Used in bioconjugation to link molecules via amine-reactive NHS ester and alkyne groups. The PEG2 spacer enhances solubility and flexibility, improving reaction efficiency in aqueous and mixed solvents. The propargyl group enables click chemistry, especially copper-catalyzed azide-alkyne cycloaddition (CuAAC), for labeling biomolecules like proteins, peptides, and nucleic acids. Commonly applied in developing antibody-drug conjugates (ADCs), fluorescent probes, and functionalized surfaces in diagnostic and therapeutic research. Stable under standard handling conditions but should be protected from moisture to preserve NHS ester activity.