Synthesis and Characterization of Four Diastereomers of Monorhamnolipids

Abstract

Rhamnolipids are amphiphilic glycolipids biosynthesized by bacteria that, due to their low toxicity and biodegradability, are potential replacements for synthetic surfactants. The previously limited access to pure materials at the gram scale has hindered extensive characterization of rhamnolipid structure-performance behavior. Here, we present an efficient and versatile synthetic methodology from which four diastereomers of the most common monorhamnolipid, α-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate, are prepared and subsequently characterized. Exploration of their behavior at the air-water interface is reported and analyzed in terms of the absolute configuration of the lipid tail carbinols at pH 4.0 and 8.0. All diastereomers exhibit a minimum surface tension of about 28 mN/m without a significant difference between the protonated (nonionic) or deprotonated (anionic) states. At pH 4.0 (nonionic), all diastereomers have a critical micelle concentration (CMC) in the micromolar range. At pH 8.0 (anionic), CMC values for the (R,R), (S,S), and (S,R) diastereomers are approximately an order of magnitude higher than in their nonionic states, whereas the (R,S) diastereomer exhibits a CMC about five times larger.

Structural Properties of Nonionic Monorhamnolipid Aggregates in Water Studied by Classical Molecular Dynamics Simulations

“…The experimental surface area per molecule at the complete surface coverage is reported as ~117 ± 12 Å 2 . 28 There is a good agreement between the experiment and calculations, which supports the performance of the force field.…”

Ion Flotation of La3+, Cd2+, and Cs+ using Monorhamnolipid Collector

“…[20,45,55,56]. Finally, because the production of both biologically synthesized and chemically synthesized [57] rhamnolipids have not been adequately evaluated at industrial scales, the economics of large-scale production should be studied to elucidate the long-term potential of rhamnolipid applications.…”

Specific optical rotation is a versatile tool for the identification of critical micelle concentration and micellar growth of tartaric acid–based diastereomeric amphiphiles

“…Pemberton et al reported that two diastereomers Rhamnolipids and their enantiomers exhibited the similar values of minimum surface tension (~28 mN/m), CMC, and aggregation behavior at pH 4, when the surfactants exist in the nonionic state. However, at pH 8 when the surfactants exits in the ionic state, the CMC and the aggregation behavior of the diastereomers and their enantiomers were somewhat different . Basically, it could be inferred that the spatial orientations of the head group is important in determining the physicochemical properties of diastereomeric surfactants.…”

“…However, at pH 8 when the surfactants exits in the ionic state, the CMC and the aggregation behavior of the diastereomers and their enantiomers were somewhat different. 55 Basically, it could be inferred that the spatial orientations of the head group is important in determining the physicochemical properties of diastereomeric surfactants. Interestingly, the diastereomers investigated here show identical surface tension profiles, with CMC at 0.3 mM, indicating that the head groups have similar orientation at the interface.…”

“…Variations among surface activities, as well as chiroptical properties, of diastereomeric amphiphiles have not been investigated to date. Physicochemical properties of some diastereomeric surfactants 55,56 are known but the chiroptical properties of surface active diastereomers are not known. Recently, we reported a novel chiral ionic liquid, 39 derived from mono lauryl ester of diacetyl-Ltartaric acid (L-T12OH) and (S)-methylbenzylamine (MBA), with surface active properties.…”