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 x 10(-4), K-a1 = 1.0 x 10(-4), K-a2 = 3.2 x 10(-8), K-Ct1 = 1.0 x 10(-7), K-Ct2 = 1.3 x 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.
ISI Document Delivery No.: 136KGTimes Cited: 18
Cited Reference Count: 46
Melo, Maria J. Sousa, Micaela Parola, A. Jorge Seixas de Melo, J. Srgio Catarino, Fernando Marcalo, Joaquim Pina, Fernando
Melo, Maria Joao/C-8594-2011; Seixas de Melo, Sergio/A-5388-2008; Pina, Fernando/C-8161-2011; Parola, A. Jorge/F-4048-2010; REQUIMTE, AL/H-9106-2013; Marcalo, Joaquim/J-5476-2013
Seixas de Melo, Sergio/0000-0001-9708-5079; Parola, A. Jorge/0000-0002-1333-9076; Marcalo, Joaquim/0000-0001-7580-057X
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