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Boris G Shpeizer

Publications and source records attributed to Boris G Shpeizer.

4 recordsLinked to original sources
PubMed2007

Structure of a paramagnetic supermicroporous silica-based material via a multinuclear solid-state NMR monitoring.

The paramagnetic Si/Al material doped with 19.8% (weight) of Mn2+ has been characterized by the 1H, 13C, 27Al, 29Si MAS NMR spectra and the 1H, 29Si T1MAS relaxation measurements as a gel dried at 130 degrees C and as samples calcined at 504, 540 and 650 degrees C. It has been demonstrated that in spite of strong paramagnetic effects, NMR monitoring in combination with 29Si T1 relaxation experiments can be successful for structural descriptions of porous materials.

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PubMed2006

Solid-state NMR spectra of paramagnetic silica-based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions.

Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the 29Si and 27Al nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies.

Journal Article↗
PubMed2006

29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations.

The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1-6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2-4 with relatively small Mn2+ contents. Because the relaxation curves for 1-6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn2+ concentrations in terms of incorporation of the Mn2+ ions into the silica lattice when their concentration is small (<or=2.5 wt%). At higher concentrations, most of the manganese is located on the surface of the silica.

Journal Article↗