Luc Picton

Analysis of a complex polysaccharide (gum arabic) by multi-angle laser light scattering coupled on-line to size exclusion chromatography and flow field flow fractionation

The heterogeneous polysaccharide gum arabic has been characterized using size exclusion chromatography (SEC) and flow field flow fractionation (F4) coupled on-line to multi-angle laser light scattering (MALLS). Two distinct populations have been shown. About 80% of the material consist of highly branched arabinogalactan (AG) units. The rest is mainly composed of heterogeneous arabinogalactan–protein complex (AGP) of high molecular weight. The F4/MALLS method is shown to allow the complete analysis of gum arabic whereas SEC gave only partial information. From light-scattering-based radii of gyration (Rg) and F4-based hydrodynamic radii (Rh) we found that the ratio Rg/Rh is near 0.8 for AGP. This value is reasonably consistent with a globular conformation and gives further evidence in favour of the “wattle blossom model” proposed by Connolly et al.

New amphiphilic and pH-sensitive hydrogel for controlled release of a model poorly water-soluble drug.

This paper presents the development of new pH-sensitive, amphiphilic and biocompatible hydrogels based on alginate-g-PCL, cross-linked with calcium ions to form beads, prepared for controlled delivery of poorly water-soluble drug. We have focused our study on the effect of the length of PCL chains (530 and 1250 g mol(-1)). Swelling profiles obtained clearly indicated that these hydrogels swell slightly (10-14%) in a simulated gastric fluid (pH 1.2), and strongly (700-1300% before disintegration) in a simulated intestinal fluid (pH 6.8). In both media, rates of swelling were lower for beads based on amphiphilic derivatives than for alginate/Ca2+ ones due to the hydrophobic PCL grafts, and decreased when hydrophobic character increased. A model drug, theophylline, was entrapped into these hydrogels and release studies were carried out. The drug was protected in acidic fluid (only 14-20% of release for alginate-g-PCL hydrogel against 35% of release for alginate hydrogel during 350 min). The drug is released completely in neutral fluid due to ion exchanges and disintegration of the hydrogel. PCL leads to decrease in the release kinetics in SIF (2h for alginate-g-PCL/Ca2+ beads against 1h for alginate/Ca2+ beads). It was demonstrated that the establishment of clusters inside beads by intramolecular interactions between PCL grafts of 530 g mol(-1) in salt media allowed to retain the drug and to slow down its release considerably.

Aggregation of amphiphilic pullulan derivatives evidenced by on-line flow field flow fractionation/multi-angle laser light scattering.

Size-exclusion chromatography (SEC) is a useful steric separation technique for the analysis of water-soluble polysaccharides in aqueous solution. However, in the case of amphiphilic derivatives, the usefulness is limited because of interactions between hydrophobic segments and the stationary phase. Alkyl-bearing pullulans differing from the extent and the length of alkyl groups were characterized using flow-field flow fractionation with on-line coupling multi-angle laser light scattering (F4/MALLS). Comparison of SEC and F4 is presented and the interest of F4 in the field of amphiphilic derivatives is demonstrated.

Associative pullulan gels and their interaction with biological active substances.

This paper studies the synthesis and properties of anionic and/or amphiphilic pullulan microparticles crosslinked with epichlorohydrine or with sodium trimethaphosphate. The polysaccharide gels were physicochemically characterized and their interaction with enzymes (lysozyme) was studied with the aim to appreciate the performances for separation/purification/immobilization of the enzymes or controlled release drug systems.

Production and characterization of new families of polyglucuronic acids from TEMPO-NaOCl oxidation of curdlan

Curdlan from Agrobacterium sp. was oxidized using 2,2,6,6,-tetramethylpiperidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems at pH 11. The effects of oxidation conditions on degrees of oxidation and polymerization of the products obtained were studied using SEC-MALLS, NMR and IR analyses. Different families of water-soluble beta-(1,3)-polyglucuronic and beta-(1,3)-polyglucoglucuronic acid sodium salts were quantitatively generated with a yield of 80% and without significant loss of their molecular weights. Given that beta-(1,3)-polyglucuronic acids prepared from the regioselective oxidation of curdlan by the TEMPO-NaBr-NaClO systems regularly consist of the glucuronic acid repeating unit; they may open new biotechnological fields for the utilizations of water soluble forms of curdlan.

Enhancement of the Solubility and Efficacy of Poorly Water-Soluble Drugs by Hydrophobically-Modified Polysaccharide Derivatives

PurposeThis work was intended to develop and evaluate a new polymeric system based on amphiphilic carboxymethylpullulans (CMP49C8 and CMP12C8) that can spontaneously self-assemble in aqueous solutions and efficiently solubilize hydrophobic drugs.MethodsThe self-assembling properties of CMP49C8 and CMP12C8 were characterized by fluorescence spectroscopy and surface tension measurements. The solubilization of benzophenone and docetaxel was assessed from surface tension measurements, UV spectrometry and HPLC assays. The in vitro cytoxicity of CMP49C8 solutions and the docetaxel commercial vehicle (Tween 80®/Ethanol–water) were evaluated in the absence and in the presence of docetaxel.ResultsCompared to CMP12C8, CMP49C8 in aqueous solutions appeared to self-organize into monomolecular aggregates containing hydrophobic nanodomains, and to significantly increase the apparent solubility of benzophenone. Docetaxel solubility could also be improved in the presence of CMP49C8 but to a lower extent due to the surface properties of the drug. Nevertheless, in vitro, the cytotoxicity studies revealed that against cancer cells, the CMP49C8-docetaxel formulation was equipotent to the commercial docetaxel one. Furthermore, in the absence of the drug, CMP49C8 appeared less cytotoxic against macrophages than the Tween® 80/Ethanol–water.ConclusionsCMP49C8 is a good candidate for solubilizing hydrophobic drugs and could be applied to docetaxel formulations.

Adsorption of cellulose derivatives onto montmorillonite: a SEC–MALLS study of molar masses influence

Abstract Adsorption properties of two commercial neutral cellulose derivatives: hydroxyethylcellulose (HEC) and hydrophobically modified hydroxyethylcellulose (HMHEC) onto montmorillonite were investigated in pure water and in salt solution. Regardless of the polymer, the adsorption onto clay is always larger in pure water than in salt solutions. In other respects, adsorption of the associative HMHEC is always slightly enhanced in comparison with its parent HEC. For both polymers, only simple layer type of adsorption is evidenced (Scatchard linearisation). Finally, a SEC–MALLS study conducted with HEC has shown that adsorption on clay occurs preferentially for the lower molar masses. The adsorbed amount of HEC on clay is larger for the lower molar masses.

Hypothesis: Hyperstructures regulate bacterial structure and the cell cycle

A myriad different constituents or elements (genes, proteins, lipids, ions, small molecules etc.) participate in numerous physico-chemical processes to create bacteria that can adapt to their environments to survive, grow and, via the cell cycle, reproduce. We explore the possibility that it is too difficult to explain cell cycle progression in terms of these elements and that an intermediate level of explanation is needed. This level is that of hyperstructures. A hyperstructure is large, has usually one particular function, and contains many elements. Non-equilibrium, or even dissipative, hyperstructures that, for example, assemble to transport and metabolize nutrients may comprise membrane domains of transporters plus cytoplasmic metabolons plus the genes that encode the hyperstructures enzymes. The processes involved in the putative formation of hyperstructures include: metabolite-induced changes to protein affinities that result in metabolon formation, lipid-organizing forces that result in lateral and transverse asymmetries, post-translational modifications, equilibration of water structures that may alter distributions of other molecules, transertion, ion currents, emission of electromagnetic radiation and long range mechanical vibrations. Equilibrium hyperstructures may also exist such as topological arrays of DNA in the form of cholesteric liquid crystals. We present here the beginning of a picture of the bacterial cell in which hyperstructures form to maximize efficiency and in which the properties of hyperstructures drive the cell cycle.

Highly sulphated galactan from Halymenia durvillei (Halymeniales, Rhodophyta), a red seaweed of Madagascar marine coasts.

Halymenia durvillei is a red seaweed with a great potential as sulphated galactan producer collected in the coastal waters of small island of Madagascar (Nosy-be in Indian Ocean). To elucidate the structure of its polysaccharide, NMR (1H and 13C), FTIR, HPAEC and different colorimetric methods were carried out. It has been shown that this polysaccharide, consisted mainly of galactose, was branched by xylose and galactose in minor amounts. Arabinose and fucose were also detected. This galactan was found highly sulphated (42%, w/w) and pyruvylated (1.8%, w/w). Analysis of glycosidic linkages by CPG-MS and 13C NMR indicated that the polysaccharide has the defining linear backbone of alternating 3-beta-D-galactopyranosyl units and 4-linked alpha-L/D-galactopyranosyl residues. 3,6-Anhydrogalactose units have been also detected in minor quantity. This lambda-carrageenan like polysaccharide has shown original sulphatation patterns with 2-O (26%) or 2/6-O (58%) sulphated 3-linked beta-D-galactopyranosyl units and 6-O (19%) or 2/6-O (47%) 4-linked alpha-L/D-galactopyranosyl residues.

Effect of chitosan coating on the swelling and controlled release of a poorly water-soluble drug from an amphiphilic and pH-sensitive hydrogel.

In the present work, a new particulate controlled release system was prepared, by coating alginate-g-PCL/Ca(2+) beads with chitosan. The swelling behaviour and controlled release of a poorly water-soluble drug (theophylline) model were studied in media of varying pH, by simulating human fluids at 37 degrees C. In a simulated gastric fluid (SGF, pH 1.2), coated beads presented weak swelling (8-22%) and weak release rates (24-32% within 120min), and were able to protect the drug from this harsh environment. In a simulated intestinal fluid (SIF, pH 6.8), the swelling rates of amphiphilic beads (before disintegration) were strongly reduced (300-1100%) comparatively with those of uncoated beads (700-1700%). This can be explained by the strong electrostatic interactions between the amino groups of chitosan and the carboxylate groups of alginate-g-PCL, leading to the formation of a protective membrane of strong polyelectrolyte complex around the beads. This outermost layer effectively promoted the stability of beads under gastro-intestinal tract conditions, while the hydrophobic interactions between theophylline and PCL grafts allowed a considerable slowing down of the drug release. It was found out that combination of the protective effect of the polyelectrolyte membrane in SIF associated with the hydrophobicity of PCL grafts allowed to release a poorly water-soluble drug, in a controlled manner, for 7h, along a simulated gastro-intestinal tract.