DSC study of cold and heat denaturation processes of β-lactoglobulin A with guanidine hydrochloride

The cold and heat denaturations of bovine P-lactoglobulin A ((β-lg A) has been studied in solutions of guanidine hydrochloride (GuHCI) by differential scanning calorimetry (DSC). The experimental results are presented and discussed. It is shown that the number of protons bound by the monomeric molecules of β-lg A was unchanged before and after its heat denaturation below pH 3, and that the activation energy of the heat denaturation was depressed owing to the presence of GuHCI. In the solutions with 2.50 and 3.06 mol/L of GuHCI, both the cold and heat denaturations of P-lg A were observed. In comparison with the heat denaturation, the activation energy of cold denaturation was far lower and the number of GuHCl molecules bound by the unfolded polypeptide chains after culd denaturation increased a lot. The absolute value of the enthalpy of cold denaturation was larger than that of heat denaturation. It was found by the analysis that the contribution to the total denaturational enthalpy of conformational change itself of the monomeric molecules of β-lg A was the lowest among the globulins, according to the average of the number of heavy atoms. Project supported by the National Natural Science Foundation of China, and by the fund for excellent items under Director of the Institute of Chemistry.     

Oxidation reactions of indapamide. A novel route to the indole derivative,N-(3-sulfamyl-4-chlorobenzamido)-2-methylindole

Indapamide ( 1 ) is readily oxidized with mild oxidizing agents to the indole derivative 2 . Dehydrogenation of indapamide is a convenient one step synthesis of a complex indole compound.     

Aromatization of methane over different Mo-supported catalysts in the absence of oxygen

Both acidity and structure of the support are important factors in converting methane to aromatics. Lower SiO₂/Al₂O₃ ratio seems to favor the aromatization of methane over the Mo/HZSM-5 catalyst. When Pt is added as a modifier the activity of Mo/HZSM-5 catalyst will decrease slightly, but coke formation will enhanced.     

Thermodynamic studies of monuron

Monuron (C₉H₁₁ClN₂O; N,N-dimethyl-N′-(4-chlorophenyl) urea, CAS 150-68-5) was synthesized and the heat capacities of the compound were measured in the temperature range from 79 to 385 K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The enthalpy and entropy data of the compound relative to the reference temperature 298.15 K were derived based on the heat capacity data. The thermodynamic properties of the compound were further investigated through DSC and TG analysis. The melting point, the molar enthalpy, and entropy of fusion were determined to be 447.6±0.1 K, 29.3±0.2 kJ mol⁻¹, and 65.4 J K⁻¹ mol⁻¹, respectively.     

Catalytic Oxidation of Dimethyl Ether to Dimethoxymethane over Cs Modified HaPW12O40/SiO2 Catalysts

The attractive utilization route for one-step catalytic oxidation of dimethyl ether to dimethoxymethane was successfully carried out over the H3PW12O40（40%）/SiO2 catalyst, modified by Cs, K, Ni, and V. The Cs modification of H3PW12O40（40%）/SiO2 gave the most promising result of 20% dimethyl ether conversion and 34.8% dimethoxymethane selectivity. Dimethoxymethane could be synthe- sized via methoxy groups decomposed from dimethyl ether through the synergistic effect between the acid sites and the redox sites of Cs modified H3PW12O40（40%）/SiO2.     

非晶SiO2纳米灯笼的制备和表征

在1000 ℃用活性炭把二氧化锡粉末还原成单质锡, 锡作为催化剂, 硅片作为硅源同时作为收集衬底, 在硅片上制备出了非晶SiO2纳米灯笼. 灯笼的一端连在硅片上, 另一端为一个锡球, 中间是一些圆弧状的SiO2纳米线把两端相连. 纳米灯笼具有良好的对称性. 利用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、选区电子衍射(SAED) 和HRTEM自带的能谱分析仪(EDS)对样品的表面形貌、微观结构和成分进行了分析研究. 结果表明, 灯笼中SiO2纳米线为非晶态, 结点是晶态锡, 结点表面覆盖一层非晶态的硅的氧化物. 结合实验条件对纳米灯笼的生长机理进行了讨论, 提出了纳米灯笼生长的一个模型.     

High-resolution electron microscopy of montmorillonite and montmorillonite/epoxy nanocomposites

With the use of high-resolution transmission electron microscopy the structure and morphology of montmorillonite (MMT), a material of current interest for use in polymer nanocomposites, was characterized. Using both imaging theory and experiment, the procedures needed to generate lattice images from MMT were established. These procedures involve careful control of the microscope's objective lens defocus to maximize contrast from features of a certain size, as well as limiting the total dose of electrons received by the sample. Direct images of the MMT lattice were obtained from neat Na+ MMT, organically modified MMT, and organically modified MMT/epoxy nanocomposites. The degree of crystallinity and turbostratic disorder were characterized using electron diffraction and high-resolution electron microscopy (HREM). Also, the extent of the MMT sheets to bend when processed into an epoxy matrix was directly visualized. A minimum radius of curvature tolerable for a single MMT sheet during bending deformation was estimated to be 15 nm, and from this value a critical failure strain of 0.033 was calculated. HREM can be used to improve the understanding of the structure of polymer nanocomposites at the nanometer-length scale.     

用峰鉴别技术反相高效液相色谱法测定火锅汤料中微量吗啡

本文报道了以峰鉴别技术为定性依据的测定火锅汤料中微量吗啡的反相高效液相色谱法。本法采用改良的Ｓｔａｓ－ｏｔｔｏ法分离提取复杂样品中的微量吗啡。由于采用峰鉴别技术，增加了定性参数，大大提高了定性方法的准确性。本法简便、快速。最低检出浓度为０．０４ｍｇ／Ｌ。在数十例样品分析中，与其它仪器分析结果比照，非常符合。     

Syntheses and configurations of some heterocyclic amidoximes. X-Ray crystal structure of 3-phenyl-5,6-dihydro-2(1H)-pyrazinone-O-methyloxime

O-Methyl-α-ketophenylacetohydroximoyl chloride ( 1 ) was prepared by the reaction of O-methyl-α-methoxyphenylacetohydroximoyl chloride ( 5 ) with N-bromosuccinimide and concentrated hydrobromic acid. Reaction of 1 with ethylenediamine gave 3-phenyl-5,6-dihydro-2(1H)-pyrazinone-O-methyloxime ( 6 ). 3-Phenyl-5,6-cyclohexano-5,6-dihydro-2(1H)-pyrazininone-O-methyloxime ( 7 ) was prepared by reaction of 1 with trans-1,2-diaminocyclohexane. The X-ray structure of 6 has been determined. The crystals are orthorhombic, space group Pbca with a = 10.264(3), b = 18.262(4), c = 23.530(4)Å, V = 4411(2)ų, and Z = 16. The structure, which was refined to R = 0.038 using 1652 observed reflections, shows the amidoxime moiety to be the Z configuration. Reaction of benzohydroximoyl chloride with aziridine gave (Z)-aziridinylbenzaldoxime ( 16a ). Ultraviolet irradiation of a benzene solution of 16a gave a mixture of the Z and E isomers 16a and 16b . The E isomer 16b underwent thermal isomerization to 16a at 100°. Reaction of 16a with dimethyl sulfate in sodium hydroxide solution gave (Z)-O-methylaziridinylbenzaldoxime ( 17a ). Photoisomerization of a hexane solution of 17a gave a mixture of the Z and E isomers 17a and 17b which were separated by preparative glc. The isomers 17a and 17b are resistant to thermal Z = E isomerization. The mechanisms of thermal isomerization of benzamidoximes are discussed.     

Chemical synthesis and firefly luciferase produced dehydroluciferyl-coenzyme A

Dehydroluciferyl-coenzyme A (L-CoA) was chemically synthesized and characterized by MS, UV-vis spectrometry and RP-HPLC. The identity of the chemically synthesized compound with the one that was produced by firefly luciferase was confirmed. Moreover, the reversibility of the enzymatic conversion of dehydroluciferin ? dehydroluciferyl-adenylate ? L-CoA was also confirmed. The chemical synthesis of L-CoA, described here, may help the clarification of the activator effect of CoA on luciferase bioluminescent assays, in which the enzyme catalyzed formation of L-CoA and the consequent destruction of L-AMP is one of the possible explanations for that effect.