DFT study of conjugated biheterocyclic oligomers exhibiting a very low HOMO–LUMO energy gap

Density functional theory (DFT) is applied to study the structure and electronic properties of oligomers based on bithiophene bridged by a sp² carbon substituted by a chalcogen atom (O, S, Se and Te), and their polybifurane and polybipyrrole analogues. The important reduction of the energy gap which is observed for the whole series of biheterocyclic compounds, when going down the chalcogen group, is explained on the basis of an orbital interaction analysis. Bithiophene polymers bridged by a selenium or a tellurium substituted carbon atom are expected to exhibit very low energy band gaps.     

Preparation and Evaluation of Sustained-Release Solid Dispersions of Drugs with Eudragit Polymers

Coevaporates of paracetamol and rifampicin with Eudragit polymers of different natures (anionic, cationic, and zwitterionic) were prepared. Determination of dissolution rate of these coevaporates in dissolution media simulating those of the gastrointestinal tract (GIT) revealed that the release rate of paracetamol is retarded from all the coevaporates studied. In this respect, Eudragit L100-SS shows the highest sustainment of drug release, while Eudragit E100 shows the lowest. Conversely, the release of rifampicin from its coevaporates with the anionic Eudragit S100 polymer is more retarded than the corresponding coevaporate with the zwitterionic Eudragit RL100 or from coevaporates with equal mixtures of the two polymers.

Increasing the polymer weight fraction in rifampicin coevaporates with Eudragit S100 up to 0.5 resulted in a corresponding decrease in the dissolution rate. However, beyond this weight fraction, the polymer effect on the dissolution rate of the drug becomes minimized. The results confirmed that the process of dissolution of the two drugs from their coevaporates is a diffusion-controlled release process.

The biological performance of paracetamol coevaporates was monitored in rabbits; paracetamol level in plasma was found to follow first-order kinetics. for all the investigated paracetamol coevaporates, the peak plasma level was less than 50 μg/ml compared to a value of 60, μg/ml for the drug per se. The coevaporates of the drug with Eudragit L100-55 showed slowest rates of absorption and elimination as well as greatest half-peak and half-life times. Biological peformance of rifampicin coevaporates was assessed in human subjects receiving a single oral dose equivalent to 300 mg of the drug. The results depicted sustainment of drug release as a function of polymer weight fraction. A strict correlation was shown to exist between the total amount of drug excreted during 24 hr post dosing of the coevaporates and its in vitro dissolution rate.

The results depicted that paracetamol can be formulated in the form of a coevaporate with Eudragit L100-55 to prepare a more safe sustained-release formulation with minimal side effects, and also revealed the advantages of administration of rifampicin in the form of a coevaporate with Eudragit S100 (4:1) at a single oral dose equivalent to 600 mg of drug.     

Co-precipitation synthesis and AC conductivity of Sn0.94Zn0.04O2 nanoparticles,using impedance spectroscopy

The co-precipitation method is used for the preparation of Sn_0.94Zn_0.04O₂ nanoparticles. The formation of typical rutile-type was confirmed by X-ray diffraction studies, and it was found to be a tetragonal phase at room temperature. In addition, the complex measurement has been investigated in the temperature range 473–713 K and in the frequency range 200 Hz–5 MHz. The results have been analyzed in the complex plane formalism and suitable equivalent circuits have been proposed in different regions. The direct current conductivity shows typical Arrhenuis behavior, when observed as a function of temperature. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts function: Φ(t) = exp [(?t/τ)^β]. The near value of activation energies obtained from the analyses of modulus and conductivity data confirms that the transport is through ion hopping mechanism in the investigated materials.     

Inversion of three-stage stress-strain relation for stainless steel in tension and compression

Presented in this paper is a new stress-strain relation for stainless steel alloys that provides the stress as an explicit function of the strain. The relation is an approximate inversion of a recently proposed three-stage stress-strain relation based on a modified Ramberg-Osgood equation. The three-stage relation is a much more accurate formulation than the previous two-stage formulations and is applicable to both tensile as well as compressive stresses. The new relation is derived by making a rational function assumption on the fractional deviation of the actual stress-strain curve from an idealized linear elastic behaviour. The new expression is valid over the full range of the stress well beyond the elastic region. The validity of the inverted expression is tested over a wide range of material parameters. These tests demonstrate that, the new expression results in stress-strain curves which are both qualitatively and quantitatively in excellent agreement with the fully iterated numerical solution of the full-range stress-strain relation with a maximum error below 4%.     

Isolation of a yeast,Trichosporon cutaneum,able to use low molecular weight phenolic compounds: application to olive mill waste water treatment

This study deals with the degradation of phenolic compounds in olive oil mill waste; a highly polluting material in olive oil‐producing countries because of its abundance and the toxicity of its phenolic compound content. This investigation confirms the ability of an isolated yeast, identified as Trichosporon cutaneum, to degrade phenolic compounds extracted from olive mill waste water (OMW). The yeast was adapted to the OMW by an enrichment culture. The results of this biotransformation were a decrease in the phenolic content and hence a reduction in the phytotoxic effects of the effluent after the yeast treatment. The kinetic growth of the isolated yeast on phenol over a range of concentrations (0.3–3.0 g dm^?3) was studied. The ability of the strain to assimilate simple monomeric phenols and alkyl phenols, at a concentration of 1 g dm^?3, in a synthetic liquid medium used as the sole carbon source was investigated in a batch culture. The aromatic ring cleavage pathway occurred in the yeast through catechol oxidation. Using various concentrations of ethyl acetate extract from OMW as the sole carbon source, the yeast exhibited growth on the substrate up to 7 g dm^?3 equivalent of phenols. A significant reduction of COD after the treatment of the OMW extract by the yeast isolate was noticed. The removal of phenol and COD exceeded 80% of the original loading after 8 days of treatment, for extracts containing initial COD in the range 19 to 72 g dm^?3. Copyright © 2004 Society of Chemical Industry     

Study of the freezing temperature of benzoic acid as a standard reference material in thermometry

Measurements of the liquidus temperature of 99.97% pure benzoic acid by using platinum resistance thermometer has been carried out. The average value is found to be 122.358 ± 0.005°C. A laboratory technique for the purification of benzoic acid to be used as a standard reference material for thermometric and calorimetric work is also described.     

Comparative clinical pharmacology of rocuronium, cisatracurium, and their combination

BACKGROUND: The comparative clinical pharmacology of cisatracurium and rocuronium and their combinations has not been reported. In this study, the authors compared the relative potency and the clinical profile and characterized the interaction of both drugs. METHODS: Two hundred twenty adults classified as American Society of Anesthesiologists physical status I and anesthetized with propofol-fentanyl-nitrous oxide were studied. In part 1, the neuromuscular-blocking effects of cisatracurium and rocuronium were assessed after administration of bolus doses of 20-50 microg/kg and 100-300 microg/kg, respectively. In part 2, we compared the time course of 1xED50, 1, 1.5, and 2xED95 doses of both drugs (where ED50 and ED95 are, respectively, the doses producing 50% and 95% depression of the first twitch height [T1]). In part 3, equieffective combinations of both drugs were studied to characterize their interaction. RESULTS: The calculated ED50 values and their 95% confidence intervals were 111 (107-115) and 26.2 (25.8-26.5) microg/kg [corrected] for rocuronium and cisatracurium, respectively. Compared with equipotent doses of cisatracurium, rocuronium had a faster onset, and a faster spontaneous T1 and train-of-four recovery times that were significant except at maximum recovery with the 2xED95 dose. The interaction between rocuronium and cisatracurium was synergistic, and the time profile of the combination group was different from that of the single-dose groups. CONCLUSIONS: Cisatracurium is four to five times more potent than rocuronium. Rocuronium had a faster onset of action, a shorter clinical duration, and a faster spontaneous recovery rate compared with equipotent doses of cisatracurium.     

A low-dispersion 3-D second-order in time fourth-order in space FDTD scheme (M3d/sub 24/)

A second-order in time fourth-order in space modified finite-difference time-domain (FDTD) scheme for three dimensional electromagnetic problems "M3d/sub 24/" is presented. The algorithm enables the numerical phase error to be minimized, so that it leads to high accuracy with low resolution grids. The advantage of this method is demonstrated by considering the long distance propagation of the wave radiated from a time harmonic elementary dipole using a low resolution grid, and comparing the results with other FDTD schemes.     

Laparoscopy for the impalpable testes. Initial experience of one center

Endoscopic treatment of acute pancreatitis has been proposed in different conditions: acute biliary pancreatitis, pancreatitis related to pancreas divisum or in case of pseudocysts. The efficacy of such endoscopic procedure is discussed.