Strong electronic correlations in Lix_xZnPc organic metals

Nuclear magnetic resonance, electron paramagnetic resonance and magnetization measurements show that bulk Li$_x$ZnPc are strongly correlated one-dimensional metals. The temperature dependence of the nuclear spin-lattice relaxation rate $1/T_1$ and of the static uniform susceptibility $\chi_S$ on approaching room temperature are characteristic of a Fermi liquid. Moreover, while for $x\simeq 2$ the electrons are delocalized down to low temperature, for $x\to 4$ a tendency towards localization is noticed upon cooling, yielding an increase both in $1/T_1$ and $\chi_s$. The $x$-dependence of the effective density of states at the Fermi level $D(E_F)$ displays a sharp enhancement for $x\simeq 2$, at the half filling of the ZnPc lowest unoccupied molecular orbitals. This suggests that Li$_x$ZnPc is on the edge of a metal-insulator transition where enhanced superconducting fluctuations could develop.Comment: 5 pages, 4 figure

Spectroscopic and magnetic studies of wild-type and mutant forms of the Fe(II)- and 2-oxoglutarate-dependent decarboxylase ALKBH4

The Fe(II)/2OG (2-oxoglutarate)-dependent dioxygenase superfamily comprises proteins that couple substrate oxidation to decarboxylation of 2OG to succinate. A member of this class of mononuclear non-haem Fe proteins is the Escherichia coli DNA/RNA repair enzyme AlkB. In the present work, we describe the magnetic and optical properties of the yet uncharacterized human ALKBH4 (AlkB homologue). Through EPR and UV–visible spectroscopy studies, we address the Fe-binding environment of the proposed catalytic centre of wild-type ALKBH4 and an Fe(II)-binding mutant. We could observe a novel unusual Fe(III) high-spin EPR-active species in the presence of sulfide with a gmax of 8.2. The Fe(II) site was probed with NO. An intact histidine-carboxylate site is necessary for productive Fe binding. We also report the presence of a unique cysteine-rich motif conserved in the N-terminus of ALKBH4 orthologues, and investigate its possible Fe-binding ability. Furthermore, we show that recombinant ALKBH4 mediates decarboxylation of 2OG in absence of primary substrate. This activity is dependent on Fe as well as on residues predicted to be involved in Fe(II) co-ordination. The present results demonstrate that ALKBH4 represents an active Fe(II)/2OG-dependent decarboxylase and suggest that the cysteine cluster is involved in processes other than Fe co-ordination

Light-Induced Defect Formation and Pt Single Atoms Synergistically Boost Photocatalytic H2 Production in 2D TiO2-Bronze Nanosheets ?

Ultrathin two-dimensional (2D) semiconductor nanosheets decorated with single atomic species (SAs) have recently attracted increasing attention due to their abundant surface-exposed reactive sites and maximum SAs binding capabilities thus lowering the catalyst cost, without sacrificing high performance for photocatalytic hydrogen (H2) production from water. Here, we present a strategy to prepare titanium dioxide-bronze nanosheets (TiO2-BNS) and H2-reduced TiO2 nanosheets (TiO2- HRNS) synthesized, characterized, and applied for photocatalytic H2 production. Surprisingly, black TiO2-HRNS show complete photo inactivity, while the TiO2-BNS-Pt0.05 nanohybrid shows excellent H2 production rate with a very low loading of 0.05 wt % Pt. TiO2-BNS-Pt0.05 presents around 10 and 99 times higher photocatalytic rate than pristine TiO2-BNS under solar and 365 nm UV-LED light irradiation, respectively. Due to the 2D morphology and the presence of abundant coordinating sites, the successful formation of widely dispersed Pt SAs was achieved. Most excitingly, the in situ formation of surface-exposed defect sites (Ti3+) was observed for TiO2-BNS under light illumination, suggesting their significant role in enhancing the H2 production rate. This self-activation and amplification behavior of TiO2-BNS can be extended to other 2D systems and applied to other photocatalytic reactions, thus providing a facile approach for fully utilizing noble metal catalysts via the successful formation of SAs

Excitation Wavelength- and Medium-Dependent Photoluminescence of Reduced Nanostructured TiO2 Films

The performance of TiO2 nanomaterials in solar energy conversion applications can be tuned by means of thermal treatments in reducing atmospheres, which introduce defects (such as oxygen vacancies), allowing, for instance, a better charge transport or a higher photocatalytic activity. The characterization of these defects and the understanding of their role are pivotal to carefully engineer the properties of TiO2, and, among various methods, they have been addressed by photoluminescence (PL) spectroscopy. A definitive framework to describe the PL properties of TiO2, however, is still lacking. In this work, we report on the PL of nanostructured anatase TiO2 thin films, annealed in different atmospheres (oxidizing and reducing), and consider the effects of different excitation energies and different surrounding media on their PL spectra. A broad PL signal centered around 1.8–2.0 eV is found for all the films with UV excitation in air as well as in vacuum, while the same measurements in ethanol lead to a blueshift and to intensity changes in the spectra. On the other hand, measurements with different sub-bandgap excitations show PL peaking at 1.8 eV, with an intensity trend only dependent on the thermal treatment and not on the surrounding medium. The results of PL spectroscopy, together with electron paramagnetic resonance spectroscopy, suggest the critical role of oxygen vacancies and Ti3+ ions as radiative recombination centers. The complex relationship between thermal treatments and PL data in the explored conditions is discussed, suggesting the importance of such investigations for a deeper understanding on the relationship between defects in TiO2 and photoactivity

Linear-Structure Single-Atom Gold(I) Catalyst for Dehydrogenative Coupling of Organosilanes with Alcohols

A strategyfor the synthesisof a gold-basedsingle-atom catalyst(SAC) via a one-steproom temperaturereductionofAu(III)salt and stabilizationof Au(I) ions on nitrile-functionalizedgraphene(cyanographene;G-CN)is described.The graphene-supportedG(CN)-Aucatalystexhibitsa unique linear structureofthe Au(I) active sites promotinga multistepmode of action indehydrogenativecouplingof organosilaneswith alcoholsundermild reactionconditionsas provenby advancedXPS, XAFS,XANES,and EPR techniquesalong with DFT calculations.Thelinear structurebeing perfectlyaccessibletowardthe reactantmoleculesand the cyanographene-inducedcharge transferresultingin the exclusiveAu(I) valencestate contributeto the superiorefficiencyof the emergingtwo-dimensionalSAC. The developedG(CN)-AuSAC, despiteits low metal loading(ca. 0.6 wt %),appearto be the most efficientcatalystfor Si−H bond activationwith a turnoverfrequencyof up to 139,494h−1and highselectivities,significantlyovercomingall reportedhomogeneousgold catalysts.Moreover,it can be easily preparedin a multigrambatch scale, is recyclable,and works well toward more than 40 organosilanes.This work opens the door for applicationsof SACs witha linear structureof the active site for advancedcatalyticapplications

Surface-Confined Metal?Organic Nanostructures from Co-Directed Assembly of Linear Terphenyl-dicarbonitrile Linkers on Ag(111)

A detailed structural analysis of the surface supported self-assembly of terphenyl-4,4′′-dicarbonitrile molecules (NC−Ph3−CN) linked by Co adatoms on Ag(111) reveals different surface patterns depending on the constraints applied to the system. Without constraints, i.e., sufficient mobility and absence of space limitations at the surface, extended regular honeycomb nanomeshes are formed. On the basis of high-resolution scanning tunneling microscopy images, an atomistic model is derived showing the crystallographic orientation of the molecules and a commensurate alignment of the honeycomb networks, which exist in two rotational domains on the Ag(111) atomic lattice. For Co deficiency, an additional star-like Co-directed motif has been identified, and fully disordered networks are present if space limitations are imposed. In these cases, nodal motifs exist showing between 3- and 6-fold coordination of Co centers

Metal-organic honeycomb nanomeshes with tunable cavity size

We present a systematic study of metal-organic honeycomb lattices assembled from simple ditopic molecular bricks and Co atoms on Ag(111). This approach enables us to fabricate size- and shape-controlled open nanomeshes with pore dimensions up to 5.7 nm. The networks are thermally robust while extending over mu m(2) large areas as single domains. They are shape resistant in the presence of further deposited materials and represent templates to organize guest species and realize molecular rotary systems

Engineering shape anisotropy of Fe3O4-¿-Fe2O3 hollow nanoparticles for magnetic hyperthermia

The use of microwave-assisted synthesis (in water) of a-Fe2O3 nanomaterials followed by their transformation onto iron oxide Fe3O4-¿-Fe2O3 hollow nanoparticles encoding well-defined sizes and shapes [nanorings (NRs) and nanotubes (NTs)] is henceforth described. The impact of experimental variables such as concentration of reactants, volume of solvent employed, and reaction times/temperatures during the shape-controlled synthesis revealed that the key factor that gated generation of morphologically diverse nanoparticles was associated to the initial concentration of phosphate anions employed in the reactant mixture. All the nanomaterials presented were fully characterized by powder X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared, Mössbauer spectroscopy, and superconducting quantum interference device (SQUID). The hollow nanoparticles that expressed the most promising magnetic responses, NTs and NRs, were further tested in terms of efficiencies in controlling the magnetic hyperthermia, in view of their possible use for biomedical applications, supported by their excellent viability as screened by in vitro cytotoxicity tests. These systems NTs and NRs expressed very good magneto-hyperthermia properties, results that were further validated by micromagnetic simulations. The observed specific absorption rate (SAR) and intrinsic loss power of the NRs and NTs peaked the values of 340 W/g and 2.45 nH m2 kg-1 (NRs) and 465 W/g and 3.3 nH m2 kg-1 (NTs), respectively, at the maximum clinical field 450 Oe and under a frequency of 107 kHz and are the highest values among those reported so far in the hollow iron-oxide family. The higher SAR in NTs accounts the importance of magnetic shape anisotropy, which is well-predicted by the modified dynamic hysteresis (ß-MDH) theoretical model