Proton rich solid phases

For the present discussion, we define a solid phase as any phase where the rotational mobility of the molecules involved is sufficiently slow so that the 

A clear demonstration of the effects of the magnetic coupling are shown in Fig. 16 where the liquid proton signal intensity is plotted as a function of the frequency offset of a preparation pulse (84,87). The essence of the 

The importance of the magnetic coupling is easily seen in Fig. 17 which shows two water proton MRD profiles for serum albumin solutions at the same composition (89). The approximately Lorentzian dispersion is obtained for the solution, and reports the effective rotational correlation time for the protein. The magnetic coupling between the protein and the water protons carries the information on the slow reorientation of the protein to the water spins by chemical exchange of the water molecules and protons between the protein and the bulk solution. When the protein is cross-linked with itself at the same total concentration of protein, the rotational motion of the protein 

There are a variety of models for the magnetic field dependence for polymers and variously ordered phases coming largely from the groups of Kimmich and Noack. We focus here on the protein system that provides unique structural and physical characteristics. Recent advances in the speed of current-switched field-cycling instruments have provided a direct measure of the MRD profile of the protein protons as shown in Fig. 18. The relaxation 

Three characteristics of the MRD profile change when the protein is hydrated with either H2O or D2O. Both terms of Eq. (6) are required to provide an accurate fit to the data. The second or perpendicular term dominates once the transverse modes become important. The power law for the MRD profile is retained, but the exponent takes values between 0.78 and 0.5 depending on the degree of hydration. A low frequency plateau is apparent for samples containing H2O which derives from two sources the field limitation of the local proton dipolar field as mentioned above, and from limitations in the magnetization transfer rates that may be a bottleneck in bringing the liquid spins into equilibrium with the solid spins. 

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B. Natural systems Proton rich solid phases... 

According to this interpretation a small proportion of the non-framework Si-OH is able to interact with pyridine. Does this mean that these Si-OH groups behave as Bronsted sites Such a surprisingly acidic behaviour is unlikely. Adsorption experiments performed on silica-rich amorphous silica-alumina indicate that the Si-OH band located at 3745 cm 1 is partly affected by pyridine adsorption, even after evacuation at 723 K. Taking into account that non-protonated pyridine species are detected under such conditions, the perturbation of the Si-OH would result from an indirect interaction with pyridine adsorbed on near-by Lewis acid sites. The same phenomenon is likely to occur for non-framework Si-OH present in modified zeolites since the solids are known to contain a large amount of extra-framework Lewis sites (4). Moreover this interpretation would support the presence of a silica rich extra-framework phase in HT as well as in HTA solids. 

Proton spin-temperature equilibration between the hard- and soft-segment-rich domains of the polyurethane elastomer on the order of 10-100 ms might be considered fast relative to a macroscopically phase-separated blend [26] or copolymer, but slow relative to a strongly interacting mixture [25]. This is reasonable for a microphase-separated material whose solid state morphology has been the subject of considerable theoretical and experimental research. Under fortuitous circumstances, intimate (near-neighbor) contact between dissimilar molecules in a mixture can be studied via direct measurement of proton spin diffusion in a two-dimensional application of the 1H-CRAM PS experiment (Combined Rotation And Multiple Pulse Spectroscopy). Belfiore et al. [17,25,31] have detected intermolecular dipolar communication in a hydrogen-bonded cocrystallized solid solution of poly(ethylene oxide) and resorcinol on the f00-/xs time scale, whereas Ernst and coworkers [26] report the absence of proton spin diffusion on the 100-ms time scale for an immiscible blend of polystyrene and poly(vinyl methyl ether), cast from chloroform. 

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