Octanol-watcr partitioning

Monkiedje et al. [10] investigated the fate of niclosamide in aquatic system both under laboratory and field conditions. The octanol/watcr partition coefficient (Kaw) of niclosamide was 5.880 x 10 4. Adsorption isotherm studies indicated that the Freundlich parameters (K, n) for niclosamide were 0.02 and 4.93, respectively, for powder activated carbon (PAC), and 9.85 x 10 5 and 2.81, respectively, for silt loam soil. The adsorption coefficient (Aoc) for the drug was 0.02 for PAC, and 4.34 x 10-3 for the same soil. Hydrolysis of niclosamide occurred in distilled water buffer at pH above 7. No photolysis of the drug was observed in water after exposure to long-wave UV light for 4 h. Similarly, neither chemically volatilized from water following 5 h of sample aeration. Under field conditions, niclosamide persisted in ponds for over 14 days. The half-life of niclosamide was 3.40 days. 

As presented in Chapter 4, DEHP has a relatively low vapor pressure and Henry s law constant, as well as a relatively high octanol/watcr partition coefficient and soil sorption coefficient. This combination of properties is consistent with a chemical that is found to only a limited extent in air (see Staples et al. 1997). Nonetheless, DEHP appears to be a common air contaminant that is present globally in the bw ng/m3... 

Geyer, H., Politzki, G., Freitag, D. (1984) Prediction of ecotoxicological behaviour of chemicals Relationship between n-octanol/watcr partition coefficient and bioaccumulation of organic chemicals by Alga Chlorella. Chemosphere 13, 269-284. 

Gossett RW, Brown DA, Young DR. 1983. Predicting the bioaccumulation of organic compounds in marine organisms using octanol/watcr partition coefficients. Marine Poll Bull 14 (10) 387-392. 

Let s plot BR versus PC (partition coefficient). Figure 2-5 shows the scatter and an attempt at determining a linear fit fur the relationship. Note that compounds I and 11 lie at a considerable distance from the remtiining nine compounds. In addition to the I3.8(X) times difference in activity, there is a 33.9(X) time,s difference in the octanol/watcr partition coefficient. Al.so. the regression line whose equation is... 

No other physicochemical property has attracted as much interest in QSAR as the 1-octanol/watcr partition coefficient (log P). This is because of its direct relationship to membrane permeation and numerous other biological processes (also see Chapter 9). At first sight, the experimental measurement of log P seems to be a straightforward exercise. In practice, this is not the case because many factors affect the experimental determination of log P such as temperature, pH, and stability to degradation. As a result identical replicate samples can give very different log P values, and measurement by different... 

Meylan WM et al., Improved method for estimating bioconcentration/bioaccumulation factor from octanol/watcr partition coefficient, Environ. Toxicol. Chem., 18, 664, 1999. 

Wang, W., Wang, L., Tian, L., Zhang, Z., Qiu, J. (1987) Partition coefficients of the intermediate of pyrethroid in n-octanol/watcr system. Huazhong Gongxueyuan Xuebao 15, 135-137. 

With this representation in mind, a partial explanation can bc presented as to why the /i-octanol/water partitioning system seems to mimic the lipid mcmbranc.s/watcr sy.stctns found in the body. It turns nut that /i-octanol is not as nonpolar as initially might be predicted. Water-saturated octanol contains 2..1 M water because the small water molecule easily clusters around oclunoTs hydroxy moiety. -Ocianol-satur-ated water contains little of the organic phase bccau.se of the large hydrophobic 8-carbon chain of octanol. The water in the /t-octanol phase apparently approximates the polar prop-... 

Drug paniiioning. 18-21. I9f /i-octanol/watcr system and. 19-20 partition coefficient and, 19-21 Drug-reccpior interactions. 3, 8-9. 27-.3.5 activc sitc-dircctcd irreversible inhibition in. 29... 

Fig. 8. Relation between decane/watcr partition eoeffident (abscissa) and octanol/water partition coefficient (ordinate) for some steroids. Data from Giorgi and Stein [19]. The straight lines have slopes as indicated. Steroids are numbered as follows 41, progesterone 42, corticosterone 43, cortisone 44, cortisol 45, dexamethasone 46, (5,o)-dihydrotestosterone 47, testosterone 48, (l7, )-estradiol 49,...

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