Wavelength-Dependent Activation of Photoacids and Bases.

Photoacids and bases allow remote control over pH in reaction solutions, which is of fundamental importance to an array of applications. Herein, we determine the wavelength-by-wavelength resolved photoreactivity of triarylsulfonium hexafluorophosphate salts as a representative photoacid generator and p-(benzoyl)benzyl triethylammonium tetraphenylborate as a photobase generator, constructing a wavelength-resolved photochemical action plot for each of the compounds. We monitor the pH change of the solution on-line within the cavity of the laser vial and demonstrate a marked mismatch between the absorption spectrum of the photoacid and base with the photochemical action plot, unveiling reactivity at very low absorptivities. Our findings are of critical importance for the use of photoacids and bases, unambiguously demonstrating that absorption is no guide to chemical reactivity with critical consequences for the wavelength employed in applications of photoacids and bases.

Design of Organic Cathode Material Based on Quinone and Pyrazine Motifs for Rechargeable Lithium and Zinc Batteries.

Despite the rapid expansion of the organic cathode materials field, we still face a shortage of materials obtained through simple synthesis that have stable cycling and high energy density. Herein, we report a two-step synthesis of a small organic molecule from commercially available precursors that can be used as a cathode material. Oxidized tetraquinoxalinecatechol (OTQC) was derived from tetraquinoxalinecatechol (TQC) by the introduction of additional quinone redox-active centers into the structure. The modification increased the voltage and capacity of the material. The OTQC delivers a high specific capacity of 327 mAh g-1 with an average voltage of 2.63 V vs Li/Li+ in the Li-ion battery. That corresponds to an energy density of 860 Wh kg-1 on the OTQC material level. Furthermore, the material demonstrated excellent cycling stability, having a capacity retention of 82% after 400 cycles. Similarly, the OTQC demonstrates increased average voltage and specific capacity in comparison with TQC in aqueous Zn-organic battery, reaching the specific capacity of 326 mAh g-1 with an average voltage of 0.86 V vs Zn/Zn2+. Apart from good electrochemical performance, this work provides an additional in-depth analysis of the redox mechanism and degradation mechanism related to capacity fading.

Dynamic Properties of Di(cyclopentadienecarboxylic Acid) Dimethyl Esters.

Di(cyclopentadienecarboxylic acid) dimethyl ester (DCPDME) is a potential dynamic covalent system. When such molecules are used as dynamic crosslinkers in polymers, understanding the reversibility of cyclopentadiene dimerization is crucial to determine optimal melt processing conditions. To this end, we synthesized DCPDME, which consists of three regioisomers with different physicochemical properties, which were investigated by isolating them and further characterizing them using 1H NMR, FTIR and DSC. There have been many attempts to improve the synthesis process to increase the reaction yield and purity of isomer 3, and this goal remains a challenge today. In this work, we show that pure isomers 1 and 2 irreversibly convert to the more stable DCPDME isomer 3 at temperatures between 120 and 140 °C in N2. This shows that isolation of the pure isomer 3 from the DCPDME isomer mixture is not necessary. The DCPDME isomer 3 is reversibly cleaved to the monomeric cyclopentadienecarboxylic acid methyl ester (CPME), as confirmed with GC-MS and the resulting mass spectrum. The conversion of DCPDME isomers 1 and 2 to isomer 3 was confirmed by heating the synthesized mixture of DCPDME isomers at 135 °C for 5 min in N2, producing an almost pure isomer 3 which increased its synthesis yield by 35%.

Chemical Recycling of Flexible Polyurethane Foams by Aminolysis to Recover High-Quality Polyols.

Polyurethane foams (PUFs) are widely used commodity materials, but most of them end up in landfills at the end of their life, which is not in line with the circular economy approach. Here, we introduce microwave-assisted aminolysis with amine reagents that contain primary and tertiary amino groups in the structure. These reagents enable complete degradation of the urethane groups in the structure of the flexible PUFs with a much lower amount of degradation reagent than is typically required for solvolysis reactions. The purified, recovered polyols are close equivalents to the corresponding virgin polyols in terms of their structural and molar mass characteristics. Therefore, they can be used for the production of high-quality PUFs without having to adapt the synthesis process. The flexible PUFs made from recovered polyols have comparable mechanical properties to those made from virgin polyols.

Determination of End-Group Functionality of Propylene Oxide-Based Polyether Polyols Recovered from Polyurethane Foams by Chemical Recycling.

Chemical recycling of polyurethane foams (PUFs) leads to partially aromatic, amino-functionalized polyol chains when the urethane groups in the PUF structure are incompletely degraded. Since the reactivity of amino and hydroxyl groups with isocyanate groups is significantly different, information on the type of the end-group functionality of recycled polyols is important to adjust the catalyst system accordingly to produce PUFs from recycled polyols of suitable quality. Therefore, we present here a liquid adsorption chromatography (LAC) method using a SHARC 1 column that separates polyol chains according to their end-group functionality based on their ability to form hydrogen bonds with the stationary phase. To correlate end-group functionality of recycled polyol with chain size, LAC was coupled with size-exclusion chromatography (SEC) to form a two-dimensional liquid chromatography system. For accurate identification of peaks in LAC chromatograms, the results were correlated with those obtained by characterization of recycled polyols using nuclear magnetic resonance, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and SEC coupled with a multi-detection system. The developed method allows the quantification of fully hydroxyl-functionalized chains in recycled polyols using an evaporative light scattering detector and appropriate calibration curve.

Tuning the Properties of Ester-Based Degradable Polymers by Inserting Epoxides into Poly(ϵ-caprolactone).

A series of ester-ether copolymers were obtained via the reaction between α,ω-dihydroxyl poly(ϵ-caprolactone) (PCL) and ethylene oxide (EO) or monosubstituted epoxides catalyzed by strong phosphazene bases. The two types of monomeric units were distributed in highly random manners due to the concurrence of epoxide ring-opening and fast transesterification reactions. The substituent of epoxide showed an interesting bidirectional effect on the enzymatic degradability of the copolymer. Compared with PCL, copolymers derived from EO exhibited enhanced hydrophilicity and decreased crystallinity which then resulted in higher degradability. For the copolymers derived from propylene oxide and 1,2-butylene oxide, the hydrophobic alkyl pendant groups also allowed lower crystallinity of the copolymers thus higher degradation rates. However, further enlarging the pendant groups by using styrene oxide or 2-ethylhexyl glycidyl ether caused a decrease in the degradation rate, which might be ascribed to the higher bulkiness hindering the contact of ester groups with lipase.

Water as a monomer: synthesis of an aliphatic polyethersulfone from divinyl sulfone and water.

Using water as a monomer in polymerization reactions presents a unique and exquisite strategy towards more sustainable chemistry. Herein, the feasibility thereof is demonstrated by the introduction of the oxa-Michael polyaddition of water and divinyl sulfone. Upon nucleophilic or base catalysis, the corresponding aliphatic polyethersulfone is obtained in an interfacial polymerization at room temperature in high yield (>97%) within an hour. The polyethersulfone is characterized by relatively high molar mass averages and a dispersity around 2.5. The polymer was tested as a solid polymer electrolyte with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the salt. Free-standing amorphous membranes were prepared by a melt process in a solvent-free manner. The polymer electrolyte containing 15 wt% LiTFSI featured an oxidative stability of up to 5.5 V vs. Li/Li+ at 45 °C and a conductivity of 1.45 × 10-8 S cm-1 at room temperature.

Influence of Microstructure on the Elution Behavior of Gradient Copolymers in Different Modes of Liquid Interaction Chromatography.

We studied the influence of microstructure on the chromatographic behavior of gradient copolymers with different gradient strengths and block copolymer with completely segregated blocks by using gradient liquid adsorption chromatography (gLAC) and liquid chromatography at critical conditions (LCCC) for one of the copolymer constituents. The copolymers consist of repeating units of poly(propylene oxide) and poly(propylene phthalate) and have comparable average chemical composition and molar mass, and a narrow molar mass distribution to avoid as much as possible the influence of these parameters on the elution behavior of the copolymers. On both reversed stationary phases, the elution volume of gradient copolymers increases with the increasing strength of the gradient. The results indicate that for both modes of liquid interaction chromatography, it is important to consider the effect of microstructure on the elution behavior of the gradient copolymers in addition to the copolymer chemical composition and molar mass in the case of gLAC and the length of the chromatographically visible copolymer constituent in the case of LCCC.

Insight into Chemical Recycling of Flexible Polyurethane Foams by Acidolysis.

Acidolysis is emerging as a promising method for recycling polyurethane foam (PUF) waste. Here, we present highly efficient acidolysis of PUFs with adipic acid (AA) by heating the reaction mixtures with microwaves. The influence of experimental conditions, such as reaction temperature, time, and amount of the degradation reagent, on the polyol functionality, molecular weight characteristics, the presence of side products, and the degree of degradation of the remaining PUF hard segments was studied by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS), nuclear magnetic resonance (NMR), size-exclusion chromatography (SEC) coupled to a multidetection system, and Fourier transform infrared (FT-IR) spectroscopy. The purified recycled polyols were used for the synthesis of flexible PUFs. The morphology and mechanical properties of the PUFs show that the degree of functionalization of the polyol by the carboxylic end groups, which is higher for larger amounts of AA used to degrade the PUFs, significantly affects the quality and performance of the flexible PUFs from the recycled polyols.

Designed folding pathway of modular coiled-coil-based proteins.

Natural proteins are characterised by a complex folding pathway defined uniquely for each fold. Designed coiled-coil protein origami (CCPO) cages are distinct from natural compact proteins, since their fold is prescribed by discrete long-range interactions between orthogonal pairwise-interacting coiled-coil (CC) modules within a single polypeptide chain. Here, we demonstrate that CCPO proteins fold in a stepwise sequential pathway. Molecular dynamics simulations and stopped-flow Förster resonance energy transfer (FRET) measurements reveal that CCPO folding is dominated by the effective intra-chain distance between CC modules in the primary sequence and subsequent folding intermediates, allowing identical CC modules to be employed for multiple cage edges and thus relaxing CCPO cage design requirements. The number of orthogonal modules required for constructing a CCPO tetrahedron can be reduced from six to as little as three different CC modules. The stepwise modular nature of the folding pathway offers insights into the folding of tandem repeat proteins and can be exploited for the design of modular protein structures based on a given set of orthogonal modules.

Noncovalent Protection for Direct Synthesis of α-Amino-ω-hydroxyl Poly(ethylene oxide).

The synthesis of poly(ethylene oxide) (PEO) with amino end group, a key functionality for PEGylation, is a long-standing challenge. Multistep routes based on postmodification or covalent protection have been adopted to circumvent ethoxylation of the amino group by ethylene oxide (EO). Here, we report a noncovalent protection strategy for one-step synthesis of PEO amine. An amino (di)alcohol is mixed with a small amount of mild phosphazene base and excess triethylborane (Et3B) before addition of EO. The complexation of the amino group with Et3B guarantees that polymerization of EO occurs selectively from the hydroxyl group through the bicomponent metal-free catalysis. Simply by precipitation in diethyl ether, the protective Et3B as well as the catalyst can be removed to afford α-amino-ω-hydroxyl PEO with controlled molar mass, low dispersity, and complete end functionality. The effect of initiator structure and retention of Et3B on the storage (oxidative) stability of PEO amine is also revealed.

Chemical Recycling of Aliphatic Polyamides by Microwave-Assisted Hydrolysis for Efficient Monomer Recovery.

We report on a simple and efficient chemical recycling process for aliphatic polyamides (PA 66, PA 1010, PA 11, and PA 12), whereby PAs are converted exclusively into their constituent monomers even in the presence of reinforcement additives, such as carbon- and glass-fibers. In this process, the rate of PA hydrolysis reaction, performed under microwave irradiation in the presence of HCl as an acid catalyst, depends on the PA type, the HCl/amide mole ratio, and the type and amount of reinforcement additives. PA 66 is completely converted into the constituent monomers at 200 °C and a 1.25 HCl/amide mole ratio in 10 min. Long-chain PAs (PA 11, PA 12, and PA 1010) and PAs containing glass- or carbon-fiber reinforcement additives need at the same experimental conditions longer reaction times. Alternatively, they can be completely hydrolyzed at 200 °C within a comparable reaction time at a higher HCl/amide mole ratio of 2.5. Complete and straightforward conversion of PAs into the constituent monomers in the absence of side reactions simplifies the isolation and purification of monomers and reinforcement additives, which have been recovered in high yields and quality comparable to those of commercially available chemicals.

Porous Polystyrene Monoliths Prepared from in Situ Simultaneous Interpenetrating Polymer Networks: Modulation of Morphology by Polymerization Kinetics.

Semi-interpenetrating polymer networks (semi-IPNs) were prepared by in situ simultaneous orthogonal polymerizations, where the linear poly(ε-caprolactone) (PCL) was synthesized by ring-opening polymerization of ε-caprolactone and the poly(styrene-co-divinylbenzene) (PS) network was formed by free-radical polymerization of styrene/divinylbenzene. Semi-IPNs were used as the precursors for the preparation of porous PS monoliths. To this end, the PCL domains were selectively removed by hydrolysis under basic conditions. By changing the amount of organocatalyst used for the ring-opening polymerization of ε-caprolactone, the relative polymerization kinetics of both monomers was varied, which has a pronounced effect on the morphology of thus-obtained PS frameworks.

Structural basis for the multitasking nature of the potato virus Y coat protein.

Potato virus Y (PVY) is among the most economically important plant pathogens. Using cryoelectron microscopy, we determined the near-atomic structure of PVY's flexuous virions, revealing a previously unknown lumenal interplay between extended carboxyl-terminal regions of the coat protein units and viral RNA. RNA-coat protein interactions are crucial for the helical configuration and stability of the virion, as revealed by the unique near-atomic structure of RNA-free virus-like particles. The structures offer the first evidence for plasticity of the coat protein's amino- and carboxyl-terminal regions. Together with mutational analysis and in planta experiments, we show their crucial role in PVY infectivity and explain the ability of the coat protein to perform multiple biological tasks. Moreover, the high modularity of PVY virus-like particles suggests their potential as a new molecular scaffold for nanobiotechnological applications.

Chemoselective Polymerization of Epoxides from Carboxylic Acids: Direct Access to Esterified Polyethers and Biodegradable Polyurethanes.

Carboxylic-acid-initiated ring-opening polymerization (ROP) of epoxides is a fast approach to esterified polyethers which are cleavable at the termini or centers. A major challenge lies in conventional ROP methods because of the lability of ester groups formed in the initiation step. Here, we describe chemoselective ROP of epoxides from aliphatic, aromatic, and methacrylic carboxylic acids using two-component metal-free catalysts. Transesterification is clearly absent so that well-defined α-(carboxylic ester)-ω-hydroxy polyethers are generated in one step from monocarboxylic acids. The livingness of the ROP is verified despite the slow initiation mode. The ester end group can be readily cleaved from the polyether hydrolytically. An α,ω-dihydroxy poly(propylene oxide) with two central ester groups is generated from a diacid initiator and transformed in situ by the same catalyst to polyurethane which shows distinct enzymatic degradability. This study provides convenient access to α,ω-heterobifunctional polyethers with cleavable, releasable, or modifiable end groups and to biodegradable polyether-based materials.

Nanocomposites comprised of homogeneously dispersed magnetic iron-oxide nanoparticles and poly(methyl methacrylate).

Nanocomposites with a high, uniform loading of magnetic nanoparticles are very desirable for applications such as electromagnetic shielding and cancer treatment based on magnetically induced hyperthermia. In this study, a simple and scalable route for preparing nanocomposites with a high, uniform loading of magnetic nanoparticles is presented. The magnetic iron-oxide nanoparticles were functionalized with a methacrylate-based monomer that copolymerized in a toluene solution with the methyl methacrylate (MMA) monomer. The resulting suspension of magnetic nanoparticles decorated with poly(methyl methacrylate) (PMMA) chains in toluene were colloidal, even in the presence of a magnetic field gradient. Nanocomposites were precipitated from these suspensions. The transmission electron microscopy investigation of the prepared nanocomposites revealed that the magnetic nanoparticles were homogeneously dispersed in the PMMA matrix, even in amounts up to 53 wt %. The uniform dispersion of the nanoparticles in the PMMA matrix was attributed to the good solvation of the grafted PMMA chains from the magnetic nanoparticles by the PMMA chains of the matrix. The nanocomposites were superparamagnetic and exhibited large values for the saturation magnetization of up to 36 emu/g. Moreover, the nanocomposite with the largest amount of incorporated nanoparticles exhibited relatively large values for the specific power loss when subjected to alternating magnetic fields, giving this material great potential for the magnetically induced hyperthermia-based treatment of cancer.

Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins.

Necrosis and ethylene-inducing peptide 1-like (NLP) proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. Many NLPs are cytotoxins that facilitate microbial infection of eudicot, but not of monocot plants. Here, we report glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors. Plant mutants with altered GIPC composition were more resistant to NLP toxins. Binding studies and x-ray crystallography showed that NLPs form complexes with terminal monomeric hexose moieties of GIPCs that result in conformational changes within the toxin. Insensitivity to NLP cytolysins of monocot plants may be explained by the length of the GIPC head group and the architecture of the NLP sugar-binding site. We unveil early steps in NLP cytolysin action that determine plant clade-specific toxin selectivity.

Pitfalls in Size Characterization of Soft Particles by Dynamic Light Scattering Online Coupled to Asymmetrical Flow Field-Flow Fractionation.

An asymmetrical flow field-flow fractionation (AF4) technique coupled to a multiangle light scattering (MALS) detector with an embedded dynamic light scattering (DLS) module was introduced to study the size characteristics and shape of soft particles of various size and type: polystyrene nanosphere size standards, lipid droplets (LDs), and large unilamellar vesicles (LUVs). A range of flow velocities through the LS detector, at which accurate hydrodynamic size can be extracted from the DLS in flow mode, was studied since the particles subjected to a longitudinal flow exhibit not only the Brownian motion due to diffusion but also the translational movement. In addition, the impact of the longitudinal flow velocity on the shape of the artificial LUV of two different sizes and two different compositions was studied by MALS. For comparison, the conventional batch DLS and static light scattering (SLS) experiments without prior sample separation by size were performed. From a combination of batch and flow light scattering results, we concluded that the passage flow velocities at the detector used in this study, 0.2, 0.5, and 1 mL/min, have no significant impact on the shape of spherical vesicles; however, the flow DLS experiments give accurate hydrodynamic radius (Rh) only at the lowest investigated passage flow rate at the detector (0.2 mL/min). With increasing rate of passage flow at the DLS detector, the error in the accuracy of the Rh determination rapidly increases. The error in Rh depends solely on the detector flow rate and particle size but not on the type of the soft particle.

Ring-Opening Polymerization of N-Carboxyanhydrides Initiated by a Hydroxyl Group.

We report on a method for preparation of well-defined synthetic polypeptides by ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCA) initiated by a hydroxyl group. To overcome the issue of slow initiation by hydroxyl group, an acid catalyst was used in the initiation step to catalyze opening of the NCA ring by the hydroxyl group and to simultaneously suppress further chain propagation by protonation of the formed amine group. In this way, we have separated slow initiation from the fast chain propagation, since such a combination leads to poorly defined products, and instead performed them in a successive manner. Only after completion of the initiation, the propagation was started by the addition of a base to deprotonate the ammonium group. This method was successfully applied for the synthesis of homopolypeptides by using alcohol as an initiator as well as polypeptide-based block copolymers by using poly(ethylene glycol) or poly(styrene) macroinitiator terminated with the hydroxyl group. This approach not only expands the pool of possible initiators, but also significantly facilities the preparation of polypeptide-based hybrid polymers.

Size fractionation and size characterization of nanoemulsions of lipid droplets and large unilamellar lipid vesicles by asymmetric-flow field-flow fractionation/multi-angle light scattering and dynamic light scattering.

Asymmetric-flow field-flow fractionation technique coupled to a multi-angle light-scattering detector (AF4-MALS) was used together with dynamic light-scattering (DLS) in batch mode and transmission electron microscopy (TEM) to study the size characteristics of the trioleoylglycerol lipid droplets covered by a monolayer of sphingomyelin and cholesterol, in water phase. These lipid droplet nanoemulsions (LD) were formed by ultrasonication. In parallel, the size characteristics of large unilamellar lipid vesicles (LUV) prepared by extrusion and composed of sphingomyelin and cholesterol were determined. LD and LUV were prepared at two different molar ratios (1/1, 4/1) of sphingomyelin and cholesterol. In AF4-MALS, various cross-flow conditions and mobile phase compositions were tested to optimize the separation of LD or LUV particles. The particle radii, R, as well as the root-mean-square radii, Rrms, of LD and LUV were determined by AF4-MALS, whereas the hydrodynamic radii, Rh, were obtained by DLS. TEM visualization revealed round shape particles of LD and LUV.