Molecular editing of sophorolipids by esterification of lipid moieties: Effects on interfacial properties at paraffin and synthetic crude oil-water interfaces

Abstract

Sophorolipids (SLs) are naturally produced glycolipid biosurfactants that offer safe alternatives to chemical surfactants that have been identified as ecologically-hazardous.Molecular editing of SLs by esterification of the lipid tail was used to prepare a family of SLesters whose hydrophobic moiety is extended from 18 carbons (17-HOC18:1Δ 9 ) to 20, 24, or 28 carbons, respectively. The interfacial properties of natural and SL-esters were evaluated with paraffin and a synthetic crude oil. SL-esters reduced paraffin oil/water interfacial tension (IFT) by 89-97% and had critical aggregation concentrations (CACs) between 0.02-0.008mg/mL. SLesters were also found to emulsify paraffin and synthetic crude oil with oil/surfactant ratios up to 200:1 wt/wt for 1 week with emulsion droplet sizes below 5μm. SL-hexyl ester had the lowest CAC, 0.008 mg/mL, and generally, the lowest droplet sizes, particularly at 10wt% paraffin oil.While, SL-decyl ester had the highest (97.2%) maximum %-IFT reduction and gave paraffin oil emulsions that were most stable over time. SL-ester emulsions of synthetic crude oil resulted in emulsion sizes that are similar to those with paraffin oil. However, the absence of SL-ester precipitation over the range of SL-ester/synthetic crude oil emulsions tested suggest that the affinity of SL-esters to the oil phase is enhanced by the presence of o-xylene and 1,2-dimethylcyclohexane in the crude oil formulation. A natural SL mixture consisting of 1:1 lactonic (LSL) and acidic (ASL) forms has a CAC that is about an order of magnitude larger than SL-esters. Furthermore, the natural SL mixture was unable to emulsify paraffin and synthetic oil when the ratio of oil-to-surfactant is greater than 1:1. The predictive connection between CAC and emulsion sizes is discussed. IFT and emulsion data show that SL-esters are promising surfactants for crude oil related oil compositions.

Biosurfactants from Waste: Structures and Interfacial Properties of Sophorolipids Produced from a Residual Oil Cake

“…The average droplet sizes of SL emulsions increase with the increment in the percentage of almond oil for a given time, with mean values ranging from 500 to 5000 nm. Similar trends have recently been reported for SL emulsions using almond oil (Koh et al, 2016), lemon oil (Koh and Gross, 2016a), and paraffin oil (Koh and Gross, 2016b).…”

A versatile family of sophorolipid esters: Engineering surfactant structure for stabilization of lemon oil-water interfaces

“…[14] The structure of purified SL-ester products was confirmed by Liquid Chromatography-Mass Spectrometry (LC-MS), 1 H NMR, and 13 C NMR which are identical to those previously reported. [12][13][14]…”

“…[9][10][11] While a few studies have evaluated the properties of SLs for emulsification, recent work by the Gross laboratory has described the connection between interfacial tension and emulsification performance of natural SLs as well as a homologous series of modified SLs. [12,13] The later resulted from molecular editing of SLs by esterification of the lipid tail that gave a family of SL-esters whose hydrophobic moiety is extended from 18 carbons (17-HOC18:1Δ 9 ) to 20, 24, or 28 carbons, respectively (Scheme 2). [14] These studies focused on almond oil, a C18 fatty-acid based triglyceride, and liquid paraffin that consists of a mixture of alkanes generally ranging from C16 to C50.…”

Asymmetrical, Symmetrical, Divalent, and Y-Shaped (Bola)amphiphiles: The Relationship between the Molecular Structure and Self-Assembly in Amino Derivatives of Sophorolipid Biosurfactants

“…14,18,19 This short survey shows that, despite the rich phase behavior of this class of compounds, the diversity in terms of molecular structure remains very limited and generally confined to the general formula sugar-spacer-COOH, where the spacer is commonly a C18:1 or C18:0 hydrocarbon, although more complexity can be found in rhamnolipids and cellobioselipids. 20,21 To explore new properties and broaden the application potential of the natural sophorolipids, several chemical derivatives including alkyl esters (better emulsifiers) [22][23][24][25] and polymers 26 have been recently developed, just to cite some. 27 One possible approach consists in modifying the double bond in the C18:1 backbone.…”