Chapter 3, Problem 3P

(a)

Summary Introduction

To determine: The reason as to why alanine predominantly occurs as zwitterion rather than completely uncharged at its pI.

Introduction:

Alanine is an amino acid used in the biosynthesis of polypeptides or proteins. It consists of  α-amino group and α-carboxylic group. The side chain of alanine consists of methyl group. This makes alanine a non-polar and an aliphatic amino acid.

(b)

Summary Introduction

To determine: The fraction of alanine that is present in completely uncharged form at its pI.

Introduction:

The fraction of alanine that is present in completely uncharged form at its pI can be calculated through Henderson-Hasselbalch equation, which is as follows:

$\text{pH}-{\text{pK}}_{\text{a}}=\log \frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$

Here, pH is the concentration of hydrogen ion.

pK_a is the equilibrium constant.

$\log \frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$ is the log of reactants by products.