N-(NHS ester-PEG3)-N-bis(PEG3-Mal) is a 3-arm PEG reagent with an NHS ester group and two maleimide moieties that is reactive toward thiols. Maleimide groups react specifically with sulfhydryl groups to form a stable thioether linkage when the pH is between 6.5 and 7.5. The NHS ester can be used to label the primary amines (-NH2) of proteins, amine-modified oligonucleotides, and other amine-containing molecules. Reagent grade, for research purpose. Please contact us for GMP-grade inquiries.