Effect of urea on speciation of cobalt (II) complexes of L-glutamine and succinic acid

Speciation of Coll complexes of L-glutamine (Gln) and succinic acid (Suc) in 0.0-36.83%, w/v urea-water mixtures at an ionic strength of 0.16 mol dm(-3) and temperature 303.0 +/- 0.1 K has been investigated pH-metrically. The species detected for Gln complexes are ML, MLH and ML3H and those for Suc are ML, MLH and ML2H. The stability of the complexes decreased with increased urea content due to the electrostatic forces, denaturing power and complexing ability of urea. The relative stabilities of the species in urea-water and ethylene glycol-water mixtures are compared based on the dielectric constants. The species distribution and the plausible equilibria for the formation of the species are also presented.