V. Ladizhansky et S. Vega, Polarization transfer dynamics in Lee-Goldburg cross polarization nuclear magnetic resonance experiments on rotating solids, J CHEM PHYS, 112(16), 2000, pp. 7158-7168
This paper presents a theoretical description of continuous wave (CW) high
frequency Lee-Goldburg cross polarization magic angle spinning (LG-CPMAS) n
uclear magnetic resonance experiments. The full time-dependent LG-CPMAS Ham
iltonian is replaced by its zero order time-independent Hamiltonian in the
interaction representation. Carbon signal enhancements of LG-CPMAS experime
nts are calculated for spin systems consisting of six H-1 nuclei coupled to
one C-13 nucleus. These simulations are based on Floquet theory calculatio
ns, explicitly taking into account the time dependence because of magic ang
le spinning, and calculations based on the zero-order Hamiltonian. The good
agreement between these calculations justifies the use of the zero-order H
amiltonian. The time-dependent intensities of the cross peaks in heteronucl
ear C-13-H-1 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 z
ero-order Hamiltonian. The approximated LG-CPMAS Hamiltonian can be used to
obtain structural information about a proton coupled to a single carbon. T
he simulated intensities of the carbon signals of an isolated C-13-H-1 grou
p and a C-13-H-1 group that is coupled to additional protons, measured by L
G-CPMAS experiments with increasing CP mixing times, are compared. This stu
dy suggests that the buildup curve of each LG-CPMAS carbon signal and its F
ourier transformed CP spectrum can be interpreted in terms of a single dist
ance between the observed C-13 and its nearest proton, if the additional pr
otons are removed from this carbon by at least 1.2 times this distance. (C)
2000 American Institute of Physics. [S0021-9606(00)00116-1].