Theoretical and experimental study of an absorbable gas diffusion through a fine filter

A mathematical model of the diffusion efflux of an absorbable gas into vacuum through a fine membrane with a distance between pores comparable with their diameter is proposed. The model is analyzed for a steady-state regime. The results of the theoretical analysis are compared to experiment.     

Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G^*//HF/6-31G^*+ZPE(HF/6-31G^*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe₃F₃ ⁺ cation detected in the mass spectra of μ₄-Be₄O(CF₃COO)₆ were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol⁻¹ and those of the remaining four structures lie in the range 20–40 kcal mol⁻¹. Two most favorable isomers, aC _2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC _3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol⁻¹, except for the pyramidalC _3v isomer (∼16 kcal mol⁻¹). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol⁻¹). A planarD _3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe₃H₃ ⁺ cation, a hydride analog of the OBe₃F₃ ⁺ ion; the energies of the remaining five isomers are more than 25 kcal mol⁻¹ higher. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999.     

Synthesis and Biological Evaluation of S-, O- and Se-Containing Dispirooxindoles

A series of novel S-, O- and Se-containing dispirooxindole derivatives has been synthesized using 1,3-dipolar cycloaddition reaction of azomethine ylide generated from isatines and sarcosine at the double C=C bond of 5-indolidene-2-chalcogen-imidazolones (chalcogen was oxygen, sulfur or selenium). The cytotoxicity of these dispiro derivatives was evaluated in vitro using different tumor cell lines. Several molecules have demonstrated a considerable cytotoxicity against the panel and showed good selectivity towards colorectal carcinoma HCT116 p53^+/+ over HCT116 p53^−/− cells. In particular, good results have been obtained for LNCaP prostate cell line. The performed in silico study has revealed MDM2/p53 interaction as one of the possible targets for the synthesized molecules. However, in contrast to selectivity revealed during the cell-based evaluation and the results obtained in computational study, no significant p53 activation using a reporter construction in p53wt A549 cell line was observed in a relevant concentration range.     

Studying the muon and hadron components of extensive air showers with the Carpet-2 array

The method of separating muons and hadrons recorded by the Muon Detector of the Carpet-2 air shower array of Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) is described. The results of studying characteristics of the muon and hadron components of extensive air showers (EAS) with N _e ≥ 10⁵ are presented. For the range of distances 40–55 m from shower axes the numbers of hadrons with energies higher than 30 GeV and muons with energies above 1 GeV are obtained as functions of the shower size N _e .     

Effect of vibronically induced spin-orbit coupling of electronic ππ* states on nonradiative intersystem crossing: Naphthalene

The effect of (I) S ₁(¹ B _2u ) ? T ₁(³ B _1u ) and (II) S ₁ ? T ₂ (³ B _3g ) ? T ₁ transitions in naphthalene on the rate constant K _ST ^s of the S ₁ ? T ₁ nonradiative transitions to all triplet sublevels s = z, y, x of the T ₁ state has been investigated in the approximation of vibronically induced spin-orbit couplings, taking into account all out-of-plane vibrational modes. The shapes of the vibrational modes that are most active in these transitions are determined. The calculated values K _ST = (0.33–0.75) × 10⁷ s^?1, obtained with allowance for the I and I + II transitions, are consistent with the experimental values (K _ST)_exp found by different researchers. It is established in all calculation versions that K _ST > K _ST ^z > k _ST ^x . This relation is in qualitative agreement with the known magnetooptical data.     

Theoretical study of the energies and activation barriers of elementary reactions of hydrogenation of the Ti-doped closo-aluminide cluster Al@TiAl11 and its anion Al@TiAl 11?

The potential energy surfaces, energies E, and activation barriers h of elementary reactions of addition of an H₂ molecule to the Ti-doped closo-aluminide cluster Al@TiAl₁₁ and its anion Al@Ti₁₁⁻ with an icosahedral and marquee structure in the states with different multiplicity were calculated within the B3LYP approximation of the density functional theory using the 6–31G* and 6–311+G* basis sets. The results were compared with the data calculated at the same level of theory for the related reactions of hydrogenation of bare closo-aluminides Al₁₃ and Al₁₃⁻ and their B-, C-, Si-, and Ge-doped derivatives. The computations demonstrated that, depending on the structure, charge, and multiplicity of the Al@TiAl₁₁ cluster, the hydrogenation energy varies in the range 15–23 kcal/mol. At the first stage of addition (chemisorption) of H₂, a μ-H₂ complex at the Ti atom (intermediate) forms with the distance R(Ti-H₂) ∼ 1.9–2.0 ?, which is accompanied by an energy decrease of ∼4–10 kcal/mol. The H-H bond in the μ-H₂ complex is ∼0.1 ? longer and the stretching vibration frequency V_val(HH) is ∼700–1500 cm⁻¹ (or more) lower than the corresponding characteristics of the isolated H₂ molecule. In the transition state with an imaginary frequency of ∼600i–1100i, the H₂ molecule is coordinated to the attacked edge Ti-Al_r, and its length increases to ∼0.9–1.1 ?. The activation barrier height h varies from a few kcal/mol to ∼8–10 kcal/mol when measured from the μ-H₂ complex and is within 18–22 kcal/mol when measured from the product (dihydride Al@TiAl₁₁H₂). The latter barrier (to the reverse reaction of dehydrogenation) is considerably higher than the barriers to migration of hydrogen atoms around the metal cage in the Al@TiAl₁₁H₂ dehydrides. There is a correlation between the energies E and barriers h of hydrogenation reactions and the structure, external charge, and multiplicity of the Al@TiAl₁₁ cluster. In all cases, the hydrogenation should occur significantly more readily than dehydrogenation. It was shown that these reactions can be both irreversible (for example, for an icosahedron in the singlet state) and reversible (for a marquee in the triplet state and others). The conclusion was drawn that the elementary reactions of hydrogenation and dehydrogenation for Ti-doped aluminides should occur considerably faster and under milder conditions than for bare aluminides or their analogues doped with main-group atoms. Original Russian Text ? V.K. Charkin, O.P. Kochnev, N.M. Klimenko, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 8, pp. 1345–1354.     

The electrical conductivity of poly-p-xylylene + CdS nanocomposites

The dependence of electrical conductivity on the concentration of CdS (c) and temperature (T) over the temperature range 10–300 K was studied for poly-p-xylylene-CdS (PPX + CdS) nanocomposites prepared by solid-state cryochemical synthesis. The results were discussed in terms of the heterogeneous conductivity model including various charge transfer mechanisms in various nanocomposite regions. Under the illumination of a film with c > 11 vol % by a daylight lamp, the conductivity increased, and the σ(T) dependence was metallic in character at low temperatures. The photoconductivity of films at larger concentrations c was caused by the appearance of photoexcited electrons in CdS nanoparticles, the separation of charges at the nanoparticle-matrix boundary, and percolation effects in films. The PPX matrix was shown to actively participate in electrical conductivity; electrons in this matrix jumped between phenyl rings. The experimental dependence of dark conductivity σ(T) at temperatures from 150 to 300 K was analyzed using the Mott hopping conductivity model with variable jump lengths. The main points of the Mott theory of hopping conductivity were discussed. Original Russian Text ? I.A. Misurkin, S.V. Titov, T.S. Zhuravleva, I.V. Klimenko, S.A. Zav’yalov, E.I. Grigor’ev, S.N. Chvalun, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 534–540.     

Theoretical study of isomerism, structure, and stability of dimers of C-doped aluminide clusters (C@Al12)2 and (C@Al12)(L@Al12) (L = Si, Ge)

The geometric, energetic, and vibrational characteristics of the dimers of carbon-doped aluminum clusters (C@Al₁₂)₂, (C@Al₁₂)(Si@Al₁₂), and (C@Al₁₂)(Ge@Al₁₂) have been calculated by ab initio density functional theory B3LYP method with the basis sets 6-31G* and 6-311+G*. As distinct from the silicon and germanium analogues (Si@Al₁₂)₂ and (Ge@Al₁₂)₂ with an AA lowest-lying structure, in which the Si@Al₁₂ and Ge@Al₁₂ blocks retain the shape of distorted icosahedra A, the symmetric AA structure is not typical of the (C@Al₁₂)₂ dimer (itcorresponds to a transition state) and the most favorable structures are two closely spaced BB and AD isomers, in which the C@Al₁₂ blocks have either a distorted icosahedral (A) or nonicosahedral geometry (B, a dicapped ten-vertex polyhedron; D, a marquee with a centered hexagonal base). The calculated energy of dissociation of the most favorable isomer AD into isolated C@Al₁₂ (I _h ) monomers is ～45 kcal/mol, which is 1.5–2 times as large as the corresponding dissociation energy of (Si@Al₁₂)₂ and (Ge@Al₁₂)₂. For mixed dimers of the (C@Al₁₂)(L@Al₁₂) type with L = Si or Ge, three types of low-lying isomers (AA, BA, and DA) are predicted in which the Si@Al₁₂ and Ge@Al₁₂ blocks retain their shape A and the C@Al₁₂ blocks have geometry A, B, and D, respectively. For all the isomers, the block-block bonds are comparable in length and energy to the bonds inside the blocks and have the same chemical nature. Specific features of the geometry, relative stability, ionization potentials, electron affinity, vibrational spectra, and other characteristics of doped aluminide dimers, which could be used for the identification of their isomers by spectroscopic methods, are discussed.