Nano-Sized Cyclodextrin-Based Molecularly Imprinted Polymer Adsorbents for Perfluorinated Compounds-A Mini-Review

Assessing the greenification potential of cyclodextrin-based molecularly imprinted polymers for pesticides detection

Cyclodextrins, with their unparalleled attributes of eco-friendliness, natural abundance, versatile utility, and facile functionalization, make a paramount contribution to the field of molecular imprinting. Leveraging the unique properties of cyclodextrins in molecularly imprinted polymers synthesis has revolutionized the performance of molecularly imprinted polymers, resulting in enhanced adsorption selectivity, capacity, and rapid extraction of pesticides, while also circumventing conventional limitations. As the concern for food quality and safety continues to grow, the need for standard analytical methods to detect pesticides in food and environmental samples has become paramount. Cyclodextrins, being non-toxic and biodegradable, present an attractive option for greener reagents in imprinting polymers that can also ensure environmental safety post-application. This review provides a comprehensive summary of the significance of cyclodextrins in molecular imprinting for pesticide detection in food and environmental samples. The recent advancements in the synthesis and application of molecularly imprinted polymers using cyclodextrins have been critically analyzed. Furthermore, the current limitations have been meticulously examined, and potential opportunities for greenification with cyclodextrin applications in this field have been discussed. By harnessing the advantages of cyclodextrins in molecular imprinting, it is possible to develop highly selective and efficient methods for detecting pesticides in food and environmental samples while also addressing the challenges of sustainability and environmental impact.

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.

Dramatically Increased Binding Constant of Water-Soluble Cyclodextrin Hyperbranched Polymers: Explored with Diffusion Ordered NMR Spectroscopy (DOSY)

We report that the polymerization of cyclodextrin (CD) with epichlorohydrin (ECH) dramatically increases the binding constant of CD to vanillin, from 55 to 8.4 × 10³ M^-1, by approximately 100 times, as determined by diffusion ordered spectroscopy (DOSY)-¹H NMR. The binding constant increased with an increase of the ECH content of the polymer, although ECH polymers without CDs showed no affinity at all, suggesting that the hydrophobicity of the ECH network outside of CDs helps to enhance the binding. This increased binding constant allows CD-ECH polymers to increase the drug loading ratio, which may be one of the most critical issues for drug delivery systems.

A Review of Sensors and Biosensors Modified with Conducting Polymers and Molecularly Imprinted Polymers Used in Electrochemical Detection of Amino Acids: Phenylalanine, Tyrosine, and Tryptophan

Recently, the studies on developing sensors and biosensors-with an obvious interdisciplinary character-have drawn the attention of many researchers specializing in various fundamental, but also complex domains such as chemistry, biochemistry, physics, biophysics, biology, bio-pharma-medicine, and bioengineering. Along these lines, the present paper is structured into three parts, and is aimed at synthesizing the most relevant studies on the construction and functioning of versatile devices, of electrochemical sensors and biosensors, respectively. The first part presents examples of the most representative scientific research focusing on the role and the importance of the phenylalanine, tyrosine, and tryptophan amino acids, selected depending on their chemical structure and their impact on the central nervous system. The second part is dedicated to presenting and exemplifying conductor polymers and molecularly imprinted polymers used as sensitive materials in achieving electrochemical sensors and biosensors. The last part of the review analyzes the sensors and biosensors developed so far to detect amino acids with the aid of conductor polymers and molecularly imprinted polymers from the point of view of the performances obtained, with emphasis on the detection methods, on the electrochemical reactions that take place upon detection, and on the electroanalytical performances. The present study was carried out with a view to highlighting, for the benefit of specialists in medicine and pharmacy, the possibility of achieving and purchasing efficient devices that might be used in the quality control of medicines, as well as in studying and monitoring diseases associated with these amino acids.

Structural Adaptive, Self-Separating Material for Removing Ibuprofen from Waters and Sewage

β-Cyclodextrin nanosponge (β-CD-M) was used for the adsorption of ibuprofen (IBU) from water and sewage. The obtained material was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), Harkins and Jura t-Plot, zeta potential, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and elementary analysis (EA). Batch adsorption experiments were employed to investigate the effects of the adsorbent dose, initial IBU concentration, contact time, electrolyte ions and humic acids, and sewage over adsorption efficiency. The experimental isotherms were show off using Langmuir, Freundlich, Hill, Halsey and Sips isotherm models and thermodynamic analysis. The fits of the results were estimated according to the Sips isotherm, with a maximum adsorption capacity of 86.21 mg g-1. The experimental kinetics were studied by pseudo-first-order, pseudo-second-order, Elovich, modified Freundlich, Weber Morris, Bangham's pore diffusion, and liquid film diffusion models. The performed experiments revealed that the adsorption process fits perfectly to the pseudo-second-order model. The Elovich and Freundlich models indicate chemisorption, and the kinetic adsorption model itself is complex. The data obtained throughout the study prove that this nanosponge (NS) is extremely stable, self-separating, and adjusting to the guest structure. It also represents a potential biodegradable adsorbent for the removal IBU from wastewaters.

Application of nanomaterials decorated with cyclodextrins as sensing elements for environment analysis

Environmental pollution has brought adverse socio-economic consequences. Organic pollutants and heavy metals are the main culprits of environmental pollution. It is of great importance to develop novel, simple, rapid, sensitive, and low-cost detection approaches for sensing trace pollutants in environmental samples. A lot of detection strategies which are based on varieties of nanomaterials have been developed for environmental analysis in past decades. In this review, we retrospect a variety of nanomaterials decorated with cyclodextrins (CDs), including carbon nanomaterials decorated with CDs, noble metal nanomaterials decorated with CDs and other nanomaterials decorated with CDs, and their application in environmental analysis. CDs is a type of ideal modifying molecules which could recognize targets, improve the solubility and dispersibility of corresponding functionalized materials, and enhance the detecting performance of designed sensors. CDs have been widely immobilized to carbon nanomaterials, noble metal nanomaterials, phosphorene (BP) nanocomposites, metal organic framework (MOF), and magnetic nanomaterials, and these nanocomposites have been utilized as the sensing elements for different target analytes. Immobilizing CDs on different nanomaterials could extremely expand the development of new sensing systems for environmental analysis based on these materials, greatly broaden the species of sensing targets, and apparently improve their sensing performance. Herein, the nanomaterials decorated with CDs, as sensing elements for environmental analysis, were reviewed including the types of nanomaterials decorated with CDs and their applications in various sensing strategies for environmental analysis. Finally, the perspectives of the nanomaterials decorated with CDs used as sensing elements were also discussed.

Comparison and recent progress of molecular imprinting technology and dummy template molecular imprinting technology

Molecular imprinting technology for the preparation of polymers with specific molecular recognition function had become one of the current research hotspots. It has been widely applied in chromatographic separation, antibody and receptor mimetics, solid-phase extraction, bio-sensors, and other fields in the last decades. In this study, molecular imprinting technology was summarized from the points of templates and dummy templates, and four typical target analytes were selected to compare the differences between templates and dummy templates. The current status and prospects of molecular imprinting technology were also proposed.

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.

Evaluation of adsorption ability of cyclodextrin-calixarene nanosponges towards Pb2+ ion in aqueous solution

Different cyclodextrin-calixarene nanosponges (CyCaNSs) have been characterized by means of FFC-NMR relaxometry, and used as sorbents to remove Pb²⁺ ions from aqueous solutions. Considering that the removal treatments may involve polluted waters with different characteristics, the adsorption experiments were performed on solutions without and with the addition of background salts, under different operational conditions. The adsorption abilities and affinities of the nanosponges towards Pb²⁺ ions were investigated by measuring the metal ion concentration by means of Inductively Coupled Plasma Emission Spectroscopy (ICP-OES) and Differential Pulse Anodic Stripping Voltammetry (DP-ASV). The acid-base properties of nanosponges and of metal ion as well as their interactions with the other interacting components of the systems have been considered in the evaluation of adsorption mechanism. Recycling and reuse experiments on the most efficient adsorbents were also performed. On the grounds of the results obtained, post-modified CyCaNSs appear promising materials for designing environmental remediation devices.

Recent Advances of Molecularly Imprinted Polymers Based on Cyclodextrin

Molecular imprinting polymers (MIPs), generally considered as artificial mimics that are comparable to natural receptor, are polymers with tailor-made specific recognition sites complementary to the template molecules in shape and size. As a class of supramolecular compounds, cyclodextrins (CDs) are flourishing in the field of molecular imprinting with their unique structural properties. This review presents recent advances in application of MIPs based on CDs during the past five years. The discussion is grouped according to the different role of CDs in MIPs, that is, functional monomer, carrier modifier, etc. Main focus is the application of CD-based MIP on sample preparation, detection, and sensing. Additionally, drug delivery with CD-based MIP is also briefly discussed. Finally, challenges and future prospects of application of CDs in MIP are elaborated.

Iron-Montmorillonite-Cyclodextrin Composites as Recyclable Sorbent Catalysts for the Adsorption and Surface Oxidation of Organic Pollutants

Iron-clay-cyclodextrin composites were designed as sorbent catalysts to adsorb and oxidize pollutants from water. The clay-iron backbone served as a mechanical support and as a heterogeneous Fenton catalyst, and the cyclodextrin monomers or polymers cross-linked with polyfluorinated aromatic molecules were used to accommodate adsorption of the pollutants. The composite based on iron-clay-cyclodextrin-polymers (Fe-MMT-βCD-DFB) exhibited superior adsorption and degradation of the model pollutants, bisphenol A (BPA), carbamazepine (CBZ), and perfluorooctanoic acid (PFOA), compared to the monomer-based composite and the native iron clay. The variety of adsorption sites, such as the polyfluorinated aromatic cross-linker, cyclodextrin toroid, and iron-clay surface, resulted in high adsorption affinity toward all pollutants; BPA was primarily adsorbed to the cyclodextrin functional groups, CBZ showed high affinity toward the Fe-MMT surface and the Fe-MMT-βCD-DFB composite, whereas PFOA was adsorbed mainly to the βCD-DFB polymer. Degradation, using H₂O₂, was highly efficient, reaching over 90% degradation in 1 h for BPA and CBZ and ∼80% for PFOA. The composite also showed excellent degradation efficiency in a multicomponent system with all three model pollutants. Furthermore, the composite's activity remained steady for five consecutive cycles of adsorption and degradation. The ability to remediate a broad range of pollutants, and the high overall removal exhibited by this novel material, demonstrates the potential for future application in water remediation technologies.

Guanidinocalix[5]arene for sensitive fluorescence detection and magnetic removal of perfluorinated pollutants

Perfluorinated alkyl substances, such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), are toxic materials that are known to globally contaminate water, air, and soil resources. Strategies for the simultaneous detection and removal of these compounds are desired to address this emerging health and environmental issue. Herein, we develop a type of guanidinocalix[5]arene that can selectively and strongly bind to PFOS and PFOA, which we use to demonstrate the sensitive and quantitative detection of these compounds in contaminated water through a fluorescent indicator displacement assay. Moreover, by co-assembling iron oxide nanoparticle with the amphiphilic guanidinocalix[5]arene, we are able to use simple magnetic absorption and filtration to efficiently remove PFOS and PFOA from contaminated water. This supramolecular approach that uses both molecular recognition and self-assembly of macrocyclic amphiphiles is promising for the detection and remediation of water pollution.

Research progress on the removal of hazardous perfluorochemicals: A review

Perfluorinated substances are global and ubiquitous pollutants. The persistent organic pollution of perfluorochemicals (PFCs) have drawn attentions worldwide. In view of the current need for sustainable development, many researchers began to study the remediation techniques for PFCs. Due to its unique hydrophobic and oil-phobic characteristics, the requirements for the PFCs removal process are different, so that their remediation techniques are still under continuous exploration. Hence, this review summarized the removal behaviors of various PFCs on different materials which supply a good foundation for future investigations in this field. It is evident from previous literature that every remediation techniques for PFCs has its own advantages. Among various currently evaluated removal methods, adsorption seems to be one of the most commonly used and recognized techniques for PFCs pollution control. Other innovative and promising techniques, such as physical and/or chemical methods, have also been tested for their effectiveness in removing perfluorinated compounds.

Toxicity of perfluorooctane sulfonate on Phanerochaete chrysosporium: Growth, pollutant degradation and transcriptomics

As a persistent organic pollutant listed in the Stockholm Convention, perfluorooctane sulfonate (PFOS) is extremely refractory to degradation under ambient conditions. Its potential ecotoxicity has aroused great concerns and research interests. However, little is known about the toxicity of PFOS on fungus. In this study, the white rot fungus Phanerochaete chrysosporium (P. chrysosporium) was adopted to assess the toxicity of PFOS in liquid culture. The addition of 100 mg/L PFOS potassium salt significantly decreased the fungal biomass by up to 76.4% comparing with un-amended control during the incubation period. The hyphostroma of P. chrysosporium was wizened and its cell membrane was thickened, while its vesicle structure was increased, based on the observation with scanning electron microscope (SEM) and transmission electron microscope (TEM). Nevertheless, the PFOS dosage of below 100 mg/L did not show a considerable damage to the growth of P. chrysosporium. The degradation of malachite green (MG) and 2,4-dichlorophenol (2,4-DCP) by P. chrysosporium was negatively affected by PFOS. At the initial dosage of 100 mg/L PFOS, the decolorization efficiency of MG and the degradation efficiency of 2,4-DCP decreased by 37% and 20%, respectively. This might be attributed to the inhibition of PFOS on MnP and LiP activities. The activities of MnP and LiP decreased by 20.6% and 43.4%, respectively. At a high dosage PFOS (100 mg/L), P. chrysosporium could show a high adsorption of MG but lose its pollutant degradation ability. Transcriptome analysis indicated that PFOS contamination could lead to the change of gene expression in the studied white rot fungus, and the genes regulating membrane structure, cell redox process, and cell transport, synthesis and metabolism were impacted. Membrane damage and oxidative damage were the two main mechanisms of PFOS' toxicity to P. chrysosporium.

3D-QSAR for binding constants of β-cyclodextrin host-guest complexes by utilising spectrophores as molecular descriptors

The increasing use of cyclodextrins (CDs) as host-molecules for host-guest complexes and their remediation application in environmental science requires to establish easily accessible models of "quantitative structure-activity relationships" (QSARs) to predict the binding constants. A new open-source molecular descriptor, so called spectrophores, was utilised to build 3D-QSAR models which have R² of 0.95 and RMSE of 0.20.

Nanocellulose-Block Copolymer Films for the Removal of Emerging Organic Contaminants from Aqueous Solutions

The prevalence of emerging organic contaminants (EOCs) in ground and surface water has sparked the search for more effective methods to remove EOCs from the environment. In pursuit of a solution for this environmental concern, herein we present the development of reusable films based on cellulose nanofibers (CNFs) and the block copolymer, poly(4-vinylpyridine-b-ethylene oxide) (P4VP-PEO) to adsorb sulfamethoxazole (SMX) as an EOC model compound. We hypothesize that the adsorption of SMX was achieved mainly by π-π interactions between the pyridine functionalities of the block copolymer and the electron deficient phenyl group of the SMX. Preceding preparation of the films, CNFs were modified with the alkoxysilane trimethoxy(2-phenylethyl)silane (TMPES) to increase their stability in aqueous solution. After the addition of P4VP-PEO, the process was completed by filtration followed by oven-drying. XPS and FTIR were employed to confirm the addition of TMPES and P4VP-PEO, respectively. Adsorption batch experiments were performed in aqueous solutions of SMX at a neutral pH, obtaining adsorptions of up to 0.014 mmol/g in a moderate time of 60 min. For the reusability tests, films were immersed in ethanol 95 wt.% to elude the adsorbed SMX, rinsed with deionized (DI) water, and dried at room temperature to be reused in a new adsorption cycle. We found that this new composite material could be reused several times with negligible loss of adsorption capacity. The films presented have been shown to be of substantial importance for water remediation as they find direct application in the adsorption of electron deficient aromatic compounds and are reusable.

Selective electrochemical detection of bisphenol A using a molecularly imprinted polymer nanocomposite

A molecularly imprinted nanocomposite with covalently connected polyacrylate, β-cyclodextrin and graphene is synthesized for selective capture and electrochemical detection of bisphenol A.

“Pillaring Effects” in Cross-Linked Cellulose Biopolymers: A Study of Structure and Properties

Modified cellulose materials (CLE-4, CLE-1, and CLE-0.5) were prepared by cross-linking with epichlorohydrin (EP), where the products display variable structure, morphology, and thermal stability. Adsorptive probes such as nitrogen gas and phenolic dyes in aqueous solution reveal that cross-linked cellulose has greater accessible surface area (SA) than native cellulose. The results also reveal that the SA of cross-linked cellulose increased with greater EP content, except for CLE-0.5. The attenuation of SA for CLE-0.5 may relate to surface grafting onto cellulose beyond the stoichiometric cellulose and EP ratio since ca. 30% of the hydroxyl groups of cellulose are accessible for cross-linking reaction due to its tertiary fibril nature. Scanning electron microscopy (SEM) results reveal the variable surface roughness and fibre domains of cellulose due to cross-linking. X-ray diffraction (XRD) and 13C NMR spectroscopy indicate that cellulose adopts a one-chain triclinic unit cell structure (P1 space group) with gauche-trans (gt) and trans-gauche (tg) conformations of the glucosyl linkages and hydroxymethyl groups. The structural characterization results reveal that cross-linking of cellulose occurs at the amorphous domains. By contrast, the crystalline domains are preserved according to similar features in the XRD, FTIR, and 13C NMR spectra of cellulose and its cross-linked forms. This study contributes to an improved understanding of the role of cross-linking of native cellulose in its structure and functional properties. Cross-linked cellulose has variable surface functionality, structure, and textural properties that contribute significantly to their unique physicochemical properties over its native form.

State-of-the-art applications of cyclodextrins as functional monomers in molecular imprinting techniques: a review

As a versatile tool in separation science, cyclodextrins and their derivatives, known as emerging functional monomers, have been used extensively in molecular imprinting techniques. The attributes of cyclodextrins and their derivatives are widely known to form host-guest inclusion complex processes between the polymer and template. The exploitation of the imprinting technique could produce a product of molecularly imprinted polymers, which are very robust with long-term stability, reliability, cost-efficiency, and selectivity. Hence, molecularly imprinted polymers have gained popularity in chemical separation and analysis. Molecularly imprinted polymers containing either cyclodextrin or its derivatives demonstrate superior binding effects for a target molecule. As noted in the previous studies, the functional monomers of cyclodextrins and their derivatives have been used in molecular imprinting for selective separation with a wide range of chemical compounds, including steroidals, amino acids, polysaccharides, drugs, plant hormones, proteins, pesticides, and plastic additives. Therefore, the main goal of this review is to illustrate the exotic applications of imprinting techniques employing cyclodextrins and their derivatives as single or binary functional monomers in synthesizing molecularly imprinted polymers in areas of separation science by reviewing some of the latest studies reported in the literature.

β-Cyclodextrin Attenuates Perfluorooctanoic Acid Toxicity in the Zebrafish Embryo Model

Perfluorooctanoic acid (PFOA) has been linked to negative health outcomes including cancer, thyroid disease, infertility, and developmental delays. β-Cyclodextrin (β-CD), a cyclic sugar, has been previously shown to form strong host–guest complexes with PFOA, and is proposed as a means of environmental remediation with respect to this widespread contaminant. In the present study, β-CD was directly examined with regards to possible attenuation of the toxicity of PFOA specifically employing the zebrafish (Danio rerio) embryo model. Zebrafish embryos were exposed to various concentrations of PFOA without β-CD, and with equimolar (1:1) and excess (2:1) molar ratios of β-CD to PFOA, and assessed for lethality and developmental toxicity through seven days post-fertilization (dpf). Rapid onset of lethality with limited morphological abnormalities was observed at relatively low concentrations of PFOA (LC₅₀ ≈ 50 ppm), along with effects on morphometric and neurobehavioral parameters in surviving embryos. A highly significant difference (p < 0.0001) was observed between the 2:1 treatment, and both 1:1 and PFOA only treatments, with respect to lethal concentration and apparent neurobehavioral effects, suggesting an effectively reduced toxicity of the fully complexed PFOA. In contrast, however, neither β-CD treatment reduced developmental toxicity with respect to the morphometric endpoint (i.e., interocular distance). Whereas LC₅₀ of PFOA alone did not change over 7 dpf, the 1:1 and 2:1 values decreased slightly over time, suggesting either delayed or alternative toxic effects on later developmental stages at presumptively lowered levels. This study, therefore, indicates β-CD may be an effective agent to reduce toxicity of and mitigate environmental health concerns associated with PFOA, but that further study is required to elucidate the mechanism of complexation as it relates to the attenuation of toxicity.

19F NMR Characterization of the Encapsulation of Emerging Perfluoroethercarboxylic Acids by Cyclodextrins

Legacy perfluoroalkyl substances (PFASs) are known environmental pollutants with serious adverse health effects. Perfluoroethercarboxylic acids (PFECAs), emerging PFASs now being substituted for legacy PFASs, have recently been detected in the environment. Cyclodextrins (CDs) have been proposed as agents for the remediation of problematic pollutants, including legacy PFASs. The current study uses ¹⁹F NMR spectroscopy to measure the complexation of mono-, di-, and triether PFECAs by CDs for eventual environmental applications. Eight PFECAs were characterized by ¹⁹F and ¹³C NMR. The change in chemical shift of individual fluorines upon complexation of CDs at various stoichiometric ratios was used to determine the host-guest association constants. All studied PFECAs were most strongly encapsulated by β-CD, with association constants from 10²-10⁵ M^-1 depending on chain length and number of ether functionalities. ¹⁹F-¹H heteronuclear Overhauser effect spectroscopy (HOESY) NMR experiments were performed for the β-CD complexes of two branched monoethers, PFPrOPrA ("GenX") and PFDMMOBA, to elucidate the structural details of the complexes, determine the specific orientation, and position of β-CD along the PFAS chain, and assess the roles of hydrogen-bonding and PFECA branching on the host-guest interactions. The results give new understanding into the fundamental nature of the host-guest complex between cyclodextrins and perfluorinated surfactants.

Detailed NMR investigation of cyclodextrin-perfluorinated surfactant interactions in aqueous media

Perfluorochemicals (PFCs) are contaminants of serious concern because of their toxicological properties, widespread presence in drinking water sources, and incredible stability in the environment. To assess the potential application of α-, β-, and γ-cyclodextrins for PFC remediation, we investigated their complexation with linear fluorinated carboxylic acids, sulfonates, and a sulfonamide with carbon backbones ranging from C4-C9. ¹⁹F Nuclear Magnetic Resonance (NMR) spectroscopy studies demonstrated β-CD formed the strongest complexes with these PFCs. The polar head group had a modest influence, but for PFCs with backbones longer than six carbons, strong association constants are observed for 1:1 (K_1:1∼10⁵M^-1) and 2:1 (K_2:1∼10³M^-1) β-CD:PFC complexes. Excess β-CD can be used to complex 99.5% of the longer chain PFCs. Competition studies with adamantane-carboxylic acid and phenol confirmed the nature and persistence of the β-CD:PFC complex. Detailed analyses of the individual NMR chemical shifts and Job plots indicate the favored positions of the β-CD along the PFC chain. Solution pH, ionic strength, and the presence of humic acid have modest influence on the β-CD:PFC complexes. The strong encapsulation of PFCs by β-CD under a variety of water quality conditions demonstrates the tremendous potential of CD-based materials for the environmental remediation of PFCs.

Preparation and Characterization of a Polymer-Based "Molecular Accordion"

A urethane-based polymer material, denoted HDI-1, was obtained from the addition reaction of β-cyclodextrin (β-CD) with 1,6-hexamethylene diisocyanate (HDI) at the 1:1 mole ratio. In aqueous solution and ambient temperature conditions, HDI-1 adopts a compact (coiled) morphology where the cross-linker units become coiled and are partially self-included in the annular hydroxyl (interstitial) region of β-CD. As the temperature is raised or as p-nitrophenol (PNP) was included within the β-CD cavity and the noninclusion sites of the polymer, an extended (uncoiled) morphology was adopted. The equilibrium distribution between the extended and the compact forms of HDI-1 is thermally and chemically switchable, in accordance with the hydration properties and host-guest chemistry of this responsive polymer system. The molecular structure of this water-soluble urethane polymer and its host-guest complexes with PNP were investigated using spectroscopic (Raman, (1)H NMR, induced circular dichroism), dynamic light scattering (DLS), and calorimetric (DSC) methods in aqueous solution at ambient pH, and compared with native β-CD. This study reports on the unique supramolecular properties of a polymer that resembles a thermally and chemically responsive "molecular accordion".