Preparation of novel mcl-PHA by green synthesis: influence of active small molecule via esterification effect on side chain

Abstract

Microbial production of polyhydroxyalkanoic acid (PHA) with customized features has been attempted by humans through metabolic engineering. However, few studies have explored the green chemical synthesis of customized PHA using hydroxy fatty acids. In the present study, new mcl-PHA having C16-co-C16, blocked by esterification of hydroxy groups in the side chain, was synthesized by melt polycondensation using aleuritic acid (9, 10, 16-trihydroxyhexadecanoic acid) and lactic acid as long-chain fatty acid monomers and active blocking molecule, respectively. The results showed that when the two monomers reacted at 150 °C for 24 h, the properties of PHA were largely retained, along with free hydroxyl groups as much as possible. Comparison of the effect of different ratios of active small molecule (lactic acid) on the properties of new mcl-PHA revealed that copolymerization mainly happened between the long-chain monomers, and lactic acid served as a blocker by esterification in the side chain on the hydroxy groups of mcl-PHA. Further, the properties of side chain-esterified mcl-PHA (SCE-mcl-PHA) changed from rigid to soft with increasing ratio of active lactic acid monomer. The tensile strength of mcl-PHA was similar to that of commercially available products PLA and PHBV. The mechanical properties of SCE-mcl-PHA significantly changed by adding only 5 wt% lactic acid monomer. Besides, the cell proliferation analysis showed that the new PHA had minimum cytotoxicity, which was close to PLA and PHBV. Therefore, these new mcl-PHA and SCE-mcl-PHA have great potential for application in food, medicine, cosmetics, and other fields, and hence require further investigation.