25 year-old molecular logic-based computation1,2 (MLBC) can operate inside small spaces such as living cells which semiconductor devices struggle to do. However, MLBC faces a challenge of gate integration. Now we take a step to address this by integrating a logic processor into the output of a molecular memory. Additionally, this system permits the controlled pick-up and delivery of molecular cargos in water by erection/collapse of walls. This is reported in; Daly, B., Moody, T.S., Huxley, A.J.M., Yao, C.Y., Schazmann, B., Alves-Areias, A., Malone, J.F., Gunaratne, H.Q.N., Nockemann, P. & de Silva, A.P. Molecular memory with downstream logic processing exemplified by switchable and self-indicating guest capture and release. Nat. Commun. 10, 49 (2019) [https://doi.org/10.1038/s41467-018-07902-7].
The fall of the Berlin wall is etched in the minds of many people since this event proved to be world-changing. We felt that a wall collapse or erection causing mobility or restriction of individuals could translate from the political sphere into the molecular world.
Additionally, we felt that our previous research in sensors and MLBC had focussed perhaps too tightly on atomic species. A move to molecular targets would enhance the usefulness of both these fields. Although complexation of molecular guests can be achieved by several host families, we were particularly inspired by the cyclophane research of Fraser Stoddart, Jean-Pierre Sauvage, Kenji Koga and Francois Diederich.
MLBC had been most closely associated with sensing research thus far1. So we felt it was crucial to combine concepts of MLBC with other ideas such as those underlying the delivery of drugs, bio-signalling agents and other functional molecules, which is what the current work does. Capture of toxins and pollutants are also included here. This should broaden the scope of MLBC.
A cyclophane macrocycle with several erect wall sections can corral a suitably sized and shaped guest molecule. A chemical command can collapse these walls and the constricted cavity can no longer contain the guest which is ejected into the surrounding water like a neurotransmitter being released into the synaptic cleft. This redox-induced cavity change can hold its state like a memory. Since a separate chemical command can re-erect these walls, the entire process can be reversed at will. Additionally, the cyclophane with erect walls indicates to us whether it is occupied by a guest or not via a fluorescence signal. The macrocycle with collapsed walls is optically distinguishable too. Thus, we are informed by the cyclophane as to which of the three possible states it is in.
We were able to find projections of the cyclophane x-ray crystal structures with erect and collapsed walls which roughly follow the boundaries of old west Berlin and unified Berlin respectively (Figure). So the molecular and political worlds do coincide almost exactly.
Post and image created by Brian Daly, Chaoyi Yao and AP de Silva
1. de Silva, A. P. Molecular Logic-based Computation (Royal Society of Chemistry, Cambridge, 2013).
2. de Silva, A. P., Gunaratne, H. Q. N. & McCoy, C. P. A molecular photoionic AND gate based on fluorescent signaling. Nature 364, 42–44 (1993).
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