A rotational band in82Zr

The neutron deficient nucleus⁸²Zr has been studied through the reaction⁵⁸Ni(²⁸Si, 2p 2n)⁸²Zr with a calculated cross section of 0.3% of the total fusion cross section atE(²⁸Si)=128 MeV. Gamma rays from excited states of⁸²Zr were measured and identified using the NORDBALL escape-suppression array at the Niels Bohr Institute. Reaction channel selection was performed by use of neutron and charged particle detector arrays in conjunction with the germanium detectors. A rotational band in⁸²Zr has been identified with spins up to 20 ? by analysis of reaction channel selectedγ-γ coincidence matrices. Band crossings were identified at frequencies 0.57 and 0.69 MeV.     

Nicke(II) halide complexes with hypoxanthine and xanthine

Summary Ni(LH)₃LX complexes (LH=hypoxanthine or xanthine; X=Cl, Br or I) are formed by boiling under reflux 2:1 molar mixtures of LH and hydrated NiX₂ in HC(OEt)₃–MeCO₂Et. The new complexes appear to be linear chain-like polymers, characterized by bidentate monoanionic L^– ligands singly bidging between adjacent Ni²⁺ ions. A coordination number six is attained by the presence of three terminal unidentate LH and one X ligand in the first coordination sphere of each Ni²⁺ ion. The neutral LH and monoanionic L^– ligands bind exclusivelyvia ring nitrogens to Ni^II. The probable binding sites of the uni- and bi-dentate hypoxanthine and ligands in the new complexes are discussed.Presented in part at the 3rd Chem. Congress of North America (LH=xanthine) and the XXVI ICCC (LH=hypoxanthine), see refs. 1 and 2, respectively.     

Zur Chemie der Spiro-β-lactame aus der [2+2]-Cycloaddition von Ketenen an Iminolactone

Chemistry of Spiro-β-lactams Reactions of the easily accessible spiro-β-lactams 1 are described. These comprise hydrogenation, hydrolyses and alcoholyses, reaction with hydrazine, and lead to new heterocyclic compounds. Some further transformations of the products are shown.     

13C{1H} single frequency off-resonance decoupling of secondary carbons

¹³C{¹H} single frequency off-resonance decoupled spectra of secondary carbons with two chemically non-equivalent protons are analysed theoretically and experimentally. By a careful analysis of the frequencies of all six transitions all spectral parameters, including the geminal proton-proton coupling constant, can be determined very accurately.     

COMPLEXING OF RIBOFLAVIN AND ITS 2-SUBSTITUTED ANALOGS WITH ADENOSINE AND OTHER 6-SUBSTITUTED PURINE DERIVATIVES*

Abstract Fluorescence properties of riboflavin and its 2-substituted analogs and the quenching of fluorescence which occurs upon complexing with adenosine and other 6-substituted purine derivatives have been examined at different concentrations of interactants and hydrogen ion. The 6-substituted purines and their ribosides show varying degrees of association with riboflavin. Successive N-alkylation of the 6-amino group of purine ribosides leads to more stable complexing in the order ethyl > methyl > propyl with riboflavin and its analog. These results suggest that such groups, including the 6-amino group of adenine or adenine moiety of FAD, do not directly interact with flavins by hydrophobic or hydrogen bonding. Lowering the pH to above that required to protonate the isoalloxazine system disrupts the intermolecular complexes. Hence, only the unprotonated bases can form such complexes. The 2-substituted aminoriboflavins, as well as FAD, exhibit fluorescence optima upon changing pH. The species involved appear to be a non-fluorescent form with protonated isoalloxazine and amine or adenine portions at low pH, a fluorescent form with only the amine or adenine portions protonated at moderately acid pH, and a non-fluorescent form which is intramolecularly quenched at higher pH. The general electron donating properties of the amines may be the common reason for their quenching of fluorescence in inter- and intramolecular complexes with flavins.     

An extension and simple proof of a constrained lattice fixed point theorem

We extend a result of Roth dealing with fixed points of lattice mappings which satisfy certain constraints. Presented by J. Mycielski.     

Oxygen isotope effects on electron transfer to O2 probed using chemically modified flavins bound to glucose oxidase

Apo-glucose oxidase has been reconstituted with flavins modified in the 7 and 8 positions and characterized with regard to the catalytic rate of O(2) reduction and oxygen-18 isotope effects on this process. Kinetic studies as a function of driving force indicate a reorganization energy for electron transfer to O(2) of lambda = 28 kcal mol(-)(1) at optimal pH, which is similar to the value obtained earlier from temperature dependencies of rates (Roth, J. P.; Klinman, J. P. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 62-67). For the various enzyme-bound flavins, competitive oxygen-18 kinetic isotope effects fall within the narrow range of 1.0266(5) to 1.0279(6), apparently because of the dominant contribution of outer-sphere reorganization to the activation barrier; within the context of semiclassical and quantum mechanical electron transfer theories, the magnitude of the isotope effects reveals the importance of nuclear tunneling.