The Nature of Molecular Association and Solvation of Aliphatic and Perfluorinated Aliphatic Carboxylic Acids

脂肪族和全氟脂肪族羧酸的分子缔合和溶剂化的性质

• 批准号: 0244795
• 负责人: Yoonkook Park
• 金额: $ 23万
• 依托单位: Tuskegee University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-04-01 至 2006-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0244795&HistoricalAwards=false
• 关键词: Nature; Molecular; Association; Solvation; Aliphatic

Yoonkook ParkTuskegee UniversityThe Nature of Molecular Association and Solvation of Aliphatic and Perfluorinated Aliphatic Carboxylic Acids Carboxylic acids are of significant importance in industry due to numerous uses as raw materials for other chemicals, as solvents, and in the drug, dye, textile and foodstuffs industries. In addition, carboxylic acids play an important role in biological applications. For example, short-chain fatty acids (SCFAs) such as acetic, propionic, iso- and n-butyric and iso- and n-valeric acids, serve as an indicator of bacterial activity. Hence, analysis of SCFAs is of importance in studies of health and disease in the intestinal tract. Fundamental molecular understanding of these acids can help in rational design of processes and products with desired properties. In light of the need to improve the green engineering of processes involving these species, this proposal will focus on understanding the molecular behavior of carboxylic acids in supercritical fluids.Formic acid and SCFAs represent an interesting series of molecules that provide the opportunity to study and correlate molecular structure with the tendency for these molecules to self-associate. However, solvation can have a tremendous impact on carboxylic acid self-association even in the case of carboxylic acids with modestly different alkyl groups. The influence of solvents on dimerization of some carboxylic acids has been investigated by several research groups. In earlier work, the PI and co-PIs used Fourier transform infrared (FTIR) spectroscopy and a modified lattice-fluid hydrogen-bonding (MLFHB) model to examine the effect of solvent density and solvation in formic acid association in both supercritical (SC) CO2 and C2H6. The results obtained indicated that in the presence of SC CO2 solvent, the association of formic acid decreased linearly with increases in solvent density. The interaction of CO2 (solvent) with formic acid monomer (solute) has a marked effect on the dimer formation compared to that when ethane was employed as the solvent. As a result of weaker solvent-solute interactions in ethane, the association constant of formic acid in C2H6 is thus an order of magnitude larger than that in CO2. The strong interactions of CO2 and carboxylic acid monomers has a tremendous effect on the equilibrium behavior. In addition, this behavior has been successfully modeled by using the MLFHB model. Specific Aims: SC CO2 can interact strongly with certain molecules, particularly, those with electron donating functional groups. In this study, the PIs will investigate the nature of molecular association and solvation of carboxylic acids. This study is comprised of three main areas. 1) The association equilibrium constant (KA) of carboxylic acids at various densities in a variety of solvents (e.g. SCF CO2 and C2H6) will be determined using FTIR spectroscopy. Dr. Park and his Tuskegee University undergraduate students will work with Dr. Roberts and his full-time Auburn Ph.D. student to collect the experimental data in the Roberts' lab. 2) The specific interaction between CO2 and aliphatic (and fluorinated aliphatic)carboxylic acids in an "inert" solvent, such as pentane, will also be investigated in the Roberts' lab as well as the Tuskegee laboratories. Dr. Park and his students will identify the most probable interaction site between CO2 and aliphatic (and fluorinated aliphatic) carboxylic acids theoretically. The experimentally obtained binding energies will be compared to those obtained from model potentials. 3) Molecular modeling of these systems will be carried out in Dr. Gupta's lab to improve our fundamental understanding of the experimental results and to guide the experimental studies. Both ab initio and equation of state approaches will be utilized. Broader Impact: These studies will be important in improving our understanding of solvent effects on carboxylic acid interactions in SCFs. Understanding the fundamental molecular attributes of CO2 plays a role in rational design of inexpensive and green CO2-based processes. Information about the specific interaction between CO2 and aliphatic (and fluorinated aliphatic) carboxylic acids will provide a guideline as to which factors should be considered to improve overall CO2-philicity. The proposed research program presents multiple opportunities to develop students in the areas of molecular thermodynamics and green chemistry and engineering. The mechanisms for this development include Ph.D. student and undergraduate student training, as well as incorporation of our findings and aspects of this ever important field of green chemistry within our molecular thermodynamics courses at both Tuskegee University and Auburn University.

Yoonkook ParkTuskegee University脂肪族和全氟化脂肪族羧酸的分子缔合和溶剂化的性质羧酸在工业中具有重要意义，因为它被用作其他化学品的原料、溶剂以及在制药、染料、纺织和食品工业中的用途。此外，羧酸在生物应用中也扮演着重要的角色。例如，短链脂肪酸(SCFA)，如醋酸、丙酸、异丁酸和正丁酸以及异戊酸和正戊酸，可作为细菌活动的指示剂。因此，对单链脂肪酸的分析在肠道健康和疾病的研究中具有重要意义。对这些酸的分子基础了解有助于合理设计具有所需性质的工艺和产品。鉴于改善涉及这些物种的过程的绿色工程的需要，这项建议将侧重于了解羧酸在超临界流体中的分子行为。甲酸和SCFA代表了一系列有趣的分子，提供了研究分子结构并将其与这些分子自缔合的趋势相关联的机会。然而，即使在烷基略有不同的羧酸的情况下，溶剂化也会对羧酸的自缔合产生巨大的影响。几个研究小组研究了溶剂对某些羧酸二聚反应的影响。在早期的工作中，PI和co-PI使用傅里叶变换红外光谱(FTIR)和改进的晶格-流体氢键(MLFHB)模型研究了溶剂密度和溶剂化对超临界CO2和C2H6中甲酸缔合的影响。结果表明，在超临界CO2溶剂存在下，甲酸的缔合度随溶剂浓度的增加而线性降低。与以乙烷为溶剂时相比，CO2(溶剂)与甲酸单体(溶质)的相互作用对二聚体的形成有显著的影响。由于溶剂-溶质在乙烷中的相互作用较弱，甲酸在C2H6中的缔合常数比在CO2中大一个数量级。CO2与羧酸单体的强相互作用对体系的平衡行为有很大影响。此外，使用MLFHB模型成功地模拟了这一行为。具体目标：超临界二氧化碳可以与某些分子发生强烈的相互作用，特别是那些带有给电子官能团的分子。在这项研究中，PI将研究羧酸的分子缔合和溶剂化的性质。这项研究主要由三个方面组成。1)用FTIR光谱测定了不同密度的羧酸在各种溶剂(如超临界CO2和C2H6)中的缔合平衡常数(Ka)。朴博士和他的塔斯基吉大学本科生将与罗伯茨博士和他的全日制奥本博士生一起在罗伯茨的实验室收集实验数据。2)在“惰性”溶剂(如戊烷)中，二氧化碳与脂肪族(和氟化脂肪族)羧酸之间的特定相互作用也将在Roberts实验室和Tuskegee实验室中进行研究。Park博士和他的学生将从理论上确定二氧化碳和脂肪族(以及氟化脂肪族)羧酸之间最有可能的相互作用部位。将实验得到的结合能与模型势得到的结合能进行比较。3)这些体系的分子模拟将在古普塔博士的实验室进行，以提高我们对实验结果的基本理解，并指导实验研究。从头算方法和状态方程方法都将被利用。更广泛的影响：这些研究将有助于我们更好地理解溶剂对超临界流体中羧酸相互作用的影响。了解二氧化碳的基本分子属性对合理设计廉价和绿色的基于二氧化碳的工艺具有重要作用。关于二氧化碳与脂肪族(和氟化脂肪族)羧酸之间具体相互作用的信息将提供指导方针，说明应考虑哪些因素来改善总体的二氧化碳亲和性。拟议的研究计划为发展分子热力学、绿色化学和工程领域的学生提供了多种机会。这一发展的机制包括博士生和本科生培训，以及将我们在塔斯基吉大学和奥本大学的分子热力学课程中这一始终重要的绿色化学领域的发现和方面纳入我们的研究。