Silver Sub-nanoclusters Electrocatalyze Ethanol Oxidation and Provide Protection against Ethanol Toxicity in Cultured Mammalian Cells Javier Selva, † Susana E. Martı ´nez, †,§ David Buceta, ‡ Marı ´a J. Rodrı ´guez-Va ´ zquez, ‡ M. Carmen Blanco, ‡ M. Arturo Lo ´ pez-Quintela,* ,‡ and Gustavo Egea † Departament de Biologia Cellular, Immunologia i Neurocie `ncies, Facultat de Medicina, Instituts d’InVestigacions Biome `diques August Pi i Sunyer (IDIBAPS) i de Nanocie `ncies i Nanotecnologia (IN 2 UB), UniVersitat de Barcelona, E-08036 Barcelona, Spain, and Laboratorio de Magnetismo y Nanotecnologı ´a (Nanomag), Instituto de InVestigacio ´n Tecnolo ´gica, UniVersidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain Received September 19, 2009; E-mail: malopez.quintela@usc.es Abstract: Silver atomic quantum clusters (AgAQCs), with two or three silver atoms, show electrocatalytic activities that are not found in nanoparticles or in bulk silver. AgAQCs supported on glassy carbon electrodes oxidize ethanol and other alcohols in macroscopic electrochemical cells in acidic and basic media. This electrocatalysis occurs at very low potentials (from ∼ +200 mV vs RHE), at physiological pH, and at ethanol concentrations that are found in alcoholic patients. When mammalian cells are co-exposed to ethanol and AgAQCs, alcohol-induced alterations such as rounded cell morphology, disorganization of the actin cytoskeleton, and activation of caspase-3 are all prevented. This cytoprotective effect of AgAQCs is also observed in primary cultures of newborn rat astrocytes exposed to ethanol, which is a cellular model of fetal alcohol syndrome. AgAQCs oxidize ethanol from the culture medium only when ethanol and AgAQCs are added to cells simultaneously, which suggests that cytoprotection by AgAQCs is provided by the ethanol electro-oxidation meditated by the combined action of AgAQCs and cells. Overall, these findings not only show that AgAQCs are efficient electrocatalysts at physiological pH and prevent ethanol toxicity in cultured mammalian cells, but also suggest that AgAQCs could be used to modify redox reactions and in this way promote or inhibit biological reactions. 1. Introduction Electrochemistry mediated by small metal nanoparticles is a recent, very active and promising field with enormous possibili- ties, many of which remain unexplored. 1 Molecule-like energy HOMO-LUMO (the highest occupied molecular orbital to the lowest unoccupied molecular orbital) gaps are created in nanoparticles with <100 atoms, which are called atomic clusters. The existence of these band gaps together with geometrical or electronic closed-shell structures 2 confers novel properties to atomic clusters 3-6 as well as an unexpected extremely high stability. 7-9 For example, we have recently reported the fluorescent 10 and paramagnetic 11 properties of very stable Ag n (n < 10) clusters and the excellent electrocatalytic properties shown by Au n (n ≈ 3-11) clusters for the oxygen reduction reaction. 12 As we will show later on, we also observe that silver atomic quantum clusters (AgAQCs) containing only 2 or 3 atoms are very active electrocatalysts in the oxidation of alcohols, and this occurs at very low potentials. On the basis of these properties, we hypothesized that electrocatalysis by AgAQCs for ethanol oxidation reaction is possible whenever cells provide the required electrical potential for the electro- chemical oxidation reaction. In this case, AgAQCs could prevent (or at least mitigate) some cellular injuries produced by ethanol. This is relevant in the case of fetal alcohol syndrome (FAS), a common pathology in children of women who consumed alcohol † University of Barcelona. ‡ University of Santiago de Compostela. § Present address: IMIM-Hospital del Mar, Parc de Recerca Biome `dica de Barcelona, E-08003 Barcelona, Spain. (1) Murray, R. W. Chem. ReV. 2008, 108, 2688. (2) Negishi, Y.; Chaki, N. K.; Shichibu, Y.; Whetten, R. L.; Tsukuda, T. J. Am. Chem. Soc. 2007, 129, 11322. (3) Heaven, M. W.; Dass, A.; White, P. S.; Holt, K. M.; Murray, R. W. J. Am. Chem. Soc. 2008, 130, 3754. (4) Negishi, Y.; Takasugi, Y.; Sato, S.; Yao, H.; Kimura, K.; Tsukuda, T. J. Am. Chem. Soc. 2004, 126, 6518. (5) Schaeffer, N.; Tan, B.; Dickinson, C.; Rosseinsky, M. J.; Laromaine, A.; McComb, D. W.; Stevens, M. M.; Wang, Y.; Petit, L.; Barentin, C.; Spiller, D. G.; Cooper, A. I.; Levy, R. Chem. Commun. 2008, 34, 3986. (6) Herzing, A. A.; Kiely, C. J.; Carley, A. F.; Hutchings, P. L. G. J. Science 2008, 321, 1331. 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