Mass spectrometry of the self-association and complexation of triterpene saponins and cholesterol

Electrospray ionization mass spectrometry has been used to study the self-association of α-hederin and hederacoside C (from Hedera) glycosides. The complexation of glycosides with cholesterol has been considered. It has been revealed that α-hederin forms self-associates registered in ESI mass spectra, while no self-associates have been found for hederacoside C and cholesterol. Cholesterol produces molecular complex with α-hederin, while complex formation between cholesterol and bisdesmoside hederacoside has not been observed.     

Bipolar resistive switching in heterostructures: Bismuth oxide/normal metal

Thin filmed heterojunctions Ag/Bi/BiOx/Ag were fabricated and the effect of frequency of applied ac voltage on bipolar resistive switching in the obtained heterojunctions was observed for the first time. It has been found that the frequency dependence of the effect has a universal character for some oxide compounds. This observation confirms the significant role of oxygen-ion migration in the resistive switching phenomena in structures based on oxide compounds.     

New insights into the interface between a single-crystalline metal electrode and an extremely pure ionic liquid: slow interfacial processes and the influence of temperature on interfacial dynamics

Ionic liquids are of high interest for the development of safe electrolytes in modern electrochemical cells, such as batteries, supercapacitors and dye-sensitised solar cells. However, electrochemical applications of ionic liquids are still hindered by the limited understanding of the interface between electrode materials and ionic liquids. In this article, we first review the state of the art in both experiment and theory. Then we illustrate some general trends by taking the interface between the extremely pure ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate and an Au(111) electrode as an example. For the study of this interface, electrochemical impedance spectroscopy was combined with in situ STM and in situ AFM techniques. In addition, we present new results for the temperature dependence of the interfacial capacitance and dynamics. Since the interfacial dynamics are characterised by different processes taking place on different time scales, the temperature dependence of the dynamics can only be reliably studied by recording and carefully analysing broadband capacitance spectra. Single-frequency experiments may lead to artefacts in the temperature dependence of the interfacial capacitance. We demonstrate that the fast capacitive process exhibits a Vogel-Fulcher-Tamman temperature dependence, since its time scale is governed by the ionic conductivity of the ionic liquid. In contrast, the slower capacitive process appears to be Arrhenius activated. This suggests that the time scale of this process is determined by a temperature-independent barrier, which may be related to structural reorganisations of the Au surface and/or to charge redistributions in the strongly bound innermost ion layer.     

Dipolar spirocyclic σ-complexes based on of 4,6-dinitrobenzofuroxan

The first dipolar spiro-σ-complexes with a superelectrophilic dinintrobenzofuroxan fragment and tropolone systems with diastereotopic substituents were synthesized. The kinetics of their enantiotopomerization, which occursvia cleavage-formation of the C_spiro-heteroatom bond, was studied by dynamic¹H NMR. The stereorigidity of dinitrobenzofuroxan spiro-complexes in this degenerated process increases in the series: tropolone<aminotropone<aminothiotropone≈aminotroponimine. The two last posses the highest kinetic stability compared to all known zwitterionic spiro-complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1509–1512, August, 1997.     

Chern-Lashof absolute curvature of complex submanifolds and volumes of Grassmann images

We introduce an analog of the Chern-Lashof absolute curvature for complex submanifolds in complex Euclidean spaces. A relation between this curvature and the volume of the Grassmann image of the submanifold is established.     

Extraction of caftaric and cichoric acids from Echinacea purpurea L. in subcritical water

A procedure for extracting caftaric and cichoric acids from Echinacea purpurea L. in subcritical water was developed. The procedure is ecologically clean and more effective than the traditional extraction methods based on the use of expensive and toxic organic solvents.     

Extraction of bioflavonoid mixture from onion husk by subcritical water

A new method for extraction of bioflavonoids from onion husk using subcritical water is developed. The method is environmentally friendly and more effective than traditional extraction methods using expensive and toxic organic solvents. To determine the quantitative and qualitative composition of obtained extracts, high-performance liquid chromatography combined with mass spectrometry was used.     

Constituents of the quasiparticle spectrum along the nodal direction of high-Tc cuprates

Applying the Kramers-Kronig consistent procedure, developed earlier, we investigate in detail the formation of the quasiparticle spectrum along the nodal direction of high-Tc cuprates. The heavily discussed "70 meV kink" on the renormalized dispersion exhibits a strong temperature and doping dependence when purified from structural effects such as bilayer splitting, diffraction replicas, etc. This dependence is well understood in terms of fermionic and bosonic constituents of the self-energy. The latter follows the evolution of the spin-fluctuation spectrum, emerging below some doping dependent temperature and sharpening below Tc, and is mainly responsible for the formation of the kink in question.     

Electrokinetic phenomena in a kerosene-based magnetic fluid

We propose the methods for studying electrokinetic phenomena in magnetic colloidal systems (magnetic fluids), which make it possible to use the magnetic properties of particles of the disperse phase. Electrophoresis and the sedimentation potential in a kerosene-based magnetic fluid are studied. It is shown that only a small part (approximately one-thousandth) of all disperse particles in the magnetic fluid under investigation are charged, the sign of the particle charge being negative.