Development of instramentation of vibrational circular dichroism by Fourier transform spectroscopy and conformational studies of biopolymers

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Fourier transform infrared circular dichroism spectrophotometer was developed for investigating the secondary structures of biopolymers such as proteins and nucleic acids. The system was constructed using a Michelson interferometer (JASCO IRF-10 Interferometer), incorporatin, IRCD optical unit which consists of polarization modulation system and an MCF infrared detector, and the electronic unit which processes the interferogram associated with CD signal in addition to the ordinary absorption interferogram. Circular polarization modulation was achieved by a combination of a wire grid polarizer and a photoelastic modulator (PEM) made of ZnSe. The instrument is able to measure the wavenumber region from 2200 to 800 cm^<-1> with the sensitivity DELTA A=10^<-6> OD. VCD of N-acetyl N'-methylamides of several aminoacids (Ac-Ala-NHMe, Ac-Val-NHMe, Ac-Leu-NHMe, Ac-Phe-NHMe, and Ac-Pro-NHMe) were measured and analyzed in relation to the molecular conformations. It was found that the VCD of the NH stretching vibration (amide A band) depends on not only the local conformation of oligopeptides but also the intermolecular association by intermolucular hydrogen bond. VCD of tripeptides containing proline residue (Ac-Pro-Gly-NHMe and PivPro-GIY-NHMe) was studied as a model of beta -tum structure. The results were applied to the analysis of structural change in valinomycine on complexation with metal cation.