Resonance dispersion

Crystalline polymers, as well as other crystalline solids, have been found by Fitzgerald and Bodner to exhibit unusual responses to periodic mechanical stress 

An example for polytetrafluoroethylene is shown in Fig. 16-15. The experimental points are rather well matched by curves calculated from the simple mechanical model of Fig. 16-16 with suitable values of the four parameters and an added constant background loss of 0.1 X 10 cm /dyne for J . This model differs from those usually associated with linear viscoelasticity by the inclusion of the inertial unit w//, with dimensions of mass per unit length. The values of Co and G are determined by the limiting levels of J on the two sides of the dispersion, m/l by the resonance frequency and r) by the breadth of the dispersion. The magnitude of t] is reasonable, 10 poises. However, that of m/l is too large to be identifiable physically as a real mass per unit length. This result corresponds to the elementary calculation that to produce an audio-frequency resonance with an elastic member of the shape and modulus of the sample, an inertial member with mass considerably greater than that of the sample would be required. 

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Because unidimensional NMR spectra of denatured proteins lack resonance dispersion and resemble spectra of mixtures of free amino acids, it was assumed that the denatured state behaves as a random coil (McDonald and Phillips, 1969). Calculations (Brant et al., 1967 Zimm and Bragg, 1959) and spectroscopic measurements on... 

Because of the intrinsic flexibility and poor resonance dispersion of unfolded and partly folded proteins, long-range NOEs are generally very difficult to observe and assign. While observation of a long-range NOE between two protons provides a definitive indication that they are in close proximity in at least some structures in the conformational ensemble, determination of the nature of the folded structures is difficult unless an extensive network of NOEs can be observed. This has so far been achieved in only one case (Mok et al., 1999). 

Magnetic resonance dispersion is a useful aid in the characterization of liquids in porous rocks from which one may extract oil however, the method... 

Comparison of electronic absorption spectra of the Ln-TTHA complexes in the solid state and in solution has shown that the monomeric species with Ln3+ coordination numbers 10 and 9 also occur in solution for the light and heavy lanthanides, respectively [39,41,43]. In addition, these studies suggest the presence of another species with one uncoordinated N-atom for the Nd3+ and Eu3+ systems. Absorption spectra [39,41,43],luminescence [45] and H Nuclear Magnetic Resonance Dispersion (NMRD) studies [46] have shown that oligomeric species also occur in solution, particularly below pH 5. 

Eq. (4), frequency-dependent, such that the limit for a(w) in Eq. (8) becomes physically acceptable. Under conditions appropriate to the correct limit, the normalized real and imaginary parts of the complex permittivity and the normalized dielectric conductivity take on the form depicted in Fig. (1). Here, is the relaxation time in the limit of zero frequency (diabatic limit). Irrespective of the details of the model employed, both a(w) and cs(u>) must tend toward zero as 11 + , in contrast to Eq. (8), for any relaxation process. In the case of a resonant process, not expected below the extreme far-infrared region, a(u>) is given by an expression consistent with a resonant dispersion for k (w) in Eq. (6), not the relaxation dispersion for K (m) implicit in Eq. 

Lower concentration of anomalous scatterers, especially if they exhibit some regular structure, allow the measurement of the complete resonant dispersion profiles. The case of very dilute solutions of resonant scatterers will be discussed in Section 3.4. 

The heteronuclear NMR experiments discussed above highlight how much extra resonance dispersion can be gained via this approach. The power of this added dimension becomes clear if, for example, the 3H—15N HSQC experiment shown above, where each HN atom is essentially resolved, was to be combined with a TOCSY or NOESY experiment to provide a third frequency dimension. The resulting 3D 15N-HSQC-TOCSY/NOESY spectrum would contain virtually no overlap of interresidue resonances. Such experiments are indeed possible and have been the driving force in producing uniformly 15N- and/or 13C-labeled proteins. This field has been the most intensely researched area of NMR in the past 20 years, and the strategies employed to determine protein and peptide structures using heteronuclear NMR experiments are discussed in the next section (see Chepter 9.19). 

Figure 3.42. Changes in solvent can be used to improve resonance dispersion. The proton spectrum of the sugar 3.1 is shown in (a) CDCI3 and fb) CgDe. Notice the appearance of the resonance at 3.2 ppm in (b) that was hidden at 3.6 ppm by another resonance in (a).

Fig. 7a. Proton resonance (absorption mode) in foric nitrate solution (taken from Ref.. b Proton resonance (dispersion mode) in ferric nitrate solution (taken from Ref. )...

The mobility of proton containing molecules in foods can be investigated by the acquisition of Nuclear Magnetic Resonance Dispersion (NMRD) profiles that report about the changes in the H-spin-lattice or longitudinal relaxation rate (Ri=l/Ti) as function of the applied magnetic field strength. 

A. Ordikhani Seyedlar, S. Stapf, C. Mattea, Dynamics of the ionic liquid l-butyl-3-methyKmidazolium bis(tri luoromethylsulphonyl)imide studied by nuclear magnetic resonance dispersion and diffusion, Phys. Chem. Chem. Phys. 17 (3) (2015) 1653-1659. 

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