Self-Assembly of the Bio-Surfactant Aescin in Solution: A Small-Angle X-ray Scattering and Fluorescence Study

• Published in: Colloids and interfaces Vol. 3; no. 2; p. 47
• Main Authors: Dargel, Carina, Geisler, Ramsia, Hannappel, Yvonne, Kemker, Isabell, Sewald, Norbert, Hellweg, Thomas
• Format: Journal Article
• Language: English
• Published: MDPI AG 25.04.2019
• Subjects: aescin; autofluorescence; critical micelle concentration (cmc); micelle structure; saponin; small-angle X-ray scattering (SAXS); transmission electron microscopy (TEM)
• ISSN: 2504-5377; 2504-5377
• DOI: 10.3390/colloids3020047

This work investigates the temperature-dependent micelle formation as well as the micellar structure of the saponin aescin. The critical micelle concentration ( c m c ) of aescin is determined from the concentration-dependent autofluorescence (AF) of aescin. Values between c m c aescin , AF (10 ∘ C) = 0.38 ± 0.09 mM and c m c aescin , AF (50 ∘ C) = 0.32 ± 0.13 mM were obtained. The significance of this method is verified by tensiometry measurements. The value determined from this method is within the experimental error identical with values obtained from autofluorescence ( c m c aescin , T ( WP ) (23 ∘ C) = 0.33 ± 0.02 mM). The structure of the aescin micelles was investigated by small-angle X-ray scattering (SAXS) at 10 and 40 ∘ C. At low temperature, the aescin micelles are rod-like, whereas at high temperature the structure is ellipsoidal. The radii of gyration were determined to ≈31 Å (rods) and ≈21 Å (ellipsoid). The rod-like shape of the aescin micelles at low temperature was confirmed by transmission electron microscopy (TEM). All investigations were performed at a constant pH of 7.4, because the acidic aescin has the ability to lower the pH value in aqueous solution.