Study on Optical Properties and Biological Activity of Proanthocyanidins at Different pH and Alkalinit

Abstract The UV-Vis absorption and fluorescence spectra of proanthocyanidins at different pH values were studied, and the change of absorption peak position was analyzed. The intermediate stable states of proanthocyanidins in different pH conditions, the electron transition modes and emission spectra of these steady states were analyzed. Eight parts of proanthocyanidins, each with mass of 1.00 mg, were added to acetic acid buffer solution with different pH in turn. The absorption of samples at the same pH concentration was measured by UV-visible spectrophotometer and fluorescence spectrophotometer, spectrogram analysis was carried out. The absorption peak wavelength of proanthocyanidins did not change obviously in acid condition, the quantum yield of proanthocyanidins was low in different pH solutions, and the excited molecules returned to the ground state mainly by non-radiative transition. Under the same temperature conditions, the stability of proanthocyanidins decreased with the increase of pH, and the color of the solution ranged from orange to red. The charge distribution of hydroxyl groups analyzed the ability of combining free radicals at different sites of proanthocyanidins with hydroxyl groups, which suggested that proanthocyanidins may have better antioxidant activity.