Study at Berkeley Lab traces growth of molecules into solids, life forms

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Musahid Ahmed/Courtesy

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A study involving researchers from Lawrence Berkeley National Laboratory is providing insights into the formation of molecules that are precursors to the building blocks of life.

The study, published Monday in the journal Nature Astronomy, traced the formation of pyrene, a form of polycyclic aromatic hydrocarbon, or PAH, which has a similar structure to certain DNA forms, according to Musahid Ahmed, senior scientist of chemistry at the lab. Pyrene hydrocarbons represent a step in the creation of more complex, three-dimensional molecular forms that make up solid material, Ahmed said.

The researchers simulated the formation of pyrene in combustion environments and deep space settings. Chemical experiments for the research were performed at the lab, with researchers from the University of Hawaii at Manoa and Florida International University involved in analysis.

“(It’s) exciting because (this) shows the method of how we can systematically start off building of molecules to get bigger structures that show up in meteorites or other forms of space dust,” Ahmed said.

Observations were conducted using gas-based chemical reactions and high temperatures to simulate space conditions, Ahmed said. The paper, according to Ahmed, is part of a series of studies that form a stage-by-stage approach to see how additional rings are generated in PAH molecular structures.

The simulation, which involved probing chemicals in a reactor, provides a clue to the formation of more complex molecules that form solid material. This particular study of the series showed the researchers how the four-ringed compound pyrene is produced from the acetylene’s reaction with the three-ringed compound phenanthrene.

“Before, people did not know how PAHs can be formed in space. So we provided solid evidence on the fundamental reaction mechanisms,” said Ralf Kaiser, professor of chemistry at the University of Hawaii at Manoa and one of the study’s lead authors.

Alexander Mebel, professor of physical and computational chemistry at Florida International University, said clarifying the formation mechanism of PAHs in space has implications for Earth’s environment.

“In space, they’re precursors to life, and on Earth they’re very bad pollutants,” Mebel said.

PAH manifests in combustion processes, such as burning fossil fuels, which form black carbon or soot. By better understanding how pyrene forms, techniques can be developed to minimize the formation of PAH and make combustion cleaner for airplane and car engines, Mebel said.

Ahmed said he plans to continue systematically tracking this sequence of three-dimensional molecular development. Pyrene offers an experimental pathway toward how these structures can form out of a number of possible pathways, according to Ahmed.

“We’re just going to make them bigger and bigger,” Ahmed said. “(We’re) going to make five rings, six rings, and get to a complete 3-D structure, like a buckyball.”

Contact Michele Meltzer at [email protected] and follow her on Twitter at @michele_meltzer.