Abstract
The G-3 poly(ethylene imine) ligand L2 shows a multifaceted coordination ability, being able to bind metal cations, anions and ion-pairs. The equilibrium constants for the formation of metal (Cu2+, Zn2+), anion (SO42−) and ion-pair (Cu2+/SO42−) complexes were determined in 0.1 M Me4NCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric titrations. Thanks to its dendrimeric nature, L2 can form highly nucleated metal complexes, such as Cu5L210+ and Zn4L28+, in successive and well-defined complexation steps. Protonated forms of L2 give rise to relatively weak anion complexes with SO42−, but the addition of Cu2+ significantly enhances the binding ability of the ligand toward this anion below pH 9. In more alkaline solutions, an opposite trend is observed. The coordination properties of L2 are discussed with the support of modelling calculations. According to results, L2 is a promising molecule for the preparation of solid supported materials for the recovery of cations and anions from aqueous media and/or for applications in heterogeneous catalysis.
Highlights
We showed that the G-2 poly(ethylene imine) dendrimer L1 (Figure 1) and its variously protonated forms are able to assemble stable cation, anion and ion-pair complexes in aqueous solution [1,2,3,4]
L2 showed an unprecedented behaviour toward ATP, the dendrimer being able to enhance or inhibit dephosphorylation of the nucleotide depending on the solution pH [6]
The ability of L2 to form stable highly nucleated complexes over a large pH range, as a consequence of its dendrimeric nature and of the many amine groups in its structure, make this compound a promising candidate for the preparation of solid supported materials to be used in the recovery of metal ions from aqueous media
Summary
We showed that the G-2 poly(ethylene imine) dendrimer L1 (Figure 1) and its variously protonated forms are able to assemble stable cation, anion and ion-pair complexes in aqueous solution [1,2,3,4]. Such ability appears to be a propagation and an enhancement of the properties of the parent ligand tris(2-aminoethyl)amine (tren), which is historically known to bind metal complexes and, more recently, has been accredited as a rather efficient anion receptor [5]. L2 showed an unprecedented behaviour toward ATP, the dendrimer being able to enhance or inhibit dephosphorylation of the nucleotide depending on the solution pH [6]
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