Carotenoid radical ions: A laser flash photolysis study

Ali El-Agamey, Thor B. Melø, Maha A. El-Hagrasy, Vassilia Partali, Shunichi Fukuzumi

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Laser excitation of a single precursor, namely 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (HHEMP), has been used for generating the radical cations and radical anions of various carotenoids in methanol. In the presence of oxygen, laser excitation of HHEMP undergoes an efficient α-cleavage reaction (Norrish type I) to form acyl radicals, which react with O2, in a nearly diffusion-controlled reaction, to form their corresponding strong oxidizing acylperoxyl radicals (RO2) (E = ~1.1 V (v SHE)), which are capable of oxidizing almost all carotenoids. Under argon-saturated conditions and in the presence of strong base (0.01 M NaOH or tetrabutylammonium hydroxide (TBAOH)), the initially formed 2-hydroxy-2-propyl radical (ACH), generated after LFP of HHEMP, is deprotonated to form the strong reducing acetone ketyl radical (AC•-) (E {acetone/ AC•-} = −2.1 V (v SHE)), which is capable of reducing all carbonyl-containing carotenoids. To validate this new proposed approach, retinal and β-apo-8′-carotenal (APO), with known spectroscopic data, were investigated in methanol, acetonitrile and tetrahydrofuran (THF). In addition, the radical ions of newly investigated carotenoids, namely 4-oxo-β-apo-15′-carotenoic acid (4-oxo-15′), crocetindial, 4-oxo-β-apo-10′-carotenoic acid ethyl ester (4-oxo-10′) and 4-oxo-β-apo-8′-carotenoic acid ethyl ester (4-oxo-8′) have been reported. Moreover, the scope of this approach has been extended to investigate the radical ions of chlorophyll b.

Original languageEnglish
Article number112023
JournalJournal of Photochemistry and Photobiology B: Biology
Volume212
DOIs
StatePublished - Nov 2020

Bibliographical note

Funding Information:
Dr. El-Agamey is grateful to the Egyptian Ministry of Higher Education and to King Faisal University (Scientific Research Deanship, project No. 186220) for financial support and to Dr. Hati, A.G. for his continuous help during this research and to Mr. Tony Heslop (Market Development Manager, BASF) for providing HHEMP. The authors are grateful to DSM Nutritional Products for supplying the carotenoids used in this work and a Grants-in-Aid (no. 16H02268 to S.F.) from MEXT, Japan.

Funding Information:
Dr. El-Agamey is grateful to the Egyptian Ministry of Higher Education and to King Faisal University (Scientific Research Deanship, project No. 186220) for financial support and to Dr. Hati, A.G. for his continuous help during this research and to Mr. Tony Heslop (Market Development Manager, BASF) for providing HHEMP. The authors are grateful to DSM Nutritional Products for supplying the carotenoids used in this work and a Grants-in-Aid (no. 16H02268 to S.F.) from MEXT, Japan.

Publisher Copyright:
© 2020 Elsevier B.V.

Keywords

  • Carotenoid
  • Chlorophyll b
  • Flash photolysis
  • Ketyl radical
  • Radical anion
  • Radical cation

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