Graphic data analysis and complex formation curves as modeling and optimization tools for characterization of Cu–(buffer) x –(OH) y systems involving BTP or BES in aqueous solution.

Bis-tris propane or 1,3-bis(tris(hydroxymethyl)methylamino)propane (BTP) and N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES) are pH buffers which have been used in biological experiments. To characterize BTP and BES complexation properties with Cu(II), glass electrode potentiometry and direct current polarography were conducted using total ligand to total copper concentration ratios of different orders of magnitude and pH values at 25 °C and 0.1 M KNO3ionic strength. The graphic analysis is a very powerful tool in the prediction and refinement operations of both systems. For the Cu-BTP system, six species were found to describe totally the system, CuL, CuL(OH), CuL(OH)2, CuL2, CuL2(OH), and CuL2(OH)2, with respective stability constants determined as 10.7  ±  0.1, 19.4  ±  0.4, 24.3  ±  0.2, 18.8  ±  0.1, 24.7  ±  0.2, and 29.8  ±  0.2. CuL2, CuL2(OH), and CuL2(OH)2were described for the first time. In the case of the Cu-BES system, complexation behavior was described by the model constituted by CuL, CuL(OH), and CuL(OH)2, the latter two described for the first time, with respective stability constants determined as 3.24  ±  0.08, 10.9  ±  0.2, and 16.0  ±  0.3, respectively. UV–vis results allowed us to establish coordination modes for the Cu-BTP and Cu-BES complexes. [ABSTRACT FROM AUTHOR]