Solid State Photochemistry of Hydroxylated Naphthalenes on Minerals: Probing Polycyclic Aromatic Hydrocarbon Transformation Pathways under Astrochemically-Relevant Conditions

Abstract

Oxygenated derivatives of polycyclic aromatic hydrocarbons (PAHs), or oxyPAHs, recently captured the interest of the scientific community for their photochemical reactivity in a water–ice matrix mimicking the interstellar medium. Furthermore, oxyPAHs are interesting molecules for the study of the origin of life for their prebiotic potential. However, their stability and transformation pathways under astrophysically relevant conditions have remained largely unexplored. Herein we report the photochemical behavior of 1-naphthol (1-HN) and 1,6- and 1,8-dihydroxynaphthalene (DHN) either as pure powdered solids or adsorbed on forsterite or anatase surface. All the compounds showed an extensive decrease of main vibrational bands, accompanied in the case of DHNs by the formation of new molecular species. Irradiation of 1,8-DHN at 80 K resulted in the IR-detectable generation of CO2 (2340 cm–1), a process reported by other authors following irradiation of PAHs in water–ice analogues at 14 K. These results, when compared to model autoxidation experiments, indicated a high susceptibility of hydroxylated naphthalene derivatives to UV radiation leading to free radical and carbonyl-containing extended quinone intermediates (preliminary DFT calculations) with partial degradation and decarboxylation. On the basis of these results, oxyPAH formation and photoprocessing on minerals is proposed as a plausible pathway of PAHs transformation under astrochemical conditions of prebiotic relevance.

Ultraviolet Photoprocessing of Glycine Adsorbed on Various Space-Relevant Minerals

“…These findings agree with the UV irradiation studies of amino acids adsorbed on various minerals under Martian-like conditions carried out by dos Santos et al (2016), revealing that phyllosilicates have a greater tendency to preserve GLY degradation with respect to other minerals. The lower catalytic effect of antigorite with respect to forsterite was also observed in recent works carried out in our laboratory using different classes of prebiotic molecules (Fornaro et al, 2018a;Potenti et al, 2018). The catalytic activity of some minerals may be related to a proximity effect, i.e., their ability to increase the local concentration of molecules through adsorption onto the mineral surfaces and, consequentially, the probability of molecular self-association and chemical reactions.…”

“…The growing band area of CO 2 band is clearly visible. previous works, antigorite seems to have lower catalytic effect than forsterite (Fornaro et al, 2018a;Potenti et al, 2018) or pyrite. We also observed lower catalytic properties in the case of spinel.…”

“…More details on the methods used for analyzing the degradation kinetics can be found in previous works (Fornaro et al, 2013b(Fornaro et al, , 2018aPotenti et al, 2018).…”

A Robust Fungal Allomelanin Mimic: An Antioxidant and Potent π‐Electron Donor with Free‐Radical Properties that can be Tuned by Ionic Liquids

“…Non‐nitrogenous fungal melanin mimics devoid of catechol functions are thus proposed as innovative prototypes of melanin‐based functional materials with exceptionally robust π‐electron properties and radical scavenging ability suitable for applications in biomedicine and materials science. In addition, these results may provide an improved background to inquire into the fate of PAH‐derived carbon‐containing species in potential astrochemical and prebiotic environments …”

“…In addition, these results may provide an improved background to inquire into the fate of PAH-derived carbon-containing species in potential astrochemical and prebiotic environments. [37] Experimental Section Synthetic procedures for ILs: IL1-IL4 and IL10 were prepared by addition of the alkylating agent (trimethyl phosphate or dimethylmethylphosphonate or dimethyl phosphite, 1.1 molar equivalents) to a molar equivalent of the proper alkylimidazole (methyl or butylimidazole), according to the previously reported procedure. [25] N-Methyl-N,N,N-trioctylammonium oleate (IL12) was prepared by addition of a molar equivalent of oleic acid to a methanolic solution of N-methyl-N,N,N-trioctylammonium methylcarbonate (43 %), using the same experimental conditions described in the literature.…”