Effect on permeability

Figure 3. Temperature effects on permeability of calcein through lipid bilayer membranes of Mals(Phyt)2 and DPPC.

Darcy s work was confined to the quantity of water discharged from a sand filter. Four examples of the application of Darcy s law as applied through a sand filter (actually a permeameter) is shown in Figure 3.10. Notice that the orientation of the cylinder has no effect on permeability. An example calculation of hydraulic conductivity (K) is presented in Figure 3.10 using the equation below ... 

Seo PR, Teksin ZS, Kao JP, Polli JE (2006) Lipid composition effect on permeability across PAMPA. Eur J Pharm Sci 29 259-68. 

To further investigate the pH and temperature effects on permeability, we analyzed the permeation of oxprenolol HCl under the four possible pH... 

In pacemaker cells (whether normal or ectopic), spontaneous depolarization (the pacemaker potential) occurs during diastole (phase 4, Figure 14-1). This depolarization results from a gradual increase of depolarizing current through special hyperpolarization-activated ion channels (If, also called If,) in pacemaker cells. The effect of changing extracellular potassium is more complex in a pacemaker cell than it is in a nonpacemaker cell because the effect on permeability to potassium is much more important in a pacemaker (see Effects of Potassium). In a pacemaker—especially an ectopic one—the end result of an increase in extracellular potassium is usually to slow or stop the pacemaker. Conversely, hypokalemia often facilitates ectopic pacemakers. 

Discrete and continuum models of transfer of molecules over various sorption sites of a microheterogeneous membrane were considered for systems with weak intermolecular interactions and membranes with constant composition and structure. An equation for estimating size effects on permeability coefficient II of microheterogeneous membranes was derived [188], and the possibility of applying the continuum model to calculate the n value in thin films of thickness L is numerically analyzed. The effect of the composition and structure of a uniformly microheterogeneous membrane on the permeability coefficients II was studied. The dependence of n on the composition is a convex function if the migration between different sorption sites proceeds more quickly than between identical sites and a concave one in the opposite case [189],... 

Anderson, B. D., Higuchi, W. I. and Raykar, P. V. (1988). Heterogeneity effects on permeability-partition coefficient relationships in human stratum comeum. Pharm. Res. 5 566-573. 

Several methods have been employed in the determination of the resistance of monolayers to evaporation. The evaporation rate may be determined from the increase in mass of a desiccant suspended over the monolayer, or from the loss of weight of a Petri dish containing solution and spread monolayer, under carefully controlled conditions. Such experiments are useful in determining the effect on permeability of incorporation of a plasticiser into the polymer stmcture. ... 

Biomimetic artificiai membranes-factors Effects of pH and co-solvents on the BAMPA were investigated to determine the optimal conditions for the prediction of oral absorption. The permeability (Pam) of 33 structurally diverse drugs to the PC/PE/ PS/PI/CHO/1,7-octadiene membrane system [bio-mimetic lipid (BML) membrane] was measured at pH 5.5,6.5, and 7.4. The pH dependence of Pam was in accordance with the pH partition theory. The better prediction of oral absorption (fraction of a dose absorbed) was shown under the pH 5.5 condition for determining the permeability of poorly soluble compounds were examined. Dimethysulfoxide (DMSO), ethanol (EtOH) and polyoxyethyleneglycol 400 (PEG 400) were added up to 30% to the transport medium as solubilizers. DMSO, EtOH and PEG 400 decreased Pam of hydrocortisone and propranolol. For example, DMSO (30%) decreased Pam of hydrocortisone and propanol by 60 and 70%2, respectively. DMSO and PEG 400 also decreased Pam of ketoprofen. In contrast, EtOH produced an opposite effect on permeability, that is, an increased Pam of ketoprofen. Therefore, the high concentration of these co-solvents could lead to the under- or overestimation of drug permeability. 

Figure 5.50 shows the salinity effect on the permeability reduction factor, Fkr, predicted from Eq. 5.36. This figure shows that F j decreases with salinity. However, Figure 5.40 shows that higher salinity leads to higher polymer adsorption. Therefore, the salinity effect on permeability reduction factor is different from that on polymer adsorption. In other words, because of the salinity effect, the permeability reduction based on Eqs. 5.36 and 5.37 does not... 

This paper considers Neoprene elastomers and their use as barriers to water penetration. Long time effects on permeability and composition will be discussed as will the effects on permeability of temperature and high-frequency mechanical (acoustic) agitation. 

Permeability is intensely affected by the presence of an intramolecular hydrogen bond." In this area tight SAR can occur. Any structural change that causes an internal hydrogen bond to form (or that prevents one from forming) can have a dramatic effect on permeability. The effect of a single intramolecular hydrogen bond on... 

The permolecular structure of polymers exerts a perceptible effect on permeability. Thermoplasts whose structure is not spherulitic and materials with a coarse-spherulitic structure are highly permeable because of different development levels of the microcapillary system of permolecular formations. 

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