Researchers from Wrocław University of Science and Technology and MIT have demonstrated that peptides can maintain stability and fold into diverse structures in concentrated sulfuric acid. The findings may be of key importance in the search for traces of life in the clouds of Venus.

The paper on this subject - “Peptides Adopt Stable Omega Loop Structures in Concentrated Sulfuric Acid” - has just been published in Proceedings of the National Academy of Sciences (PNAS), the journal of the National Academy of Sciences, which is one of the most cited and comprehensive interdisciplinary scientific periodicals in the world.

Its authors are Dr. Janusz Pętkowski from the Faculty of Environmental Engineering at Wrocław Tech, Jia Yi Zhang, Dr. Aurelio J. Dregni, Prof. Sara Seager, and Prof. Mei Hong (all from the Massachusetts Institute of Technology, USA).

The Mysterious Clouds of Venus and the Search for Traces of Life

According to astronomers, the clouds on Venus consist mainly of sulfuric acid droplets containing a certain amount of chlorine, iron, and other elements. As a result, the planet's surface is visible neither from Earth nor from orbital probes, and its topography is known solely through radar studies.

A few years ago, evidence was presented for the presence of phosphine - a toxic gas produced in oxygen-deprived environments - and ammonia on Venus. Both gases are described as biomarkers, which, in short, means they could potentially indicate the presence of life.

Are Venusian sulfuric acid clouds really as hostile to organic structures as previously thought? In their latest publication in PNAS, the researchers compared conditions in the clouds of Venus to those on Earth's surface regarding the stability of peptides, which serve as small proteins and basic building blocks of life.

The Sulfuric Acid Paradox: From Destruction to Stabilization

The clouds of the second planet from the Sun feature extremely low water content and very high concentrations of sulfuric acid (H₂SO₄, ranging from 80% to 98%), with temperatures in these layers swinging between approximately 0°C and 80°C. Earth’s environment, by contrast, is rich in water, which acts as an essential solvent for biological processes as we know them.

“On Earth, water enables acid-catalyzed hydrolysis of peptide bonds, leading to the breakdown of proteins in strongly acidic aqueous solutions. However, in an environment of concentrated sulfuric acid where water content is minimal, peptides can remain stable. In our study, we investigated whether these complex organic molecules could survive and adopt specific structures under conditions that seem so hostile from an Earth-centric perspective,” explains Dr. Janusz Pętkowski from the Faculty of Environmental Engineering.

Advanced 3D Structural Analysis

Advanced nuclear magnetic resonance (NMR) spectroscopy techniques were used to analyze the behavior of peptides in concentrated sulfuric acid. The methods included monitoring molecular stability over time and structural modeling, which used experimental data to generate 3D models of the structures adopted by peptides in sulfuric acid.

“The research showed that peptides demonstrate full stability in 98% sulfuric acid for at least two weeks. Comparing the spectra at the beginning and end of the experiment revealed no significant differences in the position or intensity of the peaks corresponding to individual amino acids. This demonstrates a complete absence of peptide bond hydrolysis, which would be impossible in an aqueous environment at low pH,” Dr. Pętkowski explains.

The most surprising result of the research, however, is the finding that peptides in concentrated acid do not merely avoid breakdown; they actually fold into stable, ordered structures that differ in shape from those they assume in water. These structures are stabilized by a dense network of interactions with the surrounding solvent molecules as well as intramolecular interactions (hydrogen bonds).

“Chemical shift analysis confirmed these observations. Interestingly, existing knowledge suggested that such interactions could not form stably under concentrated sulfuric acid conditions,” the Wrocław Tech researcher adds.

The results of the experiment therefore prove that concentrated sulfuric acid can serve as a favorable environment for the stability and structural differentiation of complex organic polymers like peptides.

A Breakthrough for Astrobiology

“Paradoxically, the absence of water protects these molecules from the destructive action of hydronium ions, which lead to rapid hydrolysis in aqueous solutions,” explains Dr. Pętkowski. “The discovery that peptides can adopt stable conformations under conditions mimicking the Venusian atmosphere is of fundamental importance for astrobiology. It suggests that potential chemical processes of high complexity could take place within sulfuric acid droplets in the clouds of Venus, using peptides as stable structural components,” he adds.

The findings open a new avenue in the study of life as we do not yet know it - operating on solvents other than water and governed by entirely different principles of chemical stability and reactivity.