Preparation, characterization and in vitro dissolution studies of solid systems of valdecoxib with chitosan

In the present study, the solubilizing and amorphizing properties of Valdecoxib (a poorly water soluble anti inflammatory drug) with low molecular weight chitosan (a polymer), have been investigated. Binary systems of varying drug/polymer ratios were prepared using different techniques (physical mixing, co-grinding, kneading) and were tested for dissolution. Drug carrier interactions were investigated in both the liquid and solid state, by phase solubility analysis, differential scanning calorimetry, powder X-ray diffractrometry, FT-IR spectroscopy and scanning electron microscopy. The solubility of the drug increased with increasing polymer concentration showing A(N) type phase solubility diagram. Differential scanning calorimetry, powder X-ray diffractrometry and scanning electron microscopic studies of binary systems suggested generation of amorphous form of drug (in kneading and co ground mixtures). IR spectroscopy revealed the presence of hydrogen bonding in kneading and co ground mixtures. Drug dissolution was improved with increasing the polymer concentration in the mixture (Kneaded>co ground>physical mixture), which was attributed to the amorphonization and/or decreased drug crystallinity, size and polymer wetting effect. Enhanced dissolution combined with its direct compression feasibility and anti ulcerogenic action results in low molecular weight chitosan for developing fast release oral solid dosage forms of valdecoxib.     

New Potential Biocatalysts by Laccase Immobilization in PVA Cryogel Type Carrier

Laccases are enzymes belonging to the Oxidoreductases class. These enzymes may be good biocatalysts for different processes, at laboratory and industrial levels. A successful use at industrial scale demands a higher stability of the enzyme. As an easy way to obtain longer life biocatalysts, the immobilization process is recommended. Thus, the paper presents different ways of obtaining new biocatalysts by a laccase covalent immobilization on a macroporous carrier based on poly(vinyl alcohol) cryogel. Different procedures of covalent immobilization are described, the newly obtained biocatalysts being characterized. According to the experimental data, the stability of the immobilized enzyme increased and the pH profile changed, compared with those of the free enzyme.     

Dynamics and Control Strategies for a Butanol Fermentation Process

In this work, mathematical modeling was employed to assess the dynamic behavior of the flash fermentation process for the production of butanol. This process consists of three interconnected units as follows: fermentor, cell retention system (tangential microfiltration), and vacuum flash vessel (responsible for the continuous recovery of butanol from the broth). Based on the study of the dynamics of the process, suitable feedback control strategies [single input/single output (SISO) and multiple input/multiple output (MIMO)] were elaborated to deal with disturbances related to the process. The regulatory control consisted of keeping sugar and/or butanol concentrations in the fermentor constant in the face of disturbances in the feed substrate concentration. Another objective was the maintenance of the proper operation of the flash tank (maintenance of the thermodynamic equilibrium of the liquid and vapor phases) considering that oscillations in the temperature in the tank are expected. The servo control consisted of changes in concentration set points. The performance of an advanced controller, the dynamic matrix control, and the classical proportional-integral controller was evaluated. Both controllers were able to regulate the operating conditions in order to accommodate the perturbations with the lowest possible alterations in the process outputs. However, the performance of the PI controller was superior because it showed quicker responses without oscillations.     

Electroanalytical determination of eugenol in clove oil by voltammetry of immobilized microdroplets

Journal of Solid State Electrochemistry - The determination of eugenol employing voltammetry of immobilized microdroplets (VIM) is reported in this work. The construction of the electrode was based...     

Femtosecond pump-probe measurements of solvation by hydrogen-bonding interactions.

An additional ultrafast blue shift in the transient absorption spectra of hydrogen-bonding complexes of a strong photoacid, 8-hydroxypyrene 1,3,6-trisdimethylsulfonamide (HPTA), over the solvation response of the uncomplexed HPTA and also over that of the methoxy derivative of the photoacid (MPTA) in the presence of the hydrogen-bonding base was observed on optical excitation of the photoacid. The additional 55 +/- 10 fs solvation response was found to be about 35 % and 19% of the total C(t) of HPTA in dichloromethane (DCM) when it was hydrogen-bonded to dimethylsulfoxide (DMSO) and dioxane, respectively, and about 29% of the total C(t) of HPTA in dichloroethane (DCE) when it was hydrogen-bonded to DMSO. We have assigned this additional dynamic spectral shift to a transient change in the hydrogen bond (O-H...O) that links HPTA to the complexing base, after the electronic excitation of the photoacid.     

Scaling behavior of surface irregularity in the molecular domain: From adsorption studies to fractal catalysts

For an unexpected variety of solids, the surface topography from a few up to as many as a thousand angstroms is very well described by fractal dimension,D. This follows from measurements of the number of molecules in surface monolayers, as function of adsorbate or adsorbent particle size. As an illustration, we present a first case, amorphous silica gel, whereD has been measured independently by each of the two methods. (The agreement, 3.02±0.06 and 3.04±0.05, is excellent, and the result is modeled by a heavy generalized Menger sponge.) The examples as a whole divide into amorphous and crystalline materials, but presumably all of them are to be modeled as random fractal surfaces. The observedD values exhaust the whole range between 2 and 3, suggesting that there are a number of different mechanisms by which such statistically self-similar surfaces form. We show that fractal surface dimension entails interfacial power laws much beyond what is the source of theseD values. Examples are reactive scattering events when neutrons of variable flux pass the surface (this is of interest for locating fractal substrates that may support adlayer phase transitions); the rate of diffusion-controlled chemical reactions at fractal surfaces; and the fractal implementation of the traditional idea that the active sites of a catalyst are edge and apex sites on the surface.     

Survey of multi-wire probe data processing techniques and efficient processing of four-wire probe velocity measurements in turbulent flows

 A general presentation of the two main approaches for the extraction of velocity information from multi-wire hot-wire probe measurements is first given, along with a short introduction to the different data processing techniques currently available. This global survey is intended to help researchers interested in using multi-wire probes (for velocity measurements) choose more easily a data processing technique adapted to their experiments and laboratory facilities. In the second part, a numerically efficient four-wire probe data processing technique, especially suited for flows with relatively high turbulence intensities (up to 30%), is described. With this technique, an accurate solution can be found in almost all of the probe's acceptance domain and the directional sensitivity calibration does not have to be performed in situ. The accuracy of the method is demonstrated with a 3D airfoil near-wake experiment for which four-wire probe measurements of mean velocity, full Reynolds stress tensor and triple correlations are compared with three-component LDA measurements. Received: 25 February 1999/Accepted: 17 September 1999     

Lithium insertion into titanium dioxide (anatase) electrodes: microstructure and electrolyte effects

Insertion characteristics of anatase electrodes were studied on single-crystal and polycrystalline electrodes of different microstructures. The lithium incorporation from propylene carbonate solution containing LiClO₄ and Li(CF₃SO₂)₂N was studied by means of cyclic voltammetry (CV), the quartz crystal microbalance (QCM) and the galvanostatic intermittent titration technique (GITT). The electrode microstructure affects both the accessible coefficient x and the reversibility of the process. The highest insertion activity was observed for electrodes composed of crystals with characteristic dimensions of ∼10^–8 m. The insertion properties deteriorate for higher as well as for smaller crystal sizes. Enhanced insertion was observed in Li(CF₃SO₂)₂N-containing solutions. Lithium insertion is satisfactorily reversible for mesoscopic electrodes; the reversibility in the case of compact polycrystalline and single-crystal electrodes is poor. The reversibility of the insertion improves with increasing electrolyte concentration. The lithium diffusion coefficient decreases with increasing x and ranges between 10^–15 and 10^–18 cm² s^–1. Electronic Publication