Henley Alice, Diveky Matus E, Patel Anand M, Parkes Michael A, Anderson James C, Fielding Helen H
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
Phys Chem Chem Phys. 2017 Dec 6;19(47):31572-31580. doi: 10.1039/c7cp06950b.
The photocycle of photoactive yellow protein (PYP) begins with small-scale torsional motions of the chromophore leading to large-scale movements of the protein scaffold triggering a biological response. The role of single-bond torsional molecular motions of the chromophore in the initial steps of the PYP photocycle are not fully understood. Here, we employ anion photoelectron spectroscopy measurements and quantum chemistry calculations to investigate the electronic relaxation dynamics following photoexcitation of four model chromophores, para-coumaric acid, its methyl ester, and two analogues with aliphatic bridges hindering torsional motions around the single bonds adjacent to the alkene group. Following direct photoexcitation of S at 400 nm, we find that both single bond rotations play a role in steering the PYP chromophore through the S/S conical intersection but that rotation around the single bond between the alkene moiety and the phenoxide group is particularly important. Following photoexcitation of higher lying electronic states in the range 346-310 nm, we find that rotation around the single bond between the alkene and phenoxide groups also plays a key role in the electronic relaxation from higher lying states to the S state. These results have potential applications in tuning the photoresponse of photoactive proteins and materials with chromophores based on PYP.
光活性黄色蛋白（PYP）的光循环始于发色团的小规模扭转运动，进而引发蛋白支架的大规模运动，从而触发生物反应。发色团的单键扭转分子运动在PYP光循环初始步骤中的作用尚未完全明晰。在此，我们采用阴离子光电子能谱测量和量子化学计算，来研究四种模型发色团（对香豆酸、其甲酯以及两种带有脂肪族桥阻碍与烯烃基团相邻单键扭转运动的类似物）光激发后的电子弛豫动力学。在400 nm处对S进行直接光激发后，我们发现两个单键旋转在引导PYP发色团通过S/S锥形交叉点时均发挥作用，但烯烃部分与酚盐基团之间单键的旋转尤为重要。在346 - 310 nm范围内对较高能级电子态进行光激发后，我们发现烯烃与酚盐基团之间单键的旋转在从较高能级态到S态的电子弛豫过程中也起着关键作用。这些结果在调控基于PYP发色团的光活性蛋白和材料的光响应方面具有潜在应用。
