Correlation of electrochemical performance and in situ X-ray absorption fine structure (XAFS) spectroscopy measurements on ZnO anodes for lithium-ion batteries has enabled a detailed examination of the capacity fading mechanisms in this material. ZnO electrodes were galvanostatically charged/discharged in situ for several cycles while XAFS spectra at the Zn K-edge were taken. X-ray absorption near edge structure (XANES) spectroscopy provided information on the oxidation state of Zn atoms in each charged and discharged state. Modeling of extended X-ray absorption fine structure (EXAFS) provided detailed information on the Zn-O, Zn-Zn and even Zn-Li coordination numbers and atomic distances for each charged and discharged electrode states. Based on the changes in atomic arrangement deduced from EXAFS fitting results, it is suggested that metallic Zn nanoparticles larger than 10 nm in diameter and bulk-like properties are created during the first few cycles. In the first discharged state, a small fraction of metallic Zn is oxidized back to ZnO, but such re-oxidation is only observed in the first discharged state. On subsequent cycling, the local Zn environment is unchanged, indicating that majority of zinc is no longer participating in any electrochemical reaction. The observed rapid capacity fade is correlated to the irreversible conversion of ZnO to metallic Zn and segregation of Zn atoms into the large metallic zinc nanoparticles during the first charge, which is essentially conversion of the high capacity ZnO electrode to a poorly performing metallic Zn anode.Lithium-ion batteries (LIBs) are the primary power source for portable electronic applications. Graphite is the most common anode material in commercially available products due to its excellent cycle life and specific capacity (theoretical capacity of 372 mAh g −1 ). 1,2 However, for LIBs to be viable options for large scale applications such as electric vehicles, significant improvements in energy and power densities, along with cycle life of next generation LIBs are needed. Metal oxides are often discussed as reasonable alternatives to traditional carbon anode materials as they exhibit theoretical capacities upwards of three times higher than graphitic anodes. 3−5 ZnO is one of the potential alternatives as it has a theoretical capacity of 978 mAh g −1 , 3 however it has been reported to suffer from severe capacity loss in the first few cycles, even at slow charging rates. 6−11 Attempts have been made to control the capacity fading by using nano-scale ZnO particles, 3,12−14 coating of ZnO with carbon, 15 nickel, 16 copper, 17 tin, 10,18 and even replacing oxygen with nitrogen 5 and phosphorous 19,20 resulting in modest improvements. In order to successfully stabilize cycling behavior of ZnO the overall lithation/delithiation mechanism must be understood at the atomic level to properly engineer better performing anodes. The proposed reduction-oxidation reactions are 4,5,9where ZnO is converted to Zn and Li 2 O on initial charging and, upon further chargin...

Acetylation is correlated with chromatin decondensation and transcriptional activation, but its regulation by histone deacetylase (HDAC)-bearing corepressor complexes is poorly understood. Here, we describe the mechanism of assembly of the mammalian Sin3L/Rpd3L complex facilitated by Sds3, a conserved subunit deemed critical for proper assembly. Sds3 engages a globular, helical region of the HDAC interaction domain (HID) of the scaffolding protein Sin3A through a bipartite motif comprising a helix and an adjacent extended segment. Sds3 dimerizes through not only one of the predicted coiled-coil motifs but also, the segment preceding it, forming an ∼150-Å-long antiparallel dimer. Contrary to previous findings in yeast, Sin3A rather than Sds3 functions in recruiting HDAC1 into the complex by engaging the latter through a highly conserved segment adjacent to the helical HID subdomain. In the resulting model for the ternary complex, the two copies of the HDACs are situated distally and dynamically because of a natively unstructured linker connecting the dimerization domain and the Sin3A interaction domain of Sds3; these features contrast with the static organization described previously for the NuRD (nucleosome remodeling and deacetylase) complex. The Sds3 linker features several conserved basic residues that could potentially maintain the complex on chromatin by nonspecific interactions with DNA after initial recruitment by sequence-specific DNA-binding repressors.transcription repression | histone deacetylase | corepressor complex | protein-protein interaction | structural biology H istone deacetylation constitutes the primary mechanism of erasing acetylation marks on histones, leading to a chromatin environment that is repressive to gene transcription. Histone deacetylases (HDACs) exhibit limited substrate specificity and rely on transcription factors with sequence-specific DNAbinding and/or chromatin-binding activities for their targeting specificity. Among 11 known Zn 2+ -dependent HDACs in mammals, only HDAC1, HDAC2, and HDAC3 are constitutively nuclear, regulating the transcription of a broad array of genes that impact fundamentally on cellular physiology and organism development (1-3). These HDACs are commonly found in multiprotein corepressor complexes, with the closely related HDAC1 and HDAC2 partitioning broadly into the Sin3L/Rpd3L, Sin3S/ Rpd3S, NuRD (nucleosome remodeling and deacetylase), and CoREST (corepressor of REST transcription factor) complexes, whereas HDAC3 is found exclusively in SMRT/NCoR (silencing mediator of retinoid and thyroid hormone receptor/nuclear receptor corepressor) complexes. Little is known regarding the structure and organization of these complexes, although molecular insights into HDAC recruitment into these complexes are beginning to emerge.High-resolution structures of HDAC1 and HDAC3 in complex with the MTA1 (metastatic tumor antigen 1) and SMRT subunits in the NuRD and SMRT/NCoR complexes, respectively (4, 5), revealed a shared structural theme involving the catalytic do...

alloying reaction (Equation (2)) between metallic Sn and Li-ions as follows [1,2] Sn P 9Li 9e 4Sn 3Li P 4 3 3

The practical electrosynthesis of hydrogen peroxide (H 2 O 2 ) is hindered by the lack of inexpensive and efficient catalysts for the two-electron oxygen reduction reaction (2e − ORR) in neutral electrolytes. Here, we show that Ni 3 HAB 2 (HAB = hexaaminobenzene), a two-dimensional metal organic framework (MOF), is a selective and active 2e − ORR catalyst in buffered neutral electrolytes with a linker-based redox feature that dynamically affects the ORR behaviors. Rotating ring-disk electrode measurements reveal that Ni 3 HAB 2 has high selectivity for 2e − ORR (>80% at 0.6 V vs RHE) but lower Faradaic efficiency due to this linker redox process. Operando X-ray absorption spectroscopy measurements reveal that under argon gas the charging of the organic linkers causes a dynamic Ni oxidation state, but in O 2 -saturated conditions, the electronic and physical structures of Ni 3 HAB 2 change little and oxygen-containing species strongly adsorb at potentials more cathodic than the reduction potential of the organic linker (E redox ∼ 0.3 V vs RHE). We hypothesize that a primary 2e − ORR mechanism occurs directly on the organic linkers (rather than the Ni) when E > E redox , but when E < E redox , H 2 O 2 production can also occur through Ni-mediated linker discharge. By operating the bulk electrosynthesis at a low overpotential (0.4 V vs RHE), up to 662 ppm of H 2 O 2 can be produced in a buffered neutral solution in an H-cell due to minimized strong adsorption of oxygenates. This work demonstrates the potential of conductive MOF catalysts for 2e − ORR and the importance of understanding catalytic active sites under electrochemical operation.

No abstract