Structure, dynamics and solvation in heterogeneous environments

Branka Ladanyi教授获得了化学理论，模型和计算方法计划的奖项，用于研究处理流体界面或微不均匀性发挥重要作用的系统。 几个这样的系统被认为是。 一组包括限制在表面活性剂组件或二氧化硅纳米孔中的流体。 另一个问题涉及生物相关分子溶剂化壳中水的性质。 研究方法包括统计力学理论和计算机模拟。 表面活性剂组合体中流体的研究涉及两种类型的体系。 其中之一是反胶束（RM），其中表面活性剂涂覆的水滴分散在连续的非极性相中。 原子RM模型正在开发和他们的属性正在研究作为水含量w 0 = [H2O]/[表面活性剂]，一个参数密切相关的水滴大小的函数。 继阴离子表面活性剂AOT形成的RM的模型开发工作之后，研究小组正在开发阳离子表面活性剂CTAB（十六烷基三甲基溴化铵）形成的RM的原子模型，确定结构和动力学作为w 0的函数，并将结果与相关实验数据进行比较。 下一个任务是研究分子离子在RM中的溶剂化，确定溶质-表面活性剂静电相互作用如何影响RM内的溶质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含有水和全氟辛烷磺酸表面活性剂，可作为燃料电池膜材料的模型。 水和离子的流动性正在研究在这些系统中，作为水含量的变化和表面活性剂经历层状和六方相之间的过渡。 关于二氧化硅纳米孔中流体的工作建立在对限制在不同直径的近似圆柱形孔中的水的性质的早期研究的基础上。 还在研究计算和分析限制在纳米孔中的水的准弹性中子散射（QENS）中的可观察性，并调查孔的亲水性和各向异性如何影响QENS可检测的分子旋转和平移动力学。 还从苯及其氟化类似物开始，研究由形状和极化性各向异性的分子组成的液体的界面结构和动力学。 与实验的联系是通过模拟集体极化率各向异性动态观察光学克尔效应。 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）模拟研究寡糖水溶液。 这项工作的目标是绘制出和发展更好地了解水在生物分子的溶剂化壳的动力学。 该方法包括测量不同浓度的生物分子溶液的DLS光谱，通过MD和分子理论对光谱进行建模，并根据不同物种的贡献，它们的相互作用和相关性对其进行分析。 除了低聚糖，该项目还包括低聚肽和蛋白质水溶液的研究，这些研究涉及纳米孔和表面活性剂组件中的液体以及复杂的水溶液混合物，使用理论和计算化学方法。 在分子水平上理解这些系统的性质在物理化学之外的领域是重要的。 具有离子表面活性剂的水界面是生物系统如蛋白质和细胞膜的特征。 了解这样的系统是技术上的重要性，涉及电化学，燃料电池，石油回收，环境净化等。 了解限制在纳米孔中的液体的性质在多相催化、分离、润滑和微流体中是重要的。 水溶液性质的研究提供了水与生物分子相互作用的信息，以及生物保存的分子基础。 从事该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，并将其应用于与化学，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，他们有机会学习如何将他们的工作应用于真实的系统，以及如何测量他们正在计算的量。

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.