PARTITIONING AND HYDRATION EQUILIBRIA OF ALPHA-DIKETONES IN MICELLAR SOLUTIONS

The partitioning and hydration of 2,3-butanedione and 2,3-pentanedione have been measured in sodium dodecyl sulfate micelles and AOT reverse micelles. In the latter system, the incorporation of both compounds t o the micellar pseudophase is proportional to the amount of water at w ater/AOT ratios higher than 9. This result is interpreted in terms of a dominant incorporation of the diketones to the water pools. With reg ard to both solubilization and hydration, the water of the reverse mic elle pools behaves nearly as bulk water (at water/AOT ratios higher th an 9). The addition of sodium dodecyl sulfate to an aqueous solution o f 2,3-pentanedione decreases the extent of hydration of the diketone. Measurement of the quenching of 2,3-pentanedione fluorescence by iodid e allows an evaluation of the extent of solubilization in the micellar pseudophase. From these data and the changes in absorbance of the alp ha-dicarbonyl band with the surfactant concentration (which is a measu re of the degree of hydration) the partition constant of the hydrated and nonhydrated forms of 2,3-pentanedione are evaluated. The results o btained indicate that the hydration of 2,3-pentanedione molecules boun d to sodium dodecyl sulfate micelles is nearly 4.6 times less efficien t than in bulk water.