Exchange and reduction of Cu(2+) ions in clinoptilolite

The ion-exchange and reduction processes for Cu(2+) ions in clinoptilolite from the Caimanes deposit (Moa, Cuba) were studied at different temperatures. The ion-exchange studies were done to determine the kinetic parameters of Cu(2+) removal from solution by this clinoptilolite modified previously to NH(+)(4) form, and thermodynamic parameters of Cu(2+) elution from zeolite using NH(4)Cl solution. The results show that temperature increase favors the exchange and that it is a reversible process. The external diffusion rate appreciably increases with temperature, while, the internal diffusion coefficient rises relatively little. This means that besides ion exchange other processes (such as precipitation of the low-solubility phase and/or salt adsorption) occur, which cause copper removal from solution and affect the intracrystalline diffusion of the ions. For steric reasons the exchange of [Cu(H(2)O)(6)](2+) ions from a solution must occur with a number of water molecules n smaller than 6 (6 > n > or = 0). Cu(2+) reduction by hydrogen and the formation of Cu-particles in the clinoptilolite were verified. The Cu(2+) reduction mechanism is complex, indirect, and sensitive to reduction temperature; consequently, Cu(+)(n) states intermediate between Cu(2+) and Cu(0) should be present in the reduced samples.     

On the mutually non isomorphic ℓp(ℓq) spaces

We extend a result of Pe?czyński showing that {?_p(?_q): 1 ≤ p, q ≤ ∞} is a family of mutually non isomorphic Banach spaces. Some results on complemented subspaces of ?_p(?_q) are also given.     

Hydrogen-bonded cyclic tetramers based on ureidopyrimidinones attached to a 3,6-carbazolyl spacer

Direct attachment of two 2-ureido-4-[1H]-pyrimidinone (UPy) subunits to a 3,6-carbazolyl core gives rise to a highly viscous, supramolecular polymer. However, insertion of a methylene spacer between the UPy's and the carbazole leads to a well-defined, cyclic tetramer, in a belt-shaped arrangement, as evidenced by MALDI-TOF, DOSY, and NOESY spectra.     

Linear and non-linear viscoelastic rheology of hybrid nanostructured materials from block copolymers with gold nanoparticles

A polystyrene-b-poly-4-vinypyridine (PS-b-P4VP) diblock copolymer is modified with a gold precursor to obtain an organic–inorganic (hybrid) block copolymer in bulk with gold nanoparticles selectively incorporated in the P4VP block. In the linear viscoelastic regime, temperature sweep tests over a series of these hybrid block copolymer systems revealed consistent shifts (ΔT) in the glass transition temperatures (both T _g\text-PS_{\rm g\text{-}PS} and T _g\text-P4VP_{\rm g\text{-}P4VP}) of the hybrid materials in comparison to the pristine polymers. Studying different volume fractions of the pyridine block, a level-off point was found for block copolymers with f _P4VP > 0.26, where the shifts in T _g\text-P4VP_{\rm g\text{-}P4VP} consistently increased up to ΔT = 25°C. By artificially increasing the volume fraction of the pyridine block, the nanoparticles reduce the transition regime determined in master curves. At higher volume fractions of the pyridine block, crossover frequencies were not detected after the entanglement regime, indicating that the material does not relax from topological constraints (entanglements and nanoparticles) into the terminal regime. Above a specific volume fraction of nanoparticles (Φ _P = 0.05), the flow behaviour of the hybrid materials becomes increasingly elastic, exhibiting wall-slip from the geometry at lower strain values in comparison to the pristine material. In the non-linear viscoelastic regime, Fourier-transformed rheology was used to analyse the raw signals from strain sweep experiments. It was clearly demonstrated the nanoparticle effect by following the second and third harmonic (I _2/1, I _3/1) of the stress response. Comparing the behaviour of the third and second harmonics provided an unambiguous fingerprint for the effect of the nanoparticles.     

Fragmentation and 1,2-Addition Reactions upon Action of Methyllithium on Coupling Products of Ferrocenecarbaldehyde with Dibenzoylmethane

2-Ferrocenylmethylidene-1,2-diphenylpropanedione (3), 2,4-dibenzoyl-3-ferrocenyl-1,5-diphenylpentane-1,5-dione (4), and 2,4-dibenzoyl-3-ferrocenyl-2-[(ferrocenyl)hydroxymethyl]-1,5-diphenylpentane-1,5-dione (5) react with MeLi to undergo fragmentation and 1,2-addition or only 1,2-addition at the carbonyl group. Dehydration of intermediate tertiary alcohols affords α-methylstyrene (6), 3-ferrocenyl-1-phenylprop-2-enone (7), 3,5-diferrocenyl-1-phenyl-4-(1-phenylvinyl)cyclohexene (8), 3-ferrocenylmethylidene-2,4-diphenylpenta-1,4-diene (9), 2-benzoyl-1-ferrocenyl-3-phenylbuta-1,3-diene (10), 2-benzoyl-1-ferrocenyl-3-methylindene (11), 4-ferrocenyl-2-methyl-2,6-diphenyl-3,4-dihydro-2H-pyran (19), and (Z,Z)-2,4-dibenzoyl-1,3-diferrocenyl-5-phenylhexa-1,4-diene (21), isolated by chromatography. The spatial structures of ferrocenyldihydropyran (19) and diferrocenylhexadiene (21) were established by X-ray diffraction analysis.     

An alternative thermal method for identification of pozzolanic activity in Ca(OH)2/pozzolan pastes

Pozzolans play an important role in the industry of cement and concrete. They increase the mechanical strength of cement matrices and can be used to decrease the amount of cement in concrete mixtures, thus decreasing the final economic and environmental cost of production; also, as some of them are byproducts of industrial processes (such as silica fume and fly ash) and their use can be seen as a solution for some residues, that otherwise would be disposed as a waste. Pozzolans fixate the Ca(OH)₂ generated during cement’s hydration reactions to form calcium silicate hydrates (C–S–H), calcium aluminate hydrates (C–A–H), or calcium aluminosilicate hydrates (C–A–S–H), depending on the nature of the pozzolan. Traditionally, the pozzolanic activity is identified using the Ca(OH)₂ fixation percentage which is quantified by thermogravimetric (TG) analysis, using the mass loss due to the Ca(OH)₂ dehydroxylation around 500 °C. An alternative method to identify pozzolanic activity at lower temperatures using a standard issue moisture analyzer (MA) is presented in this paper, using the mass loss due to hydrate’s dehydration generated by pozzolans in the pozzolanic reaction. Samples of Ca(OH)₂ blended with different pozzolans were prepared and tested at different hydration ages. Using TG analysis and an MA, a good correlation was found between the total mass loss of the same sample, using the two methods at the same temperature. It was concluded that the MA method can be considered a less expensive and less time-consuming alternative to identify pozzolanic activity of siliceous or aluminosiliceous materials.     

Chloro­(hist­amine)(1,10‐phenanthro­line)copper(II) chloride monohydrate

In the cationic complex present in the title compound, chloro­[2‐(4‐imidazolyl‐κN¹)­ethyl­amine‐κN](1,10‐phenanthroline‐κ²N,N′)copper(II) chloride monohydrate, [CuCl(C₅H₉­N₃)­(C₁₂H₈N₂)]Cl·H₂O, the metal centre adopts a five‐coordinate geometry, ligated by the two phenanthroline N atoms, two amine N atoms of the hist­amine ligand (one aliphatic and one from the imidazole ring) and a chloro ligand. The geometry around the Cu atom is a distorted compressed trigonal bipyramid, with one phenanthroline N and one imidazole N atom in the axial positions, and the other phenanthroline N atom, the histamine amine N atom and the chloro ligand in the equatorial positions. The structure includes an uncoordinated water mol­ecule, and a Cl⁻ ion to complete the charge. The water mol­ecule is hydrogen bonded to both Cl⁻ ions (coordinated and uncoordinated), and exhibits a close Cu⋯H contact in the equatorial plane of the bipyramid.     

Number of arm selection in two-dimensional diffusion processes

We introduce an algorithm to generate two-dimensional diffusion-limited star-branched aggregates (DLSA)attaching bi-functional monomers successively to a central colloidal particle with any desired number of reactive sites. The proposed algorithm produces star-shaped aggregates that grow forever and show a power law polydispersity in the chemical length of the arms near the central colloid. More interestingly, it gives rise to a number of arm selection consisting in that only a small number of arms (around five) define the final structure at relatively large distances from the central colloid, independently of the initial number of reactive sites and the size of the central colloid. We characterize the structure of the aggregates by means of the particle-particle correlation function, analyze its scaling properties and obtain the fractal dimension.