pH-Dependent Aggregation Behavior of a Sugar-Amine Gemini Surfactant in Water: Vesicles, Micelles, and Monolayers of Hexane-1,6-bis(hexadecyl-1′-deoxyglucitylamine)

Abstract

The pH-dependent aggregation behavior of one representative of a recently described series of sugar-amine gemini surfactants has been investigated. The surface tension (γ ) and turbidity of hexane-1,6-bis(hexadecyl-1 -deoxyglucitylamine) drop steeply between pH 5.5 and 4.0, consistent with a vesicle-to-micelle transition. The critical micelle concentration (cmc) at low pH (3.0) was determined by surface tension measurements to be 1 × 10 −3 M. This value is high, as γ is at the cmc (57 mN m −1 ). The area per headgroup (A h ) extracted from the slope of the curve of γ vs concentration below the cmc is 109Å2 . In an attempt to obtain a reasonable estimate of the headgroup area at higher pH, surface pressure vs area measurements were performed on a monolayer supported on pure water (pH 6), providing an A h of ca. 69Å 2 . The dependence of A h on pH is consistent with the proposed vesicle-to-micelle transition. Measurements of the gel-to-liquid crystalline phase transition using differential scanning calorimetry at a range of pHs revealed a drop in both the phase transition temperature and the transition enthalpy with decreasing pH. The pH dependence of the aggregation behavior can thus be summarized as follows: (1) pH 7.5-5.5, bilayer vesicles; (2) pH 5.5-4.0, a "drop region" where aggregate morphology is sensitive to small changes in pH; and (3) pH < 4.0, micelles. C 2001 Academic Press

Association behaviour of glucitol amine gemini surfactants

“…Several physico-chemical properties of the same system are reported by Bergsma et al [9]. The molecular structure of the surfactants used in those studies is shown in Figure 1.…”

“…If the glucitol groups had not been present, this might have even led to a maximum in φ 0 as is, e.g., observed for gemini surfactants of type ( [28,4]. Due to the very low critical association concentration of the glucitol amine surfactant, also reflected in the formation of vesicles [9], no experimental cmc data is available for the present system. Instead of changing the pH to change the electrostatic interactions, one can also change the ionic strength of the solution by adding salt to the solution.…”

“…Clearly, a transition from a cylindrical micelle to a lamellar-like structure is observed around pH = 6.5. Fielden et al [7,9] already suggested the existence of this transition for the corresponding real surfactant. They even suggested that such a transition might be of importance for the transfection ability of the surfactant, as long as this transition occurs in the endosomal pH range (4.0-7.4).…”

“…1. Molecular structure of the basic form of a family of glucitol amine gemini surfactants as used in references [7,9].…”

Photo-Induced Micellization of Block Copolymers

“…Molecular self-assembly is also caused by the polymers responding to stimuli, resulting in the construction of high-dimensional structures of the polymers. Stimuli inducing self-assembly of the polymers include pH [17,18], temperature [19][20][21][22], and pressure [23][24][25][26]. Recently, it has been reported that chemical reactions inducing self-assembly of the polymers; the oxidation [27], reduction [28][29][30], and disproportionation [31,32] of stable nitroxyl radicals supported on the side chains of a block copolymer, promote the micellization of the copolymer to provide micelles that function as oxidants and reductants.…”