Gisèle Volet

Preparation and characterization of water soluble high molecular weight β-cyclodextrin-epichlorohydrin polymers

Abstract Water soluble β-cyclodextrin polymers were prepared from β-cyclodextrin crosslinked with epichlorohydrin under basic conditions. The influence of preparation conditions on the molecular weight distribution has been investigated. The knowledge of this relationship allows for the choice of reaction parameters according to the desired weight distribution of the β-cyclodextrin polymer. A procedure was developed for the preparation of high molecular weight water soluble polymer ( M w higher than 10 4 ).

Polyoxazoline adsorption on silica nanoparticles mediated by host–guest interactions

The objective of this work is to develop an original method of polyoxazoline brush generation based on supramolecular chemistry onto silica nanoparticles. A first layer is realized by adsorption of a polymer bearing β-cyclodextrin units (PβCD). This allows the anchoring of a second layer made of alkyl end-capped poly(2-methyl-2-oxazoline) (POXZ-C(n)) via host-guest interactions between the alkyl end groups and the β-cyclodextrin units. The characteristics of the surface layers were studied by dynamic light scattering. A first study of PβCD adsorption allowed to define the conditions of homogeneous PβCD coverage onto the silica surfaces. Then the adsorption of the second polymer onto the PβCD coated nanoparticles was studied as a function of the POXZ-C(n) solution concentration. Brush layers with chains in extended conformation could be obtained above a critical POXZ-C(n) concentration. The large thickness sensitivity to the feeding POXZ-C(n) concentrations allowed to show that the POXZ-C(n) grafting ratio can be controlled by the POXZ-C(n) concentrations. In a limited concentration range, the nature of the anchoring end-group (C(12) or C(18)) does not influence the shape of the POXZ layer.

New procedures for glycophorin A purification with high yield and high purity

Glycophorin A (GPA) is the major glycoprotein of the human erythrocyte membrane. It is known to form, in SDS gels as well as in a membrane environment, homodimers, and also heterodimers with the homologous molecule Glycophorin B (GPB). It is shown in this report that the propensity of GPA to dimerize with GPB precludes satisfactory preparation with high yield of pure GPA using classical techniques including SEC and RPLC. It was demonstrated using multiple angle light scattering that GPA is eluted from RPLC columns as dimers. A convenient procedure was devised which allowed us to get pure GPA with high yield. This procedure consists of selectively blocking GPA-GPB heterodimer formation by selective modification of Cysteine 50 of GPB before RPLC.

Bifunctionalized dextrans for surface PEGylation via multivalent host-guest interactions

The main goal of this work was to develop a supramolecular chemistry strategy to decorate interfaces with polyethylene glycol (PEG) grafts. A series of novel bifunctionalized dextrans, bearing 40-60 PEG pending chains and 12-24 hydrophobic adamantyl groups, have been prepared by copper(I)-catalyzed azide-alkyne cycloaddition. Their binding properties toward native βCD and βCD polymers were characterized both in solution and at interface using isothermal titration microcalorimetry and surface plasmon resonance. The polymers were found to form stable layers onto neutral and positively charged βCD-polymer films pre-adsorbed on gold surfaces, due to multivalent interpolymer host-guest interactions. The thickness and stability of the layers could be tuned by varying the ratio between the degrees of substitution by PEG and adamantyl groups.

Synthesis of a new dextran-PEG-β-cyclodextrin host polymer using “Click” chemistry

The objective of this work was to synthesize a new type of dextran-based host polymer in which β-cyclodextrin (βCD) moieties are linked to the dextran backbone via flexible hydrophilic poly (ethylene glycol) (PEG) spacer. Short PEG-acrylate (Mn~375) was coupled with 5-hexynoic acid and grafted to the thiolated dextran using thiol-ene “click” chemistry. In the following step 6-monodeoxy-6-monoazido-βCD was “clicked” to the obtained alkyne terminated Dext-g-PEG copolymer (Dext-g-PEG-Hex-5-ynoate) using a copper (I)-catalyzed azide–alkyne cycloaddition. The reaction conditions and catalytic system were optimized. The synthesized Dext-g-PEG-βCD polymers have been characterized by 1H-NMR spectroscopy and isothermal titration microcalorimetry and they show good binding properties comparing with conventional cross-linked pβCD.

Cyclodextrin-Based Supramolecular Multilayer Assemblies for the Design of Biological Optical Sensors Using Tilted Fiber Bragg Gratings

In this work, we demonstrate the possibility to use optical fiber incorporating photowritten tilted fiber Bragg gratings (TFBG) as optical detection system for the real time monitoring of interfacial adsorption events and biological recognition. For this purpose, immobilization of cyclodextrin polymers onto the surface of optical fiber was envisioned through the layer-by-layer self-assembly method with the aim of developing sensing layers with well-defined host properties. To develop a biological sensor, amphiphilic dextran, acting as intermediate layer between the polyelectrolyte multilayer assembly and the biological probe, was immobilized though inclusion complex formation. The dextran layer exhibit a dual functionality: (i) it prevents non-specific proteins adsorption and (ii) it allows covalent immobilization of anti-bovine serum albumine through activation of the hydroxyl groups with 1,1’-carbonyl diimidazole. To verify the feasibility of our strategy, fluorescence microscopy was applied to evidence the effective inclusion of fluorescent macromolecular – flurorescein labelled dextran bearing adamantane as side-grafts – species within the cyclodextrin cavities present onto the optical fiber interface and at the last layer to prove the grafting of anti bovin serum albumin onto the amphiphilic dextran by a capture of fluorescein bovin serum albumin by the antibody layer. In a further step, it was demonstrated that the elaboration of the multilayer assembly can be monitored in real time using the TFBG sensor.

Study of some side reactions in the synthesis of diblock copolymers of isobutylvinylether and 2-methyl-2-oxazoline by cationic polymerization

The blocking of 2-methyl-2-oxazoline from living poly(isobutylvinylether) was studied. First, the initiation of isobutylvinylether (IBVE) by the system HI-I 2 was characterized. Experiments by the incremental monomer addition method confirmed that the system was living. A study of the homopolymerization of 2-methyl-2-oxazoline confirmed that this polymerization must be carried out at much higher temperature than the living polymerization of IBVE. A study of the behaviour of PIBVE at the temperature required to polymerize 2-methyl-2-oxazoline revealed that this polymer exhibited dealcoholation. The detrimental effect of this side reaction during polymerization of 2-methyl-2-oxazoline blocking could not be avoided by the presence of ditertiobutylpyridine (DtBP). However, block copolymers containing from 20 to 70% of IBVE were obtained and characterized.

Host–guest interaction and structural ordering in polymeric nanoassemblies: Influence of molecular design

Host-guest nanoassemblies made from spontaneous self-association of host and guest polymers in aqueous solutions have been studied. The specific motivation behind this work was to clarify the impact of the molecular design of the polymers on the interactions between them and on the inner structure of the resulting nanoassemblies. The polymers were composed of a dextran backbone, functionalized with either pendant β-cyclodextrin (CD) or adamantyl (Ada). Those groups were connected to the backbone either directly or with hydrophilic polyethylene glycol (PEG) spacers. To study the impact of those spacers we have proposed a synthetic pathway to new guest polymers. The latter relied on the use of thiol-substituted dextrans as a scaffold, which is subsequently transformed into PEG-Ada grafted guest polymers via nucleophile-mediated thiol-click reaction. Surface plasmon resonance (SPR) studies evidenced strong mutual affinities between the host and guest polymers and showed that the stoichiometry was close to the ideal one (CD/Ada = 1/1) when PEG spacers were introduced. The structure of the nanoassemblies was studied by a combination of dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). The nature of the individual host or guest polymers has a strong impact on the size and internal structure of the resulting nanoassemblies. The presence of PEG spacers in the polymers led to smaller and less compact nanoassemblies, as evidenced by their large correlation length values (4-20nm compared to 2nm without PEG spacers). At the same time, all types of nanoassemblies appear to have radial density distribution with denser cores and pending polymer chains at the periphery. This study, centered on the influence of the molecular design on the host-guest interactions and structural ordering in polymeric nanoassemblies, will help to tailor host-guest nanoassemblies with attractive drug delivery profiles.