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Porphyrins and their derivatives have been widely used in catalysis, energy conversion, photonics, and biomedicine; however, their use in biological applications is restricted by their limited solubility in aqueous systems. We have prepared a water-soluble copolymer containing moieties of naturally occurring protoporphyrin IX using direct copolymerization of a poly(ethylene glycol) (PEG) methacrylate monomer with protoporphyrin IX via free-radical polymerization. The content of protoporphyrin IX in the copolymer was determined by[.sup.1H] NMR and UV-vis absorption spectroscopies. Their solution properties and the photostability of the protoporphyrin IX moiety in the copolymer provide direct evidence of the covalent incorporation of protoporphyrin IX within the copolymer. The copolymer showed a reversible phase transition in aqueous solution due to the lower critical solution temperature (LCST). The phase transition temperature varies with the pH of the solutions because of the protonation of the carboxylic acid groups. This copolymer may be useful as an alternative thermoresponsive material for biomedical applications. Key words: protoporphyrin IX, porphyrin copolymer, thermoresponsive properties, pH sensitivity. Les porphyrines et leurs derives ont ete largement utilises en catalyse, en conversion de l'energie, en photonique et en biomedecine, mais leur utilisation dans le domaine de la biologie est restreinte en raison de leur solubilite limitee dans les systemes aqueux. Nous avons prepare un copolymere soluble dans l'eau comportant des motifs de protoporphyrine IX d'origine naturelle par copolymerisation directe du methacrylate de poly(ethylene glycol) (PEG) avec la protoporphyrine IX en presence d'un amorceur de polymerisation radicalaire. Nous avons determine la teneur du copolymere en protoporphyrine IX par spectros-copie RMN [.sup.1H] et spectroscopie d'absorption UV-vis. La solubilite du copolymere et la photostabilite du fragment protoporphy-rine IX dans celui-ci constituent une demonstration directe de l'incorporation covalente de la protoporphyrine IX dans le copolymere. Ce dernier a presente une transition de phase reversible en solution aqueuse en raison de sa temperature de solution critique inferieure (en anglais LCST pour lower critical solution temperature). La temperature de transition de phase varie selon le pH des solutions, en raison de la protonation des groupes acide carboxylique. Ce copolymere pourrait trouver des applications biomedicales comme nouveau materiau thermosensible. [Traduit par la Redaction] Mots-cles : protoporphyrine IX, copolymere de porphyrine, proprietes thermosensibles, sensibilite au pH., Introduction Porphyrins and their derivatives have shown to be promising for biomedical applications, because their photosensitizing properties make them suitable for photodynamic therapy [.sup.13C]-3) and antimicrobial photodynamic inactivation. (4-8) They [...]

Abstract: Two dimers of cholic acid were synthesized through simple covalent linkers. The dimers form invertible molecular pockets in media of different polarity; hydrophobic pockets are formed in water and [...]

Abstract: Bile acids are gaining increasing importance as building blocks in the development of novel polymeric materials. This is evidenced by the growing number of publications advocating the advantages of [...]

Polymeric microspheres responsive to pH and temperature changes have been prepared by a two-step surfactant-free emulsion polymerization with a polystyrene core and a hydrogel shell. The double sensitivity is achieved by the copolymerization in the shell layer of acrylic acid and N-isopropylacrylamide, which are pH- and thermo-responsive, respectively. Above a certain critical concentration, these microspheres are able to self-assemble into crystalline colloidal arrays, causing intense visible light diffraction. The behavior of these structures has been studied and correlated to the properties of the microspheres. The packing of these microspheres results in stimuli-sensitive colloidal crystals, with a behavior directly linked to the interactions between the particles and the surrounding media. Key words: core-shell microspheres, surfactant-free emulsion polymerization, pH and thermo-sensitivity, crystalline colloidal arrays. Des microspheres doublement sensibles et composees d'un coeur de polystyrene entoure d'une couche d'hydrogel ont ete synthetisees par polymerisation en emulsion sans tensioactif. La double sensibilite a ete obtenue grace a la copolymerisation de l'acide acrylique et du N-isopropylacrylamide, tous deux connus pour etre sensibles respectivement au pH et a la temperature. Au dessus d'une concentration critique, ces microspheres sont capables de s'auto-assembler pour former des cristaux colloidaux et affichent des couleurs intenses dues a la diffraction de la lumiere visible. Le comportement de ces structures a ete etudie en rapport avec les proprietes des particules. L'empilement de ces microspheres donne des cristaux colloidaux sensibles a leur environnement, propriete qui semble etre liee a la nature des interactions entre les particules. Mots-cles : microspheres coeur-coquille, polymerisation en emulsion sans tensioactif, sensibilite au pH et a la temperature, cristaux colloidaux., Introduction Polymer microspheres have been the subject of intense research interests for biosensor-related applications because of their high surface area, hence fast response and easy functionalization. (1) Stimuli-responsive microgels have [...]

NMR imaging techniques were used to study the effect of drug loading in cross-linked high-amylose starch tablets. The tablets contained acetaminophen with loading levels from 10 to 40 wt%. The absolute amount of the drug released increased with a larger amount of drug loading, but the percentages of drug released had only minor differences for the different tablets, probably due to the rapid formation of a gel layer for all the tablets, which slowed down drug release significantly. The release of drugs from the tablets in all cases is dominated by a diffusion mechanism before the disappearance of the dry core of the tablets. Radial and axial swelling and water uptake were found to increase with the amount of drug loading. The diffusion rates of water were comparable at the initial stage for all the tablets with different loadings, but became faster later for the tablets with higher amounts of drug loading as water diffusion may be facilitated by the hydrophilicity of the drug. Key words: NMR imaging, diffusion coefficient, high-amylose starch, drug loading. Resume : Les techniques d'imagerie RMN ont ete utilisees pour etudier l'effet de la charge en medicament dans les tablettes d'amidons reticules riche en amylose. Les tablettes contenaient un medicament, l'acetaminophene, de 10 a 40 pourcent en poids. La quantite absolue du medicament libere augmente avec une augmentation de la charge en medicament, mais les pourcentages de medicament libere n'ont que des differences mineures pour les differenies tablettes, probablement a cause d'une formation rapide d'une couche de gel aulour de toutes les tablettes qui ralenlit d'une facon significative la liberation du medicament. Les liberations de medicaments sont dominees dans tous les cas par un mecanisme de diffusion avant la disparition du coeur sec des tablettes. On a trouve que les gonflements radiaux et axiaux ainsi que ['absorption d'eau augmentent avec une augmentation de la charge en medicament. Les vitesses de diffusion de I'eau dans la periode initiale sont comparables pour toutes les tablettes comport ant des charges differenies de medicament, mais plus tard elles deviennent plus rapides pour les tablettes portam une quantite plus elevee de medicament, probablement en raison du fait que la diffusion est peut-etre facilitee par le caractere hydrophile du medicament. Mots-des : imagerie RMN, coefficient de diffusion, amidon a forte concentration d'amylose, charge en medicament., Introduction Cross-linked high-amylose starch (CHAS) has been demonstrated to be an effective controlled release matrix. (1-4) Once the CHAS tablets are bydrated, a consistent gel layer is formed very rapidly [...]

Abstract: Pulsed-field gradient NMR spectroscopy was used to study the interactions between small molecular probes and polymers bearing interacting groups. The self-diffusion coefficients of ethylene glycol and its oligomers and [...]

Abstract: Reversible addition-fragmentation chain transfer (RAFT) polymerization of N-alkyl substituted acrylamides has been carried out by the use of a trithiocarbonate (2-dodecylsulfanylthiocarbonyl-sulfanyl-2-methyl propionic acid) as the RAFT reagent. The N-alkyl [...]

The molecular weight dependence of the lower critical solution temperature of poly(N,N-diethylacrylamide) was studied with 11 samples of the polymer with a number-average molecular weight ([M.sub.n]) ranging from 9.6 x [10.sup.3] to 1.3 x [10.sup.6] g [mol.sup.-1] and relatively narrow polydispersity indices from 1.19 and 2.60. These samples were obtained by fractional precipitation of the polymer. LCST values of polymers were measured by turbidimetry and microcalorimetry. An inverse dependence of LCST on the molar mass was found and the LCST of the samples remained more or less a constant above a critical molecular weight of ca. 2 x [10.sup.5] g [mol.sup.-1]. The enthalpy and the entropy changes as well as the LCST of the polymer depend strongly on the molar mass of the polymer, especially in low molecular weight range. Key words: poly(N,N-diethylacrylamide), LEST, thermosensitive, phase diagram, effect of molecular weight.

The exchange between complexed and free dihydroxycholate ions in some aqueous dihydroxycholate-beta-cyclodextrin was investigated using nuclear magnetic resonance spectroscopy. Results showed that the complexed and free ions display separate 18-CH3 signals. The dominant exchange mechanism was observed to follow a unimolecular decomplexation step. The formation of the decomplexation reactions was found to be greatly influenced by dehydration.