Parkes Michael A, Phillips Ciara, Porter Michael J, Fielding Helen H
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
Phys Chem Chem Phys. 2016 Apr 21;18(15):10329-36. doi: 10.1039/c6cp00565a. Epub 2016 Mar 30.
Understanding how the interactions between a chromophore and its surrounding protein control the function of a photoactive protein remains a challenge. Here, we present the results of photoelectron spectroscopy measurements and quantum chemistry calculations aimed at investigating how substitution at the coumaryl tail of the photoactive yellow protein chromophore controls competing relaxation pathways following photoexcitation of isolated chromophores in the gas phase with ultraviolet light in the range 350-315 nm. The photoelectron spectra are dominated by electrons resulting from direct detachment and fast detachment from the 2(1)ππ* state but also have a low electron kinetic energy component arising from autodetachment from lower lying electronically excited states or thermionic emission from the electronic ground state. We find that substituting the hydrogen atom of the carboxylic acid group with a methyl group lowers the threshold for electron detachment but has very little effect on the competition between the different relaxation pathways, whereas substituting with a thioester group raises the threshold for electron detachment and appears to 'turn off' the competing electron emission processes from lower lying electronically excited states. This has potential implications in terms of tuning the light-induced electron donor properties of photoactive yellow protein.
理解发色团与其周围蛋白质之间的相互作用如何控制光活性蛋白的功能仍然是一个挑战。在此，我们展示了光电子能谱测量和量子化学计算的结果，旨在研究在气相中用350 - 315 nm范围内的紫外光对光活性黄色蛋白发色团的香豆酰尾部进行取代时，如何控制孤立发色团光激发后的竞争弛豫途径。光电子能谱主要由直接离解和从2(1)ππ*态快速离解产生的电子主导，但也有一个低电子动能成分，它源于较低电子激发态的自离解或电子基态的热电子发射。我们发现，用甲基取代羧酸基团的氢原子会降低电子离解的阈值，但对不同弛豫途径之间的竞争影响很小，而用硫酯基团取代则会提高电子离解的阈值，并且似乎“关闭”了来自较低电子激发态的竞争电子发射过程。这在调节光活性黄色蛋白的光诱导电子供体性质方面具有潜在意义。
