Journal of Porphyrins and Phthalocyanines

A water-soluble octabromoporphyrin 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (H₂(OBTMPyP)⁴⁺), H₂P⁴⁺) and its lithium complex, Li(OBTMPyP)³⁺, (LiP³⁺), transferred quantitatively to an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM⁺PF₆^-) with no addition of other counter ions. The acid-dissociation constants of H₂(OBTMPyP)⁴⁺ between aqueous and BMIM⁺PF₆^- phases were determined spectrophotometrically and found to be 10^-7.67 and 10^-11.33 at I = 0.1 for K_a1,IL = [H⁺]_aq[HP³⁺]_IL/[H₂P⁴⁺]_IL and K_a2,IL = [H⁺]_aq[P²⁺]_IL/[HP³⁺]_IL, respectively. Since the acid-dissociation constants involve the partition of H₂(OBTMPyP)⁴⁺ between aqueous and IL phases, the determined values are ten times as low as those observed in aqueous solution. The transfer equilibrium constants of LiP³⁺ and NaP³⁺ to IL defined by K_MP,IL = [MP³⁺]_IL/[M⁺]_aq[P²⁺]_IL (M = Li⁺ or Na⁺) were found to be 10^4.83 and 10^1.31 for K_LiP,IL and K_NaP,IL, respectively. LiP³⁺ transferred selectively in the presence of Na⁺ (K_LiP,IL/K_NaP,IL = 10^3.52) to IL phase through an ion-exchange mechanism between BMIM⁺PF₆^- and Li(OBTMPyP)³⁺.

A new synthesis of μ-oxo dimeric iron(III) porphyrins from meso-tetraarylporphyrins in one-pot procedure is reported. μ-oxo dimeric iron(III) porphyrin was obtained in high yield (up to 93%) from the reaction of meso-tetraarylporphyrin with ferrous chloride in DMF at pH 8–11. Compared with other synthetic methods of μ-oxo dimeric iron(III) porphyrin from meso-tetraarylporphyrins, the one-pot procedure has higher yields of μ-oxo dimeric iron(III) porphyrins and is a simpler and more convenient procedure. In order to evaluate the range of applicability of this method, μ-oxo dimeric iron(III) porphyrins with different substituents were prepared by the reaction of the corresponding meso-tetraarylporphyrins with ferrous chloride. The results showed that it was possible to apply this one-pot procedure to the synthesis of other μ-oxo dimeric iron porphyrins in excellent yields. A mechanism for the formation of μ-oxo dimeric iron porphyrins was proposed based on the reaction intermediates characterized by HPLC and UV-vis methods.

The results of a UV-vis and fluorescent spectral investigation of a tetra-15-crown-5-substituted aluminum phthalocyanine [(R₄Pc)Al(OH)] (1), where (R₄Pc)^2- = 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninate-dianion, in different solvents (CHCl₃, DMSO, MeOH) are reported. It was shown that compound exhibits a very strong tendency to aggregation with the formation of μ-fluoro dimer [((R₄Pc)Al)₂F]⁺ in the presence of F^- in the low-donor solvent CHCl₃. This complex is not emissive. The formation of two different emissive species [(R₄Pc)AlF₂]^- and [(R₄Pc)Al(OH)₂]^- during the reaction of 1 with anions (F^- and OH^- correspondently) in high-donor DMSO was established.

The stabilization of G-quadruplex DNA represents an attractive strategy for the design and development of novel antitumor drugs. In the present work, we have designed and synthesized nine cationic porphyrins, each with four side arms at their meso positions. The interactions of these porphyrins with both human telomeric DNA and NHE III₁ G-quadruplexes were measured by various DNA binding assays, including polymerase stop assay, circular dichroism (CD) and CD melting assay. We then proceeded to investigate their effects on the expression of c-myc oncogene in the Hep G2 cell line. The experimental results indicate that these porphyrins are capable of effectively inducing or stabilizing both human telomeric and NHE III₁ G-quadruplexes in the presence or absence of metal ions. Furthermore, we have discovered that porphyrins with a stronger stabilizing effect on c-myc G-quadruplexes lead to more pronounced down-regulation of the c-myc oncogene in the Hep G2 cell line.

Two cobalt porphyrazines, 2,3-tetrapyridoporphyrazine and 3,4-tetrapyridoporphyrazine, were examined in N,N-dimethylformamide, dimethyl sulfoxide and pyridine solutions as to their electrochemical, spectroelectrochemical and ESR spectroscopic properties. These results were compared with those of the unsubstituted cobalt phthalocyanine. At high concentrations, aggregation was observed for each investigated compound in the three solvents. The intensity of ESR signals of each derivative depends upon the extent of aggregation in its solution. The g values shift towards high field with an increase in the strength of the axial ligand and the number of axial ligands on the cobalt center. Both tetrapyridoporphyrazine complexes undergo one oxidation and three reductions in N,N-dimethylformamide, dimethyl sulfoxide or pyridine solution. Thin-layer UV-visible spectroelectrochemical results confirmed that the first oxidation and first reduction of both compounds are metal-centered while the second and third reductions are ring-centered. An overall electron transfer mechanism for both porphyrazine derivatives is proposed.

A mild method for O-alkylation of meso-hydroxyphenylporphyrin has been developed using microwave irradiation. This method is clean and efficient for many substrates and results in significant improvement in reaction yield and in a dramatic decrease in reaction time in comparison to thermal heating.

A series of tetrapyrrolic macrocycles such as porphyrins, phthalocyanines and corroles were found to have inhibitory abilities toward acetylcholinesterase (AChE). Their structure-activity relationship was studied. Several compounds were found to have good inhibitory abilities, which could be developed as potential candidates of acetylcholinesterase (AchE) inhibitors.

A series of core-modified porphyrins with different meso aryl groups (R₁), anchoring groups (R₂), and core atoms (X) were studied as light-harvesting sensitizers for dye-sensitized solar cells (DSSCs). DSSCs were fabricated using these porphyrins as well as TiO₂ nanoparticles with a particle diameter of around 25 nm. A dense layer of TiO₂ was deposited as an interfacial layer on fluorine-doped tin dioxide (FTO) substrates. A TiO₂ nanocrystalline film was then deposited on the dense layer by spin coating. The comparison of DSSC performance from different core-modified porphyrins was studied. The UV-vis absorption spectroscopy of porphyrin films attached on TiO₂ and porphyrin solutions were also measured. The results indicated that both anchoring and meso aryl groups impacted on cell performance. The cell efficiency was correlated to the absorption of porphyrin films attached on TiO₂ at the Soret band.

Hg₂²⁺ ion and 5,10,15,20-tetrakis(parasulphonato-phenyl)porphyrin anion can form 2:1 (2 clusters:1 porphyrin) and 2:2 complexes, while the formation of the 1:1 species is not observable: it is only an intermediate, similarly to the cases of other large metal ions of small charge-density. The differences between mercury(I) and mercury(II) porphyrins in the composition of monoporphyrins (2:1 vs. 1:1), in the stability and the Soret absorption based on the arrangement of 2:2 complexes (asymmetric vs. probably symmetric sandwich-structure), in the kinetic behavior (molecularities and the special dimerization of Hg^IIP^4-), in the product of the photoinduced dissociations of 2:2 bisporphyrins (free-base ligand vs. 1:1 complex) can prove that no mercury(II) porphyrins can form due to the possible disproportion of dimercury(I) ions. However, the similarities in the absorption, photophysical and photochemical features (also to other out-of-plane metalloporphyrins) suggest that the out-of-plane position of metal center and the distorted structure of complexes may be responsible for these common properties, the so-called sitting-atop characteristics. Moreover, the calculated structural data of the theoretically studied 1:1 mercury(I) porphyrin are very similar to those of Hg^IIP as a consequence of the charge separation in the cluster based on the strength of metal-nitrogen bonds. In the case of the 2:2 species, neither the increased distance (because of the Hg-Hg bond), nor the absence of 45° rotation of the two ligands can significantly modify the π-π interaction because its both measured and calculated absorption spectra are similar to those of Hg^II₂P₂.

It has long been believed that the phase transition behavior and clearing points (c.p.s.) of phthalocyanine-based metallomesogens scarcely change regardless of the kind of central metal. In this work, we have synthesized a series of novel sandwich-type phthalocyanine-based lanthanoid complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-didodecyloxyphenoxy)phthalocyaninato]lanthanoid(III) (abbreviated as {[(C₁₂O)₂PhO]₈Pc}₂M, M = La, Ce, Eu, Gd, Tb, Yb and Lu: 1–7). Their mesomorphic properties were investigated by polarization microscope, DSC and temperature-dependent X-ray diffraction techniques to compare with the phase transition behavior and c.p.s. of the complexes. Very interestingly, the c.p.s. of these seven rare-earth metal complexes increased in an order of La (1) → Ce (2) → Eu (3), reached to a maximum for Gd (4), and decreased in an order of Tb (5) → Yb (6) → Lu (7). We have noticed that their rise and fall of c.p.s. correspond to the values of total spin quantum number (S) of the central rare-earth metal ions. Thus, it was found, for the first time in metallomesogens, that the S values of central rare-earth metal ions strongly influence their c.p.s.

The binding interaction mechanism between 5-phenyl-10,15,20-tri-(4-pyridyl)-porphyrin (TriPyP) and bovine serum albumin (BSA) was investigated by the fluorescence method and presented in this paper. Based on the mechanism of fluorescence quenching of BSA caused by TriPyP, the binding constants between TriPyP and BSA were measured at different temperatures by fluorescence spectroscopy at pH 7.40. As the binding constants decreased with increasing temperature, the type of quenching between TriPyP and BSA was determined as static quenching. Based on the Förster theory of non-radiation energy transfer, the binding distance and energy transfer efficiency at 25 °C between TriPyP (acceptor of energy) and BSA (donor of energy) were obtained. The results confirmed that the interaction was similar to non-radiation energy transfer. According to the thermodynamic parameters, the main type of binding force between TriPyP and BSA could be deduced as electrostatic force. Using synchronous fluorescence spectra, the effect of TriPyP on conformation of BSA was studied, and the hydrophobicity in microenvironment was developed by TriPyP. All these experimental results and theoretical data clarified that TriPyP could bind to BSA and be effectively transported in the human body, which could be a useful guideline for further drug design.

A dendritic shell can create a distinct micro-environment within its core. It also has the advantage of possessing unique photochemical, photophysical, electrochemical, and catalytic properties. Polyphenylene dendrons, which are characterized by their shape-persistent structures and out-of-plane twisted phenyl components, have previously been successfully attached to various functional groups. We have recently developed a convenient method for synthesizing a new type of porphyrazine that contains both flexible (linear) and more rigid (dendritic) groups. The synthesis of this completely aromatic and dendronic structure is unique in that it is based on a [2+4] Diels-Alder cycloaddition of tetraphenylcyclopentadienone to an ethynyl compound, followed by the elimination of carbon monoxide. In this study, tetrapyrazinoporphyrazinato metal and metal-free complexes were prepared by mixing 2,3-dicyano-5-polyphenylpyrazines with magnesium in n-butanol. The synthesized tetrapyrazinoporphyrazines were characterized by UV-visible spectroscopy, MALDI-TOF-MS (matrix-assisted laser desorption/ionization time-of-flight mass) spectrometry, elemental analysis and ¹H NMR spectroscopy.

Bis(N,N-dimethylamino)methane has been shown to be a convenient reagent for the aminomethylation of chlorophyll a derivatives. Methylpheophorbide a (in enol form) and chlorin e₆ 13-amides were aminomethylated with bis(N,N-dimethylamino)methane. Reactivity of methylpheophorbide a exo-ring and chlorin e₆ 13-amides vinyl group were shown to be different. Selective methylpheophorbide a exo-ring aminomethylation was realized and isomerization of the exo-ring aminomethylation product with rhodochlorin 15-acrylic derivative formation was studied. The action of bis(N,N-dimethylamino)-methane in the presence of weak acid has been shown to be a simple and effective synthetic procedure to obtain a new chlorin e₆ derivative with two N,N-dimethylaminomethyl substituents in the vinyl group. The aminomethylation products' high yields, the simplicity of the procedure, the use of metal-free chlorines and the possible synthesis of new compounds, were found to be the main advantages of using bis(N,N-dimethylamino)methane as an aminomethylation reagent in chlorophyll a derivatives' chemistry.

The spectral manifestations of the distorted forms of sterically unconstrained metallocomplexes of porphyrin in rare gas and Shpol'skii matrices at cryogenic temperatures were detected. The planar and two kinds of distorted conformations of the Mg- and Zn-porphyrins in rare gas matrices have been measured simultaneously in the fluorescence and phosphorescence spectra due to external heavy atom effect. The distinctly different frequencies of the vibronic transitions have been revealed for planar and distorted forms. In the phosphorescence spectra of the Pd-porphyrin the manifestation of the two forms in the ground state has been proven also, with one of them being planar and the other being saddle-type distorted. The ratio of the planar and non-planar forms was shown to depend on the deuteration of both meso-positions of the porphyrin and n-alkane matrix. The appearance of the out-of-plane modes in the phosphorescence spectra of the Pd- and Pt-porphyrin has been demonstrated.

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.

Manganese tetraphenylporphyrin supported on nano-TiO₂ has been synthesized and structurally characterized. It has been shown to have excellent catalytic activity for the aerobic oxidation of α-pinene. Experimental results showed that this much-enhanced activity could arise from possible co-catalysis between metalloporphyrin and the nano-TiO₂ support. The catalyst can be reused several times with minor loss to its catalytic activity.

Inorganic nanoparticles combined with conducting polymers provide interesting physical properties. This research describes the aniline polymerization taking place on the nanoparticles surface by catalytic oxidative polymerization with metalloporphyrin and metallophthalocyanine. In this way, the core-shell structure of the polyaniline/TiO₂ nanocomposites was obtained. The comparison of results demonstrates that porphyrin is a better catalyst than phthalocyanine for synthesis of nanocomposite. The morphology and composition of the nanocomposites were characterized by techniques such as SEM and FT-IR spectroscopy. TGA analysis showed that the nanocomposites, synthesized with iron(III) tetrasulfonated tetraphenyl porphyrin and iron(II) tetrasulfonated phthalocyanines, contained 10% and 5% conducting polyaniline (by mass), respectively. Eventually, the voltammograms revealed that these nanocomposites were electroactive and there was a linear relationship between the anodic and cathodic peak current values and scan rates.

Cobalt phthalocyanine (CoPc), cobalt tetracarboxy phthalocyanine (CoTCPc) and cobalt octacarboxy phthalocyanine (CoOCPc), adsorbed onto glassy carbon electrodes, have been used for the electrocatalytic detection of nitrite, L-cysteine and melatonin. The modified electrodes electrocatalytically detected nitrite around 800 mV vs.Ag|AgCl, a value less positive compared to that of an unmodified glassy carbon electrode (at 950 mV vs.Ag|AgCl) and also gave detection limits in the 10^-7 M range for nitrite detection. L-cysteine was detected by the modified electrodes at potentials between 0.50 to 0.65 V vs.Ag|AgCl, with L-cysteine detection limits also in the 10^-7 M range. The detection limits for melatonin ranged from 10^-7 to 10^-6 M. CoPc-modified electrodes displayed good separation of interferents (tryptophan and ascorbic acid) in the presence of melatonin. Analyses of commercial melatonin tablets using modified electrodes gave excellent agreement with manufacturer's value for all modified electrodes of this work.