Hydrophobic Phase Research Articles

Molecular Dynamics Study on the Spontaneous Adsorption of Aromatic Carboxylic Acids to Methane Hydrate Surfaces: Implications for Hydrate Antiagglomeration

Spontaneous adsorption of aromatic carboxylic acids (phenylacetic acid, 2-napthylacetic acid, and 1-pyreneacetic acid) to the CH4 hydrate surface in both liquid hydrocarbon and aqueous phases has been investigated using molecular dynamics simulations, aiming to provide implications for hydrate antiagglomeration. Simulation results indicate that the liquid-phase environment, that is, the liquid hydrocarbon phase or aqueous phase, especially its hydrophilic/hydrophobic property, could profoundly affect the interfacial structures of CH4 hydrate and the adsorption behavior of aromatic carboxylic acids. In the hydrophobic hydrocarbon phase, with many CH4 molecules dissolved, more interfacial hydrate structures decompose and form a thin quasiliquid water film on the hydrate surface; aromatic carboxylic acids act as surfactants, that is, strongly adsorb to the hydrate/hydrocarbon interface and significantly lower the interfacial tension. Moreover, they adsorb to the interfacial water film on the hydrate surface with their carboxylic groups, which may destabilize the capillary liquid bridges formed among hydrate particles and then prevent hydrate coalescence. By contrast, fewer interfacial hydrate structures decompose in the aqueous phase, as CH4 molecules rarely dissolve in water but stay at the hydrate/water interface and stabilize the hydrate solid; only a few aromatic carboxylic acids adsorb to the hydrate/water interface by inserting their aromatic rings into the semicages on the hydrate surface, which may kinetically disturb the hydrate growth. Such adsorption is not very strong and mainly depends on the size matching between aromatic rings and semicages. Consequently, many more aromatic carboxylic acid molecules strongly adsorb to the hydrate surface in the hydrocarbon phase than in the aqueous phase, which can explain why antiagglomerants generally show a higher performance in the hydrocarbon phase and easily lose efficacy at high watercuts. Additionally, the molecular structures could also affect the adsorption behavior of aromatic carboxylic acids: with more aromatic rings, acid molecules can form stable aggregates via the π–π stacking interactions of the aromatic rings, adversely affecting the adsorption in the aqueous phase.

Extraction and separation on Au(III) and Pt(IV) from HCl media using novel piperazine-based ionic liquid as an ionic exchanger

Selective recovery of gold and platinum from secondary resources is of great significance under the crisis of resource shortage. Hence, the optimal extractant 1-(2-(dimethylamino) ethyl)-4-methyl-piperazin bis(trifluoromethylsulfonyl)imide ([C6-Et-TMEDA-PIP][Tf2N]2) was synthesized and screened out from five piperazine-based ionic liquids (ILs) to construct an IL-water system for Au(III) and Pt(IV) extraction. ILs have high hydrophobicity and low viscosity at room temperature, which can be used as both extractant and hydrophobic phase. The effects of IL dosage, metal concentration and acidity on the extraction efficiency were investigated. Under the optimal conditions, the extraction efficiency of 98.5% (Au(III)) and 97.5% (Pt(IV)) can be achieved. The anion exchange mechanism was verified through the combination of Ultraviolet visible spectroscopy (UV–vis), Nuclear magnetic spectra (NMR) and quantum chemical calculations. Besides that, the two-factor optimization of the extractant dosage and HCl concentration was carried out by Response surface methodology (RSM), and the effective separation of Au(III) and Pt(IV) was successfully achieved. Au(III)/ Pt(IV) was extracted into the IL phase as [Et-TMEDA-PIP+][AuCl4-] and can easily be stripped by reduction to Au(0)/Pt(Ⅱ) with H2C2O4/CS(NH2)2-HCl, and each extraction ability maintained after 5 turns of extraction cycle experiments. Since the excellent behaviors showed in the multi-metal selective extraction and cycle experiments, the [C6-Et-TMEDA-PIP][Tf2N]2 was regarded as the most potential system for Au(III) and Pt(IV) recovery from HCI medium.

Mesoscale hydrated morphology of perfluorosulfonic acid membranes

AbstractFuel cells are expected to play an important role in global carbon neutralization and future social development with high conversion efficiency and zero emissions. The core of the fuel cell is the proton exchange membrane (PEM). However, the unclear of the proton transport mechanism in PEMs limits the development of membranes with improved performance. Perfluorosulfonic acid (PFSA) membranes are currently the most widely used type of PEM, and exhibit varying proton transport capabilities with various chemical structures. In this study, the hydration morphology of several PFSA membranes was studied using dissipative particle dynamics. The result shows that under low water content the hydrophilic and hydrophobic phases separated and the water clusters are relatively isolated. The increased water content formed hydrophilic channels, while the increase in equivalent weight decreases the water cluster size and improves water dispersion. Aciplex 1128 shows great variation owing to the presence of a long sulfonic acid terminated side chain in water cluster size and dispersion compared with Nafion. The average diffusivity and mean square displacement results showed similar results. These results will promote the development of high performance PEM for fuel cells.

Water-pumping and purifying hydrogels driven by diurnal temperature variation

Diurnal temperature variation is an untapped energy source, although it has seldom been exploited as such. In this study, a novel system of thermo-responsive hydrogels uses diurnal temperature variation as the only power source to pump and purify water. Water is pumped at night and released during the day using an anisotropic xylem-mimetic structure whose composite phase functions as a water channel valve. The water-pumping efficiency ranges from 78% to 92%, and the weights of the pumped water per cycle are 2–3 times larger than those of the pumping materials. The anisotropic structure and the hydrophobic silicone phase are critical in determining pumping efficiency, which allow irreversible water flow upon temperature variation. Seasonal and regional temperature changes can be matched using thermo-responsive hydrogels with different volume transition temperatures. Purification of dye-contaminated water and separation of oil–water mixtures are also successfully achieved based on the hydrophilic and the pollutant-adsorbing nature of hydrogels. Since temperature changes even faster than the diurnal temperature cycle can also power this water pumping and purification system, this novel mechanism could provide a new operational solution for future water management.

Preparation of Hollow-Porous Rosin-Based Polyurethane Microspheres with pH-Responsive Characteristics

Preparation of polymer microspheres from naturally occurring resource is a challenge. Here, a rosin-based polyol (RAG) was used to prepare polyurethane resin (RPU) firstly, and then act as both self-assembled precursor and emulsifier, rosin based polyurethane microspheres (RPUMs) were prepared. In the process of self-emulsification, the RPU formed vesicles by self-assembly. The outer shell of the vesicle consisted of hydrophilic segments, while the inner shell contained the hydrophobic phase. After cross-linking the RPU and removal of the solvent in the core, the porous-hollow microspheres with pH-sensitive were obtained. The microspheres were characterized by optical microscope (OM), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The effect of type and amount of the hydrophilic chain extender, and solvent on the morphology, particle size and distribution, and buffer volume of the microspheres were determined. The best conditions for synthetic RPUMs were as follows: nNCO/nOH = 1, nRAG:n1-(2-hydroxyethyl) piperazine = 4:6, with azodiisobutyronitrile level of 1.0 wt.%, based on reactive monomers, mixing speed of both emulsification and polymerization at 400 r·min−1, the RPUMs synthesized had porous-hollow structure with a buffer volume of 1.6 mL.

Novel deep eutectic solvent-based liquid phase microextraction for the extraction of estrogenic compounds from environmental samples.

Steroid hormones, such as estrone (E1), 17β-estradiol (E2), 17β-ethinylestradiol (EE2) and estriol (E3) are a group of lipophilic active substances, synthesized biologically from cholesterol or chemically. A pH-switchable hydrophobic deep eutectic solvent-based liquid phase microextraction (DES-LPME) technique was established and combined with gas chromatography-mass spectroscopy for the determination of estrogenic compounds in environmental water and wastewater samples. A DES was synthesized using l-menthol as HBA and (1S)-(+)-camphor-10-sulfonic acid (CSA) as HBD, and used as a green extraction solvent. By adjusting the pH of the solution, the unique behavior of the DES in the phase transition and extraction of the desired analytes was investigated. The homogenization process of the mixture is done only by manual shaking in less than 30 seconds and the phase separation is done only by changing the pH and without centrifugation. Some effective parameters on the extraction and derivatization, such as molar ratio of DES components, DES volume, KOH concentration, HCl volume, salt addition, extraction and derivatization time and derivatization prior or after extraction were studied and optimized. Under the optimum conditions, relative standard deviation (RSD) values for intra-day and inter-day of the method based on 7 replicate measurements of 20 ng L−1 of estrogenic compounds and 10 ng L−1 for internal standard in different samples were in the range of 2.2–4.6% and 3.9–5.7%, respectively. The calibration graphs were linear in the range of 0.5–100 ng L−1 and the limits of detection (LODs) were in the range of 0.2–1.0 ng L−1. The relative recoveries of environmental water and wastewater samples which have been spiked with different levels of target compounds were 91.0–108.8%.

Development of highly hydrophobic fabric phase sorptive extraction membranes and exploring their applications for the rapid determination of tocopherols in edible oils analyzed by high pressure liquid chromatography-diode array detection

Α novel, green, and facile fabric phase sorptive extraction (FPSE) prior to high pressure liquid chromatography with diode array detection (HPLC-DAD) methodology was developed for the efficient extraction and quantitative determination of tocopherols (α-, sum of (β+γ), and δ-) in edible oils. Among several highly hydrophobic FPSE membranes, sol-gel polycaprolactone-polydimethylsiloxane-polycaprolactone (sol-gel PCAP-PDMS-PCAP) coated polyester FPSE membrane was found as the most efficient in extracting tocopherol homologues from edible oil samples. To maximize the extraction efficiency of FPSE membrane, major parameters of FPSE including the membrane size, sample loading time, the choice of the appropriate elution solvent and the elution solvent volume, desorption time, and the influence of stirring were systematically optimized. The developed FPSE-HPLC-DAD methodology was validated and presented adequately low limits of detection (LODs) and limits of quantification (LOQs) over the ranges 0.05–0.10 μg/g, and 0.17–0.33 μg/g, respectively. The RSD% of the within-day and between-day assays were lower than 1.3, and 11.8, respectively, demonstrating good method precision. The trueness of the method was assessed by means of relative percentage of recovery and ranged between 90.8 and 95.1% for within-day assay, and between 88.7–92.8% for between-day assay. The developed methodology was applied in the analysis of edible oils.

Improving the Durability and Performance of Sulfonated Poly(arylene ether)s by Introducing 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide Structure for Fuel Cell Application.

Polymer electrolyte membranes in which the hydrophilic and hydrophobic domains phase separate exhibit improved properties and stability. Such a phase separation of hydrophilic and hydrophobic domains can be achieved by polymerizing a 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide-bisphenol A (DOPO-BPA) and 1,4-bis(4-fluorobenzoyl)benzene (1,4-FBB) monomer. In this work, sulfonated polymer membranes with various degrees of sulfonation (DS) were prepared and their physicochemical and electrochemical properties were studied. In addition, the effect of molecular structure on the durability of the copolymers was investigated. The sulfonated copolymers were characterized by Fourier-transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. Then, sulfonated membranes were prepared using these copolymers by the solvent casting method, and their morphologies were investigated by atomic force microscopy. The effect of DS on the thermal, mechanical, and oxidative stabilities, water uptake behavior, and ion-exchange capacity of the membranes was determined. The results showed that compared with the commercially available Nafion 212 polymer electrolyte membrane, the electrolyte membrane based on DOPO-BPA and 1,4-FBB exhibited a lower water uptake and excellent dimensional stability despite having a relatively high ion-exchange capacity. The low water uptake is an important characteristic that ensures the stability of the polymer electrolyte membrane in fuel cell applications.

Carbohydrate-based aqueous biphasic systems for biomolecules extraction

Any potential of new biotechnological processes would be assuredly canceled in the absence of efficient separation strategies. This work comprehensively addresses the solutes partitioning behavior in biocompatible carbohydrate-polymer aqueous biphasic systems (ABSs) to explore the separation performance of these systems. The complete liquid–liquid phase diagrams were determined for sucrose/glucose-polypropylene glycol (PPG) ABSs at 25 °C and atmospheric pressure. Then, the partitioning pattern of four biomolecules, including caffeine, codeine, vanillin, and curcumin, was investigated in the carbohydrate-PPG ABSs. The obtained results show that caffeine, vanillin, and curcumin are mostly electrically neutral in the medium of the studied ABSs and preferentially concentrate in the more hydrophobic PPG-rich phase with the maximum partition coefficients (K) of 2.05, 19.75, and 246.37, respectively. However, codeine, being present mainly in the cationic form in the ABSs investigated, has a high tendency for the more hydrophilic carbohydrate-rich phase with the highest K−1 = 16.85. The magnitude of log K values for all the target biomolecules linearly increases by decreasing the water content ratio of the coexisting phases. The maximum value of the caffeine/codeine selectivity index was estimated to be 34.5 at optimum conditions. The best value of K did not necessarily correspond to the maximum recovery percentage (R) because the volume ratio of phases is another factor that can affect the R values. The curcumin partitioning behavior in carbohydrate-propanol ABSs was also investigated to provide a competitive platform. The gathered results indicate that although both carbohydrate-PPG and carbohydrate-propanol ABSs provide satisfactory partitioning performance for vanillin and curcumin, carbohydrate-PPG ABSs own a higher selectivity index for the alkaloids studied.

Optimization of the Composition of the Ointment with Phytoecdysteroids Serpisten

Introduction. Phytoecdysteroids are a group of natural compounds related in structure and physiological effect to ecdysone - the hormone of insect molting. Phytoecdisteroids have been found to have an antiflammatory effect, which suggests that they have regenerative properties. The development of a soft dosage form containing phytoecdysteroids is of interest.Aim. Improvement of ointment compositions with phytoecdysteroids by optimizing the composition of base adjuvants.Materials and methods. As an active substance was used Serpisten, containing the sum of phytoecdysteroids, the main of which is 20-hydroxyecdysone and obtained from the leaves of Serratulaecoronatae. Raw materials "Serpukhi crowned leaves" were registered by the Federal Service Rospotrebnadzor (Moscow) for the production of dietary supplements (Gr. No. 77.99.23.3.U.1922.3.08), substance Serpisten (Gr. No. 77.99.23.3.U.1923.3.08. TU 9369-002-15092611-2008). In work were used the excipients allowed for medical use: the monoglycerides distilled, T-2 emulsifier, tween 80, sodium - carboxymethylcellulose, polyvinyl alcohol, hydroxide of aluminum, aero forces, vaseline, oil vaseline, sunflower oil. Optimization of ointment auxiliary substances composition was carried out according to the Greco-Latin 4 x 4 square plan with repeated observations. The concentration of hydrogen ions from aqueous ointments was evaluated as process parameters; acid number; release of serpistene from ointment into agar gel, thermal stability of structure. The structural and mechanical properties of the optimal composition ointment composition were determined on a RV type REOTEST 2.1 rotary viscometer (RHEOTEST Medingen GmbH, Germany). Ointment Bepanten (GP Grenzach Produktions GmbH, Germany) was used as a comparison preparation.Results and discussion. During optimization of the composition of the diphilic ointment with serpistene, was found that the ratio of hydrophobic and hydrophilic phases should be 1 : 1, it is advisable to introduce into the ointment base an emulsifier T-2, aerosil and a mixture of vaseline and vaseline oil in the proportion of 1 : 1. As a result of the carried out studies on the optimization of ointment compositions, the following serpisten ointment composition is proposed: serpisten - 0.02; emulsifier T-2 - 3.0; aerosil - 3.0; vaseline - 23.0; vaseline oil - 23.0; ethyl alcohol 40 % - 1 ml; purified water to 100.0. Comparative analysis of effective viscosity showed that the proposed composition is as close as possible to the Bepanten ointment.Conclusion. A set of technological studies was carried out to optimize the composition of the Serpisten, 0.02 °% ointment on a diphilic basis. The developed composition and technology made it possible to obtain a composition with thermal stability, bring the hydrogen index of the ointment closer to the pH of human skin and achieve the parameters included in the rheological optimum for dermatological ointments (0.34-108 Pa • s).

Comb-shaped SEBS-based anion exchange membranes with obvious microphase separation morphology

The trade-off between stability and hydroxide conductivity plays an important role in the development of anion exchange membranes (AEMs) and AEM applications. Aiming at the problems of low OH− ion conductivity and poor stability of AEMs, poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) was used as the polymer backbone and combined with tertiary amines with different carbon chain lengths to synthesize a series of comb-shaped membranes through Menshutkin reaction. The well-designed architecture of comb-shaped membranes was responsible for precisely adjusting the hydrophilic and hydrophobic phases to promote the self-aggregation of ion clusters in the membrane from the separated state and gradually form interconnected ion channels. This continuous channel significantly increased the ion conductivity (57.5 mS cm−1 at 80 °C), while the increased hydrophobic chain reduced the swelling ratio (14.17% at 80 °C) of the comb-shaped membranes which improved the dimensional stability. In the single cell evaluation, the comb-shaped membrane achieves a maximum power density of 176 mW cm−2 at 80 °C under H2/O2 conditions. Additionally, the comb-shaped structure can effectively ameliorate the solubility of the polymer, which can solve the gelation problem in the process of functional modification of SEBS. On balance, this work presents a new technology with such uncomplicated and controllable mode for the synthesis of highly efficient AEMs, thus opening an effective and adjustable means of anion exchange membrane fuel cell applications.

Supercritical fluid chromatography for the analysis of natural dyes: From carotenoids to flavonoids.

Plant-derived natural dyes are used in a variety of formulated products, from food to cosmetics and pharmaceutics. In addition to their color, they also provide some bioactivity. While they are mostly analyzed with high-performance liquid chromatography, supercritical fluid chromatography was also employed for several dye families, mostly for carotenoids and chlorophylls, and more recently for anthraquinones and flavonoids. These supercritical fluid chromatography methods are described in this review. Because the dyes have different structures and structural variations (polarity, isomers, etc.), the best chromatographic system to achieve their separation is not always the same. Hydrophobic stationary phases are preferred for the most hydrophobic dyes (chlorophylls and carotenoids) while polar stationary phases are preferred for the polar dyes (anthraquinones and flavonoids). Regarding the mobile phase composition, chlorophylls and carotenoids are best eluted with moderate proportions of co-solvent in CO2 (about 40%), while the most polar glycosylated flavonoids require higher proportions of co-solvent and acidic additives. Because dyes are colorful, ultraviolet-visible detection is often sufficient, while mass spectrometry offers additional structural information. Furthermore, fundamental information can also be gained through chromatographic analysis of dyes: either solubility in supercritical fluids, in view of their extraction, or retention behavior providing an understanding of stationary phase properties.

The Central PXXP Motif Is Crucial for PMAP-23 Translocation across the Lipid Bilayer.

PMAP-23, a cathelicidin-derived host defense peptide, does not cause severe membrane permeabilization, but exerts strong and broad-spectrum bactericidal activity. We have previously shown that it forms an amphipathic α-helical structure with a central hinge induced by the PXXP motif, which is implicated in the interaction of PMAP-23 with negatively charged bacterial membranes. Here, we studied the potential roles of the PXXP motif in PMAP-23 translocation across the lipid bilayer by replacing Pro residues with either α-helix former Ala (PMAP-PA) or α-helix breaker Gly (PMAP-PG). Although both PMAP-PA and PMAP-PG led to effective membrane depolarization and permeabilization, they showed less antimicrobial activity than wild-type PMAP-23. Interestingly, we observed that PMAP-23 crossed lipid bilayers much more efficiently than its Pro-substituted derivatives. The fact that the Gly-induced hinge was unable to replace the PXXP motif in PMAP-23 translocation suggests that the PXXP motif has unique structural properties other than the central hinge. Surface plasmon resonance sensorgrams showed that the running buffer almost entirely dissociated PMAP-23 from the membrane surface, while its Pro-substituted derivatives remained significantly bound to the membrane. In addition, kinetic analysis of the sensorgrams revealed that the central PXXP motif allows PMAP-23 to rapidly translocate at the interface between the hydrophilic and hydrophobic phases. Taken together, we propose that the structural and kinetic understanding of the PXXP motif in peptide translocation could greatly aid the development of novel antimicrobial peptides with intracellular targets by promoting peptide entry into bacterial cells.

Relative significance of hydrophilic partitioning and surface adsorption to the retention of polar compounds in hydrophilic interaction chromatography

It is commonly acknowledged that the retention of non-ionized polar analytes on polar stationary phases is governed by hydrophilic partitioning and surface adsorption. However, it has been difficult to evaluate whether partitioning or adsorption is the dominant mechanism for a specific polar compound on a polar stationary phase. We have developed a simple method based on the thermodynamic principle of partitioning to quantitatively investigate the retention contributed by the partitioning or adsorption mechanism. By varying phase ratio through changing salt concentration in the mobile phase, we were able to determine the distribution coefficients of cytosine between the adsorbed water layer and the mobile phase containing various levels of acetonitrile. The retention factors of cytosine attributed to partitioning and adsorption were quantitatively determined. The results demonstrate that the dominant retention mechanism for cytosine is hydrophilic partitioning on ZIC-HILIC, XBridge Amide and LUNA-HILIC columns.

Chromatographic Approach to Isolate Exfoliated Graphene.

A chromatographic approach for separating exfoliated graphene from natural flake graphite is presented. Graphene is an extremely strong, electrically and thermally conductive two-dimensional hexagonal array of carbon atoms with the potential to transform applications such as supercapacitors, composites, biosensors, ultra-thin touchscreens, and solar cells. However, many of these applications require the use of exfoliated graphene, and the current cost of this material can be prohibitive. The most cost-effective source of graphene is exfoliated graphite, and numerous approaches have been proposed for exfoliating graphite to graphene. Solution approaches are the most common, with graphite often exfoliated by extended sonication treatment followed by separation of graphene from graphite using centrifugation. This time-consuming approach results in low concentrations of small lateral dimension graphene, often in high-boiling-point organic solvents or containing stabilizers. In this study, a chromatographic approach is used in combination with a solvent interface trapping method of graphite exfoliation to isolate graphene. The interface trapping exfoliation approach uses a hydrophobic/hydrophilic solvent interface to spontaneously exfoliate graphite and form a graphene-stabilized water-in-oil emulsion. This emulsion contains both graphene and graphite, and when added to water-wet glass beads, graphene adsorbs onto the glass surface, leaving graphite in the hydrophobic mobile phase, where it is removed by washing with an additional oil phase. The efficiency of this scalable approach to separation is demonstrated by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and Tyndall effect scattering.

Biopolymer‐based microparticles for encapsulation of all‐trans‐retinoic acid

AbstractThis work aims to investigate the potential of complex coacervation technique to encapsulate and protect all‐trans retinoic acid (RA). Gelatin and κ‐carrageenan were used as wall material and pequi oil was employed as a hydrophobic phase. Three formulations with different protein: polysaccharide ratio and pH were defined to produce the microparticles based on the zeta potential and turbidity analysis: (F1) ratio 3:1 and pH 3.5, (F2) ratio 8:1 and pH 3.5, and (F3) ratio 8:1 and pH 5.0. Microparticles were evaluated regarding their morphology, yield, encapsulation efficiency (EE), and stability. The properties of microparticles were mainly affected by the protein: polysaccharide ratio and the turbidity of the mixtures, which is directly related to the protein‐polysaccharide interaction. Formulation 1 showed the optimal values of yield (75.6%), EE (100.2%), and stability (85% of the encapsulated RA remained in the particle). The results demonstrated the high potential of this innovative technique to encapsulate RA for a future application in topical formulations.

A hydra tentacle-inspired hydrogel with underwater ultra-stretchability for adhering adipose surfaces

Adhesive hydrogels hold great significance in various biomedical applications. However, the maintenance of high extensibility and adhesion to adipose matters still remain challenging. Inspired by hydra tentacles, we utilise flexible polymeric ionic crosslinkers for constructing densely crosslinked networks. The derived hydrogel was ultra-stretchable (over 54 times) even in the fully swollen state in water. Due to dense electrostatic bonding sites and hydrophobic phases, it displayed fast (~30 sec), repeatable and long-lasting (over 14 days) underwater adhesion to adipose surfaces such as fat, octopus and fish epidermis in aqueous environments. Moreover, the excellent cytocompatibility and antibacterial ability made it suitable for a variety of applications related to biomedicine and flexible electronics. This biomimetic work addresses new possibility for the design rationale for highly stretchable and lipophilic underwater adhesives.

Liquid chromatography-tandem mass spectrometry with a new separation mode for rapid profiling of the Z/E isomers of plant glucosylceramides

Plant glucosylceramide (GlcCer) is characterized by various long-chain bases (LCBs) containing a Z/E isomeric unsaturated bond at the Δ8 position. The isomer ratio of GlcCer is highly diversified among plant species and is involved in tolerance to membrane fluidity-associated stresses such as chilling and aluminum toxicity. Therefore, a plant GlcCer isomer-selective quantitative method is required, allowing further sphingolipidomic studies for crop breeding. We here report a new technique for rapid determination of the Z/E isomers of plant GlcCer. A Cholester column contains cholesteryl groups as the hydrophobic stationary phase and separated the GlcCer isomers more efficiently than a conventional C18 column. We also investigated various mobile phases and column temperatures. The optimized column, solvent, and temperature conditions provided comprehensive profiles of the Z/E ratios of GlcCer in crude extracts of plant materials in less than 20 min. This high-throughput method will facilitate the large-scale profiling of plant GlcCer isomers.

Surfactant Adsorption to Different Fluid Interfaces

Surfactant adsorption to fluid interfaces is ubiquitous in biological systems, industrial applications, and scientific fields. Herein, we unravel the impact of the hydrophobic phase (air and oil) and the role of oil polarity on the adsorption of surfactants to fluid interfaces. We investigated the adsorption of anionic (sodium dodecyl sulfate), cationic (dodecyltrimethylammonium bromide), and non-ionic (polyoxyethylene-(23)-monododecyl ether) surfactants at different interfaces, including air and oils, with a wide range of polarities. The surfactant-induced interfacial tension decrease, called the interfacial pressure, correlates linearly with the initial interfacial tension of the clean oil-water interface and describes the experimental results of over 30 studies from the literature. The higher interfacial competition of surfactant and polar oil molecules caused the number of adsorbed molecules at the interface to drop. Further, we found that the critical micelle concentration of surfactants in water correlates to the solubility of the oil molecules in water. Hence, the nature of the oil affects the adsorption behavior and equilibrium state of the surfactant at fluid interfaces. These results broaden our understanding and enable better predictability of the interactions of surfactants with hydrophobic phases, which is essential for emulsion, foam, and capsule formation, pharmaceutical commodities, cosmetics, and many food products.

Analysis and outlook of mass transport in ultralow Pt loading proton exchange membrane fuel cells

<p indent=0mm>Proton exchange membrane fuel cells (PEMFCs) for automotive propulsions have been regarded as an ideal and the most promising alternative to replace fossil-fuel based internal combustion engines due to the high performance, high energy efficiency and zero-emission. However, the high cost has severely impeded the commercialization of PEMFCs, especially the high cost of Pt-based precious metal catalyst used for the cathode oxygen reduction reaction (ORR). It is critical to reducing the amount of Pt and thus decreasing the cost of fuel cell stacks, which would lead to numbers of new challenges. On the one hand, the reduction of Pt load could increase the oxygen transport resistance in cathode catalyst layers (CCLs). In fact, the oxygen transport resistance could be divided into several constituent parts, i.e., oxygen transport resistances in CCLs, gas diffusion layers (GDLs) and the flow channels, where the transport resistance in CCLs is much higher than other resistances. Further, CCLs are constructed as heterogeneous composites of ORR electrocatalysts, conductive polymer such as perfluorinated sulfonic acid (PFSA) ionomer as well as the pore space determined. Hence, the oxygen transport resistance in CCLs includes the bulk transport resistance caused by oxygen diffusion in the nanopore and the local transport resistance caused by oxygen permeation through the ultrathin ionomer film covering on the Pt surface. Local oxygen transport behavior could be divided into three processes: (1) Oxygen adsorption from gas phase into ionomer, (2) oxygen diffusion inside the ionomer, and (3) oxygen adsorption from the ionomer to Pt surfaces. As the Pt loading decreases, local oxygen transport resistance would increase significantly, thus leading to a dramatical performance degradation at high current density of fuel cells. In specific, the oxygen adsorption at gas/ionomer interface used to be considered as Henry’s adsorption. However, it is proved recently that this type of adsorption should be quasi-logarithmic, due to the finiteness of the adsorption site on ionomer surface. In addition, the bulk oxygen transport resistance depends on the porosity and pore size distribution inside the electrodes. We summarized plenty of experimental results of effective oxygen diffusivities reported by different research groups, and found that all the experimental values are obviously smaller than the calculated results based on the classical Bruggeman approximation. It is believed that the effective porosity plays a more important role relative to the geometrical porosity in the estimation of bulk oxygen transport resistance in PEMFCs. On the other hand, confining effect of the ultrathin ionomer film could weaken the separation of hydrophilic and hydrophobic phases and then cut down the pathway of proton migration. There are two proton conduction mechanisms in CCLs: Grotthuss hopping and vehicular mechanism. The proton conduction in CCLs could be affected by numerous factors, such as temperature, ionomer structure, thickness of ionomer film, as well as cation contaminants in the ionomer film. Both high oxygen transport resistance and low proton conduction in ultra-low Pt membrane electrode assemblies would damage the performance and the lifetime of PEMFCs. In this review, the bulk and local transport behavior, proton transport in CCLs, as well as the corresponding influence on fuel cell performance are systematically analyzed, and a series of coping strategies are presented.