Abstract:Four new organic hosts are described that contain a phthalocyanine core to which four crown ether rings are attached.These hosts include a free base phthalocyanine with 18-crown-6 rings and three copper phthalocyanines with 15-crown-5, 18-crown-6, and 21-crown-7 rings. The macrocycles are synthesized from benzo crown ethers in three steps. In solution the phthalocyanines tend to form aggregates. This aggregation is affected by the polarity of the solvent and the presence of alkali-metal salts, which coordinate to the crowns. Cations with diameters that match the diameters of the crown ether rings form 4:4 host-guest complexes with the new hosts. Complexes with 8:4 host-guest stoichiometry are formed when the diameters of the cations exceed that of the crown ether rings. Binding free energies of the copper phthalocyanine hosts are presented and compared to those of benzo crown ethers. The binding profiles support the results of UV-vis experiments; i.e., that large cations induce aggregation of the macrocycles.
We describe a synthetic model of a natural channel-forming ionophore. It is based on a polymer with a rigid backbone, viz. a polymer of an isocyanide, [R-N = C < ] n. Each of the polymer side chains R contains a crown ether ring. Due to the rigid 4/1 helical structure of the polymer the crown ether rings are cofacially stacked and form four channels which run parallel to the polymer helix axis. The channels are better ion-complexing agents than low molecular weight crown ethers. Evidence is presented th a t the channel structures can be incorporated in the bilayers of dihexadecyl phosphate vesicles. Electron microscopic data, fluorescence experiments, as well as entrapm ent studies indicate th a t the vesicle bilayers are not disrupted by the channels. Ion transport studies are presented which reveal th a t the channel structures enhance the perm eability of the dihexadecyl phosphate m em branes by forming transm em branous pores.
The Cytochrome P-450 dependent monooxygenases are mem brane-bound enzymes that catalyze a great variety of reactions, among which is the epoxidation of alkenes by molecular oxygen.1 > = < -I-0 2 -+ 2H 4-2e O
>^< -1 -HoOThe active center of the enzymes contains an iron(III) proto porphyrin IX and axial thiolate ligand. After being reduced to iron(II) this center binds and cleaves molecular oxygen, whereupon water and a high-valent iron-oxo complex are formed. The latter species transfers its oxygen to a substrate molecule.1,2 The electrons required in the process are provided by N A D PH via a coupled electron transferring enzyme system.1 We describe here a synthetic model system of cytochrome P-450 which incorporates all the features of the natural enzyme system, i.e., (i) a membraneously bound metalloporphyrin (complex 1), (ii) an axial ligand (A^-methylimidazole), (iii) an electron donor (colloidal P t-H 2),2a (iv) an electron carrier (methylene blue), and (v) a membrane system (polymerized vesicles of 2) which holds com ponents within its bilayer or within its inner aqueous compartment (Figure 1).[Tetrakis[4-(hexadecyloxy)phenyl]porphyrinato]manganese-(III) acetate (1) was synthesized from the corresponding tetrakis(hydroxyphenyl) derivative and «-hexadecyl bromide by reaction with base in 3:1 v/v DMF-toluene. Compound 1 (2.7 X 1 0~5 M) and the isocyano surfactant 23 (5 X 10"3 M) were cosonicated for 30 min in water at 25.0 °C. Subsequent polymerization3 with nickel capronate (8.5 X 10-5 M) for 24 h yielded polymerized vesicles which had 1 incorporated into their bilayers. This was checked by dialysis and chromatographic procedures in combi nation with UV-vis. In a similar way, using an aqueous solution of K2PtCl4 (10~3 M), polymerized vesicles were prepared which, after passing over an anion-exchange resin (Dowex 1-X2, Cl_-(1) White, R. E.; Coon, H. J. Annu. Rev. Biochem. 1980, 49, 315-356. (2) For model studies on cytochrome P-450, see: (a) Tabushi, I.; Morimitsu, K. J. Am. Chem. Soc. 1984, 106, 6871-6872. (b)
An artificial ion channel, composed of stacks of crown ether rings, forms a pore in bilayers of dihexadecyl phosphate vesicles and facilitates the transmembranous transport of cobalt ions.
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