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31.
文章对5种碳五位(C5)的不同取代基海因的质子北合能(PA),在亚稳状态下采用“动能法”进行了研究。以5,5-甲基海因作为参照,确定了5种样品亲质子能的顺序。 相似文献
32.
P. A. Stuzhin E. A. Pozdysheva O. V. Mal’chugina I. A. Popkova C. Ercolani 《Chemistry of Heterocyclic Compounds》2005,41(2):246-254
AM1 calculations gave the proton affinities of different types of donor sites in tetrakis-3,4-(1,2,5-thiadiazolo)porphyrazine, H2{[SN2)4PA}, and protonation of the meso-nitrogen atoms was found to be favored. A spectrometric study showed that the basicity of the meso-nitrogen atoms of the porphyrazine macrocycle is strongly diminished and these atoms in CF3CO2H are involved in an incomplete acid-base interaction (ABI) to give acid solvates, while a complete ABI (protonation) is found only in the presence of sulfuric acid. The basicity constants of the meso-nitrogen atoms were determined spectrophotometrically in CF3CO2H-H2SO4. The kinetics of decomposition of the macrocyclic chromophore in concentrated sulfuric acid was studied and a possible mechanism for this process was proposed.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 278–287, February, 2005. 相似文献
33.
Using a multireferent MBPT method (CIPSI) the electronic affinity (EA) of F, CN and HCC is computed. Results show how UMP2 gives unbalanced truncation of the MP series, while ROMP2 has the correct (balanced) behaviour. The good agreement with the experimental EA found for some compounds is accidental and associated to an error compensation. The good agreement with the experimental data found for the ROMP2 and CIPSI EAs is analysed.This paper was presented at the International Conference on The Impact of Supercomputers on Chemistry, held at the University of London, London, UK, 13–16 April 1987 相似文献
34.
Hiratake J 《Chemical record (New York, N.Y.)》2005,5(4):209-228
Carefully designed molecules that are intimately related to the reaction mechanism of enzymes are often highly selective and potent inhibitors that serve as extremely useful chemical probes for understanding the reaction mechanism and structure of enzymes. This article describes the design, synthesis, and applications of specific inhibitors of two mechanistically distinct groups of enzymes, ATP-dependent amide ligases and Ser- and Thr-hydrolases. Our strategy is based on the premise that stable analogues of the transition state (transition-state analogues) are highly potent inhibitors that serve as good mechanistic probes, and that a key structure of a good inhibitor of one enzyme is also utilized for the inhibitors of other enzymes that share the same chemistry in their catalyzed reactions, irrespective of the degree of structural similarity and evolutionary link between the enzymes. According to these principles, we designed and synthesized a series of phosphinate- and sulfoximine-based transition-state analogue inhibitors of glutathione synthetase, gamma-glutamylcysteine synthetase and asparagine synthetase. For the second group of enzymes, we synthesized a gamma-monofluorophosphono glutamate analogue for mechanism-based affinity labeling of gamma-glutamyltranspeptidase and fluorescent phosphonic acid esters for the active-site titration of lipase. These inhibitors were used successfully as ligands for detailed kinetic analyses, X-ray crystallography, and mass analysis of the enzymes to identify the key amino acid residues responsible for catalysis and substrate recognition in the transition state. 相似文献
35.
A Triton X-100-4.0G-D (4.0G-D refers to a 4.0-generation dendrimer) was brought forward as a new phosphorescence labeling reagent. Two types of specific affinity adsorption (AA) reactions (direct method and sandwich method) were carried out between the labeling product of Triton X-100-4:0G-D-Wheat germ agglutinin (WGA) and alkaline phosphatase (ALP), the product of AA reaction preserved the good characteristics of room temperature phosphorescence (RTP) of 4.0G-D and △Ip of the product was proportional to the content of ALP. According to the fact stated above, a new method for the determination of trace ALP by affinity adsorption solid substrate-room temperature phosphorimetry (AA-SS-RTP) was established on the basis of WGA labeled with the Triton X-100-4.0G-D. The detection limits were 0.20 ag·spot^-1 (corresponding concentration: 5.0×10^-16 g·mL^-1, namely 5.0×10^-18 mol·L^-1) for a direct method and 0.14 ag·spot^-1 (corresponding concentration: 3.5×10^-16 g·mL^-1, namely 3.5×10^-18 mol·L^-1) for a sandwich method, respectively. For their high sensitivity, good repeatability and high accuracy, the direct method and sandwich method have been successfully appfied to determine the content of ALP in human serum, and the results were coincided with the clinical detection results of the enzyme-linked immunosorbent assay method by the Zhangzhou Hospital of Traditional Chinese Medicine. Meanwhile, the mechanism for the determination of trace ALP by AA-SS-RTP was discussed. 相似文献
36.
Geometries and electronic structures of W4 and W clusters were studied by use of density functional methods B3LYP, B3P86, B3PW91, BHLYP, BLYP, and MPW1PW91. The calculated results indicate that the three‐dimensional structure of singlet state with either D2d symmetry (B3LYP, B3P86, B3PW91, BLYP, and MPW1PW91) or C2v symmetry (BHLYP) is the ground state for the W4 cluster. For the W cluster, the doublet state is preferred, and the most stable structure is also 3D with either D2d symmetry (B3LYP, B3PW91, BHLYP, BLYP) or C2v symmetry (B3P86 and MPW1PW91). The calculated electron affinity at B3P86 gives the best performance compared with experiment. For the dissociation channel, W + W3 is suggested to be the possible route for the W4 cluster. For the W cluster, W + W is the most likely route for dissociation, in agreement with experiment. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
37.
The proton affinity on each of the possible sites in the antitumor 2‐(4‐aminophenyl)benzazoles has been calculated at the B3LYP/6‐311G** level of theory in the gas phase and in solution. The N3‐site of protonation is found to be strongly favored over the NH2‐site for the studied compounds both in gas phase and in solution. The stability of N3‐protonated species is explained by the resonance interaction of the NH2‐group with the heterocyclic ring. The potential energy surface (PES) for the protonation process was studied at the density functional theory (DFT)/B3LYP/6‐311++G** level of theory. Solvent effects on the PES were also examined using two models: Onsager self‐consistent field and polarizable continuum model (PCM). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
38.
Kulikov R. N. Kostenko E. V. Kuznetsova M. A. Novopashina D. S. Chernonosov A. A. Vorob"ev P. E. Ven"yaminova A. G. Zenkova M. A. Vlassov V. V. 《Russian Chemical Bulletin》2003,52(1):247-257
The site-specific modification of the 5"-terminal fragment of PGY1/MDR1 mRNA by oligodeoxyribonucleotide conjugates bearing residues of bleomycin A5 (Blm), cobalt(ii) tetracarboxyphthalocyanine (Phcn), 4-[N-(2-chloroethyl)-N-methylamino]benzylamine (RCl), or perfluoroarylazide (Az) was studied. Conjugates of oligonucleotides complementary to the RNA sequences 123—138 and 155—166 selectively modify RNA in the vicinity of these regions. The highest efficacy (up to 50%) was achieved in reactions with alkylating and perfluoroarylazide conjugates of oligonucleotides. Conjugates of perfluoroarylazide with 2"-O-modified oligonucleotides are much more efficient than analogous conjugates with oligodeoxyribonucleotides (extents of RNA modification are 40—50% and 20%, respectively). 相似文献
39.
FANG Fang ZHU Yu ZHAO Qian JIANG Gang WANG Hong-Yan 《结构化学》2007,26(9):1092-1096
Geometric and electronic properties of Pdn–1Pb and Pdn (n≤8) clusters have been studied by using density functional theory with effective core potentials, focusing on the differences between mono- and bimetallic clusters. The average bond length of Pdn–1Pb (n≤8) bimetallic clusters is longer than that of pure palladium clusters except for n = 2 and 3. The most stable structure of Pdn–1Pb (n≤7) is the singlet where there is at least a Pd or Pb atom on its excited state. The energy gaps of Pd–Pb binary clusters are narrower than those of Pdn clusters, and then the chemical activity is strengthened when Pdn clusters are doped with Pb. 相似文献
40.
A small amount (≤ 10−6 mol fraction) of four alkaline earth metals, tin and yttrium were introduced into five, premixed, fuel-rich, H2–O2–N2 flames at atmospheric pressure in the temperature range 1820–2400 K. Aqueous salt solutions of the metals were sprayed into the premixed flame gas as an aerosol using an atomizer technique. Ions in a flame were observed by sampling flame gas through a nozzle into a mass spectrometer. The concentrations of the major neutral metallic species present in the flame were calculated from thermodynamic data currently available. The principal metallic ions observed were AOH+ (A = Mg, Ca, Sr, Ba, Sn) and A(OH)2+ (A = Y), formed initially by proton transfer to AO and OAOH from H3O+, a natural flame ion. Except for Mg, the ions were also produced by chemi-ionization processes. By adjusting the concentration(s) of the salt solution in the atomizer, it was found that a pair of ions could be brought into equilibrium within the time scale of the flame; the pairs included H3O+ with a metal ion or two metallic ions. Because water is a major product of combustion, a very large difference in proton affinity PA0(AO) − PA0(H2O) ≤ 490 kJ mol−1 (117 kcal mol−1) could be attempted for the proton transfer equilibrium. Using PA0(H2O) = 691.0 kJ mol−1 (165.2 kcal mol−1) as a reference base to anchor the proton affinity scale, ion ratio measurements led to proton affinity PA0 values of 766, 912, 1004, 1184, 1201, and 1222 kJ mol−1 (183, 218, 240, 283, 287, and 292 kcal mol−1) corrected to 298 K for OYOH, SnO, MgO, CaO, SrO, and BaO, respectively; of these, only the value for OYOH has not been reported previously. If it is assumed that the neutral thermodynamic data are correct (although some appear to be in error), the uncertainties in the PA results reported here are ± 21 kJ mol−1 (5 kcal mol−1). The realization that these equilibria can be achieved in flames provides a new approach to consolidate and build the high end of the proton affinity ladder, primarily of metallic species which are not accessible at lower temperatures. 相似文献