XANES study of sulfur oxidation by Ag and Cu atomic quantum clusters in cysteine and glutathione

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

Campinas

Congreso; 28th Annual Users Meeting (RAU); 2018

CNPEM

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[1]. In addition, it has been reported the capacity of Atomic Quantum Clusters (AQCs) as oxidation catalysts[2]. In this work, we have studied the oxidative capacity of Ag and Cu 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 XANES spectroscopy. Ag L3 (3351 eV) and S K-edge (2470 eV) XANES experiments were performed at de SXS beamline and Cu K-edge (8988 eV) XAFS experiments at the XAFS-2 beamline at the Laboratório Nacional de Luz Síncrotron (LNLS, Campinas, Brazil). For Cysteine and Gluthatione characterization, a fraction of solution were deposited by drop casting on carbon disks in order to have a S concentration in a detectable value. PBS buffer 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 by AQCs, from -2 to +6 . However, decreasing the AQC concentration between three and six times, a lower oxidation reaction also take place for cysteine. Disulfide species, with external groups corresponding to aliphatic-disulfide species can be also identified by XANES. This effect is not clearly observed for glutathione, due to this conformational structure and S-atoms localization. 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. REFERENCES: [1] Thomas, J., Poland, B., Honzatko, R. Arch Biochem Biophys. 1995;319(1):1-9 [2] Corma, A.; Concepción, P.; Boronat, M.; Sabater, M. J.; Navas, J.; Yacaman, M. J.; Larios, E.; Posadas, A.; López-Quintela, M. A.; Buceta, D.; et al. Nat. Chem. 2013, 5, 775?781