Abstract
In a protein environment, proton transfer events can be initiated by configurational changes of pigments (e.g., trans-cis isomerization) or changes in the redox states of cofactors upon photoactivation. These changes lead to alteration of pKa of hydrogen-bond (H-bond) donor and acceptor moieties. In particular, when the pKa values of the two moieties match, a “symmetric H-bond” can be formed. Formation of an unusually short, symmetric H-bond appears to be essential for proton transfer events via H-bonds, and has been observed in photoreceptor proteins.
