Gaussian basis sets for calculation of spin densities in first-row atoms

Summary The suitability of Gaussian basis sets for ab initio calculation of Fermi contact spin densities is established by application to the prototype first-row atoms B-F having open shell p electrons. Small multiconfiguration self-consistent-field wave functions are used to describe relevant spin and orbital polarization effects. Basis sets are evaluated by comparing the results to highly precise numerical grid calculations previously carried out with the same wave function models. It is found that modest contracted Gaussian basis sets developed primarily for Hartree-Fock calculations can give semiquantitative results if augmented by diffuse functions and if further uncontracted in the outer core-inner valence region.     

Contracted polarization functions for B to Ar

Using optimal exponents for B through Ne given by Dunning and those for Al through Ar by Woon and Dunning, d-type contracted polarization functions (2d/1d), (3d/1d), and (3d/2d) are generated from natural orbitals of atomic single and double excitation configuration interaction (SDCI) calculations, where the numbers before and after the slash are those of the primitive and contracted Gaussian type functions. The resulting contracted functions are tested on N₂ and P₂ molecules by self-consistent field and SDCI calculations, which clarify characteristics of the present polarization functions. Received: 5 June 1997 / Accepted: 20 August 1997     

Degrees of unsolvability of first order decision problems for finitely presented groups

We show that for any arithmetical -degree there is a first order decision problem such that has -degree for the free 2-step nilpotent group of rank 2. This implies a conjecture of Sacerdote.

     

Glass capillary gas chromatography of amino acid enantiomers

Glass capillaries coated with Chirasil-Val, a chirally functionalised polysiloxane, are capable in principle of resolving all protein amino-acid enantiomers in a single run and within a short analysis time, thus allowing for example the quantitative amino acid determination by enantiomer labelling. The elution characteristics of the individual amino acids however are also dependent upon the chemical nature of the capillary wall surface, and a surface pretreatment is found to be necessary if all protein amino acids are to be analysed. Of the various methods of pretreatment tested, etching of borosilicate glass with gaseous HCl followed by deposition of colloidal silicic acid is considered to be the most suitable.     

Influence of mechanical properties of pectin films on charge density and charge density distribution in pectin macromolecule

The hydration and mechanical properties of citrus pectin films were examined in conditions relevant to those in the plant cell wall. The pectins used for this study varied in the degree of esterification (DE) (high or low) and charge distribution on the backbone (random or block). The hydration of the films was controlled in an osmotic pressure experiment using polyethylene glycol solutions (PEG 20000). Hysteresis tests at constant deformation rate (stress vs deformation) were used for investigating the mechanical behaviour of films. Mechanical and hydration properties of pectin films were examined as a function of charge density, charge density distribution and counterion environment—K⁺, Ca²⁺, Mg²⁺. Swelling decreased with increasing counterion concentration. The effect is stronger in the case of Ca²⁺ and Mg²⁺ for low esterified pectins and therefore crosslinks from divalent ions could be assumed. The crosslink effect is confirmed in mechanical experiments where an increase in the film tensile modulus is observed with increasing counterion concentration. It is shown for the first time that in case of highly concentrated pectin solutions Mg²⁺ cations also act as a crosslinker for pectin macromolecules.     

导数阴极溶出方波伏安法测定卡那霉素注射液含量

研究了汞 卡那霉素络合物的电化学行为 ,并建立了导数阴极溶出方波伏安法测定卡那霉素注射液含量的方法。在 pH 4 .7的HOAc NaOAc缓冲溶液中 ,在约 0 .12 6V (vs.SCE)处出现一个汞 卡那霉素络合物的还原峰 ,卡那霉素的浓度在 0 .0 2～ 1.5mg·ml- 1之间与导数方波伏安图的峰高存在良好的线性关系 ,回归方程ip(10 - 4A) =3.6C(mg·ml- 1) + 0 .4 6 ,相关系数为 0 .992 0。方法简便、灵敏、准确 ,可用于卡那霉素注射液含量测定     

一阶导数吸光光度法同时测定纯硅中铁和铝的研究

提出了用一阶导数光光度法同时测定铁和铝的方法，在ｐＨ６．５乙二胺缓冲溶液中，乳化剂ＯＰ存在下，Ｆｅ＾３＋Ａｌ＾３＋与络天青Ｓ形成Ｆｅ＾３＋，Ａｌ＾３＋－ＣＡＳ－ＯＰ三元络合物，络合物一阶导数光谱等吸收点分别在６０６．２，６３８．０ｎｍ记录混合体系在两波长处一阶导数数值可以分别测定铝，铁含量，互不影响，铁，铝含量分别在１．０～１６μｇ／２５ｍｌ，０．３～１０μｇ／２５ｍｌ范围内呈良好线性，用于测定纯     

一阶导数光谱K系数法同时测定硝基酚钠三组分

研究和建立了同时测定硝基酚钠混合三组份的新方法——一阶导数光谱K系数法。确定了最佳实验条件和测定波长,方法简便、快速、准确。通过对动植物细胞赋活增进剂中邻硝基酚钠、对硝基酚钠、5-硝基愈创木酚钠三组份的直接测定,其相对误差小于2%,相对标准偏差小于3%,回收率为99～103%。     

MoS2纳米管包覆单壁碳纳米管束的制备

MoS₂ nanotube coated SWNT (Single wall carbon nanotube) bundles have been successfully prepared by adsorbing (NH₄)₂MoS₄ onto SWNT bundles and subsequent heat treatment under H₂ at 900 ℃ in a tube furnace. The morphologies, structure and composition of the as-prepared sample were investigated by XRD, SEM, HRTEM coupled with EDS. The formation mechanism has also been preliminarily discussed.