INVESTIGATING MITOCHONDRIA PENETRATING PEPTIDES WITH SOLID STATE NMR USING MODEL MEMBRANES

Penetrating peptides are unique peptides that can translocate across membranes in a non-lytic fashion. A new class of penetrating peptides that can target the mitochondria with high specificity have been developed. Targeting the mitochondria is therapeutically valuable, given the organelle’s role in energy production and apoptosis. The peptide we studied is sufficiently cationic and hydrophobic and is hypothesized to reach the mitochondrial matrix. However, the mechanism of translocation remains unknown. In our work, we use solid state NMR to gain insight into the mechanism of translocation of this mitochondria-penetrating peptide. We use static 31P NMR the membrane morphology and peptide-induced structure changes. The paramagnetic relaxation effect examined through 13C MAS NMR was used for insertion depth determination and to distinguish bilayer sidedness. We found that the peptide does not disrupt the lamellarity. Also, at low peptide concentrations the peptide binds to the outer leaflet and at high concentrations crosses the hydrophobic bilayer core and is distributed in both leaflets. Our findings support the electroporation model of translocation, but we did not observe complete translocation of the peptide. We examine the energy associated with crossing the inner mitochondrial membrane to determine the feasibility of the peptide reaching the mitochondrial matrix

Niobium tungsten oxides for high-rate lithium-ion energy storage.

The maximum power output and minimum charging time of a lithium-ion battery depend on both ionic and electronic transport. Ionic diffusion within the electrochemically active particles generally represents a fundamental limitation to the rate at which a battery can be charged and discharged. To compensate for the relatively slow solid-state ionic diffusion and to enable high power and rapid charging, the active particles are frequently reduced to nanometre dimensions, to the detriment of volumetric packing density, cost, stability and sustainability. As an alternative to nanoscaling, here we show that two complex niobium tungsten oxides-Nb16W5O55 and Nb18W16O93, which adopt crystallographic shear and bronze-like structures, respectively-can intercalate large quantities of lithium at high rates, even when the sizes of the niobium tungsten oxide particles are of the order of micrometres. Measurements of lithium-ion diffusion coefficients in both structures reveal room-temperature values that are several orders of magnitude higher than those in typical electrode materials such as Li4Ti5O12 and LiMn2O4. Multielectron redox, buffered volume expansion, topologically frustrated niobium/tungsten polyhedral arrangements and rapid solid-state lithium transport lead to extremely high volumetric capacities and rate performance. Unconventional materials and mechanisms that enable lithiation of micrometre-sized particles in minutes have implications for high-power applications, fast-charging devices, all-solid-state energy storage systems, electrode design and material discovery.K.J.G. gratefully acknowledges support from The Winston Churchill Foundation of the United States, the Herchel Smith Scholarship, and the Science and Technology Facilities Council Futures Early Career Award. K.J.G and C.P.G thank the EPSRC via the LIBATT grant (EP/P003532/1). L.E.M. was funded by the European Union’s Horizon 2020 – European Union research and innovation program under the Marie Skłodowska–Curie grant agreement No. 750294. We thank Dr. Ieuan Seymour, University of Cambridge, and Prof. Bruce Dunn, University of California, Los Angeles, for fruitful discussions. We thank Drs. Jeremy Skepper and Heather Greer, University of Cambridge, for assistance with the electron microscopy and Dr. Maxim Avdeev, Bragg Institute, for his bond valence sum mapping program. We thank Dr. Olaf Borkiewicz, Advanced Photon Source, Argonne National Laboratory and Alisha Kasam, University of Cambridge for diffraction data reduction scripts. We thank Diamond Light Source for access to beamline B18 (SP14956, SP16387, SP17913) that contributed to the results presented here. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE- AC02-06CH11357

7Li NMR Chemical Shift Imaging To Detect Microstructural Growth of Lithium in All-Solid-State Batteries.

All-solid-state batteries potentially offer safe, high-energy-density electrochemical energy storage, yet are plagued with issues surrounding Li microstructural growth and subsequent cell death. We use 7Li NMR chemical shift imaging and electron microscopy to track Li microstructural growth in the garnet-type solid electrolyte, Li6.5La3Zr1.5Ta0.5O12. Here, we follow the early stages of Li microstructural growth during galvanostatic cycling, from the formation of Li on the electrode surface to dendritic Li connecting both electrodes in symmetrical cells, and correlate these changes with alterations observed in the voltage profiles during cycling and impedance measurements. During these experiments, we observe transformations at both the stripping and plating interfaces, indicating heterogeneities in both Li removal and deposition. At low current densities, 7Li magnetic resonance imaging detects the formation of Li microstructures in cells before short-circuits are observed and allows changes in the electrochemical profiles to be rationalized

Realistic atomistic structure of amorphous silicon from machine-learning-driven molecular dynamics

Amorphous silicon (a-Si) is a widely studied noncrystalline material, and yet the subtle details of its atomistic structure are still unclear. Here, we show that accurate structural models of a-Si can be obtained using a machine-learning-based interatomic potential. Our best a-Si network is obtained by simulated cooling from the melt at a rate of 1011 K/s (that is, on the 10 ns time scale), contains less than 2% defects, and agrees with experiments regarding excess energies, diffraction data, and 29Si NMR chemical shifts. We show that this level of quality is impossible to achieve with faster quench simulations. We then generate a 4096-atom system that correctly reproduces the magnitude of the first sharp diffraction peak (FSDP) in the structure factor, achieving the closest agreement with experiments to date. Our study demonstrates the broader impact of machine-learning potentials for elucidating structures and properties of technologically important amorphous materials

Establishing Ultralow Activation Energies for Lithium Transport in Garnet Electrolytes.

Garnet-type structured lithium ion conducting ceramics represent a promising alternative to liquid-based electrolytes for all-solid-state batteries. However, their performance is limited by their polycrystalline nature and inherent inhomogeneous current distribution due to different ion dynamics at grains, grain boundaries, and interfaces. In this study, we use a combination of electrochemical impedance spectroscopy, distribution of relaxation time analysis, and solid-state nuclear magnetic resonance (NMR), in order to understand the role that bulk, grain boundary, and interfacial processes play in the ionic transport and electrochemical performance of garnet-based cells. Variable temperature impedance analysis reveals the lowest activation energy for Li transport in the bulk of the garnet electrolyte (0.15 eV), consistent with pulsed field gradient NMR spectroscopy measurements (0.14 eV). We also show a decrease in grain boundary activation energy at temperatures below 0 °C, that is followed by the total conductivity, suggesting that the bottleneck to ionic transport resides in the grain boundaries. We reveal that the grain boundary activation energy is heavily affected by its composition that, in turn, is mainly affected by the segregation of dopants and Li. We suggest that by controlling the grain boundary composition, it would be possible to pave the way toward targeted engineering of garnet-type electrolytes and ameliorate their electrochemical performance in order to enable their use in commercial devices

Identifying the Structural Basis for the Increased Stability of the Solid Electrolyte Interphase Formed on Silicon with the Additive Fluoroethylene Carbonate.

To elucidate the role of fluoroethylene carbonate (FEC) as an additive in the standard carbonate-based electrolyte for Li-ion batteries, the solid electrolyte interphase (SEI) formed during electrochemical cycling on silicon anodes was analyzed with a combination of solution and solid-state NMR techniques, including dynamic nuclear polarization. To facilitate characterization via 1D and 2D NMR, we synthesized 13C-enriched FEC, ultimately allowing a detailed structural assignment of the organic SEI. We find that the soluble poly(ethylene oxide)-like linear oligomeric electrolyte breakdown products that are observed after cycling in the standard ethylene carbonate-based electrolyte are suppressed in the presence of 10 vol% FEC additive. FEC is first defluorinated to form soluble vinylene carbonate and vinoxyl species, which react to form both soluble and insoluble branched ethylene-oxide-based polymers. No evidence for branched polymers is observed in the absence of FEC

Investigating the Order Parameters of Saturated Lipid Molecules under Various Curvature Conditions on Spherical Supported Lipid Bilayers

The conformations and motions of lipid molecules under different membrane curvatures have important implications for transmembrane protein function, binding events, and overall membrane organization. This work reports on the local order parameters of saturated lipid molecules, as measured by ¹³C NMR relaxation, under several curvature conditions to probe structural changes as a function of lipid bilayer curvature. Different curvature conditions are created by depositing phosphatidylcholine membranes on spherical beads of various diameters. The findings reveal that the order parameters are not a continuous function of the membrane curvature. While small (30 nm) and large (110 nm) diameter bilayers exhibit similar order parameters, bilayers with curvatures of 60–80 nm diameter show a consistently increased order parameter along the entire lipid molecule, indicating a higher packing density and lateral tension. Order parameters for curvatures between 60 and 80 nm also show molecular evidence for interdigitation

Recovery and Reuse of Composite Cathode Binder in Lithium Ion Batteries

Abstract Here, we investigate the recovery and reuse of polyvinylidene fluoride (PVDF) binders from both homemade and commercial cathode films in Li ion batteries. We find that PVDF solubility depends on whether the polymer is an isolated powder or cast into a composite film. A mixture of tetrahydrofuran:N‐methyl‐2‐pyrrolidone (THF : NMP, 50 : 50 v/v) at 90 °C delaminates composite cathodes from Al current collectors and yields pure PVDF as characterized by 1H nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), wide‐angle X‐ray scattering (WAXS), and scanning electron microscopy (SEM). PVDF recovered from Li ion cells post‐cycling exhibits similar performance to pristine PVDF. These data suggest that PVDF can be extracted and reused during Li ion battery recycling while simultaneously eliminating the formation of HF etchants, providing an incentive for use in direct cathode recycling

Phase Transformations and Phase Segregation during Potassiation of Sn x P y Anodes.

K-ion batteries (KIBs) have the potential to offer a cheaper alternative to Li-ion batteries (LIBs) using widely abundant materials. Conversion/alloying anodes have high theoretical capacities in KIBs, but it is believed that electrode damage from volume expansion and phase segregation by the accommodation of large K-ions leads to capacity loss during electrochemical cycling. To date, the exact phase transformations that occur during potassiation and depotassiation of conversion/alloying anodes are relatively unexplored. In this work, we synthesize two distinct compositions of tin phosphides, Sn4P3 and SnP3, and compare their conversion/alloying mechanisms with solid-state nuclear magnetic resonance (SSNMR) spectroscopy, powder X-ray diffraction (XRD), and density functional theory (DFT) calculations. Ex situ 31P and 119Sn SSNMR analyses reveal that while both Sn4P3 and SnP3 exhibit phase separation of elemental P and the formation of KSnP-type environments (which are predicted to be stable based on DFT calculations) during potassiation, only Sn4P3 produces metallic Sn as a byproduct. In both anode materials, K reacts with elemental P to form K-rich compounds containing isolated P sites that resemble K3P but K does not alloy with Sn during potassiation of Sn4P3. During charge, K is only fully removed from the K3P-type structures, suggesting that the formation of ternary regions in the anode and phase separation contribute to capacity loss upon reaction of K with tin phosphides