AlCn及AlC+n(n=1-4)原子簇的理论研究

用ab initio能量解析梯度法，在UHF（RHF）／3－21G水平上优化得到AlCn，AlCn+（n＝1～3）的四十三个构型，在RHF（UHF）／3－21G水平上优化得到AlC4，AlC4+的二十六个构型，CISD能量．从能量角度所研究的AlCn，AlCn+（n=1～4）构型中，最稳定的构型均是线性构型，且Al全都在端点上，同文献报导的理论和实验结果相一致．此外，还研究了原子簇的离子化能，原子平均结合能以及原子簇的碎片化通道和碎片化能，并计算了上述最稳定构型的谐振动光谱常数．     

Facts and artifacts about aromatic stability estimation

The stability of a set of 105 five-membered π-electron systems (involving aromatic, non-aromatic and anti-aromatic species) was evaluated using six isodesmic reactions of which two belong to the subclass of homodesmotic reactions, which are based on cyclic and acyclic reference systems. We demonstrate that the ‘Resonance Energies’ derived from isodesmotic schemes have obvious flaws and do not correct or cancel other contributions to the energy, such as the changes of hybridization, homoconjugation of heterosubstituted cyclopentadienes, conjugative interactions of CC or CX (X=N or P) with a π or pseudo π orbital at Y (Y=O, S, NH, PH), strain, etc. as effectively as possible. Likewise, ‘aromatic stabilization energies (ASE)’ derived from homodesmotic schemes based on the acyclic reference compounds do not give satisfactory results. We strongly recommend that only cyclic reference compounds should be used for ASE and other aromaticity evaluations. The analysis is based on ab initio optimized geometries at B3LYP/6-311+G^∗∗.     

硝酸钐水合物热分解过程的研究

Sm(NO_3)_3·6H_2O热分解过程的研究工作虽有文献报道,但结果不尽相同。文献[2]不同于文献[1,3],认为分解过程中存在无水盐阶段;文献[3]不同于文献[1,2],认为分解过程中存在低水合物。而且文献尚缺低水合物热分解机理的报道。我们也曾做过一些工作,但脱水阶段也不详尽。为此,我们详细地研究了Sm(NO_3)_3·nH_2O(n=     

On the accuracy of correlation energy calculated by the correlation factor method: first- and second-row atoms

Summary The correlation energy of two- and four-isoelectronic series, a representative example for which the existing spin-density functionals fails, is calculated using the Colle and Salvetti method, considering mono- and multideterminantal wave functions. The results are in agreement with experimental data, and show the potentiality of this method when it is applied to wave functions including the most relevant configurational features. Also, results for the ionization energies and electron affinities of first- and second-row atoms are reported.     

Cu(II)-Cu(Hg)体系在蔗糖水溶液中的电化学行为

糖及其聚合物有着重要的生理功能,研究它们的热力学性质具有重要的意义[1 5]。本文考察Cu(II)在蔗糖水溶液中的电化学行为,获得了一些重要信息。1　实验部分使用试剂均为分析纯。蔗糖(北京化学试剂总厂)在343K时真空干燥6h。LiClO4(上海化学试剂总厂)在403K时减压干燥后保存在干燥器中。硝酸铜(北京化学试剂总厂)。所用溶液均采用重量法用二次蒸馏水配制。配好的溶液测定前用通过焦性没食子酸溶液的氮气来除氧。测定温度为298±1K。极谱和伏安测定在微机电化学分析系统(LK98A型)上进行,该机由天津市兰力科化学电子高技术有限公司制…     

Improved third-order Møller-Plesset perturbation theory

Based on a partitioning of the total correlation energy into contributions from parallel‐ and antiparallel‐spin pairs of electrons, a modified third‐order Møller–Plesset (MP) perturbation theory is developed. The method, termed SCS–MP3 (SCS for spin‐component‐scaled) continues previous work on an improved version of MP2 (S. Grimme, J Chem Phys 2003, 118, 9095). A benchmark set of 32 isogyric reaction energies, 11 atomization energies, and 11 stretched geometries is used to assess to performance of the model in comparison to the standard quantum chemical approaches MP2, MP3, and QCISD(T). It is found, that the new method performs significantly better than usual MP2/MP3 and even outperforms the more costly QCISD method. Opposite to the usual MP series, the SCS third‐order correction uniformly improves the results. Dramatic enhancements are especially observed for the more difficult atomization energies, some of the stretched geometries, and reaction and ionization energies involving transition metal compounds where the method seems to be competitive or even superior to the widely used density functional approaches. Further tests performed for other complex systems (biradicals, C₂₀ isomers, transition states) demonstrate that the SCS–MP3 model yields often results of QCISD(T) accuracy. The uniformity with which the new approach improves for very different correlation problems indicates significant robustness, and suggests it as a valuable quantum chemical method of general use. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1529–1537, 2003     

Geometries,vibrational frequencies,and electron affinities of X2Cl (X=C,Si,Ge) clusters

Ab initio quantum chemical calculations have been performed on X₂Cl^? and X₂Cl (X = C, Si, Ge) clusters. The geometrical structures, vibrational frequencies, electronic properties and dissociation energies are investigated at the Hartree–Fock (HF), Møller–Plesset second‐ and fourth‐order (MP2, MP4), CCSD(T) level with the 6‐311+G(d) basis set. The X₂Cl (X = C, Si, Ge) and X₂Cl^? (X = Si, Ge) take a bent shape obtained at the ground state, while C₂Cl^? has a linear structure. The impact on internal electron transfer between the X₂Cl and the corresponding anional clusters is studied. The three different types of electron affinities (EAs) at the CCSD(T) are reported. The most reliable adiabatic electronic affinities, obtained at the CCSD(T)/cc‐pvqz level of theory, are predicted to be 3.30, 2.62, and 1.98 eV for C₂Cl, Si₂Cl, and Ge₂Cl, respectively. The calculated EAs of C₂Cl and Ge₂Cl are in good agreement with theoretical results reported. The correlation effects and basis sets effects on the geometrical structures and dissociation energies are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Free energies of transfer of complexes of the type MCl2py4 between pyridine and other solvent media

Solubility isotherms are reported for the NiCl₂·4py, MnCl₂·4py, and MnCl₂·2py solid pyridinates in a number of pyridine+diluent mixtures at 25°C. Activity coefficients of the solvent components have been derived from the total vapor pressures measured by a static method. The standard free energies of transfer for the NiCl₂py₄ and MnCl₂py₄ complexes are the same, within the experimental error, in the pyridine+aprotic diluent mixtures, while marked differences are observed in the pyridine+chloroform mixtures. Marked deviations are observed for chloroform and 1,2-dichloroethane from a correlation between the standard free energy of transfer of the complexes, on one hand, and the Hildebrand's solubility parameter of the solvent, on the other, the latter correlation being roughly valid for aprotic solvents. The deviations are tentatively ascribed to hydrogen bond formation of the type H... between the protic solvents and the coordinated pyridine molecules, enhanced by the d electron delocalization.     

Double photoionisation spectra of small molecules and a new empirical rule for double ionisation energies

Complete double photoelectron spectra are presented for 18 small molecules where the location of charges in the cations and dications is relatively clearly defined. The data demonstrate the importance of a coulombic repulsion contribution to the double ionisation energies. Examination of data for a wide range of molecules leads to a new empirical rule to calculate double ionisation energies from the molecules’ single ionisation energies and maximum dimensions. Where single and double ionisation energies are known the rule allows the deduction of plausible intercharge distances.     

A structural and energetics analysis of the binding of a series of N-acetylneuraminic-acid-based inhibitors to influenza virus sialidase

Summary A molecular dynamics/energy-minimisation protocol has been used to analyse the structural and energetic effects of functional group substitution on the binding of a series of C4-modified 2-deoxy-2,3-didehydro-N-acetylneuraminic acid inhibitors to influenza virus sialidase. Based on the crystal structure of sialidase, a conformational searching protocol, incorporating multiple randomisation steps in a molecular dynamics simulation was used to generate a range of minimum-energy structures. The calculations were useful for predicting the number, location, and orientation of structural water molecules within protein-ligand complexes. Relative binding energies were calculated for the series of complexes using several empirical molecular modelling approaches. Energies were computed using molecular-mechanics-derived interactions as the sum of pairwise atomic nonbonded energies, and in a more rigorous manner including solvation effects as the change in total electrostatic energy of complexation, using a continuum-electrostatics (CE) approach. The CE approach exhibited the superior correlation with observed affinities. Both methods showed definite trends in observed and calculated binding affinities; in both cases inhibitors with a positively charged C4 substituent formed the tightest binding to the enzyme, as observed experimentally.This paper is based on a presentation given at the 14th Molecular Graphics and Modelling Society Conference, held in Cairns, Australia, August 27–September 1, 1995.Presently on a visiting postdoctoral fellowship in the Department of Biomolecular Structure, Glaxo Research & Development Ltd, Greenford, Middlesex UB6 OHE, U.K.