Simplifying the synthesis of dendrimers: accelerated approaches.

Dendrimers are highly branched and monodisperse macromolecules that display an exact and large number of functional groups distributed with unprecedented control on the dendritic framework. Based on their globular structure, compared to linear polymers of the same molecular weight, dendrimers are foreseen to deliver extraordinary features for applications in areas such as cancer therapy, biosensors for diagnostics and light harvesting scaffolds. Of the large number of reports on dendrimer synthesis only a few have reached commercial availability. This limitation can be traced back to challenges in the synthetic paths including a large number of reaction steps required to obtain dendritic structures with desired features. Along with an increased number of reaction steps come not only increased waste of chemical and valuable starting materials but also an increased probability to introduce structural defects in the dendritic framework. This tutorial review briefly covers traditional growth approaches to dendrimers and mainly highlights accelerated approaches to dendrimers. A special focus capitalizes on the impact of the click chemistry concept on dendrimer synthesis and the promise it has to successfully accomplish highly sophisticated dendrimers, both traditional as well as heterofunctional, in a minimum number of chemical steps. It is clear that accelerated synthetic approaches are of greatest importance as these will encourage the scientific community to synthesize and access dendrimers for specific applications. The final goal of accelerated synthesis is to deliver economically justified dendritic materials for future applications without compromising the environmental perspective.

Hybrid one-dimensional nanostructures: one-pot preparation of nanoparticle chains via directed self-assembly of in situ synthesized discrete Au nanoparticles.

The fabrication of well-defined one-dimensional (1D) arrays is becoming a challenge for the development of the next generation of advanced nanodevices. Herein, a simple concept is proposed for the in situ synthesis and self-assembly of gold nanoparticles (AuNPs) into 1D arrays via a one-step process. The results demonstrated the formation of nanoparticle chains (NPC) with high aspect ratio based on discrete Au nanoparticles stabilized by short thiol ligands. A model was proposed to explain the self-assembly based on the investigation of several parameters such as pH, solvent, temperature, and nature of the ligand on the 1D assembly formation. Hydrogen bonding was identified as a key factor to direct the self-assembly of the hybrid organic-inorganic nanomaterials into the well-defined 1D nanostructures. This simple and cost-effective concept could potentially be extended to the fabrication of a variety of hybrid 1D nanostructures possessing unique physical properties leading to a wide range of applications including catalysis, bionanotechnology, nanoelectronics, and photonics.

Stability and biocompatibility of a library of polyester dendrimers in comparison to polyamidoamine dendrimers.

Dendrimers can be designed for several biomedical applications due to their well-defined structure, functionality and dimensions. The present study focused on the in vitro biocompatibility evaluation of a library of aliphatic polyester dendrimers based on 2,2-bis(methylol)propionic acid (bis-MPA) with an overall diameter of 0.5-2 nm. In addition, dendrimers with two different chemical surfaces (neutral with hydroxyl end group and anionic with carboxylic end group) and dendrons corresponding to the structural fragments of the dendrimers were evaluated. Commercial polyamidoamine dendrimers (PAMAM) with cationic (amine) or neutral (hydroxyl) end group were also included for comparison. Cell viability studies were conducted in human cervical cancer (HeLa) and acute monocytic leukemia cells (THP.1) differentiated into macrophage-like cells as well as in primary human monocyte-derived macrophages. Excellent biocompatibility was observed for the entire hydroxyl functional bis-MPA dendrimer library, whereas the cationic, but not the neutral PAMAM exerted dose-dependent cytotoxicity in cell lines and primary macrophages. Studies to evaluate material stability as a function of pH, temperature, and time, demonstrated that the stability of the 4th generation hydroxyl functional bis-MPA dendrimer increased at acidic pH. Taken together, bis-MPA dendrimers are degradable and non-cytotoxic to human cell lines and primary cells.