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No description available.

Life supporting biological membranes are barriers to toxic chemicals. One of the factors determining the toxicity of chemical compounds is their distribution between membranes and their an environment. An octanol-water system is frequently used as a model for biological membranes to estimate the toxic potency of environmental pollutants. The distribution of a chemical between the octanol and the water phase is described by the octanol-water partition coefficient Kow. This study is concerned with the relationship between Kow and the molecular structure of the toxic chemical. In the study the following trihalophenols were included: 2,4,6-trifluorophenol (TriFP), 2,4,6-trichlorophenol (TriCP); 2,4,6-tribromophenol (TriBP) and 2,4,6-triiodophenol (TrilP). The distribution of halophenols between octanol and water was measured as a function of the pH. Experimental results were analyzed in terms of a two compartment distribution model which accounts for the pH dependent dissociation of the trihalophenol. We showed that, with the exception of TriIP, the pH dependence of the distribution coefficient of 2,4,6 trihalophenols can be understood with this model. From the fit of the distribution model to the experimental results, the following log(Kow) of the neutral molecules were determined: 1.96 (TriFP), 3.65 (TriCP}, 4.11 (TriBP) and approximately 4.42 (TrilP). For the ionized species the log(Kow) are 1.38 (TriFP), 0.15 (TriCP), 0.08 (TriBP) and 1.16 (TriIP). In relation with these distribution studies, the following values for the dissociation constants pKa were obtained: 7.12 (TriFP}, 6.15 (TriCP), 5.9 (TriBP) and 6.6 (TriIP). We also found that octanol dissolved in the water phase does not significantly affect the dissociation of TriIP. The relationship between Kaw and trihalophenol molecular structure was studied in two models. Linear relationships were found between log(Kow) and the surface area as well as between log(Kow) and molar volume for both the neutral and the ionized halophenols. It was not possible to discriminate between the two models. Distribution coefficients of the ionized and unionized 2,4,6-trihalophenols are proportional to the each other. The proportionality factor, (3.54±1.49)x104, is a measure of the effect of electric charge on the transfer across the water-octanol interface.

The accumulation of xenobiotics, such as halogenated phenols, in soils, sediments, and living organisms is primarily a partitioning process between an aquatic and organic phase. It is traditional to use a bulk octanol-water system to model the partitioning of a compound between complex biological lipid membranes and aqueous media. The octanol-water partition coefficient Kow successfully approximates the lipid membrane-water partition coefficient Ki;pw of neutral compounds. However, the ionized species of substituted phenols were shown (Smejtek, et al. 1993; Escher, et al. 1996) to have a higher affinity for lipid membranes than predicted from octanol-water results. Data on the octanol-water partition coefficients of molecular ions is limited. In order to compare the partitioning of neutral and charged species of halogenated phenols between the lipid membrane-water and octanol-water systems, we measured the pH dependent distribution of ionized and neutral 2,3,4,6-tetrachlorophenol (TeCP), pentafluorphenol (PFP), pentachlorophenol (PCP), and pentabromophenol (PBP). For the neutral (HA) species of each phenol, log Kow was found to be 4.28 (TeCP), 2.79 (PFP), 4.77 (PCP), and approximately 4.67 (PBP). For the ionized (A-) species of each phenol, log Kow was found to be 0.48 (TeCP), -0.85 (PFP), 1.16 (PCP), and 1.77 (PBP). These results are compared with sorption data on halophenols in a lipid membrane-water system (Smejtek, et al. 1996). This study shows that ionized halophenols have an affinity for lipid membranes about two to three orders of magnitude greater than for octanol. The usefulness of the octanol-water model as a predictor of lipid membrane-water partitioning for ionizable compounds, such as halogenated phenols, is questioned in view of the present results. Two thermodynamic Kow prediction models based on molecular properties are discussed in the context of the octanol-water partitioning of ionized and neutral compounds. The partition coefficients predicted by the molar volume based model (Gobas, et al. 1988) correlates with the experimental Kow results of this study better than Kow results predicted from the molecular surface area based model (Smejtek, et al. 1996). Results of this study support the hypothesis that partitioning of xenobiotics in the octanol-water system is fundamentally different than partitioning in lipid membrane-water systems.

Thesis (Ph. D.)--Oregon Graduate Center, 1979.

Thesis (Ph. D. - Hydrology and Water Resources)--University of Arizona, 1983. / Includes bibliographical references (leaves 137-144).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references : leaf 72.

Physical and geochemical tracer measurements were collected at one oceanographic station (Station A: 72 N 143 W) in the southern Canada Basin from 1989 to 1995, along sections from the Beaufort Shelf to this station in 1993 and 1995, and along a section westward of Banks Island in 1995. These measurements were examined to see how recent events in three upstream Arctic Ocean sub-basins impacted upon Canada Basin waters. Upstream events included Atlantic layer warming, relocation of the Atlantic/Pacific water mass boundary, and increased ventilation of boundary current waters. Early signals of change appeared first in the Canada Basin in 1993 along the continental margin and, by 1995, were evident at Station A in the basin interior and farther downstream. Differences in physical and geochemical properties (nutrients, oxygen, ¹²⁹I and CFCs) were observed throughout much of the water column to depths greater than 1600 m. In particular, the boundary distinguishing Pacific from Atlantic-origin water was found to be shallower and Atlantic-origin water occupied more of the Canada Basin water column. By 1995, Atlantic-origin water in the lower halocline at Station A was found to be colder and more ventilated. Likewise, within the Atlantic layer, Fram Strait Branch (FSB) water was colder, fresher, and more ventilated, and Barents Sea Branch (BSB) water was warmer, fresher, and more ventilated than during previous years. By comparing observations at Station A with eastern Nansen Basin observations, the main source of these changes was traced to dense water outflow from the Barents Sea. Studies indicated that in early 1989 Barents Sea waters were 2°C warmer and that, between 1988 and 1989, a large volume of dense water had left the shelf. These events coincided with an atmospheric shift to increased cyclonic circulation in 1989, a transition unprecedented in its magnitude, geographic reach, and apparent oceanographic impact. The effects of a large outflow of dense Barents Sea water were observed some 5000 km away downstream in the Canada Basin where the BSB component of the Atlantic layer had increased 20% by 1995. / Graduate

No description available.

No description available.