Aqueous complexation studies of lead(II) and cadmium(II) with 1,3-bis(tris(hydroxymethyl)methylamino)propane pH buffer

Abstract

Hydrogen buffers are important in biological studies, as a steady hydrogen concentration is of great importance in most scientific studies. One of these buffers is 1,3-bis(tris(hydroxymethyl)methylamino)propane (BTP), which, considering its structure, has complexing capabilities, as previously shown for other metals. In order to know the stability constants for Cd(II) or Pb(II) with BTP, glass electrode potentiometry and direct current polarography studies were carried out. Our results show that both metals form metal complexes, with Pb(II) forming stronger complexes with BTP as evidenced by its higher stability constants. In the Pb-BTP system, five species were described; PbHL, PbL, PbL 2 , PbL 2 (OH), and PbL 2 (OH) 2 , and their stability constants were determined to be 11.4 ± 0.3, 4.7 ± 0.3, 8.8 ± 0.2, 14.4 ± 0.3, and 18.4 ± 0.3, respectively. For the Cd-BTP system, four complexes were detected; CdHL, CdL, CdL(OH), and CdL(OH) 2 , and their stability constants were also determined as 10.9 ± 0.4, 4.10 ± 0.07, 8.2 ± 0.2, and 10.9 ± 0.2, respectively. These complexes decrease considerably the amount of free metal in solution within the buffering pH range. This fact should be considered when planning experiments were BTP and Pb(II) and/or Cd(II) ions are present.

(Un)suitability of the use of pH buffers in biological, biochemical and environmental studies and their interaction with metal ions – a review

“…TES, TAPSO and tricine have stability constants described for most of the metals. 8,23,25,26,43,[48][49][50][51][52][53][54] Renganathan et al 7 found interferences in Cu inhibition of photosystem II electron transport due to bonding between Cu and TES, Tris and tricine. For TAPSO and TAPS, there is evidence of complexation with Cd, Co, Cu, Pb, Ni and Zn.…”

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

“…The model described in the literature for the Cu-BTP system is comprised of three species [CuL, CuL(OH), and CuL(OH) 2 ]. However, the analysis of the structure of BTP (figure 1) together with the models described for other divalent metal-BTP systems [8,9], and the one described in the literature for Cu-BTP system [10] support the idea that this system is not properly described by the current model. N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES) is one of the buffers originally proposed by Good et al [1].…”

“…The structure of BTP suggests that it should be a strong complexing agent. In fact, previous studies have shown that BTP forms strong complexes with Cd(II), Co(II), Ni (II), Pb(II), and Zn(II) [8,9], and Cu(II) ions [10]. The model described in the literature for the Cu-BTP system is comprised of three species [CuL, CuL(OH), and CuL(OH) 2 ].…”