Journal of Porphyrins and Phthalocyanines

Meso-tetraphenylporphyrinatooxidovanadium(IV) [V^IVO(TPP)] (1) and 2,3,7,8,12,13, 17,18-octabromo-meso-tetraphenylporphyrinatooxidovanadium(IV) [V^IVO(TPPBr${}_8)$] (2) were synthesized and characterized by various spectroscopic techniques. 1 and 2 were utilized as efficient catalysts for the selective epoxidation of olefins. Catalyst 2 shows very high catalytic activity (TOF = 8783–13108 h${}^{-1})$ as compared to 1 (TOF = 2175–3296 h${}^{-1})$. The catalysts are recyclable, as their recyclability was checked for four cycles and show only minor reduction of their efficiency.

UV, FL and IR spectra of isomer A (in DCM) and isomer B (in DMAc) of N-confused 5,10,15,20-tetra($o$-methoxyphenyl)porphyrin ($o$-isomer, 1), N-confused 5,10,15,20-tetra($m$-methoxyphenyl)porphyrin ($m$-isomer, 2) and N-confused 5,10,15,20-tetra($p$-methoxyphenyl)porphyrin ($p$-isomer, 3) were investigated. Significant red shifts are observed from $o$-isomer (1) to $p$-isomer (3) in UV-vis absorption and fluorescence spectra. The fluorescence lifetime (${\tau }_{\text{fl}})$ of isomer A and isomer B of the samples (1, 2 and 3) are ca. 1.39$\sim$1.79 ns and 1.68$\sim$2.09 ns, respectively. In addition, the order of fluorescence quantum yield for isomer A is 1 >2 > 3, but for isomer B it is 1 < 3 <2. The isomer B of 2shows the strongest emission in accord with the strongest absorption. The isomer A of 1shows the strongest emission with the fluorescence quantum yield of 0.045, which is nearly double that of 3. The introduction of the methoxy group at the orthoposition increases steric hindrance, the molecular rigidity and the flow of $\pi$-electron, thereby favourable to the fluorescence enhancement. The IR absorption peaks of 1, 2 and 3 were investigated and empirically assigned. The effects of the position of the substituents on the absorption frequency were also discussed. The absorption frequency of the C=C phenyl stretching in plane changed obviously by conjugative effect and steric effect when the methoxy group was at the orthoormetaposition in comparison with paraposition.

The Mn(III)-oxophlorin complexes with imidazole, pyridine and t-butylcyanide as axial ligands have been studied using B3LYP, Bv86p, and M06-2X methods. All of the possible optimized geometries are specified, while the M06-2X is employed. Results obtained show that the isomers of Mn(III)-oxophlorin with imidazole or pyridine are the most stable at quintet state, compared to singlet and triplet spin states. Besides, there are two and four $\alpha$-electrons on manganese in each of these complexes at triplet and quintet states, respectively. Also, Mn(III)-oxophlorin with t-butylcyanide as axial ligand is only stable at singlet state. Non-specific solvent effects show that dispersion and London forces have the basic role in stability of complexes in a solvent. Note that latter interactions can occur in medium with dielectric constant ($𝜖$) of $\sim$8, such as $𝜖$ for position of oxophlorin in heme oxygenase enzyme. NBO analysis show that there is no degeneracy between d orbitals of Mn in the five-coordinated Mn(III)-oxophlorin at singlet and triplet spin states, but two d orbitals of manganese are degenerated in latter complexes at quintet state. Such degeneracy of d orbitals is observed in a complex with square pyramid structure. Then five-coordinated Mn(III)-oxophlorin with imidazole or pyridine is the most stable at quintet spin state, because of its geometry corresponding to square pyramid configuration of atoms. Also, nonbounding interaction between Mn and the ring of oxophlorin or Mn and ligand are more effective in Mn(III)-oxophlorin with imidazole as axial ligand, compared to pyridine and t-butylcyanide.

By using quantum chemical calculation data obtained by the DFT method with the OPBE/TZVP and B3PW91/TZVP levels, the principal possibility of the existence of three heteroligand complexes of nickel, each of which was shown to contain in the inner coordination sphere either porphyrazine or di[benzo]- and tetra[benzo]porphyrazine, oxygen (O${}^{2-})$ and fluorine (F${}^{-})$ ions. The data on the geometric parameters of the molecular structure of these complexes are presented; which shows that NiN₄ chelate nodes, all metal-chelate and non-chelate cycles in each of these complexes, are strictly planar. The bond angles between two donor nitrogen atoms and a nickel atom are equal to 90${}^{\circ }$, while the bond angles between donor atoms N, Ni, and O or F, in most cases, albeit insignificantly, differ from this value. Nevertheless, the bond angles formed by Ni, O and F atoms are exactly 180${}^{\circ }$. NBO analysis data for these complexes are presented; it was noted that the ground state of all these complexes was a spin doublet. It has been shown that a good agreement between the data obtained using the above two versions of the DFT method occurs. Also, standard thermodynamic parameters of formation (standard enthalpy $\mathrm{\Delta }{H}_{f,298}^0$, entropy $S_{f,298}^0$ and Gibbs’s energy $\mathrm{\Delta }{G}_{f,298}^0)$ for the macrocyclic compounds under consideration were calculated.

We successfully synthesized the 5, 10, 15, 20-(4-sulphonatophenyl)porphyrin (TSPP) by the most environmentally friendly method, afterwhich, we proposed a novel fluorescent “on-off-on” sensor for monohydrogen phosphate (HPO${}_4^{2-})$ in the nutrient solution using the appealing fluorescence of TSPP. The switchable sensor based on TSPP was developed to determine HPO${}_4^{2-}$ via fluorescence quenching of TSPP solution by Fe${}^{3+}$ (off) and recovery by HPO${}_4^{2-}$ (on). Under optimal conditions, the limit of detection (LOD) for HPO${}_4^{2-}$ was 0.31 $\mu$M (S/N=3), and a good linearity is showed in the range of 0–54.7 $\mu$M with R²=0.9989. This method displayed several excellent properties including convenience, high selectivity and fast fluorescence response.

The emergence of antibiotic-resistant bacterial strains has recently resulted in a large focus on designing new antimicrobial agents, including those based on natural compounds. We have previously synthesized two disubstituted arginine-containing derivatives of hemin (HD) (4) and (5) that demonstrated pronounced antimicrobial activity against planktonic cells in vitro [1, 2]. These HDs are leading and promising for the creation of antibacterial agents on their basis. This research is aimed at improving the synthesis of HDs (4) and (5) to increase their yield, simplify the process and minimize the side reactions, as well as to establish their antimicrobial and destructive effect on biofilms, including those consisting of antibiotic-resistant bacteria. As a result, we were able to increase the yields of the protected dipeptide of ZArg(Z${}_2)$SerNH₂ (3) and the corresponding HD (4) up to 97 and 93%, respectively, and also to minimize the side reaction of the formation of ornithine-containing HD. For the arginine amide modified HD (5), we have also proposed an improved synthesis scheme. The ability of HD to cause the bacteria death in the composition of formed biofilms, including those consisting of resistant bacteria, was shown. After the effect of HDs on the biofilm at concentrations of 80 and 100 $\mu$g/ml, the CFU decrease was 3–5/ml. The fluorescent microscopy confirmed the bacteria mortality in the biofilm. Electron microscopy showed structural damage (fragmentation) of the formed bacterial biofilm under the effect of HDs.

Donor-Acceptor (D-A) systems based on phenoxazine – phthalocyanine (PXZ-Pc) and phenoxazine – zinc phthalocyanine (PXZ-ZnPc) have been designed and synthesized. Both D-A systems are characterized using various spectroscopic and electrochemical techniques including in-situ methods. Optical absorption studies suggest that both Soret and Q bands of these D-A systems are hypsochromically and bathochromically shifted, when compared to its individual constituents. The study supported by theoretical calculations shows clearly that there exists a negligible electronic communication in the ground state between donor phenoxazine and acceptor phthalocyanine. However, attractively, both D-A systems exhibit noteworthy fluorescence emission quenching (90–99%) of the phthalocyanine emission compared to its reference compounds. The fluorescence emission quenching featured at the excited-state intramolecular photoinduced electron transfer from ground state of phenoxazine to the excited state of phthalocyaine/zinc phthalocyanine. The rates of electron-transfer ($k_{ET})$ of these D-A systems are found in the range of 5.7 × 10⁸ to 2.8 × 10⁹ s${}^{-1}$ and are according to solvent polarity.

A new meso-tetrakis(3,5-di-tert-butylphenyl) substituted porphycene and its cobalt complex were synthesized and characterized. Several meso-tetraarylporphycene cobalt complexes having different substituents showed catalytic activity for the hydrogen gas evolution reaction (HER) in the presence of trifluoroacetic acid (TFA) under electrochemical reductive conditions. The electrochemical potential of the HER was -1.50V vs. Ag/AgCl in THF. The active species of this reaction were determined to be the ligand reduced species of Co(II) porphycenes. The catalytic efficiencies of the cobalt complexes of meso-aryl substituted porphycenes and meso-tetraphenylporphyrin were compared and meso-tetraphenyl porphycene cobalt complex exhibited the best current efficiency of 72%. Based on these experimental results and theoretical calculations, we proposed a possible HER mechanism of this system.