Perfluorooctanoate in Aqueous Urea Solutions: Micelle Formation, Structure, and Microenvironment

Dispersive liquid-liquid microextraction followed by sweeping micellar electrokinetic chromatography-tandem mass spectrometry for determination of six breast cancer drugs in human plasma

Herein, we have developed a novel method of aqueous-sample dispersive liquid-liquid microextraction (AqS-DLLME) followed by sweeping micellar electrokinetic chromatography-tandem mass spectrometry (MEKC-MS/MS) for simultaneous determination of breast cancer drugs letrozole, anastrozole, palbociclib, ribociclib, abemaciclib, and fulvestrant in human plasma. Coupling of MEKC to MS was possible due to the use of ammonium perfluorooctanoate (APFO) as a volatile surfactant. The MEKC and MS conditions were optimized to achieve a fast, sensitive, selective, and green analysis enabling full separation of the analytes within 16 min. Electrophoretic buffer was 125 mM APFO at apparent pH 10.5 in 32 % MeOH, while sheath liquid was 70 % MeOH with 0.2 % formic acid, delivered at 10 µL/min. Excellent extraction recoveries from plasma ranging from 89.4 to 104.9 % were obtained with a combination of protein precipitation and DLLME. The developed method was validated according to the ICH guidelines. Remarkable selectivity, accuracy (bias < 6.7 %), precision (RSD < 15.8 %), and stability (bias < 10.4 %) with insignificant matrix effect (RSD < 14.0 %) and no carry-over were obtained over a wide range of concentrations. Linearity with inter-day slope RSD lower than 8.7 % was demonstrated. With this method, very low concentrations could be detected after the injection of only 68.7 nL of the sample. The method was applied to plasma samples from six women currently receiving breast cancer treatment. Determined concentrations of the drugs of interest agreed with concentrations found in clinical studies, thus proving the suitability of the developed method for therapeutic drug monitoring as a superior alternative to published LC-MS methods.

Ultrasonic-microwave synergistic supramolecular solvent liquid-liquid microextraction of trace biogenic amines in fish and beer based on solidification of floating organic droplet

It is important to detect the presence of biogenic amines (BAs) as indicators of food freshness. The purpose of this study was to develop a novel ultrasonic-microwave synergistic supramolecular solvent liquid-liquid microextraction based on solidification of floating organic droplet (UMS-SUPRAS-SFO-LLME) combined with high-performance liquid chromatography for the determination of BAs. The physical properties and microstructure of SUPRAS based on 1-dodecanol and tetrahydrofuran were studied, and the extraction conditions such as the SUPRAS volume, the UMS process, and the centrifugal conditions were optimized. The results for the extraction kinetics and thermodynamics showed that UMS-SUPRAS-SFO-LLME is a spontaneous, endothermic diffusion process. The linear ranges of this method are 0.1-2.0 × 105 ng·mL-1 (R2 > 0.994), the limits of detection are 4.0 × 10-3-6.0 × 10-2 ng·mL-1, and the recoveries were 96.28-103.15%. Compared with existing analysis methods, UMS-SUPRAS-SFO-LLME is a sensitive, green and economical sample pretreatment method for analyzing the enrichment of BAs in beer and fish.

Research Priorities for the Environmental Risk Assessment of Per- and Polyfluorinated Substances

Per- and polyfluorinated substances (PFAS) are a group of thousands of ubiquitously applied persistent industrial chemicals. The field of PFAS environmental research is developing rapidly, but suffers from substantial biases toward specific compounds, environmental compartments, and organisms. The aim of our study was therefore to highlight current developments and to identify knowledge gaps and subsequent research needs that would contribute to a comprehensive environmental risk assessment for PFAS. To this end, we consulted the open literature and databases and found that knowledge of the environmental fate of PFAS is based on the analysis of <1% of the compounds categorized as PFAS. Moreover, soils and suspended particulate matter remain largely understudied. The bioavailability, bioaccumulation, and food web transfer studies of PFAS also focus on a very limited number of compounds and are biased toward aquatic biota, predominantly fish, and less frequently aquatic invertebrates and macrophytes. The available ecotoxicity data revealed that only a few PFAS have been well studied for their environmental hazards, and that PFAS ecotoxicity data are also strongly biased toward aquatic organisms. Ecotoxicity studies in the terrestrial environment are needed, as well as chronic, multigenerational, and community ecotoxicity research, in light of the persistency and bioaccumulation of PFAS. Finally, we identified an urgent need to unravel the relationships among sorption, bioaccumulation, and ecotoxicity on the one hand and molecular descriptors of PFAS chemical structures and physicochemical properties on the other, to allow predictions of exposure, bioaccumulation, and toxicity. Environ Toxicol Chem 2023;42:2302-2316. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Separation of unsaturated C18 fatty acids using perfluorinated-micellar electrokinetic chromatography: I. Optimization and separation process

Ammonium perfluorooctanoate (APFOA) was used as a surfactant for the separation of free unsaturated C18 fatty acids by micellar electrokinetic chromatography. A simple background electrolyte of 50 mM APFOA water/methanol (90:10, v/v) at pH = 10 enabled the repeatable separation of oleic acid, elaidic acid, linoleic acid, and alpha-linolenic acid in less than 20 min. Separation conditions were optimized regarding various parameters (organic solvent, counterion, APFOA concentration, and pH). Because the repulsive interactions between fluorocarbon chains and hydrogenated chains are known to lead to segregation and phase separation, the choice of perfluorinated micelles to separate such perhydrogenated long-chain acids could appear astonishing. Therefore, the critical micelle concentration, the charge density, and the mobility of the micelles have been determined, resulting in a first description of the separation process.

GenX in water: Interactions and self-assembly

2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoate, a.k.a. "GenX", is a surfactant introduced as a safer alternative to replace perfluorooctanoate (PFOA) in the manufacturing of fluorinated polymers, however, GenX is shown to cause adverse health effects similar to, or even worse than, those of the legacy PFOA. With an overarching goal to understand the behavior of GenX molecules in aqueous media, we report here on GenX micelle formation and structure in aqueous solutions, on the basis of results obtained from a combination of experimental techniques such as surface tension, fluorescence, viscosity, and small-angle neutron scattering (SANS), and molecular dynamics (MD) simulations. To our best knowledge, this is the first report on GenX micelles. The critical micelle concentration (CMC) of GenX ammonium salt in water is 175 mM. GenX forms small micelles with association number 6-8 and 10 Å radius. GenX molecules prefer to align along the micelle surface, and the ether oxygen of GenX has very little interaction with and exposure to water. Information on the surfactant and interfacial properties of GenX is crucial, since such properties are manifestations of interactions between GenX molecules and between GenX and water molecules and, in turn, the amphiphilic character of GenX dictates its fate and transport in the aqueous environment, its interactions with various biomolecules, and its binding to adsorbent materials.

Co-delivery of proanthocyanidin and mitoxantrone induce synergistic immunogenic cell death to potentiate cancer immunotherapy

Immunological checkpoint inhibitors provide a revolutionary method for cancer treatment. However, due to low tumor mutations and insufficient infiltration of immune cells in the tumor microenvironment, 85% of colorectal cancer...

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

The Physical Chemistry and Chemical Physics Section (PCCP Section) is one of the youngest among the sections of the International Journal of Molecular Sciences (IJMS)—the year 2021 will only mark three years since its inception [...]

Characterization of hydrophobic interaction of galactomannan in aqueous solutions using fluorescence-based technique

Fluorescence probing was used to study hydrophobic interactions of galactomannan (GM) obtained from fenugreek gum (FG), guar gum (GG), and locust bean gum (LBG) at different M/G ratios. The I₁/I₃ ratio of pyrene changed from 1.73 to 1.29, 1.22, and 1.29 for FG, GG and LBG, respectively, as the concentration of GM increased from 0.01 to 8.0 g/L at 30 °C. The critical aggregation concentration of FG, GG, and LBG increased from 1.04 to 3.84 g/L, 1.15 to 3.73 g/L, and 0.94 to 3.63 g/L, respectively, as temperature increased from 10 to 70 °C. Addition of Na₂SO₄ and NaSCN increased the I₁/I₃ ratio in dilute solution, but reduced it in semi-dilute solution, whereas adding urea reduced I₁/I₃ in dilute solution but increased it in semi-dilute solution. These results indicated that the CAC of GM, polarity and number of hydrophobic microdomains were highly dependent on the M/G ratio and galactose distribution.

Properties of some nonionic fluorocarbon surfactants and their mixtures with hydrocarbon ones

The adsorption of Zonyl FSN-100 (FSN100, having an average 14 oxyethylene units and 6 -CF₂ groups) and Zonyl FSO-100 (FSO100, having an average 10 oxyethylene units and 5 -CF₂ groups) as well as of their mixtures with p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols) having 10, 16 and 8 oxyethylene groups in molecule (TX100, TX165, TX114) and cetyltrimethylammonium bromide (CTAB) at the solution-air and polytetrafluoroethylene (PTFE)-solution and polymethyl methacrylate (PMMA)-solution interfaces as well as the composition of the surface mixed layer was discussed based on the literature data. The adsorption properties of nonionic fluorocarbon surfactants were compared to those of the classical ones on the basis of the Gibbs standard free energy of adsorption determined by different ways and the intermolecular interactions of the surfactant molecules through the water phase. The synergetic effect in the reduction of the water surface tension by the mixture of fluorocarbon and classical nonionic surfactant was shown and explained by the comparison of the composition of the mixed surface layer to those in the bulk phase. The composition of the mixed fluorocarbon and classical surfactant layer at the solution-air interface was compared to that formed at the PTFE-solution and PMMA-solution interfaces. The changes of the surface tension of the aqueous solution of the fluorocarbon surfactants and their mixtures with classical hydrocarbon ones and their adsorption were analyzed taking into account the PTFE and PMMA surface wettability. This analysis was also based on the components and parameters of the head and tail of the surfactants surface tension as well as those of PTFE and PMMA. Apart from adsorption and wetting properties the aggregation of the fluorocarbon surfactants and their mixtures was discussed. A specific attention was paid to the possibility of two CMC values in the case of nonionic fluorocarbon surfactants as well as the synergism in CMC of mixtures of nonionic fluorocarbon and hydrocarbon surfactants.

Structure and Interactions in Perfluorooctanoate Micellar Solutions Revealed by Small-Angle Neutron Scattering and Molecular Dynamics Simulations Studies: Effect of Urea

The self-assembly of surfactants in aqueous solution can be modulated by the presence of additives including urea, which is a well-known protein denaturant and also present in physiological fluids and agricultural runoff. This study addresses the effects of urea on the structure of micelles formed in water by the fluorinated surfactant perfluoro-n-octanoic acid ammonium salt (PFOA). Analysis of small-angle neutron scattering (SANS) experiments and atomistic molecular dynamics (MD) simulations provide consensus strong evidence for the direct mechanism of urea action on micellization: urea helps solvate the hydrophobic micelle core by localizing at the surface of the core in the place of some water molecules. Consequently, urea decreases electrostatic interactions at the micelle shell, changes the micelle shape from prolate ellipsoid to sphere, and decreases the number of surfactant molecules associating in a micelle. These findings inform the interactions and behavior of surface active per- and polyfluoroalkyl substances (PFAS) released in the aqueous environment and biota.

Controlling the self-assembly of perfluorinated surfactants in aqueous environments

Surface active per- and polyfluoroalkyl substances (PFAS) released in the environment generate great concern in the US and worldwide. The sequestration of PFAS amphiphiles from aqueous media can be limited by their strong tendency to form micelles that plug the pores in the adsorbent material, rendering most of the active surface inaccessible. A joint experimental and simulation approach has been used to investigate the structure of perfluorooctanoate ammonium (PFOA) micelles in aqueous solutions, focusing on the understanding of ethanol addition on PFOA micelle formation and structure. Structurally compact and slightly ellipsoidal in shape, PFOA micelles in pure water become more diffuse with increasing ethanol content, and break into smaller PFOA clusters in aqueous solutions with high ethanol concentration. A transition from a co-surfactant to a co-solvent behavior with the increase of ethanol concentration has been observed by both experiments and simulations, while the latter also provide insight on how to achieve co-solvent conditions with other additives. An improved understanding of how to modulate PFAS surfactant self-assembly in water can inform the fate and transport of PFAS in the environment and the PFAS sequestration from aqueous media.

Fluorinated Surfactant Adsorption on Mineral Surfaces: Implications for PFAS Fate and Transport in the Environment

Fluorinated surfactants, which fall under the class of per- and polyfluoroalkyl substances (PFAS), are amphiphilic molecules that comprise hydrophobic fluorocarbon chains and hydrophilic head-groups. Fluorinated surfactants have been utilized in many applications, e.g., fire-fighting foams, paints, household/kitchenware items, product packaging, and fabrics. These compounds then made their way into the environment, and have been detected in soil, fresh water, and seawater. From there, they can enter human bodies. Fluorinated surfactants are persistent in water and soil environments, and their adsorption onto mineral surfaces contributes to this persistence. This review examines how fluorinated surfactants adsorb onto mineral surfaces, by analyzing the thermodynamics and kinetics of adsorption, and the underlying mechanisms. Adsorption of fluorinated surfactants onto mineral surfaces can be explained by electrostatic interactions, hydrophobic interactions, hydrogen bonding, and ligand and ion exchange. The aqueous pH, varying salt or humic acid concentrations, and the surfactant chemistry can influence the adsorption of fluorinated surfactants onto mineral surfaces. Further research is needed on fluorinated surfactant adsorbent materials to treat drinking water, and on strategies that can modulate the fate of these compounds in specific environmental locations.

Association between Nonionic Amphiphilic Polymer and Ionic Surfactant in Aqueous Solutions: Effect of Polymer Hydrophobicity and Micellization

The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO₁₀₀PO₆₅EO₁₀₀) and Pluronic P123 (EO₁₉PO₆₉EO₁₉), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.