Analysis of Protonation Equilibria of Amino Acids in Aqueous Solutions Using Microsoft Excel

A Microsoft Excel workbook has been developed to simplify the quantitative analysis of experimentally measured titration curves for diprotic and triprotic amino acids such as glycine, arginine, histidine, and glutamate. Students perform the titration, enter the data into the worksheet, and manually adjust the resulting pKa values to achieve the closest agreement between the experimental and calculated titration curves. At the same time, the students can observe changes in the speciation diagram that illustrates the transitions of differently protonated molecular species during the titration. Through a combination of graphical visualization and analysis, supported by computer software, students learn the most important aspects of the protonation equilibria of amino acid solutions. The knowledge gained can serve as the basis for understanding the behavior of more complex polyprotic acids in aqueous solution and the pKa values of amino acid residues in proteins.