PROLINE-BASED CHIRAL STATIONARY PHASES: INSIGHTS INTO THE MECHANISM OF CHIRAL SELECTIVITY

Proline (Pro) is a unique amino acid that has been examined previously as a potential chiral selector for high-performance liquid chromatography. In recent years, a new class of promising Pro based enantioselective stationary phases has been studied and the longer peptides were found to be competitive with commercial chiral stationary phases (CSPs). Here, we aim to perform a comprehensive examination of a t-butoxycarbonyl- (t-Boc-) terminated monoproline selector. This selector was grafted through an amide linkage to an aminopropyl siloxane-terminated Si (111) wafer and to a silicon atomic force microscopy tip. To ensure a flat, homogeneous overlayer of selectors suitable for force spectrometric measurements, the prepared surfaces were characterized using XPS, AFM and contact angle measurements. Chemical force spectrometry (CFS) has been used to examine the chiral discrimination in our monoproline CSP by measuring the interaction forces between two D- or L-monoproline monolayers in water and in the presence of a series of amino acids in solution to explore the degree to which binding of amino acids impacts self-selectivity. Chemical force titration (CFT) has been used to observe the influence of variations in pH on the binding interaction of proline modified chiral surfaces. Here we aim to explore the connection between side-chain hydrophobicity and differences in the nature of the binding between different ionic forms of amino acids and the t-Boc-Pro interface, and thereby to gain insight into the mechanism of chiral selectivity. The CFS results show several trends for different proline selector/amino acid combinations and indicate that the binding characteristics of amino acid to the proline surface is strongly dependent on the amino acid side chain where hydrophilic side chain amino acids exhibit a selectivity opposite to that seen for those with hydrophobic side chains. The CFT studies also provide valuable insights into interactions between the proline selector and the amino acids under a wide range of pH conditions, indicating that protonated amine groups of alanine and serine are closely involved in the binding mechanism to proline surfaces. On the other hand, the presence of the second carboxylic group in aspartic acid plays an important role while interacting with proline.

Analysis of Non-Stationary Flows Using Eulerian and Lagrangian Frameworks

Recent developments have made researchers to reconsider Lagrangian measurement techniques as an alternative to their Eulerian counterpart when investigating non-stationary flows. This thesis advances the state-of-the-art of Lagrangian measurement techniques by pursuing three different objectives: (i) developing new Lagrangian measurement techniques for difficult-to-measure, in situ flow environments; (ii) developing new post-processing strategies designed for unstructured Lagrangian data, as well as providing guidelines towards their use; and (iii) presenting the advantages that the Lagrangian framework has over their Eulerian counterpart in various non-stationary flow problems. Towards the first objective, a large-scale particle tracking velocimetry apparatus is designed for atmospheric surface layer measurements. Towards the second objective, two techniques, one for identifying Lagrangian Coherent Structures (LCS) and the other for characterizing entrainment directly from unstructured Lagrangian data, are developed. Finally, towards the third objective, the advantages of Lagrangian-based measurements are showcased in two unsteady flow problems: the atmospheric surface layer, and entrainment in a non-stationary turbulent flow. Through developing new experimental and post-processing strategies for Lagrangian data, and through showcasing the advantages of Lagrangian data in various non-stationary flows, the thesis works to help investigators to more easily adopt Lagrangian-based measurement techniques.