Aqueous self-assembly of a wide range of sophorolipid and glucolipid microbial bioamphiphiles (biosurfactants): considerations about the structure-properties relationship

Hypothesis

Sophorolipids are well-known scaled-up microbial glycolipid biosurfactants with strong commercialization potential for their biological origin, mildness compared to classical surfactants. However, their properties are still poorly understood, they cannot be predicted and their behaviour in solution challenges half a century of knowledge generated in the field of surfactant science. By studying forty different types of sophorolipids, this work contributes to better tackle their structure-property relationship and identify which chemical groups in their molecular structure have a critical influence towards their self-assembly properties in water.

Experiments

This work explores the self-assembly properties at room temperature of sophorolipids and sophorosides in water using small angle X-ray scattering (SAXS), optical and cryogenic transmission electron microscopy (cryo-TEM). Structural features like the number of sugar headgroups, acetylation, end-chain functional group, (un)saturation, lactonization and length of chain are varied both to rationalize their impact and to understand their effect on the self-assembly.

Findings

The number of sugar groups, pH, (un)saturation and lactonization were found to have a critical impact in respect to the sophorolipids self-assembly. The chemical nature of the end-chain functional group and the chain length were found to have a possibly critical impact, depending on the specific type of chemical function (COOH and long chains are critical). Mono- and diacetylation, as well as position of sophorose on the fatty acid (ω, ω-1), are not critical, i.e., do not significantly influence the sophorolipids self-assembly.

Hypothesis

Sophorolipids are well-known scaled-up microbial glycolipid biosurfactants with strong commercialization potential for their biological origin, mildness compared to classical surfactants. However, their properties are still poorly understood, they cannot be predicted and their behaviour in solution challenges half a century of knowledge generated in the field of surfactant science. By studying forty different types of sophorolipids, this work contributes to better tackle their structure-property relationship and identify which chemical groups in their molecular structure have a critical influence towards their self-assembly properties in water.

Experiments

This work explores the self-assembly properties at room temperature of sophorolipids and sophorosides in water using small angle X-ray scattering (SAXS), optical and cryogenic transmission electron microscopy (cryo-TEM). Structural features like the number of sugar headgroups, acetylation, end-chain functional group, (un)saturation, lactonization and length of chain are varied both to rationalize their impact and to understand their effect on the self-assembly.

Findings

The number of sugar groups, pH, (un)saturation and lactonization were found to have a critical impact in respect to the sophorolipids self-assembly. The chemical nature of the end-chain functional group and the chain length were found to have a possibly critical impact, depending on the specific type of chemical function (COOH and long chains are critical). Mono- and diacetylation, as well as position of sophorose on the fatty acid (ω, ω-1), are not critical, i.e., do not significantly influence the sophorolipids self-assembly.