Cerium doped zirconium dioxide as a potential new photocatalytic material. the role of the preparation method on the properties of the material

partially_open6noSmall amounts of Ce4+ ions dispersed in the bulk of ZrO2 give to this material unexpected properties of photoactivity under visible light. Three different samples have been synthesized following different methods and using different precursors and all show some degree of photoactivity. This has been monitored via EPR spectroscopy in terms of charge separation (electrons and holes formation) under polychromatic light having lambda > 420 nm. This behaviour, unimaginable for bare zirconia due to the large band gap of this oxide (around 5 eV), is possible because of the presence in the solid of empty 4f Ce states located in the middle of the band gap which act as intermediate levels in a double excitation mechanism. The doped oxide here described can be considered an example of third generation photoactive material operating under visible light. (C) 2015 Elsevier B.V. All rights reserved.openGionco, C.; Paganini, M.C.; Chiesa, M.; Maurelli, S.; Livraghi, S.; Giamello, E.Gionco, C.; Paganini, M. C.; Chiesa, M.; Maurelli, S.; Livraghi, S.; Giamello, E

The effect of a C298D mutation in CaHydA [FeFe]-hydrogenase: Insights into the protein-metal cluster interaction by EPR and FTIR spectroscopic investigation

AbstractA conserved cysteine located in the signature motif of the catalytic center (H-cluster) of [FeFe]-hydrogenases functions in proton transfer. This residue corresponds to C298 in Clostridium acetobutylicum CaHydA. Despite the chemical and structural difference, the mutant C298D retains fast catalytic activity, while replacement with any other amino acid causes significant activity loss. Given the proximity of C298 to the H-cluster, the effect of the C298D mutation on the catalytic center was studied by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) and by Fourier transform infrared (FTIR) spectroscopies.Comparison of the C298D mutant with the wild type CaHydA by CW and pulse EPR showed that the electronic structure of the center is not altered. FTIR spectroscopy confirmed that absorption peak values observed in the mutant are virtually identical to those observed in the wild type, indicating that the H-cluster is not generally affected by the mutation. Significant differences were observed only in the inhibited state Hox–CO: the vibrational modes assigned to the COexo and Fed-CO in this state are shifted to lower values in C298D, suggesting different interaction of these ligands with the protein moiety when C298 is changed to D298. More relevant to the catalytic cycle, the redox equilibrium between the Hox and Hred states is modified by the mutation, causing a prevalence of the oxidized state.This work highlights how the interactions between the protein environment and the H-cluster, a dynamic closely interconnected system, can be engineered and studied in the perspective of designing bio-inspired catalysts and mimics