Effect of ion bombardment on the phase composition and mechanical properties of diamond-like carbon films

It is established that the addition of hydrogen to methane in the reaction mixture upon the fabrication of diamond-like carbon films via the plasma-enhanced chemical vapor deposition method decreases residual stresses in the obtained films and significantly reduces their growth rate. The films were investigated via atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Irradiation of the prepared films with P⁺ and PF ₄ ⁺ ions results in strong sample swelling with increasing dose, as well as in a decrease in the compressive stress up to transition to tensile one reaching saturation. Moreover, the fraction of sp ³ bonds increases with increasing ion dose while the fraction of sp ² bonds decreases symmetrically with the processes proceeding faster upon irradiation with molecular ions. Qualitative mechanisms explaining the experimental results are proposed.     

New meroterpenoids from the marine sponge Aka coralliphaga

Three new sulfated meroterpenoids containing sesquiterpene and hydroquinone moieties, namely siphonodictyal A sulfate (1), akadisulfate A (2) and akadisulfate B (3), along with the known siphonodictyal B3 and bis(sulfato)-cyclosiphonodictyol A were isolated from the sponge Aka coralliphaga. Their structures were elucidated on the basis of spectroscopic data. Akadisulfate B and siphonodictyal B3 showed a radical-scavenging activity comparable with that of the known lipophylic antioxidant BHT.     

Half-life measurements of stored fully ionized and hydrogen-like 122 I ions

The half-lives of fully ionized and hydrogen-like (H-like) ¹²²I ions have been measured in a heavy-ion storage ring. The $ \beta^{+}_{}$ -decay constants for both charge states and the electron capture (EC) decay constant of H-like ions have been determined. The EC-decay constant in H-like ¹²²I ions $\ensuremath \lambda^{\text{H-like}}_{\rm EC}=7.35(33)\cdot10^{-4}{\,\mbox{s}}^{-1}$ is, within the uncertainty, the same as the one in neutral atoms. This result is in agreement with the estimates of recent theoretical considerations on the EC-decay of few-electron ions that explicitly take into account the conservation of the total angular momentum of the nucleus plus lepton(s) system and its projections. No firm confirmation could be concluded from our results on the predicted effect that allowed Gamow-Teller transitions become forbidden if the initial and final total angular momenta are not equal.-1     

Nitrite impurities are responsible for the reaction observed between vitamin B12 and nitric oxide in acidic aqueous solution

The reaction between aquacobalamin, Cbl(H2O), and NO was studied at low pH. As previously reported, the final product of the reaction is the same as that obtained in the reaction of NO and reduced Cbl(H2O), viz. Cbl(NO-). Nevertheless, this reductive nitrosylation is preceded by a faster reaction (accompanied by small absorbance changes) that depends on the HNO2 concentration but not on the NO concentration. Kinetic and UV-vis spectroscopic data show that Cbl(NO2-) is generated during this reaction. Spectroscopic data show that the dimethylbenzimidazole group trans to the NO2- ligand is protonated and partially dechelated at pH 1, by which a reaction with NO is induced. DFT calculations were performed to compare the ability of NO and NO2- to bind to cobalamin and their influence on the stability of the dimethylbenzimidazole group. The reductive nitrosylation reaction shows a quadratic dependence on the HNO2 concentration and an inverse dependence on the NO concentration. It also strongly depends on pH and is no longer observed at pH > 4. On the basis of earlier work performed on a series of Co(III) porphyrins, a mechanism is proposed that can quantitatively account for the HNO2 and NO dependencies. The reductive nitrosylation reaction is practically dominated by a back reaction, i.e., the reaction between Cbl(NO-) and HNO2, which accounts for the strange NO and HNO2 concentration dependencies observed.     

Dynamics of localized excitons in a superlattice grown by molecular-beam epitaxy with submonolayers of CdSe

The low-temperature photoluminescence spectrum and the recombination dynamics of localized excitons have been studied in a short-period superlattice of CdSe/ZnSe submonolayers. As distinct from structures with isolated submonolayers, which exhibit one narrow photoluminescence peak, the photoluminescence and photoluminescence excitation spectra of a superlattice have two peaks, separated by ∼50 meV. The amount of splitting, as well as the temporal characteristics of the damping of the photoluminescence, are interpreted in terms of a model of a disordered superlattice of extended islands, sited randomly in the submonolayers making up the superlattice. Fiz. Tverd. Tela (St. Petersburg) 40, 837–838 (May 1998)     

Desmethylubiquinone Q2 from the Far-Eastern ascidian Aplidium glabrum: structure and synthesis

Two new diprenylquinones, glabruquinone A (desmethylubiquinone Q₂) having cancer preventive properties and its minor isomer Glabruquinone B were isolated from the ascidian Aplidium glabrum. Their structures have been elucidated by NMR and mass spectra and confirmed by synthesis.     

Coordination and organometallic chemistry of relevance to the rhodium-based catalyst for ethylene hydroamination

The RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI catalytic system for the hydroamination of ethylene by aniline is shown to be thermally stable by a recycle experiment and by a kinetic profile study. The hypothesis of the reduction under catalytic conditions to a Rh(I) species is supported by the observation of a high catalytic activity for complex [RhI(PPh(3))(2)](2). New solution equilibrium studies on [RhX(PPh(3))(2)](2) (X = Cl, I) in the presence of ligands of relevance to the catalytic reaction (PPh(3), C(2)H(4), PhNH(2), X(-), and the model Et(2)NH amine) are reported. Complex [RhCl(PPh(3))(2)](2) shows broadening of the (31)P NMR signal upon addition of PhNH(2), indicating rapid equilibrium with a less thermodynamically stable adduct. The reaction with Et(2)NH gives extensive conversion into cis-RhCl(PPh(3))(2)(NHEt(2)), which is however in equilibrium with the starting material and free Et(2)NH. Excess NHEt(2) yields a H-bonded adduct cis-RhCl(PPh(3))(2)(Et(2)NH)···NHEt(2), in equilibrium with the precursors, as shown by IR spectroscopy. The iodide analogue [RhI(PPh(3))(2)](2) shows less pronounced reactions (no change with PhNH(2), less extensive addition of Et(2)NH with formation of cis-RhI(PPh(3))(2)(NHEt(2)), less extensive reaction of the latter with additional Et(2)NH to yield cis-RhI(PPh(3))(2)(Et(2)NH)···NHEt(2). The two [RhX(PPh(3))(2)](2) compounds do not show any evidence for addition of the corresponding X(-) to yield a putative [RhX(2)(PPh(3))(2)](-) adduct. The product of C(2)H(4) addition to [RhI(PPh(3))(2)](2), trans-RhI(PPh(3))(2)(C(2)H(4)), has been characterized in solution. Treatment of the RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI/PhNH(2) mixture under catalytic conditions yields mostly [RhCl(PPh(3))(2)](2), and no significant halide exchange, demonstrating that the promoting effect of iodide must take place at the level of high energy catalytic intermediates. The equilibria have also been investigated at the computational level by DFT with treatment at the full QM level including solvation effects. The calculations confirm that the bridge splitting reaction is slightly less favorable for the iodido derivative. Overall, the study confirms the active role of rhodium(I) species in ethylene hydroamination catalyzed by RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI and suggest that the catalyst resting state is [RhCl(PPh(3))(2)](2) or its C(2)H(4) adduct, RhCl(PPh(3))(2)(C(2)H(4)), under high ethylene pressure.     

Neutron Activation Analysis of Samples of Unknown Composition

The advantages of relative analytical methods over absolute methods for calculating element concentrations have been demonstrated. A procedure for the neutron activation analysis of samples of unknown composition was proposed based on the numerical simulation of the gamma spectra of test samples.     

Anomalous Duff reaction with 2,4-di-tert-butylphenol

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, p. 2186, September, 1988.