Sustainable enzymatic preparation of polyaspartate using a bacterial protease

Diethyl L-aspartate was polymerized by a bacterial protease from Bacillus subtilis (BS) in organic solvent at a temperature between 30 and 50 °C to yield α-linked poly(ethyl L-aspartate) having an M_w of up to 3700 and a maximum polymer yield of 85%. The best polymerization conditions were the 40 °C polymerization of diethyl L-aspartate using 30% protease BS containing 4.5 vol % water in acetonitrile for 2 days. Poly(ethyl L-aspartate) was readily depolymerized by the enzyme into the oligomeric and monomeric L-aspartate in aqueous acetonitrile. Poly(sodium aspartate) prepared by the saponification of poly(ethyl L-aspartate) was readily biodegradable by activated sludge obtained from the municipal sewage treatment plant. Also, poly(sodium aspartate) was depolymerized by the hydrolase enzyme into the monomeric aspartate. These results may indicate the sustainable chemical recycling and biorecycling of this polymer.