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PubMed2007

Electronic effects of peripheral substituents at porphyrin meso positions.

Porphyrins are stable molecules with a macrocyclic conjugated system and often peripheral substituents. This unique structure makes the electronic properties of the four meso-carbons (the methine bridges) nearly identical. Replacement of the weakly electron-polarizing 2,4-vinyl groups of protoporphyrin IX with strongly electron-polarizing acetyl groups not only leads to much lower meso-carbon reactivities toward electrophilic aromatic substitution but also results in a significant meso-selectivity (the beta- and gamma-meso-positions become much more nucleophilic (basic) than the alpha- and delta-meso-positions). To further investigate the relationship between the porphyrin meso-carbon reactivities and the peripheral substituents, two monoacetylporphyrin analogues also were synthesized. This investigation not only leads to empirical rules for predicting porphyrin meso-carbon selectivities but also provides important models for theoretical calculations of porphyrin aromaticity.

Electrons↗

PubMed2005

Excited states of porphyrin isomers and porphycene derivatives: a SAC-CI study.

Excited states of free-base porphyrin isomers, porphycene (Pc), corrphycene (Cor), and hemiporphycene (hPc), were studied by the Symmetry-Adapted Cluster (SAC)/SAC-Configuration Interaction (CI) method. The absorption peaks of the porphyrin isomers were assigned on the basis of the SAC-CI spectra. The X, Y, X', and Y' bands of the porphyrin isomers, which have weak intensities, are identified. The differences in the Q-band absorptions among the isomers were clearly explained by the four-orbital model. In Cor and hPc, the wave function of the B-band corresponds to the mixture of the four-orbital excitations and the optically forbidden excitation of free-base porphin (P), due to the molecular symmetry lowering in the isomers. The B-band character is described by the five-orbital model in Pc and the six-orbital model in Cor and hPc. Two tetrazaporphycenes and two ring-extended (dibenzo) porphycenes were designed, and the Q-band transition moment was successfully controlled. These examples show that the control of the four-orbital energy levels is the guiding principle for pigment design in porphyrin compounds.

Electrochemistry↗

PubMed2005

Amphiphilic cyclodextrin carriers embedding porphyrins: charge and size modulation of colloidal stability in heterotopic aggregates.

The interaction between the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin (TPPS) and cationic vesicles formed by heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-cyclodextrin (SC6CDNH2) has been investigated in detail through a combination of elastic light scattering (ELS), quasi-elastic light scattering (QELS), zeta potential measurements, and time-resolved fluorescence anisotropy. ELS experiments provided the first structural characterization of these cationic vesicles both in the absence and in the presence of TPPS porphyrin, modeling the system as a spherical particle described by a single thin shell form factor. The structure of mixed hetero-aggregates is modulated by charge and size of the two components as function of different porphyrin/cyclodextrin (CD) molar ratios. At the limiting molar ratio studied, the absolute value of zeta potential (/zeta/ = 12.5 mV) seems to be a reference value for the formation of stable colloidal CD vesicular aggregates at thermodynamic equilibrium. New insights on the structure of these heterotopic colloids have been obtained by analysis of rotational correlation times at different molar ratios exploiting time-resolved fluorescence anisotropy experiments. At high porphyrin loads, the anisotropy decays behave as monoexponentials and the rotational correlation times (1-2 ns) together with the r(0) values close to zero suggest the presence of small amounts of TPPS embedded in a hydrophobic environment either in monomeric or in aggregated form. At the lower porphyrin/CD molar ratios, the anisotropy decays exhibit a double-exponential behavior showing a predominant component with a slow rotational correlation time (20-25 ns) and limiting anisotropy values of approximately 0.15. This component has been assigned to molecules that are more stabilized onto the CD vesicles, that is, porphyrins embedded into the oligo-ethylene "wall" of the CD vesicles. Scanning near-field optical microscopy of the samples evaporated on glass surfaces gave further insights on the morphology and optical properties of these systems, confirming the embedding of TPPS on the vesicles and evidencing the role of the solvent.

Anions↗

PubMed2006

Nonlinear absorption and nonlinear refraction of self-assembled porphyrins.

Nonlinear refraction and nonlinear absorption of self-assembled porphyrins in the nanosecond and picosecond regimes were studied at 532 nm by the Z-scan technique. First, a marked difference in nonlinear refraction was observed between self-assembled zinc porphyrins and free base porphyrins; however, the effects of self-assembly and metallization on nonlinear absorption are small. Second, an enhancement of nonlinear absorption was observed for the monomeric components of self-assembled structures by adding pyridine, while their nonlinear refractions remained almost unchanged as pyridine was added. It is expected that the metallization and addition of ligand can provide more convenient routes to alter the optical nonlinearities of porphyrins than the modifications of molecular structures of traditional covalent-bond organic materials.

Lasers↗

PubMed2004

Self-organization of self-assembled tetrameric porphyrin arrays on surfaces.

The incorporation of designed self-assembled supramolecular structures into devices requires deposition onto surfaces with retention of both structure and function. This remains a challenge and can present a significant barrier to developing devices using self-organizing materials. To examine the role of peripheral groups in the self-organization of self-assembled multiporphyrinic arrays on surfaces, Pd(II)-linked square and Pt(II)-linked trapezoidal tetrameric porphyrin arrays with peripheral tert-butylphenyl or dodecyloxyphenyl functionalities were investigated using various spectroscopies and atomic force microscopy. The Pd(II) assembled squares disassemble upon deposition on glass surfaces, while the Pt(II) assembled trapezoids are more robust and can be routinely cast on these surfaces. The orientation and length of the peripheral alkyl substituents influence the resultant structures on surfaces. The tert-butylphenyl-substituted porphyrin array forms discrete columnar stacks, which assemble in a vertical direction via pi-stacking interactions among the macrocycles. The tetrameric porphyrin array with dodecyloxyphenyl groups forms a continuous film via van der Waals interactions among the peripheral hydrocarbon chains. The super-molecules with liquid crystal-forming moieties also form three-dimensional crystalline structures at higher deposition concentrations. These observations clearly demonstrate that the number, position, and nature of the peripheral groups and the supramolecular structure and dynamics, as well as the energetics of interactions with the surface, are of key importance to the two-dimensional and three-dimensional self-organization of assemblies such as porphyrin arrays on surfaces.

Dimerization↗

PubMed2004

Synthesis and supramolecular self-assembly study of a novel porphyrin molecule in Langmuir and Langmuir-Blodgett films.

The self-assembly and supramolecular engineering of porphyrins into ordered arrays have recently attracted much interest because of their promising application potential in molecular and electronic devices, spintronics, energy harvesting and storage, catalysis, and sensor development. We herein report the synthesis and supramolecular self-assembly study of a novel porphyrin molecule, 2Por-TAZ, in Langmuir and Langmuir-Blodgett films. The 2Por-TAZ molecule contains two porphyrin macrocycles attached to a triaminotriazine headgroup. Triaminotriazines are known to form a highly ordered linear supramolecular self-assembly through complementary hydrogen bonding with barbituric acid molecules at the air-water interface. Surface pressure-area isotherm measurements and polarized UV-vis absorption spectroscopic studies indicate that the 2Por-TAZ molecules adopted an edge-on orientation at the air-water interface. Polarized UV-vis absorption study also revealed that the 2Por-TAZ molecules formed linear supramolecular networks on pure water and barbituric acid subphase with porphyrin flat planes facing toward the compression direction. The binding of barbituric acid with 2Por-TAZ molecules was observed from the expansion of the Langmuir monolayer film. Compared to the transferred LB film from pure water subphase, both the UV-vis absorbance and fluorescence emission intensity of the LB film transferred from barbituric acid subphase increased significantly.

Hydrogen Bonding↗

PubMed2005

Probing of porphyrin surface chemistry in systems with laser-ablated Ag nanoparticle hydrosol: role of thiosulfate anions.

The influence of sodium thiosulfate (THS) concentration in Ag colloid/THS/H(2)TMPyP and Ag colloid/H2TMPyP/THS systems (H2TMPyP = 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin) was investigated by a combination of surface-enhanced resonance Raman scattering (SERRS) spectroscopy, surface plasmon extinction (SPE) measurements, and transmission electron microscopy (TEM). THS was found to have a strong impact on Ag nanoparticle surface structure and aggregation state and on interaction with H2TMPyP probe molecules, as evidenced by variations of the SERRS spectrum. In the Ag colloid/THS/H2TMPyP system, when laser-ablated Ag colloid was THS pretreated prior to the porphyrin addition, a critical threshold THS concentration (4 x 10(-5) M) was discovered. At concentrations below the threshold, THS mainly reduces the number of Ag+ adsorption sites. This leads to increased Ag nanoparticle aggregation prior to the porphyrin addition and significant weakening of the overall SERRS signal. Dominant contributions in the SERRS spectrum correspond to free base H2TMPyP and Ag+ containing the AgTMPyP form. At concentrations above the threshold, THS mediates also the formation and stabilization of new adsorption sites, probably Ag(0) sites. This induces a turn in the aggregation state of the pretreated Ag-c/THS system, an increase of the overall SERRS signal, and the appearance of a new spectral form of Ag metalated porphyrin.

Anions↗

PubMed2004

Incorporation of glycoconjugated porphyrin derivatives into phospholipid monolayers: a screening method for the evaluation of their interaction with a cell membrane.

The use of porphyrin derivatives in photodynamic therapy is of excellent prospect for the treatment of superficial or easily reachable tumors. The selection of porphyrin derivatives by tumor cells depends to a large extent of their ability to interact with the biological membrane. The evaluation of porphyrin interaction with phospholipids can thus be used as a screening method. In this work we report on the assessment of the interaction of three new porphyrin derivatives with various phospholipids forming Langmuir films by surface tension and surface pressure measurements, grazing incidence X-ray diffraction, and liquid chromatography on an IAM stationary phase. The results show that the hydroxylated phenylporphyrin (m-THPP) is able to interact with all studied phospholipids and to significantly disorganize the structure of their monolayers. Obviously, the interaction occurs at the level of the hydrophobic chains of a phospholipid. A triglucoconjugated phenylporphyrin (m-TPP(Glu)3) also interacts with the phospholipids though to a lesser extent. Conversely, the tetraglucoconjugated derivative (m-TPP(Glu)4) exhibits both a weak surface activity and a poor affinity for the studied phospholipids. Thus, whereas m-THPP and m-TPP(Glu)3 are expected to penetrate into a biological membrane, m-TPP(Glu)4 seems unlikely to do so.

Cell Membrane↗

PubMed1987

Destruction of erythroleukaemic cells by photoactivation of endogenous porphyrins.

Selective destruction of Friend erythroleukaemic cells (FELC) was potentiated by stimulation of endogenous porphyrin synthesis followed by light sensitization. Endogenous porphyrin biosynthesis in FELC was induced by supplementation of 5-amino levulinic acid (5-ALA) at a concentration of 5 X 10(-4) M. The main accumulated product, after 4 days culture, was uroporphyrin, while after 8 days culture the cells were loaded with protoporphyrin, up to 1.5 micrograms 10(-7) cells. Photoirradiation of the cells for 2 min, accumulating endogenous porphyrins, induced cardinal deformations and cell disintegration in greater than 95% of the cells, as examined by scanning electron microscopy (SEM). The photodynamic destruction effects were dependent on cultivation time with 5-ALA. Flow cytometry analysis showed an immediate expansion of cell volume subsequent to irradiation, presumably a consequence of water influx. Transmission electron microscopy (TEM) of photosensitized cells after different time intervals of culture in 5-ALA medium, revealed initial damage to mitochondria and water influx into the nuclear envelope, after 2 days. After 3-4 days in culture the water influx phenomenon was pronounced, chromatin condensation took place and slight rupture of the outer membrane was detected. Cells photosensitized after 5-6 days of culture were completely disintegrated leaving a nuclear remnant and an enormously swollen nuclear envelope. The culture time dependence of the process, showed an interrelationship between the photodynamic effect and porphyrin accumulation sites in cellular compartments. The study presents a specific method for erythroleukaemic cell inactivation.

Aminolevulinic Acid↗

PubMed1992

Porphyrin metabolism in some malignant diseases.

Porphyrin metabolism was studied in 21 children of both sexes suffering from acute lymphoblastic leukaemia (ALL) and 34 adult patients of different ages and sexes suffering from ALL (n = 14), non-Hodgkin's lymphoma (NHL), n = 14, or Hodgkin's disease (HD), n = 6. In addition, two groups of healthy children (n = 14), and adults (n = 17) were studied for comparison. It was apparent from this study that the activity of uroporphyrinogen-1-synthetase (URO-1-S, E.C. 4.3.1.8) was highly significantly activated in the blood of children, while the activities of blood 5-aminolevulinic acid dehydrase (E.C. 4.2.1.24) and ferrochelatase (E.C. 4.99.1.1.), as expressed by protoporphyrin/haem ratio, were inhibited in those children. Also, free erythrocyte total porphyrins were increased, while the haem content was reduced. The concentrations of 5-aminolevulinic acid, coproporphyprin and uroporphyrin were increased in the urine of children with ALL. On the other hand, some dramatic changes were found in porphyrin metabolism in adult patients suffering from ALL, NHL and HD. The aforementioned disturbances were discussed in the light of some factors which may affect the enzymatic activities in the synthesis of porphyrins.

Adult↗

PubMed2003

Synthesis, characterization and molecular structures of six-coordinate manganese nitrosyl porphyrins.

Manganese(II) porphyrins are isoelectronic with iron(III) porphyrins, and previously reported work suggests that manganese nitrosyl porphyrins are good structural models for their kinetically unstable and biologically relevant ferric-NO analogues. We have prepared a new set of six-coordinate manganese nitrosyl porphyrins of the general form (por)Mn(NO)(L)(por = TTP, T(p-OCH3)PP; L = piperidine, methanol, 1-methylimidazole) in moderate to high yields. The (por)Mn(NO)(pip) complexes were prepared from the reductive nitrosylation of the (por)MnCl compounds with NO in the presence of piperidine. The IR spectra of the (por)Mn(NO)(pip) compounds as KBr pellets show new strong bands at 1746 cm(-1)(for TTP) and 1748 cm(-1)(for (T(p-OCH3)PP) due to the NO ligands. Attempted crystallization of one of these compounds (por = TTP) from dichloromethane-methanol resulted in the generation of the methanol complex (TTP)Mn(NO)(CH3OH). Reaction of the (por)Mn(NO)(pip) compounds with excess 1-methylimidazole gave the (por)Mn(NO)(1-MeIm) derivatives in good yields. The IR spectra of these compounds show nu(NO) bands that are approximately 12 cm(-1) lower than those of the (por)Mn(NO)(pip) precursors, indicative of greater Mn-->NO pi-backdonation in the 1-MeIm derivatives. X-Ray crystal structures of three of these compounds, namely (TTP)Mn(NO)(CH3OH), (TTP)Mn(NO)(1-MeIm) and (T(p-OCH3)PP)Mn(NO)(1-MeIm) were obtained, and reveal that the NO ligands in these complexes are linear.

Manganese↗

PubMed2004

Porphyrin-fullerene linked systems as artificial photosynthetic mimics.

We have prepared a variety of porphyrin-fullerene linked systems to mimic photoinduced energy and electron transfer (ET) processes in photosynthesis. Photodynamical studies on porphyrin and analogs-fullerene linked systems have revealed the acceleration of photoinduced electron transfer and charge-shift and the deceleration of charge recombination, which is reasonably explained by the small reorganization energies of electron transfer in fullerenes. In this context, we have proposed two strategies, photoinduced single-step and multi-step electron transfers, for prolonging the lifetime of a charge-separated state in donor-acceptor linked systems. The single-step ET strategy allowed a zinc chlorin-fullerene linked dyad to extend the lifetime up to 120 seconds in frozen PhCN at 123 K, which is the longest value of charge separation ever reported for donor-acceptor linked systems. Unfortunately, however, the quantum yield of formation of the charge-separated state was as low as 12%, probably due to the decay of the precursor exciplex state to the ground state rather than to the favorable complete charge-separated state. In contrast, the multi-step ET strategy has been successfully applied to porphyrin-fullerene linked triads, tetrads, and a pentad. In particular, a ferrocene-porphyrin trimer-fullerene pentad revealed formation of a long-lived charge-separated state (0.53 s in frozen DMF at 163 K) with an extremely high quantum yield (83%), which is comparable to natural bacterial reaction centers. These results not only provide valuable information for a better understanding of photoinduced energy and electron transfer processes in photosynthesis, but also open the door for the development of photoinitiated molecular devices and machines.

Algorithms↗

PubMed2006

Synthesis of supramolecular fullerene-porphyrin-Cu(phen)(2)-ferrocene architectures. A heteroleptic approach towards tetrads.

Four supramolecular fullerene-porphyrin-Cu(phen)(2)-ferrocene architectures were accessed by a twofold coordination strategy. At first, the phenanthroline-linked zinc porphyrins , conceived as supramolecular synthons, were combined with a ferrocene module, 3,8-(diferrocenylethynyl)phenanthroline, by a Cu(i)-mediated heteroleptic bisphenanthroline complexation (HETPHEN) protocol to furnish the porphyrin-Cu(phen)(2)-ferrocene aggregates . Subsequently, the fullerene module was incorporated by axial pyridyl coordination to the zinc porphyrin, affording . Their suitability as tetrads was interrogated using electrochemical and photophysical data.

Electrochemistry↗

PubMed1977

Molar absorption coefficients of porphyrin esters in chloroform determined by copper titration.

Chromatographically pure porphyrin esters free from metalloporphyrins were titrated with Cu2+ to determine the molar amount of porphyrin present. The end point of the titration was defined by a t.l.c. method detecting traces of metal-free porphyrin ester in admxture to its copper complex. From spectrometric measurement at the Soret maximum and the molar amounts found by the titration, epsilonM was calculated for proto-, copro-, penta-, hexa- and hepta-carboxylic and uro-porphyrin permethyl esters. The values for uroporphyrin showed perfect agreement with those of previous workers, whereas those for coproporphyrin were about 5% lower and those for protoporphyrin more than 20% lower. The implications of the findings are discussed. Determinations of epsilonM of some higher esters (ethyl to pentyl) and some partial methyl esters with one carboxyl group free are also presented.

Chloroform↗

PubMed2000

Phosphorescent porphyrin probes in biosensors and sensitive bioassays.

Platinum(II) and palladium(II) complexes of porphyrins and related tetrapyrrolic pigments emit strong phosphorescence at room temperatures, which is characterized by long lifetimes falling into the sub-millisecond range and long-wave spectral characteristics. These features make the dyes useful as probes for a number of bioanalytical applications, particularly those employing time-resolved fluorescent detection. They can provide high sensitivity and selectivity, together with rather simple instrumental set-up. A number of analytical systems are now under development that are based on the use of phosphorescent porphyrin probes. Experimental results are presented on the following systems: (i) fibre-optic phosphorescence lifetime-based oxygen sensor on the basis of hydrophobic platinum-porphyrins and development of advanced sensing materials and prototype instrumentation; (ii) practical applications of the optical oxygen sensor, including a sensitive immunosensor that employs glucose oxidase labels, a rapid screening method for cell viability in microtitre-plate format, non-destructive measurement of oxygen in packaged foods and reagentless biosensors for metabolites (glucose, lactate); and (iii) the use of water-soluble platinum- and palladium-porphyrins as labels for ultra-sensitive time-resolved phosphorescence immunoassays.

Biological Assay↗

PubMed1977

Porphyrins in erythrocytes and blood plasma: preliminary studies with qualitative thin-layer chromatography.

1. A simple chromatographic method for the study of porphyrins in erythrocytes and blood plasma, requiring little technician time, is described. The findings in adults and neonates are presented as well as those from severely ill patients. 2. The regular occurrence of uro-, copro- and proto-porphyrin in erythrocytes is deomonstrable as well as sporadic occurrence of tri-, penta-, hexa- and hepta-carboxylic porphyrin. The method gives, however, irregular values for protoporphyrin, which seems to occur in a more labile form in some subjects than in others; this is especially the case in erythropoietic protoporphyria. 3. In blood plasma, uroporphyrin occurs regularly, and coproporphyrin less regularly. Protoporphyrin and penta- to hepta-carboxylic porphyrin are found only occasionally.

Adult↗

PubMed2002

Extending supramolecular fullerene-porphyrin chemistry to pillared metal-organic frameworks.

Porphyrins and fullerenes are spontaneously attracted to each other. This supramolecular recognition element can be exploited to produce ordered arrays of interleaved porphyrins and fullerenes. C(60) x H(2)TpyP x Pb(NO(3))(2) x 1.5TCE (H(2)TpyP = tetra-4-pyridylporphyrin; TCE = 1,1,2,2-tetrachloroethane) crystallizes in the tetragonal P4/n space group and the structure has been solved to high resolution. The Pb(2+) ions connect the pyridylporphyrins in infinite sheets with an interlayer spacing of 12.1 A. The fullerenes are intercalated between these layers, acting as pillars. The 6:6 ring juncture bonds of C(60) are centered over the porphyrins, bringing the layers into strict tetragonal register. This arrangement identifies the fullerene-porphyrin interaction as a structure-defining element. The same motif is seen in a related ribbon structure having C(70) intercalated into HgI(2)-linked H(2)TpyTP. The supramolecular design principles involved in assembling these chromophores may have applications in materials science.

Carbon↗

PubMed1974

Repression by hematin of porphyrin biosynthesis in erythrocyte precursors in congenital erythropoietic porphyria.

Hematin administered intravenously in a patient with congenital erythropoietic porphyria evidently entered erythrocyte precursors in the bone marrow, producing the well-known negative feedback repression of porphyrin biosynthesis with marked decline of porphyrin concentrations in urine, circulating plasma, and erythrocytes. A delay in the major segment of this effect corresponded roughly with the sum of the average transit times through the maturation compartments of the erythrocyte precursors. This delay was considerably longer than previously observed in the decline of porphyrin precursors after administration of hematin in patients with hepatic porphyria. The effect of hematin was compared with that of packed erythrocyte transfusions given at regular intervals in the same patient over a period of 2.5 years. In general, administration of hematin results in a reduction of porphyrin formation of the same order of magnitude, but of shorter duration, possibly in relation to the relatively small amounts of hematin infused.

Adult↗