In this article, you will become more familiar with how to draw titration curves of amino acids. A titration curve of an amino acid tracks how the pH changes and how the amino acid looks at different pH values as a strong base (OH equivalents) is added. Two important points to recognize on a titration curve are the:
- 100% deprotonation points; the points where enough base is added to deprotonate all the acid. These are the steepest points on the graph
- Half equivalents points; the points where half the amino acid is protonated and half is deprotonated. These are the flattest points on the graph. The flatness of the graph indicates that the solution is highly buffered i.e., there is little change in pH as the base is added. The pH = pKa at the half equivalents points
Problem: Draw the structure of aspartic acid at points B, D and F on the following titration curve. Determine the overall charge of the amino acid at each point, and calculate the isoelectric point (pI). Note: Constituents will be deprotonated in the order from lowest to highest pKa.