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PubMed2003

Activation and functionalization of molecular nitrogen by metal complexes.

Molecular nitrogen is intrinsically unreactive, so much so that it has confounded chemists for decades in attempts to functionalize this abundant diatomic molecule. While biological systems and industrial processes can fix nitrogen to form ammonia, the challenge is to discover a process that involves a homogeneous catalyst that can utilize N(2) as a feedstock to generate higher value organonitrogen materials. In this review, the activation of molecular nitrogen by transition metal complexes is reviewed with the view to present new kinds of transformations for coordinated dinitrogen. Moreover, some reaction types that are as yet unknown are outlined to try and stimulate further research in this area.

Nitrogen↗
PubMed2004

Development of apatite-type oxide ion conductors.

Research into materials displaying oxide ion conductivity is attracting considerable attention due to their potential technological applications in devices such as Solid Oxide Fuel Cells. In this paper, recent work on apatite-type oxide ion conductors is reviewed, showing that a wide range of cation substitutions are possible, due to the flexibility of the apatite structure in accommodating a range of ion sizes. The conductivity studies on these doped samples show that to achieve high oxide ion conduction, non-stoichiometry in terms of cation vacancies and/or oxygen excess is required, with the latter resulting in the highest conductivities. In contrast to most common oxide ion conductors, e.g. perovskite and fluorite in which oxide ion conduction proceeds via oxygen vacancies, the research on these apatite systems suggests that the conductivity involves interstitial oxide ions. With further optimization of these materials, particularly in terms of the Ge-containing systems, significant improvements in conductivity are likely, leading to the very real possibility of the application of apatite-type electrolytes in fuel cell and other applications.

Apatites↗
PubMed2005

The surface chemistry of heterogeneous catalysis: mechanisms, selectivity, and active sites.

The role of chemical kinetics in defining the requirements for the active sites of heterogeneous catalysts is discussed. A personal view is presented, with specific examples from our laboratory to illustrate the role of the chemical composition, structure, and electronic properties of specific surface sites in determining reaction activity and selectivity. Manipulation of catalytic behavior via the addition of chemical modifiers and by tuning of the reaction conditions is also introduced.

Adsorption↗
PubMed2001

Group Theoretical Calculation for Infrared Spectra of Triatomic Molecules.

The rotation-vibration levels of the molecule COS are described using the model U(5). The transition matrix elements for the molecular levels are calculated by means of a group theoretical approach. The infrared absorption line intensities for the molecule COS are calculated. The results are in good agreement with the experimental values. Copyright 2001 Academic Press.

Journal Article↗
PubMedDate not supplied

Nuclear spin-lattice relaxation in transition metal alloys and intermetallics.

General analytical formulae describing the various contributions to the total spin-lattice relaxation rate in metallic materials (single crystals or powders) are presented. The formulae are obtained in the tight-binding approximation and can be easily used for any point-group symmetry. The cubic (O(h)), hexagonal (D(3h)), and tetragonal (D(2d)) symmetries are considered in detail.

Alloys↗
PubMed1996

Composite carcinoid-adenocarcinoma tumor of the stomach: report of a case.

We describe herein the case of an extremely unusual composite carcinoid-adenocarcinoma tumor of the stomach, most of which was found to be carcinoid. The carcinoid tumor component exhibited argyrophilic granules, immunohistochemical localization of chromogranin, and serotonin immunoreaction. Conversely, none of the adenocarcinoma component reacted with argyrophilia, chromogranin, or serotonin. DNA flow cytometric analysis revealed a near-diploid pattern in the carcinoid element and an aneuploid pattern in the adenocarcinoma element. The transitional zone and continuity between the two tumor components were observed. These findings suggest that the tumor originated from the endocrine system, although part of it showed nonendocrine differentiation. The patient died approximately 6 months after the onset of symptoms and an autopsy could not be performed.

Adenocarcinoma↗
PubMed2002

Does the anaerobic formation of hydroxyl radicals by paraquat monocation radicals and hydrogen peroxide require the presence of transition metals?

This in vitro study investigated the formation of hydroxyl radicals (*OH) under anaerobic conditions through the direct reaction between paraquat radicals (PQ(+)*) and hydrogen peroxide (H(2)O(2)) by quantitative UV-VIS and electron spin resonance (ESR) spectroscopy. PQ(+)* was formed by paraquat reduction using either sodium dithionite or the xanthine/xanthine oxidase reaction as electron donors. The anaerobic formation of PQ(+)* was quantified both by measuring light absorption at 605 nm or by ESR techniques respectively, using either the absorption coefficient or ultramarine as a stable spin standard. Detection of *OH took place with aid of the spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline- N-oxide (DEPMPO). Generation or addition of H(2)O(2) to PQ(+)* eliminates the 35-line ESR signal of PQ(+)* and subsequently generates the 8-line ESR signal of the DEPMPO-OH adduct. The elimination of PQ(+)* as well as the formation of OH-DEPMPO adduct was not influenced by 1.0 mM deferoxamine, indicating that iron or other transition metals are, at least under anoxic conditions, not necessarily involved in the generation of the most aggressive reactive oxygen species *OH.

Anaerobiosis↗
PubMed2002

Onset of cataract in early infancy associated with a 32G-->C transition in the iron responsive element of L-ferritin.

UNLABELLED: We describe the onset of cataract in early infancy in a family with hereditary hyperferritinaemia-cataract syndrome. The two probands presented with isolated hyperferritinaemia and had developed cataracts at the age of 18 months. Two members of their family with high ferritin levels (1270-1450 microg/l) had suffered from cataract since childhood. The mutation responsible was a 32G-->C change in the lateral bulge of the stem structure of the iron responsive element of the L-ferritin subunit gene. Mutations at this level cause particularly high ferritin levels, whereas the age of cataract onset and its severity are controversial subjects. In our family, early ophthalmic examination ruled out the possibility that cataract was due to age-related persistence of high ferritin levels in the lens and suggested that other factors may modulate the phenotype. CONCLUSION: cataract may appear early in hereditary hyperferritinaemia-cataract syndrome and this syndrome should be suspected and ferritin levels measured in all cases of cataract in children, even when the onset is in early infancy.

Adolescent↗
PubMed2005

Binding of transition metal complexes to guanine and guanine-cytosine: hydrogen bonding and covalent effects.

Density functional calculations and Atoms in Molecules analysis are used to investigate the role of covalent and hydrogen bondings in determining the binding of transition metal complexes to guanine, and the subsequent effect on pairing with cytosine. Hydrogen bonding is ubiquitous, and typically contributes ca. 10% to overall binding, a value that varies with the coordination site on guanine, as well as metal and ligands. Early transition metals show a clear preference for the O6 position, while later ones prefer N7, the crossover point coming at the vanadium group. Metallation at N7 causes a redistribution of hydrogen bonding strength between guanine and cytosine, but does not greatly affect the overall pairing energy. In contrast, metallation at O6 strongly reduces the pairing energy, as may be expected given the role of O6 in pairing guanine with cytosine. This effect can be quantified using electron density properties, and seems to be due to both electrostatic repulsion from the positive metal centre and a redistribution of electron density within guanine itself. Qualitative agreement with experimental mass spectroscopic results is obtained.

Base Pairing↗
PubMed2006

Transition metal complexes as mediator-titrants in protein redox potentiometry.

A selection of nine macrocyclic Fe(III/II) and Co(III/II) transition metal complexes has been chosen to serve as a universal set of mediator-titrants in redox potentiometry of protein samples. The potential range spanned by these mediators is approximately from +300 to -700 mV vs the normal hydrogen electrode, which covers the range of most protein redox potentials accessible in aqueous solution. The complexes employed exhibit stability in both their oxidized and their reduced forms as well as pH-independent redox potentials within the range 6 < pH < 9. The mediators were also chosen on the basis of their very weak visible absorption maxima in both oxidation states, which will enable (for the first time) optical redox potentiometric titrations of proteins with relatively low extinction coefficients. This has previously been impractical with organic mediators, such as indoles, viologens and quinones, whose optical spectra interfere strongly with those of the protein.

Cobalt↗
PubMed2006

Natural orbitals for chemical valence as descriptors of chemical bonding in transition metal complexes.

Natural orbitals for chemical valence (NOCV) are defined as the eigenvectors of the chemical valence operator defined by Nalewajski et al.; they decompose the deformation density (differential density, Deltarho) into diagonal contributions. NOCV were used in a description of the chemical bond between the organometallic fragment and the ligand in example transition-metal complexes: heme-CO ([FeN(5)C(20)H(15)]-CO), [Ni-diimine hydride]-ethylene ([N;N-Ni-H]-C(2)H(4), N;N = -NH-CH-CH-NH-), and [Ni(NH(3))(3)]-CO. DFT calculations were performed using gradient-corrected density functional theory (DFT) in the fragments resolution, using the fragment/ligand Kohn-Sham orbitals as a basis set in calculations for the whole fragment-ligand complex. It has been found that NOCV lead to a very compact description of the fragment-ligand bond, with only a few orbitals exhibiting non-zero eigenvalues. Results of NOCV analysis, compared with Mulliken populations analysis and Zigler-Rauk interaction-energy decomposition, demonstrate that the use of the natural valence orbitals allows for a separation of the sigma-donation and pi-back-donation contributions to the ligand-fragment bond. They can be also useful in comparison of these contributions in different complexes.

Metals↗
PubMed2004

Production of electrical energy from carbohydrates using a transition metal-catalysed liquid alkaline fuel cell.

Biomass may be converted to energy by enzymatic hydrolysis to monomer components and fermentative conversion of those products to ethanol for use as fuel. Both glucose and xylose in aqueous solution were directly converted to electrical energy using a liquid alkaline fuel cell (AFC) at room temperature. Hydrolysis products derived from the action of cellulase and amylase on cellulose and starch, respectively, were also used as fuels in the AFC system. We suggest that this approach may provide a more direct means of accessing some of the energy available from biomass.

Alkalies↗
PubMed2006

Transition metal-mediated liposomal encapsulation of irinotecan (CPT-11) stabilizes the drug in the therapeutically active lactone conformation.

PURPOSE: To determine whether entrapped transition metals could mediate the active encapsulation of the anticancer drug irinotecan into preformed liposomes. Further, to establish that metal complexation could stabilize liposomal irinotecan in the therapeutically active lactone conformation. MATERIALS AND METHODS: Irinotecan was added to preformed 1,2-distearoyl-sn-glycero-phosphocholine/cholesterol (DSPC/chol) liposomes prepared in CuSO4, ZnSO4, MnSO4, or CoSO4 solutions, and drug encapsulation was determined over time. The roles of the transmembrane pH gradient and internal pH were evaluated. TLC and HPLC were used to monitor drug stability and liposome morphology was assessed by cryo-TEM. RESULTS: Irinotecan was rapidly and efficiently loaded into preformed liposomes prepared in unbuffered (approximately pH 3.5) 300 mM CuSO4 or ZnSO4. For Cu-containing liposomes, results suggested that irinotecan loading occurred when the interior pH and the exterior pH were matched; however, addition of nigericin to collapse any residual transmembrane pH gradient inhibited irinotecan loading. Greater than 90% of the encapsulated drug was in its active lactone form and cryo-TEM analysis indicated dark intravesicular electron-dense spots. CONCLUSION: Irinotecan is stably entrapped in the active lactone conformation within preformed copper-containing liposomes as a result of metal-drug complexation.

Antineoplastic Agents, Phytogenic↗
PubMed1975

Electron microscopy of the placenta and related structures of the marmoset.

The marmoset has recently become an important animal in oncologic research, especially with respect to herpes deoxyribonucleic acid viral tumors. As a prototype of the primitive New World monkey, it is also valuable for the study of primate evolution. For these reasons this ultrastructural description of its placenta is presented, including the first electron micrographs of the basal plate and amnion. The main placental mass is pseudo-labyrinthine, or trabecular. The ultrastructural features of the cellular and syncytial trophoblast and endothelium closely resemble those of higher primates. The junctional region shows numerous clumps of moderately well-differentiated trophoblast, an acellular junctional zone, and a poorly developed decidual reaction. Trabecular connective tissue is sparser and transitional trophoblastic elements are less prominent than those in the human placenta. The amnion is ultrastructurally indistinguishable from that of the higher primates. Although the marmoset's placenta retains certain primitive gross and histologic features, such as the large persistent yolk sac and the trabecular condition, it is ultrastructurally quite similar to that of man.

Amnion↗
PubMed2004

A high-performance liquid chromatography method for determining transition metal content in proteins.

Transition metals are common components of cellular proteins and the detailed study of metalloproteins necessitates the identification and quantification of bound metal ions. Screening for metals is also an informative step in the initial characterization of the numerous unknown and unclassified proteins now coming through the proteomic pipeline. We have developed a high-performance liquid chromatography method for the quantitative determination of the most prevalent biological transition metals: manganese, iron, cobalt, nickel, copper, and zinc. The method is accurate and simple and can be adapted for automated high-throughput studies. The metal analysis involves acid hydrolysis to release the metal ions into solution, followed by ion separation on a mixed-bead ion-exchange column and absorbance detection after postcolumn derivatization with the metallochromic indicator 4-(2-pyridylazo)resorcinol. The potential interferences by common components of protein solutions were investigated. The metal content of a variety of metalloproteins was analyzed and the data were compared to data obtained from inductively coupled plasma-atomic emission spectroscopy. The sensitivity of the assay allows for the detection of 0.1-0.8 nmol, depending on the metal. The amount of protein required is governed by the size of the protein and the fraction of protein with metal bound. For routine analysis 50 microg was used but for many proteins 10 microg would be sufficient. The advantages, disadvantages, and possible applications of this method are discussed.

Animals↗
PubMed2005

Reference assignment: using language breakdown to choose between theoretical approaches.

We report results of an experimental study with Dutch agrammatic aphasics that investigated their ability to interpret pronominal elements in transitive clauses and Exceptional Case Marking constructions (ECM). Using the obtained experimental results as a tool, we distinguish between three competing linguistic theories that aim at determining principles responsible for pronoun distribution: Government and Binding (Chomsky, 1981), Reflexivity (Reinhart & Reuland, 1993), and Primitives of Binding (Reuland, 2001). The obtained results are inconsistent with Government and Binding, but consistent with the latter two theories. We further show that the Primitives of Binding framework most naturally explains our results. Our proposal is based on the different performance demonstrated by patients in transitive clauses and ECM constructions, in combination with the often-made claim in the literature regarding the limitation of processing resources in this population (e.g., Haarmann and Kolk, 1991, Haarmann and Kolk, 1994 and Zurif et al., 1993, among others).

Adult↗