Non-aqueous capillary electrophoresis of the positional isomers of a sulfated monosaccharide

A non-aqueous capillary electrophoresis (NACE) method coupled to indirect absorbance detection has been developed for the separation of the three positional isomers of monosulfated fucose. The optimized electrolyte was composed of 12 mM ethanolamine, 2 mM trimesic acid buffer in a methanol-ethanol (1:1, v/v) mixture. As the retained electrolyte entails no separating agent other than the pH buffer, the NACE separation of the positional isomers has been ascribed mainly to selective ion-pairing with the electrolyte counter-ion and the possibility of a selective solvation effect in the alcohol mixture. In the absence of pure isomeric standards, peak identification was completed by MS and NMR spectroscopy and selective enzymatic desulfation. This method should be of interest for the structure elucidation of monosulfated fucose-based polysaccharides and for the screening of sulfoesterase of unknown activity.     

Bildung siliciumorganischer Verbindungen. LVI. Reaktionen Si- und C-chlorierter 1,3,5-Trisilapentane mit CH3MgCl

Formation of Organosilicon Compounds. LVI. Reactions of Si- and C-Chlorinated 1,3,5-Trisilapentanes with CH₃MgCl (Cl₃Si? CCl₂)₂SiCl₂ (1) reacts with an excess of meMgCl (me = CH₃) forming me₃Si? C?C? Sime₃ (2), Sime₄, H₂C?C(Sime₃)[CH(Sime₃)₂] (3) as main products and (me₃Si)₂C? CH(Sime₃) and as by-products. The cleavage reaction of (1) to (2) and (3) does not occur when the meMgCl-concentration is lowered. The reaction is started by the formation of a GRIGNARD reagent at a CCl-group in compound (1). Cl₃Si? CCl₂? SiCl₂? CH₂? SiCl₃ forms with ; me₃Si? CCl₂? SiCl₂? CHCl? SiCl₃ forms (me₃Si)₂C?CH(Sime₃). A reaction sequence is given.     

Synthesis of an ethidium nucleoside and its acyclic analog

The protected ethidium nucleosides 8-(3′,5′-di-O-benzoyl-2′-deoxy-d-ribofuranosyl)-3-acetamido-5-ethyl-6-phenyl-phenanthridinium (5), 8-(3′,5′-di-O-acetyl-2′-deoxy-d-ribofuranosyl)-3-acetamido-5-ethyl-6-phenyl-phenanthridinium (6), and the acyclic analog 8-[(3R)-1,3-dihydroxy-4-yl]-acetamido-3-amino-5-ethyl-6-phenyl-phenanthridinium (3) were prepared. Based on to their different stability, only the acyclic derivative 3 seems to be suitable for oligonucleotide synthesis. Furthermore, the acyclic ethidium nucleoside analog 3 exhibits comparable absorption and emission properties of the underivatized ethidium (1).     

Enantioselective synthesis of alpha-methyl-D-cysteine and lanthionine building blocks via alpha-methyl-D-serine-beta-lactone

[reaction: see text] We report here the enantioselective synthesis of Boc-alpha-methyl-d-cysteine(PMB)-OH and lanthionine building blocks through the regioselective ring opening of key intermediate Boc-alpha-methyl-d-serine-beta-lactone.     

Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: polymer hosts for high-efficiency light-emitting diodes

A carbazole homopolymer and carbazole copolymers based on 9,9'-dialkyl-[3,3']-bicarbazolyl, 2,5-diphenyl-[1,3,4]-oxadiazole and 9,9-bis(4-[3,7-dimethyloctyloxy]phenyl)fluorene were synthesized and their electrical and photophysical properties were characterized with respect to their application as host in phosphorescent polymer light-emitting diodes. It is shown that the triplet energy of a polymer depends on the specific connections between its building blocks. Without changing the composition of the polymer, its triplet energy can be increased from 2.3 to 2.6 eV by changing the way in which the different building blocks are coupled together. For poly(9-vinylcarbazole) (PVK), a carbazole polymer often used as host for high-energy triplet emitters in polymer light-emitting diodes, a large hole-injection barrier of about 1 eV exists due to the low-lying HOMO level of PVK. For all carbazole polymers presented here, the HOMO levels are much closer to the Fermi level of a commonly used anode such as ITO and/or a commonly used hole-injection layer such as PEDOT:PSS. This makes high current densities and consequently high luminance levels possible at moderate applied voltages in polymer light-emitting diodes. A double-layer polymer light-emitting diode is constructed comprising a PEDOT:PSS layer as hole-injection layer and a carbazole-oxadiazole copolymer doped with a green triplet emitter as emissive layer that shows an efficacy of 23 cd/A independent of current density and light output.     

Bildung und Reaktionen P-funktioneller Phosphane

Formation and Reaction of P-functional Phosphanes The reaction of (me₃Si)₂PLi · 2 THF a (me = CH₃) with PCl₃ b at ?78°C via the intermediate (me₃Si)₂P? PCl₂ 1 yields [(me₃Si)₂P]₂PCl 2 and [(me₃Si)₂P]₂P? P(Sime₃)₂ 3 . By addition of me₃CLi c to the reaction mixture of a and b (molar ratio a:b:c (molar ratio a:b:c = 1:1:1) at ?60°C, 2 is formed as a main product, which reacts on to yield [(me₃Si)₂P]₂PH 4 (white crystals, mp = 73°C). By reactions of a:b:c in a molar ratio of 1:1:2 the cyclotetraphosphane (me₃C)₃ (me₃Si)P₄ 7 is accessible, and the additional formation of (me₃Si)₂PLi · 2 THF, (me₃Si)₃P and Li₃P₇ · 3 THF 13 was detected. Warming (me₃Si)₂P? PCl(Cme₃) 5 to 20°C produces cis- and trans-cyclotetraphosphanes (me₃Si)₂(me₃C)₂P₄. By running the reaction of a and b at ?78°C and adding me₃CLi only after 24 h, additionally to (me₃Si)₂P? PH Cme₃) and (me₃Si)₃P also (me₃Si)₂P? P(Cme₃)? P(Cme₃)? P (Sime₃)₂ is obtained, which is formed by metallation of (me₃Si)₂P? PCl(Cme₃) with me₃CLi and by further reaction of the intermediate (me₃Si)₂P? PLi(Cme₃) with (me₃Si)₂P? PCl(Cme₃). The reaction of (me₃Si₃)P with PCl₃ at ?78°C only yields (me₃Si)₂P? PCl₂ 1 and me₃SiCl. On addition of me₃CLi (?78°C, molar ratio = 1:1:1) preferrably 2 and (me₃Si)₂P? PCl(Cme₃) are formed, whereas after warming the mixture to 20°C, 4 and (me₃Si)₂P? PH(Cme₃) are found to be the main products. These reactions are induced by the cleavage of 1 by means of me₃CLi, and by the formation of (me₃Si)₂PLi and me₃C? PCl₂.     

Luminescent core-shell photonic crystals from poly(phenylene ethynylene) coated silica spheres

We describe the preparation and characterization of a photonic crystal filled with a luminescent conjugated polyelectrolyte, sulfonated poly(phenylene ethynylene). The conjugated polymer was coated onto the nanospheres by the layer-by-layer method and assembled directly into a fluorescent opal structure avoiding the defects associated with post-filling schemes. These structures exhibit strong angle-dependent luminescent properties. By using multiple layers, we further demonstrate control over the emissive bands of the opal.     

Investigation of the electrocatalytic oxidation of formate and ethanol at platinum black under microbial fuel cell conditions

In this communication, we discuss the electro-oxidation of the fermentation products formate and ethanol at platinum black modified electrodes under microbial fuel cell conditions, i.e., at neutral pH, room temperature, and in microbial culture solutions. The electrocatalytic oxidation was studied using cyclic voltammetry, chronoamperometry, and potentiostatic coulometry. Current densities up to 6 mA cm⁻² at 0.2 V oxidation potential and 97% coulombic efficiency were observed for the electro-oxidation of 100 mM solutions of formate in pH 7 buffer solution. Electrode deactivation could be successfully prevented using an oxidative potential reactivation procedure. Polymer coating, however, fully stopped the formate oxidation. As expected, the electro-oxidation of ethanol was less efficient—with a limiting current density being 600 μA cm⁻².Dedicated to Professor Dr. Alan M. Bond on the occasion of this 60th birthday.     

Charge-mediated recognition of N-terminal tryptophan in aqueous solution by a synthetic host

The molecular recognition of peptides and proteins in aqueous solution by designed molecules remains an elusive goal with broad implications for basic biochemical research and for sensors and separations technologies. This paper describes the recognition of N-terminal tryptophan in aqueous solution by the synthetic host cucurbit[8]uril (Q8). Q8 is known to form 1:1:1 heteroternary complexes with methyl viologen (MV) and a second aromatic guest. Here, the complexes of Q8.MV with (i) the four natural aromatic alpha-amino acids, (ii) four singly charged tryptophan derivatives, and (iii) four tryptophan-containing tripeptides were characterized by isothermal titration calorimetry, mass spectrometry, and UV-visible, fluorescence, and (1)H NMR spectroscopy. We find that Q8.MV binds Trp-Gly-Gly with high affinity (K(a) = 1.3 x 10(5) M(-1)), with 6-fold specificity over Gly-Trp-Gly, and with 40-fold specificity over Gly-Gly-Trp. Analysis of the nine indole-containing compounds suggests that peptide recognition is mediated by the electrostatic charge(s) proximal to the indole, and that the mode of binding is consistent for these compounds. Complex formation is accompanied by the growth of a visible charge-transfer band and the quenching of indole fluorescence. These optical properties, combined with the stability and selectivity of this system, are promising for applications in sensing and separating specific peptides.     

Structural characterization of a pentacene monolayer on an amorphous SiO2 substrate with grazing incidence x-ray diffraction

Grazing incidence X-ray diffraction reveals that a pentacene monolayer, grown on an amorphous SiO2 substrate that is commonly used as a dielectric layer in organic thin film transistors (OTFTs), is crystalline. A preliminary energy-minimized model of the monolayer, based on the GIXD data, reveals that the pentacene molecules adopt a herringbone arrangement with their long axes tilted slightly from the substrate normal. Although this arrangement resembles the general packing features of the (001) layer in single crystals of bulk pentacene, the monolayer lattice parameters and crystal structure differ from those of the bulk. Because carrier transport in pentacene OTFTs is presumed to occur in the semiconductor layers near the dielectric interface, the discovery of a crystalline monolayer structure on amorphous SiO2 has important implications for transport in OTFTs.