Oxidative Grafting for Catalyst Synthesis in Surface Organometallic Chemistry.

The development of new methods of catalyst synthesis with the potential to generate active site structures orthogonal to those accessible by traditional protocols is of great importance for discovering new materials for addressing challenges in the evolving energy and chemical economy. In this work, the generality of oxidative grafting of organometallic and well-defined molecular metal precursors onto redox-active surfaces such as manganese dioxide (MnO2) and lithium manganese oxide (LiMn2O4) is investigated. Nine molecular metal precursors are explored, spanning groups 4-11 and each of the three periods of the transition metal series. The byproducts of the oxidative grafting reaction, a mixture of protodemetalation and ligand homocoupling for several organometallic precursors, was found to provide insights into the mechanism of the grafting reaction, suggesting oxidation of both the metal d-orbitals, as well as the metal-carbon σ-bonds, resulting in ejection of the ligand radical fragment. Analysis of the supported structures and oxidation state by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) suggests that several of the chemisorbed metal ions are intercalated into interstitial vacancies of the surface structure while other complexes form intact molecular fragments on the surface. Proof of concept for the use of this metalation protocol to generate diverse, metal-dependent catalytic performance is demonstrated by the application of these materials in the conversion of cyclohexane to K/A oil (cyclohexanol and cyclohexanone) with tert-butyl hydroperoxide, as well as in the low-temperature (T ≤ 50 °C) oxidation of carbon monoxide to carbon dioxide.

Synthesis, structural and electrochemical properties of V4O9 cathode for lithium batteries.

Single-phase three-dimensional vanadium oxide (V4O9) was synthesized by reduction of V2O5 using a gas stream of ammonia/argon (NH3/Ar). The as-synthesized oxide, prepared by this simple gas reduction method was subsequently electrochemically transformed into a disordered rock salt type-"Li3.7V4O9" phase while cycling over the voltage window 3.5 to 1.8 V versus Li. The Li-deficient phase delivers an initial reversible capacity of ∼260 mAhg-1 at an average voltage of 2.5 V vs. Li+/Li0. Further cycling to 50 cycles yields a steady 225 mAhg-1. Ex situ X-ray diffraction studies confirmed that (de) intercalation phenomena follows a solid-solution electrochemical reaction mechanism. As demonstrated, the reversibility and capacity utilization of this V4O9 is found to be superior to battery grade, micron-sized V2O5 cathodes in lithium cells.

A room temperature rechargeable Li2O-based lithium-air battery enabled by a solid electrolyte.

A lithium-air battery based on lithium oxide (Li2O) formation can theoretically deliver an energy density that is comparable to that of gasoline. Lithium oxide formation involves a four-electron reaction that is more difficult to achieve than the one- and two-electron reaction processes that result in lithium superoxide (LiO2) and lithium peroxide (Li2O2), respectively. By using a composite polymer electrolyte based on Li10GeP2S12 nanoparticles embedded in a modified polyethylene oxide polymer matrix, we found that Li2O is the main product in a room temperature solid-state lithium-air battery. The battery is rechargeable for 1000 cycles with a low polarization gap and can operate at high rates. The four-electron reaction is enabled by a mixed ion-electron-conducting discharge product and its interface with air.

A Carboranyl Electrolyte Enabling Highly Reversible Sodium Metal Anodes via a "Fluorine-Free" SEI.

Realization of practical sodium metal batteries (SMBs) is hindered due to lack of compatible electrolyte components, dendrite propagation, and poor understanding of anodic interphasial chemistries. Chemically robust liquid electrolytes that facilitate both favorable sodium metal deposition and a stable solid-electrolyte interphase (SEI) are ideal to enable sodium metal and anode-free cells. Herein we present advanced characterization of a novel fluorine-free electrolyte utilizing the [HCB11 H11 ]1- anion. Symmetrical Na cells operated with this electrolyte exhibit a remarkably low overpotential of 0.032 V at a current density of 2.0 mA cm-2 and a high coulombic efficiency of 99.5 % in half-cell configurations. Surface characterization of electrodes post-operation reveals the absence of dendritic sodium nucleation and a surprisingly stable fluorine-free SEI. Furthermore, weak ion-pairing is identified as key towards the successful development of fluorine-free sodium electrolytes.

Theory-guided experimental design in battery materials research.

A reliable energy storage ecosystem is imperative for a renewable energy future, and continued research is needed to develop promising rechargeable battery chemistries. To this end, better theoretical and experimental understanding of electrochemical mechanisms and structure-property relationships will allow us to accelerate the development of safer batteries with higher energy densities and longer lifetimes. This Review discusses the interplay between theory and experiment in battery materials research, enabling us to not only uncover hitherto unknown mechanisms but also rationally design more promising electrode and electrolyte materials. We examine specific case studies of theory-guided experimental design in lithium-ion, lithium-metal, sodium-metal, and all-solid-state batteries. We also offer insights into how this framework can be extended to multivalent batteries. To close the loop, we outline recent efforts in coupling machine learning with high-throughput computations and experiments. Last, recommendations for effective collaboration between theorists and experimentalists are provided.

Detection of 13C labeling of glutamate and glutamine in human brain by proton magnetic resonance spectroscopy.

A proton magnetic resonance spectroscopy (MRS) technique was used to measure 13C enrichments of glutamate and glutamine in a 3.5 × 1.8 × 2 cm3 voxel placed in the dorsal anterior cingulate cortex of five healthy participants after oral administration of [U-13C]glucose. Strong pseudo singlets of glutamate and glutamine were induced to enhance the signal strength of glutamate and glutamine. This study demonstrated that 13C labeling of glutamate and glutamine can be measured with the high sensitivity and spatial resolution of 1H MRS using a proton-only MRS technique with standard commercial hardware. Furthermore, it is feasible to measure 13C labeling of glutamate and glutamine in limbic structures, which play major roles in behavioral and emotional responses and whose abnormalities are involved in many neuropsychiatric disorders.

Carbonic anhydrase activity in the frontal lobe of human brain.

Carbonic anhydrase (CA) plays an important role in many biological processes. Recent technological advances have demonstrated the feasibility of measuring CA activity in the occipital lobe of human subjects in vivo. In this work we report, for the first time, in vivo measurement of CA activity in the frontal lobe of human brain, where structural and function abnormalities are strongly associated with symptoms of major psychiatric disorders. Despite the much larger magnetic field distortion in the frontal lobe, the pseudo first-order bicarbonate dehydration rate constant was determined with high precision using in vivo 13 C magnetic resonance magnetization transfer spectroscopy following oral administration of [U-13 C6 ]glucose. Nuclear Overhauser effect pulses were used to increase the signal-to-noise ratio; no proton decoupling was applied. The unidirectional dehydration rate constant of bicarbonate was found to be 0.26 ± 0.07 s-1 , which is not statistically different from the dehydration rate constant in the occipital lobe determined in our previous study, indicating that CA activity in the two brain regions is essentially indistinguishable. These results demonstrate the feasibility of characterizing CA activity in the frontal lobe for future psychiatric studies.

Kinetically Stable Oxide Overlayers on Mo3 P Nanoparticles Enabling Lithium-Air Batteries with Low Overpotentials and Long Cycle Life.

The main drawbacks of today's state-of-the-art lithium-air (Li-air) batteries are their low energy efficiency and limited cycle life due to the lack of earth-abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo3 P) nanoparticles with an exceptional activity-ORR and OER current densities of 7.21 and 6.85 mA cm-2 at 2.0 and 4.2 V versus Li/Li+ , respectively-in an oxygen-saturated non-aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance-Tafel slopes of 35 and 38 mV dec-1 for ORR and OER, respectively-resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li-air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo3 P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials.

Photo-accelerated fast charging of lithium-ion batteries.

Due to their exceptional high energy density, lithium-ion batteries are of central importance in many modern electrical devices. A serious limitation, however, is the slow charging rate used to obtain the full capacity. Thus far, there have been no ways to increase the charging rate without losses in energy density and electrochemical performance. Here we show that the charging rate of a cathode can be dramatically increased via interaction with white light. We find that a direct exposure of light to an operating LiMn2O4 cathode during charging leads to a remarkable lowering of the battery charging time by a factor of two or more. This enhancement is enabled by the induction of a microsecond long-lived charge separated state, consisting of Mn4+ (hole) plus electron. This results in more oxidized metal centers and ejected lithium ions are created under light and with voltage bias. We anticipate that this discovery could pave the way to the development of new fast recharging battery technologies.

Interspace between Popliteal Artery and posterior Capsule of the Knee (IPACK) Injectate Spread: A Cadaver Study.

OBJECTIVES: Local anesthetic injection into the interspace between the popliteal artery and the posterior capsule of the knee (IPACK) has the potential to provide motor-sparing analgesia to the posterior knee after total knee arthroplasty. The primary objective of this cadaveric study was to evaluate injectate spread to relevant anatomic structures with IPACK injection. METHODS: After receipt of Institutional Review Board Biospecimen Subcommittee approval, IPACK injection was performed on fresh-frozen cadavers. The popliteal fossa in each specimen was dissected and examined for injectate spread. RESULTS: Ten fresh-frozen cadaver knees were included in the study. Injectate was observed to spread in the popliteal fossa at a mean ± SD of 6.1 ± 0.7 cm in the medial-lateral dimension and 10.1 ± 3.2 cm in the proximal-distal dimension. No injectate was noted to be in contact with the proximal segment of the sciatic nerve, but 3 specimens showed injectate spread to the tibial nerve. In 3 specimens, the injectate showed possible contact with the common peroneal nerve. The middle genicular artery was consistently surrounded by injectate. CONCLUSIONS: This cadaver study of IPACK injection demonstrated spread throughout the popliteal fossa without proximal sciatic involvement. However, the potential for injectate to spread to the tibial or common peroneal nerve was demonstrated. Consistent surrounding of the middle genicular artery with injectate suggests a potential mechanism of analgesia for the IPACK block, due to the predictable relationship between articular sensory nerves and this artery. Further study is needed to determine the ideal site of IPACK injection.

Determining the Rate of Carbonic Anhydrase Reaction in the Human Brain.

Carbonic anhydrase plays important role in life. This study sought to demonstrate the feasibility of detecting carbonic anhydrase activity in the human brain in vivo. After oral administration of [U-13C6]glucose, 13C saturation transfer experiments were performed with interleaved control spectra and carbon dioxide saturation spectra. Proton nuclear Overhauser effect pulses were used to increase signal to noise ratio; no proton decoupling was applied. Results showed that the 13C signal of bicarbonate was reduced by 72% ± 0.03 upon saturating carbon dioxide. The unidirectional dehydration rate constant of the carbonic anhydrase reaction was found to be 0.28 ± 0.02 sec-1 in the human brain. These findings demonstrate the feasibility of measuring carbonic anhydrase activity in vivo in the human brain, which makes it possible to characterize this important enzyme in patients with brain disorders.

Ultrasound-Guided Posterior Femoral Cutaneous Nerve Block: A Cadaveric Study.

OBJECTIVES: To identify any anatomic barriers to local anesthetic spread between the sciatic nerve (SN) and the posterior femoral cutaneous nerve (PFCN) at the level of the infragluteal crease and to describe a potential technique for an ultrasound (US)-guided subgluteal PFCN block in a cadaveric model. METHODS: Bilateral US-guided subgluteal injections of a colored latex solution were performed around the SN (15 mL) and PFCN (10 mL) in 4 unembalmed cadavers, for a total of 8 cadaver thighs. The specimens were dissected after latex polymerization to observe the spread of the latex solutions. RESULTS: With US guidance, the PFCN was visualized deep to the gluteus maximus and slightly superficial or lateral to the SN at the level of the infragluteal crease. The SN and PFCN were found on dissection to be coated with their respective colored latex in all 8 thighs. The SN and PFCN were consistently separated by the deep investing muscular fascia of the thigh, with only 2 thighs showing substantial mixing of latex injectates. CONCLUSIONS: The deep investing muscular fascia of the thigh appears to impede the spread of injectate between the SN and PFCN in a most unembalmed cadaver specimens. A US-guided subgluteal PFCN blockade may be a feasible technique to complement an SN block when complete anesthesia of the posterior thigh is required.

Microwave-Assisted Synthesis of NaCoPO4 Red-Phase and Initial Characterization as High Voltage Cathode for Sodium-Ion Batteries.

Transition metal-containing polyanion compounds are attractive for use as cathode materials in sodium-ion batteries (SIB) because they possess elevated higher intrinsic electrochemical potentials versus oxide analogs given the same Mn+/(n+1)+ redox couple, which leads to higher energy densities. NaMPO4 (M = transition metal) compounds have a driving force to form into the electrochemically inactive maricite phase when using conventional methods. Herein we report on the synthesis of a NaCoPO4 (NCP) polymorph ("Red"-phase) by a microwave-assisted solvothermal process at 200 °C using tetraethylene glycol as the solvent. Ex situ XRD, XANES, and electrochemical data are used to determine the reversibility of the Co2+/3+ redox center.

(13)C MRS of human brain at 7 Tesla using [2-(13)C]glucose infusion and low power broadband stochastic proton decoupling.

PURPOSE: Carbon-13 ((13)C) MR spectroscopy (MRS) of the human brain at 7 Tesla (T) may pose patient safety issues due to high radiofrequency (RF) power deposition for proton decoupling. The purpose of present work is to study the feasibility of in vivo (13)C MRS of human brain at 7 T using broadband low RF power proton decoupling. METHODS: Carboxylic/amide (13)C MRS of human brain by broadband stochastic proton decoupling was demonstrated on a 7 T scanner. RF safety was evaluated using the finite-difference time-domain method. (13)C signal enhancement by nuclear Overhauser effect (NOE) and proton decoupling was evaluated in both phantoms and in vivo. RESULTS: At 7 T, the peak amplitude of carboxylic/amide (13)C signals was increased by a factor of greater than 4 due to the combined effects of NOE and proton decoupling. The 7 T (13)C MRS technique used decoupling power and average transmit power of less than 35 watts (W) and 3.6 W, respectively. CONCLUSION: In vivo (13)C MRS studies of human brain can be performed at 7 T, well below the RF safety threshold, by detecting carboxylic/amide carbons with broadband stochastic proton decoupling.

First-charge instabilities of layered-layered lithium-ion-battery materials.

Li- and Mn-rich layered oxides with composition xLi2MnO3·(1 -x)LiMO2 enable high capacity and energy density Li-ion batteries, but suffer from degradation with cycling. Evidence of atomic instabilities during the first charge are addressed in this work with X-ray absorption spectroscopy, first principles simulation at the GGA+U level, and existing literature. The pristine material of composition xLi2MnO3·(1 -x)LiMn0.5Ni0.5O2 is assumed in the simulations to have the form of LiMn2 stripes, alternating with NiMn stripes, in the metal layers. The charged state is simulated by removing Li from the Li layer, relaxing the resultant system by steepest descents, then allowing the structure to evolve by molecular dynamics at 1000 K, and finally relaxing the evolved system by steepest descents. The simulations show that about » of the oxygen ions in the Li2MnO3 domains are displaced from their original lattice sites, and form oxygen-oxygen bonds, which significantly lowers the energy, relative to that of the starting structure in which the oxygen sublattice is intact. An important consequence of the displacement of the oxygen is that it enables about ⅓ of the (Li2MnO3 domain) Mn ions to migrate to the delithiated Li layers. The decrease in the coordination of the Mn ions is about twice that of the Ni ions. The approximate agreement of simulated coordination number deficits for Mn and Ni following the first charge with analysis of EXAFS measurements on 0.3Li2MnO3·0.7LiMn0.5Ni0.5O2 suggests that the simulation captures significant features of the real material.

Nanostructured Layered Cathode for Rechargeable Mg-Ion Batteries.

Nanostructured bilayered V2O5 was electrochemically deposited within a carbon nanofoam conductive support. As-prepared electrochemically synthesized bilayered V2O5 incorporates structural water and hydroxyl groups, which effectively stabilizes the interlayers and provides coordinative preference to the Mg(2+) cation in reversible cycling. This open-framework electrode shows reversible intercalation/deintercalation of Mg(2+) ions in common electrolytes such as acetonitrile. Using a scanning transmission electron microscope we demonstrate that Mg(2+) ions can be effectively intercalated into the interlayer spacing of nanostructured V2O5, enabling electrochemical magnesiation against a Mg anode with a specific capacity of 240 mAh/g. We employ HRTEM and X-ray fluorescence (XRF) imaging to understand the role of environment in the intercalation processes. A rebuilt full cell was tested by employing a high-energy ball-milled Sn alloy anode in acetonitrile with Mg(ClO4)2 salt. XRF microscopy reveals effective insertion of Mg ions throughout the V2O5 structure during discharge and removal of Mg ions during electrode charging, in agreement with the electrode capacity. We show using XANES and XRF microscopy that reversible Mg intercalation is limited by the anode capacity.

Toward lithium ion batteries with enhanced thermal conductivity.

As batteries become more powerful and utilized in diverse applications, thermal management becomes one of the central problems in their application. We report the results on thermal properties of a set of different Li-ion battery electrodes enhanced with multiwalled carbon nanotubes. Our measurements reveal that the highest in-plane and cross-plane thermal conductivities achieved in the carbon-nanotube-enhanced electrodes reached up to 141 and 3.6 W/mK, respectively. The values for in-plane thermal conductivity are up to 2 orders of magnitude higher than those for conventional electrodes based on carbon black. The electrodes were synthesized via an inexpensive scalable filtration method, and we demonstrate that our approach can be extended to commercial electrode-active materials. The best performing electrodes contained a layer of γ-Fe2O3 nanoparticles on carbon nanotubes sandwiched between two layers of carbon nanotubes and had in-plane and cross-plane thermal conductivities of ∼50 and 3 W/mK, respectively, at room temperature. The obtained results are important for thermal management in Li-ion and other high-power-density batteries.

Association of azithromycin with mortality and cardiovascular events among older patients hospitalized with pneumonia.

IMPORTANCE: Although clinical practice guidelines recommend combination therapy with macrolides, including azithromycin, as first-line therapy for patients hospitalized with pneumonia, recent research suggests that azithromycin may be associated with increased cardiovascular events. OBJECTIVE: To examine the association of azithromycin use with all-cause mortality and cardiovascular events for patients hospitalized with pneumonia. DESIGN: Retrospective cohort study comparing older patients hospitalized with pneumonia from fiscal years 2002 through 2012 prescribed azithromycin therapy and patients receiving other guideline-concordant antibiotic therapy. SETTING: This study was conducted using national Department of Veterans Affairs administrative data of patients hospitalized at any Veterans Administration acute care hospital. PARTICIPANTS: Patients were included if they were aged 65 years or older, were hospitalized with pneumonia, and received antibiotic therapy concordant with national clinical practice guidelines. MAIN OUTCOMES AND MEASURES: Outcomes included 30- and 90-day all-cause mortality and 90-day cardiac arrhythmias, heart failure, myocardial infarction, and any cardiac event. Propensity score matching was used to control for the possible effects of known confounders with conditional logistic regression. RESULTS: Of 73,690 patients from 118 hospitals identified, propensity-matched groups were composed of 31,863 patients exposed to azithromycin and 31,863 matched patients who were not exposed. There were no significant differences in potential confounders between groups after matching. Ninety-day mortality was significantly lower in those who received azithromycin (exposed, 17.4%, vs unexposed, 22.3%; odds ratio [OR], 0.73; 95% CI, 0.70-0.76). However, we found significantly increased odds of myocardial infarction (5.1% vs 4.4%; OR, 1.17; 95% CI, 1.08-1.25) but not any cardiac event (43.0% vs 42.7%; OR, 1.01; 95% CI, 0.98-1.05), cardiac arrhythmias (25.8% vs 26.0%; OR, 0.99; 95% CI, 0.95-1.02), or heart failure (26.3% vs 26.2%; OR, 1.01; 95% CI, 0.97-1.04). CONCLUSIONS AND RELEVANCE: Among older patients hospitalized with pneumonia, treatment that included azithromycin compared with other antibiotics was associated with a lower risk of 90-day mortality and a smaller increased risk of myocardial infarction. These findings are consistent with a net benefit associated with azithromycin use.

Predictors of rehospitalization after admission for pneumonia in the veterans affairs healthcare system.

INTRODUCTION: Although some factors associated with rehospitalization after community-acquired pneumonia have been identified, other factors such as medical care utilization and medication usage have not been previously studied. We investigated novel predictors of rehospitalization in patients admitted with pneumonia. METHODS: Using Department of Veteran Affairs (VA) administrative data from October 2001 to September 2007, we examined a cohort of patients 65 years old and older, who were hospitalized with pneumonia, in 150 VA acute care hospitals. The cohort was randomly split into derivation and validation samples, and then logistic regression models were used to identify and validate predictors of all-cause rehospitalization within 30 days. RESULTS: Of the 45,134 subjects, 13% were rehospitalized within 30 days. No significant differences were noted between the derivation and validation cohorts. Factors associated with readmission included age, marital status, chronic renal disease, prior malignancy, nursing home residence, congestive heart failure, use of oral corticosteroids, number of emergency department visits a year prior, prior admission, number of outpatient clinic visits in a year prior, and length of hospital stay. The C statistics for the derivation and validation models were 0.615 and 0.613, respectively. CONCLUSIONS: Factors associated with readmission were largely unrelated to the underlying pneumonia, but were related to demographics, comorbidities, healthcare utilization, and length of stay on index admission.