Electrochemically assisted Fenton reaction: reaction of hydroxyl radicals with xenobiotics followed by on-line analysis with high-performance liquid chromatography/tandem mass spectrometry

Oxygen radicals are generated in vivo by various processes, often as toxic intermediates in different metabolic transformations, and have been shown to play an important role for a large number of diseases. In this article we introduce an electrochemical flow-through system that allows generation of hydroxyl radicals for reaction with xenobiotics and subsequent detection of the oxidation products on-line with high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). The system is based on the Fenton reaction and is predominantly aimed at the generation of hydroxyl radicals; however, by minor variations to the system, a broad range of other radicals can be produced. Optimization of the system was performed with the radical scavenger 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Under the same physical conditions, one injection through the electrochemical cell gave a higher yield of the oxidation product N-hydroxy-5,5-dimethylpyrrolidin-2-one than what was attained after 60 min with a chemical Fenton system catalyzed by ascorbic acid. Since the iron is added as Fe(3+), the initial mixture is 'inactive' until it reaches the electrochemical cell. This makes it very suitable for on-line analysis of the generated compounds, since the whole reaction mixture, including substrate, can be kept in a vial in an autosampler. The system described provides a useful tool for investigation of new radical scavengers and antioxidants. Since the hydroxyl radical adds readily to unsaturated pi-systems, the technique is also suitable for on-line generation and characterization of potential drug metabolites resulting from hydroxylation of double bonds and aromatic systems.     

Aggregate, Polymer and Cluster Formation from Metal-Imino Carboxylate Complexes

Reaction of tris-(2-aminoethyl)amine (tren) andthe sodium salt of an -ketocarboxylic acid, typically sodium pyruvate, affordsin the presence of a lanthanide ion aseries of complexes and aggregates includingmononuclear, cyclic tetranuclear and polymerspecies of [L¹]^3- ([L¹]^3-=N[CH₂CH₂N=C(CH₃)COO^-]³).The aggregation of these and related d-block elementcomplexes with Na⁺ ions leadsto the formation of polymeric materials, and thefactors influencing the formation and controlof these various aggregation states are discussed.Metal cations also template the aggregationof the fragment [Ni(L²)] ([L²]^2- =CH₂[CH₂N = C(CH₃)COO^-]₂)to give, in high yield, the polynuclearaggregates {[Ni(L²)]₆M}^x+(M = Nd, Pr, Ce, La, x = 3; M = Sr, Ba, x = 2). The structures of{[Ni(L²)]₆M}^x+ show aninterstitial twelve co-ordinate, icosahedralcation M^x+ encapsulated by six [Ni(L²)]fragments. In the presence ofNa⁺, aggregation of [Ni(L²)] fragments affords {[Ni(L²)]₉Na₄(H₂O)(MeOH)(ClO₄)}³⁺ thestructure of whichshows four Na⁺ ions templating the formation ofa distorted tricapped trigonal prismatic[Ni(L²)]₉ cage. Thus, control overconstruction of various polynuclear cages viaself-assembly at octahedral junctions can beachieved using main group, transition metaland lanthanide ion templates.     

Synthesis and characterization of an Al(69)(3-) cluster with 51 naked Al atoms: analogies and differences to the previously characterized Al(77)(2-) cluster

A disproportionation process of a metastable AlCl solution with a simultaneous ligand exchange-Cl is substituted by N(SiMe(3))(2)-leads to a [Al(69)[N(SiMe(3))(2)](18)](3-) cluster compound that can be regarded as an intermediate on the way to bulk metal formation. The cluster was characterized by an X-ray crystal structural analysis. Regarding its structure and the packing within the crystal, this metalloid cluster with 4 times more Al atoms than ligands is compared to the [Al(77)N(SiMe(3))(2)](20)](2-) cluster that has been published four years ago. Although there is a similar packing density of the Al atoms in both clusters as well as in Al metal, the X-ray structural analysis shows significant differences in topology and distance proportions. The differences between these-at a first glance almost identical-Al clusters demonstrate that results of physical measuring, e.g., of nanostructured surfaces which carry supposedly identical cluster species, have to be interpreted with great caution.     

Determination of short-lived activation products in neutron-irradiated sodium through application of hydrated antimony pentoxide

A method for the determination of short-lived activation products in neutron-irradiated sodium is described. It is based on hydrolysis of sodium with methanol, separation of Na⁺ with specially prepared antimony pentoxide (HAP) possessing very high selectivity and capacity, and subsequent gamma-spectroscopic measurement of the activation products.     

Effect of proline and glycine residues on dynamics and barriers of loop formation in polypeptide chains

Glycine and proline residues are frequently found in turn and loop structures of proteins and are believed to play an important role during chain compaction early in folding. We investigated their effect on the dynamics of intrachain loop formation in various unstructured polypeptide chains. Loop formation is significantly slower around trans prolyl peptide bonds and faster around glycine residues compared to any other amino acid. However, short loops are formed fastest around cis prolyl bonds with a time constant of 6 ns for end-to-end contact formation in a four-residue loop. Formation of short loops encounters activation energies in the range of 15 to 30 kJ/mol. The altered dynamics around glycine and trans prolyl bonds can be mainly ascribed to their effects on the activation energy. The fast dynamics around cis prolyl bonds, in contrast, originate in a higher Arrhenius pre-exponential factor, which compensates for an increased activation energy for loop formation compared to trans isomers. All-atom simulations of proline-containing peptides indicate that the conformational space for cis prolyl isomers is largely restricted compared to trans isomers. This leads to decreased average end-to-end distances and to a smaller loss in conformational entropy upon loop formation in cis isomers. The results further show that glycine and proline residues only influence formation of short loops containing between 2 and 10 residues, which is the typical loop size in native proteins. Formation of larger loops is not affected by the presence of a single glycine or proline residue.     

Measurements of side-chain 13C-13C residual dipolar couplings in uniformly deuterated proteins

13C-only spectroscopy was used to measure multiple residual (13)C-(13)C dipolar couplings (RDCs) in uniformly deuterated and (13)C-labeled proteins. We demonstrate that (13)C-start and (13)C-observe spectra can be routinely used to measure an extensive set of the side-chain residual (13)C-(13)C dipolar couplings upon partial alignment of human ubiquitin in the presence of bacteriophages Pf1. We establish that, among different broadband polarization transfer schemes, the FLOPSY family can be used to exchange magnetization between a J coupled network of spins while largely decoupling dipolar interactions between these spins. An excellent correlation between measured RDCs and the 3D structure of the protein was observed, indicating a potential use of the (13)C-(13)C RDCs in the structure determination of perdeuterated proteins.     

Short and stereoselective synthesis of C-glycosylated glycine derivatives from glycals by radical addition and reduction

Only three steps are required for the convenient synthesis of 2-C-branched glyco-amino acids from glycals with good yields and stereoselectivities.     

Thermal degradation studies of alkyl-imidazolium salts and their application in nanocomposites

Increasing the thermal stability of organically-modified layered silicates is one of the key points in the successful technical application of polymer-layered silicate nanocomposites on the industrial scale. To circumvent the detrimental effect of the lower thermal stability of alkyl ammonium-treated montmorillonite, a series of alkyl-imidazolium molten salts were prepared and characterized by elemental analysis, thermogravimetry (TGA) and thermal desorption mass spectroscopy (TDMS). The effect of counter ion, alkyl chain length and structural isomerism on the thermal stability of the imidazolium salts was investigated. Alkyl-imidazolium-treated montmorillonite clays were prepared by ion exchange of the imidazolium salts with Na-montmorillonite. These organically-modified clays were characterized by X-ray diffraction (XRD), TDMS and thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA-FTIR), and compared to the conventional quaternary alkyl ammonium montmorillonite. Results indicate that the counter ion has an effect on the thermal stability of the imidazolium salts, and that imidazolium salts with PF₆⁻, N(SO₂CF₃)₂⁻ and BF₄⁻ anions are thermally more stable than the halide salts. A relationship was observed between the chain length of the alkyl group and the thermo-oxidative stability; as the chain length increased from propyl, butyl, decyl, hexadecyl, octadecyl to eicosyl, the stability decreased. The results also show that the imidazolium-treated montmorillonite has greater thermal stability compared to the imidazolium halide. Analysis of the decomposition products by FTIR provides an insight about the decomposition products which are water, carbon dioxide and hydrocarbons.     

Stereochemie von Metallocenen, 8. Mitt.: Die Absolute Konfiguration von Optisch Aktiven Benzol-chromtricarbonyl-derivaten; Asymmetrische Synthese und Kinetische Racematspaltung von Chiralen Metallocenen

Zusammenfassung Es wird über die Synthese und Racematspaltung von drei Benzol-chromtricarbonyl-derivaten sowie der -Methyl-ferrocen-carbonsäure berichtet. Die Absolutkonfiguration von (+)-(1-Tetralon)-Cr(CO)₃ konnte als (1S) ermittelt werden. Bei den beiden isomeren Säuren (+)- bzw. (–)-(o- bzw. m-Tolylsäure)-Cr(CO)₃ gelang erstmalig die konfigurative Korrelation eines -mit einem -disubstituierten Metallocen. Die Absolutkonfiguration des auch durch asymmetrische Synthese zugänglichen (+)-(o-Tolylsäure)-Cr(CO)₃ ließ sich auf Grund der Ergebnisse der kinetischen Racematspaltung der Anhydride der beiden racem. -Methyl-metallocen-carbonsäuren mit (–)-Menthol und (–)--Phenäthylamin als (1 S) bestimmen, da die Konfiguration der Methyl-ferrocencarbonsäure (nach chemischer Korrelation) bekannt war.

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The synthesis and optical resolution of three benzene chromium tricarbonyl derivatives and of -methyl ferrocene carboxylic acid are reported. The absolute configuration of (+)-1-tetralone)-Cr(CO)₃ was established as (1S). In the case of the isomeric acids (+)-(o-toluic acid)- and (–)-(m-toluic acid)-Cr(CO)₃ resp. a configurational correlation of - and -disubstituted metallocenes was possible for the first time. The absolute configuration of (+)-(o-toluic acid)-Cr(CO)₃ (which is also accessible by asymmetric synthesis) could be established as (1S) by kinetic resolutions of the anhydrides of the two racemic -methyl metallocene carboxylic acids with (–)-menthol and (–)--phenethylamine, since (after chemical correlation) the configuration of methyl ferrocene carboxylic acid was known.

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7. Mitt.:H. Falk undK. Schlögl, Tetrahedron [London], im Druck.     

13-Acetoxy-heptadecadien-(8, 10)-ol-(1), Octadien-(3, 5)-ol-(1)-Isomere und verwandte Verbindungen

Zusammenfassung Es werden diecis,cis- undtrans,trans-Isomeren der primären Alkohole Octadien-(3,5)-ol-(1) (I), 15-Acetoxy-nonadeca-dien-(10,12)-ol-(1) (IV), 17-Acetoxy-heneikosa-dien-(10,12)-ol-(1) (V), 12-Acetoxy-pentadeca-dien-(8,10)-ol-(1) (VII) und 13-Acetoxy-heptadeca-dien-(8,10)-ol-(1) (VI) synthetisiert und zusammen mit einigen Zwischenprodukten und Analogen unter Verwendung des Seidenspinners (Bombyx mori L.) und des Schwammspinners (Lymantria dispar L.) auf Attraktivität getestet. DieL. E.-Werte der synthetisierten cis,cis-VI-Präparate liegen in der Größenordnung von 10^–9 g/ml.

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Thecis, cis- andtrans, trans-isomere of the primary alcohols octadien-(3,5)-ol-(1) (I), 15-acetoxy-nonadecadien-(10,12)-ol-(1) (IV), 17-acetoxy-heneicosadien-(10,12)-ol-(1) (V), 12-acetoxypentadecadien-(8,10)-ol-(1) (VI) have been synthesized and tested for effectiveness as attractant together with several intermediates and analogues using the Silk Moth (Bombyx mori L.) and the Gipsy Moth (Lymantria dispar L.) The values of the attractant units of the cis, cis-VI-compounds synthesized are of the order 10^–9 g/ml.

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4. Mitt. der Reihe Synthese und Wirksamkeit von Sexualduftstoff-Analogen; 3. Mitt.:R. Riemschneider, A. Kühnl undK. Brockmeyer, unveröffentlichte Versuche; 2. Mitt.:R. Riemschneider undG. Kasang, Z. Naturforschg.18 b, 646 (1963); 1. Mitt.:R. Riemschneider, Vortrag vom 1. 9. 1962 in S. Paolo.