title: Spectral diffusion at the water/lipid interface revealed by two-dimensional fourth-order optical spectroscopy: a classical simulation study.
abstract: Using a classical simulation protocol for nonlinear optical signals, we predict the two-dimensional (2D) spectra of water near a monolayer of [1,2-dimytristoyl-sn-glycero-3-phosphatidylcholine] (DMPC) generated by three IR probe pulses followed by one visible probe pulse. Sum-frequency-generation 1D spectra show two peaks of the OH stretch representing two environments: near-bulk water nonadjacent to DMPC and top-layer water adjacent to DMPC. These peaks create a 2D pattern in the fourth-order signal. The asymmetric cross-peak pattern with respect to the diagonal line is a signature of coherence transfer from the higher- to the lower-frequency modes. The nodal lines in the imaginary part of the 2D spectrum show that the near-bulk water has fast spectral diffusion resembling that of bulk water despite the orientation by the strong electrostatic field of DMPC. The top-layer water has slower spectral diffusion.
authors.affiliation: Department of Chemistry, University of California, Irvine, California 92697, United States. nagatay@uci.edu
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nagata
authors.forename: Shaul
authors.initials: S
authors.lastname: Mukamel
mesh_terms: D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D008055:Lipids / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D013057:Spectrum Analysis / Q000379:methods; D014867:Water / Q000737:chemistry*
chemical_list: D008055:Lipids; D014867:Water; D004134:Dimyristoylphosphatidylcholine