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. 2022 Sep 21;23(19):11090.
doi: 10.3390/ijms231911090.

Rhamnolipid Micellization and Adsorption Properties

Yi Zhang  1 , Tess L Placek  1 , Ruksana Jahan  1 , Paschalis Alexandridis  1 , Marina Tsianou  1
Affiliations

Rhamnolipid Micellization and Adsorption Properties

Yi Zhang et al. Int J Mol Sci. .

Abstract

Biosurfactants are naturally occurring amphiphiles that are being actively pursued as alternatives to synthetic surfactants in cleaning, personal care, and cosmetic products. On the basis of their ability to mobilize and disperse hydrocarbons, biosurfactants are also involved in the bioremediation of oil spills. Rhamnolipids are low molecular weight glycolipid biosurfactants that consist of a mono- or di-rhamnose head group and a hydrocarbon fatty acid chain. We examine here the micellization of purified mono-rhamnolipids and di-rhamnolipids in aqueous solutions and their adsorption on model solid surfaces. Rhamnolipid micellization in water is endothermic; the CMC (critical micellization concentration) of di-rhamnolipid is lower than that of mono-rhamnolipid, and both CMCs decrease upon NaCl addition. Rhamnolipid adsorption on gold surface is mostly reversible and the adsorbed layer is rigid. A better understanding of biosurfactant self-assembly and adsorption properties is important for their utilization in consumer products and environmental applications.

Keywords: bioremediation; biosurfactant; formulation; green surfactant; rhamnolipid; self-assembly; sustainability.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Chemical structures of (a) mono-rhamnolipid and (b) di-rhamnolipid.
Figure 2
Figure 2
Pyrene fluorescence intensity I1/I3 ratios for (a) R95M90, R95D90, and (b) P.R. rhamnolipid in water and in aqueous NaCl solutions.
Figure 3
Figure 3
(a) ΔH of injection per mole of injected R95D90 in aqueous solution plotted as a function of the R95D90 concentration in the calorimeter cell; (b) first derivative of the ΔH vs. surfactant concentration.
Figure 4
Figure 4
Δf and ΔD over time of a gold sensor surface responding to exposure to (a) 0.15 wt.% R95M90 aqueous solution and (b) 0.15 wt.% R95M90 in 3.5 wt.% NaCl aqueous solution. The first arrow indicates the time when the rhamnolipid solution was injected and the second arrow indicates the time when solvent rinsing was initiated. Fi and Di shown in the insert are the frequency and dissipation at ith overtone, respectively.
Figure 5
Figure 5
Δf and ΔD over time of a gold sensor surface responding to exposure to (a) 0.15 wt.% R95D90 aqueous solution and (b) 0.15 wt.% R95D90 in 3.5 wt.% NaCl aqueous solution. The first arrow indicates the time when the rhamnolipid solution was injected and the second arrow indicates the time when solvent rinsing was initiated. Fi and Di shown in the insert are the frequency and dissipation at ith overtone, respectively.
Figure 6
Figure 6
Δf and ΔD over time of a gold sensor surface responding to exposure to (a) 0.1 wt.% P.R. rhamnolipid aqueous solution and (b) 0.1 wt.% P.R. rhamnolipid in 3.5 wt.% NaCl aqueous solution. The first arrow indicates the time when the rhamnolipid solution was injected and the second arrow indicates the time when solvent rinsing was initiated. Fi and Di shown in the insert are the frequency and dissipation at ith overtone, respectively.
Figure 7
Figure 7
Equilibrium ΔD/Δf values of 0.15 wt.% R95M90 and R95D90 adsorbed layers on gold surfaces from water and 3.5 wt.% NaCl aqueous solution.
Figure 8
Figure 8
Variation of dissipation shift ΔD vs. frequency shift Δf (5th overtone) during the adsorption of P.R. rhamnolipid on a gold sensor surface from aqueous solution and from 3.5 wt.% NaCl aqueous solution.
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