Chapter 25, Problem 51PP

(a)

Interpretation Introduction

Interpretation:

The form of amino acid that predominates are the isoelectric point need to be identified.

Concept introduction:

Amino acids at a particular pH do not migrate in an electric field.  This pH is known as the isoelectric point.  The isoelectric point is also known as isoionic point.  At this isoelectric point the amino acid is neutral.  This means that the zwitterion form predominates more over the other forms.  pI is the isoelectric point and this can be given by average of the pK_a.

$\text{pI=}\frac{{\text{pK}}_{{\text{a}}_{\text{1}}}{\text{+pK}}_{{\text{a}}_{\text{2}}}}{\text{2}}$

The carboxylic acid form will predominate if, ${\text{pI<pK}}_{\text{a}}$ and carboxylate form will predominate if, ${\text{pI>pK}}_{\text{a}}$.

The uncharged amino form will predominate if, ${\text{pI>pK}}_{\text{a}}$ and the protonated amino form will predominate if, ${\text{pI<pK}}_{\text{a}}$.

For the side chain the same rule applies as of for carboxylic acid and amino group.

(b)

Interpretation Introduction

Interpretation:

The form of amino acid that predominates are the isoelectric point need to be identified.

Concept introduction:

Amino acids at a particular pH do not migrate in an electric field.  This pH is known as the isoelectric point.  The isoelectric point is also known as isoionic point.  At this isoelectric point the amino acid is neutral.  This means that the zwitterion form predominates more over the other forms.  pI is the isoelectric point and this can be given by average of the pK_a.

$\text{pI=}\frac{{\text{pK}}_{{\text{a}}_{\text{1}}}{\text{+pK}}_{{\text{a}}_{\text{2}}}}{\text{2}}$

The carboxylic acid form will predominate if, ${\text{pI<pK}}_{\text{a}}$ and carboxylate form will predominate if, ${\text{pI>pK}}_{\text{a}}$.

The uncharged amino form will predominate if, ${\text{pI>pK}}_{\text{a}}$ and the protonated amino form will predominate if, ${\text{pI<pK}}_{\text{a}}$.

For the side chain the same rule applies as of for carboxylic acid and amino group.

(c)

Interpretation Introduction

Interpretation:

The form of amino acid that predominates are the isoelectric point need to be identified.

Concept introduction:

Amino acids at a particular pH do not migrate in an electric field.  This pH is known as the isoelectric point.  The isoelectric point is also known as isoionic point.  At this isoelectric point the amino acid is neutral.  This means that the zwitterion form predominates more over the other forms.  pI is the isoelectric point and this can be given by average of the pK_a.

$\text{pI=}\frac{{\text{pK}}_{{\text{a}}_{\text{1}}}{\text{+pK}}_{{\text{a}}_{\text{2}}}}{\text{2}}$

The carboxylic acid form will predominate if, ${\text{pI<pK}}_{\text{a}}$ and carboxylate form will predominate if, ${\text{pI>pK}}_{\text{a}}$.

The uncharged amino form will predominate if, ${\text{pI>pK}}_{\text{a}}$ and the protonated amino form will predominate if, ${\text{pI<pK}}_{\text{a}}$.

For the side chain the same rule applies as of for carboxylic acid and amino group.

(d)

Interpretation Introduction

Interpretation:

The form of amino acid that predominates are the isoelectric point need to be identified.

Concept introduction:

Amino acids at a particular pH do not migrate in an electric field.  This pH is known as the isoelectric point.  The isoelectric point is also known as isoionic point.  At this isoelectric point the amino acid is neutral.  This means that the zwitterion form predominates more over the other forms.  pI is the isoelectric point and this can be given by average of the pK_a.

$\text{pI=}\frac{{\text{pK}}_{{\text{a}}_{\text{1}}}{\text{+pK}}_{{\text{a}}_{\text{2}}}}{\text{2}}$

The carboxylic acid form will predominate if, ${\text{pI<pK}}_{\text{a}}$ and carboxylate form will predominate if, ${\text{pI>pK}}_{\text{a}}$.

The uncharged amino form will predominate if, ${\text{pI>pK}}_{\text{a}}$ and the protonated amino form will predominate if, ${\text{pI<pK}}_{\text{a}}$.

For the side chain the same rule applies as of for carboxylic acid and amino group.