Probe for NMR

This revolutionary technology uses a cryogenically cooled NMR probe for NMR detection, in which the NMR coil assembly and the... 

Figure 2.9 Left Overall view of a high pressure, high temperature probe for NMR studies of supercritical water. Right detail of the ceramic sample tube and free piston pressure balancing arrangement. The stainless-steel cylinder and piston are far from the heated region and remain cool.

Figure 4 High pressure, high-resolution probe for NMR studies under gas pressures of up to 100 MPa ( H frequency 400 MHz) equipped with mixing capability [14,15]...

In another application, 19F NMR studies have provided critical information on the bioactive conformation of taxoids. Fluorine-containing taxoids have been used as probes for NMR analysis of the conformational dynamics of paclitaxel in conjunction with molecular modeling [166], The dependence of the 19F chemical shifts and the Jm--ny values of these fluorinated analogues is examined through 19F and H variable-temperature (VT) NMR measurements. The experiments clearly indicate highly dynamic behavior of these molecules and the existence of equilibrium between conformers. The analysis of the VT NMR data in combination with molecular modeling, including restrained molecular dynamics (RMD), has identified three key conformers, which were further confirmed by the 19F- H heteronuclear NOE measurements. 

A design for a high-pressure, high-resolution probe for NMR studies of... 

Schulz PS (2010) Ionic liquids as solvent probes for NMR cryoporometry. Chem Phys Chem ll(l) 87-89... 

S. P. Babailov, Lanthanide Paramagnetic Probes for NMR Spectroscopic Studies of Molecular Conformational Dynamics in Solution Applications to Macrocyclic Molecules , Prog. Nucl. Magn. Resort. Spectrosc., 2008, 52, 1. 

Lanthanide paramagnetic probes for NMR spectroscopic studies of molecular conformational d3mamics in solution Applications to macrocycUc molecules . 

Hunger M and Horvath T 1995 A new MAS NMR probe for in situ investigations of hydrooarbon oonversions on solid oatalysts under oontinuous-flow oonditions Chem. Commun. 1995 1423-4... 

The Se NMR chemical shifts of Se-N compounds cover a range of >1500 ppm and the value of the shift is characteristic of the local environment of the selenium atom. As a result, Se NMR spectra can be used to analyse the composition of a complex mixture of Se-N compounds. For example, Se NMR provides a convenient probe for analyzing the decomposition of selenium(IV) diimides RN=Se=NR e.g., R = Bu). By this method it was shown that the major decomposition products are the six-membered ring (SeN Bujs, the five-membered ring Sc3(N Bu)2 and fifteen-membered ring Sc9(N Bu)6 (Figure 3.2 and Section 6.3). 

The intensity of the absorption of microwave energy is a measure the abundance of that isotope. The potency of the NMR spectroscopy is not only its ability to quantify the concentration of an isotope, but to check the enviromnent into which an isotope is embedded. This is possible because the magnetic resonance and thus the absorption frequency prove to be sensitive to the spins of neighboring atoms and to structural features of the probe. Therefore, NMR spectroscopy is more a tool for scientific structural analyses than for daily food (colorant) inspection. For a detailed study of the NMR techniques used in food science we recommend books by Macomber and Pochapsky. - ... 

The size of sample required has been reduced by a number of technical developments including micro inverse probes and micro cells (references in Martin et al. 1998), and has been reduced even further using a newly developed 1.7-mm submicro inverse-detection gradient probe (Martin et al. 1998). The combined use of inverse detection probes with solenoid microcoils has also been developed to reduce sample volumes for NMR (Subramanian and Webb 1998). 

The application of NMR to the study of chemical reactions has been expanded to a wide range of experimental conditions, including high pressure and temperatures. In 1993, Funahashi et al. [16] reported the construction of a high pressure 3H NMR probe for stopped-flow measurements at pressures <200 MPa. In the last decade, commercial flow NMR instrumentation and probes have been developed. Currently there are commercially available NMR probes for pressures of 0.1-35 MPa and temperatures of 270-350 K (Bruker) and 0.1-3.0 MPa and 270-400 K (Varian). As reported recently, such probes can be used to perform quantitative studies of complicated reacting multicomponent mixtures [17]. 

Some examples for NMR techniques that have been used for investigating catalytic reactors (most of which will be discussed in this chapter) and the corresponding length scales which they probe are as follows ... 

Fig. 5.3.8 Photograph of the detection region of the NMR probe with radiofrequency coil. A methane—air mixture was ignited above the zeolite pellets. The mixture also contained xenon for NMR detection. Hp-129Xe NMR spectra with 30% xenon (from high-density xenon optical pumping) in 70% methane is depicted. (1) The spectrum in the absence of combustion and (2) the spectrum during combustion. Adapted from Ref. [2],...

While H NMR is an important tool, which requires some 10-100 p,g, it yields organic structural information only indirectly (viewed through the hydrogen nuclei). In principle, the 13 C nucleus is the most informative probe for organic structure determination by means of FTNMR. The special advantages, which make 13C NMR an attractive alternative to 1H NMR for the solution of analytical problems, include ... 

Hunger, M. and Horvath, T.J. (1995) A new mas NMR probe for in-situ investigations of hydrocarbon conversion on solid catalysts under continuous-flow conditions, Chem. Soc. Client. Comm., 14, 1423. 

Another point which has already been mentioned before, and which is not specific for organotin compounds, is that the diastereomers should be distinguishable by a spectroscopic method (for instance NMR) to be sure that their separation was sufficient enough to give at least one of them in pure form. Till now, this has been the case only once. The methoxy signal seems to be a good probe for this purpose (see above), but unfortunately, the anisyl-tin bond is cleaved much more rapidly than the phenyl- or naphthyl-tin bond, which might sometimes cause problems in the crucial step. 

Silver(I) trifluoromethanethiolate (AgSCF3) has been used to prepare trifluoromethyl aryl sulfides by reaction with iodide.996 A mixed silver-zinc thiolate complex [Ag4Zn2(SC6H2-Pr -2,4,6)6(OTf)2] has been prepared by reaction of AgOTf with Zn[N(TMS)2]2 in the presence of the thiol.99 Solid-state 109Ag NMR can be a sensitive environment probe for silver thiolates,998 overall for biological thiolates ligands as cysteine,999 or proteins such as metallothionein.1000,1001... 

---