A Proton Pathway with Large Proton Polarizability in Bacteriorhodopsin

Abstract

With homoconjugated B+H⋯B ⇌ B⋯H+B hydrogen bonds the proton fluctuates in a double minimum potential with a frequency larger than 1013 sec−1. With hetero-conjugated AH⋯B ⇌ A−⋯H+B hydrogen bonds with double minimum the fluctuation frequency is slightly smaller but still very large. Calculations have shown that the polarizability caused by shifts of the proton within the hydrogen bonds due to electrical fields is about two orders of magnitude larger than polarizabilities arising due to deformation of electron systems. The same is true with hydrogen- bonded chains with multiminima potentials. The presence of such hydrogen bonds is indicated by continua in the infrared spectra. They arise since these hydrogen bonds strongly interact with their environments caused by their large proton polarizability. Such bonds or hydrogen-bonded chains with large proton polarizability are indicated by such continua1, 2 (Fig 1).