USTC finds γ rays drive the conversion of aqueous-phase methane to complex organic molecules including glycine

A research group led by Prof. HUANG Weixin at the Precision and Intelligent Chemistry Key Laboratory of the University of Science and Technology of China (USTC), in collaboration with the School of Chemistry and Materials Science, observed that in the presence of oxygen at room temperature, aqueous-phase CH₄ was converted into various complex organic molecules. Additionally, the introduction of ammonia resulted in the formation of glycine. These findings were published in Angewandte Chem.In.Ed.

Complex organic molecules in the universe are thought to form progressively through chemical reactions driven by cosmic rays and the high-energy particles they produce. These reactions may be the cause of the origin of life. As a widely distributed molecule in the interstellar medium, CH₄ serves as a source of carbon (C) and hydrogen (H) for the synthesis of complex organic molecules. However, the research on simulating the evolution of interstellar molecules from methane and other small molecules is usually carried out at high vacuum and very low temperature, when methane is in solid phase, while on large solids, such as the earth or planets located in the so-called livable zone, they have relatively high pressure and temperature, and CH4 and other small molecules exist in gas or aqueous phase.

This study aimed to investigate the γ-ray-induced conversion of CH₄ under varying conditions (gas and aqueous phases), analyze its reaction networks and products, and assess its potential implications for the formation of interstellar complex molecules and the origin of life.

Utilizing gamma rays produced by the ⁶⁰Co source at the School of Chemistry and Materials Science, USTC, the researchers examined CH₄ transformation under various conditions. They proposed a reaction network and mechanism, as illustrated in Figure 2. The study found that gamma rays can facilitate CH₄ conversion at room temperature, with the conversion rate and products varying according to the reactant composition. Notably, the reactants CH₄, H₂O, O₂, and NH₃, which are all present in space, were used in the reaction. All organic products listed in Figure 2, except (CH₃)₃COH, have been identified in space. The conversion of CH₄, driven by gamma rays, adheres to the free radical mechanism. The reaction rate is contingent on the concentration of free radicals and is not significantly influenced by the reaction temperature. Consequently, in the presence of H₂O, O₂, NH_3, and other small molecules, the transformation of CH₄ induced by gamma rays could potentially be a method for producing interstellar complex molecules.

In summary, gamma rays effectively drive the aqueous-phase conversion of CH₄ at room temperature into diverse products, including hydrocarbons, oxygenated compounds, and amino acids. While gamma rays exhibit strong radiation effects, they are currently utilized safely and sustainably on a large scale, making them an accessible and viable energy source. Moreover, the gamma-ray-driven selective conversion of CH₄ to CH₃COOH under mild conditions offers a novel strategy for utilizing abundant CH₄ as a carbon source to produce value-added products.