Newly elucidated mechanism for blue flower color development

Various flower colors are in great part due to anthocyanins. Recently, we have elucidated two new mechanisms for blue flower color development on blue cornflower and blue morning glory. The composition of protocyanin, a blue pigment from cornflower, Centaurea cyanus, was determined to consist of six molecules of succinylcyanins (Sucy), six molecules of malonylflavones (Mafl), one ferric ion and one magnesium ion, [Sucy₆Mafl₆Fe³⁺]. The blue color of protocyanin was due to the LMCT (Ligand to Metal Charge Transfer) interaction between Sucy and Fe³⁺. The structure of protocyanin was examined by using Al, Mg-protocyanin. The gross structure is much similar to that of commelinin. The pigment of blue morning glory. Ipomoea tricolor, is an triacylated anthocyanin, HBA. We measured the vacuoler pH of the petal of morning glory by using a proton selective micro electrode. The pHv of the petal of purplish red bud was 6.6 and that of blue open fiower petal was 7.7. The anhydrobase anion of HBA must be stabilized by intramolecular stacking. We could solve 80 year's problems, one is about cornflower's pigment and the other is the evidence of the pH theory. In both cases hydrophobic interaction followed by formation of supra-molecule is the key of stabilization of anthocyanidin chromophore.