Abstract
The study was to calculate the quantum yields of aldehydes formed from photolysis of copper(II) – amino acid complexes in anaerobic aqueous solution under monochromatic radiation at 313 nm. 2,4-dinitrophenylhydrazine (DNPH) derivatization method combined with high-performance liquid chromatography (HPLC)-UV was applied and optimized. DNPH derivatization is a well-developed, highly sensitive method for determination of aldehyde but the reaction of DNPH with aldehydes was found to be suppressed by copper(II) in this study. Adding EDTA to chelate copper(II) could significantly reduce the inference of copper(II), and it was expected to have the same effects for other metal ion. Meanwhile, the reaction between DNPH and copper(II) is a redox reaction, and the kinetics follows the first reaction order of both aldehydes and DNPH. Regarding the photoreaction of copper complexes, the ligand to metal charge transfer (LMCT) was supposed to be responsible for the reduction of copper(II) to copper(I) following with the degradation of amino acid. Aldehydes could be parts of the photoproducts. The quantum yield ratios of copper(I) to aldehydes (ΦCu(I) / Φaldehyde) were around 3 to 6, which depends on the different amino acids as the ligands, such as Alanine, Valine, Leucine and Isoleucine. Meanwhile, the quantum yield ratios were found to have a positive correlation with the concentration of copper(II). A further oxidation of formed aldehydes to carboxyl acids is proposed to explain the trend of the quantum yield of aldehydes.