A peptide bond is a type of covalent bond that forms between two amino acids during protein synthesis. This bond occurs when the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water (this process is known as a dehydration synthesis or condensation reaction). Once formed, the peptide bond creates a dipeptide, and as more amino acids join in the same fashion, polypeptides and proteins are formed.
Pi backbonding, often referred to in the context of chemistry, particularly in coordination chemistry and organometallic chemistry, is a type of bonding interaction between a metal center and a ligand. It typically involves the donation of electron density from a filled metal d-orbital to an empty orbital of a ligand, usually a π* (pi-star) orbital, which is the antibonding orbital associated with pi bonds.