Quantification and Mechanistic Investigation of the Spontaneous H2O2 Generation at the Interfaces of Salt-Containing Aqueous Droplets.

There is now much evidence that OH radicals and H2O2 are spontaneously generated at the air-water interface of atmospheric aerosols. Here, we investigated the effect of halide anions (Cl-, Br-, I-), which are abundant in marine aerosols, on this H2O2 production. Droplets were generated via nebulization of water solutions containing Na2SO4, NaCl, NaBr, and NaI containing solutions, and H2O2 was monitored as a function of the salt concentration under atmospheric relevant conditions. The interfacial OH radical formation was also investigated by adding terephthalic acid (TA) to our salt solutions, and the product of its reaction with OH, hydroxy terephthalic acid (TAOH), was monitored. Finally, a mechanistic investigation was performed to examine the reactions participating in H2O2 production, and their respective contributions were quantified. Our results showed that only Br- contributes to the interfacial H2O2 formation, promoting the production by acting as an electron donor, while Na2SO4 and NaCl stabilized the droplets by only reducing their evaporation. TAOH was observed in the collected droplets and, for the first time, directly in the particle phase by means of online fluorescence spectroscopy, confirming the interfacial OH production. A mechanistic study suggests that H2O2 is formed by both OH and HO2 self-recombination, as well as HO2 reaction with H atoms. This work is expected to enhance our understanding of interfacial processes and assess their impact on climate, air quality, and health.

Supra-Fluorophores: Ultrabright Fluorescent Supramolecular Assemblies Derived from Conventional Fluorophores in Water.

Fluorescent organic nanoparticles (NPs) with exceptional brightness hold significant promise for demanding fluorescence bioimaging applications. Although considerable efforts are invested in developing novel organic dyes with enhanced performance, augmenting the brightness of conventional fluorophores is still one of the biggest challenges to overcome. This study presents a supramolecular strategy for constructing ultrabright fluorescent nanoparticles in aqueous media (referred to as "Supra-fluorophores") derived from conventional fluorophores. To achieve this, this course has employed a cylindrical nanoparticle with a hydrophobic microdomain, assembled by a cyclic peptide-diblock copolymer conjugate in water, as a supramolecular scaffold. The noncovalent dispersion of fluorophore moieties within the hydrophobic microdomain of the scaffold effectively mitigates the undesired aggregation-caused quenching and fluorescence quenching by water, resulting in fluorescent NPs with high brightness. This strategy is applicable to a broad spectrum of fluorophore families, covering polyaromatic hydrocarbons, coumarins, boron-dipyrromethenes, cyanines, xanthenes, and squaraines. The resulting fluorescent NPs demonstrate high fluorescence quantum yield (>30%) and brightness per volume (as high as 12 060 m-1 cm-1 nm-3). Moreover, high-performance NPs with emission in the NIR region are constructed, showcasing up to 20-fold increase in both brightness and photostability. This Supra-fluorophore strategy offers a versatile and effective method for transforming existing fluorophores into ultrabright fluorescent NPs in aqueous environments, for applications such as bioimaging.

Nitrate Radicals Suppress Biogenic New Particle Formation from Monoterpene Oxidation.

Highly oxygenated organic molecules (HOMs) are a major source of new particles that affect the Earth's climate. HOM production from the oxidation of volatile organic compounds (VOCs) occurs during both the day and night and can lead to new particle formation (NPF). However, NPF involving organic vapors has been reported much more often during the daytime than during nighttime. Here, we show that the nitrate radicals (NO3), which arise predominantly at night, inhibit NPF during the oxidation of monoterpenes based on three lines of observational evidence: NPF experiments in the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN (European Organization for Nuclear Research), radical chemistry experiments using an oxidation flow reactor, and field observations in a wetland that occasionally exhibits nocturnal NPF. Nitrooxy-peroxy radicals formed from NO3 chemistry suppress the production of ultralow-volatility organic compounds (ULVOCs) responsible for biogenic NPF, which are covalently bound peroxy radical (RO2) dimer association products. The ULVOC yield of α-pinene in the presence of NO3 is one-fifth of that resulting from ozone chemistry alone. Even trace amounts of NO3 radicals, at sub-parts per trillion level, suppress the NPF rate by a factor of 4. Ambient observations further confirm that when NO3 chemistry is involved, monoterpene NPF is completely turned off. Our results explain the frequent absence of nocturnal biogenic NPF in monoterpene (α-pinene)-rich environments.

Modular design of cyclic peptide - polymer conjugate nanotubes for delivery and tunable release of anti-cancer drug compounds.

High aspect-ratio nanomaterials have recently emerged as promising drug delivery vehicles due to evidence of strong cellular association and prolonged in vivo circulation times. Cyclic peptide - polymer conjugate nanotubes are excellent candidates due to their elongated morphology, their supramolecular composition and high degree of pliability due to the versatility in manipulating amino acid sequence and polymer type. In this work, we explore the use of a nanotube structure on which a potent anti-cancer drug, camptothecin, is attached alongside hydrophilic or amphiphilic RAFT polymers, which shield the cargo. We show that subtle modifications to the cleavable linker type and polymer architecture have a dramatic influence over the rate of drug release in biological conditions. In vitro studies revealed that multiple cancer cell lines in 2D and 3D models responded effectively to the nanotube treatment, and analogous fluorescently labelled materials revealed key mechanistic information regarding the degree of cellular uptake and intracellular fate. Importantly, the ability to instruct specific drug release profiles indicates a potential for these nanomaterials as vectors which can provide sustained drug concentrations for a maximal therapeutic effect.

Supramolecular peptide nanotubes as artificial enzymes for catalysing ester hydrolysis.

Peptide-based artificial enzymes are attracting significant interest because of their remarkable resemblance in both composition and structure to native enzymes. Herein, we report the construction of histidine-containing cyclic peptide-based supramolecular polymeric nanotubes to function as artificial enzymes for ester hydrolysis. The optimized catalyst shows a ca. 70-fold increase in reaction rate compared to the un-catalysed reaction when using 4-nitrophenyl acetate as a model substrate. Furthermore, the amphiphilic nature of the supramolecular catalysts enables an enhanced catalytic activity towards hydrophobic substrates. By incorporating an internal hydrophobic region within the self-assembled polymeric nanotube, we achieve a 55.4-fold acceleration in hydrolysis rate towards a more hydrophobic substrate, 4-nitrophenyl butyrate. This study introduces supramolecular peptide nanotubes as an innovative class of supramolecular scaffolds for fabricating artificial enzymes with better structural and chemical stability, catalysing not only ester hydrolysis, but also a broader spectrum of catalytic reactions.

Supra-Cyanines: Ultrabright Cyanine-Based Fluorescent Supramolecular Materials in Solution and in the Solid State.

Fluorescent materials with high brightness play a crucial role in the advancement of various technologies such as bioimaging, photonics, and OLEDs. While significant efforts are dedicated to designing new organic dyes with improved performance, enhancing the brightness of existing dyes holds equal importance. In this study, we present a simple supramolecular strategy to develop ultrabright cyanine-based fluorescent materials by addressing long-standing challenges associated with cyanine dyes, including undesired cis-trans photoisomerization and aggregation-caused quenching. Supra-cyanines are obtained by incorporating cyanine moieties in a cyclic peptide-based supramolecular scaffold, and exhibit high fluorescence quantum yields (up to 50 %) in both solution and in the solid state. These findings offer a versatile approach for constructing highly emissive cyanine-based supramolecular materials.

Spontaneous Iodide Activation at the Air-Water Interface of Aqueous Droplets.

We present experimental evidence that atomic and molecular iodine, I and I2, are produced spontaneously in the dark at the air-water interface of iodide-containing droplets without any added catalysts, oxidants, or irradiation. Specifically, we observe I3- formation within droplets, and I2 emission into the gas phase from NaI-containing droplets over a range of droplet sizes. The formation of both products is enhanced in the presence of electron scavengers, either in the gas phase or in solution, and it clearly follows a Langmuir-Hinshelwood mechanism, suggesting an interfacial process. These observations are consistent with iodide oxidation at the interface, possibly initiated by the strong intrinsic electric field present there, followed by well-known solution-phase reactions of the iodine atom. This interfacial chemistry could be important in many contexts, including atmospheric aerosols.

Sunlight Induces the Production of Atmospheric Volatile Organic Compounds (VOCs) from Thermokarst Ponds.

Ground subsidence caused by permafrost thawing causes the formation of thermokarst ponds, where organic compounds from eroding permafrost accumulate. We photolyzed water samples from two such ponds in Northern Quebec and discovered the emission of volatile organic compounds (VOCs) using mass spectrometry. One pond near peat-covered permafrost mounds was organic-rich, while the other near sandy mounds was organic-poor. Compounds up to C10 were detected, comprising the atoms of O, N, and S. The main compounds were methanol, acetaldehyde, and acetone. Hourly VOC fluxes under actinic fluxes similar to local solar fluxes might reach up to 1.7 nmol C m-2 s-1. Unexpectedly, the fluxes of VOCs from the organic-poor pond were greater than those from the organic-rich pond. We suggest that different segregations of organics at the air/water interface may partly explain this observation. This study indicates that sunlit thermokarst ponds are a significant source of atmospheric VOCs, which may affect the environment and climate via ozone and aerosol formation. Further work is required for understanding the relationship between the pond's organic composition and VOC emission fluxes.

Anchor Group Bottlebrush Polymers as Oil Additive Friction Modifiers.

Surface-tethered polymers have been shown to be an efficient lubrication strategy for boundary and mixed lubrication by providing a solvated film between solid surfaces. We have assessed the performance of various graft copolymers as friction modifier additives in oil and revealed important structure-property relationships for this application. The polymers consisted of an oil-soluble, grafted poly(lauryl acrylate) segment and a polar, linear poly(4-acryloylmorpholine) anchor group. Reversible addition-fragmentation chain transfer polymerization was used to access various architectures with control of the grafting density and position of the anchor group. Macrotribological studies displayed promising results with ≈50% reduction in friction coefficient at low polymer treatment rates. QCM-D experiments, neutron reflectometry, small-angle neutron scattering, and atomic force microscopy were used to gather detailed information on these polymers' surface adsorption characteristics, film structure, and solution behavior.

Investigating the Impact of Hydrophobic Polymer Segments on the Self-Assembly Behavior of Supramolecular Cyclic Peptide Systems via Asymmetric-Flow Field Flow Fractionation.

The present study examines the behavior of cyclic peptide polymer conjugates that have been designed to combine their self-assembling ability via H-bonding with the properties of amphiphilic diblock copolymers. Using a combination of asymmetric flow-field flow fractionation (AF4) and small-angle neutron scattering (SANS), we have uncovered unique insight based on the population of structures established at a 24 h equilibrium profile. Our results determine that by introducing a small quantity of hydrophobicity into the conjugated polymer corona, the resulting nanotube structures exhibit low unimer dissociation which signifies enhanced stability. Furthermore, as the hydrophobicity of the polymer corona is increased, the elongation of the nanotubes is observed due to an increase in the association of unimers. This encompasses not only the H-bonding of unimers into nanotubes but also the self-assembly of single nanotubes into segmented-nanotube structures with high aspect ratios. However, this influence relies on a subtle balance between the hydrophobicity and hydrophilicity of the polymer corona. This balance is proposed to determine the solvent entropic penalty of hydrating the system, whereby the cost scales with the hydrophobic quantity. Consequently, it has been suggested that at a critical hydrophobic quantity, the solvation penalty becomes high enough such that the self-assembly of the system deviates from ordered hydrogen bonding. The association behavior is instead dominated by the hydrophobic effect which results in the undesirable formation of disordered aggregates.

Polymer Functionalization by RAFT Interchange.

Here, we report a simple approach for end group functionalization of linear polymers and graft copolymers via an interchange process of reversible addition-fragmentation chain transfer (RAFT) polymerization chain transfer agents (CTAs). The high functional group tolerance of the RAFT process allows a library of functionalities to be introduced. Moreover, this approach allows multiple functional groups to be installed simultaneously. Furthermore, as an alternative to end group analysis, we report the utility of the supernatant of the reaction mixture to determine the degree of functionalization.

Mechanism of Action of Oxazoline-Based Antimicrobial Polymers Against Staphylococcus aureus: In Vivo Antimicrobial Activity Evaluation.

Antimicrobial-resistant pathogens have reached alarming levels, becoming one of the most pressing global health issues. Hence, new treatments are necessary for the fight against antimicrobial resistance. Synthetic nanoengineered antimicrobial polymers (SNAPs) have emerged as a promising alternative to antimicrobial peptides, overcoming some of their limitations while keeping their key features. Herein, a library of amphiphilic oxazoline-based SNAPs using cationic ring-opening polymerization (CROP) is designed. Amphipathic compounds with 70% cationic content exhibit the highest activity against clinically relevant Staphylococcus aureus isolates, maintaining good biocompatibility in vitro and in vivo. The mechanism of action of the lead compounds against S. aureus is assessed using various microscopy techniques, indicating cell membrane disruption, while the cell wall remains unaffected. Furthermore, a potential interaction of the compounds with bacterial DNA is shown, with possible implications on bacterial division. Finally, one of the compounds exhibits high efficacy in vivo in an insect infection model.

Synthetic Star Nanoengineered Antimicrobial Polymers as Antibiofilm Agents: Bacterial Membrane Disruption and Cell Aggregation.

Antimicrobial resistance has become a worldwide issue, with multiresistant bacterial strains emerging at an alarming rate. Multivalent antimicrobial polymer architectures such as bottle brush or star polymers have shown great potential, as they could lead to enhanced binding and interaction with the bacterial cell membrane. In this study, a library of amphiphilic star copolymers and their linear copolymer equivalents, based on acrylamide monomers, were synthesized via RAFT polymerization. Their monomer distribution and molecular weight were varied. Subsequently, their antimicrobial activity toward a Gram-negative bacterium (Pseudomonas aeruginosa PA14) and a Gram-positive bacterium (Staphylococcus aureus USA300) and their hemocompatibility were investigated. The statistical star copolymer, S-SP25, showed an improved antimicrobial activity compared to its linear equivalent againstP. aeruginosaPA14. The star architecture enhanced its antimicrobial activity, causing bacterial cell aggregation, as revealed via electron microscopy. However, it also induced increased red blood cell aggregation compared to its linear equivalents. Changing/shifting the position of the cationic block to the core of the structure prevents the cell aggregation effect while maintaining a potent antimicrobial activity for the smallest star copolymer. Finally, this compound showed antibiofilm properties against a robust in vitro biofilm model.

Combining SNAPs with antibiotics shows enhanced synergistic efficacy against S. aureus and P. aeruginosa biofilms.

Biofilm infections are associated with a high mortality risk for patients. Antibiotics perform poorly against biofilm communities, so high doses and prolonged treatments are often used in clinical settings. We investigated the pairwise interactions of two synthetic nano-engineered antimicrobial polymers (SNAPs). The g-D50 copolymer was synergistic with penicillin and silver sulfadiazine against planktonic Staphylococcus aureus USA300 in synthetic wound fluid. Furthermore, the combination of g-D50 and silver sulfadiazine showed a potent synergistic antibiofilm activity against S. aureus USA300 using in vitro and ex vivo wound biofilm models. The a-T50 copolymer was synergistic with colistin against planktonic Pseudomonas aeruginosa in synthetic cystic fibrosis medium, and this pair showed a potent synergistic antibiofilm activity against P. aeruginosa in an ex vivo cystic fibrosis lung model. SNAPs thus have the potential for increased antibiofilm performance in combination with certain antibiotics to shorten prolonged treatments and reduce dosages against biofilm infection.

Spontaneous dark formation of OH radicals at the interface of aqueous atmospheric droplets.

Hydroxyl radical (OH) is a key oxidant that triggers atmospheric oxidation chemistry in both gas and aqueous phases. The current understanding of its aqueous sources is mainly based on known bulk (photo)chemical processes, uptake from gaseous OH, or related to interfacial O3 and NO3 radical-driven chemistry. Here, we present experimental evidence that OH radicals are spontaneously produced at the air-water interface of aqueous droplets in the dark and the absence of known precursors, possibly due to the strong electric field that forms at such interfaces. The measured OH production rates in atmospherically relevant droplets are comparable to or significantly higher than those from known aqueous bulk sources, especially in the dark. As aqueous droplets are ubiquitous in the troposphere, this interfacial source of OH radicals should significantly impact atmospheric multiphase oxidation chemistry, with substantial implications on air quality, climate, and health.

Multiblock copolymer synthesis via RAFT emulsion polymerization.

A multiblock copolymer is a polymer of a specific structure that consists of multiple covalently linked segments, each comprising a different monomer type. The control of the monomer sequence has often been described as the "holy grail" of synthetic polymer chemistry, with the ultimate goal being synthetic access to polymers of a "perfect" structure, where each monomeric building block is placed at a desired position along the polymer chain. Given that polymer properties are intimately linked to the microstructure and monomer distribution along the constituent chains, it goes without saying that there exist seemingly endless opportunities in terms of fine-tuning the properties of such materials by careful consideration of the length of each block, the number and order of blocks, and the inclusion of monomers with specific functional groups. The area of multiblock copolymer synthesis remains relatively unexplored, in particular with regard to structure-property relationships, and there are currently significant opportunities for the design and synthesis of advanced materials. The present review focuses on the synthesis of multiblock copolymers via reversible addition-fragmentation chain transfer (RAFT) polymerization implemented as aqueous emulsion polymerization. RAFT emulsion polymerization offers intriguing opportunities not only for the advanced synthesis of multiblock copolymers, but also provides access to polymeric nanoparticles of specific morphologies. Precise multiblock copolymer synthesis coupled with self-assembly offers material morphology control on length scales ranging from a few nanometers to a micrometer. It is imperative that polymer chemists interact with physicists and material scientists to maximize the impact of these materials of the future.

Interfacial photochemistry of marine diatom lipids: Abiotic production of volatile organic compounds and new particle formation.

The global importance of abiotic oceanic production of volatile organic compounds (VOCs) still presents a source of high uncertainties related to secondary organic aerosol (SOA) formation. A better understanding of the photochemistry occurring at the ocean-atmosphere interface is particularly important in that regard, as it covers >70% of the Earth's surface. In this work, we focused on the photochemical VOCs production at the air-water interface containing organic material from authentic culture of marine diatom Chaetoceros pseudocurvisetus. Abiotic VOCs production upon irradiation of material originating from total phytoplankton culture as well as the fraction containing only dissolved material was monitored by means of PTR-ToF-MS. Furthermore, isolated dissolved lipid fraction was investigated after its deposition at the air-water interface. All samples acted as a source of VOCs, producing saturated oxygenated compounds such as aldehydes and ketones, as well as unsaturated and functionalized compounds. Additionally, a significant increase in surfactant activity following irradiation experiments observed for all samples implied biogenic material photo-transformation at the air-water interface. The highest VOCs flux normalized per gram of carbon originated from lipid material, and the produced VOCs were introduced into an atmospheric simulation chamber, where particle formation was observed after its gas-phase ozonolysis. This work clearly demonstrates abiotic production of VOCs from phytoplankton derived organic material upon irradiation, facilitated by its presence at the air/water interface, with significant potential for affecting the global climate as a precursor of particle formation.

Polymerisation-Induced Self-Assembly of Graft Copolymers.

We report the polymerisation-induced self-assembly of poly(lauryl methacrylate)-graft-poly(benzyl methacrylate) copolymers during reversible addition-fragmentation chain transfer (RAFT) grafting from polymerisation in a backbone-selective solvent. Electron microscopy images suggest the phase separation of grafts to result in a network of spherical particles, due to the ability of the branched architecture to freeze chain entanglements and to bridge core domains. Small-angle X-ray scattering data suggest the architecture promotes the formation of multicore micelles, the core morphology of which transitions from spheres to worms, vesicles, and inverted micelles with increasing volume fraction of the grafts. A time-resolved SAXS study is presented to illustrate the formation of the inverted phase during a polymerisation. The grafted architecture gives access to unusual morphologies and provides exciting new handles for controlling the polymer structure and material properties.

Probing the Effect of Rigidity on the Cellular Uptake of Core-Shell Nanoparticles: Stiffness Effects are Size Dependent.

Nanoparticles are well established vectors for the delivery of a wide range of biomedically relevant cargoes. Numerous studies have investigated the impact of size, shape, charge, and surface functionality of nanoparticles on mammalian cellular uptake. Rigidity has been studied to a far lesser extent, and its effects are still unclear. Here, the importance of this property, and its interplay with particle size, is systematically explored using a library of core-shell spherical PEGylated nanoparticles synthesized by RAFT emulsion polymerization. Rigidity of these particles is controlled by altering the intrinsic glass transition temperature of their constituting polymers. Three polymeric core rigidities are tested: hard, medium, and soft using two particle sizes, 50 and 100 nm diameters. Cellular uptake studies indicate that softer particles are taken up faster and threefold more than harder nanoparticles with the larger 100 nm particles. In addition, the study indicates major differences in the cellular uptake pathway, with harder particles being internalized through clathrin- and caveolae-mediated endocytosis as well as macropinocytosis, while softer particles are taken up bycaveolae- and non-receptormediated endocytosis. However, 50 nm derivatives do not show any appreciable differences in uptake efficiency, suggesting that rigidity as a parameter in the biological regime may be size dependent.