Question

Question 1: The pKas of the a-amino group, a-carboxylic acid, and side chain carboxylic acid are 9.6, 1.9, and 3.9, respectively. Paying attention to the ionizable group, draw the structure of L-aspartate, in a solution of pH 1. Repeat for pH 7 and 12 solutions. Question 2: Using the amino acid side chain information in Chapter 4 of our textbook, predict the relative order of silica gel Rf values hydrolyzed peptide containing the amino acids, serine, lysine, leucine, and valine. Assume the developing solvent is n-butanol, acetic acid, and water (pH=1.5).

Answer 1

Question 1:

Answer:

Aspartic acid is a polar amino acid with one additional methylene group. The methylene group is bonded with one carboxyl group. Hence aspartic acid is a dicarboxylic amino acid. The presence of second carboxyl group makes the molecule very hydrophilic.

Question 2:

Answer:

Rf value can be calculated using the formula:

The Rf values with butanol-acetic acid- water solvent are as follows:

serine 0.27, lysine 0.14, leucine 0.73, valine 0.60.