Amitav Sanyal

Double click reaction strategies for polymer conjugation and post-functionalization of polymers

Double click reaction strategies, which are a combination of different type of click reactions, allow the preparation of polymers with various topologies and the post-functionalization of polymers, which cannot be easily achieved by using only one click reaction. The most studied click reaction combinations may be listed as the Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC)–Diels–Alder, and the CuAAC–nitroxide radical coupling reactions for polymer–polymer conjugation and the CuAAC–Diels–Alder, or the CuAAC–thiol-ene reactions for post-modification of polymers.

Segment block dendrimers via Diels-Alder cycloaddition.

Segment block dendrimers consisting of polyester and polyaryl ether dendrons were synthesized using reagent free Diels-Alder cycloaddition reactions. Three generations of furan functionalized polyaryl ether dendrons were reacted with maleimide functionalized polyester dendrons of the same generation to obtain segment block dendrimers in good yields. The thermoreversible nature of these macromolecules was investigated by subjecting them to elevated temperatures in the presence of anthracene as a scavenger diene.

Stable Magnetic Colloidosomes via Click-Mediated Crosslinking of Nanoparticles at Water-Oil Interfaces

Alkyne- and azide-functionalized iron oxide nanoparticles are co-assembled at the water-oil interface and covalently linked using click chemistry under ambient conditions to create magnetic colloidosomes (see image). These colloidosomes possess high stability, size-selective permeability, and are responsive toward external magnetic stimuli.

Designing functionalizable hydrogels through thiol–epoxy coupling chemistry

A novel and modular strategy has been developed for the preparation of reactive and functionalized hydrogels. In this strategy, thiol-epoxy coupling chemistry was employed for the formation of a hydrophilic network. The hydroxyl groups, generated during the coupling process, were then engaged in anchoring a fluorescent probe to the hydrogel scaffold.

Direct Fabrication of Functional and Biofunctional Nanostructures Through Reactive Imprinting

One-step reactive imprinting of a protected maleimide polymer provides a nanopatterned maleimide surface via a retro-Diels-Alder reaction. The patterned surfaces are used as scaffolds for the generation of functional and biofunctional structures. The biofunctional surface offers a platform for aligning the cells in the direction of patterns, demonstrating the potential for applications in the field of tissue engineering.

Colloidal microcapsules: self-assembly of nanoparticles at the liquid-liquid interface.

Colloidal microcapsules (MCs) are highly modular, inherently multiscale constructs of capsules stabilized by nano-/microparticle shells, with applications in many areas of materials and biological sciences, such as drug delivery, encapsulation, and microreactors. Until recently, fabrication of colloidal MCs focused on the use of submicron-sized particles because the smaller nanoparticles (NPs) are inherently unstable at the interface owing to thermal disorder. However, stable microcapsules can now be obtained by tuning the interactions between the nanometer-sized building blocks at the liquid-liquid interface. This Review highlights recent developments in the fabrication of colloidal MCs using NPs.

Formation and Size Tuning of Colloidal Microcapsules via Host−Guest Molecular Recognition at the Liquid−Liquid Interface†

Stimuli-responsive colloidal microcapsules have been fabricated at the oil-water interface using molecular recognition between functionalized gold nanoparticles. Water-soluble beta-cyclodextrin-capped gold nanoparticles and organo-soluble adamantyl-functionalized gold nanoparticles are self-assembled at the water-toluene interface via specific host-guest molecular interactions to provide robust microcapsules. Multivalent interactions of complementary ligands on the nanoparticle surface provide stability to these capsules. Unlike covalently cross-linked microcapsules, the reversible nature of these bridging interactions can be used to manipulate the size of these capsules via introduction of competing adamantane containing amphiphilic guest molecules. Partial disruption of interfacial cross-linking allows microcapsules to coalesce with each other to form larger capsules.

FRET between BODIPY Azide Dye Clusters within PEG-Based Hydrogel: A Handle to Measure Stimuli Responsiveness

The purpose of this paper is to investigate the dynamics of the fluorescence mechanism of boradiazaindacene (BODIPY) dye molecules, which are covalently bound to a polyethylene glycol based hydrogel structure with different concentrations, using a picosecond time-resolved spectroscopic technique. Since the hydrogel structure is capable of absorbing a large amount of water, without dissolving and without losing its shape, upon swelling, the distance between the BODIPY azide dyes is controllably changed; it is observed that the intensity weighted fluorescence lifetime for the highly concentrated donor dye molecules embedded in the hydrogel cluster network changes from 2.03 to 7.14 ns. Calculations based on our experimental results suggest that the fluorescence dynamics of the BODIPY azide dye molecules confined within the hydrogel network obeys the Forster resonance energy transfer (FRET) rather than self (or contact) quenching. If the hydrogel is dry, in which the distance between donors and acceptors is minimum, the energy transfer efficiency is found to be about 72%, and the distance between the two dye molecules is calculated to be 4.59 nm. Such a close placement causes a significant reduction in the fluorescence intensity due to a strong dipole-dipole interaction of the dye molecules. As the separation increases upon hydrogel swelling, the FRET efficiency reduces to 2%, which corresponds to a separation of 10 nm between two BODIPY dyes and hence a considerable increase in the level of fluorescence intensity. For the dilute hydrogel samples, the distance between the dye molecules is larger than the critical Forster distance. Therefore, the energy transfer efficiency for this type of dilute samples is found to be much lower.

Magnetic reduced graphene oxide loaded hydrogels: Highly versatile and efficient adsorbents for dyes and selective Cr(VI) ions removal

The formation of composites of reduced graphene oxide (rGO) and magnetic nanoparticles (MP) has flourished in recent years as they combine the advantages of both nanomaterials. Most of these composite materials are prepared by in situ formation of MP onto rGO or by the post-adsorption onto rGO. We report here on a simple and highly controlled method for the fabrication of different magnetic 3D rGO-loaded hydrogels. Cellulose bound magnetic nanoparticles (MP@cellulose) were synthesized by chemical co-precipitation and loaded together with rGO into poly(ethylene glycol) dimethacrylate based hydrogels during their fabrication using photo-polymerization. The magnetic rGO-loaded hydrogels proved to be highly adaptable to different applications. The as-formed composites allowed for efficient dye removal with an adsorption capacity of 111.9±4mgg-1 in the case of methylene blue (MB). Integration of poly(ethyleneimine) (PEI) allowed for the selective capturing of Cr6+ ions with an adsorption capacity of 313±12mgg-1. Most importantly, independent of the application, the magnetic rGO-loaded hydrogel can be regenerated without loss of its adsorption capacity.

Assembly of magnetic nanoparticles into higher structures on patterned magnetic beads under the influence of magnetic field

The self-assembly of nanoparticles into higher organizations in a controlled manner has critical importance for the utility of the unique properties of nanoparticles. The behavior of magnetic Fe(3)O(4) nanoparticles (MNPs) with an average size of 6 nm under an enhanced magnetic force is reported. Upon evaporation of the solvent where the MNPs are suspended, formation of unique micrometer-sized structures is achieved only when there is a patterned surface constructed from sub-micrometer size magnetic beads in between the applied magnetic field and the MNPs. The preliminary results indicate that the combined effect of magnetic field and evaporation rate might help the control of nanoparticle behavior on surfaces and interfaces in constructing higher structures.