Elemental and structural analysis of silicon forms in herbal drugs using silicon-29 MAS NMR and WD-XRF spectroscopic methods.

The objective of this work was to study concentration of silicon and its structural forms present in herbal drugs. Equisetum arvense and Urtica dioica L. from teapot bags, dietary supplements (tablets and capsules) containing those herbs, dry extract obtained from a teapot bag of E. arvense, and samples of the latter herb harvested in wild habitat over four months were studied using wavelength dispersive X-ray spectroscopy (WD-XRF) and high-resolution solid-state (29)Si NMR. The highest concentration of Si, ca. 27mg/g, was found in the herbal material from the teapot bags containing E. arvense. The Si content in natural E. arvense (whole plants) increased from May to August by ca. 7mg/g, reaching value 26mg/g. Three different silicon forms were detected in the studied herbal samples: Si(OSi)4 (Q(4)), Si(OH)(OSi)3 (Q(3)) and Si(OH)2(OSi)2 (Q(2)). Those sites were populated in E. arvense in the following order: Q(4)≫Q(3)>Q(2). A dramatic, ca. 50-fold decrease of the Si concentration during the infusion process was observed. The infusion process and the subsequent drying procedure augmented population of the Q(4) sites at the cost of the Q(2) sites. The WD-XRF and (29)Si NMR methods occurred useful and complementary in the study of herbal materials.

2H-->1H cross-polarization in deuterated glycine.

1H spectral details and CP kinetics are discussed. We recommend perdeuterated polycrystalline glycine as a standard for setting 2H-->1H cross-polarization (CP), for 1H chemical shift referencing and for checking the setting of the magic angle and the shims.

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.

Two-dimensional J-resolved and SUPERCOSY NMR experiments in the solid state.

Two 2D experiments, novel to solid-state NMR, are demonstrated using the trimethylsilyl ester of cubic octameric silicate (Q8M8). J-Resolved 13C NMR with BLEW-12 proton homonuclear decoupling reveals the scalar 13C-1H couplings and 29Si SUPERCOSY the connectivities of silicon atoms in the distorted Q8 cube.

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 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.

Kinetics of 1H --> 31P cross-polarization in human trabecular bone.

Bloch-decay and cross-polarization (CP) 31P nuclear magnetic resonance (NMR) spectra of healthy human trabecular bone were acquired under magic-angle spinning (MAS) at 3 kHz. A single peak at 3.1 ppm was detected. Variable-contact time 1H --> 31P CP experiments revealed three signal components growing at various rates. The fast, moderate and slow components were assigned and assessed in P atom % to proton-rich (24%), hydroxyapatite (58%) and proton-deficient (18%) phosphate domains, respectively. Examination of CP kinetics is useful for the chemical characterization of bone tissue.

Kinetics of NMR cross-polarization from protons to phosphorus-31 in natural brushite.

Cross-polarization in natural brushite proceeds according to an isolated spin-pair kinetics.

1H MAS and 1H --> 31P CP/MAS NMR study of human bone mineral.

Chemical structure of human bone mineral was studied by solid-state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS). Trabecular and cortical bone samples from adult subjects were compared with mineral standards: hydroxyapatite (HA), hydrated and calcined, carbonatoapatite of type B with 9 wt% of CO3(2-) (CHA-B), brushite (BRU) and mixtures of HA with BRU. Proton spectra were acquired with excellent spectral resolution provided by ultra-high speed MAS at 40 kHz. 2D 1H-31P NMR heteronuclear correlation was achieved by cross-polarization (CP) under fast MAS at 12 kHz. 31P NMR was applied with CP from protons under slow MAS at 1 kHz. Appearance of 31P rotational sidebands together with their CP kinetics were analyzed. It was suggested that the sidebands of CP spectra are particularly suitable for monitoring the state of apatite crystal surfaces. The bone samples appeared to be deficient in structural hydroxyl groups analogous to those in HA. We found no direct evidence that the HPO4(2-) brushite-like ions are present in bone mineral. The latter problem is extensively discussed in the literature. The study proves there is a similarity between CHA-B and bone mineral expressed by their similar NMR behavior.

Solid-state NMR study of ordered mesoporous aluminosilicate MCM-41 synthesized on a liquid-crystal template.

A novel mesoporous aluminosilicate MCM-41, synthesized in a liquid-crystal system, was characterized by magic angle spinning NMR. Conventional Bloch decay and cross-polarization spectra were compared. The 27Al spectra showed that the calcined material was highly siliceous, while 29Si NMR proved that it was rich in single and geminal silanol groups. Two kinds of the silanol groups were detected: exchanging and non-exchanging protons with water on the timescale of the 1H experiment. The 13C spectra of the uncalcined material were consistent with the concept of the micellar arrangement of the cetyltrimethylammonium template inside MCM-41.

Proton magnetic resonance microimaging of human trabecular bone.

Proton magnetic resonance (1H magnetic resonance imaging (MRI)) images of human trabecular bone were acquired and discussed for two samples with different porosity. Three-dimensional 3D Spin Echo (3D SE) and Multi-Slice Multi-Echo (MSME) pulse sequences were examined. A very high slice resolution of (38 microm)2 was achieved (MSME). The intensity histograms were found useful for the characterization of the bone porosity. A spatial distribution of the spin-spin relaxation time T2 was monitored with the MSME pulse program. The work demonstrates the great potential of the proton MRI technique in the study of the trabecular bone morphology.