No abstract

Three ABAB-type cobalt meso-tetraarylporphyrins with fluorine (F-CoPor), acetic acid (AC-CoPor), and cyanoacetic acid (CN-CoPor) groups at the para-positions of phenyl rings at the 10,20-positions are synthesized and evaluated as catalysts for oxygen reduction reactions (ORRs). In density functional theory calculations, the frontier molecular orbitals of these complexes were found to be stabilized relative to model complexes with electron-withdrawing atoms or moieties on the meso-aryl rings. Electrochemical measurements suggest that electrodes with CN-CoPor (CN-CoPor/C) exhibit the most positive ORR potential values and the highest limiting current density in both acidic and alkali electrolytes, while the F-CoPor/C electrocatalyst exhibits extremely low ORR performance. The electron transfer numbers for the electrocatalysts are more than 3.0, indicating that a mixture of 2-and 4-electron transfer pathways occurs. The results demonstrate that coupling the hydrogen bonding properties and electron-withdrawing abilities through rational design of the substituent at the meso-position is an efficient way to modify the ORR performance.

The photodynamic antimicrobial chemotherapy (PACT) activities of four meso-pentafluorophenylBODIPY dyes were studied against Staphylococcus aureus to identify structure-property relationships related to the introduction of different substituents on the BODIPY core. 1,3,5,7-Tetramethyl dyes with bromine and iodine atoms at the 2,6-positions (2a and 3a) were synthesized and characterized along with 3,5-dimethyl dyes that were either tetrabrominated at the 1,2,6,7-positions (2b) or diiodinated (3b) at the 2,6-positions. The incorporation of iodine atoms on the BODIPY core at the 2,6-positions enhanced the PACT activity relative to those of the di- and tetrabrominated dyes. Replacing the methyl groups at the 1,7-positions with protons to form 3b results in greater PACT activity than is the case with 3a since the absence of steric hindrance related to methyl groups at the 1,7-positions allows the meso-aryl ring to rotate closer to the plane of the [Formula: see text]-system of the BODIPY core. The tetrabrominated dye was found to have the lowest PACT activity due to a lack of stability in solution and poor uptake by the bacteria being studied. The electron-withdrawing pentafluorophenyl group was selected to lower the dipole moment of the BODIPY core dye since poor PACT activity was observed when a 2,6-dibromo-1,3,5,7-tetramethyl BODIPY dye was prepared with a thiomethylphenyl group (2c).