Showing papers on "Porphyrin published in 1988"

Probing structure-function relations in heme-containing oxygenases and peroxidases

Abstract: Structural factors that influence functional properties are examined in the case of four heme enzymes: cytochrome P-450, chloroperoxidase, horseradish peroxidase, and secondary amine mono-oxygenase. The identity of the axial ligand, the nature of the heme environment, and the steric accessibility of the heme iron and heme edge combine to play major roles in determining the reactivity of each enzyme. The importance of synthetic porphyrin models in understanding the properties of the protein-free metal center is emphasized. The conclusions described herein have been derived from studies at the interface between biological and inorganic chemistry.

Reactive iron porphyrin derivatives related to the catalytic cycles of cytochrome P-450 and peroxidase. Studies of the mechanism of oxygen activation

Abstract: Mecanisme d'oxydation de [Fe(III) TMP(X)] par des peracides. TMP=tetramesitylporphyrine; X=Cl, OH

Photodynamic therapy with porphyrin and phthalocyanine sensitization - quantitative studies in normal rat-liver

Abstract: Selective sensitisation of malignant tumours to monochromatic light (photodynamic therapy, PDT) is a promising approach to cancer treatment, but current sensitisers are unsatisfactory and the parameters controlling effects produced in normal and neoplastic tissue are poorly understood. To quantify the effects in a relatively homogeneous organ, we carried out experiments in the livers of normal rats following systemic sensitisation with haematoporphyrin derivative (HpD) and a new sensitiser, a sulphonated aluminium phthalocyanine (AlSPc) using light from an Argon pumped tunable dye laser. Damage from PDT (dominant at 100 mW laser power) could be distinguished from that due to local hyperthermia (dominant at 400 mW). For both sensitisers, the extent of PDT necrosis increased with the applied light energy and was abolished by occluding the hepatic blood flow during therapy. With HpD, the extent of PDT necrosis was maximum with only a few hours between sensitisation and therapy, and was not detectable when this interval was increased to a week. With AlSPc, the extent of necrosis in liver changed little with sensitisation times from 1 h to 1000 h (6 weeks), and declined slowly thereafter, matching the amount of AlSPc measurable by alkali extraction, although prolonged photosensitisation was not seen with AlSPc in muscle. Less cutaneous photosensitivity was seen with AlSPc than with HpD. AlSPc is easier to produce and handle than HpD, has a more appropriate strong absorption peak (at 675 nm) and from these results, warrants further study as a photosensitiser for PDT.

PHOTOPHYSICAL PROPERTIES OF meso‐TETRAPHENYLPORPHYRIN and SOME meso‐TETRA(HYDROXYPHENYL)PORPHYRINS

Abstract: — The o-, m-, and p-isomers of 5, 10, 15, 20- tetra(hydroxyphenyl)-porphyrin have been of recent interest as potential second-generation sensitisers in tumour phototherapy. Fluorescence spectroscopy, nanosecond laser flash photolysis and pulse radiolysis have been used to characterise the singlet and triplet excited states of tetraphenylporphyrin and the o, m-, and p-isomers of tetra(hydroxyphenyl)porphyrin. This has included evaluation of fluorescence yields and lifetimes, triplet spectra, lifetimes, oxygen quenching rate constants, extinction coefficients, and yields and singlet oxygen yields. Whilst the fluorescence quantum yields were low, the triplet yields were all 0.7 ± 10% and the singlet oxygen yields 0.6 ± 10%: all these parameters are in the ranges shown by other efficient porphyrin photosensitisers. The similar photophysical properties found for these compounds suggest that their differing tumour sensitising efficiencies are likely to be due to other factors.

Oxomanganese(IV) porphyrins identified by resonance Raman and infrared spectroscopy. Weak bonds and the stability of the half-filled t2g subshell

Abstract: The Mn/sup IV/-O stretching frequency is identified at 754 cm/sup -1/ in resonance Raman (RR) and infrared (IR) spectra of Mn/sup IV/ porphyrins prepared by electrooxidation of ClMn/sup III/TMP (TMP = tetramesitylporphyrin), ClMn/sup III/TPP (TPP = tetraphenylporphyrin) and ClMn/sup III/OEP (OEP = octaethylporphyrin) in CH/sub 3/CN containing tetrabutylammonium hydroxide (TBA(OH)). This vibrational band establishes oxo-Mn/sup IV/ bond formation under these conditions and shows the bond to be anomalously weak. When the oxidation is carried out in CH/sub 2/Cl/sub 2/ containing TBA(OH), or when ClMn/sup III/TMPyP (TMPyP = tetrakis(methylpyridinium)porphyrin) is electrooxidized in aqueous 1 M NaOH, the Mn-O stretching band is seen at 711 cm/sup /minus/1/. This band is associated with a trans OH/sup /minus// adduct, as shown by its anomalous upshift, to 732 cm/sup /minus/1/, in D/sub 2/O; the lower frequency in H/sub 2/O is attributed to interaction with the Mn-O-H bend of the trans OH/sup /minus// ligand, which is relieved when H is replaced by D. EPR spectra of all these species show strong g /perpendicular/ /approximately/ 4.0 and weak g /parallel/ /approximately/ 2.0 signals characteristics of a high-spin d/sup 3/ configuration. The Mn/sup III/TMPyP species in 1 M NaOH is shown to be a trans dihydroxide adduct bymore » virtue of a 495-cm/sup /minus/1/ RR band identified, on the basis of its H/sub 2//sup 18/O and D/sub 2/O shifts, as the symmetric Mn-(OH)/sub 2/ stretch. The M-O stretching frequencies are compared for V/sup IV/, Cr/sup IV/, Mn/sup IV/, and Fe/sup IV/ porphyrins, and the anomalous weakness of the Mn/sup IV/-O bond is attributed to the special stability and low polarizability of the half-filled t/sub 2g//sup 3/ subshell. Consequences of this weak bond for manganyl reactivity are discussed.« less

Differential Cell Photosensitivity following Porphyrin Photodynamic Therapy

Abstract: Experiments were performed to determine if differences in porphyrin photosensitivity could be observed for cells with varying efficiency in DNA damage repair, as well as for cells which make up components of the vasculature. Photofrin II is undergoing current clinical evaluation for photodynamic therapy of solid tumors, and therefore the retention, dark toxicity, and photosensitizing effects of this drug on human DNA repair-deficient fibroblasts (ataxia telangiectasia and xeroderma pigmentosum) were compared to normal human fibroblasts. In addition, bovine cells of endothelial, smooth muscle, and fibroblast origin were compared for porphyrin retention, toxicity, and photosensitivity. All human fibroblasts exhibited porphyrin-induced dark toxicity, but there were no significant differences in photosensitization or porphyrin retention for any of these cell lines. However, bovine endothelial cells were considerably more photosensitive than smooth muscle or fibroblast cells treated under identical conditions. All bovine cells accumulated similar levels of porphyrin, and therefore the increased sensitivity of the endothelial cells was not due to differences in porphyrin retention. These results provide additional evidence that nuclear damage and/or repair is not a dominant factor in the cytotoxicity induced by porphyrin photosensitization. In addition, these results indicate that endothelial cell photosensitivity may play a role in the vascular damage observed following photodynamic therapy.

Achieving High Quantum Yield Charge Separation in Porphyrin-Containing Donor—Acceptor Molecules at 10 K

Abstract: In order to study the rates and energetics of electron-transfer reactions related to photosynthesis, two new fixed-distance donor-acceptor molecules have been prepared. The donors are Zn porphyrins, and the acceptor is a high-electron affinity tetracyanonaphthoquinodimethane derivative. These compounds posses very large negative free energies for charge separation at 294 K. It was found that the very low quantum yields for charge separation in low temperature solids exhibited by the porphyrin-based donor-acceptor molecules resulted in a large part from destabilization of the ion pair state in low-temperature solids relative to polar liquids. 15 references, 2 figures, 1 table.

Electrochemistry of metalloporphyrins and viologens at zeolite Y-modified electrodes: evidence for electron trapping by monomolecular porphyrin layers

Abstract: Cyclic voltammetric data are presented for electrodes coated with zeolite Y powder containing porphyrins and viologens. Half-wave potentials for viologen cations (methylviologen, benzylviologen, or N,N'-(1,3-propenyl)-2,2'-bipyridinium) do not change significantly when they are exchanged into zeolite Y, whereas the reduction potentials for cobalt and zinc tetrakis(N-methyl-4-pyridyl)porphyrins shift (relative to aqueous solution) by + 200 mV. When a viologen cation is ion exchanged into the bulk of the zeolite, and cobalt tetrakis(N-methyl-4-pyridyl)porphyrin is adsorbed onto its outer surface in monolayer quantities, current rectification and charge trapping reactions are observed. The charge untrapping reactions are similar to those previously observed at redox polymer bilayer electrodes and are attributed to a kinetically fast cross reaction between double reduced viologens inside the zeolite and cobalt(II)porphyrin on the outer surface. Rotating disk experiments show that the porphyrin monolayer effectively seals up the zeolite against exchange of encapsulated viologens with solution-phase cations.

Porphyrin and metalloporphyrin binding to DNA polymers: rate and equilibrium binding studies.

Abstract: Interactions of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin [TMpyP(4)] with poly[d(G-C)].poly[d(G-C)] [poly[d(G-C)2] and poly[d(A-T)].poly[d(A-T)] [poly[d(A-T)2] were studied by equilibrium dialysis and stopped-flow dissociation kinetics as a function of [Na+]. Metalloderivatives of TMpyP(4), NiTMpyP(4), and ZnTMpyP(4) were also investigated. The apparent equilibrium binding constants (Kobs) were approximately the same for TMpyP(4) binding to either poly[d(G-C)2] or poly[d(A-T)2] and decreased with increasing [Na+]. The slopes of the plots of log Kobs vs log [Na+] were similar, with values close to -2.7. Contrary to implications in previously reported studies, these data do not indicate that TMpyP(4) prefers to bind to GC sites at low ionic strength and to AT sites at high ionic strength. In contrast, binding of ZnTMpyP(4) to these two polymers is very different. Comparisons of Kobs values at 0.065 M [Na+] indicate that ZnTMpyP(4) binding to AT sites is approximately 200 times more favorable than binding to GC sites, a finding in agreement with previous qualitative observations. Although the binding of the Zn species to the GC polymer was too weak for us to assess the salt effect, the plot of log Kobs vs log [Na+] gave a slope of -2.0 for ZnTMpyP(4) binding to poly[d(A-T)2]. Application of condensation theory for polyelectrolytes suggests similar charge interactions for ZnTMpyP(4) and for TMpyP(4) binding to poly[d(A-T)2]. Likewise, the rates of dissociation from poly[d(A-T)2] were similar for TMpyP(4) and ZnTMpyP(4) [and also NiTMpyP(4)]. However, whereas TMpyP(4) [and NiTMpyP(4)] dissociation from poly[d(G-C)2] was measurable, that for ZnTMpyP(4) was too fast to measure.(ABSTRACT TRUNCATED AT 250 WORDS)

Metal complexes with tetrapyrrole ligands. 46. Europium(III) bis(octaethylporphyrinate), a lanthanoid porphyrin sandwich with porphyrin rings in different oxidation states, and dieuropium(III) tris(octaethylporphyrinate)

Abstract: Preparation de Eu(OEP) 2 et Eu 2 (OEP) 3 . Ils sont separes par chromatographie, et caracterises par les spectres UV-visible, proche IR, IR, RMN de H 1 , RPE et spectre de masse, structure cristalline. OEP=octaethylporphyrine

Proximal effect of the nitrogen ligands in the catalytic epoxidation of olefins by the NaOCl/manganese(III) porphyrin system

Abstract: Using synthetic manganese porphyrin complexes with an imidazole or a pyridine ligand covalently attached to the macrocycle, the control of the reaction rate, product selectivity, and stereoselectivity by the axial ligand trans to the active site of the catalyst is reported. The results clearly illustrate the proximal effect on nitrogen ligands in this cytochrome P-450 model. 33 refs., 1 fig., 2 tabs.

Photophysics of a cofacial porphyrin-quinone cage molecule and related compounds: fluorescence properties, flash transients, and electron-transfer reactions

Abstract: Fluorescence yields, fluorescence lifetimes, and flash photolysis transients have been measured for a tetrabridged cofacial porphyrin-quinone cage molecule and related derivatives. When the quinone is present and in the oxidized form, two fluorescence lifetimes are observed for the zinc complex, both shorter than the single lifetimes of control compounds. These are assigned to two conformers, with porphyrin to quinone interplanar separation of about 8.5 and 6.5 A, respectively. The fluorescence lifetime data lead to electron-transfer times for the two conformers of between 0.5 and 15 ns. The fast electron-transfer time is only weakly dependent on solvent and is independent of temperature between 290 and 124 K. Following flash photolysis of the zinc-porphyrin-quinone in polar solvents, a transient band at 415 nm grows in more slowly (150 ns) and decays much more rapidly (1.4 ..mu..s) than the triplet seen in control compounds and is assigned to a charge-separated ZnP/sup +/Q/sup -/ state. The reaction leading to this state exhibits an activation energy of only 6 kJ/mol. In contrast to the zinc chelate, the free base porphyrin-quinone shows no electron-transfer interactions. These results support a distance-sensitive nonadiabatic electron-tunneling mechanism for the transfer. Effects of solvent and protonation are interpreted in terms ofmore » conformational changes that modify the porphyrin-quinone distance.« less

Artificial allosteric systems

Abstract: The artificial allosteric molecule, gable porphyrin metal complexes, were prepared by connecting two independent metal porphyrin molecules by covalent bond. The author would like to discuss mostly on allosteric mechanism of the artificial allosteric systems. Our gable porphyrin system behaves similarly to natural Hb, binding small molecules like CO, 02: or base, cooperatively. The original structure of the dimeric porphyrin, especially when they are very strongly cooperative, usually needs chemical strain between two porphyrin rings and this strain is released by the first binding of small molecule which causes coordination change of the metal porphyrin.

Metal Complexes with Tetrapyrrole Ligands. 47. Yttrium(III) Bis(octaalkylporphyrinate)s: Synthesis and Electron Spin Resonance Spectra of Earth Metal Porphyrin Sandwich Compounds

Abstract: Reaction of tris(2,4-pentanedionato)yttrium(III) with octaethylporhyrin, H2oep in refluxing 1,2,4-trichlorobenzene (TCB) produces a trace (2%) of the double-decker, Y(oep)2 (3A) besides major amounts (72%) of the yttrium(III) monoporphyrinate, Y(oep)(acac) which are separated by chromatography. Appreciable yields of Y(oep)2 (3A) (25%) are obtained from dilithium octaethylporphyrinate, Li2(oep), formed in situ and Y(oep)(acac) in refluxing TCB. The constitution of the double-decker 3A is proved by UV/VIS, IR, 1H NMR, ESR, ENDOR, and mass spectra. The well-defined composition Y(oep)2 requires that one of the porphyrin rings is electron-deficient, i.e. the charge of the YIII ion is compensated by the normal porphyrinate dianion and a porphyrinate monoanion radical. The magnetic moment in the solid state, μeff=1.5 B.M. (5–100 K), demonstrates the radical nature of 3A as well. Under the time resolution of the methods used, the unpaired electron is delocalized between the two porphyrin rings. The wavenumber of ...

Photoproducts formed from photofrin II in cells

Abstract: Fluorescence and absorption spectra of light-exposed cells containing the tumour-localizing porphyrin preparation Photofrin II (PII) have been studied. Light exposure results in spectral changes that may be due to a photoinduced modification of the porphyrins without breakage of the porphyrin macrocycle and/or to a photoinduced displacement of the porphyrins in the cells. Photochemical reactions involving breakage of the porphyrin macrocycle also occur as can be seen from the loss of absorbance within the Soret band region during light exposure. Singlet oxygen may be involved in the photodegradation of PII in cells since the process is slowed down on bubbling N 2 through the samples and is slightly faster in suspensions in Dulbecco's phosphate buffered saline (PBS) made of D 2 O compared with suspensions in PBS made of H 2 O. During light exposure a fluorescent product is formed in the cells with fluorescence excitation and emission characteristics similar to those of the “age pigment” lipofuscin (λ exc = 350 nm, λ em = 440 nm).