Structural distortions upon oxidation in heteroleptic [Cp(2)W(dmit)] tungsten dithiolene complex: combined structural, spectroscopic, and magnetic studies

Four different cation radical salts are obtained upon electrocrystallization of [Cp(2)W(dmit)] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in the presence of the BF(4)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions. In these formally d(1) cations, the WS(2)C(2) metallacycle is folded along the S···S hinge to different extents in the four salts, an illustration of the noninnocent character of the dithiolate ligand. Structural characteristics and the charge distribution on atoms, for neutral and ionized complexes with various folding angles, were calculated using DFT methods, together with the normal vibrational modes and theoretical Raman spectra. Raman spectra of neutral complex [Cp(2)W(dmit)] and its salts formed with BF(4)(-), AsF(6)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions were measured using the red excitation (λ = 632.8 nm). A correlation between the folding angle of the metallacycle and the Raman spectroscopic properties is analyzed. The bands attributed to the C═C and C-S stretching modes shift toward higher and lower frequencies by about 0.3-0.4 cm(-1) deg(-1), respectively. The solid state structural and magnetic properties of the three salts are analyzed and compared with those of the corresponding molybdenum complexes. Temperature dependence of the magnetic susceptibility shows the presence of one-dimensional antiferromagnetic interactions in the BF(4)(-), PF(6)(-), and [Au(CN)(2)](-) salts, while an antiferromagnetic ground state is identified in the Br(-) salt below T(Ne?el) = 7 K. Interactions are systematically weaker in the tungsten salts than in the isostructural molybdenum analogs, a consequence of the decreased spin density on the dithiolene ligand in the tungsten complexes.     

The Structure of a Novel Neutral Lipid A from the Lipopolysaccharide of Bradyrhizobium elkanii Containing Three Mannose Units in the Backbone

The chemical structure of the lipid A of the lipopolysaccharide (LPS) from Bradyrhizobium elkanii USDA 76 (a member of the group of slow‐growing rhizobia) has been established. It differed considerably from lipids A of other Gram‐negative bacteria, in that it completely lacks negatively charged groups (phosphate or uronic acid residues); the glucosamine (GlcpN) disaccharide backbone is replaced by one consisting of 2,3‐dideoxy‐2,3‐diamino‐D ‐glucopyranose (GlcpN3N) and it contains two long‐chain fatty acids, which is unusual among rhizobia. The GlcpN3N disaccharide was further substituted by three D ‐mannopyranose (D ‐Manp) residues, together forming a pentasaccharide. To establish the structural details of this molecule, 1D and 2D NMR spectroscopy, chemical composition analyses and high‐resolution mass spectrometry methods (electrospray ionisation Fourier‐transform ion cyclotron resonance mass spectrometry (ESI FT‐ICR MS) and tandem mass spectrometry (MS/MS)) were applied. By using 1D and 2D NMR spectroscopy experiments, it was confirmed that one D ‐Manp was linked to C‐1 of the reducing GlcpN3N and an α‐(1→6)‐linked D ‐Manp disaccharide was located at C‐4′ of the non‐reducing GlcpN3N (α‐linkage). Fatty acid analysis identified 12:0(3‐OH) and 14:0(3‐OH), which were amide‐linked to GlcpN3N. Other lipid A constituents were long (ω‐1)‐hydroxylated fatty acids with 26–33 carbon atoms, as well as their oxo forms (28:0(27‐oxo) and 30:0(29‐oxo)). The 28:0(27‐OH) was the most abundant acyl residue. As confirmed by high‐resolution mass spectrometry techniques, these long‐chain fatty acids created two acyloxyacyl residues with the 3‐hydroxy fatty acids. Thus, lipid A from B. elkanii comprised six acyl residues. It was also shown that one of the acyloxyacyl residues could be further acylated by 3‐hydroxybutyric acid (linked to the (ω‐1)‐hydroxy group).     

Solution properties and solvatochromism of bis(<Emphasis Type="Italic">N</Emphasis>-2-pyridyl-salicylaldiminato)cobalt(II)

The bis(N-2-pyridyl-salicylaldiminato)cobalt(II) complex ([Co(sap)₂]), a reddish-pink crystalline compound has been characterized by elemental analysis, molar conductivity, cyclic voltammetry, and Vis–NIR spectroscopy. Combination of all techniques indicates a tetrahedral geometry for the complex in solid state and in the solvents used. Electronic spectroscopy was used to determine the ligand–field parameters as well as chromaticity coordinates; for discrimination of color changes CIE and CIELAB color spaces have been applied.     

Calorimetric investigations of the influence of waste aluminosilicate on the hydration of different cements

The aim of this work is to compare the influence of addition of waste aluminosilicate catalyst on the initial periods of hydration of different cements, i.e. calcium aluminate cements of different composition and Portland cement, basing on the calorimetric studies. Cement pastes containing up to 25 mass% of additive were studied, where the water/(cement+additive) ratio was 0.5. An attempt was undertaken to explain the mechanism of action of introduced aluminosilicate in the system of hydrating cement, particularly in the case of calcium aluminate cement pastes. It was found that the presence of fine-grained additive caused in all studied cases the increase of the amount of released heat in the first period after the addition of water. In the case of aluminate cements with aluminosilicate addition, a significant reduction of induction time and faster precipitation of hydration products were observed compared to the reference sample (without additive). In the experimental conditions, the additive caused the acceleration of aluminate cements hydration, and the mechanism of its action is probably complex and can encompass: nucleative action of small grains and formation of new chemical compounds.     

Modification of surface properties of a poly(dimethylsiloxane)-based elastomer, RTV11, upon exposure to seawater

Atomic force microscopy (AFM) was combined with surface analytical techniques to investigate the rarely addressed issue of the effect of seawater on the surface properties of a selected fouling-release coating, silicon elastomer RTV11 (trademark of General Electric). The exposure of the RTV11 surface to seawater resulted in a modification of its morphology and mechanical properties, as confirmed by AFM and scanning electron microscopy (SEM). Surface modification was dependent on sample preparation and curing process, namely, curing agent concentration and relative humidity during curing. The RTV11 surface remained largely unaltered for samples cured under 100% relative humidity. SEM and X-ray photoelectron spectroscopy studies confirmed that the modified surface of RTV11 had the same elemental composition as the unexposed surface of the elastomer and showed excess Ca. However, the modified surface deformed plastically under load and was stiffer than the original surface. No major change was found on surfaces exposed to nanopure water during similar times of exposure as in seawater, regardless of curing conditions. The rate of increase in the aggregate formation in seawater can be described by an exponential function, with a decay constant of approximately 4.99 x 10(-)(3) min(-)(1) and a pre-exponential factor of approximately 1.77 x 10(-)(2) microm/min.     

Simulating electron transfer attachment to a positively charged model peptide

Ab initio electronic structure methods, including stabilization method tools for handling electronically metastable states, are used to treat a model system designed to probe the electron-transfer event characterizing electron-transfer dissociation (ETD) mass spectroscopic studies of peptides. The model system consists of a cation H(3)C-(C=O)NH-CH(2)-CH(2)-NH(3)(+), containing a protonated amine site and an amide site, that undergoes collisions with a CH(3)(-) anion. Cross-sections for electron transfer from CH(3)(-) to the protonated amine site are shown to exceed those for transfer to the Coulomb-stabilized amide site by 2 orders of magnitude. Moreover, it is shown that the fates of the amine-attached and amide-attached species are similar in that both eventually lead to the same carbon-centered radical species H(3)C-((*)C-OH)NH-CH(2)-CH(2)-NH(2), although the reaction pathways by which the two species produce this radical are somewhat different. The implications for understanding peptide fragmentation patterns under ETD conditions are also discussed in light of this work's findings.     

A new tool for inorganic nitrogen speciation study: simultaneous determination of ammonium ion, nitrite and nitrate by ion chromatography with post-column ammonium derivatization by Nessler reagent and diode-array detection in rain water samples

The paper presents a new method for a simultaneous determination of inorganic nitrogen species in the oxidized (NO₂⁻, NO₃⁻) and reduced (NH₄⁺) form in rain water samples. The method is based on a system of nitrogen species separation employing ion exchange and diode-array detection. The ions are separated in a strong ion-exchanger, nitrites and nitrates are determined directly at 208 and 205 nm, respectively, while the ammonium ions are determined in the column hold-up time after a post-column derivatization by the Nessler reagent, at 425 nm. The use of a diode-array detector permits a simultaneous identification of the inorganic nitrogen species in 8 min. The detection limits obtained are: NO₂⁻, 0.1 mg L⁻¹; NO₃⁻, 0.05 mg L⁻¹; NH₄⁺, 1 mg L⁻¹. The method proposed has been successfully used for speciation analysis of inorganic nitrogen in precipitation.