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Identification of 7,4′‐Dihydroxy‐5‐methoxyflavylium in “Dragon's Blood”: To Be or Not To Be an Anthocyanin
Author(s) -
Melo Maria J.,
Sousa Micaela,
Parola A. Jorge,
de Melo J. Sérgio Seixas,
Catarino Fernando,
Marçalo Joaquim,
Pina Fernando
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600837
Subject(s) - anthocyanidin , anthocyanin , chemistry , aqueous solution , base (topology) , organic chemistry , stereochemistry , food science , mathematics , mathematical analysis
The compound 7,4′‐dihydroxy‐5‐methoxyflavylium (dracoflavylium) was identified as the major red colorant in samples of the resin “dragon's blood”, extracted from the tree Dracaena draco . The complex network of reversible chemical reactions that dracoflavylium undergoes in aqueous solution is fully described; for the first time, all the equilibrium constants that enable a complete characterisation of the system have been obtained ( K ′ a =1.6×10 −4 , K a1 =1.0×10 −4 , K a2 =3.2×10 −8 , K Ct 1 =1.0×10 −7 , K Ct 2 =1.3×10 −10 ). It is concluded that the red colour is due to a stable quinoid base, A , which is the major species at pH 4–7. It is further shown that this compound does not fit the commonly accepted definitions of anthocyanidin nor 3‐deoxyanthocyanidin. Similarly to synthetic flavylium salts, the natural compound 7,4′‐dihydroxy‐5‐methoxyflavylium gives rise to several species (multistate system) reversibly interconverted by external stimuli, such as pH.