Investigating Internal Structural Differences between Micelles and Unilamellar Vesicles of Decanoic Acid/Sodium Decanoate

Abstract

We report on the dynamics of a chromophore sequestered within the nonpolar regions of micelles and unilamellar vesicles comprised of decanoic acid/sodium decanoate. We find that there is a measurable difference in the motional dynamics of the chromophore perylene in these two nonpolar media, with the vesicle structure forming a somewhat less viscous environment than the micelle. In all cases, the chromophore reorients as a prolate rotor, implying a local environment with a nominally similar shape for both micelle and vesicle structures. These findings demonstrate that the organization of micelles is measurably different than that of bilayers.

Fatty acid vesicles

“…21 cP). The value determined for the vesicles agreed with the value determined for vesicles from 1,2-dimyristoyl-snglycero-3-phosphocholine (DMPC) below the main phase transition temperature, in the solid-ordered gel-state of the bilayers [12]. The comparison between vesicles and micelles is important also for clarifying thermodynamic and kinetic aspects of various aggregation states.…”

“…The fact that a range of fatty acid aggregates are formed just by changing the protonation/ ionization ratio of the terminal carboxylic acid and by changing the overall concentration provides an excellent opportunity to study physico-chemical properties of different aggregate structures. For example, the organization of the hydrophobic interior of fatty acid vesicles was compared with micelles in the case of the decanoic acid/sodium decanoate system by using fluorescence lifetime and anisotropy measurements of the incorporated chromophore perylene [12]. Perylene embedded in decanoic acid vesicles experienced a somewhat less viscous environment (ca.…”

Catanionic aggregates formed from drugs and lauric or capric acids enable prolonged release from gels

“…A lowering of pH and increase of ion strength lowers the cac of the carboxylic acids. Self aggregation has been reported [25,29]; however, the results from the release study point to that the vesicles found in the gel samples are catanionic aggregates, composed of both drug substance and oppositely charged surfactant.…”

“…Cac of this system was also studied by Namani and Walde who found vesicles in the pH range 8.1-6.0 [27]. The decanoic acid/sodium decanoate system was also studied, and vesicles imaged by TEM, by Stevenson and Blanchard [29]. In this study the two long chain carboxylic acids will be used as oppositely charged surfactants to form catanionic aggregates with drug substances.…”

“…An aqueous solution of lauric acid can be obtained at approximately 45 • C. Recent studies suggest that lauric acid is a natural antibacterial, antiviral and antiprotozoal agent, nonharmful to and easily digested by the human body [24]. The formation of vesicles by these fatty acids by themselves has been studied by other research groups [25][26][27][28][29]. The need of uncharged amphiphiles to form vesicles with ionic soaps with chain lengths C(8)-C(18) was noted by Hargreaves and Deamer [25].…”