Aminooxy-PEG4-alcohol is an aqueous soluble PEG reagent. The aminooxy group can react with an aldehyde to form an oxime bond. If a reductant is used, it will form a hydroxylamine linkage. The hydroxyl group enables further derivatization or replacement with other reactive functional groups. Aminooxy compounds are very reactive and sensitive; they cannot be stored for long term. Immediate use (within 1 week) is highly recommended.