Surface charge of acidic sophorolipid micelles: effect of base and time

Abstract

Acidic sophorolipids, SL-COOH, bio-derived glycolipids, are known to form micelles whose interactions vary as a function of pH. Upon partial ionization of the COOH group, intermicellar interactions take place. Here, we explore the nature of these interactions by using small angle neutron scattering (SANS) on SL-COOH solutions to which increasing amounts of NaOH are added. The effect of the nature of the base is also explored by replacing NaOH with aqueous NH3, KOH and Ca(OH)(2). Time effects up to 36 days are also discussed. All SANS data have been successfully fitted using an appropriate model of core-shell prolate ellipsoids of revolution with an interaction potential, U(r), which combines hard-sphere and screened Coulomb (described by a repulsive Yukawa potential) potentials. Modelling quantifies the effect of the base in terms of micellar size, effective surface charge and interfacial hydration, thus showing the possibility of tuning them at will

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

“…Data on the C18 :1-cis sophorolipid can be found in ref. 53,52 The asterisk identifies the chiral subterminal carbon. The image of the ribbon has been adapted from ref.…”

“…24 In the case of sophorolipids, nanoscale chirality has never been reported even if giant ribbons seem to be formed from an elaidic acid (C18:1-trans) based compound while contradictory results exists (giant ribbons versus micelles) on the behavior of oleic acid derived (C18:1-cis) sophorolipids. 50,51,52,53 In the present paper, we present the pHtriggered formation of self-assembled fibers with nanoscale chirality using a saturated sophorolipid (C18:0 sophorolipids, Figure 1b) Preparation of the supramolecular assemblies: Different amounts of acidic C18:0 sophorolipids (c= 2 mg/mL and 5 mg/mL) were solubilized in deionized water. Due to the poor solubility of the C18:0 sophorolipids, pH was first increased to 11 using a 1 M NaOH solution and then decreased to pH= 2 and 6 with µmolar amounts of 0.5 and 0.05 M HCl solutions respectively.…”

Surface-induced assembly of sophorolipids

“…They have been recovered using method 1 as reported in a previous study by Baccile et al 65 Their purity has been evaluated at about 90% of both terminal and subterminal C18:1 congener and their equilibrium state in water is micellar as described earlier. 56,62,66 Sodium dodecyl sulfate (SDS) has been purchased from Aldrich and used as received. C10-Alkylpolyglycoside (APG, commercial name: Oramix) was provided by SEPPIC (France).…”

“…60 We also reported the micellar structure and their surface charge induced by pH. 61,62 The same molecules were also reported to form giant ribbons. 55,58 We have recently shown that the micelle-ribbon duality depends on purity; a standard non-acetylated, monounsaturated, acidic sophorolipid batch forms micelles, unless it is contaminated with 15 wt% of the saturated congener, which induces the ribbon formation.…”

“…1), and in particular their pH-responsive self-assembly have been shown earlier. [55][56][57] It has also been established that the structure of the molecules greatly influenced the self-assembly. 58 Acidic monounsaturated sophorolipids form ellipsoidal micelles in water in a very broad pH range (from pH 11 to pH 3), 59 although at basic pH, formation of nanoplatelets is also observed.…”