Enhanced host–guest complexation of short chain perfluoroalkyl substances with positively charged β-cyclodextrin derivatives

2D and 3D Self-Assembly of Fluorine-Free Pillar-[5]-Arenes and Perfluorinated Diacids at All-Aqueous Interfaces

The interaction of perfluorinated molecules, also known as "forever chemicals" due to their pervasiveness, with their environment remains an important yet poorly understood topic. In this work, the self-assembly of perfluorinated molecules with multivalent hosts, pillar-[5]-arenes, is investigated. It is found that perfluoroalkyl diacids and pillar-[5]-arenes rapidly and strongly complex with each other at aqueous interfaces, forming solid interfacially templated films. Their complexation is shown to be driven primarily by fluorophilic aggregation and assisted by electrostatic interactions, as supported by the crystal structure of the complexes, and leads to the formation of quasi-2D phase-separated films. This self-assembly process can be further manipulated using aqueous two-phase system microdroplets, enabling the controlled formation of 3D micro-scaffolds.

Rim-Based Binding of Perfluorinated Acids to Pillararenes Purifies Water

Per- and polyfluoroalkyl substances (PFAS) pose a rapidly increasing global problem as their widespread use and high stability lead worldwide to water contamination, with significant detrimental health effects.[1] Supramolecular chemistry has been invoked to develop materials geared towards the specific capture of PFAS from water,[2] to reduce the concentration below advisory safety limits (e.g., 70 ng/L for the sum of perfluorooctane sulfonic acid, PFOS and perfluorooctanoic acid, PFOA). Scale-up and use in natural waters with high PFAS concentrations has hitherto posed a problem. Here we report a new type of host-guest interaction between deca-ammonium-functionalized pillar[5]arenes (DAF-P5s) and perfluoroalkyl acids. DAF-P5 complexes show an unprecedented 1 : 10 stoichiometry, as confirmed by isothermal calorimetry and X-ray crystallographic studies, and high binding constants (up to 106 M-1) to various polyfluoroalkyl acids. In addition, non-fluorinated acids do not hamper this process significantly. Immobilization of DAF-P5s allows a simple single-time filtration of PFAS-contaminated water to reduce the PFOS/PFOA concentration 106 times to 15-50 ng/L level. The effective and fast (<5 min) orthogonal binding to organic molecules without involvement of fluorinated supramolecular hosts, high breakthrough capacity (90 mg/g), and robust performance (>10 regeneration cycles without decrease in performance) set a new benchmark in PFAS-absorbing materials.

New insights into the influence of encapsulation materials on the feasibility of ultrasonic-assisted encapsulation of Mosla chinensis essential oil

The study aimed to estimate the feasibility of α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD) to encapsulate Mosla chinensis essential oil (EO) by ultrasonic-assisted method. The physical properties variations, stabilization mechanisms, and formation processes of the inclusion complexes (ICs) were investigated using experimental methods, molecular docking, and molecular dynamics (MD) simulation. Scanning electron microscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, and gas chromatography-mass spectrometry showed that the ICs were successfully prepared, which differentially improved the thermal stability and retained the chemical composition of EO. The dissolution profile showed that the Peppas model can be used to describe the diffuse release mechanism of EO. Finally, molecular docking and MD simulation theoretically confirmed the interaction and conformational changes of carvacrol (the main active component of Mosla chinensis EO) inside the cavity of CDs. The results indicate that hydrogen bonding was the primary driving force for the carvacrol spontaneous access to the cavity. Further, a binding dynamic balance occurs between carvacrol and β-CD, whereas a bind and away dynamic balance occurs in the IC between carvacrol and α-CD, γ-CD. The comprehensive results show that the medium cavity size of β-CD is a suitable host molecule for Mosla chinensis EO of encapsulation, release, and stabilization. A combination of experimental and theoretical calculations is useful for the pinpoint targeted design and optimization of CD molecular encapsulation of small entity molecules. β-CD was rationally screened as a better candidate for stabilizing EO, which provides an option for a meaningful path to realistic EO applications.

Molecular level investigation of interactions between pharmaceuticals and β-cyclodextrin (β-CD) functionalized adsorption sites for removal of pharmaceutical contaminants from water

This study describes a novel application of the use of molecular modeling tools for investigating the adsorption of organic micropollutants (OMPs) from water by nanocomposites. The partitioning of pharmaceuticals onto β-Cyclodextrin (β-CD) functionalized adsorbents was investigated at the molecular level to explore the atomistic interactions of pharmaceutical contaminants in water systems with β-CD and to provide insight into possible approaches for removal of pharmaceuticals from water. Molecular electrostatic surface potential mapping of β-CD derivatives was employed to examine the impact of substitution degree of β-CD and type of grafting agent on host-guest complexation. The stability of the complexes of selected pharmaceuticals and β-CD derivatives were assessed via molecular dynamics simulations to evaluate competitive adsorption between organic micropollutants (OMPs) and between OMPs and fulvic acid, a representative natural organic material (NOM) component found in water systems. Molecular electrostatic surface potential maps showed that grafting agents with aromatic and amine functional groups were found to provide attractive interactions for negatively charged OMPs. In addition, optimization of substitution degree of β-CD is necessary to enhance adsorption of target OMPs. Furthermore, it was found that aromatic ring bearing grafting agents can provide additional electrostatic attractions by π-π interactions with the aromatic ring of the OMPs. The impact of common water quality characteristics on adsorption was assessed and it was revealed that the effect of pH and calcium on adsorption depends on the ionizable functional groups present on the grafting agent. Molecular dynamics simulations showed that adsorption of target OMPs does not solely depend on hydrophobicity but is affected by electrostatic interactions. The simulations revealed that fulvic acid which is commonly present in environmental waters can be a competitor with ibuprofen for the β-CD cavity. Ultimately, this study showed that molecular level simulation can be effectively employed to investigate adsorption of OMPs by β-CD functionalized adsorbents and could be employed to enhance their design and subsequent environmental applications.

Chemical Tailoring of β-Cyclodextrin-Graphene Oxide for Enhanced Per- and Polyfluoroalkyl Substances (PFAS) Adsorption from Drinking Water

We report on the synthesis of β-cyclodextrin (βCD) modified graphene oxide (GO) nanosheets, having different sized alkyl linkers (GO-Cn -βCD) and their exploitation as sorbent of per- and polyfluoroalkyl substances (PFAS) from drinking water. βCD were functionalized with a pending amino group, and the resulting precursors grafted to GO nanosheets by epoxide ring opening reaction. Loading of βCD units in the range 12 %-36 % was estimated by combined XPS and elemental analysis. Adsorption tests on perfluorobutanoic acid (PFBA), a particularly persistent PFAS selected as case study, revealed a strong influence of the alkyl linker length on the adsorption efficiency, with the hexyl linker derivative GO-C6 -βCD outperforming both pristine GO and granular activated carbon (GAC), the standard sorbent benchmark. Molecular dynamic simulations ascribed this evidence to the favorable orientation of the βCD unit on the surface of GO which enables a strong contaminant molecules retention.

Porous Materials for Water Purification

Water pollution is a growing threat to humanity due to the pervasiveness of contaminants in water bodies. Significant efforts have been made to separate these hazardous components to purify polluted water through various methods. However, conventional remediation methods suffer from limitations such as low uptake capacity or selectivity, and current water quality standards cannot be met. Recently, advanced porous materials (APMs) have shown promise in improved segregation of contaminants compared to traditional porous materials in uptake capacity and selectivity. These materials feature merits of high surface area and versatile functionality, rendering them ideal platforms for the design of novel adsorbents. This Review summarizes the development and employment of APMs in a variety of water treatments accompanied by assessments of task-specific adsorption performance. Finally, we discuss our perspectives on future opportunities for APMs in water purification.

Recent Advancements in Cyclodextrin-Based Adsorbents for the Removal of Hazardous Pollutants from Waters

Water is an essential substance for the survival on Earth of all living organisms. However, population growth has disturbed the natural phenomenon of living, due to industrial growth to meet ever expanding demands, and, hence, an exponential increase in environmental pollution has been reported in the last few decades. Moreover, water pollution has drawn major attention for its adverse effects on human health and the ecosystem. Various techniques have been used to treat wastewater, including biofiltration, activated sludge, membrane filtration, active oxidation process and adsorption. Among the mentioned, the last method is becoming very popular. Moreover, among the sorbents, those based on cyclodextrin have gained worldwide attention due to their excellent properties. This review article overviewed recent contributions related to the synthesis of Cyclodextrin (CD)-based adsorbents to treat wastewater, and their applications, especially for the removal of heavy metals, dyes, and organic pollutants (pharmaceuticals and endocrine disruptor chemicals). Furthermore, new adsorption trends and trials related to CD-based materials are also discussed regarding their regenerative potential. Finally, this review could be an inspiration for new research and could also anticipate future directions and challenges associated with CD-based adsorbents.

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.

Elucidation of specific binding sites and extraction of toxic Gen X from HSA employing cyclodextrin

The presence of per and poly-fluoroalkyl substances (PFAS), commonly referred to as forever chemicals, in aquatic systems is a serious global health problem. While the remediation of PFAS from aqueous media has been extensively investigated, their interactions with and removal from biological systems have received far less attention. We report herein structural alterations to human serum albumin (HSA) upon addition of perfluoro(2-methyl-3-oxahexanoic) acid (Gen X) monitored by changes to the fluorescence and circular dichroism (CD) spectra of HSA. The equilibrium association constant for Gen X binding to HSA is 7( ± 1) × 10³ M^-1 determined from changes in HSA fluorescence emission data during titration. Site-specific HSA binding fluorophores, 8-anilinonaphthalene-1-sulfonic acid (1,8-ANS), warfarin and dansyl-L-proline were used to investigate the specific binding sites of Gen X on HSA. A competitive displacement study yields association constants for Gen X to HSA at the 1,8-ANS, warfarin, and dansyl-L-proline binding sites to be 6.25 ( ± 0.5) × 10⁴ M^-1, 1.1 × 10⁶ M^-1, and 2.5( ± 0.2) × 10⁹ M^-1 respectively. Addition of β-cyclodextrin (β-CD) and heptakis(6-deoxy-6-amino)-β-cyclodextrin heptahydrochloride to the HSA:Gen X complex leads to the effective extraction of Gen X from the complex with the return of HSA in its native form. Gen X also leads to displacement of site-specific binding fluorophores bound to HSA, while subsequent addition of β-CD extracts Gen X from HSA with the return of the characteristic fluorescence of the HSA bound site-specific agent. These results illustrate the strong and specific binding sites of Gen X on HSA and demonstrate the principles for the potential application of β-CD for the remediation of PFAS from biological systems.

Porphyrin-based colorimetric sensing of perfluorooctanoic acid as proof of concept for perfluoroalkyl substance detection

A functionalized porphyrin receptor was prepared to bind perfluorooctanoic acid. UV-Vis spectroscopic analysis showed the receptor gave a rapid colorimetric response that could also be detected visually at environmentally relevant concentrations. Spiked soil samples were used to demonstrate detection of perfluorooctanoic acid without intensive sample pre-treatment or laboratory instrument analysis.

Sensors for detecting per- and polyfluoroalkyl substances (PFAS): A critical review of development challenges, current sensors, and commercialization obstacles

Per- and polyfluoroalkyl substances (PFAS) are a class of compounds that have become environmental contaminants of emerging concern. They are highly persistent, toxic, bioaccumulative, and ubiquitous which makes them important to detect to ensure environmental and human health. Multiple instrument-based methods exist for sensitive and selective detection of PFAS in a variety of matrices, but these methods suffer from expensive costs and the need for a laboratory and highly trained personnel. There is a big need for fast, inexpensive, robust, and portable methods to detect PFAS in the field. This would allow environmental laboratories and other agencies to perform more frequent testing to comply with regulations. In addition, the general public would benefit from a fast method to evaluate the drinking water in their homes for PFAS contamination. A PFAS sensor would provide almost real-time data on PFAS concentrations that can also provide actionable information for water quality managers and consumers around the planet. In this review, we discuss the sensors that have been developed up to this point for PFAS detection by their molecular detection mechanism as well as the goals that should be considered during sensor development. Future research needs and commercialization challenges are also highlighted.