Hirano, Y., and Y. Nagao. “Effect of Polyethylene Glycol on the Synthesis of Tyr-Arg Dipeptide by a-Chymotrypsin in an Organic Medium”. Asian Journal of Chemistry, vol. 25, no. 6, Jan. 2013, pp. 3401-4, doi:10.14233/ajchem.2013.13873.