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Gas diffusion mechanisms and diffusion coefficients in microkinetic system of solid materials characterize the different performance of chemical and transport processes. These factors should be evaluated with respect to the range of diffusion coefficients based on the number of experimental methods. Here, impedance spectroscopy which is a powerful tool for understanding transport phenomena of gases in nanostructured porous solids is used. In this work, we developed a new approach to compare and evaluate diffusion coefficients of isopropanol in the zeolite H-ZSM5. Furthermore, FTIR spectroscopy was used to study the adsorption of isopropanol in H-ZSM5 at different temperatures to support the interpretation of diffusion regimes. The combination of EIS with FTIR enables to illustrate preferred interaction sites and their influence on transport processes. The activation energy for transport of molecules in the channels is also calculated. Results are compared to literature data and suggest improved applications of EIS to characterize transport processes.

Dehydration experiments were carried out on larger B(OH)4-sodalite single crystals, Na8[Al6Si6O24](B(OH)4)2, at temperatures 300°C, 350°C and 400°C. Profiles of relative intensity variations of B-(OH)/Si-O vibration could be measured by micro-Raman spectroscopy ranging typically between 5 and 40 μm into the interior of the crystals. Profile analyses reveal effective dehydration diffusion coefficients DOH between 10-11 and 10-9 cm2/s with an Arrhenius activation energy Ea ≈ 1.3 eV. H/D exchange experiments were realized at temperatures 50, 100 and 150°C in closed tubes. Profiles of OD/OH Raman intensities reveal effective H/D exchange diffusion coefficients DHD between 1.5∙10-10 and 4∙10-11 cm2/s with Ea ≈ 0.4 eV. The dehydration effect for crystalline powders was reinvestigated up to 500°C in TG experiments and by IR spectra. These data show that dehydration takes place forming NaBO(OH)2- and NaBO2-sodalite centered at temperatures 250°C and 410°C, respectively. It is discussed that diffusion coefficients DP could be estimated using the mass losses for the two stages of dehydration related to the experiments on the polycrystalline samples. Linear extrapolation of DOH, i.e. the diffusion coefficients obtained on larger single crystals, towards lower temperature well approximates DP using the dehydration effect obtained for crystalline powders between 140 and 180°C assuming spherical crystals of 0.1 μm diameters. H/D exchange could occur with proton/deuteron jumps through the four-ring windows of the sodalite framework. Larger ions or molecules predominantly pass through the six-ring windows which requires window opening.

Brain function is based on communication between individual cells, neurons and glia. From a traditional point of view, neurons play a central role in the fast transfer of information in the central nervous system while astrocytes, major type of glia, serve as housekeeping elements maintaining homeostasis of the extracellular microenvironment. This view has dramatically changed in recent years as many findings ascribe new roles to astrocytes. It is becoming evident that astrocytes communicate with neurons via chemical signals released to the extracellular space (ECS). Astrocytes also have communication systems of their own, such as calcium waves that use gap junctions in combination with purinergic signaling through the ECS. Here we discuss yet another important role for astrocytes: that they regulate diffusion of signaling molecules and therapeutic agents in the extracellular microenvironment by contributing to the structural properties of ECS. There is a wealth of morphological data showing that each astrocyte is an exclusive occupant of a small volume of brain tissue, and that many fine astrocytic processes ensheathe neuronal processes and bodies. The functional significance of these unique morphological features is largely unknown with the exception of astrocytic coverage of synaptic formations. At the synapses, astrocytic processes play an active role by restricting neurotransmitter diffusion to the synaptic cleft and its immediate vicinity. Recent work suggests that astrocytic processes work in a similar fashion throughout the ECS and thus control the diffusive spread of substances over both short and long distances.