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M Kempka

Publications and source records attributed to M Kempka.

7 recordsLinked to original sources
PubMed1999

Molecular dynamics in solid anhydrous beta-estradiol studied by 1H NMR.

Proton second moment and spin-lattice relaxation times T1 and T1p in solid anhydrous beta-estradiol are measured as a function of temperature. The results show that the C3 reorientation of the single methyl group provides the mechanism dominating relaxation at low temperatures and reveal the existence of a conformational motion of the carbon skeleton dominating relaxation at high temperatures. The activation energies of the respective motions are found to be 9.3 and 37.3 kJ/mol.

Estradiol↗
PubMed1998

Transverse gradient coil with circle current paths.

The paper describes a new type of transverse magnetic field gradient coil for applications in MRI and MRS. It uses full circle current paths rather than current arcs and has a particularly simple unit construction of symmetric form. It features a large volume of uniform transverse field gradient, high efficiency and low inductance for rapid switching. A prototype coil has been constructed and evaluated to check computer simulations. Two smaller sets have subsequently been made for NMR microscopy. This coil design may be used for all sizes.

Calibration↗
PubMed1998

Molecular dynamics in solid L-adrenaline by proton NMR.

Proton NMR measurements of the spectrum, second moment, spin-lattice relaxation time T1 and dipolar relaxation time T1D were carried out on polycrystalline L-adrenaline at 14 and 25 MHz between 55 and 400 K. Between 70 K and 250 K relaxation is dominated by C3 reorientation of the single methyl group in each molecule, characterized by an activation energy 8.3+/-0.3 kJ/mole. Below 70 K tunnelling assisted relaxation is significant, characterized by an excitation energy of 1.9+/-0.2 kJ/mole. Above 250 K an additional molecular motion becomes significant, with activation energy above 28 kJ/mole, attributed to conformational motion of the methylene group in the ethylamine side chain.

Epinephrine↗
PubMed1996

Magnetic field gradient system for nuclear magnetic resonance microimaging.

In this study we present an orthogonal magnetic field gradient system for nuclear magnetic resonance (NMR) microimaging applications. The construction details are given for a prototype assembly for proton microscopy inside a 50-mm vertical bore magnet, which is designed to fit into a commercial 300-MHz NMR probe. This system has been used to acquire images of the human spinal cord in vitro. Its performance has been evaluated and compared to that predicted by computer simulation.

Humans↗
PubMed1995

Molecular motions in solid estradiol studied by nuclear magnetic resonance spectroscopy.

The temperature dependence of the proton nuclear magnetic resonance (NMR) relaxation time T1 and second moment M2 of polycrystalline beta-estradiol hemihydrate (1,3,5-estratriene-3,17 beta-diol) is measured at frequencies of 14 and 25 MHz. Below 260 K relaxation is found to be dominated by C3 reorientation of the single methyl group in each molecule, characterized by an activation energy of 9.4 +/- 0.1 kJ/mol. Above 260 K another relaxation mechanism becomes evident, characterized by an activation energy of 22 +/- 2 kJ/mol and ascribed to motion of the water molecules in the solid.

Chemical Phenomena↗
PubMed1993

Proton NMR study of molecular motion in solid cortisone.

Polycrystalline cortisone (17,21-dihydroxy-4-pregnene-3,11,20-trione, C21H28O5) has been investigated by proton NMR methods between 56 and 400 K at 14 and 25 MHz. Reductions in second moment and two very well-resolved minima in the spin-lattice relaxation time at both frequencies are attributed to reorientation of the two methyl groups on carbons 18 and 19. The data are very well fitted over the entire temperature range to the Kubo-Tomita dipolar relaxation theory using the same parameters at both frequencies. Activation energies Ea characterizing the hindrances to the two methyl reorientations were 5.9 and 15.5 kJ/mol, an unusually large difference. The relaxation constants were 6.4 and 7.9 x 10(8) s-2.

Cortisone↗