LC Evaluation of Intestinal Transport of Praziquantel

Praziquantel (PZQ) is a highly lipophilic drug with low aqueous solubility. Despite this, it is well absorbed from the gastrointestinal tract. In this study, a simple LC method was developed and validated, in order to monitor the concentration of PZQ in TC-199 buffer in vitro, in the rat everted gut sac absorption model. PZQ was analyzed by a reversed-phase LC method with an isocratic mobile phase containing acetonitrile and water in the proportions 45:55. The flow-rate was 1 mL min⁻¹ and PZQ was determined by measuring absorbance at 215 nm, at 25 °C. The method was found to be specific, as none of the components of TC-199 or intestinal sac artefacts interfered with the drug peak. Recovery was within acceptable statistical limits. The limit of detection was 0.54 μg mL⁻¹ and the limit of quantitation was 1.63 μg mL⁻¹. The calibration curve was found to be linear in the concentration range of 10–90 μg mL⁻¹ PZQ. The proposed method was found to be rapid and selective and hence can be applied in the monitoring of the absorption of PZQ in in vitro everted gut sac absorption studies.     

Carbohydrate Hydrogels with Stabilized Phage Particles for Bacterial Biosensing: Bacterium Diffusion Studies

Bacteriophage particles have been reported as potentially useful in the development of diagnosis tools for pathogenic bacteria as they specifically recognize and lyse bacterial isolates thus confirming the presence of viable cells. One of the most representative microorganisms associated with health care services is the bacterium Pseudomonas aeruginosa, which alone is responsible for nearly 15 % of all nosocomial infections. In this context, structural and functional stabilization of phage particles within biopolymeric hydrogels, aiming at producing cheap (chromogenic) bacterial biosensing devices, has been the goal of a previous research effort. For this, a detailed knowledge of the bacterial diffusion profile into the hydrogel core, where the phage particles lie, is of utmost importance. In the present research effort, the bacterial diffusion process into the biopolymeric hydrogel core was mathematically described and the theoretical simulations duly compared with experimental results, allowing determination of the effective diffusion coefficients of P. aeruginosa in the agar and calcium alginate hydrogels tested.     

LC Evaluation of Intestinal Transport of Praziquantel

Praziquantel (PZQ) is a highly lipophilic drug with low aqueous solubility. Despite this, it is well absorbed from the gastrointestinal tract. In this study, a simple LC method was developed and validated, in order to monitor the concentration of PZQ in TC-199 buffer in vitro, in the rat everted gut sac absorption model. PZQ was analyzed by a reversed-phase LC method with an isocratic mobile phase containing acetonitrile and water in the proportions 45:55. The flow-rate was 1 mL min⁻¹ and PZQ was determined by measuring absorbance at 215 nm, at 25 °C. The method was found to be specific, as none of the components of TC-199 or intestinal sac artefacts interfered with the drug peak. Recovery was within acceptable statistical limits. The limit of detection was 0.54 μg mL⁻¹ and the limit of quantitation was 1.63 μg mL⁻¹. The calibration curve was found to be linear in the concentration range of 10–90 μg mL⁻¹ PZQ. The proposed method was found to be rapid and selective and hence can be applied in the monitoring of the absorption of PZQ in in vitro everted gut sac absorption studies.

     

Flux mapping at 77 K and local measurement at lower temperature of thin-wall YBaCuO single-domain samples oxygenated under high pressure

YBCO single-domain samples are suitable for the production of high trapped fields in the range 20–77 K using a cryocooler or liquid nitrogen. But the oxygenation process required to actually transform the single domains into superconductors induces an extensive crack network that is limiting the material performances. Thin-wall geometry has been introduced to reduce the diffusion paths and to enable a progressive oxygenation strategy. As a consequence cracks are drastically reduced. In addition the use of a high oxygen pressure (16 MPa) speeds up further the process by displacing the oxygen–temperature equilibrium towards the higher temperature of the phase diagram. The advantage of thin-wall geometry is that such an annealing can be applied directly to a much larger sample. Remarkable results are obtained without any doping by the combination of thin walls and oxygen high pressure. While classical plain samples yield 300–400 mT, a trapped field of 840 mT has been measured at 77 K on a 16 mm diameter Y123 thin-wall single-domain sample with an annealing time as short as 3 days. Local measurements with a fixed Hall probe on top of the sample were performed at lower temperature after magnetization either in a static field or in a pulse field. The trapped field is significantly higher at lower temperature. Cryocoolers become the key to compromise between performances and cryogenic cost around 40 K.     

Cracking and oxygenation of YBaCuO bulk superconductors: application to c-axis elements for current limitation

A process to elaborate crack free, oxygenated c-axis samples in YBa₂Cu₃O_x bulk superconductors is reported. This includes texturing of crack free pellets and development of an adequate oxygen annealing treatment to avoid cracking during oxygen uptake. For current limitation in c-direction such a process is needed as c-axis elements are particularly susceptible to ab-plane cracking during oxygenation. Mechanical properties have been compared for different annealing treatments by flexural strength measurements. With the load applied in ab-direction the mean flexural strength is 58 MPa in as-textured c-axis bars and 48 MPa in c-axis bars which were oxygenated using a customized annealing treatment. The conventional oxygen annealing treatments lead to macroscopic oxygenation cracks which reduced flexural strength to 10–20 MPa. Bars cut in ab-direction do not show significant variation in flexural strength (load applied in c-direction) as a function of the annealing condition with an average value of 145 MPa.     

Loading of 5-aminosalicylic in solid lipid microparticles (SLM)

5-Aminosalicylic acid (5-ASA), the active moiety of sulphasalazine, is the most commonly used drug for treating patients with inflammatory bowel disease (IBD). Its bioavailability is low, i.e. 20–30% upon oral administration and 10–35% by rectal administration. As the extent of 5-ASA absorption is very much dependent on the time-length, the drug is retained in the colon, a way to increase drug retention is the use of orally administered sustained released formulations. Solid lipid microparticles (SLM) are a viable option for site-specific targeted delivery in compressed tablets produced by direct compaction. In this study, we describe the development and characterization of 5-ASA-loaded SLM for sustained release. The solubility of 5-ASA in different types of solid lipids (e.g. cetyl palmitate, cetyl alcohol, and cetearyl alcohol) was evaluated to select the best lipid as the inert matrix-forming agent to control the release of the drug. SLM dispersions were prepared using the hot emulsification method employing the selected solid lipid, lecithin (Lipoid^®) as surfactant, dimethyl sulphoxide, and acetone stabilized with Arlacel^®. The characterization was performed by differential scanning calorimetry, thermogravimetric analysis, wide-angle x-ray diffraction, Fourier transform infrared spectroscopy measurements, optical microscopy, and scanning electron microscopy. Results show that the best lipid for dissolving the 5-ASA was cetyl palmitate and that the melting process did not affect the chemical stability of the materials. The thermal analysis suggests that 5-ASA was successfully encapsulated with the microparticles, of spherical shape and uniform size distribution.

     

Magnetic order in the pseudogap phase of high-Tc superconductors

One of the leading issues in high-T(c) superconductors is the origin of the pseudogap phase in underdoped cuprates. Using polarized elastic neutron diffraction, we identify a novel magnetic order in the YB(2)Cu(3)O(6+) system. The observed magnetic order preserves translational symmetry of the lattice as proposed for orbital moments in the circulating current theory of the pseudogap state. To date, it is the first direct evidence of a hidden order parameter characterizing the pseudogap phase in high-T(c) cuprates.     

Vortex lattice accommodation on twin boundaries in studied by neutron diffraction

An extensive study of small angle neutron scattering was performed in twinned YBa₂Cu₃O₇ crystals in its superconducting state as a function of the angle between the c-axis of the crystal and the magnetic field. The half of the twin boundaries are oriented in the horizontal plane, which also contains the neutron beam and the magnetic field. Two different diffraction patterns are studied as a function of at 5 K and B = 0.5 T, one along the c-axis of the crystal, the other one along the applied field. These variations are interpreted in the model of accommodation of the vortices on the twin planes by zigzagging from these planes to the ab-planes of the crystal, in order to minimize their energy. Received: 9 March 1998 / Revised and Accepted: 12 June 1998