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Producing Biodegradable Plastic Feedstock Through Artificial Photosynthesis

Researchers at the Osaka Metropolitan University have successfully developed a light-driven, artificial photosynthesis pathway to increase yields of chemical feedstock for biodegradable plastics.

Plastics are ubiquitous in modern life, being durable yet inexpensive and lightweight. However, they have caused no small amount of concern over their toxic effects when introduced as pollution to the environment upon disposal. Over mounting concerns about their effects on the environment, researchers have turned their focus to developing biodegradable plastics that have all of the desirable characteristics of conventional petroleum-derived plastics, yet do not harm animals, humans, and the environment.

Fortunately, researchers from the Osaka Metropolitan University have managed to develop a method to produce biodegradable plastics using acetone and CO2, in hopes of being able to reduce the environmental impacts of plastic waste and strive towards the goal of becoming a circular economy. Their work was published in Chemical Communications.

The team, headed by Professor Yutaka Amao from the Research Center for Artificial Photosynthesis at Osaka Metropolitan University, has managed to synthesise 3-hydroxybutyrate, a chemical precursor to poly-3-hydroxybutyrate (PHB) —a durable, water-resistant yet biodegradable polyester used for packaging materials.

The researchers achieved this feat by using a mixture of substances, which included a cell extract containing acetone carboxylase and 3-hydroxybutyrate dehydrogenase from cultured Rhodobacter capsulatus SB1003, NAD+, a rhodium complex, triethanolamine (TEOA), and water-soluble zinc porphyrin, in the presence of light. In this NAD+ reduction system with TEOA as the electron donor, zinc porphyrin acts as the photosensitiser while the rhodium complex and the enzymes act as catalysts for the reaction. Using this particular system resulted in an 81 per cent improved yield of 3-hydroxybutyrate compared to existing production pathways that do not involve photosynthesis-inspired, light-driven catalysts.

The light-driven catalysis of acetone and CO2 to produce raw material for biodegradable plastic was heavily inspired by photosynthesis, with the chemical pathway involving light, as well as a dark reaction that fixes CO2 and synthesised 3-hydroxybutyrate.

These findings are among the latest in the Research Center for Artificial Photosynthesis’s attempts to draw upon artificial photosynthesis pathways to derive chemical feedstock and fuels, in their push to attain a carbon-neutral society.

“These findings, detailing the synthesis of 3-hydroxybutyrate, a raw material for PHB, from CO2, is a significant contribution to addressing both the plastic and CO2 reduction issues,” said Professor Amao. His research team also hopes to explore the use of artificial photosynthesis to produce 3-hydroxybutyrate from exhaust gases from factories, for cleaner air, reduced CO2 pollution, and a more sustainable source of raw materials for biodegradable plastics. [APBN]

Source: Kita et al. (2022). Visible-light-driven 3-hydroxybutyrate synthesis from CO2 and acetone with the hybrid system of photocatalytic NADH regeneration and multi-biocatalysts. Chemical Communications, 58(79), 11131-11134.