Monday, August 18, 2008

Applied Magnetic Resonance - Vol 34, No 1 & 2

Preparation and NMR Characterization of Polyethyl-2-cyanoacrylate Nanocapsules
M. Bogdan, A. Nan, C. V. L. Pop, L. Barbu-Tudoran and I. Ardelean
The aim of this work was to prepare a nanocapsule by interfacial polymerization of ethyl-2-cyanoacrylate monomer in an oil-in-water emulsion. The chemical nature of the individual system components and the nanocapsule was investigated by high-resolution 1H and 13C nuclear magnetic resonance. The nanocapsule mean size and polydispersity were determined by photon correlation spectroscopy. The effect of different variables such as the organic solvent, oil concentration and stirring rate on the nanocapsule size was evaluated. The oil concentration was found to play a major role in controlling the size of the emulsified droplets.

Study of Thermal Mobility by Means of 1H NMR Magic-Angle Spinning Sideband Analysis
Ö. F. Erdem and D. Michel
1H nuclear magnetic resonance (NMR) magic-angle spinning (MAS) sideband patterns of molecules adsorbed in zeolites or related materials both depend on the MAS frequency and the thermal mobility. By using a statistical NMR line shape theory a valuable information on the thermal motion can be derived from the MAS sidebands. The conclusions are compared with the results of longitudinal proton spin relaxation studies at different temperatures and Larmor frequencies. The measurements are performed on samples of ethylene glycol molecules adsorbed in zeolites of the NaX and sodalite type which were prepared under well-defined conditions in vacuum. It is shown that the comparison of the respective results is very suitable for a deeper understanding of the dynamics of the adsorbed molecules.

1H NMR Relaxation Studies of Proton-Conducting Imidazolium Salts of Dicarboxylic Acids
A. Rachocki, K. Pogorzelec-Glaser and J. Tritt-Goc
The proton nuclear magnetic resonance spin–lattice relaxation time has been successfully used to evidence the reorientation of the imidazolium rings in carboxylic acid salts of imidazole: imidazolium oxalate, imidazolium adipate monohydrate and diimidazolium suberate. The process occurs in the temperature range between 325 K and the melting point of the salts (523, 379 and 360 K) and is described by a single activation energy of 20, 48 and 66 kJ/mol for imidazolium oxalate, imidazolium adipate monohydrate and diimidazolium suberate, respectively. The studied salts are considered as possible candidate materials for fuel-cell membranes.

Molecular Motion in the Biocopolymer Sequence of Glycolide and Lactide Studied by Solid-State NMRF. Nozirov, Z. Fojud, M. Jancelewicz, A. Nazirov and S. Jurga
This paper reports a nuclear magnetic resonance study of the molecular motion in copolymers derived from glycolide and L-lactide in the solid state. Variation of T 1 relaxation times with temperature reflects a local disorder and the fast segment conformational motions which can be quantified in terms of correlation times predicted by the Bloembergen–Purcell–Pound and Davidson–Cole models. At low temperatures, spin relaxation is dominated by the axial methyl rotation in lactide units described by an asymmetry parameter of the correlation time δ which takes a value of about 0.45 for all systems. Above the devitrification points the trans and gauche isomerization in glycolide segments occurs. In addition to the chemical structure characterization, solid-state magic-angle spinning spectroscopy gives an insight into the role of glycol segments in the chain mobility.

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