title: Kinetic model for astaxanthin aggregation in water-methanol mixtures.
abstract: The aggregation of astaxanthin in hydrated methanol was kinetically studied in the temperature range from 10 degrees C to 50 degrees C, at different astaxanthin concentrations and solvent composition. A kinetic model for the formation and transformation of astaxanthin aggregated has been proposed. Spectrophotometric studies showed that monomeric astaxanthin decayed to H-aggregates that after-wards formed J-aggregates when water content was 50% and the temperature lower than 20 degrees C; at higher temperatures, very stable J-aggregates were formed directly. Monomer formed very stable H-aggregates when the water content was greater than 60%; in these conditions H-aggregates decayed into J-aggregates only when the temperature was at least 50 degrees C. Through these findings it was possible to establish that the aggregation reactions took place through a two steps consecutive reaction with first order kinetic constants and that the values of these depended on the solvent composition and temperature.
authors.affiliation: Dipartimento di Scienze Ambientali, Sezione Chimica, Universita' di Camerino, Via S. Agostino 1, 62032 Camerino, MC, Italy. rita.giovannetti@unicam.it
authors.forename: Rita
authors.initials: R
authors.lastname: Giovannetti
authors.forename: Leila
authors.initials: L
authors.lastname: Alibabaei
authors.forename: Filippo
authors.initials: F
authors.lastname: Pucciarelli
mesh_terms: D007700:Kinetics; D000432:Methanol / Q000737:chemistry*; D008956:Models, Chemical; D013053:Spectrophotometry; D014867:Water / Q000737:chemistry*; D024341:Xanthophylls / Q000737:chemistry
chemical_list: D024341:Xanthophylls; D014867:Water; C005948:astaxanthine; D000432:Methanol