Abstract: ¹H、¹³C、¹¹³Cd NMR were applied to the study of the coordination sites of histidine to Cadmium (Ⅱ) in aqueous solutions with varied pH values and compositions.The chemical shifts、line broadening and NOE effects can lead to the confusion that when PH<4.0, histidine coordinates to Cd²⁺ with the carboxyl oxygen, when PH>4.0, both the carboxyl oxygen and imidazole nitrogen are capable of forming coordination bond to Cd²⁺.

Key words: Histidine, pH value, ¹¹³Cd NMR, Coordiation, coordination sites