Membrane matrix effective permeability

Various tiny structures, so-called organelles, are embedded in the cytoplasm where they make numerous cell functions possible, (s. fig. 2.9) (s. tab. 2.1) The enzyme-rich mitochondria have an outer and an inner membrane, with the latter forming creases (cristae). The outer membrane is relatively permeable for small molecules. However, the inner membrane (which surrounds the matrix) must use specific transport proteins to enable protons, calcium, phosphate and so on to pass. Energy-rich substrates are transformed into ATP in the mitochondria. The enzymes which are responsible for fatty-acid degradation and the citric-acid cycle can be found in the matrix. The inner membrane also contains the enzymes of the so-called respiratory cycle. An enormous number of energy-providing reactions and metabolic processes take effect at this site. They have a round-to-oval shape with a diameter of about 1 im. There are 1,400-2,200 mitochondria per liver cell (18-22% of the liver cell volume). They generally lie in... 

A method for determining the effect of particle size on the effective permeability values of zeolite-polymer mixed matrix membranes has been developed in this study. The model presented is a modified form of the effective medium theory, including the permeability and thickness of an additional phase, the interphase, which is assumed to surround the zeolite particles in the polymer environment. The interphase thickness and permeability values were determined by taking into consideration the assumptions that in case the size of the zeolite particles is held constant, the interphase thickness should be equal for different gases and in case the zeolite particle size is varied, the interphase permeability should remain constant for the same gas. The model seems to fit the experimental permeability data for O2, N2 and CO2 in the silicalite-PDMS mixed matrix membranes well. 

Vu et al. [122] incorporated CMS materials into polymers to form MMM films for selective gas separations. The CMS, formed by pyrolysis of a PI precursor and exhibiting an intrinsic CO2/CH4 selectivity of 200, was dispersed into a polymer matrix. Pure-gas permeation tests of such MMMs revealed the CO2/CH4 selectivity was enhanced by as much as 40%-45% relative to that of the pure polymer. The effective permeabilities of fast-gas penetrants (e.g., O2 and CO2) through these MMMs are also improved relative to the intrinsic permeabilities of the unmodified polymer matrices. For a CO2/H2 gas mixture, the CO2 will be the fastest permeating component, and H2 will be retained on the feed side to avoid repressurization, in which case the polymer matrix dictates the minimum membrane performance. Properly selected molecular sieves can only improve membrane performance in the absence of defects. The polymer matrix must be chosen so that comparable permeation occurs in the two phases (to avoid starving the sieves) and so the permeating molecules are directed toward (not around) the dispersed sieve particulates. 

E. E. Gonzo, M. L. Parentis, J. C. Gottifredi, Estimating models for predicting effective permeability of mixed matrix membranes, J. Membr. ScL, 211, 46-54 (2006). 

The experiment was done with various compounds at concentrations from 0.1 to 1000 ppbw, and in all the cases, no matrix effect due to the salt in seawater was observed. Therefore, seven VOCs could be detected simultaneously both in fresh and in salty water. The permeability through the membrane was the main factor limiting the detection sensitivity toward specific compounds. In this MI-PTRMS system, the limit of detection was at about 100 pptw for DMS at a signal-to-noise ratio 3. 

MMC membrane performance can be predicted using various theoretical expressions. Maxwell first analyzed steady-state dielectric properties in a conducting dilute suspension of identical spheres. Robeson et al. (11) applied a similar analysis to determine an effective permeability for a series of organic-organic mixed matrix membranes analogous to the desired defect-firee molecular sieve-polymer membranes noted above where fundamental transport phenomena are similar... 

Similar to hydrophilic flavonoids, hydrophobic flavonoids can affect membrane permeability. Alterations in this biophysical property of liposome bilayers lead to the release of bulky molecules entrapped into the inner aqueous space. As mentioned in the previous section, a strong correlation was found between flavonoid retention to a hydrophobic matrix and their capacity to induce membrane leakage [Ollila et al., 2002]. Interestingly, hydrophilic flavonoids, such as (—)-epicatechin and related procyanidins (dimer to hex-amer) prevented Fe2 + -mediated liposome permeabilization, although in this case the beneficial effect could be related to both their antioxidant and metal chelating capacities and their membrane stabilizing properties [Verstraeten et al., 2004],... 

Research on the various biochemical systems affected by tumor promoters, in particular TPA, has been recently reviewed by Diamond et al. (54) and Werner and coworkers (55) have reviewed the early effects of phorbol esters on the membranes of cultured cells. The latter group reports that TPA causes permeability changes in 3T3 cell membranes and experimental evidence is cited that phorbol esters interact specifically with a membrane-specific macromolecule rather than passive adsorption by the membrane lipid matrix. One of the earliest observed effects of TPA is a significant modification in the transport of potassium, sodium and phosphate. Lee and Weinstein (56) have found that the addition of phorbol esters immediately stimulated the uptake of 2-deoxyglucose in... 

Mixed-matrix membranes have been a subject of research interest for more than 15 years [28-33], The concept is illustrated in Figure 8.10. At relatively low loadings of zeolite particles, permeation occurs by a combination of diffusion through the polymer phase and diffusion through the permeable zeolite particles. The relative permeation rates through the two phases are determined by their permeabilities. At low loadings of zeolite, the effect of the permeable zeolite particles on permeation can be expressed mathematically by the expression shown below, first developed by Maxwell in the 1870s [34],... 

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