Identification of the chromophores in Corallium rubrum gem quality corals by HPLC/UV, ESI-MS and 1H NMR spectroscopy

Abstract

Gem Corallium rubrum corals are calcitic biomaterials derived from the branched skeletons of Cnidaria marine invertebrates. Until now the structure of chromophores in Corallium rubrum is still under discussion. First attempts to identify pigments in red corals from Marseille revealed the presence of canthaxanthin. In 2008 Raman spectroscopy suggested that pigments are instead due to unsubstituted polyenes. More recently (2012) ECC theory in Raman spectroscopy stated that the spectrum of Corallium rubrum lies in between carotenoids and unsubstituted polyenes spectra. To confirm and complete the experimental and theoretical results, a group of gem quality specimens of colony skeletons of Corallium rubrum was tested. Rough coral samples were before demineralized with EDTA. HPLC combined with UV was used to separate the pure fractions, on which structural characterization was carried out by ESI-MS and 1H NMR spectroscopy. Results have shown that the colouring pigment profile in Corallium rubrum seems more complex than hitherto considered. HPLC/UV chromatograms, confirmed by ESI-MS spectra, indicate the presence of two structurally modified carotenoids and of traces of astaxanthin and canthaxanthin. Owing to scarsity of material, 1H NMR spectroscopy did not yield the expected results.