Theoretical studies of separation of cis-trans isomers using dinuclear (Cu(2+)- and Zn(2+)-based) cryptates.

Theoretical investigations have been carried out using density functional theory, with the M06L functional and SMD solvent-modeling, to study the binding interactions of geometrical cis-trans isomers of fumarate (fum(2-)), maleate (male(2-)) and 1,2-cyclopropane dicarboxylate with Cu(2+)- and Zn(2+)-based dinuclear cryptates. It was found that cis-trans isomers of these groups of compounds bind strongly to metal cryptates, and the binding ability of the cryptates is controlled by the shape of the 'incoming' isomer (cis or trans); trans isomers bind more strongly than cis. Due to the size and shape of the cis and trans isomers, the cryptates can bind selectively and, to a large extent, 'recognize' the various cis-trans isomers, suggesting the tantalising possibility of isomeric separation/purification and recognition.