Stereodivergent Anion Binding Catalysis with Molecular Motors

A photoresponsive chiral catalyst based on an oligotriazole‐functionalized unidirectional molecular motor has been developed for stereodivergent anion binding catalysis. The motor function controls the helical chirality of supramolecular assemblies with chloride anions, which by means of chirality transfer enables the enantioselective addition of a silyl ketene acetal nucleophile to oxocarbenium cations. Reversal of stereoselectivity (up to 142 % Δee) was achieved through rotation of the motor core induced by photochemical and thermal isomerization steps.     

Polymer nanocomposites in medicine

A large number of recent studies deal with the application of nano materials to different medicine areas, application that led to a new discipline known as nanomedicine. It comprises the processes of diagnosing, treating, curing, preventing diseases and also dealing with traumatic injury, relieving pain and preserving/improving human health by using nano materials. Among nano materials, an important place belongs to the group of natural and synthetic polymer nanocomposites. These are made up of an organic polymer matrix and a mineral, organic or metallic nanofiller. The properties of polymer nanocomposites depend on the characteristics of the components and on the interaction polymer-nanofiller. Polymer nanocomposites offer to modern medicine new opportunities for generate products for antibacterial treatment, tissues engineering, cancer therapy, medical imaging, dental applications, drug delivery, etc.     

Polyamide nanocomposites

Polyamides are thermoplastic polymers mainly used for producing synthetic fibers. Only about 10% of polyamides are used for plastics production. The market is shared roughly equally between polyamide 6 (polycaprolactam) and polyamide 66 {poly (hexamethyleneadipamide)}. More recently, the research on polyamides led to their nanocomposites. These new hybrid polyamides are reinforced with nanofillers able to increase their main properties and also bring some new interesting characteristics. This paper deals with nanocomposites made of various polyamides and nanofillers; they find application in many engineering fields.     

Sol–gel doped TiO<Subscript>2</Subscript> nanomaterials: a comparative study

Among the great number of sol–gel prepared nanomaterials, TiO₂ has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO₂ nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO₂ and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol–gel Ag-doped TiO₂ coatings, prepared by co-gelation and sol–gel Ag-doped TiO₂ coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.     

On the microstructure of methyl acrylate-4-vinyl pyridine copolymers

Using ¹H-NMR spectra of radical copolymers of methyl acrylate (M₁) and 4-vinyl pyridine (M₂), the terminal model of copolymerization has been tested. Reactivity ratios (r₁ = 0.18 r₂ = 1.77) were found. The probability of “coisotactic” alternating addition (σ = 0.98) has been obtained as the best fit of experimental methoxy signal fractions and the theoretical curves.     

Lignin nanocomposites

Lignin is a biopolymer and one of the main constituents of woody plants where it plays the role of lining agent and is comparable in this respect to cement in steel reinforced concrete. Polymer nanocomposites containing biopolymers such as cellulose, lignin, starch, proteins, etc. are the object of recent numerous studies and are known also as bio-nanocomposites. This paper deals with lignin use in various polymer nanocomposites. It presents the preparation and uses of nanolignin as a filler and lignin uses as a matrix or a matrix component in polymer nanocomposites.     

Influence of viscosity on the diffraction of sound by a periodic array of screens

The paper contains an analysis of the transmission of a pressure wave through a periodic grating including the influence of the air viscosity. The system of equations in this case consists of the compressible Navier-Stokes equations associated with no-slip boundary conditions on solid surfaces. The problem is reduced to two hypersingular integral equations for determining the velocity components along the slits. These equations are solved by using Galerkin's method with some special trial functions. The results can be applied in designing protective screens for miniature microphones realized in the technology of micro-electro-mechanical systems (MEMS). In this case, the physical dimensions of the device are on the order of the viscous boundary layer so that the viscosity cannot be neglected. The microfluidic model of the screen consists of a periodic array of slits in a substrate. The analysis indicates that the openings in the screen should be on the order of 10 microm in order to avoid excessive attenuation of the signal.     

On a problem of Schwaiger in random normed spaces

We consider a problem of Schwaiger in the setting of random normed spaces to obtain a characterization for the completeness of these spaces by means of the stability of the Cauchy additive functional equation.