Effects-driven chemical design: the acute toxicity of CO2-triggered switchable surfactants to rainbow trout can be predicted from octanol-water partition coefficients

For both environmental protection and improved energy efficiency, CO2-triggered switchable surfactants have been developed to change surface activity and solubility upon command. Surfactant activity is turned on by introduction of one atmosphere of CO2 and reversed by purging with air or nitrogen. These surfactants have numerous potential industrial applications related to their ability to stabilize and destabilize emulsions upon command. To assess their potential environmental impacts, we tested the acute toxicity of nine switchable surfactants to rainbow trout (Oncorhyncus mykiss) at pH similar to 8.0, typical of natural surface waters. The surfactants were synthesized in several variations, differing in the structure of the hydrophobic tail group, the hydrophilic head group, or both. A strong correlation between the log of the estimated octanol/water partition coefficients (log P) and the toxicity of eight switchable surfactants formed the basis of a structure-activity relationship that was used to design a ninth compound. That new compound had the lowest toxicity of all of the switchable surfactants tested. The effect of log P on acute toxicity was similar to that reported in the literature for other organic compounds. This model shows that despite the addition of varying functional groups, switchable surfactant toxicity remains largely dependent on log P and differs little from traditional non-switchable surfactants. The log P relationship developed provides a very useful tool for screening new compounds for acute toxicity.