Rhamnolipid Micellization and Adsorption Properties

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.

Glycolipid Biosurfactants in Skincare Applications: Challenges and Recommendations for Future Exploitation

“…Surfactants with low CMC are generally considered effective as less amounts would be required to form micelles and subsequently perform surface activities, such as foaming and emulsification, in skincare formulations [149][150][151]. The significant difference in CMC between glycolipids and synthetic surfactants has been reported in several studies, where the authors indicated that the CMC of sophorolipid and rhamnolipid congeners were at least tenfold lower than the CMC of the synthetic surfactants utilised in the same study; this demonstrates a potential preferential use of these glycolipids over synthetic surfactants in skincare applications as less amounts would be required to achieve the needed surface activity [19,[152][153][154]. However, it should be acknowledged that glycolipids are readily biodegradable and can lose some activity with time depending on the concentration at which they are prepared, batch storage conditions, and variation in-house extraction/purification methods [155].…”

Rhamnolipid Self-Aggregation in Aqueous Media: A Long Journey toward the Definition of Structure–Property Relationships

“…The aggregation behavior of R1 and R2 has also been rationalized in some cases through the calculation of the critical packing parameter ( cpp ) [ 193 , 194 ], but very different values are reported in different papers, with cpp values ranging from 0.24 [ 172 ] to 1 [ 144 ] for R1 and from 0.27 [ 172 ] to 0.73 [ 179 ] for R2.…”

“…In most cases, the carboxyl group of the distal β-hydroxy fatty acid chain remains free; few congeners, however, have this group esterified with a short alkyl group [ 55 ]. The high structural diversity of different rhamnolipid molecules, resulting in a large pool of rhamnolipid homologs that approaches 60 structures, arises from the numerous combinations of the number of rhamnose moieties and the nature of the aliphatic chains, which may be saturated, monosaturated, or polyunsaturated and branched, with chain length varying from C 8 to C 16 [ 55 , 144 ]. As an example, Table 1 presents the rhamnolipid congeners produced by Pseudomonas aeruginosa grown using two different carbon sources: glycerol and soy [ 145 ].…”

Thermodynamic Characterization of Rhamnolipid, Triton X-165 and Ethanol as well as Their Mixture Behaviour at the Water-Air Interface

“…In fact, rhamnolipid is a mixture of up to 26 different compounds [ 21 ]. Therefore one can find differ opinions on its adsorption and aggregation activity in the literature [ 22 , 23 ]. It should be noted that most of the available papers deal with mono-rhamnolipid.…”