From Flexible to Constrained Tris(tetraamine) Ligands: Synthesis, Acid-Base Properties, and Structural Effect on the Coordination Process with Nucleotides
Résumé
This work presents the synthesis and characterization of L2 and L3, which formed with the previously described ligand L1 a family of three tris(tetraamine) ligands based on a mesitylenyl spacer. The trimeric ligands differ from one to the other by the nature of their tetraamine moieties: triethylenetetraamine (L1), cyclen (L2), and constrained cyclen (L3). The impact of the rigidification of the structure from L1 to L3 on the acid–base properties is investigated, and the behavior of the ligands towards triphosphate (TriP), adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) anion receptors is explored by potentiometric investigations. To characterize and understand the driving forces implicated in the supramolecular assemblies, results are supported by 1H and 31P NMR measurements performed over a wide pH range. ATP appears as the most complexed anion and particular attention is given to comparison with its inorganic triphosphate analogue to highlight the contribution of π-stacking interactions. Results unambiguously show the various coordination scheme induced by the structure of the ligands.