WP1/2:
First, focus was on the preparation of a core rotary switch unit that could be operated with light. A series of novel hydrazone photoswitches diversely functionalized were synthesized. Light-induced isomerization model studies confirmed it was possible to switch between both isomers of the hydrazone systems with light of selected wavelength. The best switching efficiencies were obtained for the original system, achieving almost full conversion between E and Z isomers with no sign of fatigue. As the operation of this rotary photoswitch had the added benefit of not generating waste products, main effort was in the application of this switching process to the proposed molecular transporters, at the expense of the second objective of this project (use of a chemical fuel).
WP3:
A molecular structure for a ‘bucket-brigade’ device was designed that allowed to directly exchange the molecular cargo between two robotic arms without the need of an intermediate station. This machine had two different arms to ensure the cargo is transported only from left to right in an irreversible transfer step.
The synthesis of each module was carried out. The development of each half-machine model consisted in the sequential formation of the track fragment bearing an aldehyde station, connection to the rotary hydrazone switch core, installing of the corresponding thiol-based arm and loading of the cargo in the left-half machine or attachment to the central linker for the right half-machine. The preparation of each half-machine entailed 15-20 synthetic steps, and an overall 40 steps for the final machine. A strategy based on late formation of the hydrazone switch was successfully optimized that allowed to obtain the left and right half-machine models separately. At the conclusion of the project, focus is on the synthesis of an operative full machine by connecting the two half parts.
In terms of operation, cargo transfer conditions based on the use of acidic media were established that will be implemented for the operation of the full machine.
WP4:
A molecular model for the construction of a robotic transporter with an extendable arm was designed based on the incorporation of a second light-switchable unit, an azobenzene. The synthesis of molecular models corresponding to the left and the right half parts of the full machine were synthesized via a synthetic route consisting of 20 steps each. A full machine model was also obtained through a 28-step procedure.
Model studies on the orthogonal switching of azobenzene and hydrazone compounds using light allowed to select the best irradiation wavelengths for both processes and confirmed that the presence of one compound in the solution does not affect the switching efficiency of the other. Switching conditions were applied to the cargo transport and realease of the half-machine compounds. At the conclusion of the project, tests for the exchange of the molecular cargo under operating conditions are being carried out.
During the period of remote working, the Researcher elaborated two reviews about the use of switchable and programmable molecular machines in catalysis and the active template synthesis of mechanically interlocked molecules.
The results obtained were presented by the Researcher at the Symposium on the Synthesis and Characterization of Functional Molecules and Molecular Machines in Brussels, Belgium, in 2019. The Researcher also participated in the event hosted by Manchester Museum during the European Researchers’ Night celebrated in September 2019, where he represented the Leigh Group and the ProgNanoRobot Project, introducing the field of molecular machines to a general audience with hands-on displays and demonstrations. Other dissemination and outreach activities envisioned during the project were cancelled due to the COVID-19 pandemic global situation.
