Dansyl

Dansyl refers to the dansyl fluorophore, a sulfonylated naphthalene group widely used as a fluorescent tagging moiety in biochemistry. It is most commonly encountered as dansyl chloride (DNS‑Cl), which reacts with primary amines to form stable dansylated derivatives via sulfonamide linkages. The dansyl group is chemically known as 5-dimethylaminonaphthalene-1-sulfonyl.

Spectroscopic properties make dansyl useful for labeling and detection. The group absorbs in the near-UV (typically around 335–360 nm) and emits in the green region (roughly 510–550 nm), with the emission strongly influenced by the local environment. This solvatochromic behavior means fluorescence can report on polarity and conformational changes near the labeled site. The quantum yield is generally favorable, contributing to sensitive fluorescence detection.

Applications and methods of use. Dansyl chloride is widely employed to tag primary amines, including the N-terminus of proteins and the side chains of lysine residues, as well as amino acids and peptides for analytical detection. The resulting dansylated products can be detected by fluorescence in HPLC, thin-layer chromatography, or gel-based methods. In addition to general labeling, dansyl derivatives serve as solvatochromic probes to study protein folding, binding events, and microenvironment polarity.

Considerations. Labeling conditions are typically mildly basic to promote reaction with amines, and the reaction can be nonselective when multiple amine groups are present. Dansyl compounds can be subject to photobleaching, and safety data sheets should be consulted for handling, as reagents like dansyl chloride are moisture-sensitive and irritant.