Salting Effects Of Langmuir Monolayer And Interfacial Proteins Investigated By Nonlinear Vibrational Ectroscopies

Specific ion effects exist everywhere because of their prevalent presence in nature and human bodies. It has been recognized that the ions play a crucial role in mediation of the interfacial molecular structures on catalysts, metals, cell membranes. The ion effects on diverse systems have been extensively investigated by experimental and theoretical tech-niques since German scientist Franz Hofmeister discovered that the effects of different ions follow the Hofmeister series.In the past decades, sum frequency generation vibrational spectroscopy (SFG-VS) has been developed into a powerful and versatile technique to study interfacial molecu-lar structures and dynamics at the molecular level in situ in different chemical environ-ments. Recently, our group has developed a compatible multiple nonlinear vibrational spectroscopy system that can be used for recording SFG and infrared-infrared-visible three-pump-field four-wave-mixing (IIV-TPF-FWM) vibrational spectra of the same samples by using the same experimental geometry(the same input laser beams, the same detection lines, monochromator and photomultiplier tube, the same experimental parameters and without removing/adding any optics).In this dissertation, SFG-VS and IIV-TPF-FWM has been applied, supplemented by surface pressure (Ï€)-area (A) isotherms measurements, UV-Vis absorbance spectroscopy, and Brewster angle microscopy images, to investigate the assembly of Langmuir mono-layer, the interaction between peptide and lipid bilayer in different pH and ionic solution environments. Detailed molecular structures has been achieved, which will aid in recog-nizing the nature of driving force and weak molecular interaction in pH and ionic environ-ments, and providing important clues to control interfacial processes in a desired manner. The organization of the dissertation is as follows.In Chapter1, the recent researches on the interfacial salting effects are reviewed.Chapter2introduces the principles of sum frequency generation vibrational spec-troscopy and procedures of orientational analysis, as well as its applications in the study of interfacial proteins.Chapter3studies the interaction between a modeling peptide(mastoparan:MP) and cell membranes in ionic environments. The action mechanism and driving forces in the interaction are elucidated. Chapter4investigates the PARC18monolayer at air/solution interface. The structural transition mechanism and self-assembly aggregation model are elucidated. The reaction kinetics is also investigated.Chapter5introduces the newly developed IIV-TPF-FWM technique based on the Ek-spla commercial SFG laser system, as well as its applications.