Sweet Confinement: Glucose and Carbohydrate Osmolytes in Reverse Micelles

Abstract

The research presented here reports the surprising observation that adding glucose and other carbohydrate osmolytes to the polar phase of water-containing reverse micelles causes the particles to shrink. This apparent change in reverse micelle size is attributed to two factors: an increase in the surface area per surfactant molecule induced by the presence of carbohydrate and changes in the particle shape eccentricity. The studies reported here not only focus on glucose but also explore other carbohydrate osmolytes, specifically ethylene glycol, glycerol, erythritol, xylitol, sorbitol, myo-inositol, and trehalose, in the nanoconfined environments of reverse micelles. Through two-dimensional proton nuclear Overhauser enhancement nuclear magnetic resonance spectroscopy, the osmolytes were determined to reside solvated in the aqueous interior of the reverse micelles. This paper reports the loading limit of carbohydrates into AOT [sodium bis­(2-ethylhexyl)­sulfosuccinate] reverse micelles, demonstrates the location of the carbohydrates in the reverse micelles, and shows an unexpected effect where the carbohydrates add to the reverse micelle volume without causing an apparent increase in the reverse micelle diameter.

Nanoconfinement Raises the Energy Barrier to Hydrogen Atom Exchange between Water and Glucose

“…We also considered the possibility of glucose stacking within the reverse micelles. Although glucose–glucose aggregation could block water from accessing glucose hydroxyl groups, reducing exchange rates, previous 2D NOESY NMR measurements showed no close interactions between glucose molecules that would support the existence of glucose aggregation …”

“…Although glucose−glucose aggregation could block water from accessing glucose hydroxyl groups, reducing exchange rates, previous 2D NOESY NMR measurements showed no close interactions between glucose molecules that would support the existence of glucose aggregation. 27 To interpret trends in the hydrogen atom exchange rates between glucose positions (scatter plot shown in Figure 5) and their associated activation energies, we consider two data cohorts: the 6α and 6β hydroxyl groups and all other hydroxyl groups. The first cohort, i.e., 6α and 6β hydroxyl groups, demonstrates consistently higher exchange rates than the latter cohort.…”

“…Inexpensive and nontoxic, AOT is the most widely used surfactant when preparing reverse micelles and is the amphiphile used in this study. Characterization by small-angle X-ray scattering, small-angle neutron scattering, and dynamic light scattering has given scientists a good understanding of AOT reverse micelles. , The encapsulated water molecules that form the core of the reverse micelle can interact with other molecules dissolved in the reverse micelle, for example, osmolytes, proteins, and probe molecules. − …”

Discerning the Structure Factor of Charged Micelles in Water and Supercooled Solvent by Contrast Variation X-ray Scattering

“…The structural parameters of micelles obtained by both SANS and SAXS are consistent (Table S2). The influence of sugars on self-assembly characteristics of amphiphiles has been extensively studied in bilayer membranes, reverse micelles, and vesicles owing to its importance in cryopreservation. − Though sugars influence many of the physicochemical properties of lipid bilayers, its mechanism of action is still clearly not understood. For example, previous studies indicated that the flexibility of hydrated bilayers is influenced by the presence of cryoprotectants such as glucose, sucrose, trehalose, etc .…”

Dynamic effect of polymers at the surfactant–water interface: an ultrafast study

“…Since the polymers interact with the interface, it is important to characterize any alterations to the overall structure of the RM such as changes in the diameter or heterogeneity, which have been observed in analogous systems. 39,45,46 DLS RM size measurements were performed on the RMs with 5 wt% polymer and monomer concentrations (Table S1, ESI †). The DLS measurements show no significant changes across samples, and in addition, the sizes are comparable to previous measurements of these RM systems.…”