Antibacterial resistance is becoming increasingly prominent, causing a great need for novel antibacterial products. This work focuses on developing an understanding of the relationship between counterion identity on colloidal and antibacterial activity for cationic amphiphiles. In an amphiphile series with three hydrophilic quaternary ammonium bromide head groups and one hydrophobic tail, the amphiphile with a linear hydrocarbon chain with 18 carbons is more antibacterial than those with longer or shorter tails. Counterion exchange of the bromide counterions with various Hofmeister series anions significantly affects both antibacterial and colloidal activity. The logarithm of critical aggregation concentration [log(CAC)] was found to have a linear correlation with Gibbs free energy of hydration (ΔGhydr), enthalpy of hydration (ΔHhydr), partial molar volume (Vi0), and surface tension (σ) of counterions present. These trends were found to correlate with an inverse Hofmeister effect, which is common for cationic species in the presence of low anion concentration. At this point no specific trend between the Hofmeister series and amphiphile antibacterial potency have been observed, although significant changes in potency have been seen with varying ions. Chloride and iodide counterions improve the potency of triple-headed amphiphiles with one or two hydrophobic tails, especially when combating Gram-negative bacteria.

Effect of Hofmeister series counterions on the colloidal and antimicrobial properties of triple-headed cationic amphiphiles

254th National Meeting (2017)

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