Mixed-ligand complexes of palladium(II). Part 2. Diaqua(ethylenediamine) palladium(II) complexes of L-asparagine and L-glutamine

Abstract

The reactions of [Pd(en)(OH₂)₂]²⁺(en = ethylenediamine) with L-asparagine monohydrate and L-glutamine in 0.5 mol dm^–3 K[NO₃] have been studied by potentiometric titrations. The results obtained can be explained by equilibria (i) and (ii) where L^–= H₂NCOCH₂CH(NH₂)CO₂^– or H₂NCOCH₂CH₂CH(NH₂)CO₂^–, and log K₁ and [Pd(en)(OH)₂]²⁺+ L^–[graphic omitted][Pd(en)L]⁺(i), [Pd(en)L]⁺[graphic omitted][Pd(en)L′]+ H⁺(ii) pK_a′ are 10.46 and 6.46 for asparagine and 10.76 and 9.03 for glutamine respectively. The mode of co-ordination of the two ligands in their protonated and deprotonated complexes is discussed on the basis of these parameters.