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PubMed2005

Spectrophotometric detection of pentachlorophenol (PCP) in water using immobilized and water-soluble porphyrins.

The spectrophotometric properties of porphyrins are altered upon interaction with chlorophenols and other organochlorine pollutants. Meso-tetra(4-sulfonatophenyl)porphyrin (TPPS), zinc meso-tetra(4-sulfonato phenyl)porphyrin (Zn-TPPS), monosulfonate-tetraphenylporphyrin (TPPS1), meso-tri(4-sulfonatophenyl)mono(4-carboxyphenyl)porphyrin (C1TPP), meso-tetra(4-carboxyphenyl)porphyrin (C4TPP), and copper meso-tetra(4-carboxyphenyl)porphyrin (Cu-C4TPP) in solution exhibit a broad absorbance in the range 400-450 nm Soret region. The interaction of the above mentioned porphyrins in solution with pentachlorophenol (PCP) induces a red shift in the Soret spectrum with absorbance losses at 413, 418, 403, 405, 407, and 404 nm, respectively, and the appearance of new peaks at 421, 427, 431, 416, 417, and 416 nm, respectively. The intensity of the Soret spectral change is proportional to the pentachlorophenol concentration with a detection limit of 1, 0.5, 1.16, 1, 0.5, and 0.5 ppb, respectively. The interaction of (C4TPP) and (Cu-C4TPP) in solution with PCP shows to concentration dependent for concentrations less than 4 ppb the dependence was log-linear. However, for concentrations greater than 4 ppb the relation was linear. Monosulfonate-tetraphenylporphyrin immobilized as a monolayer on a Kimwipe tissue exhibits an absorbance peak in the Soret region at 422 nm. The interaction of the porphyrin with PCP induces a red shift in the Soret spectrum with absorbance loss at 419 nm and the appearance of new peaks at 446 nm. The intensity of the Soret spectral change is proportional to the log of PCP concentration. The detection limit with immobilized TPPS1 for PCP is 0.5 ppb. These results suggest the potential for development of spectrophotometric chemosensor for PCP residues in water with detection limits less than US EPA maximum contaminate level (MCL) of 1 ppb. The immobilized TPPS1 on the Kimwipe will make it possible to develop a wiping sensors to monitor the PCP or other pesticides residues on the vegetables or wood products.

Adsorption↗
PubMed2005

Binding and photocleavage of cationic porphyrin-phenylpiperazine hybrids to DNA.

The binding properties of cationic porphyrin-phenylpiperazine hybrids to calf thymus (CT) DNA were investigated by using absorption, fluorescence and circular dichroism (CD) spectra, and the apparent affinity binding constants (K(app)) of the porphyrins for CT DNA were determined by using a competition method with ethidium bromide (EB). Intercalation of porphyrin into CT DNA occurred when two phenylpiperazines were introduced at cis position onto the periphery of cationic porphyrin. The photocleavages of pBR322 plasmid DNA by the porphyrins were consistent with the values of K(app). With [porphyrin]/[DNA base pairs] ratio increased, the binding mode tended to be outside binding, and the cleavage abilities of the porphyrins varied. In the presence of sodium azide, a quencher of 1O2, the cleavage of DNA by the porphyrin of intercalation was less inhibited.

Animals↗
PubMed2004

Nitric oxide transfer from the NO-donor S-nitroso-N-acetylpenicillamine to monomers and dimers of water-soluble iron-porphyrins.

The nitrosylation of two water-soluble iron-porphyrins, the anionic Fe(III)-meso-tetrakis(p-sulfonatophenyl)porphyrin (FeTPPS(4)) and the cationic Fe(III)-meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (FeTMPyP), by the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) was studied using optical absorption spectroscopy. The influence of ionic and non-ionic micelles on rates of nitric oxide transfer was investigated. Initially, the effect of the micelles on the pH-dependent equilibrium between monomeric and micro-oxo-dimeric species of the iron-porphyrins was examined. It is not affected in micelle-porphyrin systems with electric charges identical in sign. The non-ionic micelles of polidocanol induce a small negative pK shift. In contrast, the dimerization equilibrium of porphyrins in oppositely charged micellar phases is displaced to lower pH by approximately 2 units. Nitric oxide binding to monomers and micro-oxo-dimers was examined at pH 5.0 and 8.0, respectively. Contrary to nitrosylation by NO gas, SNAP induces reductive nitrosylation. There was no observed NO-Fe(III)porphyrin intermediate. Nitrosylation rates were obtained and compared in aqueous buffer and in micellar systems. Monomers nitrosylate much faster than micro-oxo-dimers. Oppositely charged micelles prevent nitrosylation of the iron-porphyrins or considerably enhance nitrosylation times. Nitrosylation rates are comparable to transnitrosylation rates between several S-nitrosothiols and thiol-containing proteins, suggesting biological relevance for the process.

Dimerization↗
PubMed2006

Cobalt(IV) corroles as catalysts for the electroreduction of O2: reactions of heterobimetallic dyads containing a face-to-face linked Fe(III) or Mn(III) porphyrin.

A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O(2) to H(2)O and/or H(2)O(2) when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1M HClO(4). The examined compounds are represented as (PCY)M(III)ClCo(IV)Cl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H(2)Co, and on the other hand to dicobalt porphyrin-corrole dyads of the form (PCY)Co(2) which were shown to efficiently electrocatalyze the four electron reduction of O(2) at a graphite electrode in acid media. Comparisons between the four series of porphyrin-corrole dyads, (PCY)Co(2), (PCY)H(2)Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O(2) electroreduction at potentials more positive by an average 110mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E(1/2) values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co(2) and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H(2)Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co(2) contains a Co(II) porphyrin and a Co(IV) corrole.

Binding Sites↗
PubMed1998

Capillary electrophoretic separation of cationic porphyrins.

Cationic porphyrins have a wide variety of uses including those as nucleic acid binding and cleaving agents, as potential pharmacological agents, as electron donor/acceptors in intramolecular electron transfer processes and as analytical reagents. Herein, we report the separation of cationic porphyrins by capillary electrophoresis on fused silica in phosphate buffer at pH 2-5. The porphyrins studied in this work were synthesized from alkylation of the parent tetrapyridylporphyrin (TPyP) to give various pyridinium porphyrins. For example, methylation of TPyP gives a mixture of the mono-, cis-di-, trans-di-, tri- and tetramethylated porphyrins [e.g., 5,10,15,20-tetrakis(N-methyl-4-pyridiniumyl)-21H,23H-p orphyrin, TMPyP(4)]. Capillary electrophoresis on a synthetic mixture showed separation of four of these compounds. Mixtures after alkylation with iodopropionic acid and bromopropylamine were also separated. The cis-di- and trimethylated TMPyP derivatives were separated on a small preparative scale by centrifugal partition chromatography. Capillary electrophoresis was also used to separate metallo TMPyP(4) complexes including those of cobalt, copper, iron, manganese, palladium, tin, vanadium and zinc. The conformational isomers (atropisomers) of 5,10,15,20-tetrakis(N-methyl-2-pyridiniumyl)-21H,23H-p orphyrin, TMPyP(2), were also separated. Net charge, molecular mass and molecular shape all contribute to the differential retention of cationic porphyrins under capillary electrophoresis conditions. Additional factors affecting the separations, including aggregation and protonation of the porphyrins, were probed by evaluating the separation of TMPyP(4) and its butyl and octyl analogs as a function of solution conditions. Cationic porphyrins are difficult to separate using traditional chromatographic methods; capillary electrophoresis and centrifugal partition chromatography provide excellent new techniques for separation of this class of compounds.

Cations↗
PubMed1997

A series of meso-tris (N-methyl-pyridiniumyl)-(4-alkylamidophenyl) porphyrins: synthesis, interaction with DNA and antibacterial activity.

A series of meso-5,10,15-tris(N-methyl-4-pyridiniumyl)-20-(4-alkylamidophen yl) porphyrins were synthesized by derivatizing the amino group on the phenyl ring with the following hydrophobic groups: -C(O)C7F15, -C(O)CH=CH2, C(O)CH3, -C(O)C7H15, and -C(O)C15H31. The cationic tris-pyridiumyl porphyrin core serves as a DNA binding motif and a photosensitizer to photomodify DNA molecules. The changes of the UV-Vis absorption spectra during the titration of these porphyrins with calf thymus DNA revealed a large bathochromic shift (up to 14 nm) and a hypochromicity (up to 55%) of the porphyrins Soret bands, usually considered as proof of porphyrin intercalation into DNA. Association constants (K) calculated according to the McGhee and von Hippel model, were in the range of 10(6)-10(7) M(-1). An increase in hydrophobicity of the substituents at the 20-meso-position produced higher binding affinity. These porphyrins caused photomodification of the supercoiled plasmid DNA when a green laser beam at 532 nm was applied. Those with higher surface activity acted more efficiently as DNA photomodifiers. The porphyrin with a perfluorinated alkyl chain (-COC7F15) at the meso-20-position inhibited the growth of gram-positive bacteria (S. aureus, or S. epidermidis). Other porphyrins exhibited moderate activity against both gram-negative and gram-positive organisms.

Anti-Bacterial Agents↗
PubMed2001

Intercalation of water-soluble bis-porphyrins into poly(dA)-poly(dT) double helix.

The association constants (K) of nucleic acid monomers with a series of water-soluble bis-porphyrins (bisMC1, bisMC3, bisMC5, bisMC7, and bisMC11) in which two porphyrin units were linked by a methylene chain of various lengths were estimated spectrophotometrically. Among the bis-porphyrins, the K values are similar for each nucleic acid monomer, indicating that the bridging chain length does not affect the association of the bis-porphyrins with the nucleic acid monomers. The melting curves of poly(dA)-poly(dT) in the presence of bisMC3 or bisMC5 were found to be biphasic, suggesting that bisMC3 and bisMC5 are bound to poly(dA)-poly(dT) with a binding mode different from the groove binding exhibited by the corresponding porphyrin monomers. A negative-induced CD peak in the Soret region of bisMC3 and bisMC5 with poly(dA)-poly(dT) is observed and the visible spectral changes of bisMC3 and bisMC5 upon addition of poly(dA)-poly(dT) are accompanied by a large red shift of the Soret band (bisMC3: 21 nm, bisMC5: 23 nm) with substantial hypochromicity (bisMC3: 49%, bisMC5: 40%). Therefore, it is reasonable to conclude that both of the porphyrin units of bisMC3 and bisMC5 intercalate into poly(dA)-poly(dT). In contrast to poly(dA)-poly(dT), the melting curves of poly(dA.dT)(2) in the presence of the bis-porphyrins did not show such biphasic behavior. Together with the CD and visible absorption data, it is certain that these bis-porphyrins do not intercalate into poly(dA.dT)(2).

Biochemistry↗
PubMed1999

Biomimetic degradation of lignin and lignin model compounds by synthetic anionic and cationic water soluble manganese and iron porphyrins.

The biomimetic oxidation of 5-5' condensed and diphenylmethane lignin model compounds with several water soluble anionic and cationic iron and manganese porphyrins in the presence of hydrogen peroxide is reported. The oxidative efficiency of manganese and iron meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrin chloride (TDCSPPMnCl and TDCSPPFeCl, respectively), meso-tetra-3-sulphonatophenyl porphyrin chloride (TSPPMnCl) and manganese meso-tetra(N-methylpyridinio)porphyrin pentaacetate (TPyMePMn(CH3COO)5) was compared on the basis of the oxidation extent of the models tested. Manganese porphyrins were found more effective in degrading lignin substructures than iron ones. Among them the cationic TPyMePMn (CH3COO)5, never used before in lignin oxidation, showed to be the best catalyst. The catalytic activity of porphyrins in hydrogen peroxide oxidation of residual kraft lignin was also investigated. The use of quantitative 31P NMR allowed the focusing on the occurrence of different degradative pathways depending on the catalyst used. TPyMePMn(CH3COO)5 was able to perform the most extensive degradation of the lignin structure, as demonstrated by the decrease of aliphatic hydroxyl groups and carboxylic acids. Noteworthy, no significant condensation reactions occurred during manganese porphyrins catalyzed oxidations of residual kraft lignin, while in the presence of iron porphyrins a substantial increase of condensed substructures was detected.

Anions↗
PubMed1997

Melanin-porphyrin interaction monitored by delayed luminescence and photoacoustics.

Even though melanin is commonly viewed as a photoprotective agent, the molecular mechanism of the melanin-related photoprotective action remains unclear. We studied the interaction of a synthetic dopa melanin with positively and negatively charged porphyrins using an array of spectroscopic techniques. Thus absorption, fluorescence, time-resolved delayed luminescence in the microsecond time range, and photoacoustic spectra at different modulation frequencies of both porphyrins and their mixtures with dopa melanin were measured in buffered aqueous solution at room temperature. It has been confirmed that dopa melanin forms a complex with the cationic porphyrin in its ground state, which significantly modifies the optical properties of the dye molecule. Although no such complex can be detected for the anionic porphyrin, some interaction between melanin and the porphyrin molecule can be detected in its excited state. Both porphyrins show delayed luminescence with a decay time of 35-38 microseconds, which is substantially reduced by melanin. Our photoacoustic measurements indicate that upon photoexcitation, melanin efficiently liberates heat. Our data also suggest that the thermal properties of melanin can be modified by porphyrins, particularly by the cationic form of the dye. The ionic complexes of dopa melanin with the positively charged porphyrin exhibit properties typical for a supermolecular system that liberates heat as a whole.

Dihydroxyphenylalanine↗
PubMed2003

Raman and infrared spectral study of meso-sulfonatophenyl substituted porphyrins (TPPSn, n = 1, 2A, 2O, 3, 4).

Raman and IR spectra of the free base p-sulfonatophenyl and phenyl meso-substituted porphyrins [5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4); 5,10,15-tris(4-sulfonatophenyl)-20-phenyl-porphyrin (TPPS3); 5,10-bis(4-sulfonatophenyl)-15,20-diphenylporphyrin (TPPS2A); 5,15-bis(4-sulfonatophenyl)-10,20-diphenylporphyrin (TPPS2O); and 5-(4-sulfonatophenyl)-10, 15,20-trisphenylporphyrin (TPPS1)] and their N-diprotonated derivatives (porphyrin diacids) were studied. The Raman spectra of the deuterated analogues of these porphyrins, in which the central hydrogen atoms were substituted with deuterium, were also measured. The observed vibrational bands were assigned on the basis of the deuteration shifts and compared with the structural analogues of these compounds. In IR spectra of the free-base porphyrins, the p-sulfonation of phenyl groups results in evident alteration for the phenyl modes and the porphyrin skeleton modes that are strongly coupled with phenyl vibrations. While the p-sulfonation of phenyl groups causes only slight changes for the high-frequency Raman bands (> 850 cm(-1)), dramatic shifts and band splitting were observed in the low-frequency region (< 500 cm(-1)) of Raman spectra. The observed differences of low-frequency Raman spectra were attributed to the alteration of the structure of the porphyrin ring, especially the CalphaCmCalpha bond-angles, by different meso-sulfonatophenyl substitutions. In addition, different packing style of TPPSn molecules in the aggregates is also responsible for the alteration of the vibrational spectra of the aggregated TPPSn.

Models, Chemical↗
PubMed1983

Interactions of porphyrins with nucleic acids.

The interactions of nucleic acids with water-soluble porphyrins and metalloporphyrins have been investigated by stopped-flow and temperature-jump techniques. Both natural DNA (calf thymus) and synthetic homopolymers [poly(dG-dC) and poly(dA-dT)] have been employed. The porphyrins studied belong to the tetrakis(4-N-methylpyridyl)porphine (H2TMpyP-4) series and can be divided into two groups: (i) those which have no axial ligands when bound to nucleic acids [e.g., Ni(II), Cu(II), and the nonmetallic derivatives] and (ii) those which maintain axial ligands upon binding [e.g., Mn(III), Fe(III), Co(III), and Zn(II) derivatives]. The reaction of both axially and nonaxially liganded porphyrins at AT sites is too rapid to be measured by the kinetic methods utilized, whereas at GC sites the interaction of the nonaxially liganded porphyrins is in the millisecond time range and can be monitored by both stopped-flow and temperature-jump techniques. These results corroborate previous static studies, utilizing visible spectroscopy and circular dichroism, which indicate that the formation of an intercalated complex occurs only at GC base pair sites with porphyrins which do not possess axial ligands. With all the porphyrins investigated, the complexes formed at AT sites are envisioned as being of an "external" type involving some degree of overlap between the porphyrin and the bases of the duplex. In relaxation experiments of poly-(dG-dC) with H2TMpyP-4, a large, reproducible effect is observed which can be analyzed as a single exponential. Rate constants for association and dissociation of the H2TMpyP-4/poly(dG-dC) complex are 3.7 X 10(5) M-1 s-1 and 1.8 s-1, respectively. Relaxation studies of mixtures of poly(dA-dT) and poly(dG-dC) with H2TMpyP-4 indicate that the transfer of the porphyrin from one homopolymer to another occurs via a mechanism involving dissociation rather than direct transfer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Crystal structures of the PNA-porphyrin complex in the presence and absence of lactose: mapping the conformational changes on lactose binding, interacting surfaces, and supramolecular aggregations.

The extraordinary recognition specificity of lectins for carbohydrate ligands appears to be violated as they also bind to porphyrins and other noncarbohydrate ligands. In this study, crystal structures of meso-tetrasulfonatophenylporphyrin (H(2)TPPS) bound to peanut agglutinin (PNA) in the presence and absence of lactose were determined. The binding of H(2)TPPS with PNA involved 11 molecules of H(2)TPPS in different supramolecular stacking arrangements associated with a tetramer of PNA in the crystals of the PNA-H(2)TPPS binary complex as well as the PNA-H(2)TPPS-lactose ternary complex. The ternary complex involved lactose binding only to two subunits of the PNA tetramer, which did not have porphyrin interacting in the vicinity of the carbohydrate-binding site. Comparison of the two structures highlighted the plasticity of the carbohydrate-binding site expressed in terms of the conformational change in lactose binding. The unusual quaternary structure of PNA, which results in exposed protein-protein interaction sites, might be responsible for the porphyrin binding. The association of porphyrin in diverse oligomeric stacking arrangements observed in the PNA-H(2)TPPS complex suggested the possibility of protein-porphyrin aggregation under abnormal physiological conditions. The structures described here provide a possible native conformation of the carbohydrate-binding site of PNA in the absence of the ligand, highlight mapping of the unsaturated binding surfaces of PNA using porphyrin interactions, indicate new leads toward possible application of this lectin in photodynamic therapy, and exhibit diverse modes of porphyrin-lectin interactions with implications to porphyria, a disease that results from abnormal accumulation of porphyrins.

Binding Sites↗
PubMed2005

NMR and EPR studies of low-spin Fe(III) complexes of meso-tetra-(2,6-disubstituted phenyl)porphyrinates complexed to imidazoles and pyridines of widely differing basicities.

A series of bis-axially ligated complexes of iron(III) tetramesitylporphyrin, TMPFe(III), tetra-(2,6-dibromophenyl)porphyrin, (2,6-Br2)4TPPFe(III), tetra-(2,6-dichlorophenyl)porphyrin, (2,6-Cl2)4TPPFe(III), tetra-(2,6-difluorophenyl)porphyrin, (2,6-F2)4TPPFe(III), and tetra-(2,6-dimethoxyphenyl)porphyrin, (2,6-(OMe)2)4TPPFe(III), where the axial ligands are 1-methylimidazole, 2-methylimidazole, and a series of nine substituted pyridines ranging in basicity from 4-(dimethylamino)pyridine (pK(a)(PyH(+)) = 9.70) to 3- and 4-cyanopyridine (pKa(PyH+) = 1.45 and 1.1, respectively), have been prepared and characterized by EPR and 1H NMR spectroscopy. The EPR spectra, recorded at 4.2 K, show "large g(max)", rhombic, or axial signals, depending on the iron porphyrinate and axial ligand, with the g(max) value decreasing as the basicity of the pyridine decreases, thus indicating a change in electron configuration from (d(xy))2(d(xz),d(yz)3 to (d(xz),d(yz))4(d(xy))1 through each series at this low temperature. Over the temperature range of the NMR investigations (183-313 K), most of the high-basicity pyridine complexes of all five iron(III) porphyrinates exhibit simple Curie temperature dependence of their pyrrole-H paramagnetic shifts and beta-pyrrole spin densities, rho(C) approximately 0.015-0.017, that are indicative of the S = 1/2 (d(xy))(2)(d(xz),d(yz))(3) electron configuration, while the temperature dependences of the pyrrole-H resonances of the lower-basicity pyridine complexes (pK(a)(PyH(+)) < 6.00) show significant deviations from simple Curie behavior which could be fit to an expanded version of the Curie law using a temperature-dependent fitting program developed in this laboratory that includes consideration of a thermally accessible excited state. In most cases, the ground state of the lower-basicity pyridine complexes is an S = 1/2 state with a mixed (d(xy))2(d(xz),d(yz))3/(d(xz),d(yz))4(d(xy))1 electron configuration, indicating that these two are so close in energy that they cannot be separated by analysis of the NMR shifts; however, for the TMPFe(III) complexes with 3- and 4-CNPy, the ground states were found to be fairly pure (d(xz),d(yz))4(d(xy))1 electron configurations. In all but one case of the intermediate- to low-basicity pyridine complexes of the five iron(III) porphyrinates, the excited state is found to be S = 3/2, with a (d(xz),d(yz))3(d(xy))1(d(z)2)1 electron configuration, lying some 120-680 cm(-1) higher in energy, depending on the particular porphyrinate and axial ligand. Full analysis of the paramagnetic shifts to allow separation of the contact and pseudocontact contributions could be achieved only for the [TMPFe(L)2]+ series of complexes.

Electron Spin Resonance Spectroscopy↗
PubMed2002

Light-harvesting heptadecameric porphyrin assemblies.

New porphyrin assemblies containing 17 porphyrin molecules are constructed by using free base TPP-type porphyrins having eight pyrazine moieties 1. Spectroscopic titration of dimeric [meso-tetrakis(2-carboxy-4-nonylphenyl)porphyrinato]zinc(II) 2 with these porphyrins shows that the processes of the formation of the heptadecameric porphyrin assemblies may be analyzed as eight independent equilibrium processes with an identical binding constant. All binding constants are larger than 5 x 107 M-1 which is the determinable upper limit of the present titration method. In all cases, the fluorescence spectrum of the 1:8 mixture of 1 and 2 consists of the major fluorescence of 1 and the minor one of 2.pyrazine complex even in the presence of the large excess of the antenna pigments. The observed spectra are well reconstructed by the form of faF1 + fbF2, where F1 and F2 are the fluorescence of 1 and the 2.pyrazine complex measured separately at the corresponding concentrations. Interestingly, the general trend that values of fa are nearly equal to those of r564 x (1 - fb) in all cases is found, where r564 is the absorption ratios of the 2.pyrazine moiety and the central free base porphyrin in the assemblies at 564 nm. The observation indicates the excitation of the central porphyrin is directly enhanced by the absorption of the antenna pigments even in such large scale assemblies. Thus, the antenna effect for 1 having largest r564 results in 77 times fluorescence enhancement of the central free base porphyrin. The systems also show interesting dependency of energy-transfer efficiencies on the topological arrangement of the antenna elements.

Metalloporphyrins↗
PubMed2005

Anion chelation-induced porphyrin protonation and its application for chloride anion sensing.

The protonation of a simple meso-tetraphenylporphyrin in an organic-aqueous system was found to be induced by the counteranions. During the process of protonation, the counteranion of the proton sources binds with the porphyrin core and thus promotes the complexation of the porphyrin and protons. The interaction of porphyrin and anion was characterized by fluorescence, UV-visible, cyclic voltammetry, (1)H NMR, and IR. Moreover, it could be exploited in selective fluorescent sensing of Cl(-). The sensing mechanism was based on extraction of protons from the aqueous phase into the organic phase by free base porphyrin and simultaneous coextraction of Cl(-), which promoted porphyrin protonation, and hence resulted in significant changes of the porphyrin fluorescence spectra. Selectivity trends turned out to be dependent upon the lipophilicity of anion and the binding affinity and structure complementarity between the protonated porphyrin and anions. The fluorescence enhancement of the porphyrin band at 684 nm showed modest selectivity for Cl(-) and NO(3)(-).

Anions↗
PubMed2005

Porphyrin effects on zwitterionic HPS micelles as investigated by small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR).

In this work, small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) studies on the interaction of three anionic mesotetrakis (4-sulfonatophenyl) porphyrins, TPPS4, FeTPPS4, and ZnTPPS4, at concentrations in the 2-10 mM range, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) at pH 4.0 and 9.0 are reported. The SAXS results demonstrate that, upon addition of all species of porphyrins, the HPS micelle of prolate shape reduces its axial ratio from 1.8 +/- 0.2 (in the absence of porphyrin) to 1.5 +/- 0.1. Such an effect is accompanied by a shrinking of the paraffinic shortest semiaxis from 22.5 +/- 0.5 A to 18.0 +/- 0.2 A. This shows that the micellar hydrophobic core is affected by porphyrin incorporation, independent of the type of porphyrin and pH. Concurrently, EPR results demonstrate an increase in the micellar packing as noticed from the increase in motional restriction for both nitroxides. Furthermore, increase of the porphyrin concentration induces the appearance of a repulsive interference function over the SAXS curve of zwitterionic micelles, which is typical of an interaction between surface-charged micelles. Such a finding gives strong evidence that the negatively charged porphyrin molecule must accommodate in the HPS micelle dipole layer close to the inner positive charges (near the hydrophobic core), inducing a surface charge (probably a negative one associated with the HPS sulfonate external groups) in the original zwitterionic (overall neutral) micelle. Such a porphyrin location is favored by both electrostatic and hydrophobic contributions, giving rise to binding constant values that are quite large compared to the binding of cationic drugs to HPS micelles (Caetano, W.; Barbosa, L. R. S.; Itri, R.; Tabak, M. J. Coll. Int. Sci. 2003, 260, 414).

Electron Spin Resonance Spectroscopy↗
PubMed1998

Ab initio calculations on iron-porphyrin model systems for intermediates in the oxidative cycle of cytochrome P450s.

Geometry optimizations for several spin states of the iron(III)-S-methyl- porphyrin complex, the iron (III)-oxo-S-methyl-porphyrin complex and the respective anions were performed in order to examine models for intermediates in the oxidative cycle of cytochrome P450. The aim of this study was to obtain insights into the ground states of the intermediates of this catalytic cycle and to use the ab initio calculated geometries and charge distributions to suggest better and more realistic parameters for forcefields which are generally used for modeling P450s. The results indicate that the ground states of both the iron(III)-S-methyl-porphyrin complex and the iron(III)-oxo-S-methyl-porphyrin complex are sextet spin states (high spin). The ground states of the anions of both complexes are probably quintet spin states. The fact that experimentally a shift from low spin to high spin is observed upon binding of the substrate suggests that the ab initio calculations for the iron(III)-S-methyl-porphyrin complex in vacuum give a correct representation of the (hydrophobic) substrate-bound state of the active site of P450. The ab initio geometries of the iron-porphyrin complexes are very similar to the experimentally observed geometries, except for the longer iron-sulfur bond in ab initio calculations, which is probably caused by the omission of polarization functions on the sulfur atom during the geometry optimization. The charge distribution in all ab initio calculated complexes can be described by a series of concentric rings of alternating charge, thus allowing a relatively large positive charge on the iron atom. The commonly used forcefields generally underestimate the charge differences between the iron atom and the different parts of the porphyrin moiety or ignore the charges completely. Although forcefield calculations can reproduce the experimental geometry of iron-porphyrin moieties, extension of the forcefields with charges obtained from ab initio calculations should give a better description of the heme moiety in protein modeling and docking experiments.

Animals↗
PubMed1992

Evaluation of tumour and tissue distribution of porphyrins for use in photodynamic therapy.

A range of pure, monomeric porphyrins were synthesised and their localising capacities compared to HpD and Hp at 6 h and 24 h post injection in the mouse C6 intracerebral glioma model as well as in normal brain, skin, muscle, kidney, spleen, liver, lung and whole blood. The partition coefficients were examined between PBS and 2-octanol over the pH range 7.4-6.6 and pH profiles were established. A parabolic relationship was observed between log (porphyrin tumour concentration) at pH 7.4, with maximal tumour localisation at log (partition coefficient), pi, of approximately zero. Porphyrins with side chains with nett cationic character also exhibited up upward (parabolic) dependence on pi for most tissues studied, with maximal porphyrin localisation at pi of 0-0.5. In contrast, those porphyrins with nett anionic character exhibited a downward (negative) parabolic trend for all eight tissues studied, with minimal porphyrin localisation at pi of approximately zero. Four porphyrins (4, 11, 12, 13) exhibited similar or better tumour localisation than HpD, and two (11 and 12) offer promise as lead compounds for the design of improved porphyrins for use in PDT.

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