Dipolar broadening

This method, which had already been recognized in 1953 by Andrew and his co-workers 4), eliminates dipolar broadening and brings forth spectra almost analogous, to those of the low-viscous liquid state. Therefore, it also permits the use of chemical shifts for the identification of nuclei in different chemical environments and motional states. 

The Dipolar Broadening of Magnetic Resonance Lines in Crystals. Physic. 

FIGURE 10.4 Anisotropy averaging in the EPR of TEMPO as a function of temperature. The spectra are from a solution of 1 mM TEMPO in water/glycerol (10/90). The blow-up of the middle 14N (/ = 1) hyperfine line in the 90°C spectrum has been separately recorded on a more dilute sample (100 pM) to minimize dipolar broadening and, using a reduced modulation amplitude of 0.05 gauss, to minimize overmodulation. The multiline structure results from hyperfine interaction with several protons. 

To further reduce the linewidth of the spectra, doping in isostructural Y3+, La3+ or Lu3+ host is usually performed to minimize dipolar broadening and spin-spin relaxation. 

Molecules in the solid state are in fixed orientations with respect to the magnetic field. This produces chemical shift anisotropic powder patterns for each carbon atom since all orientations are possible (Fig. 2). It was shown as early as 1958 that rapid sample rotation of solids narrowed dipolar-broadened signals [18]. Several years later, it was recognized that spinning could remove broadening caused by CSA yet retain the isotropic chemical shift [19]. 

Andrew, E.R., Bradbury, A., and Eades, R.G. (1959) Removal of dipolar broadening of nuclear magnetic resonance spectra of solids by specimen rotation. Nature, 183, 1802. 

Examination of the ESR spectra measured in this study, Figures 1 and 2, shows no indication of the dipolar broadened line at 77 K in the networks studied even when the samples were cooled to 77 K from ambient temperature during more than four hours. We particularly checked the S-band spectra for this line. We expect the dipolar broadening to be the same at the two frequencies but much more conspicuous at S-band because the spectrum from isolated ions is spread over a smaller range of magnetic fields at this microwave frequency. The absence of the broad line indicates that in all the networks measured Cu(ll) hydrated by freezable, or bulk, water is not detected. These results are in agreement with those presented in ref. 25 which indicate the absence of bulk water in water absorbed on silica gels with pores smaller than 6 nm. 

Dipolar broadening constitutes a routinely-overcome barrier in high-resolution NMR of solids, and the consequences are readily removed in the... 

When a spin-labelled derivative of phosphatidylinositol 4,5-bisphosphate was bound to MARCKS (Myristoylated Alanine-Rich C Kinase Substrate) the frozen solution EPR spectra exhibited dipolar broadening consistent with distances on the order of 18-22 A, which indicated that more than one spin-labelled substrate was bound to each MARCKS.65... 

Fourier Deconvolution. Pairs of spin labels were introduced in the N-terminus of a-spectrin.66 Distances in the range of 8.3 to 11.7 A were determined by Fourier deconvolution of the dipolar broadening. The trends in distances for positions i to i+2, i + 3, i+4, and i + 5 were consistent with an a-helix. 

However, the Lorentzian form of the dipolar broadening function, which has the advantage of mathematical simplicity, is not suitable for an interpretation in terms of second moments it is replaced with a Gaussian dipolar function S(oa, AG), where the parameters AG correspond to the appropriate fractions of the square root of the intra-group rigid lattice second moments. With appropriate values for AG, calculated and experimental line shapes I(oo) are found to be in a good agreement for cross-linked polyethylene oxide) swollen in chloroform 1U). 

The dipolar broadening parameter AG, independent of the type of solvent used, is related to the residual second moment (AM2b) ... 

Fig. 23. Plot of the dipolar broadening parameter AG (left scale) and its relation to the square root of rigid lattice second moment, AM2 = 15 kHz (right scale), for polystyrene networks crosslinked with DVB (solid symbols) and EDM (open symbols) swollen to equilibrium, vs l/n, the reciprocal nominal number of C—C bonds between crosslinks points. Solvents CC14 ( ), CDC13 (A),...

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