Sánchez Arenillas, M., Gálvez Martínez, S., Mateo Marti, E. 2017. Sulfur amino acids and alanine on pyrite (100) by X-ray photoemission spectroscopy: Surface or molecular role?. Applied Surface Science 414, 303-312, DOI: 10.1016/j.apsusc.2017.04.049

This paper describes the first successful adsorption of the cysteine, cystine, methionine and alanine amino acids on the pyrite (100) surface under ultra-high vacuum conditions with crucial chemical adsorption parameters driving the process. We have demonstrated by X-ray photoemission spectroscopy (XPS) that the surface pretreatment annealing process on pyrite surfaces is a critical parameter driving surface reactivity. The presence of enriched monosulfide species on the pyrite (100) surface favours the amino acid NH2 chemical form, whereas a longer annealing surface pretreatment of over 3 h repairs the sulfur vacancies in the pyrite, enriching disulfide species on the pyrite surface, which promotes NH3+ adsorption due to the sulfur vacancies in the pyrite being replaced by sulfur atom dimers (S-2(2-)) on the surface. Furthermore, even if the surface chemistry (monosulfide or disulfide species enrichment) is the main factor promoting a partial conversion from NH2 to NH3+ species, the unique chemical structure of each amino acid provides a particular fingerprint in the process. (C) 2017 Elsevier B.V. All rights reserved.