NMR relaxation techniques

The presence of four kinds of nuclear magnetic resonance (NMR) observable nuclei ( H, uB, 13C, and 29Si) allows poly(m-carborane-siloxane) to be readily investigated using NMR spectroscopy. In addition, H spin-echo NMR relaxation techniques can provide an insight into polymer segmental chain dynamics and therefore useful information on material viscoelastic characteristics. 

Solvent polarity is known to affect catalytic activity, yet consistent correlations between activity and solvent dielectric (e) have not been observed [12,102]. However, a striking correlation was found between the catalytic efficiency of salt-activated subtilisin Carlsberg and the mobility of water molecules (as determined using NMR relaxation techniques) associated with the enzyme in solvents of varying polarities (Figure 3.11) [103]. As the solvent polarity increased, the water mobility of the enzyme increased, yet the catalytic activity of the enzyme decreased. This is consistent with previous EPR and molecular dynamics (MD) studies, which indicated that enzyme flexibility increases with increasing solvent dielectric [104]. 

We have been able to demonstrate the basic validity of the assumptions on which the dual mode model is based and we have shown the usefulness of NMR relaxation techniques in the study of this model,"... 

We have been able to critically examine the dual mode model by pulsed NMR relaxation techniques ... 

Network structure analysis is discussed in Chapters 7, 8,10 and 13. These chapters deal with the characterisation of the structure of chemical and physical networks, rubber-filler physical network, network defects and its heterogeneity using NMR relaxation techniques and NMR imaging. 

The double proton transfer in cyclic dimers of crystalline benzoic acid has been studied by various authors using NMR relaxation techniques [72, 73]. For a recent account of this work the reader is referred to the study of Horsewill et al. [74] who published the correlation times of the HH, HD and DD reactions given by... 

Gardino AK, Kern D (2007) Eunctional dynamics of response regulators using NMR relaxation techniques. Methods Enzymol 423 195-205... 

Several studies have been carried out on the electron exchange and transfer reactions of Pseudomonas aeruginosa azurin. The AzCu(I)/(II) exchange rate constant has been measured at 4 °C by fast-flow/rapid-freeze EPR methods and at 25 °C using H NMR relaxation techniques/ and shows only a small dependence on pH (4.5-9.0). The rate constants for electron transfer reactions between... 

To make the significance of the NMR technique as an experimental tool in surfactant science more apparent, it is important to compare the strengths and the weaknesses of the NMR relaxation technique in relation to other experimental techniques. In comparison with other experimental techniques to study, for example, microemulsion droplet size, the NMR relaxation technique has two major advantages, both of which are associated with the fact that it is reorientational motions that are measured. One is that the relaxation rate, i.e., R2, is sensitive to small variations in micellar size. For example, in the case of a sphere, the rotational correlation time is proportional to the cube of the radius. This can be compared with the translational self-diffusion coefficient, which varies linearly with the radius. The second, and perhaps the most important, advantage is the fact that the rotational diffusion of particles in solution is essentially independent of interparticle interactions (electrostatic and hydrodynamic). This is in contrast to most other techniques available to study surfactant systems or colloidal systems in general, such as viscosity, collective and self-diffusion, and scattered light intensity. A weakness of the NMR relaxation approach to aggregate size determinations, compared with form factor determinations, would be the difficulties in absolute calibration, since the transformation from information on dynamics to information on structure must be performed by means of a motional model. 

As mentioned above, the strength of the NMR relaxation technique in comparison to other (say, scattering) techniques for studying micelles and microemulsions is related to the fact that rotational dynamics are monitored. This has the advantage that the dynamics are (1) sensitive to small size variations and (2) essentially independent of interactions. In an extensive study of a three-component microemulsion system composed of the nonionic surfactant pentaethylene oxide dodecyl ether, water, and decane oil-swollen micelles dispersed in water were investigated over a large concentration range [58]. 

The fact that the -SiO(CH3)2- chain units that were grafted to the silica surface and those in the middle portion of the chain show the same chemical shift in the and Si spectra precluded the use of chemically selective NMR relaxation techniques for characterizing the PDMS-silica inteifacial layer. We therefore performed nonselective low resolution NMR relaxation experiments to characterize the structure of the PDMS grafted layer. 

Because molecular solids exhibit significant compressibility even in the pressure range 0.1 to 900 MPa one can use high pressure NMR relaxation techniques to investigate phase transitions. The high degree of molecular rational freedom in plastic crystals (orientationally disordered crystals)... 

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