Structure-activity relationships for organotin compounds

Abstract

Abstract The LC50 concentrations of a series of 15 structurally distinct diorganotins (R2SnX2) and triorganotins (R3SnX) were determined for zoeae of the mud crab Rhithropanopeus harrisii. Zoeae were exposed from hatching until metamorphosis, at ˜14 d. The LC50 values varied by almost 4 orders of magnitude, from the least toxic aquated species, dimethyltin (LC50 = 92,276 nM) to the most toxic, tricyclohexyltin (LC50 = 19.8 nM). Within a homologous series, the diorganotin was less toxic than the corresponding triorganotin, but the toxicity of the two classes overlapped, e.g., dicyclohexyltin was more toxic than trimethyltin and about as toxic as triethyltin. Correlations between the Hansch π parameter and the LC50, and between total surface area and the LC50, suggest that aqueous thermodynamic activity (hydrophobicity), a function of the organic ligand attached to tin, controls bioconcentration and thus the lethal dose. This conclusion is substantiated by the observation of a single linear relationship between a sum of Hansch fragment constants and the LC50 values for both the di- and triorganotins. The difference in toxicity between di- and trialkyltins results from a decrease in hydrophobic character when a hydroxyl group is substituted for an organic ligand in the former. Any electronic effect of the organic ligand is overwhelmed by the factors that control hydrophobic behavior, as evidenced by the observed poor correlations with χ.