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Sample records for transfer reaction catalyzed

  1. Recent advances in transition metal-catalyzed N -atom transfer reactions of azides

    Science.gov (United States)

    Driver, Tom G.

    2011-01-01

    Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids. PMID:20617243

  2. Pentanidium-catalyzed enantioselective phase-transfer conjugate addition reactions

    KAUST Repository

    Ma, Ting

    2011-03-09

    A new chiral entity, pentanidium, has been shown to be an excellent chiral phase-transfer catalyst. The enantioselective Michael addition reactions of tert-butyl glycinate-benzophenone Schiff base with various α,β- unsaturated acceptors provide adducts with high enantioselectivities. A successful gram-scale experiment at a low catalyst loading of 0.05 mol % indicates the potential for practical applications of this methodology. Phosphoglycine ester analogues can also be utilized as the Michael donor, affording enantioenriched α-aminophosphonic acid derivatives and phosphonic analogues of (S)-proline. © 2011 American Chemical Society.

  3. Modeling of mass transfer in combination with a homogeneously catalyzed reaction

    NARCIS (Netherlands)

    Hoorn, J.A.A.; Versteeg, G. F.

    The mass transfer rates of a gaseous reactant into a liquid where the reactions are catalyzed by homogeneous catalysts have been evaluated by the numerical solution of the diffusion-reaction equations according to Higbie's penetration theory. The concentration profiles as well as enhancement factors

  4. Recyclable polystyrene-supported siloxane-transfer agent for palladium-catalyzed cross-coupling reactions.

    Science.gov (United States)

    Nguyen, Minh H; Smith, Amos B

    2014-04-04

    The rational design, synthesis, and validation of a significantly improved insoluble polymer-supported siloxane-transfer agent has been achieved that permits efficient palladium-catalyzed cross-coupling reactions. The cross-linked polystyrene support facilitates product purification with excellent siloxane recycling. Drawbacks of a previous polymer-supported siloxane-transfer agent, relating to reaction efficiency and polymer stability after repeated cycles, have been addressed.

  5. Investigation of transition metal-catalyzed nitrene transfer reactions in water.

    Science.gov (United States)

    Alderson, Juliet M; Corbin, Joshua R; Schomaker, Jennifer M

    2018-04-11

    Transition metal-catalyzed nitrene transfer is a powerful method for incorporating new CN bonds into relatively unfunctionalized scaffolds. In this communication, we report the first examples of site- and chemoselective CH bond amination reactions in aqueous media. The unexpected ability to employ water as the solvent in these reactions is advantageous in that it eliminates toxic solvent use and enables reactions to be run at increased concentrations with lower oxidant loadings. Using water as the reaction medium has potential to expand the scope of nitrene transfer to encompass a variety of biomolecules and highly polar substrates, as well as enable pH control over the site-selectivity of CH bond amination. Copyright © 2018 Elsevier Ltd. All rights reserved.

  6. Enantio- and Diastereoselective Nitro-Mannich Reaction of α-Aryl Nitromethanes with Amidosulfones Catalyzed by Phase-Transfer Catalysts.

    Science.gov (United States)

    Lu, Ning; Li, Ruxu; Wei, Zhonglin; Cao, Jungang; Liang, Dapeng; Lin, Yingjie; Duan, Haifeng

    2017-05-05

    A high-yield, highly diastereo- and enantioselective nitro-Mannich reaction of α-aryl nitromethanes with amidosulfones catalyzed by a novel chiral phase-transfer catalyst, bearing multiple H-bonding donors, derived from quinine was developed. A variety of α-aryl nitromethanes and amidosulfones were investigated; and the corresponding products were obtained in excellent yields with excellent diastereo- and enantioselectivities (up to 99% yield, > 99:1 dr and >99% ee). As a demonstration of synthetic utility, the resulting β-nitroamines could be converted to corresponding meso-symmetric and optically pure unsymmetric anti-1,2-diarylethylenediamines.

  7. 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.

  8. Mixed quantum-classical simulation of the hydride transfer reaction catalyzed by dihydrofolate reductase based on a mapped system-harmonic bath model

    Science.gov (United States)

    Xu, Yang; Song, Kai; Shi, Qiang

    2018-03-01

    The hydride transfer reaction catalyzed by dihydrofolate reductase is studied using a recently developed mixed quantum-classical method to investigate the nuclear quantum effects on the reaction. Molecular dynamics simulation is first performed based on a two-state empirical valence bond potential to map the atomistic model to an effective double-well potential coupled to a harmonic bath. In the mixed quantum-classical simulation, the hydride degree of freedom is quantized, and the effective harmonic oscillator modes are treated classically. It is shown that the hydride transfer reaction rate using the mapped effective double-well/harmonic-bath model is dominated by the contribution from the ground vibrational state. Further comparison with the adiabatic reaction rate constant based on the Kramers theory confirms that the reaction is primarily vibrationally adiabatic, which agrees well with the high transmission coefficients found in previous theoretical studies. The calculated kinetic isotope effect is also consistent with the experimental and recent theoretical results.

  9. Thermodynamics of Enzyme-Catalyzed Reactions Database

    Science.gov (United States)

    SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

  10. Reversible Hydride Transfer to N,N'-Diarylimidazolinium Cations from Hydrogen Catalyzed by Transition Metal Complexes Mimicking the Reaction of [Fe]-Hydrogenase.

    Science.gov (United States)

    Hatazawa, Masahiro; Yoshie, Naoko; Seino, Hidetake

    2017-07-17

    [Fe]-hydrogenase is a key enzyme involved in methanogenesis and facilitates reversible hydride transfer from H 2 to N 5 ,N 10 -methenyltetrahydromethanopterin (CH-H 4 MPT + ). In this study, a reaction system was developed to model the enzymatic function of [Fe]-hydrogenase by using N,N'-diphenylimidazolinium cation (1 + ) as a structurally related alternative to CH-H 4 MPT + . In connection with the enzymatic mechanism via heterolytic cleavage of H 2 at the single metal active site, several transition metal complex catalysts capable of such activation were utilized in the model system. Reduction of 1[BF 4 ] to N,N'-diphenylimidazolidine (2) was achieved under 1 atm H 2 at ambient temperature in the presence of an equimolar amount of NEt 3 as a proton acceptor. The proposed catalytic pathways involved the generation of active hydride complexes and subsequent intermolecular hydride transfer to 1 + . The reverse reaction was accomplished by treatment of 2 with HNMe 2 Ph + as the proton source, where [(η 5 -C 5 Me 5 )Ir{(p-MeC 6 H 4 SO 2 )NCHPhCHPhNH}] was found to catalyze the formation of 1 + and H 2 with high efficiency. These results are consistent with the fact that use of 2,6-lutidine in the forward reaction or 2,6-lutidinium in the reverse reaction resulted in incomplete conversion. By combining these reactions using the above Ir amido catalyst, the reversible hydride transfer interconverting 1 + /H 2 and 2/H + was performed successfully. This system demonstrated the hydride-accepting and hydride-donating modes of biologically relevant N-heterocycles coupled with proton concentration. The influence of substituents on the forward and reverse reactivities was examined for the derivatives of 1 + and 2 bearing one para-substituted N-phenyl group.

  11. Efficient transfer hydrogenation reaction Catalyzed by a dearomatized PN 3P ruthenium pincer complex under base-free Conditions

    KAUST Repository

    He, Lipeng

    2012-03-01

    A dearomatized complex [RuH(PN 3P)(CO)] (PN 3PN, N′-bis(di-tert-butylphosphino)-2,6-diaminopyridine) (3) was prepared by reaction of the aromatic complex [RuH(Cl)(PN 3P)(CO)] (2) with t-BuOK in THF. Further treatment of 3 with formic acid led to the formation of a rearomatized complex (4). These new complexes were fully characterized and the molecular structure of complex 4 was further confirmed by X-ray crystallography. In complex 4, a distorted square-pyramidal geometry around the ruthenium center was observed, with the CO ligand trans to the pyridinic nitrogen atom and the hydride located in the apical position. The dearomatized complex 3 displays efficient catalytic activity for hydrogen transfer of ketones in isopropanol. © 2011 Elsevier B.V. All rights reserved.

  12. Versatile In Situ Generated N-Boc-Imines: Application to Phase-Transfer-Catalyzed Asymmetric Mannich-Type Reactions.

    Science.gov (United States)

    Kano, Taichi; Kobayashi, Ryohei; Maruoka, Keiji

    2015-07-13

    The efficient construction of nitrogen-containing organic compounds is a major challenge in chemical synthesis. Imines are one of the most important classes of electrophiles for this transformation. However, both the available imines and applicable nucleophiles for them are quite limited given the existing preparative methods. Described herein are imine precursors which generate reactive imines with a wide variety of substituents under mild basic conditions. This approach enables the construction of various nitrogen-containing molecules which cannot be accessed by the traditional approach. The utility of the novel imine precursor was demonstrated in the asymmetric Mannich-type reaction under phase-transfer conditions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Palladium-catalyzed coupling reactions

    CERN Document Server

    Molnár, Árpád

    2013-01-01

    This handbook and ready reference brings together all significant issues of practical importance for interested readers in one single volume. While covering homogeneous and heterogeneous catalysis, the text is unique in focusing on such important aspects as using different reaction media, microwave techniques or catalyst recycling. It also provides a comprehensive treatment of modern-day coupling reactions and emphasizes those topics that show potential for future development, such as continuous flow systems, water as a reaction medium, and catalyst immobilization, among others. With i

  14. Electron transfer reactions

    CERN Document Server

    Cannon, R D

    2013-01-01

    Electron Transfer Reactions deals with the mechanisms of electron transfer reactions between metal ions in solution, as well as the electron exchange between atoms or molecules in either the gaseous or solid state. The book is divided into three parts. Part 1 covers the electron transfer between atoms and molecules in the gas state. Part 2 tackles the reaction paths of oxidation states and binuclear intermediates, as well as the mechanisms of electron transfer. Part 3 discusses the theories and models of the electron transfer process; theories and experiments involving bridged electron transfe

  15. Representing Rate Equations for Enzyme-Catalyzed Reactions

    Science.gov (United States)

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

  16. Reactions of ethyl diazoacetate catalyzed by methylrhenium trioxide

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Z.; Espenson, H. [Iowa State Univ., Ames, IA (United States)

    1995-11-03

    Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) has found wise use in catalysis, including the epoxidation and metathesis of olefins, aldehyde olefination, and oxygen transfer. Extensive reports have now appeared in the area of MTO-catalyzed substrate oxidations with hydrogen peroxide. Certain catalytic applications of MTO for organic reactions that do not utilize peroxide have now been realized. In particular, a catalytic amount of MTO with ethyl diazoacetate (EDA) will convert aromatic imines to aziridines and convert aldehydes and ketones to epoxides. The aziridine preparation proceeds in high yields under anaerobic conditions more conveniently than with existing methods. Compounds with a three-membered heterocyclic ring can be obtained with the EDA/MTO catalytic system. Aromatic imines undergo cycloaddition reactions to give aziridines under mild conditions.

  17. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides ...

    Indian Academy of Sciences (India)

    016-1096-y. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides/. Isocyanate leading to Guanidines/Urea derivatives formation. JAYEETA BHATTACHARJEE, MITALI SACHDEVA, INDRANI BANERJEE and. TARUN K PANDA.

  18. Recent advances in osmium-catalyzed hydrogenation and dehydrogenation reactions.

    Science.gov (United States)

    Chelucci, Giorgio; Baldino, Salvatore; Baratta, Walter

    2015-02-17

    CONSPECTUS: A current issue in metal-catalyzed reactions is the search for highly efficient transition-metal complexes affording high productivity and selectivity in a variety of processes. Moreover, there is also a great interest in multitasking catalysts that are able to efficiently promote different organic transformations by careful switching of the reaction parameters, such as temperature, solvent, and cocatalyst. In this context, osmium complexes have shown the ability to catalyze efficiently different types of reactions involving hydrogen, proving at the same time high thermal stability and simple synthesis. In the catalytic reduction of C═X (X = O, N) bonds by both hydrogenation (HY) and transfer hydrogenation (TH) reactions, the most interest has been focused on homogeneous systems based on rhodium, iridium, and in particular ruthenium catalysts, which have proved to catalyze chemo- and stereoselective hydrogenations with remarkable efficiency. By contrast, osmium catalysts have received much less attention because they are considered less active on account of their slower ligand exchange kinetics. Thus, this area remained almost neglected until recent studies refuted these prejudices. The aim of this Account is to highlight the impressive developments achieved over the past few years by our and other groups on the design of new classes of osmium complexes and their applications in homogeneous catalytic reactions involving the hydrogenation of carbon-oxygen and carbon-nitrogen bonds by both HY and TH reactions as well as in alcohol deydrogenation (DHY) reactions. The work described in this Account demonstrates that osmium complexes are emerging as powerful catalysts for asymmetric and non-asymmetric syntheses, showing a remarkably high catalytic activity in HY and TH reactions of ketones, aldehydes, imines, and esters as well in DHY reactions of alcohols. Thus, for instance, the introduction of ligands with an NH function, possibly in combination with a

  19. Efficient, crosswise catalytic promiscuity among enzymes that catalyze phosphoryl transfer.

    Science.gov (United States)

    Mohamed, Mark F; Hollfelder, Florian

    2013-01-01

    The observation that one enzyme can accelerate several chemically distinct reactions was at one time surprising because the enormous efficiency of catalysis was often seen as inextricably linked to specialization for one reaction. Originally underreported, and considered a quirk rather than a fundamental property, enzyme promiscuity is now understood to be important as a springboard for adaptive evolution. Owing to the large number of promiscuous enzymes that have been identified over the last decade, and the increased appreciation for promiscuity's evolutionary importance, the focus of research has shifted to developing a better understanding of the mechanistic basis for promiscuity and the origins of tolerant or restrictive specificity. We review the evidence for widespread crosswise promiscuity amongst enzymes that catalyze phosphoryl transfer, including several members of the alkaline phosphatase superfamily, where large rate accelerations between 10(6) and 10(17) are observed for both native and multiple promiscuous reactions. This article is part of a Special Issue entitled: Chemistry and mechanism of phosphatases, diesterases and triesterases. Copyright © 2012 Elsevier B.V. All rights reserved.

  20. Cyclodextrin-Catalyzed Organic Synthesis: Reactions, Mechanisms, and Applications

    Directory of Open Access Journals (Sweden)

    Chang Cai Bai

    2017-09-01

    Full Text Available Cyclodextrins are well-known macrocyclic oligosaccharides that consist of α-(1,4 linked glucose units and have been widely used as artificial enzymes, chiral separators, chemical sensors, and drug excipients, owing to their hydrophobic and chiral interiors. Due to their remarkable inclusion capabilities with small organic molecules, more recent interests focus on organic reactions catalyzed by cyclodextrins. This contribution outlines the current progress in cyclodextrin-catalyzed organic reactions. Particular emphases are given to the organic reaction mechanisms and their applications. In the end, the future directions of research in this field are proposed.

  1. Cyclodextrin-Catalyzed Organic Synthesis: Reactions, Mechanisms, and Applications.

    Science.gov (United States)

    Bai, Chang Cai; Tian, Bing Ren; Zhao, Tian; Huang, Qing; Wang, Zhi Zhong

    2017-09-07

    Cyclodextrins are well-known macrocyclic oligosaccharides that consist of α-(1,4) linked glucose units and have been widely used as artificial enzymes, chiral separators, chemical sensors, and drug excipients, owing to their hydrophobic and chiral interiors. Due to their remarkable inclusion capabilities with small organic molecules, more recent interests focus on organic reactions catalyzed by cyclodextrins. This contribution outlines the current progress in cyclodextrin-catalyzed organic reactions. Particular emphases are given to the organic reaction mechanisms and their applications. In the end, the future directions of research in this field are proposed.

  2. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides ...

    Indian Academy of Sciences (India)

    DOI 10.1007/s12039-016-1096-y. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides/ ... A possible mechanism involving penta-coordinated zinc transition state for the catalytic reaction is presented. Keywords. Carbodiimide ... or receptors through hydrogen bonds and electrostatic interactions. They are ...

  3. Metal-catalyzed asymmetric aldol reactions

    Energy Technology Data Exchange (ETDEWEB)

    Dias, Luiz C.; Lucca Junior, Emilio C. de; Ferreira, Marco A. B.; Polo, Ellen C., E-mail: ldias@iqm.unicamp.br [Universidade de Campinas (UNICAMP), SP (Brazil). Inst. de Quimica

    2012-12-15

    The aldol reaction is one of the most powerful and versatile methods for the construction of C-C bonds. Traditionally, this reaction was developed in a stoichiometric version; however, great efforts in the development of chiral catalysts for aldol reactions were performed in recent years. Thus, in this review article, the development of metal-mediated chiral catalysts in Mukaiyama-type aldol reaction, reductive aldol reaction and direct aldol reaction are discussed. Moreover, the application of these catalysts in the total synthesis of complex molecules is discussed. (author)

  4. Method for predicting enzyme-catalyzed reactions

    Science.gov (United States)

    Hlavacek, William S.; Unkefer, Clifford J.; Mu, Fangping; Unkefer, Pat J.

    2013-03-19

    The reactivity of given metabolites is assessed using selected empirical atomic properties in the potential reaction center. Metabolic reactions are represented as biotransformation rules. These rules are generalized from the patterns in reactions. These patterns are not unique to reactants but are widely distributed among metabolites. Using a metabolite database, potential substructures are identified in the metabolites for a given biotransformation. These substructures are divided into reactants or non-reactants, depending on whether they participate in the biotransformation or not. Each potential substructure is then modeled using descriptors of the topological and electronic properties of atoms in the potential reaction center; molecular properties can also be used. A Support Vector Machine (SVM) or classifier is trained to classify a potential reactant as a true or false reactant using these properties.

  5. Exploring possible reaction pathways for the o-atom transfer reactions to unsaturated substrates catalyzed by a [Ni-NO2 ] ↔ [Ni-NO] redox couple using DFT methods.

    Science.gov (United States)

    Tsipis, Athanassios C

    2017-07-15

    The (nitro)(N-methyldithiocarbamato)(trimethylphospane)nickel(II), [Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] complex catalyses efficiently the O-atom transfer reactions to CO and acetylene. Energetically feasible sequence of elementary steps involved in the catalytic cycle of the air oxidation of CO and acetylene are proposed promoted by the Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] ↔ Ni(NO 2 )(S 2 CNHMe)(PMe 3 ) redox couple using DFT methods both in vacuum and dichloromethane solutions. The catalytic air oxidation of HC≡CH involves formation of a five-member metallacycle intermediate, via a [3 + 2] cyclo-addition reaction of HC≡CH to the Ni-N = O moiety of the Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] complex, followed by a β H-atom migration toward the C α carbon atom of the coordinated acetylene and release of the oxidation product (ketene). The geometric and energetic reaction profile for the reversible [Ni( κN1-NO 2 )(S 2 CNHMe)(PMe 3 )] ⇌ [Ni( κO,O2-ONO)(S 2 CNHMe)(PMe 3 )] linkage isomerization has also been modeled by DFT calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  6. Insight into solid-liquid phase transfer catalyzed synthesis of ...

    Indian Academy of Sciences (India)

    Ganapati D Yadav

    2017-11-16

    Nov 16, 2017 ... https://doi.org/10.1007/s12039-017-1368-1. REGULAR ARTICLE. Special Issue on Recent Trends in the Design and Development of Catalysts and their Applications. Insight into solid-liquid phase transfer catalyzed synthesis of. Mecoprop ester using K2CO3 as base and development of new kinetic model ...

  7. Insight into solid-liquid phase transfer catalyzed synthesis of ...

    Indian Academy of Sciences (India)

    Insight into solid-liquid phase transfer catalyzed synthesis of Mecoprop ester using K₂CO₃ as base and development of new kinetic model involving liquid product and two solid co-products. GANAPATI D YADAV GUNJAN P DESHMUKH. REGULAR ARTICLE Volume 129 Issue 11 November 2017 pp 1677-1685 ...

  8. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides ...

    Indian Academy of Sciences (India)

    ... Journal of Chemical Sciences; Volume 128; Issue 6. Zinc catalyzed Guanylation reaction of Amines with Carbodiimides/ Isocyanate leading to Guanidines/Urea derivatives formation. JAYEETA BHATTACHARJEE MITALI SACHDEVA INDRANI BANERJEE TARUN K PANDA. Regular Article Volume 128 Issue 6 June 2016 ...

  9. Development of a Lewis Base Catalyzed Selenocyclization Reaction

    Science.gov (United States)

    Collins, William

    2009-01-01

    The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

  10. List-Barbas-Mannich reaction catalyzed by modularly designed organocatalysts.

    Science.gov (United States)

    Perera, Sandun; Sinha, Debarshi; Rana, Nirmal K; Trieu-Do, Van; Zhao, John Cong-Gui

    2013-11-01

    The List-Barbas-Mannich reaction of ethyl (p-methoxyphenylimino)acetate (p-methoxyphenyl = PMP) with unmodified aldehydes or ketones catalyzed by modularly designed organocatalysts (MDOs) that are self-assembled from proline and cinchona alkaloid thioureas (such as a quinidine-derived thiourea) produces the corresponding γ-oxo-α-amino acid derivatives in high yields and excellent stereoselectivities. No solvent is necessary for this reaction. Aldehydes are especially good substrates for this reaction: The reaction takes only a few minutes to yield the corresponding List-Barbas-Mannich products in excellent dr (up to >99:1) and ee values (up to >99% ee).

  11. Manduca sexta lipid transfer particle acts upon a lipoprotein to catalyze lipid and apoprotein disproportionation.

    Science.gov (United States)

    Ryan, R O; Van Antwerpen, R; Van der Horst, D J; Beenakkers, A M; Law, J H

    1990-01-05

    A novel reaction, catalyzed by Manduca sexta lipid transfer particle (LTP), transforms low density lipophorin (LDLp) into two distinct lipoprotein species. A population of LDLp particles serves as lipid donor or acceptor in LTP-catalyzed production of a very low density lipophorin (VLDLp) and a high density lipophorin (HDLp) product. The products result from facilitated net transfer of lipid mass from donor LDLp particles to acceptor LDLp particles. Transfer of apolipophorin III (apoLp-III) from donor to acceptor lipoprotein occurs during the reaction to produce a lipid- and apoLp-III-enriched VLDLp species and lipid- and apoLp-III-depleted HDLp species. The VLDLp produced in this in vitro reaction contains more lipid and apoLp-III than any previous lipophorin species reported and further demonstrates the scope of the lipid binding capacity of lipophorin. Lipid analysis and radiolabeling studies confirmed that unidirectional net transfer of lipid mass and apoLp-III from donor to acceptor occurs. When 3H-lipid-LDLp was used as substrate in the LTP-catalyzed disproportionation reaction the density distribution of radioactivity and protein provided evidence of vectorial transfer of diacylglycerol, phospholipid, and free fatty acids. Electron micrographs of the original LDLp population and of the LTP-induced product lipoprotein population provided further support for the interpretation derived from biochemical studies. This LTP-catalyzed disproportionation was observed only with apoLp-III-rich LDLp suggesting that the presence of increased amounts of this apoprotein dramatically affects the properties of the particle and appears to be directly related to the capacity of the lipoprotein to bind lipid.

  12. Heterogeneously Catalyzed Oxidation Reactions Using Molecular Oxygen

    DEFF Research Database (Denmark)

    Beier, Matthias Josef

    properties to the widely discussed gold catalysts. Literature results were summarized for alcohol oxidation, epoxidation, amine oxidation, phenol hydroxylation, silane and sulfide oxidation, (side-chain) oxidation of alkyl aromatic compounds, hydroquinone oxidation and cyclohexane oxidation. It was found...... that both copper and silver can function as complementary catalyst materials to gold showing different catalytic properties and being more suitable for hydrocarbon oxidation reactions. Potential opportunities for future research were outlined. In an experimental study, the potential of silver as a catalyst...... contact while leaching could be excluded. The silver catalyst was most active when calcined over a short time at 500 °C potentially due to the formation of silver-oxygen species. Removal of these species might be a deactivation mechanism as was suggested by X-ray absorption spectroscopy (XAS) analysis...

  13. Asymmetric Stetter reactions catalyzed by thiamine diphosphate-dependent enzymes.

    Science.gov (United States)

    Kasparyan, Elena; Richter, Michael; Dresen, Carola; Walter, Lydia S; Fuchs, Georg; Leeper, Finian J; Wacker, Tobias; Andrade, Susana L A; Kolter, Geraldine; Pohl, Martina; Müller, Michael

    2014-12-01

    The intermolecular asymmetric Stetter reaction is an almost unexplored transformation for biocatalysts. Previously reported thiamine diphosphate (ThDP)-dependent PigD from Serratia marcescens is the first enzyme identified to catalyze the Stetter reaction of α,β-unsaturated ketones (Michael acceptor substrates) and α-keto acids. PigD is involved in the biosynthesis of the potent cytotoxic agent prodigiosin. Here, we describe the investigation of two new ThDP-dependent enzymes, SeAAS from Saccharopolyspora erythraea and HapD from Hahella chejuensis. Both show a high degree of homology to the amino acid sequence of PigD (39 and 51 %, respectively). The new enzymes were heterologously overproduced in Escherichia coli, and the yield of soluble protein was enhanced by co-expression of the chaperone genes groEL/ES. SeAAS and HapD catalyze intermolecular Stetter reactions in vitro with high enantioselectivity. The enzymes possess a characteristic substrate range with respect to Michael acceptor substrates. This provides support for a new type of ThDP-dependent enzymatic activity, which is abundant in various species and not restricted to prodigiosin biosynthesis in different strains. Moreover, PigD, SeAAS, and HapD are also able to catalyze asymmetric carbon-carbon bond formation reactions of aldehydes and α-keto acids, resulting in 2-hydroxy ketones.

  14. Nanoparticulate-catalyzed oxygen transfer processes

    Science.gov (United States)

    Hunt, Andrew T [Atlanta, GA; Breitkopf, Richard C [Dunwoody, GA

    2009-12-01

    Nanoparticulates of oxygen transfer materials that are oxides of rare earth metals, combinations of rare earth metals, and combinations of transition metals and rare earth metals are used as catalysts in a variety of processes. Unexpectedly large thermal efficiencies are achieved relative to micron sized particulates. Processes that use these catalysts are exemplified in a multistage reactor. The exemplified reactor cracks C6 to C20 hydrocarbons, desulfurizes the hydrocarbon stream and reforms the hydrocarbons in the stream to produce hydrogen. In a first reactor stage the steam and hydrocarbon are passed through particulate mixed rare earth metal oxide to crack larger hydrocarbon molecules. In a second stage, the steam and hydrocarbon are passed through particulate material that desulfurizes the hydrocarbon. In a third stage, the hydrocarbon and steam are passed through a heated, mixed transition metal/rare earth metal oxide to reform the lower hydrocarbons and thereby produce hydrogen. Stages can be alone or combined. Parallel reactors can provide continuous reactant flow. Each of the processes can be carried out individually.

  15. Acid catalyzed reactions of cyclohexanol in liquid phase

    OpenAIRE

    Liu, Yuanshuai

    2017-01-01

    Hydronium ions in aqueous phase catalyze the dehydration of cyclohexanol via monomolecular precursors. In confines such as zeolite pores they are more active than in water, which is caused by an enhanced association between the hydronium ion and alcohol, as well as a greater activation entropy. Alcohol dimers, forming in apolar solvents, reduce the rate of reaction by stabilizing the ground state. Alkylation of arene rings with cyclohexanol requires the formation of a cyclohexyl carbenium ion...

  16. Catalyst-Controlled and Tunable, Chemoselective Silver-Catalyzed Intermolecular Nitrene Transfer: Experimental and Computational Studies.

    Science.gov (United States)

    Dolan, Nicholas S; Scamp, Ryan J; Yang, Tzuhsiung; Berry, John F; Schomaker, Jennifer M

    2016-11-09

    The development of new catalysts for selective nitrene transfer is a continuing area of interest. In particular, the ability to control the chemoselectivity of intermolecular reactions in the presence of multiple reactive sites has been a long-standing challenge in the field. In this paper, we demonstrate examples of silver-catalyzed, nondirected, intermolecular nitrene transfer reactions that are both chemoselective and flexible for aziridination or C-H insertion, depending on the choice of ligand. Experimental probes present a puzzling picture of the mechanistic details of the pathways mediated by [( t Bu 3 tpy)AgOTf] 2 and (tpa)AgOTf. Computational studies elucidate these subtleties and provide guidance for the future development of new catalysts exhibiting improved tunability in group transfer reactions.

  17. Gold-catalyzed cyclization reactions of allenol and alkynol derivatives.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro

    2014-03-18

    Although gold is chemically inert as a bulk metal, the landmark discovery that gold nanoparticles can be effective catalysts has opened up new and exciting research opportunities in the field. In recent years, there has been growth in the number of reactions catalyzed by gold complexes [gold(I) and gold(III)], usually as homogeneous catalysts, because they are soft Lewis acids. In addition, alkynes and allenes have interesting reactivities and selectivities, notably their ability to produce complex structures in very few steps. In this Account, we describe our work in gold catalysis with a focus on the formation of C-C and C-O bonds using allenes and alkynes as starting materials. Of these, oxa- and carbo-cyclizations are perhaps the best known and most frequently studied. We have divided those contributions into sections arranged according to the nature of the starting material (allene versus alkyne). Gold-catalyzed carbocyclizations in allenyl C2-linked indoles, allenyl-β-lactams, and allenyl sugars follow different mechanistic pathways. The cyclization of indole-tethered allenols results in the efficient synthesis of carbazole derivatives, for example. However, the compound produced from gold-catalyzed 9-endo carbocyclization of (aryloxy)allenyl-tethered 2-azetidinones is in noticeable contrast to the 5-exo hydroalkylation product that results from allenyl sugars. We have illustrated the unusual preference for the 4-exo-dig cyclization in allene chemistry, as well as the rare β-hydride elimination reaction, in gold catalysis from readily available α-allenols. We have also observed in γ-allenols that a (methoxymethyl)oxy protecting group not only masks a hydroxyl functionality but also exerts directing effects as a controlling unit in a gold-catalyzed regioselectivity reversal. Our recent work has also led to a combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled

  18. Ti-catalyzed Barbier-type allylations and related reactions.

    Science.gov (United States)

    Estévez, Rosa E; Justicia, José; Bazdi, Btissam; Fuentes, Noelia; Paradas, Miguel; Choquesillo-Lazarte, Duane; García-Ruiz, Juan M; Robles, Rafael; Gansäuer, Andreas; Cuerva, Juan M; Oltra, J Enrique

    2009-01-01

    Titanocene(III) complexes, easily generated in situ from commercial Ti(IV) precursors, catalyze Barbier-type allylations, intramolecular crotylations (cyclizations), and prenylations of a wide range of aldehydes and ketones. The reaction displays surprising and unprecedented mechanistic subtleties. In cyclizations a fast and irreversible addition of an allyl radical to a Ti(III)-coordinated carbonyl group seems to occur. Intermolecular additions to conjugated aldehydes proceed through a coupling of a Ti(IV)-bound ketyl radical with an allyl radical. Reactions of ketones with allylic halides take place by the classical addition of an allylic organometallic reagent. The radical coupling processes enable transformations such as the highly regioselective alpha-prenylation that are otherwise difficult to achieve. The mild reaction conditions and the possibility to employ titanocene complexes in only catalytic quantities are highly attractive features of our protocol. These unusual properties have been taken advantage of for the straightforward synthesis of the natural products rosiridol, shikalkin, and 12-hydroxysqualene.

  19. Investigation of the complex reaction coordinate of acid catalyzed amide hydrolysis from molecular dynamics simulations

    International Nuclear Information System (INIS)

    Zahn, Dirk

    2004-01-01

    The rate-determining step of acid catalyzed peptide hydrolysis is the nucleophilic attack of a water molecule to the carbon atom of the amide group. Therein the addition of the hydroxyl group to the amide carbon atom involves the association of a water molecule transferring one of its protons to an adjacent water molecule. The protonation of the amide nitrogen atom follows as a separate reaction step. Since the nucleophilic attack involves the breaking and formation of several bonds, the underlying reaction coordinate is rather complex. We investigate this reaction step from path sampling Car-Parrinello molecular dynamics simulations. This approach does not require the predefinition of reaction coordinates and is thus particularly suited for investigating reaction mechanisms. From our simulations the most relevant components of the reaction coordinate are elaborated. Though the C···O distance of the oxygen atom of the water molecule performing the nucleophilic attack and the corresponding amide carbon atom is a descriptor of the reaction progress, a complete picture of the reaction coordinate must include all three molecules taking part in the reaction. Moreover, the proton transfer is found to depend on favorable solvent configurations. Thus, also the arrangement of non-reacting, i.e. solvent water molecules needs to be considered in the reaction coordinate

  20. Synthesis of heterocycles through transition-metal-catalyzed isomerization reactions

    DEFF Research Database (Denmark)

    Ishøy, Mette; Nielsen, Thomas Eiland

    2014-01-01

    of structurally complex and diverse heterocycles. In this Concept article, we attempt to cover this area of research through a selection of recent versatile examples. A sea of opportunities! Transition-metal-catalyzed isomerization of N- and O-allylic compounds provides a mild, selective and synthetically...... versatile method to form iminium and oxocarbenium ions. Given the number of reactions involving these highly electrophilic intermediates, this concept provides a sea of opportunities for heterocycle synthesis, (see scheme; Nu=nucleophile). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim....

  1. Deoxyribonucleoside kinases: two enzyme families catalyze the same reaction

    DEFF Research Database (Denmark)

    Sandrini, Michael; Piskur, Jure

    2005-01-01

    Mammals have four deoxyribonucleoside kinases, the cytoplasmic (TK1) and mitochondrial (TK2) thymidine kinases, and the deoxycytidine (dCK) and deoxyguanosine (dGK) kinases, which salvage the precursors for nucleic acids synthesis. In addition to the native deoxyribonucleoside substrates, the kin......, the kinases can phosphorylate and thereby activate a variety of anti-cancer and antiviral prodrugs. Recently, the crystal structure of human TK1 has been solved and has revealed that enzymes with fundamentally different origins and folds catalyze similar, crucial cellular reactions....

  2. Aza-Morita-Baylis-Hillman reactions catalyzed by a cyclopropenylidene.

    Science.gov (United States)

    Lu, Xun; Schneider, Uwe

    2016-10-27

    Catalysis using a bis(dialkylamino)cyclopropenylidene (BAC) has been developed, which relies on a formal umpolung activation of Michael acceptor pro-nucleophiles. Various aza-Morita-Baylis-Hillman reactions between aromatic, heteroaromatic, or aliphatic imines and acyclic or cyclic α,β-unsaturated ketones and carboxylic acid derivatives have been catalyzed by a BAC under mild conditions. Functionalities such as unprotected amino and hydroxy groups have been tolerated. The catalyst loading was decreased to 1 mol% without loss of activity. The BAC catalyst was shown to be substantially more active than a cyclic (alkyl)(amino) carbene (CAAC), N-heterocyclic carbenes (NHCs), and P- or N-centered Lewis bases.

  3. Physio-pathological roles of transglutaminase-catalyzed reactions.

    Science.gov (United States)

    Ricotta, Mariangela; Iannuzzi, Maura; Vivo, Giulia De; Gentile, Vittorio

    2010-05-26

    Transglutaminases (TGs) are a large family of related and ubiquitous enzymes that catalyze post-translational modifications of proteins. The main activity of these enzymes is the cross-linking of a glutaminyl residue of a protein/peptide substrate to a lysyl residue of a protein/peptide co-substrate. In addition to lysyl residues, other second nucleophilic co-substrates may include monoamines or polyamines (to form mono- or bi-substituted /crosslinked adducts) or -OH groups (to form ester linkages). In the absence of co-substrates, the nucleophile may be water, resulting in the net deamidation of the glutaminyl residue. The TG enzymes are also capable of catalyzing other reactions important for cell viability. The distribution and the physiological roles of TG enzymes have been widely studied in numerous cell types and tissues and their roles in several diseases have begun to be identified. "Tissue" TG (TG2), a member of the TG family of enzymes, has definitely been shown to be involved in the molecular mechanisms responsible for a very widespread human pathology: i.e. celiac disease (CD). TG activity has also been hypothesized to be directly involved in the pathogenetic mechanisms responsible for several other human diseases, including neurodegenerative diseases, which are often associated with CD. Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, supranuclear palsy, Huntington's disease and other recently identified polyglutamine diseases, are characterized, in part, by aberrant cerebral TG activity and by increased cross-linked proteins in affected brains. In this review, we discuss the physio-pathological role of TG-catalyzed reactions, with particular interest in the molecular mechanisms that could involve these enzymes in the physio-pathological processes responsible for human neurodegenerative diseases.

  4. Insect lipid transfer particle catalyzes bidirectional vectorial transfer of diacylglycerol from lipophorin to human low density lipoprotein.

    Science.gov (United States)

    Ryan, R O; Wessler, A N; Price, H M; Ando, S; Yokoyama, S

    1990-06-25

    Insect plasma lipid transfer particle (LTP) catalyzes vectorial net transfer of diacylglycerol (DAG) from Manduca sexta larval high density lipophorin (HDLp-L) to human low density lipoprotein (LDL) producing an LDL of lower density and lipophorin subspecies of higher density. At equilibrium, a stable DAG-depleted very high density lipophorin species (density = 1.25 g/ml) is formed. Electrophoretic analysis of the substrate and product lipoproteins showed that apoprotein exchange or transfer between human LDL and lipophorin did not occur during the lipid transfer reaction. Facilitated net transfer of cholesteryl ester, free cholesterol, and phospholipid occurred to a much lower extent than DAG net transfer, indicating that under these conditions, LDL serves as a sink for lipophorin-associated DAG. This reaction, therefore, provides a method whereby the mass of lipid associated with human LDL can be modified in vitro without alteration of its apoprotein component. The DAG content of LDL increased in a linear manner with respect to LTP concentration and time during the initial phase of the reaction, demonstrating the utility of this system as a quantitative assay method for LTP-mediated net DAG transfer. When [3H]DAG-labeled LDL was prepared and employed in transfer experiments with unlabeled lipophorin, labeled DAG was recovered in the HDLp-L fraction. The amount of labeled DAG recovered in the HDLp-L fraction was dependent on the ratio of LDL to HDLp-L in the reaction. Thus, in this system, LTP-mediated DAG redistribution is bidirectional, suggesting that the final equilibrium distribution of lipid may be dictated by the properties of potential donor/acceptor lipoproteins rather than by an inherent particle substrate specificity of LTP.

  5. Synthesis of Sulfoximine Carbamates by Rhodium-Catalyzed Nitrene Transfer of Carbamates to Sulfoxides.

    Science.gov (United States)

    Zenzola, Marina; Doran, Robert; Luisi, Renzo; Bull, James A

    2015-06-19

    Sulfoximines are of considerable interest for incorporation into medicinal compounds. A convenient synthesis of N-protected sulfoximines is achieved, under mild conditions, by rhodium-catalyzed transfer of carbamates to sulfoxides. The first examples of 4-membered thietane-oximines are prepared. Sulfoximines bearing Boc and Cbz groups are stable to further cross coupling reactions, and readily deprotected. This method may facilitate the preparation of NH-sulfoximines providing improved (global) deprotection strategies, which is illustrated in the synthesis of methionine sulfoxide (MSO).

  6. Mechanism of Pd(NHC)-catalyzed transfer hydrogenation of alkynes.

    Science.gov (United States)

    Hauwert, Peter; Boerleider, Romilda; Warsink, Stefan; Weigand, Jan J; Elsevier, Cornelis J

    2010-12-01

    The transfer semihydrogenation of alkynes to (Z)-alkenes shows excellent chemo- and stereoselectivity when using a zerovalent palladium(NHC)(maleic anhydride)-complex as precatalyst and triethylammonium formate as hydrogen donor. Studies on the kinetics under reaction conditions showed a broken positive order in substrate and first order in catalyst and hydrogen donor. Deuterium-labeling studies on the hydrogen donor showed that both hydrogens of formic acid display a primary kinetic isotope effect, indicating that proton and hydride transfers are separate rate-determining steps. By monitoring the reaction with NMR, we observed the presence of a coordinated formate anion and found that part of the maleic anhydride remains coordinated during the reaction. From these observations, we propose a mechanism in which hydrogen transfer from coordinated formate anion to zerovalent palladium(NHC)(MA)(alkyne)-complex is followed by migratory insertion of hydride, after which the product alkene is liberated by proton transfer from the triethylammonium cation. The explanation for the high selectivity observed lies in the competition between strongly coordinating solvent and alkyne for a Pd(alkene)-intermediate.

  7. Effect of osmolytes on protein dynamics in the lactate dehydrogenase-catalyzed reaction.

    Science.gov (United States)

    Zhadin, Nickolay; Callender, Robert

    2011-03-15

    Laser-induced temperature jump relaxation spectroscopy was used to probe the effect of osmolytes on the microscopic rate constants of the lactate dehydrogenase-catalyzed reaction. NADH fluorescence and absorption relaxation kinetics were measured for the lactate dehydrogenase (LDH) reaction system in the presence of varying amounts of trimethylamine N-oxide (TMAO), a protein-stabilizing osmolyte, or urea, a protein-destabilizing osmolyte. Trimethylamine N-oxide (TMAO) at a concentration of 1 M strongly increases the rate of hydride transfer, nearly nullifies its activation energy, and also slightly increases the enthalpy of hydride transfer. In 1 M urea, the hydride transfer enthalpy is almost nullified, but the activation energy of the step is not affected significantly. TMAO increases the preference of the closed conformation of the active site loop in the LDH·NAD(+)·lactate complex; urea decreases it. The loop opening rate in the LDH·NADH·pyruvate complex changes its temperature dependence to inverse Arrhenius with TMAO. In this complex, urea accelerates the loop motion, without changing the loop opening enthalpy. A strong, non-Arrhenius decrease in the pyruvate binding rate in the presence of TMAO offers a decrease in the fraction of the open loop, pyruvate binding competent form at higher temperatures. The pyruvate off rate is not affected by urea but decreases with TMAO. Thus, the osmolytes strongly affect the rates and thermodynamics of specific events along the LDH-catalyzed reaction: binding of substrates, loop closure, and the chemical event. Qualitatively, these results can be understood as an osmolyte-induced change in the energy landscape of the protein complexes, shifting the conformational nature of functional substates within the protein ensemble.

  8. Nucleon transfer reactions with radioactive beams

    Science.gov (United States)

    Wimmer, K.

    2018-03-01

    Transfer reactions are a valuable tool to study the single-particle structure of nuclei. At radioactive beam facilities transfer reactions have to be performed in inverse kinematics. This creates a number of experimental challenges, but it also has some advantages over normal kinematics measurements. An overview of the experimental and theoretical methods for transfer reactions, especially with radioactive beams, is presented. Recent experimental results and highlights on shell evolution in exotic nuclei are discussed.

  9. Tandem Three-Component Reactions of Aldehyde, Alkyl Acrylate, and Dialkylmalonate Catalyzed by Ethyl Diphenylphosphine

    Directory of Open Access Journals (Sweden)

    Utpal Das

    2012-03-01

    Full Text Available A new highly efficient three-component reaction of alkyl acrylate, aldehyde and dialkyl malonate using ethyl diphenylphosphine as organocatalyst has been described. Various highly functional compounds bearing hydroxyl groups and the ester functions can be easily prepared in moderate to good yields according to our one-step procedure. The reactions are believed to proceed via Morita-Baylis-Hillman reactions of alkyl acrylate and aldehydes, followed by the Michael addition reactions of dialkyl malonates. Our reactions indicated that the intermediate species formed in the phosphine-catalyzed MBH reaction are an effective organic base to catalyze the Michael addition reactions of dialkyl malonates to the preformed MBH adducts.

  10. Stereochemical course of enzyme-catalyzed aminopropyl transfer: spermidine synthase

    Energy Technology Data Exchange (ETDEWEB)

    Kullberg, D.W.; Orr, G.R.; Coward, J.K.

    1986-05-01

    The R and S enantionmers of S-adenosyl-3-(/sup 2/H)3-(methylthio)-1-propylamine (decarboxylated S-adenosylmethionine), previously synthesized in this laboratory, were incubated with (1,4-/sup 2/H/sub 4/)-putrescine in the presence of spermidine synthase from E. coli. The resulting chiral (/sup 2/H/sub 5/)spermidines were isolated and converted to their N/sub 1/,N/sub 7/-dibocspermidine-N/sub 4/-(1S,4R)-camphanamides. The derivatives were analyzed by 500 MHz /sup 1/H-NMR and the configuration of the chiral center assigned by correlation with the spectra of synthetic chiral (/sup 2/H/sub 3/)dibocspermidine camphanamide standards. The enzyme-catalyzed aminopropyl transfer was shown to occur with net retention of configuration, indicative of a double-displacement mechanism. This result concurs with that of a previous steady-state kinetics study of spermidine synthase isolated from E. coli, but contradicts the single-displacement mechanism suggested by a stereochemical analysis of chiral spermidines biosynthesized in E. coli treated with chirally deuterated methionines. It also indicates that this aminopropyltransferase is mechanistically distinct from the methyltransferases, which have been shown to act via a single-displacement mechanism (net inversion at -CH/sub 3/) in all cases studied to date.

  11. Scattering and transfer reactions with heavy ions

    International Nuclear Information System (INIS)

    Hussein, M.S.

    From the elastic scattering analysis the input parameters are found for the inelastic scattering analysis and the transfer reactions of the heavy ion reactions. The main theme reported is the likeness and conection among these processes. (L.C.) [pt

  12. Revised Theoretical Model on Enantiocontrol in Phosphoric Acid Catalyzed H-Transfer Hydrogenation of Quinoline.

    Science.gov (United States)

    Pastor, Julien; Rezabal, Elixabete; Voituriez, Arnaud; Betzer, Jean-François; Marinetti, Angela; Frison, Gilles

    2018-03-02

    The enantioselective H-transfer hydrogenation of quinoline by Hantzsch ester is a relevant example of Brønsted acid catalyzed cascade reactions, with phosphoric acid being a privileged catalyst. The generally accepted mechanism points out the hydride transfer step as the rate- and stereodetermining step, however computations based on these models do not totally fit with experimental observations. We hereby present a computational study that enlightens the stereochemical outcome and quantitatively reproduces the experimental enantiomeric excesses in a series of H-transfer hydrogenations. Our calculations suggest that the high stereocontrol usually attained with BINOL-derived phosphoric acids results mostly from the steric constraints generated by an aryl substituent of the catalyst, which hinders the access of the Hantzsch ester to the catalytic site and enforces approach through a specific way. It relies on a new model involving the preferential assembly of one of the stereomeric complexes formed by the chiral phosphoric acid and the two reaction partners. The stereodetermining step thus occurs prior to the H-transfer step.

  13. Proton transfer reaction - mass spectrometry

    International Nuclear Information System (INIS)

    Cappellin, L.

    2012-01-01

    Proton transfer reaction mass spectrometry (PTR-MS) provides on-line monitoring of volatile organic compounds (VOCs) with a low detection threshold and a fast response time. Commercially available set-ups are usually based on quadrupole analysers but recently new instruments based on time-of-flight (PTR-ToF-MS) analysers have been proposed and commercialized. PTR-MS has been successfully applied to a variety of fields including environmental science, food science and technology, plant physiology and medical science. Many new challenges arise from the newly available PTR-ToF-MS instruments, ranging from mass calibration and absolute VOC concentration determination to data mining and sample classification. This thesis addresses some of these problems in a coherent framework. Moreover, relevant applications in food science and technology are presented. It includes twelve papers published in peer reviewed journals. Some of them address methodological issues regarding PTR-ToF-MS; the others contain applicative studies of PTR-ToF-MS to food science and technology. Among them, there are the first two published applications of PTR-ToF-MS in this field. (author)

  14. Inter- and intramolecular aldol reactions promiscuously catalyzed by a proline-based tautomerase

    NARCIS (Netherlands)

    Rahimi, Mehran; Geertsema, Edzard M; Miao, Yufeng; van der Meer, Jan-Ytzen; Bosch, van den Thea; de Haan, Pim; Zandvoort, Ellen; Poelarends, Gerrit J

    2017-01-01

    The enzyme 4-oxalocrotonate tautomerase (4-OT), which in nature catalyzes a tautomerization step as part of a catabolic pathway for aromatic hydrocarbons, was found to promiscuously catalyze different types of aldol reactions. These include the self-condensation of propanal, the cross-coupling of

  15. A unified diabatic description for electron transfer reactions, isomerization reactions, proton transfer reactions, and aromaticity.

    Science.gov (United States)

    Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

    2015-10-14

    While diabatic approaches are ubiquitous for the understanding of electron-transfer reactions and have been mooted as being of general relevance, alternate applications have not been able to unify the same wide range of observed spectroscopic and kinetic properties. The cause of this is identified as the fundamentally different orbital configurations involved: charge-transfer phenomena involve typically either 1 or 3 electrons in two orbitals whereas most reactions are typically closed shell. As a result, two vibrationally coupled electronic states depict charge-transfer scenarios whereas three coupled states arise for closed-shell reactions of non-degenerate molecules and seven states for the reactions implicated in the aromaticity of benzene. Previous diabatic treatments of closed-shell processes have considered only two arbitrarily chosen states as being critical, mapping these states to those for electron transfer. We show that such effective two-state diabatic models are feasible but involve renormalized electronic coupling and vibrational coupling parameters, with this renormalization being property dependent. With this caveat, diabatic models are shown to provide excellent descriptions of the spectroscopy and kinetics of the ammonia inversion reaction, proton transfer in N2H7(+), and aromaticity in benzene. This allows for the development of a single simple theory that can semi-quantitatively describe all of these chemical phenomena, as well as of course electron-transfer reactions. It forms a basis for understanding many technologically relevant aspects of chemical reactions, condensed-matter physics, chemical quantum entanglement, nanotechnology, and natural or artificial solar energy capture and conversion.

  16. First Novozym 435 lipase-catalyzed Morita-Baylis-Hillman reaction in the presence of amides.

    Science.gov (United States)

    Tian, Xuemei; Zhang, Suoqin; Zheng, Liangyu

    2016-03-01

    The first Novozym 435 lipase-catalyzed Morita-Baylis-Hillman (MBH) reaction with amides as co-catalyst was realized. Results showed that neither Novozym 435 nor amide can independently catalyze the reaction. This co-catalytic system that used a catalytic amount of Novozym 435 with a corresponding amount of amide was established and optimized. The MBH reaction strongly depended on the structure of aldehyde substrate, amide co-catalyst, and reaction additives. The optimized reaction yield (43.4%) was achieved in the Novozym 435-catalyzed MBH reaction of 2, 4-dinitrobenzaldehyde and cyclohexenone with isonicotinamide as co-catalyst and β-cyclodextrin as additive only in 2 days. Although enantioselectivity of Novozym 435 was not found, the results were still significant because an MBH reaction using lipase as biocatalyst was realized for the first time. Copyright © 2015 Elsevier Inc. All rights reserved.

  17. C (sp2)–C (sp2) cross coupling reaction catalyzed by a palladacycle ...

    Indian Academy of Sciences (India)

    (sp2) cross coupling reaction catalyzed by a palladacycle phosphine complex: A simple and sustainable protocol in aqueous media. Seyyed Javad Sabounchei Marjan Hosseinzadeh. Articles Volume 127 Issue 11 November 2015 pp 1919- ...

  18. Gold(III)-catalyzed three-component coupling reaction (TCC) selective toward furans.

    Science.gov (United States)

    Li, Jian; Liu, Li; Ding, Dong; Sun, Jiangtao; Ji, Yangxuan; Dong, Jialing

    2013-06-07

    An efficient three-component coupling reaction toward a variety of furan derivatives has been developed. This cascade transformation proceeds via the gold-catalyzed coupling reaction of phenylglyoxal derivatives, secondary amines, and terminal alkynes, under the reaction conditions, that undergoes cyclization into the furan core.

  19. Benchmarking Quantum Mechanics/Molecular Mechanics (QM/MM) Methods on the Thymidylate Synthase-Catalyzed Hydride Transfer.

    Science.gov (United States)

    Świderek, Katarzyna; Arafet, Kemel; Kohen, Amnon; Moliner, Vicent

    2017-03-14

    Given the ubiquity of hydride-transfer reactions in enzyme-catalyzed processes, identifying the appropriate computational method for evaluating such biological reactions is crucial to perform theoretical studies of these processes. In this paper, the hydride-transfer step catalyzed by thymidylate synthase (TSase) is studied by examining hybrid quantum mechanics/molecular mechanics (QM/MM) potentials via multiple semiempirical methods and the M06-2X hybrid density functional. Calculations of protium and tritium transfer in these reactions across a range of temperatures allowed calculation of the temperature dependence of kinetic isotope effects (KIE). Dynamics and quantum-tunneling effects are revealed to have little effect on the reaction rate, but are significant in determining the KIEs and their temperature dependence. A good agreement with experiments is found, especially when computed for RM1/MM simulations. The small temperature dependence of quantum tunneling corrections and the quasiclassical contribution term cancel each other, while the recrossing transmission coefficient seems to be temperature-independent over the interval of 5-40 °C.

  20. Recent developments in gold-catalyzed cycloaddition reactions

    Directory of Open Access Journals (Sweden)

    Fernando López

    2011-08-01

    Full Text Available In the last years there have been extraordinary advances in the development of gold-catalyzed cycloaddition processes. In this review we will summarize some of the most remarkable examples, and present the mechanistic rational underlying the transformations.

  1. DNA and Protein Requirements for Substrate Conformational Changes Necessary for Human Flap Endonuclease-1-catalyzed Reaction*

    Science.gov (United States)

    Algasaier, Sana I.; Exell, Jack C.; Bennet, Ian A.; Thompson, Mark J.; Gotham, Victoria J. B.; Shaw, Steven J.; Craggs, Timothy D.; Finger, L. David; Grasby, Jane A.

    2016-01-01

    Human flap endonuclease-1 (hFEN1) catalyzes the essential removal of single-stranded flaps arising at DNA junctions during replication and repair processes. hFEN1 biological function must be precisely controlled, and consequently, the protein relies on a combination of protein and substrate conformational changes as a prerequisite for reaction. These include substrate bending at the duplex-duplex junction and transfer of unpaired reacting duplex end into the active site. When present, 5′-flaps are thought to thread under the helical cap, limiting reaction to flaps with free 5′-termini in vivo. Here we monitored DNA bending by FRET and DNA unpairing using 2-aminopurine exciton pair CD to determine the DNA and protein requirements for these substrate conformational changes. Binding of DNA to hFEN1 in a bent conformation occurred independently of 5′-flap accommodation and did not require active site metal ions or the presence of conserved active site residues. More stringent requirements exist for transfer of the substrate to the active site. Placement of the scissile phosphate diester in the active site required the presence of divalent metal ions, a free 5′-flap (if present), a Watson-Crick base pair at the terminus of the reacting duplex, and the intact secondary structure of the enzyme helical cap. Optimal positioning of the scissile phosphate additionally required active site conserved residues Tyr40, Asp181, and Arg100 and a reacting duplex 5′-phosphate. These studies suggest a FEN1 reaction mechanism where junctions are bound and 5′-flaps are threaded (when present), and finally the substrate is transferred onto active site metals initiating cleavage. PMID:26884332

  2. Quantifying electron transfer reactions in biological systems

    DEFF Research Database (Denmark)

    Sjulstok, Emil Sjulstok; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-01-01

    to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe...

  3. Water-Gas Shift Reaction Catalyzed by Redox Enzymes on Conducting Graphite Platelets

    OpenAIRE

    Lazarus, Oliver; Woolerton, Thomas W.; Parkin, Alison; Lukey, Michael J.; Reisner, Erwin; Seravalli, Javier; Pierce, Elizabeth; Ragsdale, Stephen W.; Sargent, Frank; Armstrong, Fraser A.

    2009-01-01

    The water-gas shift (WGS) reaction (CO + H2O ⇆ CO2 + H2) is of major industrial significance in the production of H2 from hydrocarbon sources. High temperatures are required, typically in excess of 200 °C, using d-metal catalysts on oxide supports. In our study the WGS process is separated into two half-cell electrochemical reactions (H+ reduction and CO oxidation), catalyzed by enzymes attached to a conducting particle. The H+ reduction reaction is catalyzed by a hydrogenase, Hyd-2, from Esc...

  4. 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.

  5. Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of “hunger hormone” ghrelin

    Science.gov (United States)

    Yao, Jianzhuang; Yuan, Yaxia; Zheng, Fang; Zhan, Chang-Guo

    2016-02-01

    Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway.

  6. Palladium-Catalyzed Cross-Coupling Reactions of Perfluoro Organic Compounds

    Directory of Open Access Journals (Sweden)

    Masato Ohashi

    2014-09-01

    Full Text Available In this review, we summarize our recent development of palladium(0-catalyzed cross-coupling reactions of perfluoro organic compounds with organometallic reagents. The oxidative addition of a C–F bond of tetrafluoroethylene (TFE to palladium(0 was promoted by the addition of lithium iodide, affording a trifluorovinyl palladium(II iodide. Based on this finding, the first palladium-catalyzed cross-coupling reaction of TFE with diarylzinc was developed in the presence of lithium iodide, affording α,β,β-trifluorostyrene derivatives in excellent yield. This coupling reaction was expanded to the novel Pd(0/PR3-catalyzed cross-coupling reaction of TFE with arylboronates. In this reaction, the trifluorovinyl palladium(II fluoride was a key reaction intermediate that required neither an extraneous base to enhance the reactivity of organoboronates nor a Lewis acid additive to promote the oxidative addition of a C–F bond. In addition, our strategy utilizing the synergetic effect of Pd(0 and lithium iodide could be applied to the C–F bond cleavage of unreactive hexafluorobenzene (C6F6, leading to the first Pd(0-catalyzed cross-coupling reaction of C6F6 with diarylzinc compounds.

  7. Ru(II)-catalyzed amidation reactions of 8-methylquinolines with azides via C(sp(3))-H activation.

    Science.gov (United States)

    Liu, Bingxian; Li, Bin; Wang, Baiquan

    2015-11-25

    Ru(II)-catalyzed amidation reactions of 8-methylquinolines with azides have been developed. They are the first examples of [(p-cymene)RuCl2]2-catalyzed C(sp(3))-H bond intermolecular amidation reactions which give quinolin-8-ylmethanamines under mild reaction conditions in good yields.

  8. One enzyme, many reactions: structural basis for the various reactions catalyzed by naphthalene 1,2-dioxygenase

    Directory of Open Access Journals (Sweden)

    Daniel J. Ferraro

    2017-09-01

    Full Text Available Rieske nonheme iron oxygenases (ROs are a well studied class of enzymes. Naphthalene 1,2-dioxygenase (NDO is used as a model to study ROs. Previous work has shown how side-on binding of oxygen to the mononuclear iron provides this enzyme with the ability to catalyze stereospecific and regiospecific cis-dihydroxylation reactions. It has been well documented that ROs catalyze a variety of other reactions, including mono-oxygenation, desaturation, O- and N-dealkylation, sulfoxidation etc. NDO itself catalyzes a variety of these reactions. Structures of NDO in complex with a number of different substrates show that the orientation of the substrate in the active site controls not only the regiospecificity and stereospecificity, but also the type of reaction catalyzed. It is proposed that the mononuclear iron-activated dioxygen attacks the atoms of the substrate that are most proximal to it. The promiscuity of delivering two products (apparently by two different reactions from the same substrate can be explained by the possible binding of the substrate in slightly different orientations aided by the observed flexibility of residues in the binding pocket.

  9. Multistep enzyme catalyzed reactions for unnatural amino acids.

    Science.gov (United States)

    D'Arrigo, Paola; Tessaro, Davide

    2012-01-01

    The use of unnatural amino acids, particularly synthetic α-amino acids, for modern drug discovery research requires the availability of enantiomerically pure isomers. Starting from a racemate, one single enantiomer can be obtained using a deracemization process. The two more common strategies of deracemization are those obtained by stereoinversion and by dynamic kinetic resolution. Both techniques will be here described using as a substrate the D,L-3-(2-naphthyl)-alanine, a non-natural amino acid: the first one employing a multi-enzymatic redox system, the second one combining an hydrolytic enzyme together with a base-catalyzed substrate racemization. In both cases, the final product, L-3-(2-naphthyl)alanine, is recovered with good yield and excellent enantiomeric excess.

  10. The Oxidative Mannich Reaction Catalyzed by Dirhodium Caprolactamate

    Science.gov (United States)

    Catino, Arthur J.; Nichols, Jason M.; Nettles, Brian J.; Doyle, Michael P.

    2008-01-01

    Dirhodium caprolactamate [Rh2(cap)4] is a highly effective catalyst for the oxidative Mannich reaction. The reaction proceeds via C-H oxidation of a tertiary amine followed by nucleophilic capture. This green transformation is conducted in protic solvent using inexpensive T-HYDRO® (70% t–BuOOH in water). Synthetically valuable γ-aminoalkyl-butenolides are obtained. PMID:16637627

  11. Lipase-catalyzed reactions in organic media: competition and applications.

    Science.gov (United States)

    Deleuze, H; Langrand, G; Millet, H; Baratti, J; Buono, G; Triantaphylides, C

    1987-01-05

    Lipases (triacylglycerol acylhydrolase, EC 3.1.1.3) have been used in organic media for the catalysis of reactions such as hydrolysis, esterification and transesterification. In these conditions it was confirmed that all reactions proceed through an acyl enzyme intermediate in two successive steps: acyl enzyme formation and solvolysis. The competition between two acyl acceptors (acyl donors) for reaction with a donor (acceptor) is described for the first time. A kinetic model is proposed using a competitive factor which is in good accordance with experimental results. The model was used successfully for the prediction of alcohol (acid) separations and resolutions by lipases.

  12. Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

    OpenAIRE

    Zhenghua Tang; Wen Wu; Kai Wang

    2018-01-01

    Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction ...

  13. Iron-Catalyzed Asymmetric Nitro-Mannich Reaction.

    Science.gov (United States)

    Dudek, Agata; Mlynarski, Jacek

    2017-10-20

    The first enantioselective addition of nitroalkanes to imines (nitro-Mannich reaction), mediated by an iron(II) catalyst assembled by a hindered hydroxyethyl-pybox ligand, is described. This valuable carbon-carbon bond-forming reaction proceeds smoothly at room temperature to afford enantioenriched β-nitro amines in good yields and high enantioselectivity, up to 98% with unprecedentedly low iron catalyst loading (5 mol %).

  14. Carbocyclization versus oxycyclization on the metal-catalyzed reactions of oxyallenyl C3-linked indoles.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro; Alonso, José M; Fernández, Israel

    2013-07-05

    The preparation of previously unknown (indol-3-yl)-α-allenols and -allenones was accomplished from indole-3-carbaldehydes, through indium-mediated Barbier allenylation reaction taking advantage of the N-(2-pyridyl)sulfonyl group. Metal-catalyzed cyclizations of oxyallenyl C3-linked indoles proceeded in two ways depending on the presence or absence of the N-(2-pyridyl)sulfonyl group. For allenols, gold-catalyzed oxycyclization occurred in the presence of the protecting group; in the absence of the protecting group, palladium- and gold-catalyzed benzannulations operated. On the contrary, under gold catalysis furyl-indoles were obtained as exclusive products from NH-allenones, while 5-endo carbocyclization adducts were the major components starting from N-SO2py-protected allenones. These cyclization reactions have been developed experimentally, and their mechanisms have additionally been investigated by a computational study.

  15. Recent Developments in Electron Transfer Reactions.

    Science.gov (United States)

    1987-05-29

    Developments in ElectronTransfer Reactions by R.A. Marcus Prepared for Publication in Nouveau J. Chimie California Institute of Technology Noyes... coordination shell of the reactants. Comparison of the various predictions with the experimental data has been described in the review with Sutin.1 Electron

  16. Ag-catalyzed InAs nanowires grown on transferable graphite flakes

    DEFF Research Database (Denmark)

    Meyer-Holdt, Jakob; Kanne, Thomas; Sestoft, Joachim E.

    2016-01-01

    on exfoliated graphite flakes by molecular beam epitaxy. Ag catalyzes the InAs nanowire growth selectively on the graphite flakes and not on the underlying InAs substrates. This allows for easy transfer of the flexible graphite flakes with as-grown nanowire ensembles to arbitrary substrates by a micro-needle...

  17. Nickel-catalyzed reactions of enone with ethylene

    International Nuclear Information System (INIS)

    Nishimura, A; Haba, T; Ohashi, M; Ogoshi, S

    2010-01-01

    The reaction of (E)-1-phenylbut-2-en-1-one with ethylene in the presence of a catalytic amount of Ni(cod) 2 and PCy 3 at room temperature gave two kinds of three-component addition products; one is 1,6-enone composed of an enone and two ethylene molecules, and the other is 1,5-diketone composed of two enones and an ethylene. The reactions might proceed via oxidative cyclization of an enone and an ethylene with nickel(0).

  18. A novel reactor for determination of kinetics for solid catalyzed gas reactions

    NARCIS (Netherlands)

    Borman, P.C.; Borman, P.C.; Bos, A.N.R.; Bos, A.N.R.; Westerterp, K.R.

    1994-01-01

    A novel perfectly mixed laboratory reactor for determining kinetics of heterogeneously catalyzed gas-phase reactions has been developed. Perfect mixing is achieved by circulating the gas in the reactor using an axial flow impeller in a well streamlined enclosure. Pellets are fixed in a rectangular

  19. Synthesis of (-)-Δ9-trans-Tetrahydrocannabinol - Stereocontrol via Mo-catalyzed Asymmetric Allylic Alkylation Reaction

    Science.gov (United States)

    Trost, Barry M.; Dogra, Kalindi

    2008-01-01

    Δ9-THC is synthesized in enantiomericaly pure form, where all of the stereochemistry is derived from the molybdenum catalyzed asymmetric alkylation reaction of the extremely sterically congested bis-ortho substituted cinnamyl carbonate in high regio- and enantioselectivity. PMID:17266321

  20. A simple model for chiral amplification in the aminoalcohol-catalyzed reaction of aldehydes with dialkylzinc

    Directory of Open Access Journals (Sweden)

    IVAN GUTMAN

    1999-08-01

    Full Text Available A simple explanation is offered for the recently discovered chiral amplification in the alkylation reaction of benzaldehyde by means of dialkylzinc, catalyzed by (dimethylaminoisoborneol. The model presentd is similar to, yet somewhat simpler than, the model put forward by Noyori et al.

  1. Copper-catalyzed asymmetric allylic substitution reactions with organozinc and Grignard reagents

    NARCIS (Netherlands)

    Geurts, Koen; Fletcher, Stephen P.; van Zijl, Anthoni W.; Minnaard, Adriaan J.; Feringa, Ben L.; Bignall, H. E.; Jauncey, D. L.; Lovell, J. E. J.; Tzioumis, A. K.; Kedziora-Chudczer, L. L.; MacQuart, J. P.; Tingay, S. J.; Rayner, D. P.; Clay, R. W.

    Asymmetric allylic alkylations (AAAs) are among the most powerful C-C bond-forming reactions. We present a brief overview of copper-catalyzed AAAs with organometallic reagents and discuss our own contributions to this field. Work with zinc reagents and phosphoramidite ligands provided a framework

  2. Tunable Metal-Catalyzed Heterocyclization Reactions of Allenic Amino Alcohols: An Experimental and Theoretical Study.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro; Aragoncillo, Cristina; Gómez-Campillos, Gonzalo; Quirós, M Teresa; Soriano, Elena

    2016-08-10

    Controlled preparation of 2,5-dihydro-1H-pyrroles, 3,6-dihydro-2H-pyrans, and pyrroles has been achieved through switchable chemo- and regioselectivity in the metal-catalyzed heterocyclization reactions of allenic amino alcohols. The gold-catalyzed cycloisomerization reaction of α-amino-β-hydroxyallenes was effective as 5-endo cyclization by addition of amino functionality to the distal allene carbon to yield enantiopure 2,5-dihydro-1H-pyrroles, whereas their palladium-catalyzed cyclizative coupling reactions furnished 3,6-dihydro-2H-pyrans through a chemo- and regioselective 6-endo cycloetherification. Conversely, the gold-catalyzed heterocyclization reaction of β-amino-γ-hydroxyallenes generated exclusively pyrrole derivatives. These results could be explained through a chemo- and regioselective 5-exo aminocyclization to the central allene carbon followed by aromatization. Chemo- and regioselectivity depend on both linker elongation as well as the type of catalyst. This behavior can be justified by means of density functional theory calculations.

  3. Enantioconvergent synthesis by sequential asymmetric Horner-Wadsworth-Emmons and palladium-catalyzed allylic substitution reactions

    DEFF Research Database (Denmark)

    Pedersen, Torben Møller; Hansen, E. Louise; Kane, John

    2001-01-01

    A new method for enantioconvergent synthesis has been developed. The strategy relies on the combination of an asymmetric Horner-Wadsworth-Emmons (HWE) reaction and a palladium-catalyzed allylic substitution. Different $alpha@-oxygen-substituted, racemic aldehydes were initially transformed by asy...

  4. The Manganese-Catalyzed Cross-Coupling Reaction and the Influence of Trace Metals

    DEFF Research Database (Denmark)

    Santilli, Carola; Beigbaghlou, Somayyeh Sarvi; Ahlburg, Andreas

    2017-01-01

    The substrate scope of the MnCl2-catalyzed cross-coupling between aryl halides and Grignard reagents has been extended to several methyl-substituted aryl iodides by performing the reaction at elevated temperature in a microwave oven. A radical clock experiment revealed the presence of an aryl...

  5. S,O-Ligand-Promoted Palladium-Catalyzed C-H Functionalization Reactions of Nondirected Arenes

    NARCIS (Netherlands)

    Naksomboon, K.; Valderas, C.; Gomez-Martinez, M.; Alvarez-Casao, Y.; Fernández Ibáñez, M.A.

    Pd(II)-catalyzed C-H functionalization of non directed arenes has been realized using an inexpensive and easily accessible type of bidentate S,O-ligand. The catalytic system shows high efficiency in the C-H olefination reaction of electron-rich and electron-poor arenes. This methodology is

  6. An enantioselective Brønsted acid catalyzed enamine Mannich reaction.

    Science.gov (United States)

    Tillman, A Louise; Dixon, Darren J

    2007-02-21

    An enantioselective Brønsted acid catalyzed Mannich reaction between acetophenone derived enamines and N-Boc imines has been developed. Simple diol (S)-H(8)-BINOL has been identified as the optimal catalyst, to afford versatile beta-amino aryl ketones in good yield and enantiomeric excess.

  7. Palladium(II) Acetate Catalyzed Reductive Heck Reaction of Enones; A Practical Approach

    NARCIS (Netherlands)

    Mannathan, Subramaniyan; Raoufmoghaddam, Saeed; Reek, Joost N. H.; de Vries, Johannes G.; Minnaard, Adriaan J.

    2015-01-01

    A surprisingly practical Pd(OAc)(2) or Pd(TFA)(2)-catalyzed reductive Heck reaction between aryl iodides and alpha,beta-unsaturated ketones is described using N,N-diisopropylethylamine (DIPEA, Hunigs base) as the reductant. In general, 1 mol% of Pd(OAc)(2) is sufficient to afford good yields using

  8. Homogeneously catalyzed reactions under high-pressure conditions; Homogen katalysierte Reaktionen unter hohen Druecken

    Energy Technology Data Exchange (ETDEWEB)

    Albers, J.

    2003-05-01

    One of the most important process parameters of chemical reactions with involvement of gaseous substrates is the pressure. In the range of high pressures (> 5000 bar) the physical-chemical principles have not been broadly investigated yet. In particular, the influence of high pressure on homogeneously catalyzed reactions is still widely unknown. In this work the influence of high pressure on selectivities and yields is studied for two homogeneously rhodium catalyzed reactions. In both reactions, the hydroformylation of olefins and the cooligomerization of 1,3-butadiene and CO{sub 2} significant changes in the product distribution are observed. The experiments have been performed in a newly constructed equipment, that enables to carry out experiments reproducibly under inert gas conditions in two different reactors at pressures up to 150 bar and up to 7000 bar, respectively. (orig.)

  9. Insight into solid-liquid phase transfer catalyzed synthesis of ...

    Indian Academy of Sciences (India)

    2-Methyl-4-chlorophenoxy propionic acid (Mecoprop) is a widely used household herbicide. In the current work, a simple synthetic method is developed for Mecoprop methyl ester using solid-liquid phase transfer catalysis (S-L PTC) with K₂CO₃ as mild base and toluene as solvent. Conversion of 95% was achieved with ...

  10. The three transglycosylation reactions catalyzed by cyclodextrin glycosyltransferase from Bacillus circulans (strain 251) proceed via different kinetic mechanisms

    NARCIS (Netherlands)

    Veen, Bart A. van der; Alebeek, Gert-Jan W.M. van; Uitdehaag, Joost C.M.; Dijkstra, Bauke W.; Dijkhuizen, Lubbert

    Cyclodextrin glycosyltransferase (CGTase) catalyzes three transglycosylation reactions via a double displacement mechanism involving a covalent enzyme-intermediate complex (substituted-enzyme intermediate). Characterization of the three transglycosylation reactions, however, revealed that they

  11. Efficient Synthesis of Spirobarbiturates and Spirothiobarbiturates Bearing Cyclopropane Rings by Rhodium(II)-Catalyzed Reactions of Cyclic Diazo Compounds

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xue; Lee, Yong Rok [Yeungnam Univ., Gyeongsan (Korea, Republic of)

    2013-06-15

    Rhodium(II)-catalyzed reactions of cyclic diazo compounds derived from barbituric acid and thiobarbituric acid with a variety of styrene moieties were examined. These reactions provide rapid synthetic routes to the preparations of spirobarbiturates and spirothiobarbiturates bearing cyclopropane rings.

  12. Visible light catalyzed Mannich reaction between tert-amines and silyl diazoenolates.

    Science.gov (United States)

    Pramanik, Mukund M D; Nagode, Savita B; Kant, Ruchir; Rastogi, Namrata

    2017-09-13

    The present work documents the α-C-H functionalization of tertiary amines via the visible light catalyzed Mannich reaction with silyl diazoenolates. The reaction takes place at room temperature with an organic dye, Rose Bengal, as a photocatalyst and oxygen as the oxidant. The resulting multifunctional products bearing an α-diazo-β-keto group undergo Rh-carbenoid mediated cyclization, affording stable ammonium ylides in high yields.

  13. Synthesis of Indolines by a Zn-Mediated Mannich Reaction/Pd-Catalyzed Amination Sequence.

    Science.gov (United States)

    Presset, Marc; Pignon, Antoine; Paul, Jérôme; Le Gall, Erwan; Léonel, Eric; Martens, Thierry

    2017-03-17

    1,2-Disubstituted indolines have been prepared in fair to good yields by a Zn-mediated organometallic Mannich reaction, followed by an intramolecular Pd-catalyzed aromatic amination. The reactions are easy to set up and compatible with a large variety of simple or commercially available reagents. The method was further extended to the preparation of a 1,2,3-trisubstituted indoline.

  14. Palladium-catalyzed cross-coupling reactions of aryl boronic acids with aryl halides in water.

    Science.gov (United States)

    Wang, Shaoyan; Zhang, Zhiqiang; Hu, Zhizhi; Wang, Yue; Lei, Peng; Chi, Haijun

    2009-01-01

    An efficient Suzuki cross-coupling reaction using a variety of aryl halides in neat water was developed. The Pd-catalyzed reaction between aryl bromides or chlorides and phenyl boronic acids was compatible with various functional groups and affords biphenyls in good to excellent yields without requirement of organic cosolvents. The air stability and solubility in water of the palladium-phosphinous acid complexes were considered to facilitate operation of the coupling reaction and product isolation. The reaction conditions including Pd catalyst selection, temperature, base and catalyst recoverability were also investigated.

  15. Intramolecular energy transfer reactions in polymetallic

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, J.

    1990-11-01

    This report is concerned with intramolecular, energy-transfer reactions. The concept of preparing synthetically a complex molecular species, capable of absorbing a photon at one metal center (antenna fragment), transferring that energy to a second metal center (reactive fragment) via a bridging ligand was first reported by our group in 1979. It is now apparent that a major emphasis in inorganic chemistry in the future will involve these types of molecular ensembles. Complexes discussed include Rh, Ru, and Cu complexes. 23 refs., 14 tabs.

  16. Transfer hydrogenation reactions catalyzed by chiral half-sandwich ...

    Indian Academy of Sciences (India)

    The 2-aminomethylpyrrolidine L4 ligand was pre- pared from the L-proline amide which on reduction with lithium aluminium hydride afforded the 2-amino- methylpyrrolidine L4 ligand (Scheme 3).39 Formation of ligands was confirmed by 1H and 13C NMR spec- troscopy. Metal complexes were synthesized by carrying out.

  17. Transfer hydrogenation reactions catalyzed by chiral half-sandwich ...

    Indian Academy of Sciences (India)

    Chiral ruthenium half-sandwich complexes were prepared using a chelating diamine made from proline with a phenyl, ethyl, or benzyl group, instead of hydrogen on one of the coordinating arms. Three of these complexes were obtained as single diastereoisomers and their configuration identified by X-ray crystallography.

  18. Enantioselective Henry reaction catalyzed by "ship in a bottle" complexes.

    Science.gov (United States)

    Bania, Kusum K; Karunakar, Galla V; Goutham, Kommuru; Deka, Ramesh C

    2013-07-15

    Two chiral Schiff-base complexes of copper(II) have been successfully encapsulated inside the cavity of zeolite-NaY via a "ship in a bottle" synthesis method. The presence of the two complexes inside the cages of zeolite-Y has been confirmed based on various spectrochemical and physicochemical techniques, viz. FTIR, UV-vis/DRS, ESR, XPS, CV, EDX, SEM, and TGA. Zeolite-encapsulated chiral copper(II) Schiff-base complexes are found to give a high-enantioselective (84% ee, R conformation) nitro-aldol product at -20 °C. The encapsulated copper complexes are found to show higher catalytic efficiency than their homogeneous counterparts under identical conditions. Density functional theory (DFT) calculation has been implemented to understand the effect of the zeolite matrix on structural, electronic, and reactivity properties of the synthesized complexes. Theoretical calculation predicts that upon encapsulation into the zeolite matrix the Cu center becomes more susceptible to nucleophilic attack, favoring a nitro-aldol reaction. A plausible mechanism is suggested based on the experimental and theoretical results. The structures of reaction intermediates and transition state(s) involved in the catalytic cycle are derived using DFT.

  19. Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

    Directory of Open Access Journals (Sweden)

    Zhenghua Tang

    2018-02-01

    Full Text Available Highly-efficient catalysts for the oxygen reduction reaction (ORR have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs. The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications.

  20. Enzyme-catalyzed and binding reaction kinetics determined by titration calorimetry.

    Science.gov (United States)

    Hansen, Lee D; Transtrum, Mark K; Quinn, Colette; Demarse, Neil

    2016-05-01

    Isothermal calorimetry allows monitoring of reaction rates via direct measurement of the rate of heat produced by the reaction. Calorimetry is one of very few techniques that can be used to measure rates without taking a derivative of the primary data. Because heat is a universal indicator of chemical reactions, calorimetry can be used to measure kinetics in opaque solutions, suspensions, and multiple phase systems and does not require chemical labeling. The only significant limitation of calorimetry for kinetic measurements is that the time constant of the reaction must be greater than the time constant of the calorimeter which can range from a few seconds to a few minutes. Calorimetry has the unique ability to provide both kinetic and thermodynamic data. This article describes the calorimetric methodology for determining reaction kinetics and reviews examples from recent literature that demonstrate applications of titration calorimetry to determine kinetics of enzyme-catalyzed and ligand binding reactions. A complete model for the temperature dependence of enzyme activity is presented. A previous method commonly used for blank corrections in determinations of equilibrium constants and enthalpy changes for binding reactions is shown to be subject to significant systematic error. Methods for determination of the kinetics of enzyme-catalyzed reactions and for simultaneous determination of thermodynamics and kinetics of ligand binding reactions are reviewed. Copyright © 2015 Elsevier B.V. All rights reserved.

  1. Complementary Strategies for Directed C(sp3)-H Functionalization: A Comparison of Transition-Metal-Catalyzed Activation, Hydrogen Atom Transfer, and Carbene/Nitrene Transfer.

    Science.gov (United States)

    Chu, John C K; Rovis, Tomislav

    2018-01-02

    The functionalization of C(sp 3 )-H bonds streamlines chemical synthesis by allowing the use of simple molecules and providing novel synthetic disconnections. Intensive recent efforts in the development of new reactions based on C-H functionalization have led to its wider adoption across a range of research areas. This Review discusses the strengths and weaknesses of three main approaches: transition-metal-catalyzed C-H activation, 1,n-hydrogen atom transfer, and transition-metal-catalyzed carbene/nitrene transfer, for the directed functionalization of unactivated C(sp 3 )-H bonds. For each strategy, the scope, the reactivity of different C-H bonds, the position of the reacting C-H bonds relative to the directing group, and stereochemical outcomes are illustrated with examples in the literature. The aim of this Review is to provide guidance for the use of C-H functionalization reactions and inspire future research in this area. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Applications of Palladium-Catalyzed C–N Cross-Coupling Reactions

    Science.gov (United States)

    2016-01-01

    Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts. PMID:27689804

  3. Development of Fluorous Lewis Acid-Catalyzed Reactions

    Directory of Open Access Journals (Sweden)

    Joji Nishikido

    2006-08-01

    Full Text Available Organic synthetic methodology in the 21st century aims to conform to the principles of green sustainable chemistry (GSC and we may expect that in the future, the realization of GSC will be an important objective for chemical industries. An important aim of synthetic organic chemistry is to implement waste-free and environmentally-benign industrial processes using Lewis acids as versatile as aluminum choride. A key technological objective of our work in this area has been to achieve a “catalyst recycling system that utilizes the high activity and structural features of fluorous Lewis acid catalysts”. Thus, we have developed a series of novel fluorous Lewis acid catalysts, namely the ytterbium(III, scandium(III, tin(IV or hafnium(IV bis(perfluoroalkanesulfonylamides or tris(perfluoro- alkanesulfonylmethides. Our catalysts are recyclable and effective for acylations of alcohols and aromatics, Baeyer-Villiger reactions, direct esterifications and transesterifications in a fluorous biphasic system (FBS, in supercritical carbon dioxide and on fluorous silica gel supports.

  4. Gold versus silver catalyzed intramolecular hydroarylation reactions of [(3-arylprop-2-ynyl)oxy]benzene derivatives.

    Science.gov (United States)

    Arcadi, Antonio; Blesi, Federico; Cacchi, Sandro; Fabrizi, Giancarlo; Goggiamani, Antonella; Marinelli, Fabio

    2012-12-28

    The scope and the generality of gold versus silver catalyzed intramolecular hydroarylation reactions of 3-[(3-arylprop-2-ynyl)oxy]benzene derivatives in terms of rings substitution were investigated. Only products deriving from 6-endo cyclization were exclusively formed. The features of substituents had a considerable effect on the reaction outcome in the presence of silver catalysis, whereas gold catalysis revealed a unique blend of reactivity and selectivity and represented the only choice for the intramolecular hydroarylation reaction of the starting substrates bearing electron deficient arenes.

  5. Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

    Directory of Open Access Journals (Sweden)

    Katrina Tait

    2016-10-01

    Full Text Available Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene derivatives using alcohol nucleophiles were investigated. The optimal conditions were found to be 10 mol % PdCl2(CH3CN2 in methanol, offering yields up to 92%. The reaction was successful using primary, secondary and tertiary alcohol nucleophiles and was compatible with a variety of substituents on cyclopropanated oxabenzonorbornadiene. With unsymmetrical C1-substituted cyclopropanated 7-oxabenzonorbornadienes, the regioselectivity of the reaction was excellent, forming only one regioisomer in all cases.

  6. Hydrogen transfer reaction on rare earth oxides

    International Nuclear Information System (INIS)

    Minachev, Kh.M.; Atal'yan, O.K.; Markov, M.A.

    1978-01-01

    The ketone reduction by alcohols is studied on a large group of rare earth oxides. The reactions of octanol-2 with cyclohexan one, n. butanol with dipropyl ketone and acetone have been chosen for a model. It has been shown that La,Nd,Sm,Gd,Dy,Er and Y oxides are active in the reactions of hydrogen transfer from n. butanol to dipropyl ketone and acetone and from octanol-2 to cyclohexanone the last reaction being the most selective. The comparative reactivity of ketones-acceptors of hydrogen at their interaction with n. butanol is in conformity with the values of their normal oxidative potentials. By addition of ketone to n. butanol the general degree of catalytic transformation of the latter increases and the selectivity in ketonization ratio decreases. It has been established that catalyst activity increases with the temperature rise

  7. Glutathiolactaldehyde as a probe of the overall stereochemical course of glyoxalase-I catalyzed reactions

    International Nuclear Information System (INIS)

    Brush, E.J.; Kozarich, J.W.

    1986-01-01

    The overall stereochemical course of the reactions catalyzed by glyoxalase-I (GX-I) has remained elusive as the substrates are equilibrium mixtures of rapidly interconverting diastereomeric thiohemiacetals. However, with the discovery of inverse substrate processing by Kozarich and coworkers, it is possible to design GX-I substrate analogs that are intrinsically more stable than the thiohemiacetals. Hence, Chari and Kozarich reported that glutathiohydroxyacetone (GHA, GSCH 2 COCH 2 OH) undergoes GX-I catalyzed exchange of the pro-S hydroxymethyl proton with solvent deuterium. Their data suggest that GX-I processes a single diastereomeric thiohemiacetal, and are consistent with a cis-enediol intermediate. To test this hypothesis and to follow the overall stereochemistry on a single substrate, they have prepared glutathiolactaldehyde (GLA, GSCH 2 CHOHCHO) as a potential inverse substrate. Human erythrocyte GX-I catalyzes the isomerization of GLA to GHA as evidenced by UV and NMR spectra of the product. Solvent deuterium is incorporated into the hydroxymethyl position, and NMR data suggest that incorporation is stereospecific. Furthermore, 50% of the expected amount of GHA is produced indicating that only one diastereomer of GLA is processed by GX-I. Identification of the absolute stereochemistry of the substrate diastereomer will lead to a clarification of the overall stereochemical and mechanistic course of GX-I catalyzed reactions

  8. Folylpolyglutamate synthetase: direct evidence for an acyl phosphate intermediate in the enzyme-catalyzed reaction

    Energy Technology Data Exchange (ETDEWEB)

    Banerjee, R.; McGuire, J.J.; Shane, B.; Coward, J.K.

    1986-05-01

    The nature of the intermediate in the reaction catalyzed by folylpoly-..gamma..-glutamate synthetase (FPGS) has been investigated. Incubation of ..cap alpha..,..gamma..-(/sup 18/O)methotrexate with ATP, glutamate, and FPGS resulted in the formation of (/sup 18/O)phosphate, thus providing strong evidence for the formation of a ..gamma..-glutamyl phosphate during catalysis. The inorganic phosphate formed in the enzyme-catalyzed reaction was separated from other products and substrates by chromatography on DEAE-cellulose, then converted to the trimethyl ester, and analyzed by mass spectroscopy. Stoichiometric formation of (/sup 18/O)phosphate was observed in the case of the E. coli enzyme, isolated from a transformant containing the cloned FPGS-dihydrofolate synthetase (folC) gene. In addition, /sup 31/P-NMR analysis of the phosphate isolated from the reaction using E. coli FPGS showed the expected /sup 18/O-isotopic perturbations due to both singly bonded and doubly bonded P-/sup 18/O species. Similar experiments were carried out with FPGS isolated from hog liver. In this case, the small amounts of pure enzyme available precluded use of the NMR technique. However, mass spectral analysis of the derivatized phosphate product revealed the presence of (/sup 18/O)-trimethyl phosphate, thus indicating that the reaction catalyzed by the mammalian enzyme also proceeds via an acyl phosphate intermediate.

  9. Diastereo- and Enantioselective Iridium Catalyzed Carbonyl (α-Cyclopropyl)allylation via Transfer Hydrogenation.

    Science.gov (United States)

    Tsutsumi, Ryosuke; Hong, Suckchang; Krische, Michael J

    2015-09-07

    The first examples of diastereo- and enantioselective carbonyl α-(cyclopropyl)allylation are reported. Under the conditions of iridium catalyzed transfer hydrogenation using the chiral precatalyst (R)-Ir-I modified by SEGPHOS, carbonyl α-(cyclopropyl)allylation may be achieved with equal facility from alcohol or aldehyde oxidation levels. This methodology provides a conduit to hitherto inaccessible inaccessible enantiomerically enriched cyclopropane-containing architectures. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Studies on electron transfer reactions of Keggin-type mixed ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 121; Issue 2. Studies on electron transfer reactions of Keggin-type mixed addenda heteropolytungstovanadophosphates with NADH ... Nicotinamide adenine dinucleotide (NADH); heteropoly-tungstovanadophosphate; outer sphere electron transfer reactions.

  11. Dirhodium carboxylates catalyzed enantioselective coupling reactions of α-diazophosphonates, anilines, and electron-deficient aldehydes.

    Science.gov (United States)

    Zhou, Cong-Ying; Wang, Jing-Cui; Wei, Jinhu; Xu, Zhen-Jiang; Guo, Zhen; Low, Kam-Hung; Che, Chi-Ming

    2012-11-05

    Chiral dirhodium carboxylate complexes ([Rh(2)(S-PTAD)(4)] or [Rh(2)(S-PTTL)(4)]) efficiently catalyze asymmetric three-component coupling reactions of α-diazophosphonates, anilines, and electron-deficient aldehydes to give α-amino-β-hydroxyphosphonates. The high level of enantiocontrol provides evidence for the intermediacy of metal-bound ammonium ylide in the product-forming step. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Photo-induced excitations in the ruthenium-catalyzed Belousov Zhabotinsky reaction

    Science.gov (United States)

    Wang, Jichang

    2001-02-01

    Photo-induced excitations in the tris-(bipyridyl)Ru(II)-catalyzed Belousov-Zhabotinsky reaction are studied numerically using the Oregonator model, modified to describe photosensitivity. An abrupt change in bromide concentration induced by a pulse-light perturbation causes a large excursion. The mimimal light intensity for initiating an excitation decreases while the system approaches to a bifurcation point. This study provides an alternative explanation for a recent experimental research.

  13. Polycyclization Enabled by Relay Catalysis: One-Pot Manganese-Catalyzed C-H Allylation and Silver-Catalyzed Povarov Reaction.

    Science.gov (United States)

    Chen, Shi-Yong; Li, Qingjiang; Liu, Xu-Ge; Wu, Jia-Qiang; Zhang, Shang-Shi; Wang, Honggen

    2017-06-09

    In this study, a Mn I /Ag I -based relay catalysis process is described for the one-pot synthesis of polycyclic products by a formal [3+2] and [4+2] cycloaddition reaction cascade. A manganese(I) complex catalyzed the first example of directed C-H allylation with allenes, setting the stage for an in situ Povarov cyclization catalyzed by silver(I). The reaction proceeds with high bond-forming efficiency (three C-C bonds), broad substrate scope, high regio- and stereoselectivity, and 100 % atom economy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Transition-metal-catalyzed hydrogen-transfer annulations: access to heterocyclic scaffolds.

    Science.gov (United States)

    Nandakumar, Avanashiappan; Midya, Siba Prasad; Landge, Vinod Gokulkrishna; Balaraman, Ekambaram

    2015-09-14

    The ability of hydrogen-transfer transition-metal catalysts, which enable increasingly rapid access to important structural scaffolds from simple starting materials, has led to a plethora of research efforts on the construction of heterocyclic scaffolds. Transition-metal-catalyzed hydrogen-transfer annulations are environmentally benign and highly atom-economical as they release of water and hydrogen as by-product and utilize renewable feedstock alcohols as starting materials. Recent advances in this field with respect to the annulations of alcohols with various nucleophilic partners, thus leading to the formation of heterocyclic scaffolds, are highlighted herein. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Practical synthesis of 1,3-oleoyl 2-docosahexaenoylglycerol by lipase-catalyzed reactions: An evaluation of different reaction routes

    DEFF Research Database (Denmark)

    Zhang, Hong; Onal, G.; Wijesundera, C.

    2009-01-01

    Three new synthetic routes were critically evaluated for the lipase-catalyzed production of 1,3-oleoyl-2 docosahexaenoylglycerol (ODD) in relatively large-scale (approximately 200 g). First, the production of 1,3-diolein by the reaction of glycerol and oleic acid followed by incorporation...... of single cell oil (SCO) in excess oleic acid using Novozym 435 as the catalyst occurred twice as fast in solvent (tert-butanol) compared to a solvent-free system, and 63% oleic acid was incorporated into SCO. However, the regio-isomeric purity of the product was poor. Finally, the ethanolysis of SCO...... to produce DHA-enriched 2-monoacylglycerol followed by esterification with oleic acid or ethyl oleate was investigated. ODO was obtained in 50.9% regio-purity by Lipozyme RM IM-catalyzed esterification. The latter method was the most feasible for preparing ODD in large-scale. This synthetic route could...

  16. Transition-metal-catalyzed enantioselective heteroatom-hydrogen bond insertion reactions.

    Science.gov (United States)

    Zhu, Shou-Fei; Zhou, Qi-Lin

    2012-08-21

    Carbon-heteroatom bonds (C-X) are ubiquitous and are among the most reactive components of organic compounds. Therefore investigations of the construction of C-X bonds are fundamental and vibrant fields in organic chemistry. Transition-metal-catalyzed heteroatom-hydrogen bond (X-H) insertions via a metal carbene or carbenoid intermediate represent one of the most efficient approaches to form C-X bonds. Because of the availability of substrates, neutral and mild reaction conditions, and high reactivity of these transformations, researchers have widely applied transition-metal-catalyzed X-H insertions in organic synthesis. Researchers have developed a variety of rhodium-catalyzed asymmetric C-H insertion reactions with high to excellent enantioselectivities for a wide range of substrates. However, at the time that we launched our research, very few highly enantioselective X-H insertions had been documented primarily because of a lack of efficient chiral catalysts and indistinct insertion mechanisms. In this Account, we describe our recent studies of copper- and iron-catalyzed asymmetric X-H insertion reactions by using chiral spiro-bisoxazoline and diimine ligands. The copper complexes of chiral spiro-bisoxazoline ligands proved to be highly enantioselective catalysts for N-H insertions of α-diazoesters into anilines, O-H insertions of α-diazoesters into phenols and water, O-H insertions of α-diazophosphonates into alcohols, and S-H insertions of α-diazoesters into mercaptans. The iron complexes of chiral spiro-bisoxazoline ligands afforded the O-H insertion of α-diazoesters into alcohols and water with unprecedented enantioselectivities. The copper complexes of chiral spiro-diimine ligands exhibited excellent reactivity and enantioselectivity in the Si-H insertion of α-diazoacetates into a wide range of silanes. These transition-metal-catalyzed X-H insertions have many potential applications in organic synthesis because the insertion products, including chiral

  17. Yttrium (III chloride catalyzed Mannich reaction: An efficient procedure for the synthesis of β-amino carbonyl compounds

    Directory of Open Access Journals (Sweden)

    Venkateswarlu Yekkirala

    2014-12-01

    Full Text Available Yttrium (III chloride catalyzed Mannich reaction of aldehydes with ketones and amines in acetonitrile at reflux temperature to give various β-amino carbonyl compounds in very good yields.

  18. Kinetics and optimization on discoloration of dyeing wastewater by schorl-catalyzed fenton-like reaction

    Directory of Open Access Journals (Sweden)

    Xu Huan-Yan

    2014-01-01

    Full Text Available Kinetics and optimization on the discoloration of an active commercial dye, Argazol Blue BFBR (ABB by heterogeneous Fenton-like reaction catalyzed by natural schorl were investigated in this study. Kinetic investigations revealed that the first-order kinetic model was more favorable to describe the discoloration of ABB at different reaction conditions than the second-order and Behnajady-Modirshahla-Ghanbery models. The relationship between the reaction rate constant k and reaction temperature T followed the Arrhenius equation, with the apparent activation energy Ea of 51.31kJ•mol-1. The central composite design under the response surface methodology was employed for the experimental design and optimization of the ABB discoloration process. The significance of a second order polynomial model for predicting the optimal values of ABB discoloration was evaluated by the analysis of variance and 3D response surface plots for the interactions between two variables were constructed. Then, the optimum conditions were determined.

  19. Mechanism of Cytochrome P450 17A1-Catalyzed Hydroxylase and Lyase Reactions

    DEFF Research Database (Denmark)

    Bonomo, Silvia; Jorgensen, Flemming Steen; Olsen, Lars

    2017-01-01

    Cytochrome P450 17A1 (CYP17A1) catalyzes C17 hydroxylation of pregnenolone and progesterone and the subsequent C17–C20 bond cleavage (lyase reaction) to form androgen precursors. Compound I (Cpd I) and peroxo anion (POA) are the heme-reactive species underlying the two reactions. We have...... states (TSs) for the two reactions into the active site of CYP17A1 showed that the TS for the C17 hydroxylation needs to be distorted by 13 kJ·mol–1, whereas the TS for the 17,20 lyase reaction easily can be accommodated in the protein. Finally, differences in the hydrogen-bond pattern of the substrates...

  20. Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

    Energy Technology Data Exchange (ETDEWEB)

    Klobukowski, Erik [Iowa State Univ., Ames, IA (United States)

    2011-01-01

    This work involves two projects. The first project entails the study of bulk gold as a catalyst in oxidation reactions of isocyanides and amines. The main goal of this project was to study the activation and reactions of molecules at metal surfaces in order to assess how organometallic principles for homogeneous processes apply to heterogeneous catalysis. Since previous work had used oxygen as an oxidant in bulk gold catalyzed reactions, the generality of gold catalysis with other oxidants was examined. Amine N-oxides were chosen for study, due to their properties and use in the oxidation of carbonyl ligands in organometallic complexes. When amine N-oxides were used as an oxidant in the reaction of isocyanides with amines, the system was able to produce ureas from a variety of isocyanides, amines, and amine N-oxides. In addition, the rate was found to generally increase as the amine N-oxide concentration increased, and decrease with increased concentrations of the amine. Mechanistic studies revealed that the reaction likely involves transfer of an oxygen atom from the amine N-oxide to the adsorbed isocyanide to generate an isocyanate intermediate. Subsequent nucleophilic attack by the amine yields the urea. This is in contrast to the bulk gold-catalyzed reaction mechanism of isocyanides with amines and oxygen. Formation of urea in this case was proposed to proceed through a diaminocarbene intermediate. Moreover, formation of the proposed isocyanate intermediate is consistent with the reactions of metal carbonyl ligands, which are isoelectronic to isocyanides. Nucleophilic attack at coordinated CO by amine N-oxides produces CO{sub 2} and is analogous to the production of an isocyanate in this gold system. When the bulk gold-catalyzed oxidative dehydrogenation of amines was examined with amine N-oxides, the same products were afforded as when O{sub 2} was used as the oxidant. When the two types of oxidants were directly compared using the same reaction system and

  1. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    Science.gov (United States)

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

  2. Inter- and intramolecular aldol reactions promiscuously catalyzed by a proline-based tautomerase.

    Science.gov (United States)

    Rahimi, Mehran; Geertsema, Edzard M; Miao, Yufeng; van der Meer, Jan-Ytzen; van den Bosch, Thea; de Haan, Pim; Zandvoort, Ellen; Poelarends, Gerrit J

    2017-03-28

    The enzyme 4-oxalocrotonate tautomerase (4-OT), which in nature catalyzes a tautomerization step as part of a catabolic pathway for aromatic hydrocarbons, was found to promiscuously catalyze different types of aldol reactions. These include the self-condensation of propanal, the cross-coupling of propanal and benzaldehyde, the cross-coupling of propanal and pyruvate, and the intramolecular cyclizations of hexanedial and heptanedial. Mutation of the catalytic amino-terminal proline (P1A) greatly reduces 4-OT's aldolase activities, whereas mutation of another active site residue (F50A) strongly enhances 4-OT's aldolase activities, indicating that aldolization is an active site process. This catalytic promiscuity of 4-OT could be exploited as starting point to create tailor-made, artificial aldolases for challenging self- and cross-aldolizations.

  3. A Selective and Functional Group-Tolerant Ruthenium-Catalyzed Olefin Metathesis/Transfer Hydrogenation Tandem Sequence Using Formic Acid as Hydrogen Source.

    Science.gov (United States)

    Zieliński, Grzegorz K; Majtczak, Jarosława; Gutowski, Maciej; Grela, Karol

    2018-03-02

    A ruthenium-catalyzed transfer hydrogenation of olefins utilizing formic acid as a hydrogen donor is described. The application of commercially available alkylidene ruthenium complexes opens access to attractive C(sp3)-C(sp3) bond formation in an olefin metathesis/transfer hydrogenation sequence under tandem catalysis conditions. High chemoselectivity of the developed methodology provides a remarkable synthetic tool for the reduction of various functionalized alkenes under mild reaction conditions. The developed methodology is applied for the formal synthesis of the drugs pentoxyverine and bencyclane.

  4. Sulfuric, hydrochloric, and nitric acid-catalyzed triacetone triperoxide (TATP) reaction mixtures: an aging study.

    Science.gov (United States)

    Fitzgerald, Mark; Bilusich, Daniel

    2011-09-01

    The organic peroxide explosive triacetone triperoxide (TATP) is regularly encountered by law enforcement agents in various stages of its production. This study utilizes solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) to examine sulfuric acid-, hydrochloric acid-, and nitric acid-catalyzed TATP syntheses during the initial 24 h of these reactions at low temperatures (5-9°C). Additionally, aging of the reaction mixtures was examined at both low and ambient temperatures (19-21°C) for a further 9 days. For each experiment, TATP could be readily identified in the headspace above the reaction mixture 1 h subsequent to the combination of reagents; at 24 h, TATP and diacetone diperoxide (DADP) were prominent. TATP degraded more rapidly than DADP. Additionally, chlorinated acetones chloroacetone and 1,1,-dichloroacetone were identified in the headspace above the hydrochloric acid-catalyzed TATP reaction mixture. These were not present when the catalyst was sulfuric acid or nitric acid. 2011 American Academy of Forensic Sciences. Published 2011. This article is a U.S. Government work and is in the public domain in the U.S.A.

  5. Precision Synthesis of Functional Polysaccharide Materials by Phosphorylase-Catalyzed Enzymatic Reactions

    Directory of Open Access Journals (Sweden)

    Jun-ichi Kadokawa

    2016-04-01

    Full Text Available In this review article, the precise synthesis of functional polysaccharide materials using phosphorylase-catalyzed enzymatic reactions is presented. This particular enzymatic approach has been identified as a powerful tool in preparing well-defined polysaccharide materials. Phosphorylase is an enzyme that has been employed in the synthesis of pure amylose with a precisely controlled structure. Similarly, using a phosphorylase-catalyzed enzymatic polymerization, the chemoenzymatic synthesis of amylose-grafted heteropolysaccharides containing different main-chain polysaccharide structures (e.g., chitin/chitosan, cellulose, alginate, xanthan gum, and carboxymethyl cellulose was achieved. Amylose-based block, star, and branched polymeric materials have also been prepared using this enzymatic polymerization. Since phosphorylase shows a loose specificity for the recognition of substrates, different sugar residues have been introduced to the non-reducing ends of maltooligosaccharides by phosphorylase-catalyzed glycosylations using analog substrates such as α-d-glucuronic acid and α-d-glucosamine 1-phosphates. By means of such reactions, an amphoteric glycogen and its corresponding hydrogel were successfully prepared. Thermostable phosphorylase was able to tolerate a greater variance in the substrate structures with respect to recognition than potato phosphorylase, and as a result, the enzymatic polymerization of α-d-glucosamine 1-phosphate to produce a chitosan stereoisomer was carried out using this enzyme catalyst, which was then subsequently converted to the chitin stereoisomer by N-acetylation. Amylose supramolecular inclusion complexes with polymeric guests were obtained when the phosphorylase-catalyzed enzymatic polymerization was conducted in the presence of the guest polymers. Since the structure of this polymeric system is similar to the way that a plant vine twines around a rod, this polymerization system has been named

  6. Three Metal Ions Participate in the Reaction Catalyzed by T5 Flap Endonuclease*S⃞

    Science.gov (United States)

    Syson, Karl; Tomlinson, Christopher; Chapados, Brian R.; Sayers, Jon R.; Tainer, John A.; Williams, Nicholas H.; Grasby, Jane A.

    2008-01-01

    Protein nucleases and RNA enzymes depend on divalent metal ions to catalyze the rapid hydrolysis of phosphate diester linkages of nucleic acids during DNA replication, DNA repair, RNA processing, and RNA degradation. These enzymes are widely proposed to catalyze phosphate diester hydrolysis using a “two-metal-ion mechanism.” Yet, analyses of flap endonuclease (FEN) family members, which occur in all domains of life and act in DNA replication and repair, exemplify controversies regarding the classical two-metal-ion mechanism for phosphate diester hydrolysis. Whereas substrate-free structures of FENs identify two active site metal ions, their typical separation of >4 Å appears incompatible with this mechanism. To clarify the roles played by FEN metal ions, we report here a detailed evaluation of the magnesium ion response of T5FEN. Kinetic investigations reveal that overall the T5FEN-catalyzed reaction requires at least three magnesium ions, implying that an additional metal ion is bound. The presence of at least two ions bound with differing affinity is required to catalyze phosphate diester hydrolysis. Analysis of the inhibition of reactions by calcium ions is consistent with a requirement for two viable cofactors (Mg2+ or Mn2+). The apparent substrate association constant is maximized by binding two magnesium ions. This may reflect a metal-dependent unpairing of duplex substrate required to position the scissile phosphate in contact with metal ion(s). The combined results suggest that T5FEN primarily uses a two-metal-ion mechanism for chemical catalysis, but that its overall metallobiochemistry is more complex and requires three ions. PMID:18697748

  7. Formation of C–C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation

    Science.gov (United States)

    Bower, John F.; Krische, Michael J.

    2011-01-01

    The formation of C–C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C–C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and π-unsaturated reactants generates electrophile–nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C–H bonds. PMID:21822399

  8. [Study of ATP-independent stages of reaction catalyzed by phage T4 RNA-ligase].

    Science.gov (United States)

    Zagrebel'nyĭ, S N; Zernov, Iu P

    1986-01-01

    The isotope exchange between [5'-32P]pAP and A(5')ppAp catalyzed by enzyme was shown not to take place in the absence of the acceptor; i. e. the necessity of the acceptor presence during the second step of the process was demonstrated. The isotope exchange reaction between [5'32P]pAp and (pA)5p was studied. It was demonstrated that acceptor (pA)4, slightly whereas the acceptor (pU)4 completely inhibits the isotope reaction. The isotope reaction exchange between [5'-32P]pAp and (pU)4pAp does not take place. The question of existence of adenylated donor elimination mechanism in the presence of "poor" acceptors is considered on the basis of the data obtained.

  9. Electron transfer and reaction mechanism of laccases.

    Science.gov (United States)

    Jones, Stephen M; Solomon, Edward I

    2015-03-01

    Laccases are part of the family of multicopper oxidases (MCOs), which couple the oxidation of substrates to the four electron reduction of O2 to H2O. MCOs contain a minimum of four Cu's divided into Type 1 (T1), Type 2 (T2), and binuclear Type 3 (T3) Cu sites that are distinguished based on unique spectroscopic features. Substrate oxidation occurs near the T1, and electrons are transferred approximately 13 Å through the protein via the Cys-His pathway to the T2/T3 trinuclear copper cluster (TNC), where dioxygen reduction occurs. This review outlines the electron transfer (ET) process in laccases, and the mechanism of O2 reduction as elucidated through spectroscopic, kinetic, and computational data. Marcus theory is used to describe the relevant factors which impact ET rates including the driving force, reorganization energy, and electronic coupling matrix element. Then, the mechanism of O2 reaction is detailed with particular focus on the intermediates formed during the two 2e(-) reduction steps. The first 2e(-) step forms the peroxide intermediate, followed by the second 2e(-) step to form the native intermediate, which has been shown to be the catalytically relevant fully oxidized form of the enzyme.

  10. Transition-Metal-Catalyzed Asymmetric Hydrogenation and Transfer Hydrogenation: Sustainable Chemistry to Access Bioactive Molecules.

    Science.gov (United States)

    Ayad, Tahar; Phansavath, Phannarath; Ratovelomanana-Vidal, Virginie

    2016-12-01

    Over the last few decades, the development of new and highly efficient synthetic methods to obtain chiral compounds has become an increasingly important and challenging research area in modern synthetic organic chemistry. In this account, we review recent work from our laboratory toward the synthesis of valuable chiral building blocks through transition-metal-catalyzed asymmetric hydrogenation and transfer hydrogenation of C=O, C=N and C=C bonds. Application to the synthesis of biologically relevant products is also described. © 2016 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Palladium-atom catalyzed formic acid decomposition and the switch of reaction mechanism with temperature.

    Science.gov (United States)

    He, Nan; Li, Zhen Hua

    2016-04-21

    Formic acid decomposition (FAD) reaction has been an innovative way for hydrogen energy. Noble metal catalysts, especially palladium-containing nanoparticles, supported or unsupported, perform well in this reaction. Herein, we considered the simplest model, wherein one Pd atom is used as the FAD catalyst. With high-level theoretical calculations of CCSD(T)/CBS quality, we investigated all possible FAD pathways. The results show that FAD catalyzed by one Pd atom follows a different mechanism compared with that catalyzed by surfaces or larger clusters. At the initial stage of the reaction, FAD follows a dehydration route and is quickly poisoned by CO due to the formation of very stable PdCO. PdCO then becomes the actual catalyst for FAD at temperatures approximately below 1050 K. Beyond 1050 K, there is a switch of catalyst from PdCO to Pd atom. The results also show that dehydration is always favoured over dehydrogenation on either the Pd-atom or PdCO catalyst. On the Pd-atom catalyst, neither dehydrogenation nor dehydration follows the formate mechanism. In contrast, on the PdCO catalyst, dehydrogenation follows the formate mechanism, whereas dehydration does not. We also systematically investigated the performance of 24 density functional theory methods. We found that the performance of the double hybrid mPW2PLYP functional is the best, followed by the B3LYP, B3PW91, N12SX, M11, and B2PLYP functionals.

  12. Ruthenium-catalyzed reactions--a treasure trove of atom-economic transformations.

    Science.gov (United States)

    Trost, Barry M; Frederiksen, Mathias U; Rudd, Michael T

    2005-10-21

    The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.

  13. Solid nanoparticles that catalyze biofuel upgrade reactions at the water/oil interface.

    Science.gov (United States)

    Crossley, Steven; Faria, Jimmy; Shen, Min; Resasco, Daniel E

    2010-01-01

    A recoverable catalyst that simultaneously stabilizes emulsions would be highly advantageous in streamlining processes such as biomass refining, in which the immiscibility and thermal instability of crude products greatly complicates purification procedures. Here, we report a family of solid catalysts that can stabilize water-oil emulsions and catalyze reactions at the liquid/liquid interface. By depositing palladium onto carbon nanotube-inorganic oxide hybrid nanoparticles, we demonstrate biphasic hydrodeoxygenation and condensation catalysis in three substrate classes of interest in biomass refining. Microscopic characterization of the emulsions supports localization of the hybrid particles at the interface.

  14. Cure reaction of epoxy resins catalyzed by graphite-based nanofiller

    Science.gov (United States)

    Corcione, C. Esposito; Acocella, Maria Rosaria; Giuri, Antonella; Maffezzoli, Alfonso; Guerra, Gaetano

    2015-12-01

    A significant effort was directed to the synthesis of graphene stacks/epoxy nanocomposites and to the analysis of the effect of a graphene precursor on cure reaction of a model epoxy matrix. A comparative thermal analysis of epoxy resins filled with an exfoliated graphite oxide eGO were conducted. The main aim was to understand the molecular origin of the influence of eGO on the Tg of epoxy resins. The higher Tg values previously observed for low curing temperatures, for epoxy resins with graphite-based nanofillers, were easily rationalized by a catalytic activity of graphitic layers on the reaction between the epoxy and amine groups of the resin, which leads to higher crosslinking density in milder conditions. A kinetic analysis of the cure mechanism of the epoxy resin associated to the catalytical activity of the graphite based filler was performed by isothermal DSC measurements. The DSC results showed that the addition of graphite based filler greatly increased the enthalpy of epoxy reaction and the reaction rate, confirming the presence of a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine). A kinetic modelling analysis, arising from an auto-catalyzed reaction mechanism, was finally applied to isothermal DSC data, in order to predict the cure mechanism of the epoxy resin in presence of the graphite based nanofiller.

  15. Mechanistic Implications for the Ni(I-Catalyzed Kumada Cross-Coupling Reaction

    Directory of Open Access Journals (Sweden)

    Linda Iffland

    2017-11-01

    Full Text Available Herein we report on the cross-coupling reaction of phenylmagnesium bromide with aryl halides using the well-defined tetrahedral Ni(I complex, [(TriphosNiICl] (Triphos = 1,1,1-tris(diphenylphosphinomethylethane. In the presence of 0.5 mol % [(TriphosNiICl], good to excellent yields (75–97% of the respective coupling products within a reaction time of only 2.5 h at room temperature were achieved. Likewise, the tripodal Ni(IIcomplexes [(κ2-TriphosNiIICl2] and [(κ3-TriphosNiIICl](X (X = ClO4, BF4 were tested as potential pre-catalysts for the Kumada cross-coupling reaction. While the Ni(II complexes also afford the coupling products in comparable yields, mechanistic investigations by UV/Vis and electron paramagnetic resonance (EPR spectroscopy indicate a Ni(I intermediate as the catalytically active species in the Kumada cross-coupling reaction. Based on experimental findings and density functional theory (DFT calculations, a plausible Ni(I-catalyzed reaction mechanism for the Kumada cross-coupling reaction is presented.

  16. Au-Cu core-shell nanocube-catalyzed click reactions for efficient synthesis of diverse triazoles.

    Science.gov (United States)

    Madasu, Mahesh; Hsia, Chi-Fu; Huang, Michael H

    2017-06-01

    Au-Cu core-shell nanocubes and octahedra synthesized in aqueous solution were employed to catalyze a 1,3-dipolar cycloaddition reaction between phenylacetylene and benzyl azide in water at 50 °C for 3 h. Interestingly, the nanocubes were far more efficient in catalyzing this reaction, giving 91% yield of a regioselective 1,4-triazole product, while octahedra only recorded 46% yield. The Au-Cu nanocubes were subsequently employed to catalyze the click reaction between benzyl azide and a broad range of aromatic and aliphatic alkynes. The product yields ranged from 78 to 99%. Clearly the Au-Cu cubes exposing {100} surfaces are an excellent and green catalyst for click reactions.

  17. Construction of Benzene Rings by Copper-Catalyzed Cycloaddition Reactions of Oximes and Maleimides: An Access to Fused Phthalimides.

    Science.gov (United States)

    Yang, Jie; Zhao, Bo; Xi, Yue; Sun, Si; Yang, Zhen; Ye, Ying; Jiang, Kun; Wei, Ye

    2018-02-16

    A useful Cu-catalyzed cycloaddition protocol for the construction of benzene rings has been achieved. The reactions, utilizing readily available oximes and maleimides as starting materials, proceed under mild reaction conditions to generate a series of structurally interesting fused-phthalimides that are difficult to be prepared by conventional methods.

  18. The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications

    KAUST Repository

    Ebner, Davidâ C.

    2009-12-07

    The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.

  19. Study of single nucleon transfer in α + 12C reaction

    International Nuclear Information System (INIS)

    Pandey, R.; Rana, T.K.; Dey, A.; Bhattacharya, C.; Kundu, S.; Banerjee, K.; Mukherjee, G.; Ghosh, T.K.; Meena, J.K.; Pai, H.; Gohil, M.; Bhattacharya, S.; Biswas, M.

    2011-01-01

    Nucleon transfer reactions are of great significance for understanding the nuclear structure both for direct reaction studies as well as for production of nuclear states. Transfer reactions are simplest to interpret when either the initial and final state of the target nucleus has spin zero and when the conditions are such that the transition from the initial and final states occurs to a good approximation in a single step. In this paper, the measurement of angular momentum distribution and calculation of the spectroscopic factor for one nucleon transfer reaction in α + 12 C reaction have been reported

  20. On the Effect of Microwave Energy on Lipase-Catalyzed Polycondensation Reactions

    Directory of Open Access Journals (Sweden)

    Alessandro Pellis

    2016-09-01

    Full Text Available Microwave energy (MWe is, nowadays, widely used as a clean synthesis tool to improve several chemical reactions, such as drug molecule synthesis, carbohydrate conversion and biomass pyrolysis. On the other hand, its exploitation in enzymatic reactions has only been fleetingly investigated and, hence, further study of MWe is required to reach a precise understanding of its potential in this field. Starting from the authors’ experience in clean synthesis and biocatalyzed reactions, this study sheds light on the possibility of using MWe for enhancing enzyme-catalyzed polycondensation reactions and pre-polymer formation. Several systems and set ups were investigated involving bulk and organic media (solution phase reactions, different enzymatic preparations and various starting bio-based monomers. Results show that MWe enables the biocatalyzed synthesis of polyesters and pre-polymers in a similar way to that reported using conventional heating with an oil bath, but in a few cases, notably bulk phase polycondensations under intense microwave irradiation, MWe leads to a rapid enzyme deactivation.

  1. Two-nucleon transfer reactions with form factor models

    International Nuclear Information System (INIS)

    Osman, A.

    1980-04-01

    The theory of two-nucleon transfer reactions is considered. Nuclear reactions are considered with triton or 3 He particles which are used as projectiles in stripping reactions and as detected particles in pick-up reactions. In each channel we have a four-particle problem, three of them are nucleons and the fourth is a heavy particle. These transfer reactions are studied on the basis of the generaled R-matrix method. Different channel functions of the sub-clusters in the triton and 3 He particles are included. Model form factors are obtained and are used in two-nucleon transfer reactions. Differential cross-sections of different two-nucleon transfer reactions are calculated and are found in good agreement with the experimental data. The correct normalization and spectroscopic factors are obtained. (author)

  2. Mechanistic Studies of Hafnium-Pyridyl Amido-Catalyzed 1-Octene Polymerization and Chain Transfer Using Quench-Labeling Methods.

    Science.gov (United States)

    Cueny, Eric S; Johnson, Heather C; Anding, Bernie J; Landis, Clark R

    2017-08-30

    Chromophore quench-labeling applied to 1-octene polymerization as catalyzed by hafnium-pyridyl amido precursors enables quantification of the amount of active catalyst and observation of the molecular weight distribution (MWD) of Hf-bound polymers via UV-GPC analysis. Comparison of the UV-detected MWD with the MWD of the "bulk" (all polymers, from RI-GPC analysis) provides important mechanistic information. The time evolution of the dual-detection GPC data, concentration of active catalyst, and monomer consumption suggests optimal activation conditions for the Hf pre-catalyst in the presence of the activator [Ph 3 C][B(C 6 F 5 ) 4 ]. The chromophore quench-labeling agents do not react with the chain-transfer agent ZnEt 2 under the reaction conditions. Thus, Hf-bound polymeryls are selectively labeled in the presence of zinc-polymeryls. Quench-labeling studies in the presence of ZnEt 2 reveal that ZnEt 2 does not influence the rate of propagation at the Hf center, and chain transfer of Hf-bound polymers to ZnEt 2 is fast and quasi-irreversible. The quench-label techniques represent a means to study commercial polymerization catalysts that operate with high efficiency at low catalyst concentrations without the need for specialized equipment.

  3. State of the art and prospective of lipase-catalyzed transesterification reaction for biodiesel production

    International Nuclear Information System (INIS)

    Amini, Zeynab; Ilham, Zul; Ong, Hwai Chyuan; Mazaheri, Hoora; Chen, Wei-Hsin

    2017-01-01

    Highlights: • Enzymatic transesterification process is less energy intensive and robust. • Nano-materials are promising immobilization supports for lipase. • Packed-bed reactors are appropriate for scale-up use. • Potential recombinant, whole cell and recombinant whole cell lipases were enlisted. • Genetic engineering is a promising prospect in biodiesel area. - Abstract: The world demand for fuel as energy sources have arisen the need for generating alternatives such as biofuel. Biodiesel is a renewable fuel used particularly in diesel engines. Currently, biodiesel is mainly produced through transesterification reactions catalyzed by chemical catalysts, which produces higher fatty acid alkyl esters in shorter reaction time. Although extensive investigations on enzymatic transesterification by downstream processing were carried out, enzymatic transesterification has yet to be used in scale-up since commercial lipases are chiefly limited to the cost as well as long reaction time. While numerous lipases were studied and proven to have the high catalytic capacity, still enzymatic reaction requires more investigation. To fill this gap, finding optimal conditions for the reaction such as alcohol and oil choice, water content, reaction time and temperature through proper reaction modelling and simulations as well as the appropriate design and use of reactors for large scale production are crucial issues that need to be accurately addressed. Furthermore, lipase concentration, alternative lipase resources through whole cell technology and genetic engineering, recent immobilizing materials including nanoparticles, and the capacity of enzyme to be reused are important criteria to be neatly investigated. The present work reviews the current biodiesel feedstock, catalysis, general and novel immobilizing materials, bioreactors for enzymatic transesterification, potential lipase resources, intensification technics, and process modelling for enzymatic

  4. Computational Mechanistic Study of Redox-Neutral Rh(III)-Catalyzed C-H Activation Reactions of Arylnitrones with Alkynes: Role of Noncovalent Interactions in Controlling Selectivity.

    Science.gov (United States)

    Xing, Yang-Yang; Liu, Jian-Biao; Tian, Ying-Ying; Sun, Chuan-Zhi; Huang, Fang; Chen, De-Zhan

    2016-11-23

    The mechanism of redox-neutral Rh(III)-catalyzed coupling reactions of arylnitrones with alkynes was investigated by density functional theory (DFT) calculations. The free energy profiles associated with the catalytic cycle, involving C(sp 2 )-H activation, insertion of alkyne, transfer of O atom, cyclization and protodemetalation, are presented and analyzed. An overwhelming preference for alkyne insertion into Rh-C over Rh-O is observed among all pathways, and the most favorable route is determined. The pivalate-assisted C-H activation step is turnover-limiting, and the cyclization step determines the diastereoselectivity of the reaction, with the stereoselectivity arising mainly from the difference of noncovalent interactions in key transition states. The detailed mechanism of O atom transfer, Rh III -Rh I -Rh III versus Rh III -Rh V -Rh III cycle, is discussed.

  5. Theoretical studies on proton transfer reaction of 3 (5)-substituted ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 126; Issue 1. Theoretical studies on proton transfer reaction of 3(5)-substituted pyrazoles ... Abstract. The inter and intra molecular proton transfer reactions of a series of pyrazole derivatives have been studied by using density functional theory (DFT) andMP2 methods ...

  6. Variation of kinetic isotope effect in multiple proton transfer reactions

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 124; Issue 1. Variation of kinetic isotope ... An extension of this to the concerted multiple proton transfer reactions implies that the kinetic isotope effect in such reaction depends exponentially on the number of protons that are being transferred. Computational evidence ...

  7. Biocatalytic carbon capture via reversible reaction cycle catalyzed by isocitrate dehydrogenase.

    Science.gov (United States)

    Xia, Shunxiang; Frigo-Vaz, Benjamin; Zhao, Xueyan; Kim, Jungbae; Wang, Ping

    2014-09-12

    The practice of carbon capture and storage (CCS) requires efficient capture and separation of carbon dioxide from its gaseous mixtures such as flue gas, followed by releasing it as a pure gas which can be subsequently compressed and injected into underground storage sites. This has been mostly achieved via reversible thermochemical reactions which are generally energy-intensive. The current work examines a biocatalytic approach for carbon capture using an NADP(H)-dependent isocitrate dehydrogenase (ICDH) which catalyzes reversibly carboxylation and decarboxylation reactions. Different from chemical carbon capture processes that rely on thermal energy to realize purification of carbon dioxide, the biocatalytic strategy utilizes pH to leverage the reaction equilibrium, thereby realizing energy-efficient carbon capture under ambient conditions. Results showed that over 25 mol of carbon dioxide could be captured and purified from its gas mixture for each gram of ICDH applied for each carboxylation/decarboxylation reaction cycle by varying pH between 6 and 9. This work demonstrates the promising potentials of pH-sensitive biocatalysis as a green-chemistry route for carbon capture. Copyright © 2014. Published by Elsevier Inc.

  8. Studies on the specificity of Candida rugosa lipase catalyzed esterification reactions in organic media

    Directory of Open Access Journals (Sweden)

    DEJAN BEZBRADICA

    2006-01-01

    Full Text Available In this study, the feasibility of the synthesis of various flavor esters catalyzed by a commercial lipase from Candida rugosa was investigated and the process parameters were optimized. Lipase from C. rugosa successfully catalyzed the synthesis of 19 esters. The highest yields, of more than 90 % after 20 h, were observed in the synthesis of short-chain esters, pentyl propanoate, isopentyl butanoate, and butyl butanoate. Increasing the number of carbon atoms of both substrates above 8 caused a significant decrease of the initial reaction rates and the final yields. The enzyme showed surprisingly low affinity towards pentanoic acid and hexanoic acid, compared with the higher homologues, octanoic acid and decanoic acid. In addition to the number of carbon atoms, the structure of the substrates had a significant influence on the enzyme activity. Namely, the activity of the enzyme towards isopropanol was significantly lower compared with n-propanol. Additionally, cis-9-octadecenoic acid was a better substrate than octadecanoic acid, its saturated analogue.

  9. Insight into the electronic effect of phosphine ligand on Rh catalyzed CO2 hydrogenation by investigating the reaction mechanism.

    Science.gov (United States)

    Ni, Shao-Fei; Dang, Li

    2016-02-14

    Improving the catalytic efficiency of CO2 hydrogenation is a big challenge in catalysed CO2 recycling and H2 conservation. The detailed mechanism of [Rh(PCH2X(R)CH2P)2](+) (X(R) = CH2, N-CH3, CF2) catalyzed CO2 hydrogenation is studied to obtain insights into the electronic effect of the substituents at diphosphine ligand on the catalytic efficiency. The most favorable reaction mechanism is found to be composed of three steps: (1) oxidative addition of dihydrogen onto the Rh center of the catalyst; (2) the first hydride abstraction by base from the Rh dihydride complexes; (3) the second hydride transfer from the Rh hydride complexes to CO2. It was found that the transition state for the first hydride abstraction from the Rh dihydride complex is the TOF-determining transition state (TDTS) in the most favorable mechanism. The energetic span (δE) of the cycle is suggested related to the thermodynamic hydricity of the Rh dihydride complex. Model catalyst [Rh(PCH2CF2CH2P)2](+) with a strong σ electron withdrawing group on the diphosphine ligand provides higher hydricity in the Rh dihydride complex and lower activation energy when compared with the other two catalysts. Our study shows that it is the σ electron withdrawing ability rather than the electron donating ability that enhances the catalytic efficiency in catalyzed CO2 hydrogenation. This finding will benefit ligand design in transition metal catalysts and lead to more efficient methods for CO2 transformation.

  10. Understanding the role of water in aqueous ruthenium-catalyzed transfer hydrogenation of ketones

    NARCIS (Netherlands)

    Pavlova, A.; Meijer, E.J.

    2012-01-01

    We report an accurate computational study of the role of water in transfer hydrogenation of formaldehyde with a ruthenium-based catalyst using a water-specific model. Our results suggest that the reaction mechanism in aqueous solution is significantly different from that in the gas phase or in

  11. Highly Chemo- and Stereoselective Transfer Semihydrogenation of Alkynes Catalyzed by a Stable, Well-defined Manganese(II) Complex

    KAUST Repository

    Brzozowska, Aleksandra

    2018-03-30

    The first example of manganese catalyzed semihydrogenation of internal alkynes to (Z)-alkenes using ammonia borane as a hydrogen donor is reported. The reaction is catalyzed by a pincer complex of the earth abundant manganese(II) salt in the absence of any additives, base or super hydride. The ammonia borane smoothly reduces the manganese pre-catalyst [Mn(II)-PNP][Cl]2 to the catalytically active species [Mn(I)-PNP]-hydride in the triplet spin state. This manganese hydride is highly stabilized by complexation with the alkyne substrate. Computational DFT analysis studies of the reaction mechanism rationalizes the origin of stereoselectivity towards formation of (Z)-alkenes.

  12. Determination of selenium via the fluorescence quenching effect of selenium on hemoglobin-catalyzed peroxidative reaction.

    Science.gov (United States)

    Chen, Ya-Hong; Zhang, Ya-Nan; Tian, Feng-Shou

    2015-05-01

    A new method for the determination of selenium based on its fluorescence quenching on the hemoglobin-catalyzed reaction of H2 O2 and l-tyrosine has been established. The effect of pH, foreign ions and the optimization of variables on the determination of selenium was examined. The calibration curve was found to be linear between the fluorescence quenching (F0 /F) and the concentration of selenium within the range of 0.16-4.00 µg/mL. The detection limit was 1.96 ng/mL and the relative standard deviation was 3.14%. This method can be used for the determination of selenium in Se-enriched garlic bulbs with satisfactory results. Copyright © 2014 John Wiley & Sons, Ltd.

  13. Heterometallic Metal-Organic Frameworks That Catalyze Two Different Reactions Sequentially.

    Science.gov (United States)

    Saha, Debraj; Hazra, Dipak K; Maity, Tanmoy; Koner, Subratanath

    2016-06-20

    A series of copper- and alkaline-earth-metal-based multidimensional metal-organic frameworks, {[CuMg(pdc)2(H2O)4]·2H2O}n (1), [CuCa(pdc)2]n (2), [CuSr(pdc)2(H2O)3]n (3), and {[CuBa(pdc)2(H2O)5]·H2O}n (4), where H2Pdc = pyridine-2,5-dicarboxylic acid, were hydrothermally synthesized and characterized. Two different metals act as the active center to catalyze two kinds of reactions, viz., olefin to its epoxide followed by epoxide ring opening to afford the corresponding vicinal diol in a sequential manner.

  14. Transition Metal Catalyzed Reactions of Carbohydrates: a Nonoxidative Approach to Oxygenated Organics

    Energy Technology Data Exchange (ETDEWEB)

    Andrews, Mark

    1997-01-08

    There is a critical need for new environmentally friendly processes in the United States chemical industry as legislative and economic pressures push the industry to zero-waste and cradle-to-grave responsibility for the products they produce. Carbohydrates represent a plentiful, renewable resource, which for some processes might economically replace fossil feedstocks. While the conversion of biomass to fuels, is still not generally economical, the selective synthesis of a commodity or fine chemical, however, could compete effectively if appropriate catalytic conversion systems can be found. Oxygenated organics, found in a variety of products such as nylon and polyester, are particularly attractive targets. We believe that with concerted research efforts, homogeneous transition metal catalyzed reactions could play a significant role in bringing about this future green chemistry technology.

  15. Gold (I)-Catalyzed Diastereo- and Enantioselective 1,3-Dipolar Cycloaddition and Mannich Reactions of Azlactones

    Science.gov (United States)

    Melhado, Asa D.; Amarante, Giovanni W.; Wang, Z. Jane; Luparia, Marco; Toste, F. Dean

    2011-01-01

    Azlactones participate in stereoselective reactions with electron-deficient alkenes and N-sulfonyl aldimines to give products of 1,3-dipolar cycloaddition and Mannich addition reactions respectively. Both of these reactions proceed with good to excellent diastereo- and enantioselectivity using a single class of gold-catalysts, namely C2-symmetric bis(phosphinegold(I) carboxylate)complexes. The development of the azlactone Mannich reaction to provide fully protected anti-α,β-diamino acid derivatives is described. 1,3-Dipolar cycloaddition reactions of several acyclic 1,2-disubstituted alkenes, and the chemistry of the resultant cycloadducts, are examined to probe the stereochemical course of this reaction. Reaction kinetics and tandem MS studies of both the cycloaddition and Mannich reactions are reported. These studies support a mechanism in which the gold complexes catalyze addition reactions through nucleophile activation rather than the more typical activation of the electrophilic reaction component. PMID:21341677

  16. Studies on electron transfer reactions: Reduction of heteropoly 10 ...

    Indian Academy of Sciences (India)

    Rates of electron transfer reaction of thioglycolic acid with vanadium(V) substituted Keggintype heteropolyanion, [PVVVVW10O40]5-, in acetate-acetic acid buffers have been measured spectrophotometrically at 25°C. The order of the reaction with respect to substrate and oxidant is unity. The reaction shows simple second ...

  17. Droplet heat transfer and chemical reactions during direct containment heating

    International Nuclear Information System (INIS)

    Baker, L. Jr.

    1986-01-01

    A simplified model of heat transfer and chemical reaction has been adapted to evaluate the expected behavior of droplets containing unreacted Zircaloy and stainless steel moving through the containment atmosphere during postulated accidents involving direct containment heating. The model includes internal and external diffusive resistances to reaction. The results indicate that reactions will be incomplete for many conditions characteristic of direct containment heating sequences

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

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several.

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

    Indian Academy of Sciences (India)

    Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several other ...

  20. Kinetic study of free fatty acid esterification reaction catalyzed by recoverable and reusable hydrochloric acid.

    Science.gov (United States)

    Su, Chia-Hung

    2013-02-01

    The catalytic performance and recoverability of several homogeneous acid catalysts (hydrochloric, sulfuric, and nitric acids) for the esterification of enzyme-hydrolyzed free fatty acid (FFA) and methanol were studied. Although all tested catalysts drove the reaction to a high yield, hydrochloric acid was the only catalyst that could be considerably recovered and reused. The kinetics of the esterification reaction catalyzed by hydrochloric acid was investigated under varying catalyst loading (0.1-1M), reaction temperature (303-343K), and methanol/FFA molar ratio (1:1-20:1). In addition, a pseudo-homogeneous kinetic model incorporating the above factors was developed. A good agreement (r(2)=0.98) between the experimental and calculated data was obtained, thus proving the reliability of the model. Furthermore, the reusability of hydrochloric acid in FFA esterification can be predicted by the developed model. The recoverable hydrochloric acid achieved high yields of FFA esterification within five times of reuse. Copyright © 2012 Elsevier Ltd. All rights reserved.

  1. New Stetter reactions catalyzed by thiamine diphosphate dependent MenD from E. coli.

    Science.gov (United States)

    Beigi, Maryam; Waltzer, Simon; Zarei, Mostafa; Müller, Michael

    2014-12-10

    The intermolecular asymmetric Stetter reaction is a rarely found biocatalysts transformation. MenD, the second enzyme of the menaquinone biosynthetic pathway, catalyzes as a physiological reaction a Stetter-like addition of α-ketoglutarate to isochorismate. The substrate range of MenD for similar 1,4-additions is highly restricted. All other thiamine diphosphate dependent enzymes known to act as stetterases are members of the PigD enzyme subfamily, which accept aliphatic and aromatic α,β-unsaturated ketones and thioesters as Michael acceptor substrates. Here, we describe the unexpected activity of MenD with short-chain α,β-unsaturated acids and derivatives as substrates in Stetter reactions. MenD possesses a characteristic substrate range with respect to Michael acceptor substrates which is distinctly different from the classical stetterases. This provides biocatalytic access to new types of products which are not related to the products currently accessible by thiamine diphosphate dependent enzyme catalysis. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Bimolecular reactions of carbenes: Proton transfer mechanism

    Science.gov (United States)

    Abu-Saleh, Abd Al-Aziz A.; Almatarneh, Mansour H.; Poirier, Raymond A.

    2018-04-01

    Here we report the bimolecular reaction of trifluoromethylhydroxycarbene conformers and the water-mediated mechanism of the 1,2-proton shift for the unimolecular trans-conformer by using quantum chemical calculations. The CCSD(T)/cc-pVTZ//MP2/cc-pVDZ potential-energy profile of the bimolecular reaction of cis- and trans-trifluoromethylhydroxycarbene, shows the lowest gas-phase barrier height of 13 kJ mol-1 compared to the recently reported value of 128 kJ mol-1 for the unimolecular reaction. We expect bimolecular reactions of carbene's stereoisomers will open a valuable field for new and useful synthetic strategies.

  3. Hydride Transfer versus Deprotonation Kinetics in the Isobutane–Propene Alkylation Reaction: A Computational Study

    Science.gov (United States)

    2017-01-01

    The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane–propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate of hydride transfer in comparison to the competitive oligomerization and deprotonation reactions resulting in catalyst deactivation. Our calculations reveal that hydride transfer from isobutane to a carbenium ion occurs via a concerted C–C bond formation between a tert-butyl fragment and an additional olefin, or via deprotonation of the tert-butyl fragment to generate isobutene. A combination of high isobutane concentration and low propene concentration at the reaction center favor the selective alkylation. The key reaction step that has to be suppressed to increase the catalyst lifetime is the deprotonation of carbenium intermediates that are part of the hydride transfer reaction cycle. PMID:29226012

  4. Hydride Transfer versus Deprotonation Kinetics in the Isobutane-Propene Alkylation Reaction: A Computational Study.

    Science.gov (United States)

    Liu, Chong; van Santen, Rutger A; Poursaeidesfahani, Ali; Vlugt, Thijs J H; Pidko, Evgeny A; Hensen, Emiel J M

    2017-12-01

    The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane-propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate of hydride transfer in comparison to the competitive oligomerization and deprotonation reactions resulting in catalyst deactivation. Our calculations reveal that hydride transfer from isobutane to a carbenium ion occurs via a concerted C-C bond formation between a tert -butyl fragment and an additional olefin, or via deprotonation of the tert -butyl fragment to generate isobutene. A combination of high isobutane concentration and low propene concentration at the reaction center favor the selective alkylation. The key reaction step that has to be suppressed to increase the catalyst lifetime is the deprotonation of carbenium intermediates that are part of the hydride transfer reaction cycle.

  5. Heavy ion transfer reactions: Status and perspectives

    Indian Academy of Sciences (India)

    Abstract. With the large solid angle magnetic spectrometer (PRISMA) coupled to the γ-array (CLARA), extensive investigations of nuclear structure and reaction dynamics have been carried out. In the present paper aspects of these studies will be presented, focussing more closely on the reaction mechanism, in particular on ...

  6. Hydrogen-deuterium exchange reaction of 2-methylpyridine catalyzed by several fatty acids

    International Nuclear Information System (INIS)

    Hirata, Hirohumi; Fukuzumi, Kazuo.

    1976-01-01

    Hydrogen-deuterium exchange reaction of 2-methylpyridine has been studied by using several fatty acids as catalysts. The reaction was carried out in a sealed pyrex tube at 120 0 C, and the contents of the products were determined by mass spectrometry. Reaction of 2-methylpyridine with monodeuteroacetic acid (1 : 1, mol/mol) arrived at a equilibrium (d 0 reversible d 1 reversible d 2 reversible d 3 ) in 2 hr (d 0 41%, d 1 42%, d 2 15%, d 3 2%). No exchange was observed for the reaction of pyridine with monodeuteroacetic acid. The conversion-time curves of typical series reactions (d 0 → d 1 → d 2 → d 3 ) were obtained for the fatty acid catalyzed exchange in deuterium oxide. The effect of the fatty acid RCO 2 H (substrate : fatty acid : D 2 O=1 : 0.86 : 27.6, mol/mol/mol) on the conversion was in the order of R; C 1 --C 3 4 --C 10 , where the reaction mixtures were homogeneous in the case of C 1 --C 3 and were heterogeneous in the case of C 4 --C 10 . The effects of the initial concentration of the substrates and the catalysts (RCO 2 H) on the total conversion were studied by using some fatty acids (R; C 2 , C 4 and C 9 ) in deuterium oxide (for 2 hr). The total conversion of the substrate increases with increasing the concentration of the acids. The total conversion decreases in the case of R=C 9 , but, increases in the case of R=C 2 with increasing the concentration of the substrate. In the case of reactions with low concentrations of the substrate, the reactivity was in the order of C 9 >C 4 >C 2 , while with high concentrations, the reactivity was in the order of C 4 >C 2 >C 9 and C 9 >C 4 >C 2 with high and low concentrations of the acids, respectively. A possible reaction mechanism was proposed and discussed. (auth.)

  7. Cu-Catalyzed carbon-heteroatom coupling reactions under mild conditions promoted by resin-bound organic ionic bases.

    Science.gov (United States)

    Huang, Yao-Bing; Yang, Chu-Ting; Yi, Jun; Deng, Xiao-Jian; Fu, Yao; Liu, Lei

    2011-02-04

    Resin-bound organic ionic bases (RBOIBs) were developed in which tetraalkyl-ammonium or phosphonium cations are covalently attached to solid resins. The application tests showed that the performance of the tetraalkyl-ammonium-type RBOIBs is slightly better than that of the corresponding Cs salts in Cu-catalyzed C-N cross-couplings, while the tetraalkylphosphonium-type RBOIBs are significantly better than all the inorganic bases. With these newly developed RBOIBs, room-temperature Cu-catalyzed C-N coupling with various nonactivated aryl iodides and even aryl bromides can be readily accomplished. Moreover, RBOIBs can be easily recycled and reused for a number of times without much drop of activity. The good performances of RBOIBs are proposed to arise from the relatively weak binding forces between the cationic polymer backbone and basic anions, as opposed to the strong metal-anion interactions in the inorganic bases. Further applications of RBOIBs in Ni-catalyzed Suzuki-type couplings at room temperature, Cu-catalyzed C-N couplings at -30 °C, a Pd-catalyzed Heck reaction at 60 °C, and Cu-catalyzed C-S couplings at room temperature demonstrate that RBOIBs are generally applicable bases with improved performance for many other types of organic transformations.

  8. Nafion®-catalyzed microwave-assisted Ritter reaction: An atom-economic solvent-free synthesis of amides

    Science.gov (United States)

    An atom-economic solvent-free synthesis of amides by the Ritter reaction of alcohols and nitriles under microwave irradiation is reported. This green protocol is catalyzed by solid supported Nafion®NR50 with improved efficiency and reduced waste production.

  9. Kinetic studies on the Rhizomucor miehei lipase catalyzed esterification reaction of oleic acid with 1-butanol in a biphasic system

    NARCIS (Netherlands)

    Kraai, G.N.; Winkelman, J.G.M.; de Vries, Johannes; Heeres, H.J.

    2008-01-01

    The kinetics of the esterification of oleic acid with 1 -butanol catalyzed by free Rhizomucor miehei lipase in a biphasic system was studied in a batch reactor. The reaction appeared to proceed via a Ping Pong bi-bi mechanism with I -butanol inhibition. The kinetic constants of the model were

  10. 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.

  11. Insights into the formation of carlactone from in-depth analysis of the CCD8-catalyzed reactions

    KAUST Repository

    Bruno, Mark

    2017-02-10

    Strigolactones (SLs) are a new class of phytohormones synthesized from carotenoids via carlactone. The complex structure of carlactone is not easily deducible from its precursor, a cis-configured β-carotene cleavage product, and is thus formed via a poorly understood series of reactions and molecular rearrangements, all catalyzed by only one enzyme, the carotenoid cleavage dioxygenase 8 (CCD8). Moreover, the reactions leading to carlactone are expected to form a second, yet unidentified product. In this study, we used (13) C and (18) O-labelling to shed light on the reactions catalyzed by CCD8. The characterization of the resulting carlactone by LC-MS and NMR, and the identification of the assumed, less accessible second product allowed us to formulate a minimal reaction mechanism for carlactone generation. This article is protected by copyright. All rights reserved.

  12. Configurationally stable, enantioenriched organometallic nucleophiles in stereospecific Pd-catalyzed cross-coupling reactions: an alternative approach to asymmetric synthesis

    Science.gov (United States)

    Wang, Chao-Yuan; Derosa, Joseph

    2015-01-01

    Several research groups have recently developed methods to employ configurationally stable, enantioenriched organometallic nucleophiles in stereospecific Pd-catalyzed cross-coupling reactions. By establishing the absolute configuration of a chiral alkyltin or alkylboron nucleophile prior to its use in cross-coupling reactions, new stereogenic centers may be rapidly and reliably generated with preservation of the known initial stereochemistry. While this area of research is still in its infancy, such stereospecific cross-coupling reactions may emerge as simple, general methods to access diverse, optically active products from common enantioenriched organometallic building blocks. This minireview highlights recent progress towards the development of general, stereospecific Pd-catalyzed cross-coupling reactions using configurationally stable organometallic nucleophiles. PMID:26388985

  13. Fundamental Reaction Pathway and Free Energy Profile for Butyrylcholinesterase-Catalyzed Hydrolysis of Heroin

    Science.gov (United States)

    Qiao, Yan; Han, Keli; Zhan, Chang-Guo

    2013-01-01

    The pharmacological function of heroin requires an activation process which transforms heroin into 6-monoacetylmorphine (6-MAM) which is the most active form. The primary enzyme responsible for this activation process in human plasma is butyrylcholinesterase (BChE). The detailed reaction pathway of the activation process via BChE-catalyzed hydrolysis has been explored computationally, for the first time, in the present study by performing molecular dynamics simulation and first-principles quantum mechanical/molecular mechanical free energy calculations. It has been demonstrated that the whole reaction process includes acylation and deacylation stages. The acylation consists of two reaction steps, i.e. the nucleophilic attack on the carbonyl carbon of 3-acetyl group of heroin by the hydroxyl oxygen of Ser198 side chain and the dissociation of 6-MAM. The deacylation also consists of two reaction steps, i.e. the nucleophilic attack on the carbonyl carbon of the acyl-enzyme intermediate by a water molecule and the dissociation of the acetic acid from Ser198. The calculated free energy profile reveals that the second transition state (TS2) should be rate-determining. The structural analysis reveals that the oxyanion hole of BChE plays an important role in the stabilization of the rate-determining transition state TS2. The free energy barrier (15.9±0.2 or 16.1±0.2 kcal/mol) calculated for the rate-determining step is in good agreement with the experimentally-derived activation free energy (~16.2 kcal/mol), suggesting that the mechanistic insights obtained from the present computational study are reliable. The obtained structural and mechanistic insights could be valuable for use in future rational design of a novel therapeutic treatment of heroin abuse. PMID:23992153

  14. Electron-transfer rates govern product distribution in electrochemically-driven P450-catalyzed dioxygen reduction.

    Science.gov (United States)

    van der Felt, Clairisse; Hindoyan, Kevork; Choi, Kang; Javdan, Nazafarin; Goldman, Peter; Bustos, Rose; Star, Andrew G; Hunter, Bryan M; Hill, Michael G; Nersissian, Aram; Udit, Andrew K

    2011-10-01

    Developing electrode-driven biocatalytic systems utilizing the P450 cytochromes for selective oxidations depends not only on achieving electron transfer (ET) but also doing so at rates that favor native-like turnover. Herein we report studies that correlate rates of heme reduction with ET pathways and resulting product distributions. We utilized single-surface cysteine mutants of the heme domain of P450 from Bacillus megaterium and modified the thiols with N-(1-pyrene)-iodoacetamide, affording proteins that could bond to basal-plane graphite. Of the proteins examined, Cys mutants at position 62, 383, and 387 were able to form electroactive monolayers with similar E(1/2) values (-335 to -340mV vs AgCl/Ag). Respective ET rates (k(s)(o)) and heme-cysteine distances for 62, 383, and 387 are 50 s(-1) and 16Ǻ, 0.8 s(-1) and 25Ǻ, and 650 s(-1) and 19Ǻ. Experiments utilizing rotated-disk electrodes were conducted to determine the products of P450-catalyzed dioxygen reduction. We found good agreement between ET rates and product distributions for the various mutants, with larger k(s)(o) values correlating with more electrons transferred per dioxygen during catalysis. Copyright © 2011 Elsevier Inc. All rights reserved.

  15. Synthesis of 2-monoacylglycerols and structured triacylglycerols rich in polyunsaturated fatty acids by enzyme catalyzed reactions.

    Science.gov (United States)

    Rodríguez, Alicia; Esteban, Luis; Martín, Lorena; Jiménez, María José; Hita, Estrella; Castillo, Beatriz; González, Pedro A; Robles, Alfonso

    2012-08-10

    This paper studies the synthesis of structured triacylglycerols (STAGs) by a four-step process: (i) obtaining 2-monoacylglycerols (2-MAGs) by alcoholysis of cod liver oil with several alcohols, catalyzed by lipases Novozym 435, from Candida antartica and DF, from Rhizopus oryzae, (ii) purification of 2-MAGs, (iii) formation of STAGs by esterification of 2-MAGs with caprylic acid catalyzed by lipase DF, from R. oryzae, and (iv) purification of these STAGs. For the alcoholysis of cod liver oil, absolute ethanol, ethanol 96% (v/v) and 1-butanol were compared; the conditions with ethanol 96% were then optimized and 2-MAG yields of around 54-57% were attained using Novozym 435. In these 2-MAGs, DHA accounted for 24-31% of total fatty acids. In the operational conditions this lipase maintained a stable level of activity over at least 11 uses. These results were compared with those obtained with lipase DF, which deactivated after only three uses. The alcoholysis of cod liver oil and ethanol 96% catalyzed by Novozym 435 was scaled up by multiplying the reactant amounts 100-fold and maintaining the intensity of treatment constant (IOT=3g lipase h/g oil). In these conditions, the 2-MAG yield attained was about 67%; these 2-MAGs contained 36.6% DHA. The synthesized 2-MAGs were separated and purified from the alcoholysis reaction products by solvent extraction using solvents of low toxicity (ethanol and hexane); 2-MAG recovery yield and purity of the target product were approximately 96.4% and 83.9%, respectively. These 2-MAGs were transformed to STAGs using the optimal conditions obtained in a previous work. After synthesis and purification, 93% pure STAGs were obtained, containing 38% DHA at sn-2 position and 60% caprylic acid (CA) at sn-1,3 positions (of total fatty acids at these positions), i.e. the major TAG is the STAG with the structure CA-DHA-CA. Copyright © 2012 Elsevier Inc. All rights reserved.

  16. Lipase-Catalyzed Synthesis of Indolyl 4H-Chromenes via a Multicomponent Reaction in Ionic Liquid

    Directory of Open Access Journals (Sweden)

    Weian Zhang

    2017-06-01

    Full Text Available Synthesis of indolyl 4H-chromenes via a three-component reaction catalyzed by lipase in ionic liquidsis reported here for the first time. High yields (77–98% were obtained when Mucor miehei lipase was used as the catalyst in [EMIM][BF4]. Furthermore, [EMIM][BF4] exhibited good reusability in this enzymatic reaction. This study affords a new example of lipase catalytic promiscuity and broadens the application range of ionic liquid in biocatalysis.

  17. Enantioselective Direct Mannich-Type Reactions Catalyzed by Frustrated Lewis Acid/Brønsted Base Complexes.

    Science.gov (United States)

    Shang, Ming; Cao, Min; Wang, Qifan; Wasa, Masayuki

    2017-10-16

    An enantioselective direct Mannich-type reaction catalyzed by a sterically frustrated Lewis acid/Brønsted base complex is disclosed. Cooperative functioning of the chiral Lewis acid and achiral Brønsted base components gives rise to in situ enolate generation from monocarbonyl compounds. Subsequent reaction with hydrogen-bond-activated aldimines delivers β-aminocarbonyl compounds with high enantiomeric purity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Polyoxymetalate liquid-catalyzed polyol fuel cell and the related photoelectrochemical reaction mechanism study

    Science.gov (United States)

    Wu, Weibing; Liu, Wei; Mu, Wei; Deng, Yulin

    2016-06-01

    A novel design of liquid catalyzed fuel cell (LCFC), which uses polyoxometalates (POMs) as the photocatalyst and charge carrier has been reported previously. In this paper, the adaptability of biomass fuels (e.g., glycerol and glucose) to the LCFC and corresponding cell performance were studied in detail here. An interesting finding that greatly differs from conventional fuel cell is that high molecular weight fuels rather than small molecule fuels (e.g., methanol and ethylene glycol) are favored by the novel LCFC with respect to the power densities. The power output of LCFC strongly depends on the number and structure of hydroxyl groups in the biomass fuels. The evidence of UV-Vis and 1H NMR spectra shows that the preassociation between POM and alcohol fuels, which determines the photoelectrochemical reaction pathway of POM, is enhanced as the number of hydroxyl increases. Experimental results also demonstrate that more hydroxyl groups in the molecules lead to faster photoelectrochemical reaction between POM and fuels, higher reduction degree of POM, and further higher power output of LCFC. Our study reveals that biomass-based polyhydroxyl compounds such as starch, hemicellulose and cellulose are potential high-performance fuels for LCFC.

  19. Methyl Ester Production via Heterogeneous Acid-Catalyzed Simultaneous Transesterification and Esterification Reactions

    Science.gov (United States)

    Indrayanah, S.; Erwin; Marsih, I. N.; Suprapto; Murwani, I. K.

    2017-05-01

    The heterogeneous acid catalysts (MgF2 and ZnF2) have been used to catalyze the simultaneous transesterification and esterification reactions of crude palm oil (CPO) with methanol. Catalysts were synthesized by sol-gel method (combination of fluorolysis and hydrolysis). The physicochemical, structural, textural, thermal stability of the prepared catalysts was investigated by N2 adsorption-desorption, XRD, FT-IR, SEM and TG/DTG. Both MgF2 and ZnF2 have rutile structures with a different phase. The surface area of ZnF2 is smaller than that of MgF2, but the pore size and volume of ZnF2 are larger than those of MgF2. However, these materials are thermally stable. The performance of the catalysts is determined from the yield of catalysts toward the formation of methyl ester determined based on the product of methyl ester obtained from the reaction. The catalytic activity of ZnF2 is higher than MgF2 amounted to 85.21% and 26.82% with the optimum condition. The high activity of ZnF2 could be attributed to its pore diameter and pore volume but was not correlated with its surface area. The yield of methyl ester decreased along with the increase in molar ratio of methanol/CPO from 85.21 to 80.99 for ZnF2, respectively.

  20. Possible pathophysiological roles of transglutaminase-catalyzed reactions in the pathogenesis of human neurodegenerative diseases

    Directory of Open Access Journals (Sweden)

    Enrica Serretiello

    2015-09-01

    Full Text Available Transglutaminases (TG, E.C. 2.3.2.13 are related and ubiquitous enzymes that catalyze the cross linking of a glutaminyl residue of a protein/peptide substrate to a lysyl residue of a protein/peptide co-substrate. These enzymes are also capable of catalyzing other post-translational reactions important for cell life. The distribution and the physiological roles of human TGs have been widely studied in numerous cell types and tissues and recently their roles in several diseases have begun to be identified. It has been hypothesized that transglutaminase activity is directly involved in the pathogenetic mechanisms responsible for several human diseases. In particular, tissue TG (tTG, TG2, a member of the TG enzyme family, has been recently shown to be involved in the molecular mechanisms responsible for a very widespread human pathology, Celiac Disease (CD, one of the most common food intolerances described in the western population. The main food agent that provokes the strong and diffuse clinical symptoms has been known for several years to be gliadin, a protein present in a very large number of human foods derived from vegetables. Recently, some biochemical and immunological aspects of this very common disease have been clarified, and “tissue” transglutaminase, a multifunctional and ubiquitous enzyme, has been identified as one of the major factors. The aim of this review is to summarize the most recent findings concerning the relationships between the biochemical properties of the transglutaminase activity and the basic molecular mechanisms responsible for some human diseases, with particular reference to neuropsychiatric disorders. Possible molecular links between CD and neuropsychiatric disorders, and the use of transglutaminase inhibitors are also discussed.

  1. The bacterial catabolism of polycyclic aromatic hydrocarbons: Characterization of three hydratase-aldolase-catalyzed reactions

    Directory of Open Access Journals (Sweden)

    Jake A. LeVieux

    2016-12-01

    Full Text Available Polycyclic aromatic hydrocarbons (PAHs are highly toxic, pervasive environmental pollutants with mutagenic, teratogenic, and carcinogenic properties. There is interest in exploiting the nutritional capabilities of microbes to remove PAHs from various environments including those impacted by improper disposal or spills. Although there is a considerable body of literature on PAH degradation, the substrates and products for many of the enzymes have never been identified and many proposed activities have never been confirmed. This is particularly true for high molecular weight PAHs (e.g., phenanthrene, fluoranthene, and pyrene. As a result, pathways for the degradation of these compounds are proposed to follow one elucidated for naphthalene with limited experimental verification. In this pathway, ring fission produces a species that can undergo a non-enzymatic cyclization reaction. An isomerase opens the ring and catalyzes a cis to trans double bond isomerization. The resulting product is the substrate for a hydratase-aldolase, which catalyzes the addition of water to the double bond of an α,β-unsaturated ketone, followed by a retro-aldol cleavage. Initial kinetic and mechanistic studies of the hydratase-aldolase in the naphthalene pathway (designated NahE and two hydratase-aldolases in the phenanthrene pathway (PhdG and PhdJ have been completed. Crystallographic work on two of the enzymes (NahE and PhdJ provides a rudimentary picture of the mechanism and a platform for future work to identify the structural basis for catalysis and the individual specificities of these hydratase-aldolases.

  2. Understanding the mechanisms of cobalt-catalyzed hydrogenation and dehydrogenation reactions.

    Science.gov (United States)

    Zhang, Guoqi; Vasudevan, Kalyan V; Scott, Brian L; Hanson, Susan K

    2013-06-12

    Cobalt(II) alkyl complexes of aliphatic PNP pincer ligands have been synthesized and characterized. The cationic cobalt(II) alkyl complex [(PNHP(Cy))Co(CH2SiMe3)]BAr(F)4 (4) (PNHP(Cy) = bis[(2-dicyclohexylphosphino)ethyl]amine) is an active precatalyst for the hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols. To elucidate the possible involvement of the N-H group on the pincer ligand in the catalysis via a metal-ligand cooperative interaction, the reactivities of 4 and [(PNMeP(Cy))Co(CH2SiMe3)]BAr(F)4 (7) were compared. Complex 7 was found to be an active precatalyst for the hydrogenation of olefins. In contrast, no catalytic activity was observed using 7 as a precatalyst for the hydrogenation of acetophenone under mild conditions. For the acceptorless dehydrogenation of 1-phenylethanol, complex 7 displayed similar activity to complex 4, affording acetophenone in high yield. When the acceptorless dehydrogenation of 1-phenylethanol with precatalyst 4 was monitored by NMR spectroscopy, the formation of the cobalt(III) acetylphenyl hydride complex [(PNHP(Cy))Co(III)(κ(2)-O,C-C6H4C(O)CH3)(H)]BAr(F)4 (13) was detected. Isolated complex 13 was found to be an effective catalyst for the acceptorless dehydrogenation of alcohols, implicating 13 as a catalyst resting state during the alcohol dehydrogenation reaction. Complex 13 catalyzed the hydrogenation of styrene but showed no catalytic activity for the room temperature hydrogenation of acetophenone. These results support the involvement of metal-ligand cooperativity in the room temperature hydrogenation of ketones but not the hydrogenation of olefins or the acceptorless dehydrogenation of alcohols. Mechanisms consistent with these observations are presented for the cobalt-catalyzed hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols.

  3. Palladium-Catalyzed Atom-Transfer Radical Cyclization at Remote Unactivated C(sp3 )-H Sites: Hydrogen-Atom Transfer of Hybrid Vinyl Palladium Radical Intermediates.

    Science.gov (United States)

    Ratushnyy, Maxim; Parasram, Marvin; Wang, Yang; Gevorgyan, Vladimir

    2018-03-01

    A novel mild, visible-light-induced palladium-catalyzed hydrogen atom translocation/atom-transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5-HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo- and heterocyclic structures. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Probing cluster structures through sub-barrier transfer reactions

    Directory of Open Access Journals (Sweden)

    Rafferty D. C.

    2016-01-01

    Full Text Available Multinucleon transfer probabilities and excitation energy distributions have been measured in 16,18O, 19F + 208Pb at energies between 90% - 100% of the Coulomb barrier. A strong 2p2n enhancement is observed for all reactions, though most spectacularly in the 18O induced reaction. Results are interpreted in terms of the Semiclassical model, which seems to suggest α-cluster transfer in all studied systems. The relation to cluster-states in the projectile is discussed, with the experimental results consistent with previous structure studies. Dissipation of energy in the collisions of 18O is compared between different reaction modes, with cluster transfer associated with dissipation over a large number of internal states. Cluster transfer is shown to be a long range dissipation mechanism, which will inform the development of future models to treat these dynamic processes in reactions.

  5. Charge transfer reactions in electrochemical and chemical processes

    International Nuclear Information System (INIS)

    Krishtalik, L.I.

    1986-01-01

    This book presents information on the following topics: the Bronsted relation and the activation energy of electrode reactions; the chemical potential of an electron, absolute potential drop, and solvation energy in electrochemical kinetics; kinetic equations for discharge; the discharge of hydronium ions at a mercury cathode; the evolution of hydrogen at a silver cathode; some theoretical problems; an ion in a polar solvent; the elementary act of electron transfer; quantum and classical degrees of freedom-proton transfer; the effect of the potential and the nature of proton donors on the preexponential factor and the kinetic isotope effect; the chlorine evolution reaction at ruthenium dioxide-titanium dioxide anodes; the hydrogen evolution at certain liquid alloys; proton transfer in enzymatic hydrolysis reactions - kinetic isotope effect; and simultaneous transfer of two charges - coupling of endoergic and exoergic reactions

  6. One-nucleon transfer reactions and the optical potential

    CERN Document Server

    Nunes, F M; Ross, A; Titus, L J; Charity, R J; Dickhoff, W H; Mahzoon, M H; Sarich, J; Wild, S M

    2015-01-01

    We provide a summary of new developments in the area of direct reaction theory with a particular focus on one-nucleon transfer reactions. We provide a status of the methods available for describing (d,p) reactions. We discuss the effects of nonlocality in the optical potential in transfer reactions. The results of a purely phenomenological potential and the optical potential obtained from the dispersive optical model are compared; both point toward the importance of including nonlocality in transfer reactions explicitly. Given the large ambiguities associated with optical potentials, we discuss some new developments toward the quantification of this uncertainty. We conclude with some general comments and a brief account of new advances that are in the pipeline.

  7. Metal-Catalyzed Cyclization Reactions of 2,3,4-Trien-1-ols: A Joint Experimental-Computational Study.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro; Cembellín, Sara; Fernández, Israel; Martínez Del Campo, Teresa

    2016-08-08

    Controlled preparation of tri- and tetrasubstituted furans, as well as carbazoles has been achieved through chemo- and regioselective metal-catalyzed cyclization reactions of cumulenic alcohols. The gold- and palladium-catalyzed cycloisomerization reactions of cumulenols, including indole-tethered 2,3,4-trien-1-ols, to trisubstituted furans was effective, due to a 5-endo-dig oxycyclization by attack of the hydroxy group onto the central cumulene double bond. In contrast, palladium-catalyzed heterocyclization/coupling reactions with 3-bromoprop-1-enes furnished tetrasubstituted furans. Also studied was the palladium-catalyzed cyclization/coupling sequence involving protected indole-tethered 2,3,4-trien-1-ols and 3-bromoprop-1-enes that exclusively generated trisubstituted carbazole derivatives. These results could be explained through a selective 6-endo-dig cumulenic hydroarylation, followed by aromatization. DFT calculations were carried out to understand this difference in reactivity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Synechocystis DrgA protein functioning as nitroreductase and ferric reductase is capable of catalyzing the Fenton reaction.

    Science.gov (United States)

    Takeda, Kouji; Iizuka, Mayumi; Watanabe, Toshihiro; Nakagawa, Junichi; Kawasaki, Shinji; Niimura, Youichi

    2007-03-01

    In order to identify an enzyme capable of Fenton reaction in Synechocystis, we purified an enzyme catalyzing one-electron reduction of t-butyl hydroperoxide in the presence of FAD and Fe(III)-EDTA. The enzyme was a 26 kDa protein, and its N-terminal amino acid sequencing revealed it to be DrgA protein previously reported as quinone reductase [Matsuo M, Endo T and Asada K (1998) Plant Cell Physiol39, 751-755]. The DrgA protein exhibited potent quinone reductase activity and, furthermore, we newly found that it contained FMN and highly catalyzed nitroreductase, flavin reductase and ferric reductase activities. This is the first demonstration of nitroreductase activity of DrgA protein previously identified by a drgA mutant phenotype. DrgA protein strongly catalyzed the Fenton reaction in the presence of synthetic chelate compounds, but did so poorly in the presence of natural chelate compounds. Its ferric reductase activity was observed with both natural and synthetic chelate compounds with a better efficiency with the latter. In addition to small molecular-weight chemical chelators, an iron transporter protein, transferrin, and an iron storage protein, ferritin, turned out to be substrates of the DrgA protein, suggesting it might play a role in iron metabolism under physiological conditions and possibly catalyze the Fenton reaction under hyper-reductive conditions in this microorganism.

  9. Inhibited proton transfer enhances Au-catalyzed CO2-to-fuels selectivity

    Science.gov (United States)

    Wuttig, Anna; Yaguchi, Momo; Motobayashi, Kenta; Osawa, Masatoshi; Surendranath, Yogesh

    2016-01-01

    CO2 reduction in aqueous electrolytes suffers efficiency losses because of the simultaneous reduction of water to H2. We combine in situ surface-enhanced IR absorption spectroscopy (SEIRAS) and electrochemical kinetic studies to probe the mechanistic basis for kinetic bifurcation between H2 and CO production on polycrystalline Au electrodes. Under the conditions of CO2 reduction catalysis, electrogenerated CO species are irreversibly bound to Au in a bridging mode at a surface coverage of ∼0.2 and act as kinetically inert spectators. Electrokinetic data are consistent with a mechanism of CO production involving rate-limiting, single-electron transfer to CO2 with concomitant adsorption to surface active sites followed by rapid one-electron, two-proton transfer and CO liberation from the surface. In contrast, the data suggest an H2 evolution mechanism involving rate-limiting, single-electron transfer coupled with proton transfer from bicarbonate, hydronium, and/or carbonic acid to form adsorbed H species followed by rapid one-electron, one-proton, or H recombination reactions. The disparate proton coupling requirements for CO and H2 production establish a mechanistic basis for reaction selectivity in electrocatalytic fuel formation, and the high population of spectator CO species highlights the complex heterogeneity of electrode surfaces under conditions of fuel-forming electrocatalysis. PMID:27450088

  10. Transfer reactions at the neutron dripline with triton target

    CERN Multimedia

    Two-neutron transfer to $^{9}$Li will populate the ground state of $^{11}$Li as well as low-lying resonances in a way that is complementary to studies of these states performed at higher beam energies. We aim at detecting the charged particles from the transfer reactions as well as neutrons coming from the decay of possible $^{11}$Li resonances.

  11. Parallel proton transfer pathways in aqueous acid-base reactions

    NARCIS (Netherlands)

    Cox, M.J.; Bakker, H.J.

    2008-01-01

    We study the mechanism of proton transfer (PT) between the photoacid 8-hydroxy-1,3, 6-pyrenetrisulfonic acid (HPTS) and the base chloroacetate in aqueous solution. We investigate both proton and deuteron transfer reactions in solutions with base concentrations ranging from 0.25M to 4M. Using

  12. Transfer reactions at the neutron dripline with triton target

    CERN Document Server

    Borge, M J G; Fynbo, H O U; Gomez Camacho, J; Johansen, J; Johansson, H T; Jonson, B; Krücken, R; Kurcewicz, J; Martel, I; Moro, A; Mücher, D; Nilsson, T; Nyman, G; Raabe, R; Randisi, G; Riisager, K; Sambi, S; Sanchez-Benitez, AM; Tengblad, O

    2012-01-01

    Two-neutron transfer to $^{9}$Li will populate the ground state of $^{11}$Li as well as low-lying resonances in a way that is complementary to studies of these states performed at higher beam energies. We aim at detecting the charged particles from the transfer reactions as well as neutrons coming from the decay of possible $^{11}$Li resonances.

  13. Mechanism of electron transfer reaction of ternary ...

    Indian Academy of Sciences (India)

    )(OX)(H2O)]− (DPA = dipicolinate and OX = oxalate) by periodate in aqueous acidic medium has been studied spectrophotometrically over the pH range of 4.45-5.57 at different temperatures. The reaction is first order with respect to both [IO 4 ...

  14. Mechanism of Triplet Energy Transfer in Photosynthetic Bacterial Reaction Centers.

    Science.gov (United States)

    Mandal, Sarthak; Carey, Anne-Marie; Locsin, Joshua; Gao, Bing-Rong; Williams, JoAnn C; Allen, James P; Lin, Su; Woodbury, Neal W

    2017-07-13

    In purple bacterial reaction centers, triplet excitation energy transfer occurs from the primary donor P, a bacteriochlorophyll dimer, to a neighboring carotenoid to prevent photodamage from the generation of reactive oxygen species. The B B bacteriochlorophyll molecule that lies between P and the carotenoid on the inactive electron transfer branch is involved in triplet energy transfer between P and the carotenoid. To expand the high-resolution spectral and kinetic information available for describing the mechanism, we investigated the triplet excited state formation and energy transfer pathways in the reaction center of Rhodobacter sphaeroides using pump-probe transient absorption spectroscopy over a broad spectral region on the nanosecond to microsecond time scale at both room temperature and at 77 K. Wild-type reaction centers were compared with a reaction center mutant (M182HL) in which B B is replaced by a bacteriopheophytin (Φ), as well as to reaction centers that lack the carotenoid. In wild-type reaction centers, the triplet energy transfer efficiency from P to the carotenoid was essentially unity at room temperature and at 77 K. However, in the M182HL mutant reaction centers, both the rate and efficiency of triplet energy transfer were decreased at room temperature, and at 77 K, no triplet energy transfer was observed, attributable to a higher triplet state energy of the bacteriopheophytin that replaces bacteriochlorophyll in this mutant. Finally, detailed time-resolved spectral analysis of P, carotenoid, and B B (Φ in the M182HL mutant) reveals that the triplet state of the carotenoid is coupled fairly strongly to the bridging intermediate B B in wild-type and Φ in the M182HL mutant, a fact that is probably responsible for the lack of any obvious intermediate 3 B B / 3 Φ transient formation during triplet energy transfer.

  15. Studies on electron transfer reactions of Keggin-type mixed ...

    Indian Academy of Sciences (India)

    Administrator

    (PV2) in aqueous phosphate buffer of pH 6 at ambient temperature. Electrochemical and optical studies show that the stoichiometry of the reaction is 1: 2 (NADH : HPA). EPR and optical studies show that HPA act as one electron acceptor and the products of electron transfer reactions are one elec- tron reduced heteropoly ...

  16. Understanding the role of water in aqueous ruthenium-catalyzed transfer hydrogenation of ketones.

    Science.gov (United States)

    Pavlova, Anna; Meijer, Evert Jan

    2012-10-22

    We report an accurate computational study of the role of water in transfer hydrogenation of formaldehyde with a ruthenium-based catalyst using a water-specific model. Our results suggest that the reaction mechanism in aqueous solution is significantly different from that in the gas phase or in methanol solution. Previous theoretical studies have shown a concerted hydride and proton transfer in the gas phase (M. Yamakawa, H. Ito, R. Noyori, J. Am. Chem. Soc. 2000, 122, 1466-1478;J.-W. Handgraaf, J. N. H. Reek, E. J. Meijer, Organometallics 2003, 22, 3150-3157; D. A. Alonso, P. Brandt, S. J. M. Nordin, P. G. Andersson, J. Am. Chem. Soc. 1999, 121, 9580-9588; D. G. I. Petra, J. N. H. Reek, J.-W. Handgraaf, E. J. Meijer, P. Dierkes, P. C. J. Kamer, J. Brussee, H. E. Schoemaker, P. W. N. M. van Leeuwen, Chem. Eur. J. 2000, 6, 2818-2829), whereas a delayed, solvent-mediated proton transfer has been observed in methanol solution (J.-W. Handgraaf, E. J. Meijer, J. Am. Chem. Soc. 2007, 129, 3099-3103). In aqueous solution, a concerted transition state is observed, as in the previous studies. However, only the hydride is transferred at that point, whereas the proton is transferred later by a water molecule instead of the catalyst. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Excited state charge transfer reaction in (mixed solvent + electrolyte ...

    Indian Academy of Sciences (India)

    to the relatively more polar charge transfer (CT) state with a forward reaction rate constant, kf . Note that the. LE→CT conversion reaction in P4C is associated with an activation barrier21 of ∼ 6kB T. Subsequently, the CT state either regenerates the LE state by participating in the reverse reaction with a rate constant, kr, or, ...

  18. Electron Transfer and Reaction Mechanism of Laccases

    OpenAIRE

    Jones, Stephen M.; Solomon, Edward I.

    2015-01-01

    Laccases are part of the family of multicopper oxidases (MCOs), which couple the oxidation of substrates to the four electron reduction of O2 to H2O. MCOs contain a minimum of four Cu's divided into Type 1 (T1), Type 2 (T2), and binuclear Type 3 (T3) Cu sites that are distinguished based on unique spectroscopic features. Substrate oxidation occurs near the T1, and electrons are transferred approximately 13 Å through the protein via the Cys-His pathway to the T2/T3 trinuclear copper cluster (T...

  19. Intrinsic barriers for H-atom transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Camaioni, D.M.; Autrey, S.T.; Franz, J.A.

    1994-08-01

    Hydrogen transfer reactions play a well-recognized role in coal liquefaction. While H-abstraction reactions between radicals and H-donors have been well-studied, understanding of structure-reactivity relationships remains surprisingly incomplete. Another form of hydrogen transfer known as radical hydrogen transfer (radical donation of H to an unsaturated compound) is currently the subject of much speculation. The barriers for identity reactions are key parameters in the Evans-Polanyi equation for estimating reaction barriers and are fundamentally significant for the insight they provide about bond reorganization energies for formation of transition state structures. Although knowable from experiment, relatively few H-abstraction identity barriers and no barriers for hydrocarbon radical hydrogen transfer reactions have been measured. This paper seeks to supplement and extend existing experimental data with results obtained by calculation. The authors have used ab initio and semiempirical molecular orbital methods (MNDO-PM3) to calculate barriers for a series of H-atom abstraction and radical-hydrogen-transfer identity reactions for alkyl, alkenyl, arylalkyl and hydroaryl systems. Details of this methodology and analyses of how barrier heights correlate with reactant and transition state properties will be presented and discussed.

  20. Use of intermediate partitioning to calculate intrinsic isotope effects for the reaction catalyzed by malic enzyme

    International Nuclear Information System (INIS)

    Grissom, C.B.; Cleland, W.W.

    1985-01-01

    For those enzymes that proceed via a stepwise reaction mechanism with a discrete chemical intermediate and where deuterium and 13 C isotope effects are on separate steps, a new method has been developed to solve for the intrinsic deuterium and 13 C kinetic isotope effects that relies on directly observing the partitioning of the intermediate between the forward and reverse directions. This observed partitioning ratio, along with the values of the primary deuterium, tritium, and 13 C kinetic isotope effects on V/K for the substrate with the label being followed, allows an exact solution for the intrinsic deuterium and 13 C isotope effects, the forward commitment for the deuterium-sensitive step, and the partition ratio for the intermediate in the reaction. This method allows portions of the reaction coordinate diagram to be defined precisely and the relative energy levels of certain activation barriers to be assigned exactly. With chicken liver triphosphopyridine nucleotide (TPN) malic enzyme activated by Mg 2+ , the partitioning of oxalacetate to pyruvate vs. malate in the presence of TPNH, 0.47, plus previously determined isotope effects gives an intrinsic deuterium isotope effect of 5.7 on hydride transfer and a 13 C isotope effect of 1.044 on decarboxylation. Reverse hydride transfer is 10 times faster than decarboxylation, and the forward commitment for hydride transfer is 3.3. The 13 C isotope effect is not significantly different with reduced acetylpyridine adenine dinucleotide phosphate replacing TPNH (although the pyruvate/malate partitioning ratio for oxalactate is now 9.9), but replacement of Mg 2+ by Mn 2+ raises the value to 1.065 (partition ratio 0.99)

  1. Structure of a Novel Enzyme That Catalyzes Acyl Transfer to Alcohols in Aqueous Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Mathews, I.; Soltis, M.; Saldajeno, M.; Ganshaw, G.; Sala, R.; Weyler, W.; Cervin, M.A.; Whited, G.; Bott, R.

    2009-06-03

    The unusual architecture of the enzyme (MsAcT) isolated from Mycobacterium smegmatis forms the mechanistic basis for favoring alcoholysis over hydrolysis in water. Unlike hydrolases that perform alcoholysis only under anhydrous conditions, MsAcT demonstrates alcoholysis in substantially aqueous media and, in the presence of hydrogen peroxide, has a perhydrolysis:hydrolysis ratio 50-fold greater than that of the best lipase tested. The crystal structures of the apoenzyme and an inhibitor-bound form have been determined to 1.5 {angstrom} resolution. MsAcT is an octamer in the asymmetric unit and forms a tightly associated aggregate in solution. Relative to other structurally similar monomers, MsAcT contains several insertions that contribute to the oligomerization and greatly restrict the shape of the active site, thereby limiting its accessibility. These properties create an environment by which MsAcT can catalyze transesterification reactions in an aqueous medium and suggests how a serine hydrolase can be engineered to be an efficient acyltransferase.

  2. Graphene Charge Transfer, Spectroscopy, and Photochemical Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Brus, Louis [Columbia Univ., New York, NY (United States)

    2017-01-31

    This project focused on the special electronic and optical properties of graphene and adsorbed molecular species. Graphene makes an excellent substrate for current collection in nanostructured photovoltaic designs. Graphene is almost transparent, and can be used as a solar cell window. It also has no surface states, and thus current is efficiently transported over long distances. Progress in graphene synthesis indicates that there will soon be practical methods for making large pieces of graphene for devices. We now need to understand exactly what happens to both ground state and electronically excited molecules and Qdots near graphene, if we are going to use them to absorb light in a nano-structured photovoltaic device using graphene to collect photocurrent. We also need to understand how to shift the graphene Fermi level, to optimize the kinetics of electron transfer to graphene. And we need to learn how to convert local graphene areas to semiconductor structure, to make useful spatially patterned graphenes. In this final report, we describe how we addressed these goals. We explored the question of possible Surface Enhanced Raman spectroscopy from molecular Charge Transfer onto Graphene substrates. We observed strong hole doping of graphene by adsorbed halogens as indicated by the shift of the graphene G Raman band. In the case of iodine adsorption, we also observed the anionic species made by hole doping. At low frequency in the Raman spectrum, we saw quite intense lines from I3- and I5- , suggesting possible SERS. We reported on Fresnel calculations on this thin film system, which did not show any net electromagnetic field enhancement.

  3. Two-neutron transfer reactions with heavy-deformed nuclei

    International Nuclear Information System (INIS)

    Price, C.; Landowne, S.; Esbensen, H.

    1988-01-01

    In a recent communication we pointed out that one can combine the macroscopic model for two-particle transfer reactions on deformed nuclei with the sudden limit approximation for rotational excitation, and thereby obtain a practical method for calculating transfer reactions leading to high-spin states. As an example, we presented results for the reaction 162 Dy( 58 Ni, 60 Ni) 160 Dy populating the ground-state rotational band up to the spin I = 14 + state. We have also tested the validity of the sudden limit for the inelastic excitation of high spin states and we have noted how the macroscopic model may be modified to allow for more microscopic nuclear structure effects in an application to diabolic pair-transfer processes. This paper describes our subsequent work in which we investigated the systematic features of pair-transfer reactions within the macroscopic model by using heavier projectiles to generate higher spins and by decomposing the cross sections according to the multipolarity of the transfer interaction. Particular attention is paid to characteristic structures in the angular distributions for the lower spin states and how they depend on the angular momentum carried by the transferred particles. 11 refs., 3 figs

  4. Inverting Steric Effects: Using "Attractive" Noncovalent Interactions To Direct Silver-Catalyzed Nitrene Transfer.

    Science.gov (United States)

    Huang, Minxue; Yang, Tzuhsiung; Paretsky, Jonathan D; Berry, John F; Schomaker, Jennifer M

    2017-12-06

    Nitrene transfer (NT) reactions represent powerful and direct methods to convert C-H bonds into amine groups that are prevalent in many commodity chemicals and pharmaceuticals. The importance of the C-N bond has stimulated the development of numerous transition-metal complexes to effect chemo-, regio-, and diastereoselective NT. An ongoing challenge is to understand how subtle interactions between catalyst and substrate influence the site-selectivity of the C-H amination event. In this work, we explore the underlying reasons why Ag(tpa)OTf (tpa = tris(pyridylmethyl)amine) prefers to activate α-conjugated C-H bonds over 3° alkyl C(sp 3 )-H bonds and apply these insights to reaction optimization and catalyst design. Experimental results suggest possible roles of noncovalent interactions (NCIs) in directing the NT; computational studies support the involvement of π···π and Ag···π interactions between catalyst and substrate, primarily by lowering the energy of the directed transition state and reaction conformers. A simple Hess's law relationship can be employed to predict selectivities for new substrates containing competing NCIs. The insights presented herein are poised to inspire the design of other catalyst-controlled C-H functionalization reactions.

  5. Dinuclear Tetrapyrazolyl Palladium Complexes Exhibiting Facile Tandem Transfer Hydrogenation/Suzuki Coupling Reaction of Fluoroarylketone

    KAUST Repository

    Dehury, Niranjan

    2016-07-18

    Herein, we report an unprecedented example of dinuclear pyrazolyl-based Pd complexes exhibiting facile tandem catalysis for fluoroarylketone: Tetrapyrazolyl di-palladium complexes with varying Pd-Pd distances efficiently catalyze the tandem reaction involving transfer hydrogenation of fluoroarylketone to the corresponding alcohol and Suzuki-Miyaura cross coupling reaction of the resulting fluoroarylalcohol under moderate reaction conditions, to biaryl alcohol. The complex with the shortest Pd-Pd distance exhibits the highest tandem activity among its di-metallic analogues, and exceeds in terms of activity and selectivity the analogous mononuclear compound. The kinetics of the reaction indicates clearly that reductive transformation of haloarylketone into haloaryalcohol is the rate determining step in the tandem reaction. Interestingly while fluoroarylketone undergoes the multistep tandem catalysis, the chloro- and bromo-arylketones undergo only a single step C-C coupling reaction resulting in biarylketone as the final product. Unlike the pyrazole based Pd compounds, the precursor PdCl2 and the phosphine based relevant complexes (PPh3)2PdCl2 and (PPh3)4Pd are found to be unable to exhibit the tandem catalysis.

  6. N-Heterocyclic Carbene-Catalyzed Vinylogous Mukaiyama Aldol Reaction of α-Keto Esters and α-Trifluoromethyl Ketones

    KAUST Repository

    Du, Guang-Fen

    2015-11-05

    © Georg Thieme Verlag Stuttgart · New York · Synthesis 2016. N-Heterocyclic carbene (NHC)-catalyzed vinylogous Mukaiyama aldol reaction of ketones was developed. Under the catalysis of 5 mol% NHC, α-keto esters and α-trifluoromethyl ketones reacted with 2-(trimethysilyloxy)furan efficiently to produce γ-substituted butenolides containing adjacent quaternary and tertiary carbon centers in high yields with good diastereoselectivities.

  7. Rh(I)-catalyzed CO gas-free carbonylative cyclization reactions of alkynes with 2-bromophenylboronic acids using formaldehyde.

    Science.gov (United States)

    Morimoto, Tsumoru; Yamasaki, Kae; Hirano, Akihisa; Tsutsumi, Ken; Kagawa, Natsuko; Kakiuchi, Kiyomi; Harada, Yasuyuki; Fukumoto, Yoshiya; Chatani, Naoto; Nishioka, Takanori

    2009-04-16

    The rhodium(I)-catalyzed reaction of alkynes with 2-bromophenylboronic acids in the presence of paraformaldehyde resulted in a CO gas-free carbonylative cyclization, yielding indenone derivatives. [RhCl(BINAP)](2) and [RhCl(cod)](2) were responsible for the decarbonylation of formaldehyde and the subsequent carbonylation of alkynes with 2-haloboronic acids, respectively, leading to efficient whole carbonylation. Sterically bulky and electron-withdrawing groups on unsymmetrically substituted alkynes favored the alpha-position of indenones.

  8. Recent Advances in Recoverable Systems for the Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction (CuAAC

    Directory of Open Access Journals (Sweden)

    Alessandro Mandoli

    2016-09-01

    Full Text Available The explosively-growing applications of the Cu-catalyzed Huisgen 1,3-dipolar cycloaddition reaction between organic azides and alkynes (CuAAC have stimulated an impressive number of reports, in the last years, focusing on recoverable variants of the homogeneous or quasi-homogeneous catalysts. Recent advances in the field are reviewed, with particular emphasis on systems immobilized onto polymeric organic or inorganic supports.

  9. 1H NMR studies of substrate hydrogen exchange reactions catalyzed by L-methionine gamma-lyase

    International Nuclear Information System (INIS)

    Esaki, N.; Nakayama, T.; Sawada, S.; Tanaka, H.; Soda, K.

    1985-01-01

    Hydrogen exchange reactions of various L-amino acids catalyzed by L-methionine gamma-lyase (EC 4.4.1.11) have been studied. The enzyme catalyzes the rapid exchange of the alpha- and beta-hydrogens of L-methionine and S-methyl-L-cysteine with deuterium from the solvent. The rate of alpha-hydrogen exchange was about 40 times faster than that of the enzymatic elimination reaction of the sulfur-containing amino acids. The enzyme also catalyzes the exchange reaction of alpha- and beta-hydrogens of the straight-chain L-amino acids which are not susceptible to elimination. The exchange rates of the alpha-hydrogen and the total beta-hydrogens of L-alanine and L-alpha-aminobutyrate with deuterium followed first-order kinetics. For L-norvaline, L-norleucine, S-methyl-L-cysteine, and L-methionine, the rate of alpha-hydrogen exchange followed first-order kinetics, but the rate of total beta-hydrogen exchange decreased due to a primary isotope effect at the alpha-position. L-Phenylalanine and L-tryptophan slowly underwent alpha-hydrogen exchange. The pro-R hydrogen of glycine was deuterated stereospecifically

  10. Tunable, Chemo- and Site-Selective Nitrene Transfer Reactions through the Rational Design of Silver(I) Catalysts.

    Science.gov (United States)

    Alderson, Juliet M; Corbin, Joshua R; Schomaker, Jennifer M

    2017-09-19

    Carbon-nitrogen (C-N) bonds are ubiquitous in pharmaceuticals, agrochemicals, diverse bioactive natural products, and ligands for transition metal catalysts. An effective strategy for introducing a new C-N bond into a molecule is through transition metal-catalyzed nitrene transfer chemistry. In these reactions, a metal-supported nitrene can either add across a C═C bond to form an aziridine or insert into a C-H bond to furnish the corresponding amine. Typical catalysts for nitrene transfer include Rh 2 L n and Ru 2 L n complexes supported by bridging carboxylate and related ligands, as well as complexes based on Cu, Co, Ir, Fe, and Mn supported by porphyrins and related ligands. A limitation of metal-catalyzed nitrene transfer is the ability to predictably select which specific site will undergo amination in the presence of multiple reactive groups; thus, many reactions rely primarily on substrate control. Achieving true catalyst-control over nitrene transfer would open up exciting possibilities for flexible installation of new C-N bonds into hydrocarbons, natural product-inspired scaffolds, existing pharmaceuticals or biorenewable building blocks. Silver-catalyzed nitrene transfer enables flexible control over the position at which a new C-N bond is introduced. Ag(I) supported by simple N-donor ligands accommodates a diverse range of coordination geometries, from linear to tetrahedral to seesaw, enabling the electronic and steric parameters of the catalyst to be tuned independently. In addition, the ligand, Ag salt counteranion, Ag/ligand ratio and the solvent all influence the fluxional and dynamic behavior of Ag(I) complexes in solution. Understanding the interplay of these parameters to manipulate the behavior of Ag-nitrenes in a predictable manner is a key design feature of our work. In this Account, we describe successful applications of a variety of design principles to tunable, Ag-catalyzed aminations, including (1) changing Ag/ligand ratios to influence

  11. Combined cross-linked enzyme aggregates of horseradish peroxidase and glucose oxidase for catalyzing cascade chemical reactions.

    Science.gov (United States)

    Nguyen, Le Truc; Yang, Kun-Lin

    2017-05-01

    Cascade reactions involved unstable intermediates are often encountered in biological systems. In this study, we developed combined cross-linked enzyme aggregates (combi-CLEA) to catalyze a cascade reaction which involves unstable hydrogen peroxide as an intermediate. The combi-CLEA contains two enzymes̶ glucose oxidase (GOx) and horseradish peroxidase (HRP) which are cross-linked together as solid aggregates. The first enzyme GOx catalyzes the oxidation of glucose and produces hydrogen peroxide, which is used by the second enzyme HRP to oxidize 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). The apparent reaction rate of the cascade reaction reaches 10.5±0.5μM/min when the enzyme ratio is 150:1 (GOx:HRP). Interestingly, even in the presence of catalase, an enzyme that quickly decomposes hydrogen peroxide, the reaction rate only decreases by 18.7% to 8.3±0.3μM/min. This result suggests that the intermediate hydrogen peroxide is not decomposed by catalase due to a short diffusion distance between GOx and HRP in the combi-CLEA. Scanning electron microscopy images suggest that combi-CLEA particles are hollow spheres and have an average diameter around 250nm. Because of their size, combi-CLEA particles can be entrapped inside a nylon membrane for detecting glucose by using the cascade reaction. Copyright © 2017 Elsevier Inc. All rights reserved.

  12. Carbene Transfer Reactions Catalysed by Dyes of the Metalloporphyrin Group

    Directory of Open Access Journals (Sweden)

    Mário M. Q. Simões

    2018-03-01

    Full Text Available Carbene transfer reactions are very important transformations in organic synthesis, allowing the generation of structurally challenging products by catalysed cyclopropanation, cyclopropenation, carbene C-H, N-H, O-H, S-H, and Si-H insertion, and olefination of carbonyl compounds. In particular, chiral and achiral metalloporphyrins have been successfully explored as biomimetic catalysts for these carbene transfer reactions under both homogeneous and heterogeneous conditions. In this work the use of synthetic metalloporphyrins (MPorph, M = Fe, Ru, Os, Co, Rh, Ir, Sn as homogeneous or heterogeneous catalysts for carbene transfer reactions in the last years is reviewed, almost exclusively focused on the literature since the year 2010, except when reference to older publications was deemed to be crucial.

  13. Energy-Related Small Molecule Activation Reactions: Oxygen Reduction and Hydrogen and Oxygen Evolution Reactions Catalyzed by Porphyrin- and Corrole-Based Systems.

    Science.gov (United States)

    Zhang, Wei; Lai, Wenzhen; Cao, Rui

    2017-02-22

    Globally increasing energy demands and environmental concerns related to the use of fossil fuels have stimulated extensive research to identify new energy systems and economies that are sustainable, clean, low cost, and environmentally benign. Hydrogen generation from solar-driven water splitting is a promising strategy to store solar energy in chemical bonds. The subsequent combustion of hydrogen in fuel cells produces electric energy, and the only exhaust is water. These two reactions compose an ideal process to provide clean and sustainable energy. In such a process, a hydrogen evolution reaction (HER), an oxygen evolution reaction (OER) during water splitting, and an oxygen reduction reaction (ORR) as a fuel cell cathodic reaction are key steps that affect the efficiency of the overall energy conversion. Catalysts play key roles in this process by improving the kinetics of these reactions. Porphyrin-based and corrole-based systems are versatile and can efficiently catalyze the ORR, OER, and HER. Because of the significance of energy-related small molecule activation, this review covers recent progress in hydrogen evolution, oxygen evolution, and oxygen reduction reactions catalyzed by porphyrins and corroles.

  14. Study of charge transfer reactions in a microbial fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Martin, E.; Savadogo, O. [Ecole Polytechnique, Montreal, PQ (Canada). Dept. de Genie Chimique; National Research Council of Canada, Montreal, PQ (Canada). Biotechnology Research Inst.; Tartakovsky, B. [National Research Council of Canada, Montreal, PQ (Canada). Biotechnology Research Inst.

    2008-07-01

    Electron transfer reactions in a microbial fuel cell (MFC) were evaluated. The MFC was inoculated with anaerobic mesophilic sludge and operated with carbon felt, carbon cloth, and platinum (Pt) coated carbon cloth. The MFC was then fed with either acetate or glucose as a source of fuel and operated at a temperature of 25 degrees C and a pH of 7. Scanning electron microscopy (SEM) micrographs demonstrated that the micro-organisms colonized the anodes. Cyclic voltammetry and polarization tests were conducted using different fractions of the anodophilic biofilm in order to determine charge transfer routes. The study characterized the electron transfer mechanisms used by the exoelectrogenic micro-organisms to produce electricity. It was concluded that further research is needed to characterize reaction transfer routes. 2 refs., 1 fig.

  15. Tests on measuring astrophysical S-factors with transfer reactions

    CERN Document Server

    Crespo, R

    2002-01-01

    We propose a general method to test the uniqueness property of the Asymptotic Normalization Constant, ANC. We apply this method for the case of the vertex sup 1 sup 0 B -> sup 9 Be+p using a set of different proton-transfer reactions at different energies. Given the limited sets of data for peripheral transfer reactions, we underline the present difficulties in extracting astrophysical S-factors and point out the inadequacy of some of the available data. Finally, we make some suggestions for future experiments in order to make this test conclusive.

  16. Intrinsic barriers for H-atom transfer reactions involving hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Camaioni, D.M.; Autrey, S.T.; Franz, J.A.

    1994-08-01

    Intrinsic barriers (formally the barrier in the absence of driving force) for H-atom transfer reactions are key parameters in Evans-Polyanyi and Marcus equations for estimating exothermic reaction barriers and are fundamentally significant for the insight they provide about bond reorganization energies for formation of transition state structures. Although knowable from experiment, relatively few of these barriers have been measured due to experimental difficulties in measuring rates for identity reactions. Thus, the authors have used semiempirical Molecular Orbital theoretical methods (MNDO/PM3) to calculate barriers for a series of H-atom transfer identity reactions involving alkyl, alkenyl, arylalkyl and hydroaryl radicals and donors. Briefly stated, they find that barriers decrease with the degree of alkyl substitution at the radical site whereas barriers increase with the degree of conjugation with the radical site. Details of the methodology and analyses of how these barrier heights correlate with reactant and transition state properties will be presented and discussed.

  17. Effect of electrostatic interactions on electron-transfer reactions

    International Nuclear Information System (INIS)

    Hickel, B.

    1987-01-01

    Fast reactions of electron transfer are studied by pulsed radiolysis. By this technique radicals and ionic radicals with high redox potentials are created homogeneously in the solution in about 10 -8 second. For solvated electron effect of electrostatic interaction on kinetics of reactions limited by diffusion is obtained with a good approximation by the Debye equation when ion mobility is known. Deviation from the theory occurs in ion pair formation, which is evidenced experimentally in reactions between anions when cations are complexed by a cryptate. Slow reactions k 8 M -1 s -1 are more sensitive to electrostatic interactions than reactions limited by diffusion. When there is no ion pair formation the velocity constant depends upon dielectric constant of the solvent and reaction distance. 17 refs

  18. Mass transfer with complex reversible chemical reactions. II: Parallel reversible chemical reactions

    NARCIS (Netherlands)

    Versteeg, Geert; van Beckum, F.P.H.; Kuipers, J.A.M.; van Swaaij, Willibrordus Petrus Maria

    1990-01-01

    An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and

  19. Non-Catalyzed Click Reactions of ADIBO Derivatives with 5-Methyluridine Azides and Conformational Study of the Resulting Triazoles.

    Directory of Open Access Journals (Sweden)

    Petra Smyslova

    Full Text Available Copper-free click reactions between a dibenzoazocine derivative and azides derived from 5-methyluridine were investigated. The non-catalyzed reaction yielded both regioisomers in an approximately equivalent ratio. The NMR spectra of each regioisomer revealed conformational isomery. The ratio of isomers was dependent on the type of regioisomer and the type of solvent. The synthesis of various analogs, a detailed NMR study and computational modeling provided evidence that the isomery was dependent on the interaction of the azocine and pyrimidine parts.

  20. Iron-Catalyzed Reaction of Urea with Alcohols and Amines: A Safe Alternative for the Synthesis of Primary Carbamates.

    Science.gov (United States)

    Peña-López, Miguel; Neumann, Helfried; Beller, Matthias

    2016-08-23

    A general study of the iron-catalyzed reaction of urea with nucleophiles is here presented. The carbamoylation of alcohols allows for the synthesis of N-unsubstituted (primary) carbamates, including present drugs (Felbamate and Meprobamate), without the necessity to apply phosgene and related derivatives. Using amines as nucleophiles gave rise to the respective mono- and disubstituted ureas via selective transamidation reaction. These atom-economical transformations provide a direct and selective access to valuable compounds from cheap and readily available urea using a simple Lewis-acidic iron(II) catalyst. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Rhodium-Catalyzed Insertion Reaction of PhP Group of Pentaphenylcyclopentaphosphine with Acyclic and Cyclic Disulfides.

    Science.gov (United States)

    Arisawa, Mieko; Sawahata, Kyosuke; Yamada, Tomoki; Sarkar, Debayan; Yamaguchi, Masahiko

    2018-02-16

    Organophosphorus compounds with a phosphorus atom attached to a phenyl group and two organothio/organoseleno groups were synthesized using the rhodium-catalyzed insertion reaction of the PhP group of pentaphenylcyclopentaphosphine (PhP) 5 with acyclic disulfides and diselenides. The method was applied to the synthesis of heterocyclic compounds containing the S-P-S group by the reaction of (PhP) 5 and cyclic disulfides such as 1,2-dithietes, 1,2-dithiocane, 1,4,5-dithiopane, and 1,2-dithiolanes.

  2. Rh-Catalyzed reductive Mannich-type reaction and its application towards the synthesis of (±-ezetimibe

    Directory of Open Access Journals (Sweden)

    Motoyuki Isoda

    2016-07-01

    Full Text Available An effective synthesis for syn-β-lactams was achieved using a Rh-catalyzed reductive Mannich-type reaction. A rhodium–hydride complex (Rh–H derived from diethylzinc (Et2Zn and a Rh catalyst was used for the 1,4-reduction of an α,β-unsaturated ester to give a Reformatsky-type reagent, which in turn, reacted with an imine to give the syn-β-lactam. Additionally, the reaction was applied to the synthesis of (±-ezetimibe, a potent β-lactamic cholesterol absorption inhibitor.

  3. Rh-Catalyzed reductive Mannich-type reaction and its application towards the synthesis of (±)-ezetimibe.

    Science.gov (United States)

    Isoda, Motoyuki; Sato, Kazuyuki; Kunugi, Yurika; Tokonishi, Satsuki; Tarui, Atsushi; Omote, Masaaki; Minami, Hideki; Ando, Akira

    2016-01-01

    An effective synthesis for syn-β-lactams was achieved using a Rh-catalyzed reductive Mannich-type reaction. A rhodium-hydride complex (Rh-H) derived from diethylzinc (Et2Zn) and a Rh catalyst was used for the 1,4-reduction of an α,β-unsaturated ester to give a Reformatsky-type reagent, which in turn, reacted with an imine to give the syn-β-lactam. Additionally, the reaction was applied to the synthesis of (±)-ezetimibe, a potent β-lactamic cholesterol absorption inhibitor.

  4. Silylium ion-catalyzed challenging Diels-Alder reactions: the danger of hidden proton catalysis with strong Lewis acids.

    Science.gov (United States)

    Schmidt, Ruth K; Müther, Kristine; Mück-Lichtenfeld, Christian; Grimme, Stefan; Oestreich, Martin

    2012-03-07

    The pronounced Lewis acidity of tricoordinate silicon cations brings about unusual reactivity in Lewis acid catalysis. The downside of catalysis with strong Lewis acids is, though, that these do have the potential to mediate the formation of protons by various mechanisms, and the thus released Brønsted acid might even outcompete the Lewis acid as the true catalyst. That is an often ignored point. One way of eliminating a hidden proton-catalyzed pathway is to add a proton scavenger. The low-temperature Diels-Alder reactions catalyzed by our ferrocene-stabilized silicon cation are such a case where the possibility of proton catalysis must be meticulously examined. Addition of the common hindered base 2,6-di-tert-butylpyridine resulted, however, in slow decomposition along with formation of the corresponding pyridinium ion. Quantitative deprotonation of the silicon cation was observed with more basic (Mes)(3)P to yield the phosphonium ion. A deuterium-labeling experiment verified that the proton is abstracted from the ferrocene backbone. A reasonable mechanism of the proton formation is proposed on the basis of quantum-chemical calculations. This is, admittedly, a particular case but suggests that the use of proton scavengers must be carefully scrutinized, as proton formation might be provoked rather than prevented. Proton-catalyzed Diels-Alder reactions are not well-documented in the literature, and a representative survey employing TfOH is included here. The outcome of these catalyses is compared with our silylium ion-catalyzed Diels-Alder reactions, thereby clearly corroborating that hidden Brønsted acid catalysis is not operating with our Lewis acid. Several simple-looking but challenging Diels-Alder reactions with exceptionally rare dienophile/enophile combinations are reported. Another indication is obtained from the chemoselectivity of the catalyses. The silylium ion-catalyzed Diels-Alder reaction is general with regard to the oxidation level of the

  5. Base-catalyzed controllable reaction of 3-ylideneoxindoles with O-Boc hydroxycarbamates for the synthesis of amidoacrylates and spiroaziridine oxindoles.

    Science.gov (United States)

    Liu, Yi-Yin; Duan, Shu-Wen; Zhang, Rui; Liu, Yun-Hang; Chen, Jia-Rong; Xiao, Wen-Jing

    2016-06-21

    A base-catalyzed divergent reaction of 3-ylideneoxindoles with O-Boc hydroxycarbamates has been developed to provide efficient access to various amidoacrylates and spiroaziridine oxindoles with generally high yields, which should be potentially useful in drug discovery.

  6. Selective Production of Renewable para-Xylene by Tungsten Carbide Catalyzed Atom-Economic Cascade Reactions.

    Science.gov (United States)

    Dai, Tao; Li, Changzhi; Li, Lin; Zhao, Zongbao Kent; Zhang, Bo; Cong, Yu; Wang, Aiqin

    2018-02-12

    Tungsten carbide was employed as the catalyst in an atom-economic and renewable synthesis of para-xylene with excellent selectivity and yield from 4-methyl-3-cyclohexene-1-carbonylaldehyde (4-MCHCA). This intermediate is the product of the Diels-Alder reaction between the two readily available bio-based building blocks acrolein and isoprene. Our results suggest that 4-MCHCA undergoes a novel dehydroaromatization-hydrodeoxygenation cascade process by intramolecular hydrogen transfer that does not involve an external hydrogen source, and that the hydrodeoxygenation occurs through the direct dissociation of the C=O bond on the W 2 C surface. Notably, this process is readily applicable to the synthesis of various (multi)methylated arenes from bio-based building blocks, thus potentially providing a petroleum-independent solution to valuable aromatic compounds. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Variation of kinetic isotope effect in multiple proton transfer reactions

    Indian Academy of Sciences (India)

    Proton transfer; promoter modes; kinetic isotope effect. 1. Introduction. Kinetic isotope effect (KIE) is the dependence of the rate constant on the mass of the isotope of the atom in a chemical reaction. The primary kinetic isotope effect is the KIE when the bonds connecting that atom to the rest of the molecular frame are broken ...

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

    Indian Academy of Sciences (India)

    TECS

    primary amino group, shows dual emission in polar solvents. Absorption and emission ... for understanding the primary processes of vision ... demonstrated ICT in some fluoro-substituted amino benzonitrile deriva- tive and very recently Stalin et al. 10–12 reported charge-transfer reaction in p-amino benzoic acid, 3-.

  9. Electron transfer reactions involving porphyrins and chlorophyll a

    International Nuclear Information System (INIS)

    Neta, P.; Scherz, A.; Levanon, H.

    1979-01-01

    Electron transfer reactions involving porphyrins (P) and quinones (Q) have been studied by pulse radiolysis. The porphyrins used were tetraphenylporphyrin (H 2 TPP), its tetracarboxy derivative (H 2 TCPP), the sodium and zinc compounds (Na 2 TPP and ZnTPP), and chlorophyll a (Chl a). These compounds were found to be rapidly reduced by electron transfer from (CH 3 ) 2 CO - . Reduction by (CH 3 ) 2 COH was rapid in aqueous solutions but relatively slow in i-PrOH solutions. Transient spectra of the anion radicals were determined and, in the case of H 2 TCPP - ., a pK = 9.7 was derived for its protonation. Electron-transfer reactions from the anion radical of H 2 TCPP to benzoquinone, duroquinone, 9,10-anthraquinone 2-sulfonate, and methylviologen occur in aqueous solutions with rate constants approx. 10 7 -10 9 M -1 s -1 which depend on the pH and the quinone reduction potential. Reactions of Na 2 TPP - ., ZnTPP - ., and Chl a - . with anthraquinone in basic i-PrOH solutions occur with rate constants approx. 10 9 M -1 s -1 . The spectral changes associated with these electron-transfer reactions as observed over a period of approx. 1 ms indicated, in some cases, the formation of an intermediate complex [P...Q - .]. 8 figures, 2 tables

  10. Studies on electron transfer reactions: Reduction of heteropoly 10 ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Rates of electron transfer reaction of thioglycolic acid with vanadium(V) substituted Keggin- type heteropolyanion, [PV ... By applying Rehm–Weller relationship, self exchange rate constant for the. –. SCH2COO. –. /S. •. CH2COO. – .... is much more higher than that of mono-anion. HSCH2COO–. 3.4 Marcus theory.

  11. Excited state intramolecular charge transfer reaction of 4 ...

    Indian Academy of Sciences (India)

    An intramolecular charge transfer (ICT) molecule with an extra hetero atom in its donor moiety has been synthesized in order to investigate how ICT reaction is affected by hetero atom replacement. Photo-physical and photo-dynamical properties of this molecule, 4-(morpholenyl)benzonitrile (M6C), have been studied in 20 ...

  12. Hydrogen transfer reaction of cyclohexanone with 2-propanol ...

    Indian Academy of Sciences (India)

    Unknown

    Addition of ceria into zinc oxide was found to increase the catalytic activity for hydrogen transfer reaction. The catalytic activity also depended on the method of preparation. Citrate process results in uniformly dispersed mixed oxide with higher catalytic activity. Keywords. Cyclohexanone; ceria; ZnO; diffuse reflectance; EPR.

  13. Towards Neutron Drip Line via Transfer-Type Reactions

    CERN Document Server

    Penionzhkevich, Yu E; Antonenko, N V

    2005-01-01

    Possibilities of production of light neutron-rich isotopes $^{24,26}$O, $^{32}$Ne, $^{36,38}$Mg, $^{42}$Si and $^{56,58,60}$Ca in transfer-type reactions are analyzed. The optimal conditions for their production are suggested. The measurement of the excitation function can allow us to estimate the binding energy of exotic nuclei.

  14. Single-particle and collective states in transfer reactions

    International Nuclear Information System (INIS)

    Lhenry, I.; Suomijaervi, T.; Giai, N. van

    1993-01-01

    The possibility to excite collective states in transfer reactions induced by heavy ions is studied. Collective states are described within the Random Phase Approximation (RPA) and the collectivity is defined according to the number of configurations contributing to a given state. The particle transfer is described within the Distorted Wave Born Approximation (DWBA). Calculations are performed for two different stripping reactions: 207 Pb( 20 Ne, 19 Ne) 208 Pb and 59 Co( 20 Ne, 19 F) 60 Ni at 48 MeV/nucleon for which experimental data are available. The calculation shows that a sizeable fraction of collective strength can be excited in these reactions. The comparison with experiment shows that this parameter-free calculation qualitatively explains the data. (author) 19 refs.; 10 figs

  15. Neutron transfer reactions in the fp-shell region

    International Nuclear Information System (INIS)

    Mahgoub, Mahmoud

    2008-01-01

    Neutron transfer reactions were used to study the stability of the magic number N=28 near 56 Ni. On one hand the one-neutron pickup (d,p) reaction was used for precision spectroscopy of single-particle levels in 55 Fe. On the other hand we investigated the two-neutron transfer mechanism into 56 Ni using the pickup reaction 58 Ni(vectorp,t) 56 Ni. In addition the reliability of inverse kinematics reactions at low energy to study exotic nuclei was tested by the neutron transfer reactions t( 40 Ar,p) 42 Ar and d( 54 Fe,p) 55 Fe using tritium and deuterium targets, respectively, and by comparing the results with those of the normal kinematics reactions. The experimental data, differential cross-section and analyzing powers, are compared to DWBA and coupled channel calculations utilizing the code CHUCK3. By performing the single-neutron stripping reaction (vectord,p) on 54 Fe the 1f 7/2 shell in the ground state configuration was found to be partly broken. The instability of the 1f 7/2 shell and the magic number N=28 was confirmed once by observing a number of levels with J π = 7/2 - at low excitation energies, which should not be populated if 54 Fe has a closed 1f 7/2 shell, and also by comparing our high precision experimental data with a large scale shell model calculation using the ANTOINE code [5]. Calculations including a partly broken 1f 7/2 shell show better agreement with the experiment. The instability of the 1f 7/2 shell was confirmed also by performing the two-neutron pick-up reaction (vectorp,t) on 58 Ni to study 56 Ni, where a considerable improvement in the DWBA calculation was observed after considering 1f 7/2 as a broken shell. To prove the reliability of inverse kinematics transfer reactions at low energies (∝ 2 AMeV), the aforementioned single-neutron transfer reaction (d,p) was repeated using a beam of 54 Fe ions and a deuteron target. From this inverse kinematics experiment we were able to reproduce the absolute cross-section and angular

  16. Kinetic and thermodynamic study of the reaction catalyzed by glucose-6-phosphate dehydrogenase with nicotinamide adenine dinucleotide

    International Nuclear Information System (INIS)

    Martin del Campo, Julia S.; Patino, Rodrigo

    2011-01-01

    Research highlights: → The reaction catalyzed by one enzyme of the pentose phosphate pathway was studied. → A spectrophotometric method is proposed for kinetic and thermodynamic analysis. → The pH and the temperature influences are reported on physical chemical properties. → Relative concentrations of substrates are also important in the catalytic process. - Abstract: The enzyme glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) from Leuconostoc mesenteroides has a dual coenzyme specificity with oxidized nicotinamide adenine dinucleotide (NAD ox ) and oxidized nicotinamide adenine dinucleotide phosphate as electron acceptors. The G6PD coenzyme selection is determined by the metabolic cellular prevailing conditions. In this study a kinetic and thermodynamic analysis is presented for the reaction catalyzed by G6PD from L. mesenteroides with NAD ox as coenzyme in phosphate buffer. For this work, an in situ spectrophotometric technique was employed based on the detection of one product of the reaction. Substrate and coenzyme concentrations as well as temperature and pH effects were evaluated. The apparent equilibrium constant, the Michaelis constant, and the turnover number were determined as a function of each experimental condition. The standard transformed Gibbs energy of reaction was determined from equilibrium constants at different initial conditions. For the product 6-phospho-D-glucono-1,5-lactone, a value of the standard Gibbs energy of formation is proposed, Δ f G o = -1784 ± 5 kJ mol -1 .

  17. A thermodynamic study of ketoreductase-catalyzed reactions 5. Reduction of substituted ketones in n-hexane

    International Nuclear Information System (INIS)

    Tewari, Yadu B.; Vanderah, David J.; Schantz, Michele M.; Goldberg, Robert N.; Rozzell, J. David; Liebman, Joel F.; Hui, Raymond Wai-Man; Nissenbaum, Yitzy; Parniani, Ahmad Reza

    2008-01-01

    The equilibrium constants K for the ketoreductase-catalyzed reduction reactions of 1-benzyl-3-pyrrolidinone, ethyl 2-oxo-4-phenylbutyrate, ethyl 4-chloroacetoacetate, 1-benzyl-4-piperidone, and 1-benzyl-3-piperidone were measured in n-hexane at T = 298.15 K by using gas chromatography. The equilibrium constants for the reaction involving 1-benzyl-4-piperidone were also measured as a function of temperature (288.15 to 308.05) K. The calculated thermodynamic quantities for the reaction (1-benzyl-4-piperidone + 2-propanol = 1-benzyl-4-hydroxypiperidine + acetone) reaction carried out in n-hexane at T = 298.15 K are: K = (26.2 ± 1.7); Δ r G m 0 =-(8.10±0.16)kJ.mol -1 ; Δ r H m 0 =-(3.44±0.42)kJ.mol -1 ; and Δ r S m 0 =(15.6±1.4)J.K -1 .mol -1 . The chirality of the hydroxyl products of the reactions has also been investigated. The results showed that the stereoselectivity of the hydroxyl products formed can be controlled by the selection of the solvent and enzyme used in these reactions. The thermochemical results for these reactions are compared with the results for reactions that have analogous structural features as well as with the results of quantum chemical calculations

  18. A thermodynamic study of ketoreductase-catalyzed reactions 5. Reduction of substituted ketones in n-hexane

    Energy Technology Data Exchange (ETDEWEB)

    Tewari, Yadu B. [Biochemical Science and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)], E-mail: yadu.tewari@nist.gov; Vanderah, David J. [Biochemical Science and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)], E-mail: david.vanderah@nist.gov; Schantz, Michele M. [Biochemical Science and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)], E-mail: michele.schantz@nist.gov; Goldberg, Robert N. [Biochemical Science and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)], E-mail: robert.goldberg@nist.gov; Rozzell, J. David [Codexis, Inc., 129 N. Hill Avenue, Pasadena, CA 91106 (United States)], E-mail: david.rozzell@codexis.com; Liebman, Joel F. [Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD 21250 (United States)], E-mail: jliebman@umbc.edu; Hui, Raymond Wai-Man; Nissenbaum, Yitzy; Parniani, Ahmad Reza [Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD 21250 (United States)

    2008-04-15

    The equilibrium constants K for the ketoreductase-catalyzed reduction reactions of 1-benzyl-3-pyrrolidinone, ethyl 2-oxo-4-phenylbutyrate, ethyl 4-chloroacetoacetate, 1-benzyl-4-piperidone, and 1-benzyl-3-piperidone were measured in n-hexane at T = 298.15 K by using gas chromatography. The equilibrium constants for the reaction involving 1-benzyl-4-piperidone were also measured as a function of temperature (288.15 to 308.05) K. The calculated thermodynamic quantities for the reaction (1-benzyl-4-piperidone + 2-propanol = 1-benzyl-4-hydroxypiperidine + acetone) reaction carried out in n-hexane at T = 298.15 K are: K = (26.2 {+-} 1.7); {delta}{sub r}G{sub m}{sup 0}=-(8.10{+-}0.16)kJ.mol{sup -1}; {delta}{sub r}H{sub m}{sup 0}=-(3.44{+-}0.42)kJ.mol{sup -1}; and {delta}{sub r}S{sub m}{sup 0}=(15.6{+-}1.4)J.K{sup -1}.mol{sup -1}. The chirality of the hydroxyl products of the reactions has also been investigated. The results showed that the stereoselectivity of the hydroxyl products formed can be controlled by the selection of the solvent and enzyme used in these reactions. The thermochemical results for these reactions are compared with the results for reactions that have analogous structural features as well as with the results of quantum chemical calculations.

  19. Theory of nuclear heavy-ion direct transfer reactions

    International Nuclear Information System (INIS)

    Crowley, B.J.B.

    1979-01-01

    We review the distorted-wave approach to direct transfer reactions and draw attention to some of the shortcomings of current theories. We show that a reformulated form of the distorted-wave Born approximation (DWBA) for transfer can lead to important simplifications of the theory, which are valid for nuclear heavy-ion induced reactions at energies > or approx. =MeV/nucleon. In particular, in the semiclassical limit, it leads to a new and simple formula for the transfer t-matrix which includes all the essential physics while offering several important advantages over standard ''full-recoil finite-range'' DWBA. One such advantage is that the new formula is more transparent in that it is amendable to interpretation and analytical manipulation. At high-energy it is shown to reduce to one earlier deduced using eikonal-DWBA. The conditions for the validity of the new theory are discussed in detail. They are shown to be generally well satisfied for small-mass transfer between heavy-ions at energies at or above those particularly favour transfer (> or approx. =10 MeV/nucleon for transfer of valence nucleons). The restriction to small mass is not due to any recoil approximation; in fact, it is only a necessary restriction at certain energies. The theory treats recoil exactly. Consideration of the optimum dynamical conditions for transfer leads to a set of matching conditions. The presence of hitherto neglected absorption, arising from dynamical effects of poor matching, it suggested and qualitatively discussed. Condition under which such absorption may be neglected are derived. Results of numerical calculations are presented showing that the theory is capable of good agreement with standard full-recoil finite-range DWBA, and that it is capable of giving at least as good an account of experimental data for nucleon-transfer between heavy-ions at energies approx.10 MeV/nucleon

  20. Beta-D-xylosidase from Selenomonas ruminantium: thermodynamics of enzyme-catalyzed and noncatalyzed reactions

    Science.gov (United States)

    Beta-D-xylosidase/alpha-L-arabinofuranosidase from Selenomonas ruminantium (SXA) is the most active enzyme known for catalyzing hydrolysis of 1,4-beta-D-xylooligosaccharides to D-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-beta-D-xylopyranoside (4NPX), 4-nitrophenyl-alpha-L-arabi...

  1. Nickel-Catalyzed Decarbonylative Silylation, Borylation, and Amination of Arylamides via a Deamidative Reaction Pathway

    KAUST Repository

    Rueping, Magnus

    2017-10-23

    A nickel-catalyzed decarbonylative silylation, borylation, and amination of amides has been developed. This new methodology allows the direct interconversion of amides to arylsilanes, arylboronates, and arylamines and enables a facile route for carbon–heteroatom bond formations in a straightforward and mild fashion.

  2. Optimizing Metalloporphyrin-Catalyzed Reduction Reactions for In Situ Remediation of DOE Contaminants

    Energy Technology Data Exchange (ETDEWEB)

    Schlautman, Mark A. [Clemson University, Clemson, SC (United States)

    2013-07-14

    Past activities have resulted in a legacy of contaminated soil and groundwater at Department of Energy facilities nationwide. Uranium and chromium are among the most frequently encountered and highest-priority metal and radionuclide contaminants at DOE installations. Abiotic chemical reduction of uranium and chromium at contaminated DOE sites can be beneficial because the reduced metal species are less soluble in water, less mobile in the environment, and less toxic to humans and ecosystems. Although direct biological reduction has been reported for U(VI) and Cr(VI) in laboratory studies and at some field sites, the reactions can sometimes be slow or even inhibited due to unfavorable environmental conditions. One promising approach for the in-situ remediation of DOE contaminants is to develop electron shuttle catalysts that can be delivered precisely to the specific subsurface locations where contaminants reside. Previous research has shown that reduction of oxidized organic and inorganic contaminants often can be catalyzed by electron shuttle systems. Metalloporphyrins and their derivatives are well known electron shuttles for many biogeochemical systems, and thus were selected to study their catalytic capabilities for the reduction of chromium and uranium in the presence of reducing agents. Zero valent iron (ZVI) was chosen as the primary electron donor in most experimental systems. Research proceeded in three phases and the key findings of each phase are reported here. Phase I examined Cr(VI) reduction and utilized micro- and nano-sized ZVI as the electron donors. Electron shuttle catalysts tested were cobalt- and iron-containing metalloporphyrins and Vitamin B12. To aid in the recycle and reuse of the nano-sized ZVI and soluble catalysts, sol-gels and calcium-alginate gel beads were tested as immobilization/support matrices. Although the nano-sized ZVI could be incorporated within the alginate gel beads, preliminary attempts to trap it in sol-gels were not

  3. Optimizing Metalloporphyrin-Catalyzed Reduction Reactions for In Situ Remediation of DOE Contaminants

    International Nuclear Information System (INIS)

    Schlautman, Mark A.

    2013-01-01

    Past activities have resulted in a legacy of contaminated soil and groundwater at Department of Energy facilities nationwide. Uranium and chromium are among the most frequently encountered and highest-priority metal and radionuclide contaminants at DOE installations. Abiotic chemical reduction of uranium and chromium at contaminated DOE sites can be beneficial because the reduced metal species are less soluble in water, less mobile in the environment, and less toxic to humans and ecosystems. Although direct biological reduction has been reported for U(VI) and Cr(VI) in laboratory studies and at some field sites, the reactions can sometimes be slow or even inhibited due to unfavorable environmental conditions. One promising approach for the in-situ remediation of DOE contaminants is to develop electron shuttle catalysts that can be delivered precisely to the specific subsurface locations where contaminants reside. Previous research has shown that reduction of oxidized organic and inorganic contaminants often can be catalyzed by electron shuttle systems. Metalloporphyrins and their derivatives are well known electron shuttles for many biogeochemical systems, and thus were selected to study their catalytic capabilities for the reduction of chromium and uranium in the presence of reducing agents. Zero valent iron (ZVI) was chosen as the primary electron donor in most experimental systems. Research proceeded in three phases and the key findings of each phase are reported here. Phase I examined Cr(VI) reduction and utilized micro- and nano-sized ZVI as the electron donors. Electron shuttle catalysts tested were cobalt- and iron-containing metalloporphyrins and Vitamin B12. To aid in the recycle and reuse of the nano-sized ZVI and soluble catalysts, sol-gels and calcium-alginate gel beads were tested as immobilization/support matrices. Although the nano-sized ZVI could be incorporated within the alginate gel beads, preliminary attempts to trap it in sol-gels were not

  4. Palladium-Catalyzed Intramolecular Trost-Oppolzer-Type Alder-Ene Reaction of Dienyl Acetates to Cyclopentadienes.

    Science.gov (United States)

    Bankar, Siddheshwar K; Singh, Bara; Tung, Pinku; Ramasastry, S S V

    2018-02-05

    A new approach to the synthesis of highly substituted cyclopentadienes, indenes, and cyclopentene-fused heteroarenes by means of the Pd-catalyzed Trost-Oppolzer-type intramolecular Alder-ene reaction of 2,4-pentadienyl acetates is described. This unprecedented transformation combines the electrophilic features of the Tsuji-Trost reaction with the nucleophilic features of the Alder-ene reaction. The overall outcome can be perceived as a hitherto unknown "acid-free" iso-Nazarov-type cyclization. The versatility of this strategy was further demonstrated by the formal synthesis of paucifloral F, a resveratrol-based natural product. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Effects of electrostatic interactions on electron transfer reactions

    International Nuclear Information System (INIS)

    Hickel, B.

    1987-01-01

    The fast reactions of electron transfer are studied by pulse radiolysis. This technique allows the creation in about 10 -8 second radicals and radical ions with high redox potentials. For solvated electrons electrostatic interaction on the kinetics of reactions limited by diffusion is described by Debye's equation when ion mobility is known. Deviation from theory can occur in ion pairs formation. This is evidenced experimentally for anions by cation complexation with a cryptate. Relatively slow reactions are more sensitive to electrostatic interactions than limited by diffusion. If ion pairs are not formed kinetics constant depends on dielectric constant of solvent and reaction radius. Experimentally is studied the effect of electrostatic interaction on the rate constants of solvated electrons with anions and cations in water-ethanol mixtures where the dielectric constant change from 80 to 25 at room temperature. 17 refs

  6. Effects of nonlocal potentials on (p ,d ) transfer reactions

    Science.gov (United States)

    Ross, A.; Titus, L. J.; Nunes, F. M.; Mahzoon, M. H.; Dickhoff, W. H.; Charity, R. J.

    2015-10-01

    Background: Although local phenomenological optical potentials have been standardly used to interpret nuclear reactions, recent studies suggest the effects of nonlocality should not be neglected. Purpose: In this work we investigate the effects of nonlocality in (p ,d ) transfer reactions using nonlocal optical potentials. We compare results obtained with the dispersive optical model to those obtained using the Perey-Buck interaction. Method: We solve the scattering and bound-state equations for the nonlocal version of the dispersive optical model. Then, using the distorted-wave Born approximation, we calculate the transfer cross section for (p ,d ) on 40Ca at Ep=20 , 35, and 50 MeV. Results: The inclusion of nonlocality in the bound state has a larger effect than that in the scattering states. The overall effect on the transfer cross section is very significant. We found an increase due to nonlocality in the transfer cross section of ≈30 - 50 % when using the Perey-Buck interaction and of ≈15 - 50 % when using the dispersive optical potential. Conclusions: Although the details of the nonlocal interaction can change the magnitude of the effects, our study shows that qualitatively the results obtained using the dispersive optical potential and the Perey-Buck interaction are consistent, in both cases the transfer cross sections are significantly increased.

  7. A thermodynamic study of ketoreductase-catalyzed reactions 4. Reduction of 2-substituted cyclohexanones in n-hexane

    International Nuclear Information System (INIS)

    Tewari, Yadu B.; Liebman, Joel F.; Rozzell, J. David; Vanderah, David J.; Schantz, Michele M.

    2007-01-01

    The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone+2-propanol=cis- and trans-2-substituted cyclohexanol+acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T=288.15 to 308.05K. The thermodynamic quantities at T=298.15K are: K=(2.13+/-0.06); Δ r G m o =-(1.87+/-0.06)kJ.mol -1 ; Δ r H m o =-(6.56+/-2.68)kJ.mol -1 ; and Δ r S m o =-(15.7+/-9.2)J.K -1 .mol -1 for the reaction involving cis-2-methylcyclohexanol, and K=(10.7+/-0.2); Δ r G m o =-(5.87+/-0.04)kJ.mol -1 ; Δ r H m o =-(2.54+/-1.8)kJ.mol -1 ; and Δ r S m o =(11.2+/-6.4)J.K -1 .mol -1 for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes Δ r G m o for the reactions (trans-2-substituted cyclohexanol=cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective

  8. A thermodynamic study of ketoreductase-catalyzed reactions 4. Reduction of 2-substituted cyclohexanones in n-hexane

    Energy Technology Data Exchange (ETDEWEB)

    Tewari, Yadu B. [Biochemical Science Division and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)]. E-mail: yadu.tewari@nist.gov; Liebman, Joel F. [Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD 21250 (United States)]. E-mail: jliebman@umbc.edu; Rozzell, J. David [BioCatalytics, Inc., 129 N. Hill Avenue, Pasadena, CA 91106 (United States)]. E-mail: davidrozzell@biocatalytics.com; Vanderah, David J. [Biochemical Science Division and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)]. E-mail: david.vanderah@nist.gov; Schantz, Michele M. [Biochemical Science Division and Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States)]. E-mail: michele.schantz@nist.gov

    2007-07-15

    The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone+2-propanol=cis- and trans-2-substituted cyclohexanol+acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T=288.15 to 308.05K. The thermodynamic quantities at T=298.15K are: K=(2.13+/-0.06); {delta}{sub r}G{sub m}{sup o}=-(1.87+/-0.06)kJ.mol{sup -1}; {delta}{sub r}H{sub m}{sup o}=-(6.56+/-2.68)kJ.mol{sup -1}; and {delta}{sub r}S{sub m}{sup o}=-(15.7+/-9.2)J.K{sup -1}.mol{sup -1} for the reaction involving cis-2-methylcyclohexanol, and K=(10.7+/-0.2); {delta}{sub r}G{sub m}{sup o}=-(5.87+/-0.04)kJ.mol{sup -1}; {delta}{sub r}H{sub m}{sup o}=-(2.54+/-1.8)kJ.mol{sup -1}; and {delta}{sub r}S{sub m}{sup o}=(11.2+/-6.4)J.K{sup -1}.mol{sup -1} for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes {delta}{sub r}G{sub m}{sup o} for the reactions (trans-2-substituted cyclohexanol=cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective.

  9. Reaction mechanism and spectroscopy of transfer reactions induced by heavy ions

    International Nuclear Information System (INIS)

    Lemaire, M.-C.

    1977-01-01

    The specific features displayed by data on heavy ion elastic and inelastic angular distributions are discussed, and their physical origin is pointed out from semi-classical calculations in counterpart ambiguities in the phenomenological description of the optical potential appear. Two nucleon transfer reactions induced by heavy ions successfully point out important contributions of a two-step process where the transfer is proceeding via target and residual nucleus inelastic excitation. At incident energies not too high above the Coulomb barrier, such process produces clear shape changes between different final state angular distributions. At higher incident energy, the angular distributions are forward peaked and display oscillations for both mechanisms. As for four-nucleon transfer reactions, the existing data suggest that the nucleons are well transferred into a Os relative

  10. Studies of Grafted and Sulfonated Spiro Poly(isatin-ethersulfone Membranes by Super Acid-Catalyzed Reaction

    Directory of Open Access Journals (Sweden)

    Lei Jin

    2016-03-01

    Full Text Available Spiro poly(isatin-ethersulfone polymers were prepared from isatin and bis-2,6-dimethylphenoxyphenylsulfone by super acid catalyzed polyhydroxyalkylation reactions. We designed and synthesized bis-2,6-dimethylphenoxyphenylsulfone, which is structured at the meta position steric hindrance by two methyl groups, because this structure minimized crosslinking reaction during super acid catalyzed polymerization. In addition, sulfonic acid groups were structured in both side chains and main chains to form better polymer chain morphology and improve proton conductivity. The sulfonation reactions were performed in two steps which are: in 3-bromo-1-propanesulfonic acid potassium salt and in con. sulfuric acid. The membrane morphology was studied by tapping mode atomic force microscope (AFM. The phase difference between the hydrophobic polymer main chain and hydrophilic sulfonated units of the polymer was shown to be the reasonable result of the well phase separated structure. The correlations of proton conductivity, ion exchange capacity (IEC and single cell performance were clearly described with the membrane morphology.

  11. Laccase-catalyzed removal of the antimicrobials chlorophene and dichlorophen from water: Reaction kinetics, pathway and toxicity evaluation.

    Science.gov (United States)

    Shi, Huanhuan; Peng, Jianbiao; Li, Jianhua; Mao, Liang; Wang, Zunyao; Gao, Shixiang

    2016-11-05

    As active agents in cleaning and disinfecting products, antimicrobials have been widely spread in the environment and have drawn extensive attention as potential threats to the ecological system and human health. In this study, the laccase-catalyzed removal of two emerging antimicrobials, chlorophene (CP) and dichlorophen (DCP), was investigated under simulated environmental conditions. Intrinsic reaction kinetics showed that the removal of CP and DCP followed second-order reaction kinetics, first-order with respect to both the enzyme and the substrate concentration. It was also found that fulvic acid could suppress the transformation of CP and DCP by reversing the oxidation reactions through its action as a scavenger of the free radical intermediates produced from reactions between laccase and the substrates. Several reaction products were identified by a quadrupole time-of-flight mass spectrometer, and detailed reaction pathways were proposed. For both CP and DCP, direct polymerization was the principal pathway, and the coupling patterns were further corroborated based on molecular modeling. The nucleophilic substitution of chlorine by the hydroxyl group was observed, and further oxidation products capable of coupling with each other were also found. Additionally, toxicity evaluation tests using Scenedesmus obliquus confirmed that the toxicity of CP and DCP was effectively eliminated during the reaction processes. Copyright © 2016 Elsevier B.V. All rights reserved.

  12. The reaction mechanism for dehydration process catalyzed by type I dehydroquinate dehydratase from Gram-negative Salmonella enterica

    Science.gov (United States)

    Yao, Yuan; Li, Ze-Sheng

    2012-01-01

    The fundamental reaction mechanism for the dehydration process catalyzed by type I dehydroquinate dehydratase from Gram-negative Salmonella enterica has been studied by density functional theory calculations. The results indicate that the dehydration process undergoes a two-step cis-elimination mechanism, which is different from the previously proposed one. The catalytic roles of both the highly conserved residue His143 and the Schiff base formed between the substrate and Lys170 have also been elucidated. The structural and mechanistic insight presented here may direct the design of type I dehydroquinate dehydratase enzyme inhibitors as non-toxic antimicrobials, anti-fungals, and herbicides.

  13. Stereoselective ZrCl4-Catalyzed Mannich-type Reaction of β-Keto Esters with Chiral Trifluoromethyl Aldimines.

    Science.gov (United States)

    Parise, Luca; Pellacani, Lucio; Sciubba, Fabio; Trulli, Laura; Fioravanti, Stefania

    2015-08-21

    A method for the synthesis of fluorinated β'-amino β-dicarbonyl compounds using a Zr-catalyzed Mannich-type reaction has been developed, starting from N-protected trifluoromethyl aldimines and cyclic or acyclic β-keto esters bearing different ester residues. The in situ generated metallic complex reacted with optically pure trifluoromethyl aldimine derived from (R)-α-methylbenzylamine, giving a highly diastereoselective asymmetric Mannich-type addition with formation of a chiral quaternary center. The absolute configuration at the new chiral centers was assigned through two-dimensional nuclear Overhauser effect spectroscopic analysis coupled with computational studies.

  14. The effect of an illumination jump on wave propagation in the Ru-catalyzed Belousov-Zhabotinsky reaction

    Science.gov (United States)

    Ram Reddy, M. K.; Dahlem, M.; Zykov, V. S.; Müller, S. C.

    1995-04-01

    The influence of visible light on the trigger wave propagation in a thin layer of the Ru(bpy) 32+-catalyzed Belousov-Zhabotinsky reaction is investigated. The velocity evolution of a wave propagating in the dark was followed after switching on the light. The velocity starts to decrease immediately, but a new stationary value is attained only after about 10 s. The inhibitory effect on the propagation velocity was more pronounced in thin reactive layers than in thick ones. The experimental data were compared with computational results obtained with a modified Oregonator model.

  15. Transfer reactions in the investigation of light-nuclei nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Guimaraes, V.; Camargo, O.; Lichtenthaler, R.; Scarduelli, V. [Instituto de Fisica, Universidade de Sao Paulo, P. O. Box 66318, 05389-970 Sao Paulo (Brazil); Kolata, J. J. [Department of Physics, University of Notre Dame, Notre Dame, 46556 Indiana (United States); Amro, H.; Becchetti, F. D.; Jiang, H. [Department of Physics, University of Michigan, Ann Arbor, 48109-1120 Michigan (United States); Aguilera, E. F.; Lizcano, D.; Martinez Q, E.; Garcia, H. [ININ, La Marquesa, 52750 Estado de Mexico (Mexico)

    2008-12-15

    Cross sections for the {sup 6}Li(p,{gamma}){sup 7}Be, {sup 7}Li(n,{gamma}){sup 8}Li{sup 8}Li(n,{gamma}){sup 9}Li and {sup 8}Li(p,{gamma}){sup 9}Be capture reactions have been investigated in the framework of the potential model. The main ingredients of the potential model are the potentials used to generate the continuum and bound-state wave functions and spectroscopic factors of the corresponding bound systems. The spectroscopic factors for the {sup 7}Lin={sup 8}Li{sub gs}, {sup 8}Lin={sup 9}Li{sub gs} bound systems were obtained from a FR-DWBA analysis of neutron transfer reactions induced by {sup 8}Li radioactive beam on a {sup 9}Be target, while spectroscopic factor for the {sup 8}Lip={sup 9}Be{sub gs} bound system were obtained from a proton transfer reaction. From the obtained capture reaction cross section, reaction rate for the {sup 8}Li(n,{gamma}){sup 9}Li and {sup 8}Li(p,{gamma}){sup 9}Be direct neutron and proton capture were determined and compared with other experimental and calculated values. (Author)

  16. Intermolecular hydrogen transfer catalyzed by a flavodehydrogenase, bakers' yeast flavocytochrome b2

    International Nuclear Information System (INIS)

    Urban, P.; Lederer, F.

    1985-01-01

    Bakers yeast flavocytochrome b2 is a flavin-dependent L-2-hydroxy acid dehydrogenase which also exhibits transhydrogenase activity. When a reaction takes place between [2- 3 H]lactate and a halogenopyruvate, tritium is found in water and at the halogenolactate C2 position. When the halogenopyruvate undergoes halide ion elimination, tritium is also found at the C3 position of the resulting pyruvate. The amount tau of this intermolecular tritium transfer depends on the initial keto acid-acceptor concentration. At infinite acceptor concentration, extrapolation yields a maximal transfer of 97 +/- 11%. This indicates that the hydroxy acid-derived hydrogen resides transiently on enzyme monoprotic heteroatoms and that exchange with bulk solvent occurs only at the level of free reduced enzyme. Using a minimal kinetic scheme, the rate constant for hydrogen exchange between Ered and solvent is calculated to be on the order of 10(2) M-1 S-1, which leads to an estimated pK approximately equal to 15 for the ionization of the substrate-derived proton while on the enzyme. It is suggested that this hydrogen could be shared between the active site base and Flred N5 anion. It is furthermore shown that some tritium is incorporated into the products when the transhydrogenation is carried out in tritiated water. Finally, with [2-2H]lactate-reduced enzyme, a deuterium isotope effect is observed on the rate of bromopyruvate disappearance. Extrapolation to infinite bromopyruvate concentration yields DV = 4.4. An apparent inverse isotope effect is determined for bromide ion elimination. These results strengthen the idea that oxidoreduction and elimination pathways involve a common carbanionic intermediate

  17. Density Functional Theory Study on the Demethylation Reaction between Methylamine, Dimethylamine, Trimethylamine, and Tamoxifen Catalyzed by a Fe(IV)-Oxo Porphyrin Complex.

    Science.gov (United States)

    Alberro, Nerea; Torrent-Sucarrat, Miquel; Arrieta, Ana; Rubiales, Gloria; Cossío, Fernando P

    2018-02-15

    In this work, we studied computationally the N-demethylation reaction of methylamine, dimethylamine, and trimethylamine as archetypal examples of primary, secondary, and tertiary amines catalyzed by high-field low-spin Fe-containing enzymes such as cytochromes P450. Using DFT calculations, we found that the expected C-H hydroxylation process was achieved for trimethylamine. When dimethylamine and methylamine were studied, two different reaction mechanisms (C-H hydroxylation and a double hydrogen atom transfer) were computed to be energetically accessible and both are equally preferred. Both processes led to the formation of formaldehyde and the N-demethylated substrate. Finally, as an illustrative example, the relative contribution of the three primary oxidation routes of tamoxifen was rationalized through energetic barriers obtained from density functional calculations and docking experiments involving CYP3A4 and CYP2D6 isoforms. We found that the N-demethylation process was the intrinsically favored one, whereas other oxidation reactions required most likely preorganization imposed by the residues close to the active sites.

  18. Two-nucleon transfer reactions uphold supersymmetry in atomic nuclei.

    Science.gov (United States)

    Barea, J; Bijker, R; Frank, A

    2005-04-22

    The spectroscopic strengths of two-nucleon transfer reactions constitute a stringent test for two-nucleon correlations in the nuclear wave functions. A set of closed analytic expressions for ratios of spectroscopic factors is derived in the framework of nuclear supersymmetry. These ratios are parameter independent and provide a direct test of the wave functions. A comparison between the recently measured 198Hg(d-->,alpha)196Au reaction and the predictions from the nuclear quartet supersymmetry lends further support to the validity of supersymmetry in nuclear physics.

  19. Acid-, base-, and lewis-acid-catalyzed heterolysis of methoxide from an alpha-hydroxy-beta-methoxy radical: models for reactions catalyzed by coenzyme B12-dependent diol dehydratase.

    Science.gov (United States)

    Xu, Libin; Newcomb, Martin

    2005-11-11

    [Reaction: see text].A model for glycol radicals was employed in laser flash photolysis kinetic studies of catalysis of the fragmentation of a methoxy group adjacent to an alpha-hydroxy radical center. Photolysis of a phenylselenylmethylcyclopropane precursor gave a cyclopropylcarbinyl radical that rapidly ring opened to the target alpha-hydroxy-beta-methoxy radical (3). Heterolysis of the methoxy group in 3 gave an enolyl radical (4a) or an enol ether radical cation (4b), depending upon pH. Radicals 4 contain a 2,2-diphenylcyclopropane reporter group, and they rapidly opened to give UV-observable diphenylalkyl radicals as the final products. No heterolysis was observed for radical 3 under neutral conditions. In basic aqueous acetonitrile solutions, specific base catalysis of the heterolysis was observed; the pK(a) of radical 3 was determined to be 12.5 from kinetic titration plots, and the ketyl radical formed by deprotonation of 3 eliminated methoxide with a rate constant of 5 x 10(7) s(-1). In the presence of carboxylic acids in acetonitrile solutions, radical 3 eliminated methanol in a general acid-catalyzed reaction, and rate constants for protonation of the methoxy group in 3 by several acids were measured. Radical 3 also reacted by fragmentation of methoxide in Lewis-acid-catalyzed heterolysis reactions; ZnBr2, Sc(OTf)3, and BF3 were found to be efficient catalysts. Catalytic rate constants for the heterolysis reactions were in the range of 3 x 10(4) to 2 x 10(6) s(-1). The Lewis-acid-catalyzed heterolysis reactions are fast enough for kinetic competence in coenzyme B12 dependent enzyme-catalyzed reactions of glycols, and Lewis-acid-catalyzed cleavages of beta-ethers in radicals might be applied in synthetic reactions.

  20. ATP binding and hydrolysis-driven rate-determining events in the RFC-catalyzed PCNA clamp loading reaction.

    Science.gov (United States)

    Sakato, Miho; Zhou, Yayan; Hingorani, Manju M

    2012-02-17

    The multi-subunit replication factor C (RFC) complex loads circular proliferating cell nuclear antigen (PCNA) clamps onto DNA where they serve as mobile tethers for polymerases and coordinate the functions of many other DNA metabolic proteins. The clamp loading reaction is complex, involving multiple components (RFC, PCNA, DNA, and ATP) and events (minimally: PCNA opening/closing, DNA binding/release, and ATP binding/hydrolysis) that yield a topologically linked clamp·DNA product in less than a second. Here, we report pre-steady-state measurements of several steps in the reaction catalyzed by Saccharomyces cerevisiae RFC and present a comprehensive kinetic model based on global analysis of the data. Highlights of the reaction mechanism are that ATP binding to RFC initiates slow activation of the clamp loader, enabling it to open PCNA (at ~2 s(-1)) and bind primer-template DNA (ptDNA). Rapid binding of ptDNA leads to formation of the RFC·ATP·PCNA(open)·ptDNA complex, which catalyzes a burst of ATP hydrolysis. Another slow step in the reaction follows ATP hydrolysis and is associated with PCNA closure around ptDNA (8 s(-1)). Dissociation of PCNA·ptDNA from RFC leads to catalytic turnover. We propose that these early and late rate-determining events are intramolecular conformational changes in RFC and PCNA that control clamp opening and closure, and that ATP binding and hydrolysis switch RFC between conformations with high and low affinities, respectively, for open PCNA and ptDNA, and thus bookend the clamp loading reaction. Copyright © 2011 Elsevier Ltd. All rights reserved.

  1. Synthesis of heterobimetallic Ru-Mn complexes and the coupling reactions of epoxides with carbon dioxide catalyzed by these complexes.

    Science.gov (United States)

    Man, Man Lok; Lam, King Chung; Sit, Wing Nga; Ng, Siu Man; Zhou, Zhongyuan; Lin, Zhenyang; Lau, Chak Po

    2006-01-23

    The heterobimetallic complexes [(eta5-C5H5)Ru(CO)(mu-dppm)Mn(CO)4] and [(eta5-C5Me5)Ru(mu-dppm)(mu-CO)2Mn(CO)3] (dppm = bis-diphenylphosphinomethane) have been prepared by reacting the hydridic complexes [(eta5-C5H5)Ru(dppm)H] and [(eta5-C5Me5)Ru(dppm)H], respectively, with the protonic [HMn(CO)5] complex. The bimetallic complexes can also be synthesized through metathetical reactions between [(eta5-C5R5)Ru(dppm)Cl] (R = H or Me) and Li+[Mn(CO)5]-. Although the complexes fail to catalyze the hydrogenation of CO2 to formic acid, they catalyze the coupling reactions of epoxides with carbon dioxide to yield cyclic carbonates. Two possible reaction pathways for the coupling reactions have been proposed. Both routes begin with heterolytic cleavage of the RuMn bond and coordination of an epoxide molecule to the Lewis acidic ruthenium center. In Route I, the Lewis basic manganese center activates the CO2 by forming the metallocarboxylate anion which then ring-opens the epoxide; subsequent ring-closure gives the cyclic carbonate. In Route II, the nucleophilic manganese center ring-opens the ruthenium-attached epoxide to afford an alkoxide intermediate; CO2 insertion into the RuO bond followed by ring-closure yields the product. Density functional calculations at the B3LYP level of theory were carried out to understand the structural and energetic aspects of the two possible reaction pathways. The results of the calculations indicate that Route II is favored over Route I.

  2. Collision Frequency for Energy Transfer in Unimolecular Reactions.

    Science.gov (United States)

    Matsugi, Akira

    2018-03-01

    Pressure dependence of unimolecular reaction rates is governed by the energy transfer in collisions of reactants with bath gas molecules. Pressure-dependent rate constants can be theoretically determined by solving master equations for unimolecular reactions. In general, master equation formulations describe energy transfer processes using a collision frequency and a probability distribution model of the energy transferred per collision. The present study proposes a novel method for determining the collision frequency from the results of classical trajectory calculations. Classical trajectories for collisions of several polyatomic molecules (ethane, methane, tetrafluoromethane, and cyclohexane) with monatomic colliders (Ar, Kr, and Xe) were calculated on potential energy surfaces described by the third-order density-functional tight-binding method in combination with simple pairwise interaction potentials. Low-order (including non-integer-order) moments of the energy transferred in deactivating collisions were extracted from the trajectories and compared with those derived using some probability distribution models. The comparison demonstrates the inadequacy of the conventional Lennard-Jones collision model for representing the collision frequency and suggests a robust method for evaluating the collision frequency that is consistent with a given probability distribution model, such as the exponential-down model. The resulting collision frequencies for the exponential-down model are substantially higher than the Lennard-Jones collision frequencies and are close to the (hypothetical) capture rate constants for dispersion interactions. The practical adequacy of the exponential-down model is also briefly discussed.

  3. Kinetic study for the ethanolysis of fish oil catalyzed by lipozyme(®) 435 in different reaction media.

    Science.gov (United States)

    Bucio, Silvia Liliana; Solaesa, Ángela García; Sanz, María Teresa; Melgosa, Rodrigo; Beltrán, Sagrario; Sovová, Helena

    2015-01-01

    The ethanolysis of fish oil in various reaction medium (tert-pentanol, n-hexane and solvent free system) catalyzed by the immobilized commercial lipase Lipozyme(®) 435 (Candida Antarctica) at atmospheric pressure has been studied in this work. The effect of some kinetic parameters, such as the amount of lipase, temperature and the initial reactant molar ratio ethanol:oil on monoacyglyceride and ethyl ester yield has been analyzed. Experimental data were successfully correlated by a simple kinetic model based on the elementary reactions proposed in this work. At high initial reactant molar ratio the three elementary steps can be considered as irreversible. However the reaction rate constants ratio for the deacylation of monoglyceride to glycerol decreased by decreasing the molar ratio ethanol:oil. The reaction rates are slower in n-hexane as reaction medium compared to tert-pentanol and a solvent-free system, at the experimental conditions essayed in this work. In this last case, ethanol acts as solvent for reaction and as reactant.

  4. Mass transfer with complex reversible chemical reactions I. Single reversible chemical reaction

    NARCIS (Netherlands)

    Versteeg, Geert; Kuipers, J.A.M.; van Beckum, F.P.H.; van Swaaij, Willibrordus Petrus Maria

    1989-01-01

    An improved numerical technique was used in order to develop an absorption model with which it is possible to calculate rapidly absorption rates for the phenomenon of mass transfer accompanied by a complex reversible chemical reaction. This model can be applied for the calculation of the mass

  5. Synthesis of the copper chelator TGTA and evaluation of its ability to protect biomolecules from copper induced degradation during copper catalyzed azide-alkyne bioconjugation reactions.

    Science.gov (United States)

    Ekholm, F S; Pynnönen, H; Vilkman, A; Koponen, J; Helin, J; Satomaa, T

    2016-01-21

    One of the most successful bioconjugation strategies to date is the copper(I)-catalyzed cycloaddition reaction (CuAAC), however, the typically applied reaction conditions have been found to degrade sensitive biomolecules. Herein, we present a water soluble copper chelator which can be utilized to protect biomolecules from copper induced degradation.

  6. Ligand-Controlled Synthesis of Azoles via Ir-Catalyzed Reactions of Sulfoxonium Ylides with 2-Amino Heterocycles.

    Science.gov (United States)

    Phelps, Alicia M; Chan, Vincent S; Napolitano, José G; Krabbe, Scott W; Schomaker, Jennifer M; Shekhar, Shashank

    2016-05-20

    An iridium-catalyzed method was developed for the synthesis of imidazo-fused pyrrolopyrazines. The presence or absence of a nitrogenated ligand controlled the outcome of the reaction, leading to simple β-keto amine products in the absence of added ligand and the cyclized 7- and 8-substituted-imidazo[1,2-a]pyrrolo[2,3-e]pyrazine products in the presence of ligand. This catalyst control was conserved across a variety of ylide and amine coupling partners. The substrate was shown to act as a ligand for the iridium catalyst in the absence of other ligands via NMR spectroscopy. Kinetic studies indicated that formation of the Ir-carbene was reversible and the slow step of the reaction. These mechanistic investigations suggest that the β-keto amine products form via an intramolecular carbene N-H insertion, and the imidazopyrrolopyrazines form via an intermolecular carbene N-H insertion.

  7. Switchable Diastereoselectivity in the Fluoride Promoted Vinylogous Mukaiyama-Michael Reaction of 2-Trimethylsilyloxyfuran Catalyzed by Crown Ethers

    KAUST Repository

    Della Sala, Giorgio

    2017-05-31

    The fluoride promoted vinylogous Mukaiyama-Michael reaction (VMMR) of 2-trimethylsilyloxyfuran with diverse α,β-unsaturated ketones is described. The TBAF catalyzed VMMR afforded high anti-diastereoselectivity irrespective of the solvents used. The KF/crown ethers catalytic systems proved to be highly efficient in terms of yields and resulted in a highly diastereoselective unprecedented solvent/catalyst switchable reaction. Anti-adducts were obtained as single diastereomers or with excellent diastereoselectivities when benzo-15-crown-5 in CH2Cl2 was employed. On the other hand, high syn-diastereoselectivities (from 76:24 to 96:4) were achieved by employing dicyclohexane-18-crown-6 in toluene. Based on DFT calculations, the catalysts/solvents-dependent switchable diastereoselectivities are proposed to be the result of loose or tight cation-dienolate ion pairs.

  8. Products and kinetics of the liquid-phase reaction of glyoxal catalyzed by ammonium ions (NH4(+)).

    Science.gov (United States)

    Nozière, Barbara; Dziedzic, Pawel; Córdova, Armando

    2009-01-08

    Glyoxal, a common atmospheric gas, has been reported to be depleted in some regions of the atmosphere. The corresponding sink could be accounted for by reactions in or at the surface of atmospheric particles, but these reactions were not identified. Recently, we showed that inorganic ammonium ions, NH(4)(+), are efficient catalysts for reactions of carbonyl compounds, including glyoxal, in the liquid phase. To determine whether ammonium-catalyzed reactions can contribute to depletion of glyoxal in the atmosphere, the reactivity of this compound in aqueous solutions containing ammonium salts (ammonium sulfate, chloride, fluoride, and phosphate) at 298 K has been studied. The products identified by LC-HRMS and UV absorption revealed a mechanism involving two distinct pathways: a Bronsted acid pathway and an iminium pathway. The kinetics of the iminium pathway was studied by monitoring formation of a specific product. This pathway was second order in glyoxal in most of the solutions studied and should therefore be second order in most ammonium-containing aerosols in the atmosphere. The corresponding rate constant, k(II) (M(-1) s(-1)), increased strongly with ammonium ion activity, a(NH(4)(+)), and pH: k(II) (M(-1) s(-1)) = (2 +/- 1) x 10(-10) exp((1.5 +/- 0.8)aNH(4)(+)) exp((2.5 +/- 0.2)pH). This iminium pathway is a lower limit for the ammonium-catalyzed consumption of glyoxal, but the contribution of the acid pathway is expected to be small in tropospheric aerosols. With these results the reactive uptake of glyoxal on ammonium-containing aerosols was estimated and shown to be a possible explanation for depletion of this compound in Mexico City.

  9. Cationic Pd(II-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

    Directory of Open Access Journals (Sweden)

    Takashi Nishikata

    2016-05-01

    Full Text Available Cationic palladium(II complexes have been found to be highly reactive towards aromatic C–H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN4](BF42 or a nitrile-free cationic palladium(II complex generated in situ from the reaction of Pd(OAc2 and HBF4, effectively catalyzes C–H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C–H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1 C–H activation to generate a cationic palladacycle; (2 reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3 regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied.

  10. Effects of delocalization on intrinsic barriers for H-atom transfer: Implications for the radical hydrogen transfer reaction

    Energy Technology Data Exchange (ETDEWEB)

    Camaioni, D.M.; Autrey, S.T.; Ferris, K.F.; Franz, J.A.

    1992-08-01

    PM3 calculations of transition states (TS) for both normal H-atom transfer and radical hydrogen transfer (RHT) reactions of a a wide-variety of hydrocarbon structures have enabled development of quantitative structure-reactivity relationships. Results indicate that activation barriers for RHT reactions are large enough that thermoneutral and endothermic reactions should not compete with alternative multistep pathways.

  11. Redox Reactions of Metalloporphyrins and their Role in Catalyzed Reduction of Carbon Dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Neta, P.

    2002-09-01

    Pulse radiolysis and laser photolysis are used to study redox processes of metalloporphyrins and related complexes in order to evaluate these light absorbing molecules as sensitizers and intermediates in solar energy conversion schemes. The main thrust of the current studies is to investigate the role of reduced metalloporphyrins as intermediates in the catalyzed reduction of carbon dioxide. Studies involve cobalt and iron porphyrins, phthalocyanines, corroles, and corrins as homogeneous catalysts for reduction of carbon dioxide in solution. The main aim is to understand the mechanisms of these photochemical schemes in order to facilitate their potential utilization.

  12. Tailored Cyclic and Linear Polycarbosilazanes by Barium-Catalyzed N-H/H-Si Dehydrocoupling Reactions.

    Science.gov (United States)

    Bellini, Clément; Orione, Clément; Carpentier, Jean-François; Sarazin, Yann

    2016-03-07

    Ba[CH(SiMe3 )2 ]2 (THF)3 catalyzes the fast and controlled dehydrogenative polymerization of Ph2 SiH2 and p-xylylenediamine to afford polycarbosilazanes. The structure (cyclic versus linear; end-groups) and molecular weight of the macromolecules can be tuned by adjusting the Ph2 SiH2 /diamine feed ratio. A detailed analysis of the resulting materials (mol. wt up to ca. 10 000 g mol(-1) ) is provided. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Mechanistic Investigations of the Iron(III)-Catalyzed Carbonyl-Olefin Metathesis Reaction.

    Science.gov (United States)

    Ludwig, Jacob R; Phan, Susan; McAtee, Christopher C; Zimmerman, Paul M; Devery, James J; Schindler, Corinna S

    2017-08-09

    Iron(III)-catalyzed carbonyl-olefin ring-closing metathesis represents a new approach toward the assembly of molecules traditionally generated by olefin-olefin metathesis or olefination. Herein, we report detailed synthetic, spectroscopic, kinetic, and computational studies to determine the mechanistic features imparted by iron(III), substrate, and temperature to the catalytic cycle. These data are consistent with an iron(III)-mediated asynchronous, concerted [2+2]-cycloaddition to form an intermediate oxetane as the turnover-limiting step. Fragmentation of the oxetane via Lewis acid-activation results in the formation of five- and six-membered unsaturated carbocycles.

  14. Effect of water content and temperature on Carica papaya lipase catalyzed esterification and transesterification reactions

    Directory of Open Access Journals (Sweden)

    Turon Fabrice

    2003-09-01

    Full Text Available Temperature and water activity (a w of the reaction medium are two factors that govern enzyme reactions. We studied the influence of these two parameters on the esterification and transesterification activity of Carica papaya lipase in water and solvent free reactions. It was found that over the course of reaction the catalytic activity of C. papaya lipase was dependent on these factors. The best lipase activity for both reactions was at a temperature of 55°C and water activity of 0.22, which corresponds to 2 g of water per 100 g of C. papaya latex.

  15. Mass transfer effects in the H2SO4 catalyzed pivalic acid synthesis

    NARCIS (Netherlands)

    Brilman, D.W.F.; Meesters, N.G.; Swaaij, W.P.M. van; Versteeg, G.F.

    2001-01-01

    The synthesis of carboxylic acids from alkenes, carbon monoxide and water according to the Koch process is usually carried out in a stirred gas–liquid–liquid multiphase reactor. Due to the complex reaction system with fast, equilibrium reactions and fast, irreversible reactions the yield and product

  16. Mass transfer effects in H2SO4 catalyzed pivalic acid synthesis

    NARCIS (Netherlands)

    Brilman, Derk Willem Frederik; Meesters, N.G.; van Swaaij, Willibrordus Petrus Maria; Versteeg, Geert

    2001-01-01

    The synthesis of carboxylic acids from alkenes, carbon monoxide and water according to the Koch process is usually carried out in a stirred gas–liquid–liquid multiphase reactor. Due to the complex reaction system with fast, equilibrium reactions and fast, irreversible reactions the yield and product

  17. Ultrasound assisted lipase catalyzed synthesis of cinnamyl acetate via transesterification reaction in a solvent free medium.

    Science.gov (United States)

    Tomke, Prerana D; Rathod, Virendra K

    2015-11-01

    Cinnamyl acetate is known for its use as flavor and fragrance material in different industries such as food, pharmaceutical, cosmetic etc. This work focuses on ultrasound assisted lipase (Novozym 435) catalyzed synthesis of cinnamyl acetate via transesterification of cinnamyl alcohol and vinyl acetate in non-aqueous, solvent free system. Optimization of various parameters shows that a higher yield of 99.99% can be obtained at cinnamyl alcohol to vinyl acetate ratio of 1:2 with 0.2% of catalyst, at 40°C and 150 rpm, with lower ultrasound power input of 50 W (Ultrasound intensity 0.81 W/cm(2)), at 25 kHz frequency, 50% duty cycle. Further, the time required for the maximum conversion is reduced to 20 min as compared to 60 min of conventional process. Similarly, the enzyme can be successfully reused seven times without loss of enzyme activity. Thus, ultrasound helps to enhance the enzyme catalyzed synthesis of flavors. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. Microbial activity catalyzes oxygen transfer in membrane-aerated nitritating biofilm reactors

    DEFF Research Database (Denmark)

    Pellicer i Nàcher, Carles; Domingo Felez, Carlos; Lackner, Susanne

    2013-01-01

    The remarkable oxygen transfer efficiencies attainable in membrane-aerated biofilm reactors (MABRs) are expected to favor their prompt industrial implementation. However, tests in clean water, currently used for the estimation of their oxygen transfer potential, lead to wrong estimates once biofilm...... is present, significantly complicating reactor modelling and control. This study shows for the first time the factors affecting oxygen mass transfer across membranes during clean water tests and reactor operation via undisturbed microelectrode inspection and bulk measurements. The mass transfer resistance...... of the liquid boundary layer developed at the membrane-liquid interface during clean water tests accounted for two thirds of the total mass transfer resistance, suggesting a strong underestimation of the oxygen transfer rates when it is absent (e.g. after biofilm growth). Reactor operation to attain partial...

  19. Cobalt catalyzed peroxymonosulfate oxidation of tetrabromobisphenol A: Kinetics, reaction pathways, and formation of brominated by-products

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Yuefei [Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing 210095 (China); Kong, Deyang [Nanjing Institute of Environmental Science, Ministry of Environmental Protection of PRC, Nanjing 210042 (China); Lu, Junhe, E-mail: jhlu@njau.edu.cn [Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing 210095 (China); Jin, Hao; Kang, Fuxing; Yin, Xiaoming; Zhou, Quansuo [Department of Environmental Science and Engineering, Nanjing Agricultural University, Nanjing 210095 (China)

    2016-08-05

    Highlights: • Cobalt catalyzed peroxymonosulfate oxidation of tetrabromobisphenol A. • Phenolic moiety was the reactive site for sulfate radical attack. • Pathways include β-scission, oxidation, debromination and coupling reactions. • Brominated disinfection by-products were found during TBBPA degradation. • Humic acid inhibited TBBPA degradation but promoted DBPs formation. - Abstract: Degradation of tetrabromobisphenol A (TBBPA), a flame retardant widely spread in the environment, in Co(II) catalyzed peroxymonosulfate (PMS) oxidation process was systematically explored. The second-order-rate constant for reaction of sulfate radical (SO{sub 4}{sup ·−}) with TBBPA was determined to be 5.27 × 10{sup 10} M{sup −1} s{sup −1}. Apparently, degradation of TBBPA showed first-order kinetics to the concentrations of both Co(II) and PMS. The presence of humic acid (HA) and bicarbonate inhibited TBBPA degradation, most likely due to their competition for SO{sub 4}{sup ·−}. Degradation of TBBPA was initiated by an electron abstraction from one of the phenolic rings. Detailed transformation pathways were proposed, including β-scission of isopropyl bridge, phenolic ring oxidation, debromination and coupling reactions. Further oxidative degradation of intermediates in Co(II)/PMS process yielded brominated disinfection by-products (Br-DBPs) such as bromoform and brominated acetic acids. Evolution profile of Br-DBPs showed an initially increasing and then decreasing pattern with maximum concentrations occurring around 6–10 h. The presence of HA enhanced the formation of Br-DBPs significantly. These findings reveal potentially important, but previously unrecognized, formation of Br-DBPs during sulfate radical-based oxidation of bromide-containing organic compounds that may pose toxicological risks to human health.

  20. L-proline-catalyzed enantioselective one-pot cross-Mannich reaction of aldehydes.

    Science.gov (United States)

    Hayashi, Yujiro; Urushima, Tatsuya; Tsuboi, Wataru; Shoji, Mitsuru

    2007-01-01

    This protocol describes a procedure for the synthesis of syn-beta-amino alpha-substituted aldehydes, versatile intermediates in synthetic organic chemistry, via asymmetric, direct, one-pot, three-component, cross-Mannich reaction of two different aldehydes. The reaction consists of two steps; one is the formation of imine by the reaction of aldehyde and p-anisidine in the presence of Pro, and the second step is the enantioselective addition reaction of enamine generated from the other aldehyde and Pro with the imine generated in the first step. As the aldehyde easily racemizes, gamma-amino alcohol was isolated and characterized after reduction. The yield and diastereo- and enantioselectivities are generally excellent. It will take approximately 26 h to complete the protocol: 0.5 h to set up the reaction, 20.5 h for the reaction and 5 h for the isolation and purification.

  1. Development and Applications of the Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC as a Bioorthogonal Reaction

    Directory of Open Access Journals (Sweden)

    Li Li

    2016-10-01

    Full Text Available The emergence of bioorthogonal reactions has greatly broadened the scope of biomolecule labeling and detecting. Of all the bioorthogonal reactions that have been developed, the copper-catalyzed azide-alkyne cycloaddition (CuAAC is the most widely applied one, mainly because of its relatively fast kinetics and high efficiency. However, the introduction of copper species to in vivo systems raises the issue of potential toxicity. In order to reduce the copper-induced toxicity and further improve the reaction kinetics and efficiency, different strategies have been adopted, including the development of diverse copper chelating ligands to assist the catalytic cycle and the development of chelating azides as reagents. Up to now, the optimization of CuAAC has facilitated its applications in labeling and identifying either specific biomolecule species or on the omics level. Herein, we mainly discuss the efforts in the development of CuAAC to better fit the bioorthogonal reaction criteria and its bioorthogonal applications both in vivo and in vitro.

  2. Elucidating Latent Mechanistic Complexity in Competing Acid-Catalyzed Reactions of Salicylaldehyde-Derived Baylis-Hillman Adducts.

    Science.gov (United States)

    Olomola, Temitope O; Klein, Rosalyn; Caira, Mino R; Kaye, Perry T

    2016-01-04

    (1)H NMR-based kinetic studies have revealed the latent mechanistic complexity of deceptively simple hydrochloric acid-catalyzed reactions of salicylaldehyde-derived Baylis-Hillman adducts. Reactions conducted at 0 °C afforded 2-(chloromethyl)cinnamic acid derivatives as the major products and the corresponding 3-(chloromethyl)coumarin derivatives as the minor products. In reactions conducted in refluxing acetic acid, however, the 3-(chloromethyl)coumarin derivatives are the sole products. Variable-temperature (1)H NMR analysis permitted the determination of the rate constants and kinetic parameters involved in the pseudo-first-order formation of (Z)-2-(chloromethyl)-3-(2-hydroxyphenyl)-2-propenoic acid. The kinetic data clearly preclude the operation of classical kinetic versus thermodynamic control and indicate the operation of three independent reaction pathways. Theoretical studies of these pathways undertaken at the B3LYP/6-31G(d) level permitted rationalization of the experimental data and provided insights into the possible mechanism of the enzymic E-Z isomerization and cyclization of (E)-cinnamic acid analogues to afford coumarins.

  3. Refined transition-state models for proline-catalyzed asymmetric Michael reactions under basic and base-free conditions.

    Science.gov (United States)

    Sharma, Akhilesh K; Sunoj, Raghavan B

    2012-12-07

    The stereocontrolling transition state (TS) models for C-C bond formation relying on hydrogen bonding have generally been successful in proline-catalyzed aldol, Mannich, α-amination, and α-aminoxylation reactions. However, the suitability of the hydrogen-bonding model in protic and aprotic conditions as well as under basic and base-free conditions has not been well established for Michael reactions. Through a comprehensive density functional theory investigation, we herein analyze different TS models for the stereocontrolling C-C bond formation, both in the presence and absence of a base in an aprotic solvent (THF). A refined stereocontrolling TS for the Michael reaction between cyclohexanone and nitrostyrene is proposed. The new TS devoid of hydrogen bonding between the nitro group of nitrostyrene and carboxylic acid of proline, under base-free conditions, is found to be more preferred over the conventional hydrogen-bonding model besides being able to reproduce the experimentally observed stereochemical outcome. A DBU-bound TS is identified as more suitable for rationalizing the origin of asymmetric induction under basic reaction conditions. In both cases, the most preferred approach of nitrostyrene is identified as occurring from the face anti to the carboxylic acid of proline-enamine. The predicted enantio- and diastereoselectivities are in very good agreement with the experimental observations.

  4. Chaotic scattering in heavy-ion reactions with mass transfer

    International Nuclear Information System (INIS)

    Rodriguez Padron, Emilio; Guzman Martinez, Fernando

    1998-01-01

    The role of the mass transfer in heavy ion collisions is analyzed in the framework of a simple semi phenomenological model searching for chaotic scattering effects. The model couples the relative motion of the ions to a collective degree of freedom. The collective degree of freedom is identified by the mass asymmetry of the system. A Saxon-Woods potential is used for nucleus-nucleus interaction whiles a harmonic potential rules the temporal behaviour of the collective degree of freedom. This model shows chaotic scattering which could be an explanation for certain types of cross-section fluctuations observed in this kind of reactions

  5. Radiolytic and electron-transfer reactions in supercritical CO2

    International Nuclear Information System (INIS)

    Bartels, D. M.; Dimitrijevic, N. M.; Jonah, C. D.; Takahashi, K.

    2000-01-01

    Using supercritical fluids as solvents is useful for both practical and theoretical reasons. It has been proposed to use supercritical CO 2 as a solvent for synthesis because it eliminates the air pollution arising from other solvents. The properties of supercritical fluids can be easily varied with only modest changes in temperature and density, so they provide a way of testing theories of chemical reactions. It has also been proposed to use supercritical fluids for the treatment of hazardous mixed waste. For these reasons the authors have studied the production of radiolytic species in supercritical CO 2 and have measured their reactivity as a function of density. They have shown that the C 2 O 4 + is formed. They also have shown that the electron transfer reactions of dimethylaniline to C 2 O 4 + and CO 2 (e - ) to benzoquinone are diffusion controlled over a considerable density range

  6. Transfer Hydrogenation of Alkenes Using Ethanol Catalyzed by a NCP Pincer Iridium Complex: Scope and Mechanism.

    Science.gov (United States)

    Wang, Yulei; Huang, Zhidao; Leng, Xuebing; Zhu, Huping; Liu, Guixia; Huang, Zheng

    2018-03-28

    The first general catalytic approach to effecting transfer hydrogenation (TH) of unactivated alkenes using ethanol as the hydrogen source is described. A new NCP-type pincer iridium complex ( BQ -NC O P)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C-C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct. A wide variety of alkenes, including multisubstituted alkyl alkenes, aryl alkenes, and heteroatom-substituted alkenes, as well as O- or N-containing heteroarenes and internal alkynes, are suitable substrates. Importantly, the ( BQ -NC O P)Ir/EtOH system exhibits high chemoselectivity for alkene hydrogenation in the presence of reactive functional groups, such as ketones and carboxylic acids. Furthermore, the reaction with C 2 D 5 OD provides a convenient route to deuterium-labeled compounds. Detailed kinetic and mechanistic studies have revealed that monosubstituted alkenes (e.g., 1-octene, styrene) and multisubstituted alkenes (e.g., cyclooctene (COE)) exhibit fundamental mechanistic difference. The OH group of ethanol displays a normal kinetic isotope effect (KIE) in the reaction of styrene, but a substantial inverse KIE in the case of COE. The catalysis of styrene or 1-octene with relatively strong binding affinity to the Ir(I) center has ( BQ -NC O P)Ir I (alkene) adduct as an off-cycle catalyst resting state, and the rate law shows a positive order in EtOH, inverse first-order in styrene, and first-order in the catalyst. In contrast, the catalysis of COE has an off-cycle catalyst resting state of ( BQ -NC O P)Ir III (H)[O(Et)···HO(Et)···HOEt] that features a six-membered iridacycle consisting of two hydrogen-bonds between one EtO ligand and two EtOH molecules, one of which is coordinated to the Ir(III) center. The rate law shows a negative order in EtOH, zeroth-order in COE, and first-order in the catalyst. The observed inverse KIE corresponds to an inverse equilibrium

  7. Proton transfer reactions and dynamics in protonated water clusters.

    Science.gov (United States)

    Lao-Ngam, Charoensak; Asawakun, Prapasri; Wannarat, Sornthep; Sagarik, Kritsana

    2011-03-14

    Proton transfer reactions and dynamics were theoretically studied using the hydrogen-bond (H-bond) complexes formed from H(3)O(+) and nH(2)O, n = 1-4, as model systems. The investigations began with searching for characteristics of transferring protons in the gas phase and continuum aqueous solution using DFT method at the B3LYP/TZVP level, followed by Born-Oppenheimer molecular dynamics (BOMD) simulations at 350 K. B3LYP/TZVP calculations revealed the threshold asymmetric O-H stretching frequencies (ν(OH)*) for the proton transfers in the Zundel complex (H(5)O) in the gas phase and continuum aqueous solution at 1984 and 1881 cm(-1), respectively. BOMD simulations suggested lower threshold frequencies (ν(OH,MD)* = 1917 and 1736 cm(-1), respectively), with two characteristic ν(OH,MD) being the IR spectral signatures of the transferring protons. The low-frequency band could be associated with the "oscillatory shuttling motion" and the high-frequency band with the "structural diffusion motion". These can be regarded as the spectroscopic evidences of the formations of the shared-proton structure (O···H(+)···O) and the H(3)O(+)-H(2)O contact structure (O-H(+)···O), respectively. Since the quasi-dynamic equilibrium between the Zundel and Eigen complexes was suggested to be the rate-determining step, in order to achieve an "ideal" maximum efficiency of proton transfer, a concerted reaction pathway should be taken. The most effective interconversion between the two proton states, the shared-proton structure and the H(3)O(+)-H(2)O contact structure, can be reflected from comparable intensities of the oscillatory shuttling and structural diffusion bands. The present results iterated the previous conclusions that static proton transfer potentials cannot provide complete description of the structural diffusion process and it is essential to incorporate thermal energy fluctuations and dynamics in the model calculations.

  8. Gold(I)/Gold(III)-Catalyzed Selective Synthesis of N-Sulfonyl Enaminone Isomers from Sulfonamides and Ynones via Two Distinct Reaction Pathways.

    Science.gov (United States)

    Lee, Dabon; Kim, Sang Min; Hirao, Hajime; Hong, Soon Hyeok

    2017-09-15

    Au-catalyzed chemoselective methods for synthesizing N-sulfonyl enaminones are developed. Two different isomers are obtained in a chemocontrolled manner by employing the different properties of Au(I) and Au(III) catalysts. Hydroamidation and proton-assisted carbonyl activation followed by Meyer-Schuster rearrangement are proposed as the working mechanisms for the reactions. A wide range of substrates afforded moderate to excellent yields and selectivities. These reactions represent the first examples of transition-metal-catalyzed enamine synthesis from sulfonamides and alkynes.

  9. Alternative Pathway for the Reaction Catalyzed by DNA Dealkylase AlkB from Ab Initio QM/MM Calculations.

    Science.gov (United States)

    Fang, Dong; Cisneros, G Andrés

    2014-11-11

    AlkB is the title enzyme of a family of DNA dealkylases that catalyze the direct oxidative dealkylation of nucleobases. The conventional mechanism for the dealkylation of N 1 -methyl adenine (1-meA) catalyzed by AlkB after the formation of Fe IV -oxo is comprised by a reorientation of the oxo moiety, hydrogen abstraction, OH rebound from the Fe atom to the methyl adduct, and the dissociation of the resulting methoxide to obtain the repaired adenine base and formaldehyde. An alternative pathway with hydroxide as a ligand bound to the iron atom is proposed and investigated by QM/MM simulations. The results show OH - has a small impact on the barriers for the hydrogen abstraction and OH rebound steps. The effects of the enzyme and the OH - ligand on the hydrogen abstraction by the Fe IV -oxo moiety are discussed in detail. The new OH rebound step is coupled with a proton transfer to the OH - ligand and results in a novel zwitterion intermediate. This zwitterion structure can also be characterized as Fe-O-C complex and facilitates the formation of formaldehyde. In contrast, for the pathway with H 2 O bound to iron, the hydroxyl product of the OH rebound step first needs to unbind from the metal center before transferring a proton to Glu136 or other residue/substrate. The consistency between our theoretical results and experimental findings is discussed. This study provides new insights into the oxidative repair mechanism of DNA repair by nonheme Fe II and α-ketoglutarate (α-KG) dependent dioxygenases and a possible explanation for the substrate preference of AlkB.

  10. Influence of gamma radiation reaction on the hydroesterification of butenes catalyzed by metal carbonyls

    International Nuclear Information System (INIS)

    Velde, J. van der.

    1976-01-01

    In the hydro carboxylation reaction, which first has been studied by Reppe, olefine and acetylene compounds are processed with carbon monoxide and water at high pressures and high temperatures in the presence of metal carbonyls. This reaction can be enhanced considerably by application of ionizing radiation. Lower pressures and in particular lower temperatures can be used if gamma irradiation is performed during carboxylation. For the experiments a mixture of buten-1 and buten-2 as well as pure buten-1 and pure buten-2 has been used to study the behaviour of these olefines with respect to the isomerization of the reaction products and to the olefines not transformed in the reaction process. Replacing water, methanol has been used as a reaction component, thus obtaining directly the respective carbonyl acid esters, which can be analysed quantitatively and qualitatively with respect to their isomeric composition by gaschromatography. (orig./HK) [de

  11. A thermodynamic study of ketoreductase-catalyzed reactions 2. Reduction of cycloalkanones in non-aqueous solvents

    International Nuclear Information System (INIS)

    Tewari, Yadu B.; Phinney, Karen W.; Liebman, Joel F.

    2006-01-01

    The equilibrium constants for the ketoreductase-catalyzed reactions (cycloalkanone+2-propanol=cycloalkanol+acetone) have been measured in n-hexane, n-pentane, and supercritical carbon dioxide SCCO 2 (pressure=(8.0 to 12.0)MPa). The cycloalkanones included in this study were: cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone, and cyclooctanone. The equilibrium constants for the reactions involving cyclobutanone and cyclohexanone were measured in n-hexane over the range T=(288.35 to 308.05)K. The thermodynamic quantities at T=298.15K are: K=(0.763+/-0.001); Δ r G m - bar =(0.670+/-0.002)kJ.mol -1 ; Δ r H m - bar =-(1.09+/-0.11)kJ.mol -1 , and Δ r S m - bar =-(5.9+/-0.4)J.K -1 .mol -1 for the reaction involving cyclobutanone; and K=(15.7+/-0.2); Δ r G m - bar =-(6.82+/-0.02)kJ.mol -1 ; Δ r H m - bar =-(4.6+/-1.0)kJ.mol -1 , and Δ r S m - bar =(7.4+/-3.3)J.K -1 .mol -1 for the reaction involving cyclohexanone, respectively. An inspection of the equilibrium constants for these reactions in n-hexane, n-pentane, and SCCO 2 shows that solvent dependence is not significant. The equilibrium constants of cycloalkanones decrease with increasing value of the number of carbons, N C with the exception of cyclohexanone. The cyclohexanol, which adopts a nearly strainless, idealized tetrahedral conformation around each carbon, is thermodynamically favored and more stable compared to other cycloalkanol rings, and this is reflected in the significantly higher value of the equilibrium constant obtained for this reaction. Comparisons with results obtained by using two independent thermochemical routes are also made

  12. A novel mechanism of sulfur transfer catalyzed by O-acetylhomoserine sulfhydrylase in the methionine-biosynthetic pathway of Wolinella succinogenes

    Energy Technology Data Exchange (ETDEWEB)

    Tran, Timothy H. [Cornell University, Ithaca, New York 14853-1301 (United States); Krishnamoorthy, Kalyanaraman; Begley, Tadhg P., E-mail: begley@tamu.edu [Texas A& M University, College Station, TX 77842 (United States); Ealick, Steven E., E-mail: begley@tamu.edu [Cornell University, Ithaca, New York 14853-1301 (United States)

    2011-10-01

    MetY is the first reported structure of an O-acetylhomoserine sulfhydrylase that utilizes a protein thiocarboxylate intermediate as the sulfur source in a novel methionine-biosynthetic pathway instead of catalyzing a direct sulfhydrylation reaction. O-Acetylhomoserine sulfhydrylase (OAHS) is a pyridoxal 5′-phosphate (PLP) dependent sulfide-utilizing enzyme in the l-cysteine and l-methionine biosynthetic pathways of various enteric bacteria and fungi. OAHS catalyzes the conversion of O-acetylhomoserine to homocysteine using sulfide in a process known as direct sulfhydrylation. However, the source of the sulfur has not been identified and no structures of OAHS have been reported in the literature. Here, the crystal structure of Wolinella succinogenes OAHS (MetY) determined at 2.2 Å resolution is reported. MetY crystallized in space group C2 with two monomers in the asymmetric unit. Size-exclusion chromatography, dynamic light scattering and crystal packing indicate that the biological unit is a tetramer in solution. This is further supported by the crystal structure, in which a tetramer is formed using a combination of noncrystallographic and crystallographic twofold axes. A search for structurally homologous proteins revealed that MetY has the same fold as cystathionine γ-lyase and methionine γ-lyase. The active sites of these enzymes, which are also PLP-dependent, share a high degree of structural similarity, suggesting that MetY belongs to the γ-elimination subclass of the Cys/Met metabolism PLP-dependent family of enzymes. The structure of MetY, together with biochemical data, provides insight into the mechanism of sulfur transfer to a small molecule via a protein thiocarboxylate intermediate.

  13. In tandem or alone: a remarkably selective transfer hydrogenation of alkenes catalyzed by ruthenium olefin metathesis catalysts.

    Science.gov (United States)

    Zieliński, Grzegorz Krzysztof; Samojłowicz, Cezary; Wdowik, Tomasz; Grela, Karol

    2015-03-07

    A system for transfer hydrogenation of alkenes, composed of a ruthenium metathesis catalyst and HCOOH, is presented. This operationally simple system can be formed directly after a metathesis reaction to effect hydrogenation of the metathesis product in a single-pot. These hydrogenation conditions are applicable to a wide range of alkenes and offer remarkable selectivity.

  14. Steady and nonsteady rates of reaction in a heterogeneously catalyzed reaction: Oxidation of CO on platinum, experiments and simulations

    Science.gov (United States)

    Ehsasi, M.; Matloch, M.; Frank, O.; Block, J. H.; Christmann, K.; Rys, F. S.; Hirschwald, W.

    1989-10-01

    The rate of reaction for oxidation of CO over (210) and (111) single-crystal surfaces of platinum has been studied as a function of reactant pressures (PO2,PCO) and sample temperature (T), both experimentally and by computer simulation. Experimental results on both surfaces show regions with a steady high rate of reaction followed by a nonsteady transition region and, at high CO pressures, a region with low reactivity caused by CO poisoning of the surface. At constant sample temperature, the transition region can be narrow and depends critically on the ratio of the gas phase concentration of reactants (PCO/PO2). The temperature dependences of the experimental data indicate that the critical ratio and the details for the occurrence of CO poisoning are strongly affected by surface processes such as adsorption, desorption, and diffusion ordering and reconstruction phenomena. A computer simulation model of the Langmuir-Hinshelwood surface reaction as developed by Ziff et al. was used for the simulation of the reaction under flow conditions. The initial fair agreement between this model and the experiment can be significantly improved if processes such as adsorption, desorption, and diffusion are taken into account in an extended simulation model which in turn provides an insight into the kinetics of adsorbate poisoning and the effect of adsorbate-induced processes on the reaction.

  15. Reversed hydroxamate-bearing thermolysin inhibitors mimic a high-energy intermediate along the enzyme-catalyzed proteolytic reaction pathway.

    Science.gov (United States)

    Park, Jung Dae; Kim, Dong H

    2003-10-06

    A series of inhibitors that bear a reversed hydroxamate moiety have been evaluated as transition state analogue inhibitors for thermolysin. A linear correlation is observed between the K(i) values of these inhibitors and the kinetic parameters (K(M)/k(cat)) of the parallel series of related substrates, satisfying the criterion stipulated for transition state analogue inhibitors by Bartlett and Marlowe. Furthermore, examination of the binding mode of a related reversed hydroxamate bearing thermolysin inhibitor, in comparison with a transition state postulated for the enzyme-catalyzed proteolytic reaction revealed that the inhibitors under study mimic the electronic as well as the geometric characteristics of the transition state. On the basis of these results it may be concluded that the hydroxamate-bearing zinc protease inhibitors are a new type of transition state analogue inhibitors.

  16. Sodium ascorbate kills Candida albicans in vitro via iron-catalyzed Fenton reaction: importance of oxygenation and metabolism.

    Science.gov (United States)

    Avci, Pinar; Freire, Fernanda; Banvolgyi, Andras; Mylonakis, Eleftherios; Wikonkal, Norbert M; Hamblin, Michael R

    2016-12-01

    Ascorbate can inhibit growth and even decrease viability of various microbial species including Candida albicans. However the optimum conditions and the mechanism of action are unclear. Materials/methodology: Candida albicans shaken for 90 min in a buffered solution of ascorbate (90 mM) gave a 5-log reduction of cell viability, while there was no killing without shaking, in growth media with different carbon sources or at 4°C. Killing was inhibited by the iron chelator 2,2'-bipyridyl. Hydroxyphenyl fluorescein probe showed the intracellular generation of hydroxyl radicals. Ascorbate-mediated killing of C. albicans depends on oxygenation and metabolism, involves iron-catalyzed generation of hydroxyl radicals via Fenton reaction and depletion of intracellular NADH. Ascorbate could serve as a component of a topical antifungal therapy.

  17. 179Ta and 180Ta structure by transfer reactions

    International Nuclear Information System (INIS)

    Warde, Elias.

    1979-01-01

    Transfer reactions (α,t); ( 3 He,d); (p,t) and (p,d) have been used to study the nuclear spectroscopy of 179 Ta and 180 Ta. In 179 Ta, 5/2 - and 9/2 - states of the 1/2(541) configuration have been identified. The core-quasiproton interaction has to be taken into account in order to explain the two-nucleon transfer intensities in the 181 Ta(p,t) 179 Ta reaction. A level scheme has been proposed for 180 Ta for the first time. Especially the ground state is identified with the (1 + ,1) level of the [7/2 + (404)sub(p), 9/2 + (624)sub(n)] configuration and spin (9 - ,9) of the configuration [9/2 - (514)sub(p), 9/2 + (624)sub(n)] has been assigned to the long-lived isomer. From the observed configurations in 180 Ta, the matrix elements of the effective residual interaction vsub(np) have been deduced and compared to theoretical predictions [fr

  18. Transfer reactions in inverse kinematics at REX-ISOLDE

    CERN Document Server

    Tengborn, E

    Research on the structure of exotic nuclei is one of the most intriguing topics in present day nuclear physics. With the use of facilities for isotope separation on-line, such as ISOLDE at CERN, short-lived isotopes can be studied experimentally. Since 2002, the REX-ISOLDE facility enables radioactive ions produced by ISOLDE to be post-accelerated, increasing the energy of the ions enough to do nuclear transfer reactions in inverse kinematics. In this thesis, transfer reactions are used to study the structure of neutron-rich lithium isotopes through a series of experiments at REX-ISOLDE. The first experiment used a 9Li beam at 2.36 MeV/u impinging on a deuterated polyethylene target to study 10Li, 9Li and 8Li. For the (d,p)-channel the resonance ground state and a first excited state are observed and the results agree with theoretical calculations. The elastic channel agrees with Optical Model, OM, calculations. For the (d,t)-channel the shape of the angular distribution agrees with Distorted Wave Born Approx...

  19. Electron transfer reactions to probe the electrode/solution interface

    Energy Technology Data Exchange (ETDEWEB)

    Capitanio, F.; Guerrini, E.; Colombo, A.; Trasatti, S. [Milan Univ., Milan (Italy). Dept. of Physical Chemistry and Electrochemistry

    2008-07-01

    The reactions that occur at the interface between an electrode and an electrolyte were examined with particular reference to the interaction of different electrode surfaces with redox couples. A semi-integration or convolution technique was used to study the kinetics of electron transfer on different electrode materials with different hydrophilic behaviour, such as Boron-Doped-Diamond (BDD), Au and Pt. Standard reversible redox couples were also investigated, including (Fe3+/2+, Fe(CN)63-/4-, Ru(NH3)63+/2+, Co(NH3)63+/2+, Ir4+/3+, V4+/5+ and V3+/2+). The proposed method proved to be simple, straightforward and reliable since the obtained kinetic information was in good agreement with data in the literature. It was concluded that the kinetics of the electrode transfer reactions depend on the chemical nature of the redox couple and electrode material. The method should be further extended to irreversible couples and other electrode materials such as mixed oxide electrodes. 3 refs., 2 figs.

  20. Pd-catalyzed coupling reaction on the organic monolayer: Sonogashira reaction on the silicon (1 1 1) surfaces

    International Nuclear Information System (INIS)

    Qu Mengnan; Zhang Yuan; He Jinmei; Cao Xiaoping; Zhang Junyan

    2008-01-01

    Iodophenyl-terminated organic monolayers were prepared by thermally induced hydrosilylation on hydrogen-terminated silicon (1 1 1) surfaces. The films were characterized by ellipsometry, contact-angle goniometry, and X-ray photoelectron spectroscopy (XPS). To modify the surface chemistry and the structure of the monolayers, the Sonogashira coupling reaction was performed on the as-prepared monolayers. The iodophenyl groups on the film surfaces reacted with 1-ethynyl-4-fluorobenzene or the 1-chloro-4-ethynylbenzene under the standard Sonogashira reaction conditions for attaching conjugated molecules via the formation of C-C bonds. It is expected that this surface coupling reaction will present a new method to modify the surface chemistry and the structure of monolayers

  1. Influence of the reaction conditions on the enzyme catalyzed transesterification of castor oil

    DEFF Research Database (Denmark)

    Andrade, Thalles Allan; Errico, Massimiliano; Christensen, Knud Villy

    2017-01-01

    The identification of the influence of the reaction parameters is of paramount importance when defining a process design. In this work, non-edible castor oil was reacted with methanol to produce a possible component for biodiesel blends, using liquid enzymes as the catalyst. Temperature, alcohol-to-oil...... molar ratio, enzyme and added water contents were the reaction parameters evaluated in the transesterification reactions. The optimal conditions, giving the optimal final FAME yield and FFA content in the methyl ester-phase was identified. At 35 °C, 6.0 methanol-to-oil molar ratio, 5 wt% of enzyme and 5...

  2. Low-temperature superacid catalysis: Reactions of n - butane and propane catalyzed by iron- and manganese-promoted sulfated zirconia

    Energy Technology Data Exchange (ETDEWEB)

    Tsz-Keung, Cheung; d`Itri, J.L.; Lange, F.C.; Gates, B.C. [Univ. of California, Davis, CA (United States)

    1995-12-31

    The primary goal of this project is to evaluate the potential value of solid superacid catalysts of the sulfated zirconia type for light hydrocarbon conversion. The key experiments catalytic testing of the performance of such catalysts in a flow reactor fed with streams containing, for example, n-butane or propane. Fe- and Mn-promoted sulfated zirconia was used to catalyze the conversion of n-butane at atmospheric pressure, 225-450{degrees}C, and n-butane partial pressures in the range of 0.0025-0.01 atm. At temperatures <225{degrees}C, these reactions were accompanied by cracking; at temperatures >350{degrees}C, cracking and isomerization occurred. Catalyst deactivation, resulting at least in part from coke formation, was rapid. The primary cracking products were methane, ethane, ethylene, and propylene. The observation of these products along with an ethane/ethylene molar ratio of nearly 1 at 450{degrees}C is consistent with cracking occurring, at least in part, by the Haag-Dessau mechanism, whereby the strongly acidic catalyst protonates n-butane to give carbonium ions. The rate of methane formation from n-butane cracking catalyzed by Fe- and Mn-promoted sulfated zirconia at 450{degrees}C was about 3 x 10{sup -8} mol/(g of catalyst {center_dot}s). The observation of butanes, pentanes, and methane as products is consistent with Olah superacid chemistry, whereby propane is first protonated by a very strong acid to form a carbonium ion. The carbonium ion then decomposes into methane and an ethyl cation which undergoes oligocondensation reactions with propane to form higher molecular weight alkanes. The results are consistent with the identification of iron- and manganese-promoted sulfated zirconia as a superacid.

  3. Single-collision studies of energy transfer and chemical reaction

    Energy Technology Data Exchange (ETDEWEB)

    Valentini, J.J. [Columbia Univ., New York, NY (United States)

    1993-12-01

    The research focus in this group is state-to-state dynamics of reaction and energy transfer in collisions of free radicals such as H, OH, and CH{sub 3} with H{sub 2}, alkanes, alcohols and other hydrogen-containing molecules. The motivation for the work is the desire to provide a detailed understanding of the chemical dynamics of prototype reactions that are important in the production and utilization of energy sources, most importantly in combustion. The work is primarily experimental, but with an important and growing theoretical/computational component. The focus of this research program is now on reactions in which at least one of the reactants and one of the products is polyatomic. The objective is to determine how the high dimensionality of the reactants and products differentiates such reactions from atom + diatom reactions of the same kinematics and energetics. The experiments use highly time-resolved laser spectroscopic methods to prepare reactant states and analyze the states of the products on a single-collision time scale. The primary spectroscopic tool for product state analysis is coherent anti-Stokes Raman scattering (CARS) spectroscopy. CARS is used because of its generality and because the extraction of quantum state populations from CARS spectra is straightforward. The combination of the generality and easy analysis of CARS makes possible absolute cross section measurements (both state-to-state and total), a particularly valuable capability for characterizing reactive and inelastic collisions. Reactant free radicals are produced by laser photolysis of appropriate precursors. For reactant vibrational excitation stimulated Raman techniques are being developed and implemented.

  4. Silyl Ketene Acetals/B(C₆F₅)₃ Lewis Pair-Catalyzed Living Group Transfer Polymerization of Renewable Cyclic Acrylic Monomers.

    Science.gov (United States)

    Hu, Lu; Zhao, Wuchao; He, Jianghua; Zhang, Yuetao

    2018-03-15

    This work reveals the silyl ketene acetal (SKA)/B(C₆F₅)₃ Lewis pair-catalyzed room-temperature group transfer polymerization (GTP) of polar acrylic monomers, including methyl linear methacrylate (MMA), and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL) as well. The in situ NMR monitored reaction of SKA with B(C₆F₅)₃ indicated the formation of Frustrated Lewis Pairs (FLPs), although it is sluggish for MMA polymerization, such a FLP system exhibits highly activity and living GTP of MMBL and MBL. Detailed investigations, including the characterization of key reaction intermediates, polymerization kinetics and polymer structures have led to a polymerization mechanism, in which the polymerization is initiated with an intermolecular Michael addition of the ester enolate group of SKA to the vinyl group of B(C₆F₅)₃-activated monomer, while the silyl group is transferred to the carbonyl group of the B(C₆F₅)₃-activated monomer to generate the single-monomer-addition species or the active propagating species; the coordinated B(C₆F₅)₃ is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. Such neutral SKA analogues are the real active species for the polymerization and are retained in the whole process as confirmed by experimental data and the chain-end analysis by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS). Moreover, using this method, we have successfully synthesized well-defined PMMBL- b -PMBL, PMMBL- b -PMBL- b -PMMBL and random copolymers with the predicated molecular weights ( M n ) and narrow molecular weight distribution (MWD).

  5. Silyl Ketene Acetals/B(C6F53 Lewis Pair-Catalyzed Living Group Transfer Polymerization of Renewable Cyclic Acrylic Monomers

    Directory of Open Access Journals (Sweden)

    Lu Hu

    2018-03-01

    Full Text Available This work reveals the silyl ketene acetal (SKA/B(C6F53 Lewis pair-catalyzed room-temperature group transfer polymerization (GTP of polar acrylic monomers, including methyl linear methacrylate (MMA, and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL and α-methylene-γ-butyrolactone (MBL as well. The in situ NMR monitored reaction of SKA with B(C6F53 indicated the formation of Frustrated Lewis Pairs (FLPs, although it is sluggish for MMA polymerization, such a FLP system exhibits highly activity and living GTP of MMBL and MBL. Detailed investigations, including the characterization of key reaction intermediates, polymerization kinetics and polymer structures have led to a polymerization mechanism, in which the polymerization is initiated with an intermolecular Michael addition of the ester enolate group of SKA to the vinyl group of B(C6F53-activated monomer, while the silyl group is transferred to the carbonyl group of the B(C6F53-activated monomer to generate the single-monomer-addition species or the active propagating species; the coordinated B(C6F53 is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. Such neutral SKA analogues are the real active species for the polymerization and are retained in the whole process as confirmed by experimental data and the chain-end analysis by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS. Moreover, using this method, we have successfully synthesized well-defined PMMBL-b-PMBL, PMMBL-b-PMBL-b-PMMBL and random copolymers with the predicated molecular weights (Mn and narrow molecular weight distribution (MWD.

  6. Probing the pairing interaction through two-neutron transfer reactions

    Directory of Open Access Journals (Sweden)

    Margueron J.

    2012-12-01

    Full Text Available The treatment of the pairing interaction in mean-field-based models is addressed. In particular, the possibility to use pair transfers as A tool to better constrain this interaction is discussed. First, pairing inter-actions with various density dependencies (surface/volume mixing are used in the microscopic Hartree-Fock-Bogoliubov + quasiparticle random-phase approximation model to generate the form factors to be used in reaction calculations. Cross sections for (p,t two-neutron transfer reactions are calculated in the one-step zero-range distorted-wave Born approximation for some Tin isotopes and for incident proton energies from 15 to 35 MeV. Three different surface/volume mixings of A zero-range density-dependent pairing interaction are employed in the microscopic calculations and the sensitivity of the cross sections to the different mixings is analyzed. Differences among the three different theoretical predictions are found espacially for the nucleus 136Sn and they are more important at the incident proton energy of 15 MeV. We thus indicate (p,t two-neutron transfer reactions with very neutron-rich Sn isotopes and at proton energies around 15 MeV as good experimental cases where the surface/volume mixing of the pairing interaction may be probed. In the second part of the manuscript, ground-state to ground-state transitions are investigated. Approximations made to estimate two-nucleon transfer probabilities in ground-state to ground-state transitions and the physical interpretation of these probabilities are discussed. Probabilities are often calculated by approximating both ground states of the initial nucleus A and of the final nucleus A±2 by the same quasiparticle vacuum. We analyze two improvements of this approach. First, the effect of using two different ground states with average numbers of particles A and A±2 is quantified. Second, by using projection techniques, the role of particle number restoration is analyzed. Our analysis

  7. Transition metal catalyzed carbonylation reactions carbonylative activation of C-X bonds

    CERN Document Server

    Beller, Matthias

    2014-01-01

    This book provides students and researchers in organic synthesis with a detailed discussion of carbonylation from the basics through to applications. It discusses the past, present and future of carbonylation reactions.

  8. DNA-Catalyzed Henry Reaction in Pure Water and the Striking Influence of Organic Buffer Systems

    Directory of Open Access Journals (Sweden)

    Marleen Häring

    2015-03-01

    Full Text Available In this manuscript we report a critical evaluation of the ability of natural DNA to mediate the nitroaldol (Henry reaction at physiological temperature in pure water. Under these conditions, no background reaction took place (i.e., control experiment without DNA. Both heteroaromatic aldehydes (e.g., 2-pyridinecarboxaldehyde and aromatic aldehydes bearing strong or moderate electron-withdrawing groups reacted satisfactorily with nitromethane obeying first order kinetics and affording the corresponding β-nitroalcohols in good yields within 24 h. In contrast, aliphatic aldehydes and aromatic aldehydes having electron-donating groups either did not react or were poorly converted. Moreover, we discovered that a number of metal-free organic buffers efficiently promote the Henry reaction when they were used as reaction media without adding external catalysts. This constitutes an important observation because the influence of organic buffers in chemical processes has been traditionally underestimated.

  9. Metal-catalyzed double migratory cascade reactions of propargylic esters and phosphates.

    Science.gov (United States)

    Kazem Shiroodi, Roohollah; Gevorgyan, Vladimir

    2013-06-21

    Propargylic esters and phosphates are easily accessible substrates, which exhibit rich and tunable reactivities in the presence of transition metal catalysts. π-Acidic metals, mostly gold and platinum salts, activate these substrates for an initial 1,2- or 1,3-acyloxy and phosphatyloxy migration process to form reactive intermediates. These intermediates are able to undergo further cascade reactions leading to a variety of diverse structures. This tutorial review systematically introduces the double migratory reactions of propargylic esters and phosphates as a novel synthetic method, in which further cascade reaction of the reactive intermediate is accompanied by a second migration of a different group, thus offering a rapid route to a wide range of functionalized products. The serendipitous observations, as well as designed approaches involving the double migratory cascade reactions, will be discussed with emphasis placed on the mechanistic aspects and the synthetic utilities of the obtained products.

  10. The Acid Catalyzed Reaction of α-Pinene Over Y-Zeolite

    Directory of Open Access Journals (Sweden)

    Nanik Wijayati

    2013-05-01

    Full Text Available The hydration of α-pinene has been studied in the presence of Y-zeolite (Si/Al = 2.89 as a solid acid catalyst. The reaction was performed in batch reactor in isopropyl alcohol at various temperature and reaction time with magnetic stirrer. The acid catalyst hydration reaction of a-pinene yields a complex mixture of monoterpenes, alcohols and hydrocarbons. The selectivity of α-terpineol (the monocyclic alcohol as main product was 59.20% with a conversion of 83.83% and the non alcoholic as the isomerization co-product as 30% after 60 min at 65 °C. The conversion and selectivity to α-terpineol increase significantly with in increase in temperature and reaction times.

  11. Asymmetric Glyoxylate-Ene Reactions Catalyzed by Chiral Pd(II Complexes in the Ionic Liquid [bmim][PF6

    Directory of Open Access Journals (Sweden)

    Nan Sun

    2007-06-01

    Full Text Available The room temperature ionic liquid [bmim][PF6] was employed as the reactionmedium in the asymmetric glyoxylate-ene reaction of α-methyl styrene (4a with ethylglyoxylate using chiral palladium(II complexes as the catalysts. [Pd(S-BINAP(3,5-CF3-PhCN2](SbF62 (1b showed the highest catalytic activity. Under the reaction conditionsof 40 oC, 0.5 h, and 1b/4a molar ratio of 0.05, ethyl α-hydroxy-4-phenyl-4-pentenoate wasobtained in excellent chemical yield (94 % with high enantioselectivity (70 %. Otherα-hydroxy esters can also be obtained in high chemical yields and enantioselectitiesthrough the glyoxylate-ene reactions of alkenes with glyoxylates catalyzed by 1b in[bmim][PF6]. Moreover, the ionic liquid [bmim][PF6] which contained the palladium(IIcomplex could be recycled and reused several times without significant loss of the catalyticactivity.

  12. DFT Methods to Study the Reaction Mechanism of Iridium-Catalyzed Hydrogenation of Olefins: Which Functional Should be Chosen?

    Science.gov (United States)

    Sun, Yihua; Chen, Hui

    2016-01-04

    To enable the selection of more accurate computational methods for the future theoretical exploration of the reaction mechanism of Ir-catalyzed olefin hydrogenation, we compared high-level ab initio coupled cluster and DFT calculations with a simplified model of Pfaltz's Ir/P,N-type catalyst for all four previously proposed Ir(I) /Ir(III) and Ir(III) /Ir(V) mechanisms. Through the systematic assessment of the DFT performances, the DFT empirical dispersion correction (DFT-D3) is found to be indispensable for improving the accuracy of relative energies between the Ir(I) /Ir(III) and Ir(III) /Ir(V) mechanisms. After including the DFT-D3 correction, the three best performing density functionals (DFs) are B2-PLYP, BP86, and TPSSh. In these recommended DFs, the computationally more expensive double-hybrid functional B2-PLYP-D3 has a balanced and outstanding performance for calculations of the reaction barriers, reaction energies, and energy gaps between different mechanisms, whereas the less costly BP86-D3 and TPSSh-D3 methods have outstanding, but relatively less uniform performances. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Recent progress in transition-metal-catalyzed reduction of molecular dinitrogen under ambient reaction conditions.

    Science.gov (United States)

    Nishibayashi, Yoshiaki

    2015-10-05

    This paper describes our recent progress in catalytic nitrogen fixation by using transition-metal-dinitrogen complexes as catalysts. Two reaction systems for the catalytic transformation of molecular dinitrogen into ammonia and its equivalent such as silylamine under ambient reaction conditions have been achieved by the molybdenum-, iron-, and cobalt-dinitrogen complexes as catalysts. Many new findings presented here may provide new access to the development of economical nitrogen fixation in place of the Haber-Bosch process.

  14. Pd(II/HPMoV-Catalyzed Direct Oxidative Coupling Reaction of Benzenes with Olefins

    Directory of Open Access Journals (Sweden)

    Yasutaka Ishii

    2010-03-01

    Full Text Available The direct aerobic coupling reaction of arenes with olefins was successfully achieved by the use of Pd(OAc2/molybdovanadophosphoric acid (HPMoV as a key catalyst under 1 atm of dioxygen. This catalytic system could be extended to the coupling reaction of various substituted benzenes with olefins such as acrylates, aclrolein, and ethylene through the direct aromatic C-H bond activation.

  15. Direct Asymmetric Vinylogous and Bisvinylogous Mannich-Type Reaction Catalyzed by a Copper(I) Complex.

    Science.gov (United States)

    Zhang, Hai-Jun; Shi, Chang-Yun; Zhong, Feng; Yin, Liang

    2017-02-15

    A direct catalytic asymmetric vinylogous Mannich-type reaction has been disclosed in good yield, excellent regio-, diastereo- and enantioselectivity. The key to control the regioselectivity is the combination of a bulky N-acylpyrazole and a bulky bisphosphine ligand. The catalytic system was extended to a bisvinylogous Mannich-type reaction by changing the ligand. The synthetic utility of the vinylogous products was demonstrated by several transformations.

  16. Laboratory Studies of Hydrogen Gas Generation Using the Cobalt Chloride Catalyzed Sodium Borohydride-Water Reaction

    Science.gov (United States)

    2015-07-01

    used. We believe that the chloramine in tap water and dissolved organics in seawater form complexes with the catalyst impeding its ability to...resulted in a very viscous sludge due to the precipitation of NaBO2 hydrate crystals, foaming, and reaction temperatures approaching 90 °C. We used...laced a hose connected to the outlet of the reaction vessel inside the cylinder from the bottom . As hydrogen gas is generated, it bubbles inside the

  17. Measuring one nucleon transfer reaction 24Mg( p, d)23Mg for astrophysical reaction rates

    Science.gov (United States)

    Lee, E. J.; Chae, K. Y.

    2017-12-01

    The level structure of a radionuclide 23Mg has been studied by using the 24Mg( p, d)23Mg one nucleon transfer reaction measurement for the astrophysical 19Ne(α, γ)23Mg reaction rate. A 41 MeV proton beam was produced and accelerated at the 25 MV tandem accelerator of the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory in the United States. The beam particles impinged on an isotopically-enriched 24Mg solid target. Angular distributions of recoiling deuterons were extracted by using a large area silicon strip detector array. By comparing the experimentally-obtained angular distributions with zero range distorted wave Born approximation calculations, spins and parities of three energy levels of 23Mg could be constrained for the first time, which is very important information needed to understand the 19Ne(α, γ)23Mg reaction rate.

  18. Sonication effect on the reaction of 4-bromo-1-methylbenzene with sodium sulfide in liquid-liquid multi-site phase-transfer catalysis condition - kinetic study.

    Science.gov (United States)

    Abimannan, Pachaiyappan; Selvaraj, Varathan; Rajendran, Venugopal

    2015-03-01

    The synthesis of di-p-tolylsulfane from the reaction of 4-bromo-1-methylbenzene (BMB) with sodium sulfide was carried out using a multi-site phase-transfer catalyst (MPTC) viz., 1,4-dihexyl-1,4-diazoniabicyclo[2.2.2]octanium dibromide and ultrasonic irradiation in a liquid-liquid reaction condition. The overall reaction rate is greatly enhanced when catalyzed by multi-site phase-transfer catalyst (MPTC) combined with sonication (40 kHz, 300 W) in a batch reactor than catalyzed by MPTC without sonication. Effects on the reaction due to various operating conditions, such as agitation speed, different ultrasound frequencies, different phase-transfer catalysts, different organic solvents, the amount of MPTC, temperature, amount of sodium sulfide, effect of sodium hydroxide, volume of n-hexane and the concentration of 4-bromo-1-methylbenzene. The reaction obeys a pseudo first-order rate law and a suitable mechanism was proposed based on the experimental observation. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. DFT and AFIR Study on the Mechanism and the Origin of Enantioselectivity in Iron-Catalyzed Cross-Coupling Reactions.

    Science.gov (United States)

    Sharma, Akhilesh K; Sameera, W M C; Jin, Masayoshi; Adak, Laksmikanta; Okuzono, Chiemi; Iwamoto, Takahiro; Kato, Masako; Nakamura, Masaharu; Morokuma, Keiji

    2017-11-15

    The mechanism of the full catalytic cycle for Fe-chiral-bisphosphine-catalyzed cross-coupling reaction between alkyl halides and Grignard reagents (Nakamura and co-workers, J. Am. Chem. Soc. 2015, 137, 7128) was rationalized by using density functional theory (DFT) and multicomponent artificial force-induced reaction (MC-AFIR) methods. The computed mechanism consists of (a) C-Cl activation, (b) transmetalation, (c) C-Fe bond formation, and (d) C-C bond formation through reductive elimination. Our survey on the prereactant complexes suggested that formation of Fe II (BenzP*)Ph 2 and Fe I (BenzP*)Ph complexes are thermodynamically feasible. Fe I (BenzP*)Cl complex is the active intermediate for C-Cl activation. Fe II (BenzP*)Ph 2 complex can be formed if the concentration of Grignard reagent is high. However, it leads to biphenyl (byproduct) instead of the cross-coupling product. This explains why slow addition of Grignard reagent is critical for the cross-coupling reaction. The MC-AFIR method was used for systematic determination of transition states for C-Fe bond formation and C-C bond formation starting from the key intermediate Fe II (BenzP*)PhCl. According to our detailed analysis, C-C bond formation is the selectivity-determining step. The computed enantiomeric ratio of 95:5 is in good agreement with the experimental ratio (90:10). Energy decomposition analysis suggested that the origin of the enantioselectivity is the deformation of Ph-ligand in Fe-complex, which is induced by the bulky tert-butyl group of BenzP* ligand. Our study provides important mechanistic insights for the cross-coupling reaction between alkyl halides and Grignard reagents and guides the design of efficient Fe-based catalysts for cross-coupling reactions.

  20. Electrocatalysis of anodic and cathodic oxygen-transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Wels, B.R.

    1990-09-21

    The electrocatalysis of oxygen-transfer reactions is discussed in two parts. In Part I, the reduction of iodate (IO{sub 3}{sup {minus}}) is examined as an example of cathodic oxygen transfer. On oxide-covered Pt electrodes (PtO), a large cathodic current is observed in the presence of IO{sub 3}{sup {minus}} to coincide with the reduction of PtO. The total cathodic charge exceeds the amount required for reduction of PtO and IO{sub 3}{sup {minus}} to produce an adsorbed product. An electrocatalytic link between reduction of IO{sub 3}{sup {minus}} and reduction of PtO is indicated. In addition, on oxide-free Pt electrodes, the reduction of IO{sub 3}{sup {minus}} is determined to be sensitive to surface treatment. The electrocatalytic oxidation of CN{sup {minus}} is presented as an example of anodic oxygen transfer in Part II. The voltametric response of CN{sup {minus}} is virtually nonexistent at PbO{sub 2} electrodes. The response is significantly improved by doping PbO{sub 2} with Cu. Cyanide is also oxidized effectively at CuO-film electrodes. Copper is concluded to serve as an adsorption site for CN{sup {minus}}. It is proposed that an oxygen tunneling mechanism comparable to electron tunneling does not occur at the electrode-solution interface. The adsorption of CN{sup {minus}} is therefore considered to be a necessary prerequisite for oxygen transfer. 201 refs., 23 figs., 2 tabs.

  1. 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.

  2. Catalyzed oxidation reactions. IV. Picolinic acid catalysis of chromic acid oxidations

    International Nuclear Information System (INIS)

    Rocek, J.; Peng, T.Y.

    1977-01-01

    Picolinic acid and several closely related acids are effective catalysts in the chromic acid oxidation of primary and secondary alcohols; the oxidation of other substrates is accelerated only moderately. The reaction is first order in chromium-(VI), alcohol, and picolinic acid; it is second order in hydrogen ions at low acidity and approaches acidity independence at high perchloric acid concentrations. A primary deuterium kinetic isotope effect is observed at high but not at low acidities. At low acidity the reaction has a considerably lower activation energy and more negative activation entropy than at higher acidities. The reactive intermediate in the proposed mechanism is a negatively charged termolecular complex formed from chromic acid, picolinic acid, and alcohol. The rate-limiting step of the reaction changes with the acidity of the solution. At higher acidities the intermediate termolecular complex is formed reversibly and the overall reaction rate is determined by the rate of its decomposition into reaction products; at low acidities the formation of the complex is irreversible and hence rate limiting. Picolinic acids with a substituent in the 6 position show a greatly reduced catalytic activity. This observation is interpreted as suggesting a square pyramidal or octahedral structure for the reactive chromium (VI) intermediate. The temperature dependence of the deuterium isotope effect has been determined and the significance of the observed large values for E/sub a//sup D/ - E/sub a//sup H/ and A/sup D//A/sup H/ is discussed

  3. Degradation of Anthraquinone Dye Reactive Blue 4 in Pyrite Ash Catalyzed Fenton Reaction

    Directory of Open Access Journals (Sweden)

    Milena Becelic-Tomin

    2014-01-01

    Full Text Available Pyrite ash (PA is created by burning pyrite in the chemical production of sulphuric acid. The high concentration of iron oxide, mostly hematite, present in pyrite ash, gives the basis for its application as a source of catalytic iron in a modified Fenton process for anthraquinone dye reactive blue 4 (RB4 degradation. The effect of various operating variables such as catalyst and oxidant concentration, initial pH and RB4 concentration on the abatement of total organic carbon, and dye has been assessed in this study. Here we show that degradation of RB4 in the modified Fenton reaction was efficient under the following conditions: pH=2.5; [PA]0=0.2 g L−1; [H2O2]0=5 mM and initial RB4 concentration up to 100 mg L−1. The pyrite ash Fenton reaction can overcome limitations observed from the classic Fenton reaction, such as the early termination of the Fenton reaction. Metal (Pb, Zn, and Cu content of the solution after the process suggests that an additional treatment step is necessary to remove the remaining metals from the water. These results provide basic knowledge to better understand the modified, heterogeneous Fenton process and apply the PA Fenton reaction for the treatment of wastewaters which contains anthraquinone dyes.

  4. Degradation of Anthraquinone Dye Reactive Blue 4 in Pyrite Ash Catalyzed Fenton Reaction

    Science.gov (United States)

    Becelic-Tomin, Milena; Dalmacija, Bozo; Rajic, Ljiljana; Tomasevic, Dragana; Kerkez, Djurdja; Watson, Malcolm; Prica, Miljana

    2014-01-01

    Pyrite ash (PA) is created by burning pyrite in the chemical production of sulphuric acid. The high concentration of iron oxide, mostly hematite, present in pyrite ash, gives the basis for its application as a source of catalytic iron in a modified Fenton process for anthraquinone dye reactive blue 4 (RB4) degradation. The effect of various operating variables such as catalyst and oxidant concentration, initial pH and RB4 concentration on the abatement of total organic carbon, and dye has been assessed in this study. Here we show that degradation of RB4 in the modified Fenton reaction was efficient under the following conditions: pH = 2.5; [PA]0 = 0.2 g L−1; [H2O2]0 = 5 mM and initial RB4 concentration up to 100 mg L−1. The pyrite ash Fenton reaction can overcome limitations observed from the classic Fenton reaction, such as the early termination of the Fenton reaction. Metal (Pb, Zn, and Cu) content of the solution after the process suggests that an additional treatment step is necessary to remove the remaining metals from the water. These results provide basic knowledge to better understand the modified, heterogeneous Fenton process and apply the PA Fenton reaction for the treatment of wastewaters which contains anthraquinone dyes. PMID:24526885

  5. Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

    Science.gov (United States)

    Basilevsky, M. V.; Odinokov, A. V.; Titov, S. V.; Mitina, E. A.

    2013-12-01

    The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ0 = ℏω0/kBT where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the

  6. Incremental Identification of Reaction and Mass-Transfer Kinetics Using the Concept of Extents

    OpenAIRE

    Bhatt, Nirav; Amrhein, Michael; Bonvin, Dominique

    2011-01-01

    This paper proposes a variation of the incremental approach to identify reaction and mass-transfer kinetics (rate expressions and the corresponding rate parameters) from concentration measurements for both homogeneous and gas-liquid reaction systems. This incremental approach proceeds in two steps: (i) computation of the extents of reaction and mass transfer from concentration measurements without explicit knowledge of the reaction and mass-transfer rate expressions, and (ii) estimation of ...

  7. [Mechanism of reaction catalyzed by RNA-ligase from bacteriophage T4].

    Science.gov (United States)

    Zagrebel'nyĭ, S N; Zernov, Iu P

    1987-01-01

    The dissociation constants of the complexes of RNA-ligase with acceptors, donors and the adenylylated donor A(5')ppAp have been determined on the basis of the inhibition of ATP-pyrophosphate exchange reaction. The dissociation constants of the complexes of the enzyme with "poor" acceptors (oligouridilates) have been shown to be slightly different from those with "good" acceptors (oligoadenylates). The dependence of the reaction velocity of the formation of ligation products on the concentration of acceptors (pA)4, (pU)4 and the adenylylated donor A(5)ppAp has been studied. On the basis of the data obtained the conclusion about the random addition mechanism has been drawn. The reaction takes place in the steady-state conditions in the case of (pA)4 and in the equilibrium conditions--in the case of (pU)4.

  8. Chemoselective Boron-Catalyzed Nucleophilic Activation of Carboxylic Acids for Mannich-Type Reactions.

    Science.gov (United States)

    Morita, Yuya; Yamamoto, Tomohiro; Nagai, Hideoki; Shimizu, Yohei; Kanai, Motomu

    2015-06-10

    The carboxyl group (COOH) is an omnipresent functional group in organic molecules, and its direct catalytic activation represents an attractive synthetic method. Herein, we describe the first example of a direct catalytic nucleophilic activation of carboxylic acids with BH3·SMe2, after which the acids are able to act as carbon nucleophiles, i.e. enolates, in Mannich-type reactions. This reaction proceeds with a mild organic base (DBU) and exhibits high levels of functional group tolerance. The boron catalyst is highly chemoselective toward the COOH group, even in the presence of other carbonyl moieties, such as amides, esters, or ketones. Furthermore, this catalytic method can be extended to highly enantioselective Mannich-type reactions by using a (R)-3,3'-I2-BINOL-substituted boron catalyst.

  9. Charged-particle transfer reactions and nuclear astrophysics problems

    International Nuclear Information System (INIS)

    Artemov, S.V.; Yarmukhamedov, R.; Yuldashev, B.S.; Burtebaev, N.; Duysebaev, A.; Kadyrzhanov, K.K.

    2002-01-01

    In the report a review of the recent results of calculation of the astrophysical S-factors S(E) for the D(α, γ) 6 Li, 3 He(α, γ) 7 Be, 7 Be(p, γ) 8 Be, 12,13 C(p, γ) 13, 14 N and 12 C(p,γ) 16 O* reactions at extremely low energies E, including value E=0 , performed within the framework of a new method taking into account the additional information about the nuclear vertex constant (Nc) (or the respective asymptotic normalization coefficient) are presented. The required values of Nc can be obtained from an analysis of measured differential cross-sections of proton and α-particle transfer reactions (for example A( 3 He,d)B, 6 Li(d, 6 Li)d, 6 Li(α, 6 Li)α, 12 C( 6 Li, d) 16 O* etc.). A comparative analysis between the results obtained by different authors is also done. Taking into account an important role of the NVC's values for the nuclear astrophysical A(p, γ)B and A(α, γ)B reactions, a possibility of obtaining the reliable NVC values for the virtual decay B→A+p and B→A+α from the analysis of differential cross sections both sub- and above-barrier A( 3 He, d) and A( 6,7 Li, 2,3 H)B reactions is discussed in detail. In this line the use the isochronous cyclotron U-150 M, the 'DC-60' heavy ion machine and electrostatic charge-exchanging accelerator UKP-2-1 of Institute of Nuclear Physics of National Nuclear Center of the Republic of Kazakhstan for carrying out the needed experiments is considered and the possibility of the obtained data application for the astrophysical interest is also discussed

  10. Electron transfer reactions of macrocyclic compounds of cobalt

    Energy Technology Data Exchange (ETDEWEB)

    Heckman, R.A.

    1978-08-01

    The kinetics and mechanisms of reduction of H/sub 2/O/sub 2/, Br/sub 2/, and I/sub 2/ by various macrocyclic tetraaza complexes of cobalt(II), including Vitamin B/sub 12r/, were studied. The synthetic macrocycles studied were all 14-membered rings which varied in the degree of unsaturation,substitution of methyl groups on the periphery of the ring, and substitution within the ring itself. Scavenging experiments demonstrated that the reductions of H/sub 2/O/sub 2/ produce free hydroxyl radicals only in the case of Co((14)ane)/sup 2 +/ but with none of the others. In the latter instances apparently H/sub 2/O/sub 2/ simultaneously oxidizes the metal center and the ligand. The reductions of Br/sub 2/ and I/sub 2/ produce an aquohalocobalt(III) product for all reductants (except B/sub 12r/ + Br/sub 2/, which was complicated by bromination of the corrin ring). The mechanism of halogen reduction was found to involve rate-limiting inner-sphere electron transfer from cobalt to halogen to produce a dihalide anion coordinated to the cobalt center. This intermediate subsequently decomposes in rapid reactions to halocobalt(III) and halogen atom species or reacts with another cobalt(II) center to give two molecules of halocobalt(III). The reductions of halomethylcobaloximes and related compounds and diamminecobaloxime by Cr/sup 2 +/ were also studied. The reaction was found to be biphasic in all cases with the reaction products being halomethane (for the halomethylcobaloximes), Co/sup 2 +/ (in less than 100 percent yield), a Cr(III)-dimethylglyoxime species, a small amount of free dmgH/sub 2/, and a highly-charged species containing both cobalt and chromium. The first-stage reaction occurs with a stoichiometry of 1:1 producing an intermediate with an absorption maximum at 460 nm for all starting reagents. The results were interpreted in terms of inner-sphere coordination of the cobaloxime to the Cr(II) and electron transfer through the oxime N-O bond.

  11. Uptake kinetics and biodistribution of C-14-D-luciferin-a radiolabeled substrate for the firefly luciferase catalyzed bioluminescence reaction : impact on bioluminescence based reporter gene imaging

    NARCIS (Netherlands)

    Berger, Frank; Paulmurugan, Ramasamy; Bhaumik, Srabani; Gambhir, Sanjiv Sam

    2008-01-01

    Purpose Firefly luciferase catalyzes the oxidative decarboxylation of D-luciferin to oxyluciferin in the presence of cofactors, producing bioluminescence. This reaction is used in optical bioluminescence-based molecular imaging approaches to detect the expression of the firefly luciferase reporter

  12. One-pot synthesis of 2H-pyrans by indium(III) chloride-catalyzed reactions. efficient synthesis of pyranocoumarins, pyranophenalenones, and pyranoquinolinones

    International Nuclear Information System (INIS)

    Lee, Yong Rok; Kim, Do Hoon; Shim, Jae Jin; Kim, Seog K.; Park, Jung Hag; Cha, Jin Soon; Lee, Chong Soon

    2002-01-01

    An efficient synthesis of 2H-pyrans is achieved by indium (III) chloride-catalyzed reactions of 1,3-dicarbonyl compounds with a variety of α.β-unsaturated aldehydes in moderates yields. This method has been applied to the synthesis of pyranocoumarins, pyranophenaleneones, and pyranoquinolinone alkaloids

  13. "N"-Heterocyclic Carbene-Catalyzed Reaction of Chalcone and Cinnamaldehyde to Give 1,3,4-Triphenylcyclopentene Using Organocatalysis to Form a Homoenolate Equivalent

    Science.gov (United States)

    Snider, Barry B.

    2015-01-01

    In this experiment, students carry out a modern organocatalytic reaction using IMes·HCl and NaOH to catalyze the formation of 1,3,4-triphenylcyclopentene from cinnamaldehyde and chalcone in water. Deprotonation of IMes·HCl with NaOH forms the "N"-heterocyclic carbene IMes that reacts with cinnamaldehyde to form a homoenolate equivalent…

  14. The Effect of Temperature on the Enzyme-Catalyzed Reaction: Insights from Thermodynamics

    Science.gov (United States)

    Aledo, Juan Carlos; Jimenez-Riveres, Susana; Tena, Manuel

    2010-01-01

    When teaching the effect of temperature on biochemical reactions, the problem is usually oversimplified by confining the thermal effect to the catalytic constant, which is identified with the rate constant of the elementary limiting step. Therefore, only positive values for activation energies and values greater than 1 for temperature coefficients…

  15. Inverted supercritical carbon dioxide/aqueous biphasic media for rhodium-catalyzed hydrogenation reactions.

    Science.gov (United States)

    Burgemeister, Katja; Franciò, Giancarlo; Gego, Volker H; Greiner, Lasse; Hugl, Herbert; Leitner, Walter

    2007-01-01

    An inverted supercritical carbon dioxide (scCO(2))/aqueous biphasic system has been used as reaction media for Rh-catalysed hydrogenation of polar substrates. Chiral and achiral CO(2)-philic catalysts were efficiently immobilised in scCO(2) as the stationary phase, while the polar substrates and products were contained in water as the mobile phase. Notably, product separation and catalyst recycling were conducted without depressurisation of the autoclave. The catalyst phase was reused several times with high conversion and product recovery of more than 85 %. Loss of rhodium and phosphorus by leaching were found to be below the detection limit after the first two cycles in the majority of repetitive experiments. The reaction conditions were optimised with a minimum of experiments by using a simplex algorithm in a sequential optimisation. Total turnover numbers (TTNs) of up to 1600, turnover frequencies (TOFs) of up to 340 h(-1) and ee's up to 99 % were obtained in repetitive batch operations. The scope of the devised catalytic system has been investigated and a semicontinuous reaction setup has been implemented. The chiral ligand (R,S)-3-H(2)F(6)-BINAPHOS allowed highly enantioselective hydrogenation of itaconic acid and methyl-2-acetamidoacrylate combined with a considerable catalyst stability in these reaction media.

  16. (SalenMn(III Catalyzed Asymmetric Epoxidation Reactions by Hydrogen Peroxide in Water: A Green Protocol

    Directory of Open Access Journals (Sweden)

    Francesco Paolo Ballistreri

    2016-07-01

    Full Text Available Enantioselective epoxidation reactions of some chosen reactive alkenes by a chiral Mn(III salen catalyst were performed in H2O employing H2O2 as oxidant and diethyltetradecylamine N-oxide (AOE-14 as surfactant. This procedure represents an environmentally benign protocol which leads to e.e. values ranging from good to excellent (up to 95%.

  17. Metal-catalyzed Asymmetric Hetero-Diels-Alder Reactions of Unactivated Dienes with Glyoxylates

    DEFF Research Database (Denmark)

    Johannsen, Mogens; Yao, Sulan; Graven, Anette

    1998-01-01

    The development of a catalytic asymmetric hetero-Diels-Alder methodology for the reaction of unactivated dienes with glyoxylates is presented. Several different asymmetric catalysts can be used, but copper-bisoxazolines and aluminium-BINOL give the highest yield, and the best chemo- and enantiose...

  18. RUTHENIUM-CATALYZED TANDEM OLEFIN MIGRATION-ALDOL AND MANNICH-TYPE REACTIONS IN IONIC LIQUID.

    Science.gov (United States)

    In the presence of a catalytic amount of RuCl2(PPh3)3, a cross-coupling of 3-buten-2-ol with aldehydes and imines was developed via a tandem olefin migration--aldol--Mannich reaction in bmim[PF6]. With In(OAc)3 as a co-catalyst, a-vinylbenzyl alcohol and aldehydes underwent sim...

  19. Chiral ammonium betaine-catalyzed asymmetric Mannich-type reaction of oxindoles.

    Science.gov (United States)

    Torii, Masahiro; Kato, Kohsuke; Uraguchi, Daisuke; Ooi, Takashi

    2016-01-01

    A highly diastereo- and enantioselective Mannich-type reaction of 3-aryloxindoles with N -Boc aldimines was achieved under the catalysis of axially chiral ammonium betaines. This catalytic method provides a new tool for the construction of consecutive quaternary and tertiary stereogenic carbon centers on biologically intriguing molecular frameworks with high fidelity.

  20. Highly Enantioselective Three-Component Direct Mannich Reactions of Unfunctionalized Ketones Catalyzed by Bifunctional Organocatalysts

    Science.gov (United States)

    Guo, Qunsheng; Zhao, John Cong-Gui

    2013-01-01

    A highly stereoselective three-component direct Mannich reaction between aromatic aldehydes, p-toluenesulfonamide, and unfunctionalized ketones was achieved through an enolate mechanism for the first time with a bifunctional quinidine thiourea catalyst. The corresponding N-tosylated β-aminoketones were obtained in high yields and excellent diastereo- and enantioselectivities (up to >99:1 dr and >99% ee). PMID:23343472

  1. Chiral ammonium betaine-catalyzed asymmetric Mannich-type reaction of oxindoles

    Directory of Open Access Journals (Sweden)

    Masahiro Torii

    2016-09-01

    Full Text Available A highly diastereo- and enantioselective Mannich-type reaction of 3-aryloxindoles with N-Boc aldimines was achieved under the catalysis of axially chiral ammonium betaines. This catalytic method provides a new tool for the construction of consecutive quaternary and tertiary stereogenic carbon centers on biologically intriguing molecular frameworks with high fidelity.

  2. A programmable soft chemo-mechanical actuator exploiting a catalyzed photochemical water-oxidation reaction.

    Science.gov (United States)

    Yuan, P; McCracken, J M; Gross, D E; Braun, P V; Moore, J S; Nuzzo, R G

    2017-10-18

    We describe a composite hydrogel containing an embedding coupled chemistry for light-sensitized catalytic reactions that enables chemo-mechanical actuation of poly(acrylic acid)-based gels. In these materials, a photosensitizer and catalyst-ruthenium trisbipyridine and iridium dioxide nanoparticles, respectively-are incorporated into the hydrogel where together, with visible light irradiation, they undergo a catalytic water-oxidation reaction that lowers the pH and induces a dissipative/chemically-driven strain change in the gel. To demonstrate the capacity for 3D chemo-mechanical actuation, a layer of non-pH responsive poly(2-hydroxyethyl methacrylate) is added to the photo-active composite gel to create a model bimorph actuator. Triggering and terminating the water-oxidation reaction leads to a programmatic expansion and contraction of the active layer, which induces different modes of biomimetic curling motions in the bimorph actuator in light and dark environments. The efficiency of this system is fundamentally limited by the system-level design, which provides no capacity to sustain a local pH gradient against diffusive mixing. Even so, if the initial pH of the background solution is reestablished either actively or passively between each reaction cycle, it is possible to realize multiple cycles of reversible actuation. We describe a thermodynamic analysis of this system which identifies specific features mediating efficiency losses and conceptual requirements for mesoscopic design rules for optimization of this system and for advancing soft actuation systems in general.

  3. Mass transfer in porous media with heterogeneous chemical reaction

    Directory of Open Access Journals (Sweden)

    Souza S.M.A.G.Ulson de

    2003-01-01

    Full Text Available In this paper, the modeling of the mass transfer process in packed-bed reactors is presented and takes into account dispersion in the main fluid phase, internal diffusion of the reactant in the pores of the catalyst, and surface reaction inside the catalyst. The method of volume averaging is applied to obtain the governing equation for use on a small scale. The local mass equilibrium is assumed for obtaining the one-equation model for use on a large scale. The closure problems are developed subject to the length-scale constraints and the model of a spatially periodic porous medium. The expressions for effective diffusivity, hydrodynamic dispersion, total dispersion and the Darcy's law permeability tensors are presented. Solution of the set of final equations permits the variations of velocity and concentration of the chemical species along the packed-bed reactors to be obtained.

  4. Membrane introduction proton-transfer-reaction mass spectrometry

    International Nuclear Information System (INIS)

    Alexander, M.; Boscaini, E.; Maerk, T.; Lindinger, W.

    2002-01-01

    Proton-transfer-reaction mass spectrometry (PTR-MS) is a rapidly expanding field with multiple applications in ion physics, atmospheric chemistry, food chemistry, volatile organic compounds monitoring and biology. Initial studies that combine PTR-MS and membrane introduction mass spectrometry (MIMS) were researched and outlined. First using PTR-MS, certain fundamental physical properties of a poly-dimethylsiloxane (PDMS) membrane including solubilities and diffusion coefficients were measured. Second, it was shown how the chemical selectivity of the (PDMS) can be used to extend the capabilities of the PTR-MS instrument by eliminating certain isobaric interferences and excluding water from volatile organic compounds (VOCs). Experiments with mixtures of several VOCs (toluene, benzene, acetone, propanal, methanol) are presented. (nevyjel)

  5. A practical and green approach toward synthesis of N3-substituted dihydropyrimidinones: using Aza-Michael addition reaction catalyzed by KF/Al2O3.

    Science.gov (United States)

    Wang, Xicun; Quan, Zhengjun; Wang, Jun-Ke; Zhang, Zhang; Wang, Mangang

    2006-09-01

    A simple and efficient method for the synthesis of N3-substituted 3,4-dihydropyrimidinones by aza-Michael addition reactions of 3,4-dihydropyrimidinones to alpha,beta-ethylenic compounds catalyzed by KF/Al(2)O(3) is described. The advantage of this method is high regioselectivity, high purity, and the use of a cheaper, milder, and efficient catalyst for the hetero-Michael addition reaction.

  6. Nickel-catalyzed Suzuki-Miyaura type cross-coupling reactions of (2,2-difluorovinyl)benzene derivatives with arylboronic acids.

    Science.gov (United States)

    Xiong, Yang; Huang, Tao; Ji, Xinfei; Wu, Jingjing; Cao, Song

    2015-07-21

    An unprecedented highly stereoselective example of nickel-catalyzed Suzuki-Miyaura type cross-coupling reactions of (2,2-difluorovinyl)benzene derivatives with arylboronic acids was developed. The reaction proceeded efficiently in the presence of 5 mol% NiCl2(PCy3)2 and K3PO4, affording the Z-fluorostyrene derivatives in good to high yields with excellent regioselectivity.

  7. Palladium-catalyzed intramolecular asymmetric C-H functionalization/cyclization reaction of metallocenes: an efficient approach toward the synthesis of planar chiral metallocene compounds.

    Science.gov (United States)

    Deng, Ruixian; Huang, Yunze; Ma, Xinna; Li, Gencheng; Zhu, Rui; Wang, Bin; Kang, Yan-Biao; Gu, Zhenhua

    2014-03-26

    A palladium-catalyzed asymmetric synthesis of planar chiral metallocene compounds is reported. The reaction stereoselectively functionalized one of the ortho C-H bonds of Cp rings by intramolecular cyclization to form indenone derivatives in high yields with excellent enantioselectivity. The mild set of reaction conditions allowed a wide variety of chiral metallocene compounds to be synthesized with broad functional group tolerance. The influences of preinstalled chiralities on the other Cp-ring were also investigated.

  8. Brønsted acid catalyzed regioselective aza-Ferrier reaction : A novel synthetic method of α-(N-Boc-2-pyrrolidinyl)aldehydes

    OpenAIRE

    Tayama, Eiji; Otoyama, Seijun; Isaka, Wataru

    2008-01-01

    The 1,4-elimination reaction of (Z)-N-Boc-2-(4-methoxy-2-alkenyloxy)pyrrolidines (1) is shown to proceed with high (1E,3E)-stereoselectivity to afford N-Boc-2-(1,3-dienyloxy)pyrrolidines (2); the Bronsted acid catalyzed aza-Ferrier reaction of the N-Boc-2-(1,3-dienyloxy)pyrrolidines (2) provides a-(N-Boc-2-pyrrolidinyl) aldehydes (3) in excellent yields with high a-regioselectivities.

  9. Enzymatic Synthesis and Structural Characterization of Theanderose through Transfructosylation Reaction Catalyzed by Levansucrase from Bacillus subtilis CECT 39.

    Science.gov (United States)

    Ruiz-Aceituno, Laura; Sanz, Maria Luz; de Las Rivas, Blanca; Muñoz, Rosario; Kolida, Sofia; Jimeno, Maria Luisa; Moreno, F Javier

    2017-12-06

    This work addresses the high-yield and fast enzymatic production of theanderose, a naturally occurring carbohydrate, also known as isomaltosucrose, whose chemical structure determined by NMR is α-d-glucopyranosyl-(1 → 6)-α-d-glucopyranosyl-(1 → 2)-β-d-fructofuranose. The ability of isomaltose to act as an acceptor in the Bacillus subtilis CECT 39 levansucrase-catalyzed transfructosylation reaction to efficiently produce theanderose in the presence of sucrose as a donor is described by using four different sucrose:isomaltose concentration ratios. The maximum theanderose concentration ranged from 122.4 to 130.4 g L -1 , was obtained after only 1 h and at a moderate temperature (37 °C), leading to high productivity (109.7-130.4 g L -1 h -1 ) and yield (up to 37.3%) values. The enzymatic synthesis was highly regiospecific, since no other detectable acceptor reaction products were formed. The development of efficient and cost-effective procedures for the biosynthesis of unexplored but appealing oligosaccharides as potential sweeteners, such as theanderose, could help to expand its potential applications which are currently limited by their low availability.

  10. A Phase Transfer Catalyzed Permanganate Oxidation: Preparation of Vanillin from Isoeugenol Acetate.

    Science.gov (United States)

    Lampman, Gary M.; Sharpe, Steven D.

    1983-01-01

    Background information, laboratory procedures, and results are provided for the preparation of vanillin from isoeugenol acetate. Reaction scheme used to prepare the vanillin and a table indicating the different oxidation experiments carried out on isoeugenol or isoeugenol acetate are also provided. (JN)

  11. Photoexcited chemical wave in the ruthenium-catalyzed Belousov-Zhabotinsky reaction.

    Science.gov (United States)

    Nakata, Satoshi; Matsushita, Mariko; Sato, Taisuke; Suematsu, Nobuhiko J; Kitahata, Hiroyuki; Amemiya, Takashi; Mori, Yoshihito

    2011-07-07

    The excitation of the photosensitive Belousov-Zhabotinsky (BZ) reaction induced by light stimulation was systematically investigated. A stepwise increase in the light intensity induced the excitation, whereas a stepwise decrease did not induce the excitation. The threshold values for the excitation were found to be a function of the initial and final light intensities, time variation in light intensity, and the concentration of NaBrO(3). The experimental results were qualitatively reproduced by a theoretical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that although the steady light irradiation is known to inhibit oscillation and chemical waves in the BZ system under almost all conditions, the stepwise increase in the light irradiation leads to the rapid production of an activator, resulting in the photoexcitation.

  12. Synthesis of L-Ascorbyl Flurbiprofenate by Lipase-Catalyzed Esterification and Transesterification Reactions

    OpenAIRE

    Xin, Jia-ying; Sun, Li-rui; Chen, Shu-ming; Wang, Yan; Xia, Chun-gu

    2017-01-01

    The synthesis of L-ascorbyl flurbiprofenate was achieved by esterification and transesterification in nonaqueous organic medium with Novozym 435 lipase as biocatalyst. The conversion was greatly influenced by the kinds of organic solvents, speed of agitation, catalyst loading amount, reaction time, and molar ratio of acyl donor to L-ascorbic acid. A series of solvents were investigated, and tert-butanol was found to be the most suitable from the standpoint of the substrate solubility and the ...

  13. Chiral Phosphoric Acid Catalyzed Diastereo- and Enantioselective Mannich-Type Reaction between Enamides and Thiazolones.

    Science.gov (United States)

    Kikuchi, Jun; Momiyama, Norie; Terada, Masahiro

    2016-06-03

    An enantioselective Mannich-type reaction between enamides, serving as aliphatic imine equivalents, and thiazolones or an azlactone, serving as α-amino acid derived pronucleophiles, was investigated using a chiral phosphoric acid catalyst. By using thiazolones, Mannich adducts with a tetrasubstituted chiral carbon center at the α-position and an aliphatic substituent at the β-position were efficiently obtained with high diastereo- and enantioselectivities.

  14. Multinucleon transfer in the 136Xe+208Pb reaction

    Science.gov (United States)

    Li, Cheng; Zhang, Fan; Li, Jingjing; Zhu, Long; Tian, Junlong; Wang, Ning; Zhang, Feng-Shou

    2016-01-01

    The dynamic mechanics in the multinucleon transfer reaction 136Xe+208Pb at an incident energy of Ec .m .=450 MeV is investigated by using the improved quantum molecular dynamics model (ImQMD). The lifetime of the neck directly influences the nucleon exchange and energy dissipation between the projectile and the target. The total-kinetic-energy-mass distributions and excitation energy division of primary binary fragments and the mass distributions of primary fragments at different impact parameters are calculated. The thermal equilibrium between two reaction partners has been observed at the lifetime of a neck larger than 480 fm /c . By using the statistical decay code gemini to describe the de-excitation process of the primary fragments, the isotope production cross sections from Pt to At are compared with the prediction by the dinuclear system and GRAZING model. The calculations indicate that the GRAZING model is suitable for estimating the isotope production cross sections only for Δ Z =-1 to +2; the DNS + gemini calculations underestimate the cross sections in the neutron-rich and neutron-deficient regions; and the ImQMD + gemini calculations give reasonable predictions of the isotope production cross sections for Δ Z =-3 to 0.

  15. Computational Characterization of the Origin of Selectivity in Cycloaddition Reactions Catalyzed by Phosphoric Acid Derivatives.

    Science.gov (United States)

    Liu, Chunhui; Besora, Maria; Maseras, Feliu

    2016-02-04

    The mechanism of the organocatalyzed [4+2] cycloaddition of ο-hydroxybenzaldimines to 2,3-dihydro-2 H-furan (DHF) to form furanobenzopyrans has been investigated by using computational methods. Experiments have shown that this reaction produces different products (trans-fused or cis-fused) if different phosphoric acid derivatives are applied. Our study shows the reaction proceeds through a mechanism in which the imine re-arranges into an amine, which subsequently reacts with DHF with mediation from the catalyst. The rate-limiting step in this process is the formation of two new bonds, which is also the key step in determining the reaction selectivity. The selectivity is controlled by a balance of noncovalent interactions between the catalyst and the substrates. The discriminating factor between the two catalysts is the presence of a triflyl substituent on one of catalysts, which constraints the relative orientations of the substrates. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. E- and Z-Selective Transfer Semihydrogenation of Alkynes Catalyzed by Standard Ruthenium Olefin Metathesis Catalysts.

    Science.gov (United States)

    Kusy, Rafał; Grela, Karol

    2016-12-02

    Selective transfer semihydrogenation of alkynes to yield alkenes was achieved with commercial first and second generation Hoveyda-Grubbs catalysts and formic acid as a hydrogen donor. This catalytic system is distinguished by its selectivity and compatibility with many functional groups (halogens, cyano, nitro, sulfide, alkenes). The metathetic activity of the ruthenium catalysts may be utilized in tandem sequences of olefin metathesis plus alkyne reduction.

  17. Structural requirements and reaction pathways in dimethyl ether combustion catalyzed by supported Pt clusters.

    Science.gov (United States)

    Ishikawa, Akio; Neurock, Matthew; Iglesia, Enrique

    2007-10-31

    The identity and reversibility of the elementary steps required for catalytic combustion of dimethyl ether (DME) on Pt clusters were determined by combining isotopic and kinetic analyses with density functional theory estimates of reaction energies and activation barriers to probe the lowest energy paths. Reaction rates are limited by C-H bond activation in DME molecules adsorbed on surfaces of Pt clusters containing chemisorbed oxygen atoms at near-saturation coverages. Reaction energies and activation barriers for C-H bond activation in DME to form methoxymethyl and hydroxyl surface intermediates show that this step is more favorable than the activation of C-O bonds to form two methoxides, consistent with measured rates and kinetic isotope effects. This kinetic preference is driven by the greater stability of the CH3OCH2* and OH* intermediates relative to chemisorbed methoxides. Experimental activation barriers on Pt clusters agree with density functional theory (DFT)-derived barriers on oxygen-covered Pt(111). Measured DME turnover rates increased with increasing DME pressure, but decreased as the O2 pressure increased, because vacancies (*) on Pt surfaces nearly saturated with chemisorbed oxygen are required for DME chemisorption. DFT calculations show that although these surface vacancies are required, higher oxygen coverages lead to lower C-H activation barriers, because the basicity of oxygen adatoms increases with coverage and they become more effective in hydrogen abstraction from DME. Water inhibits reaction rates via quasi-equilibrated adsorption on vacancy sites, consistent with DFT results indicating that water binds more strongly than DME on vacancies. These conclusions are consistent with the measured kinetic response of combustion rates to DME, O2, and H2O, with H/D kinetic isotope effects, and with the absence of isotopic scrambling in reactants containing isotopic mixtures of 18O2-16O2 or 12CH3O12CH3-13CH3O13CH3. Turnover rates increased with Pt

  18. How low does iron go? Chasing the active species in fe-catalyzed cross-coupling reactions.

    Science.gov (United States)

    Bedford, Robin B

    2015-05-19

    The catalytic cross-coupling reactions of organic halides or related substrates with organometallic nucleophiles form the cornerstone of many carbon-carbon bond-forming processes. While palladium-based catalysts typically mediate such reactions, there are increasing concerns about the long-term sustainability of palladium in synthesis. This is due to the high cost of palladium, coupled with its low natural abundance, environmentally deleterious extraction (∼6 g of metal are produced per ton of ore), toxicity, and competition for its use from the automotive and consumer electronics sectors. Therefore, there is a growing interest in replacing palladium-based catalysts with those incorporating more earth-abundant elements. With its low cost, high natural abundance, and low toxicity, iron makes a particularly appealing alternative, and accordingly, the development of iron-catalyzed cross-coupling is undergoing explosive growth. However, our understanding of the mechanisms that underpin the iron-based catalytic cycles is still very much in its infancy. Mechanistic insight into catalytic reactions is not only academically important but also allows us to maximize the efficiency of processes or even to develop entirely new transformations. Key to the development of robust mechanistic models for cross-coupling is knowing the lowest oxidation state in the cycle. Once this is established, we can explore subsequent redox processes and build the catalytic manifold. Until we know with confidence what the lowest oxidation state is, any cycles proposed are largely just guesswork. To date, Fe(-II), Fe(-I), Fe(0), Fe(I), and Fe(II) have been proposed as contenders for the lowest-oxidation-state species in the cycle in iron-catalyzed cross-coupling; the aim of this Account is to pull together the various pieces of evidence in support, or otherwise, of each of these suggestions in turn. There currently exists no direct evidence that oxidation states below Fe(0) are active in the

  19. An Alternative Reaction Pathway for Iridium Catalyzed Water Oxidation Driven by CAN

    KAUST Repository

    Bucci, Alberto

    2016-06-10

    The generation of solar fuels by means of a photosynthetic apparatus strongly relies on the development of an efficient water oxidation catalyst (WOC). Cerium ammonium nitrate (CAN) is the most commonly used sacrificial oxidant to explore the potentiality of WOCs. It is usually assumed that CAN has the unique role to oxidatively energize WOCs, making them capable to offer a low energy reaction pathway to transform H2O to O2. Herein we show that CAN might have a much more relevant and direct role in WO, mainly related to the capture and liberation of O–O containing molecular moieties.

  20. Linear Polystyrene-Stabilized PdO Nanoparticle-Catalyzed Mizoroki-Heck Reactions in Water

    Directory of Open Access Journals (Sweden)

    Takuto Teratani

    2011-10-01

    Full Text Available Linear polystyrene-stabilized PdO nanoparticles (PS-PdONPs were prepared by thermal decomposition of Pd(OAc2 in the presence of polystyrene. X-ray diffraction (XRD and transmission electron microscopy (TEM indicated the production of PdO nanoparticles. The loading of palladium was determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES. PS-PdONPs exhibited high catalytic activity for Mizoroki-Heck reactions under air in water and could be recycled without loss of activity.

  1. Three-Component Asymmetric Mannich Reaction Catalyzed by a Lewis Acid with Rhodium-Centered Chirality.

    Science.gov (United States)

    Feng, Lihe; Dai, Xuemei; Meggers, Eric; Gong, Lei

    2017-05-04

    A highly efficient direct asymmetric three-component Mannich reaction of an N-acylpyrazole, an aldehyde and a primary or secondary amine, was enabled by a rhodium-based Lewis-acid catalyst with metal-centered chirality. Excellent enantioselectivities were achieved for a variety of substrates at a typical catalyst loading of merely 0.5 mol % (23 examples, up to 98 % ee). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Universal, colorimetric microRNA detection strategy based on target-catalyzed toehold-mediated strand displacement reaction

    Science.gov (United States)

    Park, Yeonkyung; Lee, Chang Yeol; Kang, Shinyoung; Kim, Hansol; Park, Ki Soo; Park, Hyun Gyu

    2018-02-01

    In this work, we developed a novel, label-free, and enzyme-free strategy for the colorimetric detection of microRNA (miRNA), which relies on a target-catalyzed toehold-mediated strand displacement (TMSD) reaction. The system employs a detection probe that specifically binds to the target miRNA and sequentially releases a catalyst strand (CS) intended to trigger the subsequent TMSD reaction. Thus, the presence of target miRNA releases the CS that mediates the formation of an active G-quadruplex DNAzyme which is initially caged and inactivated by a blocker strand. In addition, a fuel strand that is supplemented for the recycling of the CS promotes another TMSD reaction, consequently generating a large number of active G-quadruplex DNAzymes. As a result, a distinct colorimetric signal is produced by the ABTS oxidation promoted by the peroxidase mimicking activity of the released G-quadruplex DNAzymes. Based on this novel strategy, we successfully detected miR-141, a promising biomarker for human prostate cancer, with high selectivity. The diagnostic capability of this system was also demonstrated by reliably determining target miR-141 in human serum, showing its great potential towards real clinical applications. Importantly, the proposed approach is composed of separate target recognition and signal transduction modules. Thus, it could be extended to analyze different target miRNAs by simply redesigning the detection probe while keeping the same signal transduction module as a universal signal amplification unit, which was successfully demonstrated by analyzing another target miRNA, let-7d.

  3. Monitoring enzyme-catalyzed reactions in micromachined nanoliter wells using a conventional microscope-based microarray reader

    Science.gov (United States)

    van den Doel, L. Richard; Moerman, R.; van Dedem, G. W. K.; Young, Ian T.; van Vliet, Lucas J.

    2002-06-01

    Yeast-Saccharomyces cerevisiae - it widely used as a model system for other higher eukaryotes, including man. One of the basic fermentation processes in yeast is the glycolytic pathway, which is the conversion of glucose to ethanol and carbon dioxide. This pathway consists of 12 enzyme-catalyzed reactions. With the approach of microarray technology we want to explore the metabolic regulation of this pathway in yeast. This paper will focus on the design of a conventional microscope based microarray reader, which is used to monitor these enzymatic reactions in microarrays. These microarrays are fabricated in silicon and have sizes of 300 by 300 micrometers 2. The depth varies from 20 to 50 micrometers . Enzyme activity levels can be derived by monitoring the production or consumption rate of NAD(P)H, which is excited at 360nm and emits around 450nm. This fluorophore is involved in all 12 reactions of the pathway. The microarray reader is equipped with a back-illuminated CCD camera in order to obtain a high quantum efficiency for the lower wavelengths. The dynamic range of our microarray reader varies form 5(mu) Molar to 1mMolar NAD(P)H. With this microarray reader enzyme activity levels down to 0.01 unit per milliliter can be monitored. The acquisition time per well is 0.1s. The total scan cycle time for a 5 X 5 microarray is less than half a minute. The number of cycles for a proper estimation of the enzyme activity is inversely proportional to the enzyme activity: long measurement times are needed to determine low enzyme activity levels.

  4. A chemically modified lipase preparation for catalyzing the transesterification reaction in even highly polar organic solvents.

    Science.gov (United States)

    Solanki, Kusum; Gupta, Munishwar Nath

    2011-05-15

    Acylation of Pseudomonas cepacia lipase with Pyromellitic dianhydride to modify 72% of total amino groups was carried out. Different organic solvents were screened for precipitation of modified lipase. It was found that 1,2-dimethoxyethane was the best precipitant which precipitated 97% protein and complete activity. PCMC (protein coated microcrystals), CLPCMC (crosslinked protein coated microcrystals), EPROS (enzyme precipitated and rinsed with organic solvents) and pH tuned preparations of modified and unmodified lipase were prepared and used for carrying out transesterification reaction with n-octane and dimethyl formamide (DMF) as reaction medium. In n-octane, among all the preparations, CLPCMC of modified lipase gave highest rate (1970 nmol min(-1)mg(-1)) as compared to unmodified pH tuned lipase (128 nmol min(-1) mg(-1)). In DMF, with both 1% (v/v) and 5% (v/v) water content, CLPCMC showed highest initial rate of 0.72 and 7.2 nmol min(-1) mg(-1), respectively. Unmodified pH tuned lipase showed no activity at all in DMF with both 1% and 5% (v/v) water content. Copyright © 2011 Elsevier Ltd. All rights reserved.

  5. Asymmetric effect of mechanical stress on the forward and reverse reaction catalyzed by an enzyme.

    Directory of Open Access Journals (Sweden)

    Collin Joseph

    Full Text Available The concept of modulating enzymatic activity by exerting a mechanical stress on the enzyme has been established in previous work. Mechanical perturbation is also a tool for probing conformational motion accompanying the enzymatic cycle. Here we report measurements of the forward and reverse kinetics of the enzyme Guanylate Kinase from yeast (Saccharomyces cerevisiae. The enzyme is held in a state of stress using the DNA spring method. The observation that mechanical stress has different effects on the forward and reverse reaction kinetics suggests that forward and reverse reactions follow different paths, on average, in the enzyme's conformational space. Comparing the kinetics of the stressed and unstressed enzyme we also show that the maximum speed of the enzyme is comparable to the predictions of the relaxation model of enzyme action, where we use the independently determined dissipation coefficient [Formula: see text] for the enzyme's conformational motion. The present experiments provide a mean to explore enzyme kinetics beyond the static energy landscape picture of transition state theory.

  6. Coupling Reactions of Carbon Dioxide with Epoxides Catalyzed by Vanadium Aminophenolate Complexes.

    Science.gov (United States)

    Elkurtehi, Ali I; Kerton, Francesca M

    2017-03-22

    A series of vanadium compounds supported by tetradentate aminobis(phenolate) ligands were screened for catalytic reactivity in the reaction of propylene oxide (PO) with CO 2 : [VO(OMe)(O 2 NO BuMeMeth )], [VO(OMe)(ON 2 O BuMe )], [VO(OMe)(O 2 NN BuBuPy )], and [VO(OMe)(O 2 NO BuBuFurf )]. They showed similar reactivities, but reaction rates were higher for [VO(OMe)(ON 2 O BuMe )], which was studied in more detail. Turnover frequencies for conversion of PO over 500 h -1 were observed. Activation energies were determined experimentally through in situ IR spectroscopy for propylene carbonate (48.2 kJ mol -1 ), styrene carbonate (45.6 kJ mol -1 ), and cyclohexene carbonate (54.7 kJ mol -1 ) formation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Chemical Reactions Catalyzed by Metalloporphyrin-Based Metal-Organic Frameworks

    Directory of Open Access Journals (Sweden)

    Kelly Aparecida Dias de Freitas Castro

    2013-06-01

    Full Text Available The synthetic versatility and the potential application of metalloporphyrins (MP in different fields have aroused researchers’ interest in studying these complexes, in an attempt to mimic biological systems such as cytochrome P-450. Over the last 40 years, synthetic MPs have been mainly used as catalysts for homogeneous or heterogeneous chemical reactions. To employ them in heterogeneous catalysis, chemists have prepared new MP-based solids by immobilizing MP onto rigid inorganic supports, a strategy that affords hybrid inorganic-organic materials. More recently, materials obtained by supramolecular assembly processes and containing MPs as building blocks have been applied in a variety of areas, like gas storage, photonic devices, separation, molecular sensing, magnets, and heterogeneous catalysis, among others. These coordination polymers, known as metal-organic frameworks (MOFs, contain organic ligands or complexes connected by metal ions or clusters, which give rise to a 1-, 2- or 3-D network. These kinds of materials presents large surface areas, Brønsted or redox sites, and high porosity, all of which are desirable features in catalysts with potential use in heterogeneous phases. Building MOFs based on MP is a good way to obtain solid catalysts that offer the advantages of bioinspired systems and zeolitic materials. In this mini review, we will adopt a historical approach to present the most relevant MP-based MOFs applicable to catalytic reactions such as oxidation, reduction, insertion of functional groups, and exchange of organic functions.

  8. Graphene oxide for acid catalyzed-reactions: Effect of drying process

    Science.gov (United States)

    Gong, H. P.; Hua, W. M.; Yue, Y. H.; Gao, Z.

    2017-03-01

    Graphene oxides (GOs) were prepared by Hummers method through various drying processes, and characterized by XRD, SEM, FTIR, XPS and N2 adsorption. Their acidities were measured using potentiometric titration and acid-base titration. The catalytic properties were investigated in the alkylation of anisole with benzyl alcohol and transesterification of triacetin with methanol. GOs are active catalysts for both reaction, whose activity is greatly affected by their drying processes. Vacuum drying GO exhibits the best performance in transesterification while freezing drying GO is most active for alkylation. The excellent catalytic behavior comes from abundant surface acid sites as well as proper surface functional groups, which can be obtained by selecting appropriate drying process.

  9. Cooperative Effects Between Arginine and Glutamic Acid in the Amino Acid-Catalyzed Aldol Reaction.

    Science.gov (United States)

    Valero, Guillem; Moyano, Albert

    2016-08-01

    Catalysis of the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde by mixtures of L-Arg and of L-Glu in wet dimethyl sulfoxide (DMSO) takes place with higher enantioselectivity (up to a 7-fold enhancement in the anti-aldol for the 1:1 mixture) than that observed when either L-Glu or L-Arg alone are used as the catalysts. These results can be explained by the formation of a catalytically active hydrogen-bonded complex between both amino acids, and demonstrate the possibility of positive cooperative effects in catalysis by two different α-amino acids. Chirality 28:599-605, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  10. Transient state kinetic studies of the MutT-catalyzed nucleoside triphosphate pyrophosphohydrolase reaction.

    Science.gov (United States)

    Xia, Zuyong; Azurmendi, Hugo F; Mildvan, Albert S

    2005-11-22

    The MutT pyrophosphohydrolase, in the presence of Mg2+, catalyzes the hydrolysis of nucleoside triphosphates by nucleophilic substitution at Pbeta, to yield the nucleotide and PP(i). The best substrate for MutT is the mutagenic 8-oxo-dGTP, on the basis of its Km being 540-fold lower than that of dGTP. Product inhibition studies have led to a proposed uni-bi-iso kinetic mechanism, in which PP(i) dissociates first from the enzyme-product complex (k3), followed by NMP (k4), leaving a product-binding form of the enzyme (F) which converts to the substrate-binding form (E) in a partially rate-limiting step (k5) [Saraswat, V., et al. (2002) Biochemistry 41, 15566-15577]. Single- and multiple-turnover kinetic studies of the hydrolysis of dGTP and 8-oxo-dGTP and global fitting of the data to this mechanism have yielded all of the nine rate constants. Consistent with an "iso" mechanism, single-turnover studies with dGTP and 8-oxo-dGTP hydrolysis showed slow apparent second-order rate constants for substrate binding similar to their kcat/Km values, but well below the diffusion limit (approximately 10(9) M(-1) s(-1)): k(on)app = 7.2 x 10(4) M(-1) s(-1) for dGTP and k(on)app = 2.8 x 10(7) M(-1) s(-1) for 8-oxo-dGTP. These low k(on)app values are fitted by assuming a slow iso step (k5 = 12.1 s(-1)) followed by fast rate constants for substrate binding: k1 = 1.9 x 10(6) M(-1) s(-1) for dGTP and k1 = 0.75 x 10(9) M(-1) s(-1) for 8-oxo-dGTP (the latter near the diffusion limit). With dGTP as the substrate, replacing Mg2+ with Mn2+ does not change k1, consistent with the formation of a second-sphere MutT-M2+-(H2O)-dGTP complex, but slows the iso step (k5) 5.8-fold, and its reverse (k(-5)) 25-fold, suggesting that the iso step involves a change in metal coordination, likely the dissociation of Glu-53 from the enzyme-bound metal so that it can function as the general base. Multiple-turnover studies with dGTP and 8-oxo-dGTP show bursts of product formation, indicating partially rate

  11. Phosphorus-31 NMR magnetization transfer measurements of metabolic reaction rates in the rat heart and kidney in vivo

    International Nuclear Information System (INIS)

    Koretsky, A.P.

    1984-01-01

    31 P NMR is a unique tool to study bioenergetics in living cells. The application of magnetization transfer techniques to the measurement of steady-state enzyme reaction rates provides a new approach to understanding the regulation of high energy phosphate metabolism. This dissertation is concerned with the measurement of the rates of ATP synthesis in the rat kidney and of the creatine kinase catalyzed reaction in the rat heart in situ. The theoretical considerations of applying magnetization transfer techniques to intact organs are discussed with emphasis on the problems associated with multiple exchange reactions and compartmentation of reactants. Experimental measurements of the ATP synthesis rate were compared to whole kidney oxygen consumption and Na + reabsorption rates to derive ATP/O values. The problems associated with ATP synthesis rate measurements in kidney, e.g. the heterogeneity of the inorganic phosphate resonance, are discussed and experiments to overcome these problems proposed. In heart, the forward rate through creatine kinase was measured to be larger than the reverse rate. To account for the difference in forward and reverse rates a model is proposed based on the compartmentation of a small pool of ATP

  12. Pre-steady state transients in the Drosophila alcohol dehydrogenase catalyzed reaction: isotope effects and stereospecificity

    International Nuclear Information System (INIS)

    Place, A.R.; Eccleston, J.F.

    1987-01-01

    The alcohol dehydrogenase (ADH) isolated from Drosophila is unique among alcohol metabolizing enzymes by not requiring metals for catalysis, by showing 4-pro-S (B-sided) hydride transfer stereospecificity, and by possessing a greater catalytic turnover rate for secondary alcohols than for primary alcohols. They have extended their studies on the kinetic mechanism for this enzyme by examining the pre-steady state transients of ternary complex interconversion using stopped-flow fluorescence methods. When enzyme and a 30-fold molar excess of NADH is mixed with excess acetadehyde, methyl ethyl ketone (MEK), or cyclohexanone a rapid (> 100 s -1 ) transient is observe before the steady-state. The rates are insensitive to isotope substitution. With the substrate MEK, the rate and amplitude suggests a single turnover of the enzyme. Similar pre-steady state transients are observed when enzyme and a 50-fold molar excess of NAD + is mixed with ethanol, 2-propanol, and cyclohexanol. The rates show a hyperbolic concentration dependence and a deuterium isotope effect. With d 6 -deuteroethanol the transient no longer occurs in the pre-steady state. When the optical isomers of secondary alcohols are used as substrates, transients are observed only in the R-(-) isomers for all chain lengths. With 2-S(+)-heptanol and 2-S(+)-octanol no transients occur

  13. Starting D-optimal designs for batch kinetics studies of enzyme-catalyzed reactions in the presence of enzyme deactivation.

    Science.gov (United States)

    Malcata, F X

    1992-09-01

    This paper describes a strategy for the starting experimental design of experiments required by general research in the field of biochemical kinetics. The type of experiments that qualify for this analysis involve batch reactions catalyzed by soluble enzymes where the activity of the enzyme decays with time. Assuming that the catalytic action of the enzyme obeys a Michaelis-Menten rate expression and that the deactivation of the enzyme follows a first-order decay, the present analysis employs the dimensionless, integrated form of the overall rate expression to obtain a criterion (based on the maximization of the determinant of the derivative matrix) that relates the a priori estimates of the parameters with the times at which samples should be withdrawn from the reacting mixture. The analysis indicates that the initial concentration of substrate should be as large as possible, and that the samples should be taken at times corresponding to substrate concentrations of approximately 2/3, 1/4, and I/epsilon of the initial concentration (where epsilon should be as large as possible).

  14. Synthesis of deuterium-labeled desipramine through acid-catalyzed exchange reactions and the stability of deuterium labeling

    International Nuclear Information System (INIS)

    Baba, Shigeo; Sasaki, Yukihito

    1987-01-01

    Synthesis of three forms of selectively deuterated desipramine with high isotopic purity through acid-catalyzed hydrogen-deuterium exchange reactions and the stability of deuterium labeling are described. Deuterated desipramine labeled at positions 2,4,6 and 8 [DMI-d 4 (I)] was prepared directly by heating desipramine in 10% DCI-D 2 O at 80deg C for 8 hours. Desipramine labeled at all eight aromatic positions (DMI-d 8 ) was synthesized from iminodibenzyl-1,2,3,4,6,7,8,9-d 8 . Desipramine labeled at positions 1,3,7 and 9 [DMI-d 4 (II)] was obtained by the ''back-exchange'' of DMI-d 8 under the protio condition according to the exchange procedure of DMI-d 4 (I). Deuterium atoms labeled at positions 2,4,6 and 8 of desipramine were eliminated rapidly in 1N HCl at 80deg C, but those labeled at positions 1,3,7 and 9 of desipramine were quite chemically stable. (author)

  15. Synthesis of L-Ascorbyl Flurbiprofenate by Lipase-Catalyzed Esterification and Transesterification Reactions.

    Science.gov (United States)

    Xin, Jia-Ying; Sun, Li-Rui; Chen, Shu-Ming; Wang, Yan; Xia, Chun-Gu

    2017-01-01

    The synthesis of L-ascorbyl flurbiprofenate was achieved by esterification and transesterification in nonaqueous organic medium with Novozym 435 lipase as biocatalyst. The conversion was greatly influenced by the kinds of organic solvents, speed of agitation, catalyst loading amount, reaction time, and molar ratio of acyl donor to L-ascorbic acid. A series of solvents were investigated, and tert-butanol was found to be the most suitable from the standpoint of the substrate solubility and the conversion for both the esterification and transesterification. When flurbiprofen was used as acyl donor, 61.0% of L-ascorbic acid was converted against 46.4% in the presence of flurbiprofen methyl ester. The optimal conversion of L-ascorbic acid was obtained when the initial molar ratio of acyl donor to ascorbic acid was 5 : 1. kinetics parameters were solved by Lineweaver-Burk equation under nonsubstrate inhibition condition. Since transesterification has lower conversion, from the standpoint of productivity and the amount of steps required, esterification is a better method compared to transesterification.

  16. Synthesis of L-Ascorbyl Flurbiprofenate by Lipase-Catalyzed Esterification and Transesterification Reactions

    Directory of Open Access Journals (Sweden)

    Jia-ying Xin

    2017-01-01

    Full Text Available The synthesis of L-ascorbyl flurbiprofenate was achieved by esterification and transesterification in nonaqueous organic medium with Novozym 435 lipase as biocatalyst. The conversion was greatly influenced by the kinds of organic solvents, speed of agitation, catalyst loading amount, reaction time, and molar ratio of acyl donor to L-ascorbic acid. A series of solvents were investigated, and tert-butanol was found to be the most suitable from the standpoint of the substrate solubility and the conversion for both the esterification and transesterification. When flurbiprofen was used as acyl donor, 61.0% of L-ascorbic acid was converted against 46.4% in the presence of flurbiprofen methyl ester. The optimal conversion of L-ascorbic acid was obtained when the initial molar ratio of acyl donor to ascorbic acid was 5 : 1. kinetics parameters were solved by Lineweaver-Burk equation under nonsubstrate inhibition condition. Since transesterification has lower conversion, from the standpoint of productivity and the amount of steps required, esterification is a better method compared to transesterification.

  17. Mission to Mars by catalyzed nuclear reactions of the commercialized cold fusion power

    Energy Technology Data Exchange (ETDEWEB)

    Woo, Tae Ho [Yonsei University, Wonju (Korea, Republic of)

    2016-05-15

    The chemical compound source is deficient to reach to the power as much as the journey to Mars, unless the massive equipment is installed like the nuclear fusion reactor. However, there is very significant limitations of making up the facility due to the propellant power. Therefore, the light and cheap energy source, Low energy nuclear reactions (LENRs), powered rocket has been proposed. In this paper, the power conditions by LENRs are analyzed. After the successful Apollo mission to Moon of the National Aeronautics and Space Administration (NASA) in the U.S. government, the civilian companies have proposed for the manned mission to Mars for the commercial journey purposes. The nuclear power has been a critical issue for the energy source in the travel, especially, by the LENR of LENUCO, Champaign, USA. As the velocity of the rocket increases, the mass flow rate decreases. It could be imaginable to take the reasonable velocity of spacecraft. The energy of the travel system is and will be created for the better one in economical and safe method. There is the imagination of boarding pass for spacecraft ticket shows the selected companies of cold fusion products. In order to solve the limitations of the conventional power sources like the chemical and solar energies, it is reasonable to design LENR concept. Since the economical and safe spacecraft is very important in the long journey on and beyond the Mars orbit, a new energy source, LENR, should be studied much more.

  18. Homogeneous Catalyzed Reactions of Levulinic Acid: To γ-Valerolactone and Beyond.

    Science.gov (United States)

    Omoruyi, Uwaila; Page, Samuel; Hallett, Jason; Miller, Philip W

    2016-08-23

    Platform chemicals derived from lignocellulosic plant biomass are viewed as a sustainable replacement for crude oil-based feedstocks. Levulinic acid (LA) is one such biomass-derived chemical that has been widely studied for further catalytic transformation to γ-valerolactone (GVL), an important 'green' fuel additive, solvent, and fine chemical intermediate. Although the transformation of LA to GVL can be achieved using heterogeneous catalysis, homogeneous catalytic systems that operate under milder reactions, give higher selectivities and can be recycled continuously are attracting considerable attention. A range of new homogeneous catalysts have now been demonstrated to efficiently convert LA to GVL and to transform LA directly to other value-added chemicals such as 1,4-pentanediol (1,4-PDO) and 2-methyltetrahydrofuran (2-MTHF). This Minireview covers recent advances in the area of homogeneous catalysis for the conversion of levulinic acid and levulinic ester derivatives to GVL and chemicals beyond GVL. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Pd-catalyzed ethylene methoxycarbonylation with Brønsted acid ionic liquids as promoter and phase-separable reaction media

    DEFF Research Database (Denmark)

    Garcia-Suarez, Eduardo J.; Khokarale, Santosh Govind; Nguyen van Buu, Olivier

    2014-01-01

    Brønsted acid ionic liquids (BAILs) were prepared and applied as combined acid promoters and reaction media in Pd–phosphine catalyzed methoxycarbonylation of ethylene to produce methyl propionate. The BAILs served as alternatives to common mineral acids required for the reaction, e.......g. methanesulfonic acid or sulfuric acid, resulting in high catalytic activity and selectivity towards methyl propionate. In addition, the BAILs yielded a biphasic system with the product and provided stability to palladium intermediates avoiding the undesirable formation of palladium black after reaction...

  20. An efficient process for pd-catalyzed C-N cross-coupling reactions of aryl iodides: insight into controlling factors.

    Science.gov (United States)

    Fors, Brett P; Davis, Nicole R; Buchwald, Stephen L

    2009-04-29

    An investigation into Pd-catalyzed C-N cross-coupling reactions of aryl iodides is described. NaI is shown to have a significant inhibitory effect on these processes. By switching to a solvent system in which the iodide byproduct was insoluble, reactions of aryl iodides were accomplished with the same efficiencies as aryl chlorides and bromides. Using catalyst systems based on certain biarylphosphine ligands, aryl iodides were successfully reacted with an array of primary and secondary amines in high yields. Lastly, reactions of heteroarylamines and heteroaryliodides were also conducted in high yields.

  1. Production of L-malic acid with fixation of HCO3(-) by malic enzyme-catalyzed reaction based on regeneration of coenzyme on electrode modified by layer-by-layer self-assembly method.

    Science.gov (United States)

    Zheng, Haitao; Ohno, Yoko; Nakamori, Toshihiko; Suye, Shin-Ichiro

    2009-01-01

    Malic enzyme prepared and purified from Brevundimonas diminuta IFO13182 catalyzed the decarboxylation reaction of malate to pyruvate and CO2 using NAD+ as the coenzyme, and the reverse reaction was used in the present study for L-malic acid production with fixation of HCO3(-) as a model compound for carbon source. The L-malic acid production was based on electrochemical regeneration of NADH on a carbon plate electrode modified by layer-by-layer adsorption of polymer-bound mediator (Alginic acid bound viologen derivative, Alg-V), polymer-bound coenzyme (Alginic acid bound NAD+, Alg-NAD+), and lipoamide dehydrogenase (LipDH). Electrochemical reduction of immobilized NAD+ catalyzed by LipDH in a multilayer film was achieved, and the L-malic acid production with HCO3(-) fixation system with layer-by-layer immobilization of Alg-V/LipDH/Alg-NAD+/malic enzyme multilayer film on the electrode gave an L-malic acid production of nearly 11.9 mmol and an HCO3(-) fixation rate of nearly 47.4% in a buffer containing only KHCO3 and pyruvic acid potassium salt, using a cation exchange membrane. The total turnover number of NADH within 48 h was about 19,000, which suggests that efficient NADH regeneration and fast electron transfer were achieved within the multilayer film, and that the modified electrode is a potential method for the fixation of HCO3(-) without addition of free coenzyme.

  2. Enantioselective Alkylation of 2-Oxindoles Catalyzed by a Bifunctional Phase-Transfer Catalyst: Synthesis of (-)-Debromoflustramine B.

    Science.gov (United States)

    Craig, Ryan; Sorrentino, Emiliano; Connon, Stephen J

    2018-03-26

    A new bifunctional phase-transfer catalyst that employs hydrogen bonding as a control element was developed to promote efficient enantioselective S N 2 reactions for the construction all-carbon quaternary stereocenters in high yield and excellent enantioselectivity (up to 97 % ee) utilizing the alkylation of a malleable oxindole substrate. The utility of the methodology was demonstrated through a concise and highly enantioselective synthesis of (-)-debromoflustramine B. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Atomically Dispersed Au-(OH)x Species Bound on Titania Catalyze the Low-Temperature Water-Gas Shift Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ming; Allard, Lawrence F; Flytzani-Stephanopoulos, Maria [Tufts; (ORNL)

    2013-03-27

    We report a new method for stabilizing appreciable loadings (~1 wt %) of isolated gold atoms on titania and show that these catalyze the low-temperature water-gas shift reaction. The method combines a typical gold deposition/precipitation method with UV irradiation of the titania support suspended in ethanol. Dissociation of H2O on the thus-created Au–O–TiOx sites is facile. At higher gold loadings, nanoparticles are formed, but they were shown to add no further activity to the atomically bound gold on titania. Removal of this “excess” gold by sodium cyanide leaching leaves the activity intact and the atomically dispersed gold still bound on titania. The new materials may catalyze a number of other reactions that require oxidized active metal sites.

  4. Computational studies on the regioselectivity of metal-catalyzed synthesis of 1,2,3 triazoles via click reaction: a review.

    Science.gov (United States)

    Hosseinnejad, Tayebeh; Fattahi, Bahareh; Heravi, Majid M

    2015-10-01

    Recently, the experimental and computational chemists have been attracted widely to the click synthesis of 1,2,3 triazoles and their derivatives, mainly due to the fact that they are interesting from structural and mechanistic points of view. Moreover, catalyzed click have been well established as a successful strategy showing high regioselectivity and high yield for the synthesis of 1,2,3-triazoles. In this review, we try to highlight the recently reported computational assessments on the origins and predection of regioselectivity in the catalyzed click synthesis of triazoles from the mechanistic and thermodynamical points of view. In this light, density functional theory (DFT) calculations on the free energy profiles of azide-alkyne cycloaddition reactions have been underscored. The stereoelectronic features for the role of copper, ruthenium, and iridium as catalyst on regioselectivity of click reactions have also be discussed. Graphical Abstract Computational origins for the regioselective behavior of 1,2,3 triazoles click synthesis.

  5. Mass transfer with complex chemical reaction in gas–liquid systems—I. Consecutive reversible reactions with equal diffusivities

    NARCIS (Netherlands)

    Vas Bhat, R.D.; Swaaij, W.P.M. van; Kuipers, J.A.M.; Versteeg, G.F.

    1999-01-01

    A fundamental description of gas–liquid mass transfer with reversible consecutive reaction has been derived. The Higbie penetration theory has been used and numerical simulations were carried out for isothermal absorption. Although the model can be adapted to reactions of general stoichiometric and

  6. Mass transfer with complex chemical reaction in gas–liquid systems—II : Effect of unequal diffusivities on consecutive reactions

    NARCIS (Netherlands)

    Vas Bhat, R.D.; Swaaij, W.P.M. van; Kuipers, J.A.M.; Versteeg, G.F.

    1999-01-01

    A fundamental description of gas–liquid mass transfer with reversible consecutive reaction has been given. The Higbie penetration theory has been used and numerical simulations were carried out for isothermal absorption. Although the model can be adapted to reactions of general stoichiometric and

  7. Mass transfer with complex chemical reaction in gas-liquid systems - I. Consecutive reversible reactions with equal diffusivities

    NARCIS (Netherlands)

    Vas bhat, R.D.; van Swaaij, Willibrordus Petrus Maria; Kuipers, J.A.M.; Versteeg, Geert

    1999-01-01

    A fundamental description of gas¿liquid mass transfer with reversible consecutive reaction has been derived. The Higbie penetration theory has been used and numerical simulations were carried out for isothermal absorption. Although the model can be adapted to reactions of general stoichiometric and

  8. Rh2(II)-catalyzed intramolecular aliphatic C-H bond amination reactions using aryl azides as the N-atom source.

    Science.gov (United States)

    Nguyen, Quyen; Sun, Ke; Driver, Tom G

    2012-05-02

    Rhodium(II) dicarboxylate complexes were discovered to catalyze the intramolecular amination of unactivated primary, secondary, or tertiary aliphatic C-H bonds using aryl azides as the N-atom precursor. While a strong electron-withdrawing group on the nitrogen atom is typically required to achieve this reaction, we found that both electron-rich and electron-poor aryl azides are efficient sources for the metal nitrene reactive intermediate. © 2012 American Chemical Society

  9. Rh2(II)-Catalyzed Intramolecular Aliphatic C–H Bond Amination Reactions Using Aryl Azides as the N-Atom Source

    Science.gov (United States)

    Nguyen, Quyen; Sun, Ke; Driver, Tom G.

    2012-01-01

    Rhodium(II) dicarboxylate complexes were discovered to catalyze the intramolecular amination of unactivated primary-, secondary-, or tertiary aliphatic C–H bonds using aryl azides as the N-atom precursor. While a strong electron-withdrawing group on the nitrogen atom is typically required to achieve this reaction, we found that both electron-rich- and electron-poor aryl azides are efficient sources for the metal nitrene reactive intermediate. PMID:22519742

  10. Vinyl azides derived from allenes: thermolysis leading to multisubstituted 1,4-pyrazines and Mn(III)-catalyzed photochemical reaction leading to pyrroles.

    Science.gov (United States)

    Sajna, K V; Kumara Swamy, K C

    2012-10-05

    Thermolysis of phosphorus-based vinyl azides under solvent- and catalyst-free conditions furnished a new route for 1,4-pyrazines. A simple one-pot, Mn(III)-catalyzed photochemical route has been developed for multisubstituted pyrroles starting from allenes and 1,3-dicarbonyls via in situ-generated vinyl azides. The utility of new phosphorus-based pyrroles is also demonstrated in the Horner reaction. The structures of key products are unequivocally confirmed by X-ray crystallography.

  11. Cyclic aldimines as superior electrophiles for Cu-catalyzed decarboxylative Mannich reaction of β-ketoacids with a broad scope and high enantioselectivity.

    Science.gov (United States)

    Zhang, Heng-Xia; Nie, Jing; Cai, Hua; Ma, Jun-An

    2014-05-02

    A novel Cu-catalyzed enantioselective decarboxylative Mannich reaction of cyclic aldimines with β-ketoacids is described. The cyclic structure of these aldimines, in which the C═N bond is constrained in the Z geometry, appears to be important, allowing Mannich condensation to proceed in high yields with excellent enantioselectivities. A chiral chroman-4-amine was synthesized from the decarboxylative Mannich product in several steps without loss of enantioselectivity.

  12. Visible-Light Photoredox-Catalyzed Giese Reaction: Decarboxylative Addition of Amino Acid Derived α-Amino Radicals to Electron-Deficient Olefins

    KAUST Repository

    Millet, Anthony

    2016-06-20

    A tin- and halide-free, visible-light photoredox-catalyzed Giese reaction was developed. Primary and secondary α-amino radicals were generated readily from amino acids in the presence of catalytic amounts of an iridium photocatalyst. The reactivity of the α-amino radicals has been evaluated for the functionalization of a variety of activated olefins. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  13. Chemical reaction on MHD flow and heat transfer of a nanofluid ...

    African Journals Online (AJOL)

    Chemical reaction on MHD flow and heat transfer of a nanofluid near the stagnation point over a permeable stretching surface with non-uniform heat source/sink. ... and is found to be in excellent agreement. Keywords: Stagnation point flow; Chemical reaction; Heat transfer; Stretching surface; Nanofluid; Numerical solution.

  14. Carboxyl-catalyzed prototropic rearrangements in histidine peptide radicals upon electron transfer: effects of peptide sequence and conformation.

    Science.gov (United States)

    Turecek, Frantisek; Panja, Subhasis; Wyer, Jean A; Ehlerding, Anneli; Zettergren, Henning; Nielsen, Steen Brøndsted; Hvelplund, Preben; Bythell, Benjamin; Paizs, Béla

    2009-11-18

    We report an unusual prototropic rearrangement in gas-phase radicals formed by collisional electron transfer from cesium atoms to protonated peptides HAL, AHL, and ALH at 50 keV. The rearrangement depends on the peptide amino acid sequence and presence or steric accessibility of a free carboxyl group. Upon electron transfer, protonated HAL and ALH rearrange to tautomers that are detected as nondissociated anions in charge-reversal mass spectra. The isomerization is minor in protonated ALH and virtually absent in HAL amide. Electron structure calculations indicate that the gas-phase ions are preferentially protonated in the His imidazole ring and consist of multiple conformers that differ in their hydrogen bonding patterns. Electron transfer to protonated HAL and AHL triggers an exothermic and dynamically barrierless transfer of the carboxyl proton onto the C-2' position of the His ring that occurs on a 120-240 ns time scale. The kinetics of this isomerization are controlled by internal rotations in the radicals to assume conformations favoring the proton transfer. The radical conformations also affect subsequent proton migrations in zwitterionic His imidazoline intermediates that reform the COOH group and result in His ring isomerization. This autocatalytic prototropic rearrangement in gas-phase peptide radicals is analogous to enzyme catalytic reactions involving His and acidic amino acid residues. In contrast to HAL and AHL, the C-2' position is sterically inaccessible in ALH radicals. These radicals undergo proton migrations to the His ring C-5' positions that have moderate energy barriers and are less efficient. RRKM calculations on the combined B3LYP and PMP2/6-311++G(2d,p) potential energy surface of the ground doublet electronic state of the peptide radicals provided rate constants that were quantitatively consistent with the dissociations observed in the gas phase. The formation of minor sequence z(1) and z(2) fragments from AHL was interpreted as occurring

  15. Intrinsic isotope effects suggest that the reaction coordinate symmetry for the cytochrome P-450 catalyzed hydroxylation of octane is isozyme independent

    International Nuclear Information System (INIS)

    Jones, J.P.; Rettie, A.E.; Trager, W.F.

    1990-01-01

    The mechanism of the omega-hydroxylation of octane by three catalytically distinct, purified forms of cytochrome P-450, namely, P-450b, P-450c, and P-450LM2, was investigated by using deuterium isotope effects. The deuterium isotope effects associated with the omega-hydroxylation of octane-1,1,1-2H3, octane-1,8-2H2, and octane-1,1,8,8-2H4 by all three isozymes were determined. From these data the intrinsic isotope effects were calculated and separated into their primary and secondary components. The primary intrinsic isotope effect for the reaction ranged from 7.69 to 9.18 while the secondary intrinsic isotope effect ranged from 1.13 to 1.25. Neither the primary nor secondary isotope effect values were statistically different for any of the isozymes investigated. These data are consistent with a symmetrical transition state for a mechanism involving initial hydrogen atom abstraction followed by hydroxyl radical recombination which is essentially independent of the specific isozyme catalyzing the reaction. It is concluded that (1) in general the porphyrin-[FeO]3+ complex behaves as a source of a triplet-like oxygen atom, (2) the regioselectivity for the site of oxidation is dictated by the apoprotein of the specific isozyme of cytochrome P-450 catalyzing the reaction, and (3) the maximum primary intrinsic isotope effect for any cytochrome P-450 catalyzed oxidation of a carbon center is about 9, assuming no tunneling effects

  16. The (3He,α) reaction mechanism. A study of the angular momentum transfer

    International Nuclear Information System (INIS)

    Guttormsen, M.; Bergholt, L.; Ingebretsen, F.; Loevhoeiden, G.; Messelt, S.; Rekstad, J.; Tveter, T.S.; Helstrup, H.; Thorsteinsen, T.F.

    1994-01-01

    The γ-rays emitted after the 163 Dy( 3 He,αxn) reactions at E( 3 He) = 45 MeV have been measured. The transferred angular momentum in the reaction is deduced from the side-feeding γ-intensities of the ground bands in the residual 162-x Dy isotopes. With decreasing α-energy the average spin transfer increases from similar 5h to similar 11h. The ( 3 He,α) reaction at these energies is dominated by direct processes. Even at the highest spin transfer the contribution from the compound reaction channel is negligible. ((orig.))

  17. Selective population of high-j states via heavy-ion-induced transfer reactions

    International Nuclear Information System (INIS)

    Bond, P.D.

    1982-01-01

    One of the early hopes of heavy-ion-induced transfer reactions was to populate states not seen easily or at all by other means. To date, however, I believe it is fair to say that spectroscopic studies of previously unknown states have had, at best, limited success. Despite the early demonstration of selectivity with cluster transfer to high-lying states in light nuclei, the study of heavy-ion-induced transfer reactions has emphasized the reaction mechanism. The value of using two of these reactions for spectroscopy of high spin states is demonstrated: 143 Nd( 16 O, 15 O) 144 Nd and 170 Er( 16 O, 15 Oγ) 171 Er

  18. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive...... theory of charge transfer in polar media offers convenient tools for the treatment of experimental data for such systems, with due account of large-amplitude strongly anharmonic intramolecular reorganization. Equations for the activation barrier and free energy relationships are provided, incorporating...

  19. N3S-ligated Copper(II) Complex Catalyzed Selective Oxidation of Benzylic Alcohols to Aldehydes under Mild Reaction Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Dharmalingam, Sivanesan; Yoon, Sungho; Park, Gyoosoon [Kookmin Univ., Seoul (Korea, Republic of); Koo, Eunhae [Korea Institute of Ceramic Engineering and Technology, Seoul (Korea, Republic of)

    2014-03-15

    A Cu(II) complex with an three nitrogens and one sulfur coordination environment was synthesized and characterized. Its redox potential was observed at 0.483 V vs. NHE, very similar to that of a Cu-containing fungal enzyme, galactose oxidase, which catalyzes the oxidation of alcohols to corresponding aldehydes with the concomitant reduction of molecular oxygen to water. The Cu(II) complex selectively oxidizes the benzylic alcohols using TEMPO/O{sub 2} under mild reaction conditions to corresponding aldehydes without forming any over-oxidation product. Moreover, the catalyst can be recovered and reused multiple times for further oxidation reactions, thus minimizing the waste generation.

  20. Synthesis of 4-Aryl Isoquinolinedione Derivatives by a Palladium-Catalyzed Coupling Reaction of Aryl Halides with Isoquinoline-1,3(2H,4H)-diones.

    Science.gov (United States)

    Yang, Yuanyong; Li, Yingxian; Cheng, Cheng; Yang, Guo; Zhang, Jiquan; Zhang, Yi; Zhao, Yonglong; Zhang, Lin; Li, Chun; Tang, Lei

    2018-02-23

    The palladium-catalyzed cross-coupling reaction of aryl halides with isoquinoline-1,3(2H,4H)-diones for the synthesis of 4-aryl isoquinoline-1,3(2H,4H)-diones was developed. The reaction conditions exhibit remarkable compatibility with various aryl halides and isoquinoline-1,3(2H,4H)-diones, and the product could be conveniently transformed to 4-aryl tetrahydroisoquinolines. (±) Dichlorofensine was synthesized using this protocol in two steps with an overall yield of 71%.

  1. One-Pot Synthesis of Novel Chiral β-Amino Acid Derivatives by Enantioselective Mannich Reactions Catalyzed by Squaramide Cinchona Alkaloids

    Directory of Open Access Journals (Sweden)

    Kankan Zhang

    2013-05-01

    Full Text Available An efficient one-pot synthesis of novel β-amino acid derivatives containing a thiadiazole moiety was developed using a chiral squaramide cinchona alkaloid as organocatalyst. The reactions afforded chiral β-amino acid derivatives in moderate yields and with moderate to excellent enantioselectivities. The present study demonstrated for the first time the use of a Mannich reaction catalyzed by a chiral bifunctional organocatalyst for the one-pot synthesis of novel β-amino acid derivatives bearing a 1,3,4-thiadiazole moiety on nitrogen.

  2. Zn-ProPhenol Catalyzed Enantio- and Diastereoselective Direct Vinylogous Mannich Reactions between α,β- and β,γ-Butenolides and Aldimines.

    Science.gov (United States)

    Trost, Barry M; Gnanamani, Elumalai; Tracy, Jacob S; Kalnmals, Christopher A

    2017-12-20

    We report a Zn-ProPhenol catalyzed reaction between butenolides and imines to obtain tetrasubstituted vinylogous Mannich products in good yield and diastereoselectivity with excellent enantioselectivity (97 to >99.5% ee). Notably, both α,β- and β,γ-butenolides can be utilized as nucleophiles in this transformation. The imine partner bears the synthetically versatile N-Cbz group, avoiding the use of the specialized aryl directing groups previously required in related work. Additionally, the reaction can be performed on gram scale with reduced catalyst loading as low as 2 mol %. The functional group-rich products can be further elaborated using a variety of methods.

  3. Mechanism of the orotidine 5'-monophosphate decarboxylase-catalyzed reaction: importance of residues in the orotate binding site.

    Science.gov (United States)

    Iiams, Vanessa; Desai, Bijoy J; Fedorov, Alexander A; Fedorov, Elena V; Almo, Steven C; Gerlt, John A

    2011-10-04

    The reaction catalyzed by orotidine 5'-monophosphate decarboxylase (OMPDC) is accompanied by exceptional values for rate enhancement (k(cat)/k(non) = 7.1 × 10(16)) and catalytic proficiency [(k(cat)/K(M))/k(non) = 4.8 × 10(22) M(-1)]. Although a stabilized vinyl carbanion/carbene intermediate is located on the reaction coordinate, the structural strategies by which the reduction in the activation energy barrier is realized remain incompletely understood. This laboratory recently reported that "substrate destabilization" by Asp 70 in the OMPDC from Methanothermobacter thermoautotrophicus (MtOMPDC) lowers the activation energy barrier by ∼5 kcal/mol (contributing ~2.7 × 10(3) to the rate enhancement) [Chan, K. K., Wood, B. M., Fedorov, A. A., Fedorov, E. V., Imker, H. J., Amyes, T. L., Richard, J. P., Almo, S. C., and Gerlt, J. A. (2009) Biochemistry 48, 5518-5531]. We now report that substitutions of hydrophobic residues in a pocket proximal to the carboxylate group of the substrate (Ile 96, Leu 123, and Val 155) with neutral hydrophilic residues decrease the value of k(cat) by as much as 400-fold but have a minimal effect on the value of k(ex) for exchange of H6 of the FUMP product analogue with solvent deuterium; we hypothesize that this pocket destabilizes the substrate by preventing hydration of the substrate carboxylate group. We also report that substitutions of Ser 127 that is proximal to O4 of the orotate ring decrease the value of k(cat)/K(M), with the S127P substitution that eliminates hydrogen bonding interactions with O4 producing a 2.5 × 10(6)-fold reduction; this effect is consistent with delocalization of the negative charge of the carbanionic intermediate on O4 that produces an anionic carbene intermediate and thereby provides a structural strategy for stabilization of the intermediate. These observations provide additional information about the identities of the active site residues that contribute to the rate enhancement and, therefore

  4. Hydride Transfer versus Deprotonation Kinetics in the Isobutane–Propene Alkylation Reaction: A Computational Study

    OpenAIRE

    Liu, Chong; van Santen, Rutger A.; Poursaeidesfahani, Ali; Vlugt, Thijs J. H.; Pidko, Evgeny A.; Hensen, Emiel J. M.

    2017-01-01

    The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane–propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate o...

  5. Laser ion source for multi-nucleon transfer reaction products

    Science.gov (United States)

    Hirayama, Y.; Watanabe, Y. X.; Imai, N.; Ishiyama, H.; Jeong, S. C.; Miyatake, H.; Oyaizu, M.; Kimura, S.; Mukai, M.; Kim, Y. H.; Sonoda, T.; Wada, M.; Huyse, M.; Kudryavtsev, Yu.; Van Duppen, P.

    2015-06-01

    We have developed a laser ion source for the target-like fragments (TLFs) produced in multi-nucleon transfer (MNT) reactions. The operation principle of the source is based on the in-gas laser ionization and spectroscopy (IGLIS) approach. In the source TLFs are thermalized and neutralized in high pressure and high purity argon gas, and are extracted after being selectively re-ionized in a multi-step laser resonance ionization process. The laser ion source has been implemented at the KEK Isotope Separation System (KISS) for β-decay spectroscopy of neutron-rich isotopes with N = 126 of nuclear astrophysical interest. The simulations of gas flow and ion-beam optics have been performed to optimize the gas cell for efficient thermalization and fast transporting the TLFs, and the mass-separator for efficient transport with high mass-resolving power, respectively. To confirm the performances expected at the design stage, off-line experiments have been performed by using 56Fe atoms evaporated from a filament in the gas cell. The gas-transport time of 230 ms in the argon cell and the measured KISS mass-resolving power of 900 are consistent with the designed values. The high purity of the gas-cell system, which is extremely important for efficient and highly-selective production of laser ions, was achieved and confirmed from the mass distribution of the extracted ions. After the off-line tests, on-line experiments were conducted by directly injecting energetic 56Fe beam into the gas cell. After thermalization of the injected 56Fe beam, laser-produced singly-charged 56Fe+ ions were extracted. The extraction efficiency and selectivity of the gas cell in the presence of plasma induced by 56Fe beam injection as well as the time profile of the extracted ions were investigated; extraction efficiency of 0.25%, a beam purity of >99% and an extraction time of 270 ms. It has been confirmed that the performance of the KISS laser ion source is satisfactory to start the measurements of

  6. Chemical Exchange Saturation Transfer in Chemical Reactions: A Mechanistic Tool for NMR Detection and Characterization of Transient Intermediates.

    Science.gov (United States)

    Lokesh, N; Seegerer, Andreas; Hioe, Johnny; Gschwind, Ruth M

    2018-02-07

    The low sensitivity of NMR and transient key intermediates below detection limit are the central problems studying reaction mechanisms by NMR. Sensitivity can be enhanced by hyperpolarization techniques such as dynamic nuclear polarization or the incorporation/interaction of special hyperpolarized molecules. However, all of these techniques require special equipment, are restricted to selective reactions, or undesirably influence the reaction pathways. Here, we apply the chemical exchange saturation transfer (CEST) technique for the first time to NMR detect and characterize previously unobserved transient reaction intermediates in organocatalysis. The higher sensitivity of CEST and chemical equilibria present in the reaction pathway are exploited to access population and kinetics information on low populated intermediates. The potential of the method is demonstrated on the proline-catalyzed enamine formation for unprecedented in situ detection of a DPU stabilized zwitterionic iminium species, the elusive key intermediate between enamine and oxazolidinones. The quantitative analysis of CEST data at 250 K revealed the population ratio of [Z-iminium]/[exo-oxazolidinone] 0.02, relative free energy +8.1 kJ/mol (calculated +7.3 kJ/mol), and free energy barrier of +45.9 kJ/mol (ΔG ⧧ calc. (268 K) = +42.2 kJ/mol) for Z-iminium → exo-oxazolidinone. The findings underpin the iminium ion participation in enamine formation pathway corroborating our earlier theoretical prediction and help in better understanding. The reliability of CEST is validated using 1D EXSY-build-up techniques at low temperature (213 K). The CEST method thus serves as a new tool for mechanistic investigations in organocatalysis to access key information, such as chemical shifts, populations, and reaction kinetics of intermediates below the standard NMR detection limit.

  7. Observation of the one- to six-neutron transfer reactions at sub-barrier energies

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, C.L.; Rehm, K.E.; Gehring, J. [and others

    1995-08-01

    It was suggested many years ago that when two heavy nuclei are in contact during a grazing collision, the transfer of several correlated neutron-pairs could occur. Despite considerable experimental effort, however, so far only cross sections for up to four-neutron transfers have been uniquely identified. The main difficulties in the study of multi-neutron transfer reactions are the small cross sections encountered at incident energies close to the barrier, and various experimental uncertainties which can complicate the analysis of these reactions. We have for the first time found evidence for multi-neutron transfer reactions covering the full sequence from one- to six-neutron transfer reactions at sub-barrier energies in the system {sup 58}Ni + {sup 100}Mo.

  8. Visible-light-induced, Ir-catalyzed reactions of N-methyl-N-((trimethylsilylmethylaniline with cyclic α,β-unsaturated carbonyl compounds

    Directory of Open Access Journals (Sweden)

    Dominik Lenhart

    2014-04-01

    Full Text Available N-Methyl-N-((trimethylsilylmethylaniline was employed as reagent in visible-light-induced, iridium-catalyzed addition reactions to cyclic α,β-unsaturated carbonyl compounds. Typical reaction conditions included the use of one equivalent of the reaction substrate, 1.5 equivalents of the aniline and 2.5 mol % (in MeOH or 1.0 mol % (in CH2Cl2 [Ir(ppy2(dtbbpy]BF4 as the catalyst. Two major reaction products were obtained in combined yields of 30–67%. One product resulted from aminomethyl radical addition, the other product was a tricyclic compound, which is likely formed by attack of the intermediately formed α-carbonyl radical at the phenyl ring. For five-membered α,β-unsaturated lactone and lactam substrates, the latter products were the only products isolated. For the six-membered lactones and lactams and for cyclopentenone the simple addition products prevailed.

  9. Reaction kinetics in open reactors and serial transfers between closed reactors

    Science.gov (United States)

    Blokhuis, Alex; Lacoste, David; Gaspard, Pierre

    2018-04-01

    Kinetic theory and thermodynamics of reaction networks are extended to the out-of-equilibrium dynamics of continuous-flow stirred tank reactors (CSTR) and serial transfers. On the basis of their stoichiometry matrix, the conservation laws and the cycles of the network are determined for both dynamics. It is shown that the CSTR and serial transfer dynamics are equivalent in the limit where the time interval between the transfers tends to zero proportionally to the ratio of the fractions of fresh to transferred solutions. These results are illustrated with a finite cross-catalytic reaction network and an infinite reaction network describing mass exchange between polymers. Serial transfer dynamics is typically used in molecular evolution experiments in the context of research on the origins of life. The present study is shedding a new light on the role played by serial transfer parameters in these experiments.

  10. Following Solid-Acid-Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase -Zeolite-Catalyzed Conversion of Cyclohexanol in Water

    Energy Technology Data Exchange (ETDEWEB)

    Vjunov, Aleksei [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Hu, Mary Y. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Feng, Ju [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Camaioni, Donald M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Mei, Donghai [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Hu, Jian Z. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Zhao, Chen [TU Munchen, Garching (Germany); Lercher, Johannes A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); TU Munchen, Garching (Germany)

    2014-01-07

    The catalytic conversion of cyclohexanol on zeolite HBEA in hot liquid water leads to dehydration as well as alkylation products. A novel micro autoclave suitable for application in MAS NMR at high temperatures and pressures is developed and successfully applied to obtain new insight into the mechanistic pathway leading to an understanding of the reactions under selected experimental conditions.

  11. Excited state charge transfer reaction in (mixed solvent+ electrolyte ...

    Indian Academy of Sciences (India)

    The reaction time constant in low polar mixtures, which becomes faster on addition of electrolyte, lengthens on increasing the mole fraction of the relatively less polar solvent component of the mixture. These observations have been qualitatively explained in terms of the measured solvent reorganization energy and reaction ...

  12. Thermodynamic chemical energy transfer mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium chemical reactions

    International Nuclear Information System (INIS)

    Roh, Heui-Seol

    2015-01-01

    Chemical energy transfer mechanisms at finite temperature are explored by a chemical energy transfer theory which is capable of investigating various chemical mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium. Gibbs energy fluxes are obtained as a function of chemical potential, time, and displacement. Diffusion, convection, internal convection, and internal equilibrium chemical energy fluxes are demonstrated. The theory reveals that there are chemical energy flux gaps and broken discrete symmetries at the activation chemical potential, time, and displacement. The statistical, thermodynamic theory is the unification of diffusion and internal convection chemical reactions which reduces to the non-equilibrium generalization beyond the quasi-equilibrium theories of migration and diffusion processes. The relationship between kinetic theories of chemical and electrochemical reactions is also explored. The theory is applied to explore non-equilibrium chemical reactions as an illustration. Three variable separation constants indicate particle number constants and play key roles in describing the distinct chemical reaction mechanisms. The kinetics of chemical energy transfer accounts for the four control mechanisms of chemical reactions such as activation, concentration, transition, and film chemical reactions. - Highlights: • Chemical energy transfer theory is proposed for non-, quasi-, and equilibrium. • Gibbs energy fluxes are expressed by chemical potential, time, and displacement. • Relationship between chemical and electrochemical reactions is discussed. • Theory is applied to explore nonequilibrium energy transfer in chemical reactions. • Kinetics of non-equilibrium chemical reactions shows the four control mechanisms

  13. The acid-catalyzed hydrolysis of an α-pinene-derived organic nitrate: kinetics, products, reaction mechanisms, and atmospheric impact

    Science.gov (United States)

    Rindelaub, Joel D.; Borca, Carlos H.; Hostetler, Matthew A.; Slade, Jonathan H.; Lipton, Mark A.; Slipchenko, Lyudmila V.; Shepson, Paul B.

    2016-12-01

    The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO + NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long-range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, the hydrolysis mechanism and rate constants were elucidated for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the tertiary APN lifetime ranging from 8.3 min at acidic pH (0.25) to 8.8 h at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant

  14. Reaction Mechanisms of CO2 Reduction to Formaldehyde Catalyzed by Hourglass Ru, Fe, and Os Complexes: A Density Functional Theory Study

    Directory of Open Access Journals (Sweden)

    Chunhua Dong

    2016-12-01

    Full Text Available The reaction mechanisms for the reduction of carbon dioxide to formaldehyde catalyzed by bis(tricyclopentylphosphine metal complexes, [RuH2(H2(PCyp32] (1Ru, [FeH2(H2(PCyp32] (1Fe and [OsH4(PCyp32] (1Os, were studied computationally by using the density functional theory (DFT. 1Ru is a recently reported highly efficient catalyst for this reaction. 1Fe and 1Os are two analogues of 1Ru with the Ru atom replaced by Fe and Os, respectively. The total free energy barriers of the reactions catalyzed by 1Ru, 1Fe and 1Os are 24.2, 24.0 and 29.0 kcal/mol, respectively. With a barrier close to the experimentally observed Ru complex, the newly proposed iron complex is a potential low-cost catalyst for the reduction of carbon dioxide to formaldehyde under mild conditions. The electronic structures of intermediates and transition states in these reactions were analyzed by using the natural bond orbital theory.

  15. A molecular dynamics study of intramolecular proton transfer reaction of malonaldehyde in solutions based upon mixed quantum-classical approximation. I. Proton transfer reaction in water.

    Science.gov (United States)

    Yamada, Atsushi; Kojima, Hidekazu; Okazaki, Susumu

    2014-08-28

    In order to investigate proton transfer reaction in solution, mixed quantum-classical molecular dynamics calculations have been carried out based on our previously proposed quantum equation of motion for the reacting system [A. Yamada and S. Okazaki, J. Chem. Phys. 128, 044507 (2008)]. Surface hopping method was applied to describe forces acting on the solvent classical degrees of freedom. In a series of our studies, quantum and solvent effects on the reaction dynamics in solutions have been analysed in detail. Here, we report our mixed quantum-classical molecular dynamics calculations for intramolecular proton transfer of malonaldehyde in water. Thermally activated proton transfer process, i.e., vibrational excitation in the reactant state followed by transition to the product state and vibrational relaxation in the product state, as well as tunneling reaction can be described by solving the equation of motion. Zero point energy is, of course, included, too. The quantum simulation in water has been compared with the fully classical one and the wave packet calculation in vacuum. The calculated quantum reaction rate in water was 0.70 ps(-1), which is about 2.5 times faster than that in vacuum, 0.27 ps(-1). This indicates that the solvent water accelerates the reaction. Further, the quantum calculation resulted in the reaction rate about 2 times faster than the fully classical calculation, which indicates that quantum effect enhances the reaction rate, too. Contribution from three reaction mechanisms, i.e., tunneling, thermal activation, and barrier vanishing reactions, is 33:46:21 in the mixed quantum-classical calculations. This clearly shows that the tunneling effect is important in the reaction.

  16. Transition-metal-catalyzed C-N bond forming reactions using organic azides as the nitrogen source: a journey for the mild and versatile C-H amination.

    Science.gov (United States)

    Shin, Kwangmin; Kim, Hyunwoo; Chang, Sukbok

    2015-04-21

    Owing to the prevalence of nitrogen-containing compounds in functional materials, natural products and important pharmaceutical agents, chemists have actively searched for the development of efficient and selective methodologies allowing for the facile construction of carbon-nitrogen bonds. While metal-catalyzed C-N cross-coupling reactions have been established as one of the most general protocols for C-N bond formation, these methods require starting materials equipped with functional groups such as (hetero)aryl halides or their equivalents, thus generating stoichiometric amounts of halide salts as byproducts. To address this aspect, a transition-metal-catalyzed direct C-H amination approach has emerged as a step- and atom-economical alternative to the conventional C-N cross-coupling reactions. However, despite the significant recent advances in metal-mediated direct C-H amination reactions, most available procedures need harsh conditions requiring stoichiometric external oxidants. In this context, we were curious to see whether a transition-metal-catalyzed mild C-H amination protocol could be achieved using organic azides as the amino source. We envisaged that a dual role of organic azides as an environmentally benign amino source and also as an internal oxidant via N-N2 bond cleavage would be key to develop efficient C-H amination reactions employing azides. An additional advantage of this approach was anticipated: that a sole byproduct is molecular nitrogen (N2) under the perspective catalytic conditions. This Account mainly describes our research efforts on the development of rhodium- and iridium-catalyzed direct C-H amination reactions with organic azides. Under our initially optimized Rh(III)-catalyzed amination conditions, not only sulfonyl azides but also aryl- and alkyl azides could be utilized as facile amino sources in reaction with various types of C(sp(2))-H bonds bearing such directing groups as pyridine, amide, or ketoxime. More recently, a new

  17. Mathematical model of the MenD-catalyzed 1,4-addition (Stetter reaction) of α-ketoglutaric acid to acrylonitrile.

    Science.gov (United States)

    Sudar, Martina; Vasić-Rački, Đurđa; Müller, Michael; Walter, Alexandra; Blažević, Zvjezdana Findrik

    2018-02-20

    The Stetter reaction, a conjugate umpolung reaction, is well known for cyanide-catalyzed transformations of mostly aromatic aldehydes. Enzymatic Stetter reactions, however, have been largely unexplored, especially with respect to preparative transformations. We have investigated the kinetics of the MenD-catalyzed 1,4-addition of α-ketoglutaric acid to acrylonitrile which has shown that acrylonitrile, while an interesting candidate, is a poor substrate for MenD due to low affinity of the enzyme for this substrate. The kinetic model of the reaction was simplified to double substrate Michaelis-Menten kinetics where the reaction rate linearly depends on acrylonitrile concentration. Experiments at different initial concentrations of acrylonitrile under batch, repetitive batch, and fed-batch reactor conditions were carried out to validate the developed mathematical model. Thiamine diphosphate dependent MenD proved to be quite a robust enzyme; nevertheless, enzyme operational stability decay occurs in the reactor. The spontaneous reactivity of acrylonitrile towards polymerization was also taken into account during mathematical modeling. Almost quantitative conversion of acrylonitrile was achieved in all batch reactor experiments, while the yield of the desired product was dependent on initial acrylonitrile concentration (i.e., the concentration of the stabilizer additive). Using the optimized reactor parameters, it was possible to synthesize the product, 6-cyano-4-oxohexanoic acid, in a concentration of 250 mM. The highest concentration of product was achieved in a repetitive batch reactor experiment. A fed-batch reactor experiment also delivered promising results, especially regarding the short reaction time needed to achieve a 200 mM concentration of product. Hence, the enzymatic Stetter reaction with a highly reactive acceptor substrate can be performed on a preparative scale, which should enable similar transformations with acrylate, methacrylate, and methyl

  18. Measurement of Proton-Induced Transfer Reactions with JENSA

    Science.gov (United States)

    Chatterjee, Sidharth; Chipps, Kelly; Pain, Steven; Cizewski, Jolie; Jensa Collaboration

    2017-09-01

    Reaction measurements of radioactive nuclei on light targets are important to understanding the origin of and the trends in the structure of nuclei. To efficiently measure nuclear reactions, measurements require highly localized and pure light targets and need to accommodate arrays of light charged particles, gamma rays, and recoiling heavy ions. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) jet target system was designed to facilitate high resolution, low background nuclear reaction studies. To demonstrate the capability of the JENSA system, the 20Ne(p,3He)18F reaction was studied during the commissioning phase. The radioisotope 18F is one of the galactic gamma-ray sources targeted by next-generation space-based telescopes. In addition, the 20Ne(p,3He) reaction has not been previously used for the spectroscopic study of 18F. The JENSA system gives us the opportunity to study this reaction with high resolution and low background. The measurement was performed with a proton beam from the Holifield Radioactive Ion Beam Facility tandem on a neon jet of natural isotopic abundance from JENSA. The experimental setup of JENSA and preliminary results will be discussed. Oak Ridge National Laboratory; Rutgers University Department of Physics and Astronomy.

  19. Stereo-specificity for pro-(R) hydrogen of NAD(P)H during enzyme-catalyzed hydride transfer to CL-20

    International Nuclear Information System (INIS)

    Bhushan, Bharat; Halasz, Annamaria; Hawari, Jalal

    2005-01-01

    A dehydrogenase from Clostridium sp. EDB2 and a diaphorase from Clostridium kluyveri were reacted with CL-20 to gain insights into the enzyme-catalyzed hydride transfer to CL-20, and the enzyme's stereo-specificity for either pro-R or pro-S hydrogens of NAD(P)H. Both enzymes biotransformed CL-20 at rates of 18.5 and 24 nmol/h/mg protein, using NADH and NADPH as hydride-source, respectively, to produce a N-denitrohydrogenated product with a molecular weight of 393 Da. In enzyme kinetics studies using reduced deuterated pyridine nucleotides, we found a kinetic deuterium isotopic effect of 2-fold on CL-20 biotransformation rate using dehydrogenase enzyme against (R)NADD as a hydride-source compared to either (S)NADD or NADH. Whereas, in case of diaphorase, the kinetic deuterium isotopic effect of about 1.5-fold was observed on CL-20 biotransformation rate using (R)NADPD as hydride-source. In a comparative study with LC-MS, using deuterated and non-deuterated NAD(P)H, we found a positive mass-shift of 1 Da in the N-denitrohydrogenated product suggesting the involvement of a deuteride (D - ) transfer from NAD(P)D. The present study thus revealed that both dehydrogenase and diaphorase enzymes from the two Clostridium species catalyzed a hydride transfer to CL-20 and showed stereo-specificity for pro-R hydrogen of NAD(P)H

  20. A note on the Noyori model for chiral amplification in the aminoalcohol-catalyzed reaction of aldehydes with dialkylzinc

    Directory of Open Access Journals (Sweden)

    IVAN GUTMAN

    1999-11-01

    Full Text Available The Noyori model of chiral amplification in the alkylation of aldehydes by means of dialkylzinc, catalyzed by chiral aminoalcohols, is further elaborated. A direct, but approximate, relation is obtained between the enantiomeric excess of the catalyst added and the enantiomeric excess of the product.

  1. Spectroscopic Analyses on Reaction Intermediates Formed during Chlorination of Alkanes with NaOCl Catalyzed by a Nickel Complex

    NARCIS (Netherlands)

    Draksharapu, Apparao; Codolà, Zoel; Gómez, Laura; Lloret-Fillol, Julio; Browne, Wesley R; Costas, Miquel

    2015-01-01

    The spectroscopic, electrochemical, and crystallographic characterization of [((Me,H)PyTACN)Ni(II)(CH3CN)2](OTf)2 (1) ((Me,H)PyTACN = 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane, OTf = CF3SO3) is described together with its reactivity with NaOCl. 1 catalyzes the chlorination of alkanes

  2. Four mechanisms in the reactions of 3-aminopyrrole with 1,3,5-triazines: inverse electron demand Diels-Alder cycloadditions vs S(N)Ar reactions via uncatalyzed and acid-catalyzed pathways.

    Science.gov (United States)

    De Rosa, Michael; Arnold, David; Hartline, Douglas

    2013-09-06

    Reaction of 3-aminopyrrole with seven 1,3,5-triazines was studied in a one-step reaction (in situ formation of 3-aminopyrrole) and a two-step reaction (using the tetraphenylborate salt and an amine base). An inverse-electron demand Diels-Alder reaction (IEDDA) was observed with R1 = CF3, CO2Et, and H with the formation of 5H-pyrrolo[3,2-d]pyrimidine derivatives. S(N)Ar was observed when 2,4,6-trifluoro- or 2,4,6-trichloro-1,3,5-triazine were used--1,3,5-triazines that had leaving groups. If excess 1,3,5-triazine was present the initial S(N)Ar product reacted further, in the presence of acid and water, with another equivalent of 1,3,5-triazine to give compounds containing three linked heterocyclic rings. No reaction was observed with R1 = C6H5 and OCH3. Four mechanisms are proposed to explain the experimental results: uncatalyzed and acid catalyzed inverse electron demand Diels-Alder cascades leading to cycloaddition, and uncatalyzed and acid-catalyzed S(N)Ar reactions leading, respectively, to single and double substitution products. Acid catalysis was a factor when there was reduced reactivity in either reactant.

  3. Following solid-acid-catalyzed reactions by MAS NMR spectroscopy in liquid phase--zeolite-catalyzed conversion of cyclohexanol in water.

    Science.gov (United States)

    Vjunov, Aleksei; Hu, Mary Y; Feng, Ju; Camaioni, Donald M; Mei, Donghai; Hu, Jian Z; Zhao, Chen; Lercher, Johannes A

    2014-01-07

    A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid-liquid-gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The (13) C spectra show that dehydration of 1-(13) C-cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the (13) C label. A simplified kinetic model shows the E1-type elimination fully accounts for the initial rates of 1-(13) C-cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2-hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl-1-cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100-fold faster per proton. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Studies on catalysis by molten metals. X. Hydrogen transfer reactions between alcohols and ketones on liquid indium catalyst

    International Nuclear Information System (INIS)

    Miyamoto, A.; Ogino, Y.

    1976-01-01

    Hydrogen transfer reactions between alcohols and ketones were studied on liquid indium catalyst by using a pulse reaction technique, and a plausible reaction model is proposed to explain the experimental results including deuterium isotope effects. Further, the stereoselectivity observed in the transfer hydrogenation of methylcyclohexanones and the selectivities observed in the transfer hydrogenation of unsaturated ketones are discussed in terms of the proposed model

  5. A reevaluation of fluid flow, heat transfer and chemical reaction in catalyst filled tubes

    OpenAIRE

    Daszkowski, Thomas; Eigenberger, Gerhart

    1992-01-01

    The problem of heat transfer through the wall in catalyst filled tubes with a tube to particle diameter ratio greater than 4 - 5 and industrial flow rates with and without chemical reaction has been reevaluated through detailed experiments and model calculations. The results confirm and extend findings of Vortmeyer et al. that reaction and heat transfer can only be modeled with independently determined parameters if the radial variation of the axial mass flow velocity is properly considered. ...

  6. The influence of phase transfer catalyst structure on reaction selectivity

    International Nuclear Information System (INIS)

    Demlov, Eh.V.

    1995-01-01

    A concise review is given of systematic studies which are concerned with the tuning of regio, frequentio-, chemo-, and diastereoselectivity by the structure or type of phase transfer catalyst. Use of MEI as an alkylating agent is described. Refs. 36, figs. 11

  7. Synthesis and Reactions of Five-Membered Heterocycles Using Phase Transfer Catalyst (PTC Techniques

    Directory of Open Access Journals (Sweden)

    Ahmed M. El-Sayed

    2014-01-01

    Full Text Available Phase transfer catalysts (PTCs have been widely used for the synthesis of organic compounds particularly in both liquid-liquid and solid-liquid heterogeneous reaction mixtures. They are known to accelerate reaction rates by facilitating formation of interphase transfer of species and making reactions between reagents in two immiscible phases possible. Application of PTC instead of traditional technologies for industrial processes of organic synthesis provides substantial benefits for the environment. On the basis of numerous reports it is evident that phase-transfer catalysis is the most efficient way for generation and reactions of many active intermediates. In this review we report various uses of PTC in syntheses and reactions of five-membered heterocycles compounds and their multifused rings.

  8. Lecithin-cholesterol acyltransferase (LCAT) catalyzes transacylation of intact cholesteryl esters. Evidence for the partial reversal of the forward LCAT reaction

    International Nuclear Information System (INIS)

    Sorci-Thomas, M.; Babiak, J.; Rudel, L.L.

    1990-01-01

    Lecithin-cholesterol acyltransferase (LCAT) catalyzes the intravascular synthesis of lipoprotein cholesteryl esters by converting cholesterol and lecithin to cholesteryl ester and lysolecithin. LCAT is unique in that it catalyzes sequential reactions within a single polypeptide sequence. In this report we find that LCAT mediates a partial reverse reaction, the transacylation of lipoprotein cholesteryl oleate, in whole plasma and in a purified, reconstituted system. As a result of the reverse transacylation reaction, a linear accumulation of [3H]cholesterol occurred during incubations of plasma containing high density lipoprotein labeled with [3H]cholesteryl oleate. When high density lipoprotein labeled with cholesteryl [14C]oleate was also included in the incubation the labeled fatty acyl moiety remained in the cholesteryl [14C]oleate pool showing that the formation of labeled cholesterol did not result from hydrolysis of the doubly labeled cholesteryl esters. The rate of release of [3H]cholesterol was only about 10% of the forward rate of esterification of cholesterol using partially purified human LCAT and was approximately 7% in whole monkey plasma. Therefore, net production of cholesterol via the reverse LCAT reaction would not occur. [3H]Cholesterol production from [3H]cholesteryl oleate was almost completely inhibited by a final concentration of 1.4 mM 5,5'-dithiobis(nitrobenzoic acid) during incubation with either purified LCAT or whole plasma. Addition of excess lysolecithin to the incubation system did not result in the formation of [14C]oleate-labeled lecithin, showing that the reverse reaction found here for LCAT was limited to the last step of the reaction. To explain these results we hypothesize that LCAT forms a [14C]oleate enzyme thioester intermediate after its attack on the cholesteryl oleate molecule

  9. Definition and determination of the triplet-triplet energy transfer reaction coordinate

    Energy Technology Data Exchange (ETDEWEB)

    Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Frutos, Luis Manuel, E-mail: luisma.frutos@uah.es [Departamento de Química Física, Universidad de Alcalá, 28871 Alcalá de Henares, Madrid (Spain); Acuña, A. Ulises [Instituto de Química Física “Rocasolano”, C.S.I.C., Serrano 119, 28006 Madrid (Spain)

    2014-01-21

    A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

  10. Definition and determination of the triplet-triplet energy transfer reaction coordinate.

    Science.gov (United States)

    Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Acuña, A Ulises; Frutos, Luis Manuel

    2014-01-21

    A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

  11. A chiral Brønsted acid-catalyzed highly enantioselective Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines.

    Science.gov (United States)

    Unhale, Rajshekhar A; Sadhu, Milon M; Ray, Sumit K; Biswas, Rayhan G; Singh, Vinod K

    2018-04-03

    A chiral phosphoric acid-catalyzed asymmetric Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines, derived from 3-hydroxyisoindolinones has been demonstrated in this communication. A variety of isoindolinone-based α-amino diazo esters bearing a quaternary stereogenic center were afforded in high yields (up to 99%) with excellent enantioselectivities (up to 99% ee). Furthermore, the synthetic utility of the products has been depicted by the hydrogenation of the diazo moiety of adducts.

  12. The 2H(e, e' p)n reaction at large energy transfers

    NARCIS (Netherlands)

    Willering, Hendrik Willem

    2003-01-01

    At the ELSA accelerator facillity in Bonn, Germany, we have measured the deutron "breakup" reaction 2H(e,e' p)n at four-momentum transfers around Q2 = -0 .20(GeV/c)2 with an electron beam energy of E0 = 1.6 GeV. The cross section has been determined for energy transfers extending from the

  13. Mass transfer accompanied with complete reversible chemical reactions in gas-liquid systems: an overview

    NARCIS (Netherlands)

    van Swaaij, Willibrordus Petrus Maria; Versteeg, Geert

    1992-01-01

    In many processes in the chemical industry mass transfer accompanied with reversible, complex chemical reactions in gas-liquid systems are frequently encountered. In point of view of design purposes it is very important that the absorption rates of the transferred reactants can estimated

  14. Excited state intramolecular charge transfer reaction of 4 ...

    Indian Academy of Sciences (India)

    Administrator

    In spite of the above discus- sion, conclusions drawn from this work remain un- altered as the calculation of average equilibrium constant (Keq) involves only the amplitudes of the decay components, not the reaction time constants. 4. Conclusion. To summarize, the replacement of the carbon atom para to the nitrogen atom ...

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

    Indian Academy of Sciences (India)

    is found to produce a linear increase of confined solvent viscosity but leads to a non-monotonic electrolyte concentration ... The observed huge reduction in reaction rate constant is attributed to the effects of decreased solution polarity, enhanced vis- .... twisting mode while reacting inside a confined pool. We have used the ...

  16. Specific Features of Intramolecular Proton Transfer Reaction in Schiff Bases

    Directory of Open Access Journals (Sweden)

    Aleksander Koll

    2003-06-01

    Full Text Available Abstract: The differences between the intramolecular proton transfer in Mannich and Schiff bases are discussed. The tautomeric forms being in equilibrium in both types of molecules are seriously different. In Mannich bases there are in equilibrium the forms of phenols and phenolates. In Schiff bases each of tautomers is strongly influenced by resonance between zwitterionic and keto structures. Despite the common opinion that the proton transfer forms in compounds with internal π-electronic coupling are mainly keto forms it is shown in this work, that in Schiff bases the content of keto structure is slightly less than zwitterionic one. Almost equal participation of both forms leads to effective resonance between them and stabilization of intramolecular hydrogen bond in this way.

  17. Arsenate stabilized Cu₂O nanoparticle catalyst for one-electron transfer reversible reaction.

    Science.gov (United States)

    Sahoo, Ramkrishna; Dutta, Soumen; Pradhan, Mukul; Ray, Chaiti; Roy, Anindita; Pal, Tarasankar; Pal, Anjali

    2014-05-14

    The befitting capping capabilities of AsO4(3-) provide a stable Cu2O nanocatalyst from a galvanic reaction between a Cu(II) precursor salt and As(0) nanoparticles. This stable Cu2O hydrosol appears to be a suitable catalyst for the one-electron transfer reversible redox reaction between Eosin Y and NaBH4. The progress of the reaction relates to three different kinetic stages. In the presence of the new catalyst the reversible redox reaction of Eosin Y in air shows a periodic color change providing a new crowd-pleasing demonstration, i.e. a "clock reaction".

  18. Spectrophotometric determination of anilines based on charge-transfer reaction

    Science.gov (United States)

    Wu, Hao; Du, Li Ming

    2007-07-01

    The molecular interactions between aniline, p-toluidines, benzidine and p-phenylenediamine as electron donors and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as acceptor have been investigated by spectrophotometric method. Different variables affecting the reaction were studies and optimized. At the optimum reaction conditions Beer's law was obeyed in a concentration limit of 0.6-3.0, 0.3-3.0, 0.3-3.0 and 0.3-2.7 μg ml -1 for aniline, p-toluidines, benzidine and p-phenylenediamine. The developed methods were applied successfully for the determination of the studied compounds in waste water and relative standard deviation of the methods were 0.8-3.0%. Percentage recoveries ranged from 97.22% to 102.78%.

  19. Two-proton transfer reactions on even Ni and Zn isotopes

    International Nuclear Information System (INIS)

    Boucenna, A.; Kraus, L.; Linck, I.; Tsan Ung Chan

    1988-01-01

    Two-proton transfer reactions induced by 112 MeV 12 C ions on even Ni and Zn isotopes are found to be less selective than the analogous two-neutron transfer reactions induced on the same targets in a similar incident energy range. The additional collective aspects observed in the proton transfer are examined in view of a semiphenomenological model of two quasi-particles coupled to a triaxial asymmetric rotor. Tentative spin and parity assignments emerge from this comparison, from crude shell model calculations and from systematic trends

  20. Observation of new neutron-deficient isotopes with Z≥92 in multinucleon transfer reactions

    Directory of Open Access Journals (Sweden)

    H.M. Devaraja

    2015-09-01

    Full Text Available In deep inelastic multinucleon transfer reactions of 48Ca + 248Cm we observed about 100 residual nuclei with proton numbers between Z=82 and Z=100. Among them, there are five new neutron-deficient isotopes: 216U, 219Np, 223Am, 229Am and 233Bk. As separator for the transfer products we used the velocity filter SHIP of GSI while the isotope identification was performed via the α decay chains of the nuclei. These first results reveal that multinucleon transfer reactions together with here applied fast and sensitive separation and detection techniques are promising for the synthesis of new isotopes in the region of heaviest nuclei.

  1. Neutron transfer reactions: Surrogates for neutron capture for basic and applied nuclear science

    Energy Technology Data Exchange (ETDEWEB)

    Cizewski, J. A. [Rutgers University; Jones, K. L. [University of Tennessee; Kozub, R. L. [Tennessee Technological University; Pain, Steven D [ORNL; Peters, W. A. [Rutgers University; Adekola, Aderemi S [ORNL; Allen, J. [Rutgers University; Bardayan, Daniel W [ORNL; Becker, J. [Lawrence Livermore National Laboratory (LLNL); Blackmon, Jeff C [ORNL; Chae, K. Y. [University of Tennessee; Chipps, K. [Colorado School of Mines, Golden; Erikson, Luke [Colorado School of Mines, Golden; Gaddis, A. L. [Furman University; Harlin, Christopher W [ORNL; Hatarik, Robert [Rutgers University; Howard, Joshua A [ORNL; Jandel, M. [Los Alamos National Laboratory (LANL); Johnson, Micah [ORNL; Kapler, R. [University of Tennessee; Krolas, W. [University of Warsaw; Liang, J Felix [ORNL; Livesay, Jake [ORNL; Ma, Zhanwen [ORNL; Matei, Catalin [Oak Ridge Associated Universities (ORAU); Matthews, C. [Rutgers University; Moazen, Brian [University of Tennessee; Nesaraja, Caroline D [ORNL; O' Malley, Patrick [Rutgers University; Patterson, N. P. [University of Surrey, UK; Paulauskas, Stanley [University of Tennessee; Pelham, T. [University of Surrey, UK; Pittman, S. T. [University of Tennessee, Knoxville (UTK); Radford, David C [ORNL; Rogers, J. [Tennessee Technological University; Schmitt, Kyle [University of Tennessee; Shapira, Dan [ORNL; ShrinerJr., J. F. [Tennessee Technological University; Sissom, D. J. [Tennessee Technological University; Smith, Michael Scott [ORNL; Swan, T. P. [University of Surrey, UK; Thomas, J. S. [Rutgers University; Vieira, D. J. [Los Alamos National Laboratory (LANL); Wilhelmy, J. B. [Los Alamos National Laboratory (LANL); Wilson, Gemma L [ORNL

    2009-04-01

    Neutron capture reactions on unstable nuclei are important for both basic and applied nuclear science. A program has been developed at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory to study single-neutron transfer (d,p) reactions with rare isotope beams to provide information on neutron-induced reactions on unstable nuclei. Results from (d,p) studies on {sup 130,132}Sn, {sup 134}Te and {sup 75}As are discussed.

  2. Excitation functions for quasi-elastic transfer reactions induced with heavy ions in bismuth

    International Nuclear Information System (INIS)

    Gardes, D.; Bimbot, R.; Maison, J.; Reilhac, L. de; Rivet, M.F.; Fleury, A.; Hubert, F.; Llabador, Y.

    1977-01-01

    The excitation functions for the production of 210 Bi, 210 Po, sup(207-211)At and 211 Rn through quasi-elastic transfer reactions induced with heavy ions in 209 Bi have been measured. The corresponding reactions involved the transfer of one neutron, one proton, two and three charges from projectile to target. The projectiles used were 12 C, 14 N, 16 O, 19 F, 20 Ne, 40 Ca, 56 Fe and 63 Cu. The experimental techniques involved target irradiations and off-line α and γ activity measurements. Chemical separations were used to solve specific problems. Careful measurements of incident energies and cross sections were performed close to the reaction thresholds

  3. Recent aspects of the proton transfer reaction in H-bonded complexes

    Science.gov (United States)

    Szafran, Mirosław

    1996-07-01

    Proton transfer processes cover a very wide range of situations and time scales and they are of great interest from the viewpoint of chemical reactions in solution. These processes can occur via thermally activated crossing or tunneling. This review considers various aspects of this many-faceted field. Spectroscopic, dielectric, colligative and energetic properties and structures of various species with H-bonds are examined. Proton transfer reactions in water and organic solvents, and the contribution of various H-bonded species and ions to these processes are discussed. Among other topics, this survey includes the effects of solvent, acid-base stoichiometry, concentration, temperature and impurity on proton transfer reactions in complexes of phenols and carboxylic acids with amines, pyridines and pyridine N-oxides. The contribution of the nonstoichiometric acid-base complexes and ionic species to the reversible proton transfer mechanism is discussed.

  4. Electronic state selectivity in dication-molecule single electron transfer reactions: NO(2+) + NO.

    Science.gov (United States)

    Parkes, Michael A; Lockyear, Jessica F; Schröder, Detlef; Roithová, Jana; Price, Stephen D

    2011-11-07

    The single-electron transfer reaction between NO(2+) and NO, which initially forms a pair of NO(+) ions, has been studied using a position-sensitive coincidence technique. The reactivity in this class of collision system, which involves the interaction of a dication with its neutral precursor, provides a sensitive test of recent ideas concerning electronic state selectivity in dicationic single-electron transfer reactions. In stark contrast to the recently observed single-electron transfer reactivity in the analogous CO(2)(2+)/CO(2) and O(2)(2+)/O(2) collision systems, electron transfer between NO(2+) and NO generates two product NO(+) ions which behave in an identical manner, whether the ions are formed from NO(2+) or NO. This observed behaviour is in excellent accord with the recently proposed rationalization of the state selectivity in dication-molecule SET reactions using simple propensity rules involving one-electron transitions. This journal is © the Owner Societies 2011

  5. Product distributions for some thermal energy charge transfer reactions of rare gas ions

    Science.gov (United States)

    Anicich, V. G.; Laudenslager, J. B.; Huntress, W. T., Jr.; Futrell, J. H.

    1977-01-01

    Ion cyclotron resonance methods were used to measure the product distributions for thermal-energy charge-transfer reactions of He(+), Ne(+), and Ar(+) ions with N2, O2, CO, NO, CO2, and N2O. Except for the He(+)-N2 reaction, no molecular ions were formed by thermal-energy charge transfer from He(+) and Ne(+) with these target molecules. The propensity for dissociative ionization channels in these highly exothermic charge-transfer reactions at thermal energies contrasts with the propensity for formation of parent molecular ions observed in photoionization experiments and in high-energy charge-transfer processes. This difference is explained in terms of more stringent requirements for energy resonance and favorable Franck-Condon factors at thermal ion velocities.

  6. Development of Novel Electrode Materials for the Electrocatalysis of Oxygen-Transfer and Hydrogen-Transfer Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Simpson, Brett Kimball [Iowa State Univ., Ames, IA (United States)

    2002-01-01

    Throughout this thesis, the fundamental aspects involved in the electrocatalysis of anodic O-transfer reactions and cathodic H-transfer reactions have been studied. The investigation into anodic O-transfer reactions at undoped and Fe(III)[doped MnO2 films] revealed that MnO2 film electrodes prepared by a cycling voltammetry deposition show improved response for DMSO oxidation at the film electrodes vs. the Au substrate. Doping of the MnO2 films with Fe(III) further enhanced electrode activity. Reasons for this increase are believed to involve the adsorption of DMSO by the Fe(III) sites. The investigation into anodic O-transfer reactions at undoped and Fe(III)-doped RuO2 films showed that the Fe(III)-doped RuO2-film electrodes are applicable for anodic detection of sulfur compounds. The Fe(III) sites in the Fe-RuO2 films are speculated to act as adsorption sites for the sulfur species while the Ru(IV) sites function for anodic discharge of H2O to generate the adsorbed OH species. The investigation into cathodic H-transfer reactions, specifically nitrate reduction, at various pure metals and their alloys demonstrated that the incorporation of metals into alloy materials can create a material that exhibits bifunctional properties for the various steps involved in the overall nitrate reduction reaction. The Sb10Sn20Ti70, Cu63Ni37 and Cu25Ni75 alloy electrodes exhibited improved activity for nitrate reduction as compared to their pure component metals. The Cu63Ni37 alloy displayed the highest activity for nitrate reduction. The final investigation was a detailed study of the electrocatalytic activity of cathodic H-transfer reactions (nitrate reduction) at various compositions of Cu-Ni alloy electrodes. Voltammetric response for NO3- at the Cu-Ni alloy electrode is superior to

  7. 31P NMR saturation-transfer measurements in Saccharomyces cerevisiae: characterization of phosphate exchange reactions by iodoacetate and antimycin A inhibition

    International Nuclear Information System (INIS)

    Campbell-Burk, S.L.; Jones, K.A.; Shulman, R.G.

    1987-01-01

    31 P nuclear magnetic resonance (NMR) saturation-transfer (ST) techniques have been used to measure steady-state flows through phosphate-adenosine 5'-triphosphate (ATP) exchange reactions in glucose-grown derepressed yeast. The results have revealed that the reactions catalyzed by glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase (GAPDH/PGK) and by the mitochondrial ATPase contribute to the observed ST. Contributions from these reactions were evaluated by performing ST studies under various metabolic conditions in the presence and absence of either iodoacetate, a specific inhibitor of GAPDH, or the respiratory chain inhibitor antimycin A. Intracellular phosphate (P/sub i/) longitudinal relaxation times were determined by performing inversion recovery experiments during steady-state ATP/sub λ/ saturation and were used in combination with ST data to determine P/sub i/ consumption rates. 13 C NMR and O 2 electrode measurements were also conducted to monitor changes in rates of glucose consumption and O 2 consumption, respectively, under the various metabolic conditions examined. The results suggest that GAPDH/PGK-catalyzed P/sub i/-ATP exchange is responsible for antimycin-resistant saturation transfer observed in anaerobic and aerobic glucose-fed yeast. Kinetics through GAPDH/PGK were found to depend on metabolic conditions. The coupled system appears to operate in a unidirectional manner during anaerobic glucose metabolism and bidirectionally when the cells are respiring on exogenously supplied ethanol. Additionally, mitochondrial ATPase activity appears to be responsible for the transfer observed in iodoacetate-treated aerobic cells supplied with either glucose or ethanol, with synthesis of ATP occurring unidirectionally

  8. Isotopically sensitive branching and its effect on the observed intramolecular isotope effects in cytochrome P-450 catalyzed reactions: a new method for the estimation of intrinsic isotope effects

    International Nuclear Information System (INIS)

    Jones, J.P.; Korzekwa, K.R.; Rettie, A.E.; Trager, W.F.

    1986-01-01

    Two selectively deuterated n-octanes (octane-1- 2 H 3 and octane-1,2,3- 2 H 7 ) were synthesized and subjected to hydroxylation by phenobarbital-induced rat liver microsomes and purified cytochrome P-450b. The results of these experiments provide evidence which clarifies the interplay between a branched reaction pathway and the equilibration of an enzyme-substrate complex, in determining the magnitude of an observed isotope effect. An equation is derived that allows limits to placed on the intrinsic isotope effect. The equation is based on the observed isotope effect and the regioselectivity of a branch reaction pathway, catalyzed by an enzyme that forms two products via a single enzyme-substrate complex. The intrinsic isotope effect for the formation of 1-octanol was determined by this equation to lie between 9.5 and 9.8

  9. Theoretical Mechanism Studies on the Enantioselectivity of aza-MBH-type Reaction of Nitroalkene to N-tosylimine Catalyzed by Thiourea-tertiary Amine

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Nan; Wang, Huatian; Wang, Yangping [Shandong Agricultural Univ., Taian (China)

    2013-12-15

    The enantioselective aza-Morita Baylis Hillman reaction of nitroalkene and N-tosylimine catalyzed by thiourea-tertiary amine has been investigated using density functional theory. Enantioselectivity is dominated by the cooperative effect of non-covalent and weak covalent interactions imposed by different units of catalyst. As Lewis base, the tertiary amine unit activates nitroalkene via weak covalent bond. The weak covalent interaction orients the reaction in a major path with smaller variations of this bond. The aromatic ring unit activates N-tosylimine via π-π stacking. The non-covalent interaction selects the major path with smaller changes of the efficient packing areas. Thiourea unit donates more compact H-bonded network for species of the major path. The calculated ee value in xylene solution phase (97.6%) is much higher than that in N,N-Dimethylformamide (27.2%). Our conclusion is also supported by NBO analysis.

  10. Investigation of Pd-catalyzed Co(III-EDTA/hypophosphite inhibition reaction kinetics, mechanism and the evaluation of its analytical application possibilities

    Directory of Open Access Journals (Sweden)

    M. AKCAY

    2004-02-01

    Full Text Available The reaction between Co(III-EDTA and hypophosphite ion, catalyzed by Pd(II was chosen as the indicator reaction. The inhibition kinetics of this catalytic reaction have been investigated by a mechanistic approach in the presence of some inhibitors. Catalysts other than PdCl2, that is Pt, Au, Ni salts, did not exhibit any effect on the reaction. An original reaction mechanism is proposed based on the experimental data. The important variables were optimized for maximum sensitivity. The calibration graph, which was prepared following the inhibition kinetic method, showed a linear relationship (r = – 0.9878 between the initial rate and iodide in the concentration range of 2–35 ng/cm3 I- with a detection limit of 1.2 ng/cm3 I- (3Sb/m criterion. The RSDs of the method, (N = 5 for 7 and 14 ng/cm3 were 1.19 and 0.81 %, respectively, depended on iodide concentration. The method was only applied to the determination of iodide in water, urine, iodized table salt and some drug samples and was compared with the modified Sandell–Kolthoff method.

  11. Attempts To Catalyze the Electrochemical CO2-to-Methanol Conversion by Biomimetic 2e(-) + 2H(+) Transferring Molecules.

    Science.gov (United States)

    Saveant, Jean-Michel; Tard, Cédric

    2016-01-27

    In the context of the electrochemical and photochemical conversion of CO2 to liquid fuels, one of the most important issues of contemporary energy and environmental issues, the possibility of pushing the reduction beyond the CO and formate level and catalytically generate products such as methanol is particularly attractive. Biomimetic 2e(-) + 2H(+) is often viewed as a potential hydride donor. This has been the object of a recent interesting attempt (J. Am. Chem. Soc. 2014, 136, 14007) in which 6,7-dimethyl-4-hydroxy-2-mercaptopteridine was reported as a catalyst of the electrochemical conversion of CO2 to methanol and formate, based on cyclic voltammetric, (13)C NMR, IR, and GC analyses. After checking electrolysis at the reported potential and at a more negative potential to speed up the reaction, it appears, on (1)H NMR and gas chromatographic grounds, that there is neither catalysis nor methanol and nor formate production. (1)H NMR (with H2O presaturation) brings about an unambiguous answer to the eventual production of methanol and formate, much more so than (13)C NMR, which can even be misleading when no internal standard is used as in the above-mentioned paper. IR analysis is even less conclusive. Use of a GC technique with sufficient sensitivity confirmed the lack of methanol formation. The direct or indirect hydride transfer electrochemical reduction of CO2 to formate and to methanol remains an open question. Original ideas and efforts such as those discussed here are certainly worth tempting. However, in view of the importance of the stakes, it appears necessary to carefully check reports in this area.

  12. Comparison of dynamical aspects of nonadiabatic electron, proton, and proton-coupled electron transfer reactions

    International Nuclear Information System (INIS)

    Hatcher, Elizabeth; Soudackov, Alexander; Hammes-Schiffer, Sharon

    2005-01-01

    The dynamical aspects of a model proton-coupled electron transfer (PCET) reaction in solution are analyzed with molecular dynamics simulations. The rate for nonadiabatic PCET is expressed in terms of a time-dependent probability flux correlation function. The impact of the proton donor-acceptor and solvent dynamics on the probability flux is examined. The dynamical behavior of the probability flux correlation function is dominated by a solvent damping term that depends on the energy gap correlation function. The proton donor-acceptor motion does not impact the dynamical behavior of the probability flux correlation function but does influence the magnitude of the rate. The approximations previously invoked for the calculation of PCET rates are tested. The effects of solvent damping on the proton donor-acceptor vibrational motion are found to be negligible, and the short-time solvent approximation, in which only equilibrium fluctuations of the solvent are considered, is determined to be valid for these types of reactions. The analysis of PCET reactions is compared to previous analyses of single electron and proton transfer reactions. The dynamical behavior is qualitatively similar for all three types of reactions, but the time scale of the decay of the probability flux correlation function is significantly longer for single proton transfer than for PCET and single electron transfer due to a smaller solvent reorganization energy for proton transfer

  13. Bond-formation versus electron transfer: C-C-coupling reactions of hydrocarbon dications with benzene.

    Science.gov (United States)

    Roithová, Jana; Schröder, Detlef

    2007-02-14

    The bimolecular reactions of several hydrocarbon dications C(m)H(n)(2+) (m = 6-10, n = 4-9) with neutral benzene are investigated by tandem mass spectrometry using a multipole instrument. Not surprisingly, the major reaction of C(m)H(n)(2+) with benzene corresponds to electron transfer from the neutral arene to the dication resulting in the pair of monocationic products C(m)H(n)(+) + C(6)H(6)(+). In addition, also dissociative electron transfer takes place, whereas proton transfer from the C(m)H(n)(2+) dication to neutral benzene is almost negligible. Interestingly, the excess energy liberated upon electron transfer from the neutral arene to the C(m)H(n)(2+) dication is not equally partitioned in the monocationic products in that the cations arising from the dicationic precursor have a higher internal energy content than the monocations formed from the neutral reaction partner. In addition to the reactions leading to monocationic product ions, bond-forming reactions with maintenance of the two-fold charge are observed, which lead to a condensation of the C(m)H(n)(2+) dications with neutral benzene under formation of intermediate C(m+6)H(n+6)(2+) species and then undergo subsequent losses of molecular hydrogen or neutral acetylene. This reaction complements a recently proposed dicationic route for the formation of polycyclic aromatic hydrocarbons under extreme conditions such as they exist in interstellar environments.

  14. Observing Proton Transfer Reactions Inside the MALDI Plume: Experimental and Theoretical Insight into MALDI Gas-Phase Reactions

    Science.gov (United States)

    Mirabelli, Mario F.; Zenobi, Renato

    2017-08-01

    We evaluated the contribution of gas-phase in-plume proton transfer reactions to the formation of protonated and deprotonated molecules in the MALDI process. A split sample holder was used to separately deposit two different samples, which avoids any mixing during sample preparation. The two samples were brought very close to each other and desorbed/ionized by the same laser pulse. By using a combination of deuterated and non-deuterated matrices, it was possible to observe exclusively in-plume proton transfer processes. The hydrogen/deuterium exchange (HDX) kinetics were evaluated by varying the delayed extraction (DE) time, allowing the desorbed ions and neutrals to interact inside the plume for a variable period of time before being extracted and detected. Quantum mechanical calculations showed that the HDX energy barriers are relatively low for such reactions, corroborating the importance of gas-phase proton transfer in the MALDI plume. The experimental results, supported by theoretical simulations, confirm that the plume is a very reactive environment, where HDX reactions could be observed from 0 ns up to 400 ns after the laser pulse. These results could be used to evaluate the relevance of previously proposed (and partially conflicting) ionization models for MALDI.

  15. Nobel Prize 1992: Rudolph A. Marcus: theory of electron transfer reactions in chemical systems

    International Nuclear Information System (INIS)

    Ulate Segura, Diego Guillermo

    2011-01-01

    A review of the theory developed by Rudolph A. Marcus is presented, who for his rating to the theory of electron transfer in chemical systems was awarded the Nobel Prize in Chemistry in 1992. Marcus theory has constituted not only a good extension of the use of a spectroscopic principle, but also has provided an energy balance and the application of energy conservation for electron transfer reactions. A better understanding of the reaction coordinate is exposed in terms energetic and establishing the principles that govern the transfer of electrons, protons and some labile small molecular groups as studied at present. Also, the postulates and equations described have established predictive models of reaction time, very useful for industrial environments, biological, metabolic, and others that involve redox processes. Marcus theory itself has also constituted a large contribution to the theory of complex transition [es

  16. The Mannich Reaction of Malonates with Simple Imines Catalyzed by Bifunctional Cinchona Alkaloids: Enantioselective Synthesis of β-Amino Acids

    Science.gov (United States)

    Song, Jun; Wang, Yi; Deng, Li

    2011-01-01

    We describe the first efficient, direct asymmetric Mannich reactions with malonates and N-Boc aryl and alkyl imines by cooperative hydrogen bonding catalysis with a cinchona alkaloid bearing a thiourea functionality. We have also extended the scope of this reaction to β-ketoesters. The synthetic value of this new reaction is demonstrated in the establishment of a convergent enantioselective route toward the biologically important β-amino acids under mild and air- and moisture-tolerant conditions. PMID:16669669

  17. Rhodium-catalyzed [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes and CO: reaction design, development, application in natural product synthesis, and inspiration for developing new reactions for synthesis of eight-membered carbocycles.

    Science.gov (United States)

    Wang, Yi; Yu, Zhi-Xiang

    2015-08-18

    Practical syntheses of natural products and their analogues with eight-membered carbocyclic skeletons are important for medicinal and biological investigations. However, methods and strategies to construct the eight-membered carbocycles are limited. Therefore, developing new methods to synthesize the eight-membered carbocycles is highly desired. In this Account, we describe our development of three rhodium-catalyzed cycloadditions for the construction of the eight-membered carbocycles, which have great potential in addressing the challenges in the synthesis of medium-sized ring systems. The first reaction described in this Account is our computationally designed rhodium-catalyzed two-component [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes (ene-VCPs) and CO for the diastereoselective construction of bi- and tricyclic cyclooctenones. The design of this reaction is based on the hypothesis that the C(sp(3))-C(sp(3)) reductive elimination of the eight-membered rhodacycle intermediate generated from the rhodium-catalyzed cyclopropane cleavage and alkene insertion, giving Wender's [5 + 2] cycloadduct, is not easy. Under CO atmosphere, CO insertion may occur rapidly, converting the eight-membered rhodacycle into a nine-membered rhodacycle, which then undergoes an easy C(sp(2))-C(sp(3)) reductive elimination process and furnishes the [5 + 2 + 1] product. This hypothesis was supported by our preliminary DFT studies and also served as inspiration for the development of two [7 + 1] cycloadditions: the [7 + 1] cycloaddition of buta-1,3-dienylcyclopropanes (BDCPs) and CO for the construction of cyclooctadienones, and the benzo/[7 + 1] cycloaddition of cyclopropyl-benzocyclobutenes (CP-BCBs) and CO to synthesize the benzocyclooctenones. The efficiency of these rhodium-catalyzed cycloadditions can be revealed by the application in natural product synthesis. Two eight-membered ring-containing natural products, (±)-asterisca-3(15),6-diene and (+)-asteriscanolide, have been

  18. Direct Carboxylation of C(sp3-H and C(sp2-H Bonds with CO2 by Transition-Metal-Catalyzed and Base-Mediated Reactions

    Directory of Open Access Journals (Sweden)

    Immacolata Tommasi

    2017-12-01

    Full Text Available This review focuses on recent advances in the field of direct carboxylation reactions of C(sp3-H and C(sp2-H bonds using CO2 encompassing both transition-metal-catalysis and base-mediated approach. The review is not intended to be comprehensive, but aims to analyze representative examples from the literature, including transition-metal catalyzed carboxylation of benzylic and allylic C(sp3-H functionalities using CO2 which is at a “nascent stage”. Examples of light-driven carboxylation reactions of unactivated C(sp3-H bonds are also considered. Concerning C(sp3-H and C(sp2-H deprotonation reactions mediated by bases with subsequent carboxylation of the carbon nucleophile, few examples of catalytic processes are reported in the literature. In spite of this, several examples of base-promoted reactions integrating “base recycling” or “base regeneration (through electrosynthesis” steps have been reported. Representative examples of synthetically efficient, base-promoted processes are included in the review.

  19. 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......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...

  20. Analysis of trace gases at ppb levels by proton transfer reaction mass spectrometry (PTR-MS)

    International Nuclear Information System (INIS)

    Lindinger, W.; Hansel, A.

    1996-01-01

    A proton transfer reaction mass spectrometry (PTR-MS) system has been developed which allows for on-line measurements of trace gas components with concentrations as low as 1 ppb. The method is based on reactions of H 3 O + ions, which perform non-dissociative proton transfer to most of the common organic trace constituents but do not react with any of the components present in clean air. Examples of medical information obtained by means of breath analysis, of environmental trace analysis, and examples in the field of food chemistry demonstrate the wide applicability of the method. (Authors)

  1. Characterization of Porphyrin-Co(III)-‘Nitrene Radical’ Species Relevant in Catalytic Nitrene Transfer Reactions

    OpenAIRE

    Goswami, Monalisa; Lyaskovskyy, Volodymyr; Domingos, Sérgio R.; Buma, Wybren Jan; Woutersen, Sander; Troeppner, Oliver; Ivanović-Burmazović, Ivana; Lu, Hongjian; Cui, Xin; Zhang, X. Peter; Reijerse, Edward J.; DeBeer, Serena; van Schooneveld, Matti M.; Pfaff, Florian Felix; Ray, Kallol

    2015-01-01

    To fully characterize the CoIII–‘nitrene radical’ species that are proposed as intermediates in nitrene transfer reactions mediated by cobalt(II) porphyrins, different combinations of cobalt(II) complexes of porphyrins and nitrene transfer reagents were combined, and the generated species were studied using EPR, UV–vis, IR, VCD, UHR-ESIMS, and XANES/XAFS measurements. Reactions of cobalt-(II) porphyrins 1P1 (P1 = meso-tetraphenylporphyrin (TPP)) and 1P2 (P2 = 3,5-DitBu-ChenPhyrin) with organi...

  2. Interplay of break-up and transfer processes in reactions involving weakly-bound systems

    Science.gov (United States)

    Vitturi, Andrea; Moschini, Laura

    2018-02-01

    In this note we illustrate some applications of a simple model which has been devised to clarify the reaction mechanism and the interplay of different reaction channels (elastic, inelastic, transfer, break-up) in heavy-ion collisions. The model involves two potential wells moving in one dimension and few active particles; in spite of its simplicity, it is supposed to maintain the main features, the properties and the physics of the full three-dimensional case. Special attention is given to the role of continuum states in reactions involving weakly-bound systems, and different approximation schemes (as first-order or coupled-channels) as well as different continuum discretization procedures are tested. In the case of two active particles the reaction mechanism associated with two-particle transfer and the effect of pairing intearction are investigated. Work done in collaboration with Antonio Moro and Kouichi Hagino

  3. Cyclic Multiblock Copolymers via Combination of Iterative Cu(0)-Mediated Radical Polymerization and Cu(I)-Catalyzed Azide-Alkyne Cycloaddition Reaction.

    Science.gov (United States)

    Xiao, Lifen; Zhu, Wen; Chen, Jiqiang; Zhang, Ke

    2017-02-01

    Cyclic multiblock polymers with high-order blocks are synthesized via the combination of single-electron transfer living radical polymerization (SET-LRP) and copper-catalyzed azide-alkyne cycloaddition (CuAAC). The linear α,ω-telechelic multiblock copolymer is prepared via SET-LRP by sequential addition of different monomers. The SET-LRP approach allows well control of the block length and sequence as A-B-C-D-E, etc. The CuAAC is then performed to intramolecularly couple the azide and alkyne end groups of the linear copolymer and produce the corresponding cyclic copolymer. The block sequence and the cyclic topology of the resultant cyclic copolymer are confirmed by the characterization of 1 H nuclear magnetic resonance spectroscopy, gel permeation chromatography, Fourier transform infrared spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. The medium reorganization energy for the charge transfer reactions in proteins.

    Science.gov (United States)

    Krishtalik, Lev I

    2011-11-01

    A low static dielectric permittivity of proteins causes the low reorganization energies for the charge transfer reactions inside them. This reorganization energy does not depend on the pre-existing intraprotein electric field. The charge transferred inside the protein interacts with its aqueous surroundings; for many globular proteins, the effect of this surroundings on the reorganization energy is comparable with the effect of reorganization of the protein itself while for the charge transfer in the middle of membrane the aqueous phase plays a minor role. Reorganization energy depends strongly on the system considered, and hence there is no sense to speak on the "protein reorganization energy" as some permanent characteristic parameter. We employed a simple algorithm for calculation of the medium reorganization energy using the numerical solution of the Poisson-Boltzmann equation. Namely, the reaction field energy was computed in two versions - all media having optical dielectric permittivity, and all the media with the static one; the difference of these two quantities gives the reorganization energy. We have calculated reorganization energies for electron transfer in cytochrome c, various ammine-ruthenated cytochromes c, azurin, ferredoxin, cytochrome c oxidase, complex of methylamine dehydrogenase with amicyanin, and for proton transfer in α-chymotrypsin. It is shown that calculation of the medium reorganization energy can be a useful tool in analysis of the mechanisms of the charge transfer reactions in proteins. 2011 Elsevier B.V. All rights reserved.

  5. Electron transfer reaction of butane -1,3-diol and cr(vi) in aqueous ...

    African Journals Online (AJOL)

    Kinetic and mechanistic studies of electron transfer reaction of butane-1,3-diol and Cr(VI) ion in aqueous acidic medium have been carried out in aqueous medium at 271°C, I = 1.0 mol dm-3 (NaCl), [H +] = 0.5mol dm-3 (HCl). The reaction was inhibited by added anions and showed negative salt effect. Spectroscopic ...

  6. Unprecedented cobalt-catalyzed isomerization reactions to single skipped 2,4,7-trienes applied in the synthesis of urushiol.

    Science.gov (United States)

    Schmidt, Anastasia; Hilt, Gerhard

    2014-09-01

    The cobalt-catalyzed isomerization of 1,3-dienes to 2Z,4E-dienes was realized for the very challenging substrates with an additional double bond in the side chain. An isomerization to the conjugated 3,5,7-triene derivative was not observed, which is in stark contrast to observations with many other isomerization catalysts. Accordingly, the synthesis of the natural product urushiol, which has a sensitive 2Z,4E,7Z-triene subunit in the side chain, was investigated. The O-protected urushiol derivative was generated selectively without isomerization to the conjugated 3,5,7-triene or Z/E-isomerization of the double bond at position 7. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Evaluation of the Optimal Reaction Conditions for the Methanolysis and Ethanolysis of Castor Oil Catalyzed by Immobilized Enzymes

    DEFF Research Database (Denmark)

    Andrade, Thalles Allan; Al-Kabalawi, Ibrahim; Errico, Massimiliano

    This study aims to compare the efficiency of the transesterification of castor oil with methanol and ethanol as part of the biodiesel production, using immobilized enzyme Lipozyme IM as catalyst. Different reaction conditions were evaluated and optimized, including the reaction temperature, alcohol-to-oil...

  8. Palladium on Carbon-Catalyzed Suzuki-Miyaura Coupling Reaction Using an Efficient and Continuous Flow System

    Directory of Open Access Journals (Sweden)

    Tomohiro Hattori

    2015-01-01

    Full Text Available The continuous flow Suzuki-Miyaura reaction between various haloarenes and arylboronic acids was successfully achieved within only ca. 20 s during the single-pass through a cartridge filled with palladium on carbon (Pd/C. No palladium leaching was observed in the collected reaction solution by atomic absorption spectrometry (detection limit: 1 ppm.

  9. Equilibrium coverage of OHad in correlation with platinum catalyzed fuel cell reactions in HClO4

    DEFF Research Database (Denmark)

    Deng, Yujia; Arenz, Matthias; Wiberg, Gustav Karl Henrik

    2015-01-01

    We employ a recently developed stripping protocol to examine the equilibrium coverage of oxygenated species and their influence on the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR). In particular we aim to distinguish between dynamic and steady state conditions...

  10. Bismuth(III) trifluoromethanesulfonate catalyzed ring opening reaction of mono epoxy oleochemicals to form keto and diketo derivatives

    Science.gov (United States)

    Using a catalytic system, methyl oleate is transformed into long chain keto and diketo derivatives via an epoxide route. Methyl 9(10)-oxooctadecanoate and methyl 9,10-dioxooctadecanoate were made by a ring opening reaction of epoxidized methyl oleate using bismuth triflate catalyst. Lower reaction t...

  11. Influence of the chain-transfer reactions on the emulsion post-polymerization process

    International Nuclear Information System (INIS)

    Lukhovitskij, V.I.; Polikarpov, V.V.; Pozdeeva, R.M.

    1975-01-01

    A probability of free radical exit from latex particle in the course of chain transfer reaction is defined by properties of the radical itself. In the case of emulsive post-polymerization of styrene in the presence of H-dodecylmercantane the value α for CCL 3 is about 3x10 -2 , for radical C 12 H 25 it is close to zero and for the radical generated under transfer to the monomer it is approximately 10 -2 . The effect of transfer to the monomer on the emulsive post-polymerization is discussed: it is responsible for the high degree of monomer conversion

  12. Development of a methodology based on metal-catalyzed oxidation reactions and mass spectrometry to determine the metal binding sites in copper metalloproteins.

    Science.gov (United States)

    Lim, Jihyeon; Vachet, Richard W

    2003-03-01

    Efforts have been made to develop a method that uses metal-catalyzed oxidation (MCO) reactions and mass spectrometry (MS) to identify the binding site of copper in metalloproteins. This method uses MCO reactions to oxidize the amino acids in the metal-binding site and MS to identify the amino acids that have been oxidized. Several reaction conditions, including Cu(II)/ascorbate/O2, Cu(II)/O2/H2O2, and Cu(II)/ascorbate/O2/H2O2, have been tested at varying concentrations to find the optimum conditions for specific oxidation of only the amino acids bound to copper. For small peptides, such as angiotensin I (Agt I) and [Gln11]-amyloid-beta-protein fragment 1-16 (A beta(1-16)), the optimum conditions for specific modification involve the use of Cu(II)/ascorbate/O2. For a larger protein, azurin, the speed and specificity of the MCO reactions are enhanced by the presence of a relatively high concentration of ascorbate (100 mM) and a small concentration of H2O2 (1 mM). Optimized reaction conditions combined with MS/MS and MSn analysis on a quadrupole ion trap mass spectrometer allow the copper-binding sites to be specifically identified. For Agt I and A beta(1-16), the amino acids bound to copper can be identified without any false positives. For azurin, four of the five amino acids bound to copper are identified with one false positive. This false positive, however, corresponds to the oxidation of Met44, which is probably due to its susceptibility to oxidation and its proximity to the only residue not identified (i.e., Gly45). The results altogether suggest that MCO reactions and MS provide a very promising approach for identifying the amino acid residues bound to copper in metalloproteins.

  13. 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...

  14. 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.

  15. New process of the preparation of catalyzed gas diffusion electrode for PEM fuel cells based on ultrasonic direct solution spray reaction method

    Energy Technology Data Exchange (ETDEWEB)

    Oishi, K.; Savadogo, O. [Ecole Polytechnique de Montreal, Montreal, PQ (Canada). Laboratoire de nouveaux materiaux pour l' energie et l' electrochimie

    2008-07-01

    This paper reported on a newly developed process for in-situ catalyst deposition on gas diffusion electrodes (GDE) for polymer electrolyte fuel cells. This process has the potential to reduce the number of steps for catalyzed GDE fabrication. In addition, the process offers economic advantages for the fuel cell commercialization. In this study, a home-made catalyst maker with ultrasonic spray method was used to prepare a solution of the carbon supported platinum catalyst on the GDL. The sprayed catalyst powder consisted of carbon support. The catalyst particles did not prevent gas flow channels on the GDL. The catalyst layer was shown to be located only on the top surface of the GDL and was not packed into its flow channel. Results of Cross-section SEM image, crystallization, micro structure and electro-catalytic activity for the oxygen reduction reaction were also discussed. 1 ref., 1 fig.

  16. Mass transfer model for two-layer TBP oxidation reactions: Revision 1

    International Nuclear Information System (INIS)

    Laurinat, J.E.

    1994-01-01

    To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the Canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. Bubbles containing reaction products enhance the rate of transfer of water from the aqueous layer to the organic layer. These bubbles are generated by the oxidation of TBP and its reaction products in the organic layer and by the oxidation of butanol in the aqueous layer. Butanol is formed by the hydrolysis of TBP in the organic layer. For aqueous-layer bubbling to occur, butanol must transfer into the aqueous layer. Consequently, the rate of oxidation and bubble generation in the aqueous layer strongly depends on the rate of transfer of butanol from the organic to the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments

  17. A novel 4-aminoantipyrine-Pd(II complex catalyzes Suzuki–Miyaura cross-coupling reactions of aryl halides

    Directory of Open Access Journals (Sweden)

    Claudia A. Contreras-Celedón

    2014-12-01

    Full Text Available A simple and efficient catalytic system based on a Pd complex of 4-aminoantipyrine, 4-AAP–Pd(II, was found to be highly active for Suzuki–Miyaura cross-coupling of aryl iodides and bromides with phenylboronic acids under mild reaction conditions. Good to excellent product yields from the cross-coupling reaction can be achieved when the reaction is carried out in ethanol, in the open air, using low loading of 4-AAP–Pd(II as a precatalyst, and in the presence of aqueous K2CO3 as the base. A variety of functional groups are tolerated.

  18. Direct Kinetic Evidence for the Formation of an Acylpyridinium Intermediate in Synthetic p-Nitrophenyl Esterase-Catalyzed Hydrolysis Reactions

    National Research Council Canada - National Science Library

    Wang, Guang-Jia

    1996-01-01

    .... The deacylation rate was also found to exhibit a maximum for the same substrate 2 (n=6). These results are similar to those previously reported with cholesterol esterase as catalyst for the same hydrolysis reaction...

  19. Rapid Access to Nanographenes and Fused Heteroaromatics by Palladium-Catalyzed Annulative π-Extension Reaction of Unfunctionalized Aromatics with Diiodobiaryls.

    Science.gov (United States)

    Matsuoka, Wataru; Ito, Hideto; Itami, Kenichiro

    2017-09-25

    Efficient and rapid access to nanographenes and π-extended fused heteroaromatics is important in materials science. Herein, we report a palladium-catalyzed efficient one-step annulative π-extension (APEX) reaction of polycyclic aromatic hydrocarbons (PAHs) and heteroaromatics, producing various π-extended aromatics. In the presence of a cationic Pd complex, triflic acid, silver pivalate, and diiodobiaryls, diverse unfunctionalized PAHs and heteroaromatics were directly transformed into larger PAHs, nanographenes, and π-extended fused heteroaromatics in a single step. In the reactions that afford [5]helicene substructures, simultaneous dehydrogenative ring closures occur at the fjord regions to form unprecedented larger nanographenes. This successive APEX reaction is notable as it stiches five aryl-aryl bonds by C-H functionalization in a single operation. Moreover, the unique molecular structures, crystal-packing structures, photophysical properties, and frontier molecular orbitals of the thus-formed nanographenes were elucidated. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Photo-Mediated Copper(I)-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) "Click" Reactions for Forming Polymer Networks as Shape Memory Materials.

    Science.gov (United States)

    McBride, Matthew K; Gong, Tao; Nair, Devatha P; Bowman, Christopher N

    2014-11-05

    The formation of polymer networks polymerized with the Copper (I) - catalyzed azide - alkyne cycloaddition (CuAAC) click reaction is described along with their accompanying utilization as shape memory polymers. Due to the click nature of the reaction and the synthetic accessibility of azide and alkyne functional-monomers, the polymer architecture was readily controlled through monomer design to manipulate crosslink density, ability for further functionalization, and the glass transition temperature (55 to 120°C). Free strain recovery is used to quantify the shape memory properties of a model CuAAC network resulting in excellent shape fixity and recovery of 99%. The step growth nature of this polymerization results in homogenous network formation with narrow glass transitions ranges having half widths of the transition close to 15°C for these materials resulting in shape recovery sharpness of 3.9 %/°C in a model system comparable to similarly crosslinked chain growth polymers. Utilization of the CuAAC reaction to form shape memory materials opens a range of possibilities and behaviors that are not readily achieved in other shape memory materials such as (meth) acrylates, thiolene, thiol-Michael, and poly(caprolactone) based shape memory materials.

  1. Photo-Mediated Copper(I)-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) “Click” Reactions for Forming Polymer Networks as Shape Memory Materials

    Science.gov (United States)

    McBride, Matthew K.; Gong, Tao; Nair, Devatha P.; Bowman, Christopher N.

    2014-01-01

    The formation of polymer networks polymerized with the Copper (I) – catalyzed azide – alkyne cycloaddition (CuAAC) click reaction is described along with their accompanying utilization as shape memory polymers. Due to the click nature of the reaction and the synthetic accessibility of azide and alkyne functional-monomers, the polymer architecture was readily controlled through monomer design to manipulate crosslink density, ability for further functionalization, and the glass transition temperature (55 to 120°C). Free strain recovery is used to quantify the shape memory properties of a model CuAAC network resulting in excellent shape fixity and recovery of 99%. The step growth nature of this polymerization results in homogenous network formation with narrow glass transitions ranges having half widths of the transition close to 15°C for these materials resulting in shape recovery sharpness of 3.9 %/°C in a model system comparable to similarly crosslinked chain growth polymers. Utilization of the CuAAC reaction to form shape memory materials opens a range of possibilities and behaviors that are not readily achieved in other shape memory materials such as (meth) acrylates, thiolene, thiol-Michael, and poly(caprolactone) based shape memory materials. PMID:25378717

  2. Isolation of Key Organometallic Aryl-Co(III) Intermediates in Cobalt-Catalyzed C(sp2)-H Functionalizations and New Insights into Alkyne Annulation Reaction Mechanisms.

    Science.gov (United States)

    Planas, Oriol; Whiteoak, Christopher J; Martin-Diaconescu, Vlad; Gamba, Ilaria; Luis, Josep M; Parella, Teodor; Company, Anna; Ribas, Xavi

    2016-11-02

    The selective annulation reaction of alkynes with substrates containing inert C-H bonds using cobalt as catalyst is currently a topic attracting significant interest. Unfortunately, the mechanism of this transformation is still relatively poorly understood, with little experimental evidence for intermediates, although an organometallic Co(III) species is generally implicated. Herein, we describe a rare example of the preparation and characterization of benchtop-stable organometallic aryl-Co(III) compounds (NMR, HRMS, XAS, and XRD) prepared through a C(sp 2 )-H activation, using a model macrocyclic arene substrate. Furthermore, we provide crystallographic evidence of an organometallic aryl-Co(III) intermediate proposed in 8-aminoquinoline-directed Co-catalyzed C-H activation processes. Subsequent insights obtained from the application of our new organometallic aryl-Co(III) compounds in alkyne annulation reactions are also disclosed. Evidence obtained from the resulting regioselectivity of the annulation reactions and DFT studies indicates that a mechanism involving an organometallic aryl-Co(III)-alkynyl intermediate species is preferred for terminal alkynes, in contrast to the generally accepted migratory insertion pathway.

  3. Palladium-catalyzed cascade reactions of 1-(3-arylprop-2-ynyloxy)-2-bromo benzene derivatives with organoboron compounds.

    Science.gov (United States)

    Arcadi, Antonio; Blesi, Federico; Cacchi, Sandro; Fabrizi, Giancarlo; Goggiamani, Antonella; Marinelli, Fabio

    2013-05-03

    Applications of the cascade cyclocarbopalladation reaction followed by Suzuki-Miyaura coupling reactions of the readily available aryl-substituted propargylic aryl ethers with arylboronic acid and potassium trans-β-styryltrifluoroborate accomplish a new versatile entry in the synthesis of benzofuran derivatives. Notably, a new approach to the challenging synthesis of C3 functionalized 2-unsubstituted benzofurans has been developed by a cyclocarbopalladation/cross-coupling/aromatization process.

  4. 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.

  5. Carbon-based Solid Acid Catalyzed One-pot Mannich Reaction: A Facile Synthesis of β-Amino Carbonyl Compounds

    Energy Technology Data Exchange (ETDEWEB)

    Davoodnia, Abolghasem; Tavakoli-Nishaburi, Afsaneh; Tavakoli-Hoseini, Niloofar [Islamic Azad University, Mashhad (Iran, Islamic Republic of)

    2011-02-15

    A simple and efficient method for the synthesis of β-amino carbonyl compounds by one-pot three-component Mannich reaction of acetophenone, aromatic aldehydes and aromatic amines using a carbon-based solid acid (CBSA), as an effective and reusable catalyst, is described. The present methodology offers several advantages such as simple procedure with an easy work-up, shorter reaction times, and high yields.

  6. Asymmetric Mannich Reaction of Isatin-Based Ketimines with α-Diazomethylphosphonates Catalyzed by Chiral Silver Phosphate.

    Science.gov (United States)

    Chen, Jing; Wen, Xiaojing; Wang, Yan; Du, Fei; Cai, Liu; Peng, Yungui

    2016-09-02

    An efficient asymmetric Mannich reaction of isatin-based ketimines with α-diazomethylphosphonates has been developed using a chiral binaphthanol-derived silver phosphate as the catalyst. This reaction allowed the construction of a series of chiral oxindoles bearing a quaternary stereocenter and amino group at the C3 position with up to 95% yields and 99% ee. Those products could be further transformed into promising densely functionalized compounds by merging of the oxindole and β-aminophosphonate.

  7. Chemo- and Diastereoselective N-Heterocyclic Carbene-Catalyzed Cross-Benzoin Reactions Using N-Boc-α-amino Aldehydes.

    Science.gov (United States)

    Haghshenas, Pouyan; Gravel, Michel

    2016-09-16

    N-Boc-α-amino aldehydes are shown to be excellent partners in cross-benzoin reactions with aliphatic or heteroaromatic aldehydes. The chemoselectivity of the reaction and the facial selectivity on the amino aldehyde allow cross-benzoin products to be obtained in good yields and good diastereomeric ratios. The developed method is utilized as the key step in a concise total synthesis of d-arabino-phytosphingosine.

  8. Base free N-alkylation of anilines with ArCH2OH and transfer hydrogenation of aldehydes/ketones catalyzed by the complexes of η5-Cp*Ir(iii) with chalcogenated Schiff bases of anthracene-9-carbaldehyde.

    Science.gov (United States)

    Dubey, Pooja; Gupta, Sonu; Singh, Ajai K

    2018-03-12

    The condensation of anthracene-9-carbaldehyde with 2-(phenylthio/seleno)ethylamine results in Schiff bases [PhS(CH 2 ) 2 C[double bond, length as m-dash]N-9-C 14 H 9 ](L1) and [PhSe(CH 2 ) 2 C[double bond, length as m-dash]N-9-C 14 H 9 ] (L2). On their reaction with [(η 5 -Cp*)IrCl(μ-Cl)] 2 and CH 3 COONa at 50 °C followed by treatment with NH 4 PF 6 , iridacycles, [(η 5 -Cp*)Ir(L-H)][PF 6 ] (1: L = L1; 2: L = L2), result. The same reaction in the absence of CH 3 COONa gives complexes [(η 5 -Cp*)Ir(L)Cl][PF 6 ] (3-4) in which L = L1(3)/L2(4) ligates in a bidentate mode. The ligands and complexes were authenticated with HR-MS and NMR spectra [ 1 H, 13 C{ 1 H} and 77 Se{ 1 H} (in the case of L2 and its complexes only)]. Single crystal structures of L2 and half sandwich complexes 1-4 were established with X-ray crystallography. Three coordination sites of Ir in each complex are covered with η 5 -Cp* and on the remaining three, donor atoms present are: N, S/Se and C - /Cl - , resulting in a piano-stool structure. The moisture and air insensitive 1-4 act as efficient catalysts under mild conditions for base free N-alkylation of amines with benzyl alcohols and transfer hydrogenation (TH) of aldehydes/ketones. The optimum loading of 1-4 as a catalyst is 0.1-0.5 mol% for both the activations. The best reaction temperature is 80 °C for transfer hydrogenation and 100 °C for N-alkylation. The mercury poisoning test supports a homogeneous pathway for both the reactions catalyzed by 1-4. The two catalytic processes are most efficient with 3 followed by 4 > 1 > 2. The mechanism proposed on the basis of HR-MS of the reaction mixtures of the two catalytic processes taken after 1-2 h involves the formation of an alkoxy and hydrido species. The real catalytic species proposed in the case of iridacycles results due to the loss of the Cp* ring.

  9. Curing reactions of bismaleimide resins catalyzed by triphenylphosphine. High resolution solid-state 13C NMR study

    International Nuclear Information System (INIS)

    Shibahara, Sumio; Enoki, Takashi; Yamamoto, Takahisa; Motoyoshiya, Jiro; Hayashi, Sadao.

    1996-01-01

    The curing reactions of bismaleimide resins consisted of N,N'-4,4'-diphenylmethanebismaleimide (BMI) and o,o'-diallylbisphenol-A (DABA) in the presence of triphenylphosphine (TPP) as a catalyst were investigated. DSC measurements showed that the catalytic effect of TPP on the curing reaction of BMI was more in the presence of DABA than in its absence. In order to explore this curing reaction, N-phenylmaleimide (PMI) and o-allylphenol (AP) were selected as model compounds. The products of the PMI/TPP system were oligomers and polymers of PMI, whereas the main product of the PMI/AP/TPP system was the PMI trimer which had the five-membered ring formed via the phosphonium ylide intermediate. In these model reactions, 13 C NMR was found to be useful to distinguish between trimerization and polymerization of PMI. On the basis of the results of the model reactions, the curing reactions of bismaleimide resins were investigated by high resolution solid state 13 C NMR techniques. In the BMI/TPP system, maleimides polymerize above 175degC, but the polymerization does not proceed at 120degC. On the other hand, maleimides trimerize above 120degC in the presence of DABA and TPP. The mechanism of the trimerization is briefly discussed. (author)

  10. Severe immediate allergic reactions to grapes: part of a lipid transfer protein-associated clinical syndrome

    NARCIS (Netherlands)

    Vassilopoulou, Emilia; Zuidmeer, Laurian; Akkerdaas, Jaap; Tassios, Ioannis; Rigby, Neil R.; Mills, E. N. Clare; van Ree, Ronald; Saxoni-Papageorgiou, Photini; Papadopoulos, Nikolaos G.

    2007-01-01

    BACKGROUND: Grape allergy is considered rare; grape lipid transfer protein (LTP; Vit v 1), an endochitinase and a thaumatin-like protein (TLP) have been reported as grape allergens. A considerable number of patients have referred to our department for severe reactions to grapes, and several IgE

  11. Electron transfer reactions, cyanide and O2 binding of truncated hemoglobin from Bacillus subtilis

    DEFF Research Database (Denmark)

    Fernandez, Esther; Larsson, Jonas T.; McLean, Kirsty J.

    2013-01-01

    The truncated hemoglobin from Bacillus subtilis (trHb-Bs) possesses a surprisingly high affinity for oxygen and resistance to (auto)oxidation; its physiological role in the bacterium is not understood and may be connected with its very special redox and ligand binding reactions. Electron transfer...

  12. Mechanism of the Primary Charge Transfer Reaction in the Cytochrome bc1 Complex

    DEFF Research Database (Denmark)

    Barragan, Angela M; Schulten, Klaus; Solov'yov, Ilia A

    2016-01-01

    , the quinol-protein interaction, which initiates the Q-cycle, has not yet been completely described. Furthermore, the initial charge transfer reactions of the Q-cycle lack a physical description. The present investigation utilizes classical molecular dynamics simulations in tandem with quantum density...

  13. Numerical analysis of inter-phase mass transfer with chemical reaction

    African Journals Online (AJOL)

    The numerical analysis in the present study simulates inter-phase mass transfer with chemical reaction of two immiscible liquids by simultaneously solving the Higbie Penetration model. The transport equations are solved numerically for concentration and temperature profiles at the inter-phase using finite volume method ...

  14. Cluster-transfer reactions with radioactive beams: a spectroscopic tool for neutron-rich nuclei

    CERN Document Server

    AUTHOR|(CDS)2086156; Raabe, Riccardo; Bracco, Angela

    In this thesis work, an exploratory experiment to investigate cluster-transfer reactions with radioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier, as a possible mean to perform $\\gamma$ spectroscopy studies of exotic neutron-rich nuclei at medium-high energies and spins. The experiment was performed at ISOLDE (CERN), employing the heavy-ion reaction $^{98}$Rb + $^{7}$Li at 2.85 MeV/A. Cluster-transfer reaction channels were studied through particle-$\\gamma$ coincidence measurements, using the MINIBALL Ge array coupled to the charged particle Si detectors T-REX. Sr, Y and Zr neutron-rich nuclei with A $\\approx$ 100 were populated by either triton- or $\\alpha$ transfer from $^{7}$Li to the beam nuclei and the emitted complementary charged fragment was detected in coincidence with the $\\gamma$ cascade of the residues, after few neutrons evaporation. The measured $\\gamma$ spectra were studied in detail and t...

  15. Offline thermal-desorption proton-transfer-reaction mass spectrometry to study composition of organic aerosol

    NARCIS (Netherlands)

    Timkovsky, J.; Dusek, U.|info:eu-repo/dai/nl/314134166; Henzing, J. S.; Kuipers, T. L.; Röckmann, T.|info:eu-repo/dai/nl/304838233; Holzinger, R.|info:eu-repo/dai/nl/337989338

    2015-01-01

    We present a novel approach to study the organic composition of aerosol filter samples using thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) in the laboratory. The method is tested and validated based on the comparison with in situ TD-PTR-MS measurements. In general, we

  16. Functional LH1 antenna complexes influence electron transfer in bacterial photosynthetic reaction centers.

    NARCIS (Netherlands)

    Visschers, R.W.; Vulto, S.I.E.; Jones, M.R.; van Grondelle, R.; Kraayenhof, R.

    1999-01-01

    The effect of the light harvesting 1 (LH1) antenna complex on the driving force for light-driven electron transfer in the Rhodobacter sphaeroides reaction center has been examined. Equilibrium redox titrations show that the presence of the LH1 antenna complex influences the free energy change for

  17. Functional LH1 antenna complexes influence electron transfer in bacterial photosynthetic reaction centers

    NARCIS (Netherlands)

    Visschers, R.W.; Vulto, S.I.E.; Jones, M.R.; van Grondelle, R.; Kraayenhof, R.

    1999-01-01

    The effect of the light harvesting 1 (LH1) antenna complex on the driving force for light-driven electron transfer in the Rhodobacter sphaeroides reaction center has been examined. Equilibrium redox titrations show that the presence of the LH1 antenna complex influences the free energy change for

  18. Mass transfer with complex reversible chemical reactions—I. Single reversible chemical reaction

    NARCIS (Netherlands)

    Versteeg, G.F.; Kuipers, J.A.M.; Beckum, F.P.H. van; Swaaij, W.P.M. van

    1989-01-01

    An improved numerical technique was used in order to develop an absorption model with which it is possible to calculate rapidly absorption rates for the phenomenon of mass transfer accompanied by a complex reversible chemical reaction. This model can be applied for the calculation of the mass

  19. Transfer reactions in sup(32,36)S + sup(144,154)Sm

    International Nuclear Information System (INIS)

    Pacheco, A.J.; Tada, M. di; Fernandez Niello, J.; Testoni, J.E.

    1990-01-01

    The deformation of spherical nuclei in transfer reactions near to the coulomb barrier is studied. The sup(32,36)S + sup(144,154)Sm reactions were carried out using sup(32)S beams produced by TANDAR accelerator in Buenos Aires with energies of 148 MeV and 160 MeV and sup(36)S beams produced by tandem accelerator of Laboratorio Nazionale di Legnaro with energies of 142 MeV and 155 MeV. The angular distributions were measured for sup(32)S reaction using gas ionization chamber and position sensitive detector. The mass spectra of reaction products were obtained measuring time of flight between time detectors, in the sup(36)S reaction. (M.C.K.)

  20. The Palladium Acetate-Catalyzed Microwave-Assisted Hirao Reaction without an Added Phosphorus Ligand as a "Green" Protocol: A Quantum Chemical Study on the Mechanism.

    Science.gov (United States)

    Keglevich, György; Henyecz, Réka; Mucsi, Zoltán; Kiss, Nóra Zs

    2017-12-19

    It was proved by our experiments that on microwave irradiation, the mono- or bidentate phosphorus ligands generally applied in the palladium(II)-catalyzed P-C coupling reaction of aryl bromides and dialkyl phosphites or secondary phosphine oxides may be substituted by the excess of the >P(O)H reagent that exists under a tautomeric equilibrium. Taking into account that the reduction of the palladium(II) salt and the ligation of the palladium(0) so formed requires 3 equivalents of the P-species for the catalyst applied in a quantity of 5-10%, all together, 15-30% of the P-reagent is necessary beyond its stoichiometric quantity. In the coupling reaction of diphenylphosphine oxide, it was possible to apply diethyl phosphite as the reducing agent and as the P-ligand. The reactivities of the diethyl phosphite and diphenylphosphine oxide reagents were compared in a competitive reaction. The mechanism and the energetics of this new variation of the Hirao reaction of bromobenzene with Y 2 P(O)H reagents (Y=EtO and Ph) was explored by quantum chemical calculations. The first detailed study on simple reaction models justified our assumption that, under the conditions of the reaction, the trivalent form of the >P(O)H reagent may serve as the P-ligand in the palladium(0) catalyst, and shed light on the fine mechanism of the reaction sequence. The existence of the earlier described bis(palladium complex) {[H(OPh 2 P) 2 PdOAc] 2 } was refuted by high level theoretical calculations. This kind of complex may be formed only with chloride anions instead of the acetate anion. The interaction of palladium acetate and Y 2 P(O)H may result in only the formation of the [(HO)Y 2 P] 2 Pd complex that is the active catalyst in the Hirao reaction. The new variation of the Hirao reaction is of a more general value, and represents the greenest protocol, as there is no need for the usual P-ligands. Instead, the >P(O)H reagent should be used in an excess of up to 30%. Hence, the costs and