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Two novel esterases from the anaerobe Clostridium botulinum ATCC 3502 (Cbotu_EstA and Cbotu_EstB) were expressed in Escherichia coli BL21-Gold(DE3) and were found to hydrolyze the polyester poly(butylene adipate-co-butylene terephthalate) (PBAT). The active site residues (triad Ser, Asp, His) are present in both enzymes at the same location only with some amino acid variations near the active site at the surrounding of aspartate. Yet, Cbotu_EstA showed higher kcat values on para-nitrophenyl butyrate and para-nitrophenyl acetate and was considerably more active (sixfold) on PBAT. The entrance to the active site of the modeled Cbotu_EstB appears more narrowed compared to the crystal structure of Cbotu_EstA and the N-terminus is shorter which could explain its lower activity on PBAT. The Cbotu_EstA crystal structure consists of two regions that may act as movable cap domains and a zinc metal binding site.

Recently, a variety of biodegradable polymers have been developed as alternatives to recalcitrant materials. Although many studies on polyester biodegradability have focused on aerobic environments, there is much less known on biodegradation of polyesters in natural and artificial anaerobic habitats. Consequently, the potential of anaerobic biogas sludge to hydrolyze the synthetic compostable polyester PBAT (poly(butylene adipate-co-butylene terephthalate) was evaluated in this study. On the basis of reverse-phase high-performance liquid chromatography (RP-HPLC) analysis, accumulation of terephthalic acid (Ta) was observed in all anaerobic batches within the first 14 days. Thereafter, a decline of Ta was observed, which occurred presumably due to consumption by the microbial population. The esterase Chath_Est1 from the anaerobic risk 1 strain Clostridium hathewayi DSM-13479 was found to hydrolyze PBAT. Detailed characterization of this esterase including elucidation of the crystal structure was performed. The crystal structure indicates that Chath_Est1 belongs to the α/β-hydrolases family. This study gives a clear hint that also micro-organisms in anaerobic habitats can degrade manmade PBAT.

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The synthesis of novel methylcoumarin end-functionalized poly(methyl methacrylate) of different molecular weights using atom transfer radical polymerization (ATRP) is reported. 7-(2′-Bromoisobutyryloxy)-4-methylcoumarin was used as the ATRP initiator at 70 °C using copper(I) bromide/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) as the catalyst system. The theoretical and experimental number-average molecular weights M n with narrow polydispersities (M w /M n ) 1.1-1.4) agreed very well. Photochemical drug loading of the methylcoumarin end-functionalized polymer was performed in solution (chloroform/acetone 1:2) with benzophenone as additional photosensitizer using a 50-fold excess of the pro-drug 1-heptanoyl-5-fluorouracil (H5FU). UV/vis and NMR spectroscopy were used for the characterization of the polymer drug conjugate and indicated an almost quantitative conversion of coumarin moieties into photodimers. The change of polymer properties like thermal stability, glass transition, and molecular weight after photochemical drug immobilization was also studied. The glass transition temperature increased only negligibly, whereas the thermal decomposition commenced at considerably lower temperature for the polymer drug conjugate. The molecular weight distribution of the H5FU-loaded polymer showed no detectable chain degradation due to the applied UV irradiation. The characterization of the photoinduced drug release was investigated for a single photon absorption (SPA) process. The polymer drug conjugate was irradiated at λ ) 266 nm to cleave the cyclobutane linker between the methylcoumarin moiety and the pro-drug H5FU. The drug release was monitored and quantified using highperformance liquid chromatography (HPLC). Assuming quantitative hydrolysis of H5FU, 4.76 µg of 5-fluorouracil (5FU) per 1 mg of polymer drug conjugate was released on irradiation.