Abstract:
Chemical speciation of binary complexes of Co(II), and Zn(II) with ethylenediamine was studied
pH– metrically in various concentrations (0-2.5% v/v) of SDS-water mixtures maintaining an
ionic strength of 0.12molL-1 (NaCl) at 298.0 K. SDS is used to mimic the low dielectric constant
at the active site cavities in bioactive molecules like enzymes and proteins. The active forms of
the ligand were LH22+, LH+, and L. Alkalimetric titrations were carried out in different relative
concentrations (M: L = 1:1, 1:2, 1:3) of metal (M) to ethylenediamine (L) with sodium hydroxide
as titrant. The predominant species detected for Co(II) and Zn(II) were ML (at pH 4.5 to 7.5),
ML2 (at pH 6.5 to 9.0) and ML3(at pH 9 and above) .The models containing different numbers of
species were refined by using MINIQUAD75 algorism. The best-fit chemical models that
represent the experimental data were arrived at based on statistical parameters like, sum of
square of the residuals,X2, R-factor, skewness and kurtosis. The trend in variation of stability
constant (log ) is due to increases in the concentration of surfactants. Effect of errors in the
ingredients on the values of stability constants was also studied. The species distribution
diagrams with pH at different compositions of SDS were also presented. The most probable
structures of plausible binary complexes were suggested in the study
