Jingyi Rao

Enzyme Sensitive Synthetic Polymer Micelles Based on the Azobenzene Motif

In this study, we investigate the potential of an artificial structural motif, azobenzene, in the preparation of enzyme sensitive polymeric nanostructures. For this purpose, an azobenzene linkage is established at the copolymer junction of an amphiphilic diblock copolymer. This polymer assembles into a micellar structure in water. Treatment with the enzyme azoreductase, in the presence of coenzyme NADPH, results in the cleavage of the azo-based copolymer junction and disruption of the micellar assembly. These results suggest that azobenezene is a useful non-natural structural motif for the preparation of enzyme responsive polymer nanoparticles. Due to the presence of azoreductase in the human intestine, such nanomaterials are anticipated to find applicability in the arena of colon-specific delivery systems.

Large‐Area Alignment of Tungsten Oxide Nanowires over Flat and Patterned Substrates for Room‐Temperature Gas Sensing

Alignment of nanowires over a large area of flat and patterned substrates is a prerequisite to use their collective properties in devices such as gas sensors. In this work, uniform single-crystalline ultrathin W18 O49 nanowires with diameters less than 2 nm and aspect ratios larger than 100 have been synthesized, and, despite their flexibility, assembled into thin films with high orientational order over a macroscopic area by the Langmuir-Blodgett technique. Alignment of the tungsten oxide nanowires was also possible on top of sensor substrates equipped with electrodes. Such sensor devices were found to exhibit outstanding sensitivity to H2 at room temperature.

Enzyme-Triggered Cascade Reactions and Assembly of Abiotic Block Copolymers into Micellar Nanostructures

Catalytic action of an enzyme is shown to transform a non-assembling block copolymer, composed of a completely non-natural repeat unit structure, into a self-assembling polymer building block. To achieve this, poly(styrene) is combined with an enzyme-sensitive methacrylate-based polymer segment carrying carefully designed azobenzene side chains. Once exposed to the enzyme azoreductase, in the presence of coenzyme NADPH, the azobenzene linkages undergo a bond scission reaction. This triggers a spontaneous 1,6-self-elimination cascade process and transforms the initially hydrophobic methacrylate polymer segment into a hydrophilic hydroxyethyl methacrylate structure. This change in chemical polarity of one of the polymer blocks confers an amphiphilic character to the diblock copolymer and permits it to self-assemble into a micellar nanostructure in water.

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.

Synthesis and self-assembly of dynamic covalent block copolymers

A diblock copolymer is designed to have incompatible blocks, unsymmetrical block lengths, and a reversible linkage. This copolymer self-assembles into nanostructured cylindrical morphology in thin films. Removal of the nanosized cylinders by breaking the reversible linkage then affords nanoporous membranes featuring a chemically reactive functionality in the pores.

Enzymatic ‘charging’ of synthetic polymers

Actuated by an enzyme, a purely synthetic and chemically neutral polymer chain transforms into a chemically charged cationic structure. This biologically triggered structural change enables the polymer chain to recognize a negatively charged biomolecule (RNA) through electrostatic interactions in aqueous environment. The supramolecular recognition event ultimately leads to the assembly of oppositely charged, artificial and natural polymer chains, into the polyion complex-based nanoparticles.

Using reversibility of the dynamic covalent bond to create porosity in highly ordered polymer thin films under mild conditions and nano-pore functionalization in the gas phase

Phase-separating polystyrene (PS) and polyethylene glycol (PEG) polymers are connected through a hydrazone-based reversible covalent bond to afford a PS–CHN–PEG diblock copolymer. This novel dynamic covalent copolymer assembles into a nano-structured cylindrical morphology in thin films. Reversal of the hydrazone linkage and removal of PEG–hydrazide under mild conditions afford a nano-porous membrane featuring a chemically reactive functionality in the nano-pores. Availability of these reactive groups for further thin film functionalization is demonstrated by re-establishing the imine bond with a small molecule amine. This modification strategy does not require any coupling reagent, solvent, or high temperature. Therefore, a gas-phase technique is sufficient for film functionalization purposes.

Self-assembly of an interacting binary blend of diblock copolymers in thin films

Self-assembly of a binary mixture of poly(styrene)336-block-poly(4-vinyl pyridine)25 (PS336-b-P4VP25) and poly(ethylene glycol)113-block-poly(4-hydroxy styrene)25 (PEG113-b-P4HS25) is shown to give rise to a cylindrical morphology in thin films through pyridine/phenol-based hetero-complementary hydrogen bonding interactions between the P4VP and P4HS copolymer segments. Removal of the cylindrical phase (PEG-b-P4HS) allowed access to porous materials having a pore surface decorated with P4VP polymer blocks. These segments could be transformed into cationic polyelectrolytes through quaternization of the pyridine nitrogen atom. The resulting positively charged nanopore surface could recognize negatively charged gold nanoparticles through electrostatic interactions. This work, therefore, outlines the utility of the supramolecular AB/CD type of block copolymer towards preparation of ordered porous thin films carrying a chemically defined channel surface with a large number of reactive sites.

Introducing a reversible linkage to block copolymer self-assembly: towards controlling nanopore chemistry.

Block copolymer self-assembly[1] has shown remarkable potential towards preparation of highly ordered nanoporous membranes.[2] In this approach, covalently connected yet chemically dissimilar polymer blocks phase separate into ordered nanostructures with length scales on the order of ten to a hundred nanometres. Selective removal of the minor phase from these nanostructured polymer thin films affords nanoporous membranes. Such membranes have found use in surface patterning, templated nanomaterial synthesis, separation, filtration, catalysis, sensing, and drug delivery applications. The far-ranging applicability and performance of these porous materials will further enhance if the surface of the nanopore can carry chemically reactive functionalities that can be altered under ambient conditions. So far, strategies for covalent chemical functionalization of the nanopores in highly ordered porous thin films remains undeveloped. To this end, we designed and synthesized a diblock copolymer featuring incompatible blocks, unsymmetrical block lengths, and a reversible copolymer linkage (Fig. 1 and Scheme 1).[3] Self-assembly of this copolymer results in nanostructured thin films exhibiting highly ordered cylindrical morphology (Fig. 2). Removal of the nanosized cylinders by reversing the dynamic covalent – oxy-imine – linkage then affords ordered nanoporous membranes that contain chemically reactive oxy-amine functionalities. Covalent and non-covalent membrane-functionalization were carried out both by reestablishing imine bonds with fluorescent organic molecules and via forming metal complexes. Received: May 7, 2012