Dendrimer analysis

Just as gel electrophoresis methodology is commonly used to determine homogeneity, as well as molecular weights of proteins these techniques may be used similarly for dendrimer analysis. Other uses have included the assessment of DNA/dendrimer binding constants which have been studied using gel electrophoresis. Application of gel electrophoresis in dendritic science will be discussed from these three aspects. 

A chromatographic technique frequently used in polymer and dendrimer analysis is size exclusion chromatography (SEC) [13], which is often also called gel permeation chromatography (GPC). It is a straightforward method of determining the relative molar mass, the molar mass distribution, and the polydispersity index (PDI) with compatively modest consumption of material and time. 

The only mass spectrometric methods available during the era of the first cascade synthesis in 1978 [30] were electron impact (El) and field desorption (FD) mass spectrometry [31]. Fast atom bombardment (FAB) mass spectrometry is limited to fairly low mass ranges and not very suitable for compounds of low polarity. It was not until the development of new and gentle ionisation methods such as MALDI (matrix-assisted laser desorption ionization) [32] and ESI (electrospray ionization) [33] that the conditions were fulfilled for the start of intense research in the field of dendrimer chemistry. The following section will present the special features of these mass-spectrometric methods and their importance in dendrimer analysis. 

Although MALDI-MS plays an outstanding role in dendrimer analysis, additional use is also made of modern ESI mass spectrometers for monitoring syntheses, for determination of relative molecular masses, and for studying the purity and polydispersity of dendrimers, including those of higher generations [34]. 

In addition to CW ESR, ENDOR, and pulsed techniques (HYSCORE spectra, 2D-ESTN, and ESEEM) were also used for dendrimer analysis. The ESR techniques have provided useful information on the dendrimers structure, properties, and applications, and their interactions with selected species. 

Percec, V. et al. Synthesis and retrostructural analysis of hbraries of AB3 and constitutional isomeric AB2 phenyl propyl ether-based supramolecular dendrimers, J. Am. Chem. Soc., 128, 3324, 2005. 

When tetranuclear platinum complex (35) bridged by tetra(4-ethynylphenyl)-methane was used as the core (Fig. 6), dendrimers having more platinum atoms than those prepared from trinuclear platinum core 30 in the molecule were obtained up to the third generation. GPC analysis of these dendrimers revealed that the dendrimers with a tetraplatinum core have a similar molecular size to those with the triplatinum core 30. 

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. 

According to the synthetic strategy just described, a series of water-soluble carbosi-lane dendrimers were made, bearing peripheral galabiose trimers interspaced by 29 A, adjusted to the binding-site distances (Fig. 75).432 The binding affinity to SLT-I and SLT-II B subunits were determined by Scatchard plot analysis. Hexavalent compound 610 showed KD values of 1.3 and 1.6 /M for SLT-I and SLT-II,... 

The chemical composition of particles can be just as varied as their shape. Commercial particles can consist of polymers or copolymers, inorganic constructs, metals and semiconductors, superparamagnetic composites, biodegradable constructs, and synthetic dendrimers and dendrons. Often, both the composition of a particle and its shape govern its suitability for a particular purpose. For instance, composite particles containing superparamagnetic iron oxide typically are used for small-scale affinity separations, especially for cell separations followed by flow cytometry analysis or fluorescence-activated cell sorting (FACS). Core-shell semiconductor particles, by... 

Islam, M.T., Majoros, I.J., and Baker Jr., J.R. (2005) HPLC analysis of PAMAM dendrimer based multifunctional devices. J. Chrom. B822, 21-26. 

Percec, V., Cho, W.D., Mosier, P.E., Ungar, G., and Yeardley, D.J.P. (1998) Structural analysis of cylindrical and spherical supramolecular dendrimers quantifies the concept of monodendron shape control by generation number./. Am. Chem. Soc. 120, 11061-11070. 

The synthesis of well-defined LCB polymers have progressed considerably beyond the original star polymers prepared by anionic polymerization between 1970 and 1980. Characterization of these new polymers has often been limited to NMR and SEC analysis. The physical properties of these polymers in dilute solution and in the bulk merit attention, especially in the case of completely new architectures such as the dendritic polymers. Many other branched polymers have been prepared, e.g. rigid polymers like nylon [123], polyimide [124] poly(aspartite) [125] and branched poly(thiophene) [126], There seems to be ample room for further development via the use of dendrimers and hyperbran-... 

Gel electrophoresis is widely used in the routine analysis and separation of many well-known biopolymers such as proteins or nucleic acids. Little has been reported concerning the use of this methodology for the analysis of synthetic polymers, undoubtedly since in many cases these polymers are not soluble in aqueous solution - a medium normally used for electrophoresis. Even for those water-soluble synthetic polymers, the broad molecular weight dispersities usually associated with traditional polymers generally preclude the use of electrophoretic methods. Dendrimers, however, especially those constructed using semi-controlled or controlled structure synthesis (Chapters 8 and 9), possess narrow molecular weight distribution and those that are sufficiently water solubile, usually are ideal analytes for electrophoretic methods. More specifically, poly(amidoamine) (PAMAM) and related dendrimers have been proven amendable to gel electrophoresis, as will be discussed in this chapter. 

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