Permeability coefficient for water

Permeability coefficients for water have remarkably similar magnitude in all of the species studied. 

Pfaff RT, Agca Y, Liu J, Woods EJ, Peter AT, Critser JK (2000) Cryobiology of rat embryos, I determination of zygote membrane permeability coefficients for water and cryoprotectants, their activation energies, and the development of improved cryopreservation methods. Biol Reprod 63 1294-1302. 

Nodes, E.E., Mazur, P., Watson, P.F., Kleinhans, F.W., Critser, J.K. (1993). Determination of water permeability coefficient for human spermatozoa and its activation energy. Biol, of Reprod. 48,... 

Figure 22 Correlation between the log permeability coefficient for a series of peptides across a Caco-2 cell monolayer in the Transwell system and A log PC, which is defined as log PC(n-octanol/water) — log PC (isooctane/water). [Redrawn from Burton et al. (1992) with permission from the publisher.]...

Figure 5 compares the experimental data with predictions based on the new pore model. The theoretical calculations were done using Equation 6 together with the experimental 3-estradiol solubility data and the experimental ethanol-water concentration gradient data (Figure 4). The partition coefficients in the pores were derived from the solubility data using Equation 4. Henry s law seems to be obeyed, as evidenced by the similar permeability coefficients for 3-estradiol obtained from tracer level as well as saturated solution experiments (Figure 1).

Fig. 4.9 (a) Logarithm of the apparent permeability coefficient, for perfusion experiments in rats (filled symbols) and Caco-2 (empty symbols) versus logarithm of the intrinsic permeability coefficients based on PAMPA. (b) The unstirred water layer effect in the Caco-2 data. 

Most of the permeability coefficients for small solutes crossing the plasma membrane range from 10-10 to 10-6 m s-1. Hence, a cell wall generally has a higher permeability coefficient than does a membrane, which means that the cell wall is usually more permeable for small solutes than is the plasma membrane. For comparison, let us consider a permeability coefficient appropriate for an unstirred liquid layer adjacent to a cell wall or membrane. Specifically, Dj for a small solute may be 1 x 10-9 m2 s-1 in water, Kj is 1 in the aqueous solution, and let us assume that Ax is 30 pm for the unstirred... 

The possibility of ethanol-induced alterations in the protein domains of SC was considered by Kurihara-Bergstrom et al. [124], who examined human SC treated with perdeuterated ethanol-water systems by FT-IR. The penetration studies showed that the maximal permeability coefficient for salicylic acid and ethanol from saturated ethanol-water delivery systems was achieved at 0.63 volume fraction of ethanol. Infrared spectra of SC samples immersed in EtOD-D20 systems for 6 hours revealed the presence of keratin, predominantly in the a-helical conformation, up to 0.25 volume fraction EtOD. Above this concentration, the appearance of shoulders at 1688 and 1615 cm near the Amide I band at 1650 cm was interpreted as the formation of extended chains or distorted P-strands within the protein domain. An evaluation of lipid extraction was also made by comparing the intensities of the infrared bands arising primarily from stratum comeum proteins to those associated with lipid domains. A decreased absorbance of the C-H stretching bands relative to the N-H stretching band would indicate that some degree of lipid extraction had occurred. The ratio of these two bands decreased from 0.96 to 0.76 as volume fraction ethanol increased from 0.4 to 1.00, respectively, indicating lipid extraction. 

Of the human skin permeation data compiled by Flynn (1990) and analyzed by Potts and Guy (1992), only six of the 92 compounds have log values less than zero, and only two of those six have log K values less than negative 1. Clearly, the regression performed by Potts and Guy (1992) for human skin data was weighted almost entirely by relatively lipophilic permeants. In light of this fact, it seems worthwhile to focus on the polar permeants included in the analyses of Potts and Guy (1992) to see how well the proposed correlations actually predict the permeability coefficients for these permeants. Of the permeants included in the human skin analysis, sucrose and water are the most polar (log == -3.7 and -1.4, respectively). The correlation that results from the fit of the compiled data to the equation proposed by Potts and... 

Guy predicts permeability coefficients for sucrose and water that are factors of 150 and 3 times lower than the experimental values reported in Flynn s (1990) compilation. The fit between predicted and experimental permeability of the permeants with log values between -1 and 0 is more satisfactory. Glucose is the most polar compound included in the data reported by Acker-mann et al. (1987). The correlation resulting from the analysis of Potts and Guy for Ackermann s data set underestimates the permeability of glucose by a factor of 10. The magnitudes and direction of these discrepancies cause some doubt as to the adequacy of the proposed correlations in the polarity and MW range of sucrose and glucose. 

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]. 

Figure 2 shows the oxygen permeability coefficient for EvOH-32 as a function of water content at 20C. The oxygen barrier effectiveness of EvOH-32 decreases markedly with the absorption of water because of plasticization of the EvOH-32 matrix. 

The partition coefficients for water in p-HEMA and p-HEMA crosslinked with 1 mole % EGDMA are 0.52 and 0.51 respectively. However, from Sung s data (5), it is possible to define partition coefficients for water into the various subclasses of water in the hydrogel membranes. For p-HEMA, these values of Ko are bulk water 0.30, bulk + intermediate water 0.41, and bulk + intermediate + bound water 0.52. For p-HEMA with 1 mole % EGDMA, the values are bulk water 0.21, bulk + intermediate water 0.36, and bulk + intermediate + bound water 0.50. A comparison of these values with the experimental values found in Tables I and II indicates that the sugars partition primarily into bulk water of both membranes and, therefore, that the diffusion of these solutes occurs primarily in the bulk water of the membranes. This result is consistent with the observed very low permeability of inositol and raffinose in p-HEMA with 5 mole % EGDMA. These membranes have 1 i ttl e or no bul k water (5.). 

Table A3 tabulates and Figure 15.3 shows 17 permeability coefficient values for 11 compoimds (14 fully validated and 3 excluded data points 10 fully validated compoimds) measured in rat skin. This database is small and consists mainly of phenols, alcohols, and water. Because all chemicals in this database are of relatively low MW and many are structurally related (meaning that MW and log are correlated), log is more clearly linear with log than in Figure 15.1 and Figure 15.2. Water permeability coefficients are similar to human skin (i.e., 1.47 x 10" cm h" in rats compared to 1.18 x 10" cm h in humans). However, the permeability coefficient for paraquat in the rat is significantly higher than in humans (i.e., 3.07 X 10" cm h in rats compared to 8.70 x lO- cm h" in humans, a ratio of about 35). Paraquat permeability was similar in the haired and hairless rat.

The permeability coefficients of water and urea in rat were taken without modification from Table 1. Urea was more than 10% unionized in the vehicle. The exposure time was 8 h, which was sufficient for steady state to be obtained. We learned the following from personal communication with Barber (1996) (1) The temperature used in the water permeation smdies was 30°C (2) urea was delivered in a vehicle with pH 7.1 (3) the membrane was isolated SC and (4) the authors are not aware of any inaccuracies in the document. The authors also listed permeability coeffidrait values for six other compounds that could be added to this database. These compounds are 2-ethoxypropionzte, diethylene glycol monobutyl ethCT, di(2-ethylhexyl) phthalate, 2-ethylhexanol, ethyl 3-ethoxypropioniate, and 2-propoxyethanol. 

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