Tritopic phenanthroline and pyridine tail-tied aza-scorpiands

Abstract

The synthesis of two new tritopic double-scorpiand receptors in which two equivalent 5-(2-aminoethyl)-2,5,8-triaza[9]-(2,6)-pyridinophane moieties have been linked with 2,6-dimethylpyridine (L1) or 2,9-dimethylphenanthroline (L2) units is reported for the first time. Their acid–base behaviour and Zn²⁺ coordination chemistry have been studied by pH-metric titrations, molecular dynamic calculations, NMR, UV-Vis and steady-state fluorescence techniques. L1 and L2 behave, respectively, as hexaprotic and heptaprotic bases in the experimental conditions used (298.1 ± 0.1 K, 0.15 mol dm⁻³ NaCl, pH range under study 2.0–11.0). These ligands are able to form mono-, bi- and trinuclear Zn²⁺ complexes depending on the Zn²⁺-receptor molar ratio. Interaction of L1 and L2 with pyrophosphate (PPi), tripolyphosphate (TPP) and adenosine 5′-triphosphate (ATP) has been followed by pH-metric titrations, ¹H and ³¹P NMR techniques and molecular dynamic analysis. Finally, formation of mixed complexes Zn²⁺-L-PPi, Zn²⁺-L-TPP and Zn²⁺-L-ATP has been studied for both receptors by potentiometric titrations.