TERNARY COMPLEXES IN SOLUTION - COMPARISON OF THE COORDINATION TENDENCY OF SOME BIOLOGICALLY IMPORTANT ZWITTERIONIC BUFFERS TOWARD THE BINARY COMPLEXES OF CU(II) AND ADENOSINE 5'-MONOPHOSPHATE, 5'-DIPHOSPHATE,AND 5'-TRIPHOSPHATE

Potentiometric equilibrium measurements have been made at 25.0 +/- 0.1 degrees C and ionic strength I = 0.1 mol dm(-3) KNO3 for the interact ion of adenosine 5'-mono-, 5'-di-, and 5'-triphosphate (AMP, ADP and A TP) and Cu(II) with biologically important secondary ligand zwitterion ic buffers (N,N-bis-(2-hydroxyethyl)-2-aminoethanesulphonic acid (BES) , tris-(hydroxymethyl)-methyl-2-aminoethanesulphonic acid (TES), N,N-b is-(2-hydroxyethyl)-glycine (Bicine) and tris-(hydroxymethyl)-methylam inopropane sulphonic acid (TAPS)) in a 1:1:1 ratio and the formation o f various 1:1:1 mixed ligand complex species inferred from the potenti ometric pH titration curves. Initial estimates of the formation consta nts of the resulting species and the acid dissociation constants of AM P, ADP, ATP, and secondary ligands have been refined with the SUPERQUA D computer program. Negative and positive Delta log K values were obta ined for the ternary systems studied. In some Cu(II) ternary systems s tudied the interligand interactions or some cooperativity between the coordinate ligands, possibly H bond formation, has been found to be mo st effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increase in the or der AMP < ADP < ATP. The trend in stability constants of the mixed-lig and complexes of the title zwitterionic buffer ligands is found to be TAPS > Bicine > TES > BES.