Physicochemical properties of pH-controlled polyion complex (PIC) micelles of poly(acrylic acid)-based double hydrophilic block copolymers and various polyamines.

The physicochemical properties of polyion complex (PIC) micelles were investigated in order to characterize the cores constituted of electrostatic complexes of two oppositely charged polyelectrolytes. The pH-sensitive micelles were obtained with double hydrophilic block copolymers containing a poly(acrylic acid) block linked to a modified poly(ethylene oxide) block and various polyamines (polylysine, linear and branched polyethyleneimine, polyvinylpyridine, and polyallylamine). The pH range of micellization in which both components are ionized was determined for each polyamine. The resulting PIC micelles were characterized using dynamic light scattering and small-angle X-ray scattering experiments (SAXS). The PIC micelles presented a core-corona nanostructure with variable polymer density contrasts between the core and the corona, as revealed by the analysis of the SAXS curves. It was shown that PIC micelle cores constituted by polyacrylate chains and polyamines were more or less dense depending on the nature of the polyamine. It was also determined that the density of the cores of the PIC micelles depended strongly on the nature of the polyamine. These homogeneous cores were surrounded by a large hairy corona of hydrated polyethylene oxide block chains. Auramine O (AO) was successfully entrapped in the PIC micelles, and its fluorescence properties were used to get more insight on the core properties. Fluorescence data confirmed that the cores of such micelles are quite compact and that their microviscosity depended on the nature of the polyamine. The results obtained on these core-shell micelles allow contemplating a wide range of applications in which the AO probe would be replaced by various cationic drugs or other similarly charged species to form drug nanocarriers or new functional nanodevices.

Inclusion of ibuprofen in mesoporous templated silica: drug loading and release property.

The aim of this study is to determine the feasibility of loading biologically active molecules into templated mesoporous silica (MCM 41). This material shows an important mesoporosity associated to hexagonally organized channels, a narrow pore size distribution and a large surface area. Ibuprofen was selected as a model molecule since it is a well documented and much used anti-inflammatory drug. Furthermore, it has a lipophilic character and its molecular size is suitable for inclusion within the mesopores of the MCM 41 material. In order to load ibuprofen within the mesopores, adsorption experiments using various solvents or successive impregnations with solutions of ibuprofen in ethanol were performed. At each step of the loading process, the pore filling was characterized by nitrogen adsorption experiments and by X-ray diffraction. The impregnation procedure results in a significant improvement of the amount of ibuprofen loaded into MCM 41. The in vitro drug release was investigated with simulated biological fluids (gastric and intestinal). Hundred percent release is observed at the end of the in vitro experiment.

Preparation and characterization of siliceous material using liposomes as template.

Material synthesis using unilamellar liposomes with a high sol-gel temperature transition phase as a template leads to a new silica material.

A demonstration model for a selective and recyclable uptake of metals from water: Fe(III) ions complexation and release by a supported natural fluorescent chelator.

We describe here the preliminary stage of development of a process aiming at the selective uptake and release of metal ions from water. The process envisioned involves the encapsulation of highly selective natural chelates secreted by bacteria or other living species in mesoporous solids that could be used as usual resins. To demonstrate the feasibility of the concept, we use a model system involving pyoverdin, a natural Fe(III) ions chelator from a Pseudomonas fluorescens strain, encapsulated in a mesoporous templated silica. For this model study, the native fluorescence of the chelator allows a simpler follow-up and quantification of the uptake and release processes.

Analytical applications of retinoid-cyclodextrin inclusion complexes. 1. Characterization of a retinal-beta-cyclodextrin complex.

In studies in these laboratories on the supramolecular chemistry of the retinoids, it has been recently confirmed that inclusion of these substances within the cavity of cyclodextrins protects their excited states, thus improving their photochemical stability. In the present paper, the isolation is described of a crystalline stable complex between retinal and beta-cyclodextrin, which has been characterized by means of several techniques including atomic force microscopy (AFM). The complex shows distinct spectroscopic differences from both retinal and beta-cyclodextrin. Thus, it absorbs at lambda(max) = 380 nm in water whereas retinal is insoluble; it shows room-temperature luminescence, which retinal does not; finally, it give 1H-NMR and 13C-NMR spectra in d6-DMSO with clear differences in chemical shifts with respect to those of beta-cyclodextrin. Besides these studies in solution, the behaviour of the complex in the solid state has been compared with that of physical mixtures of retinal and beta-cyclodextrin. IR spectroscopy shows clear differences, particularly a shift in the retinal carbonyl absorption (1644-1672 cm-1). AFM studies reveal the existence of aggregates; X-ray diffractometry also supports the formation of a cyclodextrin-retinal complex.

Use of micellar media for the fluorimetric determination of ellipticine in aqueous solutions.

Ellipticine is a pyridocarbazole alkaloid with interesting antitumour activity. Use of neutral ellipticine is hampered by its very low water solubility and therefore this compound has been administered as a salt; however, nitrogen quaternization modifies the antitumour properties of ellipticine. Potential alternatives to quaternization include the use of cyclodextrins, and also the use of micellar media. The latter possibility is explored in this work as an analytical tool. The results obtained with model anionic (SDS), cationic (CTAB) and neutral (Brij-35) surfactants are described. Fluorimetric analysis shows that ellipticine solubilizes completely in the presence of all these compounds, as a result of its aromatic, planar structure. The use of micellar media considerably increases the slopes of the calibration curves with improved correlation coefficients (e.g. 0.8904 in water and 0.9982 with SDS). Micellar media also modify proton transfer processes, as a consequence of the apolar environment of the micellar phase. Deprotonation of ellipticine is hampered in SDS because of the relationship between this process and the surface charge of the micelles. Finally, fluorescence quenching in micellar media has been studied, it being found that surfactants provide protection towards this phenomenon.

Photoisomerization kinetics of cefuroxime axetil and related compounds.

The photoisomerization kinetics of aqueous solutions of cefuroxime axetil under irradiation at 254 nm was investigated by HPLC. The overall degradation is the result of a competition between the isomerization of the alkoxyimino group and the photolysis of the beta-lactam ring. Cefuroxime axetil exists as a mixture of two diastereomers which are shown to react at different rates. This is true not only for the photoisomerization step but also for ground-state hydrolysis in alkaline conditions. Photoisomerization of the alkoxyimino group is also observed for the anti isomer of cefuroxime axetil and for some of its degradation products. The quantum yields for all these photoisomerizations are always lower than 1%, which explains the relative importance of the photolysis step. A stationary syn to anti ratio of 1 is measured for cefuroxime axetil and of 2.1 for cefuroxime. From this and previous studies, it appears that cefuroxime axetil is the most sensitive under irradiation at 254 nm when compared to other antibiotics bearing the alkoxyimino group. Azetreonam is the most stable followed by cefotaxime, cefuroxime, and cefuroxime axetil.

Identification of proteolytic processing sites within the Gag and Pol polyproteins of feline immunodeficiency virus.

N-terminal amino acid sequencing, ion spray mass spectrometry, and cleavage of synthetic peptide substrates were used to identify the N and C termini of the mature Gag and Pol proteins of feline immunodeficiency virus (FIV). The Gag polyprotein encodes matrix (MA), capsid (CA), and nucleocapsid (NC) proteins. The Gag-Pol polyprotein encodes, in addition to the above proteins, protease (PR), reverse transcriptase (RT), dUTPase (DU), and integrase (IN). Secondary cleavage of RT at Trp-595-Tyr-596 of Pol yields a truncated form lacking the C-terminal RNase H domain. The observed and expected molecular masses of the viral proteins were in agreement, with three exceptions. (i) The molecular mass of MA was 14,735 Da, compared with a predicted mass of 14,649 Da, based on a single cleavage at Tyr-135-Pro-136 of Gag. The observed molecular mass is consistent with myristoylation of MA, which was confirmed by metabolic labeling of FIV MA with [3H]myristic acid. (ii) The N terminus of the NC protein is generated via cleavage at Gln-366-Val-367 of Gag, which predicts a mass of 25,523 for CA and 9,101 for the major form of NC. The observed mass of CA was 24,569, consistent with loss of nine C-terminal amino acids by a second cleavage of CA at Leu-357-Leu-358. Synthetic FIV protease accurately cleaved synthetic peptide substrates containing this site. (iii) The actual mass of NC (7,120 Da) was approximately 2 kDa smaller than the mass predicted by synthesis to the stop codon at the end of Gag (9,101 Da). Experiments are in progress to characterize additional cleavage(s) in NC.

Photodegradation kinetics under UV light of aztreonam solutions.

A photodegradation study of aztreonam solutions exposed to UV irradiation showed that the major product of degradation was the anti-isomer together with some unidentified products. This result was similar to that obtained with cefotaxime and it is postulated that this would be generally true of compounds containing an alkoxyimino group.

Photodegradation paths of cefotaxime.

The degradation kinetics of cefotaxime sodium salt in aqueous solution, under UV light at 254 nm, was investigated by HPLC and antibiotic activity. This degradation is the result of two competitive processes, an isomerization and a photolysis. This study is mostly about the isomerization step. The measured quantum yields for the cefotaxime to its anti-isomer and anti-isomer to cefotaxime isomerizations are, respectively, 0.10 and 0.12. A photostationary state characterized by an anti:syn ratio of 1.2 is obtained after 30 min of irradiation. The competitive photolysis, which actually consists of at least two processes (one on the delta 3-cephem ring and the second on the methoxyimino group), leads to an intense yellowing of the solution corresponding to the destruction of the molecule. The comparative evolution of the absorption spectra, under irradiation at 254 nm, of cefotaxime, thiazoximic acid, and 7-aminocephalosporanic acid shows that it is the delta 3-cephem ring photolysis which gives the yellow color. The major conclusion of this work is to call attention to the photoisomerization step which leads efficiently to the inactive anti-isomer, without giving any visible notice of degradation. Such a process is to be expected in all antibiotics containing an alkoxyimino linkage on the C-7 substitution.