31P solid-state NMR study of spin diffusion in the molecular sieve VPI-5 using variable-speed MAS

Near-Infrared (NIR) Spectroscopy of Synthetic Hydroxyapatites and Human Dental Tissues

Near-infrared spectroscopy (NIR) was used to analyze synthetic hydroxyapatite calcined at various temperatures, synthetic carbonated hydroxyapatite, and human hard dental tissues (enamel and dentin). The NIR bands of those materials in the combination, first-overtone, and second-overtone spectral regions were assigned and evaluated for structural characterization. They were attributed to adsorbed and structural water, structural hydroxyl (OH) groups and surface P-OH groups. The NIR spectral features were quantitatively discussed in view of proton solid-state magic-angle spinning nuclear magnetic resonance ((1)H MAS NMR) results. We conclude that the NIR spectra of apatites are useful in the structural characterization of synthetic and biogenic apatites.

A solid-state NMR study of the molecular sieve VPI-5 synthesized in the presence of a CTABr surfactant

Silicon-free and silicon-rich large-pore aluminophosphate VPI-5, synthesized with various contents of AIPO-H3 impurity, was studied by Bloch decay (BD) and cross polarization (CP) NMR under magic angle spinning (MAS). The 1H-->31P CP peaks were considerably stronger from AIPO-H3 than from VPI-5. A detailed examination of the CP kinetics and a careful comparison of the CP and BD spectra are prerequisites for the unequivocal interpretation of 1H-->31P CP in porous aluminophosphates.

Proton spin diffusion for spatial heterogeneity and morphology investigations of polymers

The diffusion of Zeeman spin order in the laboratory frame for a system with microscopic spatial heterogeneity, due to either molecular mobility or chemical heterogeneity, has been analysed by solving the diffusion equation in the limit of two different models. By simulation of proton spin diffusion nuclear magnetic resonance (NMR) spectral areas for poly(ethylene oxide) we have demonstrated, for both models, the sensitivity of these observables to phase domain size and to the dimensionality of the diffusion process. The possibility to obtain information about the morphology is analysed. Results from calculations based on the two models are compared with experimental spin diffusion results from 1H NMR spectra of poly(ethylene oxide). Two methods for filtering the z-magnetization from the different phase domains in a solid are discussed. The efficiency of a magnetization dipolar filter based on magic and polarization echoes is presented.

27Al-->1H cross-polarization in aluminosilicates

Solid-state nuclear magnetic resonance (NMR) cross-polarization (CP) from 27Al to 1H was set on kaolinite, verified by a variable-contact time experiment and applied to ultrastable zeolite Y. The technique is useful for the selective NMR observation of AlOH sites in aluminosilicates, especially those from extraframework species in zeolites.

Solid-state NMR study of ultrastable zeolite Y modified with orthophosphoric acid

29Si, 27Al and 31P solid-state NMR under magic-angle spinning was used for the study of ultrastable zeolite Y modified with H3PO4. The material is a potential candidate for a new generation of oil-cracking catalysts. Bloch decay and cross-polarization spectra were compared. It was found that amorphous aluminium phosphate is formed during the P-impregnation and the following activation, and that it occupies the zeolite surface and internal voids. For a high P-content under steaming conditions, aluminium phosphate is converted into a crystalline form. No evidence has been found for incorporation of P atoms into the zeolite framework.

A method for detection of spectral spin diffusion from minor peaks, and its application to 19F MAS NMR of antimony(III)-doped fluorapatite

A new technique for detecting spectral spin diffusion in solids under MAS NMR conditions that is particularly well suited for accurately measuring cross-relaxation from minor spectral components is presented. The pulse sequence, SINK (Saturation Inter-Nuclear Kinetics), selectively saturates the magnetization of a minor spectral component with a series of rotor-synchronized DANTE pulse trains and monitors spin diffusion to other peaks with a non-selective 90 degrees pulse. We have used SINK with 19F MAS NMR on samples of calcium fluorapatite doped with Sb3+ to measure spin diffusion between a weak peak at 68.6 ppm due to fluoride ions associated with Sb3+ and other peaks in the spectrum. The SINK experiment clearly demonstrates that spin diffusion from the former peak to the main resonance of fluorapatite at 64.0 ppm is faster than spin diffusion to a second antimony-related peak at 65.6 ppm. These results strengthen our previous conclusion that antimony(III) occupies a phosphate site in the apatite lattice, with an SbO3(3-) group replacing a PO4(3-) group. The SINK experiment also enables the detection of a "hidden" peak at approximately 62.9 ppm that is otherwise obscured by the intense main peak at 64.0 ppm.