NMR Detection

Therefore, in NMR, one observes collective nuclear spin motions at the Lannor frequency. Thus the frequency of NMR detection is proportional to Nuclear magnetic moments are connnonly measured either... 

Closs G L and Miller R J 1979 Laser flash photolysis with NMR detection. Microsecond time-resolved CIDNP separation of geminate and random-phase polarization J. Am. Chem. Soc. 101 1639—41... 

The physical and chemical properties of sufficiently small particles, in particular their magnetism, must depend on their size, whence the idea of using NMR to study them. Because of the theoretical and technical difficulties associated with the NMR detection of metals, and specially since only a few can be detected, NMR work has been mainly devoted to the indirect study of metallic properties, by the intenuediary of easily detected chemisorbed phases ( F1, C) or of physically adsorbed probes ( Xe). We will develop the cases of Pt and Pd. 

CW Continuous wave or frequency sweep, the older, less sensitive, more time consuming basic technique of NMR detection... 

Several problems m basic methodologies have persisted over the 25 years since F-NMR spectroscopy was first apphed to a biochemical question Most hmiting IS that of NMR sensitivity High substrate concentrabons, relative to the naturally occumng biological levels, are required for NMR detection Although most NMR studies use millimolar and somebmes submilhmolar concenbatrons, many bio molecules exist at micromolar or lower levels... 

A restricted number of applicable fluonne markers may also be viewed as a Imutabon The tnfluoroacetyl moiety has been the most commonly used group, used m sbidies of ammo acids, steroids, and carbohydrates Enhanced F NMR detection should be possible with specifically designed agents of opumal biological and spectral properbes... 

The isotope has a nuclear spin quantum number I and so is potentially useful in nmr experiments (receptivity to nmr detection 17 X 10 that of the proton). The resonance was first observed in 1951 but the low natural abundance i>i S(0.75%) and the quadrupolar broadening of many of the signals has so far restricted the amount of chemically significant work appearing on this rcsonance, However, more results are expected now that pulsed fourier-transform techniques have become generally available. 

A derivative of 5-(indol-2 -yl)dihydropyridazine 44 (R = H) exists in DMSO-iig solution exclusively as tautomer 44a (within the limits of 400-MHz H NMR detection). However, the introduction of methyl groups both into the indole ring and into the pyridazine ring favors a shift of the tautomeric equilibrium... 

Grootveld et al. (1994) employed this technique to investigate radiolytic, damage to biomolecules present in human body fluids. 7-Radiolysis of healthy or rheumatoid human serum (5.00 kGy) in the presence of atmospheric O2 gave rise to reproducible elevations in the concentration of NMR-detectable acetate, which are predominantly ascribable to the prior oxidation of lactate to pyruvate by OH radical followed by oxidative decarboxylation of pyruvate by radiolytically generated H2O2 and/or further OH radicals (Equations 1.7 and 1.8). 

An important consideration for making NMR and MRI suitable for applications in chemical engineering is to provide for flexibility in handling samples of various sizes, materials, shapes or temperatures, while ensuring sufficiently high NMR detection sensitivity. In this chapter, we present a novel technique known as NMR and MRI remote detection [11,12], which addresses these problems in a fundamental fashion, as well as a few examples where remote detection has been applied successfully. 

In order to use Eqs. (2.6.1) and (2.6.2) to estimate the sensitivity gain obtained by remote detection, knowledge of the relative sensitivity of the detector and the encoding circuit, A, is required. Here we discuss the sensitivity of an rf coil detector as an example, because all the experiments presented in this text use inductive detection at high field. The signal-to-noise ratio of inductive NMR detection can be approximated by the following simplified equation [12] ... 

With the rare exception of xenon gas NMR of fluidized beds, which we discuss later, granular flow studies by NMR detect signals from the particles and not the surrounding medium. Because it is technically easier to obtain NMR signals from liquids rather than solids, the majority of granular NMR studies so far use solid particles containing liquids. 

Figure 5.3.8 displays a photograph of the actual combustion zone. The methane-xenon gas was mixed with air before entering the NMR detection cell in the probe head. The gas mixture was blown through an area with molecular sieve pellets (i.e.,... 

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],...

SFC-NMR is available from 200 to 800 MHz, and is suitable for all common NMR-detected nuclei. SFC/SFE-NMR requires dedicated probe-heads for high pressure (up to 350 bar) and elevated temperature (up to 100 °C). SFC-NMR is carried out with conventional packed columns, using modifier, pressure and temperature gradients. The resolution of 1H NMR spectra obtained in SFE-NMR and SFC-NMR coupling under continuous-flow conditions approaches that of conventionally recorded NMR spectra. However, due to the supercritical measuring conditions, the 111 spin-lattice relaxation times 7) are doubled. 

In summary, NMR spectroscopy is an extremely versatile tool useful that enables researchers to understand the structure of natural products such as carotenoids. For a full structural assignment, the compound of interest has to be separated from coeluents. Thus, it is a prerequisite to employ tailored stationary phases with high shape selectivity for the separation in the closed-loop on-line LC-NMR system. For the NMR detection, microcoils prove to be advantageous for small quantities of sample. Overall, the closed-loop system of HPLC and NMR detection is very advantageous for the structural elucidation of air- and UV-sensitive carotenoids. 

In practise, if using one of these reagents to follow the course of a chiral separation, it is essential to determine whether resolution is possible, by performing a test experiment either on a sample of racemate, or at least a sample known to contain significant quantities of both enantiomers. Once useable resolution has been established, the technique can be used to monitor solutions of unknown enantiomer ratios with reasonable accuracy, down to normal NMR detection limits. 

Brindle K, Williams S-P, Boulton M (1989) 19F NMR detection of a fluorine-labelled enzyme in vivo. FEBS Lett 255 121-124... 

The same group recently reported that the TBB defects can be brought below the nuclear magnetic resonance (NMR) detection limit by employing similar polymerization conditions (i-BuOK in THF at room temperature) in the synthesis of naphthyl-substituted PPVs 51-53 [112]. Although the absorption and PL spectra of all three polymers are similar, the EL can be finely tuned between 486 nm (for 52) and 542 nm (for 53). The external QE (studied for ITO/PEDOT/polymer/Ba/Al device) is also sensitive to the substituents pattern in the naphthyl pendant group 0.08% for 51, 0.02% for 52, and 0.54% for 53. 

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