Unexpected discovery of calcium cryptates with exceptional stability

Abstract

A 2,2'-bipyridine-N,N′-dioxide-based cryptand has been found to exhibit exceptional apparent complex stability for Ca²⁺ and unusually shows very high selectivity for Ca²⁺ over trivalent lanthanoid cations. The calcium cryptate is kinetically inert to an extent that it even withstands competition experiments with a 77-fold excess of free DOTA ligand, which is currently the chelator with the highest formation constant for calcium.