Amino Acids Essay

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Experiment #2- Amino Acids October 16, 2013 Jessica Ramirez Kara Lue Chem 353- Section Instructor: Professor G. Santillan Purpose The purpose of this experiment is to become familiar with the dual nature of amino acids and their unique ability to be electrically neutral, or zwitterion. When amino acids sit in the blood stream they act as proton acceptors or donors, and this change in pH affects the overall charge of the amino acid. The titration curve is used to determine an amino acid through estimated pKa values of the ionizable groups of the amino acid. Knowing the pI helps us understand the acid-base behavior of an amino acid. Principles Amino Acids are weak polyprotic acids, which means contain more than one mole ionizable hydronium ions per mole of acid. Since amino acids can be present in zwitterion form at a neutral pH this allows the amphoteric molecules to be titrated with both acid and base. A main characteristic of all amino acids is that they have an acidic group (COOH) and basic group (NH2) that are attached to a carbon, and also contain ionizable groups that act as weak acids or bases. These give off or take on protons which results in altered pH. Amino acids are considered to be strong acids because they have a strong charge on the amino group. This strong charge on the amino group creates an affinity for carboxylic acids to lose a proton. The isoelectric point, pI, is the pH of an aqueous solution of an amino acid at which the molecules have no net charge. In other words, the positively charged groups are exactly balanced by the negatively charged groups. When this dissolved amino acid is titrated with an acid it reacts like a base, and when titrated with base it acts like an acid. This ability makes amino acids an amphoteric molecule. This gives an isoelectric point known as pI, which is when the positively positive charged groups
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