Enzymatic Transformation of Bacterial Polyhydroxyalkanoates into Repolymerizable Oligomers Directed towards Chemical Recycling

• Published in: Macromolecular Bioscience
• Main Authors: Kaihara, Sachiko, Osanai, Yasushi, Nishikawa, Kimihito, Toshima, Kazunobu, Doi, Yoshiharu, Matsumura, Shuichi
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2005
• Subjects: Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1002/mabi.200500030; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fmabi.200500030; https://onlinelibrary.wiley.com/doi/pdf/10.1002/mabi.200500030

Abstract Summary: The enzymatic transformation into an oligomer was carried out with the objective of developing the chemical recycling of bacterial polyesters. Poly( R ‐3‐hydroxyalkanoate)s (PHAs), such as poly[( R ‐3‐hydroxybutyrate)‐ co ‐12%( R ‐3‐hydroxyhexanoate)] and poly[( R ‐3‐hydroxybutyrate)‐ co ‐12%( R ‐3‐hydroxyvalerate)], were degraded by granulated Candida antarctica lipase B immobilized on hydrophilic silica (lipase GCA) in a diluted organic solvent at 70 °C. The degradation products were cyclic oligomers having a molecular weight of a few hundreds. The obtained cyclic oligomer was readily repolymerized by the same lipase (lipase GCA) to produce the corresponding polyester in a concentrated solution. The cyclic oligomer was copolymerized with ε ‐caprolactone using lipase to produce the corresponding terpolymers having an $\overline M _{\rm w}$ of 21 000. This is the first example of the enzymatic chemical recycling of bacterial PHAs using lipase. Poly( R ‐3‐hydroxybutyrate) [P(3HB)] was also degraded into the linear‐type R ‐3HB monomer to trimer by P(3HB)‐depolymerase (PHBDP) in phosphate buffer at 37 °C. The degradation using PHBDP required a longer reaction time compared with the lipase‐catalyzed degradation in organic solvent. The monomer composition of the oligomer depended on the origin of the PHBDP. The R ‐3HB monomer was predominately produced by PHBDP from Pseudomonas stutzeri , while the R ‐3HB dimer was produced by PHBDP from Alcaligenes faecalis T1. Repolymerization of these oligomers by lipase in concentrated organic solvent produced a relatively low‐molecular‐weight P(3HB) (e.g., $\overline M _{\rm w}$ = 2 000). Degradation of P(3HB) by lipase in organic solvent into repolymerizable cyclic oligomer and degradation of P(3HB) by PHBDP in buffer into hydroxy acid type R ‐3HB dimer. magnified image Degradation of P(3HB) by lipase in organic solvent into repolymerizable cyclic oligomer and degradation of P(3HB) by PHBDP in buffer into hydroxy acid type R ‐3HB dimer.