Novel tetrahedral tetranickel cluster with alkylidyne ligand (NiCp)4(μ3-CR)

A novel tetrahedral (μ₃-alkylidyne)tetranickel cluster (NiCp)₄(μ₃-C(CH₂)₄CH₃) (4) was obtained in the reaction of nickelocene with potassium and 1-hexene. Compound 4 was characterised by means of MS and X-ray diffraction analysis. It crystallizes in the orthorhombic crystal system and Pna2₁ (No. 33) space group. Unit cell dimensions: a = 28.406(6) Å, b = 8.928(2) Å, c = 9.541(2) Å; Z = 4. The compound possesses 63 valence electrons, three more than the expected “magic number” for such type of clusters, and three of the four nickel atoms do not fulfil the 18VE rule. It is paramagnetic with the magnetic moment 3.54 μ_B, what corresponds to three unpaired electrons per molecule. This was confirmed by molecular orbital calculations using the density functional theory (DFT).     

Polarizability and inductive effect contributions to solvent–cation binding observed in electrospray ionization mass spectrometry

Electrospray ionization (ESI) mass spectrometry (MS) has been used in conjunction with computer modeling to investigate binding tendencies of alkali metal cations to low molecular weight solvents. Intensities of peaks in ESI mass spectra corresponding to solvent-bound alkali metal cations were found to decrease with increasing ionic radii (Li⁺ > Na⁺ > K⁺ > Cs⁺) in either dimethylacetamide (DMAc) or dimethylformamide (DMF). When a lithium or sodium salt was added to an equimolar mixture of DMF, DMAc, and dimethylpropionamide (DMP), the intensities of gas-phase [solvent + alkali cation]⁺ peaks observed in ESI mass spectra decreased in the order DMP > DMAc ≫ DMF. A parallel ranking was obtained for alkali metal cation affinities in ESI-MS/MS experiments employing the kinetic method. These trends have been attributed to a combination of at least three factors. An inductive effect exhibited by the alkyl group adjacent to the carbonyl function on each solvent contributes through-bond electron donation to stabilize the alkali metal cation attached to the carbonyl oxygen. The shift in the partial negative charge at the oxygen binding site with increasing n-alkyl chain length (evaluated via computer modeling), however, cannot fully account for the mass spectrometric data. The increasing polarizability and the augmented ability to dissipate thermal energy with increasing size of the solvent molecule are postulated to act in conjunction with the inductive effect. Further evidence of these contributions to solvent–cation binding in ESI-MS is given by the relative intensities of [solvent + Li]⁺ peaks in mixtures containing equimolar quantities of alcohols, indicating preferential solvation of Li⁺ in the order n-propanol > ethanol > methanol. These experiments suggest a combined role of polarizability, the inductive effect, and solvent molecule size in determining relative intensities of solvated cation peaks in ESI mass spectra of equimolar mixtures of homologous solvents.     

Dicarboxylic acids and hydroxy fatty acids in different species of fungi

Secondary metabolites of fungi can be responsible for allergies; therefore, the identification of compounds produced by these organisms is very important. Fungi produce large amounts of secondary metabolites, which belong to groups of chemicals such as: dicarboxylic acids, hydroxy acids, alcohols, hydrocarbons, esters, fatty acids, sterols, amino acids and mycotoxins. The presence of all these compounds in human proximity contributes to many diseases. Therefore, the aim of the study was a qualitative and quantitative analysis of hydroxy and dicarboxylic acids produced by fungi occurring in student hostel in Poland, in the province of Pomerania. The following species of fungi were subjected to extraction: Aspergillus niger, Aspergillus fumigatus, Aspergillus candidus, Rhizopus sp., Geotrichum candidum, and Penicillium chrysogenum. A mixture of ethyl acetate and methanol was used for the extraction. The obtained extracts were further analyzed by gas chromatography mass spectrometry (GC–MS). In all samples of fungi, the presence of a total of 22 acids, including 13 dicarboxylic and 9 hydroxy acids, was confirmed. Most acids (17 different acids) were identified in A. fumigatus. Only 10 acids were identified in the mycelium of G. candidum and A. niger. Acids which were identified in all samples of the mycelium were 22-hydroxydocosanoic acid, 24-hydroxytetracosanoic acid and adipic acid. The most abundant compounds were 22-hydroxydocosanoic acid in A. fumigatus, A. candidus, Rhizopus sp., G. candidum and P. chrysogenum, and succinic acid in A. niger. More experiments are needed to understand the physiological role of hydroxy and dicarboxylic acids. We hope that our results are an important contribution to further studies on the human health.     

Field-amplified sample injection coupled with pseudo-isotachophoresis technique for sensitive determination of selected psychiatric drugs in human urine samples after dispersive liquid–liquid microextraction

A field-amplified sample injection (FASI) technique was elaborated for fast and sensitive determination of selected central nervous system drugs in human urine samples. Factors affecting the sensitivity enhancement, such as background electrolyte (BGE) and the analytical matrix composition were optimized and discussed. Pseudo-isotachophoresis (p-ITP) mechanism contribution in preconcentration mechanism was discussed. All separations were performed in uncoated fused silica capillaries 50 μm × 57 cm at 22 kV. The optimized analytical matrix was composed of 0.25 mM HCOOH in 90% (v/v) methanol, while BGE contained 45 mM TRIS/HCl (pH 2.20). The head-column injection was performed in 0.25 mM HCOOH water solution (3 s, 3.45 kPa). Sample was introduced into the capillary by electrokinetic injection (70 s, 5 kV) followed by short BGE plug (3 s, 3.45 kPa). Seven psychiatric drugs (olanzapine, prochlorperazine dimaleate, trifluoperazine dihydrochloride, perphenazine, promazine hydrochloride, clomipramine hydrochloride, and chlorprothixene hydrochloride) were separated in about 6 min. The elaborated method was additionally supported with dispersive liquid–liquid microextraction (DLLME) technique which in summary with FASI provided about 8000–13,000-fold sensitivity enhancement in comparison to the capillary zone electrophoresis (CZE) method with standard hydrodynamic injection (5 s, 3.45 kPa).     

Strong connections on quantum principal bundles

A gauge invariant notion of a strong connection is presented and characterized. It is then used to justify the way in which a global curvature form is defined. Strong connections are interpreted as those that are induced from the base space of a quantum bundle. Examples of both strong and non-strong connections are provided. In particular, such connections are constructed on a quantum deformation of the two-sphere fibrationS ²→RP ². A certain class of strongU _q (2)-connections on a trivial quantum principal bundle is shown to be equivalent to the class of connections on a free module that are compatible with theq-dependent hermitian metric. A particular form of the Yang-Mills action on a trivialU _q (2)-bundle is investigated. It is proved to coincide with the Yang-Mills action constructed by A. Connes and M. Rieffel. Furthermore, it is shown that the moduli space of critical points of this action functional is independent ofq. This work was in part supported by the NSF grant 1-443964-21858-2. Writing up the revised version was partially supported by the KBN grant 2 P301 020 07 and by a visiting fellowship at the International Centre for Theoretical Physics in Trieste.     

Symmetries of quantum spaces. Subgroups and quotient spaces of quantumSU(2) andSO(3) groups

We prove that each action of a compact matrix quantum group on a compact quantum space can be decomposed into irreducible representations of the group. We give the formula for the corresponding multiplicities in the case of the quotient quantum spaces. We describe the subgroups and the quotient spaces of quantumSU(2) andSO(3) groups.     

On sequential properties of Banach spaces,spaces of measures and densities

We show that a conjunction of Mazur and Gelfand-Phillips properties of a Banach space E can be naturally expressed in terms of weak* continuity of seminorms on the unit ball of E*.     

Random groups do not split

We prove that random groups in the Gromov density model, at any density, satisfy property (FA), i.e. they do not act non-trivially on simplicial trees. This implies that their Gromov boundaries, defined at density less than \frac12{\frac{1}{2}} , are Menger curves.     

Mechanism of 4‐methyl‐1,2,4‐triazol‐3‐thiole reaction with formaldehyde. A DFT study

Contrary to the typical nucleophilic substitution, occurring on the sulfur atom of 4‐methyl‐1,2,4‐ triazol‐3‐thiole, the reaction with formaldehyde leads to the formation of the N? C bond rather than the S? C bond. The mechanism of this reaction has been characterized theoretically. Calculations indicate that the reaction proceeds via a cyclic transition state involving one solvent molecule with the Gibbs free activation energy of only 2 kcal/mol. The alternative pathway that leads to the S? C bond formation is about 5 kcal/mol more energetically demanding. Copyright © 2007 John Wiley & Sons, Ltd.