A new model for the structure of chalcogenide glasses: The closed cluster model

A new model is proposed for the structure of low atomic coordination chalcogenide glasses. The closed clusters model is based on the various types of clusters, packed by van der Waals forces in a molecular-type packing. Arguments are given to support the new model, taken as example the typical chalcogenide glass As₂S₃.     

Validated method for the determination of the novel organo-ruthenium anticancer drug NAMI-A in human biological fluids by Zeeman atomic absorption spectrometry

NAMI-A is a novel ruthenium-containing experimental anticancer agent. We have developed and validated a rapid and sensitive analytical method to determine NAMI-A in human plasma, plasma ultrafiltrate and urine using atomic absorption spectrometry with Zeeman correction. The sample pretreatment procedure is straightforward, involving only dilution with an appropriate hydrochloric acid buffer-solution. Because the response signal of the spectrometer depended on the composition of the sample matrix, in particular on the amount of human plasma in the sample, all unknown samples were diluted to match the matrix composition in which the standard line was prepared (plasma-buffer 1 : 10 v/v). This procedure enabled the measurement of samples of different biological matrices in a single run. The validated range of determination was 1.1–220 μM NAMI-A for plasma and urine, and 0.22–44 μM for plasma ultrafiltrate. The lower limit of detection was 0.85 μM in plasma and urine and 0.17 μM in plasma ultrafiltrate. The lower limit of quantitation was 1.1 and 0.22 μM, respectively. The performance of the method, in terms of precision and accuracy, was according to the generally accepted criteria for validation of analytical methodologies. The applicability of the method was demonstrated in a patient who was treated in a pharmacokinetic phase I trial with intravenous NAMI-A. Received: 1 September 2000 / Revised: 1 November 2000 / Accepted: 12 November 2000     

Determination of arsenic,cadmium and zinc in river water by neutron activation analysis

A concentration apparatus has been developed for the determination of As, Cd and Zn in water by neutron activation. The preconcentration technique used for this purpose is based on the retention of As, Cd and Zn on the Rexyn 201 resin at pH 10. The apparatus used minimizes the manipulations needed for preconcentration and contamination by trace elements present in reagents. Eleven samples of water from rivers in the Montreal region were analyzed and the following concentrations were found (in μg/1): As 0.86–1.95, Cd 0.61–0.98 and Zn 4.6–12.9.     

Aromatic polyamides with pendent acetoxybenzamide groups and thin films made therefrom

New aromatic polyamides containing 1,3,4-oxadiazole or benzonitrile units in the main chain and 5-(4-acetoxybenzamido) groups in the side chain have been synthesized and their properties have been characterized and compared with those of related polyamides and polyoxadiazole-amides. These polymers show good thermal stability, with initial decomposition temperature being at about 300 °C and glass transition temperature in the range of 260-280 °C. They are easily soluble in certain solvents such as N-methylpyrrolidinone (NMP), N,N^′-dimethylacetamide (DMA) and N,N^′-dimethylformamide (DMF) and can be cast from solutions into thin flexible films. The polymer films had tensile strengths in the range of 77-97 MPa, tensile moduli in the range of 2.3-2.6 GPa and elongation at break values ranging from 6% to 24%. One of the polymers containing the 1,3,4-oxadiazole ring exhibited blue fluorescence.     

Di- and tetranuclear palladium complexes incorporating phospha- and diphosphaferrocenes as ligands

Monophosphaferrocenes and 4 react with [Pd(COD)Cl2] (COD = cyclooctadiene) to afford cis- [Pd(1 or 4)2Cl2] complexes that slowly decompose in solution to give dimeric complexes 3 and 6 of general formula [[Pd(1 or 4)Cl]2]. In these dimers, which incorporate a Pd-Pd bond, phosphaferrocenes act as four electron donors through the phosphorus-atom lone pair (mu2-bonded) and through one orbital of appropriate symmetry at iron. These dimers can also be more conventionally prepared from the reaction of cis- [Pd(1 or 4) Cl2] complexes with [Pd(dba)2] (dba = dibenzylidene acetone). The reaction of octaethyldiphosphaferrocene (7) with [Pd(COD)Cl2] yields a dinuclear complex [Pd2(7)2Cl4] (8) in which the two ligands 7 are coordinated in a trans fashion through the phosphorus-atom lone pairs. Decomposition of 8 in solution yields a dimeric dicationic complex of general formula [[Pd2(7)2Cl]2]2+[FeCl4]2- (9a) incorporating four palladium atoms. In each ligand. one phospholyl ring behaves as a two-electron donor through the phosphorus-atom lone pair whereas the second binds two palladium centers in a mu2-fashion. A plausible mechanism that explains the formation of dimers 3, 6, and 9a involves the preliminary oxidation of the mono- or diphosphaferrocene ligand. Parallel experiments aimed at confirming this hypothesis have shown that complex 9a can be synthesized from the reaction of FeCl2 with complex 8. Also presented is another synthetic approach to the synthesis of the tetranuclear complex 9b (counterion is GaCl4-) from the reaction of the palladium(0) complex [Pd(7)2] (10) with [Pd(COD)Cl2] the presence of GaCl3 as chloride abstractor.     

Modified Diatomaceous earth as a principal stationary phase component in TLC

Modified natural diatomaceous earth (DE) is a principal component of the stationary phase in normal thin-layer chromatography (TLC) applications and is mixed with commercial silica gel 60GF254 (Si-60GF254). Modification is carried out by flux calcination and refluxing with acid. Natural DE, modified DEs [flux calcinated (FC)DE and FCDE-I), and Si-60GF254 are characterized by scanning electron microscopy and Fourier-transform-IR spectroscopy. Particle size, specific surface area, pore distribution, pore volume, and surface hydroxyl group density parameters of materials are determined by various techniques. FCDE-I and Si-60GF254 are investigated for their usefulness in the stationary phase of TLC both individually and in composition. Commercially available red and blue ink samples are run on layers of Si-60GF254 and FCDE-I individually, and on various FCDE-I and Si-60GF254 mixtures. Butanol-ethanol-2M ammonia (3:1:1, v/v) and butanol-acetic acid-water (12:3:5, v/v) mixtures are used as mobile phases. The polarities of stationary phases decrease, and the retention factor (Rf) values of ink components increase when the FCDE-I content of the stationary phase increases. The properties of the stationary phase can be optimized by adding FCDE-I to Si-60GF254. This study may be useful in understanding both the systematic effects of stationary phase properties [e.g., specific surface area and surface hydroxyl group density, aOH(s)] and those of the mobile phase (e.g., polarity and acidity) on Rf values and the separability of components.     

On the copolymerization model and microstructure of methyl acrylate - styrene radical copolymer. Influence of ZnCl2

Bulk radical copolymerization of methyl acrylate (MeA, M₁) with styrene (St, M₂) in presence and absence of ZnCl₂ as complexing agent was studied. ¹H-NMR spectra were used to establish copolymer composition and sequence distribution. The methoxy group signal was observed to be split due to pentads, but the analysis of sequence distribution is possible only at triad level. Both composition and sequence distribution data confirmed that bulk radical copolymerization respects quite well the terminal addition model; the values of r₁ = 0.14 ± 0.02 (from composition data) and r₁ = 0.25 ± 0.03 (from sequence distribution data) and r₂ = 0.83 ± 0.10 (from composition data) were found. The presence of ZnCl₂ increases the probability of alternating addition, e.g., for [ZnCl₂]/[MeA] = 0.2, r₁ = 0.03 ± 0.02 and r₂ = 0.17 ± 0.03. The radical copolymer obtained in bulk in the absence of ZnCl₂ presents a coisotactic configuration with σ = 0.75 ± 0.03, but the presence of the complexing agent reduces the probability of coisotactic addition, e.g., for [ZnCl₂]/[MeA] = 0.2, σ = 0.52 ± 0.03.     

Quasi-power increasing sequence for generalized absolute summability

In this paper, we prove a theorem given in [E. Sava?, On almost increasing sequences for generalized absolute summability, Math. Inequal. Appl., Preprint] on summability factors under weaker conditions by using a quasi-β$\beta$-power increasing sequence instead of an almost increasing sequence.     

On generalized absolute summability factors

In this paper, a general theorem on _|A,δ|k${|A,\delta |}_k$-summability factors which generalize a theorem of Sava? [E. Sava?, On a recent result on absolute summability factors, Appl. Math. Lett. 18 (2005) 1273–1280] on _|A|k${\left|A\right|}_k$-summability factors has been proved.