EPR Study of the Astaxanthin n-Octanoic Acid Monoester and Diester Radicals on Silica-Alumina

A L Focsan, M K Bowman, Julia Shamshina, Matthew D. Krzyaniak, Adam Magyar, Nikolay E. Polyakov, Lowell D Kispert

Research output: Contribution to journalArticlepeer-review

Abstract

The radical intermediates of the n-octanoic monoester and n-octanoic diester of astaxanthin were detected by pulsed EPR measurements carried out on the UV-produced radicals on silica–alumina artificial matrix and characterized by density functional theory (DFT) calculations. Previous Mims ENDOR for astaxanthin detected the radical cation and neutral radicals formed by proton loss from the C3 (or C3′) position and from the methyl groups. Deprotonation of the astaxanthin neutral radical formed at the C3 (or C3′) position resulted in a radical anion. DFT calculations for astaxanthin showed that the lowest energy neutral radical forms by proton loss at the C3 (or C3′) position of the terminal ring followed by proton loss at the methyl groups of the polyene chain. Contrary to astaxanthin where proton loss can occur at either end of the symmetrical radical, for the diester of astaxanthin, this loss is prevented at the cyclohexene ends and is favored for its methyl groups. The
Original languageEnglish
Pages (from-to)13200-13210
JournalJ. Phys. Chem. B
DOIs
StatePublished - 2012

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