European Journal of Scientific Research - EuroJournals

Investigation of Complex Formation PDTC with Ni(II) in Physiological Conditions 334
In this work, complex formation of nickel (II) ion with PDTC was investigated by job's method
using UV-vis spectroscopy at serum pH.
Experimental
Reagents: Pyrrolidine dithiocarbamate (PDTC) was purchased from Sigma and NiCl2.6H2O purchased
from Merck. Other chemicals were obtained from Sigma.
Method: Stock solution of Ni(II), was prepared by dissolving this chloride in twice-distilled water.
Electronic absorption spectra of the free ligand and its complex in 0.1M (hepes) containing 5mM
sodium bicarbonate were recorded using Cintra5 double-beam UV-Vis spectrophotometer. The
composition of the complex in solution was determined by continuous variation methods [13,14]. All
chemicals used were of without purification. The pH-metric titrations solutions of the free ligand and
its mixtures with metal ion was carried out as described earlier [15] using a digital Metrohm pH-meter
713 with a conventional pH-electrode. Using equations of Irving and Rossotti [16] the curves were
used to calculate the formation constants of the following equilibria
And
M 2+ +HL ML + + H +
ML + +HL K2 � ML2 + H +
Results and Discussion
Determination of pKa for PDTC ligand
The free PDTC titration was used to calculate ligand pka value of 3.300 with a very good fit σpH=
0.002 (fig. 1). This value corresponds to the protonation of the thio groups. However, there is chemical
evidence that suggests, PDTC is more stable at pH 7.4 and it can be expected for oral chelator (bidentat
ligand) [6].