Multivalued anisotropy of electric conductivity in Si near to the <111>-direction

The current voltage characteristics and the dependence of the transverse electric field on applied voltage is studied experimentally and theoretically forn-Si at 27 K for the current close to the <111>-direction. A solution in form of a loop is split off from the solution with nearly equal carrier population in all three valleys and corresponds to predominant population of only one valley. The solutions corresponding to predominant population of either one of the three valleys may coexist in the sample in the form of layers parallel to the current. A transverse magnetic inductionB may change the size of the layers and by appropriateB it is possible to induce either one of these three layers or any combination of them into the sample.     

Separation and determination of traces of ammonia in air by means of chromatomembrane cells

Chromatomembrane cells are new devices for gaseous/liquid and liquid/liquid extractions consisting of porous hydrophobic material (PTFE) with two types of pores, i.e., micropores and macropores. Their application benefits from established procedures of preconcentration and continuous extraction being used at the present to automate sample preparation in analytical chemistry. A method is reported to separate traces of ammonia from air by means of a chromatomembrane cell with subsequent potentiometric determination. The measuring system responds proportionally to both gas phase concentration of ammonia and preconcentration time.     

Role of base in palladium-catalyzed arylation of carbanions

The arylation reaction of carbanions, derived from certain sulfones, cyanoacetic ester and malononitrile, with aryl bromides (using the catalytic system of Pd₂dba₃/3L, L=PPh₃, PtBu₃) as well as the reaction of the carbanions with one equivalent of 4-CF₃C₆H₄ Pd(PPh₃)₂Br has been studied. These reactions proceed smoothly provided that the base stronger than the initial carbanion is present in the reaction mixture. In the absence of the above type of base the reactions do not proceed at all. Taking that into account we have proposed a novel mechanism of palladium-catalyzed arylation of CH-acids. The main feature of this mechanism is the accelaration of the reductive elimination due to the deprotonation of the intermediate ArPdL₂CHXY. The correlation between the carbanion reactivity and the pK_a values for related CH-acids as well as the ligand effect are discussed in the framework of the proposed mechanism.     

The use ofN-alkylcarbamates in sample mapping of terpene alcohols

Carbamates (I) of terpene alcohols (e.g. menthol, borneol, citronellol, nerol, geraniol) were used to develop a method for characterization and mapping of alcohol components in complex essential oils using GC, GC-MS and GC-FTIR data and the almost quantitative reaction of the primary and secondary alcohols with isocyanates. The comparison of the data of original and derivatized samples is thus the basis for assignment of components to the primary, secondary and tertiary alcohol types (e.g. Sandalwood Oil, Rose Oil) in sample mapping procedure.The NH-deformation absorption band of (I) in vapour phase FTIR-spectroscopy at 1492–1494 cm^–1 proved to be of great use in the selective registration of derivatized alcohols in complex samples.     

Solvothermal Morphology Studies: Alkali and Alkaline Earth Molybdates

A convenient and systematic solvothermal pathway towards alkali and alkaline‐earth molybdates has been established. The solvothermal treatment of a molybdenum‐based precursor material (yellow molybdic acid, MoO₃?2 H₂O) with ionic additives (alkali or alkaline‐earth halides) provides access to a spectrum of molybdates. Their particle morphology can further be addressed by optimizing the reaction conditions. The resulting products cover a wide scope of sizes and morphologies, ranging from molybdenum oxide fibres with high aspect ratios and nanoscale diameters to millimeter‐sized crystals of novel alkali molybdates. Both anionic and cationic additives exhibit certain synthetic profiles that offer the perspective of turning this approach into a ‘toolbox’ for the tailoring of molybdate‐based materials.     

Solid-state NMR spectroscopic methods in chemistry

Over the last decades, NMR spectroscopy has grown into an indispensable tool for chemical analysis, structure determination, and the study of dynamics in organic, inorganic, and biological systems. It is commonly used for a wide range of applications from the characterization of synthetic products to the study of molecular structures of systems such as catalysts, polymers, and proteins. Although most NMR experiments are performed on liquid-state samples, solid-state NMR is rapidly emerging as a powerful method for the study of solid samples and materials. This Review outlines some of the developments of solid-state NMR spectroscopy, including techniques such as cross-polarization, magic-angle spinning, multiple-pulse sequences, homo- and heteronuclear decoupling and recoupling techniques, multiple-quantum spectroscopy, and dynamic angle spinning, as well as their applications to structure determination. Modern solid-state NMR spectroscopic techniques not only produce spectra with a resolution close to that of liquid-state spectra, but also capitalize on anisotropic interactions, which are often unavailable for liquid samples. With this background, the future of solid-state NMR spectroscopy in chemistry appears to be promising, indeed.     

Cyclization of N-cyanovinyl-lactam imines to condensed 4-aminopyridines or substituted aminopyrazole

N-Cyanovinyl-lactam imines 2 react with hydrazine giving aminopyrazole 4a while lactam imine 3 is split off. Treatment of 2 with strong bases gives intramolecular cyclization to condensed 4-aminopyridines 5 . The progress of reaction was observed by polarographic method.     

Sol–Gel Processed Functional Nanosized TiO2 and SiO2-Based Films for Photocatalysts and Other Applications

Titania and silica-based porous coatings have been produced via sol–gel route in the presence of pore-creating agents PEG and viscous solvent -terpineol, or template agents CTAB, as well as triblock copolimer Pluronic P123. Porous titania films were characterised by HR TEM, UV-Vis, XRD, ellipsometry, ARS methods. The dispersion of the refractive index, the porosity (32–39%) and the thickness of the samples were estimated by integrating sphere transmission and reflection spectra with 3D angular resolved light scattering. The catalytic activity of mesoporous TiO₂ and TiO₂/ZrO₂ as well as SiO₂-benzophenone films in the process of Cr^VI to Cr^III and Ag⁺ to Ag⁰ photoreduction have been studied.