Dendrimers density

The dendrimer density z (atomic mass units per unit volume) clearly minimizes... 

Figure 1.20 Comparison of densities as a function of generation for (A) asymmetrical branch cell in DenkewaIter-type dendrimers, (B) symmetrical branch cell in Tomalia-type dendrimers ([densities calculated from experimental hydrodynamic diameters and theoretical, D.A. Tomalia, M. Hall, D.M. Hedstrand, J. Am. Chem. Soc., 109,1601 (1987))...

The dendrimer density z (atomic mass units per unit volume) clearly minimizes between generations 4 and 5, then begins to increase as a function of generation due to the increasingly larger, exponential accumulation of surface groups. Since refractive indices are directly related to density parameters, their values minimize and parallel the above density relationship. 

The presence of a large number of chain-ends in the fully synthesized dendrimer molecules makes them highly soluble and also readily miscible, for example with other dendrimer solutions. The solubility is controlled by the nature of the end-groups, so that dendrimers with hydrophilic groups, such as hydroxyl or carboxylic acid, at the ends of the branches are soluble in polar solvents, whereas dendrimers with hydrophobic end-groups are soluble in non-polar solvents. The density of the end-groups at the surface of the dendrimer molecule means that they have proportionately more influence on the solubility than in linear polymers. Hence a dendritic polyester has been shown to be more soluble in tetrahydrofuran than an equivalent linear polyester. 

The same research group extended their studies, proposing a systematic investigation of the core activities for different carbohydrate densities during biosensing processes.279 Three new mannosylated dendrimers with a Ru(bipy)3 core unit were synthesized, and the influence of the number and size of dendritic branches on the rate of electron and energy transfer, as well as the lectin-biosensing abilities (Scheme 41),... 

Regardless of how they are made, the higher the dendrimer generation the greater the density of its branching becomes. Dendrimers of small size have an internally open configuration that freely permits the flow of small molecules within their inner structure. As dendrimers increase in diameter from G-0 through G-7, their appearance and size becomes more and more similar to... 

Figure 7.25 The multivalent nature of dendrimers can be used to add increased functionality to surfaces. Aminopropyl silane surfaces can be activated with either PDITC or through use of a cyclic anhydride plus DCC/ NHS to give amine-reactive surfaces. These reactive surfaces can be used to couple amine-dendrimers to provide a high density of amine groups on the surface for further bioconjugation.

Testing of G-l, G-2, and G-3 dendrimers in this application provided insight into the density of surface modification needed to passivate completely the particles and prevent aggregation. The G-l dendron was insufficient in this regard, but both the G-2 and G-3 dendron were big enough to create a surface barrier, which resulted in excellent colloidal stability of the particles in solution. 

Figure 7.26 Dendrimers made with a disulfide-containing core can be reduced to produce dendrons having free thiol groups for surface modification. Dative binding of these thiol-dendrons to gold or metallic surfaces can provide a high density of amine groups for coupling proteins or other molecules.

Srikant, P., Singh, A.K., McElhanon, J.R., and Dentinger, P.M. (2004) Dendrimer-activated surfaces for high density and high activity protein chip applications. Langmuir 20(15), 6075-6079. 

Stears, R.L., Getts, R.C., and Gullans, S.R. (2000) A novel, sensitive detection system for high-density microarrays using dendrimer technology. Physiol. Genomics 3, 93-99. 

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