Spin-locked multiple quantum coherence for signal enhancement in heteronuclear multidimensional NMR experiments.
For methine sites the relaxation rate of 13C-1H two-spin coherence is generally slower than the relaxation rate of the individual 13C and 1H single spin coherences. The slower decay of two-spin coherence can be used to increase the sensitivity and resolution in heteronuclear experiments, particularly those that require correlation of H alpha and C alpha chemical shifts. To avoid dephasing of the two-spin coherence caused by 1H-1H J-couplings, the 1H spin is locked by the application of a weak rf field, resulting in a spin-locked multiple quantum coherence. For a sample of calcium-free calmodulin, use of the multiple quantum approach yields significant signal enhancement over the conventional constant-time 2D HSQC experiment. The approach is applicable to many multidimensional NMR experiments, as demonstrated for a 3D 13C-separated ROESY CT-HMQC spectrum.
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
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D000818:Animals; D002147:Calmodulin / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D013113:Spin Labels
D002147:Calmodulin; D013113:Spin Labels