Molecularly imprinted polystyrene–titania hybrids with both ionic and π–π interactions: a case study with pyrenebutyric acid

We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO₂) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO₂ and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO₂. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films.

Changes in surface composition of Fe-Si-Cr-K oxide alkylation catalyst: the marked role of potassium ferrites

The influence of gas-phase methylation of phenol on the state of the Fe-Si-Cr-K oxide catalyst surface was investigated by thermodesorption of K atoms and ions. Changes in potassium desorption energies, as determined from Arrhenius-like plots, varied from 3.07 eV to 1.21 eV for the atoms and from 2.59 eV to 2.89 eV for ion desorption from the active and deactivated samples, respectively. The results were discussed in terms of transformation of the catalyst surface and formation of β-ferrite.     

Frictional Phenomena in Dynamical Systemwith Two-Frequency Excitation

The paper deals with investigation of a self-excited vibrating system with dry friction. The system is composed of a mass connected by viscoelastic element with the referring frame and interacting with a moving belt by means of dry friction. An experimentally identified, multi-parametric dry friction model for the pair composed of soft and hard elements like steel–polyester pair, describing both the case of stick-slip and quasi-harmonic vibration, has been applied. Additionally, the system is influenced by external, two-frequency kinematic excitation. The results of computer simulation for different excitation conditions are submitted in the present paper.     

Trichloroethylene in organic synthesis: II. reaction of trichloroethylene with secondary amines

In a novel reaction, trichloroethylene reacts with secondary aliphatic amines in the presence of aqueous solution of NaOH and catalytic quantity of benzyltriethylammonium chloride to give the corresponding N,N,N,'N'-tetraalkylsubstituted glycinamides. The following glycinamides were obtained with high yield: /N-morpholine/acetic acid morpholide, N-/piperidineacetyl/piperidine, N,N,N,'N'-tetra-n-butylglycinamide and N,N,N,'N'-tetraethlyglycinamide. Mechanism of the reaction is discussed.     

Crystal,molecular structure and tautomerism of (5-methyl-1H-[1,2,4]triazol-3-ylsulfanyl)-acetic acid

Molecular structure, relative stability of conformers, and tautomers of (5-methyl-1H-[1,2,4]triazol-3-ylsulfanyl)-acetic acid (MTSA) have been investigated by experimental (X-ray diffraction) and theoretical (B3LYP/aug-cc-pVDZ) methods. It was demonstrated that in the solid state MTSA exists in N1H tautomeric form. This tautomer is not the most stable in gas phase and its stabilization is provided by environment effects.     

Binary operations and canonical forms for factorial and related models

Binary operations on commutative Jordan algebras are used to extend the grouping of treatments in blocks and the taking of fractional replicates to models where factors have arbitrary number of levels. Up to now these techniques had been restricted to models whose factors have a prime or a power of a prime number of levels. Moreover, the binary operations will enable the use of simple models as building blocks for more complex designs.     

Neighborhood unions and extremal spanning trees

We generalize a known sufficient condition for the traceability of a graph to a condition for the existence of a spanning tree with a bounded number of leaves. Both of the conditions involve neighborhood unions. Further, we present two results on spanning spiders (trees with a single branching vertex). We pose a number of open questions concerning extremal spanning trees.