古细菌RNase HⅡ与金属离子结合的热力学研究

RNase H是一种专一性水解RNA:DNA杂合链中RNA链的核糖核酸酶,它广泛存在于从原核生物到人的生物体中.本文通过等温滴定量热技术研究了Mg2+,Mn2+和Ca2+与一种古细菌Methanococcusjannaschii中的Ⅱ型RNase H结合的热力学.首次用这种方法获得了这一结合过程的热力学参数.并证实了这些金属离子与RNaseHⅡ按1:1结合.为RNase HⅡ酶反应机理和折叠研究提供了重要信息.     

氧化苦参碱与牛血清白蛋白相互作用的热力学研究

在298.15 K下, 应用等温滴定量热法和圆二色谱法研究了氧化苦参碱(OMT)与牛血清白蛋白(BSA)的相互作用, 并讨论了二者结合过程热力学性质的改变. 研究结果表明, BSA大分子上存在可结合OMT分子的两类位点. OMT分子与第一类位点相结合时, 结合过程的平衡常数、标准摩尔焓变和标准摩尔吉布斯自由能变分别为 ＝(2.14±0.31)×105, ＝(－1.07±0.50) kJ•mol－1, ＝(－30.4±0.4) kJ•mol－1, 最大可结合位点数为 N1＝(10.0±0.2), 该过程是以熵驱动为主的焓熵协同驱动过程. OMT 分子与第二类位点相结合时, ＝(6.84±0.32)×103, ＝(1.91±0.03) kJ•mol－1, ＝(－21.9±0.4) kJ•mol－1, N2＝(25.0±0.3), 该过程是熵驱动过程. 圆二色谱测试结果表明, 两类结合过程中, OMT与BSA的相互作用均导致了蛋白质二级结构构象及不同结构单元相对含量的变化.     

二价金属离子影响乳酸脱氢酶活性的单扫伏安研究

探讨了５种二价金属离子对乳酸脱氢酶在辅酶ＮＡＤＨ存在下转化丙酮酸为乳酸催化体系的影响、结果表明，Ｚｎ＾２＋，Ｃａ＾２＋与ＬＤＨ活性无影响，Ｍｎ＾２＋有抑制作用，而Ｃｕ＾２＋，Ｍｇ＾２＋在低浓度时有微弱的促进作用。     

链式与面式两种不对称疏水结构表面活性剂之间的相互作用热力学

本文通过等温滴定量热法(ITC)、电导法和浊度法研究了阴离子生物表面活性剂脱氧胆酸钠(NaDC)及其与相反电荷的十二烷基三甲基溴化铵(DTAB)在水溶液中的自组装热力学.ITC结果支持了NaDC在水溶液中先生成预胶束再形成稳定胶束的分步聚集模型,由此得到了NaDC的预胶束和胶束化过程的一系列热力学参数,并讨论了它们形成的热力学机理.进一步研究了具有头-尾链式和疏水-亲水刚性面式非对称结构的DTAB/NaDC混合体系的聚集热力学行为,得到了富NaDC临界混合胶束浓度(cmcmix)、富DTAB临界胶束浓度(CM)及对应过程的转变焓.结果表明,NaDC面式结构与DTAB链式结构的对称性差异以及相反电荷的相互作用,导致混合体系有别于单一表面活性剂或头-尾链式结构的混合体系的聚集行为.混合溶液的聚集行为受控于表面活性剂浓度和摩尔分数的变化.富NaDC胶束化过程为熵驱动,而富DTAB的两种胶束形态转变过程为熵焓共同驱动的热力学机理.这些结果对于从热力学角度认识胆汁酸盐的自组装机理以及与传统的头-尾链式结构的表面活性剂相互作用机理和相行为有重要的意义.     

基于等温滴定量热法表征的红细胞凝集反应热动力学特性研究

采用等温滴定量热法研究植物凝集素(PHA)作用于20%家兔血红细胞(RBC)的凝集反应过程, 以生物热动力学参数表达凝集反应动力学特征. 结果表明, PHA与家兔血红细胞凝集反应的平衡常数K为3.24×10⁵ L•mol^－1, 反应焓变( )为－238.548 kJ•mol^－1, 反应自由能( )为－32.722 kJ•mol^－1, 反应熵变( )为－0.664 kJ•mol^－1•K^－1. 反应为放热反应(Q＞0), 可自发进行(ΔG＜0), 反应为焓驱动、熵减过程(ΔH＜0, ΔS＜0, |ΔH|＞|TΔS|), 由化学键合作用、氢键和范德华力推动, 反应体系最终处于稳定有序状态. 所建立的微量量热法可以客观表征凝集反应的热动力学过程, 也为其他抗原抗体类型反应的过程评价方法提供新的技术参考.     

D－葡萄糖、D－果糖与Ca~（2＋）、Mg~（2＋）、Cu~（2＋）、Zn~（2＋）、Cd~（2＋）反应的热力学函数

Ｄ－葡萄糖、Ｄ－果糖与Ｃａ~（２＋）、Ｍｇ~（２＋）、Ｃｕ~（２＋）、Ｚｎ~（２＋）、Ｃｄ~（２＋）反应的热力学函数张保林（南京大学配位化学研究所，配位化学国家重点实验室，南京，２１０００８）王文清，陶祖贻（北京大学技术物理系，北京）（兰州大学现代物理系?..     

锌离子的血清蛋白质输运机制研究

采用等温滴定量热法研究血清白蛋白输运锌离子的相互作用机制,测定反应体系的结合参数与热力学参数,并讨论结合反应的分子作用机理。结果表明,血清白蛋白输运锌离子过程中,锌离子与血清白蛋白的结合反应符合langmuir模型,拥有强、弱两类结合位点。强结合位点的结合常数K1=1.86×105L.mol-1,结合位点数N1=1.17;弱结合位点的结合常数K2=7.16×103L.mol-1,结合位点数N2=2.85。分析血清白蛋白输运锌离子的热力学参数表明,两类结合过程均为自发过程,两类结合过程的主要作用力为静电作用力,且均表现为以焓驱动为主的焓熵协同驱动过程。     

新型臂式氮杂冠醚的合成及其多价螯合的热力学特征

通过采用微波方法提高了1,10-二氧-4,7,13,16-四氮杂18-冠-6 (L1)的合成产率.以该化合物作为母体与溴乙酸乙酯反应合成了两种新型的臂式冠醚L2和L3.采用等温滴定量热法测定了这三种氮杂冠醚与Ca(Ⅱ)键合的热力学参数,量热滴定拟合结果表明,除母体氮杂冠醚外,臂式氮杂冠醚L2和L3均能与Ca(Ⅱ)形成1:1的稳定配合物,其稳定性主要来自于多价螯合的焓贡献.     

金属硫蛋白与Cd2+、Pb2+络合反应的微量量热滴定

金属硫蛋白（ｍｅｔａｌｌｏｔｈｉｏｎｅｉｎ,简称ＭＴ）是一类低分子量、富含半胱氨酸的金属结合蛋白,具有调节体内微量金属元素（Ｚｎ、Ｃｕ等）代谢、重金属解毒和清除自由基等多种生物学功能［１］．ＭＴ与金属离子的络合作用是发挥其功能的物质基础,哺乳动物ＭＴ每分子含２０个半胱氨酸巯基,可结合７个二价金属离子或１２个一价金属离子;通常,各种金属离子的结合能力与典型的硫酸盐型络合物的顺序一致,即 Ｚｎ（Ⅱ）＜ Ｐｂ（Ⅱ）＜ Ｃｄ（Ⅱ）＜ Ｃｕ（Ⅰ）, Ｈｇ（Ⅰ）, Ｈｇ（Ⅱ）, Ｂｉ（Ⅲ）［２］．哺乳动物Ｃｄ７－…     

二价金属离子对磷脂聚集体的影响

通过浊度分析和激光光散射光谱研究了二价金属离子（Ca2＋、Cu2＋和Mn2＋）对蛋黄卵磷脂(EYPC)聚集态的影响.结果表明，自由的二价金属离子对EYPC囊泡有破坏作用,并使EYPC囊泡发生相转变,形成胶束;而与牛磺胆酸钠(TC)结合的二价金属离子使EYPC囊泡半径减小,但不破坏EYPC囊泡.     

A Thermodynamic Study on the Binding of PEG-Stearic Acid Copolymer with Lysozyme

The thermodynamics of the interaction between a copolymer of polyethyleneglycol400-stearic acid, S400, and lysozyme was investigated at pH=7.0 and 27 °C in phosphate buffer by isothermal titration calorimetry, ITC. The extended solvation model was used to reproduce the enthalpies of the S400 + lysozyme interactions. The solvation parameters recovered from the extended solvation model are attributed to the structural change of lysozyme and its biological activity. The binding parameters found for the interaction of S400 with lysozyme indicate that at low concentrations of S400, the lysozyme structure was destabilized but at higher concentrations of S400 lysozyme it was stabilized by S400. It is suggested that S400 interacts with a set of three identical binding sites on lysozyme.     

A Thermodynamic Study on the Binding of Calcium Ion with Myelin Basic Protein

The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent calcium ion was studied by isothermal titration calorimetry at 27 °C in aqueous solution. The extended solvation model was used to reproduce the enthalpies of Ca²⁺-MBP interaction over the whole range of Ca²⁺ concentrations. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction. It was found that there is a set of two identical and non-interacting binding sites for Ca²⁺ ions. The association equilibrium constant is 0.021 μmol⋅dm⁻³. The molar enthalpy of binding is ΔH=−15.10 kJ⋅mol⁻¹.     

A New Approach for Thermodynamic Studies on Binding of Some Metal Ions with Human Growth Hormone

A thermodynamic study on the interaction between Mg²⁺, Ni²⁺ and Co²⁺ ions (M²⁺) and human growth hormone (hGH) was made at 27 °C in aqueous NaCl solutions using isothermal titration calorimetry. Gholamreza Rezaei Behbehani’s solvation model (GRB) was used to model the enthalpies of M²⁺+hGH interactions over the studied range of metal ion concentrations. The solvation parameters derived from the solvation model were attributed to a structural change of hGH due to its interactions with the metal ion.     

A Thermodynamic Study on the Binding of Human Serum Albumin with New Synthesized Anti Cancer Pd (II) Complex

The thermodynamics of the interaction between new synthesized anti-cancer drug (2,2′-bipyridin n-butyl dithiocarbamato Pd (II), ButPd), and HSA was investigated at pH=7 by isothermal titration calorimetry. A new solvation model was used to reproduce the enthalpies of HSA interaction by ButPd within a broad range of complex concentrations. The solvation parameters attained from the new model were attributed to the structural change and biological activity of HSA. The binding parameters for the interaction of ButPd and HSA indicated that the considerable conformational changes in HSA were not observed after being bound with ButPd. It was found that HSA has three identical and cooperative binding sites for ButPd.     

A Thermodynamic Study on the Binding of Human Serum Albumin with Lanthanum Ion

Thermodynamics of the interaction between lanthanum(III) ion, La³⁺, and human serum albumin (HSA), was investigated at pH 7.0 and 300 K in Tris‐HCl buffer by isothermal titration calorimetry. A solvation model was used to reproduce the enthalpies of HSA interaction with La³⁺. The solvation parameters recovered from our new model were attributed to the structural change of HSA and its biological activity. The interaction of HSA with La³⁺ showed a set of two binding sites with negative cooperativity.     

Thermodynamic study of CN~- ion inhibition of Jack bean urease using the extended solvation theory

Cyanide ion was studied as an inhibitor of Jack bean urease at 300 K in 30 mmol/L tris buffer,pH 7.The inhibition was investigated by isothermal titration calorimetry(ITC).The extended solvation model was used for CN~- + JBU interaction over the whole range of CN~- concentrations.The binding parameters recovered from the solvation model were attributed to the cyanide ion interaction.It was found that cyanide ion acted as a non-cooperative inhibitor of urease,and there is a set of 12±0.12 identical and in...     

Thermodynamic Study of the Inclusion Interaction between Gemini Surfactants and Cyclodextrins by Isothermal Titration Microcalorimetry

The inclusion complexes of a series of bis-quarternary ammonium surfactants, (C _n N)₂Cl₂ (where n = 12, 14, 16) and sodium bis(2-ethylhexyl) sulfosuccinae (AOT), with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) in aqueous solutions were investigated by using isothermal titration calorimetry (ITC) at 298.15 K. The stability constants, stoichiometry, and formation enthalpies, entropies and Gibbs energies for the complexes in aqueous solutions have been derived from the calorimetric data. The values of the binding constant, K ^∘ _i , are very large, which indicates that these complexes are quite stable in their aqueous solutions. The enthalpy changes (ΔH ^∘) for all of the inclusion processes are negative, showing that the complex process is enthalpy driven. The entropy effect (TΔS ^∘) is negative, so the inclusion process is entropically unfavorable. The large negative Gibbs energy changes indicate that formation of host-guest inclusion complexes is generally a spontaneous process. The thermodynamic parameters are discussed in the light of the different structures of the host and guest molecules.     

Thermodynamic study on the interaction between anti-tumor drug tegafur and human serum albumin

The changes of thermodynamic properties of the system on interaction between tegafur and human serum albumin (HSA) and the changes of secondary structure units of HSA in the system at 298.15 K have been investigated by the Nano-Watt-Scale isothermal titration calorimetry (ITC), the Langmuir’s binding model and the circular dichroism (CD) spectrometry.     

A New Approach for Titration Calorimetric Data Analysis on the Binding of Magnesium Ion with Myelin Basic Protein

The interaction of the myelin basic protein (MBP) from the bovine central nervous system with divalent magnesium ion was studied by isothermal titration calorimetry at 27 °C in aqueous solution. A simple rapid method for determination of the dissociation binding constants for Mg²⁺-MBP interaction was introduced using the isothermal titration calometric data. The binding isotherm for Mg²⁺-MBP interaction is easily obtained by carrying out a titration calorimetric experiment using only one set of concentrations of MBP. There are two identical independent intrinsic association constants equal to 0.021 μmol⋅L⁻¹ in the first- and second-binding sites, respectively.     

金属硫蛋白与Cd2+、Pb2+络合反应的微量量热滴定

Metallothionein, a class of low molecular weight, metal- and cysteine-rich Proteins, are postulated to play a central role in metal-related biological processes such as the detoxification of Cd2+and Pb2+. The thermal Properties of the interactions of rabbit liver Zn_7MT2 and apo-MT2 with Cd2+ and Pb2+ were studied using isothermal titration calorimeter. The same product Cd_7MT formed in the reactions of Cd2+ with Zn_7MT2 and apo-MT2, while the reactions of Ph2+ with Zn_7MT2 and apo-MT2 Produced two MT species Ph_7MT and Ph_7MT'. The thermodynamic parameters (△H、 △G、 △S, etc. ) for the reactions of MT with 1 mol metal ions were measured at 293.15 K, pH 4.70. All of these reactions are spontaneous, exothermic processes. The values of △G and K show that Cd2+ is more affinitive to MT than Ph2+. The equilibrium constants K of the replacement reactions of Zn_7MT2 by 1 mol Cd2+ and Pb2+ are 2. 7×105 and 1. 3×105 respectively, that means the concentrations of free Cd2+ and Pb2+ are depressed to about 1. 0×10-5 after the reactions with Zn_7MT2. These data can be used to evaluate quantitatively the ability of MT in Cd2+ and Pb2+ detoxificatio.