Dendrimers measurements

Fig. 12 Variation of nh for the exocyclic amine proton of the 24-Fe dendrimer measured by NMR spectroscopy upon addition of n-Bu4NCl or n-Bu4NBr. Comparison with monometallic [FeCp (7j6-c3H5NHPh)][PF6] (1-Fe) and tripodal PhCFhNFIChCFhbO (CH2)3NH-[)76-PhFeCp ][PF6] 3 (3-Fe) showing the positive dendritic effect...

Molar weight of the dendrimers measured by MALDl-TOF (matrix assisted laser desorption ionization-time-of-flight mass spectrometry)... 

The first-generation dendrimer 51 was directly observed by transmission electron microscopy (TEM). The TEM image showed that the dimensions of individual molecules are about 50 A, which is consistent with the calculated one [36]. Third-order NLO measurements showed a significant enhancement of two-photon absorption upon proceeding from the constituent molecules to the dendritic complex [35]. 

Quantitative analysis of the results obtained has shown that a single eosin guest is sufficient to completely quench the fluorescence of any excited dansyl unit of the hosting dendrimer. Fluorescence lifetime measurements indicated that the dye molecules can occupy two different sites (or two families of substantially different sites) in the interior of the dendritic structure. 

An important goal of this study is to characterize the noncentrosymmetric arrangement of the azobenzene branches in dendrimers and the effect of these dendrimers on macroscopic second-order susceptibihty. The NLO activity of the dendrimers can be characterized by their molecular hyperpolarizabihty. The hyper-Rayleigh scattering (HRS) method is a reliable way of measuring the mol-... 

Fig. 3. Comparison of transfection efficiencies obtained using PolyFect Reagent, a dendrimer-based transfection reagent, and a calcium phosphate-mediated procedure. COS-7 and HeLa cells were transfected in srx-weU plates with a /3-galactosidase expression plasmid using the appropriate protocol. For the calcium phosphate-mediated transfection, 6 pg of plasmid DNA was used and the medium was changed after 5 h incubation. Transfections were performed in triplicate, and transfection efficiency was measured by monitoring the /3-galactosidase activity of extracts obtained from the transfected cells. The amoimt of /3-galactosidase activity in the extracts correlates with the transfection efficiency. Cells were harvested 48 h post-trans-fection...

Dendrimer encapsulated Pt nanoparticles (DENs) were prepared via literature methods (1, 11). PtCl42 and dendrimer solutions (20 1 Pt2+ dendrimer molar ratio) were mixed and stirred under N2 at room temperature for 3 days. After reduction with 30 equivalents of BH4 overnight, dialysis of the resulted light brown solution (2 days) yielded Pt2o nanoparticle stock solution. The stock solution was filtered through a fine frit and Pt concentration was determined with Atomic Absorption Spectroscopy (11). Details on catalyst characterization and activity measurements have been published previously (11). 

Dipole moments for dioxan solutions of both CHO or P-Cl terminated dendrimers were measured at 25 °C. Remarkably, values of dipole moment vs generation increase exponentially from 8.43 (10-[G1])to258 (10-[G10]) and from 8.27 (10-[G ]) to 328 (10-[GnD debyes (Fig. 10a), the highest dipole moment values... 

The conformational flexibility and the lack of difference of the electronic properties of the polyether branches in 32 have been forwarded to explain this zero rotation. Therefore a similar dendrimer 34 has been prepared which carries a more sterically demanding branch, leading to a more rigid structure [66] interestingly, this dendrimer indeed exhibited a very small but measurable optical activity, which underlines the thesis that nanoscopic chirality depends on the rigidity of the investigated structure. 

Fig. 21. lst-Generation dendrimer 57 with nitro groups at the periphery and 2nd-generation dendrimers 58-60 used for optical and H-NMR measurements [1,89]... 

The CF3 groups not only had interesting effects upon certain synthetic steps on the way to such dendrimers [93], but also could be used as probes the 19F-NMR spectra which were measured in different solvents and at different temperatures exhibited a clear-cut difference between the inner CF3 groups and those close to the periphery. 

A comparison of the thus calculated with the measured specific rotations of the 0th- to 4th-generation dendrimers of this kind gave a close resemblance, with a curve, approaching asymptotically a limiting value (Fig. 26). It was also shown that the shape of this curve was independent of solvent, concentration and temperature. This was not the case when CD spectra of these dendrimers were compared (Fig. 27) in solvents such as CH2C12 and f-butyl methyl ether a constant rise of the Cotton effect was observed, which correlates with the increasing amount of benzene chromophores in the dendrimers. However, in the... 

Fig. 26. a Specific optical rotations for the model building blocks for core 78, interior building block 79 and peripheral unit 80 of dendrimers of type 77 b calculated average optical rotations for the doubly branching dendrimers of Oth to 4th generation c measured optical rotations in CHC13 at different temperatures and concentrations [94]... 

The latter effect has been demonstrated by Meijer et al., who attached chiral aminoalcohols to the peripheral NH2-groups of polypropylene imine) dendrimers of different generations [100]. In the enantioselective addition of diethyl-zinc to benzaldehyde (mediated by these aminoalcohol appendages) both the yields and the enantioselectivities decreased with increasing size of the dendrimer (Fig. 28). The catalyst obtained from the 5th-generation dendrimer carrying 64 aminoalcohol groups at its periphery showed almost no preference for one enantiomer over the other. This behavior coincides with the absence of measurable optical rotation as mentioned in Sect. 3 above. The loss of activity and selectivity was ascribed to multiple interactions on the surface which were... 

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