A portable ultrahigh‐vacuum system for advanced synchrotron radiation studies of thin films and nanostructures: EuSi2 nano‐islands

A portable ultrahigh‐vacuum system optimized for in situ variable‐temperature X‐ray scattering and spectroscopy experiments at synchrotron radiation beamlines was constructed and brought into operation at the synchrotron radiation facility ANKA of the Karlsruhe Institute of Technology, Germany. Here the main features of the new instrument are described and its capabilities demonstrated. The surface morphology, structure and stoichiometry of EuSi₂ nano‐islands are determined by in situ grazing‐incidence small‐angle X‐ray scattering and X‐ray absorption spectroscopy. A size reduction of about a factor of two of the nano‐islands due to silicide decomposition and Eu desorption is observed after sample annealing at 1270 K for 30 min.     

Catalytic Dendrophanes as Enzyme Mimics: Synthesis,Binding Properties,Micropolarity Effect,and Catalytic Activity of Dendritic Thiazolio-cyclophanes

Catalytic dendrophanes 9 and 10 were prepared as functional mimics of the thiamine-diphosphate-dependent enzyme pyruvate oxidase, and studied as catalysts in the oxidation of naphthalene-2-carbaldehyde ( 4 ) to methyl naphthalene-2-carboxylate ( 8 ) (Scheme 1). They are composed of a thiazolio-cyclophane initiator core with four generation 2 (G-2) poly(etheramide) dendrons attached. The two dendrophanes were synthesized by a convergent growth strategy by coupling dendrons 11 and 12 , respectively (Scheme 2) with (chloromethyl)-cyclophane 42 (Scheme 5) and subsequent conversion with 4-methylthiazole (Scheme 7). The X-ray crystal structures of cyclophane precursors 30 (Scheme 3), 37 , and 38 (Scheme 5) on the way to dendrophanes were determined (Fig. 1). The crystal-structure analysis of the benzene clathrate of 37 revealed the formation of channel-like stacks by the cyclophane which incorporate its morpholinomethyl side chain and the enclathrated benzene molecule (Fig. 2). The interactions of the enclathrated benzene molecule with the phenyl rings of the two adjacent cyclophane molecules in the stack closely resemble those between neighboring benzene molecules in crystalline benzene (Fig. 3). The characterization by MALDI-TOF-MS (Fig. 4), and ¹H- and ¹³C-NMR spectroscopy (Fig. 5) proved the monodispersity of the G-2 dendrophanes 9 and 10 with molecular weights up to 11500 Da (for 10 ). ¹H-NMR and fluorescence binding titrations in H₂O and aqueous MeOH showed that 9 and 10 form stable 1 : 1 complexes with naphthalene-2-carbaldehyde ( 4 ) and 6-(p-toluidino)naphthalene-2-sulfonate ( 48 , TNS) (Tables 1 and 2). The evaluation of the fluorescence emission maxima of bound TNS revealed that the dendritic branching creates a microenvironment of distinctly reduced polarity at the cyclophane core by limiting its exposure to bulk solvent. Initial rate studies for the oxidation of naphthalene-2-carbaldehyde to methyl naphthalene-2-carboxylate in basic aqueous MeOH in the presence of flavin derivative 6 revealed only a weak catalytic activity of dendrophanes 9 and 10 (Table 3), despite the favorable micropolarity at the cyclophane active site. The low catalytic activity in the interior of the macromolecules was explained by steric hindrance of reaction transition states by the dendritic branches.     

Hexakis‐Adducts of [60]Fullerene with Different Addition Patterns: Templated Synthesis,Physical Properties,and Chemical Reactivity

Representatives of two classes of hexakis‐adducts of C₆₀ were prepared by templated synthesis strategies. Compound 8 with a dipyridylmethano addend in a pseudo‐octahedral addition pattern was obtained by DMA‐templated addition (DMA=9,10‐dimethylanthracene; Scheme 1) and served as the starting material for the first supramolecular fullerene dimer 2 . Hexakis‐adduct 12 also possesses a pseudo‐octahedral addition pattern and was obtained by a sequence of tether‐directed remote functionalization, tether removal, and regioselective bis‐functionalization (Scheme 2). With its two diethynylmethano addends in trans‐1 position, it is a precursor for fascinating new oligomers and polymers that feature C₆₀ moieties as part of the polymeric backbone (Fig. 1). With the residual fullerene π‐electron chromophore reduced to a `cubic cyclophane'‐type sub‐structure (Fig. 4), and for steric reasons, 8 and 12 no longer display electrophilic reactivity. As a representative of the second class of hexakis‐adducts, (±)‐ 1 , which features six addends in a distinct helical array along an equatorial belt, was prepared by a route that involved two sequential tether‐directed remote functionalization steps (Schemes 3 and 5). In compound (±)‐ 1 , π‐electron conjugation between the two unsubstituted poles of the carbon sphere is maintained via two (E)‐stilbene‐like bridges (Fig. 4). As a result, (±)‐ 1 features very different chemical reactivity and physical properties when compared to hexakis‐adducts with a pseudo‐octahedral addition pattern. Its reduction under cyclic voltammetric conditions is greatly facilitated (by 570 mV), and it readily undergoes additional, electronically favored Bingel additions at the two sterically well‐accessible central polar 6‐6 bonds under formation of heptakis‐ and octakis‐adducts, (±)‐ 30 and (±)‐ 31 , respectively (Scheme 6). The different extent of the residual π‐electron delocalization in the fullerene sphere is also reflected in the optical properties of the two types of hexakis‐adducts. Whereas 8 and 12 are bright‐yellow (end‐absorption around 450 nm), compound (±)‐ 1 is shiny‐red, with an end‐absorption around 600 nm. This study once more demonstrates the power of templated functionalization strategies in fullerene chemistry, providing addition patterns that are not accessible by stepwise synthetic approaches.     

Single-Molecule Two-Color Coincidence Detection of Unlabeled alpha-Synuclein Aggregates

Protein misfolding and aggregation into oligomeric and fibrillar structures is a common feature of many neurogenerative disorders. Single-molecule techniques have enabled characterization of these lowly abundant, highly heterogeneous protein aggregates, previously inaccessible using ensemble averaging techniques. However, they usually rely on the use of recombinantly-expressed labeled protein, or on the addition of amyloid stains that are not protein-specific. To circumvent these challenges, we have made use of a high affinity antibody labeled with orthogonal fluorophores combined with fast-flow microfluidics and single-molecule confocal microscopy to specifically detect α-synuclein, the protein associated with Parkinson's disease. We used this approach to determine the number and size of α-synuclein aggregates down to picomolar concentrations in biologically relevant samples.     

ChemInform Abstract: The Stability of Gold Iodides in the Gas Phase and the Solid State.

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