Electrospray ionization mass spectrometric study of the metal cation complexation capabilities of a novel, doubly cage-annulated molecular box

Abstract

An unusual molecular box, 4, obtained as a mixture of diastereoisomeric, doubly cage-annulated host molecules, i.e., 4a and 4b, has been prepared. The metal cation complexation properties of the mixture of 4a and 4b thereby obtained have been assessed, with comparison to another bis crown 2, via application of electrospray ionization mass spectrometric (ESI-MS) methods. Both host systems 2 and 4 bind selectively to Li + and Na + , thereby demonstrating preference over the other larger alkali metals. Addition of Ag + to the solutions containing alkali metals does not result in substantial Ag + complexation. Analysis of a solution containing only transition metal, not alkali metal, cations indicates that 4 forms complexes with Zn + and Ag + along with substantial complexation of Na + from residual sodium present in the solvents.