Synthesis of boron-doped Si particles by ball milling and application in Li-ion batteries

International audienceBoron-doped Si particles were prepared by high-energy ball-milling of pure B and Si in various proportions (0, 10^2^0, 10^2^1, 10^2^2 and 10^2^3 atoms B per mole Si). Despite the fact that only a fraction of the added B atoms were incorporated into the Si lattice, a significant decrease of the Si electrical resistivity was observed, leading to a minimum electrical resistivity of 0.13Ωcm for the sample milled with 10^2^1 atoms B per mole Si compared to 190Ωcm for the boron-free sample. Electrochemical investigations focused on these two samples showed that the B-doping of Si does not improve significantly the performance of the composite Si-based electrode for Li-ion batteries in terms of cycle life, coulombic efficiency and high-rate chargeability. Through an analysis of anodic polarization curves, it was also shown that the delithiation reaction is mainly controlled by the Li-diffusion kinetics from a rate of ~4C on both electrodes. Lastly, it was shown that the use of a resonant acoustic mixer for the mixing of the (Si+carbon black+carboxymethyl cellulose) components increases the cycle life of the composite electrode

Mycobacterium tuberculosis DNA gyrase possesses two functional GyrA-boxes.

International audienceIn contrast with most bacteria which possess two type II topoisomerases (topoisomerase IV and DNA gyrase), Mycobacterium tuberculosis possesses only one, DNA gyrase, which is functionally a hybrid enzyme. Functional differences between the two type IIA topoisomerases are thought to be specified by a CTD (C-terminal DNA-binding domain), which controls DNA recognition. To explore the molecular mechanism responsible for the hybrid functions of the M. tuberculosis DNA gyrase, we conducted a series of sequence analyses and structural and biochemical experiments with the isolated GyrA CTD and the holoenzyme. Although the CTD displayed a global structure similar to that of bona fide GyrA and ParC paralogues, it harbours a second key motif similar in all respects to that of the conserved GyrA-box sequence motif. Biochemical assays showed that the GyrA-box is responsible for DNA supercoiling, whereas the second GyrA-box-l (GyrA-box-like motif) is responsible for the enhanced decatenation activity, suggesting that the mechanistic originality of M. tuberculosis DNA gyrase depends largely on the particular DNA path around the CTD allowed for by the presence of GyrA-box-l. The results of the present study also provide, through phylogenetic exploration of the entire Corynebacterineae suborder, a new and broader insight into the functional diversity of bacterial type IIA topoisomerases