1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine as a substrate of cytochrome P450 2D6: allosteric effects of NADPH-cytochrome P450 reductase

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that produces Parkinsonism symptoms in man, has been examined as a substrate of recombinant human cytochrome P450 2D6. When cumene hydroperoxide is used as an oxygen and electron donor, a single product is formed, identified as 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) for formation of this product (130 microM) is in agreement with the dissociation constants for MPTP binding to the enzyme determined by optical and nuclear magnetic resonance (NMR) spectroscopy. When the reaction is carried out with nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) and recombinant human NADPH-cytochrome P450 reductase, a second product, identified as 1-methyl-4-(4'-hydroxyphenyl)-1,2,3,6-tetrahydropyridine, is formed in addition to 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) values for formation of these two products are 19 microM and 120 microM, respectively. Paramagnetic relaxation experiments have been used to measure distances between the protons of bound MPTP and the heme iron, and these have been used to construct models for the position and orientation of MPTP in the active site. For the cytochrome alone, a single mode of binding was observed, with the N-methyl close to the heme iron in a position appropriate for the observed N-demethylation reaction. In the presence of the reductase, the data were not consistent with a single mode of binding but could be explained by the existence of two alternative orientations of MPTP in the active site. One of these, characterized by a dissociation constant of 150 microM, is essentially identical to that observed in the absence of the reductase. In the second, which has a K(d) of 25 microM, the MPTP is oriented so that the aromatic ring is close to the heme iron, in a position appropriate for p-hydroxylation leading to the formation of the product seen only in the presence of the reductase. In the case of codeine, another substrate for cytochrome P450 2D6, the addition of reductase had no effect on the nature of the product formed, the dissociation constant, or the orientation in the binding site. These observations show that NADPH-cytochrome P450 reductase has an allosteric effect on the active site of cytochrome P450 2D6 that affects the binding of some substrates but not others.     

高速冷带轧机垂直自激振动稳定性分析的数值计算方法

本文在充分考虑轧机垂直振动过程中辊缝非线性的基础上，利用轧制理论方程和机械振动理论中的能量判据，给出了更精确的分析高速冷轧机垂直自激振动稳定性的数值计算方法。     

低银医用X光胶片的研制

对几种增黑剂进行了筛选实验研究，选用了两种增黑剂组合使用，提高了遮盖力，使医用Ｘ光胶片涂布银量由原业的９ｇ／ｍ２降到了６．８ｇ／ｍ２，与美国医用Ｘ光胶片涂布银量（６．７ｇ／ｍ２）相当，照相性能不低于国产医用Ｘ光胶片。     

Fabrication and Characterization of Carbon Nanotube–Titanium Nitride Composites with Enhanced Electrical and Electrochemical Properties

This work reports the fabrication and the characterization of a new composite consisting of multiwalled carbon nanotubes (CNTs) and conducting titanium nitride (TiN) with a higher specific surface area ( S _BET), enhanced electrical conductivity (σ), and specific capacitance. With increasing CNT content, the electrical conductivity and electrochemical performance of the CNT–TiN composites gradually increase. In the presence of 5 wt% (12.0 vol%) CNTs, the electrical conductivity and the weight-specific capacitance of CNT–TiN composite are increased by 3.6 times and 54.8% compared with pure TiN, respectively.     

汽车空调冷凝器腐蚀试验的表征与评价

介绍了汽车空调冷凝器的腐蚀试验程度及方法，对试验后的冷凝器进行了密封性检查，并用光学显微镜和扫描电镜检测和分析了材料的显微结构，焊接质量，腐蚀性质及其腐蚀深度等。通过对冷凝器的宏微观检查与表征，评价了冷凝器质量的优劣，提出了改进措施与建议。     

热轧高强钢平整机辊径参数设计技术研究

基于高强钢平整机的生产工艺特点,结合板形与辊耗问题,将带材的出口前张力与辊间压力横向分布都均匀作为目标函数,把保证所有被平整高强钢产品的机械性能满足产品大纲要求作为约束条件,提出了一套针对热轧高强钢平整机的工作辊与支承辊辊径参数设计模型.其研究结果对指导宝钢分公司1880 mm热轧平整机的工艺参数的确定与技术谈判发挥了重要作用,并具有进一步的推广价值.     

火焰原子吸收法测定高铋物料中的铅

本文介绍了在以高铋物料为基体 ,5 %的HNO3 介质中 ,波长 2 17nm处进行火焰原子吸收法测定铅的试验 ,采用标准加入法进行回收率的试验 ,回收率大于 98% ,特征浓度为 0 .0 7μg/ml,结果令人满意 ,能满足炉前样分析的要求     

金属—PAN—S配合物的极谱研究——Ⅱ:Fe~(3+)—PAN—S—TEA—NH_3·H_2O—NH_4Cl体系配合吸附波

在NH_3·H_2O—NH_4Cl—三乙醇胺底液中Fe(Ⅲ)与PAN—S产生一灵敏的配合吸附波,峰电位在—0.50伏(vs.SCE)。峰电位与铁离子浓度在2.8×10~8～3.4×10~(-6)mol/L范围内线性良好,检出下限可达2.8×10~(-8)mol/L。该法用于乳粉、头发、血清等样品的测定,结果满意。     

柴达木盆地北缘的右行走滑冲断系统及其动力学

通过对于断裂系统分析和地球物理资料的解释,证实了柴达木盆地北缘西段的主要构造形成时间为上新世以后,变形样式为一系列右行走滑冲断构造。走滑冲断构造带内部的断层在平面上呈分支复合,剖面上表现为正花状构造,断层上、下盘地层层序无法直接对比。右行走滑冲断构造形成于南祁连由北向南的斜向推覆作用,而主要应力来源于柴达木地块北缘由南向北的陆内俯冲作用。用一个运动学模型解释了柴北缘的右行走滑冲断作用机制。     

Preparation of nanosized titania powder via the controlled hydrolysis of titanium alkoxide

By controlling the hydrolysis of titanium butoxide, followed with or without an ethanol washing process, the preparation of nanoscale titania powder was studied in detail. The characteristics of different powders produced by the direct precipitation (without an ethanol wash) and ethanol wash processes were studied by X-ray diffraction, transmission electron microscopy, BET, thermogravimetry and differential thermal analysis techniques. By comparison, it was found that both the direct precipitation and ethanol wash methods can obtain slightly agglomerated nanoscale titania powders of less than 15 nm, but the ethanol wash can further reduce the agglomeration. The particle sizes of titania powders can be modified while still retaining the anatase structure.