On the Reaction of Dithioarsonites,L‐As(SPh)2 (L = Ar,R), with Octasulfur in the Presence of Triethylamine as an Activator. The Crystal Structure of the Sesquisulfide (2‐O2N‐C6H4‐As)2S3

Octasulfur (elemental sulfur) does not react at room temperature with a variety of As^III compounds of the type Ar‐As(SPh)₂ and R‐As(SPh)₂. However, in the presence of catalytic amounts of triethylamine, which probably acts as an activator of octasulfur, reactions do take place. The products isolated from the aromatic dithioarsonites are not the expected Ar‐As(S)(SPh)₂ but the sulfide, cyclo‐(PhAsS)₄, and the sesquisulfides, (ArAs)₂S₃, which are the same with those obtained by reduction of arylarsonic acids with hydrogen sulfide. The action of S₈/Et₃N on aliphatic dithioarsonites did not give any As^V products but gave mixtures of non‐separable oligomeric (RAsS)_x. Probable mechanistic routes for these reactions are proposed. The known cyclo‐(PhAsS)₄ and (PhAs)₂S₃ and the new (2‐O₂N‐C₆H₄‐As)₂S₃ have been structurally characterized: (2‐O₂N‐C₆H₄‐As)₂S₃, monoclinic, C2/c, a = 13.564(9)Å, b = 7.982(6)Å, c = 16.67(1)Å, β = 117.63(2)°, V = 1599(2)ų, Z = 4, wR2 0.0640. The 1, 4‐diarsa‐2, 3, 5‐trithiacyclopentane ring is puckered and the two As^III atoms are pseudo tetrahedral.     

Spectrofluorimetric determination of anthranilic acid derivatives based on terbium sensitized fluorescence.

Terbium sensitized fluorescence was used to develop a sensitive and simple spectrofluorimetric method for the determination of the anthranilic acid derivatives furosemide and mefenamic and tolfenamic acids. The method makes use of radiative energy transfer from anthranilates to terbium ions in alkaline methanolic solutions. Optimum conditions for the formation of the anthranilate-Tb3+ complexes were investigated. Under optimized conditions, the detection limits are 6 x 10(-9), 1.4 x 10(-8) and 9.0 x 10(-9) mol l-1 for furosemide, mefenamic acids and tolfenamic acid, respectively. The range of application is 2.5 x 10(-8)-5.0 x 10(-5) mol l-1 for all three drugs. The method was successfully applied to the determination of furosemide and mefenamic and tolfenamic acids in serum after extraction of the samples with ethyl acetate, evaporation of the organic layer under a stream of nitrogen at 40 degrees C and reconstitution of the residue with alkaline methanolic terbium solution prior to instrumental measurement. The mean recoveries from serum samples spiked with furosemide (5.0 x 10(-7), 2.0 x 10(-6) and 8.0 x 10(-6) mol l-1), mefenamic acid (3.0 x 10(-6), 9.0 x 10(-6) and 3.0 x 10(-5) mol l-1) and tolfenamic acid (3.1 x 10(-6), 12.5 x 10(-6) and 2.5 x 10(-5) mol l-1) were 96 +/- 8, 101 +/- 5 and 98 +/- 7%, respectively. The within-run precision (RSD) for the method for two serum samples of each drug varied from 2 to 8% and the day-to-day precision for two concentration levels varied from 2 to 13%.     

Advances in molecular techniques for the detection and quantification of genetically modified organisms

Progress in genetic engineering has led to the introduction of genetically modified organisms (GMOs) whose genomes have been altered by the integration of a novel sequence conferring a new trait. To allow consumers an informed choice, many countries require food products to be labeled if the GMO content exceeds a certain threshold. Consequently, the development of analytical methods for GMO screening and quantification is of great interest. Exponential amplification by the polymerase chain reaction (PCR) remains a central step in molecular methods of GMO detection and quantification. In order to meet the challenge posed by the continuously increasing number of GMOs, various multiplex assays have been developed for the simultaneous amplification and/or detection of several GMOs. Classical agarose gel electrophoresis is being replaced by capillary electrophoresis (CE) systems, including CE chips, for the rapid and automatable separation of amplified fragments. Microtiter well-based hybridization assays allow high-throughput analysis of many samples in a single plate. Microarrays have been introduced in GMO screening as a technique for the simultaneous multianalyte detection of amplified sequences. Various types of biosensors, including surface plasmon resonance sensors, quartz crystal microbalance piezoelectric sensors, thin-film optical sensors, dry-reagent dipstick-type sensors and electrochemical sensors were introduced in GMO screening because they offer simplicity and lower cost. GMO quantification is performed by real-time PCR (rt-QPCR) and competitive PCR. New endogenous reference genes have been validated. rt-QPCR is the most widely used approach. Multiplexing is another trend in this field. Strategies for high-throughput multiplex competitive quantitative PCR have been reported.     

Nucleus shape at the scission point at different kinetic energies of fission fragments

Deformations of fission fragments at fixed kinetic energies of a light fragment have been calculated within the droplet model. The calculations performed demonstrate the existence of a spherical shape with A ₁ = 76 and A _h = 134 (β₁, β_h ≈ 0). Fragments with A ₁ < 76 and A _h < 130 pass from the spherical to flattened shape. Fragments with A _h < 126 again acquire an elongated shape.     

Dolastanes from the brown alga Dilophus spiralis: absolute stereochemistry and evaluation of cytotoxicity

Five new dolastanes (1-5) were isolated from the brown alga Dilophus spiralis. The structural elucidation of the isolated compounds and the assignment of relative stereochemistry were based on analyses of their spectroscopic data. The structure proposed for 1 was confirmed by single crystal X-ray diffraction analysis, whereas its absolute stereochemistry was determined using the modified Mosher's method. The cytotoxicity of 1-4 was evaluated against seven cell lines.     

Characterization of LaBr<Subscript>3</Subscript>: Ce and LaCl<Subscript>3</Subscript>: Ce scintillators for gamma-ray spectroscopy

This study aims to investigate the performance of relatively new cerium-doped scintillators, LaCl₃ and LaBr₃, for gamma-ray spectroscopy. The study involved recording of detected spectra and measurement of energy resolution, as well as photo-fraction. The Monte Carlo package, GATE, was used to validate the experiments. In general, the energy resolution figures achieved were twice as good as that of NaI(Tl). In conclusion, LaBr₃: Ce and LaCl₃: Ce crystals have excellent energy resolution, (2.13±0.03)% and (2.92±0.04)% at 1332 keV, respectively, and comparable photo-fraction to NaI(Tl). Hence, these crystals, particularly LaBr₃: Ce, have the potential to replace NaI(Tl) as the scintillator of choice for γ-ray spectroscopy.     

A greedy look-ahead heuristic for the vehicle routing problem with time windows

In this paper we consider the problem of physically distributing finished goods from a central facility to geographically dispersed customers, which pose daily demands for items produced in the facility and act as sales points for consumers. The management of the facility is responsible for satisfying all demand, and promises deliveries to the customers within fixed time intervals that represent the earliest and latest times during the day that a delivery can take place. We formulate a comprehensive mathematical model to capture all aspects of the problem, and incorporate in the model all critical practical concerns such as vehicle capacity, delivery time intervals and all relevant costs. The model, which is a case of the vehicle routing problem with time windows, is solved using a new heuristic technique. Our solution method, which is based upon Atkinson's greedy look-ahead heuristic, enhances traditional vehicle routing approaches, and provides surprisingly good performance results with respect to a set of standard test problems from the literature. The approach is used to determine the vehicle fleet size and the daily route of each vehicle in an industrial example from the food industry. This actual problem, with approximately two thousand customers, is presented and solved by our heuristic, using an interface to a Geographical Information System to determine inter-customer and depot–customer distances. The results indicate that the method is well suited for determining the required number of vehicles and the delivery schedules on a daily basis, in real life applications.     

Syntheses of arsinolipids: non‐isosteric analogues of phospholipids

Reaction of alkaline benzenearsonous and 2,3‐dihydroxypropylarsonous acids with rac‐glycidol affords the corresponding arsinic acids, which after reduction with thiophenol are acylated with either fatty‐acid chlorides/pyridine or fatty acids/dicyclohexylcarbodiimide/4‐dimethylaminopyridine and oxidized with hydrogen peroxide to give the arsinolipids (rac‐2,3‐diacyloxypropyl)phenylarsinic and bis‐(rac‐2,3‐diacyloxypropyl)arsinic acids. The latter is a non‐isosteric analogue of bisphosphatidic acid. Copyright © 2000 John Wiley & Sons, Ltd.     

On the direct reduction of arsonic acids to arsenoso compounds: mechanisms and preparations†

By using a variety of reducing agents, either alone or in the presence of iodide as a catalyst, the reduction of arsonic acids to arsenoso compounds and/or arsonous acids has been studied. The solvent and temperature are important for a clean reduction. The mechanism of the reduction involves prior protonation of the  AsO₃H₂ group, and can be rationalized in the framework of the ‘hard and soft acids and bases’ principle, which is used to predict other reducing systems and to explain other literature data. For preparative purposes, triphenylphosphine/iodine, hexamethylphosphorous triamide/iodine and ascorbic acid/iodine give flexibility of choice depending on the substrate. The first two of these systems decompose arsonic acids with a weak C–As bond but the last system is sufficiently mild towards the same arsonic acids. Copyright © 2000 John Wiley & Sons, Ltd.