Complex thermal behavior of 11-cis-retinal, the ligand of the visual pigments.
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.
Silva López
Carlos
C
Departamento de Quimica Organica, Facultade de Quimica, Universidade de Vigo, Lagoas Marcosende, E-36310, Vigo, Spain.
Alvarez
Rosana
R
Domínguez
Marta
M
Nieto Faza
Olalla
O
de Lera
Angel R
AR
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
D008024:Ligands; D012243:Rhodopsin; D012172:Retinaldehyde