Isomerization of trans-astaxanthin to cis-isomers in organic solvents.
The isomerization of trans-astaxanthin to cis-isomers in organic solvents was investigated. trans-Astaxanthin was dissolved in dimethyl sulfoxide, dichloromethane, chloroform, acetone, methanol, acetonitrile, and a mixture of dichloromethane and methanol (25:75) respectively, and heated at 35 degrees C followed by analyzing cis- and trans-astaxanthins in the solutions using HPLC. The isomerization rates of trans-astaxanthin were dependent on the solvent, and the following order was found: dichloromethane > chloroform > the mixture of dichloromethane and methanol (25:75) > methanol > acetonitrile > acetone > dimethyl sulfoxide. In different solvents, the relative contents of 9-cis- and 13-cis-astaxanthins formed during isomerization were different. In all solvents, 13-cis-isomer was the main cis-isomer from trans-astaxanthin. trans-Astaxanthin dissolved in dichloromethane or chloroform was very readily isomerized to cis-isomers, especially for dichloromethane, in which a maximum isomerization percentage was found and an equilibrium practically was reached after an appropriate time interval. Results also indicated that a higher temperature could promote markedly the isomerization of trans-astaxanthin.
Yuan
J P
JP
Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong.
Chen
F
F
D007700:Kinetics; D008958:Models, Molecular; D012997:Solvents; D013053:Spectrophotometry; D013237:Stereoisomerism; D024341:Xanthophylls; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000737:chemistry
D012997:Solvents; D024341:Xanthophylls; D019207:beta Carotene; C005948:astaxanthine