title: Cooperative tuneable interactions between a designed peptide biosurfactant and positional isomers of SDOBS at the air-water interface.
abstract: Rationally designed peptide biosurfactant AM1 was mixed with sodium dodecyl benzene sulfonate (SDOBS) to self-assemble a mixed surfactant-biosurfactant layer at the air-water interface. Under optimal conditions in the presence of Zn2+, the interfacial elasticity of the mixed layer was approximately 5-fold higher than for biosurfactant alone. Two head positional isomers, SDOBS-2 and SDOBS-6, were compared for their ability to enhance interfacial film strength. SDOBS-6 forms a stronger layer with AM1 than does SDOBS-2. The highest interfacial elasticity of the AM1/SDOBS-6 layer was 640 mN m(-1) whereas the maximum value for the AM1/SDOBS-2 layer was 440 mN m(-1). Neutron reflection was used to investigate the structure of AM1/SDOBS films at varied bulk SDOBS concentrations. Both deuterated and nondeuterated SDOBS-2 and SDOBS-6 were used to provide contrast variation. It was shown that there is cooperative interaction between AM1 and SDOBS at low SDOBS concentration in the presence of 100 microM Zn2+, promoting AM1 adsorption atthe interface to form a two-layered structure of AM1 resulting in a mechanically strong interfacial film. In the presence of EDTA, only a single AM1 layer was formed at the same SDOBS concentration, and the film did not show lateral force transmission capability. Further increasing the SDOBS concentration to a molar excess of > 10x decreased the peptide population at the interface and resulted in a mechanically weak layer. Compared to SDOBS-6, SDOBS-2 depletes AM1 at a lower bulk concentration. These results demonstrate that the film strength of a self-assembled surfactant-biosurfactant mixed layer can be fine tuned by changing the isomer type and concentration of surfactant and by adding or removing metal ions.
authors.affiliation: Centre for Biomolecular Engineering, Australian Institute for Bioengineering and Nanotechnology and School of Engineering, The University of Queensland, St. Lucia QLD 4072, Australia.
authors.forename: Lizhong
authors.initials: L
authors.lastname: He
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Malcolm
authors.forename: Mirjana
authors.initials: M
authors.lastname: Dimitrijev
authors.forename: Sagheer A
authors.initials: SA
authors.lastname: Onaizi
authors.forename: Hsin-Hui
authors.initials: HH
authors.lastname: Shen
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Holt
authors.forename: Annette F
authors.initials: AF
authors.lastname: Dexter
authors.forename: Robert K
authors.initials: RK
authors.lastname: Thomas
authors.forename: Anton P J
authors.initials: AP
authors.lastname: Middelberg
mesh_terms: D000388:Air; D001557:Benzenesulfonates / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry; D007536:Isomerism; D033363:Neutron Diffraction; D010455:Peptides / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D001557:Benzenesulfonates; D010455:Peptides; D013501:Surface-Active Agents; D014867:Water; C001114:dodecylbenzenesulfonic acid; D003903:Deuterium