This usually involves the application of several dynamic NMR methods, covering different time windows [8] and [20]. Among them are the separated local-field (SLF) methods focussing on the motion of heteronuclear SIn dipolar tensors, which have been first developed for structural studies [21], [22] and [23], and later became a recognized and important tool for determining order parameters of fast-limit molecular motions [24], [25] and [26]. More recently, we have shown that SLF experiments, specifically the dipolar chemical-shift

correlation (DIPSHIFT) and Lee–Goldburg cross-polarization (LGCP) experiments, can also be used to extract the rate of molecular motions in the intermediate regime, i.e., rates in the μsμs to msms range [27] and [28]. This this website was achieved by comparison of experimental results and theoretical calculations by using either numerical simulations [29] and [30] or analytical fitting selleck products formulas based on the Anderson–Weiss (AW) approximation [31] and [32]. The next step was the augmentation of the dynamic window and the sensitivity to small-angle motions in DIPSHIFT experiments by introducing REDOR-type recoupling, which was dubbed as T2-recDIPSHIFTT2-recDIPSHIFT[33].

In this method, molecular motions are reflected in both the apparent averaging of the dipolar coupling and a T2T2-type intensity decay when the dynamics is in the intermediate regime. However, due to signal-function symmetry reasons, it was so far not possible to develop a fully analytical approximation to describe the T2-recDIPSHIFTT2-recDIPSHIFT experiments. We here present the derivation and a thorough test of an AW-based fitting formula for an earlier variant [34] of the recoupled DIPSHIFT experiment based upon constant-time recoupling (tCtC-recDIPSHIFT), recognizing that this experiment does not have the

mentioned limitation. It is based upon a simple incremented time shift of the REDOR π   pulse positions, holding all other pulse sequence check details timings constant. While this experiment has a narrower dynamic window than T2-recDIPSHIFTT2-recDIPSHIFT because the data does not show an apparent T2T2 effect, tCtC-recDIPSHIFT is more robust and less prone to setup problems and other experimental imperfections [33]. Based on the AW approach [31] recently extended by Hirschinger [32], the analytical formula now allows to use tCtC-recDIPSHIFT to study intermediate-regime motions in solids via a simple fitting procedure to the experimental data, which is a great advantage and enhances the practical applicability of the technique. The resulting molecular-dynamic parameters are the order parameter and the motional rate, both being reflected in the apparent averaging of the dipolar interaction tensor between chemically bonded nuclei.