocycles with uniquely buttressed backbones and distinct loop-type three-dimensional structures. Preliminary cell proliferation screening of the pilot library revealed a potent lead compound with selective cytotoxicity toward proliferative Myc-dependent cancer cell lines.

  8. Intramolecular electron transfer in cyanide bridged adducts comprising Ru(II)/Ru(III) tetracarboxylate and [Mn(I)(CO)(CN)((t)BuNC)(4)] units.

    Science.gov (United States)

    Imhof, Wolfgang; Sterzik, Anke; Krieck, Sven; Schwierz, Markus; Hoffeld, Thomas; Spielberg, Eike T; Plass, Winfried; Patmore, Nathan

    2010-07-21

    Reaction of mixed valence ruthenium tetracarboxylates [Ru(2)(II,III)(R(1)COO)(2)(R(2)COO)(2)Cl] (R(1) = Me, R(2) = 2,4,6-(i)Pr-Ph or R(1) = R(2) = (t)Bu) with two equivalents of the octahedral manganese complex [Mn(I)(CO)(CN)((t)BuNC)(4)] leads to the formation of cyanide bridged heteronuclear coordination compounds of the general formula {[Ru(2)(II,III)(R(1)COO)(2)(R(2)COO)(2)][Mn(I)(CO)(CN)((t)BuNC)(4)](2)}Cl. In solution an intramolecular electron transfer from manganese towards the multiply bonded Ru(2) core occurs that is verified by EPR and IR spectroscopy, magnetic measurements and DFT calculations. Nevertheless, disproportionation of an initially formed {Mn(I)-Ru(2)(II,III)-Mn(I)}(+) adduct into {Mn(II)-Ru(2)(II,III)-Mn(I)}(2+) and {Mn(I)-Ru(2)(II,II)-Mn(I)} species cannot be completely ruled out.

  9. Synthesis of the AB ring system of clifednamide utilizing Claisen rearrangement and Diels-Alder reaction as key steps.

    Science.gov (United States)

    Loke, Inga; Bentzinger, Guillaume; Holz, Julia; Raja, Aruna; Bhasin, Aman; Sasse, Florenz; Köhn, Andreas; Schobert, Rainer; Laschat, Sabine

    2016-01-21

    In order to construct the functionalized AB ring system of clifednamide, member of the class of macrocyclic tetramic acid lactams, a synthesis was developed which utilized an Ireland-Claisen rearrangement and an intramolecular Diels-Alder reaction. Starting from di-O-isopropylidene-d-mannitol the allyl carboxylate precursor for the sigmatropic rearrangement was prepared. This rearrangement proceeded diastereoselectively only in the presence of an allyl silyl ether instead of the parent enone in the side chain, as suggested by deuteration experiments. A subsequent Diels-Alder reaction yielded the target ethyl hexahydro-1H-indene-carboxylate with high diastereoselectivity. Quantum-chemical investigations of this intramolecular Diels-Alder reaction support the proposed configuration of the final product.

  10. Conditions to obtain precise and true measurements of the intramolecular {sup 13}C distribution in organic molecules by isotopic {sup 13}C nuclear magnetic resonance spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Bayle, Kevin [EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3 (France); Gilbert, Alexis [Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503 (Japan); Earth–Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan); Julien, Maxime [EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3 (France); Yamada, Keita [Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503 (Japan); Silvestre, Virginie; Robins, Richard J.; Akoka, Serge [EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3 (France); Yoshida, Naohiro [Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503 (Japan); Earth–Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan); Remaud, Gérald S., E-mail: gerald.remaud@univ-nantes.fr [EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3 (France)

    2014-10-10

    Highlights: • Evaluation of the trueness and precision criteria of isotopic {sup 13}C NMR spectrometry. • Use of bi-labelled [1,2-{sup 13}C{sub 2}]acetic acid to determine the performance of the instrumental response. • Inter-calibration of the {sup 13}C intramolecular composition of acetic acid using the technique GC-Py–irm-MS. - Abstract: Intramolecular {sup 13}C composition gives access to new information on the (bio) synthetic history of a given molecule. Isotopic {sup 13}C NMR spectrometry provides a general tool for measuring the position-specific {sup 13}C content. As an emerging technique, some aspects of its performance are not yet fully delineated. This paper reports on (i) the conditions required to obtain satisfactory trueness and precision for the determination of the internal {sup 13}C distribution, and (ii) an approach to determining the “absolute” position-specific {sup 13}C content. In relation to (i), a precision of <1% can be obtained whatever the molecule on any spectrometer, once quantitative conditions are met, in particular appropriate proton decoupling efficiency. This performance is a prerequisite to the measurement of isotope fractionation either on the transformed or residual compound when a chemical reaction or process is being studied. The study of the trueness has revealed that the response of the spectrometer depends on the {sup 13}C frequency range of the studied molecule, i.e. the chemical shift range. The “absolute value” and, therefore, the trueness of the {sup 13}C NMR measurements has been assessed on acetic acid and by comparison to the results obtained on the fragments from COOH and CH{sub 3} by isotopic mass spectrometry coupled to a pyrolysis device (GC-Py–irm-MS), this technique being the reference method for acetic acid. Of the two NMR spectrometers used in this work, one gave values that corresponded to those obtained by GC-Py–irm-MS (thus, the “true” value) while the other showed a bias, which was

  11. Quasielastic reactions

    International Nuclear Information System (INIS)

    Henning, W.

    1979-01-01

    Quasielastic reaction studies, because of their capability to microscopically probe nuclear structure, are still of considerable interest in heavy-ion reactions. The recent progress in understanding various aspects of the reaction mechanism make this aim appear closer. The relation between microscopic and macroscopic behavior, as suggested, for example, by the single proton transfer data to individual final states or averaged excitation energy intervals, needs to be explored. It seems particularly useful to extend measurements to higher incident energies, to explore and understand nuclear structure aspects up to the limit of the energy range where they are important

  12. cycloaddition reactions

    Indian Academy of Sciences (India)

    Unknown

    Molecular Modeling Group, Organic Chemical Sciences, Indian Institute of Chemical Technology,. Hyderabad ... thus obtained are helpful to model the regioselectivity ... compromise to model Diels–Alder reactions involving ...... acceptance.

  13. Long-Range Intramolecular Electronic Communication in a Trinuclear Ruthenium Tropolonate Complex.

    Science.gov (United States)

    Yoshida, Jun; Kuwahara, Kyohei; Suzuki, Kota; Yuge, Hidetaka

    2017-02-20

    Dinuclear and trinuclear ruthenium complexes, [Ru(trop) 2 (C 2 trop)Ru(dppe)Cp] [2b; trop = tropolonato, C 2 trop = ethynyltropolonato, dppe = 1,2-bis(diphenylphosphino)ethane] and [Ru(trop){(C 2 trop)Ru(dppe)Cp} 2 ] (3), were synthesized, and their electronic and electrochemical properties were investigated in comparison with our previously reported complex [Ru(acac) 2 (C 2 trop)Ru(dppe)Cp] (2a). The electron-donating Ru II (dppe)Cp unit and electron-accepting Ru III O 6 unit are connected by C 2 trop in these complexes. 2a incorporates acetylacetonate as an ancillary ligand, while 2b and 3 incorporate tropolonate as an ancillary ligand. Every complex, 2a, 2b, and 3, exhibits similar UV-vis-near-IR (NIR) absorption spectra, demonstrating the lack of explicit intramolecular electronic communication between the units at least in the neutral state. The weak NIR absorption in 2a further diminished upon electrochemical oxidation, indicating almost no electronic communication between the units. In contrast, 2b and 3 exhibit broad NIR absorptions upon oxidation. Additionally, 3 exhibits four stepwise redox couples in the electrochemical study, which are formally attributed to [Ru II (trop) 3 ] - /[Ru III (trop) 3 ], two [Ru II (dppe)Cp]/[Ru III (dppe)Cp] + , and [Ru III (trop) 3 ]/[Ru IV (trop) 3 ] + couples. Clear separation of the redox couples attributed to the two terminal [Ru(dppe)Cp] units demonstrates the thermodynamic stability of the intermediate oxidation states with respect to disproportionation. Further electrochemical studies using an electrolyte including perfluorinated weakly coordinating anions and density functional theory/time-dependent density functional theory calculations confirmed the effect of ancillary ligands, acetylacetonate and tropolonate. In the case of 2a, electronic delocalization over the whole complex, especially over the [Ru(acac) 2 (trop)] unit, appears to be small. In contrast, the electronic communication between [Ru(dppe)Cp] and [Ru

  14. Intra-molecular Charge Transfer and Electron Delocalization in Non-fullerene Organic Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qinghe [Department of Chemistry, Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Guangdong 515063, P. R. China; Zhao, Donglin [Department of Chemistry, The James Franck Institute, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, United States; Goldey, Matthew B. [Institute for Molecular Engineering, The University of Chicago, 5747 South Ellis Avenue, Chicago, Illinois 60637, United States; Filatov, Alexander S. [Department of Chemistry, The James Franck Institute, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, United States; Sharapov, Valerii [Department of Chemistry, The James Franck Institute, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, United States; Colón, Yamil J. [Institute for Molecular Engineering, Materials Science Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States; Institute for Molecular Engineering, The University of Chicago, 5747 South Ellis Avenue, Chicago, Illinois 60637, United States; Cai, Zhengxu [Department of Chemistry, The James Franck Institute, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, United States; Chen, Wei [Institute for Molecular Engineering, Materials Science Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States; Institute for Molecular Engineering, The University of Chicago, 5747 South Ellis Avenue, Chicago, Illinois 60637, United States; de Pablo, Juan [Institute for Molecular Engineering, Materials Science Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States; Institute for Molecular Engineering, The University of Chicago, 5747 South Ellis Avenue, Chicago, Illinois 60637, United States; Galli, Giulia [Institute for Molecular Engineering, Materials Science Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States; Institute for Molecular Engineering, The University of Chicago, 5747 South Ellis Avenue, Chicago, Illinois 60637, United States; Yu, Luping [Department of Chemistry, The James Franck Institute, The University of Chicago, 929 E 57th Street, Chicago, Illinois 60637, United States

    2018-03-02

    Two types of electron acceptors were synthesized by coupling two kinds of electron-rich cores with four equivalent perylene diimides (PDIs) at the a position. With fully aromatic cores, TPB and TPSe have pi-orbitals spread continuously over the whole aromatic conjugated backbone, unlike TPC and TPSi, which contain isolated PDI units due to the use of a tetrahedron carbon or silicon linker. Density functional theory calculations of the projected density of states showed that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for TPB are localized in separate regions of space. Further, the LUMO of TPB shows a greater contribution from the orbitals belonging to the connective core of the molecules than that of TPC. Overall, the properties of the HOMO and LUMO point at increased intra-molecular delocalization of negative charge carriers for TPB and TPSe than for TPC and TPSi and hence at a more facile intra-molecular charge transfer for the former. The film absorption and emission spectra showed evidences for the inter -molecular electron delocalization in TPB and TPSe, which is consistent with the network structure revealed by X-ray diffraction studies on single crystals of TPB. These features benefit the formation of charge transfer states and/or facilitate charge transport. Thus, higher electron mobility and higher charge dissociation probabilities under J(sc) condition were observed in blend films of TPB:PTB7-Th and TPSe:PTB7-Th than those in TPC:PTB7Th and TPSi:PTB7-Th blend films. As a result, the J(sc) and fill factor values of 15.02 mA/cm(2), 0.58 and 14.36 mA/cm(2), 0.55 for TPB- and TPSe-based solar cell are observed, whereas those for TPC and TPSi are 11.55 mA/cm2, 0.47 and 10.35 mA/cm(2), 0.42, respectively.

  15. Hydrogen bond strengthening induces fluorescence quenching of PRODAN derivative by turning on twisted intramolecular charge transfer

    Science.gov (United States)

    Yang, Yonggang; Li, Donglin; Li, Chaozheng; Liu, YuFang; Jiang, Kai

    2017-12-01

    Researchers have proposed different effective mechanisms of hydrogen bonding (HB) on the fluorescence of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and its derivatives. Herein, excited state transition and dynamics analysis confirm that the fluorescence of PD (a derivative of PRODAN with ethyl replaced by 3-hydroxy-2,2-dimethylpropan) emits from the planar intramolecular charge transfer (PICT) state rather than twist ICT (TICT) state, because the fluorescence emission and surface hopping from the TICT state to the twist ground (T-S0) state is energy forbidden. Nevertheless, the strengthening of intramolecular-HB (intra-HB) and intermolecular-HB (inter-HB) of PD-(methanol)2 smooth the pathway of surface hopping from TICT to T-S0 state and the external conversion going to planar ground state by decreasing the energy difference of the two states. This smoothing changes the fluorescence state of PD-(methanol)2 to the TICT state in which fluorescence emission does not occur but surface hopping, leading to the partial fluorescence quenching of PD in methanol solvent. This conclusion is different from previous related reports. Moreover, the inter-HB strengthening of PD-methanol in PICT state induces the cleavage of intra-HB and a fluorescence red-shift of 54 nm compared to PD. This red-shift increases to 66 nm for PD-(methanol)2 for the strengthening of the one intra-HB and two inter-HBs. The dipole moments of PD-methanol and PD-(methanol)2 respectively increase about 10.3D and 8.1D in PICT state compared to PD. The synergistic effect of intra-HB and inter-HB induces partial quenching of PD in methanol solvent by turning on the TICT state and fluorescence red-shift. This work gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent, which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics.

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

    International Nuclear Information System (INIS)

    Heredia, Daniel; Otero, Luis; Gervaldo, Miguel; Fungo, Fernando; Dittrich, Thomas; Lin, Chih-Yen; Chi, Liang-Chen; Fang, Fu-Chuan; Wong, Ken-Tsung

    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

  17. 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.

  18. Molecular beam studies of reaction dynamics

    International Nuclear Information System (INIS)

    Lee, Yuan T.

    1991-03-01

    The major thrust of this research project is to elucidate detailed dynamics of simple elementary reactions that are theoretically important and to unravel the mechanism of complex chemical reactions or photochemical processes that play important roles in many macroscopic processes. Molecular beams of reactants are used to study individual reactive encounters between molecules or to monitor photodissociation events in a collision-free environment. Most of the information is derived from measurement of the product fragment energy, angular, and state distributions. Recent activities are centered on the mechanisms of elementary chemical reactions involving oxygen atoms with unsaturated hydrocarbons, the dynamics of endothermic substitution reactions, the dependence of the chemical reactivity of electronically excited atoms on the alignment of excited orbitals, the primary photochemical processes of polyatomic molecules, intramolecular energy transfer of chemically activated and locally excited molecules, the energetics of free radicals that are important to combustion processes, the infrared-absorption spectra of carbonium ions and hydrated hydronium ions, and bond-selective photodissociation through electric excitation

  19. Molecular beam studies of reaction dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y.T. [Lawrence Berkeley Laboratory, CA (United States)

    1993-12-01

    The major thrust of this research project is to elucidate detailed dynamics of simple elementary reactions that are theoretically important and to unravel the mechanism of complex chemical reactions or photochemical processes that play important roles in many macroscopic processes. Molecular beams of reactants are used to study individual reactive encounters between molecules or to monitor photodissociation events in a collision-free environment. Most of the information is derived from measurement of the product fragment energy, angular, and state distributions. Recent activities are centered on the mechanisms of elementary chemical reactions involving oxygen atoms with unsaturated hydrocarbons, the dynamics of endothermic substitution reactions, the dependence of the chemical reactivity of electronically excited atoms on the alignment of excited orbitals, the primary photochemical processes of polyatomic molecules, intramolecular energy transfer of chemically activated and locally excited molecules, the energetics of free radicals that are important to combustion processes, the infrared-absorption spectra of carbonium ions and hydrated hydronium ions, and bond-selective photodissociation through electric excitation.

  20. Remote Stereoinductive Intramolecular Nitrile Oxide Cycloaddition: Asymmetric Total Synthesis and Structure Revision of (-)-11β-Hydroxycurvularin.

    Science.gov (United States)

    Choe, Hyeonjeong; Pham, Thuy Trang; Lee, Joo Yun; Latif, Muhammad; Park, Haeil; Kang, Young Kee; Lee, Jongkook

    2016-03-18

    The first total synthesis and structure revision of (-)-11β-hydroxycurvularin (1b), a macrolide possessing a β-hydroxyketone moiety, were accomplished. The β-hydroxyketone moiety in this natural product was introduced by cleavage of the N-O bond in an isoxazoline ring that was formed diastereoselectively in a 1,5-remote stereocontrolled fashion by employing intramolecular nitrile oxide cycloaddition.

  1. Enantioselective synthesis of chiral 3-aryl-1-indanones through rhodium-catalyzed asymmetric intramolecular 1,4-addition.

    Science.gov (United States)

    Yu, Yue-Na; Xu, Ming-Hua

    2013-03-15

    Enantioselective synthesis of potentially useful chiral 3-aryl-1-indanones was achieved through a rhodium-catalyzed asymmetric intramolecular 1,4-addition of pinacolborane chalcone derivatives using extraordinary simple MonoPhos as chiral ligand under relatively mild conditions. This novel protocol offers an easy access to a wide variety of enantioenriched 3-aryl-1-indanone derivatives in high yields (up to 95%) with excellent enantioselectivities (up to 95% ee).

  2. 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 - others: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

  3. Chromophore-Dependent Intramolecular Exciton-Vibrational Coupling in the FMO Complex: Quantification and Importance for Exciton Dynamics.

    Science.gov (United States)

    Padula, Daniele; Lee, Myeong H; Claridge, Kirsten; Troisi, Alessandro

    2017-11-02

    In this paper, we adopt an approach suitable for monitoring the time evolution of the intramolecular contribution to the spectral density of a set of identical chromophores embedded in their respective environments. We apply the proposed method to the Fenna-Matthews-Olson (FMO) complex, with the objective to quantify the differences among site-dependent spectral densities and the impact of such differences on the exciton dynamics of the system. Our approach takes advantage of the vertical gradient approximation to reduce the computational demands of the normal modes analysis. We show that the region of the spectral density that is believed to strongly influence the exciton dynamics changes significantly in the timescale of tens of nanoseconds. We then studied the impact of the intramolecular vibrations on the exciton dynamics by considering a model of FMO in a vibronic basis and neglecting the interaction with the environment to isolate the role of the intramolecular exciton-vibration coupling. In agreement with the assumptions in the literature, we demonstrate that high frequency modes at energy much larger than the excitonic energy splitting have negligible influence on exciton dynamics despite the large exciton-vibration coupling. We also find that the impact of including the site-dependent spectral densities on exciton dynamics is not very significant, indicating that it may be acceptable to apply the same spectral density on all sites. However, care needs to be taken for the description of the exciton-vibrational coupling in the low frequency part of intramolecular modes because exciton dynamics is more susceptible to low frequency modes despite their small Huang-Rhys factors.

  4. Intramolecularly Protein-Crosslinked DNA Gels: New Biohybrid Nanomaterials with Controllable Size and Catalytic Activity.

    Science.gov (United States)

    Zhou, Li; Morel, Mathieu; Rudiuk, Sergii; Baigl, Damien

    2017-07-01

    DNA micro- and nanogels-small-sized hydrogels made of a crosslinked DNA backbone-constitute new promising materials, but their functions have mainly been limited to those brought by DNA. Here a new way is described to prepare sub-micrometer-sized DNA gels of controllable crosslinking density that are able to embed novel functions, such as an enzymatic activity. It consists of using proteins, instead of traditional base-pairing assembly or covalent approaches, to form crosslinks inside individual DNA molecules, resulting in structures referred to as intramolecularly protein-crosslinked DNA gels (IPDGs). It is first shown that the addition of streptavidin to biotinylated T4DNA results in the successful formation of thermally stable IPDGs with a controllable crosslinking density, forming structures ranging from elongated to raspberry-shaped and pearl-necklace-like morphologies. Using reversible DNA condensation strategies, this paper shows that the gels can be reversibly actuated at a low crosslinking density, or further stabilized when they are highly crosslinked. Finally, by using streptavidin-protein conjugates, IPDGs with various enzymes are successfully functionalized. It is demonstrated that the enzymes keep their catalytic activity upon their incorporation into the gels, opening perspectives ranging from biotechnologies (e.g., enzyme manipulation) to nanomedicine (e.g., vectorization). © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. An Intramolecular Chaperone Inserted in Bacteriophage P22 Coat Protein Mediates Its Chaperonin-independent Folding*

    Science.gov (United States)

    Suhanovsky, Margaret M.; Teschke, Carolyn M.

    2013-01-01

    The bacteriophage P22 coat protein has the common HK97-like fold but with a genetically inserted domain (I-domain). The role of the I-domain, positioned at the outermost surface of the capsid, is unknown. We hypothesize that the I-domain may act as an intramolecular chaperone because the coat protein folds independently, and many folding mutants are localized to the I-domain. The function of the I-domain was investigated by generating the coat protein core without its I-domain and the isolated I-domain. The core coat protein shows a pronounced folding defect. The isolated I-domain folds autonomously and has a high thermodynamic stability and fast folding kinetics in the presence of a peptidyl prolyl isomerase. Thus, the I-domain provides thermodynamic stability to the full-length coat protein so that it can fold reasonably efficiently while still allowing the HK97-like core to retain the flexibility required for conformational switching during procapsid assembly and maturation. PMID:24126914

  6. Ubiquitination of Cdc20 by the APC occurs through an intramolecular mechanism

    Science.gov (United States)

    Foe, Ian T.; Foster, Scott A.; Cheung, Stephanie K.; DeLuca, Steven Z.; Morgan, David O.; Toczyski, David P.

    2012-01-01

    SUMMARY Background Cells control progression through late mitosis by regulating Cdc20 and Cdh1, the two mitotic activators of the Anaphase Promoting Complex (APC). The control of Cdc20 protein levels during the cell cycle is not well understood. Results Here, we demonstrate that Cdc20 is degraded in budding yeast by multiple APC-dependent mechanisms. We find that the majority of Cdc20 turnover does not involve a second activator molecule, but instead depends on in cis Cdc20 autoubiquitination while it is bound to its activator-binding site on the APC core. Unlike in trans ubiquitination of Cdc20 substrates, the APC ubiquitinates Cdc20 independent of APC activation by Cdc20’s C-box. Cdc20 turnover by this intramolecular mechanism is cell cycle-regulated, contributing to the decline in Cdc20 levels that occurs after anaphase. Interestingly, high substrate levels in vitro significantly reduce Cdc20 autoubiquitination. Conclusion We show here that Cdc20 fluctuates through the cell cycle via a distinct form of APC-mediated ubiquitination. This in cis autoubiquitination may preferentially occur in early anaphase, following depletion of Cdc20 substrates. This suggests that distinct mechanisms are able to target Cdc20 for ubiquitination at different points during the cell cycle. PMID:22079111

  7. Rapid long range intramolecular electron transfer within a steroid molecule with two electron binding groups

    International Nuclear Information System (INIS)

    Huddleston, R.K.; Miller, J.R.

    1983-01-01

    Intramolecular electron transfer has been observed to have occurred in less than 100 ns in a steroid molecule having two distinct electron binding groups separated by distances distributed from 7--11 A. Experiments were carried out in organic glasses at 77 K with pulse radiolysis techniques to create trapped electrons which were captured by a group on one end of the steroid molecule. Although one of the groups, benzoate, is held to the steroid spacer by a flexible linkage, the rigidity of the glassy matrices prevented movement to alter the initial distance. Interestingly, no effects of distance were seen: all ET processes appeared to have occurred much faster than our 100 ns time resolution, consistent with measurements of the rate of intermolecular electron transfer between the same functional groups in random solutions. Solvation energetics, on the other hand, had a remarkable influence on the extent and direction of electron transfer. A change in solvent polarity was observed to reverse the direction of electron transfer. Evidence was obtained for a distribution of solvation environments for ions in glasses which may be as broad as 0.15 eV

  8. Intramolecular tautomerisation and the conformational variability of some classical mutagens – cytosine derivatives: quantum chemical study

    Directory of Open Access Journals (Sweden)

    Hovorun D. M.

    2011-04-01

    Full Text Available Aim. To determine the lifetime of the mutagenic cytosine derivatives through the investigation of the physicochemical mechanisms of their intramolecular proton transfer. Methods. Non-empirical quantum chemistry, the analysis of the electron density by means of Bader’s atoms in molecules (AIM theory and physicochemical kinetics were used. Results. It is shown that the modification of all investigated compounds, except DCyt, prevents their pairing in both mutagenic and canonical tautomeric forms with a base which is an interacting partner. This effect can inhibit their mutagenic potential. It is also established that Watson-Crick tautomeric hypothesis can be formally expanded for the investigated molecules so far as a lifetime of the mutagenic tautomers much more exceeds characteristic time for the incorporation of one nucleotides pair by DNA biosynthesis machinery. It seems that just within the frame of this hypothesis it will be possible to give an adequate explanation of the mechanisms of mutagenic action of N4-aminocytosine, N4-methoxycytosine, N4-hydroxycytosine and N4dehydrocytosine, which have much more energy advantageous imino form in comparison with amino form. Conclusions. For the first time the comprehensive conformational analysis of a number of classical mutagens, namely cytosine derivatives, has been performed using the methods of non-empirical quantum chemistry at the MP2/6-311++G (2df,pd//B3LYP/6-311++G(d,p level of theory

  9. Dependency of the regio- and stereoselectivity of intramolecular, ring-closing glycosylations upon the ring size

    Directory of Open Access Journals (Sweden)

    Patrick Claude

    2011-12-01

    Full Text Available Phenyl 3,4,6-tri-O-benzyl-2-O-(3-carboxypropionyl-1-thio-β-D-galactopyranoside (1 was condensed via its pentafluorophenyl ester 2 with 5-aminopentyl (4a, 4-aminobutyl (4b, 3-aminopropyl (4c and 2-aminoethyl 4,6-O-benzylidene-β-D-glucopyranoside (4d, prepared from the corresponding N-Cbz protected glucosides 3a–d, to give the corresponding 2-[3-(alkylcarbamoylpropionyl] tethered saccharides 5a–d. Intramolecular, ring closing glycosylation of the saccharides with NIS and TMSOTf afforded the tethered β(1→3 linked disaccharides 6a–c, the α(1→3 linked disaccharides 7a–d and the α(1→2 linked disaccharide 8d in ratios depending upon the ring size formed during glycosylation. No β(1→2 linked disaccharides were formed. Molecular modeling of saccharides 6–8 revealed that a strong aromatic stacking interaction between the aromatic parts of the benzyl and benzylidene protecting groups in the galactosyl and glucosyl moieties was mainly responsible for the observed regioselectivity and anomeric selectivity of the ring-closing glycosylation step.

  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. Ab initio study on the electronic transport properties of carbon nanotube intramolecular junctions

    Energy Technology Data Exchange (ETDEWEB)

    Wang, R.N. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Graduate School of the Chinese Academy of Sciences, 19A Yu Quan Rd, Beijing 100049 (China); Zheng, X.H.; Zeng, Z. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Song, L.L. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Graduate School of the Chinese Academy of Sciences, 19A Yu Quan Rd, Beijing 100049 (China); School of Electronic Science and Applied Physics, Hefei University of Technology, Hefei 230009 (China)

    2011-12-15

    The effects of electron doping and molecule adsorption on the electronic transport properties of carbon nanotube (CNT) junctions CNT(3,3)/n-CNT(6,0)/CNT(3,3) (n = 1-5) are simulated by first-principles calculations combined with a non-equilibrium Green's function technique. The doping effects are investigated by N substitution for the carbon atom while the molecule adsorption effects are studied by adsorbing a H{sub 2}O molecule or an OH group on the top of one carbon atom, respectively. The transmission function around the Fermi level is highly dependent on the doping or adsorption site. The effects are negligible when the site is at the interface, while it always forms a scattering barrier which causes a valley of the transmission spectra around the Fermi level when the doping/adsorption site is inside the sandwiched CNT(6,0). The conductance of CNT intramolecular junctions is very sensitive to the environment, which may provide potential of application in future nanoelectronic devices and gas sensors. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Spectroscopic and theoretical investigations on intramolecular charge transfer phenomenon in 1-3-dioxolane derivative

    Science.gov (United States)

    Zhang, Zhiyong; Zhang, Zhongzhi; Luo, Yijing; Sun, Shanshan; Zhang, Guangqing

    2018-02-01

    High fluorescence quantum yield (FQY) and large Stokes shift (SS) cannot be easily achieved simultaneously by traditional PICT or TICT fluorescent probe. However, an 1-3-dioxolane derivative named 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO) features both high FQY and large SS. The purpose of this study is to search the mechanism behind this phenomenon by theoretical method. Simulated structure changes and charge transfer suggest ICT process in MDDCO is similar to PLICT (Planarized Intramolecular Charge Transfer) process. Calculated UV-Vis spectra and fluorescence spectra show that PLICT-like state (S1 state) of MDDCO leads to large SS. Computed transient-absorption spectra and radiative decay rates indicate that PLICT-like state is key factor for high FQY of MDDCO. These findings suggest that PLICT-like state in 1,3-dioxolane derivatives can achieve both large SS and high FQY, which presents a new method for high-performance fluorescent probe design.

  13. Ruthenium-modified cytochrome c: temperature dependence of the rate of intramolecular electron transfer

    International Nuclear Information System (INIS)

    Isied, S.S.; Kuehn, C.; Worosila, G.

    1984-01-01

    The ruthenium-modified horse heart cytochrome c, Ru(III)-cyt c(III), where the ruthenium is bound to the histidines-33 residue has been synthesized and characterized by ruthenium analysis, UV-vis and CD spectra, and differential pulse polarography and cyclic voltammetry. The intermediate Ru(III)-cyt c(III) has been generated by pulse-radioanalysis with use of four different radicals, CO 2 -., (CH 3 )COH., (CH 2 OH) 3 CCHOH, and -OCCH(OH)C(OH)CO 2 -. The rate of intramolecular electron transfer within the Ru(III)-cyt c(III) complex and its temperature dependence were determined over a 40 0 C temperature range with the CO 2 -. radical. At 25 0 C, these values are k/sub u/=53 +/- s/sup -1/ (pH 7.01 M phosphate buffer, 0.1 M NaHCO 2 ), ΔH/sup +/=3.5 +/- 0.2 kcal mol/sup -1/, and ΔS/sup +/=-39 +/- 1 eu

  14. Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroanilin

    DEFF Research Database (Denmark)

    Eriksen, J.J.; Sauer, S.P.A.; Mikkelsen, K.V.

    2013-01-01

    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...... the electric dipole moments in the gas phase and for 100 solvent congurations. We find that CAM-B3LYP overestimates the amount of charge separation inherent in the ground state and TDDFT/CAM-B3LYP drastically underestimates this amount in the excited charge-transfer state. As the errors in the solvatochromatic...... 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 measure...

  15. Excited-state intramolecular proton transfer and photoswitching in hydroxyphenyl-imidazopyridine derivatives: A theoretical study

    Science.gov (United States)

    Omidyan, Reza; Iravani, Maryam

    2016-11-01

    The MP2/CC2 and CASSCF theoretical approaches have been employed to determine the excited state proton transfer and photophysical nature of the four organic compounds, having the main frame of hydroxyphenyl-imidzaopyridine (HPIP). The nitrogen insertion effect, in addition to amine (-NH2) substitution has been investigated extensively by following the transition energies and deactivation pathways of resulted HPIP derivatives. It has been predicted that the excited state intramolecular proton transfer with or without small barrier is the most important feature of these compounds. Also, for all of the considered HPIP derivatives, a conical intersection (CI) between ground and the S1 excited state has been predicted. The strong non-adiabatic coupling in the CI (S1/S0), drives the system back to the ground state in which the proton may either return to the phenoxy unit and thus close the photocycle, or the system can continue the twisting motion that results in formation of a γ-photochromic species. This latter species can be responsible for photochromism of HPIP derivative systems.

  16. Molecular dynamics simulations of single siloxane dendrimers: Molecular structure and intramolecular mobility of terminal groups

    Science.gov (United States)

    Kurbatov, A. O.; Balabaev, N. K.; Mazo, M. A.; Kramarenko, E. Yu.

    2018-01-01

    Molecular dynamics simulations of two types of isolated siloxane dendrimers of various generations (from the 2nd to the 8th) have been performed for temperatures ranging from 150 K to 600 K. The first type of dendrimer molecules has short spacers consisting of a single oxygen atom. In the dendrimers of the second type, spacers are longer and comprised of two oxygen atoms separated by a single silicon atom. A comparative analysis of molecular macroscopic parameters such as the gyration radius and the shape factor as well as atom distributions within dendrimer interior has been performed for varying generation number, temperature, and spacer length. It has been found that the short-spacer dendrimers of the 7th and 8th generations have a stressed central part with elongated bonds and deformed valence angles. Investigation of the time evolution of radial displacements of the terminal Si atoms has shown that a fraction of the Si groups have a reduced mobility. Therefore, rather long time trajectories (of the order of tens of nanoseconds) are required to study dendrimer intramolecular dynamics.

  17. Assess the Intra-molecular Cavity in PAMAM Dendrimers by Small Angle Neutron Scattering

    International Nuclear Information System (INIS)

    Chen, Wei-Ren

    2008-01-01

    In this report, we present a contrast variation small angle neutron scattering (SANS) study of a series of neutral PAMAM dendrimer in aqueous solutions using three different generations (G4-6) at a concentration of about 10 mg/ml. Varying the solvent hydrogen-deuterium ratio, the scattering contributions from the water molecules and the constituent components of PAMAM dendrimer can be determined. Using an analytical model of the scattering cross section I(Q) incorporating the effect of water penetration, we have quantified the intra-molecular space of PAMAM dendrimer by evaluating the number of guest water molecules and we draw a direct comparison to computational predictions. As expected, the overall available internal cavity was seen to increase as a function of increasing dendrimer generation. However, the fraction of water accessible volume in the internal cavity of a dendrimer was found to remain invariant for the three generation PAMAM dendrimers studied in this report. We have also estimated the average water density inside a dendrimer, which is found to be higher than that of bulk water

  18. Absence of Intramolecular Singlet Fission in Pentacene-Perylenediimide Heterodimers: The Role of Charge Transfer State.

    Science.gov (United States)

    Wang, Long; Wu, Yishi; Chen, Jianwei; Wang, Lanfen; Liu, Yanping; Yu, Zhenyi; Yao, Jiannian; Fu, Hongbing

    2017-11-16

    A new class of donor-acceptor heterodimers based on two singlet fission (SF)-active chromophores, i.e., pentacene (Pc) and perylenediimide (PDI), was developed to investigate the role of charge transfer (CT) state on the excitonic dynamics. The CT state is efficiently generated upon photoexcitation. However, the resulting CT state decays to different energy states depending on the energy levels of the CT state. It undergoes extremely rapid deactivation to the ground state in polar CH 2 Cl 2 , whereas it undergoes transformation to a Pc triplet in nonpolar toluene. The efficient triplet generation in toluene is not due to SF but CT-mediated intersystem crossing. In light of the energy landscape, it is suggested that the deep energy level of the CT state relative to that of the triplet pair state makes the CT state actually serve as a trap state that cannot undergoes an intramolecular singlet fission process. These results provide guidance for the design of SF materials and highlight the requisite for more widely applicable design principles.

  19. Intermolecular and very strong intramolecular C-SeO/N chalcogen bonds in nitrophenyl selenocyanate crystals.

    Science.gov (United States)

    Wang, Hui; Liu, Ju; Wang, Weizhou

    2018-02-14

    Single-crystal X-ray diffraction reveals that polymorphic ortho-nitrophenyl selenocyanate (o-NSC, crystals 1a and 1b) and monomorphic para-nitrophenyl selenocyanate (p-NSC, crystal 2) crystals are all stabilized mainly by intermolecular and very strong intramolecular C-SeO/N chalcogen bonds, as well as by other different interactions. Thermogravimetric (TG) and differential scanning calorimetry thermogram (DSC) analyses show that the starting decomposition temperatures and melting points of the three crystals are different, following the order 1b > 1a > 2, which is consistent with the structural characteristics of the crystals. In addition, atoms in molecules (AIM) and natural bond orbital (NBO) analyses indicate that the total strengths of the C-SeO and C-SeN chalcogen bonds decrease in the order 1b > 1a > 2. This study could be significant for engineering functional crystals based on robust C-SeO and C-SeN chalcogen bonds, and for designing drugs containing selenium as well as understanding their interaction in biosystems.

  20. The mucin-degradation strategy of Ruminococcus gnavus: The importance of intramolecular trans-sialidases.

    Science.gov (United States)

    Crost, Emmanuelle H; Tailford, Louise E; Monestier, Marie; Swarbreck, David; Henrissat, Bernard; Crossman, Lisa C; Juge, Nathalie

    2016-07-03

    We previously identified and characterized an intramolecular trans-sialidase (IT-sialidase) in the gut symbiont Ruminococcus gnavus ATCC 29149, which is associated to the ability of the strain to grow on mucins. In this work we have obtained and analyzed the draft genome sequence of another R. gnavus mucin-degrader, ATCC 35913, isolated from a healthy individual. Transcriptomics analyses of both ATCC 29149 and ATCC 35913 strains confirmed that the strategy utilized by R. gnavus for mucin-degradation is focused on the utilization of terminal mucin glycans. R. gnavus ATCC 35913 also encodes a predicted IT-sialidase and harbors a Nan cluster dedicated to sialic acid utilization. We showed that the Nan cluster was upregulated when the strains were grown in presence of mucin. In addition we demonstrated that both R. gnavus strains were able to grow on 2,7-anyhydro-Neu5Ac, the IT-sialidase transglycosylation product, as a sole carbon source. Taken together these data further support the hypothesis that IT-sialidase expressing gut microbes, provide commensal bacteria such as R. gnavus with a nutritional competitive advantage, by accessing and transforming a source of nutrient to their own benefit.

  1. 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.

  2. Photoinduced Intramolecular Bifurcate Hydrogen Bond: Unusual Mutual Influence of the Components.

    Science.gov (United States)

    Sigalov, Mark V; Shainyan, Bagrat A; Sterkhova, Irina V

    2017-09-01

    A series of 7-hydroxy-2-methylidene-2,3-dihydro-1H-inden-1-ones with 2-pyrrolyl (3), 4-dimethylaminophenyl (4), 4-nitrophenyl (5), and carboxyl group (6) as substituents at the exocyclic double bond was synthesized in the form of the E-isomers (4-6) or predominantly as the Z-isomer (3) which in solution is converted to the E-isomer. The synthesized compounds and their model analogues were studied by NMR spectroscopy, X-ray analysis, and MP2 theoretical calculations. The E-isomers having intramolecular O-H···O═C hydrogen bond are converted by UV irradiation to the Z-isomers having bifurcated O-H···O···H-X hydrogen bond. Unexpected shortening (and, thus, strengthening) of the O-H···O═C component of the bifurcated hydrogen bond upon the formation of the C═O···H-X hydrogen bond was found experimentally, proved theoretically (MP2), and explained by a roundabout interaction of the H-donor (HX) and H-acceptor (C═O) via the system of conjugated bonds.

  3. Intramolecular energy transfer at donor-acceptor interactions in model and biological membranes

    International Nuclear Information System (INIS)

    Umarova, Fatima T.

    2011-01-01

    Intramolecular triplet-triplet energy transfer between molecules of sensibilisator and photochrome for registration of protein interactions in the membrane preparation of Na,K-ATPase was investigated. Erythrosinithiocyanate (ERITC) was used as the triplet label of sensibilisator, and 4-acetoamido-4 -isothiocyanatostilbene-2,2 disullfonic acid (SITS) was used as the photochrome label. Na,K-ATPase preparations were covalently bound with ERITC in active centre of enzyme, and SITS molecules were covalently bound by NH2-groups. In model system, in chymotrypsinogene molecule, SITS and ERITC labels were used also. The cis-trans-isomerization of SITS was initiated by triplet-triplet energy transfer from light excited ERITC molecule to photochrome. The kinetics of isomerization was recorded by the SITS fluorescence measurements. The constant of rate of triplet-triplet energy transfer from ERITC to cis-isomers of SITS in Na,K-ATPase was determined as (3-7)x10 3 M -1 s -1 , and in model system it equals 1x 10 7 M 1 s -1 . The value of energy transfer between loos molecules of erythrosine and SITS in buffer solution equaled to 7x10 7 M -1 s -1 . This drop of R m y in the membrane preparation of Na,K-ATPase at 10 4 reflected the decrease in the frequency of label collisions caused by the increase in the media viscosity and steric hindrances. (author)

  4. Pentacene Dimers as a Critical Tool for the Investigation of Intramolecular Singlet Fission.

    Science.gov (United States)

    Hetzer, Constantin; Guldi, Dirk M; Tykwinski, Rik R

    2018-01-11

    Singlet fission (SF) involves the spontaneous splitting of a photoexcited singlet state into a pair of triplets, and it holds great promise toward the realization of more efficient solar cells. Although the process of SF has been known since the 1960s, debate regarding the underlying mechanism continues to this day, especially for molecular materials. A number of different chromophores have been synthesized and studied in order to better understand the process of SF. These previous reports have established that pentacene and its derivatives are especially well-suited for the study of SF, since the energetic requirement E(S 1 )≥2E(T 1 ) is fulfilled rendering the process exothermic and unidirectional. Dimeric pentacene derivatives, in which individual pentacene chromophores are tethered by a "spacer", have emerged as the system of choice toward exploring the mechanism of intramolecular singlet fission (iSF). The dimeric structure, and in particular the spacer, allows for controlling and tuning the distance, geometric relationship, and electronic coupling between the two pentacene moieties. This Minireview describes recent advances using pentacene dimers for the investigation of iSF. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Intramolecular singlet-singlet energy transfer in antenna-substituted azoalkanes.

    Science.gov (United States)

    Pischel, Uwe; Huang, Fang; Nau, Werner M

    2004-03-01

    Two novel azoalkane bichromophores and related model compounds have been synthesised and photophysically characterised. Dimethylphenylsiloxy (DPSO) or dimethylnaphthylsiloxy (DNSO) serve as aromatic donor groups (antenna) and the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as the acceptor. The UV spectral window of DBO (250-300 nm) allows selective excitation of the donor. Intramolecular singlet-singlet energy transfer to DBO is highly efficient and proceeds with quantum yields of 0.76 with DPSO and 0.99 with DNSO. The photophysical and spectral properties of the bichromophoric systems suggest that energy transfer occurs through diffusional approach of the donor and acceptor within a van der Waals contact at which the exchange mechanism is presumed to dominate. Furthermore, akin to the behaviour of electron-transfer systems in the Marcus inverted region, a rate of energy transfer 2.5 times slower was observed for the system with the more favourable energetics, i.e. singlet-singlet energy transfer from DPSO proceeded slower than from DNSO, although the process is more exergonic for DPSO (-142 kJ mol(-1) for DPSO versus-67 kJ mol(-1) for DNSO).

  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. Contrasting intermolecular and intramolecular exciplex formation of a 1,4-dicyano-2-methylnaphthalene-N,N-dimethyl-p-toluidine dyad.

    Science.gov (United States)

    Imoto, Mitsutaka; Ikeda, Hiroshi; Fujii, Takayuki; Taniguchi, Hisaji; Tamaki, Akihiro; Takeda, Motonori; Mizuno, Kazuhiko

    2010-05-07

    An intramolecular exciplex is formed upon excitation of the cyclohexane solution of the 1,4-dicyano-2-methylnaphthalene-N,N-dimethyl-p-toluidine dyad, but little if any intramolecular CT complex exists in the ground state of this substance in solution. In contrast, in the crystalline state, the dyad forms an intermolecular mixed-stack CT complex in the ground state and an intermolecular exciplex when it is photoexcited.

  8. Heat conduction in chain polymer liquids: molecular dynamics study on the contributions of inter- and intramolecular energy transfer.

    Science.gov (United States)

    Ohara, Taku; Yuan, Tan Chia; Torii, Daichi; Kikugawa, Gota; Kosugi, Naohiro

    2011-07-21

    In this paper, the molecular mechanisms which determine the thermal conductivity of long chain polymer liquids are discussed, based on the results observed in molecular dynamics simulations. Linear n-alkanes, which are typical polymer molecules, were chosen as the target of our studies. Non-equilibrium molecular dynamics simulations of bulk liquid n-alkanes under a constant temperature gradient were performed. Saturated liquids of n-alkanes with six different chain lengths were examined at the same reduced temperature (0.7T(c)), and the contributions of inter- and intramolecular energy transfer to heat conduction flux, which were identified as components of heat flux by the authors' previous study [J. Chem. Phys. 128, 044504 (2008)], were observed. The present study compared n-alkane liquids with various molecular lengths at the same reduced temperature and corresponding saturated densities, and found that the contribution of intramolecular energy transfer to the total heat flux, relative to that of intermolecular energy transfer, increased with the molecular length. The study revealed that in long chain polymer liquids, thermal energy is mainly transferred in the space along the stiff intramolecular bonds. This finding implies a connection between anisotropic thermal conductivity and the orientation of molecules in various organized structures with long polymer molecules aligned in a certain direction, which includes confined polymer liquids and self-organized structures such as membranes of amphiphilic molecules in water.

  9. Emission Spectroscopy as a Probe into Photoinduced Intramolecular Electron Transfer in Polyazine Bridged Ru(II,Rh(III Supramolecular Complexes

    Directory of Open Access Journals (Sweden)

    Karen J. Brewer

    2010-08-01

    Full Text Available Steady-state and time-resolved emission spectroscopy are valuable tools to probe photochemical processes of metal-ligand, coordination complexes. Ru(II polyazine light absorbers are efficient light harvesters absorbing in the UV and visible with emissive 3MLCT excited states known to undergo excited state energy and electron transfer. Changes in emission intensity, energy or band-shape, as well as excited state lifetime, provide insight into excited state dynamics. Photophysical processes such as intramolecular electron transfer between electron donor and electron acceptor sub-units may be investigated using these methods. This review investigates the use of steady-state and time-resolved emission spectroscopy to measure excited state intramolecular electron transfer in polyazine bridged Ru(II,Rh(III supramolecular complexes. Intramolecular electron transfer in these systems provides for conversion of the emissive 3MLCT (metal-to-ligand charge transfer excited state to a non-emissive, but potentially photoreactive, 3MMCT (metal-to-metal charge transfer excited state. The details of the photophysics of Ru(II,Rh(III and Ru(II,Rh(III,Ru(II systems as probed by steady-state and time-resolved emission spectroscopy will be highlighted.

  10. QTAIM and Stress Tensor Characterization of Intramolecular Interactions Along Dynamics Trajectories of a Light-Driven Rotary Molecular Motor.

    Science.gov (United States)

    Wang, Lingling; Huan, Guo; Momen, Roya; Azizi, Alireza; Xu, Tianlv; Kirk, Steven R; Filatov, Michael; Jenkins, Samantha

    2017-06-29

    A quantum theory of atoms in molecules (QTAIM) and stress tensor analysis was applied to analyze intramolecular interactions influencing the photoisomerization dynamics of a light-driven rotary molecular motor. For selected nonadiabatic molecular dynamics trajectories characterized by markedly different S 1 state lifetimes, the electron densities were obtained using the ensemble density functional theory method. The analysis revealed that torsional motion of the molecular motor blades from the Franck-Condon point to the S 1 energy minimum and the S 1 /S 0 conical intersection is controlled by two factors: greater numbers of intramolecular bonds before the hop-time and unusually strongly coupled bonds between the atoms of the rotor and the stator blades. This results in the effective stalling of the progress along the torsional path for an extended period of time. This finding suggests a possibility of chemical tuning of the speed of photoisomerization of molecular motors and related molecular switches by reshaping their molecular backbones to decrease or increase the degree of coupling and numbers of intramolecular bond critical points as revealed by the QTAIM/stress tensor analysis of the electron density. Additionally, the stress tensor scalar and vector analysis was found to provide new methods to follow the trajectories, and from this, new insight was gained into the behavior of the S 1 state in the vicinity of the conical intersection.

  11. Direct Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Austern, N. [University of Pittsburgh, Pittsburgh, PA (United States)

    1963-01-15

    In order to give a unified presentation of one point of view, these lectures are devoted only to a detailed development of the standard theories of direct reactions, starting from basic principles. Discussion is given of the present status of the theories, of the techniques used for practical calculation, and of possible future developments. The direct interaction (DI) aspects of a reaction are those which involve only a few of the many degrees of freedom of a nucleus. In fact the minimum number of degrees of freedom which must be involved in a reaction are those required to describe the initial and final channels, and DI studies typically consider these degrees of freedom and no others. Because of this simplicity DI theories may be worked out in painstaking detail. DI processes concern only part of the wave function for a problem. The other part involves complicated excitations of many degrees of freedom, and gives the compound nucleus (CN) effects. While it is extremely interesting to learn how to separate DI and CN effects in an orderly manner, if they are both present in a reaction, no suitable method has yet been found. Instead, current work stresses the kinds of reactions and the kinds of final states in which DI effects dominate and in which CN effects may almost be forgotten. The DI cross-sections which are studied are often extremely large, comparable to elastic scattering cross-sections. (author)

  12. Reaction mechanisms

    International Nuclear Information System (INIS)

    Nguyen Trong Anh

    1988-01-01

    The 1988 progress report of the Reaction Mechanisms laboratory (Polytechnic School, France), is presented. The research topics are: the valence bond methods, the radical chemistry, the modelling of the transition states by applying geometric constraints, the long range interactions (ion - molecule) in gaseous phase, the reaction sites in gaseous phase and the mass spectroscopy applications. The points of convergence between the investigations of the mass spectroscopy and the theoretical chemistry teams, as well as the purposes guiding the research programs, are discussed. The published papers, the conferences, the congress communications and the thesis, are also reported [fr

  13. Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

    Science.gov (United States)

    Habershon, Scott

    2016-04-12

    In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles.

  14. Allergic reactions

    Science.gov (United States)

    ... that don't bother most people (such as venom from bee stings and certain foods, medicines, and pollens) can ... person. If the allergic reaction is from a bee sting, scrape the ... more venom. If the person has emergency allergy medicine on ...

  15. Kinetics of isotope exchange reactions involving intra- and intermolecular reactions: 1. Rate law for a system with two chemical compounds and three exchangeable atoms

    International Nuclear Information System (INIS)

    Xuelei Chu; Ohmoto, Hiroshi

    1991-01-01

    For an isotopic exchange reaction between two compounds (X and AB) in a homogeneous system, such as a gaseous or aqueous system, where one (AB) of them possesses two exchangeable atoms in non-equivalent positions and where one intramolecular isotope exchange (A ↔ B) and two intermolecular isotope exchange reactions (X ↔ A and X ↔ B) may occur, its rate law no longer obeys a pseudo-first order rate equation described for simple two-component systems by many previous investigators. The change with time of the δ value of each of the three components (X, A, and B) in a closed and homogeneous system is a complicated function of the initial δ values of the three components, the chemical concentrations of the two compounds, and the overall rate constants of the forward and reverse reactions involving the two intermolecular and one intramolecular reactions of isotope exchanges. Also, for some one of the three components, the change of its δ value with time may not be monotonic, and the relationship of 1n (1 - F) with time may be non-linear in a plot of 1n (1 - F) vs. t. In addition, the rate law of the isotope exchange reaction in this system also provides a quantitative method to estimate the overall rate constants for the one-intra-and two intermolecular isotope exchanges and the equilibrium isotopic fractionation factors among the three components

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

    Directory of Open Access Journals (Sweden)

    Matthew G. Budge

    2011-06-01

    Full Text Available The syntheses and single-crystal structures of Mo(CO3(phen(dipy (1, Mo(CO3(biquin(dipy (2 and Mo(CO3(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 occur in each structure. Crystal data: 1 (C25H17MoN5O3, Mr = 531.38, monoclinic, P21/n (No. 14, Z = 4, a = 11.0965 (5 Å, b = 13.0586 (6 Å, c = 16.6138 (8 Å, b = 108.324 (1°, V = 2285.31 (18 Å3, R(F = 0.035, wR(F2 = 0.070. 2 (C31H21MoN5O3, Mr = 607.47, monoclinic, P21/n (No. 14, Z = 4, a = 11.4788 (6 Å, b = 19.073 (1 Å, c = 11.9881 (6 Å, b = 95.179 (1°, V = 2613.9 (2 Å3, R(F = 0.030, wR(F2 = 0.076. 3 (C24H19MoN5O3, Mr = 521.38, monoclinic, P21/n (No. 14, Z = 4, a = 8.4222 (3 Å, b = 21.5966 (9 Å, c = 12.5011 (5 Å, b = 94.065 (1°, V = 2268.12 (15 Å3, R(F = 0.025, wR(F2 = 0.065.

  17. 1,1,3,3-Tetramethylguanidine solvated lanthanide aryloxides: pre-catalysts for intramolecular hydroalkoxylation.

    Science.gov (United States)

    Janini, Thomas E; Rakosi, Robert; Durr, Christopher B; Bertke, Jeffrey A; Bunge, Scott D

    2009-12-21

    The synthesis and structural characterization of six 1,1,3,3-tetramethylguanidine (H-TMG) solvated lanthanide aryloxide complexes are reported. Ln[N{Si(CH3)3}2]3 (Ln = Nd, La) was reacted with two equivalents of both H-TMG and HOAr {HOAr = HOC6H2(CMe3)2-2,6 (H-DBP) or HOC6H2(CMe3)2-2,6-CH3-4 (H-4MeDBP)} and one equivelent of ethanol (HOEt) to yield the corresponding [Nd(H-TMG)2(4MeDBP)2(OEt)] (1) and [La(H-TMG)2(DBP)2(OEt)] (2). Compounds 1 and 2 were further reacted with 4-pentyn-1-ol {HO(CH2)3C[triple bond]CH} to isolate [Nd(H-TMG)2(4MeDBP)2{O(CH2)3C[triple bond]CH}] (3) and [La(H-TMG)2(DBP)2{O(CH2)3C[triple bond]CH}] (4), respectively. Three equivalents of HOAr and one equivalent of H-TMG were additionally reacted with Ln[N{Si(CH3)3}2]3 to generate [Nd(4MeDBP)3(H-TMG)] (5) and [La(DBP)3(H-TMG)] (6). In order to examine the formation of 1-6, the interaction of H-TMG and HOAr was further examined in solution and the hydrogen bonded complexes (H-TMG:HOAr), 7 and 8, were isolated. Upon successful isolation of 1-6, the utility of 1, 2, 4 and 5 as pre-catalysts for the intramolecular hydroalkoxylation of 4-pentyn-1-ol was investigated. The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, FT-IR spectroscopy, and 1H and 13C NMR investigations.

  18. Weak intramolecular interaction effects on the torsional spectra of ethylene glycol, an astrophysical species

    Energy Technology Data Exchange (ETDEWEB)

    Boussessi, R., E-mail: rahma.boussesi@iem.cfmac.csic.es [Departamento de Química y Física Teóricas, I. Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006 (Spain); Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA LR01ES09, Faculté des sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia); Senent, M. L., E-mail: ml.senent@csic.es [Departamento de Química y Física Teóricas, I. Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006 (Spain); Jaïdane, N. [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA LR01ES09, Faculté des sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia)

    2016-04-28

    An elaborate variational procedure of reduced dimensionality based on explicitly correlated coupled clusters calculations is applied to understand the far infrared spectrum of ethylene-glycol, an astrophysical species. This molecule can be classified in the double molecular symmetry group G{sub 8} and displays nine stable conformers, gauche and trans. In the gauche region, the effect of the potential energy surface anisotropy due to the formation of intramolecular hydrogen bonds is relevant. For the primary conformer, stabilized by a hydrogen bond, the ground vibrational state rotational constants are computed to be A{sub 0} = 15 369.57 MHz, B{sub 0} = 5579.87 MHz, and C{sub 0} = 4610.02 MHz corresponding to differences of 6.3 MHz, 7.2 MHz, and 3.5 MHz from the experimental parameters. Ethylene glycol displays very low torsional energy levels whose classification is not straightforward and requires a detailed analysis of the torsional wavefunctions. Tunneling splittings are significant and unpredictable due to the anisotropy of the potential energy surface PES. The ground vibrational state splits into 16 sublevels separated ∼142 cm{sup −1}. The splitting of the “G1 sublevels” was calculated to be ∼0.26 cm{sup −1} in very good agreement with the experimental data (0.2 cm{sup −1} = 6.95 MHz). Transitions corresponding to the three internal rotation modes allow assignment of previously observed Q branches. Band patterns, calculated between 362.3 cm{sup −1} and 375.2 cm{sup −1}, 504 cm{sup −1} and 517 cm{sup −1}, and 223.3 cm{sup −1} and 224.1 cm{sup −1}, that correspond to the tunnelling components of the v{sub 21} fundamental (v{sub 21} = OH-torsional mode), are assigned to the prominent experimental Q branches.

  19. Spin-selective recombination reactions of radical pairs: Experimental test of validity of reaction operators

    Energy Technology Data Exchange (ETDEWEB)

    Maeda, Kiminori [Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford (United Kingdom); Liddell, Paul; Gust, Devens [Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, 85287-1604 (United States); Hore, P. J. [Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford (United Kingdom)

    2013-12-21

    Spin-selective reactions of radical pairs are conventionally modelled using an approach that dates back to the 1970s [R. Haberkorn, Mol. Phys. 32, 1491 (1976)]. An alternative approach based on the theory of quantum measurements has recently been suggested [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010)]. We present here the first experimental attempt to discriminate between the two models. Pulsed electron paramagnetic resonance spectroscopy has been used to investigate intramolecular electron transfer in the radical pair form of a carotenoid-porphyrin-fullerene molecular triad. The rate of spin-spin relaxation of the fullerene radical in the triad was found to be inconsistent with the quantum measurement description of the spin-selective kinetics, and in accord with the conventional model when combined with spin-dephasing caused by rotational modulation of the anisotropic g-tensor of the fullerene radical.

  20. Synthesis of cyclopentadiene-fused chromanones via one-pot multicomponent reactions.

    Science.gov (United States)

    Ghandi, Mehdi; Ghomi, Ali-Tabatabaei; Kubicki, Maciej

    2013-03-15

    We have developed one-pot method for the synthesis of functionalized novel cyclopentadiene-fused chromanone scaffolds. A variety of 4-oxo-2,4-dihydrocyclopenta[c]chromene-1,2-dicarboxylates were obtained in moderate to good yields via condensation of 2-hydroxybenzaldehydes and ethyl acetoacetate with 1:1 acetylenecarboxylate-isocyanides in toluene. These reactions presumably proceed via reaction of the in situ generated 3-acetyl-2H-chromen-2-ones with acetylenecarboxylate-isocyanide zwitterionic intermediates through Michael addition/intramolecular cyclization and double [1,5] acyl shift rearrangement cascade.

  1. Kinetic isotope effects in reaction of ferment oxidation of tritium-labelled D-galactosamine

    International Nuclear Information System (INIS)

    Akulov, G.P.; Korsakova, N.A.

    1992-01-01

    Primary, secondary and intramolecular kinetic isotopic effects in reaction of ferment oxidation of D-galactosamine labelled by tritium in position 6, were measured. When comparing values of the effects with previously obtained results for similar reaction D-[6- 3 H]galactose, it was ascertained that the presence of aminogroup in galactopyranosyl mainly affects kinetics of substrate-ferment complex formation stage. The possibility to use kinetic isotope effects for increase in molar activity of D-galactosamine, labelled by tritium in position 6, is shown

  2. 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)

    Chu, Hongzhu; He, Lutao; Jiang, Qian; Fang, Yuyu; Jia, Yiming; Yuan, Xiangyang; Zou, Shuliang; Li, Xianghui; Feng, Wen; Yang, Yuanyou; Liu, Ning; Luo, Shunzhong; Yang, Yanqiu; Yang, Liang; Yuan, Lihua

    2014-01-01

    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 3+ , Eu 3+ , Yb 3+ , Th 4+ , and UO 2 2+ has been examined. The results show that 5b and 5c containing only one hydrogen bond with a less hindered rotation spacer extract La 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 3+ and Yb 3+ (or Eu 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 3+ , Th 4+ , UO 2 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

  3. Stereoselective total syntheses of three Lycopodium alkaloids, (-)-magellanine, (+)-magellaninone, and (+)-paniculatine, based on two Pauson-Khand reactions.

    Science.gov (United States)

    Kozaka, Takashi; Miyakoshi, Naoki; Mukai, Chisato

    2007-12-21

    The total syntheses of (-)-magellanine, (+)-magellaninone, and (+)-paniculatine were completed from diethyl l-tartrate via the common intermediate in a stereoselective manner. The crucial steps in these syntheses involved two intramolecular Pauson-Khand reactions of enynes: the first Pauson-Khand reaction constructed the bicyclo[4.3.0] carbon framework, the corresponding A and B rings of these alkaloids in a highly stereoselective manner, whereas the second Pauson-Khand reaction stereoselectively produced the bicyclo[3.3.0]skeleton, which could be converted into the C and D rings of the target natural products.

  4. Diarylhalotelluronium(IV) cations [(8-Me2NC10H6)2TeX]+ (X = Cl, Br, I) stabilized by intramolecularly coordinating N-donor substituents.

    Science.gov (United States)

    Beckmann, Jens; Bolsinger, Jens; Duthie, Andrew; Finke, Pamela

    2013-09-14

    The stoichiometrically controlled halogenation of the intramolecularly coordinated diaryltelluride (8-Me2NC10H6)2Te using SO2Cl2, Br2 and I2 was studied. At an equimolar ratio, the diarylhalotelluronium cations [(8-Me2NC10H6)2TeX](+) (1, X = Cl; 2, X = Br; 3, X = I) formed and were isolated as 1·Cl(-)·H2O·1/2THF, 2·Br(-), and 3·I(-), respectively. When the same reactions were carried out in the presence of KPF6, 1·PF6(-) and 22·Br(-)·PF6(-) were obtained. The chlorination of (8-Me2NC10H6)2Te with an excess of SO2Cl2 occurred with a double electrophilic substitution at the 8-dimethylaminonaphthyl residues (in the ortho- and para-positions) and afforded the diaryltellurium dichloride (5,7-Cl2-8-Me2NC10H4)2TeCl2 (4). The bromination of (8-Me2NC10H6)2Te with three equivalents of Br2 took place with a single electrophilic substitution at the 8-dimethylaminonaphthyl residues (in the para-positions) and provided the diaryltellurium dibromide (5-Br-8-Me2NC10H5)2TeBr2 (5), while an excess of Br2 produced the diarylbromotelluronium cation [(5-Br-8-Me2NC10H5)2TeBr](+) (6) that was isolated as 6·Br3(-). The reaction of (8-Me2NC10H6)2Te with two or three equivalents of iodine provided 3·I3(-) and 3·I3(-)·I2, respectively. In the presence of water, 1·Cl(-)·H2O·1/2THF, 2·Br(-), 3·I(-) and 3·I3(-) hydrolyzed to give the previously known diarylhydroxytelluronium cation [(8-Me2NC10H6)2TeOH](+) (7) that was isolated as 7·Cl(-), 7·Br(-)·H2O·THF, 7·I(-) and 7·I3(-)·H2O, respectively. The molecular structures of 1-7 were investigated in the solid-state by (125)Te MAS NMR spectroscopy and X-ray crystallography and in solution by multinuclear NMR spectroscopy ((1)H, (13)C, (125)Te), electrospray mass spectrometry and conductivity measurements. The stabilization of cations 1-3 by the intramolecular coordination was estimated by DFT calculations at the B3PW91/TZ level of theory.

  5. Molecular eigenstate spectroscopy: Application to the intramolecular dynamics of some polyatomic molecules in the 3000 to 7000 cm{sup {minus}1} region

    Energy Technology Data Exchange (ETDEWEB)

    Perry, D.S. [Univ. of Akron, OH (United States)

    1993-12-01

    Intramolecular vibrational redistribution (IVR) appears to be a universal property of polyatomic molecules in energy regions where the vibrational density of states is greater than about 5 to 30 states per cm{sup {minus}1}. Interest in IVR stems from its central importance to the spectroscopy, photochemistry, and reaction kinetics of these molecules. A bright state, {var_phi}{sub s}, which may be a C-H stretching vibration, carries the oscillator strength from the ground state. This bright state may mix with bath rotational-vibrational levels to form a clump of molecular eigenstates, each of which carries a portion of the oscillator strength from the ground state. In this work the authors explicitly resolve transitions to each of these molecular eigenstates. Detailed information about the nature of IVR is contained in the frequencies and intensities of the observed discrete transitions. The primary goal of this research is to probe the coupling mechanisms by which IVR takes place. The most fundamental distinction to be made is between anharmonic coupling which is independent of molecular rotation and rotationally-mediated coupling. The authors are also interested in the rate at which IVR takes place. Measurements are strictly in the frequency domain but information is obtained about the decay of the zero order state, {var_phi}{sub s}, which could be prepared in a hypothetical experiment as a coherent excitation of the clump of molecular eigenstates. As the coherent superposition dephases, the energy would flow from the initially prepared mode into nearby overtones and combinations of lower frequency vibrational modes. The decay of the initially prepared mode is related to a pure sequence infrared absorption spectrum by a Fourier transform.

  6. Intramolecular, Exciplex-Mediated, Proton-Coupled, Charge-Transfer Processes in N,N-Dimethyl-3-(1-pyrenyl)propan-1-ammonium Cations: Influence of Anion, Solvent Polarity, and Temperature.

    Science.gov (United States)

    Safko, Trevor M; Faleiros, Marcelo M; Atvars, Teresa D Z; Weiss, Richard G

    2016-06-16

    An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been investigated for a series of N,N-dimethyl-3-(1-pyrenyl)propan-1-ammonium cations with different anions (PyS) in solvents of low to intermediate polarity over a wide temperature range. Solvent mediates both the equilibrium between conformations of the cation that place the pyrenyl and ammonium groups in proximity (conformation C) or far from each other (conformation O) and the ability of the ammonium group to transfer a proton adiabatically in the PyS excited singlet state. Thus, exciplex emission, concurrent with the PCCT process, was observed only in hydrogen-bond accepting solvents of relatively low polarity (tetrahydrofuran, ethyl acetate, and 1,4-dioxane) and not in dichloromethane. From the exciplex emission and other spectroscopic and thermodynamic data, the acidity of the ammonium group in conformation C of the excited singlet state of PyS (pKa*) has been estimated to be ca. -3.4 in tetrahydrofuran. The ratios between the intensities of emission from the exciplex and the locally excited state (IEx/ILE) appear to be much more dependent on the nature of the anion than are the rates of exciplex formation and decay, although the excited state data do not provide a quantitative measure of the anion effect on the C-O equilibrium. The activation energies associated with exciplex formation in THF are calculated to be 0.08 to 0.15 eV lower than for the neutral amine, N,N-dimethyl-3-(1-pyrenyl)propan-1-amine. Decay of the exciplexes formed from the deprotonation of PyS is hypothesized to occur through charge-recombination processes. To our knowledge, this is the first example in which photoacidity and intramolecular exciplex formation (i.e., a PCCT reaction) are coupled.

  7. On the intramolecular origin of the blue shift of A-H stretching frequencies: triatomic hydrides HAX.

    Science.gov (United States)

    Karpfen, Alfred; Kryachko, Eugene S

    2009-04-30

    A series of intermolecular complexes formed between the triatomic hydrides HAX and various interaction partners are investigated computationally aiming (1) to demonstrate that either an appearance or nonappearance of a blue shift of the A-H stretching frequency is directly related to the sign of the intramolecular coupling that exists between the two degrees of freedom, the A-H and A-X bond lengths, and (2) to offer the following conjecture: the theoretical protonation of a triatomic neutral molecule HAX at the site X is a simple and rather efficient probe of a red or blue shift that the stretching frequency nu(A-H) undergoes upon complex formation regardless of whether this bond is directly involved in hydrogen bonding or not. In other words, to predict whether this A-H bond is capable to display a blue or red shift of nu(A-H), it suffices to compare the equilibrium structures and vibrational spectra of a given molecule with its protonated counterpart. The two above goals are achieved invoking a series of 11 triatomic molecules: HNO, HSN, HPO, and HPS characterized by a negative intramolecular coupling; HON and HNS as intermediate cases; and HOF, HOCl, HCN, HNC, and HCP with a positive intramolecular coupling. For these purposes, the latter molecules are investigated at the MP2/6-311++G(2p,2d) level in the neutral and protonated HAXH(+) forms as well as their complexes with H(2)O and with the fluoromethanes H(3)CF, H(2)CF(2), and HCF(3).

  8. Direct electrochemistry and intramolecular electron transfer of ascorbate oxidase confined on L-cysteine self-assembled gold electrode.

    Science.gov (United States)

    Patil, Bhushan; Kobayashi, Yoshiki; Fujikawa, Shigenori; Okajima, Takeyoshi; Mao, Lanqun; Ohsaka, Takeo

    2014-02-01

    A direct electrochemistry and intramolecular electron transfer of multicopper oxidases are of a great importance for the fabrication of these enzyme-based bioelectrochemical-devices. Ascorbate oxidase from Acremonium sp. (ASOM) has been successfully immobilized via a chemisorptive interaction on the l-cysteine self-assembled monolayer modified gold electrode (cys-SAM/AuE). Thermodynamics and kinetics of adsorption of ASOM on the cys-SAM/AuE were studied using cyclic voltammetry. A well-defined redox wave centered at 166±3mV (vs. Ag│AgCl│KCl(sat.)) was observed in 5.0mM phosphate buffer solution (pH7.0) at the fabricated ASOM electrode, abbreviated as ASOM/cys-SAM/AuE, confirming a direct electrochemistry, i.e., a direct electron transfer (DET) between ASOM and cys-SAM/AuE. The direct electrochemistry of ASOM was further confirmed by taking into account the chemical oxidation of ascorbic acid (AA) by O2 via an intramolecular electron transfer in the ASOM as well as the electrocatalytic oxidation of AA at the ASOM/cys-SAM/AuE. Thermodynamics and kinetics of the adsorption of ASOM on the cys-SAM/AuE have been elaborated along with its direct electron transfer at the modified electrodes on the basis of its intramolecular electron transfer and electrocatalytic activity towards ascorbic acid oxidation and O2 reduction. ASOM saturated surface area was obtained as 2.41×10(-11)molcm(-2) with the apparent adsorption coefficient of 1.63×10(6)Lmol(-1). The ASOM confined on the cys-SAM/AuE possesses its essential enzymatic function. © 2013.

  9. Quasielastic reactions

    International Nuclear Information System (INIS)

    Hansen, O.

    1983-01-01

    A brief review is presented of the experimental and theoretical situation regarding transfer reactions and inelastic scattering. In the first category there is little (very little) precision data for heavy projectiles and consequently almost no experience with quantitative theoretical analysis. For the inelastic scattering the rather extensive data strongly supports the coupled channels models with collective formfactors. At the most back angles, at intensities about 10 -5 of Rutherford scattering, a second, compound-like mechanism becomes dominant. The description of the interplay of these two opposite mechanisms provides a new challenge for our understanding

  10. Estudio computacional de transferencia electrónica intramolecular en tríadas conjugadas ferroceno-puente-aceptor

    OpenAIRE

    García López, Rafaela

    2016-01-01

    En el presente trabajo se analiza, desde el punto de vista teórico a través de cálculos mecanocuánticos, el comportamiento dador del ferroceno, de potencial utilidad en procesos de reconocimiento de cationes metálicos, así como la estabilización de deficiencias electrónicas en  a grupos ferrocenilo. Esto permite el estudio del fenómeno de transferencia electrónica intramolecular en diferentes tríadas ferroceno-puente-aceptor, así como el efecto de la naturaleza y longitud de espaciadores -c...

  11. 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)

    Perry, D.S.

    1991-05-01

    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

  12. Collisional activation by MALDI tandem time-of-flight mass spectrometry induces intramolecular migration of amide hydrogens in protonated peptides

    DEFF Research Database (Denmark)

    Jørgensen, Thomas J D; Bache, Nicolai; Roepstorff, Peter

    2005-01-01

    of doubly protonated peptides that the original regioselective deuterium pattern of these peptides is completely erased (Jørgensen, T. J. D., Gårdsvoll, H., Ploug, M., and Roepstorff, P. (2005) Intramolecular migration of amide hydrogens in protonated peptides upon collisional activation. J. Am. Chem. Soc...... randomization among all exchangeable sites (i.e. all N- and O-linked hydrogens) also occurs upon high energy collisional activation of singly protonated peptides. This intense proton/deuteron traffic precludes the use of MALDI tandem time-of-flight mass spectrometry to obtain reliable information...

  13. Coherent pulse and environmental characteristics of the intramolecular proton-transfer lasers based on 3-hydroxyflavone and fisetin

    Science.gov (United States)

    Parthenopoulos, Dimitri A.; Kasha, Michael

    1988-04-01

    Coherent stimulated emission and laser beams of good quality are reported for 3-hydroxyfiavone (3-HF) and a polyhydroxyfiavone, risetin, acting as intramolecular proton-transfer lasers. The laser beam quality of these materials is comparable to that observed for rhodamine-6G. Studies of amplified spontaneous emission of 3-hydroxyflavone in highly polar solvents are also reported. The very large changes in dipole moment upon electronic excitation of 3-HF expected according to ZINDO semiempirical molecular orbital calculations fail to give rise to spectral shifts in the high dielectric constant solvents. The results are interpreted as a masking spectral effect caused by specific hydrogen bonding by the solvent.

  14. Relaxation dynamics in quantum dissipative systems: The microscopic effect of intramolecular vibrational energy redistribution

    Energy Technology Data Exchange (ETDEWEB)

    Uranga-Piña, L. [Facultad de Física, Universidad de la Habana, San Lázaro y L, Vedado, 10400 Havana (Cuba); Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustr. 3, D-14195 Berlin (Germany); Tremblay, J. C., E-mail: jean.c.tremblay@gmail.com [Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustr. 3, D-14195 Berlin (Germany)

    2014-08-21

    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

  15. NMR of proteins (4Fe-4S): structural properties and intramolecular electron transfer

    International Nuclear Information System (INIS)

    Huber, J.G.

    1996-01-01

    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-(S γ -C β -H β )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

  16. 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

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

    KAUST Repository

    Shen, Chao; Xia, Haijun; Yan, Hua; Chen, Xinzhi; Ranjit, Sadananda; Xie, Xiaoji; Tan, Davin; Lee, Richmond; Yang, Yanmei; Xing, Bengang; Huang, Kuo-Wei; Zhang, Pengfei; Liu, Xiaogang

    2012-01-01

    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.

  18. Nuclear reactions

    International Nuclear Information System (INIS)

    Corner, J.; Richardson, K.; Fenton, N.

    1990-01-01

    Nuclear reactions' marks a new development in the study of television as an agency of public policy debate. During the Eighties, nuclear energy became a major international issue. The disasters at Three-mile Island and Chernobyl created a global anxiety about its risks and a new sensitivity to it among politicians and journalists. This book is a case-study into documentary depictions of nuclear energy in television and video programmes and into the interpretations and responses of viewers drawn from many different occupational groupings. How are the complex and specialist arguments about benefit, risk and proof conveyed through the different conventions of commentary, interview and film sequence? What symbolic associations does the visual language of television bring to portrayals of the issue? And how do viewers make sense of various and conflicting accounts, connecting what they see and hear on the screen with their pre-existing knowledge, experience and 'civic' expectations. The authors examine some of the contrasting forms and themes which have been used by programme makers to explain and persuade, and then give a sustained analysis of the nature and sources of viewers' own accounts. 'Nuclear Reactions' inquires into the public meanings surrounding energy and the environment, spelling out in its conclusion some of the implications for future media treatments of this issue. It is also a key contribution to the international literature on 'television knowledge' and the processes of active viewing. (author)

  19. Spallation reactions; Reactions de spallation

    Energy Technology Data Exchange (ETDEWEB)

    Cugon, J.

    1996-12-31

    Spallation reactions dominate the interactions of hadrons with nuclei in the GeV range (from {approx} 0.1 to {approx} 10 GeV). They correspond to a sometimes important ejection of light particles leaving most of the time a residue of mass commensurate with the target mass. The main features of the experimental data are briefly reviewed. The most successful theoretical model, namely the intranuclear cascade + evaporation model, is presented. Its physical content, results and possible improvements are critically discussed. Alternative approaches are shortly reviewed. (author). 84 refs.

  20. Comparison of IRMS and NMR spectrometry for the determination of intramolecular 13C isotope composition: application to ethanol.

    Science.gov (United States)

    Gilbert, Alexis; Hattori, Ryota; Silvestre, Virginie; Wasano, Nariaki; Akoka, Serge; Hirano, Satoshi; Yamada, Keita; Yoshida, Naohiro; Remaud, Gérald S

    2012-09-15

    Isotopic (13)C NMR is a relatively recent technique which allows the determination of intramolecular (13)C isotope composition at natural abundance. It has been used in various scientific fields such as authentication, counterfeiting or plant metabolism. Although its precision has already been evaluated, the determination of its trueness remains still challenging. To deal with that issue, a comparison with another normalized technique must be achieved. In this work, we compare the intramolecular (13)C isotope distribution of ethanol from different origins obtained using both Isotope Ratio Mass Spectrometry (IRMS) and Nuclear Magnetic Resonance (NMR) spectrometry techniques. The IRMS approach consists of the oxidation of ethanol to acetic acid followed by the degradation of the latter for the analysis of each fragments formed. We show here that the oxidation of ethanol to acetic acid does not bring any significant error on the determination of the site-specific δ(13)C (δ(13)C(i)) of ethanol using the IRMS approach. The difference between the data obtained for 16 samples from different origins using IRMS and NMR approaches is not statistically significant and remains below 0.3‰. These results are encouraging for the future studies using isotopic NMR, especially in combination with the IRMS approach. Copyright © 2012. Published by Elsevier B.V.

  1. Detection of Intramolecular Charge Transfer and Dynamic Solvation in Eosin B by Femtosecond Two-Dimensional Electronic Spectroscopy

    Science.gov (United States)

    Ghosh, Soumen; Roscioli, Jerome D.; Beck, Warren F.

    2014-06-01

    We have employed 2D electronic photon echo spectroscopy to study intramolecular charge-transfer dynamics in eosin B. After preparation of the first excited singlet state (S_1) with 40-fs excitation pulses at 520 nm, the nitro group (--NO_2) in eosin B undergoes excited state torsional motion towards a twisted intramolecular charge transfer (TICT) state. As the viscosity of the surrounding solvent increases, the charge-transfer rate decreases because the twisting of the --NO_2 group is hindered. These conclusions are supported by the time evolution of the 2D spectrum, which provides a direct measure of the the ground-to-excited-state energy gap time-correlation function, M(t). In comparison to the inertial and diffusive solvation time scales exhibited by eosin Y, which lacks the nitro group, the M(t) function for eosin B exhibits under the same conditions an additional component on the 150-fs timescale that arises from quenching of the S_1 state by crossing to the TICT state. These results indicate that 2D electronic spectroscopy can be used as a sensitive probe of the rate of charge transfer in a molecular system and of the coupling to the motions of the surrounding solvent. (Supported by grant DE-SC0010847 from the Department of Energy, Office of Basic Energy Sciences, Photosynthetic Systems program.)

  2. Study of intramolecular isotope heterogeneity of organic oxy acids in order to detect sophisticated wines and juice drinks

    Directory of Open Access Journals (Sweden)

    Kuzmina Helen

    2014-01-01

    Full Text Available According to International Code of Oenological Practices it is allowed to use acide L(+tartrique for wine acidification, while use of synthetic dihydroxysuccinic acid is forbidden. Today it is impossible to differentiate natural dihydroxysuccinic acid from synthetic one by standard techniques. Even by using very sensitive method of isotope mass spectrometry certain difficulties emerge because total isotope characteristics of carbon of dihydroxysuccinic acid of different nature have the same values. However, isotope characteristics of carbon of intramolecular structural groups of dihydroxysuccinic acid made of different raw materials differ significantly. This allows specifying the nature of dihydroxysuccinic acid that is used for making of wines and juice drinks. In Russia, scientific and research institute of beer brewing and wine-making industry carried out a work for studying isotope characteristics of intramolecular isotope heterogeneity of dihydroxysuccinic acid from different origins in order to identify wines and juice drinks. Isotope characteristics of organic oxy acids from different origins were studied including them obtained by synthetic way and numeric range of value δ13 C,‰ were specified. The obtained results allow performing identification tests of wines and juice drinks to find out the products that contain not specified additives as that allowed for its use in production process.

  3. The effect of intramolecular donor–acceptor moieties with donor–π-bridge–acceptor structure on the solar photovoltaic performance

    Directory of Open Access Journals (Sweden)

    T. L. Wang

    2015-10-01

    Full Text Available A series of intramolecular donor–acceptor polymers containing different contents of (E-1-(2-ethylhexyl-6,9-dioctyl-2-(2-(thiophen-3-ylvinyl-1H-phenanthro[9,10-d]imidazole (thiophene-DOPI moiety and 4,4-diethylhexylcyclopenta[ 2,1-b:3,4-b']dithiophene (CPDT unit was synthesized via Grignard metathesis (GRIM polymerization. The synthesized random copolymers and homopolymer of thiophene-DOPI contain the donor–π-bridge–acceptor conjugated structure to tune the absorption spectra and energy levels of the resultant polymers. UV-vis spectra of the three polymer films exhibit panchromatic absorptions ranging from 300 to 1100 nm and low band gaps from 1.38 to 1.51 eV. It is found that more thiophene-DOPI moieties result in the decrease of band gap and lower the highest occupied molecular orbital (HOMO and lowest unoccupied molecular orbital (LUMO values of polymers. Photovoltaic performance results indicate that if the content of the intramolecular donor–acceptor moiety is high enough, the copolymer structure may be better than homopolymer due to more light-harvesting afforded by both monomer units.

  4. Diffracted X-ray tracking for monitoring intramolecular motion in individual protein molecules using broad band X-ray

    Energy Technology Data Exchange (ETDEWEB)

    Ichiyanagi, Kouhei; Sasaki, Yuji C. [Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 609 Kiban Building 5-1-5 Kashiwanoha, Kahiwashi, Chiba 277-8561 (Japan); Japan Science and Technology Agency, CREST, CREST, Sasaki-Team, 609 Kiban Building, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Sekiguchi, Hiroshi; Hoshino, Masato; Kajiwara, Kentaro; Senba, Yasunori; Ohashi, Haruhiko; Ohta, Noboru [Japan Synchrotron Radiation Research Institute, SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198 (Japan); Hoshisashi, Kentaro; Jae-won, Chang; Tokue, Maki; Matsushita, Yufuku [Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 609 Kiban Building 5-1-5 Kashiwanoha, Kahiwashi, Chiba 277-8561 (Japan); Nishijima, Masaki; Inoue, Yoshihisa [Department of Applied Chemistry and Office for University-Industry Collaboration, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Yagi, Naoto [Japan Science and Technology Agency, CREST, CREST, Sasaki-Team, 609 Kiban Building, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Japan Synchrotron Radiation Research Institute, SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198 (Japan)

    2013-10-15

    Diffracted X-ray tracking (DXT) enables the tilting and twisting motions of single protein molecules to be monitored with micro- to milliradian resolution using a highly brilliant X-ray source with a wide energy bandwidth. We have developed a technique to monitor single molecules using gold nanocrystals attached to individual protein molecules using the BL28B2 beamline at SPring-8. In this paper we present the installation of a single toroidal X-ray mirror at BL28B2 to focus X-rays in an energy range of 10–20 keV (△E/E = 82% for an X-ray with a wide energy bandwidth). With this beamline we tracked diffraction spots from gold nanocrystals over a wide angle range than that using quasi-monochromatic X-rays. Application of the wide angle DXT technique to biological systems enabled us to observe the on-site motions of single protein molecules that have been functionalized in vivo. We further extend the capability of DXT by observing the fractional tilting and twisting motions of inner proteins under various conditions. As a proof of this methodology and to determine instrumental performance the intramolecular motions of a human serum albumin complex with 2-anthracenecarboxylic acid was investigated using the BL28B2 beamline. The random tilting and twisting intramolecular motions are shown to be directly linked to the movement of individual protein molecules in the buffer solution.

  5. What the heck is a Theremin?

    Science.gov (United States)

    Lambdin, Ken

    2009-10-01

    This talk will in introduce the Theremin, one of the first electronic musical instruments. The inner workings of the instrument will be examined, explaining how this bizarre instrument can be played without any physical contact!

  6. Chain reaction

    International Nuclear Information System (INIS)

    Balogh, Brian.

    1991-01-01

    Chain Reaction is a work of recent American political history. It seeks to explain how and why America came to depend so heavily on its experts after World War II, how those experts translated that authority into political clout, and why that authority and political discretion declined in the 1970s. The author's research into the internal memoranda of the Atomic Energy Commission substantiates his argument in historical detail. It was not the ravages of American anti-intellectualism, as so many scholars have argued, that brought the experts back down to earth. Rather, their decline can be traced to the very roots of their success after World War II. The need to over-state anticipated results in order to garner public support, incessant professional and bureaucratic specialization, and the sheer proliferation of expertise pushed arcane and insulated debates between experts into public forums at the same time that a broad cross section of political participants found it easier to gain access to their own expertise. These tendencies ultimately undermined the political influence of all experts. (author)

  7. SAM-dependent enzyme-catalysed pericyclic reactions in natural product biosynthesis

    Science.gov (United States)

    Ohashi, Masao; Liu, Fang; Hai, Yang; Chen, Mengbin; Tang, Man-Cheng; Yang, Zhongyue; Sato, Michio; Watanabe, Kenji; Houk, K. N.; Tang, Yi

    2017-09-01

    Pericyclic reactions—which proceed in a concerted fashion through a cyclic transition state—are among the most powerful synthetic transformations used to make multiple regioselective and stereoselective carbon-carbon bonds. They have been widely applied to the synthesis of biologically active complex natural products containing contiguous stereogenic carbon centres. Despite the prominence of pericyclic reactions in total synthesis, only three naturally existing enzymatic examples (the intramolecular Diels-Alder reaction, and the Cope and the Claisen rearrangements) have been characterized. Here we report a versatile S-adenosyl-L-methionine (SAM)-dependent enzyme, LepI, that can catalyse stereoselective dehydration followed by three pericyclic transformations: intramolecular Diels-Alder and hetero-Diels-Alder reactions via a single ambimodal transition state, and a retro-Claisen rearrangement. Together, these transformations lead to the formation of the dihydropyran core of the fungal natural product, leporin. Combined in vitro enzymatic characterization and computational studies provide insight into how LepI regulates these bifurcating biosynthetic reaction pathways by using SAM as the cofactor. These pathways converge to the desired biosynthetic end product via the (SAM-dependent) retro-Claisen rearrangement catalysed by LepI. We expect that more pericyclic biosynthetic enzymatic transformations remain to be discovered in naturally occurring enzyme ‘toolboxes’. The new role of the versatile cofactor SAM is likely to be found in other examples of enzyme catalysis.

  8. Synthesis of Quinuclidines by Intramolecular Silver-​Catalysed Amine Additions to Alkynes

    NARCIS (Netherlands)

    Breman, A.C.; Ruiz-Olalla, A.; van Maarseveen, J.H.; Ingemann, S.; Hiemstra, H.

    2014-01-01

    A new method has been developed for the synthesis of 2-​alkylidenequinuclidines based on a silver triflate catalyzed intramol. hydroamination of 4-​(prop-​2-​ynyl)​piperidines. Monosubstituted piperidines reacted less efficiently than cis-​disubstituted piperidines, and the reaction was selective

  9. Hydroamination reactions of alkynes with ortho-substituted anilines in ball mills: synthesis of benzannulated N-heterocycles by a cascade reaction.

    Science.gov (United States)

    Weiße, Maik; Zille, Markus; Jacob, Katharina; Schmidt, Robert; Stolle, Achim

    2015-04-20

    It was demonstrated that ortho-substituted anilines are prone to undergo hydroamination reactions with diethyl acetylenedicarboxylate in a planetary ball mill. A sequential coupling of the intermolecular hydroamination reaction with intramolecular ring closure was utilized for the syntheses of benzooxazines, quinoxalines, and benzothiazines from readily available building blocks, that is, electrophilic alkynes and anilines with OH, NH, or SH groups in the ortho position. For the heterocycle formation, it was shown that several stress conditions were able to initiate the reaction in the solid state. Processing in a ball mill seemed to be advantageous over comminution with mortar and pestle with respect to process control. In the latter case, significant postreaction modification occurred during solid-state analysis. Cryogenic milling proved to have an adverse effect on the molecular transformation of the reagents. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Photoinduced Ultrafast Intramolecular Excited-State Energy Transfer in the Silylene-Bridged Biphenyl and Stilbene (SBS) System: A Nonadiabatic Dynamics Point of View.

    Science.gov (United States)

    Wang, Jun; Huang, Jing; Du, Likai; Lan, Zhenggang

    2015-07-09

    The photoinduced intramolecular excited-state energy-transfer (EET) process in conjugated polymers has received a great deal of research interest because of its important role in the light harvesting and energy transport of organic photovoltaic materials in photoelectric devices. In this work, the silylene-bridged biphenyl and stilbene (SBS) system was chosen as a simplified model system to obtain physical insight into the photoinduced intramolecular energy transfer between the different building units of the SBS copolymer. In the SBS system, the vinylbiphenyl and vinylstilbene moieties serve as the donor (D) unit and the acceptor (A) unit, respectively. The ultrafast excited-state dynamics of the SBS system was investigated from the point of view of nonadiabatic dynamics with the surface-hopping method at the TDDFT level. The first two excited states (S1 and S2) are characterized by local excitations at the acceptor (vinylstilbene) and donor (vinylbiphenyl) units, respectively. Ultrafast S2-S1 decay is responsible for the intramolecular D-A excitonic energy transfer. The geometric distortion of the D moiety play an essential role in this EET process, whereas the A moiety remains unchanged during the nonadiabatic dynamics simulation. The present work provides a direct dynamical approach to understand the ultrafast intramolecular energy-transfer dynamics in SBS copolymers and other similar organic photovoltaic copolymers.

  11. An Efficient Synthesis of Substituted Furans by Cupric Halide-Mediated Intramolecular Halocyclization of 2-(1-Alkynyl)-2-alken-1-ones

    International Nuclear Information System (INIS)

    Fu, Weijun; Guo, Wenbo; Zhu, Mei; Xu, Chen; Xu, Fengjuan

    2013-01-01

    An efficient synthesis of 3-halofurans by the intramolecular cyclization of 2-(1-alkynyl)-2-alken-1-ones with cupric halide has been developed. A broad range of 3-chloro- and 3-bromofuran derivatives could be obtained in the present method in moderate to good yields. The 3-halofuran derivatives are potential synthetic intermediates for amplification of molecular complexity

  12. Ready synthesis of free N-H 2-arylindoles via the copper-catalyzed amination of 2-bromo-arylacetylenes with aqueous ammonia and sequential intramolecular cyclization.

    Science.gov (United States)

    Wang, Huifeng; Li, Yaming; Jiang, Linlin; Zhang, Rong; Jin, Kun; Zhao, Defeng; Duan, Chunying

    2011-07-07

    A wide range of free N-H 2-arylindoles were synthesised via the copper(II)-catalyzed amination of 2-bromo-arylacetylenes with aqueous ammonia and sequential intramolecular cyclization. The convenience and atom economy of aqueous ammonia, and the low cost of the copper catalytic system make this protocol readily superior in practical application.

  13. Quantum and Statistical Mechanics Applied to Singlet Carbenes, Pericyclic Reactions, and Condensed Phase Phenomena

    Science.gov (United States)

    Evanseck, Jeffrey Donald

    The completed research covers a broad range of theoretical applications in organic chemistry. It is divided into three chapters which covers the chemistry of singlet carbenes (Chapter 1), substituent effects in pericyclic rearrangements (Chapter 2), and the effects of solvent on the reactivity of organic reactions (Chapter 3). The selectivity between 1,2- and 1,4-intramolecular additions to restricted diene systems has been investigated. A decrease in activation energy for the intramolecular cycloaddition is noted for systems which approach the idealized geometry found with intermolecular addition of carbenes to olefins. Direct substitution at the carbene site dramatically effects the predicted activation barriers for 1,2-hydrogen shifts. An excellent correlation between the activation energy and a substituents sigma_sp {rm R}{rm o} parameters has been demonstrated. The long standing problem of orbital alignment influences on the selectivity of 1,2-hydrogen arrangements shows significant geometric distortions, yet has little influence on the rates of singlet alkylcarbene rearrangements. The exo-selectivities observed for 1,2-shifts in rigid systems are explained by torsional and steric interactions which develop in the transition structures. Substituent effects on pericyclic reactions have been computed for several conrotatory and disrotatory electrocyclizations. The six-electron disrotatory electrocyclization of 1-substituted hexatrienes displays a strong electronic component in determining stereoselectivity, despite incredible steric interference. The eight-electron conrotatory electrocyclization transition structure of 1-substituted octatetraene has an unusual helical transition structure which does not differentiate between substituent position. The effects of solvents on the acidity differences between E and Z esters has supplemented earlier ab initio quantum mechanical results on the enhanced acidity of Meldrum's acid. Monte Carlo simulations predict a

  14. Syntheses of the Stemona Alkaloids (±)-Stenine, (±)-Neostenine, and (±)-13-Epineostenine Using a Stereodivergent Diels-Alder/Azido-Schmidt Reaction

    Science.gov (United States)

    Frankowski, Kevin J.; Golden, Jennifer E.; Zeng, Yibin; Lei, Yao; Aubé, Jeffrey

    2009-01-01

    A tandem Diels-Alder/azido Schmidt reaction sequence provides rapid access to the core skeleton shared by several Stemona alkaloids including stenine, neostenine, tuberstemonine, and neotubererostemonine. The discovery and evolution of inter- and intramolecular variations of this process and their applications to total syntheses of (±)–stenine and (±)–neostenine is described. The stereochemical outcome of the reaction depends on both substrate type and reaction condition, enabling the preparation of both (±)–stenine and (±)–neostenine from the same diene/dienophile combination. PMID:18396881

  15. Intramolecular Hydroamination of Unbiased and Functionalized Primary Aminoalkenes Catalyzed by a Rhodium Aminophosphine Complex

    Science.gov (United States)

    Julian, Lisa D.; Hartwig, John F.

    2010-01-01

    We report a rhodium catalyst that exhibits high reactivity for the hydroamination of primary aminoalkenes that are unbiased toward cyclization and that possess functional groups that would not be tolerated in hydroaminations catalyzed by more electrophilic systems. This catalyst contains an unusual diaminophosphine ligand that binds to rhodium in a κ3-P,O,P mode. The reactions catalyzed by this complex typically proceed at mild temperatures (room temperature to 70 °C), occur with primary aminoalkenes lacking substituents on the alkyl chain that bias the system toward cyclization, occur with primary aminoalkenes containing chloride, ester, ether, enolizable ketone, nitrile, and unprotected alcohol functionality, and occur with primary aminoalkenes containing internal olefins. Mechanistic data imply that these reactions occur with a turnover-limiting step that is different from that of reactions catalyzed by late transition metal complexes of Pd, Pt, and Ir. This change in the turnover-limiting step and resulting high activity of the catalyst stem from favorable relative rates for protonolysis of the M-C bond to release the hydroamination product vs reversion of the aminoalkyl intermediate to regenerate the acyclic precursor. Probes for the origin of the reactivity of the rhodium complex of L1 imply that the aminophosphine groups lead to these favorable rates by effects beyond steric demands and simple electron donation to the metal center. PMID:20839807

  16. Ruthenium-catalyzed intramolecular metathesis of dienes and its application in the synthesis of bridged and spiro azabicycles

    Science.gov (United States)

    Kuznetsov, N. Yu; Bubnov, Yu N.

    2015-07-01

    The review presents a historical excursion into catalytic alkene metathesis, covering the problems of history of the discovery of this process, as well as investigations on the properties, structure and reactivity of the most popular ruthenium catalysts for metathesis, mechanism of their action and decomposition. The main part covers studies devoted to the syntheses of bridged azabicyclic and 1-azaspirocyclic compounds comprising the intramolecular metathesis of dienes as the key step. The formation of a bicyclic skeleton of a series of natural bridged (cocaine, ferruginine, calystegines, and anatoxin-a) and spiro (pinnaic acids, halichlorine, hystrionicotoxin, and cephalotaxine) azabicycles, as well as their analogues and compounds with larger rings is demonstrated. The methods for the synthesis of diene precursors and the conditions for final assembling of the bicyclic compounds are considered in detail. The generalization of the literature data allows one to efficiently carry out the mentioned process taking into account the most important features. The bibliography includes 129 references.

  17. Insights into the Intramolecular Properties of η6-Arene-Ru-Based Anticancer Complexes Using Quantum Calculations

    Directory of Open Access Journals (Sweden)

    Adebayo A. Adeniyi

    2013-01-01

    Full Text Available The factors that determine the stability and the effects of noncovalent interaction on the η6-arene ruthenium anticancer complexes are determined using DFT method. The intramolecular and intra-atomic properties were computed for two models of these half-sandwich ruthenium anticancer complexes and their respective hydrated forms. The results showed that the stability of these complexes depends largely on the network of hydrogen bonds (HB, strong nature of charge transfer, polarizability, and electrostatic energies that exist within the complexes. The hydrogen bonds strength was found to be related to the reported anticancer activities and the activation of the complexes by hydration. The metal–ligand bonds were found to be closed shell systems that are characterised by high positive Laplacian values of electron density. Two of the complexes are found to be predominantly characterised by LMCT while the other two are predominately characterised by MLCT.

  18. Ruthenium-catalyzed intramolecular metathesis of dienes and its application in the synthesis of bridged and spiro azabicycles

    International Nuclear Information System (INIS)

    Kuznetsov, N Yu; Bubnov, Yu N

    2015-01-01

    The review presents a historical excursion into catalytic alkene metathesis, covering the problems of history of the discovery of this process, as well as investigations on the properties, structure and reactivity of the most popular ruthenium catalysts for metathesis, mechanism of their action and decomposition. The main part covers studies devoted to the syntheses of bridged azabicyclic and 1-azaspirocyclic compounds comprising the intramolecular metathesis of dienes as the key step. The formation of a bicyclic skeleton of a series of natural bridged (cocaine, ferruginine, calystegines, and anatoxin-a) and spiro (pinnaic acids, halichlorine, hystrionicotoxin, and cephalotaxine) azabicycles, as well as their analogues and compounds with larger rings is demonstrated. The methods for the synthesis of diene precursors and the conditions for final assembling of the bicyclic compounds are considered in detail. The generalization of the literature data allows one to efficiently carry out the mentioned process taking into account the most important features. The bibliography includes 129 references

  19. Vertex function for the coupling of an electron with intramolecular phonons: Exact results in the antiadiabatic limit

    International Nuclear Information System (INIS)

    Takada, Y.; Higuchi, T.

    1995-01-01

    The Green's-function techniques, especially the one developed in the preceding paper [Takada, Phys. Rev. B 52, 12 708 (1995)], are employed to calculate the electron-phonon vertex part as well as the electronic self-energy exactly on both real- and imaginary-frequency axes in the electron-phonon Holstein model with the on-site Coulomb repulsion in the limit in which the intramolecular phonon energy ω 0 is much larger than the electronic bandwidth. The rigorous vertex part is found to diverge at the frequencies at which an electron is locked by such local phonons with an infinitely strong effective coupling. Characteristic frequencies of this divergence, which are not equal to multiples of ω 0 , are calculated as a function of the electron-phonon bare coupling constant. Our results for the self-energy are checked successfully with the exact ones obtained by the Lang-Firsov canonical transformation

  20. Intramolecular excimer formation of diastereoisomeric model compounds of polystyrene in fluid solution: their local molecular motion and photophysical properties

    International Nuclear Information System (INIS)

    Itagaki, Hideyuki; Horie, Kazuyuki; Mita, Itaru; Washio, Masakazu; Tagawa, Seiichi; Tabata, Yoneho

    1989-01-01

    The dynamic process of intramolecular excimer formation in diasteroisomeric oligomers model compounds of polystyrene, was investigated by using a picosecond pulse radiolysis technique. Monomer fluorescence of all-racemic isomers decays single-exponentially, while that of other isomers decays dual-exponentially. Multicomponent fluorescence decay curves are supposed to be mainly induced by conformational changes. The results suggest that the excimer in oligostyrenes (or polystyrene) is formed mainly in meso diad. It is definitely proved that there exists singlet energy migration in styrene trimer and tetramer systems. The conformational change in PS3 and PS4 is concluded to occur by way of cooperative motions in backbone chains bond such as a crankshaft transition, not by way of independent rotation around each carbon-carbon bond of the backbone chain. (author)