Simultaneous Determination of Hydrocortisone and Zn-Bacitracin by Spectrophotometric Derivative and Multivariate Methods

 Four spectrophotometric methods are described and applied to resolve binary mixtures of the corticosteroid hydrocortisone and the antibacterial polypeptide Zn-Bacitracin. The simultaneous determination of the two compounds was accomplished by means of derivative methods, which were satisfactory used to determine synthetic mixtures of these compounds in different ratios and in pharmaceutical preparations (only for hydrocortisone). Direct absorption spectra of compounds were used to optimise the spectral data set performs the calibration by PLS-1, PLS-2 and PCR algorithms. These calibration models were evaluated through internal validation (prediction of compounds in its own designed training set of calibration), cross-validation (obtaining statistical parameters that show the efficiency for a calibration fit model) and external validation over synthetic and pharmaceutical mixtures. The four described procedures do not require any separation step. Precision studies were achieved over two series of ten standards for each compound showing no significant differences at 95% confidence level in the two spectrophotometric methods. The results found in commercial products were compared with those obtained by means of MEKC method and similar values were found. Correspondence: Department of Analytical Chemistry and Food Technology, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain. e-mail: JoseMaria.Lemus@uclm.es Received January 25, 2002; accepted October 22, 2002     

Test strip for determination of nitrite in water

A disposable test strip is proposed for the determination of nitrite in waters. The strip is an inert rectangular strip of polyester with a 6 mm o.d. circular, transparent and colorless film attached to its surface. This film contains the chemicals required for reaction and fixation of the dye formed, sulfanilamide, N-(1-naphthyl)ethylenediamine on Nafion. When the test strip is placed in an acidified (pH 2.0) sample solution containing nitrite a red-violet color develops; the absorbance of this is measured at 536 nm. The linear range of the method depends on the time of equilibration of the test strip with the sample solution. When the equilibration time was 45 min, the linear range was 8.9-500 microg L(-1) whereas for an equilibration time of 60 min it was 4.7-200 microg L(-1). The detection limit was 1.4 microg L(-1) for an equilibration time of 60 min. The precision of the method, expressed as RSD, was 8.8 % at 100.0 microg L(-1). The method was applied, and validated chemometrically, for the determination of nitrite in different types of water (spring, mineral, tap, well, and sea).     

Mass spectrometric study of tricarbonyl (eta(6)-phenyl methanols) of chromium(0)

A mass spectrometric study of several tricarbonyl (eta(6)-phenyl methanols) of chromium(0) was performed. Electron ionization (EI), chemical ionization (CI) and fast atom bombardment (FAB) mass spectra were acquired for each molecule, and compared in order to establish a general fragmentation pattern. The suggested pathways were investigated and confirmed by means of constant b/e linked scans and high resolution data. In addition a Hammett-McLafferty correlation for some peaks derived from the molecular ions was accomplished.     

Effect of Chitosan and Temperature on Spore Germination of Aspergillus niger

Inhibition of radial growth and spore germination of Aspergillus niger in media with added chitosan were detected. The highest radial growth inhibition (73%) was determined at 24 h with 3 g · L^?1 of chitosan, and the percent inhibition of spore germination was 40% after 13 h of inoculation. Further, the CC₅₀, that is, the concentration at which spore germination is inhibited by 50%, was estimated by probit analysis (3.5 g · L^?1). The activation energies, E_A were estimated by an Arrhenius model in control and amended chitosan media, obtaining 35.6 and 36.6 kcal · mol^?1, respectively. These values were in the same order of magnitude because chitosan as inhibitor was more effective at low temperature (≤ 18 °C). Hence synergism of temperature and chitosan were only observed at 12 and 18 °C. Therefore, the maximal percentage of germinated spores, S_max was also affected by low temperatures in chitosan‐amended media with estimated values lower than 70% at temperatures < 37 °C whereas in control media S_max reached values close to 100%. Scanning electron micrographs showed that chitosan produced spore aggregation and morphological anomalies affecting swelling, germ tube emergence, and polarization.

Germinated spores percentages of Aspergillus niger in Czapeck media at several chitosan concentrations and 30 °C.     

Electrokinetics of concentrated suspensions of spherical colloidal particles with surface conductance, arbitrary zeta potential, and double-layer thickness in static electric fields

In this paper the electrophoretic mobility and the electrical conductivity of concentrated suspensions of spherical colloidal particles have been numerically studied under arbitrary conditions including zeta potential, particle volume fraction, double-layer thickness (overlapping of double layers is allowed), surface conductance by a dynamic Stern layer model (DSL), and ionic properties of the solution. We present an extensive set of numerical data of both the electrophoretic mobility and the electrical conductivity versus zeta potential and particle volume fraction, for different electrolyte concentrations. The treatment is based on the use of a cell model to account for hydrodynamic and electrical interactions between particles. Other theoretical approaches have also been considered for comparison. Furthermore, the study includes the possibility of adsorption and lateral motion of ions in the inner region of the double layers (DSL model), according to the theory developed by C. S. Mangelsdorf and L. R. White (J. Chem. Soc. Faraday Trans.86, 2859 (1990)). The results show that the correct limiting cases of low zeta potentials and thin double layers for dilute suspensions are fulfilled by our conductivity formula. Moreover, the presence of a DSL causes very important changes, even dramatic, on the values of both the electrophoretic mobility and the electrical conductivity for a great range of volume fractions and zeta potentials, specially when double layers of adjacent cells overlap, in comparison with the standard case (no Stern layer present). It can be concluded that in general the presence of a dynamic Stern layer causes the electrophoretic mobility to decrease and the electrical conductivity to increase in comparison with the standard case for every volume fraction, zeta potential, and double-layer thickness.     

Persistence of layer motifs in the crystal structures of [1,4-bis-(2-methoxy-2-carbonylethyl)piperazinium (2’)] chloride and [1,4-bis-(2-amidoethyl)piperazinium (2’)] perchlorate

Two structures of the closely related piperazinium salts, [1,4-bis-(2-methoxy-2-carbonylethyl)piperazinium (2+)] chloride (1) and [1,4-bis-(2-amidoethyl)piperazinium (2+)] perchlorate (2) reveal the persistence of a layer structure, interspersed with anions, held in place by N–H···Cl, C–H···O and C–H···Cl interactions in the case of 1, and N–H···O and C–H···O interactions in the case of 2. Compound 1 crystallizes in the triclinic space group P-1 with a=6.7667(6) ?, b = 6.9467(6) ?, c=9.3880(18) ?, α=105.845(9)°, β=99.896(16)°, γ=103.600(9)°, and Z=1. Compound 2 crystallizes in the monoclinic space group P2₁/c with a = 9.0930(8) ?, b=10.0525(11) ? c=10.2104(13) ?, β=114.279(9)°, and Z=2.     

Promotion of 1,3-dithiolanes using a bentonitic clay as catalyst

The reactions between 1,2-ethandithiol with several carbonylic compounds to form the corresponding 1,3-dithiolanes were performed using a natural clay as promotor. The target molecules are used as reagents to obtain fine chemicals, herbicides, fungicides, and pharmaceutical compounds among others applications. A kinetic study of camphorquinone and 1,2-ethandithiol showed a first-order dependence with 1,2-ethandithiol as well as with camphorquinone. The substrate transformation in percent was found to be dependent with the reaction time, the amount of catalyst, and the reagents concentration. © 2003 Wiley Periodicals, Inc. 15:71–76, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.10215     

A GRASP algorithm for the multi-criteria minimum spanning tree problem

This paper proposes a GRASP (Greedy Randomized Adaptive Search Procedure) algorithm for the multi-criteria minimum spanning tree problem, which is NP-hard. In this problem a vector of costs is defined for each edge of the graph and the problem is to find all Pareto optimal or efficient spanning trees (solutions). The algorithm is based on the optimization of different weighted utility functions. In each iteration, a weight vector is defined and a solution is built using a greedy randomized constructive procedure. The found solution is submitted to a local search trying to improve the value of the weighted utility function. We use a drop-and-add neighborhood where the spanning trees are represented by Prufer numbers. In order to find a variety of efficient solutions, we use different weight vectors, which are distributed uniformly on the Pareto frontier. The proposed algorithm is tested on problems with r=2 and 3 criteria. For non-complete graphs with n=10, 20 and 30 nodes, the performance of the algorithm is tested against a complete enumeration. For complete graphs with n=20, 30 and 50 nodes the performance of the algorithm is tested using two types of weighted utility functions. The algorithm is also compared with the multi-criteria version of the Kruskal’s algorithm, which generates supported efficient solutions. This work was funded by the Municipal Town Hall of Campos dos Goytacazes city. The used computer was acquired with resource of CNPq.     

A partial enumeration heuristic for multi-objective flowshop scheduling problems

This paper addresses the flowshop scheduling problem with multiple performance objectives in such a way as to provide the decision maker with approximate Pareto optimal solutions. It is well known that the partial enumeration constructive heuristic NEH and its adaptations perform well for single objectives such as makespan, total tardiness and flowtime. In this paper, we develop a similar heuristic using the concept of Pareto dominance when comparing partial and complete schedules. The heuristic is tested on problems involving combinations of the above criteria. For the two-machine case, and the pairs of objectives: (i) makespan and maximum tardiness, (ii) makespan and total tardiness, the heuristic is compared with branch-and-bound algorithms proposed in the literature. For two and more than two machines, and the criteria combinations considered in this article, the heuristic performance is tested against constructive heuristics reported in the literature. By means of an illustrative example, it is shown that a genetic algorithm from the literature performs better when starting from heuristic solutions rather than random solutions.     

Synthesis,characterization, DNA interaction studies and anticancer activity of platinum–clotrimazole complexes

New trans-platinum complexes of clotrimazole (CTZ) have been prepared and characterized. Their interaction with DNA and activity against tumour cell lines were evaluated. [Pt (CTZ)₂I₂] (1) was synthesized by the reaction of K₂PtCl₄, KI and CTZ, and [Pt(CTZ)₂Cl₂] (2) by direct reaction of K₂PtCl₄ with CTZ. These complexes were characterized by a combination of elemental analysis, molar conductivity, UV–Vis, IR, and NMR spectroscopy in one and two dimensions. DNA–platinum complex interactions were studied by spectroscopic, thermal denaturation and viscosity titration measurements. Covalent interaction studies were also performed. From these results we suggest that complexes 1 and 2 interact with the minor groove of DNA. Both complexes showed growth inhibitory effects on four out of the six tumour cells lines with GI₅₀ (50% growth inhibition) values in the 5–25 μM range, but there was no indication of cytotoxicity over the range of concentrations tested.