Structure, dynamics and solvation in heterogeneous environments

布兰卡·拉丹尼教授得到了化学理论、模型和计算方法计划颁发的奖项的支持，该奖项旨在研究流体界面或微非均质起重要作用的系统。考虑了几个这样的系统。一组包括限制在二氧化硅纳米孔上的表面活性剂组件中的流体。另一个问题是与生物相关的分子的溶剂化壳层中水的性质。研究方法涉及统计力学理论和计算机模拟。关于表面活性剂组件中流体的工作涉及两种类型的体系。其中之一是反胶束(RMS)，在反胶束中，表面活性剂包裹的水滴分散在连续的非极性相中。原子学的RM模型正在开发中，其性质正在作为水分含量W0=[H2O]/[表面活性剂]的函数进行研究，这是一个与水滴大小密切相关的参数。继阴离子表面活性剂AOT形成的RMS的模型开发工作之后，该研究小组正致力于开发由阳离子表面活性剂CTAB(十六烷基三甲基溴化铵)形成的RMS的原子模型，确定其结构和动力学随w0的函数，并将结果与相关实验数据进行比较。下一项任务是研究分子离子在RMS中的溶剂化作用，确定溶质-表面活性剂静电相互作用如何影响RMS中溶质的位置，以及它们如何反映在溶质时间分辨红外光谱中。正在研究的另一种系统包含水和全氟辛烷磺酸(PFOS)表面活性剂，并用作燃料电池膜材料的模型。随着水含量的变化和表面活性剂在片状和六方相之间的转变，这些体系中的水和离子的迁移率正在被研究。关于二氧化硅纳米孔中流体的工作建立在早期对水的性质的研究基础上，这些水被限制在大约不同直径的圆柱形孔隙中。还在计算和分析纳米孔中水的准弹性中子散射(QENS)可观测值，并研究孔隙亲水性和各向异性对QENS可探测的分子转动和平移动力学的影响。人们还在研究由形状和极化率各向异性的分子组成的液体的界面结构和动力学，从苯及其氟化类似物开始。通过建立由光学克尔效应观察到的集体极化各向异性动力学模型，与实验相联系。这项工作是与佩鲁贾大学的研究小组合作，使用去偏振光散射(DLS)和分子动力学(MD)模拟来研究低聚糖水溶液。这项工作的目标是绘制并更好地了解生物分子溶剂化壳层中的水的动力学。该方法包括测量不同浓度生物分子溶液的DLS光谱，通过分子动力学和分子理论对光谱进行建模，并根据不同物种的贡献、相互作用和相关性进行分析。除了低聚糖，该项目还包括研究寡肽和蛋白质的水溶液。这些研究涉及限制在纳米孔和表面活性剂组件中的液体以及复杂的水混合物，使用理论和计算化学的方法。在分子水平上了解这些体系的性质在物理化学以外的领域很重要。与离子表面活性剂的水溶液界面是蛋白质和细胞膜等生物系统的一个特征。了解这类系统具有重要的技术意义，涉及电化学、燃料电池、石油回收和环境清理等领域。了解纳米孔中液体的性质对多相催化、分离、润滑和微流体学具有重要意义。这种对水溶液性质的研究提供了关于水与生物分子相互作用和生物保存的分子基础的信息。从事这个项目的学生和博士后正在学习多体系统统计力学的理论和计算方法，并将它们应用于与化学、材料科学和生物化学相关的系统和现象。由于该提案包括与实验小组的协作工作，他们有机会了解他们的工作如何应用于真实系统，以及他们正在计算的量是如何测量的。

Prof. Branka Ladanyi is supported by an award from the Chemical Theory, Models and Computational Methods program for research dealing with systems in which fluid interfaces or microheterogeneities play an important role. Several such systems are considered. One set includes fluids confined either in surfactant assemblies on in silica nanopores. Another concerns the properties of water in solvation shells of molecules of biological relevance. The methods of approach involve statistical mechanical theory and computer simulation. The work on fluids in surfactant assemblies deals with two types of systems. One of these is reverse micelles (RMs) in which surfactant-coated water droplets are dispersed in a continuous nonpolar phase. Atomistic RM models are being developed and their properties are being investigated as functions of water content w0 = [H2O]/[surfactant], a parameter closely related to water droplet size. Following up on their work on model development of RMs formed by anionic surfactant AOT, the research group is working on developing an atomistic model for RMs formed by the cationic surfactant CTAB (cetyltrimethylammonium bromide), determining the structure and dynamics as a function of w0 and comparing the results to relevant experimental data. The next task is to investigate solvation of molecular ions in RMs, determining how solute-surfactant electrostatic interactions influence solute location within the RM and how they are reflected in the solute time-resolved infrared spectra. The other type of system under study contains water and perfluorooctane sulfonic acid (PFOS) surfactant and serves as a model for fuel cell membrane materials. Water and ion mobility is being investigated in these systems as water content varies and the surfactant undergoes transitions between lamellar and hexagonal phases. The work on fluids in silica nanopores builds on earlier studies of the properties of water confined in approximately cylindrical pores of varying diameter. Research is also being made into calculating and analyzing the observable in quasi-elastic neutron scattering (QENS) of water confined in nanopores and investigating how pore hydrophilicity and anisotropy influence molecular rotational and translational dynamics detectable by QENS. Studies are also being made into the interfacial structure and dynamics of liquids composed of molecules that are anisotropic in shape and polarizability, starting with benzene and its fluorinated analogs. Contact with experiment is made by modeling collective polarizability anisotropy dynamics observable by optical Kerr effect. The work is in collaboration with research groups at the University of Perugia in the study of aqueous oligosaccharide solutions using depolarized light scattering (DLS) and molecular dynamics (MD) simulation. The goal of this work is to map out and develop a better understanding of the dynamics of water in solvation shells of biomolecules. The approach includes measuring DLS spectra of solutions at varying concentrations of biomolecules, modeling the spectra via MD and molecular theory and analyzing them in terms of contributions from different species, their interactions and correlations. In addition to oligosaccharides, the project includes studies of aqueous solutions of oligopeptides and proteins.These studies deal with liquids confined in nanopores and surfactant assemblies as well as with complex aqueous mixtures, using methods of theoretical and computational chemistry. Understanding the properties of these systems at the molecular level is important in areas beyond physical chemistry. Aqueous interfaces with ionic surfactants are a feature of biological systems such as proteins and cell membranes. Understanding such systems is of technological importance, related to electrochemistry, fuel cells, oil recovery, and environmental clean-up, among others. Understanding the properties of liquids confined in nanopores is important in heterogeneous catalysis, separations, lubrication, and microfluidics. This research in the properties of aqueous solutions provides information on water interactions with biomolecules and about the molecular basis for biopreservation. Students and postdocs working on this project are learning theoretical and computational methods of statistical mechanics of many-body systems and applying them to systems and phenomena relevant to chemistry, materials science, and biochemistry. Since the proposal includes collaborative work with experimental groups, they have the opportunity of learning how their work applies to real systems and how the quantities that they are calculating are measured.