Blue flower colour derived from flavonol-anthocyanin co-pigmentation in Ceanothus papillosus

The pigments responsible for the blue flower colour of Ceanothus papillosus have been identified. The colour arises from co-pigmentation between the anthocyanins and flavonols. The major anthocyanins have been identified from NMR spectroscopy and degradation studies as the novel acylated delphinidin glycosides, delphinidin 3-O-rutinoside 7-O-(6-O-p-coumaroylglucoside) 3'-O-glucoside and delphinidin 3-O-rutinoside 7,3'-di-O-(6-O-p-coumaroylglucoside), and the major flavonol is kaempferol 3-O-xylosyl-(1 --> 2)-rhamnoside. The co-pigmentation effect appears to be quite specific, and does not occur to the same extent with other, more common, flavonols. The effect is particularly notable in that an extraordinary, long wavelength visible absorption maxima at 680 nm is produced which confers additional blueness. This is proposed to arise from a supramolecular complex of high stoichiometry. (C) 1997 Elsevier Science Ltd. All rights reserved.