Phenoxide coordination to Fe(III) tetraphenylporphyrin: Exploring antibacterial and electrocatalytic HER activity

• Published in: Inorganica Chimica Acta 2024-08, Vol.568, p.122084, Article 122084
• Main Authors: Patra, Moumita, Kumar Das, Tarun, Saha, Arijit, Das, Tania, Patra, Arpita, Garai, Somenath, Nayek, Abhijit, Roy, Ujjal Kanti, Bhowmik, Susovan
• Format: Article
• Language: English
• Subjects: Antibacterial; Electrochemistry; Hydrogen evolution reaction (HER); Phenoxide
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2024.122084

Three five-coordinate (unsubstituted, 4-NO2 substituted and 2,4,6 trinitro substituted) phenoxide axially ligated Fe(III)-tetraphenyl porphyrins were synthesised and characterised. Axially phenoxide coordinated Fe(III) complex demonstrated potent antibiotic activity. It also showed electrocatalytic behaviour for proton reduction to H2. So, this catalase analogue was employed to address two important global problems: antibacterial resistance and production of green fuel. [Display omitted] •Axially phenoxide coordinated Fe(III) porphyrins were synthesized and fully characterized. Two of the complexes stabilize pure high-spin (S = 5/2) state of iron. However, 2,4,6-trinitro phenoxide axial ligand stabilizes spin admixed state of iron(III) (S = 5/2, 3/2) with minute mid-spin contribution.•(TPP)FeIII-OPh demonstrated potent anti-bacterial activity.•(TPP)FeIII-OPh showed efficient electrocatalytic proton reduction to H2 upon gradual addition of acid source (PTSA: para-tolune sulphonic acid). Herein, we report synthesis, solid and solution state structure as well as properties of three five coordinate (unsubstituted, 4-NO2 substituted and 2,4,6 trinitro substituted) phenoxide axially ligated to Fe(III)-tetraphenyl porphyrins. Spectroscopic characterization revealed high-spin (S = 5/2) nature of the phenoxide bound Fe(III) porphyrins (Fe1 and Fe2). However, the 2,4,6 trinitro substituted phenoxide axially ligated Fe(III) porphyrin (Fe3) demonstrate spin admixed nature (S = 5/2, 3/2) with predominate high spin contribution. (Phenolato)(porphinato)iron(III) complexes merit attention owing to structural analogy with the catalase enzyme. In this study we investigated their antibacterial as well as electrocatalytic hydrogen evolution reaction (HER) activity. Fe1 demonstrate potent antibacterial activity against gram-negative E. coli (MTCC 443) and gram-positive Staphylococcus aureus (MTCC 3160) human pathogenic bacteria. It also produce catalytic current for electrocatalytic HER activities upon gradual addition of PTSA (para-tolunesulphonic acid) as proton source. Compounds Fe2 and Fe3 also produce enhanced catalytic wave which originate possibly from reduction of proton coupled with reduction of –NO2 group.