A research team led by scientists from Boise State University and NASA’s Goddard Space Flight Center has identified several complex cyanide compounds in a set of CM chondrite meteorites. These extraterrestrial organometallic compounds are a source of free cyanide and also bear a striking similarity to portions of the active sites of hydrogeneses (enzymes that provide energy to bacteria and archaea by breaking down hydrogen gas), which suggests that these compounds may have played an important role during the origin and early evolution of life on Earth.

“Cyanide, a carbon atom bound to a nitrogen atom, is thought to be crucial for the origin of life, as it is involved in the non-biological synthesis of organic compounds like amino acids and nucleobases, which are the building blocks of proteins and nucleic acids used by all known forms of life,” said Dr. Karen Smith, a researcher at Boise State University.

Dr. Smith and colleagues developed new analytical methods to extract and measure ancient traces of cyanide in meteorites.

They analyzed five CM chondrite meteorites (ALH 83100, LEW 85311, LEW 90500, LON 94102 and Murchison), CR (GRA 06100) and CV (RBT 04133) chondrite meteorites, and one Martian meteorite (ALH 84001).

Only CM chondrites contained cyanide compounds, with the highest concentration in LEW (Lewis Cliff) 85311.

Dr. Smith and co-authors were surprised to discover that cyanide, along with carbon monoxide (CO), were binding with iron to form stable compounds in the meteorites.

They also identified two different iron cyano-carbonyl complexes — [FeII(CN) 5 (CO)]3− and [FeII(CN) 4 (CO) 2 ]2− — in the LEW 85311 meteorite using high-resolution liquid chromatography-mass spectrometry.

“One of the most interesting observations from our study is that these iron cyano-carbonyl complexes resemble portions of the active sites of hydrogenases, which have a very distinct structure,” said Dr. Mike Callahan, from Boise State University and NASA’s Goddard Space Flight Center.

Hydrogenases are present in almost all modern bacteria and archaea and are widely believed to be ancient in origin.

They are large proteins, but the active site — the region where chemical reactions take place — happens to be a much smaller metal-organic compound contained within the protein. It is this compound that resembles cyanide compounds the team discovered in CM chondrites.

“Cyanide and carbon monoxide attached to a metal are unusual and rare in enzymes,” Dr. Smith said.

“Hydrogenases are the exception. When you compare the structure of these iron cyano-carbonyl complexes in meteorites to these active sites in hydrogenases, it makes you wonder if there was a link between the two.”

“It’s possible that iron cyano-carbonyl complexes may have been a precursor to these active sites and later incorporated into proteins billions of years ago. These complexes probably acted as sources of cyanide on early Earth as well.”

The research was described in a paper in the journal Nature Communications.

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Karen E. Smith et al. 2019. Organometallic compounds as carriers of extraterrestrial cyanide in primitive meteorites. Nature Communications 10, article number: 2777; doi: 10.1038/s41467-019-10866-x