Pulsed Field Gradient NMR Research Articles

Advanced Nuclear Magnetic Resonance Techniques for Characterizing Ionic Liquids for Lithium Ion Battery Applications; High Presssure NMR and Fast Field Cycling Relaxometry

Ionic liquids (ILs) have received widespread acclaim for their potential use as a safe and effective alternative to unstable and flammable organic solvents used in electrolytes for lithium-ion secondary batteries. The thermal and chemical stability of ILs, as well as the tunable properties of ILs by altering cation and anion species, have made them promising materials for use in multiple applications: such as textile dyeing, nuclear waste recycling, and solar cells. A limiting characteristic for IL use in secondary lithium-ion batteries is a notable lower ionic conductivity in most known species. Characterizing the effect of cation and anion structure on ionic diffusion in ILs, as well as studying molecular dynamics in IL species is of great importance for increasing their potential utility in battery chemistries. To this end, the techniques of Fast Field Cycling Nuclear Magnetic Resonance (FFCNMR) and pressure dependent NMR diffusometry are used to study ionic liquid species of interest. Fast field cycling measurements of spin-lattice relaxation times (T1) allow for access to time dependent molecular dynamics in ionic systems, as functions of both magnetic field strength and temperature. FFC measurements are complementary to high-pressure NMR experiments, which reveal pressure dependence of reorientation and tumbling processes, as well as the effects of alkyl chain length on ionic mobility in specific species. Presented here is the application of these two techniques to 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (CnMIM TFSA) ILs. Specifically, a selectively deuterated species of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) is observed and characterized. FFC results were used to extract cation self-diffusion coefficients, showing good agreement with Pulse Field Gradient (PFG) NMR measurements. High pressure T1 data on selectively deuterated cation isotopologues revealed site dependent interactions on the cation alkyl chain. The work at BNL (JFW and JH) was supported by the US-DOE Office of Science, Division of Chemical Sciences, Geosciences and Biosciences under contract DE-SC0012704.

NMR Transport Study of LiPF6 and NaPF6 in Glymes for Use in Supercapacitors

Electric double-layer capacitors (EDLC) store ionic charge electrostatically at the interface of high surface area electrodes such as carbon in a liquid electrolyte. Despite significant improvements in electrode and materials design, virtually all state-of-the-art nonaqueous electrochemical capacitors use the same electrolyte: tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile (ACN). This electrolyte has an exceptionally high conductivity which minimizes resistive losses and enables capacitors to operate at very high power. However, this electrolyte has a practical voltage window around only 2.7 V, beyond which the capacitor lifetime is significantly shortened. Since the energy stored in a capacitor increases quadratically with voltage, extending this electrochemical window could significantly improve the energy density. In this study we report on electrolytes consisting of LiPF6 or NaPF6 in tetraethylene glycol dimethyl ether (TEGDME or tetraglyme or G4), bis(2-methoxyethyl) ether (diglyme, or G2) and dimethoxyethane (DME or G1) which clearly show a 4 V electrochemical window. The extended voltage window doubles the energy density that can be achieved with any given capacitor electrode. Electrolyte conductivities range from 1-10 mS/cm, which are comparable to ionic liquids and adequate for moderate power applications. Futhermore, glyme-based electrolytes have good chemical stability and low flammability. Importantly, all salts and solvents are commercially available, which should enable these electrolytes to be as cost-effective and scalable as the current generation of commercial supercapacitor electrolytes. NMR experiments were performed on 0.1m LiPF6 and 0.1m/0.8m NaPF6, each dissolved in G1, G2, and G4. Using Pulsed Field Gradient (PFG) NMR, the solvent and ionic self-diffusion coefficients, D, of 1H, 7Li, 19F, and 23Na were measured, at both 25°C and 60°C. As NMR does not distinguish between the movement of single ions and ion pairs, it can be difficult to accurately determine the true conductivity of the material. However, the diffusion measurements were used to find the limiting conductivity, σNMR , of each material via the Nernst-Einstein equation: σNMR = F2[C]/(RT)*(Dcation+Danion) Direct comparison with conductivity values obtained by electrochemical impedance spectroscopy measurements yields the degree of ion association, α: α = 1 - (σdirect/σNMR) Both diffusion and conductivity decrease with increasing solvent size, primarily attributed to viscosity effects. However the degree of ion association is significant, determined to be 85% for both 0.1m LiPF6 and 0.1m NaPF6 in G2. In glyme solvents, ion association tends to decrease with increasing solvent molecular mass, and increase with increasing temperature. These results will be discussed in the context of practical use of glyme-based electrolytes for electrochemical capacitors.

Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries

We report on the synthesis of poly(diethylene oxide-alt-oxymethylene), P(2EO-MO), via cationic ring-opening polymerization of the cyclic ether monomer, 1,3,6-trioxocane. We use a combined experimental and computational approach to study ion transport in electrolytes comprising mixtures of P(2EO-MO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Mixtures of poly(ethylene oxide) (PEO) and LiTFSI are used as a baseline. The maximum ionic conductivities, σ, of P(2EO-MO) and PEO electrolytes at 90 °C are 1.1 × 10^(–3) and 1.5 × 10^(–3) S/cm, respectively. This difference is attributed to the T_g of P(2EO-MO)/LiTFSI (−12 °C), which is significantly higher than that of PEO/LiTFSI (−44 °C) at the same salt concentration. Self-diffusion coefficients measured using pulsed-field gradient NMR (PFG-NMR) show that both Li+ and TFSI– ions diffuse more rapidly in PEO than in P(2EO-MO). However, the NMR-based cation transference number in P(2EO-MO) (0.36) is approximately twice that in PEO (0.19). The transference number measured by the steady-state current technique, t_(+,ss), in P(2EO-MO) (0.20) is higher than in PEO (0.08) by a similar factor. We find that the product σt_(+,ss) is greater in P(2-EO-MO) electrolytes; thus, P(2EO-MO) is expected to sustain higher steady-state currents under dc polarization, making it a more efficacious electrolyte for battery applications. Molecular-level insight into the factors that govern ion transport in our electrolytes was obtained using MD simulations. These simulations show that the solvation structures around Li+ are similar in both polymers. The same is true for TFSI–. However, the density of Li+ solvation sites in P(2EO-MO) is double that in PEO. We posit that this is responsible for the observed differences in the experimentally determined transport properties of P(2EO-MO) and PEO electrolytes.

Adhesion/growth-regulatory galectins tested in combination: evidence for formation of hybrids as heterodimers.

The delineation of the physiological significance of protein (lectin)-glycan recognition and the structural analysis of individual lectins have directed our attention to studying them in combination. In this report, we tested the hypothesis of hybrid formation by using binary mixtures of homodimeric galectin-1 and -7 as well as a proteolytically truncated version of chimera-type galectin-3. Initial supportive evidence is provided by affinity chromatography using resin-presented galectin-7. Intriguingly, the extent of cell binding by cross-linking of surface counter-receptor increased significantly for monomeric galectin-3 form by the presence of galectin-1 or -7. Pulsed-field gradient NMR (nuclear magnetic resonance) diffusion measurements on these galectin mixtures indicated formation of heterodimers as opposed to larger oligomers. 15N-1H heteronuclear single quantum coherence NMR spectroscopy and molecular dynamics simulations allowed us to delineate how different galectins interact in the heterodimer. The possibility of domain exchange between galectins introduces a new concept for understanding the spectrum of their functionality, particularly when these effector molecules are spatially and temporally co-expressed as found in vivo.

Study of Dispersion in Porous Media by Pulsed Field Gradient NMR: Influence of the Fluid Rheology

Pulsed field gradient nuclear magnetic resonance (PFG-NMR) is used to measure the molecular displacements for the flow of a fluid through a capillary tube and a packed bed made of monodisperse PMMA beads. The molecules average displacement is studied using both the formalism of propagators and the cumulant method. In the Poiseuille case, the dispersion coefficients determined by the cumulant method compare satisfactorily with the theoretical values obtained. The technique is then extended to study the flow through a porous medium. We thus analyze Newtonian (water) and non-Newtonian (Xanthan) flows and put a particular emphasis on comparing the dispersion mechanisms between Newtonian and non-Newtonian fluids.

Effect of CO2 absorption on ion and water mobility in an anion exchange membrane

We report the measured water uptake, density, ionic conductivity and water transport properties in Tokuyama A201 membrane in OH−, HCO3− and Cl− forms. The water uptake of the AEM varies with anion type in the order λ(OH−) > λ(HCO3−) > λ(Cl−) for samples equilibrated with the same water vapor activity (aw). The conductivity of the AEM is reduced by absorption of CO2. Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) measurements were utilized to characterize the diffusivity of water and HCO3− ion. The anion diffusion coefficient and membrane conductivity are used to probe the applicability of the Nernst-Einstein equation in these AEMs.

Tracing compartment exchange by NMR diffusometry: Water in lithium-exchanged low-silica X zeolites

The two-region model for analyzing signal attenuation in pulsed field gradient (PFG) NMR diffusion studies with molecules in compartmented media implies that, on their trajectory, molecules get from one region (one type of compartment) into the other one with a constant (i.e. a time-invariant) probability. This pattern has proved to serve as a good approach for considering guest diffusion in beds of nanoporous host materials, with the two regions (“compartments”) identified as the intra- and intercrystalline pore spaces. It is obvious, however, that the requirements of the application of the two-region model are not strictly fulfilled given the correlation between the covered diffusion path lengths in the intracrystalline pore space and the probability of molecular “escape” from the individual crystallites. On considering water diffusion in lithium-exchanged low-silica X zeolite, we are now assuming a different position since this type of material is known to offer “traps” in the trajectories of the water molecules. Now, on attributing the water molecules in the traps and outside of the traps to these two types of regions, we perfectly comply with the requirements of the two-region model. We do, moreover, benefit from the option of high-resolution measurements owing to the combination of magic angle spinning (MAS) with PFG NMR. Data analysis via the two-region model under inclusion of the influence of nuclear magnetic relaxation yields satisfactory agreement between experimental evidence and theoretical estimates. Limitations in accuracy are shown to result from the fact that mass transfer outside of the traps is too complicated for being adequately reflected by simple Fick’s laws with but one diffusivity.

Poly(alkyl methacrylate)-Grafted Polyolefins as Viscosity Modifiers for Engine Oil: A New Mechanism for Improved Performance

Lubricant additives based on graft copolymers with polyolefin backbones and poly(alkyl methacrylate) side chains were examined for their viscosity modifying behavior in base oil. A combination of ring-opening metathesis polymerization, atom transfer radical polymerization of alkyl methacrylates, and hydrogenation was used to prepare the target materials. Viscometric measurements reveal that larger side chain molar mass provides better thickening efficiency. More importantly, increasing the side chain polarity favorably impacts the performance of these graft copolymers as viscosity modifiers. While competitive modifiers must simultaneously meet several technical requirements, the most promising graft copolymer exhibits similar or larger viscosity index at a lower concentration (treat rate) compared to state-of-the-art polymeric additives. This feature bodes well for future additive design. Dynamic light scattering and pulsed field gradient NMR on dilute solutions of the graft copolymer in dodecane (a model oil) consistently show a significant (∼30 nm) decrease in the hydrodynamic radius of the copolymer upon heating from 40 to 100 °C, in conflict with the prevailing assumed viscosification mechanism of coil expansion upon heating. Small angle neutron scattering experiments suggest that the graft copolymer chains may associate to give clusters containing methacrylate-rich domains at lower temperatures due to the solubility of the hydrocarbon backbone and insolubility of the polymethacrylate side chains. We posit that, at elevated temperatures, deaggregation into single chains occurs due to the increased solubility of the side chains. This declustering process results in an overall increase in the hydrodynamic volume of the dispersed polymers, which presumably leads to an improved viscosity modification behavior in engine oil.

Unexpected Diffusion Anisotropy of Carbon Dioxide in the Metal-Organic Framework Zn2(dobpdc).

Metal-organic frameworks are promising materials for energy-efficient gas separations, but little is known about the diffusion of adsorbates in materials featuring one-dimensional porosity at the nanoscale. An understanding of the interplay between framework structure and gas diffusion is crucial for the practical application of these materials as adsorbents or in mixed-matrix membranes, since the rate of gas diffusion within the adsorbent pores impacts the required size (and therefore cost) of the adsorbent column or membrane. Here, we investigate the diffusion of CO2 within the pores of Zn2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations. The residual chemical shift anisotropy for pore-confined CO2 allows PFG NMR measurements of self-diffusion in different crystallographic directions, and our analysis of the entire NMR line shape as a function of the applied field gradient provides a precise determination of the self-diffusion coefficients. In addition to observing CO2 diffusion through the channels parallel to the crystallographic c axis (self-diffusion coefficient D∥ = (5.8 ± 0.1) × 10-9 m2 s-1 at a pressure of 625 mbar CO2), we unexpectedly find that CO2 is also able to diffuse between the hexagonal channels in the crystallographic ab plane (D⊥ = (1.9 ± 0.2) × 10-10 m2 s-1), despite the walls of these channels appearing impermeable by single-crystal X-ray crystallography and flexible lattice MD simulations. Observation of such unexpected diffusion in the ab plane suggests the presence of defects that enable effective multidimensional CO2 transport in a metal-organic framework with nominally one-dimensional porosity.

Anisotropic Ion Diffusion and Electrochemically Driven Transport in Nanostructured Block Copolymer Electrolytes.

Nanostructured block copolymer electrolytes have the potential to enable solid-state batteries with lithium metal anodes. We present complete continuum characterization of ion transport in a lamellar polystyrene-b-poly(ethylene oxide) copolymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte as a function of salt concentration. Electrochemical measurements are used to determine the Stefan-Maxwell salt diffusion coefficients [Formula: see text], [Formula: see text], and [Formula: see text]. Individual self-diffusion coefficients of the lithium- and TFSI-containing species were measured by pulsed-field gradient NMR (PFG-NMR). The NMR data indicate that salt diffusion is locally anisotropic, and this enables determination of a diffusion coefficient parallel to the lamellae, D∥, and a diffusion coefficient through defects in the lamellae, D⊥. We quantify anisotropic diffusion by defining an NMR morphology factor and demonstrate that it is correlated to defect density seen by transmission electron microscopy. We find agreement between the electrochemically determined Stefan-Maxwell diffusion coefficients and the diffusion coefficient D⊥ determined by PFG-NMR. Our work indicates that the performance of nanostructured block copolymer electrolytes in batteries is strongly influenced by ion transport through defects.

Diffusion of methyl oleate in hierarchical micro-/mesoporous TS-1-based catalysts probed by PFG NMR spectroscopy.

Pulsed field gradient (PFG) NMR is successfully applied to trace the diffusion of methyl oleate (MO) inside the mesopores of hierarchically structured titanium silicalite-1 (TS-1)-based catalysts. Introduction of mesoporosity by post-synthetic treatment of initially microporous TS-1 provides additional active surface to improve catalytic activity in the epoxidation of MO. The present study provides experimental evidence of the accessibility of mesopores for MO resulting from alkaline treatment of TS-1. The self-diffusion coefficients of MO inside the pores of hierarchically structured TS-1 catalysts are up to two orders of magnitude lower compared to the values in the bulk liquid phase. Additionally, the methodological capability of PFG NMR for measuring self-diffusion coefficients of long-chain hydrocarbons (up to C19) confined to narrow mesopores of catalytically active is demonstrated for the first time.

Ethane diffusion in mixed linker zeolitic imidazolate framework-7-8 by pulsed field gradient NMR in combination with single crystal IR microscopy.

Pulsed field gradient (PFG) NMR was used in combination with single crystal IR microscopy (IRM) to study diffusion of ethane inside crystals of a mixed linker zeolitic imidazolate framework (ZIF) of the type ZIF-7-8 under comparable experimental conditions. These crystals contain 2-methylimidazolate (ZIF-8 linker) and benzimidazolate (ZIF-7 linker). It was observed that the PFG NMR attenuation curves measured for ethane in ZIF-7-8 exhibit deviations from the monoexponential behaviour, thereby indicating that the ethane self-diffusivity in different crystals of a crystal bed can be different. Measurements of the ethane uptake curves performed by IRM under the same conditions in different ZIF-7-8 crystals of the bed yield different transport diffusivities thus confirming that the rate of ethane diffusion is different in different ZIF-7-8 crystals. The IRM observation that the fractions of ZIF-8 and ZIF-7 linkers are different in different ZIF-7-8 crystals allowed attributing the observed heterogeneity in diffusivities to the heterogeneity in the linker fraction. The quantitative comparison of the average ethane self-diffusivities measured by PFG NMR in ZIF-7-8 with the corresponding data on corrected diffusivities from IRM measurements revealed a good agreement between the results obtained by the two techniques. In agreement with the expectation of smaller aperture sizes in ZIF-7-8 than in ZIF-8, the average ethane self-diffusivities in ZIF-7-8 were found to be significantly lower than the corresponding self-diffusivities in ZIF-8.

Inelastic and quasi-elastic neutron scattering. Application to soft-matter

Microscopic dynamical events control many of the physical processes at play in condensed matter: transport, magnetism, catalysis and even function of biological assemblies. Inelastic (INS) and Quasi-Elastic Neutron Scattering (QENS) are irreplaceable probes of these phenomena. These experimental techniques reveal the displacements of atoms and molecules over distances spanning from angstroms to a few tens of nanometers, on time scales ranging from a fraction of picoseconds to microseconds. In this context, the different INS and QENS machines (Time-of-Flight (ToF), Backscattering (BS) and Neutron spin-echo (NSE)) stand at a central position. After introducing an underlying basic theoretical toolbox for neutron scattering, the principles and key elements of a ToF measurement are described. While, here, we mainly focus on disk choppers spectrometers, all the INS/QENS instruments share a common ground: they directly and simultaneously probe correlation functions in both time and space, so that the scattering vector (Q) dependence of the systems characteristic time(s) can be measured. To illustrate, the potentialities of the technique in the field of soft-matter, we show a multiscale approach of the dynamics of a polymer melt. The system is probed from the molecular to the mesoscopic scale (1 ps to 0.6 μs and 0.1 to 40 nm), in bulk and under nanometric confinement. We address the different dynamical modes of a high mass entangled polymer chain: local monomer dynamics, Rouse modes up to the reptation process. This study exemplifies that, used in conjunction with hydrogen/deuterium isotopic effects, high resolution QENS can be bridged to the Zero Average Contrast (ZAC) method to probe, in a non destructive way, the dynamics of a single polymer chain in bulk but also under severe nanometric confinement. Connection and complementarity of the neutron derived analysis with Pulsed-Field Gradient and Relaxation NMR techniques are discussed.

Self-Diffusion and Heteroassociation in an Acetone–Chloroform Mixture at 298 K

The self-diffusion coefficients of acetone and chloroform in a binary acetone–chloroform mixture at 298 K are determined via pulsed field gradient NMR spectroscopy. It is estimated that the hydrodynamic radii of the mixture’s components, calculated using the Stokes–Einstein equation, grow as the concentrations of the components fall. It is shown that such behavior of hydrodynamic radii is due to acetone–chloroform heteroassociation. The hydrodynamic radii of monomers and heteroassociates in a 1: 1 ratio are determined along with the constant of heteroassociation, using the proposed model of an associated solution.

Toward understanding of ion dynamics in highly conductive lithium ion conductors: Some perspectives by solid state NMR techniques

Solid state lithium ion conductors are promising to replace the organic liquid electrolytes for a safer and long cycle-life lithium battery. However, solid electrolytes are still not fully explored and need extensive basic studies to understand their intrinsic conducting mechanism and interfacial properties between electrodes and electrolytes. In this review, we highlight the latest progresses in the research of lithium ion conductors by using advanced solid state nuclear magnetic resonance(SS NMR) spectroscopy, i.e. Magic angle spinning (MAS) NMR, pulsed-field gradient (PFG) NMR, spin-lattice(SLR) as well as spin-spin relaxation NMR, spin alignment echo (SAE) NMR and two-dimensional exchange (2D EXSY) NMR, and briefly review the application of these solid NMR techniques in LISICON-, NASICON- and Garnet-type lithium ion conductors in the different time/length scales, as well as the measurement in the determination of ion occupancy, ion diffusion pathways, and diffusion coefficients.

Transport and Association of Ions in Lithium Battery Electrolytes Based on Glycol Ether Mixed with Halogen-Free Orthoborate Ionic Liquid

Ion transport behaviour of halogen-free hybrid electrolytes for lithium-ion batteries based on phosphonium bis(salicylato)borate [P4,4,4,8][BScB] ionic liquid mixed with diethylene glycol dibutyl ether (DEGDBE) is investigated. The Li[BScB] salt is dissolved at different concentrations in the range from 0.15 mol kg−1 to 1.0 mol kg−1 in a mixture of [P4,4,4,8][BScB] and DEGDBE in 1:5 molar ratio. The ion transport properties of the resulting electrolytes are investigated using viscosity, electrical impedance spectroscopy and pulsed-Field Gradient (PFG) NMR. The apparent transfer numbers of ions are calculated from the diffusion coefficients measured by using PFG NMR. PFG NMR data suggested ion association upon addition of Li salt to the [P4,4,4,8][BScB] in DEGDBE solution. This is further confirmed by liquid state 7Li and 11B NMR, and FTIR spectroscopic techniques, which suggest strong interactions between the lithium cation and oxygen atoms of the [BScB]− anion in the hybrid electrolytes.

Direct Observation of Two Distinct Diffusive Modes for Polymer Rings in Linear Polymer Matrices by Pulsed Field Gradient (PFG) NMR

Using high resolution PFG NMR spectroscopy, we have studied the diffusion of well-characterized polymer rings in linear host matrices at various observation times Δ, varying both ring and host molecular weights. For the first time, to our knowledge, for higher Mw rings in entangled melts it was possible to directly distinguish two different diffusive modes: (i) fast diffusion that scales inversely with the host chain length and (ii) much slower diffusion depending much more strongly on the host molecular weight. Furthermore, we studied the diffusion of the linear chains in the host melts. The diffusion data were analyzed in terms of existing theories and compared to simulations. The two-mode structure directly verifies the hypothesis of qualitatively different mechanisms for ring diffusion in linear melts. The fast mode quantitatively agrees with the assertion of a special diffusion channel for once threaded rings, while the suggested diffusion of unthreaded rings was not found. The slow mode scales more ...

Ionic strength-dependent pre-asymptoic diffusion coefficient distribution in porous media - Determination through the pulsed field gradient technique

1H pulsed-field gradient nuclear magnetic resonance was used to study early-time water diffusivity in porous media. The method has also been proven useful to characterize porous media from the standpoint of time-dependent diffusion. In porous media such as zeolite, biological cells or reservoir rocks, water molecular diffusion is time-as well as ionic strength-dependent. Diffusion phenomena are relevant transport mechanisms in low-permeability gas reservoirs and consequently in characterization efforts. Model systems are used here to unveil effects of ionic strength and pore size on the self- and effective-diffusion coefficient distributions. For this purpose, diffusion in aqueous phase in beadpacks made up of different glass bead sizes is analyzed. Ion size, ionic strength and hydration play an important role on the resulting diffusion coefficient. Ion-ion interaction leads to an increase of the diffusion coefficient by distorting water structure (hydrogen bond). While for the diffusion coefficient distribution derived using the regularized Inverse Laplace Transform method, ionic strength has little effect on the dominant peak position. With the increase in pore size, the dominant peak shifts to larger diffusion coefficient.

Monitoring the Diffusivity of Light Hydrocarbons in a Mixture by Magic Angle Spinning Pulsed Field Gradient NMR: Methane/Ethane/Ethene in ZIF-8

1H MAS PFG NMR was applied for the measurement of the diffusivities in a three-component mixture of the light hydrocarbons: methane, ethane and ethene, which were absorbed in the micropores of ZIF-8 MOF. It has been found that diffusivity in mixture increases in the order: ethane < ethene < methane with variance of self-diffusion coefficients D from 0.22×10-10 m2 s-1 for ethane to 1.96×10-10 m2 s-1 for methane at 313 K. This tendency in increasing of diffusivity from ethane to methane is similar to the tendency for individual hydrocarbons. It is concluded that the interaction of a hydrocarbon with the micropore wall of the ZIF-8 framework influences the mobility rather than the intermolecular hydrocarbon interaction. The latter plays no role for the molecules, when they overcome the energy barrier of the window connecting neighbor cages. The activation energies Ea for diffusivity of the hydrocarbons in mixture increases in the order: methane (Ea =2.4 kJ mol-1 ) < ethene (Ea =7.2 kJ mol-1 ) < ethane (Ea =1...

Synthesis and Solution-Phase Characterization of Sulfonated Oligothioetheramides.

Nature has long demonstrated the importance of chemical sequence to induce structure and tune physical interactions. Investigating macromolecular structure and dynamics is paramount to understand macromolecular binding and target recognition. To that end, we have synthesized and characterized flexible sulfonated oligothioetheramides (oligo-TEAs) by variable temperature pulse field gradient (PFG) NMR, double electron-electron resonance (DEER), and molecular dynamics (MD) simulations to capture their room temperature structure and dynamics in water. We have examined the contributions of synthetic length (2-12mer), pendant group charge, and backbone hydrophobicity. We observe significant entropic collapse, driven in part by backbone hydrophobicity. Analysis of individual monomer contributions revealed larger changes due to the backbone compared to pendant groups. We also observe screening of intramolecular electrostatic repulsions. Finally, we comment on the combination of DEER and PFG NMR measurements via Stokes-Einstein-Sutherland diffusion theory. Overall, this sensitive characterization holds promise to enable de novo development of macromolecular structure and sequence-structure-function relationships with flexible, but biologically functional macromolecules.