Heteronuclear dipolar decoupling in liquid-crystal NMR using supercycled SW_f-TPPM sequences

摘要

Heteronuclear dipolar decoupling is an essential requirement for extracting structural information from the ~(13)C NMR spectra of liquid crystals. Efficient schemes for heteronuclear dipolar decoupling in such systems are formulated here by supercycling SW_f-TPPM, a sequence introduced recently for this purpose in rotating solids. These sequences are compared with two other commonly used decoupling schemes in liquid-crystal NMR, SPINAL-64 and SW_f-TPPM, by analyzing the intensities of various resonances in the proton decoupled ~(13)C spectrum of the liquid-crystal 4-n-pentyl-4′-cyanobiphenyl (5CB). The effectiveness of the decoupling programs with respect to experimental parameters such as RF field strength, decoupler offset frequency and phase angle is also presented.