Interaction of neutrons with zinc and its isotopes

Coherent neutron scattering lengths and total cross sections have been measured for elemental Zn,Zn-compounds and on isotopicly enriched samples for neutron energies from 0.5 meV up to 143 keV using different techniques. From the experimental data the following quantities were obtained:

the coherent scattering lengths (b in fm) of Zn (5.689±0.014);⁶⁴Zn (5.23±0.04);⁶⁶Zn (5.98±0.05);⁶⁷Zn (7.58±0.08;b ₊=9.4±0.5/5.8±0.5;b _?=5.0±0.7/10.1±0.7);⁶⁸Zn (6.04 ±0.03);

the potential scattering radii (R′ in fm) of Zn (6.2±0.2),⁶⁴Zn (6.0±0.3) and⁶⁶Zn (6.2 ±0.3);

the absorption cross sections (σ _γ at 0.025 eV in barn) of Zn (1.11±0.02);⁶⁴Zn (1.1 ±0.1) and⁶⁶Zn (0.62±0.06).

Derived quantities are the “zero energy” scattering cross sections (σ ₀ in barn) for Zn (4.128±0.010) and⁶⁷Zn (7.8±0.3) and the incoherent bound cross sections of Zn (0.061 ±0.023) and⁶⁷Zn (0.6±0.4). In the epithermal region the Zn-cross section can be described by introduction of two strong bound levels of⁶⁷Zn+n for which estimated parameters are given.     

Palladium(II) complexes of the reducing sugars D-arabinose,D-ribose,rac-mannose,and D-galactose

The cellulose solvent Pd-en, an aqueous solution of [(en)Pd(II)(OH)(2)] (en=ethylenediamine), reacts with the monosaccharides D-arabinose (D-Ara), D-ribose (D-Rib), rac-mannose (rac-Man), and D-galactose (D-Gal) under formation of dimetalated aldose complexes, if the molar ratio of Pd and sugar is 2:1 or larger. In the Pd(2) complexes, the aldoses are tetra-deprotonated and act as bisdiolato ligands. Two crystalline pentose complexes were isolated: [(en)(2)Pd(2)(beta-D-Arap1,2,3,4 H(-4))].5 H(2)O (1) and [(en)(2)Pd(2)(beta-D-Ribp1,2,3,4 H(-4))].6.5 H(2)O (2), along with two hexose complexes. With rac-Man, the major solution species is crystallized as the 9.4-hydrate [(en)(2)Pd(2)(beta-rac-Manp1,2,3,4 H(-4))].9.4 H(2)O (3). From the respective D-Gal solutions, [(en)(2)Pd(2)(beta-D-Galf1,3,5,6 H(-4))].5 H(2)O.C(2)H(5)OH (4), with the sugar tetraanion in its furanose form, is crystallized though it is not the major species, rather the second most abundant in purely aqueous solutions. The Galf species is enriched in the mother liquors to the extent of 25 % of total sugar content. Substitution of the en ligand by two molecules of ammonia, methylamine, or isopropylamine, respectively, results in the formation of different solution species. With the bulkiest ligand, isopropylamine, monometalation of the aldoses in the 1,2-position is exclusively observed.     

Synthesis and supramolecular properties of trimethylene-bridged clips

The novel trimethylene-bridged clips 3 and 4 have been synthesized by using repetitive stereoselective Diels-Alder reactions of the benzo- and naphthobismethylenenorbornenes 8 and 19 as dienes and norbornadiene 9 as bisdienophile, and subsequent dehydrogenation of the primary cyclobisadducts 10 and 20 by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Clips 3 and 4 serve as receptors for a variety of electron-deficient neutral and cationic aromatic substrates, comparable to the molecular tweezers 1 and 2. The thermodynamic parameters of the complex formation, K(a) and DeltaG, were determined by (1)H NMR titration experiments and, in the case of the highly stable complex TCNB 32@4, by the use of isothermal titration microcalorimetry. The finding that clip 4 forms more stable complexes than 3 can be explained by the larger van der Waals contact surfaces of the naphthalene sidewalls in 4 compared to the corresponding benzene systems in 3. In the complexes with 4 as receptor, the plane of each aromatic substrate molecule is calculated to be oriented almost parallel to the naphthalene sidewalls. However, in the complexes of tweezers 2, the substrate is usually oriented parallel to the central naphthalene spacer unit. Due to the more open topology of 4, most complexes were calculated to consist of two or more equilibrating noncovalent conformers.     

Neue Sulfonamide, 12. Mitt. 5-Halogen-substituierte Sulfanilamido-methoxy-pyrimidine

Zusammenfassung Es wird die Darstellung von 2-Sulfanilamido-4-methoxy-5-chlorpyrimidin, 2-Sulfanilamido-4-methoxy-5-jodpyrimidin sowie 4-Sulfanilamido-2-methoxy-5-chlorpyrimidin beschrieben. Die erste Verbindung wurde auf zwei voneinander unabhängigen Synthesewegen erhalten. W. Klötzer undJ. Schantl, Mh. chem.94, 1178 (1963).     

Flow-injection approach for the determination of the dynamic response characteristics of ion-selective electrodes. Part 1. Theoretical considerations

A single-line flow-injection system with a straight tube reactor is proposed for investigating the dynamic response behaviour of ion-selective electrodes. The principle of the method is based on the fact that the concentration—time curve at the electrode surface can be described theoretically in the flow-injection system under certain practically realizable conditions. The response of the ion-selective electrode to that input signal can be measured experimentally. Thus, knowing the input and the output signal of an ion-selective electrode, an appropriate model describing its dynamic behaviour can be selected among the relevant models existing in the literature. Theoretical expressions for predicting the transient response of ion-selective electrodes in the flow system when the rate-determining step is an ion-transport process through a diffusion layer or a kinetic process were elaborated.     

Determination of N-n-alkyl-dimethylmorpholines and their metabolites by high resolution GC/MS

An analytical method is described to determine simultaneously cis/trans N-n-alkyl-dimethylmorpholines and their metabolites, the 4-(ω-carboxy-n-alkyl) cis/trans-2,6-dimethylmorpholines by pyrolytic alkylation and high resolution GC/MS in aqueous systems and sediments. The substances in the sediment phase were analyzed by GC/MS after extraction with methanol and water, substances in the water phase could be directly determined by GC/MS. The analytical procedure also allows the determination of further carboxylic acids in complex aqueous systems. Received: 9 April 1996 / Revised: 10 June 1996 / Accepted: 14 June 1996     

Optimisation of high performance liquid chromatography separation of neuroprotective peptides. Fractional experimental designs combined with artificial neural networks

The study of experimental design conjunction with artificial neural networks for optimisation of isocratic ion-pair reverse phase HPLC separation of neuroprotective peptides is reported. Different types of experimental designs (full-factorial, fractional) were studied as suitable input and output data sources for ANN training and examined on mixtures of humanin derivatives. The independent input variables were: composition of mobile phase, including its pH, and column temperature. In case of a simple mixture of two peptides, the retention time of the most retentive component and resolution were used as the dependent variables (outputs). In case of a complex mixture with unknown number of components, number of peaks, sum of resolutions and retention time of ultimate peak were considered as output variables. Fractional factorial experimental design has been proved to produce sufficient input data for ANN approximation and thus further allowed decreasing the number of experiments necessary for optimisation. After the optimal separation conditions were found, fractions with peptides were collected and their analysis using off-line matrix assisted laser desorption/ionisation time of flight mass spectrometry (MALDI-TOF-MS) was performed.     

Synthesis and supramolecular properties of molecular clips with anthracene sidewalls

Novel molecular clips with anthracene sidewalls (1 a-c) were synthesized; they form stable host-guest complexes with a variety of electron-deficient aromatic and quinoid molecules. According to single-crystal structure analyses of clip 1 c and 1,2,4,5-tetracyanobenzene (TCNB) complex 14@1 b, the clips' anthracene sidewalls have to be compressed substantially during the complex formation to provide attractive pi-pi interactions between the aromatic guest molecule and the two anthracene sidewalls in the complex. The compression and expansion of aromatic sidewalls are calculated by molecular mechanics to be low-energy processes, so the energy required for compression of the anthracene sidewalls during complex formation is apparently overcompensated by the gain in energy resulting from the attractive pi-pi interactions. The finding that complexes of the clips 1 a-c are more stable than those of the corresponding clips 2 a-c can be explained in terms of the larger van der Waals contact surfaces of the anthracene sidewalls in 1 a-c (relative to the naphthalene sidewalls in 2 a-c). Color changes resulting from charge-transfer (CT) bands are observed in complex formation by 1 a-c: from colorless to red or purple with TCNB (14), and from yellow to green with 2,4,7-trinitro-9-fluorenone TNF (17). Independently, the host 1 b and guest 14 fluoresce from their respective excited singlet states, whilst in the complex 14@1 b the charge-transfer state quenches the higher-energy singlet states of the two components, and as a result luminescence is only observed from this new CT state. To the best of our knowledge, complex 14@1 b is the first example of CT luminescence from a host-guest complex. The binding constant determined for the formation of the TCNB complex 14@1 b from a UV/Vis titration experiment (Ka = 12 400 m(-1)) agrees well with the value (K(a) = 12 800 m(-1)) obtained by 1H NMR titration.