The molecular ionic surface structure and charge of the electric double layer around a nanodroplet and its structural change induced by hydrophobic effects are measured using vibrational coherent surface scattering spectroscopy, second harmonic scattering, and electrokinetic mobility measurements. Tetraalkylammonium chloride salts were added to negatively charged nanoscopic oil droplets in water. When we vary the alkyl chain length of the cation from CH3 to C4H10, both the size of the cation and its hydrophobic interaction are increased. We find that tetramethylammonium ions change the electrokinetic potential and the water structure but do not detectably adsorb to the interface. Tetrapropylammonium and tetrabutylammonium ions clearly adsorb to the interface. The corresponding (Stern) layer appears to be a mixed monolayer of anions and cations. An estimate of the amount of cations in the Stern layer is also made.

Biotechnology involves applying enzymes in organic synthesis to convert non-natural substrates into enantiomerically pure products under mild reaction conditions. Non-natural substrates are often lipophilic molecules that can hardly be accessed and converted by enzymes in their natural aqueous environment. Bicontinuous microemulsions provide a spongelike nanostructure with a large interfacial area between aqueous and oil domains, which makes them valuable alternative reaction media. In the present study, we introduced lipase B from Candida antarctica into a bicontinuous microemulsion of composition H2O/NaCl-n-octane-pentaethylene glycol monodecylether (C10E5). Phase behavior, partitioning studies, and pulsed-field-gradient NMR measurements revealed that the lipase is mostly adsorbed at the microemulsions interface. Phase diagrams showed a maximum in efficiency with increasing amount of lipase added to the water phase of the microemulsion. It was observed that the ratio between the mass of lipase that is introduced into the system and the mass of lipase that is located at the interface stays constant. Self-diffusion coefficients of all components showed that the presence of the lipase is not influencing the bicontinuity of the microemulsion.

Selective enzyme-catalysed biotransformations offer great potential in organic chemistry. However, special requirements are needed to achieve optimum enzyme activity and stability. A bicontinuous microemulsion is proposed as reaction medium because of its large connected interface between oil and water domains at which a lipase can adsorb and convert substrates in the oil phase of the microemulsion. Herein, a microemulsion consisting of buffer-n-octane-nonionic surfactant Ci Ej was used to investigate the key factors that determine hydrolyses of p-nitrophenyl esters catalysed by the lipase B from Candida antarctica (CalB). The highest CalB activity was found around 44 °C in the absence of NaCl and substrates with larger alkyl chains were better hydrolysed than their short-chained homologues. The CalB activity was determined using two different co-surfactants, namely the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and the sugar surfactant decyl β-D-glucopyranoside (β-C10 G1 ). The results show the CalB activity as linear function of both enzyme and substrate concentration with an enhanced activity when the sugar surfactant is used as co-surfactant.

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