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

1
Physical and Biophysical Chemistry, Bielefeld University, 33615 Bielefeld, Germany
2
Organic and Bioorganic Chemistry, Bielefeld University, 33615 Bielefeld, Germany
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Colloids Interfaces 2019, 3(2), 47; https://doi.org/10.3390/colloids3020047
Received: 22 February 2019 / Revised: 16 April 2019 / Accepted: 17 April 2019 / Published: 25 April 2019
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. View Full-Text
Keywords: saponin; aescin; critical micelle concentration (cmc); autofluorescence; small-angle X-ray scattering (SAXS); transmission electron microscopy (TEM); micelle structure saponin; aescin; critical micelle concentration (cmc); autofluorescence; small-angle X-ray scattering (SAXS); transmission electron microscopy (TEM); micelle structure
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MDPI and ACS Style

Dargel, C.; Geisler, R.; Hannappel, Y.; Kemker, I.; Sewald, N.; Hellweg, T. Self-Assembly of the Bio-Surfactant Aescin in Solution: A Small-Angle X-ray Scattering and Fluorescence Study. Colloids Interfaces 2019, 3, 47.

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