Spin Coherences in Photosystem I Reaction Center Proteins and Model Systems

生命过程化学（CLP）项目的这一奖项支持西北大学的Michael R. Wasielewski教授对绿色植物中关键光转导蛋白之一的光系统I （PSI）反应中心（RC）中光诱导电荷分离的多种途径的本质进行基础研究，该中心负责提供将二氧化碳还原为碳水化合物所需的化学势。含氧生物中的PSI RC是独特的，因为它是唯一有证据表明两组冗余辅因子参与电子传递的RC。PSI RC蛋白中的电子转移辅因子排列在A和B两个对称通路上，导致电荷传输到一个共同的电子受体，这表明PSI蛋白可能具有干涉仪的功能，其中穿越这两个通路的电子处于量子叠加态。该项目将解决关于量子叠加在PSI功能中的作用的两个关键问题：1)PSI内的电荷传输是否涉及使用A和B途径的独立自旋相干自由基离子对，或者同时涉及两种途径的量子叠加态？2)双通道电荷分离的固有量子相干性是否感知和控制PSI RC中过量激发能量耗散？时间分辨电子顺磁共振波谱将用于探测这些机制，而理论和合成供体-受体系统将用于模拟这种行为。了解光合生物体内多余的能量耗散对于确保自然界光合能量转导的可行性和可持续性至关重要，这是地球上生命所必需的过程。提高对这一过程的认识，为设计用于太阳能转换的人工光合系统提供了重要的概念基础。这项研究的结果将通过西北大学资助的西北大学可持续发展和能源倡议（ISEN）的广泛外联网络向公众传播。

This award in the Chemistry of Life Processes (CLP) program supports work by Professor Michael R. Wasielewski at Northwestern University to carry out fundamental studies on the nature of multiple pathways for light-induced charge separation in one of the key light transduction proteins in green plants, the Photosystem I (PSI) reaction center (RC), which is responsible for providing the chemical potential necessary to reduce carbon dioxide to carbohydrates. The PSI RC in oxygenic organisms is unique because it is the only RC for which there is evidence that both sets of redundant cofactors engage in electron transport. The electron transfer cofactors in the PSI RC protein are arranged in two symmetric pathways, A and B, which results in charge transport to a common electron acceptor, and suggests the possibility that the PSI protein may function as an interferometer in which electrons traversing the two pathways are in a quantum superposition state. This project will address two key questions regarding the role of quantum superposition in PSI function: 1) Does charge transport within PSI involve independent spin-coherent radical ion pairs using either the A and B pathways or a quantum superposition state involving both pathways simultaneously? 2) Does the inherent quantum coherent nature of the dual-pathway charge separation sense and control excess excitation energy dissipation in the PSI RC? Time-resolved electron paramagnetic resonance spectroscopy will be used to probe these mechanisms, while theory and synthetic donor-acceptor systems will be used to model this behavior.Understanding excess energy dissipation in photosynthetic organisms is critical to ensuring the viability and sustainability of photosynthetic energy transduction in nature, a process essential to life on Earth. Improved knowledge of this process provides an important conceptual basis for the design of artificial photosynthetic systems for solar energy conversion. The results of this research will be communicated to the public through the extensive outreach network of the Northwestern-funded Initiative for Sustainability and Energy at Northwestern (ISEN).