Well-Tempered Metadynamics as a Tool for Characterizing Multi-Component, Crystalline Molecular Machines

The well-tempered, smoothly converging form of the metadynamics algorithm has been implemented in classical molecular dynamics simulations and used to obtain an estimate of the free energy surface explored by the molecular rotations in the plastic crystal, octafluoronaphthalene. The biased simulations explore the full energy surface extremely efficiently, more than 4 orders of magnitude faster than unbiased molecular dynamics runs. The metadynamics collective variables used have also been expanded to include the simultaneous orientations of three neighboring octafluoronaphthalene molecules. Analysis of the resultant three-dimensional free energy surface, which is sampled to a very high degree despite its significant complexity, demonstrates that there are strong correlations between the molecular orientations. Although this correlated motion is of limited applicability in terms of exploiting dynamical motion in octafluoronaphthalene, the approach used is extremely well suited to the investigation of the function of crystalline molecular machines

2H and 27Al Solid-State NMR Study of the Local Environments in Al-Doped 2-Line Ferrihydrite, Goethite, and Lepidocrocite.

Although substitution of aluminum into iron oxides and oxyhydroxides has been extensively studied, it is difficult to obtain accurate incorporation levels. Assessing the distribution of dopants within these materials has proven especially challenging because bulk analytical techniques cannot typically determine whether dopants are substituted directly into the bulk iron oxide or oxyhydroxide phase or if they form separate, minor phase impurities. These differences have important implications for the chemistry of these iron-containing materials, which are ubiquitous in the environment. In this work, 27Al and 2H NMR experiments are performed on series of Al-substituted goethite, lepidocrocite, and 2-line ferrihydrite in order to develop an NMR method to track Al substitution. The extent of Al substitution into the structural frameworks of each compound is quantified by comparing quantitative 27Al MAS NMR results with those from elemental analysis. Magnetic measurements are performed for the goethite series to compare with NMR measurements. Static 27Al spin-echo mapping experiments are used to probe the local environments around the Al substituents, providing clear evidence that they are incorporated into the bulk iron phases. Predictions of the 2H and 27Al NMR hyperfine contact shifts in Al-doped goethite and lepidocrocite, obtained from a combined first-principles and empirical magnetic scaling approach, give further insight into the distribution of the dopants within these phases.J.K., A.J.I., D.M. and N.P. were supported by an NSF grant collaborative research grant in chemistry CHE0714183. An allocation of time upon the NANO computer cluster at the Center for Functional Nanomaterials, Brookhaven National Laboratory, U.S.A., which is supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886 is also acknowledged. D.S.M. and C.P.G. thank the EPSRC and the EU-ERC for support.This is the final version of the article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/acs.chemmater.5b0085

Real-time 3D imaging of microstructure growth in battery cells using indirect MRI.

Lithium metal is a promising anode material for Li-ion batteries due to its high theoretical specific capacity and low potential. The growth of dendrites is a major barrier to the development of high capacity, rechargeable Li batteries with lithium metal anodes, and hence, significant efforts have been undertaken to develop new electrolytes and separator materials that can prevent this process or promote smooth deposits at the anode. Central to these goals, and to the task of understanding the conditions that initiate and propagate dendrite growth, is the development of analytical and nondestructive techniques that can be applied in situ to functioning batteries. MRI has recently been demonstrated to provide noninvasive imaging methodology that can detect and localize microstructure buildup. However, until now, monitoring dendrite growth by MRI has been limited to observing the relatively insensitive metal nucleus directly, thus restricting the temporal and spatial resolution and requiring special hardware and acquisition modes. Here, we present an alternative approach to detect a broad class of metallic dendrite growth via the dendrites' indirect effects on the surrounding electrolyte, allowing for the application of fast 3D (1)H MRI experiments with high resolution. We use these experiments to reconstruct 3D images of growing Li dendrites from MRI, revealing details about the growth rate and fractal behavior. Radiofrequency and static magnetic field calculations are used alongside the images to quantify the amount of the growing structures.The NMR/MRI methodology, as well as rf and static field calculations were supported by US National Science Foundation Grant CHE 1412064. The electrochemistry and battery components of the work were supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences, under Awards DE-SC0001294 and DE-SC0012583 (in situ methodology), including NECCES matching funds from the New York State Energy Research Development Authority (to H.J.C.), by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the US DOE under Contract DE-AC02-05CH11231, under the Batteries for Advanced Transportation Technologies (BATT) Program Subcontract 7057154

Exploring scale-up, spread, and sustainability: an instrumental case study tracing an innovation to enhance dysphagia care

Background Adoption, adaptation, scale-up, spread, and sustainability are ill-defined, undertheorised, and little-researched implementation science concepts. An instrumental case study will track the adoption and adaptation, or not, of a locally developed innovation about dysphagia as a patient safety issue. The case study will examine a conceptual framework with a continuum of spread comprising hierarchical control or ‘making it happen’, participatory adaptation or ‘help it happen’, and facilitated evolution or ‘let it happen’. Methods This case study is a prospective, longitudinal design using mixed methods. The fifteen-month (October 2012 to December 2013) instrumental case study is set in large, healthcare organisation in England. The innovation refers to introducing a nationally recognised, inter-disciplinary dysphagia competency framework to guide workforce development about fundamental aspects of care. Adoption and adaptation will be examined at an organisational level and along two, contrasting care pathways: stroke and fractured neck of femur. A number of educational interventions will be deployed, including training a cadre of trainers to cascade the essentials of dysphagia management and developing a Dysphagia Toolkit as a learning resource. Mixed methods will be used to investigate scale-up, spread, and sustainability in acute and community settings. A purposive sample of senior managers and clinical leaders will be interviewed to identify path dependency or the context specific particularities of implementation. A pre- and post-evaluation, using mealtime observations and a survey, will investigate the learning effect on staff adherence to patient specific dysphagia recommendations and attitudes towards dysphagia, respectively. Official documents and an ethnographic field journal allow critical junctures, temporal aspects and confounding factors to be explored. Discussion Researching spread and sustainability presents methodological and practical challenges. These include fidelity, adaptation latitude, time, and organisational changes. An instrumental case study will allow these confounding factors to be tracked over time and in place. The case study is underpinned by, and will test a conceptual framework about spread, to explore theoretical generalizability

Probing Solid-Electrolyte Interphase (SEI) Growth and Ion Permeability at Undriven Electrolyte–Metal Interfaces Using ⁷Li NMR

We examine here the exchange of Li ions between electrolyte and metallic lithium with ⁷Li NMR spectroscopy. The measurements quantify the liquid–solid exchange processes, as well as the growth of a solid-electrolyte interphase (SEI) layer. A numerical model including diffusion in the solid phase through atom hopping, radiofrequency penetration considerations through the skin effect, as well as surface exchange explains the experimental trends. Incorporation of the growth of an SEI layer explains the “missing” Li quantities, and, as the SEI layer grows, a decreased ion permeability in dependence on the layer thickness is modeled to explain the long-term trends. These measurements provide indirect probes for SEI growth and permeabilities and also provide a means for quantifying Li diffusion in the metal