Diadenosine tetraphosphate regulates biosynthesis of GTP in Bacillus subtilis.

Diadenosine tetraphosphate (Ap4A) is a putative second messenger molecule that is conserved from bacteria to humans. Nevertheless, its physiological role and the underlying molecular mechanisms are poorly characterized. We investigated the molecular mechanism by which Ap4A regulates inosine-5'-monophosphate dehydrogenase (IMPDH, a key branching point enzyme for the biosynthesis of adenosine or guanosine nucleotides) in Bacillus subtilis. We solved the crystal structure of BsIMPDH bound to Ap4A at a resolution of 2.45 Å to show that Ap4A binds to the interface between two IMPDH subunits, acting as the glue that switches active IMPDH tetramers into less active octamers. Guided by these insights, we engineered mutant strains of B. subtilis that bypass Ap4A-dependent IMPDH regulation without perturbing intracellular Ap4A pools themselves. We used metabolomics, which suggests that these mutants have a dysregulated purine, and in particular GTP, metabolome and phenotypic analysis, which shows increased sensitivity of B. subtilis IMPDH mutant strains to heat compared with wild-type strains. Our study identifies a central role for IMPDH in remodelling metabolism and heat resistance, and provides evidence that Ap4A can function as an alarmone.

Electrochemical and Electronic Charge Transport Properties of Ni-Doped LiMn2O4 Spinel Obtained from Polyol-Mediated Synthesis.

LiNi0.5Mn1.5O4 (LNMO) spinel has been extensively investigated as one of the most promising high-voltage cathode candidates for lithium-ion batteries. The electrochemical performance of LNMO, especially its rate performance, seems to be governed by its crystallographic structure, which is strongly influenced by the preparation methods. Conventionally, LNMO materials are prepared via solid-state reactions, which typically lead to microscaled particles with only limited control over the particle size and morphology. In this work, we prepared Ni-doped LiMn2O4 (LMO) spinel via the polyol method. The cycling stability and rate capability of the synthesized material are found to be comparable to the ones reported in literature. Furthermore, its electronic charge transport properties were investigated by local electrical transport measurements on individual particles by means of a nanorobotics setup in a scanning electron microscope, as well as by performing DFT calculations. We found that the scarcity of Mn3+ in the LNMO leads to a significant decrease in electronic conductivity as compared to undoped LMO, which had no obvious effect on the rate capability of the two materials. Our results suggest that the rate capability of LNMO and LMO materials is not limited by the electronic conductivity of the fully lithiated materials.

Monitoring local redox processes in LiNi0.5Mn1.5O4 battery cathode material by in operando EPR spectroscopy.

Despite the multitude of analytical methods available to characterize battery cathode materials, identifying the factors responsible for material aging is still challenging. We present the first investigation of transient redox processes in a spinel cathode during electrochemical cycling of a lithium ion battery by in operando electron paramagnetic resonance (EPR). The battery contains a LiNi0.5Mn1.5O4 (LNMO) spinel cathode, which is a material whose magnetic interactions are well understood. The evolution of the EPR signal in combination with electrochemical measurements shows the impact of Mn3+ on the Li+ motion inside the spinel. Moreover, state of charge dependent linewidth variations confirm the formation of a solid solution for slow cycling, which is taken over by mixed models of solid solution and two-phase formation for fast cycling due to kinetic restrictions and overpotentials. Long-term measurements for 480 h showed the stability of the investigated LNMO, but also small amounts of cathode degradation products became visible. The results point out how local, exchange mediated magnetic interactions in cathode materials are linked with battery performance and can be used for material characterization.

Temperature-Switchable Agglomeration of Magnetic Particles Designed for Continuous Separation Processes in Biotechnology.

The purpose of this work was the synthesis and characterization of thermally switchable magnetic particles for use in biotechnological applications such as protein purification and enzymatic conversions. Reversible addition-fragmentation chain-transfer polymerization was employed to synthesize poly(N-isopropylacrylamide) brushes via a "graft-from" approach on the surface of magnetic microparticles. The resulting particles were characterized by infrared spectroscopy and thermogravimetric analysis and their temperature-dependent agglomeration behavior was assessed. The influence of several factors on particle agglomeration (pH, temperature, salt type, and particle concentration) was evaluated. The results showed that a low pH value (pH 3-4), a kosmotropic salt (ammonium sulfate), and a high particle concentration (4 g/L) resulted in improved agglomeration at elevated temperature (40 °C). Recycling of particles and reversibility of the temperature-switchable agglomeration were successfully demonstrated for ten heating-cooling cycles. Additionally, enhanced magnetic separation was observed for the modified particles. Ionic monomers were integrated into the polymer chain to create end-group functionalized particles as well as two- and three-block copolymer particles for protein binding. The adsorption of lactoferrin, bovine serum albumin, and lysozyme to these ion exchange particles was evaluated and showed a binding capacity of up to 135 mg/g. The dual-responsive particles combined magnetic and thermoresponsive properties for switchable agglomeration, easy separability, and efficient protein adsorption.

Magnetic microgels, a promising candidate for enhanced magnetic adsorbent particles in bioseparation: synthesis, physicochemical characterization, and separation performance.

For specific applications in the field of high gradient magnetic separation of biomaterials, magnetic nanoparticle clusters of controlled size and high magnetic moment in an external magnetic field are of particular interest. We report the synthesis and characterization of magnetic microgels designed for magnetic separation purposes, as well as the separation efficiency of the obtained microgel particles. High magnetization magnetic microgels with superparamagnetic behaviour were obtained in a two-step synthesis procedure by a miniemulsion technique using highly stable ferrofluid on a volatile nonpolar carrier. Spherical clusters of closely packed hydrophobic oleic acid-coated magnetite nanoparticles were coated with cross linked polymer shells of polyacrylic acid, poly-N-isopropylacrylamide, and poly-3-acrylamidopropyl trimethylammonium chloride. The morphology, size distribution, chemical surface composition, and magnetic properties of the magnetic microgels were determined using transmission electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. Magnetically induced phase condensation in aqueous suspensions of magnetic microgels was investigated by optical microscopy and static light scattering. The condensed phase consists of elongated oblong structures oriented in the direction of the external magnetic field and may grow up to several microns in thickness and tens or even hundreds of microns in length. The dependence of phase condensation magnetic supersaturation on the magnetic field intensity was determined. The experiments using high gradient magnetic separation show high values of separation efficiency (99.9-99.97%) for the magnetic microgels.

Phosphate recovery from wastewater using engineered superparamagnetic particles modified with layered double hydroxide ion exchangers.

An innovative nanocomposite material is proposed for phosphate recovery from wastewater using magnetic assistance. Superparamagnetic microparticles modified with layered double hydroxide (LDH) ion exchangers of various compositions act as phosphate adsorbers. Magnetic separation and chemical regeneration of the particles allows their reuse, leading to the successful recovery of phosphate. Based upon the preliminary screening of different LDH ion exchanger modifications for phosphate selectivity and uptake capacity, MgFe-Zr LDH coated magnetic particles were chosen for further characterization and application. The adsorption kinetics of phosphate from municipal wastewater was studied in dependence with particle concentration, contact time and pH. Adsorption isotherms were then determined for the selected particle system. Recovery of phosphate and regeneration of the particles was examined via testing a variety of desorption solutions. Reusability of the particles was demonstrated for 15 adsorption/desorption cycles. Adsorption in the range of 75-97% was achieved in each cycle after 1 h contact time. Phosphate recovery and enrichment was possible through repetitive application of the desorption solution. Finally, a pilot scale experiment was carried out by treating 125 L of wastewater with the particles in five subsequent 25 L batches. Solid-liquid separation on this scale was carried out with a high-gradient magnetic filter (HGMF).

Pancreatic mucinous noncystic (colloid) carcinomas and intraductal papillary mucinous carcinomas are usually microsatellite stable.

Pancreatic mucinous noncystic (colloid) carcinomas (MNCC) differ from the usual ductal adenocarcinomas in their mucin expression profile and share with many extrapancreatic mucinous carcinomas the expression of MUC2. Because mucinous carcinomas are frequently associated with mutations of the DNA mismatch repair genes, causing them to exhibit the so-called mutator phenotype, we decided to investigate whether MNCCs of the pancreas are characterized by microsatellite instability (MSI). Twelve carcinomas with a mucinous phenotype (8 mucinous noncystic carcinomas, 3 intraductal papillary-mucinous carcinomas with an invasive muconodular component, and 1 ductal adenocarcinoma with an extensive mucinous noncystic component) and 11 ductal adenocarcinomas were immunostained with monoclonal antibodies to the mismatch repair gene products hMLH1, hMSH2, and hMSH6. For MSI analysis, DNA was isolated from microdissected tissue, and five primary microsatellites (BAT 25, BAT 26, D5S346, D17S250, and D2S123) were analyzed. MSI was diagnosed in case a novel allele was found, compared with the normal tissue. The criterion for LOH was a 75% signal reduction. All carcinomas tested exhibited nuclear expression of mismatch repair gene products, except for one MNCC that also showed MSI at the molecular level. The data suggest that pancreatic carcinomas with a mucinous phenotype (MUC2+/MUC1-) do not appear to normally exhibit mutations in the mismatch repair genes and therefore differ in their carcinogenesis from those in other organs.