Quartz Crystal Temperature Sensor for MAS NMR

Quartz crystal temperature sensors (QCTS) were tested for the first time as wireless thermometers in NMR MAS rotors utilizing the NMR RF technique itself for exiting and receiving electro-mechanical quartz resonances. This new tool in MAS NMR has a high sensitivity, linearity, and precision. When compared to the frequently used calibration of the variable temperature in the NMR system by a solid state NMR chemical shift thermometer (CST), such as lead nitrate, QCTS shows a number of advantages. It is an inert thermometer in close contact with solid samples operating parallel to the NMR experiment. QCTS can be manufactured for any frequency to be near a NMR frequency of interest (typically 1 to 2 MHz below or above). Due to the strong response of the crystal, signal detection is possible without changing the tuning of the MAS probe. The NMR signal is not influenced due to the relative sharp crystal resonance, restricted excitation by finite pulses, high probeQvalues, and commonly used audio filters. The quadratic dependence of the temperature increase on spinning speed is the same for the QCTS and for the CST lead nitrate and is discussed in terms of frictional heat in accordance with the literature about lead nitrate and with the results of a simple rotor speed jump experiment with differently radial located lead nitrate in the rotor.     

Selective free-radical dechlorination of 1,1-dichloro-2,2,2-trifluoroethyl difluoromethyl ether initiated thermally or by uv light: A practical and ‘green’ method for isoflurane synthesis

Treatment of 1,1-dichloro-2,2,2-trifluoroethyl difluoromethyl ether (3) with 2-propanol followed by either irradiation with UV light or heating with radical initiators gives the inhalational anesthetic isoflurane. Unlike most other common dechlorination methods, monoreduction is the exclusive process and the by-products acetone and HCl are relatively benign. Some comments about the mechanism of the reduction will be presented, along with solutions to problems encountered during scale-up.     

Selenium-Sulfur analogs. 6. Selenoisosteres of levamisole

A series of three new isosteres of levamisole was prepared by the substitution of the phenyl ring by the thienyl and selenienyl moieties and of the thiazole group by selenazole. The physiochemical properties and infrared spectra of the sulfur- and selenium-containing analogs were very similar. Differentiation was mostapparent in the nuclear magnetic resonance spectra where the α- and β-protons of the selenienyl compounds were shifted downfield relative to those of the corresponding thienyl compounds. With deuterated thiofluoroacetic acid as the solvent, a more rapid exchange was observed for the α-proton of the selenienyl ring of compounds 17 and 18 compared to that observed for compound 16 .     

Dynamics of probability distributions over classical fields

It is shown that the original Hopf formulation for the time evolution of probability distributions over classical fields follows deductively from the space-time version of the theory.This work was supported by a grant from the National Science Foundation.