Determination of carbonyl compounds in exhaust gas by using a modified DNPH-method

The determination of carbonyl compounds in gaseous samples is usually accomplished by enrichment methods, in which 2,4-dinitrophenyl-hydrazine (DNPH) as a derivatization reagent has become established to a large extent. However, the conventional methods of DNPH-impingers and of DNPH-cartridges are applicable to emission measurements in a limited way only, depending on the NO₂-concentration in the exhaust gas. It could be proved that DNPH-derivatives, as well as DNPH, are also decomposed by NO₂ at a different speed, in which the hydrazones of unsaturated carbonyl compounds are probably more sensitive than those of the saturated carbonyl compounds. In view of this fact, the collecting methods had to be modified to avoid losses with the enrichment. The analysis of the compounds is carried out by HPLC with an effective gradient-system which is able to separate and detect the carbonyl compounds in exhaust gas within 16 min. Furthermore, a simple working-up procedure is presented which facilitates a parallel analysis by GC.     

Analysis of natural flavonoids by microchip-micellar electrokinetic chromatography with pulsed amperometric detection

Catechins (catechin and other derivatives) are naturally occurring flavonoids present in a number of plants and foods. They are also part of numerous nutraceutical formulations because they are believed to have antioxidant, cancer chemo-preventative, anti-inflammatory and antimicrobial properties. The determination of catechins has traditionally been performed by HPLC. However, this methodology is both time and sample intensive and generates large amounts of organic solvent waste. In the current report, an application of MEKC using a PDMS microchip is presented for the analysis of catechins. The system uses pulsed amperometric detection for direct analysis of important naturally occurring catechins. The effect of pH, surfactant concentration, detection potential and signal stability were analyzed. Linear relationships were found between the concentration and peak current, with good stability and limits of detection of 8 [micro sign]M for catechin, epigallocatechin gallate and epicatechin, and 14 [micro sign]M for epicatechin gallate. Optimum conditions were applied to the detection of selected catechins in a commercially available green tea extract nutraceutical and the results were compared to HPLC analysis. The analysis using microchip micellar electrokinetic chromatography and pulsed amperometric detection was completed in 4.5 min, 10 times faster than the HPLC analysis.     

Darstellung und Struktur von Ag2C4O4

Preparation and Structure of Ag₂C₄O₄ Ag₂C₄O₄ occurs in a yellow and a colourless modification. Both forms decompose to metallic silver upon heating. Ag⁺ is coordinated in two different fashions in the yellow Ag₂C₄O₄. Ag(1) shows distorted tetrahedral coordination, Ag(2) is coordinated in an unusual distorted square planar manner. The connection of Ag⁺ and C₄O₄^2? leads to a complicated three-dimensional framework. C₄O₄^2? is planar with C? O and C? C bonds lengths typical of complete delocalization of the π-electron system.     

Nickel-Catalyzed Preparations of Functionalized Organozincs

The reaction of primary alkyl bromides or chlorides with diethylzinc in the presence of Ni(acac)(2) (5 mol %) furnishes the corresponding alkylzinc halides (X = Br, Cl) via a halogen-zinc exchange reaction. The treatment of terminal alkenes with diethylzinc (neat, 25-60 degrees C) in the presence of Ni(acac)(2) as a catalyst (1-5 mol %) and 1,5-cyclooctadiene (COD) affords the corresponding dialkylzincs via a hydrozincation reaction. Whereas the conversion for simple alkenes bearing a remote functionality reaches 40 to 63%, the hydrozincation of allylic, homoallylic alcohols and allylic amines proceeds very efficiently (85-95% conversion). All the zinc organometallics obtained react with various electrophiles (allylic halides, enones, acid chlorides, alkynyl halides, ethyl propiolate) after transmetalation with CuCN.2LiCl. In the presence of the chiral catalyst 12, the dialkylzincs prepared add to aldehydes with high enantioselectivity.     

Fine structure and hyperfine structure in the excited configuration 5p 26s of the antimony I spectrum

By optical interference and VUV spectroscopy the doublet system of SbI 5p ²6s was investigated, so that now the hyperfinestructure of all 8 levels of 5p ²6s (A- andB-splitting constants) are known. From the analysis we receive a spin-orbit parameter ζ_5p =3,538(57) cm^?1 and from the hyperfine-analysis single electron splitting constantsa _5p ⁰¹ =52.4(4.6),a _5p ¹⁰ =?1.6(7.3),a _5p ¹² =72.3(2.3),a _6s ¹⁰ =91.7(4.1),b _5p ⁰² =?49.6(1.1) andb _5p ¹¹ =30.4(3.2) (all values in mK). For all calculations in the fs- and hfs-analysis the 5p ²6s ² D _3/2 has to be excluded (see discussion). With the figures given above the quadrupole moment¹²¹ Q(5p ²6s)=?0.44(3) barn was obtained. It is in good agreement with the¹²¹ Q(5p ³). For the core-polarization by the 5p electron in the innerfieldns-shells (n=1, 2, 3, 4, 5) and the unpaired 6s electron a field of +500(300) kG was obtained.     

Sequence-defined positioning of amine and amide residues to control catechol driven wet adhesion

Catechol and amine residues, both abundantly present in mussel adhesion proteins, are known to act cooperatively by displacing hydration barriers before binding to mineral surfaces. In spite of synthetic efforts toward mussel-inspired adhesives, the effect of positioning of the involved functional groups along a polymer chain is not well understood. By using sequence-defined oligomers grafted to soft hydrogel particles as adhesion probes, we study the effect of catechol–amine spacing, as well as positioning relative to the oligomer terminus. We demonstrate that the catechol–amine spacing has a significant effect on adhesion, while shifting their position has a small effect. Notably, combinations of non-charged amides and catechols can achieve similar cooperative effects on adhesion when compared to amine and catechol residues. Thus, these findings provide a blueprint for the design of next generation mussel-inspired adhesives.

The catechol driven adhesion of precision macromolecules on glass surfaces is quantified by soft colloidal probe readout. Catechol moieties are shown to synergize with amine and amide residues depending on residue spacing and residue order.     

Orientation of nonionic surfactants on solid surfaces: n-alkyl polyglycol ethers on montmorillonite

Summary Complexes of nonionic surfactantsR-(OCH₂CH₂)x OH with montmorillonite have been studied (R =n-hexadecyl,n-octadecyl and oleyl ;x=2, 10 and 20).On internal surfaces the surfactant molecules are arranged in bilayers. Withx=2 the alkyl chain and about one half of the polar group, (-R OCH₂CH₂O-) stand perpendicularly whereas the terminal —CH₂CH₂OH group is attached to the silicate surface (₁-phase). The bilayer thickness decreases stepwise with rising temperature due to the formation of kinks (i-phases). At higher temperature (52 °C withR=C₁₈H₃₇-, 43°C withR=n-C₁₆H₃₃-, and 12 °C withR = oleyl-) surfactant molecules are squeezed out of the interlayer space reversibly, the packing density decreases, the whole polar head group gets attached to the silicate surface and the alkyl chains rearrange into a gauche-block structure. This structure undergoes further structural changes at still higher temperatures ( _i -phases).The complexes withx =10 and 20 form -phases even at room temperature. These -phases take up long chain alkanol molecules under formation of -structures which rearrange at higher temperatures into -phases. Long-chain impurities of the surfactants can be intercalated in a similar way.Previous data indicating mono- or bilayers of flatly lying surfactant molecules refer to metastable phases due to steric hindrances of lattice expansion.It is proposed that the surfactant molecules build up similar films on the external surfaces, which can adopt - or -structures depending upon number of ethylene oxide groups and temperature. The films of hexadecyl polyglycol ethers for instance are about 27 Å thick in the -phases and about 17 Å in the a-phases.

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Zusammenfassung Es wurden Montmorillonitkomplexe mit nichtionogenen TensidenR(-OCH₂CH₂) _x ,OH (R =n-hexadecyl-,n-octadecyl- und oleyl-;x = 2, 10 and 20) hergestellt. Die Tensidmoleküle bilden zwischen den Silicatschichten bimolekulare Filme.Mitx=2 sind die hydrophoben Reste und die anschließende -OCH₂CH₂-Äthergruppe bei niedriger Temperatur gestreckt und senkrecht zu den Silicatschichten orientiert ( _i -Phase); nur die endständige HOCH₂CH₂-Gruppe sitzt direkt auf der Silicatschicht auf. Beim Erwärmen erniedrigt sich die Dicke der bimolekularen Tensidschicht stufenweise durch den Einbau von Kinken ( _i -Phasen). Bei höheren Temperaturen (52°C mitR =C₁₈H₃₇-, 43 °C mitR =C₁₆H_33- und 12 °C mitR = oleyl) werden Tensidmoleküle reversibel aus den Schichtzwischenräumen verdrängt, die Packungsdichte erniedrigt sich, die gesamte polare Gruppe kommt in direkten Kontakt mit der Silicatschicht und die Alkylketten ordnen sich in eine Gaucheblockstruktur ( _i -Phase). Diese kann bei noch höheren Temperaturen weitere Phasenumwandlungen erleiden.Mitx =10 undx = 20 werden auch bei Zimmertemperatur nur -Phasen gebildet. Diese -Phasen können zusätzlich langkettige Alkanolmoleküle aufnehmen und ternäre Komplexe mit -Struktur bilden, die sich beim Erhitzen reversibel in -Formen umwandeln. Langkettige polare Verunreinigungen in den Tensiden wirken ähnlich wie die Alkanolmoleküle.An den äußeren Oberflächen werden die Tensidmoleküle gleichartige Filme mit - oder -Struktur bilden, je nach der Zahl der -CH₂CH₂O-Gruppen und der Temperatur. Ein Film aus Hexadecylpolyglykoläthern wird etwa 27 Å dick sein in der -Phase und etwa 17 Å in der -Form.

     

Synthesis and auration of primary and di-primary heteroaryl-phosphines

Convenient high-yield syntheses of the primary and di-primary heteroaryl-phosphines R-PH2 and H2P-R'-PH2(with R = 2-thienyl, 2-furyl, and R'= 2,5-thiophenediyl, 2,5-furandiyl, respectively) are presented. The products and a set of precursor molecules have been characterized by analytical and spectral data, and the crystal structures of selected molecules have been determined: 2-C4H3O-PCl2, 2,5-(Cl2P)2C4H2O, 2,5-[(Et2N)2P]2C4H2E (with E = O, S). In the crystals, the two molecules with -PCl2 substituents adopt trans conformations, while the other two have the -P(NEt2)2 groups rotated into a twist conformation. The reaction of the thienyl compounds with tris[(tert-phosphine)gold]oxonium tetrafluoroborates gave almost quantitative yields of the tri- and hexanuclear gold complexes, respectively: {2-C4H3S-P[Au(PR3)]3}+BF4- and [2,5-{[(R3P)Au]3P}2C4H2S]2+(BF4(-)2, (R =tBu, Ph). The structures of the compounds with R3P =tBu3P ligands have been determined. In both cases the [2-C4H3/2S-P] units cap triangles of gold atoms in an array that can be described as three [Au(PR3)]+ cations bridged by a phosphido dianion (RP)2-.