Showing papers on "Porphyrin published in 1982"

Porphyrins with multiple crown ether voids: novel systems for cation complexation studies

Abstract: Porphyrins appended with crown ether, benzo-15-crown-5, at the methine positions have been synthesized and characterized. The fully and partially substituted porphyrins and their metallo (Co, Cu, and Zn) derivatives describe one or more ether cavities in the periphery that are capable of recognizing spherical cations. The ability of these macrocycles to complex cations (Na+, K+, Mg2+, Ca2+, Ba2+, and NH4+) is investigated by use of visible, 1H NMR, ESR, and emission spectral studies. The tetrasubstituted crown porphyrin (TCP) exhibits very high selectivity for K+. The cations (K+, Ba2+, and NH4+) that require two crown ether cavities for complexation promote dimerization of the porphyrins. The ESR study of the cation-induced porphyrin dimers reveals axial symmetry with the porphyrin planes separated by ~4.2 A. This distance increases from the fully substituted to partially substituted porphyrins. The cations (K+, Ba2+, and NH4+) quench efficiently the fluorescence of the free base porphyrins and their metallo derivatives. The quenching process is attributed to the steric geometry of the dimers.

Resonance Raman investigation of nitric oxide bonding in nitrosylhemoglobin A and -myoglobin: detection of bound nitrogen-oxygen stretching and iron-nitric oxide stretching vibrations from the hexacoordinated nitric oxide-heme complex

Abstract: With excitation at 406.7 nm, we have observed the resonance Raman enhancement of the bound v(N-O) stretch at approximately 1623 cm-1 in nitrosylhemoglobin A and nitrosylmyoglobin, indicating the existence of a charge-transfer transition underlying the strong Soret band. The v(Fe-NO) stretch at 551 cm-1 has also been detected in the Soret as well as in the Q-band region, a phenomenon similar to the v(Fe-O2) and v(Fe-CO) stretches in oxy and carbon monoxy hemoproteins. It appears that these iron-ligand vibrations ay be resonance enhanced via porphyrin pi leads to pi transitions. Upon addition of inositol hexaphosphate at pH 6.0, the v(Fe-NO) stretch at 551 cm-1 and a low-frequency mode at 301 cm-1 exhibit an intensity decrease by approximately one-half. Contrary to the work of Stong et al. [Stong, J. D., Burke, J. M., Daly, P., Wright. P., & Spiro, T. G. (1980) J. Am. Chem. Soc. 102, 5815], who employed an excitation wavelength at 454.5 nm, we observed no intensity increase at 592 cm-1 attributable to the v(Fe-NO) stretch from the pentacoordinated NO-heme complex in the alpha subunits.

Syntheses, ground electronic state, and crystal and molecular structure of the monomeric manganese(VI) porphyrin complex dimethoxy(5,10,15,20-tetraphenylporphinato)manganese(IV)

Abstract: Der Titel-Mn(IV)-Komplex (II) wird durch Oxidation des Mangan(III)-Komplexes (I) in basischem Methanol entweder mit Na-hypochlorit 126 oder mit Iodosylbenzol synthetisiert.

Determinants of porphyrin‐sensitized photooxidation characterized by fluorescence and absorption spectra

Abstract: — As a model for studies involving biologic systems, rates of hematoporphyrin and protopor-phyrin-sensitized photooxidation of tryptophan were measured in water-methanol mixtures Absorption and fluorescence-emission spectra associated with solutions of porphyrins in different water-methano! mixtures were also examined The optimal rate of photooxidation by hematoporphyrin occurred in 30% methanol; by protoporphyrin, in 60% methanol Absorption spectra were examined to characterize dispersion of hematoporphyrin into monomeric form in 90% methanol, and the dimer formation which predominates in 30% methanol With the more hydrophobic protoporphyrin, an absorption spectrum characteristic of drug monomer was seen in 100% methanol, a dimer spectrum was observed in 60% methanol At methanol concentrations < 60%, we observed impaired photooxidation and another alteration in the absorption pattern apparently reflecting drug aggregation beyond the dimer stage Fluorescence emission maxima of both porphyrins were blue-shifted with increasing solvent dielectric constant, but an additional blue shift was detected in an aqueous environment which was apparently related to porphyrin aggregation Absorption and fluorescence-emission spectra appear helpful for characterizing environmental determinants of porphyrin-sensitized photooxidation

Characterization of superoxide-metalloporphyrin reaction products: effective use of deuterium NMR spectroscopy

Abstract: Nuclear magnetic resonance spectroscopy has been utilized to define the solution electronic structures of complexes generated from combination of superoxide ion with iron(II) and manganese(II) porphyrins. Very large proton NMR line widths for the iron porphyrin product dictated the use of deuterium NMR for selectively deuterated synthetic porphyrins. On the basis of the pyrrole deuterium signal at 60 ppm (Me/sub 2/SO solvent, 28/sup 0/C, Me/sub 4/Si reference) and a solution magnetic moment of greater than or equal to5.6 ..mu../sub B/, a peroxoiron(III) porphyrin structure consistent with an earlier formulation is favored. A corresponding manganese porphyrin signal at 32 ppm and a solution magnetic moment of 5.0 ..mu../sub B/ are indicative of a superoxomanganese(II) porphyrin configuration with spin coupling between the superoxide ligand and the manganese center. This species provides an excellent model for what has been described as superoxide coupling to a low-spin iron(III) center in the oxyhemoglobin molecule. The peroxoiron porphyrin complex is likely coordinated in the second axial position by a solvent molecule. The axial ligand combination leaves the iron center in a high-spin state, but the peroxo ligand serves to reduce the zero-field-splitting value and indirectly induce large NMR line widths. Variable-temperature NMR Curie law behavior ismore » consistent with monomeric structures. Absence of splitting in the pyrrole signals suggests no attack of porphyrin nitrogen atoms by peroxide or superoxide species.« less

Cation-induced crown porphyrin dimers of oxovanadium(IV)

Abstract: Oxovanadium(1V) porphyrins appended with crown ether (benzo-15-crown-5) at the 5 (mono), the 5 and 10/15 (cis/trans bis), the 5, 10, and 15 (tris), and the 5, 10, 15, and 20 (tetrakis) positions have been synthesized. The cation complexation behavior of these cavity-bearing porphyrins has been studied by using optical aborption and ESR spectral methods. The cations K + , Cs + , NH 4 + , and Ba 2+ , which require two crown ether cavities for complexation, induce dimerization of the porphyrins. The cation-induced dimerization constants for a representative tetrasubstituted porphyrin vary as K + > Ba 2+ > Cs + ~ NH 4 + , and the relative stabilities of the dimers are dependent on the type of the substitution, tetrakis > tris > cis bis. ESR spectra recorded at a sample temperature of 77 K have low-field components attributed to ΔM h = ± 2 transitions, providing further evidence for the existence of dimers in solutions. The eclipsed sandwich dimers have V-V distances in the range 4.70 A. The relative distributions of oxovanadium crown porphyrins in terms of monomeric and dimeric forms rest on the geometric dispositions of the crown ether appendages.

Porphyrin biosynthesis in parasitic hemoflagellates: functional and defective enzymes in Trypanosoma cruzi.

Abstract: 1 Heme compounds are necessary as a growth factor for Trypanosoma cruzi in culture, this porphyrin requirement being due to the inability of the parasite to synthesize heme To obtain supporting evidence for this hypothesis, an extensive study of porphyrin biosynthesis in the epimastogote form of T cruzi (Tulahuen strain) was carried out 2 Low levels of endogenous delta-aminolevulinic acid (ALA) and porphobilinogen (PBG) were found in extracts of T cruzi Free porphyrins and heme contents were practically nil 3 The activity of succinyl CoA synthetase (Suc CoA-S) was rather high and therefore non-limiting 4 Both delta-aminolevulinic acid synthetase (ALA-S) and 45, dioxovaleric transaminase (DOVA-T), the two enzymes forming ALA, were readily detected and their activities, although low, were of the same order 5 delta-Aminolevulinic acid dehydratase (ALA-D) activity was almost negligible and both porphobilinogenase (PBGase) and deaminase were absent or inactive 6 Heme-Synthetase (Heme-S) was totally functional 7 It is concluded that T cruzi has lost part of its heme biosynthetic pathway, possibly due to mutations of several genes involved in the synthesis of the soluble enzymes ALA-D, PBGase, deaminase and probably others preceding Heme-S; while the particulate enzymes Suc CoA-S, ALA-S, DOVA-T and Heme-S are functional As a consequence, the host should supply the parasite with the porphyrin substrate to form its essential heme compounds

Chemical Properties of Water-soluble Porphyrins 3. The Reaction of Superoxide Radicals with Some Metalloporphyrins

Abstract: SummaryThe catalytic efficiency of some water soluble metalloporphyrins upon the disproportionation of the superoxide radicals has been determined by observing the rate of decay of the radical at 254 nm. The Fe(III), Mn(III), Co(III), Ni(II), Cu(II) and Zn(II) derivatives of tetrakis-(4-N-methylpyridyl) porphyrin (TMPyP), tetra(4-N,N,N-trimethylanilinium) porphyrin (TAP), and tetra(4-sulphonatophenyl) porphyrin (TPPS4) were studied. The order of catalytic efficiency found was Fe(III)TMPyP > Mn(III)TMPyP > Co(III)TMPyP ≅ Mn(TAP) > Fe(III)TPPS4. Other metalloporphyrins did not show catalytic activity. Reduction potentials of the catalytically active metalloporphyrins determined from cyclic voltamograms indicate the importance of having a second energetically accessible oxidation state available to the metal ion for catalysis. The catalytic action of the above metalloporphyrins is discussed in terms of inner and outer-sphere mechanisms. It is suggested that with the exception of Fe(III)TMPyP which reacts via...

Catalysis of Oxygen Cathodic Reduction by Adsorbed Iron(111)‐Tetra (N,N,N‐Trimethylanilinium) Porphyrin on Glassy Carbon Electrodes

Abstract: The adsorption of iron(111)‐tetra (N,N,N‐trimethylanilinium) porphyrin on glassy carbon was studied in aqueous solutions using cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and the RRDE technique. The porphyrin was found to catalyze oxygen electroreduction; the overpotential is reduced by about 400 mV and the hydrogen peroxide yield is 5% compared to 25% in the absence of catalyst.

Photovoltaic properties of meso-tetraarylporphyrins

Abstract: — The photovoltaic properties of meso-tetraphenylporphyrin and its derivatives with various para-substituents, meso-tetrakis(2,4-dimethoxyphenyl)porphyrin and meso-tetrakis (2-fluorenyl)porphyrin have been investigated The forward dark current-voltage characteristics of Al/porphyrin/Ag cells are attributed to the MIS Schottky barriers consisting of Al/Al2O3/porphyrin The barrier parameters such as the apparent diffusion potential V0 the barrier width w0 and the density of ionized impurity N are estimated by using the capacitor discharge method The action spectra of photocurrents closely follow the optical absorption spectra of the porphyrin films The photocurrents vary as ipαIγ, where I is the incident light intensity, and the Sight exponents y range between 083 and 10 The sublinear difference from unity could be related to the exponential distribution of hole traps in films of the porphyrins No obvious correlation between the photocurrent and the fluorescence quantum yields of the sublimed porphyrin films is found The electron donating substituents such as OCH3 and CH3 strikingly increase the photocurrents The photocurrent quantum yields correlate exponentially with the first ring oxidation potentials of the porphyrins and also with the substituent constants for the Hammett linear free-energy relationship The current quantum yields estimated for the porphyrins studied, range in the order of 10-4–10-2 with power conversion efficiencies 10-7–10-3

Some aspects of porphyrin neurotoxicity in vitro.

Abstract: Using a dissociated primary sensory neuron culture system, it is observed that some naturally occurring porphyrins produce dose-dependent neurotoxicity as measured by neuron death and by inhibition of the neurite outgrowth induced by Nerve Growth Factor (NGF). However, the porphyrin precursor δ-aminolcvulinic acid (δ-ALA) is not toxic up to millimolar concentrations within a 30-h time period. Two synthetic porphyrins, tetraphenylporphine sulfonate (TPPS) and hematoporphyrin derivative (HPD), have also been shown to be toxic in vitro.Cultures and cocultures of isolated populations of neurons and glia of central and peripheral nervous system origin may prove advantageous in the study of porphyrin influences on the intact nervous system. This in vitro assay system can complement in vivo paradigms and may be useful for rapid quantitative screening for neurotoxicity of radiation sensitizers including the synthetic porphyrins and other chemotherapeutic agents.