Luis E. Ochando

Quantitative X-ray diffraction phase analysis of coarse airborne particulate collected by cascade impactor sampling

Mineralogical composition of Castellon (Spanish Mediterranean coast) atmospheric aerosol was studied by X-ray diffraction by sampling with a cascade impactor without filters. Quantitative phase analysis of natural phases present in the atmospheric coarse aerosol was performed using a modified version of the computer program MENGE, that uses the standardless X-ray method developed by Rius for the quantitative analysis of multiphase mixtures, adapted for PC running. Presence of quartz, calcite and gypsum was identified in the atmospheric aerosol and we have quantified their amounts using the standardless method.

BODIPY dyes functionalized with 2-(2-dimethylaminophenyl)ethanol moieties as selective OFF–ON fluorescent chemodosimeters for the nerve agent mimics DCNP and DFP

Two OFF–ON fluorescent chemodosimeters based on a BODIPY core for the detection of nerve agent mimics have been synthesized. Their reactivity towards diethylcyanophosphonate (DCNP) and diisopropylfluorophosphate (DFP) has been tested in organic and aqueous phase. These chemodosimeters selectively detect the nerve agent mimics with good LODs. The chemodosimeters hold their sensing properties on solid supports, allowing the preparation of a hand held sensing kit. The sensing in solid–liquid phase has been demonstrated. The X-ray structure of compound 2 has been resolved.

X-ray powder diffraction phase analysis and thermomechanical properties of silica and alumina porcelains

Chemical and mineralogical characterization, using the Rietveld method, of some silica and alumina rich porcelains and its relationship with thermomechanical properties have been studied in this work. X-ray powder diffraction analysis allows to differ clearly between silica and alumina porcelains. X-ray study shows that both porcelains have a content of vitreous phase. This vitreous phase is higher in the silica than in the alumina porcelain. Dilatometric studies combined with powder diffraction methods shows a strong relationship between silica content and a lower expansion coefficients and between alumina content and a higher crash resistance. Lower contents in vitreous phase in porcelain yields to higher thermal expansion coefficients.

Phase Transitions in Tris(3,5-dimethylpyrazol-1-yl)methane. The Structure of the High-Temperature Phase from X-ray Powder Diffraction

The crystal structure of the sublimated form (m.p. = 424 K) of tris(3,5-dimethylpyrazol-l-yl)methane has been solved by a Patterson search method from laboratory X-ray powder diffraction data. Crystal data: trigonal symmetry with the unit-cell parameters a = 16.152 (1) and c = 5.353 (1) A, space group P3, C16H22N6, Z = 3, 293 K. After indexing the powder pattern by two methods, the unit-cell parameters found were refined by a least-squares technique. A whole pattern-fitting program was used to extract the integrated intensities. The structure was solved taking a related compound as a search model and the final Rietveld refinement converged to Rwp = 0.077 and Rp = 0.059. This study is one of the first examples of Patterson search structure determination from an hemihedral space group using powder data. The complexity of the structural determination is increased by the presence of three molecules in the asymmetric unit.

Redox-active crown ethers derived from biphenyl. Electrochemical and spectroscopic study of binding processes with alkali, alkali-earth and mercury salts

Abstract Three new electroactive ligands, 3a, 3b and 3c, that contain the biphenyl frameworks in their structure were prepared. These new ligands presented three interesting characteristics: 1) they exhibited a reversible oxidation, 2) the oxidation induced a conformational change in the crown moiety and 3) they had two different coordination centers, the crown ether and the dimethylamino groups. Electrochemical and spectroscopic studies using alkali, alkali-earth and mercury salts were carried out.

Quantitative Phase Analysis of Mixtures of Three Components using Rietveld and Rius Standardless Methods. Comparative Results

Eight samples, supplied by the Commission on Powder Diffraction of the International Union of Crystallography, through the Round Robin on quantitative phase analysis, were analized using standardless methods. Samples were mixtures of corundum, zincite and fluorite in different ratios. The Rietveld method, using the DBW 3.2 and FULLPROF software, and the Rius method, using MENGE-PC software, were used. Results obtained agree well with the real composition supplied (a posteriori) by the IUCr.

Inversion of selectivity in anion recognition with conformationally blocked calix[4]pyrroles

Two calixpyrrole derivatives were synthesised. A p-dimethylaminobenzoyl group was electronically attached to a pyrrole ring, establishing an intramolecular hydrogen bond in a 1,3-alternate conformation. The formation of the H-bond was corroborated by IR, NMR, and X-ray measurements. NMR titration studies reveal that the H-bond is strong enough to block the conversion to a cone conformation, allowing them to only acquire a partial cone conformation. Affinity constants for several anions were calculated, and a noticeable increase was observed for tridentate tetrahedral anions, while the K(a) of spheric or bidentate anions decreased. In the presence of several acids, the synthesised compounds can act as chemosensors by a double process: protonation of the amino group and coordination of the generated anion. In addition, a displacement approach gives rise to a proof of concept for sulphonate recognition.

BIS-CYCLIC CROWN ETHERS DERIVED FROM BIPHENYL. INFLUENCE OF CONFORMATION IN COMPLEXATION OF HG(SCN)2

Abstract Complexation studies carried out using bis-crown ethers derived from biphenyl have demostrated that the second crown units has a strong influence on the association constant in the first one. X-ray analysis shows that the situation is different in the monocrown-ether complex 5 than in the related bis-cyclic compound 6.

A tangent formula derived from Patterson-function arguments. VII. Solution of inorganic structures from powder data with accidental overlap

Accidental overlap constitutes one of the principal limitations for the solution of crystal structures from powder diffraction data, since it reduces the number of available intensities for direct-methods application. In this work, the field of application of the direct-methods sum function is extended to cope with powder patterns with relatively large amounts of accidental overlap. This is achieved by refining not only the phases of the structure factors but also the estimated intensities of the severely overlapped peaks during the structure solution process. This procedure has been specifically devised for inorganic compounds with uncertain cell contents and with probable severe atomic disorder, a situation often found when studying complex minerals with limited crystallinity. It has been successfully applied to the solution of the previously unknown crystal structure of the mineral tinticite. Finally, an estimation of the smallest ratio (number of observations to number of variables) for the procedure to be successful is given.

Experimental evidence for the homochiral aggregation of ammonium salts in solution

NMR and X-ray evidence for the homochiral aggregation of chiral ammonium picrates from racemic solutions is presented.