细胞色素ｃ氧化酶ＣｕＡ结构域蛋白的荧光猝灭研究

近年来 ,有关细胞色素 c 氧化酶的研究取得了重要进展 [1] 。细胞色素 c 氧化酶是由多个亚基组成的复合酶分子 ,其核心亚基Ⅱ中含有可溶性 Cu A 结构域蛋白 ,它是一个高度离域化的混价双核金属中心结构 [Cu 1.5 -Cu 1.5 ],两个铜离子之间由两个 Cys-S - 桥联起来 ,这是生物体     

细胞色素C氧化酶稳态动力学研究

应用分光光度计研究了细胞色素c氧化酶的稳态动力学。结果表明,酶与底物具有高低两个亲和相,催化反应受底物浓度调节,具有单底物多相反应动力学特点。     

吡啶、2-甲基吡啶存在下细胞色素c碱式异构化和配体细胞色素c配合物的电化学研究

用半胱氨酸修饰的金电极研究了吡啶、2 甲基吡啶存在下细胞色素c碱式异构化和配体结合细胞色素c的电化学。在此电极上 ,细胞色素c可发生准可逆的电极反应而吡啶结合细胞色素c和 2 甲基吡啶结合细胞色素c在循环伏安图上只给出还原峰。高浓度 (1.2 7mol·L- 1)的吡啶和 2 甲基吡啶可诱导碱式细胞色素c在中性条件下生成。进一步的研究表明 ,这种诱导作用与配体和细胞色素c的键合无关     

细胞色素c氧化酶可溶性结构域中Val162突变对蛋白结构和功能的影响

采用蛋白质工程的定点突变技术和UV-Vis,CD,荧光,EPR及快速动力学技术考察了与癌症相关的Val162的突变对细胞色素c氧化酶可溶性结构域的影响.研究发现,该突变导致了蛋白二级结构的转化和电子传递活性的降低,这为理解其致病机制提供了化学基础信息.     

细胞色素c在羟基磷灰石修饰玻碳电极上的直接电化学

采用沉淀法合成羟基磷灰石纳米晶体，由于具有独特的多吸附位点特征，羟基磷灰石可作为一种新型电子传递促进剂用于细胞色素c的直接电化学研究．在pH7．0的磷酸盐缓冲溶液中，细胞色素c在羟基磷灰石修饰玻碳电极表面于0．074V(vs．Ag/AgC1)处有一对准可逆的氧化还原峰，为细胞色素c血红素辅基Fe(Ⅲ)／Fe(Ⅱ)电对的特征峰．实验结果表明细胞色素c与羟基磷灰石之间的静电作用．促进了细胞色素c在玻碳电极表面扩散控制的准可逆单电子转移过程．讨论了电位扫描速度、溶液离子强度对细胞色素c直接电化学的影响．     

脲对细胞色素c同步荧光光谱和电化学行为的影响

研究了细胞色素C溶液的同步荧光光谱和电化学性质随加入的脲的浓度而发生的变化,发现随着脲浓度的增加,细胞色素c分子在溶液中发生降聚、细胞色素c分子中卟啉环对溶剂暴露程度的增加和卟啉环上Fe-S键的断裂等过程和相应的电化学行为的变化.提出细胞色素c在金属电极上电化学反应不可逆可能是在较浓细胞色素c的溶液中,其分子大都以电化学活性较差的多聚体的形式存在而造成的.     

细胞色素C电化学反应的静电作用模型

首次发现,简单的阴离子Ⅰ~-是细胞色素c电化学反应的良好促进剂。在碘离子修饰的金电极上能观察到细胞色素c的准可逆电化学反应。根据细胞色素c的结构特点和碘离子的吸附特性,提出了一个以静电作用为基础的细胞色素c的电化学反应的模型。     

咪唑-细胞色素c复合物的溶液结构研究

轴向配体在决定血红素蛋白结构和性能方面的作用引起人们的兴趣[1]. 细胞色素c是一个重要的电子传递蛋白, 在天然状态下轴向配体His 18和Met 80与血红素的Fe原子配位. UV光谱和NMR谱显示氧化态细胞色素c配位的Met 80在pH大于9或强外源配体存在时较易被取代[2]. 人们对外源配体配位引发细胞色素c的构象的研究得到一些重要的结构特征[3,4]. 但对整个蛋白溶液结构完整精确的描述和血红素电子结构的研究还很少. 此外, 细胞色素c在重折叠过程中形成组氨酸配位的中间体, 而咪唑能捕获和阻断中间体的形成. 为此, 本文对咪唑-细胞色素c复合物溶液结构进行了研究.     

[PtdienNO_3]Cl与细胞色素c修饰体系研究

本实验首次以稳定修饰试剂[PtdienNO_3]Cl标记细胞色素c,反应产物经CM-52阳离子交换色谱分离纯化得细胞色素c单修饰、双修饰及三修饰衍生物。用微分脉冲伏安测定各修饰产物的还原电位,并以~1H NMR波谱证实[PtdienNO_3]Cl在细胞色素c上的修饰位点为His-33和Trp-59,其中Trp-59是其它过渡金属配合物所未能标记的、与血红素以氢键相连的保守氨基酸。细胞色素c Trp-59标记衍生物的获得,为研究芳香族氨基酸在细胞色素c电子转移过程中的作用提供了有价值的实验材料。     

表面带负电荷氨基酸残基的突变对细胞色素bs与细胞色素c结合和识别的影响

利用核磁共振方法研究表面带不同负电荷氨基酸残基突变后的细胞色素b5与细胞色素c的结合与识别，结果表明，静电作用在细胞色素b5与细胞色素c的结合过程中有着重要的贡献，而且这些静电贡献在一定程度上具有 加性，E48的贡献略大于E44。同时还证明Brownian dyanmics simulations优化出的Glu48-Lys13,Clu56-Lys87,Asp60-Lys86和heme 6-propionate-Tml72（细胞色素b5的残基排在前面）的结合方式在溶液中的确存在，细胞色素b5突变体9E48，E56／A，D60／A）及[Cr(oxalate)3]^3－对细胞色素c的表面竞争实验表明，细胞色素c表面结合区SiteⅢ仍然同细胞色素b5突变体9E48，E56／A，D60／A）有结合作用，只是结合强度上相对于野生细胞色素b5同细胞色素c的结合有所降低，这表明除上述的Browni-an dynamics simulations模型外，尚有其它如Salemme模型等的结合方式，这也揭示出细胞色素b5和细胞色素c之间的结合是比较动态的。     

Energy barriers of proton transfer reactions between amino acid side chain analogs and water from ab initio calculations

Proton transfer reactions were studied in all titratable pairs of amino acid side chains where, under physiologically reasonable conditions, one amino acid may function as a donor and the other one as an acceptor. Energy barriers for shifting the proton from donor to acceptor atom were calculated by electronic structure methods at the MP2/6-31++G(d,p) level, and the well-known double-well potentials were characterized. The energy difference between both minima can be expressed by a parabola using as argument the donor-acceptor distance R(DA). In this work, the fit parameters of the quadratic expression are determined for each donor-acceptor pair. Moreover, it was found previously that the energy barriers of the reactions can be expressed by an analytical expression depending on the distance between donor and acceptor and the energy difference between donor and acceptor bound states. The validity of this approach is supported by the extensive new data set. This new parameterization of proton transfer barriers between titratable amino acid side chains allows us to very efficiently estimate proton transfer probabilities in molecular modelling studies or during classical molecular dynamics simulation of biomolecular systems.     

The Host/Guest Type of Excited‐State Proton Transfer; a General Review

Contemporary progress regarding guest/host types of excited‐state double proton transfer has been reviewed, among which are the biprotonic transfer within doubly H‐bonded host/guest complexes, the transfer through a solvent bridge relay, the intramolecular double proton transfer and solvation dynamics coupled proton transfer. Of particular emphases are the photophysical and photochemical properties of excited‐state double proton transfer (ESDPT) in 7‐azaindole and its corresponding analogues. From the chemical aspect, two types of ESDPT reaction, namely the catalytic and non‐catalytic types of ESDPT, have been classified and reviewed separately. For the case of static host/guest hydrogen‐bonded complexes both hydrogen‐bonding strength and configuration (i.e. geometry) play key roles in accounting for the reaction dynamics. In addition to the dynamical concern, excited‐state thermodynamics are of importance to fine‐tune the proton transfer reaction in the non‐catalytic host/guest type of ESDPT. The mechanisms of protic solvent assisted ESDPT, depending on host molecules and proton‐transfer models, have been reviewed where the plausible resolution is deduced. Particular attention has been given to the excited‐state proton transfer dynamics in pure water, aiming at its future perspective in biological applications. Finally, the differentiation in mechanism between solvent diffusive reorganization and solvent relaxation to affect the host/guest ESPT dynamics is made and discussed in de tail.     

细菌紫红质中氢键相互作用和质子转移机理的分子模拟

用CHARMM程序以细菌紫红质1R84晶体为模型, 模拟了在等温定容条件下细菌紫红质在1 ps过程中的变化, 分析了与质子传递相关的ASP85, ASP212和水分子与视黄醛间氢键的结构变化情况. 考虑到氨基酸残基和席夫碱质子的不同距离, 考察了EC和PC两种结构的变化情况, 探讨了紫红质中质子传递的可能途径. 模拟结果表明1R84中可能的质子连续传递的机理是质子由席夫碱向水传递, 再由水向ASP85传递. 发现Asp212在模拟过程中保持EC结构, 这样可能更有利于顺序质子传递.     

2，4-二硫基胸腺嘧啶的异构化和质子迁移的理论研究

采用密度泛函方法在B3LYP/6-31+G水平上研究了2，4-二硫基胸腺嘧啶孤立分 子和水合物的异构体的相对稳定性和可能的质子迁移反应，分析了水分子的参与对 2，4-二硫基胸腺嘧啶异构体的相对稳定性和质子迁移速率的影响。结果表 明，该分子在气相中只存在一种稳定构型，水分子的参与未改变2，4-二硫基胸腺 嘧啶各异构体的稳定性顺序，但大大降低了质子迁过程的活化能垒。     

DFT explorations of tautomerism of 2-mercaptoimidazole in aqueous solution

A systematic investigation of the proton transfer in the tautomerization of 2-mercaptoimidazole was undertaken. Calculations in aqueous solution were performed using the combined supramolecular/continuum and the direct continuum models, respectively. Complexes containing one and two water molecules around the hydrophilic site of 2-mercaptoimidazole were used for the combined supramolecular/continuum calculation. DFT results predict that the barrier height for non-water-assisted intramolecular proton transfer is very high (175.8 kJ/mol). Hydrogen bonding between 2-mercaptoimidazole and the water molecule(s) will dramatically lower the barrier by the concerted multiple proton transfer mechanism. The proton transfer process through a eight-member ring formed by 2-mercaptoimidazole and two water molecules is found to be more efficient one and the calculated barrier height is reduced to ca. 72 kJ/mol.     

Excited-state proton transfer from pyranine to acetate in methanol

Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (k ₁) is calculated to be ∼1 × 10⁹ M⁻¹ s⁻¹. This is slower by about two orders of magnitude than that in bulk water (8 × 10¹⁰ M⁻¹ s⁻¹) at 4 M acetate.     

Intra- and intermolecular proton transfer reactions in 2-phenyl substituted benzazoles

The present review describes the salient features of inter- and intramolecular proton transfer reactions of 2-(2′-aminophenyl)-, 2-(3′-aminophenyl)-, 2-(4′-aminophenyl)-, 2-(2′-hydroxyphenyl)-, 2-(3′-hydroxyphenyl)- and 2-(4′-hydroxyphenyl)-benzimidazoles, benzoxazoles and benzothiazoles. Fluorescence quantum yield of the phototautomer produced by the intramolecular hydrogen bonding decreases on going from benzimidazole to benzoxazole to benzothiazole. This indicates that the rate of internal conversion increases in the order of compounds as mentioned above. The biprotonic phototautomerism or the presence of intermolecular proton transfer has led to the formation of (i) nonfluorescent zwitterions in case of hydroxyphenyl derivatives and the ground state precursor of this species in neutral molecules, (ii) nonfluorescent monoanions from fluorescent monoanions and (iii) nonfluorescent monocations from monocations in case of aminophenyl derivatives. In the case of 2-(4′-aminophenyl)-substituted compounds, the first protonation has always led to the formation of two types of monocations; one by protonating the amino group and the other by protonating the tertiary nitrogen atom. The former is more stable in aqueous media and the latter in non-polar media.     

Theoretical study on proton tautomerism of chryosphanol and its analogues in the ground and excited states

Proton tautomerism of 1,8-dihydroxy-3-methyl-anthraquinone and its analogues were studied using HF and CIS methods with 6-31g(d,p) basis set for the ground and singlet excited states. The calculations indicate that the compound exists two strong intramolecular hydrogen bonds (IHB), and shows similar characters in its proton transfer processes considering the geometries and Mulliken charge population. Calculation results further show that intramolecular proton transfer (IPT) is not favored in view of the energy trend for chryosphanol, which has two hydrogens of hydroxyl groups bond with a common oxygen of carbonyl group and exists two IHBs in the peri region. However, it exhibits normal intramolecular proton transfer for the derivatives of chryosphanol, which have only one pair of adjacent hydroxyl group and carbonyl group existing in the peri region. Hereby, it can be conjectured from a theoretical point of view that IPT is absent in the similar structure such as hypericin’s peri region. Calculation results on the photophysical process show that the isomerization process is competitive with the intersystem crossing process, which facilitates the increase of triplet state quantum efficiency and photosensitive activity.     

分子团簇内的化学反应

本文综述了分子团簇内化学反应研究的进展, 介绍了发生在团簇内部的电子或电荷转移、质子转移、Penning 电离、激发原子与分子的反应及双分子反应等各类反应的研究现状。     

Competition of proton and electron transfers in gas-phase reactions of hydrogen-containing dications CHX2+ (X = F, Cl, Br, I) with atoms, nonpolar and polar molecules

The competition between proton and electron transfer in reactions of mass-selected dications CHX2+ (X = F, Cl, Br, and I) with rare gas atoms (Ne, Ar, Kr, and Xe) and selected molecular reagents (N2, O2, CO, H2O, and HCl) is studied in the gas phase. In the ion-molecule reactions of CHX2+ dications with atoms and nonpolar molecules, it is the energy balance of electron transfer that acts as the decisive factor: when the exothermicity of electron transfer exceeds 2 eV, this process predominates at the expense of bond-forming proton transfer. In marked contrast, the reactions between these triatomic dications and polar molecules are governed for the benefit of the thermochemically more favored products resulting from proton transfer.