Abstract
The hydrophobic effect can give rise to both clathrate hydrate formation and micellization, depending on the molecular composition of the solute, temperature, and pressure. However, only a single compound, tetrabutylammonium dodecanoate, TBAD, has been shown to induce both types of self-assembly. Here we examine a second clathrate-forming surfactant. Tetrabutylammonium 10-undecenoate, TBAU, is shown to form a clathrate with a hydration number of 22.6 and a melting point of 293.32 ± 0.16 K, and also to form micelles with a critical micelle concentration, CMC, of 0.032 ± 0.004 mol dm -3 at 298.2 ± 0.3 K. Solubilization of a hydrophobic dye, Oil Blue N, by TBAU was compared to a series of tetra-n-alkylammonium 10-undecenoates at 296 ± 2 K. The CMC decreased and the solubilization power of the surfactant increased with the number of carbons in the counterion. No special, clathrate hydrate forming effects were evident above the clathrate hydrate melting point.
Highlights
Clathrate hydrates are supramolecular frameworks composed of polyhedral water cages supported by relatively small guest molecules
Their primary application has been in soaps and detergency, but they are increasingly important in drug delivery systems. [6], [7] A surfactant that could localize guest molecules, either by clathrate formation or by micellar solubilization, might provide a simple model for multifunctional nanoparticles for drug delivery systems. [8]
The number of surfactant compounds known to form clathrate hydrates is small. [9], [10] Of the known clathrate-forming surfactants, only one, tetrabutylammonium dodecanoate, TBAD, has been shown to form micelles in aqueous solution. [11], [12] Zana [11] reported an unexpectedly small micelle aggregation number for TBAD at 298 K, but little else is known about any unusual properties of these compounds
Summary
Clathrate hydrates are supramolecular frameworks composed of polyhedral water cages supported by relatively small guest molecules. The hydrophobic region in the interior of the micelle provides a favorable environment for solubilization of hydrophobic substrates. Their primary application has been in soaps and detergency, but they are increasingly important in drug delivery systems. [6], [7] A surfactant that could localize guest molecules, either by clathrate formation or by micellar solubilization, might provide a simple model for multifunctional nanoparticles for drug delivery systems. The number of surfactant compounds known to form clathrate hydrates is small. Oil Blue N was chosen because of the resemblance of its molecular structure to that of Mitoxantrone (Figure 1), which is used to treat leukemia and prostate cancer
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