Synthesis and stereoselective evaluation of a (1R)-(–)-myrtenal-derived pseudo C2-symmetric dodecaheterocycle as a potential heterofunctional chiral auxiliary

The synthesis and diastereoselective performance of the pseudo C₂-symmetric dodecaheterocycle 3 in nucleophilic and electrophilic reactions are reported. Compound 3 proved to be a highly diastereoselective template to generate a pair of enantiomeric moieties within its structure in a programmed manner. Hence, this study describes the synthesis of a novel potential heterobifunctional chiral auxiliary.     

Synthesis,characterization and a voltammetric study of (Bu4N)2[Mo2Br6]. Oxidation-reduction mechanism of related compounds

Summary The synthesis and characterization of (Bu₄N)₂[Mo₂Br₆], obtained from Mo(CO)₆, (Bu₄N)Br and 1,2-dibromoethane, is described. The electrochemical behaviour of [Mo₂Br₆]^–2 and related species is studied, and an oxidation-reduction mechanism is proposed.     

Revisiting the addition reaction of TeCl4 to alkynes: The crystal structure and docking studies of 1-chloro-2-trichlorotelluro-3-phenyl-propen-2-ol

Tellurium tetrachloride adds to alkynes via two pathways: a concerted syn addition, that yields Z-tri- and tetra-substituted alkenes or by an anti addition that yields E-alkenes. The mechanistic aspects of these divergent pathways have been reevaluated at the light of crystallographic data. The molecules, of the title compound, in the crystal, are associated in a helical fashion with a Te…Te pitch of 6.3492(6) Å. As it exhibits inhibitory activity for cathepsin B and in order to gain more insight of the inhibition mechanism, a docking study was undertaken providing insight on why organic telluranes are more efficient inhibitors than inorganic ones as AS-101.     

Free damped oscillations of the linear viscoelastic material

This work shows that the complex dynamic viscosity ^* () can be evaluated from experimental data of free damped oscillations (FDO) when upper and lower angular displacements measured in a plate-plate geometry are analyzed by Fourier series. We deduce the equation required to evaluate experimentally the dynamic functions of linear viscoelastic materials in FDO. Two loss tangents can be defined in FDO, which are not necessarily equal to tan () of the forced oscillation test.     

Evaluation of inductively coupled plasma optical emission spectrometers with axial configuration: interfaces with end-on gas and shear gas

In this investigation, samples of whole bovine milk were diluted with water-soluble tertiary amines solution and introduced in two axially viewed inductively coupled plasma optical emission spectrometer (ICP OES) instruments equipped with different interfaces (shear gas and end-on gas interface). The accuracy and the Mg II (280.2 nm)/Mg I (285.2 nm) ratio were evaluated. Higher values for Mg II/Mg I were observed with the shear gas interface. However, these values were less affected by changes of instrumental parameters when using the end-on gas interface. Results with suitable accuracy were obtained for a certified reference material of powdered whole milk (NIST SRM 8435) using instruments equipped with each interface.     

13C NMR investigation of solid-state polymorphism in 10-deacetyl baccatin III

To investigate the origins of solid-state NMR shift differences in polymorphs, carbon NMR chemical shift tensors are measured for two forms of solid 10-deacetyl baccatin III: a dimethyl sulfoxide (DMSO) solvate and an unsolvated form. A comparison of ab initio computed tensors that includes and omits the DMSO molecules demonstrates that lattice interactions cannot fully account for the shift differences in the two forms. Instead, conformational differences in the cyclohexenyl, benzoyl, and acetyl moieties are postulated to create the differences observed. X-ray analysis of six baccatin III analogues supports the suggested changes in the cyclohexenyl and benzoyl systems. The close statistical match of the (13)C chemical shifts of both polymorphic forms with those calculated using the X-ray geometry of 10-deacetyl baccatin III supports the contention that the B, C, and D rings are fairly rigid. Therefore, the observed tensor differences appear to arise primarily from conformational variations in ring substituents and the cyclohexenyl ring.     

Insertion of unsaturated organic electrophiles into molybdenumbond-alkoxide and rheniumbond-alkoxide bonds of neutral,stable carbonyl complexes

Alkoxo complexes [Re(OR)(CO)(3)(N-N)] (R=Me, Et, tBu; N-N=2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'bipyridine (bipy'), 1,10-phenanthroline (phen)) and [M(OMe)(eta(3)-allyl)(CO)(2)(phen)] (M=Mo, W) have been synthesized in good yields and using mild conditions by the reaction of sodium alkoxides with [Re(OTf)(CO)(3)(N-N)] and [MCl(eta(3)-allyl)(CO)(2)(phen)] precursors. These have been characterized by IR and NMR spectroscopy as well as by X-ray diffraction for [W(OMe)(eta(3)-allyl)(CO)(2)(phen)] (10). The reactions of the molybdenum and rhenium alkoxo complexes with isocyanates, R'NCO, yield [L(n)M[N(R')C(O)OR]] complexes; the carbamate ligand, which results from an R'NCO insertion into the Mbond;OR bond, is monodentate through the nitrogen atom. The solid-state structures of Mo and Re examples have been determined by X-ray diffraction. The geometry around the carbamate nitrogen of these compounds is planar, and the distances indicate delocalization of the nitrogen lone pair involving mainly the carbonyl groups. Experiments carried out with the Re complexes showed that aryl isocyanates are more reactive than their alkyl counterparts, and that bulky R' groups led to slow rates of insertion. Insertion reactions were also observed with isothiocyanates, although here it is the Sbond;C bond that inserts into the Mbond;OR bond, and the resulting ligand is bound to the metal by sulfur. Competition experiments with the Re compounds indicate that isocyanates are more reactive than isothiocyanates towards the Rebond;OR bonds. Tetracyanoethylene inserts into the Rebond;OMe bond of [Re(OMe)(CO)(3)(bipy')], forming a complex with a 2-methoxytetracyanoethyl ligand; the structure of which was determined by X-ray diffraction. The formation of the xanthato complex [Re(SC(S)OtBu)(CO)(3)(bipy)] (20) by reaction of [Re(OTf)(CO)(3)(bipy)] with CS(2) and NaOtBu, but not by the reaction of CS(2) and [Re(OtBu)(CO)(3)(bipy)] (5 a), suggests that the insertion reactions do not take place by ionization of the alkoxo complexes to give the free alkoxide ion.     

Drug Delivery Systems Based on Porous Chitosan/Polyacrylic acid Microspheres

Porous microspheres have been prepared by suspension free radical polymerization of acrylic acid (AA) in the presence of chitosan (CHI). The microspheres were characterized by FTIR and environmental SEM. The PAA content of the microspheres was estimated to be in the range 45–50 wt.‐%. The swelling degree of these particles is almost constant in the range 2 < pH < 5, but it increases considerably as the pH is raised from 5 to 10. The release profiles of microspheres loaded with meclofenamic acid (MF) were determined at pH 2, 7.4, and 10. The in vitro release of MF at different pHs was modulated by the solubility of the drug. These microcapsules are biodegradable and presented good biocompatibility and biodegradability during in vivo experiments.

ESEM microphotograph of the porous PAA/CHI microspheres.     

Cationic fac-tris(pyrazole) complexes as anion receptors

New receptors fac-[Re(CO)3(pz)3]BAr'4 (pz = 3,5-dimethylpyrazole or 3(5)-tert-butylpyrazole, Ar' = 3,5-(CF3)2C6H3), synthesized from [Re(OTf)(CO)5] and the pyrazoles, have been found to show a high affinity for chloride.     

Excess molar volumes and isothermal vapor-liquid equilibrium in the binary system 1,1,1-trichloroethane with 1-chlorobutane and with pyridine at 25°C

Densities and vapor-liquid equilibrium were determined for 1-chlorobutane and pyridine with 1,1,1-trichloroethane at 25°C. From the experimental results, excess molal volumes and excess molar Gibbs energies were calculated. Information could be obtained about the possible interactions between the components of both binary systems. The Prigogine-Flory-Patterson theory was applied to calculate excess molar volumes. Liquid activity coefficients were calculated and correlated with different expressions existing in the literature.