Molecular Orientation Analysis of Alkyl Methylene Groups from Quantitative Coherent Anti-Stokes Raman Scattering Spectroscopy.
Quantitative data analysis in coherent anti-Stokes Raman scattering (CARS) spectroscopy is important for extracting molecular structural information. We developed a method to derive molecular tilt angle with respect to the surface normal based on quantitative CARS spectral analysis. We showed that the tilt angle of methylene alkyl chains on a surface can be directly obtained from the CH2 symmetric/asymmetric peak ratio in a CARS spectrum. The lipid alkyl chain tilt angle from a lipid monolayer was measured to be ∼0° and was verified by sum frequency generation spectroscopy, which probes the orientations of the lipid methyl end groups. The tilt angle of a silane monolayer alkyl chain was derived to be ∼35°, which agrees with the theoretical prediction. This method is submonolayer sensitive and can also be used to interpret polarization-dependent signals in CARS microscopy. It can be applied to elucidate detailed molecular structure from CARS spectroscopic and microscopic measurements.
†Department of Chemistry, and ‡Department of Biophysics, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
Chi
C
Zhang
†Department of Chemistry, and ‡Department of Biophysics, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
Jie
J
Wang
†Department of Chemistry, and ‡Department of Biophysics, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
Joshua
J
Jasensky
†Department of Chemistry, and ‡Department of Biophysics, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States.
Zhan
Z
Chen
D008051:Lipid Bilayers / Q000737:chemistry; D008752:Methylene Chloride / Q000737:chemistry*; D008968:Molecular Conformation; D013059:Spectrum Analysis, Raman / Q000379:methods*
D008051:Lipid Bilayers; D008752:Methylene Chloride
CARS; bond additivity; polarization; self-assembled monolayer; tilt angle