Electronic spectra and photochemistry of coordinated astaxanthin

Abstract

Astaxanthin (AXT) is a natural carotenoid which provides colorations to numerous living species such as salmon. Owing to its chelate function deprotonated astaxanthin (axt-) should be easily attached to metal ions. The complex RhIII(phpy)2(axt) with phpy- = deprotonated 2-phenylpyridine was prepared, and its electronic spectra and photochemistry were examined and compared to that of free AXT. Although different in detail, the spectra and photochemistry of AXT and Rh(phpy) 2(axt) show common features such as fluorescence and photoisomerization of the axt- ligand in ethanol as solvent. In CH2Cl2 free AXT as well as the complex undergo photooxidation owing to the reducing property of astaxanthin as an antioxidant. © 2011 Verlag der Zeitschrift für Naturforschung, Tübingen.