Lethal weapon IL: a nano-copper/tetraalkylphosphonium ionic liq-uid composite material with potent antibacterial activity

21 June 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Ionic liquid (IL) based composite materials have shown great promise as antimicrobial coatings, owing to their inherent germicidal properties, as well as their ability to stabilize metal nanoparticles (NPs), which may serve as a secondary antimicrobial reservoir. Here, we show that tetraalkylphosphonium ILs (TAPILs) on their own can annihilate pathogens by interfering with their cell membranes; however, the nature of the alkyl substituents on the central P atom and the nature of the anion play decisive roles in determining their antimicrobial activities. Con-comitantly, TAPILs can stabilize copper nanoparticles (Cu NPs) generated directly within the IL matrices without the addition of any second-ary stabilizers. The composites thus generated were thoroughly characterized and shown to be far more lethal to E. coli than just the TAPILs. The antibacterial effect demonstrated by the composite created from P[6,6,6,8]Cl (TAPIL-2) was orders of magnitude more lethal to microbes in comparison with P[6,6,6,8]Cl or copper nanoparticles alone. Neither the parent TAPIL-2 nor composite-2 were compromised by ambient storage conditions over a period of months with regards to their bactericidal effects. The composite with the best performance (composite-2) also proved to be effective against a panel of selected microbes. SEM studies were conducted to image E. coli after exposure to the TAPILs or composite-2; with the latter, only bacterial debris were noticed post-exposure, indicating total bacterial annihilation. The killing kinetic assay and regression analyses for time-dependent bactericidal activity of composite-2 against E. coli and S. aureus demonstrated increase in log re-duction values over time, indicating the effectiveness of composite-2 in reducing the viable cell counts for both bacterial strains. Finally, Cu K-edge XANES was used to investigate the fate of Cu NPs within the composites, revealing oxidative disintegration of the Cu NPs within the TAPIL matrices over time, releasing charged copper ions and/or small copper clusters which interfere with the integrity and the permeability of E. coli cell membranes, inducing cell death. This was confirmed by SEM of bacterial preparations before and after exposure to both the TAPILs themselves as well as to the composites. Exposing E. coli to composite-2 causes complete cellular destruction, leaving behind cellular debris as the only visible organic matter. Thus, these TAPIL-based composites containing ‘ion reservoir’ metal NPs are potent antimicrobial materials, deserving additional research.


ionic liquid
X-ray absorption spectroscopy

Supplementary materials

Supporting Information, additional figures
Additional figures and tables to support the contentions in the article.


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.