Ab Initio (GIAO) Calculations of Absolute Nuclear Shieldings for Representative Compounds Containing 1(2)H, 6(7)Li, 11B, 13C, 14(15)N, 17O, 19F, 29Si, 31P, 33S,and 35Cl Nuclei

Two kinds of ab initio calculations (B3LYP and HF) using the GIAO approach have been carried out for fifteen H, three Li, three B, eleven C, seven N, nine O, four F, three Si, four P, six S and five Cl containing derivatives. The calculated absolute nuclear shieldings have been compared with experimental absolute values (either measured or estimated from relative chemical shifts) when available or with relative chemical shifts (¹¹B, ³⁵Cl). The correlations range from good to excellent and only three compounds (PN, P₂H₂, SO₂) deviate significantly.     

On the High Viscosity of Aqueous Solution of Lysozyme Induced by Some Organic Solvents

A remarkably high viscosity has been induced in protein aqueous solutions by the addition of certain structurally related organic solvents. The effect has been observed for lysozyme aqueous solutions containing tetramethylurea (TMU), dimethylsulfoxide (DMSO), dimethylformamide, and hexamethylphosphortriamide. The effect has also been induced in ferrocytochrome c aqueous solutions by TMU. Critical concentrations for both the protein and organic solvent were verified for the onset of the viscosity increase. A common feature of the solvents which were able to induce the effect is a dipolar moiety (C=O, S → O and P → O) and a nonpolar region represented by the methyl groups. The resulting fluids show an extremely restricted flow and a typical non-Newtonian, pseudoplastic behavior. Use was made of¹H nuclear magnetic resonance (NMR) and Raman spectroscopy to characterize protein structural modifications and of¹³C NMR to investigate changes in relaxation times and chemical shifts in the solvent/water solutions. A systematic rheological characterization of the systems was undertaken for some of the solvents, and unusual patterns of viscous effects were identified for the solvent/water systems both with and without protein. The process was found to be at least partially reversible, as concluded from the recovered original solution rheological characteristics and the original protein¹H NMR spectrum, after eliminating the organic solvent by ultrafiltration. The whole process was characterized as consisting of two mutually independent stages. The first involves an extensive conformational transition of the polypeptide backbone, from a predominantly α-helical to increased random coiled and β-sheet structures, with the occurrence of nonorthodox protein secondary structures at regions above the solvent critical point. The second stage consists of short-lived interchain contacts leading to an entanglement of the macromolecular system as a whole. A microphase reversion in the organic solvent/water mixture, supported by¹³C NMR and rheological results, is proposed as the driving force causing the observed behavior.     

Investigation of carbon-13 nuclear magnetic resonance spectra-structure correlation based on novel atomic distance-edge (ADE) vector

A set of novel graph-theoretical parameters,called the atomic distance-edge (ADE) vector,was developed.Based on the connecting C-C bond number between central carbon atom and the other ones,various carbon atoms of alkanes were classified as four types,i.e.,type 1,2,3 and 4 for primary,secondary,ternary and quaternary carbon,respectively; and then four regression equations were obtained to link carbon-13 chemical shift (CS) of each type of atoms.Furthermore,these regression models were used to predict the carbon-13 nuclear magnetic resonance spectra of alkanes and it was found that the estimated CS were in agreement with the experimental results.     

An analysis of the total ion-solvent encounter configuration of ClO 4 − and BF 4 − with Na+ and Li+ in water,studied by various nuclear magnetic relaxation times. Part 21

Proton relaxation rates of the solvent water in NaClO₄, NaBF₄, LiClO₄, and NiBF₄ solutions together with some self-diffusion coefficients are reported and interpreted in terms of structure-breaking effects.¹⁹F relaxation rates in⁷LiBF₄ and⁶LiBF₄ solutions in D₂O have been measured, and the relaxation contribution caused by⁷Li⁺ has been evaluated to give a cation-anion model pair distribution function.⁷Li relaxation rates in H₂O and D₂O are also reported, and conclusions concerning the hydration structure of Li⁺ have been drawn. The strong relaxation effects caused by the ions BF ₄ ^– and ClO ₄ ^– on²³Na⁺ and⁷Li⁺ have been subjected to a detailed analysis, and combined ion-solvent encounter configurations are presented which yield an electric field gradient strong enough to cause the observed effect.Part 1 was presented at the Faraday Discussion Ion-Ion and Ion-Solvent Interaction, Oxford, September 1977 (see ref. 1).     

偏氟乙烯和四氟乙烯共聚反应中链自由基的反应性

应用高分辨率核磁共振仪研究了一系列不同组成的偏氟乙烯和四氟乙烯共聚物。指出,共振核—CF_2—的化学位移不仅受第一、二邻位基团的影响,也受第三邻位的影响。偏氟乙烯和四氟乙烯以无规共聚进行反应,在共聚反应中的链自由基﹏CF_2·或﹏CH_2·容易增长于CH_2=CF_2的CH_2端,而链自由基﹏CH_2·在偏氟乙烯和四氟乙烯共聚反应中的增长倾向于四氟乙烯。     

NMR频率综合器的微机控制

为实现ＰＴＳ系列频率综合器的微机控制，设计了一种简单的控制电路。在微机的控制下，通过该电路与微机的并行通讯口，用Ｃ语言编写的控制程序可以很方便的控制频率综合器的输出频率。控制程序采用菜单操作，电路所需的＋５Ｖ电源由微机提供，整个控制系统简单实用，值得推广。     

活性酚醛树脂中羟甲基含量的测定

本文提出一种酚醛树脂中羟甲基含量的化学分析法，分别以＾１３ＣＮＭＲ和化学分析法测定酚醛树脂的羟甲基含量。将两种测试结果与已知的投料量进行比较，证明所建立的化学分析法可行。