Superchaotropic Nano-ion Binding as a Gelation Motif in Cellulose Ether Solutions

Nanometer-sized anions (nano-ions) like polyoxometalates and boron clusters exhibit so-called superchaotropic behavior, which describes their strong binding to hydrated non-ionic matter in water. We show here that nano-ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non-ionic cellulose ethers (CEs), a class of widely utilized polymers known for their thickening and gel-forming ability. These phenomena arise from an interplay of attractive forces and repulsive electrostatic forces between CE-chains upon nano-ion binding. The attractive forces manifest themselves as aggregation of CE-chains into a physically crosslinked polymer network (gel). In turn, the electrostatic repulsions hamper the viscosity increase and gelation. Superchaotropic nano-ion binding emerges as a novel and general physical crosslinking motif for CE-solutions and exceeds by far the conventional thickening effects of classical salts and ionic surfactants.     

Cyclic and Macrocyclic Molecules Containing Silicon or Tin – Synthesis of Highly Rigid,Potentially Lewis-Acidic Cryptands

Herein we report the syntheses of highly rigid silicon- and tin-containing cyclic and bicyclic compounds with unsaturated organic backbones. The syntheses proceed via di-lithiated diethynylbenzene derivatives. The protocols for the known precursor compounds were significantly improved in a two-step one-pot reaction with yields up to 45 % by alternating addition of the lithiation reagent and starting material. A total of ten compounds were synthesized and the molecular structure in the solid state was elucidated for six novel compounds. Host-guest-experiments with selected molecules were conducted to investigate on the potential of the complexation of small anions. All compounds were characterized by multinuclear NMR spectroscopy and elemental analyses or mass spectrometry and in most parts by SC-XRD analyses.     

ChemInform Abstract: Soft Bending Modes of Terminal Chlorides in Gaseous Two- and Three-Coordinate Cu(II)—Cl Species.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

A Bidentate Antimony Pnictogen Bonding Host System

A bidentate pnictogen bonding host-system based on 1,8-diethynylanthracene was synthesized by a selective tin-antimony exchange reaction and investigated regarding its ability to act as a Lewis acidic host component for the complexation of Lewis basic or anionic guests. In this work, the novel C≡C−Sb(C₂F₅)₂ unit was established to study the potential of antimony(III) sites as representatives for the scarcely explored pnictogen bonding donors. The capability of this partly fluorinated host system was investigated towards halide anions (Cl⁻, Br⁻, I⁻), dimethyl chalcogenides Me₂Y (Y=O, S, Se, Te), and nitrogen heterocycles (pyridine, pyrimidine). Insights into the adduct formation behavior as well as the bonding situation of such E⋅⋅⋅Sb−C^F moieties were obtained in solution by means of NMR spectroscopy, in the solid state by X-ray diffraction, by elemental analyses, and by computational methods (DFT, QTAIM, IQA), respectively.