An improved quantum-mechanical study of environmental effects on the spectral shift of the rhodopsin system
Abstract
A theoretical study of the effect of a condensed medium upon the electronic transitions of a solute has been performed by incorporating a multiple expansion of the reaction field into the Hartree–Fock approximation. Dielectric relaxation of the medium was taken into account together with dispersion forces. The method has been applied to some models for rhodopsin, the Schiff base of retinal with the apoprotein opsin. This system is characterized by a large electronic polarizability of the chromophore and protein environment together with a large variation of dipole moment. It is found that large spectral shifts of the chromophore could originate from the electric fields of ionic residues and from fields induced in the protein environment by the electronic-charge distribution of the chromophore.