Ternary Complexes in Solution. Comparison of the Coordination Tendency of Some Biologically Important Zwitterionic Buffers toward the Binary Complexes of Some Transition Metal Ions and Some Amino Acids

摘要

Potentiometric equilibrium measurements have beenperformed at (25.0 +- 0.1) deg C and ionic strength I = 0.1 mol dm~(-3) (KNO_3) for the interaction of glycine (aminoethanoci acid), serine (2-amino-3-hydroxypropanoic acid), methionine (2-mino-4-(methylthio)butanoic acid), aspartic acid (aminobutanedioica acid), glutamic acid (2-aminopropanedioic acid), and histidine (#alpha#-amino-1H-imidazole-4-propanoic acid) and Cu(II), Co(II), Ni(II), and Zn(II) with the biologically important secondary ligand zwitterionic buffers #beta#-hydroxy-4-morpholinepropanesulfonic acid (MOPSO), 4-morpholinepropnaesulfonic acid (MOPS), 3-[bis(2-hydroxyethyl)amino]-2-hydroxy-1-propanesulfonic acid (DIPSO), and 3-[N-tris(hydroxymethyl)methyl)amino]-2-hydroxypropanesulfonic acid (TAPSO) in 1:1:1 and 1:1:2 ratios, and the formation of various 1:1:1 ternary complexes and 1:1:2 quaternary complex species was inferred from the potentiometric pH titration curves. Initial estimates of the formation constants of hte resulting species and the acid dissociation constants of the different amino acids and secondary ligands studied have been refined with the SUPERQUAD computer program. The order fo stability of the different normal ternary complexes in the systems under investigation in terms of metal ion follows generally the trend Cu(II) > Ni(II) > Co(II) > Zn(II) > Mn(II).