1. (a) This study was supported by grants from the National Institutes of Health (NIH Grant No. DK-16595), the National Science Foundation facilities programs (NSF-MRI-CHE-9724392, NSF-ARI-9602708, NSF-ARI-9601831, and NSF-ARI-ST-193-13519), the Cambridge Isotopes Laboratories (CIL Research Grant Program), and the Committee on Research of UC Riverside. Selected chemicals were also provided by Solvay, Hoffmann-LaRoche, and Leo Pharmaceuticals.