Estudio XANES de la oxidación de azufre por clusters atómicos de Ag5 en cisteína y glutatión

DEVIDA, JUAN M.; LÓPEZ-QUINTELA, M. ARTURO; BUCETA, DAVID ; GIOVANETTI, LISANDRO J.

San Luís

Encuentro; 8vo. Encuentro de Física y Química de Superficies; 2018

Universidad Nacional de San Luís

A large group or proteins and oligopeptides has been reported as essentials for their role in the redox homeostasis regulation. This regulation involves several catalytic processes that includes the oxidation, and their reduction back, of Cysteine residues (Cys-SH), which are susceptible to oxidation at physiological pH . In addition, it has been reported the capacity of Atomic Quantum Clusters (AQCs) as oxidation catalysts . In this work, we have studied the oxidative capacity of Ag AQCs on Cysteine and Glutathione as a first approach in elucidating the oxidant effect in molecules with biological interest. For this purpose, the sulfur species both before and after catalytic reaction, were characterized by S-K edge XANES spectroscopy.Ag L3 (3351 eV) and S K-edge (2470 eV) XANES experiments were performed at de SXS beamline at the Laboratório Nacional de Luz Síncrotron (LNLS, Campinas, Brazil). For Cysteine and Glutathione characterization, a fraction of solution were deposited by drop casting on carbon disks (Ted Pella, Inc ®) in order to have a Sulfur concentration in a detectable value. Phosphate buffered saline (PBS) solution was used as solvent in all the reaction mixes, with the purpose maintain a pH value according to a physiological environmental. We observed that sulfur present in Cysteine and Glutathione is deeply oxidized on AQCs presence, from -2 to +6 . However, decreasing the AQCs concentration between three and six times, a lower oxidation reaction also take place for cysteine. Disulfide species (S-1), with external groups corresponding to n-butyl, n-propyl or methyl-disulfide species can be also identified by XANES, which are originated on the formation of sulfur dimers between the lineal cysteine molecules. This effect is not clearly observed for glutathione, due to this conformational structure and S-atoms localization, preventing the S-S dimers formation at the concentrations tried. Finally, it can be shown the ability of X-ray absorption near edge structure spectroscopy on the studied molecules, allowing to characterize faithfully the chemical changes allowing the knowledge of possible reaction mechanisms.