The antimicrobial activity of oil-in-water microemulsions is predicted by their position within the microemulsion stability zone

It has been shown previously that thermodynamically stable oil-in-water microemulsions have significant antimicrobial activity against planktonic cells and biofilm cells over short periods of exposure. It was the aim of this study to identify whether the position of the microemulsion within the microemulsion stability zone of the pseudo-ternary phase structure predicts the efficiency of the antimicrobial action of the microemulsion. Microemulsions were formulated at different points within the microemulsion stability zone. Experiments were performed to observe the kinetics of killing of these microemulsions against selected test microorganisms (Pseudomonas aeruginosa ATCC 9027, Candida albicans ATCC 10231, Staphylococcus aureus ATCC 6538 and Aspergillus niger ATCC 16404). The results indicated that the antimicrobial activity of the microemulsion is dependant upon its position within the zone of stability and is greater nearer the centre of that zone. The results indicate that significant antimicrobial activity can be observed at all points within the zone of microemulsion stability, but that maximal activity is to be found at the centre of that area

Influence of process variables on the properties of simvastatin self-emulsifying granules obtained through high shear wet granulation

Improvements of the oral bioavailability of lipophilic drugs can be obtained using lipidic formulations such as the self-emulsifying drug delivery systems. The high shear wet granulation (HSWG), using microemulsions as binder, is a viable process to produce self-emulsifying granules. However only few information are present in the literature on the effect of process variables on the properties of the granules obtained with these binders. Consequently, this article compares the effects of some relevant experimental variables (impeller speed and massing time) on thefinal technological and pharmaceutical properties of the granules produced using simple water, or alternatively, a microemulsion as binder and containing simvastatin (SV) as model drug. The effects of the variables were determined by evaluating the granule median diameter, their particle size distribution, roundness, disintegration time and dissolution rate of SV. Results clearly demonstrated that the microemulsion-based process was less sensitive tooperating conditions than the water-based process. With microemulsion the nucleation process and growth regimes were more difficult to control, resulting in products with broader PSDs. At the same operatingconditions microemulsion-based granules were more brittle but rounder and showed smaller median diameter compared to water-based granules. The dissolution rate of simvastatin was not significantly affected by the operating conditions

Computation of a Theoretical Membrane Phase Diagram, and the Role of Phase in Lipid Raft-Mediated Protein Organization

Lipid phase heterogeneity in the plasma membrane is thought to be crucial for many aspects of cell signaling, but the physical basis of participating membrane domains such as "lipid rafts" remains controversial. Here we consider a lattice model yielding a phase diagram that includes several states proposed to be relevant for the cell membrane, including microemulsion - which can be related to membrane curvature - and Ising critical behavior. Using a neural network-based machine learning approach, we compute the full phase diagram of this lattice model. We analyze selected regions of this phase diagram in the context of a signaling initiation event in mast cells: recruitment of the membrane-anchored tyrosine kinase Lyn to a cluster of transmembrane of IgE-Fc{\epsilon}RI receptors. We find that model membrane systems in microemulsion and Ising critical states can mediate roughly equal levels of kinase recruitment (binding energy ~ -0.6 kBT), whereas a membrane near a tricritical point can mediate much stronger kinase recruitment (-1.7 kBT). By comparing several models for lipid heterogeneity within a single theoretical framework, this work points to testable differences between existing models. We also suggest the tricritical point as a new possibility for the basis of membrane domains that facilitate preferential partitioning of signaling components.Comment: 33 pages, 7 figures, 16 supplementary pages, 10 supplementary figure

Microemulsion breakdown by pervaporation technique: Effect of the alkyl chain length of n-alkanol, a cosurfactant of the microemulsion

Two sets of microemulsions, cyclohexane- and water-rich ones, were prepared with the following n-alkanols as cosurfactants: n-propanol, n-butanol, n-pentanol, and n-hexanol. The results showed the influence of the alkyl chain length of the n-alkanol on the permselectivity properties of the pervaporation technique in the breakdown of the microemulsions. The variations of the total flux rate J and the enrichment factor β were in parallel with the effect of the cosurfactant on the swelling extent of the PDMS membrane

Cu,Zn,Al layered double hydroxides as precursors for copper catalysts in methanol steam reforming – pH-controlled synthesis by microemulsion technique

By co-precipitation inside microemulsion droplets a Cu-based catalyst precursor was prepared with a Cu:Zn:Al ratio of 50:17:33. A pH-controlled synthesis was applied by simultaneous dosing of metal solution and precipitation agent. This technique allows for continuous operation of the synthesis and enables easy and feasible up-scaling. For comparison conventional co-precipitation was applied with the same composition. Both techniques resulted in phase pure layered double hydroxide precursors and finally (after calcination and reduction) in small Cu nanoparticles (8 nm) and ZnAl2O4. By applying the microemulsion technique smaller Cu/ZnAl2O4 aggregates with less embedded Cu particles were obtained. The microemulsion product exhibited a higher BET and specific Cu surface area and also a higher absolute catalytic activity in methanol steam reforming. However, the Cu surface area-normalized, intrinsic activity was lower. This observation was related to differences in interactions of Cu metal and oxide phase

Use of inverse gas chromatography to account for the pervaporation performance in the microemulsion breakdown

Mass transfer phenomenon that occurs in the pervaporation process when applied to the microemulsion breakdown, was confirmed by the results of inverse gas chromatography. The stationary phase for this study was polydimethylsiloxane (PDMS), a hydrophobic polymer employed as a membrane in the pervaporation technique. The retention times of the different molecule probes (toluene, cyclohexane, and n-butanol) gave an insight into the extent of the interactions between each of these molecules and the stationary phase; these molecules were the components of the two microemulsions in study. The infinite dilution conditions allowed to determine the thermodynamic and the chromatographic parameters γ∞ (the infinite dilution activity coefficient), the Flory-Huggins parameter interactions χ∞12, and V0g (the specific retention volume), respectively. The magnitudes of the latter parameters threw some light on the permselectivity of the membrane in the pervaporation operation

Phase behavior of pseudoternary brine/alkane/alcohol-secondary alkanesulfonates systems.Surfactant ratio effects of salinity and alcohol

Dodecanesulfonates (isomer mixtures) have been synthesized by the process developed in our laboratory. First, pseudoternary phase diagrams of the water or (brine) decane/ dodecanesulfonates-butan-1-ol systems were drawn and compared with those of a commercial sample (Hostapur 60). In the presence of NaCl, a three-phase region (Winsor III) appears for the two systems, and is larger with the home-made surfactants. This region is interesting in enhanced oil recovery because it leads to very low interfacial tensions. Then, the behavior of the Winsor III region was investigated as a function of the alcohol/surfactant mass ratio (C/T). At a constant salinity (2.5 wt. % NaCl) a value of 2 for C/T gives the best compromise for a larger W III region with both systems. For this ratio, optimal salinity values of 1.55 and 1.65 mass % for our sample and Hostapur 60, were found, respectivel

Clean synthesis of adipic acid from cyclohexene in microemulsions with stearyl dimethyl benzyl ammonium chloride as surfactant: From the laboratory to bench scale

Adipic acid, HOOC(CH2)4COOH, is a white crystalline solid used primarily in the manufacture of nylon-6,6 polyamide. In industry, adipic acid is mainly produced by oxidation of cyclohexane with air and nitric acidfollowing a homogeneous two-step route. However, this process leads to the formation of nitrous oxide, a greenhouse gas that has to be decomposed. The aim of this study was the development of a clean technology at pilot scale in order to obtain and recover pure adipic acid, and the evaluation of its industrial practicability. Adipic acid was synthesized from cyclohexene and hydrogen peroxide in microemulsions with stearyl dimethyl benzyl ammonium chloride as surfactant. The non-polluting catalyst sodium tungstate, which contains no heavy metal, was used and the reaction conducted under mild conditions (85 C, 8 h). Yields of up to 81% were reached at the 0.14 L scale. However at the end of the reaction the catalyst and the surfactant must be separated and recycled for subsequent cycles. The reuse of the reaction media enabled the conversion to be increased up to 92% but a loss of surfactant and/or catalyst through the cycles progressively reduced the yields. Yields at the bench scale (1.4 L) increased during the two first cycles and then decreased to conversions of between 60% and 70%. Globally the yield is a little lower at bench scale. The results obtained show that the synthesis of adipic acid by a heterogeneous one-step oxidation of cyclohexene in the presence of hydrogen peroxide is an attractive route for developing a future green industrial process

Green process for adipic acid synthesis: oxidation by hydrogen peroxide in water micromelusions using Benzalkonium Chloride C12-14 surfactant

Adipic acid was synthesized by the oxidation of cyclohexene using 30% hydrogen peroxide in a microemulsion in the presence of sodium tungstate as catalyst. The proposed green process is environmentally friendly since catalyst and surfactant are recycled and pure adipic acid is produced in high yield (70% to 79%). Microemulsions are used as a “green solvent” and give a better contact between the phases. Alkyldimethylbenzylammonium chloride (C12-C14) was used as a surfactant for the generation of the microemulsion since it enables the use of harmful organic solvents and phase-transfer catalysts to be avoided. Optimised operating conditions (temperature, reaction time, separation process) have been defined and applied to evaluate the industrial practicability. The main interest of the present work is the easy recovery of pure adipic acid and the reuse of the reaction media (surfactant and catalyst). This shows promise for developing a future green industrial process that will enable greenhouse gas emissions (N2O), among others, to be reduced