How can enzymes be so efficient?

Dudley Williams and his colleagues discuss how ligands can gain binding energy to their receptors, and substrate transition states to their enzymes, by tightening the protein structures, with a decrease in their dynamic behaviour.     

Temperature-induced gelation of concentrated silicon carbide suspensions

Due to the steric barrier provided by the adsorption of the dispersant hypermer KD1 (a polyester/polyamine condensation polymer), stable and low-viscosity suspensions of SiC, Y(2)O(3), and Al(2)O(3) powder mixtures could be prepared in methyl ethyl ketone (MEK)/ethanol (E) solvent with solids loading as high as 60 vol%. The solvency of the dispersant in MEK/E decreased dramatically on cooling. Steady shear viscosity and oscillatory measurements were performed as a function of temperature for suspensions with different solids loading. The viscosity and elastic modulus of suspension increased with decreasing temperature and became more sensitive with the increase of solids loading. The suspensions with solids loading higher than 40 vol% could be solidified with decreasing temperature, but gelation temperature and gelation stiffness decreased with decreasing solids loading. The 60 vol% solid-loaded suspension was a stable and free-flowing fluid at 20 degrees C and gradually transformed to a very highly viscous and elastic system upon cooling to about 13 degrees C. Complete solidification occurred when the temperature was decreased to 5 degrees C. The gelation mechanism was mainly based on the collapse of the adsorbed layer as the temperature decreases, which induced incipient flocculation and formed a stiff network. The gelled body was further strengthened by separation of the dispersant from the suspension.     

Density functional theory studies on the Raman and IR spectra of meso-tetraphenylporphyrin diacid

The vibrational spectra of meso-tetraphenylporphyrin diacid (H4TPP2+) have been studied with the density functional theory. Raman and IR spectra of H4TPP2+ and its N-deuterated analogue (D4TPP2+) are measured and compared with the computational results. Complete assignments of observed IR and Raman bands were proposed on the bases of calculation results. The DFT calculations reproduce 140 observed fundamentals with the RMS 8.6 cm-1. The computational as well as the experimental results reveal that the saddle-distortion of porphyrin macrocycle for the diacid leads to a significant effect on its vibrational spectra. Especially, several out-of-plane skeletal modes, which were either unobserved or very weak in the Raman spectra of CuTPP and H2TPP, are activated in the Raman spectra of the diacids. In addition, enhancement for the Raman bands of phenyl CC stretching modes were observed and attributed to the conjugation effect of pi-systems of the phenyl and the porphyrinato macrocycles.     

NMR and X-ray crystallography, complementary tools in structural proteomics of small proteins

NMR spectroscopy and X-ray crystallography, the two primary experimental methods for protein structure determination at high resolution, have different advantages and disadvantages in terms of sample preparation and data collection and analysis. It is therefore of interest to assess their complementarity when applied to small proteins. Structural genomics/proteomics projects provide an ideal opportunity to make such comparisons as they generate data in a systematic manner for large enough numbers of proteins to allow firm conclusions to be drawn. Here we report a comparison for 263 unique proteins screened by both NMR spectroscopy and X-ray crystallography in our structural proteomics pipeline. Only 21 targets (8%) were deemed amenable to both methods based on an initial 2D 15N-HSQC NMR spectrum and optimized crystallization trials. However, the use of both methods in the pipeline increased the total number of targets amenable to structure determination to 107, with 43 amenable to NMR only and 43 amenable to X-ray crystallographic methods only. We did not observe a correlation between 15N-HSQC spectral quality and the success of the same protein in crystallization screens. Similar results were found for an independent set of 159 proteins as reported in the accompanying paper by Snyder et al. Thus, we conclude that both methods are highly complementary, and in order to increase the number of proteins suited for structure determination, we suggest that both methods be used in parallel in screening of all small proteins for structure determination.     

在改性非水合成的丝光沸石上邻二甲苯异构化

1985年Bibby首次在非水体系中合成了纯硅方钠石,由此开创了一条合成分子筛的新途径。徐文旸等首次在Na_2O-SiO_2-Al_2O_3一有机胺非水体系中合成了丝光沸石(简称非水丝光沸石,用NAM表示)。晶化过程中液相无硅铝酸根离子,固相硅铝比始终保持不变,是典型的固相转化过程。利用非水体系这一特点,可以定向地合成出催化反应所需硅铝比的沸石。与水热体系相比,非水体系合成的丝光沸石在邻二甲苯异构化催化性能上要优于前者。     

催化动力学光度法测定痕量锆

研究了在弱酸性介质中，锆（Ⅳ）催化过氧化氢氧化铬蓝黑Ｒ这一新的指示反应及其动力学条件，建立了一种高灵敏、高选择性测定痕量锆的新方法，方法检出限为３．７４×１０－１１ｇ／ｍＬ，线性范围０～１．１μｇ／２５ｍＬＺｒ（Ⅳ）．用于合金钢中痕量锆的测定，结果满意．     

水中酚的膜萃取分离流动注射技术测定的研究

本文提出了硅橡胶膜在线萃取分离流动注射技术测定水样中苯酚的方法。由于水样中的苯酚透过硅橡胶进入萃取液的萃取量随时间的增加和温度的升高而增大，故采用停流技术及升高温度以降低酚的检出限。     

铋(Ⅲ)-桑色素极谱络合吸附波的研究

在0.25 mol/L HCl底液中,用单扫极谱法得到了灵敏的铋(Ⅱ)-桑色素络合吸附波,其检测下限达5.0×10~(-9)mol/L。用其测定了锰盐中的痕量铋。测得电活性络合物组成为:铋(Ⅱ):桑色素=1:1,条件稳定常数1gμ=5.0。电极反应为吸附络合物中Bi(Ⅱ)还原为Bi(Hg)。测得电极反应转移系数α=0.42,表面电化学反应的标准速率常数k_s=12.7s~(-1)。     

建立在群对称轨道(SMO)及特征组态(CD)基础上的CI方法与程序发展

ISMO－CDCI方法点群理论，特别是不可约张量方法，在量子化学理论方法发展以及简化概念与计算方面，发挥了重要作用．但在国外的量子化学计算程序（如G94）中，在后自洽场（opt－SCF）计算方面，很少用到对称约化．在文献中，只见有关hbeltah群（DZh与它的子群）对称约化用于组态相关计算的报导．由于多重耦合系数的计算复杂，蜕化不可约表示多体问题的对称约化难于得到解决．我们提出了一个统一与普遍的方法，它能解决所有分子体系多体相关的点群对称约化问题［‘－6］，这个方法的核心是群对称轨道（SMO）概念的提出．SMO的基本特…     

树脂法再生贮氢合金材料包覆液工艺中树脂吸附性能研究

本文研究并探讨了NK-ELN型离子交换树脂在再生贮氢合金材料包覆液过程中，温度、流速、溶液中离子浓度等条件对树脂交换容量和再生效率的影响，为树脂法再生贮氢合金材料包覆液工艺的制定，提供了一系列重要参数。