About Dendrimers: Structure, Physical Properties, and Applications

Convergent Dendrons and Dendrimers: from Synthesis to Applications

Dendrimers are versatile, derivatisable, well-defined, compartmentalised chemical polymers with sizes and physicochemical properties resembling those of biomolecules e.g. proteins. The present critical review (citing 158 references) briefly describes dendrimer design, nomenclature and divergent/convergent dendrimer synthesis. The characteristic physicochemical features of dendrimers are highlighted, showing the effect of solvent pH and polarity on their spatial structure. The use of dendrimers in biological systems are reviewed, with emphasis on the biocompatibility of dendrimers, such as in vitro and in vivo cytotoxicity, as well as biopermeability, biostability and immunogenicity. The review deals with numerous applications of dendrimers as tools for efficient multivalent presentation of biological ligands in biospecific recognition, inhibition and targeting.
 Dendrimers may be used as drugs for antibacterial and antiviral treatment and have found use as antitumor agents. The review highlights the use of dendrimers as drug or gene delivery devices in e.g. anticancer therapy, and the design of different host–guest binding motifs directed towards medical applications is described.
 Other specific examples are the use of dendrimers as ‘glycocarriers’ for the controlled multimeric presentation of biologically relevant carbohydrate moieties which are useful for targeting modified tissue in malignant diseases for diagnostic and therapeutic purposes. Finally, the use of specific types of dendrimers as scaffolds for presenting vaccine antigens, especially peptides, for use in vaccines is presented.

Dendrimers in drug research

The convergence of our understanding of structure-property relationships for selected biological macromolecules and our increased ability to prepare large synthetic macromolecules with a structural precision that approaches that of proteins have spawned a new area of research where chemistry and materials science join with biology. While evolution has enabled nature to perfect processes involving energy transfer or catalysis by incorporating functions such as self-replication and repair, synthetic macromolecules still depend on our synthetic skills and abilities to mesh structure and function in our designs. Clearly, we can take advantage of our understanding of natural systems to mimic the structural features that lead to optimized function. For example, numerous biological systems make use of the concept of site isolation whereby an active center or catalytic site is encapsulated, frequently within a protein, to afford properties that would not be encountered in the bulk state. The ability of the dendritic shell to encapsulate functional core moieties and to create specific site-isolated nanoenvironments, and thereby affect molecular properties, has been explored. By utilizing the distinct properties of the dendrimer architecture active sites that have either photophysical, photochemical, electrochemical, or catalytic functions have been placed at the core. Applying the general concept of site isolation to problems in materials research is likely to prove extremely fruitful in the long term, with short-term applications in areas such as the construction of improved optoelectronic devices. This review focuses on the evolution of a natural design principle that contributes to bridging the gap between biology and materials science. The recent progress in the synthesis of dendrimer-encapsulated molecules and their study by a variety of techniques is discussed. These investigations have implications that range from the preliminary design of artificial enzymes, catalysts, or light-harvesting systems to the construction of insulated molecular wires, light-emitting diodes, and fiber optics.

Dendritic Encapsulation of Function: Applying Nature's Site Isolation Principle from Biomimetics to Materials Science.

The origin of the extent of charging and the mechanism by which multiply charged ions are formed in electrospray ionization have been hotly debated for over a decade. Many factors can affect the number of charges on an analyte ion. Here, we investigate the extent of charging of poly(propyleneimine) dendrimers (generations 3.0 and 5.0), cytochrome c, poly(ethylene glycol)s, and 1,n-diaminoalkanes formed from solutions of different composition. We demonstrate that in the absence of other factors, the surface tension of the electrospray droplet late in the desolvation process is a significant factor in determining the overall analyte charge. For poly(ethylene glycol)s, 1,n-diaminoalkanes, and poly(propyleneimine) dendrimers electrosprayed from single-component solutions, there is a clear relationship between the analyte charge and the solvent surface tension. Addition of m-nitrobenzyl alcohol (m-NBA) into electrospray solutions increases the charging when the original solution has a lower surface tension tha...

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Mechanism of Charging and Supercharging Molecules in Electrospray Ionization

Four generations of a dendrimer with a fluorescent core consisting of a rubicene moiety are synthesized. The biexponential nature of fluorescence decay in toluene indicates the presence of two emitting conformations. Molecular modeling suggests that a conformation where the dendrons interact with the core is not improbable. The relative weight of the two decay times indicates that the contribution of that conformation in toluene increases as the dendrimer generation increases. In acetone and acetonitrile however the fluorescence decay is, except for the fourth generation, monoexponential. The hydrodynamical volume of the dendrimer is determined in toluene, a good solvent, acetone, a medium quality solvent, and acetonitrile, a poor solvent, with the time-resolved fluorescence depolarization technique. No change of the hydrodynamical volume is found in toluene in a temperature range between 20 and 94 °C. This suggests that the dendrimers of all the generations are fully expanded in this solvent. In acetonit...

K. Desmedt

Papers

Solvent Dependence of the Hydrodynamical Volume of Dendrimers with a Rubicene Core