Jean-Paul Guégan

Heteroleptic silylamido phenolate complexes of calcium and the larger alkaline earth metals: β-agostic Ae⋅⋅⋅Si-H stabilization and activity in the ring-opening polymerization of L-lactide.

The factors governing the stability and the reactivity towards cyclic esters of heteroleptic complexes of the large alkaline earth metals (Ae) have been probed. The synthesis and stability of a family of heteroleptic silylamido and alkoxide complexes of calcium [{LO(i)}Ca-Nu(thf)(n)] supported by mono-anionic amino ether phenolate ligands (i = 1, {LO(1)}(-) = 4-(tert-butyl)-2,6-bis(morpholinomethyl)phenolate, Nu(-) = N(SiMe(2)H)(2)(-), n = 0, 4; i = 2, {LO(2)}(-) = 2,4-di-tert-butyl-6-{[2-(methoxymethyl)pyrrolidin-1-yl]methyl}phenolate, Nu(-) = N(SiMe(2)H)(2)(-), n = 0, 5; i = 4, {LO(4)}(-) = 2-{[bis(2-methoxyethyl)amino]methyl}-4,6-di-tert-butylphenolate, Nu(-) = N(SiMe(2)H)(2)(-), n = 1, 6; Nu(-) = HC≡CCH(2)O(-), n = 0, 7) and those of the related [{LO(3)}Ae-N(SiMe(2)H)(2)] ({LO(3)}(-) = 2-[(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl]-4,6-di-tert-butylphenolate Ae = Ca, 1; Sr, 2; Ba, 3) have been investigated. The molecular structures of 1, 2, [(4)(2)], 6, and [(7)(2)] have been determined by X-ray diffraction. These highlight Ae⋅⋅⋅H-Si internal β-agostic interactions, which play a key role in the stabilization of [{LO(i)}Ae-N(SiMe(2)H)(2)] complexes against ligand redistribution reactions, in contrast to regular [{LO(i)}Ae-N(SiMe(3))(2)]. Pulse-gradient spin-echo (PGSE) NMR measurements showed that 1, 4, 6, and 7 are monomeric in solution. Complexes 1-7 mediate the ring-opening polymerization (ROP) of L-lactide highly efficiently, converting up to 5000 equivalents of monomer at 25 °C in a controlled fashion. In the immortal ROP performed with up to 100 equivalents of exogenous 9-anthracenylmethanol or benzyl or propargyl alcohols as a transfer agent, the activity of the catalyst increased with the size of the metal (1<2<3). For Ca-based complexes, the enhanced electron-donating ability of the ancillary ligand favored catalyst activity (1>6>4≈5). The nature of the alcohol had little effect over the activity of the binary catalyst system 1/ROH; in all cases, both the control and end-group fidelity were excellent. In the living ROP of L-LA, the HC≡CCH(2)O(-) initiating group (as in 7) proved superior to N(SiMe(2)H)(2)(-) or N(SiMe(3))(2)(-) (as in 6 or [{LO(4)}Ca-N(SiMe(3))(2)] (B), respectively).

Methylated β-Cyclodextrin-Capped Ruthenium Nanoparticles: Synthesis Strategies, Characterization, and Application in Hydrogenation Reactions

Colloidal suspensions of ruthenium nanoparticles (Ru0 NPs) stabilized by randomly methylated β‐cyclodextrins were easily prepared in aqueous solution by two comparative reductive approaches. The first method relies on a one‐step hydrogen reduction of ruthenium trichloride as a metal precursor in the presence of cyclodextrins (one‐pot method). The second method consists of the chemical reduction of metal salts by NaBH4, followed by the stabilization of ruthenium NPs by post‐addition of the methylated β‐cyclodextrins (cascade method). The modified β‐cyclodextrin‐capped ruthenium NPs obtained were characterized using TEM, DLS, and NMR techniques. The highly dispersed colloidal suspensions contain very small particles in the size range of 1–1.4 nm. Their catalytic performances were investigated in terms of activity and selectivity of their biphasic hydrogenation of various substrates (olefins, ketones, and disubstituted arenes) under mild conditions.

Probing β-(1→3)-d-glucans interactions with recombinant human receptors using high-resolution NMR studies

A full characterization of the high-resolution NMR spectrum of the laminarihexaose is described and used for the determination of the binding epitope of the more complex but structurally related laminarin. These biophysical data extend the current knowledge of β-glucans/Dectin-1 interactions and suggest different biological mechanisms in close relation with the size of the saccharidic chain.

Direct and one-pot conversion of polyguluronates and alginates into alkyl-L-guluronamide-based surfactant compositions

We describe here an efficient one-pot process for the synthesis of 100% bio-based L-guluronic acid based surfactant compositions as emulsion stabilizers, directly from L-polyguluronate or whole alginate, a renewable polysaccharide extracted from brown seaweeds. The transformation of these polymers into long-chain alkyl-L-guluronamides associated with D-mannuronamides when the alginate was used, has been achieved through the preparation of n-butyl uronate monosaccharide intermediates involving methane sulfonic acid-promoted hydrolysis, Fisher glycosylation and esterification reactions, followed by an in situ solvent-free aminolysis reaction with fatty amines.

Efficient solvent-free cationization of alkylpolyglycoside based surfactant compositions using natural glycine betaine

We describe here a new strategy for the preparation of 100% bio-based sugar based cationic surfactants using glycine betaine butyl ester as the cationizing agent. We first studied NaHCO3-catalyzed transesterification reactions of pure fatty alcohols and equimolar mixtures of alkyl glucosides or xylosides and fatty alcohols. Using solvent-free processes, moderate to high levels of cationization (48–90%) concerning both fatty alcohols and carbohydrates, were obtained with a certain regioselectivity toward C6 and/or C3 positions in the D-glucose and D-xylose series. This synthetic approach can also be extended to commercial alkylpolyglycosides containing large proportions of fatty alcohols (90–96%) to provide original cationized glycoside compositions, as (co-)emulsifiers.

Synthesis, spectral characterization, molecular modeling, antibacterial and antioxidant activities and stability study of binuclear Pd(II) and Ru(III) complexes with novel bis-[1-(2-[(2-hydroxynaphthalen-1-yl)methylidene]amino}ethyl)-1-ethyl-3-phenylthiourea] ligand: Application to detection of cholesterol

A novel bis-[1-(2-[(2-hydroxynaphthalen-1-yl) methylidene]amino}ethyl)-1-ethyl-3-phenylthiourea] Schiff base (L) and its binuclear palladium and ruthenium complexes have been prepared and characterized by ESI-MS, elemental analysis, NMR (1H NMR, 13C NMR, COSY, NEOSY and HSQC), FT-IR, ATR, UV-Visible spectra, TGA measurements, conductivity and cyclic voltammetry. The experimental results and the molecular parameters calculated using DFT method revealed a square planar geometry around Pd and octahedral geometry around ruthenium metal. The antibacterial activity of the ligand L and its complexes was evaluated against different human bacteria. In addition, the formation constants of the synthesized Schiff base-metal complexes and the systems formed with these chelates and cholesterol were estimated using spectrophotometric technique. The detection of cholesterol using novel Pd and Ru Schiff base complexes was studied using fluorometric method, and the measurements showed that the sensitive fluorometric response towards cholesterol analysis was determined using palladium complex. The limit of detection (LOD) of cholesterol calculated using this complex (4.6 μM) is lower (better) than LOD found using ruthenium complex (19.1 μM) and different compounds previously published around linear range of 0-5 mM.

Isolation of Bioactive Compounds from Calicotome villosa Stems

A phenylethanoid, two steroids, a flavone glucoside and a chalcone have been isolated for the first time from the stems of Calicotome villosa together with a previously isolated flavone glucoside. Their structures were determined by spectroscopic analyses (NMR, HRMS) as basalethanoïd B (1), β-sitosterol and stigmasterol (2), chrysine-7-O-β-d-glucopyranoside (3), chrysine 7-((6′′-O-acetyl)-O-β-d-glucopyranoside) (4) and calythropsin (5). The crude extracts and the isolated compounds (except 4), were evaluated for their antioxidant, antimicrobial (against two Gram-positive bacterial strains: Staphylococcus aureus, Bacillus cereus, four Gram-negative bacterial strains: Staphylococcus epidermidis, Klebsiella pneumonia, Acinetobacter baumanii, and three yeasts: Candida albicans, Candida tropicalis, and Candida glabrata), hemolytic, antidiabetic, anti-inflammatory and cytotoxic activity. The crude extracts showed good ability to scavenge the free radical DPPH. Methanol stem extract followed by the dichloromethane stem extract showed moderate antimicrobial potency; furthermore, at 1 mg/mL the methanol extract showed an inhibition of C. albicans growth comparable to nystatin. Dichloromethane, methanol, and aqueous extracts inhibited 98%, 90%, and 80% of HeLa cell proliferation at 2 mg/mL respectively. Weak hypoglycemic and hemolytic effects were exhibited by the crude extracts. Among all the tested compounds, compound 3 showed remarkable hypoglycemic potential (93% at 0.1 mg/mL) followed by compound 5 (90% at 0.3 mg/mL). Compound 5 was the most effective in the DPPH. scavenging assay (100% at 0.1 mg/mL) and cytotoxic assay on HeLa cells (99% and 90% after 24 and 48 h of treatment at 0.1 mg/mL, respectively). No anti-inflammatory effects were displayed by any of the crude extracts or the isolated compounds at any of the tested concentrations.

Structural and rheological properties of kappa (κ)-carrageenans covalently modified with cationic moieties

Cationized kappa-carrageenans containing 2-hydroxy-3-(trimethylammonium)propyl groups with various degrees of substitution (0.13–0.75) were synthesized by reaction of sulfated polysaccharides with 3-chloro-2-hydroxypropyltrimethyl ammonium chloride (QUAB 188) in alkaline solutions through the generation of the corresponding 2,3-epoxy reagent in situ. The structure of the modified algal polysaccharides was characterized without any further treatment or after methanolysis and/or enzymatic depolymerization, by means of spectroscopic tools (FT-IR, NMR, Mass spectrometry) and high-performance size exclusion chromatography (HPSEC). Significant differences in the rheological properties of these cationized kappa-carrageenans have been found depending on the DS values and the presence of KCl salt. Despite their lower molecular weights in comparison with native polysaccharides, cationized kappa-carrageenans with a DS of 0.75 exhibited high viscosity and gelling behaviors mediated by the high density of quaternary ammonium groups.