Octaethylporphyrinate haem complexes encapsulated inside aqueous detergent micelles: a spectroscopic study

Abstract

NMR and optical spectral studies have been made for monomeric aqua and hydroxo complexes of iron(III) 2,3,7,8,12,13,17,18-octaethylporphyrin in aqueous sodium dodecyl sulphate (sds) detergent micellar solutions. Both the aqua and hydroxo complexes are found to be high spin (S= 5/2). The pK_a for the aqua ⇌ hydroxo equilibrium was found to be 4.8. Iron(II) complexes of octaethylporphyrin in different spin states and co-ordination geometries have also been stabilized in aqueous micellar solution. The detailed structural disposition of the porphyrin complex and the conformation of the surfactant molecules inside the micellar cavity have also been investigated using ¹³C NMR spectra of aqueous sds detergent micelles containing the complex. The average values of the distances of the different carbon centres in a surfactant molecule from the iron obtained from spin-lattice relaxation enhancement measurements were fitted to a spherical model of micellar structure to obtain the average configuration of the detergent molecules and the position of the complex inside the micelles.