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Gold(III) porphyrin 1 is shown to undergo reduction at the central metal ion to give the first known gold(II) porphyrin overturning the long held assumption that reduction of such complexes only occurs at the macrocycle.
Photoinduced electron transfer from tetrakis(4-carboxy-phenyl porphyrin)-zinc complex (Zn-TCPP) to an acceptor molecule (methyl viologen; MV2+) has been found to be controlled by the complex formation of monoclonal antibody 03-1 for the porphyrin (TCPP) and Zn-TCPP. Although there are no ground-state interactions between Zn-TCPP and MV2+ for a 2:1 complex of antibody 03-1 and Zn-TCPP, the fluorescence of Zn-TCPP is quenched by the addition of MV2+. The Stern-Volmer plots and emission lifetime studies show that there is a long-range electron transfer through the antibody 03-1.
High-valent oxo-iron(IV) species are commonly proposed as the key intermediates in the catalytic mechanisms of iron enzymes. Water-soluble iron(III) tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphyrin (Fe(III)TMPyP) has been used as a model of heme-enzyme to catalyse the hydrogen peroxide (H(2)O(2)) oxidation of various organic compounds. However, the mechanism of the reaction of Fe(III)TMPyP with H(2)O(2) has not been fully established. In this study, we have explored the kinetic simulation of the reaction of Fe(III)TMPyP with H(2)O(2) and of the catalytic reactivity of FeTMPyP in the luminescent peroxidation of luminol. According to the mechanism that has been established in this work, Fe(III)TMPyP is oxidized by H(2)O(2) to produce (TMPyP)(*+)Fe(IV)[double bond]O (k1 = 4.5 x 10(4)/mol/L/s) as a precursor of TMPyPFe(IV)[double bond]O. The intermediate, (TMPyP)(*+)Fe(IV)[double bond]O, represented nearly 2% of Fe(III)TMPyP but it does not accumulate in sufficient concentration to be detected because its decay rate is too fast. Kinetic simulations showed that the proposed scheme is capable of reproducing the observed time courses of FeTMPyP in various oxidation states and the decay profiles of the luminol chemiluminescence. It also shows that (TMPyP)(*+)Fe(IV)[double bond]O is 100 times more reactive than TMPyPFe(IV)[double bond]O in most of the reactions. These two species are responsible for the initial sharp and the sustained luminol emissions, respectively.
Porphyrin-induced photodamage has been studied on small organic molecules, biomolecules, mitochondria and red cells. Water soluble components (e.g. tryptophan and glutamate dehydrogenase) are more easily destroyed by uroporphyrin than by protoporphyrin. On the other hand, lipophilic components (e.g. succinate dehydrogenase, mitochondria and red cell membranes) are more severely damaged by protoporphyrin. The results may be of importance to explain the different skin lesions in erythropoietic protoporphyria and in porphyria cutanea tarda. The photodamage is enhanced by D2O and reduced by azide. Reagents known to increase or decrease the yields of superoxide, peroxide or hydroxyl radicals have no effect on the photodamage. The results suggest that singlet oxygen is the most important reactive oxygen species.
Circular dichroism (CD) spectra of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) that are associated with various duplex and triplex AT oligomers were investigated in this study. A strong positive CD was apparent for both the TMPyP complexed with duplex d[(A-T)(12)](2), d(A)(12).d(T)(12) and triplex d(A)(12).d[(T)(12)](2) at a low mixing ratio. As the mixing ratio increased, bisignate excitonic CD was produced for TMPyP complexed with duplexes, whereas the positive CD signal remained the same for the TMPyP-d(A)(12).d[(T)(12)](2) complex. This difference in the CD spectrum in the presence of duplex and triplex oligomers indicates that the moderate stacking of TMPyP occurs at the major groove of the duplex and the monomeric binding occurs in (or near) the minor groove. When TMPyP forms a complex with duplex d[(A-T)(6)](2) only excitonic CD was observed, even at a very low mixing ratio. Therefore, at least seven or more basepairs are required for TMPyP to exhibit a monomeric CD spectrum. After close analysis of the CD spectrum, the TMPyP-poly[d(A-T)(2)] complex could be explained by a combination of the CD spectrum of the monomeric, moderately stacked, and extensively stacked TMPyP.
Induced CD spectra of meso-tetrakis(N-methylpyridium-4-yl)porphyrin (TMPyP) complexed with d(A)12.d(T)12, d(G)12.d(C)12 duplex and d(A)12.[d(T)12]2, d(G)12.d(C)12.d(C)12+ triplex in the Soret band were compared in this study. When TMPyP is complexed with the duplex, a monomeric CD spectrum at a low [TMPyP]/[oligomer] ratio was apparent, while at a high mixing ratio, the excitonic CD was dominant. In contrast, when TMPyP was complexed with the triplex, the excitonic CD disappears at a relatively high mixing ratio, indicating the TMPyP exciton formation is inhibited by the third strand, which is located in the major groove. This observation indicates that the exciton is formed at the major groove of both AT- and GC-rich DNA, while the monomeric TMPyP binds at (or near) the minor groove of the AT site.
Self-promoted electron transfer from a cobalt(II) porphyrin [Co(II)OEP] to p-fluoranil (F4Q) occurs, exhibiting a second-order dependence of the electron-transfer rate with respect to the F4Q concentration due to the formation of a strong complex between the dimer radical anion [(F4Q)2*-] and the resulting Co(III)OEP+.
Ab initio electron propagator methods are applied to the prediction, assignment, and interpretation of the valence photoelectron spectra of free base porphine and of magnesium and zinc porphyrins. Tests of various approximate self-energies, including the partial third (P3), the outer valence Green's function, and the nondiagonal, renormalized second-order (NR2) methods are performed. Basis set effects and reduced active orbital spaces are examined as well. The P3 method and the one-electron picture of ionization that accompanies it are validated for the first two cationic states and for states with sigma holes that are localized in nitrogen, lone pair regions. In the remaining pi-hole states, there is significant shake-up character and NR2 results provide useful diagnostics of correlation effects.
[reaction] A self-complementary V-shaped bis-porphyrin cavity has been synthesized that is capable of dimerization to form a capsule structure. Self-assembly of the dimer occurs via metal ion coordination and produces an internal volume for guest encapsulation.
A highly saddle-distorted dodecaphenylporphyrin dication (H4DPP2+) was revealed by X-ray crystallography to form positively charged porphyrin nanochannels which were 1 nm in diameter; chloride anion and redox-active hydroquinone could be incorporated in the channels.
Deficiency of the fifth enzyme in haem synthesis, uroporphyrinogen decarboxylase (UPGD), may give rise to accumulation and excretion of poly-carboxylated porphyrins, as well as to clinical manifestations in the form of a phototoxic skin reaction and liver engagement leading to cirrhosis and hepatocellular cancer. The cutaneous reaction, presenting as skin fragility and blisters on areas exposed to sun--porphyria cutanea tarda (PCT)--develops only in individuals with a remaining hepatic UPGD activity less than 20% of normal. Experimental results and clinical observation give evidence that PCT is a multifactorial disease. In some individuals a 50%, decrease in UPGD activity is a consequence of inheritance of an allele with a mutation in the gene programming for the enzyme, but in these gene carriers, as well as in the other patients with overt PCT, the activity of the hepatic enzyme is reduced below the critical level by the action of specific inhibitors. In the generation of the enzyme inhibitors, iron plays a central role by promoting the formation of reactive oxygen species, a process where a specific class of cytochrome enzymes; cytochrome P450 1A (CYP4501A), participates. The varying individual susceptibility to development of the disease can be discussed in terms of differences in a spectrum of factors that affect the availability of the free form of this element in the liver, or its pathogenic action. In the article the roles of chronic viral infection, alcohol abuse and exposition to polyhalogenated cyclic hydrocarbons are considered in the light of effects on the availability of iron in the liver. Some genetic prerequisites for susceptibility to PCT-inducing agents are included in a tentative model for the disease, i.e. mutations in the UPGD gene and in the HFE gene affected in haemochromatosis, as well as genetically steered inducibilities of the genes programming for CYP4501A and the rate-limiting enzyme in haem synthesis, 5-aminolevulinate synthase. With the pathogenic model as a basis the different therapeutic strategies that can be applied are discussed, and suggestions for a handling programme for the patient presenting with PCT put forward.
An extremely painful cutaneous condition with no or only slight visible skin changes, presenting in a child or an adult as an acute reaction to sun light, is probably a manifestation of the porphyrin metabolic disorder erythropoietic protoporphyria (EPP). The disease is the result of a genetically determined condition where a mutation in the gene for the final enzyme in the haem synthetic chain, ferrochelatase, results in impaired activity of the enzyme. In some predisposed individuals, the condition is accompanied by heavy accumulation of the substrate for the deficient enzyme, i.e. of protoporphyrin. Distributing to the skin, and there absorbing light of certain wavelengths, the metabolite generates free radicals that give rise to photodynamic cell injury. The primary event takes place in the endothelial cells of the superficial skin capillaries, but complement activation and mast cell degranulation in the surrounding tissue follow in the process. Even if the disease is primarily dermatological the hepatic and psychosocial complications are features requiring close attention by the physician. In order to provide a basis for suggestions regarding lege artis protocols for the diagnosis, treatment and monitoring of the patient with EPP, the pathophysiology of the cutaneous and hepatic manifestations are discussed in some detail in the article.
Three covalently linked porphyrin-fluorouracil compounds were synthesized. Measurement using these compounds for inhibition of mice transplanted tumor growth, cytotoxicity to mice cancer cells and the mice ear index under exposure to a light was performed. The results indicated that all these compounds were phototoxic to the cancer cells, and compound 1 was the most effective among them.
In liver cells photodamage following externally added protoporphyrin affects predominantly membrane associated components, whereas photodamage by uroporphyrin also affects water-soluble components. Following excess endogenous production of porphyrins, protoporphyrin concentrates in the mitochondria and exerts its photodamaging effect primarily on the mitochondrial system, whereas uroporphyrin concentrates in lysosomes with release and inactivation of lysosomal enzymes when irradiated. The results may be of importance to explain the different skin lesions in porphyria cutanea tarda and erythropoietic protoporphyria.
The potentiometric response characteristics of diclofenac selective electrodes based on Fe(III) tetraphenylporphyrin-chloride (Fe(III)TPP-Cl) and Fe(III) tetrakis(pentafluorophenyl)porphyrin-chloride (Fe(III)TPFPP-Cl) in different mediator solvents and ionic additives are compared. The sensitivity, working range, detection limit, response mechanism, and selectivity of the membrane sensor show a significant dependence on the type of carrier substituent and on the pH value of the sample solution. Studies performed with different amounts of cationic additive (tetra-n-octylammoniumbromide (TOABr)) and anionic additive (sodium tetraphenylborate (NaTPB)) in the membranes allowed the determination of the potentiometric mechanism of action of the used metalloporphyrins. For the analysis of real samples, Fe(III)TPFPP-Cl (type G), prepared in o-NPOE, incorporating 10 mol% of TOABr, was used. This potentiometric unit presented a linear response towards diclofenac concentrations between 10(-5) and 10(-2)mol l(-1) ( I=0.1 mol l(-1)) and slopes of about -59 mV dec(-1), exhibiting a response time of 10s in a buffered solution of ammonia-ammonium sulphate with pH 9.9. The potentiometric analysis of sodium diclofenac in pharmaceutical formulations was carried out by direct potentiometry and the obtained results were compared to those provided by HPLC, presenting relative errors inferior to 1.0%.
The tetracyanoethylene (TCNE) electron-transfer salts of meso-tetrakis(4-methoxyphenyl)- and meso-tetrakis(2-fluorophenyl)porphinatomanganese(II), [MnTOMePP][TCNE].2PhMe, 1, and [MnTFPP][TCNE].2PhMe, 2, respectively, have been structurally and magnetically characterized. 1 and 2 belong to the triclinicP&onemacr; (No. 2) space group [1, a = 9.896(2) Å, b = 10.256(3) Å, c = 14.447(2) Å, alpha = 82.64(2) degrees, beta = 92.40(1) degrees, gamma = 109.07(2) degrees, T = -80 degrees C, Z = 1, and R(F(o)) = 0.0295; 2, a = 10.185(5) Å, b = 11.081(3) Å, c = 12.378(3) Å, alpha = 107.55(2) degrees, beta = 82.88(3) degrees, gamma = 111.09(3) degrees, T = -80 degrees C, Z = 1, and R(F(o)) = 0.0421]. 1 and 2 are coordination polymers with the Mn(III) sites bridged by trans-&mgr;-sigma-[TCNE](*)(-). The [TCNE](*)(-) is orientationally disordered in 2, with the minor form being rotated by 90 degrees with respect to the major form and in the same plane as the major form in an approximate 5:1 ratio. The Mn-N and intrachain Mn.Mn distances are 2.289 and 2.313 Å and 10.256 and 10.185 Å, and the Mn-N-C and the dihedral angle between the mean MnN(4)-porphyrin and the mean [TCNE](*)(-) planes are 165.53 and 78.1 degrees and 148.6 and 55.4 degrees for 1 and the occupancy-weighted average of 2, respectively. For 1 above 250 K the susceptibility can be fit by the Curie-Weiss expression with theta = -65 K, while between 75 and 190 K an effective theta of +21 K is observed; for 2 above 225 K, theta is -71 K, while between 40 and 100 K the effective theta is +45 K. The initial negative theta values along with minima in the chiT(T) data at 134 K (X = OMe) and 240 K (X = F) are consistent with antiferromagnetic coupling. One chi"(T) and two chi'(T) peaks are observed for both 1 and 2. The higher temperature [ approximately 10 K (1) and 12.5 K (2)] chi'(T) peaks are frequency independent, lack a corresponding chi"(T) absorption, and are assigned to a transition to an antiferromagnetic state. In contrast, the lower-temperature frequency dependent [5.6 K (1) and 7.5 K (2) at 10 Hz] chi'(T) peaks have a corresponding frequency dependent chi"(T) peaks and are assigned to the transition to a spin-glass or superparamagnetic state. The T(c)'s are defined as chi'(T) data taken at 10 Hz and are listed above.
On heating, syn-diporphyrin zinc complexes fused with bis(ethano)dimethoxyanthracene, the crystal structure of which showed a unique trimeric assembly, extruded one ethylene molecule at 240-310 degrees C to give a porphyrin-naphthoporphyrin diad, and the second retro-Diels-Alder reaction and concomitant decomposition of the methoxy groups occurred at 280-350 degrees C to give the anthraquinone-fused diporphyrin, while the first thermal conversion of the anti-diporphyrin zinc complex occurred in a much lower temperature range (180-230 degrees C).
Photoexcitation of an electron donor-acceptor linked dyad containing gold(III) and zinc(II) porphyrins (ZnPQ-AuIIIPQ+) results in electron transfer from the singlet excited state of ZnPQ to the metal center of AuPQ+ to produce the charge-separated state (ZnPQ*+-AuIIPQ) which has a long lifetime (10 mus) in nonpolar solvents such as cyclohexane and toluene.