M2+•EDTA Binding Affinities: A Modern Experiment in Thermodynamics for the Physical Chemistry Laboratory

• Leah C. O'Brien ^[1] ; Hannah B. Root ^[1] ; Chin-Chuan Wei ^[1] ; Drake Jensen ^[1] ; Nahid Shabestary ^[1] ; Cristina De Meo ^[1] ; Douglas J. Eder ^[1]
  1. [1] Southern Illinois University Edwardsville

     Southern Illinois University Edwardsville

     Township of Edwardsville, Estados Unidos

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 92, Nº 9, 2015, págs. 1547-1551
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • Isothermal titration calorimetry was used to experimentally determine thermodynamic values for the ethylenediaminetetraacetic acid (EDTA)(aq) + M2+(aq) reactions (M2+ = Ca2+ and Mg2+). Students showed that for reactions in a N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (HEPES) buffer (pH = 7.4), the Mg2+ + EDTA reaction was endothermic, while Ca2+ binding to EDTA was exothermic. EDTA is triply ionized at pH 7.4 and therefore must shed a proton to the buffer prior to chelating the M2+ ion; thus the observed reaction enthalpies are strongly dependent on pH and buffer ionization enthalpy.