Hydrophilic Head Research Articles

Aminolipids in bacterial membranes and the natural environment.

Our comprehension of membrane function has predominantly advanced through research on glycerophospholipids, also known as phosphoglycerides, which are glycerol phosphate-based lipids found across all three domains of life. However, in bacteria, a perplexing group of lipids distinct from glycerol phosphate-based ones also exists. These are amino acid-containing lipids that form an amide bond between an amino acid and a fatty acid. Subsequently, a second fatty acid becomes linked, often via the 3-hydroxy group on the first fatty acid. These amide-linked aminolipids have, as of now, been exclusively identified in bacteria. Several hydrophilic head groups have been discovered in these aminolipids including ornithine, glutamine, glycine, lysine, and more recently, a sulfur-containing non-proteinogenic amino acid cysteinolic acid. Here, we aim to review current advances in the genetics, biochemistry and function of these aminolipids as well as giving an ecological perspective. We provide evidence for their potential significance in the ecophysiology of all major microbiomes i.e. gut, soil and aquatic as well as highlighting their important roles in influencing biological interactions.

Molecular modeling aided design, synthesis, and activity evaluation of N-arylindole derivatives as GPR52 agonists

G protein-coupled receptor 52 (GPR52) is considered to be a promising target to improve the symptoms of psychiatric disorders and its agonists are expected to treat schizophrenia without traditional side effects. Several research institutions have reported some small molecule GPR52 agonists, which can be the starting point for rational drug development. In this study, a series of N-arylindole derivatives were designed and synthesized based on 3g according to classical pharmacochemical methods and computer aided drug design (CADD). The designed compounds exhibited good to excellent activities and the structure-activity relationship (SAR) study was explored. The results show that the connection mode between the hydrophilic head (Part I) and the indole ring (Part II) plays an important role in the GPR52 agonist activity. Among these compounds, compounds 16 and 21 have good GPR52 agonist activity (EC50 = 93 nM and 75 nM) and can inhibit hyperactive behavior in mice induced by MK-801 (EC50 =7.94 mg/kg and 6.64 mg/kg). These designed small molecules will provide new options for the development of novel GPR52 agonists.

The effect of biochar in a specialty adsorbent on enhanced PFAS removal from surface water

An enhanced specialty adsorbent, referred to as biochar-based iron and perlite-integrated green environmental media (BIPGEM), was designed to simultaneously remove both long-chain PFAS mainly including perfluorooctanoic acid (PFOA) and Perfluorooctanesulfonic acid (PFOS) from surface water matrices. Batch-scale experiments using BIPGEM revealed that the removal efficiencies for PFOA and PFOS exceeded 98 % when treating a mixture of 3 short-chain PFAS, including perfluorobutanoic acid (PFBA), perfluorobutane sulfonic acid (PFBS), and hexafluoropropylene oxide dimer acid (GenX Chemicals). Additionally, a fixed-bed column study using BIPGEM revealed that the removal efficiencies of PFOA and PFOS were over 85 % within the first 12 h whereas the removal efficiency of PFBA was over 40 % at the fortieth hour. It was confirmed that the critical role of biochar in the removal of long-chain PFAS, particularly PFOA, can be attributed to the following factors: (1) the morphological structure and pore size of biochar restrict PFAS mobility, (2) the extensive specific surface area of biochar, with a positive charge (point of zero charge = 10.7) at the experimental condition, enhances the adsorption likelihood with the negatively charged hydrophilic heads of PFOA and PFOS, and (3) the presence of non-polar aromatic rings with high hydrophobicity in biochar facilitates the removal of PFAS through hydrophobic interactions with the functional groups of PFAS.

Molecular and energetic analysis of the interaction and specificity of Maximin 3 with lipid membranes: In vitro and in silico assessments.

In this study, the interaction of antimicrobial peptide Maximin 3 (Max3) with three different lipid bilayer models was investigated to gain insight into its mechanism of action and membrane specificity. Bilayer perturbation assays using liposome calcein leakage dose-response curves revealed that Max3 is a selective membrane-active peptide. Dynamic light scattering recordings suggest that the peptide incorporates into the liposomal structure without producing a detergent effect. Langmuir monolayer compression assays confirmed the membrane inserting capacity of the peptide. Attenuated total reflection-Fourier transform infrared spectroscopy showed that the fingerprint signals of lipid phospholipid hydrophilic head groups and hydrophobic acyl chains are altered due to Max3-membrane interaction. On the other hand, all-atom molecular dynamics simulations (MDS) of the initial interaction with the membrane surface corroborated peptide-membrane selectivity. Peptide transmembrane MDS shed light on how the peptide differentially modifies lipid bilayer properties. Molecular mechanics Poisson-Boltzmann surface area calculations revealed a specific electrostatic interaction fingerprint of the peptide for each membrane model with which they were tested. The data generated from the in silico approach could account for some of the differences observed experimentally in the activity and selectivity of Max3.

Enhancing gene delivery efficiency with amphiphilic chitosan modified by myristic acid and tertiary amino groups

The aim of this study is to synthesize new amphiphilic chitosan containing myristic acid as the hydrophobic tail and tertiary amine groups as the hydrophilic head and to evaluate the gene delivery efficiency. In this context, the primary amine groups of chitosan were first modified with myristic acid (Chi-M), followed by the modification of the methylol groups with 3-dimethylamino-1-propyl chloride hydrochloride. The chemical characterization of this chitosan formulation (Chi-MA) was determined using nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR) analysis and gel permeation chromatography-size exclusion chromatography. Chi-MA nanoparticles were prepared via ionic gelation, and particle size, polydispersity and zeta potential were determined. The nanoparticles were evaluated for their proton buffering capacity and gene complexing capacity. Additionally, the cytotoxicity of Chi-MA on HEK293T cells was determined via MTT assay, and the transfection efficiency of Chi-MA was analyzed by a flow cytometer. The results indicate a significant increase in gene complexing capacity (8-fold) and nanoparticle formation ability of Chi-MA compared to other chitosan formulations. Chi-MA nanoparticles showed no toxicity against HEK293T cells and exhibited the highest transfection efficiency with significantly lower nanoparticle: gene ratios compared to previous studies. These findings demonstrate the effective use of amphiphilic Chi-MA as a gene carrier.

Micellar (Photo−)Catalysis Driven by IR‐Active Semiconductor Surfactants

AbstractIn micellar catalysis, one uses aggregates formed by surfactants as nanoreactors for performing chemical reactions. A special class of tailor‐made surfactants containing catalytically active sites opens new perspectives in micellar catalysis. Little is known about the combination of such surfactants with photocatalysis. Molecular semiconductors are presented, which simultaneously have amphiphilic properties and are made of a hydrophilic fullerenol head group attached to dye molecules as the hydrophobic entity. The first generation of those surfactants produces reactive oxygen species (ROS) when exposed to light in the UV/Vis range. The concept of the current paper is that one can drive the photocatalytic process also using low‐energy photons in the near‐infrared region. For this purpose, NIR‐active dye molecules were selected and attached to the fullerenol head. It is shown that a fullerenol ‐ aminostilbene compound representing the second generation of semiconductor surfactants fulfills all requirements. It forms aggregates in water that are catalytically active. Moreover, two‐photon experiments with λ=780 nm were performed, indicating successful ROS production and, thus, photocatalytic activity.

Biosurfactant-mediated transport of tetracycline antibiotics in saturated porous media: Combined effects of the chemical properties of contaminants and solution chemistry conditions

The mobility of tetracycline antibiotics (TCs) in saturated aquifers is possibly affected by the presence of biosurfactants, which are widespread in the aquatic/soil environments. This study investigated the mobility characteristics of various tetracyclines—specifically tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)—within quartz sand columns in the presence of rhamnolipid, a common biosurfactant. Exogenous rhamnolipid significantly inhibited the transport of the three TCs over the pH range of 5.0–9.0 (e.g., the mass of retained TC, OTC, and CTC increased from 32.6 %, 26.9 %, and 39.2 % (in the absence rhamnolipid) to 39.4 %, 38.9 %, and 51.7 % (in the presence of rhamnolipid), respectively). This observation could be attributed to the bridging effects of this biosurfactant. Specifically, the hydrophilic head of rhamnolipid molecules is likely associated with the surfaces of sand grains through surface complexation and/or hydrogen bonding interactions. Accordingly, the hydrophobic moieties of the deposited rhamnolipid molecules (i.e., the aliphatic chains) interact with the hydrophobic groups of TCs molecules via hydrophobic interactions. Interestingly, the extent of the inhibitory effect on CTC mobility was greater than that on OTC and TC, which was related to the different hydrophobic characteristics of the three antibiotics. Furthermore, the inhibitory effect of rhamnolipid on the transport of TCs diminished as the pH of the background solution increased. This observation was attributed to the weakened bridging effects, resulting from the reduced deposition of the biosurfactant on the sand surfaces. Additionally, the cation-bridging mechanism involved in the retention of TCs in the addition of rhamnolipid when the background electrolyte was Ca2+ (i.e., Ca2+ ions served as bridging agents between the deposited rhamnolipid molecules and TCs). The insightful findings enhance our understanding of the critical roles of biosurfactants in influencing the environmental dynamics and ultimate fate of conventional antibiotic pollutants within groundwater systems.

Sodium dodecyl sulfate rearranges the conformation of transferrin and attenuates its iron-binding capacity

Sodium dodecyl sulfate (SDS), an anionic surfactant used in many cleaning and hygiene products, is known for its dermal and respiratory toxicity. However, how this surfactant influences the iron dynamics within the body and the mechanism is unknown. We explored the interaction between SDS and human transferrin (HTF), focusing on the effects on iron-binding capacity and structural changes. Results revealed that SDS exposure led to a significant release of iron from HTF in a dose-dependent manner, changing its structure and reducing the iron-binding ability. Spectroscopic analyses showed that the protein secondary structure and skeleton, as well as the micro-environment of aromatic amino acids of HTF, were destroyed after SDS binding. Isothermal titration calorimetry (ITC) results (ΔG, ΔS, and ΔH were −40.1 kcal·mol−1, 0.16 kcal·mol−1·K-1, and 10.1 kcal·mol−1, respectively) indicated a spontaneous and hydrophobic interaction with one strong binding site. Molecular docking identified the preferred binding sites, emphasizing hydrophobic forces (with the hydrophobic tail) and hydrogen bonds (with the hydrophilic head) as the primary driving forces, which aligns with the ITC results. Overall, this comprehensive analysis sheds light on the intricate interplay between SDS and HTF, providing insights into potential health risks associated with SDS exposure.

Responsive release of guest aqueous droplet in liquid crystal droplet assists the detection of organophosphorus using commercial pregnancy test strip

Here, we report a liquid crystal (LC) double-emulsion based system for organophosphorus (OPs) sensing by controllable release of guest aqueous droplets (GADs) cargo. First, double liquid crystal emulsion, water in liquid crystal in water (W/LC/W), with size between 4∼ 20 μm was prepared with GADs loaded at the center of liquid crystal droplet (LCD) through elasticity trap. The LCDs were monodispersed and response sensitively to amphiphilic surfactant with opposite charge. With the capability of ejecting GADs with human chorionic gonadotropin (hCG) as cargo located in LCD to continuous aqueous phase, responsive vehicles are obtained and applied in the repurposing of commercial pregnancy test strip (PTS). With hydrophobic alkyl chain and hydrophilic head, myristoylcholine (Myr) is a good amphiphilic surfactant to trigger the release of hCG, and substrate for the enzymatic hydrolysis of acetylcholine esterase (AChE). Provided with the inhibition effect of OPs to the hydrolysis ability of AChE, OPs correlate positively with the concentration of Myr, thus correlate well with the release of hCG in W/LC/W emulsion. Thus, OPs residue in river or food is readily visualized using commercial PTS.

Surface engineered novel cationic surfactants with enhanced surface adsorption for environmental applications

Gemini Cationic Surfactants (GCS) have garnered significant attention due to their distinctive molecular structure, featuring two hydrophilic head groups associated with a hydrophobic spacer. This distinctive configuration enables diverse applications across various fields. Hence, the current study introduces a novel series of GCSs, ethanediyl-1,2-bis[di(2-hydroxypropyl) alkylammonium] dibromide (Cn-C2-Cn[IsoPr(OH)2; n = 9, 12 and 14) and comprehensively explore their properties, highlighting their promising antimicrobial activity. The synthesis of GCSs was validated using 1H NMR and IR spectroscopy. Dynamic Light Scattering was employed to determine the dimensions of Gemini surfactant aggregates in aqueous solutions. Surface tension analysis determined critical concentrations of micelle (CMC), minimum surface area (Amin) and concentration of surface excess (Γmax). Physicochemical properties were assessed through conductivity and surface tension analyses in aqueous solutions. The CMC, Amin and Γmax values decrease as alkyl chain length extends. Surface tension data revealed strong adsorption of GCSs at interfaces. π values (mN/m) ranged from 36.7 (C14C2C14[Iso-Pr(OH)]2) to 45.3 (C9C2C9[Iso-Pr(OH)]2). Conductivity and surface tension measurements further characterized Gemini surfactants in aqueous environments at 298 K. The size of the micelle aggregates varied between C9C2C9[Iso-Pr(OH)]2 (1.2885 nm) and C14C2C14[Iso-Pr(OH)]2 (1.9210 nm), highlighting the impact of chain length on micelle size. Hence, the study highlights significant effect of the chain lengths on Gemini cationic surfactants’ self-assembly in dilute aqueous environments. Antimicrobial tests demonstrated significant activity of Cn-C2-Cn[IsoPr(OH)]2 GCSs at varying concentrations. Antimicrobial tests showed the significant antimicrobial potential of these GCS compounds, suggesting their potential and promising applications in medical, hygiene, environmental sanitation and advanced materials sectors.

Visualisation of surface coating distribution patterns on modified CaCO3

In this work, the surface modification of calcite-type calcium carbonate using the anionic surfactant sodium stearate was studied. The optimal amount of surfactant and its distribution on the surface of calcium carbonate is of great significance to the actual production. Various techniques were used to characterize these important parameters such as Fourier-transform infrared spectroscopy (FTIR), water contact angle measurements, Raman Mapping visualizationimaging, Raman depth profiling, thermogravimetric analysis (TGA), and atomic force microscopy (AFM). The results of the Fourier Transform Infrared (FTIR) suggest the formation of a coating on the surface of the modified calcium carbonate. Water contact angle measurements, Raman Mapping visualizationimaging, and TGA indicate that the optimal initial dosage of sodium stearate required to form a monolayer coating is about 2 wt%. Here, the hydrophilic heads of the sodium stearate are arranged vertically on the calcium carbonate surface forming the monolayer. As the concentration of sodium stearate increases, the hydrophobic tails of the sodium stearate or calcium stearate connect each other, forming bilayer or multilayer coatings. Furthermore, the surface coating on calcium carbonate originates from the edge vertices and gradually spreads towards the central region as the amount of sodium stearate increases until complete coverage is achieved. Raman depth profiling and AFM visualization results suggest that the thickness of the monolayer coating is approximately 5.25 nm.

Molecular insights reveal how the glycolipids in cell membrane mitigates nanomaterial's invasion

Nanomaterial-cellular membrane interaction is crucial for the cytotoxicity of such materials in theoretical investigations. However, previous research often used cellular membrane models with one or few lipid types, which deviates significantly from realistic membrane compositions. Here, employing molecular dynamics (MD) simulations, we investigate the impact of a typical nanomaterial, boron nitride (BN), on a cellular membrane model based on the realistic small intestinal epithelial cell (SIEC) membrane. This membrane contains a complex composition, including abundant glycolipids. Our MD simulations reveal that BN nanosheet can partially insert into the SIEC membrane, maintaining a stable binding conformation without causing obvious structural changes. Dynamic analyses suggest that van der Waals (vdW) interactions drive the binding process between BN and the SIEC membrane. Further simulation of the interaction between BN nanosheet and deglycosylated SIEC membrane confirms that BN nanosheet cause significant structural damage to deglycosylated SIEC membranes, completely inserting into the membrane, extracting lipids, and burying some lipid hydrophilic heads within the membrane interior. Quantitative analyses of mean squared displacements (MSD) of membranes, membrane thicknesses, area per lipid, and order parameters indicate that BN nanosheet causes more substantial damage to deglycosylated SIEC membrane than to intact SIEC membrane. This comparison suggests the molecular mechanism involved in mitigating BN invasion by SIEC membrane that the polysaccharide heads of glycolipids in the SIEC membrane form a significant steric hindrance on membrane surface, not only hindering the insertion of BN, but also resisting the lipid extraction by BN. Free energy calculations further support this conclusion. Overall, our MD simulations not only shed new light into the reduced impact of BN nanosheet on the realistic SIEC membrane but also highlight the importance of glycolipids in protecting cell membranes from nanomaterial invasion, contributing to a deeper understanding of nanomaterial-realistic cell membrane interactions.

Natural Surfactant Stabilized Aqueous MoS2 Nano-Lubricants for Reducing Friction and Wear

From the outlook of energy saving and environmental protection, the development of eco-friendly and green lubricants without compromising their lubrication performance has become a global agenda. Nevertheless, water-based lubricants suffer from low lubricity and weak load-bearing capacity, making them unsuitable for various industrial applications. Herein, using liquid-phase exfoliation, bulk MoS2 layers are delaminated into atomically thin nanosheets and stabilized in a water medium by a natural surfactant, Sapindius Mukrossi (SM). A natural SM surfactant consisting of 10 % –12 % saponin molecules has a hydrophobic tail aglycone and hydrophilic head glycone molecules that provide steric repulsive forces against the aggregation of exfoliated MoS2 nanosheets. Optimization of the surfactant concentration in water led to highly concentrated MoS2 nanosheets (∼1.23 mg/ml in a single step) with an average lateral length (<L>) and number of layers (<N>) of ∼ 150 nm and ∼ 8 layers, respectively. Owing to its high concentration and few-layers, MoS2 nanosheets based aqueous dispersion was directly tested for aqueous lubricant applications. Compared to pure water, MoS2 nanosheets (0.1 wt%) in water led to effective reductions in the coefficient of friction and wear scar diameter of ∼ 75 % and ∼ 65 %, respectively. Wear depth ∼ 15 µm on SS ball is reduced to ∼ 1 µm when 0.1 wt% of MoS2 nanosheets-SM surfactant dispersion under similar testing conditions. Post-mortem analysis suggested that the stable formation of protective tribo-film on the worn surfaces of steel surface that were tested at different intervals (1-210-400 Days) leads to an effective sliding under load. To demonstrate the practicality of this dispersion, SM surfactant stabilized MoS2 nanosheets was used as a dielectric lubricant fluid in a wire EDM for advanced metal-cutting fluid applications.

Instant in situ highlighting of latent fingerprints by a green fluorescent probe based on aggregation-induced emission

Fluorescence sensing of latent fingerprints (LFPs) has gained extensive attention due to its high sensitivity, non-destructive testing, low biotoxicity, ease of operation, and the potential for in situ visualization. However, the realization of in situ visualization of LFPs especially with green emission and rapid speed is still a challenge. Herein, we synthesized an amphibious green-emission AIE-gen TPE–NI–AOH (PLQY = 62%) for instant in situ LFP detecting, which integrates the excellent fluorescence properties of naphthalimide (NI) with a hydrophilic head and the AIE character as well as the donating property of tetraphenylethene (TPE). TPE–NI–AOH in ethanol/water binary solvent was used as an environmentally friendly LFP developer and achieved in situ green-fluorescence visualization of LFPs. The fluorescence signal achieves its 60% saturated intensity in 0.37 s and nearly 100% in 2.50 s, which is an instant process for the naked eye. Moreover, level 3 details and super-resolution images of LFPs could be observed clearly. Besides, the TPE–NI–AOH developer could be stored for at least 6 months, suitable for long-term storage. This instant in situ highlighting method does not require post-processing operations, providing a more convenient, rapid, and efficient detection method of LFPs. This work would inspire the further advancement of fluorescent sensors for fingerprint imaging.

Role of functional group orientation in the drug partitioning and micelle-mediated delivery of quinoline family drugs to the carrier protein

The understanding of the characteristics of the carrier vehicle and the specific drug it transports is required for designing an effective drug delivery system. We have done a comprehensive analysis of the distribution of three quinolines − quinine, quinidine, and cinchonidine − within hexadecyltrimethyl-ammonium bromide (HTAB) micelles. Further, we tracked their journey as they are transported to the carrier protein human serum albumin (HSA), using spectroscopy, calorimetry, and molecular docking methodologies. The mechanism of partitioning of the quinolines in HTAB micelles is explained based on thermodynamic parameters obtained from isothermal titration calorimetry (ITC). The partitioning coefficient obtained for the quinolines is in the range of 102-104 M−1 and is strongest for quinidine [(1.17 ± 0.78) × 104 M−1]. The stereochemistry and hydroxyl group orientation modulates the partitioning of the quinolines and also the delivery of the quinolines via micellar HTAB. The polar/electrostatic/H-bonding interactions of the hydrophilic polar head of HTAB hinders in efficient quinine delivery, while hydrophobic interactions through the micellar palisade layer facilitate the delivery of quinidine and cinchonidine. Such thorough exploration into the delivery of drugs via micelles is crucial in identifying functionalities necessary to optimize drug delivery systems for the successful delivery of drugs.

Liposomes in Medicine: An In-depth Analysis of Preparation Methods and Applications

Liposomes are the targeted drug administration system that offers the potential to improve the medicinal value of drugs by boosting the concentration of medication the duration of time in intended cells, thereby reducing side effects. Liposomes, which are sphere-shaped vesicles built from phospholipids and cholesterol, are being investigated extensively as a means of increasing the bioavailability and delivery of therapeutic medications. Liposomes have both hydrophilic head and hydrophobic tail and exhibit eminent properties, including reduced toxicity, better biocompatibility, easily biodegradable, easy to function and enhanced sustained release of drugs with increased therapeutic efficacy. Liposomes are said to be an ideal drug-carrier system as they enhance the delivery of anticancer drugs at the tumor site. Since liposomes are amphiphilic carriers that may be modified to have various functional characteristics, they are seen as a potential technology for a range of pharmacological and industrial uses. As a potential way to carry drug delivery across cell membranes, liposomes help medications to target specific disease sites. Liposomes are employed to deliver genetic material, such as DNA fragments, to specified cells so they may synthesize certain proteins. Thus, liposomes are investigated as adaptable nano-vesicular vehicles with potential medical applications for medicinal and diagnostic purposes. The future of liposomal formulations is projected to be a multipurpose use of imaging capabilities and medicinal components in a single liposome for diagnostic and actual-time therapy. The most promising approach for topical administration is liposomal drug delivery since it is compatible with living systems and can accommodate simultaneously hydrophobic and hydrophilic medicated substances because of the amphipathic feature of phospholipids.

Carbohydrate polymers based MnO2 nanostructures for catalytic and antibacterial activity; kinetic modeling and molecular docking analysis

In this project, cellulose nanocrystal-CNC, chitosan-CS, and starch-St doped MnO2 nanostructures (NSs) were synthesized by a co-precipitation approach. The motive of this research was to evaluate the effect of CNC, CS, and St on catalytic activity, kinetic adsorption, and antimicrobial potency with molecular docking (MD) analysis of MnO2. The hydrophilic head of polymers interacts with MnO2 NSs to regulate the growth, recombination rate, and stability of nanostructures. Notably, St-doped MnO2 exhibited the highest catalytic potency in an acidic medium in comparison to basic and neutral media. The kinetic modeling (pseudo-1st, pseudo-2nd order, Elovich, and intra-particle diffusion model) suggests that the adsorption of RhB dye by the NSs follows the pseudo-second-order kinetics. Among all samples, CNC-MnO2 and St-MnO2 proved to be an efficient antibacterial agents against E. coli and s. aureus bacteria, respectively. Findings revealed that polymer-based MnO2 nanostructures were the most efficient inhibitors of DNA gyrase against E. coli and S. aureus.

Qualitative analysis of hydrophilic headgroup water molecular space dependence and wetting effects of solution systems on polluting coal dust

The hydrophilic head groups of the surfactants affect the interfacial tension of surfactant solutions and the internal micelle structure of the bulk surfactants. Because of this, investigating the effect of the hydrophilic head groups on the adsorption performance of surfactants is helpful in terms of revealing the wetting mechanism of surfactants on coal at the molecular level. In this work we combine molecular dynamics simulations and quantum chemistry calculations with a collection of experiments to analyze the interaction patterns between sodium dodecyl sulfonate (SDSO), sodium dodecyl sulfate (SDS), sodium fatty alcohol polyoxyethylene ether carboxylate (SSN), and sodium lauryl phosphate (LSN) with coal. The radial distribution results show that SDSO formed the closest first peak of the hydrated layer at 1.31 Å, with a probability peak of 3.92, which exhibited strong hydrogen bonding interactions that are consistent with the relative concentration and average azimuthal shift trends obtained from molecular trajectory simulations. The priority interaction types between four surfactants and water molecules were determined using the energy difference of molecular orbitals in quantum mechanics. The weak interaction between hydrophilic head groups and water molecules was qualitatively and quantitatively analyzed using the Independent Gradient Model (IGMH), and the fundamental reasons affecting the wetting of long flame coal were obtained.

Self-assembling properties of mono and di-rhamnolipids characterized using small-angle X-ray scattering

Rhamnolipids are glycolipid surfactants composed by a hydrophilic head of either one (mono-RL) or two (di-RL) rhamnose moieties coupled to hydroxyaliphatic chains that can be of different lengths. In spite of their importance in different fields of applications, as bioremediation processes for instance, self-aggregation physico-chemical properties of RLs are not unique. This because a variety of aggregates morphologies (shape and size) can either exist or coexist in aqueous dispersion due to mono-RL:di-RL molar ratio, hydrophobic tails length, pH and the presence of co-surfactants and additives. Recently, a theorethical approach reported the self-assembling morphologies of either pure mono or di-RL in aqueous environment, predicting the formation of spherical to ellipsoidal micelles to worm-like and disk-like aggregates depending on RL concentration and fatty acid chain length. In order to add new information to those previously available, the present work investigated the self-assembling properties of mono-RL-C10-C10 and di-RL-C10-C10 separately in aqueous dispersion by small angle X-Ray scattering (SAXS). A novel approach was applied to the data analysis coupling the scattering length density profiles of the RLs chemical groups and Monte Carlo simulations. Such an approach allowed us to infer about the preferred mono-RL and di-RL conformations that fit better in the self-assembling morphologies. In this way, we show that mono-RL-C10-C10 self-assembles into lamella-like aggregates coexisting with 30 % of multi-lamella aggregates (circa of 5 closed stacked lamella) from a concentration ranging from 10 to 50 mM, with hydrophobic thickness of about 12 Å, a hydrated polar head thickness of 10 Å, and an area per glycolipid of 76 Å2. On the other hand, di-RL prefers to self-associate into flexible cylinder-like aggregates, from 70 mM to 110 mM concentration, with hydrophobic radius on the order of 7.5 Å, a hydrated polar shell of 21.5 Å, with hydropobic/polar interface of 110 Å2 per glycolipid. Interestingly, the parameters obtained from the best fitting to the experimental data associated to the volume fraction distribution of the chemical groups within the aggregates revealed that the hydrophobic chains are more disordered in mono-RL planar aggregates than in di-RL worm-like aggregates, as well as the hydration properties. Further, the addition of 100 mM NaCl in di-RL aqueous dispersion leads to the formation of longer worm-like aggregates. Taking together, this work opens a new avenue regarding characterization of biosurfactants self-assembling properties by using SAXS, also contributing to prepare more efficient biosurfactant dispersions depending on the desired applications in industrial sectors and bioremediation.

Insight into the mechanisms of plant growth promoting strain ZY2 in improving phytoremediation efficiency in perfluorooctanoic acid (PFOA)-contaminated soil

Perfluorooctanoic acid (PFOA) is an anthropogenic perfluorinated alkyl substance which can enter the food chain and pose health risks. The hydrophilic carboxyl head of PFOA enhances its solubility in water, making it easier for PFOA to migrate with soil water and be absorbed by plants from the soil. Plant growth promoting bacteria (PGPR) have the ability to compensate for plant growth disadvantage under unfavorable conditions and are therefore likely to reduce the negative effects of PFOA phytotoxicity on plant growth. However, the effectiveness of the PGPR-assisted plant systems for remediation of PFOA-contaminated soil has not yet been demonstrated. To this end, a novel strain of Rhizobium sp. was isolated and named as ZY2, which is tolerant to PFOA and exhibits significant plant growth-promoting trains. The results indicated that inoculation with strain ZY2 significantly increased the biomass of oilseed rape. Notably, the accumulation content of PFOA in oilseed rape roots increased significantly by 89.0 % and the removal of PFOA from the soil increased over 3 times after inoculation with ZY2. In addition, inoculated ZY2 also altered the rhizosphere soil bacterial community structure which might correlate with the production of a series of hydrolases and reductases involved in soil carbon and nitrogen cycling processes. Generally, this study offered a novel approach for establishing an effective phytoremediation system in PFOA-contaminated soil.