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

Abstract

The need to protect human and environmental health and avoid the widespread use of substances obtained from nonrenewable sources is steering research toward the discovery and development of new molecules characterized by high biocompatibility and biodegradability. Due to their very widespread use, a class of substances for which this need is particularly urgent is that of surfactants. In this respect, an attractive and promising alternative to commonly used synthetic surfactants is represented by so-called biosurfactants, amphiphiles naturally derived from microorganisms. One of the best-known families of biosurfactants is that of rhamnolipids, which are glycolipids with a headgroup formed by one or two rhamnose units. Great scientific and technological effort has been devoted to optimization of their production processes, as well as their physicochemical characterization. However, a conclusive structure–function relationship is far from being defined. In this review, we aim to move a step forward in this direction, by presenting a comprehensive and unified discussion of physicochemical properties of rhamnolipids as a function of solution conditions and rhamnolipid structure. We also discuss still unresolved issues that deserve further investigation in the future, to allow the replacement of conventional surfactants with rhamnolipids.

Cytotoxic rhamnolipid micelles drive acute virulence inPseudomonas aeruginosa

“…This is consistent with studies that have indicated that rhamnolipids self-assemble into various structures, including micelles, vesicles, lamellar structures, and even mesophases, depending on factors such as concentration, pH, temperature, presence of additives, and sample heterogeneity (congeners). (68,69) However, the micelles we have characterized here are distinctly smaller (~30 nm in diameter) than those previously characterized (~100-1000 nm). ( 70) This discrepancy may have been due to the different media used to grow the pathogen, the different methods for harvesting, and processing of the secreted products.…”

Enhancing Oil-Uptake Efficiency with an Alkyl Polyglycoside–Dodecanol Formulation

“…Biosurfactants, as an environmentally sustainable alternative to conventional surfactants, offer the potential to mitigate the environmental impact caused by the escalating production of industrial surfactant-containing formulations [1,2]. In recent years, heightened concern for environmental issues has directed scientific and technological research efforts.…”

“…While canonical synthetic surfactants are classified based on their polar head properties, Rosenberg and Ron [31] introduced a classification method for biosurfactants that centers on their molecular weight. This classification system categorizes biosurfactants into two groups: low-molecular-weight (LMW) and high-molecular-weight (HMW) variants [2,6,28,[31][32][33][34]. LMW biosurfactants, which include glycolipids and lipopeptides, are known for their ability to reduce surface and interfacial tension while enhancing wetting abilities [33][34][35][36].…”

“…On the other hand, HMW biosurfactants consist of polymeric compounds such as proteins, polysaccharides, lipoproteins, and lipopolysaccharides [6,30,34,37] and are characterized by their excellent emulsifying and surface adhesion properties. LMW biosurfactants are notable not only for their effectiveness at low concentrations and resilience under extreme pH, temperature, and salinity conditions but also for their high biodegradability, low toxicity, and enhanced environmental compatibility [2,3,18,25,32,34,38].…”

Self-Assembly of Rhamnolipid Bioamphiphiles: Understanding the Structure–Property Relationship Using Small-Angle X-ray Scattering

“…in 1995: acidic pH promotes the vesicle phase, while alkaline pH promotes the micellar phase. However, these and many other works, of which the self-assembly properties were just reviewed, were performed on sources of RLs containing both the di-rhamnolipid (RhaRhaC10C10) and monorhamnolipid (RhaC10C10), ,,− thus precluding full understanding of the structure–property relationship. Studies concentrating on either mono- or di-RLs started with the work of Chen et al ., who showed that in buffer at pH 9, RhaRhaC10C10 tends to form micelles, while RhaC10C10 tends to form vesicles.…”