Experimental and theoretical vibrational study of silyl trifluoromethanesulfonate, CF3SO2OSiH3

Infrared and Raman spectra were obtained for liquid silyl trifluoromethanesulfonate, a silylating agent of limited stability. The molecular geometry was optimized by means of density functional theory and M?ller-Plesset second order perturbation theory methods, using different basis sets. The optimized structure presents a gauche conformation, similar to that adopted by methyl trifluoromethanesulfonate, which was determined experimentally a short time ago. The wavenumbers for the normal modes of vibration and the corresponding force constants were also calculated, facilitating the interpretation of the vibrational data. The harmonic force constants given by theory were scaled to reproduce adequately the experimental wavenumbers.     

Phosphine and Thiophene Cyclopalladated Complexes: Hydrolysis Reactions in Strong Acidic Media

The mechanisms for the hydrolysis of organopalladium complexes [Pd(CNN)R]BF₄ (R=P(OPh)₃, PPh₃, and SC₄H₈) were investigated at 25 °C by using UV/Vis absorbance measurements in 10 % v/v ethanol/water mixtures containing different sulphuric acid concentrations in the 1.3–11.7 M range. In all cases, a biphasic behavior was observed with rate constants k_1obs, which corresponds to the initial step of the hydrolysis reaction, and k_2obs, where k_1obs>k_2obs. The plots of k_1obs and k_2obs versus sulfuric acid concentration suggest a change in the reaction mechanism. The change with respect to the k_1obs value corresponds to 35 %, 2 %, and 99 % of the protonated complexes for R=PPh₃, P(OPh)₃, and SC₄H₈, respectively. Regarding k_2obs, the change occurred in all cases at about 6.5 M H₂SO₄ and matched up with the results reported for the hydrolysis of the 2‐acetylpyridinephenylhydrazone (CNN) ligand. By using the excess acidity method, the mechanisms were elucidated by carefully looking at the variation of k_i,_obs (i=1,2) versus ${c_{{\rm{H}}^ + } }$ . The rate‐determining constants, k_0,A‐1, k_0,A‐2, and k_0,A‐SE2 were evaluated in all cases. The R=P(OPh)₃ complex was most reactive due to its π‐acid character, which favors the rupture of the trans nitrogen–palladium bond in the A‐2 mechanism and also that of the pyridine nitrogen–palladium bond in the A‐1 mechanism. The organometallic bond exerts no effect on the relative basicity of the complexes, which are strongly reliant on the substituent.     

A Flexible Pro‐porous Coordination Polymer: Non‐conventional Synthesis and Separation Properties Towards CO2/CH4 Mixtures

The novel coordination polymers [Cu(Hoxonic)(H₂O)]_n ( 1 ) and [Cu(Hoxonic)(bpy)_0.5]_n ? 1.5 n H₂O ( 2?H₂O ) (H₃oxonic: 4,6‐dihydroxy‐1,3,5‐triazine‐2‐carboxylic acid; bpy: 4,4′‐bipyridine) have been isolated and structurally characterised by ab initio X‐ray powder diffraction. The dense phase 1 contains 1D zig‐zag chains in which Hoxonic dianions bridge square‐pyramidal copper(II) ions, apically coordinated by water molecules. On the contrary, 2?H₂O , prepared by solution and solventless methods, is based on 2D layers of octahedral copper(II) ions bridged by Hoxonic ligands, further pillared by bpy spacers. The resulting pro‐porous 3D network possesses small hydrated cavities. The reactivity, thermal, magnetic and adsorptive properties of these materials have been investigated. Notably, the adsorption studies on 2 show that this material possesses unusual adsorption behaviour. Indeed, guest uptake is facilitated by increasing the thermal energy of both the guest and the framework. Thus, neither N₂ at 77 K nor CO₂ at 195 K are incorporated, and CH₄ is only minimally adsorbed at 273 K and high pressures (0.5 mmol g^?1 at 2500 kPa). By contrast, CO₂ is readily incorporated at 273 K (up to 2.5 mmol g^?1 at 2500 kPa). The selectivity of 2 towards CO₂ over CH₄ has been investigated by means of variable‐temperature zero coverage adsorption experiments and measurement of breakthrough curves of CO₂/CH₄ mixtures. The results show the highly selective incorporation of CO₂ in 2 , which can be rationalised on the basis of the framework flexibility and polar nature of its voids.     

Application of thiophilic chromatography to deplete serum immunoglobulins in sample preparation for bidimensional electrophoresis

Serum is a typical sample for non-invasive studies in clinical research. Its proteome characterization is challenging, since requires extensive protein depletion. Methods used nowadays for removal of high-abundance proteins are expensive or show quite often a low loading capacity, which has strong repercussions on the number of samples and replicates per analysis.In order to deplete immunoglobulins (Igs) and albumin (HSA) from 1 mL serum samples, we have developed a protocol based on a combination of thiophilic chromatography, not previously used in clinical proteomics, and a HSA-specific resin. Ig/HSA-depleted samples, immunoglobulinome and albuminone were analyzed by 2-DE. Thiophilic chromatography, coupled with HSA-depletion, allows a good 2-DE resolution as well as the visualization of new spots. Moreover, it yields enough protein to evaluate technical variability and facilitate subsequent protein identification. To validate the protocol, we carried out a preliminary comparative study between triplicate Igs/HSA-depleted serum samples from healthy control individuals and recently diagnosed/untreated rheumatoid arthritis (RA) patients. RA patients showed several acute phase proteins, as well as additional serum proteins, differentially and significantly regulated.Therefore, thiophilic chromatography can be used as an efficient and economical method in 2-DE to deplete immunoglobulins from large human serum samples before a more extensive fractioning.     

Mechanical Behavior of Polymer Gels for RDCs and RCSAs Collection: NMR Imaging Study of Buckling Phenomena

Anisotropic NMR parameters, such as residual dipolar couplings (RDCs), residual chemical shift anisotropies (RCSAs) and residual quadrupolar couplings (RQCs or Δν_Q), appear in solution‐state NMR when the molecules under study are subjected to a degree of order. The tunable alignment by reversible compression/relaxation of gels (PMMA and p‐HEMA) is an easy, user‐friendly, and very affordable method to measure them. When using this method, a fraction of isotropic NMR signals is observed in the NMR spectra, even at a maximum degree of compression. To explain the origin of these isotropic signals we decided to investigate their physical location inside the NMR tube using deuterium 1D imaging and MRI micro‐imaging experiments. It was observed that after a certain degree of compression the gels start to buckle and they generate pockets of isotropic solvent, which are never eliminated. The amount of buckling depends on the amount of cross‐linker and the length of the gel.     

Collection of NMR Scalar and Residual Dipolar Couplings Using a Single Experiment

A new DMSO‐compatible aligning gel based on cross‐linked poly(2‐hydroxylethyl methacrylate) (poly‐HEMA) has been developed. Due to a significant difference in bulk magnetic susceptibility between the DMSO inside and outside the gel, it is possible to simultaneously collect isotropic and anisotropic NMR data, such as residual dipolar couplings (RDC), in the same NMR tube. RDC‐assisted structural analysis of menthol and the alkaloid retrorsine is reported as proof of concept.     

Kinetic study of the sulfonation of hydrogenated styrene butadiene block copolymer (HSBS): Microstructural and electrical characterizations

In this work homogeneous sulfonation kinetic and both, microstructural and electrical characterizations of hydrogenated styrene butadiene block copolymer (HSBS) were studied. The incorporation of sulfonic groups was checked by infrared spectroscopy (FTIR-ATR) and the sulfonation level was determined by both, elemental analysis (E.A.) and chemical titration. Thermal behavior was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), in order to determine thermal transitions and stability, respectively. Microstructure was studied, by means of dynamic mechanical analysis (DMA). Atomic force microscopy (AFM) was studied for several samples and evidenced a morphology change when the sulfonation level increases. Finally, electrical behavior was recorded by means of electrochemical impedance spectroscopy (EIS) and the four-probe technique (FPT). Results show that sulfonation of the benzene rings, in the styrene units, has effectively occurred and that the sulfonation level increases with reaction time. When incrementing the sulfonation level, a structural change in the copolymer was observed. Interconnected clusters allow proton conduction through the membrane. The ion conductivity obtained was about 10⁻² S/cm.     

Analysis of the effects of catalytic bleaching on cotton

Hydrogen peroxide can be catalyzed to bleach cotton fibers at temperatures as low as 30°C by incorporating dinuclear tri-μ-oxo bridged manganese(IV) complex of the ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (MnTACN) as the catalyst in the bleaching solution. The catalytic system was found to be more selective under the conditions applied than the non-catalytic H₂O₂ system, showing better bleaching performance while causing slightly lower decrease in degree of polymerization (DP) of cellulose. In order to gain fundamental knowledge of the bleach effect on cotton fibers and cellulose as its main component, especially after catalytic bleaching, X-ray Photoelectron Spectroscopy (XPS) was used to study surface chemical effects. The Washburn method was applied to investigate wetting properties, and liquid porosity was used to obtain pore volume distribution (PVD) plots. Parallel analyzes performed on model cotton fabric, i.e. “clean” cotton fabric stained with morin - a pigment regularly found in native cotton fiber, helped to differentiate between pigment oxidation and other bleaching effects produced on the (regular) industrially scoured cotton fabric. Bleaching was not limited to the chemical action but also affected cotton fiber capillary parameters most likely due to the removal of non-cellulosic materials as well as chain-shortened cellulose.     

Application of TG/FTIR to the study of the regeneration process of husy and HZSM5 zeolites

The effect of regeneration conditions on the composition of the gases evolved during the catalytic pyrolysis of low density (LDPE) and high density polyethylene (HDPE) with HUSY and HZSM5 catalysts has been analysed by the TG/FTIR technique. When regenerated HUSY was employed, the evolution of the gases obtained was similar to that with fresh HUSY, indicating that the regeneration treatment did not affect its properties. Nevertheless with HZSM5, as the regeneration temperature was higher, the composition of the gases gradually became more similar to that evolved in the thermal process.     

Microwave-assisted synthesis of bipyrazolyls and pyrazolyl-substituted pyrimidines

We describe the preparation of 1,4′-bipyrazolyls and 4-pyrazolylpyrimidines by the reaction of 2-pyrazolyl-3-dimethylamino acrylate and acrylonitrile with double nucleophilic reagents such as hydrazines, urea and guanidine. Reactions were performed under microwave irradiation in 5-60 min. This is a useful procedure for the preparation of valuable compounds with applications in medicinal and coordination chemistry.