Proton-spin diffusion

The H Tip values determined from the Cot, Cp and C=0 carbon signals of pure PLA with the ot-helix form are 22, 22 and 24 ms, respectively, and those of the PLA (mixture of the p-sheet and -helix forms, 1 1) with the p-sheet form are 16, 14 and 19 ms, respectively. On the other hand, the H Tip values determined from the Cot, Cp, Cy and C=0 of pure PLV with the p-sheet form are 14, 15, 15 and 15 ms, respectively. The H Tip values for PLA with the p-sheet form are somewhat longer than those for PLV with the p-sheet form. However, the T p values for PLA in the ot-helix form are much larger than those for PLA and PLV in the p-sheet form. In the PLA/PLV (50/50) blend, the Tip values determined from the Cot, Cp and Cy of PLV in the p-sheet form are 17, 16 and 15 ms, respectively, and are thus slightly larger than those for pure PLV. The TxP values determined from the Cot and Cp of PLA in the ot-helix form, are 16 and 13 ms, respectively, and for the Cot carbon of PLA in the p-sheet form it is 19 ms. The Tip values for the ot-helix form thus decrease. Hence, these XH Tip values are very close to each other. This shows that proton spin diffusion between the PLAs in the ot-helix and p-sheet forms and PLV in the p-sheet form occurs on the H TiP time scale. 

In all of the polypeptide blend samples obtained by Method 5, the proton spin diffusion between each homopolypeptide occurs on the 3H time scale. The maximum effective diffusion distance was obtained from these Tip values. The maximum effective diffusion distance L of the proton spin diffusion is expressed by the following equation (5) from equation (4),... 

A 2D CPMAS exchange experiment in which through-space (site) correlation is established via proton spin diffusion was proposed by Wilhelm et al.292 for probing the isotropic chemical shift correlations. This technique has a number of advantages, including site selectivity, multiple correlations and broad spatial correlation range (1-200 nm). It was shown that this technique... 

For the methyl groups of the host molecule, proton spin diffusion and crosspolarization are slower compared to the methyl groups of DMA. Moreover, for the methyl groups of resorcinarene, the value of T f is larger than that found for the carbonyl peak and the T2 comes close to that of unprotonated carbonyl carbon. All parameters indicate that in the host molecule H- H and dipo-... 

A new 3D experiment that allows direct probing of proton spin-diffusion process between resolved proton spectra obtained under Lee-Goldburg homo-nuclear decoupling has been reported. It is anticipated that this class of experiments will soon be used to study poorly crystalline hybrid materials as well as finely divided or porous inorganic materials. 

Both techniques are affected by proton spin diffusion. This renders technique (i) only valuable in a qualitative sense, showing intimate mixing (Fig. 

B MAS NMR yields quantitative information about the incorporation of boron into zeolite frameworks. H MAS NMR and IR spectroscopy show that OH groups introduced into the framework by boron substitution are non-acidic. 2D proton spin diffusion measurements of the zeolite SAPO-5 reveal that defect OH groups are adjacent to acidic bridging hydroxyl groups and do not exist in an amorphous phase. Strongly adsorbed water molecules in mildly steamed zeolites H-Y can be explained by Lewis sites. 

Information on the short distance spatial proximity of different segments of molecules can be obtained using the proton spin-diffusion NMR. This is a particularly valuable method for the... 

For a CP contact time (tcp) that is small enough (100 p.s) to avoid the rotating-frame spin diffusion that scrambles the desired H— Si correlation vide supra), the geminal silanol peak at -89 ppm is the one that suffers most from H— H dipolar dephasing for 2tj-ot period. The effect of rotating frame proton spin diffusion is also clear from the spectra in Figure 34.20 if a long CP contact period (e.g., 5 ms) is employed, essentially... 

Pulse EPR methods can measure dipole-dipole couplings with precision to 0.5 MHz for most paramagnetic centers, which corresponds to a distance range up to 5 If transverse electron spin relaxation caused by proton spin diffusion is slow, a precision of 0.1 MHz corresponding to a distance of 8 nm can be achieved. This is possible for materials that do not contain methyl groups or water or when the bulk of the material is perdeuterated. If part of a supramolecular system exhibits... 

Solid state proton line shape experiments on PMP and Goldman-Shen proton spin diffusion experiments on PMP were performed on a Bruker MSL 300. The 900 pulse width was typically 2 is. The Goldman-Shen experiments were performed at a temperature of 350 K with a discrimination time of )ps. 

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