Two-dimensional exchange NMR in static powders: interchain carbon-13 spin exchange in crystalline polyethylene

Solid‐State NMR Investigation of Ligand Mobility and Reactivity in Transition Metal Complexes

“…[22] Dynamics with correlation times slower than the lifetime of the NMR signals that do not affect the NMR spectrum can be detected by 2D-exchange techniques. [23] A large array of new 2D pulse sequence is now available for spectroscopists, however, a detailed explanation of all these solid-state NMR techniques goes beyond the aim of this review, so, for a complete and rigorous description, the reader should consult authoritative texts.…”

Initial Conditions for Carbon-13 MAS NMR 1D Exchange Involving Chemically Equivalent and Inequivalent Nuclei

“…Center: Corresponding simulated spectra using Eq. [4] and parameters given in Tables 1 and 2 leading. In reality the alternate polarization of the ssb is also present in the tr-ODESSA throughout the mixing time as in normal ODESSA, but is canceled by the T R /2 delay that follows the detection pulse.…”

“…The selective excitation of carbon 1 was achieved by a rotor-synchronized SELDOM train of twenty 90°pulses with t d ϭ 1 ms. Center: Corresponding simulated spectra using Eq. [4] and parameters given in Tables 1 and 2 In the next section we apply the various sequences to the enriched tropolone sample. As discussed above, this sample exhibits exchange both between congruent and between inequivalent sites, thus allowing us to evaluate the merits and limitations of the various methods.…”

“…Simulated spectra calculated using Eq. [4] are shown in the center column. Relevant plots are given on the right-hand side.…”

Determination of Polypeptide Backbone Dihedral Angles in Solid State NMR by Double Quantum 13C Chemical Shift Anisotropy Measurements

“…For unoriented solid samples, the measurement of dihedral angles (or more generally the relative orientation of two chemical functional groups that are close in space) has received considerable attention in recent years . Dihedral angles define the relative orientation of rigid structural elements and can be determined from measurements of correlations between two spin interaction tensors on two adjacent structural elements, provided that the tensor orientations relative to the molecular frame are known (27)(28)(29)(30)(31)(32)(33)(34). In a polypeptide, the dihedral angles φ and ψ define the relative orientation of two adjacent peptide planes.…”