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

为了研究蛋白质和核酸等生物大分子的二级结构，研制了傅里叶变换红外圆二色光谱仪。该系统由迈克尔逊干涉仪(JASCO IRF-10干涉仪)、INCORPORATION、IRCD光学单元(由偏振调制系统和MCF红外探测器组成)和电子单元组成，该单元除了处理普通的吸收干涉图外，还处理与CD信号相关的干涉图。圆偏振调制是由线栅偏振器和由硫化锌制成的光弹调制器(PEM)相结合实现的。该仪器能够测量2200~800 cm的波数范围，灵敏度为Delta A=10~(-6)OD。测定和分析了几种氨基酸(Ac-Ala-NHMe、Ac-Val-NHMe、Ac-Leu-NHMe、Ac-Phe-NHMe和Ac-Pro-NHMe)的N-乙酰-N‘-甲胺的VCD与分子构象的关系。发现NH伸缩振动(酰胺A带)的VCD不仅取决于寡肽的局部构象，还取决于分子间氢键的分子间缔合。以含Pro残基的三肽(Ac-Pro-Gly-NHMe和PivPro-GIY-NHMe)为模型进行了VCD研究。该结果被应用于分析呋喃霉素与金属阳离子络合时的结构变化。

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.