Fluorous media for extraction and transport

Polybenzimidazole: a novel, fluorocarbon-free, SPME sorbent binder with good thermal and solvent resistance properties for GC and LC analysis

A novel solid-phase microextraction (SPME) coating is presented that uses polybenzimidazole (PBI) as a binder to immobilize micro-size sorbent particles onto a support. An evaluation of the developed binder's thermal and solvent desorption capabilities demonstrated its compatibility with both gas and liquid chromatography (GC and LC). The incorporation of hydrophilic-lipophilic balanced (HLB) particles provided optimal extraction coverage for an array of chemically diverse analytes possessing a range of hydrophobicities and molecular weights. The developed binder's performance was assessed by comparing it to a selection of binders commonly used in the literature, including polydimethylsiloxane (PDMS) and polyacrylonitrile (PAN), as well as the more recently developed polyvinylidene fluoride (PVDF) and polytetrafluoroethylene amorphous fluoroplastic (PTFE AF 2400). The results revealed that PBI provides better performance compared to PVDF and PTFE AF 2400 in terms of its environmental impact, while also being convenient for use in coating preparation and offering good matrix compatibility. The thermal analysis revealed that PBI exhibited more than 93% weight retention at 550 °C, which is superior to PVDF's 80.07% weight retention at 393.78 °C. To the best of our knowledge, this work is the first to use PBI as a particle binder in SPME coatings. The PBI coating maintained high extraction efficiencies under extreme conditions with pH values of 3 and 12. The performance of PBI in combination with HLB was assessed by employing it to extract several drugs of abuse and McReynolds compounds for LC and GC analysis, respectively. The results indicated that PBI performs similarly to PAN for LC but is outperformed by PDMS in GC applications with respect to extraction and desorption kinetics. Nonetheless, the thermal and solvent desorption results indicated that PBI can be used for both applications, as it remains stable at temperatures over 350 °C and is stable when solvent desorption is applied.

Green Chemistry and Molecularly Imprinted Membranes

Technological progress has made chemistry assume a role of primary importance in our daily life. However, the worsening of the level of environmental pollution is increasingly leading to the realization of more eco-friendly chemical processes due to the advent of green chemistry. The challenge of green chemistry is to produce more and better while consuming and rejecting less. It represents a profitable approach to address environmental problems and the new demands of industrial competitiveness. The concept of green chemistry finds application in several material syntheses such as organic, inorganic, and coordination materials and nanomaterials. One of the different goals pursued in the field of materials science is the application of GC for producing sustainable green polymers and membranes. In this context, extremely relevant is the application of green chemistry in the production of imprinted materials by means of its combination with molecular imprinting technology. Referring to this issue, in the present review, the application of the concept of green chemistry in the production of polymeric materials is discussed. In addition, the principles of green molecular imprinting as well as their application in developing greenificated, imprinted polymers and membranes are presented. In particular, green actions (e.g., the use of harmless chemicals, natural polymers, ultrasound-assisted synthesis and extraction, supercritical CO2, etc.) characterizing the imprinting and the post-imprinting process for producing green molecularly imprinted membranes are highlighted.

Fluorination Effect on the Gibbs Transfer Energy for Methylene Group from 1,2-Dichloroethane or 1,1,1,2,3,4,4,5,5,5-​Decafluoropentane to Water

The ion-transfer reactions of alkyl and perfluoroalkyl carboxylate ions (CH₃(CH₂)_n-2COO^- and CF₃(CF₂)_n-2COO^-) at 1,2-dichloroethane (DCE) | water (W) and 1,1,1,2,3,4,4,5,5,5-decafluoropentane (DFP) | W interfaces were investigated. These ions gave reversible or quasi-reversible voltammetric waves due to their ion transfer across the interfaces, and the formal potentials and the formal Gibbs transfer energies from a non-aqueous solvent to water, ΔG°^'_tr,α→W (α = DCE and DFP), were determined. The ΔG°^'_tr,α→W for CH₃(CH₂)_n-2COO^- and CF₃(CF₂)_n-2COO^- linearly increased with n, allowing for estimating ΔG°^'_tr,α→W for methylene groups. The estimated value of ΔG°^'_tr,DCE→W for the -CH₂- group was higher than that of ΔG°^'_tr,DCE→W for the -CH₂- group, whereas the ΔG°^'_tr,DCE→W for the -CF₂- group was lower than that of ΔG°^'_tr,DCE→W for the -CF₂- group, indicating that the -CH₂- (or -CF₂-) group is more favorably (or unfavorably) solvated in the DCE phase compared to the DFP phase. From the estimated values, the fluorination effect of alkyl chains on partitioning the alkyl group between the biphase media has also been discussed.

Enantioselective Sensing in the Fluorous Phase for Catalyst Screening: Application of a Racemic Fluorescent Probe

A perfluoroalkyl ketone-based molecular probe was found to show highly enantioselective fluorescent enhancement in the fluorous phase when treated with an amino alcohol generated from the asymmetric reaction of a meso-epoxide with an alkyl amine. The two enantiomeric probes (R)- and (S)-2 were used to screen catalysts for this asymmetric reaction. The use of the probe in the fluorous phase allowed the fluorescent sensing of the products to be conducted away from the other reaction components with minimized interference. It was further found that when (R)- or (S)-2 was used to determine the enantiomeric composition of the amino alcohol product, there was a large nonlinear effect. That is, only when one enantiomer of the substrate was in excess was there a large fluorescence enhancement for the chirality-matched probe-substrate interaction. This allowed the racemic probe rac-2 to be used to evaluate the asymmetric induction in the catalyst screening. The catalyst screening using the fluorescent probes led to the discovery of a more enantioselective and efficient method for the desymmetrization of 1,2-epoxycyclohexane with ⁱPrNH₂ to form the corresponding chiral amino alcohol. This work presents a novel method to conduct catalyst screening for asymmetric synthesis and has potential to become a high-throughput process.

A Bis-Acridinium Macrocycle as Multi-Responsive Receptor and Selective Phase-Transfer Agent of Perylene

A bis-acridinium cyclophane incorporating switchable acridinium moieties linked by a 3,5-dipyridylanisole spacer was studied as a multi-responsive host for polycyclic aromatic hydrocarbon guests. Complexation of perylene was shown to be the most effective and was characterized in particular by a charge-transfer band as signal output. Effective catch and release of the guest was triggered by both chemical (proton/hydroxide) and redox stimuli. Moreover, the dicationic host was also easily switched between organic and perfluorocarbon phases for applications related to the enrichment of perylene from a mixture of polycyclic aromatic hydrocarbons.

Enantioselective Fluorescent Recognition of Free Amino Acids: Challenges and Opportunities

Fluorescent probes that can discriminate enantiomers of amino acids in organic media or aqueous solution are discussed. This Minireview focuses on recent progress in the studies of three classes of probes including those made of cyclodextrins, 1,1'-binaphthyl compounds, and nanomaterials, and uses them to illustrate the design strategies, applications, and limitations in this area. These probes are potentially useful for rapid analysis of asymmetric reactions for amino acid synthesis as well as the real-time imaging of amino acids in biological systems. The challenges in these applications are analyzed. Working in this field of enantioselective fluorescent recognition of amino acids offers great opportunities to make new scientific discoveries and to develop important practical applications.

Ion Aggregation and R3N+-C(R)-H···NR3 Hydrogen Bonding in a Fluorous Phase

Potentiometric selectivities show that in fluorous ion-selective electrode membranes the tetrabutylammonium ion binds to fluorophilic proton ionophores. For the ionophore bis[3-(perfluorooctyl)propyl](2,2,2-trifluoroethyl)amine, this type of interaction is confirmed by the effect of the ionophore on the ionic conductivity of perfluoro(perhydrophenanthrene) solutions of a fluorophilic NBu₄⁺ salt. In this system, ion pairs, triple ions, and higher ionic aggregates dominate over single ions, and the ionophore increases the conductivity by favoring the formation of ion aggregates with a net charge. These observations are consistent with the formation of R₃N⁺-C(R)-H···NR₃ type hydrogen bonds between the nitrogen atom of the ionophore and the hydrogen atoms in the α position to the positively charged quaternary ammonium center of NBu₄⁺. Similar interactions were observed in a number of crystalline phases. To date, observations of C-H···N type hydrogen bonds in liquid phases have been very few, and solution-phase N⁺-C-H···N type hydrogen bonds have not been reported previously. Interestingly, no interactions between NBu₄⁺ and the more basic ionophore tridodecylamine were observed in conventional plasticized poly(vinyl chloride) membranes doped with the ionophore tridodecylamine, emphasizing the uniquely low polarity of fluorous phases.

Glossary of terms used in extraction (IUPAC Recommendations 2016)

Approaches for analytical-scale extraction are developing rapidly as new strategies are implemented to improve sample throughput, to minimize material use in laboratory methods, and to develop on-site capabilities. In this contribution, definitions and recommendations for symbols for the terms used in analytical extraction are presented. Exhaustive, microextraction, elevated temperature, microwave- and ultrasound-assisted, parallel batch, flow through systems, and membrane extraction approaches are discussed. An associated tutorial titled “Extraction” provides a detailed introduction to the topic.

Tag and Capture Flow Hydrogen Exchange Mass Spectrometry with a Fluorous-Immobilized Probe

Analysis of complex mixtures of proteins by hydrogen exchange (HX) mass spectrometry (MS) is limited by one's ability to resolve the protein(s) of interest from the proteins that are not of interest. One strategy for overcoming this problem is to tag the target protein(s) to allow for rapid removal from the mixture for subsequent analysis. Here we illustrate a new solution involving fluorous conjugation of a retrievable probe. The appended fluorous tag allows for facile immobilization on a fluorous surface. When a target protein is passed over the immobilized probe molecule, it can be efficiently captured and then exposed to a flowing stream of deuterated buffer for hydrogen exchange. The utility of this method is illustrated for a model system of the Elongin BC protein complex bound to a peptide from HIV Vif. Efficient capture is demonstrated, and deuteration when immobilized was identical to deuteration in conventional solution-phase hydrogen exchange MS. Protein captured from a crude bacterial cell lysate could also be deuterated without the need for separate purification steps before HX MS. The advantages and disadvantages of the method are discussed in light of miniaturization and automation.

A light incident angle switchable ZnO nanorod memristor: reversible switching behavior between two non-volatile memory devices

A light incident angle selectivity of a memory device is demonstrated. As a model system, the ZnO resistive switching device has been selected. Electrical signal is reversibly switched between memristor and resistor behaviors by modulating the light incident angle on the device. Moreover, a liquid passivation layer is introduced to achieve stable and reversible exchange between the memristor and WORM behaviors.

Creating biocompatible oil-water interfaces without synthesis: direct interactions between primary amines and carboxylated perfluorocarbon surfactants

Currently, one of the most prominent methods used to impart biocompatibility to aqueous-in-oil droplets is to synthesize a triblock copolymer surfactant composed of perfluoropolyether and polyether blocks. The resulting surfactants (EA surfactant, KryJeffa, etc.) allow generation of highly biocompatible droplet surfaces while maintaining the heat stability of the starting material. However, production of these surfactants requires expertise in synthetic organic chemistry, creating a barrier to widespread adoption in the field. Herein, we describe a simple alternative to synthetic modification of surfactants to impart biocompatibility. We have observed that aqueous-in-oil droplet surfaces can be made biocompatible and heat stable by merely exploiting binding interactions between polyetherdiamine additives in the aqueous phase and carboxylated perfluorocarbon surfactants in the oil phase. Droplets formed under these conditions are shown to possess biocompatible surfaces capable of supporting picoliter-scale protein assays, droplet polymerase chain reaction (PCR), and droplet DNA amplification with isothermal recombinase polymerase amplification (RPA). Droplets formed with polyetherdiamine aqueous additives are stable enough to withstand temperature cycling during PCR (30-40 cycles at 60-94 °C) while maintaining biocompatibility, and the reaction efficiency of RPA is shown to be similar to that with a covalently modified surfactant (KryJeffa). The binding interaction was confirmed with various methods, including FT-IR spectroscopy, NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and fluorescence microscopy. Overall, our results suggest that, by simply introducing a commercially-available, polyetherdiamine additive (Jeffamine ED-900) to the aqueous phase, researchers can avoid synthetic methods in generating biocompatible droplet surfaces capable of supporting DNA and protein analysis at the subnanoliter scale.

Teflon AF Materials

The unique combination of chemical, thermal, and mechanical stability, high fractional free volume, low refractive index, low surface energy, and wide optical transparency has led to growing interest in Teflon Amorphous Fluoropolymers (AFs) for a wide spectrum of applications ranging from chemical separations and sensors to bioassay platforms. New opportunities arise from the incorporation of nanoscale materials in Teflon AFs. In this chapter, we highlight fractional free volume - the most important property of Teflon AFs - with the aim of clarifying the unique transport behavior through Teflon AF membranes. We then review state-of-the-art developments based on Teflon AF platforms by focusing on the chemistry behind the applications.

Properties and transport behavior of perfluorotripentylamine (FC-70)-doped amorphous teflon AF 2400 films

Teflon AF 2400 films are known to imbibe solvents, making films in the presence of solvents less fluorous than they might otherwise be. Herein, we demonstrate that doping films with perfluorotripentylamine (Fluorinert FC-70) maintains the fluorous nature of Teflon AF 2400 and improves transport selectivity for fluorine-containing organic compounds. Density measurements on the FC-70-doped films reveal that free volume decreases dramatically as the dopant concentration increases (0-12 wt %) and then increases to approach that of pure FC-70. Remarkably, films from 0 to 12 wt % FC-70 have the same w/v concentration of Teflon AF 2400, indicating that FC-70 fills the free volume of Teflon AF 2400. This is consistent with the observed increased storage modulus and significant decrease (compared to undoped films) of solute diffusion coefficients in the same range of FC-70 concentrations. In contrast, FC-70 at concentrations greater than 12 wt % dilutes Teflon AF 2400, leading to a decrease of storage modulus and dramatic increase in solute diffusion coefficients. Sorption of chloroform decreases from 11.8 g of chloroform/100 g of film (pure Teflon film) to 3.8 g of chloroform/100 g of film (27 wt % FC-70-doped Teflon film), less than the solubility of chloroform in pure FC-70 (4.06 g of chloroform/100 g of FC-70). Solute partition coefficients from chloroform to FC-70-doped films generally decrease with increased dopant concentration. However, within a series of toluenes and nitrobenzenes, selectivity for F-containing solutes over analogous H-containing solutes increases as dopant concentration increases if the substitution is on the aromatic ring but not if it is on the methyl group (toluene). Transport (partitioning × diffusion) rates, as they involve both thermodynamic and kinetic factors, are not simply related to composition.