The evolution of β-diketone or β-diketophenol ligands and related complexes

Stereochemistry of lead(II) complexes with oxygen donor ligands

Recently, we reported the first artificial nucleoside for alternative DNA base pairing through metal complexation (J. Org. Chem. 1999, 64, 5002−5003). In this regard, we report here the synthesis of a hydroxypyridone-bearing nucleoside and the incorporation of a neutral Cu2+-mediated base pair of hydroxypyridone nucleobases (H−Cu−H) in a DNA duplex. When the hydroxypyridone bases are incorporated into the middle of a 15 nucleotide duplex, the duplex displays high thermal stabilization in the presence of equimolar Cu2+ ions in comparison with a duplex containing an A−T pair in place of the H−H pair. Monitoring temperature dependence of UV-absorption changes verified that a Cu2+-mediated base pair is stoichiometrically formed inside the duplex and dissociates upon thermal denaturation at elevated temperature. In addition, EPR and CD studies suggested that the radical site of a Cu2+ center is formed within the right-handed double-strand structure of the oligonucleotide. The present strategy could be develope...

Efficient incorporation of a copper hydroxypyridone base pair in DNA.

This review discusses the coordination number (CN) and the coordination geometry of the first coordination sphere of Pb(II) atoms in crystal structures of 98 lead(II) complexes with O-donor ligands and the stereochemically active lone pair of electrons (LP, E) in the terms of the valence shell electron-pair repulsion (VSEPR) model. The CN of Pb(II) atoms of the first coordination sphere has values falling into the range (3 + E) to (6 + E). The following coordination polyhedra-{psi}-tetrahedron (I), {psi}-trigonal bipyramid (II), {psi}-octahedron (III), {psi}-pentagonal bipyramid with an axial (IV) or equatorial (V) vacant position are formed. For the investigated structures of the Pb(II) complexes, the formula of each compound, the overall CN of the Pb(II) atom considered as the sum of the CN in the first coordination sphere and the number of secondary bonds, the polyhedron shape, the Pb-O bond lengths, and O-Pb-O bond angles in the first coordination sphere, secondary bond lengths, references and REFCODEs are presented in the comprehensive Tables. The quantum chemical investigations performed using density functional theory (DFT) method have confirmed the stereochemical activity of the LP of Pb(II) atoms in the studied structures of lead(II) complexes with O-donor ligands.

Stereochemistry of lead(II) complexes with oxygen donor ligands.

The mixed-ligand complexes [Cu(L)(maltol)] where L = 2,2′-bipyridine (bpy; 1), 1,10-phenanthroline (phen; 2), 1,10-phenanthroline-5,6-dione (phendione; 3), dipyrido[3,2-a:2′,3′-c]phenazine (dppz; 4), and 4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f][1,10]-phenanthroline-6,13-dione (bipyridylglycoluril; bpg; 5) have been synthesized and characterized by structural, analytical, and spectral methods. The single-crystal X-ray structures of 1, 2, and 5 exhibit a distorted square-pyramidal structure, with the polypyridyl ligands and maltol occupying equatorial positions and either a water or nitrate anion at the axial position. The N,N-dimethylformamide glass as well as the single-crystal electron paramagnetic resonance of the complexes confirms the distorted square-pyramidal structure. The DNA binding investigated using different techniques (absorption titration, viscosity, thermal melting, and fluorescence quenching) indicates the partial intercalation of the planar polypyridyl ligands into...

Mixed-Ligand Copper(II) Maltolate Complexes: Synthesis, Characterization, DNA Binding and Cleavage, and Cytotoxicity

The structures of bis-maltolato-zinc(II) and of bis-3-hydroxy-1,2-dimethyl-4-pyridinonato–zinc(II) and –lead(II)

The reaction of [M(CN)4O(OH2)]2− (M = Mo or W) with 2-acetylpyridine and methyl-or butyl-amine in a water-MeOH mixture gave [M(CN)3O(L-L)]- (L-L= Schiff base ligand), isolated as [AsPh4]+ salts. The complexes have been characterized by elemental analysis, and electronic, i.r. and1H-n.m.r. spectroscopy. The Schiff base ligands complex in a bidentate manner through the two nitrogen atoms giving mixed-ligand compounds similarly to 2,2′-bipyridyl or 1,10-phenanthroline.

Oxo-tricyano complexes of molybdenum(IV) and tungsten(IV) with bidentate Schiff bases

We report solvent effects on the piezochromic behaviour of wavelengths of maximum absorption for metal-to-ligand charge-transfer (m.l.c.t.) bands of several molybdenum–diimine–carbonyl and titanium or vanadium–cyclopentadienyl or ethylmaltolate–thiocyanate complexes. These and previously published data are collated in an attempt to establish a pattern for solvent effects on piezochromism of m.l.c.t. bands. Strategies for the design of compounds and complexes for use in establishing a clear pattern for such effects are outlined.

Solvent effects on piezochromism of transition metal complexes

Rate laws and kinetic parameters are reported for substitution at titanium(IV) complexes Ti(LL)2X2, where LLH=cyclopentadiene, the 4-pyrone ethylmaltol, several 4-pyridinones, and related ligands, and X=halide or alkoxide, in acetonitrile solution at 298.2 K. Reactivities are discussed in terms of the nature of the leaving group, the entering group and the non-leaving ligand LL−. Activation volumes of −15 and −12 cm3 mol−1 have been determined for thiocyanate attack at Ti(cp)2Cl2 and Ti(etmalt)2Cl2 respectively. Substitution mechanisms are discussed in the light of the kinetic parameters obtained.

Kinetics of substitution at ternary titanium(IV)-cyclopentadienyl, pyronato or pyridinato-halide or alkoxide complexes

The preparation and properties of tris-[3-hydroxy-1,2-dimethyl-pyridin-4(1H)-onato]cobalt(III) are described. The structure of the fac isomer has been established by X-ray diffraction techniques. Solvation characteristics of this complex have been assessed through solubility measurements in methanol–water mixtures. The complex is very inert in neutral solution but undergoes acid-catalysed aquation at lower pHs.

Simon A. Parsons

Papers

The structures of bis-maltolato-zinc(II) and of bis-3-hydroxy-1,2-dimethyl-4-pyridinonato–zinc(II) and –lead(II)

Oxo-tricyano complexes of molybdenum(IV) and tungsten(IV) with bidentate Schiff bases

Solvent effects on piezochromism of transition metal complexes

Kinetics of substitution at ternary titanium(IV)-cyclopentadienyl, pyronato or pyridinato-halide or alkoxide complexes

Tris-[3-hydroxy-1,2-dimethyl-pyridin-4(1H)-onato]cobalt(III)