Spektroskopische Untersuchungen der Metallkomplexe des 2,5-Dibenzoyl-3,4-dihydroxyselenophens

Zusammenfassung Eine Reihe von Metallkomplexen des 2,5-Dibenzoyl-3,4-dihydroxy-selenophens wurden spektroskopisch untersucht. Das Verhalten des Wismutkomplexes und die Möglichkeiten einer spektrophotometrischen Wismutbestimmung auf diesem Wege wurden eingehend studiert.

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Summary A spectroscopic examination was made of a series of metal complexes of 2,5-dibenzoyl-3,4-dihydroxyselenophen. The behavior of the bismuth complex and the possibilities of a spectrophotometric method of determining bismuth in this manner were studied thoroughly.

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Herrn Univ.-Prof. Dr.Hans Lieb zum 80. Geburtstag gewidmet.     

Underwater sediment analyses by laser induced breakdown spectroscopy and calibration procedure for fluctuating plasma parameters

Laser Induced Breakdown Spectroscopy (LIBS) was applied on sediments directly under water. The aim of the research was to develop a method for measuring the sediment elemental composition, including minor elements, which could be implemented in-situ. The plasma was generated by a double-pulse, Q-Switched Nd:YAG laser operated at 1064 nm. For signal detection, both ICCD and non-gated, compact detectors were used. The major difficulties in underwater sediment analyses are related to the natural and laser induced surface roughness, and to the sample softness. The latter is responsible for the formation of particle clouds above the surface, which scatter both the laser and plasma radiation, and often results in breakdown formation above the analyzed surface. In such cases, a broad sonoluminescence emission from water, formed during the gas bubble collapse was sometimes registered. Under optimized experimental conditions, even by using a non-gated detector and single shot acquisition, it was possible to detect several minor sediment constituents, such as titanium, barium, manganese and others. A crude estimation of the Limit of Detection (LODs) for these elements was performed by underwater measurements on certified soils/sediments. Due to strong shot-to-shot fluctuations in the plasma temperature, well correlated calibration curves, aimed for quantitative analyses, could only be obtained after applying an appropriate data processing procedure. The latter selects automatically only the spectra characterized by similar plasma parameters, which are related to their continuum spectral distribution. Application of such a procedure improves the measurement accuracy also in other surroundings and on samples different from the ones analyzed here.     

Contamination level of Danube river sediments

The paper presents a survey of the contamination level of the Danube river sediments along its course, between 849 km and 1162 km, during the period 1985–1988. Sampling was performed on several locations in the seasons with extreme hydrological conditions (spring, autumn).     

Surface recombination in breakdown time delay experiments: Effect of different cathode materials

The late afterglow in nitrogen with iron electrode is studied by the breakdown time delay method, i.e., by measuring the breakdown time delay t_d as a function of the afterglow time . It is proposed that the cause of the secondary electrons initiating the breakdown is the energy of the surface recombination of nitrogen atoms on the iron electrode. The gas-phase and macrokinetic diffusive models are used to describe the experimental breakdown time delay data. By fitting the theoretical curve to the experimental data: (1) it has been confirmed that the recombination on the molybdenum glass is of the second order and the value of the surface recombination coefficient is determined at 4 mbar; (2) it has been shown that the surface recombination on the iron electrode is of the second order, and the effective recombination coefficients are determined; (3) the analytical form of the recombination coefficient as a function of the adsorption characteristics of surfaces and the pressure of the parent gas has been derived. In addition, the orders of surface recombination on the molybdenum-, aluminum-, and gold-plated electrode were determined by the same method.     

In Situ Amperometric Detection of Vesicles and Microgel Phases in an Aggregating System: Calcium Alginate

In situ amperometric characterization of an aggregating system in terms of molecular adsorption and single microparticle interactions at the electrode interface is demonstrated using a model system: alginate/Ca(II) in an aqueous electrolyte solution. Recording of chronoamperometric curves of oxygen reduction at the dropping mercury electrode is designed for detection of dip‐shaped signals of individual gel microparticles. By addition of Ca(II) decrease of alginate adsorption is accompanied by appearance of signals indicating vesicle type association of alginate molecules and microparticles of gel phase. AFM imaging provided evidence of initial stage in calcium alginate gel formation.     

Investigation of the Flavonoids in Croatian Propolis by Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Flavonoids and phenolic acids with a variety of biological activity are considered to be the main compounds in propolis–a...     

Statistical investigations of some element distributions in healthy and pathologically altered human colon mucosa

In this paper data are presented concerning the distribution of Cr, Sb, Sc, Fe, Co, and Zn in HCM, of patients with histopathologically and clinically verified findings: Healthy—N; Colitis Chronica-CCh; Colitis Ulcerosa-CU; Adenoma Tubulare-AT; Adenocarcinoma-ACa. The data are presented on the basis of the contents of elements (C_E parameter expressed in nkg/g of lyophilized HCM) obtained by INAA and calculated by computer programs, with statistical parameters (n, XBAR, XMIN-XMAX, R, V, SE and SDEV). The values of C_E parameters of elements found in all diagnostic groups (decreasing order) are also presented. The minimal \(\bar C_E \) parameters for all elements except Zn are found in diagnostic groups AT and ACa. The maximal differences of \(\bar C_E \) parameters in DS-decreasing orders are found for Sb (78.89%) and the minimal for Zn (18.89%).     

Algebraic Kekulé structures of benzenoid hydrocarbons

An algebraic Kekulé structure of a benzenoid hydrocarbon is obtained from an ordinary Kekulé structure by inscribing into each hexagon the number of pi-electrons which (according to this Kekulé structure) belong to this hexagon. We show that in the case of catafusenes, there is a one-to-one correspondence between ordinary and algebraic Kekulé structures. On the other hand, in the case of perifusenes, one algebraic Kekulé structure may correspond to several ordinary Kekulé structures.     

Determination of Lercanidipine Hydrochloride and Its Impurities in Tablets

The reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed for determination of lercanidipine hydrochloride and its synthetic impurities, degradation and oxidative products in Carmen^® tablets. The best separation was performed on Zorbax SB C18 column, 250 x 4.6 mm, particle size 5 m. Acetonitrile-water-triethylamine 55:44.8:0.2 (v/v/v) was used as a mobile phase with flow rate 1 mL min^–1. pH was adjusted to 3.0 with orthophosphoric acid. UV detection was performed at 240 nm. Duration of chromatographic run was about 12 min for six examined compounds. The chromatographic conditions for the determination of lercanidipine hydrochloride and its related substances were the same, but the concentration of lercanidipine hydrochloride was 0.03 mg mL^–1 for assay and 0.3 mg mL^–1 for related substances. The validation of the method performance characteristics (figures of merits, quality of parameters) was established to be adequate for the intended use. The evaluation of number of parameters, such as selectivity, linearity, accuracy, specificity, precision (repetability and reproducibility), sensitivity and detection and determination limits is entailed.Acknowledgements This work was supported by the Institute of Pharmacy of Serbia, Belgrade and by the Ministry for Science, Technology and Development of Serbia, Contact: 1458     

Oxygen adsorption on hydrated gold cluster anions: experiment and theory

The discovery that supported gold clusters act as highly efficient catalysts for low-temperature oxidation reactions has led to a great deal of work aimed at understanding the origins of the catalytic activity. Several studies have shown that the presence of trace moisture is required for the catalysts to function. Using near-atmospheric pressure flow reactor techniques, we have studied humidity and temperature effects on the reactivity of gas-phase gold cluster anions with O2. Near room temperature, the humid source produces abundant gold-hydroxy cluster anions, Au(N)OH(-), and these have a reversed O2 adsorption activity: Nonreactive bare gold clusters become active when in the form Au(N)OH(-), while active bare clusters are inactive when -OH is bound. The binding energies for the stable structures obtained from density functional calculations confirm fully these findings. Moreover, the theory provides evidence that electron-transfer induced by the binding of a OH group enhances the reactivity toward molecular oxygen for odd anionic gold clusters and suppresses the reactivity for the even ones. The temperature dependence of O2 addition to Au(3)OH(-) and Au(4)(-) indicates deviations from equilibrium control at temperatures below room temperature. The effects of humidity on gold cluster adsorption activity support the conclusion drawn for the mechanism of O2 adsorption on "dry" gold cluster anions and provides insight into the possible role of water in the enhanced activity of supported gold cluster catalysts.