Metal ion/buffer interactions. Stability of binary and ternary metal ion complexes containing the anion of N,N-bis(2-hydroxyethyl)-glycine (bicine) and adenosine 5′-triphosphate (ATP)

The acidity constants of protonated N,N-bis(2-hydroxyethyl)-glycine (H2(Bic)+) have been measured by potentiometric pH titrations in aqueous solution at I=0.5 M and 1.0 M (KNO3) at 25 °C. The interaction of Bicinate (Bic−) with Co2+, Ni2+ and Cu2+ (M2+) was studied by spectrophotometry and the stability constants of the binary M(Bic)+ complexes were determined: log KCoCo(Bic)=5.08, log KNiNi(Bic)=6.02, log KCuCu(Bic)=8.24 (I=1.0 M, KNO3; 25 °C). These results are compared with the corresponding values of the patent ligand, glycinate, and of other amino acids. It is concluded that the hydroxy groups of Bicinate are heavily involved in metal ion binding in the M(Bic)+ complexes. Ternary complexes containing in addition adenosine 5′-triphosphate (ATP) were also studied: log KCo(ATP)Co(ATP)(Bic)=4.53, log KNi(ATP)Ni(ATP)(Bic)=5.44, log KCu(ATP)Cu(ATP)(Bic)=6.57. It is evident that these mixed ligand complexes are also still of a rather high stability. The structure of these complexes is discussed, as is the use of Bicine as a buffer substance in the presence of metal ions and other ligating systems.