PubMed · 17163557
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Maxim G Ryadnov. 2007. A self-assembling peptide polynanoreactor.. https://doi.org/10.1002/anie.200604014
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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.
Self-immolative dendrimers disassemble through a domino-like chain fragmentation initiated by a single cleavage at the dendrimer core. We have designed and synthesized dendritic molecules that resemble dendritic architectures present in nature. The unique design allows a cleavage signal received by any one of the multiple triggers on one side of the dendrimer to be transferred convergently to a focal point. The signal is divergently amplified through to the other side of the dendrimer, reporter units are released, and fluorescence is emitted. During signal propagation, the dendritic molecule disassembles in a self-immolative manner into small fragments. These compounds are the longest dendritic system ever reported to disassemble through sequential self-immolative reactions. The synthesized dendritic molecules have an architecture and signal-conducting activity related to that of neurons.
Characterization of amino-terminated polyamidoamine dendrimers by CE suffers from a lack of resolution for higher generations and poor between-day reproducibility of retention times. Under optimal conditions of temperature, voltage, and sample amount, 0-5 generations of dendrimers could be resolved with a bare fused-silica capillary. However, reproducibility was poor due to potential interactions of the polycationic dendrimers with the uncoated quartz capillary wall. Use of a poly(vinyl alcohol)-coated capillary significantly decreased the migration times of the nanomolecules without compromising resolution. Dendrimer mixtures containing generations 0-5 are separated as discrete, nonoverlapping peaks in about 15 min. In addition, the between-day precision of retention times was dramatically improved without the need for internal standards or data normalization. Dendrimers of various generations and cores run on different days showed an RSD of retention times of less than 4%. The poly(vinyl alcohol) coating was very stable as shown by the excellent precision of migration times obtained on a capillary used for a month with more than 100 injections. Similar to PAGE, separation of polyamidoamine dendrimers on a bare fused-silica and poly(vinyl alcohol)-coated capillary showed an exponential relationship between migration times and calculated charge density of the nanomolecules.