There are building blocks for RNA-based life at the center of our galaxy

Nitriles, a class of organic molecules having a cyano group, that is, a carbon atom bonded with a triple unsaturated bond to a nitrogen atom, are typically poisonous. But paradoxically, they are also an important precursor to molecules essential to life, such as ribonucleotides, which are composed of the nucleobases or ‘letters’ A, U, C and G linked by a ribose and phosphate group, which together forming RNA. Now, a team of researchers from Spain, Japan, Chile, Italy and the US shows that a wide variety of nitriles exist in interstellar space within the molecular cloud G+0.693-0.027, near the center of the Milky Way.

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 lead author of the new study, said: “Here we have we show that the chemistry taking place in the interstellar medium is able to efficiently form multiple nitriles, which are important molecular precursors of the ‘RNA World’ scenario.”

Possible ‘RNA-only’ world

Under this scenario, life on Earth was originally based only on RNA, and DNA and protein enzymes evolved later. RNA can perform both functions: to store and copy information such as DNA, and to catalyze reactions such as enzymes. According to the “RNA World” theory, nitriles and other building blocks for life don’t necessarily all have to have originated on Earth itself: They could also have originated in space and “lifted up” to the young Earth in meteorites and comets during the ‘Late Heavy Bombardment’ period, between 4.1 and 3.8 billion years ago. In support, nitriles and other precursor molecules to nucleotides, lipids and amino acids have been found in modern-day comets and meteors.

But where in space could these molecules come from? Primary 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, the 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 that of our sun. There is no evidence that stars are currently forming within G+0.693-0.027, although scientists suspect it could evolve into a stellar nursery in the future.

“The chemical content of G+0.693-0.027 is comparable to other star-forming regions in our galaxy, as well as to solar system objects such as comets. This means that his study could give us important insights into the chemical ingredients available in the nebula that gave rise to our planetary system,” explains Rivilla.

Electromagnetic spectra studied

Rivilla and colleagues used two telescopes in Spain to study the electromagnetic spectra 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 discovered the nitriles cyanosole (CH2CCHCN), propargyl cyanide (HCCCH2CN) and cyanopropyne, which had not yet been found in G+0.693-0.027, although they had been reported in 2019 in the TMC-1 dark cloud in the constellations Taurus and Auriga, a molecular cloud with very different conditions than G+0.693-0.027.

Rivilla et al. also found possible evidence for the occurrence in G+0.693-0.027 of cyanoformaldehyde (HCOCN) and glycolonitrile (HOCH2CN). Cyanoformaldehyde was first detected 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 within G+0.693-0.027, such as glycolaldehyde (HCOCH2OH), urea (NH2CONH2), hydroxylamine (NH2OH), and 1,2-ethenediol (C2H4O2), confirming that the interstellar chemistry is capable of is to supply the most basic ingredients for the ‘RNA world’.

Nitriles are one of 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 the current results, we now know that nitriles are among the most abundant chemical families in the universe. We’ve found them in molecular clouds at the center of our galaxy, protostars of different masses, meteorites and comets, as well as in the atmosphere of Titan, Saturn’s largest moon.”

Second author Dr. Izaskun Jiménez-Serra, also a researcher at CSIC and INTA, looked ahead: “So far we have discovered several simple precursors of ribonucleotides, the building blocks of RNA. But there are still important missing molecules that are difficult to detect. For example, we know that the origin of life on Earth probably also required other molecules, such as lipids, which are responsible for the formation of the first cells. Therefore, we also need to focus on understanding how lipids can be formed from simpler precursors available in the interstellar medium.”