Sugar-Based Gemini Surfactant with a Vesicle-to-Micelle Transition at Acidic pH and a Reversible Vesicle Flocculation near Neutral pH

Abstract

A sugar-based (reduced glucose) gemini surfactant forms vesicles in dilute aqueous solution near neutral pH. At lower pH, there is a vesicle-to-micelle transition within a narrow pH region (pH 6.0-5.6). The vesicles are transformed into large cylindrical micelles that in turn are transformed into small globular micelles at even lower pH. In the vesicular pH region, the vesicles are positively charged at pH < 7 and exhibit a good colloidal stability. However, close to pH 7, the vesicles become unstable and rapidly flocculate and eventually sediment out from the solution. We find that the flocculation correlates with low vesicle zeta-potentials and the behavior is thus well predicted by the classical DLVO theory of colloidal stability. Surprisingly, we find that the vesicles are easily redispersed by increasing the pH to above pH 7.5. We show that this is due to a vesicle surface charge reversal resulting in negatively charged vesicles at pH > 7.1. Adsorption, or binding, of hydroxide ions to the vesicular surface is likely the cause for the charge reversal, and a hydroxide ion binding constant is calculated using a Poisson-Boltzmann model.

Equilibrium Surface Tension, Dynamic Surface Tension, and Micellization Properties of Lactobionamide-Type Sugar-Based Gemini Surfactants

“…For 2C 10 Lac and 2C 12 Lac, the I 1 /I 3 ratio started to decrease slowly at concentrations around or above the cmc and reached approximately 1.2 when the concentration was 50-100 times the cmc. This behavior differed from that of 2C 8 Lac and conventional monomeric surfactants. This could be because the surfactants formed loose micelles whose interiors were not completely hydrophobic environments, because pyrene made it difficult to be solubilized in the micelles.…”

“…Figure 6 shows how the I 1 /I 3 ratio varied with the concentration for 2C n Lac. Similar to conventional monomeric surfactants, the I 1 /I 3 ratio of 2C 8 Lac decreased at a concentration around the cmc obtained by the surface tension measurements and reached approximately 1.2 when the concentration was 10 times the cmc. For 2C 10 Lac and 2C 12 Lac, the I 1 /I 3 ratio started to decrease slowly at concentrations around or above the cmc and reached approximately 1.2 when the concentration was 50-100 times the cmc.…”

“…2C 8 Lac exhibited the same behavior as 2C 8 Glu, with no change in the size of the aggregates with increasing concentration. 2C 10 Glu and 2C 12 Glu formed small aggregates like micelles at low concentrations, as was the case for 2C 10 Lac and 2C 12 Lac; as the aggregates grew, their sizes increased with increasing concentration.…”

“…Although many papers pertaining to the synthesis and properties of cationic and anionic gemini surfactants have been published, there are very few studies on nonionic and zwitterionic gemini surfactants. The majority of the conventional nonionic surfac-that the surface tension decreased in the order 2C 16 peLac 2C 12 peLac 2C 8 Glu 2C 10 Glu 2C 12 Glu. Our results showed that the introduction of a long alkyl chain and a bulky spacer rendered the surfactant less surface active.…”

Transfection mediated by pH-sensitive sugar-based gemini surfactants; potential for in vivo gene therapy applications

“…The sugar-based gemini surfactants were synthesized as previously described [30,31]. Liposomes were prepared 1 day before the experiment.…”