Tallent J R, Stuart J A, Song Q W, Schmidt E J, Martin C H, Birge R R
Department of Chemistry and W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100 USA.
Biophys J. 1998 Oct;75(4):1619-34. doi: 10.1016/S0006-3495(98)77605-2.
The preparation and photochemical properties of dried deionized blue membrane (dIbR600; lambdamax approximately 600 nm, epsilon approximately 54, 760 cm-1 M-1, f approximately 1.1) in polyvinyl alcohol films are studied. Reversible photoconversion from dIbR600 to the pink membrane (dIbR485; lambdamax approximately 485 nm) is shown to occur in these films under conditions of strong 647-nm laser irradiation. The pink membrane analog, dIbR485, has a molar extinction coefficient of approximately 39,000 cm-1 M-1 (f approximately 1.2). The ratio of pink --> blue and blue --> pink quantum efficiencies is 33 +/- 5. We observe an additional blue-shifted species (dIbR455, lambdamax approximately 455 nm) with a very low oscillator strength (f approximately 0.6, epsilon approximately 26,000 cm-1 M-1). This species is the product of fast thermal decay of dIbR485. Molecular modeling indicates that charge/charge and charge/dipole interactions introduced by the protonation of ASP85 are responsible for lowering the excited-state all-trans --> 9-cis barrier to approximately 6 kcal mol-1 while increasing the corresponding all-trans --> 13-cis barrier to approximately 4 kcal mol-1. Photochemical formation of both 9-cis and 13-cis photoproducts are now competitive, as is observed experimentally. We suggest that dIbR455 may be a 9-cis, 10-s-distorted species that partially divides the chromophore into two localized conjugated segments with a concomitant blue shift and decreased oscillator strength of the lambdamax absorption band.
研究了聚乙烯醇薄膜中干燥去离子化蓝色膜（dIbR600；最大吸收波长约600 nm，ε约54760 cm⁻¹ M⁻¹，f约1.1）的制备及其光化学性质。研究表明，在647 nm强激光照射条件下，这些薄膜中会发生从dIbR600到粉红色膜（dIbR485；最大吸收波长约485 nm）的可逆光转换。粉红色膜类似物dIbR485的摩尔消光系数约为39000 cm⁻¹ M⁻¹（f约1.2）。粉红色→蓝色和蓝色→粉红色的量子效率之比为33±5。我们观察到另一种蓝移物种（dIbR455，最大吸收波长约455 nm），其振子强度非常低（f约0.6，ε约26000 cm⁻¹ M⁻¹）。该物种是dIbR485快速热衰变的产物。分子模型表明，ASP85质子化引入的电荷/电荷和电荷/偶极相互作用，负责将激发态全反式→9-顺式势垒降低至约6 kcal mol⁻¹，同时将相应的全反式→13-顺式势垒提高至约4 kcal mol⁻¹。如实验观察到的，9-顺式和13-顺式光产物的光化学形成现在具有竞争性。我们认为dIbR455可能是一种9-顺式、10-s-扭曲的物种，它将发色团部分地分成两个局部共轭片段，同时伴随蓝移和最大吸收带振子强度的降低。
