非金属氢化物pKa定量结构性质关系(QSPR)研究

采用Tomasi的极化统一模型对非金属氢化物HmA在水相条件下进行从头算, 选取与A原子电子密度相关的7个量子化学参数对氢化物pKa进行多元回归和逐步回归, 建立的QSPR方程相关系数R分别为0.9984和0.9947, 标准偏差s分别为1.7349和2.3618, 留一法交叉验证的结果则为R=0.9689和0.9895, s=7.5985和3.3118, 表明由逐步回归建立的方程具有更高的预测可靠性, 同时也表明逐步回归分析引入的原子净电荷数NC、电荷布居数TP和最低未占分子轨道能级ELUMO 3个参数是影响HmA酸强度的关键参数. 对NC, TP和ELUMO的物理意义及其对HmA pKa影响的深入分析表明, 这3个参数是决定A原子电子密度大小的主要因素, ELUMO和TP则分别是同主族氢化物和同周期氢化物酸性强弱递变的决定因素.     

以Fe2O3为原料制备LiFePO4/C复合材料及其性能研究

以Fe2O3为铁源原料, 利用热还原法成功地制备了LiFePO4/C复合材料. 用XRD以及SEM对材料的晶体结构以及表面形貌进行了表征. 通过循环伏安和充放电测试研究了材料的电化学性能. 研究结果表明, 于700 ℃下制备的LiFePO4/C复合材料在0.1C的倍率下可以得到放电容量144.8 mA·h/g, 在循环160次后, 容量仍保持在141.4 mA·h/g. 这种以廉价的Fe2O3代替目前常用的二价铁盐原料方法, 具有减少LiFePO4合成成本的优点.     

掺杂Mn对CeO2-ZrO2-Al2O3材料性质的影响

采用共沉淀法制备了一系列Mn掺杂摩尔分数为0～5%的CeO2-ZrO2-Al2O3(CZA)复合氧化物, 并采用BET, OSC, XRD, XPS, H2-TPR等方法对所制备的材料进行了表征. 结果表明, 所制备的材料均形成了稳定的CZA固溶体, 尤其是Mn掺杂0.5%的材料在600和1000 ℃焙烧后均表现出最好的织构性能. OSC和H2-TPR的结果表明, Mn掺杂量≤1%时, 氧在材料中的体相移动是材料储氧和被还原的速控步骤, 并且Mn的掺杂量为0.2%时, 储氧量最大, 材料的还原温度也最低; Mn掺杂量>1%时, Mn物种对材料储氧和被还原的作用显著. XPS结果表明, Mn在焙烧过程中会迁移向表面, 结合H2-TPR结果可知, 新鲜样品表面的MnOx物种主要为Mn2O3, 而老化样品主要为Mn3O4.     

δ-MnO2对TiO2光催化降解甲基橙的抑制作用

采用动力学方法研究了在水悬浮液中δ-MnO2颗粒物对P-25 TiO2光催化降解甲基橙活性的影响, 并利用紫外-可见漫反射光谱(DRS)和光致发光光谱(PL)对受δ-MnO2污染前后的TiO2样品进行了表征. 动力学研究结果表明, 在3种不同初始pH值条件下, δ-MnO2对TiO2光催化剂都具有明显的致毒效应, 共存δ-MnO2的浓度越大, 致毒效应越明显. 表征结果表明, 由于δ-MnO2 与TiO2之间的界面接触, 使得TiO2吸收带边蓝移, 紫外光区的吸收强度降低, 光致发光信号(PL)明显减弱. 因此, δ-MnO2导致TiO2的禁带宽度增大, 光利用率降低, 并且是光生电子与空穴的复合中心.     

复合物LiFePO4/CaB6的结构与性能研究

采用固相法合成了纯的LiFePO4, 并通过两种不同的方法合成了不同CaB6含量的复合物LiFePO4/CaB6. 对这些产物进行了粒度、形貌、电导率、振实密度、X射线衍射和充放电性能的研究. 实验结果表明, CaB6的掺入虽然没有明显地提高产物的比容量, 但却显著地增加了产物的振实密度和电导率. 第二种方法合成的产物性能更好, 其电导率提高了5个数量级, 振实密度提高了65%.     

PMMA人工晶状体表面的CF4/O2等离子体修饰

为了改善聚甲基丙烯酸甲酯(PMMA)人工晶状体的生物相容性和透光性, 采用CF4/O2等离子体技术修饰其表面. 通过衰减全反射红外光谱(ATR-FTIR)、X射线光电子能谱(XPS)、静态接触角(CA)测定、扫描电子显微镜(SEM)、紫外-可见近红外光谱(UV-Vis)等方法进行表征, 结果表明, 经CF4/O2等离子体处理后, PMMA表面的含氟和含氧基团增加, 其表面的亲水性增强, 生物相容性改善, 紫外光的隔离效率增大. 因此, 通过CF4/O2等离子体修饰能够有效地改善PMMA人工晶状体的性质.     

Y2O3和Nd2O3介孔薄膜的制备与表征

以聚乙烯合丁烯-嵌-聚氧乙烯嵌段共聚物(PHB-PEO)作模板, 采用蒸发诱导自组装方法, 分别制备了Y2O3和Nd2O3介孔薄膜. 用小角、广角X射线衍射和透射电子显微镜对薄膜样品在不同的热处理阶段进行了表征. 结果表明, 所制备的Y2O3和Nd2O3薄膜样品呈现一种大孔径(平均孔径分别约为11.5和12.5 nm)、有序的立方扭曲球形孔排列、稳定于450 ℃并具有部分晶态孔壁结构的介孔薄膜材料.     

二价离子溶剂化自由能的计算—玻恩方程的应用

离子溶剂化自由能是一个很重要的热力学参数,求得溶剂化自由能后,不仅可以了解离子溶剂化的性质,而且由此还可以计算其它热力学函数。由于单个离子不能独立存在,所以不能由实验直接测得单个离子的溶剂化自由能。1920年,玻恩根据静电模型,提出计算单个离子溶剂化自由能的公式如下:     

用于在超临界流体CO2中直接溶解镧系和锕系元素氧化物的TRPO-HNO3络合物的性质

研究了TRPO-HNO₃络合物的一些性质. 实验结果表明, 当HNO₃/TRPO初始体积比从1/7增大到5/1时, TRPO-HNO₃络合物中HNO₃浓度从2.12增大到6.16 mol/L, [HNO₃]/[TRPO]比从0.93增大到3.38, 络合物中水含量的变化范围为0.97%~2.70%. TRPO-HNO₃络合物的比重、粘度和表面张力随络合物中HNO₃浓度的变化而变化. 采用氘锁定技术研究了TRPO-HNO₃络合物的NMR光谱, 结果表明, 在NMR谱图中, 络合物中HNO₃和H₂O的质子会快速交换, 出现一个单峰, 而当TRPO-HNO₃络合物溶入低介电常数的溶剂时, 通过NMR谱图可以发现有小的HNO₃液滴形成.     

溶剂化热力学的理论研究(Ⅴ)——含水混合溶剂中AgCl、AgBrO3溶度积的理论计算

本文以AgCl、AgBrO₃在一系列浓度的MeOH-H₂O、EtOH-H₂O、PrOH-H₂O、Me₂CO-H₂O及DMSO-H₂O混合溶剂中的离解平衡为研究对象,从离子溶剂化能的角度计算了这些难溶盐的溶度积,计算结果与文献值吻合较好.     

用离散-连续模型计算NH2-,NH3和NH4+的溶剂化自由能

通过理论计算推测NH2-,NH3和NH4+在水溶液第一溶剂化层中与之直接作用的水分子分别为2,4和4个,并采用离散-连续模型计算了NH2-,NH3,NH3和NH4+在水溶液中的溶剂化自由能.结果表明,由于离散-连续模型在从头算水平考虑了溶质分子与第一溶剂化层溶剂分子之间的作用,能更准确地描述溶剂化作用.此外,采用更加符合溶液中真实情况的溶剂化构型,能得到更准确的溶剂化性质.     

Calculation of acidic dissociation constants in water: solvation free energy terms. Their accuracy and impact

Three polarizable continuum models, DPCM, CPCM, and IEFPCM, have been applied to calculate free energy differences for nine neutral compounds and their anions. On the basis of solvation free energies, the pK_a values were obtained for the compounds in question by using three thermodynamic cycles: one, involving the combined experimental and calculated data, as well as two other cycles solely with calculated data. This paper deals with the influence of factors such as the SCRF model applied, choice of a particular thermodynamic cycle, atomic radii used to build a cavity in the solvent (water), optimization of geometry in water, inclusion of electron correlation, and the dimension of the basis set on the solvation free energies and on the calculated pK_a values. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

烷基芳基磺酸盐的分子动力学模拟与自由能微扰计算

为研究不同结构的表面活性剂分子在溶液中胶束化能力的差异, 采用分子动力学方法模拟三种烷基芳基磺酸盐在真空和水溶液环境下的结构与相互作用. 利用自由能微扰(FEP)方法计算了水合自由能, 发现与用传统热力学表面张力法测定自制的烷基芳基磺酸盐结果一致. 研究表明: 烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的, 随着分子结构中芳环向长烷基链中间位置移动, 胶束化能力和胶束稳定性均下降; 疏水基周围水分子的“冰山结构”会影响胶束的稳定性, 而水分子中氢键的生存周期是反映冰山结构变化的重要指标; 同时, 亲水基与水分子间形成氢键的数目会增强或减弱分子脱离胶束体的趋势, 从而影响胶束结构的稳定性.     

自由能微扰法研究系列烷基芳基磺酸盐的胶束化焓-熵补偿现象

为了研究不同结构的表面活性剂分子在水溶液中的胶束化焓-熵补偿现象, 采用自由能微扰(FEP)法计算了系列烷基芳基磺酸盐的溶剂化自由能, 并根据胶团化过程的质量作用模型讨论了相关热力学性质. 结果表明: 自由能微扰法得到的溶剂化自由能大小与用传统热力学表面张力法测定的吉布斯自由能相近, 能够用于比较不同结构的烷基芳基磺酸盐间胶束化能力; 烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的, 且存在焓-熵补偿现象, 补偿温度范围均在(302±2) K; 随着分子结构中芳环向长烷基链中间位置移动, 胶束化能力和胶束的稳定性均下降; 而随着芳环上短烷基链或长烷基链碳数的增加, 形成胶束的能力与稳定性均提高.     

一组和AMBER力场配合的普适波恩模型参数

提出了一套和AMBER力场相匹配的普适波恩模型参数.新的参数集包含21种原子类型的初始半径和屏蔽因子.参数通过遗传算法拟合359个小分子水合自由能的实验值得到.采用新的参数,预测了44个小分子的水合自由能,预测值和实验值能很好地吻合,而且大大优于采用Jayaram参数得到的结果.此外,采用新的参数,还预测了15个蛋白质的水合自由能,预测值和PB/SA预测得到的结果能很好地吻合.     

Theoretical study of environmental effects on proton transfer reaction through the peptide bond in a model system

This study considered the possibility of proton transfer reactions through the peptide bond under different environments using the dipeptide and the 12-mer polyglycine α-helix models, in which diglycine is substituted by the 12-mer polyglycine helix. Ab initio molecular orbital calculations were carried out at the B3LYP/6-31+G(d) level of theory. To evaluate the free energies in solution, calculations of the solvation energies were performed using PCM. The correction functions on the calculated solvation energies were provided to reproduce experimental pKa values. The proton transfer reactions through the peptide bond are concluded to be possible in the protein for a wide range of proton acceptors. His complex has two free energy minima along a putative proton transfer pathway in spite of one minimum in the other complexes. The α-helix is estimated to suppress the proton transfer reactions through the peptide bond at the termini of the helix, although it is possible to proceed when the proton affinity of the acceptor is low. Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue.     

A method to determine the Gibbs energy of specific interactions in solutions. Hydrogen bonding of proton donating solutes in basic solvents

One of two fundamental types of solute–solvent intermolecular interactions are the specific interactions, such as hydrogen bonding complexation between solute and solvent. The Gibbs energy of specific interactions is an important quantity that determines rate and equilibrium constants in solutions, but it is difficult to obtain by direct measurement. We proposed equations allowing to determine the contribution of specific interactions to the Gibbs energy of solvation in nonelectrolyte solutions. Applying it for the case of proton donating solutes with one acidic hydrogen atom dissolved in basic solvents, we obtained the values of the Gibbs energies of 1:1 complexation in pure base. These values have been compared with the Gibbs energies of 1:1 complexation in tetrachloromethane. Most of the hydrogen bonds are found to have the same energy in pure base and in CCl₄, however, some weakly bound complexes seem to become even more weakened in pure base medium. Suggested method is applicable in a general situation when multiple associates of different stoichiometry and structure are formed.     

Calculating the surface tension between a flat solid and a liquid: a theoretical and computer simulation study of three topologically different methods

We discuss three topologically different methods for calculating the surface tension between a flat solid and a liquid from theoretical and computer simulation viewpoints. The first method, commonly used in experiments, measures the contact angle at which a static droplet of liquid rests on a solid surface. We present a new analysis algorithm for this method and explore the effects of line tension on the contact angle. The second method, commonly used computer simulations, uses the pressure tensor through the virial in a system where a thick, infinitely extended slab of liquid rests on a solid surface. The third method, which is original to this paper and is closest to the thermodynamic definition of surface tension, applies to a spherical solid in contact with liquid in which the flat solid is recovered by extrapolating the sphere radius to infinity. We find that the second and third methods agree with each other, while the first method systematically underestimates surface tension values.