Prebiotic Astrochemistry from Astronomical Observations and Laboratory Spectroscopy.

The discovery of more than 200 gas-phase chemical compounds in interstellar space has led to the speculation that this nonterrestrial synthesis may play a role in the origin of life. These identifications were possible because of laboratory spectroscopy, which provides the molecular fingerprints for astronomical observations. Interstellar chemistry produces a wide range of small, organic molecules in dense clouds, such as NH2COCH3, CH3OCH3, CH3COOCH3, and CH2(OH)CHO. Carbon (C) is also carried in the fullerenes C60 and C70, which can preserve C-C bonds from circumstellar environments for future synthesis. Elusive phosphorus has now been found in molecular clouds, the sites of star formation, in the molecules PO and PN. Such clouds can collapse into solar systems, although the chemical/physical processing of the emerging planetary disk is uncertain. The presence of molecule-rich interstellar starting material, as well as the link to planetary bodies such as meteorites and comets, suggests that astrochemical processes set a prebiotic foundation.

Preparation of methanediamine (CH2(NH2)2)-A precursor to nucleobases in the interstellar medium.

Although methanediamine (CH2(NH2)2) has historically been the subject of theoretical scrutiny, it has never been isolated to date. Here, we report the preparation of methanediamine (CH2(NH2)2)-the simplest diamine. Low-temperature interstellar analog ices composed of ammonia and methylamine were exposed to energetic electrons which act as proxies for secondary electrons produced in the track of galactic cosmic rays. These experimental conditions, which simulate the conditions within cold molecular clouds, result in radical formation and initiate aminomethyl (CH2NH2) and amino ([Formula: see text]2) radical chemistry. Exploiting tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReToF-MS) to make isomer-specific assignments, methanediamine was identified in the gas phase upon sublimation, while its isomer methylhydrazine (CH3NHNH2) was not observed. The molecular formula was confirmed to be CH6N2 through the use of isotopically labeled reactants. Methanediamine is the simplest molecule to contain the NCN moiety and could be a vital intermediate in the abiotic formation of heterocyclic and aromatic systems such as nucleobases, which all contain the NCN moiety.

Synthesis of methanediol [CH2(OH)2]: The simplest geminal diol.

Geminal diols-organic molecules carrying two hydroxyl groups at the same carbon atom-have been recognized as key reactive intermediates by the physical (organic) chemistry and atmospheric science communities as fundamental transients in the aerosol cycle and in the atmospheric ozonolysis reaction sequence. Anticipating short lifetimes and their tendency to fragment to water plus the aldehyde or ketone, free geminal diols represent one of the most elusive classes of organic reactive intermediates. Here, we afford an exceptional glance into the preparation of the previously elusive methanediol [CH2(OH)2] transient-the simplest geminal diol-via energetic processing of low-temperature methanol-oxygen ices. Methanediol was identified in the gas phase upon sublimation via isomer-selective photoionization reflectron time-of-flight mass spectrometry combined with isotopic substitution studies. Electronic structure calculations reveal that methanediol is formed via excited state dynamics through insertion of electronically excited atomic oxygen into a carbon-hydrogen bond of the methyl group of methanol followed by stabilization in the icy matrix. The first preparation and detection of methanediol demonstrates its gas-phase stability as supported by a significant barrier hindering unimolecular decomposition to formaldehyde and water. These findings advance our perception of the fundamental chemistry and chemical bonding of geminal diols and signify their role as an efficient sink of aldehydes and ketones in atmospheric environments eventually coupling the atmospheric chemistry of geminal diols and Criegee intermediates.

The emergence of interstellar molecular complexity explained by interacting networks.

Recent years have witnessed the detection of an increasing number of complex organic molecules in interstellar space, some of them being of prebiotic interest. Disentangling the origin of interstellar prebiotic chemistry and its connection to biochemistry and ultimately, to biology is an enormously challenging scientific goal where the application of complexity theory and network science has not been fully exploited. Encouraged by this idea, we present a theoretical and computational framework to model the evolution of simple networked structures toward complexity. In our environment, complex networks represent simplified chemical compounds and interact optimizing the dynamical importance of their nodes. We describe the emergence of a transition from simple networks toward complexity when the parameter representing the environment reaches a critical value. Notably, although our system does not attempt to model the rules of real chemistry nor is dependent on external input data, the results describe the emergence of complexity in the evolution of chemical diversity in the interstellar medium. Furthermore, they reveal an as yet unknown relationship between the abundances of molecules in dark clouds and the potential number of chemical reactions that yield them as products, supporting the ability of the conceptual framework presented here to shed light on real scenarios. Our work reinforces the notion that some of the properties that condition the extremely complex journey from the chemistry in space to prebiotic chemistry and finally, to life could show relatively simple and universal patterns.

From Meteorite to Life's Building Blocks: A possible Electrochemical Pathway to Amino Acids and Peptide Bonds.

This study explores the electrochemical properties of the carbonaceous Allende CV3 meteorite, focusing on its potential as a Fe-based catalyst derived from Mackinawite iron sulfide for electrocatalytic reactions facilitating nitrogen (N2) fixation into ammonia. Through comprehensive analysis, we not only monitored the evolution of key compounds such as CN-, sulfur/H2S, H2 and carbonyl compounds, but also identified potential reagent carriers, indicating significant implications for the Strecker synthesis of amino acids in space environments. Initial examination revealed the presence of polypeptides, notably sequences including dimer Ala-α-HO-Gly, pentamer Gly3-Ala2, and hexamer Gly4-(HO-Gly)2. These discoveries greatly enhance our understanding of astrobiological chemistry, offering valuable insights into prebiotic processes and the potential presence of life-building blocks throughout the universe.

Theoretical Rotational and Vibrational Spectral Data for the Hypermagnesium Oxide Species Mg2O and Mg2O.

While magnesium is astronomically observed in small molecules, it largely serves as a contributor to silicate grains, though how these grains form is not well-understood. The smallest hypermagnesium oxide compounds (Mg 2 ${{}_{2}}$ O/Mg 2 ${{}_{2}}$ O + ${{}^{+}}$ ) may play a role in silicate formation, but little vibrational reference data exist. As such, anharmonic spectroscopic data are computed for X ˜ 1 Σ g + ${{{\tilde{\rm {X}}}}^1 {\rm{\Sigma }}_g^+ }$ Mg 2 ${{}_{2}}$ O, a ˜ 1 Σ u + ${{{\tilde{\rm {a}}}}^1 {\rm{\Sigma }}_u^+ }$ Mg 2 ${{}_{2}}$ O, and X ˜ 2 Σ g + ${{{\tilde{\rm {X}}}}^2 {\rm{\Sigma }}_g^+ }$ Mg 2 ${{}_{2}}$ O + ${{}^{+}}$ using quartic force fields (QFFs). Explicitly-correlated coupled-cluster QFFs for the neutral species perform well, implying that full multireference treatment may not be necessary for such systems if enough electron correlation is included. Equation-of-motion ionization potential (EOMIP) methods for X ˜ 2 Σ g + ${{{\tilde{\rm {X}}}}^2 {\rm{\Sigma }}_g^+ }$ Mg 2 ${{}_{2}}$ O + ${{}^{+}}$ QFFs circumvent previous symmetry breaking issues even in explicitly-correlated coupled-cluster results, motivating the need for EOMIP treatments at minimum for such systems. All three species are found to have high-intensity vibrational frequencies. Even so, the highly intense frequency ( X ˜ 1 Σ g + ${{{\tilde{\rm {X}}}}^1 {\rm{\Sigma }}_g^+ }$ Mg 2 ${{}_{2}}$ O: 894.7 cm-1/11.18 µm; a ˜ 1 Σ u + ${{{\tilde{\rm {a}}}}^1 {\rm{\Sigma }}_u^+ }$ Mg 2 ${{}_{2}}$ O: 915.0 cm-1/10.91 µm) for either neutral state may be astronomically obscured by the polycyclic aromatic hydrocarbon 11.2 µm band. Mg 2 ${{}_{2}}$ O + ${{}^{+}}$ may be less susceptible to such obfuscation, and its ν 1 ${{\nu }_{1}}$ intensity is computed to be a massive 4793 km mol-1.

Bending Relaxation of H2 O by Collision with Para- and Ortho-H2.

We extend our recent theoretical work on the bending relaxation of H2 O in collisions with H2 by including the three water modes of vibration coupled with rotation, as well as the rotation of H2 . Our full quantum close-coupling method (excluding the H2 vibration) is combined with a high-accuracy nine-dimensional potential energy surface. The collisions of para-H2 O and ortho-H2 O with the two spin modifications of H2 are considered and compared for several initial states of H2 O. The convergence of the results as a function of the size of the rotational basis set of the two colliders is discussed. In particular, near-resonant energy transfer between H2 O and H2 is found to control the vibrational relaxation process, with a dominant contribution of transitions with Δ j 2 = j 2 f - j 2 i ${{\rm{\Delta }}j_2 = j_2^f - j_2^i }$ = + 2 , + 4 ${ + 2, + 4}$ , j 2 i ${j_2^i }$ and j 2 f ${j_2^f }$ being respectively the H2 initial and final rotational quantum numbers. Finally, the calculated value of the H2 O bending relaxation rate coefficient at 295 K is found to be in excellent agreement with its experimental estimate.

Formation of Methanol via Fischer-Tropsch Catalysis by Cosmic Iron Sulphide.

Chemical reactions in the gas phase of the interstellar medium face significant challenges due to its extreme conditions (i. e., low gas densities and temperatures), necessitating the presence of dust grains to facilitate the synthesis of molecules inaccessible in the gas phase. While interstellar grains are known to enhance encounter rates and dissipate energy from exothermic reactions, their potential as chemical catalysts remain less explored. Here, we present mechanistic insights into the Fischer-Tropsch-type methanol (FTT-CH3OH) synthesis by reactivity of CO with H2 and using cosmic FeS surfaces as heterogeneous catalysts. Periodic quantum chemical calculations were employed to characterize the potential energy surface of the reactions on the (011) and (001) FeS surfaces, considering different Fe coordination environments and S vacancies. Kinetic calculations were also conducted to assess catalytic capacity and allocate reaction processes within the astrochemical framework. Our findings demonstrate the feasibility of FeS-based astrocatalysis in the FTT-CH3OH synthesis. The reactions and their energetics were elucidated from a mechanistic standpoint. Kinetic analysis demonstrates the temperature dependency of the simulated processes, underscoring the compulsory need of energy sources considering the astrophysical scenario. Our results provide insights into the presence of CH3OH in diverse regions where current models struggle to explain its observational quantity.

Exploring the Scaling Factors for Infrared Modes of PANHs - A Case Study on Cationic 3-Azafluoranthene⋠+ and Protonated 3-Azafluoranthene.

Infrared (IR) emission bands by interstellar polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic nitrogen heterocycles (PANHs) are observed towards a large variety of interstellar objects and offer detailed insights into the chemistry and physics of the interstellar medium. The analysis of the emission bands, and thus the interpretation of the molecular characteristics of the carriers, heavily relies on the use of density functional theory (DFT) calculated IR spectra. However, there are significant challenges in accurately predicting the experimental IR band positions, particularly for PANH emission vibrational modes around 6 µm. In this work, we present gas-phase mid-infrared (mid-IR) spectra of cationic 3-azafluoranthene (3AF⋅+) and protonated 3-azafluoranthene (3AFH+) to investigate their experimental IR band positions in relation to DFT calculated bands. The experimental spectra are compared to DFT simulated spectra, where different approaches were followed to correct for anharmonicities. The best agreement is achieved by scaling frequencies of modes with large nitrogen displacements with a different factor. Even though our findings might be limited to a small number of PANH structures, they indicate, that nitrogen atom incorporation needs to be accounted for by carefully adjusting the corresponding scaling factors while computing IR spectra of PANHs on DFT level.

Gas-Phase Preparation of the 14π Hückel Polycyclic Aromatic Anthracene and Phenanthrene Isomers (C14H10) via the Propargyl Addition-BenzAnnulation (PABA) Mechanism.

Polycyclic aromatic hydrocarbons (PAHs) imply the missing link between resonantly stabilized free radicals and carbonaceous nanoparticles, commonly referred to as soot particles in combustion systems and interstellar grains in deep space. Whereas gas phase formation pathways to the simplest PAH - naphthalene (C10H8) - are beginning to emerge, reaction pathways leading to the synthesis of the 14π Hückel aromatic PAHs anthracene and phenanthrene (C14H10) are still incomplete. Here, by utilizing a chemical microreactor in conjunction with vacuum ultraviolet (VUV) photoionization (PI) of the products followed by detection of the ions in a reflectron time-of-flight mass spectrometer (ReTOF-MS), the reaction between the 1'- and 2'-methylnaphthyl radicals (C11H9⋅) with the propargyl radical (C3H3⋅) accesses anthracene (C14H10) and phenanthrene (C14H10) via the Propargyl Addition-BenzAnnulation (PABA) mechanism in conjunction with a hydrogen assisted isomerization. The preferential formation of the thermodynamically less stable anthracene isomer compared to phenanthrene suggests a kinetic, rather than a thermodynamics control of the reaction.

Discovery in space of ethanolamine, the simplest phospholipid head group.

Cell membranes are a key element of life because they keep the genetic material and metabolic machinery together. All present cell membranes are made of phospholipids, yet the nature of the first membranes and the origin of phospholipids are still under debate. We report here the presence of ethanolamine in space, [Formula: see text]OH, which forms the hydrophilic head of the simplest and second-most-abundant phospholipid in membranes. The molecular column density of ethanolamine in interstellar space is N = (1.51[Formula: see text]0.07)[Formula: see text], implying a molecular abundance with respect to [Formula: see text] of [Formula: see text] Previous studies reported its presence in meteoritic material, but they suggested that it is synthesized in the meteorite itself by decomposition of amino acids. However, we find that the proportion of the molecule with respect to water in the interstellar medium is similar to the one found in the meteorite ([Formula: see text]). These results indicate that ethanolamine forms efficiently in space and, if delivered onto early Earth, could have contributed to the assembling and early evolution of primitive membranes.

Synchronous Fluorescence as a Sensor of Trace Amounts of Polycyclic Aromatic Hydrocarbons.

Synchronous fluorescence spectroscopy (SFS) is a technique that involves the simultaneous detection of fluorescence excitation and emission at a constant wavelength difference. The spectrum yields bands that are narrower and less complex than the original excitation and emission bands. The SFS bands correspond uniquely to the fluorescing molecule. Our investigation focuses on evaluating the sensitivity of the SFS technique for the detection and quantitation of PAHs relevant to astrochemistry. Results are presented for naphthalene, anthracene, and pyrene in three different solvents: n-hexane, water, and ethanol. SF bands are obtained with a constant wavelength difference between the peak excitation and emission wavelength (Δλ = λex - λem) at a concentration ranging from 10-4 to 10-10 M. Limit of detection (LOD) and limit of quantitation (LOQ) calculations are based on integrated SF band areas at different concentrations. Spectra of 23 pg/g of anthracene, 16 pg/g, and 2.6 pg/g of pyrene are recorded using ethanol as the solvent. The PAHs exhibit detection limits in the fractions of parts-per-billion (ng/g) range. Through comparison with similar prior studies employing fluorescence emission, our findings reveal a better detectability limit, demonstrating the effectiveness and applicability of the SFS technique.

Gas-Phase Infrared Action Spectroscopy of CH2Cl+ and CH3ClH+: Likely Protagonists in Chlorine Astrochemistry.

Two fundamental halocarbon ions, CH2Cl+ and CH3ClH+, were studied in the gas phase using the FELion 22-pole ion trap apparatus and the Free Electron Laser for Infrared eXperiments (FELIX) at Radboud University, Nijmegen (the Netherlands). The vibrational bands of a total of four isotopologs, CH235,37Cl+ and CH335,37ClH+, were observed in selected wavenumber regions between 500 and 2900 cm-1 and then spectroscopically assigned based on the results of anharmonic force field calculations performed at the CCSD(T) level of theory. As the infrared photodissociation spectroscopy scheme employed probes singly Ne-tagged weakly bound complexes, complementary quantum-chemical calculations of selected species were also performed. The impact of tagging on the vibrational spectra of CH2Cl+ and CH3ClH+ is found to be virtually negligible for most bands; for CH3ClH+-Ne, the observations suggest a proton-bound structural arrangement. The experimental band positions as well as the best estimate rotational molecular parameters given in this work provide a solid basis for future spectroscopic studies at high spectral resolutions.

Theoretical Study of the Thermal Rate Coefficients of the H3+ + C2H4 Reaction: Dynamics Study on a Full-Dimensional Potential Energy Surface.

Ion-molecular reactions play a significant role in molecular evolution within the interstellar medium. In this study, the entrance channel reaction, H3+ + C2H4 → H2 + C2H5+, was investigated using classical molecular dynamic (classical MD) and ring polymer molecular dynamic (RPMD) simulation techniques. We developed an analytical potential energy surface function with a permutationally invariant polynomial basis, specifically employing the monomial symmetrized approach. Our dynamic simulations reproduced the rate coefficient of 300 K for H3+ + C2H4 → H2 + C2H5+, aligning reasonably well with the values in the kinetic database commonly utilized in astrochemistry. The thermal rate coefficients obtained using both the classical MD and RPMD techniques exhibited an increase from 100 K to 300 K as the temperature rose. Additionally, we analyzed the excess energy distribution of the C2H5+ fragment with respect to temperature to investigate the indirect reaction pathway of C2H5+ → H2 + C2H3+. This result suggests that the indirect reaction pathway of C2H5+ → H2 + C2H3+ holds minor significance, although the distribution highly depends on the collisional temperature.

Exploring High-Pressure Polymorphism in Carbonic Acid through Direct Synthesis from Carbon Dioxide Clathrate Hydrate.

Carbon dioxide (CO2) is widespread in astrochemically relevant environments, often coexisting with water (H2O) ices and thus triggering a great interest regarding the possible formation of their adducts under various thermodynamic conditions. Amongst them, solid carbonic acid (H2CO3) remains elusive, yet being widely studied. Synthetic routes followed for its production have always been characterised by drastic irradiation on solid ice mixtures or complex procedures on fluid samples (such as laser heating at moderate to high pressures). Here we report about a simpler yet effective synthetic route to obtain two diverse carbonic acid crystal structures from the fast, cold compression of pristine clathrate hydrate samples. The two distinct polymorphs we obtained, differing in the water content, have been deeply characterised via spectroscopic and structural techniques to assess their composition and their astonishing pressure stability, checked up to half a megabar, also highlighting the complex correlations between them so to compile a detailed phase diagram of this system. These results may have a profound impact on the prediction and modelisation of the complex chemistry which characterises many icy bodies of our Solar System.

γ-Ray Driven Aqueous-Phase Methane Conversions into Complex Molecules up to Glycine.

Fundamental understanding of initial evolutions of molecules in the universe is of great interest and importance. CH4 is one of the abundant simple molecules in the universe. Herein we report γ-ray, high-energy photons commonly existing in cosmic rays and unstable isotope decay, as an external energy to efficiently drives aqueous-phase CH4 conversions to various products with the presence of oxygen at room temperature. Glycine also forms with an additional introduction of ammonia. Both CH4 conversions and product distributions are modified by solid granules, and a CH3COOH selectivity as high as 82% is obtained when SiO2 is added. Our results point to γ-ray driven aqueous-phase CH4 conversions as a likely formation network of initial complex organic compounds in the universe and offer an alternative strategy for efficiently utilizing CH4 as the carbon source to produce value-added products at mild conditions, a long-standing challenging task in heterogeneous catalysis.

Investigating Possible Dipole-Bound States of Cyanopolyynes: the Case for the C5 N- Anion Detected in Interstellar Space.

We present results of quantum structure calculations aimed at demonstrating the possible existence of dipole-bound states (DBS) for the anion C 5 N - ${{\rm{C}}_5 {\rm{N}}^ - }$ , a species already detected in the Interstellar medium (ISM). The positive demonstration of DBS existence using ab initio studies is an important step toward elucidating possible pathways for the formation of the more tightly bound valence bound states (VBS) in environments where free electrons from starlight ionization processes are known to be available to interact with the radical partner of the title molecule. Our current calculations show that such excited DBS states can exist in C 5 N - ${{\rm{C}}_5 {\rm{N}}^ - }$ , in agreement with what we had previously found for the smallercyanopolyyne in the series: the C 3 N - ${{\rm{C}}_3 {\rm{N}}^ - }$ anion. This system has a very weakly bound anion with binding energies of about 3 and 9 cm-1 for the 1 Σ + ${^1 \Sigma ^ + }$ and 3 Σ + ${^3 \Sigma ^ + }$ DBS, respectively.

Cryogenic Chemistry and Quantitative Non-Thermal Desorption from Pure Methanol Ices: High-Energy Electron versus X-Ray Induced Processes.

X-Ray irradiation of interstellar ice analogues has recently been proven to induce desorption of molecules, thus being a potential source for the still-unexplained presence of gaseous organics in the coldest regions of the interstellar medium, especially in protoplanetary disks. The proposed desorption mechanism involves the Auger decay of excited molecules following soft X-ray absorption, known as X-ray induced electron-stimulated desorption (XESD). Aiming to quantify electron induced desorption in XESD, we irradiated pure methanol (CH3 OH) ices at 23 K with 505 eV electrons, to simulate the Auger electrons originating from the O 1s core absorption. Desorption yields of neutral fragments and the effective methanol depletion cross-section were quantitatively determined by mass spectrometry. We derived desorption yields in molecules per incident electron for CO, CO2 , CH3 OH, CH4 /O, H2 O, H2 CO, C2 H6 and other less abundant but more complex organic products. We obtained desorption yields remarkably similar to XESD values.

Ring-polymer Molecular Dynamics Simulation for the Adsorption of H2 on Ice Clusters (H2 O)n (n=8, 10, and 12).

In the interstellar medium, the H2 adsorption and desorption on the solid water ice are crucial for chemical and physical processes. We have recently investigated the probabilities of H2 sticking on the (H2 O)8 ice, which has quadrilateral surfaces. We have extended the previous work using classical MD and ring-polymer molecular dynamics (RPMD) simulations to the larger ice clusters, (H2 O)10 and (H2 O)12 , which have pentagonal and hexagonal surfaces, respectively. The H2 sticking probabilities decreased as the temperature increased for both cluster cases, whereas the cluster-size-independent profiles were observed. It is thought that the size independence of the probabilities is qualitatively understood from the similar binding energies for all the three cluster systems. Furthermore, the RPMD sticking probabilities are smaller than the classical ones because of the reduction in the binding energies owing to nuclear quantum effects, such as vibrational quantization.

X-ray processing of a realistic ice mantle can explain the gas abundances in protoplanetary disks.

The Atacama Large Millimeter Array has allowed a detailed observation of molecules in protoplanetary disks, which can evolve toward solar systems like our own. While CO, [Formula: see text], HCO, and [Formula: see text] are often abundant species in the cold zones of the disk, [Formula: see text] or [Formula: see text] are only found in a few regions, and more-complex organic molecules are not observed. We simulate, experimentally, ice processing in disks under realistic conditions, that is, layered ices irradiated by soft X-rays. X-ray emission from young solar-type stars is thousands of times brighter than that of today's sun. The ice mantle is composed of a [Formula: see text]:[Formula: see text]:[Formula: see text] mixture, covered by a layer made of [Formula: see text] and CO. The photoproducts found desorbing from both ice layers to the gas phase during the irradiation converge with those detected in higher abundances in the gas phase of protoplanetary disks, providing important insights on the nonthermal processes that drive the chemistry in these objects.