Inclusion complexes of carotenoids with cyclodextrins: 1H NMR, EPR, and optical studies.
Direct evidence of carotenoid/cyclodextrin inclusion complex formation was obtained for the water-soluble sodium salt of beta-caroten-8'-oic acid (IV) by using 1H NMR and UV-Vis absorption spectroscopy. It was shown that this carotenoid forms a stable 1:1 inclusion complex with beta-cyclodextrin (stability constant K11 approximately 1500 M(-1)). All other carotenoids under study in the presence of cyclodextrins (CDs) form large aggregates in aqueous solution as demonstrated by very broad absorption spectra and considerable change in color. By using the EPR spin trapping technique, the scavenging ability of IV toward OOH radicals was compared in DMSO and in the aqueous CD solution. A considerable decrease in PBN/OOH spin adduct yield was detected in the presence of uncomplexed IV because of a competing reaction of the carotenoid with OOH radical. No such decrease occurred in the presence of the IV/CD complex. Moreover, a small increase in spin adduct yield (pro-oxidant effect) is most likely due to the reaction of the carotenoid with Fe3+ to regenerate Fe2+, which in turn regenerates the OOH radical. Our data show that CD protects the carotenoid from reactive oxygen species. On the other hand, complexation with CD results in considerable decrease in antioxidant ability of the carotenoid.
Polyakov
Nikolai E
NE
Institute of Chemical Kinetics and Combustion, Novosibirsk 630090, Russia.
Leshina
Tatyana V
TV
Konovalova
Tatyana A
TA
Hand
Elli O
EO
Kispert
Lowell D
LD
D002338:Carotenoids / Q000737:chemistry*; D003505:Cyclodextrins / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D019097:Spin Trapping
D003505:Cyclodextrins; D002338:Carotenoids