51
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Maurelli S, Chiesa M, Giamello E, Di Nardo G, V. Ferrero VE, Gilardi G, Van Doorslaer S. Direct spectroscopic evidence for binding of anastrozole to the iron heme of human aromatase. Peering into the mechanism of aromatase inhibition. Chem Commun (Camb) 2011; 47:10737-9. [DOI: 10.1039/c1cc13872c] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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52
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Livraghi S, Corazzari I, Paganini MC, Ceccone G, Giamello E, Fubini B, Fenoglio I. Decreasing the oxidative potential of TiO(2) nanoparticles through modification of the surface with carbon: a new strategy for the production of safe UV filters. Chem Commun (Camb) 2010; 46:8478-80. [PMID: 20938530 DOI: 10.1039/c0cc02537b] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A safe UV filter may be obtained by inhibiting the photo-generation of free radicals through modification of the surface of TiO(2) nanoparticles with carbon.
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53
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Napoli F, Chiesa M, Giamello E, Preda G, Di Valentin C, Pacchioni G. Formation of superoxo species by interaction of O(2) with Na atoms deposited on MgO powders: a combined continuous-wave EPR (CW-EPR), hyperfine sublevel correlation (HYSCORE) and DFT study. Chemistry 2010; 16:6776-85. [PMID: 20514645 DOI: 10.1002/chem.201000546] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The formation of O(2) (-) radical anions by contact of O(2) molecules with a Na pre-covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O(2). The typical EPR signal of isolated Na atoms disappears when the reaction with O(2) takes place and new paramagnetic species are observed, which are attributed to different surface-stabilised O(2) (-) radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O(2) (-)Na(+) species to be determined, demonstrating the direct coordination of the O(2) (-) adsorbate to surface Na(+) cations. DFT calculations enable the structural details of the formed species to be determined. Matrix-isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface-stabilised Na(+)-O(2) (-) complexes.
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54
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Gallino F, Di Valentin C, Pacchioni G, Chiesa M, Giamello E. Nitrogen impurity states in polycrystalline ZnO. A combined EPR and theoretical study. ACTA ACUST UNITED AC 2010. [DOI: 10.1039/b915578c] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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55
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Gonchar A, Risse T, Giamello E, Freund HJ. Additive coloring of thin, single crystalline MgO(001) films. Phys Chem Chem Phys 2010; 12:12520-4. [DOI: 10.1039/c0cp00197j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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56
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Chiesa M, Giamello E, Van Doorslaer S. Ammoniated electrons stabilized at the surface of MgO. J Am Chem Soc 2009; 131:12664-70. [PMID: 19673518 DOI: 10.1021/ja903179b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The reaction of excess electrons at the surface of MgO with ammonia leads to surface ammoniated electrons analogous to those formed when alkali metals are dissolved in anhydrous ammonia. Surface excess electrons are found to be solvated by up to three ammonia molecules, and well-resolved CW and pulsed EPR spectra allow for a precise description of the unpaired electron spin density distribution over the solvent molecules. The large majority of the electron spin density resides in the first-shell nitrogen fragments. HYSCORE spectra allow obtaining for the first time the full hyperfine interaction of the solvated electron with the ammonia protons, which is consistent with a small and negative spin density in the (1)H 1s orbital. Furthermore, the hyperfine and nuclear quadrupole tenors of the second-shell nitrogens could be unravelled.
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57
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Chiesa M, Giamello E, Che M. EPR Characterization and Reactivity of Surface-Localized Inorganic Radicals and Radical Ions. Chem Rev 2009; 110:1320-47. [DOI: 10.1021/cr800366v] [Citation(s) in RCA: 151] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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58
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Morandi S, Paganini M, Giamello E, Bini M, Capsoni D, Massarotti V, Ghiotti G. Structural and spectroscopic characterization of Mo1−xWxO3−δ mixed oxides. J SOLID STATE CHEM 2009. [DOI: 10.1016/j.jssc.2009.09.025] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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59
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Napoli F, Chiesa M, Livraghi S, Giamello E, Agnoli S, Granozzi G, Pacchioni G, Di Valentin C. The nitrogen photoactive centre in N-doped titanium dioxide formed via interaction of N atoms with the solid. Nature and energy level of the species. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2009.06.050] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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60
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Livraghi S, Elghniji K, Czoska A, Paganini M, Giamello E, Ksibi M. Nitrogen-doped and nitrogen–fluorine-codoped titanium dioxide. Nature and concentration of the photoactive species and their role in determining the photocatalytic activity under visible light. J Photochem Photobiol A Chem 2009. [DOI: 10.1016/j.jphotochem.2009.04.010] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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61
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Livraghi S, Czoska A, Paganini M, Giamello E. Preparation and spectroscopic characterization of visible light sensitized N doped TiO2 (rutile). J SOLID STATE CHEM 2009. [DOI: 10.1016/j.jssc.2008.10.012] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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62
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Preda G, Pacchioni G, Chiesa M, Giamello E. The reactivity of CO2 with K atoms adsorbed on MgO powders. Phys Chem Chem Phys 2009; 11:8156-64. [DOI: 10.1039/b906192d] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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63
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Moreira IDP, Wojdeł JC, Illas F, Chiesa M, Giamello E. Evidence of magnetic ordering of paramagnetic surface defects on partially hydroxylated MgO nanocrystals. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.07.060] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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64
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Pacchioni G, Sicolo S, Valentin CD, Chiesa M, Giamello E. A Route toward the Generation of Thermally Stable Au Cluster Anions Supported on the MgO Surface. J Am Chem Soc 2008; 130:8690-5. [DOI: 10.1021/ja710969t] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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65
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Finazzi E, Di Valentin C, Pacchioni G, Chiesa M, Giamello E, Gao H, Lian J, Risse T, Freund HJ. Properties of Alkali Metal Atoms Deposited on a MgO Surface: A Systematic Experimental and Theoretical Study. Chemistry 2008; 14:4404-14. [DOI: 10.1002/chem.200702012] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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66
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Di Valentin C, Finazzi E, Pacchioni G, Selloni A, Livraghi S, Paganini MC, Giamello E. N-doped TiO2: Theory and experiment. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2007.07.020] [Citation(s) in RCA: 677] [Impact Index Per Article: 39.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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67
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Berger T, Diwald O, Knözinger E, Napoli F, Chiesa M, Giamello E. Hydrogen activation at TiO2 anatase nanocrystals. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2007.06.021] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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68
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Livraghi S, Paganini MC, Chiesa M, Giamello E. Trapped molecular species in N-doped TiO2. RESEARCH ON CHEMICAL INTERMEDIATES 2007. [DOI: 10.1163/156856707782169462] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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69
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Napoli F, Chiesa M, Giamello E, Finazzi E, Valentin CD, Pacchioni G. Partially Hydroxylated Polycrystalline Ionic Oxides: A New Route toward Electron-Rich Surfaces. J Am Chem Soc 2007; 129:10575-81. [PMID: 17685526 DOI: 10.1021/ja073114k] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Charge traps at the surface of oxide materials play a fundamental role in various chemical processes, such as the activation of supported metal clusters. In this study, combining electron paramagnetic resonance with cluster model DFT calculations, we show that excess electrons at the surface of MgO, CaO, and SrO polycrystalline materials can be generated by preparing weakly hydroxylated surfaces followed by deposition of small amounts of alkali metals. The residual OH groups present on specific sites of the partially dehydroxylated surface act as stable traps for electrons donated by the alkali metal (Na in this case) which forms a Na+ ion distant from the trapped electron. This process results in the formation of thermally stable (H+)(e-) color centers at the surface of the oxide. The procedure could be of interest for the stabilization and activation of supported metal nanoparticles with potential use in catalysis.
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70
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Chiesa M, Giamello E, Annino G, Massa C, Murphy D. Multi-frequency high-field EPR study of (H+)(e−) pairs localized at the surface of polycrystalline MgO. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.03.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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71
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Chiesa M, Giamello E. Carbon Dioxide Activation by Surface Excess Electrons: An EPR Study of the CO2− Radical Ion Adsorbed on the Surface of MgO. Chemistry 2007; 13:1261-7. [PMID: 17149776 DOI: 10.1002/chem.200600792] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The CO2- radical anion has been generated at the surface of MgO by direct electron transfer from surface trapped excess electrons and characterized by electron paramagnetic resonance spectroscopy. Both 13C and 17O hyperfine structures have been resolved for the first time, leading to a detailed mapping of the unpaired electron spin density distribution over the entire radical anion. The magnetic equivalence of the two O nuclei has been ascertained allowing a side-on adsorption structure at low-coordinate Mg2+ ions to be proposed for the surface stabilized radical.
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72
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Livraghi S, Paganini MC, Giamello E, Selloni A, Di Valentin C, Pacchioni G. Origin of Photoactivity of Nitrogen-Doped Titanium Dioxide under Visible Light. J Am Chem Soc 2006; 128:15666-71. [PMID: 17147376 DOI: 10.1021/ja064164c] [Citation(s) in RCA: 385] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nitrogen-doped titanium dioxide (N-TiO2), a photocatalytic material active in visible light, has been investigated by a combined experimental and theoretical approach. The material contains single-atom nitrogen impurities that form either diamagnetic (Nb-) or paramagnetic (Nb*) bulk centers. Both types of Nb centers give rise to localized states in the band gap of the oxide. The relative abundance of these species depends on the oxidation state of the solid, as, upon reduction, electron transfer from Ti3+ ions to Nb* results in the formation of Ti4+ and Nb-. EPR spectra measured under irradiation show that Nb centers are responsible for visible light absorption with promotion of electrons from the band gap localized states to the conduction band or to surface-adsorbed electron scavengers. These results provide a characterization of the electronic states associated with N impurities in TiO2 and, for the first time, a picture of the processes occurring in the solid under irradiation with visible light.
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73
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Chiesa M, Paganini MC, Giamello E, Murphy DM, Di Valentin C, Pacchioni G. Excess electrons stabilized on ionic oxide surfaces. Acc Chem Res 2006; 39:861-7. [PMID: 17115726 DOI: 10.1021/ar068144r] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Surface excess electrons are remarkable chemical entities that provide great opportunities for the design of new materials with precisely tuned electronic and magnetic properties. In this Account, we describe the structure and electronic properties of excess electron centers generated at the surface of insulating oxides. We also outline the elementary mechanisms that are at the basis of the generation of excess electrons at solid surfaces, setting a comparison to the general problem of excess electron localization in condensed media. Emphasis is given to morphological aspects relative to the surface-trapping sites as deduced from combined electron paramagnetic resonance and accurate quantum chemical calculations. The remarkable reactivity featured by the so formed "electron-rich" surfaces is illustrated, describing the reduction of simple diatomic molecules that form adsorbed radical anions via direct surface to adsorbate electron transfer.
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74
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Livraghi S, Paganini MC, Chiesa M, Giamello E. Reduction and fragmentation of CS2 at the surface of electron-rich MgO: an EPR study. RESEARCH ON CHEMICAL INTERMEDIATES 2006. [DOI: 10.1163/156856706778606516] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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75
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Paganini MC, Chiesa M, Dolci F, Martino P, Giamello E. EPR Study of the Surface Basicity of Calcium Oxide. 3. Surface Reactivity and Nonstoichiometry. J Phys Chem B 2006; 110:11918-23. [PMID: 16800495 DOI: 10.1021/jp061131a] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High surface area polycrystalline calcium oxide forms ozonide O3- ions upon O2 adsorption and NO3(2-) anions under low pressures of NO. Both radical anions, detected by electron paramagnetic resonance (EPR), are not observed in the case of the homologous magnesium oxide. This behavior reveals the presence, in CaO, of anomalies with respect to the ideal composition of an ionic oxide which are identified in terms of two main types of defects. The first type consists of positive holes dispersed in the bulk and originated by the unavoidable presence of Na+ ions in the composition of the solid. The decomposition of the surface ozonide shows the formation of a transient surface stabilized O- (the chemical notation of a positive hole associated to an oxide ion) which is for the first time reported at the surface of CaO. The second type of defect consists of surface peroxide groups (present at particular surface sites where they are formed by pairing of two distinct O-) which react with nitric oxide (NO) yielding NO3(2-) radical anions. The presence of peroxide is not related to the presence of impurities but, rather, to a certain propensity of the solid to form such ions at the surface along the dehydration process.
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