Complex formation between cadmium(II) and histidine or ornithine.

The behaviour of histidine and ornithine as ligands (L) towards cadmium(II) has been studied at 25-degrees-C. Complex formation between histidine and cadmium(II) has been investigated in two ionic media 1 M NaCl and 1 M NaClO4, while the system ornithine - cadmium(II) has been studied in 1 M NaCl. Experimental data, obtained by measuring the electromotive force of galvanic cells containing glass and stationary diluted cadmium amalgam, were explained by assuming formation of CdL+, CdHL2+, CdH2L3+, CdL2, CdHL2+, and CdH2L22+. In 1 M NaClO4 species CdH2L22+ was not present in appreciable concentration. The stability constants of each complex have been determined showing that protonated species prevail in a wide range of concentration of reagents, even in neutral or moderately alkaline solution. The results have been discussed and compared with those obtained for aspartate and glutamate