High binding yet accelerated guest rotation within a cucurbit[7]uril complex. Toward paramagnetic gyroscopes and rolling nanomachines †

International audienceThe (15-oxo-3,7,11-triazadispiro[5.1.5.3]hexadec-7-yl)oxidanyl, a bis-spiropiperidinium nitroxide derived from TEMPONE, can be included in cucurbit[7]uril to form a strong (K a ∼ 2 × 10 5 M −1) CB[7]@bPTO complex. EPR and MS spectra, DFT calculations, and unparalleled increased resistance (a factor of ∼10 3) toward ascorbic acid reduction show evidence of deep inclusion of bPTO inside CB[7]. The unusual shape of the CB[7]@bPTO EPR spectrum can be explained by an anisotropic Brownian rotational diffusion, the global tumbling of the complex being slower than rotation of bPTO around its " long molecular axis " inside CB[7]. The CB[7] (stator) with the encapsulated bPTO (rotator) behaves as a supramolecular para-magnetic rotor with increased rotational speed of the rotator that has great potential for advanced nano-scale machines requiring wheels such as cucurbiturils with virtually no friction between the wheel and the axle for optimum wheel rotation (i.e. nanopulleys and nanocars)

Antibiotic spider silk: site-specific functionalisation of recombinant spider silk using ‘click’- chemistry

The use of functionalised recombinant spider silk as a sustainable advanced biomaterial is currently an area of intense interest owing to spider silk’s intrinsic strength, toughness, biocompatibility and biodegradability. This paper demonstrates, for the first time, the site-specific chemical conjugation of different organic ligands that confer either antibiotic or fluorescent properties to spider silk. This has been achieved by the incorporation of the non-natural methionine analogue L-azidohomoalanine (L-Aha) using an E. coli methionine auxotroph and subsequent copper catalysed azide-alkyne cycloaddition (CuAAC) or ‘click chemistry’ functionalisation of 4RepCT3Aha. The 4RepCT3Aha protein can be modified either prior to, or post fibre formation increasing the versatility of this approach as demonstrated here by the formation of silk fibres bearing a defined ratio of two different fluorophores uniformly distributed along the fibres. Silk decorated with the fluoroquinone family broad spectrum antibiotic levofloxacin via a labile linker is shown to have significant antibiotic activity over a period of at least 5 days. The inherent low immunogenicity and pyrogenicity of spider silk should allow a diverse range of functionalised silks to be produced using these approaches that are tailored to applications including wound dressings and as tissue regeneration scaffolds

Nitroxide bound β-cyclodextrin : is there an inclusion complex ?

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The differential effect of apoferritin-PbS nanocomposites on cell cycle progression in normal and cancerous cells

We report the effects induced by near-infrared apoferritin-PbS (AFt-PbS) nanocomposites on cell cycle progression in non-tumorigenic and cancerous human cells. By using flow cytometry and Annexin V assay, we show that the cell cycle of non-tumorigenic cells is not altered by exposure to AFt-PbS nanoparticles at concentrations up to 1 mg mL -1. In contrast, exposure of human-derived breast cancer cell lines to AFt-PbS at concentrations > 0.2 mg mL -1 triggers apoptotic cell death. The selective death of cancerous cells and the near-infrared fluorescence properties of AFt-PbS could be exploited in both nanomedicine and in vivo imaging studies. © 2012 The Royal Society of Chemistry

Spin exchange monitoring of the strong positive homotropic allosteric binding of a tetraradical by a synthetic receptor in water

International audienceThe flexible tetranitroxide 4T has been prepared and was shown to exhibit a nine line EPR spectrum in water, characteristic of significant through space spin exchange (Jij) between four electron spins interacting with four nitrogen nuclei (Jij ≫ aN). Addition of CB[8] to 4T decreases dramatically all the Jij couplings, and the nine line spectrum is replaced by the characteristic three line spectrum of a mononitroxide. The supramolecular association between 4T and CB[8] involves a highly cooperative asymmetric complexation by two CB[8] (K1 = 4027 M–1; K2 = 202 800 M–1; α = 201) leading to a rigid complex with remote nitroxide moieties. The remarkable enhancement for the affinity of the second CB[8] corresponds to an allosteric interaction energy of ≈13 kJ mol–1, which is comparable to that of the binding of oxygen by hemoglobin. These results are confirmed by competition and reduction experiments, DFT and molecular dynamics calculations, mass spectrometry, and liquid state NMR of the corresponding reduced complex bearing hydroxylamine moieties. This study shows that suitably designed molecules can generate allosteric complexation with CB[8]. The molecule must (i) carry several recognizable groups for CB[8] and (ii) be folded so that the first binding event reorganizes the molecule (unfold) for a better subsequent recognition. The presence of accessible protonable amines and H-bond donors to fit with the second point are also further stabilizing groups of CB[8] complexation. In these conditions, the spin exchange coupling between four radicals has been efficiently and finely tuned and the resulting allosteric complexation induced a dramatic stabilization enhancement of the included paramagnetic moieties in highly reducing conditions through the formation of the supramolecular 4T@CB[8]2 complex