FT-IR and MAS NMR analysis of montmorillonite K10 supported MF2 reagents and their activity as catalysis /

ZnF2, CdF2, and CUF2 have been adsorbed onto the surface of montmorillonite K10, and the infrared and 19F, 27 AI, and 29Si MAS NMR spectra of the reagents over a range of loadings have been obtained. CUF2 was observed to attack the Si02 layer and form the complex CuSiF6, Zn F2 tends to attack the aluminium oxide layer, in which Zn isomorphously replaces AI, and forms AIF3 and AIF4 - complexes. All the spectroscopic evidence ruled out the formation of any AI-F and/or Si-F free species as CdF2 is adsorbed on the surface of montmorillonite K10. The reactivity of MF2-K10 reagents towards Friedel-Crafts benzylation of benzene with benzyl chloride varied from one reagent to another. ZnF2-K10 was observed to be the most reactive and CUF2 was the least reactive.

Festkörper-NMR an polymeren Kompositmaterialien

In dieser Arbeit wurden polymere Kompositmaterialien mit Hilfe von Festkörper-NMR-Techniken untersucht, um den Einfluß von Polymer-Festkörper-Kontakten auf molekulare Materialeigenschaften zu betrachten. Dabei wurden sowohl Analysen am Polymer als auch am Füllmaterial durchgeführt.rnrnIm ersten Teil der Arbeit wurde die Dynamik von Poly(ethylmethacrylat) (PEMA) in sphärischen Bürstenpartikeln gemessen. Diese Bürsten bestanden aus einem Poly(silsesquioxan)-Kern und verpfropften PEMA-Ketten, die über ATRP (atom transfer radical polymerization) an verschiedenen Kettensequenzen mit 13C an der Carboxylgruppe markiert wurden. Statische 13C-NMR-Messungen konnten zeigen, dass die Dynamik dieser Sequenzen unabhängig vom Abstand zur Oberfläche verlangsamt ist, was auf eine eingeschränkte Reptation zurückgeführt wurde.rnrnDer zweite Teil der Arbeit beschäftigt sich mit den molekularen Unterschieden von Silika-Naturkautschuk-Kompositen, die über mechanisches Mischen bzw. über eine Sol-Gel-Reaktion hergestellt wurden. Durch kinetische 1H-NMR-Messungen wurde der Umsatz der Sol-Gel-Reaktion bestimmt. Mittels heteronuklearen 29Si{1H}-NMR-Korrelationsexperimenten wurde ein direkter räumlicher Kontakt zwischen dem Inneren der Partikel und dem Polymer nachgewiesen. Dies belegt experimentell, dass im Kompositmaterial die Polymerketten in den durch Sol-Gel-Reaktion hergestellten Silikapartikeln eingeschlossen sind.

A structural investigation relating to the pozzolanic activity of rice husk ashes

Various factors determine the applicability of rice husk ash (RHA) as a pozzolanic material. The amount and accessibility of reactive sites is thought to be a key factor. A structural study of RHA samples in relation to their reactivity has been performed; Silica in RHA formed by burning rice husk in a laboratory furnace under continuous supply of air have been characterized as a function of incineration temperature, time and cooling regime. The characterization methods included chemical analyses, conductivity measurements, microscopic analysis, X-ray diffraction (XRD) and 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR). In line with earlier observations, the analyses show that the highest amounts of amorphous silica occur in samples burnt in the range of 500 °C–700 °C. The 29Si NMR data allow direct identification of the reactive silanol sites in the RHA samples. De-convolution of the NMR spectra clearly shows that the quickly cooled RHA resulting from burning rice husk for 12 h at 500 °C has the highest amount of silanol groups. This sample also induced the largest drop in conductivity when added to a saturated calcium hydroxide solution giving an indication of its reactivity towards lime. Therefore, this RHA is the favorable sample to be used as pozzolanic cement additive

Compostos luminescentes em matrizes macroporosas de sílica obtidas por tratamento hidrotérmico a partir de vidro pyrex

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Síntese e caracterização espectroscópica de novos vanadosilicatos utilizando templates orgânicos derivados de piperidinas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Novel silica membrane material for molecular sieve applications

Development of new silica membranes properties, e.g., molecular sieving properties, has been increasingly gaining importance in the last few years. A novel unsupported silica membrane, referred to as hydrophobic metal-doped silica, was developed by cobalt-doping within the organic templated silica matrix. The novel material was prepared by the acid-catalyzed hydrolysis and condensation process of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES), which is the precursor for methyl ligand covalently bounded to the silica matrix. The synthesis and surface properties of the novel unsupported silica membrane as well as the unsupported blank silica and modified silica membranes were revealed by surface and microstructural techniques, such as water contact angle measurement, FTIR, X-ray, Solid-state 29Si MAS NMR, TGA and N2 and CO2 adsorption measurements. The results showed that the thermal stability of the organic templated silica matrix was enhanced by cobalt-doping process. A hydrophobic microporous silica membrane material with high thermal stability up to ∼560 °C in oxidizing atmosphere and a narrow pore size distribution centered at 1.1 nm was obtained. Therefore, a novel precursor material for molecular sieve silica membranes applications has been achieved and developed.

Spectroscopic, calorimetric, and catalytic evidences of hydrophobicity on Ti-MCM-41 silylated materials for olefin epoxidations

Hydrophobic Ti-MCM-41 samples prepared by post-synthesis silylation treatment demonstrate to be highly active and selective catalysts in olefins epoxidation by using organic hydroperoxides as oxidizing agents in liquid phase reaction systems. Epoxide yields show important enhancements with increased silylation degrees of the Ti-mesoporous samples. Catalytic studies are combined and correlated with spectroscopic techniques (e.g. XRD, XANES, UV-Visible, 29Si MAS-NMR) and calorimetric measurements to better understand the changes in the surface chemistry of Ti-MCM-41 samples due to the post-synthesis silylation treatment and to ascertain the role of these trimethylsilyl groups incorporated in olefin epoxidation. In such manner, the effect of the organic moieties on solids, and both water and glycol molecules contents on the catalytic activity and selectivity are analyzed in detail. Results show that the hydrophobicity level of the samples is responsible for the decrease in water adsorption and, consequently, the negligible formation of the non-desired glycol during the catalytic process. Thus, catalyst deactivation by glycol poisoning of Ti active sites is greatly diminished, this increasing catalyst stability and leading to practically quantitative production of the corresponding epoxide. The extended use of these hydrophobic Ti-MCM-41 catalysts together with organic hydroperoxides for the highly efficient and selective epoxidation of natural terpenes is also exemplified.

Studies in clay chemistry

A study of clay chemistry has been approached with three aims: - to modify the conducting properties by intercalation of tetrathiafulvalene, - to study the electrochemistry of redox-active coordination compounds immobilised on clay coated electrodes, and - to study the role of clays as reagents in inorganic glass forming reactions using mainly solid-state magic-angle-spinning NMR. TTF was intercalated by smectites containing different interlayer and lattice cations. Evidence from ESR and 57Fe Mossbauer indicated charge-transfer from TTF to structural iron in natural montmorillonite, and to interlayer Cu2+ in Cu2+ exchanged laponite. No charge transfer was observed for laponite (Na+ form) itself. Ion exchange of TTF3(BF4)2 with laponite was found to proceed quantitatively. The intercalated species were believed to be (TTF)2+ dimers. Conductivity data showed an order of magnitude increase for the intercalated clays. The mechanism is thought to be ionic rather than CT as Na+ laponite showed a similar enhancement in conductivity. Mechanically robust colloidal clay films were prepared on platinum electrodes. After immersion in solutions containing redox active complexes [Co(bpy)3]3+ and [Cr(bpy)3]3+, the films became electroactive when a potential was applied. Cyclic voltammograms obtained for both complexes were found to be of the diffusion controlled type. For [Co(bpy)3]3+ immobilised on clay coated electrodes, a one-step oxidation and four-step reduction wave was observed corresponding to a one electron stepwise reversible reduction of Co(III), through Co(II), Co(I), Co(O) to Co(I) oxidation state. For [Cr(bpy)3]3+ the electrochemistry was complicated by the presence of additional waves corresponding to the dissociation of [Cr(bpy)3]3+ into the diaquo complex. ESR and diffuse reflectance data supported such a mechanism. 29Si, 27Al and 23Na MAS NMR spectroscopy, supported by powder XRD and FTIR, was used to probe the role of clays as reagents in glass forming reactions. 29Si MAS NMR was found to be a very sensitive technique for identifying the presence and relative abundance of crystalline and non-crystalline phases. In thermal reactions of laponite formation of new mineral phases such as forsterite, akermanite, sillimanite and diopside were detected. The relative abundance of each phase was dependent on thermal history, chemical nature and concentration of the modifier oxide present. In continuing work, the effect of selected oxides on the glass forming reactions of a model feldspar composition was investigated using solid state NMR alone. Addition of network modifying oxides generally produced less negative 29Si chemical shifts and larger linewidths corresponding to a wider distribution of Si-O-Si bond angles and lengths, and a dominant aluminosilicate phase with a less polymerised structure than the starting material. 29Si linewidths and 27Al chemical shifts were respectively correlated with cationic potential and Lewis acidity of the oxide cations. Anomalous Al(4) chemical shifts were thought to be due to precipitation of aluminate phases rather than a breakdown in Lowenstein's aluminium avoidance principle.

Solid state NMR chemical shifts as an alternative to diffraction data in the determination of SIC polytypic structures

Silicon carbide, which has many polytypic modifications of a very simple and very symmetric structure, is an excellent model system for exploring, the relationship between chemical shift, long-range dipolar shielding, and crystal structure in network solids. A simple McConnell equation treatment of bond anisotropy effects in a poly type predicts chemical shifts for silicon and carbon sites which agree well with the experiment, provided that contributions from bonds up to 100 A are included in the calculation. The calculated chemical shifts depend on three factors: the layer stacking sequence, electrical centre of gravity, and the spacings between silicon and carbon layers. The assignment of peaks to lattice sites is proved possible for three polytypes (6H, 15R, and 3C). The fact that the calculated chemical shifts are very sensitive to layer spacings provides us a potential way to detennine and refine a crystal structure. In this work, the layer spacings of 6H SiC have been calculated and are within X-ray standard deviations. Under this premise, the layer spacings of 15R have been detennined. 29Si and 13C single crystal nmr studies of 6H SiC polytype indicate that all silicons and carbons are magnetically anisotropic. The relationship between a magnetic shielding tensor component and layer spacings has been derived. The comparisons between experimental and semi-empirical chemical shielding tensor components indicate that the paramagnetic shielding of silicon should be included in the single crystal chemical shift calculation.

Solvent induced NMR chemical shifts that arise from molecular encounters

Recently Homer and Percival have postulated that intermolecular van der Waals dispersion forces can be characterized by three mechanisms. The first arises via the mean square reaction field < R1; 2> due to the transient dipole of a particular solute molecule that is considered situated in a cavity surrounded by solvent molecules; this was characterized by an extended Onsager approach. The second stems from the extra cavity mean square reaction field < R2; 2> of the near neighbour solvent molecules. The third originates from square field electric fields E2BI due to a newly characterized effect in which solute atoms are `buffeted' by the peripheral atoms of adjacent solvent molecules. The present work concerns more detailed studies of the buffeting screening, which is governed by sterically controlled parameter (2T - T)2, where and are geometric structural parameters. The original approach is used to characterise the buffeting shifts induced by large solvent molecules and the approach is found to be inadequate. Consequently, improved methods of calculating and are reported. Using the improved approach it is shown that buffeting is dependent on the nature of the solvent as well as the nature of the solute molecule. Detailed investigation of the buffeting component of the van der Waals chemical shifts of selected solutes in a range of solvents containing either H or Cl as peripheral atoms have enabled the determination of a theoretical acceptable value for the classical screening coefficient B for protons. 1H and 13C resonance studies of tetraethylmethane and 1H, 13C and 29Si resonance studies of TMS have been used to support the original contention that three (< R1; 2> , < R2; 2> and E2BI) components of intermolecular van der Waals dispersion fields are required to characterise vdW chemical shifts.

An examination of the calcium and strontium site distribution in bioactive glasses through isomorphic neutron diffraction, X-ray diffraction, EXAFS and multinuclear solid state NMR.

Strontium has been substituted for calcium in the glass series (SiO2)49.46(Na2O)26.38(P2O5)1.07(CaO)23.08x(SrO)x (where x = 0, 11.54, 23.08) to elucidate their underlying atomic-scale structural characteristics as a basis for understanding features related to the bioactivity. These bioactive glasses have been investigated using isomorphic neutron and X-ray diffraction, Sr K-edge EXAFS and solid state 17O, 23Na, 29Si, 31P and 43Ca magic-angle-spinning (MAS) NMR. An effective isomorphic substitution first-order difference function has been applied to the neutron diffraction data, confirming that Ca and Sr behave in a similar manner within the glass network, with residual differences attributed to solely the variation in ionic radius between the two species. The diffraction data provides the first direct experimental evidence of split Ca–O nearest-neighbour correlations in these melt quench bioactive glasses, together with an analogous splitting of the Sr–O correlations; the correlations are attributed to the metal ions correlated either to bridging or to non-bridging oxygen atoms. Triple quantum (3Q) 43Ca MAS NMR corroborates the split Ca–O correlations. Successful simplification of the 2 < r (A) < 3 region via the difference method has also revealed two distinct Na environments. These environments are attributed to sodium correlated either to bridging or to nonbridging oxygen atoms. Complementary multinuclear MAS NMR, Sr K-edge EXAFS and X-ray diffraction data supports the structural model presented. The structural sites present will be intimately related to their release properties in physiological fluids such as plasma and saliva, and hence the bioactivity of the material. Detailed structural knowledge is therefore a prerequisite for optimising material design.

Authenticity study of Phyllanthus species by NMR and FT-IR Techniques coupled with chemometric methods

The importance of medicinal plants and their use in industrial applications is increasing worldwide, especially in Brazil. Phyllanthus species, popularly known as quebra-pedras in Brazil, are used in folk medicine for treating urinary infections and renal calculus. This paper reports an authenticity study, based on herbal drugs from Phyllanthus species, involving commercial and authentic samples using spectroscopic techniques: FT-IR, ¹H HR-MAS NMR and ¹H NMR in solution, combined with chemometric analysis. The spectroscopic techniques evaluated, coupled with chemometric methods, have great potential in the investigation of complex matrices. Furthermore, several metabolites were identified by the NMR techniques.

Synthesis of novel O-acylated-D-ribono-1,5-lactones and structural assignment supported by conventional NOESY-NMR and x-ray analysis

A practical method for the structural assignment of 3,4-O-benzylidene-D-ribono-1,5-lactones and analogues using conventional NMR techniques and NOESY measurements in solution is described. 2-O-Acyl-3,4-O-benzylidene-D-ribono-1,5-lactones were prepared in good yields by acylation of Zinner’s lactone with acyl chlorides under mildly basic conditions. Structural determination of 2-O-(4-nitrobenzoyl)-3,4-O-benzylidene-D-ribono-1,5-lactone was achieved by single crystal x-ray diffraction, which supports the results based on spectroscopic data.

Synthesis and total H-1- and C-13-NMR assignment of cephem derivatives for use in ADEPT approaches

We report the synthesis and total NMR characterization of 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[[[(4''-nitrophenoxy)carbonyl]oxy]-methyl]-8-oxo-7[(2-thienyloxoacetyl)amino]-diphenylmethyl ester-5-dioxide (5), a new cephalosporin derivative. This compound can be used as the carrier of a wide range of drugs containing an amino group. The preparation of the intermediate product, 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[methyl-4-(6-methoxyquinolin-8-ylamino) pentylcarbamate]-8-oxo-7-[(2-thienyloxoacetyl)amino]-diphenylmethyl ester-5-dioxide (6), as well as the synthesis of the antimalarial primaquine prodrug 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[methyl-4-(6-methoxyquinolin-8-ylamino) pentylcarbamate]-8-oxo-7-[(2-thienyloxoacetyl)amino]-5-dioxide (7) are also described, together with their total H-1- and C-13-NMR assignments.

Resistively detected NMR of the nu=1 quantum Hall state: A tilted magnetic field study

Previous resistively detected NMR (RDNMR) studies on the nu approximate to 1 quantum Hall state have reported a ""dispersionlike"" line shape and extremely short nuclear-spin-lattice relaxation times, observations which have been attributed to the formation of a skyrme lattice. Here we examine the evolution of the RDNMR line shape and nuclear-spin relaxation for Zeeman: Coulomb energy ratios ranging from 0.012 to 0.036. According to theory, suppression of the skyrme crystal, along with the associated Goldstone mode nuclear-spin-relaxation mechanism, is expected at the upper end of this range. However, we find that the anomalous line shape persists at high Zeeman energy, and only a modest decrease in the RDNMR-detected nuclear-spin-relaxation rate is observed.