[Study on complex formation of quercetin reacting with Cu2+ using UV-Vis absorption spectroscopy]

Using an intensified spectroscopic detector ICCD, the real-time UV-Vis absorption spectra of quercetin (Q) reacting with Cu2+ under neutral and acid conditions were acquired. The exposure time was 0. 1 ms for each spectrum, and the molar ratio of Cu2+:Q was 0.2, 0.5, 1.0, 2.0, 5.0 and 10.0, respectively. Results indicate that the changes in absorption bands of reaction solutions with different ratio of Cu2+:Q were similar if other conditions were the same, and the greater the molar ratio, the shorter the reaction time; the reaction processes of complex formation were different under neutral and acid conditions. There was an intermediate product with the absorption peak at 428 nm that occurred during the reaction under neutral condition, but the final product was directly formed under acid condition, and the final products under both conditions had the same absorption bands centered at 296 nm; reaction processes with air and without air showed no difference. The present work first observed that there was an intermediate product formed during the complex formation of quercetin reacting with Cu2+ and the absorption band of the final complex was centered at 296 nm. Results obtained here provide useful experimental evidence for the study of complex mechanism of quercetin with Cu2+.