Abstract
We characterized the adsorption of triglycine molecules on a pyrite surface under several simulated environmental conditions by X-ray photoemission spectroscopy. The triglycine molecular adsorption on a pyrite surface under vacuum conditions (absence of oxygen) shows the presence of two different states for the amine functional group (NH2 and NH3+), therefore two chemical species (anionic and zwitterionic). On the other hand, molecular adsorption from a solution discriminates the NH2 as a unique molecular adsorption form, however, the amount adsorbed in this case is higher than under vacuum conditions. Furthermore, molecular adsorption on the mineral surface is even favored if the pyrite surface has been irradiated before the molecular adsorption occurs. Pyrite surface chemistry is highly sensitive to the chemical changes induced by UV irradiation, as XPS analysis shows the presence of Fe2O3 and Fe2SO4—like environments on the surface. Surface chemical changes induced by UV help to increase the probability of adsorption of molecular species and their subsequent concentration on the pyrite surface.
Highlights
Minerals can be very promising surfaces for studying biomolecule surface processes, which are of principal relevance in the origin of life and a source of chemical complexity [1,2]
It is important to explore the role-played by the mineral surfaces related to the prebiotic chemistry processes, such as molecular adsorption and geochemistry, and we focused our study on investigating the possible role played by mineral surface reactivity
Regarding the pyrite clean surface, the sulfur peak showed three components: The main one at 162.8 eV, which corresponded to the S2 22−−, clean pyrite surface (FeS2, 77%), in agreement main one at 162.8 eV, which corresponded to the S2, clean pyrite surface (FeS2, 77%), in agreement with the literature [31,32,33]; a second component at 164.7 eV assigned to a polysulfide species
Summary
Minerals can be very promising surfaces for studying biomolecule surface processes, which are of principal relevance in the origin of life and a source of chemical complexity [1,2]. Bernal proposed that mineral surface adsorption could help to overcome the problem of the extremely dilute concentration of amino acids in prebiotic oceans [3]. Minerals such as silicates, oxides and sulfides were probably present on early Earth in several environments [4,5], and among them, pyrite (FeS2 ) is one of the most important and abundant sulfide minerals on Earth. The presence of iron-sulfur cores in several modern proteins, such as ferredoxins, has been offered as additional evidence for the “iron-sulfur” world hypothesis
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