NOESY around the critical point Omega Tauc = 1.12. Precise determination of protonproton distances and reorientation correlation times with two-field NOESY

When nuclear Overhauser enhancement spectroscopy (NOESY) experiments are performed around the critical point Omega Tauc = 1.12, internuclear cross-relaxation rates are dependent on the resonance frequency omega, where tauc is the reorientation time of the distance vector between two magnetic dipoles. Therefore, the correlation times and, consequently, the internuclear distances can be determined precisely by measuring the cross-relaxation rates under two magnetic fields. An application with a cyclic pentapeptide is given as an example, demonstrating the use of the two-field NOESY method in molecular structure studies. NOESY experiments with mixing times beyond 500ms are discussed.