The production of anthocyanins and anthocyanidins.—Part III

Abstract

The work of W illstatter,f of W illstatter and Mallison,* and of W illstatter and Zechmeister, § that has followed upon the proposal by the present author of a structural formula for the anthocyan pigments,|| has clearly demonstrated the correctness of the formula proposed, and of the conclu sions of the present author as to the relationship th at exists between the anthocyan and flavonol groups, exemplified thus :- Although it has thus been proved that anthocyanidins can be produced from flavonols, and that the flavonol glucosides pass, likewise, to antho cyanins, it does not of necessity follow that the anthocyan pigments are thus formed in plants and flowers, although this is probable, and in the present paper chemical evidence is produced which strengthens this proba bility.It was with a view to an examination of some points that may prove of value in connection with the tracing of the formation of the anthocyan pigments in Nature that the author began the investigations, of which this is a preliminary announcement. In view of the fact th at the work, which was begun during the summer of 1914, has had of necessity to stand aside, and must continue to do so for some time, and of the publication of further work by Willstatter and his collaborators,IT some of which touches upon the same ground, the author feels that the publication of the present preliminary observations will not be out of place. Both W illstatter and the author have noticed that when fiavonols are reduced as described by them, with formation of anthocyans, a considerable proportion of the yellow compound remains unacted upon-as the result of quantitative estimation W illstatter found, in one case, only 4 per cent, of anthocyan present after reduction-but this is, to some extent at least, due to the difficulty in regulating the reduction of the pigment, and it is quite conceivable that in Nature conditions may be more favourable to anthocyan formation than in the experiments thus far described.I t would appear desirable that evidence should be collected upon which conclusions might be drawn as to whether the anthocyan pigments are produced in plants vid flavonols, or, as the result of direct pendent of the presence of flavonols.If they are produced vid flavonols, then, unless the conditions present in Nature allow the reaction causing the conversion of the flavonol into anthocyan to proceed to completion, and the reaction proceeds more rapidly than th at whereby the flavonol is synthesised, and, further, that there is no reconversion from anthocyan to flavonol as the result of re-oxidation, it is to be anticipated that flowers, fruit, etc., containing an anthocyan pigment will also contain some quantity, great or small, of a flavonol, and indeed of the particular flavonol that corresponds to the anthocyan present. Thus, where the anthocyan pigment is one of the cyanidin glucosides, a corre sponding quercetin glucoside would be expected, whereas if the anthocyan were a glucoside of pelargonidin, then a corresponding glucoside of kaempferol shoul...

Demonstrating Purple Color Development to Students by Showing the Highly Visual Effects of Aluminum Ions and pH on Aqueous Anthocyanin Solutions

“…The blue cornflower Centaurea cyanus has protocyanin pigment, which also undergoes metal complexation. − Thus, metal ions affect blue-tone coloration. − The mapping of metal complexes in blue sepal tissues has recently been reported for Hydrangea macrophilla , a popular flowering plant, where the coexistence of anthocyanin, aluminum ions (Al 3+ ), and copigment molecules gives a stable blue color . Al 3+ ions can trigger the development of a blue color. − In addition, coexistence of aromatic acids such as chlorogenic acid can protect against hydration and modify the spectra. , For example, Al 3+ ions, anthocyanin, and neochlorogenic acid chelate in blue hydrangea flowers …”