Loppnow G R, Mathies R A
Department of Chemistry, University of California, Berkeley 94720.
Biophys J. 1988 Jul;54(1):35-43. doi: 10.1016/S0006-3495(88)82928-X.
Resonance Raman excitation profiles have been measured for the bovine visual pigment rhodopsin using excitation wavelengths ranging from 457.9 to 647.1 nm. A complete Franck-Condon analysis of the absorption spectrum and resonance Raman excitation profiles has been performed using an excited-state, time-dependent wavepacket propagation technique. This has enabled us to determine the change in geometry upon electronic excitation of rhodopsin's 11-cis-retinal protonated Schiff base chromophore along 25 normal coordinates. Intense low-frequency Raman lines are observed at 98, 135, 249, 336, and 461 cm-1 whose intensities provide quantitative, mode-specific information about the excited-state torsional deformations that lead to isomerization. The dominant contribution to the width of the absorption band in rhodopsin results from Franck-Condon progressions in the 1,549 cm-1 ethylenic normal mode. The lack of vibronic structure in the absorption spectrum is shown to be caused by extensive progressions in low-frequency torsional modes and a large homogeneous linewidth (170 cm-1 half-width) together with thermal population of low-frequency modes and inhomogeneous site distribution effects. The resonance Raman cross-sections of rhodopsin are unusually weak because the excited-state wavepacket moves rapidly (approximately 35 fs) and permanently away from the Franck-Condon geometry along skeletal stretching and torsional coordinates.
利用457.9至647.1 nm范围内的激发波长，测量了牛视觉色素视紫红质的共振拉曼激发谱。使用激发态含时波包传播技术，对吸收光谱和共振拉曼激发谱进行了完整的弗兰克-康登分析。这使我们能够确定视紫红质的11-顺式视黄醛质子化席夫碱发色团在电子激发时沿25个正则坐标的几何结构变化。在98、135、249、336和461 cm-1处观察到强烈的低频拉曼线，其强度提供了有关导致异构化的激发态扭转变形的定量、模式特异性信息。视紫红质吸收带宽度的主要贡献来自1549 cm-1乙烯正则模式下的弗兰克-康登进展。吸收光谱中缺乏振动结构表明是由低频扭转模式的广泛进展、较大的均匀线宽（半高宽170 cm-1）以及低频模式的热占据和非均匀位点分布效应共同导致的。视紫红质的共振拉曼截面异常微弱，因为激发态波包沿着骨架拉伸和扭转坐标迅速（约35 fs）且永久地远离弗兰克-康登几何结构。
