Rita Wagner

Effect of the substituents on the spin coupling between iminosemiquinone π-radicals mediated by diamagnetic metal ions: l.s. Co(III)vsGa(III)

Exchange coupling between the radical iminosemiquinone ligands changes from ferromagnetic to antiferromagnetic in l.s. Co(III) complexes, whereas the same coupling in Ga(III) complexes is always antiferromagnetic.

Radical−Ligand-Derived C−N Coupling, Ga(III)−Radical vs Low-Spin Co(III)−Radical Reactivity

The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di- tert-butylphenol, H 2L (OCH3), results in, as expected, a trisradical complex with a low-spin Co(III) center, [Co (III)(L (OCH3) (*)) 3] ( 1), whereas the Ga(III) center yields a coordinated new hexadentate monoradical ligand, [Ga (III)L (*) 1] ( 2), presumably due to the ligand-derived redox activity involving C-H activation.

The Reactions of the Hydroxymethyl Radical with 1,3-dimethyluracil and 1,3-dimethylthymine

Hydroxymethyl radicals .CH2OH, generated by the radiolysis of methanol (0.5 mol dm-3) in N2O-saturated aqueous solutions, were reacted with 1,3-dimethyluracil or 1,3-dimethylthymine (10(-3) mol dm-3). The products were identified and their G values determined. It has been concluded that in 1,3-dimethyluracil .CH2OH attack occurs only at C(6) while in 1,3-dimethylthymine there is partitioning between addition (two-thirds) and H-abstraction from the C(5)-methyl group (one-third). A rate constant for CH2OH addition to 1,3-dimethyluracil of about 10(4) dm3 mol-1 s-1 is estimated. Complexities that may arise in the radiolysis of pyrimidines such as 1,3-dimethylthymine, apparently as a consequence of the formation of 5-alkylidenepyrimidines, are discussed. A value of 0.15 has been estimated for the disproportionation/combination ratio for the hydroxymethyl radical self-termination reaction.

A magnetostructural study of linear NiIIMnIIINiII, NiIICrIIINiII and triangular NiII3 species containing (pyridine-2-aldoximato)nickel(II) unit as a building block

Three trinuclear complexes, NiII MnIII NiII, NiII CrIII NiII and Ni(II)3 based on (pyridine-2-aldoximato)nickel(II) units are described. Two of them, and , contain metal-centers in linear arrangement, as is revealed by X-ray diffraction. Complex is a homonuclear complex in which the three nickel(II) centers are disposed in a triangular fashion. The compounds were characterized by various physical methods including cyclic voltammetric and variable-temperature (2-290 K) susceptibility measurements. Complexes and display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent Ni II and Cr III ions in is observed. The experimental magnetic data were simulated by using appropriate models.

γ-Radiolysis of 2′-Deoxycytidine-5′-phosphate in Deoxygenated Aqueous Solutions. OH Radical-Induced Alterations at the Sugar Moiety

Abstract In order to elucidate some aspects of the mechanism of radical-induced strand break formation in DNA, the γ-radiolysis of N2O-saturated aqueous solutions of 2′-deoxycytidine-5′-phosphate has been studied as a model system. At pH 4 it has been observed that upon OH attack at the sugar moiety phosphate (G ≈ 0.6) and cytosine (G = 1) are released and the following cytosine-free sugars are formed: 2,5-dideoxypentos-3,4-diulose, 1 (G = O.22), 2-deoxy-pentos-4-ulose, 2 (G = 0.18), 2-deoxy-pentos-4-ulose-5-phosphate, 3 (G=0.06), 2-deoxypentonic acid-5-phosphate and its lactone, 5 (G ≈ 0.5). Some 2-deoxyribose-5-phosphate, 4 is also formed. Upon addition of H2O2 (up to 10-2 M) prior to irradiation, G(1) is drastically reduced without giving rise to another cytosine-free product. G(3) increases at the expense of G(2). G (4 + 5) also increase upon H2O2 addition. The formation of these products and the change of their G values as a function of H2O2 concentration are discussed in the light of well-documented radical reactions of carbohydrates and related compounds. The precursor of 1 has been considered to be the radical at C-3′, that of 2 and 3 the radical at C-4′ and that of 5 the radical at C-1′. Product 4 is thought to arise from a radical-induced destruction of the cytosine moiety. These primary radicals which may undergo rearrangement, or eliminate phosphate, are readily oxidised by H2O2, a reaction which leads to the change of product distribution mentioned above.