Relation of chemical structure to activity of iodine compounds against the developmental stages of horse strongyles

Abstract

In a study of the toxicity of 43 iodine compounds for the developmental stages of horse strongyles in feces, compounds which were lethal at a concentration of 0.0005 M or less were iodic acid, periodic acid, barium iodide, cadmium iodide, calcium iodide, lithium iodide, plumbous iodide, strontium iodide, zinc iodide, trimethylene iodide, and pentamethylene iodide. In a series of 16 alkyl monoiodides, all n-alkyl iodides with five or less carbon atoms were inactive at a concentration of 0.01 M. The most toxic member of the series was n-octyl iodide (0.0025 M). Compounds with more carbon atoms were increasingly less active. The three alpha-omega diiodides, ethylene iodide, trimethylene iodide and pentamethylene iodide, were much more active than their related n-alkyl monoiodides. In an analysis of the results obtained in this and a previous study, it has been shown that the toxicity of the compounds is closely related to the availability of the iodine atom. Those compounds in which it is ionized as an iodide ion (inorganic ionized compounds, quaternary ammonium iodides, quaternary heterocyclic nitrogen iodides, and iodonium iodides) were highly toxic, while inorganic un-ionized compounds, aryl iodides and polyiodo compounds, in which the iodine is tightly bound, were relatively non-toxic. Alkyl iodides, in which the iodine is less tightly bound, were intermediate in toxicity. Alpha-iodo and beta-iodo carbonyl compounds, in which the iodine is still more loosely bound, were as toxic as the ionized compounds.