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PubMed2003

Theoretical analysis of the porphyrin-porphyrin exciton interaction in circular dichroism spectra of dimeric tetraarylporphyrins.

Chiral bis-porphyrins are currently the subject of intense interest as chiral receptors and as probes in the determination of structure and stereochemistry. To provide an improved framework for interpreting the circular dichroism (CD) spectra of bis-porphyrins, we have calculated the CD spectra of chiral bis-porphyrins from three classes: I, where porphyrins can adopt a relatively wide range of orientations relative to each other; II, porphyrins have a fixed relative orientation; III, porphyrins undergo pi-stacking. The calculations primarily utilized the classical polarizability theory of DeVoe, but were supplemented by the quantum mechanical matrix method. Class I was represented by three isomers of the diester of 5alpha-cholestane-3,17-diol with 5-(4'-carboxyphenyl)-10,15,20-triphenylporphin (2-alphabeta, 2-betaalpha, 2-betabeta). Careful analysis of the torsional degrees of freedom led to two to four minimum-energy conformers for each isomer, in each of which the phenyl-porphyrin bonds had torsional angles near 90 degrees. Libration about these bonds is relatively unrestricted over a range of +/-45 degrees. CD spectra in the Soret region were calculated as Boltzmann-weighted averages over the low-energy conformers for each isomer. Three models were used: the effective transition moment model, in which only one of the degenerate Soret components is considered, along the 5-15 direction; the circular oscillator model, in which both Soret components are given equal weight; and the hybrid model, in which the 10-20 oscillator is given half the weight of the 5-15 oscillator, to mimic the effect of extensive librational averaging about the 5-15 direction. All three models predict Soret exciton couplets with signs in agreement with experiment. Quantitatively, the best results are given by the hybrid and circular oscillator models. These results validate the widely used effective transition moment model for qualitative assignments of bis-porphyrin chirality and thus permit application of the exciton chirality model. However, for quantitative studies, the circular oscillator or hybrid models should be used. The simplified effective transition moment and hybrid models are justified by the librational averaging in the class I bis-porphyrins and should only be used with such systems. Two class II bis-porphyrins were also studied by DeVoe method calculations in the circular oscillator model, which yielded good agreement with experiment. Class III bis-porphyrins were represented by 2-alphaalpha, for which the calculations gave qualitative agreement. However, limitations in the conformational analysis with the close contacts and dynamic effects in these pi-stacked systems preclude quantitative results.

Circular Dichroism↗

PubMed1998

Validity of spot urine samples as a surrogate measure of 24-hour porphyrin excretion rates. Evaluation of diurnal variations in porphyrin, mercury, and creatinine concentrations among subjects with very low occupational mercury exposure.

Porphyrin, mercury, and creatinine levels in single-void urine specimens ("spot samples") were compared with calculated 24-hour urine concentrations among 146 (77 male and 69 female) practicing dentists who are participating in an ongoing study of urinary porphyrin changes as a biomarker of mercury body burden. All subjects had urinary mercury concentrations < or = 5 micrograms/L, a level comparable to that of the general US population and which is below that determined to be associated with mercury-induced changes in urinary porphyrin excretion rates. The results confirmed previous findings of no significant diurnal variation in any of the porphyrin levels normally found in urine or in total porphyrin levels combined among males but describe significant diurnal variations in most porphyrin levels as well as concentrations of total porphyrins combined among females. Similarly, no evidence of large diurnal variation in mercury excretion among males was apparent, whereas significant diurnal variation in the mercury excretion rate among females was found. Creatinine adjustment of porphyrin or mercury concentrations had no significant effect on these findings. Moreover, no evidence of diurnal variation in urinary creatinine excretion among either male or female subjects was obtained, despite substantial between-subject variability in this parameter. These results support the view that spot urine samples may be utilized to derive reasonably accurate estimates of 24-hour porphyrin and mercury excretion rates in male subjects. In contrast, time of day appears to be of considerably greater importance when spot samples are utilized as 24-hour estimates of either porphyrin or mercury excretion rates among females. Additionally, time of day may be an important consideration in studies involving serial (repeated) porphyrin or mercury measurements using spot urine samples, irrespective of gender distribution of study subjects.

Adult↗

PubMed2002

Allosteric Binding of an Ag+ Ion to Cerium(IV) Bis-porphyrinates Enhances the Rotational Activity of Porphyrin Ligands.

A series of cerium(IV) bis-porphyrinate double-deckers [Ce(bbpp)(2)] (BBPP=5,15-bis(4-butoxyphenyl)porphyrin dianion), [Ce(tmpp)(2)] (TMPP=5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin dianion), [Ce(tfpp)(2)] (TFPP=5,10,15,20-tetrakis(4-fluorophenyl)porphyrin dianion), [Ce(tmcpp)(2)] (TMCPP=5,10,15,20-tetrakis(4-methoxycarbonylphenyl)porphyrin dianion), and [Ce(tmpp)(tmcpp)] was prepared. They bind three Ag(+) ions to their concave porphyrin pi subunits (pi-clefts) according to a positive homotropic allosteric mechanism with Hill coefficients (n(H)) of 1.7-2.7. The rotation rates of the porphyrin ligands in [Ce(bbpp)(2)] were evaluated to be 200 s(-1) at 20 degrees C (DeltaG$\rm{^{\ne }_{293}}$=14.1 kcal mol(-1)) and 220 s(-1) at -40 degrees C (DeltaG$\rm{^{\ne }_{233}}$=11.0 kcal mol(-1)) without and with Ag(+) ions, respectively. These results consistently support our unexpected finding that Ag(+) binding can accelerate rotation of the porphyrin ligand. On the basis of UV-visible, (1)H NMR, and resonance Raman spectral measurements, the rate enhancement of the rotational speed of the porphyrin ligands is attributed to conformational changes of the porphyrin in cerium(IV) bis-porphyrinate induced by binding of Ag(+) guest ions in the clefts. This novel concept of positive homotropic allosterism is applicable to the molecular design of various supramolecular and switch-functionalized systems.

Journal Article↗

PubMed1998

Photophysics of the cationic 5,10,15,20-tetrakis (4-N-methylpyridyl) porphyrin bound to DNA, [poly (dA-dT)]2 and [poly (dG-dC)]2: interaction with molecular oxygen studied by porphyrin triplet-triplet absorption and singlet oxygen luminescence.

Interaction between molecular oxygen and the cationic free-base 5,10,15,20-tetrakis (4-N-methylpyridyl) porphyrin (H2TMpyP4+) complexed with [poly (dA-dT)]2, [poly (dG-dC)]2 and calf thymus DNA, has been monitored in air-saturated heavy water solutions through porphyrin triplet-triplet absorption and singlet oxygen luminescence. Three different rate constants of porphyrin triplet state quenching have been found which correspond to different accessibilities of molecular oxygen to porphyrins embedded in the duplexes. The longest triplet state lifetime (30 microseconds), found for porphyrin bound to [poly (dG-dC)]2, corresponds to molecules well protected from oxygen. This supports the hypothesis of an intercalative binding mode of the porphyrin between GC base-pairs ('type A' sites). The fraction fT delta of the porphyrin triplet states quenched by molecular oxygen with singlet oxygen generation, is unity. In [poly (dA-dT)]2-porphyrin complexes, two sites ('type B' and 'C' sites of interaction) are involved, yielding very different triplet state lifetimes (5.5 microseconds and 20.5 microseconds) and efficiencies of singlet oxygen generation (fT delta = 0.50 and 0.82). The fT delta decreases can likely be explained in terms of competition between energy and electron transfer from the porphyrin excited triplet state to molecular oxygen. All three types (A, B and C) of interaction sites can be expected in porphyrin-DNA complexes.

Absorption↗

PubMed1985

Interactions with glutathione S-transferases of porphyrins used in photodynamic therapy and naturally occurring porphyrins.

Several naturally occurring porphyrins and porphyrins used in photodynamic therapy inhibit glutathione S-transferase isoenzymes either purified from rat liver or lung or in cytosol from normal and from cancerous (Morris 7288C hepatoma) liver. Although differences occur in the type and amount of transferases in normal and cancerous liver and in the liver of rats bearing an extrahepatic tumour, these enzymes are potential binding sites for porphyrins. Porphyrin structure is an important factor in determining the affinity of binding, as shown by the relative inhibitory effectiveness. Of the dicarboxylic porphyrins in the mixture used clinically, OO'-diacetylhaematoporphyrin and monohydroxyethylmonovinyldeuteroporphyrin are more effective inhibitors than haematoporphyrin and protoporphyrin IX. Of the naturally occurring porphyrins the order of effectiveness is protoporphyrin IX (dicarboxylic) greater than coproporphyrin (tetracarboxylic) greater than uroporphyrin (octacarboxylic) and type I greater than type III isomers of both uroporphyrin and coproporphyrin, and the synthetic tetra-meso-phenylporphinetetrasulphonate is a better inhibitor (apparent Ki = 250 nM) than coproporphyrin, which contains a comparable number of negative charges. In addition, iron-porphyrin chelates are more effective inhibitors of the transferases, with 25-fold decrease in Ki value, than the free porphyrins. These results indicate that one means whereby porphyrins accumulate in tissues is the occupation of intracellular binding sites, such as the transferases. Since porphyrins inhibit the activity of these important detoxifying enzymes, there will be metabolic consequences to the cell.

Animals↗

PubMed2002

Allosteric binding of an Ag+ ion to cerium(IV) bis-porphyrinates enhances the rotational activity of porphyrin ligands.

A series of cerium(IV) bisporphyrinate double-deckers [Ce(bbpp)2] (BBPP = 5,15-bis(4-butoxyphenyl) porphyrin dianion), [Ce(tmpp)2] (TMPP = 5,10,15,20-tetrakis(4-methoxyphenyl)-porphyrin dianion), [Ce(tfpp)2] (TFPP = 5,10,15,20-tetrakis(4-fluorophenyl)porphyrin dianion), [Ce(tmcpp)2] (TMCPP = 5,10,15,20-tetrakis(4-methoxycarbonylphenyl)porphyrin dianion), and [Ce(tmpp)(tmcpp)] was prepared. They bind three Ag+ ions to their concave porphyrin pi subunits (pi-clefts) according to a positive homotropic allosteric mechanism with Hill coefficients (nH) of 1.7-2.7. The rotation rates of the porphyrin ligands in [Ce(bbpp)2] were evaluated to be 200 s-1 at 20 degrees C (delta G++293 = 14.1 kcal mol-1) and 220 s-1 at -40 degrees C (delta G++233 = 11.0 kcal mol-1) without and with Ag+ ions, respectively. These results consistently support our unexpected finding that Ag+ binding can accelerate rotation of the porphyrin ligand. On the basis of UV-visible, 1H NMR, and resonance Raman spectral measurements, the rate enhancement of the rotational speed of the porphyrin ligands is attributed to conformational changes of the porphyrin in cerium(IV) bis-porphyrinate induced by binding of Ag+ guest ions in the clefts. This novel concept of positive homotropic allosterism is applicable to the molecular design of various supramolecular and switch-functionalized systems.

Journal Article↗

PubMed2006

5-Aminolaevulinic acid (ALA) induced formation of different fluorescent porphyrins: a study of the biosynthesis of porphyrins by bacteria of the human digestive tract.

Aminolaevulinic acid (ALA) induces porphyrin formation in almost all living cells. The fluorescence spectra of porphyrins produced from a variety of 31 bacterial strains from the human oral cavity and other parts of digestive tract have been examined. Many of the bacteria exposed to ALA were able to induce protoporphyrin IX (PpIX) fluorescence, but under aerobic condition some bacteria can also produced different fluorescent porphyrins, in particular water-soluble porphyrins that can arise from an oxidation of the corresponding porphyrinogen precursors. The formation of fluorescent porphyrins can be different from one bacterial strain to another, but also one specific bacterium can form different fluorescent porphyrins. Irradiation of the ALA incubated cultures led to a rapid formation of water-soluble porphyrins exhibiting fluorescence maxima at wavelengths of 618-620 nm. This light induced formation of water-soluble porphyrins could be attributed to a photooxidation of the non-fluorescent (Uro/Copro)-porphyrinogen precursors. Addition of detergents to some of the bacterial cultures led to a strong PpIX fluorescence increase, indicating that some of the PpIX originally produced can be present in a non-fluorescent, probably aggregated, form. The large abundance of bacteria in the oral cavity and other parts of digestive tract, with their capacity to easily produce fluorescent porphyrins, indicates that such bacterial fluorescence should be suppressed during the ALA-based diagnosis of tumours in order to eliminate false positive results.

Aminolevulinic Acid↗

PubMed2000

Porphyrin-Fe(III)-hydroperoxide and porphyrin-Fe(III)-peroxide anion as catalytic intermediates in cytochrome P450-catalyzed hydroxylation reactions: a molecular orbital study.

The hydroxylation of fluorobenzene and aniline, catalyzed by the porphyrin-Fe(III)-peroxide anion with either a cysteinate- or a histidyl-type of axial ligand as well as the hydroxylation of fluorobenzene, catalyzed by porphyrin-Fe(III)-hydroperoxide with a cysteinate-type of axial ligand as catalytic intermediates, have been investigated by electronic structure calculations in local spin-density approximation. Non-repulsive potential curves are, in contrast with porphyrin-Fe(III)-hydroperoxide, obtained only in the case of porphyrin-Fe(III)-peroxide anion as catalytic intermediate. The mutual substrate-porphyrin orientation with a dihedral angle between the plane of the substrate and the porphyrin plane of 45 degrees is more favorable compared with the parallel orientation between these two planes. This orientation differs for the case of fluorobenzene hydroxylation from the corresponding one calculated by us with the ferryl-oxo-pi-cation radical complex as a catalytic intermediate. The calculated reaction profiles show also the effectiveness of the histidyl-type coordinated porphyrin-Fe(III)-peroxide involved in P450 type of hydroxylation reactions. The calculations demonstrate the predominant role of the O1-O2 moiety of the porphyrin-Fe(III)-peroxide anion in the hydroxylation process of the substrates. The results indicate that the porphyrin-Fe(III)-peroxide anion is an effective catalytic species in hydroxylation reactions. In all the studied cases irrespective of the substrate and the nature of the axial ligand, the potential curves reach minimum at approximately 130-140 pm, expressing the length of an aromatic C-O bond.

Aniline Compounds↗

PubMed2004

Swallowtail porphyrins: synthesis, characterization and incorporation into porphyrin dyads.

The incorporation of symmetrically branched tridecyl ("swallowtail") substituents at the meso positions of porphyrins results in highly soluble building blocks. Synthetic routes have been investigated to obtain porphyrin building blocks bearing 1-4 swallowtail groups. Porphyrin dyads have been synthesized in which the zinc or free base (Fb) porphyrins are joined by a 4,4'-diphenylethyne linker and bear swallowtail (or n-pentyl) groups at the nonlinking meso positions. The swallowtail-substituted Zn(2)- and ZnFb-dyads are readily soluble in common organic solvents. Static absorption and fluorescence spectra and electrochemical data show that the presence of the swallowtail groups slightly raises the energy level of the filled a(2u)(pi) HOMO. EPR studies of the pi-cation radicals of the swallowtail porphyrins indicate that the torsional angle between the proton on the alkyl carbon and p-orbital on the meso carbon of the porphyrin is different from that of a porphyrin bearing linear pentyl groups. Regardless, the swallowtail substituents do not significantly affect the photophysical properties of the porphyrins or the electronic interactions between the porphyrins in the dyads. In particular, time-resolved spectroscopic studies indicate that facile excited-state energy transfer occurs in the ZnFb dyad, and EPR studies of the monocation radical of the Zn(2)-dyad show that interporphyrin ground-state hole transfer is rapid.

Electrochemistry↗

PubMed1993

The effect of porphyrins on cellular redox systems: a study on the dark effect of porphyrins on phagocytes.

Erythropoietic protoporphyria (EPP) and porphyria cutanea tarda (PCT) are characterized by skin morbidity, induced by pro-inflammatory reactive oxygen species generated by the photosensitizing properties of protoporphyrin IX and uroporphyrin I. How these porphyrins exert a toxic effect on the liver in the absence of light is poorly understood. We tested the hypothesis that porphyrins can interference with cellular redox systems, by studying the dark effects of protoporphyrin (PP), haematoporphyrin (HP), deuteroporphyrin (DP) and uroporphyrin (UP) on the cellular redox system of phagocytes, and on enzymatic oxyradical generating systems. Both in phagocytic cells and enzymatic systems, a dose-dependent inhibition of chemiluminescence was observed by all porphyrins added. Catalase and SOD-like activity of porphyrins was excluded by oxygraph and ferricytochrome c reduction. However, ferrocytochrome c oxidation was inhibited by porphyrins indicating ferrireductase-like activity. In a Fenton type reaction between H2O2 and PP, we could demonstrate the generation of .OH, or an electronically excited porphyrin species. No influence on phagocyte chemotaxis, phagocytosis and killing-capacity was observed. We conclude that porphyrins do interfere with (cellular) redox systems and can both inhibit and enhance oxygen free radical generation, dependent on the type of redox reaction. Porphyrins can thus affect cellular metabolism. Since H2O2 and PP both readily dissolve in biological membranes, their interaction in the presence of transition metals may contribute to the toxic dark effects of porphyrins as observed in patients with EPP and PCT.

Cytochrome c Group↗

PubMed1972