Mass spectrometric study of thermal desorption of water from surface of titanosilica

A study has been made of the thermal desorption of water from the surface of titanosilica (TS) obtained by high-temperature hydrolysis (HTH) and low-temperature hydrolysis (LTE), and containing up to 37% TiO₂ by weight. For the samples of TS obtained by either method, only one thermal desorption maximum is observed; the position of the maximum does not depend on the content of the titanium dioxide phase in the TS, but it does depend on the method of preparation: For the LTH, T_max = 480 K; and for the ETH, T_max = 400 K. The shift of the temperature corresponding to the maximum of the H₂O⁺ desorption peak for the TS obtained by HTH may be due to migration of adsorbed water molecules along the surface to sections of titanium-siloxane bonds Si-O-Ti, from which the water molecules are then desorbed.Institute of Surface Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 6, pp. 734–736, November–December, 1991. Original article submitted February 20, 1989.     

Electron transport in monodisperse metal nanostructures

Electron transport in monodisperse granular Cu, Ni, and Pd structures with conduction near the percolation threshold is investigated. An activation conduction law is observed in the oxidized Cu structures, whereas the Efros-Shklovskii law is observed in the initial Cu structures and in the Ni and Pd structures. This behavior is discussed within the framework of a model in which variable range hopping conduction is considered with regard to both the disorder potential and spread of the sizes of grain assemblies.     

Synthesis and structure of [(p-phenylenedimethylene) Bis [diphenylphosphine]]-Bis[(acetylacetonato) carbonylrhodium(I) and its reaction product with inorganic azides,azidocarbonylbis (triphenylphosphine) rhodium(I)

Journal of Structural Chemistry -     

Size Dependences of the Magnetic Properties of Superconducting Lead–Porous Glass Nanostructures

Superconducting structures Pb–PG formed by filling a porous glass matrix with the lead from melt under pressure have been investigated. Samples with characteristic pore structure diameters of d ≈ 7, 3, and 2 nm have been studied. It has been found that the critical temperature of the superconducting transition in the samples under study is similar to the corresponding value T_c ≈ 7.2 K for bulk lead. At the same time, it has been observed that the critical magnetic field of the nanocomposites, which attains H_c(T = 0 K) ≈ 165 kOe for Pb–PG (3 nm), exceeds several times the value H_c(0) = 803 Oe for bulk lead. The low-temperature magnetic- field dependences of magnetic moment M(H) contain quasi-periodic flux jumps, which vanish with a decrease in the lead nanostructure diameter. A qualitative model of the observed effects is considered.     

Orbital ac spin-Hall effect in the hopping regime

The Rashba and Dresselhaus spin-orbit interactions are both shown to yield the low temperature spin-Hall effect for strongly localized electrons coupled to phonons. A frequency-dependent electric field E(omega) generates a spin-polarization current, normal to E, due to interference of hopping paths. At zero temperature the corresponding spin-Hall conductivity is real and is proportional to omega2. At nonzero temperatures the coupling to the phonons yields an imaginary term proportional to omega. The interference also yields persistent spin currents at thermal equilibrium, at E=0. The contributions from the Dresselhaus and Rashba interactions to the interference oppose each other.     

Synthesis, structure, and biological activity of the cis-[4-amino-2,2,6,6-tetramethylpiperidine-N,N′]dichloropalladium(ii) complex

A previously unknown palladium complex was synthesized by the reaction of 4-amino-2,2,6,6-tetramethylpiperidine with PdCl₂. The X-ray diffraction study showed that the complex formed by 4-amino-2,2,6,6-tetramethylpiperidine with PdCl₂ is a chelate, in which the bidentate ligand adopts a boat conformation with the nitrogen atoms occupying cis positions at the palladium atom. The resulting cis-[4-amino-2,2,6,6-tetramethylpiperidine-N,N′]dichloro-palladium(ii) complex exhibits strong antimetastatic activity against experimental B16 melanoma at moderate toxicity.     

Mechanisms involved in the cell cycle and apoptosis of HT-29 cells pre-treated with MK-886 prior to photodynamic therapy with hypericin

In our previous study we have proved that colon cancer cells HT-29 pre-treated with specific 5-lipoxygenase inhibitor MK-886 became more susceptible to photodynamic therapy (PDT) with hypericin and we also found that this mutual combination induced cell cycle arrest and stimulated onset of apoptosis (Kleban et al., 2007. J. Photochem. Photobiol. B 84, 2). To further explain events associated with MK-886 mediated sensitization of tumor cells toward PDT with hypericin, more detailed study of signaling pathways leading to increase in apoptosis as well as cell cycle perturbations was performed and is presented herein. Intensive accumulation of HT-29 cells in G0/G1 phase of cell cycle led to expression analyses of several G0/G1 checkpoint molecules (cyclin A, cyclin E, cdk-2, pRb). Similarly, accumulation of apoptotic cells invoked analyses of key molecules involved in apoptotic signaling (caspase-3, -8, -9; PARP; Lamin B; Mcl-1; Bax) by Western blotting and caspase activity assay. Long term survival of cells was examined by clonogenicity test. As the effect of PDT is mediated by ROS production, levels of hydrogen peroxides and superoxide anion were monitored by flow cytometric analyses. In addition, an impact of MK-886 on LTB4 production and expression of 5-LOX was monitored. Massive G0/G1 arrest in the cell cycle accompanied by increase in cyclin E level and decrease/absention of cyclin A, cdk-2 and pRb expression indicated incapability for G1/S transition. Minimal changes in cleavage of procaspases observed in cells treated with non-toxic concentrations of either agent alone or their mutual combination were not quite in line with their activity (caspase-3, -8, -9) which was significantly increased mainly in combinations. Treatment with non-toxic concentration of MK-886 had minimal influence over ROS production compared to control cells. In contrast, hypericin alone markedly increased the level of ROS, but no additional effect of MK-886 pre-treatment was detected. Further analyses of particular ROS groups unveiled an impact of increasing MK-886 concentration on superoxide accumulation accompanied with depletion of hydrogen peroxide level within the cells. The clonogenicity test revealed disruption of colony formation after mutual combination of both agents as compared to MK-886 or PDT alone. In conclusion, we presume that stimulation of apoptosis in our experimental model was accomplished preferentially through the mitochondrial pathway, although caspase-8 activation was also noticed. Interestingly, pre-treatment with MK-886 modulated distribution of ROS production in mutual combination with PDT.