ISSN:
0377-0486
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The carotenoids astaxanthin, lutein and zeaxanthin form high molecular weight aggregates in aqueous solvent systems. The absorption spectra of the aggregates, compared to those of the monomer molecules, show significant bandwidth narrowing and blue shifts of 600-800 Å. The resonance Raman spectra of these aggregated polyenes are anomalous in that ν C=C occurs near 1518 cm-1 whereas a well-established νC=C vs 1/λmax correlation predicts that νC=C should be near 1560 cm-1. The Raman and absorption data together demonstrate that strong excited state interactions are taking place and these results illustrate the utility of the resonance Raman technique for recognizing excited state perturbations. Raman excitation profiles (the variation of Raman intensity with wavelength) on aggregated astaxanthin and low temperature (-100 °C) absorption spectra on aggregates of astaxanthin and lutein establish that a pronounced change in vibronic structure occurs upon aggregation. In contrast to astaxanthin or lutein monomers whose electronic absorption spectra are made up of 0-0, 0-1, 0-2,… transitions, only the 0-0 transition is seen in the aggregates. The results are explained in terms of the molecular exciton model.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jrs.1250060605
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