Fig. 2
From: Solid-state NMR at natural isotopic abundance for bioenergy applications
Technical aspects of ssNMR spectroscopy. a Commonly utilized NMR-active nuclei in biomolecular research, highlighting their relative sensitivities and natural abundances. 13C and 1H nuclei are predominantly employed in studies of lignocellulosic materials. b NMR interactions in solids: overview of key NMR interactions such as Zeeman, dipolar couplings, and chemical shielding interactions. These ranges highlight typical observations, though variations may occur based on molecular structure and local environments. c Chemical shift range for 13C nuclei, spanning from 0 to 220 ppm, utilized for structural elucidation. d Diagram illustrating the relationships among the magic angle (θr), the laboratory frame, the rotor frame, and the principal axis system, with the sample rotor oriented at the magic angle of 54.7°. e Representative solid-state NMR pulse sequences of initial polarization, including direct polarization (DP), cross-polarization (CP), and dynamic nuclear polarization (DNP). The asterisk (*) indicates RAMP-CP, which mitigates rf inhomogeneities and enhances polarization transfer efficiency. The ramp can be applied on either the 1H or X channel. f Modified CP sequences for side-band suppression and quantitative detection. g 1D 13C NMR spectra of glycine acquired under static conditions and at various magic angle spinning (MAS) rates. The asterisks (*) denote spinning sidebands, which decrease in intensity with increasing MAS frequency, leading to enhanced resolution of the isotropic chemical shifts. h 1D 13C NMR spectra of glycine recorded with and without heteronuclear dipolar decoupling. The spectrum without decoupling exhibits significant line broadening due to 1H–13C dipolar interactions, while the application of decoupling yields sharper 13C resonances, enhancing spectral resolution. All experiments in g and h were conducted on a 600-MHz spectrometer with a 4-mm HXY Phoenix probe, under 13.5 kHz MAS at 290 K, with swept-frequency two-pulse phase modulation (SWf-TPPM) heteronuclear dipolar decoupling sequence at the NREL