Drug release from hydrogel devices with ratecontrolling barriers

Zero order release of a drug from monolithic polymer devices fails because the drug concentration gradient within the matrix falls with time. In principle, it should be possible to maintain this concentration gradient constant via the introduction of a ratelimiting barrier to solute diffusion at the surface of the device. In this study, progesterone-dispersed monolithic devices were prepared from either polyhydroxyethyl methacrylate (HEMA) or a copolymer of HEMA and methoxyethoxyethyl methacrylate (MEEMA). These monolithic devices were soaked in an ethanol solution of ethylene glycol dimethacrylate (EGDMA) followed by exposure to UV light to create a crosslinked zone at the outer edge. The cross-linked zone has a much lower permeability to solute than the central region of the device and therefore serves as a rate-limiting barrier. Progesterone release studies demonstrated a zero order release from devices with the crosslinked outer layer. Drug release rates were dependent upon the UV treatment time, the EGDMA concentration, and the device soaking time in the EGDMA solution.     

Darstellung und Kristallstruktur von Calciumimid,CaNH

Synthesis and Crystal Structure of Calcium Imide, CaNH Single-crystals of calcium imide were obtained for the first time by the reaction of a mixture of calcium amide with sodium amide at 850°C in an autoclave for salt melts. After cooling the autoclave to room temperature the crystals are embedded in solid Na which was extracted by liquid ammonia. The structure of calcium imide was determined from single-crystal diffractometer data: space group Fm3 m, Z = 4, a = 5.143(1) Å, R/R_w = 0.032/0.028 mit N(F ${}_{\text{º}}^{\text{2}}$ ? 3σ(F ${}_{\text{º}}^{\text{2}}$ )) = 26, N(Var.) = 5. Ca and N atoms are arranged in the motif of the NaCl structure type. The hydrogen atoms of the imide groups are disordered within the Ca octahedra, and they occupy a six fold split position.     

Alfréd Rényi

Probability Theory and Related Fields -     

Group VA effects on surfactant aggregation number and dye solubilization efficiency

The effects of changing the charge-bearing atom in the polar head of a surfactant ion on micelle size and dye solubilization efficiency were investigated. Replacement of nitrogen in decyltrimethylammonium bromide by phosphorus or arsenic increases the micellar aggregation number by at least 20% in 0.5 m NaBr solutions. The ability of the surfactants to solubilize the dye Orange-OT is only slightly affected by the substitution of phosphorus for nitrogen, but it is lowered appreciably by the substitution of arsenic.     

Defect interactions in intrinsic silver chloride

Approximate formulae are developed for the activity coefficients of vacancies and interstitials in intrinsic silver chloride. The numerical values are compared with the Debye-Hückel approximation and the useful range of the formulae is discussed.     

Efficient dynamic kinetic resolution of secondary amines with Pd on alkaline earth salts and a lipase

Combination of Pd, supported on alkaline earth type supports with a lipase results in a selective catalytic system for dynamic kinetic resolution of benzylic amines.