Thermodynamic of metal complexation of the macrocylic antibiotic rifampicin

I. Shehatta, I. Kenawy, A. H. Askalany, A. A. Hassan

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


The acid-base and complexation equilibria of rifampicin with H+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+ were studied by means of potentiometry. The stoichiometric equilibrium constants were determined in 50% (v/v) methanol-water medium at different temperatures and constant ionic strength (0.05 M KCl). It was established that rifampicin has two proton-binding sites. The distribution diagram of the corresponding ionic species as a function of pH is given and indicated that rifampicin exists predominantly in the zwitterionic form at pH ≤ 5. The thermodynamic parameters of protonation and complexation were derived and discussed. The formation of the complexes is spontaneous, more favourable at lower temperatures, entropically unfavourable, and an enthalpy-driven process. The order of the changes in Gibbs energy and enthalpy accompanying the complexation was found to be Mn2+ < Co2+ < Ni2+ < Cu2+ > Pb2+ > Zn2+ > Cd2+ > Hg2+ in accordance with the well-known sequence of Irving and Williams. The transition series contraction energy (Er(Mn-Zn)), and the ligand field stabilization energy (δH) were calculated from the enthalpy changes.

Original languageEnglish
Pages (from-to)42-49
Number of pages8
JournalCanadian Journal of Chemistry
Issue number1
Publication statusPublished - 2001


  • Complexation
  • Potentiometry
  • Rifampicin
  • Thermodynamics

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry


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