RESUMEN
Toroid detectors are resonators for high-pressure in situ NMR spectroscopy or one-dimensional rotating-frame imaging. One of their unique qualities is a mathematically well-defined nonuniform radiofrequency field confined to the inside of the detector. A single parameter (i.e., the torus factor) is sufficient to describe the relationship between this radiofrequency field and the radial distance from the center axis of the torus. Because accurate determination of the torus factor is essential to optimize toroid cavity NMR experiments or conduct toroid cavity imaging, a fast numerical algorithm for accurate, precise, and convenient determination of torus factors from pulse width-dependent signal intensities is introduced. In addition, the new algorithm provides for 99% confidence intervals around the refined torus factors. A computer program in which the optimization progress is visualized during the torus factor refinement is presented. Upon completion of the program, the best-fit simulated data and the residuals between best fit and experimental data are provided. Copyright 2000 Academic Press.
RESUMEN
A finite-difference approach has been developed for precisely determining diffusion coefficient and T(1) relaxation time in fluid samples analyzed by magnetization-grating rotating-frame imaging (MAGROFI) with either a surface coil or a toroid cavity detector (TCD). This approach avoids shortcomings of phenomenologically based approximations, such as neglect of sample geometries with singularities at the confines of the sample volume, and accounts for the diffusive edge enhancement observed in fluid imaging. Error limits are discussed. The new method has been applied to the determination of the self-diffusion coefficient for MAGROFI experiments using TCDs filled with acetone. Copyright 2000 Academic Press.
RESUMEN
A new "CO2-philic" chiral rhodium diphosphinite complex was synthesized and applied as catalyst precursor in the asymmetric hydrogenation of dimethyl itaconate in scCO2, scC2H6 and various liquid organic solvents. Deuterium labeling studies and parahydrogen-induced polarization (PHIP) NMR experiments were used to provide the first detailed mechanistic insight into the activation and transfer of the dihydrogen molecule during hydrogenation in scCO2. Chemical interactions between CO2 and reactive intermediates of the catalytic pathway could be excluded as possible explanations for the experimentally verified difference in the catalytic behavior in scCO2 and hexane.