Natural ferroelectric order near ambient temperature in HoFeO3: A member of RFeO3 orthoferrites

Current scenario in multiferroics demands a breakthrough discovery of promising materials after BiFeO3. Recently, the controversial discovery of room temperature ferroelectricity (FE) in SmFeO3 [PRL 107, 117201 (2011); 113, 217203 (2014)] inspires the investigation of HoFeO3. Here, we report a natural ferroelectric order below 210 K (TFE) along c-axis with reasonably large polarization and low-field strong magnetoelectric coupling. Synchrotron and neutron diffraction results confirm that a shift of O atoms along c-axis of polar Pbn21 structure causes FE in HoFeO3. The exchange striction mechanism is suggested to elucidate the ferroelectric order. The results create a renewed attention for searching promising candidates with a natural ferroelectric order and higher TFE in the rest of the RFeO3 series

Regulación aguda de la musculatura lisa intestinal de ileon y colon de ratón por poliaminas.

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Evidence for lipid alterations in lipid rafts from alzheimer´s disease human brain.

Lipid rafts are membrane microdomains involved in cell signalling and characterized by their high contents of sphingolipids, cholesterol and saturated fatty acids. In this study, we have purified lipid rafts of human frontal brain cortex from normal and Alzheimer’s disease (AD) cell membranes and analyzed their lipid composition. Compared to non-AD brains, lipid rafts from AD brains displayed low levels of n-3 long chain highly unsaturated fatty acids (HUFA) specially 22:6n-3 (docosahexaenoic acid) and n-9 monoenes (specially 18:1n-9, oleic acid). Changes in lipid structure of AD lipid rafts also involved significant reductions in the unsaturation and peroxidability indexes as well as increased unsaturated/cholesterol unsaturated/sphingomyelin and saturates/n-3 HUFA ratios. These results indicate that the mechanisms preserving lipid raft order and viscosity in normal frontal cortex are disrupted in AD brains, which partially might explain the abnormal intracellular signalling mechanisms observed during AD.Versión de edito

Synthesis, crystal structure, and magnetic characterization of the three-dimensional compound [Co2(cbut)(H2O) 3]n (H4cbut = 1,2,3,4- cyclobutanetetracarboxylic acid)

A novel cobalt(II) complex of formula [Co2(cbut)(H 2O)3]n (1) (H4cbut = 1,2,3,4-cyclobutanetetracarboxylic acid) has been synthesized under hydrothermal conditions and its crystal structure has been determined by means of synchrotron radiation and neutron powder diffraction. The crystal structure of 1 consists of layers of cobalt(II) ions extending in the bc-plane which are pillared along the crystallographic a-axis through the skeleton of the cbut 4- ligand. Three crystallographically independent cobalt(II) ions [Co(1), Co(2), and Co(3)] occur in 1. They are all six-coordinate with four carboxylate-oxygens [Co(1)-Co(3)] and two cis-[Co(1)] or trans-water molecules [Co(2) and Co(3)] building distorted octahedral surroundings. Regular alternating double oxo(carboxylate) [between Co(1) and Co(1a)] and oxo(carboxylate) plus one aqua and a syn-syn carboxylate bridges [between Co(1) and Co(2)] occur along the crystallographic b-axis, the values of the cobalt-cobalt separation being 3.1259(8) and 3.1555(6) Å, respectively. These chains are connected to the Co(3) atoms through the OCO carboxylate along the [01̄1] direction leading to the organic-inorganic bc-layers with Co(1)-OCO(anti-syn)-Co(3) and Co(2)-OCO(anti-anti)-Co(3) distances of 5.750(2) and 4.872(1) Å. The shortest interlayer cobalt-cobalt separation through the cbut4- skeleton along the crystallographic a-axis is 7.028(2) Å. Variable-temperature magnetic susceptibility measurements show the occurrence of antiferromagnetic ordering with a Néel temperature of 5.0 K, followed by a field-induced ferromagnetic transition under applied dc fields larger than 1500 Oe. The magnetic structure of 1 has been elucidated at low temperatures in zero field by neutron powder diffraction measurements and was found to be formed by ferromagnetic chains running along the b-axis which are antiferromagnetically coupled with the Co(3) ions through the c-axis giving rise to noncompensated magnetic moments within each bc-layer (ferrimagnetic plane). The occurrence of an antitranslation operation between these layers produces a weak interlayer antiferromagnetic coupling along the a-axis which is overcome by dc fields greater than 1500 Oe resulting in a phase transition toward a ferromagnetic state (metamagnetic behavior). © 2014 American Chemical Society.Partial funding for this work is provided by the Ministerio Español de Ciencia e Innovación through projects MAT2010-16981, CTQ2010-15364, DPI2010-21103- C04-03, MAT2011-27233-C02-02, MAT2011-25991 and “Factoría de Cristalización” (Consolider-Ingenio2010, CSD2006-00015), the Generalitat Valenciana (ISIC/2012/ 002), and the CEI Canarias: Campus Atlántico Tricontinental. P.D.-G. also thanks to Ministerio Español de Economia y Competitividad through FPI program for predoctoral contracts.Peer Reviewe