量子力学是描述亚原子粒子、原子、分子、分子组装等微观粒子属性的基本理论。量子力学在纳米和亚纳米尺度上运行,是光合作用、呼吸和视觉等基本生命过程的基础。在量子力学中,所有物体都具有波动特性:当它们相互作用时,量子相干性描述了由于波动特性导致的描述这些物体的物理量之间的相关性。在光合作用、呼吸和视觉方面,过去开发的模型基本上是量子力学的。研究人员已经描述了基于表面跳跃框架的能量转移和电子转移。这些模型描述的动力学通常是“指数”的,并且遵循费米黄金法则[1,2]的应用。由于是在准连续的最终态的分布上求平均转移率,计算的动力学不再显示相干性和干涉现象。在1990年代进行的大量研究中,研究人员已经在光合反应中心和光捕获复合体中观察到了振荡现象,通常将其归因于振动或混合电子-振动波包的形成。据报道,在光合系统的激发能量转移过程中检测到非常长寿命(660fs和更长)的电子量子相干性,重新激发了人们对“非平凡”量子力学在解释生物体基本生命过程中的作用的兴趣[3]。然而,量子现象(如相干性)可能在宏观生命系统中发挥功能作用的想法并不新鲜。1932年,在量子物理学家尼尔斯·玻尔(Niels Bohr)因其在原子结构方面的工作而获得诺贝尔奖10年后,他在哥本哈根国际光疗法大会上发表了题为“光与生命”的演讲[4]。这提出了一个问题,即量子理论是否有助于对生命系统的科学理解。出席会议的有一位充满兴趣的年轻物理学家 Max Delbrück,他后来帮助建立了分子生物学领域,并因在遗传学方面的发现于1969年获得诺贝尔奖[5]。所有生命系统都由分子组成,基本上所有分子都由量子力学描述。然而,传统上,量子力学描述的系统与生物学研究的系统之间巨大的尺度差异,生命和无生命看似不同的性质,使得两个知识体系之间一直存在某种隔阂。最近,超快光谱[6]、单分子光谱[7-11]、时间分辨显微镜[12-14]和单粒子成像[15-18]等实验技术的发展,使得研究人员能够在越来越小的分辨率兼时间尺度上研究生物动力学。他们揭示了生命系统功能所必需的各种过程,这些过程依赖于量子和经典物理效应之间微妙的相互作用。量子生物学将量子理论应用于经典物理学无法准确描述的生物学方面。尽管已有这个简单的定义,关于该领域在科学界的目标和作用仍然存在争议。本文提供了对量子生物学当前地位的看法,并指出在该领域取得进一步进展的潜在途径。
关于量子生物学的第一本书是 Pascual Jordan [132] 撰写的《有机分子之谜的物理学》(Physics of the mystery of organic molecules)。然而,自1932年出版以来,关于生命本质的许多谜团仍然存在。很明显,粗粒化的经典模型无法准确描述生命系统中发生的一系列过程。那么,持续争论的问题是量子效应在这种生物过程中发挥重要作用的程度。回答这个问题的一个有用途径是通过生物启发量子技术的工程设计,这些技术可以胜过为相同目的(例如用于能量利用或环境传感)而设计的经典设备。一些自然过程在生理温度和极其复杂的系统中经过了数十亿年完善,如果宏观尺度上的量子效应可以在其中发挥作用,使其良好运转,那么生物世界中存在大量信息可以从中为人类自己的技术汲取灵感。在这个方向上,人们提出了一种原型量子热机,它清楚地说明了量子设计原理,即电子自由度和振动自由度之间的单一能量量子的相干交换可以增强光收集系统的功率,超过单独使用热机制可能实现的功率。它使用热力学性能测量的量子优势已被量化,并且该原理对现实生物结构的适用性得到了证明[133]。量子生物学研究生物功能和该功能的调节,其与静态无序相关。单分子光谱给我们一个独特强大的透镜来观察静态无序的作用,它连接生物功能(投影到宏观/有机尺度)和量子力学现象。同时,量子生物学还关注长度和时间尺度分离的动力学现象之间的相互作用,从纳米级分子组装中的飞秒能量转移过程,到整个生物尺度内生态系统中的生存和繁殖。虽然在未来几十年内,量子生物学将证明受生物启发的量子设备在多大程度上优于经典类似物,但更深层次的问题是,纳米尺度的量子动力学现象如何为整个生物体提供选择优势。严格解决这个问题需要说明,对有机体适应性具有重要意义的宏观物理可观测量如何可预测地依赖于纳米级量子动力学变量。相反,我们还必须考虑,纳米级的量子子系统如何通过进化依赖于生物体的宏观动态。这个问题的进展可能会得到一个理论框架的帮助,该框架允许有机体尺度模型通过纳米尺度模型进行参数化。这可以由复杂系统理论领域内的多尺度分析工具提供。我们还可以设想一些实验,在这些实验中,已知在纳米尺度上表现出长寿命量子相干过程的野生型生物与已知不存在此类过程的转基因生物竞争。这样的实验——类似于生物学家定期进行的那些实验——可以提供清楚的洞见,表明量子生物学现象是否可以为生物体提供选择优势,并增加量子生物学作为生物学的一个领域的可信度。
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