Polarization transfer from remote protons in 13C CP/MAS.
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.
Tripon
Carmen
C
National Institute for R&D of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj, Romania.
Aluas
Mihaela
M
Filip
Xenia
X
Filip
Claudiu
C
D000409:Alanine / Q000032:analysis* / Q000737:chemistry*; D002247:Carbon Isotopes / Q000032:analysis / Q000737:chemistry; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D011522:Protons
D002247:Carbon Isotopes; D011522:Protons; D000409:Alanine