Lipoamido-PEG4-acid contains the functional form of lipoic acid, lipoamide, through the formation of an amide bond as well as a terminal carboxylic acid. The lipoic acid is a co-factor that is used in biological systems such as the citric acid cycle. The carboxylic acid can react with primary amines in the presence of activators such as EDC and DCC to form stable amide bonds. The hydrophilic PEG spacer increases the compound's solubility in aqueous environments. The water solubility properties of the PEG linker are enhanced with longer PEG chains.