The Nature of the Delocalized Cations in Azulenic Bacteriorhodopsin Analogs

Depending on the size and shape of their azulenic chromophores, azulenic bacteriorhodopsin (bR) pigment analogs can exist as either an initial pigment P1, a more red-shifted final pigment P2 or an equilibrium mixture of both. The absorption spectra of red-shifted bR analogs exhibit characteristic na...

Full description

Saved in:
Bibliographic Details
Published in:Photochemistry and photobiology 2001-12, Vol.74 (6), p.837-845
Main Authors: Muthyala, Rajeev, Watanabe, Dana, Asato, Alfred E., Liu, Robert S. H.
Format: Article
Language:English
Subjects:
Bacteriorhodopsins - chemistry
Bacteriorhodopsins - radiation effects
Cations
Magnetic Resonance Spectroscopy
Photochemistry
PHOTOMEDICINE
Retinaldehyde - chemistry
Schiff Bases - chemistry
Spectrophotometry
Citations: Items that this one cites
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Depending on the size and shape of their azulenic chromophores, azulenic bacteriorhodopsin (bR) pigment analogs can exist as either an initial pigment P1, a more red-shifted final pigment P2 or an equilibrium mixture of both. The absorption spectra of red-shifted bR analogs exhibit characteristic narrow-band shapes similar to charge fully delocalized cyanine-like dyes. Therefore, all such red-shifted pigments are believed to be highly delocalized, bond-equalized carbocations. We have determined structural requirements that facilitate their formation. To describe fully the red-shift potentials of these retinal analogs, we have introduced a new parameter—percent red-shift (PRS). A large PRS value not only reflects the extent of red-shift, but is also suggestive of extensive delocalization of the positive charge. Relevance of these findings in consideration of the possibility of forming stable O-intermediates is presented. The postulated resonance hybrid-like structures for different cations of the positively charged protonated Schiff base chromophores are in fact structurally distinct species, equilibrating in response to local perturbations within the supramolecular protein environment.
ISSN:0031-8655
1751-1097
DOI:10.1562/0031-8655(2001)074<0837:TNOTDC>2.0.CO;2