Improved capillary electrophoretic separation of nine (fluoro)quinolones with fluorescence detection for biological and environmental samples

A capillary electrophoretic method has been developed for the separation of nine (fluoro)quinolones. Detection is done by fluorescence measurement with broad wavelength band excitation between 240 and 400 nm. Best separation is achieved in a carrier electrolyte containing 50 mM H3PO4 adjusted to pH 7.55-acetonitrile (60:40, v/v). Detection limits are in the low microgl(-1) range. The suitability to real samples has been demonstrated by analyzing blood samples and surface water samples. Sample preconcentration and sample clean-up can easily be done by solid-phase extraction. Different phases based on alkyl- or phenyl-modified silica as well as on polymers have been investigated for this purpose. The method should also be useful for determination of residues of (fluoro)quinolones in food or other matrices.     

Preparation of thermosensitive nanogels by photo-cross-linking

 A novel method to prepare thermosensitive nanogels from photocross-linkable copolymers of N-isopropylacrylamide and dimethyl maleinimido acrylamide (DMIAAm) was developed. The colloidal nanogels were formed by UV irradiation of solutions of thermosensitive polymers in water at 45 °C. The compositions of the photopolymer solutions were varied by changing the amount of DMIAAm in the photopolymer chains (2–10 mol%) or by varying the sodium dodecyl sulfate (SDS) concentration. The resultant nanogel particles were rather spherical and showed large changes in hydrodynamic diameters in the vicinity of the phase transition temperature of the corresponding linear photopolymers. The particle sizes of the nanogels and their swellability could be controlled through the UV irradiation time, the chromophore content and the SDS concentration. An increase in the chromophore content and the SDS concentration resulted in nanogels with smaller dimensions. The hydrodynamic diameters of the nanogels decreased significantly from 2 to 10 min UV irradiation time but not significantly after that. The phase transition of the photopolymer solutions and the respective nanogels could be adjusted by the chromophore content or the SDS concentration. An increase in the chromophore content leads to lower phase-transition temperatures, whilst an increase in the SDS concentration elevated them. Pulsed-field-gradient NMR proved a useful tool to investigate the network formation in the nanogels by determining changes in the diffusion coefficients. Received: 14 May 2001 Accepted: 1 June 2001     

Crystal and molecular structure of the symmetrical bidentate ligand 3,3-di(1-pyrazolyl)pentane, CH3CH2C(C3H3N2)2CH2CH3

The title compound crystallizes in the centrosymmetric space group C2/c with a = 14.4005(23), b = 7.0494(12), c = 11.2462(20) Å, = 101.572(13)° and Z = 4; the molecule lies on a crystallographic C ₂ axis. Hydrogen atoms were both located and refined.     

Basics of temperature pulse voltammetry

A new electrochemical technique is presented that allows peak-shaped voltammograms to be recorded at local temperature values from room temperature to above boiling point. This new method, temperature pulse voltammetry (TPV), is analogous to differential pulse voltammetry (DPV), but makes use of temperature jumps instead of potential pulses. Fundamentals are presented and potentialities demonstrated. As an example, ferrocyanide is investigated using a new kind of heated electrode on the basis of screen-printed gold layer structures on low-temperature cofired ceramics (LTCC) substrates. Received: 12 January 2000 / Revised: 9 March 2000 / Accepted: 13 March 2000     

Dynamic tabu list management using the reverse elimination method

Tabu search is a metastrategy for guiding known heuristics to overcome local optimality. Successful applications of this kind of metaheuristic to a great variety of problems have been reported in the literature. However, up to now mainly static tabu list management ideas have been applied. In this paper we describe a dynamic strategy, the reverse elimination method, and give directions on improving its computational effort. The impact of the method will be shown with respect to a multiconstraint version of the zero-one knapsack problem. Numerical results are presented comparing it with a simulated annealing approach.     

Experiments concerning sequential versus simultaneous maximization of objective function and distance

Suppose two solution vectors are needed that have good objective function values and are different from each other. The following question has not yet been systematically researched: Should the two vectors be generated sequentially or simultaneously? We provide evidence that for broad ranges of practically achievable distances, sequential generation usually requires less computational effort and produces solutions that are at least as good as produced by simultaneous generation. This is done using experiments based on publicly available instances of the multi-constrained, zero-one knapsack problem, which are corroborated using experiments conducted with the linear assignment problem.     

Dynamical heterogeneity and diffusion in high-density Al2O3·2SiO2 melts

Dynamical heterogeneity (DH) in high-density Al₂O₃·2SiO₂ melts has been studied in a model containing 3025 atoms via molecular dynamics (MD) simulation and at the fixed density of 4.0 g/cm³. Non-Gaussian parameter of atomic species in the system has been found and discussed. We found a clear evidence of the existence of DH in high-density Al₂O₃·2SiO₂, which has specific features differed from those observed in the lower-density one. The most mobile and immobile atoms in the system have a tendency to form clusters and temperature dependence of their mean cluster size was found. On the other hand, diffusion constant of atomic species in the system has been calculated at temperatures ranged from 3150 to 7000 K. Calculations show that at relatively not high temperatures, temperature dependence of diffusion constant shows an Arrhenius law and at higher temperatures it shows a power law: D∝(T−T_C)^γ. Diffusion data of high-density melts have been compared with those for the low-density ones. Diffusion mechanism in the system has been discussed via the temperature dependence of diffusion constant ratio and activation energy. And we found the existence of cooperative diffusion mechanism in the system.     

Содержания работ, выш едших толъко в чешско м издании настояшего ж урнала (Československý časopis pro fysiku)

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Abstracts of papers which have appeared only in the czech edition of this journal (eskoslovenský asopis pro fysiku)