Polarization inversion applied to proton MAS-NMR spectroscopy – Methylene and methine free proton NMR spectra

• Published in: Journal of magnetic resonance (1997) 2018-11, Vol.296, p.181-187
• Main Authors: Potnuru, Lokeswara Rao, Ramanathan, K.V.
• Format: Article
• Language: English
• Subjects: CPPI; Cross-polarization; Polarization inversion; Proton MAS NMR; Solid-state NMR; Spectral editing
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2018.09.011

[Display omitted] •Polarization-inversion proposed for editing solid state proton MAS spectra.•Absence of peaks of protons with attached carbon simplifies the spectrum.•Protons attached to nitrogen, oxygen or sulphur can be exclusively identified.•Increased resolution enables better estimate of chemical shifts.•Method also provides a means of estimating CH dipolar coupling. Polarization-inversion (PI) has been applied to proton magic angle spinning (MAS) NMR spectra recorded under fast MAS conditions. The combination of cross-polarization (CP) from carbon to proton and subsequent polarization-inversion produces strong oscillatory behavior in the proton signal intensities at high MAS speeds of 60 kHz. It is observed that by a suitable choice of the polarization-inversion time, a proton spectrum free of methylene and methine protons can be obtained. Such a spectrum, on the one hand, increases the resolution of the crowded proton spectrum and on the other hand provides exclusively chemical shifts of protons such as NH, OH and SH which might otherwise overlap with carbon attached protons. The oscillations observed during PI can also be used to estimate the dipolar coupling between proton and carbon by Fourier transformation of data acquired at equally incremented time periods. The utility of the above ideas has been demonstrated on a set of molecules with both 13C labeled and 13C in natural abundance.