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Title: Carotenoid cation radicals produced by the interaction of carotenoids with iodine

Abstract

Electron paramagnetic resonance (EPR) and optical absorption spectra of 1,2-dichloroethane and dichloromethane solutions of ..beta..-carotene (C/sub 40/H/sub 56/) and iodine have been studied. EPR studies showed that ..beta..-carotene cation radicals are formed. These radicals form complexes at 77 K, in highly concentrated (0.1 M) iodine solutions, with higher order polyiodide anions, I/sub 5//sup -/, I/sub 7//sup -/, I/sub 9//sup -/ (as evidenced by g value shifts and line-width increases), while at room temperature and in dilute (10/sup -4/-10/sup -5/ M) solutions of iodine only I/sub 3//sup -/ counterions are involved. In dilute solutions (total molar concentratino = 2 x 10/sup -4/ M), a Job plot showed the stoichiometry to be 2:3, indicating the reaction 2C/sub 40/H/sub 56/ + 31/sub 2/ /r equilibrium/ 2C/sub 40/H/sub 56//sup .+/ + 2I/sub 3//sup -/. The radical fraction (EPR) is /approximately/ 2% at 77 K and 0.4% at 300 K (for a 2 mM ..beta..-carotene/0.1 M I/sub 2/ solution); it increases at lower ..beta..-carotene concentrations. Dimers and trimers of ..beta..-carotene cation radicals are formed in dilute solution (I/sub 2/ < 10/sup -4/ M) if (I/sub 2/)/(..beta..-carotene) < 1, and an intense absorption band occurs at lambda/sub max/ /approximately/ 1030 nm. Canthaxanthin and ..beta..-apo-8'-carotenal with I/submore » 2/ produce new absorption bands with lambda/sub max/ < 1000 nm; the g values are independent of iodine concentration, suggesting a poorer ability to form complexes with the polyiodide anions. All three carotenoids react with other electron acceptors (7,7,8,8-tetracyanoquinodimethane (TCNQ), tetrachloro-1,4-benzoquinone (chloranil), and Br/sub 2/) according to the electron affinity of the acceptor used.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Univ. of Alabama, Tuscaloosa (USA)
OSTI Identifier:
6298883
DOE Contract Number:  
FG05-86ER13465
Resource Type:
Journal Article
Journal Name:
J. Phys. Chem.; (United States)
Additional Journal Information:
Journal Volume: 92:16
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CAROTENOIDS; CHEMICAL REACTIONS; IODINE; ABSORPTION SPECTROSCOPY; CATIONS; ELECTRON SPIN RESONANCE; EXPERIMENTAL DATA; INFRARED SPECTRA; LOW TEMPERATURE; RADICALS; CHARGED PARTICLES; DATA; ELEMENTS; HALOGENS; HYDROCARBONS; INFORMATION; IONS; MAGNETIC RESONANCE; NONMETALS; NUMERICAL DATA; ORGANIC COMPOUNDS; PIGMENTS; RESONANCE; SPECTRA; SPECTROSCOPY; TERPENES; 400201* - Chemical & Physicochemical Properties

Citation Formats

Ding, R, Grant, J L, Metzger, R M, and Kispert, L D. Carotenoid cation radicals produced by the interaction of carotenoids with iodine. United States: N. p., 1988. Web. doi:10.1021/j100327a010.
Ding, R, Grant, J L, Metzger, R M, & Kispert, L D. Carotenoid cation radicals produced by the interaction of carotenoids with iodine. United States. https://doi.org/10.1021/j100327a010
Ding, R, Grant, J L, Metzger, R M, and Kispert, L D. 1988. "Carotenoid cation radicals produced by the interaction of carotenoids with iodine". United States. https://doi.org/10.1021/j100327a010.
@article{osti_6298883,
title = {Carotenoid cation radicals produced by the interaction of carotenoids with iodine},
author = {Ding, R and Grant, J L and Metzger, R M and Kispert, L D},
abstractNote = {Electron paramagnetic resonance (EPR) and optical absorption spectra of 1,2-dichloroethane and dichloromethane solutions of ..beta..-carotene (C/sub 40/H/sub 56/) and iodine have been studied. EPR studies showed that ..beta..-carotene cation radicals are formed. These radicals form complexes at 77 K, in highly concentrated (0.1 M) iodine solutions, with higher order polyiodide anions, I/sub 5//sup -/, I/sub 7//sup -/, I/sub 9//sup -/ (as evidenced by g value shifts and line-width increases), while at room temperature and in dilute (10/sup -4/-10/sup -5/ M) solutions of iodine only I/sub 3//sup -/ counterions are involved. In dilute solutions (total molar concentratino = 2 x 10/sup -4/ M), a Job plot showed the stoichiometry to be 2:3, indicating the reaction 2C/sub 40/H/sub 56/ + 31/sub 2/ /r equilibrium/ 2C/sub 40/H/sub 56//sup .+/ + 2I/sub 3//sup -/. The radical fraction (EPR) is /approximately/ 2% at 77 K and 0.4% at 300 K (for a 2 mM ..beta..-carotene/0.1 M I/sub 2/ solution); it increases at lower ..beta..-carotene concentrations. Dimers and trimers of ..beta..-carotene cation radicals are formed in dilute solution (I/sub 2/ < 10/sup -4/ M) if (I/sub 2/)/(..beta..-carotene) < 1, and an intense absorption band occurs at lambda/sub max/ /approximately/ 1030 nm. Canthaxanthin and ..beta..-apo-8'-carotenal with I/sub 2/ produce new absorption bands with lambda/sub max/ < 1000 nm; the g values are independent of iodine concentration, suggesting a poorer ability to form complexes with the polyiodide anions. All three carotenoids react with other electron acceptors (7,7,8,8-tetracyanoquinodimethane (TCNQ), tetrachloro-1,4-benzoquinone (chloranil), and Br/sub 2/) according to the electron affinity of the acceptor used.},
doi = {10.1021/j100327a010},
url = {https://www.osti.gov/biblio/6298883}, journal = {J. Phys. Chem.; (United States)},
number = ,
volume = 92:16,
place = {United States},
year = {Thu Aug 11 00:00:00 EDT 1988},
month = {Thu Aug 11 00:00:00 EDT 1988}
}