In situ Raman spectroscopy on silicon nanowire anodes integrated in lithium ion batteries

Rapid decay of silicon anodes during lithiation poses a significant challenge in application of silicon as an anode material in lithium ion batteries. In situ Raman spectroscopy is a powerful method to study the relationship between structural and electrochemical data during electrode cycling and to allow the observation of amorphous as well as liquid and transient species in a battery cell. Herein, we present in situ Raman spectroscopy on high capacity electrode using uncoated and carbon-coated silicon nanowires during first lithiation and delithiation cycle in an optimized lithium ion battery setup and complement the results with operando X-ray reflection diffraction measurements. During lithiation, we were able to detect a new Raman signal at 1859 cm−1 especially on uncoated silicon nanowires. The detailed in situ Raman measurement of the first lithiation/delithiation cycle allowed to differentiate between morphology changes of the electrode as well as interphase formation from electrolyte components

A Complete Pathway Model for Lipid A Biosynthesis in Escherichia coli.

Lipid A is a highly conserved component of lipopolysaccharide (LPS), itself a major component of the outer membrane of Gram-negative bacteria. Lipid A is essential to cells and elicits a strong immune response from humans and other animals. We developed a quantitative model of the nine enzyme-catalyzed steps of Escherichia coli lipid A biosynthesis, drawing parameters from the experimental literature. This model accounts for biosynthesis regulation, which occurs through regulated degradation of the LpxC and WaaA (also called KdtA) enzymes. The LpxC degradation signal appears to arise from the lipid A disaccharide concentration, which we deduced from prior results, model results, and new LpxK overexpression results. The model agrees reasonably well with many experimental findings, including the lipid A production rate, the behaviors of mutants with defective LpxA enzymes, correlations between LpxC half-lives and cell generation times, and the effects of LpxK overexpression on LpxC concentrations. Its predictions also differ from some experimental results, which suggest modifications to the current understanding of the lipid A pathway, such as the possibility that LpxD can replace LpxA and that there may be metabolic channeling between LpxH and LpxB. The model shows that WaaA regulation may serve to regulate the lipid A production rate when the 3-deoxy-D-manno-oct-2-ulosonic acid (KDO) concentration is low and/or to control the number of KDO residues that get attached to lipid A. Computation of flux control coefficients showed that LpxC is the rate-limiting enzyme if pathway regulation is ignored, but that LpxK is the rate-limiting enzyme if pathway regulation is present, as it is in real cells. Control also shifts to other enzymes if the pathway substrate concentrations are not in excess. Based on these results, we suggest that LpxK may be a much better drug target than LpxC, which has been pursued most often

Regulation of the Escherichia coli HipBA Toxin-Antitoxin System by Proteolysis

Bacterial populations produce antibiotic-tolerant persister cells. A number of recent studies point to the involvement of toxin/antitoxin (TA) modules in persister formation. hipBA is a type II TA module that codes for the HipB antitoxin and the HipA toxin. HipA is an EF-Tu kinase, which causes protein synthesis inhibition and dormancy upon phosphorylation of its substrate. Antitoxins are labile proteins that are degraded by one of the cytosolic ATP-dependent proteases. We followed the rate of HipB degradation in different protease deficient strains and found that HipB was stabilized in a lon- background. These findings were confirmed in an in vitro degradation assay, showing that Lon is the main protease responsible for HipB proteolysis. Moreover, we demonstrated that degradation of HipB is dependent on the presence of an unstructured carboxy-terminal stretch of HipB that encompasses the last 16 amino acid residues. Further, substitution of the conserved carboxy-terminal tryptophan of HipB to alanine or even the complete removal of this 16 residue fragment did not alter the affinity of HipB for hipBA operator DNA or for HipA indicating that the major role of this region of HipB is to control HipB degradation and hence HipA-mediated persistence

Interplay between wet-dry-cycles and corrosion initiation due to chloride accumulation on AA1050 - A simple experimental approach

Generally aluminum alloys are susceptible to pitting corrosion in chloride containing environments, e. g. in marine climates. A well-known but not well-documented fact is the increasing of chloride concentration over a number of wet-dry cycles which are the outstanding feature of atmospheric corrosion. Moreover, time and frequency of wet-dry cycles and consequently the adsorption of chlorides are quite randomly under natural weathering, complicating the quantification of results. For example reported accumulation rates of chloride from the atmosphere on indoor aluminum surfaces range between 0.01 and 0.13μgcm-2a-1 [1]. In a simple experimental approach the authors simulated a number of natural wet-dry-cycles on an aluminum alloy AA1050. The chloride concentration was monitored by a Cl- -ion sensitive electrode and the electrode potential of the aluminum sample by measurement of the open circuit potential. The choronovoltametric experiments were complemented by FT-IRRAS-technique to investigate the development of oxide films and corrosion products. The deposition of sodium chloride itself cannot be directly detected by IRRAS because NaCl is infrared inactive. However, the influence of chloride ions can be deduced indirectly due to the formation of characteristic corrosion products and the oxide film composition (e.g. occurrence of cadwaladerite). Additionally, owing to the hygroscopic properties of the sodium chloride salt, the amount of adsorbed water is an indication of the salt deposition on the surface. The use of the IRRAS mode allows the study of very thin layers down to less than 1μm. This implies the possibility to detect alteration of the native surface layer before the corrosion attacks emerge. Post experimental microscopic investigation complete the study

FtsH-Dependent Degradation of Phage Shock Protein C in Yersinia enterocolitica and Escherichia coli▿

The widely conserved phage shock protein (Psp) extracytoplasmic stress response has been studied extensively in Escherichia coli and Yersinia enterocolitica. Both species have the PspF, -A, -B, and -C proteins, which have been linked to robust phenotypes, including Y. enterocolitica virulence. PspB and PspC are cytoplasmic membrane proteins required for stress-dependent induction of psp gene expression and for bacterial survival during the mislocalization of outer membrane secretin proteins. Previously, we reported that Y. enterocolitica PspB functions to positively control the amount of PspC by an uncharacterized posttranscriptional mechanism. In this study, we have discovered that the cytoplasmic membrane protease FtsH is involved in this phenomenon. FtsH destabilizes PspC in Y. enterocolitica, but coproduction of PspC with its binding partner PspB was sufficient to prevent this destabilization. In contrast, FtsH did not affect any other core component of the Psp system. These data suggested that uncomplexed PspC might be particularly deleterious to the bacterial cell and that FtsH acts as an important quality control mechanism to remove it. This was supported by the observation that toxicity caused by PspC production was reduced either by coproduction of PspB or by increased synthesis of FtsH. We also found that the phenomenon of FtsH-dependent PspC destabilization is conserved between Y. enterocolitica and E. coli