The role of the local environment in ultrafast non-adiabatic dynamics: primary events in the photocycle of the yellow protein

在这个项目中，理论-包括电子结构和动力学计算，以及理论公式和建模-将与飞秒时间分辨实验相结合，以在分子水平上理解光活性黄色蛋白（PYP）的初始光事件。我们关注的是在光循环中观察到的最早的事件（~700秒），这些事件被认为涉及对羟基肉桂基阴离子发色团中乙烯双键的部分反式到顺式异构化，以及发色团与蛋白质结合的硫酯键的扭曲运动。动力学强烈依赖于蛋白质环境的局部约束（主要是由于静电效应和氢键）：事实上，在溶液中，变性PYP或稍微改变的发色团的动力学要慢得多（10 ps）。我们的理论分析将基于发色团的电子结构计算和非绝热超快动力学分析，这可能与圆锥相交的存在有关。该理论将通过先前对天然蛋白质的实验以及在溶液和修饰纳米空间环境中对PYP发色团的新实验研究来提供信息。将特别强调提取关键的微观特征，这些特征使这些事件对当地环境如此敏感，非常重要的是，这些特征可以更普遍地适用于其他生物光系统。事实上，相关问题在广泛的生物相关光物理过程中具有重要意义，特别是视觉视紫红质和细菌视紫红质的光循环。该项目的一个重要方面是必要的理论框架的发展，以描述和计算，强耦合量子发色团/环境超分子系统的动力学。这将需要来自法国和德国团队在理论方面（气相动力学理论，凝聚相反应理论）的专业知识的强烈互动组合。

In this project, theory - including electronic structure and dynamical calculations, as well as theory formulation and modelling - will be combined with femtosecond time-resolved experiments to understand the initial photoevents for the photoactive yellow protein (PYP) at the molecular level. We focus on the very earliest events observed in the photocycle (~700 fs) that are believed to involve a partial trans-to-cis isomerization of the ethylenic double bond in the p-hydroxycinnamyl anion chromophore, along with a twisting motion of the thioester linkage by which the chromophore is bound to the protein. The dynamics is strongly dependent on the local constraints of the protein environment (primarily due to electrostatic effects and hydrogen bonding): in fact, the dynamics of either the denatured PYP or a slightly altered chromophore in solution is much slower (10 ps). Our theoretical analysis will be based on electronic structure calculations for the chromophore, and analysis of the non-adiabatic ultrafast dynamics which is presumably related to the presence of a conical intersection. The theory will be informed by previous experiments on the native protein and new experimental investigations of the PYP chromophore in solution and in modified nanospace environments. Special emphasis will be placed on extracting the key microscopic features which make these events so sensitive to the local environment and -- very importantly -- which could be more generally applicable to other biological photosystems. Indeed, related questions are of importance in a wide range of biologically relevant photophysical processes, in particular the photocycles of visual rhodopsin and bacteriorhodopsin. An essential aspect of the project is the necessary development of a theoretical framework to describe, and to calculate, the dynamics of the strongly coupled quantum chromophore/environment supermolecular system. This will require a strongly interacting combination of expertises on the theory side (gas phase dynamical theory, condensed phase reaction theory) from the French and German teams involved in this project.