Surface-charged dendrimers

Surface-charged dendrimers are those in which chaises are located only at the termini of the elaborated branches, while the core and branch system are uncharged. In general, the species of this category, which have been constructed, have involved anionic sites, specifically carboxylate anions, at the termini of the branches. 

Fluorescence lifetime measurements on the aggregate have shown that the rate constant of the intermolecular energy transfer from the zinc porphyrin unit to the free-base porphyrin unit has been evaluated to be 3.0 x 109 s-1. This value is reasonable from a model in which dendritic donor 6b and acceptor 5a contact each other directly at their exterior surfaces (Scheme 2). Therefore, electrostatic assembly of positively and negatively charged dendrimers provides a promising supramolecular approach to construct photofunctional materials with nanometric precision. 

Dendrimers used for DNA delivery most commonly have positive net surface charges. The most well studied molecules for gene delivery are those based on an ethylene diamine or ammonia core with polyamidoamine (PAMAM) dendrites or those based on bufylenediamine cores and polypropylenimine (PPI) dendrites. Solubility of PAMAM dendrimers can be enhanced by partial acetylation of the reactive amino groups and they can be conjugated with various targeting entities such as folic acid to target receptors on specific cancer cells (42). 

Figure 6 The PIC micelles loading photosensitizers for photodynamic therapy. PEG-P(Asp) (block polyanions) and PEG-P(Lys) (block polycations) are selected according to the surface charge of Zn-porphyrin-dendrimer s.

A dendrimer is a hyperbranched polymer molecule that has a well-defined molecular weight. It has a globular architecture with several dendrons (dendron a tree-like polymer molecule with a trunk) that are connected to a central core. Its distinctive features include a controlled size (15 nm in diameter), multivalency, and the surface charge of ionizable dendrimer terminal groups, which can vary in the generation number [4]. 

Ghosh, S., Priyam, A., and Saha, A. 2009. Surface charge tunabdity and size dependent luminescence anisotropy of aqueous synthesized ZnS/dendrimer nanocomposites. J. Nanosci. Nanotechnol. 9 6726-6735. 

Surface functionalization of dendrimer nanoparticles with suitable ligands, size, surface groups, and surface charge plays a key role on the cellular internalization by endocytosis, phagocytosis, miCTopinocytosis, or fluid-phase endocytosis. 

Y. Yang, S. Sunogrot, C. Stowell, J. Ji, C.W. Lee, J.W. Kim, S.A. Khan, S. Hong, Effect of size, surface charge, and hydropho-bicity of poly(amidoamine) dendrimers on their skin penetration. Biomacromolecules 13 (2012)2154—2162. 

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