The building blocks for RNA-based life abound at the center of our galaxy

08 July 2022

(Nanowerk News) Nitriles, a class of organic molecules with a cyano group, i.e. a carbon atom bonded by an unsaturated triple bond to a nitrogen atom, are usually toxic. But paradoxically, they are also key precursors to molecules essential for life, such as ribonucleotides, which are made up of nucleobases or ‘letters’ A, U, C, and G joined by ribose and phosphate groups, which together make up RNA.

Now, a team of researchers from Spain, Japan, Chile, Italy and the US are showing that various nitriles occur in interstellar space in the G+0.693-0.027 molecular cloud, near the center of the Milky Way (Frontiers in Astronomy and Space Science“Molecular precursors of the RNA world in space: new nitriles in the molecular cloud G+0.693-0.027”).

Dr Víctor M. Rivilla, a researcher at the Center for Astrobiology of the Spanish National Research Council (CSIC) and the National Institute of Aerospace Technology (INTA) in Madrid, Spain, and first author of the new study, said: “Here we show that the chemistry that occurs in the medium interstellar capable of efficiently forming multiple nitriles, which are key molecular precursors of the ‘RNA World’ scenario.”

Possible ‘RNA-only’ world

According to this scenario, life on Earth was originally based solely on RNA, and DNA and protein enzymes evolved later. RNA can fulfill both functions: store and copy information like DNA, and catalyze reactions like enzymes. According to the ‘RNA World’ theory, nitriles and other building blocks for life did not need to have all appeared on Earth itself: they probably also came from outer space and ‘hitted’ to young Earth in meteorites and comets during the ‘End of the Heavy Bombardment Period, between 4.1 and 3.8 billion years ago. As supports, nitriles and other precursor molecules for nucleotides, lipids, and amino acids have been found in contemporary comets and meteors.

But where do these molecules come from? The main candidates are molecular clouds, which are dense and cold regions of the interstellar medium, and are suitable for the formation of complex molecules. For example, a molecular cloud G+0.693-0.027 has a temperature of about 100 K and is about three light-years across, with a mass about a thousand times the mass of our Sun. There is no evidence that the star is currently forming within G+0.693-0.027, although scientists suspect that it may develop into a stellar nursery in the future.

“The chemistry of G+0.693-0.027 is similar to other star-forming regions in our galaxy, and also to solar system objects such as comets. This means that its study can provide us with important insights into the chemicals available in the nebulae that gave rise to our planetary system.” Rivilla.

Electromagnetic spectrum studied

Rivilla and his colleagues used two telescopes in Spain to study the electromagnetic spectrum emitted by G+0.693-0.027: the 30-meter-wide IRAM telescope in Granada, and the 40-meter-wide Yebes telescope in Guadalajara. They detected nitrile cyanoallene (CH2CCHCN), propargyl cyanide (HCCCH2CN), and cyanopropyne, which has not been found at G+0.693-0.027, although it has been reported in 2019 in the dark cloud TMC-1 in the constellations Taurus and Auriga, molecular clouds with very different conditions from G +0.693-0.027.

Rivilla et al. also found possible evidence for the occurrence in G+0.693-0.027 cyanoformaldehyde (HCOCN) and glycolonitrile (HOCH2CN). Cyanoformaldehyde was detected for the first time in the molecular clouds TMC-1 and Sgr B2 in the constellation Sagittarius, and glycolonitrile in the Sun-like protostar IRAS16293-2422 B in the constellation Ophiuchus.

Other recent studies have also reported other RNA precursors in G+0.693-0.027 such as glycolaldehyde (HCOCH2OH), urea (NH2CONH2), hydroxylamine (NH2OH), and 1,2-ethenadiol (C2H4HI2), confirming that interstellar chemistry is capable of providing the most basic material for the ‘RNA World’.

Nitriles are among the most abundant chemical families in space

Final author Dr Miguel A Requena-Torres, a lecturer at Towson University in Maryland, USA, concluded: “Thanks to our observations over the past few years, including our current results, we now know that nitriles are one of the most abundant chemical families in the universe. We have found them in molecular clouds at the center of our galaxy, protostars of different masses, meteorites and comets, and also in the atmosphere of Titan, Saturn’s largest moon.”

Second author Dr Izaskun Jiménez-Serra, also a researcher at CSIC and INTA, looked ahead: “We have detected so far some simple precursors of ribonucleotides, the building blocks of RNA. But there are still key missing molecules that are difficult to detect. For example, we know that the origin of life on Earth may also require other molecules such as lipids, which were responsible for the formation of the first cells. Therefore, we should also focus on understanding how lipids can form from simple precursors available in the interstellar medium.”

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