Embedded cluster calculation of the Ce3+ impurity in Lu2SiO5 crystals including crystal lattice relaxation and polarization

Results of electronic structure studies of the Ce³⁺ impurity in Lu₂SiO₅ crystals allowing for lattice polarization and relaxation are given. The calculations were performed by the embedded cluster method combining the scattered wave and molecular static methods. The effect of lattice deformation induced by the defect on the results of calculations is discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1046–1052, November–December, 1997.     

THE PHOTOSENSITIZED OXIDATION OF SULPHIDES

Abstract— The rates of photosensitized oxidation of a number of sulphides were determined under standard conditions in 1, 1, 2,2-tetrachloroethane and in methanol. It was found that the ratio of the rates of reaction in the two solvents was not constant for different sulphides and that t -butyl sulphide does not react in methanol. It is inferred that the presence of an H atom in the α position is essential for reaction in polar solvents and an appropriate mechanism is suggested. The results indicate that reaction in chlorinated solvents may take place by a different mechanism which possibly involves H-abstraction by triplet sensitizer.     

An investigation of the structure of butadiene by high resolution infra-red and raman spectroscopy

The rotational Raman spectra of butadiene and butadiene-d₆ are found to consist of discrete lines having small ≈0·4 cm⁻¹) yet almost constant spacings, as would be expected for symmetric or nearly symmetric top molecules. An infra-red absorption band (Type C) of butadiene at 908 cm⁻¹ is observed to have a spacing of about 2·5 cm⁻¹. Both the Raman and infra-red spectra provide evidence for the trans structure of the butadiene molecule. From the rotational constants A″ and ″ the following structural parameters were obtained: C=C---C) = 122·9 ± 0·5° rC---C) = 1·47₆ ± 0·010 Å dy]somewhat shorter than recently determined from electron-diffraction experiments).     

Preparation-Proprietes physico-chimiques enthalpie de formation de l'hydrure d'aluminium AlH3α′

Résumé L'hydrure d'aluminium AlH₃- a été obtenu par action de LiAlH₄ sur AlCl₃ ou ZnCl₂ dans l'éther éthylique. La décomposition thermique a été étudiée par thermogravimé trie sous pression réduite (10^–2 torr). La capacité calorifique molaire à 298 K, l'enthalpie de décomposition, ainsi que l'enthalpie de formation ont été déterminées avec un microcalorimètre Calvet.

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Aluminium hydride,-AlH₃, was prepared by reaction of LiAlH₄ on A1C1₃ or ZnCl₂ in diethyl ether. Thermogravimetry was used to investigate its thermal decomposition under low pressure (10^–2 torr). The molar heat capacity at 298 K, the heat of decomposition, and the heat of formation, were measured with a Calvet microcalorimeter.

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Zusammenfassung Aluminiumhydrid AlH₃- wurde durch Einwirkung von LiAlH₄ auf AlCl₃ oder ZnCl₂ in DiÄthylether hergestellt. Die Thermo gravimetrie wurde zur Untersuchung der thermischen Zersetzung bei niedrigem Druck (10^–2 torr) herangezogen. Die molare WÄrmekapazitÄt bei 298 K, die Zersetzungsenthalpie sowie die Bildungsenthalpie wurden mit einem Calvet-Mikrokalorimeter bestimmt.

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— - l₃ LiAlH₄ ll₃ ZnCl₂ . (10^–2 ) . 298 , .

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Ce travail a été effectué dans le cadre d'un contrat de recherches passé par le laboratoire de Thermochimie Minérale avec la Direction des Recherches et Moyen d'Essai. Nous remercions bien vivement cet organisme de l'aide qu'il nous a apportée.     

CHEMICALLY MODIFIED PHOTOSYNTHETIC BACTERIAL REACTION CENTERS: CIRCULAR DICHROISM, RAMAN RESONANCE, LOW TEMPERATURE ABSORPTION, FLUORESCENCE AND ODMR SPECTRA AND POLYPEPTIDE COMPOSITION OF BOROHYDRIDE TREATED REACTION CENTERS FROM Rhodobacter sphaeroides R26

Abstract— Reaction centers from Rhodobacter sphaeroides have been modified by treatment with sodium borohydride similar to the original procedure [Ditson et al., Biochim. Biophys. Acta 766 , 623 (1984)], and investigated spectroscopically and by gel electrophoresis.
(1) Low temperature (1.2 K) absorption, fluorescence, absorption- and fluorescence-detected ODMR, and microwave-induced singlet-triplet absorption difference spectra (MIA) suggest that the treatment produces a spectroscopically homogeneous preparation with one of the 'additional' bacteriochlorophylls being removed. The modification does not alter the zero field splitting parameters of the primary donor triplet (^TP870).
(2) From the circular dichroism and Raman resonance spectra in the1500–1800 cm^-1 region, the removed pigment is assigned to Bchl_M, e.g. the "extra" Bchl on the "inactive" M-branch.
(3) A strong coupling among all pigment molecules is deduced from the circular dichroism spectra, because pronounced band-shifts and/or intensity changes occur in the spectral components assigned to all pigments. This is supported by distinct differences among the MIA spectra of untreated and modified reaction centers, as well as by Raman resonance.
(4) The modification is accompanied by partial proteolytic cleavage of the M-subunit. The preparation is thus spectroscopically homogeneous, but biochemically heterogenous.     

Oxygen uptake photosensitized by disorganized chlorophyll in model systems and thylakoids of greening barley

Light-dependent oxygen uptake was observed and studied in thylakoids from early greening barley in comparison to oxygen uptake in chlorophyll solutions and in thylakoids from fully green leaves. Substantial oxygen uptake was observed in chlorophyll solutions supplemented with tryptophan, histidine, ascorbic acid or linoleic acid. This uptake was diminished by adding azide, beta-carotene and alpha-tocopherol, which are specific singlet-oxygen quenchers. Illuminated thylakoids from greening barley also exhibited marked oxygen uptake that, likewise, was strongly quenched by azide. In comparison, azide was found not to affect oxygen uptake that is associated with the methyl viologen-catalyzed Mehler reaction. It is reasoned that in the first two cases the oxygen uptake arises from chlorophyll-photosensitized activation of oxygen to the singlet state and its consumption by exogenous or endogenous substrates. In greening, we propose that disorganized chlorophyll photo-sensitizes the oxygen uptake.     

Phosphorus-containing podands 7. Complexing properties of ortho-diphenylphosphinyl-substituted diphenyl ethers of oligoethylene glycols with respect to alkali-metal cations

Stability constants of complexes of alkali-metal cations with oligoethylene glycol diethers RO(CH₂CH₂O)_nR (n=1–5), where R=2-Ph₂P(O)C₆H₄ and 2-Ph₂(O)-4-t-BuC₆H₃P, have been determined conductometrically in a tetrahydrofuran-chloroform mixture (41 by volume). The dependence of complexing ability on a number of monopodand donor centers for Li⁺ and Na⁺ has multiple extrema. For K⁺, Rb⁺, and Cs⁺ the complexing abilities steadily increase with the length of the ligand polyether chain. Monopodands based on triethylene glycol and its pyrocatechol analog are highly effective (log K=6.7–7.0) with respect to Li⁺. The synthesis of ligands with a lipophilic tert-butyl substituent in the terminal group is described.For previous communication, see [1]. The number of the communication in [2] is 5, not 4 as printed in error.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1992–2000, September, 1991.     

Initiation of the internal-conversion process in the phenyl benzoate molecule

The INDO and CNDO/S methods were used to calculate changes in the energy of the ground state and the energy of the first singlet-singlet transition of phenyl benzoate permitted with respect to its multiplet nature with consistent rotation of phenyl groups of the molecule in the cis conformation. It was found that in the lowest excited singlet state of the phenyl benzoate molecule an adiabatic photoreaction can occur, as a result of which the energy of the S₀-S₁ electron transition decreases to values of 2 eV. With motion of the molecular system along the coordinate of the photoreaction, an internal-conversion process is initiated, which leads to the experimentally observed absence of luminescence of phenyl benzoate solutions.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 21, No. 3, pp. 365–367, May–June, 1985.     

Selective suppression of some radical reactions by iron pentacarbonyl

Conclusions On the example of the homolytic reaction of methallyl chloride with CCl₄ it was found that iron pentacarbonyl in catalytic amounts can selectively suppress the radical process involving chlorine atoms, and at the same time it catalyzes the chain reaction with trichloromethyl radicals, which act as carriers of the kinetic chain.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2320–2322, October, 1972.     

Synthesis of peptides based onβ-(N1-uracilyl)-α-alanine

The synthesis of peptides which include a DL--(N₁-uracilyl)--alanine (DL-willardiine) residue as an N-terminal or C-terminal group was investigated, dipeptides of DL-willardiine with glycine and L-tyrosine were obtained, and DL-willardiyl-DL-willardiine was synthesized; the latter is the simplest representative of the family of monotonic homopeptides which contain, as a repeating side substituent, a natural nucleic base capable of participation in intermolecular interactions of the complementary type.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 404–408, March, 1971.