Showing papers in "ChemInform in 1987"
TL;DR: A review of metalloporphyrin-porphyrin (π-π) interactions in the solid state can be found in this article, where a variety of important conformational aspects of metmorphyrin and their properties on physical properties are presented.
Abstract: Information pertaining to the stereochemistry of metalloporphyrins and other tetrapyrroles continues to expand. The present article reviews important developments of this structural chemistry. Detailed updates on the relationship of the structure and physical properties of iron derivatives are given. Metalloporphyrins with unusually high or low oxidation states are reviewed. Surveys of recent work on π-cation radical complexes, bound O2 species, tetrapyrroles with N-substituents, the stereochemistry of ring-reduced tetrapyrroles and a variety of novel species are given. Newly developed data concerning experimental electron density studies are summarized. Detailed reviews of porphyrin-porphyrin (π-π) interactions in the solid state are given. A variety of important conformational aspects of metalloporphyrins and their consequent results on physical properties are presented. Finally, a number of isomorphous series and crystal packing effects in tetrapyrroles have been detailed.
401 citations
TL;DR: In this article, the role of the Zeeman perturbation is considered in relation with the magnetic and EPR properties of the heterobimetallic complexes. And the authors propose a model for the isotropic interaction based on the concept of natural magnetic orbitals.
Abstract: The field of heteropolymetallic systems with magnetic metal centers occupies a crossing point between biology and physics. For instance the Cu(II)-Fe(III) interaction in cytochrome oxidase is of the same nature as the Cu(II)-Mn(II) interaction in a novel system which could be the first molecular ferromagnet. The mechanism of the interaction is discussed, both from a phenomenological view point using a spin Hamiltonian, and from an orbital view point. An orbital model for the isotropic interaction is presented. It is based on the concept of natural magnetic orbitals. The mechanism of the anisotropic and antisymmetric interactions is more briefly treated. The role of the Zeeman perturbation is then considered in relation with the magnetic and EPR properties of the heterobimetallic complexes. Several examples are presented to emphasize that the nature, ferro- or antiferromagnetic of the isotropic interaction is controlled by the symmetry of the magnetic orbitals. The concept of overlap density is introduced. It permits an estimation of the magnitude of the ferromagnetic stabilization in the case of orthogonality of the magnetic orbitals. The Cu(II)-Fe(III) interaction, in relation to the situation encountered in cytochrome oxidase, the Cu(II)-Ni(II) interaction and a few additional selected examples are discussed. A section deals with the case where one of the interacting ions has an orbital degeneracy. Afterwards, the heterotrinuclear complexes are studied. The important concept of regular and irregular spin state structure is developped and the Mn(II)Cu(II)Mn(II) triad is presented as a spectacular example of irregular spin state structure. A section is devoted to the ordered bimetallic chains. The theory is presented, both at a qualitative and quantitative levels and the already reported compounds of this kind are discussed. One of them may be considered as one of the first molecular ferromagnets. The last but one section concerns the systems with even more subtle spin orders. In conclusion, the vast perspectives of this area are outlined.
400 citations
246 citations
TL;DR: In this paper, a variety of gold catalysts are used to catalyze the oxidation of carbon monoxide at temperatures as low as −70 °C and are stable in a moistened gas atmosphere.
Abstract: A variety of gold catalysts can be used to catalyze the oxidation of carbon monoxide at temperatures as low as −70 °C and are stable in a moistened gas atmosphere. The novel catalysts, prepared by coprecipitation, are composed of ultra-fine gold particles and one of the oxides of 3d transition metals of group VIII, namely, Fe, Co, and Ni.
195 citations
TL;DR: The species Cl2O2 has been generated in a gaseous flow system at 220-240 K by reacting Cl atoms with one of three different ClO precursors as mentioned in this paper.
Abstract: The species Cl2O2 has been generated in a gaseous flow system at 220-240 K by reacting Cl atoms with one of three different ClO precursors: O3, Cl2O, or OClO. The infrared spectra of the reactive mixture indicate that at least two different dimers are produced: a predominant form with bands centered at 1225 and 1057/cm attributed to ClOOCl, and a second form with a band at 650/cm attributed to ClOClO. The UV spectrum of the predominant form shows a maximum absorption cross section of about 6.5 x 10 to the -18th sq cm/molecule around 270 nm, with a wing extending beyond 300 nm. The implications of these results for the chemistry of the stratosphere are discussed.
129 citations
126 citations
118 citations
107 citations
TL;DR: Photodynamic Action of Hypericin Cercosporin's Role in Plant Disease Light-Activated Antimicrobial Chemicals Photodynamic Herbicides photoactivated Compounds as Pesticides.
Abstract: Photoactivated Compounds as Pesticides Mechanisms of Photodynamic Action Photomodification and Singlet Oxygen Generation Identifying Singlet Oxygen Singlet Oxygen Quantum Yields Biochemistry of Photodynamic Action Photodynamic Modification of Excitable Cell Function Physiological Effects of Photodynamic Action Multiple Mechanisms of Dye-induced Toxicity Photooxidative Dyes as Insecticides Photodecomposition of Naturally Occurring Biocides *a-Terthienyl as a Photoactive Insecticide Using Bacterial Mutants and Transforming DNA Phototoxicity as a Defense Against Insects Furanocoumarins Fungicidal Activity Polycetylene Photoactivity Thiophenes and Acetylenes Photodynamic Action of Hypericin Cercosporin's Role in Plant Disease Light-Activated Antimicrobial Chemicals Photodynamic Herbicides
TL;DR: Rietveld analysis of time-of-flight pulsed neutron diffraction of powders shows a nearly isotropic shrinkage of the structures of both the rutile and anatase polymorphs of TiO/sub 2/ upon cooling from 295 to 15 K as mentioned in this paper.
Abstract: Rietveld analysis of time-of-flight pulsed neutron diffraction of powders shows a nearly isotropic shrinkage of the structures of both the rutile and anatase polymorphs of TiO/sub 2/ upon cooling from 295 to 15 K and no change in the sense of the distortion of the TiO/sub 6/ octahedra (two long and four short Ti-O distances in both): rutile at 295 (first) and 15 K (second), a/sub 0/ 4.593 08 (4), 4.586 66 (4), c/sub 0/, 2.958 89 (3), 2.954 07 (3), x/sub oxygen/, 0.304 76 (6), 0.304 69 (6), Ti-O(4x), 1.9486 (3), 1.9459 (3), Ti-O(2X), 1.9796 (4), 1.9764 (4); anatase at 295 and 15 K, a/sub 0/, 3.784 79 (3), c/sub 0/, 9.502 26 (12), 0.504 65 (12), x/sub oxygen/, 0.16686 (5), 0.166 75 (4), Ti-O(4x), 1.9338 (1), 1.9322 (1), Ti-O(2X), 1.9799 (5), 1.9788 (4): all distances (A) referenced to silicon (a = 5.430 88 A). Both tight-binding calculations on the crystalline solids and molecular mechanics computations on the oxide lattice alone lead to a model in which the balance of attractive Ti-O and repulsive O-O interactions control the details of the overall structures. The relative bond lengths around metal centers in some other systems are predicted.
TL;DR: A solution to get the problem off, have you found it? Really? What kind of solution do you resolve the problem? From what sources? Well, there are so many questions that we utter every day as discussed by the authors.
Abstract: A solution to get the problem off, have you found it? Really? What kind of solution do you resolve the problem? From what sources? Well, there are so many questions that we utter every day. No matter how you will get the solution, it will mean better. You can take the reference from some books. And the fourier transform mass spectrometry evolution innovation and applications is one book that we really recommend you to read, to get more solutions in solving this problem.
TL;DR: Porphyrins with Covalently Attached Ouinonc Groups ................................................................. 142 3.3.3 CheIatedHemes.
Abstract: 3. CheIatedHemes ......................................................................................................................... 127 3. A. Porphyrins HavingCovalently Attached Imidazole or Pyridine Ligands ......................................... 127 3.B. Porphyrins Having Covalently Attached Sulfur Ligands................................................................ 137 3.C. Porphyrins with Covalently Attached Ouinonc Groups ................................................................. 142 3. D. Porphvrins with Covalentlv Attached Interactive Groups .............................................................. 146
TL;DR: In this article, the authors describe the various aspects of the vibrational spectra of carbohydrates and present a harmonic approximation in which any motion of the molecule is resolved in a sum of displacements parallel to the Cartesian coordinates and these are called fundamental, normal modes of vibration.
Abstract: Publisher Summary This chapter describes the various aspects of the vibrational spectra of carbohydrates. Vibrational spectroscopy is one of the techniques most adapted techniques for the study of hydrogen bonding, which is the indicator of molecular interaction in the aqueous solutions of sugars. A polyatomic molecule, such as sugar, may be regarded as a system of masses joined by bonds having spring-like properties. The vibration of each of the masses (atoms) can be resolved into components parallel to the x, y, and z axis of a Cartesian system of coordinates. The harmonic approximation is applied in which any motion of the molecule is resolved in a sum of displacements parallel to the Cartesian coordinates and these are called “fundamental, normal modes of vibration.” The analysis of crystallographic results shows the important role played by anomeric center in the structure of sugars. Infrared dichroism in polysaccharides was applied to obtain information on the orientation of chemical groups in the crystalline structure. The computational calculation of the frequencies of carbohydrates' vibration is also elaborated in the chapter.
TL;DR: In this article, the Gibbs-Duhem equation was used to calculate the activity coefficients for Fe(OH)/sub 3/ (log lambda/sub Cr(OH)3/ = -1.60 + 0.79(1 - x)/sup 3/ + log x).
Abstract: Neutralization of acidic solutions containing Cr(III) and Fe(III) at room temperatures results in coprecipitation of these elements as an amorphous solid solution (Cr/sub x/Fe/sub 1-x/(OH)/sub 3/). The solubilities of the Cr/sub x/Fe/sub 1-x/(OC)/sub 3/ precipitates prepared with different mole fractions (x) of Cr(OH)/sub 3/ (0.99, 0.89, 0.69, 0.49, 0.36, 0.15, 0.09, 0.01, 0.00) were determined in 0.01 M prechlorate solutions between pH 2 and 6 in an N/sub 2/ atmosphere. The Cr concentrations in 0.0018-..mu..m filtrates at various times between 5 and 210 days, from initially undersaturated and oversaturated solutions, show that equilibrium was attained within about 7 days when x < 0.5 and more slowly when higher mole fractions of Cr(OH)/sub 3/ were used. In general, aqueous Cr concentrations decrease with decreasing Cr contents in the solids, suggesting that Cr/sub x/Fe/sub 1-x/(OH)/sub 3/ behaves thermodynamically like a solid solution. Activity coefficients for Cr(OH)/sub 3/ in the solid solutions were calculated from the solubility data and are given by the equation log lambda/sub Cr(OH)3/ = -1.60 + 0.28(1 - x)/sup 2/ - 1.79(1 - x)/sup 3/ for 0.01 less than or equal to x less than or equal to 0.69. Aqueous Fe activities were generally too low for reliable measurement;more » therefore, the corresponding activity coefficients for Fe(OH)/sub 3/ (log lambda/sub Fe(OH)3/ = -2.26x/sup 2/ + 1.39x/sup 3/) were calculated by a Gibbs-Duhem equation. A general relationship (log (CrOH/sup 2 +/) = -2pH + 4.18 + 0.28(1 - x)/sup 2/ - 1.79(1 - x)/sup 3/ + log x) developed from these data can be used to calculate Cr concentrations in solutions between pH 2 and 6 that are in equilibrium with Cr-bearing ferric hydroxides with known Cr content. 12 references, 6 figures, 1 table.« less
TL;DR: Etude cinetique du transfert d'electron entre la perhydrodiethano-1,4:6,9 pyridazino [1,2]-pyridazine et son cation dans l'acetonitrile as mentioned in this paper.
Abstract: Etude cinetique du transfert d'electron entre la perhydrodiethano-1,4:6,9 pyridazino [1,2-a] pyridazine et son cation dans l'acetonitrile
TL;DR: This book highlights the applications of supercomputers to electronic structure, transport, kinetics, and simulations, and explains why, in many cases, the computational mode of science offers important advantages over the experimental, observational mode.
Abstract: This book highlights the applications of supercomputers to electronic structure, transport, kinetics, and simulations. Explores how supercomputers are used to solve important problems that combine both scientific complexity and engineering practicality. Explains why, in many cases, the computational mode of science offers important advantages over the experimental, observational mode. Covers four major sections: electronic structure, equilibrium properties and spectra, microscopic dynamics, and transport.
TL;DR: The chemistry of interstellar molecular clouds is reviewed in this article, where a review of the recent observational and theoretical advances in the detection of molecular species in the molecular clouds and their properties is given.
Abstract: The chemistry of interstellar molecular clouds is reviewed. Emphasis has been given to recent observational and theoretical advances. At present approximately 70 identified molecular species have been detected in interstellar molecular clouds and circumstellar shells. Identification of the newly detected species rests mainly on the exacting test between interstellar and laboratory spectra. A large number of unidentified interstellar lines indicates the wide chemical variety in synthesizing molecules in a low temperature, low density environment. Although most of the interstellar molecules are organic, (presently 53) some of the most abundant interstellar molecules are inorganic, such as H2, H2O, NH3. The recent detection of the H2D+ molecular ion is astro-chemically important, since the existence of the primary ion H 3 + has been postulated by the ion-molecule gas phase reaction scheme. Amongst the newly detected molecules are additional carbon chain molecules and the first two ring molecules SiCC and C3H2.
TL;DR: In this article, the authors discuss the chemical mechanisms of RNA-catalyzed reactions with emphasis on the self-splicing ribosomal RNA precursor of Tetrahymena and the enzymatic activities of its intervening sequence RNA.
Abstract: Proteins are not the only catalysts of cellular reactions; there is a growing list of RNA molecules that catalyze RNA cleavage and joining reactions. The chemical mechanisms of RNA-catalyzed reactions are discussed with emphasis on the self-splicing ribosomal RNA precursor of Tetrahymena and the enzymatic activities of its intervening sequence RNA. Wherever appropriate, catalysis by RNA is compared to catalysis by protein enzymes.
TL;DR: In this article, thermal parameters for duplex formation by self-complementary oligomers ICCGGC, CGGCCI, ICCGG, and GGCCI are reported.
Abstract: Thermodynamic parameters for duplex formation by self-complementary oligomers ICCGGC, CGGCCI, ICCGG, and GGCCI are reported.
TL;DR: The majority of ruthenium(II) compounds which have been observed to be luminescent are complexes of aromatic heterocyclic chelating ligands.
Abstract: The majority of ruthenium(II) compounds which have been observed to be luminescent are complexes of aromatic heterocyclic chelating ligands. Methods of synthesizing such complexes are reviewed and recommendations made (where considered possible) as to the best procedures.
TL;DR: In this article, a laser-heated diamond-anvil cell was used to synthesize SiO3 at a pressure of 127 gigapascals at temperatures exceeding 2000 K. The perovskite phase was identified and its unitcell dimensions measured by in situ x-ray diffraction at elevated pressure and room temperature.
Abstract: Silicate perovskite of composition (Mg0.88Fe0.12) SiO3 has been synthesized in a laser-heated diamond-anvil cell to a pressure of 127 gigapascals at temperatures exceeding 2000 K. The perovskite phase was identified and its unit-cell dimensions measured by in situ x-ray diffraction at elevated pressure and room temperature. An analysis of these data yields the first high-precision equation of state for this mineral, with values of the zero-pressure isothermal bulk modulus and its pressure derivative being K0T = 266 ± 6 gigapascals and K90T = 3.9 ± 0.4. In addition, the orthorhombic distortion of the silicate-perovskite structure away from ideal cubic symmetry remains constant with pressure: the lattice parameter ratios are b/a = 1.032 ± 0.002 and c/a = 1.444 ± 0.006. These results, which prove that silicate perovskite is stable to ultrahigh pressures, demonstrate that perovskite can exist throughout the pressure range of the lower mantle and that it is therefore likely to be the most abundant mineral in Earth.