Dendritic molecules/architecture

Recent developments in the design of dendritic molecules has provided both new methodology and molecular architecture which are structure controlled macromolecules, globular-shaped, dendritic-branched tree-like structures with nanoscscale dimensions [1], Dendrimers generally consist of a focal core, many building blocks (monomer units) and a mathematically defined number of ex-... 

Chapters 2 and 3 have already introduced the reader to the general principles of the architecture, synthesis, and functionalisation of dendritic molecules - including hyperbranched and dendronised (linear) polymers (denpols). This chapter will now consider specific molecular scaffolds and syntheses of important types of dendrimers and their individual properties. More specialised and appli-cations-relevant properties of particular dendrimers are compiled in Chapter 8. 

Siloxanes, prepared in 1989 as representatives of silicon-based dendritic molecules ( silicodendrimers ), were the first dendrimers to contain heteroatoms other than the usual ones (N, O, S, halogens) [68]. As with the phosphodendri-mers (Section 4.1.10), their readily modifiable architecture and their pronounced thermostability hold promise of applications, for example, in the form of carbo-silanes as liquid-crystalline materials and catalyst supports. They can be subdivided into a number of basic types and their properties are presented below with the aid of characteristic representatives ... 

Kramer and coworkers recently reported on water-soluble dendritic coreshell architectures and studied the influence of the attached carbohydrate shell on the formation and stabilization of metal nanoparticles in water. For this purpose, they used hyperbranched poly(ethylenimine) (PEI) as core molecules and covalently attached different carbohydrates as shells, i.e., glycidol, gluconolactone and lactobionic acid, to obtain the corresponding PEI-glycol, PEI-gluconamide and PEI-lactobionamide. Different molecular weights of PEIX (x = 0.8, 5, 21 or 25 with different Mw = xlO3) were employed [81]. 

Consideration of the generally globular, or pseudo-spherical. 3-dimensional architecture of dendritic molecules"." naturally leads to a comparison with the idealized concept of micellar organization and properties (Fig. 1). From the perspective of classical, charged... 

Perfectly branched dendrimers have potentially better properties for applications in the field of biomedicine than hyperbranched polymers due to their well-defined and predictable structure and narrow mass distribution, which is important for in vitro and in vivo applications. However, hyperbranched polymers have one very significant advantage, which is their easier preparation by a one-step synthesis. Therefore, hyperbranched polymers are also used in technical applications, for example, as additives, blends, or coating components and as multifunctional cross-linkers. But both, dendrimers and hyperbranched polymers, have been extensively studied in the fields of encapsulation and delivery of drugs, dyes, and genes because of their original branched architecture (Fig. 5.15). Small molecules of interest can be incorporated in the interior cavities of dendritic molecules or bound to their outer functional groups. 

Percec et al. [41,42] studied and reviewed various complex self-assembled structures in detail that can be obtained from dendritic molecules. Especially multicompartment capsules obtained by the self-assembly of a library of amphiphilic Janus-type dendrimers are impressive. The chemical linkage of two dissimilar dendritic building blocks results in Janus dendrimers and produces a break in the spherical symmetry characteristic to dendrimers. Consequently, these stmctures spontaneously promote the self-assembly upon injection of its ethanol solution to form stable unilamellar vesicular nanostructures and other complex architectures (Eig. 6.17). Dendriniersom.es... 

The polymers were viscous liquids that were eventually colored yellowish by residual catalyst. They were very soluble in toluene, chloroform, THF, n-hexane, petrolether or acetone, but did not dissolve in water and lower alcohols like methanol or ethanol. The effect of improved solubilities of dendritic molecules compared to linear polymers has been mentioned before and attributed to their architecture and their functional groups [35]. 

Dendronized polymers, a type of dendritic molecule, exhibit properties not only from the dendron they possess - high functionality and regularity - but also from the polymer segments that are connected to dendrons or used to coimect several dendrons. Many different architectures of dendronized polymers can be prepared, depending on the t5q)e of polymer used, where the dendrons are attached, and how many are introduced. These architectures include, among others, dendron-coil, dendron-rod, dendron-rod-coil, and dendron-coil-dendron. The dendron-mediated assembly of dendronized polymers has been reviewed by Rosen et al7 ... 

In summary, the unique architecture of dendritic molecules has proven to be amenable to the formation of gel-phase assembhes. We propose that the inherent branched architecture of dendritic macromolecules will be further exploited in the near future to yield a new generation of functional, dendritic, soft nanomaterials. 

There is considerable interest in the properties of new mesomorphic materials, which are composed of molecules with novel architectures. These include rod-coil molecules [1], polyphilic molecules [2, 3], block-copolymers [4] and dendritic molecules [5]. In many of these systems microphase separation can be used to build new materials containing structures that are ordered on the nanoscale. Examples include the formation of spheres or rods within a uniform matrix of dififerent chemical... 

At the current time, we have no way, other than chemical intuition, of predicting which bulk structures will be formed from novel molecular architectures. Here then is a major challenge for simulation can we predict what phase, or sequence of phases, will be formed by complex multiblock oligomers, polymers, or dendritic molecules composed of several different groups Can we predict the properties of these phases Can we use simulation to engineer new materials, designing them from scratch to create the desired structure at the nanoscale ... 

Based on the various hybridization states of carbon and other elements in the periodic table, small molecule synthesis has led to at least four major architectural patterns. The major architectural classes may be visualized as described in Figure 2 and includes (I) Linear, (II) Bridged, (HI) Branched, and (IV) Dendritic (cascade) architectures. 

The only topological type in this small molecule area that has not been exploited extensively as a neutral ligand in supramolecular chemistry was the Class IV dendritic (cascade)-type architecture. Vogtle introduced this fourth major small molecule architecture in the late 1970s in a single isolated communication [33]. These low molecular weight dendritic (cascade) molecules served as... 

Intensive studies in the area of dendritic macromolecules, which include applied research and are generally interdisciplinary, have created a need for a more systematic approach to dendritic architectures development that employs a multi-scale modeling and simulation approach. A possible way is to determine the atomic-scale characteristics of dendritic molecules using computer simulation and computational approaches. Computer simulation, as a powerful and modem tool for solving scientific problems, can be performed for dendritic architectures without synthesizing them. Computer simulation not only used to reproduce experiment to elucidate the invisible microscopic details and further explain experiments, but also can be used as a useful predictive tool. Currently, Monte Carlo, Brownian dynamics and molecular dynamics are the most widely used simulation methods for molecular systems [5]. 

Dendritic architectures (Rg. 3.8a) show very benefidal properties for the development of drug delivery systems and thus many different systems based on dendrimers,dendroms or hyperbranched polymers have been developed (Oliveira et al., 2010). In general, one can distinguish between two different release mechanisms from dendritic molecules depending on the way the... 

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