Redox‐Controlled Interaction of Biferrocenyl‐Terminated Dendrimers with β‐Cyclodextrin Molecular Printboards

Abstract

This paper describes the synthesis and electrochemistry of biferrocenyl‐terminated dendrimers and their β‐cyclodextrin (β‐CD) inclusion complexes in aqueous solution and at surfaces. Three generations of poly(propylene imine) (PPI) dendrimers, decorated with 4, 8, and 16 biferrocenyl (BFc) units, respectively, were synthesized. A water‐soluble BFc derivative forms stable inclusion complexes with β‐CD. The intrinsic binding constant is Ki=2.5×104 M−1. The BFc dendrimers were solubilized in water by complexation of the end groups with β‐CD, resulting in large water‐soluble supramolecular assemblies. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) showed that all the end groups are complexed to β‐CD. Adsorption of the dendrimers at self‐assembled monolayers (SAMs) of heptathioether‐functionalized β‐CD on gold (“molecular printboards”) resulted in stable monolayers of the dendrimers due to the formation of multivalent host–guest interactions between the BFc end groups of the dendrimers and the immobilized β‐CD molecules. The number of interacting end groups is 3, 4, and 4 for dendrimer generations 1, 2, and 3, respectively. The complexation of BFc to β‐CD is sensitive to the oxidation state of the BFc unit. Oxidation of neutral BFc‐Fe2(II,II) to the cationic, mixed‐valence biferrocenium BFc‐Fe2(II,III)+ resulted in dissociation of the host–guest complexes. Scan‐rate‐dependent CV and DPV analyses of the dendrimer–β‐CD assemblies immobilized at the β‐CD host surface and in solution revealed that the dendrimers are oxidized in three steps. First, the surface‐β‐CD‐bound BFc moieties are oxidized to the mixed‐valence state, Fe2(II,III)+, followed by the oxidation of the non‐surface‐interacting BFc groups to the Fe2(II,III)+ state. The third step involves the oxidation of all the BFc moieties to the Fe2(III,III)2+ state.

Electrochemical impedimetry of electrodeposited poly(propylene imine) dendrimer monolayer

“…Rather, only dendrimer which have been functionalised with redox molecules such as pyridines of transition metal complexes on polyamidoamine (PA-MAM) [11] and ferrocynyl and cobaltocene on PPI [12,13] are those reported as electroactive and their electroactive nature was ascribed to the functionality. PPI has also been studied at liquid-liquid interface with interesting electrochemistry [14] but it was in fact referred to as nonredox active.…”

Orthogonal Supramolecular Interaction Motifs for Functional Monolayer Architectures

“…Huskens and Reinhoudt et al introduced the concept of "molecular printboards", for the stable positioning and assembly of guest functionalized dendrimers, [43] nanoparticles, [44] proteins, [45] and fluorescent small molecules [46] onto CD SAMs. Molecular patterns of (bio)molecules have also been prepared on these molecular printboards by using lithographic techniques such as microcontact printing and dip-pen nanolithography.…”

Cyclodextrins and Polymer Nanoparticles

“…Dendrimers have been prepared with different types of subunits: polyamidoamine (PAMAM) [94,[96][97][98] and polypropylenimine [99][100][101]. They are characterized by high surface charge density and water solubility enabling electrostatic interactions with nucleic acids, allowing the formation of dendrimer-DNA complexes, which can be used for efficient transfection of cells [94].…”