H. Grondey

Dipolar dephasing between quadrupolar and spin-12 nuclei. REDOR and TEDOR NMR experiments on VPI-5

Abstract In this work we examine the use of dipolar-dephasing magic-angle spinning NMR to study mixed pairs of quadrupolar and spin- 1 2 nuclei in solids. Dipolar connectivities are examined in both directions between the 27 Al ( I =5/2) spins in the very large pore aluminophosphate VPI-5, which is considered representative of a range of inorganic framework materials. Rotational-echo double-resonance (REDOR) and transferred-echo double-resonance (TEDOR) experiments are demonstrated, as well as a two-dimensional extension of the TEDOR experiment. These experiments restore the heteronuclear dipolar coupling under MAS conditions via a train of radiofrequency pulses, thereby providing information about connectivities and distances between coupled nuclei in these inorganic solids.

1D and 2D solid state NMR investigations of the framework structure of As-synthesized AlPO4-14

The framework structure of As-synthesized AlPO4-14 has been investigated with a combination of different one-dimensional 27Al and 31P solid state NMR techniques and 27Al/31P double resonance methods. The results are found to be fully consistent with the assumed structural model. 27Al MAS and DOR experiments at three different magnetic field strengths together with simulations show the presence of two tetrahedral sites, one pentacoordinated and one octahedral aluminum site. The 27Al quadrupolar coupling constants and the 31P isotropic chemical shifts of the tetrahedral sites correlate well with tetrahedral shear-strain parameters and mean P-O-Al bond angles, respectively. These correlations allow one to assign all of the NMR resonances to specific T-sites in the proposed framework structure. The assignments are then further confirmed by the application of three different two-dimensional heteronuclear correlation methods (i.e., 27Al-->31P TEDOR, CP, and INEPT) which reveal the connectivities between AlOx and PO4 polyhedra. The two-dimensional INEPT experiment is applied here for the first time in the solid state.

NMR imaging investigations of drug delivery devices using a flow-through USP dissolution apparatus

A system for performing NMR imaging experiments on drug delivery devices within a flow-through dissolution apparatus, USP Apparatus 4, has been developed. The system was used to image the physical changes that occur in solid dosage forms during dissolution in the flow-through apparatus. Simultaneous cumulative drug release measurements were also made. The NMR images obtained under these conditions and the drug release data provide a better understanding of the processes involved in the release of drugs from drug delivery systems based on diffusion, dissolution and osmosis mechanisms.

Use of NMR imaging in the optimization of a compression-coated regulated release system

Nuclear magnetic resonance (NMR) imaging is routinely used to detect the protons of mobile water molecules within samples. In this investigation, this non-destructive, non-invasive technique was used to determine the cause for faster than predicted drug release from a dissolution-based regulated-release tablet. The NMR images of tablets, from two different formulations, taken at various intervals of time while immersed in static USP dissolution medium showed that the tablet with faster than predicted drug release had a porous coating. The porous coat exposed more of the core surface area to the dissolution medium than desired and this caused an increase in the rate of dissolution of the core. The data presented in this paper demonstrate the usefulness of NMR imaging in solid dosage form development.

Evaluation of chemical shift—structure correlations from a combination of X-ray diffraction and 2D MAS NMR data for highly siliceous zeolite frameworks

Abstract 29Si MAS NMR chemical shift data and the corresponding T-site assignments from two-dimensional INADEQUATE experiments have been correlated with various structural parameters from five high quality sets of X-ray diffraction data on highly siliceous zeolites. Good correlations with a variety of structure related functions were obtained for the best data sets on single crystals of ZSM-5. Inaccuracies in atomic positional parameters derived from diffraction data are identified as the limiting feature in such correlations.

Investigation of the three-dimensional SiOSi connectivities in the monoclinic form of zeolite ZSM-5 by two-dimensional 29Si INADEQUATE experiments

Abstract Two-dimensional 29 Si MAS NMR INADEQUATE experiments have been used to investigate the three-dimensional silicon bonding network in the monoclinic form of zeolite ZSM-5. Thirty-eight of the expected forty-eight SiOSi connectivities are clearly observed, giving rise to two possible assignments of the 29 Si MAS NMR spectrum, reflecting the unit cell symmetry. An unambiguous choice of the correct assignment is made by correlation of the 29 Si chemical shifts with local geometric parameters from X-ray diffraction data.

Pulsed field gradient multiple-quantum MAS NMR spectroscopy of half-integer spin quadrupolar nuclei

Abstract Pulsed field gradients (PFGs) have been applied to select coherence transfer pathways in multiple-quantum (MQ) MAS NMR spectra of half-integer spin quadrupolar nuclei in rigid solids. 27 Al triple-quantum (3Q) MAS NMR spectra of the aluminophosphate molecular sieves VPI-5 and AlPO 4 -18 have been used to demonstrate the selection of the (0)→(3)→(−1) coherence transfer pathway using PFGs and no phase cycling. Compared to MQMAS experiments that employ phase cycling schemes, the main advantage of the PFG-MQMAS technique is its simplicity, which should facilitate the combination of MQMAS with other pulse sequences.

Two-dimensional 29Si MAS n.m.r. investigation of the three-dimensional structure of zeolite DD3R

The three-dimensional connectivities in the (solid-state) structure of zeolite DD3R have been investigated by two-dimensional29SiMAS n.m.r. techniques. 2D COSY experiments on an 85%29Si-enriched sample are in agreement with the expected connectivities using a partial assignment of the resonances based on their relative intensities. In addition, the results indicate that the structure is of lower symmetry than expected as there are two T1 environments. 2D INADEQUATE experiments confirm these results, including the lower symmetry of the structure, and, in this case, all of the expected connectivities are observed. A high-temperature INADEQUATE experiment shows that the symmetry of the structure increases to that expected from the previous single crystal X-ray diffraction experiment on the as-synthesized material.

The structure of zeolite ZSM-23 (MTT) refined from synchrotron X-ray powder data

The structure of zeolite ZSM-23 (structure-type code MTT) loaded with NH 4 F [a o =11.129 (1), b o =5.025 (1) and c o =21.519 (1) A and β=89.85 (4) o ] was refined from high-resolution synchrotron X-ray powder data. The Rietveld refinement converged in space group P12 1 1 (No. 4) to R F =0.090 and R wp =0.085, confirming the proposed model of the silicate framework. The use of complementary methods (synchrotron X-ray powder diffraction, 29 Si magic-angle-spinning nuclear-magnetic-resonance spectroscopy, and distance and angle least-squares refinements) was essential for the determination of the true space-group symmetry, a prerequisite for the successful Rietveld structure refinement

Magnetic Resonance Imaging Evaluation of Photodynamic Therapy‐Induced Hemorrhagic Necrosis in the Murine M1 Tumor Model

Abstract— Proton magnetic resonance imaging (MRI) and histological methods were used to evaluate photodynamic therapy (PDT)‐induced hemorrhagic necrosis in the murine Ml tumor within 72 h of treatment of male DBA/2 mice. The effects of three photosensitizing drugs were investigated: Photofrin (n = 4), Zn (II) phthalocyanine (n = 7) and benzoporphyrin derivative monoacid ring A (n = 11). As noted in previous studies of PDT using MRI, MRI makes possible serial, noninvasive, in vivo observation of tissue response to PDT. Our serial study of MRI and histological data confirms that tumors responded in the same way to PDT treatment using the three photosensitizing drugs: vascular damage followed by hemorrhagic necrosis. Most importantly and unlike previous MRI studies of PDT, we used a very high field magnet that enhanced the effect of magnetic susceptibility on image signal when blood is processed by the body after PDT‐induced hemorrhagic necrosis. This last finding demonstrates the utility of high field magnets and the importance of localized, serial experiments in future magnetic resonance studies of PDT.