Final answer:
The a-amino group in α-amino acids is typically less basic than amine groups in simple amines due to the influence of the adjacent carboxyl group. These a-amino groups accept a proton to form NH3+, exhibiting their basic character, but remain less basic compared to their simple amine counterparts.
Step-by-step explanation:
The a-amino group in amino acids is typically less basic than the amine groups found in simple amines. This is due to the electronegativity of the adjacent carboxyl group in α-amino acids which can pull electron density away from the amine group, making it less basic.
Additionally, when an a-amino group accepts a proton (H*), it forms NH3+, indicating its basic nature as it can remove H* from solution. However, in comparison to simple amine groups, which exist as independent entities, the basicity of an a-amino group is moderated by the presence of the carboxylic acid group.
In the case of basic amino acids which have basic side chains and are hydrophilic, these amino acids have basic primary or secondary amine groups in their side chains.
For example, histidine has an amine group with a pKa of 6.04, which although not ionized at physiological pH (7.4), is still considered a basic amino acid as it ionizes at a pH below 6.0. The presence of these amine groups influences the water solubility of the amino acids as well as their behavior in different pH environments.