Shim Sangdeok, Dasgupta Jyotishman, Mathies Richard A
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Am Chem Soc. 2009 Jun 10;131(22):7592-7. doi: 10.1021/ja809137x.
Light-activated proton translocation in halobacteria is driven by photoisomerization of the retinal chromophore within the membrane-bound protein bacteriorhodopsin. The molecular mechanism of this process has been widely debated due to the absence of structural information on the time scale of the reactive dynamics (the initial 0.1-1 ps). Here we use tunable femtosecond stimulated Raman spectroscopy to obtain time-resolved resonance Raman vibrational spectra of bacteriorhodopsin's key J and K photoisomerization intermediates. The appearance of the J state is delayed by approximately 150 fs relative to the zero of time and rises after this dwell with a 450 fs time constant. The J state is characterized by a 16 cm(-1) red-shifted C=C stretch, which blue shifts by 5 cm(-1) coincident with the rise of the K state. The delayed 3 ps rise of the C(15)-H HOOP mode with enhanced intensity in K reveals the appearance of strain near the Schiff's base once the 13-cis configuration is fully formed. The delay in the initial appearance of J is assigned to nuclear dynamics on the excited state that precede the formation of the proper geometry for reactive internal conversion.
嗜盐菌中光激活的质子转运是由膜结合蛋白细菌视紫红质内视黄醛发色团的光异构化驱动的。由于缺乏反应动力学时间尺度（最初的0.1 - 1皮秒）上的结构信息，这一过程的分子机制一直存在广泛争议。在此，我们使用可调谐飞秒受激拉曼光谱来获取细菌视紫红质关键的J和K光异构化中间体的时间分辨共振拉曼振动光谱。相对于时间零点，J态的出现延迟约150飞秒，并在此停留后以450飞秒的时间常数上升。J态的特征是C = C伸缩振动红移16厘米⁻¹，随着K态的上升蓝移5厘米⁻¹。在K态中强度增强的C(15)-H HOOP模式延迟3皮秒上升，这表明一旦13 - 顺式构型完全形成，席夫碱附近就会出现应变。J态初始出现的延迟归因于激发态上的核动力学，这发生在反应性内转换的适当几何构型形成之前。
