A new foam-based method for the (bio)degradation of hydrocarbons in contaminated vadose zone.

An innovative foam-based method for Fenton reagents (FR) and bacteria delivery was assessed for the in situ remediation of a petroleum hydrocarbon-contaminated unsaturated zone. The surfactant foam was first injected, then reagent solutions were delivered and propagated through the network of foam lamellae with a piston-like effect. Bench-scale experiments demonstrated the feasibility of the various treatments with hydrocarbon (HC) removal efficiencies as high as 96 %. Compared to the direct injection of FR solutions, the foam-based method led to larger radii of influence and more isotropic reagents delivery, whereas it did not show any detrimental effect regarding HC oxidation. Despite 25 % of HCs were expelled from the treated zone because of high foam viscosity, average degradation rates were increased by 20 %. At field-scale, foam and reagent solutions injections in soil were tracked both using visual observation and differential electric resistivity tomography. The latter demonstrated the controlled delivery of the reactive solutions using the foam-based method. Even if the foam-based method duration is about 5-times longer than the direct injection of amendment solutions, it provides important benefits, such as the confinement of harmful volatile hydrocarbons during Fenton treatments, the enhanced reagents delivery and the 30 % lower consumption of the latter.

Self-assembly of a diferrous triple-stranded helicate with bis(2,2'-bipyridine) ligands: thermodynamic and kinetic intermediates.

The protonation and iron(II) coordination properties of a bis(2,2'-bipyridine) ligand L were investigated in methanol. The protonated forms showed allosteric effects due to the flexibility of the strand. Speciation studies of the corresponding ferrous complexes were carried out as a function of pH and iron(II) concentrations. A combination of electrospray mass spectroscopy, potentiometry, and spectrophotometry allowed the determination in solution of three ferrous complexes, one mononuclear (L2Fe2+) and two dinuclear (L2Fe2(4+) and L3Fe2(4+)) species. Their structure was deduced from the metal spin state and confirmed by 1H NMR measurements and molecular modeling. The dissociation process of the triple-stranded diferrous helicate L3Fe2(4+) by OH- revealed two rate-limiting steps. The former leads to the formation of a monoferrous triple-stranded compound via a classical mechanism, which involves hydroxy-ferrous complexes. A similar process was observed in the latter step for the release of the ferrous cation from the mononuclear intermediate. Taking into account the structural, thermodynamic, and kinetic features provided by the present study, we could propose a self-assembling mechanism of the triple-stranded diferrous helicate.

Comparative pharmacokinetic study of a floating multiple-unit capsule, a high-density multiple-unit capsule and an immediate-release tablet containing 25 mg atenolol.

The purpose of this study was to evaluate the possible advantages of floating and high-density dosage forms and their influence on pharmacokinetic parameters. Atenolol was chosen as a model drug because of its poor absorption in the lower gastrointestinal tract. Three formulations containing 25 mg atenolol, a floating multiple-unit capsule, a high-density multiple-unit capsule, and an immediate-release tablet were compared with respect to estimated pharmacokinetic parameters. The two multiple-unit dosage forms were composed of compressed minitablets and had sustained release properties. The bioavailability of the two gastroretentive preparations with sustained release characteristics was significantly decreased when compared to the immediate-release tablet. The floating minitablets seemed to be retained longer in the stomach than the high-density dosage form. The first atenolol concentration detectable in the plasma and the time to peak Tmax were delayed for the floating dosage form. For the parameters Cmax and AUC 0-infinity, the lower limit of the 90% confidence interval was outside the bioequivalence range (0.80-1.25). This study showed that it was not possible to increase the bioavailability of a poorly absorbed drug such as atenolol using gastroretentive formulations. Atenolol absorption was delayed and the maximum plasma concentration was diminished.

Buoyancy and drug release patterns of floating minitablets containing piretanide and atenolol as model drugs.

The purpose of this study was to evaluate factors for improving the in vitro buoyancy and the drug release characteristics of floating minitablets containing either piretanide or atenolol as model drugs. The buoyancy of the minitablets was achieved either by the swelling of the excipient or by incorporation of the gas-generating agent sodium bicarbonate. Resultant-weight kinetics were performed in order to evaluate the buoyancy. The release rate of the poorly soluble drug piretanide was enhanced by increasing its solubility or by promoting the erosion of the minitablets. For the sparingly soluble drug atenolol, the minitablets were coated with different ratio of insoluble polymer in order to diminish the release rate of this drug. The swelling of a hydrophilic excipient was not sufficient to obtain floating minitablets. The buoyancy of the minitablets containing either piretanide or atenolol was greatly improved by adding sodium bicarbonate as well as by a wet granulation. The most satisfactory improvement in the release rate of piretanide was achieved using a solid dispersion with povidone, thus increasing the drug solubility concomitantly with the increase of the minitablets' erosion. Regarding atenolol, minitablets containing 7% sodium bicarbonate and coated with Eudragit NE30D:RS 70:30 gave satisfactory results concerning buoyancy and drug release rate. This study showed that it was possible to produce minitablets containing either piretanide or atenolol, which have a positive resultant-weight during more than 6 hr and satisfactory release profiles.