亮氨酸与异亮氨酸的表面增强拉曼光谱

报道了在蛋白质氨基酸中唯一一对异构体氨基酸——亮氨酸和异亮氨酸的FT-拉曼光谱和在银胶基底上的表面增强拉曼光谱(SERS). 归属了各振动、增强峰位并分析了异构体氨基酸分子内不同振动模式引起的拉曼位移及其在不同pH值下SERS的变化. 分子内不同的振动模式主要源于异构体氨基酸中一个甲基和主链的不同连接次序, 表现在拉曼光谱; 亮氨酸的甲基摇摆ρ(CH₃)和非对称变形δ_as(CH₃)在962, 945, 924和1454, 1408 cm^－1; 异亮氨酸的ρ(CH₃), δ_as(CH₃)在922和1448, 1420, 1394 cm^－1. C—CO, C—C, H—O…H及骨架晶格振动峰位基本对应. 饱和液态的拉曼光谱和SERS中, 各基团振动峰位的差异表现得更为明显. 初步推测了这对氨基酸异构体在银表面吸附状态的模型.

Surface Enhanced Raman Spectroscopy of Leucine and Isoleucine

FT-Raman and surface enhanced Raman spectra (SERS) of leucine and isoleucine, the only isomer in proteinic amino acids, on the silver colloidal substrate are recorded. The vibrational and enhanced peaks are assigned; the Raman shifts that stem from different vibrational model in the molecular inner structure, and the variations of SERS at different pH values are analyzed. One methyl’s different connection to the main chains of the isomer amino acid resulted in different vibrational model in inner molecule, expressed in Raman spectra: ρ(CH₃) and δ_as(CH₃) of leucine are at 962, 945, 924 and 1454, 1408 cm^－1, by the comparation, isoleucine’s are at 922 and 1448, 1420, 1394 cm^－1. Vibrations involved in C—CO, C—C, H—O…H and lattice vibration mode are identical. In saturated solution’s Raman spectra and SERS, all the different shifts are expressed more clearly than those in solid state’s Raman spectra. The adsorption models of the isomer amino acid on the silver surface are speculated.