Journal of the American Chemical Society, Vol.120, No.40, 10453-10462, 1998
C-13-C-13 correlations and internuclear distance measurements with 2D-MELODRAMA
Under magic-angle spinning (MAS), the 2D-MELODRAMA pulse sequence reintroduces homonuclear dipolar couplings, thereby allowing internuclear correlations to be determined. The evolution of the density matrix under the average Hamiltonian established under the 2D-MELODRAMA pulse sequence has been evaluated, and closed-form expressions for the dependence of cross-peak intensity as a function of the dipolar mixing time are presented. In the case of sodium proprionate-2-3-C-13(2) (>90% C-13) it is shown that analysis of cross-peak intensity vs mixing times allows estimates of dipolar coupling with an accuracy comparable with the 1D-MELODRAMA experiment. The potential for simultaneous multiple internuclear correlations and distance measurements in spin systems for which there is not a large difference in resonance frequencies is illustrated with glucose-C-13(6) (36% uniformly labeled). It is shown that multiple correlations for each ring carbon can be detected and good estimates of the corresponding internuclear distances can be extracted from analysis of cross-peak intensities as a function of the dipolar recoupling time.
Keywords:NUCLEAR-MAGNETIC-RESONANCE;ANGLE SPINNING NMR;ROTATINGSOLIDS;DIPOLAR COUPLINGS;CONFORMATION;SPECTROSCOPY;DYNAMICS