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 formation between zinc(II) and arginine is studied, at 25 A degrees C and in 1.00 mol dm(-3) NaCl as ionic medium. The investigation 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 mononuclear 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 beta (1,1,1) = 16.11 +/- A 0.07), ZnH2L2 (log beta (1,2,2) = 33.41 +/- A 0.05), ZnH3L3 (log beta (1,3,3) = 45.93), ZnH2L3 (log beta (1,2,3) = 36.04), and ZnHL3(log beta (1,1,3) = 27.15), where L represents the completely deprotonated arginine.