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Some novel monoalkyl-N-aryl-substituted iminopyridine iron chloride complexes, differing in the nature of the substituent at the iminic carbon and at the ortho position of the aryl ring, were synthesized and characterized. For one of them, single crystals were obtained, which allowed for the determination of its crystalline structure, in which the iron center is coordinated to the chlorides and to the two nitrogen atoms of the ligand. The coordination around iron is distorted tetrahedral, a coordination mode rarely identified for FeCl2 adducts with bidentate nitrogen ligands. All the complexes were used, in combination with methylaluminoxane, for the polymerization of 1,3-butadiene and isoprene, providing syndiotactic 1,2 poly(1,3-butadiene)s and poly(isoprene)s with a predominantly cis-1,4/3,4 alternating structure, in which short cis-1,4 sequences of three or five units, whose length depends on the nature of the ligand on the iron atom, are present. A detailed NMR characterization (1H-, 13C-, and 2D experiments) of the resultant poly(isoprene)s is reported, and a tentative scheme for the formation of the novel isoprene polymers is proposed.

This article has an erratum: https://doi.org/10.1051/e3sconf/20198802003Présentation d'une communication à la conférence internationale i-DUST 2018 – Inter-Disciplinary Underground Science & Technology (2018/06/04-05), Avignon (FRA); International audience; Groundwater is a major source of water for irrigation of vegetables, especially in the Mediterranean basin. Contamination of aquifer by pathogens has been responsible for numerous disease outbreaks worldwide. Several studies reported that groundwater dissolved organic matter (DOM) can serve as a source of carbon and energy for heterotrophic metabolism of pathogens. In this study, we aimed to investigate the DOM composition of groundwater collected at Avignon. Six liters of groundwater were filtered (0.2 µm) and freeze-dried following appropriate cleaning procedure. The bulk analyses of powder sample were performed using 1D and 2D nuclear magnetic resonance spectroscopy and liquid chromatography coupled with mass spectroscopy. Several components were found at concentrations around 1 µM and comprise : (i) humic and fulvic acids originated from land-derived material or soils and, (ii) various acids, esters and alcohols of different sizes including acetate, lactate and formate, these may result from microbial metabolism. In conclusion, the Avignon groundwater DOM contains a heterogeneous mixture of dissolved organic components with a rather low potential bioreactivity based on the low level of labile biogeochemicals such as carbohydrates.

International audience; In this work, three novel long-chain alkyl substituted 1,4-benzothiazine derivatives have been synthesized by alkylation reactions under phase transfer catalysis conditions. The obtained compounds (4, 5 and 6) obtained were characterized using 1H- and 13C- NMR spectroscopy and X-ray. Their molecular and crystal structures have been determined by single-crystal X-ray diffraction techniques. The experimental data, were compared with the predicted ones spectral data were also obtained using density functional theory (DFT) at the B3LYP/6-31G(d,p) level of theory. In addition, the closest contacts between the active atoms of the compounds were identified through Hirshfeld surface analyses. According to Monte Carlo simulations, the new compounds can act as good corrosion inhibitors for iron and as moderate ones for copper and aluminum metals.

Sixteen new quinoline derivatives (3e18) have been synthesized through cyclocondensation, nucleophilic substitution and alkylation reactions. All the obtained compounds have been characterized using 1 H-, 13C and 19F NMR spectroscopic measurements. The molecular and crystal structures of four of these compounds (10, 11, 15 and 18) have also been further examined by single crystal X-ray crystallography. The predicted spectral data were also obtained and compared to the experimental results using density functional theory (DFT). in order to understand the non-bonding intermolecular interactions in solid phase crystal packing. The closest contacts between active atoms of the four studied molecules were identified through both 2D and 3D Hirshfeld surface analyses. The different structures of the four compounds are optimized and their both energies highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO), as well as their clouds are evaluated. The obtained experimental results are correlated to the calculated ones and showed great compatibility. Finally, molecular docking studies are performed to investigate the binding patterns of the title compounds with the Protein Data Bank (PDB: 1M17) inhibitor targets and showed good insights on the possible interactions using the Auto-Dock Vina program. Author would like to thank Prof. Jerry P. Jasinski acknowledges the NSF-MRI program (Grant No. CHE-1039027) for funds to purchase the X-ray diffractometer. T. H. is grateful to Hacettepe University Scientific Research Project Unit (Grant No. 013 D04 602 004).

The interest of research groups and pharmaceutical companies to discover novel GSK-3&beta, inhibitors has increased over the years considering the involvement of this enzyme in many pathophysiological processes and diseases. Along this line, we recently reported on 1H-indazole-3-carboxamide (INDZ) derivatives 1&ndash, 6, showing good GSK-3&beta, inhibition activity. However, they suffered from generally poor central nervous system (CNS) permeability. Here, we describe the design, synthesis, and in vitro characterization of novel imidazo[1,5-a]pyridine-1-carboxamide (IMID 1) and imidazo[1,5-a]pyridine-3-carboxamide (IMID 2) compounds (7&ndash, 18) to overcome such liability. In detail, structure-based approaches and fine-tuning of physicochemical properties guided the design of derivatives 7&ndash, 18 resulting in ameliorated absorption, distribution, metabolism, and excretion (ADME) properties. A crystal structure of 16 in complex with GSK-3&beta, enzyme (PDB entry 6Y9S) confirmed the in silico models. Despite the nanomolar inhibition activity, the new core compounds showed a reduction in potency with respect to INDZ derivatives 1&ndash, 6. In this context, Molecular Dynamics (MD) and Quantum Mechanics (QM) based approaches along with NMR investigation helped to rationalize the observed structure activity relationship (SAR). With these findings, the key role of the acidic hydrogen of the central core for a tight interaction within the ATP pocket of the enzyme reflecting in good GSK-3&beta, affinity was demonstrated.

In this study, lignin with fine structures and facile enzymatic saccharifying residue were successively dissociated based on the lignin-first biomass deconstruction strategy. In the lignin-first process, aldehyde-protected lignin fractions were firstly isolated by acid-catalyzed dioxane extraction in the presence of formaldehyde (FA) and acetaldehyde (AA) and then analyzed by advanced nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The optimized hydrogenolysis of the extracted lignin (LFA and LAA) resulted in a high yield (42.57% and 33.00%) of lignin monomers with high product selectivity (mainly 2,6-dimethoxy-4-propylphenol) (39.93% and 46.61%). Moreover, the cellulose-rich residues were saccharified into fermentable glucose for bioethanol production. The glucose yield of the substrate (RAA) reached to 75.12%, which was significantly higher than that (15.4%) of the substrate (RFA). In short, the lignin-first biomass deconstruction by adding AA is a promising and sustainable process for producing value-added products (energy and fine chemicals) from lignocellulosic biomass.

A camphor-derived sulfonimine with a conjugated carbonyl group, oxoimine 1 (O2SNC10H13O), reacts with amino acids (glycine, L-alanine, L-phenylalanine, L-leucine) to form a compound O2SNC10H13NC10H14NSO2 (2) which was characterized by spectroscopic means (MS and NMR) and supported by DFT calculations. The product, a single diastereoisomer, contains two oxoimine units connected by a –N= bridge, and thus has a structural analogy to the colored product Ruhemann´s purple obtained by the ninhydrin reaction with amino acids. A plausible reaction mechanism that involves zwitterions, a Strecker degradation of an intermediate imine and water-catalyzed tautomerizations was developed by means of DFT calculations on potential transition states.

Dioscorea pentaphylla L., a wild tuber is used both as food and medicines among different ethnic groups of Similipal Biosphere Reserve, India. Tubers are used against skin infections. In order to establish and confirm tribal claims, methanol extract was subjected to fractionation. The active fraction (DP1) was subsequently used for further purification and NMR (Nuclear magnetic resonance) characterization. The phytochemical analysis revealed the presence of saponin groups. The antibacterial activity of DP1 was done against selected bacterial strains (Salmonella typhi, Shigella flexneri, Streptococcus pyogenes, Streptococcus mutans and Vibrio cholerae) using DD (disc diffusion), AWD (agar well diffusion) and broth dilution assay. The activity was compared with antibiotics Penicillin and Kanamycin. It was observed that DP1 showed significant inhibitory activity against the tested bacteria. The characterization of DP1 through NMR analysis and presence of proton in carbon position at C-3, C-19, C-18, C-21 and C-27 was same as the known compound “Diosgenin”. Therefore, isolated compound was confirmed to be Diosgenin. The study for the first time showed that, diosgenin present in D. pentaphylla tuber was responsible for antibacterial and antioxidant potential. Present study highlights the importance of Dioscorea species as sources of diverse secondary metabolites for the isolation of active compound(s).

Two new polypropionates, named exiguapyrone (2) and exiguaone (3) along with the known haminol-1 (4) and -2 (5), have been isolated from the lipidic extract of the Mediterranean cephalaspidean mollusc Haminoea exigua. The regular propionate skeletons, structurally related to other polypropionates from the congener Haminoea fusari, have been elucidated by means of NMR techniques as natural (2 and 3) and alpha-/gamma-pyrone methyl derivatives (2a and 2b). This is a further report showing the co-occurrence of alkyl-pyridines and polypropionates in Haminoea molluscs strengthening the role of polypropionates as chemical markers among cephalaspideans. (C) 2015 Elsevier Ltd. All rights reserved.

MIF is a chemokine-like cytokine that plays a role in the pathogenesis of inflammatory and cardiovascular disorders. It binds to the chemokine-receptors CXCR2/CXCR4 to trigger atherogenic leukocyte migration albeit lacking canonical chemokine structures. We recently characterized an N-like-loop and the Pro-2-residue of MIF as critical molecular determinants of the CXCR4/MIF binding-site and identified allosteric agonism as a mechanism that distinguishes CXCR4-binding to MIF from that to the cognate ligand CXCL12. By using peptide spot-array technology, site-directed mutagenesis, structure-activity-relationships, and molecular docking, we identified the Arg-Leu-Arg (RLR) sequence-region 87–89 that – in three-dimensional space – ‘extends’ the N-like-loop to control site-1-binding to CXCR4. Contrary to wildtype MIF, mutant R87A-L88A-R89A-MIF fails to bind to the N-terminal of CXCR4 and the contribution of RLR to the MIF/CXCR4-interaction is underpinned by an ablation of MIF/CXCR4-specific signaling and reduction in CXCR4-dependent chemotactic leukocyte migration of the RLR-mutant of MIF. Alanine-scanning, functional competition by RLR-containing peptides, and molecular docking indicate that the RLR residues directly participate in contacts between MIF and CXCR4 and highlight the importance of charge-interactions at this interface. Identification of the RLR region adds important structural information to the MIF/CXCR4 binding-site that distinguishes this interface from CXCR4/CXCL12 and will help to design MIF-specific drug-targeting approaches.

l-arginine is often covalently linked to vectors for gene or drug delivery as a means of increasing their transfection activity and reducing toxicity. This strategy relies on the protection of basic nitrogen atoms, for example, by employing the tert-butoxycarbonyl group. Our aim in the present work was to prepare the widely described α N, ω N, ω′ N-tris(tert-butyloxycarbonyl)-l-arginine as a single isomer in high yield and with high levels of purity for use in the esterification of dendrimers with several peripheral hydroxyl groups. Following three reported protocols which assured this goal, we observed the unexpected formation of four additional isomers. Using the first procedure, α N, ω N, ω′ N-tris(tert-butyloxycarbonyl)-l-arginine was never obtained. The second procedure delivered the desired compound as a mixture of geometric isomers (E/Z), while the third protocol led to a single isomer in high yield and purity, but with an unreported symmetrical structure. Since Boc protection is transient, this discovery would seem to be of little interest, but preliminary results from an ongoing investigation of the behavior of each of the isomers obtained in the esterification reactions of interest has shown that their reactivity depends on their structure. Although this research is ongoing, here we report a detailed description of these unexpected results, along with an NMR investigation focusing on the double-bond geometry and position which enabled confirmation of the structures.

Novel allyl cobalt complexes, i.e., (?3 -C4 H7 )(?4 -C4 H6 )Co(PCyPh2 ) (1), (?3-C4H7)(?4-C4H6)Co(PMePh2) (2) and (?3-C5H9)(?4-C5H8)Co(PMePh2) (3), were synthesized by reacting CoCl2(PRPh2)2 (R = methyl, cyclohexyl) with 1,3-butadiene or isoprene in presence of metallic zinc. The complexes were fully characterized by Nuclear Magnetic Resonance (NMR) spectroscopy (1H and 2D experiments); in case of 1, single crystals, suitable for X-ray analysis, were obtained and the molecular structure was determined. The allyl cobalt phosphine complexes alone gave highly crystalline 1,2 polymers from 1,2-propadiene, but they did not polymerize 1,3-dienes. Nevertheless, in the presence of a stoichiometric amount of methylaluminoxane (MAO), they were able to polymerize 1,3-butadiene and substituted 1,3-butadienes such as isoprene, (E)-1,3-pentadiene, (E)-1,3-hexadiene, and (E)-3-methyl-1,3-pentadiene. Specifically, 1/MAO gave predominantly syndiotactic 1,2 polymers from 1,3-butadiene and terminally substituted 1,3-butadienes (e.g., 1,3-pentadiene and 1,3-hexadiene), but it was practically not active in the polymerization of internally substituted 1,3-butadienes (e.g., isoprene and 3-methyl-1,3-pentadiene); 2/MAO and 3/MAO exhibited instead an opposite behavior, giving predominantly isotactic 1,2 polymers from 3-methyl-1,3-pentadiene, and showing very low activity in the polymerization of 1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene. The results obtained are interesting from the mechanistic point of view, and some hypotheses to explain this particular behavior were formulated.

Herein, the polyphenolic content in extracts of Ruppia cirrhosa (Petagna) Grande and Ruppia maritima L.was fully characterized for the first time. High amounts of the main compound chicoric acid (CA) (≤30.2 ± 4.3 mg/g) were found in both Ruppia species. In addition, eight flavonoids, namely the 3-O-glucopyranosides and 3-O-galactopyranosides, as well as malonylated 3-O-glycosides of quercetin and isorhamnetin, were isolated and identified. The antioxidant activity of Ruppia cirrhosa extracts and isolated compounds was investigated spectrophotometrically by a 1,1-diphenyl-2-picrylhydrazyl (DPPH·) radical scavenging assay. IC50 values were 31.8–175.7 μg/mL for Ruppia cirrhosa extracts and 12.1–88.4 μg/mL for isolated flavonoids. Both individual and total phenolic and flavonoid content were quantified in crude extracts using analytical HPLC. The relative high amount of total flavonoids ranged from 5.9 to 14.7 mg/g in both species, with concentrations of individual flavonoids ranging from 0.4 to 2.9 mg/g dry weight. The content of chicoric acid was twofold more in Ruppia maritima than in Ruppia cirrhosa. Seasonal variation of the quantitative content in Ruppia cirrhosa was examined. Total flavonoid content ranged from 8.4 mg/g in October to 14.7 mg/g in August, whereas the highest concentration of chicoric acid was observed in March (29.2 mg/g). publishedVersion

The comparative study on the pyrolysis of two Polypropylene samples, with a similar high isotactic character but quite distinct molecular weights, reveals a significant difference in their thermal performances. The detailed qualitative analysis of the parameters, which are expected to govern the thermal degradation, leads to reasonably assume a main role of the molecular weight in their relative early stabilities. Furthermore, the correlation found between the sharp initial build-up of the Eact and the selective cleavage of isotactic stereosequences in both samples, suggests the relevance of the stereoregular length into the energy required for chain scission, The authors acknowledge the financial support of project MAT2016-79869-C2-1-P (AEI/FEDER, UE), as well as the kindly assistance of Repsol for the supply of samples.

Pressed potato fibre (PPF) has a high water holding capacity (WHC) affecting its processing as an animal feed. The aim of this study was to characterize cell wall polysaccharides (CWPs) in PPF and investigate their WHC. This was done via sequential extractions. Half of all CWPs were recovered in the hot buffer soluble solids extract as pectins (uronic acid and rhamnose) and galactans wherein most pectins (76%) from PPF were water soluble. Most likely, the network of CWPs is loosened during processing of potatoes. PPF showed a WHC of 7.4 expressed as the amount of water held per g of dry matter (mL/g). Reconstituting hot buffer soluble solids with buffer insoluble solids in water gave a WHC comparable to that of PPF. Removal of alkali soluble solids, which mainly comprised xyloglucans, lowered the WHC of the final residue. The results indicated that interactions between CWPs could affect the WHC of PPF.

International audience; Post functionalization of aryl ether perfluorocyclobutyl (PFCB) polymers with fluoroalkyl side chains was accomplished with Umemoto's FITS reagents. The fluoroalkylated PFCB polymers (20 % functionalized) showed increases in both hydrophobicity and oleophobicity. Static contact angle for hexadecane was increased after fluoroalkylation from 0° to greater than 30° for the two PFCB polymers tested. Increased oil repellency makes these materials potential candidates for various coatings applications.

Lignin is a complex polyphenolic constituent of plant secondary cell walls. Inspired largely by the recalcitrance of lignin to biomass processing, plant engineering efforts have routinely sought to alter lignin quantity, composition, and structure by exploiting the inherent plasticity of lignin biosynthesis. More recently, researchers are attempting to strategically design plants for increased degradability by incorporating monomers that lead to a lower degree of polymerisation, reduced hydrophobicity, fewer bonds to other cell wall constituents, or novel chemically labile linkages in the polymer backbone. In addition, the incorporation of value-added structures could help valorise lignin. Designer lignins may satisfy the biological requirement for lignification in plants while improving the overall efficiency of biomass utilisation.

Biomass pyrolysis is a promising path toward renewable liquid fuels. However, the calorific value of the pyrolysis oil (PO), also known as bio-oil, is low due to the high content of organic oxygenates and water. The oxygen content of PO can be reduced by hydrodeoxygenation, in which hydrogen is used to remove oxygen. An economic disadvantage of hydrodeoxygenation pathway is its dependence on hydrogen as an expensive feedstock. An alternative technology is to upgrade PO in hot, high pressure water, known as hydrothermal processing. The present paper studies upgrading pyrolysis oil derived from Norwegian spruce by (1) hydrodeoxygenation in a liquid hydrocarbon solvent using nanodispersed sulphide catalysts and (2) hydrothermal treatment in near-supercritical water. Experimental results and simulation studies suggested that if water soluble products are reformed for hydrogen production, the hydrodeoxygenation pathway would be a net consumer of hydrogen, whilst the hydrothermal pathway could produce a significant hydrogen excess. By comparison, the fuel yield from hydrodeoxygenation was significantly higher than hydrothermally treated fuel. Therefore, in the present study, an integrated model was proposed which demonstrates that the synergistic integration of hydrothermal and hydrodeoxygenation upgrading technologies can yield an optimal configuration which maximises fuel production, whilst obviating the need to purchase hydrogen. In this optimal configuration, 32% of raw pyrolysis-oil is hydrothermally treated and the rest is sent for hydrodeoxygenation. The results of a techno-economic analysis suggests that if the proposed integrated approach is used, it is possible to produce biofuel (43% gasoline, and 57% diesel) at a very competitive minimum selling price of 428 $ m −3 (1.62 $/gallon).

We report on a new spectrofluorimetric assay for the measurement of reductase activity of proteins belonging to the superfamily of thioredoxins such as protein disulfide isomerase (PDI). The assay relies on the preparation of a fluorescence-quenched substrate easily accessible in two steps through functional group transformations of the peptide Gly-Cys-Asp. In the first step fluorescein isothiocyanate is linked to the Gly-NH2 terminus and in the second step the Cys-SH groups are converted into a disulfide bond. Both intermediate and final substrate have been fully characterized by mass spectrometric and nuclear magnetic resonance measurements. Dimethyl sulfoxide is here reported to be a mild oxidizing agent allowing us to obtain in good overall yield the assay substrate in a single synthetic step. A reliable estimation of PDI reductase activity is obtained via the detection of a strong fluorescence enhancement after enzymatic reduction. Moreover, our assay provides further support for the key role played by thioredoxin reductase in enabling disulfide reductase activity of PDI.

An empirical equation, describing the relationship between the porphyrin methyl hyperfine shifts and the position of the axial ligand(s), has been applied to an artificial heme-protein in order to obtain insight into the active site properties of heme-protein models.

International audience; N-Heterocyclic carbenes (NHCs), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1) and 1, 3-bis(di-tert-butyl)imidazol-2-ylidene (2) were employed as neutral organocatalysts to bring about the group transfer polymerization (GTP) of both methacrylic and acrylic monomers, including methyl methacrylate (MMA), tert-butylacrylate (tBA), and n-butylacrylate (nBA). This could be achieved at room temperature using 1-methoxy-2-methyl-1-trimethylsiloxypropene (MTS) as initiator in polar or apolar medium. In this way, polymethacrylates and polyacrylates with molar masses in the range 10 000-300 000 g.mol(-1), corresponding to the initial [monomer]/[MTS] ratio and with polydispersities lower than 1.2, were obtained in quantitative yields. The kinetics of GTP of MMA catalyzed by 1 or 2 was further investigated. Though the first-order kinetic plot ln[M](0)/[M] versus time deviated from linearity at high monomer conversion, no inhibition period was noted at low monomer conversion. Moreover, the polymerization rate dramatically increased as the concentration of initiator increased, with first-order dependence in initiator. When mixed in 1/1 molar ratio, MTS and NHC I did not reveal the formation of enolate-type species by Si-29 or 13 C NMR spectroscopy. Based on these observations, we propose that NHCs activate the silyl ketene acetal initiator and further propagate GTP via an associative mechanism. The fact that In[M](0)/[M] does not evolve linearly with time in the terminal phase of the polymerization can be understood by a reduced diffusion of the catalyst to the trimethylsilyl end groups. The proposed associative mechanism can also account for the successful control of NHC-catalyzed GTP of acrylates during which termination reactions such as backbiting or internal isomerization could be drastically minimized. Next, was described the synthesis of all acrylic block copolymers based on polyacrylates and polymethacrylates (e.g., PMMA-b-PnBA-b-PMMA), utilizing the same NHC as catalyst in sequential GTP. It is again argued that such block copolymer formation is favored by an associative mechanism forming highly unstable activated silicon intermediates.

Melanin granules (MGs) have been extracted from human Chinese black hairs by either acid hydrolysis (CH-type MGs) or enzymatic digestion (CP-type MGs), and their chemical structure investigated at the solid state by means of (13)C cross polarization magic angle spinning (CPMAS NMR) and EPR spectroscopy. Both types of MGs contain a large amount of protein that is tightly bound to the true melanin polymer, with CP-type MGs having a larger protein content than CH-type ones. Moreover, MGs may also contain variable amounts of lipid-like material. A high amount of paramagnetic metals is detected by EPR in CP-type MGs, in particular Fe(III). Iron can be bound in two chemical forms: as isolated high spin Fe(III) ions with rhombic symmetry and as small oxy-hydroxy Fe(III) aggregates. Iron is poorly available to chelators. CH-type MGs contain much fewer metals. CP-type MGs have then been subjected to partial bleaching by hydrogen peroxide in ammonia, yielding a residual solid, called residual oxidized melanin (ROM) and a soluble but still pigmented fraction called melanin free acid (MFA). MFA can be isolated by precipitation at acidic pH. The (13)C-CPMAS NMR and EPR spectra of these derivatives indicated that ROM has a structure very similar to that of parent MGs, whereas MFA shows a decrease of the protein content with respect to the melanin and a decreased amount of bound iron. Thus, the oxidative degradation of CP-type MGs is a process not involving the bulk of MGs, but rather it proceeds from the solvent-exposed outer parts to the interior.

Hyaluronan-based hydrogels were synthesised using different crosslinking agents, such as 1,3-diaminopropane (1,3-DAP) and 1,6-diaminohexane (1,6-DAE). The hydrogels were sulfated to provide materials (Hyal-1,3-DAP, Hyal-1,6-DAE, HyalS-1,3-DAP and HyalS-1,6-DAE) that were characterised by both high- and low-resolution nuclear magnetic resonance (NMR) spectroscopy. The (13)C NMR spectra of the materials were analysed to identify, characterise and study the crosslinking degree of the hydrogels. The crosslinking degree was also determined by potentiometric titration and the effectiveness of the two techniques was compared. Measurements of longitudinal relaxation times (spin-lattice) and of NOE enhancement were used to study the mobility of the hydrogels. Low-resolution NMR studies allowed the determination of the water transport properties in the hydrogels. In addition, the swelling degree for the various hydrogels was calculated as a function of the longitudinal and transversal relaxation times of the water molecules. Lastly, the self-diffusion coefficients of the water in interaction with the four polysaccharides were measured by the pulsed field gradient spin echo (PFGSE) sequence.

International audience; Several conditions for the sol-gel polymerisation of hybrid silica-zirconia and silica-titania have been studied using specially tailored electrochemical probes. One of the probes has been designed to bind to the silica backbone, while the other has been designed to bind to the transition metal species. The results show that the silicon and the transition metal species play a quite different role in the polymerization course, and especially large differences between the zirconium and the titanium behaviour have been observed. It is shown unambiguously that while the zirconia species bind irreversibly to the silica gel, the titania, ones remain very mobile whatever the advancement of the reaction and probably act only as catalysts for the siloxane polycondensation.

New siloxanes with acid-sensitive substituents have been synthesized by means of hydrosilylation, starting from methylhydrosiloxanes. Details of the preparation and characterization are reported. p -t-Butoxycarbonyloxystyrene, p -t-butoxystyrene and t-butyl methacrylate turned out to be excellent reagents in these experiments. 1 H, 13 C and 29 Si nuclear magnetic resonance techniques were used for characterization. The ratio between α and β addition appears to be strongly dependent on the substituents at the vinyl group of the organic moieties.