PUB - Publikationen an der Universität Bielefeld

Bicontinuous microemulsions exhibit a sponge-like domain structure of oil and water separated by an enormous surfactant interface. These systems are therefore an excellent reaction medium \cite{gar99, hol88, sta99, car00, ros08}. The enzyme diisopropyl fluorophosphatase (DFPase) from the squid \textit{Loligo vulgaris} is of great importance for enzymatically catalysed hydrolysis of highly toxic organophosphates. Related to this application, the phase stability and the internal structure of microemulsions under extreme conditions are of great interest.\\ This work covers the influence of the chain length and headgroup of pure sugar surfactants on the internal structure sizes of the microemulsion system cyclohexane, n-pentanol and water characterized by small angle neutron (SANS) and X-Ray (SAXS) scattering. The phase behaviour of microemulsions based on isononyl isononanoate (Lanol99), sugar surfactant Simulsol SL55 (C$_{12/14}$ G$_{1.3}$), D$_{2}$O / water and the cosurfactant benzyl alcohol is studied and the bicontinuous phase is identified. Using SANS, the internal structure of the bicontinuous phase is characterized. A temperature range of \unit [261]{K} to \unit [343]{K} was covered in the experiments. The prepared microemulsions were found to exhibit nearly no temperature dependence with respect to their structure and phase behaviour. The last part of this thesis focuses on enzymatic reactions in sugar surfactant based microemulsions. A simple model for catalyzing the hydrolysis of highly toxic organophosphates by the DFPase was searched. With the NADH-dependent alcohol dehydrogenase (ADH200) which reduces acetophenone, a simple model was found whereby the enzym is located in the polar phase, and is not surface-active. The substrate is located in the organic phase. This enzymatic reaction was kinetically characterized using the UV/vis spectroscopy. Finally the influence of the internal structure of the microemulsion systems which were studied by SANS and SAXS scattering on the enzyme kinetic are discussed.