The aryl-chroman nucleus in anthocyanin pigments can act as either an acid or a base, depending upon the pH (acidity or alkalinity) of the solution it is in. At acidic pH calues, about 4.5 to 5.5, the acid from of anthocyanin is formed; it has a positive (+) charge. There is a neutral form, which is uncharged, at pH values around ca. 6. At higher pH values, 7 and above, the basic form of the anthocyanin nucleus is formed, with one or more negative charges.
Delphinidin has the possibility of a second basic ionization, to give a doubly negative charged molecule.
