Ionic liquids with dual biological function: sweet and anti-microbial, hydrophobic quaternary ammonium-based salts

Abstract

The dual nature of ionic liquids has been exploited to synthesize materials that contain two independent biological functions by combining anti-bacterial quaternary ammonium compounds with artificial sweetener anions. The synthesis and physical properties of eight new ionic liquids, didecyldimethylammonium saccharinate ([DDA][Sac]), didecyldimethylammonium acesulfamate ([DDA][Ace]), benzalkonium saccharinate ([BA][Sac]), benzalkonium acesulfamate ([BA][Ace]), hexadecylpyridinium saccharinate ([HEX][Sac]), hexadecylpyridinium acesulfamate ([HEX][Ace]), 3-hydroxy-1-octyloxymethylpyridinium saccharinate ([1-(OctOMe)-3-OH-Py][Sac]), and 3-hydroxy-1-octyloxymethylpyridinium acesulfamate ([1-(OctOMe)-3-OH-Py][Ace]), are reported, as well as the single crystal structures for [HEX][Ace] and [1-(OctOMe)-3-OH-Py][Sac]. Determination of anti-microbial activities is described for six of the ILs. While some exhibited decreased anti-microbial activity others showed a dramatic increase. For two of the ionic liquids, [DDA][Sac] and [DDA][ACE], oral toxicity, skin irritation, and deterrent activity was also established. Unfortunately, both ILs received a Category 4 (harmful) rating for oral toxicity and skin irritation. However, deterrent activity experiments point to use as an insect deterrent, as both ILs scored either “very good” or “good” against several types of insects.