Showing papers by "Georgina M. Rosair published in 2011"

Bis-phenanthroline copper(II) phthalate complexes are potent in vitro antitumour agents with ‘self-activating’ metallo-nuclease and DNA binding properties

Abstract: Three, structurally characterised, bis-phen Cu(II) complexes of the phthalate isomers display rapid, low micromolar in vitro cytotoxicity against a range of epithelial tumour cells. The complexes induce relaxation of supercoiled plasmid DNA in the absence of external reducing agents and display efficient CT-DNA, Poly[d(A–T)]2 and Poly[d(G–C)]2 binding.

Weak interactions modulating the dimensionality in supramolecular architectures in three new nickel(II)-hydrazone complexes, magnetostructural correlation, and catalytic potential for epoxidation of alkenes under phase transfer conditions.

Abstract: Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL1), 2-hydroxyacetophenone (HL2), and 2, 3-dihydroxybenzaldehyde (HL3). These tridentate ligands are reacted with Ni(OOCCF3)2·xH2O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L1)(OOCCF3)(CH3OH)]2 (1), [Ni(L2)(OOCCF3)(H2O)]2 (2), and [Ni(L3)(L3H)](OOCCF3)(H2O)1.65(CH3OH)0.35 (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV–vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O–H···O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand ...

Isolation of four new CoII/CoIII and NiII complexes with a pentadentate Schiff base ligand: syntheses, structural descriptions and magnetic studies.

Abstract: In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new CoII/CoIII and NiII complexes with a pentadentate Schiff base ligand H3L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1 : 2 molar ratio. The room temperature syntheses involving CoII and NiII nitrates and the ligand H3L lead to the isolation of the dinuclear species [Co2L2(H2O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [CoII2CoIII2L2(μ3-OMe)2(NO3)(H2O)2]NO3·2(H2O) (2), and [Ni4L2(μ3-OMe)2(H2O)2]·2H2O (4). 1 is found to be a simple mono alkoxo-bridged CoIII dinuclear species, whereas 2 and 4 are both rhomb-like tetrameric complexes with double oxo bridges and μ3-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2 shows six coordinate ordered CoII and CoIII ions and 4 has both six- and five-coordinate NiII centers. Compound 3 is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, 1H-NMR and ESI mass study results and is supposed to have one NiII center coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2 and 4 is performed which indicate for both 2 and 4 the presence of intracluster dominant ferromagnetic interactions.

Spectroscopic, structural, computational and (spectro)electrochemical studies of icosahedral carboranes bearing fluorinated aryl groups

Abstract: The icosahedral carboranes 1-C6F5-2-Ph-1,2-closo-C2B10H10 (1), 1-(4′-F3CC6H4)-2-Ph-1,2-closo-C2B10H10 (2), 1,2-(4′-F3CC6H4)2-1,2-closo-C2B10H10 (3), 1-(4′-H3CC6F4)-2-Ph-1,2-closo-C2B10H10 (4), 1-(4′-F3CC6F4)-2-Ph-1,2-closo-C2B10H10 (5), 1,2-(4′-F3CC6F4)2-1,2-closo-C2B10H10 (6), 1,7-(4′-F3CC6F4)2-1,7-closo-C2B10H10 (7) and 1,12-(4′-F3CC6F4)2-1,12-closo-C2B10H10 (8), with fluorinated aryl substituents on cage carbon atoms, have been prepared in good to high yields and characterised by microanalysis, 1H, 11B and 19F NMR spectroscopies, mass spectrometry, single-crystal X-ray diffraction and (spectro)electrochemistry. By analysis of , the weighted average 11B chemical shift, a ranking order for the orthocarboranes 1–6 is established based on the combined electron-withdrawing properties of the C-substituents, and is in perfect agreement with that established independently by electrochemical study. In a parallel computational study the effects of a wide range of different substituents on the redox properties of carboranes have been probed by comparison of ΔE values, where ΔE is the energy gap between the DFT-optimised [7,9-R2-7,9-nido-C2B10]2− anion and its DFT-optimised basket-shaped first oxidation product. The overall conclusion from the NMR spectroscopic, electrochemical and computational studies is that strongly electron withdrawing substituents significantly stabilise [7,9-nido-C2B10]2− dianions with respect to oxidation, and that the best practical substituent is 4-F3CC6F4. Thus attention focussed on the reduction of 1,2-(4′-F3CC6F4)2-1,2-closo-C2B10H10, compound 6. The sequence 6/[6]−/[6]2− appears reversible on the cyclic voltammetric timescale but on the longer timescale of macroelectrolysis the radical anion is only partially stable. EPR study of the electrogenerated monoanions from the ortho-carboranes 1–6 confirms the cage-centred nature of the redox processes. In contrast, the reduction of the meta- and para-carboranes 7 and 8, respectively, appears to be centred on the aromatic substituents, a conclusion supported by the results of DFT calculation of the LUMOs of compounds 6–8. Bulk 2-electron reduction of 6 affords a dianion which is remarkably stable to reoxidation, surviving for several hours in the open laboratory in the absence of halogenated solvents.

Elucidation of a structural basis for the inhibitor-driven, p62 (SQSTM1)-dependent intracellular redistribution of cAMP phosphodiesterase-4A4 (PDE4A4).

Abstract: A survey of PDE4 inhibitors reveals that some compounds trigger intracellular aggregation of PDE4A4 into accretion foci through association with the ubiquitin-binding scaffold protein p62 (SQSTM1). We show that this effect is driven by inhibitor occupancy of the catalytic pocket and stabilization of a "capped state" in which a sequence within the enzyme's upstream conserved region 2 (UCR2) module folds across the catalytic pocket. Only certain inhibitors cause PDE4A4 foci formation, and the structural features responsible for driving the process are defined. Switching to the UCR2-capped state induces conformational transition in the enzyme's regulatory N-terminal portion, facilitating protein association events responsible for reversible aggregate assembly. PDE4-selective inhibitors able to trigger relocalization of PDE4A4 into foci can therefore be expected to exert actions on cells that extend beyond simple inhibition of PDE4 catalytic activity and that may arise from reconfiguring the enzyme's protein association partnerships.

A Two-Dimensional Zinc(II)–Schiff Base Coordination Polymer Formed by Six-Membered Metallacyclic Repeating Motif: Structural Aspects, Thermal and Photophysical Properties

Abstract: A dicyanoamide-bridged 2D polynuclear zinc(II) complex having formula [Zn2(L)(μ-dca-κN1κN5)2]n, 1 has been synthesized using the Schiff base ligand N,N′-bis(salicylidene)-1,3-diaminopentane, (H2L) ...

Cobalt(II), Manganese(IV) Mononuclear and Zinc(II) Symmetric Dinuclear Complexes of an Aliphatic Hydrazone Schiff Base Ligand with Diversity in Coordination Behaviors and Supramolecular Architectures : Syntheses, Structural Elucidations, and Spectroscopic Characterizations

Abstract: Three new complexes of cobalt, manganese, and zinc have been synthesized using a hydrazone Schiff base ligand {(E)-N′-[1-(2-hydroxyphenyl)ethylidene]acetohydrazide} (LH2) produced by the 1:1 conden...

New chemistry of 1,2-closo-P2B10H10 and 1,2-closo-As2B10H10; in silico and gas electron diffraction structures, and new metalladiphospha- and metalladiarsaboranes.

Abstract: The molecular structures of 1,2-closo-P2B10H10 (1) and 1,2-closo-As2B10H10 (2) have been determined by gas electron diffraction and the results obtained compared with those from computation at the MP2/6-31G** level of theory. The level of agreement is good for 2 (root-mean-square [rms] misfit for As and B atoms 0.0297 A) and very good for 1 (rms misfit for P and B atoms 0.0082 A). In comparing the structures of 1 and 2 with that of 1,2-closo-C2B10H12 (I) it is evident that expansion of the polyhedron from I to 1 to 2 is restricted only to the heteroatom vertices and the B6 face to which these are bound. Following deboronation (at B3) and subsequent metallation, compounds 1 and 2 have been converted into the new metalladiheteroboranes 3-(η-C9H7)-3,1,2-closo-CoAs2B9H9 (4), 3-(η-C10H14)-3,1,2-closo-RuAs2B9H9 (5), 3-(η-C5H5)-3,1,2-closo-CoP2B9H9 (6), 3-(η-C9H7)-3,1,2-closo-CoP2B9H9 (7) and 3-(η-C10H14)-3,1,2-closo-RuP2B9H9 (8), the last three constituting the first examples of metalladiphosphaboranes. Together with the known compound 3-(η-C5H5)-3,1,2-closo-CoAs2B9H9 (3), compounds 4–8 have been analysed by NMR spectroscopy and (except for 8) single-crystal X-ray diffraction. The 11B NMR spectra of analogous pairs of metalladiphosphaborane and metalladiarsaborane (6 and 3, 7 and 4, 8 and 5) reveal a consistently narrower (9–10 ppm) chemical shift range for the metalladiarsaboranes, the combined result of a deshielding of the lowest frequency resonance (B6) and an increased shielding of the highest frequency resonance (B8) via an antipodal effect. In crystallographic studies, compounds 3 and 5B (one of two crystallographically-independent molecules) suffer As/B disorder, but in both cases it was possible to refine distinct, ordered, components of the disorder, the first time this has been reported for metalladiarsaboranes. Moreover, whilst the Cp compounds 6 and 3 are disordered, their indenyl analogues 7 and 4 are either ordered or significantly less disordered, a consequence of both the reduced symmetry of an indenyl ligand compared to a Cp ligand and the preference of the former for a distinct conformation relative to the cage heteroatoms. Unexpectedly, whilst this conformation in the cobaltadiphosphaborane 7 is cis-staggered (similar to that previously established for the analogous cobaltadicarborane), in the cobaltadiarsaborane 4 the conformation is close to cis-eclipsed.

Diphosphaborane and Metalladiphosphaborane: Ligands for Transition‐Metal Chemistry

Abstract: Through an impressive series of papers by Wesemann and coworkers, the dianionic stannaborate [closo-SnB11H11] 2 has been shown to be a powerful and versatile s-donating ligand in coordination chemistry through the lone pair of electrons on the Sn atom. In marked contrast, the neutral stannacarborane 3,1,2-closo-SnC2B9H11 and its derivatives and supraicosahedral analogues show clear Lewis acid behavior, readily forming adducts with bases such as pyridine or 2,2’-bipyridine. 3] In the stannacarboranes the lone pair on Sn appears to be stereochemically active but chemically inert. The monoanionic stannacarborate [1,2-closo-SnCB10H11] displays intermediate behavior, having both s-donor and pacceptor properties. We recently reported the structure and the first deboronation followed by metallation of the diphosphaborane 1,2closo-P2B10H10, [5] a compound originally prepared by Todd et al. in 1989. Based on the above precedents it was not clear that the neutral compounds 1,2-closo-P2B10H10 and 3,1,2closo-MP2B9 (M = transition metal) would necessarily show Lewis base behavior, and certainly no examples of these species acting in this way has previously been reported. We now describe the first examples of diphosphaborane and metalladiphosphaborane as s-bonded ligands in transitionmetal chemistry. In seeking to convert 1,2-closo-P2B10H10 to a supraicosahedral species we recognized that we could not use the standard method of polyhedral expansion, that is, reduction followed by capitation, since 2-electron reduction of 1,2closo-P2B10H10 leads to loss of a P vertex and formation of [7nido-PB10H12] , following aqueous work-up. An alternative approach to polyhedral expansion of carboranes, developed by Stone and co-workers many years ago, is that of direct insertion of a highly nucleophilic metal fragment, but whilst direct insertion of a Pt or Pd unit is generally successful with subicosahedral carboranes, insertion into icosahedral carboranes has only been shown to work with Co fragments. However, whilst reaction of 1,2-closo-P2B10H10 with [Co(PEt3)4] [11] did not yield supraicosahedral products it did afford [HCo(1,2-closo-P2B10H10)2(PEt3)2] (1). Compound 1 was initially characterized spectroscopically. The B{H} NMR spectrum is relatively uninformative, containing four resonances in a 1:1:6:2 pattern (high frequency to low frequency) between d =+ 14 and 1 ppm. The H spectrum displays the usual quartet and triplet resonances associated with Et groups, but additionally an apparent septet in the hydride region (at d = 14.55 ppm) with an integral 1/ 12 that of the quartet resonance. In the P NMR spectrum are three resonances of equal integral at d = 49.4 (br.), 33.0 and 13.5 ppm. From a H-P correlation experiment the resonance at d = 33.0 ppm in the P spectrum is assigned to PEt3. H{Pselective} experiments collapse the hydride resonance from an apparent septet to 1:2:1 triplets with coupling constants of 17.2 Hz (decoupling at dP = 49.4 ppm) and 33.6 Hz (decoupling at dP = 33.0 ppm). Collectively these results suggest that in 1 one of the two P atoms in 1,2-closoP2B10H10 is coordinated to a {HCo} fragment. Moreover, the two-bond JHP coupling constant to the diphosphaborane P atom, 33.6 Hz, is nearly twice that to the triethylphosphine P atom, 17.2 Hz. The structure of 1 determined crystallographically is shown in Figure 1. There are four crystallographically independent molecules (AB, CD, EF and GH) in the asymmetric fraction of the unit cell. Although the precision of the determination is not high the structural identity of the species is unambiguous. Not unexpectedly the hydride ligand

Synthesis, X-ray Crystal Structure and Magnetic Study of a μ1,5-dca Bridged Dimeric Copper(II) Complex

Abstract: The reaction of aqueous solution of copper(II) nitrate trihydrate with methanolic solution of the ligand HL and sodium dicyanamide in aqueous medium results in the formation of a dimeric dicyanamide complex of Cu(II), [Cu2(L)2(μ1,5-dca)2]·0.5 H2O (1) [where L = 1-(N-salicylideneamine)-2-(N-ethyl)-aminoethane]. The single crystal X-ray structure reveals that the asymmetric unit of complex 1 consists of two dinuclear units. The complex crystallizes in the monoclinic space group P21 with cell parameters, a = 9.8828(19) A, b = 19.018(4) A, c = 14.851(3) A, (°) = 92.979(6) and Z = 4. χM T, stays in the 0.94–0.91 cm3 mol−1 K range between 300 and 2 K, which is slightly higher than the spin-only value (χM T = 0.75 cm3 mol−1 K) for two uncoupled copper(II) (S = ½) ions assuming g = 2.0, thus indicating that the complex 1 behaves like a simple paramagnet.