New favorite of renewable energy? Chinese scientists "turn waste into treasure" and may solve a century-old problem

For more than a century, scientists have been trying to turn certain substances into "treasures".

This substance is lignin, one of the most abundant organic polymers on earth, second only to cellulose in content.

However, their efforts largely ended in failure.

Now, this frustrating feeling of failure may be about to change.

Recently, a research team from Washington State University, Pacific Northwest National Laboratory (PNNL) and their collaborators synthesized an artificial enzyme that can effectively decompose lignin.

This work is a major breakthrough in the field and scientists are expected to develop a new type of catalyst that can truly address the limitations of biological and chemical catalysts.

The related research paper, titled “Highly stable and tunable peptoid/hemin enzymatic mimetics with natural peroxidase-like activities”, was published in the scientific journal Nature Communications.

(Source: Nature Communications)

The research team said that if this new artificial enzyme can be further improved in subsequent research to increase the overall conversion rate and produce more selective products, it will have the potential for larger-scale production.

What is lignin?

To understand the impact of lignin on our lives, we need to first know what substance (thing) it is.

A very academic answer is the picture below.

(Source: Wikipedia)

If you don’t understand, it’s okay, in fact not many people can understand it.

In simple terms, lignin is one of the most abundant organic polymers on earth, and it has very important biological functions in plant growth, development and resistance.

During the lignification process of plant cell walls, lignin penetrates into the cell walls and fills into the cell wall structure, which can increase the hardness of the cell walls, enhance the mechanical support of the cells, promote the formation of mechanical tissue, and help consolidate and support the plant body and water conduction and other functions.

In addition, since lignin is a cross-linked phenolic polymer and belongs to the aromatic high molecular polymer, its pyrolysis products will give smoked foods such as barbecue a unique aroma and taste.

More importantly, lignin has the potential to become a huge renewable energy source.

The disciple is better than the master

Although lignin seems so useful, it is treated as a "waste product" in actual production activities.

For example, in the production process such as papermaking, since lignin turns yellow when exposed to air, tens of millions of tons of lignin are treated as "impurities" and either discharged directly into natural water bodies or burned inefficiently to produce fuel and electricity. In fact, less than 20% of the lignin is effectively utilized, and even less is used as a resource, which can be said to be quite a waste.

However, as the second most abundant organic polymer on earth and the only non-petroleum resource in nature that can provide renewable aromatic compounds, lignin theoretically has the potential to "turn waste into treasure."

In nature, fungi and bacteria are able to use their enzymes to break down lignin and convert it into different products. For example, white rot fungi that grow on trees can break down lignin for reuse by soil organisms.

Figure｜White rot fungi growing on trees. (Source: PNNL)

Moreover, the degradation process involving natural enzymes is more environmentally friendly than chemical degradation, because chemical degradation requires high heat and consumes more energy than it produces.

However, natural enzymes in nature degrade over time, making them difficult to use in large-scale industrial production and are also very expensive.

Over the past few decades, new insights into how natural enzymes work have provided researchers with new insights into how to design this new class of artificial enzymes.

In this study, inspired by natural enzymes, the research team replaced the polypeptides around the active sites of natural enzymes with a protein-like molecule (i.e., peptoid).

These peptoids then automatically assemble into nanoscale transistors (crystalline tubes) and sheets.

Peptoids were first developed in the 1990s to mimic the functions of proteins. They have characteristics such as high stability and have helped scientists solve the shortcomings of natural enzymes.

In this case, they provide a high density of active sites that is not available in natural enzymes.

Figure | Xiao Zhang and Chun-long Chen, the corresponding authors of the paper, are studying the products of lignin degradation by a new biomimetic peptide catalyst. (Source: PNNL)

The researchers say they can use this artificial enzyme to precisely organize these active sites, tuning their local environment to promote catalytic activity. "So we have a higher density of active sites instead of just one active site."

As expected, the artificial enzymes were also more stable than natural enzymes and could operate at temperatures up to 60 degrees Celsius, a temperature that would destroy the activity of natural enzymes.

Experiments have shown that this artificial enzyme can effectively break down lignin, producing compounds that can be used in biofuel and chemical production.

In addition, the technology provides new pathways for renewable materials for aviation biofuels and bio-based materials, among other applications.

Researchers are currently seeking to speed up this reaction to tap into this underutilized resource.

Overall, this work does open up new opportunities to convert lignin into valuable products using environmentally friendly methods.

References:

https://www.nature.com/articles/s41467-022-30285-9

https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cctc.201901480

https://www.pnnl.gov/news-media/synthesizing-nanomaterials-natures-blueprints

https://www.pnnl.gov/news-media/new-artificial-enzyme-breaks-down-tough-woody-lignin

https://en.wikipedia.org/wiki/Lignin