Vibrational sum-frequency spectroscopic investigations of the orientation and conformation of amphiphiles at oil/water and vapor/water interfaces.

摘要

Recently there has been a resurgence in the attention given to understanding the properties of adsorbates at liquid surfaces. The intermolecular interactions that affect the orientation and conformation of adsorbates at liquid surfaces are the keys to understanding such diverse systems as detergents and cell membranes. This dissertation examines a series of molecular adsorbates at liquid surfaces that have particular relevance to biological and environmental topics of current interest.; Vibrational sum-frequency spectroscopy is a recently developed technique that allows for the direct study of liquid interfaces. As a vibrational technique, it probes the molecular species at an interface. This technique is employed here to investigate surfactants, phospholipids, amino acids, and anesthetic at vapor/water and CCl₄/water interfaces.; The adsorption of dodecylsulfonate and dodecylbenzenesulfonate at organic/water and air/water interfaces are compared. The change in aromatic ring orientation as a function of surface concentration is quite different for the dodecylbenzenesulfonate at the two interfaces. The alkyl chains of the dodecylbenzenesulfonate are highly disordered at both interfaces in stark contrast to what is observed for the dodecylsulfonate.; The conformational order of phospholipid monolayers at an oil/water interface was determined. Halothane was introduced into the monolayers, and the resulting changes in acyl chain order examined. Both neutral (zwitterionic) and charged lipid monolayers were studied. Chain lengths of 14 and 16 carbons and four headgroups were studied (choline, ethanolamine, glycerol, and serine). Each monolayer exhibits significant disorder. The conformational order of each monolayer is perturbed after the introduction of halothane.; Monolayers of L-phenylalanine, L-lysine, L-leucine, L-isoleucine, L-methionine, L-tryptophan, L-threonine, L-tyrosine and L-mandelic acid adsorbed at the CCl₄/water interface are studied. Conformations for all, and orientational tilt angles for some, of the amino acids have been obtained. These results demonstrate the ability to monitor side chain orientation in complex molecules.; The orientation and conformation of phospholipid monolayers and the structure of water associated with these monolayers adsorbed at the vapor/water interface have been investigated. Comparisons are made between the monolayers based on chain length and headgroup differences.