Two novel protocols for the chemical valorization of polyhydroxybutyrate (PHB) were developed, aiming at the production of two bio-based molecules: methyl 3-hydroxybutyrate (MHB) and methyl 3-methoxybutyrate (MMB). Optimized reaction conditions were applied to pure PHB and PHB inclusions inside bacterial cells as starting materials. MHB was synthesized through a single-step catalytic methanolysis, while MMB was synthesized through a three-step process: thermolytic distillation to give crotonic acid (CA), esterification to give methyl crotonate (MC), and oxa-Michael addition of MeOH. The obtained MHB and MMB were tested as solvents for the recovery of PHB itself both from freeze-dried single strain cultures (SSC) and mixed microbial cultures (MMC) with low to medium contents of PHB (22–57 wt %). High PHB recovery was achieved: up to 96 ± 1% through MHB and up to 98 ± 1% through MMB. Extraction from MMC slurry (with a PHB content of 39% on dry weight) was also performed, recovering 77 ± 2% using MHB and 92 ± 2% using MMB. High purities and excellent molecular weights and polydispersity indexes of extracted PHB were obtained with both MHB and MMB. Solubility in water, octanol/water partition coefficients (log K_ow), and aerobic ready biodegradability of both solvents were also evaluated.

中文翻译：

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将聚羟基丁酸酯 (PHB) 化学回收为生物基溶剂及其在循环 PHB 萃取中的应用

开发了两种用于聚羟基丁酸 (PHB) 化学价值化的新方案，旨在生产两种生物基分子：3-羟基丁酸甲酯 (MHB) 和 3-甲氧基丁酸甲酯 (MMB)。将优化的反应条件应用于细菌细胞内的纯 PHB 和 PHB 包裹体作为起始材料。MHB 通过一步催化甲醇分解合成，而 MMB 通过三步过程合成：热解蒸馏得到巴豆酸 (CA)，酯化得到巴豆酸甲酯 (MC)，以及 MeOH 的氧杂-迈克尔加成。将获得的 MHB 和 MMB 作为溶剂从冷冻干燥的单菌株培养物 (SSC) 和混合微生物培养物 (MMC) 中回收 PHB 本身，其中 PHB 含量低至中等 (22–57 wt%)。实现了高 PHB 回收率：通过 MHB 高达 96 ± 1%，通过 MMB 高达 98 ± 1%。还进行了从 MMC 浆液中提取（PHB 含量为干重的 39%），使用 MHB 回收 77±2%，使用 MMB 回收 92±2%。使用 MHB 和 MMB 均获得了高纯度和优异的提取 PHB 的分子量和多分散性指数。水中溶解度，辛醇/水分配系数（logķ_流），以及两种溶剂的好氧生物降解能力进行了评价。