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, PbL₂, PbL₂(OH), and PbL₂(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.

Graphical Abstract

Keywords:

• Biological buffer
• Metal depletion
• Metal complexation
• Speciation simulations
• Stability constants

Additional information

Funding

Funding. This work is financed by FEDER funds through Programa Operacional Factores de Competitividade – COMPETE and by National Funds through FCT – Fundação para a Ciência e a Tecnologia in the ambit of project Pest-C/EQB/LA0006/2013. The authors thank Prof. Ignacy Cukrowski from the University of Pretoria (South Africa) for polarographic modeling software (3D-CFC program) and Prof. Carlos Gomes from the Faculty of Sciences/Porto University for the COPOTISY program.