Water, Air, and Soil Pollution

, Volume 183, Issue 1, pp 467–472

Differential Complexation between Zn2+ and Cd2+ with Fulvic Acid: A Computational Chemistry Study

  • Teodorico de Castro Ramalho
  • Elaine F. F. da Cunha
  • Ricardo Bicca de Alencastro
  • Aïda Espínola
Article

DOI: 10.1007/s11270-007-9364-6

Cite this article as:
de Castro Ramalho, T., da Cunha, E.F.F., de Alencastro, R.B. et al. Water Air Soil Pollut (2007) 183: 467. doi:10.1007/s11270-007-9364-6

Abstract

Fulvic (FA) and humic acids (HA) from the solubilization of organic matter are significant agents of the complex of metallic ions in soil and water. Cadmium ions are important natural water pollutants which are discharged along with electroplating and zinc metallurgy liquid wastes, zinc and cadmium being always associated with isomorphic substitution. In this paper we study the complexes formed by Zn2+ and Cd2+ with fulvic acids, using computational chemistry. We carried out relative free energy calculations using a thermodynamic cycle and Free Energy Pertubation (FEP) and Density Functional Theory (DFT-B3LYP/6-31G**) methods. We also computed the interaction energies between orbitals from Natural Bond Order (NBO) calculations. Cd-FA complexes, octahedral with four water molecules in the coordination sphere are more stable than Zn-FA complexes, tetrahedral with two water molecules. This means that FA should be a better ligand for Cd2+ bioavailability and toxicity in natural aquatic environments.

Keywords

ComplexationDFTEnvironmental chemistry

Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Teodorico de Castro Ramalho
    • 1
  • Elaine F. F. da Cunha
    • 1
    • 2
  • Ricardo Bicca de Alencastro
    • 4
  • Aïda Espínola
    • 3
  1. 1.Departamento de QuímicaUniversidade Federal de Lavras–UFLALavrasBrazil
  2. 2.Centro Brasileiro de Pesquisas Físicas (CBPF)Rio de JaneiroBrazil
  3. 3.Programa de Engenharia Metalúrgica e de Materiais, COPPE/UFRJUniversidade Federal do Rio de JaneiroRio de JaneiroBrazil
  4. 4.Grupo de Físico-Química Orgânica, Departamento de Química Orgânica, Instituto de QuímicaUniversidade Federal do Rio de JaneiroRio de JaneiroBrazil