Chemoenzymatic oxidation of citronellol and geraniol: Synthesis and antibacterial activity assessment

Essential oils (EOs) are potential bio-sourced candidates to be grafted on polymer surfaces to fight against bacterial infections by either restricting the growth of bacteria (bacteriostatic effect) or killing bacterial cells (bactericidal effect). This paper deals with the modification of terpenoid molecules intended to be later grafted on polymer-plasma-activated surfaces. Citronellol (CT) and geraniol (GR) were chosen for their antimicrobial activity and were successfully modified to obtain better reactive function towards polymer grafting. They were transformed into CT-oxide (CT-ox) and GR-oxide (GR-ox) through an accessible and green chemo enzymatic oxidation method. Microbiological tests were undertaken to estimate the antibacterial effects of CT and GR before and after modification. Three bacterial species have been used: Escherichia coli (E. coli, diderm Gram-negative), Staphylococcus aureus (S. aureus, monoderm Gram-positive), and Corynebacterium glutamicum (C. glutamicum, diderm Gram-positive). The results showed that antibacterial effects remained after epoxidation: tested molecules exhibited different impacts on the three bacterial strains. The tested molecules exhibited antibacterial activities by targeting bacterial cell envelopes, disrupting membrane integrity, and altering hydrophobicity. These actions led to the inhibition of bacterial growth or death of the bacteria, as evidenced by Zeta Potential (ZP) measurements, Scanning Electron Microscopy (SEM) imaging, and surface energy assessments. Our study conclusively confirmed the antibacterial effectiveness of CT-ox and GR-ox.