Study of DNA-ellipticine interaction by capillary electrophoresis with laser-induced fluorescence detection

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), an alkaloid isolated from Apocynaceae plants, exhibits an antitumor activity, which is exceptionally high against several specific types of tumors. Ellipticine is also interesting as an anticancer drug as it has limited side effects and lacks of hematological toxicity. Various methods to study intercalating activity of this drug have been developed. However, to our best knowledge, capillary electrophoresis (CE) as a technique combining high separation resolution with various detection options has never been used for these purposes. In this study, a novel separation method based on CE with laser-induced fluorescence (CE-LIF) detection has been developed for the determination of ellipticine and for the monitoring of ellipticine-DNA interaction. Sodium acetate (50 mM, pH 4.5) was used as a background electrolyte and LIF detection at λ(ex) = 488 nm. The limit of detection for ellipticine was determined to be 5 × 10?? M. A total of 20% dimethyl sulfoxide was found optimal as sample solvent. Additionally, intercalation of ellipticine into the double-stranded DNA was investigated. Signal corresponding to ellipticine was decreasing and a new peak appeared and was growing. It can be concluded that CE-LIF is a method applicable to in vitro studies of ellipticine-DNA complexes.     

Structural changes in metallothionein isoforms revealed by capillary electrophoresis and Brdicka reaction

Metallothionein (MT) as a potential cancer marker is at the center of interest and its properties, functions and behavior under various conditions is intensively studied. In the present study, two major mammalian MT isoforms (MT‐1 and MT‐2) were separated using capillary electrophoresis (CE) coupled with UV detector in order to describe their basic behavior. Under the optimized conditions, the separation of both isoforms was enabled as well as estimation of detection limits as subunits and units of ng per μL for MT‐2 and MT‐1, respectively. Further, the effects of thermal treatment and the presence of denaturing agent such as urea on MT‐1 and MT‐2 isoforms were studied by CE‐UV. Thermal treatment caused an increase in the signals of both isoforms. A new parameter called precipitation rate has been defined based on this finding. This parameter can be expressed as a slope of the linear regression of the time dependency curve recalculated on the MT concentration. The thermal precipitation rate for MT‐1 and MT‐2 was determined as 1.1 and 0.9 ng of MT/min, respectively. The chemical precipitation rate calculated from the linear regression for both isoforms provided the same value of 0.25 ng of MT/min. The results were confirmed by manual spectrometric measurements and by differential pulse voltammetry Brdicka reaction. Based on these results, a model of MT behavior under the conditions studied was suggested.     

A new type of strong metal-support interaction and the production of H2 through the transformation of water on Pt/CeO2(111) and Pt/CeO(x)/TiO2(110) catalysts

The electronic properties of Pt nanoparticles deposited on CeO(2)(111) and CeO(x)/TiO(2)(110) model catalysts have been examined using valence photoemission experiments and density functional theory (DFT) calculations. The valence photoemission and DFT results point to a new type of "strong metal-support interaction" that produces large electronic perturbations for small Pt particles in contact with ceria and significantly enhances the ability of the admetal to dissociate the O-H bonds in water. When going from Pt(111) to Pt(8)/CeO(2)(111), the dissociation of water becomes a very exothermic process. The ceria-supported Pt(8) appears as a fluxional system that can change geometry and charge distribution to accommodate adsorbates better. In comparison with other water-gas shift (WGS) catalysts [Cu(111), Pt(111), Cu/CeO(2)(111), and Au/CeO(2)(111)], the Pt/CeO(2)(111) surface has the unique property that the admetal is able to dissociate water in an efficient way. Furthermore, for the codeposition of Pt and CeO(x) nanoparticles on TiO(2)(110), we have found a transfer of O from the ceria to Pt that opens new paths for the WGS process and makes the mixed-metal oxide an extremely active catalyst for the production of hydrogen.     

On color critical graphs

It is shown that the minimal number of edges which have to be omitted from a (k + 1)-critical graph on n vertices in order to make it bipartite is at least ^k₂ for n large enough. This bound is best possible. Various related questions are considered.     

Zeptomole Detection of Streptavidin Using Carbon Paste Electrode and Square‐Wave Voltammetry

We compared the suitability of avidin and streptavidin for avidin‐biotin technology in view of the sensitivity of the analysis using square‐wave voltammetry. We found out during our preliminary experiments that streptavidin gave approximately 100 times higher electrochemical response in comparison with avidin at the same experimental conditions and concentration. Thus, we used two approaches for streptavidin determination – analysis directly in electrochemical cell and analysis by adsorptive transfer technique (AdTS). Ten minutes long accumulation on carbon paste electrode surface was ascertained as optimal in both cases. Limits of detection were 0.3 aM (electrochemical cell) and 30 aM (AdTS).     

Reaction of SO2 with AuCeO2(111): importance of O vacancies in the activation of gold

Synchrotron-based high-resolution photoemission was used to study the adsorption and chemistry of SO(2) on AuCeO(2)(111) and AuO(x)CeO(2) surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO(2)(111) was 4-7 kcalmol larger than on Au(111). However, there was negligible dissociation of SO(2) on the AuCeO(2)(111) surfaces. The full decomposition of SO(2) was observed only after introducing O vacancies in the ceria support. AuO(x)CeO(2) surfaces were found to be much less chemically active than AuCeO(2)(111) or AuCeO(2-x)(111) surfaces. The active sites in {Au + AuO(x)}ceria catalysts should involve pure gold nanoparticles in contact with O vacancies.     

OH functionality of germanium(II) compounds for the formation of heterobimetallic oxides

Two novel germanium(II) mu-oxo heterobimetallic oxides with different oxidation states at the metal centers have been reported. The reaction of LGeOH [L = N(Ar)C(Me)CHC(Me)N(Ar) (Ar = 2,6-i-Pr(2)C(6)H(3))] with Cp(2)MMe(2) (M = Zr, Hf) in Et(2)O afforded LGeOM(Me)Cp(2) [M = Zr (2), Hf (3)] in moderate yield. Compounds 2 and 3 were characterized by elemental analysis, IR, NMR, EI-MS, and single X-ray structural analysis. Compounds 2 and 3 crystallized in the space group P, and the geometry at the metal centers is tetrahedral. The Ge-O bond lengths of 2 and 3 are very similar (1.797(2) and 1.799(3) Angstroms, respectively), and a bent M-O-M' angle in 2 (143.8(1) degrees) and 3 (141.9(2) degrees) features both oxide systems. Different orientations of the Cp and Me groups of the metal centers were observed, and deviations of the Cp groups were exhibited.     

Chemistry of NO2 on oxide surfaces: formation of NO3 on TiO2(110) and NO2<-->O vacancy interactions

Synchrotron-based high-resolution photoemission, X-ray absorption near-edge spectroscopy, and first-principles density functional (DF) slab calculations were used to study the interaction of NO(2) with a TiO(2)(110) single crystal and powders of titania. The main product of the adsorption of NO(2) on TiO(2)(110) is surface nitrate with a small amount of chemisorbed NO(2). A similar result is obtained after the reaction of NO(2) with polycrystalline powders of TiO(2) or other oxide powders. This trend, however, does not imply that the metal centers of the oxides are unreactive toward NO(2). An unexpected mechanism is seen for the formation of NO(3). Photoemission data and DF calculations indicate that the surface nitrate forms through the disproportionation of NO(2) on Ti sites (2NO(2,ads) --> NO(3,ads) + NO(gas)) rather than direct adsorption of NO(2) on O centers of titania. Complex interactions take place between NO(2) and O vacancies of TiO(2)(110). Electronic states associated with O vacancies play a predominant role in the bonding and surface chemistry of NO(2). The adsorbed NO(2), on its part, affects the thermochemical stability of O vacancies, facilitating their migration from the bulk to the surface of titania. The behavior of the NO(2)/titania system illustrates the importance of surface and subsurface defects when using an oxide for trapping or destroying NO(x)() species in the prevention of environmental pollution (DeNOx operations).     

Molecular level study of the formation and the spread of MoO3 on Au(111) by scanning tunneling microscopy and X-ray photoelectron spectroscopy

The formation of MoO(3) and its spontaneous spread over an Au (111) surface have been studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Metallic Mo clusters grown by Mo(CO)(6) chemical vapor deposition (CVD) have a constant size independent of the Mo coverage. Molecular oxygen does not react with low coverage of Mo, probably due to the encapsulation of the Mo clusters by Au. At higher coverage, O(2) reacts with Mo, partially transforming the metallic Mo to Mo(4+). NO(2) can oxidize Mo efficiently to Mo(6+) and Mo(5+) species at all coverages investigated. XPS experiments show that the integrated intensity of the Mo 3d peaks increases by a factor of 2 upon the oxidation, suggesting the spread of the MoO(3) over the surface. The STM study confirms this suggestion and provides the mechanistic details of the spreading. Mo oxide forms ramified two-dimensional islands covering a substantially larger fraction of the Au surface than the metallic Mo. We propose that the morphology change starts with the diffusion of oxide clusters (ramified-cluster-diffusion mechanism), followed by their breakdown to highly disordered two-dimensional islands of molecular MoO(3).     

Coverage effects and the nature of the metal-sulfur bond in S/Au(111): high-resolution photoemission and density-functional studies

The bonding of sulfur to surfaces of gold is an important subject in several areas of chemistry, physics, and materials science. Synchrotron-based high-resolution photoemission and first-principles density-functional (DF) slab calculations were used to study the interaction of sulfur with a well-defined Au(111) surface and polycrystalline gold. Our experimental and theoretical results show a complex behavior for the sulfur/Au(111) interface as a function of coverage and temperature. At small sulfur coverages, the adsorption of S on fcc hollow sites of the gold substrate is energetically more favorable than adsorption on bridge or a-top sites. Under these conditions, S behaves as a weak electron acceptor but substantially reduces the density-of-states that gold exhibits near the Fermi edge. As the sulfur coverage increases, there is a weakening of the Au-S bonds (with a simultaneous reduction in the Au --> S charge transfer and a modification in the S sp hybridization) that facilitates changes in adsorption site and eventually leads to S-S bonding. At sulfur coverages above 0.4 ML, S(2) and not atomic S is the more stable species on the gold surface. Formation of S(n)(n > 2) species occurs at sulfur coverages higher than a monolayer. Very similar trends were observed for the adsorption of sulfur on polycrystalline surfaces of gold. The S atoms bonded to Au(111) display a unique mobility/reactivity not seen on surfaces of early or late transition metals.