Identification of polyphenolic compounds in red and white grape varieties grown in R. Macedonia and changes of their content during ripening

The composition of polyphenols in the skin, seed and pulp extracts of the grapes of Vranec and Smederevka varieties, and Merlot and Chardonnay as well, was analyzed by liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) and MS/MS techniques. Thirty-one phenolic compounds, including anthocyanins, flavonols and flavan-3-ols, as well as phenolic acids derivatives, have been identified in the extracts prepared from the grapes at physiological maturity, by mass spectrometry applying electrospray ionization operated in alternating ion mode and by performing tandem MS experiments in the ion trap mass analyzer. Grapes were analyzed at three different phases: (i) veraison, (ii) physiological ripeness and (iii) late harvest, in order to follow the evolution of polyphenolic content during berry development, applying spectrophotometric methods. Vranec had a higher polyphenolic content compared to Merlot due to the higher levels of total phenolics and flavonoids in the skins and seeds as well as a higher content of flavan-3-ols and anthocyanins in the skins, allowing discriminating the varieties. HPLC-DAD-MS analysis presented significantly higher relative amounts of anthocyanin monoglucosides and p-coumaroylglucosides in Vranec grapes. Smederevka seeds had a higher amount of flavan-3-ols than Chardonnay, while a higher content of total phenolics and flavonoids was found in the skins of the Chardonnay variety. Anthocyanin content in both red varieties increased during the berry ripening, while flavan-3-ols in seeds were mainly accumulated in the veraison phase followed by decrease of the content with ripening.     

Effect of defects of the domain structure on the optical properties of ferroelectric crystals

The effect of irregularities of a periodic domain structure on the efficiency of the second harmonic generation has been numerically investigated in the case where the structure is formed by the high-voltage method. The irregularities associated with the uncontrollable motion of domain walls from under electrodes, as well as with the presence of internal defects in the crystal, have been analyzed.     

Formation of active sites in titanium-containing zeolites with MFI structure in propylene epoxidation with hydrogen peroxide

Propylene epoxidation with hydrogen peroxide on titanosilicates with different Si/Ti ratios and various states of titanium in the catalysts, prepared by hydrothermal crystallization according to two different procedures, has been investigated. It has been demonstrated that a change in the pH of the crystallizing gel leads to a change in the sequence of titanium insertion in the zeolite structure at a hydrothermal synthesis temperature of 170°C. It was shown that titanium incorporated in the zeolite framework in the tetrahedral positions is an active site in the epoxidation reaction, whereas titanium in the form of titanium dioxide leads to unproductive degradation of hydrogen peroxide.     

Thermoelectric properties of a Pb0.2Sn0.8Te solid solution prepared through thermal decomposition of salts

We have studied the thermoelectric properties of microcrystalline samples of the Pb_0.2Sn_0.8Te solid solution prepared by hot-pressing fine powders obtained through the thermal decomposition of lead acetate trihydrate and tin oxalate in the presence of tellurium powder. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the samples have been measured at room temperature and in the temperature range 300–700 K and correlated with the particle size of the powders and heat-treatment conditions. We have compared the thermoelectric properties of hot-pressed samples from powders prepared through the thermal decomposition of salts and by mechanical grinding of ingots.     

Dramatic Effect of Vibrations on Dynamics of Rotating Hydrodynamic Systems

The results of theoretical and experimental investigation of the average dynamics of inhomogeneous systems in rotating cavity in the presence of oscillating force field are highlighted and analyzed. Average behavior of nonisothermal liquid as well as different multiphase systems (two liquids, liquid and gas, solid in liquid, granular matter in liquid) in quickly rotating horizontal cylinder subjected to vibrations of different direction is described. The specificity of dynamics of all the systems is determined by the Coriolis force which defines not only the average flows but the fluid oscillations also. The resonant excitation of inertial oscillations of liquid results in generation of intensive mean flows. The structure of vibrational streams is essentially determined by the type of inertial waves. So, excitation of an azimuthal wave generates azimuthal streams (outrunning or lagging, depending on frequency of the wave), three-dimensional standing waves (in the systems with deformable interface) generate regular spatial flows of high intensity. Under the resonant conditions the influence of vibrations appears to be very strong, the speed of mean streaming can achieve the values comparable with the speed of rotation of the container.     

Production of isobutylene from acetone over micro–mesoporous catalysts

The production of isobutylene from acetone over micro–mesoporous catalysts with different mesopore contents, which have been prepared using hydrothermal recrystallization of mordenite (MOR) zeolite modified with cesium acetate by incipient wetness impregnation, has been studied. It has been shown that cesium is inserted into the cation positions during the modification, at the same time the number of Brønsted acid sites in the samples decreased. It has been found that an increase in the content of mesopores in the catalyst leads to an increase in the initial rates of acetone conversion and isobutylene formation as a result of removing diffusion limitations. Brønsted acid sites have been shown to be preferable for the selective production of isobutylene from acetone. Micro–mesoporous materials operate more stably as compared to microporous materials.