Exploring Versatile Sulfhydryl Chemistry in the Chain End of a Synthetic Polylactide

Synthesis of an end-functionalized polylactide by ring-opening polymerization of lactide monomer using a functional initiator containing pyridyl disulfide group is reported. Molecular weight of the polymer determined by GPC matched very well with that determined by end-group analysis using the UV/vis method, suggesting survival of the end-group functionality during polymerization. DTT-induced reduction of the pyridyl disulfide group produced free sulfhydryl group quantitatively which was utilized for versatile chain-end modifications using various thiol-mediated high-yielding chemical transformations including thiol–ene, thiol–maleimide, and thiol–acrylate “click” reactions. This strategy was further extended to link two macromolecules by reaction of sulfhydryl-functionalized polylactide and acrylate-terminated poly­(ethylene oxide) (PEO) which produced a block copolymer with an acid-labile β-thiopropionate linker between the two constituent blocks. This functional group could be cleaved under mild acidic condition to produce the individual parent polymers. Further as-synthesized pyridyl disulfide-terminated polylactide was treated with thiol-functionalized sugar moiety and n-type semiconducting naphthalene diimide (NDI) chromophore which also generated quantitative chain-end functionalization by thiol–disulfide exchange reaction. NDI-functionalized polylactide showed white light emission due to mixed emission from monomeric and excimer-type species. Further atomic force microscopic (AFM) studies revealed NDI-functionalized polymer formed uniform spherical aggregates upon drying of a drop-casted film on silicon surface possibly due to solvent-evaporation-induced defined organization of the polymer chain dictated by strong π-stacking interaction among the NDI chromophores

Photophysical study of P3HT/NDI based hybrid nanoparticles

Electron donor-acceptor based hybrid novel structure remains a frontier area of research to design optoelectronic, photovoltaic, and light harvesting devices. Here, we report the synthesis of interdyad and intradyad nanoparticles by using the electron donating polymer Poly-3-(hexylthiophine)) (P3HT) and the electron accepting molecule 1, 4, 5, 8 naphthalene tetracarboxylic diimide (NDI). The intradyad nanostructures are fabricated in situ by adding donor and acceptor molecules simultaneously whereas interdyad nanoparticles are fabricated by attaching the donor and acceptor nanoparticles electrostatically. The differential scanning calorimetry (DSC) confirms the segmental motion of the polymer chain and the uniform packing in intradyad nanostructures which is absent in the interdyad system. The photoluminescence quenching and the shortening of decay time of the excited state of the donor molecule were observed with increasing the concentration of acceptor molecule in the intradyad system which is attributed to the photoinduced electron transfer from donor to the acceptor molecule. However, in the case of the interdyad system, the change in photoluminescence quenching and the decay time is less significant due to different photophysical processes

Understanding the Role of H‑Bonding in Aqueous Self-Assembly of Two Naphthalene Diimide (NDI)-Conjugated Amphiphiles

Supramolecular architectures with the synchronized combination of various directional noncovalent forces are ubiquitous in biological systems. However, reports of such abiotic synthetic systems involving H-bonding in aqueous medium are rare due to the challenge faced in the formation of such structures by overcoming the competition from the water molecules. In this paper we have studied self-assembly of two structurally related naphthalene-diimide (NDI) conjugated bola-amphiphiles (NDI-1 and NDI-2) in water with an aim to realize the specific role of H-bonding among the hydrazide units present in one of the two building blocks (NDI-2) on the self-assembly. Both chromophores showed vesicular assembly in aqueous solution driven primarily by π-stacking among the NDI chromophores, which could be probed by UV–vis absorption spectra. Contrary to common belief, the lack of an H-bonding group in NDI-1 was found to be a boon in disguise in terms of the stability of the aggregates. Whereas NDI-2 aggregates showed LCST around 65–70 °C owing to the breaking of the H-bonds with increased temperature, the NDI-1 aggregates were found to be structurally intact until 90 °C, which may be attributed to the increased hydrophobicity introduced by the absence of the polar hydrazide group. Further concentration- and solvent-dependent UV–vis studies showed that NDI-1 formed assembled structure at greatly dilute solution and also in a solvent such as THF, confirming greater propensity for its self-assembly. As both bola-amphiphiles contain an electron-deficient NDI chromophore, interaction of their vesicles was studied with an externally added electron-rich pyrene derivative. Surprisingly, NDI-1 did not show any charge-transfer interaction with the donor, whereas NDI-2 could effectively intercalate, leading to a functional membrane with tunable surface functionalities. This was attributed to the additional stability of the intercalated state by H-bonding among the hydrazide units

Protein-Induced Supramolecular Disassembly of Amphiphilic Polypeptide Nanoassemblies

Mimicking noncovalent interaction based processes in nature has been an important goal of supramolecular chemistry. Here, we report on amphiphilic polypeptides that self-assemble to form nanoscale supramolecular assemblies and are programmed to disassemble in response to a specific protein. Benzenesulfonamide and carbonic anhydrase have been chosen as the ligand and protein, respectively, to demonstrate this possibility. Since the amphiphilic nanoassembly sequesters hydrophobic guest molecules, the protein-specific disassembly event provides a protein-sensitive molecular release as well. We envision that the binding induced disassembly and guest release might open up new opportunities for the next generation of supramolecular assemblies for protein-specific delivery and diagnostics

Temporal and Triggered Evolution of Host–Guest Characteristics in Amphiphilic Polymer Assemblies

An amphiphilic polymer with cleavable side chain and main chain functional groups has been designed and synthesized. Specific cleavage of either of its functional groups was found to have an effect on the morphology of the assembly. Degradation of the main chain is shown to cause morphology of the supramolecular assembly to evolve with time from a micelle-like assembly to a vesicular assembly. On the other hand, stimulus-induced cleavage of the side chains causes these nanoassemblies to disassemble. These temporal (main chain) and triggered (side chain) degradation processes have implications in the design of degradable polymers as supramolecular scaffolds for biological applications

Unlocking a Caged Lysosomal Protein from a Polymeric Nanogel with a pH Trigger

A polymeric nanogel has been used to sequester and turn off a lysosomal protein, acid α-glucosidase (GAA). The nanogel contains a β-thiopropionate cross-linker, which endows the nanogel with pH-sensitivity. While encapsulation of the enzyme fully turns off its activity, approximately 75% of the activity is recovered upon reducing the pH to 5.0. The recovered activity is ascribed to pH-induced degradation of the β-thiopropionate cross-linker causing the swelling of the nanogel and ultimately causing the release of the enzyme. We envision that strategies for sequestering protein molecules and releasing them at lysosomal pH might open up new directions for therapeutic treatment of lysosomal storage diseases