Dipolar coupling constant

Kramer, F., Deshmukh, M. V., Kessler, H., Glaser, S. J. Residual dipolar coupling constants an elementary derivation of key equations. Cone. Magn. Reson. A... 

Rotational-echo double-resonance (REDOR)(75,79) is a new solid-state NMR technique which is sensitive to through-space carbon-nitrogen interactions between selectively 13C and 15N-enriched sites separated by up to 5A (20-22). The parameter directly measured in a REDOR experiment is the heteronuclear dipolar coupling constant DCN, which is in itself proportional to the inverse third power of the intemuclear distance, rCN. It is this dependence on (icn)3 which accounts both for REDOR s ability to accurately measure short distances and its insensitivity to longer-range interactions. As a technique which can probe, in detail, intermolecular interactions over a distance range of 5A, REDOR is well suited to studying the distribution of small selectively-labeled molecules in polymer delivery systems. 

Fig. 14. (A) Ac-L-Ala-NHMe structure with best-fit dipolar coupling constants (Hz).

Fitting of these curves yields the sum of the dipolar coupling plus the /-coupling. Referencing to a spectrum without alignment allows extraction of the dipolar coupling constant. 

Fig. 11.7 a Pulse sequence for rotational-resonance recoupling of homonuclear spin pairs, b The spinning frequency is matched to the isotropic chemical-shift difference, and one of the resonances is selectively inverted and the polarization exchange measured as a function of the mixing time, c The difference polarization as a function of the mixing can be evaluated to give the dipolar coupling constant. 

In the following, we will discuss heteronuclear polarization-transfer techniques in four different contexts. They can be used as a polarization-transfer method to increase the sensitivity of a nucleus and to shorten the recycle delay of an experiment as it is widely used in 1H-13C or 1H-15N cross polarization. Heteronuclear polarization-transfer methods can also be used as the correlation mechanism in a multi-dimensional NMR experiment where, for example, the chemical shifts of two different spins are correlated. The third application is in measuring dipolar coupling constants in order to obtain distance information between selected nuclei as is often done in the REDOR experiment. Finally, heteronuclear polarization transfer also plays a role in measuring dihedral angles by generating heteronuclear double-quantum coherences. 

The H magnetic resonance spectra of pyrrole- 15N in two nematic solvents have been reported91. The dipolar coupling constants were used to derive relative intemu-clear distances, and it was found that the N—H bond distance relative to the distance... 

As mentioned in Sections I.B.2.b and II.A, the dipolar coupling between Li- C may complicate solid state NMR spectra of organolithium compounds and its elimination is often desirable. On the other hand, dipolar coupling constants are related to atomic distances and their determination can yield important structural information. It is therefore of general interest that the REDOR technique, briefly described in Section I.B.2.b, provides a means to determine these parameters. 

Dipolar coupling constants for the protons of n-hexane in the uniaxial phase, DZJ. 

The conformations of flexible chain molecules incorporated in a nematic environment are investigated. Proton-proton and carbon-carbon dipolar coupling constant measurements are attempted for 1,2-dimethoxyethane and 1,2-diphenoxyethane, in addition to 2H NMR observations of quadrupolar splittings. These conformation-dependent properties are analyzed according to the RIS scheme. Studies are further extended to a mixture of 1,2-diphenoxyethane with a nematic liquid crystal, 4,4 -azoxyanisole. 

In this case, the frequencies of the Pake pattern are shifted by J and the frequency of the edge (0y) and peak (0/) of the Pake pattern do not behave like2 l (Fig. 16.8) what they do if J is zero (Fig. 16.2C). However, if the full Pake pattern is observed both contributions can be disentangled and quantified. From the frequencies at which the peaks and edges of the Pake pattern appear, the dipolar coupling constant vdd and J can be calculated using Eqs. (16.8) and (16.9) derived from Eqs. (16.7) and (16.3) (Milov etal, 1998) ... 

By monitoring the H MAS spectra, it has been suggested that the loss of water from bone tissue is an irreversible process under air drying conditions.38 It has been shown that CP transfer within an isolated heteronuclear spin pair will exhibit a characteristic oscillation, from which the dipolar coupling constant can be accurately determined.197 The technique of LG-CPMAS can probe this oscillation pattern due to a dominating 31P-1H interaction in a dipolar coupled network, if any. However, such oscillation is seldom observed in 31P 1H CPMAS measurements of biominerals because of the damping effect of the homonu-clear dipole-dipole interaction. Thus, it is rather remarkable that the buildup curve of 31P 1H LG-CPMAS obtained for a sample of powdered femoral cortical bone, which is partially hydrated, shows a distinctive... 

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