Alessandra Crispini

Crystal architecture and mesophase structure of long-chain N-alkylpyridinium tetrachlorometallates

The N -hexadecylpyridinium derivatives [C16Py] 2 [MCl 4 ] (M=Cd ( 1 ), Zn ( 2 )) were prepared and structurally characterized by X-ray diffraction methods. The crystal structure of 1 reveals a layered arrangement with alternation of monolayers of interdigitated cations with layers of isolated [CdCl 4 ] 2− anions. CH⋯ClCd interactions reinforce the association between anions and cations in the polar region of the supramolecular structure. Both 1 and 2 display a thermotropic smectic A phase in addition to some high-temperature crystalline modifications. The thermal polymorphism of the salts was studied by X-ray powder diffraction, differential scanning calorimetry (DSC), and thermal optical microscopy. The structural and mesomorphic characteristics of 1 and 2 are compared with those of the analogous salts along the series [C16Py] 2 [MCl 4 ] (M=Co, Ni, Cu, Zn, Pd, Cd).

Dinuclear cyclopalladated azobenzene complexes : a comparative study on model compounds for organometallic liquid-crystalline materials

The series of dinuclear 4,4′-bis(hexyloxy)azobenzene, [H(Azo-6)], cyclopalladated complexes of general formula [Azo-6)Pd(µ-X)]2, (X = Cl, Br, I, N3, SCN, OAc) and [Azo-6)2Pd2(µ-Ox)] (Ox = oxalate) have been synthesized and investigated for mesomorphism and spectroscopic properties. Single-crystal X-ray analysis of the dinuclear bromo- and iodo-bridged complexes has been performed. The structural data, compared with those of the known homologous chloro compound, show that all the [Azo-6)Pd(µ-X)]2)] (X = Cl, Br, I) molecules crystallize in the monoclinic space group P21/c and are isomorphous. They are arranged in slipped pairs with intermolecular non-bonding Pd–Pd contacts ranging from 3.668(1) A(X = Cl) to 3.758(3) A(X = I). The different nature of the bridging group allows variation of the distance between the palladium atoms and the bond environment experienced by the metal centers. Thus, this comparative study reveals that the effectiveness of the bridging group in promoting thermotropic mesophases is greater for chloride, bromide, azide or oxalate than for iodide, thiocyanate or acetate. The greatest range of liquid-crystal behavior was displayed by [Azo−6)2Pd2(µ−Ox)]. Remarkably, this compound is the first example of a metallomesogen containing the bridging oxalate group. The bimetallic complexes exhibit different absorption spectra (i.e. colors) depending, in general terms, on the nature of the bridge connecting the two cyclometalated [H(Azo-6)] moieties, which can be varied so as to tune the optical properties. Blocking the azo group in the trans position results in several cases in weakly luminescent complexes, with luminescence efficiencies ϕ ≈10−4 and luminescence lifetimes of the order of nanoseconds. Using the data obtained from the 4,4′-bis(hexyloxy)azoxybenzene [H(Azoxy-6)] derivative, [Azoxy-6)Pd(µ -Cl)]2, from the mononuclear acetylacetonate (acac) complexes [(Azo-6)Pd(acac)] and [(Azoxy-6)Pd(acac)], and from the uncomplexed [H(Azo-6)] and [H(Azoxy-6)] ligands, the nature of the excited states relevant to the photophysical behavior are discussed. Copyright

Synthesis and characterization of a homologous series of mononuclear palladium complexes containing different cyclometalated ligands

Abstract New mononuclear palladium(II) complexes formed by with 2-hydroxy-4-( n -hexyloxybenzylidene)-4′- n -hexyaniline ( HL ) and 2-phenylpyridine ( I ), benzo[h]quinoline ( II ), azobenzene ( III ), 2-benzoylpyridine ( IV ) or phenyl-2-pyridylketone-2,4-dinitrophenylhydrazone ( V ) have been synthesized and characterized by analytical and spectroscopic methods and the single-crystal structures of [(IVa)Pd(L)] and [(Va)Pd(L)] have been established. The spectroscopic and diffractrometric data account for molecular structures wherein the palladium(II) center is part of two chelate rings involving HL and one of the I – V ligands which form a five-member N,C{[(Ia)PdL], [(IIa)Pd(L)] and [(IIIa)Pd(L)]}, a six-member N,C{[(IVa)Pd(L)]}, or a six-member N , N ′{[(Va)Pd(L)]} metallacycle. The electronic spectra of [(IIIa)Pd(L)] and [(Va)Pd(L)] show an absorption maxima, at 495 ( e ∼3×10 3 M −1 cm −1 ) and 531 nm ( e ∼2×10 4 M −1 cm −1 ), respectively, which results are significantly affected by the polarity of the solvent. These chromophores should therefore be of interest for the preparation of nonlinear optical materials.

DNA binding and cytotoxicity of fluorescent curcumin-based Zn(II) complexes

Two new heteroleptic pentacoordinated Zn(II) complexes (1 and 2) containing 4,4′-disubstituted 2,2′-bipyridines as the main ligand and curcumin (curc) as an ancillary ligand have been synthesized, spectroscopically and structurally characterized, and tested in vitro towards different human cancer cell lines. While the nitrogen ligands are almost inactive, Zn(II) curc derivatives 1 and 2 show promising and selective anticancer properties. In particular the curc Zn(II) complex 1 shows the strongest growth inhibition in all cell lines, being even more effective than the pure curc in the LAN-5 neuroblastoma cell line. Furthermore, the curc moiety makes the complexes 1 and 2 fluorescent, a feature enabling investigation of their interaction with DNA through a new optical method previously tested with the reference fluorescent intercalator ethidium bromide. This analysis demonstrates that the interaction mode of curc, 1 and 2 with DNA in the double helix favors their alignment perpendicular to the DNA axis, suggesting a partial inter-base intercalation of these Zn(II) complexes.

Cyclopalladated complexes. Synthesis and crystal structure of di-μ-chloro-bis{[2,6-dimethyl-N-(benzylidene) phenylaminato-C2′, N]palladium(II)}

Abstract The X-ray crystal structure of the cyclometallated palladium(II) complex [{Pd(L2)(μ-Cl)} 2 ], L2=2,6-dimethyl- N - (benzylidene)phenylaminate, is described. Crystals were orthorhombic, space group Pna 2 1 with a = 17.307(3) A, b = 17.732(4) A, c = 9.075(2) A, Z = 4, U = 2785.0(10) A 3 . The palladated dimer, with asymmetrically bridging chlorine atoms, exhibits a Pd 2 Cl 2 unit folded at 36.7(1)° and a non-bonding Pd ⋯ Pd separation of 3.425(1) A.

Improving the bioactivity of Zn(II)-curcumin based complexes

New Zn(II)-curcumin based heteroleptic complexes (1-5) have been synthesized and fully characterized, with the aim to improve the bioactivity of the precursor derivative [(bpy-9)Zn(curc)Cl] (A), a potentially intercalating antitumor agent recently reported. Some structural changes have been made starting from the reference complex A, in order to introduce new functionalities, such as electrostatic and/or covalent interactions. In particular, keeping the same N,N chelating ligand, namely bpy-9, two completely different Zn(II) species have been obtained: a tetracoordinated Zn(II) cation with tetrafluoroborate as counterion (1) and a dimeric neutral complex in which the sulfate anion acts as a bridging group through two Zn(II) centres (2). Moreover, by changing the N,N chelating unit, [(L(n))Zn(curc)Cl] complexes (3-5), in which the Zn(II) ion shows the same pentacoordination seen in the precursor complex A, have been obtained. The antitumour activity of all new Zn(II) complexes was tested in vitro against the human neuroblastoma cell line SH-SY5Y in a biohybrid membrane system and the results indicate that all species exhibit strong cytotoxic activity. In particular the ionic tetrafluoroborate Zn(II) complex, 1, and the neutral phenanthroline based Zn(II) derivative, 4, show the strongest growth inhibition, being even more effective than the model complex A. Both complexes have a dose-dependent anti-proliferative effect on cells as demonstrated by the decrease of viability and the increase of Annexin V and PI-positive cells with the increase of their concentration. Cells treated with complexes 1 and 4 undergo apoptosis that involves the activation of JNK, caspase 3 and MMP changes. Finally, complex 1 is more effective in the induction of caspase-3 activation demonstrating its ability to trigger the execution-phase of cell apoptosis.

Transition metals complexed to ordered mesophases: VIII. Cyclopalladated p-azoxyanisole complexes. Crystal structure of [N-(phenyl)-2-salicylideneaminato]-[4′-(methoxyphenyl-NNO-azoxy-N2-4-methoxyphenyl-2-ato]palladium(II)☆

The synthesis and characterization of the cyclopalladated p-azoxyyanisole chloro-bridged dimer [Pd(Azoxy)Cl]2, 1, is reported and its reactions with some salicylideneaniline derivatives (HL1–5) are described. 1H NMR spectral observations indicate that except for [Pd(Azoxy)(L4)] the mononuclear [Pd(Azoxy)(L)] products are ca 5:1 mixtures of N-trans and N-cis isomers. In the HL4 case (HL4 = salicylidene(2,4-dimethyl)aniline) the only product which was detected is the N-trans isomer. The crystal structure of trans-[Pd(Azoxy)(L1)] (HL1 = salicylideneaniline) (3-trans) is monoclinic.

Metal-Containing Amphiphiles: Orthometallated Iridium(III) Complexes with Substituted 6′-Phenyl-2,2′-bipyridines

The reaction of 4′-functionalized 6′-phenyl-2,2′-bipyridine ligands (L-n) with the dimer [(ppy)2IrCl]2 (ppy = 2-phenylpyridine anion) and subsequent counterion exchange affords a new series of cationic orthometallated iridium(III) complexes, [(ppy)2Ir(L-n)][PF6] (1–5), which have been characterized by spectroscopic methods. These complexes have a large shape anisotropy and significant amphiphilic character. The crystal structure of 4 has been determined by X-ray diffraction.

A fluorescent curcumin-based Zn(II)-complex reactivates mutant (R175H and R273H) p53 in cancer cells

BackgroundMutations of the p53 oncosuppressor gene are amongst the most frequent aberration seen in human cancer. Some mutant (mt) p53 proteins are prone to loss of Zn(II) ion that is bound to the wild-type (wt) core, promoting protein aggregation and therefore unfolding. Misfolded p53 protein conformation impairs wtp53-DNA binding and transactivation activities, favouring tumor growth and resistance to antitumor therapies. Screening studies, devoted to identify small molecules that reactivate mtp53, represent therefore an attractive anti-cancer therapeutic strategy. Here we tested a novel fluorescent curcumin-based Zn(II)-complex (Zn-curc) to evaluate its effect on mtp53 reactivation in cancer cells.MethodsP53 protein conformation was examined after Zn-curc treatment by immunoprecipitation and immunofluorescence assays, using conformation-specific antibodies. The mtp53 reactivation was evaluated by chromatin-immunoprecipitation (ChIP) and semi-quantitative RT-PCR analyses of wild-type p53 target genes. The intratumoral Zn-curc localization was evaluated by immunofluorescence analysis of glioblastoma tissues of an ortothopic mice model.ResultsThe Zn-curc complex induced conformational change in p53-R175H and -R273H mutant proteins, two of the most common p53 mutations. Zn-curc treatment restored wtp53-DNA binding and transactivation functions and induced apoptotic cell death. In vivo studies showed that the Zn-curc complex reached glioblastoma tissues of an ortothopic mice model, highlighting its ability to crossed the blood-tumor barrier.ConclusionsOur results demonstrate that Zn-curc complex may reactivate specific mtp53 proteins and that may cross the blood-tumor barrier, becoming a promising compound for the development of drugs to halt tumor growth.

N,N′-Dodecamethylene-bis(pyridinium) goes lamellar. Role of C–H⋯I, C–H⋯M, and I⋯I interactions in the crystal structure of its hexaiododipalladate(II) derivative

Weak C–H⋯I and C–H⋯Pd hydrogen bonds and short I⋯I interactions strongly contribute to build up a lamellar ordering of organic cations and inorganic anions in the crystal structure of the organic–inorganic hybrid [Py-C12-Py][Pd2I6].