Dendrimers Based on a Three-Dimensionally Disposed AB4 Monomer

Electrochemical One-Step Immunoassay Based on Switching Peptides and Pyrolyzed Carbon Electrodes

Switching peptides were designed to bind reversibly to the binding pocket of antibodies (IgG) by interacting with frame regions (FRs). These peptides can be quantitatively released when antigens bind to IgG. As FRs have conserved amino acid sequences, switching peptides can be used as antibodies for different antigens and different source animals. In this study, an electrochemical one-step immunoassay was conducted using switching peptides labeled with ferrocene for the quantitative measurement of analytes. For the effective amperometry of the switching peptides labeled with ferrocene, a pyrolyzed carbon electrode was prepared by pyrolysis of the parylene-C film. The feasibility of the pyrolyzed carbon electrode for the electrochemical one-step immunoassay was determined by analyzing its electrochemical properties, such as its low double-layer capacitance (C_dl), high electron transfer rate (k_app), and wide electrochemical window. In addition, the factors influencing the amperometry of switching peptides labeled with ferrocene were analyzed according to the hydrodynamic radius, the number of intrahydrogen bonds, dipole moments, and diffusion coefficients. Finally, the applicability of the electrochemical one-step immunoassay for the medical diagnosis of the human hepatitis B surface antigen (hHBsAg) was assessed.

Modular Synthetic Approach for Adjusting the Disassembly Rates of Enzyme-Responsive Polymeric Micelles

Self-assembled nanostructures and their stimuli-responsive degradation have been recently explored to meet the increasing need for advanced biocompatible and biodegradable materials for various biomedical applications. Incorporation of enzymes as triggers that can stimulate the degradation and disassembly of polymeric assemblies may be highly advantageous owing to their high selectivity and natural abundance in all living organisms. One of the key factors to consider when designing enzyme-responsive polymers is the ability to fine-tune the sensitivity of the platform toward its target enzyme in order to control the disassembly rate. In this work, a series of enzyme-responsive amphiphilic PEG-dendron hybrids with increasing number of hydrophobic cleavable end-groups was synthesized, characterized, and compared. These hybrids were shown to self-assemble in aqueous media into nanosized polymeric micelles, which could encapsulate small hydrophobic guests in their cores and release them upon enzymatic stimulus. Utilization of dendritic scaffolds as the responsive blocks granted ultimate control over the number of enzymatically cleavable end-groups. Remarkably, as we increased the number of end-groups, the micellar stability increased significantly and the range of enzymatic sensitivity spanned from highly responsive micelles to practically nondegradable ones. The reported results highlight the remarkable role of hydrophobicity in determining the micellar stability toward enzymatic degradation and its great sensitivity to small structural changes of the hydrophobic block, which govern the accessibility of the cleavable hydrophobic groups to the activating enzyme.

Expanding the Structural Diversity of Self-Assembling Dendrons and Supramolecular Dendrimers via Complex Building Blocks

The design and synthesis of the first examples of AB4 and AB5 dendritic building blocks with complex architecture are reported. Structural and retrostructural analysis of supramolecular dendrimers self-assembled from hybrid dendrons based on different combinations of AB4 and AB5 building blocks with AB2 and AB3 benzyl ether dendrons demonstrated that none of these new hybrid dendrons exhibit the previously encountered conformations of libraries of benzyl ether dendrons. These hybrid dendrons enabled the discovery of some highly unusual tapered and conical dendrons generated by the intramolecular back-folding of their repeat units and of their apex. The new back-folded tapered dendrons have double thickness and self-assemble into pine-tree-like columns exhibiting a long-range 7/2 helical order. The back-folded conical dendrons self-assemble into spherical dendrimers. Non-back-folded truncated conical dendrons were also discovered. They self-assemble into spherical dendrimers with a less densely packed center. The discovery of dendrons displaying a novel crown-like conformation is also reported. Crown-like dendrons self-assemble into long-range 5/1 helical pyramidal columns. The long-range 7/2 and 5/1 helical structures were established by applying, for the first time, the helical diffraction theory to the analysis of X-ray patterns obtained from oriented fibers of supramolecular dendrimers.

Redox Active, Hybrid Dendrimers Containing Fréchet- and Newkome-Type Blocks

A new series of dendrimers was prepared by covalently attaching a Newkome dendron, a Fréchet dendron, and a redox active, aminoferrocene group to a central triazine core. Growth of the Newkome dendron has a more pronounced effect on the half-wave potential for the one-electron oxidation of the ferrocene residue than growth of the Fréchet dendron. All dendrimers show reversible or quasireversible voltammetric behavior at scan rates in the range 0.10-2.0 V s-1.

Study of peptide dendrimers having a ferrocene core supported on mercaptoundecanoic acid

Hydrogen-bonding interactions between the carboxylic acid groups of mercaptoundecanoic acid (MUA) coated gold substrates and the ester surface of peptide dendrimers allows the formation of glutamic acid dendrimers films. Dendrimer films were prepared for generations 1-6 (G1-G6) and analyzed by spectroscopic and electrochemical techniques. Electrochemical studies using cyclic voltammetry and differential pulse voltammetry show that all films except those of G6 were electrochemically active. Lack of activity of G6 films is rationalized by the total encapsulation of the ferrocene redox probe by the dendritic sheath and lack of ion pairing, which prevents its oxidation.

A New Class of Intramolecularly Hydrogen-Bonded Dendrons Based on a 2-Methoxyisophthalamide Repeat Unit

The synthesis and conformational properties of folded dendrons based on a 2-methoxyisophthalamide (2-OMe-IPA) repeat unit are described. The hydrodynamic properties of dendrons preorganized via the syn-syn conformational preference of 2-methoxyisophthalamide are compared with 2,6-pyridinedicarboxamide (2,6-pydic) analogues. The effect of subtle differences in the nature of the conformational equilibria that exist within the 2-OMe-IPA and 2,6-pydic repeat units on the global structural properties of the corresponding dendrons was explored computationally, by (1)H-DOSY NMR spectroscopy and time-resolved fluorescence anisotropy (TRFA) measurements. Whereas the syn-syn preference of the 2-OMe-IPA branched repeat unit is stabilized entirely by intramolecular hydrogen-bonding interactions, this preference in the 2,6-pydic system is a consequence of both intramolecular hydrogen-bonding and dipole minimization effects. However, nonspecific solvophobic compression is more important in determining hydrodynamic properties than solvent-dependent shifts in the conformational equilibria of the repeat unit for both dendron series.

Electrochemical and Guest Binding Properties of Fréchet- and Newkome-Type Dendrimers with a Single Viologen Unit Located at Their Apical Positions

Several new series of dendrimers containing a single redox-active 4,4'-bipyridinium (viologen) residue were synthesized and characterized. In these dendrimers, the viologen group is covalently attached to the apical position of a Newkome- or Frechet-type dendron, ranging in size from first to third generation of growth. The half-wave potentials corresponding to the two consecutive one-electron reductions of the viologen residue are affected by the size of the dendritic component. The size effects are more pronounced in the Newkome-type dendrimers and seem to result from the polarity contrast between the microenvironments provided by the solution and the internal phase of the dendrimer. Unlike in many other dendrimers having a redox-active core, the voltammetric behavior remains fast (reversible) even in third generation dendrimers. Pulse gradient stimulated echo NMR diffusion coefficient measurements on the Newkome-type dendrimers reveal that their hydrodynamic radii are relatively invariant in solvents of widely different polarities (dichloromethane to dimethyl sulfoxide). The host-guest binding interactions between the viologen residue in these dendrimers and the crown ether host bis-p-phenylene-34-crown-8 were also investigated. While in Newkome-type dendrimers the growth of the dendron caused a substantial attenuation of the binding constant values, this size effect was not observed in the Frechet-type dendrimers. These electrochemical and binding measurements underscore some of the structural differences between these two common types of dendritic architectures.