Rules for Ion Pairing in Aqueous Interfacial Structures

在化学系大分子、超分子和纳米化学项目的支持下，宾夕法尼亚州立大学的保罗·S·克里默教授将探索化学处理界面上离子配对的规则。许多有机物质的表面在水中带电。例子包括从水性涂料中的胶体到存在于细胞膜中的蛋白质。带负电的表面从相邻的溶液中吸引带正电的金属离子。这项研究将有助于确定盐中的金属离子如何与带负电的表面相互作用。这个问题的答案一方面与生物和环境科学有关，另一方面与材料科学和工程问题有关。这项研究还将使用涉及激光的实验物理化学技术组合来培训新一代学生。学生们还将从与理论合作者的合作中获得经验，这些合作者将帮助建立离子对数据的模型。这些结果不仅将提供离子与带电表面结合的紧密程度的信息，还将提供有关表面化学成分如何影响离子结合的重要细节。研究结果将适用于广泛的实际问题，从软化饮用水的最有效方法到指导药品生产。还将与高中化学教师合作，为高中生开发为期一周的新实验室，利用离子配对将食品着色剂划分为富盐液体。其目标将是创建无需复杂设备或昂贵化学物质即可进行的实验。实验将使用红外可见和频振动光谱(SFVS)来探测Hofmeister离子与长链表面活性剂在空气/水界面的朗缪尔单分子膜的相互作用。振动光谱应该包含界面水结构、烷基链序和头基水合的信息。在这些实验中，将同时使用带正电荷和带负电荷的头组。这将包括对羧酸盐、硫酸盐、磺酸盐、磷酸盐和磷酸盐阴离子头基以及胺和三甲胺阳离子头基的研究。这些实验的一个主要特点是作为界面电荷密度的函数进行测量。这将通过使用长链脂肪醇作为填充表面活性剂来调节带电头基的摩尔分数来实现。将注意到反离子的结合顺序，并将测量所使用的每个反离子的平衡结合常数。还将特别注意导致接触离子对形成的条件，而不是溶剂共享的离子配对。在适当的情况下，将通过使用多曲线分辨率拉曼光谱获得关于离子配对的主体溶液中的补充数据。这些类型的系统测量应该能够阐明一套规则，这些规则作为化学特性和界面结构的函数来管理大分子界面上的反离子配对。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor Paul S. Cremer of Pennsylvania State University will explore the rules for ion pairing at chemically treated interfaces. The surfaces of many organic-based substances are charged in water. Examples include everything from colloids in water-based paints to proteins residing in cell membranes. Negatively charged surfaces attract positively charged metal ions from the adjacent solution. This study will help determine how metal ions from salts interact with negatively charged surfaces. The answers to this question have relevance in the biological and environmental sciences on the one hand, and materials science and engineering problems on the other. This research will also train a new generation of students using a combination of experimental physical chemistry techniques that involve laser light. The students will also get experience from working with theoretical collaborators who will help model ion-pairing data. The results are expected to provide information not only on how tightly ions bind to charged surfaces but also give important details on how the chemical composition of a surface influences ion binding. The results will be applicable to a wide range of practical problems ranging from the most effective way to soften drinking water to the guidance of pharmaceutical drug manufacturing. Work will also be conducted in association with high school chemistry teachers to develop new week-long laboratories for high school students that take advantage of ion pairing to partition food coloring into salt rich liquid phases. The goal will be to create experiments that can be conducted without the need for complex equipment or expensive chemicals.Experiments will be performed using infrared-visible sum frequency vibrational spectroscopy (SFVS) to probe the interactions of Hofmeister ions with Langmuir monolayers of long chain surfactants at the air/water interface. The vibrational spectra should contain information on interfacial water structure, alkyl chain ordering and headgroup hydration. In these experiments, both positively and negatively charged headgroups will be employed. This will include studies of carboxylate, sulfate, sulfonate, phosphate, and phosphate anionic headgroups as well as amine and trimethylamine cationic headgroups. A key feature of these experiments will be to conduct measurements as a function of interfacial charge density. This will be accomplished by using long chain fatty alcohols as filler surfactants to tune the mole fraction of charged headgroups. The order of binding for counterions will be noted and equilibrium binding constants will be measured for each counterion that is employed. Special attention will also be paid to conditions that lead to contact ion pair formation as opposed to solvent-shared ion pairing. Where appropriate, complementary data in bulk solution on ion pairing will be obtained by using multicurve resolution Raman spectroscopy. These types of systematic measurements should enable the elucidation of a set of rules that govern counterion pairing at macromolecular interfaces as a function of chemical identity and interfacial structure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.