Showing papers on "Porphyrin published in 1981"
634 citations
TL;DR: In this paper, a positively charged, water-soluble zinc porphyrin photosensitises the reduction of water to H2 with high efficiency, using MV2+ as electron relay and EDTA as sacrificial electron donor.
Abstract: We have confirmed an earlier report by Kalanasundaram and Gratzel that a positively charged, water-soluble zinc porphyrin photosensitises the reduction of water to H2 with high efficiency. Using MV2+ as electron relay and EDTA as sacrificial electron donor, the quantum yield for production of ½H2 is ca. 0.6. The reaction mechanism involves reduction of MV2+ by triplet porphyrin and the porphyrin π-radical cation so produced is reduced by EDTA. The concentrations of reactants have been optimised for production of H2 and to limit destruction of the porphyrin. Under optimised conditions the turnover with respect to the porphyrin can reach 6000.In addition, some consideration has been given to ways of improving oH2 and of increasing the fraction of sunlight that can be harvested. In this respect, Cd porphyrins may possess suitable properties.Finally, we note that the porphyrin π-radical cation may possess the thermodynamic capacity to oxidise water to O2, but this is very much borderline.
141 citations
TL;DR: Comparison of experimentally obtained average pi-electron spin densities with theoretical predictions for a 4-fold symmetric porphyrin pi-cation radical is supportive of a 2A2u assignment for the radical's electronic state.
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103 citations
Journal Article•
TL;DR: Hydrophilic components of HPD were gradually accumulated by L1210 cells via a mode of binding not readily dissociated by washing and appear to be responsible for the preferential affinity of this product for neoplastic cells.
Abstract: A hematoporphyrin derivative (abbreviated in the literature as "HPD") has been used successfully for phototherapy of tumors in the clinic. The chemical nature of HPD, a complex mixture of porphyrins, is not fully understood. This study was designed to provide an explanation for the superior tumor-localizing ability of HPD. Chromatographic behavior, hydrophobicity, transport, binding, and photosensitizing capacity of different porphyrins were examined and compared. Biological studies were carried out using murine leukemia L1210 cells in vitro. The initial rate of porphyrin uptake was a function of drug hydrophobicity. The most hydrophobic components of HPD were therefore the most potent photosensitizers when irradiation followed a 10-min porphyrin-loading incubation. But these and other hydrophobic porphyrins were readily washed from cells by medium containing serum. Hydrophilic components of HPD were gradually accumulated by L1210 cells via a mode of binding not readily dissociated by washing and appear to be responsible for the preferential affinity of this product for neoplastic cells. A portion of the tightly bound porphyrin could not be dissociated by sodium dodecyl sulfate:polyacrylamide gel electrophoresis but remained bound to a low-molecular weight membrane component.
100 citations
TL;DR: The results unequivocally establish that the 4-alkyl groups in DDC and dDEP are the source of the N-alksyl group in N-methyl- and N-ethylprotoporphyrin IX, respectively, and strongly suggest that the alkyl group is transferred to the prosthetic heme of cytochrome P-450 during catalytic processing of the substrate by the enzyme.
95 citations
TL;DR: It is suggested that singlet oxygen is the most important reactive oxygen species in small organic molecules, biomolecules, mitochondria and red cells.
93 citations
TL;DR: Strong support is provided by the structure of this porphyrin for the contention that the prosthetic heme of cytochrome P-450 is alkylated during attempted transfer of the catalytically-activated oxygen to the pi-bond of destructive unsaturated substrates.
TL;DR: In this paper, a charge iterative extended Hueckel calculations are presented for compound II, the one-electron oxidation intermediate of horseradish peroxidase (HRP), and for compounds I, the two-electRON oxidation transients of HRP and catalase (CAT) observed in the catalytic cycles of the hydroperoxidases enzymes.
Abstract: Charge iterative extended Hueckel calculations are presented for compound II, the one-electron oxidation intermediate of horseradish peroxidase (HRP), and for compounds I, the two-electron oxidation transients of HRP and catalase (CAT) observed in the catalytic cycles of the hydroperoxidase enzymes. Compound II is described in terms of a ferryl configuration (O = Fe/sup IV/), and compounds I are described as ferrylporphyrin ..pi..-cation radicals. The validity of the iron ..pi..-cation calculations is supported by favorable comparison of parallel computations for porphyrin ..pi.. cations of diamagnetic metals with new and previously reported ESR results for radicals of zinc tetrabenz-, meso-tetramethyl, (/sup 14/N and /sup 15/N) tetraphenyl-, and magnesium (/sup 1/H and /sup 2/H) octaethylporphyrins. The calculated electronic configurations and unpaired spin density profiles for the ferryl ..pi.. cations satisfactorily account for the physical properties reported for compounds I of HRP (in the native protoporphyrin IX form or reconstituted with deuteroporphyrin), chloroperoxidase, and CAT. The ground states of the ..pi.. cations, a/sub 1u/ or a/sub 2u/, are determined by peripheral substitution and axial ligation, and the axial ligand of CAT I is predicted to differ from that of HRP I. The combination of model studies and calculations suggests that /sup 2/H, /sup 13/C,more » and /sup 15/N NMR studies of isotopically substituted proto and deutero HRP I would confirm the electronic profiles predicted. /sup 15/N NMR in particular would clearly discriminate between a/sub 1u/ and a/sub 2u/ configurations. As an additional test of the ferryl ..pi..-cation hypothesis, calculations are presented for a proposed ferrylchlorin ..pi.. cation of Neurospora crassa catalase, which contains an iron chlorin prosthetic group. Compound I of this unusual heme is predicted to occupy an a/sub 2/ ground state with the spin distribution and optical spectra reported here for synthetic chlorin radicals.« less
TL;DR: In this article, the tripmultiplet states result from interaction between the metal d-orbitals and the porphyrin (ππ*) excited triplet states, and the rate constants for deactivation of the tri-parameter states depend markedly upon the nature of the central metal ion and are much faster for MnIII and FeIII than for CuII and CrIII.
Abstract: The absorption spectra of paramagnetic transition metal porphyrins consist of (ππ*), charge-transfer and tripmultiplet transitions. The tripmultiplet states result from interaction between the metal d-orbitals and the porphyrin (ππ*) excited triplet states. For CuIITPP, luminescence occurs from the lowest energy tripquartet state whilst CrIIITPP shows luminescence from tripquartet and tripsextet states. Luminescence from MnIIITPP and FeIIITPP is much less efficient and originates from the second tripmultiplet state. The rate constants for deactivation of the tripmultiplet states depend markedly upon the nature of the central metal ion and are much faster for MnIII and FeIII than for CuII and CrIII. Luminescence was not observed for FeIITPP, possibly due to the presence of a low-lying c.t. state.
TL;DR: Kinetic studies of the hematoporphyrin–sensitized photooxidation of l‐tryptophan and tryptamine at pH 10 in either homogeneous aqueous solutions or in aqueously dispersions of Triton X–100 and cetyltrimethylammonium bromide micelles indicate that the indole substrates are attacked via a mixed type I/type II mechanism.
Abstract: — Kinetic studies of the hematoporphyrin–sensitized photooxidation of l-tryptophan and tryptamine at pH 10 in either homogeneous aqueous solutions or in aqueous dispersions of Triton X–100 and cetyltrimethylammonium bromide micelles indicate that the indole substrates are attacked via a mixed type I (electron transfer from triplet dye)/type II (1O2-involving) mechanism. Both reactive intermediates, generated by micelle-solubilized hematoporphyrin, can diffuse to attack substrate molecules located in either the bulk aqueous phase or a different micelle. In particular, incorporation of the substrate into a micelle has only minor effects on its reactivity toward1O2, although the 1O2—indole interaction appears to be more efficient in cationic micelles owing to a favourable orientation of the target with respect to the attacking species. On the other hand, the electron transfer from triplet porphyrin to a micellized substrate is virtually non-operative when the latter is located in an anionic micelle, whereas in neutral or cationic micelles, the efficiency of the process is again controlled by the substrate orientation. Studies of tryptamine photooxidation sensitized by meso-tetra-(4-sulfonato-phenyl) porphine in the presence of sodium dodecylsulphate micelles lend further support to the abovementioned conclusions.
TL;DR: Correlations between the observed frequency of a polarized mode in the 1560-1600-cm-1 region and the heme iron spin and coordination geometry have been developed, and normal coordinate analysis developed by Abe and co-workers is used to rationalize the dependence of the various modes on porphyrin geometry and peripheral substitution.
Abstract: Laser lines in resonance with the Soret band optical transitions of several heme proteins and heme model compounds have been used to obtain Raman spectra of these species. Correlations between the observed frequency of a polarized mode in the 1560-1600-cm-1 region and the heme iron spin and coordination geometry have been developed. The position of this band is also a function of the pattern of porphyrin pyrrole ring beta-carbon substitution, and therefore structural information can be extracted from the Raman data only after this dependence has been taken into account. Quantitative correlations between the frequency of this band and the porphyrin core size are presented for three commonly occurring classes of heme compounds: (a) protoheme derivatives, (b) iron porphyrins in which all ring positions are saturated, and (c) heme alpha species. A polarized mode in the 1470-1510-cm-1 region is also consistently enhanced upon Soret excitation of these compounds, but is relatively insensitive to peripheral substituents, and can be used in conjunction with the polarized mode described above to assign heme geometries. In the frequency region above 1600 cm-1, a vibration is observed which also responds to changes in porphyrin geometry. However, this band is sometimes obscured by vibrations of unsaturated beta-carbon substituents, particularly in the case of protoheme derivatives. The normal coordinate analysis developed by Abe and co-workers [Abe, M., Kitagawa, T., & Kyogoku, Y. (1978) J Chem. Phys. 69, 4526-4534] is used to rationalize the dependence of the various modes on porphyrin geometry and peripheral substitution.
TL;DR: The hepatic pigment accumulated in 3,5-diethoxycarbonyl-1,4-dihydrocollidine-treated rats, which has been reported to inhibit ferrochelatase, has been isolated and purified and the four isomers of N-methylprotoporphyrin IX have been chemically synthesized, independently characterized, and used to confirm the structures of the biologically products.
Abstract: The hepatic pigment accumulated in 3,5-diethoxycarbonyl-1,4-dihydrocollidine-treated rats, which has been reported to inhibit ferrochelatase, has been isolated and purified. The pigment has been resolved into one major, one minor, and two trace components, all of which appear to be isomeric porphyrins. The major fraction has been unambiguously identified by spectroscopic methods as the isomer of N-methylprotoporphyrin IX (isolated as the dimethyl ester) in which vinyl-substituted pyrrole ring A is methylated. The minor product appears to be an isomer of the same porphyrin with the N-methyl group on propionic acid-substituted ring C, and the trace components have the same high-pressure liquid chromatography retention times as the other two possible isomers of the porphyrin. The four isomers of N-methylprotoporphyrin IX have been chemically synthesized, independently characterized, and used to confirm the structures of the biologically products.
TL;DR: In this article, photo-induced redox reactions employing the anionic porphyrins meso-tetrakis(p-sulfonatophenyl)porphyrin and its palladium(II) complex (2) as excited substrates and various alkylviologens as quenchers have been studied in homogeneous aqueous solution and in the presence of the charged detergents sodium dodecyl sulfate (SDS) and cetyltrimethylammonium chloride (CTAC) above the critical micelle concentration
Abstract: Photoinduced redox reactions employing the anionic porphyrins meso-tetrakis(p-sulfonatophenyl)porphyrin (1) and its palladium(II) complex (2) as excited substrates and various alkylviologens as quenchers have been studied in homogeneous aqueous solution and in the presence of the charged detergents sodium dodecyl sulfate (SDS) and cetyltrimethylammonium chloride (CTAC) above the critical micelle concentration (cmc). In homogeneous solution strong ground-state association between the porphyrins and the viologens occurs; even dynamic quenching processes result in no separation of electron transfer product ions. Addition of either SDS or CTAC reduces the quenching rates but allows the detection of product ions surviving up to ca. 100 ms in some cases. The back-reactions are sensitive to a variety of factors including added electrolyte, hydrophobicity of the viologen and its one-electron reduction product, and the charge on the surfactant. The long-lived products can be selectively intercepted by a variety of reagents. In the case of quenching of the palladium porphyrin (2) by methylviologen, the oxidized porphyrin can be reduced by iodide while the reduced viologen can be oxidized via either a colloidal catalyst or reaction with molecular oxygen. These reactions illustrate the possibility for obtaining net chemical conversion in a process whereby both the light-absorbing substrate and the quenchermore » are recycled.« less
TL;DR: In this paper, the synthesis of capsized porphyrin (C3-capped porphrin) and cobalt (II) complexes has been studied, which serve as models for the active site of the oxygen binding haemoproteins.
TL;DR: The feasibility of synthesizing porphyrins with a variety of reactive side groups suggests that it may be possible to introduce suitable gamma-emitters while retaining the tumour-localizing properties.
Abstract: A series of radioactively labelled porphyrin analogues have been synthesized and compared for tissue distribution and tumour uptake against 67Ga in the same tumour-mouse system. The compounds were: 14C-ms-tetraphenylporphine sulphonate (14C-TPPS), 35S-ms-tetraphenylporphine sulphonate (TPP35S), 35S-ms-tetra[β-naphthyl]porphine sulphonate (TNP35S), 14C-ms-thienylphenylporphine sulphonate (14C-TTPPS) and 35S-ms-tetra[ptolyl]porphine sulphonate (TTP35S). 14C-TPPS and TNP35S appear to concentrate in tumours to a greater extent than 67Ga (ratios of tumour uptake for TPPS/67Ga and TNPS/67Ga were about two and three respectively) but their uptake in kidneys and lungs was also greater than that of gallium. The type of side group attached to the central tetrapyrrole ring appears to have a substantial effect on the tumour-localizing properties of these compounds. Comparison of 14C and 35S-labelled TPPS indicates that the sulphonate groups are split off in vivo and that compounds with highly aromatic side g...
TL;DR: The structure of the green porphyrin implicates a cytochrome P-450 destructive mechanism in which a species formed by catalytic oxidation of the acetylenic moiety reacts with the nitrogens of prosthetic heme.
Abstract: Hepatic microsomal cytochrome P-450 from phenobarbital-pretreated rats is destroyed by propyne in a reduced nicotinamide adenine dinucleotide dependent process which also results in vivo in the accumulation of an abnormal green porphyrin. The green porphyrin has been identified by its electronic absorption, mass spectrometric, and nuclear magnetic resonance properties as the isomer of N-(2-oxopropyl)protoporphyrin IX in which the alkylated nitrogen is that of pyrrole ring A. Alkylation of the other nitrogens in the parent heme is quantitatively unimportant, although evidence for traces of the resulting adducts has been obtained. The green porphyrin exhibits a circular dichroism spectrum and is therefore the result of a chirally selective or specific interaction. The structure of the green porphyrin implicates a cytochrome P-450 destructive mechanism in which a species formed by catalytic oxidation of the acetylenic moiety reacts with the nitrogens of prosthetic heme. The possible nature of the reactive intermediate is discussed.
TL;DR: The data are suggested to be consistent with the idea that at least two slowly interconverting conformational substrates of the protein are populated, depending sensitively on small changes in rings I and II of the macrocycle and temperature.
Abstract: Well-defined 1:1 complexes have been formed between apomyoglobin (apoMb) and a number of chlorophyllide derivatives. The chlorophyllides substitute for heme in the pocket of myoglobin. These include magnesium chlorophyllide a, magnesium and zinc pyrochlorophyllide a, zinc pyrochlorophyllide b, zinc pyrochlorophyllide d, zinc pyromesochlorophyllide a, zinc 2-acetyl-2-devinylpyrochlorophyllide a, zinc protopyrochlorophyllide a, and zinc bacteriopyrochlorophyllide a. The effects of the protein on the electronic absorption, circular dichroism (CD), magnetic circular dichroism, and triplet state electron spin resonance spectra and fluorescence lifetimes in solution are compared with appropriate models in organic solvents. With the exception of the CD spectra, the protein causes shifts and intensity changes which are within the range observed for solvent effects. The CD spectra change substantially: the signs of several transitions are entirely reversed in the chlorins, and 3-6-fold intensity increases are observed with zinc bacteriochlorophyllide a. High-field 1H NMR spectra of ring current shifted Val-E11 methyl protons for the series porphyrin-, chlorin-, and bacteriochlorin-apoMb are used to establish the probable absolute orientation of the chromophore in the heme pocket. Doubled peaks in the NMR spectra of certain complexes are shown to arise from interconvertible species. The temperature dependence of the peak intensities and saturation transfer studies show that the species giving rise to the doubled peaks exchange on the time scale of about 1-60 s. Arguments are presented against inversion of the macrocycle in the heme pocket by either an inter- or an intramolecular mechanism as the origin of doubled peaks, and simple two-site exchange is ruled out by the NMR data. We suggest that the data are consistent with the idea that at least two slowly interconverting conformational substrates of the protein are populated, depending sensitively on small changes in rings I and II of the macrocycle and temperature.