Solute relationship between permeability

Diclofenac sodium was absorbed across the buccal mucosa at a zero-order rate from a saturated drug solution. The measured rate showed significant variation between animals but the mean value was 2.8 mg/cm. h. Since the pH of the solutions was substantially above the pKa of this acidic drug, this result suggests that the buccal permeability of the ionized form was substantial. Further investigation of the relationship between permeability and solution pH is required before any firm conclusions can be drawn. 

Most of the research work has been focused on polymer membrane materials involving a solution-diffusion mechanism. The performances of such materials generally fall within the trade-off relationship between permeability and selectivity suggested by Robeson [5], with an upper bound limit for the membrane performances. 

For ionizable molecules, the membrane permeability, P (Pc in cellular models), depends on pH of the bulk aqueous solution. The maximum possible Pm is designated Pq, the intrinsic permeabiUty of the uncharged species. For monoprotic weak acids and bases, the relationship between P and Pq may be stated in terms of the fraction of the uncharged species,, as Pm= Pofo, i-e. ... 

Accurate interpretation of the formation properties (porosity, permeability and irreducible water saturation) requires reliable estimates of NMR fluid properties or the relationship between diffusivity and relaxation time. Estimation of oil viscosity and solution-gas content require their correlation with NMR measurable fluid properties. These include the hydrogen index, bulk fluid relaxation time and bulk fluid diffusivity [8]. 

If initial solute uptake rate is determined from intestinal tissue incubated in drug solution, uptake must be normalized for intestinal tissue weight. Alternative capacity normalizations are required for vesicular or cellular uptake of solute (see Section VII). Cellular transport parameters can be defined either in terms of kinetic rate-time constants or in terms of concentration normalized flux [Eq. (5)]. Relationships between kinetic and transport descriptions can be made on the basis of information on solute transport distances. Note that division of Eq. (11) or (12) by transport distance defines a transport resistance of reciprocal permeability (conductance). 

In summary, the relationship between TER and solute permeability shown here and by Madara and Hecht (1989) emphasizes that these two measures of paracellular leakage are related but not directly correlated. The most obvious feature is that permeability as a function of TER is dependent upon the solute characteristics, primarily molecular size but also charge. The degree of correlation becomes worse as the molecular size of the solute increases. Consequently, the interrelationship between TER and solute permeability must be measured for each cell model before a minimum TER value can be selected as a prerequisite for flux studies. 

Zeidel, M. L., The relationship between membrane fluidity and permeabilities to water, solutes, ammonia, and protons, J. Gen. Physiol. 1995, 306, 67-84. 

Figure 27. Relationship between water-hexadecane partition coefficients and membrane permeabilities for a broad selection of solutes. (Data collected by Walter and Gutknecht [124]. Reproduced with permission from the American Chemical Society)...

In case of solutions of high Molecular weight compounds, the selection of semi-permeable membrane is easier, because the solvent and the solute molecules are quite different in their size. The relationship between the Osmotic pressure of solution of a macromolecular compound and the Molecular weight is widely used for determination of Molecular weights and in the study of the interaction between the solvent and the solute molecules in the solution. 

The challenge for modeling the water balance in CCL is to link the composite, porous morphology properly with liquid water accumulation, transport phenomena, electrochemical kinetics, and performance. At the materials level, this task requires relations between composihon, porous structure, liquid water accumulation, and effective properhes. Relevant properties include proton conductivity, gas diffusivihes, liquid permeability, electrochemical source term, and vaporizahon source term. Discussions of functional relationships between effective properties and structure can be found in fhe liferafure. Because fhe liquid wafer saturation, 5,(2)/ is a spatially varying function at/o > 0, these effective properties also vary spatially in an operating cell, warranting a self-consistent solution for effective properties and performance. 

INSIGHT uses the fundamental correlation between the electrical and permeability properties of skin. Skin permeability shows a strong correlation with skin impedance, as shown in Figure 4B. Figure 4B shows 150 independent and simultaneous measurements of mannitol skin permeability and skin impedance for six different enhancer formulations. The relationship between skin impedance and permeability to hydrophilic solutes confirms that the former can be used as a surrogate measure for the later. Skin conductance is quick and easy to obtain and does not require additional sample handling and analysis. 

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... 

For ionizable molecules, the membrane permeability, Pm, determined from the PAM PA system, may be derived from the effective permeability, Pe, when the effects of the UWL are taken into account [49]. The maximum possible value of Pm is realized at the pH where the solute is in its uncharged form. This limiting Pm is designated P0, the (intrinsic) permeability of the uncharged species. The relationship between Pm and P0 may be stated as ... 

The question of the osmotic relationship between a cestode and its environment is complicated by the fact that some substances can pass through membranes by means other than diffusion (p. 42). Hence the actual osmotic pressure of a solution as measured by physico-chemical means may not be as significant to a worm as the actual content to which the tegument of the worm is permeable - using the word in its widest sense as indicated above. The reason for this is that substances in the medium which (theoretically) contribute to the total osmotic pressure of the medium do not actually exert osmotic pressure across the tegument of the worm, which separates the worm from its environment. 

Robeson [4] showed that there exists a trade-off relationship between selectivity and permeability for dense polymer membranes. This plot was later updated by Singh and Koros [9] (see Figure 4.1). Molecular transport of light gases in such membranes typically occurs by a solution diffusion mechanism (as discussed in Section 4.2.1). For a polymer membrane to be commercially considered for the removal of CO2 from H2, CH4, or air, both the CO2 permeability and selectivity must be competitively high. Since the gases in the mixture with CO2 often are smaller (H2) or about the same size as CO2, they may diffuse more rapidly through the polymers, and it follows that the diffusion selectivity will be <1. The only way... 

The lipid composition of the SC varies between the different regions of the body. A study by Elias et al. demonstrated a quantitative relationship between the rate of percutaneous transport of salicylic acid across the SC at two different body sites (abdomen and leg) and the lipid weight percent at the corresponding sites. The results showed that the lower the lipid content, the higher the penetration rate of salicylic acid, which appeared to be in line with the role of the lipid pathway to the non-polar solute pene-tration.f A more in-depth study by Lampe et al. also found the same variations in lipid weight percent, with face > abdomen > leg > plantar SC in the exact inverse of their known permeability. ... 

---