title: 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.
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Soil, Water and Environmental Science, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Palos Pacheco
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Soil, Water and Environmental Science, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Eismin
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Soil, Water and Environmental Science, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Clifford S
authors.initials: CS
authors.lastname: Coss
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Soil, Water and Environmental Science, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Soil, Water and Environmental Science, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Raina M
authors.initials: RM
authors.lastname: Maier
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Soil, Water and Environmental Science, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Robin
authors.initials: R
authors.lastname: Polt
authors.affiliation: Department of Chemistry and Biochemistry and ‡Department of Soil, Water and Environmental Science, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Jeanne E
authors.identifier: http://orcid.org/0000-0002-1710-2922
authors.initials: JE
authors.lastname: Pemberton