||NBD-Cl is widely used to label peptides, proteins, drugs and other biomolecules. It is also a popular derivatizing reagent for HPLC analysis. NBD-Cl is non-fluorescent, and generates fluorescent adducts upon reacting with aliphatic amines or thiol compounds. It reacts with amino groups such as aliphatic amines, amino acids, peptides, and proteins to form highly fluorescent compounds. The NBD-amine adducts have _ex = 464 nm and _em = 512 nm in aqueous solutions. The fluorescence spectra of NBD-amine adducts are highly environment-sensitive, the fluorescence intensity decreases significantly in aqueous solutions. NBD-Cl also reacts with thiol group to form fluorescent adducts, but the thiol adducts are much less fluorescent than the amine adducts.