95--670 GHz EPR studies of canthaxanthin radical cation stabilized on a silica-alumina surface
- Univ. of Alabama, Tuscaloosa, AL (United States). Dept. of Chemistry
- Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab.
- University College London (United Kingdom). Dept. of Biology
The 95--670 GHz EPR measurements at 5 K were performed on canthaxanthin radical cation chemically generated on silica-alumina. The 327 GHz and higher frequency EPR spectra were resolved into two principal components of the g tensor. Spectral simulation indicated this to be the result of g anisotropy where g{sub {parallel}} = 2.0032 and g{sub {perpendicular}} = 2.0023. This type of g tensor is consistent with the theory for polyacene {pi}-radical cations, which states that the g tensor becomes cylindrically symmetric with increasing chain length. This also demonstrates that the symmetrical unresolved EPR line at 9 GHz is due to a carotenoid {pi}-radical cation with electron density distributed throughout the whole chain as predicted by RHF-INDO/SP molecular orbital calculations. The lack of temperature dependence of the EPR line widths over the range of 5--80 K at 327 GHz suggests rapid rotation of methyl groups even at 5 K that averages out the proton couplings from three oriented {beta}-protons. In fact, similar line widths at 5 K were observed at 670 GHz. Simulation of EPR spectra at 95--250 GHz gives only symmetrical unresolved lines. The present work shows that the 327--670 GHz EPR measurements are sufficient to resolve the individual g tensors of C-H containing {pi}-radicals in powder and frozen glasses. Symmetry differences can be deduced from which radical identification can be made.
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- FG02-86ER13465
- OSTI ID:
- 682113
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 28; Other Information: PBD: 15 Jul 1999
- Country of Publication:
- United States
- Language:
- English
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