Dimerization of tetracationic porphyrins: ionic strength dependence

Water-Soluble Star Polymer as a Potential Photoactivated Nanotool for Lysozyme Degradation

The development of nanotools for chemical sensing and macromolecular modifications is a new challenge in the biomedical field, with emphasis on artificial peptidases designed to cleave peptide bonds at specific sites. In this landscape, metal porphyrins are attractive due to their ability to form stable complexes with amino acids and to generate reactive oxygen species when irradiated by light of appropriate wavelengths. The issues of hydrophobic behavior and aggregation in aqueous environments of porphyrins can be solved by using its PEGylated derivatives. This work proposes the design of an artificial photo-protease agent based on a PEGylated mercury porphyrin, able to form a stable complex with l-Tryptophan, an amino acid present also in the lysozyme structure (a well-known protein model). The sensing and photodegradation features of PEGylated mercury porphyrin were exploited to detect and degrade both l-Trp and lysozyme using ROS, generated under green (532 nm) and red (650 nm) light lasers. The obtained system (Star3600_Hg) and its behavior as a photo-protease agent were studied by means of several spectroscopies (UV-Vis, fluorescence and circular dichroism), and MALDI-TOF mass spectrometry, showing the cleavage of lysozyme and the appearance of several short-chain residues. The approach of this study paves the way for potential applications in theranostics and targeted bio-medical therapies.

Peripheral Groups of Dicationic Pyrazinoporphyrins Regulate Lipid Membrane Binding

Photodynamic therapy (PDT) is a widely used technique for skin cancer treatment and antimicrobial therapy. An improvement in PDT efficiency requires not only an increase in quantum yield of photosensitizer (PS) molecules but also their applicability for biological systems. Recently, we demonstrated that the activity of porphyrin-based PSs in the lipid membrane environment depends on the nature of the cation in the macrocycle due to its interactions with the lipid phosphate moiety, as well as the orientation of the PS molecules inside the membrane. Here, we report the synthesis, membrane binding properties and photodynamic efficiency of novel dicationic free-base, Ni(II) and Zn(II) pyrazinoporphyrins with terminal tetraalkylammonium units (2H-1, Ni-1 and Zn-1), to show the possibility to enhance the membrane binding of PS molecules, regardless of the central cation. All of these substances adsorb at the lipid membrane, while free-base and Zn(II) porphyrins actively generate singlet oxygen (SO) in the membranes. Thus, this study reveals a new way to tune the PDT activity of PSs in biological membranes through designing the structure of the peripheral groups in the macrocyclic photosensitizer.

Detonation nanodiamonds as enhancers of E. coli photodynamic inactivation by phthalocyanines in a high molarity buffer solution

Antimicrobial therapy, especially inactivation of multi-antibiotic-resistant strains, requires creating new approaches for drug action and targeted delivery in different environmental conditions. In this work, detonation nanodiamonds (DNDs) were used to deliver polycationic zinc phthalocyanines to E. coli cells. It is shown that in aqueous solutions, zinc phthalocyanines with cholinyl peripheral substituents form complexes with negatively charged DND based on electrostatic interactions. About 40-70 phthalocyanine molecules can bind to a single DND particle, depending on the number of charged groups of the dye molecule. During the complex formation, quenching of phthalocyanine fluorescence and a decrease in its ability to generate reactive oxygen species were observed. In the presence of bacterial cells, phthalocyanine left the complex and induced a photodynamic effect, the magnitude of which depended on the phthalocyanine charge, the molarity of the buffer solution, and the stoichiometry of the phthalocyanine-DND complex. It was found that at physiological values of the ionic strength of the solution, the photodynamic effect of phthalocyanine with a charge of 8+ in combination with a DND is higher than that of the initial phthalocyanine. Thus, nanodiamonds are a promising platform for the delivery of photosensitizers in antimicrobial therapy.

Influence of the SPR Experimental Conditions on the G-Quadruplex DNA Recognition by Porphyrin Derivatives

Surface plasmon resonance (SPR) is a powerful technique to study the interactions of ligands with analytes and therefore a number of biosensor surfaces and injection methods have been developed so far. However, many experimental parameters can affect the interactions and consequently the affinity measurements. In particular, the interactions of positively charged analytes (often used for anionic nucleic acids targets) can be influenced by the sensing surfaces (e.g., negatively charged), leading to significant nonspecific interactions as well as regeneration problems. The aim of the present work is to investigate the effect of different parameters, including ionic strength, SPR biosensor (i.e., nature of the surfaces), and the injection method on the recognition of porphyrin G-quadruplex ligands. We demonstrate that the injection method does not influence the affinity whereas the ionic strength and the nature of the surface impact the recognition properties of the porphyrin for the G-quadruplex DNA. We also found that self-assembled monolayer coating surface presents many advantages in comparison with carboxymethylated dextran surface for SPR studies of G-quadruplex DNA/ligand interactions: (i) the electrostatic interaction with charged analytes is less important, (ii) its structure/composition is less sensitive to the ionic concentration and less prone to unspecific adsorption, (iii) it is easily homemade, and (iv) the cost is approximately 10 times cheaper.

A new water-soluble sulfonated cobalt(II) phthalocyanines: Synthesis, spectral, coordination and catalytic properties

Novel complexes of cobalt(II) with sulfonated derivatives of phthalocyanines are synthesized. The influence of the sulfonated group's number in peripheral substituent on solubility of macrocycle and ability to form ordered structures in solution is showed. Transition from H-aggregates to monomeric phthalocyanine structures and sandwich-type dimers was found during formation of metallophthalocyanine complexes with 1,4-diazabicyclo[2.2.2]octane. The catalytic activity of metallophthalocyanines was studied on the model of Merox process.

Thermodynamic investigation of manganese(III) 5-(1-(4-carboxybutyl)pyridinium-4-yl) 10,15,20-tris-(1-methylpyridinium-4-yl)porphyrin with calf thymus DNA

Binding properties of two water-soluble porphyrins, manganese(III) 5-(1-(4-carboxybutyl)pyridinium-4-yl) 10,15,20-tris(1-methylpyridinium-4-yl)porphyrin ( Mn(III)5-CBPyP ) and manganese(III) 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin ( Mn(III)TMPyP ), in the presence of various concentration of calf thymus DNA (ct-DNA), has been studied in 7.5 mM phosphate buffer, pH = 7.2 and at various temperatures by UV-vis absorption, resonance light scattering (RLS) and fluorescence spectroscopy and viscosity measurement. Optical absorption and RLS measurements have demonstrated three different species of both porphyrins form in DNA solution. The thermodynamic parameters were calculated by van't Hoff equation at various temperatures. The values of -4.89 kJ.mol-1 and +65.98 J.mol-1.K-1 for Mn(III)5-CBPyP and -14.92 kJ.mol-1 and +15.46 J mol-1.K-1 for TMPyP were estimated for enthalpy and entropy changes of interaction, respectively. The data indicate that the process is exothermic and enthalpy- and entropy-driven, suggesting that electrostatic forces play a considerable role in the interaction process. The binding of both porphyins to DNA quenches fluorescence emission of ethidium bromide (EB) and the quenching process obeys linear Stern-Volmer relationship, indicating the quenching of electron transfer of EB from its binding sites by these porphyrins. The results of using these techniques indicate the external mode of binding for both porphyrins and a higher binding affinity of Mn(III)5-CBPyP with respect to Mn(III)TMPyP .

Meso tetrakis ortho-, meta-, and para-N-alkylpyridiniopor-phyrins: kinetics of copper(II) and zinc(II) incorporation and zinc porphyrin demetalation

The relative reactivities of the tetrakis( N -alkylpyridinium- X - yl )-porphyrins where X = 4 (alkyl = methyl, ethyl, n -propyl) , X = 3 (methyl) , and X = 2 (methyl, ethyl, n -propyl, n -butyl, n -hexyl, n -octyl) were studied in aqueous solution. From the ionic strength dependence of the metalation rate constants, the effective charge of a particular cationic porphyrin was usually larger when copper(II) rather than zinc(II) was the reactant. The kinetics of ZnOH + incorporation and the acid catalyzed removal of zinc from the porphyrins in 1.0 M HCl were also studied. In general, the more basic 4- (para-) and 3- (meta-) isomers were the most reactive, followed by the less basic 2- (ortho-) methyl to n -butyl derivatives, with the lipophilic ortho n -hexyl and n -octyl porphyrins the least reactive.

Effect of molecular complex formation of metallophthalocyanines with pyridine on their aggregation

The results for aggregation equilibrium of metallophthalocyanines in buffer and buffer-pyridine solutions were obtained and generalized. The influence of specific interactions of the metallophthalocyanines with pyridine on their aggregation state in solution was estimated.

Spectral properties of cationic water-soluble metallo-porphyrins immobilized in a perfluorosulfonated ion-exchange membrane

The behavior of palladium(II), platinum(II) and rhodium(III) complexes with two cationic water-soluble porphyrins: meso-tetrakis(4-N-methylpyridyl)porphyrin and meso-tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin in Nafion® membrane and in Nafion® solution have been studied by UV-visible absorption and emission spectroscopy. All metalloporphyrins are localized in the interfacial region of Nafion®. The six-coordinate Rh(III) complexes are monomeric inside Nafion®, but immobilized four-coordinate Pd(II) and Pt(II) complexes form face-to-face dimers with a characteristic blue shifted Soret band. All immobilized complexes exhibit a strong red phosphorescence at room temperature in the absence of oxygen. Phosphorescence decays for all metalloporphyrins were found to be a single exponential but phosphorescence lifetimes noticeably increased in the Nafion® membrane as compared to lifetimes in aqueous solution.

Physiologically relevant concentrations of NaCl and KCl increase DNA photocleavage by an N-substituted 9-aminomethylanthracene dye

This paper describes the synthesis of a new 9-aminomethylanthracene dye N-substituted with a pyridinylpolyamine side chain (4). The effects of NaCl and KCl on anthracene/DNA interactions were then studied, with the goal of simulating the conditions of high ionic strength that a DNA photosensitizer might encounter in the cell nucleus (~150 mM of NaCl and 260 mM of KCl). As exemplified by methylene blue (5), the expected effect of increasing ionic strength is to decrease DNA binding and photocleavage yields. In contrast, the addition of 150 mM of NaCl in combination with 260 mM of KCl to photocleavage reactions containing micromolar concentrations of 4 triggers the conversion of supercoiled, nicked, and linear forms of pUC19 plasmid into a highly degraded band of DNA fragments (350 nm hν, pH 7.0). Circular dichroism spectra point to a correlation between salt-induced unwinding of the DNA helix and the increase in DNA photocleavage yields. The results of circular dichroism, UV-vis absorption, fluorescence emission, thermal denaturation, and photocleavage inhibition experiments suggest that the combination of salts causes a change in the DNA binding mode of 4 from intercalation to an external interaction. This in turn leads to an increase in the anthracene-sensitized production of DNA-damaging reactive oxygen species.

Self-aggregation processes of 1,6-diphenyl-1,3,5-hexatriene in water/ethanol mixtures with high water percentages

This work describes the behavior of 1,6-diphenyl-1,3,5-hexatriene (DPH) in ethanol/water mixtures. The dependence of DPH photophysical properties (absorption and fluorescence emission) on the water percentage in ethanol indicates that DPH undergoes self-aggregation processes in solvent conditions above a critical water content. Evidence such as an additional absorption band, Beer's law deviation, kinetic behavior, and other experimental results obtained from temperature variation and surfactant addition demonstrated the presence of several types of DPH aggregates. Resonance light scattering measurements proved that the aggregate grew in water-rich media by a self-catalyzed process.

Binding of nickel(II) tetrakis(dimethylpyrazolium-4-yl)porphyrin to poly(dG-dC)2 and poly(dA-dT)2

The interaction of nickel(II) complex of cationic porphyrins bearing five-membered rings, meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrinatonickel(II) (NiPzP) , with synthetic polynucleotides poly(dG-dC)2 and poly(dA-dT)2 has been characterized by viscometric, visible absorption, CD and MCD spectroscopic, and melting temperature measurements. The nickel(II) complex NiPzP is intercalated into poly(dG-dC)2 but outside bound to the major groove of poly(dA-dT)2. The binding constants of NiPzP to poly(dG-dC)2 and poly(dA-dT)2 are in the order of 106 M-1 and comparable to those of other reported cationic metalloporphyrins. The binding process of NiPzP to poly(dG-dC)2 and poly(dA-dT)2 is endothermic and entropically driven.

Spectroscopic studies on the interaction of a water-soluble cationic porphyrin with proteins

The interaction of a water-soluble cationic porphyrin, meso-tetrakis (4-N,N,N-trimethylanilinium) porphyrin (TMAP), with two proteins, bovine serum albumin (BSA) and human serum albumin (HSA), was studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, fluorescence anisotropy and synchronous fluorescence spectroscopy at neutral aqueous solutions. Free base TMAP bound to proteins as monomers and no aggregation was observed. The binding of TMAP quenched the fluorescence of the protein. On the contrary, the fluorescence of TMAP was enhanced and the fluorescence anisotropy increased due to the binding. The direct static binding mechanism could account for the quenching by TMAP and the binding constants were calculated. TMAP showed a higher quenching efficiency and binding constant of HSA than BSA. The binding of TMAP had no obvious effect on the molecular conformation of the protein. There was only one binding site for TMAP and it was located on the surface of the protein molecule. Electrostatic force played an important role in the binding due to the opposite charges on porphyrin and the proteins.

Interaction of cationic meso-porphyrins with liposomes, mitochondria and erythrocytes

Two series of cationic porphyrins meso-(3N-methylpyridinium)phenylporphyrin (3P1, 3P2c, 3P2t, 3P3 and 3P4) and meso-(4N-methylpyridinium)phenylporphyrin (4P1, 4P2c, 4P2t, 4P3 and 4P4) were studied to obtain a comprehensive understanding of factors that influence the binding of cationic porphyrins to liposomes and mitochondria, as well as their photodynamic efficiencies in erythrocytes. Binding and photodynamic efficiency were found to be inversely proportional to the number of positively charged groups and directly proportional to n-octanol/water partition coefficients (log P(OW)), except for the cis molecules 3P2c and 4P2c. In the cis molecules, binding and photodynamic efficiency were much higher than expected, indicating that specific interactions not accounted by log P(OW) enhance photodynamic efficiency. The effect of mitochondrial transmembrane electrochemical potentials on cationic porphyrin binding constants was estimated to be as large as 15%, and may be useful to selectively target this organelle when promoting photodynamic therapy to induce apoptosis.

Binding of tetrakis(pyrazoliumyl)porphyrin and its copper(II) and zinc(II) complexes to poly(dG-dC)2 and poly(dA-dT)2

Interactions of cationic porphyrins bearing five-membered rings at the meso position, meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrin (MPzP; M is H2, Cu(II) or Zn(II)), with synthetic polynucleotides poly(dG-dC)2 and poly(dA-dT)2 have been characterized by viscometric, visible absorption, circular dichroisim and magnetic circular dichroism spectroscopic and melting temperature measurements. Both H2PzP and CuPzP are intercalated into poly(dG-dC)2 and are outside-bound to the major groove of poly(dA-dT)2, while ZnPzP is outside-bound to the minor groove of poly(dA-dT)2 and surprisingly is intercalated into poly(dG-dC)2. The binding constants of the porphyrin and poly(dG-dC)2 and poly(dA-dT)2 are on the order of 10(6) M(-1) and are comparable to those of other cationic porphyrins so far reported. The process of the binding of the porphyrin to poly(dG-dC)2 and poly(dA-dT)2 is exothermic and enthalpically driven for H2PzP, whereas it is endothermic and entropically driven for CuPzP and ZnPzP. These results have revealed that the kind of the central metal ion of metalloporphyrins influences the characteristics of the binding of the porphyrins to DNA.

Synthesis of novel types of copper-bipyridyl porphyrins and characterization of their interactions and reactivity with DNA

The inherent ability to interact with DNA makes cationic metallo-porphyrins attractive targets as antitumor drugs. Many studies describe their interaction with DNA and the mechanism by which they induce DNA cleavage. Since porphyrins can be used as anchors for chemically reactive groups, it is possible to modify them to generate a family of compounds with specific functions. In the present work, we used chemical groups such as copper-bipyridinium (Cu-bpy), which hydrolyze phosphodiester bonds, and a porphyrin core to synthesize two novel Cu(2)-bpy-porphyrins. Their interactions with DNA have been characterized using classic spectroscopic methods, and their oxidative and hydrolytic reactivity toward supercoiled plasmid DNA has been studied in vitro. Our results show that Cu(2)-bpy-porphyrins interact with DNA via external association and intercalation and that their ability to cleave DNA and the mechanisms depends on the experimental conditions.

Metalloporphyrin probes for antimalarial drug action

Metal-substituted protoporphyrin IXs (Co(III)PPIX (1), Cr(III)PPIX (2), Mn(III)PPIX (3), Cu(II)PPIX (4), Mg(II)PPIX (5), Zn(II)PPIX (6) and Sn(IV)PPIX (7)), phthalocyanine tetrasulfonates (PcS (8) and Ni(II)PcS (9)), and anionic and cationic porphyrins (meso-tetra(4-sulfonatophenyl)porphine (TPPS4, 10), meso-tetra(4-carboxyphenyl)porphine (TPPC4, 11), tetrakis(4-N-trimethylaminophenyl)porphine (TMAP, 12) and meso-tetra(N-methyl-4-pyridyl)porphine (TMPyP4, 13)) have been used as probes to compare two different assays for the inhibition of beta-hematin formation. The results demonstrate that the efficacy of these probes in either the beta-hematin inhibition assay (9, 7, 6, 5>4>11, 3>10, 8>2, 1; 12 and 13 did not inhibit.) or the bionucleating template assay (8>1>11>9, 2>4>3>7>10>5>6; 12 and 13 did not inhibit.) differ significantly. These differences are examined in light of possible interactions between the inhibitor probes, heme, beta-hematin and the bionucleating template. This detailed analysis highlights the fact that while dominant modes of interactions may be occasionally identified, the precise mechanism of inhibition undoubtedly consists of the interplay between multiple interactions.

Inactivation of human immunodeficiency virus type 1 by porphyrins

We have evaluated the anti-human immunodeficiency virus (HIV) activity of a series of natural and synthetic porphyrins to identify compounds that could potentially be used as microbicides to provide a defense against infection by sexually transmitted virus. For assays we used an epithelial HeLa-CD4 cell line with an integrated long terminal repeat-beta-galactosidase gene. For structure-activity analysis, we divided the porphyrins tested into three classes: (i) natural porphyrins, (ii) metallo-tetraphenylporphyrin tetrasulfonate (metallo-TPPS4) derivatives, and (iii) sulfonated tetra-arylporphyrin derivatives. None of the natural porphyrins studied reduced infection by more than 80% at a concentration of 5 micro g/ml in these assays. Some metal chelates of TPPS4 were more active, and a number of sulfonated tetra-aryl derivatives showed significantly higher activity. Some of the most active compounds were the sulfonated tetranaphthyl porphyrin (TNapPS), sulfonated tetra-anthracenyl porphyrin (TAnthPS), and sulfonated 2,6-difluoro-meso-tetraphenylporphine [TPP(2,6-F2)S] and its copper chelate [TPP(2,6-F2)S,Cu], which reduced infection by 99, 96, 94, and 96%, respectively. Our observations indicate that at least some of these compounds are virucidal, i.e., that they render the virus noninfectious. The active compounds were found to inhibit binding of the HIV type 1 gp120 to CD4 and also to completely inhibit the ability of Env proteins expressed from recombinant vectors to induce cell fusion with receptor-bearing target cells. These results support the conclusion that modified porphyrins exhibit substantial activity against HIV and that their target is the HIV Env protein.

Rotation of periphery methylpyridine of meso-tetrakis(n-N-methylpyridiniumyl)porphyrin (n = 2, 3, 4) and its selective binding to native and synthetic DNAs

By utilizing circular and linear dichroism, the binding mode of meso-tetrakis(n-N-methylpyridiniumyl)porphyrin (n = 2, 3, 4) to various DNAs was studied in this work. 2-N-(methylpyridiniumyl)porphyrin(o-TMPyP), in which rotation of the periphery pyridinium ring is prevented, exhibits similar spectral properties when bound to DNA, poly[d(G-C)(2)] and poly[d(A-T)(2)], suggesting a similar binding mode. Close analysis of the spectral properties led us to conclude that o-TMPyP sits in the major groove. However, both 3-N- and 4-N-(methylpyridiniumyl)porphyrin (m- and p-TMPyP), of which the periphery pyridinium ring is free to rotate, intercalate between the basepairs of DNA and poly[d(G-C)(2)]. In the presence of poly[d(A-T)(2)], m-TMPyP exhibits a typical bisignate excitonic CD spectrum in the Soret band, while p-TMPyP shows two positive CD bands. The excitonic CD spectrum of the m-TMPyP-poly[d(A-T)(2)] complex and the positive CD band of the o-TMPyP-poly[d(A-T)(2)] complex were not affected by the presence of the minor groove binding drug, 4',6-diamidino-2-phenylindole (DAPI), indicating that this porphyrin is bound in the major groove. In contrast, two positive CD bands of the p-TMPyP-poly[d(A-T)(2)] complex altered in the presence of DAPI. From the changes in CD spectrum and other spectral properties, a few possible binding modes for p-TMPyP to poly[d(A-T)(2)] are suggested.

Self-association of disulfonated deuteroporphyrin and its esters in aqueous solution and photosensitized production of singlet oxygen by the dimers

Dimerization of free acid and ester forms of disulfonated deuteroporphyrin is investigated in aqueous solution by absorbance and fluorescence spectroscopies. The dimerization equilibrium constant increases with the extent of esterification. In phosphate buffer saline (pH 7.4, 20 degrees C), it ranges from 1.4 x 10(6) M(-1) to 7.8 x 10(7) M(-1) for the free acid and the diethyl ester forms, respectively. The dimer formation is favored by an increase of ionic strength, as predicted by the Debye-Hückel law. The dimers display a marked shift to the blue of their Soret band. In agreement with the exciton model, a cofacial stacking of the molecules with some offset is postulated. The sulfonate groups on each molecule are likely to stand on opposite directions to reduce repulsion. Both the analysis of porphyrin self-association and careful examination of the fluorescence excitation spectra show that the dimers of disulfonated deuteroporphyrins do not fluoresce at all. The quantum yield of formation of singlet oxygen by the disulfonated deuteroporphyrins in deuterated methanol is 0.71, a value typical of monomers. In deuterated water, the yield is 0.44 for all the compounds studied though they are dimerized. The fact that nonfluorescent dimers of porphyrins can be efficient photosensitizers is emphasized.

Solution properties and photonuclease activity of cationic bis-porphyrins linked with a series of aliphatic diamines

The development of efficient photo-induced DNA cleavage agents has been of particular interest for biomedical applications such as cancer photodynamic therapy (PDT). Toward this objective, we synthesized a series of cationic bis-porphyrins with various lengths of diamino alkyl linkage, N,N'-bis[4-[10,15,20-tris(1-methylpyridinium-4-yl)porphyrin-5-yl]benzoyl]oligomethylenediamine hexaiodide. They were expected to show more efficient photocleavage of DNA than unichromophore meso-tetrakis(4-N-methylpyridiniumyl)porphine (TMPyP), which is well known to cleave DNA effectively on illumination. The cationic bis-porphyrins were found to self-aggregate in aqueous solution, and the aggregation property was accounted for by the formation of an intermolecular dimer. Because conservative-type circular dichroism spectra of the bis-porphyrins were induced in the Soret region on binding to calf thymus DNA, we assigned their binding mode to outside self-stacking on the DNA surface. Their photonuclease activity using plasmid DNA decreased as the number of their linker hydrocarbons increased, and was well correlated with their tendency for dimerization. The inhibitory effect of azide anion, N3-, and the enhancement effect of D2O suggest that singlet oxygen was probably involved in the photocleavage of DNA.

Interaction of metallopyrazoliumylporphyrins with calf thymus DNA

The interaction of transition metal complexes of cationic porphyrins bearing five membered rings, meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrin (MPzP, M=Mn(III), Ni(II), Cu(II) or Zn(II)), with calf thymus DNA (ctDNA) has been studied. Metalloporphyrins NiPzP and CuPzP are intercalated into the 5'GC3' step of ctDNA. MnPzP is bound edge-on at the 5'TA3' step of the minor groove of ctDNA, while ZnPzP is bound face-on at the 5'TA3' step of the major groove of ctDNA. The binding constants of the metalloporphyrins to ctDNA range from 1.05x10(5) to 2.66x10(6) M(-1) and are comparable to those of other reported cationic porphyrins. The binding process of the metallopyrazoliumylporphyrins to ctDNA is endothermic and entropically driven. These results have revealed that the kind of central metal ions of metalloporphyrins influences the binding characteristics of the porphyrin to DNA.

Metalloporphyrins inhibit beta-hematin (hemozoin) formation

Metal-substituted protoporphyrin IXs (Cr(III)PPIX (1), Co(III)PPIX (2), Mn(III)PPIX (3), Cu(II)PPIX (4), Mg(II)PPIX (5), Zn(II)PPIX (6), and Sn(IV)PPIX (7)) act as inhibitors to beta-hematin (hemozoin) formation, a critical detoxification biopolymer of malarial parasites. The central metal ion plays a significant role in the efficacy of the metalloprotoporphyrins to inhibit beta-hematin formation. The efficacy of these compounds correlates well with the water exchange rate for the octahedral aqua complexes of the porphyrin's central metal ion. Under these in vitro reaction conditions, metalloporphyrins 5, 6 and 7 are as much as six times more efficacious than the free ligand protoporphyrin IX in preventing beta-hematin formation and four times as efficacious as chloroquine, while metalloporphyrins 3 and 4 are three to four times more effective at preventing beta-hematin formation than the free protoporphyrin IX base. In contrast, the relatively exchange inert metalloporphyrins 1 and 2 are only as efficacious as the free ligand and only two-thirds as effective as chloroquine. Aggregation studies of the heme:MPPIX using UV-Vis and fluorescence spectroscopies are indicative of the formation of pi-pi hetero-metalloporphyrin assemblies. Thus, hemozoin inhibition is likely prevented by the formation of heme:MPPIX complexes through pi-stacking interactions. The ramifications of such hetero-metalloporphyrin assemblies, in the context of the emerging structural picture of hemozoin, are discussed.

Super-Charged Porphyrazines: Synthesis and Physical Properties of Octacationic Tetraazaporphyrins

We report the synthesis of octacationic macrocycles based on the porphyrazine (tetraazaporphyrin) core. The first stage is the synthesis of Mg(II) 2,3,7,8,12,13,17,18-octakis(4-pyridyl)porphyrazine, [Mgpz(pyr)(8)], and the parent [H(2)pz(pyr)(8)]. Both compounds are freely soluble in aqueous acid due to protonation of the pyridyl groups but with concomitant loss of Mg(2+) by the latter. Methylation of [H(2)pz(pyr)(8)] gives the octacation, 2,3,7,8,12,13,17,18-octakis(N-methyl-4-pyridiniumyl)porphyrazine, [H(2)pz(Me-pyr)(8)](8+), which is freely soluble in water as the chloride salt. The peripheral charges greatly lower the pK(a) values of the pyrrole protons of [H(2)pz(Me-pyr)(8)](8+) in aqueous solution. Global fitting of optical pH titration curves gives pK(a) values for the first and second deprotonations of 6.3 and 8.8 in 2.0 M NaCl and 4.1 and 5.6 at 0.1 M NaCl. The analysis further gives the UV-visible spectra of the [H(2)pz(Me-pyr)(8)](8+), [Hpz(Me-pyr)(8)](7+), and [pz(Me-pyr)(8)](6+) species. The free-base compound [H(2)pz(Me-pyr)(8)](8+) rapidly incorporates a variety of metal ions (Ba(II), Cd(II), Co(II), Cu(II), Mn(III), Ni(II), Pd(II), and Zn(II)) to form [Mpz(Me-pyr)(8)](8+). We present the complete synthesis and characterization of the [Nipz(Me-pyr)(8)](8+) and [Cupz(Me-pyr)(8)](8+) derivatives.

Cationic porphyrins bearing diazolium rings: synthesis and their interaction with calf thymus DNA

Two novel cationic porphyrins bearing five-membered rings at the meso-positions, meso-tetrakis(1,3-dimethylimidazolium-2-yl)porphyrin (H2TDMImP) and meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrin (H2TDMPzP), have been synthesized. These two compounds interact with calf thymus DNA (CTDNA) in different binding modes from that of mesotetrakis(N-methylpyridinium-4-yl)porphyrin (H2TMPyP). H2TDMImP outside binds to the minor groove of CTDNA while H2TDMPzP intercalates into CTDNA. These two novel cationic porphyrins strongly bind to CTDNA even at high ionic strength and the binding constant of H2TDMPzP to CTDNA is comparable to that of H2TMPyP. The binding of H2TDMImP to CTDNA is enthalpically driven. The favorable free energy changes in binding of H2TDMPzP to CTDNA come from the large negative enthalpy changes accompanied by small positive entropy changes.

Binding of the Mn(III) complex of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin to DNA. Effect of ionic strength

Interactions of the water-soluble Mn(III) complex of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin (Mn(III)TMPyP) with DNA in aqueous solutions at low (0.01 M) and high (0.2 M) ionic strengths have been studied by optical absorption, resonance light scattering (RLS) and 1H NMR spectroscopies. Optical absorption and RLS measurements have demonstrated that in DNA solutions at low ionic strength the Mn(III)TMPyP form aggregates, which are decomposed at DNA excess. At high ionic strength the aggregation was not observed. We explain this effect by assuming that upon increase in ionic strength, Mn(III) TMPyP dislocates from the DNA sites, which produces better conditions for the porphyrin aggregation, to sites where the aggregation is hindered. The 1H NMR data demonstrated that the aggregation observed at low ionic strength reduces the paramagnetism of Mn(III)TMPyP. This phenomenon was not observed at the high ionic strength in the absence of aggregation.