Proton-Coupled Electron Transfer (PCET) is ubiquitous in nature, essential to life but particularly difficult to study because of the complexity of natural systems. We recently developed a new experimental framework to permit fine-tuning of proton-transfer kinetics without perturbing the thermodynamics. The regulation took advantage of the “flip-flop” diffusion of proton carriers inside lipid membranes. Unfortunately, the diffusion happens spontaneously and more precise control could be beneficial. As a result, we designed the first synthetic photoresponsive proton gate incorporated in a lipid layer. The new proton carrier features a boronic acid head-group for proton transfer, a stiff stilbene body for photoresponsiveness, and an alkyl tail for lipid incorporation. The light-induced cross-membrane proton transfer was quantified by the activity of an O₂ reduction catalyst buried under the lipid layer by electrochemistry. This molecular switch mimics the natural system to precisely control proton relocation without perturbing the proton thermodynamics (Scheme 1).

Scheme 1.  Illustration of photoresponsive transmembrane proton transfer.