Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, IL 60637, USA.
Proc Natl Acad Sci U S A. 2011 Dec 27;108(52):20908-12. doi: 10.1073/pnas.1105234108. Epub 2011 Dec 13.
The photosynthetic light-harvesting apparatus moves energy from absorbed photons to the reaction center with remarkable quantum efficiency. Recently, long-lived quantum coherence has been proposed to influence efficiency and robustness of photosynthetic energy transfer in light-harvesting antennae. The quantum aspect of these dynamics has generated great interest both because of the possibility for efficient long-range energy transfer and because biology is typically considered to operate entirely in the classical regime. Yet, experiments to date show only that coherence persists long enough that it can influence dynamics, but they have not directly shown that coherence does influence energy transfer. Here, we provide experimental evidence that interaction between the bacteriochlorophyll chromophores and the protein environment surrounding them not only prolongs quantum coherence, but also spawns reversible, oscillatory energy transfer among excited states. Using two-dimensional electronic spectroscopy, we observe oscillatory excited-state populations demonstrating that quantum transport of energy occurs in biological systems. The observed population oscillation suggests that these light-harvesting antennae trade energy reversibly between the protein and the chromophores. Resolving design principles evident in this biological antenna could provide inspiration for new solar energy applications.
光合作用的光捕获装置以显著的量子效率将能量从吸收的光子转移到反应中心。最近，长寿命量子相干被提议影响光捕获天线中光合作用能量转移的效率和鲁棒性。由于可能进行有效的长程能量转移，并且生物学通常被认为完全在经典范围内运行，这些动力学的量子方面引起了极大的兴趣。然而，迄今为止的实验仅表明相干持续的时间足够长，以至于可以影响动力学，但它们并没有直接表明相干确实会影响能量转移。在这里，我们提供了实验证据，证明细菌叶绿素发色团与周围蛋白质环境之间的相互作用不仅延长了量子相干，而且还在激发态之间引发了可逆的、振荡的能量转移。使用二维电子光谱学，我们观察到振荡的激发态种群，证明能量在生物系统中进行量子输运。观察到的种群振荡表明，这些光捕获天线在蛋白质和发色团之间可逆地交换能量。解析这种生物天线中明显的设计原则可能为新的太阳能应用提供灵感。
