Studies of the effect of anesthetic molecules, halothane and isoflurane, on the aggregation behavior of POE-POP-POE triblock copolymers, P84, F88, P104, in aqueous solution have been carried out using fluorescence spectroscopy and light-scattering techniques. The hydrodynamic radius of block copolymer aggregates and the I/III vibronic intensity ratio of pyrene in 5 wt % aqueous solutions of F88, P84, and P104 were obtained over a wide temperature range, 10-60 °C. Large-sized clusters form at low temperatures for P104, but they do not have a well-defined hydrophobic core. Low concentrations of the anesthetics are found to induce the aggregation of F88 and P84 at 25 °C, and this effect is similar to that of increasing the temperature. The effect of halothane and isoflurane concentration on the change of hydrodynamic radius of copolymer aggregates and the I/III vibronic ratio of pyrene in F88, P84, and P104 were investigated at 25 °C. The addition of 1 mM of anesthetic is equivalent to ca. a 1-2 °C increase in temperature. It is deduced that the anesthetic molecules are distributed in both the hydrophobic core and hydrophilic corona of the polymer micelles. However, whereas an increase in temperature removes water of hydration from around the POP and POE segments, the anesthetic molecules tend to replace water of hydration around these segments. It is inferred that anesthetic molecules could disturb the water of hydration around biological macromolecules, and it is proposed that the dehydration effect of inhalation anesthetics may play an important role in the process of anesthesia.

Thermodynamic data for the formation of iodine complexes with pyrone-(4) (I) and 1-thiopyrone-4 (11) have been obtained from measurements of the blue-shifted iodine band. The thiocarbonyl analogs of I and I1 are found to undergo irreversible reactions with iodine. The values of AHo and A G O 2 9 8 indicate that I1 is only slightly more basic toward iodine than is I. From a comparison of thermodynamic data for iodine complexes of ethers, thioethers, and ketones with that reported here for I and I1 with iodine, it is evident that the bonding site in I and I1 is the carbonyl oxygen. The differences between I and I1 may be explained mainly in terms of the electron density at the carbonyl oxygen.