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

Abstract

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 pK a 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 pK a values of amino acid residues in proteins.

Oligozwitterions in coordination polymers and frameworks – a structural view

“…An obvious omission in the introductory remarks above is that of the zwitterion chemistry of amino acids, formally a matter for inclusion in this section. This, however, is a vast [18][19][20][21] and exceptionally important topic demanding separate treatment and, as well, is excluded here by limiting considerations to where the N-atom of the positive site of the zwitterion cannot become involved, through deprotonation, in metal ion coordination.…”

Spreadsheet Methodology for the Calculation of Equilibrium Diagrams Including Precipitation Reactions and Formation of Mixed Ligand and Polynuclear Hydroxo Complexes

“…Several papers published over the years in the Journal of Chemical Education stress the importance of fraction of species (relative abundance or speciation) and of Pourbaix diagrams for the characterization and understanding of chemical systems under equilibrium conditions. − The MERC proposed in this work has been tested in the classroom for almost 3 consecutive years with undergraduate students in an analytical chemistry course, corresponding to the sixth semester of the bachelor’s degree in chemistry. This course aims to give the students a firm understanding of the operations involved in classical analytical and basic separation methods (i.e., titrimetry, gravimetry, and separations by precipitation, liquid–liquid extraction, and ion exchange).…”

Prelaboratory Practice with a Titration Simulation Program for Carbonate Mixtures

“…In this study, a LabVIEW program was developed to solve equations that conform to the restrictive principles of chemical equilibrium, mass balance, and charge balance. , The program can precisely simulate the concentration changes of each component when titrating the carbonate mixture or each individual pure component with HCl. Students need to undertake comprehensive exercises and employ software simulation tools to acquire proficiency in judging the components of the mixtures based on the titration curves’ characteristics, , grasp the change process of distribution fractions for each component in relation to pH value (or titrant volume) during the titration process, and understand the principle of indicator selection. In addition, the software’s test function can test whether the student can correctly obtain the relevant information on the titration curve (randomly generated by the software), as well as the judgment of the mixtures’ components and the quantitative analysis ability.…”