Toward inorganic electrides

Electrides are materials in which alkali metals (Li through Cs) ionize to form bound alkali cations and "excess" electrons. The electrons reside in large cavities or channels or both in the host lattice. We report here the first synthesis of thermally stable inorganic electrides with cation-to-electron ratios of 1:1 as in organic electrides. Although alkali metal adducts to alumino-silicate zeolites are well known, the cation-to-electron ratio is generally 3:1 or greater because these zeolites contain alkali cations prior to incorporation of the alkali metal. In this work, two pure silica zeolites, ITQ-4and ITQ-7, with pore diameters of approximately 7 A, absorb up to 40 wt % cesium from the vapor phase (even at room temperature). The other alkali metals (except Li) can also be introduced at elevated temperatures. The optical and magnetic properties of the cesium-loaded samples suggest ionization to form Cs+ and e- with substantial electron-spin pairing. The metal-loaded samples are stable to at least 100 degrees C and are able to reduce small aromatic molecules such as benzene and naphthalene to the radical anions within the pores of the zeolite.     

Synthesis of novel tryptamine and β-carboline derivatives via palladium-catalyzed reaction of bromotryptamine with organic boronic acids

New tryptamine 5, 7 and β-carboline derivatives 3 were preparated by palladium-catalyzed coupling reaction of 5-bromotryptamine 1 with aryl boronic acids. Dedicated to Professor András Lipták on his 70^th birthday.     

Xyloketal G,a Novel Metabolite from the Mangrove Fungus <Emphasis Type="Italic">Xylaria sp.</Emphasis> 2508

A novel metabolite 1, named xyloketal G, was isolated from cultures of marine derived mangrove fungus Xylaria sp. 2508. Its structure was elucidated by analysis of spectroscopic data.__________Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 22–23, January–February, 2005.     

Assessment of the Fe-Sn-Zn phase diagram at 450°C

The Fe-Sn-Zn system is of interest because Sn is one element added to the Zn galvanizing bath to overcome the drawbacks due to the presence of Si in semi-killed steels. This work has been undertaken with the aim to understand the tin effect on the microstructure and the layers growth in batch galvanized coatings on low alloyed steels. Various experimental techniques such as metallography, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDX) are used in order to characterize the microstructure and the properties of such coatings elaborated in a zinc bath enriched with tin. Solidification phenomena and layers growth mechanisms during galvanization are explained by means of the ternary phase diagram Fe-Sn-Zn at 450°C. The Calphad method allows to obtain this phase diagram from the three optimized binary phase diagrams Fe-Sn, Fe-Zn and Sn-Zn and some experimental data inside the ternary Fe-Sn-Zn system.     

A re-statement of the Hohenberg–Kohn theorem and its extension to finite subspaces

Bearing in mind the insight into the Hohenberg–Kohn theorem for Coulomb systems provided recently by Kryachko (Int J Quantum Chem 103:818, 2005), we present a re-statement of this theorem through an elaboration on Lieb’s proof as well as an extension of this theorem to finite subspaces. Contribution to the Serafin Fraga Memorial Issue.     

Pozzolanic properties of a residual FCC catalyst during the early stages of cement hydration

The catalyst used in fluidized catalytic cracking (FCC) units of refineries after several recovery cycles in regeneration units, reduces its activity and it is partially substituted by new catalyst in the process. As it has a high silicon and aluminum oxides content, the pozzolanic properties of a Brazilian FCC spent residual catalyst, used in different substitution degrees to cement, were evaluated by three thermal analysis techniques during the early stages of hydration of a type II Portland cement. NCDTA curves show in real time that the residual catalyst, accelerates the stages of cement hydration. TG and DSC curves of respective pastes after 24 h of hydration evidence the pozzolanic activity of the waste, respectively, by the lower water mass loss during the dehydroxylation of the residual calcium hydroxide and by the lower dehydroxylation endothermal effect. Within the analyzed period, the higher is the cement substitution degree, the higher is the pozzolanic activity of the residual catalyst.     

Sorption behavior of Co(II) on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the presence of humic acid

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including cosorbing or complexing. In this work, the effects of pH, humic acid HA/Co(II) addition orders, ionic strength, concentration of HA, and foreign cations on the Co(II) sorption on γ-Al₂O₃ in the presence of HA were investigated. The sorption isotherms of Co(II) on γ-Al₂O₃ in the absence and presence HA were also studied and described by using S-type sorption model. The experimental results showed that the Co(II) sorption is strongly dependent on the pH values, concentration of HA, but independent of HA/Co(II) addition orders, ionic strength, and foreign cations in the presence of HA under our experimental conditions. The results also indicated that HA enhanced the Co(II) sorption at low pH, but reduced the Co(II) sorption at high pH. It was hypothesized that the significantly positive influence of HA at low pH on the Co(II) sorption on γ-Al₂O₃ was attributed to strong surface binding of HA on γ-Al₂O₃ and subsequently the formation of ternary surface complexes such as ≡S-OOC-R-(COO⁻) _x Co^2−x . Chemi-complexation may be the main mechanism of the Co(II) sorption on γ-Al₂O₃ in the presence of HA.     

Complexes formed between nitrilotris(methylenephosphonic acid) and M(2+) transition metals: isostructural organic-inorganic hybrids

Nitrilotris(methylenephosphonic acid) (NTP, [N(CH(2)PO(3)H(2))(3)]) recently has been found to form three-dimensional porous structures with encapsulation of templates as well as layered and linear structures with template intercalation. It was, therefore, of interest to examine the type of organic-inorganic hybrids that would form with metal cations. Mn(II) was found to replace two of the six acid protons, while a third proton bonds to the nitrilo nitrogen, forming a zwitter ion. Two types of compounds were obtained. When the ratio of acid to Mn(II) was less than 10, a trihydrate, Mn[HN(CH(2)PO(3)H)(3)(H(2)O)(3)] (2) formed. Compound 2 is monoclinic P2(1)/c, with a = 9.283(2) A, b = 16.027(3) A, c = 9.7742(2) A, beta = 115.209(3) degrees, V = 1315.0(5) A(3), and Z = 4. The Mn atoms form zigzag chains bridged by two of the three phosphonate groups. The third phosphonate group is only involved in hydrogen bonding. The metal atoms are octahedrally coordinated with three of the sites occupied by water molecules. Adjacent chains are hydrogen-bonded to each other through POH and HN donors, and the additional participation of all the water hydrogens in H-bonding results in a corrugated sheet-like structure. Use of excess NTP at a ratio to metal of 10 to 1 yields an anhydrous compound Mn[HN(CH(2)PO(3)H)(3)] (1), P2(1)/n, a = 9.129(1) A, b = 8.408(1) A, c = 13.453(1) A, beta = 97.830(2) degrees, V = 1023.0(2) A(3), and Z = 4. Manganese is five coordinate forming a distorted square pyramid with oxygens from five different phosphonate groups. The sixth oxygen is 2.85 A from an adjacent Mn, preventing octahedral coordination. All the protonated atoms, three phosphonate oxygens and N, form moderately strong hydrogen bonds in a compact three-dimensional structure. The open-structured trihydrate forms a series of isostructural compounds with other divalent transition metal ions as well as with mixed-metal compositions. This is indicative that the hydrogen bonding controls the type of structure formed irrespective of the cation.     

C-Glycosylidene derivatives (exo-glycals): their synthesis by reaction of protected sugar lactones with tributylphosphonium ylids, conformational analysis and stereoselective reduction

Stabilised tributylphosphonium ylids Bu₃PCHCH(EWG), where EWG is CO₂Me, CO₂^tBu or CN, react with protected sugar lactones under mild conditions to give high yields of glycosylidene derivatives (4 and 5) with good Z/E selectivity. X-Ray crystallography shows that in the solid state the tetra-O-benzyl protected (Z)-glucosylideneacetonitrile (Z)-4c adopts a conformation intermediate between a boat and a twist-boat, whereas the isomeric galactose derivative (Z)-5c exists as a distorted chair. NMR data suggest that in solution chair-like conformations are again more favoured for galactosylidene derivatives than for their glucosylidene analogues. Solution phase NMR studies and molecular modelling show that the (E)-double bond geometry disfavours the chair-like geometry of the ring, even in the galactose series; this is consistent with the avoidance of allylic 1,3-strain. Reduction of the glycosylidene double bond to give stereoselective formation of β-C-glycoside derivatives may be achieved by using Et₃SiH-CF₃CO₂H or Et₃SiH-BF₃·Et₂O.     

Preconcentration and separation of copper(II), cadmium(II) and chromium(III) in a syringe filled with 3-aminopropyltriethoxysilane supported on silica gel

In this study, a syringe was filled with silica gel loaded with 3-aminopropyltriethoxysilane, for the separation and preconcentration of copper, cadmium and chromium prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS) in seawater. For this purpose, a syringe was filled with 0.5 g of modified silica gel and the sample solution was drawn into the syringe and ejected back again. The analyte elements were quantitatively retained at pH 5. Then, the elements sorbed by the silica gel were eluted with 2.0 M of HCl and determined by GFAAS. At optimum conditions, the recovery of Cu, Cd and Cr were 96-98%. Detection limits (3delta) were 6.6, 7.5 and 6.0 micro g L(-1) for Cu, Cd and Cr, respectively. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only once. Cu, Cd and Cr added to a seawater sample were quantitatively recovered (>95%) in the range of the 95% confidence level. The method proposed in this paper was compared with a column technique. Optimum experimental conditions, reproducibility, precision and recoveries of both techniques are the same, but the syringe technique is much faster, easier and more practical than the column technique. It is a portable system and allows one to make the sorption process in the source of sample. In addition, the risk of contamination is less than in the column technique.