M2+鈥DTA Binding Affinities: A Modern Experiment in Thermodynamics for the Physical Chemistry Laboratory
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- 作者：Leah C. O鈥橞rien ; Hannah B. Root ; Chin-Chuan Wei ; Drake Jensen ; Nahid Shabestary ; Cristina De Meo ; Douglas J. Eder
- 刊名：Journal of Chemical Education
- 出版年：2015
- 出版时间：September 8, 2015
- 年：2015
- 卷：92
- 期：9
- 页码：1547-1551
- 全文大小：276K
- ISSN：1938-1328
文摘
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鈥?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.