Alkyne-PEG3-NHS ester is a bifunctional molecule containing NHS ester and alkyne functional groups. NHS ester group is used for the labeling of amine groups, like lysine and N-terminal NH2, in proteins and peptides. And terminal alkyne group is useful for copper catalyzed Click chemistry (CuAAc) or Sonogashira coupling.
PEG3 linker is hydrophilic, and provides a good separation between the parts of the conjugate.