Design of Spatial Disposition of Anionic Porphyrins in Matrices of Ammonium Bilayer Membranes

A methodology to place charged porphyrin derivatives in specific spatial arrangements in matrices of ammonium bilayer membranes was explored. Aqueous mixtures of anionic copper(II) porphyrins and bilayer dispersions of single-chain and double-chain ammonium amphiphiles were cast on Teflon sheets to produce regular multilayer films. The orientation of doped copper(II) porphyrins was determined by anisotropies of ESR spectral patterns that were dependent on the disposition of the cast film in the magnetic field. Quantitative estimates of the porphyrin orientation were made possible by elaborate computer simulation of the observed spectra. The mode of porphyrin orientation is determined by the distribution of anionic substituents on guest porphyrins and the supramolecular structure of host bilayers. Type III porphyrins, which possess evenly distributed anionic substituents, are incorporated horizontally on the ammonium bilayer surface. Type I porphyrins, in which anionic substituents are localized on one side of the porphyrin ring, are incorporated into the spacer portion of the bilayer parallel to the molecular axis in the case of the double-chain ammonium amphiphile. In contrast, these porphyrins cannot penetrate into the bilayer interior of the single-chain amphiphile and show random incorporation. A type II porphyrin with three sulfonate substituents gives a horizontal orientation on the nonpenetrable bilayer of the single-chain amphiphile and a random orientation in the bilayer of the double-chain amphiphile. The standard deviation of the porphyrin orientation was always 15°, implying that the orientational fluctuation is derived from undulation of the cast film. The microscopic orientation is thus highly specific. The present findings should be instrumental in designing biomimetic functional systems.