Ernesto MacNamara

Multiplex sample NMR: an approach to high-throughput NMR using a parallel coil probe

A new parallel coil NMR probe is described which can detect simultaneously the signals arising from four individual samples. The signals are differentiated using field gradients and analyzed in software yielding either a table of peaks assigned to each sample or individual spectra. When suitably developed, this method should be useful for increasing the throughput of NMR measurements, an important issue in applications such as process monitoring or the screening of large molecular libraries using NMR detection.

NMR analysis of multiple samples using parallel coils: improved performance using reference deconvolution and multidimensional methods

Improvements in the Multiplex Sample NMR method are investigated to explore its capabilities of analyzing multiple samples simultaneously. Issues of quantitation and resolution in the multiple-coil probe are examined in one- and two-dimensional experiments. Improvements in quantitation are shown to result from the use of reference deconvolution for one-dimensional experiments, while the use of two-dimensional methods has much improved resolution and shows the potential for significantly increased parallelism. A multiplicative scheme is shown to be an easily implemented, effective method for generating individual sub-spectra from individual samples.

A versatile computer-controlled pulsed nuclear quadrupole resonance spectrometer

A new, pulsed nuclear quadrupole resonance (NQR) spectrometer capable of performing a variety of pulsed and swept experiments is described. The spectrometer features phase locked, superheterodyne detection using a commercial spectrum analyzer and a fully automatic, computer-controlled tuning and matching network. The tuning and matching network employs stepper motors which turn high power air gap capacitors in a “moving grid” optimization strategy to minimize the reflected power from a directional coupler. In the duplexer circuit, digitally controlled relays are used to switch different lengths of coax cable appropriate for the different radio frequencies. A home-built pulse programmer card controls the timing of radio frequency pulses sent to the probe, while data acquisition and control software is written in Microsoft Quick Basic. Spin-echo acquisition experiments are typically used to acquire the data, although a variety of pulse sequences can be employed. Scan times range from one to several hours de...

Cross-relaxation dynamics between laser-polarized xenon and a surface species using a simple three-spin model

Abstract We present an analysis of the cross-relaxation dynamics between optically polarized 129 Xe and surface 13 C and 1 H spins in methanol adsorbed on a SiO 2 surface. Analytical expressions for the 13 C polarization are derived, which show that the 13 C polarization is determined by cross-relaxation with both 129 Xe and 1 H spins. The 1 H spins act as a polarization sink; however, saturation of the protons results in a further increase in signal intensity. Replacing the 1 H spin reservoir with 2 H increases the 13 C signal by a factor of 12 (25 as compared to room-temperature data). Further improvements are anticipated using higher-powered lasers.