13C PGSE NMR Experiment with Heteronuclear Dipolar Decoupling to Measure Diffusion in Liquid Crystals and Solids

103

Application of rapid sample rotation and radiofrequency irradiation in magic angle spinning (MAS) NMR of lipid bilayers can significantly increase the sample temperature. In this work, we studied the extent of heating during the acquisition of 1H-decoupled 13C MAS spectra of hydrated dimyristoylphosphatidylcholine (DMPC) in the L(alpha) phase. First, we describe a simple procedure for determining the increase in temperature by observing the shift of the 1H water signal. The method is then used to identify and assess the various factors that contribute to the sample heating. The important factors discussed in this paper include: (i) the spinning speed, (ii) the variable-temperature gas pressure, (iii) the rotor geometry, (iv) the power, duration and frequency of the radiofrequency irradiation and (v) the hydration level. A comparison of different heteronuclear decoupling schemes in terms of their ability to produce highly resolved 13C spectra of DMPC is also reported.

Section: Efficiency Of Heteronuclear Decouplingmentioning

confidence: 99%

Heating caused by radiofrequency irradiation and sample rotation in ¹³C magic angle spinning NMR studies of lipid membranes

Dvinskikh

Castro

Sandström

2004

103

“…64,114 In case of heteronuclear dipole-dipole coupling as the dominant source of line broadening, heteronuclear instead of homonuclear decoupling can be applied. 113 on the signal decay in a gradient experiment can be simply described by replacing the term g 2 D in Eqn (3), yielding…”

Section: Sample and Gradient Orientationmentioning

confidence: 99%

NMR methods applied to anisotropic diffusion

Furó

Dvinskikh

2002

The methodology of NMR experiments intended to measure anisotropic diffusion is reviewed. Experiments of this kind preferably require oriented samples and/or orientation-dependent spin coupling and/or magnetic field gradients in different directions. One strategy of diffusion experiments in anisotropic systems with broad NMR lines employs line narrowing techniques, thereby allowing for efficient gradient encoding/decoding. Depending on the nuclei, spin couplings and samples, the preferred methods vary from decoupling through echo techniques to magic angle sample orientation and spinning. Another avenue to efficient gradient encoding/decoding is through very strong magnetic field gradients. Either way, anisotropic diffusion reveals new structural features as illustrated by a few selected examples in liquid crystals and in biological tissues.

“…Nevertheless, none of these decays can be considered for properly determining diffusion coefficients. The remedy employed by Furó [13] consists in selecting a slice for which the modification of the B 0 field is not large, leading to a moderate defocusing and thus to an efficient decoupling. However, in this case, one is dealing with dipolar couplings, and the use of decoupling during gradient pulses seems mandatory in order to avoid a large spread in resonance frequencies that could be incompatible with the effects of gradients.…”

Section: Resultsmentioning

confidence: 99%

“…The gradient was incremented in 32 steps between 2% and 95% of this maximum value, each step corresponding to a separate experiment. The diffusion interval was set at 600 ms; this unusual large value is allowed by the fact that 13 C longitudinal relaxation times (T 1 ) are generally relatively long (3-5 s). The time elapsed between two consecutive experiments is assumed to be five times the longest T 1 .…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Self‐diffusion coefficients obtained from proton‐decoupled carbon‐13 spectra for analyzing a mixture of terpenes

Yemloul¹,

Castola²,

Leclerc³

et al. 2009

In the limit of sufficient sensitivity, natural abundance 13C offers a much better spectral resolution than proton NMR. This is due to an important chemical shift range and to proton-decoupling conditions that yield one peak per carbon with practically no overlap. However, pulsed gradient spin echo experiments, which lead to the diffusion coefficient associated with each peak, have scarcely been employed. In this article, we present and compare different ways to access this quantity and we have effectively verified that, without any precaution, diffusion coefficients cannot be properly determined from standard procedures. The cause of such a failure is decoupling during the gradient pulses. We have used a very simple remedy that proved to be very successful on a model mixture of three monoterpenes and that appears as being of general applicability.