An amino acid from plastic, air, and water

A hybrid catalytic system can synthesize the amino acid alanine directly from used bioplastic, air, and water (Angew. Chem. Int. Ed. 2025, DOI: 10.1002/anie.202511466). The system could enable the recycling of waste plastic but also makes a valuable product from a cheap feedstock and without dangerous or expensive reagents.

One of the simpler amino acids, alanine is widely used across the food, pharmaceutical, and agricultural sectors. Currently the bulk of this global demand is met by microbial fermentation. Chemical syntheses typically employ toxic cyanide reagents and high-cost ammonia generated through the energy-intensive Haber–Bosch process.

But an interdisciplinary team led by Bocheng Qiu at Nanjing Agricultural University has overcome these limitations by combining thermochemical, plasma, and electrochemical processes to convert end-of-life polylactic acid (PLA) plastic into alanine.

First, a catalyst that the team developed oxidatively depolymerizes PLA, breaking it down into lactic acid monomers before oxidizing those to pyruvic acid. In parallel, a plasma discharge device activated molecular nitrogen in air to generate nitrogen dioxide, which was immediately dissolved in water to form nitric acid.

The team then combined these two unpurified feedstock streams into an electrochemical reactor, where a reductive process, mediated by a copper-bismuth alloy, give the final product, alanine. The reaction achieved an overall yield of 66% at a 100 g scale, and the robust sequence is capable of tolerating the typical impurities present in postconsumer waste such as cups, straws, and nonwoven fabrics, the team says.

For each step, the researchers completed a detailed mechanistic analysis and a thorough characterization of the respective catalysts. The group also performed lifecycle assessment and techno-economic analysis on the overall process, comparing the hybrid sequence against a thermocatalytic route employing ammonia as the nitrogen source. While the new synthesis showed increased profitability and a reduced carbon footprint, Eva Nichols, a catalysis and electrochemistry researcher at the University of British Columbia who was not involved in the work, believes it is unlikely to replace current methods of manufacture. The plasma step, which like the Haber–Bosch process also has a high energy demand, is potentially difficult to scale, particularly as the reaction produces toxic NO₂ as an intermediate.

Nichols is incredibly positive about the work, although she says an important, and overlooked, consideration is that of the enantioselectivity of the entire process. “In terms of manufacturing an amino acid, it’s important to know, are we preserving a stereocenter, or is there racemization along the way? Depending on the input source of PLA plastic, it may be an enantiopure or a racemic mixture,” she says.

Despite this, Nichols says she is inspired by the creativity and thoroughness of Qiu’s approach. “I was very impressed by the breadth of this paper. It’s rare to see so much under one title,” she says. “The impressive combination of catalyst development, characterization of each system, the creative combination of the reactions, and just the sheer number of approaches that were used to interrogate all of those systems I thought was really quite exceptional.”