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Singlet Molecular Oxygen Quenching Ability of Carotenoids in a Reverse‐micelle Membrane Mimetic System ¶
Author(s) -
Montenegro Mariana A.,
Nazareno Mónica A.,
Durantini Edgardo N.,
Borsarelli Claudio D.
Publication year - 2002
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2002)0750353smoqao2.0.co2
Subject(s) - chemistry , singlet oxygen , photochemistry , quenching (fluorescence) , micelle , rose bengal , photobleaching , double bond , oxygen , reaction rate constant , hexane , photooxygenation , organic chemistry , fluorescence , aqueous solution , kinetics , physics , quantum mechanics
The influence of the medium heterogeneity upon the bimolecular rate constants for the physical quenching, k q , and chemical quenching, k r , of singlet molecular oxygen O 2 ( 1 Δ g ) by seven natural and three synthetic carotenoids (CAR) with different substituent patterns was studied in a reverse micelle system of sodium bis(2‐ethylhexyl)sulfosuccinate, hexane and water. Because O 2 ( 1 Δ g ) was generated inside the water pools of the reverse micelles by photosensitization of the water‐soluble dye rose bengal and the CAR are mainly located in the external hexane pseudophase, the quenching process was interpreted using a pseudophase model for the partition of O 2 ( 1 Δ g ) between the water pools and the organic pseudophases. The k q values were mainly dependent on the extent of the double‐bond conjugation of the CAR, as demonstrated by a good empirical relationship between log( k q ) and the energy E (S) of the longest wavelength transition π→π* of the CAR. In contrast, the k r values were almost independent of the extent of the double‐bond–conjugated system and about four orders of magnitude lower than k q . However, in all cases, CAR photobleaching was observed with the formation of various oxidation products, depending on the photosensitization time. Chromatographic and spectroscopic product analysis for the reaction products of β‐carotene with O 2 ( 1 Δ g ) indicated the formation of the β‐carotene‐5,8‐endoperoxide as the primary oxidation product.