Transformation pathways of polycyclic aromatic hydrocarbons and biomolecule precursors of astrochemical origin under model conditions of prebiotic relevance

The emergence of life on Earth and the possibility of life elsewhere in the Universe are central questions explored by astrochemists and astrobiologists. Various hypotheses have been proposed to understand the processes leading to the formation of life's building blocks. Research suggests that abiogenesis could have occurred on early Earth under extreme conditions, with Miller's experiments supporting the idea of amino acid formation from gaseous methane, ammonia, and water under electrical discharge. Hydrothermal systems and volcanic rock pools have been considered potential niches for organic compound synthesis due to the availability of essential geochemical variables.In this connection the relevance of geothermal sites like Solfatara, a volcanic area near Naples, is highlighted for their similarity to early Earth conditions. Additionally, the panspermia hypothesis gained attraction as long chain carboxylic acids, amino acids, bases, and sugars were identified on celestial bodies like meteorites and comets. The building blocks of biomacromolecules may have formed from complex organic molecules (COMs) such as formamide, formaldehyde, methanol and acetaldehyde originating in the interstellar medium (ISM) during the evolution of dense clouds to the protoplanetary disks.In this scenario polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic nitrogen heterocycles (PANHs), detected in the ISM as well as on comets and meteorites, may have played a crucial role in the formation of life-related molecules, serving both as potential carbon sources and as catalysts.Starting from this observation, the research activity of my PhD course has been aimed at elucidating the nature of the reaction products deriving from PAHs and oxyPAHs under solid-state irradiation and heating conditions and the catalytic role of their polymers in prebiotically relevant processes. By pursuing this approach, the work has been structured in two parts dealing with:1. the study of the photochemical susceptibility of PAHs, oxyPAHs and COMs under simulated interstellar conditions;2. the study of the role played by PAHs and oxyPAHs in the chemical transformations occurring under early Earth conditions.In both cases, the aim was to assess the potential role of some representative components of the putative astrochemical pool of PAHs and oxyPAHs, namely naphthalene (NAPH), 1-naphthol (1-HN), and 1,8 dihydroxynaphthalene (1,8-DHN), in the origin of life scenario.High-energy proton beam irradiation of oxyPAHs adsorbed on meteorites revealed the conversion of 1-HN and 1,8-DHN into complex mixtures including quinones and polyhydroxylated derivatives. The addition of urea expanded the range of identified species, suggesting a possible mechanism for C-N bond formation. Photo-processing and thermal desorption of PA(N)Hs and COMs on ice dust grains highlighted the formation of key molecules, including prebiotic molecules and molecules detected in the interstellar medium. Exploring the role played by hydrothermal environments in the reactivity of PAHs, three main pathways of PAH transformation were observed when reacting in the mud of Solfatara: functionalization, erosion and polymerization. Furthermore, the catalytic effect of oxyPAH-polymers in the formation of the peptide bond from the amino acid glycine under wet-dry conditions was disclosed. Overall, the main outcomes of this research contributed to understanding the potential role of PAHs in astrochemical processes and their relevance to the origin of life scenarios, shedding light on the complex pathways that may have led to the emergence of life on Earth.