Microencapsulation of cholesteryl alkanoate by polymerization‐induced phase separation and its association with drugs

A new microencapsulation technique is presented in which cholesteryl nonanoate (CN)/poly(methyl methacrylate) (PMMA) microcapsules are produced by the induction of phase separation between CN and PMMA within the droplets during the polymerization. The concentration of CN is the most important factor determining the final morphology of the microcapsules. For example, a polynuclear type is obtained at a low concentration (<20 wt %), a mononuclear type is obtained at a medium concentration (20–30 wt %), and an irregular phase is obtained at a high concentration (>40 wt %). To evaluate the effectiveness of the technique for stabilizing an unstable drug, we selected retinol (vitamin A) as a model drug and loaded it into the CN/PMMA microcapsules. We used a process called solute codiffusion, in which a fine solvent emulsion containing the retinol was diffused uniformly into the CN/PMMA microcapsules. The loading efficiency of retinol was predicted successfully with the aid of a thermodynamic equation. In the thermal stability test of retinol, we found that an effective association with the CN phase was the most important factor determining the limit of its molecular stability. The technique reported in this article has great potential for the microencapsulation of soft materials via a simple process and for the stabilization of unstable drugs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2202–2213, 2004     

Adsorption structure and spin polarization of pentacene on a magnetized Fe(1 0 0) substrate: SPMDS and ERDA study

The adsorption structure and spin-resolved electronic structure of pentacene on Fe(1 0 0) surfaces were investigated using elastic recoil detection analysis (ERDA) and spin-polarized metastable deexcitation spectroscopy (SPMDS), respectively. It was found that the pentacene molecule adsorbs with its molecular plane parallel to the surface in the initial stage of growth, while the molecular plane tilted from the surface with the increase of the coverage. In the pentacene-Fe surface interaction, a donation and backdonation interaction was indicated. It was found that the polarity of the spin polarization induced in the pentacene molecular orbitals was opposite to each other between the orbitals contributing to the donation and those contributing to the backdonation.     

脉冲时滞抛物型方程解的振动性

本文研究了两类边界条件下有振动系数的脉冲时滞抛物型方程解的振动性,得到了若干解振动的判别准则。其结果即使用于有固定符号系数的方程,也显著地改进了已有的结果。     

Universal self-similarity of porous media equation with absorption: the critical exponent case

In this paper we study the large time behavior of non-negative solutions to the Cauchy problem of u_t=Δu^m−u^q in R^N×(0,∞), where m>1 and q=q_c≡m+2/N is a critical exponent. For non-negative initial value u(x,0)=u₀(x)∈L¹(R^N), we show that the solution converges, if u₀(x)(1+|x|)^k is bounded for some k>N, to a unique fundamental solution of u_t=Δu^m, independent of the initial value, with additional logarithmic anomalous decay exponent in time as t→∞.     

The concept of minimal attractor and maximal attractors of partial differential equations of the Kuramoto-Sivashinsky type

The first part of the paper is devoted to definition of the smallest set that may be regarded as the attractor of the dissipative system. Simple properties of this set are discussed. In the second part some geometrical facts concerning attractors of the partial differential equations are revealed. They include well-known results for the two-dimensional Navier-Stokes equation and new ones for the Kuramoto-Sivashinsky and similar equations.     

Local structure of highly dispersed lead species incorporated within zeolite: experimental and theoretical studies

XAFS (both XANES and FT-EXAFS) measurements revealed that the Pb²⁺ /ZSM-5 catalyst prepared from precursor H-ZSM-5 by a conventional ion-exchange method includes a highly dispersed 3-fold coordinated Pb²⁺ ion species within the zeolite framework. UV-irradiation of Pb²⁺ /ZSM-5 led to effective decomposition of NO and N₂O producing N₂. The photocatalytic decomposition of NO is found to be slightly preferable than that of N₂O. The isolated Pb²⁺ ions play a significant role in the decomposition of pollutant NO _x . Ab initio and DFT quantum chemical studies at the HF/Lanl2dz and B3PW91/Lanl2dz levels further shed light on local structures of the Pb²⁺ active site of lead-containing zeolites, as well as on their interactions with pollutant NO and N₂O molecules. In agreement with experiments, 3-fold coordination was found to be the most favorable state for the Pb²⁺ site within the zeolite framework.     

含吡啶二脲配体汞(II)、镉(II)配合物的合成及其晶体结构

以2,2′-二氨基二苯醚和4-吡啶异氰酸酯反应合成了含吡啶二脲配体(L),并分别与HgCl_2和Cd(ClO_4)2进行了配位反应,得到2个配位聚合物{[Hg(L)Cl_2]·2DMF}_n(1)和{[Cd(L)_2(H_2O)_2](ClO_4)_2·4DMF·2H_2O·2CH_3OH}_n(2),采用1H NMR、MS、FTIR和元素分析等对化合物L进行了表征。通过X射线单晶衍射技术测定了配体及2个配合物的单晶结构,结构解析表明,2个配合物均为一维链状结构。进一步考察了2个配合物的热稳定性及其对甲醇蒸气的吸附性能。     

Equilibrium and dynamic surface properties of long-chain quaternary ammonium hydroxides with different chain length and number

The equilibrium and dynamic surface tensions of five long-chain alkyl ammonium hydroxides (AAH) at the air/aqueous solution interface were investigated, and the effects of the length and number of alkyl chain on surface tensions had been discussed. With the increase of the length, the equilibrium surface tension (EST) increased from 28.65 to 40.52?mN/m. While, for the double chains at the critical micelle concentration (CMC), the EST decreased from 32.71 to 26.61?mN/m with the length increasing. In addition, the adsorption behaviors of the AAH were analyzed and the effective diffusion coefficients (D_eff) were calculated on basis of the Ward–Tordai equation. Moreover, the time required to attain the EST decreases with the increase of surfactant concentration. The longer the C–H chain is, the lower surface tension at initial concentration is. What’s more, the diffusion processing of the AAH to air/water interface mainly depends on the surfactant concentration, and the adsorption is controlled by diffusion mechanism in a dilute concentration, while under a high concentration the adsorption is controlled by mixed diffusion–kinetic mechanism.