No abstract

The second of two reactions in a recently discovered pathway through which saturated fatty acids are converted to alkanes (and unsaturated fatty acids to alkenes) in cyanobacteria entails scission of the C1–C2 bond of a fatty aldehyde intermediate by the enzyme aldehyde decarbonylase (AD), a ferritin-like protein with a dinuclear metal cofactor of unknown composition. We tested for and failed to detect carbon monoxide (CO), the proposed C1-derived co-product of alkane synthesis, following the in vitro conversion of octadecanal (R-CHO, where R = n-C17H35) to heptadecane (R-H) by the Nostoc punctiforme AD isolated following its overproduction in Escherichia coli. Instead, we identified formate (HCO2−) as the stoichiometric co-product of the reaction. Results of isotope-tracer experiments indicate that the aldehyde hydrogen is retained in the HCO2− and the hydrogen in the nascent methyl group of the alkane originates, at least in part, from solvent. With these characteristics, the reaction appears to be formally hydrolytic, but the improbability of a hydrolytic mechanism having the primary carbanion as the leaving group, the structural similarity of the ADs to other O2-activating non-heme di-iron proteins, and the dependence of in vitro AD activity on the presence of a reducing system implicate some type of redox mechanism. Two possible resolutions to this conundrum are suggested.

Best of both worlds: A heterostructured material is synthesized that comprises a core of layered lithium-rich material and an outer layer of nanospinel material. This spinel/layered heterostructured material maximizes the inherent advantages of the 3D Li(+) insertion/extraction framework of the spinel structure and the high Li(+) storage capacity of the layered structure. The material exhibits super-high reversible capacities, outstanding rate capability and excellent cycling ability.

Hierarchical Li1.2 Ni0.2 Mn0.6 O2 nanoplates with exposed {010} planes are designed and synthesized. In combination with the advantages from the hierarchical archi-tecture and the exposed electrochemically active {010} planes of layered materials, this material satisfies both efficient ion and electron transport and thus shows superior rate capability and excellent cycling stability.

The view that the theoretical capacity of spinel Li4Ti5O12 is limited by the number of available octahedral sites to accommodate lithium ions is debated. Combining the electrochemical and XRD results with the crystal structure of Li4Ti5O12, we demonstrate the corresponding reaction mechanism of the low-potential intercalation behavior of Li4Ti5O12 and modify the classical viewpoint on the theoretical capacity of Li4Ti5O12. The theoretical capacity of Li4Ti5O12 is limited by the number of tetravalent titanium ions, but not the octahedral or tetrahedral sites to accommodate lithium ions in the voltage range of 2.5 to 0.01 V, corresponding to 293 mAhg−1, but not 175 mAhg−1.