Anthocyanins. VI. Chelation Studies on Anthocyanins and Other Related Compounds

SUMMARY The metal-complexing properties of malvidin-3-monoglucoside, petunidin-3-monoglucoside, and 3′-methoxy-apigeninidin-chloride-4′-methyl-ether were studied polarographically and spectrophotometrically to complement bacteriological findings previously made. The molar ratios at which malvidin-3- monoglucoside combined with cupric ions depended on the pH of the supporting electrolyte solutions. The molar ratio of cupric ion to malvidin-3-monoglucoside was 2:1 at pH 3.9; the molar ratios were 1:2 at pH 3.5 and 4.5, but these ratios were 1:1 at pH 5.0 and 6.0. The absorption peaks of malvidin-3-monoglucoside were shifted to shorter wavelengths in the visible range but to longer wavelengths in the UV range upon addition of various concentrations of cupric ions. The absorption peaks of petunidin-3-monoglucoside were shifted to shorter wavelength in both the UV and the visible light ranges upon addition of various concentrations of cupric ions. The infrared absorbancies of 3′-metboxy-apigeninidin-chloride-4′-methyl-ether at 11 to 14.5 μ disappeared upon the addition of Ca and Mg ions.