Evgenia Spodine

Electrochemical studies of copper(II) complexes with Schiff-base ligands

Abstract The electrochemical reduction of copper(II) complexes with salen Schiff-base ligands derived from ethylenediamine or (R,R) or (S,S)-1,2-diphenylethylenediamine and 5-methoxy, 5-bromo and 5-nitrosalicylaldehyde have been studied by cyclic voltammetry in the potential range +1 to −2.3 V in dimethyl sulfoxide (DMSO) as a solvent. The resulting voltammograms consist of a single quasi-reversible one-electron transfer attributable to the couple [Cu(II)L]/[Cu(I)L]−. Trends in cathodic peak potential (Epc) values are observed which can be correlated with the electronic effects of the 5-substituents of the Schiff-base ligands. Changes in the basicity of the ligand groups are determinant for such electrochemical trends.

SYNTHESES AND CHARACTERIZATION OF COPPER(II) COMPLEXES WITH SCHIFF-BASE LIGANDS DERIVED FROM ETHYLENEDIAMINE, DIPHENYLETHYLENEDIAMINE AND NITRO, BROMO AND METHOXY SALICYLALDEHYDE

Abstract Copper(II) quelates with Schiff bases derived from ethylenediamine, 1R,2R-(+)- or 1S,2S-(−)-1,2-diphenylethylenediamine and 5-X-salicylaldehyde (X=OCH3, H, Br, NO2) have been synthesized and characterized by elemental analysis and IR and UV-visible spectroscopies. The ORD and CD spectra of the chiral ligands and their related complexes have also been measured. The absorption and CD spectra of the metal complexes in the visible region are consistent with near square planar coordination geometries. Trends in absorption spectra over the series of complexes can be correlated with electronic effects of the substituents at position 5 of the salicylaldehyde. The sign patterns of the CD spectra in both UV and visible regions suggest the prevalence of δ and λ conformations for the chelate ring in the complexes of Schiff bases derived, respectively, from R,R- and S,S-diamines. Specific features of the CD spectra of the metal complexes are discussed in terms of the exciton chirality method.

Oxygen insertion in organic substrates catalyzed by copper compounds

Models systems for tyrosinase, dopamine β-hydroxylase, peptidylglycine α-amidating monooxygenase: active copper site of these proteins, oxygen activation mechanisms related to biological systems in which the metalloenzymes are involved.

Molecular structure and magnetic properties of [Gd(LH4)(NO3)2(H2O)]NO3(H2O)2, [Sm(LH4)(NO3)2(H2O)]NO3 (H2O)1.5(CH3OH)0.5 and [Cu2(LH2)(H2O)2](NO3)2 complexes (LH4: Schiff base ligand derived from 4-methyl-2,6-diformylphenol and 1,3-diaminopropanol)

Abstract Novel lanthanide(III) complexes (Ln=Gd (1), Sm (2), La (3)) of the macrocyclic ligand LH4 have been prepared and characterized. The binuclear copper(II) complex (Cu2(LH2)(H2O)2)(NO3)2 (4), has been obtained by transmetalation of complex 3 with Cu(CF3COO)2. The macrocyclic Schiff base ligand (LH4) is formed by the condensation of two molecules of 4-methyl-2,6-diformylphenol with two molecules of 1,3-diaminopropanol in the presence of the lanthanide ions. The alcohol group of the macrocycle does not coordinate to the copper(II) centers of the binuclear complex. However, one of the secondary alcohol groups of the ligand coordinates in an asymmetric mode to the lanthanide ion in the corresponding three complexes. The X-ray crystal structures of (Gd(LH4)(NO3)2(H2O))(NO3)(H2O)2 (1), (Sm(LH4)(NO3)2(H2O))(NO3)(H2O)1.5(CH3OH)0.5 (2), and (Cu2(LH2)(H2O)2)(NO3)2 (4) have been determined. Magnetic susceptibility measurements in the 5–300 K range were obtained for these complexes.

Oxidation of 3,5-ditert-butylcatechol catalyzed by copper(II) complexes. A kinetic study

Abstract Copper(II) complexes of the ligands (6-methyl-2,2′-dipridyl)methane (MeDPM) and (6,6′-dimethyl-2,2′-dipyridyl)methane (diMeDPM) were prepared and used as catalysts for the oxidation of 3,5-ditertbutylcatechol to 3,5-ditert-butyl-o-benzoquinone. The rate of reaction was determined in the presence and absence of base (KOH) in methanol. The kinetic data are interpretated, postulating two reactive species towards molecular oxygen: a copper(I) complex and a species described as a ternary copper(II) catecholate complex.

Crystal Structure and Magnetic Properties of a New Chiral Manganese(II) Three-Dimensional Framework: Na3[Mn3(HCOO)9]

A structural and magnetic characterization of a trinuclear chiral Mn(II) formate three-dimensional framework exhibiting a triangular arrangement is presented. Compound Na(3)[Mn(3)(HCOO)(9)] was obtained by solvothermal synthesis and crystallizes in the chiral cubic space group P2(1)3 and is well described by a Delta conformation. The structure displays triangular Mn(3) building blocks, in which the metal centers are bonded by formate ligands in a syn-anti mode (Mn-Mn 5.697(1) A). The coordination sphere of manganese(II) is completed by six oxygen atoms from six formate ligands, resulting in an octahedral geometry. Magnetic susceptibility measurements showed antiferromagnetic interactions at high temperature and a strongly field dependent magnetic behavior below 40 K. At fields higher than 1.0 kOe only the antiferromagnetic interactions can be observed. At applied fields lower than 1.0 kOe magnetic susceptibility becomes irreversible with maxima observed at 22 and 34 K. These maxima suggest a weak ferromagnetic behavior because of spin canting, allowed by the presence of the noncentrosymmetric syn-anti HCOO bridges linking the Mn sites. This non-collinear antiferromagnetism and irreversible behavior can be due to the existence of a high degree of frustration in this unique lattice composed of linked triangular arrangements of interacting magnetic centers.

A discrete dinuclear Cu(II)–Gd(III) complex derived from a Schiff base ligand, [CuGd(ems)(NO3)3H2O]Cu(ems) (ems: N,N′-ethylene-bis-5-methoxy salicylaldiimine)

Abstract A Cu(II)–Gd(III) heteronuclear complex with N,N′-ethylene-bis-5-methoxy salicylaldiimine (ems) as ligand has been synthesized. The complex crystallizes in the monoclinic system C2/c space group. The structure consists of two different discrete molecules: a mononuclear unit containing a single Cu(II) center, and a dinuclear one containing both a nine coordinated Gd(III) plus a four coordinated Cu(II) cation [CuGd(H2O)(NO3)(ems)]. The complex was characterized by magnetic susceptibility and electron paramagnetic resonance. The Cu(II)–Gd(III) complex presents a ferromagnetic interaction (J=1.88 cm−1); its effective magnetic moment was found to increase with decreasing temperature. Both electronic and structural parameters are shown to influence the magnitude of the magnetic interaction.

Epoxidation of styrene with iodosylbenzene in the presence of copper(II) Schiff-base complexes

Copper(II) complexes with salen Schiff-base ligands derived from ethylenediamine or (S,S)-1,2-diphenylethylenediamine and salicylaldehyde or 5-methoxy, 5-bromo and 5-nitrosalicylaldehyde have been tested as catalysts for the epoxidation of styrene with iodosylbenzene, in dichoromethane as a solvent. The reactions were followed by gas chromatographic analysis and mass spectrometry. Catalytic activities were found to be dependent upon both the Lewis acidity of the metal complexes and the presence of phenyl substituents on the ethylene moiety. Moderate styrene conversions and epoxide yields were obtained. Pseudo-first-order kinetics was observed for the styrene conversion. Possible reaction mechanisms are outlined.

Synthesis, Characterization and Antitumor Activity ofcis-bis(acylthioureato) platinum(II) Complexes, cis-[PtL2] [HL1=N,N-Diphenyl-N'-Benzoylthiourea or HL2=N,N-diphenyl-N'-(p-nitrobenzoyl)thiourea]

A low-molecular weight chromium-containing fraction of the material resulting from dichromate reduction by bovine liver homogenate was investigated by NMR and ES-MS. The ES-MS spectrum showed a readily detectable peak at m/z 786.1. The same molecular weight reasonably agreed with the relatively low diffusion coefficient measured by NMR-DOSY experiments on the main species observed in the 1H NMR spectrum. At least two downfield shifted and broad paramagnetic signals were apparent in the 1H NMR spectrum. Temperature dependence of chemical shift was exploited in order to estimate the diamagnetic shift of the signals in the diamagnetic region of the spectrum. 2D TOCSY, NOESY, COSY and 1H-13C HMQC spectra revealed the presence of aromatic protons (which were assigned as His residues), Gly and some other short chain amino-acids. Combinations of the molecular masses of such components together with acetate (which is present in the solution) and chromium atoms allowed a tentative proposal of a model for the compound.

Synthesis, Characterization, and In Vitro Cytotoxic Activities of Benzaldehyde Thiosemicarbazone Derivatives and Their Palladium (II) and Platinum (II) Complexes against Various Human Tumor Cell Lines

The palladium (II) bis-chelate Pd (L1−3)2 and platinum (II) tetranuclear Pt4(L4)4 complexes of benzaldehyde thiosemicarbazone derivatives have been synthesized, and characterized by elemental analysis and IR, FAB(+)-mass and NMR (1H, 13C) spectroscopy. The complex Pd(L2)2 [HL2 = m-CN-benzaldehyde thiosemicarbazone] shows a square-planar geometry with two deprotonated ligands (L) coordinated to PdII through the nitrogen and sulphur atoms in a transarrangement, while the complex Pt4(L4)4 [HL4 = 4-phenyl-1-benzaldehyde thiosemicarbazone] has a tetranuclear geometry with four tridentate ligands coordinated to four PtII ions through the carbon (aromatic ring), nitrogen, and sulphur atoms where the ligands are deprotonated at the NH group. The in vitro antitumor activity of the ligands and their complexes was determined against different human tumor cell lines, which revealed that the palladium (II) and platinum (II) complexes are more cytotoxic than their ligands with IC50 values at the range of 0.07–3.67 μM. The tetranuclear complex Pt4(L4)4, with the phenyl group in the terminal amine of the ligand, showed higher antiproliferative activity (CI50 = 0.07–0.12 μM) than the other tested palladium (II) complexes.