Ju Feng

Following the Transient Reactions in Lithium–Sulfur Batteries Using an In Situ Nuclear Magnetic Resonance Technique

A fundamental understanding of electrochemical reaction pathways is critical to improving the performance of Li-S batteries, but few techniques can be used to directly identify and quantify the reaction species during disharge/charge cycling processes in real time. Here, an in situ (7)Li NMR technique employing a specially designed cylindrical microbattery was used to probe the transient electrochemical and chemical reactions occurring during the cycling of a Li-S system. In situ NMR provides real time, semiquantitative information related to the temporal evolution of lithium polysulfide allotropes during both discharge/charge processes. This technique uniquely reveals that the polysulfide redox reactions involve charged free radicals as intermediate species that are difficult to detect in ex situ NMR studies. Additionally, it also uncovers vital information about the (7)Li chemical environments during the electrochemical and parasitic reactions on the Li metal anode. These new molecular-level insights about transient species and the associated anode failure mechanism are crucial to delineating effective strategies to accelerate the development of Li-S battery technologies.

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.

(1)H NMR Metabolomics Study of Metastatic Melanoma in C57BL/6J Mouse Spleen.

Melanoma is a malignant tumor of melanocytes. Although extensive investigations have been done to study metabolic changes in primary melanoma in vivo and in vitro, little effort has been devoted to metabolic profiling of metastatic tumors in organs other than lymph nodes. In this work, NMR-based metabolomics combined with multivariate data analysis is used to study metastatic B16-F10 melanoma in C57BL/6J mouse spleen. Principal component analysis, an unsupervised multivariate data analysis method, is used to detect possible outliers, while orthogonal projection to latent structure (OPLS), a supervised multivariate data analysis method, is employed to find important metabolites responsible for discriminating the control and the melanoma groups. Two different strategies, i.e. spectral binning and spectral deconvolution, are used to reduce the original spectral data before statistical analysis. Spectral deconvolution is found to be superior for identifying a set of discriminatory metabolites between the control and the melanoma groups, especially when the sample size is small. OPLS results show that the melanoma group can be well separated from its control group. It is found that taurine, glutamate, aspartate, O-phosphoethanolamine, niacinamide, ATP, lipids and glycerol derivatives are decreased statistically and significantly while alanine, malate, xanthine, histamine, dCTP, GTP, thymidine, 2′-deoxyguanosine are statistically and significantly elevated. These significantly changed metabolites are associated with multiple biological pathways and may be potential biomarkers for metastatic melanoma in spleen.

Energetics of Defects on Graphene through Fluorination

Functionalized graphene sheets (FGSs) comprise a unique member of the carbon family, demonstrating excellent electrical conductivity and mechanical strength. However, the detailed chemical composition of this material is still unclear. Herein, we take advantage of the fluorination process to semiquantitatively probe the defects and functional groups on graphene surface. Functionalized graphene sheets are used as substrate for low-temperature (<150 °C) direct fluorination. The fluorine content has been modified to investigate the formation mechanism of different functional groups such as C-F, CF2, O-CF2 and (C=O)F during fluorination. The detailed structure and chemical bonds are simulated by density functional theory (DFT) and quantified experimentally by nuclear magnetic resonance (NMR). The electrochemical properties of fluorinated graphene are also discussed extending the use of graphene from fundamental research to practical applications.