EPR study of the electronic properties and weak exchange interactions in bis(L-phenylalaninamidato)Cu(II)

We performed EPR measurements in powder and single crystal samples of bis(L-phenylalaninamidato)Cu(II) (C18H22CuN4O2). We evaluated the crystal and molecular g-factors, and estimate an exchange interaction of 0.15 K< or = J(AB)/k < or =0.32 K between coppers spaced apart 6.24 A, transmitted through an amidate bridge Cu-O-C-N-Cu. An unusual line shape is observed in powder samples arising from the relative orientation of symmetry-related molecules in the structure. The dipolar interaction and the layered structure of the copper ions produce a strong temperature variation of the spectral shape when the copper spins are polarized by the applied magnetic field.     

Diaquabis(3,6-dioxaheptanoato)copper(II): crystal structure and EPR characteristics

The structure of the title compound has been determined by X-ray diffraction at 190 K. The complex has an all trans configuration with an elongated tetragonally distorted octahedral CuO6 chromophore. The elongated axis corresponding to the trans-Cu–O(ether) bonds. The ligand molecules are bidentate via the carboxyl and the 3-ether O atoms; the 6-ether O atoms are not coordinated and are remote from the Cu centres. The bond lengths to the Cu centres are Cu–O(ether) 2.355 Å, Cu–O(Carboxyl) 1.933 Å and Cu–OH2 1.995 Å.The EPR spectrum of both the powder and frozen solution forms is typical of a rhombic system with a dx2−y21 electronic configuration. There were no significant differences in spectra recorded over the temperature range 77 K to room temperature. These results are discussed in relation to earlier published results on closely related oxa-carboxyl complexes.     

Crystal packing and hydrogen bonding in platinum(II) nucleotide complexes: X-ray crystal structure of [Pt(MeSCH(2)CH(2)SMe)(5'-GMP-N7)(2)].6H(2)O

We have synthesised the complex [Pt(CH(3)SCH(2)CH(2)SCH(3))(5'-GMP-N7)(2)].6H(2)O (1), where 5'-GMP is 5'-guanosine monophosphate, and determined its X-ray crystal structure. Pt(II) adopts a square-planar geometry in which the bases are coordinated head-to-tail (HT) in the Delta configuration. The nucleotide conformation in this complex is almost identical to that in the previously reported complex [Pt(en)(5'-GMP-N7)(2)].9H(2)O (2), in which there is outer sphere macrochelation via intramolecular H-bonding between the monoanionic phosphate groups and the coordinated ethylenediamine (en) NH. It is therefore apparent that intermolecular interactions rather than intramolecular H-bonding determines the orientation of the sugar-phosphate side-chain in these Pt(II) bisnucleotide complexes in the solid state.     

Reactions of peroxyl radicals with Fe(H(2)O)(6)(2+)

The reactions of RO(2)* radicals with Fe(H(2)O)(6)(2+) were studied, R[double bond]H; CH(3); CH(2)COOH; CH(2)CN; CH(2)C(CH(3))(2)OH; CH(2)OH; CHCl(2)/CCl(3). All these processes involve the following reactions: Fe(H(2)O)(6)(2+)+RO(2)*<==>(H(2)O)(5)Fe(III)[bond]OOR(2+) K(1) approximately 250 M(-1); (H(2)O)(5)Fe(III)[bond]OOR(2+)+H(3)O(+)/H(2)O-->Fe(H(2)O)(6)(3+)+ROOH+H(2)O/OH(-); (H(2)O)(5)Fe(III)[bond]OOR(2+)+2Fe(H(2)O)(6)(2+)-->3Fe(H(2)O)(6)(3+)+ROH; 2 RO(2)*-->Products; RO(2)*+(H(2)O)(5)Fe(III)[bond]OOR(2+)-->Fe(H(2)O)(6)(2+)+products. The values of k(1) and k(3) [reaction is clearly not an elementary reaction] approach the ligand exchange rate of Fe(H(2)O)(6)(2+), i.e. these reactions follow an inner sphere mechanism and the rate determining step is the ligand exchange step. The rate of reaction is several orders of magnitude faster than that of the Fenton reaction. Surprisingly enough the K(1) values are nearly independent of the redox potential of the radical and are considerably higher than calculated from the relevant redox potentials. These results indicate that the ROO(-) ligands considerably stabilise the Fe(III) complex, this stabilisation is smaller for radicals with electron withdrawing groups which raise the redox potential of the radical but decrease the basicity of the ROO(-) ligands, two effects which seem to nearly cancel each other. Finally, the results clearly indicate that reaction (5) is relatively fast and affects the nature of the final products. The contribution of these reactions to oxidation processes involving 'Fenton-like' processes is discussed.     

Two new scorpionates vanadium haloperoxidases model complexes: synthesis and structure of VO(O2)(pzH)(HB(pz)3) and VO(O2)(pzH)(B(pz)4) (pzH = pyrazole(C3H4N2))

Using vanadate, poly(1H-pyrazol-1-yl)borate and pyrazole as starting materials, two new neutral peroxovanadium(V) complexes with poly(1H-pyrazol-1-yl)borate, VO(O(2))(pzH)(HB(pz)(3))(1) and VO(O(2))(pzH)(B(pz)(4))(2), were synthesized successfully. Both complexes were characterized by elemental analysis, IR, UV-vis and NMR spectra. And the structure of complex 1 was determined by X-ray diffraction, which is somewhat relevant for haloperoxidase enzymes. Cytotoxic effects also are discussed on 3T3 cell proliferation. In the concentration range (0.1-100mumol), both complexes have an inhibiting cellular proliferation effect. When the cells cultivated with the complexes at high dose, the toxicity effect of both complexes is more and more predominant.     

Synthesis, characterisation and antimicrobial activity of copper(II) and manganese(II) complexes of coumarin-6,7-dioxyacetic acid (cdoaH2) and 4-methylcoumarin-6,7-dioxyacetic acid (4-MecdoaH2): X-ray crystal structures of [Cu(cdoa)(phen)2].8.8H(2)O and [Cu(4-Mecdoa)(phen)2].13H2O (phen=1,10-phenanthroline)

Two novel coumarin-based ligands, coumarin-6,7-dioxyacetic acid (1) (cdoaH(2)) and 4-methylcoumarin-6,7-dioxyacetic acid (2) (4-MecdoaH(2)), were reacted with copper(II) and manganese(II) salts to give [Cu(cdoa)(H(2)O)(2)].1.5H(2)O (3), [Cu(4-Mecdoa)(H(2)O)(2)] (4), [Mn(cdoa)(H(2)O)(2)] (5) and [Mn(4-Mecdoa)(H(2)O)(2)].0.5H(2)O (6). The metal complexes, 3-6, were characterised by elemental analysis, IR and UV-Vis spectroscopy, and magnetic susceptibility measurements and were assigned a polymeric structure. 1 and 2 react with Cu(II) in the presence of excess 1,10-phenanthroline (phen) giving [Cu(cdoa)(phen)(2)].8.8H(2)O (7) and [Cu(4-Mecdoa)(phen)(2)].13H(2)O (8), respectively. The X-ray crystal structures of 7 and 8 confirmed trigonal bipyramidal geometries, with the metals bonded to the four nitrogen atoms of the two chelating phen molecules and to a single carboxylate oxygen of the dicarboxylate ligand. The complexes were screened for their antimicrobial activity against a number of microbial species, including methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Candida albicans. The metal-free ligands 1 and 2 were active against all of the microbes. Complexes 3-6 demonstrated no significant activity whilst the phen adducts 7 and 8 were active against MRSA (MIC(80)=12.1microM), E. coli (MIC(80)=14.9microM) and Patonea agglumerans (MIC(80)=12.6microM). Complex 7 also demonstrated anti-Candida activity (MIC(80)=22microM) comparable to that of the commercially available antifungal agent ketoconazole (MIC(80)=25microM).     

Re(CO)(3)(H(2)O)(3)(+) binding to lysozyme: structure and reactivity

The reaction of Re(CO)(3)(H(2)O)(3)(+) with hen egg white lysozyme in aqueous solution results in a single covalent adduct. Both NMR spectroscopy and single crystal X-ray diffraction show that the rhenium tricarbonyl cation binds to His15 via replacement of one of the coordinated water molecules. The formation of this adduct does not greatly affect the structure of the protein.     

Speciation study of the anti-inflammatory drug tenoxicam (Htenox) with Cu(II): X-ray crystal structure of [Cu(tenox)(2)(py)(2)].EtOH

A speciation study was carried out in aqueous solution of the anti-inflammatory drug tenoxicam (Htenox), under quasi-physiological conditions (temperature of 37 degrees C and ionic strength 0.15 M NaCl) in order to determine the acidity constants from spectrophotometric studies, the pK(a) values found being pK(1)=1.143+/-0.008 and pK(2)=4.970+/-0.004. Subsequently, the spectrophotometrical speciation of the different complexes of Cu(II) with the drug was performed under the same conditions of temperature and ionic strength, observing the formation of Cu(Htenox)(2)(2+) with log beta(212)=20.05+/-0.01, Cu(tenox)(2) with log beta(012)=13.6+/-0.1, Cu(Htenox)(2+) with log beta(111)=10.52+/-0.08, as well as Cu(tenox)(+) with log beta(011)=7.0+/-0.2, all of them in solution, and solid species Cu(tenox)(2)(s) with an estimated value of log beta(012)(s) approximately 18.7. The crystalline structure of the complex [Cu(tenox)(2)(py)(2)]. EtOH, was also determined, and it was observed that tenoxicam employs the oxygen of the amide group and the pyridyl nitrogen to bond to the cation.     

Molecular structure, bioavailability and bioactivity of [Cu(o-phen)2(cnge)](NO3)2.2H2O and [Cu(o-phen)(cnge)(H2O)(NO3)2] complexes

Two Cu(II) complexes with cyanoguanidine (cnge) and o-phenanthroline, [Cu(o-phen)(2)(cnge)](NO(3))(2).2H(2)O (1) and [Cu(o-phen)(cnge)(H(2)O)(NO(3))(2)] (2), have been synthesized using different experimental techniques and characterized by elemental analyses, FTIR, diffuse and UV-vis spectra and EPR and magnetic moment measurements techniques. The crystal structures of both complexes were solved by X-ray diffraction methods. Complex (1) crystallizes in the monoclinic space group C2/c with a=12.621(5), b=31.968(3), c=15.39(1)A, beta=111.68(4) degrees, and Z=8 and complex (2) in the monoclinic space group P2(1)/n with a=10.245(1), b=13.923(2), c=12.391(2)A, beta=98.07(1) degrees, and Z=4. The environments of the copper(II) center are trigonal bipyramidal (TBP) for [Cu(o-phen)(2)(cnge)](2+) and an elongated octahedron for [Cu(o-phen)(cnge)(H(2)O)(NO(3))(2)]. Solution studies have been performed to determine the species distribution. The superoxide dismutase (SOD) activities of both complexes have also been tested in order to determine if these compounds mimic the enzymatic action of the enzyme SOD that protects cells against peroxide radicals.     

Stereospecific formation of alpha-hydroxycarboxylato oxo peroxo complexes of vanadium(V). Crystal structure of (NBu4)2[V2O2(O2)2(L-lact)2] x 2H2O and (NBu4)2[V2O2(O2)2(D-lact)(L-lact)] x 2H2O

An overview of structurally characterized alpha-hydroxycarboxylatodioxo- and alpha-hydroxycarboxylatooxoperoxovanadates(V) is presented and the geometric parameters of the V2O2 bridging core are discussed. The first case of a stereospecific formation of oxoperoxovanadates(V) is reported: The crystal structures of the isomeric compounds (NBu4)2[V2O2(O2)2(L-lact)2] x 2H2O and (NBu4)2[V2O2(O2)2(D-lact)(L-lact)] x 2H2O (lact = C3H4O3(2-), the anion of the lactic acid) differ mainly in the arrangement of the V2O2 core and in mutual orientation of the V=O bonds. The complexes with achiral ligands adopt the same structural type as the complexes formed from a racemic mixture of a chiral ligand, while the structure obtained using an enantiopure L,L-hydroxycarboxylate is different.     

Triboluminescence and crystal structure of the centrosymmetric complex [Tb(NO3)2(Acac)(Phen)2]·H2O

The atomic structure of crystals of the complex [Tb(NO₃)₂(Acac)(Phen)₂]·H₂O, (AA – acetylacetonate anion, Phen – 1,10‐phenanthroline) characterized by an intensive luminescence and triboluminescence has been determined by means of an X‐ray structural analysis method. Centrosymmetric crystals have a monoclinic syngony: a = 11.2298(1), b = 9.6492(1), c = 13.2745(1) Å, β = 101.290(1), space group P2/n, Z = 2, ρ_calc = 1.790 g/cm³. The crystal structure is represented by individual С₂₉Н₂₅N₆O₉Tb complexes linked through van der Waals interactions with clearly expressed cleavage planes. The Tb(III) atom coordination polyhedron reflects the state of a distorted square antiprism. The structural aspects of the suggested model of formation of the triboluminescent properties were considered and the role of the cleavage planes discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

The preparation and crystal structure analysis of bis(L-Arginine)Cu(II)(acetate)2trihydrate

The crystal structure of bis(L-arginine)Cu(II)(acetate)₂trihydrate has been determined by X-ray analysis. The complex crystallizes in the monoclinic space group P2₁, with cell dimensions a = 15.948(2), b = 16.878(2), c = 10.378(2) Å, β = 108.47(1)°, Z = 4. There are two independent formula units in the asymmetric unit. The Cu atoms were located from a Patterson synthesis and the remaining atoms from difference Fourier syntheses. The structure was refined by least-squares to R = 0.079 and R = 0.11. Each copper atom has an essentially square planar coordination with the two arginine molecules chelated via the carboxy oxygens and the α-amino nitrogens, but with distorted six-fold coordinations completed by weak Cu…O (acetate) interactions. Electrostatic interactions between the acetates and the protonated ends of the amino acid residues link the two independent [Cu(L-arginine)₂(acetate)₂] units into dimers, which are then connected via hydrogen bonds, also involving the water molecules, into an infinite network.     

Supramolecular networks of dinuclear copper(II): Synthesis, crystal structure and magnetic study

The complexes [Cu₂(ox)(phen)₂(H₂O)₂](NO₃)₂ (1), [Cu₂(sq)(pmdien)₂(H₂O)₂](ClO₄)₂ (2) and {[Cu₃(pdc)₃(4,4′-bipy)_1.5(H₂O)_2.25] · 2.5(H₂O)}_n (3) [phen = 1,10-phenanthroline; pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine; 4,4′-bipy = 4,4′-bipyridine; ox = oxalate dianion; sq = squarate dianion and pdc = pyridine 2,6-dicarboxylate] have been synthesized and characterized by X-ray single crystal structure determination, low temperature magnetic measurement and thermal study. Structure determination reveals that 1 and 2 are dinuclear copper(II) complexes bridged by oxalate and squarate dianions, respectively, while 3 is a hexanuclear species formed by three Cu(pdc)(H₂O)-(4,4′-bipy)-Cu(pdc)(H₂O) fragments, connected through long Cu-O(pdc) bonds in a centrosymmetric arrangement. In complex 1 H-bonds occurring between the coordinated water molecules and lattice nitrate anions result in eight-membered ring clusters with the concomitant formation of 1D supramolecular chain. The adjacent chains undergo π-π stacking forming a 2D architecture. In the crystal of 3 an extensive H-bonding scheme gives rise to a 3D supramolecular network. Low temperature magnetic study shows a strong antiferromagnetic coupling in 1 (J = −288 ± 2 cm⁻¹, g = 2.21 ± 0.01, R = 1.2 × 10⁻⁶); and a very weak interaction in 2 and 3, the best-fit parameters being: J = −0.21 cm⁻¹, g = 2.12 ± 0.01, R = 1.1 × 10⁻⁶ (2) and J = −1.34 cm⁻¹ ± 0.1, g = 2.14 ± 0.01, R = 1.2 × 10⁻⁶ (3) (R defines as .     

Acetato, formato and chloride copper(II) complexes with 2-(aminomethyl)pyridine: Synthesis, crystal structure, magnetic properties and EPR results

By the reactions of Cu(OAc)₂ · H₂O and Cu(HCOO)₂ · 4H₂O with 2-(aminomethyl)pyridine in different proportions, the compounds Cu(OAc)₂(2-amp) (1), Cu(HCOO)₂(2-amp) (2), Cu(HCOO)₂(2-amp)_1/2 (5), Cu(OAc)₂(2-amp)₂ · H₂O (6) and Cu(HCOO)₂(2-amp)₂ · H₂O (7) were obtained. In 1 the copper shows an elongated rhombic octahedral stereochemistry determined by a 2-amp molecule and two asymmetrical bidentate acetate groups. The hydrogen bonds between the NH₂ groups and O atoms yield to the formation of a double chain. Compound 2 instead consists in monodimensional chains of Cu(2-amp)(HCOO) units, with monodentate formate groups, linked by syn-anti bridging formate groups. Sheets are formed by hydrogen bonds between the chains. By crystallization of a solution of 6 in chloroform, CuCl₂(2-amp)₂ (3) was obtained. It presents a highly distorted square pyramidal geometry around the copper atom. The sheets, formed by the hydrogen bonds between NH₂ and Cl, are interpenetrated and shows π stacking. Magnetic properties and EPR spectra for these new compounds have been studied. Also the magnetic behaviour of Cu(OAc)₂(2-amp)_1/2 (4) is described.     

Pd(II)- and Pt(II)-cimetidine complexes. Crystal structure of trans-[Pt(N,S-cimetidine)(2)]Cl(2)(*)12H(2)O

The influence of cimetidine on patients under cisplatin treatment for cancer is controversial. It has moderate or no effects on several types of cancer and its effects on the nephrotoxicity induced by cisplatin are uncertain. To examine the binding properties and antiproliferative effects of the known anticancer noble metals, cimetidine (cim) was complexed to platinum(II) and palladium(II). The crystal structure of the Pt-cim compound shows two molecules of cimetidine coordinated to the metal through thioether sulfur and imidazolic nitrogen whereas spectroscopic studies in solution for Pd-cim reveal that the ratio of the metal to cimetidine is 1:1 with identical coordination environments. To determine the antitumor activity of the drugs, the interaction of the metallic complexes and free cimetidine with DNA was assessed. Their cytotoxic activity was compared with that of cisplatin.     

Synthesis, characterization, crystal structure and biological activity of a novel heterotetranuclear complex: [NiLPb(SCN)2(DMF)(H2O)]2, bis-{[mu-N,N'-bis(salicylidene)-1,3-propanediaminato-aqua-nickel(II)](thiocyanato)(mu-thiocyanato)(mu-N,N'-dimethylformamide)lead(II)}

The mononuclear nickel complex NiL (LH2 = N,N'-bis(salicylidene)-1,3-diaminopropane) can be transformed into the tetranuclear complex [NiL(H2O)Pb(SCN)2(DMF)]2 in the aid of SCN-, DMF (dimethylformamide) and Pb(II) ions. The complex was characterized by elemental analysis and FTIR investigation. The crystal structure reveals it is a nonlinear Ni(II)-Pb(II)-Pb(II)i-Ni(II)i (i: 1-x, 1-y, 1-z) heterotetranuclear complex and crystallizes in the triclinic space group P1. The Ni(II) and Pb(II) ions have a distorted octahedral coordination geometry. There are three kinds of mu-bridge in the molecule between the metal ions. Each pair of Ni and Pb ions in the asymmetric unit is equatorially linked by two phenolic oxygen bridging atoms of N,N'-bis(salicylidene)-1,3-propanediaminato (salpd(2-), C17H16N2O2(2-)) ligand. The dinuclear centres from tetranuclear clusters Ni-Pb(i) and Ni(i)-Pb pairs are bridged by two mu-1,3-SCN groups. Pb(II) and Pb(II)i ions are also bridged by the oxygen atoms of DMF molecules. The tetranuclear units are hydrogen bonded by two O-H...N intermolecular interactions along the c-axis. The complex was screened for antibacterial and antifungal activities by the disc diffusion and microtiter plate techniques using DMF as solvent. The minimum inhibitory concentration values were calculated. It has been found that antimicrobial activities of the complexes are higher than the free ligand.