Jaeduk Yoo

Selective Sensing of Anions with Calix[4]pyrroles Strapped with Chromogenic Dipyrrolylquinoxalines

New calix[4]pyrroles bearing dipyrrolylquinoxaline as strapping elements have been synthesized and characterized by spectroscopic means. The binding behavior of these receptors at 25 degrees C was investigated first by proton NMR spectroscopy in CD(3)CN/DMSO-d(6) (9:1 v/v), as well as by UV-vis spectroscopy and isothermal titration calorimetry (ITC) in CH(3)CN/DMSO (97:3 v/v). The receptors displayed a selective colorimetric response when exposed to the fluoride, dihydrogen phosphate, and acetate anions (studied in the form of the corresponding tetrabutylammonium salts) and an enhanced affinity as compared to a comparable calix[4]pyrrole system lacking the dipyrrolylquinoxaline-containing strap.

Strapped Calix[4]pyrroles Bearing a 1,3-Indanedione at a β-Pyrrolic Position: Chemodosimeters for the Cyanide Anion

A strapped calix[4]pyrrole bearing a 1,3-indanedione group at a beta-pyrrolic position has been synthesized and studied as a ratiometric cyanide-selective chemosensor. A concentration-dependent bleaching of the initial yellow color was observed upon addition of the cyanide anion. The bleaching, which was observed exclusively with the cyanide anion, occurred even in the presence of other anions. Spectroscopic studies provide support for a mechanistic interpretation wherein the cyanide anion forms a complex with the receptor (K = 2.78 x 10(4) M(-1)) through a fast equilibrium, which is followed by slow nucleophilic addition to the beta-position of the 1,3-indanedione group. A minimum inhibitory effect from other anions was observed, a feature that could be beneficial in the selective sensing of the cyanide anion.

Oligoether-strapped calix[4]pyrrole: an ion-pair receptor displaying cation-dependent chloride anion transport

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1·F](-) and [1·Cl](-)) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li(+), Na(+), K(+), Cs(+), as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1·F](-), no appreciable interaction with the K(+) ion was seen. On the other hand, when this complex was treated with Li(+) or Na(+) ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li(+), Na(+), K(+), treating [1·F](-) with Cs(+) ions gave rise to a stable, host-separated ion-pair complex, [F·1·Cs], which contains the Cs(+) ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1·Cl](-). Here, no appreciable interaction was observed with Na(+) or K(+). In contrast, treating with Li(+) produces a tight ion-pair complex, [1·Li·Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1·F](-), treatment of [1·Cl](-) with Cs(+) ions gives rise to a host-separated ion-pair complex, [Cl·1·Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism.

Conformational and spectroscopic properties of π-extended, bipyrrole-fused rubyrin and sapphyrin derivatives.

Two new expanded porphyrins, naphthorubyrin and naphthosapphyrin, were synthesized. The π-extended rubyrin was isolated and structurally characterized in its monoprotonated form. The sapphyrin congener undergoes pyrrole inversion as a function of the protonation state. These conformational effects are reflected in the spectroscopic features, including the excited singlet state lifetimes.

Calix[4]pyrrole‐Based Heteroditopic Ion‐Pair Receptor That Displays Anion‐Modulated, Cation‐Binding Behavior

A new ditopic ion-pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl(3). Treatment of the halide-ion complexes of 1 with Group I and II metal ions (Li(+), Na(+), K(+), Cs(+), Mg(2+), and Ca(2+); studied as their perchlorate salts in CD(3)CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [1⋅F](-) (preformed as the tetrabutylammonium (TBA(+)) complex), little evidence of interaction with the K(+) ion was seen. In contrast, when this same complex (i.e., [1⋅F](-) as the TBA(+) salt) was treated with the Li(+) or Na(+) ions, complete decomplexation of the receptor-bound fluoride ion was observed. In sharp contrast to what was seen with Li(+), Na(+), and K(+), treating complex [1⋅F](-) with the Cs(+) ion gave rise to a stable, receptor-bound ion-pair complex [Cs⋅1⋅F] that contains the Cs(+) ion complexed within the cup-like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [1⋅Cl](-). In this case, no appreciable interaction was observed with Na(+) or K(+). In addition, treating [1⋅Cl](-) with Li(+) produces a tightly hydrated dimeric ion-pair complex [1⋅LiCl(H(2)O)](2) in which two Li(+) ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [1⋅F](-), exposure of [1⋅Cl](-) to the Cs(+) ion gives rise to an ion-pair complex [Cs⋅1⋅Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts.

Fluorophore-appended calix[4]pyrroles: Conformationally flexible fluorometric chemosensors

Calix[4]pyrroles bearing appended pyrenyl groups at the meso-positions on one side of the calix[4]pyrrole have been synthesised and characterised. These species act as hosts that exhibit a selective increase in their fluorescence intensity upon the addition of Pb2 + or Cu2 + . When excess chloride anion is added after subjecting the host to pre-complexation with Pb2 + , the cation-induced enhancement in fluorescence is sustained. On the contrary, no changes in fluorescence are observed when the calix[4]pyrrole host is first treated with chloride anion, followed by the addition of Pb2 + . These results are consistent with pre-complexation of Pb2 + not serving to inhibit the binding of chloride anion, while, by contrast, the initial interaction between a chloride anion and the calix[4]pyrrole cavity acts to inhibit the subsequent binding of Pb2 + , possibly due to anion-binding-based constraints on the conformational flexibility.