Breakthrough: Catalyzing a Zero-Carbon World by Harvesting Energy From Living Cells

Krebs cycle metabolites fall in energy-rich carbon feedstock.
Credit: Issey Takahashi

Scientists from Nagoya University have achieved a breakthrough in converting energy-deficient metabolites to a biorenewable resource thanks to a versatile catalyst.

The imminent environmental crisis calls for an urgent transition to a green economy. A team of scientists at Nagoya University, Japan, led by Professor Susumu Saito, has recently found an interesting way to make this happen — by leveraging an important metabolic pathway in living cells. Their aim was to turn the energy-poor pathway products into biorenewable ones that can potentially power our world in a sustainable manner.

In most plants, animals, fungi, and bacteria, a pathway called the “Krebs cycle” is responsible for providing fuel for cells to carry out their functions. Operating in the mitochondria, this cycle ultimately results in the formation of both energy-rich compounds like NADH and FADH2 (which are used to power the organism) and energy-deficient metabolites like C4-, C5-, and C6-polycarboxylic acids (PCAs). Recently, the idea of modifying highly functionalized PCAs into biorenewable molecules has been explored, by restoring the carbon-hydrogen (C-H) bonds that were lost in their creation. This would need these biomolecules to undergo reactions called “dehydration” and “reduction,” that is, the reversal of the Krebs cycle — a complicated process.

In their new study, which was published in Science Advances, Prof Saito and his team rose to the challenge by aiming to find an artificial “catalyst,” a molecule that could facilitate this modification. They focused on a powerful, versatile precatalyst called “phosphine-bipyridine-phosphine (PNNP)iridium (Ir)-bipyridyl complex.” Prof Saito says, “Single-active-metal catalyst such as the (PNNP)Ir catalyst can facilitate the selective hydrogenation and dehydration of highly functionalized (highly oxidized and oxygenated) biomass feedstock like Krebs cycle metabolites.”

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