Science.gov

Sample records for acyl transfer reaction

  1. Kinetics of acyl transfer reactions in organic media catalysed by Candida antarctica lipase B.

    PubMed

    Martinelle, M; Hult, K

    1995-09-01

    The acyl transfer reactions catalysed by Candida antartica lipase B in organic media followed a bi-bi ping-pong mechanism, with competitive substrate inhibition by the alcohols used as acyl acceptors. The effect of organic solvents on Vm and Km was investigated. The Vm values in acetonitrile was 40-50% of those in heptane. High Km values in acetonitrile compared to those in heptane could partly be explained by an increased solvation of the substrates in acetonitrile. Substrate solvation caused a 10-fold change in substrate specificity, defined as (Vm/Km)ethyl octanoate/(Vm/Km)octanoic acid, going from heptane to acetonitrile. Deacylation was the rate determining step for the acyl transfer in heptane with vinyl- and ethyl octanoate as acyl donors and (R)-2-octanol as acyl acceptor. With 1-octanol, a rate determining deacylation step in heptane was indicated using the same acyl donors. Using 1-octanol as acceptor in heptane, S-ethyl thiooctanoate had a 25- to 30-fold lower Vm/Km value and vinyl octanoate a 4-fold higher Vm/Km value than that for ethyl octanoate. The difference showed to be a Km effect for vinyl octanoate and mainly a Km effect for S-ethyl thiooctanoate. The Vm values of the esterification of octanoic acid with different alcohols was 10-30-times lower than those for the corresponding transesterification of ethyl octanoate. The low activity could be explained by a low pH around the enzyme caused by the acid or a withdrawing of active enzyme by nonproductive binding by the acid. PMID:7669809

  2. Protease-catalyzed peptide synthesis using inverse substrates: the influence of reaction conditions on the trypsin acyl transfer efficiency.

    PubMed

    Schellenberger, V; Jakubke, H D; Zapevalova, N P; Mitin, Y V

    1991-06-01

    Benzyloxycarbonyl-L-alanine p-guanidinophenyl ester behaves as a trypsin "inverse substrate," i.e., a cationic center is included in the leaving group instead of being in the acyl moiety. Using this substrate as an acyl donor, trypsin catalyzes the synthesis of peptide bonds that cannot be split by this enzyme. An optimal acyl transfer efficiency was achieved between pH 8 and 9 at 30 degrees C.The addition of as much as 50% cosolvent was shown to be of minor influence on the acyl transfer efficiency, whereas the reaction velocity decreases by more than one order of magnitude. The efficiency of H-Leu-NH(2) and H-Val-NH(2) in deacylation is almost the same for "inverse" and normal type substrates. PMID:18600704

  3. Monogalactosyldiacylglycerol biosynthesis by direct acyl transfer in Anabaene variabilis

    SciTech Connect

    Chen, H.H.; Wickrema, A.; Jaworski, J.

    1987-04-01

    The authors previously reported the direct acylation of monogalactosyldiacylglycerol (MGDG) by an enzyme in the membranes of the cyanobacterium Anabaena variabilis. The enzyme requires acyl-acyl carrier protein (acyl-ACP) as substrate, but had no other additional cofactor requirements. Palmitoyl-, stearoyl- and oleoyl-ACP were all effective substrates. The A. variabilis membranes also had a hydrolase activity which metabolized the acyl-ACP to yield free fatty acid and ACP. Possible mechanisms for the acylation reaction include either acyl exchange with existing MGDG or direct acyl transfer to a lyso-MGDG, with concomitant release of free ACP. The mechanism of this reaction has been resolved using a double labelled (/sup 14/C)acyl-(/sup 14/)ACP substrate prepared with E. coli acyl-ACP synthetase. Following incubation with the enzyme, the unreacted (/sup 14/)acyl-(/sup 14/)ACP was isolated and the (/sup 14/)acyl/(/sup 14/)ACP ratio determined. Comparison of this ratio to that of the original substrate indicated no change and eliminated acyl exchange as a possible mechanism. Therefore, the direct acylation of lyso-MGDG is the proposed mechanism for this enzyme.

  4. Monogalactosyldiacylglycerol biosynthesis by direct acyl transfer in Anabaena variabilis. [Anabaena variabilis

    SciTech Connect

    Chen, H.H.; Wickrema, A.; Jaworski, J.

    1987-05-01

    The authors previously reported the direct acylation of monogalactosyldiacylglycerol (MGDG) by an enzyme in the membranes of the cyanobacterium (Anabaena variabilis. The enzyme requires acyl-acyl carrier protein (acyl-ACP) as substrate, but had no other additional cofactor requirements. Palmitoyl-, stearoyl- and oleoyl-ACP were all effective substrates. The A. variabilis membranes also had a hydrolase activity which metabolized the acyl-ACP to yield free fatty acid and ACP. Possible mechanisms for the acylation reaction include either acyl exchange with existing MGDG or direct acyl transfer to a lyso-MGDG, with concomitant release of free ACP. The mechanism of this reaction has been resolved using a double labelled (/sup 14/C)acyl-(/sup 14/C)ACP substrate prepared with E. coli acyl-ACP synthetase. Following incubation with the enzyme, the unreacted (/sup 14/C)acyl-(/sup 14/C)ACP was isolated and the (/sup 14/C)acyl/(/sup 14/C)ACP ratio determined. Comparison of this ratio to that of the original substrate indicated no change and eliminated acyl exchange as a possible mechanism. Therefore, the direct acylation of lyso-MGDG is the proposed mechanism for this enzyme. The reaction is apparently specific for MGDG synthesis, as other glycolipids and phospholipids were not labelled during incubations.

  5. Plant Acyl-CoA:Lysophosphatidylcholine Acyltransferases (LPCATs) Have Different Specificities in Their Forward and Reverse Reactions*

    PubMed Central

    Lager, Ida; Yilmaz, Jenny Lindberg; Zhou, Xue-Rong; Jasieniecka, Katarzyna; Kazachkov, Michael; Wang, Peng; Zou, Jitao; Weselake, Randall; Smith, Mark A.; Bayon, Shen; Dyer, John M.; Shockey, Jay M.; Heinz, Ernst; Green, Allan; Banas, Antoni; Stymne, Sten

    2013-01-01

    Acyl-CoA:lysophosphatidylcholine acyltransferase (LPCAT) enzymes have central roles in acyl editing of phosphatidylcholine (PC). Plant LPCAT genes were expressed in yeast and characterized biochemically in microsomal preparations of the cells. Specificities for different acyl-CoAs were similar for seven LPCATs from five different species, including species accumulating hydroxylated acyl groups in their seed oil, with a preference for C18-unsaturated acyl-CoA and low activity with palmitoyl-CoA and ricinoleoyl (12-hydroxyoctadec-9-enoyl)-CoA. We showed that Arabidopsis LPCAT1 and LPCAT2 enzymes catalyzed the acylation and de-acylation of both sn positions of PC, with a preference for the sn-2 position. When acyl specificities of the Arabidopsis LPCATs were measured in the reverse reaction, sn-2-bound oleoyl, linoleoyl, and linolenoyl groups from PC were transferred to acyl-CoA to a similar extent. However, a ricinoleoyl group at the sn-2-position of PC was removed 4–6-fold faster than an oleoyl group in the reverse reaction, despite poor utilization in the forward reaction. The data presented, taken together with earlier published reports on in vivo lipid metabolism, support the hypothesis that plant LPCAT enzymes play an important role in regulating the acyl-CoA composition in plant cells by transferring polyunsaturated and hydroxy fatty acids produced on PC directly to the acyl-CoA pool for further metabolism or catabolism. PMID:24189065

  6. Comparison of the lipase activity in hydrolysis and acyl transfer reactions of two latex plant extracts from babaco (Vasconcellea x Heilbornii Cv.) and Plumeria rubra: Effect of the Aqueous microenvironment.

    PubMed

    Cambon, Emmanuelle; Gouzou, Fanny; Pina, Michel; Barea, Bruno; Barouh, Nathalie; Lago, Regina; Ruales, Jenny; Tsai, Shau-Wei; Villeneuve, Pierre

    2006-04-01

    The enzymatic properties of Plumeria rubra latex have been evaluated for the first time, showing a high activity in both hydrolysis and synthesis reactions, and compared to the biocatalytic behavior of babaco (Vasconcellea x Heilbornii cv.) latex. Both biocatalysts have been optimized by studying the various parameters that influence reaction kinetics. The optimum temperatures for hydrolysis reactions were 50 and 55 degrees C for babaco and Plumeria, respectively. The optimum pH for babaco latex was 7, whereas for Plumeria latex, two optimal pH values (4 and 7) were observed. With regard to esterification and acyl transfer reactions such as alcoholysis and interesterification, the influence of thermodynamic water activity on reaction yields was determined and correlated with water sorption and desorption isotherms. When babaco latex is used as a biocatalyst, optimal synthesis reaction yields are obtained when the enzymatic extract is stabilized at a water activity value of 0.38, which corresponds to a water content of 5.7%. This optimal level of hydration is located on the linear portion of the biocatalyst's sorption isotherm, where the water molecules exhibit high-energy interactions with the protein network. In synthesis reactions (esterification, alcoholysis, and interesterification) biocatalyzed by Plumeria latex, correlation between best reaction yields and water activity cannot be done. Indeed, the sorption isotherm plot has an atypical shape, indicating that water might be trapped in the latex matrix and, consequently, that the water content of the biocatalyst is highly dependent on the hydration history of the latex. PMID:16569067

  7. Chemical and Biochemical Transfer of Acyl Groups: A New Look at an Old Mechanism

    ERIC Educational Resources Information Center

    Douglas, Kenneth T.; Williams, Andrew

    1976-01-01

    Examines recent studies of the elimination-addition mechanism of acyl group transfer, in which an acid function moves from one acceptor to another. Presents diagnostic evidence for this mechanism and discusses acyl group transfers in metabolism. (MLH)

  8. Quantum chemical study of penicillin: Reactions after acylation

    NASA Astrophysics Data System (ADS)

    Li, Rui; Feng, Dacheng; Zhu, Feng

    The density functional theory methods were used on the model molecules of penicillin to determine the possible reactions after their acylation on ?-lactamase, and the results were compared with sulbactam we have studied. The results show that, the acylated-enzyme tetrahedral intermediate can evolves with opening of ?-lactam ring as well as the thiazole ring; the thiazole ring-open products may be formed via ?-lactam ring-open product or from tetrahedral intermediate directly. Those products, in imine or enamine form, can tautomerize via hydrogen migration. In virtue of the water-assisted, their energy barriers are obviously reduced.

  9. Enantioselective acyl transfer catalysis by a combination of common catalytic motifs and electrostatic interactions

    PubMed Central

    Mandai, Hiroki; Fujii, Kazuki; Yasuhara, Hiroshi; Abe, Kenko; Mitsudo, Koichi; Korenaga, Toshinobu; Suga, Seiji

    2016-01-01

    Catalysts that can promote acyl transfer processes are important to enantioselective synthesis and their development has received significant attention in recent years. Despite noteworthy advances, discovery of small-molecule catalysts that are robust, efficient, recyclable and promote reactions with high enantioselectivity can be easily and cost-effectively prepared in significant quantities (that is, >10 g) has remained elusive. Here, we demonstrate that by attaching a binaphthyl moiety, appropriately modified to establish H-bonding interactions within the key intermediates in the catalytic cycle, and a 4-aminopyridyl unit, exceptionally efficient organic molecules can be prepared that facilitate enantioselective acyl transfer reactions. As little as 0.5 mol% of a member of the new catalyst class is sufficient to generate acyl-substituted all-carbon quaternary stereogenic centres in quantitative yield and in up to 98:2 enantiomeric ratio (er) in 5 h. Kinetic resolution or desymmetrization of 1,2-diol can be performed with high efficiency and enantioselectivity as well. PMID:27079273

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

    PubMed Central

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

    2016-01-01

    The detection of protein lysine acylations remains a challenge due to a lack of specific antibodies for acylations with various chain lengths. This problem can be addressed by metabolic labeling techniques using carboxylates with reactive functionalities. Subsequent chemoselective reactions with a complementary moiety connected to a detection tag enable the visualization and quantification of the protein lysine acylome. In this study, we present EDTA-Pd(II) as a novel catalyst for the oxidative Heck reaction on protein-bound alkenes, which allows employment of fully aqueous reaction conditions. We used this reaction to monitor histone lysine acylation in vitro after metabolic incorporation of olefinic carboxylates as chemical reporters. PMID:25672493

  11. beta-Lactamase-catalyzed hydrolysis of acyclic depsipeptides and acyl transfer to specific amino acid acceptors.

    PubMed Central

    Pratt, R F; Govardhan, C P

    1984-01-01

    beta-Lactamases from all three classes, A, B, and C, catalyze the hydrolysis of specific acyclic depsipeptide (PhCH2CONHCR1R2CO2CHR3CO2H) analogs of acyl-D-alanyl-D-alanine peptides. The depsipeptides investigated, which are chemically as reactive toward nucleophiles as penicillins, are in general poor substrates, although differences between the classes of beta-lactamases have been observed: the order of effectiveness seems to be C greater than B greater than A. Certain class A and C beta-lactamases also catalyze phenylacetylglycyl transfer between phenylacetylglycyl depsipeptides and specific amino acid acceptors, a type of reaction hitherto identified more closely with D-alanyl-D-alanine transpeptidases than with beta-lactamases. Preliminary indications of an acyl-enzyme intermediate in these reactions have been obtained. These results support the suggestion [Tipper, D.J. and Strominger, J.L. (1965) Proc. Natl. Acad. Sci. USA 54, 1133-1141] that beta-lactamases are evolutionary descendants of bacterial cell wall D-alanyl-D-alanine transpeptidases. PMID:6424114

  12. Acetic anhydride: an intermediate analogue in the acyl-exchange reaction of citramalate lyase.

    PubMed

    Buckel, W

    1976-04-15

    1. Reactivation of deacetyl citramalate lyase by acetic anhydride proceeds through an enzyme-anhydride complex prior to actual acetylation. The reaction is inhibited by citramalate which is competitive with acetic anhydride. 2. A corresponding complex is an intermediate in the carboxymethylation of deacetyl enzyme by iodoacetate. However, the inhibition of this reaction by S-citramalate appears to be non-competitive with iodoacetate. 3. The results lead to the conclusion that acetic anhydride can be regarded as a structural analogue of citramalic acetic anhydride, the proposed intermediate in the acyl exchange reaction on citramalate lyase. 4. The formation of 6-citryl thiolester from the 1-thiolester via the cyclic citric anhydride provides a chemicla model for enzymic acyl exchange. 5. The data suggest that anhydrides are of general importance in acyl exchange reactions of thiolesters. PMID:1278157

  13. Mass Transfer with Chemical Reaction.

    ERIC Educational Resources Information Center

    DeCoursey, W. J.

    1987-01-01

    Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

  14. Acyl-acyl carrier protein: Lysomonogalactosyldiacylglycerol acyl transferase in Anabaena variabilis

    SciTech Connect

    Chen, H.H.

    1989-01-01

    Monogalactosyldiacylglycerol was produced when membranes isolated from the cyanobacterium, Anabaena variabilis, and washed free of soluble endogenous constituents, were incubated with ({sup 14}C)acyl-acyl carrier protein. This enzymatic synthesis of monogalactosyldiacylglycerol localized in the membranes was not dependent on any added cofactors, such as ATP, coenzyme A, and dithiothreitol. Palmitoyl-, stearoyl-, and oleoyl-acyl carrier proteins were approximately equally active as substrates with Km of 0.37, 0.36, and 0.23 {mu}M, respectively. The ({sup 14}C)acyl group was exclusively transferred to the sn-1 hydroxyl of the glycerol backbone of monogalactosyldiacylglycerol as demonstrated by hydrolysis of all incorporated acyl groups by the lipase from Rhizopus arrhizus delamar. Using a double labelled ({sup 14}C)acyl-({sup 14}C)acyl carrier protein, this enzyme catalyzed the direct transfer of the acyl group from acyl-acyl carrier protein to an endogenous lysomonogalactosyldiacylglycerol to form monogalactosyldiacylglycerol. The transfer reaction mechanism was also confirmed by the increased activity with the addition of the lysomonogalactosyldiacylglycerol suspension. A specific galactolipid acyl hydrolase activity was released into the soluble protein fraction when the membranes of Anabaena variabilis were treated with 2% Triton X-100. The positional specificity of this acyl hydrolase was demonstrated to be similar to that of Rhizopus lipase, i.e. only the acyl group at the sn-1 position was hydrolyzed. The acyl hydrolase which was also localized in the membrane fraction of Anabaena variabilis was presumably responsible for producing endogenous lysomonogalactosyldiacylglycerol used by the acyltransferase.

  15. Concerted Amidation of Activated Esters: Reaction Path and Origins of Selectivity in the Kinetic Resolution of Cyclic Amines via N-Heterocyclic Carbenes and Hydroxamic Acid Cocatalyzed Acyl Transfer

    PubMed Central

    2015-01-01

    The N-heterocyclic carbene and hydroxamic acid cocatalyzed kinetic resolution of cyclic amines generates enantioenriched amines and amides with selectivity factors up to 127. In this report, a quantum mechanical study of the reaction mechanism indicates that the selectivity-determining aminolysis step occurs via a novel concerted pathway in which the hydroxamic acid plays a key role in directing proton transfer from the incoming amine. This modality was found to be general in amide bond formation from a number of activated esters including those generated from HOBt and HOAt, reagents that are broadly used in peptide coupling. For the kinetic resolution, the proposed model accurately predicts the faster reacting enantiomer. A breakdown of the steric and electronic control elements shows that a gearing effect in the transition state is responsible for the observed selectivity. PMID:25050843

  16. Kinetic resolution of acids in acylation reactions in the presence of chiral tertiary amines

    SciTech Connect

    Potapov, V.M.; Dem'yanovich, V.M.; Khlebnikov, V.A.

    1988-07-10

    Asymmetric synthesis has now become an important method for the production of optically active compounds, and its most attractive form is asymmetric catalysis. This work was devoted to an investigation into asymmetric catalysis with chiral tertiary amines in acylation reactions. During the acylation of alcohols and amines by the action of racemic 2-phenylpropionic and 2-methyl-3-phenylpropionic acids in the presence of S-nicotine the initial acids are resolved kinetically. The (R)-2-phenylpropionic acid obtained in this way had an optical purity of 0.5-1.5%.

  17. The Liganding of Glycolipid Transfer Protein Is Controlled by Glycolipid Acyl Structure

    PubMed Central

    Kanack, Alex T; Lu, Min; Abagyan, Ruben; Brown, Rhoderick E; Patel, Dinshaw J

    2006-01-01

    Glycosphingolipids (GSLs) play major roles in cellular growth and development. Mammalian glycolipid transfer proteins (GLTPs) are potential regulators of cell processes mediated by GSLs and display a unique architecture among lipid binding/transfer proteins. The GLTP fold represents a novel membrane targeting/interaction domain among peripheral proteins. Here we report crystal structures of human GLTP bound to GSLs of diverse acyl chain length, unsaturation, and sugar composition. Structural comparisons show a highly conserved anchoring of galactosyl- and lactosyl-amide headgroups by the GLTP recognition center. By contrast, acyl chain chemical structure and occupancy of the hydrophobic tunnel dictate partitioning between sphingosine-in and newly-observed sphingosine-out ligand-binding modes. The structural insights, combined with computed interaction propensity distributions, suggest a concerted sequence of events mediated by GLTP conformational changes during GSL transfer to and/or from membranes, as well as during GSL presentation and/or transfer to other proteins. PMID:17105344

  18. Reaction of /alpha/,/beta/-unsaturated acyl isothiocyanates with salts of dithiocarbamic acids

    SciTech Connect

    Krus, K.; Masias, A.; Beletskaya, I.P.

    1989-01-10

    The reaction of unsaturated isothiocyanates with the sodium and calcium salts of N-alkyl- and N,N-dialkyldithiocarbamic acids was studied. Depending on the structure of the dithiocarbamate, the reaction products are thiazines or acyl dithiocarbamates. For the salts of methyldithiocarbamic acid the effect of the concentration and the nature of the metal on the relative yields of 6-phenyl-3-methylpropiorhodanine and 6-phenylpropiorhodanine was studied. A method is proposed for the synthesis of 3-substituted propiorhodanines.

  19. Effects of Nanoparticle Morphology and Acyl Chain Length on Spontaneous Lipid Transfer Rates

    DOE PAGESBeta

    Xia, Yan; Li, Ming; Charubin, Kamil; Liu, Ying; Heberle, Frederick A.; Katsaras, John; Jing, Benxin; Zhu, Yingxi; Nieh, Mu-Ping

    2015-11-05

    In this paper, we report on studies of lipid transfer rates between different morphology nanoparticles and lipids with different length acyl chains. The lipid transfer rate of dimyristoylphosphatidylcholine (di-C14, DMPC) in discoidal “bicelles” (0.156 h–1) is 2 orders of magnitude greater than that of DMPC vesicles (ULVs) (1.1 × 10–3 h–1). For both bicellar and ULV morphologies, increasing the acyl chain length by two carbons [going from di-C14 DMPC to di-C16, dipalmitoylphosphatidylcholine (DPPC)] causes lipid transfer rates to decrease by more than 2 orders of magnitude. Results from small angle neutron scattering (SANS), differential scanning calorimetry (DSC), and fluorescence correlationmore » spectroscopy (FCS) are in good agreement. Finally, the present studies highlight the importance of lipid dynamic processes taking place in different morphology biomimetic membranes.« less

  20. Effects of Nanoparticle Morphology and Acyl Chain Length on Spontaneous Lipid Transfer Rates

    SciTech Connect

    Xia, Yan; Li, Ming; Charubin, Kamil; Liu, Ying; Heberle, Frederick A.; Katsaras, John; Jing, Benxin; Zhu, Yingxi; Nieh, Mu-Ping

    2015-11-05

    In this paper, we report on studies of lipid transfer rates between different morphology nanoparticles and lipids with different length acyl chains. The lipid transfer rate of dimyristoylphosphatidylcholine (di-C14, DMPC) in discoidal “bicelles” (0.156 h–1) is 2 orders of magnitude greater than that of DMPC vesicles (ULVs) (1.1 × 10–3 h–1). For both bicellar and ULV morphologies, increasing the acyl chain length by two carbons [going from di-C14 DMPC to di-C16, dipalmitoylphosphatidylcholine (DPPC)] causes lipid transfer rates to decrease by more than 2 orders of magnitude. Results from small angle neutron scattering (SANS), differential scanning calorimetry (DSC), and fluorescence correlation spectroscopy (FCS) are in good agreement. Finally, the present studies highlight the importance of lipid dynamic processes taking place in different morphology biomimetic membranes.

  1. Reaction coordinates for electron transfer reactions

    SciTech Connect

    Rasaiah, Jayendran C.; Zhu Jianjun

    2008-12-07

    The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

  2. Clarification of the Mechanism of Acylation Reaction and Origin of Substrate Specificity of the Serine-Carboxyl Peptidase Sedolisin through QM/MM Free Energy Simulations

    SciTech Connect

    Xu, Qin; Yao, Jianzhuang; Wiodawer, Alexander; Guo, Hong

    2011-01-01

    Quantum mechanical/molecular mechanical (QM/MM) free energy simulations are applied for understanding the mechanism of the acylation reaction catalyzed by sedolisin, a representative serine-carboxyl peptidase, leading to the acyl-enzyme (AE) and first product from the enzyme-catalyzed reaction. One of the interesting questions to be addressed in this work is the origin of the substrate specificity of sedolisin that shows a relatively high activity on the substrates with Glu at P1 site. It is shown that the bond making and breaking events of the acylation reaction involving a peptide substrate (LLE*FL) seem to be accompanied by local conformational changes, proton transfers as well as the formation of alternative hydrogen bonds. The results of the simulations indicate that the conformational change of Glu at P1 site and its formation of a low barrier hydrogen bond with Asp-170 (along with the transient proton transfer) during the acylation reaction might play a role in the relatively high specificity for the substrate with Glu at P1 site. The role of some key residues in the catalysis is confirmed through free energy simulations. Glu-80 is found to act as a general base to accept a proton from Ser-287 during the nucleophilic attack and then as a general acid to protonate the leaving group (N H of P1 -Phe) during the cleavage of the scissile peptide bond. Another acidic residue, Asp-170, acts as a general acid catalyst to protonate the carbonyl of P1-Glu during the formation of the tetrahedral intermediate and as a general base for the formation of the acyl-enzyme. The energetic results from the free energy simulations support the importance of proton transfer from Asp-170 to the carbonyl of P1-Glu in the stabilization of the tetrahedral intermediate and the formation of a low-barrier hydrogen bond between the carboxyl group of P1-Glu and Asp-170 in the lowering of the free energy barrier for the cleavage of the peptide bond. Detailed analyses of the proton transfers

  3. A redox beginning: Which came first phosphoryl, acyl, or electron transfer ?. [Abstract only

    NASA Technical Reports Server (NTRS)

    Weber, Arthur L.

    1994-01-01

    Thermodynamic and kinetic information available on the synthesis of prebiotic monomers and polymers will be examined in order to illuminate the prebiotic plausibility of polymer syntheses based on (a) phosphoryl transfer that yields phosphodiester polymers, (b) acyl transfer that gives polyamides, and (c) electron transfer that produces polydisulfide or poly(thio)ester polymers. New experimental results on the oxidative polymerization of 2,3-dimercaptopropanol by ferric ions on the surface of ferric hydroxide oxide will be discussed as a chemical model of polymerization by electron transfer. This redox polymerization that yields polymers with a polydisulfide backbone was found to give oligomers up to the 15-mer from 1 mM of 2,3-dimercaptopropanol after one day at 25 C. High pressure liquid chromatography (HPLC) analysis of the oligomers was carried out on an Alltech OH-100 column eluted with acetonitrile-water.

  4. Transfer reactions in nuclear astrophysics

    NASA Astrophysics Data System (ADS)

    Bardayan, D. W.

    2016-08-01

    To a high degree many aspects of the large-scale behavior of objects in the Universe are governed by the underlying nuclear physics. In fact the shell structure of nuclear physics is directly imprinted into the chemical abundances of the elements. The tranquility of the night sky is a direct result of the relatively slow rate of nuclear reactions that control and determines a star’s fate. Understanding the nuclear structure and reaction rates between nuclei is vital to understanding our Universe. Nuclear-transfer reactions make accessible a wealth of knowledge from which we can extract much of the required nuclear physics information. A review of transfer reactions for nuclear astrophysics is presented with an emphasis on the experimental challenges and opportunities for future development.

  5. Ligand binding to the ACBD6 protein regulates the acyl-CoA transferase reactions in membranes.

    PubMed

    Soupene, Eric; Kuypers, Frans A

    2015-10-01

    The binding determinants of the human acyl-CoA binding domain-containing protein (ACBD) 6 and its function in lipid renewal of membranes were investigated. ACBD6 binds acyl-CoAs of a chain length of 6 to 20 carbons. The stoichiometry of the association could not be fitted to a 1-to-1 model. Saturation of ACBD6 by C16:0-CoA required higher concentration than less abundant acyl-CoAs. In contrast to ACBD1 and ACBD3, ligand binding did not result in the dimerization of ACBD6. The presence of fatty acids affected the binding of C18:1-CoA to ACBD6, dependent on the length, the degree of unsaturation, and the stereoisomeric conformation of their aliphatic chain. ACBD1 and ACBD6 negatively affected the formation of phosphatidylcholine (PC) and phosphatidylethanolamine in the red blood cell membrane. The acylation rate of lysophosphatidylcholine into PC catalyzed by the red cell lysophosphatidylcholine-acyltransferase 1 protein was limited by the transfer of the acyl-CoA substrate from ACBD6 to the acyltransferase enzyme. These findings provide evidence that the binding properties of ACBD6 are adapted to prevent its constant saturation by the very abundant C16:0-CoA and protect membrane systems from the detergent nature of free acyl-CoAs by controlling their release to acyl-CoA-utilizing enzymes. PMID:26290611

  6. Transfer reactions with heavy elements

    SciTech Connect

    Hoffman, D.C.

    1986-04-01

    Transfer reactions for several transuranium elements are studied. (/sup 248/Cm, /sup 249/Bk, /sup 249/CF, /sup 254/Es), /sup 16,18/O, /sup 20,22/Ne, and /sup 40,48/Ca projectiles are used. The production of neutron-rich heavy actinides is enhanced by the use of neutron-rich projectiles /sup 18/O and /sup 22/Ne. The maxima of the isotopic distributions occur at only 2 to 3 mass numbers larger for /sup 48/Ca than for /sup 40/Ca reactions with /sup 248/Cm. The cross sections decrease rapidly with the number of nucleons transferred. The use of neutron-rich targets favors the production of neutron-rich isotopes. ''Cold'' heavy targets are produced. Comparisons with simple calculations of the product excitation energies assuming binary transfers indicate that the maxima of the isotopic distributions occur at the lightest product isotope for which the energy exceeds the reaction barrier. The cross sections for transfer of the same nucleon clusters appear to be comparable for a wide variety of systems. 23 refs., 4 figs., 4 tabs.

  7. Rapid Covalent Fluorescence Labeling of Membrane Proteins on Live Cells via Coiled-Coil Templated Acyl Transfer.

    PubMed

    Reinhardt, Ulrike; Lotze, Jonathan; Mörl, Karin; Beck-Sickinger, Annette G; Seitz, Oliver

    2015-10-21

    Fluorescently labeled proteins enable the microscopic imaging of protein localization and function in live cells. In labeling reactions targeted against specific tag sequences, the size of the fluorophore-tag is of major concern. The tag should be small to prevent interference with protein function. Furthermore, rapid and covalent labeling methods are desired to enable the analysis of fast biological processes. Herein, we describe the development of a method in which the formation of a parallel coiled coil triggers the transfer of a fluorescence dye from a thioester-linked coil peptide conjugate onto a cysteine-modified coil peptide. This labeling method requires only small tag sequences (max 23 aa) and occurs with high tag specificity. We show that size matching of the coil peptides and a suitable thioester reactivity allow the acyl transfer reaction to proceed within minutes (rather than hours). We demonstrate the versatility of this method by applying it to the labeling of different G-protein coupled membrane receptors including the human neuropeptide Y receptors 1, 2, 4, 5, the neuropeptide FF receptors 1 and 2, and the dopamine receptor 1. The labeled receptors are fully functional and able to bind the respective ligand with high affinity. Activity is not impaired as demonstrated by activation, internalization, and recycling experiments. PMID:26367072

  8. N-Acylsaccharins: Stable Electrophilic Amide-Based Acyl Transfer Reagents in Pd-Catalyzed Suzuki-Miyaura Coupling via N-C Cleavage.

    PubMed

    Liu, Chengwei; Meng, Guangrong; Liu, Yongmei; Liu, Ruzhang; Lalancette, Roger; Szostak, Roman; Szostak, Michal

    2016-09-01

    The development of efficient catalytic methods for N-C bond cleavage in amides remains an important synthetic challenge. The first Pd-catalyzed Suzuki-Miyaura cross-coupling of N-acylsaccharins with boronic acids by selective N-C bond activation is reported. The reaction enables preparation of a variety of functionalized diaryl and alkyl-aryl ketones with broad functional group tolerance and in good to excellent yields. Of general interest, N-acylsaccharins serve as new, highly reactive, bench-stable, economical, amide-based, electrophilic acyl transfer reagents via acyl-metal intermediates. Mechanistic studies strongly support the amide N-C(O) bond twist as the enabling feature of N-acylsaccharins in the N-C bond cleavage. PMID:27513821

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

    SciTech Connect

    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.

  10. Merging Photoredox with Palladium Catalysis: Decarboxylative ortho-Acylation of Acetanilides with α-Oxocarboxylic Acids under Mild Reaction Conditions.

    PubMed

    Zhou, Chao; Li, Pinhua; Zhu, Xianjin; Wang, Lei

    2015-12-18

    A room temperature decarboxylative ortho-acylation of acetanilides with α-oxocarboxylic acids has been developed via a novel Eosin Y with Pd dual catalytic system. This dual catalytic reaction shows a broad substrate scope and good functional group tolerance, and an array of ortho-acylacetanilides can be afforded in high yields under mild conditions. PMID:26646667

  11. Transfer Reaction Studies with JENSA

    NASA Astrophysics Data System (ADS)

    Thompson, P.; Bardayan, D. W.; Blackmon, J. C.; Chipps, K. A.; Greife, U.; Linhardt, L. E.; Kontos, A.; Kozub, R. L.; Matos, M.; Montes, F.; Pain, S. D.; Pittman, S. T.; Sachs, A.; Schatz, H.; Schmitt, K. T.; Smith, M. S.; Jensa Collaboration

    2015-10-01

    The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target system was designed to provide a gas target that was pure, localized, and dense. Several commissioning experiments with the JENSA target, performed at Oak Ridge National Laboratory (ORNL), were undertaken to demonstrate the unique capability of JENSA for transfer reaction studies. JENSA has since completed its move from ORNL to the ReA3 reaccelerated beam hall at the National Superconducting Cyclotron Laboratory (NSCL). An overview of the JENSA design and operation will be presented, as well as a brief discussion of the experiments performed at ORNL with JENSA, with a focus on preliminary results from the 20Ne(p,t)18Ne commissioning experiment.

  12. Reaction of Glyconitriles with Organometallic Reagents: Access to Acyl β-C-Glycosides.

    PubMed

    Guisot, Nicolas E S; Ella Obame, Idriss; Ireddy, Prathap; Nourry, Arnaud; Saluzzo, Christine; Dujardin, Gilles; Dubreuil, Didier; Pipelier, Muriel; Guillarme, Stéphane

    2016-03-18

    A new strategy for the synthesis of acyl β-C-glycosides is described. The reactivity of glyconitriles toward organometallic reagents such as organomagnesium or organolithium derivatives was studied, affording acyl β-C-glycosides in moderate to good yields. In this study, glycal formation was efficiently prevented by deprotonating the hydroxyl group in position 2 of the glyconitriles during the process. PMID:26926714

  13. Enantioselective N-Heterocyclic Carbene-Catalyzed β-Hydroxylation of Enals Using Nitroarenes: An Atom Transfer Reaction That Proceeds via Single Electron Transfer

    PubMed Central

    2015-01-01

    A novel oxidative N-heterocyclic carbene-catalyzed reaction pathway has been discovered. Alkyl and aryl enals undergo β-hydroxylation via oxygen atom transfer from electron-deficient nitrobenzenes, followed by trapping of the resultant acyl azolium by the solvent. The proposed mechanism involves a single electron transfer event to initiate the reaction followed by radical recombination. This represents a profound mechanistic departure from the established two-electron disconnects in NHC catalysis. PMID:25302860

  14. Pseudo-enzymatic S-acylation of a myristoylated yes protein tyrosine kinase peptide in vitro may reflect non-enzymatic S-acylation in vivo.

    PubMed Central

    Bañó, M C; Jackson, C S; Magee, A I

    1998-01-01

    Covalent attachment of a variety of lipid groups to proteins is now recognized as a major group of post-translational modifications. S-acylation of proteins at cysteine residues is the only modification considered dynamic and thus has the potential for regulating protein function and/or localization. The activities that catalyse reversible S-acylation have not been well characterized and it is not clear whether both the acylation and the deacylation steps are regulated, since in principle it would be sufficient to control only one of them. Both apparently enzymatic and non-enzymatic S-acylation of proteins have previously been reported. Here we show that a synthetic myristoylated c-Yes protein tyrosine kinase undecapeptide undergoes spontaneous S-acylation in vitro when using a long chain acyl-CoA as acyl donor in the absence of any protein. The S-acylation was dependent on myristoylation of the substrate, the length of the incubation period, temperature and substrate concentration. When COS cell fractions were added to the S-acylation reaction no additional peptide:S-acyltransferase activity was detected. These results are consistent with the possibility that membrane-associated proteins may undergo S-acylation in vivo by non-enzymatic transfer of acyl groups from acyl-CoA. In this case, the S-acylation-deacylation process could be controlled by a regulated depalmitoylation mechanism. PMID:9480882

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

    PubMed

    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. PMID:26193994

  16. Fluorescent metal-organic polymers of zinc and cadmium from hydrothermal in situ acylation reaction.

    PubMed

    Yu, Xiao-Yang; Ye, Ling; Zhang, Xiao; Cui, Xiao-Bing; Zhang, Jian-Po; Xu, Ji-Qing; Hou, Qin; Wang, Tie-Gang

    2010-11-28

    A series of metal-organic complexes based on d(10) metals and the ligand H(4)bbh (H(4)bbh = benzene-1, 2, 4, 5-biformhydrazide), formed through hydrothermal in situ acylate reaction of H(4)bta (H(4)bta = benzene-1, 2, 4, 5-tetracarboxylic acid) with hydrazine hydrate (N(2)H(4)·H(2)O), have been prepared and structurally characterized by single-crystal X-ray diffraction. Compounds [Zn(μ(2)-H(2)bbh)(phen)(H(2)O)](2) (1) (phen = 1, 10-phenanthroline) and [Zn(μ(2)-H(2)bbh)(2, 2'-bpy)](2) (2) (2, 2'-bpy = 2, 2'-bipyridine) are both dinuclear complexes in which bridging ligands H(2)bbh(2-) display different μ(2)- coordination modes. [Zn(μ(2)-H(2)bbh)(1/2)(μ(2)-H(2)bbh)(1/2)(H(2)O)](n) (3) exhibits a two-dimensional (2-D) layer structure containing simultaneously two kinds of different coordination modes of H(2)bbh(2-): μ(2)-bidentate and μ(4)-tetradentate. [Cd(μ(3)-H(2)bbh)(phen)](n) (4) consists of one-dimensional (1-D) double-metal chains. The crystal structures of these compounds are stabilized by hydrogen bonds and π···π interactions, forming three-dimensional supramolecular networks. All of the compounds were characterized by IR, UV-vis spectra and elemental analysis and they show good fluorescence properties in the solid state at room temperature. In order to understand the emission mechanism, we carried out TDDFT calculations on the excited electronic states of compound 2. PMID:20886135

  17. Chemoselective O-acylation of hydroxyamino acids and amino alcohols under acidic reaction conditions: History, scope and applications.

    PubMed

    Kristensen, Tor E

    2015-01-01

    Amino acids, whether natural, semisynthetic or synthetic, are among the most important and useful chiral building blocks available for organic chemical synthesis. In principle, they can function as inexpensive, chiral and densely functionalized starting materials. On the other hand, the use of amino acid starting materials routinely necessitates protective group chemistry, and in reality, large-scale preparations of even the simplest side-chain derivatives of many amino acids often become annoyingly strenuous due to the necessity of employing protecting groups, on one or more of the amino acid functionalities, during the synthetic sequence. However, in the case of hydroxyamino acids such as hydroxyproline, serine, threonine, tyrosine and 3,4-dihydroxyphenylalanine (DOPA), many O-acyl side-chain derivatives are directly accessible via a particularly expedient and scalable method not commonly applied until recently. Direct acylation of unprotected hydroxyamino acids with acyl halides or carboxylic anhydrides under appropriately acidic reaction conditions renders possible chemoselective O-acylation, furnishing the corresponding side-chain esters directly, on multigram-scale, in a single step, and without chromatographic purification. Assuming a certain degree of stability under acidic reaction conditions, the method is also applicable for a number of related compounds, such as various amino alcohols and the thiol-functional amino acid cysteine. While the basic methodology underlying this approach has been known for decades, it has evolved through recent developments connected to amino acid-derived chiral organocatalysts to become a more widely recognized procedure for large-scale preparation of many useful side-chain derivatives of hydroxyamino acids and related compounds. Such derivatives are useful in peptide chemistry and drug development, as amino acid amphiphiles for asymmetric catalysis, and as amino acid acrylic precursors for preparation of catalytically

  18. Chemoselective O-acylation of hydroxyamino acids and amino alcohols under acidic reaction conditions: History, scope and applications

    PubMed Central

    2015-01-01

    Summary Amino acids, whether natural, semisynthetic or synthetic, are among the most important and useful chiral building blocks available for organic chemical synthesis. In principle, they can function as inexpensive, chiral and densely functionalized starting materials. On the other hand, the use of amino acid starting materials routinely necessitates protective group chemistry, and in reality, large-scale preparations of even the simplest side-chain derivatives of many amino acids often become annoyingly strenuous due to the necessity of employing protecting groups, on one or more of the amino acid functionalities, during the synthetic sequence. However, in the case of hydroxyamino acids such as hydroxyproline, serine, threonine, tyrosine and 3,4-dihydroxyphenylalanine (DOPA), many O-acyl side-chain derivatives are directly accessible via a particularly expedient and scalable method not commonly applied until recently. Direct acylation of unprotected hydroxyamino acids with acyl halides or carboxylic anhydrides under appropriately acidic reaction conditions renders possible chemoselective O-acylation, furnishing the corresponding side-chain esters directly, on multigram-scale, in a single step, and without chromatographic purification. Assuming a certain degree of stability under acidic reaction conditions, the method is also applicable for a number of related compounds, such as various amino alcohols and the thiol-functional amino acid cysteine. While the basic methodology underlying this approach has been known for decades, it has evolved through recent developments connected to amino acid-derived chiral organocatalysts to become a more widely recognized procedure for large-scale preparation of many useful side-chain derivatives of hydroxyamino acids and related compounds. Such derivatives are useful in peptide chemistry and drug development, as amino acid amphiphiles for asymmetric catalysis, and as amino acid acrylic precursors for preparation of

  19. Neutron transfer reactions at large distances

    SciTech Connect

    Rehm, K.E.; Glagola, B.G.; Kutschera, W.; Wolfs, F.L.H.; Wuosmaa, A.H. )

    1993-06-01

    [sup 58]Ni-induced one- and two-neutron transfer reactions have been measured on [sup 232]Th at [ital E][sub lab]=500 MeV. The transfer probabilities at large internuclear distances measured for the deformed [sup 232]Th target are compared with similar data on spherical [sup 208]Pb. For one-neutron transfer reactions good agreement between experiment and the prediction from the tunneling model is observed in both cases. The transfer probabilities for two-neutron transfer reactions deviate from the semiclassical predictions. The disagreement increases at higher bombarding energies. These deviations can be explained by the influence of diffractive effects which become more important at higher bombarding energies.

  20. Oxidative acylation using thioacids

    NASA Technical Reports Server (NTRS)

    Liu, R.; Orgel, L. E.

    1997-01-01

    Several important prebiotic reactions, including the coupling of amino acids into polypeptides by the formation of amide linkages, involve acylation. Theae reactions present a challenge to the understanding of prebiotic synthesis. Condensation reactions relying on dehydrating agents are either inefficient in aqueous solution or require strongly acidic conditions and high temperatures. Activated amino acids such as thioester derivatives have therefore been suggested as likely substrates for prebiotic peptide synthesis. Here we propose a closely related route to amide bond formation involving oxidative acylation by thioacids. We find that phenylalanine, leucine and phenylphosphate are acylated efficiently in aqueous solution by thioacetic acid and an oxidizing agent. From a prebiotic point of view, oxidative acylation has the advantage of proceeding efficiently in solution and under mild conditions. We anticipate that oxidative acylation should prove to be a general method for activating carboxylic acids, including amino acids.

  1. Hydrogen-Atom Transfer Reactions.

    PubMed

    Wang, Liang; Xiao, Jian

    2016-04-01

    The cascade [1,n]-hydrogen transfer/cyclization, recognized as the tert-amino effect one century ago, has received considerable interest in recent decades, and great achievements have been made. With the aid of this strategy, the inert C(sp(3))-H bonds can be directly functionalized into C-C, C-N, C-O bonds under catalysis of Lewis acids, Brønsted acids, as well as organocatalysts, and even merely under thermal conditions. Hydrogen can be transferred intramolecularly from hydrogen donor to acceptor in the form of hydride, or proton, followed by cyclization to furnish the cyclic products in processes featuring high atom economy. Methylene/methine adjacent to heteroatoms, e.g., nitrogen, oxygen, sulfur, can be exploited as hydride donor as well as methylene/methine without heteroatom assistance. Miscellaneous electrophilic subunits or intermediates, e.g., alkylidene malonate, carbophilic metal activated alkyne or allene, α,β-unsaturated aldehydes/ketone, saturated aldehydes/iminium, ketenimine/carbodiimide, metal carbenoid, electron-withdrawing groups activated allene/alkyne, in situ generated carbocation, can serve as hydride acceptors. This methodology has shown preeminent power to construct 5-, 6-, or 7-membered heterocyclic as well as carbon rings. In this chapter, various hydrogen donors and acceptors are adequately discussed. PMID:27573142

  2. Iridium-Catalyzed Hydrogen Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Saidi, Ourida; Williams, Jonathan M. J.

    This chapter describes the application of iridium complexes to catalytic hydrogen transfer reactions. Transfer hydrogenation reactions provide an alternative to direct hydrogenation for the reduction of a range of substrates. A hydrogen donor, typically an alcohol or formic acid, can be used as the source of hydrogen for the reduction of carbonyl compounds, imines, and alkenes. Heteroaromatic compounds and even carbon dioxide have also been reduced by transfer hydrogenation reactions. In the reverse process, the oxidation of alcohols to carbonyl compounds can be achieved by iridium-catalyzed hydrogen transfer reactions, where a ketone or alkene is used as a suitable hydrogen acceptor. The reversible nature of many hydrogen transfer processes has been exploited for the racemization of alcohols, where temporary removal of hydrogen generates an achiral ketone intermediate. In addition, there is a growing body of work where temporary removal of hydrogen provides an opportunity for using alcohols as alkylating agents. In this chemistry, an iridium catalyst "borrows" hydrogen from an alcohol to give an aldehyde or ketone intermediate, which can be transformed into either an imine or alkene under the reaction conditions. Return of the hydrogen from the catalyst provides methodology for the formation of amines or C-C bonds where the only by-product is typically water.

  3. A DFT study of the mechanism of NHC catalysed annulation reactions involving α,β-unsaturated acyl azoliums and β-naphthol.

    PubMed

    Aurell, M José; Domingo, Luis R; Arnó, Manuel; Zaragozá, Ramón J

    2016-09-21

    The mechanism of NHC catalysed annulation reactions involving an α,β-unsaturated acyl azolium and β-naphthol has been studied using DFT methods at the MPWB1K/6-311G(d,p) level in toluene. For the C-C bond formation step, which corresponds to the rate- and stereo-determining step of this NHC catalysed reaction, the two competitive addition modes, i.e. the 1,2- and the 1,4-additions, have been studied. In toluene, acyl azolium forms an ion pair (IP) with the counterion chloride anion. Interestingly, β-naphthol forms a hydrogen bond with the chloride anion of IP, increasing the nucleophilic character of β-naphthol and the electrophilic character of the acyl azolium moiety. For the first time, the transition state (TS) associated with the 1,2-addition is found and characterised. An analysis of the activation Gibbs free energies involved in the two competitive pathways makes it possible to rule out the pathway associated with the 1,2-addition. The relative Gibbs free energy of stereoisomeric TSs present in the 1,4-additions, accounts for the experimentally observed stereoselectivity. Finally, a comparative study of the pathways associated with the 1,2- and the 1,4-addition of β-naphthalenethiol to the acyl azolium moiety of IP accounts for the low reactivity of β-naphthalenethiol in these NHC catalysed annulation reactions involving α,β-unsaturated acyl azoliums. PMID:27530598

  4. Acylation of Ferrocene: A Greener Approach

    ERIC Educational Resources Information Center

    Birdwhistell, Kurt R.; Nguyen, Andy; Ramos, Eric J.; Kobelja, Robert

    2008-01-01

    The acylation of ferrocene is a common reaction used in organic laboratories to demonstrate Friedel-Crafts acylation and the purification of compounds using column chromatography. This article describes an acylation of ferrocene experiment that is more eco-friendly than the conventional acylation experiment. The traditional experiment was modified…

  5. Direct evidence for an acyl phosphate intermediate in the folylpoly-. gamma. -glutamate synthetase and dihydrofolate synthetase-catalyzed reactions

    SciTech Connect

    Banerjee, R.

    1987-01-01

    The mechanism of the reactions catalyzed by two enzymes, namely dihydrofolate synthetase (DHFS) and folylpoly-..gamma..-glutamate synthetase (FPGS), has been investigated. The nature of the intermediate in each of the two reactions was monitored simultaneously in the multifunctional enzyme, FPGS/DHFS from E. coli. The latter was isolated from a transformant containing the cloned FPGS/DHFS gene. Incubation of (/sup 18/O)-H/sub 2/Pte and (/sup 17/O)-glutamate with ATP and the enzyme, resulted in the formation of (/sup 18/O)- and (/sup 17/O)-P/sub i/, thus providing strong evidence for the formation of an acyl phosphate species during catalysis of each reaction. The inorganic phosphate formed in the enzyme-catalyzed reaction was purified by chromatography on DEAE-cellulose, then converted to the trimethyl ester and analyzed by mass spectroscopy /sup 17/O NMR and /sup 31/P NMR. Stoichiometric formation of (/sup 17/O)- and (/sup 18/O)-Pi was observed. /sup 31/P NMR analysis showed the expected /sup 18/O-induced isotopic perturbations. The presence of (/sup 17/O)-trimethyl phosphate was revealed by /sup 17/O NMR. The mechanism of the FPGS-catalyzed reaction was also investigated with the antifolate (/sup 18/O)-methotrexate.

  6. Insight into Coenzyme A cofactor binding and the mechanism of acyl-transfer in an acylating aldehyde dehydrogenase from Clostridium phytofermentans

    PubMed Central

    Tuck, Laura R.; Altenbach, Kirsten; Ang, Thiau Fu; Crawshaw, Adam D.; Campopiano, Dominic J.; Clarke, David J.; Marles-Wright, Jon

    2016-01-01

    The breakdown of fucose and rhamnose released from plant cell walls by the cellulolytic soil bacterium Clostridium phytofermentans produces toxic aldehyde intermediates. To enable growth on these carbon sources, the pathway for the breakdown of fucose and rhamnose is encapsulated within a bacterial microcompartment (BMC). These proteinaceous organelles sequester the toxic aldehyde intermediates and allow the efficient action of acylating aldehyde dehydrogenase enzymes to produce an acyl-CoA that is ultimately used in substrate-level phosphorylation to produce ATP. Here we analyse the kinetics of the aldehyde dehydrogenase enzyme from the fucose/rhamnose utilisation BMC with different short-chain fatty aldehydes and show that it has activity against substrates with up to six carbon atoms, with optimal activity against propionaldehyde. We have also determined the X-ray crystal structure of this enzyme in complex with CoA and show that the adenine nucleotide of this cofactor is bound in a distinct pocket to the same group in NAD+. This work is the first report of the structure of CoA bound to an aldehyde dehydrogenase enzyme and our crystallographic model provides important insight into the differences within the active site that distinguish the acylating from non-acylating aldehyde dehydrogenase enzymes. PMID:26899032

  7. Insight into Coenzyme A cofactor binding and the mechanism of acyl-transfer in an acylating aldehyde dehydrogenase from Clostridium phytofermentans.

    PubMed

    Tuck, Laura R; Altenbach, Kirsten; Ang, Thiau Fu; Crawshaw, Adam D; Campopiano, Dominic J; Clarke, David J; Marles-Wright, Jon

    2016-01-01

    The breakdown of fucose and rhamnose released from plant cell walls by the cellulolytic soil bacterium Clostridium phytofermentans produces toxic aldehyde intermediates. To enable growth on these carbon sources, the pathway for the breakdown of fucose and rhamnose is encapsulated within a bacterial microcompartment (BMC). These proteinaceous organelles sequester the toxic aldehyde intermediates and allow the efficient action of acylating aldehyde dehydrogenase enzymes to produce an acyl-CoA that is ultimately used in substrate-level phosphorylation to produce ATP. Here we analyse the kinetics of the aldehyde dehydrogenase enzyme from the fucose/rhamnose utilisation BMC with different short-chain fatty aldehydes and show that it has activity against substrates with up to six carbon atoms, with optimal activity against propionaldehyde. We have also determined the X-ray crystal structure of this enzyme in complex with CoA and show that the adenine nucleotide of this cofactor is bound in a distinct pocket to the same group in NAD(+). This work is the first report of the structure of CoA bound to an aldehyde dehydrogenase enzyme and our crystallographic model provides important insight into the differences within the active site that distinguish the acylating from non-acylating aldehyde dehydrogenase enzymes. PMID:26899032

  8. Effects of nonlocality on transfer reactions

    NASA Astrophysics Data System (ADS)

    Titus, Luke

    Nuclear reactions play a key role in the study of nuclei away from stability. Single-nucleon transfer reactions involving deuterons provide an exceptional tool to study the single-particle structure of nuclei. Theoretically, these reactions are attractive as they can be cast into a three-body problem composed of a neutron, proton, and the target nucleus. Optical potentials are a common ingredient in reactions studies. Traditionally, nucleon-nucleus optical potentials are made local for convenience. The effects of nonlocal potentials have historically been included approximately by applying a correction factor to the solution of the corresponding equation for the local equivalent interaction. This is usually referred to as the Perey correction factor. In this thesis, we have systematically investigated the effects of nonlocality on (p,d) and (d,p) transfer reactions, and the validity of the Perey correction factor. We implemented a method to solve the single channel nonlocal equation for both bound and scattering states. We also developed an improved formalism for nonlocal interactions that includes deuteron breakup in transfer reactions. This new formalism, the nonlocal adiabatic distorted wave approximation, was used to study the effects of including nonlocality consistently in ( d,p) transfer reactions. For the (p,d) transfer reactions, we solved the nonlocal scattering and bound state equations using the Perey-Buck type interaction, and compared to local equivalent calculations. Using the distorted wave Born approximation we construct the T-matrix for (p,d) transfer on 17O, 41Ca, 49Ca, 127 Sn, 133Sn, and 209Pb at 20 and 50 MeV. Additionally we studied (p,d) reactions on 40Ca using the the nonlocal dispersive optical model. We have also included nonlocality consistently into the adiabatic distorted wave approximation and have investigated the effects of nonlocality on on (d,p) transfer reactions for deuterons impinged on 16O, 40Ca, 48Ca, 126Sn, 132Sn, 208Pb at 10

  9. Molecular polarizabilities in aqueous proton transfer reactions

    NASA Astrophysics Data System (ADS)

    Buin, Andrei; Iftimie, Radu

    2009-12-01

    Dipole polarizabilities of individual ions and molecules are computed from first principles in three condensed-phase systems: pure water, pure hydrofluoric acid, and an equimolar mixture of water and hydrofluoric acid in which HF is mostly ionized. We find that the polarizability of fluorine and oxygen centers varies linearly with the value of the bond order, which measures the local degree of advancement of the ionization reaction F-H+H2O⇄[Fδ -ṡHṡOδ+H2]⇄F-+H3O+. This observation explains the validity of the Lorentz-Lorenz formula for mixtures of acids and water and could have important practical consequences concerning the construction of empirical polarizable reactive force fields. Our results are consistent with the Mulliken charge-transfer picture of proton transfer reactions. The present results also suggest that the average isotropic polarizability of a chemical entity changes substantially only when that entity is involved in charge-transfer processes.

  10. Free Energy Contribution Analysis Using Response Kernel Approximation: Insights into the Acylation Reaction of a Beta-Lactamase.

    PubMed

    Asada, Toshio; Ando, Kanta; Bandyopadhyay, Pradipta; Koseki, Shiro

    2016-09-01

    A widely applicable free energy contribution analysis (FECA) method based on the quantum mechanical/molecular mechanical (QM/MM) approximation using response kernel approaches has been proposed to investigate the influences of environmental residues and/or atoms in the QM region on the free energy profile. This method can evaluate atomic contributions to the free energy along the reaction path including polarization effects on the QM region within a dramatically reduced computational time. The rate-limiting step in the deactivation of the β-lactam antibiotic cefalotin (CLS) by β-lactamase was studied using this method. The experimentally observed activation barrier was successfully reproduced by free energy perturbation calculations along the optimized reaction path that involved activation by the carboxylate moiety in CLS. It was found that the free energy profile in the QM region was slightly higher than the isolated energy and that two residues, Lys67 and Lys315, as well as water molecules deeply influenced the QM atoms associated with the bond alternation reaction in the acyl-enzyme intermediate. These facts suggested that the surrounding residues are favorable for the reactant complex and prevent the intermediate from being too stabilized to proceed to the following deacylation reaction. We have demonstrated that the free energy contribution analysis should be a useful method to investigate enzyme catalysis and to facilitate intelligent molecular design. PMID:27501066

  11. Intramolecular energy transfer reactions in polymetallic

    SciTech Connect

    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.

  12. Nickel nanoparticles in hydrogen transfer reactions.

    PubMed

    Alonso, Francisco; Riente, Paola; Yus, Miguel

    2011-05-17

    The transfer hydrogenation of organic compounds is a much safer and more environmentally benign process than reduction reactions involving molecular hydrogen, metal hydrides, or dissolving metals. In transfer hydrogenation, 2-propanol is often preferred as the source of hydrogen because it is cheap, easy to remove, and environmentally friendly. This class of transformation has been mostly pursued through the use of expensive noble metals, such as Ru, Pd, and so forth; research involving cheaper catalytically active metals has been relatively neglected. On the other hand, alcohols have recently emerged as desirable alkylating agents, a useful alternative to organic halides, in reactions of hydrogen autotransfer, also known as the "borrowing of hydrogen" methodology. For instance, the α-alkylation of ketones with alcohols is an atom-efficient process that produces water as the only byproduct in the presence of a noble metal catalyst. Hydrogen autotransfer is also successful in the synthesis of amines through a reductive aza-Wittig reaction, which involves an iminophosphorane and primary alcohol under iridium catalysis. The in situ oxidation-Wittig olefination of primary alcohols with stabilized phosphorus ylides is a commonly practiced method in organic synthesis that precludes the necessity of handling aldehydes. These reactions are normally performed in one pot but sequentially; thus the course of the alcohol oxidation needs monitoring before the ylide addition. In this Account, we describe the development of our discovery that nickel(0), in the form of nanoparticles, can replace the more expensive noble metals in both transfer hydrogenation and hydrogen autotransfer reactions. These nanoparticles were found to catalyze the transfer hydrogenation of olefins and carbonyl compounds, as well as the reductive amination of aldehydes, with 2-propanol as the hydrogen donor. All reactions proceeded in the absence of base, and the catalyst could be easily and successfully

  13. Plant acyl-CoA:lysophosphatidylcholine acyltransferases (LPCATs) have different specificities in their forward and reverse reactions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Acyl-CoA:lysophosphatidylcholine acyltransferase (LPCAT) enzymes have central roles inacyl editing of phosphatidylcholine (PC). Plant LPCAT genes were expressed in yeast and characterized biochemically in microsomal preparations of the cells. Specificities for different acyl-CoAs were similar for se...

  14. Molecular polarizabilities in aqueous proton transfer reactions

    SciTech Connect

    Buin, Andrei; Iftimie, Radu

    2009-12-21

    Dipole polarizabilities of individual ions and molecules are computed from first principles in three condensed-phase systems: pure water, pure hydrofluoric acid, and an equimolar mixture of water and hydrofluoric acid in which HF is mostly ionized. We find that the polarizability of fluorine and oxygen centers varies linearly with the value of the bond order, which measures the local degree of advancement of the ionization reaction F-H+H{sub 2}O<-->[F{sup {delta}-}{center_dot}H{center_dot}{sup {delta}+}OH{sub 2}]<-->F{sup -}+H{sub 3}O{sup +}. This observation explains the validity of the Lorentz-Lorenz formula for mixtures of acids and water and could have important practical consequences concerning the construction of empirical polarizable reactive force fields. Our results are consistent with the Mulliken charge-transfer picture of proton transfer reactions. The present results also suggest that the average isotropic polarizability of a chemical entity changes substantially only when that entity is involved in charge-transfer processes.

  15. Electron-transfer reactions in polymer matrices

    NASA Astrophysics Data System (ADS)

    Vannikov, Anatolii V.; Grishina, Antonina D.

    1989-12-01

    This paper discusses the dark reactions and photoreactions that occur with transfer of an electron from a donor to an acceptor in polymer matrices under electron tunnelling conditions and when forming change-transfer complexes. The main emphasis is on an analysis of the factors that determine the rate of electron transfer, which, in accordance with the advanced theory of electron transfer, are the magnitude of the exchange interaction, the free energy of the process, and the reorganisation energies of the medium and the reacting donor and acceptor molecules. The existing models for the movement of charge carriers between single-type transport sites are discussed. The limits of applicability of the different models have been determined. The reorganisation energy of a polymer matrix is shown to have a considerable effect on the rate of movement of charge carriers on introduced transport molecules. The effect of the dielectric properties and free volume of polymer matrices on the characteristics of electron phototransfer in donor-acceptor complexes is discussed. The bibliography includes 126 references.

  16. Proton Transfer Reaction Ion Trap Mass Spectrometer

    SciTech Connect

    Prazeller, Peter; Palmer, Peter T.; Boscaini, Elena; Jobson, B Tom T.; Alexander, M. Lizabeth

    2003-06-11

    Proton transfer reaction mass spectrometry is a relatively new field that has attracted a great deal of interest in the last few years. This technique uses H₃Oþ as a chemical ionization (CI) reagent to measure volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) to parts per trillion by volume (pptv) range. Mass spectra acquired with a proton transfer reaction mass spectrometer (PTR-MS) are simple because proton transfer chemical ionization is ‘soft’ and results in little or no fragmentation. Unfortunately, peak identification can still be difficult due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). The use of an ITMS is appealing because of its ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates are possible that will allow for detection of multiple compounds. Here we present the first results from a proton transfer reaction ion trap mass spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype instrument in order to estimate possible detection limits of a second-generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated. Modifications are suggested that will enable further reduction in detection limits to the low-ppbv to high-pptv range. Furthermore, the applicability of MS/MS in differentiating between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making differentiation possible, even when a mixture of both species is present in the same sample. However, MS/MS spectra of acetone and propanal produce fragments with the same molecular masses but with different intensity ratios

  17. Monitoring Wnt Protein Acylation Using an In Vitro Cyclo-Addition Reaction

    PubMed Central

    Tuladhar, Rubina; Yarravarapu, Nageswari; Lum, Lawrence

    2016-01-01

    We describe here a technique for visualizing the lipidation status of Wnt proteins using azide-alkyne cycloaddition chemistry (click chemistry) and SDS-PAGE. This protocol incorporates in vivo labeling of a Wnt-IgG Fc fusion protein using an alkynylated palmitate probe but departs from a traditional approach by incorporating a secondary cycloaddition reaction performed on single-step purified Wnt protein immobilized on protein A resin. This approach mitigates experimental noise by decreasing the contribution of labeling from other palmitoylated proteins and by providing a robust method for normalizing labeling efficiency based on protein abundance. PMID:27590147

  18. Monitoring Wnt Protein Acylation Using an In Vitro Cyclo-Addition Reaction.

    PubMed

    Tuladhar, Rubina; Yarravarapu, Nageswari; Lum, Lawrence

    2016-01-01

    We describe here a technique for visualizing the lipidation status of Wnt proteins using azide-alkyne cycloaddition chemistry (click chemistry) and SDS-PAGE. This protocol incorporates in vivo labeling of a Wnt-IgG Fc fusion protein using an alkynylated palmitate probe but departs from a traditional approach by incorporating a secondary cycloaddition reaction performed on single-step purified Wnt protein immobilized on protein A resin. This approach mitigates experimental noise by decreasing the contribution of labeling from other palmitoylated proteins and by providing a robust method for normalizing labeling efficiency based on protein abundance. PMID:27590147

  19. Enzymatic acylation of starch.

    PubMed

    Alissandratos, Apostolos; Halling, Peter J

    2012-07-01

    Starch a cheap, abundant and renewable natural material has been chemically modified for many years. The popular modification acylation has been used to adjust rheological properties as well as deliver polymers with internal plasticizers and other potential uses. However the harsh reaction conditions required to produce these esters may limit their use, especially in sensitive applications (foods, pharmaceuticals, etc.). The use of enzymes to catalyse acylation may provide a suitable alternative due to high selectivities and mild reaction conditions. Traditional hydrolase-catalysed synthesis in non-aqueous apolar media is hard due to lack of polysaccharide solubility. However, acylated starch derivatives have recently been successfully produced in other non-conventional systems: (a) surfactant-solubilised subtilisin and suspended amylose in organic media; (b) starch nanoparticles dispersed in organic medium with immobilised lipase; (c) aqueous starch gels with lipase and dispersed fatty acids. We attempt a systematic review that draws parallels between the seemingly unrelated approaches described. PMID:22138593

  20. Charge transfer reaction laser with preionization means

    NASA Technical Reports Server (NTRS)

    Lauderslager, J. B.; Pacala, T. J. (Inventor)

    1978-01-01

    A helium-nitrogen laser is described in which energy in the visible range is emitted as a result of charge transfer reaction between helium ions and nitrogen molecules. The helium and nitrogen are present in a gas mixture at several atmospheres pressure, with a nitrogen partial pressure on the order of a pair of main discharge electrodes, the gas mixture is preionized to prevent arcing when the discharge pulse is applied. The preionization is achieved by the application of a high voltage across a pair of secondary electrodes which are spaced apart in a direction perpendicular to the spacing direction of the main discharge electrodes and the longitudinal axis of the space in which the gas mixture is contained. Feedback, by means of a pair of appropriately spaced mirrors, is provided, to produce coherent energy pulses at a selected wavelength.

  1. Electron Transfer and Reaction Mechanism of Laccases

    PubMed Central

    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 (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 (ΔG°), reorganization energy (λ), and electronic coupling matrix element (HDA). 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 (PI), followed by the second 2e− step to form the native intermediate (NI), which has been shown to be the catalytically relevant fully oxidized form of the enzyme. PMID:25572295

  2. (Mechanistic examination of organometallic electron transfer reactions: Annual report, 1989)

    SciTech Connect

    Not Available

    1989-01-01

    Our mechanistic examination of electron transfer reactions between organometallic complexes has required data from our stopped-flow infrared spectrophotometer that was constructed in the first year. Our research on organometallic electron transfer reaction mechanisms was recognized by an invitation to the Symposium on Organometallic Reaction Mechanisms at the National ACS meeting in Miami. We have obtained a reasonable understanding of the electron transfer reactions between metal cations and anions and between metal carbonyl anions and metal carbonyl dimers. In addition we have begun to obtain data on the outer sphere electron transfer between metal carbonyl anions and coordination complexes and on reactions involving cluster anions.

  3. [Mechanistic examination of organometallic electron transfer reactions: Annual report, 1989

    SciTech Connect

    Not Available

    1989-12-31

    Our mechanistic examination of electron transfer reactions between organometallic complexes has required data from our stopped-flow infrared spectrophotometer that was constructed in the first year. Our research on organometallic electron transfer reaction mechanisms was recognized by an invitation to the Symposium on Organometallic Reaction Mechanisms at the National ACS meeting in Miami. We have obtained a reasonable understanding of the electron transfer reactions between metal cations and anions and between metal carbonyl anions and metal carbonyl dimers. In addition we have begun to obtain data on the outer sphere electron transfer between metal carbonyl anions and coordination complexes and on reactions involving cluster anions.

  4. Activation entropy of electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Milischuk, Anatoli A.; Matyushov, Dmitry V.; Newton, Marshall D.

    2006-05-01

    We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by continuum models is not supported by the microscopic theory. Also, the reorganization and overall solvation entropies are substantially larger in the microscopic theory compared to continuum models.

  5. Proton Transfer Reaction Ion Trap Mass Spectrometer

    SciTech Connect

    Prazeller, Peter; Palmer, Peter T.; Boscaini, Elena; Jobson, B Tom; Alexander, M. Lizabeth

    2003-07-07

    Proton Transfer Reaction Mass Spectrometry (PTR-MS) is a relatively new field that has attracted a great deal of interest in the last several years. This technique uses H3O+ as a chemical ionization (CI) agent for measuring volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) - parts per trillion by volume (pptv) range. PTR-MS mass spectra are simple because the ionization method of proton transfer is “soft”, resulting in little or no fragmentation. Unfortunately, the simplicity of the mass spectra can cause problems in peak identification due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). ITMS is appealing because of the ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates can be realized for detection of multiple compounds. We present here the first results from a Proton Transfer Reaction Ion Trap Mass Spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype interface in order to estimate possible detection limits of a second generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated for the PTR-ITMS. Modifications are suggested that will enable further reduction in detection limits to the low ppbv to pptv range. Furthermore the applicability of MS/MS to differentiate between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making a differentiation possible even when a mixture of both species is present in the same sample. MS/MS spectra of acetone and propanal produce fragments with the same molecular weight but different ratios, allowing quantitative distinction only if one species

  6. Transfer-type products accompanying cold fusion reactions

    SciTech Connect

    Adamian, G.G.; Antonenko, N.V.

    2005-12-15

    Production of nuclei heavier than the target is treated for projectile-target combinations used in cold fusion reactions leading to superheavy nuclei. These products are related to transfer-type or to asymmetry-exit-channel quasifission reactions. The production of isotopes in the transfer-type reactions emitting of {alpha} particles with large energies is discussed.

  7. Direct synthesis of C-glycosides from unprotected 2-N-acyl-aldohexoses via aldol condensation-oxa-Michael reactions with unactivated ketones.

    PubMed

    Johnson, Sherida; Tanaka, Fujie

    2016-01-01

    C-glycosides are important compounds as they are used as bioactive molecules and building blocks. We have developed methods to concisely synthesize C-glycosides from unprotected 2-N-acyl-aldohexoses and unactivated ketones; we designed aldol-condensation-oxa-Michael addition reactions catalyzed by amine-based catalysts using additives. Depending on the conditions used, C-glycosides were stereoselectively obtained. Our methods allowed the C-C bond formations at the anomeric centers of unprotected carbohydrates under mild conditions to lead the C-glycosides in atom- and step-economical ways. PMID:26565955

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

    SciTech Connect

    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.

  9. Biological phosphoryl-transfer reactions: understanding mechanism and catalysis.

    PubMed

    Lassila, Jonathan K; Zalatan, Jesse G; Herschlag, Daniel

    2011-01-01

    Phosphoryl-transfer reactions are central to biology. These reactions also have some of the slowest nonenzymatic rates and thus require enormous rate accelerations from biological catalysts. Despite the central importance of phosphoryl transfer and the fascinating catalytic challenges it presents, substantial confusion persists about the properties of these reactions. This confusion exists despite decades of research on the chemical mechanisms underlying these reactions. Here we review phosphoryl-transfer reactions with the goal of providing the reader with the conceptual and experimental background to understand this body of work, to evaluate new results and proposals, and to apply this understanding to enzymes. We describe likely resolutions to some controversies, while emphasizing the limits of our current approaches and understanding. We apply this understanding to enzyme-catalyzed phosphoryl transfer and provide illustrative examples of how this mechanistic background can guide and deepen our understanding of enzymes and their mechanisms of action. Finally, we present important future challenges for this field. PMID:21513457

  10. KOtBu: A Privileged Reagent for Electron Transfer Reactions?

    PubMed

    Barham, Joshua P; Coulthard, Graeme; Emery, Katie J; Doni, Eswararao; Cumine, Florimond; Nocera, Giuseppe; John, Matthew P; Berlouis, Leonard E A; McGuire, Thomas; Tuttle, Tell; Murphy, John A

    2016-06-15

    Many recent studies have used KOtBu in organic reactions that involve single electron transfer; in the literature, the electron transfer is proposed to occur either directly from the metal alkoxide or indirectly, following reaction of the alkoxide with a solvent or additive. These reaction classes include coupling reactions of halobenzenes and arenes, reductive cleavages of dithianes, and SRN1 reactions. Direct electron transfer would imply that alkali metal alkoxides are willing partners in these electron transfer reactions, but the literature reports provide little or no experimental evidence for this. This paper examines each of these classes of reaction in turn, and contests the roles proposed for KOtBu; instead, it provides new mechanistic information that in each case supports the in situ formation of organic electron donors. We go on to show that direct electron transfer from KOtBu can however occur in appropriate cases, where the electron acceptor has a reduction potential near the oxidation potential of KOtBu, and the example that we use is CBr4. In this case, computational results support electrochemical data in backing a direct electron transfer reaction. PMID:27183183

  11. RNA SHAPE chemistry with aromatic acylating reagents.

    PubMed

    Nodin, Laura; Noël, Olivier; Chaminade, Françoise; Maskri, Ouerdia; Barbier, Vincent; David, Olivier; Fossé, Philippe; Xie, Juan

    2015-02-01

    As chemical methods for RNA secondary structure determination, SHAPE chemistry (selective 2'-hydroxyl acylation analyzed by primer extension) has been developed to specifically target flexible nucleotides (often unpaired nucleotides) independently to their purine or pyrimidine nature. In order to improve the specificity of acylating reagents towards unpaired nucleotides, we have explored the reactivity of symmetric anhydrides, acyl fluorides, active esters like succinimidyl ester and cyanomethyl esters for 2'-O-acylation reaction. Among the tested compounds, only the acyl fluoride 4 showed a low reactivity (compared to NMIA). However, this study is the first to show that nucleophilic catalysts like DMAP greatly improved the selective 2'-hydroxyl acylation by symmetric anhydrides, acyl fluorides and succinimidyl ester, with the 2-fluorobenzoic anhydride 5 being the most reactive. PMID:25557357

  12. Structural Milestones in the Reaction Pathway of an Amide Hydrolase: Substrate, Acyl, and Product Complexes of Cephalothin with AmpC [beta]-Lactamase

    SciTech Connect

    Beadle, Beth M.; Trehan, Indi; Focia, Pamela J.; Shoichet, Brian K.

    2010-03-05

    {beta}-lactamases hydrolyze {beta}-lactam antibiotics and are the leading cause of bacterial resistance to these drugs. Although {beta}-lactamases have been extensively studied, structures of the substrate-enzyme and product-enzyme complexes have proven elusive. Here, the structure of a mutant AmpC in complex with the {beta}-lactam cephalothin in its substrate and product forms was determined by X-ray crystallography to 1.53 {angstrom} resolution. The acyl-enzyme intermediate between AmpC and cephalothin was determined to 2.06 {angstrom} resolution. The ligand undergoes a dramatic conformational change as the reaction progresses, with the characteristic six-membered dihydrothiazine ring of cephalothin rotating by 109{sup o}. These structures correspond to all three intermediates along the reaction path and provide insight into substrate recognition, catalysis, and product expulsion.

  13. [The detection of 10-acyl derivatives of phenothiazine by staining reactions and a spectrophotometric method for their hydrolysis products].

    PubMed

    Egorov, A P

    1998-01-01

    Identification of phenothiazine 10-acyl derivatives by staining and spectrophotometry of their hydrolysis products 2-chlorophenothiazine, 2-trifluoromethylphenothiazine, and 2-carboxyaminophenothiazine appreciably improved the sensitivity and specificity of their detection. Staining on silufol plates detects at least 0.05 to 0.15 microgram per spot. The specific parameters of hydrolysis products absorption are notably superior to those of the native compounds and are (in chloroform, U1%1 cm): 1821 for 2-chlorophenothiazine, 1400 for 2-trifluoromethylphenothiazine, and 1656 for 2-carboxyaminophenothiazine. PMID:9567678

  14. Study of transfer and breakup reactions with the plastic box

    SciTech Connect

    Stokstad, R.G.; Albiston, C.R.; Bantel, M.; Chan, Y.; Countryman, P.J.; Gazes, S.; Harvey, B.G.; Homeyer, H.; Murphy, M.J.; Tserruya, I.

    1984-12-01

    The study of transfer reactions with heavy-ion projectiles is complicated by the frequent presence of three or more nuclei in the final state. One prolific source of three-body reactions is the production of a primary ejectile in an excited state above a particle threshold. A subset of transfer reactions, viz., those producing ejectiles in bound states, can be identified experimentally. This has been accomplished with a 4..pi.. detector constructed of one-millimeter-thick scintillator paddles of dimension 20 cm x 20 cm. The paddles are arranged in the form of a cube centered around the target with small entrance and exit apertures for the beam and the projectile-like fragments, (PLF). The detection of a light particle (e.g., a proton or an alpha particle) in coincidence with a PLF indicates a breakup reaction. The absence of any such coincidence indicates a reaction in which all the charge lost by the projectile was transferred to the target. With this technique we have studied the transfer and breakup reactions induced by 220 and 341 MeV /sup 20/Ne ions on a gold target. Ejectiles from Li to Ne have been measured at several scattering angles. The absolute cross sections, angular distributions and energy spectra for the transfer and breakup reactions are presented. Relatively large cross sections are observed for the complete transfer of up to seven units of charge (i.e., a nitrogen nucleus). The relatively large probabilities for ejectiles to be produced in particle-bound states suggest that on the average, most of the excitation energy in a collision resides in the heavy fragment when mass is transferred from the lighter to the heavier fragment. The gross features and trends in the energy spectra for transfer and breakup reactions are similar. 20 references.

  15. Coherent and semi-coherent neutron transfer reactions

    SciTech Connect

    Hagelstein, P.L.

    1992-01-01

    Neutron transfer reactions are proposed to account for anomalies reported in Pons-Fleischmann experiments. The prototypical reaction involves the transfer of a neutron (mediated by low frequency electric or magnetic fields) from a donor nucleus to virtual continuum states, followed by the capture of the virtual neutron by an acceptor nucleus. In this work we summarize basic principles, recent results and the ultimate goals of the theoretical effort.

  16. Coherent and semi-coherent neutron transfer reactions

    SciTech Connect

    Hagelstein, P.L.

    1992-12-31

    Neutron transfer reactions are proposed to account for anomalies reported in Pons-Fleischmann experiments. The prototypical reaction involves the transfer of a neutron (mediated by low frequency electric or magnetic fields) from a donor nucleus to virtual continuum states, followed by the capture of the virtual neutron by an acceptor nucleus. In this work we summarize basic principles, recent results and the ultimate goals of the theoretical effort.

  17. Dynamic salt effect on intramolecular charge-transfer reactions

    SciTech Connect

    Zhu Jianjun; Ma Rong; Lu Yan; Stell, George

    2005-12-08

    The dynamic salt effect in charge-transfer reactions is investigated theoretically in this paper. Free-energy surfaces are derived based on a nonequilibrium free-energy functional. Reaction coordinates are clearly defined. The solution of the reaction-diffusion equation leads to a rate constant depending on the time correlation function of the reaction coordinates. The time correlation function of the ion-atmosphere coordinate is derived from the solution of the Debye-Falkenhagen equation. It is shown that the dynamic salt effect plays an important role in controlling the rate of charge-transfer reactions in the narrow-window limit but is balanced by the energetics and the dynamics of the polar-solvent coordinate. The simplest version of the theory is compared with an experiment, and the agreement is fairly good. The theory can also be extended to charge-transfer in the class of electrolytes that has come to be called 'ionic fluids'.

  18. Fission Study Using Multi-Nucleon Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Nishio, K.; Hirose, K.; Lėguillon, R.; Makii, H.; Nishinaka, I.; Orlandi, R.; Smallcombe, J.; Ishii, T.; Tsukada, K.; Asai, M.; Chiba, S.; Ohtsuki, T.; Tatsuzawa, R.; Takaki, N.

    2015-06-01

    Fission study using multi-nucleon transfer reaction will be discussed. This approach has an advantage that we can study fission of neutron-rich nuclei which cannot be accessed by particle or charged-particle capture reactions. Unique feature in our setup is that we can produce fission data for many nuclei using many transfer-channels. Also wide excitation energy range can be covered in this set up, allowing us to measure the excitation energy dependence of the fission properties. Preliminary data obtained in the 18O + 238U reaction will be presented..

  19. Intrinsic barriers for H-atom transfer reactions

    SciTech Connect

    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. Carboxyl group participation in sulfate and sulfamate group transfer reactions

    SciTech Connect

    Hopkins, A.; Williams, A.

    1982-04-23

    The pH dependence for the hydrolysis of N-(2-carboxyphenyl)sulfamic acid exhibits a plateau region corresponding to participation of the carboxyl function. A normal deuterium oxide solvent isotope effect indicates that proton transfer from the carboxylic acid is concerted with sulfamate group transfer to water. Hydrolysis of salicylic sulfate and N-(2-carboxyphenyl)sulfamate in /sup 18/O-enriched water yields salicylic acid and anthranilic acids with no enrichment, excluding catalysis by neighboring nucleophilic attack on sulfur by the carboxylate group. Intermolecular catalysis by carboxylic acids is demonstrated in the hydrolysis of N-(1-naphthyl)sulfamic acid; the mechanism is shown to involve preequilibrium protonation of the nitrogen followed by nucleophilic attack on sulfur by the carboxylate anion. Fast decomposition of the acyl sulfate completes the hydrolysis; this mechanism is considered to be the most efficient but is excluded in the intramolecular case which is constrained by the electronic requirements of displacement at the sulfur atom (6-ENDO-tet).

  1. Electron transfer reactions in microporous solids

    SciTech Connect

    Mallouk, T.E.

    1992-05-01

    We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently dry'' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

  2. Electron transfer reactions in microporous solids

    NASA Astrophysics Data System (ADS)

    Mallouk, T. E.

    1992-05-01

    We have studied electron transfer quenching of the excited state of Ru3(2+) in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows two remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently 'dry' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV(2+) ion in these zeolites, determined by this technique, is 10(exp -7) sq cm sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2 to 3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K(4-x)H(x)Nb6O17 - nH2O(x approx. = 2.5) yields photocatalysts for the production of H2 and I3(-) in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

  3. Proton transfer reactions for improved peptide characterisation.

    PubMed

    Rožman, Marko; Schneider, Andrea; Gaskell, Simon J

    2011-06-01

    The combination of deprotonation (via ion/molecule and ion/ion reactions) and low-energy collision-induced dissociation (CID) has been explored for the enhanced characterisation of tryptic peptides via access to different precursor charge states. This approach allows instant access to fragmentation properties of singly and doubly protonated precursors (arising from the availability of mobile protons) in a single experiment. Considering both charge states extended our base of structurally informative data (in comparison with considering just a single charge state) due to generation of additional sequence ions and by obtaining supplementary structural information derived from selective cleavages. Roughly 37% of combined data sets (CID spectra of doubly and singly charged precursor) showed a greater database identification confidence than each set alone. Moreover, comparison between a number of sequence ions of the singly charged precursor and the doubly charged precursor provided a mean of distinguishing the two classes of tryptic peptides (arginine or lysine containing). PMID:21630380

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

    SciTech Connect

    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 WSDy(VYNi,WNi) WDy 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.

  5. Organocatalytic Asymmetric Michael/Cyclization Cascade Reactions of 3-Hydroxyoxindoles/3-Aminooxindoles with α,β-Unsaturated Acyl Phosphonates for the Construction of Spirocyclic Oxindole-γ-lactones/lactams.

    PubMed

    Chen, Lin; Wu, Zhi-Jun; Zhang, Ming-Liang; Yue, Deng-Feng; Zhang, Xiao-Mei; Xu, Xiao-Ying; Yuan, Wei-Cheng

    2015-12-18

    Enantioselective Michael/cyclization cascade reactions of 3-hydroxyoxindoles/3-aminooxindoles with α,β-unsaturated acyl phosphonates by using a cinchonine derived squaramide as the catalyst were developed. A broad range of spirocyclic oxindole-γ-lactones/lactams could be obtained in moderate to excellent yields (up to 98%) with good to excellent diastereo- and enantioselectivities (up to >99:1 dr and 97% ee) under mild conditions. This work represents the first example about the α,β-unsaturated acyl phosphonates for the asymmetric construction of spirocyclic oxindoles. PMID:26550839

  6. Heat transfer to a supercritical hydrocarbon fuel with endothermic reaction.

    SciTech Connect

    Yu, W.; France, D. M.; Wambsganss, M. W.; Energy Technology; Univ. of Illinois at Chicago

    2000-01-01

    Supercritical fuel reforming is being studied as a technology for reducing emissions of industrial gas turbine engines. In this study, experiments were performed in a 2.67-mm-inside-diameter stainless steel tube with a heated length of 0.610 m for the purpose of investigating the characteristics of supercritical heat transfer with endothermic fuel reforming. Thermocouples were positioned along the tube both in the fluid stream and on the heated wall for local heat transfer measurements. Both heat transfer coefficients and endotherms were calculated from the measured results. State-of-the-art correlations for heat transfer were evaluated, and a correlation for supercritical heat transfer to hydrocarbon fuel has been developed. The results provide a basis for supercritical fuel heat-exchanger/reactor design and its practical applications, in an area that has received relatively little attention in the engineering literature, viz., supercritical forced convection heat transfer with endothermic chemical reaction.

  7. Exclusive Reactions at High Momentum Transfer

    NASA Astrophysics Data System (ADS)

    Radyushkin, Anatoly; Stoler, Paul

    2008-03-01

    Hard exclusive scattering at JLab / P. Kroll -- AdS/CFT and exclusive processes in QCD / S. J. Brodsky and G. F. de Téramond -- Hadron structure matters in collisions at high energy and momentum / A. W. Thomas -- Inclusive perspectives / P. Hoyer -- Fitting DVCS at NLO and beyond / K. Kumericki, D. Müller and K. Passek-Kumericki -- Spin-orbit correlations and single-spin asymmetries / M. Burkardt -- Electroproduction of soft pions at large momentum transfers / V. M. Braun, D. Yu. Ivanov and A. Peters -- Color transparency: 33 years and still running / M. Strikman -- Meson clouds and nucleon electromagnetic form factors / G. A. Miller -- Covariance, dynamics and symmetries, and hadron form factors / M. S. Bhagwat, I. C. Cloët and C. D. Roberts -- N to [symbol] electromagnetic and axial form factors in full QCD / C. Alexandrou -- Real and virtual compton scattering in perturbative QCD / C.-R. Ji and R. Thomson -- Deeply virtual compton scattering at Jefferson Lab / F. Sabatie -- DVCS at HERMES: recent results / F. Ellinghaus -- Deeply virtual compton scattering with CLAS / F. X. Girod -- Deeply virtual compton scattering off the neutron at JLab Hall A / M. Mazouz -- The future DVCS experiments in Hall A at JLab / J. Roche -- Deeply virtual compton scattering with CLAS12 / L. Elouadrhiri -- Quark helicity flip and the transverse spin dependence of inclusive DIS / A. Afanasev, M. Strikman and C. Weiss -- Deeply virtual pseudoscalar meson production / V. Kubarovsky and P. Stoler -- Exclusive p[symbol] electroproduction on the proton: GPDs or not GPDs? / M. Guidal and S. Morrow -- p[symbol] transverse target spin asymmetry at HERMES / A. Airapetian -- Electroproduction of ø(1020) mesons / J. P. Santoro and E. S. Smith -- Generalized parton distributions from hadronic observables / S. Ahmad ... [et al.] -- Imaging the proton via hard exclusive production in diffractive pp scattering / G. E. Hyde ... [et al.] -- Regge contributions to exclusive electro-production / A

  8. Exclusive Reactions at High Momentum Transfer

    NASA Astrophysics Data System (ADS)

    Radyushkin, Anatoly; Stoler, Paul

    2008-03-01

    Hard exclusive scattering at JLab / P. Kroll -- AdS/CFT and exclusive processes in QCD / S. J. Brodsky and G. F. de Téramond -- Hadron structure matters in collisions at high energy and momentum / A. W. Thomas -- Inclusive perspectives / P. Hoyer -- Fitting DVCS at NLO and beyond / K. Kumericki, D. Müller and K. Passek-Kumericki -- Spin-orbit correlations and single-spin asymmetries / M. Burkardt -- Electroproduction of soft pions at large momentum transfers / V. M. Braun, D. Yu. Ivanov and A. Peters -- Color transparency: 33 years and still running / M. Strikman -- Meson clouds and nucleon electromagnetic form factors / G. A. Miller -- Covariance, dynamics and symmetries, and hadron form factors / M. S. Bhagwat, I. C. Cloët and C. D. Roberts -- N to [symbol] electromagnetic and axial form factors in full QCD / C. Alexandrou -- Real and virtual compton scattering in perturbative QCD / C.-R. Ji and R. Thomson -- Deeply virtual compton scattering at Jefferson Lab / F. Sabatie -- DVCS at HERMES: recent results / F. Ellinghaus -- Deeply virtual compton scattering with CLAS / F. X. Girod -- Deeply virtual compton scattering off the neutron at JLab Hall A / M. Mazouz -- The future DVCS experiments in Hall A at JLab / J. Roche -- Deeply virtual compton scattering with CLAS12 / L. Elouadrhiri -- Quark helicity flip and the transverse spin dependence of inclusive DIS / A. Afanasev, M. Strikman and C. Weiss -- Deeply virtual pseudoscalar meson production / V. Kubarovsky and P. Stoler -- Exclusive p[symbol] electroproduction on the proton: GPDs or not GPDs? / M. Guidal and S. Morrow -- p[symbol] transverse target spin asymmetry at HERMES / A. Airapetian -- Electroproduction of ø(1020) mesons / J. P. Santoro and E. S. Smith -- Generalized parton distributions from hadronic observables / S. Ahmad ... [et al.] -- Imaging the proton via hard exclusive production in diffractive pp scattering / G. E. Hyde ... [et al.] -- Regge contributions to exclusive electro-production / A

  9. Theoretical studies on shaking processes in nuclear transfer reactions

    NASA Astrophysics Data System (ADS)

    Sharma, Prashant; Nandi, Tapan

    2015-09-01

    The probabilities of shaking processes during nuclear transfer reactions have been studied using the Mukoyama formalism after the re-examination of formalism for β-decay processes. Electron shakeoff probabilities have been calculated for the α-transfer reaction in the range of Z = 10- 50. The Z-dependence on the shakeoff probabilities so obtained has been represented by an analytical equation with two parameters. The formalism has been applied on a typical nuclear transfer reaction Fe5626 +C126 →Ni6028 +Be84 and it is found that electron shakeup, shakedown and shakeoff probabilities dominate for low l quantum number of the respective shells of the projectile-like fragment ion. However, for a particular value of l these processes show high probabilities for low values of n quantum number.

  10. Facile Detection of Acyl- and Peptidyl- intermediates on Thiotemplate Carrier Domains via Phosphopantetheinyl Elimination Reactions During Tandem Mass Spectrometry

    PubMed Central

    Dorrestein, Pieter C.; Bumpus, Stefanie B.; Calderone, Christopher T.; Garneau-Tsodikova, Sylvie; Aron, Zachary D.; Straight, Paul D.; Kolter, Roberto; Walsh, Christopher T.; Kelleher, Neil L.

    2008-01-01

    With the emergence of drug resistance and the genomic revolution there has been a renewed interest in the genes that are responsible for the generation of bioactive natural products. Secondary metabolites of one major class are biosynthesized at one or more sites by ultra large enzymes that carry covalent intermediates on phosphopantetheine arms. Because such intermediates are difficult to characterize in vitro, we have developed a new approach for streamlined detection of substrates, intermediates and products attached to a phosphopantetheinyl arm of the carrier site. During vibrational activation of gas phase carrier domains, facile elimination occurs in benchtop and Fourier-Transform mass spectrometers alike. Phosphopantetheinyl ejections quickly reduce >100 kDa megaenzymes to <1000 Da ions for structural assignment of intermediates at <0.007 Da mass accuracy without proteolytic digestion. This “Top Down” approach quickly illuminated diverse acyl-intermediates on the carrier domains of the nonribosomal peptide synthetases (NRPSs) or polyketide synthases (PKSs) found in the biosynthetic pathways of prodigiosin, pyoluteorin, mycosubtilin, nikkomycin, enterobactin, gramicidin and several proteins from the orphan pksX gene cluster from Bacillus subtilis. By focusing on just those regions undergoing covalent chemistry, the method delivered clean proof for the reversible dehydration of hydroxymethylglutaryl-S-PksL via incorporation of 2H or 18O from the buffer. The facile nature of this revised assay will allow diverse laboratories to spearhead their NRPS/PKS projects with benchtop mass spectrometers. PMID:17042494

  11. Femtochemistry of Intramolecular Charge and Proton Transfer Reactions in Solution

    SciTech Connect

    Douhal, Abderrazzak; Sanz, Mikel; Carranza, Maria Angeles; Organero, Juan Angel; Tormo, Laura

    2005-03-17

    We report on the first observation of ultrafast intramolecular charge- and proton-transfer reactions in 4'-dimethylaminoflavonol (DAMF) in solution. Upon femtosecond excitation of a non-planar structure of DMAF in apolar medium, the intramolecular charge transfer (ICT) does not occur, and a slow (2 ps) proton motion takes place. However, in polar solvents, the ICT is very fast (100-200 fs) and the produced structure is stabilized that proton motion takes place in few or tens of ps.

  12. Probing active electron transfer branch in photosystem I reaction center.

    NASA Astrophysics Data System (ADS)

    Savikhin, Sergei; Dashdorj, Naranbaatar; Xu, Wu; Martinsson, Peter; Chitnis, Parag

    2003-03-01

    Complimentary point mutations were introduced at the primary electron acceptor sites in A and B branches of the photosystem I (PS I) reaction center (RC) from Synechocystis sp. PCC 6803 and their effect on the kinetics of the electron transfer process was studied by means of ultrafast pump-probe spectroscopy. The results indicate that in these species the electron transfer occurs primarily along the A-branch. Previous optical experiments on PS I complexes from Chlorella sorokiniana demonstrated that both branches of RC are equally active. That suggests that the directionality of electron transfer in PS I is species dependent.

  13. Electron Transfer versus Proton Transfer in Gas-Phase Ion/Ion Reactions of Polyprotonated Peptides

    PubMed Central

    Gunawardena, Harsha P.; He, Min; Chrisman, Paul A.; Pitteri, Sharon J.; Hogan, Jason M.; Hodges, Brittany D. M.; McLuckey, Scott A.

    2005-01-01

    The ion/ion reactions of several dozen reagent anions with triply protonated cations of the model peptide KGAILKGAILR have been examined to evaluate predictions of a Landau–Zener-based model for the likelihood for electron transfer. Evidence for electron transfer was provided by the appearance of fragment ions unique to electron transfer or electron capture dissociation. Proton transfer and electron transfer are competitive processes for any combination of anionic and cationic reactants. For reagent anions in reactions with protonated peptides, proton transfer is usually significantly more exothermic than electron transfer. If charge transfer occurs at relatively long distances, electron transfer should, therefore, be favored on kinetic grounds because the reactant and product channels cross at greater distances, provided conditions are favorable for electron transfer at the crossing point. The results are consistent with a model based on Landau–Zener theory that indicates both thermodynamic and geometric criteria apply for electron transfer involving polyatomic anions. Both the model and the data suggest that electron affinities associated with the anionic reagents greater than about 60–70 kcal/mol minimize the likelihood that electron transfer will be observed. Provided the electron affinity is not too high, the Franck–Condon factors associated with the anion and its corresponding neutral must not be too low. When one or the other of these criteria is not met, proton transfer tends to occur essentially exclusively. Experiments involving ion/ion attachment products also suggest that a significant barrier exists to the isomerization between chemical complexes that, if formed, lead to either proton transfer or electron transfer. PMID:16144411

  14. Mechanisms for control of biological electron transfer reactions

    PubMed Central

    Williamson, Heather R.; Dow, Brian A.; Davidson, Victor L.

    2014-01-01

    Electron transfer (ET) through and between proteins is a fundamental biological process. The rates and mechanisms of these ET reactions are controlled by the proteins in which the redox centers that donate and accept electrons reside. The protein influences the magnitudes of the ET parameters, the electronic coupling and reorganization energy that are associated with the ET reaction. The protein can regulate the rates of the ET reaction by requiring reaction steps to optimize the system for ET, leading to kinetic mechanisms of gated or coupled ET. Amino acid residues in the segment of the protein through which long range ET occurs can also modulate the ET rate by serving as staging points for hopping mechanisms of ET. Specific examples are presented to illustrate these mechanisms by which proteins control rates of ET reactions. PMID:25085775

  15. Chemical reactions and gas transfer in natural waters

    SciTech Connect

    O`Connor, D.J. |

    1998-02-01

    Many chemical reactions of environmental significance involve reactants or end products that exchange with the atmosphere. The transferable constituents are the atmospheric gases--oxygen, carbon dioxide, and, to a more limited degree, nitrogen--and volatile substances that are not usually present in the atmosphere, such as ammonia, sulfur dioxide, and hydrogen sulfide. Reactions of this type have many applications in natural water systems, as well as water and waste treatment processes. It is the general purpose of this paper to present a mathematical approach to the analysis of these reactions and to demonstrate the application to various environmental problems. Both variable and constant pH conditions are addressed. The latter frequently characterizes laboratory experiments in batch reactions, in which a constant pH is maintained. The former is commonly present in natural waters, in which the pH changes through the course of the chemical reaction.

  16. Role of Double Hydrogen Atom Transfer Reactions in Atmospheric Chemistry.

    PubMed

    Kumar, Manoj; Sinha, Amitabha; Francisco, Joseph S

    2016-05-17

    Hydrogen atom transfer (HAT) reactions are ubiquitous and play a crucial role in chemistries occurring in the atmosphere, biology, and industry. In the atmosphere, the most common and traditional HAT reaction is that associated with the OH radical abstracting a hydrogen atom from the plethora of organic molecules in the troposphere via R-H + OH → R + H2O. This reaction motif involves a single hydrogen transfer. More recently, in the literature, there is an emerging framework for a new class of HAT reactions that involves double hydrogen transfers. These reactions are broadly classified into four categories: (i) addition, (ii) elimination, (iii) substitution, and (iv) rearrangement. Hydration and dehydration are classic examples of addition and elimination reactions, respectively whereas tautomerization or isomerization belongs to a class of rearrangement reactions. Atmospheric acids and water typically mediate these reactions. Organic and inorganic acids are present in appreciable levels in the atmosphere and are capable of facilitating two-point hydrogen bonding interactions with oxygenates possessing an hydroxyl and/or carbonyl-type functionality. As a result, acids influence the reactivity of oxygenates and, thus, the energetics and kinetics of their HAT-based chemistries. The steric and electronic effects of acids play an important role in determining the efficacy of acid catalysis. Acids that reduce the steric strain of 1:1 substrate···acid complex are generally better catalysts. Among a family of monocarboxylic acids, the electronic effects become important; barrier to the catalyzed reaction correlates strongly with the pKa of the acid. Under acid catalysis, the hydration of carbonyl compounds leads to the barrierless formation of diols, which can serve as seed particles for atmospheric aerosol growth. The hydration of sulfur trioxide, which is the principle mechanism for atmospheric sulfuric acid formation, also becomes barrierless under acid catalysis

  17. Multi-neutron transfer reactions at sub-barrier energies.

    SciTech Connect

    Rehm, K. E.

    1998-01-20

    The optimum conditions for multi-neutron transfer have been studied in the system {sup 58}Ni + {sup 124}Sn at bombarding energies at and below the Coulomb barrier. The experiments were performed in inverse kinematics with a {sup 124}Sn beam bombarding a {sup 58}Ni target. The particles were identified with respect to mass and Z in the split-pole spectrograph with a hybrid focal plane detector with mass and Z-resolutions of A/{Delta}A = 150 and Z/{Delta}Z = 70. At all energies the transfer of up to 6 neutrons was observed. The yields for these transfer reactions are found to decrease by about a factor of four for each transferred neutron.

  18. Friedel-Crafts Acylation with Amides

    PubMed Central

    Raja, Erum K.; DeSchepper, Daniel J.; Nilsson Lill, Sten O.; Klumpp, Douglas A.

    2012-01-01

    Friedel-Crafts acylation has been known since the 1870s and it is an important organic synthetic reaction leading to aromatic ketone products. Friedel-Crafts acylation is usually done with carboxylic acid chlorides or anhydrides while amides are generally not useful substrates in these reactions. Despite being the least reactive carboxylic acid derivative, we have found a series of amides capable of providing aromatic ketones in good yields (55–96%, 17 examples). We propose a mechanism involving diminished C-N resonance through superelectrophilic activation and subsequent cleavage to acyl cations. PMID:22690740

  19. Proton-Coupled Electron Transfer Reactions with Photometric Bases Reveal Free Energy Relationships for Proton Transfer.

    PubMed

    Eisenhart, Thomas T; Howland, William C; Dempsey, Jillian L

    2016-08-18

    The proton-coupled electron transfer (PCET) oxidation of p-aminophenol in acetonitrile was initiated via stopped-flow rapid-mixing and spectroscopically monitored. For oxidation by ferrocenium in the presence of 7-(dimethylamino)quinoline proton acceptors, both the electron transfer and proton transfer components could be optically monitored in the visible region; the decay of the ferrocenium absorbance is readily monitored (λmax = 620 nm), and the absorbance of the 2,4-substituted 7-(dimethylamino)quinoline derivatives (λmax = 370-392 nm) red-shifts substantially (ca. 70 nm) upon protonation. Spectral analysis revealed the reaction proceeds via a stepwise electron transfer-proton transfer process, and modeling of the kinetics traces monitoring the ferrocenium and quinolinium signals provided rate constants for elementary proton and electron transfer steps. As the pKa values of the conjugate acids of the 2,4-R-7-(dimethylamino)quinoline derivatives employed were readily tuned by varying the substituents at the 2- and 4-positions of the quinoline backbone, the driving force for proton transfer was systematically varied. Proton transfer rate constants (kPT,2 = (1.5-7.5) × 10(8) M(-1) s(-1), kPT,4 = (0.55-3.0) × 10(7) M(-1) s(-1)) were found to correlate with the pKa of the conjugate acid of the proton acceptor, in agreement with anticipated free energy relationships for proton transfer processes in PCET reactions. PMID:27500804

  20. Study of multi-nucleon transfer reactions with light nuclei

    SciTech Connect

    Benzoni, G.; Montanari, D.; Bracco, A.; Blasi, N.; Camera, F.; Crespi, F. C. L.; Corsi, A.; Leoni, S.; Million, B.; Nicolini, R.; Wieland, O.; Zalite, A.; Zocca, F.; Azaiez, F.; Franchoo, S.; Stefan, I.; Ibrahim, F.; Verney, D.; Battacharyya, S.; De France, G.

    2008-05-12

    Multi-nucleon transfer reactions are useful tools to populate exotic nuclei, particularly the neutron-rich ones. In this view, two different experiments have been performed employing a stable ({sup 22}Ne) and a radioactive ({sup 24}Ne) beam, both impinging on a {sup 208}Pb target. The first reaction has been studied using the CLARA-PRISMA-DANTE set-up at Laboratori Nazionali di Legnaro (Legnaro-Italy), while the second reaction was performed at Ganil (Caen-France) employing a SPIRAL radioactive beam of {sup 24}Ne. In this case recoils and coincident {gamma} rays were detected with the VAMOS-EXOGAM set-up.The data show that MNT reactions can selectively populate states of different nature and, therefore, are a good tool to study nuclear structure further away from stability.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Acyl-CoA synthetase catalyzes the synthesis of diadenosine hexaphosphate (Ap6A).

    PubMed

    Fontes, R; Günther Sillero, M A; Sillero, A

    1999-03-01

    The synthesis of diadenosine hexaphosphate (Ap6A), a potent vasoconstrictor, is catalyzed by acyl-CoA synthetase from Pseudomonas fragi. In a first step AMP is transferred from ATP to tetrapolyphosphate (P4) originating adenosine pentaphosphate (p5A) which, subsequently, is the acceptor of another AMP moiety from ATP generating diadenosine hexaphosphate (Ap6A). Diadenosine pentaphosphate (Ap5A) and diadenosine tetraphosphate (Ap4A) were also synthesized in the course of the reaction. In view of the variety of biological effects described for these compounds the potential capacity of synthesis of diadenosine polyphosphates by the mammalian acyl-CoA synthetases may be relevant. PMID:10385004

  3. An ab-initio study of some homolytic substitution reactions of acyl radicals at silicon, germanium and tint.

    PubMed

    Matsubara, Hiroshi; Schiesser, Carl H

    2003-12-01

    Ab initio calculations using the 6-311G**, cc-pVDZ, and (valence) double-zeta pseudopotential (DZP) basis sets, with (MP2, QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional (BHandHLYP, B3LYP) calculations predict that homolytic substitution reactions of acetyl radicals at the silicon atoms in disilane can proceed via both backside and frontside attack mechanisms. At the highest level of theory (CCSD(T)/cc-pVDZ//MP2/cc-pVDZ), energy barriers (deltaE double dagger) of 77.2 and 81.9 kJ mol(-1) are calculated for the backside and frontside reactions respectively. Similar results are obtained for reactions involving germanium and tin with energy barriers (deltaE double dagger) of 53.7-84.2, and 55.0-89.7 kJ mol(-1) for the backside and frontside mechanisms, respectively. These data suggest that both homolytic substitution mechanisms are feasible for homolytic substitution reactions of acetyl radicals at silicon, germanium, and tin. BHandHLYP calculations provide geometries and energy barriers for backside and frontside transition states in good agreement with those obtained by traditional ab initio techniques. PMID:14685338

  4. Electron transfer pathways in photosystem I reaction centers

    NASA Astrophysics Data System (ADS)

    Ivashin, Nikolaj; Larsson, Sven

    2003-07-01

    Electron transfer following charge separation in the photosystem I (PSI) reaction center of Synechococcus elongatus is studied using theoretical methods. The difference in rate between two almost symmetrical A- and B-branches is caused by a difference in a single residue (Trp B673 versus Gly A693), close to the F X iron-sulfur cluster. Partly due to its polar environment, Trp B673 acts as an electron acceptor in its π-system. The rate increases on the B-side due to shortened distances for electron transfer.

  5. Light induced electron transfer reactions of metal complexes

    SciTech Connect

    Sutin, N.; Creutz, C.

    1980-01-01

    Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excited states are discussed and interpreted in terms of the driving force for the reaction and the distortions of the excited states relative to the corresponding ground states. General considerations relevant to the conversion of light into chemical energy are presented and progress in the use of polypyridine complexes to effect the light decomposition of water into hydrogen and oxygen is reviewed.

  6. Structure-activity relationships for degradation reaction of 1-beta-o-acyl glucuronides: kinetic description and prediction of intrinsic electrophilic reactivity under physiological conditions.

    PubMed

    Baba, Akiko; Yoshioka, Tadao

    2009-01-01

    1-beta-O-Acyl glucuronides (betaGAs) are potentially reactive metabolites capable of binding to proteins, and they have been implicated in adverse drug reactions of the carboxylic acid drugs. To explore their electrophilic reactivity, we studied structure-activity relationships (SARs) to characterize the factors affecting the degradation rate constants (k values) of betaGAs and ultimately to predict k values of structurally diverse betaGAs. Twenty-seven betaGAs and four related compounds were synthesized, and their k values were determined under physiological conditions (pH 7.4 and 37 degrees C). 1-beta-O-Benzoyl glucuronide (BAGA) and glucopyranoside (BAG) showed almost the same k values, whereas their 1-alpha-O-benzoyl isomers degraded approximately 40-fold faster than BAGA and BAG. BAGA methyl ester showed almost the same rate constant as BAGA in the cleavage of their 1-beta-O-benzoyl linkages. A pH-log k profile obtained indicated kinetics catalyzed by both specific and general bases. The log k of betaGAs derived from m- and p-substituted benzoic acids correlated with Hammett's sigma constants. A similar correlation was observed with delta(COOH), (1)H NMR chemical shifts of the parent benzoic acids including ones with less sterically bulky o-substituents. Alternative descriptors of delta(CO) and delta((CO)OH), (13)C chemical shifts for ester carbonyl carbons of betaGAs and for carbonyl carbons of the parent benzoic acids, respectively, correlated well with the log k of all 16 betaGAs derived from benzoic acids including ones with bulkier o-substituents. Of the betaGA isomers derived from (2R)- and (2S)-alpha-methyl-4-biphenylylacetic acid, the (2R)-isomer degraded approximately 2-fold faster than the (2S)-isomer. The alpha-methyl group in the (2S)-isomer would encumber the intramolecular acyl migration. The log k of betaGAs derived from n-aralkyl carboxylic acids and of the (2R)-isomer correlated with their delta(COOH). However, the log k of betaGAs derived

  7. Preparation of fatty-acylated derivatives of acyl carrier protein using Vibrio harveyi acyl-ACP synthetase.

    PubMed

    Shen, Z; Fice, D; Byers, D M

    1992-07-01

    A simple two-step purification of Vibrio harveyi fatty acyl-acyl carrier protein (acyl-ACP) synthetase, which is useful for the quantitative preparation and analysis of fatty-acylated derivatives of ACP, is described. Acyl-ACP synthetase can be partially purified from extracts of this bioluminescent bacterium by Cibacron blue chromatography and Sephacryl S-300 gel filtration and is stable for months at -20 degrees C in the presence of glycerol. Incubation of ACP from Escherichia coli with ATP and radiolabeled fatty acids (6 to 16 carbons in length) in the presence of the enzyme resulted in quantitative conversion to biologically active acylated derivatives. The enzyme reaction can be monitored by a filter disk assay to quantitate levels of ACP or by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography to detect ACP in cell extracts. With its broad fatty acid chain length specificity and optimal activity in mild nondenaturing buffers, the soluble V. harveyi acyl-ACP synthetase provides an attractive alternative to current chemical and enzymatic methods of acyl-ACP preparation and analysis. PMID:1514693

  8. Multiple Acyl-CoA Dehydrogenation Deficiency (Glutaric Aciduria Type II) with a Novel Mutation of Electron Transfer Flavoprotein-Dehydrogenase in a Cat.

    PubMed

    Wakitani, Shoichi; Torisu, Shidow; Yoshino, Taiki; Hattanda, Kazuhisa; Yamato, Osamu; Tasaki, Ryuji; Fujita, Haruo; Nishino, Koichiro

    2014-01-01

    Multiple acyl-CoA dehydrogenation deficiency (MADD; also known as glutaric aciduria type II) is a human autosomal recessive disease classified as one of the mitochondrial fatty-acid oxidation disorders. MADD is caused by a defect in the electron transfer flavoprotein (ETF) or ETF dehydrogenase (ETFDH) molecule, but as yet, inherited MADD has not been reported in animals. Here we present the first report of MADD in a cat. The affected animal presented with symptoms characteristic of MADD including hypoglycemia, hyperammonemia, vomiting, diagnostic organic aciduria, and accumulation of medium- and long-chain fatty acids in plasma. Treatment with riboflavin and L-carnitine ameliorated the symptoms. To detect the gene mutation responsible for MADD in this case, we determined the complete cDNA sequences of feline ETFα, ETFβ, and ETFDH. Finally, we identified the feline patient-specific mutation, c.692T>G (p.F231C) in ETFDH. The affected animal only carries mutant alleles of ETFDH. p.F231 in feline ETFDH is completely conserved in eukaryotes, and is located on the apical surface of ETFDH, receiving electrons from ETF. This study thus identified the mutation strongly suspected to have been the cause of MADD in this cat. PMID:24142280

  9. Modelling charge transfer reactions with the frozen density embedding formalism

    SciTech Connect

    Pavanello, Michele; Neugebauer, Johannes

    2011-12-21

    The frozen density embedding (FDE) subsystem formulation of density-functional theory is a useful tool for studying charge transfer reactions. In this work charge-localized, diabatic states are generated directly with FDE and used to calculate electronic couplings of hole transfer reactions in two {pi}-stacked nucleobase dimers of B-DNA: 5{sup '}-GG-3{sup '} and 5{sup '}-GT-3{sup '}. The calculations rely on two assumptions: the two-state model, and a small differential overlap between donor and acceptor subsystem densities. The resulting electronic couplings agree well with benchmark values for those exchange-correlation functionals that contain a high percentage of exact exchange. Instead, when semilocal GGA functionals are used the electronic couplings are grossly overestimated.

  10. Light Nuclei Studied with Nucleon Transfer Reactions Using Exotic Beams

    SciTech Connect

    Wuosmaa, A. H.; Rehm, K. E.; Greene, J. P.; Henderson, D. J.; Janssens, R. V. F.; Jiang, C. L.; Moore, E. F.; Pardo, R. C.; Peterson, D.; Pieper, S. C.; Savard, G.; Schiffer, J. P.; Sinha, S.; Tang, X.; Wiringa, R. B.; Jisonna, L.; Segel, R. E.; Paul, M.

    2006-04-26

    Single-neutron transfer with the (d,p) reaction in inverse kinematics has been used to study the properties of the light nuclei 9Li and 7He. The results for 9Li and 7He are compared to the predictions of ab-initio models of nuclear structure. Different possibilities for excited states in 7He are discussed in the context of other recent experimental studies of 7He.

  11. Momentum transfer in relativistic heavy ion charge-exchange reactions

    NASA Technical Reports Server (NTRS)

    Townsend, L. W.; Wilson, J. W.; Khan, F.; Khandelwal, G. S.

    1991-01-01

    Relativistic heavy ion charge-exchange reactions yield fragments (Delta-Z = + 1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (Delta-Z = 1, -2,...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.

  12. Fission of actinide nuclei using multi-nucleon transfer reactions

    NASA Astrophysics Data System (ADS)

    Léguillon, Romain; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, Riccardo; Makii, Hiroyuki; Nishinaka, Ichiro; Ishii, Tetsuro; Tsukada, Kazuaki; Asai, Masato; Chiba, Satoshi; Ohtsuki, Tsutomu; Araki, Shohei; Watanabe, Yukinobu; Tatsuzawa, Ryotaro; Takaki, Naoyuki

    2014-09-01

    We are promoting a campaign to measure fission-fragment mass distributions for neutron-rich actinide nuclei populated by transfer reactions from their ground state up to an excitation energy of several tens MeV. We thus obtain the excitation energy dependence of the mass distribution. The experiment was carried out at the 20 MV JAEA tandem facility at Tokai. We report on the data obtained in the direct reaction 18 O + 232 Th . Transfer-channels and excitation energies of the fissioning nuclei were identified using silicon dE-E detectors located at forward angle. Two fission fragments were detected in coincidence using multi-wire proportional counters. Fission fragment masses were determined by kinematic consideration. We obtained the fission fragment mass distributions for 13 nuclei from actinium to uranium and some fission barrier heights. We are promoting a campaign to measure fission-fragment mass distributions for neutron-rich actinide nuclei populated by transfer reactions from their ground state up to an excitation energy of several tens MeV. We thus obtain the excitation energy dependence of the mass distribution. The experiment was carried out at the 20 MV JAEA tandem facility at Tokai. We report on the data obtained in the direct reaction 18 O + 232 Th . Transfer-channels and excitation energies of the fissioning nuclei were identified using silicon dE-E detectors located at forward angle. Two fission fragments were detected in coincidence using multi-wire proportional counters. Fission fragment masses were determined by kinematic consideration. We obtained the fission fragment mass distributions for 13 nuclei from actinium to uranium and some fission barrier heights. Present study is supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan.

  13. Acyl silicates and acyl aluminates as activated intermediates in peptide formation on clays

    NASA Technical Reports Server (NTRS)

    White, D. H.; Kennedy, R. M.; Macklin, J.

    1984-01-01

    Glycine reacts with heating on dried clays and other minerals to give peptides in much better yield than in the absence of mineral. This reaction was proposed to occur by way of an activated intermediate such as an acyl silicate or acyl aluminate analogous to acyl phosphates involved in several biochemical reactions including peptide bond synthesis. The proposed mechanism has been confirmed by trapping the intermediate, as well as by direct spectroscopic observation of a related intermediate. The reaction of amino acids on periodically dried mineral surfaces represents a widespead, geologically realistic setting for prebiotic peptide formation via in situ activation.

  14. Laser driven hydrogen transfer reactions in atmospheric chemistry

    NASA Astrophysics Data System (ADS)

    Lester, Marsha I.

    2015-03-01

    Ozonolysis of alkenes, an important non-photolytic source of OH radicals in the troposphere, proceeds through energized Criegee intermediates that undergo unimolecular decay to produce OH radicals. In this work, infrared laser activation of cold methyl-substituted Criegee intermediates is utilized to drive hydrogen transfer from the methyl group to the terminal oxygen, followed by dissociation to OH radicals. State-selective excitation of the Criegee intermediates in the CH stretch overtone region combined with sensitive OH detection reveals the infrared spectra of CH3CHOO and (CH3)2 COO, effective barrier heights for the critical hydrogen transfer step, and rapid decay dynamics to OH products. Complementary theory provides insights on the infrared overtone spectra as well as vibrational excitations, structural changes, and energy required to move from the minimum energy configuration of the Criegee intermediates to the transition state for the hydrogen transfer reaction. Research supported by the National Science Foundation.

  15. Neutron transfer reactions induced by Li8 on Be9

    NASA Astrophysics Data System (ADS)

    Guimarães, V.; Lichtenthäler, R.; Camargo, O.; Barioni, A.; Assunção, M.; Kolata, J. J.; Amro, H.; Becchetti, F. D.; Jiang, Hao; Aguilera, E. F.; Lizcano, D.; Martines-Quiroz, E.; Garcia, H.

    2007-05-01

    Angular distributions for the elastic scattering of Li8 on Be9 and the neutron transfer reactions Be9(Li8,Li7)Be10 and Be9(Li8,Li9)Be8 were measured with a 27 MeV Li8 radioactive nuclear beam. Spectr- oscopic factors for Li8 ⊗n= Li9 and Li7 ⊗n= Li8 bound systems were obtained from the comparison between the experimental differential cross section and finite-range distorted-wave Born approximation calculations with the code FRESCO. The spectroscopic factors obtained were compared to shell model calculations and to other experimental values from (d,p) reactions. Using the present values for the spectroscopic factor, cross sections for the direct neutron-capture reactions Li7(n,γ)Li8 and Li8(n,γ)Li9 were calculated in the framework of a potential model.

  16. Fluctuations in Biological and Bioinspired Electron-Transfer Reactions

    PubMed Central

    Skourtis, Spiros S.; Waldeck, David H.; Beratan, David N.

    2010-01-01

    Central to theories of electron transfer (ET) is the idea that nuclear motion generates a transition state that enables electron flow to proceed, but nuclear motion also induces fluctuations in the donor-acceptor (DA) electronic coupling that is the rate-limiting parameter for nonadiabatic ET. The interplay between the DA energy gap and DA coupling fluctuations is particularly noteworthy in biological ET, where flexible protein and mobile water bridges take center stage. Here, we discuss the critical timescales at play for ET reactions in fluctuating media, highlighting issues of the Condon approximation, average medium versus fluctuation-controlled electron tunneling, gated and solvent relaxation controlled electron transfer, and the influence of inelastic tunneling on electronic coupling pathway interferences. Taken together, one may use this framework to establish principles to describe how macromolecular structure and structural fluctuations influence ET reactions. This framework deepens our understanding of ET chemistry in fluctuating media. Moreover, it provides a unifying perspective for biophysical charge-transfer processes and helps to frame new questions associated with energy harvesting and transduction in fluctuating media. PMID:20192814

  17. Electrical double layer effects on ion transfer reactions.

    PubMed

    Lin, Chuhong; Laborda, Eduardo; Batchelor-McAuley, Christopher; Compton, Richard G

    2016-04-14

    The potential dependence of the thermodynamics and kinetics of ion transfer reactions as influenced by the electrical double layer are studied via two-dimensional free energy surfaces calculated with an extension of the Anderson-Newns Hamiltonian. The Gibbs energy difference between the reduced and oxidized states, the activation barrier and the resulting current-potential curves are investigated as a function of the potential of zero charge and the Debye length, which are applied to characterize the external electric field. It is found that the current-potential curves of different redox systems are distinctly affected by the electrical double layer depending on the charges of the solution-phase and adsorbed species. For the redox couples sensitive to double layer effects, it is shown that the external electric field can cause a decrease in the driving force for the ion transfer process, which leads to the reversible peak current deviating significantly from the ideal, Nernstian predictions and the effective transfer coefficient being less than 1 even though the ion transfer is kinetically fully reversible. PMID:27001630

  18. Chemical reaction fouling model for single-phase heat transfer

    SciTech Connect

    Panchal, C.B.; Watkinson, A.P.

    1993-08-01

    A fouling model was developed on the premise that the chemical reaction for generation of precursor can take place in the bulk fluid, in the thermalboundary layer, or at the fluid/wall interface, depending upon the interactive effects of flu id dynamics, heat and mass transfer, and the controlling chemical reaction. The analysis was used to examine the experimental data for fouling deposition of polyperoxides produced by autoxidation of indene in kerosene. The effects of fluid and wall temperatures for two flow geometries were analyzed. The results showed that the relative effects of physical parameters on the fouling rate would differ for the three fouling mechanisms; therefore, it is important to identify the controlling mechanism in applying the closed-flow-loop data to industrial conditions.

  19. Catalytic Transfer Hydogenation Reactions for Undergraduate Practical Programs

    NASA Astrophysics Data System (ADS)

    Hanson, R. W.

    1997-04-01

    A brief review of catalytic transfer hydrogenation (CTH) reactions is given. Attention is drawn, particularly, to the utility of ammonium formate as the hydrogen donor in this type of reaction. The reduction of aryl carbonyl compounds to the corresponding methylene derivatives by ammonium formate in the presence of 10% Pd/C at 110°C is compared to their reductive ammonation which occurs at higher temperatures in the absence of the catalyst (the Leuckart reaction). It is suggested that the low cost and simplicity of CTH reactions using ammonium formate as the hydrogen donor, together with the high yields obtained in many cases, make them excellent candidates for inclusion in undergraduate practical programmes. Laboratory instructions are given for the reduction of nitrobenzene to aniline (isolated as benzanilide), benzophenone to diphenylmethanol and fluorenone to fluorene, in all cases using ammonium formate as the hydrogen donor and 10% Pd/C as the catalyst. Thin layer chromatography shows that in each case the product is homogeneous; the yields are essentially quantitative.

  20. Decoupling interfacial reactions between plasmas and liquids: charge transfer vs plasma neutral reactions.

    PubMed

    Rumbach, Paul; Witzke, Megan; Sankaran, R Mohan; Go, David B

    2013-11-01

    Plasmas (gas discharges) formed at the surface of liquids can promote a complex mixture of reactions in solution. Here, we decouple two classes of reactions, those initiated by electrons (electrolysis) and those initiated by gaseous neutral species, by examining an atmospheric-pressure microplasma formed in different ambients at the surface of aqueous saline (NaCl) solutions. Electrolytic reactions between plasma electrons and aqueous ions yield an excess of hydroxide ions (OH(-)), making the solution more basic, while reactions between reactive neutral species formed in the plasma phase and the solution lead to nitrous acid (HNO2), nitric acid (HNO3), and hydrogen peroxide (H2O2), making the solution more acidic. The relative importance of either reaction path is quantified by pH measurements, and we find that it depends directly on the composition of the ambient background gas. With a background gas of oxygen or argon, electron transfer reactions yielding excess OH(-) dominate, while HNO2 and HNO3 formed in the plasma and by the dissolution of nitrogen oxide (NOx) species dominate in the case of air and nitrogen. For pure nitrogen (N2) gas, we observe a unique coupling between both reactions, where oxygen (O2) gas formed via water electrolysis reacts in the bulk of the plasma to form NOx, HNO2, and HNO3. PMID:24144120

  1. Labelling of endogenous target protein via N-S acyl transfer-mediated activation of N-sulfanylethylanilide.

    PubMed

    Denda, Masaya; Morisaki, Takuya; Kohiki, Taiki; Yamamoto, Jun; Sato, Kohei; Sagawa, Ikuko; Inokuma, Tsubasa; Sato, Youichi; Yamauchi, Aiko; Shigenaga, Akira; Otaka, Akira

    2016-07-14

    The ligand-dependent incorporation of a reporter molecule (e.g., fluorescence dye or biotin) onto a endogenous target protein has emerged as an important strategy for elucidating protein function using various affinity-based labelling reagents consisting of reporter, ligand and reactive units. Conventional labelling reagents generally use a weakly activated reactive unit, which can result in the non-specific labelling of proteins in a ligand-independent manner. In this context, the activation of a labelling reagent through a targeted protein-ligand interaction could potentially overcome the problems associated with conventional affinity-based labelling reagents. We hypothesized that this type of protein-ligand-interaction-mediated activation could be accomplished using N-sulfanylethylanilide (SEAlide) as the reactive unit in the labelling reagent. Electrophilically unreactive amide-type SEAlide can be activated by its conversion to the corresponding active thioester in the presence of a phosphate salt, which can act as an acid-base catalyst. It has been suggested that protein surfaces consisting of hydrophilic residues such as amino, carboxyl and imidazole groups could function as acid-base catalysts. We therefore envisioned that a SEAlide-based labelling reagent (SEAL) bearing SEAlide as a reactive unit could be activated through the binding of the SEAL with a target protein. Several SEALs were readily prepared in this study using standard 9-fluorenylmethyloxycarbonyl (Fmoc)-based solid-phase protocols. These SEAL systems were subsequently applied to the ligand-dependent labelling of human carbonic anhydrase (hCA) and cyclooxyganese 1. Although we have not yet obtained any direct evidence for the target protein-mediated activation of the SEAlide unit, our results for the reaction of these SEALs with hCA1 or butylamine indirectly support our hypothesis. The SEALs reported in this study represent valuable new entries to the field of affinity-based labelling reagents

  2. Ion/ion proton transfer reactions for protein mixture analysis.

    PubMed

    Stephenson, J L; McLuckey, S A

    1996-11-15

    Ion/ion proton transfer reactions are shown to be an effective means to facilitate the resolution of ions in electrospray mass spectrometry that differ in mass and charge but are similar in mass-to-charge ratio. Examples are shown in which a minor contaminant protein in a ribonuclease B solution is clearly apparent after ion/ion proton transfer but not in the conventional electrospray mass spectrum. A further example involving a mixture of bovine serum albumin and bovine transferrin also showed the identification of previously unnoticed "contaminant" polymer. The latter mixture also illustrated important issues in the use of the quadrupole ion trap as a reaction vessel and mass analyzer for high mass-to-charge ratio ions. The results suggest that the use of ion trap operating parameters specifically tailored for storage, ejection, detection, and mass-to-charge analysis of high mass-to-charge ratio ions can have attractive analytical figures of merit for determining mixtures of relatively high-mass proteins and, by extension, other types of high-mass biopolymers. PMID:8916454

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

    SciTech Connect

    Valentini, J.J.

    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. Double group transfer reactions: role of activation strain and aromaticity in reaction barriers.

    PubMed

    Fernández, Israel; Bickelhaupt, F Matthias; Cossío, Fernando P

    2009-12-01

    Double group transfer (DGT) reactions, such as the bimolecular automerization of ethane plus ethene, are known to have high reaction barriers despite the fact that their cyclic transition states have a pronounced in-plane aromatic character, as indicated by NMR spectroscopic parameters. To arrive at a way of understanding this somewhat paradoxical and incompletely understood phenomenon of high-energy aromatic transition states, we have explored six archetypal DGT reactions using density functional theory (DFT) at the OLYP/TZ2P level. The main trends in reactivity are rationalized using the activation strain model of chemical reactivity. In this model, the shape of the reaction profile DeltaE(zeta) and the height of the overall reaction barrier DeltaE( not equal)=DeltaE(zeta=zeta(TS)) is interpreted in terms of the strain energy DeltaE(strain)(zeta) associated with deforming the reactants along the reaction coordinate zeta plus the interaction energy DeltaE(int)(zeta) between these deformed reactants: DeltaE(zeta)=DeltaE(strain)(zeta)+DeltaE(int)(zeta). We also use an alternative fragmentation and a valence bond model for analyzing the character of the transition states. PMID:19852009

  5. Electrocatalysis of anodic and cathodic oxygen-transfer reactions

    SciTech Connect

    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.

  6. Anatomy of a simple acyl intermediate in enzyme catalysis: combined biophysical and modeling studies on ornithine acetyl transferase.

    PubMed

    Iqbal, Aman; Clifton, Ian J; Bagonis, Maria; Kershaw, Nadia J; Domene, Carmen; Claridge, Timothy D W; Wharton, Christopher W; Schofield, Christopher J

    2009-01-21

    Acyl-enzyme complexes are intermediates in reactions catalyzed by many hydrolases and related enzymes which employ nucleophilic catalysis. However, most of the reported structural data on acyl-enzyme complexes has been acquired under noncatalytic conditions. Recent IR analyses have indicated that some acyl-enzyme complexes may be more flexible than most crystallographic analyses have implied. OAT2 is a member of the N-terminal nucleophile (Ntn) hydrolase enzyme superfamily and catalyzes the reversible transfer of an acetyl group between the alpha-amino groups of ornithine and glutamate in a mechanism proposed to involve an acyl-enzyme complex. We have carried out biophysical analyses on ornithine acetyl transferase (OAT2), both in solution and in the crystalline state. Mass spectrometric studies identified Thr-181 as the residue acetylated during OAT2 catalysis; (13)C NMR analyses implied the presence of an acyl-enzyme complex in solution. Crystallization of OAT2 in the presence of N-alpha-acetyl-L-glutamate led to a structure in which Thr-181 was acetylated; the carbonyl oxygen of the acyl-enzyme complex was located in an oxyanion hole and positioned to hydrogen bond with the backbone amide NH of Gly-112 and the alcohol of Thr-111. While the crystallographic analyses revealed only one structure, IR spectroscopy demonstrated the presence of two distinct acyl-enzyme complex structures with carbonyl stretching frequencies at 1691 and 1701 cm(-1). Modeling studies implied two possible acyl-enzyme complex structures, one of which correlates with that observed in the crystal structure and with the 1691 cm(-1) IR absorption. The second acyl-enzyme complex structure, which has only a single oxyanion hole hydrogen bond, is proposed to give rise to the 1701 cm(-1) IR absorption. The two acyl-enzyme complex structures can interconvert by movement of the Thr-111 side-chain alcohol hydrogen away from the oxyanion hole to hydrogen bond with the backbone carbonyl of the acylated

  7. Population of high spin states in very heavy ion transfer reactions. The experimental evidence

    SciTech Connect

    Guidry, M.W.

    1985-01-01

    Transfer reactions have been studied for some time with light heavy ions such as oxygen. Although states of spin I approx.10 h are sometimes populated in such reactions, it is assumed that collective excitation is small, and the transferred particles are responsible for the angular momentum transfer. In this paper we will discuss a qualitatively different kind of transfer reaction using very heavy ions (A greater than or equal to 40). In these reactions the collective excitation in both the entrance and exit channels is strong, and there may be appreciable angular momentum transfer associated with inelastic excitation. 12 refs., 13 figs.

  8. Multinucleon transfer in the 136Xe+208Pb reaction

    NASA Astrophysics Data System (ADS)

    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.

  9. LIGNIN ACYLATION IN GRASSES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Acylation of lignin during growth and development is a commonly found among some plant species. Grasses form unique acylated lignins involving p-coumarate (pCA). In corn rind tissue, it is exclusively attached to the gamma-carbon of lignin monomers, with a strong preference (over 90%) for attachment...

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

    SciTech Connect

    Basilevsky, M. V.; Mitina, E. A.; Odinokov, A. V.; National Research Nuclear University “MEPhI,” 31, Kashirskoye shosse, Moscow ; Titov, S. V.

    2013-12-21

    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 ξ{sub 0}=ℏω{sub 0}/k{sub B}T where ω{sub 0} is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ{sub 0} < 1 − 3) and for low (ξ{sub 0}≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T→ 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic 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

  11. Electron Transfer Reactions in Colloidal Quantum Dot-Ligand Complexes

    NASA Astrophysics Data System (ADS)

    Morris-Cohen, Adam Joshua

    This thesis describes a quantitative analysis of the chemical composition of colloidal II-VI quantum dot (QD)-ligand complexes and transient absorption experiments analyzing the rates of electron transfer reactions in these complexes functionalized with redox active ligands. Chemical analysis reveals that phosphonate impurities in the surfactants used to synthesize CdSe QDs are the dominant ligands on the surface of the QDs, and these phosphonate impurities cause size-dependent Cd-enrichment of the QD surface. A study of the adsorption equilibrium of solution-phase CdS quantum dots and acid-derivatized viologen ligands (V2+) reveals that the structure of the surfaces of the QDs depends on the concentration of the QDs. A new model based on the Langmuir isotherm that treats both the number of adsorbed ligands per QD and the number of available binding sites per QD as binomially-distributed quantities is described. Transient absorption spectroscopy of solution-phase mixtures of colloidal CdS QDs and V2+ indicates electron transfer occurs from the conduction band of the QD to the LUMO of V2+. The rate constant for photoinduced electron transfer (PET) is independent of the number of methylene groups in the alkyl chain on the acid-derivatized viologen. The insensitivity of the electron transfer rate constant to the length of the functional groups on the viologen suggests a van der Waals (vdW) pathway for PET, where the electron bypasses the alkylcarboxylate and tunnels through the orbitals of the QD and of the bipyridinium core. The rate of PET from colloidal CdSe quantum dots (QDs) to oxo-centered triruthenium clusters (Ru 3O) depends on the structure of the chemical headgroup by which the Ru3O clusters adsorb to the QDs. Complexes comprising QDs and Ru 3O clusters adsorbed through a pyridine-4-carboxylic acid ligand have a PET rate constant of (4.9 ± 0.9)×109 s -1 whereas complexes comprising QDs and Ru3O clusters adsorbed through a 4-mercaptopyridine ligand have an

  12. Next-generation transfer reaction studies with JENSA

    NASA Astrophysics Data System (ADS)

    Chipps, K. A.

    2015-04-01

    Next generation radioactive ion beam facilities are being planned and built across the globe, and with them an incredible new array of exotic isotopes will be available for study. To keep pace with the state of nuclear physics research, both new detector systems and new target systems are needed. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target is one of these new target systems, designed to provide a target of light gas that is localized, dense, and pure. The JENSA gas jet target was originally constructed at Oak Ridge National Laboratory for testing and characterization, and has now moved to the ReA3 reaccelerated beam hall at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University for use with radioactive beams. The availability of a pure, localized target of light gases will enable exceptional scattering and transfer reaction studies with these exotic beams. Some examples will be given, and future plans will be discussed. This work is supported by the US DOE Office of Science (Office of Nuclear Physics) and the NSF.

  13. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

  14. Primary electron transfer reactions in modified reaction centers from Rhodopseudomonas sphaeroides

    PubMed Central

    Shuvalov, V. A.; Duysens, L. N. M.

    1986-01-01

    Absorption spectra were measured by means of an optical multichannel analyzer in Rhodopseudomonas sphaeroides R-26 reaction centers (RCs) modified by treatment with NaBH4 at various times (≥1 ps) after the onset of a short excitation flash at 880 nm. Most of these RCs (75-95%) have only one “monomeric” bacteriochlorophyll-800 (B1) molecule and are as active as the original RCs. The duration of the excitation and measuring pulses was ≈33 ps. If the center of the excitation pulse preceded the center of the measuring pulse by 36-40 ps, the formation of a state PE (early state), which is converted to the state PF (P+ bacteriopheophytin-) in 4 ± 1 ps (1/e time), was observed. Also the kinetics and the spectrum of the stimulated emission (reflecting the kinetics and the emission spectrum of the excited state P*) were determined. The difference spectrum of the state PE approximately equals the sum of the spectra of the states P* (≈65%) and 1[P+B1-] (≈35%). This indicates that B1- is an intermediate in the electron transfer from P* to bacteriopheophytin, H1, transferring this electron with a rate constant of (4 × 0.35 ps)-1 = 7 × 1011 s-1. PMID:16593664

  15. Selectivity of celite-immobilized patatin (lipid acyl hydrolase) from potato (Solanum tuberosum L.) tubers in esterification reactions As influenced by water activity and glycerol analogues as alcohol acceptors.

    PubMed

    Pinsirodom, P; Parkin, K L

    2000-02-01

    Lipid acyl hydrolase (LAH; patatin) was purified from potato tubers by ammonium sulfate fractionation followed by anion-exchange and affinity chromatography. The major protein band of 40-43 kDa on SDS-PAGE appeared to be patatin, and it stained positive for lipase activity on native PAGE. Selectivity of a Celite-immobilized potato LAH in esterification reactions with n-acyl fatty acids (FA; C4, C6, C8, C10, C12, C14, C16, and C18) and alcohol acceptors (n-propanol, 2-propanol, 1,3-propanediol, and glycerol; 1,2-propanediol was not sufficiently reactive) was studied in isooctane. Immobilized LAH was highly selective for medium chain FAs (C8/C10) with a secondary optimum for chain lengths of C14/16. Water activity (a(w)) influenced activity and FA selectivity of the enzyme. Initial rates of ester synthesis were greatest at a(w) of 0.90 for all alcohol acceptors except for glycerol, where greatest initial rates were observed at a(w) of 0.19. Immobilized LAH preparations exhibited a bell-shape pH profile with optimum activity at pH 6-7 for ester synthesis, and no effect of pH on FA selectivity was observed. PMID:10691609

  16. Concentrations of long-chain acyl-acyl carrier proteins during fatty acid synthesis by chloroplasts isolated from pea (Pisum sativum), safflower (Carthamus tinctoris), and amaranthus (Amaranthus lividus) leaves

    SciTech Connect

    Roughan, G.; Nishida, I. )

    1990-01-01

    Fatty acid synthesis from (1-14C)acetate by chloroplasts isolated from peas and amaranthus was linear for at least 15 min, whereas incorporation of the tracer into long-chain acyl-acyl carrier protein (ACP) did not increase after 2-3 min. When reactions were transferred to the dark after 3-5 min, long-chain acyl-ACPs lost about 90% of their radioactivity and total fatty acids retained all of theirs. Half-lives of the long-chain acyl-ACPs were estimated to be 10-15 s. Concentrations of palmitoyl-, stearoyl-, and oleoyl-ACP as indicated by equilibrium labeling during steady-state fatty acid synthesis, ranged from 0.6-1.1, 0.2-0.7, and 0.4-1.6 microM, respectively, for peas and from 1.6-1.9, 1.3-2.6, and 0.6-1.4 microM, respectively, for amaranthus. These values are based on a chloroplast volume of 47 microliters/mg chlorophyll and varied according to the mode of the incubation. A slow increase in activity of the fatty acid synthetase in safflower chloroplasts resulted in long-chain acyl-ACPs continuing to incorporate labeled acetate for 10 min. Upon re-illumination following a dark break, however, both fatty acid synthetase activity and acyl-ACP concentrations increased very rapidly. Palmitoyl-ACP was present at concentrations up to 2.5 microM in safflower chloroplasts, whereas those of stearoyl- and oleoyl-ACPs were in the lower ranges measured for peas. Acyl-ACPs were routinely separated from extracts of chloroplasts that had been synthesising long-chain fatty acids from labeled acetate by a minor modification of the method of Mancha et al. The results compared favorably with those obtained using alternative analytical methods such as adsorption to filter paper and partition chromatography on silicic acid columns.

  17. Acyl Silicates and Acyl Aluminates as Activated Intermediates in Peptide Formation on Clays

    NASA Astrophysics Data System (ADS)

    White, David H.; Kennedy, Robert M.; Macklin, John

    1984-12-01

    Glycine reacts with heating on dried clays and other minerals to give peptides in much better yield than in the absence of mineral. This reaction was proposed to occur by way of an activated intermediate such as an acyl silicate or acyl aluminate (i.e., the anhydride of a carboxylic acid with Si-OH or Al-OH), analogous to acyl phosphates involved in several biochemical reactions including peptide bond synthesis. We confirmed the proposed mechanism by trapping the intermediate, as well as by direct spectroscopic observation of a related intermediate. The reaction of amino acids on periodically dried mineral surfaces represents a widespread, geologically realistic setting for prebiotic peptide formation via in situ activation.

  18. Sonochemical enzyme-catalyzed regioselective acylation of flavonoid glycosides.

    PubMed

    Ziaullah; Rupasinghe, H P Vasantha

    2016-04-01

    This work compares a highly efficient and alternative method of sonication-assisted lipase catalyzed acylation of quercetin-3-O-glucoside and phloretin-2'-glucoside, using Candida antarctica lipase B (Novozyme 435(®)), with a range of fatty acids. In this study, sonication-assisted irradiation coupled with stirring has been found to be more efficient and economical than conventional reaction conditions. Sonication-assisted acylation accelerated the reactions and reduced the time required by 4-5 folds. PMID:26829593

  19. Reaction electronic flux and its role in DNA intramolecular proton transfers.

    PubMed

    Durán, Rocío; Vöhringer-Martinez, Esteban; Toro-Labbé, Alejandro; Herrera, Bárbara

    2016-06-01

    Proton transfer reactions present a key step in many biological and chemical processes. Here, we focused on the electronic changes in the proton transfer reactions of the four DNA bases. In combination with the previous structural analysis the reaction electronic flux together with local descriptors as the Hirshfeld-I charges allow us to identify chemical events and rationalize the underlying reaction mechanism. Our results show that imine-enamine in adenine and citosyne, and keto-enol tautomerizations in thymine and guanine have different reaction mechanisms. The former involve net structural rearrangements driven by favoured electrostatic interactions between the proton and the acceptor atom whereas the keto-enol tautomerizations require electronic changes reflected in the reaction electronic flux and changes in the NBO bond orders which favour the proton transfer reaction. PMID:27256316

  20. Laser ion source for multi-nucleon transfer reaction products

    NASA Astrophysics Data System (ADS)

    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

  1. Observation of the one- to six-neutron transfer reactions at sub-barrier energies

    SciTech Connect

    Jiang, C.L.; Rehm, K.E.; Gehring, J.

    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.

  2. Characterization of an Archaeal Medium-Chain Acyl Coenzyme A Synthetase from Methanosarcina acetivorans▿

    PubMed Central

    Meng, Yu; Ingram-Smith, Cheryl; Cooper, Leroy L.; Smith, Kerry S.

    2010-01-01

    Short- and medium-chain acyl coenzyme A (acyl-CoA) synthetases catalyze the formation of acyl-CoA from an acyl substrate, ATP, and CoA. These enzymes catalyze mechanistically similar two-step reactions that proceed through an enzyme-bound acyl-AMP intermediate. Here we describe the characterization of a member of this enzyme family from the methane-producing archaeon Methanosarcina acetivorans. This enzyme, a medium-chain acyl-CoA synthetase designated MacsMa, utilizes 2-methylbutyrate as its preferred substrate for acyl-CoA synthesis but cannot utilize acetate and thus cannot catalyze the first step of acetoclastic methanogenesis in M. acetivorans. When propionate or other less favorable acyl substrates, such as butyrate, 2-methylpropionate, or 2-methylvalerate, were utilized, the acyl-CoA was not produced or was produced at reduced levels. Instead, acyl-AMP and PPi were released in the absence of CoA, whereas in the presence of CoA, the intermediate was broken down into AMP and the acyl substrate, which were released along with PPi. These results suggest that although acyl-CoA synthetases may have the ability to utilize a broad range of substrates for the acyl-adenylate-forming first step of the reaction, the intermediate may not be suitable for the thioester-forming second step. The MacsMa structure has revealed the putative acyl substrate- and CoA-binding pockets. Six residues proposed to form the acyl substrate-binding pocket, Lys256, Cys298, Gly351, Trp259, Trp237, and Trp254, were targeted for alteration. Characterization of the enzyme variants indicates that these six residues are critical in acyl substrate binding and catalysis, and even conservative alterations significantly reduced the catalytic ability of the enzyme. PMID:20851904

  3. Cluster-transfer reactions with radioactive beams: A spectroscopic tool for neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Bottoni, S.; Leoni, S.; Fornal, B.; Raabe, R.; Rusek, K.; Benzoni, G.; Bracco, A.; Crespi, F. C. L.; Morales, A. I.; Bednarczyk, P.; Cieplicka-Oryńczak, N.; Królas, W.; Maj, A.; Szpak, B.; Callens, M.; Bouma, J.; Elseviers, J.; De Witte, H.; Flavigny, F.; Orlandi, R.; Reiter, P.; Seidlitz, M.; Warr, N.; Siebeck, B.; Hellgartner, S.; Mücher, D.; Pakarinen, J.; Vermeulen, M.; Bauer, C.; Georgiev, G.; Janssens, R. V. F.; Balabanski, D.; Sferrazza, M.; Kowalska, M.; Rapisarda, E.; Voulot, D.; Lozano Benito, M.; Wenander, F.

    2015-08-01

    An exploratory experiment performed at REX-ISOLDE 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 mechanism to explore the structure of exotic neutron-rich nuclei. The reactions 7Li(98Rb,α xn ) and 7Li(98Rb,t xn ) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cluster-transfer reactions can be described well as a direct process and that they can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.

  4. Theory of transfer reactions in peripheral heavy-ion collisions

    SciTech Connect

    Rapisarda, A. Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Corso Italia 57, I-95129 Catania, Italy ); Baldo, M. ); Broglia, R.A. The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen O, Denmark ); Winther, A. )

    1990-03-01

    The total absorption from the elastic channel due to transfer and inelastic processes in peripheral heavy-ion collisions at low bombarding energies is calculated in a microscopic coupled-channel approach. It is demonstrated for the first time that considering the depopulation of the entrance channel as an incoherent depopulation due to transfer processes is a good approximation. Using the corresponding absorptive potential within the framework of the Born approximation to calculate the transfer to individual channels, the results of full coupled-channels calculations are accurately reproduced.

  5. Study of intermediates from transition metal excited-state electron-transfer reactions

    SciTech Connect

    Hoffman, M.Z.

    1992-07-31

    Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

  6. Examining the effect of nonlocality in (d ,n ) transfer reactions

    NASA Astrophysics Data System (ADS)

    Ross, A.; Titus, L. J.; Nunes, F. M.

    2016-07-01

    Background: In the past year we have been exploring the effect of the explicit inclusion of nonlocality in (d ,p ) reactions. Purpose: The goal of this paper is to extend previous studies to (d ,n ) reactions, which, although similar to (d ,p ) reactions, have specific properties that merit inspection. Method: We apply our methods (both the distorted-wave Born approximation and the adiabatic wave approximation) to (d ,n ) reactions on 16O,40Ca,48Ca,126Sn,132Sn , and 208Pb at 20 and 50 MeV. Results: We look separately at the modifications introduced by nonlocality in the final bound and scattering states as well as the consequences reflected on the differential angular distributions. The cross sections obtained when using nonlocality explicitly are significantly different than those using the local approximation, just as in (d ,p ) reactions. Due to the particular role of the Coulomb force in the bound state, often we found the effects of nonlocality to be larger in (d ,n ) than in (d ,p ) reactions. Conclusions: Our results confirm the importance of including nonlocality explicitly in deuteron-induced reactions.

  7. 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

    SciTech Connect

    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{sup −1}, which is about 2.5 times faster than that in vacuum, 0.27 ps{sup −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.

  8. Ab initio study on the transition state of acylation step of trypsin catalysis.

    PubMed

    Kubodera, H; Nakagawa, S; Umeyama, H

    1990-03-01

    The transition state of acylation step of trypsin catalysis was determined by molecular orbital calculations. The calculations were carried out at the RHF-LCAO-SCF approximation level with double zeta basis set (plus polarization functions). The role of His57 residue in the acylation step of the catalytic reaction of trypsin was analysed from a quantum mechanical point of view. The influences of surrounding residues, such as oxyanion hole and Asp102-, and the electrostatic effect of the other regions of the enzyme were also studied. His57 was proved to capture the proton from Ser195 side chain terminus with its lone pair and to transfer it to substrate with electrostatic assistance of Asp102- and oxyanion hole. PMID:2165153

  9. Acyl-ACP Substrate Recognition in Burkholderia mallei BmaI1 Acyl-Homoserine Lactone Synthase

    PubMed Central

    2015-01-01

    The acyl-homoserine lactone (AHL) autoinducer mediated quorum sensing regulates virulence in several pathogenic bacteria. The hallmark of an efficient quorum sensing system relies on the tight specificity in the signal generated by each bacterium. Since AHL signal specificity is derived from the acyl-chain of the acyl-ACP (ACP = acyl carrier protein) substrate, AHL synthase enzymes must recognize and react with the native acyl-ACP with high catalytic efficiency while keeping reaction rates with non-native acyl-ACPs low. The mechanism of acyl-ACP substrate recognition in these enzymes, however, remains elusive. In this study, we investigated differences in catalytic efficiencies for shorter and longer chain acyl-ACP substrates reacting with an octanoyl-homoserine lactone synthase Burkholderia mallei BmaI1. With the exception of two-carbon shorter hexanoyl-ACP, the catalytic efficiencies of butyryl-ACP, decanoyl-ACP, and octanoyl-CoA reacting with BmaI1 decreased by greater than 20-fold compared to the native octanoyl-ACP substrate. Furthermore, we also noticed kinetic cooperativity when BmaI1 reacted with non-native acyl-donor substrates. Our kinetic data suggest that non-native acyl-ACP substrates are unable to form a stable and productive BmaI1·acyl-ACP·SAM ternary complex and are thus effectively discriminated by the enzyme. These results offer insights into the molecular basis of substrate recognition for the BmaI1 enzyme. PMID:25215658

  10. Does electron-transfer theory explain large rate differences in singlet and triplet excited state electron-transfer reactions?

    SciTech Connect

    Zusman, L.D.; Kurnikov, I.V.; Beratan, D.N.

    1995-12-31

    Gray and coworkers have shown that intramolecular electron-transfer rates from singlet and triplet excited states in iridium(spacer)pyridinium complexes can be vastly different (>5 orders of magnitude). We have analyzed the possible sources of these differences, including effects that may arise from reorganization energies, free energies, and tunneling matrix elements. When distance dependent reorganization energies and energy dependent tunneling matrix elements are included, a systematic framework emerges to describe these electron-transfer reactions.

  11. Charge transfer reactions in multiply charged ion-atom collisions. [in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Steigman, G.

    1975-01-01

    Charge-transfer reactions in collisions between highly charged ions and neutral atoms of hydrogen and/or helium may be rapid at thermal energies. If these reactions are rapid, they will suppress highly charged ions in H I regions and guarantee that the observed absorption features from such ions cannot originate in the interstellar gas. A discussion of such charge-transfer reactions is presented and compared with the available experimental data. The possible implications of these reactions for observations of the interstellar medium, H II regions, and planetary nebulae are outlined.

  12. Acylation of N-p-Toluenesulfonylpyrrole Under Friedel-Crafts Conditions. Evidence for Organoaluminum Intermediates

    PubMed Central

    Huffman, John W.; Smith, Valerie J.; Padgett, Lea W.

    2008-01-01

    The Friedel-Crafts acylation of N-p-toluenesulfonylpyrrole under Friedel-Crafts conditions has been reinvestigated. Evidence is presented in support of the hypothesis that when AlCl3 is used as the Lewis acid, acylation proceeds via reaction of an organoaluminum intermediate with the acyl halide. This leads to the production of the 3-acyl derivative as the major product. With weaker Lewis acids (EtAlCl2, Et2AlCl) or less than one equivalent of AlCl3 the relative amount of 2-acyl product is increased. A mechanistic rationalization is presented to explain these data. PMID:19247425

  13. Electron-Wavepacket Reaction Dynamics in Proton Transfer of Formamide

    NASA Astrophysics Data System (ADS)

    Nagashima, Kengo; Takatsuka, Kazuo

    2009-10-01

    We apply the semiclassical Ehrenfest theory, which provides electron wavepacket dynamics coupled to nuclear motion, to a study of water-assisted proton relay in formamide compared with a forced proton transfer in gas phase, both of which are associated with the tautomerization. We start with the enol (imidic acid) form HO-CH═NH and track its proton transfer process to the keto (amide) form O═CH-NH2. Identifying the fact that this is indeed a "proton transfer process" rather than hydrogen-atom migration in terms of radical character on the proton, we show a collective quantum flux of electrons, which flows backward against the proton motion. This backward flux compensates the electrons tightly covering the proton, as represented in the Mulliken charge. The enol form formamide is one of the simplest species in the group O═CR1-NHR2, which is a unit of polypeptide. In the gas phase, the nitrogen atom may have a pyramidal structure as in the ammonium molecule; therefore, the C-N bond may allow low barrier rotation along it. This rotation is strongly prohibited by the formation of the double bond C═N induced by the proton transfer. Not only the dynamical process of proton transfer itself but also the electronic structures left behind are greatly affected by the presence of water molecule(s) and polar solvents. In discussing the relative stability of the formamide after the proton transfer, the following resonance structures are frequently mentioned, O--CH═N+H2 ↔ O═CH-NH2. Here we address the dynamical manifestation of the resonance structures in terms of our dynamical electron theory.

  14. Acyl-lipid metabolism.

    PubMed

    Li-Beisson, Yonghua; Shorrosh, Basil; Beisson, Fred; Andersson, Mats X; Arondel, Vincent; Bates, Philip D; Baud, Sébastien; Bird, David; Debono, Allan; Durrett, Timothy P; Franke, Rochus B; Graham, Ian A; Katayama, Kenta; Kelly, Amélie A; Larson, Tony; Markham, Jonathan E; Miquel, Martine; Molina, Isabel; Nishida, Ikuo; Rowland, Owen; Samuels, Lacey; Schmid, Katherine M; Wada, Hajime; Welti, Ruth; Xu, Changcheng; Zallot, Rémi; Ohlrogge, John

    2013-01-01

    Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables. PMID:23505340

  15. Acyl-lipid metabolism.

    PubMed

    Li-Beisson, Yonghua; Shorrosh, Basil; Beisson, Fred; Andersson, Mats X; Arondel, Vincent; Bates, Philip D; Baud, Sébastien; Bird, David; Debono, Allan; Durrett, Timothy P; Franke, Rochus B; Graham, Ian A; Katayama, Kenta; Kelly, Amélie A; Larson, Tony; Markham, Jonathan E; Miquel, Martine; Molina, Isabel; Nishida, Ikuo; Rowland, Owen; Samuels, Lacey; Schmid, Katherine M; Wada, Hajime; Welti, Ruth; Xu, Changcheng; Zallot, Rémi; Ohlrogge, John

    2010-01-01

    Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables. PMID:22303259

  16. Acyl-Lipid Metabolism

    PubMed Central

    Li-Beisson, Yonghua; Shorrosh, Basil; Beisson, Fred; Andersson, Mats X.; Arondel, Vincent; Bates, Philip D.; Baud, Sébastien; Bird, David; DeBono, Allan; Durrett, Timothy P.; Franke, Rochus B.; Graham, Ian A.; Katayama, Kenta; Kelly, Amélie A.; Larson, Tony; Markham, Jonathan E.; Miquel, Martine; Molina, Isabel; Nishida, Ikuo; Rowland, Owen; Samuels, Lacey; Schmid, Katherine M.; Wada, Hajime; Welti, Ruth; Xu, Changcheng; Zallot, Rémi; Ohlrogge, John

    2010-01-01

    Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables. PMID:22303259

  17. Acyl-Lipid Metabolism

    PubMed Central

    Li-Beisson, Yonghua; Shorrosh, Basil; Beisson, Fred; Andersson, Mats X.; Arondel, Vincent; Bates, Philip D.; Baud, Sébastien; Bird, David; DeBono, Allan; Durrett, Timothy P.; Franke, Rochus B.; Graham, Ian A.; Katayama, Kenta; Kelly, Amélie A.; Larson, Tony; Markham, Jonathan E.; Miquel, Martine; Molina, Isabel; Nishida, Ikuo; Rowland, Owen; Samuels, Lacey; Schmid, Katherine M.; Wada, Hajime; Welti, Ruth; Xu, Changcheng; Zallot, Rémi; Ohlrogge, John

    2013-01-01

    Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables. PMID:23505340

  18. Cross sections for deeply inelastic transfer reactions induced by heavy ions in rare-earth targets

    NASA Astrophysics Data System (ADS)

    Rivet, M. F.; Bimbot, R.; Gardès, D.; Fleury, A.; Hubert, F.; Llabador, Y.

    1982-04-01

    Cross sections have been measured for deeply inelastic transfer reactions leading to the production of several radio-nuclides. Rare-earth targets were used and the projectiles were Ar, Cr, Fe and Cu ions. The reactions studied corresponded to transfers of two to nine protons and variable numbers of neutrons. The results obtained were used to study the evolution of some characteristics of these reactions, such as integrated cross sections and widths of the isotopic distributions, versus incident mass and transferred mass. These results confirm that mass transfer is driven by the potential energy of the composite system. The decrease of cross sections for increasing charge transfer may be quantitatively explained by assuming thermodynamical equilibrium of the mass asymmetry degree of freedom.

  19. On the Rate and Mechanism of Proton Transfer Reactions in Proteins

    NASA Astrophysics Data System (ADS)

    Xie, Aihua; Li, Yunxing; Manda, Edward; Nie, Beining; Hoff, Wouter; Martin, Richard

    2009-03-01

    One of the fundamental processes in molecular biology is proton transfer reactions in proteins. Proton transfer is essential for the biological functions of proteins responsible in bioenergetics, biological signaling, and enzymatic catalysis. The mechanism of proton transfer is of great interests in order to understand the structural basis of biological functions. Despite of extensive experimental and computational efforts, it remains elusive what causes a proton to move from the proton donor to the proton acceptor. We will report a proof of concept study regarding a general mechanism of internal proton transfer reactions in proteins. Density functional theory, B3LYP/6-311+G(2d,p), is employed in this study. The results of our study provide deep insights into the structural basis to the rate and mechanism of proton transfer reactions in proteins, such as bacteriorhodopsin and green fluorescence protein.

  20. Hydrogen transfer in SAM-mediated enzymatic radical reactions.

    PubMed

    Hioe, Johnny; Zipse, Hendrik

    2012-12-14

    S-adenosylmethionine (SAM) plays an essential role in a variety of enzyme-mediated radical reactions. One-electron reduction of SAM is currently believed to generate the C5'-desoxyadenosyl radical, which subsequently abstracts a hydrogen atom from the actual substrate in a catalytic or a non-catalytic fashion. Using a combination of theoretical and experimental bond dissociation energy (BDE) data, the energetics of these radical processes have now been quantified. SAM-derived radicals are found to react with their respective substrates in an exothermic fashion in enzymes using SAM in a stoichiometric (non-catalytic) way. In contrast, the catalytic use of SAM appears to be linked to a sequence of moderately endothermic and exothermic reaction steps. The use of SAM in spore photoproduct lyase (SPL) appears to fit neither of these general categories and appears to constitute the first example of a SAM-initiated radical reaction propagated independently of the cofactor. PMID:23139189

  1. Structure of Light Neutron-rich Nuclei Studied with Transfer Reactions

    SciTech Connect

    Wuosmaa, A. H.

    2015-01-01

    Transfer reactions have been used for many years to understand the shell structure of nuclei. Recent studies with rare-isotope beams extend this work and make it possible to probe the evolution of shell structure far beyond the valley of stability, requiring measurements in inverse kinematics. We present a novel technical approach to measurements in inverse kinematics, and apply this method to different transfer reactions, each of which probes different properties of light, neutron-rich nuclei.

  2. Syntheses of transuranium isotopes with atomic numbers Z ≤ 103 in multi-nucleon transfer reactions

    NASA Astrophysics Data System (ADS)

    Kratz, J. V.; Loveland, W.; Moody, K. J.

    2015-12-01

    In Section 1 we will discuss multi-nucleon transfer reactions with light heavy ions, which can be thought of as competing with complete fusion at higher impact parameters. Quasi-elastic and multi-nucleon transfer reactions with the heaviest projectiles will be discussed in Section 2. In Section 3 we will cover recent developments focusing on theoretical predictions of cross sections of superheavy nuclei, cover some new possibilities and look into the existing experimental challenges.

  3. Proton transfer reaction-mass spectrometry applications in medical research.

    PubMed

    Herbig, Jens; Amann, Anton

    2009-06-01

    Gathering information about a subject's physiological and pathophysiological condition from the `smell' of breath is an idea that dates back to antiquity. This intriguing concept of non-invasive diagnosis has been revitalized by `exhaled breath analysis' in recent decades. A main driving force was the development of sensitive and versatile gas-chromatographic and mass-spectrometric instruments for trace gas analysis. Ironically, only non-smelling constituents of breath, such as O(2), CO(2), H(2), and NO have so far been included in routine clinical breath analysis. The `smell' of human breath, on the other hand, arises through a combination of volatile organic compounds (VOCs) of which several hundred have been identified to date. Most of these volatiles are systemic and are released in the gas-exchange between blood and air in the alveoli. The concentration of these compounds in the alveolar breath is related to the respective concentrations in blood. Measuring VOCs in exhaled breath allows for screening of disease markers, studying the uptake and effect of medication (pharmacokinetics), or monitoring physiological processes. There is a range of requirements for instruments for the analysis of a complex matrix, such as human breath. Mass-spectrometric techniques are particularly well suited for this task since they offer the possibility of detecting a large variety of interesting compounds. A further requirement is the ability to measure accurately in the concentration range of breath VOCs, i.e. between parts-per-trillion (pptv) and parts-per-million (ppmv) range. In the mid 1990's proton transfer reaction-mass spectrometry (PTR-MS) was developed as a powerful and promising tool for the analysis of VOCs in gaseous media. Soon thereafter these instruments became commercially available to a still growing user community and have now become standard equipment in many fields including environmental research, food and flavour science, as well as life sciences. Their

  4. Efficient photoinduced orthogonal energy and electron transfer reactions via phospholipid membrane-bound donors and acceptors

    SciTech Connect

    Clapp, P.J.; Armitage, B.; Roosa, P.; O'Brien, D.F. )

    1994-10-05

    A three component, liposome-bound photochemical molecular device (PMD) consisting of energy and electron transfer reactions is described. Bilayer membrane surface-associated dyes, 5,10,15,20-tetrakis[4-(trimethylammonio)-phenyl]-21H,2 3H-porphine tetra-p-tosylate salt and N,N[prime]-bis[(3-trimethylammonio)propyl]thiadicarbocya nine tribromide, are the energy donor and acceptor, respectively, in a blue light stimulated energy transfer reaction along the vesicle surface. The electronically excited cyanine is quenched by electron transfer from the phospholipid membrane bound triphenylbenzyl borate anion, which is located in the lipid bilayer interior. The PMD exhibits sequential reactions following electronic excitation with the novel feature that the steps proceed with orthogonal orientation: energy transfer occurs parallel to the membrane surface, and electron transfer occurs perpendicular to the surface. Photobleaching and fluorescence quenching experiments verify the transfer reactions, and Stern-Volmer analysis was used to estimate the reaction rate constants. At the highest concentrations examined of energy and electron acceptor ca. 60% of the photoexcited porphyrins were quenched by energy transfer to the cyanine. 56 refs., 6 figs., 3 tabs.

  5. Theory for electron-transfer reactions involving two Marcus surfaces with a different force constant

    SciTech Connect

    Tang, Jau

    1994-02-01

    Theory for electron-transfer reactions at high temperature involving two Marcus parabolic surfaces with a different force constant is presented. The dynamic solvent effects are also considered using the stochastic Liouville equation, assuming an overdamped Debye solvent. An analytical expression for the adiabatic/nonadiabatic electron-transfer rate constant is derived.

  6. Posttraining Interventions To Enhance Transfer: The Moderating Effects of Work Environments. [and] Invited Reaction: Posttraining Interventions To Enhance Transfer.

    ERIC Educational Resources Information Center

    Richman-Hirsch, Wendy L.

    2001-01-01

    After 267 workers were trained, one group received goal-setting training, a second group self-management training, and a third no additional training. Goal setting improved perceptions of transfer; both interventions were more effective in supportive work environments. (Dale M. Brethower's invited reaction critiques the study from the perspective…

  7. Population of mixed-symmetry states via {alpha} transfer reactions

    SciTech Connect

    Alonso, C. E.; Arias, J. M.; Fortunato, L.; Vitturi, A.; Pietralla, N.

    2008-07-15

    Within the neutron-proton interacting boson model we study the population of mixed-symmetry states via {alpha} transfer processes. Closed expressions are deduced in the case of the limiting U{sub {pi}}{sub +{nu}}(5) and SU{sub {pi}}{sub +{nu}}(3). We find that the population of the lowest mixed-symmetry 2{sup +} state, vanishing along the N{sub {pi}}=N{sub {nu}} line, depends on the number of active bosons and is normally smaller than that of the lowest full symmetric 2{sup +} state. In particular, for deformed nuclei where the number of bosons is normally large, the relative population of the mixed-symmetry 2{sup +} state is of the order of a few percent. More favorable cases can be found near shell closures, as in the case of {alpha} transfer leading to {sup 140}Ba.

  8. Negative ion-uranium hexafluoride charge transfer reactions

    NASA Astrophysics Data System (ADS)

    Streit, Gerald E.; Newton, T. W.

    1980-10-01

    The flowing afterglow technique has been used to study the process of charge transfer from selected negative ions (F-, Cl-, Br-, I-, SF6-) to UF6. The sole ionic product in all cases was observed to be UF6-. Data analysis was complicated by an unexpected coupling of chemical and diffusive ion loss processes when UF6- product ions were present. The rate coefficients for the charge transfer processes are (k in 10-9 cm3 molecule-1 s-1) F-, 1.3; Cl-, 1.1; Br-, 0.93; I-, 0.77; and SF6-, 0.69. The rate constants agree quite well with the classical Langevin predictions.

  9. Phylogenetic and experimental characterization of an acyl-ACP thioesterase family reveals significant diversity in enzymatic specificity and activity

    PubMed Central

    2011-01-01

    Background Acyl-acyl carrier protein thioesterases (acyl-ACP TEs) catalyze the hydrolysis of the thioester bond that links the acyl chain to the sulfhydryl group of the phosphopantetheine prosthetic group of ACP. This reaction terminates acyl chain elongation of fatty acid biosynthesis, and in plant seeds it is the biochemical determinant of the fatty acid compositions of storage lipids. Results To explore acyl-ACP TE diversity and to identify novel acyl ACP-TEs, 31 acyl-ACP TEs from wide-ranging phylogenetic sources were characterized to ascertain their in vivo activities and substrate specificities. These acyl-ACP TEs were chosen by two different approaches: 1) 24 TEs were selected from public databases on the basis of phylogenetic analysis and fatty acid profile knowledge of their source organisms; and 2) seven TEs were molecularly cloned from oil palm (Elaeis guineensis), coconut (Cocos nucifera) and Cuphea viscosissima, organisms that produce medium-chain and short-chain fatty acids in their seeds. The in vivo substrate specificities of the acyl-ACP TEs were determined in E. coli. Based on their specificities, these enzymes were clustered into three classes: 1) Class I acyl-ACP TEs act primarily on 14- and 16-carbon acyl-ACP substrates; 2) Class II acyl-ACP TEs have broad substrate specificities, with major activities toward 8- and 14-carbon acyl-ACP substrates; and 3) Class III acyl-ACP TEs act predominantly on 8-carbon acyl-ACPs. Several novel acyl-ACP TEs act on short-chain and unsaturated acyl-ACP or 3-ketoacyl-ACP substrates, indicating the diversity of enzymatic specificity in this enzyme family. Conclusion These acyl-ACP TEs can potentially be used to diversify the fatty acid biosynthesis pathway to produce novel fatty acids. PMID:21831316

  10. Electron transfer reactions within zeolites: Radical cation from benzonorbornadiene

    SciTech Connect

    Pitchumani, K.; Ramamurthy, V.; Corbin, D.R.

    1996-08-28

    Zeolites are being used as solid acid catalysts in a number of commercial processes. Occasionally zeolites are also reported to perform as electron transfer agents. Recently, we observed that radical cations of certain olefins and thiophene oligomers can be generated spontaneously within ZSM-5 zeolites. We noticed that these radical cations generated from diphenyl polyenes and thiophene oligomers were remarkably stable (at room temperature) within ZSM-5 and can be characterized spectroscopically at leisure. We have initiated a program on electron transfer processes within large pore zeolites. The basis of this approach is that once a cation radical is generated within a large pore zeolite, it will have sufficient room to undergo a molecular transformation. Our aim is to identify a condition under which electron transfer can be routinely and reliably carried out within large pore zeolites such as faujasites. To our great surprise, when benzonorbornadiene A and a number of olefins were included in divalent cation exchanged faujasites. they were transformed into products very quickly (<15 min). This observation allowed us to explore the use of zeolites as oxidants. Results of our studies on benzonorbornadiene are presented in this communication. 16 refs., 1 fig.

  11. A comparison of tunneling transfer theories for asymmetric isomerization reactions

    NASA Astrophysics Data System (ADS)

    Cribb, Peter H.; Nordholm, Sture; Hush, N. S.

    1982-08-01

    In this paper, we discuss the basis of the transition state/trasmission coefficient theory of tunneling contributions to the rate of isomerization reactions. This theory, which is currently widely used, is found to deviate both quantitatively and qualitatively from an alternative theory, we have developed on the basis of a more rigorous interpretation of the reaction mechanism in accord with the original suggestion of Lindermann. We focus attention on the discrepancies which arise when there is asymmetry between the reactant and product potential wells. Comparative calculations are reported for a model potential advanced on the basis of spectroscopic measurements to represent the level spectrum associated with the ring- puckering motion in azetidine. Large differences are shown to exist between the predictions of the two types of theories.

  12. Neutron Transfer Reactions: Surrogates for Neutron Capture for Basic and Applied Nuclear Science

    SciTech Connect

    Cizewski, J. A.; Peters, W. A.; Allen, J.; Hatarik, R.; Matthews, C.; O'Malley, P.; Jones, K. L.; Kozub, R. L.; Howard, J.; Patterson, N.; Paulauskas, S. V.; Rogers, J.; Sissom, D. J.; Pain, S. D.; Adekola, A.; Bardayan, D. W.; Blackmon, J. C.; Liang, F.; Nesaraja, C. D.; Pittman, S. T.

    2009-03-10

    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.

  13. Neutron transfer reactions: Surrogates for neutron capture for basic and applied nuclear science

    SciTech Connect

    Cizewski, J. A.; Jones, K. L.; Kozub, R. L.; Pain, Steven D; Peters, W. A.; Adekola, Aderemi S; Allen, J.; Bardayan, Daniel W; Becker, J.; Blackmon, Jeff C; Chae, K. Y.; Chipps, K.; Erikson, Luke; Gaddis, A. L.; Harlin, Christopher W; Hatarik, Robert; Howard, Joshua A; Jandel, M.; Johnson, Micah; Kapler, R.; Krolas, W.; Liang, J Felix; Livesay, Jake; Ma, Zhanwen; Matei, Catalin; Matthews, C.; Moazen, Brian; Nesaraja, Caroline D; O'Malley, Patrick; Patterson, N. P.; Paulauskas, Stanley; Pelham, T.; Pittman, S. T.; Radford, David C; Rogers, J.; Schmitt, Kyle; Shapira, Dan; ShrinerJr., J. F.; Sissom, D. J.; Smith, Michael Scott; Swan, T. P.; Thomas, J. S.; Vieira, D. J.; Wilhelmy, J. B.; Wilson, Gemma L

    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.

  14. Purification and characterization of fatty acyl-acyl carrier protein synthetase from Vibrio harveyi.

    PubMed Central

    Fice, D; Shen, Z; Byers, D M

    1993-01-01

    A Vibrio harveyi enzyme which catalyzes the ATP-dependent ligation of fatty acids to acyl carrier protein (ACP) has been purified 6,000-fold to apparent homogeneity by anion-exchange, gel filtration, and ACP-Sepharose affinity chromatography. Purified acyl-ACP synthetase migrated as a single 62-kDa band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and as an 80-kDa protein by gel filtration under reducing conditions. Activity of the purified enzyme was lost within hours in the absence of glycerol and low concentrations of Triton X-100. Acyl-ACP synthetase exhibited Kms for myristic acid, ACP, and ATP of 7 microM, 18 microM, and 0.3 mM, respectively. The enzyme was specific for adenine-containing nucleotides, and AMP was the product of the reaction. No covalent acyl-enzyme intermediate was observed. Enzyme activity was stimulated up to 50% by iodoacetamide but inhibited > 80% by N-ethylmaleimide: inhibition by the latter was prevented by ATP and ACP but not myristic acid. Dithiothreitol and sulfhydryl-directed reagents also influenced enzyme size, activity, and elution pattern on anion-exchange resins. The function of acyl-ACP synthetase has not been established, but it may be related to the capacity of V. harveyi to elongate exogenous fatty acids by an ACP-dependent mechanism. Images PMID:8384617

  15. Fission Study of Actinide Nuclei Using Multi-nucleon Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Nishio, Katsuhisa; Hirose, Kentaro; Léguillon, R.; Makii, Hiroyuki; Nishinaka, Ichiro; Orlandi, Riccardo; Smallcombe, James; Tsukada, Kazuaki; Chiba, Satoshi; Ohtsuki, Tsutomu; Tatsuzawa, Ryotaro; Takaki, Naoyuki

    We have developed a set up to measure fission properties of excited compound nuclei populated by multi-nucleon transfer reactions. This approach has an advantage that we can study fission of neutron-rich nuclei which cannot be accessed by particle or charged-particle capture reactions. Unique feature in our setup is that we can produce fission data for many nuclei depending on different transfer channels. Also wide excitation energy range can be covered in this set up, allowing us to measure the excitation energy dependence of the fission properties. Preliminary data obtained in the 18O + 238U reaction will be presented.

  16. Au25 Clusters as Electron-Transfer Catalysts Induced the Intramolecular Cascade Reaction of 2-nitrobenzonitrile

    PubMed Central

    Chong, Hanbao; Li, Peng; Wang, Shuxin; Fu, Fangyu; Xiang, Ji; Zhu, Manzhou; Li, Yadong

    2013-01-01

    Design of atomically precise metal nanocluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. Here, for the first time, Au25z nanoslusters were employed as electron transfer catalysts to induce an intramolecular cascade reaction at ambient conditions and gave rise to high conversion (87%) and selectivity (96%). Electron spin-resonance spectra indeed confirmed the consecutive electron transfer process and the formation of N radical. UV-vis absorption spectra also verified Au25z was intact after the catalytic circle. Our research may open up wide opportunities for extensive organic reactions catalyzed by Au25z. PMID:24225495

  17. Proton transfer reactions and hydrogen-bond networks in protein environments.

    PubMed

    Ishikita, Hiroshi; Saito, Keisuke

    2014-02-01

    In protein environments, proton transfer reactions occur along polar or charged residues and isolated water molecules. These species consist of H-bond networks that serve as proton transfer pathways; therefore, thorough understanding of H-bond energetics is essential when investigating proton transfer reactions in protein environments. When the pKa values (or proton affinity) of the H-bond donor and acceptor moieties are equal, significantly short, symmetric H-bonds can be formed between the two, and proton transfer reactions can occur in an efficient manner. However, such short, symmetric H-bonds are not necessarily stable when they are situated near the protein bulk surface, because the condition of matching pKa values is opposite to that required for the formation of strong salt bridges, which play a key role in protein-protein interactions. To satisfy the pKa matching condition and allow for proton transfer reactions, proteins often adjust the pKa via electron transfer reactions or H-bond pattern changes. In particular, when a symmetric H-bond is formed near the protein bulk surface as a result of one of these phenomena, its instability often results in breakage, leading to large changes in protein conformation. PMID:24284891

  18. Proton transfer reactions and hydrogen-bond networks in protein environments

    PubMed Central

    Ishikita, Hiroshi; Saito, Keisuke

    2014-01-01

    In protein environments, proton transfer reactions occur along polar or charged residues and isolated water molecules. These species consist of H-bond networks that serve as proton transfer pathways; therefore, thorough understanding of H-bond energetics is essential when investigating proton transfer reactions in protein environments. When the pKa values (or proton affinity) of the H-bond donor and acceptor moieties are equal, significantly short, symmetric H-bonds can be formed between the two, and proton transfer reactions can occur in an efficient manner. However, such short, symmetric H-bonds are not necessarily stable when they are situated near the protein bulk surface, because the condition of matching pKa values is opposite to that required for the formation of strong salt bridges, which play a key role in protein–protein interactions. To satisfy the pKa matching condition and allow for proton transfer reactions, proteins often adjust the pKa via electron transfer reactions or H-bond pattern changes. In particular, when a symmetric H-bond is formed near the protein bulk surface as a result of one of these phenomena, its instability often results in breakage, leading to large changes in protein conformation. PMID:24284891

  19. An acyl group makes a difference in the reactivity patterns of cytochrome P450 catalyzed N-demethylation of substituted N,N-dimethylbenzamides-high spin selective reactions.

    PubMed

    Wang, Yong; Li, Dongmei; Han, Keli; Shaik, Sason

    2010-03-01

    This paper addresses the experimentally observed mechanistic differences between the cytochrome P450-catalyzed N-demethylation of substituted N,N-dimethylanilines (DMA) and of N,N-dimethylbenzamides (DMBA). The two reactions of these substrates are initiated by C-H activation of the methyl groups on the nitrogen. Thus, the DMA reactions exhibit small deuterium kinetic isotope effects (KIEs), and these KIEs and the corresponding reaction rates exhibit a linear response to the electronic nature of the para substituent. By contrast, the DMBA reactions exhibit large KIEs; the KIEs and reaction rates do not at all respond to the nature of the para substituent. Accordingly, the present paper uses density functional theoretical calculations to address these reactivity patterns in para-substituted DMBA and compare these results to those obtained for the DMA reactions previously (Wang, Y.; Kumar, D.; Yang, C. L.; Han, K. L.; Shaik, S. J. Phys. Chem. B 2007, 111, 7700). The theoretical calculations reproduce the experimental trends of narrow variations in rates and KIEs. It is shown that the above mechanistic differences between the two reaction series of DMA and DMBA are caused by the ability of the para substituent to maintain a conjugation path between the C-H reaction center and the aryl moiety. Furthermore, the computational results show a new feature of reactivity, namely, that the N-demethylation of DMBA proceeds by a spin-selective reaction via the high spin state of the active species of the enzyme. This conclusion is reinforced by the match of the calculated and experimental KIE values. PMID:20146528

  20. Hydride transfer reaction dynamics of OD{sup +}+C{sub 3}H{sub 6}

    SciTech Connect

    Liu, Li; Richards, Elizabeth S.; Farrar, James M.

    2007-06-28

    The hydride transfer reaction between OD{sup +} and C{sub 3}H{sub 6} has been studied experimentally and theoretically over the center of mass collision energy range from 0.21 to 0.92 eV using the crossed beam technique and density functional theory calculations. The center of mass flux distributions of the product ions at three different energies are highly asymmetric, with maxima close to the velocity and direction of the precursor propylene beam, characteristic of direct reactions. In the hydride transfer process, the entire reaction exothermicity is transformed into product internal excitation, consistent with mixed energy release in which the hydride ion is transferred with both the breaking and forming bonds extended. At higher collision energies, at least 85% of the incremental translational energy appears in product translation, providing a clear example of induced repulsive energy release. Compared to the related reaction of OD{sup +} with C{sub 2}H{sub 4}, reaction along the pathway initiated by addition of OD{sup +} to the C=C bond in propylene has a critical bottleneck caused by the torsional motion of the methyl substituent on the double bond. This bottleneck suppresses reaction through an intermediate complex in favor of direct hydride abstraction. Hydride abstraction appears to be a sequential process initiated by electron transfer in the triplet manifold, followed by rapid intersystem crossing and subsequent hydrogen atom transfer to form ground state allyl cation and HOD.

  1. Phenomenological manifestations of large-curvature tunneling in hydride-transfer reactions

    SciTech Connect

    Kreevoy, M.M.; Ostovic, D.; Truhlar, D.G.; Garrett, B.C.

    1986-01-01

    An important consequence of recent dynamical theories of tunneling is that, because of large curvature of the reaction path in a typical H(+), or H(-) transfer, light-isotope transfer occurs in more extended nuclear frameworks than heavy-isotope transfer. This is now incorporated into the Marcus phenomenological theory relating reaction rate constants to equilibrium constants. It leads to Bronsted slope parameters that depend on the isotope transferred. The new theoretical formulation is tested on experimental data for hydride and deuteride transfer between nicotinamide adenine dinucleotide analogs and on computational data for hydrogen-atom and deuterium atom transfer between pseudo-atoms. The experimental kinetic isotope effects (KIE's) are shown to vary with reaction equilibrium constant (K/sub ij/) in a way that is quantitatively consistent with the theory. The critical configurations generated by the calculations vary from the saddle point and from each other in the way anticipated by the theory. However, the calculated KIE values are a rather scattered function of K/sub ij/, because the tunneling corrections are large and somewhat system specific. Overall, we believe that this combination of experimental and calculated results provides considerable support for the idea that large-curvature results provides considerable support for the idea that large-curvature tunneling needs to be considered in hydrogen transfer reactions.

  2. Development of Novel Electrode Materials for the Electrocatalysis of Oxygen-Transfer and Hydrogen-Transfer Reactions

    SciTech Connect

    Brett Kimball Simpson

    2002-08-27

    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 MnO{sub 2} films] revealed that MnO{sub 2} 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 MnO{sub 2} 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 RuO{sub 2} films showed that the Fe(III)-doped RuO{sub 2}-film electrodes are applicable for anodic detection of sulfur compounds. The Fe(III) sites in the Fe-RuO{sub 2} films are speculated to act as adsorption sites for the sulfur species while the Ru(IV) sites function for anodic discharge of H{sub 2}O 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 Sb{sub 10}Sn{sub 20}Ti{sub 70}, Cu{sub 63}Ni{sub 37} and Cu{sub 25}Ni{sub 75} alloy electrodes exhibited improved activity for nitrate reduction as compared to their pure component metals. The Cu{sub 63}Ni{sub 37} 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 NO{sub 3}{sup -} at the Cu-Ni alloy electrode is superior to the response at the pure Cu and Ni electrodes. This is explained on the basis of the

  3. Photoinitiated electron-transfer reactions of aromatic imides with phenylcyclopropanes. Formation of radical ion pair cycloadducts. Mechanism of the reaction

    SciTech Connect

    Somich, C.; Mazzocchi, P.H.; Edwards, M.; Morgan, T.; Ammon, H.L. )

    1990-04-27

    Few investigations have addressed the cyclization of a radical anion-radical cation pair resulting from photoinitiated electron transfer. One system taht meets the criteria necessary to observe this phenomenon is the acceptor-donor pair N-methylphthalimide (NMP) and phenylcyclopropane (PC). Irradiation of NMP or N-methyl-2,3-naphthalimide (NMN) in the presence of PC in acetonitrile gave rise to two spiro tetrahydrofuranyl lactams. The regiochemistry and relative stereochemistry of these compounds were determined by NMR techniques and X-ray crystallography. The mechanism of the reaction proceeds via electron transfer from PC to the imide followed by coupling of the radical ion pair at the 1,2-position of the carbonyl to the cyclopropane ring in a stepwise fashion. Fluorescence quenching experiments, reaction efficiency, and the free energy for electron transfer using various aromatic substituted phenylcyclopropanes provided strong evidence that electron transfer occurs. The reaction of cis-2-deutero-1-phenylcyclopropane (PC-d) with NMN established that cycloaddition is stepwise rather than concerted and that both syn and anti reactive intermediates are equally accessible.

  4. The effect of the environment on the methyl transfer reaction mechanism between trimethylsulfonium and phenolate.

    PubMed

    Saez, David Adrian; Vogt-Geisse, Stefan; Inostroza-Rivera, Ricardo; Kubař, Tomáš; Elstner, Marcus; Toro-Labbé, Alejandro; Vöhringer-Martinez, Esteban

    2016-09-14

    Methyl transfer reactions play an important role in biology and are catalyzed by various enzymes. Here, the influence of the molecular environment on the reaction mechanism was studied using advanced ab initio methods, implicit solvation models and QM/MM molecular dynamics simulations. Various conceptual DFT and electronic structure descriptors identified different processes along the reaction coordinate e.g. electron transfer. The results show that the polarity of the solvent increases the energy required for the electron transfer and that this spontaneous process is located in the transition state region identified by the (mean) reaction force analysis and takes place through the bonds which are broken and formed. The inclusion of entropic contributions and hydrogen bond interactions in QM/MM molecular dynamics simulations with a validated DFTB3 Hamiltonian yields activation barriers in good agreement with the experimental values in contrast to the values obtained using two implicit solvation models. PMID:27524496

  5. Nucleophilic substitution of bromonorbornenes and derivatives by electron transfer reactions.

    PubMed

    Crespo Andrada, Karina F; Peisino, Lucas E; Güney, Murat; Daştan, Arif; Pierini, Adriana B

    2013-02-14

    The photoinitiated substitution reactions of anti-7-bromobenzonorbornadiene (5), its syn isomer 6, exo-anti-13-bromobenzocyclobutanorbornene (7), syn-7-bromonorbornene (8) and bromonorbornane (9) with Me(3)Sn(-) and Ph(2)P(-) anions, in liquid ammonia, are here informed to occur with good yields of substitution. The stereochemical outcome is discussed in terms of calculations with the B3LYP functional and the 6-31+G* basis set; the solvent being included as a continuum through the PCM model. The experimental relative chemical reactivity of pairs of substrates toward a given anion is also presented. PMID:23263719

  6. Photoinduced Electron and H-atom Transfer Reactions of Xanthone by Laser Flash Photolysis

    NASA Astrophysics Data System (ADS)

    Wang, Jin-ting; Pan, Yang; Zhang, Li-min; Yu, Shu-qin

    2007-08-01

    The property of the lowest excited triplet states of xanthone in acetonitrile was investigated using time-resolved laser flash photolysis at 355 nm. The transient absorption spectra and the quenching rate constants (kq) of the excited xanthone with several amines were determined. Good correlation between lgkq and the driving force of the reactions suggests the electron transfer mechanism, except aniline and 3-nitroaniline (3-NO2-A) which showed energy transfer mechanism. With the appearance of ketyl radical, hydrogen atom transfer also happened between xanthone and dimethyl-p-toluidine, 3,5,N,N-tetramethylaniline, N,N-dimethylaniline, and triethylamine. Therefore, both electron transfer and H-atom transfer occured in these systems. Great discrepancies of kq values were discovered in H-atom abstraction reactions for alcohols and phenols, which can be explained by different abstraction mechanisms. The quenching rate constants between xanthone and alcohols correlate well with the α-C-H bonding energy of alcohols.

  7. Photochemical electron-transfer reactions of 1,1-diarylethylenes

    SciTech Connect

    Mattes, S.L.; Farid, S.

    1986-11-12

    The dimerizations, nucleophilic additions, and oxygenation reactions of 1,1-diarylethylene (1), induced by photoexcited cyanoanthracenes, have been investigated. 1,1-Diphenylethylene (1a) yields 2 + 2 and 2 + 4 cyclodimers and one dehydrodimer, whereas 1,1-dianisylethylene (1b) gives two dehydrodimers, and 1,1-bis(4-(dimethylamino)phenyl)ethylene (1c) forms no dimers. Formation of the dehydrodimers is accompanied by reduction of the cyanoanthracene sensitizer. For the dimerization of 1b, the quantum yields and product ratios can be altered by the addition of quinones. The hydroquinone then replaces the reduced sensitizer. The reaction constant for nucleophilic addition of methanol to 1a/sup .+/ is 1.6 x 10/sup 9/ M/sup -1/s/sup -1/; for addition to 1b/sup .+/ it is approx.10/sup 7/ M/sup -1/s/sup -1/. Methanol does not add efficiently to 1c/sup .+ / . Photooxygenation of the diarylethylene yields mainly the corresponding 3,3,6,6-tetraaryl-1,2-dioxane in a chain process. In the presence of methanol and oxygen, 1a yields mainly 1-hydroperoxy-2-methyoxy-1,1-diphenylethane.

  8. Reaction dynamics and proton coupled electron transfer: studies of tyrosine-based charge transfer in natural and biomimetic systems.

    PubMed

    Barry, Bridgette A

    2015-01-01

    In bioenergetic reactions, electrons are transferred long distances via a hopping mechanism. In photosynthesis and DNA synthesis, the aromatic amino acid residue, tyrosine, functions as an intermediate that is transiently oxidized and reduced during long distance electron transfer. At physiological pH values, oxidation of tyrosine is associated with a deprotonation of the phenolic oxygen, giving rise to a proton coupled electron transfer (PCET) reaction. Tyrosine-based PCET reactions are important in photosystem II, which carries out the light-induced oxidation of water, and in ribonucleotide reductase, which reduces ribonucleotides to form deoxynucleotides. Photosystem II contains two redox-active tyrosines, YD (Y160 in the D2 polypeptide) and YZ (Y161 in the D1 polypeptide). YD forms a light-induced stable radical, while YZ functions as an essential charge relay, oxidizing the catalytic Mn₄CaO₅ cluster on each of four photo-oxidation reactions. In Escherichia coli class 1a RNR, the β2 subunit contains the radical initiator, Y122O•, which is reversibly reduced and oxidized in long range electron transfer with the α2 subunit. In the isolated E. coli β2 subunit, Y122O• is a stable radical, but Y122O• is activated for rapid PCET in an α2β2 substrate/effector complex. Recent results concerning the structure and function of YD, YZ, and Y122 are reviewed here. Comparison is made to recent results derived from bioengineered proteins and biomimetic compounds, in which tyrosine-based charge transfer mechanisms have been investigated. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. PMID:25260243

  9. Novel approach in LC-MS/MS using MRM to generate a full profile of acyl-CoAs: discovery of acyl-dephospho-CoAs[S

    PubMed Central

    Li, Qingling; Zhang, Shenghui; Berthiaume, Jessica M.; Simons, Brigitte; Zhang, Guo-Fang

    2014-01-01

    A metabolomic approach to selectively profile all acyl-CoAs was developed using a programmed multiple reaction monitoring (MRM) method in LC-MS/MS and was employed in the analysis of various rat organs. The programmed MRM method possessed 300 mass ion transitions with the mass difference of 507 between precursor ion (Q1) and product ion (Q3), and the precursor ion started from m/z 768 and progressively increased one mass unit at each step. Acyl-dephospho-CoAs resulting from the dephosphorylation of acyl-CoAs were identified by accurate MS and fragmentation. Acyl-dephospho-CoAs were also quantitatively scanned by the MRM method with the mass difference of 427 between Q1 and Q3 mass ions. Acyl-CoAs and dephospho-CoAs were assayed with limits of detection ranging from 2 to 133 nM. The accuracy of the method was demonstrated by assaying a range of concentrations of spiked acyl-CoAs with the results of 80–114%. The distribution of acyl-CoAs reflects the metabolic status of each organ. The physiological role of dephosphorylation of acyl-CoAs remains to be further characterized. The methodology described herein provides a novel strategy in metabolomic studies to quantitatively and qualitatively profile all potential acyl-CoAs and acyl-dephospho-CoAs. PMID:24367045

  10. The kinetics of electron transfer reaction of methylene green and titanium trichloride in different solvents

    NASA Astrophysics Data System (ADS)

    Saeed, Rehana; Nadeem, Syed Muhammad Saqib

    2016-06-01

    The kinetics of the electron transfer reaction of methylene green and titanium trichloride was investigated in different solvents by spectrophotometry at different temperatures. The the reaction rate was determined by monitoring the absorbance as a function of time at λmax 655 nm. The reaction is pseudo-first order, dependent only on the concentration of titanium trichloride at a fixed concentration of methylene green. The effect of an aqueous alcoholic solvent was studied in the acidic range of pH from 4 to 7. It was observed that the reaction rate increased with an increase in polarity of the reaction medium. The the reaction rate was high in acidic conditions and decreased with a further increase in acidity. The increase in temperature increased the rate of the electron transfer reaction of methylene green and titanium trichloride. The activation energy ( E a) was calculated by the Arrhenius relation. The absence of any reaction intermediate was confirmed by spectroscopic and kinetic investigations. A plausible mechanism for the reaction in line with outer-sphere reaction pathway has been proposed. Thermodynamic parameters such as the activation energy ( E a), enthalpy change (Δ H), free energy change (Δ G), and entropy change (Δ S) were also evaluated

  11. Asymmetric Allylboration of Acyl Imines Catalyzed by Chiral Diols

    PubMed Central

    Lou, Sha; Moquist, Philip N.; Schaus, Scott E.

    2008-01-01

    Chiral BINOL-derived diols catalyze the enantioselective asymmetric allylboration of acyl imines. The reaction requires 15 mol% of (S)-3,3′-Ph2-BINOL as the catalyst and allyldiisopropoxyborane as the nucleophile. The reaction products are obtained in good yields (75 – 94%) and high enantiomeric ratios (95:5 – 99.5:0.5) for aromatic and aliphatic imines. High diastereoselectivities (dr > 98:2) and enantioselectivities (er > 98:2) are obtained in the reactions of acyl imines with crotyldiisopropoxyboranes. This asymmetric transformation is directly applied to the synthesis of maraviroc, the selective CCR5 antagonist with potent activity against HIV-1 infection. Mechanistic investigations of the allylboration reaction including IR, NMR, and mass spectrometry study indicate that acyclic boronates are activated by chiral diols via exchange of one of the boronate alkoxy groups with activation of the acyl imine via hydrogen bonding. PMID:18020334

  12. Neutron Transfer Reactions with Exotic Neutron-Rich Beams: Surrogates for Neutron-Capture Reactions

    SciTech Connect

    Cizewski, Jolie; Grzywacz-Jones, Kate L; Pain, Steven D; Thomas, Jeffrey S; Bardayan, Daniel W; Blackmon, Jeff C; Smith, Michael Scott; KOZUB, RAYMOND L; Johnson, Micah

    2006-03-01

    A new program to measure (d,p) reactions on rare isotopes of fission fragments has been established at Oak Ridge National Laboratory. Initial measurements on N=50 isotones and prospects for Z=50 experiments are reported.

  13. Alkylation and acylation of cyclotriphosphazenes.

    PubMed

    Benson, Mark A; Zacchini, Stefano; Boomishankar, Ramamoorthy; Chan, Yuri; Steiner, Alexander

    2007-08-20

    Phosphazenes (RNH)6P3N3 (R = n-propyl, isobutyl, isopropyl, cyclohexyl, tert-butyl, benzyl) are readily alkylated at ring N sites by alkyl halides forming N-alkyl phosphazenium cations. Alkylation of two ring N sites occurred after prolonged heating in the presence of methyl iodide or immediately at room temperature with methyl triflate yielding N,N'-dimethyl phosphazenium dications. Geminal dichloro derivatives Cl2(RNH)4P3N3 are methylated by methyl iodide at the ring N site adjacent to both P centers carrying four RNH groups. X-ray crystal structures showed that the alkylation of ring N sites leads to substantial elongation of the associated P-N bonds. Both N-alkyl and N,N'-dialkyl phosphazenium salts form complex supramolecular networks in the solid state via NH...X interactions. Systems carrying less-bulky RNH groups show additional NH...N bonds between N-alkyl phosphazenium ions. N-Alkyl phosphazenium halides form complexes with silver ions upon treatment with silver nitrate. Depending on the steric demand of RNH substituents, either one or both of the vacant ring N sites engage in coordination to silver ions. Treatment of (RNH)6P3N3 (R = isopropyl) with acetyl chloride and benzoyl chloride, respectively, yielded N-acyl phosphazenium ions. X-ray crystal structures revealed that elongation of P-N bonds adjacent to the acylated ring N site is more pronounced than it is in the case of N-alkylated species. Salts containing N-alkyl phosphazenium ions are stable toward water and other mild nucleophiles, while N,N'-dialkyl and N-acyl phosphazenium salts are readily hydrolyzed. The reaction of (RNH)6P3N3 with bromoacetic acid led to N-alkylation at one ring N site in addition to formation of an amide via condensation of an adjacent RNH substituent with the carboxylic acid group. The resulting bromide salt contains mono cations of composition (RNH)5P3N3CH2CONR in which a CH2-C(O) unit is embedded between a ring N and an exocyclic N site of the phosphazene. PMID

  14. Ultrafast Electron Transfer Kinetics in the LM Dimer of Bacterial Photosynthetic Reaction Center from Rhodobacter sphaeroides.

    PubMed

    Sun, Chang; Carey, Anne-Marie; Gao, Bing-Rong; Wraight, Colin A; Woodbury, Neal W; Lin, Su

    2016-06-23

    It has become increasingly clear that dynamics plays a major role in the function of many protein systems. One system that has proven particularly facile for studying the effects of dynamics on protein-mediated chemistry is the bacterial photosynthetic reaction center from Rhodobacter sphaeroides. Previous experimental and computational analysis have suggested that the dynamics of the protein matrix surrounding the primary quinone acceptor, QA, may be particularly important in electron transfer involving this cofactor. One can substantially increase the flexibility of this region by removing one of the reaction center subunits, the H-subunit. Even with this large change in structure, photoinduced electron transfer to the quinone still takes place. To evaluate the effect of H-subunit removal on electron transfer to QA, we have compared the kinetics of electron transfer and associated spectral evolution for the LM dimer with that of the intact reaction center complex on picosecond to millisecond time scales. The transient absorption spectra associated with all measured electron transfer reactions are similar, with the exception of a broadening in the QX transition and a blue-shift in the QY transition bands of the special pair of bacteriochlorophylls (P) in the LM dimer. The kinetics of the electron transfer reactions not involving quinones are unaffected. There is, however, a 4-fold decrease in the electron transfer rate from the reduced bacteriopheophytin to QA in the LM dimer compared to the intact reaction center and a similar decrease in the recombination rate of the resulting charge-separated state (P(+)QA(-)). These results are consistent with the concept that the removal of the H-subunit results in increased flexibility in the region around the quinone and an associated shift in the reorganization energy associated with charge separation and recombination. PMID:27243380

  15. Dihydrofolate synthetase and folylpolyglutamate synthetase: direct evidence for intervention of acyl phosphate intermediates

    SciTech Connect

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

    1988-12-13

    The transfer of /sup 17/O and/or /sup 18/O from (COOH-/sup 17/O or -/sup 18/O) enriched substrates to inorganic phosphate (P/sub i/) has been demonstrated for two enzyme-catalyzed reactions involved in folate biosynthesis and glutamylation. COOH-/sup 18/O-labeled folate, methotrexate, and dihydropteroate, in addition to (/sup 17/O)-glutamate, were synthesized and used as substrates for folylpolyglutamate synthetase (FPGS) isolated from Escherichia coli, hog liver, and rat liver and for dihydrofolate synthetase (DHFS) isolated from E. coli. P/sub i/ was purified from the reaction mixtures and converted to trimethyl phosphate (TMP), which was then analyzed for /sup 17/O and /sup 18/O enrichment by nuclear magnetic resonance (NMR) spectroscopy and/or mass spectroscopy. In the reactions catalyzed by the E. coli enzymes, both NMR and quantitative mass spectral analyses established that transfer of the oxygen isotope from the substrate /sup 18/O-enriched carboxyl group to P/sub i/ occurred, thereby providing strong evidence for an acyl phosphate intermediate in both the FPGS- and DHFS-catalyzed reactions. Similar oxygen-transfer experiments were carried out by use of two mammalian enzymes. The small amounts of P/sub i/ obtained from reactions catalyzed by these less abundant FPGS proteins precluded the use of NMR techniques. However, mass spectral analysis of the TMP derived from the mammalian FPGS-catalyzed reactions showed clearly that /sup 18/O transfer had occurred.

  16. Electrocatalysis of anodic oxygen-transfer reactions: Evolution of ozone

    SciTech Connect

    Feng, J.; Johnson, D.C. ); Lowery, S.N.; Carey, J.J. . Kodak Research Labs.)

    1994-10-01

    Current efficiencies are compared for the generation of O[sub 3] simultaneously with O[sub 2] during anodic discharge of H[sub 2]O at pure and iron(III)-doped [beta]-lead dioxide film electrodes in phosphate buffer (pH 7.5, 10 C) containing 2.5 mM KF. Also examined is the effect of applied current density. A current efficiency of 14.6% was obtained for the Fe(III)-doped PbO[sub 2] film electrode deposited on a internally cooled (10 C) tubular titanium substrate at a current density of 200 mA cm[sup [minus]2] as compared to only 6.1% at the undoped PbO[sub 2] electrode under the same conditions. This result is tentatively explained on the basis of a mechanism involving the transfer of oxygen from hydroxyl radicals adsorbed on Pb(IV) sites adjacent to Fe(III) sites to O[sub 2] adsorbed at the Fe(III) sites in the surface of the Fe(III)-doped PbO[sub 2] electrodes.

  17. 2D NMR studies of aminoglycoside antibiotics. Use of relayed coherence transfer for /sub 1/H resonance assignment and in situ structure elucidation of amikacin derivatives in reaction mixtures

    SciTech Connect

    Andersen, N.H.; Eaton, H.L.; Nguyen, K.T.; Hartzell, C.; Nelson, R.J.; Priest, J.H.

    1988-04-19

    Phase-sensitive 2D /sup 1/H//sup 1/H COSY spectra can be used to identify the structures of individual pure specimens of the aminoglycoside antibiotic amikacin and its N-hemisuccinyl derivatives. However, even at 500 MHz the 2D chemical shift dispersion does not allow for unambiguous assignment of all cross-peaks. By use of 2D relayed coherence transfer experiments (RELAY) optimized to detect two-step /sup 1/H//sup 1/H scalar interactions in which one of the J-values is small, sufficient additional correlations can be obtained from the frequency-isolated resonances to allow facile tracing of all scalar connectivities. Complete assignments of the /sup 1/H NMR spectra of amikacin, its 6'-N-hemisuccinamide, and a novel bis(acylate) (..gamma..-N-(p-vinylbenzoyl)amikacin 6'-N-hemisuccinamide) were obtained for aqueous media. The NMR spectrum of amikacin free base was also assigned in dimethyl sulfoxide solution. The RELAY experiment can be extended to the analysis of reaction mixtures, which allows for the identification and resonance assignment of regioisomeric amikacin haptens in the mixture state. All of the N-monohemisuccinyl isomers of amikacin have been identified in reaction mixtures through the RELAY experiment. The relative reactivities of the amino functions of amikacin toward acylating agents were found to be 6'-N > 3-N greater than or equal to 3''-N greater than or equal to ..gamma..-N. However, this reactivity order is altered after the initial acylation event.

  18. Benzoylation of Ergosterol through Nucleophilic Acyl Substitution and Subsequent Formation of Ergosterol Benzoate Endoperoxide by Reaction with Singlet Oxygen Generated by Photosensitization

    ERIC Educational Resources Information Center

    Roslaniec, Mary C.; Sanford, Elizabeth M.

    2011-01-01

    Reactive oxygen species such as singlet oxygen have been a major focus of research in medicine. The effect of singlet oxygen on sterols within biological membranes is becoming increasingly more important. Ergosterol, a vitamin D precursor, is one such sterol. The benzoylation of ergosterol and subsequent reaction with singlet oxygen to form an…

  19. Camptothecins guanine interactions: mechanism of charge transfer reaction upon photoactivation

    NASA Astrophysics Data System (ADS)

    Steenkeste, K.; Guiot, E.; Tfibel, F.; Pernot, P.; Mérola, F.; Georges, P.; Fontaine-Aupart, M. P.

    2002-01-01

    The potent activity exhibited by the antitumoral camptothecin (CPT) and its analog irinotecan (CPT-11) is known to be related to a close contact between the drug and the nucleic acid base guanine. This specificity of interaction between these two chromophores was examined by following changes in the photophysical properties of the drug using steady-state as well as time-resolved absorption and fluorescence methods. The observed effects on absorption, fluorescence emission and singlet excited state lifetimes give evidence for the occurrence of a stacking complex formation restricted to the quinoline part of CPT or CPT-11 and the guanine base but also with the adenine base. The triplet excited state properties of the drugs have been also characterized in absence and in presence of guanosine monophosphate and reveal the occurrence of an electron transfer from the guanine base to the drug. Support for this conclusion was obtained from the studies of a set of biological targets of various oxido-reduction potentials, adenosine monophosphate, cytidine, cytosine, tryptophan, tyrosine and phenylalanine. This finding gives an interpretation of the CPT-induced guanine photolesions previously reported in the literature. These data taken together are discussed in connection with the drug activity. The stacking complex CPT/guanine is necessary but not sufficient to explain the role of the chirality and of the lactone structure in the function of the drug. A stereospecific interaction with the enzyme topoisomerase I seems necessary to stabilize the stacking complex. The first experiments using time-resolved fluorescence by two-photon excitation confirms that CPT does not bind to the isolated enzyme.

  20. High Throughput Engineering to Revitalize a Vestigial Electron Transfer Pathway in Bacterial Photosynthetic Reaction Centers*

    PubMed Central

    Faries, Kaitlyn M.; Kressel, Lucas L.; Wander, Marc J.; Holten, Dewey; Laible, Philip D.; Kirmaier, Christine; Hanson, Deborah K.

    2012-01-01

    Photosynthetic reaction centers convert light energy into chemical energy in a series of transmembrane electron transfer reactions, each with near 100% yield. The structures of reaction centers reveal two symmetry-related branches of cofactors (denoted A and B) that are functionally asymmetric; purple bacterial reaction centers use the A pathway exclusively. Previously, site-specific mutagenesis has yielded reaction centers capable of transmembrane charge separation solely via the B branch cofactors, but the best overall electron transfer yields are still low. In an attempt to better realize the architectural and energetic factors that underlie the directionality and yields of electron transfer, sites within the protein-cofactor complex were targeted in a directed molecular evolution strategy that implements streamlined mutagenesis and high throughput spectroscopic screening. The polycistronic approach enables efficient construction and expression of a large number of variants of a heteroligomeric complex that has two intimately regulated subunits with high sequence similarity, common features of many prokaryotic and eukaryotic transmembrane protein assemblies. The strategy has succeeded in the discovery of several mutant reaction centers with increased efficiency of the B pathway; they carry multiple substitutions that have not been explored or linked using traditional approaches. This work expands our understanding of the structure-function relationships that dictate the efficiency of biological energy-conversion reactions, concepts that will aid the design of bio-inspired assemblies capable of both efficient charge separation and charge stabilization. PMID:22247556

  1. Study of intermediates from transition metal excited-state electron-transfer reactions

    SciTech Connect

    Hoffman, M.Z.

    1991-12-31

    During this period, conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used for the characterization of the intermediates that are involved in transition metal excited-state electron-transfer reactions. The intermediates of interest were the excited states of Ru(II) and Cr(III) photosensitizers, their reduced forms, and the species formed in the reactions of redox quenchers and electron-transfer agents. Of particular concern has been the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes.

  2. Human acetyl-CoA:glucosamine-6-phosphate N-acetyltransferase 1 has a relaxed donor specificity and transfers acyl groups up to four carbons in length.

    PubMed

    Brockhausen, Inka; Nair, Dileep G; Chen, Min; Yang, Xiaojing; Allingham, John S; Szarek, Walter A; Anastassiades, Tassos

    2016-04-01

    Glucosamine-6-phosphate N-acetyltransferase1 (GNA1) catalyses the transfer of an acetyl group from acetyl coenzyme A (AcCoA) to glucosamine-6-phosphate (GlcN6P) to form N-acetylglucosamine-6-phosphate (GlcNAc6P), which is an essential intermediate in UDP-GlcNAc biosynthesis. An analog of GlcNAc, N-butyrylglucosamine (GlcNBu) has shown healing properties for bone and articular cartilage in animal models of arthritis. The goal of this work was to examine whether GNA1 has the ability to transfer a butyryl group from butyryl-CoA to GlcN6P to form GlcNBu6P, which can then be converted to GlcNBu. We developed fluorescent and radioactive assays and examined the donor specificity of human GNA1. Acetyl, propionyl, n-butyryl, and isobutyryl groups were all transferred to GlcN6P, but isovaleryl-CoA and decanoyl-CoA did not serve as donor substrates. Site-specific mutants were produced to examine the role of amino acids potentially affecting the size and properties of the AcCoA binding pocket. All of the wild type and mutant enzymes showed activities of both acetyl and butyryl transfer and can therefore be used for the enzymatic synthesis of GlcNBu for biomedical applications. PMID:26935656

  3. Non-Markovian electron transfer reactions with frequency-dependent friction

    SciTech Connect

    Tang, J.

    1993-12-31

    A modified non-Markovian Zusman equation for electron transfer reactions with frequency-dependent friction is presented. The derivation is based on the spin-boson model with a two-level system coupled to a non-Debye polar solvent bath with frequency-dependent friction. The diffusion constant in the Smoluchowski diffusion operator of the ordinary Zusman equation should be replaced by a convolution of a retarded time-dependent diffusion constant. An analytical expression for the electron transfer rate constant was derived using the Green`s function method. In the adiabatic regime, electron transfer process is generally nonexponential. Because of the time-retardation, initial electron transfer reaction is influenced more by the higher frequency components in the solvent relaxation.

  4. Single and Multi-Nucleon Transfer Reactions for Nuclear Moment Studies Toward Radioactive-Ion Beams

    SciTech Connect

    Lozeva, R. L.; Georgiev, G. P.; Audi, G.; Cabaret, S.; Fiori, E.; Gaulard, C.; Hauschilda, K.; Lopez-Martens, A.; Risegari, L.; Blazhev, A.; Jolie, J.; Moschner, K.; Zell, K.-O.; Daugas, J.-M.; Faul, T.; Morel, P.; Roig, O.; Ferraton, M.; Ibrahim, F.

    2010-04-30

    This study is a part of an experimental program to measure nuclear moments in transfer reactions. It aims to probe for a first time the nuclear -spin orientation in multi-nucleon transfer. Fist experiments were performed to measure the quadrupole moment of an isomeric state in {sup 66}Cu (I{sup p}i 6{sup -}, E{sub x} = 1154 keV, T{sub 1/2} = 595(20) ns) in single nucleon transfer and the population of mus isomers in {sup 66}Cu and {sup 63}Ni in multi-nucleon transfer. The experimentally tested methodology allows broad applications toward more exotic species and feasibility of these reactions to produce species away from stability.

  5. Observation of the one- to six-neutron transfer reactions at sub- barrier energies

    SciTech Connect

    Jiang, C.L.; Rehm, K.E.; Gehring, J.; Glagola, B.; Kutschera, W.; Rhein, M.; Wuosmaa, A.H.

    1994-04-01

    An unambiguous determination of the cross sections for the one- to six neutron transfer reactions has been made in the system {sup 58}Ni + {sup 100}Mo. The cross sections for multi-neutron transfer processes show an exponential falloff in agreement with recent theoretical calculations. Upper limits for the absolute yields to the ground states have been extracted which are smaller by a factor of ten as compared to theoretical predictions.

  6. Theory of rotational population patterns in heavy-ion transfer reactions: Even-even thorium nuclei

    SciTech Connect

    Chu, S.Y.; Rasmussen, J.O.; Donangelo, R.; Stoyer, M.A.; Frauendorf, S.; Shimizu, Y.R.

    1992-11-01

    A Hamiltonian matrix diagonalization (HMD) method is applied to calculate the lowest several bands in {sup 230,232,234}Th. Neutron pair transfer strength distributions are calculated and compared between HMD and cranked Hartree-Fock-Bogoliubov plus Random Phase Approximation (CHFB+RPA). Sudden-approximation methods are applied to estimate pair transfer population patterns in {sup 206}Pb + {sup 232}Th reactions. Band-crossing, pairing, and spin alignment properties are also discussed.

  7. Theory of rotational population patterns in heavy-ion transfer reactions: Even-even thorium nuclei

    SciTech Connect

    Chu, S.Y.; Rasmussen, J.O. ); Donangelo, R. ); Stoyer, M.A. ); Frauendorf, S. ); Shimizu, Y.R. . Dept. of Physics)

    1992-11-01

    A Hamiltonian matrix diagonalization (HMD) method is applied to calculate the lowest several bands in [sup 230,232,234]Th. Neutron pair transfer strength distributions are calculated and compared between HMD and cranked Hartree-Fock-Bogoliubov plus Random Phase Approximation (CHFB+RPA). Sudden-approximation methods are applied to estimate pair transfer population patterns in [sup 206]Pb + [sup 232]Th reactions. Band-crossing, pairing, and spin alignment properties are also discussed.

  8. Analysis of coupled mass transfer and sol-gel reaction in a two-phase system

    NASA Astrophysics Data System (ADS)

    Castelijns, H. J.; Huinink, H. P.; Pel, L.; Zitha, P. L. J.

    2006-07-01

    The coupled mass transfer and chemical reactions of a gel-forming compound in a two-phase system were studied in detail. Tetra-methyl-ortho-silicate (TMOS) is often used as a precursor in sol-gel chemistry to produce silica gels in aqueous systems. TMOS can also be mixed with many hydrocarbons without chemical reaction, which allows for various applications in multiphase systems. In this study, TMOS was mixed with n-hexadecane and placed together with water in small cylinders. Upon contact of the mixture with the water, TMOS transfers completely to the aqueous phase where it forms a gel through a heterogeneous reaction. Nuclear magnetic resonance imaging and relaxation time measurements were employed to monitor the mass transfer of TMOS from the oleic to the aqueous phase. The longitudinal relaxation time (T1) was calibrated and used to determine the concentration of TMOS in n-hexadecane during the transfer. The mass transfer rate was obtained at various temperatures (25-45°C) and for several initial concentrations of TMOS. In the aqueous phase a sharp decrease in the transversal relaxation time (T2) is observed which is attributed to the gel reaction, in particular the formation of methanol in the initial stage. The minimum in T2 indicates the gelation point, and was found to be strongly dependent on temperature and concentration.

  9. Ion-atom charge-transfer reactions and a hot intercloud medium. [in interstellar space

    NASA Technical Reports Server (NTRS)

    Steigman, G.

    1975-01-01

    An investigation is conducted concerning the ionization equilibrium of carbon in a hot intercloud medium (ICM), taking into account various charge-transfer reactions. Attention is given to problems related to observations of carbon along the lines of sight to several unreddened stars. It is pointed out that the observed underabundance of C III and overabundance of C I can be consistent with the presence of a hot, partially ionized ICM, provided that two of the charge-transfer reactions considered are rapid at thermal energies.

  10. Possibility of production of neutron-rich isotopes in transfer-type reactions at intermediate energies

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Lukyanov, S. M.; Penionzhkevich, Yu. E.

    2008-08-15

    The production cross sections of neutron-rich isotopes of Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, and Ti in the multinucleon transfer reactions {sup 48}Ca(64 MeV/nucleon, 140 MeV/nucleon) + {sup 181}Ta and {sup 48}Ca(142 MeV/nucleon) + {sup nat}W are estimated. A good agreement of the calculated results with the available experimental data confirms the mechanism of multinucleon transfer at almost peripheral collisions at intermediate energies. The global trend of production cross section with the charge (mass) number of target in reactions with {sup 48}Ca beam is discussed for the future experiments.

  11. Structures of Fluoranthene Reagent Anions Used in Electron Transfer Dissociation and Proton Transfer Reaction Tandem Mass Spectrometry.

    PubMed

    Martens, Jonathan; Berden, Giel; Oomens, Jos

    2016-06-21

    Ion/ion reactions have in recent years seen widespread use in ion activation methods such as electron transfer dissociation (ETD) tandem mass spectrometry (MS/MS) as well as in charge manipulation of highly charged peptides/proteins and their fragments by proton transfer reaction (PTR). These techniques have, in combination, enabled top-down proteomics on limited-resolution benchtop mass spectrometry platforms such as quadrupole ion traps. Anions generated by chemical ionization of fluoranthene are often used for both ETD and PTR reactions; the radical anion of fluoranthene (m/z 202) for ETD and the closed-shell anion resulting from H atom attachment to the radical anion (m/z 203) for PTR. Here we use infrared ion spectroscopy in combination with density functional theory calculations to identify the structures of these reagent anions. We establish that the m/z 203 PTR reagent anion possesses a structure that deviates from what has been suggested previously and provides some insight into the reaction mechanism involved in PTR. PMID:27228406

  12. 17O excess transfer during the NO2 + O3 → NO3 + O2 reaction

    NASA Astrophysics Data System (ADS)

    Berhanu, Tesfaye Ayalneh; Savarino, Joël; Bhattacharya, S. K.; Vicars, Willliam C.

    2012-01-01

    The ozone molecule possesses a unique and distinctive 17O excess (Δ17O), which can be transferred to some of the atmospheric molecules via oxidation. This isotopic signal can be used to trace oxidation reactions in the atmosphere. However, such an approach depends on a robust and quantitative understanding of the oxygen transfer mechanism, which is currently lacking for the gas-phase NO2 + O3 reaction, an important step in the nocturnal production of atmospheric nitrate. In the present study, the transfer of Δ17O from ozone to nitrate radical (NO3) during the gas-phase NO2 + O3 → NO3 + O2 reaction was investigated in a series of laboratory experiments. The isotopic composition (δ17O, δ18O) of the bulk ozone and the oxygen gas produced in the reaction was determined via isotope ratio mass spectrometry. The Δ17O transfer function for the NO2 + O3 reaction was determined to be: Δ17O(O3*) = (1.23 ± 0.19) × Δ17O(O3)bulk + (9.02 ± 0.99). The intramolecular oxygen isotope distribution of ozone was evaluated and results suggest that the excess enrichment resides predominantly on the terminal oxygen atoms of ozone. The results obtained in this study will be useful in the interpretation of high Δ17O values measured for atmospheric nitrate, thus leading to a better understanding of the natural cycling of atmospheric reactive nitrogen.

  13. Electron and energy transfer as probes of interparticle ion-exchange reactions in zeolite Y

    SciTech Connect

    Brigham, E.S.; Snowden, P.T.; Kim, Y.I.; Mallouk, T.E. )

    1993-08-19

    Photoinduced electron transfer and energy transfer reactions of tris(2,2[prime]-bipyridyl)ruthenium(II) (Ru(bpy)[sub 3][sup 2+]) with methylviologen (MV[sup 2+]) and tris(2,2[prime]-bipyridyl)osmium(II) (Os(bpy)[sub 3][sup 2+]) ion-exchanged onto/into separate zeolite Y particles were studied by emission spectroscopy. The kinetics of interparticle exchange were probed by observing the quenching of the MLCT excited state of-Ru(bpy)[sub 3][sup 2+] by mobile MV[sup 2+] or OS(bpy)[sub 3][sup 2+] ions. The exchange reactions occur on time scales of seconds to hours, depending on the ionic strength of the surrounding medium. The time-dependent luminescence data were fitted to a dispersed kinetics model, from which average rate constants for the exchange reactions could be extracted. Time constants for interparticle exchange of MV[sup 2+] and Os(bpy)[sub 3][sup 2+] ions, in the range 10[sup 3]-10[sup 5] s at electrolyte concentrations of 0.1-3 mM, are significantly longer than the time scales (10[sup [minus]7]-10[sup 1] s) of most electrochemical and photochemical intrazeolitic reactions involving these and similar electroactive ions. These results argue for reaction mechanisms that invoke intrazeolite electron transfer, rather than exchange of electroactive ions followed by solution-phase electron transfer, in these systems. 25 refs., 6 figs., 1 tab.

  14. On the theory of tunnelling in electron and proton transfer reactions.

    NASA Technical Reports Server (NTRS)

    Sen, R. K.; Bockris, J. O.

    1973-01-01

    The concept of tunnelling in the theory of electron and proton transfer reactions has recently been questioned on the ground that the situation is a nonstationary one. It has been suggested that time-dependent perturbation theory should be applied to obtain the quantum mechanical transition probability. We have done this for a square barrier. The result for most reactions is the same as obtained by the WKB approximation.

  15. Transfer reactions using a low-energy {sup 11}Be beam

    SciTech Connect

    Johansen, Jacob

    2011-10-28

    A series of experiments have been performed to investigate neutron rich beryllium isotopes. Scattering as well as one neutron transfer reactions have been studied using a {sup 11}Be beam on deuteron targets. Bound states of {sup 10,11,12}Be have been studied and reaction cross sections have been calculated. The elastic scattering cross section has shown remarkable structure due to the halo structure of {sup 11}Be.

  16. Analysis of the role of neutron transfer in asymmetric fusion reactions at subbarrier energies

    NASA Astrophysics Data System (ADS)

    Ogloblin, A. A.; Zhang, H. Q.; Lin, C. J.; Jia, H. M.; Khlebnikov, S. V.; Kuzmin, E. A.; Danilov, A. N.; Demyanova, A. S.; Trzaska, W. H.; Xu, X. X.; Yang, F.; Sargsyan, V. V.; Adamian, G. G.; Antonenko, N. V.; Scheid, W.

    2015-12-01

    The excitation functions were measured for the 28Si + 208Pb complete-fusion (capture) reaction at deep subbarrier energies. The results were compared with the cross sections predicted within the quantum diffusion approach. The role of neutron transfer in the case of positive Q values in the 28Si + 124Sn, 208Pb; 30Si + 124Sn, 208Pb; 20Ne + 208Pb; 40Ca + 96Zr; and 134Te + 40Ca complete-fusion (capture) reactions is discussed.

  17. Visualization of the Electron Transfer Associated with Biochemical Reaction Process by the Ultra-Slow Muon

    NASA Astrophysics Data System (ADS)

    Niimura, Nobuo; Tanaka, Ichiro; Kobayashi, Masayoshi

    The µSR experiments on trypsin-BPTI complex are proposed. The proton and electron transfer processes are continuously occurring in a trypsin-BPTI complex and the process induces the local magnetic field. The µ+ would be captured at the negatively charged oxyanion hole close to the reaction center of trypsin. As a control system of the µSR experiment, trypsin- monoisopropylphosphoryl (MIP) system is adequate, because there the catalytic reaction is absolutely stopped.

  18. Possible Role of Different Yeast and Plant Lysophospholipid:Acyl-CoA Acyltransferases (LPLATs) in Acyl Remodelling of Phospholipids.

    PubMed

    Jasieniecka-Gazarkiewicz, Katarzyna; Demski, Kamil; Lager, Ida; Stymne, Sten; Banaś, Antoni

    2016-01-01

    Recent results have suggested that plant lysophosphatidylcholine:acyl-coenzyme A acyltransferases (LPCATs) can operate in reverse in vivo and thereby catalyse an acyl exchange between the acyl-coenzyme A (CoA) pool and the phosphatidylcholine. We have investigated the abilities of Arabidopsis AtLPCAT2, Arabidopsis lysophosphatidylethanolamine acyltransferase (LPEAT2), S. cerevisiae lysophospholipid acyltransferase (Ale1) and S. cerevisiae lysophosphatidic acid acyltransferase (SLC1) to acylate lysoPtdCho, lysoPtdEtn and lysoPtdOH and act reversibly on the products of the acylation; the PtdCho, PtdEtn and PtdOH. The tested LPLATs were expressed in an S. cervisiae ale1 strain and enzyme activities were assessed in assays using microsomal preparations of the different transformants. The results show that, despite high activity towards lysoPtdCho, lysoPtdEtn and lysoPtdOH by the ALE1, its capacities to operate reversibly on the products of the acylation were very low. Slc1 readily acylated lysoPtdOH, lysoPtdCho and lysoPtdEtn but showed no reversibility towards PtdCho, very little reversibility towards PtdEtn and very high reversibility towards PtdOH. LPEAT2 showed the highest levels of reversibility towards PtdCho and PtdEtn of all LPLATs tested but low ability to operate reversibly on PtdOH. AtLPCAT2 showed good reversible activity towards PtdCho and PtdEtn and very low reversibility towards PtdOH. Thus, it appears that some of the LPLATs have developed properties that, to a much higher degree than other LPLATs, promote the reverse reaction during the same assay conditions and with the same phospholipid. The results also show that the capacity of reversibility can be specific for a particular phospholipid, albeit the lysophospholipid derivatives of other phospholipids serve as good acyl acceptors for the forward reaction of the enzyme. PMID:26643989

  19. Transfer cross sections from reactions with /sup 254/Es as a target

    SciTech Connect

    Schadel, M.; Bruechle, W.; Bruegger, M.; Gaggeler, H.; Moody, K.J.; Schardt, D.; Suemmerer, K.; Hulet, E.K.; Dougan, A.D.; Dougan, R.J.

    1986-04-01

    We report radiochemically determined cross sections for the heaviest known actinides produced in transfer reactions of /sup 16,18/O and /sup 22/Ne with /sup 254/Es as a target. A comparison with data for similar transfers from /sup 248/Cm targets is made. Transfer cross sections are extrapolated for the production of the unknown, neutron-rich isotopes of elements 101 through 105, and the unique potential of /sup 254/Es as a target to make these exotic nuclei accessible is demonstrated.

  20. Acylated monogalactosyl diacylglycerol: prevalence in the plant kingdom and identification of an enzyme catalyzing galactolipid head group acylation in Arabidopsis thaliana.

    PubMed

    Nilsson, Anders K; Johansson, Oskar N; Fahlberg, Per; Kommuri, Murali; Töpel, Mats; Bodin, Lovisa J; Sikora, Per; Modarres, Masoomeh; Ekengren, Sophia; Nguyen, Chi T; Farmer, Edward E; Olsson, Olof; Ellerström, Mats; Andersson, Mats X

    2015-12-01

    The lipid phase of the thylakoid membrane is mainly composed of the galactolipids mono- and digalactosyl diacylglycerol (MGDG and DGDG, respectively). It has been known since the late 1960s that MGDG can be acylated with a third fatty acid to the galactose head group (acyl-MGDG) in plant leaf homogenates. In certain brassicaceous plants like Arabidopsis thaliana, the acyl-MGDG frequently incorporates oxidized fatty acids in the form of the jasmonic acid precursor 12-oxo-phytodienoic acid (OPDA). In the present study we further investigated the distribution of acylated and OPDA-containing galactolipids in the plant kingdom. While acyl-MGDG was found to be ubiquitous in green tissue of plants ranging from non-vascular plants to angiosperms, OPDA-containing galactolipids were only present in plants from a few genera. A candidate protein responsible for the acyl transfer was identified in Avena sativa (oat) leaf tissue using biochemical fractionation and proteomics. Knockout of the orthologous gene in A. thaliana resulted in an almost total elimination of the ability to form both non-oxidized and OPDA-containing acyl-MGDG. In addition, heterologous expression of the A. thaliana gene in E. coli demonstrated that the protein catalyzed acylation of MGDG. We thus demonstrate that a phylogenetically conserved enzyme is responsible for the accumulation of acyl-MGDG in A. thaliana. The activity of this enzyme in vivo is strongly enhanced by freezing damage and the hypersensitive response. PMID:26566971

  1. Measurements and coupled reaction channels analysis of one and two proton transfer reactions for 28Si+90,94Zr systems

    NASA Astrophysics Data System (ADS)

    Kalkal, Sunil; Mandal, S.; Jhingan, A.; Gehlot, J.; Sugathan, P.; Golda, K. S.; Madhavan, N.; Garg, Ritika; Goyal, Savi; Mohanto, Gayatri; Verma, S.; Sandal, Rohit; Behera, Bivash; Eleonora, G.; Wollersheim, H. J.; Singh, R.

    2011-10-01

    Measurements of angular distributions for one and two proton stripping reactions for 28Si+90,94Zr systems were performed at lab energy 120 MeV with 28Si beam at Inter University Accelerator Center, New Delhi. Theoretical calculations performed using the quantum mechanical coupled reaction channels code FRESCO (including various intermediate states involving target and projectile excitations before and/or after transfer along with sequential transfer) were able to reproduce one and two proton transfer angular distributions for both the systems reasonably well. It was found that the DWBA calculations could describe the one proton transfer data well for both the systems but failed to reproduce the angular distributions for two proton transfer channels. The present measurements underline the importance of sequential transfer at energies much above the Coulomb barrier. We had also performed transfer reaction measurements for these systems in the sub- and near barrier region using recoil mass separator.

  2. Atomic decomposition of conceptual DFT descriptors: application to proton transfer reactions.

    PubMed

    Inostroza-Rivera, Ricardo; Yahia-Ouahmed, Meziane; Tognetti, Vincent; Joubert, Laurent; Herrera, Bárbara; Toro-Labbé, Alejandro

    2015-07-21

    In this study, we present an atomic decomposition, in principle exact, at any point on a given reaction path, of the molecular energy, reaction force and reaction flux, which is based on Bader's atoms-in-molecules theory and on Pendás' interacting quantum atoms scheme. This decomposition enables the assessment of the importance and the contribution of each atom or molecular group to these global properties, and may cast the light on the physical factors governing bond formation or bond breaking. The potential use of this partition is finally illustrated by proton transfers in model biological systems. PMID:26089126

  3. Transfer to the continuum calculations of quasifree (p,pn) and (p,2p) reactions

    NASA Astrophysics Data System (ADS)

    Gomez-Ramos, M.; Moro, A. M.

    2016-05-01

    Nucleon removal (p, pn) and (p, 2p) reactions at intermediate energies have gained renewed attention in recent years as a tool to extract information from exotic nuclei. The information obtained from these experiments is expected to be sensitive to deeper portions of the wave function of the removed nucleon than knockout reactions with heavier targets. In this contribution, we present calculations for (p, 2p) and (p, pn) reactions performed within the so-called transfer to the continuum method (TR*). Results for stable and unstable nuclei are presented, and compared with experimental data, when available.

  4. Single-drop reactive extraction/extractive reaction with forced convective diffusion and interphase mass transfer

    NASA Technical Reports Server (NTRS)

    Kleinman, Leonid S.; Reed, X. B., Jr.

    1995-01-01

    An algorithm has been developed for the forced convective diffusion-reaction problem for convection inside and outside a droplet by a recirculating flow field hydrodynamically coupled at the droplet interface with an external flow field that at infinity becomes a uniform streaming flow. The concentration field inside the droplet is likewise coupled with that outside by boundary conditions at the interface. A chemical reaction can take place either inside or outside the droplet or reactions can take place in both phases. The algorithm has been implemented and results are shown here for the case of no reaction and for the case of an external first order reaction, both for unsteady behavior. For pure interphase mass transfer, concentration isocontours, local and average Sherwood numbers, and average droplet concentrations have been obtained as a function of the physical properties and external flow field. For mass transfer enhanced by an external reaction, in addition to the above forms of results, we present the enhancement factor, with the results now also depending upon the (dimensionless) rate of reaction.

  5. Single-drop reactive extraction/extractive reaction with forced convective diffusion and interphase mass transfer

    NASA Technical Reports Server (NTRS)

    Kleinman, Leonid S.; Red, X. B., Jr.

    1995-01-01

    An algorithm has been developed for time-dependent forced convective diffusion-reaction having convection by a recirculating flow field within the drop that is hydrodynamically coupled at the interface with a convective external flow field that at infinity becomes a uniform free-streaming flow. The concentration field inside the droplet is likewise coupled with that outside by boundary conditions at the interface. A chemical reaction can take place either inside or outside the droplet, or reactions can take place in both phases. The algorithm has been implemented, and for comparison results are shown here for the case of no reaction in either phase and for the case of an external first order reaction, both for unsteady behavior. For pure interphase mass transfer, concentration isocontours, local and average Sherwood numbers, and average droplet concentrations have been obtained as a function of the physical properties and external flow field. For mass transfer enhanced by an external reaction, in addition to the above forms of results, we present the enhancement factor, with the results now also depending upon the (dimensionless) rate of reaction.

  6. Faddeev-type calculation of (d ,n ) transfer reactions in three-body nuclear systems

    NASA Astrophysics Data System (ADS)

    Deltuva, A.

    2015-12-01

    Exact Faddeev-type three-body equations are applied to the study of the proton transfer reactions (d ,n ) in the system consisting of a nuclear core and two nucleons. The integral equations for the three-body transition operators are solved in the momentum-space framework including the Coulomb interaction via the screening and renormalization method. For a weakly bound final nucleus the calculation of the (d ,n ) reaction is more demanding in terms of the screening radius as compared to the (d ,p ) reaction. Well-converged differential cross section results are obtained for 7Be (d ,n ) 8B, 12C (d ,n ) 13N, and 16O (d ,n ) 17$ reactions. A comparison with the corresponding (d ,p ) reactions is made. The calculations fail to reproduce the shape of the angular distribution for reactions on 12C but provide quite successful description for reactions on 16O, especially for the transfer to the 17F excited state 1 /2+ when using a nonlocal optical potential.

  7. A theoretical and experimental study of unimolecular and biomolecular radical hydrogen transfer reactions

    SciTech Connect

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

    1991-04-01

    We have examined the intramolecular radical hydrogen transfer (RHT) reaction of the 2-(2-phenylethyl)cyclohexadienyl radical. Intramolecular hydrogen shift from the cyclohexadienyl ring to the ipso position of the phenyl ring, followed by {beta}-scission would have given benzene and ethylbenzene as products. Competing with this reaction is {beta}-scission to give benzyl radical and isotoluene, or hydrogen loss to give bibenzyl. Studies to date suggest a barrier for thermoneutral hydrogen transfer in the RHT reaction between aromatic systems of ca. 18 kcal/mole. None of the studies of RHT or equivalent mechanisms have attempted to directly observe H{sub 2}, and direct determination of Arrhenius parameters and a detailed examination of the pathway of the hydrogen transfer process remains to be carried out. To better understand the structural and energetic aspects of RHT, we have carried out a semiempirical molecular orbital study of bimolecular and intramolecular RHT reactions for a variety of aromatic systems. We also examined in detail the energetics of hydrogen transfer between ethyl radical and ethylene via RHT, an addition/metathesis/scission pathway, and a hybrid concerted'' pathway. 11 refs., 1 fig., 4 tabs.

  8. Near-Barrier Neutron Transfer in Reactions 3,6He+197Au

    NASA Astrophysics Data System (ADS)

    Samarin, V. V.; Naumenko, M. A.; Penionzhkevich, Yu. E.; Skobelev, N. K.; Kroha, V.; Mrazek, J.

    2015-06-01

    Experimental excitation functions for near-barrier neutron transfer in 3,6He+197Au reactions have been measured and analyzed. Time-dependent Schrödinger equation and coupled channel equations for external neutrons of 3,6He and 197Au nuclei have been solved numerically taking into account spin-orbit interaction and Pauli exclusion principle.

  9. Toward neutron-rich nuclei via transfer reactions with stable and radioactive beams

    NASA Astrophysics Data System (ADS)

    Mun, Myeong-Hwan; Adamian, G. G.; Antonenko, N. V.; Oh, Yongseok; Kim, Youngman

    2015-05-01

    The possibilities of production of yet-undiscovered neutron-rich isotopes of Ca, Gd, Dy, Er, Yb, Hf, W, Os, Hg, Pb, and Th are explored in various multinucleon transfer reactions with stable and radioactive beams. The probable projectile-target combinations and bombarding energies to produce these neutron-rich isotopes are suggested for future experiments.

  10. Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions

    ERIC Educational Resources Information Center

    Silverstein, Todd P.

    2012-01-01

    Although it is generally true that thermodynamics do not influence kinetics, this is NOT the case for electron transfer reactions in solution. Marcus Theory explains why this is so, using straightforward physical chemical principles such as transition state theory, Arrhenius' Law, and the Franck-Condon Principle. Here the background and…

  11. Separation and quantification of 2-acyl-1-lysophospholipids and 1-acyl-2-lysophospholipids in biological samples by LC-MS/MS

    PubMed Central

    Okudaira, Michiyo; Inoue, Asuka; Shuto, Akira; Nakanaga, Keita; Kano, Kuniyuki; Makide, Kumiko; Saigusa, Daisuke; Tomioka, Yoshihisa; Aoki, Junken

    2014-01-01

    Lysophospholipids (LysoGPs) serve as lipid mediators and precursors for synthesis of diacyl phospholipids (GPs). LysoGPs detected in cells have various acyl chains attached at either the sn-1 or sn-2 position of the glycerol backbone. In general, acyl chains at the sn-2 position of 2-acyl-1-LysoGPs readily move to the sn-1 position, generating 1-acyl-2-lyso isomers by a nonenzymatic reaction called intra-molecular acyl migration, which has hampered the detection of 2-acyl-1-LysoGPs in biological samples. In this study, we developed a simple and versatile method to separate and quantify 2-acyl-1- and 1-acyl-2-LysoGPs. The main point of the method was to extract LysoGPs at pH 4 and 4°C, conditions that were found to completely eliminate the intra-molecular acyl migration. Under the present conditions, the relative amounts of 2-acyl-1-LysoGPs and 1-acyl-2-LysoGPs did not change at least for 1 week. Further, in LysoGPs extracted from cells and tissues under the present conditions, most of the saturated fatty acids (16:0 and 18:0) were found in the sn-1 position of LysoGPs, while most of the PUFAs (18:2, 20:4, 22:6) were found in the sn-2 position. Thus the method can be used to elucidate the in vivo role of 2-acyl-1-LysoGPs. PMID:25114169

  12. Acyl-acyl carrier protein as a source of fatty acids for bacterial bioluminescence

    SciTech Connect

    Byers, D.M.; Meighen, E.A.

    1985-09-01

    Pulse-chase experiments with (/sup 3/H)tetradecanoic acid and ATP showed that the bioluminescence-related 32-kDa acyltransferase from Vibrio harveyi can specifically catalyze the deacylation of a /sup 3/H-labeled 18-kDa protein observed in extracts of this bacterium. The 18-kDa protein has been partially purified and its physical and chemical properties strongly indicate that it is fatty acyl-acyl carrier protein (acyl-ACP). Both this V. harveyi (/sup 3/H)acylprotein and (/sup 3/H)palmitoyl-ACP from Escherichia coli were substrates in vitro for either the V. harveyi 32-kDa acyltransferase or the analogous enzyme (34K) from Photobacterium phosphoreum. TLC analysis indicated that the hexane-soluble product of the reaction is fatty acid. No significant cleavage of either E. coli or V. harveyi tetradecanoyl-ACP was observed in extracts of these bacteria unless the 32-kDa or 34K acyltransferase was present. Since these enzymes are believed to be responsible for the supply of fatty acids for reduction to form the aldehyde substrate of luciferase, the above results suggest that long-chain acyl-ACP is the source of fatty acids for bioluminescence.

  13. Impact of Mutation on Proton Transfer Reactions in Ketosteroid Isomerase: Insights from Molecular Dynamics Simulations

    PubMed Central

    Chakravorty, Dhruva K.; Hammes-Schiffer, Sharon

    2010-01-01

    The two proton transfer reactions catalyzed by ketosteroid isomerase (KSI) involve a dienolate intermediate stabilized by hydrogen bonds with Tyr14 and Asp99. Molecular dynamics simulations based on an empirical valence bond model are used to examine the impact of mutating these residues on the hydrogen-bonding patterns, conformational changes, and van der Waals and electrostatic interactions during the proton transfer reactions. While the rate constants for the two proton transfer steps are similar for wild-type (WT) KSI, the simulations suggest that the rate constant for the first proton transfer step is smaller in the mutants due to the significantly higher free energy of the dienolate intermediate relative to the reactant. The calculated rate constants for the mutants D99L, Y14F, and Y14F/D99L relative to WT KSI are qualitatively consistent with the kinetic experiments indicating a significant reduction in the catalytic rates along the series of mutants. In the simulations, WT KSI retained two hydrogen-bonding interactions between the substrate and the active site, while the mutants typically retained only one hydrogen-bonding interaction. A new hydrogen-bonding interaction between the substrate and Tyr55 was observed in the double mutant, leading to the prediction that mutation of Tyr55 will have a greater impact on the proton transfer rates for the double mutant than for WT KSI. The electrostatic stabilization of the dienolate intermediate relative to the reactant was greater for WT KSI than for the mutants, providing a qualitative explanation for the significantly reduced rates of the mutants. The active site exhibited highly restricted motion during the proton transfer reactions, but small conformational changes occurred to facilitate the proton transfer reactions by strengthening the hydrogen-bonding interactions and by bringing the proton donor and acceptor closer to each other with the proper orientation for proton transfer. Thus, these calculations

  14. Fine structure in the transition region: reaction force analyses of water-assisted proton transfers.

    PubMed

    Yepes, Diana; Murray, Jane S; Santos, Juan C; Toro-Labbé, Alejandro; Politzer, Peter; Jaque, Pablo

    2013-07-01

    We have analyzed the variation of the reaction force F(ξ) and the reaction force constant κ(ξ) along the intrinsic reaction coordinates ξ of the water-assisted proton transfer reactions of HX-N = Y (X,Y = O,S). The profile of the force constant of the vibration associated with the reactive mode, k ξ (ξ), was also determined. We compare our results to the corresponding intramolecular proton transfers in the absence of a water molecule. The presence of water promotes the proton transfers, decreasing the energy barriers by about 12 - 15 kcal mol(-1). This is due in part to much smaller bond angle changes being needed than when water is absent. The κ(ξ) profiles along the intrinsic reaction coordinates for the water-assisted processes show striking and intriguing differences in the transition regions. For the HS-N = S and HO-N = S systems, two κ(ξ) minima are obtained, whereas for HO-N = O only one minimum is found. The k ξ (ξ) show similar behavior in the transition regions. We propose that this fine structure reflects the degree of synchronicity of the two proton migrations in each case. PMID:22733272

  15. Two-neutron transfer analysis of the 16O(18O,16O)18O reaction

    NASA Astrophysics Data System (ADS)

    Ermamatov, M. J.; Cappuzzello, F.; Lubian, J.; Cubero, M.; Agodi, C.; Carbone, D.; Cavallaro, M.; Ferreira, J. L.; Foti, A.; Garcia, V. N.; Gargano, A.; Lay, J. A.; Lenzi, S. M.; Linares, R.; Santagati, G.; Vitturi, A.

    2016-08-01

    Recently a quantitative description of the two-neutron transfer reaction 12C(18O,16O)14C was performed and the measured cross sections were successfully reproduced [M. Cavallaro et al., Phys. Rev. C 88, 054601 (2013), 10.1103/PhysRevC.88.054601]. This task was accomplished by combining nuclear structure calculations of spectroscopic amplitudes and a full quantum description of the reaction mechanism. Verification of such a theoretical approach to other heavy nuclear systems is mandatory in order to use (18O,16O ) reactions to assess pair configurations in nuclear states. In this work we apply this methodology to the 16O(18O,16O)18O reaction at 84 MeV. Experimental angular distributions for the two-neutron transfer to the ground state and 21+ state of 18O were obtained using the MAGNEX spectrometer at INFN-LNS. The roles of one- and two-step processes are analyzed under the exact finite range coupled reaction channel and the second order distorted wave Born approximation. We conclude that the one-step transfer mechanism is dominant in this system.

  16. Production of heavy neutron-rich nuclei in transfer reactions within the dinuclear system model

    NASA Astrophysics Data System (ADS)

    Zhu, Long; Feng, Zhao-Qing; Zhang, Feng-Shou

    2015-08-01

    The dynamics of nucleon transfer processes in heavy-ion collisions is investigated within the dinuclear system model. The production cross sections of nuclei in the reactions 136Xe+208Pb and 238U+248Cm are calculated, and the calculations are in good agreement with the experimental data. The transfer cross sections for the 58Ni+208Pb reaction are calculated and compared with the experimental data. We predict the production cross sections of neutron-rich nuclei 165-168 Eu, 169-173 Tb, 173-178 Ho, and 181-185Yb based on the reaction 176Yb+238U. It can be seen that the production cross sections of the neutron-rich nuclei 165Eu, 169Tb, 173Ho, and 181Yb are 2.84 μb, 6.90 μb, 46.24 μb, and 53.61 μb, respectively, which could be synthesized in experiment.

  17. Characterizing Active Site Conformational Heterogeneity along the Trajectory of an Enzymatic Phosphoryl Transfer Reaction.

    PubMed

    Zeymer, Cathleen; Werbeck, Nicolas D; Zimmermann, Sabine; Reinstein, Jochen; Hansen, D Flemming

    2016-09-12

    States along the phosphoryl transfer reaction catalyzed by the nucleoside monophosphate kinase UmpK were captured and changes in the conformational heterogeneity of conserved active site arginine side-chains were quantified by NMR spin-relaxation methods. In addition to apo and ligand-bound UmpK, a transition state analog (TSA) complex was utilized to evaluate the extent to which active site conformational entropy contributes to the transition state free energy. The catalytically essential arginine side-chain guanidino groups were found to be remarkably rigid in the TSA complex, indicating that the enzyme has evolved to restrict the conformational freedom along its reaction path over the energy landscape, which in turn allows the phosphoryl transfer to occur selectively by avoiding side reactions. PMID:27534930

  18. Two-quasiparticle states in {sup 250}Bk studied by decay scheme and transfer reaction spectroscopy

    SciTech Connect

    Ahmad, I.; Kondev, F. G.; Koenig, Z. M.; McHarris, Wm. C.; Yates, S. W.

    2008-05-15

    Two-quasiparticle states in {sup 250}Bk were investigated with decay scheme studies and the single-neutron transfer reaction {sup 249}Bk(d,p){sup 250}Bk. Mass-separated sources of {sup 254}Es were used for {alpha} singles and {alpha}-{gamma} coincidence measurements. These studies, plus previous studies of {sup 254}Es{sup m} {alpha} decay and the {sup 249}Bk(n,{gamma}) reaction, provide spins and parities of the observed levels. The transfer reaction {sup 249}Bk(d,p){sup 250}Bk was used to deduce neutron single-particle components of the observed bands. Six pairs of singlet and triplet states, formed by the coupling of proton and neutron one-quasiparticle states, were identified. The splitting energies between the triplet and singlet states were found to be in agreement with previous calculations.

  19. Transfer of learning in choice reactions: contributions of specific and general components of manual responses.

    PubMed

    Yamaguchi, Motonori; Proctor, Robert W

    2009-01-01

    Manifestations of learned skills and knowledge are known to be context-dependent. However, a study of perceptual-motor learning [Tagliabue, M., Zorzi, M., & Umiltà, C. (2002). Cross-modal re-mapping influences the Simon effect. Memory and Cognition, 30, 18-23] reported context-independent transfer of a learned stimulus-response (S-R) mapping to a task in which the mapping is no longer relevant. Although similar results were observed in subsequent studies, these studies also provided an indication that the transfer is context-dependent. The present study investigated the issue of context-dependence of the transfer of a learned S-R mapping. In experiment 1, groups of participants performed choice-reaction tasks with either the same or different response modes (keypresses or joystick movements) in the practice and transfer sessions. Smaller transfer effects were observed for those who switched response mode in the transfer session than for those who did not, indicating that transfer of the learned mapping is context-dependent. However, transfer also occurred for the former group, indicating that the transfer effect is dependent on both general and specific response components. In experiment 2, the same task conditions were examined, but with action effects consistent across the practice and transfer sessions, which were assumed to introduce a contextual feature that was common to the two sessions. The influence of action effects on transfer depended on the practiced response. The results are discussed in terms of feature overlap between the learning and test contexts, and an association network model of learning and response selection. PMID:18952202

  20. Direct simulation of proton-coupled electron transfer reaction dynamics and mechanisms

    NASA Astrophysics Data System (ADS)

    Kretchmer, Joshua S.; Miller, Thomas F., III

    2014-03-01

    Proton-coupled electron transfer (PCET) reactions, in which both an electron and an associated proton undergo reactive transfer, play an important role in many chemical and biological systems. Due to the complexity of this class of reactions, a variety of different mechanisms fall under the umbrella of PCET. However, the physical driving forces that determine the preferred mechanism in a given system still remain poorly understood. Towards this end, we extend ring polymer molecular dynamics (RPMD), a path-integral quantum dynamics method, to enable the direct simulation and characterization of PCET reaction dynamics in both fully atomistic and system-bath models of organometallic catalysts. In addition to providing validation for the simulation method via extensive comparison with existing PCET rate theories, we analyze the RPMD trajectories to investigate the competition between the concerted and sequential reaction mechanisms for PCET, elucidating the large role of the solvent in controlling the preferred mechanism. We further employ RPMD to determine the kinetics and mechanistic features of concerted PCET reactions across different regimes of electronic and vibrational coupling, providing evidence for a new and distinct PCET reaction mechanism.

  1. Measurements and coupled reaction channels analysis of one- and two-proton transfer reactions for the 28Si + 90,94Zr systems

    NASA Astrophysics Data System (ADS)

    Kalkal, Sunil; Mandal, S.; Jhingan, A.; Gehlot, J.; Sugathan, P.; Golda, K. S.; Madhavan, N.; Garg, Ritika; Goyal, Savi; Mohanto, Gayatri; Sandal, Rohit; Chakraborty, Santosh; Verma, Shashi; Behera, Bivash; Eleonora, G.; Wollersheim, H. J.; Singh, R.

    2012-03-01

    Measurements of angular distributions for one- and two-proton stripping reactions for 28Si + 90,94Zr systems were performed at 120 MeV. The experiment was carried out with the 28Si beam at Inter University Accelerator Center, New Delhi. The theoretical calculations were performed using the quantum mechanical coupled reaction channels code fresco. The distorted wave Born approximation calculations reproduced the experimental angular distributions for the one-proton transfer channel for both the systems reasonably well but failed for the two-proton transfer channel. Coupled channels calculations including various intermediate states (involving target and projectile inelastic excitations before and/or after transfer) along with the sequential transfer were able to reproduce the two-proton transfer angular distributions for both the systems reasonably well. It seems that at an energy above the Coulomb barrier, there is significant contribution of the indirect multistep and sequential transfer to the two-proton stripping reaction.

  2. Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.

    PubMed

    Odobel, Fabrice; Séverac, Marjorie; Pellegrin, Yann; Blart, Errol; Fosse, Céline; Cannizzo, Caroline; Mayer, Cédric R; Elliott, Kristopher J; Harriman, Anthony

    2009-01-01

    Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide. PMID:19197929

  3. Mass and charge transfer in the heavy ion reactions 208Ni and 208Ni

    NASA Astrophysics Data System (ADS)

    Sapotta, K.; Bass, R.; Hartmann, V.; Noll, H.; Renfordt, R. E.; Stelzer, K.

    1985-04-01

    Target-like reaction products corresponding to the transfer of one or several nucleons have been measured as a function of the total kinetic energy loss in the reactions 208Ni (1215 MeV) and 208Ni (1107 MeV) with a focusing time-of-flight spectrometer which provided a unique mass and charge separation and good energy resolution. The analysis of the experimental data covered the range from elastic scattering to deep-inelastic collisions. In the quasielastic region, neutron transfer dominates. The transfer probabilities as a function of the distance of closest approach can be described by a semiclassical theory of tunneling. Quasielastic transfer from the Ni targets to the 208Pb projectile is strongly inhibited by the reaction Q values. For the intermediate and deep-inelastic collisions, the mean values and variances of the mass and charge distributions as a function of the dissipated energy, as well as the correlations between neutron and proton transport, are discussed in a statistical diffusion theory. The important influence of the static potential energy surface on nucleon transport in the deep-inelastic region is demonstrated. Deviations from the simple diffusion model, observed at small to medium energy losses, are discussed.

  4. Correcting reaction rates measured by saturation-transfer magnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Gabr, Refaat E.; Weiss, Robert G.; Bottomley, Paul A.

    2008-04-01

    Off-resonance or spillover irradiation and incomplete saturation can introduce significant errors in the estimates of chemical rate constants measured by saturation-transfer magnetic resonance spectroscopy (MRS). Existing methods of correction are effective only over a limited parameter range. Here, a general approach of numerically solving the Bloch-McConnell equations to calculate exchange rates, relaxation times and concentrations for the saturation-transfer experiment is investigated, but found to require more measurements and higher signal-to-noise ratios than in vivo studies can practically afford. As an alternative, correction formulae for the reaction rate are provided which account for the expected parameter ranges and limited measurements available in vivo. The correction term is a quadratic function of experimental measurements. In computer simulations, the new formulae showed negligible bias and reduced the maximum error in the rate constants by about 3-fold compared to traditional formulae, and the error scatter by about 4-fold, over a wide range of parameters for conventional saturation transfer employing progressive saturation, and for the four-angle saturation-transfer method applied to the creatine kinase (CK) reaction in the human heart at 1.5 T. In normal in vivo spectra affected by spillover, the correction increases the mean calculated forward CK reaction rate by 6-16% over traditional and prior correction formulae.

  5. Diagnostic Criteria for the Characterization of Electrode Reactions with Chemically Coupled Reactions Preceding the Electron Transfer by Cyclic Square Wave Voltammetry.

    PubMed

    Helfrick, John C; Mann, Megan A; Bottomley, Lawrence A

    2016-08-18

    Theory for cyclic square wave voltammetry of electrode reactions with chemical reactions preceding the electron transfer is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics. PMID:27443581

  6. Mechanistic studies of malonic acid-mediated in situ acylation.

    PubMed

    Chandra, Koushik; Naoum, Johnny N; Roy, Tapta Kanchan; Gilon, Chaim; Gerber, R Benny; Friedler, Assaf

    2015-09-01

    We have previously introduced an easy to perform, cost-effective and highly efficient acetylation technique for solid phase synthesis (SPPS). Malonic acid is used as a precursor and the reaction proceeds via a reactive ketene that acetylates the target amine. Here we present a detailed mechanistic study of the malonic acid-mediated acylation. The influence of reaction conditions, peptide sequence and reagents was systematically studied. Our results show that the methodology can be successfully applied to different types of peptides and nonpeptidic molecules irrespective of their structure, sequence, or conformation. Using alkyl, phenyl, and benzyl malonic acid, we synthesized various acyl peptides with almost quantitative yields. The ketenes obtained from the different malonic acid derived precursors were characterized by in situ (1) H-NMR. The reaction proceeded in short reaction times and resulted in excellent yields when using uronium-based coupling agents, DIPEA as a base, DMF/DMSO/NMP as solvents, Rink amide/Wang/Merrifield resins, temperature of 20°C, pH 8-12 and 5 min preactivation at inert atmosphere. The reaction was unaffected by Lewis acids, transition metal ions, surfactants, or salt. DFT studies support the kinetically favorable concerted mechanism for CO2 and ketene formation that leads to the thermodynamically stable acylated products. We conclude that the malonic acid-mediated acylation is a general method applicable to various target molecules. PMID:25846609

  7. Probing the critical residues for intramolecular fructosyl transfer reaction of a levan fructotransferase.

    PubMed

    Moon, Keum-Ok; Choi, Kyoung-Hwa; Kang, Ho-Young; Oh, Jeong-Il; Jang, Se Bok; Park, Cheon-Seok; Lee, Jong-Hoon; Cha, Jaeho

    2008-06-01

    Levan fructotransferase (LFTase) preferentially catalyzes the transfructosylation reaction in addition to levan hydrolysis, whereas other levan-degrading enzymes hydrolyze levan into a levan-oligosaccharide and fructose. Based on sequence comparisons and enzymatic properties, the fructosyl transfer activity of LFTase is proposed to have evolved from levanase. In order to probe the residues that are critical to the intramolecular fructosyl transfer reaction of the Microbacterium sp. AL-210 LFTase, an error-prone PCR mutagenesis process was carried out, and the mutants that led to a shift in activity from transfructosylation towards hydrolysis of levan were screened by the DNS method. After two rounds of mutagenesis, TLC and HPLC analyses of the reaction products by the selected mutants revealed two major products; one is a di-D-fructose- 2,6':6,2'-dianhydride (DFAIV) and the other is a levanbiose. The newly detected levanbiose corresponds to the reaction product from LFTase lacking transferring activity. Two mutants (2-F8 and 2-G9) showed a high yield of levanbiose (38-40%) compared with the wild-type enzyme, and thus behaved as levanases. Sequence analysis of the individual mutants responsible for the enhanced hydrolytic activity indicated that Asn-85 was highly involved in the transfructosylation activity of LFTase. PMID:18600048

  8. Mass Transfer from Gas Bubbles to Impinging Flow of Biological Fluids with Chemical Reaction

    PubMed Central

    Yang, Wen-Jei; Echigo, R.; Wotton, D. R.; Ou, J. W.; Hwang, J. B.

    1972-01-01

    The rates of mass transfer from a gas bubble to an impinging flow of a biological fluid such as whole blood and plasma are investigated analytically and experimentally. Gases commonly found dissolved in body fluids are included. Consideration is given to the effects of the chemical reaction between the dissolved gas and the liquid on the rate of mass transfer. Through the application of boundary layer theory the over-all transfer is found to be Sh/(Re)1/2 = 0.845 Sc1/3 in the absence of chemical reaction, and Sh/(Re) 1/2 = F′ (0) in the presence of chemical reaction, where Sh, Re, and Sc are the Sherwood, Reynolds, and Schmidt numbers, respectively, and F′ (0) is a function of Sc and the dimensionless reaction rate constant. Analytical results are also obtained for the bubble lifetime and the bubble radius-time history. These results, which are not incompatible with experimental results, can be applied to predict the dissolution of the entrapped gas emboli in the circulatory system of the human body. PMID:4642218

  9. Interactions of the acyl chain with the Saccharomyces cerevisiae acyl carrier protein.

    PubMed

    Perez, Daniel R; Leibundgut, Marc; Wider, Gerhard

    2015-04-01

    Acyl carrier protein (ACP) domains are critical integral components of multifunctional type I fatty acid synthases (FAS I) and polyketide synthases (PKSs), where they shuttle the growing adducts of the synthesis between the catalytic domains. In contrast to ACP of mammalian FAS I, PKSs, and the dissociated fatty acid synthase type II systems (FAS II) of bacteria, fungal FAS I ACP consists of two subdomains, one comprising the canonical ACP fold observed in all FAS systems and the other representing an extra structural subdomain. While ACPs of dissociated FAS II are able to sequester the reaction intermediates during substrate shuttling, such a transport mechanism has not been observed in ACP domains of multifunctional FAS I and PKS systems. For a better understanding of the interaction between the canonical subdomain of fungal ACP with the growing acyl chain and the role of the structural subdomain, we determined the structure of the isolated Saccharomyces cerevisiae acyl carrier protein (ScACP) domain by NMR spectroscopy and investigated the interactions between ScACP and covalently attached substrate acyl chains of varying length by monitoring chemical shift perturbations. The interactions were mapped to the hydrophobic core of the canonical subdomain, while no perturbations were detected in the structural subdomain. A population analysis revealed that only approximately 15% of covalently attached decanoyl chains are sequestered by the ACP core, comparable to the mammalian FAS I and multifunctional PKS systems, which do not sequester their substrates. Finally, denaturation experiments show that both ScACP subdomains unfold cooperatively and that the weak interaction of the acyl chain with the hydrophobic core does not significantly affect the ACP stability. PMID:25774789

  10. Probing surface distributions of α clusters in 20Ne via α -transfer reaction

    NASA Astrophysics Data System (ADS)

    Fukui, Tokuro; Taniguchi, Yasutaka; Suhara, Tadahiro; Kanada-En'yo, Yoshiko; Ogata, Kazuyuki

    2016-03-01

    Background: Direct evidence of the α -cluster manifestation in bound states has not been obtained yet, although a number of experimental studies were carried out to extract the information of the clustering. In particular in conventional analyses of α -transfer reactions, there exist a few significant problems on reaction models, which are insufficient to qualitatively discuss the cluster structure. Purpose: We aim to verify the manifestation of the α -cluster structure from observables. As the first application, we plan to extract the spatial information of the cluster structure of the 20Ne nucleus in its ground state through the cross section of the α -transfer reaction 16O(6Li,d )20Ne. Methods: For the analysis of the transfer reaction, we work with the coupled-channel Born approximation (CCBA) approach, in which the breakup effect of 6Li is explicitly taken into account by means of the continuum-discretized coupled-channel method based on the three-body α +d +16O model. The two methods are adopted to calculate the overlap function between 20Ne and α +16O ; one is the microscopic cluster model (MCM) with the generator coordinate method, and the other is the phenomenological two-body potential model (PM). Results: We show that the CCBA calculation with the MCM wave function gives a significant improvement of the theoretical result on the angular distribution of the transfer cross section, which is consistent with the experimental data. Employing the PM, it is discussed which region of the cluster wave function is probed on the transfer cross section. Conclusions: It is found that the surface region of the cluster wave function is sensitive to the cross section. The present work is situated as the first step in obtaining important information to systematically investigate the cluster structure.

  11. Development of ORRUBA: A Silicon Array for the Measurement of Transfer Reactions in Inverse Kinematics

    SciTech Connect

    Pain, S. D.; Bardayan, Daniel W; Blackmon, Jeff C; Chae, K. Y.; Chipps, K.; Cizewski, J. A.; Hatarik, Robert; Johnson, Micah; Jones, K. L.; Kapler, R.; Kozub, R. L.; Livesay, Jake; Matei, Catalin; Moazen, Brian; Nesaraja, Caroline D; O'Malley, Patrick; Smith, Michael Scott; Swan, T. P.; Thomas, J. S.; Wilson, Gemma L

    2009-01-01

    The development of high quality radioactive beams has made possible the measurement of transfer reactions in inverse kinematics on unstable nuclei. Measurement of (d,p) reactions on neutron-rich nuclei yield data on the evolution of nuclear structure away from stability, and are of astrophysical interest. Experimentally, (d,p) reactions on heavy (Z=50) fission fragments are complicated by the strongly inverse kinematics, and relatively low beam intensities. Consequently, ejectile detection with high resolution in position and energy, a high dynamic range and a high solid angular coverage is required. The Oak Ridge Rutgers University Barrel Array (ORRUBA) is a new silicon detector array optimized for the measurement of (d,p) reactions in inverse kinematics.

  12. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    PubMed Central

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

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment 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 specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome–a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor. PMID:26689792

  13. Key Role of Active-Site Water Molecules in Bacteriorhodopsin Proton-Transfer Reactions

    SciTech Connect

    Bondar, A.N.; Baudry, Jerome Y; Suhai, Sandor; Fischer, S.; Smith, Jeremy C

    2008-10-01

    The functional mechanism of the light-driven proton pump protein bacteriorhodopsin depends on the location of water molecules in the active site at various stages of the photocycle and on their roles in the proton-transfer steps. Here, free energy computations indicate that electrostatic interactions favor the presence of a cytoplasmic-side water molecule hydrogen bonding to the retinal Schiff base in the state preceding proton transfer from the retinal Schiff base to Asp85. However, the nonequilibrium nature of the pumping process means that the probability of occupancy of a water molecule in a given site depends both on the free energies of insertion of the water molecule in this and other sites during the preceding photocycle steps and on the kinetic accessibility of these sites on the time scale of the reaction steps. The presence of the cytoplasmic-side water molecule has a dramatic effect on the mechanism of proton transfer: the proton is channeled on the Thr89 side of the retinal, whereas the transfer on the Asp212 side is hindered. Reaction-path simulations and molecular dynamics simulations indicate that the presence of the cytoplasmic-side water molecule permits a low-energy bacteriorhodopsin conformer in which the water molecule bridges the twisted retinal Schiff base and the proton acceptor Asp85. From this low-energy conformer, proton transfer occurs via a concerted mechanism in which the water molecule participates as an intermediate proton carrier.

  14. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment 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 specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  15. Protein Dynamics Control of Electron Transfer in Photosynthetic Reaction Centers from Rps. Sulfoviridis

    PubMed Central

    Medvedev, E. S.; Kotelnikov, A. I.; Barinov, A. V.; Psikha, B. L.; Ortega, J. M.; Popović, D. M.; Stuchebrukhov, A. A.

    2009-01-01

    In the cycle of photosynthetic reaction centers, the initially oxidized special pair of bacteriochlorophyll molecules is subsequently reduced by an electron transferred over a chain of four hemes of the complex. Here, we examine the kinetics of electron transfer between the proximal heme c-559 of the chain and the oxidized special pair in the reaction center from Rps. sulfoviridis in the range of temperatures from 294 to 40 K. The experimental data were obtained for three redox states of the reaction center, in which one, two, or three nearest hemes of the chain are reduced prior to special pair oxidation. The experimental kinetic data are analyzed in terms of a Sumi–Marcus-type model developed in our previous paper,1 in which similar measurements were reported on the reaction centers from Rps. viridis. The model allows us to establish a connection between the observed nonexponential electron-transfer kinetics and the local structural relaxation dynamics of the reaction center protein on the microsecond time scale. The activation energy for relaxation dynamics of the protein medium has been found to be around 0.1 eV for all three redox states, which is in contrast to a value around 0.4–0.6 eV in Rps. viridis.1 The possible nature of the difference between the reaction centers from Rps. viridis and Rps. sulfoviridis, which are believed to be very similar, is discussed. The role of the protein glass transition at low temperatures and that of internal water molecules in the process are analyzed. PMID:18284231

  16. Protein dynamics control of electron transfer in photosynthetic reaction centers from Rps. sulfoviridis.

    PubMed

    Medvedev, E S; Kotelnikov, A I; Barinov, A V; Psikha, B L; Ortega, J M; Popović, D M; Stuchebrukhov, A A

    2008-03-13

    In the cycle of photosynthetic reaction centers, the initially oxidized special pair of bacteriochlorophyll molecules is subsequently reduced by an electron transferred over a chain of four hemes of the complex. Here, we examine the kinetics of electron transfer between the proximal heme c-559 of the chain and the oxidized special pair in the reaction center from Rps. sulfoviridis in the range of temperatures from 294 to 40 K. The experimental data were obtained for three redox states of the reaction center, in which one, two, or three nearest hemes of the chain are reduced prior to special pair oxidation. The experimental kinetic data are analyzed in terms of a Sumi-Marcus-type model developed in our previous paper,1 in which similar measurements were reported on the reaction centers from Rps. viridis. The model allows us to establish a connection between the observed nonexponential electron-transfer kinetics and the local structural relaxation dynamics of the reaction center protein on the microsecond time scale. The activation energy for relaxation dynamics of the protein medium has been found to be around 0.1 eV for all three redox states, which is in contrast to a value around 0.4-0.6 eV in Rps. viridis.1 The possible nature of the difference between the reaction centers from Rps. viridis and Rps. sulfoviridis, which are believed to be very similar, is discussed. The role of the protein glass transition at low temperatures and that of internal water molecules in the process are analyzed. PMID:18284231

  17. A water-soluble ruthenium glycosylated porphyrin catalyst for carbenoid transfer reactions in aqueous media with applications in bioconjugation reactions.

    PubMed

    Ho, Chi-Ming; Zhang, Jun-Long; Zhou, Cong-Ying; Chan, On-Yee; Yan, Jessie Jing; Zhang, Fu-Yi; Huang, Jie-Sheng; Che, Chi-Ming

    2010-02-17

    Water-soluble [Ru(II)(4-Glc-TPP)(CO)] (1, 4-Glc-TPP = meso-tetrakis(4-(beta-D-glucosyl)phenyl)porphyrinato dianion) is an active catalyst for the following carbenoid transfer reactions in aqueous media with good selectivities and up to 100% conversions: intermolecular cyclopropanation of styrenes (up to 76% yield), intramolecular cyclopropanation of an allylic diazoacetate (68% yield), intramolecular ammonium/sulfonium ylide formation/[2,3]-sigmatroptic rearrangement reactions (up to 91% yield), and intermolecular carbenoid insertion into N-H bonds of primary arylamines (up to 83% yield). This ruthenium glycosylated porphyrin complex can selectively catalyze alkylation of the N-terminus of peptides (8 examples) and mediate N-terminal modification of proteins (four examples) using a fluorescent-tethered diazo compound (15). A fluorescent group was conjugated to ubiquitin via 1-catalyzed alkene cyclopropanation with 15 in aqueous solution in two steps: (1) incorporation of an alkenic group by the reaction of N-hydroxysuccinimide ester 19 with ubiquitin and (2) cyclopropanation of the alkene-tethered Lys(6) ubiquitin (23) with the fluorescent-labeled diazoacetate 15 in the presence of a catalytic amount of 1. The corresponding cyclopropanation product (24) was obtained with approximately 55% conversion based on MALDI-TOF mass spectrometry. The products 23, 24, and the N-terminal modified peptides and proteins were characterized by LC-MS/MS and/or SDS-PAGE analyses. PMID:20088517

  18. Differential Quantum Tunneling Contributions in Nitroalkane Oxidase Catalyzed and the Uncatalyzed Proton Transfer Reaction

    SciTech Connect

    Major , D.; Heroux , A; Orville , A; Valley , M; Fitzpatrick , P; Gao , J

    2009-01-01

    The proton transfer reaction between the substrate nitroethane and Asp-402 catalyzed by nitroalkane oxidase and the uncatalyzed process in water have been investigated using a path-integral free-energy perturbation method. Although the dominating effect in rate acceleration by the enzyme is the lowering of the quasiclassical free energy barrier, nuclear quantum effects also contribute to catalysis in nitroalkane oxidase. In particular, the overall nuclear quantum effects have greater contributions to lowering the classical barrier in the enzyme, and there is a larger difference in quantum effects between proton and deuteron transfer for the enzymatic reaction than that in water. Both experiment and computation show that primary KIEs are enhanced in the enzyme, and the computed Swain-Schaad exponent for the enzymatic reaction is exacerbated relative to that in the absence of the enzyme. In addition, the computed tunneling transmission coefficient is approximately three times greater for the enzyme reaction than the uncatalyzed reaction, and the origin of the difference may be attributed to a narrowing effect in the effective potentials for tunneling in the enzyme than that in aqueous solution.

  19. Differential quantum tunneling contributions in nitroalkane oxidase catalyzed and the uncatalyzed proton transfer reaction.

    PubMed

    Major, Dan T; Heroux, Annie; Orville, Allen M; Valley, Michael P; Fitzpatrick, Paul F; Gao, Jiali

    2009-12-01

    The proton transfer reaction between the substrate nitroethane and Asp-402 catalyzed by nitroalkane oxidase and the uncatalyzed process in water have been investigated using a path-integral free-energy perturbation method. Although the dominating effect in rate acceleration by the enzyme is the lowering of the quasiclassical free energy barrier, nuclear quantum effects also contribute to catalysis in nitroalkane oxidase. In particular, the overall nuclear quantum effects have greater contributions to lowering the classical barrier in the enzyme, and there is a larger difference in quantum effects between proton and deuteron transfer for the enzymatic reaction than that in water. Both experiment and computation show that primary KIEs are enhanced in the enzyme, and the computed Swain-Schaad exponent for the enzymatic reaction is exacerbated relative to that in the absence of the enzyme. In addition, the computed tunneling transmission coefficient is approximately three times greater for the enzyme reaction than the uncatalyzed reaction, and the origin of the difference may be attributed to a narrowing effect in the effective potentials for tunneling in the enzyme than that in aqueous solution. PMID:19926855

  20. GALS - setup for production and study of multinucleon transfer reaction products: present status

    NASA Astrophysics Data System (ADS)

    Zemlyanoy, S.; Zagrebaev, V.; Kozulin, E.; Kudryavtsev, Yu; Fedosseev, V.; Bark, R.; Janas, Z.

    2016-06-01

    This is a brief report on the current status of the new GAs cell based Laser ionization Setup (GALS) at Flerov Laboratory for Nuclear Reactions (FLNR) - JINR, Dubna. GALS is planned to exploit available beams from the U-400M cyclotron in low energy multi-nucleon transfer reactions to study exotic neutron-rich nuclei located in the "north-east" region of nuclear map. Products from 4.5 to 9 MeV/nucleon heavy-ion collisions, such as 136Xe on 208Pb, are to be captured in a gas cell and selectively laser-ionized in a sextupole (quadrupole) ion guide extraction system.

  1. Experimental time scale of Gerischer's distribution curves for electron-transfer reactions at semiconductor electrodes

    SciTech Connect

    Willig, F.; Eichberger, R.; Sundaresan, N.S. ); Parkinson, B.A. )

    1990-03-28

    Fluorescence decay of adsorbed cresyl violet molecules was measured on n-SnS{sub 2} electrodes where their stationary photoelectrochemical current approached the yield of one electron per absorbed photon. At very low coverage, {theta} {approx} 10{sup {minus}2}, the fluorescence decay was faster than 10 ps and was identified with electron injection from excited dye monomers into the wide conduction band of the semiconductor. The reaction path was adiabatic or at least borderline to the adiabatic case. The measurement provides a time scale for Gerischer's distribution curves that are commonly applied in the discussion of electron-transfer reactions at electrodes.

  2. Production of new heavy isotopes in low-energy multinucleon transfer reactions.

    PubMed

    Zagrebaev, Valery; Greiner, Walter

    2008-09-19

    It is shown that the multinucleon transfer reactions in low-energy collisions of heavy ions may be used for production of new neutron-rich nuclei at the "northeast" part of the nuclear map along the neutron closed shell N=126 which plays an important role in the r process of nucleosynthesis. More than 50 unknown nuclei might be produced in such reactions (in particular, in collision of 136Xe with 208Pb) with cross sections of not less than 1 microb. PMID:18851367

  3. Analysis of the role of neutron transfer in asymmetric fusion reactions at subbarrier energies

    SciTech Connect

    Ogloblin, A. A.; Zhang, H. Q.; Lin, C. J.; Jia, H. M.; Khlebnikov, S. V.; Kuzmin, E. A.; Danilov, A. N.; Demyanova, A. S.; Trzaska, W. H.; Xu, X. X.; Yang, F.; Sargsyan, V. V. Adamian, G. G.; Antonenko, N. V.; Scheid, W.

    2015-12-15

    The excitation functions were measured for the {sup 28}Si + {sup 208}Pb complete-fusion (capture) reaction at deep subbarrier energies. The results were compared with the cross sections predicted within the quantum diffusion approach. The role of neutron transfer in the case of positive Q values in the {sup 28}Si + {sup 124}Sn, {sup 208}Pb; {sup 30}Si + {sup 124}Sn, {sup 208}Pb; {sup 20}Ne + {sup 208}Pb; {sup 40}Ca + {sup 96}Zr; and {sup 134}Te + {sup 40}Ca complete-fusion (capture) reactions is discussed.

  4. X-ray Crystal Structures Elucidate the Nucleotidyl Transfer Reaction of Transcript Initiation Using Two Nucleotides

    SciTech Connect

    M Gleghorn; E Davydova; R Basu; L Rothman-Denes; K Murakami

    2011-12-31

    We have determined the X-ray crystal structures of the pre- and postcatalytic forms of the initiation complex of bacteriophage N4 RNA polymerase that provide the complete set of atomic images depicting the process of transcript initiation by a single-subunit RNA polymerase. As observed during T7 RNA polymerase transcript elongation, substrate loading for the initiation process also drives a conformational change of the O helix, but only the correct base pairing between the +2 substrate and DNA base is able to complete the O-helix conformational transition. Substrate binding also facilitates catalytic metal binding that leads to alignment of the reactive groups of substrates for the nucleotidyl transfer reaction. Although all nucleic acid polymerases use two divalent metals for catalysis, they differ in the requirements and the timing of binding of each metal. In the case of bacteriophage RNA polymerase, we propose that catalytic metal binding is the last step before the nucleotidyl transfer reaction.

  5. Proton transfer reaction mass spectrometry: on-line trace gas analysis at the ppb level

    NASA Astrophysics Data System (ADS)

    Hansel, A.; Jordan, A.; Holzinger, R.; Prazeller, P.; Vogel, W.; Lindinger, W.

    1995-11-01

    A system for trace gas analysis using proton transfer reaction mass spectrometry (PTR-MS) has been developed which allows for on-line measurements of components with concentrations as low as 1 ppb. The method is based on reactions of H3O+ 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 analysis of breath taken from smokers and non-smokers as well as from patients suffering from cirrhosis of the liver, and of air in buildings as well as of ambient air taken at a road crossing demonstrate the wide range of applicability of this method. An enhanced level of acetonitrile in the breath is a most suitable indicator that a person is a smoker. Enhanced levels of propanol strongly indicate that a person has a severe liver deficiency.

  6. Room temperature, hybrid sodium-based flow batteries with multi-electron transfer redox reactions

    SciTech Connect

    Shamie, Jack S.; Liu, Caihong; Shaw, Leon L.; Sprenkle, Vincent L.

    2015-06-11

    We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volume of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multielectron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. Furthermore, the critical barriers to mature this new HNFBs have also been explored.

  7. Protein modifications affecting triplet energy transfer in bacterial photosynthetic reaction centers.

    SciTech Connect

    Laible, P. D.; Chynwat, V.; Thurnauer, M. C.; Schiffer, M.; Hanson, D. K.; Frank, H. A.; Univ.of Connecticut; Univ. of Connecticut

    1998-05-01

    The efficiency of triplet energy transfer from the special pair (P) to the carotenoid (C) in photosynthetic reaction centers (RCs) from a large family of mutant strains has been investigated. The mutants carry substitutions at positions L181 and/or M208 near chlorophyll-based cofactors on the inactive and active sides of the complex, respectively. Light-modulated electron paramagnetic resonance at 10 K, where triplet energy transfer is thermally prohibited, reveals that the mutations do not perturb the electronic distribution of P. At temperatures > or = 70 K, we observe reduced signals from the carotenoid in most of the RCs with L181 substitutions. In particular, triplet transfer efficiency is reduced in all RCs in which a lysine at L181 donates a sixth ligand to the monomeric bacteriochlorophyll B(B). Replacement of the native Tyr at M208 on the active side of the complex with several polar residues increased transfer efficiency. The difference in the efficiencies of transfer in the RCs demonstrates the ability of the protein environment to influence the electronic overlap of the chromophores and thus the thermal barrier for triplet energy transfer.

  8. Probing nucleon-nucleon correlations in heavy-ion transfer reactions

    NASA Astrophysics Data System (ADS)

    Szilner, S.

    2016-05-01

    The γ-particle coincident measurements, performed by coupling of the PRISMA spectrometer to the large γ arrays (CLARA and AGATA), demonstrate a strong interplay between single-particle and collective degrees of freedom that is pertinent to the reaction dynamics. By using the unique PRISMA performance in terms of both resolution and efficiency, measurements at very low bombarding energies have been performed. Via transfer of nucleon pairs, valuable information on the component responsible for particle correlations has been derived.

  9. Lubricity characteristics of seed oils modified by acylation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Chemically modified seed oils via acylation of epoxidized and polyhydroxylated derivatives were investigated for their potential as candidates for lubrication. The native oil was preliminarily epoxidized and ring-opened in a one-pot reaction using formic acid-H2O2 followed by aqueous HCl treatment t...

  10. The 2.1Å Crystal Structure of an Acyl-CoA Synthetase from Methanosarcina acetivorans reveals an alternate acyl binding pocket for small branched acyl substrates†,‡

    PubMed Central

    Shah, Manish B.; Ingram-Smith, Cheryl; Cooper, Leroy L.; Qu, Jun; Meng, Yu; Smith, Kerry S.; Gulick, Andrew M.

    2009-01-01

    The acyl-AMP forming family of adenylating enzymes catalyze two-step reactions to activate a carboxylate with the chemical energy derived from ATP hydrolysis. X-ray crystal structures have been determined for multiple members of this family and, together with biochemical studies, provide insights into the active site and catalytic mechanisms used by these enzymes. These studies have shown that the enzymes use a domain rotation of 140° to reconfigure a single active site to catalyze the two partial reactions. We present here the crystal structure of a new medium chain acyl-CoA synthetase from Methanosarcina acetivorans. The binding pocket for the three substrates is analyzed, with many conserved residues present in the AMP binding pocket. The CoA binding pocket is compared to the pockets of both acetyl-CoA synthetase and 4-chlorobenzoate:CoA ligase. Most interestingly, the acyl binding pocket of the new structure is compared with other acyl- and aryl-CoA synthetases. A comparison of the acyl-binding pocket of the acyl-CoA synthetase from M. acetivorans with other structures identifies a shallow pocket that is used to bind the medium chain carboxylates. These insights emphasize the high sequence and structural diversity among this family in the area of the acyl binding pocket. PMID:19544569

  11. Electron transfer in reactions of ketones with organolithium reagents. A carbon-14 kinetic isotope effect probe

    SciTech Connect

    Yamataka, H.; Fujimura, N.; Kawafuji, Y.; Hanafusa, T.

    1987-07-08

    Kinetic isotope effects have been determined for reactions of ketones labeled with carbon-14 at the carbonyl carbon with MeLi and Me/sub 2/CuLi in diethyl ether at 0/sup 0/C. Observed isotope effects were as follows: (C/sub 6/H/sub 5/)/sub 2/C double bonds O + MeLi, /sup 12/k//sup 14/k = 1.000 +/- 0.002; (C/sub 6/H/sub 5/)/sub 2/C double bonds O + Me/sub 2/CuLi, 1.029 +/- 0.005; 2,4,6-Me/sub 3/C/sub 6/H/sub 2/COC/sub 6/H/sub 5/ + MeLi, 1.023 +/- 0.004. The relative reactivities of ortho-, meta-, and para-substituted benzophenones with these reagents were also determined by the competition experiments. These results are consistent with an electron-transfer step which is followed by a carbon-carbon bond-forming step that is or is not rate determining depending on the structure of ketones and reagents. The reaction of benzophenone with MeLi proceeds via rate-determining electron transfer; the change in nucleophile from MeLi to Me/sub 2/CuLi shifts the rate-determining step from electron transfer to recombination; the change in ketone from benzophenone to 2,4,6-trimethylbenzophenone also shifts the rate-determining step from electron transfer to recombination because the latter step becomes slower for the more hindered ketone. The extent of the geometrical change of the substrate at the electron-transfer transition state of the reaction of benzophenone with MeLi was estimated to be small on the basis of the magnitude of the KIE and the rho value of the Hammett correlation.

  12. Spectroscopy of 46Ar by the (t ,p ) two-neutron transfer reaction

    NASA Astrophysics Data System (ADS)

    Nowak, K.; Wimmer, K.; Hellgartner, S.; Mücher, D.; Bildstein, V.; Diriken, J.; Elseviers, J.; Gaffney, L. P.; Gernhäuser, R.; Iwanicki, J.; Johansen, J. G.; Huyse, M.; Konki, J.; Kröll, T.; Krücken, R.; Lutter, R.; Orlandi, R.; Pakarinen, J.; Raabe, R.; Reiter, P.; Roger, T.; Schrieder, G.; Seidlitz, M.; Sorlin, O.; Van Duppen, P.; Warr, N.; De Witte, H.; Zielińska, M.

    2016-04-01

    States in the N =28 nucleus 46Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive 44Ar at an energy of 2.16 AMeV and a tritium-loaded titanium target were used to populate 46Ar by the 3H(44Ar,p ) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in 46Ar have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695 keV was identified as Jπ=0+ . The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell-model calculations using state-of-the-art effective interactions.

  13. Electrocatalysis of anodic oxygen-transfer reactions at modified lead dioxide electrodes

    SciTech Connect

    Hsiao, Yun-Lin.

    1990-09-21

    The electrocatalytic activities were compared for pure and chloride-doped beta-PbO{sub 2} (Cl-PbO{sub 2}) films on gold and platinum substrates. Rate constants were increased significantly for oxidations of Mn{sup 2+}, toluene, benzyl alcohol, dimethylsulphoxide (DMSO) and benzaldehyde in acidic media by the incorporation of Cl{sup {minus}} into the oxide films. These reactions are concluded to occur by the electrocatalytic transfer of oxygen from H{sub 2}O to the reaction products. Results of x-ray diffraction studies indicate the Cl-PbO{sub 2} film continues to have the slightly distorted rutile structure of pure beta-PbO{sub 2}. The observed electrocatalytic phenomena are concluded to be the beneficial consequence of surface defects generated when Cl{sup {minus}} serves for charge compensation within the surface matrix and, thereby, increases the number of surface sites capable of adsorbing hydroxyl radicals which are transferred in the electrocatalytic O-transfer reactions. 91 refs., 44 figs., 10 tabs.

  14. Proton Coupled Electron Transfer Reactions at the Surface of Metal Oxide Nanomaterials

    NASA Astrophysics Data System (ADS)

    Braten, Miles N.

    Nanostructured metal oxide materials are found in many products and processes in our society today, but they play a particularly important role in the conversion and storage of energy. The materials are used as catalysts and redox active supports in devices such as dye sensitized solar cells, solid oxide fuel cells, and flow batteries, where they transfer and store electrons and charge balancing cations. Oftentimes electron transfer is modulated by the cations and when the cation is a proton, these redox reactions are known as proton coupled electron transfer (PCET) reactions. The work described in this dissertation focuses on understanding the PCET reactivity of nanocrystalline metal oxide materials. Chapter 1 introduces the concept of PCET and provides background information on the zinc oxide (ZnO) nanocrystals (NCs) which the majority of the research is focused on. Chapter 2 examines the chemistry that occurs during the photoreduction of ZnO NCs. Chapter 3 describes experiments probing how ZnO NC capping ligand concentration and NC size modulate PCET reaction rates. Chapter 4 describes experiments that compare the PCET reactivity of ZnO NCs with different numbers of electrons and protons stored on them. Chapter 5 describes attempts to observe the electrochemical reduction of ZnO NCs attached to gold electrodes. Finally, Chapter 6 contains attempts to identify a nanostructured metal oxide alkane oxidation catalyst for use in fuel cell.

  15. Stagnation Point Flow and Mass Transfer with Chemical Reaction past a Stretching/Shrinking Cylinder

    PubMed Central

    Najib, Najwa; Bachok, Norfifah; Arifin, Norihan Md.; Ishak, Anuar

    2014-01-01

    This paper is about the stagnation point flow and mass transfer with chemical reaction past a stretching/shrinking cylinder. The governing partial differential equations in cylindrical form are transformed into ordinary differential equations by a similarity transformation. The transformed equations are solved numerically using a shooting method. Results for the skin friction coefficient, Schmidt number, velocity profiles as well as concentration profiles are presented for different values of the governing parameters. Effects of the curvature parameter, stretching/shrinking parameter and Schmidt number on the flow and mass transfer characteristics are examined. The study indicates that dual solutions exist for the shrinking cylinder but for the stretching cylinder, the solution is unique. It is observed that the surface shear stress and the mass transfer rate at the surface increase as the curvature parameter increases. PMID:24569547

  16. Regioselective Acylation of Diols and Triols: The Cyanide Effect.

    PubMed

    Peng, Peng; Linseis, Michael; Winter, Rainer F; Schmidt, Richard R

    2016-05-11

    Central topics of carbohydrate chemistry embrace structural modifications of carbohydrates and oligosaccharide synthesis. Both require regioselectively protected building blocks that are mainly available via indirect multistep procedures. Hence, direct protection methods targeting a specific hydroxy group are demanded. Dual hydrogen bonding will eventually differentiate between differently positioned hydroxy groups. As cyanide is capable of various kinds of hydrogen bonding and as it is a quite strong sterically nondemanding base, regioselective O-acylations should be possible at low temperatures even at sterically congested positions, thus permitting formation and also isolation of the kinetic product. Indeed, 1,2-cis-diols, having an equatorial and an axial hydroxy group, benzoyl cyanide or acetyl cyanide as an acylating agent, and DMAP as a catalyst yield at -78 °C the thermodynamically unfavorable axial O-acylation product; acyl migration is not observed under these conditions. This phenomenon was substantiated with 3,4-O-unproteced galacto- and fucopyranosides and 2,3-O-unprotected mannopyranosides. Even for 3,4,6-O-unprotected galactopyranosides as triols, axial 4-O-acylation is appreciably faster than O-acylation of the primary 6-hydroxy group. The importance of hydrogen bonding for this unusual regioselectivity could be confirmed by NMR studies and DFT calculations, which indicate favorable hydrogen bonding of cyanide to the most acidic axial hydroxy group supported by hydrogen bonding of the equatorial hydroxy group to the axial oxygen. Thus, the "cyanide effect" is due to dual hydrogen bonding of the axial hydroxy group which enhances the nucleophilicity of the respective oxygen atom, permitting an even faster reaction for diols than for mono-ols. In contrast, fluoride as a counterion favors dual hydrogen bonding to both hydroxy groups leading to equatorial O-acylation. PMID:27104625

  17. A computational study of the phosphoryl transfer reaction between ATP and Dha in aqueous solution.

    PubMed

    Bordes, I; Ruiz-Pernía, J J; Castillo, R; Moliner, V

    2015-10-28

    Phosphoryl transfer reactions are ubiquitous in biology, being involved in processes ranging from energy and signal transduction to the replication genetic material. Dihydroxyacetone phosphate (Dha-P), an intermediate of the synthesis of pyruvate and a very important building block in nature, can be generated by converting free dihydroxyacetone (Dha) through the action of the dihydroxyacetone kinase enzyme. In this paper the reference uncatalyzed reaction in solution has been studied in order to define the foundations of the chemical reaction and to determine the most adequate computational method to describe this electronically complex reaction. In particular, the phosphorylation reaction mechanism between adenosine triphosphate (ATP) and Dha in aqueous solution has been studied by means of quantum mechanics/molecular mechanics (QM/MM) Molecular Dynamics (MD) simulations with the QM subset of atoms described with semi-empirical and DFT methods. The results appear to be strongly dependent on the level of calculation, which will have to be taken into account for future studies of the reaction catalyzed by enzymes. In particular, PM3/MM renders lower free energy barriers and a less endergonic process than AM1d/MM and PM6/MM methods. Nevertheless, the concerted pathway was not located with the former combination of potentials. PMID:26303076

  18. Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.; Salter, Latasha M.; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

  19. Effect of friction on electron transfer: The two reaction coordinate case

    NASA Astrophysics Data System (ADS)

    Onuchic, José Nelson

    1987-04-01

    Electron transfer is a very important reaction in many biological processes such as photosynthesis and oxidative phosphorylation. In many of these reactions, most of the interesting dynamics can be included by using two reaction coordinates: one fast (local high frequency vibration modes) and one slow (outersphere modes such as solvent polarization). We report a model to describe this problem, which uses path integral techniques to calculate electron transfer rates, and also to obtain the Fokker-Planck equations associated with this model. Different limiting cases lead to qualitatively different results such as exponential or nonexponential time decay for the donor survival probability. Conditions for the validity of the adiabatic or the nonadiabatic limits will be discussed. Application of this model to real systems is proposed, in particular for a porphyrin rigidly linked to a quinone, which is a very interesting model compound for primary events of photosynthesis. This model can also be used for other multicoordinate biological reactions such as ligand binding to heme proteins. Also, in the concluding part of Sec. III, we discuss the important limit where the fast vibronic mode is much faster than all the other nuclear modes coupled to the problem. In this limit the fast mode ``renormalizes'' the electronic matrix element, and this considerably simplifies the treatment of the problem, reducing it to coupling only to the slow modes.

  20. Dynamics of the F(-) + CH3I → HF + CH2I(-) Proton Transfer Reaction.

    PubMed

    Zhang, Jiaxu; Xie, Jing; Hase, William L

    2015-12-17

    Direct chemical dynamics simulations, at collision energies Erel of 0.32 and 1.53 eV, were performed to obtain an atomistic understanding of the F(-) + CH3I reaction dynamics. There is only the F(-) + CH3I → CH3F + I(-) bimolecular nucleophilic substitution SN2 product channel at 0.32 eV. Increasing Erel to 1.53 eV opens the endothermic F(-) + CH3I → HF + CH2I(-) proton transfer reaction, which is less competitive than the SN2 reaction. The simulations reveal proton transfer occurs by two direct atomic-level mechanisms, rebound and stripping, and indirect mechanisms, involving formation of the F(-)···HCH2I complex and the roundabout. For the indirect trajectories all of the CH2I(-) is formed with zero-point energy (ZPE), while for the direct trajectories 50% form CH2I(-) without ZPE. Without a ZPE constraint for CH2I(-), the reaction cross sections for the rebound, stripping, and indirect mechanisms are 0.2 ± 0.1, 1.2 ± 0.4, and 0.7 ± 0.2 Å(2), respectively. Discarding trajectories that do not form CH2I(-) with ZPE reduces the rebound and stripping cross sections to 0.1 ± 0.1 and 0.7 ± 0.5 Å(2). The HF product is formed rotationally and vibrationally unexcited. The average value of J is 2.6 and with histogram binning n = 0. CH2I(-) is formed rotationally excited. The partitioning between CH2I(-) vibration and HF + CH2I(-) relative translation energy depends on the treatment of CH2I(-) ZPE. Without a CH2I(-) ZPE constraint the energy partitioning is primarily to relative translation with little CH2I(-) vibration. With a ZPE constraint, energy partitioning to CH2I(-) rotation, CH2I(-) vibration, and relative translation are statistically the same. The overall F(-) + CH3I rate constant at Erel of both 0.32 and 1.53 eV is in good agreement with experiment and negligibly affected by the treatment of CH2I(-) ZPE, since the SN2 reaction is the major contributor to the total reaction rate constant. The potential energy surface and reaction dynamics for F

  1. First proton transfer reaction to study 18F+p resonances of novae interest

    SciTech Connect

    Adekola, Aderemi S; Bardayan, Daniel W; Blackmon, Jeff C; Brune, C.; Chae, K. Y.; Domizioli, Carlo P; Greife, U.; Heinen, Z.; Hornish, M.; Jones, K. L.; Kozub, R. L.; Livesay, Jake; Ma, Zhanwen; Massey, T.; Moazen, Brian; Nesaraja, Caroline D; Pain, S. D.; ShrinerJr., J. F.; Smith, Nathan A; Smith, Michael Scott; Thomas, J. S.; Visser, D. W.; Voinov, A.

    2011-01-01

    The 18F(p,a)15O reaction is recognized as the predominant destruction mechanism of 18F in novae, and its rate is therefore important for understanding 18F production in nova outbursts. We have studied the properties of resonances in the 18F + p system using the proton-transfer reaction 18F(d, n) for the first time. We have observed fifteen 19Ne levels, five of which are below the proton threshold, including a subthreshold state at Ex = 6.289 MeV which has significant lp = 0 strength. The proton asymptotic normalization coefficient for this state and proton widths of states above the proton threshold, are extracted from angular distributions. The 18F(p,a)15O S-factor and reaction rate are re-evaluated, taking into account the subthreshold resonance and other new information determined in this experiment.

  2. Free energy, entropy and volume of activation for electron transfer reactions in a polar solvent

    SciTech Connect

    Manjari, Swati R.; Kim, Hyung J.

    2006-07-07

    A continuum theory with account of cavity size fluctuations is employed to study free energy, volume and entropy of activation for nonadiabatic electron transfer (ET) reactions in polar solvents. By using a two-sphere cavity description, model calculations are performed for charge separation and recombination processes in acetonitrile under ambient conditions. It is found that the cavity size at the transition state varies with the free energy of reaction as well as with the thermodynamic conditions. In contrast to the Marcus theory predictions, the volume and entropy of activation show a monotonic behavior with the free energy of reaction and a strong correlation with each other. For example, for a given ET process, the volume and entropy of activation have the same sign. Their values for the charge separation and recombination processes are opposite in sign. These findings are in good qualitative agreement with measurements.

  3. Proton transfer reactions between nitric acid and acetone, hydroxyacetone, acetaldehyde and benzaldehyde in the solid phase.

    PubMed

    Lasne, Jérôme; Laffon, Carine; Parent, Philippe

    2012-12-01

    The heterogeneous and homogeneous reactions of acetone, hydroxyacetone, acetaldehyde and benzaldehyde with solid nitric acid (HNO(3)) films have been studied with Reflection-Absorption Infrared Spectroscopy (RAIRS) under Ultra-High Vacuum (UHV) conditions in the 90-170 K temperature range. In the bulk or at the surface of the films, nitric acid transfers its proton to the carbonyl function of the organic molecules, producing protonated acetone-H(+), hydroxyacetone-H(+), acetaldehyde-H(+) and benzaldehyde-H(+), and nitrate anions NO(3)(-), a reaction not observed when nitric acid is previously hydrated [J. Lasne, C. Laffon and Ph. Parent, Phys. Chem. Chem. Phys., 2012, 14, 697]. This provides a molecular-scale description of the carbonyl protonation reaction in an acid medium, the first step of the acid-catalyzed condensation of carbonyl compounds, fuelling the growth of secondary organic aerosols (SOA) in the atmosphere. PMID:23090634

  4. The 9Be(8Li,9Be)8Li elastic-transfer reaction

    NASA Astrophysics Data System (ADS)

    Camargo, O.; Guimarães, V.; Lichtenthäler, R.; Scarduelli, V.; Kolata, J. J.; Bertulani, C. A.; Amro, H.; Becchetti, F. D.; Jiang, Hao; Aguilera, E. F.; Lizcano, D.; Martinez-Quiroz, E.; Garcia, H.

    2008-09-01

    Angular distributions for the 9Be(8Li,9Be)8Li elastic-transfer reaction have been measured with a 27-MeV Li8 radioactive nuclear beam. Spectroscopic factors for the <9Be|8Li+p> bound system were obtained from the comparison between the experimental differential cross sections and finite-range distorted-wave Born approximation calculations made with the code FRESCO. The spectroscopic factors so obtained are compared with shell-model calculations and other experimental values. Using the present value for the spectroscopic factors, cross sections and reaction rates for the 8Li(p,γ)9Be direct proton-capture reaction of astrophysical interest were calculated in the framework of the potential model.

  5. Proton and charge transfer reactions dynamics of a hydroxyflavone derivative in a polar solvent and in a cyclodextrin nanocavity

    NASA Astrophysics Data System (ADS)

    Sanz, M.; Organero, J. A.; Douhal, A.

    2007-09-01

    In this work, we report on the observation of ultrafast intramolecular charge- and proton-transfer reactions of 4'-dimethylaminoflavonol (DMAF) in N, N-dimethyl formamide and in γ-cyclodextrin (γ-CD) solution. Upon femtosecond excitation an intramolecular charge transfer (ICT) reaction takes place to produce an ICT structure in ˜200 fs. This structure may undergo a proton transfer reaction to generate a zwitterionic (Z) form in 2-3 ps, or relaxes in its potential energy well, to later equilibrate with that of Z in hundreds of ps. Addition of γ-CD does not significantly affect the fast dynamics of the formed anion. The fs-emission signals of the parent molecule, 3-hydroxyflavone, indicate that the dimethyl amino group in DMAF enhances the rate constant of intermolecular proton-transfer and intramolecular charge-transfer reactions.

  6. Quasielastic transfer in the {sup 136}Xe+{sup 64}Ni reaction

    SciTech Connect

    Sanders, S.J.; Dummer, A.K.; Farrar, K.A.; Prosser, F.W.; Fornal, B. |; Janssens, R.V.; Carpenter, M.P.; Khoo, T.L.; Beck, C.; Mahboub, D.; Haas, F.; Sferrazza, M.; Mayer, R.; Nisius, D.; de Angelis, G.

    1997-05-01

    Single and multinucleon transfer yields for the {sup 136}Xe+{sup 64}Ni reaction at a scattering energy {approx}5{percent} above the Coulomb barrier energy are studied using particle{endash}{gamma}-ray coincidence data. Q-value and scattering-angle distributions are extracted for the stronger channels. A fast transfer mechanism dominates the yields to these channels over an extended Q-value range, leading to a concentration of the cross section near the grazing angle. Analysis of the angular distributions based on a semiclassical barrier penetration model suggests that the single-nucleon and two-neutron exchange channels are dominated, respectively, by direct and two-step sequential transfer from the ground or low-lying excited states of the participating nuclei. The multiproton transfer channels have angular distributions that indicate a more complex mechanism, although direct cluster transfer from an excited configuration cannot be fully discounted. In a separate analysis, the relative population of different mass channels is found to be in general agreement with the expectations of a {open_quotes}random walk{close_quotes} model of particle exchange. {copyright} {ital 1997} {ital The American Physical Society}

  7. pH-dependent electron transfer reaction and direct bioelectrocatalysis of the quinohemoprotein pyranose dehydrogenase.

    PubMed

    Takeda, Kouta; Matsumura, Hirotoshi; Ishida, Takuya; Yoshida, Makoto; Igarashi, Kiyohiko; Samejima, Masahiro; Ohno, Hiroyuki; Nakamura, Nobuhumi

    2016-08-26

    A pyranose dehydrogenase from Coprinopsis cinerea (CcPDH) is an extracellular quinohemoeprotein, which consists a b-type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of CcPDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c) reacted via the cytochrome domain of intact CcPDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of CcPDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron to a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of l-fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of CcPDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. PMID:27338639

  8. Regioselective self-acylating cyclodextrins in organic solvent

    PubMed Central

    Cho, Eunae; Yun, Deokgyu; Jeong, Daham; Im, Jieun; Kim, Hyunki; Dindulkar, Someshwar D.; Choi, Youngjin; Jung, Seunho

    2016-01-01

    Amphiphilic cyclodextrins have been synthesized with self-acylating reaction using vinyl esters in dimethylformamide. In the present study no base, catalyst, or enzyme was used, and the structural analyses using thin layer chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry show that the cyclodextrin is substituted preferentially by one acyl moiety at the C2 position of the glucose unit, suggesting that cyclodextrin functions as a regioselective catalytic carbohydrate in organic solvent. In the self-acylation, the most acidic OH group at the 2-position and the inclusion complexing ability of cyclodextrin were considered to be significant. The substrate preference was also observed in favor of the long-chain acyl group, which could be attributed to the inclusion ability of cyclodextrin cavity. Furthermore, using the model amphiphilic building block, 2-O-mono-lauryl β-cyclodextrin, the self-organized supramolecular architecture with nano-vesicular morphology in water was investigated by fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. The cavity-type nano-assembled vesicle and the novel synthetic methods for the preparation of mono-acylated cyclodextrin should be of great interest with regard to drug/gene delivery systems, functional surfactants, and carbohydrate derivatization methods. PMID:27020946

  9. Regioselective self-acylating cyclodextrins in organic solvent.

    PubMed

    Cho, Eunae; Yun, Deokgyu; Jeong, Daham; Im, Jieun; Kim, Hyunki; Dindulkar, Someshwar D; Choi, Youngjin; Jung, Seunho

    2016-01-01

    Amphiphilic cyclodextrins have been synthesized with self-acylating reaction using vinyl esters in dimethylformamide. In the present study no base, catalyst, or enzyme was used, and the structural analyses using thin layer chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry show that the cyclodextrin is substituted preferentially by one acyl moiety at the C2 position of the glucose unit, suggesting that cyclodextrin functions as a regioselective catalytic carbohydrate in organic solvent. In the self-acylation, the most acidic OH group at the 2-position and the inclusion complexing ability of cyclodextrin were considered to be significant. The substrate preference was also observed in favor of the long-chain acyl group, which could be attributed to the inclusion ability of cyclodextrin cavity. Furthermore, using the model amphiphilic building block, 2-O-mono-lauryl β-cyclodextrin, the self-organized supramolecular architecture with nano-vesicular morphology in water was investigated by fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. The cavity-type nano-assembled vesicle and the novel synthetic methods for the preparation of mono-acylated cyclodextrin should be of great interest with regard to drug/gene delivery systems, functional surfactants, and carbohydrate derivatization methods. PMID:27020946

  10. Regioselective self-acylating cyclodextrins in organic solvent

    NASA Astrophysics Data System (ADS)

    Cho, Eunae; Yun, Deokgyu; Jeong, Daham; Im, Jieun; Kim, Hyunki; Dindulkar, Someshwar D.; Choi, Youngjin; Jung, Seunho

    2016-03-01

    Amphiphilic cyclodextrins have been synthesized with self-acylating reaction using vinyl esters in dimethylformamide. In the present study no base, catalyst, or enzyme was used, and the structural analyses using thin layer chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry show that the cyclodextrin is substituted preferentially by one acyl moiety at the C2 position of the glucose unit, suggesting that cyclodextrin functions as a regioselective catalytic carbohydrate in organic solvent. In the self-acylation, the most acidic OH group at the 2-position and the inclusion complexing ability of cyclodextrin were considered to be significant. The substrate preference was also observed in favor of the long-chain acyl group, which could be attributed to the inclusion ability of cyclodextrin cavity. Furthermore, using the model amphiphilic building block, 2-O-mono-lauryl β-cyclodextrin, the self-organized supramolecular architecture with nano-vesicular morphology in water was investigated by fluorescence spectroscopy, dynamic light scattering and transmission electron microscopy. The cavity-type nano-assembled vesicle and the novel synthetic methods for the preparation of mono-acylated cyclodextrin should be of great interest with regard to drug/gene delivery systems, functional surfactants, and carbohydrate derivatization methods.

  11. Theoretical study of chain transfer to solvent reactions of alkyl acrylates.

    PubMed

    Moghadam, Nazanin; Srinivasan, Sriraj; Grady, Michael C; Rappe, Andrew M; Soroush, Masoud

    2014-07-24

    This computational and theoretical study deals with chain transfer to solvent (CTS) reactions of methyl acrylate (MA), ethyl acrylate (EA), and n-butyl acrylate (n-BA) self-initiated homopolymerization in solvents such as butanol (polar, protic), methyl ethyl ketone (MEK) (polar, aprotic), and p-xylene (nonpolar). The results indicate that abstraction of a hydrogen atom from the methylene group next to the oxygen atom in n-butanol, from the methylene group in MEK, and from a methyl group in p-xylene by a live polymer chain are the most likely mechanisms of CTS reactions in MA, EA, and n-BA. Energy barriers and molecular geometries of reactants, products, and transition states are predicted. The sensitivity of the predictions to three hybrid functionals (B3LYP, X3LYP, and M06-2X) and three different basis sets (6-31G(d,p), 6-311G(d), and 6-311G(d,p)) is investigated. Among n-butanol, sec-butanol, and tert-butanol, tert-butanol has the highest CTS energy barrier and the lowest rate constant. Although the application of the conductor-like screening model (COSMO) does not affect the predicted CTS kinetic parameter values, the application of the polarizable continuum model (PCM) results in higher CTS energy barriers. This increase in the predicted CTS energy barriers is larger for butanol and MEK than for p-xylene. The higher rate constants of chain transfer to n-butanol reactions compared to those of chain transfer to MEK and p-xylene reactions suggest the higher CTS reactivity of n-butanol. PMID:24971646

  12. In Situ Catalyst Modification in Atom Transfer Radical Reactions with Ruthenium Benzylidene Complexes.

    PubMed

    Lee, Juneyoung; Grandner, Jessica M; Engle, Keary M; Houk, K N; Grubbs, Robert H

    2016-06-01

    Ruthenium benzylidene complexes are well-known as olefin metathesis catalysts. Several reports have demonstrated the ability of these catalysts to also facilitate atom transfer radical (ATR) reactions, such as atom transfer radical addition (ATRA) and atom transfer radical polymerization (ATRP). However, while the mechanism of olefin metathesis with ruthenium benzylidenes has been well-studied, the mechanism by which ruthenium benzylidenes promote ATR reactions remains unknown. To probe this question, we have analyzed seven different ruthenium benzylidene complexes for ATR reactivity. Kinetic studies by (1)H NMR revealed that ruthenium benzylidene complexes are rapidly converted into new ATRA-active, metathesis-inactive species under typical ATRA conditions. When ruthenium benzylidene complexes were activated prior to substrate addition, the resulting activated species exhibited enhanced kinetic reactivity in ATRA with no significant difference in overall product yield compared to the original complexes. Even at low temperature, where the original intact complexes did not catalyze the reaction, preactivated catalysts successfully reacted. Only the ruthenium benzylidene complexes that could be rapidly transformed into ATRA-active species could successfully catalyze ATRP, whereas other complexes preferred redox-initiated free radical polymerization. Kinetic measurements along with additional mechanistic and computational studies show that a metathesis-inactive ruthenium species, generated in situ from the ruthenium benzylidene complexes, is the active catalyst in ATR reactions. Based on data from (1) H, (13)C, and (31)P NMR spectroscopy and X-ray crystallography, we suspect that this ATRA-active species is a RuxCly(PCy3)z complex. PMID:27186790

  13. Prediction of Kinetic Isotope Effects for Various Hydride Transfer Reactions Using a New Kinetic Model.

    PubMed

    Shen, Guang-Bin; Xia, Ke; Li, Xiu-Tao; Li, Jun-Ling; Fu, Yan-Hua; Yuan, Lin; Zhu, Xiao-Qing

    2016-03-24

    In this work, kinetic isotope effect (KIEself) values of 68 hydride self-exchange reactions, XH(D) + X(+) → X(+) + XH(D), in acetonitrile at 298 K were determined using a new experimental method. KIE values of 4556 hydride cross transfer reactions, XH(D) + Y(+) → X(+) + YH(D), in acetonitrile were estimated from the 68 determined KIEself values of hydride self-exchange reactions using a new KIE relation formula derived from Zhu's kinetic equation and the reliability of the estimations was verified using different experimental methods. A new KIE kinetic model to explain and predict KIE values was developed according to Zhu's kinetic model using two different Morse free energy curves instead of one Morse free energy curve in the traditional KIE theories to describe the free energy changes of X-H bond and X-D bond dissociation in chemical reactions. The most significant contribution of this paper to KIE theory is to build a new KIE kinetic model, which can be used to not only uniformly explain the various (normal, enormous and inverse) KIE values but also safely prodict KIE values of various chemical reactions. PMID:26938149

  14. Metal ion-catalyzed cycloaddition vs hydride transfer reactions of NADH analogues with p-benzoquinones.

    PubMed

    Fukuzumi, S; Fujii, Y; Suenobu, T

    2001-10-24

    1-Benzyl-4-tert-butyl-1,4-dihydronicotinamide (t-BuBNAH) reacts efficiently with p-benzoquinone (Q) to yield a [2+3] cycloadduct (1) in the presence of Sc(OTf)(3) (OTf = OSO(2)CF(3)) in deaerated acetonitrile (MeCN) at room temperature, while no reaction occurs in the absence of Sc(3+). The crystal structure of 1 has been determined by the X-ray crystal analysis. When t-BuBNAH is replaced by 1-benzyl-1,4-dihydronicotinamide (BNAH), the Sc(3+)-catalyzed cycloaddition reaction of BNAH with Q also occurs to yield the [2+3] cycloadduct. Sc(3+) forms 1:4 complexes with t-BuBNAH and BNAH in MeCN, whereas there is no interaction between Sc(3+) and Q. The observed second-order rate constant (k(obs)) shows a first-order dependence on [Sc(3+)] at low concentrations and a second-order dependence at higher concentrations. The first-order and the second-order dependence of the rate constant (k(et)) on [Sc(3+)] was also observed for the Sc(3+)-promoted electron transfer from CoTPP (TPP = tetraphenylporphyrin dianion) to Q. Such dependence of k(et) on [Sc(3+)] is ascribed to formation of 1:1 and 1:2 complexes between Q(*)(-) and Sc(3+) at the low and high concentrations of Sc(3+), respectively, which results in acceleration of the rate of electron transfer. The formation constants for the 1:2 complex (K(2)) between the radical anions of a series of p-benzoquinone derivatives (X-Q(*)(-)) and Sc(3+) are determined from the dependence of k(et) on [Sc(3+)]. The K(2) values agree well with those determined from the dependence of k(obs) on [Sc(3+)] for the Sc(3+)-catalyzed addition reaction of t-BuBNAH and BNAH with X-Q. Such an agreement together with the absence of the deuterium kinetic isotope effects indicates that the addition proceeds via the Sc(3+)-promoted electron transfer from t-BuBNAH and BNAH to Q. When Sc(OTf)(3) is replaced by weaker Lewis acids such as Lu(OTf)(3), Y(OTf)(3), and Mg(ClO(4))(2), the hydride transfer reaction from BNAH to Q also occurs besides the

  15. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation

    SciTech Connect

    Schwartz, B.J.

    1992-11-01

    The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured and effects of external hydrogen-bonding interactions on the proton transfer are studied. The proton transfer takes place in {approximately}240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH{sub 2}I{sub 2} and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a {approximately}350 fsec time scale. Results show that recombination yields but not rates depend on the solvent environment and suggest that recombination kinetics are dominated by a single collision with surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. Data show no simple correlation between hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes, implying that the isomerization does not provide a suitable for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial steps of the photochromic reaction process occur extremely rapidly. Laser system and computer codes for data analysis are discussed.

  16. Excited state structural evolution during charge-transfer reactions in betaine-30.

    PubMed

    Ruchira Silva, W; Frontiera, Renee R

    2016-07-27

    Ultrafast photo-induced charge-transfer reactions are fundamental to a number of photovoltaic and photocatalytic devices, yet the multidimensional nature of the reaction coordinate makes these processes difficult to model theoretically. Here we use femtosecond stimulated Raman spectroscopy to probe experimentally the structural changes occurring following photoexcitation in betaine-30, a canonical intramolecular charge-transfer complex. We observe changes in vibrational mode frequencies and amplitudes on the femtosecond timescale, which for some modes results in frequency shifts of over 20 cm(-1) during the first 200 fs following photoexcitation. These rapid mode-specific frequency changes track the planarization of the molecule on the 400 ± 100 fs timescale. Oscillatory amplitude modulations of the observed high frequency Raman modes indicate coupling between specific high frequency and low frequency vibrational motions, which we quantify for 6 low frequency modes and 4 high frequency modes. Analysis of the mode-specific kinetics is suggestive of the existence of a newly discovered electronic state involved in a relaxation pathway, which may be a low-lying triplet state. These results directly track the multiple nuclear coordinates involved in betaine-30's reactive pathway, and should be of use in rationally designing molecular systems with rapid electron transfer processes. PMID:26725657

  17. Bimolecular electron transfer reactions in coumarin amine systems: Donor acceptor orientational effect on diffusion-controlled reaction rates

    NASA Astrophysics Data System (ADS)

    Satpati, A. K.; Nath, S.; Kumbhakar, M.; Maity, D. K.; Senthilkumar, S.; Pal, H.

    2008-04-01

    Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants ( kq) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating kq values with the free energy changes (Δ G0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where kq increases with -Δ G0 at the lower exergonicity (-Δ G0) region but ultimately saturate to a diffusion-limited value (kqDC) at the higher exergonicity region. It is, however, interestingly observed that the kqDC values vary largely depending on the type of the amines used. Thus, kqDC is much higher with ArAs than AlAs. Similarly, the kqDC for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the kqDC value obtained for other noncyclic AlAs. These differences in the kqDC values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the π-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the kqDC values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of

  18. Charge transfer reaction of multi-charged oxygen ions with O2

    NASA Astrophysics Data System (ADS)

    Holzscheiter, H. M.; Church, D. A.

    1981-10-01

    The reaction rates for charge transfer from O2 to doubly and triply charged oxygen atoms are measured in a demonstration of the measurement capabilities of a system at ultrahigh vacuum with low-energy magnetically confined ions. Ions were produced by electron impact ionization of gas within a Penning-type ion trap, with selective removal of unwanted ionization states by radio-frequency resonant excitation. Ion number mass-to-charge ratio spectra obtained at partial pressures of O2 from 9.9 x 10 to the -9th to 1.5 x 10 to the -7th torr yield rate constants of 1.0 x 10 to the -9th cu cm/sec and 2.5 x 10 to the -9th cu cm/sec for the O(2+) and O(3+) reactions, respectively. Measurements made at a 30% increase of the effective axial well depth of the trap demonstrate that the rate constant is essentially energy independent in the energy range studies, implying that the O(2+) cross section for charge transfer has an inverse velocity dependence of the Langevin type, despite a reaction rate lower than the Langevin valve.

  19. Electron transfer reactions in the alkene mono-oxygenase complex from Nocardia corallina B-276.

    PubMed Central

    Gallagher, S C; Cammack, R; Dalton, H

    1999-01-01

    Nocardia corallina B-276 possesses a multi-component enzyme, alkene mono-oxygenase (AMO), that catalyses the stereoselective epoxygenation of alkenes. The reductase component of this system has been shown by EPR and fluorescence spectroscopy to contain two prosthetic groups, an FAD centre and a [2Fe-2S] cluster. The role of these centres in the epoxygenation reaction was determined by midpoint potential measurements and electron transfer kinetics. The order of potentials of the prosthetic groups of the reductase were FAD/FAD.=-216 mV, [2Fe-2S]/[2Fe-2S].=-160 mV and FAD./FAD.=-134 mV. Combined, these data implied that the reductase component supplied the energy required for the epoxygenation reaction and allowed a prediction of the mechanism of electron transfer within the AMO complex. The FAD moiety was reduced by bound NADH in a two-electron reaction. The electrons were then transported to the [2Fe-2S] centre one at a time, which in turn reduced the di-iron centre of the epoxygenase. Reduction of the di-iron centre is required for oxygen binding and substrate oxidation. PMID:10085230

  20. Direct observation of ultrafast-electron-transfer reactions unravels high effectiveness of reductive DNA damage.

    PubMed

    Nguyen, Jenny; Ma, Yuhan; Luo, Ting; Bristow, Robert G; Jaffray, David A; Lu, Qing-Bin

    2011-07-19

    Both water and electron-transfer reactions play important roles in chemistry, physics, biology, and the environment. Oxidative DNA damage is a well-known mechanism, whereas the relative role of reductive DNA damage is unknown. The prehydrated electron (e(pre)-), a novel species of electrons in water, is a fascinating species due to its fundamental importance in chemistry, biology, and the environment. e(pre)- is an ideal agent to observe reductive DNA damage. Here, we report both the first in situ femtosecond time-resolved laser spectroscopy measurements of ultrafast-electron-transfer (UET) reactions of e(pre)- with various scavengers (KNO(3), isopropanol, and dimethyl sulfoxide) and the first gel electrophoresis measurements of DNA strand breaks induced by e(pre)- and OH(•) radicals co-produced by two-UV-photon photolysis of water. We strikingly found that the yield of reductive DNA strand breaks induced by each e(pre)- is twice the yield of oxidative DNA strand breaks induced by each OH(•) radical. Our results not only unravel the long-standing mystery about the relative role of radicals in inducing DNA damage under ionizing radiation, but also challenge the conventional notion that oxidative damage is the main pathway for DNA damage. The results also show the potential of femtomedicine as a new transdisciplinary frontier and the broad significance of UET reactions of e(pre)- in many processes in chemistry, physics, biology, and the environment. PMID:21730183

  1. Electron-transfer reactions and functionalization of cytochrome P450cam monooxygenase system in reverse micelles.

    PubMed

    Ichinose, Hirofumi; Michizoe, Junji; Maruyama, Tatsuo; Kamiya, Noriho; Goto, Masahiro

    2004-06-22

    Enzyme-based electron-transfer reactions involved in the cytochrome P450 monooxygenase system were investigated in nanostructural reverse micelles. A bacterial flavoprotein, putidaredoxin reductase (PdR), was activated and shown to be capable of catalyzing the electron transport from NADH to electron-carrier proteins such as cytochrome b5 (tCyt-b5) and putidaredoxin (Pdx) in reverse micelles. Ferric tCyt-b5 in reverse micelles was effectively converted to its ferrous form by the exogenous addition of separately prepared reverse micellar solution harboring PdR and NADH. The fact that direct interactions of macromolecular proteins should be possible in the reverse micellar system encouraged us to functionalize a multicomponent monooxygenase system composed of the bacterial cytochrome P450cam (P450cam), putidaredoxin (Pdx), and PdR in reverse micelles. The successful camphor hydroxylation reaction catalyzed by P450cam was significantly dependent on the coexistence of Pdx, PdR, and NADH but not H2O2, suggesting that the oxygen-transfer reactions proceeded via a "monooxygenation" mechanism. This is the first report of a multicomponent cytochrome P450 system exhibiting enzymatic activity in organic media. PMID:15986701

  2. A spectroscopist's view of energy states, energy transfers, and chemical reactions.

    PubMed

    Moore, C Bradley

    2007-01-01

    This chapter describes a research career beginning at Berkeley in 1960, shortly after Sputnik and the invention of the laser. Following thesis work on vibrational spectroscopy and the chemical reactivity of small molecules, we studied vibrational energy transfers in my own lab. Collision-induced transfers among vibrations of a single molecule, from one molecule to another, and from vibration to rotation and translation were elucidated. My research group also studied the competition between vibrational relaxation and chemical reaction for potentially reactive collisions with one molecule vibrationally excited. Lasers were used to enrich isotopes by the excitation of a predissociative transition of a selected isotopomer. We also tested the hypotheses of transition-state theory for unimolecular reactions of ketene, formaldehyde, and formyl fluoride by (a) resolving individual molecular eigenstates above a dissociation threshold, (b) locating vibrational levels at the transition state, (c) observing quantum resonances in the barrier region for motion along a reaction coordinate, and (d) studying energy release to fragments. PMID:17034339

  3. In situ Regeneration of NADH via Lipoamide Dehydrogenase-catalyzed Electron Transfer Reaction Evidenced by Spectroelectrochemistry

    SciTech Connect

    Tam, Tsz Kin; Chen, Baowei; Lei, Chenghong; Liu, Jun

    2012-08-01

    NAD/NADH is a coenzyme found in all living cells, carrying electrons from one reaction to another. We report on characterizations of in situ regeneration of NADH via lipoamide dehydrogenase (LD)-catalyzed electron transfer reaction to regenerate NADH using UV-vis spectroelectrochemistry. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of NADH regeneration were measured as 0.80 {+-} 0.15 mM and 1.91 {+-} 0.09 {micro}M s-1 in a 1-mm thin-layer spectroelectrochemical cell using gold gauze as the working electrode at the applied potential -0.75 V (vs. Ag/AgCl). The electrocatalytic reduction of the NAD system was further coupled with the enzymatic conversion of pyruvate to lactate by lactate dehydrogenase to examine the coenzymatic activity of the regenerated NADH. Although the reproducible electrocatalytic reduction of NAD into NADH is known to be difficult compared to the electrocatalytic oxidation of NADH, our spectroelectrochemical results indicate that the in situ regeneration of NADH via LD-catalyzed electron transfer reaction is fast and sustainable and can be potentially applied to many NAD/NADH-dependent enzyme systems.

  4. Probable new type of reaction mechanism: Double. cap alpha. direct transfer process

    SciTech Connect

    Xu Shu-wei; Wu Guo-hua; Miao Rong-zhi; Han Fei

    1983-10-01

    It is assumed that /sup 8/Be consists of two ..cap alpha.. particles which are close to each other in configuration space. A spectroscopic density of /sup 8/Be cluster in the residue nuclei is then obtained, which is proportional to the square of the preformation probability of ..cap alpha.. particle at nuclear surface. Using the improved method of parametrization of EFR-DWBA overlap integral,/sup 1//sup en-dash//sup 2/ we calculate the double differential energy spectra and angular distributions of ..cap alpha.. particles for the reactions /sup 209/Bi (/sup 12/C, ..cap alpha..) /sup 217/Fr and extract the preformation probability of ..cap alpha.. particle at the surface of /sup 217/Fr nuclei from fitting the experimental data. The agreement within the range of calculation error between the preformation probabilities extracted from transfer reactions and ..cap alpha.. decay suggests that the reaction /sup 209/Bi(/sup 12/C, ..cap alpha..) /sup 217/Fr may be explained as a double ..cap alpha.. direct transfer process.

  5. Imaging Proton Transfer and Dihalide Formation Pathways in Reactions of F– + CH3I

    PubMed Central

    2016-01-01

    Ion–molecule reactions of the type X– + CH3Y are commonly assumed to produce Y– through bimolecular nucleophilic substitution (SN2). Beyond this reaction, additional reaction products have been observed throughout the last decades and have been ascribed to different entrance channel geometries differing from the commonly assumed collinear approach. We have performed a crossed beam velocity map imaging experiment on the F– + CH3I reaction at different relative collision energies between 0.4 and 2.9 eV. We find three additional channels competing with nucleophilic substitution at high energies. Experimental branching ratios and angle- and energy differential cross sections are presented for each product channel. The proton transfer product CH2I– is the main reaction channel, which competes with nucleophilic substitution up to 2.9 eV relative collision energy. At this level, the second additional channel, the formation of IF– via halogen abstraction, becomes more efficient. In addition, we present the first evidence for an [FHI]− product ion. This [FHI]− product ion is present only for a narrow range of collision energies, indicating possible dissociation at high energies. All three products show a similar trend with respect to their velocity- and scattering angle distributions, with isotropic scattering and forward scattering of the product ions occurring at low and high energies, respectively. Reactions leading to all three reaction channels present a considerable amount of energy partitioning in product internal excitation. The internally excited fraction shows a collision energy dependence only for CH2I–. A similar trend is observed for the isoelectronic OH– + CH3I system. The comparison of our experimental data at 1.55 eV collision energy with a recent theoretical calculation for the same system shows a slightly higher fraction of internal excitation than predicted, which is, however, compatible within the experimental accuracy. PMID:26799548

  6. Imaging Proton Transfer and Dihalide Formation Pathways in Reactions of F(-) + CH3I.

    PubMed

    Carrascosa, Eduardo; Michaelsen, Tim; Stei, Martin; Bastian, Björn; Meyer, Jennifer; Mikosch, Jochen; Wester, Roland

    2016-07-14

    Ion-molecule reactions of the type X(-) + CH3Y are commonly assumed to produce Y(-) through bimolecular nucleophilic substitution (SN2). Beyond this reaction, additional reaction products have been observed throughout the last decades and have been ascribed to different entrance channel geometries differing from the commonly assumed collinear approach. We have performed a crossed beam velocity map imaging experiment on the F(-) + CH3I reaction at different relative collision energies between 0.4 and 2.9 eV. We find three additional channels competing with nucleophilic substitution at high energies. Experimental branching ratios and angle- and energy differential cross sections are presented for each product channel. The proton transfer product CH2I(-) is the main reaction channel, which competes with nucleophilic substitution up to 2.9 eV relative collision energy. At this level, the second additional channel, the formation of IF(-) via halogen abstraction, becomes more efficient. In addition, we present the first evidence for an [FHI](-) product ion. This [FHI](-) product ion is present only for a narrow range of collision energies, indicating possible dissociation at high energies. All three products show a similar trend with respect to their velocity- and scattering angle distributions, with isotropic scattering and forward scattering of the product ions occurring at low and high energies, respectively. Reactions leading to all three reaction channels present a considerable amount of energy partitioning in product internal excitation. The internally excited fraction shows a collision energy dependence only for CH2I(-). A similar trend is observed for the isoelectronic OH(-) + CH3I system. The comparison of our experimental data at 1.55 eV collision energy with a recent theoretical calculation for the same system shows a slightly higher fraction of internal excitation than predicted, which is, however, compatible within the experimental accuracy. PMID:26799548

  7. Deacylation Mechanism and Kinetics of Acyl-Enzyme Complex of Class C β-Lactamase and Cephalothin.

    PubMed

    Tripathi, Ravi; Nair, Nisanth N

    2016-03-17

    Understanding the molecular details of antibiotic resistance by the bacterial enzymes β-lactamases is vital for the development of novel antibiotics and inhibitors. In this spirit, the detailed mechanism of deacylation of the acyl-enzyme complex formed by cephalothin and class C β-lactamase is investigated here using hybrid quantum-mechanical/molecular-mechanical molecular dynamics methods. The roles of various active-site residues and substrate in the deacylation reaction are elucidated. We identify the base that activates the hydrolyzing water molecule and the residue that protonates the catalytic serine (Ser64). Conformational changes in the active sites and proton transfers that potentiate the efficiency of the deacylation reaction are presented. We have also characterized the oxyanion holes and other H-bonding interactions that stabilize the reaction intermediates. Together with the kinetic and mechanistic details of the acylation reaction, we analyze the complete mechanism and the overall kinetics of the drug hydrolysis. Finally, the apparent rate-determining step in the drug hydrolysis is scrutinized. PMID:26918257

  8. Effect of mass transfer on the oxygen reduction reaction catalyzed by platinum dendrimer encapsulated nanoparticles

    PubMed Central

    Dumitrescu, Ioana; Crooks, Richard M.

    2012-01-01

    Here we report on the effect of the mass transfer rate (kt) on the oxygen reduction reaction (ORR) catalyzed by Pt dendrimer-encapsulated nanoparticles (DENs) comprised of 147 and 55 atoms (Pt147 and Pt55). The experiments were carried out using a dual-electrode microelectrochemical device, which enables the study of the ORR under high kt conditions with simultaneous detection of H2O2. At low kt (0.02 to 0.12 cm s-1) the effective number of electrons involved in ORR, neff, is 3.7 for Pt147 and 3.4 for Pt55. As kt is increased, the mass-transfer-limited current for the ORR becomes significantly lower than the value predicted by the Levich equation for a 4-electron process regardless of catalyst size. However, the percentage of H2O2 detected remains constant, such that neff barely changes over the entire kt range explored (0.02 cm s-1). This suggests that mass transfer does not affect neff, which has implications for the mechanism of the ORR on Pt nanoparticles. Interestingly, there is a significant difference in neff for the two sizes of Pt DENs (neff = 3.7 and 3.5 for Pt147 and Pt55, respectively) that cannot be assigned to mass transfer effects and that we therefore attribute to a particle size effect. PMID:22665772

  9. Mutations to R. sphaeroides Reaction Center Perturb Energy Levels and Vibronic Coupling but Not Observed Energy Transfer Rates.

    PubMed

    Flanagan, Moira L; Long, Phillip D; Dahlberg, Peter D; Rolczynski, Brian S; Massey, Sara C; Engel, Gregory S

    2016-03-10

    The bacterial reaction center is capable of both efficiently collecting and quickly transferring energy within the complex; therefore, the reaction center serves as a convenient model for both energy transfer and charge separation. To spectroscopically probe the interactions between the electronic excited states on the chromophores and their intricate relationship with vibrational motions in their environment, we examine coherences between the excited states. Here, we investigate this question by introducing a series of point mutations within 12 Å of the special pair of bacteriochlorophylls in the Rhodobacter sphaeroides reaction center. Using two-dimensional spectroscopy, we find that the time scales of energy transfer dynamics remain unperturbed by these mutations. However, within these spectra, we detect changes in the mixed vibrational-electronic coherences in these reaction centers. Our results indicate that resonance between bacteriochlorophyll vibrational modes and excitonic energy gaps promote electronic coherences and support current vibronic models of photosynthetic energy transfer. PMID:26630123

  10. Electronic shift register memory based on molecular electron-transfer reactions

    NASA Technical Reports Server (NTRS)

    Hopfield, J. J.; Onuchic, Jose Nelson; Beratan, David N.

    1989-01-01

    The design of a shift register memory at the molecular level is described in detail. The memory elements are based on a chain of electron-transfer molecules incorporated on a very large scale integrated (VLSI) substrate, and the information is shifted by photoinduced electron-transfer reactions. The design requirements for such a system are discussed, and several realistic strategies for synthesizing these systems are presented. The immediate advantage of such a hybrid molecular/VLSI device would arise from the possible information storage density. The prospect of considerable savings of energy per bit processed also exists. This molecular shift register memory element design solves the conceptual problems associated with integrating molecular size components with larger (micron) size features on a chip.

  11. Electron transfer reactions of osmium(II) complexes with phenols and phenolic acids

    NASA Astrophysics Data System (ADS)

    Rajeswari, Angusamy; Ramdass, Arumugam; Muthu Mareeswaran, Paulpandian; Velayudham, Murugesan; Rajagopal, Seenivasan

    2016-07-01

    Three [Os(NN)3]2+ complexes (NN = polypyridine) with ligands of varying hydrophobicity were synthesized and characterized by NMR spectral techniques. The geometry of the molecules are optimized by DFT calculations. The interaction between [Os(NN)3]2+ complexes and phenolate ion in ground state is confirmed by absorption spectral study and the binding constant values are in the range of 3-740 M-1. The photoinduced electron transfer reaction of these [Os(NN)3]2+ complexes with phenols and phenolic acids at pH 12.5 leads to the formation of phenoxyl radical confirmed through transient absorption spectral study. Binding constants and electron transfer rate constants within the [Os(NN)3]2+-phenolate ion adduct account for the change for the overall quenching constant with the change of structure of reactants.

  12. Surface complexation reaction for phase transfer of hydrophobic quantum dot from nonpolar to polar medium.

    PubMed

    Bhandari, Satyapriya; Roy, Shilaj; Pramanik, Sabyasachi; Chattopadhyay, Arun

    2014-09-01

    Chemical reaction between oleate-capped Zn(x)Cd(1-x)S quantum dots (Qdots) and 8-hydroxyquinoline (HQ) led to formation of a surface complex, which was accompanied by transfer of hydrophobic Qdots from nonpolar (hexane) to polar (water) medium with high efficiency. The stability of the complex on the surface was achieved via involvement of dangling sulfide bonds. Moreover, the transferred hydrophilic Qdots--herein called as quantum dot complex (QDC)--exhibited new and superior optical properties in comparison to bare inorganic complexes with retention of the dimension and core structure of the Qdots. Finally, the new and superior optical properties of water-soluble QDC make them potentially useful for biological--in addition to light emitting device (LED)--applications. PMID:25133937

  13. Species differences in unlocking B-side electron transfer in bacterial reaction centers.

    PubMed

    Dylla, Nicholas P; Faries, Kaitlyn M; Wyllie, Ryan M; Swenson, Angela M; Hanson, Deborah K; Holten, Dewey; Kirmaier, Christine; Laible, Philip D

    2016-08-01

    The structure of the bacterial photosynthetic reaction center (RC) reveals symmetry-related electron transfer (ET) pathways, but only one path is used in native RCs. Analogous mutations have been made in two Rhodobacter (R.) species. A glutamic acid at position 133 in the M subunit increases transmembrane charge separation via the naturally inactive (B-side) path through impacts on primary ET in mutant R. sphaeroidesRCs. Prior work showed that the analogous substitution in the R. capsulatusRC also increases B-side activity, but mainly affects secondary ET. The overall yields of transmembrane ET are similar, but enabled in fundamentally different ways. PMID:27325608

  14. Theoretical study on the effect of solvent and intermolecular fluctuations in proton transfer reactions: General theory

    SciTech Connect

    Kato, Nobuhiko; Ida, Tomonori; Endo, Kazunaka

    2004-04-30

    We present a theory of proton transfer reactions which incorporate the modulation of the proton's potential surface by intermolecular vibrations and the effect of coupling to solvent degree of freedom. The proton tunnels between states corresponding to it being localized in the wells of a double minimum potential. The resulting tunnel splitting depends on the intermolecular separation. The solvent response to the proton's charge is modeled as that of a continuous distribution of harmonic oscillators and the intermolecular stretching mode is also damped because of the interaction with solvent degree of freedom. The transition rate is given by the Fermi Gorlden Rule expression.

  15. Fission probabilities of 242Am,243Cm , and 244Cm induced by transfer reactions

    NASA Astrophysics Data System (ADS)

    Kessedjian, G.; Jurado, B.; Barreau, G.; Marini, P.; Mathieu, L.; Tsekhanovich, I.; Aiche, M.; Boutoux, G.; Czajkowski, S.; Ducasse, Q.

    2015-04-01

    We have measured the fission probabilities of 242Am,243Cm , and 244Cm induced by the transfer reactions 243Am(3He,4He) ,243Am(3He,t ) , and 243Am(3He,d ) , respectively. The details of the experimental procedure and a rigorous uncertainty analysis, including a correlation matrix, are presented. For 243Cm our data show clear structures well below the fission threshold. To our knowledge, it is the first time that these structures have been observed for this nucleus. We have compared the measured fission probabilities to calculations based on the statistical model to obtain information on the fission barriers of the produced fissioning nuclei.

  16. Interplay between aromaticity and strain in double group transfer reactions to 1,2-benzyne.

    PubMed

    Fernández, Israel; Cossío, Fernando P

    2016-05-30

    Density Functional Theory calculations are used to explore the double hydrogen atom transfer from different alkanes to 1,2-benzyne. State-of-the-art calculations including the Activation Strain Model of reactivity, Energy Decomposition Analysis, and Valence Bond methods, reveal the origins of the relatively low activation barriers computed for these processes compared to the analogous reaction involving acetylene. In addition, the interplay between the in-plane aromaticity of the corresponding transition states and the variation of the π-aromaticity associated with the benzyne moiety as well as their influence on the barrier heights of the transformations are analyzed in detail. © 2016 Wiley Periodicals, Inc. PMID:26864872

  17. Heat and Mass Transfer in Unsteady Rotating Fluid Flow with Binary Chemical Reaction and Activation Energy

    PubMed Central

    Awad, Faiz G.; Motsa, Sandile; Khumalo, Melusi

    2014-01-01

    In this study, the Spectral Relaxation Method (SRM) is used to solve the coupled highly nonlinear system of partial differential equations due to an unsteady flow over a stretching surface in an incompressible rotating viscous fluid in presence of binary chemical reaction and Arrhenius activation energy. The velocity, temperature and concentration distributions as well as the skin-friction, heat and mass transfer coefficients have been obtained and discussed for various physical parametric values. The numerical results obtained by (SRM) are then presented graphically and discussed to highlight the physical implications of the simulations. PMID:25250830

  18. Studies of nuclei close to {sup 132}Sn using single-neutron transfer reactions

    SciTech Connect

    Jones, K. J.; Pain, S. D.; Kozub, R. L.; Howard, J. A.; O'Malley, P. D.; Paulauskas, S. V.; Shriner, J. F.; Sissom, D. J.; Adekola, A. S.; Bardayan, D. W.; Blackmon, J. C.; Liang, J. F.; Nesaraja, C. D.; Shapira, D.; Smith, M. S.; Catford, W. N.; Harlin, C.; Patterson, N. P.; Swan, T. P.; Wilson, G. L.

    2009-03-04

    Neutron transfer reactions were performed in inverse kinematics using radioactive ion beams of {sup 132}Sn, {sup 130}Sn, and {sup 134}Te and deuterated polyethylene targets. Preliminary results are presented. The Q-value spectra for {sup 133}Sn, {sup 131}Sn and {sup 135}Te reveal a number of previously unobserved peaks. The angular distributions are compatible with the expected lf{sub 7/2} nature of the ground state of {sup 133}Sn, and 2p{sub 3/2} for the 3.4 MeV state in {sup 131}Sn.

  19. Studies of Nuclei Close to 132Sn Using Single-Neutron Transfer Reactions

    SciTech Connect

    Jones, K. L.; Pain, S. D.; Kozub, R. L.; Adekola, Aderemi S; Bardayan, Daniel W; Blackmon, Jeff C; Catford, Wilton N; Chae, K. Y.; Chipps, K.; Cizewski, J. A.; Erikson, Luke; Gaddis, A. L.; Greife, U.; Grzywacz, R. K.; Harlin, Christopher W; Hatarik, Robert; Howard, Joshua A; James, J.; Kapler, R.; Krolas, W.; Liang, J Felix; Ma, Zhanwen; Matei, Catalin; Moazen, Brian; Nesaraja, Caroline D; O'Malley, Patrick; Patterson, N. P.; Paulauskas, Stanley; Shapira, Dan; ShrinerJr., J. F.; Sikora, M.; Sissom, D. J.; Smith, Michael Scott; Swan, T. P.; Thomas, J. S.; Wilson, Gemma L

    2009-01-01

    Neutron transfer reactions were performed in inverse kinematics using radioactive ion beams of 132Sn, 130Sn, and 134Te and deuterated polyethylene targets. Preliminary results are presented. The Q-value spectra for 133Sn, 131Sn and 135Te reveal a number of previously unobserved peaks. The angular distributions are compatible with the expected lf7/2 nature of the ground state of 133Sn, and 2p3/2 for the 3.4 MeV state in 131Sn.

  20. Operando NMR spectroscopic analysis of proton transfer in heterogeneous photocatalytic reactions

    PubMed Central

    Wang, Xue Lu; Liu, Wenqing; Yu, Yan-Yan; Song, Yanhong; Fang, Wen Qi; Wei, Daxiu; Gong, Xue-Qing; Yao, Ye-Feng; Yang, Hua Gui

    2016-01-01

    Proton transfer (PT) processes in solid–liquid phases play central roles throughout chemistry, biology and materials science. Identification of PT routes deep into the realistic catalytic process is experimentally challenging, thus leaving a gap in our understanding. Here we demonstrate an approach using operando nuclear magnetic resonance (NMR) spectroscopy that allows to quantitatively describe the complex species dynamics of generated H2/HD gases and liquid intermediates in pmol resolution during photocatalytic hydrogen evolution reaction (HER). In this system, the effective protons for HER are mainly from H2O, and CH3OH evidently serves as an outstanding sacrificial agent reacting with holes, further supported by our density functional theory calculations. This results rule out controversy about the complicated proton sources for HER. The operando NMR method provides a direct molecular-level insight with the methodology offering exciting possibilities for the quantitative studies of mechanisms of proton-involved catalytic reactions in solid–liquid phases. PMID:27311326

  1. Non-Markov dissipative dynamics of electron transfer in a photosynthetic reaction center

    NASA Astrophysics Data System (ADS)

    Poddubnyy, V. V.; Glebov, I. O.; Eremin, V. V.

    2014-02-01

    We consider the dissipative dynamics of electron transfer in the photosynthetic reaction center of purple bacteria and propose a model where the transition between electron states arises only due to the interaction between a chromophore system and the protein environment and is not accompanied by the motion of nuclei of the reaction subsystem. We establish applicability conditions for the Markov approximation in the framework of this model and show that these conditions are not necessarily satisfied in the protein medium. We represent the spectral function of the "system+heat bath" interaction in the form of one or several Gaussian functions to study specific characteristics of non-Markov dynamics of the final state population, the presence of an induction period and vibrations. The consistency of the computational results obtained for non-Markov dynamics with experimental data confirms the correctness of the proposed approach.

  2. Neutron spectroscopic factors of Ar34 and Ar46 from (p,d) transfer reactions

    NASA Astrophysics Data System (ADS)

    Lee, Jenny; Tsang, M. B.; Bazin, D.; Coupland, D.; Henzl, V.; Henzlova, D.; Kilburn, M.; Lynch, W. G.; Rogers, A. M.; Sanetullaev, A.; Sun, Z. Y.; Youngs, M.; Charity, R. J.; Sobotka, L. G.; Famiano, M.; Hudan, S.; Shapira, D.; O'Malley, P.; Peters, W. A.; Chae, K. Y.; Schmitt, K.

    2011-01-01

    Single-neutron-transfer measurements using (p,d) reactions have been performed at 33 MeV per nucleon with proton-rich Ar34 and neutron-rich Ar46 beams in inverse kinematics. The extracted spectroscopic factors are compared to the large-basis shell-model calculations. Relatively weak quenching of the spectroscopic factors is observed between Ar34 and Ar46. The experimental results suggest that neutron correlations have a weak dependence on the asymmetry of the nucleus over this isotopic region. The present results are consistent with the systematics established from extensive studies of spectroscopic factors and dispersive optical-model analyses of Ca40-49 isotopes. They are, however, inconsistent with the trends obtained in knockout-reaction measurements.

  3. Relayed 13C magnetization transfer: Detection of malate dehydrogenase reaction in vivo

    NASA Astrophysics Data System (ADS)

    Yang, Jehoon; Shen, Jun

    2007-02-01

    Malate dehydrogenase catalyzes rapid interconversion between dilute metabolites oxaloacetate and malate. Both oxaloacetate and malate are below the detection threshold of in vivo MRS. Oxaloacetate is also in rapid exchange with aspartate catalyzed by aspartate aminotransferase, the latter metabolite is observable in vivo using 13C MRS. We hypothesized that the rapid turnover of oxaloacetate can effectively relay perturbation of magnetization between malate and aspartate. Here, we report indirect observation of the malate dehydrogenase reaction by saturating malate C2 resonance at 71.2 ppm and detecting a reduced aspartate C2 signal at 53.2 ppm due to relayed magnetization transfer via oxaloacetate C2 at 201.3 ppm. Using this strategy the rate of the cerebral malate dehydrogenase reaction was determined to be 9 ± 2 μmol/g wet weight/min (means ± SD, n = 5) at 11.7 Tesla in anesthetized adult rats infused with [1,6- 13C 2]glucose.

  4. Operando NMR spectroscopic analysis of proton transfer in heterogeneous photocatalytic reactions.

    PubMed

    Wang, Xue Lu; Liu, Wenqing; Yu, Yan-Yan; Song, Yanhong; Fang, Wen Qi; Wei, Daxiu; Gong, Xue-Qing; Yao, Ye-Feng; Yang, Hua Gui

    2016-01-01

    Proton transfer (PT) processes in solid-liquid phases play central roles throughout chemistry, biology and materials science. Identification of PT routes deep into the realistic catalytic process is experimentally challenging, thus leaving a gap in our understanding. Here we demonstrate an approach using operando nuclear magnetic resonance (NMR) spectroscopy that allows to quantitatively describe the complex species dynamics of generated H2/HD gases and liquid intermediates in pmol resolution during photocatalytic hydrogen evolution reaction (HER). In this system, the effective protons for HER are mainly from H2O, and CH3OH evidently serves as an outstanding sacrificial agent reacting with holes, further supported by our density functional theory calculations. This results rule out controversy about the complicated proton sources for HER. The operando NMR method provides a direct molecular-level insight with the methodology offering exciting possibilities for the quantitative studies of mechanisms of proton-involved catalytic reactions in solid-liquid phases. PMID:27311326

  5. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation

    SciTech Connect

    Wasielewski, M.R.; Wiederrecht, G.P.; Svec, W.A.

    1993-05-01

    Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

  6. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation

    SciTech Connect

    Wasielewski, M.R.; Wiederrecht, G.P.; Svec, W.A.

    1993-01-01

    Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

  7. BALANCE : a computer program for calculating mass transfer for geochemical reactions in ground water

    USGS Publications Warehouse

    Parkhurst, David L.; Plummer, L. Niel; Thorstenson, Donald C.

    1982-01-01

    BALANCE is a Fortran computer designed to define and quantify chemical reactions between ground water and minerals. Using (1) the chemical compositions of two waters along a flow path and (2) a set of mineral phases hypothesized to be the reactive constituents in the system, the program calculates the mass transfer (amounts of the phases entering or leaving the aqueous phase) necessary to account for the observed changes in composition between the two waters. Additional constraints can be included in the problem formulation to account for mixing of two end-member waters, redox reactions, and, in a simplified form, isotopic composition. The computer code and a description of the input necessary to run the program are presented. Three examples typical of ground-water systems are described. (USGS)

  8. Lifetime and g-factor measurements of excited states using Coulomb excitation and alpha transfer reactions

    NASA Astrophysics Data System (ADS)

    Guevara, Z. E.; Torres, D. A.

    2016-07-01

    In this contribution the challenges in the use of a setup to simultaneously measure lifetimes and g-factor values will be presented. The simultaneous use of the transient field technique and the Doppler Shift Attenuation Method, to measure magnetic moments and lifetimes respectively, allows to obtain a complete characterization of the currents of nucleons and the deformation in excited states close to the ground state. The technique is at the moment limited to Coulomb excitation and alpha-transfer reactions, what opens an interesting perspective to consider this type of experiments with radioactive beams. The use of deep-inelastic and fusion-evaporation reactions will be discussed. An example of a setup that makes use of a beam of 106Cd to study excited states of 110Sn and the beam nuclei itself will be presented.

  9. Experimental study of the asymmetric charge transfer reaction between Ar+ ions and Fe atoms.

    PubMed

    Korolov, I; Bánó, G; Donkó, Z; Derzsi, A; Hartmann, P

    2011-02-14

    We investigate the Ar(+)-Fe asymmetric charge transfer (ACT) reaction using a combination of plasma diagnostics methods and a kinetic model of the afterglow plasma, which allow monitoring of the temporal evolution of the densities of different species. The iron vapor is created inside a discharge cell by cathode sputtering; its density is measured by atomic absorption spectroscopy. The rate coefficient of the reaction is evaluated from the emission intensity decay of Fe(+)∗ lines pumped by the ACT process in the He-Ar-Fe and Ar-Fe afterglow plasmas. The measurements yield a rate coefficient k = 7.6( ± 3.0) × 10(-9) cm(3) s(-1) at T = 300 K. PMID:21322681

  10. Acylation, Diastereoselective Alkylation, and Cleavage of an Oxazolidinone Chiral Auxiliary: A Multistep Asymmetric Synthesis Experiment for Advanced Undergraduates

    ERIC Educational Resources Information Center

    Smith, Thomas E.; Richardson, David P.; Truran, George A.; Belecki, Katherine; Onishi, Megumi

    2008-01-01

    An introduction to the concepts and experimental techniques of diastereoselective synthesis using a chiral auxiliary is described. The 4-benzyl-2-oxazolidinone chiral auxiliary developed by Evans is acylated with propionic anhydride under mild conditions using DMAP as an acyl transfer catalyst. Deprotonation with NaN(TMS)[subscript 2] at -78…

  11. Solvent Effects in Chemical Processes. Water-Assisted Proton Transfer Reaction of Pterin in Aqueous Environment

    NASA Astrophysics Data System (ADS)

    Jaramillo, Paula; Coutinho, Kaline; Canuto, Sylvio

    2009-09-01

    Pterins are members of a family of heterocyclic compounds present in a wide variety of biological systems and may exist in two forms, corresponding to an acid and a basic tautomer. In this work, the proton transfer reaction between these tautomeric forms was investigated in the gas phase and in aqueous solution. In gas phase, the intramolecular mechanism was carried out for the isolated pterin by quantum mechanical second-order Møller-Plesset perturbation theory (MP2/aug-cc-pVDZ) calculations and it indicates that the acid form is more stable than the basic form by -1.4 kcal/mol with a barrier of 34.2 kcal/mol with respect to the basic form. In aqueous solution, the role of the water molecules in the proton transfer reaction was analyzed in two separated parts, the direct participation of one water molecule in the reaction path, called water-assisted mechanism, and the complementary participation of the aqueous solvation. The water-assisted mechanism was carried out for one pterin-water cluster by quantum mechanical calculations and it indicates that the acid form is still more stable by -3.3 kcal/mol with a drastic reduction of 70% of the barrier. The bulk solution effect on the intramolecular and water-assisted mechanisms was included by free energy perturbation implemented on Monte Carlo simulations. The bulk water effect is found to be substantial and decisive when the reaction path involves the water-assisted mechanism. In this case, the free energy barrier is only 6.7 kcal/mol and the calculated relative Gibbs free energy for the two tautomers is -11.2 kcal/mol. This value is used to calculate the pKa value of 8.2 ± 0.6 that is in excellent agreement with the experimental result of 7.9.

  12. Production of heavy and superheavy neutron-rich nuclei in transfer reactions

    SciTech Connect

    Zagrebaev, V. I.; Greiner, Walter

    2011-04-15

    The problem of production and study of heavy neutron-rich nuclei has been intensively discussed during recent years. Many reasons arouse a great interest in this problem. The present limits of the upper part of the nuclear map are very close to the {beta} stability line while the unexplored area of heavy neutron-rich nuclides (also those located along the neutron closed shell N=126 to the right-hand side of the stability line) is extremely important for nuclear astrophysic investigations and, in particular, for the understanding of the r process of astrophysical nucleogenesis. For elements with Z>100 only neutron deficient isotopes (located to the left of the stability line) have been synthesized so far. The 'northeast' area of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes widely used nowadays for the production of new nuclei. Multinucleon transfer processes in near barrier collisions of heavy (and very heavy, U-like) ions seem to be the only reaction mechanism allowing us to produce and explore neutron-rich heavy nuclei including those located at the superheavy island of stability. In this paper several transfer reactions for different projectile-target combinations are studied in detail. Besides the predictions for the cross sections of such processes, we also analyze the angular and energy distributions of primary and survived reaction products in the laboratory frame. These results, as well as predicted excitation functions for the yields of neutron-rich superheavy isotopes, might be useful for the design of appropriate experimental equipment and for carrying out experiments of such kind.

  13. Synthesis of Long-Chain Acyl-CoA in Chloroplast Envelope Membranes 1

    PubMed Central

    Joyard, Jacques; Stumpf, Paul K.

    1981-01-01

    The chloroplast envelope is the site of a very active long-chain acylcoenzyme A (CoA) synthetase. Furthermore, we have recently shown that an acyl CoA thioesterase is also associated with envelope membrane (Joyard J, PK Stumpf 1980 Plant Physiol 65: 1039-1043). To clarify the interacting roles of both the acyl-CoA thioesterase and the acyl-CoA synthetase, the formation of acyl-CoA in envelope membranes was examined with different techniques which permitted the measurement of the actual rates of acyl-CoA formation. Using [14C]ATP or [14C]oleic acid as labeled substrates, it can be shown that the envelope acyl-CoA synthetase required both Mg2+ and dithiothreitol. Triton X-100 slightly stimulated the activity. The specificity of the acyl-CoA synthetase was determined either with [14C]ATP or with [3H]CoA as substrates. The results obtained in both cases were similar, that is, as substrates, the unsaturated fatty acids were more effective than saturated fatty acids, the velocity of the reaction increased from lauric acid to palmitic acid, and the maximum velocity was obtained with unsaturated C18 fatty acids. The results obtained suggest that the acyl-CoA thioesterase associated with envelope membranes could be an ultimate control to prevent the transport (outside of the chloroplast) or the insertion (into chloroplast lipids) of fatty acids with chains shorter than C16. PMID:16661656

  14. Development of a measurement system for the determination of (n , γ) cross-sections using multi-nucleon transfer reactions

    NASA Astrophysics Data System (ADS)

    Makii, H.; Ota, S.; Ishii, T.; Wakabayashi, Y.; Furutaka, K.; Nishio, K.; Nishinaka, I.; Chiba, S.; Igashira, M.; Czeszumska, A.

    2015-10-01

    We have installed a new experimental apparatus to measure γ-rays from highly excited states populated by the multi-nucleon transfer reactions with heavy-ion projectiles to determine the (n, γ) cross-sections by means of the surrogate reaction method. An apparatus consists of two anti-Compton LaBr3(Ce) spectrometers to measure the γ-rays and a Si ΔE-E detector system to detect outgoing projectile-like particles. Reactions of 153-MeV 18O beams with 155Gd and 157Gd targets were used to study the performance of apparatus. By using the LaBr3(Ce) scintillators with relatively large volume (101.6 mm in diameter and 127 mm in length), we have successfully measured γ-rays from the compound nuclei, which have excitation energy above neutron separation energy, populated by 155Gd(18O, 16O)157Gd and 157Gd(18O, 16O)159Gd two-neutron transfer reactions. To measure in-beam γ-rays through heavy-ion-induced transfer reaction, it is important to assign the reaction channel clearly, since the cross-sections of the transfer reactions are much smaller than those of competing reactions such as Coulomb excitation and fusion reactions. The Si ΔE-E detector system was used to separate outgoing particles. The present study has demonstrated high capability of apparatus to measure the de-excitation γ-rays in the compound nuclei produced by the multi-nucleon transfer reactions for determination of the (n, γ) cross-sections by using the surrogate reaction method.

  15. Peroxyl Radical Reactions in Water Solution: A Gym for Proton-Coupled Electron-Transfer Theories.

    PubMed

    Amorati, Riccardo; Baschieri, Andrea; Morroni, Gloria; Gambino, Rossana; Valgimigli, Luca

    2016-06-01

    The reactions of alkylperoxyl radicals with phenols have remained difficult to investigate in water. We describe herein a simple and reliable method based on the inhibited autoxidation of water/THF mixtures, which we calibrated against pulse radiolysis. With this method we measured the rate constants kinh for the reactions of 2-tetrahydrofuranylperoxyl radicals with reference compounds: urate, ascorbate, ferrocenes, 2,2,5,7,8-pentamethyl-6-chromanol, Trolox, 6-hydroxy-2,5,7,8-tetramethylchroman-2-acetic acid, 2,6-di-tert-butyl-4-methoxyphenol, 4-methoxyphenol, catechol and 3,5-di-tert-butylcatechol. The role of pH was investigated: the value of kinh for Trolox and 4-methoxyphenol increased 11- and 50-fold from pH 2.1 to 12, respectively, which indicate the occurrence of a SPLET-like mechanism. H(D) kinetic isotope effects combined with pH and solvent effects suggest that different types of proton-coupled electron transfer (PCET) mechanisms are involved in water: less electron-rich phenols react at low pH by concerted electron-proton transfer (EPT) to the peroxyl radical, whereas more electron-rich phenols and phenoxide anions react by multi-site EPT in which water acts as proton relay. PMID:27111024

  16. Ionic hydrogenations of hindered olefins at low temperature. Hydride transfer reactions of transition metal hydrides

    SciTech Connect

    Bullock, R.M.; Song, J.S. )

    1994-09-21

    Sterically hindered olefins can be hydrogenated at -50[degree]C in dichloromethane using triflic acid (CF[sub 3]SO[sub 3]H) and a hydride donor. Mechanistic studies indicate that these reactions proceed by hydride transfer to the carbenium ion that is formed by protonation of the olefin. Olefins that form tertiary carbenium ions upon protonation are hydrogenated in high yields (90-100%). Styrenes generally produce lower yields of hydrogenated products (50-60%). Suitable hydride donors include HSiE[sub 3] and several transition metal carbonyl hydrides HW(CO)[sub 3]Cp, HW(CO)[sub 3]Cp[sup +], HMo-(CO)[sub 3]Cp, HMn(CO)[sub 5], HRe(CO)[sub 3], and HO[sub 3](CO)[sub 1]Cp*; Cp = [eta][sup 5]-C[sub 3]H[sub 5+], Cp* = [eta][sup 5]-C[sub 5]Me[sub 5]. A characteristic that is required for transition metal hydrides to be effective is that the cationic dihydrides (or dihydrogen complexes) that result from their protonation must have sufficient acidity to transfer a proton to the olefin, as well as sufficient thermal stability to avoid significant decomposition on the time scale of the hydrogenation reaction. Metal hydrides that fall due to insufficient stability of their protonated forms include HMo(CO)[sub 2](PPH[sub 3])Cp, HMo(CO)[sub 3]Cp*, and HFe(CO)[sub 2]Cp*. 62 refs., 2 tabs.

  17. Room temperature, hybrid sodium-based flow batteries with multi-electron transfer redox reactions

    DOE PAGESBeta

    Shamie, Jack S.; Liu, Caihong; Shaw, Leon L.; Sprenkle, Vincent L.

    2015-06-11

    We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volumemore » of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multielectron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. Furthermore, the critical barriers to mature this new HNFBs have also been explored.« less

  18. Surprisingly Long-Lived Ascorbyl Radicals in Acetonitrile: Concerted Proton-Electron Transfer Reactions and Thermochemistry

    PubMed Central

    Warren, Jeffrey J.; Mayer, James M.

    2008-01-01

    Proton-coupled electron transfer (PCET) reactions and thermochemistry of 5,6-isopropylidene ascorbate (iAscH−) have been examined in acetonitrile solvent.iAscH− is oxidized by 2,4,6-tBu3C6H2O• and by excess TEMPO• to give the corresponding 5,6-isopropylidene ascorbyl radical anion (iAsc•−), which persists for hours at 298 K in dry MeCN solution. The stability of iAsc•− is surprising in light of the transience of the ascorbyl radical in aqueous solutions, and is due to the lack of the protons needed for radical disproportionation. A concerted proton-electron transfer (CPET) mechanism is indicated for the reactions of iAscH−. Redox potential, pKa and equilibrium measurements define the thermochemical landscape for 5,6-isopropylidene ascorbic acid and its derivatives in MeCN. These measurements give an O–H bond dissociation free energy (BDFE) for iAscH−of 65.4 ± 1.5 kcal mol−1 in MeCN. Similar studies on underivatized ascorbate indicate a BDFE of 67.8 ± 1.2 kcal mol−1. These values are much lower than the aqueous BDFE for ascorbate of 74.0 ± 1.5 kcal mol−1 derived from reported data. PMID:18505256

  19. Surprisingly long-lived ascorbyl radicals in acetonitrile: concerted proton-electron transfer reactions and thermochemistry.

    PubMed

    Warren, Jeffrey J; Mayer, James M

    2008-06-18

    Proton-coupled electron transfer (PCET) reactions and thermochemistry of 5,6-isopropylidene ascorbate (iAscH-) have been examined in acetonitrile solvent. iAscH- is oxidized by 2,4,6-tBu3C6H2O. and by excess TEMPO. to give the corresponding 5,6-isopropylidene ascorbyl radical anion (iAsc.-), which persists for hours at 298 K in dry MeCN solution. The stability of iAsc.- is surprising in light of the transience of the ascorbyl radical in aqueous solutions and is due to the lack of the protons needed for radical disproportionation. A concerted proton-electron transfer (CPET) mechanism is indicated for the reactions of iAscH-. Redox potential, pKa and equilibrium measurements define the thermochemical landscape for 5,6-isopropylidene ascorbic acid and its derivatives in MeCN. These measurements give an O-H bond dissociation free energy (BDFE) for iAscH- of 65.4 +/- 1.5 kcal mol-1 in MeCN. Similar studies on underivatized ascorbate indicate a BDFE of 67.8 +/- 1.2 kcal mol-1. These values are much lower than the aqueous BDFE for ascorbate of 74.0 +/- 1.5 kcal mol-1 derived from reported data. PMID:18505256

  20. Room Temperature, Hybrid Sodium-Based Flow Batteries with Multi-Electron Transfer Redox Reactions

    PubMed Central

    Shamie, Jack S.; Liu, Caihong; Shaw, Leon L.; Sprenkle, Vincent L.

    2015-01-01

    We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volume of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multi-electron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. The critical barriers to mature this new HNFBs have also been explored. PMID:26063629

  1. Cu-N dopants boost electron transfer and photooxidation reactions of carbon dots.

    PubMed

    Wu, Wenting; Zhan, Liying; Fan, Weiyu; Song, Jizhong; Li, Xiaoming; Li, Zhongtao; Wang, Ruiqin; Zhang, Jinqiang; Zheng, Jingtang; Wu, Mingbo; Zeng, Haibo

    2015-05-26

    The broadband light-absorption ability of carbon dots (CDs) has inspired their application in photocatalysis, however this has been impeded by poor electron transfer inside the CDs. Herein, we report the preparation of Cu-N-doped CDs (Cu-CDs) and investigate both the doping-promoted electron transfer and the performance of the CDs in photooxidation reactions. The Cu-N doping was achieved through a one-step pyrolytic synthesis of CDs with Na2 [Cu(EDTA)] as precursor. As confirmed by ESR, FTIR, and X-ray photoelectron spectroscopies, the Cu species chelates with the carbon matrix through Cu-N complexes. As a result of the Cu-N doping, the electron-accepting and -donating abilities were enhanced 2.5 and 1.5 times, and the electric conductivity was also increased to 171.8 μs cm(-1) . As a result of these enhanced properties, the photocatalytic efficiency of CDs in the photooxidation reaction of 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate is improved 3.5-fold after CD doping. PMID:25881689

  2. Primary electron transfer processes in photosynthetic reaction centers from oxygenic organisms.

    PubMed

    Mamedov, Mahir; Govindjee; Nadtochenko, Victor; Semenov, Alexey

    2015-08-01

    This minireview is written in honor of Vladimir A. Shuvalov, a pioneer in the area of primary photochemistry of both oxygenic and anoxygenic photosyntheses (See a News Report: Allakhverdiev et al. 2014). In the present paper, we describe the current state of the formation of the primary and secondary ion-radical pairs within photosystems (PS) II and I in oxygenic organisms. Spectral-kinetic studies of primary events in PS II and PS I, upon excitation by ~20 fs laser pulses, are now available and reviewed here; for PS II, excitation was centered at 710 nm, and for PS I, it was at 720 nm. In PS I, conditions were chosen to maximally increase the relative contribution of the direct excitation of the reaction center (RC) in order to separate the kinetics of the primary steps of charge separation in the RC from that of the excitation energy transfer in the antenna. Our results suggest that the sequence of the primary electron transfer reactions is P680 → ChlD1 → PheD1 → QA (PS II) and P700 → A 0A/A 0B → A 1A/A 1B (PS I). However, alternate routes of charge separation in PS II, under different excitation conditions, are not ruled out. PMID:25648636

  3. Room Temperature, Hybrid Sodium-Based Flow Batteries with Multi-Electron Transfer Redox Reactions

    NASA Astrophysics Data System (ADS)

    Shamie, Jack S.; Liu, Caihong; Shaw, Leon L.; Sprenkle, Vincent L.

    2015-06-01

    We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volume of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multi-electron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. The critical barriers to mature this new HNFBs have also been explored.

  4. Des-acyl ghrelin prevents heatstroke-like symptoms in rats exposed to high temperature and high humidity.

    PubMed

    Inoue, Yoshiyuki; Hayashi, Yujiro; Kangawa, Kenji; Suzuki, Yoshihiro; Murakami, Noboru; Nakahara, Keiko

    2016-02-26

    We have shown previously that des-acyl ghrelin decreases body temperature in rats through activation of the parasympathetic nervous system. Here we investigated whether des-acyl ghrelin ameliorates heatstroke in rats exposed to high temperature. Peripheral administration of des-acyl ghrelin significantly attenuated hyperthermia induced by exposure to high-temperature (35°C) together with high humidity (70-80%). Although biochemical analysis revealed that exposure to high temperature significantly increased hematocrit and the serum levels of aspartate amino transferase (AST), alanine transaminase (ALT), blood urea nitrogen (BUN), creatinine and electrolytes (Na(+), K(+), Cl(-)), most of these heatstroke-associated reactions were significantly reduced by treatment with des-acyl ghrelin. The level of des-acyl ghrelin in plasma was also found to be significantly increased under high-temperature conditions. These results suggest that des-acyl ghrelin could be useful for preventing heatstroke under high temperature condition. PMID:26773867

  5. Chlamydia trachomatis Scavenges Host Fatty Acids for Phospholipid Synthesis via an Acyl-Acyl Carrier Protein Synthetase.

    PubMed

    Yao, Jiangwei; Dodson, V Joshua; Frank, Matthew W; Rock, Charles O

    2015-09-01

    The obligate intracellular parasite Chlamydia trachomatis has a reduced genome but relies on de novo fatty acid and phospholipid biosynthesis to produce its membrane phospholipids. Lipidomic analyses showed that 8% of the phospholipid molecular species synthesized by C. trachomatis contained oleic acid, an abundant host fatty acid that cannot be made by the bacterium. Mass tracing experiments showed that isotopically labeled palmitic, myristic, and lauric acids added to the medium were incorporated into C. trachomatis-derived phospholipid molecular species. HeLa cells did not elongate lauric acid, but infected HeLa cell cultures elongated laurate to myristate and palmitate. The elongated fatty acids were incorporated exclusively into C. trachomatis-produced phospholipid molecular species. C. trachomatis has adjacent genes encoding the separate domains of the bifunctional acyl-acyl carrier protein (ACP) synthetase/2-acylglycerolphosphoethanolamine acyltransferase gene (aas) of Escherichia coli. The CT775 gene encodes an acyltransferase (LpaT) that selectively transfers fatty acids from acyl-ACP to the 1-position of 2-acyl-glycerophospholipids. The CT776 gene encodes an acyl-ACP synthetase (AasC) with a substrate preference for palmitic compared with oleic acid in vitro. Exogenous fatty acids were elongated and incorporated into phospholipids by Escherichia coli-expressing AasC, illustrating its function as an acyl-ACP synthetase in vivo. These data point to an AasC-dependent pathway in C. trachomatis that selectively scavenges host saturated fatty acids to be used for the de novo synthesis of its membrane constituents. PMID:26195634

  6. Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: Temperature dependence

    SciTech Connect

    Pradhan, Tuhin; Gazi, Harun Al Rasid; Biswas, Ranjit

    2009-08-07

    Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO{sub 4}) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-{Delta}G{sub r}) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO{sub 4} concentrations, and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (-{Delta}G{sub r}), the former in ethanol and ACN increases only linearly with the increase in driving force (-{Delta}G{sub r}). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.

  7. Validated spectrophotometric methods for determination of sodium valproate based on charge transfer complexation reactions

    NASA Astrophysics Data System (ADS)

    Belal, Tarek S.; El-Kafrawy, Dina S.; Mahrous, Mohamed S.; Abdel-Khalek, Magdi M.; Abo-Gharam, Amira H.

    2016-02-01

    This work presents the development, validation and application of four simple and direct spectrophotometric methods for determination of sodium valproate (VP) through charge transfer complexation reactions. The first method is based on the reaction of the drug with p-chloranilic acid (p-CA) in acetone to give a purple colored product with maximum absorbance at 524 nm. The second method depends on the reaction of VP with dichlone (DC) in dimethylformamide forming a reddish orange product measured at 490 nm. The third method is based upon the interaction of VP and picric acid (PA) in chloroform resulting in the formation of a yellow complex measured at 415 nm. The fourth method involves the formation of a yellow complex peaking at 361 nm upon the reaction of the drug with iodine in chloroform. Experimental conditions affecting the color development were studied and optimized. Stoichiometry of the reactions was determined. The proposed spectrophotometric procedures were effectively validated with respect to linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curves of the formed color products with p-CA, DC, PA and iodine showed good linear relationships over the concentration ranges 24-144, 40-200, 2-20 and 1-8 μg/mL respectively. The proposed methods were successfully applied to the assay of sodium valproate in tablets and oral solution dosage forms with good accuracy and precision. Assay results were statistically compared to a reference pharmacopoeial HPLC method where no significant differences were observed between the proposed methods and reference method.

  8. Baicalin inhibits the fenton reaction by enhancing electron transfer from Fe (2+) to dissolved oxygen.

    PubMed

    Nishizaki, Daisuke; Iwahashi, Hideo

    2015-01-01

    Sho-saiko-to is an herbal medicine that is known to have diverse pharmacological activities and has been used for the treatment of various infectious diseases. Here, we examined the effects of baicalin, a compound isolated from Sho-saiko-to, and the effects of the iron chelator quinolinic acid on the Fenton reaction. The control reaction mixture contained 0.1 M 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 0.2 mM H 2 O 2, 0.2 mM FeSO 4( NH 4)2 SO 4, and 40 mM sodium phosphate buffer (pH 7.4). Upon the addition of 0.6 mM baicalin or quinolinic acid to the control reaction mixture, the ESR peak heights of DMPO/OH radical adducts were measured as 32% ± 1% (baicalin) and 166% ± 27% (quinolinic acid) of that of the control mixture. In order to clarify why baicalin and quinolinic acid exerted opposite effects on the formation of hydroxyl radicals, we measured oxygen consumption in the presence of either compound. Upon the addition of 0.6 mM baicalin (or quinolinic acid) to the control reaction mixture without DMPO and H 2 O 2, the relative oxygen consumption rates were found to be 449% ± 40% (baicalin) and 18% ± 9% (quinolinic acid) of that of the control mixture without DMPO and H 2 O 2, indicating that baicalin facilitated the transfer of electrons from Fe (2+) to dissolved oxygen. Thus, the great majority of Fe (2+) turned into Fe (3+), and the formation of hydroxyl radicals was subsequently inhibited in this reaction. PMID:25640849

  9. Validated spectrophotometric methods for determination of sodium valproate based on charge transfer complexation reactions.

    PubMed

    Belal, Tarek S; El-Kafrawy, Dina S; Mahrous, Mohamed S; Abdel-Khalek, Magdi M; Abo-Gharam, Amira H

    2016-02-15

    This work presents the development, validation and application of four simple and direct spectrophotometric methods for determination of sodium valproate (VP) through charge transfer complexation reactions. The first method is based on the reaction of the drug with p-chloranilic acid (p-CA) in acetone to give a purple colored product with maximum absorbance at 524nm. The second method depends on the reaction of VP with dichlone (DC) in dimethylformamide forming a reddish orange product measured at 490nm. The third method is based upon the interaction of VP and picric acid (PA) in chloroform resulting in the formation of a yellow complex measured at 415nm. The fourth method involves the formation of a yellow complex peaking at 361nm upon the reaction of the drug with iodine in chloroform. Experimental conditions affecting the color development were studied and optimized. Stoichiometry of the reactions was determined. The proposed spectrophotometric procedures were effectively validated with respect to linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curves of the formed color products with p-CA, DC, PA and iodine showed good linear relationships over the concentration ranges 24-144, 40-200, 2-20 and 1-8μg/mL respectively. The proposed methods were successfully applied to the assay of sodium valproate in tablets and oral solution dosage forms with good accuracy and precision. Assay results were statistically compared to a reference pharmacopoeial HPLC method where no significant differences were observed between the proposed methods and reference method. PMID:26574649

  10. A general theoretical model for electron transfer reactions in complex systems.

    PubMed

    Amadei, Andrea; Daidone, Isabella; Aschi, Massimiliano

    2012-01-28

    In this paper we present a general theoretical-computational model for treating electron transfer reactions in complex atomic-molecular systems. The underlying idea of the approach, based on unbiased first-principles calculations at the atomistic level, utilizes the definition and the construction of the Diabatic Perturbed states of the involved reactive partners (i.e. the quantum centres in our perturbation approach) as provided by the interaction with their environment, including their mutual interaction. In this way we reconstruct the true Adiabatic states of the reactive partners characterizing the electron transfer process as the fluctuation of the electronic density due to the fluctuating perturbation. Results obtained by using a combination of Molecular Dynamics simulation and the Perturbed Matrix Method on a prototypical intramolecular electron transfer (from 2-(9,9'-dimethyl)fluorene to the 2-naphthalene group separated by a steroidal 5-α-androstane skeleton) well illustrate the accuracy of the method in reproducing both the thermodynamics and the kinetics of the process. PMID:22158942

  11. Intramolecular proton transfer and tunnelling reactions of hydroxyphenylbenzoxazole derivatives in Xenon at 15 K

    NASA Astrophysics Data System (ADS)

    Walla, Peter J.; Nickel, Bernhard

    2005-06-01

    We investigated the site dependence and the tunnelling processes of the intramolecular proton and deuteron transfer in the triplet state of the compounds 2-(2‧-hydroxy-4‧-methylphenyl)benzoxazole (m-MeHBO) and 2-(2‧-hydroxy-3‧-methylphenyl)benzoxazoles (o-MeHBO) and their deuterio-oxy analogues in a solid xenon matrix. After singlet excitation there occurs an ultrafast intramolecular enol → keto proton transfer and subsequent intersystem crossing mainly to the keto triplet state. In the triplet state of m-MeHBO, the proton transfer back to the lower enol triplet state is governed by tunnelling processes. In o-MeHBO, however, the enol triplet state is higher and therefore normally no tunnel reaction can be observed. Because of the external heavy atom-effect in a xenon matrix, we were able to investigate the reverse enol-keto-tunnelling after exciting directly the enol triplet state of deuterated o-MeHBO. The time constants of the reverse enol-keto tautomerization are similar to those of the normal keto-enol tautomerization. In a xenon matrix, the observed site-selective phosphorescence spectra are very well-resolved vibrationally. This allowed the study of the tunnel rates in different well-defined sites. The vibrational energies obtained in the spectra are in good agreement with vibrational energies found in resonant Raman and IR spectra of 2-(2‧-hydroxyphenyl)benzoxazole (HBO).

  12. Understanding Charge Transfer Reactions at the Interface of Plasmas in Contact with Liquids

    NASA Astrophysics Data System (ADS)

    Go, David

    2015-09-01

    Plasmas in and in contact with liquids offer a very rich physical and chemical environment where a multitude of species (electrons, ions, neutrals) and physical phenomena (light, electric fields) intersect. With emerging applications in medicine, environmental remediation, and materials synthesis, it has become paramount to understand the many processes occurring at the interface in order to design and optimize new technologies. Perhaps the most important plasma species is the electron, and it thus reasonable to assume it can play a critical role when plasmas are brought in contact with liquids as well. Over the past several years, our group has focused on deciphering the nature of electron transfer from a plasma to liquid and the subsequent chemistry the electrons induce. Our experimental configuration is the plasma equivalent of an electrochemical or electrolytic cell, where the cathode and anode are submerged in an electrolyte solution and current is carried by reduction reactions at the cathode and oxidation reactions at the anode. When the cathode is replaced by a plasma, the circuit is explicitly completed by the injection of plasma electrons into the solution where they stably solvate before inducing reduction reactions. Recently, we have demonstrated the first direct detection of these stably solvated electrons using a novel total internal reflection absorption spectroscopy experiment, resulting in the first measurement of the optical absorption spectrum for plasma-solvated electrons. Further, we have shown that the lifetime of these electrons can be significantly reduced if suitable solution- and plasma-phase scavengers are used to react quickly with these electrons. These results highlight the complexity of the plasma-liquid interface and how charge-transfer processes often compete with other chemistry that occurs at the plasma-liquid interface, such as the dissolution of plasma species into the liquid. This work was supported by the U.S. Army Research

  13. Online exhaled gas measurements for radiotherapy patients by proton transfer reaction mass spectrometry.

    PubMed

    Zou, Xue; Zhou, Wenzhao; Shen, Chengyin; Wang, Hongmei; Lu, Yan; Wang, Hongzhi; Chu, Yannan

    2016-08-01

    The present study assessed whether exhaled breath analysis using proton transfer reaction mass spectrometry (PTR-MS) could screen for radiation exposure. As the intensity of proton transfer reaction reagent ion H3(16)O(+) can be calculated with the intensity of H3(18)O(+), the intensity of H3(18)O(+) was monitored to observe the stability of the PTR-MS instrument during the experiment. The PTR-MS was applied for detecting the volatile organic compounds (VOCs) in the exhaled breath from 42 radiotherapy patients and other 61 patients who had not received radiotherapy. All patients were enrolled in the local cancer hospital. In the experiment, the subjects breathe slowly to the PTR-MS through a direct inlet system without any sampling bag or tube. The breath mass spectrometric data was statistically analyzed using Mann-Whitney U test and stepwise discriminant analysis to find the characteristic ions of radiation exposure. Receiver operating characteristics (ROC) analysis was applied for a combination of the characteristic ions. The PTR-MS instrument was stable as the intensity of reaction ion H3(16)O(+) was maintained in 1.1%. Through statistically analysis, we found 6 kinds of characteristic ions of radiation exposure, specifically mass-to-charge ratio (m/z) 93, m/z 41, m/z 102, m/z 79, m/z 131, and m/z 143. The sensitivity (true positive rate) and specificity (true negative rate) were 78.6% and 82.0% respectively. The integrated area under the ROC curve (AUC) was 0.869. The results in our study demonstrated the potential of the online breath tester PTR-MS as a non-invasive screening for radiation exposure. PMID:27209162

  14. Isolation, Characterization of an Intermediate in an Oxygen Atom-Transfer Reaction, and the Determination of the Bond Dissociation Energy

    SciTech Connect

    Nemykin, Victor N.; Laskin, Julia; Basu, Partha

    2004-07-19

    Redox reactions coupled with the formal loss or gain of an oxygen atom are ubiquitous in chemical processes. Such reactions proceed through the reduction of the donor center (XO) and the oxidation of the acceptor (Y) molecule. Among many examples of the metal centered oxygen atom transfer (OAT) reactivity, those involving molybdenum complexes have been widely investigated due to their involvement in mononuclear molybdenum enzymes. The heat of reaction of the overall atom transfer process can be expressed as a difference between the bond dissociation energies (BDEs) of the oxygen-donor(X) and oxygen-acceptor(Y) bond, i.e., H=DX=o-DY=O.

  15. Efficiencies of photoinduced electron-transfer reactions: Role of the Marcus inverted region in return electron transfer within geminate radical-ion pairs

    SciTech Connect

    Gould, I.R.; Ege, D.; Moser, J.E.; Farid, S. )

    1990-05-23

    In photoinduced electron-transfer processes the primary step is conversion of the electronic energy of an excited state into chemical energy retained in the form of a redox (geminate radical-ion) pair (A + D {sup hv}{yields} A{sup {sm bullet}{minus}}/D{sup {sm bullet}+}). In polar solvents, separation of the geminate pair occurs with formation of free radical ions in solution. The quantum yields of product formation, from reactions of either the free ions, or of the geminate pair, are often low, however, due to the return electron transfer reaction (A{sup {sm bullet}{minus}}/D{sup {sm bullet}+} {yields} A + D), an energy-wasting step that competes with the useful reactions of the ion pair. The present study was undertaken to investigate the parameters controlling the rates of these return electron transfer reactions. Quantum yields of free radical ion formation were measured for ion pairs formed upon electron-transfer quenching of the first excited singlet states of cyanoanthracenes by simple aromatic hydrocarbon donors in aceonitrile at room temperature. The free-ion yields are determined by the competition between the rates of separation and return electron transfer.

  16. Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions

    SciTech Connect

    Mader, Elizabeth A.; Manner, Virginia W.; Markle, Todd F.; Wu, Adam; Franz, James A.; Mayer, James M.

    2009-03-10

    Reported herein are thermochemical studies of hydrogen atom transfer (HAT) reactions involving transition metal H-atom donors MIILH and oxyl radicals. [FeII(H2bip)3]2+, [FeII(H2bim)3]2+, [CoII(H2bim)3]2+ and RuII(acac)2(py-imH) [H2bip = 2,2’-bi-1,4,5,6-tetrahydro¬pyrimidine, H2bim = 2,2’-bi-imidazoline, acac = 2,4-pentandionato, py-imH = 2-(2’-pyridyl)¬imidazole)] each react with TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) or tBu3PhO• (2,4,6-tri-tert-butylphenoxyl) to give the deprotonated, oxidized metal complex MIIIL, and TEMPOH or tBu3PhOH. Solution equilibrium measurements for the reactions of Co and Fe complexes with TEMPO show a large, negative ground-state entropy for hydrogen atom transfer: ΔSºHAT = -30 ± 2 cal mol-1 K-1 for the two iron complexes and -41 ± 2 cal mol-1 K-1 for [CoII(H2bim)3]2+. The ΔSºHAT for TEMPO + RuII(acac)2(py-imH) is much closer to zero, 4.9 ± 1.1 cal mol-1 K-1. Calorimetric measurements quantitatively confirm the enthalpy of reaction for [FeII(H2bip)3]2+ + TEMPO, thus also confirming ΔSºHAT. Calorimetry on TEMPOH + tBu3PhO• gives ΔHºHAT = 11.2 ± 0.5 kcal mol-1 which matches the enthalpy predicted from the difference in literature solution BDEs. An evaluation of the literature BDEs of both TEMPOH and tBu3PhOH is briefly presented and new estimates are included on the relative enthalpy of solvation for tBu3PhO• vs. tBu3PhOH. The primary contributor to the large magnitude of the ground-state entropy |ΔSºHAT| for the metal complexes is vibrational entropy, ΔSºvib. The common assumption that ΔSºHAT ≈ 0 for HAT reactions, developed for organic and small gas phase molecules, does not hold for transition metal based HAT reactions. The trend in magnitude of |ΔSºHAT| for reactions with TEMPO, RuII(acac)2(py-imH) << [FeII(H2bip)3]2+ = [FeII(H2bim)3]2+ < [CoII(H2bim)3]2+, is surprisingly well predicted by the trends for electron transfer half-reaction entropies, ΔSºET, in aprotic solvents. ΔSºET and

  17. Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions

    PubMed Central

    Mader, Elizabeth A.; Manner, Virginia W.; Markle, Todd F.; Wu, Adam; Franz, James A.; Mayer, James M.

    2009-01-01

    Reported herein are thermochemical studies of hydrogen atom transfer (HAT) reactions involving transition metal H-atom donors MIILH and oxyl radicals. [FeII(H2bip)3]2+, [FeII(H2bim)3]2+, [CoII(H2bim)3]2+ and RuII(acac)2(py-imH) [H2bip = 2,2’-bi-1,4,5,6-tetrahydropyrimidine, H2bim = 2,2’-bi-imidazoline, acac = 2,4-pentandionato, py-imH = 2-(2’-pyridyl)-imidazole)] each react with TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) or tBu3PhO• (2,4,6-tri-tert-butylphenoxyl) to give the deprotonated, oxidized metal complex MIIIL, and TEMPOH or tBu3PhOH. Solution equilibrium measurements for the reaction of [CoII(H2bim)3]2+ with TEMPO show a large, negative ground-state entropy for hydrogen atom transfer, −41 ± 2 cal mol−1 K−1. This is even more negative than the ΔSoHAT = −30 ± 2 cal mol−1 K−1 for the two iron complexes and the ΔSoHAT for RuII(acac)2(py-imH) + TEMPO, 4.9 ± 1.1 cal mol−1 K−1, as reported earlier. Calorimetric measurements quantitatively confirm the enthalpy of reaction for [FeII(H2bip)3]2+ + TEMPO, thus also confirming ΔSoHAT. Calorimetry on TEMPOH + tBu3PhO• gives ΔHoHAT = −11.2 ± 0.5 kcal mol−1 which matches the enthalpy predicted from the difference in literature solution BDEs. A brief evaluation of the literature thermochemistry of TEMPOH and tBu3PhOH supports the common assumption that ΔSoHAT ≈ 0 for HAT reactions of organic and small gas-phase molecules. However, this assumption does not hold for transition metal based HAT reactions. The trend in magnitude of |ΔSoHAT| for reactions with TEMPO, RuII(acac)2(py-imH) << [FeII(H2bip)3]2+ = [FeII(H2bim)3]2+ < [CoII(H2bim)3]2+, is surprisingly well predicted by the trends for electron transfer half-reaction entropies, ΔSoET, in aprotic solvents. This is because both ΔSoET and ΔSoHAT have substantial contributions from vibrational entropy, which varies significantly with the metal center involved. The close connection between ΔSoHAT and ΔSoET provides an important

  18. Catalytic N-radical cascade reaction of hydrazones by oxidative deprotonation electron transfer and TEMPO mediation.

    PubMed

    Hu, Xiao-Qiang; Qi, Xiaotian; Chen, Jia-Rong; Zhao, Quan-Qing; Wei, Qiang; Lan, Yu; Xiao, Wen-Jing

    2016-01-01

    Compared with the popularity of various C-centred radicals, the N-centred radicals remain largely unexplored in catalytic radical cascade reactions because of a lack of convenient methods for their generation. Known methods for their generation typically require the use of N-functionalized precursors or various toxic, potentially explosive or unstable radical initiators. Recently, visible-light photocatalysis has emerged as an attractive tool for the catalytic formation of N-centred radicals, but the pre-incorporation of a photolabile groups at the nitrogen atom largely limited the reaction scope. Here, we present a visible-light photocatalytic oxidative deprotonation electron transfer/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediation strategy for catalytic N-radical cascade reaction of unsaturated hydrazones. This mild protocol provides a broadly applicable synthesis of 1,6-dihydropyradazines with complete regioselectivity and good yields. The 1,6-dihydropyradazines can be easily transformed into diazinium salts that showed promising in vitro antifungal activities against fungal pathogens. DFT calculations are conducted to explain the mechanism. PMID:27048886

  19. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction.

    PubMed

    Zhu, Hongying; Huang, Guangming

    2015-03-31

    In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m(-3), ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages. PMID:25813029

  20. Catalytic N-radical cascade reaction of hydrazones by oxidative deprotonation electron transfer and TEMPO mediation

    PubMed Central

    Hu, Xiao-Qiang; Qi, Xiaotian; Chen, Jia-Rong; Zhao, Quan-Qing; Wei, Qiang; Lan, Yu; Xiao, Wen-Jing

    2016-01-01

    Compared with the popularity of various C-centred radicals, the N-centred radicals remain largely unexplored in catalytic radical cascade reactions because of a lack of convenient methods for their generation. Known methods for their generation typically require the use of N-functionalized precursors or various toxic, potentially explosive or unstable radical initiators. Recently, visible-light photocatalysis has emerged as an attractive tool for the catalytic formation of N-centred radicals, but the pre-incorporation of a photolabile groups at the nitrogen atom largely limited the reaction scope. Here, we present a visible-light photocatalytic oxidative deprotonation electron transfer/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediation strategy for catalytic N-radical cascade reaction of unsaturated hydrazones. This mild protocol provides a broadly applicable synthesis of 1,6-dihydropyradazines with complete regioselectivity and good yields. The 1,6-dihydropyradazines can be easily transformed into diazinium salts that showed promising in vitro antifungal activities against fungal pathogens. DFT calculations are conducted to explain the mechanism. PMID:27048886

  1. Neutron transfer reactions induced by {sup 8}Li on {sup 9}Be

    SciTech Connect

    Guimaraes, V.; Lichtenthaeler, R.; Camargo, O.; Barioni, A.; Assuncao, M.; Kolata, J. J.; Amro, H.; Becchetti, F. D.; Jiang, Hao; Aguilera, E. F.; Lizcano, D.; Martines-Quiroz, E.; Garcia, H.

    2007-05-15

    Angular distributions for the elastic scattering of {sup 8}Li on {sup 9}Be and the neutron transfer reactions {sup 9}Be({sup 8}Li,{sup 7}Li){sup 10}Be and {sup 9}Be({sup 8}Li,{sup 9}Li){sup 8}Be were measured with a 27 MeV {sup 8}Li radioactive nuclear beam. Spectr- oscopic factors for {sup 8}Li (multiply-in-circle sign)n{sup 9}Li and {sup 7}Li (multiply-in-circle sign)n{sup 8}Li bound systems were obtained from the comparison between the experimental differential cross section and finite-range distorted-wave Born approximation calculations with the code FRESCO. The spectroscopic factors obtained were compared to shell model calculations and to other experimental values from (d,p) reactions. Using the present values for the spectroscopic factor, cross sections for the direct neutron-capture reactions {sup 7}Li(n,{gamma}){sup 8}Li and {sup 8}Li(n,{gamma}){sup 9}Li were calculated in the framework of a potential model.

  2. Multinucleon transfer in O,1816,19F+208Pb reactions at energies near the fusion barrier

    NASA Astrophysics Data System (ADS)

    Rafferty, D. C.; Dasgupta, M.; Hinde, D. J.; Simenel, C.; Simpson, E. C.; Williams, E.; Carter, I. P.; Cook, K. J.; Luong, D. H.; McNeil, S. D.; Ramachandran, K.; Vo-Phuoc, K.; Wakhle, A.

    2016-08-01

    Background: Nuclear reactions are complex, involving collisions between composite systems where many-body dynamics determines outcomes. Successful models have been developed to explain particular reaction outcomes in distinct energy and mass regimes, but a unifying picture remains elusive. The irreversible transfer of kinetic energy from the relative motion of the collision partners to their internal states, as is known to occur in deep inelastic collisions, has yet to be successfully incorporated explicitly into fully quantal reaction models. The influence of these processes on fusion is not yet quantitatively understood. Purpose: To investigate the population of high excitation energies in transfer reactions at sub-barrier energies, which are precursors to deep inelastic processes, and their dependence on the internuclear separation. Methods: Transfer probabilities and excitation energy spectra have been measured in collisions of O,1816,19F+208Pb , at various energies below and around the fusion barrier, by detecting the backscattered projectile-like fragments in a Δ E -E telescope. Results: The relative yields of different transfer outcomes are strongly driven by Q values, but change with the internuclear separation. In 16O+208Pb , single nucleon transfer dominates, with a strong contribution from -2 p transfer close to the Coulomb barrier, though this channel becomes less significant in relation to the -2 p 2 n transfer channel at larger separations. For 18O+208Pb , the -2 p 2 n channel is the dominant charge transfer mode at all separations. In the reactions with 19F,-3 p 2 n transfer is significant close to the barrier, but falls off rapidly with energy. Multinucleon transfer processes are shown to lead to high excitation energies (up to ˜15 MeV), which is distinct from single nucleon transfer modes which predominantly populate states at low excitation energy. Conclusions: Kinetic energy is transferred into internal excitations following transfer, with this

  3. Theoretical analysis of co-solvent effect on the proton transfer reaction of glycine in a water–acetonitrile mixture

    SciTech Connect

    Kasai, Yukako; Yoshida, Norio Nakano, Haruyuki

    2015-05-28

    The co-solvent effect on the proton transfer reaction of glycine in a water–acetonitrile mixture was examined using the reference interaction-site model self-consistent field theory. The free energy profiles of the proton transfer reaction of glycine between the carboxyl oxygen and amino nitrogen were computed in a water–acetonitrile mixture solvent at various molar fractions. Two types of reactions, the intramolecular proton transfer and water-mediated proton transfer, were considered. In both types of the reactions, a similar tendency was observed. In the pure water solvent, the zwitterionic form, where the carboxyl oxygen is deprotonated while the amino nitrogen is protonated, is more stable than the neutral form. The reaction free energy is −10.6 kcal mol{sup −1}. On the other hand, in the pure acetonitrile solvent, glycine takes only the neutral form. The reaction free energy from the neutral to zwitterionic form gradually increases with increasing acetonitrile concentration, and in an equally mixed solvent, the zwitterionic and neutral forms are almost isoenergetic, with a difference of only 0.3 kcal mol{sup −1}. The free energy component analysis based on the thermodynamic cycle of the reaction also revealed that the free energy change of the neutral form is insensitive to the change of solvent environment but the zwitterionic form shows drastic changes. In particular, the excess chemical potential, one of the components of the solvation free energy, is dominant and contributes to the stabilization of the zwitterionic form.

  4. Theoretical analysis of co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture

    NASA Astrophysics Data System (ADS)

    Kasai, Yukako; Yoshida, Norio; Nakano, Haruyuki

    2015-05-01

    The co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture was examined using the reference interaction-site model self-consistent field theory. The free energy profiles of the proton transfer reaction of glycine between the carboxyl oxygen and amino nitrogen were computed in a water-acetonitrile mixture solvent at various molar fractions. Two types of reactions, the intramolecular proton transfer and water-mediated proton transfer, were considered. In both types of the reactions, a similar tendency was observed. In the pure water solvent, the zwitterionic form, where the carboxyl oxygen is deprotonated while the amino nitrogen is protonated, is more stable than the neutral form. The reaction free energy is -10.6 kcal mol-1. On the other hand, in the pure acetonitrile solvent, glycine takes only the neutral form. The reaction free energy from the neutral to zwitterionic form gradually increases with increasing acetonitrile concentration, and in an equally mixed solvent, the zwitterionic and neutral forms are almost isoenergetic, with a difference of only 0.3 kcal mol-1. The free energy component analysis based on the thermodynamic cycle of the reaction also revealed that the free energy change of the neutral form is insensitive to the change of solvent environment but the zwitterionic form shows drastic changes. In particular, the excess chemical potential, one of the components of the solvation free energy, is dominant and contributes to the stabilization of the zwitterionic form.

  5. Effect of mass transfer on the oxygen reduction reaction catalyzed by platinum dendrimer encapsulated nanoparticles.

    PubMed

    Dumitrescu, Ioana; Crooks, Richard M

    2012-07-17

    Here we report on the effect of the mass transfer rate (k(t)) on the oxygen reduction reaction (ORR) catalyzed by Pt dendrimer-encapsulated nanoparticles (DENs) comprised of 147 and 55 atoms (Pt(147) and Pt(55)). The experiments were carried out using a dual-electrode microelectrochemical device, which enables the study of the ORR under high k(t) conditions with simultaneous detection of H(2)O(2). At low k(t) (0.02 to 0.12 cm s(-1)) the effective number of electrons involved in ORR, n(eff), is 3.7 for Pt(147) and 3.4 for Pt(55). As k(t) is increased, the mass-transfer-limited current for the ORR becomes significantly lower than the value predicted by the Levich equation for a 4-electron process regardless of catalyst size. However, the percentage of H(2)O(2) detected remains constant, such that n(eff) barely changes over the entire k(t) range explored (0.02 cm s(-1)). This suggests that mass transfer does not affect n(eff), which has implications for the mechanism of the ORR on Pt nanoparticles. Interestingly, there is a significant difference in n(eff) for the two sizes of Pt DENs (n(eff) = 3.7 and 3.5 for Pt(147) and Pt(55), respectively) that cannot be assigned to mass transfer effects and that we therefore attribute to a particle size effect. PMID:22665772

  6. Dimerization and activation of porcine pancreatic phospholipase A2 via substrate level acylation of lysine 56.

    PubMed

    Tomasselli, A G; Hui, J; Fisher, J; Zürcher-Neely, H; Reardon, I M; Oriaku, E; Kézdy, F J; Heinrikson, R L

    1989-06-15

    The porcine pancreatic phospholipase A2-catalyzed hydrolysis of the water-soluble chromogenic substrate 4-nitro-3-octanoyloxybenzoate shows an initial latency phase similar to the one observed in the hydrolysis of aggregated phospholipids by the same enzyme. We report here that during the latency phase the enzyme undergoes a slow, autocatalytic, substrate-level acylation whereby in a few of the catalytic events the scissile octanoyl group of the substrate, normally transferred to water, is transferred to the epsilon-amino group of lysine 56. The N epsilon 56-octanoylphospholipase shows a strong tendency to dimerize in solution and thus may be separated from the monomeric native enzyme by gel filtration. Octanoylation of Lys-56 activates the enzyme some 180-fold toward 4-nitro-3-octanoyloxybenzoate and more than 100-fold toward monolayers of 1,2-didecanoyl-sn-glycero-3-phosphocholine. Acylation also attends the enzymatic hydrolysis of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine with the incorporation of 1 eq of palmitate. Kinetic analysis of the early phase of reaction with 4-nitro-3-octanoyloxybenzoate shows that in this initial step the rate of activation is first order with respect to enzyme and substrate. A much more rapid, autocatalytic activation occurs in the later phases of the reaction where the activation of the enzyme is catalyzed by the activated enzyme itself. These findings with porcine pancreatic phospholipase A2, together with those relative to a snake venom enzyme monomer (Cho, W., Tomasselli, A. G., Heinrikson, R. L., and Kézdy, F. J. (1988) J. Biol. Chem. 263, 11237-11241), strongly support the proposal that interfacial activation of monomeric phospholipases is due to substrate-level autoacylation resulting in fully potentiated dimeric enzymes. PMID:2498336

  7. Structural and dynamical control of the reaction rate in protein electron transfer

    NASA Astrophysics Data System (ADS)

    Balabin, Ilya A.

    Electron transfer (ET) reactions in proteins are key steps in many vital bioenergetic processes, and the reaction rate is known to be highly sensitive to the protein structure in some cases. For most bioenergetic reactions, as described by the Fermi Golden rule, the rate is proportional to a product of the average square of the effective electronic donor to acceptor coupling and a Franck-Condon factor, which accounts for the nuclear control of the energy gap. The nuclear factor is reasonably well described in Marcus theory and its modifications, and this work is focused on the mechanisms that control the effective coupling. About ten years ago, the Pathways model described for the first time how protein environment may control the effective coupling. In this work, a novel theoretical approach is developed to explore the mechanisms of structural and dynamical control beyond the qualitative level of the Pathways model. In Chapter 1, the assumptions of the Pathways model, its limitations and effects of the structure and the electronic Hamiltonian are investigated for model chain-like bridges using the Dyson's equations. In Chapter II, the framework to explore the sensitivity of the effective coupling to quality of the electronic Hamiltonian, the interference among the dominant pathways and the bridge dynamics is presented. This analysis employs the Green's function technique and includes combined molecular dynamics and electronic structure calculations. Finally, in Chapter III, this framework is tested on the bacterial photosynthetic reaction center, and the mechanisms of the structural and dynamical control for different ET steps are discussed.

  8. Femtosecond Dynamics of Fundamental Reaction Processes in Liquids: Proton Transfer, Geminate Recombination, Isomerization and Vibrational Relaxation.

    NASA Astrophysics Data System (ADS)

    Schwartz, Benjamin Joel

    Femtosecond and picosecond transient absorption spectroscopy are used to probe several fundamental aspects of chemical reactivity in the condensed phase including proton transfer, germinate recombination, isomerization and vibrational relaxation. The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured for the first time, and the effects of external hydrogen-bonding interactions on the proton transfer are studied in detail. The proton transfer takes place in ~240 fsec in non-polar environments, but becomes faster than the instrumental resolution of 110 fsec in methanol solutions. A simple model is proposed to explain these results. The dynamics following photodissociation of CH _2I_2 and other small molecules provide the first direct observations of germinate recombination. The recombination of many different photodissociating species occurs on a ~350 fsec time scale. Results also show that recombination yields but not rates depend on the molecular details of the solvent environment and suggest that recombination kinetics are dominated by a single collision with the surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. The data show no simple correlation between the hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes. This strongly implies that the isomerization of these systems does not provide a suitable testing ground for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in the photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial

  9. Enhanced Enzymatic Preparation of Biodiesel Using Ricinoleic Acid as Acyl Donor: Optimization Using Response Surface Methodology.

    PubMed

    Wang, Ping; Sun, Shangde

    2016-09-01

    Castor oil methyl ester is a kind of biodiesel from castor oil. However, in those previous methods for biodiesel preparation using castor oil as feedstock, glycerol was the main by-product, which had a strong blocking effect on the immobilized enzyme activity and affected the mass transfer of reaction system. For avoiding the negative effect of glycerol on the enzymatic esterification, biodiesel was prepared using ricinoleic acid (RA) as acyl donor. Enzyme screening was also studied, and the effects of reaction temperature, molar ratio of ricinoleic acid and methanol, enzyme load, and reaction time, on the preparation of castor methyl ester were also evaluated. Response surface methodology (RSM) was used to optimize the interaction effect of reaction variables (reaction temperature (30-70°C), enzyme load (2-7%; relative to the weight of total substrates), molar ratio of methanol to ricinoleic acid (2:1-10:1), and reaction time (0.5-2.5 h)) on the acid value (AV) and the degree of esterification (DE). Validation of the RSM model was verified by the good agreement between the experimental and the predicted values of AV and DE. The optimum preparation conditions were as follows: reaction temperature, 48.2°C; enzyme load, 5.8%; molar ratio of methanol to ricinoleic acid, 5.56:1; reaction time, 2.36 h. Under these conditions, the AV and DE of the esterification reaction are 10.36±1.05 mgKOH/g and 94.03±0.60%, respectively. The relationship between initial reaction rate and temperature was also established, and the activation energy (Ea) of the enzymatic esterification is 33.87 KJ/mol. PMID:27477073

  10. Population of isomeric states in fusion and transfer reactions in beams of loosely bound nuclei near the Coulomb barrier

    SciTech Connect

    Skobelev, N. K.

    2015-07-15

    The influence of the mechanisms of nuclear reactions on the population of {sup 195m}Hg and {sup 197m}Hg(7/2{sup −}), {sup 198m}Tl and {sup 196m}Tl(7{sup +}), and {sup 196m}Au and {sub 198m}Au(12{sup −}) isomeric nuclear states obtained in reactions induced by beams of {sup 3}He, {sup 6}Li, and {sup 6}He weakly bound nuclei is studied. The behavior of excitation functions and high values of isomeric ratios (δ{sub m}/δ{sub g}) for products of nuclear reactions proceeding through a compound nucleus and involving neutron evaporation are explained within statistical models. Reactions in which the emission of charged particles occurs have various isomeric ratios depending on the reaction type. The isomeric ratio is lower in direct transfer reactions involving charged-particle emission than in reactions where the evaporation of charged particles occurs. Reactions accompanied by neutron transfer usually have a lower isomeric ratio, which behaves differently for different direct-reaction types (stripping versus pickup reactions)

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

    PubMed

    Kojima, H; Yamada, A; Okazaki, S

    2015-05-01

    The intramolecular proton transfer reaction of malonaldehyde in neon solvent has been investigated by mixed quantum-classical molecular dynamics (QCMD) calculations and fully classical molecular dynamics (FCMD) calculations. Comparing these calculated results with those for malonaldehyde in water reported in Part I [A. Yamada, H. Kojima, and S. Okazaki, J. Chem. Phys. 141, 084509 (2014)], the solvent dependence of the reaction rate, the reaction mechanism involved, and the quantum effect therein have been investigated. With FCMD, the reaction rate in weakly interacting neon is lower than that in strongly interacting water. However, with QCMD, the order of the reaction rates is reversed. To investigate the mechanisms in detail, the reactions were categorized into three mechanisms: tunneling, thermal activation, and barrier vanishing. Then, the quantum and solvent effects were analyzed from the viewpoint of the reaction mechanism focusing on the shape of potential energy curve and its fluctuations. The higher reaction rate that was found for neon in QCMD compared with that found for water solvent arises from the tunneling reactions because of the nearly symmetric double-well shape of the potential curve in neon. The thermal activation and barrier vanishing reactions were also accelerated by the zero-point energy. The number of reactions based on these two mechanisms in water was greater than that in neon in both QCMD and FCMD because these reactions are dominated by the strength of solute-solvent interactions. PMID:25956108

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    SciTech Connect

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

    2015-05-07

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

  14. DHHC Protein S-Acyltransferases Use Similar Ping-Pong Kinetic Mechanisms but Display Different Acyl-CoA Specificities*

    PubMed Central

    Jennings, Benjamin C.; Linder, Maurine E.

    2012-01-01

    DHHC proteins catalyze the reversible S-acylation of proteins at cysteine residues, a modification important for regulating protein localization, stability, and activity. However, little is known about the kinetic mechanism of DHHC proteins. A high-performance liquid chromatography (HPLC), fluorescent peptide-based assay for protein S-acylation activity was developed to characterize mammalian DHHC2 and DHHC3. Time courses and substrate saturation curves allowed the determination of Vmax and Km values for both the peptide N-myristoylated-GCG and palmitoyl-coenzyme A. DHHC proteins acylate themselves upon incubation with palmitoyl-CoA, which is hypothesized to reflect a transient acyl enzyme transfer intermediate. Single turnover assays with DHHC2 and DHHC3 demonstrated that a radiolabeled acyl group on the enzyme transferred to the protein substrate, consistent with a two-step ping-pong mechanism. Enzyme autoacylation and acyltransfer to substrate displayed the same acyl-CoA specificities, further supporting a two-step mechanism. Interestingly, DHHC2 efficiently transferred acyl chains 14 carbons and longer, whereas DHHC3 activity was greatly reduced by acyl-CoAs with chain lengths longer than 16 carbons. The rate and extent of autoacylation of DHHC3, as well as the rate of acyl chain transfer to protein substrate, were reduced with stearoyl-CoA when compared with palmitoyl-CoA. This is the first observation of lipid substrate specificity among DHHC proteins and may account for the differential S-acylation of proteins observed in cells. PMID:22247542

  15. Neutron spectroscopic factors of 55Ni hole-states from (p,d) transfer reactions

    NASA Astrophysics Data System (ADS)

    Sanetullaev, A.; Tsang, M. B.; Lynch, W. G.; Lee, Jenny; Bazin, D.; Chan, K. P.; Coupland, D.; Henzl, V.; Henzlova, D.; Kilburn, M.; Rogers, A. M.; Sun, Z. Y.; Youngs, M.; Charity, R. J.; Sobotka, L. G.; Famiano, M.; Hudan, S.; Shapira, D.; Peters, W. A.; Barbieri, C.; Hjorth-Jensen, M.; Horoi, M.; Otsuka, T.; Suzuki, T.; Utsuno, Y.

    2014-09-01

    Spectroscopic information has been extracted on the hole-states of 55Ni, the least known of the quartet of nuclei (55Ni, 57Ni, 55Co and 57Cu), one nucleon away from 56Ni, the N=Z=28 double magic nucleus. Using the H1(Ni56,d)Ni55 transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f7/2, p3/2 and the s1/2 hole-states of 55Ni. These new data provide a benchmark for large basis calculations that include nucleonic orbits in both the sd and pf shells. State of the art calculations have been performed to describe the excitation energies and spectroscopic factors of the s1/2 hole-state below Fermi energy.

  16. Electron transfer reactions in microporous solids. Progress report, September 1990--January 1993

    SciTech Connect

    Mallouk, T.E.

    1993-01-01

    Basic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H{sub 2} and I{sub 3}{sup {minus}}, or H{sub 2} and O{sub 2)} from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies.

  17. Determination of Minor Actinides Fission Cross Sections by Means of Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Aiche, M.; Barreau, G.; Boyer, S.; Czajkowski, S.; Dassié, D.; Grosjean, C.; Guiral, A.; Haas, B.; Jurado, B.; Osmanov, B.; Bauge, E.; Petit, M.; Berthoumieux, E.; Gunsing, F.; Perrot, L.; Theisen, C.; Michel-Sendis, F.; Billebaud, A.; Wilson, J. N.; Ahmad, I.; Greene, J. P.; Janssens, R. V. F.

    2006-04-01

    An inventive method that allows to determine neutron-induced cross sections of very short-lived minor actinides is presented. We have successfully applied this method, based on the use of transfer reactions, to 233Pa, a key nucleus in the 232Th-233U fuel cycle. A recent experiment using this technique has also been performed in order to obtain the neutron-induced fission cross sections of 242, 243, 244Cm and 241Am which are present in the nuclear waste of the current U-Pu fuel cycle. These cross sections are highly relevant for the design of reactors capable to incinerate minor actinides. Preliminary experimental results will be presented.

  18. New recoil transfer chamber for thermalization of heavy ions produced in fusion-evaporation reactions

    NASA Astrophysics Data System (ADS)

    Alfonso, M. C.; Tereshatov, E. E.; DeVanzo, M. J.; Sefcik, J. A.; Bennett, M. E.; Mayorov, D. A.; Werke, T. A.; Folden, C. M.

    2015-10-01

    A new Recoil Transfer Chamber (RTC) has been designed, fabricated, and characterized at the Cyclotron Institute at Texas A&M University. The design is based on a gas stopper that was previously in routine use at the National Superconducting Cyclotron Laboratory. This new RTC uses He gas to stop ions, and a combination of a static electric field and gas flow to maximize the extraction efficiency. In offline experiments, a 228Th source was used to produce 216Po which was successfully extracted even though it has a short half-life. In online experiments using the products of the 118Sn(40Ar, 6n)152Er reaction, an efficiency of several tens of percent was measured.

  19. Model Based Determination of Detection Limits for Proton Transfer Reaction Mass Spectrometer

    NASA Astrophysics Data System (ADS)

    Amann, Anton; Schwarz, Konrad; Wimmer, Gejza; Witkovský, Viktor

    2010-01-01

    Proton Transfer Reaction Mass Spectrometry (PTR-MS) is a chemical ionization mass spectrometric technique which allows to measure trace gases as, for example, in exhaled human breath. The quantification of compounds at low concentrations is desirable for medical diagnostics. Typically, an increase of measuring accuracy can be achieved if the duration of the measuring process is extended. For real time measurements the time windows for measurement are relatively short, in order to get a good time resolution (e.g. with breath-to-breath resolution during exercise on a stationary bicycle). Determination of statistical detection limits is typically based on calibration measurements, but this approach is limited, especially for very low concentrations. To overcome this problem, a calculation of limit of quantification (LOQ) and limit of detection (LOD), respectively, based on a theoretical model of the measurement process is outlined.

  20. First measurement of transferred polarization in the exclusive ep-->e'K+Lambda--> reaction.

    PubMed

    Carman, D S; Joo, K; Mestayer, M D; Raue, B A; Adams, G; Ambrozewicz, P; Anciant, E; Anghinolfi, M; Armstrong, D S; Asavapibhop, B; Audit, G; Auger, T; Avakian, H; Bagdasaryan, H; Ball, J P; Barrow, S P; Battaglieri, M; Beard, K; Bektasoglu, M; Bellis, M; Bennhold, C; Bianchi, N; Biselli, A S; Boiarinov, S; Bonner, B E; Bouchigny, S; Bradford, R; Branford, D; Briscoe, W J; Brooks, W K; Burkert, V D; Butuceanu, C; Calarco, J R; Carnahan, B; Cazes, A; Cetina, C; Ciciani, L; Clark, R; Cole, P L; Coleman, A; Cords, D; Corvisiero, P; Crabb, D; Crannell, H; Cummings, J P; DeSanctis, E; Degtyarenko, P V; Denizli, H; Dennis, L; DeVita, R; Dharmawardane, K V; Dhuga, K S; Djalali, C; Dodge, G E; Doughty, D; Dragovitsch, P; Dugger, M; Dytman, S; Dzyubak, O P; Eckhause, M; Egiyan, H; Egiyan, K S; Elouadrhiri, L; Empl, A; Eugenio, P; Fatemi, R; Fedotov, G; Feuerbach, R J; Ficenec, J; Forest, T A; Funsten, H; Gaff, S J; Gai, M; Garçon, M; Gavalian, G; Gilad, S; Gilfoyle, G P; Giovanetti, K L; Girard, P; Golovach, E; Gordon, C I O; Griffioen, K; Grimes, S; Guidal, M; Guillo, M; Guo, L; Gyurjyan, V; Hadjidakis, C; Hakobyan, R S; Hardie, J; Heddle, D; Heimberg, P; Hersman, F W; Hicks, K; Hicks, R S; Holtrop, M; Hu, J; Hyde-Wright, C E; Ishkhanov, B; Ito, M M; Jenkins, D; Kelley, J H; Kellie, J D; Khandaker, M; Kim, K Y; Kim, K; Kim, W; Klein, A; Klein, F J; Klimenko, A V; Klusman, M; Kossov, M; Kramer, L H; Kuang, Y; Kuhn, S E; Kuhn, J; Lachniet, J; Laget, J M; Lawrence, D; Li, J; Livingston, K; Longhi, A; Lukashin, K; Manak, J J; Marchand, C; Mart, T; McAleer, S; McCarthy, J; McNabb, J W C; Mecking, B A; Mehrabyan, S; Melone, J J; Meyer, C A; Mikhailov, K; Minehart, R; Mirazita, M; Miskimen, R; Mokeev, V; Morand, L; Morrow, S A; Mozer, M U; Muccifora, V; Mueller, J; Murphy, L Y; Mutchler, G S; Napolitano, J; Nasseripour, R; Nelson, S O; Niccolai, S; Niculescu, G; Niculescu, I; Niczyporuk, B B; Niyazov, R A; Nozar, M; O'Rielly, G V; Opper, A K; Osipenko, M; Park, K; Paschke, K; Pasyuk, E; Peterson, G; Pivnyuk, N; Pocanic, D; Pogorelko, O; Polli, E; Pozdniakov, S; Preedom, B M; Price, J W; Prok, Y; Protopopescu, D; Qin, L M; Riccardi, G; Ricco, G; Ripani, M; Ritchie, B G; Ronchetti, F; Rossi, P; Rowntree, D; Rubin, P; Sabatié, F; Sabourov, K; Salgado, C; Santoro, J; Sapunenko, V; Schumacher, R A; Serov, V S; Sharabian, Y G; Shaw, J; Simionatto, S; Skabelin, A V; Smith, E S; Smith, L C; Sober, D I; Spraker, M; Stavinsky, A; Stepanyan, S; Stoler, P; Taiuti, M; Taylor, S; Tedeschi, D J; Thoma, U; Thompson, R; Todor, L; Tur, C; Ungaro, M; Vineyard, M F; Vlassov, A V; Wang, K; Weinstein, L B; Weller, H; Weygand, D P; Whisnant, C S; Wolin, E; Wood, M H; Yegneswaran, A; Yun, J; Zhang, B; Zhao, J; Zhou, Z

    2003-04-01

    The first measurements of the transferred polarization for the exclusive e-->p-->e(')K+Lambda--> reaction have been performed at Jefferson Laboratory using the CLAS spectrometer. A 2.567 GeV beam was used to measure the hyperon polarization over Q2 from 0.3 to 1.5 (GeV/c)(2), W from 1.6 to 2.15 GeV, and over the full K+ center-of-mass angular range. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. A nonrelativistic quark-model interpretation of our data suggests that the ssmacr; quark pair is produced with spins predominantly antialigned. Implications for the validity of the most widely used quark-pair creation operator are discussed. PMID:12689277

  1. Hole-states of 55Ni from (p,d) transfer reactions

    NASA Astrophysics Data System (ADS)

    Tsang, Betty; Sanetullaev, Alisher; Lynch, William; Lee, Jenny; Bazin, Daniel; Chan, K. P.; Coupland, Daniel; Henzl, Vlad; Henzlova, Daniela; Kilburn, Micha; Rogers, Andrew; Sun, Z. Y.; Youngs, Michael; Charity, Robert; Sobotka, Lee; Famiano, Michael; Hudan, Sylvie; Shapira, Daniel; Peters, W. A.; Barbieri, C.; Hjorth-Jensen, M.; Horoi, M.; Otsuka, T.; Suzuki, T.; Utsuno, Y.

    2014-09-01

    Spectroscopic information has been extracted on the hole-states of 55Ni. Using the 1H(56Ni,d)55Ni transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f7/2, p3/2 and the s1/2 hole-states of 55Ni. These new data provide a benchmark for large basis calculations that include nucleonic orbits in both the sd and pf shells. Most shell models describe the ground state and the first p3/2 excited state very well. However, most models have difficulties describing the deep hole state in the sd orbits. In this talk, we will compare the experimental energy levels and spectroscopic factors to state of the art shell model calculations. Spectroscopic information has been extracted on the hole-states of 55Ni. Using the 1H(56Ni,d)55Ni transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f7/2, p3/2 and the s1/2 hole-states of 55Ni. These new data provide a benchmark for large basis calculations that include nucleonic orbits in both the sd and pf shells. Most shell models describe the ground state and the first p3/2 excited state very well. However, most models have difficulties describing the deep hole state in the sd orbits. In this talk, we will compare the experimental energy levels and spectroscopic factors to state of the art shell model calculations. PHY-1102511.

  2. Proton-transfer reaction dynamics and energetics in calcification and decalcification.

    PubMed

    Suwa, Ryota; Hatta, Masayuki; Ichikawa, Kazuhiko

    2014-10-13

    CaCO3 -saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca(2+) +HCO3 (-) ⇌CaCO3 +H(+) ; and reversible static physical precipitation/dissolution, Ca(2+) +CO3 (2-) ⇌CaCO3 . The former reversible reaction was determined using a strong base and acid titration. The saturation state described by the pH/PCO2 -independent solubility product, [Ca(2+) ][CO3 (2-) ], may not be observed at pH below 8.5 because [Ca(2+) ][CO3 (2-) ]/([Ca(2+) ][HCO3 (-) ]) ≪1. Since proton transfer dynamics controls all reversible acid dissociation reactions in saline waters, the concentrations of calcium ion and dissolved inorganic carbon (DIC) were expressed as a function of dual variables, pH and PCO2 . The negative impact of ocean acidification on marine calcifying organisms was confirmed by applying the experimental culture data of each PCO2 /pH-dependent coral polyp skeleton weight (Wskel) to the proton transfer idea. The skeleton formation of each coral polyp was performed in microspaces beneath its aboral ectoderm. This resulted in a decalcification of 14 weight %, a normalized CaCO3 saturation state Λ of 1.3 at PCO2 ≈400 ppm and pH ≈8.0, and serious decalcification of 45 % and Λ 2.5 at PCO2 ≈1000 ppm and pH ≈7.8. PMID:25179204

  3. Inter-and intraspecific variation in excited-state triplet energy transfer rates in reaction centers of photosynthetic bacteria.

    SciTech Connect

    Laible, P. D.; Morris, Z. S.; Thurnauer, M. C.; Schiffer, M.; Hanson, D. K.

    2003-08-01

    In protein-cofactor reaction center (RC) complexes of purple photosynthetic bacteria, the major role of the bound carotenoid (C) is to quench the triplet state formed on the primary electron donor (P) before its sensitization of the excited singlet state of molecular oxygen from its ground triplet state. This triplet energy is transferred from P to C via the bacteriochlorophyll monomer B{sub B}. Using time-resolved electron paramagnetic resonance (TREPR), we have examined the temperature dependence of the rates of this triplet energy transfer reaction in the RC of three wild-type species of purple nonsulfur bacteria. Species-specific differences in the rate of transfer were observed. Wild-type Rhodobacter capsulatus RCs were less efficient at the triplet transfer reaction than Rhodobacter sphaeroides RCs, but were more efficient than Rhodospirillum rubrum RCs. In addition, RCs from three mutant strains of R. capsulatus carrying substitutions of amino acids near P and B{sub B} were examined. Two of the mutant RCs showed decreased triplet transfer rates compared with wild-type RCs, whereas one of the mutant RCs demonstrated a slight increase in triplet transfer rate at low temperatures. The results show that site-specific changes within the RC of R. capsulatus can mimic interspecies differences in the rates of triplet energy transfer. This application of TREPR was instrumental in defining critical energetic and coupling factors that dictate the efficiency of this photoprotective process.

  4. Electron Transfer Reactions in Biological Systems: The Reduction of Ferricytochrome c by Chromous Ions

    PubMed Central

    Grimes, Carol J.; Piszkiewicz, Dennis; Fleischer, Everly B.

    1974-01-01

    Chromous ion reacts with ferricytochrome c to yield a one-to-one Cr(III)-ferrocytochrome c complex. This material, when hydrolyzed by trypsin and subjected to chromatographic procedures, yielded two fragments containing chromium. The amino-acid compositions and chemical characteristics of each of these fragments indicated that the chromium had crosslinked two segments of polypeptide chain; these were residues 40-53-Cr(III)-residues 61-72 and residues 40-53-Cr(III)-residues 61-73. Examination of a model of the ferricytochrome c molecule indicated that only two residues of the crosslinked peptides were sufficiently close to allow crosslinking to take place. These residues were tyrosine 67 and asparagine 52. Enzymatic hydrolysis of one of those fragments by aminopeptidase M supported this identification. The position of the chromic ion implies what is the path of electron transfer from the chromous ion to the ferric ion in this chemical reduction of cytochrome c, and suggests a possible path of electron transfer in biological oxidation-reduction reactions. PMID:4364536

  5. Phosphoryl transfer reaction snapshots in crystals: Insights into the mechanism of protein kinase a catalytic subunit

    DOE PAGESBeta

    Das, Amit; Gerlits, Oksana O.; Heller, William T.; Kovalevskyi, Andrii Y.; Langan, Paul; Tian, Jianhui

    2015-06-19

    To study the catalytic mechanism of phosphorylation catalyzed by cAMP-dependent protein kinase (PKA) a structure of the enzyme-substrate complex representing the Michaelis complex is of specific interest as it can shed light on the structure of the transition state. However, all previous crystal structures of the Michaelis complex mimics of the PKA catalytic subunit (PKAc) were obtained with either peptide inhibitors or ATP analogs. Here we utilized Ca2+ ions and sulfur in place of the nucleophilic oxygen in a 20-residue pseudo-substrate peptide (CP20) and ATP to produce a close mimic of the Michaelis complex. In the ternary reactant complex, themore » thiol group of Cys-21 of the peptide is facing Asp-166 and the sulfur atom is positioned for an in-line phosphoryl transfer. Replacement of Ca2+ cations with Mg2+ ions resulted in a complex with trapped products of ATP hydrolysis: phosphate ion and ADP. As a result, the present structural results in combination with the previously reported structures of the transition state mimic and phosphorylated product complexes complete the snapshots of the phosphoryl transfer reaction by PKAc, providing us with the most thorough picture of the catalytic mechanism to date.« less

  6. Transfer reactions in inverse kinematics: An experimental approach for fission investigations

    NASA Astrophysics Data System (ADS)

    Rodríguez-Tajes, C.; Farget, F.; Derkx, X.; Caamaño, M.; Delaune, O.; Schmidt, K.-H.; Clément, E.; Dijon, A.; Heinz, A.; Roger, T.; Audouin, L.; Benlliure, J.; Casarejos, E.; Cortina, D.; Doré, D.; Fernández-Domínguez, B.; Jacquot, B.; Jurado, B.; Navin, A.; Paradela, C.; Ramos, D.; Romain, P.; Salsac, M. D.; Schmitt, C.

    2014-02-01

    Inelastic and multinucleon transfer reactions between a 238U beam, accelerated at 6.14 MeV/u, and a 12C target were used for the production of neutron-rich, fissioning systems from U to Cm. A Si telescope, devoted to the detection of the targetlike nuclei, provided a characterization of the fissioning systems in atomic and mass numbers, as well as in excitation energy. Cross sections and angular and excitation-energy distributions were measured for the inelastic and transfer channels. Possible excitations of the targetlike nuclei were experimentally investigated for the first time, by means of γ-ray measurements. The decays from the first excited states of 12C, 11B, and 10Be were observed with probabilities of 0.12-0.14, while no evidence for the population of higher-lying states was found. Moreover, the fission probabilities of 238U, 239Np and 240,241,242Pu and 244Cm were determined as a function of the excitation energy.

  7. Phosphoryl transfer reaction snapshots in crystals: Insights into the mechanism of protein kinase a catalytic subunit

    SciTech Connect

    Das, Amit; Gerlits, Oksana O.; Heller, William T.; Kovalevskyi, Andrii Y.; Langan, Paul; Tian, Jianhui

    2015-06-19

    To study the catalytic mechanism of phosphorylation catalyzed by cAMP-dependent protein kinase (PKA) a structure of the enzyme-substrate complex representing the Michaelis complex is of specific interest as it can shed light on the structure of the transition state. However, all previous crystal structures of the Michaelis complex mimics of the PKA catalytic subunit (PKAc) were obtained with either peptide inhibitors or ATP analogs. Here we utilized Ca2+ ions and sulfur in place of the nucleophilic oxygen in a 20-residue pseudo-substrate peptide (CP20) and ATP to produce a close mimic of the Michaelis complex. In the ternary reactant complex, the thiol group of Cys-21 of the peptide is facing Asp-166 and the sulfur atom is positioned for an in-line phosphoryl transfer. Replacement of Ca2+ cations with Mg2+ ions resulted in a complex with trapped products of ATP hydrolysis: phosphate ion and ADP. As a result, the present structural results in combination with the previously reported structures of the transition state mimic and phosphorylated product complexes complete the snapshots of the phosphoryl transfer reaction by PKAc, providing us with the most thorough picture of the catalytic mechanism to date.

  8. Metalloprotein electron transfer reactions: analysis of reactivity of horse heart cytochrome c with inorganic complexes.

    PubMed Central

    Wherland, S; Gray, H B

    1976-01-01

    The reactions of horse heart cytochrome c with Fe(ethylenediaminetetraacetate)2-, Co(1,10-phenanthroline)3(3+), Ru(NH3)6(2+), and Fe(CN)6(3-) have been analyzed within the formalism of the Marcus theory of outer-sphere electron transfer, including compensation for electrostatic interactions. Calculated protein self-exchange rate constants based on crossreactions are found to vary over three orders of magnitude, decreasing according to Fe(CN)6(3-) greater than Ru(NH3)6(2+) greater than Fe(EDTA)2-. The reactivity order suggests that the mechanism of electron transfer involves attack by the small molecule reagents near the most nearly exposed region of the heme; this attack is affected by electrostatic interactions with the positively charged protein, by hydrophobic interactions that permit reagent penetration of the protein surface, and by the availability of pi symmetry ligand (or extended metal) orbitals that can overlap with the pi redox orbitals of the heme group. PMID:184452

  9. Modified acyl-ACP desaturase

    DOEpatents

    Cahoon, Edgar B.; Shanklin, John; Lindgvist, Ylva; Schneider, Gunter

    1998-01-06

    Disclosed is a methods for modifying the chain length and double bond positional specificities of a soluble plant fatty acid desaturase. More specifically, the method involves modifying amino acid contact residues in the substrate binding channel of the soluble fatty acid desaturase which contact the fatty acid. Specifically disclosed is the modification of an acyl-ACP desaturase. Amino acid contact residues which lie within the substrate binding channel are identified, and subsequently replaced with different residues to effect the modification of activity.

  10. Modified Acyl-ACP desaturase

    DOEpatents

    Cahoon, Edgar B.; Shanklin, John; Lindqvist, Ylva; Schneider, Gunter

    1999-03-30

    Disclosed is a method for modifying the chain length and double bond positional specificities of a soluble plant fatty acid desaturase. More specifically, the method involves modifying amino acid contact residues in the substrate binding channel of the soluble fatty acid desaturase which contact the fatty acid. Specifically disclosed is the modification of an acyl-ACP desaturase. Amino acid contact residues which lie within the substrate binding channel are identified, and subsequently replaced with different residues to effect the modification of activity.

  11. Multiparameter Estimation in Voltammetry When an Electron Transfer Process Is Coupled to a Chemical Reaction.

    PubMed

    Simonov, Alexandr N; Morris, Graham P; Mashkina, Elena; Bethwaite, Blair; Gillow, Kathryn; Baker, Ruth E; Gavaghan, David J; Bond, Alan M

    2016-05-01

    Estimation of thermodynamic and kinetic parameters in electrochemical studies is usually undertaken via comparison of the experimental results with theory based on a model that mimics the experiment. The present study examines the credibility of transient d.c. and a.c. voltammetric theory-experiment comparisons for recovery of the parameters needed to model the ubiquitous mechanism when an electron transfer (E) reaction is followed by a chemical (C) step in the EC process ([Formula: see text]). The data analysis has been undertaken using optimization methods facilitated in some cases by grid computing. These techniques have been applied to the simulated (5% noise added) and experimental (reduction of trans-stilbene) voltammograms to assess the capabilities of parameter recovery of E(0) (reversible potential for the E step), k(0) (heterogeneous electron transfer rate constant at E(0)), α (charge transfer coefficient for the E step), and k(f) and k(b) (forward and backward rate constants for the C step) under different kinetic regimes. The advantages provided by the use of a.c. instead of d.c. voltammetry and data optimization methods over heuristic approaches to "experiment"-theory comparisons are discussed, as are the limitations in the efficient recovery of a unique set of parameters for the EC mechanism. In the particular experimental case examined herein, results for the protonation of the electrochemically generated stilbene dianion demonstrate that, notwithstanding significant advances in experiment and theory of voltammetric analysis, reliable recovery of the parameters for the EC mechanism with a fast chemical process remains a stiff problem. PMID:27041344

  12. Electron-transfer reactions of the reductase component of soluble methane monooxygenase from Methylococcus capsulatus (Bath).

    PubMed

    Kopp, D A; Gassner, G T; Blazyk, J L; Lippard, S J

    2001-12-11

    Soluble methane monooxygenase (sMMO) catalyzes the hydroxylation of methane by dioxygen to afford methanol and water, the first step of carbon assimilation in methanotrophic bacteria. This enzyme comprises three protein components: a hydroxylase (MMOH) that contains a dinuclear nonheme iron active site; a reductase (MMOR) that facilitates electron transfer from NADH to the diiron site of MMOH; and a coupling protein (MMOB). MMOR uses a noncovalently bound FAD cofactor and a [2Fe-2S] cluster to mediate electron transfer. The gene encoding MMOR was cloned from Methylococcus capsulatus (Bath) and expressed in Escherichia coli in high yield. Purified recombinant MMOR was indistinguishable from the native protein in all aspects examined, including activity, mass, cofactor content, and EPR spectrum of the [2Fe-2S] cluster. Redox potentials for the FAD and [2Fe-2S] cofactors, determined by reductive titrations in the presence of indicator dyes, are FAD(ox/sq), -176 +/- 7 mV; FAD(sq/hq), -266 +/- 15 mV; and [2Fe-2S](ox/red), -209 +/- 14 mV. The midpoint potentials of MMOR are not altered by the addition of MMOH, MMOB, or both MMOH and MMOB. The reaction of MMOR with NADH was investigated by stopped-flow UV-visible spectroscopy, and the kinetic and spectral properties of intermediates are described. The effects of pH on the redox properties of MMOR are described and exploited in pH jump kinetic studies to measure the rate constant of 130 +/- 17 s(-)(1) for electron transfer between the FAD and [2Fe-2S] cofactors in two-electron-reduced MMOR. The thermodynamic and kinetic parameters determined significantly extend our understanding of the sMMO system. PMID:11732913

  13. Direct observation of the transition state of ultrafast electron transfer reaction of a radiosensitizing drug bromodeoxyuridine

    SciTech Connect

    Wang, C.-R.; Hu, A.; Lu, Q.-B.

    2006-06-28

    Replacement of thymidine in DNA by bromodeoxyuridine (BrdU) has long been known to enhance DNA damage and cell death induced by ionizing/UV radiation, but the mechanism of action of BrdU at the molecular level is poor understood. Using time-resolved femtosecond laser spectroscopy, we obtain the real-time observation of the transition state of the ultrafast electron transfer (ET) reaction of BrdU with the precursor to the hydrated electron, which is a general product in ionizing/UV radiation. The results show that the ET reaction is completed within 0.2 picosecond (ps) after the electronic excitation, leading to the formation of a transition state BrdU*{sup -} with a lifetime of {approx}1.5 ps that then dissociates into Br{sup -} and a high reactive radical dU{sup *}. The present results can greatly enhance our understanding not only of the mechanism of BrdU as a radio-/photosensitizer but of the role of prehydrated electrons in electron-initiated processes in biological and environmental systems.

  14. Polymerization of Acetonitrile via a Hydrogen Transfer Reaction from CH3 to CN under Extreme Conditions

    DOE PAGESBeta

    Zheng, Haiyan; Li, Kuo; Cody, George D.; Tulk, Christopher A.; Dong, Xiao; Gao, Guoying; Molaison, Jamie J.; Liu, Zhenxian; Feygenson, Mikhail; Yang, Wenge; et al

    2016-08-25

    Acetonitrile (CH3CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. In this study, it is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH3 to CN along the CH···N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed sp2 and sp3more » bonded carbon. Lastly, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst.« less

  15. Direct observation of the transition state of ultrafast electron transfer reaction of a radiosensitizing drug bromodeoxyuridine

    NASA Astrophysics Data System (ADS)

    Wang, C.-R.; Hu, A.; Lu, Q.-B.

    2006-06-01

    Replacement of thymidine in DNA by bromodeoxyuridine (BrdU) has long been known to enhance DNA damage and cell death induced by ionizing/UV radiation, but the mechanism of action of BrdU at the molecular level is poor understood. Using time-resolved femtosecond laser spectroscopy, we obtain the real-time observation of the transition state of the ultrafast electron transfer (ET) reaction of BrdU with the precursor to the hydrated electron, which is a general product in ionizing/UV radiation. The results show that the ET reaction is completed within 0.2picosecond (ps) after the electronic excitation, leading to the formation of a transition state BrdU*- with a lifetime of ˜1.5ps that then dissociates into Br- and a high reactive radical dU*. The present results can greatly enhance our understanding not only of the mechanism of BrdU as a radio-/photosensitizer but of the role of prehydrated electrons in electron-initiated processes in biological and environmental systems.

  16. Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

    PubMed Central

    Chen, Chao; Lu, Chunxin; Zheng, Qing; Zhang, Min

    2015-01-01

    Summary Ruthenium complexes [Ru(L1)2(CH3CN)2](PF6)2 (1), [RuL1(CH3CN)4](PF6)2 (2) and [RuL2(CH3CN)3](PF6)2 (3) (L1= 3-methyl-1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetallation reaction of the corresponding nickel–NHC complexes with [Ru(p-cymene)2Cl2]2 in refluxing acetonitrile solution. The crystal structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands displaying the typical octahedral geometry. The reaction of [RuL1(CH3CN)4](PF6)2 with triphenylphosphine and 1,10-phenanthroline resulted in the substitution of one and two coordinated acetonitrile ligands and afforded [RuL1(PPh3)(CH3CN)3](PF6)2 (4) and [RuL1(phen)(CH3CN)2](PF6)2 (5), respectively. The molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones. PMID:26664598

  17. Polymerization of Acetonitrile via a Hydrogen Transfer Reaction from CH3 to CN under Extreme Conditions.

    PubMed

    Zheng, Haiyan; Li, Kuo; Cody, George D; Tulk, Christopher A; Dong, Xiao; Gao, Guoying; Molaison, Jamie J; Liu, Zhenxian; Feygenson, Mikhail; Yang, Wenge; Ivanov, Ilia N; Basile, Leonardo; Idrobo, Juan-Carlos; Guthrie, Malcolm; Mao, Ho-Kwang

    2016-09-19

    Acetonitrile (CH3 CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. It is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH3 to CN along the CH⋅⋅⋅N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed sp(2) and sp(3) bonded carbon. Finally, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst. PMID:27561179

  18. Radiolytic and electron-transfer reactions in supercritical CO{sub 2}

    SciTech Connect

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

    2000-01-19

    Using supercritical fluids as solvents is useful for both practical and theoretical reasons. It has been proposed to use supercritical CO{sub 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{sub 2} and have measured their reactivity as a function of density. They have shown that the C{sub 2}O{sub 4}{sup +} is formed. They also have shown that the electron transfer reactions of dimethylaniline to C{sub 2}O{sub 4}{sup +} and CO{sub 2}(e{sup {minus}}) to benzoquinone are diffusion controlled over a considerable density range.

  19. Survey of {sup 17}O excited states selectively populated by five-particle transfer reactions

    SciTech Connect

    Crisp, A. M.; Roeder, B. T.; Momotyuk, O. A.; Kemper, K. W.; Weintraub, W.; Wiedeking, M.; Keeley, N.

    2008-04-15

    The highly selective reactions {sup 12}C({sup 7}Li,d){sup 17}O and {sup 12}C({sup 6}Li,p){sup 17}O have been used to populate high-lying excited states in {sup 17}O up to 16 MeV in excitation. Several of the states are newly observed, and the existence of others in a previous study of {sup 12}C({sup 6}Li,p){sup 17}O is confirmed. The observed spectra show a clear gap of about 3 MeV, indicating an energy gap between 3p-2h and 5p-4h states in {sup 17}O. Differential cross section angular distributions have been extracted from the data for both reactions and they have been compared with finite-range DWBA calculations by assuming a ''{sup 5}He'' cluster transfer. Possible spins and parities are reported for states at 11.82 MeV (7/2{sup +}), 12.00 MeV (9/2{sup +}),12.22 MeV (7/2{sup -}), and 12.42 MeV (9/2{sup +})

  20. Single-collision studies of hot atom energy transfer and chemical reaction

    SciTech Connect

    Valentini, J.J. )

    1991-01-01

    This report discusses research in the collision dynamics of translationally hot atoms, with funding with DOE for the project Single-Collision Studies of Hot Atom Energy Transfer and Chemical Reaction,'' Grant Number DE-FG03-85ER13453. The work reported here was done during the period September 9, 1988 through October 31, 1991. During this period this DOE-funded work has been focused on several different efforts: (1) experimental studies of the state-to-state dynamics of the H + RH {yields} H{sub 2} R reactions where RH is CH{sub 4}, C{sub 2}H{sub 6}, or C{sub 3}H{sub 8}, (2) theoretical (quasiclassical trajectory) studies of hot hydrogen atom collision dynamics, (3) the development of photochemical sources of translationally hot molecular free radicals and characterization of the high resolution CARS spectroscopy of molecular free radicals, (4) the implementation of stimulated Raman excitation (SRE) techniques for the preparation of vibrationally state-selected molecular reactants.

  1. Single-collision studies of hot atom energy transfer and chemical reaction. Final report

    SciTech Connect

    Valentini, J.J.

    1991-12-31

    This report discusses research in the collision dynamics of translationally hot atoms, with funding with DOE for the project ``Single-Collision Studies of Hot Atom Energy Transfer and Chemical Reaction,`` Grant Number DE-FG03-85ER13453. The work reported here was done during the period September 9, 1988 through October 31, 1991. During this period this DOE-funded work has been focused on several different efforts: (1) experimental studies of the state-to-state dynamics of the H + RH {yields} H{sub 2} R reactions where RH is CH{sub 4}, C{sub 2}H{sub 6}, or C{sub 3}H{sub 8}, (2) theoretical (quasiclassical trajectory) studies of hot hydrogen atom collision dynamics, (3) the development of photochemical sources of translationally hot molecular free radicals and characterization of the high resolution CARS spectroscopy of molecular free radicals, (4) the implementation of stimulated Raman excitation (SRE) techniques for the preparation of vibrationally state-selected molecular reactants.

  2. Nitrogen-doped graphene prepared by a transfer doping approach for the oxygen reduction reaction application

    NASA Astrophysics Data System (ADS)

    Mo, Zaiyong; Zheng, Ruiping; Peng, Hongliang; Liang, Huagen; Liao, Shijun

    2014-01-01

    Well defined nitrogen-doped graphene (NG) is prepared by a transfer doping approach, in which the graphene oxide (GO) is deoxidized and nitrogen doped by the vaporized polyaniline, and the GO is prepared by a thermal expansion method from graphite oxide. The content of doped nitrogen in the doped graphene is high up to 6.25 at% by the results of elements analysis, and oxygen content is lowered to 5.17 at%. As a non-precious metal cathode electrocatalyst, the NG catalyst exhibits excellent activity toward the oxygen reduction reaction, as well as excellent tolerance toward methanol. In 0.1 M KOH solution, its onset potential, half-wave potential and limiting current density for the oxygen reduction reaction reach 0.98 V (vs. RHE), 0.87 V (vs. RHE) and 5.38 mA cm-2, respectively, which are comparable to those of commercial 20 wt% Pt/C catalyst. The well defined graphene structure of the catalyst is revealed clearly by HRTEM and Raman spectra. It is suggested that the nitrogen-doping and large surface area of the NG sheets give the main contribution to the high ORR catalytic activity.

  3. Study of fluorescence characteristics of the charge-transfer reaction of quinolone agents with bromanil

    NASA Astrophysics Data System (ADS)

    Li, Wen-Ying; Chen, Xiao-Fang; Xuan, Chun-Sheng

    2009-01-01

    A spectrofluorimetric method was discussed for the determination of three antibacterial quinolone derivatives, ofloxacin (OFL), norfloxacin (NOR) and ciprofloxacin (CIP) through charge-transfer complexation (CTC) with 2,3,5,6-tetrabromo-1,4-benzoquinone (bromanil, TBBQ). The method was based on the reaction of these drugs as n-electron donors with the π-acceptor TBBQ. TBBQ was found to react with these drugs to produce a kind of yellow complexes and the fluorescence intensities of the complexes were enhanced by 29-36 times more than those of the corresponding monomers. UV-vis, 1H NMR and XPS techniques were used to study the complexes formed. The various experimental parameters affecting the fluorescence intensity were studied and optimized. Under optimal reaction conditions, the rectilinear calibration graphs were obtained in the concentration range of 0.021-2.42 μg mL -1, 0.017-2.63 μg mL -1 and 0.019-2.14 μg mL -1 for OFL, NOR and CIP, respectively. The methods developed were applied successfully to the determination of the subject drugs in their pharmaceutical dosage forms with good precision and accuracy compared to official and reported methods as revealed by t- and F-tests.

  4. Probing Nonadiabaticity in the Proton-Coupled Electron Transfer Reaction Catalyzed by Soybean Lipoxygenase

    PubMed Central

    2014-01-01

    Proton-coupled electron transfer (PCET) plays a vital role in many biological and chemical processes. PCET rate constant expressions are available for various well-defined regimes, and determining which expression is appropriate for a given system is essential for reliable modeling. Quantitative diagnostics have been devised to characterize the vibronic nonadiabaticity between the electron–proton quantum subsystem and the classical nuclei, as well as the electron–proton nonadiabaticity between the electrons and proton(s) within the quantum subsystem. Herein these diagnostics are applied to a model of the active site of the enzyme soybean lipoxygenase, which catalyzes a PCET reaction that exhibits unusually high deuterium kinetic isotope effects at room temperature. Both semiclassical and electronic charge density diagnostics illustrate vibronic and electron–proton nonadiabaticity for this PCET reaction, supporting the use of the Golden rule nonadiabatic rate constant expression with a specific form of the vibronic coupling. This type of characterization will be useful for theoretical modeling of a broad range of PCET processes. PMID:25258676

  5. Solvent free energy curves for electron transfer reactions: A nonlinear solvent response model

    NASA Astrophysics Data System (ADS)

    Ichiye, Toshiko

    1996-05-01

    Marcus theory for electron transfer assumes a linear response of the solvent so that both the reactant and product free energy curves are parabolic functions of the solvent polarization, each with the same solvent force constant k characterizing the curvature. Simulation data by other workers indicate that the assumption of parabolic free energy curves is good for the Fe2+-Fe3+ self-exchange reaction but that the k of the reactant and product free energy curves are different for the reaction D0+A0→D1-+A1+. However, the fluctuations sampled in these simulations were not large enough to reach the activation barrier region, which was thus treated either by umbrella sampling or by parabolic extrapolation. Here, we present free energy curves calculated from a simple model of ionic solvation developed in an earlier paper by Hyun, Babu, and Ichiye, which we refer to here as the HBI model. The HBI model describes the nonlinearity of the solvent response due to the orientation of polar solvent molecules. Since it is a continuum model, it may be considered the first-order nonlinear correction to the linear response Born model. Moreover, in the limit of zero charge or infinite radius, the Born model and the Marcus relations are recovered. Here, the full free energy curves are calculated using analytic expressions from the HBI model. The HBI reactant and product curves have different k for D0+A0→D1-+A1+ as in the simulations, but examining the full curves shows they are nonparabolic due to the nonlinear response of the solvent. On the other hand, the HBI curves are close to parabolic for the Fe2+-Fe3+ reaction, also in agreement with simulations, while those for another self-exchange reaction D0-A1+ show greater deviations from parabolic behavior than the Fe2+-Fe3+ reaction. This indicates that transitions from neutral to charged species will have the largest deviations. Thus, the second moment of the polarization is shown to be a measure of the deviation from Marcus

  6. Fatty acylation of proteins: The long and the short of it.

    PubMed

    Resh, Marilyn D

    2016-07-01

    Long, short and medium chain fatty acids are covalently attached to hundreds of proteins. Each fatty acid confers distinct biochemical properties, enabling fatty acylation to regulate intracellular trafficking, subcellular localization, protein-protein and protein-lipid interactions. Myristate and palmitate represent the most common fatty acid modifying groups. New insights into how fatty acylation reactions are catalyzed, and how fatty acylation regulates protein structure and function continue to emerge. Myristate is typically linked to an N-terminal glycine, but recent studies reveal that lysines can also be myristoylated. Enzymes that remove N-terminal myristoyl-glycine or myristate from lysines have now been identified. DHHC proteins catalyze S-palmitoylation, but the mechanisms that regulate substrate recognition by individual DHHC family members remain to be determined. New studies continue to reveal thioesterases that remove palmitate from S-acylated proteins. Another area of rapid expansion is fatty acylation of the secreted proteins hedgehog, Wnt and Ghrelin, by Hhat, Porcupine and GOAT, respectively. Understanding how these membrane bound O-acyl transferases recognize their protein and fatty acyl CoA substrates is an active area of investigation, and is punctuated by the finding that these enzymes are potential drug targets in human diseases. PMID:27233110

  7. Measurement of atmospheric sesquiterpenes by proton transfer reaction-mass spectrometry (PTR-MS)

    NASA Astrophysics Data System (ADS)

    Kim, S.; Karl, T.; Helmig, D.; Daly, R.; Rasmussen, R.; Guenther, A.

    2009-04-01

    The ability to measure sesquiterpenes (SQT; C15H24) by a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) was investigated. SQT calibration standards were prepared by a capillary diffusion method and the PTR-MS-estimated mixing ratios were derived from the counts of product ions and proton transfer reaction constants. These values were compared with mixing ratios determined by a calibrated Gas Chromatograph (GC) coupled to a Flame Ionization Detector (GC-FID). Product ion distributions from soft-ionization occurring in a selected ion drift tube via proton transfer were measured as a function of collision energies. Results after the consideration of the mass discrimination of the PTR-MS system suggest that quantitative SQT measurements within 20% accuracy can be achieved with PTR-MS if two major product ions (m/z 149+ and 205+), out of seven major product ions (m/z 81+, 95+, 109+, 123+, 135+, 149+ and 205+), are accounted for. Considerable fragmentation of bicyclic sesquiterpenes, i.e. β-caryophyllene and α-humulene, cause the accuracy to be reduced to 50% if only the parent ion (m/z 205+) is considered. These findings were applied to a field dataset collected above a deciduous forest at the PROPHET (Program for Research on Oxidants: Photochemistry, Emissions, and Transport) research station in 2005. Inferred average daytime ecosystem scale mixing ratios (fluxes) of isoprene, sum of monoterpenes (MT), and sum of SQT exhibited values of 15 μg m-3 (4.5 mg m-2 h-1), 1.2 μg m-3 (0.21 mg m-2 h-1), and 0.0016 μg m-3 (0.10 mg m-2 h-1), respectively. A range of MT and SQT reactivities with respect to the OH radical was calculated and compared to an earlier study inferring significantly underestimated OH reactivities due to unknown terpenes above this deciduous forest. The results indicate that incorporating these MT and SQT results can resolve ~30% of missing OH reactivity reported for this site.

  8. Measurement of atmospheric sesquiterpenes by proton transfer reaction-mass spectrometry (PTR-MS)

    NASA Astrophysics Data System (ADS)

    Kim, S.; Karl, T.; Helmig, D.; Daly, R.; Rasmussen, R.; Guenther, A.

    2008-12-01

    The ability to measure sesquiterpenes (SQT; C15H24) by a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) was investigated with SQT standards, prepared by a capillary diffusion method, and the estimated mixing ratios, derived from the counts of product ions and proton transfer reaction constants were intercompared with measured mixing ratios, measured by a complementary Gas Chromatograph (GC) coupled to a Flame Ionization Detector (GC-FID). Product ion distributions due to soft-ionization occurring in a selected ion drift tube via proton transfer were measured as a function of collision energies. Results after the consideration of the mass discrimination of the PTR-MS system suggest that quantitative SQT measurements within 20% accuracy can be achieved with PTR-MS if two major product ions (m/z 149+ and 205+) out of seven major product ions (m/z 81+, 95+, 109+, 123+, 135+, 149+ and 205+) are accounted for. Bicyclic sesquiterpenes, i.e. β-caryophyllene and α-humulene, showed considerable fragmentation causing the accuracy of their analysis to be reduced to 50% if only the parent ion (m/z 205) is considered. These findings were applied to a field dataset collected above a deciduous forest at the PROPHET (Program for Research on Oxidants: Photochemistry, Emissions, and Transport) research station in 2005. Inferred Average daytime ecosystem scale mixing ratios (fluxes) of isoprene, sum of monoterpenes (MT), and sum of SQT exhibited values of 15 μg m-3 (4.5 mg m-2 h-1), 1.2 μg m-3 (0.21 mg m-2 h-1) and 0.0016 μg m-3 (0.10 mgm-2 h-1) respectively. A range of MT and SQT reactivities with respect to the OH radical was calculated and compared to an earlier study inferring significantly underestimated OH reactivities due to unknown terpenes above this deciduous forest. The results indicate that MT and SQT can resolve ~30% of missing OH reactivity, reported from this site.

  9. Synthesis and Hydride Transfer Reactions of Cobalt and Nickel Hydride Complexes to BX3 Compounds

    SciTech Connect

    Mock, Michael T.; Potter, Robert G.; O'Hagan, Molly J.; Camaioni, Donald M.; Dougherty, William G.; Kassel, W. S.; DuBois, Daniel L.

    2011-12-05

    Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H{sub 2} gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe){sub 2}, dmpe = 1,2-bis(dimethylphosphinoethane) was capable of reducing a variety of BX{sub 3} compounds having hydride affinity (HA) greater than or equal to HA of BEt{sub 3}. This study examines the reactivity of less expensive cobalt and nickel hydride complexes, (HCo(dmpe){sub 2} and [HNi(dmpe){sub 2}]{sup +}), to form B-H bonds. The hydride donor abilities ({Delta}G{sub H{sup -}}{sup o}) of HCo(dmpe){sub 2} and [HNi(dmpe){sub 2}]{sup +} were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX{sub 3} compounds. The collective data guided our selection of BX{sub 3} compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe){sub 2} was observed to transfer H{sup -} to BX{sub 3} compounds with X = H, OC{sub 6}F{sub 5} and SPh. The reaction with B(SPh){sub 3} is accompanied by formation of (BH{sub 3}){sub 2}-dmpe and (BH{sub 2}SPh){sub 2}-dmpe products that follow from reduction of multiple BSPh bonds and loss of a dmpe ligand from Co. Reactions between HCo(dmpe){sub 2} and B(SPh){sub 3} in the presence of triethylamine result in formation of Et{sub 3}N-BH{sub 2}SPh and Et{sub 3}N-BH{sub 3} with no loss of dmpe ligand. Reactions of the cationic complex [HNi(dmpe){sub 2}]{sup +} with B(SPh){sub 3} under analogous conditions give Et{sub 3}N-BH{sub 2}SPh as the final product along with the nickel-thiolate complex [Ni(dmpe){sub 2}(SPh)]{sup +}. The synthesis and characterization of HCo(dedpe){sub 2} (dedpe = diethyldiphenyl(phosphino)ethane) from H{sub 2} and a base is also discussed; including the formation of an uncommon trans

  10. Synthesis and Hydride Transfer Reactions of Cobalt and Nickel Hydride Complexes to BX₃ Compounds

    SciTech Connect

    Mock, Michael T.; Potter, Robert G.; O'Hagan, Molly; Camaioni, Donald M.; Dougherty, William G.; Kassel, W. Scott; DuBois, Daniel L.

    2011-10-31

    Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H₂ gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe)₂ (dmpe = 1,2-bis(dimethylphosphinoethane)) was capable of reducing a variety of BX₃ compounds having a hydride affinity (HA) greater than or equal to the HA of BEt₃. This study examines the reactivity of less expensive cobalt and nickel hydride complexes, HCo(dmpe)₂ and [HNi(dmpe)₂]+, to form B–H bonds. The hydride donor abilities (ΔGH °) of HCo(dmpe)₂ and [HNi(dmpe)₂]+ were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX₃ compounds. The collective data guided our selection of BX₃ compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe)₂ was observed to transfer H to BX₃ compounds with X = H, OC₆F₅, and SPh. The reaction with B(SPh)₃ is accompanied by the formation of dmpe-(BH₃)₂ and dmpe-(BH₂(SPh))₂ products that follow from a reduction of multiple B–SPh bonds and a loss of dmpe ligands from cobalt. Reactions between HCo(dmpe)₂ and B(SPh)₃ in the presence of triethylamine result in the formation of Et₃N–BH₂SPh and Et₃N–BH₃ with no loss of a dmpe ligand. Reactions of the cationic complex [HNi(dmpe)₂]+ with B(SPh)₃ under analogous conditions give Et₃N–BH₂SPh as the final product along with the nickel–thiolate complex [Ni(dmpe)₂(SPh)]+. The synthesis and characterization of HCo(dedpe)₂ (dedpe = Et₂PCH₂CH₂PPh₂) from H₂ and a base is also discussed, including the formation of an uncommon trans dihydride species, trans-[(H)₂Co(dedpe)₂][BF₄].

  11. Synthesis and hydride transfer reactions of cobalt and nickel hydride complexes to BX3 compounds.

    PubMed

    Mock, Michael T; Potter, Robert G; O'Hagan, Molly J; Camaioni, Donald M; Dougherty, William G; Kassel, W Scott; DuBois, Daniel L

    2011-12-01

    Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H(2) gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe)(2) (dmpe = 1,2-bis(dimethylphosphinoethane)) was capable of reducing a variety of BX(3) compounds having a hydride affinity (HA) greater than or equal to the HA of BEt(3). This study examines the reactivity of less expensive cobalt and nickel hydride complexes, HCo(dmpe)(2) and [HNi(dmpe)(2)](+), to form B-H bonds. The hydride donor abilities (ΔG(H(-))°) of HCo(dmpe)(2) and [HNi(dmpe)(2)](+) were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX(3) compounds. The collective data guided our selection of BX(3) compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe)(2) was observed to transfer H(-) to BX(3) compounds with X = H, OC(6)F(5), and SPh. The reaction with B(SPh)(3) is accompanied by the formation of dmpe-(BH(3))(2) and dmpe-(BH(2)(SPh))(2) products that follow from a reduction of multiple B-SPh bonds and a loss of dmpe ligands from cobalt. Reactions between HCo(dmpe)(2) and B(SPh)(3) in the presence of triethylamine result in the formation of Et(3)N-BH(2)SPh and Et(3)N-BH(3) with no loss of a dmpe ligand. Reactions of the cationic complex [HNi(dmpe)(2)](+) with B(SPh)(3) under analogous conditions give Et(3)N-BH(2)SPh as the final product along with the nickel-thiolate complex [Ni(dmpe)(2)(SPh)](+). The synthesis and characterization of HCo(dedpe)(2) (dedpe = Et(2)PCH(2)CH(2)PPh(2)) from H(2) and a base is also discussed, including the formation of an uncommon trans dihydride species, trans-[(H)(2)Co(dedpe)(2)][BF(4)]. PMID:22040085

  12. Evolution of the acyl-CoA binding protein (ACBP)

    PubMed Central

    Burton, Mark; Rose, Timothy M.; Færgeman, Nils J.; Knudsen, Jens

    2005-01-01

    Acyl-CoA-binding protein (ACBP) is a 10 kDa protein that binds C12–C22 acyl-CoA esters with high affinity. In vitro and in vivo experiments suggest that it is involved in multiple cellular tasks including modulation of fatty acid biosynthesis, enzyme regulation, regulation of the intracellular acyl-CoA pool size, donation of acyl-CoA esters for β-oxidation, vesicular trafficking, complex lipid synthesis and gene regulation. In the present study, we delineate the evolutionary history of ACBP to get a complete picture of its evolution and distribution among species. ACBP homologues were identified in all four eukaryotic kingdoms, Animalia, Plantae, Fungi and Protista, and eleven eubacterial species. ACBP homologues were not detected in any other known bacterial species, or in archaea. Nearly all of the ACBP-containing bacteria are pathogenic to plants or animals, suggesting that an ACBP gene could have been acquired from a eukaryotic host by horizontal gene transfer. Many bacterial, fungal and higher eukaryotic species only harbour a single ACBP homologue. However, a number of species, ranging from protozoa to vertebrates, have evolved two to six lineage-specific paralogues through gene duplication and/or retrotransposition events. The ACBP protein is highly conserved across phylums, and the majority of ACBP genes are subjected to strong purifying selection. Experimental evidence indicates that the function of ACBP has been conserved from yeast to humans and that the multiple lineage-specific paralogues have evolved altered functions. The appearance of ACBP very early on in evolution points towards a fundamental role of ACBP in acyl-CoA metabolism, including ceramide synthesis and in signalling. PMID:16018771

  13. Nucleon-nucleon correlations in heavy ion transfer reactions: Recent investigations at energies far below the Coulomb barrier

    SciTech Connect

    Corradi, Lorenzo

    2015-10-15

    Excitation functions of one- and two-neutron transfer channels have been measured for the {sup 96}Zr+{sup 40}Ca and {sup 116}Sn+{sup 60}Ni systems at bombarding energies ranging from the Coulomb barrier to ∼25% below. Target-like recoils have been identified in A, Z and velocity with the large solid angle magnetic spectrometer PRISMA. The experimental transfer probabilities have been compared, in absolute values and in slope, with semiclassical microscopic calculations which incorporate nucleon-nucleon pairing correlations. For the first time in a heavy ion collision, one was able to provide a consistent description of one and two neutron transfer reactions by incorporating, in the reaction mechanism, all known structure information of entrance and exit channels nuclei. In particular, there is no need to introduce any enhancement factor for the description of two neutron transfer, of course very important are the correlations induced by the pairing interaction.

  14. Effect of carbon chain length in acyl coenzyme A on the efficiency of enzymatic transformation of okadaic acid to 7-O-acyl okadaic acid.

    PubMed

    Furumochi, Sachie; Onoda, Tatsuya; Cho, Yuko; Fuwa, Haruhiko; Sasaki, Makoto; Yotsu-Yamashita, Mari; Konoki, Keiichi

    2016-07-01

    Okadaic acid (OA), a product of dinoflagellate Prorocentrum spp., is transformed into 7-O-acyl OA in various bivalve species. The structural transformation proceeds enzymatically in vitro in the presence of the microsomal fraction from the digestive gland of bivalves. We have been using LC-MS/MS to identify OA-transforming enzymes by detecting 7-O-acyl OA, also known as dinophysistoxin 3 (DTX3). However, an alternative assay for DTX3 is required because the OA-transforming enzyme is a membrane protein, and surfactants for solubilizing membrane proteins decrease the sensitivity of LC-MS/MS. The present study examined saturated fatty acyl CoAs with a carbon chain length of 10 (decanoyl), 12 (dodecanoyl), 14 (tetradecanoyl), 16 (hexadecanoyl) and 18 (octadecanoyl) as the substrate for the in vitro acylation reaction. Saturated fatty acyl CoAs with a carbon chain length of 14, 16 and 18 exhibited higher yields than those with a carbon chain length of 10 or 12. Acyl CoAs with carbon chain lengths from 14 to 18 and containing either a diene unit, an alkyne unit, or an azide unit in the carbon chain were synthesized and shown to provide the corresponding DTX3 with a yield comparable to that of hexadecanoyl CoA. The three functional units can be conjugated with fluorescent reagents and are applicable to the development of a novel assay for DTX3. PMID:27231127

  15. Enantioselective Phase-Transfer-Catalyzed Synthesis of Chiral N-Substituted 3,3-Dinitroazetidines by Aza-Michael Reaction.

    PubMed

    Lee, Hyo-Jun; Cho, Chang-Woo

    2015-11-20

    An efficient and highly enantioselective phase-transfer-catalyzed aza-Michael reaction of 3,3-dinitroazetidine, as N-centered nucleophile, to α,β-unsaturated ketones has been achieved using a quinidine-based phase-transfer catalyst (0.5-1 mol %), providing chiral N-substituted 3,3-dinitroazetidines in good yields (up to 99%) and excellent enantioselectivities (90-95% ee). This is the first example of the use of azetidines as N-centered nucleophiles in catalytic enantioselective aza-Michael reactions. PMID:26503134

  16. Transfer reactions with JENSA: study of the levels in 12N using 14N(p,t)

    NASA Astrophysics Data System (ADS)

    Chipps, K. A.; Jensa Collaboration

    2015-10-01

    The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target, recently recommissioned in the ReA3 facility at the NSCL, will provide a state-of-the-art, dense, localized, and pure target of light, gaseous elements for various reaction studies. As one of a series of commissioning physics measurements to demonstrate the benefit of the new Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target for enabling next-generation transfer reaction studies, the 14N(p,t)12N reaction was studied using a pure 300 psig jet of nitrogen, in order to help elucidate the structure of 12N. The experiment and lessons learned for future gas jet transfer reaction measurements will be discussed. Research supported by the U. S. Department of Energy Office of Science and NSF.

  17. Insight into the kinetics and thermodynamics of the hydride transfer reactions between quinones and lumiflavin: a density functional theory study.

    PubMed

    Reinhardt, Clorice R; Jaglinski, Tanner C; Kastenschmidt, Ashly M; Song, Eun H; Gross, Adam K; Krause, Alyssa J; Gollmar, Jonathan M; Meise, Kristin J; Stenerson, Zachary S; Weibel, Tyler J; Dison, Andrew; Finnegan, Mackenzie R; Griesi, Daniel S; Heltne, Michael D; Hughes, Tom G; Hunt, Connor D; Jansen, Kayla A; Xiong, Adam H; Hati, Sanchita; Bhattacharyya, Sudeep

    2016-09-01

    The kinetics and equilibrium of the hydride transfer reaction between lumiflavin and a number of substituted quinones was studied using density functional theory. The impact of electron withdrawing/donating substituents on the redox potentials of quinones was studied. In addition, the role of these substituents on the kinetics of the hydride transfer reaction with lumiflavin was investigated in detail under the transition state (TS) theory assumption. The hydride transfer reactions were found to be more favorable for an electron-withdrawing substituent. The activation barrier exhibited a quadratic relationship with the driving force of these reactions as derived under the formalism of modified Marcus theory. The present study found a significant extent of electron delocalization in the TS that is stabilized by enhanced electrostatic, polarization, and exchange interactions. Analysis of geometry, bond-orders, and energetics revealed a predominant parallel (Leffler-Hammond) effect on the TS. Closer scrutiny reveals that electron-withdrawing substituents, although located on the acceptor ring, reduce the N-H bond order of the donor fragment in the precursor complex. Carried out in the gas-phase, this is the first ever report of a theoretical study of flavin's hydride transfer reactions with quinones, providing an unfiltered view of the electronic effect on the nuclear reorganization of donor-acceptor complexes. PMID:27491848

  18. Slow Hydrogen Transfer Reactions of Oxo— and Hydroxo— Vanadium Compounds: the Importance of Intrinsic Barriers

    PubMed Central

    Waidmann, Christopher R.; Zhou, Xin; Tsai, Erin A.; Kaminsky, Werner; Hrovat, David A.; Borden, Weston Thatcher; Mayer, James M.

    2009-01-01

    Reactions are described that interconvert vanadium(IV) oxo-hydroxo complexes [VIVO(OH)(R2bpy)2]BF4 (1a-c) and vanadium(V) dioxo complexes [VVO2(R2bpy)2]BF4 (2a-c) [R2bpy = 4,4′-di-t-butyl-2,2′-bipyridine (tBu2bpy), a; 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), b; 2,2′-bipyridine (bpy), c]. These are rare examples of pairs of isolated, sterically unencumbered, first-row metal-oxo/hydroxo complexes that differ by a hydrogen atom (H+ + e−). The VIV– tBu2bpy derivative 1a has a useful 1H NMR spectrum, despite being paramagnetic. Complex 2a abstracts H• from organic substrates with weak O–H and C–H bonds, converting 2,6-tBu2-4-MeO-C6H2OH (ArOH) and 2,2,6,6-tetramethyl-N-hydroxy-piperidine (TEMPOH) to their corresponding radicals ArO• and TEMPO, hydroquinone to benzoquinone, and dihydroanthracene to anthracene. The equilibrium constant for 2a + ArOH ⇋ 1a + ArO• is (4 ± 2) × 10−3, implying that the VO–H bond dissociation free energy (BDFE) is 70.6 ± 1.2 kcal mol−1. Consistent with this value, 1a is oxidized by 2,4,6-tBu3C6H2O•. All of these reactions are surprisingly slow, typically occurring over hours at ambient temperatures. The net hydrogen-atom pseudo-self-exchange 1a + 2b ⇋ 2a + 1b, using the tBu- and Me-bpy substituents as labels, also occurs slowly, with kse = 1.3 × 10−2 M−1 s−1 at 298 K, ΔH‡ = 15 ± 2 kcal mol−1, and ΔS‡= 16 ± 5 cal mol−1 K. Using this kse and the BDFE, the vanadium reactions are shown to follow the Marcus cross relation moderately well, with calculated rate constants within 102 of the observed values. The vanadium self-exchange reaction is ca. 106 slower than that for the related RuIVO(py)(bpy)22+ / RuIIIOH(py)(bpy)22+ self-exchange. The origin of this dramatic difference has been probed with DFT calculations on the self-exchange reactions of 1c + 2c and on mono-cationic ruthenium complexes with pyrrolate or fluoride in place of the py ligands. The calculations reproduce the difference in

  19. Investigation of acyl migration in mono- and dicaffeoylquinic acids under aqueous basic, aqueous acidic, and dry roasting conditions.

    PubMed

    Deshpande, Sagar; Jaiswal, Rakesh; Matei, Marius Febi; Kuhnert, Nikolai

    2014-09-17

    Acyl migration in chlorogenic acids describes the process of migration of cinnamoyl moieties from one quinic acid alcohol group to another, thus interconverting chlorogenic acid regioisomers. It therefore constitutes a special case of transesterification reaction. Acyl migration constitutes an important reaction pathway in both coffee roasting and brewing, altering the structure of chlorogenic acid initially present in the green coffee bean. In this contribution we describe detailed and comprehensive mechanistic studies comparing inter- and intramolecular acyl migration involving the seven most common chlorogenic acids in coffee. We employe aqueous acidic and basic conditions mimicking the brewing of coffee along with dry roasting conditions. We show that under aqueous basic conditions intramolecular acyl migration is fully reversible with basic hydrolysis competing with acyl migration. 3-Caffeoylquinic acid was shown to be most labile to basic hydrolysis. We additionally show that the acyl migration process is strongly pH dependent with increased transesterification taking place at basic pH. Under dry roasting conditions acyl migration competes with dehydration to form lactones. We argue that acyl migration precedes lactonization, with 3-caffeoylquinic acid lactone being the predominant product. PMID:25116442

  20. Measurement of tissue acyl-CoAs using flow-injection tandem mass spectrometry: acyl-CoA profiles in short-chain fatty acid oxidation defects

    PubMed Central

    Palladino, Andrew A.; Chen, Jie; Kallish, Staci; Stanley, Charles A.; Bennett, Michael J.

    2013-01-01

    The primary accumulating metabolites in fatty acid oxidation defects are intramitochondrial acyl-CoAs. Typically, secondary metabolites such as acylcarnitines, acylglycines and dicarboxylic acids are measured to study these disorders. Methods have not been adapted for tissue acyl-CoA measurement in defects with primarily acyl-CoA accumulation. Our objective was to develop a method to measure fatty acyl-CoA species that are present in tissues of mice with fatty acid oxidation defects using flow-injection tandem mass spectrometry. Following the addition of internal standards of [13C2] acetyl-CoA, [13C8] octanoyl-CoA, and [C17] heptadecanoic CoA, acyl-CoA’s are extracted from tissue samples and are injected directly into the mass spectrometer. Data is acquired using a 506.9 neutral loss scan and multiple reaction-monitoring (MRM). This method can identify all long, medium and short-chain acyl-CoA species in wild type mouse liver including predicted 3-hydroxyacyl-CoA species. We validated the method using liver of the short-chain-acyl-CoA dehydrogenase (SCAD) knock-out mice. As expected, there is a significant increase in [C4] butyryl-CoA species in the SCAD −/− mouse liver compared to wild type. We then tested the assay in liver from the short-chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD) deficient mice to determine the profile of acyl-CoA accumulation in this less predictable model. There was more modest accumulation of medium chain species including 3-hydroxyacyl-CoA’s consistent with the known chain-length specificity of the SCHAD enzyme. PMID:23117082

  1. Possibility of production of neutron-rich Zn and Ge isotopes in multinucleon transfer reactions at low energies

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Sargsyan, V. V.; Scheid, W.

    2010-02-15

    The production cross sections of new neutron-rich {sup 84,86}Zn and {sup 90,92}Ge isotopes beyond N=50 are estimated for the first time in the multinucleon transfer reactions {sup 48}Ca + {sup 238}U and {sup 48}Ca + {sup 244}Pu. The production of new isotopes in reactions with a {sup 48}Ca beam is discussed for future experiments.

  2. The Physiology of Protein S-acylation

    PubMed Central

    Chamberlain, Luke H.; Shipston, Michael J.

    2015-01-01

    Protein S-acylation, the only fully reversible posttranslational lipid modification of proteins, is emerging as a ubiquitous mechanism to control the properties and function of a diverse array of proteins and consequently physiological processes. S-acylation results from the enzymatic addition of long-chain lipids, most typically palmitate, onto intracellular cysteine residues of soluble and transmembrane proteins via a labile thioester linkage. Addition of lipid results in increases in protein hydrophobicity that can impact on protein structure, assembly, maturation, trafficking, and function. The recent explosion in global S-acylation (palmitoyl) proteomic profiling as a result of improved biochemical tools to assay S-acylation, in conjunction with the recent identification of enzymes that control protein S-acylation and de-acylation, has opened a new vista into the physiological function of S-acylation. This review introduces key features of S-acylation and tools to interrogate this process, and highlights the eclectic array of proteins regulated including membrane receptors, ion channels and transporters, enzymes and kinases, signaling adapters and chaperones, cell adhesion, and structural proteins. We highlight recent findings correlating disruption of S-acylation to pathophysiology and disease and discuss some of the major challenges and opportunities in this rapidly expanding field. PMID:25834228

  3. A molecular Debye-Hückel approach to the reorganization energy of electron transfer reactions in an electric cell.

    PubMed

    Xiao, Tiejun; Song, Xueyu

    2014-10-01

    Electron transfer near an electrode immersed in ionic fluids is studied using the linear response approximation, namely, mean value of the vertical energy gap can be used to evaluate the reorganization energy, and hence any linear response model that can treat Coulomb interactions successfully can be used for the reorganization energy calculation. Specifically, a molecular Debye-Hückel theory is used to calculate the reorganization energy of electron transfer reactions in an electric cell. Applications to electron transfer near an electrode in molten salts show that the reorganization energies from our molecular Debye-Hückel theory agree well with the results from MD simulations. PMID:25296781

  4. A molecular Debye-Hückel approach to the reorganization energy of electron transfer reactions in an electric cell

    SciTech Connect

    Xiao, Tiejun; Song, Xueyu

    2014-10-07

    Electron transfer near an electrode immersed in ionic fluids is studied using the linear response approximation, namely, mean value of the vertical energy gap can be used to evaluate the reorganization energy, and hence any linear response model that can treat Coulomb interactions successfully can be used for the reorganization energy calculation. Specifically, a molecular Debye-Hückel theory is used to calculate the reorganization energy of electron transfer reactions in an electric cell. Applications to electron transfer near an electrode in molten salts show that the reorganization energies from our molecular Debye-Hückel theory agree well with the results from MD simulations.

  5. The ^2H(e,e'p)n Reaction at High Four-Momentum Transfer

    SciTech Connect

    Hassan Ibrahim

    2006-12-31

    This dissertation presents the highest four-momentum transfer, Q^2,quasielastic (x_Bj = 1) results from Experiment E01-020 which systematically explored the 2He(e,e'p)n reaction ("Electro-disintegration" of the deuteron) at three different four-momentum transfers, Q^2 = 0.8, 2.1, and 3.5 GeV^2 and missing momenta, P_miss = 0, 100, 200, 300, 400, and 500 GeV including separations of the longitudinal-transverse interference response function, R_LT, and extractoin of the longitudinal-transverse asymmetry, A_LT. This systematic approach will help to understand the reaction mechanism and the deuteron structure down to the short range part of the nucleon-nucleon interaction which is one of the fundamental missions of nuclear physics. By studying the very short distance structure of the deuteron, one may also determine whether or to what extent the description of nuclei in terms of nucleon/meson degrees of freedom must be supplemented by inclusion of explicit quark effects. The unique combination of energy, current, duty factor, and control of systematics for Hall A at Jefferson Lab made Jefferson Lab the only facility in the world where these systematic studies of the deuteron can be undertaken. This is especially true when we want to understand the short range structure of the deuteron where high energies and high luminosity/duty factor are needed. All these features of Jefferson Lab allow us to examine large missing momenta (short range scales) at kinematics where the effects of final state interactions (FSI), meson exchange currents (MEC), and isobar currents (IC) are minimal, making the extraction of the deuteron structure less model-dependent. Jefferson Lab also provides the kinematical flexibility to perform the separation of R_LT over a broad range of missing momenta and momentum transfers. Experiment E01-020 use the standard Hall A equipment in coincidence configuration in addition to the cryogenic target system. The low and middle Q^2 kinematics were completed

  6. Ring-opening metathesis polymerization-based recyclable magnetic acylation reagents.

    PubMed

    Kainz, Quirin M; Linhardt, Roland; Maity, Pradip K; Hanson, Paul R; Reiser, Oliver

    2013-04-01

    An operationally simple method for the acylation of amines utilizing carbon-coated metal nanoparticles as recyclable supports is reported. Highly magnetic carbon-coated cobalt (Co/C) and iron (Fe/C) nanobeads were functionalized with a norbornene tag (Nb-tag) through a "click" reaction followed by surface activation employing Grubbs-II catalyst and subsequent grafting of acylated N-hydroxysuccinimide ROMPgels (ROMP=ring-opening metathesis polymerization). The high loading (up to 2.6 mmolg(-1) ) hybrid material was applied in the acylation of various primary and secondary amines. The products were isolated in high yields (86-99%) and excellent purities (all >95 % by NMR spectroscopy) after rapid magnetic decantation and simple evaporation of the solvents. The spent resins were successfully re-acylated by acid chlorides, anhydrides, and carboxylic acids and reused for up to five consecutive cycles without considerable loss of activity. PMID:23427021

  7. Enhanced Activity of Nanocrystalline Beta Zeolite for Acylation of Veratrole with Acetic Anhydride.

    PubMed

    Aisha Mahmood Abdulkareem, Al-Turkustani; Selvin, Rosilda

    2016-04-01

    Friedel-Craft acylation of veratrole using homogeneous acid catalysts such as AlCl3, FeCl3, ZnCl2, and HF etc. produces acetoveratrone, (3',4'-dimethoxyacetophenone), which is the intermediate for synthesis of papavarine alkaloids. The problems associated with these homogeneous catalysts can be overcome by using heterogeneous solid catalysts. Since acetoveratrone is a larger molecule, large pore Beta zeolites with smaller particle sizes are beneficial for the liquid-phase acylation of veratrole, for easy diffusion of reactants and products. The present study aims in the acylation of veratrole with acetic anhydride using nanocrystalline Beta Zeolite catalyst. A systematic investigation of the effects of various reaction parameters was done. The catalysts were characterized for their structural features by using XRD, TEM and DLS analyses. The catalytic activity of nanocrystalline Beta zeolite was compared with commercial Beta zeolite for the acylation and was found that nanocrystalline Beta zeolite possessed superior activity. PMID:27451793

  8. Effect of different hand positions on trunk and shoulder kinematics and reaction forces in sitting pivot transfer

    PubMed Central

    Kim, Sung Shin; Her, Jin Gan; Ko, Tae Sung

    2015-01-01

    [Purpose] The purpose of this study was to compare the changes in trunk and shoulder angles, and reaction forces under the two hands elicited by different hand base of support positions during sitting pivot transfer. [Subjects and Methods] Eighteen unimpaired subjects performed independent sitting pivot transfer. Subjects performed sitting pivot transfer between an initial seat to a target seat by only using their hands positioned at the same height as and lower than the seat position. Trunk and shoulder kinematics, and reaction forces on the trailing and leading hands were calculated. Mean peak joint angles and forces were compared between the hand positions using the pared t-test for the lift phase of the transfer. [Results] There were significant increases in the trunk angles of forward and lateral flexion, even though rotation decreased while transferring in the lower hand position. Increased shoulder flexion, anterior/posterior forces and reduced lateral forces were also shown. [Conclusion] Placing the hands of the supporting arms lower than the seat position during sitting pivot transfer was identified as having biomechanical advantages. Therefore, the lower hand position can be recommended as an effective and safe method for sitting pivot transfer by patients with spinal cord injury and can be utilized as a reference data for considering the appropriate height of aids for a wheelchair. PMID:26310994

  9. Effect of different hand positions on trunk and shoulder kinematics and reaction forces in sitting pivot transfer.

    PubMed

    Kim, Sung Shin; Her, Jin Gan; Ko, Tae Sung

    2015-07-01

    [Purpose] The purpose of this study was to compare the changes in trunk and shoulder angles, and reaction forces under the two hands elicited by different hand base of support positions during sitting pivot transfer. [Subjects and Methods] Eighteen unimpaired subjects performed independent sitting pivot transfer. Subjects performed sitting pivot transfer between an initial seat to a target seat by only using their hands positioned at the same height as and lower than the seat position. Trunk and shoulder kinematics, and reaction forces on the trailing and leading hands were calculated. Mean peak joint angles and forces were compared between the hand positions using the pared t-test for the lift phase of the transfer. [Results] There were significant increases in the trunk angles of forward and lateral flexion, even though rotation decreased while transferring in the lower hand position. Increased shoulder flexion, anterior/posterior forces and reduced lateral forces were also shown. [Conclusion] Placing the hands of the supporting arms lower than the seat position during sitting pivot transfer was identified as having biomechanical advantages. Therefore, the lower hand position can be recommended as an effective and safe method for sitting pivot transfer by patients with spinal cord injury and can be utilized as a reference data for considering the appropriate height of aids for a wheelchair. PMID:26310994

  10. Enhancement of nucleate pool boiling heat transfer to dilute binary mixtures using endothermic chemical reactions around the smoothed horizontal cylinder

    NASA Astrophysics Data System (ADS)

    Sarafraz, M. M.; Peyghambarzadeh, S. M.; Alavifazel, S. A.

    2012-10-01

    Experimental studies on enhancing the pool boiling heat transfer coefficient of binary dilute mixtures of water/glycerol, water/MEG (Mono-ethylene glycol) and water/DEG (di-ethylene glycol) have been carried out. Some particular endothermic chemical reactions related to ammonium salts were used to enhance the pool boiling heat transfer coefficient, simultaneously with occurrence of pool boiling heat transfer. Accordingly, 100 g of Ammonium nitrate, ammonium perborate and Ammonium sulfate were selected to dissolve into mixtures. High and extreme solution enthalpies of each of these ammonium salt powders are employed to reduce the surface temperature around the horizontal cylinder locally. Results demonstrated that presence of ammonium salts into the mixtures deteriorates the surface temperature of cylinder and as the result, higher pool boiling heat transfer coefficient is reported for tested solutions. Results are also reported and compared for different ammonium salts to find the influence of inducing different enthalpies of solution on pool boiling heat transfer coefficient. Obtained results also indicated that presence of endothermic reaction besides the pool boiling heat transfer enhances the heat transfer coefficients in comparison with nucleate pool boiling phenomenon solely.

  11. Calculated coupling of electron and proton transfer in the photosynthetic reaction center of Rhodopseudomonas viridis.

    PubMed Central

    Lancaster, C R; Michel, H; Honig, B; Gunner, M R

    1996-01-01

    Based on new Rhodopseudomonas (Rp.) viridis reaction center (RC) coordinates with a reliable structure of the secondary acceptor quinone (QB) site, a continuum dielectric model and finite difference technique have been used to identify clusters of electrostatically interacting ionizable residues. Twenty-three residues within a distance of 25 A from QB (QB cluster) have been shown to be strongly electrostatically coupled to QB, either directly or indirectly. An analogous cluster of 24 residues is found to interact with QA (QA cluster). Both clusters extend to the cytoplasmic surface in at least two directions. However, the QB cluster differs from the QA cluster in that it has a surplus of acidic residues, more strong electrostatic interactions, is less solvated, and experiences a strong positive electrostatic field arising from the polypeptide backbone. Consequently, upon reduction of QA or QB, it is the QB cluster, and not the QA cluster, which is responsible for substoichiometric proton uptake at neutral pH. The bulk of the changes in the QB cluster are calculated to be due to the protonation of a tightly coupled cluster of the three Glu residues (L212, H177, and M234) within the QB cluster. If the lifetime of the doubly reduced state QB2- is long enough, Asp M43 and Ser L223 are predicted to also become protonated. The calculated complex titration behavior of the strongly interacting residues of the QB cluster and the resulting electrostatic response to electron transfer may be a common feature in proton-transferring membrane protein complexes. Images FIGURE 2 p2482-a FIGURE 6 FIGURE 8 FIGURE 10 PMID:8744288

  12. Calculated coupling of electron and proton transfer in the photosynthetic reaction center of Rhodopseudomonas viridis.

    PubMed

    Lancaster, C R; Michel, H; Honig, B; Gunner, M R

    1996-06-01

    Based on new Rhodopseudomonas (Rp.) viridis reaction center (RC) coordinates with a reliable structure of the secondary acceptor quinone (QB) site, a continuum dielectric model and finite difference technique have been used to identify clusters of electrostatically interacting ionizable residues. Twenty-three residues within a distance of 25 A from QB (QB cluster) have been shown to be strongly electrostatically coupled to QB, either directly or indirectly. An analogous cluster of 24 residues is found to interact with QA (QA cluster). Both clusters extend to the cytoplasmic surface in at least two directions. However, the QB cluster differs from the QA cluster in that it has a surplus of acidic residues, more strong electrostatic interactions, is less solvated, and experiences a strong positive electrostatic field arising from the polypeptide backbone. Consequently, upon reduction of QA or QB, it is the QB cluster, and not the QA cluster, which is responsible for substoichiometric proton uptake at neutral pH. The bulk of the changes in the QB cluster are calculated to be due to the protonation of a tightly coupled cluster of the three Glu residues (L212, H177, and M234) within the QB cluster. If the lifetime of the doubly reduced state QB2- is long enough, Asp M43 and Ser L223 are predicted to also become protonated. The calculated complex titration behavior of the strongly interacting residues of the QB cluster and the resulting electrostatic response to electron transfer may be a common feature in proton-transferring membrane protein complexes. PMID:8744288

  13. Chemical evolution of a travertine-depositing stream: geochemical processes and mass transfer reactions

    SciTech Connect

    Lorah, M.M.; Herman, J.S.

    1988-09-01

    This field study focuses on quantitatively defining the chemical changes occurring in Falling Spring Creek, a travertine-depositing stream located in Alleghany County, Virginia. The processes of CO/sub 2/ outgassing and calcite precipitation or dissolution control the chemical evolution of the stream. The observed chemical composition of the water was used with the computerized geochemical model WATEQF to calculate aqueous speciation, saturation indices, and CO/sub 2/ partial pressure values. Mass balance calculations were performed to obtain mass transfers of CO/sub 2/ and calcite. Reaction times, estimated from stream discharge, were used with the mass transfer results to calculate rates of CO/sub 2/ outgassing and calcite precipitation between consecutive sampling points. The stream, which is fed by a carbonate spring, is supersaturated with respect to CO/sub 2/ along the entire 5.2-km flow path. Outgassing of CO/sub 2/ drives the solution to high degrees of supersaturation with respect to calcite. Metabolic uptake of CO/sub 2/ by photosynthetic plants is insignificant, because the high supply rate of dissolved carbon dioxide and the extreme agitation of the stream at waterfalls and rapids causes a much greater amount of inorganic CO/sub 2/ outgassing to occur. Calcite precipitation is kinetically inhibited until near the crest of a 20-m vertical waterfall. Calcite precipitation rates then reach a maximum at the waterfall where greater water turbulence allows the most rapid escape of CO/sub 2/. Physical evidence for calcite precipitation exists in the travertine deposits which are first observed immediately above the waterfall and extend for at least 1.0 km below the falls. Net calcite precipitation occurs at all times of the year but is greatest during low-flow conditions in the summer and early fall.

  14. Control and Automation of Fluid Flow, Mass Transfer and Chemical Reactions in Microscale Segmented Flow

    NASA Astrophysics Data System (ADS)

    Abolhasani, Milad

    Flowing trains of uniformly sized bubbles/droplets (i.e., segmented flows) and the associated mass transfer enhancement over their single-phase counterparts have been studied extensively during the past fifty years. Although the scaling behaviour of segmented flow formation is increasingly well understood, the predictive adjustment of the desired flow characteristics that influence the mixing and residence times, remains a challenge. Currently, a time consuming, slow and often inconsistent manual manipulation of experimental conditions is required to address this task. In my thesis, I have overcome the above-mentioned challenges and developed an experimental strategy that for the first time provided predictive control over segmented flows in a hands-off manner. A computer-controlled platform that consisted of a real-time image processing module within an integral controller, a silicon-based microreactor and automated fluid delivery technique was designed, implemented and validated. In a first part of my thesis I utilized this approach for the automated screening of physical mass transfer and solubility characteristics of carbon dioxide (CO2) in a physical solvent at a well-defined temperature and pressure and a throughput of 12 conditions per hour. Second, by applying the segmented flow approach to a recently discovered CO2 chemical absorbent, frustrated Lewis pairs (FLPs), I determined the thermodynamic characteristics of the CO2-FLP reaction. Finally, the segmented flow approach was employed for characterization and investigation of CO2-governed liquid-liquid phase separation process. The second part of my thesis utilized the segmented flow platform for the preparation and shape control of high quality colloidal nanomaterials (e.g., CdSe/CdS) via the automated control of residence times up to approximately 5 minutes. By introducing a novel oscillatory segmented flow concept, I was able to further extend the residence time limitation to 24 hours. A case study of a

  15. Evidence for involvement of medium chain acyl-CoA dehydrogenase in the metabolism of phenylbutyrate

    PubMed Central

    Kormanik, Kaitlyn; Kang, Heejung; Cuebas, Dean; Vockley, Jerry; Mohsen, Al-Walid

    2012-01-01

    Sodium phenylbutyrate is used for treating urea cycle disorders, providing an alternative for ammonia excretion. Following conversion to its CoA ester, phenylbutyryl-CoA is postulated to undergo one round of β-oxidation to phenylacetyl-CoA, the active metabolite. Molecular modeling suggests that medium chain acyl-CoA dehydrogenase (MCAD; EC 1.3.99.3), a key enzyme in straight chain fatty acid β-oxidation, could utilize phenylbutyryl-CoA as substrate. Moreover, phenylpropionyl-CoA has been shown to be a substrate for MCAD and its intermediates accumulate in patients with MCAD deficiency. We have examined the involvement of MCAD and other acyl-CoA dehydrogenases (ACADs) in the metabolism of phenylbutyryl-CoA. Anaerobic titration of purified recombinant human MCAD with phenylbutyryl-CoA caused changes in the MCAD spectrum that are similar to those induced by octanoyl-CoA, its bona fide substrate, and unique to the development of the charge transfer ternary complex. The calculated apparent dissociation constant (KD app) for these substrates was 2.16 μM and 0.12 μM, respectively. The MCAD reductive and oxidative half reactions were monitored using the electron transfer flavoprotein (ETF) fluorescence reduction assay. The catalytic efficiency and the Km for phenylbutyryl-CoA were 0.2 mM−1· sec−1 and 5.3 μM compared to 4.0 mM−1· sec−1 and 2.8 μM for octanoyl-CoA. Extracts of wild type and MCAD-deficient lymphoblast cells were tested for the ability to reduce ETF using phenylbutyryl-CoA as substrate. While ETF reduction activity was detected in extracts of wild type cells, it was undetectable in extracts of cells deficient in MCAD. The results are consistent with MCAD playing a key role in phenylbutyrate metabolism. PMID:23141465

  16. Switchover of the Mechanism between Electron Transfer and Hydrogen-Atom Transfer for a Protonated Manganese(IV)-Oxo Complex by Changing Only the Reaction Temperature.

    PubMed

    Jung, Jieun; Kim, Surin; Lee, Yong-Min; Nam, Wonwoo; Fukuzumi, Shunichi

    2016-06-20

    Hydroxylation of mesitylene by a nonheme manganese(IV)-oxo complex, [(N4Py)Mn(IV) (O)](2+) (1), proceeds via one-step hydrogen-atom transfer (HAT) with a large deuterium kinetic isotope effect (KIE) of 3.2(3) at 293 K. In contrast, the same reaction with a triflic acid-bound manganese(IV)-oxo complex, [(N4Py)Mn(IV) (O)](2+) -(HOTf)2 (2), proceeds via electron transfer (ET) with no KIE at 293 K. Interestingly, when the reaction temperature is lowered to less than 263 K in the reaction of 2, however, the mechanism changes again from ET to HAT with a large KIE of 2.9(3). Such a switchover of the reaction mechanism from ET to HAT is shown to occur by changing only temperature in the boundary region between ET and HAT pathways when the driving force of ET from toluene derivatives to 2 is around -0.5 eV. The present results provide a valuable and general guide to predict a switchover of the reaction mechanism from ET to the others, including HAT. PMID:27191357

  17. Enantioselective addition of boronates to acyl imines catalyzed by chiral biphenols.

    PubMed

    Bishop, Joshua A; Lou, Sha; Schaus, Scott E

    2009-01-01

    On the big screen: A chiral biphenol catalyst screening protocol was developed for the rapid identification of enantioselective nucleophilic boronate reactions with acyl imines (see scheme). The approach successfully identified a unique catalyst for the reaction of aryl, vinyl, and alkynyl boronates. Mechanistic studies demonstrate boronate ligand exchange with the catalyst is necessary for activation towards nucleophilic addition. PMID:19431168

  18. Iridium-Catalyzed Synthesis of Acylpyridines by [2 + 2 + 2] Cycloaddition of Diynes with Acyl Cyanides.

    PubMed

    Hashimoto, Toru; Kato, Kaoru; Yano, Reiko; Natori, Tomoki; Miura, Hiroki; Takeuchi, Ryo

    2016-07-01

    2-Acylpyridines were prepared by iridium-catalyzed [2 + 2 + 2] cycloaddition of α,ω-diynes with acyl cyanides. [Ir(cod)Cl]2/rac-BINAP or F-DPPE is an efficient catalyst for this reaction. The scope and limitations of this reaction have been disclosed. PMID:27275734

  19. Kinetic and Vibrational Isotope Effects of Proton Transfer Reactions in Channelrhodopsin-2

    PubMed Central

    Resler, Tom; Schultz, Bernd-Joachim; Lórenz-Fonfría, Víctor A.; Schlesinger, Ramona; Heberle, Joachim

    2015-01-01

    Channelrhodopsins (ChRs) are light-gated cation channels. After blue-light excitation, the protein undergoes a photocycle with different intermediates. Here, we have recorded transient absorbance changes of ChR2 from Chlamydomonas reinhardtii in the visible and infrared regions with nanosecond time resolution, the latter being accomplished using tunable quantum cascade lasers. Because proton transfer reactions play a key role in channel gating, we determined vibrational as well as kinetic isotope effects (VIEs and KIEs) of carboxylic groups of various key aspartic and glutamic acid residues by monitoring their C=O stretching vibrations in H2O and in D2O. D156 exhibits a substantial KIE (>2) in its deprotonation and reprotonation, which substantiates its role as the internal proton donor to the retinal Schiff base. The unusual VIE of D156, upshifted from 1736 cm−1 to 1738 cm−1 in D2O, was scrutinized by studying the D156E variant. The C=O stretch of E156 shifted down by 8 cm−1 in D2O, providing evidence for the accessibility of the carboxylic group. The C=O stretching band of E90 exhibits a VIE of 9 cm−1 and a KIE of ∼2 for the de- and the reprotonation reactions during the lifetime of the late desensitized state. The KIE of 1 determined in the time range from 20 ns to 5 ms is incompatible with early deprotonation of E90. PMID:26200864

  20. Kinetic and vibrational isotope effects of proton transfer reactions in channelrhodopsin-2.

    PubMed

    Resler, Tom; Schultz, Bernd-Joachim; Lórenz-Fonfría, Víctor A; Schlesinger, Ramona; Heberle, Joachim

    2015-07-21

    Channelrhodopsins (ChRs) are light-gated cation channels. After blue-light excitation, the protein undergoes a photocycle with different intermediates. Here, we have recorded transient absorbance changes of ChR2 from Chlamydomonas reinhardtii in the visible and infrared regions with nanosecond time resolution, the latter being accomplished using tunable quantum cascade lasers. Because proton transfer reactions play a key role in channel gating, we determined vibrational as well as kinetic isotope effects (VIEs and KIEs) of carboxylic groups of various key aspartic and glutamic acid residues by monitoring their C=O stretching vibrations in H2O and in D2O. D156 exhibits a substantial KIE (>2) in its deprotonation and reprotonation, which substantiates its role as the internal proton donor to the retinal Schiff base. The unusual VIE of D156, upshifted from 1736 cm(-1) to 1738 cm(-1) in D2O, was scrutinized by studying the D156E variant. The C=O stretch of E156 shifted down by 8 cm(-1) in D2O, providing evidence for the accessibility of the carboxylic group. The C=O stretching band of E90 exhibits a VIE of 9 cm(-1) and a KIE of ∼2 for the de- and the reprotonation reactions during the lifetime of the late desensitized state. The KIE of 1 determined in the time range from 20 ns to 5 ms is incompatible with early deprotonation of E90. PMID:26200864

  1. Analysis of secondary organic aerosols from ozonolysis of isoprene by proton transfer reaction mass spectrometry

    NASA Astrophysics Data System (ADS)

    Inomata, Satoshi; Sato, Kei; Hirokawa, Jun; Sakamoto, Yosuke; Tanimoto, Hiroshi; Okumura, Motonori; Tohno, Susumu; Imamura, Takashi

    2014-11-01

    To understand the mechanism of formation of the secondary organic aerosols (SOAs) produced by the ozonolysis of isoprene, proton transfer reaction mass spectrometry (PTR-MS) was used to identify the semi-volatile organic compounds (SVOCs) produced in both the gaseous and the aerosol phases and to estimate the gas-aerosol partitioning of each SVOC in chamber experiments. To aid in the identification of the SVOCs, the products were also studied with negative ion-chemical ionization mass spectrometry (NI-CIMS), which can selectively detect carboxylic acids and hydroperoxides. The gaseous products were observed by on-line PTR-MS and NI-CIMS, whereas the SVOCs in SOAs collected on a filter were vaporized by heating the filter and were then analysed by off-line PTR-MS and NI-CIMS. The formation of oligomeric hydroperoxides involving a Criegee intermediate as a chain unit was observed in both the gaseous and the aerosol phases by NI-CIMS. PTR-MS also detected oligomeric hydroperoxides as protonated molecules from which a H2O molecule was eliminated, [M-OH]+. In the aerosol phase, oligomers involving formaldehyde and methacrolein as chain units were observed by PTR-MS in addition to oligomeric hydroperoxides. The gas-aerosol partitioning of each component was calculated from the ion signals in the gaseous and aerosol phases measured by PTR-MS. From the gas-aerosol partitioning, the saturated vapour pressures of the oligomeric hydroperoxides were estimated. Measurements by a fast-mobility-particle-sizer spectrometer revealed that the increase of the number density of the particles was complete within a few hundred seconds from the start of the reaction.

  2. Fusion and neutron transfer reactions with weakly bound nuclei within time-dependent and coupled channel approaches

    NASA Astrophysics Data System (ADS)

    Samarin, V. V.

    2016-05-01

    The time-dependent Schrödinger equation and the coupled channel approach based on the method of perturbed stationary two-center states are used to describe nucleon transfers and fusion in low-energy nuclear reactions. Results of the cross sections calculation for the formation of the 198Au and fusion in the 6He+197Au reaction and for the formation of the 65Zn in 6He+64Zn reaction agree satisfactorily with the experimental data near the barrier. The Feynman's continual integrals calculations for a few-body systems were used for the proposal of the new form of the shell model mean field for helium isotopes.

  3. Acylation of 1,3-butadiene with acetylfluorosulfonate

    SciTech Connect

    Gavrishova, T.N.; Shastin, A.V.; Balenkova, E.S.; Novikov, N.A.

    1987-11-20

    1-Acetylbutadiene (I) is widely used in diene syntheses, and is also a valuable starting material for the preparation of otherwise difficulty accessible 1-substituted butadienes, which are then used in the synthesis of natural products. At the present time, however, there is no convenient one-step method for the preparation of acetylbutadiene (I). Acylation of butadiene (II) in the presence of Lewis acids is accompanied by extensive polymerization, and the maximum yield of acylated product in these reactions is only 10%. The authors have now successfully carried out the acylation of butadiene (II) with acetyfluorosulfonate. Workup of the reaction mixture with triethylamine gave acetylbutadiene (I) in 33% yield. The E-configuration of compound (I) was established based on the values of the spin-spin coupling constants for interaction of the olefinic protons, /sup 3/J(H/sup a/-H/sup b/) 15.4 Hz, which was determined by NMR spectroscopy. The presence of a characteristic absorption band at 965 cm/sup -1/ in the IR spectrum also confirms the E-configuration of compound (I).

  4. A review of proton transfer reactions between various carbon-acids and amine bases in aprotic solvents

    NASA Astrophysics Data System (ADS)

    Jarczewski, Arnold; Hubbard, Colin D.

    2003-04-01

    The subject of proton transfer between carbon acids and nitrogen bases in aprotic solvents is reviewed. Equilibrium and rate constants that characterize such reactions are most often determined utilizing UV-visible spectrophotometry. At ambient temperature reaction rates are sufficiently rapid that fast reaction methods, for example, the stopped-flow and temperature-jump techniques are required in many cases. Variation of the properties of the donor and acceptor reaction pairs enables electronic and steric effects upon thermodynamic and kinetic parameters of proton transfer to be assessed. Determination of the kinetic isotope effect (KIE), i.e. k(protium)/ k(deuterium) led to the conclusion that, under certain circumstances and when the KIE is greater than seven, the proton undergoes reaction with a significant degree of quantum mechanical tunneling, consistent with a theoretical prediction advanced several decades earlier. In fact this aspect may be one of the most significant outgrowths of these studies. Many reactions have been characterized (by tunneling) but rarely are the reacting systems experimentally amenable to obtaining all the experimental criteria that support tunneling. Controversy that has arisen regarding treatment of experimental data and resulting conclusions from them is visited in this review. The structural nature of the product state of reaction is formulated based on spectroscopic evidence, in favorable cases, and probable structures of the transition state can be inferred.

  5. Site-Selective Acylations with Tailor-Made Catalysts.

    PubMed

    Huber, Florian; Kirsch, Stefan F

    2016-04-18

    The acylation of alcohols catalyzed by N,N-dimethylamino pyridine (DMAP) is, despite its widespread use, sometimes confronted with substrate-specific problems: For example, target compounds with multiple hydroxy groups may show insufficient selectivity for one hydroxyl, and the resulting product mixtures are hardly separable. Here we describe a concept that aims at tailor-made catalysts for the site-specific acylation. To this end, we introduce a catalyst library where each entry is constructed by connecting a variable and readily tuned peptide scaffold with a catalytically active unit based on DMAP. For selected examples, we demonstrate how library screening leads to the identification of optimized catalysts, and the substrates of interest can be converted with a markedly enhanced site-selectivity compared with only DMAP. Furthermore, substrate-optimized catalysts of this type can be used to selectively convert "their" substrate in the presence of structurally similar compounds, an important requisite for reactions with mixtures of substances. PMID:26970553

  6. A Short Account of RRKM Theory of Unimolecular Reactions and of Marcus Theory of Electron Transfer in a Historical Perspective

    ERIC Educational Resources Information Center

    Di Giacomo, Francesco

    2015-01-01

    The RRKM Theory of Unimolecular Reactions and Marcus Theory of Electron Transfer are here briefly discussed in a historical perspective. In the final section, after a general discussion on the educational usefulness of teaching chemistry in a historical framework, hints are given on how some characteristics of Marcus' work could be introduced in…

  7. Direct Diazo-Transfer Reaction on β-lactam: Synthesis and Preliminary Biological Activities of 6-Triazolylpenicillanic Acids

    PubMed Central

    Chen, Po C.; Emrich, Rebekah E.; Patel, Pratiq A.

    2009-01-01

    In this study we report the first example of a direct diazo-transfer reaction on readily available 6-aminopenicillanates to give 6-azidopenicillanates in high yield. Subsequent Cu(I)-catalyzed Huisgen cycloaddition between these 6-azidopenicillanates and assorted terminal alkynes facilely furnished 6-triazolylpenicillanic acids was. Preliminary biological screening indicates that these triazolylpenicillanic acids possess low to moderate antibacterial activities. PMID:17855098

  8. Reaction kinetics in dehydrochlorination of. cap alpha. -isomer of hexachlorocyclohexane in the presence of a phase transfer catalyst

    SciTech Connect

    Sirovskii, F.S.; Chimishkyan, A.L.; Panova, M.V.; Treger, Y.A.; Velichko, S.M.

    1986-01-01

    This paper presents a kinetic study of the reaction of aqueous caustic dehydrochlorination of the alpha-isomer of hexachlorocyclohexane (alpha-HCCH) with catalysis by tetrabutyl-ammonium hydroxide. It has been shown that the process is described by a scheme of phase transfer catalysis.

  9. Modified Acyl-ACP desaturase

    DOEpatents

    Cahoon, E.B.; Shanklin, J.; Lindqvist, Y.; Schneider, G.

    1999-03-30

    Disclosed is a method for modifying the chain length and double bond positional specificities of a soluble plant fatty acid desaturase. More specifically, the method involves modifying amino acid contact residues in the substrate binding channel of the soluble fatty acid desaturase which contact the fatty acid. Specifically disclosed is the modification of an acyl-ACP desaturase. Amino acid contact residues which lie within the substrate binding channel are identified, and subsequently replaced with different residues to effect the modification of activity. 2 figs.

  10. Modified acyl-ACP desaturase

    DOEpatents

    Cahoon, E.B.; Shanklin, J.; Lindgvist, Y.; Schneider, G.

    1998-01-06

    Disclosed is a method for modifying the chain length and double bond positional specificities of a soluble plant fatty acid desaturase. More specifically, the method involves modifying amino acid contact residues in the substrate binding channel of the soluble fatty acid desaturase which contact the fatty acid. Specifically disclosed is the modification of an acyl-ACP desaturase. Amino acid contact residues which lie within the substrate binding channel are identified, and subsequently replaced with different residues to effect the modification of activity. 1 fig.

  11. Analysis of kinetic isotope effects for proton-coupled electron transfer reactions.

    PubMed

    Edwards, Sarah J; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2009-03-12

    A series of rate constant expressions for nonadiabatic proton-coupled electron transfer (PCET) reactions are analyzed and compared. The approximations underlying each expression are enumerated, and the regimes of validity for each expression are illustrated by calculations on model systems. In addition, the kinetic isotope effects (KIEs) for a series of model PCET reactions are analyzed to elucidate the fundamental physical principles dictating the magnitude of the KIE and the dependence of the KIE on the physical properties of the system, including temperature, reorganization energy, driving force, equilibrium proton donor-acceptor distance, and effective frequency of the proton donor-acceptor mode. These calculations lead to three physical insights that are directly relevant to experimental data. First, these calculations provide an explanation for a decrease in the KIE as the proton donor-acceptor distance increases, even though typically the KIE will increase with increasing equilibrium proton donor-acceptor distance if all other parameters remain fixed. Often the proton donor-acceptor frequency decreases as the proton donor-acceptor distance increases, and these two effects impact the KIE in opposite directions, so either trend could be observed. Second, these calculations provide an explanation for an increase in the KIE as the temperature increases, even though typically the KIE will decrease with increasing temperature if all other parameters remain fixed. The combination of a rigid hydrogen bond, which corresponds to a high proton donor-acceptor frequency, and low solvent polarity, which corresponds to small solvent reorganization energy, allows the KIE to either increase or decrease with temperature, depending on the other properties of the system. Third, these calculations provide insight into the dependence of the rate constant and KIE on the driving force, which has been studied experimentally for a wide range of PCET systems. The rate constant

  12. Multi-capillary-column proton-transfer-reaction time-of-flight mass spectrometry☆

    PubMed Central

    Ruzsanyi, Veronika; Fischer, Lukas; Herbig, Jens; Ager, Clemes; Amann, Anton

    2013-01-01

    Proton-transfer-reaction time-of-flight mass-spectrometry (PTR-TOFMS) exhibits high selectivity with a resolution of around 5000 m/Δm. While isobars can be separated with this resolution, discrimination of isomeric compounds is usually not possible. The coupling of a multi-capillary column (MCC) with a PTR-TOFMS overcomes these problems as demonstrated in this paper for the ketone isomers 3-heptanone and 2-methyl-3-hexanone and for different aldehydes. Moreover, fragmentation of compounds can be studied in detail which might even improve the identification. LODs for compounds tested are in the range of low ppbv and peak positions of the respective separated substances show good repeatability (RSD of the peak positions <3.2%). Due to its special characteristics, such as isothermal operation, compact size, the MCC setup is suitable to be installed inside the instrument and the overall retention time for a complete spectrum is only a few minutes: this allows near real-time measurements in the optional MCC mode. In contrast to other methods that yield additional separation, such as the use of pre-cursor ions other than H3O+, this method yields additional information without increasing complexity. PMID:24119758

  13. Reaction-diffusion systems in natural sciences and new technology transfer

    NASA Astrophysics Data System (ADS)

    Keller, André A.

    2012-12-01

    Diffusion mechanisms in natural sciences and innovation management involve partial differential equations (PDEs). This is due to their spatio-temporal dimensions. Functional semi-discretized PDEs (with lattice spatial structures or time delays) may be even more adapted to real world problems. In the modeling process, PDEs can also formalize behaviors, such as the logistic growth of populations with migration, and the adopters’ dynamics of new products in innovation models. In biology, these events are related to variations in the environment, population densities and overcrowding, migration and spreading of humans, animals, plants and other cells and organisms. In chemical reactions, molecules of different species interact locally and diffuse. In the management of new technologies, the diffusion processes of innovations in the marketplace (e.g., the mobile phone) are a major subject. These innovation diffusion models refer mainly to epidemic models. This contribution introduces that modeling process by using PDEs and reviews the essential features of the dynamics and control in biological, chemical and new technology transfer. This paper is essentially user-oriented with basic nonlinear evolution equations, delay PDEs, several analytical and numerical methods for solving, different solutions, and with the use of mathematical packages, notebooks and codes. The computations are carried out by using the software Wolfram Mathematica®7, and C++ codes.

  14. Characterization of an olfactometer by proton-transfer-reaction mass spectrometry

    NASA Astrophysics Data System (ADS)

    Beauchamp, J.; Frasnelli, J.; Buettner, A.; Scheibe, M.; Hansel, A.; Hummel, T.

    2010-02-01

    The performance of a commercial olfactometer instrument, which produces odorant pulses of defined duration and concentration, was characterized using proton-transfer-reaction mass spectrometry (PTR-MS). Direct coupling of the PTR-MS instrument with the olfactometer enabled on-line evaluation of the rapidly delivered aroma pulses. Tests were made with a selection of four odorous compounds: hydrogen sulfide, 2,3-butanedione, ethyl butanoate and ethyl hexanoate. Odour concentrations and stimulus durations for these compounds were monitored directly at the olfactometer delivery port via the respective PTR-MS signals. The performance of the olfactometer was found to be dependent on pulse duration. A decrease over time in maximum intensity for identical pulses over an extended duration showed headspace concentration depletions for compounds sourced from a water solution, indicative of gas/liquid partitioning. Such changes were not present using odours sourced from a cylinder or, presumably, when using liquid odours at neat concentrations. In conclusion, while an olfactometer provides stimuli with good reproducibility, the concept is subject to certain limitations that must be appreciated by the experimenter for accurate application of this technique.

  15. First Measurement of Transferred Polarization in the Exclusive e p --> e' K+ Lambda Reaction

    SciTech Connect

    Daniel S. Carman; Et. Al.

    2003-04-04

    The first measurements of the transferred polarization for the exclusive {rvec e}p {yields} e{prime}K{sup +}{rvec {Lambda}} reaction have been performed in Hall B at the Thomas Jefferson National Accelerator Facility using the CLAS spectrometer. A 2.567 GeV electron beam was used to measure the hyperon polarization over a range of Q{sup 2} from 0.3 to 1.5 (GeV/c){sup 2}, W from 1.6 to 2.15 GeV, and over the full center-of-mass angular range of the K{sup +} meson. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. A non-relativistic quark model interpretation of our data suggests that the s{bar s} quark pair is produced with spins predominantly anti-aligned. Implications for the validity of the widely used {sup 3}P{sub o} quark-pair creation operator are discussed.

  16. On the performance of proton-transfer-reaction mass spectrometry for breath-relevant gas matrices

    NASA Astrophysics Data System (ADS)

    Beauchamp, J.; Herbig, J.; Dunkl, J.; Singer, W.; Hansel, A.

    2013-12-01

    The accuracy of quantitative volatile organic compound (VOC) detection by proton-transfer-reaction mass spectrometry (PTR-MS) is substantially enhanced if the instrument is calibrated. Although quantification of a compound is in principle possible by mathematical methods based on kinetic theory, the underlying picture can become complicated depending on the gas matrix, leading to error. A simple, reliable method to overcome this is to calibrate the instrument using standard gas mixtures containing VOCs at known concentrations, which enables the compound-dependent sensitivity of the instrument to be determined. A dynamic gas calibration unit was developed to generate variable but known quantities of selected standard compounds in a carrier gas of variable relative humidity (RH; up to 100% at 37 °C) and CO2 content (≤10%v) to reflect the changing conditions of a breath-gas sample matrix. Besides individual compound sensitivities, calibration also yields the limits of detection and quantification of the experimental method. Extensive calibrations of PTR-MS with several breath-relevant compounds were made at varying RH and CO2. Gas matrix effects of several compounds were negligible when appropriate mass-dependent transmission correction and normalization to the primary ions (m/z 21 and m/z 37) were applied. Two compounds are discussed in particular, namely acetaldehyde, which interferes with a CO2-related background, and formaldehyde, which shows a nonlinear dependence on sample gas humidity.

  17. Monitoring benzene formation from benzoate in model systems by proton transfer reaction-mass spectrometry

    NASA Astrophysics Data System (ADS)

    Aprea, Eugenio; Biasioli, Franco; Carlin, Silvia; Märk, Tilmann D.; Gasperi, Flavia

    2008-08-01

    The presence of benzene in food and in particular in soft drinks has been reported in several studies and should be considered in fundamental investigations about formation of this carcinogen compound as well as in quality control. Proton transfer reaction-mass spectrometry (PTR-MS) has been used here for rapid, direct quantification of benzene and to monitor its formation in model systems related to the use of benzoate, a common preservative, in presence of ascorbic acid: a widespread situation that yields benzene in, e.g., soft drinks and fruit juices. Firstly, we demonstrate here that PTR-MS allows a rapid determination of benzene that is in quantitative agreement with independent solid phase micro-extraction/gas chromatography (SPME/GC) analysis. Secondly, as a case study, the effect of different sugars (sucrose, fructose and glucose) on benzene formation is investigated indicating that they inhibit its formation and that this effect is enhanced for reducing sugars. The sugar-induced inhibition of benzene formation depends on several parameters (type and concentration of sugar, temperature, time) but can be more than 80% in situations that can be expected in the storage of commercial soft drinks. This is consistent with the reported observations of higher benzene concentrations in sugar-free soft drinks.

  18. The NO+O{sub 3} reaction: A triple oxygen isotope perspective on the reaction dynamics and atmospheric implications for the transfer of the ozone isotope anomaly

    SciTech Connect

    Savarino, J.; Morin, S.; Baroni, M.; Bhattacharya, S. K.; Doussin, J.-F.

    2008-05-21

    Atmospheric nitrate shows a large oxygen isotope anomaly ({delta} {sup 17}O), characterized by an excess enrichment of {sup 17}O over {sup 18}O, similar to the ozone molecule. Modeling and observations assign this specific isotopic composition mainly to the photochemical steady state that exists in the atmosphere between ozone and nitrate precursors, namely, the nitrogen oxides (NO{sub x}=NO+NO{sub 2}). However, this transfer is poorly quantified and is built on unverified assumptions about which oxygen atoms of ozone are transferred to NO{sub x}, greatly weakening any interpretation of the nitrate oxygen isotopic composition in terms of chemical reaction pathways and the oxidation state of the atmosphere. With the aim to improve our understanding and quantify how nitrate inherits this unusual isotopic composition, we have carried out a triple isotope study of the reaction NO+O{sub 3}. Using ozone intramolecular isotope distributions available in the literature, we have found that the central atom of the ozone is abstracted by NO with a probability of (8{+-}5)%({+-}2{sigma}) at room temperature. This result is at least qualitatively supported by dynamical reaction experiments, the non-Arrhenius behavior of the kinetic rate of this reaction, and the kinetic isotope fractionation factor. Finally, we have established the transfer function of the isotope anomaly of O{sub 3} to NO{sub 2}, which is described by the linear relationship {delta} {sup 17}O(NO{sub 2})=Ax{delta} {sup 17}O(O{sub 3})+B, with A=1.18{+-}0.07({+-}1{sigma}) and B=(6.6{+-}1.5) per mille ({+-}1{sigma}). Such a relationship can be easily incorporated into models dealing with the propagation of the ozone isotope anomaly among oxygen-bearing species in the atmosphere and should help to better interpret the oxygen isotope anomaly of atmospheric nitrate in terms of its formation reaction pathways.

  19. The NO +O3 reaction: A triple oxygen isotope perspective on the reaction dynamics and atmospheric implications for the transfer of the ozone isotope anomaly

    NASA Astrophysics Data System (ADS)

    Savarino, J.; Bhattacharya, S. K.; Morin, S.; Baroni, M.; Doussin, J.-F.

    2008-05-01

    Atmospheric nitrate shows a large oxygen isotope anomaly (ΔO17), characterized by an excess enrichment of O17 over O18, similar to the ozone molecule. Modeling and observations assign this specific isotopic composition mainly to the photochemical steady state that exists in the atmosphere between ozone and nitrate precursors, namely, the nitrogen oxides (NOx=NO+NO2). However, this transfer is poorly quantified and is built on unverified assumptions about which oxygen atoms of ozone are transferred to NOx, greatly weakening any interpretation of the nitrate oxygen isotopic composition in terms of chemical reaction pathways and the oxidation state of the atmosphere. With the aim to improve our understanding and quantify how nitrate inherits this unusual isotopic composition, we have carried out a triple isotope study of the reaction NO +O3. Using ozone intramolecular isotope distributions available in the literature, we have found that the central atom of the ozone is abstracted by NO with a probability of (8±5)%(±2σ) at room temperature. This result is at least qualitatively supported by dynamical reaction experiments, the non-Arrhenius behavior of the kinetic rate of this reaction, and the kinetic isotope fractionation factor. Finally, we have established the transfer function of the isotope anomaly of O3 to NO2, which is described by the linear relationship ΔO17(NO2)=A ×ΔO17(O3)+B, with A =1.18±0.07(±1σ) and B =(6.6±1.5)‰(±1σ). Such a relationship can be easily incorporated into models dealing with the propagation of the ozone isotope anomaly among oxygen-bearing species in the atmosphere and should help to better interpret the oxygen isotope anomaly of atmospheric nitrate in terms of its formation reaction pathways.

  20. Production of heavy isotopes in transfer reactions by collisions of {sup 238}U+{sup 238}U

    SciTech Connect

    Feng Zhaoqing; Jin Genming; Li Junqing

    2009-12-15

    The dynamics of transfer reactions in collisions of two very heavy nuclei {sup 238}U+{sup 238}U is studied within the dinuclear system (DNS) model. Collisions of two actinide nuclei form a superheavy composite system during a very short time, in which a large number of charge and mass transfers may take place. Such reactions have been investigated experimentally as an alternative way for the production of heavy and superheavy nuclei. The role of collision orientation in the production cross sections of heavy nuclides is analyzed systematically. Calculations show that the cross sections decrease drastically as the charged numbers of the heavy fragments increase. The transfer mechanism is favorable to synthesizing heavy neutron-rich isotopes, such as nuclei around the subclosure at N=162 from No (Z=102) to Db (Z=105)

  1. Mechanism of the nucleotidyl-transfer reaction in DNA polymerase revealed by time-resolved protein crystallography

    PubMed Central

    Nakamura, Teruya; Zhao, Ye; Yamagata, Yuriko; Hua, Yue-jin; Yang, Wei

    2013-01-01

    Nucleotidyl-transfer reaction catalyzed by DNA polymerase is a fundamental enzymatic reaction for DNA synthesis. Until now, a number of structural and kinetic studies on DNA polymerases have proposed a two-metalion mechanism of the nucleotidyl-transfer reaction. However, the actual reaction process has never been visualized. Recently, we have followed the nucleotidyl-transfer reaction process by human DNA polymerase η using time-resolved protein crystallography. In sequence, two Mg2+ ions bind to the active site, the nucleophile 3′-OH is deprotonated, the deoxyribose at the primer end converts from C2′-endo to C3′-endo, and the nucleophile and the α-phosphate of the substrate dATP approach each other to form the new bond. In this process, we observed transient elements, which are a water molecule to deprotonate the 3′-OH and an additional Mg2+ ion to stabilize the intermediate state. Particularly, the third Mg2+ ion observed in this study may be a general feature of the two-metalion mechanism.

  2. Electron transfer and bond-forming reactions following collisions of I2+ with CO and CS2

    NASA Astrophysics Data System (ADS)

    Fletcher, James D.; Parkes, Michael A.; Price, Stephen D.

    2015-08-01

    Collisions between I2+ and CO have been investigated using time-of-flight mass spectrometry at a range of centre-of-mass collision energies between 0.5 and 3.0 eV. Following I2++CO collisions, we detect I++CO+ from a single-electron transfer reaction and IO++C+ from bond-forming reactivity. Reaction-window calculations, based on Landau-Zener theory, have been used to rationalise the electron transfer reactivity and computational chemistry has been used to explore the [I-CO]2+ potential energy surface to account for the observation of IO+. In addition, collisions between I2+ and CS2 have been investigated over a range of centre-of-mass collision energies between 0.8 and 6.0 eV. Both single- and double-electron transfer reactions are observed in the I2+/CS2 collision system, an observation again rationalised by reaction-window theory. The monocations IS+ and IC+ are also detected following collisions of I2+ with CS2, and these ions are clearly products from a bond-forming reaction. We present a simple model based on the structure of the [I-CS2]2+ collision complex to rationalise the significantly larger yield of IS+ than IC+ in this bond-forming process.

  3. Rate-promoting vibrations and coupled hydrogen-electron transfer reactions in the condensed phase: A model for enzymatic catalysis

    NASA Astrophysics Data System (ADS)

    Mincer, Joshua S.; Schwartz, Steven D.

    2004-04-01

    A model is presented for coupled hydrogen-electron transfer reactions in condensed phase in the presence of a rate promoting vibration. Large kinetic isotope effects (KIEs) are found when the hydrogen is substituted with deuterium. While these KIEs are essentially temperature independent, reaction rates do exhibit temperature dependence. These findings agree with recent experimental data for various enzyme-catalyzed reactions, such as the amine dehydrogenases and soybean lipoxygenase. Consistent with earlier results, turning off the promoting vibration results in an increased KIE. Increasing the barrier height increases the KIE, while increasing the rate of electron transfer decreases it. These results are discussed in light of other views of vibrationally enhanced tunneling in enzymes.

  4. Carbon-, sulfur-, and phosphorus-based charge transfer reactions in inductively coupled plasma-atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Grindlay, Guillermo; Gras, Luis; Mora, Juan; de Loos-Vollebregt, Margaretha T. C.

    2016-01-01

    In this work, the influence of carbon-, sulfur-, and phosphorus-based charge transfer reactions on the emission signal of 34 elements (Ag, Al, As, Au, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, I, In, Ir, K, Li, Mg, Mn, Na, Ni, P, Pb, Pd, Pt, S, Sb, Se, Sr, Te, and Zn) in axially viewed inductively coupled plasma-atomic emission spectrometry has been investigated. To this end, atomic and ionic emission signals for diluted glycerol, sulfuric acid, and phosphoric acid solutions were registered and results were compared to those obtained for a 1% w w- 1 nitric acid solution. Experimental results show that the emission intensities of As, Se, and Te atomic lines are enhanced by charge transfer from carbon, sulfur, and phosphorus ions. Iodine and P atomic emission is enhanced by carbon- and sulfur-based charge transfer whereas the Hg atomic emission signal is enhanced only by carbon. Though signal enhancement due to charge transfer reactions is also expected for ionic emission lines of the above-mentioned elements, no experimental evidence has been found with the exception of Hg ionic lines operating carbon solutions. The effect of carbon, sulfur, and phosphorus charge transfer reactions on atomic emission depends on (i) wavelength characteristics. In general, signal enhancement is more pronounced for electronic transitions involving the highest upper energy levels; (ii) plasma experimental conditions. The use of robust conditions (i.e. high r.f. power and lower nebulizer gas flow rates) improves carbon, sulfur, and phosphorus ionization in the plasma and, hence, signal enhancement; and (iii) the presence of other concomitants (e.g. K or Ca). Easily ionizable elements reduce ionization in the plasma and consequently reduce signal enhancement due to charge transfer reactions.

  5. Lanthanum Tricyanide-Catalyzed Acyl Silane-Ketone Benzoin Additions and Kinetic Resolution of Resultant α-Silyloxyketones

    PubMed Central

    Tarr, James C.

    2010-01-01

    We report the full account of our efforts on the lanthanum tricyanide-catalyzed acyl silane-ketone benzoin reaction. The reaction exhibits a wide scope in both acyl silane (aryl, alkyl) and ketone (aryl-alkyl, alkyl-alkyl, aryl-aryl, alkenyl-alkyl, alkynyl-alkyl) coupling partners. The diastereoselectivity of the reaction has been examined in both cyclic and acyclic systems. Cyclohexanones give products arising from equatorial attack by the acyl silane. The diastereoselectivity of acyl silane addition to acyclic α-hydroxy ketones can be controlled by varying the protecting group to obtain either Felkin-Ahn or chelation control. The resultant α-silyloxyketone products can be resolved with selectivity factors from 10 to 15 by subjecting racemic ketone benzoin products to CBS reduction. PMID:20392127

  6. Acyl-Carbon Bond Cleaving Cytochrome P450 Enzymes: CYP17A1, CYP19A1 and CYP51A1.

    PubMed

    Akhtar, Muhammad; Wright, J Neville

    2015-01-01

    Cytochrome P450 (P450 or CYP) enzymes in their resting state contain the heme-iron in a high-spin FeIII state. Binding of a substrate to a P450 enzyme allows transfer of the first electron, producing a Fe(II) species that reacts with oxygen to generate a low-spin iron superoxide intermediate (FeIII-O-O•) ready to accept the second electron to produce an iron peroxy anion intermediate (a, FeIII-O-O-). In classical monooxygenation reactions, the peroxy anion upon protonation fragments to form the reactive Compound I intermediate (Por•+FeIV=O), or its ferryl radical resonance form (FeIV-O•). However, when the substrate projects a carbonyl functionality, of the type b, at the active site as is the case for reactions catalyzed by CYP17A1, CYP19A1 and CYP51A1, the peroxy anion (FeIII-O-O-) is trapped, yielding a tetrahedral intermediate (c) that fragments to an acyl-carbon cleavage product (d plus an acid). Analogous acyl-carbon cleavage reactions are also catalyzed by certain hepatic P450s and CYP125A1 from Mycobacterium tuberculosis. A further improvisation on the theme is provided by aldehyde deformylases that convert long-chain aliphatic aldehydes to hydrocarbons. CYP17A1 is involved in the biosynthesis of corticoids as well as androgens. The flux toward these two classes of hormones seems to be regulated by cytochrome b 5, at the level of the acyl-carbon cleavage reaction. It is this regulation of CYP17A1 that provides a safety mechanism, ensuring that during corticoid biosynthesis, which requires 17α-hydroxylation by CYP17A1, androgen formation is avoided (Fig. 4.1). PMID:26002733

  7. Residual Water Modulates QA−-to-QB Electron Transfer in Bacterial Reaction Centers Embedded in Trehalose Amorphous Matrices

    PubMed Central

    Francia, Francesco; Palazzo, Gerardo; Mallardi, Antonia; Cordone, Lorenzo; Venturoli, Giovanni

    2003-01-01

    The role of protein dynamics in the electron transfer from the reduced primary quinone, QA−, to the secondary quinone, QB, was studied at room temperature in isolated reaction centers (RC) from the photosynthetic bacterium Rhodobacter sphaeroides by incorporating the protein in trehalose water systems of different trehalose/water ratios. The effects of dehydration on the reaction kinetics were examined by analyzing charge recombination after different regimes of RC photoexcitation (single laser pulse, double flash, and continuous light) as well as by monitoring flash-induced electrochromic effects in the near infrared spectral region. Independent approaches show that dehydration of RC-containing matrices causes reversible, inhomogeneous inhibition of QA−-to-QB electron transfer, involving two subpopulations of RCs. In one of these populations (i.e., active), the electron transfer to QB is slowed but still successfully competing with P+QA− recombination, even in the driest samples; in the other (i.e., inactive), electron transfer to QB after a laser pulse is hindered, inasmuch as only recombination of the P+QA− state is observed. Small residual water variations (∼7 wt %) modulate fully the relative fraction of the two populations, with the active one decreasing to zero in the driest samples. Analysis of charge recombination after continuous illumination indicates that, in the inactive subpopulation, the conformational changes that rate-limit electron transfer can be slowed by >4 orders of magnitude. The reported effects are consistent with conformational gating of the reaction and demonstrate that the conformational dynamics controlling electron transfer to QB is strongly enslaved to the structure and dynamics of the surrounding medium. Comparing the effects of dehydration on P+QA−→PQA recombination and QA−QB→QAQB− electron transfer suggests that conformational changes gating the latter process are distinct from those stabilizing the primary

  8. Lipid Acyl Chain Remodeling in Yeast

    PubMed Central

    Renne, Mike F.; Bao, Xue; De Smet, Cedric H.; de Kroon, Anton I. P. M.

    2015-01-01

    Membrane lipid homeostasis is maintained by de novo synthesis, intracellular transport, remodeling, and degradation of lipid molecules. Glycerophospholipids, the most abundant structural component of eukaryotic membranes, are subject to acyl chain remodeling, which is defined as the post-synthetic process in which one or both acyl chains are exchanged. Here, we review studies addressing acyl chain remodeling of membrane glycerophospholipids in Saccharomyces cerevisiae, a model organism that has been successfully used to investigate lipid synthesis and its regulation. Experimental evidence for the occurrence of phospholipid acyl chain exchange in cardiolipin, phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine is summarized, including methods and tools that have been used for detecting remodeling. Progress in the identification of the enzymes involved is reported, and putative functions of acyl chain remodeling in yeast are discussed. PMID:26819558

  9. Deuteron-induced nucleon transfer reactions within an ab initio framework: First application to p -shell nuclei

    NASA Astrophysics Data System (ADS)

    Raimondi, Francesco; Hupin, Guillaume; Navrátil, Petr; Quaglioni, Sofia

    2016-05-01

    Background: Low-energy transfer reactions in which a proton is stripped from a deuteron projectile and dropped into a target play a crucial role in the formation of nuclei in both primordial and stellar nucleosynthesis, as well as in the study of exotic nuclei using radioactive beam facilities and inverse kinematics. Ab initio approaches have been successfully applied to describe the 3H (d ,n )4He and 3He(d ,p )4He fusion processes. Purpose: An ab initio treatment of transfer reactions would also be desirable for heavier targets. In this work, we extend the ab initio description of (d ,p ) reactions to processes with light p -shell nuclei. As a first application, we study the elastic scattering of deuterium on 7Li and the 7Li(d ,p )8Li transfer reaction based on a two-body Hamiltonian. Methods: We use the no-core shell model to compute the wave functions of the nuclei involved in the reaction, and describe the dynamics between targets and projectiles with the help of microscopic-cluster states in the spirit of the resonating group method. Results: The shapes of the excitation functions for deuterons impinging on 7Li are qualitatively reproduced up to the deuteron breakup energy. The interplay between d -7Li and p -8Li particle-decay channels determines some features of the 9Be spectrum above the d +7Li threshold. Our prediction for the parity of the 17.298 MeV resonance is at odds with the experimental assignment. Conclusions: Deuteron stripping reactions with p -shell targets can now be computed ab initio, but calculations are very demanding. A quantitative description of the 7Li(d ,p )8Li reaction will require further work to include the effect of three-nucleon forces and additional decay channels and to improve the convergence rate of our calculations.

  10. Bis(pentamethylcyclopentadienyl) ytterbium: Electron-transfer reactions with organotransition metal complexes

    SciTech Connect

    Matsunaga, P.T.

    1991-11-01

    The divalent lanthanide complex, (Me{sub 5}C{sub 5}){sub 2}Yb, reacts with methylcopper to produce the base-free, ytterbium-methyl complex, (Me{sub 5}C{sub 5}){sub 2}YbMe. This product forms a asymmetric, methyl-bridged dimer in the solid state. The bulky alkyl complex, (Me{sub 5}C{sub 5}){sub 2}YbCH(SiMe{sub 3}){sub 2}, displays similar chemistry to (Me{sub 5}C{sub 5}){sub 2}YbMe, but at a reduced reaction rate due to the limited accessibility of the metal in (Me{sub 5}C{sub 5}){sub 2}YbCH(SiMe{sub 3}){sub 2}. Copper and silver halide salts react with (Me{sub 5}C{sub 5}){sub 2}V to produce the trivalent halide derivatives, (Me{sub 5}C{sub 5}){sub 2}VX (X + F, Cl, Br, I). The chloride complex, (Me{sub 5}C{sub 5}){sub 2}VCl, reacts with lithium reagents to form the phenyl and borohydride species. Nitrous oxide transfers an oxygen atom to (Me{sub 5}C{sub 5}){sub 2}V producing the vanadium-oxo complex, (Me{sub 5}Ce{sub 5}){sub 2}VO. The trivalent titanium species, (Me{sub 5}C{sub 5}){sub 2}TiX (X = Cl, Br, Me, BH{sub 4}), form bimetallic coordination complexes with (Me{sub 5}C{sub 5}){sub 2}Yb. The magnetic behavior of the products indicates that electron transfer has not occurred. The solid state structures of the chloride and bromide complexes show unusual bend angles for the halide bridges between ytterbium and titanium. A model based on frontier orbital theory has been proposed to account for the bending behavior in these species. The bimetallic methyl complex contains a linear methyl bridge between ytterbium and titanium.

  11. Stability-increasing effects of anthocyanin glycosyl acylation.

    PubMed

    Zhao, Chang-Ling; Yu, Yu-Qi; Chen, Zhong-Jian; Wen, Guo-Song; Wei, Fu-Gang; Zheng, Quan; Wang, Chong-De; Xiao, Xing-Lei

    2017-01-01

    This review comprehensively summarizes the existing knowledge regarding the chemical implications of anthocyanin glycosyl acylation, the effects of acylation on the stability of acylated anthocyanins and the corresponding mechanisms. Anthocyanin glycosyl acylation commonly refers to the phenomenon in which the hydroxyl groups of anthocyanin glycosyls are esterified by aliphatic or aromatic acids, which is synthetically represented by the acylation sites as well as the types and numbers of acyl groups. Generally, glycosyl acylation increases the in vitro and in vivo chemical stability of acylated anthocyanins, and the mechanisms primarily involve physicochemical, stereochemical, photochemical, biochemical or environmental aspects under specific conditions. Additionally, the acylation sites as well as the types and numbers of acyl groups influence the stability of acylated anthocyanins to different degrees. This review could provide insight into the optimization of the stability of anthocyanins as well as the application of suitable anthocyanins in food, pharmaceutical and cosmetic industries. PMID:27507456

  12. Characterization of Proton Transfer Reaction Mass Spectrometry for the detection of sesquiterpenes

    NASA Astrophysics Data System (ADS)

    Demarcke, M.; Amelynck, C.; Schoon, N.; Dewulf, J.; van Langenhove, H.

    2009-04-01

    It is well-known that terrestrial vegetation is an important source of non-methane volatile organic compounds (NMVOC) of which terpenoid compounds, such as isoprene, monoterpenes and sesquiterpenes, constitute an important fraction. Measurements of sesquiterpenes (C15H24) are still sparse and hard to perform because of the low volatility of these compounds and their high reactivity with the main atmospheric oxidants (OH, O3, NO3). Nevertheless, they may well play an important role in atmospheric chemistry because of their high reactivity and their high potential to contribute to secondary organic aerosol (SOA) formation. Important efforts have been made lately to develop and improve analytical techniques for sesquiterpene detection and recently proton transfer reaction mass spectrometry (PTR-MS) has also been applied for sesquiterpene detection by a limited number of research groups. Further exploitation of the PTR-MS technique for this class of terpenoid compounds may benefit from a better characterization of the ion chemistry inside the PTR-MS reactor at varying instrumental and environmental parameters. Therefore, product ion distributions of four important sesquiterpenes (beta-caryophyllene, alpha-humulene, longifolene and alpha-cedrene) have been measured in a commercial high sensitivity PTR-MS instrument (Ionicon Analytik GmbH) at different values of the ratio of the electric field strength to the buffer gas number density in the reactor (E/N) and at different water vapour pressures in the inlet line. Although the nascent excited complex, which is formed in the H3O+.(H2O)n/sesquiterpene reaction, partially decomposes into a variety of fragment ions, the protonated sesquiterpene remains the major product ion for all four species studied. The product ion distributions show a large dependence on E/N, but, interestingly, are not found to be much influenced by changing relative humidities. From the results it is expected that sesquiterpene detection sensitivity

  13. Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions

    SciTech Connect

    Kumbhakar, Manoj; Nath, Sukhendu; Mukherjee, Tulsi; Pal, Haridas

    2005-07-15

    Photoinduced electron transfer (ET) between coumarin dyes and aromatic amine has been investigated in two cationic micelles, namely, cetyltrimethyl ammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the results have been compared with those observed earlier in sodium dodecyl sulphate (SDS) and triton-X-100 (TX-100) micelles for similar donor-acceptor pairs. Due to a reasonably high effective concentration of the amines in the micellar Stern layer, the steady-state fluorescence results show significant static quenching. In the time-resolved (TR) measurements with subnanosecond time resolution, contribution from static quenching is avoided. Correlations of the dynamic quenching constants (k{sub q}{sup TR}), as estimated from the TR measurements, show the typical bell-shaped curves with the free-energy changes ({delta}G{sup 0}) of the ET reactions, as predicted by the Marcus outersphere ET theory. Comparing present results with those obtained earlier for similar coumarin-amine systems in SDS and TX-100 micelles, it is seen that the inversion in the present micelles occurs at an exergonicity (-{delta}G{sup 0}>{approx}1.2-1.3 eV) much higher than that observed in SDS and TX-100 micelles (-{delta}G{sup 0}>{approx}0.7 eV), which has been rationalized based on the relative propensities of the ET and solvation rates in different micelles. In CTAB and DTAB micelles, the k{sub q}{sup TR} values are lower than the solvation rates, which result in the full contribution of the solvent reorganization energy ({lambda}{sub s}) towards the activation barrier for the ET reaction. Contrary to this, in SDS and TX-100 micelles, k{sub q}{sup TR} values are either higher or comparable with the solvation rates, causing only a partial contribution of {lambda}{sub s} in these cases. Thus, Marcus inversion in present cationic micelles is inferred to be the true inversion, whereas that in the anionic SDS and neutral TX-100 micelles are understood to be the apparent

  14. Energetics of charge transfer reactions in solvents of dipolar and higher order multipolar character. II. Results

    NASA Astrophysics Data System (ADS)

    Perng, Baw-Ching; Newton, Marshall D.; Raineri, Fernando O.; Friedman, Harold L.

    1996-05-01

    We apply the theories developed in the preceding paper (paper I) to calculate various energy quantities of charge transfer (CT) reactions in nine solvents that cover a wide range of polarity, and for which interaction site models (ISM's) may be found in the literature. Besides the two surrogate Hamiltonian theories developed in paper I, the renormalized site-density theory (RST) and the renormalized dielectric theory (RDT), we also investigate a simple harmonic approximation (HXA) for the diabatic free energy profiles, whose characteristic parameters are calculated taking specific advantage of the expression given by the extended reference interaction site method (XRISM) for the free energy of solvation. For each CT process we analyze (a) the solvent reorganization energy λ, (b) the shift of the absorption transition energy due to the solvatochromic effect, and (c) the solvent contribution to the free energy change ΔA. In addition, for a few selected examples, we also report the detailed diabatic free energy profiles. The calculations reported rely on solute-solvent and solvent-solvent pair correlation functions obtained with the XRISM integral equation method applied to nonpolarizable (with fixed mean partial charges) ISM representations of the solute and solvent molecules. To rectify the omission of the solvent electronic degrees of freedom, we correct the dielectric part of the solvent reorganization energy with an additive term designed to compensate for the use of fixed charge ISM models. Contact with theories in which the solvent is represented as a dielectric continuum medium (with or without spatial dispersion) and the solute as a set of charges inside spherical cavities carved out of the dielectric is made straightforwardly within the RDT theory by considering a particularly simple form of the solute-solvent RISM site-site direct correlation functions. Using simple ISM models for several solute species, including Reichardt's betaine-30 dye and a

  15. Photoinduced electron-transfer reactions of poly(pyridine)ruthenium(II) complexes with europium(III/II) cryptates

    SciTech Connect

    Sabbatini, N.; Dellonte, S.; Bonazzi, A.; Ciano, M.; Balzani, V.

    1986-05-21

    Rate constants for electron-transfer reactions between poly(pyridine)ruthenium(II) (RuL/sub 3//sup 2 +/) excited states and the europium cryptates (Eu contains 2.2.1)/sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/ have been measured in aqueous solution by luminescence quenching techniques. The rate constants for a few electron-transfer back-reactions between the photogenerated RuL/sub 3//sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/ or RuL/sub 3//sup +/ and (Eu contains 2.2.1)/sup 3 +/ species have also been measured by flash photolysis experiments. The results obtained have been elaborated and discussed on the basis of current electron-transfer theories. Comparison of the results obtained with those previously available for the Eu/sub aq//sup 3 +/ and Eu/sub aq//sup 2 +/ ions shows that cryptation decreases the intrinsic barrier and/or increases the adiabaticity coefficient of the electron-transfer reaction. A plot of the rate constants vs. the free energy changes of the electron-transfer processes shows that the data concerning (Eu contains 2.2.1)/sup 3 +/ reduction do not correlate with those concerning (Eu contains 2.2.1)/sup 2 +/ oxidation. Possible reasons for this asymmetric behavior include (i) different shapes of the potential energy wells for (Eu contains 2.2.1)/sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/, (ii) different work terms for the formation of the precursor complex, and (iii) different distances of closest approach of (Eu contains 2.2.1)/sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/ with the hydrophobic RuL/sub 3//sup n+/ reaction partners.

  16. Calibration and intercomparison of acetic acid measurements using proton transfer reaction mass spectrometry (PTR-MS)

    USGS Publications Warehouse

    Haase, K.B.; Keene, W.C.; Pszenny, A.A.P.; Mayne, H.R.; Talbot, R.W.; Sive, B.C.

    2012-01-01

    Acetic acid is one of the most abundant organic acids in the ambient atmosphere, with maximum mixing ratios reaching into the tens of parts per billion by volume (ppbv) range. The identities and associated magnitudes of the major sources and sinks for acetic acid are poorly characterized, due in part to the limitation in available measurement techniques. This paper demonstrates that Proton Transfer Reaction Mass Spectrometry (PTR-MS) can reliably quantify acetic acid vapor in ambient air. Three different PTR-MS configurations were calibrated at low ppbv mixing ratios using permeation tubes, which yielded calibration factors between 7.0 and 10.9 normalized counts per second per ppbv (ncps ppbv−1) at a drift tube field strength of 132 townsend (Td). Detection limits ranged from 0.06 to 0.32 ppbv with dwell times of 5 s. These calibration factors showed negligible humidity dependence. Using the experimentally determined calibration factors, PTR-MS measurements of acetic acid during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign were validated against results obtained using Mist Chambers coupled with Ion Chromatography (MC/IC). An orthogonal least squares linear regression of paired data yielded a slope of 1.14 ± 0.06 (2σ), an intercept of 0.049 ± 20 (2σ) ppbv, and an R2 of 0.78. The median mixing ratio of acetic acid on Appledore Island, ME during the ICARTT campaign was 0.530 ± 0.025 ppbv with a minimum of 0.075 ± 0.004 ppbv, and a maximum of 3.555 ± 0.171 ppbv.

  17. Advanced online monitoring of cell culture off-gas using proton transfer reaction mass spectrometry.

    PubMed

    Schmidberger, Timo; Gutmann, Rene; Bayer, Karl; Kronthaler, Jennifer; Huber, Robert

    2014-01-01

    Mass spectrometry has been frequently applied to monitor the O₂ and CO₂ content in the off-gas of animal cell culture fermentations. In contrast to classical mass spectrometry the proton transfer reaction mass spectrometry (PTR-MS) provides additional information of volatile organic compounds by application of a soft ionization technology. Hence, the spectra show less fragments and can more accurately assigned to particular compounds. In order to discriminate between compounds of non-metabolic and metabolic origin cell free experiments and fed-batch cultivations with a recombinant CHO cell line were conducted. As a result, in total eight volatiles showing high relevance to individual cultivation or cultivation conditions could be identified. Among the detected compounds methanethiol, with a mass-to-charge ratio of 49, qualifies as a key candidate in process monitoring due to its strong connectivity to lactate formation. Moreover, the versatile and complex data sets acquired by PTR MS provide a valuable resource for statistical modeling to predict non direct measurable parameters. Hence, partial least square regression was applied to the complete spectra of volatiles measured and important cell culture parameters such as viable cell density estimated (R²  = 0.86). As a whole, the results of this study clearly show that PTR-MS provides a powerful tool to improve bioprocess-monitoring for mammalian cell culture. Thus, specific volatiles emitted by cells and measured online by the PTR-MS and complex variables gained through statistical modeling will contribute to a deeper process understanding in the future and open promising perspectives to bioprocess control. PMID:24376199

  18. Experimental study of the 66Ni(d ,p ) 67Ni one-neutron transfer reaction

    NASA Astrophysics Data System (ADS)

    Diriken, J.; Patronis, N.; Andreyev, A.; Antalic, S.; Bildstein, V.; Blazhev, A.; Darby, I. G.; De Witte, H.; Eberth, J.; Elseviers, J.; Fedosseev, V. N.; Flavigny, F.; Fransen, Ch.; Georgiev, G.; Gernhauser, R.; Hess, H.; Huyse, M.; Jolie, J.; Kröll, Th.; Krücken, R.; Lutter, R.; Marsh, B. A.; Mertzimekis, T.; Muecher, D.; Orlandi, R.; Pakou, A.; Raabe, R.; Randisi, G.; Reiter, P.; Roger, T.; Seidlitz, M.; Seliverstov, M.; Sotty, C.; Tornqvist, H.; Van De Walle, J.; Van Duppen, P.; Voulot, D.; Warr, N.; Wenander, F.; Wimmer, K.

    2015-05-01

    The quasi-SU(3) sequence of the positive parity ν g9 /2,d5 /2,s1 /2 orbitals above the N =40 shell gap are assumed to induce strong quadrupole collectivity in the neutron-rich Fe (Z =26 ) and Cr (Z =24 ) isotopes below the nickel region. In this paper the position and strength of these single-particle orbitals are characterized in the neighborhood of 68Ni (Z =28 ,N =40 ) through the 66Ni(d ,p )67Ni one-neutron transfer reaction at 2.95 MeV/nucleon in inverse kinematics, performed at the REX-ISOLDE facility in CERN. A combination of the Miniball γ -array and T-REX particle-detection setup was used and a delayed coincidence technique was employed to investigate the 13.3-μ s isomer at 1007 keV in 67Ni. Excited states up to an excitation energy of 5.8 MeV have been populated. Feeding of the ν g9 /2 (1007 keV) and ν d5 /2 (2207 keV and 3277 keV) positive-parity neutron states and negative parity (ν p f ) states have been observed at low excitation energy. The extracted relative spectroscopic factors, based on a distorted-wave Born approximation analysis, show that the ν d5 /2 single-particle strength is mostly split over these two excited states. The results are also compared to the distribution of the proton single-particle strength in the 90Zr region (Z =40 ,N =50 ) .

  19. Equivalent inhibition of half-site and full-site retroviral strand transfer reactions by structurally diverse compounds.

    PubMed Central

    Hazuda, D; Felock, P; Hastings, J; Pramanik, B; Wolfe, A; Goodarzi, G; Vora, A; Brackmann, K; Grandgenett, D

    1997-01-01

    In vitro assay systems which use recombinant retroviral integrase (IN) and short DNA oligonucleotides fail to recapitulate the full-site integration reaction as it is known to occur in vivo. The relevance of using such circumscribed in vitro assays to define inhibitors of retroviral integration has not been formerly demonstrated. Therefore, we analyzed a series of structurally diverse inhibitors with respect to inhibition of both half-site and full-site strand transfer reactions with either recombinant or virion-produced IN. Half-site and full-site reactions catalyzed by avian myeloblastosis virus and human immunodeficiency virus type 1 (HIV-1) IN from virions are shown to be equivalently sensitive to inhibition by compounds which inhibit half-site reactions catalyzed by the recombinant HIV-1 IN. These studies therefore support the utility of using in vitro assays employing either recombinant or virion-derived IN to identify inhibitors of integration. PMID:8985421

  20. Near-barrier neutron transfer in reactions 3,6He + 45Sc and 3,6He + 197Au

    NASA Astrophysics Data System (ADS)

    Samarin, V. V.; Naumenko, M. A.; Penionzhkevich, Yu E.; Skobelev, N. K.; Kroha, V.; Mrazek, J.

    2016-06-01

    Experimental cross sections for formation of 196,198Au isotopes in reactions 3,6He + 197Au and cross sections for formation of 44,46Sc isotopes in reactions 3,6He + 45Sc have been analyzed. To calculate neutron transfer probabilities and cross sections the time- dependent Schrödinger equation for external neutrons of 3He, 6He, 45Sc and 197Au nuclei has been solved numerically. It is shown that the contribution of fusion and subsequent evaporation is significant in the case of reactions 3,6He + 45Sc, whereas in the case of reactions 3,6He + 197Au, it is negligible. Fusion-evaporation was taken into account using NRV evaporation code. Results of calculations demonstrate overall satisfactory agreement with experimental data.

  1. Fluorescent probes for tracking the transfer of iron-sulfur cluster and other metal cofactors in biosynthetic reaction pathways.

    PubMed

    Vranish, James N; Russell, William K; Yu, Lusa E; Cox, Rachael M; Russell, David H; Barondeau, David P

    2015-01-14

    Iron-sulfur (Fe-S) clusters are protein cofactors that are constructed and delivered to target proteins by elaborate biosynthetic machinery. Mechanistic insights into these processes have been limited by the lack of sensitive probes for tracking Fe-S cluster synthesis and transfer reactions. Here we present fusion protein- and intein-based fluorescent labeling strategies that can probe Fe-S cluster binding. The fluorescence is sensitive to different cluster types ([2Fe-2S] and [4Fe-4S] clusters), ligand environments ([2Fe-2S] clusters on Rieske, ferredoxin (Fdx), and glutaredoxin), and cluster oxidation states. The power of this approach is highlighted with an extreme example in which the kinetics of Fe-S cluster transfer reactions are monitored between two Fdx molecules that have identical Fe-S spectroscopic properties. This exchange reaction between labeled and unlabeled Fdx is catalyzed by dithiothreitol (DTT), a result that was confirmed by mass spectrometry. DTT likely functions in a ligand substitution reaction that generates a [2Fe-2S]-DTT species, which can transfer the cluster to either labeled or unlabeled Fdx. The ability to monitor this challenging cluster exchange reaction indicates that real-time Fe-S cluster incorporation can be tracked for a specific labeled protein in multicomponent assays that include several unlabeled Fe-S binding proteins or other chromophores. Such advanced kinetic experiments are required to untangle the intricate networks of transfer pathways and the factors affecting flux through branch points. High sensitivity and suitability with high-throughput methodology are additional benefits of this approach. We anticipate that this cluster detection methodology will transform the study of Fe-S cluster pathways and potentially other metal cofactor biosynthetic pathways. PMID:25478817

  2. Nuclear transfer reaction measurements at the ESR—for the investigation of the astrophysical 15O(α,γ)19Ne reaction

    NASA Astrophysics Data System (ADS)

    Doherty, D. T.; Woods, P. J.; Litvinov, Yu A.; Najafi, M. Ali; Bagchi, S.; Bishop, S.; Bo, M.; Brandau, C.; Davinson, T.; Dillmann, I.; Estrade, A.; Egelhof, P.; Evdokimov, A.; Gumberidze, A.; Heil, M.; Lederer, C.; Litvinov, S. A.; Lotay, G.; Kalantar-Nayestanaki, N.; Kiselev, O.; Kozhuharov, C.; Kröll, T.; Mahjour-Shafei, M.; Mutterer, M.; Nolden, F.; Petridis, N.; Popp, U.; Reifarth, R.; Rigollet, C.; Roy, S.; Steck, M.; Stöhlker, Th; Streicher, B.; Trotsenko, S.; von Schmid, M.; Yan, X. L.; Zamora, J. C.

    2015-11-01

    Astrophysical x-ray bursts are thought to be a result of thermonuclear explosions on the atmosphere of an accreting neutron star. Between these bursts, energy is thought to be generated by the hot CNO cycles. The 15O(α,γ)19Ne reaction is one reaction that allows breakout from these CNO cycles and into the rp-process to fuel outbursts. The reaction is expected to be dominated by a single 3/2+ resonance at 4.033 MeV in 19Ne, however, limited information is available on this key state. This work reports on a pioneering study of the 20Ne(p,d)19Ne reaction, performed in inverse kinematics at the experimental storage ring (ESR) as a means of accessing the astrophysically important 4.033 MeV state in 19Ne. The unique, background free, high luminosity conditions of the storage ring were utilized for this, the first transfer reaction performed at the ESR. The results of this pioneering test experiment are presented along with suggestions for future measurements at storage ring facilities.

  3. Photochemical reactions of electron-deficient olefins with N,N,N‧,N‧-tetramethylbenzidine via photoinduced electron-transfer

    NASA Astrophysics Data System (ADS)

    Pan, Yang; Zhao, Junshu; Ji, Yuanyuan; Yan, Lei; Yu, Shuqin

    2006-01-01

    Photoinduced electron transfer reactions of several electron-deficient olefins with N, N, N', N'-tetramethylbenzidine (TMB) in acetonitrile solution have been studied by using laser flash photolysis technique and steady-state fluorescence quenching method. Laser pulse excitation of TMB yields 3TMB* after rapid intersystem crossing from 1TMB*. The triplet which located at 480 nm is found to undergo fast quenching with the electron acceptors fumaronitrile (FN), dimethyl fumarate (DMF), diethyl fumarate (DEF), cinnamonitrile (CN), α-acetoxyacrylonitrile (AAN), crotononitrile (CrN) and 3-methoxyacrylonitrile (MAN). Substituents binding to olefin molecule own different electron-donating/withdrawing powers, which determine the electron-deficient property (π-cloud density) of olefin molecule as well as control the electron transfer rate constant directly. The detection of ion radical intermediates in the photolysis reactions confirms the proposed electron transfer mechanism, as expected from thermodynamics. The quenching rate constants of triplet TMB by these olefins have been determined at 510 nm to avoid the disturbance of formed TMB cation radical around 475 nm. All the kqT values approach or reach to the diffusion-controlled limit. In addition, fluorescence quenching rate constants kqS have been also obtained by calculating with Stern-Volmer equation. A correlation between experimental electron transfer rate constants and free energy changes has been explained by Marcus theory of adiabatic outer-sphere electron transfer. Disharmonic kq values for CN and CrN in endergonic region may be the disturbance of exciplexs formation.

  4. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander; Hammes-Schiffer, Sharon

    2015-11-17

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency regimes for the proton donor-acceptor vibrational mode. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term does not significantly impact the rate constants derived using the cumulant expansion approach in any of the regimes studied. The effects of the quadratic term may become significant when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant, however, particularly at high temperatures and for proton transfer interfaces with extremely soft proton donor-acceptor modes that are associated with extraordinarily weak hydrogen bonds. Even with the thermal averaging procedure, the effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances, and the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes. We are grateful for support from National Institutes of Health Grant GM056207 (applications to enzymes) and the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy

  5. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander V.; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  6. New players in the fatty acyl ethanolamide metabolism.

    PubMed

    Rahman, Iffat Ara Sonia; Tsuboi, Kazuhito; Uyama, Toru; Ueda, Natsuo

    2014-08-01

    Fatty acyl ethanolamides represent a class of endogenous bioactive lipid molecules and are generally referred to as N-acylethanolamines (NAEs). NAEs include palmitoylethanolamide (anti-inflammatory and analgesic substance), oleoylethanolamide (anorexic substance), and anandamide (endocannabinoid). The endogenous levels of NAEs are mainly regulated by enzymes responsible for their biosynthesis and degradation. In mammalian tissues, the major biosynthetic pathway starts from glycerophospholipids and is composed of two enzyme reactions. The first step is N-acylation of ethanolamine phospholipids catalyzed by Ca(2+)-dependent N-acyltransferase and the second step is the release of NAEs from N-acylated ethanolamine phospholipids by N-acylphosphatidylethanolamine (NAPE)-hydrolyzing phospholipase D (NAPE-PLD). As for the degradation of NAEs, fatty acid amide hydrolase plays the central role. However, recent studies strongly suggest the involvement of other enzymes in the NAE metabolism. These enzymes include members of the HRAS-like suppressor family (also called phospholipase A/acyltransferase family), which were originally discovered as tumor suppressors but can function as Ca(2+)-independent NAPE-forming N-acyltransferases; multiple enzymes involved in the NAPE-PLD-independent multi-step pathways to generate NAE from NAPE, which came to light by the analysis of NAPE-PLD-deficient mice; and a lysosomal NAE-hydrolyzing acid amidase as a second NAE hydrolase. These newly recognized enzymes may become the targets for the development of new therapeutic drugs. Here, we focus on recent enzymological findings in this area. PMID:24747663

  7. A general stochastic Liouville theory for sequential and superexchange electron-transfer reactions involving three Marcus potential surfaces

    SciTech Connect

    Tang, J.

    1994-03-01

    A general theory for nonadiabatic electron-transfer reactions at high temperature involving Marcus parabolic potential surfaces is presented. The theory can be applied to a three-component system with a donor, a bridging intermediate and an acceptor as well as to a system with charge separation from a photo-excited state followed by charge recombination to a third or ground state. Using the nonperturbative stochastic Liouville approach, analytical expressions are derived for the superexchange and the sequential electron-transfer rate constants covering all three conditions: the ``nondegenerate,`` the ``degenerate`` and the ``quasi-degenerate`` regimes.

  8. Real-time analysis of conformational control in electron transfer reactions of human cytochrome P450 reductase with cytochrome c.

    PubMed

    Hedison, Tobias M; Hay, Sam; Scrutton, Nigel S

    2015-11-01

    Protein domain dynamics and electron transfer chemistry are often associated, but real-time analysis of domain motion in enzyme-catalysed reactions and the elucidation of mechanistic schemes that relate these motions to the reaction chemistry are major challenges for biological catalysis research. Previously we suggested that reduction of human cytochrome P450 reductase with the reducing coenzyme NADPH is accompanied by major structural re-orientation of the FMN- and FAD-binding domains through an inferred dynamic cycle of 'open' and 'closed' conformations of the enzyme (PLoS Biol, 2011, e1001222). However, these studies were restricted to stopped-flow/FRET analysis of the reductive half-reaction, and were compromised by fluorescence quenching of the acceptor by the flavin cofactors. Here we have improved the design of the FRET system, by using dye pairs with near-IR fluorescence, and extended studies on human cytochrome P450 reductase to the oxidative half-reaction using a double-mixing stopped-flow assay, thereby analysing in real-time conformational dynamics throughout the complete catalytic cycle. We correlate redox changes accompanying the reaction chemistry with protein dynamic changes observed by FRET, and show that redox chemistry drives a major re-orientation of the protein domains in both the reductive and oxidative half-reactions. Our studies using the tractable (soluble) surrogate electron acceptor cytochrome c provide a framework for analysing mechanisms of electron transfer in the endoplasmic reticulum between cytochrome P450 reductase and cognate P450 enzymes. More generally, our work emphasizes the importance of protein dynamics in intra- and inter-protein electron transfer, and establishes methodology for real-time analysis of structural changes throughout the catalytic cycle of complex redox proteins. PMID:26307151

  9. Effect of laser intensity on the determination of intermolecular electron transfer rate constants—Observation of Marcus inverted region in photoinduced back electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Weng, Yu-Xiang; Chan, Kwok-Chu; Tzeng, Biing-Chiau; Che, Chi-Ming

    1998-10-01

    The light intensity and concentration dependence of the photoproduct yield are investigated in a monophotonic process. The relationship of the photoproduct yield with the laser intensity and the complex concentration for a monophotonic process is derived under laser flash photolysis. The relationship is confirmed experimentally in a monophotonic process, i.e., triplet-triplet transition for a Cu(I) complex Cu6(DMNSN')6 (DMNSN'=4,6-dimethylpyrimidine-2-thiolate). At low light intensity, the relationship can be approximated by a linear inverse square root dependence on the light intensity. Based on this equation, a method is proposed to determine the intrinsic back electron transfer rate constant kETb in photoinduced intermolecular electron transfer reactions, precluding the effect from the diffusional encounter pairs. The Marcus "inverted region" is observed by using the method in photoinduced back electron transfer reactions of [Au2(dppm)2](ClO4)2 (dppm=bis(diphenylphosphino)methane) with a series of substituted pyridinium acceptors.

  10. Nuclear spectroscopy study of the isotopes populated via multinucleon transfer in the 90Zr + 208Pb reaction

    SciTech Connect

    Ur, C. A.; Corradi, L.; Stefanini, A. M.; Behera, B. R.; Fioretto, E.; Gadea, A.; Latina, A.; Szilner, S.; Beghini, S.; Farnea, E.; Montagnoli, G.; Scarlassara, F.; Haas, F.; Pollarolo, G.

    2006-08-14

    The present work takes advantage of the multinucleon transfer mechanism between heavy reaction partners to study the population pattern of excited nuclear states in near spherical Zirconium isotopes following the 90Zr + 208Pb reaction at an energy closed to the Coulomb barrier. Both the projectile and the target are well known closed shell nuclei offering an optimum situation for clean experimental and theoretical conditions. Total kinetic energy loss (TKEL) distributions were compared with calculations performed with the GRAZING code. The ability to use the TKEL as a selection tool for the states at different excitation energies was shown.

  11. Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate

    PubMed Central

    Fructos, Manuel R; Urbano, Juan

    2015-01-01

    Summary Kinetic experiments based on the measurement of nitrogen evolution in the reaction of ethyl diazoacetate (N2CHCO2Et, EDA) and styrene or methanol catalyzed by the [IPrAu]+ core (IPr = 1,3-bis(diisopropylphenyl)imidazole-2-ylidene) have provided evidence that the transfer of the carbene group CHCO2Et to the substrate (styrene or methanol) takes place in the coordination sphere of Au(I) by means of an inner-sphere mechanism, in contrast to the generally accepted proposal of outer-sphere mechanisms for Au(I)-catalyzed reactions. PMID:26664649

  12. Neutron Transfer Reactions on Neutron-Rich N=50 and N=82 Nuclei Near the r-Process Path

    SciTech Connect

    Cizewski, J. A.; Jones, K. L.; Kozub, R. L.; Pain, S. D.; Thomas, J. S.; Arbanas, Goran; Adekola, Aderemi S; Bardayan, Daniel W; Blackmon, Jeff C; Chae, K. Y.; Chipps, K.; Dean, David Jarvis; Erikson, Luke; Gaddis, A. L.; Harlin, Christopher W; Hatarik, Robert; Howard, Joshua A; Johnson, Micah; Kapler, R.; Krolas, W.; Liang, J Felix; Livesay, Jake; Ma, Zhanwen; Matei, Catalin; Moazen, Brian; Nesaraja, Caroline D; O'Malley, Patrick; Paulauskas, Stanley V; Shapira, Dan; ShrinerJr., J. F.; Sissom, D. J.; Smith, Michael Scott; Swan, T. P.; Wilson, Gemma L

    2009-01-01

    Neutron transfer (d,p) reaction studies on the N = 50 isotones, 82Ge and 84Se, and A{approx}130 nuclei, 130,132Sn and 134Te, have been measured. Direct neutron capture cross sections for 82Ge and 84Se (n,?) have been calculated and are combined with Hauser-Feshbach expectations to estimate total (n,?) cross sections. The A{approx}130 studies used an early implementation of the ORRUBA array of position-sensitive silicon strip detectors for reaction proton measurements. Preliminary excitation energy and angular distribution results from the A{approx}130 measurements are reported.

  13. Thermodynamic Integration Networks and Their Application to Charge Transfer Reactions within the AauDyPI Fungal Peroxidase.

    PubMed

    Bauß, Anna; Langenmaier, Michael; Strittmatter, Eric; Plattner, Dietmar A; Koslowski, Thorsten

    2016-06-01

    We present a computer simulation study of the thermodynamics and kinetics of charge transfer reactions within the fungal peroxidase AauDyPI from Auricularia auriculae-judae. Driving forces and reorganization energies are obtained from a thermodynamic integration scheme based upon molecular dynamics simulations. To enhance the numerical accuracy, the free energies are analyzed within a least-squares scheme of a closely knit thermodynamic network. We identify Tyr147, Tyr229, and Trp105 as oxidative agents, and find Trp377 to be a long-lived reaction intermediate. The results are compared to recent experimental findings. PMID:27182684

  14. Copper(II)-catalyzed room temperature aerobic oxidation of hydroxamic acids and hydrazides to acyl-nitroso and azo intermediates, and their Diels-Alder trapping.

    PubMed

    Chaiyaveij, Duangduan; Cleary, Leah; Batsanov, Andrei S; Marder, Todd B; Shea, Kenneth J; Whiting, Andrew

    2011-07-01

    CuCl(2), in the presence of a 2-ethyl-2-oxazoline ligand, is an effective catalyst for the room temperature, aerobic oxidation of hydroxamic acids and hydrazides, to acyl-nitroso and azo dienophiles respectively, which are efficiently trapped in situ via both inter- and intramolecular hetero-Diels-Alder reactions with dienes. Both inter- and intramolecular variants of the Diels-Alder reaction are suitable under the reaction conditions using a variety of solvents. Under the same conditions, an acyl hydrazide was also oxidized to give an acyl-azo dienophile which was trapped intramolecularly by a diene. PMID:21644530

  15. A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern.

    PubMed

    Gauthier, Nicolas; Wu, Jiang Wei; Wang, Shu Pei; Allard, Pierre; Mamer, Orval A; Sweetman, Lawrence; Moser, Ann B; Kratz, Lisa; Alvarez, Fernando; Robitaille, Yves; Lépine, François; Mitchell, Grant A

    2013-01-01

    Most conditions detected by expanded newborn screening result from deficiency of one of the enzymes that degrade acyl-coenzyme A (CoA) esters in mitochondria. The role of acyl-CoAs in the pathophysiology of these disorders is poorly understood, in part because CoA esters are intracellular and samples are not generally available from human patients. We created a mouse model of one such condition, deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase (HL), in liver (HLLKO mice). HL catalyses a reaction of ketone body synthesis and of leucine degradation. Chronic HL deficiency and acute crises each produced distinct abnormal liver acyl-CoA patterns, which would not be predictable from levels of urine organic acids and plasma acylcarnitines. In HLLKO hepatocytes, ketogenesis was undetectable. Carboxylation of [2-(14)C] pyruvate diminished following incubation of HLLKO hepatocytes with the leucine metabolite 2-ketoisocaproate (KIC). HLLKO mice also had suppression of the normal hyperglycemic response to a systemic pyruvate load, a measure of gluconeogenesis. Hyperammonemia and hypoglycemia, cardinal features of many inborn errors of acyl-CoA metabolism, occurred spontaneously in some HLLKO mice and were inducible by administering KIC. KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels. Ultrastructurally, hepatocyte mitochondria of KIC-treated HLLKO mice show marked swelling. KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function, demonstrating an acyl-CoA-related mechanism for this complication. PMID:23861731

  16. A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern

    PubMed Central

    Gauthier, Nicolas; Wu, Jiang Wei; Wang, Shu Pei; Allard, Pierre; Mamer, Orval A.; Sweetman, Lawrence; Moser, Ann B.; Kratz, Lisa; Alvarez, Fernando; Robitaille, Yves; Lépine, François; Mitchell, Grant A.

    2013-01-01

    Most conditions detected by expanded newborn screening result from deficiency of one of the enzymes that degrade acyl-coenzyme A (CoA) esters in mitochondria. The role of acyl-CoAs in the pathophysiology of these disorders is poorly understood, in part because CoA esters are intracellular and samples are not generally available from human patients. We created a mouse model of one such condition, deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase (HL), in liver (HLLKO mice). HL catalyses a reaction of ketone body synthesis and of leucine degradation. Chronic HL deficiency and acute crises each produced distinct abnormal liver acyl-CoA patterns, which would not be predictable from levels of urine organic acids and plasma acylcarnitines. In HLLKO hepatocytes, ketogenesis was undetectable. Carboxylation of [2-14C] pyruvate diminished following incubation of HLLKO hepatocytes with the leucine metabolite 2-ketoisocaproate (KIC). HLLKO mice also had suppression of the normal hyperglycemic response to a systemic pyruvate load, a measure of gluconeogenesis. Hyperammonemia and hypoglycemia, cardinal features of many inborn errors of acyl-CoA metabolism, occurred spontaneously in some HLLKO mice and were inducible by administering KIC. KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels. Ultrastructurally, hepatocyte mitochondria of KIC-treated HLLKO mice show marked swelling. KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function, demonstrating an acyl-CoA-related mechanism for this complication. PMID:23861731

  17. Long-term mass transfer and mixing-controlled reactions of a DNAPL plume from persistent residuals

    NASA Astrophysics Data System (ADS)

    Liu, Yuan; Illangasekare, Tissa H.; Kitanidis, Peter K.

    2014-02-01

    Understanding and being able to predict the long-term behavior of DNAPL (i.e., PCE and TCE) residuals after active remediation has ceased have become increasingly important as attention at many sites turns from aggressive remediation to monitored natural attenuation and long-term stewardship. However, plume behavior due to mass loading and reactions during these later phases is less studied as they involve large spatial and temporal scales. We apply both theoretical analysis and pore-scale simulations to investigate mass transfer from DNAPL residuals and subsequent reactions within the generated plume, and, in particular, to show the differences between early- and late-time behaviors of the plume. In the zone of entry of the DNAPL entrapment zone where the concentration boundary layer in the flowing groundwater has not fully developed, the pore-scale simulations confirm the past findings based on laboratory studies that the mass transfer increases as a power-law function of the Peclét number, and is enhanced due to reactions in the plume. Away from the entry zone and further down gradient, the long-term reactions are limited by the available additive and mixing in the porous medium, thereby behave considerably differently from the entry zone. For the reaction between the contaminant and an additive with intrinsic second-order bimolecular kinetics, the late-time reaction demonstrates a first-order decay macroscopically with respect to the mass of the limiting additive, not with respect to that of the contaminant. The late-time decay rate only depends on the intrinsic reaction rate and the solubility of the entrapped DNAPL. At the intermediate time, the additive decays exponentially with the square of time (t2), instead of time (t). Moreover, the intermediate decay rate also depends on the initial conditions, the spatial distribution of DNAPL residuals, and the effective dispersion coefficient.

  18. Pincer-Type Complexes for Catalytic (De)Hydrogenation and Transfer (De)Hydrogenation Reactions: Recent Progress.

    PubMed

    Werkmeister, Svenja; Neumann, Jacob; Junge, Kathrin; Beller, Matthias

    2015-08-24

    Pincer complexes are becoming increasingly important for organometallic chemistry and organic synthesis. Since numerous applications for such catalysts have been developed in recent decades, this Minireview covers progress in their use as catalysts for (de)hydrogenation and transfer (de)hydrogenation reactions during the last four years. Aside from noble-metal-based pincer complexes, the corresponding base metal complexes are also highlighted and their applications summarized. PMID:26179375

  19. Coupled Electron and Proton Transfer Reactions during the O→E Transition in Bovine Cytochrome c Oxidase

    PubMed Central

    Popović, Dragan M.; Stuchebrukhov, Alexei A.

    2014-01-01

    A combined DFT/electrostatic approach is employed to study the coupling of proton and electron transfer reactions in cytochrome c oxidase (CcO) and its proton pumping mechanism. The coupling of the chemical proton to the internal electron transfer between heme a and the binuclear center is examined for the O→E transition. The novel features of the His291 pumping model are proposed, which involve timely well-synchronized sequence of the proton-coupled electron transfer reactions. The obtained pKas and Ems of the key ionizable and redox-active groups at the different stages of the O→E transition are consistent with available experimental data. The PT step from E242 to H291 is examined in detail for various redox states of the hemes and various conformations of E242 side-chain. Redox potential calculations of the successive steps in the reaction cycle during the O→E transition are able to explain a cascade of equilibria between the different intermediate states and electron redistribution between the metal centers during the course of the catalytic activity. All four electrometric phases are discussed in the light of the obtained results, providing a robust support for the His291 model of proton pumping in CcO. PMID:22086149

  20. Electron transfer within a reaction path model calibrated by constrained DFT calculations: application to mixed-valence organic compounds.

    PubMed

    Mangaud, E; de la Lande, A; Meier, C; Desouter-Lecomte, M

    2015-12-14

    The quantum dynamics of electron transfer in mixed-valence organic compounds is investigated using a reaction path model calibrated by constrained density functional theory (cDFT). Constrained DFT is used to define diabatic states relevant for describing the electron transfer, to obtain equilibrium structures for each of these states and to estimate the electronic coupling between them. The harmonic analysis at the diabatic minima yields normal modes forming the dissipative bath coupled to the electronic states. In order to decrease the system-bath coupling, an effective one dimensional vibronic Hamiltonian is constructed by partitioning the modes into a linear reaction path which connects both equilibrium positions and a set of secondary vibrational modes, coupled to this reaction coordinate. Using this vibronic model Hamiltonian, dissipative quantum dynamics is carried out using Redfield theory, based on a spectral density which is determined from the cDFT results. In a first benchmark case, the model is applied to a series of mixed-valence organic compounds formed by two 1,4-dimethoxy-3-methylphenylene fragments linked by an increasing number of phenylene bridges. This allows us to examine the coherent electron transfer in extreme situations leading to a ground adiabatic state with or without a barrier and therefore to the trapping of the charge or to an easy delocalization. PMID:26041466