About the intrinsic photochemical properties of the 11-cis retinal chromophore: Computational clues for a trap state and a lever effect in Rhodopsin catalysis

Alessandro Cembran, Remedios González-Luque, Luis Serrano-Andrés, Manuela Merchán, Marco Garavelli

Research output: Contribution to journalArticle

28 Scopus citations

Abstract

CASPT2//CASSCF/6-31G*computations are used on the singlet S 1 and S 2 states to map the photoisomerization process of the 11-cis retinal protonated Schiff base in vacuo and to characterize its optical properties. It is shown that the spectroscopic observations recorded in Rhodopsin are reproduced quite well, calling for a substantially neutral effect of the protein. Furthermore, a rationale is proposed for the unreactive population recently observed in Rhodopsin, which is here addressed to the accessible S 2 state, behaving as a trap. The experimental transient absorption and (absorption-wavelength dependent) emission are discussed and interpreted under the light of this novel model. Finally, a planarization of the β-ionone ring is observed on S 1, which may cause a steric lever effect into the protein pocket, thus assisting photoisomerization catalysis. The reported results constitute a solid reference for further studies aimed to rationalize the effect of the environment on the photochemical reactivity of retinal chromophores.

Original languageEnglish (US)
Pages (from-to)173-183
Number of pages11
JournalTheoretical Chemistry Accounts
Volume118
Issue number1
DOIs
StatePublished - Jul 1 2007

Keywords

  • Ab initio calculations
  • Conical intersections
  • Photoisomerization
  • Reaction mechanisms
  • Retinal

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