Self-assembly and antimicrobial activity of long-chain amide-functionalized ionic liquids in aqueous solution

Abstract

Surface active amide-functionalized ionic liquids (ILs) consisting of a long alkyl chain (C6C14) connected to a polar head group (methylimidazolium or pyridinium cation) via an amide functional group were synthesized and their thermal stability, micellar properties and antimicrobial activity in aqueous solution investigated. The incorporation of an amide group increased the thermal stability of the functionalized ionic liquids compared to simple alkyl chain substituted ionic liquids. The surface activity and aggregation behaviour in aqueous solution of amide-functionalized ionic liquids were examined by tensiometry, conductivity and spectrofluorimetry. Amide-functionalized ILs displayed surface activity and their critical micelle concentration (cmc) in aqueous media decreased with the elongation of the alkyl side chain as occurs for typical surfactants. Compared to non-functionalized ILs bearing the same alkyl chain, ionic liquids with an amide moiety possess higher surface activity (pC20) and lower cmc values. The introduction of an amide group in the hydrophobic chain close to the polar head enhances adsorption at the air/water interface and micellization which could be attributed to the H-bonding in the headgroup region. The antimicrobial activity was evaluated against a panel of representative Gram-negative and Gram-positive bacteria and fungi. Amide-functionalized ILs with more than eight carbon atoms in the side chain showed broad antimicrobial activity. Antibacterial activities were found to increase with the alkyl chain length being the C12 homologous the most effective antimicrobial agents. The introduction of an amide group enhanced significantly the antifungal activity as compared to non-functionalized ILs.

Catanionic surfactant formation from the interaction of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) and the ionic liquid 1-butyl-3-methylimidazolium octyl sulfate (bmim-octyl SO4) in aqueous solution

“…In the case of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) the effect of ILs on the surfactant cmc confirms the trend above described [8][9][10][11][12][13]. However, when IL posses surface activity as reported for long alkyl chain ionic liquids [14][15][16][17][18][19][20][21] and some short alkyl chain ILs [22,23] the ionic liquid / surfactant mixture behaves as a typical binary surfactant system [24][25][26]. In these binary systems the mixed micelle composition X 1 M as well as the  M interaction parameter quantifying the synergism can be obtained by applying the equations of the Regular Solution Theory [27].…”

Ultraviolet-responsive self-assembled metallomicelles for photocontrollable catalysis of asymmetric sulfoxidation in water

“…Photoisomerization of azobenzene from trans-form to more hydrophilic cis-form should account for the increased CMC value. 16 The results suggested the UVcontrolled self-assembly behavior of PN 427 A 10 -C.…”

Long alkyl-chain imidazolium ionic liquids: Antibiofilm activity against phototrophic biofilms

“…Several studies have reported the antimicrobial properties of ionic liquids, although there are limited studies on biofilm control [40]. As such, the toxicity of an IL depends on cation, anion and side chain, thus modification of these groups allows designing either less or more toxic compounds.…”

“…Recently, Garcia et al, (2014) reported antimicrobial activity of amide-functionalised methylimidazolium or pyridinium ionic liquids against bacterial and fungal strains [40].…”