13C NMR studies of liquid crystals

Efficient heteronuclear dipolar decoupling in solid-state NMR using frequency-swept SPINAL sequences

“…Highly efficient dipolar decoupling is also an important requirement in 13 C NMR studies of oriented media, in particular membrane [25,26] and liquid crystalline (LC) systems [24]. The demands for decoupling differ from those needed for rigid crystalline solids, as in the LC phase the dipolar interactions are scaled down by anisotropic thermal motions of the molecules.…”

“…In the area of oriented media, the application of efficient spin decoupling is especially important. Thus, NMR of liquid crystalline [24] and membrane systems [25,26] benefits from the resolution improvements that may be gained from high-performance proton decoupling. SPINAL was initially intended for liquid crystalline systems, but showed good efficiency also for rigid solid materials [6][7][8].…”

Recent NMR Studies of Thermotropic Liquid Crystals

“…Even though the use of 13 C T 1 relaxation in LCs has not been employed as much as other nuclei like proton and deuteron, numerous 13 C NMR studies in the past have been carried out to unravel order and molecular structure in various mesophases using either aligned or off-magic angle spinning LC samples [222,223]. In the case of aligned samples, 13 C NMR static spectra are characterized by relatively sharp signals with each chemical shift < δ i > of carbon i depending on an isotropic contribution, plus an anisotropic component.…”

“…Another straightforward way of getting the S 0 and D 0 of a phenyl ring is to make use of the C-H dipolar couplings (D CH ) from the two quaternary and two protonated (methine) carbons on a phenyl ring, according to [222,223]:…”

Improved heteronuclear dipolar decoupling sequences for liquid-crystal NMR

“…This affects the observation of both 1 H and 13 C nuclear spins on account of homonuclear and heteronuclear dipolar couplings. Unravelling information from 13 C spectra requires efficient heteronuclear dipolar decoupling at lower radiofrequency (RF) powers as RF heating can be deleterious to such systems [1][2][3]. Details of the use of NMR experiments, especially 13 C NMR, to the study of liquid crystals can be found in recent reviews [2,4].…”