The complex-formation equilibria of [Pd(EDDA)(H2O)(2)](2+), where EDDA=ethylenediamine N,N'-diacetic acid, with various biologically relevant ligands containing different functional groups are investigated. The ligands (L) used are amino acids, peptides and DNA unit constituents. The results show the formation of 1: 1 complexes with amino acids. Peptides form both 1: 1 complexes and the corresponding deprotonated amide species. DNA constituents formed both 1: 1 and 1:2 complexes. Stoichiometries and stability constants of the complexes were determined at 25 degrees C and at ionic strength of 0.1 mol dm(-3) (NaNO3). The concentration distribution of the complexes in solution was evaluated. (C) 2009 Elsevier B.V. All rights reserved.