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101.
M. Mora M. E. Castro A. Nio F. J. Melendez C. Muoz‐Caro 《International journal of quantum chemistry》2005,103(1):25-33
This work presents an analysis of the equivalence of MP2 and DFT (B3LYP functional) conformational populations. As a test case, we select three cholinergic agents (trans‐nicotine, acetylcholine, and the nicotinic analgesic ABT‐594), where the minima on the conformational energy hypersurfaces expand a large range of energies (~0–30 kJ mol?1). From energetic and structural data obtained in vacuo at the MP2 and B3LYP/cc‐pVDZ levels, we build conformational partition functions, including the effect of the conformational kinetic energy and the rotovibrational coupling. Our results at a physiological temperature (37°C) show qualitative agreement in all cases. Quantitative agreement, however, is only found for trans‐nicotine and ABT‐594. In the first case, energy minima differ by <0.2 kJ mol?1. Therefore, the equivalence of structural results translates in the equivalence of the conformational distribution. For ABT‐594, the minima are separated by as much as 8.0 kJ mol?1, and the conformational energy determines the conformational distribution. In this case, the slight relative variation of conformational energy, between B3LYP and MP2, does not affect the population, since the secondary minima are high in energy and very low in population. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
102.
1,2,4-Thiadiazolo[2,3-a]pyridinium chlorides undergo a very facile base promoted transformation to give bispyridilimino-1,2,4-thiadiazolidines. The unequivocal structural assignment of these last compounds was achieved by spectroscopic 1H, 13C and 15N two dimensional methods. 相似文献
103.
German Urbina-Villalba Leonardo J. Rodriguez German R. Castro Fernando Ruette 《Journal of computational chemistry》1992,13(7):867-873
The electronic structure of cobalt silicide clusters Co7Si7 and Si7Co7 was studied in comparison to that of Co19 and Si17 clusters under the scope of the MINDO/SR method. Clusters Co7Si7 and Si7Co7 represent the environment of a cobalt atom and that of a silicon atom in the cobalt monosilicide bulk, respectively. It is found that the Co? Si bond is essentially sp in character with an indirect participation (by electrostatic interaction) of the cobalt d orbitals. Our calculations show a charge transfer from silicon to the d orbitals of cobalt via sp–sp interaction with an internal sp–d hybridization. The theoretical density of states for cobalt silicide clusters are reported and compared with experimental results of surface spectroscopies. © 1992 by John Wiley & Sons, Inc. 相似文献
104.
Determination of rate constants and reaction orders with an open-closed flow-injection configuration
A new, very useful application of open-closed configurations to kinetic studies is reported. The multipeak recordings provided by the manifold used, which features a single conventional photometric detector, were used to calculate the rate constants and reaction orders of a chemical system, namely the ligand displacement reaction between the cobalt(II)-EGTA complex and PAR. 相似文献
105.
A. Z. Dubničková S. Dubnička M. E. Biagini A. Castro 《Czechoslovak Journal of Physics》1991,41(12):1177-1188
The behaviour of the -hyperon electric and magnetic form factors is predicted within the modified three resonance ((783), (1020), (1680)) vector-meson dominance (VMD) model with correct analytic properties and the asymptotic behaviour predestinated by the quark model for baryons. The resonance couplings to are evaluated from the known couplings to nucleons by utilizing theSU(3) symmetry and normalization conditions for Dirac and Pauli form factors. The masses and widths of the considered vector mesons are fixed at the world averaged values. The optimal position of the effective inelastic threshold, common for Dirac and Pauli form factors, is determined from the fit of the only existing Orsay DM2 point on the
cross section att=5·693 GeV2. The mean square charge and magnetic radii of the -hyperon are found to be r
E
2
=0·018 F2 and r
M
2
=–0·027 F2, respectively.The authors are very much indebted to Prof. R. Baldini-Ferroli for calling their attention to the problem of -hyperon e.m. ff 's in connection with the FENICE experiment. 相似文献
106.
107.
S. R. de Miguel J. C. Heinen A. A. Castro O. A. Scelza 《Reaction Kinetics and Catalysis Letters》1989,40(2):331-335
The enhancement of the activity of a carbon treated with HF is due to the drastic diminution of its inorganic impurities, which produces an increase of the surface area of the carbon, a stronger Pt-C interaction and a higher Pt dispersity.
, HF, , , Pt-C Pt.相似文献
108.
The use of photochemical reactions in flow injection (FI) is reported. The irradiation of an FI reactor with a suitable source facilitates the development of the iron(III)-oxalate reaction, allowing the amperometric determination of the anion in the range 1.0-13.0 micrograms ml-1, with a relative standard deviation of 1.1% and a sampling frequency of 40 h-1. The proposed method was applied successfully to the determination of oxalate in urine samples. 相似文献
109.
The joint action of trisdimethylaminophosphine (TDAP) and carbon tetrachloride on some vicinal diols
The joint action of trisdimethylaminophosphine and carbon tetrachloride on vicinal diols affords either trans epoxides or spirophosphoranes. The mutarotation of these spirophosphoranes is described by 1H NMR and 31P NMR spectra. The mechanism of reaction providing either epoxides or spirophosphoranes is discussed. 相似文献
110.
Liliana Castro Patricio Reyes Consuelo Montes de Correa 《Journal of Sol-Gel Science and Technology》2002,25(2):159-168
Fe-ZrO2 and Cu-ZrO2 xerogels were prepared by a sol-gel method. The effect of the hydrolysis catalyst during the gelation step, namely H2SO4 or NH4OH, on the properties of the resulting materials was investigated by XRD, BET, TGA/DTA, TPD of ammonia, FTIR, and TPR. Fe-ZrO2 and Cu-ZrO2 xerogels, with sulfuric acid introduced as the hydrolysis catalyst, mainly crystallyzed in the tetragonal phase and exhibited larger surface area and acid amount than those obtained with NH4OH. Ammonia TPD shows that copper promoted sulfated zirconia is the most acidic material. TGA and FTIR reveal that under oxidizing conditions sulfated zirconia promoted with iron and copper retains more sulfate species than unpromoted sulfated zirconia. Regardless of the hydrolysis catalyst employed, copper promoted catalysts calcined at 600°C, contain a large fraction of copper oxide specieseasily reduced at low temperatures. These copper oxide species are believed to have different environment and interactions with the surface oxygen vacancies of the zirconia support. A FeO-like phase appears to be the most probable one after reduction of Fe-ZrO2 catalysts prepared with NH4OH as the hydrolysis catalyst. The formation of Fe° species may be hindered by the high dispersion and interaction of Fe2+ ions with the zirconia support. On the other hand, the reduction peaks of iron oxide and sulfate species exhibit a considerable overlap in the TPR profiles of sulfated Fe-ZrO2 samples. Hence, the nature of the supported phase in the latter samples is rather uncertain. 相似文献