Symmetry Analysis for the Ruddlesden-Popper Systems, Ca3Mn2O7 and Ca3Ti2O7

We perform a symmetry analysis of the zero-temperature instabilities of the tetragonal phase of Ca3Mn2O7 and Ca3Ti2O7 which is stable at high temperature. We introduce order parameters to characterize each of the possible lattice distortions in order to construct a Landau free energy which elucidates the proposed group-subgroup relations for structural transitions in these systems. We include the coupling between the unstable distortion modes and the macroscopic strain tensor. We also analyze the symmetry of the dominantly antiferromagnetic ordering which allows weak ferromagnetism. We show that in this phase the weak ferromagnetic moment and the spontaneous ferroelectric polarization are coupled, so that rotating one of these ordering by applying an external electric or magnetic field one can rotate the other ordering. We discuss the number of different domains (including phase domains) which exist in each of the phases and indicate how these may be observed.Comment: 21 pages, 14 figure

Excitation Spectrum and Superexchange Pathways in the Spin Dimer VODPO_4 . 1/2 D_2O

Magnetic excitations have been investigated in the spin dimer material VODPO_4 \cdot 1/2 D_2O using inelastic neutron scattering. A dispersionless magnetic mode was observed at an energy of 7.81(4) meV. The wavevector dependence of the scattering intensityfrom this mode is consistent with the excitation of isolated V^{4+} spin dimers with a V-V separation of 4.43(7) \AA. This result is unexpected since the V-V pair previously thought to constitute themagnetic dimer has a separation of 3.09 \AA. We identify an alternative V-V pair as the likely magnetic dimer, which involves superexchange pathways through a covalently bonded PO_4 group. This surprising result casts doubt on the interpretation of (VO)_2P_2O_7 as a spin ladder.Comment: 4 pages, 4 postscript figures - identical to previous paper but figure 2 and 3 hopefully more compatible .p

Influence of very low doses of mediators on fungal laccase activity - nonlinearity beyond imagination

Laccase, an enzyme responsible for aerobic transformations of natural phenolics, in industrial applications requires the presence of low-molecular substances known as mediators, which accelerate oxidation processes. However, the use of mediators is limited by their toxicity and the high costs of exploitation. The activation of extracellular laccase in growing fungal culture with highly diluted mediators, ABTS and HBT is described. Two high laccase-producing fungal strains, Trametes versicolor and Cerrena unicolor, were used in this study as a source of enzyme. Selected dilutions of the mediators significantly increased the activity of extracellular laccase during 14 days of cultivation what was distinctly visible in PAGE technique and in colorimetric tests. The same mediator dilutions increased demethylation properties of laccase, which was demonstrated during incubation of enzyme with veratric acid. It was established that the activation effect was assigned to specific dilutions of mediators. Our dose-response dilution process smoothly passes into the range of action of homeopathic dilutions and is of interest for homeopaths

One-pot synthesis of nano-crystalline MCM-22

[EN] Nano-crystalline MCM-22 zeolite was synthesized in a one-pot procedure by the use of an organosilane (dimethyl-octadecyl-(3-trimethoxysilylpropyl)-ammonium chloride, TPOAC) in the zeolite synthesis gel. This crystal growth inhibition procedure introduced mesopores in the MCM-22 crystallites. The lower mechanical stability of the nano-crystalline MCM-22 zeolite compared with bulk MCM-22 can be countered to some extent by pillaring. The increased external surface of the microporous zeolite domains resulted in increased accessibility of the Bronsted acid sites, as followed from the better performance in liquid-phase benzene alkylation with propylene as compared with bulk MCM-22. The increased accessibility of the internal acid sites in Mo-loaded hierarchical MCM-22 was also evident from the improved benzene selectivity during methane aromatization. Silylation of hierarchical Mo/MCM-22 was detrimental for the catalytic performance in MDA. The nano-crystalline MCM-22 has physico-chemical and catalytic properties intermediate between those of MCM-22 and ITQ-2 with the benefit over ITQ-2 that it can be synthesized in a single step. (C) 2015 Elsevier Inc. All rights reserved.Funding from the 7th Framework Program of the European Commission through the Collaborative Project Next-GTL (agreement no 229183) and financial support by the Spanish Government-MINECO through "Severo Ochoa" (SEV 2012-0267), Consolider Ingenio 2010-Multicat (CSD2009-00050) and MAT2012-31657 are acknowledged. Marta E. Martinez Armero thanks MINECO for economical support through pre-doctoral fellowship for doctors training (BES-2013-066800). The authors thank B. Esparcia for technical assistance.Tempelman, CHL.; Portilla Ovejero, MT.; Martínez Armero, ME.; Mezari, B.; De Caluwe, NGR.; Martínez, C.; Hensen, EJM. (2016). One-pot synthesis of nano-crystalline MCM-22. Microporous and Mesoporous Materials. 220:28-38. https://doi.org/10.1016/j.micromeso.2015.08.018S283822