Ammonium persulfate (APS) is a widely used reagent in biochemistry and molecular biology for the preparation of polyacrylamide gels. APS forms oxygen free radicals in aqueous solution by a base-catalyzed mechanism. The bases, most commonly used as catalysts, are tertiary amines such as TEMED (N,N,N′,N′-tetramethylethylenediamine) or DMAPN (3-dimethylaminopropionitrile). The free radicals will cause the polymerization of acrylamide and bis-acrylamide to form a gel matrix, which can be used for separating macromolecules by size. APS has also been utilized to study protein-protein interactions via photoinitiated crosslinking chemistry.