据美国物理学家组织网报道，美国研究人员日前开发出一种探测植物光合作用过程的新方法。该技术有助于加深人们对光合作用这一利用太阳能最有效的方式的理解，改进现有太阳能电池的设计，提高其转换效率。相关论文发表在美国物理学学会期刊《化学物理学期刊》（Journal of Chemical Physics）上。
植物和其他光合生物之所以能够吸收太阳能并将其转化为能量，都是由于它们拥有的一种独特的天线蛋白。这种蛋白由多种吸光色素组成，能够捕获太阳能并通过一系列的化学反应将其储存起来。由于反应发生在一个极小的尺度上，天线蛋白之间会出现量子现象。当色素分子吸收光线时就会被激活成高能态，如果一个蛋白上的多种色素分子同时被激发就会出现量子叠加状态，这种量子效应会使光合作用中产生的能量找到“最优路径”，以近乎无损的方式进行传递，这也是光合作用在转换效率上如此高效的“秘密”所在。
实验室中再现光合作用“最优路径”
负责该项研究的美国加州大学伯克利分校的格雷厄姆·弗莱明和他的同事选用了一种天线蛋白作为研究对象。通过分析透过蛋白质的激光的变化，就能判断出其中是否出现了量子叠加状态。
研究人员首先用两种不同频率的激光对其进行激活，而后再用第三种激光脉冲照射蛋白质，使其释放能量。结果发现他们所接收到的激光的频率与起初发射出的并不相同，这意味着在蛋白质中成功实现了量子相干。
弗莱明说，以激光促使天线蛋白发生量子叠加的方法虽然此前也有科学家提出，但新方法不需要精确的时控脉冲，只需改变激光的频率即可，相对而言更为简单有效。
美国加州大学欧文分校的化学家沙乌尔·莫肯姆说，这一实验很有趣，开创了一种激活天线蛋白的全新方式。对光合作用中能级和色素耦合的深入理解，将有助于构建出拥有类似功能的系统。
美国罗格斯大学化学家、《化学物理学》编辑埃德·卡斯纳说：“粗略计算表明，太阳一小时内照射到地球表面的能量就能满足人类一年的能源需求。解决目前人类所面临的能源、可持续发展等问题，离不开对光合作用机制的深入理解。该研究有助于科学家们设计出更高效的太阳能电池，或许有一天我们就能通过光合作用的方式来轻松获取能源。”
生物探索推荐英文论文摘要：
Mapping the spatial overlap of excitons in a photosynthetic complex via coherent nonlinear frequency generation
We experimentally demonstrate a nonlinear spectroscopic method that is sensitive to exciton-exciton interactions in a Frenkel exciton system. Spatial overlap of one-exciton wavefunctions leads to coupling between them, resulting in two-exciton eigenstates that have the character of many single-exciton pairs. The mixed character of the two-exciton wavefunctions gives rise to a four-wave-mixing nonlinear frequency generation signal. When only part of the linear excitation spectrum of the complex is excited with three spectrally tailored pulses with separate spatial directions, a frequency-shifted third-order nonlinear signal emerges in the phase-matched direction. We employ the nonlinear response function formalism to show that the emergence of the signal is mediated by and carries information about the two-exciton eigenstates of the system. We report experimental results for nonlinear frequency generation in the Fenna-Matthews-Olson (FMO) photosynthetic pigment-protein complex. Our theoretical analysis of the signal from FMO confirms that the emergence of the frequency-shifted signal is due to the interaction of spatially overlapped excitons. In this method, the signal intensity is directly measured in the frequency domain and does not require scanning of pulse delays or signal phase retrieval. The wavefunctions of the two-exciton states contain information about the spatial overlap of excitons and can be helpful in identifying coupling strengths and relaxation pathways. We propose this method as a facile experimental means of studying exciton correlations in systems with complicated electronic structures.
