Fluorescence and Aggregation Behavior of Poly(amidoamine) Dendrimers Peripherally Modified with Aromatic Chromophores:  the Effect of Dendritic Architectures

Abstract

PAMAM dendrimers of the zeroth to fifth generation (G0-5) have been peripherally modified with phenyl, naphthyl, pyrenyl, and dansyl chromophores. Their fluorescence behaviors are strongly affected by the dendritic architectures at different generations. These dendrimers modified with hydrophobic chromphores can self-organize into vesicular aggregates at the low generations G0-3 in water. The size and aggregation number of these vesicles decrease with increasing generation from G0 to G3. Critical aggregation concentration determined by fluorescence spectroscopy reveals that these aggregates can be favorably formed in the order of G3 > G2 > G1. In contrast to the vesicles made from traditional amphiphilic compounds, these dendrimer-based vesicles are very adhesive due to the H-bonding interaction and entanglement of dendritic branches located in the outer layer. A large number of multivesicle assemblies, i.e., "twins" and "quins" consisting of two and five vesicles, were clearly identifiable with transmission electron (TEM) and atomic force microscopy. For the dendrimers with peripheral pyrenyl chromophores, triangle-like vesicles were observed in water. The hydrophobic interphase thickness of the vesicular bilayer is ca. 2.0-3.2 nm determined by fluorescence resonance energy transfer methods, which agrees well with the thickness directly observed with TEM.

Effects of glutamic acid shelled PAMAM dendrimers on the crystallization of calcium phosphate in diffusion systems

“…Thus, it may be the functionalized terminii that account for the adsorption onto crystal surfaces. Although it was reported that PAMAM could self-assemble due to the amphiphilic effect [33], PAMAM-MG does not show this behavior because the core and terminii are both hydrophilic. As a result, PAMAM-MG is not likely to adopt a self-assembled conformation to adsorb onto crystals surfaces.…”

Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation

“…Over the years, the synthesis of several pyrene-labeled dendrimers has been reported in the literature [36,37,44,[120][121][122][123][124][125][126][127][128][129][130][131][132][133][134], but in many instances, the pyrene-labeled constructs were synthesised as pyrene-labeled dendrons to be attached onto a focal point bearing an acceptor molecule capable of communicating with the pyrenyl pendants [36,44,[120][121][122][123]. Consequently, these investigations focused on the photophysical process taking place between the pyrene donor and the acceptor rather than on excimer formation between pyrene pendants covalently attached to the chain ends of dendrimers.…”

“…Consequently, these investigations focused on the photophysical process taking place between the pyrene donor and the acceptor rather than on excimer formation between pyrene pendants covalently attached to the chain ends of dendrimers. In effect, pyrene excimer formation has been investigated in earnest in only seven reports [44,120,[126][127][128]130,134] and the results of these are now described.…”

“…An increase in η × (I E /I M ) SS with increasing pyrene content was also found by Duhamel et al [126] for a series of four poly(2,2-bis(hydroxymethyl)-propionic acid) dendrimers of generations 1-4 which were labeled with 1-pyrenebutyl pendants ( Table 1). As can be seen in Figure 2 Reference [120]; (×) Reference [134] assuming that each chain end of the dendrimer is labeled with a pyrenyl pendant; (▲) Reference [127]; (∆) Reference [130], dendrimer in acetonitrile; (♦) Reference [128]; (■) Reference [44]; (□) Reference [126].…”

“…Interestingly, whereas the study of the pyrene excimer formation of pyrene-labeled linear polymers has been astonishingly successful at characterizing the internal dynamics of these macromolecules [73][74][75], much fewer pyrene-labeled dendrimers have been prepared to study intramolecular excimer formation [117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134]. Surprisingly for such a rather small set of studies, many of these studies yield trends that are, in the opinion of the author, both internally and externally inconsistent and which, if taken at their face value, would lead the non-expert in fluorescence to the erroneous conclusion that pyrene excimer formation cannot be successfully applied to characterize the internal dynamics of dendrimers.…”