A potentiometric and NMR investigation of triphosphate recognition by linear and bismacrocyclic octaamines possessing a 1,4-xylenyl linker

Abstract

The host–guest binding interaction between two symmetrical octaazaligands containing a para-xylenyl spacer and triphosphate anion is reported. The ligands studied here are the para-xylenylbiscyclam (AMD3100) and its linear analogue the para-xylenylbis-1,4,8,11-tetraazaundecane, obtained by linking the two corresponding cyclic or open-chain tetraamines. The purpose of this study is to evaluate the effect of these two different architectures on the factors governing the recognition of the triphosphate anion. The results clearly indicate that compared to its biscyclam analogue, the linear octaamine presents a better triphosphate recognition in the whole p[H] range. On the one hand, the capacity of the octaamine to form easily polyprotonated species constitutes the driving force favouring the formation of ternary species, and, on the other hand, the adaptability of this receptor in organizing hydrogen bonds represents also a benefit for the binding of triphosphate substrate. The polyprotonated ligand is sufficiently flexible to wrap itself round the anion in a way to achieve an optimal fit for the best host–guest recognition.