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

Pullulan-cyclodextrin microspheres. A chromatographic approach for the evaluation of the drug-cyclodextrin interactions and the determination of the drug release profiles

Pullulan microspheres containing cyclodextrin (CyD) were obtained by chemical crosslinking with epichlorohydrin of an alkaline solution of pullulan (Pul) and alpha-, beta- or gamma-CyD. The amount of alpha-, beta- and gamma-CyD in microspheres was 120, 156, and 138 micromol/g, respectively, as determined from the percentage of iodine incorporated in the hydrophobic cavity of CyD's. Microspheres were packed in a glass column and the liquid chromatographic behaviour by isocratic elution of different drugs or typical organic compounds (TOC), taken as model drugs, was investigated. The increase of the retention volume (V(R)) of each compound, depending on the interaction(s) between CyD's cavity and the considered molecule, is characterized by a broadening of the peaks. The interaction coefficient K, corresponding to the ratio between the V(R) value of each tested molecule on Pul-alpha-, Pul-beta- and Pul-gamma-CyD active stationary phase and the V(R) value of benzoic acid on St/maltodextrin neutral stationary phase, was determined. According to K values, the accurate prediction can be done on the potential drugs to be conditioned in suitable CyD cavity. Values of K allow to anticipate the release profiles of drugs considered.

Synthesis and enzymatic degradation of epichlorohydrin cross-linked pectins

The water solubility of pectin was successfully decreased by cross-linking with increasing amounts of epichlorohydrin in the reaction media. The initial molar ratios of epichlorohydrin/ galacturonic acid monomer in the reaction mixtures were 0, 0.37, 0.56, 0.74, 1.00, 1.47, and 2.44. The resulting epichlorohydrin cross-linked pectins were thus referred to as C-LP0, C-LP37, C-LP56, C-LP75, C-LP100, C-LP150, and C-LP250, respectively. Methoxylation degrees ranged from 60.5 +/- 0.9% to 68.0 +/- 0.6%, and the effective cross-linking degrees, determined by quantification of the hydroxyl anions consumed during the reaction, were 0, 17.8, 26.0, 38.3, 46.5, 53.5, and 58.7%. respectively. After incubating the different cross-linked pectins (0.5% w/v) in 25 mL of 0.05 M acetate-phosphate buffer (pH 4.5), containing 50 microL of Pectinex Ultra SP-L (pectinolytic enzymes), between 60 and 80% of the pectin osidic bounds were broken in less than 1 hr. Moreover, increasing the cross-linking degree only resulted in a weak slowing on the enzymatic degradation velocity.

Insight into the chiral recognition of warfarin enantiomers by epichlorhydrin/beta-cyclodextrin polymer-based supports: determination of stoichiometry and stability of warfarin/beta-cyclodextrin polymer complexes

The complexation of warfarin (W) enantiomers by a hydrosoluble high-molecular-weight beta-cyclodextrin/epichlohydrin polymer (EP/beta-CD polymer) was studied using HPLC with a mobile phase of methanol/0.1 M Na acetate/acetic acid (pH 4) at 22 degrees C. It was found that the complexes (W/beta-CD unit) have a 1:1 stoichiometry. The stability constants of the complex involving each enantiomer and the polymer beta-CD units were determined in the mobile phase, and the highest stability of the complex (S-warfarin/beta-CD unit) was observed. From the chromatographic separations of warfarin enantiomers on different beta-CD or its derivative supports, we have deduced the role of the simultaneous presence of several glyceryl (-O-CH(2)-CHOH-CH(2)-O-) and dihydroxypropyl (-O-CH(2)-CHOH-CH(2)OH) groups on one beta-CD ring in promoting the chiral recognition of warfarin enantiomers.

Carbohydrate/monomer complexes in aqueous polymerizations: methylated-beta-cyclodextrin mediated aqueous polymerization of hydrophobic methacrylic monomers

Hydrophobic methacrylic monomers were polymerized in aqueous media using methylated (1.8)-beta-cyclodextrin (MeCD) additives. Hydrophobic monomers tert-butyl methacrylate (tBuMA), cyclohexyl methacrylate (CMA), and 2-ethylhexyl methacrylate (2EHMA) were each dissolved in chloroform with MeCD. Chloroform was then evaporated to yield solid monomer/cyclodextrin complexes. Complexes were shown by 1H NMR and thermogravimetric analysis (TGA) to have molar ratios of monomer to MeCD as high as 0.72/1.00. The water-soluble complexes were readily polymerized in aqueous media using free radical initiation. During polymerization, hydrophobic methacrylic polymers precipitated and the majority of MeCD remained in solution. Poly(alkyl methacrylates) synthesized via this method exhibited number-average molecular weights ranging from 50,000 to 150,000 with polydispersities from 3.2 to 5.5 depending on monomer structure, and isolated yields were as high as 86%. Additionally, corresponding methacrylic/carbohydrate films were prepared and examined. High molecular weight poly(tBuMA), poly(CMA), and poly(2EHMA) were blended with MeCD to produce optically clear films with as high as 20 wt % MeCD. Differential scanning calorimetry (DSC) characterization indicated that the glass transition temperatures of these novel carbohydrate blends were controllable over a 20 degrees C range depending on the relative concentration of each component.

High-performance liquid chromatographic study of the interactions between immobilized beta-cyclodextrin polymers and hydrophobically end-capped polyethylene glycols

The formation of inclusion complexes between polyethylene glycols (PEGs) bearing hydrophobic ends (naphtyl and phenyladamantyl) and beta-cyclodextrin polymers (poly beta-CD) immobilized onto silica particles was studied by high-performance liquid chromatography (HPLC). It was shown that hydrophobic interactions were involved in the retention mechanism of these compounds, since retention volumes decreased when organic solvents were added to the mobile phase while it was the contrary in the presence of salts. Moreover, the association could be reversed by adding a competitor (hydroxypropyl beta-cyclodextrin) to the mobile phase. A theoretical model permitted the evaluation of affinity constants of 1:1 complexes formed between the modified PEGs and the immobilized poly beta-CD which depended on the type of hydrophobic groups grafted to the PEG.

Study of the retention properties of warfarin enantiomers on a beta-cyclodextrin polymeric support

High-performance liquid chromatography was used to study the retention properties of (R)- and (S)-warfarins on a silica support coated with a beta-cyclodextrin polymer. The influence of the methanol content of the acetate buffer eluent was investigated at pH 4. The measure of the variations of retention time with temperature enables one to determine the enthalpy and the entropy of adsorption. The plot of the two thermodynamic functions shows a minimum around 30% (v/v) methanol. At low methanol contents, the decrease of the hydrophobic interactions with increasing methanol content explains the decrease of the enthalpic and entropic terms. Above 40% (v/v) methanol, the decrease of the adsorption enthalpy absolute value is due to the solvation by the organic component. From the analysis of peak shape in mass-overload conditions, the column capacity toward each enantiomer was determined. A lower capacity was found toward (S)-warfarin, the more retained enantiomer. Peak shape analysis in mass-overload conditions was used to determine the adsorption isotherm. A Langmuir-type adsorption isotherm accounts well for the experimental data.

Polymers of malic acid and 3-alkylmalic acid as synthetic PHAs in the design of biocompatible hydrolyzable devices

Poly(beta-malic acid) and poly(beta-3-alkylmalic acid) derivatives, as synthetic polyhydroxyalkanoates (PHAs), present several advantages as macromolecular materials for temporary biomedical applications. Indeed, such polymers, which can be synthesized through different chemical and biological routes, have cleavable ester bonds in their backbone for hydrolytic degradation, stereogenic centres in the monomers units for controlling the macromolecular structure. bioassimilable or non-toxic repeating units and lateral chemical functions which can be adapted to specific requirements. The strategy for building such complex architectures, with one or several specific pendant groups, is based on the anionic ring-opening polymerization or copolymerization of the large family of malolactonic and 3-alkylmalolactonic acid esters. Because we are able to control the monomer synthesis and the polymerization step, we have been able to prepare different degradable materials for the biomedical field, such as: degradable associating networks made up by the association of random copolyesters containing a small percentage of hydrophobic moieties and beta-cyclodextrin copolymers; degradable macromolecular micelles constituted by degradable amphiphilic block copolymers of poly(beta-malic acid) as hydrophilic segments and poly(beta-alkylmalic acid alkyl esters) as hydrophobic blocks; and degradable nanoparticles made up by hydrophobic poly(beta-malic acid alkyl esters) derivatives. We have also prepared a terpolymer which exhibits growth factor-like properties in vivo. Finally, poly(beta-malic acid) has been used as an additive in the preparation of peritoneal dialysis bags.