CH3NO as a potential intermediate for early atmospheric HCN: a quantum chemical insight

A Comprehensive Review of HCN-Derived Polymers

HCN-derived polymers are a heterogeneous group of complex substances synthesized from pure HCN; from its salts; from its oligomers, specifically its trimer and tetramer, amino-nalono-nitrile (AMN) and diamino-maleo-nitrile (DAMN), respectively; or from its hydrolysis products, such as formamide, under a wide range of experimental conditions. The characteristics and properties of HCN-derived polymers depend directly on the synthetic conditions used for their production and, by extension, their potential applications. These puzzling systems have been known mainly in the fields of prebiotic chemistry and in studies on the origins of life and astrobiology since the first prebiotic production of adenine by Oró in the early years of the 1960s. However, the first reference regarding their possible role in prebiotic chemistry was mentioned in the 19th century by Pflüger. Currently, HCN-derived polymers are considered keys in the formation of the first and primeval protometabolic and informational systems, and they may be among the most readily formed organic macromolecules in the solar system. In addition, HCN-derived polymers have attracted a growing interest in materials science due to their potential biomedical applications as coatings and adhesives; they have also been proposed as valuable models for multifunctional materials with emergent properties such as semi-conductivity, ferroelectricity, catalysis and photocatalysis, and heterogeneous organo-synthesis. However, the real structures and the formation pathways of these fascinating substances have not yet been fully elucidated; several models based on either computational approaches or spectroscopic and analytical techniques have endeavored to shed light on their complete nature. In this review, a comprehensive perspective of HCN-derived polymers is presented, taking into account all the aspects indicated above.

Towards H2O catalyzed N2-fixation over TiO2 doped Run clusters (n = 5, 6): a mechanistic and kinetic approach

H2O driven N2 fixation is known as the best alternative pathway to synthesise NH3 under ambient conditions. The thermodynamic non-spontaneous reaction can be accomplished by a photocatalytic water splitting reaction over a TiO2 supported surface with oxygen vacancies. Previous experiments have also shown N2 activation over a neutral Ru cluster whose catalytic activity was remarkably enhanced by TiO2 doping. In this article, we have investigated the detailed mechanism and kinetics of the H2O catalyzed nitrogen reduction reaction (NRR) over bare and TiO2 doped Ru5 clusters in conjunction with DFT and TST calculations. The lack of photochemical activity of the small model cluster provoked us to explore an alternative route of NH3 formation via H2O catalysis. For this, we have considered H2 as co-reactant. The partial reduction of N2 into NH3 or N2H4 could be achieved by a H2O oxidation reaction, however, catalytic regeneration requires additional H2 which effectively makes the overall reaction catalyzed by H2O. Above all, the present investigation suggests that NH3 is most favorably produced through the distal mechanism. Analysis of the rate constants demonstrates that the doping with TiO2 accelerates the kinetics of NRR by a few orders of magnitude. Furthermore, an increase of the size of the metal cluster would not significantly enhance the overall performance of NRR.

Structure, Stability, and Spectroscopic Properties of Small Acetonitrile Cation Clusters

Ionization and fragmentation pathways induced by ionizing agents are key to understanding the formation of complex molecules in astrophysical environments. Acetonitrile (CH₃CN), the simplest organic nitrile, is an important molecule present in the interstellar medium. In this work, DFT and MP2 calculations were performed in order to obtain the low energy structures of the most relevant cations formed from electron-stimulated ion desorption of CH₃CN ices. Selected reaction pathways and spectroscopic properties were also calculated. Our results indicate that the most stable acetonitrile cation structure is CH₂CNH⁺ and that hydrogenation can occur successively without isomerization steps until its complete saturation. Moreover, the stability of distinct cluster families formed from the interaction of acetonitrile with small fragments, such as CH_n⁺, C₂H_n⁺, and CH_nCNH⁺, is discussed in terms of their respective binding energies. Some of these molecular clusters are stabilized by hydrogen bonds, leading to species whose infrared features are characterized by a strong redshift of the N-H stretching mode. Finally, the rotational spectra of CH₃CN and protonated acetonitrile, CH₃CNH⁺, were simulated using distinct computational protocols based on DFT, MP2, and CCSD(T) considering centrifugal distortion, vibrational-rotational coupling, and vibrational anharmonicity corrections. By adopting an empirical scaling procedure for calculating spectroscopic parameters, we were able to estimate the rotational frequencies of CH₃CNH⁺ with an expected average error below 1 MHz for J values up to 10.

Theoretical Investigations on the Possibility of Prebiotic HCN Formation via O-Addition Reactions

Until now, reactions between methane photolysis products (CH₃^•, CH₂) and active N atom or reactive NO radical are proposed as routes of HCN formation in the prebiotic Earth. Scientists think that the reducing atmosphere of primitive Earth was made of H₂, He, N₂, NO, CH₄, H₂O, CO₂, etc., and there was no molecular oxygen. However, it has been evident from experiments that the vacuum ultraviolet (VUV) photolysis of CO₂ can produce atomic oxygen. Therefore, it can be presumed that atomic oxygen was likely present in early Earth's atmosphere. Was there any impact of atomic oxygen in production of early atmospheric HCN for the emergence of life? To hunt for the answer, we have employed computational methods to study the mechanism and kinetics of CH₃NO + O(¹D) and CH₂NO^• + O(³P) addition reactions. Current study suggests that the addition of O(¹D) into nitrosomethane (CH₃NO) and the addition of O(³P) into nitrosomethylene radical (CH₂NO^•) can efficiently produce HCN through an effectively barrierless pathway. At STP, Bartis-Widom phenomenological loss rate coefficients of O(¹D) and O(³P) are obtained as 2.47 × 10^-12 and 4.67 × 10^-11 cm³ molecule^-1 s^-1, respectively. We propose that addition reactions of atomic oxygen with CH₃NO and CH₂NO^• might act as a potential source for early atmospheric HCN.

Recent Results on Computational Molecular Modeling of The Origins of Life

In the last decade of research in the origins of life, there has been an increase in the interest on theoretical molecular modeling methods aimed to improve the accuracy and speed of the algorithms that solve the molecular mechanics and chemical reactions of the matter. Research on the scenarios of prebiotic chemistry has also advanced. The presented work attempts to discuss the latest computational techniques and trends implemented so far. Although it is difficult to cover the full extent of the current publications, we tried to orient the reader into the modern tendencies and challenges faced by those who are in the origins of life field.