Four Generations of Water‐Soluble Dendrimers with 9 to 243 Benzoate Tethers: Synthesis and Dendritic Effects on Their Ion Pairing with Acetylcholine, Benzyltriethylammonium, and Dopamine in Water

Abstract

Water-soluble benzoate-terminated dendrimers of four generations (from G0 with 9 branches to G3 with 243 branches) were synthesized and fully characterized. They form water-soluble assemblies by ion-pairing interactions with three cations of medicinal interest (acetylcoline, benzyltriethylammonium, and dopamine), which were characterized and investigated by 1H NMR spectroscopy, whereas such interactions do not provoke any significant shift of 1H NMR signals with the monomeric benzoate anion. The calculated association constants confirm that the dendritic carboxylate termini reversibly form ion pairs and aggregates. Diffusion coefficients and hydrodynamic diameters of the dendrimers, as well as changes thereof on interaction with the cations, were evaluated by DOSY experiments. The lack of increase of dendrimer size on addition of the cations and the upfield shifts of the 1H NMR signals of the cation indicate encapsulation within the hydrophobic dendrimer interiors together with probable backfolding of the benzoate termini.

Dendritic and Ion-Pairing Effects in Oxo-anion Recognition by Giant Alkylferrocenyl Dendrimers

“…Such ion pairing at the periphery encapsulating the guest ions has already been invoked with benzoate-terminated dendrimers forming contact ion pairs with cationic guests such as acetylcholine in the interior of the dendrimer. 26 Among the dendritic ferrocenes, the rather constant ΔE 1/2 value is indicative of a lack of dendritic effect within this series, which contrasts with the families of small amidoferrocenyl dendrimers, for which dramatic dendritic effects were observed. 8 This lack of dendritic effect in the present series could be due to the presence of long alkyl tethers.…”

Binding Mechanisms in Supramolecular Complexes

“…[43] The presence of multiple binding centers for fullerenes in appropriate dendrimers results, for example, in substantial increases in the binding constants for the complex, even in cases where a 1:1 stoichiometry has been confirmed. [47] These examples show that observed increases in binding affinity do not require the assumption of unique dendrimer or cluster effects, [25c] or of special cooperativities. [46] Anionic dendrimers bind dopamine more strongly by orders of magnitude than the analogous monomeric benzoate.…”

Paramagnetic NMR Investigation of Dendrimer-Based Host-Guest Interactions

“…In a separate study by the Meijer group, palmitic acid modified PPI dendrimers were successfully used for the extraction of anionic xanthene dyes from aqueous solution [18]. These pioneer studies significantly promote the interests of scientific community in dendrimer-based host-guest systems [12], [19], [20], [21].…”