Study Of Some Problems In Dynamic Nuclear Magnetic Resonance

Nuclear magnetic resonance has proved to be very useful in studying molecular dynamics. This dissertation is focused on some problems in study of ~1H-~1H homonuclear cross relaxation and chemical exchange. The contents include: 1) The proton-proton intemuclear distances for the rigid part of a small peptide, a cyclic pentapeptide, have been measured. 2). The isolated spin pair approximation (ISPA) method can be used only when a single correlation time is assumed. When correlation times in a molecule differ greatly, it has been suggested that the correlation times be grouped into a few groups and the ISPA method can be still useful. 3). A new method, called two-field (2F) NOESY method, has been developed for measuring the correlation times of the proton-proton vectors for the cyclic pentapeptide. The method is based on the standard NOE theory without any approximation and is suitable for study of molecules under the critical point (ωτ_c≈1.12). 4). When the full matrix analysis method failed for multiple-site exchange system where the exchange rates differ in great deal, it has been demonstrated that the geometric method can give a satisfactory result. 5) The structure of microcystin-LR has been studied by 2D NOESY method and the structure of its cyclic part has been determined. 6) The inversion-recovery data for a fast exchange system have been discussed.In this dissertation, the correlation times of a small peptide is discussed. The Stokes-Einstein model is used. Through 2D NOESY experiments at different temperatures, the rigid parts of cyclo-(Arg-Gly-Asp-D-Phe-Val-) pentapeptide and its isomer cyclo-(D-Val-Phe-D-Asp-Gly-D-Arg-) pentapeptide are specified. The correlation times of the proton-proton vectors and simultaneously the intemuclear distances are determined. It is found that when the...