Dynamically Self-Assembling Metalloenzyme Models Based on Calixarenes

Metal-Coordination-Assisted Folding and Guest Binding in Helical Aromatic Oligoamide Molecular Capsules

The development of foldamer-based receptors is driven by the design of monomers with specific properties. Herein, we introduce a pyridazine-pyridine-pyridazine diacid monomer and its incorporation into helical aromatic oligoamide foldamer containers. This monomer codes for a wide helix diameter and can sequester metal ions on the inner wall of the helix cavity. Crystallographic studies and NMR titrations show that part of the metal coordination sphere remains available and may then promote the binding of a guest within the cavity. In addition to metal coordination, binding of the guest is assisted by cooperative interactions with the helix host, thereby resulting in significant enhancements depending on the foldamer sequence, and in slow guest capture and release on the NMR time scale. In the absence of metal ions, the pyridazine-pyridine-pyridazine monomer promotes an extended conformation of the foldamer that results in aggregation, including the formation of an intertwined duplex.

P-Sulfocalix[6]arene as Nanocarrier for Controlled Delivery of Doxorubicin

Given the high toxicity of the anthracycline antibiotic doxorubicin (DOX), it is relevant to search for nanocarriers that decrease the side effects of the drug and are able to transport it towards a therapeutic target Here, the encapsulation of DOX by p-sulfocalix[6]arene (calix) has been studied. The interaction of DOX with the macrocycle, as well as with DNA, has been investigated and the equilibrium constant for each binding process estimated. The results showed that the binding constant of DOX to DNA, K_DNA , is three orders of magnitude higher than that to calix, K_calix . The ability of calixarenes to encapsulate DOX molecules, as well as the capability of the DOX molecules included into the inner cavity of the macrocycle to bind with DNA have been examined. Cytotoxicity measurements were done in different cancer and normal cell lines to probe the decrease in the toxicity of the encapsulated DOX. The low toxicity of calixarenes has also been demonstrated for different cell lines.

Synthesis, photophysical and electrochemical properties of a new class of fluorescent amidoanthracenophanes

The synthesized amidoanthracenophanes1–4exhibit intense fluorescence emission and electrochemical oxidation reduction characteristic of a flourophoric unit.

Nano-supramolecular assemblies constructed from water-soluble bis(calix[5]arenes) with porphyrins and their photoinduced electron transfer properties

Possessing 2D netlike and 1D linear morphologies, two nano-supramolecular architectures A1 and A2 are constructed by tetracationic porphyrin (G1) and dicationic porphyrin (G2), respectively, upon complexation with the novel water-soluble bis(p-sulfonatocalix[5]arenes) bridged at the lower rim (H2). Corresponding to the molecular design, the aggregation morphologies are well manipulated by the inherent binding sites of the building blocks through host-guest interactions as well as charge interactions. In comparison to the simple p-sulfonatocalix[5]arene H1 which can only form particle-type complexes C1 and C2 with porphyrin guests, H2 provides excellent pre-organized structure to construct highly complex nano-supramolecular assemblies. The exhibited electron-transfer process of the supramolecular systems is further investigated by steady-state and time-resolved fluorescence spectroscopy, electrochemical measurements, and transient absorption spectroscopy. The results obtained show that calixarenes are also effective electron donors in PET besides acting as significant building blocks, which gives them many advantages in constructing well-ordered nanomaterials with the capability of electron and energy transport.

Nitroxide Radicals as Probes for Exploring the Binding Properties of the Cucurbit[7]uril Host

EPR spectroscopy was used for the first time to explore the binding properties of cucurbit[7]uril (CB7), a representative member of the cucurbituril family. Evidence for the formation of a complex between nitroxide radicals and the host system in an aqueous solution was provided by large changes in the nitrogen hyperfine splitting, attributed to the different polar environments experienced by the included radical. In the presence of alkali cations, the EPR spectra of benzyl tert-butyl nitroxide were characterised by new signals attributed to the radical hosted in the CB7 cavity in which one metal cation is in close contact with the nitroxidic oxygen. The formation of the coordination complex results in a substantial increase in the electron spin density on the nitrogen in inverse order with respect to the size of the cation owing to increased localisation of negative charge on the oxygen atom from bonding to the alkali cation. The EPR spectra showed selective line-broadening effects as a result of metal exchange between bulk water and the coordination complex. Analysis of the EPR linewidth variations allowed us to measure the corresponding kinetic rate constants for the first time. NMR spectroscopy showed that this behaviour is not peculiar to nitroxides but is also exhibited by the related carbonyl compounds. These data allowed us to quantify the template effect and to reach the conclusion that, in the presence of a guest having a coordinating lone pair, the formation of ternary metal-guest-CB complexes must be taken into account when discussing the complexation behaviour of cucurbituril derivatives in the presence of salts.