Natural Biosurfactants Research Articles

Enhancing performance and durability of PVDF-ceramic composite membranes in microbial fuel cells using natural rhamnolipids

Ceramic membranes are widely used in microbial fuel cells (MFCs) owing to their cost-effectiveness and availability. However, these membranes often face challenges such as biofouling and negative mass-transfer effects. This study explored the use of a polymer layer to mitigate these issues, focusing on a polyvinylidene fluoride (PVDF) nanofibre membrane with various surface modifications. The modifications included alkaline treatment (PVDF-OH), rhamnolipids treatment (PVDF/BS), and a combination of both (PVDF-OH/BS). The ceramic membrane integrated with PVDF-OH/BS achieved the highest power density of 13.8 W m−3, which was 38 % higher than that of the unmodified ceramic membrane. Additionally, during the long-term study (days 90–101), the Ceramic + PVDF-OH/BS maintained a 64 % higher power performance compared to the unmodified ceramic membrane, indicating superior antifouling properties. Electrochemical and surface characterisation revealed that rhamnolipid-modified PVDF nanofibers enhanced fouling resistance. The findings demonstrate that natural biosurfactants which can be produced in situ within MFCs, can form a protective layer over membranes and significantly enhance their long-term power performance. This study represents the first instance of using natural microbial biosurfactants to improve membrane efficiency in a bioelectrochemical system.

Потенциал биоразложения пластика базидиальными грибами и актинобактериями (обзор)

With the ever-increasing production and consumption of plastics, inadequate management of plastic waste and its improper disposal pose a significant threat to the environment, affecting all forms of life, natural ecosystems and economies worldwide. In the face of this threat the search for alternative environmentally friendly solutions such as biodegradation instead of traditional recycling is of paramount importance. Currently knowledge about the mechanisms and effectiveness of plastics biodegradation is focused mainly on such groups of microorganisms as Gram-negative bacteria and fungi ascomycetes. The aim of this review is to highlight the ideas available in the literature about the potential decomposition of the most common plastic waste (polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate and polyurethane) as a result of biotic processes. Basidial fungi and actinobacteria have not yet found practical application in the technologies of processing and utilization of synthetic plastics. We discuss the ability of specific representatives of the two above taxonomic groups to decompose various synthetic polymers. The unique strategies of basidial fungi such as a powerful enzymatic system, the ability to absorb and produce natural biosurfactants – hydrophobins, allowed fungi to use plastics as a source of carbon and energy are considered. The possible contribution of mainly thermophilic actinobacteria of the genera Thermobifida, Thermoactinomyces, Thermomonospora, Saccharomonospora, Actinomadura, Microbispora and Streptomyces in improving the plastic waste disposal in order to create effective and sustainable plastic management practices has been characterized.

Ammonium Glycyrrhizate: A natural biosurfactant for the design of innovative nanocarriers

In this paper, the surfactant properties of Ammonium Glycyrrhizate, a bioactive compound present in Licorice root were studied. Considering the ability of this bioactive molecule to form micelles, we investigated for the first time the self-assemble of Ammonium Glycyrrhizate in vesicle structures. The organization of Ammonium Glycyrrhizate in vesicles allows to increase its bioavailability and, so, efficacy but also to use them as carrier of other drugs for potential combination therapy. Niosomes made up of Ammonium Glycyrrhizate were prepared using thin layer evaporation technique without the use of additional excipients and characterized in term of size, polydispersion index, Zeta potential and colloidal stability. Moreover, the performance of these innovative vesicles as carriers of hydrophilic drug (Fluorescein sodium) or a lipophilic molecule (Curcumin), was evaluated. Nanocarriers showed nanometric sizes, hexagonal shape, high colloidal stability and ability to encapsulate both hydrophilic and hydrophobic molecules. These vesicles did not showed cytotoxicity nor antimicrobial activityMoreover, it was found that these niosomes enhanced skin permeation and diffusion in several media and an important ability to interact with mucin. Considering its antinflammatory nature, in vitro inhibition of albumin denaturation assay was also carried out to test if the drug maintains these properties also when organized in colloidal structures. The obtained results highlighted an important antinflammatory activity suggesting the potential role of these nanodevices alone or loaded with other therapeutic molecules for the treatment of inflammatory-based diseases.

Microbial Biosurfactant as an Alternate to Chemical Surfactants for Application in Cosmetics Industries in Personal and Skin Care Products: A Critical Review.

Cosmetics and personal care items are used worldwide and administered straight to the skin. The hazardous nature of the chemical surfactant utilized in the production of cosmetics has caused alarm on a global scale. Therefore, bacterial biosurfactants (BS) are becoming increasingly popular in industrial product production as a biocompatible, low-toxic alternative surfactant. Chemical surfactants can induce allergic responses and skin irritations; thus, they should be replaced with less harmful substances for skin health. The cosmetic industry seeks novel biological alternatives to replace chemical compounds and improve product qualities. Most of these chemicals have a biological origin and can be obtained from plant, bacterial, fungal, and algal sources. Various biological molecules have intriguing capabilities, such as biosurfactants, vitamins, antioxidants, pigments, enzymes, and peptides. These are safe, biodegradable, and environmentally friendly than chemical options. Plant-based biosurfactants, such as saponins, offer numerous advantages over synthetic surfactants, i.e., biodegradable, nontoxic, and environmentally friendly nature. Saponins are a promising source of natural biosurfactants for various industrial and academic applications. However, microbial glycolipids and lipopeptides have been used in biotechnology and cosmetics due to their multifunctional character, including detergency, emulsifying, foaming, and skin moisturizing capabilities. In addition, some of them have the potential to be used as antibacterial agents. In this review, we like to enlighten the application of microbial biosurfactants for replacing chemical surfactants in existing cosmetic and personal skincare pharmaceutical formulations due to their antibacterial, skin surface moisturizing, and low toxicity characteristics.

Enhanced antimicrobial and antioxidant capacity of Thymus vulgaris, Lippia sidoides, and Cymbopogon citratus emulsions when combined with mannosylerythritol a lipid biosurfactant

Essential oils (EOs) are natural and effective agents for controlling microorganisms which cause biodeterioration and disease. However, their application is hampered/restricted due to hydrophobicity and rapid vaporization of these compounds. Encapsulation technology provides an effective approach to maintain EO stabilization and prevent the loss of volatile ingredients. Meanwhile, using a synthetic surfactant is seen as counter-productive; therefore, a natural biosurfactant is more reasonable and can potentially increase activity due to its other biological proprieties. This work aims to evaluate the mannosylerythritol lipid (MEL) biosurfactant combined with Thymus vulgaris, Lippia sidoides, and Cymbopogon citratus essential oil emulsions (O/W) and evaluate its antimicrobial and antioxidant capacity. The biosurfactant MEL demonstrated activity against Bacillus subtilis and Penicillium sp. After emulsification, the antimicrobial activity of Thymus vulgaris and Lippia sidoides was increased against Escherichia coli (500 µg/mL), Staphylococcus aureus (600 µg/mL), Bacillus subtilis (120 µg/mL), Pseudomonas aeruginosa (1500 µg/mL), Penicillium sp. (62.25 µg/mL), Aspergillus flavus (250 µg/mL), Fusarium oxysporum (100 and 250 µg/mL), and Candida albicans (125 and 250 µg/mL). We report that emulsions prepared with MEL have high inhibitory activity, maintain the active concentration, and increase antioxidant capacity by 7.33% (Thymus vulgaris), 13.71% (Lippia sidoides), and 3.15% (Cymbopogon citratus).

Biocomposites based on bentonite and lecithin: An experimental approach supported by molecular dynamics

Natural bio-surfactants have recently attracted much more attention due to their biodegradability and biocompatibility. They are often associated with clay materials to synthesize organoclays and can therefore be ideal materials for environmentally friendly oil-based drilling fluids. In this study, a bio-organoclay was obtained by modifying bentonite with natural soybean lecithin, and the effects of reaction temperature, time, pH, and lecithin concentration on the properties of modified bentonite were analyzed. Structural insights such as clay properties, intercalation process and lecithin organization were obtained using a large variety of experimental techniques and molecular dynamics simulations. The results of this study suggest that some experimental conditions have an important impact on the basal space of the bentonite. Reaction time and temperature did not have a significant effect on the final properties of the modified bentonite. However, by increasing the pH of the clay material or with a high concentration of lecithin, the interlayer space fluctuates from 1.21 to 5.96 nm. The lecithin molecules adopt a new spatial conformation in the interlayer space becoming perpendicular to the clay surface, which largely increase the interlayer space.

Solubilization of lipolysis products in mixed micelles is enhanced in presence of bile salts and Tween 80 as revealed by a model study (oleic acid) and emulsified chia-oil

In the last few decades, there has been a growing interest in understanding the mechanisms involved in lipid digestion with the purpose of developing strategies to control this complex physiological process. Bile salts (BS) are natural bio-surfactants that play crucial functions in this process and may represent a key strategy to modulate the lipolysis. One of the main functions is the removal of lipolysis products present at the interface of lipid droplets by solubilizing them in BS micelles, thus avoiding the reaction inhibition. However, there are few studies that analyzed the effects that could have the emulsion components on the solubilization capacity of BS micelles. Thus, the main purpose of the present work was to evaluate the impact of a typical food emulsifier (Tween 80) on the fatty acid (FA) solubilization capacity of BS micelles by using a method recently developed, involving a combination of turbidity and dynamic light scattering (DLS) determinations. As FA solubilization into BS micelles may strongly affect the kinetics of lipolysis, the lipolysis of T80-stabilized oil-in-water (O/W) emulsions was also studied. The results showed that a higher concentration of the emulsifier in the duodenal medium causes the lipolysis rate to be maximum for a longer time. The mechanism involved could be the contribution of T80 to increase the solubilization of FA (and possibly other products of the lipolysis) in the duodenal medium, consequently affecting the potential bioavailability of fatty acids.

Biomimetic strategy for electrophoretic deposition of composite ferroelectric poly(vinylidene, fluoride-co-hexafluoropropylene) – ferrimagnetic NiFe2O4 films

This investigation is motivated by interest in fabrication of composite films combining ferrimagnetic properties of spinel ferrites with multifunctional properties of ferroelectric polymers. It addresses the need in the development of surface modification techniques for inorganic materials and polymers and their electrophoretic deposition (EPD) for the fabrication of composite films. This article describes for the first time the fabrication of composite ferroelectric poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) - ferrimagnetic NiFe2O4 films by EPD. The approach is based on feasibility of fabrication, surface modification and EPD of PVDF-HFP particles using natural biosurfactants, such as catecholate-type caffeic acid (CA) and bile acid-type cholic acid (ChA). The analysis of chemical structure of CA and ChA provides an insight into the surface modification mechanisms and EPD efficiency. Film morphologies and corrosion protection properties are analyzed. An important finding is the ability of CA to act as a charging dispersant for materials of different types, such as PVDF-HFP polymer particles and inorganic nanoparticles of NiFe2O4 spinel and fabrication of composite films by EPD. The film deposition yield, morphology and composition of PVDF-HFP - NiFe2O4 films are analyzed. NiFe2O4 content and magnetic properties of the composites are varied by variation of EPD bath composition. This investigation provides a platform for EPD of composite films combining ferrimagnetic properties of spinel ferrites with multifunctional properties of ferroelectric polymers.

Application of Rhamnolipids as Dispersing Agents for the Fabrication of Composite MnO2-Carbon Nanotube Electrodes for Supercapacitors.

The high theoretical capacitance of MnO2 renders it a promising material for the cathodes of asymmetric supercapacitors. The good dispersion of MnO2 and conductive additives in a nanocomposite electrode is a key factor for efficient electrode performance. This article describes, for the first time, the application of rhamnolipids (RL) as efficient natural biosurfactants for the fabrication of nanocomposite MnO2-carbon nanotube electrodes for supercapacitors. RL act as co-dispersants for MnO2 and carbon nanotubes and facilitate their efficient mixing, which allows for advanced capacitive properties at an active mass of 40 mg cm−2 in Na2SO4 electrolytes. The highest capacitance obtained from the cyclic voltammetry data at a scan rate of 2 mV s−1 is 8.10 F cm−2 (202.6 F g−1). The highest capacitance obtained from the galvanostatic charge–discharge data at a current density of 3 mA cm−2 is 8.65 F cm−2 (216.16 F g−1). The obtained capacitances are higher than the capacitances of MnO2-based electrodes of the same active mass reported in the literature. The approach developed in this investigation is simple compared to other techniques used for the fabrication of electrodes with high active mass. It offers advantages of using a biocompatible RL biosurfactant.

A Versatile Strategy for the Fabrication of Poly(ethyl methacrylate) Composites

Poly(ethyl methacrylate) (PEMA) is dissolved in ethanol, known to be a non-solvent for PEMA, due to the solubilizing ability of an added bile acid biosurfactant, lithocholic acid (LA). The ability to avoid traditional toxic and carcinogenic solvents is important for the fabrication of composites for biomedical applications. The formation of concentrated solutions of high molecular weight PEMA is a key factor for the film deposition using the dip coating method. PEMA films provide corrosion protection for stainless steel. Composite films are prepared, containing bioceramics, such as hydroxyapatite and silica, for biomedical applications. LA facilitates dispersion of hydroxyapatite and silica in suspensions for film deposition. Ibuprofen and tetracycline are used as model drugs for the fabrication of composite films. PEMA-nanocellulose films are successfully prepared using the dip coating method. The microstructure and composition of the films are investigated. The conceptually new approach developed in this investigation represents a versatile strategy for the fabrication of composites for biomedical and other applications, using natural biosurfactants as solubilizing and dispersing agents.

Natural Biosurfactant as Antimicrobial Agent: Strategy to Action Against Fungal and Bacterial Activities.

Natural surfactants have gained importance as the usage of synthetic surfactants shows economical aspects, health, and environmental effect. This study examined the anti-microbial activity of safflower seed waste (Ssw) isolated surfactant against dandruff-causing Malassezia furfur and skin diseases causing bacterial strains. Saponin was the major component and non-ionic surfactants derived from plants, which have a special molecular structure with hydrophilic glycoside backbone and lipophilic triterpene derivative. The antimicrobial activity of isolated surfactants was confirmed by the MIC and kill-time assays. Our results showed that the isolated saponin may interact with the cell wall and membrane first and destroy the cell wall and membranes, which finally results in bacterial death. Besides, isolated saponin penetrates the cytoplasmic membrane or enters inside the cell after the destruction of cell structure, and then inhibits the normal synthesis of DNA and proteins that are required for bacterial growth. These results suggested that the effects of the Ssw isolated saponin on the growth inhibition of selected bacterial strains may be at the molecular level rather than only physical damage. Extraction of Biosurfactant (saponin) from Safflower seed waste and its antimicrobial activity.

Structures and antitumor activities of ten new and twenty known surfactins from the deep-sea bacterium Limimaricola sp. SCSIO 53532

Surfactins are natural biosurfactants with myriad potential applications in the areas of healthcare and environment. However, surfactins were almost exclusively produced by the bacterium Bacillus species in previous reported literatures, together with difficulty in isolating pure monomer, which resulted in making extensive effort to remove duplication and little discovery of new surfactins in recent years. In the present study, the result of Molecular Networking indicated that Limimaricola sp. SCSIO 53532 might well be a potential resource for surfacin-like compounds based on OSMAC strategy. To search for new surfactins with significant biological activity, further study was undertaken on the strain. As a result, ten new surfactins (1–10), along with twenty known surfactins (11–30), were isolated from the ethyl acetate extract of SCSIO 53532. Their chemical structures were established by detailed 1D and 2D NMR spectroscopy, HRESIMS data, secondary ion mass spectrometry (MS/MS) analysis, and chemical degradation (Marfey’s method) analysis. Cytotoxic activities of twenty-seven compounds against five human tumor cell lines were tested, and five compounds showed significant antitumor activities with IC50 values less than 10 μM. Furtherly, analysis of structure–activity relationships revealed that the branch of side chain, the esterification of Glu or Asp residue, and the amino acid residue of position 7 possessed a great influence on antitumor activity.

Functional and Structural Characterization of Pediococcus pentosaceus-Derived Biosurfactant and Its Biomedical Potential against Bacterial Adhesion, Quorum Sensing, and Biofilm Formation.

Biosurfactants are surface-active molecules of microbial origin and alternatives to synthetic surfactants with various applications. Due to their environmental-friendliness, biocompatibility, biodegradability, effectiveness to work under various environmental conditions, and non-toxic nature, they have been recently recognized as potential agents with therapeutic and commercial importance. The biosurfactant produced by various probiotic lactic acid bacteria (LAB) has enormous applications in different fields. Thus, in vitro assessment of biofilm development prevention or disruption by natural biosurfactants derived from probiotic LAB is a plausible approach that can lead to the discovery of novel antimicrobials. Primarily, this study aims to isolate, screen, and characterize the functional and biomedical potential of biosurfactant synthesized by probiotic LAB Pediococcus pentosaceus (P. pentosaceus). Characterization consists of the assessment of critical micelle concentration (CMC), reduction in surface tension, and emulsification index (% EI24). Evaluation of antibacterial, antibiofilm, anti-QS, and anti-adhesive activities of cell-bound biosurfactants were carried out against different human pathogenic bacteria (B. subtilis, P. aeruginosa, S. aureus, and E. coli). Moreover, bacterial cell damage, viability of cells within the biofilm, and exopolysaccharide (EPS) production were also evaluated. As a result, P. pentosaceus was found to produce 4.75 ± 0.17 g/L biosurfactant, which displayed a CMC of 2.4 ± 0.68 g/L and reduced the surface tension from 71.11 ± 1.12 mN/m to 38.18 ± 0.58 mN/m. P. pentosaceus cells bound to the crude biosurfactant were found to be effective against all tested bacterial pathogens. It exhibited an anti-adhesion ability and impeded the architecture of the biofilm matrix by affecting the viability and integrity of bacterial cells within biofilms and reducing the total EPS content. Furthermore, the crude biosurfactant derived from P. pentosaceus was structurally characterized as a lipoprotein by GC-MS analysis, which confirms the presence of lipids and proteins. Thus, our findings represent the potent anti-adhesion and antibiofilm potential of P. pentosaceus crude biosurfactant for the first time, which may be explored further as an alternative to antibiotics or chemically synthesized toxic antibiofilm agents.

Characterization of Iturin V, a Novel Antimicrobial Lipopeptide from a Potential Probiotic Strain Lactobacillus sp. M31

Members of lactic acid bacteria group are known to produce various antimicrobial substances. Cyclic lipopeptides are one such potent class of amphipathic natural biosurfactants that exhibit bactericidal and immunomodulatory properties. In this study, we aimed to investigate antimicrobial and immunomodulatory activities of a lipopeptide secreted by a LAB isolate strain M31 identified as a member of the genus Lactobacillus. The lipopeptide that was purified using a combination of chromatographic techniques and matrix-assisted laser desorption/ionization-time of flight of pure lipopeptide displayed a molecular weight of 1002Da. MS/MS analysis confirmed the presence of 7 amino acids (Asp-Tyr-Asp-Val-Pro-Asp-Ser) and a C13 beta-hydroxy fatty acid. The amino acid composition assigned lipopeptide to iturin class. However, the replacement of Gln with Val revealed it to represent a novel iturin named as iturin V. Iturin V showed antibacterial activity and did not cause hemolysis or cytotoxicity upto 125µg/mL. It induced secretion of pro-inflammatory cytokines TNF-alpha and IL-12 in murine dendritic cells. Probiotic features of strain M31 coupled with notable activity of iturin V against species of the genera Pseudomonas and Vibrio suggest that strain M31 has potential application for pathogen intervention treatments in processing of aquatic food products.

Identification of Novel Proteins in Foam Nests of the Japanese Forest Green Tree Frog, Rhacophorus arboreus.

Foam nests of frogs are natural biosurfactants that contain potential compounds for biocompatible materials, Drug Delivery System (DDS), emulsifiers, and bioremediation. To elucidate the protein components in the foam nests of Rhacophorus arboreus, which is an endemic Japanese frog species commonly seen during the rainy season, we performed amino acid analysis, SDS-PAGE electrophoresis, and matrix-assisted laser desorption/ionization mass spectrometry using intact foam nests. Many proteins were detected in these foam nests, ranging from a few to several hundred kDa, with both essential and non-essential amino acids. Next, we performed transcriptome analysis using a next-generation sequencer on total RNAs extracted from oviducts before egg-laying. The soluble foam nests were purified by LC-MS and analyzed using Edman degradation, and the identified N-terminal sequences were matched to the transcriptome data. Four proteins that shared significant sequence homologies with extracellular superoxide dismutase of Nanorana parkeri, vitelline membrane outer layer protein 1 homolog of Xenopus tropicalis, ranasmurfin of Polypedates leucomystax, and alpha-1-antichymotrypsin of Sorex araneus were identified. Prior to purification of the foam nests, they were treated with both a reducing reagent and an alkylating agent, and LC-MS/ MS analyses were performed. We identified 22 proteins in the foam nests that were homologous with proteinase inhibitors, ribonuclease, glycoproteins, antimicrobial protein and barrier, immunoglobulin-binding proteins, glycoprotein binding protein, colored protein, and keratin-associated protein. The presence of these proteins in foam nests, along with small molecules, such as carbohydrates and sugars, would protect them against microbial and parasitic attack, oxidative stress, and a shortage of moisture.

Spectrophotometric and conductometric study of the interaction of saponin with chromium(VI) and lead(II)

The removal of heavy metals from contaminated soil/water by biosurfactants depends on the ability of biosurfactant to form complexes with metals. The interaction of quillaja saponin, a nonionic natural biosurfactant, with heavy metal ions, viz. chromium(VI) and lead(II), has been studied spectrophotometrically and conductometrically in order to obtain detailed information for the saponin–metal complexes. Both the methods indicate complex formation between saponin and metal ions. Critical micelle concentration of saponin in the absence and presence of metal ions obtained by both the methods was in good agreement. The thermodynamic parameters, viz. free energy, enthalpy and entropy change, for micellization have been determined.

A Natural Triterpene Saponin-Based Pickering Emulsion.

The abuse of chemical surfactants in pesticide formulations is a potential threat to agricultural development and environmental safety. Thereby, developing an efficient eco-friendly pesticide formulation is of great significance. In this research, a biocompatible and ultrastable pesticide formulation has been developed in which merely 1 wt % natural glycyrrhizic acid (GA) was used to emulsify and stabilize 80 wt % agricultural oils. During the preparation process, amphiphilic GA molecules initially self-assembled into 1D nanofibers with a favorable surfactivity, and then afforded GA-based Pickering emulsions with fine droplets. Consequently, the Pickering emulsions transformed into gel-like Pickering emulsions as a result of the formation of a 3D network of nanofibers. On account of the unique chemical structure and admirable assembly behavior of GA, the gel-like Pickering emulsions exhibit ultrastability, thixotropy, and broad pH resistance. In addition, this formulation was investigated for its potential application to pesticides by using pure carbosulfan as the oil phase; up to 60 wt % carbosulfan could be coated, which is more than in the current commercial formulations. This work not only provides new insights into the application of natural biosurfactants to pesticides, but also proposes a biocompatible and eco-friendly pesticide formulation for use in ecological agriculture.

Liposomal encapsulation of silver nanoparticles enhances cytotoxicity and causes induction of reactive oxygen species-independent apoptosis.

Silver nanoparticles (AgNP) are one of the most widely investigated metallic NPs due to their promising antibacterial activities. In recent years, AgNP research has shifted beyond antimicrobial use to potential applications in the medical arena. This shift coupled with the extensive commercial applications of AgNP will further increase human exposure and the subsequent risk of adverse effects that may result from repeated exposures and inefficient delivery, meaning research into improved AgNP delivery is of paramount importance. In this study, AgNP were encapsulated in a natural biosurfactant, dipalmitoylphosphatidylcholine, in an attempt to enhance the intracellular delivery and simultaneously mediate the associated cytotoxicity of the AgNP. It was noted that because of the encapsulation, liposomal AgNP (Lipo-AgNP) at 0.625μg ml-1 induced significant cell death in THP1 cell lines a notably lower dose than that of the uncoated AgNP induced cytotoxicity. The induced cytotoxicity was shown to result in an increased level of DNA fragmentation resulting in a cell cycle interruption at the S phase. It was shown that the predominate form of cell death upon exposure to both uncoated AgNP and Lipo-AgNP was apoptosis. However, a reactive oxygen species-independent activation of the executioner caspases 3/7 occurred when exposed to the Lipo-AgNP. These findings showed that encapsulation of AgNP enhance AgNP cytotoxicity and mediates a reactive oxygen species-independent induction of apoptosis.

Extracting Natural Biosurfactants from Humus Deposits for Subsurface Engineering Applications

Environmentally benign, economical, and effective surfactants and additives are needed in engineering subsurface energy recovery processes. Biosurfactants have some advantages over chemically synthesized surfactants, but the high costs of microbial-biosynthesis limit their applications in subsurface engineering. Here we propose to use naturally occurring biosurfactants contained within Earth’s readily available and inexpensive humus deposits for subsurface engineering applications. We collected humus samples of different types from four different regions, and developed a simple method for extracting natural biosurfactant (NBS) using only four common chemicals. The average NBS extraction yields are 16 ± 3% of the raw humus. No significant differences in elemental composition and functional group chemistry were found among the NBS extracted from humus of different origins, suggesting that any humus deposit can be used for NBS extraction. Measurements of interfacial tensions between air–water and supercritic...

Self-Assembly of Escin Molecules at the Air-Water Interface as Studied by Molecular Dynamics.

Escin belongs to a large class of natural biosurfactants, called saponins, that are present in more than 500 plant species. Saponins are applied in the pharmaceutical, cosmetics, and food and beverage industries due to their variously expressed bioactivity and surface activity. In particular, escin adsorption layers at the air-water interface exhibit an unusually high surface elastic modulus (>1100 mN/m) and a high surface viscosity (ca. 130 N·s/m). The molecular origin of these unusual surface rheological properties is still unclear. We performed classical atomistic dynamics simulations of adsorbed neutral and ionized escin molecules to clarify their orientation and interactions on the water surface. The orientation and position of the escin molecules with respect to the interface, the intermolecular interactions, and the kinetics of molecular aggregation into surface clusters are characterized in detail. Significant differences in the behavior of the neutral and the charged escin molecules are observed. The neutral escin rapidly assembles in a compact and stable surface cluster. This process is explained by the action of long-range attraction between the hydrophobic aglycones, combined with intermediate dipole-dipole attraction and short-range hydrogen bonds between the sugar residues in escin molecules. The same interactions are expected to control the viscoelastic properties of escin adsorption layers.