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101.
Compounds 1-6 of the type MoO2X2L2 (X=F, Cl, Br; L=OPMePh2, OPPh3) have been prepared in order to investigate the variation in catalytic activity with changes in electronic and steric properties. All six complexes catalyze the epoxidation of cyclohexene with tert-butylhydroperoxide, and the species with X=Cl and L=OPMePh2 (2) displays the best activity with 83% conversion and 90% selectivity in one hour at ambient atmosphere. These inexpensive and easily prepared dioxo catalysts are stable to air and water. Reactions of the dioxo compounds with H2O2 and t-BuOOH have also been carried out. The structures of MoO2F2(OPMePh2)2 (1) and the product of its reaction with H2O2, MoO(O2)2(OPMePh2)2 (7) have been solved by single crystal X-ray diffraction. 相似文献
102.
Kannan Raghuraman 《Inorganica chimica acta》2004,357(10):2933-2938
RhCl3 · xH2O catalyst-mediated hydrogenation reactions of vinyl phosphonic diethyl ester H2CCH-P(O)(OEt)2 (1) have been investigated. Results demonstrate that the hydrogenation of H2CCH-P(O)(OEt)2 (1) to CH3CH2-P(O)(OEt)(OH) (2) proceeds in the presence of RhCl3 · xH2O catalyst, without any external hydrogen source and ancillary ligands, to near qualitative yields in ethanol and water media. 31P, 13C and 1H NMR and deuterium-labeling experiments provide evidence for the non-concerted mechanistic pathway associated with the hydrogenation of 1 to 2. 相似文献
103.
Single-channel properties and pH sensitivity of two-pore domain K+ channels of the TALK family 总被引:6,自引:0,他引:6
The two-pore K2P channel family comprises TASK, TREK, TWIK, TRESK, TALK, and THIK subfamilies, and TALK-1, TALK-2, and TASK-2 are functional members of the TALK subfamily. Here we report for the first time the single-channel properties of TALK-2 and its pHo sensitivity, and compare them to those of TALK-1 and TASK-2. In transfected COS-7 cells, the three TALK K2P channels could be identified easily by their differences in single-channel conductance and gating kinetics. The single-channel conductances of TALK-1, TALK-2, and TASK-2 in symmetrical 150 mM KCl were 21, 33, and 70 pS (-60 mV), respectively. TALK-2 was sensitive mainly to the alkaline range (pH 7-10), whereas TALK-1 and TASK-2 were sensitive to a wider pHo range (6-10). The effect of pH changes was mainly on the opening frequency. Thus, members of the TALK family expressed in native tissues may be identified based on their single-channel kinetics and pHo sensitivity. 相似文献
104.
Versées W Loverix S Vandemeulebroucke A Geerlings P Steyaert J 《Journal of molecular biology》2004,338(1):1-6
General acid catalysis is a powerful and widely used strategy in enzymatic nucleophilic displacement reactions. For example, hydrolysis/phosphorolysis of the N-glycosidic bond in nucleosides and nucleotides commonly involves the protonation of the leaving nucleobase concomitant with nucleophilic attack. However, in the nucleoside hydrolase of the parasite Trypanosoma vivax, crystallographic and mutagenesis studies failed to identify a general acid. This enzyme binds the purine base of the substrate between the aromatic side-chains of Trp83 and Trp260. Here, we show via quantum chemical calculations that face-to-face stacking can raise the pKa of a heterocyclic aromatic compound by several units. Site-directed mutagenesis combined with substrate engineering demonstrates that Trp260 catalyzes the cleavage of the glycosidic bond by promoting the protonation of the purine base at N-7, hence functioning as an alternative to general acid catalysis. 相似文献
105.
柠檬酸合酶的分子生物学研究进展 总被引:1,自引:0,他引:1
柠檬酸合酶(citrate synthase,CS)是细胞内多种重要代谢途径的关键酶。CS可催化草酰乙酸和乙酰辅酶A之间的缩合反应生成柠檬酸和辅酶A。通常革兰氏阳性细菌、古菌以及真核细胞的CS为同源二聚体,而革兰氏阴性细菌的CS为同源六聚体。根据其在细胞内的定位不同,CS可分为线粒体CS、乙醛酸循环体CS、过氧化物酶体CS。这些同工酶在能量代谢、植物脂肪的代谢、脂肪酸的氧化及细胞解毒过程中起着重要作用。不同来源的CS空间结构、催化机制和动力学性质十分相似。针对其生化特性、空间结构特点、催化机制以及分子进化等研究进展进行综述。 相似文献
106.
The synthesis of new platinum bipy (bipy = 2,2′-bipyridyl) complexes containing phenoxide ligands is reported, together with kinetic studies of their oxidative addition reactions with MeI to produce phenoxo platinum(IV) complexes. Complexes of the form [(bipy)Pt(OC6H4-4-X)2] (X = OCH3, CH3, H, Br, Cl) are prepared by the reaction of the chloro complex [(bipy)PtCl2] with substituted phenols and KOH in a two phase system of water and chloroform in the presence of benzyl triphenylphosphonium chloride. Platinum(IV) complexes are formed by oxidative addition of MeI to the platinum(II) complexes obtained. The complexes are characterized by elemental analysis, UV-Vis, IR, mass spectrometry and 1H and 13C NMR spectroscopy.The reaction of methyl iodide with [(bipy)Pt(OC6H4-4-OMe)2] to give [(bipy)PtMe(I)(OC6H4-4-OMe)2] follows the rate law rate = k2[(bipy)Pt(OC6H4-4-OMe)2][MeI]. The values of k2 increase with increasing polarity of the solvent, suggesting a polar transition state for the reaction. 相似文献
107.
Erica Farnetti Author Vitae 《Inorganica chimica acta》2010,363(3):467-473
The ability of organoiridium derivatives of catalyzing oligomerization and polymerization of terminal alkynes is markedly influenced by the nature of non-participative ligands coordinated to the metal. The dimeric species [Ir(cod)Cl]2 and [Ir(cod)(OMe)]2 (cod = 1,5-cyclooctadiene) as well as the phosphine complexes HIr(cod)(PR3)2 (PR3 = PPh3, P(p-MeOC6H4)3, P(o-MeOC6H4)Ph2, PCyPh2) catalyze the polymerization reaction, whereas the diphosphine derivatives HIr(cod)(P-P) (P-P = Ph2P(CH2)nPPh2 (n = 1-4), o-C6H4(PPh2)2) promote the regioselective formation of 1,2,4-trisubstituted benzenes. On the other hand, the iridium complexes with nitrogen chelating ligands Ir(cod)(N-N)X and Ir(hd)(N-N)X (hd = 1,5-hexadiene; N-N = 1,10-phenanthroline and substituted derivatives; X = halogen) catalyze alkynes polymerization. In most cases one catalytic reaction predominates over the other possible routes, so that polymerization often takes place in the absence of oligomerization side reactions, and conversely cyclotrimerization is rarely accompanied by formation of either polyene or dimers. 相似文献
108.
The enantioselective epoxidation of 6-cyano-2,2-dimethylchromene (Chrom) catalysed by the Jacobsen catalyst, using sodium hypochlorite (NaOCl) as oxygen source, at room temperature, was performed in a series of 1,3-dialkylimidazolium and tetra-alkyl-dimethylguanidium based ionic liquids. All the room temperature ionic liquids (RTILs) could be used as reaction media for the enantioselective epoxidation of the alkene giving, generally, moderate to good epoxide yields and enantiomeric excesses (ee%).For the series of ionic liquids derived from the 1,3-dialkylimidazolium cation, it was observed some relationship between the RTILs physical properties and the catalytic reaction parameters, exemplified by linear correlations between (i) the ee% and the α Kamlet-Taft parameter (hydrogen bond acidity of the solvent) for CH2Cl2 and [C4mnim][BF4] ionic liquids (n = 1 or 2), and (ii) the ee% and the β Kamlet-Taft parameter (hydrogen bond basicity of the solvent) for CH2Cl2 and [C4mim][X] ionic liquids (X = PF6, NTf2 or BF4).All the RTILs could be reused in further catalytic cycles, with the exception of [C8mim][PF6]. The reutilisation of the Jacobsen catalyst for four times generally led to a decrease in the epoxide yield and to a slight decrease in the enantioselectivity. The recycling of the catalyst could be improved by imparting an ionic character to the complex through abstraction of the axially coordinated chloride anion (Cat 2). Other oxygen sources, such as iodosylbenzene, hydrogen peroxide and urea-hydrogen peroxide adduct, were also tested coupled with Jacobsen catalyst, but the best results were achieved with NaOCl. 相似文献
109.
The dinuclear V(V) complexes (VOL)2O (L = SAE (1), SAMP (2), SAP (3)) have been synthesized from VO(acac)2 and the corresponding tridentate ligands LH2 in methanol under reflux conditions and subsequent air oxidation in organic solvent. They have been characterized by IR and NMR spectroscopy, by thermogravimetric analysis, and by single crystal X-ray diffraction for 1 and 2. DFT calculations were carried out for a better understanding of the vibrational pattern, principally the V-O related vibrations. Complex [VO(SAP)]2O (3) catalyzes the epoxidation of cyclooctene by TBHP in water in the absence of any added solvent with good selectivity. 相似文献
110.
Martina Pressová Miloš Buděšínský Ivana Košiová Vladimír Kopecký Jr. Josef Cvačka Václav Kašička Ondřej Šimák Zdeněk Točík Ivan Rosenberg 《Biopolymers》2010,93(3):277-289
In an attempt to prepare a library of short oligoadenylate analogues featuring both the enzyme‐stable internucleotide linkage and the 5′‐O‐methylphosphonate moiety and thus obtain a pool of potential RNase L agonists/antagonists, we studied the spontaneous polycondensation of the adenosin‐5′‐O‐ylmethylphosphonic acid (pcA), an isopolar AMP analogue, and its imidazolide derivatives employing N,N′‐dicyclohexylcarbodiimide under nonaqueous conditions and uranyl ions under aqueous conditions, respectively. The RP LC–MS analyses of the reaction mixtures per se, and those obtained after the periodate treatment, along with analyses and separations by capillary zone electrophoresis, allowed us to characterize major linear and cyclic oligoadenylates obtained. The structure of selected compounds was supported, after their isolation, by NMR spectroscopy. Ab initio calculation of the model structures simulating the AMP‐imidazolide and pcA‐imidazolide offered the explanation why the latter compound exerted, in contrast to AMP‐imidazolide, a very low stability in aqueous solutions. © 2009 Wiley Periodicals, Inc. Biopolymers 93: 277–289, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com 相似文献