A helix-forming αβγ-chimeric peptide with catalytic activity: a hybrid peptide ligase

We describe the catalytic activity of the first chimeric ligase containing a foldameric sequence of β- and γ-amino acids. The chimeric backbone provides for the spatial arrangement of all functional groups involved in the formation of the catalytic site to allow efficient catalysis to take place. Our finding indicates significant progress in the field of functionally active artificial motifs.     

Stilbazulenyl nitrone (STAZN): a nitronyl-substituted hydrocarbon with the potency of classical phenolic chain-breaking antioxidants

Stilbazulenyl nitrone (STAZN), 8, a nitronyl-substituted hydrocarbon, is a novel second-generation azulenyl nitrone with significantly enhanced potency as a chain-breaking antioxidant vs conventional alpha-phenyl nitrones previously investigated as antioxidant therapeutics. A convenient (1)H NMR-based assay for assessing the potency of chain-breaking antioxidants has shown that STAZN is ca. 300 times more potent in inhibiting the free radical-mediated aerobic peroxidation of cumene than is PBN and the experimental stroke drug NXY-059. Such levels of antioxidant efficacy are unprecedented among archetypal alpha-phenyl nitrone spin traps. Furthermore, STAZN outperforms such classical phenolic antioxidants as BHT and probucol and rivals the antioxidant potency of Vitamin E in a polar medium comprised of 80% cumene and 20% methanol. The Volodarskii electron-transfer mechanism involving the intermediacy of the STAZN radical cation has been implicated in attempts to ascertain the basis for the increased potency of STAZN over the three alpha-phenyl nitrones PBN, S-PBN, and NXY-059.     

Rotationally‐hindered furyl fulgides

Fulgides are a representative class of photochromic organic molecules which exhibit several interesting properties for diverse applications in fields such as data storage or high‐resolution spectroscopy. The crystal structures of three furyl fulgides with different steric constraints were determined and for two of the compounds both the E and Z isomer structures were defined. The compounds are 3‐[(E)‐1,3‐dimethyl‐4,5,6,7‐tetrahydro‐2‐benzofuran‐4‐ylidene]‐4‐isopropylidenetetrahydrofuran‐2,5‐dione, C₁₇H₁₈O₄, (I‐E), 3‐[(E)‐1,3‐dimethyl‐5,6,7,8‐tetrahydro‐4H‐cyclohepta[c]furan‐4‐ylidene]‐4‐isopropylidenetetrahydrofuran‐2,5‐dione, C₁₈H₂₀O₄, (II‐E), and the Z isomer, (II‐Z), and 3‐isopropylidene‐4‐[(E)‐1‐(5‐methoxy‐2‐methyl‐1‐benzofuran‐3‐yl)ethylidene]tetrahydrofuran‐2,5‐dione, C₁₉H₁₈O₅, (III‐E), with two molecules in the asymmetric unit, and the Z isomer, (III‐Z). The structures of the E and Z isomers show only little differences in the bond lengths and angles inside the hexatriene unit. Because of the strained geometry there are deviations in the torsion angles. Furthermore, small differences in the distances between the bond‐forming C atoms in the electrocyclization process give no explanation for the unequal photochromic behaviour.     

Mechanistic and spectroscopic identification of initial reaction intermediates for prenal decomposition on a platinum model catalyst

The prediction of a reaction mechanism and the identification of the corresponding chemical intermediates is a major challenge in surface science and heterogeneous catalysis, due to a complex network of elementary steps and surface species. Here we demonstrate how to overcome this difficulty by tracking the temperature dependent formation of the initial reaction intermediates and identifying the decomposition pathways in the case of prenal, an α,β-unsaturated aldehyde, on the Pt(111) model catalyst surface by combining vibrational spectroscopy, thermal reaction/desorption spectroscopy (TPRS) experiments and detailed theoretical analysis. TPRS characterization of this reaction up to 600 K shows a series of desorption states of H(2) (～280 K, 410 K and 473 K) and CO (～414 K), giving valuable insights into the sequence of elementary steps suggesting that the loss of hydrogen and the carbonyl functions are among the first elementary steps. HREELS experiments recorded after annealing to specific temperatures result in complex spectra, which can be assigned to several subsequently formed and transformed surface intermediates. Starting from stable prenal adsorption structures, complementary DFT calculations allow the determination of the most likely reaction pathway for the initial decomposition steps and the identification of the corresponding intermediates by comparison with HREELS. The decomposition occurs from the strongly bonded prenal adsorption structures via a dehydro-η(3)-triσ(CCC)-H1 intermediate to the highly stable η(1)-isobutylidyne species at high temperatures.     

Polymer microfluidic devices

Since the introduction of lab-on-a-chip devices in the early 1990s, glass has been the dominant substrate material for their fabrication (J. Chromatogr. 593 (1992) 253; Science 261 (1993) 895). This is primarily driven by the fact that fabrication methods were well established by the semiconductor industry, and surface properties and derivatization methods were well characterized and developed by the chromatography industry among others. Several material properties of glass make it a very attractive material for use in microfluidic systems; however, the cost of producing systems in glass is driving commercial producers to seek other materials. Commercial manufacturers of microfluidic devices see many benefits in employing plastics that include reduced cost and simplified manufacturing procedures, particularly when compared to glass and silicon. An additional benefit that is extremely attractive is the wide range of available plastic materials which allows the manufacturer to choose materials' properties suitable for their specific application. In this article, we present a review of polymer-based microfluidic systems including their material properties, fabrication methods, device applications, and finally an analysis of the market that drives their development.     

Photochemistry of the anthracene chromophore: Triplet-sensitized isomerizations of dianthrylethanes

The photochemical isomerization of 1,2-di(9-anthryl)ethane can be sensitized by biacetyl to proceed by intramolecular Diels-Alder reaction. The molecular geometry of dianthrylethanes affects their triplet state reactivity.     

Further correlations between fragment ion intensity and critical energy. Unimolecular covalent bond fragmentation

A correlation of fragment ion intensity with critical energy found in the collisional activation spectra of [C₄Ph]⁺˙ ions produced by electron impact can also be found in the unimolecular mass-analysed ion kinetic energy spectra of these ions. The P(E) functions of the unimolecular and collisionally activated ions should differ not only in width but also in structure and therefore, the hypothesis that P(E) functions do not have an important effect on these correlations is tested successfully.     

High-performance liquid chromatography of non-polar retinoid isomers

Normal-phase high-performance liquid chromatograms of retinal, retinol and retinyl palmitate isomers using n-heptane-tert.-butyl methyl ether as mobile phase are presented. Methods for the synthesis of various isomers of these retinoids are described. This enables one to produce standard chromatograms and to select various isomers for cochromatography and the identification of the various peaks under study. Assignment of the peaks is based on chromatograms published previously in this journal. For the main isomers it is possible to get baseline separation of the commonly occurring isomeric forms in a reasonably short analysis time.     

Acyl- und Alkylidenphosphane. XXVII [I.]. Molekül- und Kristallstruktur des Methyl[(N-phenyl,N-tri-methylsilyl)thiocarbamoyl]trimethylsilylphosphans

Acyl- and Alkylidenephosphines. XXVII. Molecular and Crystal Structure of Methyl-[(N-phenyl, N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphine . Methyl[(N-phenyl, N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphine 1a formed via an addition of methylbis(trimethylsilyl)phosphine to phenyl isothiocyanate [1], crystallizes in the monoclinic centrosymmetric space group P2₁/n with following dimensions of the unit cell determined at a temperature of measurement of ?80±3°C: a=1041.2(4);b=1706.9(12);c=1001.1(6)pm; β=106.41(4)°; Z = 4. An X-ray structure determination (R_w = 0.039) confirms the constitution of the compound as already derived from its nmr spectra. One trimethylsilyl group is bound to the phosphorus atom, whereas the other is connected with the sp²-hybridized nitrogen atom. Characteristic rounded bond lenghts and angles are: P? Si 231, P? CH₃ 184, P? C(S) 187, C?S 167, N? C(S) 137, and N? Si 181 pm as well as P? C? S 122°, P? C? N 117°, and S? C? N 121°.