Synthesis, crystal structures, DNA binding and cleavage activity of L-glutamine copper(II) complexes of heterocyclic bases

Ternary L-glutamine (L-gln) copper(II) complexes [Cu(L-gln)(B)(H2O)](X) (B = 2,2'-bipyridine (bpy), X = 0.5SO(4)(2-), 1; B = 1,10-phenanthroline (phen), X = ClO4-, 2) and [Cu(L-gln)(dpq)(ClO4)] (3) (dpq, dipyridoquinoxaline) are prepared and characterized by physicochemical methods. The DNA binding and cleavage activity of the complexes have been studied. Complexes 1-3 are structurally characterized by X-ray crystallography. The complexes show distorted square pyramidal (4+1) CuN3O2 coordination geometry in which the N,O-donor amino acid and the N, N-donor heterocyclic base bind at the basal plane with a H2O or perchlorate as the axial ligand. The crystal structures of the complexes exhibit chemically significant hydrogen bonding interactions besides showing coordination polymer formation. The complexes display a d-d electronic band in the range of 610-630 nm in aqueous-dimethylformamide (DMF) solution (9:1 v/v). The quasireversible cyclic voltammetric response observed near -0.1 V versus SCE in DMF-TBAP is assignable to the Cu(II)/Cu(I) couple. The binding affinity of the complexes to calf thymus (CT) DNA follows the order: 3 (dpq) > 2 (phen) >> 1 (bpy). Complexes 2 and 3 show DNA cleavage activity in dark in the presence of 3-mercaptopropionic acid (MPA) as a reducing agent via a mechanistic pathway forming hydroxyl radical as the reactive species. The dpq complex 3 shows efficient photoinduced DNA cleavage activity on irradiation with a monochromatic UV light of 365 nm in absence of any external reagent. The cleavage efficiency of the DNA minor groove binding complexes follows the order:3 > 2 >> 1. The dpq complex exhibits photocleavage of DNA on irradiation with visible light of 647.1 nm. Mechanistic data on the photo-induced DNA cleavage reactions reveal the involvement of singlet oxygen (O-1(2)) as the reactive species in a type-II pathway. (C) 2008 Elsevier B.V. All rights reserved.

New main group ligands for complexation with transition and inner transition elements

Symmetrical and unsymmetrical diphosphinoamines of the type X(2)PN(R)PX(2) and X(2)PN(R)YY' offer vast scope for the synthesis of a variety of transition metal organometallic complexes. Diphosphinoamines can be converted into their dioxides which are also accessible from appropriate (chloro)phosphane oxide precursors. The diphosphazane dioxides form an interesting series of complexes with lanthanide and actinide elements. Structural and spectroscopic studies have been carried out on a wide range of transition metal complexes incorporating linear P-N-P ligands and judiciously functionalized cyclophosphazanes and cyclo-phosphazenes.

Tungsten(0)-carbonyl complexes of naphthylazoimidazoles

The reaction of W(CO)(6) with 1-alkyl-2-(naphthyl-alpha-azo)imidazole (alpha-NaiR) has synthesized [W(CO)(5)(alpha-NaiR-N)] (alpha-NaiR-N refers to the monodentate imidazole-N donor ligand) at room temperature. The structure of[W(CO)(5)(alpha-NaiMe-N)] shows a monodentate imidazole-N coordination of 1-methyl-2-(naphthyl-alpha-azo)imidazole (alpha-NaiMe). The complexes are characterized by elemental, mass and other spectroscopic data (IR, UV-Vis, NMR). On refluxing in THF at 323 K, [W(CO)(5)(alpha-NaiR-N)] undergoes decarbonylation to give [W(CO)(4)(alpha-NaiR-N,N')] (alpha-NaiR-N,N' refers to the imidazole-N(N), azo-N(N') bidentate chelator). Cyclic voltammetry shows metal oxidation (W-0/W-1) and ligand reductions (azo/azo(-), azo(-)/azo(=)). The redox and electronic properties are explained by theoretical calculations using an optimized geometry. DFT computation of [W(CO)(5)(alpha-NaiMe-N)] suggests that the major contribution to the HOMO/HOMO - 1 come from W cl-orbitals and the orbitals of CO. The LUMOs are occupied by alpha-NaiMe functions. The back bonding interaction thus originates from the W(CO)(n) moiety to the LUMO of alpha-NaiR. A TD-DFT calculation has ascribed that HOMO/HOMO - 1 -> LUMO is a mixture of metal-to-ligand and ligand-to-ligand charge transfer underlying the CO -> azoimine contribution. The complexes show emission spectra at room temperature. [W(CO)(4)(alpha-NaiR-N,N')] shows a higher fluorescence quantum yield (phi = 0.05-0.07) than [W(CO)(5)(alpha-NaiR-N)] (phi = 0.01-0.02). (C) 2008 Elsevier Ltd. All rights reserved.

First principles study of magnetism in divalent Eu perovskites

A comparative first principles study has been carried out for EuLiH3 (ELH) and EuTiO3 (ETO) using the generalized gradient approximation +U approach. While ELH exhibits ferromagnetic ground state for all volumes, the magnetic ground state of ETO has the tendency to switch from G-type antiferromagnetic to a ferromagnetic state with change in volume. The marked difference in magnetic behavior and magnitude of the nearest neighbors exchange interaction of both the compounds are shown to be related to the difference in their respective electronic structure near the Fermi level. The Ti 3d states are shown to play predominant role in weakening the strength of the exchange interaction in ETO.

Hydrogen and fluorine in crystal engineering: systematics from crystallographic studies of hydrogen bonded tartrate-amine complexes and fluoro-substituted coumarins, styrylcoumarins and butadienes

Three aspects of crystal engineering in molecular crystals are presented to emphasize the role of intermolecular interactions and factors influencing crystal packing. Hydrogen bonded tartrate-amine complexes have been analyzed with the propensity for formation of multidirectional hydrogen bonding as a key design element in the generation of materials for second harmonic generation (SHG). The invariance of the framework in DBT and its possible implications on SHG is outlined. The role of Fluorine in orienting molecules of coumarins, styrylcoumarins and butadienes for photodimerization is described with particular emphasis on its steering capability. Usage of coumarin as an design element for the generation of polymorphs of substituted styrylcoumarins is examined with specific examples.

Metal-Ion-Dependent Oxidative DNA Cleavage by Transition Metal Complexes of a New Water-Soluble Salen Derivative

A new water-soluble, salen [salen = bis(salicylidene) ethylenediamine]-based ligand, 3 was developed. Two of the metal complexes of this ligand, i.e., 3a, [Mn(III)] and 3b, [Ni(II)], in the presence of cooxidant magnesium monoperoxyphthalate (MMPP) cleaved plasmid DNA pTZ19R efficiently and rapidly at a concentration similar to 1 mu M. In contrast, under comparable conditions, other metal complexes 3c, [Cu(II)] or 3d, [Cr(III)] could not induce any significant DNA nicking. The findings with Ni(II) complex suggest that the DNA cleavage processes can be modulated by the disposition of charges around the ligand.

Transition metal complexes of a potential anticancer quinazoline ligand

A new heterocycle, namely 2-(furyl)-3-(furfuralimino)-1,2-dihydroquinazolin-4(3H)-one (ffdq) was formed by the ondensation of 2-aminobenzoylhydrazide with furfural and characterized by physico-chemical, spectroscopic, and single crystal X-ray diffraction studies. A series of complexes of ffdq have been synthesized and characterized by physico-chemical, spectroscopic, and thermal studies. According to the i.r. and 1H-n.m.r. spectra ffdq behaves as a bidentate ligand coordinating through quinazoline oxygen and azomethine nitrogen. The FAB-mass spectrum of the Cd(II) complex indicates the monomeric nature of this complex. The X-band e.p.r. spectrum of the Cu(II) complex and thermal stabilities of the Co(II) and Ni(II) complexes are discussed.

Copper(II) Complexes of l-Arginine as Netropsin Mimics Showing DNA Cleavage Activity in Red Light

Copper(II) complexes [Cu(L-arg)(2)](NO3)(2) (1) and [Cu(L-arg)(B)Cl]Cl (2-5), where B is a heterocyclic base, namely, 2,2'-bipyridine (bpy, 2), 1,10-phenanthroline (phen, 3), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 4), and dipyrido[3,2-a:2',3'-c)phenazine (dppz, 5), are prepared and their DNA binding and photoinduced DNA cleavage activity studied. Ternary complex 3, structurally characterized using X-ray crystallography, shows a square-pyramidal (4 + 1) coordination geometry in which the N,O-donor L-arginine and N,N-donor 1,10-phenanthroline form the basal plane with one chloride at the elongated axial site. The complex has a pendant cationic guanidinium moiety. The one-electron paramagnetic complexes display a metal-centered d-d band in the range of 590-690 nm in aqueous DMF They show quasireversible cyclic voltammetric response due to the Cu(II)/Cu(I) couple in the range of -0.1 to -0.3 V versus a saturated calomel electrode in a DMF-Tris HCl buffer (pH 7.2). The DNA binding propensity of the complexes is studied using various techniques. Copper(II) bis-arginate 1 mimics the minor groove binder netropsin by showing preferential binding to the AT-rich sequence of double-strand (ds) DNA. DNA binding study using calf thymus DNA gives an order: 5 (L-arg-dppz) >= 1 (biS-L-arg) > 4 (L-arg-dpq) > 3 (L-arg-phen) >> 2 (L-arg-bpy). Molecular docking calculations reveal that the complexes bind through extensive hydrogen bonding and electrostatic interactions with ds-DNA. The complexes cleave supercoiled pUC19 DNA in the presence of 3-mercaptopropionic acid as a reducing agent forming hydroxyl ((OH)-O-center dot) radicals. The complexes show oxidative photoinduced DNA cleavage activity in UV-A light of 365 nm and red light of 647.1 nm (Ar-Kr mixed-gas-ion laser) in a metal-assisted photoexcitation process forming singlet oxygen (O-1(2)) species in a type-II pathway. All of the complexes, barring complex 2, show efficient DNA photocleavage activity. Complexes 4 and 5 exhibit significant double-strand breaks of DNA in red light of 647.1 nm due to the presence of two photosensitizers, namely, L-arginine and dpq or dppz in the molecules.

Photoinduced DNA and Protein Cleavage Activity of Ferrocene-Appended L-Methionine Reduced Schiff Base Copper(II) Complexes of Phenanthroline Bases

Ferrocene-appended ternary copper(H) complexes of phenanthroline bases having CuN3OS coordination with an axial Cu-S bond derived from L-methionine reduced Schiff base shows red light induced oxidative DNA cleavage activity following a hydroxyl radical pathway. The dipyridophenazine complex, in addition, displays photoinduced oxidative cleavage of bovine serum albumin protein in UV-A light.

Three-dimensional 3d-4f heterometallic polymers containing both azide and carboxylate as co-ligands

The hydrothermal reaction of Ln(NO3)(3), Ni(NO3)(2), NaN3, and isonicotinic acid (L) yielded two novel 3-D coordination frameworks (1 and 2) of general formula [Ni(2)Ln(L)(5)(N-3)(2)(H2O)(3)] center dot 2H(2)O (Ln = Pr(III) for 1 and Nd(III) for 2), containing Ni-Pr or Ni-Nd hybrid extended three-dimensional networks containing both azido and carboxylate as co-ligands. Both the compounds are found to be isostructural and crystallize in monoclinic system having P2(1)/n space group. Here the lanthanide ions are found to be nonacoordinated. Both bidentate and monodentate modes of binding of the carboxylate with the lanthanides have been observed in the above complexes. Variable temperature magnetic studies of the above two complexes have been investigated in the temperature range 2-300 K which showed dominant antiferromagnetic interaction in both the cases and these experimental results are analyzed with the theoretical models. (c) 2008 Elsevier B.V. All rights reserved.

Syntheses and characterization of trans-[NiL2(NCS)2][L = 2-(aminomethyl) pyridine], trans-[NiL02(NSC)2][L0 = 2-(2-aminoethyl)pyridine] and trans-[NiL00 2(NSC)2] [L00 = 2-(2-methylaminoethyl)pyridine] complexes: X-ray single crystal structure of trans-[NiL02(NSC)2] [L0 = 2-(2-aminoethyl)pyridine]

[NiL2(NCS)2] (1) [L = 2-(aminomethyl)pyridine], [NiL02(NCS)2] (2) [(L0) = 2-(2-aminoethyl)pyridine and [NiL00 2(NCS)2] (3) [L00 = 2-(2-methylaminoethyl)pyridine] have been synthesized from solution. All the complexes possess trans geometry as is evident from solid state UV–Vis spectral study and X-ray single crystal structure analysis of complex 2 unambiguously proves trans geometry of the species.

Determination of the enthalpies of sublimation and evaporation from thermogravimetric data: Application to metalorganic complexes of Al and Cr

A series of bimetallic acetylacetonate (acac) complexes, AlxCr1-x(acac)(3), 0 <= x <= 1, have been synthesized for application as precursors for the CVD Of Substituted oxides, such as (AlxCr1-x)(2)O-3. Detailed thermal analysis has been carried out on these complexes, which are solids that begin subliming at low temperatures, followed by melting, and evaporation from the melt. By applying the Langmuir equation to differential thermogravimetry data, the vapour pressure of these complexes is estimated. From these vapour pressure data, the distinctly different enthalpies of sublimation and evaporation are calculated, using the Clausius-Clapeyron equation. Such a determination of both the enthalpies of sublimation and evaporation of complexes, which sublime and melt congruently, does not appear to have been reported in the literature to date.

Synthesis, crystal structures and protease activity of amino acid Schiff base iron(III) complexes

Iron(III) complexes, (NHEt3)[Fe(III)(sal-met)(2)] and (NHEt3)[Fe(III)(sal-phe)(2)], of amino acid Schiffbase ligands, viz., N-salicylidene-L-methionine and N-salicylidene L-phenylalanine, have been prepared and their binding to bovine serum albumin (BSA) and photo-induced BSA cleavage activity have been investigated. The complexes are structurally characterized by single crystal X-ray crystallography. The crystal Structures of the discrete mononuclear rnonoanionic complexes show FeN2O4 octahedral coordination geometry in which the tridentate dianionic amino acid Schiff base ligand binds through phenolate and carboxylate oxygen and imine nitrogen atoms. The imine nitrogen atoms are trans to each other. The Fe-O and Fe-N bond distances range between 1.9 and 2.1 angstrom. The sal-met complex has two pendant thiomethyl groups. The high-spin iron(III) complexes (mu(eff) similar to 5.9 mu(B)) exhibit quasi-reversible Fe(III)/Fe(II) redox process near -0.6 V vs. SCE in water. These complexes display a visible electronic hand near 480 nm in tris-HCl buffer assignable to the phenolate-to-iron(III) charge transfer transition. The water soluble complexes bind to BSA giving binding constant values of similar to 10(5) M-1. The Complexes show non-specific oxidative cleavage of BSA protein on photo-irradiation with UV-A light of 365 nm.

Structure of nonactin-calcium perchlorate, C40H64O12.Ca(ClO4)2, and a comparative study of metal-nonactin complexes

M r= 975.9, orthorhombic, Pnna, a = 20.262 (3), b= 15.717 (2), c= 15.038 (1)A, V= 4788.97 A 3, z = 4, D x = 1.35 Mg m -3, Cu Kct radiation, 2 = 1.5418 A, /t = 2.79 mm -1, F(000) -= 2072, T = 293 K, R = 0.08, 3335 observed reflections. The molecular structure and the crystal packing are similar to those observed in the nonactin complexes of sodium thiocyanate and potassium thiocyanate. The eight metal-O distances are nearly the same in the potassium complex whereas the four distances involving carbonyl O atoms are shorter than the remaining four involving the tetrahydrofuran-ring O atoms in the Na and the Ca complexes. This observation can be explained in terms of the small ionic radii of Na + and Ca 2+, and leads to a plausible structural rationale for the stronger affinity of nonactin for K + than for the other two metal ions.

NMR-Studies of Octahedral Dicyano-(2,2' Bipyridine) and Tetracyano-(2,2'-Bipyridine) Iron(ii) Complexes

Coordination compounds of the polypyridines, 2,2 ' -bipyridine (bipy) and 1,10-penanthroline (phen) have offered renewed interest on account of their manifold applications and from the point of view of understanding their structure-reactivity relationships.1 Iron(II) reacts with them to form tris-complexes possessing spin-paired ground states. Cyanide ion greatly enhances the rate of displacement of bipy or phen to form the Schilt class of compounds. Fe(bipy)2(CN)2 and Fe(phen)2(CN)2. They display varying colours in solution depending upon the nature of the solvent and react reversibly with acids to form diprotonated species.2 Magnetic circular dichroism studies have been reported to describe their lowest electronic excitation.