%0 Journal Article
%A Mendoza, Johan
%A Basílio, Nuno
%A Freitas, Victor de
%A Pina, Fernando
%D 2019
%T New Procedure To Calculate All Equilibrium Constants
in Flavylium Compounds: Application to the Copigmentation of Anthocyanins
%U https://acs.figshare.com/articles/journal_contribution/New_Procedure_To_Calculate_All_Equilibrium_Constants_in_Flavylium_Compounds_Application_to_the_Copigmentation_of_Anthocyanins/8863523
%R 10.1021/acsomega.9b01066.s001
%2 https://acs.figshare.com/ndownloader/files/16249562
%K ci
%K hemiketal
%K constant
%K caffeine
%K pH
%K pseudo-equilibrium
%K species
%K quinoidal base
%K equilibrium
%K medium
%K hydroxyflavylium
%K anthocyanin
%K compound
%K chalcone
%K copigmentation
%K tran
%K flavylium cation
%K interaction
%K model
%K procedure
%X A new experimental
procedure to calculate all equilibrium constants
of the multistate of species of anthocyanins and related compounds,
including those in basic medium, is reported. The procedure is based
on a series of pH jumps monitored by stopped flow from an extended
pH range of solutions at pseudo-equilibrium (when there is no significant
formation of trans-chalcones) or at equilibrium to
pH = 1.0. The experimental procedure is described for the anthocyanin
model compound 4′-hydroxyflavylium, which exhibits a peculiar
behavior in moderately acidic medium, because the quinoidal base,
hemiketal, and cis-chalcone have similar mole fractions
at pseudo-equilibrium, permitting good discrimination among these
species. The experimental procedure can be extended to the copigmentation
phenomenon and allow the calculation of the 1:1 copigmentation constants
of the flavylium cation, quinoidal base, hemiketal, and cis- and trans-chalcones (this last from the equilibrium)
and their respective ionized forms. The method was applied to calculate
the copigmentation constants of the model compound 4′-hydroxyflavylium
as well as malvidin-3-glucoside with caffeine. In the last compound,
the strongest interaction takes place with the quinoidal base (K = 303 M–1) and flavylium cation (K = 134 M–1) and, to a lesser extent,
with the ionized quinoidal base (K = 43 M–1) and cis-chalcone (K = 17 M–1). The caffeine interaction with the hemiketal and
the other ionized species is negligible.
%I ACS Publications