Kinetic study of the formation reaction of colloidal silica spheres in microgravity using aircraft

Polymerization reactions of colloidal silica spheres via the hydrolysis and dehydration processes of tetraethyl orthosilicate with ammonia and a tiny amount of water in ethyl alcohol have been studied in microgravity by the parabolic flights of a MU-300 rear-jet aircraft. Induction periods and polymerization rates are determined by fast-scanning transmitted-light-intensity measurements and the fast-scanning dynamic light-scattering method. Direct observation of the reaction mixtures is also made with a charge-coupled device video camera. Reproducible and reliable data are obtained in microgravity compared with those in gravity. Increases in the induction times and decreases in the polymerization rates are observed in microgravity compared with those in gravity. One of the main reasons for these observations is the fact that the translational Brownian movement of the reactants and/or product spheres is free from downward translational movement in microgravity. Very weak convection of the reaction suspensions in microgravity is another important factor. Received: 10 November 1998 Accepted in revised form: 12 January 1999     

Selenophilic reaction of organolithium and magnesium reagents with phosphinoselenoic chlorides

The reaction of phosphinoselenoic chlorides 1 with various organolithium and magnesium reagents was studied. Sequential reaction of phosphinoselenoic chlorides 1 with organolithium and magnesium reagents and elemental selenium gave two types of products, phosphine selenides 2 and phosphinodiselenoic acid esters 3 . The esters 3 appeared to be formed via the selenophilic reaction of organolithium and magnesium reagents with the chlorides 1 . Molecular orbital calculations were carried out for model compounds H₂P(E)Cl (E = O, S and Se) to determine their electronic structures. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:185–191, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20091     

Lithium potassium borate and lithium rubidium borate: new non‐linear optical crystals

The title compounds, LiKB₄O₇ and LiRbB₄O₇, are newly developed non‐linear optical crystals containing two kinds of anionic groups, namely (B₃O₈)^7? and (B₅O₁₀)^5?. The (B₃O₈)^7? groups form infinite spiral chains parallel to the [100] direction, which are interconnected by sharing O atoms with (B₅O₁₀)^5? groups.     

Viscosity change in aqueous hectorite suspension activated by DC electric field

The change in the viscosity of deionized aqueous hectorite suspensions by applying an electric field was investigated. The deionized suspensions had low viscosity, which was almost the same as that of its solvent, water. Upon applying a DC electric field of the order of a few volt per millimeter to the deionized suspension, the viscosity started to increase gradually and reached a constant value that was high enough relative to the original value. Regarding the mechanism of the electrically induced stress increase, it is highly plausible that a three-dimensional network structure formed under the electric field due to a deformation of the electrical double layer.     

Importance of the electrical double layers for the rheological properties of colloidal liquids

Rheological studies of the colloidal liquids of silica spheres in the exhaustively deionized aqueous media are reported. Diameters of the spheres are between 5 nm and 60 nm. The suspensions showed liquid or weakly structured liquid. The shear viscosities in the highly deionized system are substantially higher than those expected from Einsteins equation. When sodium chloride is added, the shear and the dynamic viscosities decrease sharply, which suggests that the electrical double layer plays an important role for the rheological properties. The ratio of the viscosity observed divided by the viscosity calculated from Einsteins equation shows a maximum value for the spheres of 45 nm in diameter. It is highly plausible that the viscosity of the suspension is influenced substantially by the ratio of the thickness of the electrical double layer and sphere sizes. The effective volume fraction of sphere including the electrical double layer, which is estimated from the viscoelasticity, shows a drastic increase when the effective volume fraction reaches around 0.74 corresponding to the closest packing in hexagonal lattice. The importance of electrical double layers is clear for the rheological properties of colloidal liquids.     

Intercalation compound of diclofenac sodium with layered inorganic compounds as a new drug material

The intercalation reaction of diclofenac sodium (DFS) with layered inorganic compounds, gamma-titanium phosphate (gamma-TiP), proton type titanium oxide (H-TiO2) and sodium type synthetic mica (Na-TSM), was examined on. The direct reaction of DFS in ethanol-water mixed solvent resulted in the large amount accommodation of DFS. The amount of intercalated DFS was the order of gamma-TiP>H-TiO2>Na-TSM corresponding to the order of acidity. The intercalation using phospholiopids was also examined to assist the intercalation reaction. However, the amount of intercalated DFS was rather small in comparison with those in the direct reaction. DFS accommodated in gamma-TiP dissolved into neutral and basic buffer solution stoichiometry while scarcely dissolved in the acidic solution. The mechanism of the intercalation and reverse dissolution was successfully accounted according to the ion-exchange mechanism between Na+ in DFS and H+ in gamma-TiP. The dissolution from tablet of DFS/gamma-TiP intercalation compound was examined by using a disintegrator. It was found that the dissolution rate appropriately controlled by mixing the disintegrator. The present results suggested the different possibilities in the clinical field to use layered inorganic compounds such as drug delivery system (DDS).     

Studies on pyrazines. 17.. An efficient synthesis of pteridine-6-carboxylic acids

2,4-Diaminopteridine-6-carboxylic acid ( 1 ) and pterin-6-carboxylic acid ( 2 ) were prepared by permanganate oxidation of the corresponding 6-(2-furyl)-substituted pteridines under much milder conditions. Several attempts to cleave the furan ring with other oxidizing agents are also described.     

Liposome formation of selectively-polymerized diene-containing phospholipids and their postpolymerization

Small and large unilamellar liposomes composed of 1,2-bis(2,4-octadecadienoyl)-sn-glycero-3-phosphorylcholine (DODPC) are prepared by sonication and extrusion, respectively. They are polymerized with water-insoluble radical initiator, azobis(isobutyronitrile) (AIBN) which can selectively polymerize diene groups in 1-acyl chains of the lipids. Polymerized liposomes are freeze-dried to obtain the polymerized liposome powder. There are two methods to redisperse lyophilized liposomes into water. The extrusion is an effective method to disperse them because the energy at extrusion is necessary only for redispersion, whereas the excess energy at sonication gives damage on liposome structure. There is no difference in stability between polymerized liposomes before and after redispersion with extrusion. DODPC polymers, obtained from free radical-initiated polymerization with AIBN, are linear and have polymerizable diene groups in 2-acyl chains. The liposome powder is therefore soluble in organic solvents. Reconstruction of polymerized liposomes is performed with lipid polymers having low or high molecular weight. The lipid polymers having high molecular weight provide stable large unilamellar liposomes by ethanol injection, but unstable small unilamellar liposomes are formed by sonication. The liposomes reconstructed from lipid polymers having low molecular weight are unstable regardless of their size. After reconstruction of liposomes selectively polymerized by AIBN, diene groups in 2-acyl chains are polymerized by water-soluble radical initiator or UV-irradiation to yield highly crosslinked structure. Their stability is improved remarkably by this postpolymerization.