Structural changes in amorphous Ge(x)SiO(y) on the way to nanocrystal formation.

Temperature induced changes of the local chemical structure of bulk amorphous GexSiOy are studied by Ge K-edge x-ray absorption near-edge spectroscopy and Si L2/3-edge x-ray Raman scattering spectroscopy. Different processes are revealed which lead to formation of Ge regions embedded in a Si oxide matrix due to different initial structures of as-prepared samples, depending on their Ge/Si/O ratio and temperature treatment, eventually resulting in the occurrence of nanocrystals. Here, disproportionation of GeOx and SiOx regions and/or reduction of Ge oxides by pure Si or by a surrounding Si sub-oxide matrix can be employed to tune the size of Ge nanocrystals along with the chemical composition of the embedding matrix. This is important for the optimization of the electronic and luminescent properties of the material.

An attempt to clarify the influence of glycerol, propylene glycol, isopropyl myristate and a combination of propylene glycol and isopropyl myristate on human stratum corneum.

The present study is a comparison of the influences of glycerol, propylene glycol (PG), isopropyl myristate (IPM) and a combination of PG and IPM (1/1; w/w) on human stratum corneum (SC) by means of differential scanning calorimetry (DSC) and wide and small angle X-ray-diffraction (WAXD and SAXD). The effects of glycerol and PG on SC structure can be attributed to their functional groups. In DSC transition temperatures of lipid fractions are decreased whereas SAXD long distances of lamellar phases reveal an additional interference due to an integration into hydrophilic regions of hexagonally packed lipids (PG) or orthorhombically packed lipids (glycerol). The increased repeat distance is attributed to the polar character of both molecules. However, with IPM the long distance remains unaffected. IPM is integrated into the lipophilic regions of SC lipid matrix as concluded from an increase of WAXD reflections of orthorhombical lipids and a decrease of WAXD reflections of hexagonal lipids. The combination of PG/IPM affects SC microstructure in a specific manner. DSC shows a decrease in transition temperatures of the lipid fractions, although not as much as expected from the single substances. Additionally, the combination of IPM/PG affects the short distances of orthorhombically and hexagonally packed lipids in WAXD measurements similar as PG alone, whereas the long distance seems to remain unaffected as in the case of IPM pretreatment. Adjuvants with penetration enhancing potential reveal different effects on SC lipid microstructure, which have to be kept in mind in terms of formulating systems for transdermal administration.

Role of isopropyl myristate, isopropyl alcohol and a combination of both in hydrocortisone permeation across the human stratum corneum.

The influence of isopropyl myristate (IPM), isopropyl alcohol (IPA) and a combination of both was studied in view of hydrocortisone (HC) permeation across the human stratum corneum (SC). IPM, IPA and their combination were incorporated into water-containing hydrophilic ointment (WHS), and the resulting effects on HC permeation and on HC accumulation in human SC were investigated as well as the influence of these substances on the microstructure of the SC. Differential scanning calorimetry as well as wide- and small-angle X-ray diffraction show that IPM incorporation into SC results in densely packed bilayer lipids and a loss of order of the corneocyte-bonded lipids. Both effects result in a decreased diffusion coefficient of HC in SC and thus in a decreased permeation rate compared to that of HC from WHS. On the other hand, IPA fluidizes and disrupts the bilayer structure of the intercellular lipids. These effects, concomitant with an increased amount of dissolved HC within the ointment, increase the permeation rate of HC across SC. The combination of both ingredients effects a stronger fluidization and disruption of intercellular lipids than with IPA alone. Therefore, the permeation rate of HC across SC is higher than with IPA alone. Consequently, the IPM and IPA combination acts synergistically on the microstructure of SC.