ABSTRACT
The binuclear zinc(II) complex, [Zn2(HPTP)(CH3COO)]2+ was found highly active to cleave DNA (double-strand super-coiled DNA, pBR322 and phix174) in the presence of hydrogen peroxide. However, no TBARS (2-thiobarbituric acid reactive substance) formation was detected in a solution containing 2-deoxyribose (or 2'-deoxyguanosine, etc); where (HPTP) represents N,N,N'-N'-tetrakis(2-pyridylmethyl)-1,3-diamino-2-propanol. These facts imply that DNA cleavage reaction by the binuclear Zn(II)/H2O2 system should be due to a hydrolytic mechanism, which may be attributed to the enhanced nucleophilicity but depressed electrophilicity of the peroxide ion coordinated to the zinc(II) ion. DFT (density-functional theory) calculations on the peroxide adduct of monomeric zinc(II) have supported the above consideration. Similar DFT calculations on the peroxide adducts of the Al(III) and La(III) compounds have revealed that electrophilicity of the peroxide ion in these compounds is strongly reduced. This gives an important information to elucidate the fact that La3+ can enhance the growth of plants under certain conditions.
Subject(s)
Aluminum/chemistry , DNA, Superhelical/chemistry , DNA, Viral/chemistry , Lanthanum/chemistry , Organometallic Compounds/chemistry , Peroxides/chemistry , Plasmids/chemistry , Zinc/chemistry , Bacteriophage phi X 174 , Cations/chemistry , Crystallography, X-Ray/methods , Deoxyguanosine/chemistry , Deoxyribose/chemistry , Hydrogen Peroxide , Hydrolysis , Models, Molecular , Molecular Conformation , Molecular Structure , Thiobarbituric Acid Reactive SubstancesABSTRACT
The two title compounds, [Cu(3)(C(6)H(11)O(2))(6)(C(7)H(9)N)(2)](n), (I), and [Cu(2)(C(5)H(9)O(2))(4)(C(7)H(9)N)(2)], (II), have chain and finite-molecular structures, respectively. In (I), binuclear cage units and mononuclear 2,6-dimethylpyridine complexes, both of which have inversion centres, are arranged alternately and are linked by the carboxylate ions to form one-dimensional chains along the a axis. In (II), the binuclear cage unit has an inversion centre and the coordination geometry around the Cu atom is typical square pyramidal, with 2,6-dimethylpyridine at the apical position.
ABSTRACT
Two sterically hindered tris-pyridyl methane ligands, tris(6-methyl-2-pyridyl)methane (L1) and bis(6-methyl-2-pyridyl)pyridylmethane (L2), are newly synthesized. Under aerobic conditions, Ln (n = 1 or 2) reacts with CuX2 (X = Cl or Br), oxygenated at the methine position to LnOH or LnOMe. The former alcoholate ligand creates trinuclear Cu(II) complexes [Cu3(X)(LnO)3](PF6)2 [(X, n) = (Br, 1) 1, (C1, 1) 2, (Br, 2) 3, or (C1, 2) 4] in which the alkoxide oxygen atoms bridge copper centers. The crystal structures of 1-4 are presented along with their magnetic susceptibility data. The weak antiferromagnetic coupling between the Cu(II) centers in this trinuclear arrangement is due to weak interaction of the magnetic orbitals (dz2) which are oriented along three alternate sides in a hexagon of the Cu3O3 core in 1-4. Under anaerobic conditions, L1 reacts with CuBr2 to form a square pyramidal complex [CuL1Br2] (9) with the ligand facially capping. [Cu(Br)2(L1OMe)] (10) was obtained after the suspension of 9 in MeOH was stirred under air for 48 h. In the presence of cyclohexene, 9 is converted to [Cu(Br)(L1)]m (m = 1 or 2) 5 quantitatively to give trans- 1,2-dibromocyclohexane, indicating that Br2 is generated during the reaction. The FAB MS spectrum of [18O]-1 prepared by the reaction of L1 with CuBr2 under 18O2 shows that the ligand of [18O]-1 is L1(18O-.) L1(18OH), L1OCD3, and bis(6-methyl-2-pyridyl) ketone were obtained from reaction of L1 with CuBr2 in CD3OD under 18O2. These results indicate that the origins of the O atom in L1OH and L1OMe are O2 and MeOH, respectively. On the basis of these results, a mechanism of the oxygenation of L1 in the present system will be proposed.
ABSTRACT
The title two compounds, [Cu(2)(C(5)H(9)O(2))(4)(C(4)H(8)O(2))](n), (I), and [Cu(2)(C(6)H(11)O(2))(4)(C(4)H(8)O(2))](n), (II), are isomorphous. The binuclear Cu(II) units have a cage structure and are linked by the dioxane molecules to form a zigzag chain along the c axis. The binuclear copper unit and the dioxane ligand each have a centre of symmetry.
