Monodisperse structures

This Topics volume also shows that in the development of dendrimer chemistry there is still a need for efficient synthetic methods ensuring multiple high-yield conversion and leading to more or less pure (monodisperse, structurally perfect) dendritic molecules. Large libraries of imperfect substances are often formed at higher generations, only differing in small structural details. 

We considered above processes of charge transfer in monodisperse structures composed of identical nanoparticles. If there is a considerable particle size scatter, the description of charge state of such structures becomes much more complicated. This issue has been the subject of several studies (see, e.g., Refs. [35,36]). 

Dendrimers are a relatively new class of macromolecules different from the conventional linear, crosslinked, or branched polymers. Dendrimers are particularly interesting because of their nanoscopic dimensions and their regular, well-defined, and highly branched three-dimensional architecture. In contrast to polymers, these new types of macromolecules can be viewed as an ordered ensemble of monomeric building blocks. Their tree-like, monodispersed structures lead to a number of interesting characteristics and features globular, void-containing shapes, and unusual physical properties [107-111]. 

Figure 11 (a) Structures of the click cluster delivery vehicles five monodisperse structures were developed that vary in the length of the oligoethyleneamine arms where x- 0 (9a), 1 (9b), 2 (9c), 3 (9d), and 4 (9e). (b) Luciferase reporter gene delivery experiments with the analogs described in (a) at N/P ratios 5,10,20, and 50. Transfection increases as the arm length increases, without having a dramatic effect on cytotoxicity. Adapted from Srinivasachari, S. Fichter, K. M. Reineke, T. M. J. Am. Chem. Soc. 2008, 130, 4618. ... 

Model described by Eqs. (6-1) to (6-4) for adsorbents of monodisperse structure or additional Eqs. (6-33) to (6-35) are too complicated for analytical use. As a matter of fact, the model can include four rate parameters in addition to the adsorption equilibrium constant. Those equations finally give the solutions for the first absolute moment, pi, and the second central moment, pj. These two moments are only utilized in actual experiments. Therefore, it might be helpful if comparison is made between this model and the models which include only two parameters including the equilibrium constant. As two-parameter models, typical are 1) a dispersion model that includes axial dispersion coefficient as a sole rate parameter and 2) a two-phase exchange model which has a mass transfer coefficient as an only rate parameter. These two models are considered to be the two extremes of the complicated model used in the earlier section, hence the results of... 

The value of x is determined by the geometry of the system, primarily by the particle size (radius, r, for spherical particles) and by the packing density of particles described by porosity, H. The porosity is a dimensionless characteristic defined as the ratio of the volume of pores, Vp to the total volume of the porous structure, V, that is, n = Vp/V. The x = Xir, H) dependence can be estimated from data on the degree of dispersion of the particles and the porosity of samples by employing the specific models for disperse structures. Eor example, in the case of loose monodisperse structures with spherical particles connected into crossing chains with n particles per chain between the nodes (Figure 3.17), the X function for the case when the porosity H does not exceed 48% can be described as... 

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