As indicated in Figure (3.1.2), we deduced that the synthesis process of the peptide bond was formed by dehydration condensation of Gallic acid and Polyethyleneimine. This process implied that the C-O of gallic acid was broken, and the C-N bond was formed. Subsequently, each copper ion in CuCl2•2H2O was chelated with four hydroxyl groups to obtain PGC.