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.