Chain-end modification of low molar mass polybutadienes allowed the formation of thermoreversible networks based on the Diels–Alder chemistry. Furan telechelic polybutadienes with various chain ...length were first synthesized. Addition of a bis-maleimide (BM) compound to the liquid polymer led to the formation of elastomeric networks. Properties of this material were highly affected by the chain length of the polymer precursor and the cross-linking density, monitored by changing the quantity of the BM compound. Finally, the capacity of recycling of the rubber was shown by remolding the used material over five cycles without mechanical properties loss.
To obtain and maintain rubber properties such as elasticity, strength, creep, and chemical resistance, or stiffness over time, rubbers must be chemically cross-linked, mainly by sulfur vulcanization. ...However, the materials produced in this manner result in irreversibly cross-linked networks and are consequently difficult to recycle, which leads to large quantities of rubber waste each year. In this paper, a new route to synthesize reversibly cross-linked 1,4-cis-polyisoprene (PI) and -polybutadiene (PB) based on the Diels–Alder chemistry is investigated. Furan groups are first grafted along the polymeric backbone and at chain ends. In a second step, a bis-maleimide compound is added to the modified liquid material, leading to the formation of a thermo-reversible cross-linked elastomer. Mechanical properties of the resulting rubber can be easily tuned and depend on the bis-maleimide/furan ratio as well as on the nature of the polymeric precursor (polyisoprene vs polybutadiene). The good reprocessability of these materials was demonstrated by remolding them five times without any loss of properties between the first and the last cycle.
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•Living polymerization of N-heterocyclic carbene-catalyzed polymerization of propylene oxide by addition of triethylboron.•High molar mass poly(propylene oxide) and block copolyethers ...are synthesized in mild conditions.•Water is an efficient difunctional initiator.•Synthesis of dihydroxytelechelic poly(propylene oxide).
Propylene oxide (PO) is polymerized by metal-free ring-opening polymerization (ROP) at 25 °C using N-heterocyclic carbenes (NHCs) and triethylborane (Et3B) as a bicomponent catalytic system. Poly(propylene oxide)s with predictable molar mass up to 60 000 g·mol−1 and low dispersity (Ð < 1.10) were obtained without the occurrence of undesirable transfer reaction to the monomer. In presence of an alcohol as the initiator, the ROP of PO follows an anionic mechanism assisted by monomer activation improving the efficiency of NHCs for the polymerization of substituted epoxides. Et3B is involved both in the formation of a complexed active center and in the activation of PO. Interestingly, dihydroxytelechelic PPOs can be readily synthesized not only using 1,4-benzenedimethanol but also water, both serving as difunctional initiators. Block copolyethers are also prepared by PPO chain extension experiments. All (co)polyethers have been thoroughly characterized by 1H NMR spectroscopy, SEC and MALDI-TOF mass spectrometry as means to elucidate the reaction mechanisms involved in this chemistry.
In this study, organocatalytic systems containing both basic and acidic sites, which can activate simultaneously the chain end and the monomer, were investigated in the ring-opening polymerization of ...l-lactide. To this end, equivalent amounts of (N,N-dimethylamino)pyridine (DMAP) and of its protonated form (DMAP·HX) were used as a dual catalytic system for l-lactide polymerization initiated by different alcohols. It is shown that the corresponding DMAP/DMAP·HX systems are significantly more active than DMAP alone, and yield well-controlled poly(l-lactide). Depending on the reaction conditions, the transesterification reaction can be prevented.
REF (Hevb1) and SRPP (Hevb3) are two major components of Hevea brasiliensis latex, well known for their allergenic properties. They are obviously taking part in the biosynthesis of natural rubber, ...but their exact function is still unclear. They could be involved in defense/stress mechanisms after tapping or directly acting on the isoprenoid biosynthetic pathway. The structure of these two proteins is still not described. In this work, it was discovered that REF has amyloid properties, contrary to SRPP. We investigated their structure by CD, TEM, ATR-FTIR and WAXS and neatly showed the presence of β-sheet organized aggregates for REF, whereas SRPP mainly fold as a helical protein. Both proteins are highly hydrophobic but differ in their interaction with lipid monolayers used to mimic the monomembrane surrounding the rubber particles. Ellipsometry experiments showed that REF seems to penetrate deeply into the monolayer and SRPP only binds to the lipid surface. These results could therefore clarify the role of these two paralogous proteins in latex production, either in the coagulation of natural rubber or in stress-related responses. To our knowledge, this is the first report of an amyloid formed from a plant protein. This suggests also the presence of functional amyloid in the plant kingdom.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Rubber particle membranes from the Hevea latex contain predominantly two proteins, REF1 and SRPP1 involved in poly(cis-1,4-isoprene) synthesis or rubber quality. The repartition of both proteins on ...the small or large rubber particles seems to differ, but their role in the irreversible coagulation of the rubber particle is still unknown. In this study we highlighted the different modes of interactions of both recombinant proteins with different classes of lipids extracted from Hevea brasiliensis latex, and defined as phospholipids (PL), glycolipids (GL) and neutral lipids (NL).
We combined two biophysical methods, polarization modulated-infrared reflection adsorption spectroscopy (PM-IRRAS) and ellipsometry to elucidate their interactions with monolayers of each class of lipids. REF1 and SRPP1 interactions with native lipids are clearly different; SRPP1 interacts mostly in surface with PL, GL or NL, without modification of its structure. In contrast REF1 inserts deeply in the lipid monolayers with all lipid classes. With NL, REF1 is even able to switch from α-helice conformation to β-sheet structure, as in its aggregated form (amyloid form). Interaction between REF1 and NL may therefore have a specific role in the irreversible coagulation of rubber particles.
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•PL and GL form homogeneous films, while NL form aggregates at the interface.•REF1 displays stronger accumulation in PL monolayer than SRPP1.•REF1 accumulates in GL and induces aggregation and segregation.•REF1/NL interaction seems to promote aggregation of REF1 in amyloid form.
Terpenes are industrially relevant natural compounds the biosynthesis of which relies on two well-established-mevalonic acid (MVA) and methyl erythritol phosphate (MEP)-pathways. Both pathways are ...widely distributed in all domains of life, the former is predominantly found in eukaryotes and archaea and the latter in eubacteria and chloroplasts. These two pathways supply isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), the universal building blocks of terpenes.
The potential to establish a semisynthetic third pathway to access these precursors has been investigated in the present work. We have tested the ability of a collection of 93 isopentenyl phosphate kinases (IPK) from the biodiversity to catalyse the double phosphorylation of isopentenol and dimethylallyl alcohol to give, respectively IPP and DMAPP. Five IPKs selected from a preliminary in vitro screening were evaluated in vivo in an engineered chassis E. coli strain producing carotenoids. The recombinant pathway leading to the synthesis of neurosporene and lycopene, allows a simple colorimetric assay to test the potential of IPKs for the synthesis of IPP and DMAPP starting from the corresponding alcohols. The best candidate identified was the IPK from Methanococcoides burtonii (UniProt ID: Q12TH9) which improved carotenoid and neurosporene yields ~ 18-fold and > 45-fold, respectively. In our lab scale conditions, titres of neurosporene reached up to 702.1 ± 44.7 µg/g DCW and 966.2 ± 61.6 µg/L. A scale up to 4 L in-batch cultures reached to 604.8 ± 68.3 µg/g DCW and 430.5 ± 48.6 µg/L without any optimisation shown its potential for future applications. Neurosporene was almost the only carotenoid produced under these conditions, reaching ~ 90% of total carotenoids both at lab and batch scales thus offering an easy access to this sophisticated molecule.
IPK biodiversity was screened in order to identify IPKs that optimize the final carotenoid content of engineered E. coli cells expressing the lycopene biosynthesis pathway. By simply changing the IPK and without any other metabolic engineering we improved the neurosporene content by more than 45 fold offering a new biosynthetic access to this molecule of upmost importance.
N-(3,5-Bis(trifluoromethyl)phenyl)-1H-indole-2-carboxamide 1e is an efficient hydrogen-bonding organocatalyst for the ring-opening polymerization of l-lactide. This new catalytic species does control ...the dispersity (1.08) and molecular weight (3460 g/mol vs 3064 in theory) of the poly(l-lactides) prepared in 2 h. 1H NMR analysis showed that compound 1e complexes l-lactide in CDCl3 through the two available NH groups (amide and indole). In particular, the catalytic species appeared to be mainly the H-bonding donor amide (1e in extended conformation, alone or dimer (1e)2) and, to a lesser extend, the dual H-bonding amido-indole (1e in its the pinched conformation). The first X-ray structure of the complex between a H-bonding organocatalyst and l-lactide also revealed a tight H-bonded network between the dimer (1e)2 and l-lactide.
Organocatalysis has been widely developed over the past decades as an alternative to metal-based catalysis. The actual concerns have also promoted the development of sustainable and degradable ...polymers. In this context, γ-lactones are an interesting class of monomers that count many bio-based monomers, yielding polyesters that can be readily depolymerized. Also, the use of functional substituted lactones such as the α-hydroxy-γ-butyrolactone (HBL) affords polyesters with pendant groups offering possible postmodification reactions. This article focuses on the ring-opening copolymerization (ROCP) of α-hydroxy-γ-butyrolactone (HBL) and ε-caprolactone (ε-CL) in the presence of phosphazene P4 base (tert-BuP4) as catalyst. The bulk copolymerization at high temperature (80 °C) yielded fast kinetics (5 min) and high monomer conversions (98% for ε-CL; 88% for HBL) and molar masses (14900 g/mol with Đ = 3.8). A kinetics study at 80 °C revealed a partial HBL depolymerization over time. This phenomenon induced changes in the microstructures of the copolymers. Similar high conversions and molar masses could be also achieved at room temperature for 6 h without any depolymerization. Various monomer feed ratios were also evaluated affording copolyesters with up to 31% of incorporated HBL. In addition, DFT calculations with respect to the HBL homopolymerization revealed similar activation energies between different possible reactions, which include ring-opening polymerization, branching, and backbiting reactions.
The biomembrane surrounding rubber particles from the hevea latex is well known for its content of numerous allergen proteins. HbREF (Hevb1) and HbSRPP (Hevb3) are major components, linked on rubber ...particles, and they have been shown to be involved in rubber synthesis or quality (mass regulation), but their exact function is still to be determined. In this study we highlighted the different modes of interactions of both recombinant proteins with various membrane models (lipid monolayers, liposomes or supported bilayers, and multilamellar vesicles) to mimic the latex particle membrane. We combined various biophysical methods (polarization-modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS)/ellipsometry, attenuated-total reflectance Fourier-transform infrared (ATR-FTIR), solid-state nuclear magnetic resonance (NMR), plasmon waveguide resonance (PWR), fluorescence spectroscopy) to elucidate their interactions. Small rubber particle protein (SRPP) shows less affinity than rubber elongation factor (REF) for the membranes but displays a kind of “covering” effect on the lipid headgroups without disturbing the membrane integrity. Its structure is conserved in the presence of lipids. Contrarily, REF demonstrates higher membrane affinity with changes in its aggregation properties, the amyloid nature of REF, which we previously reported, is not favored in the presence of lipids. REF binds and inserts into membranes. The membrane integrity is highly perturbed, and we suspect that REF is even able to remove lipids from the membrane leading to the formation of mixed micelles. These two homologous proteins show affinity to all membrane models tested but neatly differ in their interacting features. This could imply differential roles on the surface of rubber particles.
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•SRPP interaction with rubber particles is different than REF interaction.•REF has a stronger interaction than SRPP with membranes.•The structure of REF changes in the presence of lipids, not that of SRPP.•SRPP only binds to the membrane.•REF binds, inserts and modifies membrane integrity.
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