摘要：SummaryIn low-barrier hydrogen bonds (H-bonds), the pKavalues for the H-bond donor and acceptor moieties are nearly equal, whereas the redox potential values depend on the H+position. Spectroscopic details of low-barrier H-bonds remain unclear. Here, we report the absorption wavelength along low-barrier H-bonds in protein environments, using a quantum mechanical/molecular mechanical approach. Low-barrier H-bonds form between Glu46 andp-coumaric acid (pCA) in the intermediate pRCWstate of photoactive yellow protein and between Asp116 and the retinal Schiff base in the intermediate M-state of the sodium-pumping rhodopsin KR2. The H+displacement of only ∼0.4 Å, which does not easily occur without low-barrier H-bonds, is responsible for the ∼50 nm-shift in the absorption wavelength. This may be a basis of how photoreceptor proteins have evolved to proceed photocycles using abundant protons.Graphical abstractDisplay OmittedHighlights•The low-barrier H-bond formation is a prerequisite for proton transfer•How the absorption wavelength changes as H+moves is an open question•The H+displacement of ∼0.4 Å leads to the absorption wavelength shift of ∼50 nm•The localization of the molecular orbitals plays a key role in the wavelength shiftChemistry; Computational chemistry; Optical Materials
