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 (O-1(2)) 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 O-1(2) in the aqueous microdomains. Part of the O-1(2) diffuses into the organic compartments prior to fast physical deactivation of O-1(2) by water molecules. In the apolar domains O-1(2) quantitatively converts the model Substrate 9,10-dimethylanthracene into its corresponding endoperoxide. Near-IR chemiluminescence measurements confirm that the O-1(2) 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 O-1(2). (C) 2008 Published by Elsevier B.V.