title: Complex thermal behavior of 11-cis-retinal, the ligand of the visual pigments.
abstract: Upon heating to 80 degrees C, 11-cis-retinal yields a mixture of all-trans-retinal and 13-cis-retinal. This isomerization has been studied by means of density functional theory methods, and the computational results suggest a close competition between two mechanisms of very different nature. A classical internal rotation around the C11-C12 cis double bond, via a diradical transition state, accounts for the formation of the all-trans isomer. An intricate sequence of pericyclic reactions, namely a reversible [1,7]-H sigmatropic shift and a reversible 6-pi-oxa-electrocyclic reaction, is responsible for the formation of 13-cis-retinal. Experiments using 11-cis-retinal labeled with deuterium at C19 confirmed the mechanistic proposal and also revealed an unprecedented outcome on the product composition of isotopologues.
authors.affiliation: Departamento de Quimica Organica, Facultade de Quimica, Universidade de Vigo, Lagoas Marcosende, E-36310, Vigo, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Silva López
authors.forename: Rosana
authors.initials: R
authors.lastname: Alvarez
authors.forename: Marta
authors.initials: M
authors.lastname: Domínguez
authors.forename: Olalla
authors.initials: O
authors.lastname: Nieto Faza
authors.forename: Angel R
authors.initials: AR
authors.lastname: de Lera
mesh_terms: D006358:Hot Temperature; D007536:Isomerism; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008968:Molecular Conformation; D012172:Retinaldehyde / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D008024:Ligands; D012243:Rhodopsin; D012172:Retinaldehyde