pH-triggered formation of nanoribbons from yeast-derived glycolipid biosurfactants

Abstract

In the present paper, we show that the saturated form of acidic sophorolipids, a family of industrially scaled bolaform microbial glycolipids, unexpectedly forms chiral nanofibers only at pH below 7.5. In particular, we illustrate that this phenomenon derives from a subtle cooperative effect of molecular chirality, hydrogen bonding, van der Waals forces and steric hindrance. The pH-responsive behaviour was shown by Dynamic Light Scattering (DLS), pH-titration and Field Emission Scanning Electron Microscopy (FE-SEM) while the nanoscale chirality was evidenced by Circular Dichroism (CD) and cryo Transmission Electron Microscopy (cryo-TEM). The packing of sophorolipids within the ribbons was studied using Small Angle Neutron Scattering (SANS), Wide Angle X-ray Scattering (WAXS) and 2D (1)H-(1)H through-space correlations via Nuclear Magnetic Resonance under very fast (67 kHz) Magic Angle Spinning (MAS-NMR).