Experimental determination of pore shape and size using q-space NMR microscopy in the long diffusion-time limit

The signal obtained with q-space NMR imaging applied to a confined liquid is directly related to the pore shape in the limit where all molecules have sampled the whole pore. We investigate the diffusion of water across a approximately 50 microm thick film formed between planes of glass. The diffusion time t is changed almost three orders of magnitude. For short t, the root-mean-square displacement increases with a rate which is slightly less than for freely diffusing water. At t longer than 0.3 s, the displacement is constant at 24 microm which implies that the water is confined in the measuring direction defined by the applied gradient pulses. Perfectly smooth and aligned planes give rise to sharp diffraction-like features on the echo attenuation curve, i.e., NMR signal vs. the reciprocal space vector q. The experimental data with rather smooth local minima and maxima can be explained in terms of either surface roughness or a misalignment of the planes. We discuss the averaging effect of diffusion along a laterally inhomogeneous film and propose two model-free methods to determine the pore shape from the echo attenuation curve obtained in the long-t limit.     

Uniqueness of infinite rigid components in percolation models: the case of nonplanar lattices

We prove uniqueness of the infinite rigid component for standard bond percolation on periodic lattices in d-dimensional Euclidean space for arbitrary d, and more generally when the lattice is a quasi-transitive and amenable graph. Our approach to uniqueness of the infinite rigid component improves earlier ones, that were confined to planar settings.Research supported by the Swedish Research Council Mathematics Subject Classification (2000): 60K35, 82B43     

Fast enantioselective separation of clevidipine and a dihydropyridine substituted acid by SFC on Chiralpak AD

Conditions for the fast separation of the enantiomers of a dihydropyridine substituted acid on a 50 x 4.6 mm ID short Chiralpak AD column with 2-propanol modified carbon dioxide as the mobile phase are presented. A high throughout of samples can be accomplished through the continuous sample loading of the loop of the injector. If a continuous data collection was used 10 separations could be performed in about 5 min with a precision of 0.6% RSD for the area ratio (n = 10). The parent drug clevidipine can also be analyzed and its enantiomeric composition determined after alkaline hydrolysis into its acid, either through hydrolysis followed by extraction to dichloromethane or by direct analysis of the hydrolysis media. About 1 min is required for each run. Using 0.1 M of methanolic sodium hydroxide 2 min are sufficient for the hydrolysis, and, including weighing, only 5 min are required to analyze clevidipine.     

Aspects of the preparation of cyclohexenyl- and menthenylthioenynes via ring-opening of thiophenes

Treatment of 2,5-dimethyl-3-(1-menthenyl)4-bromothiophene (IIIa) and 2,5-dimethyl-3-(1-cyclohexenyl)4-bromothiophene (IIIb) with butyllithium gave the thiodienynes Va and Vb, respectively, via ring-opening of the corresponding 3-lithio derivatives. 2,5-Dimethyl-3-(1-menthenyl)-4-bromothiophene 1,1-dioxide (IV) gave the sulfone VI under similar conditions. The uv spectra of IIIa-b, IV, Va-b and some related compounds have been recorded and compared. The rotational barrier of compound VI was determined.     

Phosgene as a derivatizing reagent prior to gas and liquid chromatography

The use of phosgene as a derivatizing agent for bifunctional compounds prior to gas and liquid chromatographic analysis is reviewed. Applications include gas chromatographic determinations of metoprolol and its metabolites in biological fluids, enantiomeric separations of beta-blocking drugs and sympathomimetic agents on a chiral stationary phase and liquid chromatographic enantiomer separations.     

Synthesis of a regioregular zwitterionic conjugated oligoelectrolyte, usable as an optical probe for detection of amyloid fibril formation at acidic pH

Changes of the optical properties of conjugated polyelectrolytes have been utilized to monitor noncovalent interactions between biomolecules and the conjugated polyelectrolytes in sensor applications. A regioregular, zwitterionic conjugated oligoelectrolyte was synthesized in order to create a probe with a defined set of optical properties and hereby facilitate interpretation of biomolecule-oligoelectrolyte interactions. The synthesized oligoelectrolyte was used at acidic pH as a novel optical probe to detect amyloid fibril formation of bovine insulin and chicken lysozyme. Interaction of the probe with formed amyloid fibrils results in changes of the geometry and the electronic structure of the oligoelectrolyte chains, which were monitored with absorption and emission spectroscopy.