Heterocycles from ylides. Part VIII Reactivity of 2-arylmethylenebenzofuran-3-ones with stabilized sulphur ylides

2-Arylmethylenebenzofuran-3-ones react with carbonyl stabilized sulphur ylides yielding spiro-[cyclopropane-1,2′-benzofuran-3′-ones], whose structure and stereochemistry were assigned on the basis of spectroscopic data and chemical behaviour.     

Kinetics and mechanism of the gas-phase thermal reaction between bis(fluoroxy) difluoromethane CF2(OF)2 and carbon monoxide

The kinetics of the gas-phase thermal reaction between CF₂(OF)₂ and CO has been studied in a static system at temperatures ranging between 110 and 140°C. The only reaction products were CF₂O and CO₂, giving the following stoichiometry: The reaction is homogeneous. The rate is strictly second order in CF₂(OF)₂ and CO, and is not affected by the total pressure or by the presence of reaction products. Oxygen promotes a sensitized oxidation of CO and inhibits the formation of CF₂O. The experimental results in the absence of oxygen can be explained by a chain mechanism similar to that proposed for the reaction between F₂O and CO with an overall rate constant of From the experimental data obtained on the oxygen-inhibited reaction, the rate constant for the primary process can be calculated: The chain length v = 2.5 is independent of the temperature. Taking for collision diameters σ = 6 Å and σ_CO = 3.74 Å, a value α = 5.3 × 10^?3 for the steric factor is obtained.     

Analytical resolution of a parallel second‐order reaction mechanism

The competition among the three different elementary second‐order processes involving the radicals A and B, (1) (2) (3) is frequently established in many combustion and atmospheric chemistry systems. The analytical resolution of the above mechanism for k_AB = 2k_AA and k_AB = 2k_BB, that is, for a cross‐combination ratio ? = k_AB/(k_AAk_BB)^1/2 = 2, is well‐known, but it has been claimed not to exist for ? ≠ 2. In the present paper an analytical resolution of the system (1)–(3), performed under the condition k_AB ≠ 2k_AA and k_AB ≠ 2k_BB, leads to The mathematical procedure leading to this equation and the equation itself are valid independently of the nature of the products of the reactions ( 1 ), ( 2 ) and ( 3 ), that is, recombination or disproportionation products, provided that the reactants and the order of the reactions remain the same. The comparison with numerical integration for exemplary cases is performed. The solutions for the particular cases k_AB ≠ 2k_BB or k_AB ≠ 2k_AA are also presented. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 246–251, 2003     

Sur l'evolution du rapport signal-sur-bruit dans la deconvolution quand le bruit est fonction du signal,en particulier pour des recepteurs “parfaits‘

The influence on the signal-to-noise ratio in deconvolutions carried out from recordings of a perfect detector is discussed with emphasis given to the following remark: the transformation of the mean square of the noise of elementary zones is linear as well as that of the signal itself.     

Working Memory Decline in Alzheimer’s Disease Is Detected by Complexity Analysis of Multimodal EEG-fNIRS

Alzheimer’s disease (AD) is characterized by working memory (WM) failures that can be assessed at early stages through administering clinical tests. Ecological neuroimaging, such as Electroencephalography (EEG) and functional Near Infrared Spectroscopy (fNIRS), may be employed during these tests to support AD early diagnosis within clinical settings. Multimodal EEG-fNIRS could measure brain activity along with neurovascular coupling (NC) and detect their modifications associated with AD. Data analysis procedures based on signal complexity are suitable to estimate electrical and hemodynamic brain activity or their mutual information (NC) during non-structured experimental paradigms. In this study, sample entropy of whole-head EEG and frontal/prefrontal cortex fNIRS was evaluated to assess brain activity in early AD and healthy controls (HC) during WM tasks (i.e., Rey–Osterrieth complex figure and Raven’s progressive matrices). Moreover, conditional entropy between EEG and fNIRS was evaluated as indicative of NC. The findings demonstrated the capability of complexity analysis of multimodal EEG-fNIRS to detect WM decline in AD. Furthermore, a multivariate data-driven analysis, performed on these entropy metrics and based on the General Linear Model, allowed classifying AD and HC with an AUC up to 0.88. EEG-fNIRS may represent a powerful tool for the clinical evaluation of WM decline in early AD.     

A Novel Metal–Ligand Iodo‐bridged Lead(II) Compound: Synthesis,Crystal Structure,Thermal Properties,and DFT Calculations of [Pb(dmp)I2]n

. A novel 1D Pb^II coordination polymer [Pb(dmp)I₂]_n ( 1 ) (dmp = 2,9‐dimethyl‐1,10‐phenanthroline) containing a Pb₂‐(μ‐I)₂ unit was synthesized and characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectroscopy and studied by thermal analysis as well as X‐ray crystallography. The single‐crystal X‐ray data show that the coordination number of Pb^II ions is six, i.e. PbN₂I₄, with “stereo‐chemically active” electron lone pairs, and the coordination sphere is asymmetrical. They also show that the chains interact with each other through π‐π stacking interactions, which create a 3D framework. The structure of the title complex has been optimized by density functional theory calculations. The calculated structural parameters and the IR spectra of the title complex are in agreement with the crystal structure.     

The increase of iron phytoavailability in soils ammended with paper mill sludge

In soils characterized by low organic matter and high pH values (7.5-8.59) iron availability to plants is limited even if the content of total Fe(III) is high. We have studied by Hordeum distichum plants the capability of paper mill sludge to increase the iron phytoavailable fraction in an alkaline soil. The effect of paper mill sludges adding to an iron-deficient soil was evaluated both considering the phyto-available fraction of iron and the distribution of organic carbon (hydrophobic, fulvic and humic carbon) in the soil before and after sludge adding. Iron concentration was determined in the different portions of Hordeum distichum plants grown on soils with and without paper mill sludges. Application of paper mill sludge induces an increase in the concentration of available Fe. This effect is probably due to the production of Fe chelators by soil microorganisms acting on sludge organic matter. The Fe chelators produced result in the solubilization of not soluble Fe-complexes present in the soil.     

Falloff curves for the recombination reaction Cl + FC(O)O + M --> FC(O)OCl + M

The pressure dependence of the recombination reaction Cl + FC(O)O + M --> FC(O)OCl + M has been investigated at 296 K. FC(O)O radicals and Cl atoms were generated by laser flash photodissociation of FC(O)OO(O)CF at 193 nm in mixtures with Cl2 and He or SF6 over the total pressure range 8-645 Torr. The measured FC(O)O radical and F atom yields in the photolysis are 0.33 +/- 0.06 and 0.67 +/- 0.06. The reaction lies in the falloff range approaching the high-pressure limit. The extrapolations toward the limiting low- and high-pressure ranges were carried out using a reduced falloff curves formalism, which includes a recent implementation for the strong-collision broadening factors. The resulting values for the low-pressure rate coefficients are (2.2 +/- 0.4) x 10(-28)[He], (4.9 +/- 0.9) x 10(-28)[SF6], (1.9 +/- 0.3) x 10(-28)[Cl2] and (5.9 +/- 1.1) x 10(-28)[FC(O)OO(O)CF] cm3 molecule(-1) s(-1). The derived high-pressure rate coefficient is (4.4 +/- 0.8) x 10(-11) cm3 molecule(-1) s(-1). For the reaction Cl + FC(O)OCl --> Cl2 + FC(O)O a rate coefficient of (1.6 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1) was determined. The high-pressure rate coefficient was theoretically interpreted using SACM/CT calculations on an ab initio electronic potential computed at the G3S level of theory. Standard heat of formation values of -99.9 and -102.5 kcal mol(-1) were computed at the G3//B3LYP/6-311++G(3df,3pd) level of theory for cis-FC(O)OCl and trans-FC(O)OCl, respectively. The computed electronic barrier for the conversion between the trans and cis conformers is 8.9 kcal mol(-1). On the basis of the present results, the above reactions are expected to have a negligible impact on stratospheric ozone levels.     

Sonochemical Synthesis of a Novel Nanoscale Lead(II) Coordination Polymer: Synthesis,Crystal Structure,Thermal Properties,and DFT Calculations of [Pb(dmp)(μ‐N3)(μ‐NO3)]n with the Novel Pb2(μ‐N3)2(μ‐NO3)2 Unit

A new nanostructured coordination polymer of divalent lead with the ligand 2,9‐dimethyl‐1,10‐phenanthroline (dmp), [Pb(dmp)(μ‐N₃)(μ‐NO₃)]_n ( 1 ), was synthesized by sonochemical methods. The polymer was characterized by scanning electron microscopy, X‐ray powder diffraction, IR, ¹H NMR, and ¹³C NMR spectroscopy, and elemental analyses. Compound 1 was structurally characterized by single‐crystal X‐ray diffraction. The single‐crystal analysis shows that the coordination number of Pb^II ions is seven, (PbN₄O₃) has a “stereo‐chemically active” electron lone pair, and the coordination sphere is hemidirected. The chains interact with each other through π–π stacking interactions to create a 3D framework. The structure of the title complex was optimized by density functional calculations. The calculated structural parameters and the IR spectrum of the title complex are in agreement with the crystal structure.     

Electrochemical characterization of a lithiated mixed nickel-cobalt oxide (LiNi0.5Co0.5O2) prepared by sol-gel process

Lithiated transition metal oxides having a layered structure and general formula LiMO₂, have been extensively studied as positive electrode active materials for lithium or lithium-ion batteries. In particular, lithium nickel dioxide (LiNiO₂) and lithium cobalt dioxide (LiCoO₂) present a layered structure with high diffusion coefficients for the lithium ion. This latter property is very important in order to realize practical devices having high discharge rates. LiNiO₂, compared with LiCoO₂, has the advantage to be a cheaper material with a higher specific capacity for lithium cycling, but its stability upon cycling can be greatly influenced by the displacement of Ni ions from the Ni layers to the Li planes as the content in lithium is reduced over a certain value. Recently, solid solutions such as LiNi_xCo_1−xO₂ have been proposed to offer a compromise between stability, cost and capacity. In this work we have studied LiNi_0.5Co_0.5O₂ prepared by the Complex Sol-Gel Process (CSGP). The advantage of this procedure toward the solid-state process is the high homogeneity in composition and in particle dimension of the synthesized compounds. The samples have been characterized electrochemically using chronopotentiometric, voltammetric and impedance measurements in liquid electrolyte. The results indicates that CSGP-synthesized LiNi_0.5Co_0.5O₂ shows good cyclability (after 1000 cycles about 2/3 of the initial capacity can still be cycled) only if the anodic potential is limited to about 4.2 V. The quite low values of the specific capacity (∼70 mAh/g at C/1 charge-discharge rate) can be justified by the non-complete calcination reaction, as suggested by X-ray measurements. Kinetic properties have been evaluated by Electrochemical Impedance Spectroscopy measurements, which have shown quite high values for the lithium chemical diffusion coefficient (10⁻⁷÷10⁻⁸ cm²s⁻¹) and its unexpected decrease as deintercalation proceeds from x=0.5 in LiNi_0.5Co_0.5O₂. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997