Author : Yi Liu
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (94 download)
Book Synopsis Vibrational Sum Frequency Spectroscopy of Osmolytes and Ions at Aqueous Interface by : Yi Liu
Download or read book Vibrational Sum Frequency Spectroscopy of Osmolytes and Ions at Aqueous Interface written by Yi Liu and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Surfaces/interfaces are omnipresent in nature, ranging from physics and chemistry to biology and material sciences. To characterize the interfacial structures and understand the surface phenomena, many useful tools have been developed. Vibrational sum frequency generation (VSFG) spectroscopy has proven to be a powerful second-order non-linear optical technique for this purpose and is gaining more and more attention nowadays. With VSFG, two pulsed laser beams, one at infrared frequency and one at visible frequency, are incident on the surface and generate a new beam with a frequency equal to the sum of the IR and visible frequencies. When the IR frequency matches a surface vibrational mode frequency, this process would be resonantly enhanced. In this dissertation, this surface-sensitive technique was adopted to investigate several interfaces with special relevance to biology. The first topic of interest is the unusual orientation of a strong protein stabilizer, trimethylamine N-oxide (TMAO), at two aqueous/hydrophobic interfaces (air/water interface and OTS/water interface). By interpretation of the relative phase of VSFG spectra coupled with a numerical algorithm, the maximum entropy method (MEM) anaylysis of the molecular orientation, it is found that the methyl groups of TMAO prefer to point into the aqueous medium, while the oxide moieties (N+-O-) orient towards the hydrophobic air or OTS. This unusual orientation may be attributed to the more hydrophilic nature of methyl groups that is attached to a strong electron withdrawing atom such as a quaternary nitrogen. These results could help elucidate the stabilizing effect of TMAO on proteins the increased need to keep the methyl group hydrated would cause them to be excluded from protein interface and thereby lead to protein stabilization.The other major issue focused in this dissertation is based on the ion specific interactions at a charged interface, which plays a decisive role in various physico-chemical and biological processes. Binding affinity of different cations to monolayers of amphiphilic molecules (e.g. fatty acids, phospholipids) at the air/aqueous surfactant interfaces, may provide molecular level clues on various functions of cell membranes that are resembled by these amphiphilic molecules. Specifically, the binding events of several alkali cations to the hydrophilic carboxylate headgroups of long chain fatty acid, inferred from interfacial water structures, are thoroughly investigated by VSFG measurement. Results show that Li+ binds strongest to the negatively charged carboxylate groups, followed by Na+, then K+ although the difference is slight. The ranking of the alkali metal cations' binding abilities differs from the sequence predicted by the law of match water affinities (LMWA) and also varies with different headgroups in the model system, which may suggest the distinct solvation behaviors of these ions. Such findings should help to elucidate the molecular-level binding behavior to proteins in aqueous solutions.
