Researchers are unraveling the building blocks of Earth’s pigments

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Researchers are unraveling the building blocks of Earth's pigments

New data could inspire more environmentally friendly tech, study finds

A newly developed framework for understanding the photoproperties of both natural organic matter and eumelanin, a natural pigment responsible for dark colors in organisms, may inspire advanced sustainable technologies, scientists say.

Although they are some of the most widespread substances on Earth, not much is known about eumelanin, or natural organic matter (NOM) - a dark-colored substance formed by the decomposition of biological material. In humans, eumelanin is a vital pigment in skin and other tissues that protects cells from damage by ultraviolet radiation. In nature, NOM gives rivers and soils their color and affects light-driven reactions like photosynthesis.

Although these compounds have been studied individually for decades, researchers in a new study, by scrutinizing them alongside each other, have shown that eumelanin and NOM have common properties beyond their dark colors.

"Synthesizing the molecular building blocks in eumelanin and NOM is akin to two very different approaches for creating a diverse set of words," said Bern Kohler, one of the senior authors of the study and professor of chemistry and biochemistry at The Ohio State University. "Melanin synthesis is like giving someone multiple copies of the alphabet and asking them to make words, while NOM synthesis is like using scissors to cut words out of books from a library."

Now, using advanced spectroscopy and imaging to study disassembled eumelanin nanoparticles, Kohler and his colleagues were able to observe few-layered stacks only a few nanometers in size that closely resemble nanostructures seen in NOM samples. These common structures were revealed to be responsible for their similar optical properties.

Even though the starting materials and chemical pathways that lead to underlying molecules in eumelanin and NOM are remarkably different, these tiny structures show that they can assemble to form common nanostructures. These results reveal how common photoproperties can emerge in both natural and lab-made carbon-based nanomaterials despite notable differences in their chemical structures, said Kohler.

The study was recently published in ACS Central Science.

What's more, understanding eumelanin and NOM could help scientists create a swath of sustainable technologies, from more efficient solar power cells to longer-lasting batteries and electronics, said Meera Madhu, co-author of the study and a PhD student in chemistry and biochemistry at Ohio State.

"Eumelanin can absorb the entire solar spectrum, so by finding a way to convert that into energy that can be stored or used in viable ways, it's going to become one avenue to overcome the energy issues that we have," she said.

Looking ahead, the study concludes that this research serves as a valuable template for studying and designing other carbon-based nanomaterials, paving the way for new discoveries in fields like light harvesting, energy storage and bioelectronics.

"This fundamental understanding of how eumelanin and NOM absorb and respond to light could ultimately help guide rational design of carbon-based materials," said Madhu. "By bringing together two materials that have so far been studied separately, this work gives researchers a framework they can build on to understand related carbon materials."

Other co-authors include Aleksandra Ilina from Ohio State, as well as Hang Li and Garrett McKay from Texas A&M University. This work was supported by the Ohio Eminent Scholars program, the National Science Foundation and the Army Research Office.

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