Structural Transitions of Self-Nanoemulsifying Drug Delivery System of Glibenclamide,Carvedilol, and Lovastatin upon Progressive Aqueous Dilution

The dynamics of morphological transition in amphiphillic systems such as self-nanoemulsifying drug delivery system (SNEDDS) has become an increasingly active field of research in colloidal science. The present contribution deals with the morphological transition of selected optimized SNEDDS formulations of glibenclamide, carvedilol, and lovastatin on progressive aqueous dilution using transmission electron microscopy. The study emphasizes the structural aspects of the systems and stresses the effect of aqueous dilution under which the systems transform from water-in-oil (L₂) phase into bicontinuous structure and, finally, in oil-in-water (L₁) nanodroplets.     

Local inverse inelastic mean free path at interface

We calculated a local inverse inelastic mean free path (local-IIMFP) for electrons crossing a medium–medium interface, considering various incident electron energies, crossing angles and combinations of materials. We used an extension of a classical dielectric model developed by Li and co-workers for an electron crossing a surface (interface vacuum-medium). Moreover, the integration over the distance of the local-IIMFP allows to obtain the interface excitation parameter (or IEP) characterizing the change in excitation probability for an electron crossing an interface once caused by the presence of the interface in comparison with an electron for which only volume excitations are considered. We perform these calculations for angles between 0° and 80°, for electron energies between 500 and 2500 eV and for various pairs of materials, as Al/In for its academic interest or Au/Si and SiO₂/Si for their technological importance. Small but not negligible variations of the local-IIMFP and the IEP were observed for metal–metal or metal–semiconductor interfaces, while quite significant variations are obtained when one of the materials is a insulator.     

石墨消解-原子荧光光谱法测定土壤中的总硒

为准确定量土壤硒总量,提出以逆王水(1+1)-石墨消解法消解土壤,氢化物原子荧光光谱法(HG-AFS)测定土壤总硒含量的方法.其中,对消解方式、消解时间和仪器条件进行了探讨,确定最优检测条件.称取0.2 g土壤样品加入5 mL逆王水(1+1),于石墨消解仪120℃消解1.5 h,冷却至室温后用超纯水定容至25 m L,...     

荧光反猝灭法测定药剂中卡托普利

建立荧光反猝灭法测定卡托普利(CAT)的体系.碘(I-3)与罗丹明B(RhB)缔合作用使罗丹明B荧光信号强度减弱直至荧光猝灭,而卡托普利可将I-3还原为I-,使体系荧光信号再现.在2～20μmol·L-1范围内荧光强度再现值ΔF与卡托普利浓度有线性关系:ΔF=-8.438+10.774c(r=0.9986),检出限为3...     

Solid‐Phase Synthesis of a Seventh‐Generation Inverse Poly(amidoamine) Dendrimer: Importance of the Loading Ratio on the Resin

Here, this study overcomes the current barriers to efficient solid‐phase synthesis of high‐generation dendrimers by decreasing the loading ratio on the resin. G7 inverse poly(amidoamine) dendrimer is now prepared, for the first time, through a solid‐phase synthesis using only 50% of the available reactive sites and by choosing a large resin. This preparation takes only 15 d to afford highly pure product in 80% yield with precipitation being the only purification procedure used. The results clearly show the amount of the initial monomer loaded on the resin to be a vital factor for the ability to use solid‐phase synthesis to produce large dendrimers. This finding also sets stage for the applications of solid‐phase synthesis for the preparation of other macromolecules.

     

Quantitative surface analysis by Auger and x-ray photoelectron spectroscopy

Recent developments in quantitative surface analysis by Auger (AES) and x-ray photoelectron (XPS) spectroscopies are reviewed and problems relating to a more accurate quantitative interpretation of AES/XPS experimental data are discussed. Special attention is paid to consideration of elementary physical processes involved and influence of multiple scattering effects on signal line intensities. In particular, the major features of core-shell ionization by electron impact, Auger transitions and photoionization are considered qualitatively and rigorous approaches used to calculate the respective transition probabilities are analysed. It is shown that, in amorphous and polycrystalline targets, incoherent scattering of primary and signal Auger and photoelectrons can be described by solving analytically a kinetic equation with appropriate boundary conditions. The analytical results for the angular and energy distribution, the mean escape depth, and the escape probability as a function of depth of origin of signal electrons as well as that for the backscattering factor in AES are in good agreement with the corresponding Mote Carlo simulation data. Methods for inelastic background subtraction, surface composition determination and depth-profile reconstructions by angle-resolved AES/XPS are discussed. Examples of novel techniques based on x-ray induced photoemission are considered.     

Pore size distributions in microporous membranes. A critical analysis of the bubble point extended method

An extended bubble point method has been used to examine the porous morphology of several track-etched microporous polycarbonate membranes with nominal pore sizes ranging from 0.1 to 5.0 μm. The technique has been carefully analyzed and corrected to take into account the diverse non-ideal factors in flow along with the prevalence of Knudsen flow over the Hagen-Poiseuille one in the smaller pores.     

The extended Hulburt–Hirschfelder‐long‐range oscillator model for direct‐potential‐fit analysis

In the present work, an extended Hulburt–Hirschfelder oscillator model is proposed as a means of simplifying potential energy functions for direct‐potential‐fit analyses. The new potential energy function is joined smoothly to the long‐range inverse‐power dispersion energy expression. The new model is employed in direct‐potential‐fits using spectroscopic line positions that involve the ground electronic states of the principal isotopologues of hydrogen iodide and carbon monoxide, and the ground and first singlet‐sigma excited states of hydrogen fluoride and hydrogen chloride. The present methodology is found to lead to compact, flexible, and robust representations for the potential energy that compare favorably with the results of past work where more complicated models were employed.     

Surface Energy of Silica-TEOS-PDMS Ormosils

Inverse gas chromatography (IGC) was applied to characterize the surface energy of organically modified silicates (ormosils) by measuring the interaction of molecular organic probes with the ormosil surface. Ormosils were prepared by the sol-gel method by the reaction of TEOS (tetraethoxysilane), PDMS (polydimethylsiloxane) and different types of silica (Aerosil 130, Aerosil 200 and Aerosil 380). The isosteric heat of adsorption, q _st, and the dispersive component of the surface energy, _s ^D, were estimated by using the retention volume of different nonpolar and polar probes at infinite dilution. The dispersive component shows an increase as the specific surface area of the silica is increased from 29.6 mJ/m² to 51.4 mJ/m² at 60°C. Such values are lower than that obtained for aerosil particles meaning that PDMS chains impede the interaction with silanol groups located on the silica surface. The specific interaction parameter, I^SP, and the enthalpy of specific adsorption, H _a ^SP, of polar probes on the ormosil surface were also measured in order to obtain the acid-base character of ormosil surface. The H _a ^SP, was correlated with the donor, DN, and the acceptor, AN, numbers of the probes to quantify the acidic, K _A, and the basic, K _B, parameters of the substrate surface. The obtained results suggest that the silica particles were covered by PDMS chains in a different way depending on the type of silica used. The values of K _A and K _B suggest that the ormosil surface is amphoteric, with predominantly acceptor electron sites.     

反气相色谱法测定苯乙烯-氧乙烯-苯乙烯三嵌段聚合物的表面能

 采用反气相色谱法测定了苯乙烯 氧乙烯 苯乙烯三嵌段聚合物 (PS PEO PS)的色散成分的表面能 (γsd) ,研究探讨了温度及嵌段聚合物链段结构组成对γsd 的影响 ,并确定了γsd 与温度的数学关系式。研究结果表明 :在 70℃～ 12 0℃范围内 ,PS PEO PS的表面能较低 ;随着PS PEO PS表面组成中氧乙烯 (EO)成分的增加 ,色散成分的γsd 增大 ,且对温度的变化极其敏感 :随温度的升高 ,γsd 急剧地呈线性下降。