Thierry Lalot

Enzyme-mediated initiation of acrylamide polymerization: reaction mechanism

Abstract The polymerization of acrylamide in water initiated by a horseradish peroxidase-catalyzed redox system is studied. It combines hydrogen peroxide (as the oxidant) and 2,4-pentanedione (as the reductant). Several side reactions leading to the degradation of the enzyme through the formation of compound III are evidenced by polymerization experiments and UV spectroscopy; they can be avoided by adjusting the reactant concentrations. The oxidation of 2,4-pentanedione by a non-enzymic pathway is also detected by 1H NMR. Its main effect is to reduce the concentration of the enol form of 2,4-pentanedione, and hence to modify the initiation rate. From this information, a schematic picture of the reactions involved in the enzyme-catalyzed redox system is drawn, so as to optimize the polymerization conditions.

A kinetic approach to acrylamide radical polymerization by horse radish peroxidase-mediated initiation

Free-radical polymerization of acrylamide in water at room temperature involves catalysis by horse radish peroxidase to produce radical species from hydrogen peroxide and 2,4-pentanedione through an oxidoreductive pathway. In the presence of the vinylic monomer, initiation takes place, leading to polyacrylamide formation after a long and unreproducible inhibition period. Conversion-time plots are presented, and some kinetic features are compared with results of previous studies of classical acrylamide polymerization.

Enzyme-catalyzed syntheses of poly(1,6-hexanediyl isophthalate) and poly(1,6-hexanediyl terephthalate) in organic medium

SummaryThe enzyme-catalyzed synthesis of poly(1,6-hexanediyl terephthalate) and poly(1,6-hexanediyl isophthalate) is described. An unsuccessfull attempt to synthesize poly(1,6-hexanediyl o-phthalate) is also presented and the reactivity of those three monomers is discussed according to the enzymatic nature of the catalyst. The crude polyesters are characterized by 1H and 13C NMR spectroscopy and by differential scanning calorimetry. Macrocycles are isolated from poly(1,6-hexanediyl isophthalate) and characterized by steric exclusion chromatography and by mass spectrometry. The number-average molar masses and the thermal properties of the crude, linear and cyclic polyesters are also reported.

Enzyme-mediated radical initiation of acrylamide polymerization: main characteristics of molecular weight control

The free-radical polymerization of acrylamide initiated by a redox system (hydrogen peroxide/β-diketone) catalyzed by horseradish peroxidase is studied with emphasis on the control of the molecular weight of the polymer. The case where 2,4-pentanedione (Acac) is used as the β-diketone is particularly examined. It is shown that the concentration of Acac and that of the enzyme readily control the molecular weight of the polymer. The concentration of hydrogen peroxide does not influence the molecular weight to a significant extent except at extreme values for which enzyme degradation or side reactions interfere with the normal enzymatic cycle. The variations of the molecular weight induced by changes in the chemical structure of the β-diketone are attributed to the reactivity toward the enzymatic cycle. The experimental results are rationalized by the use of classical kinetic equations for free-radical polymerization and including the specific expressions of enzymatic catalysis. The tendencies indicated by the theoretical expressions account for the evolutions given by the experimental results.

Poly[{(BuSn)12O14(OH)6}(AMPS)2] and poly[methyl acrylate-co-{(BuSn)12O14(OH)6}(AMPS)2]: hybrid polymers cross-linked through electrostatic interactions

A butyltin oxo-cluster, {(BuSn)12O14(OH)6}2+, functionalized through electrostatic interactions with two 2-acrylamido-2-methyl-1-propanesulfonate anions (AMPS), has been synthesized and characterized by single crystal X-ray diffraction and multinuclear (1H, 13C and 119Sn) NMR. Its polymerization or co-polymerization with methyl acrylate yield hybrid materials where the nanobuilding blocks are fully preserved and act as nano-fillers and cross-linking agents. According to the electrostatic nature of the cross-linking, these materials can yield gels or solutions depending on the solvent used to swell them.

Einbau von magnetischen Nanopartikeln in neue Hybridnetze auf der Basis von Heteropolyanionen und Polyacrylamid

Die Copolymerisation von Acrylamid und dem tetrafunktionalisierten Polyanion [γ-SiW10O36(RSiO)4]4− (R=C3H6OC(O)C(Me)=CH2), das als Vernetzungsmittel dient, in einer wasrigen Dispersion von Maghemit(γ-Fe2O3)-Nanopartikeln fuhrt zu einem magnetischen Hybridhydrogel (siehe Schema) mit superabsorbierenden Eigenschaften. Die magnetischen Eigenschaften der Nanopartikel ermoglichen es, die Partikelbeweglichkeit im Innern des Netzes zu bestimmen und die Freisetzung der Partikel wahrend des Quellens des Hydrogels zu verfolgen.

Enzyme-catalyzed Polyester Synthesis

Abstract Enzyme-catalyzed polymer synthesis has gathered many scientists around a major topic such as the synthesis of polyesters by enzyme catalysis. Since the mid 80′s indeed, it is commonly accepted and experimented that lipases in particular are able to catalyze reverse reactions when they are used in organic media (less data are reported on esterases or proteases). Transposed to polymer chemistry, these pioneering results led to the definition of numerous reaction systems leading to the formation of polyesters. Thus AA + BB and AB + AB-type polycondensations as well as lactones and macrolides polymerizations have been achieved in various organic solvents. In this article, the creation of aliphatic, unsaturated and aromatic polyesters is reviewed with a special attention paid to the equilibria between linear chains and rings.

Enzymic hydrolysis of phthalic unit containing copolyesters as a potential tool for block length determination

The hydrolysis of poly(1,2-propanediyl fumarate), poly(1,2-propanediyl phthalate) and poly(1,2-propanediyl fumarate-co-phthalate)s was studied. In the absence of the lipase from Chromobacterium viscosum, all the samples exhibit a weight loss indicating that uncatalyzed hydrolysis and/or solubilization of shortest chains take place. In the presence of the enzyme, the weight loss is much higher except when the sample is poly(1,2-propanediyl phthalate), which means that the enzyme does not catalyze the hydrolysis of the phthalate functions. SEC and 1H-NMR analyses of the hydrolysis residues of copolymers with various aromatic unit contents showed that the weight loss is accompanied by both molecular weight decrease and aromatic content increase. The enzyme specificity was tested on a phthalic model and the results confirmed the assumption of a selective action of the lipase from Chromobacterium viscosum. If the non-specific uncatalyzed hydrolysis is controlled, the selective enzymic degradation of copolyesters will give a good opportunity to study the copolyester sequences by means of hydrolysis residue analysis.

Regioselective modification of methyl acrylate telomers by enzyme catalysis. Part 2. Influence of the telogen segment on the selectivity

It has been shown in Part 1 that the transesterification of methyl acrylate telomers by lipase catalysis in toluene at 50°C is a regioselective modification. Indeed, only the ester functions of the end-groups (A and C functions) and those of the monomer units linked to the telogen segment (B function) were modified. The reactivity of the latter was not expected according to data on the specificity of the Rhizomucor miehei lipase, so that has questioned the influence of the telogen structure on the recognition of the B methyl ester by the enzyme. In this article, methyl acrylate telomers were synthesized from new telogens and their modification by lipase catalysis was investigated under the same conditions as in Part 1. The main result is that the B function is still reactive whatever the structure of the incorporated telogen. Further investigations should be done in order to understand the peculiar contribution of the sulphur atom to the regioselective modification of the telomers. A detailed structural analysis of the telomers was performed by proton NMR spectroscopy and size exclusion chromatography. It supports the very precise action of the enzymatic catalyst. Lipase catalysis in this field opens up many potential applications of new designed acrylate oligomers.

Head and tail modification of methyl acrylate telomers by enzyme catalysis. Part 1. Reaction on the first adducts as models for longer chains

The transesterification of methyl acrylate telomers by lipase catalysis in toluene at 50°C was investigated. The specificity of the enzymatic catalyst led to modification of the ester functions of peculiar monomer units. Due to the influence of the near-neighbourhood, only the ester functions of the end-groups and those of the monomer units linked to the telogen segment were modified. It was a completely new result with respect to previous work done in our laboratory. The very precise action of the biocatalyst was characterized from the study of the modification of short telomers as models for longer chains. A detailed analysis of these compounds was made by spectrometric measurements, proton NMR spectroscopy, and size exclusion chromatography. The enzymatic modification opens up numerous possibilities for the design of new acrylate polymers according to the structures of the telogen and of the alcohol used in the transesterification.