Spring Time and Autumn Time Toxic Effects of Copper (II), 3-(2-Furyl) Prop-2-Enal Semicarbazone and [CuCl2(FASC)2] Complex in Mice

In vitro, 3-(2-furyl) prop-2-enal semicarbazone-copper (II) complex [CuCl₂(FASC)₂] presents antimitotic effects. In this work we studied the in vivo seasonal toxic effects in male Swiss mice of CuCl₂, and FASC and the [CuCl₂(FASC)₂] complex. In spring, one injection of CuCl₂8.10^-2 mmol killed 16% of animals after 24 h. Cupric chloride lethal dose was up to 64.10^-2 mmol with 100% mice dead after 24 h. FASC was well tolerated from 0.65 to 1.3 mmol. The complex was 100% lethal with 48.10^-2 mmol. In autumn, mice were more sensitive to CuCl₂ and to the complex with lethal doses up to 32.10^-2 mmol and 8.10^-2 mmol, respectively. On the other hand, FASC was well tolerated. It is concluded that the in vivo toxic effects of CuCl₂ and [CuCl₂(FASC)₂] complex are quite different in spring and autumn.     

Synthesis, structure and biological activities of cobalt(II) and zinc(II) coordination compounds with 2-benzimidazole derivatives

In this work we present the synthesis, structural and spectroscopic characterisation of a series of cobalt(II) and zinc(II) coordination compounds with benzimidazole (bz) and its 2-benzimidazole derivatives: 2-aminobenzimidazole (2ab), albendazole (abz) and tris(2-benzimidazolylmethyl)amine (ntb). The compounds were evaluated for their in vitro antimicrobial activity against Staphylococcus aureus, Micrococcus luteus, Salmonella typhi, Pseudomonas aeruginosa, Escherichia coli and Proteus vulgaris. Their cytotoxic activity was also evaluated using human cancer lines, HeLa, HCT-15 and SKLU-1. The halide tetrahedral compounds [Co(bz)₂Br₂] 3, [Zn(2ab)₂Cl₂] · 0.5H₂O 11, [Co(abz)Cl₂(H₂O)] · 3H₂O 14, [Co(abz)Br₂(H₂O)] 15, [Zn(abz)Cl₂(H₂O)] · 3H₂O 17 and [Zn(abz)Br₂(H₂O)] · H₂O 18 displayed similar minimal inhibition concentration (MIC) values against Micrococcus luteus and Escherichia coli, comparable to those of amoxicillin and chloramphenicol. Additionally, 11 showed a wide range of activity towards Gram(+) and Gram(−) microorganisms. The tetradentate ntb and its trigonal bipyramidal cobalt(II) and zinc(II) compounds were active, regardless of the anion present in the complex. Compound [Co(abz)Cl₂(H₂O)] · 3H₂O 14 showed promising activity in HeLa cells, while [Co(ntb)Br]Br · H₂O 21 inhibited Hela and HCT-15 cell lines.     

Molecular structures of Fe(II) complexes with mono- and di-protonated ethylenediamine-N,N,N′,N′-tetraacetate (Hedta and H2edta), as determined by X-ray crystal analyses

The molecular structure of the title complexes [Fe(H₂O)₄][Fe(Hedta)(H₂O)]₂ · 4H₂O (I) and [Fe(H[₂edta)(H₂O)] · 2H₂O (II) have been determined by single-crystal X-ray analyses. The crystal data are as follows: I: monoclinic, P2₁/n, A = 11.794(2), B = 15.990(2), C = 9.206(2) Å, β = 90.33(1)°, V = 1736.1(5) ų, Z = 2 and R = 0.030; II: monoclinic, C2/c, A = 11.074(2), B = 9.856(2), C = 14.399(2) Å, β = 95.86(1)°, V = 1563.3(4) ų, Z = 4 and R = 0.025. I is found to be isomorphous with the Mn^II analog reported earlier and to contain a seven-coordinate and approximately pentagonal-bipyramidal (PB) [Fe^II(Hedta)(H₂O]⁻ unit in which Hedta acts as a hexadentate ligand. The [Fe^II(H₂edta)(H₂O)] unit in II has also a seven-coordinate PB structure with the two protonated equatorial glycine arms both remaining coordinated, and thus bears a structural resemblance to the seven-coordinate [Co^II(H₂edta)(H₂O)] reported previously.     

N,N′-Ethylene-bis(3-methoxysalicylideneimine) mononuclear (4f) and heterodinuclear (3d–4f) metal complexes: Synthesis, crystal structure and luminescent properties

The stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, reactions of ligand H₂L and Ln(NO₃)₃ · 6H₂O give rise to three mononuclear lanthanide complexes Ln(H₂L)(NO₃)₃ [H₂L = N,N′-ethylene-bis(3-methoxysalicylideneimine), Ln = Nd (1), Eu (2) and Tb (3)], in which N,N′-ethylene-bis(3-methoxysalicylideneimine) acts as tetradentate ligands with the O₂O₂ set of donor atoms capable of effective coordination. These species are fairly stable and have been isolated. Then, addition of Cu(Ac)₂ · H₂O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes Cu(L)Ln(NO₃)₃ · H₂O [Ln = Nd (4) and Eu (5)] where the Cu(II) ion is inserted to the inner N₂O₂ cavity. Luminescent analysis reveals that complex 3 exhibits characteristic metal-centered fluorescence of Tb(III) ion. However, the characteristic luminescence of both Sm(III) and Eu(III) ions is not observed both in solution and solid state of the complexes.     

Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

Development and characterization in vitro of a catalase-based biosensor for hydrogen peroxide monitoring

There is increasing evidence that hydrogen peroxide (H₂O₂) may act as a neuromodulator in the brain, as well as contributing to neurodegeneration in diseased states, such as Parkinson's disease. The ability to monitor changes in endogenous H₂O₂ in vivo with high temporal resolution is essential in order to further elucidate the roles of H₂O₂ in the central nervous system. Here, we describe the in vitro characterization of an implantable catalase-based H₂O₂ biosensor. The biosensor comprises two amperometric electrodes, one with catalase immobilized on the surface and one without enzyme (blank). The analytical signal is then the difference between the two electrodes. The H₂O₂ sensitivity of various designs was compared, and ranged from 0 to 56 ± 4 mA cm⁻² M⁻¹. The most successful design incorporated a Nafion^® layer followed by a poly-o-phenylenediamine (PPD) polymer layer. Catalase was adsorbed onto the PPD layer and then cross-linked with glutaraldehyde. The ability of the biosensors to exclude interference from ascorbic acid, and other interference species found in vivo, was also tested. A variety of the catalase-based biosensor designs described here show promise for in vivo monitoring of endogenous H₂O₂ in the brain.     

Structural determinations, magnetic and EPR studies of complexes involving the Cr(OH)2Cr unit

Five heterometallic compounds with formulae [Ba(H₂O)₄Cr₂(μ-OH)₂(nta)₂] · 3H₂O (I), [M(bpy)₂(H₂O)₂] [Cr₂(OH)₂(nta)₂] · 7H₂O, where M²⁺ = Zn, (II); Ni, (III); Co, (IV) and [Mn(H₂O)₃(bpy)Cr₂(OH)₂(nta)₂] · (bpy) · 5H₂O (V); bpy = 2,2′-bipyridine, (nta = nitrilotriacetate ion) have been prepared by reaction of I with the corresponding M^II-sulfates in the presence of 2,2′-bipyridine. Substances I–V have been characterized by magnetic susceptibility measurements, EPR and X-ray determinations. I represents a 2D coordination polymer formed by coordination of centrosymmetrical dimeric chromium(III) units and Barium cations. The 10-coordinate Ba polyhedron is completed by four water molecules. Compounds II–IV are isostructural and consist of non-centrosymmetric dimeric anions [Cr₂(μ-OH)₂(nta)₂]²⁻, complex cations [M^II(bpy)₂(H₂O)₂]²⁺ and solvate water molecules. The octahedral coordination of chromium atoms implies four donor atoms of the nta³⁻ ligands and two bridging OH groups. Multiple hydrogen bonds of coordinated and solvate water molecules link anions and cations in a 3D network. A similar [Cr₂(μ-OH)₂(nta)₂]²⁻ unit is found in V. The bridging function is performed by a carboxylate oxygen atom of the nta ligand that leads to the formation of a trinuclear complex [Mn(bpy)(H₂O)₂Cr₂(μ-OH)₂(nta)₂]. Experimental and calculated frequency and temperature dependences of EPR spectra of these compounds are presented. The fine structure appearing on the EPR spectra of compound V is analyzed in detail at different temperatures. It is established that the main part of the EPR signals is due to the transitions in the spin states of a spin multiplet with S = 2. Analyses of experimental and calculated spectra confirm the absence of interaction between metal ions (M^II) and Cr-dimers in complexes III and IV and the presence of weak Mn–Cr interactions in V. The temperature dependence of magnetic susceptibilities for I–V was fitted on the basis of the expression derived from isotropic Hamiltonian including a bi-quadratic exchange term.     

Synthesis and characterisation of copper(II), zinc(II) and cobalt(II) complexes of salicylglycine, a metabolite of aspirin

Copper(II), nickel(II) and cobalt(II) complexes of the aspirin metabolite salicylglycine (H₂L), of stoichiometry M(HL)₂·solvate, have been prepared and characterised. In these complexes salicylglycinate is coordinated to the metal via its carboxylato group and possibly also its amide oxygen in the copper(II) complex. Under basic conditions copper(II) forms the complex Cu(LH₋₁)·2H₂O·MeOH, in which the ligand is coordinated to the metal via its carboxylate and phenolate oxygen atoms and the deprotonated peptide nitrogen atom.     

Tetrakis-[1-methylimidazoline-2(3H)-thione]-μ2-[1-methylimidazoline- 2(3H)-thione]-Di-Copper(I) sulphate trihydrate: Preparation, thermal analysis and crystal structure

1-emthylimidazoline-2(3H)-thione (mimtH) reacts with copper(II) sulphate pentahydrate in aqueous acetone to produce the dinuclear complex, Cu₂(mimtH)₅SO₄ · 3H₂O; the formula has been established by a combination of chemical and thermal analysis. The monoclinic crystals, (space group P_c, Z = 2), contain dinuclear cations, sulphate ions and water molecules. The dinuclear cation, Cu₂(mimtH)₅²⁺, consists of two trigonal copper(I) atoms, four terminal, monodentate, S-donating mimtH molecules and one S-bridging (μ₂) mimtH molecule. Some average dimensions are:Cu---S, 2.258 Å and S---Cu---S, 120.0°; the Cu---S---Cu bridging angle is 94.8° and the Cu---Cu separation distance is 3.308 Å.     

The crystal and molecular structures of lithium trimethylenediaminetetraacetatoferrate(III) trihydrate Li[Fe(trdta)]·3H2O and sodium ethylenediamine-N,N′-diacetato-N,N′-di-3-propionatoferrate(II) pentahydrate Na[Fe(eddda)]·5H2O

The crystal structures of Li[Fe(trtda)]·3H₂O and Na[Fe(eddda)]·5H₂O (trtda = trimethylenediaminetetraacetate and eddda = ethylenediamine-N,N′-diacetate-N,N′-di-3-propionate) have been determined by single crystal X-ray diffraction techniques. The former crystal was monoclinic with the space group P2₁/n,a = 17.775(3),b = 10.261(1),c = 8.883(2)Å, β = 95.86(4)° and Z = 4. The latter was also monoclinic with the space group P2₁/n,a = 6.894(2),b = 20.710(6),c = 13.966(3)Å, β = 101.44(2)° and Z = 4. Both complex anions were found to adopt an octahedral six-coordinated structure with all of six ligand atoms of trdta⁴⁻ or eddda⁴⁻ coordinated to the Fe(III) ion, unlike the corresponding edta⁴⁻ complex which is usually seven-coordinate with the seventh coordination site occupied by H₂O. Of the three geometrical isomers possible for the eddda complex, the trans(O₅) isomer was actually found in the latter crystal. Factors determining the structural types of metal–edta complexes are discussed in detail.     

Syntheses, structures and magnetic properties of mono- and di-manganese inclusion compounds

Mono- and di-manganese inclusion compounds 1 and 2 are reported. Two mono-manganese molecules Mn(bpy)₂(NO₃)₂ (bpy=2,2′-bipyridine) and [Mn(bpy)₂(NO₃)(H₂O)]·NO₃ coexist in the mole ratio of 1:1 in the structure of 1, while two di-manganese molecules [Mn₂O(bpy)₂(phtha)₂(H₂O)₂]·(NO₃)₂ (phtha=phthalate) and [Mn₂O(bpy)₂(phtha)₂(NO₃)(H₂O)]·NO₃ in the structure of 2. Refluxing Mn(NO₃)₂/bpy/phthalic acid reaction mixtures in CH₃CN leads to the isolation of 1, further concentration of the reaction solution in raising temperature results in 2. The Mn₁ and Mn₂ units in the inclusion compounds 1 and 2 are similar to other reported Mn₁ and Mn₂ analogs, respectively. The Jahn–Teller distortion was observed to give rise to the elongation along the O_terminal---Mn---O_carboxyl axes for all the four Mn(III) sites in 2, leading to unexpected longer Mn(III)---O_aqua than Mn(II)---O_aqua in 1. Extensive hydrogen bonding interactions among H₂O, NO₃ ⁻ and COOH were observed in the two inclusion compounds. Cyclic voltammetry of 2 in DMF displays two quasi-reversible redox couples at +0.10/+0.22 and −0.43/−0.36 V assigned to the Mn(III)Mn(IV)/2Mn(III) and 2Mn(III)/Mn(III)Mn(II), respectively. Variable temperature magnetic susceptibilities of 1 and 2 were measured. The data were fit to a model including axial zero-field splitting term and a good fit was found with D=1.77 cm⁻¹, g=1.98 and F=1.48×10⁻⁵ for 1. For 2, the least-squares fitting of the experimental data led to J=2.37 cm⁻¹, g=2.02 and D=0.75 cm⁻¹ with R=1.45×10⁻³.     

Structures and magnetism of rubidium and cesium salts of dimeric oxovanadium(IV) tartrate(4−) complexes

Complexes of type A₄[VO(tart)]₂·nH₂O, where A = Rb or Cs and tart =d,l-tartrate(4−) (n = 2) or d,d-tartrate(4−) (n = 2 for Rb and n = 3 for Cs), were prepared from an aqueous mixture of V₂O₅, AOH and H₄tart. These complexes were studied by single-crystal X-ray diffraction methods: Rb₄[VO(d,l-tart)]₂·2H₂O, space group P1 with a = 8.156(1),b = 8.246(1),c = 8.719(1)Å, = 66.09(1)°, β = 65.07(1)°, γ = 82.40(1)°,Z = 2, 1917 observed reflections, and final R_w = 0.035; Cs₄[VO(d,l-tart)]₂·2H₂O, space group P₂₁/c with a = 9.350(1),b = 13.728(2),c = 8.479(1)Å, β = 106.77(1)°,Z = 4, 2235 observed reflections, and final R_w = 0.054; Rb₄[VO(d,d-tart)]₂·2H₂O, space group P₄₁₂₂ with a = 8.072(1),c = 32.006(3)Å,Z = 8, 1014 observed reflections and final R_w = 0.038; Cs₄[VO(d,d-tart)]₂·3H₂O, space group P₁₂₂ with a = 8.184(1),c = 33.680(5)Å,Z = 8, 1310 observed reflections, and final R_w = 0.063. Bulk magnetic susceptibility data (1.5–300 K) for these compounds and A₄[VOl,l-tart)]₂·nH₂O (A = Rb, Cs) were obtained on polycrystalline samples. These data were analyzed in terms of a Van Vleck exchange coupled S = 1/2 model which was modified to include an interdimer exchange parameters Θ. Analysis of the low-temperature (1.5–20 K) susceptibility data gave 2J = +1.30 cm⁻¹ and Θ = −1.86 K for Rb₄[VO(d,l-tart)]₂·2H₂O, 2J = +1.16 cm⁻¹ and Θ = −1.69 K for Cs₄[VO(d,l-tart)]₂·2H₂O, 2J = +1.90 cm⁻¹ and Θ = −0.82 K for Rb₄[VO(d,d-tart)]₂·2H₂O, 2J = +2.04 cm⁻¹ and Θ = −0.80 K for Rb₄[VO(l,l-tart)]₂·2H₂O, 2J = +1.52 cm⁻¹ and Θ = −0.25 K for Cs₄[VO(d,d-tart)]₂·3H₂O, and 2J = +1.64 cm⁻¹ and Θ = −0.31 K for Cs₄[VO(l,l-tart)]₂·3H₂O. These results suggest the magnitudes of intradimer (ferromagnetic and interdimer (antiferromagnetic) exchange interactions are similar in these complexes, as observed for the analogous Na salts.     

Synthesis, crystal structure and magnetic properties of the first structurally characterized 1,2-dithiocroconato-containing Cu(II) complex, [Cu(bpca)(H2O)]2[Cu(1,2-dtcr)2]·2H2O

The first crystal and molecular structure of a transition metal complex containing 1,2-dithiocroconate (1,2-dtcr, dianion of 1,2-dimercaptocylopent-1-ene-3,4,5-trione), [Cu(bpca)(H₂O)]₂[Cu(1,2-dtcr)₂]·2H₂O (where bpca is the bis(2-pyrdidylcarbonyl)amide anion), has been determined by single crystal X-ray diffraction methods. The compound crystallizesin the monoclinic syste, space group P2₁/c, with a = 11.661(3), b = 20.255(6), c = 8.265(3) Å, ß = 107.26(2)° and Z = 2. The structure is formally built of [Cu(1,2-dtcr)₂]²⁻ and [Cu(bpca)(H₂O)]⁺ ions and water of hydration. The copper atom of the anion is situated at a crystallographic inversion centre, bonded to four sulfur atoms in a planar, approximately square arrangement. In the cation the copper equatorial plane is formed by the three nitrogen atoms of the bpca ligand and a water oxygen atom. In addition there is a very weak axial bond to one of the sulfur atoms of a 1,2-dtcr ligand in the anion. Through these latter weak bonds each anion is connected to, and sandwiched between, two cations, resulting in neutral, trinuclear, centrosymmetric formula units. The triple-decker molecules are arranged in stacks along the crystallographic a-axis creating close contacts between the terminal copper atoms and bpca groups of the neighbouring molecules. This intermolecular interaction is, however, too weak to define the structure as a chain compound. The distance between adjacent copper atoms within the trinuclear unit is 4.189(1) Å, while the shortest intra-stack metal-metal separation between terminal copper atoms is 5.281(1) Å. Variable-temperature magnetic susceptibility measurements in the temperature r.2–140 K reveal that a Curie law is followed; with three non-interacting copper(II) ions in the formula unit.     

One-dimensional polymeric chlorocadmate(II) systems of N-methylpiperazinium and N,N′-dimethylpiperazinium compounds: synthesis, structural and thermal properties

The chlorocadmate(II) systems of (H₂me₂pipz)[Cd₂Cl₆(H₂O)₂] (1) and (H₂mepipz)₂[Cd₃Cl₁₀(H₂O)] (2) (L = me₂pipz = N,N′-dimethylpiperazine; L′ = mepipz = N-methylpiperazine) were prepared and their structural and thermal properties investigated. Compound 1 is monoclinic, space group P2₁/c, A = 7.664(1), B = 7.472(4), C = 15.347(1) Å, β = 99.468(7)°, Z = 2, R = 0.024. The crystal structure consists of organic cations and infinite one-dimensional chains of [CdCl₃(H₂O)]_n³⁻ anions. Each Cd atom is octahedrally surrounded by bridged and terminal chlorine atoms and by a water molecule, which is in trans position with respect to the terminal chlorine atom. Inter- and intrachain hydrogen bond interactions between the terminal chlorine atoms and the water molecules contribute to the crystal packing. Compound 2 is orthorhombic, space group Cmc2₁, A = 15.286(3), B = 13.354(3), C = 13.154(3) Å, R = 0.023. The crystal structure consists of organic dications and infinite chains of [Cd₂Cl₆(CdCl₄H₂O]_n⁴⁻ units running along the [001] axis. Each unit is formed of regularly alternate six-coordinated Cd atoms, one of them linking one pentacoordinated Cd atom which completes its coordination througha water molecule. A strong hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential scanning calorimetry measurements did not show the presence of any structural phase transitions. The structures are compared with those of (H₂pipz)[Cd₂Cl₆(H₂O)₂] (3), (H₂mepipz)[Cd₂Cl₆(H₂O)₂]·H₂O (4) and (H₂mepipz)[Cd₂Cl₆] (5) (L = pipz = piperazine, L′ = mepipz = N-ethylpiperazine).     

A dicopper complex of N,N′-bis[2,2-dimethyl-4-(2-hydroxyphenyl)-3-aza-3-buten] oxamide. Structure and magnetic behaviour of the mono hydrated form

The ligand N, N′-bis[2,2-dimethyl-4-(2-hydroxyphenyl)-3-aza-3-buten] oxamide with two identical coordination sites reacts with copper ions in its tetradeprotonated form to yield the dinuclear complex [Cu₂(C₂₄H₂₆N₄O₄)]·H₂O. The structure of this compound has been determined by the X-ray diffraction method. The crystals are orthorhombic with a = 11.744(1), B = 16.369(2), C = 26.340(3) Å, V = 5064(1) ų, Z = 8, space group Pbca. The oxamide is in a trans conformation with two different environments for the copper centres, a (4 + 1) coordination mode for the first one and a square planar environment for the other one. The water molecule is not directly bound to a copper centre, but involved in hydrogen bonding with the two oxygen atoms of an N₂O₂ coordination site. Indeed, extra coordination comes from a phenolic oxygen atom belonging to an adjacent dinuclear unit. Static susceptibility measurements point to a strong intrapair antiferromagnetic exchange interaction of 2J = −520(±4) cm⁻¹ and possibly an interpair ferromagnetic exchange interaction of 10(±5) cm⁻¹.     

Studies of the oxovanadium(IV)—oxalate system: syntheses and crystal structures of binuclear (Ph4P)2[(VO)2(H2O)2(C2O4)3]·4H2O and of the one-dimensional chain material, (Ph4P)[VOCl(C2O4)]

The hydrothermal reactions of (Ph₄P)[VO₂Cl₂] and H₂C₂O₄ at 150 and 125°C yield (Ph₄P)₂[V₂O₂(H₂O)₂(C₂O₄)₃]·4H₂O (1) and (Ph₄P)[VOCl(C₂O₄)] (2), respectively. The structure of the molecular anion of 1 consists of a binuclear unit of oxovanadium(IV) octahedra bridged by a bisbidentate oxalate group. The VO₆ coordination geometry at each vanadium site is defined by a terminal oxo group, an aquo ligand, and four oxygen donors — two from the bisbidentate bridging oxalate and two from the terminal bidentate oxalate. The structure of 2 consists of discrete Ph₄P⁺ cations occupying regions between [VOCl(C₂O₄)]⁻_∞ spiral chains. The structure of the one-dimensional anionic chain exhibits V(IV) octahedra bridged by bisbidentate oxalate groups. Crystal data: 1·4H₂O, monoclinic P2₁/n, A = 12.694(3), B = 12.531(3), C = 17.17(3) Å, β = 106.32(2)°, V = 2621.3(13) ų, Z = 2, D_calc = 1.501 g cm⁻³, structure solution and refinement converged at a conventional residual of 0.0518; 2, tetragonal P4₃, A = 12.145(2), C = 15.991(3) Å, V = 2358.7(12) ų, Z = 4, R = 0.0452.     

Nitric oxide and peroxynitrite. The ugly, the uglier and the not so good: a personal view of recent controversies

Nitric oxide, a gaseous free radical, is poorly reactive with most biomolecules but highly reactive with other free radicals. Its ability to scavenge peroxyl and other damaging radicals may make it an important antioxidant in vivo, particular in the cardiovascular system, although this ability has been somewhat eclipsed in the literature by a focus on the toxicity of peroxynitrite, generated by reaction of O^·-₂ with NO^· (or of NO^- with O₂). On balance, experimental and theoretical data support the view that ONOO^- can lead to hydroxyl radical (OH^·) generation at pH 7.4, but it seems unlikely that OH^· contributes much to the cytotoxicity of ONOO^-. The cytotoxicity of ONOO^- may have been over-emphasized: its formation and rapid reaction with antioxidants may provide a mechanism of using NO^· to dispose of excess O^·-₂, or even of using O^·-₂ to dispose of excess NO^·, in order to maintain the correct balance between these radicals in vivo. Injection or instillation of “bolus” ONOO^- into animals has produced tissue injury, however, although more experiments generating ONOO^- at steady rates in vivo are required. The presence of 3-nitrotyrosine in tissues is still frequently taken as evidence of ONOO^- generation in vivo, but abundant evidence now exists to support the view that it is a biomarker of several “reactive nitrogen species”. Another under-addressed problem is the reliability of assays used to detect and measure 3-nitrotyrosine in tissues and body fluids: immunostaining results vary between laboratories and simple HPLC methods are susceptible to artefacts. Exposure of biological material to low pH (e.g. during acidic hydrolysis to liberate nitrotyrosine from proteins) or to H₂O₂ might cause artefactual generation of nitrotyrosine from NO^-₂ in the samples. This may be the origin of some of the very large values for tissue nitrotyrosine levels quoted in the literature. Nitrous acid causes not only tyrosine nitration but also DNA base deamination at low pH: these events are relevant to the human stomach since saliva and many foods are rich in nitrite. Several plant phenolics inhibit nitration and deamination in vitro, an effect that could conceivably contribute to their protective effects against gastric cancer development.     

Mixed anion lanthanide(III) crown ether complexes: crystal structures of [LaCl2(NO3)(12-crown-4)]2, [La(NO3)(OH2)4-(12-crown-4)]Cl2·CH3CN and [LaCl2(NO3)(18-crown-6)]

Reaction of LaCl₃·7H₂O containing small amounts of La(NO₃)₃·7H₂O as an impurity with 12-crown-4 or 18-crown-6 in 3:1 CH₃CN:CH₃OH resulted in the isolation of the mixed anion complexes [LaCl₂(NO₃)(12-crown-4)]₂, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN and [LaCl₂(NO₃)(18-crown-6)]. The nine-coordinate dimer, [LaCl₂(NO₃)(12-crown-4)]₂, has all of the anions in the inner coordination sphere and La³⁺ has a capped square antiprismatic geometry. It crystallizes in the orthorhombic space group Pbca with (at −150 °C) a = 12.938(6), B = 15.704(3), C = 13.962(2) Å, and D_calc = 2.08 g cm⁻³ for Z = 4. The second complex isolated from the same reaction, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN, has the bidentate nitrate anion in the inner coordination sphere but the two chloride anions are in a hydrogen bonded outer sphere. This complex is ten-coordinate 4A,6B-expanded dodecahedral and crystallizes in the monoclinic space group P2₁ with (at 20 °C) A = 7.651(2), B = 11.704(7), C = 11.608(4) Å, β = 95.11(2)°, and D_calc = 1.80 g cm⁻³ for Z = 2. The 18-crown-6 complex, [LaCl₂(NO₃)(18-crown-6)], has all inner sphere anions and has ten-coordinate 4A,6B-expanded dodecahedral La³⁺ centers. It crystallizes in the orthorhombic space group Pbca with (at 20 °C) a = 14.122(7), B = 13.563(5), C = 19.311(9) Å, and D_calc = 1.89 g cm⁻³ for Z = 8.     

1D copper(II) and zinc(II) coordination polymers containing an unusual twisted oxalate bridge

Two new copper(II) complexes, Cu(L1)(ClO₄)₂ (1), {[(μ-oxalate)Cu(L1)] · 5H₂O}_n (2), and a zinc(II) complex, {[(μ-oxalate)Zn(L2)] · 3H₂O · 0.5DMF}_n (3) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane), have been synthesized and characterized by X-ray crystallography. In 1, the ligand conformation is planar, and the octahedral coordination about the copper(II) ion is completed by weakly interacting ions. In 2 and 3, bridging oxalate ligands coordinate to copper(II) or zinc(II) ions in an unusually twisted bis-monodentate (trans-1,1′-bicoordination) mode.

The rigidity and steric hindrance of macrocycles L1 and L2 by the introduction of two cyclohexane rings and methyl groups on a cyclam (1,4,8,11-tetraazacyclotetradecane) skeleton cause the bridging oxalate ligands to adopt such unusual geometries in 2 and 3.     

Synthesis, structure, and heterogeneous catalytic activity of tungsten chalcogenide cubane cluster containing alkaline earth metal complex

A new compound containing a cubane tungsten chalcogenide cluster [W₄(μ₃-Te)₄(CN)₁₂]⁶⁻ and Ca²⁺ complex units has been prepared by the reaction of aqueous solution of K₆[W₄(μ₃-Te)₄(CN)₁₂] · 5H₂O with the solution of a Ca(NO₃)₂ and phen(1,10-phenanthroline) (1:2 molar ratio) in a solvent mixture of H₂O/EtOH. The structure of [{Ca(phen)₂(H₂O)}{Ca(phen)(H₂O)₄}{Ca(phen)₂(H₂O)₃}][W₄Te₄(CN)₁₂] · 5H₂O 1 has been determined by X-ray crystallography. Compound 1 contains [{Ca(phen)(H₂O)₄}{Ca(phen)₂(H₂O)₃}][W₄(μ₃- Te)₄(CN)₁₂] units bridged by {Ca(phen)₂(H₂O)}²⁺ units to form an one-dimensional zigzag chain structure. Interestingly, compound 1 showed a heterogeneous catalytic activity in the transesterification of a range of esters with methanol under the mild conditions. Moreover, it can be reused without any loss of activity through 10 runs with ester.