Showing papers on "Porphyrin published in 1996"

Assignment of Protoheme Resonance Raman Spectrum by Heme Labeling in Myoglobin

Abstract: Resonance Raman (RR) spectra are reported for myoglobin reconstituted with seven heme isotopomers which are labeled with 15N and meso-D4 in the porphyrin skeleton or at the vinyl and propionate substituents. The RR bands are assigned to the porphyrin in-plane and out-of-plane modes as well as to the internal vibrations of substituents on the basis of the observed isotope shifts. The issue of vinyl substituent effects is revisited, and bands are assigned to the 2- or 4-vinyl group from selective deuteration shifts. Contributions of the aliphatic propionate groups are also revealed in the RR spectrum. The protein influence on the heme structure is reflected in the activation of several out-of-plane modes in the low-frequency region.

Meso-substituted cationic porphyrins as efficient photosensitizers of gram-positive and gram-negative bacteria.

Abstract: Previous studies on the photosensitization of bacterial cells with different neutral or negatively charged porphyrins and phthalocyanines have demonstrated that, although Gram-positive bacteria are efficiently photoinactivated, Gram-negatrive bacteria become photosensitive only after modification of the permeability of their outer membrane. The results described in this paper show that two meso-substituted cationic porphyrins, namely tetra(4N-methyl-pyridyl) porphine tetraiodide and the tetra(4N,N,N,-trimethyl-anilinium) porphine, efficiently photosensitive the inactivation of Gram-negative bacteria, such as Vibrio anguillarum and Escherichia coli. A negatively charged meso-substituted porphyrin, tetra(4-sulphonatophenyl)porphine, has no appreciable photosensitizing activity towards Gram-negative bacteria, although all three porphyrins exhibit a similar subcellular distribution pattern, being mainly localized in the protoplasts or spheroplasts. Moreover, the three porphyrins show similar efficiency in the photoinactivation of the Gram-positive bacterium Entorecoccus seriolicida.

A catalytic DNA for porphyrin metallation.

Abstract: A guanine-rich DNA oligomer (33 nucleotides), isolated by in vitro selection from a random-sequence DNA library, catalyses the insertion of copper(II) and zinc ions into mesoporphyrin IX.

Energy and Photoinduced Electron Transfer in Porphyrin−Fullerene Dyads

Abstract: Time-resolved fluorescence and absorption techniques have been used to investigate energy and photoinduced electron transfer in a covalently linked free-base porphyrin−fullerene dyad and its zinc analog. In toluene, the porphyrin first excited singlet states decay in about 20 ps by singlet−singlet energy transfer to the fullerene. The fullerene first excited singlet state is not quenched and undergoes intersystem crossing to the triplet, which exists in equilibrium with the porphyrin triplet state. In benzonitrile, photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene competes with energy transfer. The fullerene excited singlet state is also quenched by electron transfer from the porphyrin. Overall, the charge-separated state is produced with a quantum yield approaching unity. This state lives for 290 ps in the free-base dyad and 50 ps in the zinc analog. These long lifetimes suggest that such dyads may be useful as components of more complex light-harvesting systems.

Soluble Synthetic Multiporphyrin Arrays. 2. Photodynamics of Energy-Transfer Processes

Abstract: Soluble ethyne-linked tetraarylporphyrin arrays that mimic natural light-harvesting complexes by absorbing light and directing excited-state energy have been investigated by static and time-resolved absorption and fluorescence spectroscopies. Of particular interest is the role of the diarylethyne linkers in mediating energy transfer. The major conclusions from this study, which is limited to the examination of arrays containing Zn and free-base (Fb) porphyrins, include the following: (1) Singlet excited-state energy transfer from the Zn porphyrin to the Fb porphyrin is extremely efficient (95−99%). Competitive electron-transfer reactions are not observed. (2) The rate of energy transfer is slowed up to 4-fold by the addition of groups to the linker that limit the ability of the linker and porphyrin to adopt geometries tending toward coplanarity. Thus, the mechanism of energy transfer predominantly involves through-bond communication via the linker. Consistent with this notion, the measured lifetimes of t...

Studies on the mechanism of bacteria photosensitization by meso-substituted cationic porphyrins

Abstract: Cationic porphyrins have been shown to photoinduce the direct inactivation of Gram-positive (G+) and Gram-negative (G−) bacteria, thereby differing from anionic or neutral porphyrins which can photosensitize the G− bacteria only after permeabilization of their outer membrane. The present data show that the differences between these positively and negatively charged porphyrins are not related by a difference in the intrinsic photosensitizing efficiency, as determined by the photo-oxidation of model substrates or the yield of 1O2 generation; moreover, there are only minor differences in the quantum yield of porphyrin photobleaching. Rather, it appears that the positive charge promotes an electrostatic binding of the porphyrin to the outer cell surface inducing an initial limited damage which favours the penetration of the photosensitizer. Actually, the overall photoprocess is inhibited by the preincorporation of the porphyrin into liposomes, while it is enhanced by using amphiphilic dicationic porphyrins which bind to endocellular sites in larger amounts and in a more stable form.

Aggregation of Tetraaryl-Substituted Porphyrins in Homogeneous Solution

Abstract: Electronic absorption, fluorescence and fluorescence excitation spectra, and vibrational Raman spectra of selected homogeneous solution phase, free-base tetraaryl-substituted porphyrinsspecifically, tetraphenylporphine (TPPH2), tetra(p-pyridyl)porphine (TPyPH2), tetra(p-N-methylpyridyl)porphine (TMPyPH2), tetra(p-carboxylphenyl)porphine (TCPPH2), and tetra(p-sulfonatophenyl)porphine (TSPPH2)as well as their protonated diacids are acquired and analyzed. N-protonation induces a structural change in which the free-base porphyrin is converted from a configuration in which the aryl moiety is twisted relative to the macrocycle plane to one in which it is nearly coplanar, thus promoting aggregation. However, spectroscopic investigations of the tetraaryl-substituted porphyrins reveal that coplanarity, although necessary, is insufficient for aggregation to occur. Also required is that the doubly protonated porphyrin have a net zero charge, i.e., be zwitterionic. The structural alignments of monomers in tetraaryl-s...

Soluble Synthetic Multiporphyrin Arrays. 1. Modular Design and Synthesis

Abstract: A set of porphyrin building blocks has been developed for the construction of light-harvesting model compounds and related molecular photonic devices. The porphyrins are facially encumbered to enhance solubility in organic solvents, are employed in a defined metalation state (free base (Fb) or zinc chelate), and bear peripheral functional groups such as iodo or ethyne for joining the porphyrins via covalent bonds. The coupling of an iodophenylporphyrin and an ethynylphenylporphyrin via mild Pd-mediated reactions (2−4 mM of each porphyrin in toluene/triethylamine (5:1) with Pd2(dba)3 and AsPh3 at 35 °C for 2 h) yields the corresponding diphenylethyne-linked multiporphyrin array in 70−80% yield. The arrays are easily purified by a sequence of flash silica chromatography, preparative size exclusion chromatography, and gravity elution silica chromatography. The diphenylethyne linkers give a center-to-center separation of the porphyrins of ∼20 A. Model light-harvesting compounds are easily prepared using Zn an...

Acetylenyl-Linked, Porphyrin-Bridged, Donor−Acceptor Molecules: A Theoretical Analysis of the Molecular First Hyperpolarizability in Highly Conjugated Push−Pull Chromophore Structures

Abstract: We describe the theoretical basis for the exceptionally large molecular first hyperpolarizabilities inherent to (5,15-diethynylporphinato)metal-bridged donor−acceptor (D−A) molecules. β values relevant for hyper-Rayleigh experiments are calculated at 1.064 and 0.830 μm for a complex with such a structure, [5-((4‘-(dimethylamino)phenyl)ethynyl)-15-((4‘‘-nitrophenyl)ethynyl)-10,20-diphenylporphinato]zinc(II), and are 472 × 10-30 and 8152 × 10-30 cm5/esu, respectively. The values are 1 order of magnitude larger than that calculated for any other porphyrin bridged donor−acceptor chromophore studied to date. The considerably enhanced hyperpolarizability arises from the significant excited-state electronic asymmetry manifest in such structures (derived from the strong bridge-mediated D−A coupling enabled by the largely porphyrin-based excited state) and the large bridge-centered oscillator strength in this new class of D−bridge−A molecules. Our analysis of NLO properties (based upon INDO/SCI calculations within...

Photophysical and photochemical properties of potential porphyrin and chlorin photosensitizers for PDT

Abstract: Structural and optical properties as well as photophysical and photochemical parameters (excited S1 and T1 state lifetimes at 77 K and in the presence of O2 in solution at 293 K; efficiencies of singlet oxygen, 1Δg, generation) are presented for porphyrins and chlorins with potential for the PDT of cancer: chlorin p6 and its trimethyl ester, chlorin e6 and its Na3 and K3 salts, purpurin-18 and its monomethylester, 5,10,15,20-tetrakis(3-methoxyphenyl)porphyrin (TPPM), 5,10,15,20-tetrakis(2,4-difluoro-3-methoxyphenyl)porphyrin (TPPMF) and GaTTP in different solvents (ethanol, toluene, pyridine and buffer pH 7.4) at 77–300 K. It has been shown that for monomeric chlorin e6, chlorin p6 and its derivatives the photophysical parameters are similar, as follows: fluorescence lifetimes τs in the presence of oxygen are 3.2–4.5 ns at 293 K; fluorescence quantum yields φ1 vary from 0.1 to 0.2 depending on the solvent; phosphorescence quantum yields φ1 are of t order 10−5; T1 state lifetimes τT = 1.5–2.0 ms at 77 K and 250–390 ns at 293 K in the presence of O2. By use of the direct kinetic measurement of singlet oxygen emission at 1.27 μm on laserexcitation the quantum yields of 1Δg generation by chlorins have been measured: φΔ = 0.35−0.68. In this case values of φ1 and φΔ depend strongly on the solve probably because of the formation of aggregates. For TPPM, TPPMF and Ga-TPP the φΔ values measured are higher (0.87–0.98) and are explained by the higher intersystem crossing S1 → T1 quantum yields.

Structure of DNA-porphyrin complex.

Abstract: We report the 2.4 A resolution X-ray structure of a complex in which a small molecule flips a base out of a DNA helical stack. The small molecule is a metalloporphyrin, CuTMPyP4 [copper(II) meso-tetra(N-methyl-4-pyridyl)porphyrin], and the DNA is a hexamer duplex, [d(CGATCG)]2. The porphyrin system, with the copper atom near the helical axis, is located within the helical stack. The porphyrin binds by normal intercalation between the C and G of 5' TCG 3' and by extruding the C of 5' CGA 3'. The DNA forms a distorted right-handed helix with only four normal cross-strand Watson-Crick base pairs. Two pyridyl rings are located in each groove of the DNA. The complex appears to be extensively stabilized by electrostatic interactions between positively charged nitrogen atoms of the pyridyl rings and negatively charged phosphate oxygen atoms of the DNA. Favorable electrostatic interactions appear to draw the porphyrin into the duplex interior, offsetting unfavorable steric clashes between the pyridyl rings and the DNA backbone. These pyridyl-backbone clashes extend the DNA along its axis and preclude formation of van der Waals stacking contacts in the interior of the complex. Stacking contacts are the primary contributor to stability of DNA. The unusual lack of van der Waals stacking contacts in the porphyrin complex destabilizes the DNA duplex and decreases the energetic cost of local melting. Thus extrusion of a base appears to be facilitated by pyridyl-DNA steric clashes.

Structural Studies by Exciton Coupled Circular Dichroism over a Large Distance: Porphyrin Derivatives of Steroids, Dimeric Steroids, and Brevetoxin B⊥

Abstract: The present study (see ref 1) delineates the scope and limitations of porphyrin chromophores for structural studies by the exciton coupled circular dichroic (CD) method. A distance dependency of the porphyrin coupling was investigated in the range between 10 and 50 A. Over short interchromophoric distances, significant changes in the conformational distribution introduced by the bulky porphyrin chromophores were observed. Over longer distances, the porphyrins showed ca. 10-fold sensitivity increase over commonly used chromophores, and an effective direction for the interacting porphyrin transition moments was assigned by comparison. Porphyrins at the termini of dimeric steroids and brevetoxin B exhibited exciton coupling over interchromophoric distances up to 50 A. These results represent the porphyrins as promising reporter chromophores for extending the exciton coupled CD method to structural studies of biopolymers.

Soluble Synthetic Multiporphyrin Arrays. 3. Static Spectroscopic and Electrochemical Probes of Electronic Communication

Abstract: A comprehensive electrochemical (cyclic and square-wave voltammetry, coulometry) and static spectroscopic (absorption, resonance Raman (RR), electron paramagnetic resonance (EPR)) study is reported for a series of dimeric and trimeric porphyrin-based arrays. All the arrays consist of tetraarylporphyrins linked via ethyne groups at the p-positions of the aryl rings. The complexes investigated include zinc-free base and bis-zinc dimers which contain varying degees of torsional constraint between the porphyrin rings and the aryl group of the linker, and linear and right-angle trimers in which two zinc porphyrins are bridged by either a zinc or free base porphyrin. The spectroscopic studies were performed on singly and multiply oxidized complexes as well as the natural species. The electrochemical and spectral properties of the arrays indicate that the electronic communication between the macrocycles is relatively weak in the ground and excited electronic states. This communication is through-bond, rather than through-space, and is mediated by the diarylethyne linker. The EPR spectra of the oxidized arrays exhibit complex temperature-dependent signatures that reflect hole/electron hopping and/or spin exchange interactions in the ground electronic state. Exchange interactions in the multiply oxidized arrays are significant (probably 1000 MHz pr greater) in both liquid and frozen solutions and, in certain cases,more » are enhanced upon solvent freezing. 45 refs., 12 figs., 3 tabs.« less

Singlet Oxygen Production in Water: Aggregation and Charge-Transfer Effects

Abstract: Precise quantum yields for generation of singlet molecular oxygen, O2(1Δg), have been measured for tetrakis(4-sulfonatophenyl)porphyrin (TSPP), closely-related water-soluble porphyrin derivatives, ...

Photophysical properties of metal complexes of meso-tetrakis(4-sulphonatophenyl)porphyrin

Abstract: Laser kinetic spectroscopy was used to determine the photophysical parameters (fluorescence and triplet-triplet (T-T) spectra, lifetimes of the triplet and singlet states, bimolecular constant for oxygen quenching, fluorescence quantum yield and quantum yield of formation of the triplet state) of the water-soluble complexes of Ag(II), Cd(II), Co(II), Cu(II), Mg(II), Ni(II), Pd(II), Pt(II) and Zn(II) with the tetrasodium salt of meso-tetrakis(4-sulphonatophenyl)porphyrin (H 2 TPPS 4 ). The complexes of metals with d 0 and d 10 electron configurations (Cd(II), Mg(II) and Zn(II)) are characterized by high triplet quantum yields and strong fluorescence in the red spectral region and are thus more efficient photosensitizers than the ligand alone.

Fluorescence Decay Kinetics and Structure of Aggregated Tetrakis(p-Sulfonatophenyl)Porphyrin

Abstract: Fluorescence decay dynamics and structure of a meso-tetrakis(p-sulfonatophenyl)porphyrin, referred to herein as either H2TSPP4- or TSPP, which aggregates in highly acidic homogeneous solution, are discussed. The fluorescence lifetime of the aggregate is found to depend on whether electronic excitation is to the B (Soret) state or the Q state. This finding is interpreted as indicating that the aggregate's effective size differs in the two cases. Also, a discussion is provided of possible nonradiative pathways that might affect measured fluorescence lifetimes. Specific structural changes that occur within the porphyrin upon N-protonation and incorporation within the aggregate are also discussed. Additionally, vibrational frequencies are assigned to specific bonds of the porphinato macrocycle, and comparisons are made between bond lengths in the aggregate environment and those of the monomeric dianion.

Layer-by-Layer Growth of Electrostatically Assembled Multilayer Porphyrin Films

Abstract: The feasibility of preparing multilayer porphyrin films with monolayer control of composition and thickness is demonstrated. Successive dip-coating of tetraruthenated zinc porphyrin, [ZnTPyPBpy]4+, and meso-tetraphenylporphyrin sulfonate, [M-TPPS]4-, is shown to result in linear growth of the film thickness (12.7(6) A/bilayer) and optical absorbance as a function of the number of bilayers. These results strongly suggest a layer-by-layer assembly of compositionally homogeneous films of up to 30 bilayers. The assembled multilayer composite films have been characterized by UV−vis spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and electrochemical methods. Electrodes modified with these films exhibit a reversible wave at 0.94 V and are photocatalytically active toward the reduction of O2. Our findings suggest that the layer-by-layer growth method may be a general route to compositionally modulated porphyrin films of arbitrary thickness and rationally tail...

Exceptional electronic modulation of porphyrins through meso-arylethynyl groups. Electronic spectroscopy, electronic structure, and electrochemistry of [5,15-bis](aryl)ethynyl]-10,20-diphenylporphinato]zinc(II) complexes

Abstract: A new class of porphyrins in which intervening ethynyl moieties connect aryl groups to the porphyrin 5- and 15-positions is described. The synthesis and optical spectroscopy of five new compounds are reported: [5,15-bis[(4‘-dimethylaminophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), [5,15-bis[(4‘-methoxyphenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), [5,15-bis[(phenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), [5,15-bis[(4‘-fluorophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), and [5,15-bis[(4‘-nitrophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II). The X-ray structure of one of these complexes, [5,15-bis[(4‘-fluorophenyl)ethynyl]-10,20-diphenylporphinato]zinc(II), is unusual in that it shows the arylethynyl-phenyl rings to be coplanar with the porphyrin macrocycle. This arrangement of aryl rings with respect to the porphyrin macrocycle underscores the fact that the steric barrier to rotation between the porphyrin and arylethynyl-phenyl aromatic systems has been removed and highlights the enha...

Porphyrin metalation catalyzed by a small RNA molecule

Abstract: We report here the isolation and characterization of a 35-nucleotide (nt) RNA that catalyzes the related Cu(II) insertion into mesoporphyrin IX with a k{sub cat}/K{sub m} value of 2100 M{sup -1} s{sup -1}, close to the value for the metalation of mesoporphyrin with Fe(II) catalyzed by recombinant human ferrochelatase. This work demonstrates the ability of RNA to catalyze a reaction closely related to that required for the biosynthesis of the essential cofactor, heme. The small size of the catalytic sequence motif found here should facilitate structural studies. Moreover, mutants of this RNA may be selected to display other porphyrin-based activities: ferrochelatase activity, reversible oxygen binding with RNA-bound heme, peroxidase activity, or complementation of ferrochelatase-deficient (heme H{sup -}) auxotrophs which could ultimately lead to in vivo complementation of ferrochelatase deficiency using gene transfer techniques. 25 refs., 2 figs., 1 tab.

Synthesis of Hybrid Organo−Mineral Materials: Anionic Tetraphenylporphyrins in Layered Double Hydroxides

Abstract: meso-Tetrakis(p-carboxyphenyl)porphyrin (pTCPP), the atropoisomer (αααα) of meso-tetrakis(o-carboxyphenyl)porphyrin (oTCPP), and the ammonium salt of the meso-tetrakis(p-sulfonatophenyl)porphyrin (noted pTSPP) were intercalated into [Zn−Al] layered double hydroxide (LDH) using different preparative methods. Coprecipitation at constant pH in a porphyrinic solution of zinc and aluminum salts or anionic exchange of pTCPP on a [Zn−Al−Cl] precursor led to pure LDH phases, while products obtained from the calcination−reconstruction method on a [Zn−Al−Cl] precursor contain a significant amount of ZnO. Powder X-ray diffraction and UV−visible diffuse reflectance spectroscopy of LDH intercalated with pTCPP, oTCPP, and pTSPP show complete intercalation. Interlayer spacing ranging from 18.54 A for [Zn−Al−oTCPP] to 22.91 A for [Zn−Al−pTSPP] and 22.73 A for [Zn−Al−pTCPP], determined from PXRD patterns, reveal different orientations of the anionic macrocyles between the hyroxylated layers. This selective arrangement is ...

Structural factors governing hemin dissociation from metmyoglobin

Abstract: Rates of hemin dissociation from approximately 100 different metmyoglobin mutants were measured to determine which amino acid residues are important for retaining the prosthetic group. Most of the amino acids examined are within 4 A of the porphyrin ring, but replacements of a number of noncontact residues were also made. Mutations of His93(F8) and Leu89(F4) can result in > 100-fold increases in the rate of hemin loss at pH 5 and 7. Some replacements of the contact residues His64(E7), Val68(E11), His97(FG3), Ile99(FG5), Thr39(C4), and Tyr103(G4) cause > 10-fold changes in the rate of hemin dissociation. Substitutions of the noncontact residues Leu29(B10), Phe46(CD4), and Gly65(E8) can also increase the rate of hemin loss > 10-fold. The key structural factors stabilizing bound hemin in myoglobin are (1) hydrophobic interactions between apolar residues in the heme pocket and the porphyrin ring, (2) the covalent bond between His93(F8) and the Fe3+ atom, and (3) hydrogen bonding between distal residues and coordinated water. Specific electrostatic interactions between the heme propionates and amino acids at the surface of the protein appear to be less important. Loss of these polar interactions can be compensated by increasing the apolar character of either the heme group by esterification of the propionates or replacement of charged surface residues with large apolar side chains [e.g., replacing His97(FG3) with Phe].

Porphyrin Synthesis by the “3+1” Approach: New Applications for an Old Methodology

Abstract: Acid-catalyzed condensation of tripyrranes with pyrrole-2,5-dicarboxaldehydes, followed by oxidation with an electron-deficient quinone, affords porphyrin products in excellent yields. This previously little used methodology has now been exploited in the synthesis of novel porphyrin structures, including tetrapyrrolic compounds with fused aromatic rings. By utilizing other aromatic or unsaturated dialdehydes, the “3+1” approach also allows the synthesis of new aromatic porphyrinoid systems, including benzene- and pyridine-containing macrocycles and carbaporphyrins.

Conformational Flexibility in Dodecasubstituted Porphyrins

Abstract: In contrast to regular porphyrins, dodecasubstituted porphyrins have not so far been demonstrated to possess a high degree of conformational flexibility. To determine if this is a general feature of dodecasubstituted porphyrins, we have undertaken an investigation of the conformational properties of the dodecaarylporphyrins 4-6. We show herein that crystal structures of these porphyrins provide ample evidence of the significant conformational flexibility that can be observed for dodecasubstituted porphyrins; the structures we report include the first highly ruffled dodecasubstituted porphyrin, the first examples of multiple conformations in a single dodecasubstituted porphyrin, and the first `wave` core structure of a dodecasubstituted porphyrin, which is also the most nonplanar wave structure reported to date for any porphyrin. The structure reported herein for nickel(II) complexes and metal-free porphyrins 4-6 clearly indicate that these porphyrins possess a higher degree of conformational flexibility than has previously been observed for other dodecasubstituted porphyrins. 6 refs., 2 figs.