HISTIDINE AND ORNITHINE AS LIGANDS TOWARDS LEAD(II)

The behaviours of histidine and ornithine as ligands of lead(II) have been studied by measuring the electromotive force of galvanic cells containing glass and diluted lead amalgam electrodes at 25-degrees-C in 1.00 M NaCl. The system lead(II)-histidine has been studied in 1.00 M NaClO4, as well. The experimental data were explained in terms of complex formation by also assuming the presence of protonated species. In 1.00 M NaCl for both histidine and ornithine, the species PbL, PbHL, PbH2L, PbL2, PbHL2, PbH2L2, PbH3L2 and PbH4L2 with their relative stability constants were found, while in 1.00 M NaClO4 the species PbL, PbHL, PbH2L, PbL2, PbHL2, PbH2L2, PbH3L2 with relative stability constants were found. The protonation constants of histidine al 25-degrees-C and in 1.00 M NaClO4 were determined, by using a H-2 electrode. The good agreement between experimental data and calculated curves supports the validity of the results.