PENDANT-CAPPED PORPHYRINS .2. STRUCTURAL-ANALYSIS AND DYNAMICS OF THE BIPHENYL PENDANT-CAPPED PORPHYRIN MODEL OF CATALASE AND ITS FE(III) COMPLEX BY ONE-DIMENSIONAL AND 2-DIMENSIONAL H-1-NMR SPECTROSCOPY AND DISTANCE GEOMETRY MOLECULAR MODELING REFINEMENT

The solution structure of a phenol pendant-capped porphyrin [(PHPCP)H-2] has been determined by two-dimensional NMR spectroscopy and Distance Geometry calculations. Sixteen internuclear distances have been obtained from rotating frame NOE (ROESY) experiments. The refined structure shows a spiral shape of the cap allowing a minimum exposure of the porphyrin core to solvent. Docking of Fe(III) into the solution structure of (PHPCP)H-2 shows that the phenolate oxygen moves 1.5 angstrom toward the porphyrin plane and the porphyrin ring flattens. The assignment of C-13 resonances for (PHPCP)H-2 (heteronuclear C-13-H-1 chemical shift correlation) and partial assignment of C-13 resonances for (PPCP)Fe(III) have been done. The C-13 T1 relaxation times and restrained molecular dynamics calculations for (PHPCP)H-2 show a rigid structure of the cap and a pulsing motion along the z-axis. The overall rotational coefficient was found to be 3.71 x 10(-10) s. A variable temperature study of H-1 resonances establishes a structural change of (PHPCP)H-2 between 27-28-degrees-C. Low-temperature study on (PHPCP)H-2 shows that the coalescence temperature of the beta'beta'' pyrrole protons is -40-degrees-C, while for the NH amide protons <-93-degrees-C. Molecular dynamics studies on (PHPCP)H-2 and (PPCP)Fe(III) shows a flexibility of the former and a rigidity of the latter.