Mechanism by which Tungsten Oxide Promotes the Activity of Supported V2 O5 /TiO2 Catalysts for NOX Abatement: Structural Effects Revealed by 51 V MAS NMR Spectroscopy.

The selective catalytic reduction (SCR) of NOx with NH3 to N2 with supported V2 O5 (-WO3 )/TiO2 catalysts is an industrial technology used to mitigate toxic emissions. Long-standing uncertainties in the molecular structures of surface vanadia are clarified, whereby progressive addition of vanadia to TiO2 forms oligomeric vanadia structures and reveals a proportional relationship of SCR reaction rate to [surface VOx concentration]2 , implying a 2-site mechanism. Unreactive surface tungsta (WO3 ) also promote the formation of oligomeric vanadia (V2 O5 ) sites, showing that promoter incorporation enhances the SCR reaction by a structural effect generating adjacent surface sites and not from electronic effects as previously proposed. The findings outline a method to assess structural effects of promoter incorporation on catalysts and reveal both the dual-site requirement for the SCR reaction and the important structural promotional effect that tungsten oxide offers for the SCR reaction by V2 O5 /TiO2 catalysts.

Mechanism of Phenol Alkylation in Zeolite H-BEA Using In Situ Solid-State NMR Spectroscopy.

The reaction mechanism of solid-acid-catalyzed phenol alkylation with cyclohexanol and cyclohexene in the apolar solvent decalin has been studied using in situ 13C MAS NMR spectroscopy. Phenol alkylation with cyclohexanol sets in only after a majority of cyclohexanol is dehydrated to cyclohexene. As phenol and cyclohexanol show similar adsorption strength, this strict reaction sequence is not caused by the limited access of phenol to cyclohexanol, but is due to the absence of a reactive electrophile as long as a significant fraction of cyclohexanol is present. 13C isotope labeling demonstrates that the reactive electrophile, the cyclohexyl carbenium ion, is directly formed in a protonation step when cyclohexene is the coreactant. In the presence of cyclohexanol, its protonated dimers at Brønsted acid sites hinder the adsorption of cyclohexene and the formation of a carbenium ion. Thus, it is demonstrated that protonated cyclohexanol dimers dehydrate without the formation of a carbenium ion, which would otherwise have contributed to the alkylation in the kinetically relevant step. Isotope scrambling shows that intramolecular rearrangement of cyclohexyl phenyl ether does not significantly contribute to alkylation at the aromatic ring.

In Situ Natural Abundance 17O and 25Mg NMR Investigation of Aqueous Mg(OH)2 Dissolution in the Presence of Supercritical CO2.

We report an in situ high-pressure NMR capability that permits natural abundance 17O and 25Mg NMR characterization of dissolved species in aqueous solution and in the presence of supercritical CO2 fluid (scCO2). The dissolution of Mg(OH)2 (brucite) in a multiphase water/scCO2 fluid at 90 atm pressure and 50 °C was studied in situ, with relevance to geological carbon sequestration. 17O NMR spectra allowed identification and distinction of various fluid species including dissolved CO2 in the H2O-rich phase, scCO2, aqueous H2O, and HCO3-. The widely separated spectral peaks for various species can all be observed both dynamically and quantitatively at concentrations as low as 20 mM. Measurement of the concentrations of these individual species also allows an in situ estimate of the hydrogen ion concentration, or pCH+ values, of the reacting solutions. The concentration of Mg2+ can be observed by natural abundance 25Mg NMR at a concentration as low as 10 mM. Quantum chemistry calculations of the NMR chemical shifts on cluster models aided in the interpretation of the experimental results. Evidence for the formation of polymeric Mg2+ clusters at high concentrations in the H2O-rich phase, a possible critical step needed for magnesium carbonate formation, was found.

Probing lithium germanide phase evolution and structural change in a germanium-in-carbon nanotube energy storage system.

Lithium alloys of group IV elements such as silicon and germanium are attractive candidates for use as anodes in high-energy-density lithium-ion batteries. However, the poor capacity retention arising from volume swing during lithium cycling restricts their widespread application. Herein, we report high reversible capacity and superior rate capability from core-shell structure consisting of germanium nanorods embedded in multiwall carbon nanotubes. To understand how the core-shell structure helps to mitigate volume swings and buffer against mechanical instability, transmission electron microscopy, X-ray diffraction, and in situ (7)Li nuclear magnetic resonance were used to probe the structural rearrangements and phase evolution of various Li-Ge alloy phases during (de)alloying reactions with lithium. The results provide insights into amorphous-to-crystalline transition and lithium germanide alloy phase transformation, which are important reactions controlling performance in this system.

Following solid-acid-catalyzed reactions by MAS NMR spectroscopy in liquid phase--zeolite-catalyzed conversion of cyclohexanol in water.

A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid-liquid-gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The (13) C spectra show that dehydration of 1-(13) C-cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the (13) C label. A simplified kinetic model shows the E1-type elimination fully accounts for the initial rates of 1-(13) C-cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2-hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl-1-cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100-fold faster per proton.

Prospective derivation and validation of a clinical prediction rule for recurrent Clostridium difficile infection.

BACKGROUND & AIMS: Prevention of recurrent Clostridium difficile infection (CDI) is a substantial therapeutic challenge. A previous prospective study of 63 patients with CDI identified risk factors associated with recurrence. This study aimed to develop a prediction rule for recurrent CDI using the above derivation cohort and prospectively evaluate the performance of this rule in an independent validation cohort. METHODS: The clinical prediction rule was developed by multivariate logistic regression analysis and included the following variables: age>65 years, severe or fulminant illness (by the Horn index), and additional antibiotic use after CDI therapy. A second rule combined data on serum concentrations of immunoglobulin G (IgG) against toxin A with the clinical predictors. Both rules were then evaluated prospectively in an independent cohort of 89 patients with CDI. RESULTS: The clinical prediction rule discriminated between patients with and without recurrent CDI, with an area under the curve of the receiver-operating-characteristic curve of 0.83 (95% confidence interval [CI]: 0.70-0.95) in the derivation cohort and 0.80 (95% CI: 0.67-0.92) in the validation cohort. The rule correctly classified 77.3% (95% CI: 62.2%-88.5%) and 71.9% (95% CI: 59.2%-82.4%) of patients in the derivation and validation cohorts, respectively. The combined rule performed well in the derivation cohort but not in the validation cohort (area under the curve of the receiver-operating-characteristic curve, 0.89 vs 0.62; diagnostic accuracy, 93.8% vs 69.2%, respectively). CONCLUSIONS: We prospectively derived and validated a clinical prediction rule for recurrent CDI that is simple, reliable, and accurate and can be used to identify high-risk patients most likely to benefit from measures to prevent recurrence.

A prospective study of risk factors and historical trends in metronidazole failure for Clostridium difficile infection.

BACKGROUND & AIMS: Recent studies of Clostridium difficile infection (CDI) have indicated a dramatic increase in metronidazole failure. The aims of this study were to compare current and historical rates of metronidazole failure and to identify risk factors for metronidazole failure. METHODS: Eighty-nine patients with CDI in 2004 to 2006 were followed for 60 days and were compared with a historical cohort of 63 CDI patients studied prospectively in 1998. Metronidazole failure was defined as persistent diarrhea after 10 days of therapy or a change of therapy to vancomycin. Stool samples were analyzed for the presence of the North American pulsed-field gel electrophoresis type-1 (NAP-1) strain. RESULTS: Metronidazole failure rates were 35% in both cohorts. There was no difference in the median time to resolution of diarrhea (8 vs 5 d; P = .52) or the proportion with >10 days of diarrhea (35% vs 29%; P = .51). Risk factors for metronidazole failure included recent cephalosporin use (odds ratio [OR], 32; 95% confidence interval [CI], 5-219), CDI on admission (OR, 23; 95% CI, 3-156), and transfer from another hospital (OR, 11; 95% CI, 2-72). The frequency of NAP-1 infection in patients with and without metronidazole failure was similar (26% vs 21%; P = .67). CONCLUSIONS: We found no difference in metronidazole failure rates in 1998 and 2004 to 2006. Patients with recent cephalosporin use, CDI on admission, and transfer from another hospital were more likely to metronidazole failure. Infection with the epidemic NAP-1 strain was not associated with metronidazole failure in endemic CDI.

In situ and ex situ NMR for battery research.

A rechargeable battery stores readily convertible chemical energy to operate a variety of devices such as mobile phones, laptop computers, electric automobiles, etc. A battery generally consists of four components: a cathode, an anode, a separator and electrolytes. The properties of these components jointly determine the safety, the lifetime, and the electrochemical performance. They also include, but are not limited to, the power density and the charge as well as the recharge time/rate associated with a battery system. An extensive amount of research is dedicated to understanding the physical and chemical properties associated with each of the four components aimed at developing new generations of battery systems with greatly enhanced safety and electrochemical performance at a significantly reduced cost for large scale applications. Advanced characterization tools are a prerequisite to fundamentally understanding battery materials. Considering that some of the key electrochemical processes can only exist under in situ conditions, which can only be captured under working battery conditions when electric wires are attached and current and voltage are applied, make in situ detection critical. Nuclear magnetic resonance (NMR), a non-invasive and atomic specific tool, is capable of detecting all phases, including crystalline, amorphous, liquid and gaseous phases simultaneously and is ideal for in situ detection on a working battery system. Ex situ NMR on the other hand can provide more detailed molecular or structural information on stable species with better spectral resolution and sensitivity. The combination of in situ and ex situ NMR, thus, offers a powerful tool for investigating the detailed electrochemistry in batteries.

Multinuclear NMR Study of the Solid Electrolyte Interface Formed in Lithium Metal Batteries.

The composition of the solid electrolyte interphase (SEI) layers formed in Cu|Li cells using lithium bis(fluorosulfonyi)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,2-dimethoxyethane (DME) electrolytes is determined by a multinuclear solid-state MAS NMR study at high magnetic field. It is found that the "dead" metallic Li is largely reduced in the SEI layers formed in a 4 M LiFSI-DME electrolyte system compared with those formed in a 1 M LiFSI-DME electrolyte system. This finding relates directly to the safety of Li metal batteries, as one of the main safety concerns for these batteries is associated with the "dead" metallic Li formed after long-term cycling. It is also found that a large amount of LiF, which exhibits superior mechanical strength and good Li+ ionic conductivity, is observed in the SEI layer formed in the concentrated 4 M LiFSI-DME and 3 M LiTFSI-DME systems but not in the diluted 1 M LiFSI-DME system. Quantitative 6Li MAS NMR results indicate that the SEI associated with the 4 M LiFSI-DME electrolyte is denser than those formed in the 1 M LiFSI-DME and 3 M LiTFSI-DME systems. These studies reveal the fundamental mechanisms behind the excellent electrochemical performance associated with higher concentration LiFSI-DME electrolyte systems.

Sealed rotors for in situ high temperature high pressure MAS NMR.

Here we present the design of reusable and perfectly sealed all-zirconia MAS rotors. The rotors are used to study AlPO4-5 molecular sieve crystallization under hydrothermal conditions, high temperature high pressure cyclohexanol dehydration reaction, and low temperature metabolomics of intact biological tissue.

A fundamental study on the [(µ-Cl)3Mg2(THF)6]+ dimer electrolytes for rechargeable Mg batteries.

The long sought solvated [MgCl](+) species in the Mg-dimer electrolytes was characterized by soft mass spectrometry. The presented study provides an insightful understanding on the electrolyte chemistry of rechargeable Mg batteries.

Reduction mechanism of fluoroethylene carbonate for stable solid­electrolyte interphase film on silicon anode.

Fluoroethylene carbonate (FEC) is an effective electrolyte additive that can significantly improve the cycling ability of silicon and other anode materials. However, the fundamental mechanism of this improvement is still not well understood. Based on the results obtained from (6)Li NMR and X-ray photoelectron spectroscopy studies, we propose a molecular-level mechanism for how FEC affects the formation of solid electrolyte interphase (SEI) film: 1) FEC is reduced through the opening of the five-membered ring leading to the formation of lithium poly(vinyl carbonate), LiF, and some dimers; 2) the FEC-derived lithium poly(vinyl carbonate) enhances the stability of the SEI film. The proposed reduction mechanism opens a new path to explore new electrolyte additives that can improve the cycling stability of silicon-based electrodes.

MMX mesalamine: a novel high-dose, once-daily 5-aminosalicylate formulation for the treatment of ulcerative colitis.

BACKGROUND: 5-Aminosalicylate (5-ASA) agents are the first-line therapy for ulcerative colitis (UC). A high-dose, once-daily formulation of 5-ASA known as MMX mesalamine has recently been approved for the treatment of UC. OBJECTIVE: To summarize current data on MMX mesalamine and to discuss its impact on management of UC. METHODS: A systematic review of published literature was performed on PubMed using the search terms 'MMX mesalamine' and 'Lialda'. Abstracts presented at US gastroenterology conferences between 2006 and 2007, were also reviewed. RESULTS: MMX mesalamine uses a novel multi-matrix delivery system to achieve a sustained release of 5-ASA throughout the colon. Clinical trials have demonstrated MMX mesalamine 2.4 g/day or 4.8 g/day to be superior to placebo in inducing remission in active mild to moderate UC. The drug is well tolerated with a safety profile comparable to other oral 5-ASA agents. With a high-dose formulation of 1.2 g 5-ASA per tablet, MMX mesalamine can be administered conveniently at two to four pills once a day. CONCLUSION: MMX mesalamine is the first and only approved once-daily 5-ASA treatment option for patients with UC. It is efficacious for the induction of remission in mild to moderate UC and has a favorable safety profile. With the advantage of low pill burden and easy dosing schedule, it may potentially improve patient compliance and treatment success.

Early diagnosis of hemochromatosis-related cardiomyopathy with magnetic resonance imaging.

The hallmark of hemochromatosis is the deposition of iron in multiple tissue types, most notably the skin, liver, pancreas, thyroid, and heart. Definitive diagnosis of iron deposition generally requires invasive methods, such as direct tissue biopsy. We describe a 40 year-old woman with end-stage liver disease secondary to hereditary hemochromatosis and alcohol abuse, who was referred to the cardiology service as part of an evaluation for orthotopic liver transplant. The patient had no cardiac history but a dobutamine stress echocardiogram, performed as a portion of the pre-operative cardiac evaluation, could not be completed due to intermittent, supraventricular tachycardia. Additional cardiac testing, including electrocardiography and resting echocardiography, raised suspicion for cardiomyopathy related to hemochromatosis but was non-diagnostic. Cardiac magnetic resonance (MR) of this patient revealed deposition of iron in the myocardium and established the diagnosis of hemachromatosis-related cardiomyopathy. These findings suggest that cardiac MR may be more sensitive than other non-invasive, diagnostic tools in the initial evaluation of hemochromatosis-related cardiomyopathy and may be used as an alternative to myocardial biopsy. We propose that conventional T1- and T2-weighted spin echo MR sequences can be used routinely as non-invasive modalities to assess the presence of iron deposition in the tissues of patients with hemochromatosis.