P-coumaric acid-zinc basic salt nanohybrid for controlled release and sustained antioxidant activity

P-coumaric acid (pCA) has been intercalated in zinc basic salt (ZBS) to design an organic-inorganic nanohybrid material with controlled release and sustained antioxidant activity. According to the powder X-ray diffraction patterns and FT-IR spectra, pCA molecules were intercalated into ZBS without any noticeable alterations in their structural integrity. In vitro release test showed a biphasic discharge of pCA out of the interlayer space of two-dimensional ZBS lattice consisting of an initial burst release followed by a slow and sustained release. The pCA-ZBS nanohybrid exhibited comparable antioxidant activity to that of the free pCA.     

Spectral manifestations of the splitting of the lowest triplet levels in Pd complexes of nonsymmetric porphyrins

Based on the study of the phosphorescence and phosphorescence excitation spectra of Pd(II) tetramethylporphyrin (PdTMP) and Pd(II) tetramethyldiethylporphyrin (PdTMDEP) in solutions in 2-methyltetrahydrofuran and dodecane in the temperature range 77–283 K, the occurrence of the splitting of the lowest degenerate singlet (S ₁) and triplet (T ₁, T ₂) levels of porphyrin molecules is established. In the absorption of molecules of the compounds studied, two components, S ₁ and S ₂, are revealed in the range of allowed long-wavelength Q(0,0) transitions (530–550 nm) and four components, T ₁–T ₄, are observed in the range of spin-forbidden intersystem crossing transitions S ₀ → T _n (560–670 nm), with all the triplet levels T ₁-T ₄ being located below the S ₁ level on the energy scale. It is shown that an increase in the degree of deformation of the porphyrin macrocycle caused by steric interactions between β alkyls and hydrogen meso atoms is accompanied by an increase in the splitting in the system of singlet levels δE(S ₂–S ₁) from 120 cm^?1 for PdTMDEP to 215 cm^?1 for PdTMP, as well as by an increase in the splitting in the system of triplet levels δE(T ₂–T ₁) from 190 cm^?1 for PdTMDEP to 250 cm^?1 for PdTMP.     

Influence of incoherent scattering on stochastic deflection of high-energy negative particle beams in bent crystals

An investigation on stochastic deflection of high-energy negatively charged particles in a bent crystal was carried out. On the basis of analytical calculation and numerical simulation it was shown that there is a maximum angle at which most of the beam is deflected. The existence of a maximum, which is taken in the correspondence of the optimal radius of curvature, is a novelty with respect to the case of positively charged particles, for which the deflection angle can be freely increased by increasing the crystal length. This difference has to be ascribed to the stronger contribution of incoherent scattering affecting the dynamics of negative particles that move closer to atomic nuclei and electrons. We therefore identified the ideal parameters for the exploitation of axial confinement for negatively charged particle beam manipulation in future high-energy accelerators, e.g., ILC or muon colliders.     

Transition radiation from relativistic charged particles interacting with atomic strings in a crystal

The problem of transition radiation generated by relativistic particles incident on atomic strings in a crystal at a small angle is considered. Conditions are obtained under which the problem of transition radiation reduces to that of radiation generated by a collision with a filament-like target. It is shown that the angular distribution of transition radiation is symmetric with respect to the atomic-string axis.     

Compatibility and Marginality

We present a way of introducing joint distibution function and its marginal distribution functions for non-compatible observables. Each such marginal distribution function has the property of commutativity. Models based on this approach can be used to better explain some classical phenomena in stochastic processes.     

Y2SiO5:Tb phosphor particles prepared from colloidal and aqueous solutions by spray pyrolysis

Green-emitting Y₂SiO₅:Tb phosphor particles with fine size, spherical shape, filled morphology, high crystallinity, and good brightness were synthesized by a spray pyrolysis process. The effect of silicon precursor type on the morphology, crystal structure, crystallinity, and photoluminescence efficiency of Y₂SiO₅:Tb phosphor particles was investigated. The particles prepared from an artificial colloidal solution obtained by dispersing fumed silica particles had a pure monoclinic X2 crystalline phase, which is more appropriate for application to displays, after post-treatment at 1300 °C. On the other hand, the particles prepared from 100% tetraethyl orthosilicate (TEOS) reagent had an X2 phase and small amounts of X1 and impurity phases such as Y₂Si₂O₇ and Y_4.67Si₃O₁₃ due to the phase-segregation characteristics of the TEOS precursor. The photoluminescence characteristics of Y₂SiO₅:Tb phosphor particles were strongly affected by the silicon source used. The photoluminescence intensities increased with the fumed silica/TEOS ratio. The particles prepared from 100% fumed silica showed the maximum photoluminescence intensity, which is 22% higher than that of particles prepared from 100% TEOS. PACS 81.20.Rg; 78.55.Hx; 78.40.Ha; 81.05.Hd; 81.40.Tv     

Characterization of fluorinated multiwalled carbon nanotubes by x-ray absorption spectroscopy

The C 1s and F 1s x-ray absorption spectra of fluorinated multiwalled carbon nanotubes with different fluorine contents and reference compounds (highly oriented pyrolytic graphite crystals and “white” graphite fluoride) were measured using the equipment of the Russian-German beamline at the BESSY II storage ring with a high energy resolution. The spectra obtained were analyzed with the aim of characterizing multiwalled carbon nanotubes and their products formed upon treatment of the nanotubes with fluorine at a temperature of 420°C. It was established that, within the probing depth (～15 nm) of carbon nanotubes, the process of fluorination occurs uniformly and does not depend on the fluorine concentration. The interaction of fluorine atoms with multiwalled carbon nanotubes in this case proceeds through the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton and is accompanied by a change in the hybridization of the 2s and 2p valence electron states of the carbon atom from the trigonal (sp ²) to tetrahedral (sp ³) hybridization.     

Dynamics of nanoparticle agglomeration in a magnetic fluid in a varying magnetic field

It is found that the dependence of the magnetic nanoparticle agglomerate length in a magnetic fluid on the applied magnetic field has three characteristic segments: a substantial increase in the agglomerate length with the magnetic field in the range of weak fields, a segment with an insignificant increase in the average length of agglomerates upon an increase in the field, and a sharp increase in the agglomerate length with a further increase in the field. It is shown that the agglomerate length increases in the range of strong magnetic fields due to a decrease in the spacing between adjacent agglomerates down to their complete coalescence. The total number of agglomerates decreases thereby.     

p-type porous-silicon transducer for cation detection: effect of the porosity, pore morphology, temperature and ion valency on the sensor response and generalisation of the Nernst equation

This paper shows the possibility of using oxidised porous silicon (PS) as a transducer material for ion-sensor applications. It aims to study the over-Nernstian behaviour of the porous electrodes towards the concentration of cations in contact. The dependence of the sensitivity on the porosity of the samples prepared from highly doped substrates has been studied. Maximal values of over-Nernstian sensitivities around 240 mV/pNa and ∼92 mV/pCu, corresponding to a PS-layer porosity of about 65%, obtained respectively from p⁻ and p⁺ silicon substrates, have been registered. Furthermore, the effect of the porous nanostructure morphology has been studied, by preparing PS samples from weakly doped wafers. The porous-silicon-based sensor behaviour for different PS-layer thicknesses has also been experimentally investigated. According to these results, a physical model has been proposed to explain the mechanisms which govern the charge-carrier transfer from one side to the other of the functionalised oxide layer, and leads to the over-Nernstian adsorption of the cationic species at the electrolyte/SiO₂ interface. Afterwards, the Nernst relation has been generalised accordingly, on one hand, to the previous experimental results, and on the other hand, to the results obtained about the ion-valency and the electrolyte-temperature effects on the sensor responses. Received: 15 December 2000 / Accepted: 18 December 2000 / Published online: 23 March 2001     

Synthesis of New Ursane-Type Hybrids with Morpholinomethyl-, Dialkylamino-, and Hydroxyl-Substituted Azoles

Chemistry of Natural Compounds - Ursane-type triterpenoids containing functionalized heterocyclic substituents were chemically modified. Aminomethylation of ursane hybrids with 1,3,4-oxadiazole-...