The Role of Mineral Surfaces on the Reactivity of Prebiotic Chemical Species: an ab initio Study on Energetic and Spectroscopic Features

The abiotic origin of biomolecules is a fundamental question in understanding the emergence of life. Numerous models have been developed to explore how molecular complexity arose on the ancient Earth, but many aspects remain unclear. One widely recognized hypothesis is that mineral surfaces acted as catalysts, concentrators, scaffolds and protecting agents, playing a key role in abiogenesis. This thesis aims to characterize the interactions between prebiotic molecules and mineral surfaces representative of the primordial Earth's chemical inventory.N-methylformamide (NMF) and glycolaldehyde (GA) were selected as target molecules. NMF due to its similarity to formamide, which has been extensively studied as a precursor of nitrogenous compounds and intermediates of the Krebs Cycle. GA, on the other hand, is a crucial precursor of sugars as it is a key intermediated in the early steps of the formose reaction. The chosen mineral substrates, on the other hand, titanium dioxide (TiO₂) and edingtonite (EDI), represent oxides and silicates—minerals abundant in the Earth's crust during the Hadean Eon.Computational simulations were performed employing both periodic and cluster approaches using the CRYSTAL17 and Gaussian 16 quantum chemical packages, respectively. Geometry optimizations and harmonic frequency calculations were carried out using the B3LYP functional combined with DFT-D3 dispersion correction. Double-ζ basis sets were employed: cc-pVDZ for GA and NMF, pob-DZVP for periodic models of EDI, and 86-51G*/8-411G for titanium and oxygen atoms in TiO₂. Thermodynamically stable surfaces were modeled, specifically anatase (101), rutile (110), and edingtonite (100). Upon the thus obtained structures energetic results were refined applying higher levels of theory. The adsorption of NMF on TiO₂ was investigated under various conditions. Computations revealed that the cis-NMF conformer is favored due to its potential of forming a dual interaction with the surface; both physisorption and chemisorption mechanisms were simulated on both polymorphs. Introducing co-adsorbed water molecules resulted in favoring physisorption, with cis- and trans-NMF exhibiting similar behavior. Spectroscopic features of adsorbed NMF were compared to gas-phase data, with vibrational shifts highlighting the effect of the adsorption. In addition to quantum chemical simulations, the adsorption interaction of NMF on both anatase and rutile was investigated experimentally by Diffuse Reflectance Infrared Fourier Transform Spectroscopy. Both experimental evidence and computational results point to an adsorption process that involves anchoring through both the CO and NH groups of NMF.The interaction between GA and EDI focused on the silica-mediated second step of the formose reaction, where formaldehyde (FA) adds to GA to form glyceraldehyde (GCA). The reaction mechanism was explored by quantum chemical simulations performed at various degrees of sophistication to shed light on the thermochemical and kinetic feasibility of the reaction. The same pathway was also investigated in the gas-phase, in order to disentangle the role played by the zeolitic mineral. The obtained results show that the endothermic reaction between GA and hydroxymethylene (HCOH, an active conformer of FA) yields GCA by a submerged reaction path, both in the gas-phase and on the edingtonite surface. The mineral substrate provides further stabilization, by about 20 kcal∙mol-1, of all the species involved in the reaction pathway and acts as a scaffold favoring the interaction of the two reactantsIn summary, the research carried out sheds light into the atomistic details of the interactions between prebiotic molecules and minerals present on the primordial Earth to get insights into the role they could have played in promoting molecular evolution.