Nucleic acid interactions with pyrite surfaces E. Mateo-Martí a, * , C. Briones a , C. Rogero a , C. Gomez-Navarro b , Ch. Methivier c , C.M. Pradier c , J.A. Martín-Gago a,b a Centro de Astrobiología (CSIC-INTA), Ctra. Ajalvir, Km. 4, 28850-Torrejón de Ardoz, Madrid, Spain b Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco, 28049-Madrid, Spain c Laboratoire de Réactivité de Surface, UMR CNRS 7609. Université Pierre et Marie Curie, 4, Pl Jussieu, 75005-Paris, France article info Article history: Received 18 December 2007 Accepted 15 May 2008 Available online 20 May 2008 Keywords: Peptide nucleic acid Deoxyribonucleic acid Pyrite surface Nucleic acid–surface interaction X-ray photoemission spectroscopy Infrared spectroscopy Atomic force microscopy abstract The study of the interaction of nucleic acid molecules with mineral surfaces is a field of growing interest in organic chemistry, origin of life, material science and biotechnology. We have characterized the adsorption of single-stranded peptide nucleic acid (ssPNA) on a natural pyrite surface, as well as the fur- ther adsorption of ssDNA on a PNA-modified pyrite surface. The characterization has been performed by means of reflection absorption infrared spectroscopy (RAIRS), atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS) techniques. The N(1s) and S(2p) XPS core level peaks of PNA and PNA + DNA have been decomposed in curve-components that we have assigned to different chemical species. RAIRS spectra recorded for different concentrations show the presence of positive and negative adsorption bands, related to the semiconducting nature of the surface. The combination of the informa- tion gathered by these techniques confirms that PNA adsorbs on pyrite surface, interacting through nitro- gen-containing groups of the nucleobases and the iron atoms of the surface, instead of the thiol group of the molecule. The strong PNA/pyrite interaction inhibits further hybridization of PNA with complemen- tary ssDNA, contrary to the behavior reported on gold surfaces. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Recent trends in molecular adsorption reveal an increasing interest on different aspects of the chemistry and physics of min- eral surfaces. In particular, the surface reactivity of pyrite (FeS 2 ) is a relevant issue, as pyrite is one of the most ubiquitous metal sulfides on Earth. Pyrite plays a crucial role in environmental chemistry since its oxidation in liquid media produces iron oxides, sulfate species and protons that lead to the acidification of mine drainage waters. Therefore, pyrite is known to be extremely sensi- tive to the exposure to atmospheric air or aqueous solutions [1,2]. Due to its electronic conductivity behavior, pyrite has a catalytic activity towards the air oxidation of many sulfides and also some reductive properties towards organic compounds, such as thiols. It is currently assumed that the adsorption of organic molecules or biopolymers on mineral surfaces may substantially alter mineral morphology, surface composition and reactivity, tailoring their properties. Thus, the presence or absence of molecular bioactivity on mineral surfaces has a broad range of implications, including technological aspects related to biomaterials [3–6], and environ- mental chemistry [7]. However, albeit their importance, few studies have addressed the physicochemical features of biomolecular interactions on nat- ural mineral surfaces, in particular on pyrite. Thus, although many studies have been performed to characterize the formation of self- assembled monolayers (SAMs) of biomolecules on metal surfaces, most of them have been carried out on well-suited noble metal surfaces, and there is a lack of information on the adsorption pro- cesses and mechanisms on mineral surfaces. One of the research fields in which the understanding of the mechanisms of nucleic acid interaction with mineral surfaces is of a valuable importance is the origin of life [8,9]. In order to provide a more realistic sce- nario for the origin of life models, the challenge has been afforded replacing a metal surface for a natural mineral surface. The mineral surfaces have the potential to facilitate prebiotic polymerization; minerals might adsorb and concentrate these biomolecules, and may catalyze reactions; however the precise nature of the interac- tion between the mineral host and the biomolecule guest has to be understood. This approach is more demanding than other studies on ‘perfect systems’, meaning that both surface and ligand are complex, and many possible interactions can be established between them. In this sense, the use of mineral surfaces and complex biomolecules allow us to move a step beyond in the knowledge of biomolecular interactions: to switch from an ideal system into a real system. With this aim in mind, two are the main questions that we address 0301-0104/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2008.05.004 * Corresponding author. E-mail address: mateome@inta.es (E. Mateo-Martí). Chemical Physics 352 (2008) 11–18 Contents lists available at ScienceDirect Chemical Physics journal homepage: www.elsevier.com/locate/chemphys