An efficient approach to homochiral indane nucleosides

A series of new chiral 6-substituted purinyl and 8-aza-purinyl carbonucleosides based on indanol were synthesized from the commercially available (1R,2S)-1-amino-2-indanol and (1S,2R)-1-amino-2-indanol based on a well-known methodology.     

Spectrofluorimetry in organized media coupled to second-order multivariate calibration for the determination of galantamine in the presence of uncalibrated interferences

The present article describes the spectrofluorimetric determination of galantamine, a widely used acetylcholinesterase inhibitor, through excitation-emission fluorescence matrices and second-order calibration. With the purpose of enhancing the fluorescence intensity of this substance, the effect of different organized assemblies was evaluated. Although the interaction of galantamine with different cyclodextrins is weak, it was corroborated that the fluorescence intensity of this pharmaceutical in the presence of α-cyclodextrin is increased by a twofold factor. Among the studied micellar media, the anionic surfactant sodium dodecyl sulfate produced the largest signals for the compound of interest (sixfold enhancement), and was selected as auxiliary reagent for the subsequent determinations. The developed approach enabled the determination of galantamine at the ng mL⁻¹ level without the necessity of applying separation steps, and in the presence of uncalibrated interferences. The applied second-order chemometric tools were parallel factor analysis (PARAFAC), unfolded partial least-squares coupled to residual bilinearization (U-PLS/RBL), and multidimensional partial least-squares coupled to residual bilinearization (N-PLS/RBL). The ability of U-PLS/RBL to successfully overcome spectral interference problems is demonstrated. The quality of the proposed method was established with the determination of galantamine in both artificial and natural water samples.     

Noncentral elliptical configuration density

The noncentral configuration density, derived under an elliptical model, generalizes and corrects the Gaussian configuration and some Pearson results. Partition theory is then used to obtain explicit configuration densities associated with matrix variate symmetric Kotz type distributions (including the normal distribution), matrix variate Pearson type VII distributions (including t and Cauchy distributions), the matrix variate symmetric Bessel distribution (including the Laplace distribution) and the matrix variate symmetric Jensen-logistic distribution.     

Synthesis of silicalite-1 from organo-silicic gels

Well crystallized silicalite-1 has been obtained from three sources of amorphous silica, namely, rice hull ashes, commercial Davisil, and a fume silica from Aldrich. The silicas were first dissolved in glycerol according to a recently described reaction. This reaction transforms rapidly and efficiently large surface area silicates into poly-alkoxide gels. It can be schematized as an etherification of an alcohol function of glycerol by the weakly acid surface silanol groups. The facile hydrolysis of the alkoxide permits the preparation of relatively pure and reactive silica, keeping the mesoporous character of the parent starting material. We insist on the mesoporous character of the solids obtained upon hydrolyzing the organo-silicic gel because we believe the gel plays a role of template in the secondary synthesis of mesoporous structures. The hydrolysis is carried out in presence of a structure directing agent, namely tetra-propylammonium hydroxide, TPAOH. After aging, the residue is dried and calcined. The first advantage of using the organo-silicic gel is probably related to the high degree of depolymerization of silica, witness by the C/Si ratio. The second one, more subtle to define, is to provide an intermediate silica with hydrophilic a hydrophobic regions, interfering differently with the surfactant. After calcination at 500 degrees C, well crystallized silicalite-1 is obtained. The texture of the starting silica influences the textural characteristics of the final silicalite-1.     

Catalytic combustion of ethyl acetate over ceria-promoted platinum supported on Al2O3 and ZrO2 catalysts

Platinum-supported catalysts prepared by impregnation of mixed CeO₂/Al₂O₃ and CeO₂/ZrO₂ oxides using the sol-gel method were characterized and used in the combustion of ethyl acetate. In each series, the effect of CeO₂ loading (3 and 5 wt%) was studied. Characterization data from the studied catalysts (specific area measurements, hydrogen chemisorption, programmed temperature reduction (TPR), X-ray diffraction (XRD), photoelectron spectra (XPS) and transmission electron microscopy (TEM)) revealed significant changes in porosity and metal dispersion in each series. The catalytic activity of the solids, evaluated in the total combustion of ethyl acetate, exhibited a positive effect with the addition of Ce in the zirconia series whereas no significant changes was observed in the alumina series.     

Modeling the Electrochemical Response of Mesoporous Materials Toward Its Application to Biomolecular Detection

The performance of an electrochemical sensor based on the ability of a probe to cross a mesoporous membrane partially blocked by an analyte is predicted using a numerical model. The system comprehends a membrane placed close to the working electrode and the signal is generated by applying square wave voltammetry. The digital simulation allows comparing the responses for different situations regarding the way in which the membrane is blocked by the sample. The developed model is compared with experimental results. The effect of the sizes of the pore, analyte and probe on the system response is evaluated.     

Synthesis of 5-phenyl-2,3,8,9-tetramethoxy-11H-indeno[1,2-c]isoquinoline

A novel approach to the title compound 10 starting with a conveniently available cinnamic acid is proposed. It involves a Friedel-Crafts reaction followed by the synthesis of the amide and subsequent cyclodehydration via a Bischler-Napieralski reaction.     

Conformational analysis of 1,2,3,4-tetrahydroisoquinolines

Ring and nitrogen inversion account for the conformational equilibria of 3-phenyl-1, 2,3, 4-tetrahydroiso-quinolines. In order to quantitate the relative contribution of each conformer to the equilibrium, we undertook a molecular mechanics study on several substituted 3-phenyl-1, 2, 3, 4-tetrahydroisoquinolines. Predictions from calculations were checked against cmr chemical shift data. No boat conformation contributed significantly to the equilibrium. A general result of our calculations is that in all cases the 3-phenyl group in the equatorial position is strongly favored (by at least 2.50 kcal/mole). For 3-phenyl-1, 2, 3, 4-tetrahydroisoquinolines without substitution at nitrogen, N-H in equatorial position is preferred over the axial conformer, although the energy difference between both is always small (0.30–1.10 kcal/mole). For the cis-1,3-disubstituted compounds the le'3e conformers are the only species present (at least 99.8%). The calculated energy differences between the la′3a conformer and the le′3e conformer are always large (3.80–6.10 kcal/mole for the NHe conformers and 3.60–3.80 kcal/mole for the NHa conformers). The lack of a γ_1a upfield shift at C3 also points to the preference for the pseudoequatorial-equatorial conformer. For N-methyl-3-phenyl-1,2,3,4-tetrahydroisoquinoline a preference for the NMe group in the equatorial position is predicted (0.60–2.00 kcal/mole). The small downfield shift at C4 (γ_Na = 0.5 ppm) is consistent with the equatorial NMe preference. For the cis-1,2,3-trisubstituted compounds no significant γ_1a effect at C3 (γ_1a = -0.2 and 1.0 ppm) or γ_Na effect at C4 (γ_Na = 0.1 and 0.4 ppm) is observed. For these compounds, deformations due to steric congestion are evidenced by the deviation from the values of the C4a-C8a-Cl-N and C4a-C4-C3-N torsional angles, as compared to less crowded 3-phenyl-1,2,3,4-tetrahydroisoquinolines. Here the heterocyclic ring adopts a distorted half-chair conformation.     

Crystal chemistry and thermal behavior of metal salts and complexes of unsaturated dicarboxylic acids: aquabis(hydrogen itaconato)barium(II), [Ba(C5H5O4)2(OH2)]

[Ba(C₅H₅O₄)₂(OH₂)] is monoclinic, C2/c, with a = 4.472(1), b = 13.312(3), c = 22.236(5) Å, = 92.90(1)°, Z = 4, and D _m = 2.06 g cm^–3. The barium atom is 10-coordinate with Ba—O distances in the range 2.749(2)–2.989(2) Å. The material suffers a complex decomposition process upon heating at temperatures between 25 and 600°C in dynamic nitrogen and static air atmospheres. FT-IR and gas chromatography analyses indicate that water, CO, CO₂, methane, ethane, ethylene, propane, propylene, and butane, are evolved during the heating process, leaving a residue of BaCO₃. ¹H-NMR spectra of a sample heated at 200°C, showed isomerization of barium itaconate to barium methylmaleate.