Effect of monofluorosulphonate, difluorophosphate and fluoroborate ions on the iodine uptake of the thyroid gland.

Abstract

SEVERAL inorganic anions have been found to interfere with the normal function of the thyroid gland1–3, the perchlorate and thiocyanate ions being outstanding in this group. On the other hand, it has been shown that other common anions, including chloride, bromide, fluoride, sulphate, phosphate and bromate ions, have no significant effect on the iodine uptake and retention in the gland. The effect of perchlorate ions suggests a competition for some sites in the thyroid1. This assumption is supported by the fact that perchlorate ions concentrate in the gland4. Further, it was shown4 that perchlorate ions do not undergo metabolization, thus excluding the possibility that they are involved in some enzymatic redox system. This behaviour of the perchlorate ion distinguishes it from other inorganic thyroid blocking agents like thiocyanate ions which have been shown to be metabolized and not to accumulate in the gland2. It occurred to us that the competition between perchlorate and iodide ions may be due to their similar monovalency and size. It is hard to compare the size of a spherical ion like iodide with that of a tetrahedral complex ion like perchlorate. Still we may compare the calculated volumes. The volume of ClO4 − may be calculated taking r(O=) = 1.33 A. From the radius of I−, r(I−) = 2.16 A., we may find its volume. We find for the volumes of ClO4 − and I− the values 3.94 and 4.23 × 10−23 cm.3 respectively. The experimental value6 for the ionic volume of ClO4 − is 4.05 × 10−23 cm.3.