Smaller building blocks form larger assemblies: aggregation behavior of biaryl-based dendritic facial amphiphiles.

Synthesis and micellar behavior of biaryl-based benzyl ether dendritic molecules prepared from a new biaryl building block are described. The key objective of the study is to tune the size of individual dendritic molecules and investigate its effect on aggregation behavior of the resulting micelle-like assemblies. We show that the functional group placement in the building block influences flexibility of the dendritic backbone and interior volume available for packing the hydrophobic groups, which is reflected in different aggregation behavior and aggregate size of the two types of micellar assemblies.

Supramolecular assemblies from amphiphilic homopolymers: Testing the scope.

It has been shown by us in a recent communication that homopolymers, in which each repeat unit contains a hydrophilic and a hydrophobic head group, are capable of forming environment-dependent micellar or inverse micellar assemblies. A systematic structure-property relationship study is carried out here to test the scope of the design. We show here that the molecular design is indeed broadly applicable and that there is a significant gain in the critical aggregation concentrations of these polymers, as compared to the small molecule counterparts. We also show that the design can be tuned to achieve vesicle-type assemblies, which further expands the repertoire of amphiphilic homopolymers in a variety of areas. Characterizations of these assemblies have been carried out using transmission electron microscopy, dynamic light scattering, static light scattering, and dye incorporation experiments.

Selective sensing of metalloproteins from nonselective binding using a fluorogenic amphiphilic polymer.

Nonconjugated fluorogenic amphiphilic polymers containing an anthracene chromophore exhibit fluorescence quenching in the presence of metalloproteins, although the binding of the polymer to proteins is not selective. The reason for this difference is that the possible conformational changes that protein binding could bring about on a polymer do not affect the fluorescence properties of a pendent chromophore in nonconjugated polymers. This is in contrast to the nonspecific binding and response found with conjugated polymers to proteins.

Temperature-sensitive dendritic micelles.

Syntheses up to three generations have been achieved of biaryl-based amphiphilic dendrons with a charge-neutral pentaethylene glycol as the hydrophilic part and a decyl chain as the hydrophobic part. Studies on the temperature-dependent characteristics revealed that these dendrons exhibit a generation-dependent lower critical solution temperature (LCST). This behavior is attributed to the combination of the amphipathic nature of the hydrophilic pentaethylene glycol side chain and dendritic effect. Interestingly, this biaryl-based scaffold also maintains the ability to form a micelle-like assembly in polar solvents and an inverted micelle-like assembly in apolar solvents. Polarity of the dendritic interior was investigated using dye-based microenvironment studies. The aggregation behavior of these micelles was analyzed by fluorescence spectroscopy and dynamic light scattering. Critical micelle concentrations (CMC) of these assemblies were investigated using fluorescence excitation spectra of the sequestered guest molecule, pyrene.

Effect of guest molecule flexibility in access to dendritic interiors.

[structure: see text] Dendrimers are attractive scaffolds for catalysis, since catalytic sites can be isolated and the catalysts are recoverable and reusable. Herein, we show that conformationally constrained molecules have better access to dendritic cores compared to the more flexible counterparts. The results reported here should have implications in utilizing dendrimers as scaffolds for artificial selectivity in catalysis.

Probing every layer in dendrons.

Dendrons with a fluorescent probe in a specific location have been synthesized and characterized. Accessibility of guest molecules to each of these layers was then analyzed using an intermolecular photoinduced electron-transfer process. Comparisons of the accessibility among each layer of the dendron and among the generations are provided.