Showing papers on "Porphyrin published in 1975"

7 Cytochromes c

Abstract: Publisher Summary The term cytochrome c is both a spectral and a structural classification, related more to the heme and its attachment to the polypeptide chain than to the protein which surrounds it. The most familiar member of the class is cytochrome c from the mitochondria1 respiratory chain, which has a single heme group per chain of 103–113 amino acids, and a reduction potential of +260 mV. Cytochromes all have a characteristic three-banded absorption spectrum in the reduced state. One of the most striking features of the heme group is the delocalization of electrons among the π orbitals of the porphyrin ring. The Soret band in the absorption spectrum represents the excitation of delocalized π electrons to unoccupied levels of the porphyrin ring of similar angular momentum. The absorption spectrum of cytochrome c, which is the basis for classification, depends on the side groups around the porphyrin ring and the way that they are connected to the protein chain. All cytochromes c are oxidation-reduction proteins involved in either respiration or photosynthesis.

Cytochrome c Interaction with Membranes

Abstract: A cytochrome c derivative from which iron is removed has been prepared and characterized. Several lines of evidence indicate that native and porphyrin cytochrome c have similar conformations: they have similar elution characteristics on Sephadex gel chromatography; in both proteins the tryptophan fluorescence is quenched and the pK values of protonation of the porphyrin are identical. Porphyrin cytochrome c does not substitute for native cytochrome c in either the oxidase reaction or in restoring electron transport in cytochrome-c-depleted mitochondria. It does however competitively inhibit native cytochrome c in these reactions, the Ki for inhibition being larger than the Km for reaction. The absorption and emission spectra, and the polarized excitation spectrum of the porphyrin cytochrome c are characteristic of free base porphyrin. The absence of fluorescence quenching of porphyrin cytochrome c when the protein is bound to cytochrome oxidase suggests that heme to heme distance between these proteins is larger than 0.5 to 0.9 nm depending upon orientation. Binding of the porphyrin cytochrome c to phospholipids or to mitochondria increases the fluorescence polarization of a positively polarized absorption band, which indicates that the bound form of the protein does not rotate freely within the time scale of relaxation from the excited state.

Structure and reactivity of ruthenium (II) porphyrin complexes. Photochemical ligand ejection and formation of ruthenium porphyrin dimers.

Abstract: Ruthenium(l1) carbonyloctaethylporphyrin pyridinate (1) i n degassed pyridine solution is photochemically converted to ruthenium(l1) octaethylporphyrin dipyridinate (2). The structure of 2 was determined by X-ray crystallography; the two pyridines are symmetrically coordinated to the ruthenium (Ru-N bond distance = 2.1 %.) which lies in the plane of the porphyrin. irradiation of 1 in other solvents capable of complexing with the metal leads to the corresponding diligand complexes. However, irradiation of 1 in degassed benzene results only in incomplete and reversible decarbonylation. The airstable crystalline solid 2, when heated to 220° under vacuum, produces a microcrystalline dimeric solid which is soluble in benzene. The dimer is stable in benzene solution but is oxidized when in contact with air or dissolved in other solvents. Spectral data support the assignment of a dimer structure and suggest that the dimer has a strong metal-metal bond with the porphyrin rings eclipsed. In recent years the study of metalloporphyrin complexes has been expanded by the synthesis of species containing secondand third-row transition metal ions,2 including ruthenium(I1, III).3-6 The study of carbonyl complexes of ruthenium porphyrins is of general importance with respect to the carbonyl complexes of the corresponding hemes. Although the ruthenium and iron porphyrins exhibit marked chemical differences, both the ruthenium and iron complexes of the type M(CO)(base)(porphyrin) are presumably pseudooctahedral low-spin diamagnetic compound^.^^^ Hence, studies of these systems, when M = Ru, are not totally unrelated to the biological hemes. Although many studies of iron( 11) porphyrins have been conducted, they are made difficult by the extreme ease with which iron(I1) is oxidized. Such considerations led us to synthesize, as a more easily studied analog of the iron( 11) porphyrins, carbonyl porphyrin derivatives of the similarly d6 ruthenium(I1). In a preliminary communicationh we reported an investigation of the photochemistry of ruthenium(I1) porphyrin carbonyl complexes. In this work we reported a facile photoreaction in which C O was ejected with subsequent formation of a porphyrin dimer. Contrary to previous indications, we find that the monomeric but diligated ruthenium(I1) porphyrins are the first isolable products of C O photoejection in solution. In the present paper we report a more detailed investigation of this reaction with various ruthenium(l1) porphyrins as well as a study of their thermal reactions. Stable ruthenium porphyrin dimers can be formed as subsequent products, but their formation results from a thermal reaction of the photoproduct. Along with the chemical study of these reactions, we report the complementary results of an X-ray study of octaethylporphyrinruthenium(I1) dipyridinate, the initial product of C O photoejection from Ru\"(CO)(py)OEP in ~ y r i d i n e . ~ Experimental Section Spectra. Ultraviolet and visible spectra were recorded either on a Cary Model 14 recording spectrophotometer or a Unicam Model SP-800B. Infrared spectra were recorded on a Perkin-Elmer Model 421. Proton nmr spectra were obtained through use of a Varian XL-100 with IO-mm sample tubes. All mass spectra were recorded on an AEI MS-902. Emission spectra were recorded on a Hitachi Perkin-Elmer MPF-2A spectrophotometer. Electrochemical measurements were done with previously described equipment'\" in 0.1 M TBAH. Materials. Octaethylporphyrin, etioporphyrin I , and tetraphenylporphine were prepared as described by literature methods. Ruthenium(l1) carbonyl porphyrins were prepared by the method of Tsutsui, et Pyridine (reagent grade) was distilled from potassium hydroxide and calcium oxide prior to use. Other solvents (except spectrograde solvents) were purified by distillation. Preparative Photodecarbonylation Reactions. Irradiations were carried out on solutions (-0.01 M ) of ruthenium(l1) carbonyl porphyrins in an appropriate ligating solvent. Pyrex ampoules of solution were degassed by at least three freeze-pump-thaw cycles and irradiated by a medium-pressure mercury lamp (450-W Hanovia) with a Pyrex filter until reaction was complete. The diligate product, which precipitated as reaction occurred, was filtered on a glass frit and washed with cold solvent, then vacuum dried at room tem-

Unusual metalloporphyrin complexes of rhenium and technetium.

Abstract: : Monometallic and bimetallic porphyrin complexes of rhenium and technetium were synthesized. Visible spectroscopy indicates that first the monometallic and then the bimetallic porphyrin complex is formed. The monometallic complex of rhenium can further react with either Re2(CO)10 or Tc2(CO)10 to form the homo- and heterodinuclear metalloporphyrin complexes. Structural data for the homodinuclear metalloporphyrin complexes of both rhenium and technetium were obtained by single crystal X-ray diffraction. Both the rhenium and technetium homodinuclear porphyrins are centrosymmetric complexes having two metals bonded to the porphyrin, one above and one below the plane of the macrocycle while the porphyrin macrocycle is highly distorted. Proton magnetic resonance spectra gave evidence for the proposed structures. A fluxional character of both Re and Tc monometallic porphyrin complexes was observed by variable-temperature pmr spectral studies. A novel thermal disproportionation of (H-MP)Tc(CO)3 was also observed.

Electronic Spectra of Tetraphenylporphinatoiron(III) Methoxide

Abstract: Tetraphenylporphinatoiron(III) methoxide in the high-spin state S=5⁄2 gives rise to an absorption spectrum which has been assigned to that of low-spin iron(III) porphyrins. The excited states characteristic of the spectrum of high-spin iron(III) porphyrins are the configuration-interaction admixtures of the lowest triplet and singlet porphyrin (π,π*) excited states and the low-lying “porphyrin to iron (III)” charge-transfer excited states. The charge-transfer excited states in tetraphenylporphinatoiron(III) methoxide, however, are so high that the chargetransfer excited states are not sufficiently mixed with the lowest triplet (π,π*) excited states. Thus the high-spin methoxo complex does not exhibit a spectrum characteristic of high-spin iron(III) porphyrins.

The nuclear magnetic resonance spectra of porphyrins. Part X. Carbon-13 nuclear magnetic resonance spectra of some meso-tetraarylporphyrins and their metal chelates

Abstract: The 13C n.m.r. spectra of meso-tetraphenylporphyrin (TPP), the zinc(II), cadmium(II), bis[mercury(II) acetate], and various thallium(III) derivatives, and some related analogues are reported and assigned. In meso-tetra-(o-tolyl)-porphyrin and meso-tetra-(1-naphthyl)porphyrin only one species was observed. The introduction of zinc(II), cadmium(II), or bis[mercury(II) acetate] into the TPP nucleus does not significantly change the 13C shifts, but the thallium(II) derivative shows both extensive TI–13C couplings and non-equivalence of o-phenyl carbon atoms, the latter being due to the exoplanar position of the thallium atom. Specific TI–13C couplings to the o-phenyl carbon atoms are also observed.The phenomenon of slow protonation (TPP ⇄ TPPH22+) was identified and examined by using 13C and 1H n.m.r. spectroscopy, and the 13C shifts and assignments for the dication are reported. The large protonation shifts of TPP and high ΔG value for this process (ca. 16·3 kcal mol–1) are consistent with the further buckling of the macrocycle on protonation, due to decrease in the angle between the macrocycle and the phenyl rings. In contrast, the protonation shifts of meso-tetra-(o-tolyl)porphyrin are ‘normal’ owing to the additional steric requirements of the o-methyl groups. A hitherto unrecorded effect is the shift of the tetramethylsilane reference in trifluoroacetic acid compared with deuteriochloroform of 1·5 p.p.m. upfield with respect to other reference compounds.Identification of the coalescence temperature for the NH tautomerism in both the 13C and 1H spectra allows the kinetic parameters for this process to be determined (ΔG303ca. 12·3 kcal mol–1, ΔH ca. 9·2 kcal mol–1, and ΔS ca.–10 cal K–1 mol–1). These, and the isotope effect (KNH/KND) of ca. 12 (measured at one temperature to remove entropy of activation effects) are consistent with a two-step (rather than a concerted) process.

Photosynthesis and porphyrin excited state redox reactions

Abstract: The necessity of unraveling the complex reactions of photosynthesis inspired this comprehensive study into the irreversible oxidation and reduction properties of the triplet state of zinc uroporphyrin (ZnUP). The similarities in the redox and spectral properties between ZnUP and chlorophyll excited states rendered this study relevant. In addition, the eight ionized acetic and propionic acid groups on the periphery of the uroporphyrin molecule permitted the determination of a distance of electron transfer from the triplet state t o various acceptors. The importance of these findings t o porphyrin photochemistry and photosynthesis will be presented in this report. The absorption spectra and decay kinetics of some free base and metalloporphyrin triplet states have been That the ground state of metalloporphyrins undergo successive one-electron aromatic ring oxidations6-'0 and reductions1 '-' is well documented. Similarly, one-electron electrochemical oxidations of tetraphenylporphin,' and successive one-electron electrochemical reductions of various free-base porphyrins have been reported.' 6 i 1 Photochemical reductions of uroporphyrin' 8 -2 and zinc porphin2 have been demonstrated, although the reactive state was not conclusively identified. The one-electron reduction of ground state zinc etioporphyrinZ3 and the one-electron oxidations of the triplet state of zinc t e t r a p h e n y l p ~ r p h y r i n ~ ~ by chemical means have also been reported. PhotoreductionSv2 5 , 2 6 and p h o t o ~ x i d a t i o n ~ > ~ 6 9 2 7 of chlorophyll and chlorophyll-related2 8 30 compounds have also been studied, and reaction from the triplet state was demonstrated in several cases.26-28g30 A quantitative mechanistic study, however, has not been reported and will be presented for triplet state ZnUP in this report.

Editorial: Hematin and porphyria.

Abstract: The discovery that hematin represses induction of δ-aminolevulinic acid synthetase (ALA-S), the rate-limiting enzyme for hepatic porphyrin and heme synthesis,1 is central to recent studies seeking to provide a means of terminating or ameliorating the acute attack of acute intermittent porphyria, porphyria variegata or hepatic coproporphyria. The induction of ALA-S in the acute attack of AIP, acute intermittent porphyria, porphyria variegata or hepatic coproporphyria markedly increases the porphyrin precursors, ALA and porphobilinogen (PBG), in liver, blood plasma and urine. The enzyme is induced because of heme deficiency in the liver secondary to the genetic partial lack of uroporphyrinogen synthetase (UPG-S) . . .

The use of thin layer chromatography in the separation of free porphyrins and porphyrin methyl esters.

Abstract: SUMMARY Thin layer chromatographic techniques for the separation and subsequent quantification of free porphyrins, coproporphyrin isomers and the methyl esters of porphyrins are described including a 2-dimensional system. The relevant RFs for a wide range of porphyrins are given. These methods have been in use in Cardiff and Barcelona for a number of years and were used in the survey of cases described by Pinol et al. (1975) which resulted in the discovery of the new porphyria, hepato-erythrocytic porphyria.

A Convenient Preparation of meso-Tetra(4-sulfonatophenyl)porphyrin

Abstract: The sulfonation of meso-tetraphenylporphyrin, in concentrated sulfuric acid followed by neutralization and dialysis, provides an efficient and convenient route to meso-tetra(4-sulfonatophenyl)porph...

Monomer–dimer equilibration of water-soluble porphyrins as a function of the co-ordinated metal ion

Abstract: Tetrakis-(4-sulphophenyl)porphyrin and its four co-ordinate metal complexes dimerize, while the five- or six-ligated metalloporphyrins are monomers in aqueous, electrolyte-containing solutions.

Condensation of ethyl diazoacetate with cobalt porphyrins.

Abstract: Condensation of ethyl diazoacetate with various cobalt complexes of octaethylporphyrin causes insertion of ethoxycarbonylcarbene into a cobalt–nitrogen bond to give a salt (VI) of the cobalt(III) adduct. Reduction of the salt (VI) with chromium(II) salts causes the formation of neutral halogenocobalt(II) complexes of N-ethoxy-carbonylmethyloctaethylporphyrin, e.g.(XIII). The action of acid under oxidative conditions on (VI) yields first a halogenocobalt(II)N-ethoxycarbonylhalogenomethyloctaethylporphyrin (XI), and then, after removal of the metal, 21,22-ethoxycarbonylmethyleneoctaethylporphyrin, the first example of a cis-21,22-bridged porphyrin. The parent 21,22-methyleneoctaethylporphyrin is obtained by condensation of di-iodomethane with octaethylporphyrin.