Single-Electron Catalysis of Reversible Cycloadditions under Nanoconfinement

Electron transfer (ET) is crucial in many chemical reactions,
but
its mechanism and role are hardly understood in nanobiotechnology
due to the complexity of reaction species and pathways involved. By
modulating and monitoring electron behavior at the single-molecule
level, we can better understand the fundamental mechanisms and ways
to control them for technological use. Here, we unravel a mechanism
of single-electron catalysis under positively charged nanoconfinement.
We demonstrate that both (2 + 2) and (4 + 4) cycloadditions can be
catalyzed reversibly by a single electron. Key reaction pathways are
discovered by monitoring sequential electrical signals in the cycloadditions
through advanced single-molecule detection platforms. Experimental
and theoretical results consistently demonstrate that combining single
ET processes with nanoconfinement involving cucurbit[8]uril can lower
the reaction energy barrier and promote reversible cycloaddition.
Moreover, we show that the bias voltage can fine-tune ET processes
and chemical equilibria in bond formation and cleavage. Our results
provide a novel approach to elucidate, modulate, and design electron-involved
reactions and functionalized devices.