Showing papers on "Porphyrin published in 2006"
TL;DR: Accumulated evidence shows that the ferryl species [Fe(IV)O](2+) can be formed under a variety of conditions including those related to the ferrous ion-hydrogen peroxide system known as Fenton's reagent, indicating that the oxygen rebound pathway is a ubiquitous mechanism for hydrocarbon oxygenation by both heme and non-heme iron enzymes.
540 citations
TL;DR: It is demonstrated that ABCB6 is uniquely located in the outer mitochondrial membrane and is required for mitochondrial porphyrin uptake and is challenging previous assumptions about the intracellular movement of porphyrs and the factors controlling haem biosynthesis.
Abstract: The transport of porphyrins across the mitochondrial membrane is important for cellular processes. The ABC transporter Abcb6 (an energy-requiring transporter) plays a key role not only in mitochondrial porphyrin transport but also in the upregulation of haeme biosynthesis. The movement of anionic porphyrins (for example, haem) across intracellular membranes is crucial to many biological processes, but their mitochondrial translocation and coordination with haem biosynthesis is not understood. Transport of porphyrins into isolated mitochondria is energy-dependent1,2,3, as expected for the movement of anions into a negatively charged environment. ATP-binding cassette transporters actively facilitate the transmembrane movement of substances. We found that the mitochondrial ATP-binding cassette transporter ABCB6 is upregulated (messenger RNA and protein in human and mouse cells) by elevation of cellular porphyrins and postulated that ABCB6 has a function in porphyrin transport. We also predicted that ABCB6 is functionally linked to haem biosynthesis, because its mRNA is found in both human bone marrow and CD71+ early erythroid cells (by database searching), and because our results show that ABCB6 is highly expressed in human fetal liver, and Abcb6 in mouse embryonic liver. Here we demonstrate that ABCB6 is uniquely located in the outer mitochondrial membrane and is required for mitochondrial porphyrin uptake. After ABCB6 is upregulated in response to increased intracellular porphyrin, mitochondrial porphyrin uptake activates de novo porphyrin biosynthesis. This process is blocked when the Abcb6 gene is silenced. Our results challenge previous assumptions about the intracellular movement of porphyrins and the factors controlling haem biosynthesis.
337 citations
TL;DR: A time-gated luminescence imaging technique that can fully eliminate the short-lived background fluorescence from TMPyP and cell components has been successfully developed for monitoring the time-dependent generation of (1)O2 in living cells.
Abstract: A new europium(III) complex, [4‘-(10-methyl-9-anthryl)-2,2‘:6‘,2‘ ‘-terpyridine-6,6‘ ‘-diyl]bis(methylenenitrilo) tetrakis(acetate)−Eu3+, was designed and synthesized as a highly sensitive and selective time-gated luminescence probe for singlet oxygen (1O2). The new probe is highly water soluble with a large stability constant of ∼1021 and a wide pH available range (pH 3−10), and can specifically react with 1O2 to form its endoperoxide (EP-MTTA−Eu3+) with a high reaction rate constant at 1010 M-1 s-1, accompanied by the remarkable increases of luminescence quantum yield from 0.90% to 13.8% and lifetime from 0.80 to 1.29 ms, respectively. The wide applicability of the probe was demonstrated by detection of 1O2 generated from a MoO42-/H2O2 system, a photosensitization system of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP), and a horseradish peroxidase catalyzed aerobic oxidation system of indole-3-acetic acid (IAA). In addition, it was found that the new probe could b...
335 citations
TL;DR: In this article, the structure and photochemical properties of porphyrins in inorganic host materials such as clays, layered semiconductors, nanotubes, and mesoporous materials are described.
Abstract: Porphyrin derivatives are known as useful functional dyes. Porphyrin derivatives exhibit various properties in complexes with inorganic host materials that are much different from those in homogeneous solutions. In this paper, the structure and photochemical properties of porphyrins in inorganic host materials such as clays, layered semiconductors, nanotubes, and mesoporous materials are described. The photochemical properties, including the absorption properties and excited lifetimes, are much affected by the complex formation with inorganic materials. Aggregation phenomena, structural perturbations, and selected chemical reactions such as metalation and protonation affect the photochemical properties of porphyrins accommodated in inorganic host materials. The combination of porphyrin derivatives and inorganic materials should be promising for the construction of novel hybrid materials. Inorganic materials can act as novel environments for photochemical reactions. The utilization of inorganic materials for photochemical reactions is also described.
246 citations
TL;DR: An expanded porphyrin [26]hexaphyrin (1.1.2.1) was exploited as a fluorescent chemodosimeter for Ag + ions with high sensitivity and selectivity via near-infrared luminescence above 900 nm, a region that is free from optical interference in the visible wavelength range induced by the commonly used matrix and other organic compounds.
Abstract: An expanded porphyrin [26]hexaphyrin(1.1.1.1.1.1) was exploited as a fluorescent chemodosimeter for Ag + ions with high sensitivity and selectivity via near-infrared luminescence above 900 nm, a region that is free from optical interference in the visible wavelength range induced by the commonly used matrix and other organic compounds. The association constant for the Ag + –porphyrin complexation was evaluated by spectroscopic titration method to be 7.24 10 10 M 1 .
245 citations
TL;DR: In situ metalation provides a convenient way to produce adsorbed monolayers of more reactive or thermally unstable metalloporphyrins that are difficult to evaporate or even to obtain as pure compounds at room temperature.
Abstract: We demonstrate that well-defined monolayers of a metal complex on a surface can be prepared by direct vapor deposition of the metal atoms on monolayers of the ligand. In particular, ordered monolayers of adsorbed tetraphenylporphyrin (2H-TPP) on a silver surface were exposed to cobalt vapors, resulting in the complexation of the metal by the porphyrin. The formation of the metal complexes was monitored by means of X-ray photoelectron spectroscopy (XPS), which reveals that this metalation reaction leads to a chemical equivalence of all four nitrogen atoms. The described in situ metalation provides a convenient way to produce adsorbed monolayers of more reactive (e.g., air- or solvent-sensitive) or thermally unstable metalloporphyrins that are difficult to evaporate or even to obtain as pure compounds at room temperature.
231 citations
TL;DR: Complementary transient absorption measurements not only corroborate the fast decay of the photoexcited tetraphenylporphyrin but also confirm that intraconjugate charge separation evolves from the excited porphyrin to the SWNTs.
Abstract: We describe the synthesis and characterization of a series of single-wall carbon nanotubes (SWNTs) functionalized with polyamidoamine dendrimers. Importantly, the dendrimers are linked directly to the SWNT surface using a divergent methodology. This approach allows the number of functional groups on the nanotubes to be increased without provoking significant damage to the conjugated π-system of the SWNTs. Several tetraphenylporphyrin moieties can be linked to the periphery of the dendrimers, and the photophysical properties of the resulting nanoconjugates have been investigated with a series of steady-state and time-resolved spectroscopy. The fluorescence kinetics provide evidence for two transient decays, one very short-lived (i.e., 0.04 ± 0.01 ns) and one long-lived (i.e., 8.6 ± 1.2 ns). A possible explanation is that some porphyrin units do not interact with the nanotubes, thus exhibiting a fluorescence lifetime similar to that of the free porphyrin. Complementary transient absorption measurements not ...
220 citations
TL;DR: The porphyrin sheet 3 forms stable 1:2 complexes with guest molecules G1 and G2, whose 1H NMR spectra exhibit remarkable downfield shifts for the guest protons that are located just above the cyclooctatetraene (COT) core of 3, hence competing with and cancelling the weak diatropic ring currents of the local zinc(II) porphirin local cores.
Abstract: Oxidation of a directly meso−meso linked cyclic porphyrin tetramer 2 gave a porphyrin sheet 3. The symmetric square structure of 3 is indicated by its simple 1H NMR spectrum that exhibits only two signals for the porphyrin β-protons. The absorption spectrum of 3 displays characteristic Soret-like broad bands and weak Q-bands, and its magnetic circular dichroism (MCD) spectrum exhibits a negative Faraday A term at the 762 nm band as a rare case, indicating the absorption as a transition from a nondegenerate level to a degenerate level. A slightly longer S1-state (1.1 ps) and smaller TPA cross section (2750 GM) than a tetrameric linear porphyrin tape also indicate its unique electronic properties. The porphyrin sheet 3 forms stable 1:2 complexes with guest molecules G1 and G2, whose 1H NMR spectra exhibit remarkable downfield shifts for the guest protons that are located just above the cyclooctatetraene (COT) core of 3, whereas the imidazolyl protons bound to the zinc(II) porphyrin local cores are observed ...
212 citations
TL;DR: Single-wall carbon nanotube (SWNT) field effect transistors (FETs), functionalized noncovalently with a zinc porphyrin derivative, were used to directly detect a photoinduced electron transfer (PET) within a donor/acceptor (D/A) system.
Abstract: Single-wall carbon nanotube (SWNT) field effect transistors (FETs), functionalized noncovalently with a zinc porphyrin derivative, were used to directly detect a photoinduced electron transfer (PET) within a donor/acceptor (D/A) system. We report here that the SWNTs act as the electron donor and the porphyrin molecules as the electron acceptor. The magnitude of the PET was measured to be a function of both the wavelength and intensity of applied light, with a maximum value of 0.37 electrons per porphyrin for light at 420 nm and 100 W/m2. A complete understanding of the photophysics of this D/A system is necessary, as it may form the basis for applications in artificial photosynthesis and alternative energy sources such as solar cells.
209 citations
TL;DR: The reported results confirm that the presence of positively charged groups on porphyrin frame is fundamental for PSs antibacterial activity, however the data suggest that a moderate degree of lipophilicity, achievable by the introduction of aromatic hydrocarbon side chains on the pyridyl moieties, may improve PSs efficiency.
Abstract: Background Photodynamic therapy exploits visible light and photosensitizers to inactivate cells and this methodology is currently used for the treatment of several types of malignancy. Although various tumours are successfully treated with PSs and light, the application on microorganisms (photodynamic antimicrobial chemotherapy) has not yet found specific medical applications and still remains an open field of fundamental research. Purpose The assessment of the effect of a panel of seven tetraaryl-porphyrins, two commercial (PS 1 and 2 ) and five synthetic (PS 3 – 7 ) in in vitro experiments against Escherichia coli , Pseudomonas aeruginosa and Staphylococcus aureus . Methods Three of the new photosensitizers (PS 3 , 4 and 5 ) are tetracationic porphyrins and were prepared by N -alkylation of 5,10,15,20-tetra-4-pyridylporphyrin with a large excess of different benzyl chlorides; compound 7 is a dicationic porphyrin and was obtained in a similar way using a lower excess of 4-methoxybenzyl chloride. The neutral porphyrin (PS 6 ) was previously described. Dose–response curves were obtained titrating the survivors of cell suspensions (10 8 cfu/ml) exposed to the PSs and irradiated with visible light (total fluence rate 266 J/cm 2 ). Results The non ionic porphyrin 6 was the least active PS against all the tested bacteria. Cationic PSs 3 , 4 , 5 and 7 were more active than the commercial 1 and 2 . The Gram positive S. aureus was more sensitive to all the PSs than the Gram negative E. coli and P. aeruginosa , the latter being the more resistant one. Compound 7 was found particularly efficient against P. aeruginosa , causing a 7 log units reduction of survivors at a concentration of 8 μM. Conclusions The reported results confirm that the presence of positively charged groups on porphyrin frame is fundamental for PSs antibacterial activity, however our data suggest that a moderate degree of lipophilicity, achievable by the introduction of aromatic hydrocarbon side chains on the pyridyl moieties, may improve PSs efficiency. Furthermore dicationic porphyrin 7 seems to be more efficient than the corresponding tetracationic derivatives thus emphasizing an interesting feature involved in the PSs activity.
200 citations
TL;DR: In this article, a novel covalently porphyrin-functionalized single-walled carbon nanotubes (SWNTs) have been synthesized by the reaction of SWNTs with in situ generated porphrin diazonium compounds.
Abstract: Novel covalently porphyrin-functionalized single-walled carbon nanotubes (SWNTs) have been synthesized by the reaction of SWNTs with in situ generated porphyrin diazonium compounds. The resulting nanohybrid was characterized by spectroscopic (UV-Vis-NIR, FTIR and Raman) and microscopic (TEM and AFM) methods. The Raman and absorption spectroscopy data showed that the electronic properties of the modified tubes were mostly retained, without damaging their one-dimensional electronic properties. The fluorescence from the porphyrin moiety was almost completely quenched by SWNTs, indicating that the unique direct linkage mode facilitated the effective energy and electron transfer between the excited porphyrin moiety and the extended π-system of SWNTs. This novel nanohybrid material also exhibited excellent optical limiting properties.
TL;DR: A strong correlation between pi-conjugation (aromaticity) and TPA properties in porphyrin assemblies is demonstrated.
Abstract: Recently, covalently linked or self-assembled porphyrin array systems have attracted much attention for their enhanced two-photon absorption (TPA) behaviors. In this study, we have investigated the TPA properties of various dihedral angle controlled, directly linked porphyrin dimers and arrays to elucidate the relationship between the π-conjugation pathway and TPA properties. We have demonstrated a strong correlation between π-conjugation (aromaticity) and TPA properties in porphyrin assemblies.
TL;DR: It is demonstrated that, in the coplanar double-strand arrays, self-assembled upon addition of 4,4'-bipyridyl, the conjugation length increases dramatically, leading to very strong cooperative enhancement of 2PA, and the finding of extremely strong 2PA cross section, sigma2 approximately 105 GM, in double-Strand oligomers peaking at 1.3 mum can find use for signal processing in fiber-optic devices.
Abstract: We present the two-photon absorption (2PA) spectra of a series of conjugated porphyrin oligomers containing N = 2, 4, 8, and ca. 13 monomer units, meso−meso connected with butadiyne linkers. We demonstrate that, in the coplanar double-strand arrays, self-assembled upon addition of 4,4‘-bipyridyl, the conjugation length increases dramatically, leading to very strong cooperative enhancement of 2PA. We analyze the scaling of 2PA in both the double-strand and rotationally free single-strand arrays and show how the effective conjugation length in both cases is linked to the observed 2PA properties. By introducing a “conjugation signature” for the 2PA strength, we show that, in double-strand arrangement, the conjugation embraces the whole molecule up to the tetramer level, whereas in single-strand arrangement, it is always less than N, except for N = 2, but keeps increasing until N = 8. Our finding of extremely strong 2PA cross section, σ2 ≈ 105 GM, in double-strand oligomers peaking at 1.3 μm can find use for ...
TL;DR: Femtosecond pump-probe spectroscopy experiments confirm the decay of the excited porphyrin in the SWCNT-H4P2+ assembly as it injects electrons intoSWCNT.
Abstract: Photochemical solar cells have been constructed from organized assemblies of single-walled carbon nanotubes (SWCNT) and protonated porphyrin on nanostructured SnO2 electrodes. The protonated form of porphyrin (H4P2+) and SWCNT composites form 0.5−3.0 μm-sized rodlike structures and they can be assembled onto nanostructured SnO2 films [optically transparent electrode OTE/SnO2] by an electrophoretic deposition method. These organized assemblies are photoactive and absorb strongly in the entire visible region. The incident photon to photocurrent efficiency (IPCE) of OTE/SnO2/SWCNT-H4P2+ is ∼13% at an applied potential of 0.2 V versus saturated calomel electrode. Femtosecond pump−probe spectroscopy experiments confirm the decay of the excited porphyrin in the SWCNT−H4P2+ assembly as it injects electrons into SWCNT. The dual role of SWCNT in promoting photoinduced charge separation and facilitating charge transport is presented.
TL;DR: In this paper, an unprecedented two-dimensional porphyrin network featuring dynamic pores capable of hosting fullerenes is realized following a bottom-up approach at a single-crystal silver surface.
Abstract: An unprecedented two-dimensional porphyrin network featuring dynamic pores capable of hosting fullerenes is realized following a bottom-up approach at a single-crystal silver surface. Surface- and porphyrin-driven long-range interactions between the C-60 guest molecules and porphyrin layer result in the formation of exceptionally large supramolecular hybrid chains and islands (see Figure and Cover).
TL;DR: Coordinative directed assembly has been used by a number of research groups to obtain molecular squares featuring porphyrin components as discussed by the authors, and the syntheses and functional behavior of these compounds are reviewed.
TL;DR: In this paper, the effects of highly deformed porphyrin ring on the electronic structures of iron(III)-porphyrinates have been described, including the electron configurations in low-spin (S ǫ= 1/2) ruffled complexes, the contribution of the intermediate-spin state in the spin-admixed (Sǫ = 5/2, 3/2), and the novel spin crossover phenomenon in saddled complexes.
TL;DR: Experimental evidence that binding of the trans ligand weakens the Fe-NO bond is provided and further experimental and computational evidence is provided that complex 1 has noticeable Fe(I)NO+ character relative to 2, which is an Fe(II)NO(radical) complex.
Abstract: In this paper, the differences in the spectroscopic properties and electronic structures of five- and six-coordinate iron(II) porphyrin NO complexes are explored using [Fe(TPP)(NO)] (1; TPP = tetraphenylporphyrin) and [Fe(TPP)(MI)(NO)] (2; MI = 1-methylimidazole) type systems. Binding of N-donor ligands in axial position trans to NO to five-coordinate complexes of type 1 is investigated using UV−vis absorption and 1H NMR spectroscopies. This way, the corresponding binding constants Keq are determined and the 1H NMR spectra of 1 and 2 are assigned for the first time. In addition, 1H NMR allows for the determination of the degree of denitrosylation in solutions of 1 with excess base. The influence of the axial ligand on the properties of the coordinated NO is then investigated. Vibrational spectra (IR and Raman) of 1 and 2 are presented and assigned using isotope substitution and normal-coordinate analysis. Obtained force constants are 12.53 (N−O) and 2.98 mdyn/A (Fe−NO) for 1 compared to 11.55 (N−O) and 2....
TL;DR: A direct relationship between supramolecular binding of a fullerene guest to a bisporphyrin host and the appearance of a broad NIR absorption band have been established, establishing its origin in porphyrin-to-fullerene charge transfer.
Abstract: A calix[4]arene scaffolding has been used to construct bisporphyrin (“jaws” porphyrin) hosts for supramolecular binding of fullerene guests. Fullerene affinities were optimized by varying the nature of the covalent linkage of the porphyrins to the calixarenes. Binding constants for C60 and C70 in toluene were explored as a function of substituents at the periphery of the porphyrin, and 3,5-di-tert-butylphenyl groups gave rise to the highest fullerene affinities (26 000 M-1 for C60). The origin of this high fullerene affinity has been traced to differential solvation effects rather than to electronic effects. Studies of binding constants as a function of solvent (toluene < benzonitrile < dichloromethane ≪ cyclohexane) correlate inversely with fullerene solubility, indicating that desolvation of the fullerene is a major factor determining the magnitude of binding constants. The energetics of fullerene binding have been determined in terms of ΔH and ΔS and are consistent with an enthalpy-driven, solvation-de...
TL;DR: Formation of the Compound I derivative of a P450 enzyme is reported by laser flash photolysis oxidation of the corresponding Compound II species, an iron(IV)-oxo neutral porphyrin intermediate.
Abstract: Cytochrome P450 enzymes (P450s) comprise a large class of enzymes that effect numerous oxidations in nature. The active oxidants in P450s are thought to be iron(IV)−oxo porphyrin radical cations termed Compounds I, and these intermediates have been sought since the discovery of P450s 40 years ago. We report formation of the Compound I derivative of a P450 enzyme by laser flash photolysis oxidation of the corresponding Compound II species, an iron(IV)−oxo neutral porphyrin intermediate. The Compound II derivative in turn was produced by oxidation of the P450 with peroxynitrite, which effected a net one-electron, oxo-transfer reaction to the iron(III) atom of the resting enzyme. For the P450 studied in this work, CYP119 from the thermophile Sulfolobus solfactaricus, the P450 Compound II derivative was stable for seconds at ambient temperature, and the Compound I transient decayed with a lifetime of ca. 200 ms.
TL;DR: A highly soluble, conjugated Zn-porphyrin polymer was synthesized and found to strongly interact with the surface of single-walled carbon nanotubes, producing a soluble polymer-nanotube complex.
Abstract: A highly soluble, conjugated Zn-porphyrin polymer was synthesized and found to strongly interact with the surface of single-walled carbon nanotubes, producing a soluble polymer-nanotube complex. Successful complexation required the addition of trifluoroacetic acid to the solvent (THF). It was found that the complex remained soluble after excess free polymer was removed from solution, and could be centrifuged at high speed with no observable sedimentation. Furthermore, the polymer-nanotube assembly resulted in enhanced planarization and conjugation within the porphyrin polymer, which was manifested in a 127 nm bathochromic shift of the Q-band absorption. Control experiments with the Zn-porphyrin monomer indicated that homogeneous solutions could be prepared by means of sonication, but the monomer-nanotube interactions were significantly weaker, leading to nanotube precipitation within minutes. Atomic force microscopy (AFM) studies indicated that the polymer enables exfoliation of nanotube bundles and is able to "stitch" multiple nanotubes together into a series of long, interconnected strands.
TL;DR: A review of the developments that have occurred in heteroporphyrin chemistry during 1999-2005 can be found in this article, where the authors discuss the synthesis of chlorins, corroles, confused porphyrins, covalent and non-covalent porphrin assemblies.
TL;DR: The C-H bonds of hydrocarbons are oxidized catalytically by the electron-deficient Pacman porphyrin, (DPDF)Fe2O, using visible light and molecular oxygen as the terminal oxidant and oxygen atom source.
Abstract: The C-H bonds of hydrocarbons are oxidized catalytically by the electron-deficient Pacman porphyrin, (DPDF)Fe2O, using visible light and molecular oxygen as the terminal oxidant and oxygen atom source. The photocatalytic reactions proceed under mild conditions (ambient temperature and pressure) without the need for an external co-reductant.
TL;DR: In vitro data indicated a small metabolic cleavage of the O-glycoconjugates and a good stability of the S-glycoside porphyrins, and on the basis of these in vitro data, TPP(p-Deg-O-alpha-GalOH)(3) and TPP(s-glyCoside-ManOH)( 3) were selected for in vivo studies.
Abstract: Photodynamic therapy (PDT) is emerging as a new strategy for the conservative treatment of hereditary retinoblastoma. The glycoconjugated porphyrins TPP(p-Deg-O-alpha-GalOH)(3), TPP(p-Deg-O-beta-GalOH)(3), TPP(p-Deg-O-alpha-ManOH)(3), and their S-analogues were synthesized to obtain efficient photosensitizers with some retinoblastoma cell affinity. In these systems, a sugar motif and porphyrin core were linked by a diethylene glycol spacer (Deg). Cellular uptake, localization, and photoactivity have been examined in human retinoblastoma cells (Y79). After preincubation with corresponding glycosylated albumin, the uptake of TPP(p-Deg-O-beta-GalOH)(3) and TPP(p-Deg-O-alpha-ManOH)(3) was 40-45% inhibited, indicating a possible cell-sugar-receptor saturation. High photoactivity was observed for the two alpha-galacto/manno porphyrins 8 and 10 (LD(50) = 0.05 and 0.35 muM, respectively) at 514 nm and low fluence (1 J/cm(2)). Analysis by MALDI-TOF mass spectrometry only indicated a small metabolic cleavage of the O-glycoconjugates and a good stability of the S-glycoside porphyrins. On the basis of these in vitro data, TPP(p-Deg-O-alpha-GalOH)(3) and TPP(p-Deg-O-alpha-ManOH)(3) were selected for in vivo studies.
TL;DR: Porphyrin-based supramolecular macrocyclic arrays were synthesized as mimics of photosynthetic light-harvesting (LH) antennae and the radiative decay rate kF increased relative to the other decay rates with an increase in the number of ring components.
Abstract: Porphyrin-based supramolecular macrocyclic arrays were synthesized as mimics of photosynthetic light-harvesting (LH) antennae. Pentameric and hexameric macrocyclic porphyrin arrays EP5 and EP6 were constructed by complementary coordination of m-bis(ethynylene)phenylene-linked zinc-imidazolylporphyrin Zn-EP-Zn. The proton NMR spectra of noncovalently linked N-EP5 and N-EP6 indicate fast rotation of the porphyrin moieties along the ethyne axis. These macrocycles were covalently linked and identified as C-EP5 (6832 Da) and C-EP6 (8199 Da) by mass spectrometry. Fluorescence quantum yields of C-EP2 (10.0%), C-EP5 (10.1%), and C-EP6 (11.0%), even larger than that of the unit coordination dimer C-EP1 (9.3%), were significantly increased from those of the series without the ethynylene linkage. The order of increasing fluorescence quantum yields was parallel to that of decreasing fluorescence lifetimes (C-EP1 (1.65 ns), C-EP2 (1.45 ns), C-EP5 (1.42 ns), and C-EP6 (1.38 ns)), indicating that the radiative decay rat...
TL;DR: This work has designed a synthetic protocol for the preparation of flexible metal-directed supramolecular cofacial porphyrin complexes which are readily obtained in greater than 90% yield through the use of new hemilabile poiryrin ligands with bifunctional ether-phosphine or thioether- phosphine substituents at the 5 and 15 positions on the p Morphyrin ring.
Abstract: Nature routinely uses cooperative interactions to regulate cellular activity. For years, chemists have designed synthetic systems that aim toward harnessing the reactivity common to natural biological systems. By learning how to control these interactions in situ, one begins to allow for the preparation of man-made biomimetic systems that can efficiently mimic the interactions found in Nature. To this end, we have designed a synthetic protocol for the preparation of flexible metal-directed supramolecular cofacial porphyrin complexes which are readily obtained in greater than 90% yield through the use of new hemilabile porphyrin ligands with bifunctional ether-phosphine or thioether-phosphine substituents at the 5 and 15 positions on the porphyrin ring. The resulting architectures contain two hemilabile ligand-metal domains (RhI or CuI sites) and two cofacially aligned porphyrins (ZnII sites), offering orthogonal functionalities and allowing these multimetallic complexes to exist in two states, "condensed" or "open". Combining the ether-phosphine ligand with the appropriate RhI or CuI transition-metal precursors results in "open" macrocyclic products. In contrast, reacting the thioether-phosphine ligand with RhI or CuI precursors yields condensed structures that can be converted into their "open" macrocyclic forms via introduction of additional ancillary ligands. The change in cavity size that occurs allows these structures to function as allosteric catalysts for the acyl transfer reaction between X-pyridylcarbinol (where X = 2, 3, or 4) and 1-acetylimidazole. For 3- and 4-pyridylcarbinol, the "open" macrocycle accelerates the acyl transfer reaction more than the condensed analogue and significantly more than the porphyrin monomer. In contrast, an allosteric effect was not observed for 2-pyridylcarbinol, which is expected to be a weaker binder and is unfavorably constrained inside the macrocyclic cavity.
TL;DR: T tricationic porphyrin A3B3+ is an interesting sensitizer with potential applications in photodynamic inactivation of bacteria in liquid suspensions or on surfaces and studies in an anoxic condition indicate that oxygen is necessary for the mechanism of action ofPhotodynamic in activation of bacteria.
Abstract: The photodynamic effect of novel cationic porphyrins, with different pattern of meso-substitution by 4-(3-N,N,N-trimethylammoniumpropoxy)phenyl (A) and 4-(trifluoromethyl)phenyl (B) groups, have been studied in both solution bearing photooxidizable substrates and in vitro on a typical Gram-negative bacterium Escherichia coli. In these sensitizers, the cationic groups are separated from the macrocycle ring by a propoxy spacer. Thus, the charges have a high mobility and a minimal influence on photophysical properties of the porphyrin. These compounds produce singlet molecular oxygen, O2(1Δg), with quantum yields of ∼0.41–0.53 in N,N-dimethylformamide. In methanol, the L-tryptophan photodecomposition increases with the number of cationic charges in the sensitizer. In vitro investigations show that cationic porphyrins are rapidly bound to E. coli cells in ∼5 min. A higher binding was found for A3B3+ porphyrin, which is tightly bound to cells still after three washing steps. Photosensitized inactivation of E. coli cellular suspensions follows the order: A3B3+ > A44+
≫ ABAB2+ > AB3+. Under these conditions, a negligible effect was found for 5,10,15,20-tetra(4-sulfonatophenyl)porphyrin (TPPS44−) that characterizes an anionic sensitizer. Also, the results obtained for these new cationic porphyrins were compared with those of 5,10,15,20-tetra(4-N,N,N-trimethylammonium phenyl)porphyrin (TTAP4+), which is a standard active sensitizer established to eradicate E. coli. The photodynamic activity of TTAP4+ is quite similar to that produced by A44+. Studies in an anoxic condition indicate that oxygen is necessary for the mechanism of action of photodynamic inactivation of bacteria. The higher photodynamic activity of A3B3+ was confirmed by growth delay experiments. Photodynamic inactivation capacities of these sensitizers were also evaluated in E. coli cells immobilized on agar surfaces. Under these conditions, A3B3+ porphyrin retains a high activity to inactivate localized bacterial cells. Therefore, tricationic porphyrin A3B3+ is an interesting sensitizer with potential applications in photodynamic inactivation of bacteria in liquid suspensions or on surfaces.
TL;DR: Two water-soluble porphyrin self-assemblies consisting of bis acetylene- and monoacetylene-linked conjugated bis(imidazolylporphyrin) have been synthesized and were found to efficiently generate singlet oxygen upon one-photon irradiation in a manner similar to protoporphyrIn.
Abstract: Two water-soluble porphyrin self-assemblies consisting of bisacetylene- and monoacetylene-linked conjugated bis(imidazolylporphyrin) have been synthesized. Two-photon absorption (2PA) cross section values in water were determined as 7500 GM for bisacetylene- and 7900 GM for monoacetylene-linked bisporphyrin by femtosecond open-aperture Z-scan measurement. These values were almost the same as those for the similar structure reported previously in CHCl 3 . Therefore, the structure is suggested to be similar in CHCl 3 and aqueous solutions. Both compounds were found to efficiently generate singlet oxygen upon one-photon irradiation in a manner similar to protoporphyrin, as demonstrated by the time-resolved luminescence measurement at the characteristic band of 1270 nm. Photocytotoxicities for HeLa cancer cells were examined and found to be as high as those of hematoporphyrin, demonstrating that these newly prepared compounds are potential candidates as 2PA-photodynamic therapy agents.
TL;DR: The ability to employ fundamental photophysical, kinetic, and structural parameters of modular molecular architectures in assessments of the efficiency of solar-to-electrical energy conversion should facilitate the design of molecular-based solar cells.
Abstract: The efficiencies of organic solar cells that incorporate light-harvesting arrays of organic pigments were calculated under 1 sun of air mass 1.5 solar irradiation. In one set of calculations, photocurrent efficiencies were evaluated for porphyrin, phthalocyanine, chlorin, bacteriochlorin, and porphyrin-bis(perylene) pigment arrays of different length and packing densities under the assumption that each solar photon absorbed quantitatively yielded one electron in the external circuit. In another more realistic set of calculations, solar conversion efficiencies were evaluated for arrays comprising porphyrins or porphyrin-(perylene)2 units taking into account competitive excited-state relaxation pathways. A system of coupled differential equations for all reactions in the arrays was solved on the basis of previously published rate constants for (1) energy transfer between the perylene and porphyrin pigments, (2) excited-state relaxation of the perylene and porphyrin pigments, and (3) excited-state electron injection into the semiconductor. This formal analysis enables determination of the optimal number of pigments in an array for solar-to-electrical energy conversion. The optimal number of pigments depends on the molar absorption coefficient and the density at which the arrays can be packed on an electrode surface. Taken together, the ability to employ fundamental photophysical, kinetic, and structural parameters of modular molecular architectures in assessments of the efficiency of solar-to-electrical energy conversion should facilitate the design of molecular-based solar cells.