Amide Bond
Amide Bond — A covalent bond formed between a carbonyl carbon and a nitrogen atom, synonymous with peptide bond when occurring between amino acid residues.
What Is an Amide Bond?
An amide bond is the covalent linkage formed between a carboxyl group (-COOH) and an amino group (-NH2) with the loss of water. In peptide chemistry, the amide bond between the alpha-carboxyl and alpha-amino groups of adjacent amino acids is specifically called a peptide bond. Amide bonds also occur in amino acid side chains (asparagine, glutamine) and in C-terminal amidation modifications.
Chemical Properties
The amide bond has partial double-bond character (~40%) due to nitrogen lone pair delocalization into the carbonyl. This gives the bond a rotational barrier of approximately 75-85 kJ/mol, restricting the six atoms of the amide unit to a planar geometry. The resonance stabilization makes amide bonds thermodynamically stable under physiological conditions, with a half-life of ~500 years for spontaneous hydrolysis at pH 7.
Amide Bond Modifications
- N-methylation: Adding a methyl group to the amide nitrogen increases protease resistance and membrane permeability (used in cyclosporine)
- Amide bond isosteres: Replacement with reduced amide (-CH2NH-), ester, or triazole linkages creates peptidomimetics
- C-terminal amidation: Replacing the C-terminal -COOH with -CONH2 increases receptor binding and protease resistance for many bioactive peptides
Frequently Asked Questions
What is Amide Bond?
A covalent bond formed between a carbonyl carbon and a nitrogen atom, synonymous with peptide bond when occurring between amino acid residues.
Why is Amide Bond important in peptide research?
Amide Bond is a fundamental concept in chemistry as it relates to peptide science. It directly influences experimental design, compound characterization, and the reliability of research outcomes across biochemistry and molecular biology disciplines.