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

doi:10.1021/jp307421e

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

Fiber and Biopolymer Research Inst

Research output: Contribution to journal › Article › peer-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 language	English
Pages (from-to)	13200-13210
Journal	J. Phys. Chem. B
DOIs	https://doi.org/10.1021/jp307421e
State	Published - 2012

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

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",

author = "Focsan, {A L} and Bowman, {M K} and Julia Shamshina and Krzyaniak, {Matthew D.} and Adam Magyar and Polyakov, {Nikolay E.} and Kispert, {Lowell D}",

year = "2012",

doi = "10.1021/jp307421e",

language = "English",

pages = "13200--13210",

journal = "J. Phys. Chem. B",

publisher = "ACS",

}

TY - JOUR

T1 - EPR Study of the Astaxanthin n-Octanoic Acid Monoester and Diester Radicals on Silica-Alumina

AU - Focsan, A L

AU - Bowman, M K

AU - Shamshina, Julia

AU - Krzyaniak, Matthew D.

AU - Magyar, Adam

AU - Polyakov, Nikolay E.

AU - Kispert, Lowell D

PY - 2012

Y1 - 2012

N2 - 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

AB - 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

U2 - 10.1021/jp307421e

DO - 10.1021/jp307421e

M3 - Article

SP - 13200

EP - 13210

JO - J. Phys. Chem. B

JF - J. Phys. Chem. B

ER -

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

Abstract

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