Lipoamido-PEG8-acid contains a lipoic acid group and a carboxylic acid moiety. The terminal carboxylic acid can react with primary amine groups in the presence of activators (e.g. EDC, or HATU) to form a stable amide bond. Lipoic acid contains two sulfur atoms (at C6 and C8) connected by a disulfide bond and is thus considered to be oxidized although either sulfur atom can exist in higher oxidation states. The hydrophilic PEG linker increases the water solubility of the compound.