The kinetics of enzyme catalyzed alcohol oxidation has been measured in liquid water/ethanol/Brij 35 and water/1-pentanol/Brij 35 systems, essentially in the water-rich regions. For the ethanol systems it was found that the enzymatic activity sharply decreases with increasing alcohol concentration independently of the surfactant concentration between 0 and 22 mass %. In the case of the 1-pentanol systems the enzymatic activity decreases also with increasing alcohol concentration, but this decrease can considerably be attenuated by adding increasing amounts of surfactant. To explain these results at the nanometer level, small-angle neutron scattering (SANS) experiments have been carried out on these systems. The comparison of the scattering and the kinetic measurements suggests the following interpretation. In all cases, the enzymatic activity depends on the concentration of the alcohol in the aqueous phase or in the aqueous pseudophase containing the enzyme. A certain amount of alcohol may be present in an organic pseudophase formed by direct micelles. In the case of the 1-pentanol systems the alcohol participates in the structuration of the micelles and is concentrated in the micelles, whereas in the case of the ethanol systems the alcohol remains essentially in the aqueous pseudophase and even destroys the micelles. These results suggest that in some cases enzymatic activity can be used as a probe to detect some aspects of the molecular organization of a complex liquid.

The kinetics of alcohol oxidation catalyzed by the enzyme horse liver alcohol dehydrogenase (HLADH) is studied in water/alcohol/C12E23 systems with a series of n-alcohols ranging from ethanol to 1-decanol or with α,ω-alkandiols, namely, 1,5-pentanediol and 1,7-heptanediol. Essentially, the water-rich part of the ternary systems is examined, either without C12E23 or at several constant C12E23 concentrations above the cmc (1, 8, and 22 mass %). The substrate inhibition of the enzyme allows one to infer alcohol partition coefficients between the outer aqueous pseudophase and the surfactant aggregation pseudophase. In the case of short-chain n-alcohol (ethanol, 1-propanol) and alkandiol (1,5-pentanediol) systems, the alcohol seems to remain in the aqueous pseudophase, whereas in the case of middle- and long-chain n-alcohol (1-butanol to 1-decanol) and alkandiol (1,7-heptandiol) systems, the alcohol participates in the structuration of the micelle.

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