Binding of Perfluorooctanoate to Poly(ethylene oxide)

To inform the design of polymer-based adsorbent materials for sequestration of per- and polyfluoroalkyl substances (PFAS) from aqueous solution, we report here on the critical aggregation concentration (CAC), shape, size, composition, and interactions of assemblies formed in water between perfluorooctanoic acid ammonium salt (PFOA) and the nonionic polymer poly­(ethylene oxide) (PEO), obtained from complementary experiments (conductivity, surface tension, pyrene fluorescence, viscosity, and small-angle neutron scattering (SANS)) and atomistic molecular dynamics (MD) simulations. PEO–PFAS binding commences at concentrations lower than the PFOA critical micelle concentration (CMC) and is driven by PEO localizing on the micelle surface and shielding the fluorocarbon parts of PFOA from contact with water. PFOA + PEO mixed micelles have a 10% higher association number and are 40% more elongated compared to polymer-free PFOA micelles. This is the first investigation on the structure of polymer + fluorocarbon surfactant mixed micelles and contributes fundamental insights into the association of water-soluble polymers with PFAS surfactants

Adsorption Mechanism of Perfluorooctanoate on Cyclodextrin-Based Polymers: Probing the Synergy of Electrostatic and Hydrophobic Interactions with Molecular Dynamics Simulations

Contamination of natural water resources by per- and polyfluorinated alkyl substances (PFAS) has affected millions of people around the world and emphasized the need for development of novel and effective adsorbent materials. We demonstrate how atomistic molecular dynamics (MD) simulations can be used to provide molecular scale insight into the role of electrostatic and hydrophobic interactions on the adsorption of the perfluorooctanoate (PFOA) surfactant, a prominent longer-chain PFAS, on a polymer-based network in water. Specifically, the adsorption of ammonium perfluorooctanoate salt has been investigated on the β-cyclodextrin (CD) network cross-linked with decafluorobiphenyl linkers as an example of an absorbent material that has already demonstrated efficient PFAS adsorption. Examination of pairwise interactions reveals the importance of the dual pronged adsorption mechanism involving both electrostatic and hydrophobic interactions. The adsorption of ammonium counterions on the CD segments facilitates attraction of the anionic headgroup of the PFOA surfactant, while fluorinated linkers provide an additional hydrophobic attraction for the PFOA tail as well as higher affinity of the network toward PFOA in comparison with hydrocarbons. These competing interactions result in PFOA adsorption primarily outside of the CD cavity with the PFOA tail mostly interacting with fluorinated linkers. We demonstrate that simulations using “what if” scenarios are a powerful approach to infer the role of different interactions in the adsorption of PFAS

Well-Defined Homopolypeptides, Copolypeptides, and Hybrids of Poly(l-proline)

l-Proline is the only, out of 20 essential, amino acid that contains a cyclized substituted α-amino group (is formally an imino acid), which restricts its conformational shape. The synthesis of well-defined homo- and copolymers of l-proline has been plagued either by the low purity of the monomer or the inability of most initiating species to polymerize the corresponding N-carboxy anhydride (NCA) because they require a hydrogen on the 3-N position of the five-member ring of the NCA, which is missing. Herein, highly pure l-proline NCA was synthesized by using the Boc-protected, rather than the free amino acid. The protection of the amine group as well as the efficient purification method utilized resulted in the synthesis of highly pure l-proline NCA. The high purity of the monomer and the use of an amino initiator, which does not require the presence of the 3-N hydrogen, led for the first time to well-defined poly(l-proline) (PLP) homopolymers, poly(ethylene oxide)-b-poly(l-proline), and poly(l-proline)-b-poly(ethylene oxide)-b-poly(l-proline) hybrids, along with poly(γ-benzyl-l-glutamate)-b-poly(l-proline) and poly(Boc-l-lysine)-b-poly(l-proline) copolypeptides. The combined characterization (NMR, FTIR, and MS) that results for the l-proline NCA revealed its high purity. In addition, all synthesized polymers exhibit high molecular and compositional homogeneity

Ionic Liquid-Modified Porous Materials for Gas Separation and Heterogeneous Catalysis

This work examines important physicochemical and thermophysical properties of ultrathin ionic liquid (IL) layers under confinement into the pore structure of siliceous supports and brings significant advances toward understanding the effects of these properties on the gas separation and catalytic performance of the developed supported ionic liquid phase (SILP) and solid catalysts with ionic liquid layers (SCILL). SILPs were developed by making use of functionalized and nonfunctionalized ILs, such as 1-(silylpropyl)-3-methyl-imidazolium hexafluorophosphate and 1-butyl-3-methyl-imidazolium hexafluorophosphate ILs, whereas the SCILL was prepared by effectively dispersing gold nanoparticles (AuNPs) onto the IL layers inside the open pores of the SILP. The information derived from the gas absorption/diffusivity and heterogeneous catalysis experiments was exemplified in relation to the liquid crystalline ordering and orientation of the IL molecules, investigated by X-ray diffraction (XRD) and modulated differential scanning calorimetry (MDSC). The extent of pore blocking was elucidated with small angle neutron scattering (SANS) and was proven to be a decisive factor for the gas separation efficiency of the SILPs. CO₂/CO separation values above 50 were obtained in cases where liquid crystalline ordering of the IL layers and extended pore blocking had occurred. The presence of the IL layer in the developed SCILL assisted the formation of ultrasmall (2–3 nm) and well-stabilized AuNPs. The low-temperature CO oxidation efficiency was 22%. The catalytic experiments showed an additional functionality of the IL, acting as an “in-situ trap” that abstracts the product (CO₂) from the reaction site and improves yield