VIBRATIONAL OPTICAL ACTIVITY IN PEPTIDE MOLECULES

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Vibrational optical activity, comprised of vibrational circular dichroism (VCD) and Raman optical activity (ROA), will be further developed and applied to stereochemical aspects of peptide molecules. The research will make use of a recently constructed diode-array ROA spectrograph, a high-resolution Fourier transform infrared (FTIR) spectrometer equipped for VCD measurement, a dispersive, grating VCD instrument and a dispersive Raman spectrometer for survey spectra. For improved efficiency the ROA spectrograph will be configured as a stand-alone instrument with its own laser and optical surface. The amino acids, peptides, polypeptides, model compounds and derivatives will be studied as functions of solvent, pH(pD), transition metal complexation and isotopic substitution. The ROA work will follow fruitful areas of VCD investigation and survey representative molecular classes. The focus of VCD work will be to determine the extent of sensitivity of VCD in peptide molecules to secondary structure via subunit coupling and intramolecular hydrogen bonding an to rotameric side-chain distributions about the CAlpha-CBeta bond. Spectral interpretation will involve vibrational normal coordinate analysis for the simpler amino acids beyond alanine, model peptides and relevant molecular fragments. New methods of VCD and ROA intensity calculations will be carried out to compare with experiment. Recently formulated a-diabatic, non-Born-Oppenheimer expressions for vibrationally induced electronic current density will be applied to intramolecular hydrogen bonding in amino acids and peptides to test for suspected magnetic ring currents that produce large, monosignate VCD intensity in these molecules. The long range goal of this research is to describe the conformational and self-associative features of bioactive peptides that have specific biological, neurological and pharmacological relevance, such as the simple hormonal peptides, carnosine and melanostatin and the enkephalin neuropeptides. A more general goal is to further develop VCD and ROA as stereochemical probes of conformation, vibrational motion, and electronic charge and current distributions for all classes of chiral biological molecules.