Equilibrium Sorption of Structurally Diverse Organic Ions to Bovine Serum Albumin

Reliable partitioning data are essential for assessing the bioaccumulation potential and the toxicity of chemicals. In contrast to neutral organic chemicals, the partitioning behavior of ionogenic organic chemicals (IOCs) is still a black box for environmental scientists. Partitioning to serum albumin, the major protein in blood plasma, strongly influences the freely dissolved concentration of many chemicals (including IOCs), which affects their transport and distribution in the body. Because consistent data sets for partitioning of IOCs are rarely available, bovine serum albumin-water partition coefficients (K BSA/w) were measured in this study for 45 anionic and 4 cationic organic chemicals, including various substituted benzoic and naphthoic acids, sulfonates and several pesticides and pharmaceuticals. The results of this study suggest that binding to BSA is substantially influenced by the three-dimensional structure of the chemicals and the position of substitutions on the sorbing molecules. For example, we found a difference of >1.5 log units between isomeric chemicals such as 3,4-dichlorobenzoic acid and 2,6-dichlorobenzoic acid, and 1-naphthoic acid and 2-naphthoic acid. Conventional modeling approaches (e.g., based on octanol–water partition coefficients) poorly predict log K BSA/w of organic ions (R 2 ≤ 0.5), partially because they do not capture the observed steric effects. Hence, alternative modeling strategies will be required for accurate prediction of serum albumin-water partition coefficients of organic ions.