Dendrimers molecular structure

As already introduced in Section 2.4, angular dependent NEXAFS spectroscopy is a powerful tool in the study of self assembled systems, and was successfully applied to the investigation of self assembled monolayers and multilayers of molecular-based NLO materials. Among others, Bubeck and co-workers [70] investigated the interaction of Cu " with C, N and O moieties in nanocomposites containing copper ions complexed in poly(amidoamine-organosilicon), PAMAMOS (dendrimer molecular structure is shown in Fig. 4.19). 

Metal dendrimers containing photoactive units exhibit very interesting properties, both from a fundamental and applicative viewpoint. For example, well-designed photoactive dendrimers can play the role of artificial antennae in supra-molecular structures devoted to solar energy conversion [37,47]. Photophysical... 

MP35N multiphase alloy, composition of wear- resistant alloy, 7 221t MPD-1 fibers, 13 372, 373 MPDI fibers. See also Polyfira-phenylene isophthalamide) (MPDI) structure of, 19 727 uses for, 19 733-734 m-phenylenediamine (MPD), 19 714 MQ resins, 22 586-588 applications of, 22 588 manufacture of, 22 587-588 molecular structure of, 22 587 viscoelastic properties of, 22 588 MRI agents, dendrimer-based, 26 795-796 Mrigal, common and scientific names, 3 187t... 

Nevertheless, the existence of the famed maximum in the dendrimer [>7] vs G relationship, and whether this behavior could be a characteristic fingerprint property of this type of macromolecular architecture, was questioned recently [19, 23], In fact, so was the linearity of the dependence of dendrimer molecular radii on M1/3 [19], so that whether this may be the beginning of yet another controversy, remains to be seen. Perhaps the future may bring an interesting debate on these subjects, but until new data become available, one should refrain from drawing premature conclusions because the exciting architectural beauty of idealized dendrimer structures has already proven itself to easily tempt the most astonishing hypotheses that may not be readily substantiated by reality. 

Fig. 12 Molecular structure of the chromophoric unit in the dendrimer investigated by Adronov et al. [125]. X is the attachment point to the dendrimer...

Depending upon their molecular structure, dendrimers can be classified as tendentially more rigid (e.g. polyphenylene dendrimers Section 4.1.5) and ten-dentially more flexible (e.g. POPAM, PAMAM dendrimers Sections 4.1.1 and 4.1.2). 

In their theoretical considerations of molecular structure, de Gennes and Her-vet assumed an ideal dendrimer with extended branches with all terminal groups arranged at its periphery in a kind of outer ring around the dendrimer core [9]. According to this model, dendrimers should exhibit a lower segment density at the core, which increases to a maximum value on moving to the periphery. This concept is known as the dense-shell model (Fig. 1.17). 

High resolution multidimensional NMR experiments can provide the dendrimer chemist with a wealth of additional information extending far beyond the determination of the molecular structure. In the interpretation of (2D)-NOESY (NOESY=nuclear Overhauser enhancement spectroscopy) spectra, a knowledge of the spatial interrelationships between protons in different parts of the dendrimer scaffold can be acquired from proton-proton NOE interactions. At the same time, the prevailing conformation of the dendritic branches in the solvent used can be deduced from this information. Furthermore, studies of dendrimer/sol-vent interactions and the influence of solvent on the spatial structure of the dendrimer are also possible [22]. Thus the information content of such NMR experiments resembles that of small-angle scattering experiments on dissolved dendrimers (see Section 7.6). 

Even in fields in which materials science had become somewhat routine and boring, such as the development of new polymers, unexpected and promising breakthroughs have occurred. The invention of polymers that conduct an electrical current—once considered a contradiction in terms—has made possible new substances with many of the advantages of traditional polymers and the added benefit of electrical conductivity. Like most other fields of materials research today, polymer research is turning out products with almost unheard of molecular structures, such as dendrimers and hyper-branched polymers. These products are so different from any natural or previously manufactured substance that researchers scarcely know the applications in which they may he employed. 

FIGURE 16.2 Molecular structures of different glycodendrimers. (a) A carbohydrate-coated dendrimer with 24 pendant monosaccharide residues, (b) A carbohydrate-centered dendrimer with a p-cyclodextrin ((3CD) core and 14 copies of a glycosyl thiol residue, (c) A (1-D-glucosamine-based glycodendrimer comprising 16 monosaccharide residues arranged around a tetravalent polyphenylene core. 

Fig. 19 Molecular structure of [P2C (pPr1C6H4Me)Ru 6(p-donq)3(tpt)2]6+ showing the pyrenyl-modified dendrimer (P2) (space-filling model) being encapsulated in the cavity of the metalla-cage [63]...

Figure 5.29. PAMAM dendrimer multifunctional conjugates for cancer treatment. The FA group is a folic acid cancer cell target, and FITC is fluorescein isothiocyanate, used as an imaging agent. Also shown (bottom) is the molecular structure for the anticancer drug, taxol, denoting the -OH group that covalently attaches to the dendrimer. Reproduced with permission from Majoros, I. J. Myc, A. Thomas, T Mehta, C. Baker, J. R. Biomacromolecules, 2006, 7, 572. Copyright 2006 American Chemical Society.

Figure 6.32. Molecular structures of dendrimers modified with long-chain aliphatic cores. Unlike traditional dendritic structures with smaller cores, as the generation size increases, there is an available channel for external species to enter the dendrimer interior. Reproduced with permission from Watkins, D. M. Sayed-Sweet, Y Klimash, J. W Turro, N. J. Tomalia, D. A. Langmuir 1997,13, 3136. Copyright 1997 American Chemical Society.

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