Dendrimers nomenclature

It would be beyond the scope of this textbook to dive further into the details of dendrimer nomenclature. Instead, basic rules are given to create an awareness of the problems and complexity. Nevertheless, with the aid of the literature cited (see ref. [45]) it is possible to develop names for certain formulae -and vice versa. 

The pinnacle of synthetic polymer branching must reside in a new generation of polymers known as dendrimers (Fig. 2) (5,6). Dendrimers are typically branched condensation polymers in which the branching is so well controlled that the polymers grow in well-defined rows described in the dendrimer nomenclature as generations. The use of dendrimers in cosmetics is only beginning as these polymers are currently costly and not readily available in commercial quantities. 

Concerning the nomenclature of higher-dimensionality silicon polymers such as networks, ladders, cages, and dendrimers, the variety of architectures possible is too great to treat concisely here, and the reader is directed to IUPAC sources.2... 

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). 

We have used the generational nomenclature typical for PAMAM dendrimers throughout this chapter. In the scientific literature the PPl family of dendrimers is incremented by one. That is, what we call a G4 PPl dendrimer (having 64 endgroups) is often referred to as G5. 

Fig. 1.21 POPAM dendrimer according to the Newkome nomenclature 16-Cascade l, 4-diaminobu tane[4-N, N,N, N ] [ -azabutylide-ne)2 aminopropane [45]...

In the case of complex dendrimers with differing branches or differing dendryl substituents on a non-dendritic scaffold it is necessary to include further details in the name. For this reason, a more detailed cascadane nomenclature [45] has been developed, according to which the above POPAM would be called ... 

T. M. Miller, T. X. Neenan, Chem Mater. 1990, 2, 346-349. T. M. Miller, T. X. Neenan, R. Zayas, H. E. Bair, /. Am. Chem. Soc. 1992, 334, 1018-1025. We use the family name polybenzene dendrimers (generally polyarene dendrimers) instead of polyphenylene dendrimers because the rules of nomenclature restrict pheny-lene to -QHg-. 

Friedhofen and Vogtle have recently outlined a detailed nomenclature for dendrimers which is discussed in the Section Key Reference. In brief, a dendrimer is defined as comprising a series of self-resembling units, termed dendrons, linked by a common core. The dendrons are referred to as cascadyl-substituents or, if there is more than one identical dendron, the molecule is termed a cascadane. 

The new nomenclature system allows specific naming and numbering of the dendrimer substituents and thus unambiguous naming even for complex structures. 

The nomenclature according to IUPAC rules has proven particularly unwieldy in the case of dendrimers. Several proposals have been made [25]. The major classes of dendrimers described here are represented in Schemes 1-4 in short-hand form. Other particular dendritic structures will be characterized by reaction schemes or by their branch unit in the text. 

Avnir et al. llbl have examined the classical definitions and terminology of chirality and subsequently determined that they are too restrictive to describe complex objects such as large random supermolecular structures and spiral diffusion-limited aggregates (DLAs). Architecturally, these structures resemble chiral (and fractal) dendrimers therefore, new insights into chiral concepts and nomenclature are introduced that have a direct bearing on the nature of dendritic macromolecular assemblies, for example, continuous chirality measure44 and virtual enantiomers. ... 

Many additional dendrimers have been introduced in the past decade however, no additional nomenclature problems are, at present, evident. 

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 2.7 General structure and nomenclature of dendrimers. Source adapted from Dendritic Nanotechnologies Inc. (http //dnanotech.com).

It is seen that the globular dendrimer (1) may be considered as four separate dendrons (2) that branch from the core, C (3). In the nomenclature of Frechet, R is a reactive site, F is a focal point and B is a building block and branching point. At each branching point of the dendron there are two new arms formed, which, prior to the next generation, G, of reaction will have 2° reactive sites. Thus, at the completion of the reaction, the number of terminal... 

Figure 1.19. Schematic of a Dendrimer with generations (G) indicated and the building blocks B. At generation 3 this dendrimer has 32 active sites (S), which may continue reaction to generation 4. Nomenclature is explained in the text. After Frechet and Hawker (1996).

Classification and Nomenclature of Supramolecular Compounds, p. 261 Crown Ethers, p. 326 Cryptands, p. 334 Dendrimers, p. 432 Electrochemicul Sensors, p. 505 Enzyme Mimics, p. 546 Fluorescent Sensors, p. 572 Imaging and Targeting, p. 687 Ion-Selective Electrodes, p. 747 lonophores, p. 760 Kinetics of Complexation, p. 776 Lariat Ethers, p. 782... 

Classification and Nomenclature of Supramolecular Compounds, p. 261 Crown Ethers, p. 326 Cryptands, p. 334 Cyclodextrins, p. 398 Cyclodextrins, Applications, p. 405 Dendrimers, p. 432... 

Figure 1 The nomenclature of basic dendritic (a) and star (b) structures showing the core and two generations extending through a branching site of connectivity 2 in the case of the dendrimer.

Often symmetry operations cannot be used in a simple way to classify chiral forms because, e.g., the molecule consists of a number of conformations. Therefore, independent of the symmetry considerations, a chemical approach to describe chiral molecules has been introduced by the use of structural elements such as chiral centers, chiral axis, and chiral planes. Examples for a chiral center are the asymmetric carbon atom, i.e., a carbon atom with four different substituents or the asymmetric nitrogen atom where a free electron pair can be one of the four different substituents. A chiral axis exists with a biphenyl (Figure 3.2) and chiral planes are found with cyclo-phane structures [17]. Chiral elements were introduced originally to classify the absolute configuration of molecules within the R, S nomenclature [16]. In cases where the molecules are chiral as a whole, so-called inherent dissymmetric molecules, special names have often been introduced atropiso-mers, i.e., molecules with hindered rotation about a helical molecules [18], calixarenes, cyclophanes [17], dendrimers [19], and others [20]. 

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