Electron spin resonance studies on anthocyanins

The ESR characteristics of anthocyanins and their congeners have been determined using both crystalline and non-crystalline preparations. For the latter, a micro-technique has been proposed. The results show that red and violet pigments specifically exhibit a distinct signal at g=2·057 being different from blue anthocyanins. It has been suggested that the g=2·057 signal arises from the unpaired electron of pyrylium ring. Comparison of ESR spectra of isolated anthocyanins with those in fresh petals has further shown that there is no difference in the g=2 region of ESR spectra and that the appearance of the g=2·003 signal is thus not due to anthocyanins alone.