Supramolecular Host-Guest Hydrogel Based on γ-Cyclodextrin and Carboxybenzyl Viologen Showing Reversible Photochromism and Photomodulable Fluorescence.

Much effort has been devoted to the development of supramolecular hydrogels due to their broad applications and conveniently controllable properties. Here, we demonstrate a novel supramolecular host-guest hydrogel, which is constructed by the host γ-CD complexed with the guest 1-(4-carboxybenzyl)-4,4'-bipyridinium chloride (1+·Cl-) through the π···π interaction, hydrogen bonding, and host-guest interactions. The supramolecular hydrogel [1+@γ-CD]n exhibits reversible electron transfer photochromic behavior and photomodulable fluorescence. The excellent photochromic and fluorescence properties support the practical utility of the supramolecular hydrogel as a visual display and anti-counterfeiting material.

An inclusion complex of cucurbit[7]uril with benzimidazolyl benzyl viologen exhibits fluorescence and photochromic properties.

In order to investigate the photochromic mechanism of photochromic materials based on supramolecular host-guest systems, we designed and synthesized a unique viologen derivative (benzimidazolyl benzyl viologen, guest 1·Cl3), which does not contain oxygen atoms. The binding interaction of guest 13+ with host cucurbit[7]uril (Q[7]) was investigated by various techniques. The obtained supramolecular host-guest complex 13+@Q[7] exhibits interesting fluorescence emission and reversible photochromism. The ESR and XPS experimental data suggest that the photochromic process of the complex 13+@Q[7] comes from the electron transfer from the carbonyl O atoms of the host Q[7] to the bipyridinium N atoms of the guest 13+.

A light-responsive molecular switch based on cucurbit[7]uril and 1,1'-bis(benzyl)-4-[2-(4-pyridyl)-vinyl]-pyridinium dibromide displaying white light emission.

By using 1H NMR, ESI-MS and UV spectra, a novel light-responsive molecular switch constructed using 1,1'-bis(benzyl)-4-[2-(4-pyridyl)-vinyl]-pyridinium (12+) and cucurbit[7]uril (Q[7]) is demonstrated. The E- to Z-isomerization of the double bond in 12+ results in the transition of the switching states from the 1 : 2 complex E-12+@Q[7]2 to the stable 1 : 1 complex Z-12+@Q[7]. In particular, both the 1 : 2 complex and the 1 : 1 complex can emit cold white fluorescence under UV light.

Symmetrical-Tetramethyl-Cucurbit[6]uril-Driven Movement of Cucurbit[7]uril Gives Rise to Heterowheel [4]Pseudorotaxanes.

Two novel heterowheel [4]pseudorotaxanes consisting of cucurbit[7]uril (Q[7]) and symmetrical-tetramethyl-cucurbit[6]uril (TMeQ[6]) were constructed via the multirecognition mechanism, in which Q[7] can rotate freely around the horizontal axis, while TMeQ[6] cannot. In the construction process, due to strong repulsive forces between carbonyl portals of two neighboring wheels, the dethreading and movement of the wheels along the axle was observed. The dissociation of the [4]pseudorotaxanes was also discussed.

Genipin inhibits the growth of human bladder cancer cells via inactivation of PI3K/Akt signaling.

Genipin, a natural compound derived from the fruit of Gardenia jasminoides, possesses numerous biological properties. The aim of the present study was to investigate the anticancer effects of genipin in human bladder cancer. T24 and 5637 bladder cancer cells were treated with different concentrations of genipin (0-200 µM) and tested for cell viability, colony formation, cell cycle progression and apoptosis. A xenograft model of bladder cancer was established to determine the anticancer effect of genipin in vivo. The involvement of the phosphoinositide-3 kinase (PI3K)/Akt pathway in the action of genipin was examined. Genipin treatment significantly inhibited the viability and clonogenic growth of bladder cancer cells and inhibited the growth of T24 xenograft tumors, compared with vehicle controls (P<0.05). Genipin-treated cells exhibited a cell cycle arrest at the G0/G1-phase, which was accompanied by a deregulation of numerous cell cycle regulators. Genipin-treated cells demonstrated a significant increase in the percentage of apoptotic cells, loss of mitochondrial membrane potential, Bax translocation to the mitochondria and the release of cytochrome c to the cytosol. Additionally, genipin treatment significantly (P<0.05) reduced the phosphorylation levels of PI3K and Akt in bladder cancer cells. Importantly, genipin-mediated anticancer effects were reversed by the overexpression of constitutively active Akt. In conclusion, to the best of our knowledge, the present study demonstrates for the first time the growth inhibitory effects of genipin in bladder cancer cells, and indicates its potential as a natural anticancer agent for bladder cancer.

Construction of a Molecular Switch and Selector under Electrochemical Control.

In this work, we designed and synthesized a special axle guest hexyldimethyl(ferrocenylmethyl)ammonium (1 + ) bromide. The binding interactions of 1 + and its oxidized form 1 2+ with cucurbit[7]uril (Q[7]) and cyclohexanocucurbit[6]uril (Cy6Q[6]) were investigated by 1H NMR, cyclic voltammogram, and isothermal titration calorimetry techniques. Our data indicate that both hosts Cy6Q[6] and Q[7] can form stable [2]pseudorotaxanes with 1 + in their different redox states. Most importantly, the combination and dissociation of the hosts with the guest as well as the binding location can be controlled by electrochemical means, which develops a special molecular switch and selector.

Aniline-containing guests recognized by α,α',δ,δ'-tetramethyl-cucurbit[6]uril host.

The host-guest complexation of symmetrical α,α',δ,δ'-tetramethyl-cucurbit[6]uril (TMeQ[6]) and cucurbit[7]uril (Q[7]) with a series of aniline-containing guests has been investigated by various experimental techniques including NMR, ITC, and X-ray crystallography. Experimental results indicate that both TMeQ[6] and Q[7] hosts can encapsulate aniline-containing guests to form stable inclusion complexes. However, the oval cavity of TMeQ[6] is more complementary in size and shape to the aromatic ring of the guests than the spherical cavity of Q[7]. Shielding and deshielding effects of the aromatic ring on guests lead to the remarkable chemical shifts of the TMeQ[6] host protons. The rotational restriction of the guests in the oval cavity of TMeQ[6] results in the large negative values of entropy. The X-ray crystal structure of the 1:1 inclusion complex between TMeQ[6] and N,N'-diethyl-benzene-1,4-diamine unambiguously reveals that the aromatic ring of the guest resides in the oval cavity of TMeQ[6].

Host-guest complexation of di-cyclohexanocucurbit[6]uril and hexa-cyclohexanocucurbit[6]uril with alkyldiammonium ions: a comparative study.

The host-guest complexation of symmetrical di-cyclohexanocucurbit[6]uril (Cy2Q[6]) and hexa-cyclohexanocucurbit[6]uril (Cy6Q[6]) with a series of alkyldiammonium ions (H(3+)N(CH(2))nNH(3+), n = 2-8) has been studied both in solution and in the gas phase. (1)H NMR data indicate that all alkyldiammonium ions have inclusion interactions with both hosts except for the ethanediammonium ion. In addition, if the alkyl chain of the alkyldiammonium ion is longer than n = 5 methylene groups, compressed conformation may occur, which depends on the cavity shape of the hosts and the length of the alkyl chain. Isothermal titration calorimetry (ITC) studies point out that the host-guest complexations of both hosts with the latter five alkyldiammonium ions are enthalpically driven. The comparison of the thermodynamic data reveals that the enthalpies of the van der Waals interactions contribute more to the host-guest complexation enthalpy than the ion-dipole interactions. The enthalpic gain arises from the van der Waals interactions and the reduction of entropy upon the host-guest complexation is strongly affected by the cavity shape of the host. Gas phase structures of long alkyldiammonium guests within both hosts are completely different from those in aqueous solution.

Mixed behavior of p-phenylenediaminium guest binding with the inverted cucurbit[6]uril host.

The binding interaction between inverted cucurbit[6]uril (iQ[6]) and p-phenylenediaminium both in the solid state and in aqueous solution has been investigated by X-ray crystallography, (1)H NMR spectroscopy and isothermal titration calorimetry (ITC). The experimental results suggest that the binding interaction between iQ[6] and p-phenylenediaminium may generate two different types of complexes in the solid state: one is an inclusion structure and the other is a sandwich structure. In aqueous solution, the iQ[6] host has an ability to accommodate the p-phenylenediaminium guest and in-out guest exchange is fast on the NMR time scale. ITC data indicate that the complexation of iQ[6] with p-phenylenediaminium is entropy driven.