SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Chemistry (Weinheim an der Bergstrasse, Germany)

166

A little dopey: Ta-doped titania (TiO2 ) nanotube (NT) arrays can be grown by electrochemical anodization onto low-Ta-concentration (0.03-0.4 at % Ta) Ti-Ta alloys. Under optimized conditions (0.1 at % Ta, annealing at 650 °C and 7 μm thickness), Ta-doped TiO2 NT arrays show a significantly enhanced activity in photoelectrochemical water splitting under simulated sunlight conditions.

Concepts: Photoelectrochemical cell, Electrolysis

28

Twistane, C10 H16 , is a classic D2 -symmetric chiral hydrocarbon that has been studied for decades due to its fascinating stereochemical and thermodynamic properties. Here we propose and analyze in detail the contiguous linear extension of twistane with ethano (ethane-1,2-diyl) bridges to create a new chiral, C2 -symmetric hydrocarbon nanotube called polytwistane. Polytwistane, (CH)n , has the same molecular formula as polyacetylene but is composed purely of C(sp(3) )H units, all of which are chemically equivalent. The polytwistane nanotube has the smallest inner diameter (2.6 Å) of hydrocarbons considered to date. A rigorous topological analysis of idealized polytwistane and a C236 H242 prototype optimized by B3LYP density functional theory reveals that the polymer has a nonrepeating, alternating σ-helix, with an irrational periodicity parameter and an instantaneous rise (or lead) angle near 15 °. A theoretical analysis utilizing homodesmotic equations and explicit computations as high as CCSD(T)/cc-pVQZ yields the enthalpies of formation ${{\rm{\Delta }}_f H_0^ \circ }$(twistane)=-1.7 kcal mol(-1) and ${{\rm{\Delta }}_f H_0^ \circ }$(polytwistane)= +1.28 kcal (mol CH)(-1) , demonstrating that the hypothetical formation of polytwistane from acetylene is highly exothermic. Hence, polytwistane is synthetically viable both on thermodynamic grounds and also because no obvious pathways exist for its rearrangement to lower-lying isomers. The present analysis should facilitate the preparation and characterization of this new chiral hydrocarbon nanotube.

Concepts: Scientific method, Physics, Thermodynamics, Density functional theory, Hydrocarbon, Methane, Hybrid functional, Acetylene

28

The glycopeptide CcTx, isolated from the venom of the piscivorous cone snail Conus consors, belongs to the κA-family of conopeptides. These toxins elicit excitotoxic responses in the prey by acting on voltage-gated sodium channels. The structure of CcTx, a first in the κA-family, has been determined by high-resolution NMR spectroscopy together with the analysis of its O-glycan at Ser7. A new type of glycopeptide O-glycan core structure, here registered as core type 9, containing two terminal L-galactose units {α-L-Galp-(1→4)-α-D-GlcpNAc-(1→6)-[α-L-Galp-(1→2)-β-D-Galp-(1→3)-]α-D-GalpNAc-(1→O)}, is highlighted. A sequence comparison to other putative members of the κA-family suggests that O-linked glycosylation might be more common than previously thought. This observation alone underlines the requirement for more careful and in-depth investigations into this type of post-translational modification in conotoxins.

Concepts: Posttranslational modification, Sodium channel, Lysine, Conotoxin, Glycation, Threonine, Conus, Conidae

28

Biothiols, such as cysteine (Cys) and homocysteine (Hcy), play very crucial roles in biological systems. Abnormal levels of these biothiols are often associated with many types of diseases. Therefore, the detection of Cys (or Hcy) is of great importance. In this work, we have synthesized an excellent “OFF-ON” phosphorescent chemodosimeter 1 for sensing Cys and Hcy with high selectivity and naked-eye detection based on an Ir(III) complex containing a 2,4-dinitrobenzenesulfonyl (DNBS) group within its ligand. The “OFF-ON” phosphorescent response can be assigned to the electron-transfer process from Ir(III) center and C^N ligands to the DNBS group as the strong electron-acceptor, which can quench the phosphorescence of probe 1 completely. The DNBS group can be cleaved by thiols of Cys or Hcy, and both the (3) MLCT and (3) LC states are responsible for the excited-state properties of the reaction product of probe 1 and Cys (or Hcy). Thus, the phosphorescence is switched on. Based on these results, a general principle for designing “OFF-ON” phosphorescent chemodosimeters based on heavy-metal complexes has been provided. Importantly, utilizing the long emission-lifetime of phosphorescence signal, the time-resolved luminescent assay of 1 in sensing Cys was realized successfully, which can eliminate the interference from the short-lived background fluorescence and improve the signal-to-noise ratio. As far as we know, this is the first report about the time-resolved luminescent detection of biothiols. Finally, probe 1 has been used successfully for bioimaging the changes of Cys/Hcy concentration in living cells.

Concepts: Amino acid, Disulfide bond, Luminescence, Cysteine, Phosphorescence, Thiol, Methionine, Photoluminescence

28

A new modular approach based on Pd-catalyzed CC bond formation is presented for the assembly of a benzannulated azocine scaffold, the key intermediate in the synthesis of functionalized azadibenzocyclooctynes (aza-DIBOs). The intramolecular ring-closing Heck coupling was investigated by variation of the CX bond. The reaction rate is limited by the initial oxidative addition step and the regiochemistry strongly depends on the auxiliary phosphine. Under optimized conditions, the 8-endo regioisomer was obtained in 71 % yield over two steps (with no protecting group chemistry) or in one pot, inclusive of CN bond formation. The practical generation of the octyne triple bond of a prototypical N-benzoyl aza-DIBO, without the need for chromatographic purification, is also described. The structural features, including those of the ring-strained cyclic octyne, were elucidated by NMR spectroscopy and X-ray crystallographic analysis. The high reactivity of the N-benzoyl aza-DIBO synthesized is demonstrated in a strain-promoted azide-alkyne cycloaddition reaction with an alkyl azide (k=0.38 M(-1)  s(-1) ).

Concepts: Chemical reaction, Nitrogen, Chemical synthesis, X-ray crystallography, Heck reaction, Suzuki reaction, Triphenylphosphine, Reaction mechanisms

28

A highly diastereoselective (d.r. >99:1) and enantioselective (ee value up to 96 %) synthesis of trisubstituted cyclohexanols was achieved by using a one-pot sequential organocatalysis that involved a quinidine thiourea-catalyzed tandem Henry-Michael reaction between nitromethane and 7-oxo-hept-5-en-1-als followed by a tetramethyl guanidine (TMG)-catalyzed tandem retro-Henry-Henry reaction on the reaction products of the tandem Henry-Michael reaction. Through a mechanistic study, it has also been demonstrated that similar results may also be achieved with this one-pot sequential organocatalysis by using the racemic Henry product as the substrate.

Concepts: Product, Chemical reaction, Stereochemistry, Chemical synthesis, Enantiomer, Aldol reaction, Racemic mixture, Chiral resolution

28

Uniform bismuth oxide (Bi(2) O(3) ) and bismuth subcarbonate ((BiO)(2) CO(3) ) nanotubes were successfully synthesized by a facile solvothermal method without the need for any surfactants or templates. The synergistic effect of ethylene glycol (EG) and urea played a critical role in the formation of the tubular nanostructures. These Bi(2) O(3) and (BiO)(2) CO(3) nanotubes exhibited excellent Cr(VI) -removal capacity. Bi(2) O(3) nanotubes, with a maximum Cr(VI) -removal capacity of 79 mg g(-1) , possessed high removal ability in a wide range of pH values (3-11). Moreover, Bi(2) O(3) and (BiO)(2) CO(3) nanotubes also displayed highly efficient photocatalytic activity for the degradation of RhB under visible-light irradiation. This work not only demonstrates a new and facile route for the fabrication of Bi(2) O(3) and (BiO)(2) CO(3) nanotubes, but also provides new promising adsorbents for the removal of heavy-metal ions and potential photocatalysts for environmental remediation.

Concepts: PH, Synergy, Ethylene glycol, Photocatalysis, Bismuth

28

At the gate: Colorimetric enantiorecognition of one oligopeptide was realized by virtue of a D-enantiomer specific DNA aptamer as chiral selector and unmodified gold nanoparticles as indicator. Oligopeptide enantiomers as inputs were introduced into colorimetric logic gates, which have potential for enantiorecognition of oligopeptides. This system may lead to a better understanding of chiral recognition for information processing in natural systems.

Concepts: Nanoparticle, Nanotechnology, Gold, Peptides, Logic gate, Christo and Jeanne-Claude, Logic gates, Central Park

28

Three keys to success: A concise method for the construction of a tricyclic substructure (2) of haliclonin A (1) in racemic form is described. This synthesis features a new Pd-mediated chemoselective carbonyl-enone coupling reaction, an organocatalytic reaction, and a ring-closing metathesis reaction for the construction of the macrocyclic ring as key steps.

Concepts: Catalysis, Total synthesis, Olefin metathesis, Key

28

Slow relaxation: Exergonic high-spin→low-spin relaxation after photoexcitation has been found to be exceedingly slow in a class of iron(II) complexes with hexadentate imine ligands. The thermal activation barriers that arise between the quintet- and singlet-spin manifolds are the highest ever recorded for spin crossover of isolated molecules in free solution.

Concepts: Electron, Chemistry, Ligand, Solutions, Solution, ARIA Charts, Percentage solution