Related Experiment Video
Updated: Jun 21, 2026

Transpupillary Two-Photon In Vivo Imaging of the Mouse Retina
Published on: February 13, 2021
Color tuning in short wavelength-sensitive human and mouse visual pigments: ab initio quantum mechanics/molecular
Ahmet Altun1, Shozo Yokoyama, Keiji Morokuma
1Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA. aaltun@emory.edu
Abstract:
We have investigated the protonation state and photoabsorption spectrum of Schiff-base (SB) nitrogen bound 11-cis-retinal in human blue and mouse UV cone visual pigments as well as in bovine rhodopsin by hybrid quantum mechanical/molecular mechanical (QM/MM) calculations. We have employed both multireference (MRCISD+Q, MR-SORCI+Q, and MR-DDCI2+Q) and single reference (TD-B3LYP and RI-CC2) QM methods. The calculated ground-state and vertical excitation energies show that UV-sensitive pigments have deprotonated SB nitrogen, while violet-sensitive pigments have protonated SB nitrogen, in agreement with some indirect experimental evidence. A significant blue shift of the absorption maxima of violet-sensitive pigments relative to rhodopsins arises from the increase in bond length alternation of the polyene chain of 11-cis-retinal induced by polarizing fields of these pigments. The main counterion is Glu113 in both violet-sensitive vertebrate pigments and bovine rhodopsin. Neither Glu113 nor the remaining pigment has a significant influence on the first excitation energy of 11-cis-retinal in the UV-sensitive pigments that have deprotonated SB nitrogen. There is no charge transfer between the SB and beta-ionone terminals of 11-cis-retinal in the ground and first excited states.
Related Concept Videos
Photoreceptors and Visual Pathways
UV–Vis Spectroscopy: Molecular Electronic Transitions
Color Vision
UV–Vis Spectroscopy of Conjugated Systems
One of the factors influencing λmax is the extent of conjugation in the...
Ultraviolet and Visible (UV–Vis) Spectroscopy: Overview
Molecular Spectroscopy: Absorption and Emission

