Structure activity relationship of novel antibacterial phosphonium ionic liquids/organic salts in dispersions and on films: Potential antifouling coating materials

Abstract

The worldwide increasing threat from drug resistant strains, urge continuous development of novel and effective antibacterial agents to minimize nosocomial infections and associated deaths. In this direction ionic liquids (ILs) or analogous organic salts (OS) have exhibited promising potential due to their ease of designability and tunable properties. Herein, nine structurally different phosphonium based ionic liquids (ILs)/Organic Salts (OS) were developed and investigated for their structural effect on antibacterial activity in dispersions and surface coatings. This study reveals that the structural effect on bactericidal property is reversed in coatings compared to dispersions. The pure aryl phosphonium viz. (tetraphenyl phosphonium [TTP]+) cation based IL of ampicillin (Amp−) demonstrate highest bactericidal effect in dispersion compared to alkyl aryl phosphonium (ethyltriphenyl phosphonium)-ampicillin IL and the least activity was observed for pure tetra alkyl phosphonium (trihexyltetradecyl phosphonium)-ampicillin ILs. However, on coatings the activity was reversed. It is observed that optimum hydrophilic-lipophilic balance of ILs/OS dominated the bactericidal effect in dispersions whereas on coating the most lipophiphilic IL/OS demonstrated highest activity. In dispersions the bactericidal effect is a combined property of the cation and the anion while on glass coatings primarily cationic part dominate the bactericidal effect as the hydrophilic ampicillin anion is attached to the glass surface. SwissADME based skin permeation study indicate good potential of the [TPP][Amp] IL as topical antibiotics with a log Kp of 6.91 cm/s and Log P of 3.62. Thus, the present study reveals the structural effect on antibacterial properties of ILs/OS are system dependent as implied from the investigation of some phosphonium ILs/OS and provides useful information for developing washable transparent antifouling coatings.