Ionic liquids in microextraction techniques

The tremendous potential of room temperature ionic liquids as an alternative to environmentally harmful ordinary organic solvents is well recognized. Due to their unique properties, such as low volatility, tunable viscosity and miscibility, and electrolytic conductivity, ionic liquids have attracted extensive attention and gained popularity in many areas of analytical chemistry including modern sample preparation techniques.     

A New Iteration and Preconditioning Method for Elliptic PDE-Constrained Optimization Problems

Optimal control problems constrained by a partial differential equation (PDE) arise in various important applications, such as in engineering and natural sciences. Normally the problems are of very large scale, so iterative solution methods must be used. Thereby the choice of an iteration method in conjunction with an efficient preconditioner is essential. In this paper, we consider a new iteration method and a new preconditioning technique for an elliptic PDE-constrained optimal control problem with a distributed control function. Some earlier used iteration methods and preconditioners in the literature are compared, both analytically and numerically with the new iteration method and the preconditioner.     

S(N)Ar reactions of nitro-(pentafluorosulfanyl)benzenes to generate SF5 aryl ethers and sulfides

Nucleophilic aromatic substitution of the nitro group of para- and meta-nitro-(pentafluorosulfanyl)benzene with alkoxides and thiolates generates a range of substituted 4- and 3-(pentafluorosulfanyl)benzenes in a single-step reaction.     

The effects of some operational parameters in photodegradation of benzylamine and aniline and their kinetics in aqueous suspension of TiO2 and Pt -loaded TiO2

Photocatalytic degradation of benzylamine and aniline on TiO2, Pt-modified TiO2, ZnO and ZnS in aqueous solution has been investigated. The degradation of the compounds follows a pseudo-first-order kinetics according to Langmuir-Hinshelwood model. The degradation process of benzylamine and aniline was evaluated by ninhydrin spectrophotometric method using UV-visible spectrophotometer in lambda(max) = 538 and 525 nm, respectively. The results showed the order of Pt/TiO2 > TiO2 > ZnO > ZnS for photocatalytic activity. In addition increasing of the Pt-loading was found to enhance the degradation rate of the compounds up to the optimal amount of 5 wt. % onto the surface of TiO2 so that the rates of degradation were increased about two times. Rate constants for photodegradation of benzylamine and aniline were found to be 1.4 x 10(-3) min(-1) and 0.7 x 10(-3) min(-1) for TiO2 as photocatalyst, while 2.7 x 10(-3) min(-1) and 1.7 x 10(-3) min(-1) for (5 wt.%) Pt/TiO2 as photocatalyst. Running the reactions in various pH (5-11), indicated that the pH = 8 and 10 or Higher are the optimum pH for photocatalytic degradation of benzylamine and aniline respectively. The effects of some other parameters such as amount of photocatalyst, flux of oxygen and irradiation time were evaluated. Furthermore, the Langmuir-Hinshelwood rate constant k(r) and adsorption constant K(A) for the titled compounds are reported.     

Di(9-alkylcarbazol-3-yl)arylamines as Electroactive Amorphous Materials for Optoelectronics

Summary. Star-shaped molecules of di(9-alkylcarbazol-3-yl)arylamines were synthesized and found to constitute new glass-forming materials with glass transition temperatures ranging from 40 to 147°C. The electron photoemission spectra of the molecular glasses were recorded and ionisation potentials of 4.9–5.0 eV were established. Room temperature time of flight hole drift mobilities of the di(9-alkylcarbazol-3-yl)phenylamines molecularly dispersed in polycarbonate-Z approached 5 · 10⁻⁶ cm²/Vs at high electric fields. Some of the compounds were converted to cross-linkable derivatives, which are potential components for insoluble charge transport layers.     

Characterization of ion exchange stationary phases via pH transition profiles

New non-destructive method for characterization of ion exchange chromatographic columns based on transient pH formed by a step change in ionic strength of buffer solutions was examined. The method was used to distinguish between cation and anion or weak and strong ion exchange chromatographic supports and to determine the capacity of the chromatographic resins. The general scheme to distinguish between most commonly used types of ion exchange chromatographic columns was proposed. The duration of pH transient was shown to be linearly proportional to the total ionic capacity and was used to estimate protein dynamic binding capacity of the resin. The effects of pH, concentration and temperature on transient pH duration were examined.     

Adsorptive stripping voltammetry of selected cephalosporin antibiotics and their direct determination in urine

Accumulation of selected cephalosporin antibiotics cefazolin, cefotaxime, cefuroxime and ceftriaxone on hanging mercury drop electrode was studied. The effects of supporting electrolyte composition, pH, accumulation potential and time were examined and corresponding analytical parameters were established employing linear sweep (staircase) or differential pulse voltammetric detection. Britton-Robinson buffer of pH 4.0 for ceftriaxone and acetate buffer in the pH range 3.6–5.0 for the other three compounds were found to be the best media. Calibration curves were linear from micromolar down to nanomolar range with limits of detection 2 × 10^–9 moll^–1, 1 × 10^–9 moll^–1, 5 × 10^–10 moll^–1 and 5 × 10^–9 moll^–1 for cefazolin, cefotaxime, cefuroxime and ceftriaxone respectively, applying the accumulation times of 5 to 14 min. Direct and simple determination of cefazolin as a model compound in urine was established with no other manipulation of urine sample than dilution 1 + 500 with buffer and subsequent adsorptive stripping voltammetric determination. The detection limit of the method is 7 gml^–1 (1.5 × 10^–5 moll^–1) of cefazolin in urine, and the relative standard deviation of 9 measurements was found to be 2.8% at 23 gml^–1 of cefazolin in urine. Similar values were found for other three compounds as well. These values are comparable or even better than those obtained by high performance liquid Chromatographic methods and approve the suitability of the proposed method for urine level monitoring in clinical practice and pharmacological studies.     

Upward Three-Dimensional Grid Drawings of Graphs

A three-dimensional grid drawing of a graph is a placement of the vertices at distinct points with integer coordinates, such that the straight line segments representing the edges do not cross. Our aim is to produce three-dimensional grid drawings with small bounding box volume. Our first main result is that every -vertex graph with bounded degeneracy has a three-dimensional grid drawing with volume. This is the largest known class of graphs that have such drawings. A three-dimensional grid drawing of a directed acyclic graph (dag) is upward if every arc points up in the -direction. We prove that every dag has an upward three-dimensional grid drawing with volume, which is tight for the complete dag. The previous best upper bound was . Our main result concerning upward drawings is that every -colourable dag ( constant) has an upward three-dimensional grid drawing with volume. This result matches the bound in the undirected case, and improves the best known bound from for many classes of dags, including planar, series parallel, and outerplanar. Improved bounds are also obtained for tree dags. We prove a strong relationship between upward three-dimensional grid drawings, upward track layouts, and upward queue layouts. Finally, we study upward three-dimensional grid drawings with bends in the edges.Research of Vida Dujmovi is supported by NSERC. Research of David Wood is supported by the Government of Spain grant MEC SB2003-0270 and by the projects MCYT-FEDER BFM2003-00368 and Gen. Cat 2001SGR00224.