Complex formation between copper(II) and arginine in two ionic media and in a large range of reagent concentration

Arginine and copper(II) play an important role in human physiology. Arginine is a precursor of NO which is a vasodilator and the right quantity of copper(II), bound to several amino acids, is necessary for the human body. The complex formation between copper(II) and arginine is studied at 25 °C and in two different ionic media: 1.00 mol dm−3 NaClO4 and 1.00 mol dm−3 NaCl. The investigation is carried out potentiometrically, by employing in 1.00 mol dm−3 NaClO4 cells involving glass and copper amalgam electrodes. In 1.00 mol dm−3 NaCl, only the glass electrode can be used. In both ionic media, the adoption of the constant ionic medium allows to extend the investigation to a large range of reagent concentration. Experimental data can be explained by assuming the formation of mononuclear complexes in copper(II). In 1.00 mol dm−3 NaClO4, complexes with the participation of hydrogen ions are assumed. The presence of the main complex in a large hydrogen ion concentration is supported also by spectrophotometric measurements.