N. Piślewski

Molecular structure of bituminous coal studied with pulse nuclear magnetic resonance

Abstract High-volatile bituminous coal and coal saturated with fully deuterated solvents, were studied using the 1 H n.m.r. pulse technique. Free-induction decay (FID) signals were separated into Gaussian and Lorentzian components and contents of immobile and mobile phases of coal matter were calculated. Spin-spin relaxation times, T 2 , for both phases were determined. Some solvents caused a significant decrease in the content of the coal immobile phase. It is concluded that the immobile phase of coal consists of macromolecules and molecules. The latter are attached to macromolecules by electrondonor-acceptor interactions which can be destroyed by some solvents. The contents of macromolecules (60 wt%) and molecules (40 wt%) in the coal were determined.

Magnetic resonance imaging study of the swelling kinetics of hydroxypropylmethylcellulose (HPMC) in water.

Magnetic resonance imaging has been used to monitor the hydration of hydroxypropylmethylcellulose samples by two-dimensional mapping of properties such as spin density and relaxation times. The measurements were performed at two pH values of water: 2 and 6 and two temperatures 25 and 37 degrees C. It is shown that transport behavior of water into HPMC changes from being almost completely relaxation controlled (case II) at pH=2 to Fickian behavior for pH=6. It was also observed that radial swelling is larger for the system composed of HPMC and water at pH=6 than at pH=2.

An NMR relaxation study on the hydrogen dynamics in malonic acid

Abstract We have studied the temperature and angular dependences of the spin—lattice relaxation time T 1 in malonic acid. The results suggest that the hydrogen bonded protons of the cyclic dimers undergo fast simultaneous jumps between the two minima of asymmetric double well potential.

NMR chemical shift and asymmetric dipolar tensors of water protons in sodium nitroprusside (SNP)

Abstract NMR spectra of the protons in single crystals of Na 2 Fe(CN) 5 NO·2H 2 O (SNP) were measured by FT NMR techniques between 200 and 350 K. The dipolar coupling tensors of the water protons in SNP, their asymmetry parameters and the orientations of the dipole—dipole (DD) tensors relative to the crystal axes were obtained at 200, 290, 305, 315 and 340 K. The proton—proton distance r HH and the angle HOH of the water molecules in SNP were found to be 1.53 A and 106.5°, respectively. All 1 H DD tensors are not axially symmetric. These results are interpreted in terms of librational motions of the H 2 O molecules in SNP in addition to the well-established flips. At 290 K the proton shielding tensor of the water molecules in SNP has been extracted directly from wide line spectra.

MRI study of Fickian, case II and anomalous diffusion of solvents into hydroxypropylmethylcellulose

Magnetic resonance imaging was used to investigate the diffusion and swelling processes of a hydroxypropylmethylcellulose (HPMC) matrix. Polymer in the form of a cylinder was hydrated in a water solvent with pH 2, 7, and 12 at 37 °C and monitored at equal intervals on a Bruker Avance 300 MHz spectrometer. The spatially resolved spin-spin relaxation times and spin densities together with the change in the dimension of the glass core of the polymer were determined for the HPMC tablets as a function of hydration times. FromT2 parameters, the solvent molecule mobility within the gel layer of the HPMC was estimated. All studied parameters allow the determination of the diffusion of the solvent into the HPMC matrix as Fickian diffusion for alkaline solvents, case II for acidic solvent, and anomalous diffusion for neutral solvent.

1H n.m.r. spin—lattice relaxation study in bituminous coal

Abstract 1 H n.m.r. studies of spin-lattice relaxation of a bituminous coal were performed at temperatures between 128 and 308 K. The relaxation function was observed to be two-component over the whole temperature range. The component with the shorter relaxation time was assumed to be the molecular phase in coal and the component with the longer relaxation time to be the macromolecular phase. Mechanisms of spin-lattice relaxation through spin diffusion to paramagnetic centres and through modulation of dipolar interactions by molecular motions are suggested.

Spin-lattice relaxation study of the methyl proton dynamics in solid 9,10-dimethyltriptycene (DMT)

Proton spin-lattice relaxation studies are performed for powder samples of 9,10-dimethyltriptycene (DMT) and its isotopomer DMT-d(12) in which all the non-methyl protons in the molecule are replaced by deuterons. The relaxation data are interpreted in terms of the conventional relaxation theory based on the random jump model in which the Pauli correlations between the relevant spin and torsional states are discarded. The Arrhenius activation energies, obtained from the relaxation data, 25.3 and 24.8 kJ mol(-1) for DMT and DMT-d(12), respectively, are very high as for the methyl groups. The validity of the jump model in the present case is considered from the perspective of Haupt theory in which the Pauli principle is explicitly invoked. To this purpose, the dynamic quantities entering the Haupt model are reinterpreted in the spirit of the damped quantum rotation (DQR) approach introduced recently for the purpose of NMR lineshape studies of hindered molecular rotators. Theoretical modelling of the relevant methyl group dynamics, based on the DQR theory, was performed. From these calculations it is inferred that direct assessments of the torsional barrier heights, based on the Arrhenius activation energies extracted from relaxation data, should be treated with caution.

The crystal structure and evidence of the phase transition in D-amphetamine sulfate, as studied by X-ray crystallography, DSC and NMR spectroscopy

X-Ray crystallography, DSC and NMR spectroscopy methods have been used to study the phase transition of D-amphetamine sulfate. The phase transition temperature occurs at about 325 K, and belongs to the discontinuous type with a large temperature hysteresis. A change in the space group is observed from monoclinic P21 in the low temperature phase to monoclinic C2 in the high temperature phase. The transformation from phase I to phase II is a result of the ordering of the SO42−groups, allowing a T-shape interaction between D-amphetamine molecules. Proton relaxation rate data obtained for the studied compound have been analysed by assuming two dynamically-inequivalent methyl groups below the phase transition and only one type of ammonium group above the phase transition. The activation energies for the C3 reorientation of the methyl groups have been determined to be 7.31 and 11.89 kJ mol−1, whereas for the ammonium group it is 27.29 kJ mol−1.

Molecular motions and phase transitions in solid bis-n-propylammonium pentabromoantimonate

The proton nuclear magnetic resonance (NMR) second moment and spin-lattice relaxation time for polycrystalline bis-n-propylammonium pentabromoantimonate (nPBA) have been measured from 70 to 290 K. The results are interpreted in terms of the CH3 and NH3 group reorientations for which the activation parameters have been determined. A structural phase transition evidenced at about 220 K is found in the polycrystalline sample of nPBA.

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.