TY - JOUR
T1 - Identification of 7,4′-dihydroxy-5-methoxyflavylium in "dragon's blood": To be or not to be an anthocyanin
AU - Melo, Maria J.
AU - Sousa, Micaela
AU - Parola, A. Jorge
AU - Melo, J. Sérgio Seixas de
AU - Catarino, Fernando
AU - Marçalo, Joaquim
AU - Pina, Fernando
PY - 2007/6/21
Y1 - 2007/6/21
N2 - 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′ = 1.6 × 10-4, Kal = 1.0 × 10-4, Ka2 = 3.2 × 10-8, KCt1 = 1.0 × 10 -7, KCt2= 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 fur ther shown that this compound does not fit the commonly accepted definitions of anthocyanidin nor 3-deoxyan-thocyanidin. 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.
AB - 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′ = 1.6 × 10-4, Kal = 1.0 × 10-4, Ka2 = 3.2 × 10-8, KCt1 = 1.0 × 10 -7, KCt2= 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 fur ther shown that this compound does not fit the commonly accepted definitions of anthocyanidin nor 3-deoxyan-thocyanidin. 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.
KW - Dyes/pigments
KW - Flavylium salts
KW - Kinetics
KW - Multistate systems
KW - Natural products
UR - http://www.scopus.com/inward/record.url?scp=34250313986&partnerID=8YFLogxK
U2 - 10.1002/chem.200600837
DO - 10.1002/chem.200600837
M3 - Article
C2 - 17115461
AN - SCOPUS:34250313986
VL - 13
SP - 1417
EP - 1422
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 5
ER -