Oleksandr

Anion sandwich is a pincer cake: The synthesis of the first halogen bonding (XB) [3]rotaxane host system containing a four station axle is reported. Anion binding titration experiments reveal the rotaxane is selective for nitrate and operates through a dynamic pincer mechanism in which both macrocycles shuttle to the central XB anion recognition sites to form a 1:1 stoichiometric oxoanion–rotaxane sandwich complex.

[Communication]
Timothy A. Barendt, Andrew Docker, Igor Marques, Vítor Félix, Paul D. Beer
Angew. Chem. Int. Ed., July 20, 2016, DOI: 10.1002/anie.201604327. Read article

An easily removable dressing: A hydrogel-based dressing for second-degree burn wounds has been synthesized and tested in vivo. It is composed of a dendritic macromonomer and a poly(ethylene glycol) crosslinker that form a hydrogel upon mixing. An on-demand and atraumatic hydrogel dissolution proceeds through thiol–thioester exchange reaction in presence of a cysteine methyl ester solution.

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Nature Chemistry. doi:10.1038/nchem.2563

Authors: Andrea Krachmalnicoff, Richard Bounds, Salvatore Mamone, Shamim Alom, Maria Concistrè, Benno Meier, Karel Kouřil, Mark E. Light, Mark R. Johnson, Stéphane Rols, Anthony J. Horsewill, Anna Shugai, Urmas Nagel, Toomas Rõõm, Marina Carravetta, Malcolm H. Levitt & Richard J. Whitby

Hydrogen fluoride has been encapsulated in C60-fullerene using molecular surgery. The quantum rotor system has been studied by NMR and infrared spectroscopy as well as neutron scattering. The fullerene cage causes a small red-shift in the HF rotational and vibrational constants, and shields around 75% of its dipole.

The chemical industry is dependent on the olefin/paraffin separation, which is mainly accomplished by using energy-intensive processes. We report the use of reticular chemistry for the fabrication of a chemically stable fluorinated metal-organic framework (MOF) material (NbOFFIVE-1-Ni, also referred to as KAUST-7). The bridging of Ni(II)-pyrazine square-grid layers with (NbOF5)2– pillars afforded the construction of a three-dimensional MOF, enclosing a periodic array of fluoride anions in contracted square-shaped channels. The judiciously selected bulkier (NbOF5)2– caused the looked-for hindrance of the previously free-rotating pyrazine moieties, delimiting the pore system and dictating the pore aperture size and its maximum opening. The restricted MOF window resulted in the selective molecular exclusion of propane from propylene at atmospheric pressure, as evidenced through multiple cyclic mixed-gas adsorption and calorimetric studies. Authors: A. Cadiau, K. Adil, P. M. Bhatt, Y. Belmabkhout, M. Eddaoudi

Nature Chemistry. doi:10.1038/nchem.2553

Authors: Michael S. Inkpen, Stefan Scheerer, Michael Linseis, Andrew J.P. White, Rainer F. Winter, Tim Albrecht & Nicholas J. Long

Cyclic molecules often exhibit unusual properties; consider for example the resonance stabilization energy of benzene or the strong cation binding of crown ethers. Now, a family of rings comprising varying numbers of directly linked ferrocenes has been prepared. These compounds are highly symmetric in solution and undergo rapid ‘oxidation-state isomerism’ when charged.

Molecular knots occur in DNA, proteins, and other macromolecules. However, the benefits that can potentially arise from tying molecules in knots are, for the most part, unclear. Here, we report on a synthetic molecular pentafoil knot that allosterically initiates or regulates catalyzed chemical reactions by controlling the in situ generation of a carbocation formed through the knot-promoted cleavage of a carbon-halogen bond. The knot architecture is crucial to this function because it restricts the conformations that the molecular chain can adopt and prevents the formation of catalytically inactive species upon metal ion binding. Unknotted analogs are not catalytically active. Our results suggest that knotting molecules may be a useful strategy for reducing the degrees of freedom of flexible chains, enabling them to adopt what are otherwise thermodynamically inaccessible functional conformations. Authors: Vanesa Marcos, Alexander J. Stephens, Javier Jaramillo-Garcia, Alina L. Nussbaumer, Steffen L. Woltering, Alberto Valero, Jean-François Lemonnier, Iñigo J. Vitorica-Yrezabal, David A. Leigh

Organic chemistry: Plastic waste turned into fuel

Nature 534, 7608 (2016). doi:10.1038/534439c

Plastic from bottles and bags can be degraded into liquid fuels and waxes using available catalysts.Polyethylene is the world's most common plastic, but is difficult to break down, typically requiring temperatures higher than 400 °C. A team led by Zheng Huang at the Shanghai