Chemical evolution of the colour systems generated by riccionidin A, 3-deoxyanthocyanidins and anthocyanins.

ABSTRACT

The kinetics and thermodynamics (in acidic solutions) of the five chemical species reversibly interconnected by external stimuli (a multistate), such as pH and light, generated by the liverworts colorant riccionidin A were investigated. The degradation products of the multistate formed after 10 days at neutral pH were identified. The behaviour of riccionidin A multistate was compared with previous results reported for the equivalent systems based on 3-deoxyanthocyanidins (found in mosses and ferns) and anthocyanins (ubiquitous in angiosperms). The five chemical species have mutatis mutandis similar structures in the three multistates. The most dramatic difference is the extremely slow interconversion rate between flavylium cation and trans-chalcone in riccionidin A and related compounds multistates (tens of days) when compared with deoxyanthocyanins (a few days) and anthocyanins (several hours), at room temperature. The mole fraction distribution of the five species that constitute the multistate as a function of pH is also different in the three families of compounds. Some considerations regarding the chemical evolution of the three systems are given.