A convergent ring-closing metathesis approach to carbohydrate-based macrolides with potential antibiotic activity

[reaction: see text] An efficient convergent approach has been developed for the construction of novel, non-natural, carbohydrate-based macrolides. The key step in the synthesis is the formation of the macrocyclic ring via a ring-closing metathesis reaction. The obtained macrolide analogues have been screened for biological activity against gram-positive and gram-negative bacteria, including resistant strains, yeasts, and molds.     

Electrical fixing in near-stoichiometric lithium niobate crystals

Photorefractive gratings are recorded in lithium niobate crystals in the presence of externally applied electric fields close to the coercive field. After optical erasure a voltage pulse above the poling threshold is applied, and by these means a photorefractive grating reappears that can be erased optically. The results point to electrical fixing, i.e., ferroelectric domain reversal induced by a space-charge field.     

Stability theory, permutations of indiscernibles, and embedded finite models

We show that the expressive power of first-order logic over finite models embedded in a model is determined by stability-theoretic properties of . In particular, we show that if is stable, then every class of finite structures that can be defined by embedding the structures in , can be defined in pure first-order logic. We also show that if does not have the independence property, then any class of finite structures that can be defined by embedding the structures in , can be defined in first-order logic over a dense linear order. This extends known results on the definability of classes of finite structures and ordered finite structures in the setting of embedded finite models. These results depend on several results in infinite model theory. Let be a set of indiscernibles in a model and suppose is elementarily equivalent to where is -saturated. If is stable and is saturated, then every permutation of extends to an automorphism of and the theory of is stable. Let be a sequence of -indiscernibles in a model , which does not have the independence property, and suppose is elementarily equivalent to where is a complete dense linear order and is -saturated. Then -types over are order-definable and if is -saturated, every order preserving permutation of can be extended to a back-and-forth system.

     

Ruthenium(II)‐Catalyzed CH Activation/Alkyne Annulation by Weak Coordination with O2 as the Sole Oxidant

Aerobic oxidative C? H functionalizations of weakly coordinating benzoic acids have been accomplished with versatile ruthenium(II) biscarboxylates under ambient oxygen or air. Mechanistic studies identified the key factors controlling the elementary step of the oxidation of the ruthenium(0) complex.     

Influence of Ester versus Amide Linkers on the Supramolecular Polymerization Mechanisms of Planar BODIPY Dyes

We report the H‐type supramolecular polymerization of two new hydrophobic BODIPY derivatives equipped with ester and amide linkages. Whereas the ester‐containing BODIPY derivative undergoes an isodesmic supramolecular polymerization in which the monomers are parallel‐oriented, the replacement of the ester by amide groups leads to a highly cooperative self‐assembly process into H‐type aggregates with a rotational displacement of the dye molecules within the stack. The dye organization imposed by simultaneous π–π and hydrogen bonding interactions is the driving force for the cooperative supramolecular polymerization, whereas the absence of additional hydrogen bonds for the ester‐containing moiety does not suffice to induce cooperative phenomena.     

Laser welding of polymers using unsymmetrical squaraine dyes

Transmission laser welding of plastic is typically achieved by incorporating a laser absorbing dye into one of the two pieces of plastic one wishes to weld together and mediating the welding process using a laser emitting light at a suitable wavelength. Desirable properties of laser absorbing dyes include: (1) the dye is colorless in the visible region but absorbs strongly in the region at the wavelength where the laser emits, (2) the dye has a good conversion of the energy from the laser to heat, (3) the dye is stable enough to be incorporated into the molten plastic, (4) the dye is soluble in the plastic of choice to give an even distribution in the plastic, and (5) the dye is nontoxic. Here, we explore an alternative approach to achieve laser welding of colorless plastics using a laser dye that is colored, but that can be bleached after the welding process. Nonsymmetrical squaraine dyes were prepared by condensation of squaric acid and two equivalents of various 3,5-dimethoxy-N,N-dialkylanilines. After the incorporation into polyethylene and laser welding, the plastic was bleached either by heat treatment or by irradiation with a high pressure Xe-lamp giving colorless polyethylene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2245–2254