Pinch mechanism for improving proton quantum yields in model redox-initiated proton pumps

In contrast to uncoupled proton diffusion, redox-initiated proton diffusion must occur on the time scales of the initiating redox reactions. In addition, the diffusion process must occur against an opposing external bias. These two conditions can decrease the proton quantum yield below experimentally observed values. To improve the quantum yield, we present a simple hopping model that incorporates linearly decreasing proton-transfer barriers of the form -α*n. In contrast to hopping over constant barriers, opposing effects of the bias b disappear when α = 2b. This linear energy function can be related to a pinching of a proton channel at the exit end. Such a mechanism can originate from redox-linked conformational changes.