Countercation transport modeled by porous spherical molybdenum oxide based nanocapsules.

Porous nanosized polyoxomolybdate capsule anions of composition [{Mo(VI)(Mo(VI)5O21)(H2O)6}12(linker)30]n-, where (linker)30 is {Mo(V)2O4(SO4)}30 (n = 72) (1 a) or {Mo(V)2O4(SO4)}24{Mo(V)2O4(CH3COO)}6 (n = 64) (2 a), model the (competitive) cellular transmembrane transport of Li+, Na+, K+, and Ca2+ ions along ion channels. According to X-ray crystallography and 7Li and 23Na NMR spectroscopy, Li+ and Na+, the counterions for 1 a and 2 a, respectively, occupy internal sites of the capsule. This study of the counterion transport phenomenon shows that, while Li+ ions can be replaced to a large extent by Na+ and K+ ions and completely by Ca2+ ions added to a solution of 1 a, external Li+ ions do not replace the incorporated Na+ ions of 2 a in an analogous experiment. In this context, related properties of the capsules and especially of their flexible channels, in connection with the complex pathways of cation uptake, are discussed briefly. The relevance of these investigations for lithium-based therapies is also addressed.