Wen-Sheng Chung

Cooperative Recognition of a Copper Cation and Anion by a Calix[4]arene Substituted at the Lower Rim by a β‐Amino‐α,β‐Unsaturated Ketone

We report herein a new ditopic calix[4]arene receptor 25,27-bis-{[4-amino-4-(1-naphthyl)-2-oxo-3-butenyl]oxy}-26,28-dihydroxycalix[4]arene (2) for the simultaneous complexation of anionic and cationic species. The host molecule 25,27-bis{[3-(1-naphthyl)-5-isoxazolyl]methoxy}-26,28-dihydroxycalix[4]arene (1) was synthesised first and was followed by a [Mo(CO)6]-mediated ring-opening reaction to give the target receptor 2. The binding properties of ligands 1 and 2 towards metal ions in CH3CN were investigated by UV/Vis and fluorescence spectroscopies. The results showed that both ligands 1 and 2 were highly selective for Cu(II) ions. Upon titration with Cu(II), the fluorescence of 1 was severely quenched, whereas 2 showed strong fluorescence enhancement because the metal ions help to lock the conformation of the fluorophores. During the complexation of 2 with Cu(II), the Cu(II) was reduced to Cu(I) by the free phenolic OH of 2, whereas the phenol was oxidised by Cu(II), after which it assisted in the trapping of Cu(I). Ditopic behaviour was observed for the complex 2.Cu(I), which showed further enhancement of its fluorescence intensity upon complexation with anions such as acetate or fluoride.

Biscalix[4]arene Derivative As a Very Efficient Phase Selective Gelator for Oil Spill Recovery

A biscalixarene framework, without long alkyl chains, has been readily synthesized in three steps starting from the parent calix[4]arene. The biscalix[4]arene 1 was able to form organogels in various alcoholic solvents; furthermore, it exhibited an excellent phase selective gelation property that is potentially useful in oil spill recovery.

1,3-Alternate Calix[4]arene as a Homobinuclear Ditopic Fluorescent Chemosensor for Ag(+) Ions

A novel 1,3-alternate calix-[4]arene L, containing two different cationic binding sites of bis-triazoles and bis-enaminone groups, was synthesized and shown to be a homobinuclear ditopic fluorescent chemosensor for Ag(+) ions. The fluorescence intensity of L was selectively enhanced by binding with Ag(+) ions in methanol/chloroform (49:1, v/v) cosolvent. In the presence of most competing metal ions, L retains its selectivity toward Ag(+) ion. The binding constants K(1) and K(2) of the successive complexation of L with the first and second Ag(+) ions were calculated to be 4.46×10(3) and 9.20×10(4) M(-1), respectively. The higher K(2) value revealed that a positive allosteric effect participated in the complexation of L with the second equivalent of Ag(+). Based on (1)H NMR titration results, we inferred that the two distal bis-enaminone and bis-triazole groups on L cooperatively coordinated to Ag(+) ions with the help of cation-π interactions from the phenoxy rings. Furthermore, the ESI-MS spectrometry clearly proved the formation of the homobinuclear complex L·(Ag(+))(2), because a base peak at m/z of 750.1701 was detected and its isotope pattern was in excellent agreement with the calculated one.

Anthryl‐1,2,4‐oxadiazole‐Substituted Calix[4]arenes as Highly Selective Fluorescent Chemodosimeters for Fe3+

Fluorescent chemosensors 1 and 2, with 1,2,4-oxadiazoles as the binding ligands and anthracene as the fluorophore, were synthesized through sequential 1,3-dipolar cycloaddition reactions of 25,27-dioxyacetonitrilecalix[4]arenes 8 and 11. The fluorescence of 1 was severely quenched by both Fe(3+) and Cu(2+) , whereas that of 2 was selectively quenched only by Fe(3+) . Control compound 4 was also selectively quenched by Fe(3+) , which implied the importance of anthryl-1,2,4-oxadiazole core; furthermore, it was shown to give various oxidation products such as oxanthrone 13, anthraquinone 14, and imidazolyl oxanthrone 15. In addition to product separation and identification, the fluorescent quenching mechanism of these 9-anthryl-1,2,4-oxadiazolyl derivatives by Fe(3+) is also discussed. Furthermore, it should be noted that the oxadiazole-substituted anthracene 4 and calix[4]arene 2 are Fe(3+) -selective fluorescent chemodosimeters without the interference by Cu(2+) .

Evolution of nano- to microsized spherical assemblies of fluorogenic biscalix[4]arenes into supramolecular organogels

A biscalix[4]arene ( capable of spontaneous self-assembly into nanoparticles and microspheres in CH3CN was serendipitously observed, and it eventually formed stable blue-light emitting supramolecular organogels.

Design and synthesis of triazolyl coumarins as Hg2+ selective fluorescent chemosensors

A series of triazolyl coumarin derivatives L1-L4, with and without spacer groups between the coumarin and the triazole groups, were synthesized as fluorescent sensors to study their binding ability and selectivity toward metal ions. Ligand L3, which contains an acetyl linker between the triazole and the coumarin, exhibited a high selectivity toward Hg(2+) in polar protic solvents MeOH-CHCl(3) (9 : 1, v/v) with fluorescent enhancement, furthermore, it was found to bind two Hg(2+) at a high concentration (>12.5 mM) of Hg(ClO(4))(2). In contrast, L4, in which position 4 of the triazole unit was replaced by a benzyl group instead of the 4-tert-butylphenoxymethyl group used in L1-L3, showed a binding stoichiometry toward only one Hg(2+). On the basis of the fluorescent sensing, IR, and (1)H NMR titration results of ligands L1-L4, we proposed that not only the acetyl C=O but also the ether group of the 4-tert-butylphenoxymethyl of assisted the triazole nitrogen atoms in the complexation of Hg(2+) to form a 1 : 2 complex (L3·(Hg(2+))(2)).

Iodine-induced cyclization reaction of endo-thioester substituted norbornenes followed by methylthio group rearrangement

Abstract Treatment of the endo -thioester group substituted norbornenes 3a-3d with iodine in aqueous tetrahydrofuran at 25 °C gave the novel methylthio group rearranged lactonization products 4a-4d in 80% yields; iodolactonization reaction of 9 was applied to the synthesis of novel diacetal trioxa-cage compound 13 .

Inherently Chiral Biscalix[4]arenes: Design and Syntheses

Inherently chiral biscalix[4]arenes have been designed and synthesized by covalently assembling two calix[4]arene building blocks in a 1,3-position linking with 1,2-position pattern at the lower rims via two triethylene glycol bridges.

Design and Synthesis of New Biprivileged Molecular Scaffolds: Indolo-Fused Benzodiazepinyl/quinoxalinyl benzimidazoles

The present article describes the design and synthesis of new biprivileged molecular scaffolds with diverse structural features. Commercially available, simple heterocyclic building blocks such as 4-fluoro-3-nitrobenzoic acid, 2-chloro-3-nitrobenzoic acid, and indoline were utilized for the synthesis of the novel heterocycles. Pictet-Spengler-type condensation was used as a key step to construct tetracyclic indolo-benzodiazepines and indolo-quinoxalines linked with substituted benzimidazoles. Analysis of single crystals of representative compounds showed that these molecular skeletons have the potential to present various substituents with distinct three-dimensional orientations.

Synthesis of 9,10-bis-ketoenaminoanthryl and 9,10-bis-isoxazolylanthryl linked biscalix[4]arenes: atropisomers and molecular recognitions.

An efficient synthetic pathway for the synthesis of biscalix[4]arenes 5-10 using 1,3-dipolar cycloaddition reactions is reported. Biscalix[4]arene 10 is capable of forming a complex with methyl viologen because of favorable cation-π interactions and a proper cavity size to accommodate the guest. Moreover, biscalix[4]arenes 8a and 8b were found to be atropisomers at room temperature. These two conformers were unable to exchange at room temperature because of the restricted rotation of the C(9)-C(11) or C(10)-C(12) bonds of the β-amino-α,β-unsaturated ketones of anthracene.