Functional polypeptides:

Having the same backbone as proteins, synthetic peptides make interesting biomaterials. Polypeptides are often synthesized in one step using controlled ring-opening polymerization (ROP) of N-carboxyanhydride monomers (NCA), in contrast to discrete oligopeptide synthesis (SPPS). Among them we are particularly interested with polyprolines.

The cyclic side chain of polyproline differs from other homopolypeptides in that it lacks an N-H amide group. As a result, poly(L-proline) can assume either right-handed or left-handed helical conformations with all peptide bonds forming trans or cis bonds. Yet, polyproline has not been explored well, perhaps due to its low solubility. To improve thermal stability, cell penetration, bioconjugation, and other properties, non-natural residues can be attached as homo-polypeptide side chains. In a recent study, we demonstrated that polyprolines' solubility, secondary structure, and thermal stability can be tuned through their side chain functionalizations.

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Organic Ferroelectric materials using supramolecular strategy:

An external electric field reverses the spontaneous polarization of ferroelectric materials. Additionally, they can function as pyroelectrics and piezoelectrics. There are numerous applications for these materials in the electronics industry, including ferroelectric memory (FeRAM), capacitance-tunable capacitors, piezoelectric actuators, resonators, mechanical/thermal energy harvesters, pyroelectric infrared sensors, and thermal imaging. Such materials are often inorganic, such as BaTiO3, Pb(ZrxTi1-x)O3 (PZT), and LiNbO3. Toxic and rare metals, however, pose a serious threat to the environment. Comparatively to inorganic materials, organic counterparts offer several desirable traits, such as lightness, flexibility, low cost, solution-processability, and nontoxicity.

Toward designing organic ferroelectric materials, we developed a supramolecular approach in which multiple noncovalent interactions work synergistically toward dipole alignment.

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Development of organocatalyst for the ROP of Lactides:

PLA is a biocompatible, biodegradable, and biorenewable polymer produced from corn starch and sugarcane. These qualities make PLA ideal for pharmaceuticals, microelectronics, and packaging applications. In polylactides, lactide repeating units can be arranged differently (tacticity) because lactic acid is chiral. Among different microstructures, isotactic polylactides offer superior thermal and mechanical properties. In both industry and academia, it is of great interest to develop a catalyst that can control the microstructure of polylactides using a racemic monomer. It has been shown in the past that many metal alkoxides and organometallic catalysts can promote stereoregular PLA synthesis. Despite the spectacular successes of organometallic catalysts, toxic and metal contamination caused by them paved the way for the development of organocatalysts. We were interested in developing new organocatalysts that facilitate the synthesis of stereoregular polylactides.

 

 

 

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Folding of Periodically-grafted amphiphilic Polyamides:

Through-bond and through-space electron transport are two ways in which electrons can be transported in a material. Conjugated oligomers/polymers and their ability to transport electrons through bonds have been extensively used in optoelectronics applications for decades. However, in biology, long-range electron/charge transport largely relies on the spatial organization of π-surfaces such that strong electronic coupling between the frontier orbitals (through-space) of adjacent molecules takes place during molecular recognition in DNA, excitonic coupling in photosynthesis, etc. Electron transport through space requires higher-order structures such as proteins or DNA double helixes. It is for this reason that we strive to design new materials for electron transport through space.

A mimicking approach demonstrated aromatic polyamides with intramolecular H-bonding and π-stacking interactions generated an intra-chain β-sheet structure. In addition to tuning polyamide secondary structures, we are also exploring the possibility electron transport across non-bonded aromatic surfaces.

 

 

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Architectural effect on the self-assembly of amphiphilic linear and hyperbranched polyesters:

Self-assembly of amphiphilic molecules offers an easy and efficient way to generate 3D morphologies such as a sphere, rod, cylinder, and vesicles. This approach relies on the self-segregation of lipophilic segments in water via hydrophobic effects. Random copolymers, despite their poor reconfiguration ability, can also achieve similar self-assembled structures with tuneable morphology. As a result, random copolymers are appealing because they are easy to access, have a low synthetic cost, and can be scaled up easily. Furthermore, its poor primary structure often results in a dynamic self-assembled structure, which facilitates morphological transitions and stimuli responses.

To understand the architectural effects on self-assembly, we prepared a series of hyperbranched polyesters and their linear analogues. In particular, we are trying to understand how architecture affects (i) self-assembling 3D structure; (ii) compactness of the core; (ii) effectiveness as a drug delivery vehicle.

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