Recognition of Different Metal Cations by a trans‐4‐[4‐(Dimethylamino)styryl]‐1‐methylpyridinium Iodide@Tetramethylcucurbit[6]uril Probe

Abstract

Based on the study of a known host-guest inclusion complex comprising cucurbit [6]uril (Q[6]) and a hemicyanine dye, trans-4- [4-(dimethylamino)styryl]-1-pyridinium iodide (t-DSMI), a water-soluble symmetric tetramethylcucurbit[6]uril (TMeQ[6]), was selected to construct a t-DSMI-based probe to test the response to various metal cations in neutral water. The experimental results IntroductionCucurbit[n]urils (Q[n]s) [1][2][3][4][5][6] are generally characterized by a nearly neutral electro-potential cavity and two negative electro-potential carbonyl-fringed portals, in addition to a positive electro-potential outer surface: the cavities of Q[n]s can accommodate various guest molecules through hydrophobic interactions, resulting in characteristic cucurbit[n]uril chemistry known as Q[n]-based host-guest chemistry; [7][8][9][10][11][12][13][14][15][16][17] Additionally, carbonyl groups on the rims of the portals of Q[n]s can interact with metal ions through direct coordination, resulting in distinct Q[n]-based coordination chemistry; [18][19][20][21] Furthermore, the positive electro-potential outer surface of Q[n]s can induce the formation of various novel supramolecular assemblies thorough the outer surface interaction of cucurbit[n]urils, which is another emerging research field in cucurbit[n]uril chemistry. [22] To date, Q[n]-based host-guest chemistry and Q[n]based coordination chemistry have received most attention in Q[n] research, including molecular machines or switches, [23] materials science, supramolecular materials and polymers, [15,24] life science, [25] catalysis, [13,14] sensors and other applications.Cucurbit[n]urils (Q[n]s) can interact with both guests (G) and metal cations (M n+ ), respectively. but exactly how metal cations affect the interaction between cucurbit[n]urils and guests remains poorly understood. Similar, how guests affect the coordination be- [a] 1212 revealed that the probe responded to Cs + cations in alkali metal systems, Ba 2+ and Sr 2+ cations in alkaline earth metal systems, Eu 3+ , Tm 3+ and Yb 3+ cations in lanthanide systems, and Cr 3+ , Fe 3+ and Hg 2+ cations in systems containing transition and other metal cations, via obvious fluorescence quenching.

Binding Modes of a Phenylpyridinium Styryl Fluorescent Dye with Cucurbiturils

“…It is worth to compare the stabilities of the complexes formed by PhSt with cucurbiturils Me 4 CB6 and CB7 with the stabilities of the complexes of the reference dye MeSt with the same two cucurbituril hosts. The binding constant is 4.0 × 10 5 M −1 for MeSt•Me 4 CB6 (in neat water) [16], whereas it is 1.35 × 10 5 M −1 for MeSt•CB7 (in pH 7.4 buffer) [17]. Although the two values-one measured in unbuffered, the other in buffered solution-are not fully comparable, it can be said that MeSt forms complexes with Me 4 CB6 and CB7 with similar affinities.…”

“…Another interesting feature of the spectrum of PhSt•Me 4 CB 6 is the splitting of the signals of Me 4 CB 6 . This effect is due to the reduction of the symmetry on complexation [16].…”

“…The CB complexes of environment-sensitive fluorescent dyes receive much attention, in particular, because many of these complexes function as molecular optical sensors for the detection of non-fluorescent chemical species [14,15]. The phenyl pyridinium dye, MeSt is one example for the water-soluble indicators, the spectral properties of which can greatly change on complexation by cucurbiturils [13,16,17] and also by other macrocyclic receptors (cyclodextrins [18], sulfonatocalixarenes [19], and carboxylato-pillararenes [20,21]). Exploiting these effects, displacement assays have been constructed with MeSt as an indicator, for the fluorescence detection of non-fluorescent analytes [19][20][21][22][23].…”

Recognition of Lanthanide Metal Cations by t‐DSMI@Alkyl‐Substituted Cucurbit[6]uril Probes

“…[30] Other water-soluble Q [6] derivatives have also exhibited similar effects on the t-DSMI guest upon interaction. [24,31] In the present work, three water-soluble alkyl-substituted cucurbit [6]urils, Me 6 Q [3,3], (OH) 3 Me 6 Q [3,3], and TMeQ [6], are selected as hosts to study their interactions with t-DSMI as a guest. Fluorescence spectra were recorded to investigate these interactions.…”

“…[23] Our recent efforts to identify metal ions using Q[n]-based host-guest interaction systems have hitherto been somewhat limited. [24][25][26] For the present work, we selected three alkyl-substituted cucurbit [6]urils(SQ [6]s),namely symmetrical tetramethylcucurbit [6]uril(TMeQ [6]), [27] hexamethylcucurbit [3,3]uril (Me 6 Q [3,3]), [28] and tri-hydroxylated symmetrical hexamethylcucurbit [3,3]uril ((OH) 3 Me 6 Q[3,3]) [29] as hosts, and a hemicyanine dye, trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (t-DSMI), as the guest (Figure 1). We investigated the interactions of these three hosts with t-DSMI as guest and the fluorescence characteristics of t-DSMI@SQ [6].…”