Charge-transfer complexation as a general phenomenon in the copigmentation of anthocyanins.
Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E(red) approximately -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA(Anthoc) - IP(Cop), the difference between the electron affinity of the anthocyanin, EA(Anthoc), and the ionization potential of the copigment, IP(Cop). Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted.
Ferreira da Silva
Palmira
P
Centro de Química Estrutural, Instituto Superior Técnico, UTL, Lisbon, Portugal.
Lima
João C
JC
Freitas
Adilson A
AA
Shimizu
Karina
K
Maçanita
Antonio L
AL
Quina
Frank H
FH
D000872:Anthocyanins / Q000737:chemistry*; D003373:Coumaric Acids / Q000737:chemistry; D004583:Electrons; D005419:Flavonoids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry; D059808:Polyphenols; D012996:Solutions; D013057:Spectrum Analysis
D000872:Anthocyanins; D003373:Coumaric Acids; D005419:Flavonoids; D007477:Ions; D010636:Phenols; D059808:Polyphenols; D012996:Solutions; C004999:ferulic acid