M. Carmen Blanco

Characterization of La0.67Ca0.33MnO3±δ particles prepared by the sol–gel route

We report in this work the characterization of La0.67Ca0.33MnO3±δparticles synthesizedvia sol–gel technology starting from an aqueous solution of the metallic nitrates and using urea as gelificant agent. The gelification is assumed to happen through the formation of polynuclear species by condensation reactions between hydroxo complexes. Gels were decomposed at 250 °C and calcined for 3 h at temperatures ranging from 300 to 1000 °C. Complete crystallization takes place at ca. 600 °C. The powders were structurally characterized by X-ray diffraction and their structural parameters were calculated using the Rietveld method. The MnIV content of the several samples was determined to be higher than the stoichiometric 33%. TEM micrographs show elongated particles of which the polar (long) axis size increases from 40 to 300 nm as the calcination temperature increases. Magnetization and magnetoresistance studies are reported showing that the particles smaller than 80 nm behave as single magnetic domains while the large ones behave as multidomains. A magnetoresistance of 12% at 1 kOe was observed for all the particles synthesized by this sol–gel method.

Synthesis of atomic gold clusters with strong electrocatalytic activities.

Small atomic gold clusters in solution, Au n , stabilized by tetrabutyl ammonium bromide (TBABr), have been synthesized by a simple electrochemical technique, based on the anodic dissolution of a gold electrode in the presence of TBABr salt, and using acetronitrile as solvent. The presence of clusters in the range Au3-Au11 were detected by MALDI-TOF spectroscopy, and further characterized by UV-vis absorption spectroscopy, TEM, AFM, X-ray diffraction, and cyclic voltammetry. Clusters display a semiconductor behavior with a band edge of approximately 2.5 eV. We report here their extraordinarily high electrocatalytic activity toward the O2 reduction reaction in acid solutions, which can explain Zhangs results, showing that a four-electron mechanism seems to occur because of the facile reduction of H2O2 on gold clusters compared to bulk gold or larger gold nanoparticles.

Silver Sub-nanoclusters Electrocatalyze Ethanol Oxidation and Provide Protection against Ethanol Toxicity in Cultured Mammalian Cells

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 approximately +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 mediated 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.

Gold nanorod synthesis catalysed by Au clusters

Gold nanorods have been successfully synthesized by the seed mediated method using Au clusters. This synthesis does not require silver ions to obtain large amounts of Au nanorods and has good control over their aspect ratio. Au clusters are produced with the same recipe as for Au seeds, but using shorter reaction times. This very simple scheme confirms the important catalytic influence of clusters in the anisotropic growth control.

Silver Atomic Quantum Clusters of Three Atoms for Cancer Therapy: Targeting Chromatin Compaction to Increase the Therapeutic Index of Chemotherapy

Nanomaterials with very low atomicity deserve consideration as potential pharmacological agents owing to their very small size and to their properties that can be precisely tuned with minor modifications to their size. Here, it is shown that silver clusters of three atoms (Ag3 -AQCs)-developed by an ad hoc method-augment chromatin accessibility. This effect only occurs during DNA replication. Coadministration of Ag3 -AQCs increases the cytotoxic effect of DNA-acting drugs on human lung carcinoma cells. In mice with orthotopic lung tumors, the coadministration of Ag3 -AQCs increases the amount of cisplatin (CDDP) bound to the tumor DNA by fivefold without modifying CDDP levels in normal tissues. As a result, CDDP coadministered with Ag3 -AQCs more strongly reduces the tumor burden. Evidence of the significance of targeting chromatin compaction to increase the therapeutic index of chemotherapy is now provided.