Structure, dynamics and solvation in heterogeneous environments

Branka Ladanyi教授获得了化学理论、模型和计算方法项目的奖项，以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。一组包括限制在表面活性剂组件或二氧化硅纳米孔中的流体。另一个涉及水在与生物相关的分子的溶剂化壳中的性质。方法包括统计力学理论和计算机模拟。表面活性剂组合中的流体研究涉及两种类型的系统。其中之一是反胶束（RMs），其中表面活性剂包裹的水滴分散在连续的非极性相中。原子RM模型正在被开发，它们的性质被研究为水含量w0 = [H2O]/[表面活性剂]的函数，这是一个与水滴大小密切相关的参数。在阴离子表面活性剂AOT形成的RMs模型开发工作的基础上，课题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RMs的原子模型，确定其结构和动力学作为w0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中的溶质位置，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包含水和全氟辛烷磺酸（PFOS）表面活性剂，并作为燃料电池膜材料的模型。在这些体系中，随着水含量的变化和表面活性剂在片层相和六方相之间的转变，研究了水和离子的迁移率。二氧化硅纳米孔中流体的研究建立在早期对不同直径的近似圆柱形孔中水的性质的研究基础上。研究还包括计算和分析纳米孔中水的准弹性中子散射（QENS）观测结果，以及研究孔的亲水性和各向异性如何影响QENS探测到的分子旋转和平动动力学。从苯及其氟化类似物开始，还在研究由形状和极化各向异性的分子组成的液体的界面结构和动力学。通过模拟光学克尔效应观测到的集体极化率各向异性动力学，与实验联系起来。这项工作是与佩鲁贾大学的研究小组合作，利用去偏振光散射（DLS）和分子动力学（MD）模拟研究水寡糖溶液。这项工作的目标是绘制和发展更好地理解水在生物分子的溶剂化壳中的动力学。该方法包括测量不同浓度生物分子溶液的DLS光谱，通过MD和分子理论建立光谱模型，并从不同物种的贡献、它们的相互作用和相关性方面分析它们。除寡糖外，该项目还包括对寡肽和蛋白质水溶液的研究。这些研究使用理论和计算化学的方法处理纳米孔和表面活性剂组合中的液体以及复杂的水混合物。在分子水平上理解这些系统的性质在物理化学以外的领域是重要的。离子表面活性剂的水界面是蛋白质和细胞膜等生物系统的一个特征。了解这样的系统在技术上具有重要意义，涉及到电化学、燃料电池、石油回收和环境清理等。了解被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。对水溶液性质的研究为水与生物分子的相互作用以及生物保存的分子基础提供了信息。参与该项目的学生和博士后将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合作工作，他们有机会了解他们的工作如何应用于实际系统，以及他们计算的数量是如何测量的。

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.