COMPLEX-FORMATION BETWEEN CADMIUM(II) AND HISTIDINE OR ORNITHINE

The behaviour of histidine and ornithine as ligands (L) towards cadmiu m(II) has been studied at 25-degrees-C. Complex formation between hist idine and cadmium(II) has been investigated in two ionic media 1 M NaC l and 1 M NaClO4, while the system ornithine - cadmium(II) has been st udied in 1 M NaCl. Experimental data, obtained by measuring the electr omotive force of galvanic cells containing glass and stationary dilute d 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 c ompared with those obtained for aspartate and glutamate.