Oscillating Photostationary States for Molecular Cargo Transport

分子货物的受控运输是生物系统运行的基础。虽然一些细胞运输是通过扩散或被动过程进行的，但某些分子货物是在燃料条件下运输的。例如，囊泡、细胞器和脂质在三磷酸腺苷供能的条件下，通过运动蛋白和动力蛋白等运动蛋白沿细胞微管轨迹运输。这项研究项目涉及开发一种完全合成的系统，它模仿生物系统中看到的分子货物的运输，使用光能来推动分子水平的运动。该体系中的一个关键设计元素是研究得很好的偶氮苯基序，它在不同波长的光照射下，经历两种不同的几何异构体之间的切换-扩展的E构象，端到端的距离更长，收缩的Z构象，端到端的距离更短。通过将这种光化学异构体相互转化与纯化学相互转化相耦合，产生了一个由四个分子态组成的循环反应网络。通过利用环状反应网络产生的E和Z异构体之间分子构象的自发变化，可以实现分子货物的自主控制运输。这项研究将从开发一种光燃料系统开始，该系统允许酰基-一种小的有机化学基团-在两个热力学上无法区分的脂肪醇之间定向转移。偶氮苯部分将不对称地放置在两个醇之间，并充当一只“臂”，从一种醇中拿起小的有机基团，并将其放在另一种醇上。然后，将进一步开发这一系统，以允许较小的有机种群进行更远距离的运输。为了做到这一点，将使用精心设计的分子轨道，具有交替的醇基和偶氮苯“臂”。该项目目标的实现将第一次允许在分子水平上自主控制的小部分有机物质的远距离运输。这种对分子水平运动的控制不仅模仿了支撑生物系统运行的宏伟的生物分子马达，而且为未来纳米技术的发展带来了巨大的希望。

The controlled transport of molecular cargo is fundamental to the operation of biological systems. While some cellular transport occurs through diffusive or passive processes, certain molecular cargo are transported under fuelled conditions. For example, vesicles, organelles, and lipids are transported under ATP-fuelled conditions along cellular microtubule tracks by motor proteins such as kinesin and dynein. This research project involves the development of a fully synthetic system that mimics the transport of molecular cargo seen in biological systems, using light energy to fuel the molecular level motion. A key design element in the system is the well-studied azobenzene motif, which undergoes switching between two different geometric isomers-the extended E conformation with a longer distance from end to end and the contracted Z conformation with a shorter end-to-end distance-upon irradiation with different wavelengths of light. By coupling this photochemical isomer interconversion with a purely chemical interconversion, a cyclic reaction network is generated comprising four molecular states. By harnessing the spontaneous changes in molecular conformation between the E and Z isomers which arise from the cyclic reaction network, autonomous controlled transport of molecular cargo can be achieved. The research will start with the development of a light-fuelled system which allows the transfer of an acyl group-a small organic chemical group-directionally between two thermodynamically indistinguishable aliphatic alcohols. The azobenzene moiety will be positioned asymmetrically between the two alcohols and act as an "arm" to pick up the small organic group from one alcohol and put it down on the other. This system will then be further developed to allow the transport of the small organic group over extended distances. To do this a carefully designed molecular track, with alternating alcohol groups and azobenzene "arms", will be employed. Realisation of the project's aims will allow, for the first time, the autonomous controlled transport of a small organic moiety over extended distances at the molecular level. Such control of molecular level motion not only mimics the magnificent biological molecular motors which underpin the operation of biological systems but also holds great promise for the development of future nanoscale technologies.