Fig. 4 in Chemical evolution of the colour systems generated by riccionidin A, 3-deoxyanthocyanidins and anthocyanins

Fig. 4. (a) Bell-shaped curve of the reaction towards the equilibrium versus pH of luteolinidin 2.5 × 10 −5 M in ethanol:water (1:1). Fitting was achieved by means of eq. (10) for K K K = 4 × 10−9 M−1s−1; fx21 = 6.5 × 10−7 M−1s−1; k = 1.5 × 10−6 s−1; pK = 3.8; (b) Mole fraction distribution of the species at the h t i -i a equilibrium, which is basically constituted by quinoidal base in equilibrium with trans-chalcone; (c) (1) Flavylium cation at pH = 1.0, (2) quinoidal base immediately after a pH jump to pH = 5; (3) at the equilibrium at pH = 5; (4) immediately after a pH jump to pH = 8.0. Immediately after a direct pH jump to pH = 12 the colour is magenta (not shown). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)