Understanding the interaction between biomolecules, such as amino-acids, peptides or proteins, and surfaces is of importance in the fields of surface chemistry, catalysis and prebiotic chemistry. It has been found that a number of amino-acids self-organize to form well-ordered two-dimensional structures at metal surfaces (1). On the other hand, it is important to explore the role-play by different mineral surfaces related to prebiotic chemistry processes such as molecular adsorption and geochemistry. Minerals can be very promising surfaces for studying biomolecule-surface processes; among such minerals is pyrite. Pyrite (FeS2) is one of the most important and abundant sulfide minerals on earth. Additionally, due to its catalytic activity, pyrite surface plays an important role in heterogeneous catalysis. Furthermore, the study of pyrite’s physical properties and reactivity is also crucial to the ‘‘iron–sulfur world’’ (2). Wächtershäuser proposed that the first reactions that led to the formation of amino-acids did not occur in a bulk solution in the oceans (prebiotic soup theory) but on the surface of minerals (such as pyrite). In fact, minerals may adsorb and concentrate these biomolecules and catalyze reactions. Mineral surfaces could potentially have allowed for almost any type of general catalysis, with low specificity and efficiency.
Therefore, we focused our study on investigating by the use of complementary and powerful surface science techniques the possible role played by mineral surface reactivity. Furthermore, to obtain understanding on molecule/surface system, which includes information about the interaction and self-assembled processes of amino-acids on surfaces and the chemical state of the adsorbates depending on different experimental conditions like molecular coverage, environmental conditions (3-5). These studies are based on an innovative approach; molecule-surface systems under vacuum conditions. We report the results of a spectroscopic study, specifically X-ray photoemission spectroscopy (XPS) data, obtained for amino-acids adsorption on a natural pyrite surface and discuss spectroscopic evidence of different molecular adsorption mechanisms on the surface of pyrite constrained by pre-treatment conditions. This strategy is designed to be able to evaluate how diverse environments favor or inhibit molecular adsorption, and the crucial role play by pyrite surface chemically driving amino-acids interaction on the surface. The interaction of some functional groups may drive molecular interaction with the iron and sulfur chemical groups from pyrite surface. Successful adsorption of different amino-acids on a pyrite surface confirms the high reactivity of this surface, which could operate as a batch-reactor for prebiotic molecules. These studies could therefore shed light into prebiotic chemistry reactions.
Figure 1: XPS Spectroscopy evidence of pretreatment pyrite surface processes drives amino acid molecular adsorption.
(1) E. Mateo-Marti, C. Rogero, C. Gonzalez, J. Sobrado, P. De Andrés Rodriguez and J.A. Martín-Gago, Langmuir 26 (2010) 4113.
(2) G. Wächtershäuser, Chemistry&Biodiversity, 4, (2007) 584.
(3) M. Sanchez-Arenillas and E. Mateo-Marti, Chemical Physics 458 (2015) 92.
(4) M. Sánchez-Arenillas, E. Mateo-Martí, Phys.Chem.Chem.Phys, 18 (2016) 27219-27225.
(5) M. Sánchez-Arenillas, S. Galvez-Martinez, E. Mateo-Martí, Appl. Surf. Sci., 414 (2017) 303-312.