Transient Overhauser

McBrierty and Douglass [48] have used transient Overhauser measurements to obtain information about cross relaxation between the and F spin systems in static PVDF powder over the temperature range -196 to -l-160°C. The authors comment that the experiment provides good resolution of Ti components, and they were able to observe two minima, at 25 and 110°C, where other measurements were unable to detect adequately the latter (which probably relates to P relaxation). 

Floffman R A and Forsen S 1966 Transient and steady-state Overhauser experiments in the investigation of relaxation prooesses. Analogies between ohemioal exohange and relaxation J. Chem. Phys. 45 2049-60... 

Bothner-By AA, Stephens RL, Lee J-M. Stmcture determination of a tetrasaccharide transient nuclear Overhauser effects in the rotating frame. J. Am. Chem. Soc. 1984 106 811-813. 

Bothner-By AA, Stephens RL, Lee J, Warren CD, Jeanloz RW (1984) Structure Determination of a Tetrasaccharide Transient Nuclear Overhauser Effects in the Rotating Frame. J Amer Chem Soc 106 811... 

Other possibilities (e.g., Overhauser effects) exist for the complication of the patterns of polarization predicted by the simple theory. Interesting transient splittings have been observed in polarized F-spectra (Bethell et al., 1972a, b). Nevertheless, straightforward application of the simple rules seems to yield reliable conclusions in most cases, dearly, however, it is unwise to rely on CIDNP results alone in studies of organic reaction mechanisms other information is invariably necessary to ensure that the correct interpretation is chosen from among the several possibilities which CIDNP may suggest. 

All NMR experiments were performed on a Varian XL-200 spectrometer at 50.31 MHZ. Relevant instrument settings include 90 degree pulse angle, 1.0 second acquisition time, 0.5 second pulse delay, 238.5 ppm spectral width, and broad band proton decoupling. About 40,000 transients were collected for each spectrum. Temperature was maintained at 40 C. Spin-lattice relaxation time (Tl) and Nuclear Overhauser Enhancement (NOE) values for all C-13 NMR resonances were carefully measured to determine the optimum NMR experimental conditions. The spectral intensity data thus obtained were assured of having quantitative validity. 

McBrierty and Douglass have studied cross-relaxation between and F spins in poly(vinylidene fluoride) by means of the transient nuclear Overhauser effect. The results provided valuable additional data in support of previous interpretations of relaxation, in particular the measurement of motional frequencies at the hitherto inaccessible frequency of the difference between H and F frequencies (2 MHz). The same authors have used this technique to study compatibility in blends of poly(vinylidene fluoride) with poly(methyl and ethyl methacrylate)s. The cross-relaxation data indicate substantial intimate mixing. 

Gordon, S. L. and Wuethrich, K., Transient proton-proton Overhauser effects in horse ferrocytochrome c, J. Am. Chem. Soc. 100, 7094-7096 (1978). 

Spin-lattice relaxation and transient nuclear Overhauser enhancement (tnOe) experiments with C- and H-labelled substrates have been used for the conformational analysis of several mono- and di-saccharides. An investigation of the molecular dynamics of polyciystalline mono- and di-saccharides involved measurements of the temperature dependencies of proton spin-lattice relaxation times and second moments of n.m.r. lines. ... 

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