Studies on the Effect of Isomerism in Main Chain on Enzymatic Degradation of PBS-based Copolymers with Combination of Molecular Modeling

The enzymatic degradation of poly (butylene succinate-co-1,4-cyclohexane dimethanol succinate) (PBS-co-CHDMS), poly (butylene succinate-co-butylene 1, 4-cyclohexanedicarboxylic acid) (PBS-co-BCHDA) and poly (butylene succinate) (PBS) were performed with the aim to gain more underlying information about the degradation rules and differences in organic solvent. Among various hydrolytic enzymes the lipase from Pseudomonas cepacia (PC) was chosen for the studies. The rules of enzymatic degradation were investigated by. molecular weight variation and MALDI-TOF-MS analysis of the degradation products. Additionally, mechanism of the combination between substrate and enzyme was studied with molecular docking. The results indicated that PBS-based copolymers showed an obvious degradation in chloroform. Compared to PBS-co-BCHDA, PBS-co-CHDMSs all showed a greater degradation rate after 60 h enzymatic degradation. Particularly maximum degradation was observed in PBS-co-10% CHDMS with a degradation ratio of ratio about 85%. The enzymatic degradation of PBS-based copolymers produced not only linear segments, but also cyclic oligomers. Furthermore, PBS-co-CHDMS produced more oligomers than PBS-co-BCHDA. According to the results of molecular docking, the free energy of binding between PC lipase and substrate in chloroform was in the order of CMSCM > BSCM > BCAB > BSB. That is, the docking of substrate containing 1, 4-cyclohexane dimethanol succinate(CHDMS) in the active site of PC lipase was more stable than any other ones.