European Journal of Scientific Research - EuroJournals

Investigation of Complex Formation PDTC with Ni(II) in Physiological Conditions 336
The absorbance maxima at 324 nm reflect nickel binding at the two binding sites of PDTC. The
spectrum reflects that the maximum absorbance at about 324 nm increased rapidly, until the mol ratio 1
: 2 metal/ligand reached.
Figure 3: Spectrum of PDTC at 10 -6 M.
In titrations of PDTC with Ni 2+ alone, there was an isosbestic point at 296 nm (fig.4). The
binding constant of metal to ligand was determined by using the continuous variation method (Job's
method) at 324 nm (the obtained maximum absorbance from fig.4). The corrected absorbance was
plotted against the volume of fraction of PDTC, that is, VM/(VM + VL), where VM and VL are the
volumes of Ni 2+ and PDTC solutions, respectively (Fig. 5). The maximum values of VM/(VM + VL) =
0.33 and VL/(VM + VL) = 0.66 obtained from figure 5, thus VL/VM is 2, which suggested that the
complex had the formula Ni(PDTC)2. It is clear that nickel is binding to both specific metal-binding
sites of PDTC. The binding of Ni to PDTC can be quite fast. If the nickel is added as a NiCl2, then the
binding takes many seconds to reach completion. The effective Ni-PDTC binding constant is
logk=11.1±0.1, this is clearly higher than effective Ni-Tf binding constants (logk1=4.1±0.15,
logk2=3.23±0.31) [22].