Solute permeability through

Tomita M, Abe Y, Kondo T. 1982. Viscosity change after dilution with solutions of water/oil/water emulsions and solute permeability through the oil layer. J Pharm Sci 71 332-334. 

Water Permeation and Solute Separation through the Membrane. The measurements of water permeability of the 67 membranes prepared under different conditions were carried out by using an Amicon Diaflo Cell (effective membrane area, 13.9 cm2) under a pressure of 3 kg/cm2 at 25 °C. Some results are listed in Table 1067. It is apparent that much higher water absorption and permeability than the cellulosic membrane are characteristic of the 67 membranes prepared by both the casting polymerization and conventional casting. 

The permeability tests for alkali metal ions in the aqueous solution were also conducted. When an aqueous salt solution moves to cell 2 through the membrane from cell 1, the apparent diffusion coefficient of the salt D can be deduced from a relationship among the cell volumes Vj and V2, the solution concentration cx and c2, the thickness of membrane, and time t6 . In Table 12, permeabilities of potassium chloride and sodium chloride through the 67 membrane prepared by the casting polymerization technique from the monomer solution in THF or DMSO are compared with each other and with that the permeability through Visking dialyzer tubing. The... 

In accordance with observed data, this model shows that water flux increases linearly with applied pressure AP, decreases with higher salt concentration through its impact on osmotic pressure Jt, increases with a smaller membrane thickness I, and increases with temperature through the temperature dependence of the water permeability P . The model also demonstrates that the solute or salt flux J, increases linearly with applied pressure AP, increases with higher salt concentration c , increases with a smaller membrane thickness I, and increases with temperature through the temperature dependence of the solute permeability Pj. Polarization, as described early in this section, causes the wall concentration c to exceed the bulk concentration ci,. 

Most drugs are ionized in aqueous solution (Table 2.1), and can therefore exist in a neutral or a charged state, depending on the pH of the local environment. Molecules are more lipophilic when neutral than when charged. Ionization is expressed by the aqueous ionization constant, pKa. As pointed out below, log D is a p Independent term for ionizable drugs. Permeability and aqueous solubility are also pKa-dependent. Lipophilicity, pKa, permeability through artificial membranes and... 

Instead of the dilute solution approach above, concentrated solution theory can also be used to model liquid-equilibrated membranes. As done by Weber and Newman, the equations for concentrated solution theory are the same for both the one-phase and two-phase cases (eqs 32 and 33) except that chemical potential is replaced by hydraulic pressure and the transport coefficient is related to the permeability through comparison to Darcy s law. Thus, eq 33 becomes... 

Figure 13.9. Membrane permeability coefficience of solutes. Solute permeabilities across typical lipid bilayers of liposomes or lipid vesicles are presented as their respective coefficients in cm/s. In the absence of other transport processes, it would require 10 s to move Na+ across 1 cm distance. When there is a concentration difference across a membrane, multiplying the concentration difference (mole/ml equivalent to mole/cm ) by the permeability coefficient (cm/s) allows estimation of flow rate (mole/s-cm ). For example, a concentration difference of 1Q- mole/cm Na (or 1 x 10" M Na ) would provide a flow of 10 mole/cm x 10" cm/s = IQ- mole/s through 1 cm or 0.006 mole/s through 1 pm of a membrane bilayer.

Polypeptides obtained by the anionic polymerization of optically active N-carboxy-a-amino acid anhydrides are apt to have such an ordered structures as a-helices, which is useful for investigation on the relationship between the physical structure and the permeability of the membrane. Takizawa et al.44 46) studied the water permeation and solute separation through poly(n-alkyl L-glutamate) membranes 3. It was concluded that water molecules permeate through relatively large free spaces... 

MWCO), usually defined as the molar mass at which the membrane rejects 90% of solute molecules. However, as in microfiltration, the molecular shape can affect permeability through the membrane pores. For example, a membrane with a nominal cut-off of 100 kDa, which does not allow globular molecules with a molar mass of 100 kDa to flow through, may allow fibrous molecules with higher molar masses to flow across the pores. As in microfiltration, the membrane pore size is not uniform, with a normal distribution around an average value. 

Gas sensors usually incorporate a conventional ion-selective electrode surrounded by a thin film of an intermediate electrolyte solution and enclosed by a gas-permeable membrane. An internal reference electrode is usually included, so that the sensor represents a complete electrochemical cell. The gas (of interest) in the sample solution diffuses through the membrane and comes to equilibrium with the internal electrolyte solution. In the internal compartment, between the membrane and the ion-selective electrode, the gas undergoes a chemical reaction, consuming or forming an ion to be detected by the ion-selective electrode. (Protonation equilibria in conjunction with a pH electrode are most common.) Since the local activity of this ion is proportional to the amount of gas dissolved in the sample, the electrode response is directly related to the concentration of the gas in the sample. The response is usually linear over a range of typically four orders of magnitude the upper limit is determined by the concentration of the inner electrolyte solution. The permeable membrane is the key to the electrode s gas selectivity. Two types of polymeric material, microporous and homogeneous, are used to form the... 

A second commonly used pore-restriction model is defined by the permeability of a solute ion through a membrane relative to water, using the reflection coefficient, a. It was pointed out by Davson [102] that the reflection coefficient, with limits o = 1, no entry, and a = 0, no restriction on entry, correlates well with the Renkin model. In the present context, 1 - o is simply iont/ watep Where / water the iontophoretic permeability coefficient of water [68]. Plots of log (1 - a) versus r, log MV, or MV should give slopes identical to plots based on The reflective coefficient, a, is often now used to correct for differences in the extent of solute ion transport with convective flow during iontophoresis [68,103,104]. 

UnUameUar liposomes (Fig. 4) can be loaded passively with the compound of interest, the external water phase replaced by an acceptor medium, and the concentration of this compound measured in the medium as a function of time. Liposome studies allow a complete manipulation of solute environment both inside and ontside of the vesicles, thns making it a snit-able system for passive mechanistic absorption stndies. The so-called stopped-flow techniqne can be used to study permeability through liposome bUayers. The major advantage with this technique is that even very rapid permeation processes can be measured. 

The transport of gas (permeability) through a dense, polymeric membrane can be described in terms of a solution-diffusion mechanism with permeability expressed as in Equation 4.5. 

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