Optically monitoring the microenvironment of a hydrophobic cargo in amphiphilic nanogels: influence of network composition on loading and release

Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, and catalysts. Loading content and release kinetics of these compounds are controlled by type and number of hydrophobic groups in the amphiphilic copolymer network. Thus, understanding the interactions between cargo and colloidal carrier is mandatory for a tailor-made and cargo-specific ANG design. To systematically explore the influence of the network composition on these interactions, we prepared a set of ANGs of different amphiphilicity and loaded these ANGs with varying concentrations of the solvatochromic dye Nile Red (NR). Here, NR acts as a hydrophobic model cargo to optically probe the polarity of its microenvironment. Analysis of the NR emission spectra as well as measurements of the fluorescence quantum yields and decay kinetics revealed a decrease in the polarity of the NR microenvironment with increasing hydrophobicity of the hydrophobic groups in the ANG network and dye-dye interactions at higher loading concentrations. At low NR concentrations, the hydrophobic cargo NR is encapsulated in the hydrophobic domains. Increasing NR concentrations resulted in probe molecules located in a more hydrophilic environment, i.e., at the nanodomain border, and favored dye-dye interactions and NR aggregation. These results correlate well with release experiments, indicating first NR release from more hydrophilic network locations. Overall, our findings demonstrate the importance to understand carrier-drug interactions for efficient loading and controlled release profiles in amphiphilic nanogels.

From sandwich complexes to dendrimers: journey toward applications to sensing, molecular electronics, materials science, and biomedicine

This review links various areas of inorganic chemistry around the themes developed by our research group during the last four decades. It is firstly based on the electronic structure of iron sandwich complexes, showing how the metal electron count dictates their reactivities, with various applications (via C-H activation, C-C bond formation) as reducing and oxidizing agents, redox and electrocatalysts and precursors of dendrimers and catalyst templates through bursting reactions. Various electron-transfer processes and consequences are explored, including the influence of the redox state on the acidity of robust ligands and the possibility to iterate in situ C-H activation and C-C bond formation to build arene-cored dendrimers. Examples of how these dendrimers are functionalized are illustrated using the cross olefin metathesis reactions, with application to the synthesis of soft nanomaterials and biomaterials. Mixed and average valence complexes give rise to remarkable subsequent organometallic reactions, including the salt influence on these reactions. The stereo-electronic aspect of these mixed valencies is pointed out in star-shaped multi-ferrocenes with a frustration effect and other multi-organoiron systems, with the perspective of understanding electron-transfer processes among dendrimer redox sites involving electrostatic effects and application to redox sensing and polymer metallocene batteries. Dendritic redox sensing is summarized for biologically relevant anions such as ATP^2- with supramolecular exoreceptor interactions at the dendrimer periphery in parallel with the seminal work on metallocene-derived endoreceptors by Beer's group. This aspect includes the design of the first metallodendrimers that have applications in both redox sensing and micellar catalysis with nanoparticles. These properties provide the opportunity to summarize the biomedical (mostly anticancer) applications of ferrocenes, dendrimers and dendritic ferrocenes in biomedicine (in particular the contribution from our group, but not only). Finally, the use of dendrimers as templates for catalysis is illustrated with numerous reactions including C-C bond formation, click reactions and H₂ production reactions.

Novel multi-stimuli responsive functionalized PEG-based co-delivery nanovehicles toward sustainable treatments of multidrug resistant tumor

The efficacy of ongoing anticancer treatment is often compromised by some barriers, such as low drug content, nonspecific release of drug delivery system, and multidrug resistance (MDR) effect of tumors. Herein, in the research a novel functionalized PEG-based polymer cystine-(polyethylene glycol)2-b-(poly(2-methacryloyloxyethyl ferrocenecarboxylate)2) (Cys-(PEG45)2-b-(PMAOEFC)2) with multi-stimuli sensitive mechanism was constructed, in which doxorubicin (DOX) was chemical bonded through Schiff base structure to provide acid labile DOX prodrug (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2. Afterwards, paclitaxel (PTX) and its diselenide bond linked PTX dimer were encapsulated into the prodrug through physical loading, to achieve pH and triple redox responsive (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2@PTX and (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2@PTX dimer with ultrahigh drugs content. The obtained nanovehicles could self-assemble into globular micelles with good stability based on fluorescence spectra and TEM observation. Moreover, there was a remarkable "reassembly-disassembly" behavior caused by phase transition of micelles under the mimic cancerous physiological environment. DOX and PTX could be on-demand released in acid and redox stress mode, respectively. Meanwhile, in vivo anticancer studies revealed the significant tumor inhibition of nanoformulas. This work offered facile strategies to fabricate drug nanaovehicles with tunable drug content and types, it has a profound significance in overcoming MDR effect, which provided more options for sustainable cancer treatment according to the desired drug dosage and the stage of tumor growth.

Multifunctional Self-Healing Dual Network Hydrogels Constructed via Host-Guest Interaction and Dynamic Covalent Bond as Wearable Strain Sensors for Monitoring Human and Organ Motions

Hydrogel-based flexible strain sensors have shown great potential in body movement tracking, early disease diagnosis, noninvasive treatment, electronic skins, and soft robotics. The good self-healing, biocompatible, sensitive and stretchable properties are the focus of hydrogel-based flexible strain sensors. Dual network (DN) hydrogels are hopeful to fabricate self-healing hydrogels with the above properties. Here, multifunctional DN hydrogels are prepared via a combination of host-guest interaction of β-cyclodextrin and ferrocene with dynamic borate ester bonds of poly(vinyl alcohol) and borax. Carbon nanotubes are used to endow the DN hydrogels with good conductivity. The obtained DN composite hydrogels possess good biocompatibility, stretchability (436%), fracture strength (41.0 KPa), self-healing property (healing efficiency of 95%), and high tensile strain sensitivity (gauge factor of 5.9). The DN composite hydrogels are used as flexible strain sensors to detect different human motions. After cutting, the healed hydrogels also can monitor human motions and have good stability. In addition, the hydrogel sensors may track the respiratory movement of a pig lung in vitro. This work exhibits new ideas and approaches to develop multifunctional self-healing hydrogels for constructing flexible strain sensors.

Novel carboxylated ferrocene polymer nanocapsule with high reactive oxygen species sensitivity and on-demand drug release for effective cancer therapy

Multidrug resistance (MDR) is a major clinical issue leading to substantial reductions in the intracellular levels of anticancer drugs. To overcome MDR, stimulus-responsive polymeric nanotherapeutics that facilitate drug release and cellular uptake at target sites have emerged as promising tools for safe and effective cancer treatment. Among these nanotherapeutics, reactive oxygen species (ROS)-responsive nanocapsules are ideal carriers, as abnormally increased ROS levels can drive controlled drug release at target sites. In this study, we developed novel, high ROS-responsive carboxylated ferrocene nanocapsules (CFNCs) using solvents of different polarities for effective multidrug-resistant cancer therapy. The CFNCs were prepared via the self-assembly of an amphiphilic carboxylated ferrocene polymer composed of a hydrophilic COOH segment and a hydrophobic ferrocenylmethyl methacrylate segment possessing a ROS-responsive group. The size and ROS sensitivity of self-assembled CFNCs could be controlled by using solvents of different polarities during the simple nanoprecipitation process. The CFNCs showed a high loading content (approximately 30 wt%) and on-demand release of paclitaxel under both normal and tumor-mimicking conditions, and exhibited synergistic anticancer effects in multidrug-resistant colorectal cancer cells (HCT-15). Our findings suggest that CFNCs can be applied as carriers for effective cancer therapy.

Chain-end functionalization of living helical polyisocyanides through a Pd(ii)-mediated Sonogashira coupling reaction

Various functional helical polymers were constructed through chain-end functionalization of living helical polyisocyanides through a Pd(ii)-mediated Sonogashira coupling reaction.

Multiple applications of polymers containing electron-reservoir metal-sandwich complexes

Ferrocene-containing polymers have been investigated for more than six decades, and more recently modern synthetic methods have allowed the fabrication of precise polymers that contain a variety of transition-metal complexes. Trends are now oriented towards applications, such as optics, energy conversion and storage, electrochemistry, magnetics, electric conductors and biomedicine. Metal-sandwich complexes such as those of ferrocene type and other related complexes that present redox-robust groups in polymers, i.e. that are isolable in both their oxidized and reduced forms, are of particular interest, because it is possible to address them using electronic or photonic redox stimuli for application. Our research groups have called such complexes Electron-Reservoirs and introduced them in the main chain or in the side chains of well-defined polymers. For instance, polymers with ferrocene in the main chain or in the side chain are oxidized to stable polycationic polyelectrolytes only if ferrocene is part of a biferrocene unit, because biferrocene oxidation leads to the biferrocenium cation that is stabilized by the mixed valency. Then a group of several redox-robust iron sandwich complexes were fabricated and incorporated in precise polymers including multi-block copolymers whose controlled synthesis and block incorporation was achieved for instance using ring-opening-metathesis polymerization. Applications of this family of Electron-Reservoir-containing polymers includes electrochemically induced derivatization of electrodes by decorating them with these polymers, molecular recognition and redox sensing, electrochromics with multiple colours, generation of gold and silver nanoparticles of various size by reduction of gold(iii) and silver(i) precursors and their use for nanocatalysis towards depollution and biomedicine.

Synthesis, conjugating capacity and biocompatibility evaluation of a novel amphiphilic polynorbornene

Polynorbornenes, prepared by the ‘living’ and ‘controlled’ ring-opening metathesis polymerization (ROMP) method, have emerged as a stimuli-sensitive new class of polymer carriers. Herein, we reported a novel amphiphilic diblock polynorbornene, PNCHO-b-PNTEG, containing active benzaldehyde units, which exhibited good conjugating capacity to amino-containing molecules (e.g., doxorubicin (DOX)) via the pH-sensitive Schiff base linkage. The copolymer and its conjugate with DOX, DOX-PNCHO-b-PNTEG, were adequately analyzed by various techniques including ¹H NMR, ¹³C NMR, gel permeation chromatography, etc. Especially, the formed conjugate of DOX-PNCHO-b-PNTEG could self-assemble into near-spherical micelles with the diameter of 81 ± 10 nm, and exhibit acid-triggered DOX release behavior, and the release rate could be adjusted by changing the environmental pH value. The excellent biological safety of PNCHO-b-PNTEG was further demonstrated by the results from both in vitro toxicity evaluation to murine fibroblast cells (L-929 cells) and in vivo evaluation of acute developmental toxicity and cell death in zebrafish embryos. Hence, the present polynorbornene-based PNCHO-b-PNTEG possesses great potential application as a biocompatible polymeric carrier and could be employed to fabricate various pH-sensitive conjugates.

The supramolecular redox functions of metallomacromolecules

Abstract

Metallomacromolecules are frequently encountered in redox proteins including metal-tanned hide collagen and play crucial roles involving supramolecular properties in biological electron-transfer processes. They are also currently found in non-natural families, such as: metallopolymers, metallodendrimers and metallodendronic polymers. This mini-review discusses the supramolecular redox functions of such nanomaterials developed in our research group. Electron-transfer processes are first examined in mono-, bis- and hexa-nuclear ferrocenes and other electron-reservoir organoiron systems showing the influence of supramolecular and reorganization aspects on their mechanism. Then applications of electron-transfer processes using these same organoiron redox systems in metallomacromolecules and their supramolecular functions are discussed including redox recognition/sensing, catalysis templates, electrocatalysis, redox catalysis, molecular machines, electrochromes, drug delivery device and nanobatteries.

Graphical Abstract

Ferrocene-containing hybrids as potential anticancer agents: Current developments, mechanisms of action and structure-activity relationships

Cancer is one of the most fatal threatens to human health throughout the world. The major challenges in the control and eradication of cancers are the continuous emergency of drug-resistant cancer and the low specificity of anticancer agents, creating an urgent need to develop novel anticancer agents. Organometallic compounds especially ferrocene derivatives possess remarkable structural and mechanistic diversity, inherent stability towards air, heat and light, low toxicity, low cost, reversible redox, ligand exchange, and catalytic properties, making them promising drug candidates for cancer therapy. Ferrocifen, a ferrocene-phenol hybrid, has demonstrated promising anticancer properties on drug-resistant cancers. Currently, Ferrocifen is in pre-clinical trial against cancers. Obviously, ferrocene moiety is a useful template for the development of novel anticancer agents. This review will provide an overview of ferrocene-containing hybrids with potential application in the treatment of cancers covering articles published between 2010 and 2020. The mechanisms of action, the critical aspects of design and structure-activity relationships are also discussed.

Reactive oxygen species (ROS)-responsive ferrocene-polymer-based nanoparticles for controlled release of drugs

Ferrocene-containing nanoparticles show reversible redox activity that could trigger drug release mediated by reactive oxygen species (ROS).

A dual drug-based hyperbranched polymer with methotrexate and chlorambucil moieties for synergistic cancer chemotherapy

Dual drug-based hyperbranched polymer micelles simultaneously containing methotrexate and chlorambucil were constructed for synergistic cancer chemotherapy.

Ferrocene-based hyperbranched poly(phenyltriazolylcarboxylate)s: synthesis by phenylpropiolate-azide polycycloaddition and use as precursors to nanostructured magnetoceramics

Ferrocene-based hb-PPTCs with redox activity are readily prepared by the catalyst-free phenylpropiolate-azide polycycloaddition. They could be used as precursors to produce nanostructured magnetoceramics upon pyrolysis.