Abstract
The effect of an antimicrobial peptide, melittin, on the long-range collective and local undulation motions of bicontinuous microemulsions (BμEs) was evaluated using dynamic light scattering (DLS) and neutron spin echo (NSE) spectroscopy. Small-angle neutron scattering (SANS) was also used to study the effect of melittin on the structure and the correlation length of BμEs. BμEs were isolated from Winsor-III systems formed by mixing aqueous melittin solutions containing sodium dodecyl sulfate with dodecane/1-pentanol mixtures at optimal salinity. An increase of melittin concentration linearly increased the diffusivity of the microemulsions (D DLS ) and decreased the bending rigidity (κ NSE ) up to an aqueous melittin concentration of 2 g/L, thus indicating an increase of interfacial fluidity. Further increase of melittin concentration above 2 g/L did not change D DLS and slightly increased κ NSE . The changes reflect differences of interaction between melittin and BμE surfactant monolayers at different melittin concentrations. At low concentrations, melittin is highly associated with the surfactant monolayers, likely ion-paired to the sulfate surfactant head groups and perhaps partially penetrating into the surfactant tail region. Above 2 g/L, an apparent saturation concentration, added melittin is less strongly associated with the monolayers. In contrast, the bare bending constant derived from SANS data (κ bare ) underwent only a minor decrease. Noting that κ bare reflects contributions from both the elasticity and saddle-splay moduli, this suggests that κ bare is not an effective indicator of dynamics for the BμEs investigated. This study demonstrates that amphiphilic solubilizates can have a complex impact on dynamics of surfactant monolayers in microemulsions, with implications for transmembrane diffusion and the kinetics of release from the microemulsion phase, which are important characteristics for the use of BμEs as delivery vehicles and host systems for (bio)chemical reactions.
| Original language | English |
|---|---|
| Pages (from-to) | 11197-11206 |
| Number of pages | 10 |
| Journal | Journal of Physical Chemistry C |
| Volume | 123 |
| Issue number | 17 |
| DOIs | |
| State | Published - May 2 2019 |
Funding
This work was supported by the Laboratory Directed Research and Development program of Oak Ridge National Laboratory (ORNL). Neutron scattering studies were performed at the CG-3 Bio-SANS instrument at the High-Flux Isotope Reactor (HFIR) and at the SNS-NSE (BL-15) at the Spallation Neutron Source (SNS) of ORNL. The CG3 Bio-SANS instrument is sponsored by the Office of Biological and Environmental Research, U.S. Department of Energy (DOE). Research conducted at the SNS and HFIR at ORNL was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE. S.G. would like to thank Michael Monkenbusch of the Jülich Centre for Neutron Science for helpful discussions. The neutron scattering work related to NSE of S.G. was supported by the U.S. DOE, Office of Science, Basic Energy Sciences, under EPSCoR grant no. DE-SC0012432 with additional support from the Louisiana Board of Regents.