Synthesis of mesoporous Ca-MCM catalysts and their use in suitable multicomponent synthesis of polyfunctionalized pyrans

Mesoporous Ca-MCM catalysts were prepared using a mixture of CaCO₃, TEOS, cetyl trimethyl ammonium bromide (CTAB), triethanolamine (TEA), ethanol and H₂O. Three catalysts with different CaCO₃ contents, M-Ca 1 %, M-Ca 5 % and M-Ca 10 %, respectively, were prepared and characterized by N₂ physisorption, XRD, FT-IR, XPS, TPD-CO₂ and Pyridine-FTIR. A green and simple protocol was developed for the synthesis of 6-amino-4H-pyran scaffolds through a multicomponent coupling reaction of an aldehyde, malononitrile, and 1,3-dicarbonyl compound in different reaction solvents. This procedure was performed at room temperature (20 °C), obtaining good and excellent yields of 4H-pyran derivatives. The mesoporous materials are insoluble in polar media, which allows easy removal of the reaction products without affecting their catalytic activity. The leaching test showed an excellent stability, and Ca-MCM catalysts can be used three times without appreciable loss of their catalytic activity.     

Driving the resonant quantum kicked rotor via extended initial?conditions

We study the resonances of the quantum kicked rotor subjected to an extended initial distribution. For the primary resonances we obtain the dispersion relation for the map of this system. We find an analytical dependence of the statistical moments on the shape of the initial distribution. For the secondary resonances we obtain numerically a similar dependence. This allows us to devise an extended initial condition which produces an average angular momentum pointing in a preset direction which increases with time with a preset ratio.     

Nucleoside-copper(II) system in water and on 13X-zeolite studied by continuous-wave and pulsed-wave ESR

In order to study the effects of large-surface-area solids on the formation of biomacromolecules, copper(II)-nucleosides complexes were studied in water at high pH and after contact with the cavity walls of 13X-zeolite. The results were mainly collected by electron spin resonance in continuous (cw-ESR) and pulsed (ESE) wave. Particular attention was dedicated to adenosine as a nucleoside model for the formation of compounds which were fully characterized in alkaline water solution and after adsorption on commercial 13X-zeolite. In aqueous solution, adenosine was coordinated to copper(II) through deprotonated hydroxyl groups in the 2′ and 3′ positions of the ribose unit, with the formation of [Cu(adenosine)₂(H₂O)₂]²⁻. When adsorbed on zeolite, both cw-ESR and ESE showed that a fraction of the adsorbed complexes did not change their structure and showed high mobility in the zeolite faujasite cavity. The remaining fraction directly interacted with²⁷Al nuclei of the zeolite framework. Other copper(II)-nucleosides behaved in the same manner. Surprisingly enough, alkaline solutions of nucleosides were able to remove copper (II) from zeolite in the form of [Cu(adenosine)₂(H₂O)₂]²⁻ which freely moved in the supernatant aqueous liquid.     

Oxoselenido clusters of the lanthanides: rational introduction of oxo ligands and near-IR emission from Nd(III)

Reactions of Ln(SePh)3 with SeO2 in THF give octanuclear oxoselenido clusters with the general formula (THF)8Ln8O2Se2(SePh)16 (Ln = Ce, Pr, Nd, Sm). In this isomorphous series, the eight Ln(III) ions are connected in the center by a pair of mu3-O2- ligands and mu5-Se2- ligands, with 14 bridging and two terminal selenolate ligands capping the cluster surface. Thermal decomposition at 700 degrees C of the Nd compound in vacuo led to the formation of a phase mixture of NdSe2, Nd2Se3, and Nd2O3. Near-IR emission experiments on the (THF)8Nd8O2Se2(SePh)16 and the fluorinated thiolate compound (DME)2Nd(SC6F5)3 demonstrate that clusters with oxo ligands are not only highly emissive, but also they emit at wavelengths not found in conventional oxides.     

Pro-Apoptotic and Pro-Autophagic Properties of Cardenolides from Aerial Parts of Pergularia tomentosa

Pergularia tomentosa L., a milkweed tropical plant belonging to the family Asclepiadaceae, is a rich source of unusual cardiac glycosides, characterised by transfused A/B rings and a sugar moiety linked by a double link, generating a dioxanoid structure. In the present report, five cardenolides isolated from the aerial parts of the plant (calactin, calotropin, 12β-hydroxycalactin, 12β,6′-dihydroxycalotropin, and 16α-hydroxycalotropin) were investigated for their biological effects on a human hepatocarcinoma cell line. Cell viability was monitored by an MTT assay. The occurrence of apoptosis was evaluated by detecting caspase-3 activation and chromatin fragmentation. The ability of these compounds to induce autophagy was analysed by monitoring two markers of the autophagic process, LC3 and p62. Our results indicated that all cardenolides had cytotoxic effects, with IC₅₀ ranging from 0.127 to 6.285 μM. All compounds were able to induce apoptosis and autophagy, calactin being the most active one. Some of them also caused a reduction in cell migration and a partial block of the cell cycle into the S-phase. The present study suggests that selected cardenolides from aerial parts of P. tomentosa, particularly calactin, possess potentially desirable properties for further investigation as anticancer agents.     

Effect of viscous dissipation on the mixed convection heat transfer from an exponentially stretching surface

The mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent fluid is analyzed using similarity solution technique. Wall temperature and stretching velocity are assumed to have specific exponential function forms. The influence of buoyancy along with viscous dissipation on the convective transport in the boundary layer region is analyzed in both aiding and opposing flow situations. The flow is governed by the mixed convection parameter Gr/Re². The velocity and temperature inside the boundary layer are observed to be influenced by the parameters like Prandtl number Pr, Gebhart number Gb. Significant changes are observed in non-dimensional skin friction and heat transfer coefficients due to viscous dissipation in the medium. The flow and temperature distributions inside the boundary layer are analyzed and the results for non-dimensional skin friction and heat transfer coefficients are discussed through computer generated plots.     

New application of decaniobate salt as basic solid in the synthesis of 4H-pyrans by microwave assisted multicomponent reactions

Research on Chemical Intermediates - This study focuses on the search of new applications of polyoxometalates known as decaniobate ions [Nb10O28]6?. The decaniobates can be used as basic...     

Coupled chaotic oscillators and their relation to a central pattern generator for artificial quadrupeds

Animal locomotion employs different periodic patterns known as animal gaits. In 1993, Collins and Stewart recognized that gaits possessed certain symmetries and characterized the gaits of quadrupeds and bipeds using permutation symmetry groups, which impose constraints on the locomotion center called the central pattern generator (CPG) in the animal brain. They modeled the CPG by coupling four nonlinear oscillators and found that it was possible to reproduce all symmetries of the gaits by changing the coupling strength. Here we propose to extend this idea using coupled chaotic oscillators synchronized using the Pyragas method in order to characterize the CPG symmetries. We also evaluate the time series behavior when the foot is in contact with the ground: this has potential robotic applications.