Teresa M. Santos

Mesoporous Silicas Modified with Dioxomolybdenum(VI) Complexes: Synthesis and Catalysis

The dioxomolybdenum(VI) fragment MoO2X2 has been confined within the ordered mesopores of pure siliceous hexagonal MCM-41 and cubic MCM-48 molecular sieves either by direct grafting (solvent impregnation) with MoO2X2(THF)2 or by using a spacer ligand [L = NC(CH2)2Si(OEt)3]. The materials have been characterised by elemental analysis, powder X-ray diffraction, N2 adsorption, IR spectroscopy, and magic-angle spinning NMR spectroscopy (13C, 29Si). All catalysts, homogeneous and heterogenised, are active in the epoxidation of cyclooctene with tert-butyl hydroperoxide.

Synthesis and structural characterisation of new RuII[12]aneS4 complexes with polypyridylic and related ligands

The reaction between cis-[Ru(dmso)Cl2] (dmso=dimethylsulfoxide) and the macrocycle 1,4,7,10-tetrathiacyclododecane ([12]aneS4) gives the complex cation [Ru([12]aneS4)(dmso)Cl]+. A new series of RuII([12]aneS4) complexes were obtained by replacing the dmso and the chlorine ligands with polypyridylic or related monodentate ligands. Complexes with the general formula [Ru([12]aneS4)(L)]2+, where L=bidentate ligand: dipyridylamine (dipa); 5-phenyl-1,10-phenanthroline (5-phen); 1,10-phenanthroline-5,6-dione (5,6-dione); o-phenylenediamine (pda) or 4,4′-diphenyl-2,2′-dipyridyl (dbp) have been synthesised. Related complexes containing monodentate ligands, [Ru([12]aneS4)(CH3CN)Cl]+, [Ru([12]aneS4)(CH3CN)2]2+ and [Ru([12]aneS4)(ind)Cl)]+ (ind=indazole) were also prepared. The complexes were characterised by NMR, UV/Vis and IR spectroscopy and their electrochemical behaviour was studied by cyclic voltammetry. The X-ray single crystal diffraction structures of the complexes [Ru([12]aneS4)(dmso)Cl]Cl, [Ru([12]aneS4)(CH3CN)2][PF6]2, [Ru([12]aneS4)(CH3CN)Cl]PF6, [Ru([12]aneS4)(5,6-dione)][PF6]2·2CH3CN, [Ru([12]aneS4)(5-phen)][PF6]2 and [Ru([12]aneS4)(ind)Cl]PF6·CH3CN were determined. All complexes exhibit a distorted cis-octahedral environment with the macrocycle adopting a folded conformation.

Bimetallic transition metal–ruthenium(II) complexes containing bridging bipyrimidine ligands

Abstract The ruthenium(II) complex [Ru([14]aneS4)(bpym)](BF4)2 ([14]aneS4=1,4,8,11-tetrathiacyclotetradecane, bpym=2,2′-bipyrimidine) has been prepared by substitution of the labile acetonitrile ligands in the complex [Ru([14]aneS4)(CH3CN)2](BF4)2 by bpym. Both the precursor acetonitrile complex and the polypyridyl complex were characterised by Ru K-edge EXAFS spectroscopy. In addition, the crystal structures of [Ru([14]aneS4)(bpym)](X)2 (X=BF4, PF6) were determined by X-ray diffraction. The bpym-bridged bimetallic complexes [{Ru([14]aneS4)}2(bpym)](BF4)4 and [{([14]aneS4)Ru}(bpym){ReO3Me}](BF4)2 were prepared using the ruthenium(II) monomeric bpym complex as starting material. In the case of the complex containing methyltrioxorhenium(VII) coordination of both metal centres to the bidentate bridging ligand was supported by a combination of Ru K-edge and Re L-edge XAFS spectroscopy, in addition to 1H NMR.

Effect of Cr(V) on reproductive organ morphology and sperm parameters: An experimental study in mice

BackgroundCr(V) species are formed during the intracellular reduction of Cr(VI), a ubiquitous environmental pollutant. In this study, the acute toxicity of a physiologically stable Cr(V) compound, [CrV-BT]2- (BT = bis(hydroxyethyl)aminotris(hydroxymethyl)methane) was investigated in the male reproductive system of sexually mature 60-day-old male ICR-CD1 mice.MethodsEight-week-old animals were subcutaneously injected daily with a dose of ca 8 μmol of Cr/mouse, during 5 days. The control group was injected with 0.5 mL of BT buffer. Testis and epididymis morphology was evaluated using light and transmission electron microscopy. Epididymal sperm counts, motility and acrosome integrity were also assayed using standard methods.ResultsSeminiferous epithelium abnormalities were detected in the CrV-BT experimental group, including intraepithelial vacuolation, and remarkable degeneration of Sertoli cells, spermatocytes and spermatids. The premature release of germ cells into the tubular lumen was also evident. Histological evaluation of epididymal compartments revealed apparently normal features. However, the epididymal epithelium presented vacuolation. [CrV-BT]2- induced a reduction in sperm acrosome integrity. However, sperm motility and density were not significantly affected.ConclusionThis in vivo study using a Cr(V) compound, provides evidence for the potential reproductive hazards caused on male reproductive system by species containing chromium in intermediate oxidation states.

Reactions between Cr(VI) and wood and its model compounds

Summary Wood, macromolecular and simple model compounds, were reacted with CrO3 or K2CrO4 aqueous solutions. Extracted lignin, guaiacol, vanillin, vanillyl alcohol and homovanillyl alcohol were chosen as model compounds for lignin, whilst cellulose, gum Ghatti, xylan, extracted hemicellulose from pine, methyl-β-D-glucopyranoside and methyl-β-cellobioside were used as models for wood polysaccharides. The kinetics of the reduction reactions of Cr(VI) were monitored using UV-Vis spectroscopy and the results obtained for several temperatures are discussed. In general terms, wood, lignin and lignin model compounds reduced Cr(VI) faster and to a greater extent than polysaccharides or simple sugar molecules. Moreover, lignin model compounds were reduced even faster than lignin. Simple sugars showed a reduction pattern similar to that of cellulose. Extracted hemicellulose revealed to be a poorer reductant while gum Ghatti was the strongest among the polysaccharides. As expected, CrO3 aq. behaved as a more powerfull oxidant than K2CrO4 aq. for these substances. Even at 100 °C, sugars or polysaccharides did not seem to be oxidised by K2CrO4 aq. 0.01 M. These results suggest that, because of the differences in reactivity, lignin reacts preferentially when wood is treated with Cr(VI)-containing formulations, like those which are applied in wood preservation treatments.

Evaluation of in vivo reproductive toxicity of potassium chromate in male mice

To evaluate the effects of potassium chromate on mice sperm cells after a short-term exposure, male ICR-CD1 mice were administered with 5 or 10mgK(2)CrO(4)/bw for 4 consecutive days. One group of mice was sacrificed at day 5, starting from the beginning of the experiment and another group was sacrificed at day 35. Testis and epididymis histology was evaluated by light microscopy and testicular cells populations were evaluated by flow cytometry (FCM). Spermatozoa were collected from the epididymis and their morphology and several functional parameters (density, motility, viability, mitochondrial function, acrosome integrity) were evaluated. Furthermore, DNA fragmentation and chromatin status of sperm cells were assessed at both experimental periods. Besides a reduction in seminiferous tubules diameter, exposure to potassium chromate did not induce further histopathological changes in mice testis or epididymis. These results were supported by the analysis of testicular cellular subpopulations by FCM. Concerning spermatozoa morphology, an increase in the percentage of multiple abnormalities and a decrease in the percentage of normal spermatozoa were found at days 5 and 35, respectively. Although spermatozoa mitochondrial function or viability was not affected, its motility was significantly reduced by potassium chromate exposure at both experimental periods. A decrease in acrosome integrity was found in mice injected with 10mgK(2)CrO(4)/bw after 35 days. Exposure to potassium chromate did not affect either DNA fragmentation or chromatin susceptibility to acid denaturation of sperm cells. In this work, we were able to show the effects of potassium chromate on spermatozoa physiological parameters such as motility, morphology and acrosome status and also demonstrate that the doses tested did not induce DNA damage to sperm cells after one spermatogenic cycle.

Structural characterisation and DFT studies of (Cr(cyclam)(O-dmso)Cl) 2 : a new precursor complex towards potential DNA intercalators

The synthesis and structural characterisation of the complex [Cr([14]aneN4)(O -dmso)Cl](PF6)2/dmso is reported. The structural studies were carried out in gas-phase by electrospray mass spectrometry (ESMS) and in the solid state by single crystal X-ray diffraction. The metal complex shows a distorted octahedral coordination environment with the macrocycle adopting a folded cis -V conformation. The angle Naxial � /Cr� /Naxial deviates by only 128 from the ideal value of 1808 for a perfect octahedron indicating that there is a good match between the size of the macrocyclic cavity and the size of Cr(III) ion. The ESMS shows that the complex loses a proton with concomitant opening of the [14]aneN4 ring to give the [Cr([14]aneN4-H)(dmso)Cl] � ion with a CH2� /CH� / pendant chain. This group interacts with dmso leading to the loss of this ligand and to the formation of the [Cr([14]aneN4-H)Cl] � ion, which has the highest relative abundance (100%). DFT calculations reproduce the geometry of the paramagnetic complex and are consistent with its electronic spectrum. # 2003 Elsevier Science B.V. All rights reserved.

Synthesis and characterisation of ruthenium(II) complexes containing ferrocenyl-derived ligands

Ruthenium(II) complexes containing the macrocycle [14]aneS4 and pyridyl ligands with an end-capping ferrocene were prepared using [Ru([14]aneS4)(DMSO)Cl]Cl as the starting material. Substitution of the DMSO ligand by 4-ferrocenylpyridine (4-FP), ferrocenyl-4-pyridylacetylene (FPA) and pyridine (py) gave the complexes [Ru([14]aneS4)(L)Cl]Cl (L=4-FP, FPA, py). The acetonitrile complex [Ru([14]aneS4)(NCMe)2](BF4)2 was also prepared starting from [Ru([14]aneS4)(DMSO)Cl]Cl. UV/Vis absorption spectroscopy and cyclic voltammetry indicate low electronic communication between the metal centres in the heterobimetallic complexes. The crystal structure of [Ru([14]aneS4)(4-FP)Cl]Cl was determined by X-ray diffraction. Crystal data: C25.780H37.134Cl2FeNO1.288S4Ru, M=737.82, monoclinic, space group P2/n, a=13.192(1), b=7.6662(6), c=28.549(2) A, β=100.341(2)°, V=2840.4(4) A3, Z=4.

Solution studies of some chromium(III) complexes with CrS bonds2. Kinetic and equilibrium studies of cysteinato- and penicillaminato-chromate(III) complexes☆

Abstract Similar anionic complexes are formed by the sulphur-containing amino acids cysteine and penicillamine with chromium(III). The compounds form stereospecifically with CrS 2 N 2 O 2 chromophores, the sulphur atoms being trans to each other. The CrS bonds are unusually labile and the hydrolysis of these bonds has been studied by electronic and CD spectroscopies. Stopped-flow measurements of the rate of hydrolysis in acid solution have been made and the results are compared with earlier studies reported in the literature.

Synthesis, structural characterization, cytotoxic properties and DNA binding of a dinuclear copper(II) complex.

In this study a novel dinuclear copper(II) complex with adenine and phenanthroline has been synthesized and its structure determined by single crystal X-ray diffraction. In the dinuclear complex [Cu₂(μ-adenine)₂(phen)₂(H2O)2](NO3)4·0.5H2O (phen=1,10-phenanthroline) (1) the two Cu(II) centres exhibit a distorted square pyramidal coordination geometry linked by two nitrogen donors from adenine bridges leading to a Cu-Cu distance of 3.242(3)Å. Intramolecular and intermolecular π⋯π interactions as well as an H-bonding network were observed. The antitumor capacity of the complex has been tested in vitro against human cancer cell lines, cervical carcinoma (HeLa) and colorectal adenocarcinoma (Caco-2), by metabolic tests, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide as reagent. The complex 1 has remarkable low IC50 values of 0.87±0.06μM (HeLa) and 0.44±0.06μM (Caco-2), when compared with values for cisplatin against the same cell lines. The interaction of complex 1 with calf thymus DNA (CT DNA) was further investigated by absorption and fluorescence spectroscopic methods. A binding constant of 5.09×10(5)M(-1) was obtained from UV-vis absorption studies.