METAL ION-BUFFER INTERACTIONS .2. STABILITY OF BINARY AND TERNARY COMPLEXES CONTAINING 2-[BIS(2-HYDROXYETHYL)AMINO]-2(HYDROXYMETHYL)-1,3-PROPANEDIOL (BIS-TRIS) AND ADENOSINE 5'-TRIPHOSPHATE (ATP)

Google Scholar
  • 1 January 1980
    • journal article
    • research article
    • Vol. 107  (2) , 455-466
Abstract
The acidity constant of protonated 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (Bistris) was measured. The influence of hydroxo groups on the basicity of Bistris and related bases is discussed. The interaction of Bistris with the metal ions (M2+) Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ was studied by potentiometry and spectrophotometry in aqueous solution (I = 1.0 M, KNO3; 25.degree. C) and the stability constants of the M(Bistris)2+ complexes were determined. Unexpectedly Ca(Bistris)2+ is the most stable among the alkaline earth ion complexes (log .**GRAPHIC**. = 2.25; the corresponding values for the Mg2+, Sr2+ and Ba2+ complexes are 0.34, 1.44 and 0.85, respectively). The ions of the 3rd series follow the Irving-Williams sequence: log .**GRAPHIC**. = 0.70, for Cu2+ 5.27 and Zn2+ 2.38. Ternary complexes containing ATP4- as a 2nd ligand were also investigated: the values for .DELTA.log KM ( = log .**GRAPHIC**. - log .**GRAPHIC**. are in general negative (e.g., .DELTA.log KCa = -0.40 or .DELTA.log KCu = -1.65), thus indicating that the interaction of Bistris with M(ATP)2- is somewhat less pronounced than with M2+. Even in mixed-ligand systems, complex formation may still be considerable, hence great reservations should be exercised in employing Bistris as a buffer in systems containing metal ions. In several cases .DELTA.log KM is relatively high [for Mg2+-ATP4--Bistris even positive], indicating some cooperativity between the coordinated ligands, possibly hydrogen-bond formation. Distributions of the complexes in dependence on pH are given, and the structures of the binary M(Bistris)2+ and the ternary M(ATP) (Bistris)2- complexes are discussed. The participation of Bistris hydroxo groups in complex formation is evident.