External polyacrylate-coating as alternative material for preparation of photopolymerized sol-gel monolithic column

Photopolymerized sol-gel monolithic columns for use in capillary electrochromatography were prepared in 125 microm i.d. polyacrylate-coated fused-silica capillaries. The polyacrylate-coating, unlike the polyimide one, is transparent to the radiation used (approximately 370 nm), and thus, no coating removal is necessary. This is a very important particularity since intrinsic capillary column characteristics, such as flexibility and mechanical resistance, are unchanged. A mixture containing metacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photoinitiator was irradiated at 370 nm for 20 min inside the capillaries to prepare the columns through sol-gel approach. The versatility and viability of the use of polyacrilate as a new capillary external coating were shown through preparation of two columns under different conditions, which were tested in electrochromatography for separation of standard mixture containing thiourea (marker compound), propylbenzene, phenanthrene and pyrene.     

Erbium and ytterbium co-doped SiO<Subscript>2</Subscript>:GeO<Subscript>2</Subscript> planar waveguide prepared by the sol–gel route using an alternative precursor

The sol–gel method combined with a spin-coating technique has been successfully applied for the preparation of rare-earth doped silica:germania films used for the fabrication of erbium-doped waveguide amplifiers (EDWA), presenting several advantages over other methods for the preparation of thin films. As with other methods, the sol–gel route also shows some drawbacks, such as cracks related to the thickness of silica films and high hydrolysis rate of certain precursors such as germanium alkoxides. This article describes the preparation and optical characterization of erbium and ytterbium co-doped SiO₂:GeO₂ crack-free thick films prepared by the sol–gel route combined with a spin-coating technique using a chemically stable non-aqueous germanium oxide solution as an alternative precursor. The non-crystalline films obtained are planar waveguides exhibiting a single mode at 1,550 nm with an average thickness of 3.9 μm presenting low percentages of porosity evaluated by the Lorentz–Lorenz Effective Medium Approximation, and low stress, according to the refractive index values measured in both transversal electric and magnetic polarizations. Weakly confining core layers (0.3% < Δn < 0.75%) were obtained according to the refractive index difference between the core and buffer layers, suggesting that low-loss coupling EDWA may be obtained. The life time of the erbium ⁴I_13/2 metastable state was measured as a function of erbium concentration in different systems and based on these values it is possible to infer that the hydroxyl group was reduced and the formation of rare-earth clusters was avoided.     

Characterization of Mercury Contamination Surrounding a Chloralkali Production Facility in Tuzla,Bosnia and Herzegovina

Tuzla is among the most polluted cities of Bosnia and Herzegovina. The main source of pollution in the area is soil heavily contaminated by mercury released from a former chloralkali plant. This paper is focused on the characterization of mercury contaminated soil and air surrounding the chloralkali plant. In soil, the mobility and transformation of mercury were investigated by sequential extraction, while the methylation and reduction potentials were determined by the use of a radioactive tracer. Mercury emission from soil was determined by laboratory and by flux chamber measurements in the field. In addition, mercury concentrations in air were estimated by the analysis of air and the transplanted lichen Hypogymnia physodes. Mercury in soils in the vicinity of the chloralkali plant exceeded the background value by a factor of more than 3000. The fractionation of mercury in surface soil by sequential extraction showed that the mercury in soil was primarily bound to organic matter and a fraction containing elemental mercury and mercury (I) chloride is also significant. The obtained methylation and reduction potentials are low. The mercury flux from soil was estimated by two approaches. Fluxes of up to 8000?ng/m²/day were measured at the most polluted site; evaporation from soil was shown to be the primary source of elevated mercury in air. Air concentration mapping also revealed other sources of mercury; the most likely is the 715 MW coal power plant in the vicinity of former chloralkali facility.     

Sublimation/Volatilisation Kinetics of 8-hydroxyquinolines and Their Nitro-derivatives

5-Nitro-8-hydroxyquinoline (B) and 5,7-dinitro-8-hydroxyquinoline (C) were obtained from nitration of 8-hydroxyquinoline (A) and purified in acetone medium and under heating in which the formation of (B) or (C) depends on the amount of HNO₃ added. TG curves present mass loss in only one step before and after the melting point (T _m =76°C (A) and 180°C (B)) in different proportions as a function of the heating rate, characterising the sublimation and the volatilisation processes, respectively. The thermal stability of the compounds follow the order: A (77°C)<B (121°C)<C (222°C). Kinetic parameters through TG curves, dynamic process, using heating rates of 1, 2.5, 5, 10 and 20°C min^ȡ1 , enabled to obtain the following increasing order to the activation energy values of the compounds: 80.4 (A), 102.0 (B) and 153.9 kJ mol⁻¹ (C). Other kinetic parameters as pre-exponential and half-lifetime were also estimated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Behaviour of Tin(II) Complex With 8-hydroxyquinolinate in the Solid State

Tin(II) complexes with 8-hydroxyquinolinate in solid state have been obtained by adding aqueous ammonium to a solution containing stannous chloride and 8-hydroxiquinoline in medium of HCl and acetone up to pH 5 and 9, respectively. The products obtained show the same composition, Sn(C₉H₆ON)₂; however there are some differences regarding both the thermal behaviour in an oxidant atmosphere and morphology. These products were characterised by elemental and complexometric analysis, TG and DTA curves, infrared and X-ray diffractometry. TG curves show, above 448 K, the partial oxidation on air atmosphere of Sn(II) complexes to Sn(IV) complexes, SnO(C₉H₆ON)₂. This behaviour does not depend only on pH in which the compounds were obtained but also on the heating rate in TG curves. Sn(II) complexes volatilise almost completely on nitrogen atmosphere and partially on air atmosphere depending on the oxidation degree of the compound. This revised version was published online in July 2006 with corrections to the Cover Date.     

Large Communities in a Scale-Free Network

We prove the existence of a large complete subgraph w.h.p. in a preferential attachment random graph process with an edge-step. That is, we consider a dynamic stochastic process for constructing a graph in which at each step we independently decide, with probability \(p\in (0,1)\), whether the graph receives a new vertex or a new edge between existing vertices. The connections are then made according to a preferential attachment rule. We prove that the random graph \(G_{t}\) produced by this so-called generalized linear preferential (GLP) model at time t contains a complete subgraph whose vertex set cardinality is given by \(t^\alpha \), where \(\alpha = (1-\varepsilon )\frac{1-p}{2-p}\), for any small \(\varepsilon >0\) asymptotically almost surely.     

Unraveling the Photodynamic Activity of Cationic Benzoporphyrin-Based Photosensitizers against Bladder Cancer Cells

In this study, we report the preparation of new mono-charged benzoporphyrin complexes by reaction of the appropriate neutral benzoporphyrin with (2,2′-bipyridine)dichloroplatinum(II) and of the analogs’ derivatives synthesized through alkylation of the neutral scaffold with iodomethane. All derivatives were incorporated into polyvinylpyrrolidone (PVP) micelles. The ability of the resultant formulations to generate reactive oxygen species was evaluated, mainly the singlet oxygen formation. Then, the capability of the PVP formulations to act as photosensitizers against bladder cancer cells was assessed. Some of the studied formulations were the most active photosensitizers causing a decrease in HT-1376 cells’ viability. This creates an avenue to further studies related to bladder cancer cells.