Biomedical subjects

Conxita Solans

Publications and source records attributed to Conxita Solans.

7 recordsLinked to original sources

PubMed2006

Optimization of nano-emulsion preparation by low-energy methods in an ionic surfactant system.

The low-energy emulsification method Emulsion Inversion Point (EIP) was used to prepare O/W nano-emulsions in the W/potassium oleate-oleic acid-C(12)E(10)/hexadecane ionic system. This method had not practically been used in ionic systems up to now. The resulting droplet sizes, much smaller than those obtained with the high-energy emulsification methods, depend on the composition (formulation variables) and preparation variables (addition and mixing rate). Phase diagrams, rheology measurements, and experimental designs applied to nano-emulsion droplet sizes obtained were combined to study the formation of these nano-emulsions. To obtain small droplet sizes, it is necessary to cross a direct cubic liquid crystal phase along the emulsification path, and it is also crucial to remain in this phase long enough to incorporate all of the oil into the liquid crystal. When nano-emulsion forms, the oil is already intimately mixed with all of the components, and it only has to be redistributed. Results show that the smaller droplet sizes are obtained when the liquid crystal zone is wide and extends to high water content, because in this case, during the emulsification process, the system remains long enough in the liquid crystal phase to allow the incorporation of all of the oil. Around the optimal formulation variables, the liquid crystal zone crossed during emulsification is wide enough to incorporate all of the oil whatever mixing or stirring rate is used, and then the resulting droplet size is independent of preparation variables. However, when the composition is far from this optimum, the liquid crystal zone becomes narrower and the mixing of components controls the nano-emulsion formation. High agitation rates and/or low addition rates are required to ensure the dissolution of all of the oil into this phase.

Journal Article↗

PubMed2005

Studies on the formation of O/W nano-emulsions, by low-energy emulsification methods, suitable for pharmaceutical applications.

The formation of O/W nano-emulsions suitable for pharmaceutical application and the solubilisation of a practically non-water-soluble drug, lidocaine, have been studied in water/non-ionic surfactant/oil systems. Nano-emulsions were prepared by using low-energy emulsification methods, changing the composition at constant temperature. Kinetic stability was assessed by measuring droplet diameter as a function of time. Lidocaine solubilisation was studied in nano-emulsions with high water content. In the water/Cremophor EL/Miglyol 812 system the lowest droplet sizes, from 14 to 39nm at 10/90 and 40/60 oil/surfactant ratios, respectively, and 90% of water content, were obtained with an emulsification method consisting of stepwise addition of water to oil/surfactant mixtures at 70 degrees C. Nano-emulsions of this system showed high kinetic stability. Droplet diameters did not exceed 67nm after a period of at least 7 months. The maximum lidocaine concentration solubilised in nano-emulsions of the water/Cremophor EL/Miglyol 812 system with 90 and 95% of water content was 3.5 and 2.1%, respectively. These values are within the therapeutic range of lidocaine.

Chromatography, High Pressure Liquid↗

PubMed2005

Emulsion polymerization of styrene and methyl methacrylate using a hydrophobically modified inulin and comparison with other surfactants.

The use of a new class of graft polymer surfactants, based on inulin, in emulsion polymerization of poly(methyl methacrylate) (PMMA) and polystyrene (PS) particles is described. PS and PMMA were synthesized by emulsion polymerization, and stable particles with a high monomer content (50 wt %) were obtained with a very small amount of polymeric surfactant ([surfactant]/[monomer] = 0.0033). The latex dispersions were characterized by dynamic light scattering and by transmission electron microscopy to obtain the average particle size and the polydispersity index, and the stability was determined by turbidimetry measurements and expressed in terms of critical coagulation concentration. The last section gives a comparison of PMMA particles prepared by emulsion polymerization using classical surfactants from different types as emulsifiers with that obtained using the copolymer surfactant. It shows the superiority of INUTEC SP1 as it is the only one that allows stable particles at 20 wt % monomer content, with a smaller ratio [surfactant]/[monomer] = 0.002.

Journal Article↗

PubMed2005

The influence of surfactant mixing ratio on nano-emulsion formation by the pit method.

The formation of O/W nano-emulsions by the PIT emulsification method in water/mixed nonionic surfactant/oil systems has been studied. The hydrophilic-lipophilic properties of the surfactant were varied by mixing polyoxyethylene 4-lauryl ether (C12E4) and polyoxyethylene 6-lauryl ether (C12E6). Emulsification was performed in samples with constant oil concentration (20 wt%) by fast cooling from the corresponding HLB temperature to 25 degrees C. Nano-emulsions with droplet radius 60-70 nm and 25-30 nm were obtained at total surfactant concentrations of 4 and 8 wt%, respectively. Moreover, droplet size remained practically unchanged, independent of the surfactant mixing ratio, X(C12E6). At 4 wt% surfactant concentration, the polydispersity and instability of nano-emulsions increased with the increase in X(C12E6). However, at 8 wt% surfactant concentration, nano-emulsions with low polydispersity and high stability were obtained in a wide range of surfactant mixing ratios. Phase behavior studies showed that at 4 wt% surfactant concentration, three-liquid phases (W+D+O) coexist at the starting emulsification temperature. Furthermore, the excess oil phase with respect to the microemulsion D-phase increases with the increase in X(C12E6), which could explain the increase in instability. At 8 wt% surfactant concentration, a microemulsion D-phase is present when emulsification starts. The low droplet size and polydispersity and higher stability of these nano-emulsions have been attributed, in addition to the increase in the surface or interfacial activity, to the spontaneous emulsification produced in the microemulsion D-phase.

Journal Article↗

PubMed2004

Phase behavior and nano-emulsion formation by the phase inversion temperature method.

Formation of oil-in-water nano-emulsions has been studied in the water/C12E4/isohexadecane system by the phase inversion temperature emulsification method. Emulsification started at the corresponding hydrophilic-lipophilic balance temperature, and then the samples were quickly cooled to 25 degrees C. The influence of phase behavior on nano-emulsion droplet size and stability has been studied. Droplet size was determined by dynamic light scattering, and nano-emulsion stability was assessed, measuring the variation of droplet size as a function of time. The results obtained showed that the smallest droplet sizes were produced in samples where the emulsification started in a bicontinuous microemulsion (D) phase region or in a two-phase region consisting of a microemulsion (D) and a liquid crystalline phase (L(alpha)). Although the breakdown process of nano-emulsions could be attributed to the oil transference from the smaller to the bigger droplets, the increase in instability found with the increase in surfactant concentration may be related to the higher surfactant excess, favoring the oil micellar transport between the emulsion droplets.

Journal Article↗

PubMed2003

Stereoselective aldol additions catalyzed by dihydroxyacetone phosphate-dependent aldolases in emulsion systems: preparation and structural characterization of linear and cyclic iminopolyols from aminoaldehydes.

The potential of dihydroxyacetone phosphate (DHAP)-dependent aldolases to catalyze stereoselective aldol additions is, in many instances, limited by the solubility of the acceptor aldehyde in aqueous/co-solvent mixtures. Herein, we demonstrate the efficiency of emulsion systems as reaction media for the class I fructose-1,6-bisphosphate aldolase (RAMA) and class II recombinant rhamnulose-1-phosphate aldolase from E. coli (RhuA)-catalyzed aldol addition between DHAP and N-benzyloxycarbonyl (N-Cbz) aminoaldehydes. The use of emulsions improved the RAMA-catalyzed aldol conversions by three to tenfold relative to those in conventional DMF/water mixtures. RhuA was more reactive than RAMA towards the N-Cbz aminoaldehydes regardless of the reaction medium. With (S)- or (R)-Cbz-alaninal, RAMA exhibited preference for the R enantiomer, while RhuA had no enantiomeric discrimination. The linear N-Cbz aminopolyols thus obtained were submitted to catalytic intramolecular reductive amination to afford the corresponding iminocyclitols. This reaction was diastereoselective in all cases examined; the face selectivity was controlled by the stereochemistry of the newly formed hydroxyl group originating from the aldehyde. Characterization of the resulting iminocyclitols allowed the assessment of the diastereoselectivity of the enzymatic aldol reactions with respect to the N-protected aminoaldehyde. RAMA formed single diastereoisomers from N-Cbz-glycinal and from both enantiomers of N-Cbz-alaninal, while 14 % of the epimeric product was observed from N-Cbz-3-aminopropanal. Diastereoselectivity from RhuA was lower than that observed from RAMA. Interestingly, a single diastereoisomer was formed from (S)-Cbz-alaninal, whereas only a 34 % diastereomeric excess was observed from its enantiomer (i.e., (R)-Cbz-alaninal).

Journal Article↗

PubMed2000

Nitrogen Sorption Studies of Silica Particles Obtained in Emulsion and Microemulsion Media.

The internal surface structures of silica aerogel particles synthesized using different catalysts in emulsion and microemulsion media have been investigated by means of N(2) adsorption and desorption isotherms. Surface fractal dimensions have been computed using different methods: Frankel-Halsey-Hill plots of the adsorption isotherms, the thermodynamic fractal isotherm equation, and a modification of the thermodynamic fractal isotherm equation. Silica aerogels synthesized in emulsion media with an acidic catalyst have a high specific surface area without micropores and show two separate ranges of scales where the surface fractal dimensions are different and constant. Silica aerogels synthesized in emulsion media with a basic catalyst have a moderate specific surface area with a high percentage of micropores and show constant surface fractal dimensions over a larger range. Silica aerogels synthesized in microemulsion media with a basic catalyst have a low specific surface area with a moderate percentage of micropores and show a moderate range of scales over which the surface fractal dimension is constant. Analyses by both the thermodynamic and modified thermodynamic methods give similar ranges of the surface fractal dimensions of the silica particles. Copyright 2000 Academic Press.

Journal Article↗