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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. January 2004, Volume 3, Number 1, 45-54 |
Quantum Chemical Calculations for Protonated Rhodopsin and
Considerations on the Transduction Process in the Retina
Melissa Fabíola S. Pinto and Milan Trsic
Internet Electron. J. Mol. Des. 2004, 3, 45-54
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Abstract:
Our main motivation is to provide some insight in the
transduction process in the rod cells of retina upon absorption
of light. Models for the prosthetic group of rhodopsin
(protonated Schiff base of 11-cis-retinal with opsin, named as
11-cis-rhodopsin and all-trans-rhodopsin in what follows)
were studied with various theoretical procedures. The initial
geometry of the compounds was first refined with molecular
mechanics and further optimized with semi-empirical AM1
and PM3 methods. We also analyzed electrostatic potential
charges with ab initio methods. The calculations were
applied to the ground and the first excited singlet states. For a
more comprehensive description of the species under study,
accurate configuration interaction calculations for the
electronics absorption spectrum of 11-cis- and all
trans-rhodopsin with the aid of the ZINDO/S CI program were
performed. The theoretical results were almost identical with
the experimental measurements. Finally, we qualitatively
comment on the influence of an SH- group in the absorption
spectrum. Our results suggest that the excited state is
somewhat less ordered than the ground state, which may
have connections with the transduction process.
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