ISSN:
1089-7690
Quelle:
AIP Digital Archive
Thema:
Physik
,
Chemie und Pharmazie
Notizen:
This paper presents a theoretical description of continuous wave (CW) high frequency Lee–Goldburg cross polarization magic angle spinning (LG–CPMAS) nuclear magnetic resonance experiments. The full time-dependent LG–CPMAS Hamiltonian is replaced by its zero order time-independent Hamiltonian in the interaction representation. Carbon signal enhancements of LG–CPMAS experiments are calculated for spin systems consisting of six 1H nuclei coupled to one 13C nucleus. These simulations are based on Floquet theory calculations, explicitly taking into account the time dependence because of magic angle spinning, and calculations based on the zero-order Hamiltonian. The good agreement between these calculations justifies the use of the zero-order Hamiltonian. The time-dependent intensities of the cross peaks in heteronuclear 13C–1H correlation spectra, extracted from 3D LG–CPMAS experiments on a natural abundant DL–alanine sample with increasing CP mixing times, are in good agreement with the theoretical intensities simulated by using the zero-order Hamiltonian. The approximated LG–CPMAS Hamiltonian can be used to obtain structural information about a proton coupled to a single carbon. The simulated intensities of the carbon signals of an isolated 13C–1H group and a 13C–1H group that is coupled to additional protons, measured by LG–CPMAS experiments with increasing CP mixing times, are compared. This study suggests that the buildup curve of each LG–CPMAS carbon signal and its Fourier transformed CP spectrum can be interpreted in terms of a single distance between the observed 13C and its nearest proton, if the additional protons are removed from this carbon by at least 1.2 times this distance. © 2000 American Institute of Physics.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.481281
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