Anaerobic microorganisms of the Geobacter genus are effective electron sources for the synthesis of nanoparticles, for bioremediation of polluted water, and for the production of electricity in fuel cells. In multistep reactions, electrons are transferred via iron/heme cofactors of c‐type cytochromes from the inner cell membrane to extracellular metal ions, which are bound to outer membrane cytochromes. We measured electron production and electron flux rates to 5×105 e s−1 per G. sulfurreducens. Remarkably, these rates are independent of the oxidants, and follow zero order kinetics. It turned out that the microorganisms regulate electron flux rates by increasing their Fe2+/Fe3+ ratios in the multiheme cytochromes whenever the activity of the extracellular metal oxidants is diminished. By this mechanism the respiration remains constant even when oxidizing conditions are changing. This homeostasis is a vital condition for living systems, and makes G. sulfurreducens a versatile electron source.

Compartmentalization of metal ions is crucial in biology as well as in materials science. For the synthesis of single source precursors, the preorganization of different metal ions is of particular interest for the lowtemperature generation of mixed metal oxides. On the basis of a potentially Ω-shaped salen-type ligand providing an N 2 O 2 as well as an O 2 O 2 coordination site, mixed metal coordination compounds with Cu(II) or Ni(II) and alkali metal ions have been studied for their structural and optical properties. UV− vis and 1 H NMR titrations show that the obtained compounds adopt partially different structures in solution compared to the solid state. In the latter case, the coordination geometry is mainly governed by the size of the alkali metal ion as well as the transition metal ion used. ■ INTRODUCTIONThe precise arrangement and compartmentalization of metal ions are important both in biology as well as in materials science.1−5 Siderophores such as iron chelators produced by microbes are for example prototypes for metal specific uptaking agents. These could be used in industrial or environmental cleanup processes to selectively extract metal ions.6 Artificial systems such as salen (N,N′-disalicylidene-ethylenediamine) and its derivatives are commonly employed as versatile chelate ligands in coordination chemistry and obtained by a straightforward condensation reaction. 7 Containing two Schiff base 8 coordinating moieties, this family of ligands is able to bind to transition-metal ions in a tetradentate fashion forming stable complexes through its N 2 O 2 site. Furthermore, they represent versatile ligands type thanks to their tunable design. Several structural studies were undertaken on bi-or trinuclear mono-or heterometallic Schiff base complexes. 33−37Interesting trinuclear structures of Zn-salen based complexes were reported in Cai's work, by tuning the counterions, the solvent, or the reaction conditions. 68 A structural description of a binuclear Zn complex able to undergo transmetalation as well as polynuclear salen compounds was presented by Kleij and coworkers. 69,70 On the basis of salen-type ligands, Nabeshima et al. have described multiple-metal containing host−guest complexes using transmetalation reactions to incorporate the guest ions. 22,71 These ligands can adopt, depending on the ionic radius of the metal ions, a helical conformation in solution. 72,73 They also reported the first efficient and selective introduction of three different metal ions into one ligand under thermodynamic control. 4 While numerous transition metal ions were widely employed along with the salen-derived ligands for multiple purposes, the series with alkali metal ions remain however not entirely investigated. 21,74,75 Previous tests to use alkali ions as guests in larger H 2 L salen-type ligands using also transmetalation were unsuccessful.72 While a recent publication by the Nabeshima group deals with the formation of alkali metal ion complexes with macrocyclic ligands in solution, no 1

Background: Joint arthroplasty has improved the quality of life of patients worldwide, but infections of the prosthesis are frequent and cause significant morbidity. Antimicrobial coatings for implants promise to prevent these infections. Methods: We have synthesized nanocapsules of titanium dioxide in amorphous or anatase form containing silver as antibacterial agent and tested their impact on bacterial growth. Furthermore, we explored the possible effect of the nanocapsules on the immune system. First, we studied their uptake into macrophages using a combination of electron microscopy and energy-dispersive spectroscopy. Second, we exposed immune cells to the nanocapsules and checked their activation state by flow cytometry and enzyme-linked immunosorbent assay. Results: Silver-containing titanium dioxide nanocapsules show strong antimicrobial activity against both E. coli and S. aureus and even against a multidrug-resistant strain of S. aureus. We could demonstrate the presence of the nanocapsules in macrophages, but, importantly, the nanocapsules did not affect cell viability and did not activate proinflammatory responses at doses up to 20 μg/mL. Conclusion: Our bactericidal silver-containing titanium dioxide nanocapsules fulfill important prerequisites for biomedical use and represent a promising material for the coating of artificial implants.

Indium is a nonphysiological toxic metal widely used in industry. While misunderstood, its toxicity is proposed to be linked to a perturbation of Fe 3+ homeostasis through the binding of In 3+ ions to essential iron metalloproteins such as transferrins. Therefore, the monitoring of In 3+ and Fe 3+ in biological environments is of prime interest for both basic research and diagnosis. Here we report the design of a salen-type anthracene-based probe able to selectively sense and discriminate In 3+ and Fe 2+/3+ ions by fluoro-colorimetry.1

P2−Na 0.67 Mn 0.6 Fe 0.25 Al 0.15 O 2 (NaMFA) was developed as a cheaper and less-toxic cathode material for sodiumion batteries than the Co analogous, P2−Na 0.67 Mn 0.6 Fe 0.25 Co 0.15 O 2 (NaMFC). Despite cobalt being considered to stabilize layered structures upon cycling, NaMFA proved to have not only a higher specific charge 163 mAh g −1 compared to 141 mAh g −1 at a 0.1 C rate but also a better cycling stability and rate capability than NaMFC. The structural transitions occurring during sodiation/desodiation in the layered frames were characterized by operando X-ray diffraction (XRD) and Xray absorption spectroscopy (XAS) analyses. Aluminum was found to stabilize the P2-phase and favor the Mn reduction on discharge, increasing the amount of Na atoms reintercalated in the structure.