Rhodopsin and GFP Chromophores: QM/MM Absorption Spectra in Solvent and Protein

This work presents a QM/MM investigation of the spectral properties of the 11\u2010cis\u2010retinal and the GFP chromophore in polar solvents and protein. The results of the computations are in surprising agreement with the experimental values indicating the accuracy of our computational approach. In addition it has been demonstrated the key role of the solvent to create a \u201cvirtual conter\u2010ion\u201d. This effect is due to the reorientation (i.e. polarization) of the polar solvent close to the chromophore: the polarized permanent dipoles of the solvent act similarly to the counter ion, stabilizing the ground state respect to the charge transfer excited state