Encapsulation of complementary model drugs in spray-dried nanostructured materials

Two model drugs of different physico-chemical and pharmaceutical properties (ibuprofen, acetaminophen) have been incorporated together or separately in silica-based microspheres using sol–gel and spray-drying processes. A variable amount of a neutral surfactant Brij-56© has also been added. The properties of the microspheres vary significantly depending on their composition. Three kinds of texture are identified: (1) silica containing spheroid nano-domains (formed by ibuprofen; diameters between 20 and 100 nm), (2) silica containing worm-like mesophases (formed by Brij-56© and both model drugs, typical correlation distances ~6 nm), (3) silica intimately mixed with the drug (acetaminophen) without visible phase-separation. The kinetics of drug release in simulated intestinal fluid strongly depend on these textures. The association of ibuprofen and acetaminophen in a single type of microsphere and without surfactant favours a concomitant release. Possible mechanisms of materials’ formation are discussed.     

Preparation and characterization of siliceous material using liposomes as template

Material synthesis using unilamellar liposomes with a high sol-gel temperature transition phase as a template leads to a new silica material.     

Effect of ultraviolet-B radiation on salt marsh vegetation: Trends of the genus Salicornia along the Americas

The effects of natural UV-B radiation on growth, photosynthetic and photoprotective pigment composition of different Salicornia species were analyzed in salt marshes at three different sites along the Americas (Puerto Rico, southern Brazil and Patagonia, Argentina). Plants were exposed to different levels of UV-B radiation for 1-2 years in situ as well as in outdoor garden UV-B exclusion experiments. Different UV-B levels were obtained by covering plants with UV-B opaque (blocked 93-100% of ambient UV-B) and UV-B attenuating (near-ambient) filters (reduced 20-25% of UV-B). Unfiltered plants were exposed to natural irradiance. UV-B filters had significant effects on temperature and photosynthetic pigments (due to changes in PAR; 400-700 nm). The growth of Salicornia species was inhibited after 35 to 88 days of exposure to mean UV-B radiation dosages between 3.6 and 4.1 kJ m(-2) day(-1). The highest number of branches on the main shoot (S. bigelovii and S. gaudichaudiana) and longest total length of the branches (S. gaudichaudiana) were observed in the UV-B opaque treatment. Salicornia species responded to increasing levels of UV-B radiation by increasing the amount of UV-B absorbing pigments up to 330%. Chromatographic analyses of seedlings and adult S. bigelovii plants found seven different UV-B absorbing flavonoids that are likely to serve as UV-B filtering pigments. No evidence of differential sensitivity or resilience to UV-B radiation was found between Salicornia species from low-mid latitudes and a previously published study of a high-latitude population.     

Surfactant properties of ionic liquids containing short alkyl chain imidazolium cations and ibuprofenate anions

Interfacial tension, electrical conductivity, NMR self-diffusion and DLS experiments have been used to investigate the self-aggregation in water of ionic liquids associating an ibuprofenate anion and 1-alkyl-3-methylimidazolium [C(n)MIm](+) (n = 4, 6, 8) cations. Despite the short alkyl chain on imidazolium cations (n ≤ 8), these ionic liquids exhibit particularly low Critical Aggregation Concentrations (CAC), significantly lower than their parent 1-alkyl-3-methylimidazolium chloride salts. This behaviour is attributed to the formation of catanionic pairs between ibuprofenate and imidazolium.     

Drug nano-domains in spray-dried ibuprofen-silica microspheres

Silica microspheres encapsulating ibuprofen in separated domains at the nanometre scale are formed by spray-drying and sol-gel processes. A detailed (1)H and (13)C NMR study of these microspheres shows that ibuprofen molecules are mobile and are interacting through hydrogen bonds with other ibuprofen molecules. (1)H magnetisation exchange NMR experiments were employed to characterize the size of the ibuprofen domains at the nanometre scale. These domains are solely formed by ibuprofen, and their diameters are estimated to be ～40 nm in agreement with TEM observations. The nature and formation of these particular texture and drug dispersion are discussed.     

Association of Molybdenum Ionic Species with Alumina Surface

The adsorption isotherms at 25, 45, and 65 degrees C of molybdenum solutions of concentration ranges between 10(-3) and 3x10(-2) M(Mo) (pH 4-5) on different alumina samples are investigated. The analysis is conducted using a modified Frumkin isotherm which takes a more realistic account of the lateral interaction between adsorbed species and considers that the adsorption takes place on the most basic OH groups on the surface of alumina. The results are discussed in view of the difference in solutions speciation, and the changes in the pH of the remaining supernatant solutions. The solution temperature, PZC of the used aluminas, the configuration of the basic OH groups on their surface, and the pore structure have been shown to intervene effectively. Copyright 2000 Academic Press.