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Surfactin structures at interfaces and in solution: the effect of pH and cations
Hsin-Hui Shen1, Tsung-Wu Lin, Robert K Thomas
1Department of Chemistry, Oxford University, Oxford, UK. hsin-hui.shen@csiro.au
The Journal of Physical Chemistry. B
|March 31, 2011
Summary
Surfactin exhibits a ball-like structure at air/water interfaces, with its bulk phase forming micelles, rods, or lamellar structures depending on pH and cation presence. Cations neutralize surfactin
Area of Science:
- Biophysical Chemistry
- Materials Science
- Surface Science
Background:
- Surfactin is a potent biosurfactant with amphipathic properties.
- Understanding surfactin's structural behavior is crucial for its applications.
- Interfacial and bulk phase behavior are influenced by environmental factors like pH and ions.
Purpose of the Study:
- To investigate the interfacial and bulk phase structures of surfactin.
- To determine the effects of pH and mono/divalent cations on surfactin structure.
- To elucidate the mechanisms governing surfactin's structural transitions.
Main Methods:
- Neutron scattering techniques, including neutron reflectivity and small-angle neutron scattering (SANS).
- Experiments conducted at air/water and sapphire/water interfaces.
- Systematic variation of pH and ionic strength in the presence of cations.
Main Results:
- Surfactin forms a hydrophobic ball-like structure at the air/water interface, sensitive to pH and cations.
- Adsorption at the sapphire/water interface is strongly pH-dependent due to electrostatic interactions.
- Bulk phase structures are highly sensitive to pH, forming micelles (high pH), rods (pH 6.5), and lamellar structures (pH 5.5).
- Cations, especially divalent ones, neutralize surfactin's acidic groups, influencing its structure.
Conclusions:
- Surfactin's interfacial and bulk structures are dynamically regulated by pH and cation presence.
- Electrostatic interactions play a key role in surfactin adsorption onto charged surfaces.
- The observed structural transitions in bulk phases highlight surfactin's versatility and responsiveness.
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