Cation, Anion and Ion-Pair Complexes with a G-3 Poly(ethylene imine) Dendrimer in Aqueous Solution

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.

Sensing Zn2+ in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail

“…Anion complexation by L (in the absence of Zn 2+ ) takes place with all protonated forms of L ( Table 3). The stability of the complexes increases with ligand charge, as expected for polyammonium receptors [58][59][60][61][62]. Conversely, the charge of the anions does not seem to be so important, at least for phosphate, as equal (within experimental errors) binding constants were obtained for the interaction of H 2 L 2+ with the differently charged HPO 4 2− (logK = 2.77(7)) and H 2 PO 4 − (logK = 2.83(7)) anions.…”

A linear free-energy relationship for the prediction of metal ion complexing properties in hybrid carbon-based scavengers

“…The in-depth analysis of protonation equilibria and stability constants of HBPEI/H + show the first protonation step of L with a large constant (log K 1 = 9.47), similar to those of terminal amino groups in linear polyamines made of ethyleneimine functional units ((–NH n –[CH 2 CH 2 ]–) m , n = 1,2; m = 2–5)], 39 therefore, K 1 can be attributed to the protonation of terminal amino groups in HBPEI, considering their lower steric demand as primary amines, that enables the formation of intramolecular hydrogen bonds with nearby nitrogen atoms, 40 and their external location and higher mobility, that allow to locate each positive charge as much apart as possible from each other. 41…”

“…The in-depth analysis of protonation equilibria and stability constants of HBPEI/H + show the first protonation step of L with a large constant (log K 1 = 9.47), similar to those of terminal amino groups in linear polyamines made of ethyleneimine functional units ((-NH n -[CH 2 CH 2 ]-) m , n = 1,2; m = 2-5)], 39 therefore, K 1 can be attributed to the protonation of terminal amino groups in HBPEI, considering their lower steric demand as primary amines, that enables the formation of intramolecular hydrogen bonds with nearby nitrogen atoms, 40 and their external location and higher mobility, that allow to locate each positive charge as much apart as possible from each other. 41 Successive protonations of L and L 2 show a decrease in K n values due to the lowering in basicity caused by the introduction of positive charges in the surroundings of the basic centers. Thus, the small equilibrium constant of the last protonation process (log K 3 = 2.61) is the logical outcome of the large and progressive charge accumulation in HBPEI molecules, as their protonation progresses close to completion.…”

Facile synthesis and anion binding studies of fluorescein/benzo-12-crown-4 ether based bis-dipyrromethane (DPM) receptors

“…Generally, a combination of noncovalent/supramolecular interactions participates in the anion recognition chemistry, including coulombic interactions, halogen bonding, hydrogen bonding, CH-anion, anion-p interactions, p-p stacking, and other important non-covalent forces, as well. [33][34][35][36][37][38][39][40][41][42][43][44][45][46] However, most frequent moieties consisting of the active hydrogen bonding sites for instance urea, thiourea, phenol, amide, pyrrole etc., have prominently been used for the design and synthesis of the anion receptors. [47][48][49][50][51][52] Remarkably, as can be inspected from the Fig.…”