Analytical Applications of Nonlinear Infrared Spectroscopy

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This project by Professor John Wright of the University of Wisconsin is predicated on recent key experiments that have demonstrated that resonance with vibrational transitions can enhance the nuclear polarizability sufficiently to exceed the nonresonant electronic polarizability, and that mode coupling is sufficiently large that multiple resonances can multiplicatively enhance nonlinear optical processes. These experiments demonstrate the feasibility for a new family of multiresonant vibrationally enhanced nonlinear optical spectroscopies. These spectroscopies are analogous to 2-dimensional NMR methods and they are uniquely sensitive to intra- and intermolecular interactions. From a biological perspective, they can be considered as a two- color stain that allows visualization of molecular interactions and identification of the functionalities involved in the interaction. This analogy might become important in the future as the spatial imaging capabilities of the new technology are developed. The project seeks to apply these new approaches to central problems in biochemistry where interactions play a central role. There are many different molecular interactions but this proposal will focus on applying the new method to study of the spectral correlations that are induced by the hydrogen bonding in a biomolecule structure. The correlations will be evidenced both in the relative intensities of cross-peaks in the 2-D spectra, thus reflecting the interactions between the two resonances, and in the line position shifts in line-narrowed cross-peaks.At the molecular level, the structures of biomolecules depend to a large degree on the interactions known as hydrogen bonding. Although hydrogen bonding may be understood in relatively simple systems, the nature and extent of hydrogen bonding in a complex three-dimensional biomolecular structure is far more difficult to characterize. The spectroscopic experiments to be completed under the auspices of this project provide a sensitive and direct means to complete that characterization. With the role of hydrogen bonding better understood, complex biomolecular structures may be modeled and perhaps even predicted for synthetic analogs of natural molecules.