The field of single-chain nanoparticles (SCNPs) continues to mature, and an increasing range of reports have emerged that explore the application of these small nanoparticles. A key application for SCNPs is in the field of drug delivery, and recent work suggests that SCNPs can be readily internalized by cells. However, limited attention has been directed to the delivery of small-molecule drugs using SCNPs. Moreover, studies on the physicochemical effects of drug loading on SCNP performance is so far missing, despite the accepted view that such small nanoparticles should be significantly affected by the drug loading content. To address this gap, we prepared a library of SCNPs bearing different amounts of a covalently conjugated therapeutic drug-sulfasalazine (SSZ). We evaluated the impact of the conjugated drug loading on both the synthesis and biological activity of SCNPs on pancreatic cancer cells (AsPC-1). Our results reveal that covalent drug conjugation to the side chains of the SCNP polymer precursor interferes with chain collapse and cross-linking, which demands optimization of reaction conditions to reach high degrees of cross-linking efficiencies. Small-angle neutron scattering and diffusion-ordered spectroscopy nuclear magnetic resonance (DOSY NMR) analyses reveal that SCNPs with a higher drug loading display larger sizes and looser structures, as well as increased hydrophobicity associated with a higher SSZ content. Increased SSZ loading led to reduced cellular uptake when assessed in vitro, whereby SCNP aggregation on the surface of AsPC-1 cells led to reduced toxicity. This work highlights the effects of drug loading on the drug delivery efficiency and biological behavior of SCNPs.

Piezocatalysis offers a means to transduce mechanical energy into chemical potential, harnessing physical force to drive redox reactions. Working in the solid state, we show here that piezoelectric BaTiO3 nanoparticles can transduce mechanical load into a flux of reactive radical species capable of initiating solid state free radical polymerization. Activation of a BaTiO3 powder by ball milling, striking with a hammer, or repeated compressive loading generates highly reactive hydroxyl radicals (⋅OH), which readily initiate radical chain growth and crosslinking of solid acrylamide, acrylate, methacrylate and styrenic monomers. Control experiments indicate a critical role for chemisorbed water on the BaTiO3 nanoparticle surface, which is oxidized to ⋅OH via mechanoredox catalysis. The force-induced production of radicals by compressing dry piezoelectric materials represents a promising new route to harness mechanical energy for solid state radical synthesis.

Polydopamine (PDA) is a synthetic model for melanin and has a wide range of opto-electronic properties that underpin its utility in applied and biological settings, from broadband light absorbance to possessing stable free radical species. Here, we show that PDA free radicals are photo-responsive under visible light irradiation, enabling PDA to serve as a photo-redox catalyst. Steady-state and transient electron spin resonance spectroscopy reveals a reversible amplification in semiquinone radical population within PDA under visible light. This photo-response modifies the redox potential of PDA and supports sensitisation of exogenous species via photoinduced electron transfer (PET). We demonstrate the utility of this discovery by employing PDA nanoparticles to photosensitise a common diaryliodonium photoinitiator and initiate free-radical polymerisation (FRP) of vinylic monomers. In situ 1 H nuclear magnetic resonance spectroscopy reveals an interplay between PDA-driven photosensitising and radical quenching during FRP under blue, green, and red light. This work provides crucial insights into the photoactive free radical properties of melanin-like materials and reveals a promising new application for polydopamine as a photosensitiser.

The escalating level of atmospheric carbon dioxide (CO2) due to the combustion of fossil fuels has been identified as a major contributor to climate change. CO2 capture using membrane-based gas separation provides a promising route to offset anthropogenic emissions. Thin film composite (TFC) membranes offer the capability to handle large gas flux demands and represent one of the most energy-efficient, industrially viable candidates for CO2 capture. In this review, we provide an overview of trends in materials science of TFC membranes for CO2 capture from flue gas. We explore the range of synthetic approaches and diverse materials (polymers, inorganics, and carbon materials) used in TFC assemblies, and critically examine the structural and chemical properties of prospective membrane materials that can help to meet the challenges of industrial CO2 capture. A comparison of the CO2/N2 separation performance and current technical limitations of the latest TFC membranes is also provided. We conclude by sharing outstanding challenges and opportunities for future research directions in the field.

Modifying surfaces using free radical polymerization (FRP) offers a means to incorporate the diverse physicochemical properties of vinyl polymers onto new materials. Here, we harness the universal surface attachment of polydopamine (PDA) to "prime" a range of different surfaces for free radical polymer attachment, including glass, cotton, paper, sponge, and stainless steel. We show that the intrinsic free radical species present in PDA can serve as an anchor point for subsequent attachment of propagating vinyl polymer macroradicals through radical-radical coupling. Leveraging a straightforward, twofold soak-wash protocol, FRP over the PDA-functionalized surfaces results in covalent polymer attachment on both porous and nonporous substrates, imparting new properties to the functionalized materials, including enhanced hydrophobicity, fluorescence, or temperature responsiveness. Our strategy is then extended to covalently incorporate PDA nanoparticles into organo-/hydrogels via radical cross-linking, yielding tunable PDA-polymer composite networks. The propensity of PDA free radicals to quench FRP is studied using in situ 1H nuclear magnetic resonance and electron paramagnetic resonance spectroscopy, revealing a surface area-dependent macroradical scavenging mechanism that underpins PDA-polymer conjugation. By combining the arbitrary surface attachment of PDA with the broad physicochemical properties of vinyl polymers, our strategy provides a straightforward route for imparting unlimited new functionality to practically any surface.

Online, high-throughput molecular weight analysis of polymerizations is rare, with most studies relying on tedious sampling techniques and batchwise postanalysis. The ability to track both monomer conversion and molecular weight evolution in real time could underpin precision polymer development and facilitate study of rapid polymerization reactions. Here, we use a single time-resolved diffusion nuclear magnetic resonance (NMR) experiment to simultaneously study the kinetics and molecular weight evolution during a photopolymerization, with in situ irradiation inside the NMR instrument. As a model system, we used a photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The data allow diffusion coefficients and intensities to be calculated every 14 s from which the polymer size and monomer conversion can be extracted. Key to this approach is (1) the use of shuffled gradient amplitudes in the diffusion NMR experiment to access reactions of any rate, (2) the addition of a relaxation agent to increase achievable time resolution and, (3) a sliding correction that accounts for viscosity changes during polymerization. Diffusion NMR offers a uniquely simple, translatable handle for online monitoring of polymerization reactions.

Self-assembling transesterification catalyst inspired by the catalytic triad.

Inspired by the chemical structure of chymotrypsin, we report an artificial catalytic triad with high catalytic efficiency for the transesterification reaction of vinyl trifluoroacetate and methanol. Rate accelerations of (kcat/kunc)...

At the heart of an enzyme's structure is the active catalytic site, which, together with the surrounding amino-acid residues, tunes the substrate properties in the electrostatic microenvironment. Taking inspiration from nature's catalytic triad, consisting of a hydroxyl group of a serine residue, an imidazole group of a histidine residue, and a carboxyl group of an aspartic acid, a polymer scaffolded enzyme mimic is incorporated with artificial catalytic triad units. It is demonstrated that controlling the local environment of the artificial triad affects catalytic activity. Compared to a water soluble artificial catalytic triad, enhanced esterolytic activity of p-nitrophenyl benzoate was observed for the polymeric catalyst possibly due to the hydrophobic microenvironment formed by the tertiary structure of the polymer backbone. The different environments were supported by molecular dynamics simulations. It is further demonstrated that the cross-linked catalytic triad functional polystyrene could be used as a reusable solid support catalyst for esterolysis.

Star polymers are a class of branched polymers containing three or more arms that are attached by a central core. Reversible addition–fragmentation chain transfer (RAFT) polymerization is widely used for the synthesis of star polymers because it offers exceptional control of polymer molecular weights and dispersities and is compatible with a wide range of monomers. This chapter will focus on the synthetic approaches used to form star polymers, the latest synthetic developments, as well as an overview of the applications of star polymers.

Radical polymerization is one of the most widely used methods for the synthesis of polymeric materials for biomedical applications, such as drug delivery, 3D cell culture, and regenerative medicine. Among radical polymerization reactions, thiol-ene click chemistry has shown excellent orthogonality in diverse reaction conditions. However, our preliminary investigations revealed that it fails in cell culture environment. Herein, we investigate the mechanisms by which cell culture media interfere with radical photoreactions. Three different models including free radical linear photopolymerization (N,N-dimethylacrylamide photopolymerization), free radical photohydrogelation (poly(ethylene glycol) diacrylate photohydrogelation), and thiolene photohydrogelation (4-arm poly(ethylene glycol)-norbornene thiolene photohydrogelation) were investigated. We showed that common cell culture media ingredients can interfere with radical polymerization by two different pathways; namely, radical chain transfer and radical scavenging effects. Thiol-ene photoclick hydrogelation was seriously affected by cell culture media especially under the alkaline conditions of many of them, due to the impact of deprotonation of the thiol reactant. We intend these findings to serve as a reference guide to researchers employing free radical-based molecular synthesis in cell culture settings. The nonbenign impact of media components, pH, and concentration should provide a cue for future studies that aim to prepare well-defined polymeric materials in the presence of cell culture media.

Thin film composite (TFC) membranes have attracted increasing interest to meet the demands of industrial gas separation. However, the development of high performance TFC membranes within their current configuration faces two key challenges: (i) the thickness-dependent gas permeability of polymeric materials (mainly polydimethylsiloxane (PDMS)) and (ii) the geometric restriction effect due to the limited pore accessibility of porous substrates. Here we demonstrate for the first time that the incorporation of trace (~1.8 wt%) amounts of amorphous metal-organic framework (aMOF) nanosheets into the gutter layer of TFC assemblies can simultaneously address these two limitations, with experimental evidence revealing the creation of rapid gas diffusion pathways along horizontal direction. Leveraging this strategy, we successfully fabricated a novel TFC membrane, consisting of a PDMS/aMOF gutter and an ultrathin (~54 nm) poly(ethylene glycol) top selective layer via surface-initiated atom transfer radical polymerization (ATRP). The complete TFC membrane exhibits excellent processability and the highest CO 2 permeance (1,990 GPU with a CO 2 /N 2 ideal selectivity of 39) yet observed for a TFC membrane employing a PDMS gutter layer. This study reveals an avenue for the design and fabrication of a new TFC membrane system with unprecedented gas separation performance.

An urgent need exists for the development of advanced water purification technologies to meet the increasing global demand being placed on freshwater resources. Membrane-based separation technologies for size-selective contaminant removal represent a promising approach to achieve this goal. Here, a novel thin film composite nanofiltration membrane is prepared via interfacial polymerization of alpha-cyclodextrin on a commercially available polyacrylonitrile substrate. Subsequent in-situ inclusion complexation of alkyne-functionalized poly(ethylene glycol) (PEG) is then used to tune the polyrotaxane-based pores for size-dependent filtration. The resultant membrane shows excellent size-selective rejection rates for organic dye (e.g. rhodamine B, > 99%) as well as heavy-metal ions (e.g. Co(II), > 90%), while crucially maintaining high water permeance (e.g. H2O: 7.1 L h(-1) m(-2) bar(-1)). The facile and straightforward synthetic approach to the fabrication of polyrotaxane nanofiltration membranes, combined with their strong nanofiltration separation performance, holds significant promise for membrane-based water purification applications.

Carbon capture from power plants represents a powerful technique to mitigate increasing greenhouse gas emissions. In this work, we describe a thin film composite (TFC) membrane incorporating a polymer of intrinsic microporosity (PIM-1) and metal organic framework (MOF) nanoparticles for post-combustion CO2 capture. The novel TFC membrane design consists of three layers: (1) a CO2 selective layer composed of a PIM-1@MOF mixed matrix; (2) an ultrapermeable PDMS gutter layer doped with MOF nanosheets; and (3) a porous polymeric substrate. Notably, the PDMS@MOF gutter layer incorporating amorphous nanosheets provides a CO2 permeance of 10,000-11,000 GPU, suggesting less gas transport resistance in comparison with pristine PDMS gutter layers. In addition, by blending nanosized MOF particles (MOF-74-Ni and NH2-UiO-66) into PIM-1 to afford a selective layer, the resultant TFC membrane assembly delivered improved CO2 permeance of 4660-7460 GPU and CO2/N-2 selectivity of 26-33, compared with a pristine PIM-1 counterpart (CO2 permeance of 4320 GPU and CO2/N-2 selectivity of 19). Furthermore, PIM-1@MOF based TFC membranes displayed an enhanced resistance to aging effect, maintaining a stable CO2 permeance of 900-1200 GPU and CO2/N-2 selectivity of 26-30 after aging for 8 weeks. To the best of our knowledge, the high CO2 separation performance presented here is unprecedented for PIM-1 based TFC membranes reported in the open literature.

The remarkable power of enzymes to undertake catalysis frequently stems from their grouping of multiple, complementary chemical units within close proximity around the enzyme active site. Motivated by this, we report here a bioinspired surfactant catalyst that incorporates a variety of chemical functionalities common to hydrolytic enzymes. The textbook hydrolase active site, the catalytic triad, is modeled by positioning the three groups of the triad (-OH, -imidazole, and -CO2H) on a single, trifunctional surfactant molecule. To support this, we recreate the hydrogen bond donating arrangement of the oxyanion hole by imparting surfactant functionality to a guanidinium headgroup. Self-assembly of these amphiphiles in solution drives the collection of functional headgroups into close proximity around a hydrophobic nano-environment, affording hydrolysis of a model ester at rates that challenge α-chymotrypsin. Structural assessment via NMR and XRD, paired with MD simulation and QM calculation, reveals marked similarities of the co-micelle catalyst to native enzymes.

Polymers of intrinsic microporosity (PIMs) have exceptional gas separation performance for a broad range of applications. However, PIMs are highly susceptible to physical aging, which drastically reduces their long-term performance over time. In this work, we leverage complementary experimental and density functional theory (DFT) studies to decipher the inter-/intrachain changes that occur during aging of the prototypical PIM-1 and its rigidified analogue PIM-C1. By elucidating this hereto unexplored aging behavior, we reveal that the dramatic decrease in gas permeability of PIM materials during aging stems from a loss of fractional free volume (FFV) due to PIM chain relaxations induced by pi-pi interactions, hydrogen bonding, or van der Waals' forces. While the PIM-1 based membranes displayed enhanced gas pair selectivities after aging, the PIM-C1 based membranes showed an opposite trend with unexpected reductions for CO2/N-2 and CO2/CH4. This is due to the reductions in CO2/N-2 and CO2/CH4 solubility (S) selectivities and, unlike PIM-1, the spirobisindane locked PIM-C1 (i.e., maintenance of micropore sizes) has a stable diffusivity (D) selectivities that cannot offset such reductions. These fundamental insights into the intrinsic relaxation of different PIM polymer chains during physical aging can guide the future design of high-performance PIM materials with enhanced anti-aging properties.

The development of advanced materials based on well-defined polymeric architectures is proving to be a highly prosperous research direction across both industry and academia. Controlled radical polymerization techniques are receiving unprecedented attention, with reversible-deactivation chain growth procedures now routinely leveraged to prepare exquisitely precise polymer products. Reversible addition-fragmentation chain transfer (RAFT) polymerization is a powerful protocol within this domain, where the unique chemistry of thiocarbonylthio (TCT) compounds can be harnessed to control radical chain growth of vinyl polymers. With the intense recent focus on RAFT, new strategies for initiation and external control have emerged that are paving the way for preparing well-defined polymers for demanding applications. In this work, the cutting-edge innovations in RAFT that are opening up this technique to a broader suite of materials researchers are explored. Emerging strategies for activating TCTs are surveyed, which are providing access into traditionally challenging environments for reversible-deactivation radical polymerization. The latest advances and future perspectives in applying RAFT-derived polymers are also shared, with the goal to convey the rich potential of RAFT for an ever-expanding range of high-performance applications.

Microbes employ a remarkably intricate electron transport system to extract energy from the environment. The respiratory cascade of bacteria culminates in the terminal transfer of electrons onto higher redox potential acceptors in the extracellular space. This general and inducible mechanism of electron efflux during normal bacterial proliferation leads to a characteristic fall in bulk redox potential (Eh), the degree of which is dependent on growth phase, the microbial taxa, and their physiology. Here, we show that the general reducing power of bacteria can be subverted to induce the abiotic production of a carbon-centered radical species for targeted bioorthogonal molecular synthesis. Using two species, Escherichia coli and Salmonella enterica serovar Typhimurium as model microbes, a common redox active aryldiazonium salt is employed to intervene in the terminal respiratory electron flow, affording radical production that is mediated by native redox-active molecular shuttles and active bacterial metabolism. The aryl radicals are harnessed to initiate and sustain a bioorthogonal controlled radical polymerization via reversible addition-fragmentation chain transfer (BacRAFT), yielding a synthetic extracellular matrix of "living" vinyl polymers with predetermined molecular weight and low dispersity. The ability to interface the ubiquitous reducing power of bacteria into synthetic materials design offers a new means for creating engineered living materials with promising adaptive and self-regenerative capabilities.

Star polymers are highly functional materials that display unique properties in comparison to linear polymers, making them valuable in a wide range of applications. Currently, ultra-high molecular weight (UHMW) star polymers synthesized using controlled radical polymerization are prone to termination reactions that have undesirable effects, such as star star coupling. Herein, we report the synthesis of the largest star polymers to date using controlled radical techniques via xanthate-mediated photo reversible addition fragmentation chain transfer (RAFT) polymerization using a core-first approach. Polymerization from xanthate-functionalized cores was highly living, enabling the synthesis of well-defined star polymers with molecular weights in excess of 20 MDa.

Sonochemically initiated RAFT polymerization (sonoRAFT) in organic solvents is presented for the first time. Acoustic cavitation, induced by high frequency ultrasound (US) (490 kHz), caused pyrolysis of organic solvent molecules providing a source of initiating radicals. In this way, polymers could be prepared without conventional radical initiators (e.g., AIBN) or additives (e.g., piezoelectric nanoparticles). The polymerization of acrylates and acrylamides was well controlled with the prepared polymers displaying good agreement between theoretical and experimental molecular weights with low dispersities. Methacrylates were found to be less controlled. Several factors were found to influence the final monomer conversion (25-92%) and the upper limit of molecular weight (20-30 kDa) such as the monomer vapor pressure and solubility, solvent choice, and polymer type. No polymerization occurred in the absence of US demonstrating excellent temporal control, and the polymer products were found to possess high chain-end fidelity via chain extension and MALDI-TOF mass spectroscopy.