Multicomponent Polymerizations Provide Sustainable Sulfur (Selenium)-Containing Polyesters

ConspectusWith the rapid development of the polymer industry, the contradiction between synthetic polymers and the sustainable development of human society is becoming more and more prominent. The advancement of degradable plastics greatly contributes to the sustainability of our society. Synthetic polymers containing precisely placed in-chain ester groups are expected to be degradable in a controlled manner. Their potential as environmentally benign plastics is significant. For this purpose, there is a clear need for their improved performance. Incorporating sulfur functional groups into polyesters can improve the diverse crucial properties of their counterparts. However, there is a lack of related high-efficiency polymer synthesis methods.In response to this issue, we designed a series of multicomponent polymerization methods for the synthesis of a library of degradable polyesters with tunable structure and properties. This Account summarizes our recent efforts to discover the polymerization approach. The method uses readily available monomers including diols, diamines, H2O, diacrylates, carbonyl sulfide (COS), cyclic thioanhydrides, CO, and selenium powder. The polymerization is usually carried out under mild conditions: at 60 to 90 °C, for 2 to 12 h, using organobases as the catalysts or catalyst-free. This approach achieves the simultaneous incorporation of in-chain ester and sulfur/selenium functional groups including thiocarbonate, thioether, thioester, thiourethane, and selenoether.The method has a wide monomer scope and yields diverse polymers with tunable structures. The obtained polyesters possess weight-average molecular weights of up to 175.4 kDa. Most of these polyesters are thermally stable, exhibiting decomposition temperatures of >200 °C. Due to the diversity of structure, these polymers demonstrate extensively tunable performance covering crystalline plastics, thermoplastic elastomers, and amorphous plastics. These polymers exhibit a wide range of glass-transition temperatures of -60 to 72 °C and a wide range of melting temperatures of 43 to 274 °C. Notably, the polymers containing long alkyl chains (number of carbon atoms ≥ 9) exhibit polyethylene-like crystallinity and mechanical properties. The in-chain thiourethane or amide groups enable enhanced thermal and mechanical properties due to the incorporation of inter/intramolecular hydrogen bonding. These polymers are also easy to degrade via alkali hydrolysis, alcohol hydrolysis, enzymatic hydrolysis, oxidation, etc. The degradation products often have well-defined structure and value-added properties and can even be directly used for repolymerization to achieve a closed-loop chemical cycle. Overall, the multicomponent polymerization presented in this Account furnishes a facile and versatile synthesis of sustainable polymers with tunable structure and properties.

ROS-responsive nanocarrier for oral delivery of monascin and enhanced alleviation of oxidative stress

Oxidative stress, caused by excessive production of reactive oxygen species (ROS), plays a crucial role in the occurrence and development of various diseases. Monascin can scavenge ROS and alleviate oxidative stress but with a low fermentation rate and bioavailability. Here, we optimized the fermentation process to increase the production of monascin (508.6 U/mL), and then systematically characterized its structure via HPLC, HPLC-MS, 1H NMR, and 13C NMR. Additionally, we innovatively modified carboxymethylcellulose sodium with selenium (CMC-Se) to encapsulate monascin (monascin@CMC-Se), which can sensitively respond to ROS and release monascin to effectively scavenge excessive ROS. Besides, the monascin@CMC-Se can significantly increase the bioaccessibility of monascin and alleviate cellular oxidative stress by enhancing its cellular uptake rate. Collectively, our work provides proof-of-principle evidence that the CMC-Se can precise delivery of monascin to an oxidatively stressed environment with high resistance to gastric fluids, laying a foundation to overcome inflammation-related diseases in the colon.

Potential application and prospects of ROS-sensitive biomaterials in cancer therapy: a immune microenvironment triggered nanomaterial

Reactive Oxygen Species (ROS) is the collective term used for the extremely reactive molecules that are important mediators in physiological processes as well as the development of various disease conditions. Normal cells maintain a delicate equilibrium, known as redox homeostasis, between antioxidants and ROS levels. Any imbalance in the redox homeostasis of the body results in oxidative stress which can result in inflammation, necrosis, apoptosis, cell death, and eventually a disease state. Enhanced ROS levels are a key feature in cancer cells that is being explored for developing reactive oxygen species-sensitive biomaterials. The distinct variation in redox potential between normal cells and tumour cells is one of the major physiological differences between them, that has enabled the development of ROS-sensitive nanomaterials for cancer therapy. ROS-sensitive nanomaterials are sensitive to the physiological variations in the cells, like high levels of hydrogen peroxide and glutathione in the cancer cells. ROS-responsive nanomaterials have the unique property of modulating microenvironmental redox conditions in cancer cells. ROS-sensitive material can work either by scavenging the ROS or by simulating the cellular antioxidants, leading to cancer cell cytotoxicity. These ROS-sensitive nanomaterials can simulate the human body's natural antioxidants like, superoxide dismutase and peroxidase. Thus, ROS-sensitive nanomaterials hold promise as a potential platform for the treatment of cancer. The present review will cover the importance of ROS in cancer, the different types of ROS-sensitive nanomaterials available and their therapeutic application in cancer therapy.

Phenacylselenoesters allow facile selenium transfer and hydrogen selenide generation

Hydrogen selenide (H2Se) is a precursor to several selenium-containing biomolecules and is emerging as an important redox-active species in biology, with yet to be completely characterized roles. Tools that reliably generate H2Se are key to achieving a better understanding of selenium biology. Here, we report the design, synthesis and evaluation of phenacylselenoesters as sources of H2Se. These compounds are prepared in two steps from commercial compounds, some are crystalline solids, and all are stable during storage. In the presence of esterase and a thiol in pH 7.4 buffer, these compounds produce H2Se, with half-lives of 5-20 min. We developed a colorimetric assay for the detection of gaseous H2Se by trapping it as zinc selenide (ZnSe), which is then converted to lead selenide (PbSe), which serves as a convenient visual indicator for this gas. The major organic products that are formed in nearly quantitative yields are relatively benign ketones and carboxylic acids. We provide evidence for these donors producing a thioselenide, a key intermediate in biological selenium metabolism. Finally, we compared sulfur and selenium transfer, both critical processes in cells. Phenacylthiol is relatively stable to cleavage by a thiol, and requires a sulfurtransferase enzyme to produce a persulfide and H2S. By contrast, the selenium analogue reacted with a thiol in the absence of this enzyme to produce H2Se. This result underscores the greater lability of the C-Se bond as compared with a C-S bond, and may have implications in biological selenium transfer. Together, phenacylselenoesters are easy to prepare, stable and generate H2Se under mild and biocompatible conditions. We anticipate that these will be valuable additions to the growing selenium redox toolbox.

ROS-sensitive PD-L1 siRNA cationic selenide nanogels for self-inhibition of autophagy and prevention of immune escape

In the field of cancer therapy, inhibiting autophagy has emerged as a promising strategy. However, pharmacological disruption of autophagy can lead to the upregulation of programmed death-ligand 1 (PD-L1), enabling tumor immune evasion. To address this issue, we developed innovative ROS-responsive cationic poly(ethylene imine) (PEI) nanogels using selenol chemistry-mediated multicomponent reaction (MCR) technology. This procedure involved simple mixing of low-molecular-weight PEI (LMW PEI), γ-selenobutylacetone (γ-SBL), and poly(ethylene glycol) methacrylate (PEGMA). Through high-throughput screening, we constructed a library of AxSeyOz nanogels and identified the optimized A1.8Se3O0.5/siPD-L1 nanogels, which exhibited a size of approximately 200 nm, excellent colloidal stability, and the most effective PD-L1 silencing efficacy. These nanogels demonstrated enhanced uptake by tumor cells, excellent oxidative degradation ability, and inhibited autophagy by alkalinizing lysosomes. The A1.8Se3O0.5/siPD-L1 nanogels significantly downregulated PD-L1 expression and increased the expression of major histocompatibility complex class I (MHC-I), resulting in robust proliferation of specific CD8+ T cells and a decrease in MC38 tumor growth. As a result, the A1.8Se3O0.5/siPD-L1 nanogels inhibited tumor growth through self-inhibition of autophagy, upregulation of MHC-I, and downregulation of PD-L1. Designed with dynamic diselenide bonds, the A1.8Se3O0.5/siPD-L1 nanogels showed synergistic antitumor efficacy through self-inhibition of autophagy and prevention of immune escape.

Fast and Selective Main-Chain Scission of Vinyl Polymers Using the Domino Reaction in the Alternating Sequence for Transesterification

This communication reports on vinyl polymers capable of selective and fast main-chain scission (MCS). The trick is the domino reaction in an alternating sequence of methyl 2-(trimethylsiloxymethyl)acrylate and 5,6-benzo-2-methylene-1,3-dioxepane, a cyclic ketene acetal for radical ring-opening polymerization. Removal of the trimethylsilyl group using Bu4N+·F- readily led to MCS via irreversible transesterification of the ester backbone, affording a five-membered lactone fragment. The molar mass decreased drastically within 5 min, and no side reactions were observed. Control experiments suggest that the formation of a five-membered ring via a domino reaction is critical for fast and selective MCS. The terpolymers with methyl methacrylate and styrene also exhibited a large decrease in molar mass within 5 min. In addition, MCS was also observed for the heterogeneous reaction system in acidic aqueous media; treatment of the binary copolymer in a 50 wt % acetic acid solution resulted in a significant decrease in molar mass after 30 min. These results suggest efficient construction of degradable sites using a binary monomer system corresponding to the pendant trigger and ester backbone. Because this molecular design using a binary monomer system provides selective and fast MCS for terpolymers containing other vinyl monomers, it can provide various degradable vinyl polymers.

ROS-responsive hydrogels: from design and additive manufacturing to biomedical applications

Hydrogels with intricate 3D networks and high hydrophilicity have qualities resembling those of biological tissues, making them ideal candidates for use as smart biomedical materials. Reactive oxygen species (ROS) responsive hydrogels are an innovative class of smart hydrogels, and are cross-linked by ROS-responsive modules through covalent interactions, coordination interactions, or supramolecular interactions. Due to the introduction of ROS response modules, this class of hydrogels exhibits a sensitive response to the oxidative stress microenvironment existing in organisms. Simultaneously, due to the modularity of the ROS-responsive structure, ROS-responsive hydrogels can be manufactured on a large scale through additive manufacturing. This review will delve into the design, fabrication, and applications of ROS-responsive hydrogels. The main goal is to clarify the chemical principles that govern the response mechanism of these hydrogels, further providing new perspectives and methods for designing responsive hydrogel materials.

Polyurethane with β-Selenocarbonyl Structure Enabling the Combination of Plastic Degradation and Waste Upcycling

Degradable polymers offer a promising solution to mitigate global plastic pollution, but the degraded products often suffer from diminished value. Upcycling is a more sustainable approach to upgrade polymer waste into value-added products. Herein, we report a β-selenocarbonyl-containing polyurethane (SePU), which can be directly degraded under mild conditions into valuable selenium fertilizers for selenium-rich vegetable cultivation globally, enabling both plastic degradation and waste upcycling. Under oxidation condition, this polymer can be easily and selectively degraded via selenoxide elimination reaction from mixed plastic waste. The degraded product can serve as effective selenium fertilizers to increase selenium content in radish and pak choi. The SePU exhibits excellent mechanical properties. Additionally, we observed the formation of spherulites-like selenium particles within the materials during degradation for the first time. Our research offers a successful application of selenoxide elimination reaction in the field of plastic degradation for the first time, endowing plastics with both degradability and high reusable value. This strategy provides a promising solution to reduce pollution and improve economy and sustainability of plastics.

Main-chain Macromolecular Hydrazone Photoswitches

Hydrazones-consisting of a dynamic imine bond and an acidic NH proton-have recently emerged as versatile photoswitches underpinned by their ability to form thermally bistable isomers, (Z) and (E), respectively. Herein, we introduce two photoresponsive homopolymers containing structurally different hydrazones as main-chain repeating units, synthesized via head-to-tail Acyclic Diene METathesis (ADMET) polymerization. Their key difference lies in the hydrazone design, specifically the location of the aliphatic arm connecting the rotor of the hydrazone photoswitch to the aliphatic polymer backbone. Critically, we demonstrate that their main photoresponsive property, i.e., their hydrodynamic volume, changes in opposite directions upon photoisomerization (λ=410 nm) in dilute solution. Further, the polymers-independent of the design of the individual hydrazone monomer-feature a photoswitchable glass transition temperature (Tg ) by close to 10 °C. The herein established design strategy allows to photochemically manipulate macromolecular properties by simple structural changes.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Smart Responsive Microneedles for Controlled Drug Delivery

As an emerging technology, microneedles offer advantages such as painless administration, good biocompatibility, and ease of self-administration, so as to effectively treat various diseases, such as diabetes, wound repair, tumor treatment and so on. How to regulate the release behavior of loaded drugs in polymer microneedles is the core element of transdermal drug delivery. As an emerging on-demand drug-delivery technology, intelligent responsive microneedles can achieve local accurate release of drugs according to external stimuli or internal physiological environment changes. This review focuses on the research efforts in smart responsive polymer microneedles at home and abroad in recent years. It summarizes the response mechanisms based on various stimuli and their respective application scenarios. Utilizing innovative, responsive microneedle systems offers a convenient and precise targeted drug delivery method, holding significant research implications in transdermal drug administration. Safety and efficacy will remain the key areas of continuous efforts for research scholars in the future.

Thiol-triggered deconstruction of bifunctional silyl ether terpolymers via an SNAr-triggered cascade

While Si-containing polymers can often be deconstructed using chemical triggers such as fluoride, acids, and bases, they are resistant to cleavage by mild reagents such as biological nucleophiles, thus limiting their end-of-life options and potential environmental degradability. Here, using ring-opening metathesis polymerization, we synthesize terpolymers of (1) a "functional" monomer (e.g., a polyethylene glycol macromonomer or dicyclopentadiene); (2) a monomer containing an electrophilic pentafluorophenyl (PFP) substituent; and (3) a cleavable monomer based on a bifunctional silyl ether . Exposing these polymers to thiols under basic conditions triggers a cascade of nucleophilic aromatic substitution (SNAr) at the PFP groups, which liberates fluoride ions, followed by cleavage of the backbone Si-O bonds, inducing polymer backbone deconstruction. This method is shown to be effective for deconstruction of polyethylene glycol (PEG) based graft terpolymers in organic or aqueous conditions as well as polydicyclopentadiene (pDCPD) thermosets, significantly expanding upon the versatility of bifunctional silyl ether based functional polymers.

Characterization Techniques of Polymer Aging: From Beginning to End

Polymers have been widely applied in various fields in the daily routines and the manufacturing. Despite the awareness of the aggressive and inevitable aging for the polymers, it still remains a challenge to choose an appropriate characterization strategy for evaluating the aging behaviors. The difficulties lie in the fact that the polymer features from the different aging stages require different characterization methods. In this review, we present an overview of the characterization strategies preferable for the initial, accelerated, and late stages during polymer aging. The optimum strategies have been discussed to characterize the generation of radicals, variation of functional groups, substantial chain scission, formation of low-molecular products, and deterioration in the polymers' macro-performances. In view of the advantages and the limitations of these characterization techniques, their utilization in a strategic approach is considered. In addition, we highlight the structure-property relationship for the aged polymers and provide available guidance for lifetime prediction. This review could allow the readers to be knowledgeable of the features for the polymers in the different aging stages and provide access to choose the optimum characterization techniques. We believe that this review will attract the communities dedicated to materials science and chemistry.

Thioanisole ester based logic gate cascade to control ROS-triggered micellar degradation

Thioanisole ester polymer side chains hydrolyze exclusively upon thioether oxidation, showing logic gate response. ROS-induced ester hydrolysis on the hydrophobic domain leads to nanocarrier disassembly with potential for targeted drug release.

Selenium-containing nanoparticles synergistically enhance Pemetrexed&NK cell-based chemoimmunotherapy

NK cell-based immunotherapy and pemetrexed (Pem)-based chemotherapy have broad application prospects in cancer treatment. However, the over-expressed NK cell inhibitory receptor on the surface of cancer cells and the low cell internalization efficiency of Pem greatly limit their clinical application. Herein, we construct a series of selenium-containing nanoparticles to synergistically enhance Pem-based chemotherapy and NK cell-based immunotherapy. The nanoparticles could deliver Pem to tumor sites and strengthen the chemotherapy efficiency of Pem by seleninic acid, which is produced by the oxidation of β-seleno ester. Moreover, seleninic acid can block the expression of inhibitory receptors against NK cells, thereby activating the immunocompetence of NK cells. The in vitro and in vivo experiments reveal the potential chemo-enhancing and immune-activating mechanism of seleninic acid, emphasizing the promising prospects of this strategy in effective chemoimmunotherapy.

Room-Temperature Metal-Free Multicomponent Polymerizations of Elemental Selenium toward Stable Alicyclic Poly(oxaselenolane)s with High Refractive Index

Selenium-containing polymers are a group of fascinating functional polymers with unique structures, properties, and applications, which have been developed recently but only with limited examples. The challenges of developing selenium-containing polymers with structural and functional diversity include the lack of economic and safe monomers, lack of efficient and convenient synthetic approaches, and poor stability of selenium-involving covalent bonds. In this work, room-temperature metal-free multicomponent polymerizations (MCPs) of elemental selenium, diisocyanides, and dipropargyl alcohols were developed, and polymers with a selenium-containing aliphatic heterocycle, 1,3-oxaselenolane, were synthesized through these MCPs directly from elemental selenium. The alicyclic poly(oxaselenolane)s enjoyed high yields (up to 93%), high molecular weights (up to 15 600 g/mol), high thermal and chemical stability, good solubility and processability. With the structural design of the poly(oxaselenolane)s and their high selenium contents of up to 33.7 wt %, the refractive indices of their spin-coated thin films could reach 1.8026 at 633 nm and maintain 1.7770 at 1700 nm. It is anticipated that these efficient, convenient, mild, and economic multicomponent polymerizations of elemental selenium can promote the selenium-related polymer chemistry and accelerate the exploration of diversified selenium-containing functional polymer materials.

ROS-Responsive Selenium-Containing Carriers for Coencapsulation of Photosensitizer and Hypoxia-Activated Prodrug and Their Cellular Behaviors

The integration of hypoxia-activated chemotherapy with photodynamic therapy (PDT) has newly become a potent strategy for tumor treatment. Herein, a reactive oxygen species (ROS)-responsive drug carriers (PS@AQ4N/mPEG-b-PSe NPs) are fabricated based on the amphiphilic selenium-containing methoxy poly(ethylene glycol)-polycarbonate (mPEG-b-PSe), the hydrophobic photosensitizer (PS), and hypoxia-activated prodrug Banoxantrone (AQ4N). The obtained nanoparticles are spherical with an average diameter of 100 nm as characterized by transmission electron microscope (TEM) and dynamic laser scattering (DLS) respectively. The encapsulation efficiency of the PS and AQ4N reaches 92.83% and 51.04% at different conditions, respectively, by UV-vis spectrophotometer. It is found that the drug release is accelerated due to the good ROS responsiveness of mPEG-b-PSe and the cumulative release of AQ4N is up to 89% within 30 h. The cell test demonstrates that the nanoparticles dissociate when triggered by the ROS stimuli in the cancer cells, thus the PS is exposed to more oxygen and the ROS generation efficiency is enhanced accordingly. The consumption of oxygen during PDT leads to the increased tumor hypoxia, and subsequently activates AQ4N into cytotoxic counterpart to inhibit tumor growth. Therefore, the synergistic therapeutic efficacy demonstrates this drug delivery has great potential for antitumor therapy.

Recent developments in selenium-containing polymeric micelles: prospective stimuli, drug-release behaviors, and intrinsic anticancer activity

Selenium is capable of forming a dynamic covalent bond with itself and other elements and can undergo metathesis and regeneration reactions under optimum conditions. Its dynamic nature endows selenium-containing polymers with striking sensitivity towards some environmental alterations. In the past decade, several selenium-containing polymers were synthesized and used for the preparation of oxidation-, reduction-, and radiation-responsive nanocarriers. Recently, thioredoxin reductase, sonication, and osmotic pressure triggered the cleavage of Se-Se bonds and swelling or disassembly of nanostructures. Moreover, some selenium-containing nanocarriers form oxidation products such as seleninic acids and acrylates with inherent anticancer activities. Thus, selenium-containing polymers hold promise for the fabrication of ultrasensitive and multifunctional nanocarriers of radiotherapeutic, chemotherapeutic, and immunotherapeutic significance. Herein, we discuss the most recent developments in selenium-containing polymeric micelles in light of their architecture, multiple stimuli-responsive properties, emerging immunomodulatory activities, and future perspectives in the delivery and controlled release of anticancer agents.

Reactive oxygen species-sensitive polymeric nanocarriers for synergistic cancer therapy

Reactive oxygen species (ROS)-responsive nanocarriers have aroused widespread interest in recent years. On the one hand, a high ROS level has been detected in many types of tumor cells. On the other hand, ROS generation is also induced during photodynamic, sonodynamic, or chemodynamic therapy. In addition, multiple types of polymers are sensitive to ROS. Therefore, numerous ROS-responsive polymeric nanocarriers with unique ROS-responsive characteristics have been developed. This review discusses ROS-sensitive polymeric nanocarriers to improve drug delivery efficacy. In particular, ROS-responsive nanocarriers for synergistic cancer therapy are highlighted. The development of novel ROS-sensitive nanocarriers holds great potential for combining ROS-mediated therapy, such as photodynamic therapy, and other therapies to achieve synergistic anticancer efficacy. STATEMENT OF SIGNIFICANCE: Reactive oxygen species (ROS)-responsive nanocarriers aroused widespread interest in recent years. On the one hand, a high level of ROS has been found in many types of tumor cells. On the other hand, the ROS generation can also be induced during the photodynamic, sonodynamic, or chemodynamic therapy. Besides, multiple types of polymers were sensitive to the ROS. Therefore, numerous ROS-responsive polymeric nanocarriers with unique ROS responsive characteristics have been developed. This review focuses on the ROS-sensitive polymeric nanocarriers to improve drug delivery efficacy for synergistic cancer therapy.

[Reactive oxygen species stimuli-responsive nanocarriers]

纳米载体一般是由天然高分子或人工合成高分子组成的、纳米级范畴的运输系统,具有减少药物毒性、提高药物的靶向性、增加药物有效性等优点。随着生物医学技术的进步,有研究表明,作为氧化代谢产物的活性氧(ROS)在疾病部位常常伴随着过表达的异常现象。基于此,近年来ROS刺激响应纳米载体获得了关注和发展,以不同响应机制的ROS响应基团为基础,发展了一系列的ROS响应纳米载体,实现了疾病部位ROS刺激下的药物特异性可控释放。该文聚焦于近年来常用于纳米载体的ROS响应基团,依据元素划分为两大类:硫族元素类响应基团(硫醚、缩硫酮、硒化物、二硒化物、碲化物)和其他元素类响应基团(芳香硼酸酯、过氧草酸酯、二茂铁);通过不同的设计理念将其引入纳米载体,根据ROS响应纳米载体的不同响应机制(疏水-亲水相变、断裂),探讨了载体各自的ROS响应情况、体外药物释放情况,以及在活体中的应用情况。

Side-Chain Selenium-Grafted Polymers Combining Antiangiogenesis Treatment with Photodynamic Therapy and Chemotherapy

The abnormal tumor vasculature in solid tumors creates hypoxia and leads to compromising the delivery and anticancer efficiency of nanomedicine. Nanomaterials with intrinsic antiangiogenesis ability might normalize tumor vessels and improve the therapeutic effect of O₂-related treatment like PDT. Herein, we designed and prepared ROS-responsive side-chain selenium-grafted polymers, which had potential antiangiogenic activity, as vehicles to load photodynamic therapeutic agent Ce6 and chemotherapeutic drug oridonin. Under NIR irradiation, the C-Se bonds on the side chain of polymers could be cleaved in the presence of ¹O₂ produced by Ce6 and further formed organic selenic acid through selenoxide elimination reaction. The generated seleninic acid could downregulate the expression of vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP-2) to inhibit angiogenesis and further relieve hypoxia. The released oridonin could significantly increase the intracellular ROS concentration. Both could modulate cancer cells' microenvironment to reinforce PDT. Therefore, these nanomedicines could be a good candidate for synergistic treatments of antiangiogenesis treatment, PDT, and chemotherapy.

Thiophene donor for NIR-II fluorescence imaging-guided photothermal/photodynamic/chemo combination therapy

Organic fluorophores/photosensitizers have been widely used in biological imaging and photodynamic and photothermal combination therapy in the first near-infrared (NIR-I) window. However, their applications in the second near-infrared (NIR-II) window are still limited primarily due to low fluorescence quantum yields (QYs). Here, a boron dipyrromethene (BDP) is created as a molecularly engineered thiophene donor unit with high QYs to the redshift. Thiophene insertion initiates substantial redshifts of the absorbance as compared to its counterparts in which iodine is introduced. The fluorescent molecule can be triggered by an NIR laser with a single wavelength, thereby producing emission in the NIR-II windows. Single NIR laser-triggered phototherapeutic nanoparticles (NPs) are developed by encapsulating the BDP and the chemotherapeutic drug docetaxel (DTX) by using a synthetic amphiphilic poly(styrene-co-chloromethyl styrene)-graft-poly(ethylene glycol) functionalized with folic acid (FA). These BDP-T-N-DTX-FA NPs not only show superior solubility and high singlet oxygen QY (Φ_Δ=62%) but also demonstrate single NIR laser-triggered multifunctional characteristics. After intravenous administration of the NPs into 4T1 tumor-bearing mice, the accumulation of the NPs in the tumor showed a high signal-to-background ratio (11.8). Furthermore, 4T1 tumors in mice were almost eradicated by DTX released from the BDP-T-N-DTX-FA NPs under single NIR laser excitation and the combination of photodynamic therapy (PDT) and photothermic therapy (PTT). STATEMENT OF SIGNIFICANCE: The application of organic photosensitizers is still limited primarily due to low fluorescence quantum yields (QYs) in the second near-infrared (NIR-II) window. Here, a boron dipyrromethene (BDP) as a molecularly engineered thiophene donor unit with high QYs to the redshift is created. Phototherapeutic nanoparticles (NPs) are developed by encapsulating the BDP and docetaxel (DTX) using a synthetic amphiphilic poly(styrene-co-chloromethyl styrene)-graft-poly(ethylene glycol) functionalized with folic acid (FA). These BDP-T-N-DTX-FA NPs not only show high singlet oxygen QY (Φ_Δ=62%) but also demonstrate single NIR laser-triggered multifunctional characteristics and a high signal-to-background ratio (11.8). Furthermore, 4T1 tumors in mice were almost eradicated by DTX released from the BDP-T-N-DTX-FA NPs under single NIR laser excitation and the PDT/PTT combination therapy.

Recent Advances in Stimuli-Responsive Commodity Polymers

Known for their adaptability to surroundings, capability of transport control of molecules, or the ability of converting one type of energy to another as a result of external or internal stimuli, responsive polymers play a significant role in advancing scientific discoveries that may lead to an array of diverge applications. This review outlines recent advances in the developments of selected commodity polymers equipped with stimuli-responsiveness to temperature, pH, ionic strength, enzyme or glucose levels, carbon dioxide, water, redox agents, electromagnetic radiation, or electric and magnetic fields. Utilized diverse applications ranging from drug delivery to biosensing, dynamic structural components to color-changing coatings, this review focuses on commodity acrylics, epoxies, esters, carbonates, urethanes, and siloxane-based polymers containing responsive elements built into their architecture. In the context of stimuli-responsive chemistries, current technological advances as well as a critical outline of future opportunities and applications are also tackled.

Recent progress of redox-responsive polymeric nanomaterials for controlled release

This perspective focuses on the development of redox-responsive polymeric nanomaterials for controlled payload release within the last four years.

Oxidative regulation of the mechanical strength of a C-S bond

The mechanical strength of individual polymer chains is believed to underlie a number of performance metrics in bulk materials, including adhesion and fracture toughness. Methods by which the intrinsic molecular strength of the constituents of a given polymeric material might be switched are therefore potentially useful both for applications in which triggered property changes are desirable, and as tests of molecular theories for bulk behaviors. Here we report that the sequential oxidation of sulfide containing polyesters (PE-S) to the corresponding sulfoxide (PE-SO) and then sulfone (PE-SO2) first weakens (sulfoxide), and then enhances (sulfone), the effective mechanical integrity of the polymer backbone; PE-S ∼ PE-SO2 > PE-SO. The relative mechanical strength as a function of oxidation state is revealed through the use of gem-dichlorocyclopropane nonscissile mechanophores as an internal standard, and the observed order agrees well with the reported bond dissociation energies of C–S bonds in each species and with the results of CoGEF modeling.

The mechanical strength of individual polymer chains is believed to underlie a number of performance metrics in bulk materials, including adhesion and fracture toughness.

Carbon dot targeting to nitrogen signaling molecules for inhibiting neuronal death

Ultrasmall carbon dot with targeting ability to nitrogen signaling molecules inhibit neuronal death by regulating the activity of endogenous enzymes.

Fluoxetine scaffold to design tandem molecular antioxidants and green catalysts

Fluoxetine finds application in the treatment of depression and mood disorders. This selective serotonin-reuptake inhibitor (SSRI) also contrasts oxidative stress by direct ROS scavenging, modulation of the endogenous antioxidant defense system, and/or enhancement of the serotonin antioxidant capacity. We synthesised some fluoxetine analogues incorporating a selenium nucleus, thus expanding its antioxidant potential by enabling a hydroperoxides-inactivating, glutathione peroxidase (GPx)-like activity. Radical scavenging and peroxidatic activity were combined in a water-soluble, drug-like, tandem antioxidant molecule. Selenofluoxetine derivatives were reacted with H₂O₂ in water, and the mechanistic details of the reaction were unravelled combining nuclear magnetic resonance (NMR), electrospray ionisation-mass spectrometry (ESI-MS) and quantum chemistry calculations. The observed oxidation–elimination process led to the formation of seleninic acid and cinnamylamine in a trans-selective manner. This mechanism is likely to be extended to other substrates for the preparation of unsaturated cinnamylamines.

We modified fluoxetine by incorporating a selenium nucleus enabling a hydroperoxide-inactivating, glutathione peroxidase (GPx)-like activity and paving the way for its use as green catalyst.

Organoselenium chemistry-based polymer synthesis

Novel synthesis of selenium containing polymers with pre-determined structures and applications thereof.

Enzyme-responsive polymeric micelles with fluorescence fabricated through aggregation-induced copolymer self-assembly for anticancer drug delivery

The TPE moiety with AIE is employed as functional hydrophobic chain to induce copolymer self-assembly and form polymeric micelle that can show enzyme-responsive drug delivery.