Cu-nanoparticles: a chemoselective catalyst for the aza-Michael reactions of N-alkyl- and N-arylpiperazines with acrylonitrile

A novel method for effecting the aza-Michael reactions of N-alkyl- and N-arylpiperazines with acrylonitrile using Cu-nanoparticles is described. The method features the use of 10 mol % Cu (14-17 nm) nanoparticles under mild reaction conditions to afford the addition products in good to excellent yields. The Cu-nanoparticles selectively catalysed the aza-Michael reaction of N-alkyl- and N-arylpiperazines in the presence of aromatic amino or aliphatic hydroxy groups.     

Optimizing Cs-exchange in titanosilicate with the mineral pharmacosiderite topology: framework substitution of Nb and Ge

Titanosilicates with complete or partial substitution of Ge or Nb in the framework and having the mineral pharmacosiderite topology were hydrothermally prepared and their ion-exchange properties towards Cs were studied for Ti/Ge/Si, Ti/Si, Nb/Ti/Si and pure Ge phases. The basis for the differences in the ion exchange properties measured as distribution coefficients (K_d) for these materials are detailed via structural characterization using the Rietveld refinement technique on the X-ray powder diffraction data. The differences in affinity towards Cs⁺ result either from the degree of hydration of the exchanger resulting in different coordination environments or the position of cesium ion in the eight-ring channel.     

Pressure induced phase transitions in hydroquinone

High pressure behavior of alpha-hydroquinone (1,4-dihydroxybenzene) has been studied using Raman spectroscopy up to pressures of 19 GPa. Evolution of Raman spectra suggests two transitions around 3.3 and 12.0 GPa. The first transition appears to be associated with the lowering of crystal symmetry. Above 12.0 GPa, Raman bands in the internal modes region exhibit continuous broadening suggesting that the system is progressively evolving into a disordered state. This disorder is understood as arising due to distortion of the hydrogen-bonded cage across the second transition around 12 GPa.     

Selectivity for Cs and Sr in Nb-substituted titanosilicate with sitinakite topology

The 25% niobium substituted crystalline titanosilicate with the composition Na_1.5Nb_0.5Ti_1.5O₃SiO₄·2H₂O (Nb-TS) was synthesized under hydrothermal conditions. Its selectivity for radioactive ¹³⁷Cs and ⁸⁹Sr was compared with the TS, Na₂Ti₂O₃SiO₄·2H₂O, having sitinakite topology. The Nb-TS shows significantly higher uptake value for ¹³⁷Cs but lower for ⁸⁹Sr than the TS. To investigate the origin of selectivity, the ion exchanged Cs⁺ and Sr²⁺ forms with the composition, Cs_xNaH_yNb_0.5Ti_1.5O₃SiO₄·zH₂O (x=0.1, 0.2 and 0.3, x+y=0.5 and z=1-2) and Sr_0.2Na_0.6H_0.5Nb_0.5Ti_1.5O₃SiO₄·H₂O, respectively, were structurally characterized from the X-ray powder diffraction data using the Rietveld refinement technique. Simultaneously the kinetics of ¹³⁷Cs and ⁸⁹Sr uptake was investigated for the Nb^V free and doped samples. While the Cs⁺ and Sr²⁺ exchanged form of Nb-TS and the Cs⁺ exchanged form of TS retain the symmetry of the parent compound, the Sr²⁺ exchanged form of TS undergoes a symmetry change. The differences in the uptake of Cs⁺ and Sr²⁺ result from the different coordination environments of cesium and strontium in the eight-ring channel, that result from various hydration sites in the tunnel. The origin of selectivity appears to arise from the higher coordination number of cesium or strontium. Other effects due to Nb^V substitution are reflected in the increase of both, the a- and c-dimensions and thus the unit cell volume, and the population of water vs. Na⁺ in the channel to charge-balance the Nb⁵⁺↔Ti⁴⁺ substitution.     

Transition-Metal-Free Reverse Reactivity of (2-Alkynyl)-Arylaldimines: Assembly of Functionalized Amino-Indinones

Transition-metal-free regioselective synthesis of functionalized amino-indenones by the reaction of ortho-alkynylaldehydes with a broad range of primary amines by intramolecular cyclization has been described. The designed reaction proceeds through KOH-mediated Prins-type cyclization and DMSO-promoted oxidation of the cyclopent-2-en-1-one system. The proposed mechanism and role of solvent were well supported by control experiments. For the first time, we have disclosed the reverse reactivity of (2-alkynyl)-arylaldimines in a super basic system.     

Nickel(II)-Mediated Reversible Thiolate/Disulfide Conversion as a Mimic for a Key Step of the Catalytic Cycle of Methyl-Coenzyme M Reductase

According to the well-accepted mechanism, methyl-coenzyme M reductase (MCR) involves Ni-mediated thiolate-to-disulfide conversion that sustains its catalytic cycle of methane formation in the energy saving pathways of methanotrophic microbes. Model complexes that illustrate Ni-ion mediated reversible thiolate/disulfide transformation are unknown. In this paper we report the synthesis, crystal structure, spectroscopic properties and redox interconversions of a set of Ni^II complexes comprising a tridentate N₂S donor thiol and its analogous N₄S₂ donor disulfide ligands. These complexes demonstrate reversible Ni^II-thiolate/Ni^II-disulfide (both bound and unbound disulfide-S to Ni^II) transformations via thiyl and disulfide monoradical anions that resemble a primary step of MCR's catalytic cycle.     

EPR observation of a high temperature phase transition in Zn(ClO4)2·6H2O:Mn2+

The electron paramagnetic resonance of Mn²⁺ doped in single crystals of Zn(ClO₄)₂·6H₂O has been studied at X-band in the temperature range 300–380 K. A phase transition, observed at ～ 346 K, is reported for the first time.     

Ferroelectric soft-mode contribution to zero-field splitting: Paramagnetic resonance investigation of phase transition in Mn2+-doped NaNO2

The contribution of the ferroelectric soft-mode to the zero-field splitting is calculated and separated from the thermal contribution arising from the splitting due to the electron-phonon interaction. The predicted effect is compared with the measured values in Mn²⁺-doped NaNO₂.     

Pseudo-atoms, atoms and a Jordan type decomposition in effect algebras

The aim of this paper is to introduce and investigate the concept of pseudo-atoms of a real-valued function m defined on an effect algebra L; a few examples of pseudo-atoms and atoms are given in the context of null-additive, null-null-additive and pseudo-null-additive functions and also, some fundamental results for pseudo-atoms under the assumption of null-null-additivity are established. The notions of total variation |m|, positive variation m⁺ and negative variation m⁻ of a real-valued function m on L are studied elaborately and it is proved for a modular measure m (which is of bounded total variation) defined on a D-lattice L that, m is pseudo-atomic (or atomic) if and only if its total variation |m| is pseudo-atomic (or atomic). Finally, a Jordan type decomposition theorem for an extended real-valued function m of bounded total variation defined on an effect algebra L is proved and some properties on decomposed parts of m such as continuity from below, pseudo-atomicity (or atomicity) and being measure, are discussed. A characterization for the function m to be of bounded total variation is established here and used in proving above-mentioned Jordan type decomposition theorem.