Diffusion of dextran within poly(methacrylic acid) hydrogels

We describe an investigation of fluorescence correlation spectroscopy into the diffusion of fluorescein‐tagged dextran (FDEX) in a poly(methacrylic acid) (PMAA) hydrogel. The temperature dependence of FDEX diffusion is shown to follow Zimm behavior in pure water, and the decrease in the diffusion coefficient when in the PMAA hydrogel has been modeled. The addition of acid and alkali (HCl and NaOH, respectively) not only control the swelling and collapse of the hydrogel but also reveal a strong pH dependence of the dextran diffusion coefficient, which shows a (nonmonatonic) increase with pH. The addition of NaCl and CaCl₂ salts similarly showed evidence of network swelling, most notably at low salt concentration, but also that the diffusion coefficient within the gel at these low concentrations is larger than that in the equivalent solution without the hydrogel, indicating that the combination of hydrogel and salt works to increase the diffusion coefficient above that in pure water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Study of factors influencing the fabrication of Co‐porphyrin porous coordination polymer via metal–organic gel intermediate

In this work, 5, 10, 15, 20‐Tetra‐(4‐aminophenyl) porphyrin (TAPP) was used as gelator to prepare metal‐porphyrin porous coordination polymer (PCP) via solvothermal process, Soxhlet extraction and supercritical CO₂ extraction. Firstly, the metal‐porphyrin organic gel (MOG) was prepared as intermediate with solvothermal method. The generation of gels is associated with many factors. When four acetates [Co(Ac)₂?4H₂O, Zn(Ac)₂?2H₂O, Mn(Ac)₂?4H₂O and Ni(Ac)₂?7H₂O] reacted with TAPP, only the reaction between Co(Ac)₂?4H₂O and TAPP could form desired metal‐porphyrin organic gel. The influences of solvent, concentration and anions were investigated in the gelation process. Secondly, the residual reactants and solvent molecules in MOG were removed through Soxhlet extraction and supercritical CO₂ extraction. The Co‐PCP is an amorphous material with a hierarchical porous structure can effectively catalyze the oxidation of ethylbenzene and also exhibits a strong adsorptive capacity for the strong‐polar solvent molecules.     

Meticulous Doxorubicin Release from pH-Responsive Nanoparticles Entrapped within an Injectable Thermoresponsive Depot

The dual stimuli-controlled release of doxorubicin from gel-embedded nanoparticles is reported. Non-cytotoxic polymer nanoparticles are formed from poly(ethylene glycol)-b-poly(benzyl glutamate) that, uniquely, contain a central ester link. This connection renders the nanoparticles pH-responsive, enabling extensive doxorubicin release in acidic solutions (pH 6.5), but not in solutions of physiological pH (pH 7.4). Doxorubicin-loaded nanoparticles were found to be stable for at least 31 days and lethal against the three breast cancer cell lines tested. Furthermore, doxorubicin-loaded nanoparticles could be incorporated within a thermoresponsive poly(2-hydroxypropyl methacrylate) gel depot, which forms immediately upon injection of poly(2-hydroxypropyl methacrylate) in dimethyl sulfoxide solution into aqueous solution. The combination of the poly(2-hydroxypropyl methacrylate) gel and poly(ethylene glycol)-b-poly(benzyl glutamate) nanoparticles yields an injectable doxorubicin delivery system that facilities near-complete drug release when maintained at elevated temperatures (37 °C) in acidic solution (pH 6.5). In contrast, negligible payload release occurs when the material is stored at room temperature in non-acidic solution (pH 7.4). The system has great potential as a vehicle for the prolonged, site-specific release of chemotherapeutics.     

Preparation and properties of ionic‐liquid‐containing poly(ethylene glycol)‐based networked polymer films having lithium salt structures

Ionic‐liquid‐containing polymer films were prepared by swelling poly(ethylene glycol)‐based networked polymers having lithium salt structures with an ionic liquid, 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMImFSI), or with an EMImFSI solution of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). Their fundamental physical properties were investigated. The networked polymer films having lithium salt structures were prepared by curing a mixture of poly(ethylene glycol) diglycidyl ether and lithium 3‐glycidyloxypropanesulfonate or lithium 3‐(glycidyloxypropanesulfonyl)(trifluoromethanesulfonyl)imide with poly(ethylene glycol) bis(3‐aminopropyl) terminated. The obtained ionic‐liquid‐containing films were flexible and self‐standing. They showed high ionic conductivity at room temperature, 1.16–2.09 S/m for samples without LiTFSI and 0.29–0.43 S/m for those with 10 wt % LiTFSI. Their thermal decomposition temperature was above 220 °C, and melting temperature of the ionic liquid incorporated in the film was around ?16 °C. They exhibited high safety due to good nonflammability of the ionic liquid. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Highly Fluorescent Non‐Conventional Boron‐Difluoride‐Based π Organogel with Gelation‐Assisted Piezochromism

Triphenylamine‐functionalized boron 2‐(2′‐pyridyl)imidazole complex bearing no alkyl chains or H‐bond unit was found to be able to gelate a series of solvents, and the balanced intermolecular π–π interactions play an important role in its supramolecular self‐assembly. The gelator molecule is piezochromic, and the dried gel responded to pressure more sensitively than regular crystalline powder.     

Emergent Catalytic Behavior of Self‐Assembled Low Molecular Weight Peptide‐Based Aggregates and Hydrogels

We report a series of short peptides possessing the sequence (FE)_n or (EF)_n and bearing l ‐proline at their N‐terminus that self‐assemble into high aspect ratio aggregates and hydrogels. We show that these aggregates are able to catalyze the aldol reaction, whereas non‐aggregated analogues are catalytically inactive. We have undertaken an analysis of the results, considering the accessibility of catalytic sites, pK_a value shifts, and the presence of hydrophobic pockets. We conclude that the presence of hydrophobic regions is indeed relevant for substrate solubilization, but that the active site accessibility is the key factor for the observed differences in reaction rates. The results presented here provide an example of the emergence of a new chemical property caused by self‐assembly, and support the relevant role played by self‐assembled peptides in prebiotic scenarios. In this sense, the reported systems can be seen as primitive aldolase I mimics, and have been successfully tested for the synthesis of simple carbohydrate precursors.     

Construction of Alkynylplatinum(II) Bzimpy‐Functionalized Metallacycles and Their Hierarchical Self‐Assembly Behavior in Solution Promoted by Pt⋅⋅⋅Pt and π–π Interactions

A family of new alkynylplatinum(II) 2,6‐bis(benzimidazol‐2′‐yl)pyridine (bzimpy)‐functionalized supramolecular metallacycles with different shapes and sizes have been successfully prepared by coordination‐driven self‐assembly. The obtained metallacycles showed switchable emission and a strong tendency to form intermolecular Pt???Pt and π–π stacking interactions in solution that were not displayed by their individual precursors. Further investigation revealed that the existence of the metallacyclic scaffold at the core could facilitate the formation of intermolecular Pt???Pt and π–π stacking interactions of peripheral alkynylplatinum(II) bzimpy units. Moreover, the shapes and sizes of the metallacyclic scaffold have a significant influence on the hierarchical self‐assembly behavior. Among the three metallacycles, hexagonal metallacycle A , with a relatively small size, could spontaneously self‐assemble into an aromatic guest stimuli‐responsive metallogel at room temperature without a heating–cooling process.     

Dynamic covalent polymers

This Highlight presents an overview of the rapidly growing field of dynamic covalent polymers. This class of polymers combines intrinsic reversibility with the robustness of covalent bonds, thus enabling formation of mechanically stable, polymer‐based materials that are responsive to external stimuli. It will be discussed how the inherent dynamic nature of the dynamic covalent bonds on the molecular level can be translated to the macroscopic level of the polymer, giving access to a range of applications, such as stimuli‐responsive or self‐healing materials. A primary distinction will be made based on the type of dynamic covalent bond employed, while a secondary distinction will be based on the consideration whether the dynamic covalent bond is used in the main chain of the polymer or whether it is used to allow side chain modification of the polymer. Emphasis will be on the chemistry of the dynamic covalent bonds present in the polymer, in particular in relation to how the specific (dynamic) features of the bond impart functionality to the polymer material, and to the conditions under which this dynamic behavior is manifested. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3551–3577.     

Triterpenoid‐Based Self‐Healing Supramolecular Polymer Hydrogels Formed by Host–Guest Interactions

Pentacyclic triterpenoids, a class of naturally bioactive products having multiple functional groups, unique chiral centers, rigid skeletons, and good biocompatibility, are ideal building blocks for fabricating versatile supramolecular structures. In this research, the natural pentacyclic triterpenoid glycyrrhetinic acid (GA) was used as a guest molecule for β‐cyclodextrin (β‐CD) to form a GA/β‐CD (1:1) inclusion complex. By means of GA and β‐CD pendant groups in N,N′‐dimethylacrylamide copolymers, a supramolecular polymer hydrogel can be physically cross‐linked by host–guest interactions between GA and β‐CD moieties. Moreover, self‐healing of this hydrogel was observed and confirmed by step‐strain rheological measurements, whereby the maximum storage modulus occurred at a [GA]/[β‐CD] molar ratio of 1:1. Additionally, these polymers displayed outstanding biocompatibility. The introduction of a natural pentacyclic triterpenoid into a hydrogel system not only provides a biocompatible guest–host complementary GA/β‐CD pair, but also makes this hydrogel an attractive candidate for tissue engineering.