Anabaena Sensory Rhodopsin: A biological model system to decipher the quantum mechanics of photochemical reactions through conical intersections

视网膜的超快光诱导异构化，以其希夫碱形式存在于光活性蛋白（视紫红质）中，是自然界中最重要的光反应之一，因为它使高等和低级生物能够将光子转化为化学能。尽管对其进行了持续而深入的研究，但对其反应机制和蛋白质环境对其的作用仅了解部分。一个主要的未解之谜是观察到的视觉和微生物视网膜蛋白的反应的效率和时间常数的巨大差异。在本项目中，我们将利用新的超快相干非线性光谱结合量子力学计算，研究紫红藻（Anabaena Sensory Rhodopsin， ASR）中视网膜的光物理和化学性质。ASR为澄清这一难题提供了理想的实验和理论测试基础，因为可以在相同的蛋白质环境中比较两种生物活性视网膜结构（顺式和反式）的光动力学。我们将专注于光反应过程中电子动力学和振动动力学之间相互作用的实验和理论结合研究。为此，我们将开发和应用基于时间分辨振动相干光谱和二维电子光谱的最先进的超快光谱。由于这些方法对不同的分子自由度高度敏感，它们将允许在ASR的非绝热光异构化过程中完整地映射种群和相干（电子和振动）的演变。基于创新的激发态轨迹计算的量子化学模拟将被开发并应用于定量理解分子反应，包括识别有助于反应坐标的振动模式和控制反应产率的机制。

The ultrafast photo-induced isomerization of retinal, present in its Schiff base form in photoactive proteins (rhodopsins), is among the most important photo-reactions in Nature as it enables higher and lower living organisms to transform photons into chemical energy. In spite of a sustained and intensive research, only a partial understanding of the reaction mechanism and the role of the protein environment to it are available. One of the major open puzzles is the dramatic differences in the efficiency and time constants of the reaction observed for visual and microbial retinal proteins. In this project, we will investigate the retinal's photophysics and -chemistry in Anabaena Sensory Rhodopsin (ASR) by exploiting new ultrafast coherent non-linear spectroscopy combined with quantum mechanical calculations. ASR offers the ideal experimental and theoretical test ground to clarify this puzzle, since it is possible to compare the photodynamics of two biologically active retinal configurations, cis and trans, within the same protein surroundings. We will focus on a combined experimental and theoretical investigation of the interplay between electronic and vibrational dynamics along the photoreaction. To that end, we will develop and apply state-of-the-art ultrafast spectroscopies based on time-resolved Vibrational Coherence Spectroscopy and 2D Electronic Spectroscopy. Since these methods are highly sensitive to different molecular degrees of freedom, they will allow a complete mapping of the evolution of populations and coherences (electronic and vibrational) during the non-adiabatic photoisomerization of ASR. Quantum chemical simulations based on innovative excited state trajectory computations will be developed and applied to quantitatively understand the molecular reaction, including the identification of the vibrational modes contributing to the reaction coordinate and the mechanisms that control the reaction yields.