Complex formation between arginine and calcium (II) and magnesium (II)

The compositions of solutions containing arginine and calcium (II) or magnesium (II) were studied at 25°C and 1.00 mol dm−3 NaCl or 1.00 mol dm−3 NaClO4, as ionic media. The complex formation in 1.00 mol dm−3 NaCl was studied by measuring the electromotive force of a galvanic cell, involving a glass electrode, to obtain the free hydrogen ion concentration. The investigation in 1.00 mol dm−3 NaClO4 was carried out by measuring the electromotive force of two galvanic cells. The former involved a glass electrode whereas the latter used a silver electrode. The investigation was performed in a wide range of reagent concentrations so that experimental data could be explained for calcium (II) by assuming the presence of 1:1 and 1:2 complexes, both in 1.00 mol dm−3 NaCl and 1.00 mol dm−3 NaClO4. Experimental data obtained for magnesium (II) were explained by assuming only the formation of 1:1 complexes. In both cases the values of the stability constants were determined. A comparison between the results obtained in 1.00 mol dm−3 NaCl and 1.00 mol dm−3 NaClO4 was performed. An attempt to explain as the complex formation takes place in solution is proposed.