Binding of the ionic liquid cation 1-alkyl-3-methylimidazolium to p-tetranitrocalix[4]arene probed by fluorescent indicator displacement

Abstract

Acridine orange (AO) was used as a fluorescent probe molecule to study the encapsulation of an alkylimidazolium cation from a water-soluble ionic liquid (IL) within two cavitand species, p-tetranitrocalix[4]arene (1) and calix[4]resorcinarene (2), both in alkaline aqueous media. The addition of IL to the preformed [1·AO] adduct resulted in significantly increased fluorescence due to the expulsion of AO from the inclusion complex to the aqueous phase by competitive recognition of the 1-alkyl-3-methylimidazolium cation ([C(n)mim](+), n = 4 and 6) by 1. Conversely, the fluorescence signal dropped upon the addition of IL to the [2·AO] host-guest complex due to unfavorable binding between [C(n)mim](+) and 2. The formation of these postulated adducts is corroborated using ab initio calculations, which also provide evidence for the location of [bmim](+) at the lower external rim of [2·AO], providing an explanation for the observed luminescence quenching in the latter case. These results point to a number of different paths for exploration, ranging from the fluorescence monitoring of IL contamination in groundwater to the "daisy chaining" of macrocyles toward supramolecular ionic networks. They also broadly encourage the exploration of ILs in host-guest-based optical and mass spectrometric sensory systems.

Imidazolium-tagged glycan probes for non-covalent labeling of live cells

“…19 Moreover, imidazolium based ILs can form stable adducts with cation chelating/polyanion bearing molecules. 20 To further explore the potential utility of the reagent in our system, NMR titrations using model IL 3-methyl-1-imidazol-3-ium-propionate with NTA analogue N-acetyl-Na,Na-bis(carboxymethyl)-L-lysine in the absence of Ni 2+ showed that the IL interacts with the model NTA label in PBS buffer (pH 7.4) with an approximate binding constant of 22 AE 9 mM À1 (see ESI, † for details). 21 A number of cell lines, including Jurkat T-lymphocytes, breast cancer cell line MDA-MB-231 (MDA), colon cancer cell line HT29-MTX-E12 (E12), cervical cancer cells HeLa and SV40immortalized human corneal epithelium (AS) cells were incubated for 3 days 5 in the presence of a range of concentrations of 2 (0.2-200 mM).…”