PAMAM dendrimers measurements

The development of mass spectroscopic techniques such as matrix assisted laser desorption (MALDI) and electrospray mass spectrometry has allowed the absolute determination of dendrimer perfection [7,8], For divergent dendrimers such as PAMAM and PPI, single flaws in the chemical structure can be measured as a function of generation to genealogically define an unreacted site of or a side reaction producing a loop at a particular generation level. Mass spectromet-ric results on dendrimers, not only demonstrate the extreme sensitivity of the technique, but also demonstrate the uniformity of the molecular mass. The polydispersity index of Mw/Mn for a G6 PAMAM dendrimer can be 1.0006 which is substantially narrower than that of living polymers of the same molecular mass [7],... 

TEM has been used to measure the average diameter of PAMAM dendrimers from G5 to G10 [20], Figure 11.3 shows micrographs of G5, G6, G8, and GlO.The G5 micrograph also has a small amount of G10 dendrimers added to help focus the microscope and to identify the relative sizes. Single dendrimers can easily be distinguished within each of the populations shown. Individual polymer molecules can easily be seen, while conventional linear polymers in this molecu-... 

The SANS experiments [51] were performed with solutions of G8 PAMAM dendrimer in D20, methyl-d4, ethyl-d6, and n-butyl-d10 alcohol at a temperature of T = 20.0 °C. PAMAM dendrimers do not dissolve in acetone, but they readily dissolve in methyl alcohol/acetone mixtures over a wide range of composition. Solvents of different composition, were prepared and added to a weighed amount of dried G5 or G8 dendrimer. In a separate set of experiments, the NIST NG7 30 m instrument was used to measure the effects of charging on the dendrimer size. PAMAM G8 dendrimers in D20 were charged by addition of HC1 in the presence of various amounts of NaCl to the charged dendrimers to screen the electrostatic interactions. 

In fact, it has been previously observed that measured diameters of dendrimer molecules by AFM are much larger than the theoretical values, which indicates that the dendrimers spread out and flatten on the surface [25, 26], Three major factors could account for this deformation. First, the unique architecture and chemical structure of PAMAM dendrimers result in macromolecules that are not solid balls, but instead are relatively open and hence soft materials. It is expected that the rigidity will increase substantially with increasing generation number [9]. Therefore, when deposited on solid substrates, they tend to deform to different degrees as a result of the interplay between their inherent rigidity and surface energetics from the interaction between the dendrimer molecules and the mica surface. Secondly, amine-terminated PAMAM dendrimers possess a... 

PAMAM dendrimers No. of molecules MW (AFM) measured MW theoretical Relative error (%) Polydispersity... 

However, for the dendrimer nanocomposite metallic systems this change in shape was not observed. Again, due to the high stability to intense laser pulses, the anisotropy value of the gold dendrimer nanocomposite, which can be viewed as a measure of the symmetry of the particle, did not change after several repeated cycles of measurements. It is possible that the initial optical pumping of the electron-phonon modes of the metal particles is partially absorbed by the encapsulating PAMAM dendrimer. 

Table 2 Contact angle measurements, XPS analysis, Gantrez/4th Generation PAMAM dendrimer composites and ellipsometric thickness of ...

The results obtained from the analysis of TEM measurements show that the functionalization of the amino groups with carbohydrate chains leads to nanoparticles with narrower size distribution and smaller mean particle diameter than for PEI (Figs. 7 and 8). In this case, the resulting particle sizes are comparable to the ones obtained with PAMAM dendrimers [89,91,92]. 

Recently, Stechemesser and Eimer published hydrodynamic radii obtained from translational diffusion coefficients measured by means of recovery after photobleaching experiments on selected generations of PAMAM dendrimers [76]. The values of Rh obtained in methanol are compared with Rg data on the same dendrimers in Fig. 4. It can be calculated that the ratio Rh/R 1.4 for all but the tenth generation dendrimer. This ratio is somewhat higher than expect-... 

Dubin et al. measured [r ] and D0 of seven generation of carboxylated PAMAM dendrimers in NaNOs NaH2P04 aqueous buffer at pH 5.5 and 0.38 mol/1 in order to minimize electrostatic interaction [85]. The values of of... 

The PAMAM dendrimer-DNA complexes have been shown to promote transfection [152-156]. The earlier studies used reporter luciferase which allows for measurement of luciferase activity in host cells [155, 156]. Although there is some dependence on the cell type being invaded [155], experiments have shown that generations 6-8 dendrimers are most efficient in transfection [155, 156]. There is little transfection with generations 2-4 PAMAM dendrimers and no further improved efficiency with generations 9 and 10 dendrimers. The preferred dendrimer to DNA stoichiometry is 5 1 or higher [155,156]. It has since... 

These data are corroborated1851 by ASas measurements for the polyamidoamine (PAMAM) dendrimers (see Figure 2.4 9) as well as a series of compact polyethereal... 

Table 2. Size measurements on poly(amidoamine)PAMAM dendrimers (ethylenediamine core) from computer analysis of TEM images...

Experimental measurements of the hydrodynamic radius of PAMAM dendrimers with ammonia or EDA cores by size exclusion chromatography and vis-... 

Measurements of molecular density and intrinsic viscosity of PAMAM dendrimers indicate an unusual variation with dendrimer generation. Minimum density and maximum intrinsic viscosity were observed at around G4, which suggests that the fully developed dendrimers have a high accessible internal surface area in a solvent-filled intramolecular free volume that may consist of internal cavities and channels. Similar findings were reported by Mourey et al. for PBE monodendrons (based on dihydroxybenzyl alcohol) and tridendrons produced by coupling these dendrons to a trifunctional core, l,l,l-tris(4 -hydro-xyphenyl)ethane prepared by the convergent method. A maximum intrinsic viscosity occurred at G3 for tridendrons and G5 for monodendrons, consistent with the model developed by Lescanec and Muthukumar... 

There is considerable evidence from a variety of techniques for a dendrimer model composed of a relatively soft or spongy interior surrounded by a considerably harder outer molecular surface, the so-called dendritic box. C-NMR measurements of spin lattice relaxation times of specifically tagged PAMAM dendrimers have shown considerably reduced mobility in the outer surface groups relative to the interior segments. Meltzer et performed C-... 

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