Starburst effect

Three-dimensional branched architectures, generally termed dendrimers, represent a class of synthetic macromolecules that have impacted dramatically on the field of organic and polymer chemistry and created a new branch in synthetic and material chemistry. For the last two decades, dendrimer research has been at the forefront of polymer research and was first postulated in the 1940s by Flory, a pioneer in polymer research and Nobel Laureate in 1974, who proved the existence of branched chains and their potential role in three-dimensional (3D) macromolecular architectures [446-448], In 1978, Vogtle et al. developed an iterative cascade method for the synthesis of low molecular weight branched amines [449]. The real expansion of the field started after Tomalia et al. [450] and Newkome et al. [451] discovered the starburst effect, which shed light on a new chemical arena. Since then, dendrimer chemistry has been diversified... 

Fig. 1.19 Attainment of the limiting generation in dendrimer growth as a result of the starburst limit effect (schematic idealised)...

In view of recent reports, it seems prospective to use the reaction of trans sily-lation for the synthesis of other types of unsaturated compounds, particularly for the synthesis of novel organosilicon starburst compounds having a silicon-bridged -conjugated structure which is expected to have potential optoelectronic properties. The effective functionalization of l,3,5-tris(dimethylvinylsi-lyl)benzene by the respective reactions with 1,4-divinylbenzene leads to the formation of a dendrimer (Fig. la) [55]. 

Starburst/cascade dendrimer dense-packing critical branching state, nanoscopic steric effects. 

Delong, R. Stephenson, K. Loftus, T. Fisher, M. Alahari, S. Nolting, A. Juliano, R.L. Characterization of complexes of oligonucleotides with polyamidoamine starburst dendrimers and effects on intracellular delivery. J. Pharm. Sci. 1997, 86, 762-764. 

Differential extinction between the stars and the gas can also affect EW(H/3). Calzetti et al. (1994) found that the obscuration toward starburst clusters tended to be lower than that toward the ionized gas. They determined that, on average, Ay toward the stars was about one-half of that toward the gas. This is understandable if the stars have evacuated a cavity in the ionized gas through the combined effects of radiation pressure and stellar winds. The average derived obscuration for H II regions in spirals is Ay 1 mag. If Ay (stars) is only 0.5 mag, then the observed EW(H/3) will be about 40% lower than the intrinsic value. 

Measurement of the influence of different micellar environments on proton transfer from excited states of 3-hydroxyflavone allows estimates to be made of micelle concentrations from measurement of the tautomer emission yield. Proton transfer reactions of benzimidazole excited singlet states have also been studied in ionic micelles. Magnetic fields are found to affect the behaviour of radicals generated by the photodissociation of benzil in micellar media. The starburst dendrites which are formed by anionic macromolecules in interaction with both anionic and cationic surfactants have been examined by pyrene fluorescence. Benzo[k]fluoranthrene fluorescence has served as a probe of the effects of metal salts on bile salt aggregation. The incorporation and distribution of benzoquinone into liposomes containing amphilic Zn(II) porphyrin has been followed by its effect on the quenching of the excited state °. A comparison of the photochromism of spirobenzpyran derivatives in unilamellar surfactant vesicles and solvent cast surfactant films has also been reported. ... 

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