| 概 要 |
In this talk we provide a survey of our recent studies, by means of nonlinear two-dimensional infrared spectroscopy (2DIR), of structural and dynamical properties of molecular systems of different nature and complexity. On one side, strongly hydrogen bonded molecular liquids like formamide and formic acid molecular liquids have been examined.
Partially ordered, organized molecular systems like phospholipid bilayer were also considered. In both cases, the carbonyl moieties are the convenient indicators of the local architecture and dynamics; Molecular Dynamics (MD) computer simulations represent a fundamental support to the interpretation of the experimental data for the two classes of systems.
In the two hydrogen bonded liquids, broadband and narrowband excitation experiments provide information (also with the help of isotopic substitution) on the structural arrangement of the neighboring molecules and on the energy flow in these largely interconnected molecular systems; the caracteristic dephasing and correlation times are also extracted. The fundamental role of the strong inter-molecular coupling, leading to largely delocalized vibrational excitations, is pointed out.
In phospholipid membranes, 2DIR technique represents a valuable tool for understanding their complex structural details and the relation to their functional properties. Namely, molecular biology and biochemistry at the membrane polar interface can be conveniently investigated by means of non-linear IR spectroscopy of the carbonyl moiety in such systems. We investigated that nature of the infrared response of C=O groups of a single component membrane, such as DMPC, and of a binary SPM/PLPC membranes. We employed 2DIR spectroscopy to probe molecular arrangement, possible ordering, and dynamics of carbonyls in hydrated bilayers. With the help of calculated two-dimensional spectra and of the results of extensive MD simulations quantitative estimates for some structural and dynamical parameters are provided.
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