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PubMed2006

Femtosecond fluorescence dynamics of porphyrin in solution and solid films: the effects of aggregation and interfacial electron transfer between porphyrin and TiO2.

The excited-state relaxation dynamics of a synthetic porphyrin, ZnCAPEBPP, in solution, coated on a glass substrate as solid films, mixed with PMMA and coated on a glass substrate as solid films, and sensitized on nanocrystalline TiO2 films were investigated by using femtosecond fluorescence up-conversion spectroscopy with excitation in the Soret band, S2. We found that the S2--> S1 electronic relaxation of ZnCAPEBPP in solution and on PMMA films occurs in 910 and 690 fs, respectively, but it becomes extremely rapid, <100 fs, in solid films and TiO2 films due to formation of porphyrin aggregates. When probed in the S1 state of porphyrin, the fluorescence transients of the solid films show a biphasic kinetic feature with the rapid and slow components decaying in 1.9-2.4 and 19-26 ps, respectively. The transients in ZnCAPEBPP/TiO2 films also feature two relaxation processes but they occur on different time scales, 100-300 fs and 0.8-4.1 ps, and contain a small offset. According to the variation of relaxation period as a function of molecular density on a TiO2 surface, we assigned the femtosecond component of the TiO2 films as due to indirect interfacial electron transfer through a phenylethynyl bridge attached to one of four meso positions of the porphyrin ring, and the picosecond component arising from intermolecular energy transfer among porphyrins. The observed variation of aggregate-induced relaxation periods between solid and TiO2 films is due mainly to aggregation of two types: J-type aggregation is dominant in the former case whereas H-type aggregation prevails in the latter case.

Journal Article↗
PubMed2003

C70 vs. C60 in zinc porphyrin-fullerene dyads: prolonged charge separation and ultrafast energy transfer from the second excited singlet state of porphyrin.

The second excited singlet (S2) state of porphyrin was efficiently quenched by the attached fullerene C70 moiety in a zinc porphyrin-C70 dyad. The quenching is largely explained by energy transfer to C70, but the possibility of additional reactions involving the S2 state of porphyrin is discussed. Singlet energy transfer was found to be an important decay pathway also for the first excited singlet (S1) state of porphyrin. In the polar solvent benzonitrile a charge-separated state was formed, and its lifetime was 890 ps, 50% longer than in the analogous porphyrin-C60 dyad.

Journal Article↗
PubMed2005

Porphyrin-triarylamine conjugates: strong electronic communication between triarylamine redox centers via the porphyrin dication.

A set of porphyrin-triarylamine hybrids have been synthesized in good yield by Sonogashira palladium-catalyzed cross-coupling reactions between the zinc complex of 5,15-diethynyl-10,20-dimesitylporphyrin and the appropriate iodophenyldiarylamines. The crystal structure of porphyrin 1 shows that the dihedral angle between the acetylene-bonded benzene rings and the porphyrin macrocycle is 20.0 degrees. Such a structural characteristic enables effective electronic perturbations within the molecule. The electronic spectra are red-shifted and display a broad Soret band and an intense Q band relative to those of meso-substituted tetraarylporphyrins. These conjugates display four oxidations and one reduction. All the electrochemical reactions involve one-electron transfer. The first and second oxidations are reversible and can be assigned to the porphyrin-centered reactions. The third and fourth ones, separated by about 270 mV, correspond to the triarylamine units. The comproportionation constant (Kc) is calculated to be 3.67x10(4). The electron coupling between the triarylamine moieties, at a separation of >23 A, is remarkably strong. The electrochemical results and the absorption spectra show that the electronic characteristics of these porphyrins can be significantly modulated by the triarylamine substituents via the conjugated carbon-carbon triple bond. Variations of the substituents on the triarylamines can fine-tune the electronic properties of these molecules.

Journal Article↗
PubMed1977

CNDO molecular orbital calculations on porphyrins--I. Ground and excited states of porphyrin, divinylporphyrin and tetraphenylporphyrin.

Semi-empirical CNDO/2 MO calculations are reported for the ground states of porphyrin, 2,4-divinylporphyrin (DVP), and alpha, beta, gamma, delta-tetraphenylporphyrin (TPP). Results for TPP refer to the conformation with all phenyl groups perpendicular to the porphyrin ring, calculated to be 108 kJ mol-1 more stable than the coplanar conformation. The substituents withdraw electron density where they are attached to the porphyrin ring, increasing selected orbital energies. The vinyl groups also modify the electron population at nitrogen. CNDO/S calculations with extensive configuration interaction are reported for excited states. The lowest singlet states are closely similar in energy and composition for all three molecules, except for an extra state and more complex compositions in DVP above 3 eV. The lowest triplet states of porphyrin and DVP are very similar, while those of TPP are comparable in energy or composition but not both. Experimental data on the excited states are broadly consistent with the calculations, although comparisons for the excited triplets are tentative.

Molecular Conformation↗
PubMed2003

Nonplanar distortions of bis-base low-spin iron(II)-porphyrinates: absorption and resonance Raman investigations of cross-trans-linked iron(II)-basket-handle porphyrin complexes.

Electronic absorption and Soret-excited resonance Raman (RR) spectra are reported for bis-N-alkylimidazole and bis-pyridine complexes of various cross-trans-linked iron(II)-"basket-handle" porphyrins (Fe(II)-BHP) in methylene chloride. These compounds enable us to characterize the spectroscopic properties of ruffled six-coordinated low-spin Fe(II)-porphyrin complexes. The visible absorption spectra show that the Q and B bands are progressively red-shifted when the handles are shortened and/or when the steric hindrance of the axial ligands is increased. This effect is accompanied by both a decrease in RR frequency of the nu(2) mode and an increase in frequency of the nu(8) and nu(s)(Fe-ligand(2)) modes. More precisely, an inverse linear correlation is found between the frequencies of the nu(2) and nu(8) modes. For each ligation state, the positions of the absorption bands are also linearly correlated with the frequency of the nu(2) or nu(8) mode. All of these spectroscopic data reveal that the degree of ruffling of the Fe(II)-BHP complexes is increased by the N-methylimidazole --> pyridine axial substitutions, presumably because the mutual steric strains between the axial ligand rings, the porphyrin macrocycle and the porphyrin handles are increased. The present study provides a first basis for discerning ruffled conformations from planar and other nonplanar structures in ferrous heme proteins.

Ferrous Compounds↗
PubMed2000

Porphyrins with exocyclic rings. 14. Synthesis of tetraacenaphthoporphyrins, a new family of highly conjugated porphyrins with record-breaking long-wavelength electronic absorptions.

The Soret band for porphyrins is usually observed in the near-ultraviolet at approximately 400 nm, and few examples of "nonexpanded" porphyrins with this major absorption band at values above 500 nm have previously been reported in the literature. Ring fusion with aromatic ring systems such as naphthalene, anthracene, or phenanthrene generally only produces minor bathochromic shifts to this diagnostic absorption band. In this paper, the synthesis of a series of tetraacenaphthoporphyrins and their metal chelates is reported. The compact nature of the acenaphthylene ring system allows the introduction of meso substituents using the Lindsey methodology. meso-Tetraphenylporphyrin 10a shows the presence of a Soret band at 556 nm, while p-methoxy and p-nitro substituents in 10f and 10g, respectively, further shift this band to 560 and 570 nm. Addition of TFA produces the corresponding dications with slightly higher wavelength Soret bands at 565, 573, and 588 nm. These values compare to 525 nm for the dication of tetraacenaphthylene 8, which lacks the meso-aryl substituents, indicating that steric crowding and its resulting distortion of the macrocyclic conformation is responsible for a significant albeit minor portion of these shifts. The nickel(II), copper(II), and zinc chelates of 10a produce Soret bands at 528, 545, and 558 nm, respectively, demonstrating that the trend for increasing red shifts in metalloporphyrins across the periodic table is retained for this series. The lead(II) chelate 19d gave an additional "hyper" shift that brought the Soret band to 604 nm. A similar red shift could be achieved by introducing four phenylethynyl substituents at the meso positions, and this highly conjugated porphyrin (20) also showed a Soret band at 604 nm, while the corresponding dication afforded this absorption band at 629 nm. The essentially additive "hyper" shift due to lead chelation brought the Soret band for the related lead(II) complex 22d to 642 nm. These effects are by far the largest ever observed for true porphyrins and demonstrate that the Soret band can be fined tuned to virtually any part of the visible spectrum.

Magnetic Resonance Spectroscopy↗
PubMed2005

5'-Porphyrin-oligonucleotide conjugates: neutral porphyrin-DNA interactions.

[chemical reaction: see text]. Incorporation of hydrophilic tetraarylporphyrin phosphoramidites into the 5'-termimus of the DNA as well as noncharged porphyrin-DNA interactions have been studied. Porphyrin-modified oligonucleotides show lower melting temperatures than their unmodified analogues. Single-stranded DNA interacts more strongly with porphyrin and causes more intense chiral disturbance in the porphyrin environment than the corresponding double strand.

Base Composition↗
PubMed1990

[Studies on porphyrin related compounds and tumor tissue affinities. I. Synthesis of a carrier for tumor imaging agent, bifunctional chelating agent coupled porphyrin (ATN-2)].

A carrier for a new tumor imaging agent, a bifunctional chelating agent (BCA)-coupled porphyrin (ATN-2), has been synthesized from protoporphyrin dimethyl ester in 4 steps. At first, the hydrobromination of protoporphyrin dimethyl ester is carried out to obtain a monobromo derivative. The derivative is treated with ethylene glycol. The resulting porphyrin has an ether group at the either 7- or 12-position of the ring. Metallation with GaCl3 of the porphyrin having a ethylene glycol residue affords Ga-metalloporphyrin. Final condensation of the metalloporphyrin with diethylenetriaminepentaacetic acid (DT-PA) gave BCA-coupled porphyrin (ATN-2). The chelation of ATN-2 with 111InCl3 easily afforded [111In]ATN-2. This agent was used for imaging transplantable pancreatic carcinoma in Syrian golden hamster at 72 h after postinjection. The efficacy of the new agent was compared with that of [67Ga]citrate. The images with [111In]ATN-2 were found to be clearer than those with [67Ga]citrate. Therefore, ATN-2, a carrier for 111InCl3, seems to be more useful for tumor imaging agents.

Animals↗
PubMed2006

Porphyrin-induced photogeneration of hydrogen peroxide determined using the luminol chemiluminescence method in aqueous solution: A structure-activity relationship study related to the aggregation of porphyrin.

A luminol chemiluminescence method was used to evaluate the porphyrin-induced photogeneration of hydrogen peroxide (H2O2). This method enabled us to detect H202 in the presence of a high concentration of porphyrin, which was not possible using conventional colorimetry. The limit of detection was about 1 microM. We compared the ability to generate H2O2, using uroporphyrin (UP), hexacarboxylporphyrin (HCP), coproporphyrin (CP), hematoporphyrin (HP), mesoporphyrin (MP), and protoporphyrin (PP). The amount of H2O2 photoproduced was strongly related to the state of the porphyrin in the aqueous solution. UP and HCP, which existed predominantly in a monomeric form, had a good ability to produce H2O2. HP and MP, existing as dimers, showed weak activity. CP, forming a mixture of monomer and dimer, had a moderate ability to produce H2O2. PP, which was highly aggregated, had a good ability. These results demonstrated that the efficiency of porphyrins to produce H2O2 was strongly dependent on their aggregated form, and the dimer suppressed the production of H2O2.

Colorimetry↗
PubMed1995

[Methods of determination of porphyrins and their precursors--introduction of analytical methods for porphyrin metabolites].

Contrary to the belief that porphyrias are of relatively rare occurrence, there has recently been a rapidly increasing number of reported cases of the disease apparently as a result of growing interest of clinicians, the advance of biochemical and molecular biological research works and improvement and refinement of diagnostic techniques. Unfortunately, however, it is an unquestionable fact that porphyrias are not infrequently still misdiagnosed. Detection and identification of the porphyrias constitutes an important step in the treatment of the diseases and, accordingly, determination of porphyrins and their precursors is of paramount therapeutic importance. While porphyrins are normally detected in small amounts in healthy individuals, these compounds are excreted in large quantities in the urine or feces or both in hereditary and chemical porphyrias, owing to inborn errors in heme biosynthesis and in hemolytic anemia, as a result of excessive production, resulting from increased heme biosynthesis. It follows that determination of porphyrins and their precursors in clinical materials is of pivotal importance in establishing the diagnosis of porphyrias. This paper reviews the methods of determination of porphyrins and their precursors in clinical materials and techniques employed for this purpose.

Aminolevulinic Acid↗
PubMed2004

Vectorial electron relay at ITO electrodes modified with self-assembled monolayers of ferrocene-porphyrin-fullerene triads and porphyrin-fullerene Dyads for molecular photovoltaic devices.

Systematic series of indium tin oxide (ITO) electrodes modified covalently with self-assembled monolayers (SAMs) of ferrocene-porphyrin-fullerene triads and porphyrin-fullerene dyads were designed to gain valuable insight into the development of molecular photovoltaic devices. The structures of SAMs on ITO have been investigated by UV/Vis absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The photoelectrochemical and photophysical (fluorescence lifetime and time-resolved transient absorption) properties were also determined. The highest quantum yield of photocurrent generation (11 %) among donor-acceptor linked systems which are covalently attached to the surface of ITO electrodes was achieved with SAMs of ferrocene-zinc porphyrin-fullerene linked triad on ITO electrodes. The quantum yields of photocurrent generation correlate well with the charge-separation efficiency and the lifetime of the charge-separated state of the porphyrin-fullerene linked systems in solution. These results provide valuable information for the construction of photonic molecular devices and artificial photosynthetic systems on ITO electrodes.

Journal Article↗
PubMed1983

Studies of hematoporphyrin and hematoporphyrin derivative equilibria in heterogeneous systems. Porphyrin-liposome binding and porphyrin aqueous dimerization.

Two processes of porphyrins in heterogeneous systems containing aqueous and membrane phases have been studied with hematoporphyrin and hematoporphyrin derivative: Dimerization equilibrium in the aqueous phases and porphyrin-membrane binding equilibrium using liposomes as models for biological membranes. The interrelationship of aqueous aggregations and membrane binding was probed and the porphyrin aggregation state in the membrane, at equilibrium, was assessed. Fluorimetric techniques were employed. The dimerization equilibrium constants, at neutral pH and 37 degrees C were found to be 2.8 X 10(5) M-1 and 1.9 X 10(6) M-1 for hematoporphyrin and its derivative, respectively. Over a porphyrin concentration range going from monomer-dominant to dimer-dominant systems, we have found that only monomers are bound to the membrane. The respective monomer-liposome binding constants, found to be independent of the initial monomer/dimer distribution in the aqueous phase, were determined to be 1.6 X 10(3) M-1 and 4.1 X 10(3) M-1 at neutral pH and 37 degrees C for hematoporphyrin and its derivative, respectively. The monomer-liposome interaction was found to perurb the initial monomer/dimer distribution in the aqueous phase, so that the monomers residing at equilibrium in the membrane originate from both monomers and dimers in the aqueous phase.

Chemical Phenomena↗
PubMed2002

Electronic structure, chemical bond, and optical spectra of metal bis(porphyrin) complexes: a DFT/TDDFT study of the bis(porphyrin)M(IV) (M = Zr, Ce, Th) series.

The electronic absorption spectra of the bis(porphyrin) sandwich complexes of the metals Zr, Ce, and Th are studied with time-dependent density functional theory (TDDFT). A ground-state electronic structure analysis reveals that the highest occupied one-electron levels are, as expected, composed of the porphyrin a(1u) and a(2u) highest occupied orbitals (the Gouterman orbitals), but the level pattern is not simply a pair of low-lying nearly degenerate in-phase combinations and a pair of high-lying approximately degenerate antibonding combinations. Instead, the a(1u) split strongly and the a(2u) do not. Since the calculated spectrum agrees very well with experiment, the assignment leaves little doubt that although the experimental spectrum has porphyrin-like features, such as the well-known Q and B bands, the actual composition of the states is rather different from that in porphyrin. In particular the strong mixing of a(1u) --> e(g) and a(2u) --> e(g) is absent, there is mixing with excitations of non-Gouterman type, and, in Ce, ring to metal charge-transfer transitions play an important role. The composition of the states as calculated in this work does not lead to a classification of the excitations as purely "excitonic" or "charge-resonance".

Journal Article↗
PubMed1992

Model for the porphyrin-DNA binding site: ENDOR investigations of Cu-porphyrins binding to DNA.

Proton ENDOR has been observed from frozen solutions (ca. 38K degrees) of copper meso-(4-N-tetra-methylpyridyl)porphyrin (CuTMpyP(4)) complexed with Salmon sperm DNA in water and D2O. Lines from exchangeable protons of the DNA bases have been observed in these ENDOR spectra. Analyses of these ENDOR data show that the separations of these DNA protons from the copper atom are between 3.76 and 3.84 A with angles of 19.5 to 22.5 degrees between the Cu-H vectors and the gz axis. A distant ENDOR response has also been observed from phosphorous nuclei in the DNA backbone. We estimate that the phosphorous atoms producing this ENDOR signal are 7.5-10 A from the copper center of the porphyrin. These ENDOR data combined with results from an earlier NMR investigation have been used to construct a computer simulated model of the binding site in which the porphyrin is partially intercalated and extends into the major groove of DNA. The two GC base pairs at this site are slightly inequivalent. For each, the G imino proton and one of the C amino protons are at appropriate positions to account for the ENDOR signals arising from exchangeable protons. It is unlikely that this inequivalence would persist at room temperature where dynamic processes would give an apparently symmetric interaction. Although the model accounts for all reported experimental data involving tetracationic porphyrin species which have been suggested to be intercalators, it is not a unique solution.

Binding Sites↗
PubMed1999

Protonation of porphyrin in iron-free cytochrome c: spectral properties of monocation free base porphyrin, a charge analogue of ferric heme.

Charged groups reside mainly on protein surfaces, but for proteins that incorporate redox centers, a charge typically exists at the prosthetic group within the interior. How a protein accommodates a buried charge and the effect of redox changes on protein stability are thermodynamically related problems. To examine these problems in cytochrome c, the metal-free protein was used as a model. When pH is lowered, the neutral, monocation, and dication forms of the porphyrin are progressively formed as indicated by their characteristic absorption spectra. Infrared studies of the protein over this pH range show that the protein remains in a predominately alpha-helical structure, although the carboxyl groups of the dicarboxylic amino acids become protonated at lower pH. The monocation porphyrin form (which has not been previously reported in a protein and is a charge analogue of ferric heme) has a fluorescence maximum at 609 nm. The pKs for the respective one and two protonation of the porphyrin pyrrole Ns are 3.2 and 1.6 for the folded protein, and 4.4 and 3.1 for the unfolded protein. These values indicate that the protection of the polypeptide chain for protonation is approximately 3 kcal.

Amino Acid Sequence↗
PubMedDate not supplied

Transient formation of the oxo-iron(IV) porphyrin radical cation during the reaction of iron(III) tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphyrin with hydrogen peroxide in aqueous solution.

The reaction of iron(III) tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphyrin (Fe(III)TMPyP) with hydrogen peroxide (H(2)O(2)) and the catalytic activity of the reaction intermediates on the luminescent peroxidation of luminol in aqueous solution were studied by using a double-mixing stopped-flow system. The observed luminescence intensities showed biphasic decay depending on the conditions. The initial flashlight decayed within <1 s followed by a sustained emission for more than 30 s. Computer deconvolution of the time-resolved absorption spectra under the same conditions revealed that the initial flashlight appeared during the formation of the oxo-iron(IV) porphyrin, TMPyPFe(IV) = O, which is responsible for the sustained emission. The absorption spectra 0.0-0.5 s did not reproduce well by a simple combination of the two spectra of Fe(III)TMPyP and TMPyPFe(IV) = O, indicating that transient species was formed at the initial stage. Addition of uric acid (UA) caused a significant delay in the initiation of the luminol emission as well as in the formation of the TMPyPFe(IV) = O. Both of them were completely diminished in the presence of UA equimolar with H(2)O(2), while mannitol had no effect at all. The delay of the light emission as well as the appearance of TMPyPFe(IV) = O was directly proportional to the [UA](0) but other kinetic profiles were not changed significantly. Based on these observations and the kinetic analysis, we confirmed the involvement of the oxo-iron(IV) porphyrin radical cation, (TMPyP)(.+)Fe(IV) = O, as an obligatory intermediate in the rate-determining step of the overall reaction, Fe(III)TMPyP + H(2)O(2) --> TMPyPFe(IV) = O, with a rate constant of k = 4.3 x 10(4)/mol/L/s. The rate constants for the reaction between the (TMPyP)(.+)Fe(IV) = O and luminol, and between the TMPyPFe(IV) = O and luminol were estimated to be 3.6 x 10(6)/mol/L/s and 1.31 x 10(4)/mol/L/s, respectively.

Cations↗
PubMed2003

Characterization of porphyrins of rat Harderian gland by thin layer chromatography and mass spectrometry: no evidence for a tricarboxylic acid porphyrin.

Reversed-phase TLC systems using ion-pairing reagents are described for the separation without prior derivatization of the porphyrins of rat Harderian gland. Porphyrins with R(f) values greater than protoporphyrin but smaller than coproporphyrin, representing harderoporphyrin, were labile to 1 m NaOH, which converted them to protoporphyrin, inconsistent with the established literature that harderoporphyrin is a tricarboxylic acid porphyrin. It was confirmed by HPLC/electrospray ionization MS that this 'harderoporphyrin' fraction consists of the recently characterized glycoconjugate, protoporphyrin-1-O-acyl beta-xyloside, with trace amounts of protoporphyrin-1-O-acyl beta-glucoside.

Animals↗
PubMed2005

Mechanistic insights into the reversible formation of iodosylarene-iron porphyrin complexes in the reactions of oxoiron(IV) porphyrin pi-cation radicals and iodoarenes: equilibrium, epoxidizing intermediate, and oxygen exchange.

We have shown previously that iodosylbenzene-iron(III) porphyrin intermediates (2) are generated in the reactions of oxoiron(IV) porphyrin pi-cation radicals (1) and iodobenzene (PhI), that 1 and 2 are at equilibrium in the presence of PhI, and that the epoxidation of olefins by 2 affords high yields of epoxide products. In the present work, we report detailed mechanistic studies on the nature of the equilibrium between 1 and 2 in the presence of iodoarenes (ArI), the determination of reactive species responsible for olefin epoxidation when two intermediates (i.e., 1 and 2) are present in a reaction solution, and the fast oxygen exchange between 1 and H(2)18O in the presence of ArI. In the first part, we have provided strong evidence that 1 and 2 are indeed at equilibrium and that the equilibrium is controlled by factors such as the electronic nature of iron porphyrins, the electron richness of ArI, and the concentration of ArI. Secondly, we have demonstrated that 1 is the sole active oxidant in olefin epoxidation when 1 and 2 are present concurrently in a reaction solution. Finally, we have shown that the presence of ArI in a reaction solution containing 1 and H(2)18O facilitates the oxygen exchange between the oxo group of 1 and H(2)18O and that the oxygen exchange is markedly influenced by factors such as ArI incubation time, the amounts of ArI and H(2)18O used, and the electronic nature of ArI. The latter results are rationalized by the formation of an undetectable amount of 2 from the reaction of 1 and ArI through equilibrium that leads to a fast oxygen exchange between 2 and H(2)18O.

Alkenes↗