Slow-Down of 13C Spin Diffusion in Organic Solids by Fast MAS: A CODEX NMR Study

Moderate MAS enhances local 1 H spin exchange and spin diffusion

“…The reduction of dipolar couplings with increasing MAS rates causes altered spin diffusion rates, which are usually found to be the slower the faster the spinning [11][12][13][14]. Based upon our previous work [15], we here studied local spin diffusion rates under MAS, and observed increased spin diffusion coefficients at low (<10 kHz) spinning rates as compared to static conditions, with a maximum spin diffusion efficiency around 2-3 kHz MAS.…”

“…MAS reduces dipolar couplings, and hence, is supposed to always lower the spin-diffusion constant [11][12][13][14]. The results of our measurements are shown in Fig.…”

The Application of MAS Recoupling Methods in the Intermediate Motional Regime

“…This is particularly important for DMS, which has a rather long T 2 even without decoupling. For the CODEX experiment, we implemented a new and improved phase cycle (34), which was developed for this purpose.…”

15N spin diffusion rate in solid-state NMR of totally enriched proteins: The magic angle spinning frequency effect

“…A feasible way to average the dipolar interaction is fast magic angle spinning (MAS) which is a prerequisite for many experiments in any way. However, in the case of 13 C nuclei, fast MAS may affect spin diffusion only for non-protonated carbons and has a vanishingly small influence for aliphatic carbons only [7]. This is obviously due to the much stronger 13 C-1 H interaction of aliphatic carbons (around 20 kHz) which can not be averaged out by MAS.…”

“…Solid-state exchange experiments [5,6], which are sensitive to motions in the millisecond to second time scale, suffer from spin diffusion as well: both spin diffusion and molecular motions result in a change of the orientation dependent resonance frequency of the nucleus under consideration and thus produce the same effect in the exchange spectra. Their separation by experimental means is difficult and time consuming at least, if possible at all [7]. Methods to separate the two effects past-acquisition were proposed but do not solve the problem completely, since the spin diffusion still determines the upper limit of the experimentally accessible dynamic range [8,9].…”