Enhancing Gelation of Doubly Thermosensitive Hydrophilic ABC Linear Triblock Copolymers in Water by Thermoresponsive Hairy Nanoparticles

A method is reported for enhancing the gelation of doubly thermosensitive hydrophilic linear ABC triblock copolymers in water using thermoresponsive polymer brush-grafted nanoparticles (hairy NPs). A linear ABC triblock copolymer (ABC-Q) composed of a hydrophilic, charged middle block, and two thermosensitive outer blocks with different LCSTs, LCST_A of the lower LCST A block and LCST_C of the higher LCST C block, and two batches of hairy NPs with distinct thermoresponsive properties were prepared. When the temperature was raised from 0 °C to above the LCST_A but below the LCST_C, ABC-Q self-assembled into micelles in water with the lower LCST A block forming the core; further heating to above the LCST_C triggered the collapse of the C block, producing a two-compartment 3-D network micellar hydrogel when the polymer concentration was sufficiently high. Rheological studies showed that adding thermoresponsive hairy NPs with a LCST similar to the LCST_C of ABC-Q led to a significant increase in dynamic storage modulus (<i>G</i>′). For 6 wt % aqueous solutions of ABC-Q, the maximum value of <i>G</i>′ (<i>G</i>′_max) increased with increasing amount of hairy NPs; a 45% increase in <i>G</i>′_max was observed at the NP-to-polymer mass ratio of 60:100. It is believed that hairy NPs acted as “seeds” to adsorb the collapsed C block of ABC-Q, promoting the formation of bridging chains among micellar cores and NPs and thus enhancing the gelation. In contrast, no benefit was observed when adding hairy NPs with a LCST much higher than LCST_C; the <i>G</i>′_max exhibited little change with increasing NP-to-polymer mass ratio. Our explanations for the rheological observations were supported by fluorescence resonance energy transfer studies

Thermoresponsive Oligo(ethylene glycol) Functionalized Poly‑l‑cysteine

A series of new functional amino acids were prepared in high yield via thiol–ene Michael addition between l-cysteine and monomethoxy oligo­(ethylene glycol) (OEG) functionalized methacrylates (OEG_<i>x</i>MA) and acrylate (OEG_<i>x</i>A). These OEGylated cysteine derivatives were converted into polymerizable <i>N</i>-carboxyanhydride (NCA) monomers using triphosgene. Subsequent ring-opening polymerization (ROP) of these NCA monomers gave a series of OEGylated poly-l-cysteine (poly-EG_<i>x</i>MA-C or poly-EG_<i>x</i>A-C) homopolypeptides. Depending on the length of OEG side chains, poly-EG_<i>x</i>MA-C and poly-EG_<i>x</i>A-C polypeptides displayed different solubility and secondary structure in water. More importantly, the obtained polypeptides can display reversible thermoresponsive properties in water when the <i>x</i> value is between 3 and 5. The synthetic strategy represents a highly efficient method to prepare nonionic functional polypeptides with tunable thermoresponsive properties

Oxidation-Responsive OEGylated Poly‑l‑cysteine and Solution Properties Studies

The oxidation-responsive behaviors of OEGylated poly-l-cysteine homopolypeptides, that is, poly­(l-EG_<i>x</i>MA-C)_<i>n</i>, were investigated. These poly-l-cysteine derivatives adopted mixed conformation in water, in which the β-sheet accounted for a significant proportion. Upon oxidation, the thioethers in polypeptide side chains were converted to polar sulfone groups, which triggered the secondary structure transition from β-sheet preferred conformation to random coil. Accordingly, the increase of side-chain polarity together with conformation changes increased samples’ water solubility and cloud point temperature. Using mPEG₄₅-NH₂ as macroinitiator, we synthesized PEG₄₅-<i>b</i>-poly­(l-EG₂MA-C)₂₂ diblock copolymer via ring-opening polymerization (ROP) of l-EG₂MA-C <i>N</i>-carboxyanhydride (NCA). The PEG₄₅-<i>b</i>-poly­(l-EG₂MA-C)₂₂ was able to self-assemble into spherical micelles in aqueous solution, and the micelles could undergo an oxidation-triggered disassembly due to the oxidation-responsive thioethers. Such a new class of oxidation-responsive polypeptides might provide a promising platform to construct inflammation targeting drug delivery systems

Oxidation-Responsive OEGylated Poly‑l‑cysteine and Solution Properties Studies

The oxidation-responsive behaviors of OEGylated poly-l-cysteine homopolypeptides, that is, poly­(l-EG_<i>x</i>MA-C)_<i>n</i>, were investigated. These poly-l-cysteine derivatives adopted mixed conformation in water, in which the β-sheet accounted for a significant proportion. Upon oxidation, the thioethers in polypeptide side chains were converted to polar sulfone groups, which triggered the secondary structure transition from β-sheet preferred conformation to random coil. Accordingly, the increase of side-chain polarity together with conformation changes increased samples’ water solubility and cloud point temperature. Using mPEG₄₅-NH₂ as macroinitiator, we synthesized PEG₄₅-<i>b</i>-poly­(l-EG₂MA-C)₂₂ diblock copolymer via ring-opening polymerization (ROP) of l-EG₂MA-C <i>N</i>-carboxyanhydride (NCA). The PEG₄₅-<i>b</i>-poly­(l-EG₂MA-C)₂₂ was able to self-assemble into spherical micelles in aqueous solution, and the micelles could undergo an oxidation-triggered disassembly due to the oxidation-responsive thioethers. Such a new class of oxidation-responsive polypeptides might provide a promising platform to construct inflammation targeting drug delivery systems

Peptide Hydrogels Assembled from Nonionic Alkyl-polypeptide Amphiphiles Prepared by Ring-Opening Polymerization

Three alkyl-polypeptide (AP) amphiphiles were prepared using ring-opening polymerization of α-amino acid <i>N</i>-carboxyanhydride. The polypeptide segment was composed of diethylene-glycol-monomethyl-ether-functionalized poly-l-glutamate (poly-l-EG₂Glu). These AP amphiphiles can spontaneously self-assemble into transparent hydrogels in water. These hydrogels showed shear thinning properties, and their strength can be modulated by hydrophobic alkyl tails. CryoTEM and AFM characterizations suggested that these hydrogels were formed by nanoribbons arising from intermolecular interactions between nonionic poly-l-EG₂Glu segments

Janus Silica Hollow Spheres Prepared via Interfacial Biosilicification

A poly­(ethylene glycol)<i>-<i>b</i>-</i>poly­(_L-lysine)<i>-<i>b</i>-</i>poly­(styrene) (PEG-PLL-PS) triblock copolymer, which contains a cationic PLL block as the middle block, is synthesized via a combination of ring-opening polymerization (ROP) and atom-transfer radical polymerization (ATRP). The PEG-PLL-PS (ELS) triblock is employed as a macromolecular surfactant to form a stable oil-in-water (O/W) emulsion, which is subsequently used as the template to prepare Janus silica hollow spheres (JHS) via a one-pot biosilicification reaction. For the emulsion template, the middle PLL block assembles at the O/W interface and directs the biomimetic silica synthesis in the presence of phosphate buffer and silicic acid precursors. This biosilicification process takes place only in the intermediate layer between water and the organic interior phase, leading to the formation of silica JHSs with hydrophobic PS chains tethered to the inner surface and PEG attached to the outer surface. The three-layer JHSs, namely, PEG/silica-polylysine/PS composites, were verified by electron microscopy. Upon further breaking these JHSs into species, polymer-grafted Janus silica nanoplates (JPLs) can be obtained. Our studies provide an efficient one-step method for preparing hybrid silica Janus structures within minutes

Tailorable Aqueous Dispersion of Single-Walled Carbon Nanotubes Using Tetrachloroperylene-Based Bolaamphiphiles via Noncovalent Modification

The enhanced dispersing capability of these bolaamphiphiles can be attributed to the large aromatic perylene core. The aqueous dispersion efficiency of single-walled carbon nanotubes (SWCNTs) is investigated by UV–vis absorption, fluorescence emission and Raman spectra, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. It is found that the tetrachloroperylene backbone moieties could interact with SWCNT via synergistic π–π and hydrophobic interactions, and the dispersing properties are closely related to the hydrophilic part of bolaamphiles. This study not only demonstrates tetrachloroperylene derivatives are able to stabilize SWCNTs, but also provides the possibility to understand the structure–property relationship between SWCNTs and tetrachloroperylene-based surfactants

Fluorescence Regulation of Copper Nanoclusters via DNA Template Manipulation toward Design of a High Signal-to-Noise Ratio Biosensor

Because of bioaccumulation of food chain and disability of biodegradation, concentration of toxic mercury ions (Hg²⁺) in the environment dramatically varies from picomolar to micromolar, indicating the importance of well-performed Hg²⁺ analytical methods. Herein, reticular DNA is constructed by introducing thymine (T)–Hg²⁺–T nodes in poly­(T) DNA, and copper nanoclusters (CuNCs) with aggregate morphology are prepared using this reticular DNA as a template. Intriguingly, the prepared CuNCs exhibit enhanced fluorescence. Meanwhile, the reticular DNA reveals evident resistance to enzyme digestion, further clarifying the fluorescence enhancement of CuNCs. Relying on the dual function of DNA manipulation, a high signal-to-noise ratio biosensor is designed. This analytical approach can quantify Hg²⁺ in a very wide range (50 pM to 500 μM) with an ultralow detection limit (16 pM). Besides, depending on the specific interaction between Hg²⁺ and reduced l-glutathione (GSH), this biosensor is able to evaluate the inhibition of GSH toward Hg²⁺. In addition, pollution of Hg²⁺ in three lakes is tested using this method, and the obtained results are in accord with those from inductively coupled plasma mass spectrometry. In general, this work provides an alternative way to regulate the properties of DNA-templated nanomaterials and indicates the applicability of this way by fabricating an advanced biosensor

UCST-Type Thermoresponsive Polymers in Synthetic Lubricating Oil Polyalphaolefin (PAO)

This Article reports a family of UCST-type thermoresponsive polymers, poly­(alkyl methacrylate)­s with an appropriate alkyl pendant length in an industrially important nonvolatile organic liquid polyalphaolefin (PAO). The cloud point (CP) can be readily tuned over a wide temperature range by changing the alkyl pendant length; at a concentration of 1 wt % and similar polymer molecular weights, the CP varies linearly with the (average) number of carbon atoms in the alkyl pendant. PAO solutions of ABA triblock copolymers, composed of a PAO-philic middle block and thermoresponsive outer blocks with appropriate block lengths, undergo thermoreversible sol–gel transitions at sufficiently high concentrations. The discovery of thermoresponsive polymers in PAO makes it possible to explore new applications by utilizing PAO’s unique characteristics such as thermal stability, nonvolatility, superior lubrication properties, and so on. Two examples are presented: thermoresponsive physical gels for control of optical transmittance and injectable gel lubricants

Thermally Sensitive Self-Assembly of Glucose-Functionalized Tetrachloro-Perylene Bisimides: From Twisted Ribbons to Microplates

Chiral supramolecular structures are becoming increasingly attractive for their specific molecular arrangements, exceptional properties, and promising applications in chiral sensing and separation. However, constructing responsive chiral supramolecular structures remains a great challenge. Here, glucose-functionalized tetrachloro-perylene bisimides (GTPBIs) with thermally sensitive self-assembly behaviors are designed and synthesized. In a methanol/water mixture, GTPBIs self-assembled into twisted ribbons and microplates at 4 and 25 °C, respectively. Furthermore, the ribbon structure was metastable and could transform into microplates when the temperature was increased from 4 to 25 °C. Transmission electron microscopy (TEM) was used to track the evolution of morphology and study the assembly mechanisms of correponding nanostructures at different time intervals. The supramolecular structures were characterized with various techniques, including circular dichroism, TEM, scanning electron microscopy, atomic force microscopy, ultraviolet–visible absorption, and fluorescence spectra. This study provides insight into controlling molecular parameters and assembly conditions to construct chiral supramolecular structures