Pulsed field gradient probe

Pulsed field gradient probe, PFG Probe. Syn. gradient probe. An NMR... 

Samples were prepared in 99.96% D O for NMR analysis. All the H NMR spectra were recorded with a Bruker Avance 400 MHz spectrometer operating at 300 K and were acquired with a spectral width of 5995.204 Hz, 128 scans and 65536 data-points. Both 2D COSY and ROESY experiments were acquired on a Bruker DRX 500 MHz using 5 mm BBI H-BB probe or a Varian Inova 500 MHz, equipped with a triple resonance, Z pulsed field gradient probe. 2D COSY spectra displaying H- H cross correlation for free FLZ, free P-CD and FLZ P-CD mixture were acquired using 2048 data-points with 128 increments and 18 scans for each increment. 2D ROESY spectrum of FLZ P-CD was acquired... 

Gibbs, SJ Johnson, CS, Pulsed Field Gradient NMR Study of Probe Motion in Polyacrylamide Gels, Macromolecules 24, 6110, 1991. 

Pulsed field gradient NMR (PFG-NMR) spectroscopy has been successfully used for probing interactions in several research fields.44-53 The method was developed by Stejskal and Tanner more than 40 years ago54 and allows the measurement of self-diffusion coefficient, D, which is defined as the diffusion coefficient in absence of chemical potential gradient. 

Wolfender et ah, and this coupled technique is treated more comprehensively in Chapter 1. The LC-NMR technique is by nature rather insensitive however, high-field magnets and recent improvements in solvent suppression, pulse field gradients, and probe technology have made it possible to achieve useful results on various flavonoid struc-tures. The detection limit with a 60 p.1 cell in a 500 MHz instrument for a compound with a molecular weight of around 400 amu may typically be around 20 p.g, and the information provided is hitherto mainly based on NMR spectra or correlation experiments. 

When pulsed magnetic field gradients are applied to study diffusive processes, the MR technique is often referred to as pulsed field gradient or pulsed gradient spin echo (PGSE) MR. Application of PGSE MR techniques to quantify molecular diffusion was pioneered by Stejskal and Tanner 17,18), and the techniques typically probe molecular displacements of 10 -10 m over time scales of the order 10 M s. 

The on-line SEC-NMR measurements were performed on a 750 MHz spectrometer with an inverse-geometry LC-NMR probe with pulsed-field gradient coils. The detection volume of the flow cell was approximately 60 pi A Shodex linear K-805L SEC column (8 mm x 300 mm) with a maximum porosity of 4 x 106 was used for the chromatography. 

In 1989, the first applications of multidimensional NMR were applied to humic substances (Buddrus et al., 1989).This study involved the application of 13C detected J-resolved (J-Res) spectroscopy. The study was successful in that it showed multidimensional NMR was applicable to the study of humic substances. However, in 1989 the lack of various modern experiments and the corresponding hardware (mainly probes fitted with pulse field gradients) made applying NMR to humic materials very challenging. In 1997, Simpson et al. demonstrated that the more sensitive inverse-detected NMR experiments were applicable to NOM (Simpson et al., 1997). In this manuscript COSY,TOCSY and HMQC were applied (Simpson et al.,... 

Selective probe heads are used for optimal sensitivity for a particular nucleus. Sensitivity of a selective H probe head is normally greater than that of a switchable probe head with indirect observation. With a selective X-nucleus (a nucleus other than proton) probe head, decoupling of protons is normally possible. Because of their limited usefulness, selective probe heads are rare in NMR laboratories. Other probe heads are also available, for example, those for triple resonance experiments and experiments utilizing pulsed-field gradients. In addition to their suitability for 2-D experiments, the gradients are particularly suitable for solvent suppression (20). 

A Varian Unity Inova 600-MHz NMR instrument (Palo Alto, CA) equipped with a H C/ N pulse field gradient triple resonance microliow NMR probe (flow cell 60pL 3mm O.D.) was used. Reversed-phase HPLC of the samples was carried out on a Varian modular HPLC system (a 9012 pump and a 9065 photodiode array UV detector). The Varian HPLC software was also equipped with the capability for programmable stop-flow experiments based on UV peak detection. An LCQ classic MS instrument, mentioned in the previous section, was connected on-line to the HPLC-UV system of the LC-NMR by contact closure. The H resonance of the D2O was used for field-frequency lock, and the spectra were centered on the ACN methyl resonance. Suppression of resonances from HOD and methyl of ACN and its two C satellites was accomplished using a train of four selective WET pulses, each followed by a Bo gradient pulse and a composite 90-degree read pulse [41]. 

For non-deuterated complexes, NMR experiments were performed on either Vaiian Unity600 or Varian Unity+500 spectrometers. The 600 MHz instrument was equipped with a triple resonance probe and a PTS synthesizer as a pseudo fourth channel. The 500 MHz spectrometer was a four channel instrument with a triple resonance probe with an actively shielded pulsed field gradient coil. All experiments were performed at 37 C. The heteronuclear experiments shown in Figure 1 were performed as described in Zhang et al (11) and Revington et al (24). For all 3D ex riments 32 transients were required for sufficient signal to noise. This necessitated the use of fewer increments and the use of linear prediction (25)... 

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