A Chemically and Electrochemically Switchable [2]Catenane Incorporating a Tetrathiafulvalene Unit

A mechanical switch in a [2]catenane , made up of a cyclobis(paraquat-p-phenylene) tetracation interlocked with a macrocyclic polyether containing a redox-active tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene ring system, can be thrown either chemically or electrochemically. The neutral TTF unit resides “inside” the tetracationic cyclophane in the reduced state and “alongside” it in the oxidized species (TTF⁺/ TTF²⁺). Switching between the reduced (I⁴⁺) and oxidized state (I⁵⁺(I⁶⁺)) is accompanied by a dramatic color change.     

Anion Control in the Self-Assembly of a Cage Coordination Complex

An anion is encapsulated in the center of the new cage compound [Ni₆(atu)₈X]X₃ (X=Cl—for the structure see picture—or Br; Hatu=amidinothiourea). A combination of Lewis acid–base and hydrogen-bonding interactions cause the square-planar [Ni(Hatu)₂]²⁺ units, after deprotonation, to assemble to form this compound. A remarkable feature is the anion dependence of the cage formation; nitrate, acetate, and perchlorate are unsuitable as templates.     

Application of molecular mechanics to refine and understand the crystal structure of polythiophene and its oligomers

A molecular mechanics computational procedure, previously used for the refinement and the analysis of several crystalline polymers, was applied to investigate the crystal structures of the tetramer (T4) and hexamer (T6) of thiophene, as well as the crystal structure of polythiophene (PT). Simultaneous minimization of intra- and intermolecular energies of the T4 and T6 structures, obtained by Rietveld analysis of powder X-ray diffraction profiles, leads to molecular conformations showing smaller deviations from the ring co-planarity than the original models. For both oligomers the calculations confirm that the molecular centre of inversion is not a crystallographic centre of symmetry, as also revealed by X-ray diffraction of the T6 single crystal. This surprising effect appears to arise from intermolecular interactions between the terminal residues, hence is not relevant with respect to the PT polymer structure. The small energy cost for constraining the molecules at the crystallographic centre of symmetry is in agreement with experimental findings that reveal the existence of polymorphs for both T4 and T6. The calculations on the T6 single crystal were used to upgrade the MM2-like force field, which was then used to determine the minimum-energy model of the monoclinic crystal structure of polythiophene.     

Rheological and DSC studies of mixtures of gellan gum and konjac glucomannan

The interaction between gellan gum (GELL) and konjac glucomannan (KGM) with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride has been monitored using mechanical spectroscopy and differential scanning calorimetry (DSC). The rheological results indicated that the synergism occurred at sufficient low temperatures where individual helices of GELL molecules were sufficiently aggregated. With progressive addition of monovalent cations, storage shear modulus G' and loss shear modulus G” for mixtures gradually increased, and not only the helix-coil transition temperature of GELL molecules in mixtures but also the sol-gel transition temperature for mixtures shifted to higher temperatures with increasing concentration of salts. Moreover, in the presence of sufficient monovalent cations, mixtures formed an elastic gel with large thermal hysteresis. In the presence of divalent cations, the synergistic interaction was promoted up to a certain concentration, however, with more progressive addition of divalent cations, the main structure formed by aggregates of GELL helices would be smaller, so that mixtures could not form a gel in the presence of excessive divalent cations. DSC results indicated that the intermolecular binding complexes between GELL and KGM molecules would not occur, but KGM markedly influenced the disorder-order transition of GELL molecules. We have suggested that KGM was attached to the surface of large aggregates of GELL helices, and since cations promote GELL self-aggregation by a screening effect, the synergistic interaction between GELL and KGM was promoted with increasing concentration of salts. However, excessive divalent cations formed various aggregates of GELL helices with different thermal stabilities, so that the phase-separation in GELL/KGM mixtures was promoted in the presence of excessive divalent cations.     

Novel Aluminum-Containing Ring Systems: An Octanuclear Structural Analogue of a Calix[4]pyrrole

Depending on the hydrazine reagent , Me₃Al reacts to afford novel aluminum-containing macrocyclic ring structures. The reaction of Me₃Al with Me₂NNH₂ provides the octanuclear calix[4]pyrrole-like 1 , while under analogous conditions the reaction with MePhNNH₂ gives a tetranuclear complex. Both complexes are formed by incorporation of acetonitrile.