Dendrimers, description

In the typical nomenclature for DENs, the dendrimer is designated by Gx-R where x is the dendrimer generation and R is the surface group (typically -OH or -NH2, see Fig. 7.1). The stoichiometry between the dendrimer and complexed ions or reduced encapsulated nanoparticles is denoted in parentheses after the dendrimer description, e.g. (M )n or (M ). For bimetallic DENs, the metahmetal stoichiometry is typically included, e.g. G5-OH (PtigAuig). 

However, dendrimeric and hyperbranched polyesters are more soluble than the linear ones (respectively 1.05, 0.70, and 0.02 g/mL in acetone). The solution behavior has been investigated, and in the case of aromatic hyperbranched polyesters,84 a very low a-value of the Mark-Houvink-Sakurada equation 0/ = KMa) and low intrinsic viscosity were observed. Frechet presented a description of the intrinsic viscosity as a function of the molar mass85 for different architectures The hyperbranched macromolecules show a nonlinear variation for low molecular weight and a bell-shaped curve is observed in the case of dendrimers (Fig. 5.18). 

Although the first publication on dendrimers appeared in 1978 [ 1 ] it is only in 1990 that the first report on phosphorus-containing dendrimers was published [2] i.e. after numerous papers devoted to the synthesis of organic dendrimers and practically at the same time than the description of a silicon containing dendrimer. 

The emission of the metal particles may thus originate from a band-to-band transition in the metal particle, which occurs at about 516 nm for gold [60, 119]. As stated above, the nature of the interaction of the dendrimer (PAMAM) host is still uncertain, there could be very strong electrostatic interactions that may play a part in the enhancement of the metal particles quantum efficiency for emission. However, one would expect that this enhancement would result in slightly distorted emission spectra, different from what was observed for the gold dendrimer nanocomposite. Further work is necessary to completely characterize the manner in which the dendrimer encapsulation enhances the emission of the metal nanoparticles. With further synthetic work in preparation of different size nanoparticles (in other words elongated and nonspherical shape particles, including nanorods) it may be possible to develop the accurate description of a... 

Dendrimers are not really discrete chemical structures - they are non-descript materials,... 

Fig.1. Schematic description of dendritic polymers comprising dendrimers and hyper-branched polymers...

Fig. 9. Generalized description of the intrinsic viscosity as function of molar mass for linear polymers, hyperbranched polymers and dendrimers as described by Frechet [33]...

Numerical calculations inspired in the ZK method for stars have also been applied for the description of the dynamics of model dendrimers. La Ferla [232] used a freely-rotating model, including a topology-dependence stiffness parameter and preaveraged HI. With this model, he obtained a complex analytical expression for the mean size. Cai and Chen [233] used a Gaussian model without HI and performed a detailed analysis of the relaxation motions. They investigated the diffusion of the center of mass, the relaxation of the center of mass position relative to the core monomer, and also the rotational and internal modes. 

Fig. 10 a Scheme of dendrimer generation 4 and b description of surface activation to fix the dendrimers and immobilization method for covalent binding of NAs on the activated glass surface [42]... 

H. IHRE, M. JOHANSSON, E. MALMSTROM, and A. HULT Table 1. Description of Dendrimers D1-D3 ... 

In order to give a description of the overall size and shape as well as the outside surface characteristics of a dendrimer, some quantitative parameters are required. A general idea about the overall shape of a dendrimer can be inferred by the aspect... 

For a complete quantitative description of the solvent effects on the properties of the distinct diastereoisomers of dendrimers 5 (G = 1) and 6 (G = 1), a multiparameter treatment was used. The reason for using such a treatment is the observation that solute/solvent interactions, responsible for the solvent influence on a given process—such as equilibria, interconversion rates, spectroscopic absorptions, etc.—are caused by a multitude of nonspecific (ion/dipole, dipole/dipole, dipole/induced dipole, instantaneous dipole/induced dipole) and specific (hydrogen bonding, electron pair donor/acceptor, and chaige transfer interactions) intermolecular forces between the solute and solvent molecules. It is then possible to develop individual empirical parameters for each of these distinct and independent interaction mechanisms and combine them into a multiparameter equation such as Eq. 2, "... 

The only revision of the model which has been incorporated here is the formal description of the functional group concentration in the polymer rich phases. In our work with the dendrimer, nominally containing 128 terminal functional groups, we calculated the total ligand concentration within the polymer phase 1 to be... 

This section concludes with a description of tandem synthetic strategies (Section 14.1.6) in which sequential reactions involve combinations of steps such as dendrimer formations combined with cyclic peptides (Section 14.1.6.1), chemoselective cyclization combined with divergent syntheses (Section 14.1.6.3), and many thiol-based reactions and cyclizations (Sections 14.1.6.4—14.1.6.7) J18 ... 

The structure of cationic lipids and polymers is readily amenable to chemical modification [35, 36] allowing the exploration of a virtually unlimited number of combinations and strategies at the mercy of chemists creative abilities. Various reviews have been focused on cationic lipids, dendrimers and polymers in terms of their chemical structures and their transfection properties [36—41], in an attempt to shed some light on the chemical requirements necessary to mediate gene delivery. The focus of this chapter will be to explore these carriers from a synthetic perspective, with a description of the chemical strategies used for the preparation via synthetic organic chemistry (excluding polymer synthesis) of cationic lipids and dendrimers. 

This brief description provides only the simplest overview of the way in which dendrimers can he synthesized. Many variations on this scheme have been explored. For example, one might begin with a core molecule that consists of three functional groups (such as ammonia, NH3) rather than the two functional groups found in 1,4-diaminobutane. One could also provide a direction for the growth of the dendrimer by blocking one or more of the functional groups at... 

The evolving domain of radial, as well as linear, addition of modules to form an expanding moiety, in a manner akin to the development of polymers, referred to as "dendrimers", is examined and nomenclated The direct inclusion of topology in the description of isomers, once a very insignificant part of chemical nomenclature, is now a factor to be reckoned with, not only for the small class traditionally referred to as "topological" (including catenanes, rotaxanes, and knots), but also as new compositions of matter, such as the endothelial fullerenes, are formulated. 

A proposal made recently by Lambert and coworkers [Id] for the nomenclature and structural description of polysilane dendrimers treats the problem of the high redundancy of very complex names of these compounds which possess a high degree of symmetry and might be described better by different ways. 

Figure 13. (a) Formation of mixed SAM on Au electrode, (b) immobilization of Fc-D, (c) immobilization of thiolated capture probe with bifunctional linker (succinimidyl 4-(/V-maleimidomethyl)cyclohexane-l-carboxylate (SMCC)), (d) hybridization with target, (e) hybridization with biotinylated detection probe, (f) association with avidin-alkaline phosphatase, (g) description of the process of the electrocatalytic reaction of />-aminophenol (p-AP) via electronic mediation of ferrocenyl dendrimer (Adapted from Ref. [160])... 

The 6-nm dendrimers under study also adsorbed to an extent onto the actin fibrils, thus further reducing diffusion. Superimposed on the photomicrograph are nanoparticles to illustrate the problems in diffusion through such a medium adsorption, obstruction, and entrapment. The overall effect is to markedly reduce diffusion at a certain particle radius diffusion virtually ceases. These few descriptions simply underline the supreme importance of nanoparticle diameter. This is one reason why to generahze about nanoparticles is somewhat difficult when not only are the substance of nanoparticles and their surface coatings different but the fundamental property of size varies over such a wide range. This in turn means that dependent properties such as surface area and volume vary even more. 

New directions snch as description of special materials including those involving oligomers, copolymers, new strnctnres (starlike and dendrimers), inorganic polymers (e.g., tin-based antifouling paints)... 

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