N-(Aminooxy-PEG2)-N-bis(PEG3-propargyl) consists of two terminal propargyl groups and an aminooxy group. The propargyl groups reacts with azide-bearing compounds or biomolecules via copper catalyzed Click Chemistry. The aminooxy group is reactive towards aldehydes to form oxime bonds. If a reductant is used, it will form a hydroxylamine linkage. Aminooxy compounds are very reactive and sensitive; they cannot be stored for long term. Immediate use (within 1 week) is highly recommended.