Journal of Porphyrins and Phthalocyanines

Porphyrin nanorods (PNR) have been fabricated by electrostatic self-assembly of two oppositely charged porphyrin molecules. The free base meso-tetra-(4-phenylsulphonate) porphyrin (TPPS${}_4)$ served as negatively charged counterpart for the positively charged metallo meso-tetra(4-$N$-methylpyridyl) porphyrins (MTM’PyP) with either Sn, Co, Mn or In as central metal M. Films of PNR were prepared on fluorine doped tin oxide glass sheets (FTO) by using a drop-dry method. The electronic spectra revealed J-aggregation of the charged molecules for the colloid PNR as well as for the films. Transmission electron microscopy confirmed the formation of porphyrin nanorods. The laser microscope and scanning electron microscope (SEM) images of the PNR/FTO films showed the formation of three kinds of structures in the films which consist of differently branched or linear needles with their main axis grown in the direction of the solvent flow during preparation. During cyclic voltammetry either applying negative potentials from 0.0 V to -1.0 V or positive potentials from 0.0 V to $+$2.2 V irreversible reduction or oxidation reactions were detected for the films. Consistently, SEM images taken following cyclic voltammetry showed the disintegration of the PNR on the films into smaller subunits. Spectroelectrochemical measurements showed the formation of porphyrin anionic radicals during oxidation by a decrease in the absorption intensities and broadening of spectra with an additional band appearing around 900 nm. A similar trend was observed when negative potentials were applied but in this case the cationic radical was produced. In both cases the decrease of the intensity of the J-aggregate confirms a loss of intermolecular coupling, again consistent with the smaller subunits observed in SEM analysis.

Current work is devoted to covalent immobilization of sulfonated derivatives of cobalt phthalocyanines “Merox catalysts” on the surfaces of polypropylene and polyethylene terephthalate. Their catalytic activity in reaction of mild oxidation of sulfur compounds to disulfides with oxygen of the air was studied. Anchoring of the catalyst on this polymer prevents its leaching and promotes its efficient recovering and recycling without significant loss of catalytic activity.

Spectroscopic properties of Porphyrins TPyP (tetra(4-pyridil)porphyrin), TMPP (tetrakis(4-methoxypheny) porphyrin) and its zinc metaled derivatives porphyrins Zn-TPyP and Zn-TMPP respectively, were studied in homogeneous and micro heterogeneous systems, comprising nanostructured Pluronic® copolymeric micellar systems, as a promising drug delivery systems for the porphyrins investigated. Physico-chemical properties such as, hydrophobicity degree, self- aggregation in solvents of different polarities and water/ethanol mixtures (monofasic binary), as well as kinetics profile and isotherm binding, molecular organization, ${\mathrm{\Phi }}_{Fl}$ and relative localization in neutral micellar systems. The hydrophobic character was the key to relative drug location in the micellar systems. In homogenous solvents systems the porphyrins presented relatively high values of molar absorptivity and low values of ${\mathrm{\Phi }}_{Fl}$. The K${}_{\mathrm{\text{b}}}$ values obtained are modulated by the structure of porphyrins, state of aggregation, as well as, structure and macro molecular self-organization of copolymers. Fluorescence quenching studies have shown that porphyrins in F-127 are located in a less hydrophobic region than the porphyrins in P-123, which are located preferentially in a deeper micellar microenvironment. The zinc porphyrins showed high values of K${}_{\mathrm{\text{b}}}$. Thus, the association of the porphyrins with specific binding sites of micellar systems is strongly modulated by the presence of the metal coordinated to the porphyrinic ring.

Herein, the conjugation of carboxylated tetraphenylporphyrin or its derivative containing manganese cation and model protein — immunoglobulin G is presented. The obtained IgG–cTpp and IgG–Mn-cTpp conjugates were subsequently used for model immunoassays construction. The IgG–cTpp formation was confirmed using size-exclusion chromatography. Thanks to the unique properties of applied labels the assay analysis was carried out with both spectrophotometric and spectrofluorimetric detection. The assays were performed creating semi-quantitative detection system using 96-well plates. The incubation time, ensuring full saturation of the surface with secondary antibodies was also optimized. Moreover, in the case of IgG–Mn-cTpp conjugates we present the possibility of both direct and indirect determination of the label, the latter based on the catalytic activity of Mn-cTpp, which allows for amplification of the measured signal. We proved that both cTpp and Mn-cTpp may be successfully used for protein labeling and serve as universal tracers for various formats of affinity assays and sensors.

The (nitro)($N$,$N^{\prime }$-dimethyl-4-aminopyridine) complex of perfluorinated cobalt(III) phthalocyanine Co(III)F₁₆Pc(Me₂Npy)(NO${}_2)$ catalyzes the electrochemical oxygen reduction reaction (ORR) in pH 4.0, 7.0, and 10.0 buffer and 0.05 M sulfuric acid solution when deposited on a glassy carbon electrode. Cyclic voltammetry (CV), rotating disk electrode voltammetry (RDE), and rotating ring-disk electrode voltammetry (RRDE) have been used to determine the reduction product as hydrogen peroxide although in concentrations too small to observe by qualitative methods such as oxidation of NaI in solution. The dependence of the values of the peak potentials for the reduction on the pH of the solution and the -log[Me₂Npy] are consistent with protonation up to pH 7.6 and pyridine ligand loss during the reduction. The addition of nitrite at 0.1 and 1 M to pH 7.0 solutions in contact with films of CoF₁₆Pc on the glassy carbon electrode decreases the ORR current and shifts the peak potential of the ORR from -0.21 V vs. NHE to -0.19 V vs. NHE. The addition of nitrite at 0.1 and 1 M to films of Co(III)F₁₆Pc(Me₂Npy)(NO${}_2)$ on glassy carbon, however, has no effect on either the current or the potential. While the electrochemical evidence for this proposal is not definitive, modeling has been used to examine the center of reduction in the alternative mechanisms by evaluation of the LUMOs of the hypothetical intermediates in both closed and open shell cases. The formation of five-coordinate Co(II)F₁₆Pc(NO) is proposed to occur initially in the reduction mechanism. It is also possible that O₂ reduction takes place at the NO ligand center by way of a nitrogen-bound peroxynitrite intermediate. The $\text{NO/NO}{}_2{}^{\mathrm{-}}$ ligand appears to remain bound during the ORR. Direct coordination of O₂ to the metal center requiring a six-coordinate species, Co(III)F₁₆Pc(O${}_2)$(NO${}_2)$, Co(II)F₁₆Pc(O${}_2)$(NO) or [Co(II)F₁₆Pc(O${}_2)$(NO${}_2)$]${}^{-}$ and has been considered in DFT modeling studies. The instability of the two-electron reduced, protonation species, [Co(I)F₁₆Pc(NO₂OH)]${}^{-}$ in its loss of peroxynitrous acid suggests that the reduction of O₂ may occur by two one-electron reduction steps rather than a two-electron step.

The stereo electronic effects as well as hydrogen bonding effects of imidazole, pyridine and 2,6-dimethylpyridine as N-donor axial ligands on the C–H oxidation activity of high-valent manganese(V)–oxo meso-tetraphenylporphyrin (TPP) and meso-tetrakis(pentaflourophenyl)porphyrin (TPFPP), are investigated by DFT calculations. The electronic and steric properties of axial donors and porphyrin ligands affected on the activation energy of cyclohexane hydroxylation as well as the Mn–O bond strength of the oxo species in transition state. Imidazole with the strong $\pi$-donating ability and the least steric hindrance showed greater co-catalytic activity than those of pyridine and in particularly hindered 2,6-Me₂ pyridine in the presence of simple [(TPP)MnO]${}^{+}$. Nevertheless, the C–H bond activation by hindered and electron-deficient perfluorinated catalyst [(TPFPP)MnO]${}^{+}$ is in the order of pyridine >2, 6-Me₂ pyridine >imidazole. AIM analysis showed hydrogen bonding (HB) between the C–H $\sigma$ bonds of pyridine (C${}_{\mathrm{\text{sp}}2}$-H of ring) and 2,6-Me₂Py (C${}_{\mathrm{\text{sp}}3}$-H of methyl groups) with ortho-C–F bond of phenyl rings of TPFPP in Mn$=$O species (C–H…..F–C hydrogen bond) which might be responsible for this unusual behavior. These results are supported by natural bond orbital (NBO) analysis.

Six monophenyltripyridylporphyrin derivatives were synthesized and characterized by spectroscopy in order to demonstrate their potential usefulness as photosensitizers for anticancer therapy purposes. Compounds 1 and 3–5 are amphiphilic, thus they may be suitable for transfer inside cells. Photochemical parameters such as fluorescence yield and singlet oxygen yield were determined. The former parameter does not exceed 10% which makes them unsuitable for photodynamic diagnosis (PDD). However, singlet oxygen yields are high and sufficient for these compounds to be considered as potential photodynamic therapy (PDT) photosensitizers.

Theoretical studies on porphyrin-ethanol solvates containing from 1 to 8 ethanol molecules have been carried out by density functional theory (DFT) calculations using hybrid (B3LYP) and meta-GGA (M06-L) functionals. It was established that porphirin molecule can be considered as two centered protones acceptor. Specific solvation is at the base of porphyrin-(EtOH)n interactions and results in a distortion of macrocycle planar structure. The nucleophilic solvation energy of the porphirin pyrrole demonstrates dependence on the number of molecules in the ethanol solvate, being the highest for the first two ethanol molecules and decreasing with ethanol association in the solvation shell. Results obtained by this way are in good agreement with data derived from ¹H NMR.