PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “ATOM complex”

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 1,045 records · Page 58Linked to original sources
PubMed1982

Determination of nitrate content in whey and milk powders at a dairy after an occupational accident with nitric acid.

A case of accidental occupational intoxication by fumes of nitrogen oxides and the application of an indirect method for the analysis of nitrate, nitrite, and nitro groups to establish the origin of the intoxication are presented. The method is based on the formation of a copper neocuproine complex, and extraction of the complex with methyl isobutyl ketone. The amount of copper in the organic phase is directly proportional to the nitrate content. This copper complex is determined by atomic absorption spectrophotometry. The results, which showed that samples from the contaminated workroom contained 0.1-0.2% nitrate, while blanks contained less than 0.02%, strongly support the hypothesis proposed for the course of the accident.

Accidents, Occupational↗
PubMed1992

Serine proteinase inhibition by the cyclic thiolic compound YS3025: a crystallographic study.

In order to unravel the serine proteinase inhibition mechanism by cyclic thiolic compounds, the X-ray crystal structure of bovine alpha-chymotrypsin inhibited by 3-[2-(2-thiophencarboxythio)]-propanoyl-4-thioazolidin carboxylic acid (YS3025) has been studied by means of difference Fourier techniques and refined at 2.8 A resolution (R-factor = 0.174). The thiophencarbonyl moiety of YS3025 is covalently linked, in the acyl-enzyme complex, to Ser195 OG atom of bovine alpha-chymotrypsin, and located at the entrance of the proteinase primary specificity subsite (S1). The present data confirm previous hypotheses raised on the inhibition mechanism of serine proteinases, based on solution studies of human leukocyte elastase in the presence of the YS3025 parent compound 2-[3-thiophencarboxythio]-N-[dihydro-2(3H)- thiophenone-3-il]-propionamide (MR889).

Binding Sites↗
PubMed1995

Bion's use of modern logic.

This paper introduces the reader to modern logic, more particularly the branch of logic called 'Model Theory', which is extensively used by Bion. Logic today is no longer described as the study of 'valid inference', but rather by the notion of consistency of beliefs. This central concern of the logician with consistency is also seen to be that of the psychoanalyst when he aims for eventual resolution of conflict between a patient's contradictory beliefs. Models are explained as the use of the already familiar to explain the unfamiliar, as when, for example, we invoke our familiar planetary system to understand the complex structure of the atom. In psychoanalysis we seek to find the old childhood models underpinning a patient's contemporary model of himself and others. Thus both Model Theory and psychoanalysis are interested in how we 'see the new in terms of the old'. Finally, the creation of models is assimilated to the integrative tendency of depressive activity and the dissolving or collapsing of models linked to paranoid-schizoid activity. As these two processes in the individual are linked by Bion we can see human beings as continually oscillating between creating and destroying models of their inner and outer worlds.

Humans↗
PubMed2005

Theoretical study of main-group metal-borazine sandwich complexes.

Using density functional theory within the generalized gradient approximation, we have theoretically studied the formation of neutral metal-aromatic complexes R1-M and R1-M-R2, where M is either neutral lithium, calcium, or gallium and R1 or R2 is benzene or borazine. We first find that calcium atom is an effective mediator for cooperative formation of a sandwich complex with borazine, while others are not. When benzene and borazine are mixed in the presence of calcium, a 1:2:1 mixture of benzene-calcium-benzene, borazine-calcium-benzene, and borazine-calcium-borazine is expected. An "A"-shaped structure is predicted for homo- and heterocomplexes of borazine with partial B-B and B-C bonds, while two rings are planar in the case of homocomplexes of benzene. Our analysis of the electron density distributions in HOMO-1 to LUMO in terms of orbital symmetry in conjunction with analysis of l,m-projected electronic local density of states shows that this correlates with the charge transfer and the interaction of pi states of the rings mediated by empty d-states of Ca, which is ultimately related to the polarity of the B-N bond. We find that there is a large accumulation of electron density on particular atoms upon complex formation, predicting characteristic behavior in electron-transfer reaction and nucleophilic reaction different from those for pure benzene or borazine molecule. The hetero-sandwich complex is of particular interest due to its asymmetrical distribution of excess electrons.

Journal Article↗
PubMed2003

Dynamics and entropy of a calmodulin-peptide complex studied by NMR and molecular dynamics.

All-atom, explicit water molecular dynamics simulations of calcium-loaded calmodulin complexed with a peptide corresponding to the smooth muscle myosin light chain kinase target were carried out at 295 and 346 K. Amide and side chain methyl angular generalized order parameters were calculated and analyzed in the context of the protein's structure and dynamics. The agreement between amide order parameters measured by NMR and those from the simulations was found to be good, especially at the higher temperature, indicating both better convergence for the latter and excellent transferrability of the CHARMM parameters to the higher temperature. Subtle dynamical features such as helix fraying were reproduced. A large range of order parameters for the nine calmodulin methionines was observed in the NMR, and reproduced quite well in the simulations. The major determinant of the methionine order parameter was found to be the proximity to side chains of aromatic residues. An upper bound estimate of the difference in backbone entropy between loop and helical regions was extracted from the order parameters using a model of motion in an effective potential. Although loop regions are more flexible than helical regions, it was found that the entropy loss per residue upon folding was only approximately 20% less for loops than for helices. Pairwise correlated motions, which could significantly lower entropy estimates obtained from order parameter analysis alone, were found to be largely absent.

Amides↗
PubMedDate not supplied

[A stereochemical model for DNA-Na+ (H20) complex].

By computer calculation with the use of atom-atom potentials a stereochemical model of the DNA-hydrate Na+ complex was obtained according to which the Na+(H2O)6 octahedrons are localized in the narrow groove of DNA with formation of a great number of van der vaals contacts and hydrogen bonds. The model explains why the C-form of DNA is stabilized in the Na-DNA complex which is formed in the presence of 80% methanol (v/v). A possibility of the existence of such complexes in vivo at the DNA regions surrounded with media of diminished water activity (the DNA-membrane complex, chromosomes, phage heads) is discussed.

Binding Sites↗
PubMed2004

The electron conduction of photosynthetic protein complexes embedded in a membrane.

The conductivity of two photosynthetic protein-pigment complexes, a light harvesting 2 complex and a reaction center, was measured with an atomic force microscope capable of performing electrical measurements. Current-voltage measurements were performed on complexes embedded in their natural environment. Embedding the complexes in lipid bilayers made it possible to discuss the different conduction behaviors of the two complexes in light of their atomic structure.

Bacterial Proteins↗
PubMed1996

Influence of the Peripheral Ligand Atoms on the Exchange Interaction in Oxalato-Bridged Nickel(II) Complexes: An Orbital Model. Crystal Structures and Magnetic Properties of (H(3)dien)(2)[Ni(2)(ox)(5)].12H(2)O and [Ni(2)(dien)(2)(H(2)O)(2)(ox)]Cl(2).

Two nickel(II) complexes of formula (H(3)dien)(2)[Ni(2)(ox)(5)].12H(2)O (1) and [Ni(2)(dien)(2)(H(2)O)(2)(ox)]Cl(2) (2) (dien = diethylenetriamine and ox = oxalate dianion) have been synthesized and characterized by single-crystal X-ray diffraction. 1 crystallizes in the orthorhombic system, space group Abnn, with a = 15.386(4) Å, b = 15.710(4) Å, c = 17.071(4) Å, and Z = 4. 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.579(1) Å, b = 7.258(1) Å, c = 13.326(1) Å, beta = 93.52(3) degrees, and Z = 2. The structures of 1 and 2 consist of dinuclear oxalato-bridged nickel(II) units which contain bidentate oxalate (1) and tridentate dien in the fac-conformation (2) as terminal ligands. Both features, oxalato as a peripheral ligand and dien in the fac-conformation (instead of its usual mer-conformation), are unprecedented in the coordination chemistry of nickel(II). The nickel atom is six-coordinated in both compounds, the chromophores being NiO(6) (1) and NiN(3)O(3) (2). The Ni-O(ox) bond distances at the bridge (2.072(4) Å in 1 and 2.11(1) and 2.125(9) Å in 2) are somewhat longer than those concerning the terminal oxalate (2.037(5) and 2.035(3) Å in 1). Magnetic susceptibility data of 1 and 2 in the temperature range 4.2-300 K show the occurrence of intramolecular antiferromagnetic coupling with J = -22.8 (1) and -28.8 (2) cm(-)(1) (J being the parameter of the exchange Hamiltonian H = -JS(A).S(B)). The observed value of -J in the investigated oxalato-bridged nickel(II) complexes, which can vary from 22 to 39 cm(-)(1), is strongly dependent on the nature of the donor atoms from the peripheral ligands. This influence has been analyzed and rationalized through extended Hückel calculations.

Journal Article↗
PubMed1990

Evidence for multinuclear metal-ion complexes at solid/water interfaces from X-ray absorption spectroscopy.

Metals dissolved in natural waters often become sorbed onto oxide or clay minerals, so that prediction of their chemical behaviour and transport properties requires knowledge of the structure and bonding of metal species at the solid/water interface. For many sorption systems, X-ray absorption spectroscopy (XAS) can be used to determine the identity and number of nearest-neighbour atoms and interatomic distances in aqueous complexes on solid surfaces, and thus to identify the dominant type of surface complex and the partitioning mechanism. Here we describe an XAS study of divalent cobalt (Co(II)) complexes sorbed on three different solids, gamma-Al2O3, rutile (TiO2) and kaolinite (Al2Si2O5(OH)4). We find direct evidence for the presence of multinuclear sorption complexes at surface coverages below one monolayer of Co(II) atoms. Our spectroscopic data reveal distinct differences in the number of coordinating atoms and interatomic distances in the surface complexes formed on each of the solids at the same sorption density. These results suggest that different oxide and clay surfaces influence the structure and properties of aqueous surface complexes, and therefore must be accounted for in models of metal-ion sorption.

Adsorption↗
PubMed2006

Intrinsic dinitrogen activation at bare metal atoms.

There is ongoing interest in metal complexes which bind dinitrogen and facilitate either its reduction or oxidation under mild conditions. In nature, the enzyme nitrogenase catalyzes this process, and dinitrogen fixation occurs under mild and ambient conditions at a metal-sulfur cluster in the center of the MoFe protein, but the mechanism of this process remains largely unknown. In the last few years, new important discoveries have been made in this field. In this review are discussed recent findings on the interaction of N(2) with metal atoms and metal-atom dimers from all groups of the periodic table as provided by gas-phase as well as matrix-isolation experiments. Intrinsic dinitrogen activation at such bare metal atoms is then related to corresponding processes at complexes, clusters, and surfaces.

Journal Article↗
PubMed1999

Design and synthesis of a redox-active Tc-99m radiopharmaceutical with ferrocenedithiocarboxylate [FcCS = Fe(C5H4CS2)(C5H5)-].

The synthesis, at tracer level, of two Tc-99m complexes having the same chemical composition and structure, but differing by one electron in the total electron counting, is reported. These compounds have been prepared by reacting [99mTcO4]- with the piperidinium salt of the ligand ferrocenedithiocarboxylate {[Fe(II)(C5H4CS2)(C5H5)]- = FcCS}, in the presence of N-methyl S-methyldithiocarbazate as donor of N3-groups, and triphenylphosphine or SnCl2 as reducing agents. The formation of the neutral complex [99mTc(N)(FcCS)2] (compound A) and of the monocationic, mixed-valence complex [99mTc(N)(FcCS) (FcCS)]+ (compound B) {FcCS = [Fe(III)(C5H4CS2)(C5H5)]} was obtained in high yield. Both complexes comprise a terminal Tc triple bond N multiple bond and two FcCS ligands coordinated to the metal center through the two sulfur atoms of the -CS2 group, but they differ in the oxidation state of one of the two iron atoms of the coordinated FcCS ligands. In complex A, the two Fe atoms are both in the +2 oxidation state, while in B, one Fe atom is in the +2 and the other is in the +3 oxidation state. Thus, B is a mixed-valence Fe(II)-Fe(III) complex. B is easily converted into A by one-electron exchange with various reductants such as triphenylphosphine and excess SnCl2. Biodistribution studies in rats showed that complexes A and B are mostly retained in lungs and liver without any significant uptake in organs such as heart and brain.

Animals↗
PubMed2004

Mechanism of the axial ligand substitution reactions on the head-to-tail alpha-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex with olefins.

Reactions of the head-to-tail alpha-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex having equivalent two platinum atoms, Pt(N(3)O), with p-styrenesulfonate and 4-penten-1-ol were studied kinetically. Under the pseudo first-order reaction conditions in which the concentration of the Pt(III) dinuclear complex is much smaller than that of olefin, a consecutive basically four-step reaction was observed for the reaction with p-styrenesulfonate, but for the reaction with 4-penten-1-ol, the reaction was three step. The olefin pi-coordinates to one of the two equivalent Pt atoms in the first step (step 1), followed by the second pi-coordination of another olefin molecule to the other Pt atom (step 2). In the next step (step 3), the nucleophilic attack of water to the first pi-coordinated olefin initiates its pi-sigma bond conversion on the Pt atom, and the second pi-bonding olefin molecule on the other Pt atom is released. Finally, dissociation of the alkyl group on the Pt(N(3)O) and reduction of the Pt(III) dinuclear complex to the Pt(II) dinuclear complex occur (step 4). The first water substitution with olefin (step 1) consists of two paths, the reaction of the diaqua dimer complex (path a) and the reaction of the aquahydroxo dimer complex (path b), whereas the second substitution (step 2) proceeds through three reaction paths: the normal path of the direct substitution of H(2)O (path c), the path of the coordinated OH(-) substitution (path d), and the path via the coordinatively unsaturated five-coordinate intermediate (path e). The reaction with p-styrenesulfonate proceeds through paths c, d, and e, whereas the reaction with 4-penten-1-ol proceeds through paths c and d. The third step (step 3) for the reaction with p-styrenesulfonate involves the coordinatively unsaturated intermediate, but that for the 4-pentene reaction does not. The reactivities of the HH dimer and HT dimer with olefins are compared and discussed.

Journal Article↗
PubMed2001

Re tricarbonyl complexes with ligands containing P,N,N and P,N,O donor atom sets: synthesis and structural characterization.

The coordination chemistry of the heterofunctionalized phosphines HPN2 and H2PNO and of an analogue containing a relevant biomolecule, HPN-Pip (Pip = 4-(3-aminopropyl)-1-(2-methoxyphenyl)piperazine), was studied toward the synthon (NE4)2[ReBr3(CO)3]. The complexes isolated, [Re(CO)3(kappa(3)-PN2)], 3, [Re(CO)3Br(kappa(2)-H2PNO)], 4, and [Re(CO)3Br(kappa(2)-HPN-Pip)], 5, are the first examples of Re(I) compounds stabilized by such a combination of donor atoms. All of the compounds are neutral, but the phosphines, depending on the combination of atoms, act as monoanionic and tridentate (3) or as neutral and bidentate (4, 5). The characterization of 3-5 included IR, 1H NMR, and 31P NMR spectroscopy and X-ray crystallographic analysis. Colorless crystals of compounds 3 and 4 were obtained by slow evaporation of a methanolic solution of 3 and from a boiling acetonitrile solution of 4. Compound 3 crystallizes with two molecules of MeOH per asymmetric unit in the monoclinic space group P2(1)/c, a = 10.1237(8) A, b = 9.4959(4) A, c = 28.365(2) A, beta = 98.707(9) degrees, V = 2695.4(3) A(3), Z = 4; 4 crystallizes in the triclinic space group Ponebar, a = 10.0241(9) A, b = 11.2060(10) A, c = 13.0656(12) A, alpha = 84.883(11) degrees, beta = 71.163(10) degrees, gamma = 63.650(9) degrees, V = 1241.19(19) A(3), Z = 2.

Crystallography, X-Ray↗
PubMed2005

Syntheses, crystal structures and properties of novel copper(II) complexes obtained by reactions of copper(II) sulfate pentahydrate with tripodal ligands.

Three novel metal-organic frameworks (MOFs), [Cu(1)SO4].H2O (4), [Cu2(2)2(SO4)2].4H2O (5) and [Cu(3)(H2O)]SO4.5.5H2O (6), were obtained by hydrothermal reactions of CuSO4.5H2O with the corresponding ligands, which have different flexibility. The structures of the synthesized complexes were determined by single-crystal X-ray diffraction analyses. Complex 4 has a 2D network structure with two types of metallacycles. Complex 5 also has a 2D network structure in which each independent 2D sheet contains two sub-layers bridged by oxygen atoms of the sulfate anions. Complex 6 has a 2D puckered structure in which the sulfate anions serve as counter anions, which are different from those in complexes 4 (terminators) and 5 (bridges). The different structures of complexes 4, 5 and 6 indicate that the nature of organic ligands affected the structures of the assemblies greatly. The magnetic behavior of complex 5 and anion-exchange properties of complex 6 were investigated.

Journal Article↗
PubMed2001

Atomic resolution structure of Escherichia coli dUTPase determined ab initio.

Cryocooled crystals of a mercury complex of Escherichia coli dUTPase diffract to atomic resolution. Data to 1.05 A resolution were collected from a derivative crystal and the structure model was derived from a Fourier map with phases calculated from the coordinates of the Hg atom (one site per subunit of the trimeric enzyme) using the program ARP/wARP. After refinement with anisotropic temperature factors a highly accurate model of the bacterial dUTPase was obtained. Data to 1.45 A from a native crystal were also collected and the 100 K structures were compared. Inspection of the refined models reveals that a large part of the dUTPase remains rather mobile upon freezing, with 14% of the main chain being totally disordered and with numerous side chains containing disordered atoms in multiple discrete conformations. A large number of those residues surround the active-site cavity. Two glycerol molecules (the cryosolvent) occupy the deoxyribose-binding site. Comparison between the native enzyme and the mercury complex shows that the active site is not adversely affected by the binding of mercury. An unexpected effect seems to be a stabilization of the crystal lattice by means of long-range interactions, making derivatization a potentially useful tool for further studies of inhibitor-substrate-analogue complexes of this protein at very high resolution.

Binding Sites↗
PubMed1994

Identification of actinomycins by high performance liquid chromatography and fast atom bombardment mass spectrometry.

An actinomycin complex isolated from culture broth of a soil microorganism, SNUS 9305011 has been examined by High performance liquid chromatography (HPLC). From the analysis of the fractions obtained by column chromatography of the ethyl acetate extract, three actinomycin components are confirmed. The HPLC analysis is carried out with a CN-bonded nucleosil column. Comparison of the retention times of the components with those of actinomycin D, C complex X0 beta, and V suggests that they are different actinomycins. FAB mass spectra of the components also shows different molecular ions from those of standards and other reported actinomycins. The present work was has demonstrated that actinomycin components can be separated by a CN-bonded HPLC column, and that comparison of their HPLC chromatograms with authentic samples and information on their molecular ions can be successfully employed for identification of actinomycins.

Anti-Bacterial Agents↗