Nov. 02, 2017
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Nanoscale Platelet Formation by Monounsaturated and Saturated Sophorolipids under Basic pH Conditions

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This peer-reviewed scientific article is freely accessible after registration due to a friendly sponsoring by Leica Microsystems. In this study Leica Cryo-EM equipment was used to image the different structures of yeast-derived bolaamphiphile sophorolipids (SL).

Self-assembly properties of surfactants of the class of bipolar amphiphiles (bolas) lead to differently shaped aggregates such as nanotubes, rods, sheets, tubules, membranes, and discs or platelets in aqueous solution. The morphology depends on various parameters including pH in comparison to conventional surfactants. In this study Leica Cryo-EM equipment was used to image the different structures of yeast-derived bolaamphiphile sophorolipids (SL).

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A. Cuvier, F. Babonneau, J. Berton, C. V. Stevens, G. C.Fadda, G. Péhau-Arnaudet, P. Le Griel, S. Prévost, J. Perez, and N. Baccile; “Nanoscale Platelet Formation by Monounsaturated and Saturated Sophorolipids under Basic pH Conditions”; Chem. Eur. J. 2015, 21, 19265 – 19277; DOI:10.1002/chem.201502933.

Abstract
The self-assembly behavior of the yeast-derived bolaamphiphile sophorolipid (SL) is generally studied under acidic/neutral pH conditions, at which micellar and fibrillar aggregates are commonly found, according to the (un)saturation of the aliphatic chain: the cis form, which corresponds to the oleic acid form of SL, spontaneously forms micelles, whereas the saturated form, which corresponds to the stearic acid form of SL, preferentially forms chiral fibers. By using small-angle light and X-ray scattering (SLS, SAXS) combined with high-sensitivity transmission electron microscopy imaging under cryogenic conditions (cryo-TEM), the nature of the self-assembled structures formed by these two compounds above pH 10, which is the pH at which they are negatively charged due to the presence of a carboxylate group, has been explored.

Under these conditions, these compounds self-assemble into nanoscale platelets, despite the different molecular structures. This work shows that the electrostatic repulsion forces generated by COO− mainly drive the self-assembly process at basic pH, in contrast with that found at pH below neutrality, at which self-assembly is driven by van der Waals forces and hydrogen bonding, and thus, is in agreement with previous findings on carbohydrate-based gemini surfactants.

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