Spectrometer multinuclear

With the advent of FT NMR and subsequently multinuclear spectrometers broadband proton decoupling has become widespread and is usually accompanied by a NOE which is often substantial [equation (16)] and can provide a useful gain in sensitivity. However, the dependence upon the competition between dipole-dipole and other relaxation mechanisms means that the NOE can vary from one site to another which militates against reliable intensity measurements. In these circumstances it is desirable to be able to quench the NOE, and this may also be necessary for nuclei with a negative magnetogyric ratio for which a really unfortunate combination of relaxation times can lead to zero signal intensity. 

Using Li NMR, it is possible to differentiate between atoms or ions that are within the cell and those that are free in the extracellular bathing fluid.We have recorded 31 MHz Li NMR spectra, using a Bruker WP80SY multinuclear spectrometer. Cells were incubated in phosphate-buffered saline containing 20% deuterium oxide (as heteronuclear lock) and up to 5 mmol 1 dysprosium tripolyphosphate (shift reagent). 

With the power and range of modern pulse spectrometers the compass of NMR spectroscopy is now very large for a single book—but we have undertaken this. Our book covers the Periodic Table as multinuclear spectrometers do, and introductory chapters are devoted to the essentials of the NMR experiment and its products. Primary products are chemical shifts (including anisotropies), spin-spin coupling constants, and relaxation times the ultimate product is a knowledge of content and constitution, dynamic as well as static. 

Fig. 6 Double air bearing, magic-angle spinning, multinuclear probe for use in a Bruker AM-250 NMR spectrometer. For illustrative purposes, the capped rotor has only been half inserted into the stator, which is positioned at the magic angle.

A NMR spectrometer with the following capabilities (a) multinuclear observe frequencies, (b) proton decoupling, and (c) variable temperature... 

The great recent development in electrochemical techniques will certainly be helpful for the study of redox processes of a metal which can occur in so many oxidation states. Multinuclear NMR spectrometers will allow increased use of 51V resonance as a routine method for the characterization of complexes in solution. Other recent developments are the study of polynuclear complexes, metal clusters (homo and hetero-nuclear) and mixed valence complexes, and it can be anticipated that these topics will soon become important areas of vanadium coordination chemistry, although the isolation of compounds with such complex... 

The early NMR studies of molecules sorbed on zeolites used H and 19F resonances. Truly multinuclear work involving 13C, 1SN, and 129Xe in particular began in the early 1970s with the advent of modern Fourier transform spectrometers. 

The 27A1 nutation spectra were measured at 104.26 MHz using a Bruker MSL-400 multinuclear NMR spectrometer with a high-power static probe-head and a 5 mm diameter horizontal solenoidal coil. Using an aluminium nitrate solution the amplitude of the rf pulse (corf/27c) was adjusted and kept at a constant value of 70 5 kHz unless otherwise stated. Nutation experiments were performed on the same amount of each sample and the same number of transients was accumulated for samples in the same series. The rf pulse length was increased in ln.s increments from 2 M-s to 65 is. The spectral width was 125 kHz, the recycle delay 0.2 s and the number of transients accumulated in each measurement was between 2000 to 4000. 

Acquisition. Processing and Simulation of Sodium-23 NMR Spectra. Sodium-23 MASNMR spectra were obtained on 6.3, 8.45, and 11.7 Tesla multinuclear solids NMR spectrometers at Spectral Data Services and the University of Illinois in Champaign, Illinois. 

Most NMR spectrometers have 12 to 18 shim controls (Churmny and Hoult 1990). Each user will adopt their own procedure but the aim is to produce the minimum linewidth consistent with a good lineshape. In practice, some shims are much more significant than others and for particular probes different shims will be important. For solid-state operation, shimming usually needs to be carried out relatively infrequently. One possible procedure for probes tuned to H is to crudely shim on H2O. If there is no proton channel most multinuclear probes will tune to D, so D2O can be used. For CP-MAS probes that tune to - C, adamantane is a useful compound which should be shimmed under spinning and H decoupling conditions. A typical resolution for in admantane of 3-4 Hz at 7.05 T and 10 Hz at 11.7 T should be achieveable. 

The spectrometer used to perform the preliminary SINNMR experiments was a JEOL FX-90Q multinuclear iron-core magnet NMR spectrometer. Although equipped with a variable temperature system to enable the probe temperature to be... 

These early measurements stimulated my interest in NMR spectroscopy, and, on moving to the University of Kent at Canterbury (1972), we were lucky to be able to buy the first Fourier Transform NMR spectrometer in the UK. This instrument was still based on an electromagnet ( H, 100 MHz) but allowed faster acquisition of NMR spectra and enabled the development of multinuclear NMR spectroscopy. This permitted me to start collaborating with Paolo Chini who had taken up an appointment at the University of Milan where he was developing metal carbonyl cluster chemistry. In Milan, Chini had access only to an IR spectrometer that aided the clean preparation and subsequent crystallisation of clusters, and, importantly, an X-ray diffractometer for their structural characterisation. 

The application of Magnetic Resonance Imaging (MRI) in these studies provides the additional advantage that characterization can be carried out in a non-invasive manner. This is also illustrated in Figure 1. After impregnation, the extrudate is simply placed into the RF-coil of the spectrometer. A multinuclear MRI technique allows for the detection of the H, C, and Pt... 

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