Issue 23, 2020

Synthesis and self-assembly of aminyl and alkynyl substituted sophorolipids

Abstract

Sophorolipids are one of the most important microbial biosurfactants, because of their large-scale production and applications developed so far in the fields of detergency, microbiology, cosmetics or environmental science. However, the structural variety of native sophorolipids is limited/restricted, a limiting fact for the development of new properties and their potential applications. In their open acidic form, C18:1 sophorolipids (SL) are classically composed of a sophorose headgroup and a carboxylic acid (COOH) end-group. The carboxyl group gives them unique pH-responsive properties, but it is a poorly reactive group and its charge can only be negative. To develop a new generation of pH-responsive, positively charged, SL and to improve their reactivity for further functionalization, we develop here SL with an amine (–NH2) or terminal alkyne (–C[triple bond, length as m-dash]CH) end-group analogues. The amine group generates positively charged SL and is more reactive than carboxylic acids, e.g. towards aldehydes; the alkyne group provides access to copper-based click chemistry. In this work, we synthesized (C18:1) and (C18:0) –NH2 and (C18:1) –C[triple bond, length as m-dash]CH sophorolipid derivatives and we study their self-assembly properties in response to pH and/or temperature changes by means of static and dynamic light scattering, small angle (X-ray, neutron) scattering and cryogenic electron microscopy. Monounsaturated aminyl SL-C18:1-NH2 sophorolipids form a micellar phase in their neutral form at high pH and a mixed micellar-bilayer phase in their positively charged form at low pH. Saturated aminyl SL-C18:0-NH2 sophorolipids form a micellar phase in their charged form at low pH and a twisted ribbon phase in their neutral form at high pH and monounsaturated alkynyl SL-C18:1-C[triple bond, length as m-dash]CH sophorolipids form a main micellar phase at T > 51.8 °C and a twisted ribbon phase at T < 51.8 °C.

Graphical abstract: Synthesis and self-assembly of aminyl and alkynyl substituted sophorolipids

Supplementary files

Article information

Article type
Paper
Submitted
08 sep 2020
Accepted
12 okt 2020
First published
10 nov 2020

Green Chem., 2020,22, 8323-8336

Synthesis and self-assembly of aminyl and alkynyl substituted sophorolipids

A. A. Ba, J. Everaert, A. Poirier, P. Le Griel, W. Soetaert, S. L. K. W. Roelants, D. Hermida-Merino, C. V. Stevens and N. Baccile, Green Chem., 2020, 22, 8323 DOI: 10.1039/D0GC03053H

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