| Research Abstract |
PFG NMR, especially used for diffusion experiment, and CSI (cold-spray ionization)-MS has been our major subject for solution structure analysis in recent years. X-ray analysis elucidating solid structure is also contributed to this study in some cases. It was found that some steroid compounds behave as the large-scale aggregated chain structure in solution. This unprecedented phenomenon was definitely confirmed by using CSI-MS and PFG NMR Characteristic chain structures based on strong intermolecular hydrogen bonding in the case of cortisone was clearly observed in solution exhibiting series of plural clusters, which was assigned up to thirteen aggregates. On the other hand, progesterone slightly weak intermolecular interaction was predicted form CSI-MS because ion peaks assigned only up to trimeric cluster. This result is identical with that obtained from X-ray analysis. Recently, it was demonstrated that NMR diffusion studies is an useful method for the characterization of a variety
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of interaction system in solution. NMR diffusion experiments were carried out on a LA-600 by using BPP-STE method. Calibration curve obtained from observed diffusion coefficients and calculated molecular volume. In the case of progesterone, observed diffusion coefficient (6.98×10^<-10>m^2/s) is as nearly same as calculated. The reason for this result indicated that progesterone has no intermolecular interaction in solution as well as in the crystal. On the contrary, diffusion coefficient of cortisone (5.58×10^<-10>m^2/s) exhibits slightly different from calculated values, presumably because hydrogen bonding occurs to afford molecular cluster. In consequence, these steroid compounds appeared to maintain ordered clusters, based on hydrogen, bonding in diluted solution, instead diffused randomly as individual molecules, as has been generally accepted.
Multidimensional T_<1ρ^->, diffusion-filtered and diffusion-ordered NOESY techniques are very suitable techniques for identifying segments of a ligand binding with a protein receptor in the drug discovery process. Less
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