A Simple,Cost‐effective,and Environmentally Friendly Method for Determination of Ciprofloxacin in Drugs and Urine Samples Based on Electrogenerated Chemiluminescence

Ciprofloxacin is an antibiotic that belongs to the class of drugs known as quinolones and it is frequently used to treat a variety of bacterial infections. The present work aims the development of a simple, cost‐effective, and environmentally friendly method for the determination of ciprofloxacin in drugs and artificial urine samples due to the high importance of this antibiotic for the human health. The proposed method is based on the electrogenerated chemiluminescence (ECL) resulting from the reaction between the ciprofloxacin and the tris(2,2′‐bipyridyl)ruthenium(II) complex. This method exploits a screen‐printed carbon electrode positioned in an ECL cell with capacity to 50 μL of electrolytic solution. The ECL intensity was monitored with the aid of a photodiode. The ECL signal was simultaneously registered to the voltammetric measurements. Under optimized experimental conditions, the ECL method presented a linear response range for ciprofloxacin between 0.5 and 500 μmol L^?1 (or 0.0005 and 0.5 mmol L^?1). The proposed method presented a detection limit of 0.5 μmol L^?1 and it was successfully applied for the ciprofloxacin determination in drugs and artificial urine samples, with good accuracy and precision.     

Determination of molybdenum in silicates by flame atomic absorption spectrometry exploiting activated carbon as collector

An analytical procedure has been developed for molybdenum determination in geological silicate materials using flame atomic absorption spectrometry (injection method), after sorption of the molybdenum-ammonium pyrrolidinedithiocarbamate complex (MoAPDC) on activated carbon.     

Determination of Trace Elements in Carbonaceous Samples by Graphite Furnace Atomic Absorption Spectrometry: Microwave Digestion Versus Slurry Sampling

 The determination of chromium, copper, manganese, nickel and vanadium in carbonaceous samples by slurry introduction graphite furnace atomic absorption spectrometry and after microwave assisted digestion are compared. Parameters such as atomization and pyrolysis temperatures, and surfactant concentration as well as the homogenization procedure were optimized. The slurries were prepared by mixing adequate amounts of the pulverized samples with 0.05% Triton X-100, sonicating for, at least, 40 seconds during the preparation to separate aggregates and for 20 seconds immediately before being autosampled. It was not necessary to use modifiers and calibration against aqueous standards was possible for all the elements. Coke, graphite and certified coal samples were analyzed, and no significant difference was observed using both procedures. Good agreement between found and certified values was obtained. Received January 24, 2000. Revision September 26, 2000.     

Ethylene polymerization and copolymerization with 10‐undecen‐1‐ol using the catalyst system DADNi(NCS)2/MAO

The catalyst DADNi(NCS)₂ (DAD = (ArN?C(Me)? C(Me)?ArN); Ar = 2,6‐C₆H₃), activated by methylaluminoxane, was tested in ethylene polymerization at temperatures above 25 °C and variable Al/Ni ratio. The system was shown to be active even at 80 °C and when supported on silica. However, catalyst activity decreased. The catalyst system was also tested in ethylene and 10‐undecen‐1‐ol copolymerization at different ethylene pressures. The best activities were obtained at low polar monomer concentration (0.017 mol/L), using triisopropylaluminum (Al‐i‐Pr₃) to protect the polar monomer. The incorporation of the comonomer increased with the increase of polar monomer concentration. According to ¹³C NMR analyses, all the resulting polyethylenes were highly branched and the polar monomer incorporation decreased as ethylene pressure increased. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5199–5208, 2007     

Differential equations in spaces of compact operators

We study a system of differential equations in C(H), the space of all compact operators on a separable complex Hilbert space, H. The systems considered are infinite-dimensional generalizations of mathematical models of learning, implementable as artificial neural networks. In this new setting, in addition to the usual questions of existence and uniqueness of solutions, we discuss issues which are operator theoretic in nature. Under some restrictions on the initial condition, we explicitly solve the system and represent the solution in terms of the spectral representation of the initial condition. We also discuss the stability of those solutions, and describe the weak, strong, and uniform limit sets in terms of their respective spectral properties.     

Mathematical modeling of lipase and protease production by Penicillium restrictum in a batch fermenter

This work presents a mathematical model that describes time course variations of extracellular lipase and protease activities for the batch fermentation of the fungus Penicillium restrictum, a new and promising strain isolated from soil and wastes of a Brazilian babassu coconutoil industry. The fermentation process was modeled by an unstructured model, which considered the following dependent variables: cells, fat acid, dissolved oxygen concentrations, lipase and protease activities, and cell lysate concentration. The last variable represents the amount of cells that has been lysed by the shear stress and natural cell death. Proteases released to the medium, as consequence of this process, enhance lipase inactivation. The model is able to predict the effects of some operation variables such as air flow rate and agitation speed. The mathematical model was validated against batch-fermentation data obtained under several operating conditions. Because substrate concentration has antagonistic effects on lipase activity, a typical optimization scheme should be developed in order to minimize these deleterious effects while maximizing lipase activity.     

Propylene polymerization with nickel–diimine complexes containing pseudohalides

DADNiX₂ nickel–diimine complexes [DAD = 2,6‐iPr₂? C₆H₃? N?C(Me)? C(Me)?N? 2,6‐iPr₂? C₆H₃] containing nonchelating pseudohalide ligands [X = isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2 ] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X = Br for complex 3 ) activated by methylaluminoxane (MAO) were investigated (systems 1 , 2 , and 3 /MAO). The polypropylenes obtained with systems 1 , 2 , and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni = 500, unlike system 3 . Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene–ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of propylene sequences, and system 3 presented the lowest. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 458–466, 2006     

Tin(IV) complexes of 2‐benzoylpyridine N(4)‐phenyl‐thiosemicarbazone: spectral characterization,structural studies and antifungal activity

Three tin(IV) complexes of 2‐benzoylpyridine N(4)‐phenylthiosemicarbazone (H2Bz4Ph) were prepared: [Sn(L)Cl₃] (1), [BuSn(L)Cl₂] (2) and [(Bu)₂Sn(L)Cl] (3), in which L stands for the anionic ligand formed upon complexation with deprotonation and release of HCl. The complexes were characterized by a number of spectroscopic techniques. The crystal structures of H2Bz4Ph and complex 3 were determined. The antifungal activity of the ligand and its tin(IV) complexes was tested against Candida albicans. The thiosemicarbazone proved to be more active than the tin(IV) complexes. Copyright © 2003 John Wiley & Sons, Ltd.     

Diffusion on complex cellular automata patterns

We studied random walks on two-dimensional patterns formed by the sequence of configurations of complex elementary cellular automata (CA) with random initial configurations. The walkers are allowed to jump between nearest neighbours or next nearest neighbours 1 sites. On patterns of rules 22, 54, 90, 122, 126, 150 and 182, the diffusion is normal (ν=1/2). On patterns 18 and 146 the diffusion is anomalous, with ν=0.415±0.005, and the spectral dimension is D_s=1.25±0.1. From the analysis of the diffusion in the horizontal and vertical directions (space and time directions of the CA problem, respectively) of patterns 18 and 146, we obtained ν_x≈0.22 and ν_y≈0.42, because they have branches of 1 sites which are long in the vertical direction but narrow in the horizontal direction. Due to the anisotropic diffusion, the results do not satisfy the relation D_s=2D_F/D_w, with D_w=1/ν and fractal dimension D_F=2. Considering that the fractal dimension of the region visited by the walker is equal to the dimension of the substrate (D_F), we suggest the new scaling relation D_s=2(ν_x+ν_y). This relation is supported by our numerical results and may be generalized to other structures with anisotropic diffusion.     

Exciton dissociation and charge carrier recombination processes in organic semiconductors

Exciton dissociation and charge recombination processes in organic semiconductors, with thermal effects taken into account, are described in this paper. Here, we analyzed the mechanisms of polaron-excitons dissociation into free charge carriers and the consequent recombination of those carriers under thermal effects on two parallel π-conjugated polymers chains electronically coupled. Our results suggest that exciton dissociation in a single molecule give rise to localized, polaron-like charge carrier. Besides, we concluded that in the case of interchain processes, the bimolecular polaron recombination does not lead to an usual exciton state. Rather, this type of recombination leads to an oscillating dipole between the two chains. The recombination time obtained here for these processes are in agreement with the experimental results. Finally, our results show that temperature effects are essential to the relaxation process leading to polaron formation in a single chain, as in the absence of temperature, this process was not observed. In the case of two chains, we conclude that temperature effects also help the bimolecular recombination process, as observed experimentally.