title: Sum Frequency Generation of Interfacial Lipid Monolayers Shows Polarization Dependence on Experimental Geometries.
abstract: Sum frequency generation (SFG) vibrational spectroscopy has been widely employed to investigate molecular structures of biological surfaces and interfaces including model cell membranes. A variety of lipid monolayers or bilayers serving as model cell membranes and their interactions with many different molecules have been extensively studied using SFG. Here, we conducted an in-depth investigation on polarization-dependent SFG signals collected from interfacial lipid monolayers using different experimental geometries, i.e., the prism geometry (total internal reflection) and the window geometry (external reflection). The different SFG spectral features of interfacial lipid monolayers detected using different experimental geometries are due to the interplay between the varied Fresnel coefficients and second-order nonlinear susceptibility tensor terms of different vibrational modes (i.e., ss and as modes of methyl groups), which were analyzed in detail in this study. Therefore, understanding the interplay between the interfacial Fresnel coefficients and χ((2)) tensors is a prerequisite for correctly understanding the SFG spectral features with respect to different experimental geometries. More importantly, the derived information in this paper should not be limited to the methyl groups with a C3v symmetry; valid extension to interfacial functional groups with different molecular symmetries and even chiral interfaces could be expected.
authors.affiliation: State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China.
authors.forename: Bolin
authors.initials: B
authors.lastname: Li
authors.affiliation: State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Li
authors.affiliation: State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China.
authors.forename: Yong-Hao
authors.initials: YH
authors.lastname: Ma
authors.affiliation: State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Han
authors.affiliation: State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China.
authors.forename: Fu-Gen
authors.initials: FG
authors.lastname: Wu
authors.affiliation: Department of Geriatrics, Second Affiliated Hospital of Nanjing Medical University , Nanjing 210029, P. R. China.
authors.forename: Zhirui
authors.initials: Z
authors.lastname: Guo
authors.affiliation: Department of Chemistry, University of Michigan , 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
authors.forename: Zhan
authors.initials: Z
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University , Nanjing 210096, China.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Lu