Aminooxy-PEG3-bromide HCl salt is a PEG derivative containing an aminooxy group and a bromide group. The hydrophilic PEG spacer increases solubility in aqueous media. The aminooxy group can be used in bioconjugation. It reacts with an aldehyde to form an oxime bond. If a reductant is used, it will form a hydroxylamine linkage. The bromide (Br) is a very good leaving group for nucleophilic substitution reactions.