6-取代嘌呤的电化学行为及与DNA的相互作用

应用循环伏安法和微分脉冲伏安法研究了6-糠氨基嘌呤(6-KT)和6-巯基嘌呤(6-MP)在汞电极上的电化学行为及与小牛胸腺DNA的相互作用.结果发现,6-KT和6-MP的循环伏安曲线均显示两对分别表征为扩散控制和吸附控制的氧化还原波.扩散控制波的氧化峰电流随6-取代嘌呤浓度在0.1~50.0μmol.L-1范围内呈现良好的线性关系.依据预吸附时间和溶液pH值对吸附控制波的还原峰电位和峰电流的影响,讨论了6-KT和6-MP在汞电极上的吸附机理.作者认为,6-KT乃通过部分插入作用与DNA结合,而6-MP与DNA间的相互作用为静电模式.     

生理条件下对苯二酚的电化学行为及电极产物的色谱鉴定

用循环伏安法研究了对苯二酚在玻碳电极上的电化学行为，从循环伏安图上看出当在0至1．6V电位间连续扫描20次，在0．63V左右可见到一氧化峰电位，其峰电流随扫描次数的增加而减小。说明电极反应为不可逆过程。然而，如改变在-1．4～1.6V电位间扫描，仅数次扫描后即可在Epa=0．25V和Epc=-0．08V处见到一对氧化还原峰电位，说明了此过程为一可逆过程。同时，对电极反应的产物用RHPLC进行研究和鉴定，从色谱图所示结果与电化学法所得结果一致。根据此工作的研究结果对苯二酚在呼吸链中所产生的作用进行了探讨。     

抗癌中草药冬凌草甲素的吸附伏安行为

研究了抗癌药物冬凌草甲素在悬汞电极上的电化学行为。在NaAc NaOH(pH=7.8)的缓冲溶液中,冬凌草甲素有一受吸附控制的还原峰,峰电位为-1.150V,其电极反应过程是单电子转移,传递系数α为0.834,电荷传递表观速率常数KS为2.26s-1,初步探讨了其可能的电极反应机理.     

聚天青Ⅰ玻碳修饰电极对血红蛋白催化还原

报道了天青Ⅰ在玻碳电极上的电化学聚合 ,研究了聚天青I修饰电极的电化学性质。该电极在 0 .2 5mol L硫酸底液中于 +0 .8～ - 0 .8V电位范围内有 3个峰 ,峰 1,3是一对氧化还原峰。Ep1 =+0 12 3V ,Ep2 =- 0 .432V ,Ep3 =- 0 .12 5V(vs.Ag AgCl) ,并在 0 .2 5mol L硫酸溶液中研究了聚天青修饰电极对血红蛋白的催化还原 ,血红蛋白浓度在 0 .5～ 6 0mg L范围内与峰电流呈线性关系 ,其回归方程Ip=1 0 0 2× 10 - 5+0 .15 6× 10 - 5C ,r=0 .9995。文中对电催化过程进行了探讨     

去甲肾上腺素电极过程的圆二色谱电化学研究

现场圆二色薄层光谱电化学研究去甲肾上腺素的电化学氧化还原过程 .研究表明去甲肾上腺素 ( pH =7.0磷酸缓冲溶液中 )在玻碳电极上经历了不可逆的电化学氧化 ,且遵从后行化学反应 (EC)机理 ,去甲肾上腺素醌和去甲肾上腺素红的再还原遵从简单电子转移 (E)机理 .由双对数法获得去甲肾上腺素电化学氧化的式电位为E10’=0 .2 0V ,电子转移系数和电子转移数之积为αn =0 .38,标准复相电极反应常数k10 =1 .2× 1 0 -4 cm·s-1.去甲肾上腺素醌和去甲肾上腺素红的电化学还原反应参数分别为E2 0’=0 .2 5V ,αn =0 .37,k2 0 =4.4× 1 0 -5 cm·s-1和E3 0’=- 0 .2 5V ,αn =0 .33,k3 0 =1 .1× 1 0 -4 cm·s-1.     

对乙酰氨基酚在纳米金/十二烷基苯磺酸钠修饰电极上的电化学行为研究

基于电化学沉积法制备了纳米金/十二烷基苯磺酸钠修饰玻碳电极(Nano-Au/SDBS/GCE),并采用扫描电子显微镜、X-射线光电子能谱和电化学方法进行表征。研究了对乙酰氨基酚在Nano-Au/SDBS/GCE上的伏安行为,结果表明,对乙酰氨基酚由在裸玻碳电极上的不可逆氧化过程变为准可逆过程,氧化峰峰电位由0.60 V负移至0.50 V,且在0.42 V处产生一个新的还原峰,表明nano-Au/SDBS膜能催化对乙酰氨基酚的电化学反应。在优化条件下,氧化峰峰电流与对乙酰氨基酚浓度在1.0×10-6mol/L～9.0×10-6mol.L–1和1.0×10-5～1.0×10-4mol.L–1间有良好的线性关系,检出限为8.0×10-7mol.L–1(S/N=3)。     

旋转铂盘电极上Cu(phen)22+与6-巯基嘌呤的相互作用

在 Tris-NaCl(pH=7.2)缓冲溶液中,应用循环伏安法、微分脉冲伏安法、 旋转圆盘电极实验、交流阻抗法及其数据模拟等技术研究了Cu(phen)22+（phen=1,10-邻菲咯啉）与6-巯基嘌呤（6-MP）的相互作用.结果显示, Cu(phen)22+与6-MP无论在扩散控制过程或电化学控制过程都发生了相互作用. Cu(phen)22+及其与6-MP的作用产物于铂电极上均呈现一对氧化还原峰,但后者呈现的氧化还原峰负移,峰电流减小，交流阻抗结果显示,无论6-MP存在与否, Cu(phen)22+在交流阻抗谱上均呈现两个清晰的电容弧,但当6-MP存在时,电化学反应电阻和电化学吸脱附电阻均增大. Cu(phen)22+在不同转速下的阻抗拟合结果显示,随转速增大,电化学反应电阻和电化学吸脱附电阻均减小,双电层电容呈增大趋势,而吸脱附电容呈减小趋势;当6-MP存在时,仍然呈现此变化规律.     

高铁酸盐在Sn02-Sb2O3／Ti电极上的选择性电化学合成

合成了SnO2-Sb2O3／Ti电极材料．实验结果证实，在14mol／L NaOH水溶液中和完全避免析氧反应的条件下，Fe(Ⅲ)物种在该电极上进行电化学氧化并生成FeO4^2-．结果表明，Fe(OH)。在浓NaOH溶液中发生酸式电离，形成可溶于水的FeO2^-，该离子的浓度随着碱溶液浓度变化而发生明显变化，而且它还是发生化学氧化和电化学氧化的反应物．在SnO2-Sb2O3／Ti电极上，FeO4^2-的电化学还原起始电位为0．38V(vs.Hg／HgO，14mol／L NaOH)，FeO2^-电化学氧化起始电位为0．54V．结果还表明，用电化学方法氧化Fe(Ⅲ)物种生成FeO4^2-是个多步骤过程．     

青蒿素及其衍生物电化学性质的研究 Ⅰ.青蒿素在汞电极上的电化学还原

青蒿素及其衍生物代表着一类新型抗疟药.青蒿素分子中过氧基与抗疟活性密切相关.本文采用多种电化学方法研究了青蒿素分子中过氧基在Hg电极上的还原,还原电位在0.OV(vs.Ag/AgCl)附近,电极过程为不可逆还原.反应电子数n=2,半波电位E_(1/2)=0.012V,电子转移系数α=0.66,表观标准电极反应速率常数k_s~’=6.34×10~(-6)cm/s,扩散系数D=4.3×10~(-6)cm~2/s反应产物在电极表面具有吸附性.文中提出了可能的电化学反应机理.     

旋转铂盘电极上Cu(phen)_2~(2 )与6-巯基嘌呤的相互作用

在Tris-NaC1*(pH=7.2)缓冲溶液中,应用循环伏安法,微分脉冲伏安法、旋转圆盘电极实验、交流阻抗法及其数据模拟等技术研究了Cu(phen)2 25(phcn=1.10-邻菲咯啉)与6-巯基嘌呤(6-MP)的相互作用.结果显示.Cu(phen)2 2MP与6-MP无论在扩散控制过程或电化学控制过程都发生了相互作用.Cu(phen)2 2及其与6-MP的作用产物于铂电极上均呈现一对氧化还原峰,但后者呈现的氧化还原峰负移.峰电流减小.交流阻抗结果显示,无论6-MP存在与否,Cu(phen)2 2在交流阻抗谱上均呈现两个清晰的电容弧,但当6-MP存在时,电化学反应电阻和电化学吸脱附电阻均增大.Cu(phen)2 2在不同转速下的阻抗拟合结果显示.随转速增大.电化学反应电阻和电化学吸脱附电阻均减小.双电层电容呈增大趋势,而吸脱附电容呈减小趋势:当6-MP存在时.仍然呈现此变化规律.     

An ab initio study of intermolecular interactions of nitromethane dimer and nitromethane trimer

Different geometries of nitromethane dimer and nitromethane trimer have been fully optimized employing the density functional theory B3LYP method and the 6-31++G** basis set. Three-body interaction energy has been obtained with the ab initio supermolecular approach at the levels of MP2/6-31++G**//B3LYP/6-31++G** and MP2/aug-cc-pVDZ//B3LYP/6-31++G**. The internal rotation of methyl group induced by intermolecular interaction has been observed theoretically. For the optimized structures of nitromethane dimer, the strength of C--H...O--N H-bond ranges from -9.0 to -12.4 kJ mol(-1) at the MP2/aug-cc-pVDZ//B3LYP/6-31++G** level, and the B3LYP method underestimates the interaction strength compared with the MP2 method, while MP2/6-31++G**//B3LYP/6-31++G** calculated DeltaE(C) is within 2.5 kJ mol(-1) of the corresponding value at the MP4(SDTQ)/6-31G**//B3LYP/6-31++G** level. The analytic atom-atom intermolecular potential has been successfully regressed by using the MP2/6-31++G**//B3LYP/6-31++G** calculated interaction energies of nitromethane dimer. For the optimized structures of nitromethane trimer the three-body interaction energies occupy small percentage of corresponding total binding energies, but become important for the compressed nitromethane explosive. In addition, it has been discovered that the three-body interaction energy in the cyclic nitromethane trimer is more and more negative as intermolecular distances decrease from 2.2 to 1.7 A.     

双自由基CF2与O3的反应机理

主要用作致冷剂和发泡剂的氯氟烃（CFCs）是破坏臭氧层的主要物质之一．对氯氟烃类化合物及其降解产物（包括光解、光氧化、化学反应产物等）在大气中行为问题的研究是大气化学研究的重要内容．前人[1-3]从理论和实验两方面研究了自由基与臭氧的反应机制，但是氯氟烃光解过程中     

二氟硅杂环丙烯异构化反应的理论研究

近十几年来，硅烯（：SN小'一到作为活性中间体的研究引起化学界的广泛兴趣，形成了内容丰富的硅烯化学．1975年Ilass＊等研究了硅烯和乙炔的加成反应，指出该反应的中间体为硅杂环丙烯，硅杂环丙烯异构化为硅甲基乙炔．Boatz问等利用：j－ZIG（d）基组对金属杂环丙烯小［＊xZC     

A new scheme for determining the intramolecular seven-membered ring N-H...O=C hydrogen-bonding energies of glycine and alanine peptides

In this paper a new scheme was proposed to calculate the intramolecular hydrogen-bonding energies in peptides and was applied to calculate the intramolecular seven-membered ring N-H...O=C hydrogen-bonding energies of the glycine and alanine peptides. The density-functional theory B3LYP6-31G(d) and B3LYP6-311G(d,p) methods and the second-order Moller-Plesset perturbation theory MP26-31G(d) method were used to calculate the optimal geometries and frequencies of glycine and alanine peptides and related structures. MP26-311++G(d,p), MP26-311++G(3df,2p), and MP2/aug-cc-pVTZ methods were then used to evaluate the single-point energies. It was found that the B3LYP6-31G(d), MP26-31G(d), and B3LYP6-311G(d,p) methods yield almost similar structural parameters for the conformers of the glycine and alanine dipeptides. MP2/aug-cc-pVTZ predicts that the intramolecular seven-membered ring N-H...O=C hydrogen-bonding strength has a value of 5.54 kcal/mol in glycine dipeptide and 5.73 and 5.19 kcal/mol in alanine dipeptides, while the steric repulsive interactions of the seven-membered ring conformers are 4.13 kcal/mol in glycine dipeptide and 6.62 and 3.71 kcal/mol in alanine dipeptides. It was also found that MP26-311++G(3df,2p) gives as accurate intramolecular N-H...O=C hydrogen-bonding energies and steric repulsive interactions as the much more costly MP2/aug-cc-pVTZ does.     

Substituent effects on the rate of formation of azomethine ylides. A computational investigation

The effect of substituents on the rate of conrotatory thermal cleavage of aziridine has been studied at the MP2(Full)/6-311++G(d,p)//MP2(Full)/6-31+G(d) level and also using SCS-MP2 methodology. While the parent compound has a high free energy of activation (194.6 kJ mol(-1)), this value could be drastically lowered by substituent effects. Anionic species were found to be particularly effective in increasing the calculated reaction rate. The potential utility of this approach in 1,3-dipolar cycloaddition is discussed.     

3-羟基-2-吡啶亚胺异构反应的机理

在RHF-6-31G,MP2/6-31G和MP2/6-31G水平上,对3-羟基-2-吡啶亚胺的气相、水分子作为催化剂的异构化反应进行了研究,结果表明,气象异构难于进行,水分子作为催化剂参与反应过程是目标反应所循的反应路径。     

Calculated structures and relative stabilities of furoxan,some 1,2-dinitrosoethylenes and other isomers

The structures and relative stabilities of furoxan and some of its isomers, e.g., the 1,2-dinitrosoethylenes, have been determined by means of ab initio Hartee–Fock and Møller–Plesset calculations. Geometries were optimized at the HF/3-21G, HF/6-31G* and MP2/6-31G* levels, and subsequently used for computing MP2/6-31G*, MP3/6-31G*, and MP4/6-31G* energies. The results are markedly affected by the inclusion of electronic correlation, which renders three of the isomers unstable. It also emphasizes the importance of a zwitterionic contribution to the structure of furoxan, which promotes ring-opening through a cis 1,2-dinitrosoethylene intermediate/transition state that has an MP4/6-31G*//MP2/6-31G* energy that is 31.6 kcal/mol above furoxan.     

高级量子化学从头计算法研究N2和H2O分子间相互作用

在MP2/6-311++G(3d,3p)电子相关校正水平上,对N₂和H₂O分子间可能存在的氢键复合物进行全自由度能量梯度优化,发现了一个接近于直线的弱氢键总能量极小结构(1),进一步在高级电子相关校正的MP4SDTQ和CCSD(T)水平,用6-311++G(3d,3p)基组加上(3s3p2d1f)键函数,用MP4和CCSD(T)计算的结构1的结合能分别为-5.061kJ/mol和-4.715kJ/mol.     

Oxo-hydroxy tautomerism of 5-fluorouracil: water-assisted proton transfer

Post-Hartree-Fock ab initio quantum chemical calculations were performed for 5-fluorouracil in the gas phase and in a three-water cluster. Full geometry optimizations of the 5-fluorouracil-water complexes were carried out at the MP2/6-31+G(d,p) level of theory. MP4/6-31+G(d,p)//MP2/6-31+G(d,p) and MP4/6-31++G(d,p)//MP2/6-31+G(d,p) single-point calculations were performed to obtain more accurate energies. In water solution, 5-fluorouracil exists mainly in the 2,4-dioxo form (A). We propose that the populations of the 2-hydroxy-4-oxo (B) and 4-hydroxy-2-oxo (D) tautomers are 1 x 10(-4)% and 3.9 x 10(-8)%, respectively, on the basis of the relative stabilities of the tautomers calculated at the MP4/6-31++G(d,p)//MP2/6-31+G(d,p) level of theory. A profound difference between isolated and hydrated 5-fluorouracil is noted for the height of the tautomerization barrier. In the absence of water, the process of proton transfer is very slow. The addition of water molecules decreases the barrier by 2.3 times, making the process much faster. The minimum energy path (MP2/6-31+G(d,p)) for water-assisted proton transfer in trihydrated 5-fluorouracil was followed. CNDO/S-CI calculations predict singlet pi-pi(*) electron transitions at 312 nm for B and at 318 nm for D. The fluorescence spectrum of 5-fluorouracil in water confirms the presence of the hydroxy tautomer.