Frédéric Peruch

Homopolymerization and copolymerization of styrene and norbornene with Ni-based/MAO catalysts

The homopolymerization of styrene (Sty) and norbornene (NBE) was investigated in the presence of the nickel stearate (NiSt)/methylaluminoxane (MAO) catalytic system in toluene and in chlorobenzene at 20°C. The fully saturated structure of polynorbornene indicates that the two monomers polymerize by an ethylenic type addition reaction. The synthesis of true copolymers shows that one type of active species is operating for the tow monomers. Determination of reactivity ratios (rNBE = 20.8 and rSty = 0.02) indicates a much higher reactivity of NBE, which is interpreted by a coordination mechanism. The styrene-norbornene copolymers exhibit glass transition temperatures (Tg) which range from 100°C to 320°C and follow Kovacs law. The absence of crystallinity and the homogeneous repartition of monomer units along the chains yield highly transparent materials of high thermal stability.

Isopentenyl diphosphate isomerase: A checkpoint to isoprenoid biosynthesis

Even if the isopentenyl diphosphate (IPP) isomerases have been discovered in the 50s, it is only in the last decade that the genetical, enzymatical, structural richness and cellular importance of this large family of crucial enzymes has been uncovered. Present in all living kingdoms, they can be classified in two subfamilies: type 1 and type 2 IPP isomerases, which show clearly distinct characteristics. They all perform the regulatory isomerization of isopentenyl diphosphate into dimethylallyl diphosphate, a key rate-limiting step of the terpenoid biosynthesis, via a protonation/deprotonation mechanism. Due to their importance in the isoprenoid metabolism and the increasing interest of industry devoted to terpenoid production, it is foreseen that the biotechnological development of such enzymes should be under intense scrutiny in the near future.

Ring-Opening Polymerization of L-Lactide Efficiently Triggered by an Amido-Indole. X-ray Structure of a Complex between L-Lactide and the Hydrogen-Bonding Organocatalyst

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. (1)H NMR analysis showed that compound 1e complexes l-lactide in CDCl(3) 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.

Rubber Elongation Factor (REF), a Major Allergen Component in Hevea brasiliensis Latex Has Amyloid Properties

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.

Hevea brasiliensis REF (Hev b 1) and SRPP (Hev b 3): An overview on rubber particle proteins

This review article aims to gather all the knowledge on two important proteins associated with Hevea brasiliensis rubber particles: namely the rubber elongation factor (REF) and the small rubber particle protein (SRPP). It covers more then three decades of research on these two proteins and their homologues in plants, and particularly emphasizes on the different possible properties or functions of these various proteins found in plants.

Rubber particle proteins, HbREF and HbSRPP, show different interactions with model membranes ☆

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.

Ring-opening polymerization of lactones using supramolecular organocatalysts under simple conditions

Ring-opening polymerizations of δ-valerolactone (δ-VL) and e-caprolactone (e-CL) were catalyzed by a metal-free system composed of two H-bonding components, a phenol derivative to activate the monomer, and DBU, which enhanced the nucleophilicity of the initiator and the propagating chain. Compared to other H-bonding systems for the ROP of lactones, phenol + DBU catalysts had the practical advantages of being commercially available and inexpensive, efficient at room temperature and under simple experimental conditions that avoid drying of reactants and the use of a glove-box. In addition, the obtained polyesters had a narrow dispersion of molar masses which were controlled by the concentration ratio of monomer versus initiator. Moreover, the initiation of the polymerization by DBU and residual water molecules (despite no specific drying of reagents) was shown to be very minor under the experimental conditions. No initiation by the phenol catalysts was observed. Block copolyesters PVL-PLA and PCL-PLA were also prepared using these conditions.

New catalysts for olefin polymerization: from elementary processes to the synthesis of polyolefins

A general investigation of the elementary reactions involved in the activation processes of zirconocene and Ni-based derivatives by methylaluminoxane (MAO) was performed through the association of polymerization kinetics and spectroscopic investigation of the catalytic system. This study demonstrates the close correlation between polymerization activities and the changes in the UV/visible characteristic absorption bands of the transition metal derivative used as catalyst. Hex-1-ene was chosen as model monomer.

Cationic polymerization of isoprene initiated by 2-cyclohexylidene ethanol–B(C6F5)3: an insight into initiation and branching reactions

In this paper, the cationic polymerization of isoprene using 2-cyclohexylidene ethanol–B(C6F5)3 as the initiating system is investigated under various polymerization conditions. The use of this allylic alcohol allows studying the initiation as well as the mechanism of branching reactions. Intensive β-H elimination, which is the major termination process, is responsible for protic initiation and double bond loss via protonation. This latter process leads to chain branching and intramolecular cyclization, even at low conversion. Independently of the condition used (solvent polarity, temperature, presence of a proton trap, etc.) only oligomers are obtained, composed of saturated sequences and IP units almost exclusively with a 1,4-trans configuration and an olefinic terminal group.

Polyisoprene synthesized via cationic polymerization: State of the art*

In this paper, more than 70 years of cationic polymerization of isoprene (IP) are reviewed. Up to now, the controlled or living cationic polymerization of IP was never reported due to numerous side reactions, including chain transfer, cyclization, and cross-linking reactions that were very difficult to control. Cationic polyisoprenes (PIPs) are thus described to be mainly 1,4-trans with saturated/cyclized sequences. Although progress was made for their characterization due to many analysis techniques, cationic PIPs are still not yet fully characterized, particularly the saturated sequences. As a consequence, even if suggestions are proposed, polymerization mechanism is still not fully elucidated.