Effect of Anesthetic Molecules (Halothane and Isoflurane) on the Aggregation Behavior of POE−POP−POE Triblock Copolymers

Abstract

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.

Isothermal titration calorimetry and dynamic light scattering studies of interactions between gemini surfactants of different structure and Pluronic block copolymers

“…However, when C surf > C max2 , the energetically favored formation of regular gemini micelles becomes the dominant aggregation process and the hydrodynamic radius decreases to approximately that of the regular gemini micelles. The observed radii are in reasonable agreement with values reported for the copolymer micelles [2,7] and for both DTAB and aqueous 12-6-12 [21]. The larger particle, R h1 , of radius ca.…”

“…This is in contrast to the more complex system of P103, to be described in Section 3.2, where it is expected that polymer micelles exist for concentrations >0.05 wt% [1,2]. Typical plots of the enthalpy profiles are shown in Fig.…”

“…This is consistent with the formation of P103 micelles that are induced by the presence of hydrophobic 12-6-12 surfactant species. While the solution temperature is a few degrees lower than the cmt in water, the inducement of aggregate formation just below the cmt also was observed to occur when small amounts (<several mM) of hydrophobic compounds were added to aqueous solutions of these copolymers [1,2,12,17]. The rapid decrease in the larger particle size is due to the surfactant causing a breakdown of the clusters, as depicted in Fig.…”

“…Previously, it was found that the enthalpy profile of 12-EO x -12 in 0.05 wt% P103 had two overlapping peaks [17]. The one at lower surfactant concentration, peak 1, was attributed to the formation of P103 micelles at 25 • C, induced by the hydrophobic surfactant species [2,12]. While the ITC results of 12-6-12 in 0.05 wt% P103 show only a single broad peak, the DLS results discussed in subsequent sections indicate that formation of some copolymer micelles is induced by the surfactant.…”

Effects of unidirectional and mutual interactions between microstructures and azo dyes as “kinetic” probe molecules on cis→trans isomerization rate constants in aqueous P85 and F88 triblock copolymer solutions

“…Probe molecules are essential for probing properties of microdomains in organized assemblies of amphiphiles as micelles or vesicles, which emulate the amphiphilic character of membranes [1], and are considered as models for cell membranes, respectively [2]. Results are based on the comparison with the properties of the probe molecules in homogeneous solvents and solvent mixtures.…”