Supercontinuum generation in quasi-phase-matched LiNbO3 waveguide pumped by a Tm-doped fiber laser system

We demonstrate self-referencing of a Tm-doped fiber oscillator-amplifier system by performing octave-spanning supercontinuum generation in a periodically poled lithium niobate waveguide. We model the supercontinuum generation numerically and show good agreement with the experiment.     

Peptide functionalized polydiacetylene liposomes act as a fluorescent turn-on sensor for bacterial lipopolysaccharide

Mixed polydiacetylene (PDA) liposomes functionalized on their surface with a fluorescent pentalysine peptide derivative and histidine in a ratio of 1:9 can identify bacterial lipopolysaccharide (LPS). Upon photopolymerization of the self-assembled liposomes the initial fluorescence of the peptide-diacetylene amphiphiles is quenched. Interaction with LPS in aqueous solution or on the surface of E. coli DH5α restores the fluorescence. This increase in fluorescence is selective for LPS relative to other negatively charged analytes including nucleotides and ctDNA. This simple turn-on fluorescent sensor allows detecting LPS even at low micromolar concentrations.     

Li ion diffusion in the anode material Li12Si7: ultrafast quasi-1D diffusion and two distinct fast 3D jump processes separately revealed by 7Li NMR relaxometry

The intermetallic compounds Li(x)Si(y) have attracted considerable interest because of their potential use as anode materials in Li ion batteries. In addition, the crystalline phases in the Li-Si phase diagram turn out to be outstanding model systems for the measurement of fast Li ion diffusion in solids with complex structures. In the present work, the Li self-diffusivity in crystalline Li(12)Si(7) was thoroughly probed by (7)Li NMR spin-lattice relaxation (SLR) measurements. Variable-temperature and -frequency NMR measurements performed in both the laboratory and rotating frames of reference revealed three distinct diffusion processes in Li(12)Si(7). The diffusion process characterized by the highest Li diffusivity seems to be confined to one dimension. It is one of the fastest motions of Li ions in a solid at low temperatures reported to date. The Li jump rates of this hopping process followed Arrhenius behavior; the jump rate was ~10(5) s(-1) at 150 K and reached 10(9) s(-1) at 425 K, indicating an activation energy as low as 0.18 eV.     

Influence of flexible spacers on liquid-crystalline self-assembly of T-shaped bolaamphiphiles

T-shaped bolaamphiphiles composed of a biphenyl rigid core, a semiperfluorinated lateral chain, two polar 1,2-diol groups in the terminal positions and flexible alkyl spacers connecting the polar groups with the biphenyl core have been synthesized and investigated by polarizing microscopy, DSC and X-ray scattering. The influence of spacer length and position of the spacer on the self-assembly in liquid-crystalline phases was studied. A series of four different columnar phases (Col(hex)/p6mm, Col(rec)/p2gg, Col(squ)/p4gm and Col(squ)/p4mm), representing liquid-crystalline honeycomb structures composed of cylinders having hexagonal, pentagonal, and square cross section, were found on increasing the spacer length. It is also shown that introduction of aliphatic spacers in the backbone of the T-shaped bolaamphiphiles replaces the Col(rec)/c2mm phase made up of rhombic cylinders with the Col(squ)/p4mm phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Col(rec)/p2gg to Col(squ)/p4gm. A temperature-dependent second-order phase transition between these two pentagonal cylinder structures was observed for the first time. Beside these effects on cylinder shape and phase symmetry the flexible spacer units also lead to reduced phase transition temperatures and allow adjustment of cylinder side length to envelop a wider range of side-chain sizes. Electron density maps suggest that this may involve sacrificing some of the hydrogen bonds.     

Conversion of fatty aldehydes to alka(e)nes and formate by a cyanobacterial aldehyde decarbonylase: cryptic redox by an unusual dimetal oxygenase

Cyanobacterial aldehyde decarbonylase (AD) catalyzes conversion of fatty aldehydes (R-CHO) to alka(e)nes (R-H) and formate. Curiously, although this reaction appears to be redox-neutral and formally hydrolytic, AD has a ferritin-like protein architecture and a carboxylate-bridged dimetal cofactor that are both structurally similar to those found in di-iron oxidases and oxygenases. In addition, the in vitro activity of the AD from Nostoc punctiforme (Np) was shown to require a reducing system similar to the systems employed by these O(2)-utilizing di-iron enzymes. Here, we resolve this conundrum by showing that aldehyde cleavage by the Np AD also requires dioxygen and results in incorporation of (18)O from (18)O(2) into the formate product. AD thus oxygenates, without oxidizing, its substrate. We posit that (i) O(2) adds to the reduced cofactor to generate a metal-bound peroxide nucleophile that attacks the substrate carbonyl and initiates a radical scission of the C1-C2 bond, and (ii) the reducing system delivers two electrons during aldehyde cleavage, ensuring a redox-neutral outcome, and two additional electrons to return an oxidized form of the cofactor back to the reduced, O(2)-reactive form.     

Spin correlations in nonperturbative electron–positron pair creation by petawatt laser pulses colliding with a TeV proton beam

The influence of the electron spin degree of freedom on nonperturbative electron–positron pair production by high-energy proton impact on an intense laser field of circular polarization is analyzed. Predictions from the Dirac and Klein–Gordon theories are compared and a spin-resolved calculation is performed. We show that the various spin configurations possess very different production probabilities and discuss the transfer of helicity in this highly nonlinear process. Our predictions could be tested by combining the few-TeV proton beam at CERN-LHC with an intense laser pulse from a table-top petawatt laser source.     

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

Polyoxometalates (POMs) are molecular metal‐oxide anions applied in energy conversion and storage, manipulation of biomolecules, catalysis, as well as materials design and assembly. Although often overlooked, the interplay of intrinsically anionic POMs with organic and inorganic cations is crucial to control POM self‐assembly, stabilization, solubility, and function. Beyond simple alkali metals and ammonium, chemically diverse cations including dendrimers, polyvalent metals, metal complexes, amphiphiles, and alkaloids allow tailoring properties for known applications, and those yet to be discovered. This review provides an overview of fundamental POM–cation interactions in solution, the resulting solid‐state compounds, and behavior and properties that emerge from these POM–cation interactions. We will explore how application‐inspired research has exploited cation‐controlled design to discover new POM materials, which in turn has led to the quest for fundamental understanding of POM–cation interactions.     

To be,or not to be…Electrochemist?

Journal of Solid State Electrochemistry -     

Light‐Induced Ruthenium‐Catalyzed Nitrene Transfer Reactions: A Photochemical Approach towards N‐Acyl Sulfimides and Sulfoximines

1,4,2‐Dioxazol‐5‐ones are five‐membered heterocycles known to decarboxylate under thermal or photochemical conditions, thus yielding N‐acyl nitrenes. Described herein is a light‐induced ruthenium‐catalyzed N‐acyl nitrene transfer to sulfides and sulfoxides by decarboxylation of 1,4,2‐dioxazol‐5‐ones at room temperature, thus providing direct access to N‐acyl sulfimides and sulfoximines under mild reaction conditions. In addition, a one‐pot sulfur imidation/oxidation sequence catalyzed by a single ruthenium complex is reported.     

Polyoxometalate Ionic Liquids as Self‐Repairing Acid‐Resistant Corrosion Protection

Corrosion is a global problem for any metallic structure or material. Herein we show how metals can easily be protected against acid corrosion using hydrophobic polyoxometalate‐based ionic liquids (POM‐ILs). Copper metal disks were coated with room‐temperature POM‐ILs composed of transition‐metal functionalized Keggin anions [SiW₁₁O₃₉TM(H₂O)]^n? (TM=Cu^II, Fe^III) and quaternary alkylammonium cations (C_nH_{2 n+1})₄N⁺ (n=7–8). The corrosion resistance against acetic acid vapors and simulated “acid rain” was significantly improved compared with commercial ionic liquids or solid polyoxometalate coatings. Mechanical damage to the POM‐IL coating is self‐repaired in less than one minute with full retention of the acid protection properties. The coating can easily be removed and recovered by rinsing with organic solvents.