Pulsed Field Gradient Spin Echo Research Articles

Comparative Analysis of Degradation of Pristine Nafion and Catalyst Coated Membrane Subjected to Ex-Situ Fenton's Test Approach

Polyfluorinated sulfonic –acid ionomer membranes (e.g Nafion) are extensively used today as the benchmark materials for the electrolyte membrane in PEM water electrolysis. It is broadly accepted that the state of the health of PFSA membranes are adversely impacted by the chemical degradation occured during operation of PEMWE. The crossover gases on the catalytic surface generate Hydrogen Peroxide which is homolytically or in the presence of ferrous salts produce reactive oxygen species like hydroperoxyl (HO.) and hydroxyl (HO.) radicals. These radicals attack the ionomer subsequently leading to chain scission, unzipping and loss of functional groups and release of HF in the effluent water.Other than Fe3+, several transition metal ions Cu2+, Ni2+, Ti3+, Cu+, can poison the membrane significantly. The fact that membrane degradation is accelerated owing to introduction of ferrous ions is fervently implemented in ex-situ degradation tests (known as Fentons tests) to evaluate the durability of membrane materials.This work depicts a systematic investigation of degradation of pristine Nafion and catalyst coated Nafion membrane using a Fentons accelerated aging experiment. The durability of Nafion 117 and catalyst coated Nafion membrane with various counter ions against H2O2 was explored as a degradation factor of polymer electrolyte water electrolyser. Two distinct variations of the experiments were compared : (1) Nafion and CCM were dipped in only hydrogen peroxide solution, (2) Nafion and CCM were exposed to a solution containing ferrous ions and peroxide. Accelerated aging experiments were conducted over 3-7 days. The difference in degradation phenomena with and without Fe ions were evaluated in terms of the fluoride ion release. For both cases, to quantify the effect of water activity in Nafion and CCM chemical structure on both water diffusion and interfacial transport, pulse field gradient spin echo nuclear magnetic resonance (PFGSE-NMR) technique has been employed. Furthermore the equivalent weight of the Nafion and CCM can vary in presence of aforementioned chemical stressors which can be accurately quantitatively studied by confocal Raman spectroscopy. Morphological characteristic before and after aging test was also investigated. Role of H2O2 and ferous ion in mechanical behaviour of Nafion and CCM were also analyzed. The same experiment was repeated for different transition metal ions. This work sheds light on decomposition mechanism of Nafion and CCM in more detail.

Role of dynamic surface tension of silicone polyether surfactant-based silicone coatings on protein adsorption: An insight on the ‘ambiguous’ interfacial properties of Fouling Release Coatings

Non-toxic antibiofouling coatings are currently developed to avoid the negative impacts of the settlement of (micro)organisms on any water immersed surfaces. In some industries such as microalgae culture, marine sensors or even contact lenses, in addition to the need for antibiofouling efficiency, transparency and non-toxicity are prerequisite surface properties. In this work, seven amphiphilic transparent antifouling coatings have been elaborated using silicone polyether copolymer surfactants mixed in a polydimethylsiloxane-based elastomer matrix. Average molar masses (1.3–11.7 kDa) and molar mass distributions of each surfactant were assessed by pulse-field gradient spin-echo (PGSE) diffusion NMR. Surface and bulk properties of the designed coatings were characterized by measuring their surface roughness (0.03–0.07 μm), Young's modulus (1.4–2.2 MPa) as well as their wetting behavior. Results obtained from different wetting techniques have shown that coatings had initially a low surface free energy (around 20 mJ/m2) and that their surface became amphiphilic in contact with water (from 21 to 42 mJ/m2). Fitting of water contact angle measurements with the so-called O'Brien-Paranjape dynamic surface tension (DST) model enabled the calculation of the surfactant's diffusivities within the PDMS elastomer matrix (ranging from 9.96 × 10−15 to 1.77 × 10−13 m2·s−1) while providing a comprehensive insight on the kinetic interfacial variation of the overall amphiphilic coating. Coatings with the highest rates of water contact angle variation have been shown to positively affect the bovine serum albumin (BSA) protein adsorption.

Water Diffusion and Uptake in Injectable ETTMP/PEGDA Hydrogels.

Differential scanning calorimetry (DSC) and pulsed field gradient spin echo nuclear magnetic resonance (PFGSE NMR) were used to characterize water in hydrogels of ethoxylated trimethylolpropane tri-3-mercaptopropionate (ETTMP) and poly(ethylene glycol) diacrylate (PEGDA). Freezable and nonfreezable water were quantified using DSC; water diffusion coefficients were measured using PFGSE NMR. No freezable water (free or intermediate) was detected from DSC for hydrogels of 0.68 and greater polymer mass fractions. Water diffusion coefficients, from NMR, decreased with increasing polymer content and were assumed to be weighted averages of free and bound water contributions. Both techniques showed decreasing ratios of bound or nonfreezable water mass per polymer mass with increasing polymer content. Swelling studies were used to quantify the equilibrium water content (EWC) to determine which compositions would swell or deswell when placed in the body. At 30 and 37 °C, fully cured, non-degraded ETTMP/PEGDA hydrogels at polymer mass fractions of 0.25 and 0.375, respectively, were shown to be at EWC.

Synthesis of Stereoregular Uniform Oligomers Possessing a Dense 1,2,3-Triazole Backbone

Recent remarkable progress of precision polymerization techniques has allowed researchers to synthesize polymers of controlled molecular weight, tacticity, and monomer sequence with narrow distributions. However, it is still a challenging subject to synthesize uniform polymers and oligomers, which possess specific molecular weight, tacticity, and monomer sequence. Utilizing the advantages of t-butyl 4-azido-5-hexynoate (tBuAH), which we designed recently, for the synthesis of uniform polymers and oligomers, uniform oligomers of different stereoregularities possessing a dense 1,2,3-triazole backbone were synthesized using optically active tBuAH precursors by iterative procedures containing azidation, deprotection of the protecting group, and copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC). The stereoregular uniform oligomers were characterized in the solid state by powder X-ray diffraction (PXRD) and in the solution state by pulse-field-gradient spin-echo (PGSE) NMR, ultraviolet (UV) absorption, and circular dichroism (CD) spectroscopic techniques. While the solubility of stereoregular uniform oligomers was investigated using common organic solvents, gelation was observed for solutions of two octamers of different stereoregularities in some solvents, e.g., toluene, tetrahydrofuran (THF), acetone, and methanol. It is noteworthy that the intermolecular attractive interaction depended on the stereoregularity in aprotic polar solvents, i.e., THF and acetone, presumably because of the different polarities of octamers.

The structure and dynamics of bottlebrushes: Simulation and experimental studies combined

Bottlebrushes are complex macromolecular structures composed of polymer chains densely tethered to another polymer chain via a stable covalent bond linkage. Although numerous experimental techniques have been successfully applied for the characterization of bottlebrush polymers, some parameters still cannot be determined. Herein new simulation method using a dedicated machine was used to confront its applicability for complex macromolecules simulations. The bottlebrushes were synthesized by atom transfer radical polymerization (ATRP) with varied degree of polymerization (N) of the side chains, poly(methyl methacrylate) (PMMA). Poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) (PBiBEM) was used as macroinitiator with a degree of polymerization Nbb = 102. Degree of polymerization of side chains (Nsc) changed from 28 to 113. The bottlebrushes were characterized by Gel Permeation Chromatography – Multiangle Laser Light Scattering (GPC-MALLS), Pulsed-field Gradient Spin Echo Nuclear Magnetic Resonance (PGSE NMR), and combined Static and Dynamic Light Scattering methods (SLS-DLS). A novel calculation strategy via the Monte Carlo-class Dynamic Lattice Liquid (DLL) algorithm executed on a dedicated machine ARUZ was applied for theoretical studies. The experimental values concerning the scaling behavior of polymer size and dynamics were compared and confronted with simulation results.

Long-Range Li-Ion 3D Diffusion in the High-Temperature Hexagonal Phase of LiBH4 Studied by 7Li Pulsed Field Gradient NMR and MD Simulations

Lithium diffusion pathways have been determined in three dimensions using molecular dynamics simulations and 7Li pulsed-field gradient spin-echo (PGSE) NMR diffusometry. Lithium ions arrange in multiple hexagonally arranged and intertwined columns oriented at different angles on (001) surfaces. It has been found that lithium jumps are characterized by zig–zag patterns with the main diffusion tensor axis aligned along the [001] direction. Additional diffusion tensor dimensions appear in the (001) planes through multiple jumps along the [001] direction. The simulation results were confirmed by non-linear spin-echo attenuation in the 7Li PGSE NMR experiment and three-dimensional diffusion model developed for Li+-ion conductivity. The exact values of the main diffusion tensor components D⊥ = (D11 + D22)/2 and D∥ = D33 were derived from the uni-dimensional projection of diffusion tensor under macroscopic powder averaging condition. The single ionic jump in the [001] direction was related to D∥, while translation on the (001) plane required at least two jumps through the zig–zag path and related to D⊥. Lithium diffusion in the [001] direction is faster than that in the (001) planes. The activation energies for D⊥ and D∥ were determined between 105 and 130 °C and varied between 0.47 and 0.51 eV, which suggests that both diffusion coefficients are related to the same mechanism of the jump. Pre-exponential factors for D∥ and D⊥ were also determined and equal to 4.8 × 10–6 m2 s–1 for D∥ and 3.8 × 10–7 m2 s–1 for D⊥, respectively, which confirms that molecular translations between (001) surfaces are not performed in a single jump.

Studying the "Rigid-Flexible" Properties of Polymeric Micelle Core-Forming Segments with a Hydrophobic Phthalocyanine Probe Using NMR and UV Spectroscopy.

The aim of the performed studies was to thoroughly examine the internal structure of self-assembled nanocarriers (i.e., polymeric micelles—PMs) by means of a hydrophobic phthalocyanine probe in order to identify the crucial features that are required to enhance the photoactive probe stability and reactivity. PMs of hydrophilic poly(ethylene glycol) and hydrophobic poly(ε-caprolactone) (PCL) or poly(d,l-lactide) (PDLLA) were fabricated and loaded with tetra tert-butyl zinc(II) phthalocyanine (ZnPc-t-but4), a multifunctional spectroscopic probe with a profound ability to generate singlet oxygen upon irradiation. The presence of subdomains, comprising “rigid” and “flexible” regions, in the studied block copolymers’ micelles as well as their interactions with the probe molecules, were assessed by various high-resolution NMR measurements [e.g., through-space magnetic interactions by the 1D NOE effect, pulsed field gradient spin-echo, and spin–lattice relaxation time (T1) techniques]. The studies of the impact of the core-type microenvironment on the ZnPc-t-but4 photochemical performance also included photobleaching and reactive oxygen species measurements. ZnPc-t-but4 molecules were found to exhibit spatial proximity effects with both (PCL and PDLLA) hydrophobic polymer chains and interact with both subdomains, which are characterized by different rigidities. It was deduced that the interfaces between particular subdomains constitute an optimal host space for probe molecules, especially in the context of photochemical stability, photoactivity (i.e., for significant enhancement of singlet oxygen generation rates), and aggregation prevention. The present contribution proves that the combination of an appropriate probe, high-resolution NMR techniques, and UV–vis spectroscopy enables one to gain complex information about the subtle structure of PMs essential for their application as nanocarriers for photoactive compounds, for example, in photodynamic therapy, nanotheranostics, combination therapy, or photocatalysis, where the micelles constitute the optimal microenvironment for the desired photoreactions.

Structural and dynamic properties of some aqueous salt solutions.

Aqueous salt solutions are utilized and encountered in wide-ranging technological applications and natural settings. Towards improved understanding of the effect of salts on the dynamic properties of such systems, dilute aqueous salt solutions (up to 1 molar concentration) are investigated here, via experiments and molecular simulations. Four salts are considered: sodium chloride, for which published results are readily available for comparison, ammonium acetate, barium acetate and barium nitrate, for which published data are scarce. In the present work, molecular dynamics (MD) simulations are conducted to quantify viscosity and water self-diffusion coefficients, together with rheometry and Pulsed Field Gradient Spin Echo (PFGSE)-NMR experiments for validation. Simulation predictions are consistent with experimental observations in terms of trend and magnitude of salt-specific effects. Combining insights from the approaches considered, an interpretation of the results is proposed whereby the capacity of salts to influence bulk dynamics arises from their molecular interfacial area and strength of interaction with first hydration-shell water molecules. For the concentration range investigated, the interpretation could be useful in formulating aqueous systems for applications including the manufacturing of advanced catalysts.

Luminescent cyclometalated platinum(ii) complexes with acyclic diaminocarbene ligands: structural, photophysical and biological properties.

Four new cyclometalated Pt(ii) complexes bearing acyclic diaminocarbene (ADC) ligands, [Pt(C^N)Cl{C(NHXyl)(NHR)}] [C^N = 2,6-difluorophenylpyridine (dfppy), phenylquinoline (pq); R = Pr 3a, 4a, CH2Ph 3b, 4b], were prepared by the nucleophilic attack on the isocyanide [Pt(C^N)Cl(CNXyl)] (C^N = dfppy 1, pq 2) by the corresponding amine RNH2 (R = Pr, CH2Ph). Complexes 3 show in their 1H NMR spectra in CDCl3 a notable concentration dependence, with a clear variation of the δH (NHXyl) signal, suggesting an assembling process implying donor-acceptor NHXylCl bonding, also supported by 1D-PGSE (Pulse Field Gradient Spin Echo) and 2D-DOSY (Diffusion Ordered Spectroscopy) NMR experiments in solution and X-ray diffraction studies. The intermolecular interactions in compounds 3a and 3b were studied by using Hirshfeld surface analysis and Non-Covalent Interaction (NCI) methods on their X-ray structures. Their photophysical properties were investigated by absorption and emission spectroscopies and also by TD-DFT calculations performed on 3a and 4b. These complexes show green (3) or orange (4) phosphorescence, attributed to a mixed 3IL/3MLCT excited state. The carbene ligand does not affect the emission maxima but it produces an increase of the quantum yields in relation to the isocyanide in the precursors. In fluid solutions, the emission is not concentration-dependent, but the complexes may show aggregation induced emission as detailed for complexes 3a and 4a. In addition, cytotoxicity studies in the human cell lines A549 (lung carcinoma) and HeLa (cervix carcinoma) showed good activity for these complexes and 3a, 3b and 4a exhibit a strong effect on DNA electrophoretic mobility. To the best of our knowledge, compounds 3 and 4 represent the first examples of cycloplatinated complexes bearing acyclic diamino carbenes with antiproliferative properties.

Synthesis and characterization of bis(amine)palladium(II) carboxylate complexes as precursors of palladium nanoparticles.

The synthesis and characterization of the adducts of n-alkyl amine and palladium n-alkyl carboxylate, [Pd(R2NH2)2(R1COO)2] (R1 = 1, 7, and 11; R2 = 8, 12, and 16), as precursors for the synthesis of palladium nanoparticles (PdNPs) was carried out via differential scanning calorimetry, FT-IR, Raman and UV-Vis spectroscopy, NMR spectroscopy (1H, 13C pulsed field gradient spin-echo (PGSE), and 13C CP-MAS), and powder X-ray diffraction. Pd n-alkyl carboxylates were obtained by a ligand exchange reaction from palladium acetate and the appropriate aliphatic carboxylic acid. It is proposed that carboxyl moieties in the presence of amine ligands are bound to palladium ions via monodentate bonding as opposed to bridging bidentate coordination of pure palladium carboxylate which exists in the form of polymer aggregates. All the studied palladium carboxylate/amine complexes form bilayer lamellar structures and exhibit first-order melting transitions. The evidence presented in this study shows that the phase behavior of bivalent metal carboxylates is mainly controlled by the type of coordination of carboxylate head groups. For n-alkyl carboxylates, linear chain type aggregates replace the trimeric units of Pd acetate. In solution, in the presence of amine, palladium salt aggregates disintegrate and the Pd complex is isolated and stabilized by amine molecules. Using bis(amine) palladium carboxylate adducts as precursors, palladium nanoparticles were fabricated. During high temperature thermolysis, the bis(amine) Pd carboxylate complex decomposes to form small sized Pd nanoparticles. Combining NMR techniques with FTIR spectroscopy, it was possible to follow an original stabilization mechanism. PdNPs are stabilized by weakly interacting long chain aliphatic amide and carboxylic acid derived from the palladium precursor.

Proton conduction in hydronium solvate ionic liquids affected by ligand shape.

We investigated the ligand dependence of the proton conduction of hydronium solvate ionic liquids (ILs), consisting of a hydronium ion (H3O+), polyether ligands, and a bis[(trifluoromethyl)sulfonyl]amide anion (Tf2N-; Tf = CF3SO2). The ligands were changed from previously reported 18-crown-6 (18C6) to other cyclic or acyclic polyethers, namely, dicyclohexano-18-crown-6 (Dh18C6), benzo-18-crown-6 (B18C6) and pentaethylene glycol dimethyl ether (G5). Pulsed-field gradient spin echo nuclear magnetic resonance results revealed that the protons of H3O+ move faster than those of cyclic 18C6-based ligands but as fast as those of acyclic G5 ligands. Based on these results and density functional theory calculations, we propose that the coordination of a cyclic ether ligand to the H3O+ ion is essential for fast proton conduction in hydronium solvate ILs. Our results attract special interest for many electro- and bio-chemical applications such as electrolyte systems for fuel cells and artificial ion channels for biological cells.

Structure Effects on the Ionicity of Protic Ionic Liquids.

We report on the characterisation of 16 protic ionic liquids (PILs) prepared by neutralisation of primary or tertiary amines with a range of simple carboxylic acids, or salicylic acid. The extent of proton transfer was greater for simple primary amine ILs compared to tertiary amines. For the latter case, proton transfer was increased by providing a better solvation environment for the ions through the addition of a hydroxyl group, either on the tertiary amine, or by formation of PIL/molecular solvent mixtures. The library of PILs was characterised by differential scanning calorimetry and a range of transport properties (i. e. viscosity, conductivity and diffusivity) were measured. Using the (fractional) Walden rule, the conductivity and viscosity results were analysed with respect to their deviation from ideal behaviour. The validity of the Walden plot for PILs containing ions of varying sizes was also verified for a number of samples by directly measuring self-diffusion coefficients using pulsed-field gradient spin-echo (PGSE) NMR. Ionicity was found to decrease as the alkyl chain length and degree of branching of both the cations and anions was increased. These results aim to develop a better understanding of the relationship between PIL properties and structure, to help design ILs with optimal properties for applications.

Analysis of Mechanical Performance of Bitumen Modified with Waste Plastic and Rubber Additives by Rheology and Self Diffusion NMR Experiments

In this study, the mechanical and physico-chemical properties of a new kind of modified bitumen are presented. The bituminous binders have been modified in order to understand the effect on the structural properties of several compounds such as a Polymer elastomer as Styrene Butadiene Rubber (SBR), Polymer thermoplastic polypropylene (PP) and a waste plastic (Waste PP). Laboratory tests have been focused on the characterization of bitumen modified with single product and their binary combinations compared with pristine binder as a reference. Characterization has been conducted by using conventional as well as advanced methods on bitumens. Fundamental rheological tests, based on dynamic shear rheometer in the temperature range from -30 °C to +160 °C have been performed and the structure of a bitumens and modified bitumens has been analysed by the mobility of the oily maltene by self-diffusion Pulsed field gradient spin-echo (PGSE) FT-NMR experiments.

Self-Diffusion Coefficients of Coumaric and Caffeic Acids in Tetrachloromethane–Acetone-d6 Mixtures

The self-diffusion of p-coumaric and caffeic acids in a binary tetrachloromethane–acetone-d6 solution at low concentrations of the dissolved compound is studied via pulsed field gradient-spin echo 1H NMR at 278 and 298 K. According to the results, the self-diffusion coefficients of caffeic acid are lower than those of p-coumaric acid. The hydrodynamic radii of the acids in tetrachloromethane, calculated using the Stokes–Einstein equation, are lower than those in acetone-d6. This behavior is due to an increase in the degree of acid–acetone heteroassociation. Molecular association is also apparent from changes in the chemical shifts of protons in carboxyl and hydroxyl groups within molecules of the studied acids.

Evaluating the Ion Transport of 1-Ethyl-3-Methylimidazolium Acetate Solutions Containing Carbohydrate Solutes

This study evaluated the ion transport properties of 1-ethyl-3-methylimidazolium acetate (EMIAc)-based solutions containing additional acetonitrile (AN), H2O, and up to 3.0 wt-% carbohydrate solutes. Solution ion conductivity was directly measured via frequency response, and ion self-diffusivity coefficients determined via pulsed-field gradient spin-echo (PGSE) NMR. These data combined to determine solution ionicity. Multiple linear regression analysis shows ionicity is primarily impacted by the added neutral solvent, and weakly impacted by temperature. Addition of equimolar AN or H2O increases both cation and anion self-diffusivity (D+ and D−, respectively), and each of these solvent systems decreases the D+/D− quotient. Addition of carbohydrate solutes decreases cation and anion self-diffusivity, but solute additions slightly increase the D+/D− quotient. Our observation that carbohydrate solutes reduce Ac self-diffusivity by a greater fraction than EMI supports the general assertion that acetate anions are more heavily involved in solvating cellulose than EMI cations. Finally, EMIAc solutions containing microcrystalline cellulose (MCC) were evaluated by NMR spin-lattice relaxation (T1) measurements. These T1 data reveal the microviscosity of EMIAc:MCC solutions is virtually unchanged with addition of up to 3.0 wt-% solute, in agreement with the ion transport properties measured at the same scale.

Copper(I)-catalyzed azide–alkyne cycloaddition polymerization of N-butyl-N-ethynyl-4-azidobenzenesulfonamide

Aiming at synthesis of nonperiodic sequence-controlled polymers, we have been focusing on copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) polymerization of monomers possessing both azide and alkyne groups. For this purpose, we have chosen N-ethynyl-4-azidobenzenesulfonamide derivatives because the derivatives carrying various substituents can be prepared in a fewer steps using the corresponding starting materials, i.e., amines. In this study, we synthesized a new monomer, i.e., N-butyl-N-ethynyl-4-azidobenzenesulfonamide (BuEA), and carried out its dimerization and polymerization by CuAAC using a pair of copper(II) sulfate pentahydrate and sodium ascorbate. A dimer of BuEA was successfully obtained from the monomer precursors possessing azide and ethynyl groups, respectively. This observation indicates that N-ethynyl-4-azidobenzenesulfonamide derivatives are applicable to synthesis nonperiodic sequence-controlled polymers. The polymer obtained (poly(BuEA)) was well soluble in common organic solvents, e.g., dimethyl sulfoxide, N,N-dimethylformamide, tetrahydrofuran (THF), chloroform, and dichloromethane. Solution properties of poly(BuEA) were also investigated. Pulse-field-gradient spin-echo (PGSE) NMR data in THF-d8 indicated that poly(BuEA) chain takes a compact conformation. Steady state fluorescence study exhibited that poly(BuEA) emitted weak fluorescence based on the monomer unit.

Investigations of Anion Exchange Polymer – Catalyst Interfacial Interactions

Anion exchange membrane (AEM) fuel cells offer a promising alternative to proton exchange membrane fuel cells. AEMs utilize more facile electrochemical reaction kinetics by operating in a basic environment, which should theoretically allow them to utilize non-precious metal catalysts such as silver or nickel. This research focuses on the characterization of a novel block copolymer AEM and elucidating the anion exchange polymer-catalyst interface. The block copolymer system has been engineered to combine the features of high ion conductivity of a hydrophilic block with the reinforcing properties of a hydrophobic block. The ABA triblock polymer utilizes a polychloromethylstyrene-b-polypolycyclooctene-b-polychloromethylstyrene (PCMS-PCOE-PCMS) backbone and dimethylpiperidinium (MPRD) cation, which has shown excellent hydroxide stability. This work aims to first understand the bulk properties of the polymer and then subsequently compare them to the properties of the material at the catalyst interface, where potential interactions could lead to restructuring of the polymer and thus alter the transport of water, hydroxide, fuel, and electrical conduction. This will be studied by fabricating well-defined interfaces between the polyelectrolytes and catalyst surface, either as thin films on an electroactive surface of silver (Ag) or in a constrained environment of Ag colloids. If the volume fraction of Ag colloids is small, the polymer properties will be representative of those at the polymer-catalyst interface. In-plane conductivity will be measured by EIS using a four fine Pt wire electrode fixture, from which an activation energy of aqueous ionic movement can also be derived. To further understand how the mechanical properties of the polymer are affected at the catalyst interface, dynamic vapor sorption will be used assess water content as a function of relative humidity (RH) and thermogravimetric analysis will be used to determine thermal properties. Additionally, morphological changes and restructuring at the catalyst interface as a function of RH will be elucidated using AFM and GISAXS. The information obtained from these techniques will determine whether the polymer is aligned with the catalyst surface. Pulse field gradient spin echo (PFGSE) NMR spectroscopy will be used to study the movement of water molecules (1H NMR), carbonate and bicarbonate (13C NMR), and fluoride (19F NMR). When performed at varying temperature and RH, self-diffusion coefficients can be obtained, and the tortuosity of the transport pathway can be estimated. ATR FTIR spectroscopy will also be used to investigate the nature of the water content and compare it between the bulk polymer and polymer-catalyst interface. Cyclic voltammetry using a bipolar membrane fuel cell will also be used to study the adsorption and desorption on the catalyst layer. The characterization of the polymer-catalyst interface and further understanding of any restructuring that occurs will provide a knowledge base for optimizing the design of an AEM.

Deep Eutectic Solvents formed by chiral components as chiral reaction media and studies of their structural properties

We present the realization, the use as reaction media/chiral organocatalysts/acid catalysts and the structural properties of novel chiral Deep Eutectic Solvents. These liquids are formed by mixtures of chiral HBD and HBA molecules that are common, relatively cheap and commercially available (the two enantiomers of camphorsulfonic acid as HBD) or easily one-step synthesized molecules from commercially available compounds ((S)- and (R)-N,N,N-trimethyl-(1-phenylethyl)ammonium methanesulfonate as HBA). These liquids proved to be highly-structured as showed by different yields and enantiomeric excesses observed in a probe reaction, suggesting these liquids to form diastereoisomerically different liquids by changing one of the two enantiomers. Their structural features were analyzed via 1H Pulsed Field gradient Spin Echo (PGSE) NMR, NMR titration, 1H NMR analyses of formation and differences in the chemical shifts of the peaks of the liquids. Density Functional Theory (DFT) optimization helped to define the structures of these liquids. The methanesulfonate counterion of HBA molecule showed to be relevant in order to obtain these highly-structured liquids as it interacts specifically with the HBD. These chiral Deep Eutectic Solvents revealed to be promising novel high-structured media for enantioselective reactions.

Solvent-Dependent Hemilability of (2-Diphenylphosphino)Phenol in a Ru(II) para-Cymene System

The addition of Ph2P(2-C6H4OH) to [(η6-p-cymene)RuCl(μ-Cl)]2 led to the formation of three distinct products, depending on the experimental conditions. The previously reported [(η6-p-cymene)RuCl{κ2P,O-PPh2(2-C6H4O)}], 1, was obtained in 90% yield using MeOH as the solvent, in the presence of a base (Et3N). Conversely, [(η6-p-cymene)RuCl{κ2P,O-PPh2(2-C6H4OH)}]Cl, [2]Cl, was afforded (88% yield) in MeOH without using the base. However, [(η6-p-cymene)RuCl2{κP-PPh2(2-C6H4OH)}], 3, was the major species in chlorinated solvents. Compounds 1, [2]Cl, and 3 were characterized by analytical and spectroscopic (IR, NMR) methods. The X-ray structures of [2]+ and 3 were determined, with the latter forming hydrogen bond dimeric units in the solid state. The dissolution of [2]Cl into a series of deuterated solvents, except methanol, led to rapid equilibration between [2]Cl and 3, revealing the hemilabile behavior of the phosphino-phenol ligand. According to Pulsed-Field Gradient Spin Echo (PGSE)-NMR and DFT studies, the ...

Comparison of the Effects of Different 19F π Pulses on the Sensitivity and Phaseability of the 19F-13C HSQC

The 19F-13C heteronuclear single quantum coherence (HSQC) experiment is vital for the structural elucidation of polyfluorinated organic species, yet its sensitivity and phaseability are limited by difficulties in uniform excitation of the widely disperse 19F spectral window. Adiabatic pulses of different types have previously been employed to generate effective π pulses for inversion and refocussing, but a systematic comparison of various adiabatic and other inversion pulses has not been published. In this work, it was observed that the use of a broadband inversion pulse (BIP) during the t 1 evolution period resulted in properly phaseable spectra for experiments optimized to detect 1 J CF, in contrast to CHIRP or WURST adiabatic pulses. For the INEPT and reverse-INEPT transfer segments of the HSQC, optimal sensitivity for resonances distant from the transmitter frequency was afforded by optimized universal rotation (BURBOP) or CHIRP pulses. In HSQC experiments with delays optimized for two-bond correlations, only the use of BURBOP pulses in INEPT and reverse-INEPT sequences afforded spectra cleanly phaseable across the F 2 and F 1 spectral windows. This observation is supported by off-resonance pulsed field gradient spin-echo experiments.