共查询到20条相似文献,搜索用时 31 毫秒
1.
Seiji Shinkai Takaharu Yamashita Yumiko Kusano Osamu Manabe 《Tetrahedron letters》1980,21(26):2543-2546
Oxidation of aldehydes and α-keto acids to carboxylic acids ocurrs readily in the presence of a flavin, thiazolium ion, and cationic micelles, the reaction involving trapping by the flavin of the intermediate formed from the substrate-thiazolium adducts through deprotonation or decarboxylation. 相似文献
2.
Seiji Shinkai 《Journal of polymer science. Part A, Polymer chemistry》1979,17(12):3905-3912
The rate constants for the oxidation of furoin by a flavin (vitamin B2 analog) immobilized in cationic polymers were evaluated under anaerobic conditions, and the influence of reaction environments was discussed in connection with the enzymatic reactivity. It was found that (1) proton abstraction from furoin which forms the carbanionic intermediate is rate determining in the initial stage of the reaction and is facilitated by the environment of cationic polymers, (2) proton abstraction is efficiently accelerated by added cationic surfactant (CTAB), and (3) N-dodecylbenzohydroxamic acid in aqueous CTAB acts as an excellent proton-abstracting reagent. The polymers with high dodecyl group content served, in all cases, as better oxidizing reagents. As a summary of these conclusions, the importance of hydrophobic environments in flavin-mediated oxidation was emphasized. 相似文献
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《Tetrahedron》1986,42(12):3223-3243
The reactions of 10a-peroxyflavins have been examined to increase understanding of the oxidative and chemiluminescent reactions catalysed by the flavin co-enzymes. A remarkable series of structural requirements in the peroxides used has been uncovered, and in addition to serving as models for the mechanism of bacterial luciferase, they constitute a set of new chemiluminescent reactions. 相似文献
6.
Hamura T Chuda Y Nakatsuji Y Suzuki K 《Angewandte Chemie (International ed. in English)》2012,51(14):3368-3372
A fair exchange: In the title reaction, alkynyllithium serves as an initiator for benzyne generation through an iodine-lithium exchange (see scheme; Tf=trifluoromethanesulfonyl). When performed in the presence of stoichiometric amounts of a nucleophile, the generated benzyne undergoes attack by lithio nucleophiles to generate aryllithium, which is then iodinated by iodoalkyne to give the iodoarenes 1. 相似文献
7.
Numata M Koumoto K Mizu M Sakurai K Shinkai S 《Organic & biomolecular chemistry》2005,3(12):2255-2261
We already found that beta-1,3-glucan polysaccharides form polymeric complexes with certain polynucleotides, but the parallel vs. anti-parallel orientation in those complexes had remained unsolved. In this paper, this controversial problem has been discussed for curdlan/oligo(dA) complexes utilizing two different energy transfer techniques. The first system consists of a combination of fluorescein-labeled curdlan and 3'-(or 5'-)tetramethyl-rhodamine (TAMRA)-labeled oligo(dA). The second system utilizes gold nanoparticles: that is, two curdlan chains were linked by a disulfide bond and after complexation with oligo(dA), the complex was immobilized on gold nanoparticles. In this system, TAMRA was attached to the 3'(or 5') end of oligo(dA) and the gold particle acted as a fluorescence quencher (energy acceptor). These experiments have led us to conclude that in the curdlan/oligo(dA) complex, parallel orientation is more favourable than anti-parallel orientation. These findings have enabled us to envision a clearer image for the complexation mode between beta-1,3-glucan polysaccharides and polynucleotides. 相似文献
8.
A. V. Bobolev A. Yu. Loginov S. N. Vydrin 《Reaction Kinetics and Catalysis Letters》1985,29(1):159-166
It has been established that the modification of rareearth element oxides by copper or silver ions leads to the formation of paramagnetic ions of divalent silver and greatly increases the activity of catalytic and chemisorption centers on their surface in catalytic oxidation processes.
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9.
The catalytic effect of various ions on the aerial oxidation of Co(II) when extracted from weakly acidic solutions with quinolin-8-ol in chlorofom was studied. Oxidation is complete only in the presence of Fe(III) or V(V). Mixtures of Al(III), Cu(II), Fe(III) and Ni(II) with Co(II) at concentrations in the range 1–8 μg ml?1 were analysed by using a multi-component analysis program involving first-order derivative spectra. Because of the metal ion interaction, a multivariate calibration process is required. The recovery factors achieved ranged from 93 to 111%. 相似文献
10.
Summary Attempts to separate Hg(I), Pb(II), Ag(I), Hg(II), Bi(III), Cu(II), Cd(II), As(III), Sb(III) and Sn(II) in ternary, quaternary and quinary mixtures by the Weisz ring oven technique have been made, using oxalate as complexing agent and aqueous ethanol as solvent. It is found, in general, that addition of oxalate as complexing agent enables separations to be carried out which do not occur in the uncomplexed solutions. The effect of adding varying concentrations of the complexing agent to the solutions has been studied. The sequences of separation in ternary, quaternary and quinary mixtures with varying concentrations of the complexing agent have been described.
Zusammenfassung Es wurde versucht, Hg(I), Pb(II), Ag(I), Hg(II), Bi(III), Cu(II), As(III), Sb(III) und Sn(II) in Drei-, Vier- und Fünfstoffgemischen unter Verwendung von Oxalat als Komplexbildner und wäßrigem Äthanol als Lösungsmittel nach der Ringofentechnik vonWeisz zu trennen. Im allgemeinen ermöglicht die Komplexierung mit Oxalat Trennungen, die sonst nicht durchführbar sind. Die Einwirkung verschiedener Konzentrationen des Komplexbildners auf die Probelösungen wurde geprüft. Die Reihenfolge der Trennung aus den angeführten Mischungen bei verschiedener Oxalatkonzentration wird angegeben.
Résumé On a essayé de réaliser la séparation de Hg-I, Pb-II, Ag-I, Hg-II, Bi-III, Cu-II, Cd-II, As-III, Sb-III et Sn-II dans des mélanges ternaires, quaternaires et quinquénaires, au moyen de la technique du four annulaire deWeisz, en utilisant des oxalates comme agents complexants et l'éthanol aqueux comme solvant. On a trouvé que, généralement, l'addition d'oxalates comme agents complexants oblige à effectuer des séparations qui ne se rencontrent pas dans les solutions non complexées. On a étudié l'effet de l'addition de concentrations variables de l'agent complexant aux solutions. On a décrit les étapes de la séparation dans les mélanges ternaires, quaternaires et quinquénaires pour des concentrations variables de l'agent complexant.相似文献
11.
Sachiko Nakai Fumio Yoneda Tokio Yamabe Kenichi Fukui 《Theoretical chemistry accounts》1999,102(1-6):147-160
Possible inhibition mechanisms of flavin (isoalloxazine) with (−)-deprenyl as an acetylenic irreversible inhibitor have been
investigated in detail by ab initio methods with the 6-31G* basis set through the simplified model compounds 3-formyl-2-imino-1-hydropyrazine
and propargylamine. The resulting compounds have been verified by calculations with the 3-21G basis set using flavin itself
and the model of (−)-deprenyl for confirmation of the reactions through the simplified models. Two cyclic O4,N5- and C4a,N5-covalent
adducts have been found. The latter was the most stable and was considered to be the final irreversible product. The intermediates
in the reaction, the acyclic C4a- or N5-allenic compounds and their hydrogen-transferred cyanine-type compounds, are in agreement
with the results of experimental photochemical reactions. In most of the reaction processes, hydrogen migration played an
important role.
Received: 26 June 1998 / Accepted: 28 August 1998 / Published online: 11 November 1998 相似文献
12.
N-Benzoyloxyimides such as N-benzoyloxysuccinimide (NBzS) were found to act as photoinitiators for acrylonitrile (AN), methyl acrylate and methyl methacrylate. Polymerization rate (Rp) for the photopolymerization of AN with NBzS in dimethylformamide at 30° was expressed thus; The overall activation energy was 27.6 kJ/mol. A spin trapping study on the photolysis of NBzS revealed formation of acyl and phenyl radicals, indicating that simultaneous scissions of the NO and OCO bonds in NBzS occur under irradiation. An initiation mechanism is proposed and discussed. 相似文献
13.
Mohamed Y. El-Sheikh Abdel-Fattah M. Habib Fathy M. Ashmawy Ali H. Gemeay Ahmed B. Zaki 《Transition Metal Chemistry》1989,14(2):95-99
Summary The slow decomposition of H2O2 in the presence of Dowex-50 W resin in the form of an ethylenediaminecopper(II) complex ion in water is accompanied by an induction period. The reaction is first order with respect to [H2O2] and the rate constant (perg of dry resin) was deduced. Autocatalytic behaviour was found for the H2O2 decomposition with 2% crosslinked divinylbenzene. The induction period disappeared and the reaction rate increased when the decomposition was carried out with a resin in the form of a peroxo-copper complex, which proves that the formation of an intermediate (active species) retards the reaction rate. The precursor of the active species, formed during the induction period, was not the amine-copper(II) complex ion but a product of the latter with H2O2. It proved impossible to carry out the decomposition in acid or buffer solutions, in which the resin is regenerated. 相似文献
14.
Keiji Yamashita Yoshihiro Shimizu Hiroyuki Tokuda Toshiaki Kuromiya Kazuichi Tsuda 《Journal of polymer science. Part A, Polymer chemistry》1989,27(13):4389-4395
Thiazolium salt polymers were synthesized by the quarternization of thiazole polymers by alkyl halides. It was found that these polymers had high catalytic activities for the acyloin condensation of furfural. The catalytic activities of thiazolium salt polymers increased as the degree of quarternization decreased. This tendency was observed both in the polar solvents such as MeOH and in the nonpolar solvents such as dioxane. From the results of the acyloin condensation catalyzed by more hydrophobic polymer catalyst PTS+–St (which had styrene unit instead of free thiazole unit) and CnPTS+ (which had a long alkyl chain around the active site), it became clear that the hydrophobicity and the steric hindrance around the active site greatly affected the catalytic activity. 相似文献
15.
The kinetics of H2O2 decomposition have been investigated using ZrO2 supported with transition metal ions including CuII, AgI, HgII, CoII, MnII, NiII and FeIII. At pH = 6.8, the reaction rate exhibits a first order dependence on the initial H2O2 concentration at low concentrations. The order of activity of the different catalysts is strongly dependent on the [H2O2]0 used. The reaction proceed via the formation of the peroxo-intermediate which has an inhibiting effect on the reaction rate. The rate increases with increasing pH, and attains a limiting rate at higher pH's. A reaction mechanism is proposed involving liberation of HO2 radicals from the peroxo-intermediate as the rate-determining step. 相似文献
16.
Masao Tomoi Satoru Ishigaki Yasushi Arita Hiroshi Kakiuchi 《Journal of polymer science. Part A, Polymer chemistry》1988,26(8):2251-2261
Polystyrene-bound 4-(1-pyrrolidino)pyridine moieties were prepared by the reaction of chloromethylated polystyrene resins with pyrrolidinopyridine derivatives containing hydroxyl groups. The supported amines were effective catalysts for acylations of tert-alcohols or enols, acylrearrangements, and diester synthesis from epoxides and anhydrides. Some of the low ring-substituted (8–15%) catalysts exhibited high activity comparable to that of 4-(N,N-dimethylamino)pyridine, though the activity was a little lower than that of 4-(1-pyrrolidino)pyridine. The recovered catalysts can be re-used, except for acyl rearrangements, without significant decrease in activity. 相似文献
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18.
Nakamura T Busfield WK Jenkins ID Rizzardo E Thang SH Suyama S 《The Journal of organic chemistry》2000,65(1):16-23
The thermolysis of a series of tert-alkyl peroxypivalates 1 in cumene has been investigated by using the nitroxide radical-trapping technique. tert-Alkoxyl radicals generated from the thermolysis underwent the unimolecular reactions, beta-scission, and 1,5-H shift, competing with hydrogen abstraction from cumene. The absolute rate constants for beta-scission of tert-alkoxyl radicals, which vary over 4 orders of magnitude, indicate the vastly different behavior of alkoxyl radicals. However, the radical generation efficiencies of 1 varied only slightly, from 53 (R = Me) to 63% (R = Bu(t)()), supporting a mechanism involving concerted two-bond scission within the solvent cage to generate the tert-butyl radical, CO(2), and an alkoxyl radical. The thermolysis rate constants of tert-alkyl peroxypivalates 1 were influenced by both inductive and steric effects [Taft-Ingold equation, log(rel k(d)) = (0.97 +/- 0. 14)Sigmasigma - (0.31 +/- 0.04)SigmaE(s)(c), was obtained]. 相似文献
19.
[structure: see text] A model system has been used to study the interactions of dipole-containing aromatic systems with oxidized and reduced flavin. Ab initio computational and experimental studies show that dipole orientation within the host is a critical determinant for recognition and redox behavior of the flavin guest. 相似文献
20.
Abstract— Addition of tyrosine or derivatives to aqueous solutions of flavins does not significantly impede either formation of the flavin triplet or the rate of O2 oxidation of the flavin radical generated by reaction of triplet with the phenol. However, the rate of radical decay is decreased. There is only a modest effect that results from altering the nature of the group on alkyl side chains of the flavin when the substituent, e.g. phenylalanine, does not complex avidly with the isoalloxazine system. However, when a tyrosyl or O-methyltyrosyl residue is covalently attached to an alkyl side chain at the N10-position of the flavin, the considerable intramolecular complexing that results markedly decreases the formation of flavin triplet and, therefore, the radical yield. The rate of triplet decay is not much different than for noninternally complexed flavins, but extensive intramolecular radical decay occurs, and the rate of 02 oxidation of radical is decreased. A shorter alkyl chain is more effective than a longer one for decreasing triplet production, but the greater proximity of a photooxidiz-able tyrosyl residue to the flavin nucleus within the former allows a slightly higher intramolecular radical yield. Attachment of a tyrosyl residue by a short chain from the N3-position of the flavin has only a modest effect on the production of flavin triplet and its decay. There is less radical production from internal than from external tyrosyl residues, and the rate of O2 oxidation of the flavin radical generated by such intermolecular photoreductants as N-acetyl tyrosine ethyl ester or EDTA is somewhat decreased. The tyrosyl residue within the active-site peptide of mitochondrial monoamine oxidase is not so susceptible to photooxidation by the 8α-(S-L-cysteinyl)flavin involved, since the thioether linkage at this position severely reduces triplet production. Upon oxidation of the thioether to sulfone, however, the triplet yield is partially restored. Some flavin radical can then be generated from either the intra- or an intermolecular tyrosyl residue. Taken together, these results demonstrate that tyrosyl residues near the flavin-binding sites of flavo-proteins can become oxidized by the flavin triplet that is light-generated unless the proximity and steric disposition of the interactants is such as to allow dissipation of much of the energy as radiationless decay within a tight complex or unless an 8α-thioether linkage to the flavin coenzyme is involved. Also, flavin radicals, whether generated photochemically or by biochemical oxidation of substrate, are readily oxidized by O2 in the presence of tyrosyl functions unless tight complexing occurs. More remarkable, though, is the decreased rate of radical decay conferred by the association with a tyrosyl residue. This stabilization of reactive flavin radicals may have considerable consequence in the catalytic mechanism of such enzymes. 相似文献