Porphyrin Acceptor Research Articles

Dependence of electron transfer rates on donor-acceptor angle in bis-porphyrin adducts

We have prepared a series of bis-porphyrin molecules in which the angle between the donor and acceptor porphyrins is systematically varied. In these molecules, the intramolecular electron transfer rate varies by over 1 order of magnitude as the angle changes. This variance is anticipated by symmetry arguments which focus on the nodal properties of the molecules

Energy transfer in a rhodamine—porphyrin mixture monitored by optically detected magnetic resonance

Förster-type energy transfer (ET) in solutions containing rhodamine 6G and zinc-tetraphenylporphyrin has been studied using zero-field optically detected magnetic resonance (ODMR). Transitions between the porphyrin triplet sublevels monitored via the rhodamine (donor) fluorescence have the opposite sign as compared to those detected via the porphyrin (acceptor) fluorescence, due to Förster ET. Concentration quenching of porphyrin triplets and back ET from acceptor to donor results in a rather narrow concentration range for observing ODMR transitions via ET.

Photodriven transmembrane charge separation and electron transfer by a carotenoporphyrin–quinone triad

Photochemical transmembrane electron transfer processes are an integral part of natural photosynthetic solar energy conversion and are also central to the design of biomimetic energy conversion schemes1–6. Here we report the synthesis and membrane-associated photoelectrochemical properties of carotenoporphyrin–quinone triad (I), a compound containing a photochemically active porphyrin and electron donor and acceptor moieties, and with the molecular architecture necessary to span a phospholipid bilayer. On excitation of compound 1 by visible light, charge is separated across a planar phospholipid bilayer membrane (BLM) in an intramolecular step; in the presence of suitable electron donor and acceptor species in the aqueous phases, a steady-state photo-current is observed in an external circuit bridging the BLM. Artificial membranes containing I thus mimic key features of the photodriven transmembrane electron transfer processes characteristic of photosynthetic organisms.

Oxygen binding and activation with hemoproteins: model approach using iron-porphyrin complexes

Using myoglobin reconstituted with synthetic hemes, the struc— ture—oxygen binding relationship is investigated. Oxygen affinity is controlled by (1) the basicity of heme iron and (2) site specific inter— action of the peripheral substituents of heme with globin side chain. The effect of hydrophobic cavity size on the oxygen binding is examined by using the hydrocarbon chain—bridged metalloporphyrin—imidazole complexes (metal: Fe(II), Co(II)). The stability of oxy form of this model com— plexes changes with the fitness of the cavity. As oxygenase, L—tryptophan pyrrolase is taken up. Fe(II)porphyrin is shown to be the best model of its active site. This model complex effectively catalyzes the oxygenation of 3—substituted indoles to form products corresponding to formylkynurenine (the oxygenation product of L—tryptophan) with 40—50% conversion of the substrate. ESR analysis of the oxygenation system indicates cooperative electron transfer (COET) occurs from the substituted indole anion to the oxygen in the ternary system: indole anion Fe(II)porphyrin O2 This type of electron transfer is a new concept that should occur in any strong donor Fe(II)porphyrin acceptor system. The COET process for L' ''Fe(II)porphyrin. . '02 complex is discussed with the ionization potential value of L as a criterion.

Molecular complexes of porphyrins: effect on the rate of metalloporphyrin formation

Rates of the reaction between CuCl2 or ZnCl2 and protoporphyrin IX dimethyl ester have been measured in NN-dimethylformamide (dmf) or in a benzene–dimethylformamide binary solvent in the presence of the nitroarene acceptors 1,3,5-trinitrobenzene and 2,4,7-trinitrofluoren-9-one. The results show that the acceptor–porphyrin molecular complex cannot react with the metal. A mechanism for the formation of metalloporphyrins is evaluated on the basis of these studies.