On the origin of the extremely different solubilities of polyethers in water

Photodynamic antibacterial research on hypericin-loaded PEGylated mesoporous silica delivery system

In this study, a novel drug delivery system (MSN-PEG-Hypericin) was successfully fabricated using tetraethyl orthosilicate and 3-aminopropyltriethoxysilane as raw materials, and the PEGylation of the prepared aminated mesoporous silica and grafting of hypericin onto the carrier were further conducted to obtain MSN-PEG-Hypericin. The successful preparation of MSN-PEG-Hypericin was characterized by several physical-chemical techniques. Furthermore, the MSN-PEG-Hypericin system increased the ability of hypericin to generate reactive oxygen species (ROS) in vitro. The cytotoxicity assay and hemolysis analysis showed that MSN-PEG-Hypericin had good biocompatibility. For antibacterial studies, the irradiation time and incubation time of photodynamic therapy (PDT) for S. aureus and E. coli were respectively 8 min and 8 h, and the concentrations of hypericin were 2.5 and 5 μg/mL. The result of triphenyl tetrazolium chloride assay indicated that MSN-PEG-Hypericin had stronger photodynamic antibacterial activity than free hypericin, and S. aureus was more sensitive to PDT than E. coli, which was related to their cell structural differences. The antibacterial mechanism study indicated that the generated ROS could destroy the bacterial structures and cause bacterial death due to the leakage of the contents. The MSN-PEG-Hypericin system prepared in this study had potential application prospects in the antibacterial field.

Rapid-Response Water-Shrink Films with High Output Work Density Based on Polyethylene Oxide and α-Cyclodextrin for Autonomous Wound Closure

Conventional wound closure methods, including sutures and tissue adhesives, present significant challenges for self-care treatment, particularly in the context of bleeding wounds. Existing stimuli-responsive contractile materials designed for autonomous wound closure frequently lack sufficient output work density to generate the force needed to bring the wound edges into proximity or necessitate stimuli that are not compatible with the human body. Here, semi-transparent, flexible, and water-responsive shrinkable films, composed of poly(ethylene oxide) and α-cyclodextrin, are reported. These films exhibit remarkable stability under ambient conditions and demonstrate significant contraction (≈50%) within 6 s upon exposure to water, generating substantial contractile stress (up to 6 MPa) and output work density (≈1028 kJ m-3), which is 100 times larger than that of conventional hydrogel and 25 times larger than that of skeletal muscles. Remarkably, upon hydration, these films are capable of lifting objects 10 000 times their own weight. Leveraging this technology, water-shrink tapes, which, upon contact with water, effectively constrict human skin and autonomously close bleeding wounds in animal models within 10 seconds, are developed further. This work offers a novel approach to skin wound management, showing significant potential for emergency and self-care scenarios.

Fabrication of 3D-Printed Scaffolds with Multiscale Porosity

3D printing is a promising technique for producing bone implants, but there is still a need to adjust efficiency, facilitate production, and improve biocompatibility. Porous materials have a proven positive effect on the regeneration of bone tissue, but their production is associated with numerous limitations. In this work, we described a simple method of producing polymer or polymer-ceramic filaments for 3D-printing scaffolds by adding micrometer-scale porous structures on scaffold surfaces. Scaffolds included polycaprolactone (PCL) as the primary polymer, β-tricalcium phosphate (β-TCP) as the ceramic filler, and poly(ethylene glycol) (PEG) as a porogen. The pressurized filament extrusion gave flexible filaments composed of PCL, β-TCP, and PEG, which are ready to use in fused filament fabrication (FFF) 3D printers. Washing of 3D-printed scaffolds in ethanol solution removed PEG and revealed a microporous structure and ceramic particles on the scaffold's surfaces. Furthermore, 3D-printed materials exhibit good printing precision, no cytotoxic properties, and highly impact MG63 cell alignment. Although combining PCL, PEG, and β-TCP is quite popular, the presented method allows the production of porous scaffolds with a well-organized structure without advanced equipment, and the produced filaments can be used to 3D print scaffolds on a simple commercially available 3D printer.

Long-term antifouling surfaces for urinary catheters

The presence of a variety of bacteria is an inevitable/indispensable part of human life. In particular, for patients, the existence and spreading of bacteria lead to prolonged treatment period with many more complications. The widespread use of urinary catheters is one of the main causes for the prevalence of infections. The necessity of long-term use of indwelling catheters is unavoidable in terms of the development of bacteriuria and blockage. As is known, since a permanent solution to this problem has not yet been found, research and development activities continue actively. Herein, polyethylene glycol (PEG)-like thin films were synthesized by a custom designed plasma enhanced chemical vapor deposition (PE-CVD) method and the long-term effect of antifouling properties of PEG-like coated catheters was investigated against Escherichia coli and Proteus mirabilis. The contact angle measurements have revealed the increase of wettability with the increase of plasma exposure time. The antifouling activity of surface-coated catheters was analyzed against the Gram-negative/positive bacteria over a long-term period (up to 30 days). The results revealed that PE-CVD coated PEG-like thin films are highly capable of eliminating bacterial attachment on surfaces with relatively reduced protein attachment without having any toxic effect. Previous statements were supported with SEM, XPS, FTIR spectroscopy, and contact angle analysis.

Entropy Drives Interpolymer Association in Water: Insights into Molecular Mechanisms

Interpolymer association in aqueous solutions is essential for many industrial processes, new materials design, and the biochemistry of life. However, our understanding of the association mechanism is limited. Classical theories do not provide molecular details, creating a need for detailed mechanistic insights. This work consolidates previous literature with complementary isothermal titration calorimetry (ITC) measurements and molecular dynamics (MD) simulations to investigate molecular mechanisms to provide such insights. The large body of ITC data shows that intermolecular bonds, such as ionic or hydrogen bonds, cannot drive association. Instead, polymer association is entropy-driven due to the reorganization of water and ions. We propose a unifying entropy-driven association mechanism by generalizing previously suggested polyion association principles to include nonionic polymers, here termed polydipoles. In this mechanism, complementary charge densities of the polymers are the common denominators of association, for both polyions and polydipoles. The association of the polymers results mainly from two processes: charge exchange and amphiphilic association. MD simulations indicate that the amphiphilic assembly alone is enough for the initial association. Our proposed mechanism is a step toward a molecular understanding of the formation of complexes between synthetic and biological polymers under ambient or biological conditions.

Castor (Ricinus communis L.) differential cell cycle and metabolism reactivation, germinability, and seedling performance under NaCl and PEG osmoticum: Stress tolerance related to genotype-preestablished superoxide dismutase activity

Castor (Ricinus communis) is a relevant industrial oilseed feedstock for many industrial applications, being globally mainly cultivated by smallholder farmers in semiarid areas, where abiotic stresses predominate. Therefore, susceptible to generating reactive oxygen species (ROS) and subsequent oxidative stress, compromising cell metabolism upon seed imbibition and germination, seedling and crop establishment, and yield. The present study evaluated the consequences of water restriction by Polyethylene glycol (PEG) and Sodium chloride (NaCl) on cell cycle and metabolism reactivation on germinability, seedling growth, and vigor parameters in 2 commercial castor genotypes (Nordestina and Paraguaçu). PEG water restriction inhibited germination completely at -0.23 MPa or higher, presumably due to reduced oxygen availability. The restrictive effects of NaCl saline stress on germination were observed only from -0.46 MPa onwards, affecting dry mass accumulation and the production of normal seedlings. In general, superoxide dismutase (SOD) activity increased in NaCl -0.23 MPa, whereas its modulation during the onset of imbibition (24h) seemed to depend on its initial levels in dry seeds in a genotype-specific manner, therefore, resulting in the higher stress tolerance of Nordestina compared to Paraguaçu. Overall, results show that Castor germination and seedling development are more sensitive to the restrictive effects of PEG than NaCl at similar osmotic potentials, contributing to a better understanding of the responses to water restriction stresses by different Castor genotypes. Ultimately, SOD may constitute a potential marker for characterizing castor genotypes in stressful situations during germination, early seedling, and crop establishment, and a target for breeding for Castor-improved stress tolerance.

Protein Cryoprotectant Ability of the Aqueous Zwitterionic Solution

Protein cryopreservation is important for the long-term storage of unstable proteins. Recently, we found that N-acetylglucosaminyltransferase-V (GnT-V) can be cryopreserved in a deep freezer without temperature control using a dilute binary aqueous solution of 3-(1-(2-(2-methoxyethoxy)ethyl)imidazol-3-io)butane-1-carboxylate (OE2imC3C) [10 wt %, mole fraction of solute (x) = 7.75 × 10-3], an artificial zwitterion. However, it is unclear which solvent properties are required in these media to preserve unstable proteins, such as GnT-V. In this study, we investigated the melting phenomena and solution structure of dilute binary aqueous OE2imC3C solutions [x = 0-2.96 × 10-2 (0-30 wt %)] using differential scanning calorimetry (DSC) and Raman and Fourier transform infrared (FTIR) spectroscopies combined with molecular dynamics (MD) simulation to compare the cryoprotectant ability of OE2imC3C with two general cryoprotectants (CPAs), glycerol and dimethyl sulfoxide. DSC results indicated that aqueous OE2imC3C solutions can be melted at lower temperatures with less energy than the control CPA solution, with increasing x, primarily due to OE2imC3C having a higher content of unfrozen water molecules. Moreover, Raman and FTIR results showed that the high content of unfrozen water molecules in aqueous OE2imC3C solutions was due to the hydration around the ionic parts (the COO- group and imidazolium ring) and the OCH2CH2O segment. In addition, the MD simulation results showed that there were fewer structured water molecules around the OCH2CH2O segment than the hydration water molecules around the ionic parts. These solvent properties suggest that dilute aqueous OE2imC3C solutions are effective in preventing freezing, even in a deep freezer. Therefore, this medium has the potential to act as a novel cryoprotectant for proteins in biotechnology and biomedical fields.

Origin of Strong Hydrogen Bonding and Preferred Orientation of Water at Uncharged Polyethylene Glycol Polymer/Water Interface

Polyethylene glycol (PEG), a water-soluble non-ionic polymer, finds diverse applications from Li-ion batteries to drug delivery. The effectiveness of PEG in these contexts hinges on water's behavior at PEG/water interfaces. Employing heterodyne-detected vibrational sum frequency generation and Raman spectroscopy along with a novel analytical approach, termed difference spectroscopy with simultaneous curve-fitting analysis, we observed that water exhibits both "hydrogen-up" and "hydrogen-down" orientations at PEG(≥400u)/water interfaces. As the molar mass of PEG increases, the contribution of the strongly hydrogen-bonded and H-up-oriented water rises. We propose that the PEG-affected interfacial water originates from the asymmetrical hydration of the surface-adsorbed PEG, as evidenced by the resemblance between the water spectra in the hydration shell of PEG and those at the PEG/water interface. These findings elucidate the molecular mechanism underlying PEG's catalytic role in water splitting at membrane interfaces.

Antifouling polymers for nanomedicine and surfaces: recent advances

Antifouling polymers are materials that can resist nonspecific interactions with cells, proteins, and other biomolecules. Typically, they are hydrophilic polymers with polar or charged moieties that are capable of strong nonbonding interactions with water molecules. This propensity to bind water generates a surface hydration layer that reduces nonspecific interactions with other molecules and is paramount to the antifouling behavior. This property is especially useful for nanoscale applications such as nanomedicine and surface modifications at the molecular level. In nanomedicine, antifouling polymers such as poly(ethylene glycol) and its alternatives play a key role in shielding drug molecules and therapeutic proteins/genes from the immune system within nanoassemblies, thereby enabling effective delivery to target tissues. For coatings, antifouling polymers help to prevent adhesion of cells and molecules to surfaces and are thus valued in marine and biomedical device applications. In this Review, we survey recent advances in antifouling polymers in the context of nanomedicine and coatings, while shining the spotlight on the major polymer classes such as PEG, polyzwitterions, poly(oxazoline)s, and other nonionic hydrophilic polymers.

Polymorph screening at surfaces of a benzothienobenzothiophene derivative: discovering new solvate forms

The discovery of new polymorphs opens up unique applications for molecular materials since their physical properties are predominantly influenced by the crystal structure type. The deposition of molecules at surfaces offers great potential in the variation of the crystallization conditions, thereby allowing access to unknown polymorphs. With our surface crystallization approach, four new phases are found for an oligoethylene glycol-benzothienobenzothiophene molecule, and none of these phases could be identified via classical polymorph screening. The corresponding crystal lattices of three of the new phases were obtained via X-ray diffraction (XRD). Based on the volumetric considerations together with X-ray fluorescence and Raman spectroscopy data, the phases are identified as solvates containing one, two or three solvent molecules per molecule. The strong interaction of dichloromethane with the oligoethylene glycol side chains of the molecules may be responsible for the formation of the solvates. Temperature-dependent XRD reveals the low thermal stability of the new phases, contrary to the thermodynamically stable bulk form. Nevertheless, the four solvates are stable under ambient conditions for at least two years. This work illustrates that defined crystallization at surfaces enables access to multiple solvates of a given material through precise and controlled variations in the crystallization kinetics.

Effects of intramolecular chain conformation on the hydration and miscibility of polyethylene glycol in water studied by means of polymer reference interaction site model theory

To examine the conventional idea that the gauche conformation of the OCCO dihedral angle promotes the dissolution of polyethylene glycol (PEG) in water through strong hydration, the thermodynamic properties of liquid mixtures of PEG and water were studied by means of polymer reference interaction site model (PRISM) theory. The intramolecular correlation functions required as input for PRISM theory were calculated by the generator matrix method, accompanied by changes in the distribution of dihedral angles. In the infinite dilution limit, the increased probability of gauche conformation of the OCCO dihedral angles stabilizes the hydration of PEG through enhanced hydrogen bonding between the ether oxygen of PEG and water. The mixing Gibbs energies of the liquid mixtures were also calculated in the whole concentration range based on the Gibbs-Duhem equation, as per our recent proposal. A liquid-liquid phase separation was observed when all the dihedral angles of PEG were in the trans conformation; for the liquid mixture to be miscible in the whole concentration range, the introduction of the OCCO gauche conformation was found to be indispensable. The above theoretical results support the conventional idea that the OCCO gauche conformation is important for the high miscibility of PEG and water.

Polyethylene Glycol 20k. Does It Fluoresce?

Polyethylene glycol (PEG) is a polyether compound commonly used in biological research and medicine because it is biologically inert. This simple polymer exists in variable chain lengths (and molecular weights). As they are devoid of any contiguous π-system, PEGs are expected to lack fluorescence properties. However, recent studies suggested the occurrence of fluorescence properties in non-traditional fluorophores like PEGs. Herein, a thorough investigation has been conducted to explore if PEG 20k fluoresces. Results of this combined experimental and computational study suggested that although PEG 20k could exhibit "through-space" delocalization of lone pairs of electrons in aggregates/clusters, formed via intermolecular and intramolecular interactions, the actual contributor of fluorescence between 300 and 400 nm is the stabilizer molecule, i.e., 3-tert-butyl-4-hydroxyanisole present in the commercially available PEG 20k. Therefore, the reported fluorescence properties of PEG should be taken with a grain of salt, warranting further investigation.

Reversible Dehydration-Hydration of Poly(ethylene glycol) in Langmuir Monolayers of a Diblock Copolymer Inferred from Changes in Filament Curvature

We investigated changes in the hydration state of poly(ethylene glycol) (PEG) through morphological changes in Langmuir monolayers of a PEG-poly(l-lactide) (PlLA) (PEG-b-PlLA) diblock copolymer. When the PEG blocks were hydrated, we observed a remarkable morphology of bundles of ring-like filaments, arranged concentrically, yielding densely packed disk-like objects with a hollow center. We attribute the uniform curvature of these filaments to a strong mismatch between the molecular volumes occupied by PlLA blocks and hydrated PEG blocks. Under the constraint that each hydrated PEG block is attached to a hydrophobic PlLA block anchored to the air-water interface, this mismatch of molecular volumes caused strong repulsion within the PEG layer, in particular when the PlLA blocks packed tightly. Induced by a transition in the ordering of the PlLA blocks, the PEG blocks lost their hydration shell and packed into a dense polymer brush, accompanied by a reduction of the pressure within the PEG layer. During this packing process, the curvature of the filaments was eliminated and the ring-like filaments fractured into small linear pieces. Upon compression, the linear pieces coalesced and formed long filaments aligned in parallel. Importantly, upon expansion of the Langmuir film, these changes in morphology were reversible, and the PEG blocks could be rehydrated and bundles of concentrically arranged ring-like filaments were reformed. We conclude that the change in curvature of the filaments provides a means for distinguishing between the hydrated and dehydrated states of PEG.

Blood Protein Exclusion from Polymer Brushes

We report interactions between adsorbed copolymers of poly(ethylene glycol) (PEG) in the presence of two abundant blood proteins, serum albumin and an immunoglobulin G, up to physiological blood concentrations. We directly and nonintrusively measure interactions between PEG triblock copolymers (PEG-PPO-PEG) adsorbed to hydrophobic colloids and surfaces using Total Internal Reflection Microscopy, which provides kT- and nanometer-scale resolution of interaction potentials (energy vs separation). In the absence of protein, adsorbed PEG copolymer repulsion is consistent with dimensions and architectures of PEG brushes on both colloids and surfaces. In the presence of proteins, we observe concentration dependent depletion attraction and no change to brush repulsion, indicating protein exclusion from PEG brushes. Because positive and negative protein adsorption are mutually exclusive, our observations of concentration dependent depletion attraction with no change to brush repulsion unambiguously indicate the absence of protein coronas at physiological protein concentrations. These findings demonstrate a direct sensitive approach to determine interactions between proteins and particle/surface coatings important to diverse biotechnology applications.

Adaptive insertion of a hydrophobic anchor into a poly(ethylene glycol) host for programmable surface functionalization

Covalent and non-covalent molecular binding are two strategies to tailor surface properties and functions. However, the lack of responsiveness and requirement for specific binding groups makes spatiotemporal control challenging. Here, we report the adaptive insertion of a hydrophobic anchor into a poly(ethylene glycol) (PEG) host as a non-covalent binding strategy for surface functionalization. By using polycyclic aromatic hydrocarbons as the hydrophobic anchor, hydrophilic charged and non-charged functional modules were spontaneously loaded onto PEG corona in 2 min without the assistance of any catalysts and binding groups. The thermodynamically favourable insertion of the hydrophobic anchor can be reversed by pulling the functional module, enabling programmable surface functionalization. We anticipate that the adaptive molecular recognition between the hydrophobic anchor and the PEG host will challenge the hydrophilic understanding of PEG and enhance the progress in nanomedicine, advanced materials and nanotechnology.

Sticktight-inspired PEGylation for low-fouling coatings

Polyethylene glycol (PEG) has been widely used for modifying surfaces to reduce non-specific interactions with biomolecules, microorganisms, and cells. Herein, we report a sticktight-inspired PEGylation strategy to fabricate low-fouling coatings. The influence of PEG molecular architectures on the PEG density and biological adhesion were studied. Notably, an increase in the number of arms resulted in improved surface PEGylation and an improved antifouling ability against the adhesion of proteins, mammalian cells and bacteria. The molecular architecture-dependent PEGylation strategy is an attractive approach for developing advanced low-fouling coatings.

New Nanofiber Composition for Multiscale Bubble Capture and Separation

Bubble dynamics inside a liquid medium and its interactions with hydrophobic and hydrophilic surfaces are crucial for many industrial processes. Electrospinning of polymers has emerged as a promising fabrication technique capable of producing a wide variety of hydrophobic and hydrophilic polymer nanofibers and membranes at a low cost. Thus, knowledge about the bubble interactions on electrospun hydrophobic and hydrophilic nanofibers can be utilized for capturing; separating; and transporting macro-, micro-, and nanobubbles. In this study, poly(methyl methacrylate) (PMMA) and PMMA-poly(ethylene glycol) (PEG) electrospun nanofibers were fabricated to investigate gas bubble interactions with submerged nanofiber mats. To improve their durability, the nanofibers were reinforced with a plastic mesh. The ultimate tensile strengths of PMMA and PMMA-30%PEG nanofibers were measured as 0.35 and 0.30 MPa, respectively. With the use of reinforcement mesh, the mechanical properties of final membranes could be improved by a factor of 70. The gas permeability of the electrospun and reinforced nanofibers was also studied using the high-speed visualization technique and a homemade setup to investigate the effect of electrospun nanofibers on the bubble coalescence and size in addition to the frequency of released bubbles from the nanofiber mat. The diffusion rate of air bubbles in hydrophobic PMMA electrospun nanofibers was measured as 10 L/s for each square meter of the nanofiber. However, the PMMA-30%PEG mat was able to restrict the diffusion of gas bubbles through its pores owing to the van der Waals force between the water molecules and nanofiber surface as well as the high stability of the thin water layer. It has been shown that the hydrophobic electrospun nanofibers can capture and coalesce the rising gas bubbles and release them with predictable size and frequency. Consequently, the diameter of bubbles introduced to the hydrophobic PMMA membrane ranged between 2 and 25 mm, whereas the diameter of bubbles released from the hydrophobic electrospun nanofibers was measured as 8 ± 1 mm. The proposed mechanism and fabricated electrospun nanofibers can enhance the efficiency of various systems such as heat exchangers, liquid-gas separation filters, and direct air capture (DAC) systems.

Precise heteroatom doping determines aqueous solubility and self-assembly behaviors for polycyclic aromatic skeletons

Developing effective strategies to improve the hydrophilicity or aqueous solubility of hydrophobic molecular scaffolds is meaningful for both academic research and industrial applications. Herein, we demonstrate that stepwise and precise N/O heteroatoms doping on a polycyclic aromatic skeleton can gradually alter these structures from hydrophobic to hydrophilic, even resulting in excellent aqueous solubility. The Hansen solubility parameters (HSP) method shows that the three partial solubility parameters are closely related to N/O doping species, numbers and positions on the molecular panel. The hydrogen bonding solubility parameter indicates that the hydrogen bonding interactions between N/O doped molecules and water play a key role in enhancing hydrophilicity. Moreover, three optimized water-soluble molecules underwent a self-assembly process to form stable nanoparticles in water, thus facilitating better hydrogen bonding interactions disclosed by HSP calculations, NMR and single crystal X-ray analysis. These ensembles even show quasi-solid properties in water from NMR and luminescence perspectives.

Infrared Spectra and Hydrogen-Bond Configurations of Water Molecules at the Interface of Water-Insoluble Polymers under Humidified Conditions

Elucidating the state of interfacial water, especially the hydrogen-bond configurations, is considered to be key for a better understanding of the functions of polymers that are exhibited in the presence of water. Here, an analysis in this direction is conducted for two water-insoluble biocompatible polymers, poly(2-methoxyethyl acrylate) and cyclic(poly(2-methoxyethyl acrylate)), and a non-biocompatible polymer, poly(n-butyl acrylate), by measuring their IR spectra under humidified conditions and by carrying out theoretical calculations on model complex systems. It is found that the OH stretching bands of water are decomposed into four components, and while the higher-frequency components (with peaks at ∼3610 and ∼3540 cm^-1) behave in parallel with the C═O and C-O-C stretching and CH deformation bands of the polymers, the lower-frequency components (with peaks at ∼3430 and ∼3260 cm^-1) become pronounced to a greater extent with increasing humidity. From the theoretical calculations, it is shown that the OH stretching frequency that is distributed from ∼3650 to ∼3200 cm^-1 is correlated to the hydrogen-bond configurations and is mainly controlled by the electric field that is sensed by the vibrating H atom. By combining these observed and calculated results, the configurations of water at the interface of the polymers are discussed.

Designing the Surface Chemistry of Inorganic Nanocrystals for Cancer Imaging and Therapy

Inorganic nanocrystals, such as gold, iron oxide and semiconductor quantum dots, offer promising prospects for cancer diagnostics, imaging and therapy, due to their specific plasmonic, magnetic or fluorescent properties. The organic coating, or surface ligands, of these nanoparticles ensures their colloidal stability in complex biological fluids and enables their functionalization with targeting functions. It also controls the interactions of the nanoparticle with biomolecules in their environment. It therefore plays a crucial role in determining nanoparticle biodistribution and, ultimately, the imaging or therapeutic efficiency. This review summarizes the various strategies used to develop optimal surface chemistries for the in vivo preclinical and clinical application of inorganic nanocrystals. It discusses the current understanding of the influence of the nanoparticle surface chemistry on its colloidal stability, interaction with proteins, biodistribution and tumor uptake, and the requirements to develop an optimal surface chemistry.

Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes

We have prepared a series of ampholytic polymer films, using a self-initiated photografting and photopolymerization (SI-PGP) method to sequentially polymerize first anionic (deuterated methacrylic acid (dMAA)) and thereafter cationic (2-aminoethyl methacrylate (AEMA)) monomers to investigate the SI-PGP grafting process. Dry films were investigated by ellipsometry, X-ray, and neutron reflectometry, and their swelling was followed over a pH range from 4.5 to 10.5 with spectroscopic ellipsometry. The deuterated monomer allows us to separate the distributions of the two components by neutron reflectometry. Growth of both polymers proceeds via grafting of solution-polymerized fragments to the surface, and also the second layer is primarily grafted to the substrate and not as a continuation of the existing chains. The polymer films are stratified, with one layer of near 1:1 composition and the other layer enriched in one component and located either above or below the former layer. The ellipsometry results show swelling transitions at low and high pH but with no systematic variation in the pH values where these transitions occur. The results suggest that grafting density in SI-PGP-prepared homopolymers could be increased via repeated polymerization steps, but that this process does not necessarily increase the average chain length.

siRNA nanohybrid systems: false hope or feasible answer in cancer management

Finding out predisposition and makeup alterations in cancer cells has prompted the exploration of exogenous small interference RNA (siRNA) as a therapeutic agent to deal with cancer. siRNA is subjected to many limitations that hinders its cellular uptake. Various nanocarriers have been loaded with siRNA to improve their cellular transportation and have moved to clinical trials. However, many restrictions as low encapsulation efficiency, nanocarrier cytotoxicity and premature release of siRNA have impeded the single nanocarrier use. The realm of nanohybrid systems has emerged to overcome these limitations and to synergize the criteria of two or more nanocarriers. Different nanohybrid systems that were developed as cellular pathfinders for the exogenous siRNA to target cancer will be illustrated in this review.

Using polyethylene glycol to facilitate the absorption of NO2 in sulfite solutions: Kinetics and mechanism

A new method was developed to scrub NO_x compounds in flue gases during the integrated technology of WFGD associated with ozone oxidation, among which polyethylene glycol (PEG) was utilized initially as an additive to facilitate the absorption of NO₂ by sulfite solution. Notably, absorption was significantly facilitated with adding PEG into absorbent. Compared to absorption by sulfite solution alone, NO₂ removal efficiency with PEG addition increased from 58.75% to 89.17%. Furthermore, the favorable role of PEG was considered to be ascribed to the its improvement on the rate-determining step among absorption process ── mass transfer of NO₂ into the liquid phase. A potential chemical transformation pathway between NO₂, SO₃^2- and PEG was proposed, and based on the hydrogen bonding between the various compounds. Additionally, a kinetic model was established based on various operating parameters that included adsorbent pH, ionic strength of S species, temperature, flow rate, and inlet SO₂ concentration. This model provides theoretical support for practical engineering.

Covalent Surface Modification of Ti3C2Tx MXene with Chemically Active Polymeric Ligands Producing Highly Conductive and Ordered Microstructure Films

As interest continues to grow in Ti₃C₂T_x and other related MXenes, advancement in methods of manipulation of their surface functional groups beyond synthesis-based surface terminations (T_x: -F, -OH, and ═O) can provide mechanisms to enhance solution processability as well as produce improved solid-state device architectures and coatings. Here, we report a chemically important surface modification approach in which "solvent-like" polymers, polyethylene glycol carboxylic acid (PEG6-COOH), are covalently attached onto MXenes via esterification chemistry. Surface modification of Ti₃C₂T_x with PEG6-COOH with large ligand loading (up to 14% by mass) greatly enhances dispersibility in a wide range of nonpolar organic solvents (e.g., 2.88 mg/mL in chloroform) without oxidation of Ti₃C₂T_x two-dimensional flakes or changes in the structure ordering. Furthermore, cooperative interactions between polymer chains improve the nanoscale assembly of uniform microstructures of stacked MXene-PEG6 flakes into ordered thin films with excellent electrical conductivity (∼16,200 S·cm^-1). Most importantly, our covalent surface modification approach with ω-functionalized PEG6 ligands (ω-PEG6-COOH, where ω: -NH₂, -N₃, -CH═CH₂) allows for control over the degree of functionalization (incorporation of valency) of MXene. We believe that installing valency onto MXenes through short, ion conducting PEG ligands without compromising MXenes' features such as solution processability, structural stability, and electrical conductivity further enhance MXenes surface chemistry tunability and performance and widens their applications.

Through-Space Interactions in Clusteroluminescence

Conventional π-conjugated luminophores suffer from problems such as emission quenching, biotoxicity, environmental pollution, etc. The emerging nonconjugated and nonaromatic clusteroluminogens (CLgens) are expected to overcome these stubborn drawbacks, so research of CLgens shows great significance not only for practical application but also for the construction of fundamental photophysical theories. This perspective summarizes the unusual features of CLgens in comparison to traditional chromophores, such as nonconjugated molecular structures, unmatched absorption and excitation, excitation-dependent luminescence, multiple emission peaks, and room-temperature phosphorescence. Different from the theory of through-bond conjugation in π-conjugated luminophores, through-space interactions, including through-space n···n interaction and through-space n···π interaction, are regarded as the emitting sources of nonconjugated CLgens. In addition, the formation of network clusters is proposed as an efficient strategy to improve the performance of CLgens, and their potential applications of anticounterfeiting, photoelectronic devices, and bioimaging are prospected.

Hydrogen-Bonded Structure of Water in the Loop of Anchored Polyrotaxane Chain Controlled by Anchoring Density

Hydrogen-bonded network of water surrounding polymers is expected to be one of the most relevant factors affecting biocompatibility, while the specific hydrogen-bonded structure of water responsible for biocompatibility is still under debate. Here we study the hydrogen-bonded structure of water in a loop-shaped poly(ethylene glycol) chain in a polyrotaxane using synchrotron soft X-ray emission spectroscopy. By changing the density of anchoring molecules, hydrogen-bonded structure of water confined in the poly(ethylene glycol) loop was identified. The XES profile of the confined water indicates the absence of the low energy lone-pair peak, probably because the limited space of the polymer loop entropically inhibits the formation of tetrahedrally coordinated water. The volume of the confined water can be changed by the anchoring density, which implies the ability to control the biocompatibility of loop-shaped polymers.

Evidence for European presence in the Americas in AD 1021

Transatlantic exploration took place centuries before the crossing of Columbus. Physical evidence for early European presence in the Americas can be found in Newfoundland, Canada^1,2. However, it has thus far not been possible to determine when this activity took place^3-5. Here we provide evidence that the Vikings were present in Newfoundland in AD 1021. We overcome the imprecision of previous age estimates by making use of the cosmic-ray-induced upsurge in atmospheric radiocarbon concentrations in AD 993 (ref. ⁶). Our new date lays down a marker for European cognisance of the Americas, and represents the first known point at which humans encircled the globe. It also provides a definitive tie point for future research into the initial consequences of transatlantic activity, such as the transference of knowledge, and the potential exchange of genetic information, biota and pathologies^7,8.

Anomeric effect, hyperconjugation and electrostatics: lessons from complexity in a classic stereoelectronic phenomenon

Understanding the interplay of multiple components (steric, electrostatic, stereoelectronic, dispersive, etc.) that define the overall energy, structure, and reactivity of organic molecules can be a daunting task. The task becomes even more difficult when multiple approaches based on different physical premises disagree in their analysis of a multicomponent molecular system. Herein, we will use a classic conformational "oddity", the anomeric effect, to discuss the value of identifying the key contributors to reactivity that can guide chemical predictions. After providing the background related to the relevant types of hyperconjugation and a brief historic outline of the origins of the anomeric effect, we outline variations of its patterns and provide illustrative examples for the role of the anomeric effect in structure, stability, and spectroscopic properties. We show that the complete hyperconjugative model remains superior in explaining the interplay between structure and reactivity. We will use recent controversies regarding the origin of the anomeric effect to start a deeper discussion relevant to any electronic effect. Why are such questions inherently controversial? How to describe a complex quantum system using a model that is "as simple as possible, but no simpler"? What is a fair test for such a model? Perhaps, instead of asking "who is right and who is wrong?" one should ask "why do we disagree?". Stereoelectronic thinking can reconcile quantum complexity with chemical intuition and build the conceptual bridge between structure and reactivity. Even when many factors contribute to the observed structural and conformational trends, electron delocalization is a dominating force when the electronic demand is high (i.e., bonds are breaking as molecules distort from their equilibrium geometries). In these situations, the role of orbital interactions increases to the extent where they can define reactivity. For example, negative hyperconjugation can unleash the "underutilized" stereoelectronic power of unshared electrons (i.e., the lone pairs) to stabilize a developing positive charge at an anomeric carbon. This analysis paves the way for the broader discussion of the omnipresent importance of negative hyperconjugation in oxygen-containing functional groups. From that point of view, the stereoelectronic component of the anomeric effect plays a unique role in guiding reaction design.

Structure and Dynamics of a Temperature-Sensitive Hydrogel

Polyisocyanotripeptides (TriPIC) are biomimetic polymers which consist of a β-helical backbone stabilized by hydrogen bonds between amide groups. Their oligoethylene glycol side chains give aqueous TriPIC solutions a thermoresponsive behavior: at 50 °C the solution becomes a hydrogel. In this paper we study the molecular structure and water dynamics of TriPIC aqueous solutions while undergoing gelation using FT-IR spectroscopy and polarization-resolved femtosecond infrared spectroscopy (fs-IR). We find evidence that the oligoethylene glycol side chains trap part of the water molecules upon gel formation, and we propose that the interaction between the oligoethylene glycol side chains and water plays an essential role in the bundling of the polymers and thus in the formation of a hydrogel.

Enhancing the Sensitivity of DNA and Aptamer Probes in the Dextran/PEG Aqueous Two-Phase System

Increasing the local concentration of DNA-based probes is a convenient way to improve the sensitivity of biosensors. Instead of using organic solvents or ionic liquids that phase-separate with water based on hydrophobic interactions, we herein studied a classic aqueous two-phase system (ATPS) comprising polyethylene glycol (PEG) and dextran. Polymers of higher molecular weights and higher concentrations favored phase separation. DNA oligonucleotides are selectively enriched in the dextran-rich phase unless the pH was increased to 12. A higher volume ratio of PEG-to-dextran and a higher concentration of PEG also enrich more DNA probes in the dextran-rich phase. The partition efficiency of the T₁₅ DNA was enriched around seven times in the dextran phase when the volume ratio of dextran and PEG reached 1:10. The detection of limit improved by 3.6-fold in a molecular beacon-based DNA detection system with the ATPS. The ATPS also increased the sensitivity for the detection of Hg²⁺ and adenosine triphosphate, although these target molecules alone distributed equally in the two phases. This work demonstrates a simple method using water soluble polymers to improve biosensors.

Effects of solvation shell relaxation on chain association mechanisms in poly(3-hexylthiophene) solutions

Using poly(3-hexylthiophene) (P3HT) as a model conjugated polymer and atomistic molecular dynamics simulations with carefully verified force fields, we performed in-depth investigations of solvation shell properties of P3HT chains (15 repeating units per chain) in two representative groups of non-polar (or aprotic) organic solvents (better solvents: ortho-dichlorobenzene, bromobenzene, and chlorobenzene; poorer solvents: chloroform, para-xylene, and toluene). We demonstrated that solvation shell relaxation properties in P3HT solutions dictate the formation of regular π-π associations and, hence, crystallinity through the initial chain association and subsequent chain sliding. In contrast, the mean features of polymer-solvent interactions, including solvation free energy and radial distribution function, present little or no difference for all solvent media investigated. Better-solvent media were revealed to bear relatively large values of the first solvation shell relaxation time (τ1 ≫ 100 ps) as well as larger ratios of relaxation times for the first two solvation shells (τ1/τ2 > 2), and vice versa for poorer-solvent media (τ1 ≪ 100 ps and τ1/τ2 < 2). The linear hexyl side-chain unit was noted to substantially enlarge both quantities while notably reducing the solvation free energy as well. As discussed herein, these findings shed new light on the mechanistic features by which solvent quality impacts the degree of π-π association crucial for modern applications with crystalline conjugated polymers.

Molecular, Solid-State and Surface Structures of the Conformational Polymorphic Forms of Ritonavir in Relation to their Physicochemical Properties

Purpose

Application of multi-scale modelling workflows to characterise polymorphism in ritonavir with regard to its stability, bioavailability and processing.

Methods

Molecular conformation, polarizability and stability are examined using quantum mechanics (QM). Intermolecular synthons, hydrogen bonding, crystal morphology and surface chemistry are modelled using empirical force fields.

Results

The form I conformation is more stable and polarized with more efficient intermolecular packing, lower void space and higher density, however its shielded hydroxyl is only a hydrogen bond donor. In contrast, the hydroxyl in the more open but less stable and polarized form II conformation is both a donor and acceptor resulting in stronger hydrogen bonding and a more stable crystal structure but one that is less dense. Both forms have strong 1D networks of hydrogen bonds and the differences in packing energies are partially offset in form II by its conformational deformation energy difference with respect to form I. The lattice energies converge at shorter distances for form I, consistent with its preferential crystallization at high supersaturation. Both forms exhibit a needle/lath-like crystal habit with slower growing hydrophobic side and faster growing hydrophilic capping habit faces with aspect ratios increasing from polar-protic, polar-aprotic and non-polar solvents, respectively. Surface energies are higher for form II than form I and increase with solvent polarity. The higher deformation, lattice and surface energies of form II are consistent with its lower solubility and hence bioavailability.

Conclusion

Inter-relationship between molecular, solid-state and surface structures of the polymorphic forms of ritonavir are quantified in relation to their physical-chemical properties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-021-03048-2.

Valorisation of plastic waste via metal-catalysed depolymerisation

Metal-catalysed depolymerisation of plastics to reusable building blocks, including monomers, oligomers or added-value chemicals, is an attractive tool for the recycling and valorisation of these materials. The present manuscript shortly reviews the most significant contributions that appeared in the field within the period January 2010–January 2020 describing selective depolymerisation methods of plastics. Achievements are broken down according to the plastic material, namely polyolefins, polyesters, polycarbonates and polyamides. The focus is on recent advancements targeting sustainable and environmentally friendly processes. Biocatalytic or unselective processes, acid–base treatments as well as the production of fuels are not discussed, nor are the methods for the further upgrade of the depolymerisation products.

Alternative view of oxygen reduction on porous carbon electrocatalysts: the substance of complex oxygen-surface interactions

Electrochemical oxygen reduction reaction (ORR) is an important energy-related process requiring alternative catalysts to expensive platinum-based ones. Although recently some advancements in carbon catalysts have been reported, there is still a lack of understanding which surface features might enhance their efficiency for ORR. Through a detailed study of oxygen adsorption on carbon molecular sieves and using inelastic neutron scattering, we demonstrated here that the extent of oxygen adsorption/interactions with surface is an important parameter affecting ORR. It was found that both the strength of O₂ physical adsorption in small pores and its specific interactions with surface ether functionalities in the proximity of pores positively influence the ORR efficiency. We have shown that ultramicropores and hydrophobic surface rich in ether-based groups and/or electrons enhance ORR on carbon electrocatalysts and the performance parameters are similar to those measured on Pt/C with the number of electron transfer equal to 4.

A minireview on the perturbation effects of polar groups to direct nanoscale hydrophobic interaction and amphiphilic peptide assembly

Hydrophobic interaction provides the essential driving force for creating diverse native and artificial supramolecular architectures. Accumulating evidence leads to a hypothesis that the hydrophobicity of a nonpolar patch of a molecule is non-additive and susceptible to the chemical context of a judicious polar patch. However, the quantification of the hydrophobic interaction at the nanoscale remains a central challenge to validate the hypothesis. In this review, we aim to outline the recent efforts made to determine the hydrophobic interaction at a nanoscopic length scale. The advances achieved in the understanding of proximal polar groups perturbing the magnitude of hydrophobic interaction generated by the nonpolar patch are introduced. We will also discuss the influence of chemical heterogeneity on the modulation of amphiphilic peptide/protein assembly and molecular recognition.

Hydrophobic interaction provides the essential driving force for creating diverse native and artificial supramolecular architectures.

Selenium-containing heterodimeric crown ether acting as an unconventional multi-responsive amphiphile in water

A new heterodimeric crown amphiphile was fabricated, wherein the oxacrown and selencrown ethers provided the desired molecular framework for hydrophilicity and hydrophobicity, respectively. From an integrated perspective, the developed amphiphile possesses features of crown ethers, amines, and selenium-containing species, and its assembly in water can be responsive to diverse chemical effectors-H2O2 and CO2 in a switchable ON/OFF mode to achieve controlled release. It is the first case wherein the applications of cyclic polyethers with different solubilities drives the self-assembly in an aqueous medium.

A Critical Review of the Physicochemical Properties of Lignosulfonates: Chemical Structure and Behavior in Aqueous Solution, at Surfaces and Interfaces

Lignosulfonates are bio-based surfactants and specialty chemicals, which are generated by breaking the near-infinite lignin network during sulfite pulping of wood. Due to their amphiphilic nature, lignosulfonates are used in manifold applications such as plasticizer, dispersant, and stabilizer formulations. Function and performance are determined by their behavior in aqueous solution and at surfaces and interfaces, which is in turn imposed by the chemical make-up. This review hence summarizes the efforts made into delineating the physicochemical properties of lignosulfonates, while also relating to their composition and structure. Lignosulfonates are randomly branched polyelectrolytes with abundant sulfonate and carboxylic acid groups to ensure water-solubility. In aqueous solution, their conformation, colloidal state, and adsorption at surfaces or interfaces can be affected by a range of parameters, such as pH, concentration of other electrolytes, temperature, and the presence of organic solvents. These parameters may also affect the adsorption behavior, which reportedly follows Langmuir isotherm and pseudo second-order kinetics. The relative hydrophobicity, as determined by hydrophobic interaction chromatography, is an indicator that can help to relate composition and behavior of lignosulfonates. More hydrophobic materials have been found to exhibit a lower charge density. This may improve dispersion stabilization, but it can also be disadvantageous if an electrokinetic charge needs to be introduced at solid surfaces or if precipitation due to salting out is an issue. In addition, the monolignol composition, molecular weight distribution, and chemical modification may affect the physicochemical behavior of lignosulfonates. In conclusion, the properties of lignosulfonates can be tailored by controlling aspects such as the production parameters, fractionation, and by subsequent modification. Recent developments have spawned a magnitude of products and technologies, which is also reflected in the wide variety of possible application areas.