Singlet oxygenation in microemulsion catalysed by vanadium chloroperoxidase

Non-ionic microemulsions compatible with the enzyme vanadium chloroperoxidase were designed to perform singlet oxygenation of apolar substrates. The media were based on mono- and polydisperse ethoxylated fatty alcohols (CiEj), octane and aqueous buffer. “Fish” diagrams were determined to identify the Winsor-boundaries and to formulate a monophasic Winsor IV microemulsion with a minimal surfactant concentration, ensuring less singlet oxygen (1O2) loss than in an aqueous system, thus creating a high oxygenation efficiency. The enzyme was shown to be fully stable in the microemulsion for at least 10 h, converting H2O2 into a constant flow of 1O2 in the aqueous microdomains. Part of the 1O2 diffuses into the organic compartments prior to fast physical deactivation of 1O2 by water molecules. In the apolar domains 1O2 quantitatively converts the model substrate 9,10-dimethylanthracene into its corresponding endoperoxide. Near-IR chemiluminescence measurements confirm that the 1O2 signal in the microemulsion is higher than in simple aqueous buffer. In a well-stirred (water/octane) biphasic system endoperoxide formation is also observed but the conversion rate is much lower, most likely due to stronger physical quenching of 1O2.