Proton signal linewidths

So far, the majority of granular matter studies by NMR/MRI have used liquid state proton measurements in solid materials. Because proton signals are relatively insensitive to chemical environment through the chemical shift effect and because the physical environments are relatively similar in all liquids, the resonance frequency and the NMR linewidth are not good indicators of granular parameters such as particle density and velocity. 

Fig. 5.10. Predominance of dipolar, contact or Curie relaxation in signal linewidths at 800 MHz for different rotational and electron relaxation times, and for different constants for the contact interaction. Calculations have been performed for protons at 5 A from a S = 5h ion.

Fig. 31, Plots of the linewidth of His 26 N H proton signal in horse (open circles) and tuna (filled circles) ferrocytochromes c in 90%H20/10% H20 at 5 °C as a function of pH. Similar plots for HisEF5 N, H proton signal in horse Mb(CO) - are indicated by triangles, for comparison. (From ref. 123, 1997, with permission from the publisher.)...

Experimental Linewidths of the NMR Signals Arising from Cysteine H/3 Protons... 

In reduced Fe2S2 there is a localization of valences between Fe(III) and Fe(II). The for both ions is shorter than that of the Fe(II) monomer (Table I), whereas the linewidths of the signals of the Fe(III) and Fe(II) domains depend on coefficients obtainable from the solution of Eq. (4). As a result, the signals of the H/3 protons of the cysteines bound to the Fe(III) are shifted beyond 100 ppm downfield with relatively large linewidths, while those of the cysteines bound to the Fe(II) domain are closer to the diamagnetic region and 5-10 times narrower (50-53) (Fig. 2B). There are cases in which there is delocalization of the valences (54, 55) but no NMR investigation is available. 

Fig. 2. (a) Raw 300 MHz proton spectrum of a mixture of acetone and ethanol in deuteri-ochloroform (b) after reference deconvolution using the acetone signal as reference and an ideal lineshape of a 1 Hz wide Lorentzian and (c) after reference deconvolution with an ideal lineshape characterized by a negative Lorentzian width of 0.1 Hz and a Gaussian width of 0.4 Hz. The 0.1 Hz Lorentzian term represents the approximate difference in natural linewidth between the ethanol and acetone signals, and is responsible for the wings on... 

Al3+-exchanged synthetic hectorite is a good catalyst for these conversions, and the 13C NMR spectrum obtained in the interlamellar, proton-catalyzed addition of water to 2-methylpropene is indistinguishable (Fig. 79) from that of f-butanol. Doubtless studies of this kind, where natural-abundance, 3C NMR signals are used to probe the chemical identity and motional freedom of reactant and product species situated in the interlamellar spaces of clays or pillared clays (see below), will become increasingly popular. Using l3C NMR linewidths and spin-lattice relaxation studies, Matsumoto et al. (466) have succeeded in discriminating between the internal and external surfaces of pillared montmorillonites. 

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