盐离子对B-DNA到Z-DNA结构转变影响的理论研究

在已给出的与溶液盐浓度有关的DNA弹性模型基础上, 考虑到Z-DNA的碱基堆积和氢键相互 作用, 给出了一个新的B-DNA到Z-DNA的结构转变模型. 研究了盐浓度对B—Z结构转变特性的影响, 得到了力延伸曲线、折叠角概率分布以及B—Z结构转变的临界扭矩随盐浓度的变化规律.结果表明: 当盐浓度达到2.4mol/L时, 松弛DNA的Z构象开始出现, 并且随盐浓度的增加, Z构象存在的概率增大, B—Z转变所需的扭转力矩减小. 关键词： DNA弹性 盐浓度 B—Z结构转变 堆积能     

盐离子对DNA延伸力的影响

在Ahsan等给出的描述DNA分子弹性的两状态虫链模型的基础上,考虑到盐离子浓度对静电自由能的影响,得到了延伸力随盐浓度的变化规律,结果表明:在低力和高力范围延伸力受盐浓度的影响较小,相变延伸范围随盐浓度的增加非线性增加,与实验测量一致.     

B-到Z-DNA结构转变特性的理论研究

本文给出了B-到Z-DNA的结构转变模型,研究了盐浓度和外力矩对B-Z结构转变特性的影响,得到了折叠角的几率分布、B-Z转变的临界扭矩和转变能随盐浓度的变化规律.结果表明:在没有外力和外力矩的情况下,盐浓度达到2.3 mol/L时,Z构象开始出现,与实验结果一致.随盐浓度的增加,Z构象存在的几率增大,B-Z转变所需的扭转力矩减小.     

离子液体中聚氧化乙烯(PEO)相变过程中的氢键效应

我们把Flory-Huggins模型推广应用到聚合物/离子液体体系,研究聚氧化乙烯(PEO)在离子液体[EMIM][BF_4]中相变过程中的氢键效应,理论模型考虑了三种类型氢键(Ⅰ型:PEO-[EMIM]~+氢键,Ⅱ型:PEO-[BF_4]~-氢键和Ⅲ型:[EMIM]~+-[BF_4]~-氢键)的形成,分析了三种类型的氢键分数随温度、 PEO体积分数的变化.研究发现,三种类型的氢键分数随温度的升高而减少.在较小PEO体积分数条件下,增加PEO体积分数,Ⅰ型、Ⅱ型氢键分数轻微地减小;在较大PEO体积分数条件下,增加PEO体积分数,Ⅰ型、Ⅱ型氢键分数急剧减少.Ⅲ型氢键分数随着PEO体积分数的增加而急剧降低.由于三种氢键效应,第二维里系数A_2随温度的增加而减小.通过计算分析不同分子量的PEO在[EMIM][BF_4]中的相图发现,在PEO体积分数较低的条件下,Ⅰ型、Ⅱ型和Ⅲ型氢键是PEO相变的主要驱动力;在PEO体积分数较高的条件下,Ⅰ型和Ⅱ型氢键在PEO相变过程中起到主导作用.     

界面接枝羟基对碳纳米管运动和摩擦行为影响的分子动力学模拟

本文采用分子动力学模拟研究了界面间接枝羟基对碳纳米管在石墨基底上运动和摩擦行为的影响.结果表明:界面接枝羟基后碳纳米管所受的侧向力明显改变;仅石墨接枝羟基时碳纳米管侧向力波动增大;同时由于垂直碳纳米管与基底间接触面积小,碳纳米管所受的摩擦力随羟基含量的增加而增大;碳纳米管与石墨上均接枝羟基后体系中引入了氢键和库仑力作用,显著增加了界面间的摩擦,体系的滑移界面从碳纳米管与石墨间迅速转变为石墨层间,并且导致碳纳米管在垂直初始运动方向上也出现了滑移.     

水蒸气诱导聚电解质刷的构象转变

我们把Flory-Huggins模型(association models)推广应用到暴露于水蒸气中的聚电解质刷体系,考虑聚电解质-水氢键(P-W氢键)与水-水氢键(W-W氢键)、形成氢键与聚电解质链构象的耦合特性,研究水蒸气诱导的聚电解质刷构象转变的机理.研究发现,当P-W氢键效应起主导作用时,随着水蒸气浓度的增加,聚电解质刷会单调溶胀;P-W和W-W两种氢键效应,则会导致随着水蒸气浓度的增加,聚电解质刷的构象首先塌缩,然后开始溶胀的反常转变行为.基于本文的分析,可以预言,由于P-W氢键效应,聚电解质刷可以吸附水蒸气,吸附能力随聚电解质链长的增加而增强;当聚电解质链接枝密度足够高时,由于P-W和W-W两种氢键效应,增加体系中的水蒸气,会在聚电解质刷体系中形成由P-W氢键和W-W氢键交错链接的三维网络状凝胶结构.     

盐对DNA相变影响的非线性特性研究

在Prohofsky，Peyrard-Bishop等提出的描述DNA双螺旋分子结构模型以及实验测量的基础上 , 给出了与盐(指NaCl)浓度有关的哈密顿模型, 得到了非线性动力学方程及扭结孤波解.并 由此求出了DNA变性相变所需要的Peierls相变力. 进一步讨论了盐浓度对相界面和相变力的 影响, 得到的结果与实验测量一致. 关键词： DNA 盐浓度 相界面 相变力     

水蒸气诱导聚电解质刷的构象转变

我们把 Flory−Huggins 模型(association models)推广应用暴露于水蒸气中的聚电解质刷体系,考虑聚电解质-水氢键(P-W氢键)与水-水氢键(W-W氢键)、形成氢键与聚电解质链构象的耦合特性,研究水蒸气诱导的聚电解质刷构象转变的机理.研究发现,当 P-W 氢键效应起主导作用时,随着水蒸气浓度的增加,聚电解质刷会单调溶胀;P-W 和 W-W 两种氢键效应,则会导致随着水蒸气浓度的增加,聚电解质刷的构象首先塌缩,然后开始溶胀的反常转变行为。基于本文的分析,可以预言,由于 P-W 氢键效应,聚电解质刷可以吸附水蒸气,吸附能力随聚电解质链长的增加而增强;当聚电解质链接枝密度足够高时,由于 P-W 和 W-W 两种氢键效应,增加体系中的水蒸气,会在聚电解质刷体系中形成由 P-W 氢键和 W-W 氢键交错链接的三维网络状凝胶结构。     

PCL/SiO2杂化纳米相微结构与晶态成核生长特性

应用扫描电子显微镜、广角X射线衍射和差示扫描量热手段研究了有机高分子/无机组分间以物理次价力(氢键)键合的高分子量PCL/SiO2杂化材料纳米相微结构和PCL高分子链在该微结构环境中的结晶成核生长特性及其影响因素.研究结果表明:杂化体系中高分子/无机组分间的微相分离尺度在纳米数量级,高分子微区的平均相畴尺寸在70nm左右,无机相形态呈现不规则的颗粒状.两相均匀分布程度与体系中组分间的氢键键合强度有关.PCL杂化后结晶度减小,对应的微晶尺寸明显改变,平衡熔点随无机组成含量的增加而下降.高分子链在晶核表面折叠形成结晶结构所需的能量增加.这一结果归因于无机非晶SiO2和键合强度的影响.     

含水量对PAM/PVA互穿网络水凝胶性能的影响

应用分子动力学方法对PAM/PVA互穿网络水凝胶体系进行研究.发现该水凝胶体系的内聚能密度、结合能随着水含量的增加而增加,即体系的稳定性更强.由静态力学性能分析发现随体系含水量的增加,弹性系数、工程模量以及延展性均减小.此外,通过对相关函数的分析,发现H₂O分子与其周围原子、官能团之间主要是通过氢键相互作用,形成氢键的强弱关系为O_water >O_PVA >O_PAM >N_PAM,与形成氢键的可能性(难易)关系一致.     

三链DNA分子poly（dT）.poly（dA）.poly（dT）的低频振动模式

利用晶格动力学方法，首次计算了具有三螺旋结构的ｐｏｌｙ（ｄＴ）．ｐｏｌｙ（ｄＡ）．ｐｏｌｙ（ｄＴ）的低频振动模式，结果表明Ｗａｔｓｏｎ－Ｃｒｉｃｋ氢键的呼吸模式位于９０ｃｍ＾－＾１附近，而Ｈｏｏｇｅｎｓｔｅｅｎ氢键除了在９０ｃｍ＾－＾１附近存在模式外，还在更低频率上存在着几个更为强烈的呼吸模式，这一结果定性地解释了低盐度下ｐｏｌｙ（ｄＴ）．ｐｏｌｙ（ｄＡ）．ｐｏｌｙ（ｄＴ）的两步热融化。     

Hydrogen bonds at metal surfaces: Universal scaling and quantification of substrate effects

Simple bio-molecules demonstrate a propensity to form hydrogen-bonded networks. Here, individual hydrogen-bond energies are determined through topological analysis of the theoretical electron density for a variety of systems, demonstrating the existence of a universal relationship between hydrogen-bond length and strength. Comparison of local hydrogen-bond strength to global stabilisation allows the quantification of contributions to intermolecular interactions within surface overlayers in unprecedented detail.     

Temperature-dependent hydrogen-bond geometry in liquid water

We have determined the hydrogen-bond geometry in liquid water from 0 to 80 degrees C by combining measurements of the proton magnetic shielding tensor with ab initio density functional calculations. The resulting moments of the distributions of hydrogen-bond length and angle are direct measures of thermal disorder in the hydrogen-bond network. These moments, and the distribution functions that can be reconstructed from them, impose quantitative constraints on structural models of liquid water.     

Hydrogen-bond dynamics of interior and surface molecules in a water nanocluster: temperature and size effects

Molecular dynamics simulations are employed to investigate the effects of temperature and size on the hydrogen-bond dynamics of interior molecules and surface molecules in a water nanocluster. The flexible three-centred (F3C) water model is invoked in the simulations. To inspect the dynamics of the interior hydrogen bonds and the surface hydrogen bonds, a spherical water nanocluster is modelled and then divided into interior molecules and surface molecules according to the density profile of the water nanocluster. It is observed that at higher temperatures the average number of hydrogen bonds decreases and yields faster hydrogen-bond relaxation for both interior molecules and surface molecules of the water nanocluster. Furthermore, the surface molecules have a lower average number of hydrogen bonds than the interior molecules. The lifetime of the surface hydrogen bonds is slightly longer than that of the interior hydrogen bonds, whereas the hydrogen-bond structural relaxation time of the surface molecules is more obviously slower than that of the interior molecules. Regarding the size effect, a larger water nanocluster is seen to have a larger average number of hydrogen bonds and a longer hydrogen-bond structural relaxation time.     

Effects of ion atmosphere on hydrogen-bond dynamics in aqueous electrolyte solutions

We have performed a series of molecular dynamics simulations of aqueous NaCl and KCl solutions at different concentrations to investigate the effects of ion atmosphere on the dynamics of water-water hydrogen bonds at room temperature. The average number of hydrogen bonds per water molecule decreases with increase of ion concentration. The dynamics of hydrogen-bond breaking is found to accelerate somewhat and that of hydrogen-bond structural relaxation, which occurs at a longer time scale, is found to slow down with increasing ion concentration for both NaCl and KCl solutions.     

Direct observation of hydrogen-bond exchange within a single water dimer

The dynamics of water dimers was investigated at the single-molecule level by using a scanning tunneling microscope. The two molecules in a water dimer, bound on a Cu(110) surface at 6 K, were observed to exchange their roles as hydrogen-bond donor and acceptor via hydrogen-bond rearrangement. The interchange rate is approximately 60 times higher for (H2O)2 than for (D2O)2, suggesting that quantum tunneling is involved in the process. The interchange rate is enhanced upon excitation of the intermolecular mode that correlates with the reaction coordinate.     

缔合流体在高温高压下的自扩散系数研究

在统计力学理论基础上,本文提出了一个考虑氢键对自扩散系数影响的方程．这个方程为非氢键贡献部分与氢键贡献部分之积,其中自扩散系数的非氢键部分由Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ链模型求得,而一个分子中的平均氢键数随温度和密度的变化关系使用统计缔合流体理论得到。链节之间的相互作用能量参数由粘度的关联式获得,其它四个参数则由扩散系数的实验数据获得。对７个典型的缔合流体在相当宽的温度压力范围内计算的平均相对百分误差为５．９８％。     

Unusual behaviour of poly(ethylene-oxide) in aqueous mixtures

The model system of poly(ethylene-oxide) or PEO, where the changing hydrogen-bond connectivity of the water has large effect on the conformation of the polymer chain, in mixtures of water and acetonitrile, is experimentally studied. The results show the existence of a threshold water content in the system at which the 3d connectivity of the water network begins. Unusual expansion of the polymer chain, an effect larger than that observed in either of the pure solvents, is seen. Upon addition of small amounts of a monovalent salt, binding of ion to polymer takes place in pure acetonitrile solutions. Salt ions begin to co-ordinate with water molecules at the same solvent ratio as the threshold for water network formation. Ions now no longer complex to PEO; instead, hydrogen bonding of water to the polymer strongly dictates conformation in this regime.Received: 10 September 2004, Published online: 3 November 2004PACS: 61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 61.12.Ex Neutron scattering techniques (including small-angle scattering) - 36.20.Ey Conformation (statistics and dynamics)     

绿色木霉纤维素酶分子内氢键特征的研究

运用能够揭示蛋白质分子基团振动特征的激光拉曼光谱分析技术,对绿色木霉纤维素酶中的CBHⅡ在固态以及两种pH值的液态中酶分子内的氢键状态进行了分析。结果表明相对于纤维素酶固体干粉,液态中酶分子酰胺Ⅰ羰基氧原子作为氢键质子受体的能力为上升;酰胺Ⅱ与酰胺Ⅰ的β结构特征峰变化倾向相似。在3种样品中,酶蛋白中Trp均为强氢键供体,从成键能力方面证实了以往同类酶空间分析的结果。固体与pH 6.0水溶液酶蛋白中酪氨酸酚羟基成键能力也是强的。根据游离巯基分析可以判断绿色木霉CBHⅡ的成熟肽CBD与瑞氏木霉CBHⅡ的CBD有相似的二硫键构成。