Redox-controlled interaction of biferrocenyl-terminated dendrimers with beta-cyclodextrin molecular printboards.
This paper describes the synthesis and electrochemistry of biferrocenyl-terminated dendrimers and their beta-cyclodextrin (beta-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 beta-CD. The intrinsic binding constant is K(i)=2.5 x 10(4) M(-1). The BFc dendrimers were solubilized in water by complexation of the end groups with beta-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 beta-CD. Adsorption of the dendrimers at self-assembled monolayers (SAMs) of heptathioether-functionalized beta-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 beta-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 beta-CD is sensitive to the oxidation state of the BFc unit. Oxidation of neutral BFc-Fe(2) ((II,II)) to the cationic, mixed-valence biferrocenium BFc-Fe(2) ((II,III)+) resulted in dissociation of the host-guest complexes. Scan-rate-dependent CV and DPV analyses of the dendrimer-beta-CD assemblies immobilized at the beta-CD host surface and in solution revealed that the dendrimers are oxidized in three steps. First, the surface-beta-CD-bound BFc moieties are oxidized to the mixed-valence state, Fe(2) ((II,III)+), followed by the oxidation of the non-surface-interacting BFc groups to the Fe(2) ((II,III)+) state. The third step involves the oxidation of all the BFc moieties to the Fe(2) ((III,III)2+) state.
Nijhuis
Christian A
CA
Supramolecular Chemistry and Technology, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
Dolatowska
Karolina A
KA
Ravoo
Bart Jan
BJ
Huskens
Jurriaan
J
Reinhoudt
David N
DN
D050091:Dendrimers / Q000138:chemical synthesis / Q000737:chemistry*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D006358:Hot Temperature; D058085:Iron Compounds / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D012996:Solutions; D017186:Titrimetry; D047392:beta-Cyclodextrins / Q000737:chemistry*
D050091:Dendrimers; D058085:Iron Compounds; D012996:Solutions; D047392:beta-Cyclodextrins