A New Potent Antimicrobial Metalloporphyrin

A series of bis-acryl functionalized porphyrins and their corresponding metalloporphyrins (M=Co, Mn) were synthesized and investigated for their antimicrobial properties through MIC screening and bacteria time-kill kinetic studies. The Mn(III) 4-(bis)methylphenyl-substituted-porphyrins showed superior batericidal activities even in the dark with low hemotoxicity and good cytotoxicity profile.     

Diiron(III)–μ‐Fluoro Bisporphyrins: Effect of Bridging Ligand on the Metal Spin State

A hitherto unknown family of diiron(III)–μ‐fluoro bisporphyrins has been synthesized and structurally characterized. Fluoride abstraction from SbF₆^? and BF₄^? resulted in the synthesis of the μ‐fluoro complexes of ethane‐ and ethene‐bridged diiron(III) bisporphyrins. Two such complexes were structurally characterized, which revealed a single fluoro bridge between two iron centers with a remarkably bent Fe‐F‐Fe unit. Although isoelectronic with the μ‐hydroxo complexes, the μ‐fluoro species are quite divergent in terms of the electronic structure and properties. UV/Vis spectroscopy of the μ‐fluoro complex exhibits a large redshift (ca. 18 nm) of the Soret band in comparison to their μ‐hydroxo analog. Combined analysis by single crystal X‐ray structure determination and Mössbauer and ¹H NMR spectroscopy revealed the presence of two equivalent iron(III) centers in the μ‐fluoro complexes in both solid and solution phases. In contrast, the iron(III) centers of the μ‐hydroxo complexes are known to be inequivalent. Variable‐temperature magnetic studies show a weak antiferromagnetic interaction between the iron(III) centers of the μ‐fluoro complexes with coupling constants (J) ranging from ?33 to ?40 cm^?1. The experimental results were further supported by DFT calculations.     

Extra-liganding effects in Zn-octaethylporphyrin solutions in a temperature interval of 300-77 K

It is established experimentally for the first time that Zn-octaethylporphyrin in a solution of dried methyl cyclohexane is in unliganded form in the temperature interval of 293-77 K. This form is characterized by the shortest-wave position of absorption and luminescence spectra, the independence of the degrees of fluorescence and phosphorescence polarizations from the excitation wavelength, and high phosphorescence time (τ_T=126 μsec) and quantum yield (φp=0.085) at 77 K. Adding electrodonor components to the methyl cyclohexane or going over to alcohol-containing polar media leads to the formation of a monoliganded form of ZnOEP, for which we observe a bathochromic shift of ≈150–350 cm⁻¹ for Q(0,0) absorption and luminescence bands, a splitting of ≈50–100 cm⁻² for the Q(0, 0) absorption band, and phosphorescence quenching (τ_T=60 μsec, φp=0.05-0.03 at 77 K). The effects revealed are explained by a decrease in the symmetry of a ZnOEP molecule in extra liganding and by an increase in the probability of nonradiative activation for a T₁-state due to the extra ligand being involved in the exchange of electron-excitation energy and to the enhancement of a spin-orbital coupling as a result of the disturbance of the planarity, of a macrocycle. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 900–907, November–December, 1998.     

Quantum-chemical interpretation of spectral and photochemical properties of complexes of metalloporphyrins with pyridine anions

A quantum-chemical study is made of the energy minima and profiles of the potential surface of complexes of Zn-porphyrin with dilithiumpyridine in different energy states. It is shown that the axial distribution of dilithiumpyridine relative to the porphyrin ring corresponds to the energy minimum pertaining to the lower singlet state. A radically different geometry is obtained for the lower triplet state of charge transfer, and at this energy minimum the latter state represents, according to calculation data, the ground state. Based on an investigation of the profiles of potential surfaces between the energy minima, an explanation is given for the photochemical behavior of the complex. “S. I. Vavilov Institute of Optics” All-Russia Scientific Center, 12, Birzhevaya Liniya, St. Petersburg, 199034. Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 38–41, January–February, 1997.     

Hyperporous‐Carbon‐Supported Nonprecious Metal Electrocatalysts for the Oxygen Reduction Reaction

Highly porous carbonaceous nonprecious metal catalysts for the oxygen reduction reaction are prepared by carbonization of low‐cost metalloporphyrin‐based hyper‐crosslinked polymers (MPH‐X). With high surface area (2768 m² g⁻¹), hierarchical porous structure, and high metal loading (9.97 wt %), the obtained hyperporous carbon MPH‐Fe/C catalyst exhibits high oxygen reduction reaction (ORR) activity with a half‐wave potential (0.816 V) that is comparable to the 0.819 V of commercial Pt/C. Stability tests reveal that MPH‐Fe/C also exhibits outstanding long‐term durability and methanol tolerance. Our findings may offer an alternative approach to produce nonprecious metal ORR catalysts on a large scale owing to the low‐cost MPH‐X precursors with diverse metal types.     

Molecular recognition by macropolycyclic hosts

The formation of complexes between crown ethers and aklylammonium cations may, to some extent, be modelled using standard molecular mechanics methods and an appropriate charge distribution scheme. Monocyclic crown ethers may be developed to give chromoionophores suitable for use in optical fibre based ion sensors. The incorporation of two crown ether systems into polycyclic host molecules which show highly selective complexation of guest bis-alkylammonium cations is described. The scope of these ditopic receptors may be extended by using metalloporphyrins in place of one or both of the crown ether binding sites.     

Titration Calorimetric Investigation of Interactions of Zinc(II), Nickel(II), and Copper(II) Tetraphenylporphine Complexes with Pyridine in Three Solvents

Titration calorimetry was used in a thermodynamic study on the interactions of pyridine (Py) with zinc(II)-tetraphenylporphine (ZnTPP), nickel(II)-tetraphenyl-porphine (NiTPP), and copper(II)-tetraphenylporphine (CuTPP) in benzene, chloroform, and carbon tetrachloride solutions. The coordinating properties of the metalloporphyrins in relation to pyridine were found to diminish in the order ZnTPP > CuTPP > NiTPP. Solvation effects were estimated from the interactions between metalloporphyrins (MP) and Py. The more negative values of the enthalpy and entropy of reaction of ZnTPP with Py, following the order of solvents CCl₄ > C₆H₆ > CHCl₃, was found to be related to the different types of (MP–solvent) and (Py–solvent) interactions. The NiTPP and CuTPP complexes showed the opposite trend.