SEARCH · PubMed Health

Results for “Transition Elements”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources

PubMed2006

High-valent transition metal corrolazines.

High-valent metalloporphyrin intermediates have been implicated as key players in numerous mechanistic proposals for both biological (e.g., heme protein) and synthetic porphyrin mediated transformations. However, the direct observation of these species is quite challenging because of the inherently short lifetimes of many of these metalloporphyrin intermediates. This review focuses on our own efforts to synthesize and study a new class of porphyrinoid compounds called corrolazines, which are designed to stabilize high-valent species for direct analysis. These compounds are related to corroles, which also exhibit the unusual ability to stabilize high oxidation states, and the reactivity and physical properties of relevant corrole and porphyrin analogs are compared with the appropriate corrolazines. The chemistry of Cu, Co, V, and Mn are highlighted, with a particular emphasis on the reactivity of high-valent manganese-oxo complexes.

Cobalt↗

PubMed2006

Transition metal complexes of terminally protected peptides containing histidyl residues.

Histidine-containing peptide fragments of prion protein are efficient ligands to bind various transition metal ions and they have high selectivity in metal binding. The metal ion affinity follows the order: Pd(II)>>Cu(II)>>Ni(II)Zn(II)>Cd(II) approximately Co(II)>Mn(II). The high selectivity of metal binding is connected to the involvement of both imidazole and amide nitrogen atoms in metal binding for Pd(II), Cu(II) and Ni(II), while only the monodentate N(im)-coordination is possible with the other metal ions. The stoichiometry and binding mode of palladium(II) complexes show great variety depending on the metal ion to ligand ratio, pH and especially the presence of coordinating donor atoms in the side chains of peptide fragments. It is also clear from our data that the peptide fragments containing histidine outside the octarepeat (His96, His111 and His187) are more efficient ligands than the monomer peptide fragments of the octarepeat domain.

Animals↗

PubMed2006

Synthesis, crystal structures and cytotoxicities of some transition metal complexes with N-[2-{(pyridin-2-ylmethylidene)amino}ethyl]acetamide.

The synthesis and spectroscopic (IR, (1)H and (13)C NMR) characterization of new complexes of Pt(II), Pd(II), Cu(II), and Hg(II) with the Schiff base ligand MeCONHCH(2)CH(2)N=CHPy (L) (Py=pyridine) are reported, together with studies on the cytotoxicities of these complexes, L and [ReBr(CO)(3)(L)] against human leukemia (MOLT-4), breast cancer (MCF-7) and Chang Liver (non-cancerous) cells. The crystal structures of [Pt(L)Cl(2)] (2), [Cu(L)Cl(2)] (4) and [Hg(L)Cl(2)](2) (5) are also reported. Of the complexes studied, [Cu(L)Cl(2)] (4) was identified as the most cytotoxic active derivative against cells of neoplastic origin (MOLT-4, and MCF-7), while having low toxicity on cells of benign origin (Chang Liver).

Acetamides↗

PubMed2005

Application of constant-current coulometry for estimation of plasma total antioxidant capacity and its relationship with transition metal contents.

Simple and express coulometric method for the evaluation of the total antioxidant capacity (TAC) of human plasma based on the reaction with electrogenerated bromine is applied. TAC of plasma from patients with different ethiology of chronic renal failure was observed. The levels of antioxidant capacity for venous and arterial plasma are authentically different (15+/-1 kCl/L versus 11.7+/-0.7 kCl/L, p<0.01). The application of Vitamin E and ximedon as an antioxidant treatment significantly increase TAC level of plasma. Free liposoluble antioxidants in plasma in alpha-tocopherol units was determined. Redox potential of plasma is measured and its correlation with lg(TAC) is obtained. Transition metal contents of Fe, Cu, Mn, Ni, and Cr in plasma of patients with chronic renal failure is significantly higher than that for a control group. Correlation analysis has shown negative linear regression between TAC value and transition metals concentration in plasma. This confirms interrelation of processes with participation of free radicals, antioxidants and transition metals as donors of electrons in chain radical processes. Moreover, it shows utility of common parameters, TAC for example, for estimation of efficiency of antioxidant defense system in living organism, in particular its antioxidant status.

Adult↗

PubMed2004

Transition metal transport in the green microalga Chlamydomonas reinhardtii--genomic sequence analysis.

Uptake and export systems play a major role in transition metal homeostasis. The objective of this study was to identify potential metal transport mechanisms in the green microalga Chlamydomonas reinhardtii. We concentrated on the four major transition metal transporter families found in plants and other organisms: the ZIP, CDF and Nramp families, and the CPx-ATPases. Using the information available for these protein families we performed comparative sequence analysis in the recently released genome of C. reinhardtii. Using this approach we were able to identify members of all four transporter families (four ZIPs, one CDF, two CPx-ATPases, and five Nramps). These findings advance our current knowledge of the metal transport processes present in C. reinhardtii. In addition, by subsequent in silico splicing of the genomic sequence we obtained cDNA sequences which led to the identification of ESTs (expressed sequence tags) in the C. reinhardtii EST database. These identified ESTs will be valuable for the cloning and characterization of several metal transporters utilized by the alga.

Amino Acid Sequence↗

PubMed2004

Stereochemistry of new nitrogen containing heterocyclic aldehyde. Part XI. Novel ligational behaviour of quinoline as chelate ligand toward transition metal ions.

Novel complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and UO2(II) with a new Schiff base derived from 8-hydroxy-7-quinolinecarboxaldehyde and 2-aminoethanethiol (LH2) (system name: 2-(8-hydroxy-7-carboxalimino)ethanethiol.) have been prepared and characterized on the basis of analytical, thermal, magnetic moment, infrared, electronic, NMR and EPR spectral data. From the analytical, NMR and thermal data and stoichiometry of the complexes indicate that LH2 act as a dibasic tridentate ligand with ONS donors towards all the metal ions. The magnetic moment, electronic and EPR spectral data commensurate that the Mn(II), Fe(II), Ni(II) and UO2(II) complexes are dimeric with octahedral configuration while the Cu(II) and Zn(II) complexes are monomeric with square-planar and tetrahedral geometries, respectively. Various ligand field parameters Dq, B and beta for complex 5 was calculated. The complexes 3+4 have lower symmetries and the amount of distortion in terms of DT/DQ applying NSH "Hamiltonian Theory" has been evaluated which indicate that the complexes are moderately distorted.

Aldehydes↗

PubMed2005

Characterisation of prehnite by EPMA, Mössbauer, optical absorption and EPR spectroscopic methods.

A sample of prehnite from Rayalaseema zone of Andhra Pradesh, India containing about 2.565 wt.% Fe(2)O(3) is used in the present work. The mineral has been characterized by EPMA, optical absorption, EPR, NIR and Mössbauer techniques. Mössbauer studies confirm the presence of iron as an impurity in two sites. An EPR study on powder sample confirm the presence of Fe(III) impurity in the mineral. Optical absorption spectrum also indicates that Fe(III) impurity is present in two sites with octahedral structure. NIR results are due to water fundamentals.

Aluminum Silicates↗

PubMed2006

Synthesis and thermal characterization of new ternary chelates of piroxicam and tenoxicam with glycine and DL-phenylalanine and some transition metals.

The ternary chelates of piroxicam (Pir) and tenoxicam (Ten) with Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) in the presence of various amino acids such as glycine (Gly) or dl-phenylalanine (PhA) were prepared and characterized with different physicochemical methods. IR spectra confirm that Pir and Ten behave as a neutral bidentate ligand coordinated to the metal ions via the pyridine-N and carbonyl group of the amide moiety. Gly molecule acted as a uninegatively monodentate ligand and coordinate to the metal ions through its deprotonated carboxylic group. In addition, PhA acted as a uninegatively bidentate ligand and coordinate to the metal ions through its deprotonated carboxylic and amino groups. The solid reflectance spectra and magnetic moment measurements confirm that all the chelates have octahedral geometrical structures while Cu(II)- and Zn(II)-ternary chelates with PhA have square planar geometrical structures. Thermal behaviour of the complexes is extensively studied using TG and DTA techniques. TG results show that water molecules (hydrated and coordinated) and anions are removed in the first and second steps while Gly, PhA, Pir and Ten are decomposed in the next and subsequent steps. The pyrolyses of the chelates into different gases are observed in the DTA curves as exo- or endothermic peaks. Also, phase transition states are observed in some chelates. Different thermodynamic parameters are calculated using Coats-Redfern method and the results are interpreted.

Chelating Agents↗

PubMed2005

Structural characterization of tellurite glasses doped with transition metal oxides using Raman spectra and ab initio calculations.

Systems of iron tellurite glasses were prepared by melt quenching with compositions of [85%TeO2+5%Fe2O3+10%TMO], where transition metal oxides (TMO) are TiO2, V2O5, MnO, CoO, NiO and CuO. Furthermore, the main structural units of these samples have been characterized by means of Raman spectra (150-1200 cm(-1)) as well as wavenumber predictions by means of Gaussian 98 ab initio calculations for the proposed site symmetries of TeO4(4-) triagonal bipyramid (C2v) and Te2O7(6-) bridged tetrahedra (Cs and C1). Aided by normal coordinate analysis, calculated vibrational frequencies, Raman scattering activities, force constants in internal coordinates and potential energy distributions (PEDs), revised vibrational assignments for the fundamental modes have been proposed. The main structural features are correlated to the dominant units of triagonal bipyramid (tbp) or bridged tetrahedral (TeO3+1 binds to TeO3 through TeOTe bridge; corner sharing). Moreover, the Raman spectra of the investigated tellurites reflect a structural change from tbp (coordination number is four) to triagonal pyramidal (coordination number is three).

Glass↗

PubMed2006

Spectral and thermal studies of divalent transition metal with indole-2-carboxylic acid and 4-substituted hydrazinethiocarbamide.

Ternary complexes of Co(II), Ni(II) and Cu(II) with indole-2-carboxylic acid (A) and 4-substituted hydrazinethiocarbamide (L) [4-phenylhydrazinethiocarbamide (L(1)), 4-benzylhydrazinethiocarbamide (L(2)) and 4-(2-propenyl)hydrazinethiocarb-amide (L(3)) were prepared. The structure of the complexes was characterized by microchemical analysis, molar conductance, electronic, IR, (1)H-NMR, mass spectra as well as thermogravimetric studies. An octahedral structure is suggested for Co(II), Ni(II) and Cu(II) ternary complexes.

Carboxylic Acids↗

PubMed2006

Fourier transform infrared spectra of transition metal ion-containing polyanilines synthesized in different reaction conditions.

Fourier transform infrared spectroscopy has been employed to investigate the detailed chain structure changes during the chemical oxidative polymerisation of aniline in different reaction conditions including different polarity reaction medium, reaction temperature, reactants molar ratio and in the presence of different transition metal ions such as Fe2+, Co2+, Ni2+ and Cu2+. The results show that stronger polarity reaction medium and lower reaction temperature were beneficial to obtain 1,4-para-disubstituted linear chain structure polyaniline with higher electrical conductivity. The higher oxidation degree polyaniline contained more linear chain structure than that in lower oxidation degree. Polyanilines containing Fe2+ and Cu2+ had more linear chain structure than that containing Co2+ and Ni2+. These observations were in accordance with experimental measurements of electrical conductivity.

Aniline Compounds↗

PubMed2006

Studies on some salicylaldehyde Schiff base derivatives and their complexes with Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II).

The formation constants of some transition metal ions Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II) binary complexes containing Schiff bases resulting from condensation of salicylaldehyde with aniline (I), 2-aminopyridine (II), 4-aminopyridine (III) and 2-aminopyrimidine (IV) were determined pH-metrically in ethanolic medium (80%, v/v). The formation constants were determined for all binary complexes. The important infrared (IR) spectral bands corresponding to the active groups in the four ligands and the solid complexes under investigation were studied. The solid complexes have been synthesized and studied by thermogravimetric analysis. The thermal dehydration and decomposition of these complexes were studied kinetically using the integral method applying the Coats-Redfern equation. It was found that the thermal decomposition of the complexes follow second order kinetics. The thermodynamic parameters of the decomposition are also reported. The electronic absorption spectra of the investigated ligands were carried out to determine the pK(a) values spectrophotometrically.

4-Aminopyridine↗

PubMed2006

Polynuclear transition metal complexes with thiocarbohydrazide and dithiocarbamates.

Sn(tch)2{MCl2}2 was prepared from the precursor Sn(tch)2 and MCl2. It was subsequently allowed to react with diethyldithiocarbamate which yielded the trinuclear complexes of the type Sn(tch)2{M2(dtc)4}, where tch=thiocarbohydrazide, M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and dtc=diethyldithiocarbamate. They were characterized on the basis of microanalytical, thermal (TGA/DSC), spectral (IR, UV-vis, EPR, (1)H NMR) studies, conductivity measurement and magnetic moment data. On the basis of spectral data a tetrahedral geometry has been proposed for the halide complexes, Sn(tch)2{MCl2}2 except for Cu(II) which exhibits a square planar coordination although the transition metal ion in Sn(tch)2{M2(dtc)4} achieves an octahedral geometry where the dithiocarbamato moiety acts as a symmetrical bidentate ligand. The bidentate nature has been established by the appearance of a sharp single nu(C-S) around 1000 cm(-1). A downfield shift observed in NH(a) and NH(b) protons on moving from Sn(tch)2 to Sn(tch)2{MCl2}2 is due to the drift of electrons toward metal atoms. A two-step pyrolysis has been observed in the Sn(tch)2{MCl2}2 complexes while their dithiocarbamato derivatives exhibit a three-stage degradation pattern. Finally, the in vitro antibacterial activity of Sn(tch)2{M2(dtc)4} and the mononuclear Sn(tch)2 has been carried out on bacterial strains Escherichia coli and Salmonella typhi. The compounds were found to be active against the test organisms. The activity of the complexes is enhanced with increasing concentration. The maximum activity in both the strains was achieved by cobalt(II) dithiocarbamate complex. Minimum activity was found for Sn(tch)2 which generally increases with the introduction of transition metal ion in the complex.

Anti-Bacterial Agents↗

PubMed2006

Theoretical investigation of the molecular, electronic structures and vibrational spectra of a series of first transition metal phthalocyanines.

A theoretical investigation of the fully optimized geometries and electronic structures of metallophthalocyanines FePc, CoPc, NiPc, CuPc and ZnPc has been conducted with the density functional theory (DFT) method. A comparison between the different molecules for the geometry, molecular orbital, and atomic charge is made. The simulated order of the sizes of the central hole is FePc>CoPc>NiPc NiPc>CuPc>ZnPc, and the atomic charges of the central metal (M=Fe, Co, Ni, Cu, Zn) ions vary in the same order, FePc>CoPc>NiPc CoPc>FePc>CuPc>ZnPc, and the corresponding peaks predicted at 894, 896, 898, 882 and 871 cm(-1), respectively, also exhibit the same order as above-mentioned. Moreover, the lines of fit through plots of the experimental IR and Ra frequencies versus the calculated ones show very good correlations.

Electrons↗

PubMed2005

Soluble transition metals in welding fumes cause inflammation via activation of NF-kappaB and AP-1.

We previously reported that the molecular pro-inflammatory effects of welding fumes in vitro were caused by soluble transition metals via an oxidative stress-mediated mechanism. Herein, we tested the hypothesis that transition metals in welding fume drive the in vivo inflammatory response caused by welding fume. Rats were instilled with either whole, soluble extract or washed welding fume particulates or soluble extracts pre-treated with a transition metal chelator. Markers of pulmonary inflammation were measured in the bronchoalveolar lavage fluid (BALF) and nuclear translocation of transcription factor was assessed in BAL cells by electrophoretic mobility shift assay. Instillation of either whole or soluble fractions of welding fume caused a significant influx of inflammatory cells and other markers of inflammation in the BALF 24 h later. MIP-2 protein in BALF and nuclear translocation of NF-kappaB and AP-1 were significantly greater following instillation of whole and soluble fractions than in saline-instilled lungs. Chelation of the soluble fraction, to remove transition metals, abolished the ability to cause inflammation, MIP-2 increase or transcription factor translocation to the nucleus. Instillation of washed particulates alone caused no significant change in any end-point compared to saline. This study demonstrates that soluble transition metals present in welding fumes cause inflammation via activation of the redox-sensitive transcription factors NF-kappaB and AP-1 and confirms the validity of utilising in vitro models to assess inflammatory responses to such particles.

Animals↗

PubMed2005

Ultrasound supported catalysis.

An overview on the application of ultrasound in several chemical reactions is given. Ultrasound is used in the preparation of catalysts for various reactions, i.e. dehydration reactions. The beneficial effect of ultrasound results in clean reactions and short reaction times. Criteria for scale-up are also discussed.

Catalysis↗

PubMed1981

Hemoglobin-carbon monoxide binding rate. Low temperature magneto-optical detection of spin-tunneling.

The spin-tunneling model of Hb--CO binding is used to calculate the binding rate at low temperature and high magnetic fields. The rate is calculated in second order perturbation theory assuming that spin-orbit coupling mediates the Hb iron electronic state change. The reaction which occurs at the crossing of the S = 2 and S = 0 energy vs. configuration coordinate curves is nonadiabatic, having a small electronic transition matrix element. Since detection of CO binding by polarized light in the Soret band makes it possible to observe hemes at specific orientation to the field direction, the rate is calculated for arbitrary heme orientation. Comparison with measurements at low temperature in zero field is made for spin quantization along the molecular crystal field direction.

Carboxyhemoglobin↗

PubMed2003

The association of expired nitric oxide with occupational particulate metal exposure.

Toxicologic studies have shown that soluble transition metals in residual oil fly ash (ROFA) can induce pulmonary injury. In this study, we investigated the association between the fractional concentration of expired nitric oxide (FENO) and exposure to metal constituents of particulate matter with an aerodynamic mass median diameter < or =2.5 microm (PM2.5) in boilermakers exposed to ROFA and metal fume. Metals investigated included vanadium, chromium, manganese, nickel, copper, and lead. Subjects were monitored for 5 consecutive days during boiler repair overhauls in 1999 (n=20) and 2000 (n=14). In 1999, we found a significant inverse association between log-transformed FENO and PM2.5 metal concentrations. LogFENO changed by -0.03 (95% CI: -0.04, -0.01), -0.56 (95% CI: -0.88, -0.24), -0.09 (95% CI: -0.16, -0.02), and -0.04 (95% CI: -0.07, -0.02) per microg/m3 of PM2.5 vanadium, chromium, manganese, and nickel, respectively. In 2000, no significant associations were observed, most likely due to exposure misclassification resulting from the use of respirators. The inverse association between PM2.5 metal exposure and FENO in subjects with limited respirator usage suggests that soluble transition metals might be partially responsible for the adverse pulmonary responses seen in workers exposed to ROFA.

Adolescent↗