Oscillating Photostationary States for Molecular Cargo Transport

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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.