Upcycling Polyolefin Blends into High-Performance Materials by Exploiting Azidotriazine Chemistry Using Reactive Extrusion

The revalorization of incompatible polymer blends is a key obstacle in realizing a circular economy in the plastics industry. Polyolefin waste is particularly challenging because it is difficult to sort into its constituent components. Untreated blends of polyethylene and polypropylene typically exhibit poor mechanical properties that are suitable only for low-value applications. Herein, we disclose a simple azidotriazine-based grafting agent that enables polyolefin blends to be directly upcycled into high-performance materials by using reactive extrusion at industrially relevant processing temperatures. Based on a series of model experiments, the azidotriazine thermally decomposes to form a triplet nitrene species, which subsequently undergoes a complex mixture of grafting, oligomerization, and cross-linking reactions; strikingly, the oligomerization and cross-linking reactions proceed through the formation of nitrogen-nitrogen bonds. When applied to polyolefin blends during reactive extrusion, this combination of reactions leads to the generation of amorphous, phase-separated nanostructures that tend to exist at polymer-polymer interfaces. These nanostructures act as multivalent cross-linkers that reinforce the resulting material, leading to dramatically improved ductility compared with the untreated blends, along with high dimensional stability at high temperatures and excellent mechanical recyclability. We propose that this unique behavior is derived from the thermomechanically activated reversibility of the nitrogen-nitrogen bonds that make up the cross-linking structures. Finally, the scope of this chemistry is demonstrated by applying it to ternary polyolefin blends as well as postconsumer polyolefin feedstocks.

Synthesis of Benzo[c][2,7]naphthyridinones and Benzo[c][2,6]naphthyridinones via Ruthenium-Catalyzed [2+2+2] Cycloaddition between 1,7-Diynes and Cyanamides

A convenient method for the ruthenium-catalyzed synthesis of benzo[c]naphthyridinone derivatives is reported. The [2+2+2] cycloaddition from various mono- and disubstituted 1,7-diynes and cyanamides provided benzo[c][2,7]naphthyridinones as major products and benzo[c][2,6]naphthyridinones as minor ones in yields of ≤79% and regioselectivities of ≤99:1. This method is amenable to internal and terminal diynes and a number of cyanamides with diverse functional group tolerance.

Highly Efficient Synthesis of Poly(silylether)s: Access to Degradable Polymers from Renewable Resources

The design of new materials with tunable properties and intrinsic recyclability, derived from biomass under mild conditions, stands as a gold standard in polymer chemistry. Reported herein are platinum complexes which catalyze the formation of poly(silylether)s (PSEs) at low catalyst loadings. These polymers are directly obtained from dual-functional biobased building blocks such as 5-hydroxymethylfurfural (HMF) or vanillin, coupled with various dihydrosilanes. Access to different types of copolymer architectures (statistical or alternating) is highlighted by several synthetic strategies. The materials obtained were then characterized as low T_g materials (ranging from -60 to 29 °C), stable upon heating (T_-5% up to 301 °C) and resistant towards uncatalyzed methanolysis. Additionally, quantitative chemical recycling of several PSEs could be triggered by acid-catalyzed hydrolysis or methanolysis. These results emphasize the interest of biobased poly(silylether)s as sustainable materials with high recycling potential.

Silver(I) Oxide-/DBU-Promoted Synthesis of Dihydrofuran Units through Allenyl Silver Formation

A formal [3+2] cyclization mediated by silver(I) oxide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is described herein. Through a broad variety of carbonyl compounds, this system can promote cyclization reactions with high yield (up to 85 %) and diastereoselectivity (up to 95:5) for a straightforward access to complex and congested dihydrofuran derivatives in one step under mild conditions. Based on DFT studies, the proposed mechanism would involve an allenyl silver intermediate.

Unique Class of Enantiopure N-Heterocyclic Carbene Half-Sandwich Iridium(III) Complexes with Stable Configurations: Probing Five-Membered versus Six-Membered Iridacycles

A unique class of enantiopure N-heterocyclic carbene half-sandwich iridium complexes is reported. These compounds display stable configurations at the metal center, as demonstrated by their chiroptical properties. Remarkably, because of the nature of the naphthalimide molecule, two regioisomers containing five-membered [( R)-2a and ( S)-2a] and six-membered [( R)-2b and ( S)-2b] iridacycles were obtained. Density functional theory calculations are advanced to rationalize their relative stability.

Cyclometalated N-heterocyclic carbene iridium(iii) complexes with naphthalimide chromophores: a novel class of phosphorescent heteroleptic compounds

A series of cyclometalated N-heterocyclic carbene complexes of the general formula [Ir(C^N)₂(C^C:)] has been prepared. Two sets of compounds were designed, those where (C^C:) represents a bidentate naphthalimide-substituted imidazolylidene ligand and (C^N) = ppy (3a), F2ppy (4a), bzq (5a) and those where (C^C:) represents a naphthalimide-substituted benzimidazolylidene ligand and (C^N) = ppy (3b), F2ppy (4b), bzq (5b). The naphthalimide-imidazole and naphthalimide-benzimidazole ligands 1a,b and the related imidazolium and benzimidazolium salts 2a,b were also prepared and fully characterized. The N-heterocyclic carbene Ir(iii) complexes have been characterized by NMR spectroscopy, cyclic voltammetry and elemental analysis. Moreover, the molecular structures of one imidazolium salt and four Ir(iii) complexes were determined by single-crystal X-ray diffraction. The structures provide us with valuable information, most notably the orientation of the naphthalimide chromophore with respect to the N-heterocyclic carbene moiety. All compounds are luminescent at room temperature and in a frozen solvent at 77 K, exhibiting a broad emission band that extends beyond 700 nm. The presence of the naphthalimide moiety changes the character of the lowest excited state from ³MLCT to ³LC, as corroborated by DFT and TD-DFT calculations. Remarkably, replacing imidazole with a benzimidazole unit improves the quantum yields of these compounds by decreasing the k_nr values which is an important feature for optimized emission performance. These studies provide valuable insights about a novel class of N-heterocyclic carbene-based luminescent complexes containing organic chromophores and affording metal complexes emitting across the red-NIR range.

Mechanistic Aspects of the Polymerization of Lactide Using a Highly Efficient Aluminum(III) Catalytic System

We report here a unique example of an in situ generated aluminum initiator stabilized by a C₂-symmetric salen ligand which shows a hitherto unknown high activity for the ROP of rac-lactide at room temperature. Using a simple and robust catalyst system, which is prepared from a salen complex and an onium salt, this convenient route employs readily available reagents that afford polylactide in good yields with narrow polydispersity indices, without the need for time-consuming and expensive processes that are typically required for catalyst preparation and purification. In line with the experimental evidence, DFT studies reveal that initiation and propagation proceed via an external alkoxide attack on the coordinated monomer.

Zinc and cobalt complexes based on tripodal ligands: synthesis, structure and reactivity toward lactide

The coordination chemistry of a series of pro-ligands ([L¹]-[L⁶]) with cobalt and zinc derivatives has been studied. All complexes have been characterized by multinuclear NMR, elemental analysis, and by single-crystal X-ray diffraction studies. Polymerization of rac-lactide takes place at 130 °C in the presence of cobalt and zinc complexes to yield polymers under solvent free conditions with controlled molecular masses and narrow polydispersities.

Polymersomes with PEG corona: structural changes and controlled release induced by temperature variation

Thermoresponsive behavior of different kinds of polymersomes was studied using small angle neutron scattering (SANS), transmission electron microscopy (TEM), and proton nuclear magnetic resonance ((1)H NMR). The polymersomes were made of block copolymers containing a 2000 Da polyethylene glycol (PEG) as a hydrophilic block and either a liquidlike polymer (e.g., PBA: polybutylacrylate), a solidlike polymer (PS: polystyrene), or a liquid crystalline (LC) polymer as a hydrophobic block. Structural changes in polymersomes are driven in all cases by the critical dehydration temperature of PEG corona, which is closely related to the chemical structure and chain mobility of the hydrophobic block. No structural changes occur upon heating from 25 to 75 °C in the liquidlike polymersomes where the critical dehydration temperature of PEG should be higher than 75 °C. In contrast, glassy PEG-b-PS polymersomes and LC polymersomes show structural changes around 55 °C, which corresponds to the critical dehydration temperature of PEG in those block copolymers. Furthermore, the structural changes depend on the properties of the hydrophobic layer. Glassy PEG-b-PS polymersomes aggregate together above 55 °C, but the bilayer membrane is robust enough to remain intact. This aggregation is reversible, and rather separate polymersomes are recovered upon cooling. However, LC polymersomes display drastic and irreversible structural changes when heated above ∼55 °C. These changes are dependent on the LC structures of the hydrophobic layer. Nematic LC polymersomes turn into thick-walled capsules, whereas smectic LC polymersomes collapse into dense aggregates. As these drastic and irreversible changes decrease or remove the inner compartment volume of the vesicle, LC polymersomes can be used for thermal-responsive controlled release, as shown by a study of calcein release. Finally, toxicity studies proved that LC polymersomes were noncytotoxic and had no effect on cell morphology.

The design, synthesis and photochemical study of a biomimetic cyclodextrin model of photoactive yellow protein (PYP)

The design, synthesis and study of the photophysical and photochemical properties of the first biomimetic cyclodextrin (CD) model of photoactive yellow protein (PYP) are described. This model bears a deprotonated trans-p-coumaric acid chromophore, covalently linked via a cysteine moiety to a permethylated 6-monoamino β-CD. NMR and UV/Visible spectroscopy studies showed the formation of strong self-inclusion complexes in water at basic pH. Steady-state photolysis demonstrated that, unlike the free chromophore in solution, excitation of the model molecule leads to the formation of a photoproduct identified as the cis isomer by NMR spectroscopy. These observations provide evidence that the restricted CD cavity offers a promising framework for the design of biomimetic models of the PYP hydrophobic pocket.

Versatile use of hindered oxalates for the stereoselective preparation of novel 11-modified androst-5-ene derivatives

The 11alpha- and 11beta-modified androst-5-ene derivatives 3a,b as well as the exo- and endocyclic dehydrated compounds 4a-c and 5b-c were produced using the oxalate derivatives of the highly hindered 11beta-hydroxyandrost-5-enes 1a-c. The 11-tetrahydrofuran derivative 6 was produced for the first time with good diastereoselectivity by an intramolecular 5-exo cyclization under radical conditions from the corresponding oxalate as precursor.

Biomimetic copper(I)--CO complexes: a structural and dynamic study of a cali

Four novel calix[6]arene-based cuprous complexes are described. They present a biomimetic tris(imidazole) coordination core associated with a hydrophobic cavity that wraps the apical binding site. Each differs from the other by the methyl or ethyl substituents present on the phenoxyl groups (OR1) and on the imidazole arms (NR2) of the calix[6]arene structure. In solution, stable CO complexes were obtained. We have investigated their geometrical and dynamic properties with respect to the steric demand. IR and NMR studies revealed that, in solution, these complexes adopted two distinct conformations. The preferred conformation was dictated only by the size of the OR1 group. When R1 was an ethyl group, the complex preferentially adopted a flattened C3-symmetrical structure. The corresponding helical enantiomers were in conformational equilibrium, which, however, was slow on the 1H NMR time scale at -80 degrees C. When R1 was a methyl group, the low-temperature NMR spectra revealed the partial inclusion of one tBu group. The complex wobbled between three dissymmetric but equivalent conformations. Hence, small differences in the steric demand of the calixarene's skeleton changed the geometry and dynamics of the system. Indeed, this supramolecular control was promoted by the strong conformational coupling between the metal center and the host structure. Interestingly, this was not only the result of a covalent preorganization, but also stemmed from weak interactions within the hydrophobic pocket. The vibrational spectra of the bound CO were revealed to be a sensitive gauge of this supramolecular behavior, similar to copper proteins in which allosteric effects are common.

31P-NMR and 13C-NMR studies of mannose metabolism in Plesiomonas shigelloides. Toxic effect of mannose on growth

The metabolism of mannose was examined in resting cells in vivo using 13C-NMR and 31P-NMR spectroscopy, in cell-free extracts in vitro using 31P-NMR spectroscopy, and by enzyme assays. Plesiomonas shigelloides was shown to transport mannose by a phosphoenolpyruvate-dependent phosphotransferase system producing mannose 6-phosphate. However, a toxic effect was observed when P. shigelloides was grown in the presence of mannose. Investigation of mannose metabolism using in vivo 13C NMR showed mannose 6-phosphate accumulation without further metabolism. In contrast, glucose was quickly metabolized under the same conditions to lactate, ethanol, acetate and succinate. Extracts of P. shigelloides exhibited no mannose-6-phosphate isomerase activity whereas the key enzyme of the Embden-Meyerhof pathway (6-phosphofructokinase) was found. This result explains the mannose 6-phosphate accumulation observed in cells grown on mannose. The levels of phosphoenolpyruvate and Pi were estimated by in vivo 31P-NMR spectroscopy. The intracellular concentrations of phosphoenolpyruvate and Pi were relatively constant in both starved cells and mannose-metabolizing cells. In glucose-metabolizing cells, the phosphoenolpyruvate concentration was lower, and about 80% of the Pi was used during the first 10 min. It thus appears that the toxic effect of mannose on growth is not due to energy depletion but probably to a toxic effect of mannose 6-phosphate.

Six novel tetraterpenoid ethers, lycopanerols B-G, and some other constituents from the green microalga Botryococcus braunii

Six novel tetraterpenoid ethers, lycopanerols B-G, were isolated from lipidic extracts of the green microalga Botryococcus braunii (L race), along with a series of phytyl esters and alpha- and beta-tocopherols. The structures of the compounds were determined by means of spectral analyses including 2D NMR techniques. A biogenetic relationship is proposed between lycopanerols and lycopadiene, the acyclic diunsaturated tetraterpenoid hydrocarbon synthesized by the alga.

31P and 13C nuclear magnetic resonance studies of metabolic pathways in Pasteurella multocida characterization of a new mannitol-producing metabolic pathway

Glucose metabolism of Pasteurella multocida was examined in resting cells in vivo using 13C NMR spectroscopy, in cell-free extracts in vitro using 31P NMR spectroscopy and using enzyme assays. The NMR data indicate that glucose is converted by the Embden-Meyerhof and pentose phosphate pathways. The P. multocida fructose 6-phosphate phosphotransferase activity (the key enzyme of the Embden-Meyerhof pathway) was similar to that of Escherichia coli. Nevertheless, and in contrast to that of E. coli, its activity was inhibited by alpha glycerophosphate. This inhibition is consistent with the very low fructose 6-phosphate phosphotransferase activity found in cell-free extracts of P. multocida using a spectrophotometric method. The dominant end products of glucose metabolism were mannitol, acetate and succinate. Under anaerobic conditions, P. multocida was able to constitutively produce mannitol from glucose, mannose, fructose, sucrose, glucose 6-phosphate and fructose 6-phosphate. We propose a new metabolic pathway in P. multocida where fructose 6-phosphate is reduced to mannitol 1-phosphate by fructose 6-phosphate reductase. Mannitol 1-phosphate produced is then converted to mannitol by mannitol 1-phosphatase.

Fructose and mannose metabolism in Aeromonas hydrophila: identification of transport systems and catabolic pathways

Aeromonas hydrophila was examined for fructose and mannose transport systems. A. hydrophila was shown to possess a phosphoenolpyruvate (PEP): fructose phosphotransferase system (fructose-PTS) and a mannose-specific PTS, both induced by fructose and mannose. The mannose-PTS of A. hydrophila exhibited cross-reactivity with Escherichia coli mannose-PTS proteins. The fructose-PTS proteins exhibited cross-reactivities with E. coli and Xanthomonas campestris fructose-PTS proteins. In A. hydrophila grown on mannose as well as on fructose, the phosphorylated derivative accumulated from fructose was fructose 1-phosphate. Identification of fructose 1-phosphate was confirmed by 13C-NMR spectroscopy. 1-Phosphofructokinase (1-PFK), which converts the product of the PTS reaction to fructose 1,6-diphosphate, was present in A. hydrophila grown with fructose but not on mannose. An inducible phosphofructomutase (PFM) activity, an unusual enzyme converting fructose 1-phosphate to fructose 6-phosphate, was detected in extracts induced by mannose or fructose. These results suggest that in cells grown on fructose, fructose 1-phosphate could be converted to fructose 1,6-diphosphate either directly by the 1-PFK activity or via fructose 6-phosphate by the PFM and 6-phosphofructokinase activities. In cells grown on mannose, the degradation of fructose 1-phosphate via PFM and the Embden-Meyerhof pathway appeared to be a unique route.

Metabolism of a 5-nitroimidazole in susceptible and resistant isogenic strains of Bacteroides fragilis

We investigated the metabolism of dimetridazole (1,2-dimethyl-5-nitroimidazole) (DMZ) by the resting cell method in a susceptible strain of Bacteroides fragilis and in the same strain containing the nimA gene, which conferred resistance to 5-nitroimidazole drugs. In both cases, under strict anaerobic conditions DMZ was metabolized without major ring cleavage or nitrate formation. However, one of two distinct metabolic pathways is involved, depending on the susceptibility of the strain. In the susceptible strain, the classical reduction pathway of nitroaromatic compounds is followed at least as far as the nitroso-radical anion, with further formation of the azo-dimer: 5,5'-azobis-(1,2-dimethylimidazole). In the resistant strain, DMZ is reduced to the amine derivative, namely, 5-amino-1,2-dimethylimidazole, preventing the formation of the toxic form of the drug. The specificity of the six-electron reduction of the nitro group, which is restricted to 4- and 5-nitroimidazole, suggests an enzymatic reaction. We thus conclude that nimA and related genes may encode a 5-nitroimidazole reductase.