Probing the rhodopsin cavity with reduced retinal models at the CASPT2//CASSCF/AMBER level of theory.
We show that the ab initio CASPT2//CASSCF strategy previously used to investigate the ground and excited states of the chromophore of the vision receptor rhodopsin (Rh) in vacuo can be successfully implemented in a QM/MM scheme allowing for CASPT2//CASSCF/AMBER geometry optimization and excited state property evaluation in proteins. Two receptor models (Rh-1 and Rh-2) incorporating different reduced chromophores are investigated. It is shown that Rh-2 features a chromophore equilibrium structure with the correct helicity and a lambdamax that is only 52 nm blue-shifted from the observed value. This result should open the way to a qualitatively correct ab initio QM/MM modeling of the early excited state transient species involved in the vision process.
Ferré
Nicolas
N
Dipartimento di Chimica, Università di Siena, via Aldo Moro I-53100 Siena, Italy.
Olivucci
Massimo
M
D007093:Imidazoles; D008956:Models, Chemical; D008958:Models, Molecular; D011487:Protein Conformation; D011687:Purines; D011789:Quantum Theory; D012172:Retinaldehyde / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry*; D013816:Thermodynamics
C438613:8-ethyl-4-methyl-2-phenyl-4,5,7,8-tetrahydro-1H-imidazo(2,1-i)purin-5-one; D007093:Imidazoles; D011687:Purines; D012243:Rhodopsin; D012172:Retinaldehyde