Adelic geometry and polarity

In the present paper we generalise transference theorems from the classical geometry of numbers to the geometry of numbers over the ring of adeles of a number field. To this end we introduce a notion of polarity for adelic convex bodies.     

Improved broad-spectrum antibiotics against Gram-negative pathogens via darobactin biosynthetic pathway engineering

The development of new antibiotics is imperative to fight increasing mortality rates connected to infections caused by multidrug-resistant (MDR) bacteria. In this context, Gram-negative pathogens listed in the WHO priority list are particularly problematic. Darobactin is a ribosomally produced and post-translationally modified bicyclic heptapeptide antibiotic selectively killing Gram-negative bacteria by targeting the outer membrane protein BamA. The native darobactin A producer Photorhabdus khanii HGB1456 shows very limited production under laboratory cultivation conditions. Herein, we present the design and heterologous expression of a synthetically engineered darobactin biosynthetic gene cluster (BGC) in Escherichia coli to reach an average darobactin A production titre of 13.4 mg L⁻¹. Rational design of darA variants, encoding the darobactin precursor peptide with altered core sequences, resulted in the production of 13 new ‘non-natural’ darobactin derivatives and 4 previously hypothetical natural darobactins. One of the non-natural compounds, darobactin 9, was more potent than darobactin A, and showed significantly improved activity especially against Pseudomonas aeruginosa (0.125 μg mL⁻¹) and Acinetobacter baumannii (1–2 μg mL⁻¹). Importantly, it also displayed superior activity against MDR clinical isolates of E. coli (1–2 μg mL⁻¹) and Klebsiella pneumoniae (1–4 μg mL⁻¹). Independent deletions of genes from the darobactin BGC showed that only darA and darE, encoding a radical forming S-adenosyl-l-methionine-dependent enzyme, are required for darobactin formation. Co-expression of two additional genes associated with the BGCs in hypothetical producer strains identified a proteolytic detoxification mechanism as a potential self-resistance strategy in native producers. Taken together, we describe a versatile heterologous darobactin platform allowing the production of unprecedented active derivatives in good yields, and we provide first experimental evidence for darobactin biosynthesis processes.

Heterologous expression of a synthetically engineered darobactin gene cluster in E. coli yields new darobactin derivatives with improved anti-Gram-negative activity. Targeted gene deletions provide first insights into biosynthetic steps.     

Ab initio calculations of CO physisorption on ceria(1 1 1)

Applying the method of increments, we have performed MP2 and CCSD(T) calculations for the physisorption of CO on a cerium site on the ceria(1 1 1) surface. Our calculations predict an interaction energy of −0.28 eV. We have compared our calculations to previous CCSD(T) calculations for the physisorption of CO on a cerium site on the ceria(1 1 0) surface and found a difference in the interaction energy that is related to the different structure of the two surfaces. On the ceria(110) surface only 30% of the interaction energy originate from electron correlation effects, but on the ceria(111) surface almost the entire binding energy (80%) is due to electron correlation effects. Analyses of the interaction energy contributions show that most of the electron correlation part originates from the interaction of CO with the O ions in the topmost surface layer.     

Synthesis and Structure of α/δ‐Hybrid Peptides—Access to Novel Helix Patterns in Foldamers

Origami peptides : A novel class of foldamers consisting of α/δ‐hybrid peptides has been investigated theoretically and experimentally by exploiting the rigidity of the side chain of a new δ‐amino acid prepared from D ‐glucose and D ‐xylose with a furanose side chain (see figure).

     

Silver–Ethene Complexes [Ag(η2‐C2H4)n][Al(ORF)4] with n=1, 2, 3 (RF=Fluorine‐Substituted Group)

Compounds including the free or coordinated gas‐phase cations [Ag(η²‐C₂H₄)_n]⁺ (n=1–3) were stabilized with very weakly coordinating anions [A]^? (A=Al{OC(CH₃)(CF₃)₂}₄, n=1 ( 1 ); Al{OC(H)(CF₃)₂}₄, n=2 ( 3 ); Al{OC(CF₃)₃}₄, n=3 ( 5 ); {(F₃C)₃CO}₃Al‐F‐Al{OC(CF₃)₃}₃, n=3 ( 6 )). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH₂Cl₂ solution. As a reference we also prepared the isobutene complex [(Me₂C?CH₂)Ag(Al{OC(CH₃)(CF₃)₂}₄)] ( 2 ). The compounds were characterized by multinuclear solution‐NMR, solid‐state MAS‐NMR, IR and Raman spectroscopy as well as by their single crystal X‐ray structures. MAS‐NMR spectroscopy shows that the [Ag(η²‐C₂H₄)₃]⁺ cation in its [Al{OC(CF₃)₃}₄]^? salt exhibits time‐averaged D_3h‐symmetry and freely rotates around its principal z‐axis in the solid state. All routine X‐ray structures (2θ_max.<55°) converged within the 3σ limit at C?C double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active C?C stretching modes indicated red‐shifts of 38 to 45 cm^?1, suggesting a slight C?C bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the C?C distance in [M(C₂H₄)] complexes from experimental Raman data was developed and meaningful C?C distances were obtained. These spectroscopic C?C distances compare well to newly collected X‐ray data obtained at high resolution (2θ_max.=100°) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG‐cc‐pVTZ methods. In most cases several isomers were considered. Additionally, [M(C₂H₄)₃] (M=Cu⁺, Ag⁺, Au⁺, Ni⁰, Pd⁰, Pt⁰, Na⁺) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of σ donation and π back donation. Comparing the group 10 and 11 analogues, we find that the lack of π back bonding in the group 11 cations is almost compensated by increased σ donation.     

Guest‐Directed Supramolecular Architectures of {W36} Polyoxometalate Crowns

The {W₃₆} isopolyoxotungstate cluster provides a stable inorganic molecular platform for the binding of inorganic and organic guest molecules. This is achieved by a binding pocket formed by six terminal oxo ligands located in the central cavity of the all‐inorganic cation binding host. Previously it was shown that the cluster can specifically bind primary amines and importantly, functionalized diamines through a combination of electrostatic and hydrogen bonding interactions. Here we transform this assembly strategy to utilize the binding of long‐chain alkyldiammonium guest cations to physically define the supramolecular structure of the clusters with respect to each other and demonstrate the structure direction as a function of alkyl chain length. The systematic variation of the chain length gives access to five supramolecular assemblies which were all fully characterized using single crystal XRD, TGA, ¹H NMR, and elemental analysis. In compound 1 , diprotonated 1,8‐diaminooctane molecules link the {W₃₆} clusters into infinite 1D zigzag chains, whereas compounds 2 and 3 feature trimeric {W₃₆} assemblies directly connected through protonated 1,9‐diaminononane ( 2 ) or 1,10‐diaminodecane ( 3 ) linkers . Compound 4 contains dumb‐bell shaped dimeric units as a result of direct center‐to‐center linkages between the {W₃₆} clusters formed by protonated 1,12‐diaminododecane. In compound 5 , triply protonated bis(hexamethylene)triamine was employed to obtain linear 1D chains of directly connected {W₃₆} cluster units.     

The molecular composition of non-modified and acac-modified propoxide and butoxide precursors of zirconium and hafnium dioxides

Long-term storage at 0 °C of a paraffin-sealed flask with commercial 70 wt% solution of zirconium n-propoxide in n-propanol resulted in crystallization of an individual oxoalkoxide complex Zr₄O(OⁿPr)₁₄(ⁿPrOH)₂ in over 20% yield. The structure of this molecule can be described as a triangular Zr₃(μ₃-O)(OR)₁₀(ROH) core of 3 edge-sharing octahedrons with an additional Zr(OR)₄(ROH) unit attached through a pair of (μ-OR) bridges. Mass spectrometric and ¹H NMR investigation of the commercial samples of the most broadly applied zirconium and hafnium n-propoxides and n-butoxides indicate the presence of analogous species in the commercial alkoxide precursors. The content of oxo-alkoxide species in the commercial precursors has been estimated to be ~20% for n-propoxide and ~35% for zirconium n-butoxide. A new route has been presented for synthesis of the individual crystalline mixed ligand precursor [Zr(OⁿPr)(OⁱPr)₃(ⁱPrOH)]₂, from zirconium n-propoxide. A high yield has been observed (~90%), indicative of an almost complete precursor transformation. Mass spectrometry has shown that the synthesized mixed ligand precursor is dimeric, which makes it an attractive alternative to zirconium n-propoxide. Addition of 1 eq of Acetylacetone to zirconium or hafnium alkoxide precursors results in formation of dimeric [M(OR)₃(acac)]₂ in high yields. These species have limited stability (much higher for Hf than for Zr) and transform in solution into hydrolysis-insensitive M(acac)₄ through very unstable M(acac)₃(OR) intermediates containing 7-coordinated metal centers. This transformation can be followed kinetically in hydrocarbon solvents by ¹H NMR and is noticeably accelerated by addition of parent alcohols. The obtained results clearly reveal limited applicability of EXAFS and XANES techniques for the study of such systems, especially in the context of structure prediction. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Charge and magnetization inhomogeneities in diluted magnetic semiconductors

It is predicted that III-V diluted magnetic semiconductors can exhibit stripelike modulations of magnetization and carrier concentration. This inhomogeneity results from the strong dependence of the magnetization on the carrier concentration. Within Landau theory, a characteristic temperature T* below the Curie temperature is found so that below T* the equilibrium magnetization shows modulations, which are strongly anharmonic. The wavelength and amplitude of the modulation rise for decreasing temperature, starting from zero at T*. Above T*, the equilibrium state is homogeneous, but the coupling between charge and magnetization leads to the appearance of an electrically charged layer in domain walls.     

Laser-fabricated dielectric optical components for surface plasmon polaritons

Fabrication of dielectric optical components for surface plasmon polaritons (SPPs) by two-photon polymerization (2PP) is studied. This direct-write femtosecond laser technology provides a low-cost and flexible method for the fabrication and investigation of plasmonic structures and optical components. Using the 2PP technique, we fabricated narrow dielectric ridges with dimensions as small as 150 nm on metal surfaces. SPP excitation with the laser-fabricated structures and guiding along them are demonstrated.