Self-Assembly of Rhamnolipids Bioamphiphiles: Understanding Structure-Properties Relationship using Small-Angle X-Ray Scattering

TL;DR

This study investigates how the molecular structure of rhamnolipids influences their self-assembly into micelles and vesicles in water, using SAXS and cryo-TEM to elucidate structure-property relationships across different pH levels.

Contribution

It provides detailed insights into the self-assembly behavior of specific rhamnolipids and introduces a modeling approach to quantify their nanostructures based on SAXS data.

Findings

RhaC10 and RhaRhaC10C10 form micelles over a broad pH range.

RhaC10C10 transitions from micelles to vesicles at pH 6.5.

Modeling accurately estimates nanostructure parameters from SAXS data.

Abstract

The structure-properties relationship of rhamnolipids, RLs, well known microbial bioamphiphiles (biosurfactants), is exlored in detail by coupling cryogenic transmission electron microscopy (cryo-TEM) and both ex situ and in situ small angle X-ray scattering (SAXS). The self-assembly of three RLs with reasoned variation of their molecular structure (RhaC10, RhaC10C10 and RhaRhaC10C10) and a rhamnose-free C10C10 fatty acid is studied in water as a function of pH. It is found that RhaC10 and RhaRhaC10C10 form micelles in a broad pH range and RhaC10C10 undergoes a micelle-to-vesicle transition from basic to acid pH occurring at pH 6.5. Modelling coupled to fitting SAXS data allows a good estimation of the hydrophobic core radius (or length), the hydrophilic shell thickness, the aggregation number and the surface area per RL. The essentially micellar morphology found for RhaC10 and