Complex formation between zinc(II) and arginine in a large range of reagent concentration

Arginine and zinc(II) play an important role in the human physiology. Arginine is a precursor of NO which is a vasodilator and zinc(II) is frequently an enzyme activator having also therapeutic role. The complex for- mation between zinc(II) and arginine is studied, at 25 C and in 1.00 mol dm -3 NaCl as ionic medium. The inves- tigation is carried out potentiometrically, by employing cells involving glass and zinc amalgam electrodes, in a large range of reagent concentration. Experimental data can be explained by assuming the formation of mononu- clear complexes in zinc(II), but with the participation of hydrogen ions. The formation of the following species with the relative stability constant explains the experimental data: ZnHL (log b1,1,1 = 16.11 ± 0.07), ZnH2L2 (log b1,2,2 = 33.41 ± 0.05), ZnH3L3 (log b1,3,3 = 45.93), ZnH2L3 (log b1,2,3 = 36.04), and ZnHL3(log b1,1,3 = 27.15), where L represents the completely deprotonated arginine.