科研之友
微信
新浪微博
Facebook
分享链接
摘要
The aromatic amino acid tryptophan plays an important role in protein electron-transfer and in catalysis. Tryptophan is also used LIS a probe of its local protein environment and of dynamic changes in this environment. Raman spectroscopy of tryptophan has been an important tool to monitor tryptophan, its radicals, and its protein environment. The proper interpretation of the Raman spectra requires not only the correct assignment of Raman bands to vibrational normal modes hut also the correct identification of the Raman hands in the spectrum. A significant amount or experimental and computational work has been devoted to this problem, hut inconsistencies still persist. In this work. the Raman spectra of indole, 3-methylindole (3MI) tryptophan, and several of their isotopomers have been measured to determine the isotope shifts of the Raman bands. Density functional theory calculations with the B3LYP, functional and the 6-3H+g(d.p)basis set have been performed on indole, 3MI, 3-ethylindole (3EI), and several of their isotopomers in predict isotope shifts of the vibrational normal modes. Comparison of the observed and predicted isotope shifts results in a consistent assignment of Raman bands to vibrational normal modes that can he used for both assignment and identification of the Raman bands. For correct assignments, it is important to determine force held scaling factors for each molecule separately. and scaling factors of 0.9824, 0.9843. and 0.9857 are determined for indole. 3MI. and 3EI, respectively. It IS also important to use more than one parameter to assign vibrational normal modes to Raman bands, for example, the inclusion of isotope shifts other than those obtained from H/D-exchange. Finally, the results indicate that the Fermi doublet of indole may consist of just two fundamentals. whereas one fundamental and one combination band are identified for the Fermi resonance that gives rise to the doublet in 3MI and tryptophan.
- 出版日期2010-10-14
