Correlation of vibrational frequencies with absorption maxima in polyenes, rhodopsin, bacteriorhodopsin, and retinal analogues

Hiroko Kakitani, Toshiaki Kakitani, Hillary Rodman, Barry Honig, Robert Callender

Research output: Contribution to journalArticle

82 Citations (Scopus)

Abstract

The factors that influence the C=C and C=N stretching frequencies in protonated Schiff bases, visual pigments, and bacteriorhodopsin (bR) are considered. For the C=C frequency (νC=C) we show that its well-known correlation with absorption maxima (λmax) cannot be accounted for in terms of π-electron bond orders. Rather, polarizability contributions to diagonal force constants must be taken into account. The lack of any correlation of the C=N frequency (νC=N) with absorption maxima is shown to arise from complications due to mixing with the C=N-H bending vibration. Variations in this mode due to different hydrogen-bonding patterns mask any correlation between λmax and νC=N that might otherwise be expected. Independent evidence supporting this conclusion may be derived from the relative magnitude of the deuterium isotope effects in different proteins. Comparing rhodopsin and bacteriorhodopsin, we argue that protein-chromophore interactions in the respective binding sites lead to enhanced π-electron delocalization in different parts of the chromophore. The consequences of this difference for the interpretation of Raman intensities and frequencies are discussed. Finally, we point out that, for highly delocalized π systems such as the primary photoproducts of rhodopsin and bacteriorhodopsin, additional factors may come into play as determinants of νC=N. In particular, enhanced coupling with the adjacent single bond may completely reverse the effects expected on the basis of π-electron considerations.

Original languageEnglish (US)
Pages (from-to)3620-3628
Number of pages9
JournalJournal of Physical Chemistry
Volume87
Issue number19
StatePublished - 1983
Externally publishedYes

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Bacteriorhodopsins
Polyenes
Rhodopsin
Vibrational spectra
Chromophores
analogs
Electrons
chromophores
Proteins
Retinal Pigments
visual pigments
Schiff Bases
Deuterium
Binding sites
proteins
Pigments
Isotopes
Stretching
electrons
bending vibration

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Correlation of vibrational frequencies with absorption maxima in polyenes, rhodopsin, bacteriorhodopsin, and retinal analogues. / Kakitani, Hiroko; Kakitani, Toshiaki; Rodman, Hillary; Honig, Barry; Callender, Robert.

In: Journal of Physical Chemistry, Vol. 87, No. 19, 1983, p. 3620-3628.

Research output: Contribution to journalArticle

Kakitani, Hiroko ; Kakitani, Toshiaki ; Rodman, Hillary ; Honig, Barry ; Callender, Robert. / Correlation of vibrational frequencies with absorption maxima in polyenes, rhodopsin, bacteriorhodopsin, and retinal analogues. In: Journal of Physical Chemistry. 1983 ; Vol. 87, No. 19. pp. 3620-3628.
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AU - Honig, Barry

AU - Callender, Robert

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