Current Opinion in Colloid & Interface Science最新文献

Rhamnolipids are very promising sugar-based biosurfactants, generally produced by bacteria, with a wide range of properties that can be exploited at an industrial and technological level, e.g. in cosmetics, food science, or oil recovery, to provide benefits for human health and the environment. This has led to intensive research into optimizing their production to increase yields and minimize costs, which is challenging because biotechnological methods for rhamnolipid production result in complex product mixtures and require the introduction of complex separation strategies to ensure the purity of the rhamnolipid obtained. This is an important issue for the introduction of rhamnolipids to the market due to the differences that exist between the properties of the different congeners. This review attempts to provide an overview of the interfacial properties, potential applications, and recent advances in understanding the molecular mechanisms that govern the adsorption to interfaces and assembly in solution of rhamnolipids. In addition, the review also discusses some general aspects related to the production and purification methods of rhamnolipids, highlighting the need for further research to fully exploit their potential. It is hoped that this review will contribute to the growing body of knowledge about rhamnolipids and stimulate further research in this field.

In the current global context of the search for renewable resources, bioamphiphiles appear as a promising alternative to conventional oil-based surfactants. However, to commercialize these compounds, all their structural and physical properties should be known. Although their self-assembly and interfacial properties at low concentrations are currently an active research topic, their self-organization into liquid crystalline (LC) phases at high concentrations has yet hardly been addressed. This article reviews the few studies devoted to the identification of LC properties of bioamphiphiles. It highlights the fact that only two bioamphiphile families (mannosylerythritol lipids, sophorolipids) have been investigated in some detail and that much more structural and thermodynamic knowledge is still needed to reach the level of understanding achieved with conventional surfactants.

This review summarises state-of-the-art AFM experiments measuring surface tension in various liquid systems with cylinder shaped AFM probes (nanoindenters). AFM has emerged as a powerful technique, offering precise force measurements and advantages such as reduced sample contamination, analysis of small sample amounts, and access to nanoscale features such as the measurement of the single particle surface tension. These contribute to advancing our understanding of liquid systems and interfacial phenomena. However, the limited number of published studies may be attributed to challenges in AFM-based measurements using the micro-Wilhelmy method or the complexity of the perceived importance of surface tension research. Further investigation is needed to elucidate these factors. In recent years, the possibilities for producing nanoindenters have become increasingly precise which gives a new momentum to the AFM technique to measure surface tensions on a micro and nanoscale.

Gram-positive bacteria can be considered as structural building blocks adhering to interfaces and taking part in the formation of colloidal structures depending on their surface chemistry and properties. The chemical composition and spatial conformation of the Gram-positive bacterial cell wall, particularly of the species Lactobacillus, determine their surface properties and adhesion behaviors. One application of bacterial adhesion can be the stabilization of colloidal structures via a Pickering mechanism. The natural composition of Gram-positive bacteria renders abundant hydrophilic surface polysaccharides due to the presence of a thick peptidoglycan layer, making it unfavorable for their adsorption at interfaces, however, this property provides sufficient binding sites to allow surface modification. Understanding the fundamental physicochemical forces governing bacterial adhesion helps to reveal their potential applications as Pickering particles. The novelty of this work is that this review summarizes the major non-specific interactions occurring between bacteria approaching a surface, the commonalities and differences of bacteria to Pickering particles, and how a series of simple and advanced colloidal structures can be stabilized by natural and surface-modified bacteria.

Surfactants are ubiquitous in formulated products and technologies. As one of the most important commodity chemicals, their remarkable consumption leads to the necessity of finding sustainable alternatives. Although the use of renewable sources limits the available chemical space for a “Green” production, the great variety of naturally occurring precursors, i.e., fatty acids and sugars, opens a myriad of possibilities to create biosurfactants capable of replacing the fatigued fossil-derived amphiphiles. Here, we visit the concept of isomer-directed assembly applied to sugar-based surfactants, wherein amphiphile assembly and function are fine-tuned through changes in the stereochemical and regiochemical configuration of the molecule. As such, we show how isomerism defines directional interactions and solvation, ultimately dictating the assembly of surfactants. However, a general framework to understand the structure-function relationship for these is still missing, which is key to realizing this divergent set of tools for the design of new surfactants.

The neutron and X-ray scattering techniques of small-angle scattering and reflectivity are important tools for the characterisation of the key properties of surfactants, their adsorption at interfaces, and their self-assembly in solution. The increasing trend towards biosustainable and biocompatible surfactant-based formulations highlights the increasing importance of understanding the properties of biosurfactants. This review focuses on some relatively recent contributions of the use of primarily neutron scattering techniques to the understanding of surface adsorption and self-assembly of some specific microbial derived biosurfactants, rhamnolipids and sophorolipids. The review also focuses on the behaviour of their mixtures with other surfactants and shows how a detailed thermodynamical analysis is possible from the scattering data.

The public increasingly requests green formulations as a consequence of growing sustainability awareness. This may include glycolipid and lipopeptide biosurfactants (BS), which are considered renewable, biodegradable, and mild alternatives to conventional fossil-based surfactants. For developing green formulations, it is crucial to understand the phase behavior and the resulting physico-chemical characteristics of systems with BS. This is not only necessary for binary systems of BS in water, which have already been frequently studied and reviewed. But it is also important to study combinations with other surfactants and oils due to their higher relevance for applications. For this reason, we review in this article the different types of phase behavior of systems comprising BS, in particular systems with rhamnolipid, sophorolipid, mannosylerythritol lipid, cellobiose lipid, and surfactin.

Synergies between surfactants and proteins are found everywhere in everyday life. Beneficial interactions are exploited in fields such as food processing, pharmaceutical production, and laundry, leading to better products and lower energy consumption. Nevertheless, there is still room for improvement regarding sustainability. Here, biosurfactants (BS) are an attractive alternative to petrochemical surfactants. Insights into BS-protein interactions can help replacing traditional surfactants with BS and uncover new opportunities. Here, we review recent work on proteins' interactions with BS, with focus on the self-assembly of protein:BS complexes and BS’ effects on enzymatic activity. Generally, interactions are milder than those with traditional ionic surfactants, leading to modest effects on protein structure and self-assembly, while enzymatic inhibition is generally observed above BS' critical micelle concentration. Mild interactions between proteins and BS show promise in forming functional complexes with proteins, however, further studies are required to understand and minimize the detrimental effects that do occur.

Physics-based molecular simulation is a potentially transformative tool in the field of biosurfactants. Years of research and software development have culminated in reliable and accessible techniques for applying simulation to a variety of research problems. Simulation tools can be used to probe a wide range of atomic-scale phenomena from single molecule conformational behavior to large scale aggregation in solution and at interfaces. In recent years, researchers are increasingly finding ways to incorporate insights from molecular simulation into biosurfactant research. In this review, we highlight recent advances in simulation of biosurfactants, with discussion centered on the role of all-atom and coarse-grained molecular dynamics as well as some discussion of quantum mechanics. We also offer perspective on the future of biosurfactant simulation where we consider ways to improve the practical usefulness of simulation results as well as the most effective way to leverage simulation for faster and truly novel innovation.

Microbial biosurfactants have gained interest in the last decades because of their unique characteristics. The variety of chemical structures within these compounds makes them very versatile, with glycolipids and lipopeptides outstanding among the rest. The amphiphilic nature of these compounds makes them to partition into and strongly interact with phospholipid membranes, modifying their structure and function. Thus, much research has been done on the characterization of the interaction of glycolipid and lipopeptide biosurfactants with model and biological membranes. Whereas the studies involving phospholipid model membranes were mostly carried out earlier, most of the recent research has focused on biological membranes, including mammalian and microorganisms' systems. This review presents the recent developments achieved on the interaction of the main glycolipid and lipopeptide biosurfactants with model and biological membranes.