H-1 AND C-13 NMR-STUDIES ON THE STRUCTURE OF MICELLES ENCAPSULATING HEMES IN AQUEOUS SODIUM DODECYL-SULFATE SOLUTIONS

Detailed 1H and 13C NMR studies on aqueous SDS (sodium dodecyl sulfate) detergent micelles containing ferric porphyrin complexes have been carried out to determine the structural disposition of the porphyrin complex and the conformation of the surfactant molecules inside the micellar cavity. The dipolar interactions between the micellar atoms and the paramagnetic iron center gives rise to enhancement of line widths as well as changes in the chemical shifts of the micellar atoms. In the case of low-spin ferric porphyrins this intermolecular dipolar shift is dominated by g anisotropy while with high-spin ferric porphyrins this shift originates from zero-field splitting. Measurements of nuclear spin-lattice relaxation rates for the micellar atoms have been successfully used to elucidate the structural disposition of the surfactant molecules in the aqueous detergent micelles containing ferric protoporphyrin complexes. The average values of distances of different carbon centers in a surfactant molecule from the iron center obtained from the spin-lattice relaxation enhancement were fitted to different models of micellar structure to obtain the average configuration of the detergent molecules and the position of the heme complex inside the micelles. © 1990 American Chemical Society.