Interaction of triiodide anion with gangliosides in aqueous iodine

Abstract

Molecular iodine interacts with the anionic, sialic acid-containing glycosphingolipid, ganglioside, to produce triiodide anion. The “triiodide” spectrum arising from the interaction, with absorption maxima at 287 nm and 351 nm, apparently is identical with that given by sodium iodide-iodine solutions, and it is destroyed by addition of sodium thiosulfate. The interaction has been applied to an estimation of the aggregative properties of the lipid in aqueous medium in terms of the critical micelle concentration (CMC). The following CMC's were determined: Tay-Sachs ganglioside, 7.5 × 10 −5 M; monosialoganglioside, 8.5 × 10 −5 M; disialoganglioside, 9.5 × 10 −5 M; trisialoganglioside, 1 × 10 −4 M. Absorption maxima of the triiodide spectrum are the same above or below the CMC, and no change is induced by heating to 65°C. The interaction of iodine and gangliosides produces a greater molecular ratio of triiodide ion relative to ganglioside below the CMC than above. This finding is interpreted to indicate a less anionically shielded submicellar, as compared with micellar, interior for ganglioside aggregates. The lack of dependence of the triiodide absorption maxima on the degree of aggregation of ganglioside molecules is proposed to stem from a cavitation structure for the associated molecules in which the micellar interior is subject to considerable water penetration. Triiodide anion is clearly associated with ganglioside aggregates as evidenced by coprecipitation of the triiodide anion with ganglioside micelles upon ultracentrifugation.