Multiple-Pulse Mixing Sequences That Selectively Enhance Chemical Exchange or Cross-Relaxation Peaks in High-Resolution NMR Spectra

摘要: Abstract Rotating-frame NMR experiments which either emphasize or suppress cross relaxation, and simultaneously TOCSY, COSY, zero-quantum peaks in spectra, are presented analyzed. The new rely on mixing sequences follow naturally from the transverse -ROESY (Tr-ROESY) sequence of Hwang Shaka, applicable to larger molecules solution (spin diffusion limit). In first variant a modified Tr-ROESY sequence, called multiple-pulse ROESY (MP-ROESY), is used enhance cross-relaxation peak intensity compared Tr-ROESY; second, phase-modulated CLEAN chemical exchange (CLEANEX-PM), greatly attenuated. two methods thus complementary: MP-ROESY observe Overhauser peaks, CLEANEX-PM eliminate them, permitting clear observation alone. techniques examined by theory experiment. Practical guidelines that will result high-quality spectra given, including judicious use continuous weak static magnetic field gradients.