Candida Rugosa lipase reactions in nonionic w/o-microemulsion with a technical surfactant

Dynamics of proteins confined in non-ionic bicontinuous microemulsions: a FCS study

In our present work we present an approach which allows one to confine proteins in structurally nearly identical bicontinuous microemulsions with systematically decreasing water domain size. It is shown that sub-diffusive behaviour occurs already at water domain sizes below 13 nm. However, above 13 nm normal diffusion is seen. Moreover, we compare protein diffusion in microemulsions to the transport of a much smaller fluorescent dye.

Effect of Surfactant Structure on the Superactivity of Candida rugosa Lipase

In this work, we present the effects of ionic and zwitterionic surfactants on the hydrolytic activity of Candida rugosa lipase (CRL), one of the most important and widely used microbial lipases. A series of amine N-oxide surfactants was studied to explore the relationship between their molecular structures and their effect on catalytic properties of CRL. These zwitterionic amphiphiles are known for their ability to form aggregates that can increase their size, thanks to a sphere-rod transition, without any additive. Enzyme activity seemed to be improved by morphological changes of micelles from spherical to rod-like, and the structure of the monomers played a crucial role in this transition. In fact, all the amine oxides investigated provoked superactivation, but the CRL activity increased by lengthening the alkyl chain of N-oxide surfactants, whereas it decreased in the presence of bulky head groups. Superactivity was mainly because of an increase in k_cat (0.57 s^-1 in buffer, 0.80-1.99 s^-1 in surfactant solutions) and, in some cases, a decrease in K_M (2 × 10^-3 M in buffer, 1.08-4.28 × 10^-3 M in surfactant solutions). Micelles seemed to play a dual role: superactivity occurred at surfactant concentrations higher than their critical micelle concentration, but, on the other hand, micelles subtracted the substrate from the bulk, making it unavailable for the catalysis.

Structure, interfacial film properties, and thermal fluctuations of microemulsions as seen by scattering experiments

The physics of microemulsions and in particular Dominique Langevin's contributions to the understanding of microemulsion structure and bending properties using scattering techniques are reviewed. Among the many methods used by her and her co-workers, we particularly emphasize optical techniques and small angle neutron scattering (SANS), but also neutron spin echo spectroscopy (NSE). The review is then extended to more recent studies of properties of microemulsions close to surfaces, using reflectometry and grazing-incidence small angle neutron scattering (GISANS).

Protein diffusion in a bicontinuous microemulsion: inducing sub-diffusion by tuning the water domain size

We study the diffusion of an enhanced green fluorescent protein (GFP+) in bicontinuous sugar-surfactant based microemulsions. The size of the water domains in such systems is controlled by changes of the oil-to-water ratio. Hence, microemulsions allow to produce confinement effects in a controlled way. At high water content the protein is found to exhibit Fickian diffusion. Decreasing the water domain size leads to a slowing down of the protein diffusion and sub-diffusive behavior is obtained on the scale observed by fluorescence correlation spectroscopy. Further decrease of the water domain size finally nearly fixes the GFP+ in these domains and forces it to increasingly follow the breathing mode of the microemulsion matrix.

Multiple-division of self-propelled oil droplets through acetal formation

We demonstrate a novel system that exhibits both self-propelled motion and division of micrometer-sized oil droplets induced by chemical conversion of the system components. Such unique dynamics were observed in an oil-in-water emulsion of a benzaldehyde derivative, an alkanol and a cationic surfactant at a low pH.

Dramatic Enhancement of Enone Epoxidation Rates in Nonionic Microemulsions

The ability of microemulsions to dissolve polar and non-polar components with a huge internal interface can overcome the reagent incompatibilities frequently encountered in organic reactions. We investigated model epoxidation reactions of alpha,beta-unsaturated enones and alkaline hydrogen peroxide in different nonionic microemulsions, both in the presence and absence of a phase-transfer agent (PTA). The obtained reaction profiles were compared with those for the corresponding surfactant-free two-phase systems. In addition, we defined a time constant tau as a measure for the rate of turnover. The epoxidation of trans-chalcone using an n-alkyl-polyoxyethylene surfactant based microemulsion was fastest in the system with the PTA (tau=66 min) and slightly slower without the PTA (tau=77 min). It was still slower in the two-phase system with a PTA (tau=114 min) and extremely sluggish without a phase-transfer agent. With n-alkyl beta-D-glucopyranoside as the surfactant the conversion was twice as fast than in the former microemulsion systems, but the PTA did not accelerate the reaction further (tau=35 and 33 min). The epoxidation of vitamin K(3), the second model system, was extremely accelerated. It proceeded a factor of approximately 35 faster in the microemulsion (tau=1.44 min) than in the corresponding two-phase system (tau=57 min).

Enzyme catalysis in reverse micelles

Water in oil microemulsions with reverse micelles provide an interesting alternative to normal organic solvents in enzyme catalysis with hydrophobic substrates. Reverse micelles are useful microreactors because they can host proteins like enzymes. Catalytic reactions with water insoluble substrates can occur at the large internal water-oil interface inside the microemulsion. The activity and stability of biomolecules can be controlled, mainly by the concentration of water in these media. With the exact knowledge of the phase behaviour and the corresponding activity of enzymes the application of these media can lead to favourable effects compared to aqueous systems, like hyperactivity or increased stability of the enzymes.