Polarization transfer from remote protons in 13C CP/MAS

J Magn Reson. 2006 Nov;183(1):68-76. doi: 10.1016/j.jmr.2006.07.019. Epub 2006 Aug 17.

Abstract

An experimental procedure for CP/MAS polarization transfer from remote 1H nuclear spins is introduced, which is applicable to protonated carbons in organic solids. It is based on preparing a state of non-uniform polarization, where directly bonded 13C-1H nuclei are de-polarized prior to recording the CP buildup curve. This curve is then expected to quantify the polarization transfer from remote protons only. The ability of the cross-polarization/polarization-inversion (CPPI) sequence to generate an initial state suitable for remote 1H CP/MAS scheme is analyzed both theoretically and experimentally. Confining to aliphatic groups, it was found that complete de-polarization of bonded proton is possible in the case of CH, whereas for CH2 and CH3 moieties only a partial de-polarization can be achieved. The theoretical predictions have been verified in practice for the particular case of L-alanine. The significance of the results from fundamental, as well as practical point of view, is also discussed. In particular, it is shown that: (i) the coherent description of polarization transfer under CP/MAS, including 1H polarization redistribution, is valid over time-scales longer than commonly assumed in many treatments of cross-polarization, and (ii) the remote protons polarization transfer curve can be used in combination with the conventional CP/MAS curve to get additional structural and dynamical information in organic systems.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / analysis*
  • Alanine / chemistry*
  • Carbon Isotopes / analysis
  • Carbon Isotopes / chemistry
  • Computer Simulation
  • Magnetic Resonance Spectroscopy / methods*
  • Models, Chemical*
  • Models, Molecular*
  • Protons*

Substances

  • Carbon Isotopes
  • Protons
  • Alanine