Characterization and transport properties of Nafion/polyaniline composite membranes

Nafion membranes were modified by chemical polymerization of aniline using ammonium peroxodisulfate as the oxidant. The Nafion-polyaniline composite membranes were extensively characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and ion-exchange capacity measurements. The transport properties were also evaluated by conductivity and electrodialysis measurements. The data show that when a high oxidant concentration (1 M (NH4)2S2O8) is used, polyaniline is mostly formed at the surface of the Nafion membrane with a higher proportion of oligomers. On the contrary, when 0.1 M oxidant is used, polyaniline is mostly formed inside the ionic domains of Nafion, blocking the pathway to ion transport and thus reducing the transport of Zn2+ as well as the transport of H+. These data were also compared to the data obtained with poly(styrene sulfonate)-PANI composite membranes.     

Synthesis of [4.2]cyclophanes

Vinyl $\text{p}$-xylylene cross-dimerizes with other xylylene-type intermediates to yield cycloadducts of the [8+6] and [6+6] type. This reaction provides a simple entry to the [4.2]paracyclophane system as well as the analogous [4.2]cyclophanes containing furan and pyrrole moieties.     

New aspects of the protonation of biliverdins

Biliverdins undergo appreciable self association in acidic solutions especially if solvents like benzene or chloroform are employed. The population of aggregates further depends on the concentration of both the acid and the solute. In chloroform and benzene solutions at high acidity a doubly protonated species is formed. This is concluded from a combinatory evaluation of the CD and electronic absorption spectra of chiral optically active biliverdins (1–6) in benzene, chloroform, and ethanol solutions containing trifluoroacetic acid or hydrochloric acid. The aggregates formed at medium acid concentrations exhibit largeCotton effects in the long-wavelength absorption bands and thus dominate the CD spectra. Similarly, agrregates are the main contributors to theCotton effects of achiral, protonated biliverdins in (S)-(–)-ethyl lactate (SICD) at usual concentrations. The consequence and relevance of these findings with regard to the recent literature is briefly discussed.Dedicated to Prof. Dr.Karl Schlögl on occasion of his 60^th birthday.     

New dehydration in the pyrrolo[1,2–6-b]isoquinoline series. Preparation and structural identification of 3,5-dihydrobenz[f]indolizin-3-one

3,5-Dihydrobenz[f]indolizin-3-one was prepared by a novel dehydration reaction involving the heating of 1,2,3,5,10,10a-hexahydro[f]indolizine-3,10-dione with polyphosphoric acid. The structure of this new compound was established by X-ray crystallography, by nmr spectroscopy and by reduction to the known products 1,2,3,5-tetrahydrobenz[f]indolizin-3-one and 1,2,3,5,10,10a-hexahydrobenz[f]indolizin-3-one.     

Surface enrichment of proteins at quartz/water interfaces: a neutron reflectivity study

Neutron reflectivity (NR) was used to study the adsorption of human serum albumin and human fibrinogen on quartz. The proteins were individually and sequentially adsorbed from heavy water and heavy water/methanol mixtures at pH 4 and 7.0. The technique allows for the subnanometer resolution of the adsorbed layer thickness and gross morphology. Under the conditions of our measurements we found that fibrinogen formed a distinct layer that we interpret as a mat of the protein three layers thick whereas albumin formed only diffuse layers. The adsorption pattern of the two proteins changed radically when one protein was adsorbed on top of the other (previously adsorbed). In general our measurements indicate that the adsorbed protein layers on quartz are rather loosely bound and that these layers, incorporating as much as 80% water, extend further into the bulk fluid than might have been expected.     

Intermediates in the Dehydrogenation of Hydroaromatic Compounds with Quinones

Dehydrogenation of hydroaromatic compounds with quinones was reinvestigated in the light of recent criticism of the reaction mechanism. Kinetic and spectroscopic evidence shows that disappearance of substrate proceeds at the same rate as the product-forming step. A mechanism consisting in fast formation followed by slow decomposition of an intermediate can be ruled out. The order of reactivities of 1,4-cyclohexadiene ( 1 ), 1,4-dihydronaphthalene ( 8 ) and 9,10-dihydroanthracene ( 11 ) changes in going from benzoquinone to chloranil or 2,3-dichloro-5,6-dicyanobenzoquinone. It is suggested that this behaviour could be due to contribution of CT-complexes or HOMO-LUMO interactions for determining the reactivity of the substrates.     

Selective Si--C bond cleavage as synthetic entry to a functionalized lithiosilane

Treatment of the phenyl-substituted silane 4 with lithium metal afforded the functionalized lithiosilane rac-2 by selective cleavage of one Si-C bond between silicon and a phenyl group. The resulting lithiosilane rac-2 crystallizes as the dimer (2.THF)2, which represents the first example of a dimeric organyl-substituted lithiosilane in the presence of THF.     

Synthesis and NMR studies of (13)C-labeled vitamin D metabolites

Isotope-labeled drug molecules may be useful for probing by NMR spectroscopy the conformation of ligand associated with biological hosts such as membranes and proteins. Triple-labeled [7,9,19-(13)C(3)]-vitamin D(3) (56), its 25-hydroxylated and 1 alpha,25-dihydroxylated metabolites (58 and 68, respectively), and other labeled materials have been synthesized via coupling of [9-(13)C]-Grundmann's ketone 39 or its protected 25-hydroxy derivative 43 with labeled A ring enyne fragments 25 or 26. The labeled CD-ring fragment 39 was prepared by a sequence involving Grignard addition of [(13)C]-methylmagnesium iodide to Grundmann's enone 28, oxidative cleavage, functional group modifications leading to seco-iodide 38, and finally a kinetic enolate S(N)2 cycloalkylation. The C-7,19 double labeling of the A-ring enyne was achieved by the Corey-Fuchs/Wittig processes on keto aldehyde 11. By employing these labeled fragments in the Wilson-Mazur route, the C-7,9,19 triple-(13)C-labeled metabolites 56, 58, and 68 as well as other (13)C-labeled metabolites have been prepared. In an initial NMR investigation of one of the labeled metabolites prepared in this study, namely [7,9,19-(13)C(3)]-25-hydroxyvitamin D(3) (58), the three (13)C-labeled carbons of the otherwise water insoluble steroid could be clearly detected by (13)C NMR analysis at 0.1 mM in a mixture of CD(3)OD/D(2)O (60/40) or in aqueous dimethylcyclodextrin solution and at 2 mM in 20 mM sodium dodecyl sulfate (SDS) aqueous micellar solution. In the SDS micellar solution, a double half-filter NOESY experiment revealed that the distance between the H(19Z) and H(7) protons is significantly shorter than that of the corresponding distance calculated from the solid state (X-ray) structure of the free ligand. The NMR data in micelles reveals that 58 exists essentially completely in the alpha-conformer with the 3 beta-hydroxyl equatorially oriented, just as in the solid state. The shortened distance (H(19Z))-H(7)) in micellar solutions as compared to that in the solid state is most easily rationalized on the basis that the 5(10)-torsion angle in 58 is decreased in micellar solutions as compared to that in the solid state.     

Synthesis of corroles bearing up to three different meso substituents

[reaction: see text] We have developed a new method that affords regioisomerically pure corroles possessing up to three different substituents at the meso positions. The corrole formation reaction involves the acid-catalyzed condensation of a dipyrromethane-dicarbinol with pyrrole followed by oxidation with DDQ. ABC-Type corroles were synthesized for the first time according to this procedure.     

Effects of partial/asymmetrical filling of micelles and chiral selectors on capillary electrophoresis enantiomeric separation: generation of a gradient

The effect of several experimental parameters on enantiomeric separations in micellar capillary electrophoresis (MCE) was studied. A model separation system was tested. It was composed of an acidic phosphate buffer with sodium dodecyl sulfate (SDS) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as the chiral selector. A substituted angelicin was used as a chiral analyte. Changes in the concentration of SDS micelles/SDS monomers in the presence of HP-beta-CD and their impact on the enantioselective separation were investigated. Variation of the composition of electrolytes in the individual compartments of the separation system (inlet vial, capillary, and outlet vial) affected both the migration times and the resolution of the enantiomers. Current vs. time dependencies also were monitored during the separations. A mathematical model of electromigration in micellar systems with chiral selector present was proposed and a computer simulation was used to explain the observed phenomena and to confirm the generation of a CD/SDS-micelle concentration gradient under certain experimental conditions. This is the reported first attempt of a computer simulation of the complex, dynamic chiral environment of the CD-SDS-MCE system.