Pyrite surface environment drives molecular adsorption: cystine on pyrite(100) investigated by X-ray photoemission spectroscopy and low energy electron diffraction

Abstract

We have demonstrated that the annealing process for cleaning pyrite surfaces is a critical parameter in promoting ordering on the surface and driving surface reactivity. Furthermore, we describe a spectroscopic surface characterization of the presence or absence of the surface ordering, as indicated by the Low Energy Electron Diffraction (LEED) pattern, as a function of the surface annealing process. Complementary X-ray photoemission spectroscopy (XPS) results provide evidence that longer annealing processes of over 3 hours repair the sulfur vacancies in the pyrite, making FeS species partially disappear in favor of FeS species. These features play an important role in molecular adsorption. We show that in the case of the cystine amino acid on the (100) pyrite surface, the substrate structure is responsible for the chemical adsorption form. The presence of an ordered structure on the surface, as indicated by the LEED pattern, favors the cystine NH chemical form, whereas the absence of the surface ordering promotes cystine NH adsorption due to the sulfur-deficient surface. The cystine molecule could then act by changing its chemical functionalities to compensate for the iron surface coordination. The chemical molecular adsorption form can be selected by the surface annealing conditions, implying that environmental conditions could drive molecular adsorption on mineral surfaces. These findings are relevant in several surface processes, and they could play a possible role in prebiotic chemistry surface reactions and iron-sulfur scenarios.

Defects on a pyrite(100) surface produce chemical evolution of glycine under inert conditions: experimental and theoretical approaches

“…As previously reported by our group, 12 in the case of the cystine amino acid on the (100) pyrite surface, the presence of an ordered structure on the surface (disulfide enrichment surface), as indicated by the LEED pattern, favours the cystine NH 3 + chemical form, whereas the absence of surface ordering promotes cystine NH 2 adsorption due to the sulfur-deficient surface (monosulfide enrichment surface). The breaking of the S-S bonds leads to an increase in the binding energy of the Fe 2p 3/2 component, while the contribution of the component at 161.3 eV, which can be attributed to the sulfur monomers species (RS 2À ), to the S 2p 3/2 peak increases.…”

“…be favourably detached. After creating non-stoichiometric sites on pyrite and characterizing them by XPS, 12 the adsorption and unique evolution behaviour of the amino acid was identified and carefully studied by XPS. The presence of sulfur vacancy sites on the pyrite surface drives the chemical evolution of the molecularly adsorbed amino acids.…”

“…Our recent experiments suggest that amino acids can adsorb on the pyrite surface, depending on its structure, the latter being affected by the surroundings or surface pre-treatment conditions. 12,13 These studies provided some new insights into the adsorption process on pyrite surfaces; however, the understanding of amino acid-surface interactions at the atomic level remains limited. Unfortunately, only a few spectroscopic studies on the adsorption of amino acids from the gas phase onto mineral surfaces have been reported.…”

Quantifying Fenton reaction pathways driven by self-generated H2O2 on pyrite surfaces

“…A possible reconciliation comes from considering the presence of ≡Fe 3+ dangling bonds generated from the cleavage of S-S bonds. Briefly, the rupture of S-S bonds generate S − species which are highly instable and, to compensate its charge disequilibrium, donate one electron to the nearest iron atom by the autoredox reaction263132495051525354:…”

Electron Transfer between Electrically Conductive Minerals and Quinones

“…Electron transport chain has a modular structure (Yankovskaya et al, 2003) and it is possible that a first primitive fragments of a biological electron transport chain appeared from abiotic electrocatalytic interactions between minerals and redox active molecules. In this case, an ability of pyrite surfaces to adsorb and concentrate amino acids and short peptides (Wachterhauser, 1988; Sanchez-Arenillas and Mateo-Marti, 2016) could have provided the link between the early redox systems and prebiotic reaction networks based on peptides and nucleic acids.…”