Sulfite Action in Glycolytic Inhibition: In Vivo Real‐Time Observation by Hyperpolarized 13C NMR Spectroscopy

Detecting the molecular targets of xenobiotic substances in vivo poses a considerable analytical challenge. Here, we describe the use of an NMR‐based tracer methodology for the instantaneous in vivo observation of sulfur(IV) action on cellular metabolism. Specifically, we find that glycolytic flux is directed towards sulfite adducts of dihydroxyacetone phosphate and pyruvate as off‐pathway intermediates that obstruct glycolytic flux. In particular, the pyruvate–sulfite association hinders the formation of downstream metabolites. The apparent in vivo association constant of pyruvate and sulfite agrees with the apparent inhibition constant of CO₂ formation, thus supporting the importance of pyruvate interception in disturbing central metabolism and inhibiting NAD regeneration.     

Numerical evaluation of a PEM fuel cell with conventional flow fields adapted to tubular plates

In this research a 3D numerical study on a PEM fuel cell model with tubular plates is presented. The study is focused on the performance evaluation of three flow fields with cylindrical geometry (serpentine, interdigitated and straight channels) in a fuel cell. These designs are proposed not only with the aim to reduce the pressure losses that conventional designs exhibit with rectangular flow fields but also to improve the mass transport processes that take place in the fuel cell cathode. A commercial computational fluid dynamics (CFD) code was used to solve the numerical model. From the numerical solution of the fluid mechanics equations and the electrochemical model of Butler-Volmer different analysis of pressure losses, species concentration, current density, temperature and ionic conductivity were carried out. The results were obtained at the flow channels and the catalyst layers as well as in the gas diffusion layers and the membrane interfaces. Numerical results showed that cylindrical channel configurations reduced the pressure losses in the cell due to the gradual reduction of the angle at the flow path and the twist of the channel, thus facilitating the expulsion of liquid water from the gas diffusion layers and in turn promoting a high oxygen concentration at the triple phase boundary of the catalyst layers. Moreover, numerical results were compared to polarization curves and the literature data reported for similar designs. These results demonstrated that conventional flow field designs applied to conventional tubular plates have some advantages over the rectangular designs, such as uniform pressure and current density distributions among others, therefore they could be considered for fuel cell designs in portable applications.     

A comparative study of the electrical and mechanical properties of epoxy nanocomposites reinforced by CVD- and arc-grown multi-wall carbon nanotubes

In this study, three different types of multi-wall carbon nanotubes (MWCNTs) were compared as nanostructured reinforcements in epoxy polymers: commercially available CVD-MWCNTs, synthesised in an industrial process, aligned-CVD-MWCNTs and arc-grown MWCNTs, both obtained from a lab-scale processes. The nanocomposite properties were characterised by means of electron microscopy, rheological, electrical and mechanical methods. Industrial CVD-MWCNTs are favourable for the implication of an electrical conductivity in the epoxy due to their high tendency to form conducting networks. The less entangled structure of aligned-CVD-MWCNTs turns out to be favourable for an easy dispersion and low viscosity in epoxy at similar conductivities compared to the CVD-MWCNTs. Additionally, they provide the highest increase in fracture toughness (∼17%). Arc-grown MWCNTs do not offer any electrical conductivity in epoxy without sufficient purification methods. Their high level of impurities and short length further complicate the transfer of their good electrical and mechanical properties into the nanocomposite.     

Influence of nitrogen uptake and heat treatment on the microstructural characteristics and corrosion performance of X190CrVMo20-4-1 steel produced by supersolidus liquid-phase sintering

Martensitic stainless steel powder exhibits a high nitrogen uptake when densified by supersolidus liquid-phase sintering in a nitrogen atmosphere, but the optimum uptake, which is beneficial to its resistance to corrosion, is unknown. In this study, the resistance of high-carbon martensitic stainless steel X190CrVMo20-4-1 densified in a nitrogen atmosphere against pitting corrosion was explored. This was to clarify the impact of nitrogen uptake in the steel matrix in the quenched and tempered condition on its corrosion resistance in an aqueous solution. Samples were subjected to potentiodynamic polarisation tests in a de-aerated, 1 wt% NaCl solution. Results revealed that the X190 steel densified in a nitrogen atmosphere at 40-kPa pressure, subjected to deep cryogenic treatment in liquid nitrogen at an austenitising temperature of 1150°C and tempered at 200°C, had the best pitting corrosion resistance with a breakdown potential of 142 ± 11 mV/SCE and a hardness of 738 ± 4 HV10. The matrix around the M₇C₃ carbides and MX carbonitrides suffered high pitting susceptibility. The implications of this study serve as a basis for the improvement of the functional properties of steels.     

Suitability of urban wastes for crop production in Zaria,northern Nigeria: bioavailability and geochemical fractions of potentially toxic elements

A savannah soil amended with two urban wastes and planted with sorghum (Sorghum bicolor) in a pot experiment was evaluated for chemical forms and phytoavailability of Cr, Ni and Pb. The metals were partitioned into seven operationally defined chemical fractions: mobile (F1), easily mobilisable (F2), occluded in Mn oxides (F3), organically bound (F4), occluded in amorphous Fe oxides (FeOx_am, F5), occluded in crystalline Fe oxides (FeOx_c, F6), and residual (F7). Although the application of the urban wastes increased the total concentrations of the metals in the soil, there were no corresponding increases in Cr and Ni uptake by sorghum except for Pb uptake. Waste application increased mobile Ni (F1) but decreased the residual form (F7). The organically bound Pb (F4) was increased at the expense of residual Pb (F7). With respect to Cr, waste application increased Cr form occluded in non-crystalline Fe oxides (F5) in the soil. Bioassay of the test crop indicated that the uptake of Pb by sorghum (Y-Pb) correlated significantly with Pb occluded in non-crystalline and crystalline Fe oxides (F5 and F6). Since a single application of urban wastes to this savannah soil significantly increased Pb uptake by sorghum, the consequences of long-term applications under urban and peri-urban agriculture (UPA) should be of great concern; particularly with respect to children’s exposure to Pb through consumption of food and vegetables.     

An Iterative O‐Methyltransferase Catalyzes 1,11‐Dimethylation of Aspergillus fumigatus Fumaric Acid Amides

S‐adenosyl‐l ‐methionine (SAM)‐dependent methyltransfer is a common biosynthetic strategy to modify natural products. We investigated the previously uncharacterized Aspergillus fumigatus methyltransferase FtpM, which is encoded next to the bimodular fumaric acid amide synthetase FtpA. Structure elucidation of two new A. fumigatus natural products, the 1,11‐dimethyl esters of fumaryl‐l ‐tyrosine and fumaryl‐l ‐phenylalanine, together with ftpM gene disruption suggested that FtpM catalyzes iterative methylation. Final evidence that a single enzyme repeatedly acts on fumaric acid amides came from an in vitro biochemical investigation with recombinantly produced FtpM. Size‐exclusion chromatography indicated that this methyltransferase is active as a dimer. As ftpA and ftpM homologues are found clustered in other fungi, we expect our work will help to identify and annotate natural product biosynthesis genes in various species.     

Structure and Substrate Recognition of the Bottromycin Maturation Enzyme BotP

The bottromycins are a family of highly modified peptide natural products, which display potent antimicrobial activity against Gram‐positive bacteria, including methicillin‐resistant Staphylococcus aureus. Bottromycins have recently been shown to be ribosomally synthesized and post‐translationally modified peptides (RiPPs). Unique amongst RiPPs, the precursor peptide BotA contains a C‐terminal “follower” sequence, rather than the canonical N‐terminal “leader” sequence. We report herein the structural and biochemical characterization of BotP, a leucyl‐aminopeptidase‐like enzyme from the bottromycin pathway. We demonstrate that BotP is responsible for the removal of the N‐terminal methionine from the precursor peptide. Determining the crystal structures of both apo BotP and BotP in complex with Mn²⁺ allowed us to model a BotP/substrate complex and to rationalize substrate recognition. Our data represent the first step towards targeted compound modification to unlock the full antibiotic potential of bottro‐ mycin.     

Sanierung eines PCE-Schadens in einem makroskopisch oxischen Grundwasserleiter durch Stimulation anaerober dehalogenierender Bakterien

Grundwasser - Eine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem...     

Molecular Cross-Talk between Gravity- and Light-Sensing Mechanisms in Euglena gracilis

Euglena gracilis is a photosynthetic flagellate. To acquire a suitable position in its surrounding aquatic environment, it exploits light and gravity primarily as environmental cues. Several physiological studies have indicated a fine-tuned relationship between gravity sensing (gravitaxis) and light sensing in E. gracilis. However, the underlying molecular mechanism is largely unknown. The photoreceptor photoactivated adenylyl cyclase (PAC) has been studied for over a decade. Nevertheless, no direct/indirect interaction partner (upstream/downstream) has been reported for PAC. It has been shown that a specific protein, kinase A (PKA), showed to be involved in phototaxis and gravitaxis. The current study reports the localization of the specific PKA and its relationship with PAC.