Malar A. Azagarsamy

Enzyme-Triggered Disassembly of Dendrimer-Based Amphiphilic Nanocontainers

We demonstrate a new enzyme-induced disassembly of amphiphilic nanocontainers based on dendrimers. Disassembly and the ensuing release of noncovalently bound guest molecules are of great interest because of their implications in areas such as drug delivery and sensing. Achieving these with a protein as the stimulus is of even greater importance, because proteins are the primary indicators of biological imbalances. We achieved disassembly of the nanocontainers by disturbing the hydrophilic-lipophilic balance in the amphiphilic dendrimer building blocks.

Disassembly of Dendritic Micellar Containers Due to Protein Binding

Disassembling a supramolecular assembly and releasing the contents of the assembly in response to a stimulus are important goals of supramolecular chemistry. When proteins are used as the stimulus, the biological relevance of the supramolecular event dramatically increases. Although there have been efforts in which such disassembly has been achieved using enzymatic action, such events based on ligand-receptor interactions have been very limited. Here we demonstrate protein-binding-induced disassembly of dendrimer-based amphiphilic nanocontainers. We show that this disassembly is selective to the targeted protein and that the disassembly event causes a release of the sequestered guest molecules. We propose that the disassembly is caused by alteration of the hydrophilic-lipophilic balance caused by the protein binding.

Guest-Release Control in Enzyme-Sensitive, Amphiphilic-Dendrimer-Based Nanoparticles through Photochemical Crosslinking

Stimuli sensitive, facially amphiphilic dendrimers have been synthesized and their enzyme-responsive nature has been determined with dual fluorescence responses of both covalently conjugated and non-covalently bound reporter units. These dual responses are correlated to ascertain the effect of enzymatic action on micellar aggregates and the consequential guest release. The release of the guest molecule is conveniently tuned by stabilizing the micellar aggregates through photochemical crosslinking of hydrophobic coumarin units. This photo-crosslinking is also utilized as a tool to investigate the mode of enzyme-substrate interaction in the context of aggregate-monomer equilibrium.

Selective peptide binding using facially amphiphilic dendrimers

Amphiphilic dendrimers, which contain both hydrophobic and hydrophilic groups in every repeat unit, exhibit environment-dependent assemblies both in hydrophilic solvent, water, and in lipophilic solvent, toluene. Upon investigating the status of these assemblies in a mixture of immiscible solvents, these dendrimers were found to be kinetically trapped in the solvent in which they are initially assembled. This property has been exploited to selectively extract peptides from aqueous solution into an organic phase, where the peptides bind to the interior functionalities of the dendritic inverse micelles. While the corresponding small molecule surfactant does not exhibit any selective binding toward peptides, all dendrons (G1-G3) are capable of this selective binding. We show that the inverse micelle-type assembly itself is crucial for the binding event and that the assembly formed by the G1 dendron has a greater capability for binding compared to the G2 or G3 dendrons. We have also shown that the average apparent pKa of the carboxylic acid functionalities varies with generation, and this could be the reason for the observed differences in binding capacity.

Site-specific Installation and Study of Electroactive Units in Every Layer of Dendrons

Whereas encapsulation of functional groups at the core of dendrimers is well-understood, very little is known about their intermediate layers or even the periphery. Here we report on a systematic investigation of every layer of dendrimers by incorporating a single ferrocene unit in well-defined locations in dendrons. Site-specific incorporation of the ferrocene unit was achieved by utilizing the dendrimer sequencing methodology. We show here that the redox potential values of ferrocene at intermediate layers were remarkably different from those at the core and the periphery. Although redox potential values were location-dependent, no significant change in the rate of heterogeneous electron transfer (k(0)) was observed with respect to locations. This was attributed to the possibility that free rotation of dendrimer nullifies the distance between the electrode and ferrocene unit. Finally, we also show that no Faradaic current was observed for the amphiphilic assemblies of these dendrons, whereas the same dendron did exhibit significant Faradaic current in nonassembling solvent environments.

Supramolecular displacement-mediated activation of a silent fluorescence probe for label-free ligand screening.

We report a new approach for the rapid screening of analyte binding affinities for a target protein. We demonstrate that a molecular probe, with a pro-fluorophore substrate and ligand moieties, can be hindered from enzymatic access when bound to the target protein. When analytes displace the probe from the proteins binding pocket, a fluorescence profile is generated. This profile is used to discriminate analytes based on their relative binding affinities.

Magnetic resonance imaging: Making sense of disassembly

An amphiphilic molecule that contains a protein-specific ligand and an NMR-active tag forms the basis of a protein sensor. A measurable NMR signal results only in the presence of active protein that causes disassembly of clusters of the amphiphile.