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Structure of the Fundamental Lipopeptide Surfactin at the Air/Water Interface Investigated by Sum Frequency Generation Spectroscopy

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Goussous, SA 
Casford, MTL 
Murphy, AC 
Salmond, GPC 
Leeper, FJ 


The lipopeptide surfactin produced by certain strains of Bacillus subtilis is a powerful biosurfactant possessing potentially useful antimicrobial properties. In order to better understand its surface behavior, we have used surface sensitive sum frequency generation (SFG) vibrational spectroscopy in the C-H and C═O stretching regions to determine its structure at the air/water interface. Using surfactin with the leucine groups of the peptide ring perdeuterated, we have shown that a majority of the SFG signals arise from the 4 leucine residues. We find that surfactin forms a robust film, and that its structure is not affected by the number density at the interface or by pH variation of the subphase. The spectra show that the ring of the molecule lies in the plane of the surface rather than perpendicular to it, with the tail lying above this, also in the plane of the interface.



Air, Bacillus subtilis, Hydrogen-Ion Concentration, Lipopeptides, Protein Conformation, Spectrum Analysis, Surface-Active Agents, Water

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Journal of Physical Chemistry B

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American Chemical Society
Biotechnology and Biological Sciences Research Council (BB/N008081/1)
EPSRC (1505859)
Biotechnology and Biological Sciences Research Council (BB/K001833/1)
We thank Unilever R&D and the EPSRC(UK) for an iCASE studentship for S.A.G. on Grant 1505859, and the BBSRC(UK) for a postdoctoral research assistantship for A.C.M. on Grant BB/N008081/1 to G.P.C.S. and F.J.L.