19F and 31P NMR characterisation of the phosphaalkene,CF3 P=CF2, intermediate in the alkaline hydrolysis of bis(trifluoromethyl)phospine

The previously postulated phosphaalkene intermediate CF₃ P=CF₂ in the alkaline hydrolyses of (CF₃)₂ PH has been trapped and characterised by its ¹⁹F and ³¹P NMR spectra.     

Catalytic homologation of vinyltributylstannane to allyltributylstannane by Mo(IV) complexes in the presence of ethylene

We have found that CH2=CHSnBu3 is converted into CH2=CHCH2SnBu3 catalytically in the presence of Mo(IV) olefin complexes such as Mo(NAr)(CH2CH2)[biphen] (where Ar = 2,6-i-Pr2C6H3 and [biphen]2- = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate). The proposed mechanism involves formation of a metalacyclopentane (MC4) complex from ethylene and CH2=CHSnBu3, "contraction" of this MC4 complex to a metalacyclobutane (MC3) complex, and finally metathesis of the MC3 complex to give CH2=CHCH2SnBu3 and Mo(NAr)(CH2)[biphen]. These new findings suggest (inter alia) that contraction of an MC4 ring to an MC3 ring may be a much more common mode of decomposition of metalacyclopentane rings in d0 complexes than previously believed.     

Development, validation, and standardization of polymerase chain reaction-based detection of E. coli O157

A diagnostic polymerase chain reaction assay was developed for the detection of E. coli O157 as the first part of a multicenter validation and standardization project. The assay is based on amplification of sequences of the rfbE O157 gene and includes an internal amplification control. The selectivity of the assay was evaluated against 155 strains, including 32 E. coli O157, 38 E. coli non-O157, and 85 non-E. coli. It was shown to be highly inclusive (100%) and exclusive (100%). The assay has a 100% detection probability of approximately 2 x 10(3) cells per reaction.     

Essential oil variation of Salvia officinalis aerial parts during its phenological cycle

In this paper the variation in the quantity and quality of the essential oil of Salvia officinalis during its life cycle stages is reported. The oils were obtained by hydrodistillation of air-dried samples. The yield of essential oil (w/w %) in different stages was in the order: floral budding (0.9%) > vegetative (0.7%) > flowering (0.5%) > immature fruit (0.4%) > ripen fruit (0.2%). The essential oils were analyzed by GC and GC-MS. In total, 36, 41, 40, 38, and 41 constituents were identified and quantified in the subsequent stages, respectively. Oxygenated monoterpenes were the main group of compounds in the fruiting set (56.9%), vegetative (48.5%), flowering (47.7%), and floral budding (45.3%) stage. 1,8-cineole as one of the major constituents of all samples was lower in the vegetative stage and gradually increased in subsequent harvesting times to reach a maximum in flowering and then decreased in the fruiting set. In contrast, the globulol content was higher in the first stage and decreased drastically during fruit maturation. Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 16–19, January–February, 2006.     

Identification and structural characterisation of carboxy-terminal polypeptides and antibody epitopes of Alzheimer's amyloid precursor protein using high-resolution mass spectrometry

Alzheimer's disease (AD) is the most common cause for human age-related dementia, characterised by formation of diffuse plaques in brain that are directly involved in AD pathogenesis. The major component of AD plaques is beta-amyloid, a 40 to 42 amino acid polypeptide derived from the amyloid precursor protein (APP) by proteolytic degradation involving the specific proteases, beta-and gamma-secretase acting at the N- and C- terminal cleavage site, respectively. In this study we have prepared polypeptides comprising the carboxy-terminal and transmembrane sequences of APP, by bacterial expression and chemical synthesis, as substrates for studying the C-terminal processing of APP and its interaction with the gamma-secretase complex. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used as a major tool for structure analysis. Immunisation of transgenic mouse models of AD with Abeta42 has been recently shown to be effective to inhibit and disaggregate Abeta-fibrils, and to reduce AD-related neuropathology and memory impairments. However, the mechanism underlying these therapeutic effects has been as yet unclear. Using proteolytic epitope excision from immune complexes in combination with FT-ICR-MS, we identified the epitope recognised by the therapeutically active antibody as the N-terminal Abeta(4-10) sequence; this soluble, nontoxic epitope opens new lead structures for AD vaccine development. A monoclonal antibody (Jonas; JmAb) directed against the cytosolic APP domain was used in studies of APP biochemistry and metabolism. Here we report the identification of the epitope recognised by the JmAb, using the combination of epitope excision and peptide mapping by FT-ICR-MS. The epitope was determined to be located at the C-terminal APP(740-747) sequence; it was confirmed by ELISA binding assays and authentic synthetic peptides and will be an efficient tool in the development of new specific vaccines. These results demonstrate high-resolution FT-ICR-MS as a powerful method for characterising biochemical pathways and molecular recognition structures of APP.     

Molecular complexation of free base meso-tetraarylporphyrins with antimony(III) chloride in free solvent media

The reaction of meso-tetraarylporphyrins (H₂t(Xp)p) with SbCl₃ under free solvent conditions affords green complexes with a 1:1 H₂t(X)pp:SbCl₃ ratio. These complexes have dimeric structures with a (μ-Cl)₂bridge. UV–VIS, ¹H NMR and ¹³C NMR spectra data show that the porphyrin core of [(H₂t(Xp)p)₂Sb₂Cl₆], similar to 1:2 (donor:acceptor) molecular complexes of meso-tetraarylporphyrins and porphyrin diacid, is distorted, thus two nitrogen atoms of pyrrolenine in a side of the porphyrin plane act as electron donors to an antimony atom of SbCl₃. Molecular complexation of meso-tetraarylporphyrins with SbCl₃ produces a large downfield shift for the NH signal, although there is no hydrogen bonding present.     

The effect of pH and ionic strength on the transport of alumina nanofluids in water-saturated porous media

Alumina nanofluids are one of the most useful nanofluids, especially for increasing the thermal conductivity. Due to importance of porous media in the improvement of heat transfer, this study investigates the transport and retention of gamma alumina/water nanofluid in the water-saturated porous media. For this purpose, alumina nanofluids were introduced to the porous media consisting of water-saturated glass beads possessing various pH values (4, 7 and 10) and different ionic strengths (0.001 M of KCl, CaCl₂, AlCl₃, K₂SO₄, CaSO₄, Al₂(SO₄)₃, K₂CO₃ and CaCO₃). Then the break through curve of each experiment was drawn and modeled by combining classical filtration theory with advection–dispersion equation. Single collector efficiency (η₀) and attachment efficiency (α) were calculated by classical filtration theory. Also curve fitting of experiments and modeling was achieved by minimizing the sum of squared residuals, to calculate retardation factor (R) and hydrodynamic dispersion coefficient (D) of each experiment. According to the results, in general, increase in pH and ionic strength will enhance the removal rate coefficient, retardation factor and retention while decreasing the steady-state break through concentration and the hydrodynamic dispersion coefficient. The opposite of this rule was observed and analyzed for aluminum salts. The lowest retention of nanoparticles at 31.04% can be related to their transport in background solution with pH = 4 [α = \(3.87 \times 10^{ - 2}\), K_att = \(3.33 \times 10^{ - 3}\) (min⁻¹), R = 3.93, D = 0.91 (cm² min⁻¹)], and the highest retention in nanoparticle content of 94.29% was observed in background solution containing CaCO₃ [α = \(14.33 \times 10^{ - 2}\), K_att = \(137.82 \times 10^{ - 3}\) (min⁻¹), R = 12.02, D = 0.62 (cm² min⁻¹)]. Therefore, chemistry of water plays an important role in transport and retention parameters. The classical filtration theory and the advection–dispersion model are able to perfectly model and quantify the parameters of the alumina nanofluid transport in saturated porous media.

     

Some tetranuclear carbonyl complexes of cobalt,rhodium and iridium containing trifluorophosphine

Syntheses of Co₂Rh₂(CO)₈(PF₃)₄ and Co₂Rh₂(CO)₁₀(PF₃)₂ are described and their structures are discussed. Evidence is presented for an intermolecular ligand exchange between several tetranuclear cluster complexes. ¹⁹F and ³¹P NMR and mass spectroscopic data are presented and discussed. The complexes Rh₄(CO)₄(PF₃)₈ and Co₂Ir₂(CO)₈(PF₃)₄ have been identified by their mass spectra.     

Electrocatalytic Reduction of Dioxygen on the Surface of Glassy Carbon Electrodes Modified with Cobalt Porphyrin Complexes

The preparation and electrocatalytic behavior of glassy carbon electrodes modified with three different cobalt porphyrin complexes were investigated. The electrocatalytic ability of the modified electrodes for the reduction of dioxygen to hydrogen peroxide and water in air‐saturated aqueous solutions was examined by cyclic voltammetry and chronoamperometry techniques. The porphyrin‐adsorbed glassy carbon electrodes possess excellent electrocatalytic abilities for dioxygen reduction with overpotential about 0.5 V lower than that at a plain glassy carbon electrode. The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The possible effects of the electron‐donating properties of groups in the meso‐position of the porphyrin ring were investigated.     

A Thermodynamic Study of Complex Formation Between 18-Crown-6 with T1 + , Hg 2+ and Ag + Metal Cations in Some Binary Mixed Non-aqueous Solvents Using the Conductometric Method

The complexation reactions betweenT1⁺, Hg²⁺ andAg⁺ metal cations with 18-Crown-6 (18C6)were studied in acetonitrile (AN)-methanol (MeOH) andbenzonitrile (BN)-methanol (MeOH) binary mixtures at differenttemperatures using the conductometric method. The conductance datashow that the stoichiometry of the complexes in most cases is1 : 1 (ML), but in the case of theTl⁺ cation, in addition to a1 : 1 complex, a 1 : 2 (ML₂)complex is formed in solutions. A non-linear behaviourwas observed for the variation of log K_fof the complexes vs the composition of the binary mixed solvents. The stability of 18C6 complexes with T1⁺, Hg²⁺ and Ag⁺ cations is sensitive to solvent composition and in some cases, the stability order is changed with changingthe composition of the mixed solvents. The values of the thermodynamic parameters (Δ H_c°, Δ S_c°) for formation of 18C6-T1⁺, 18C6-Hg⁺² and the 18C6-Ag⁺ complexes were obtained from the temperature dependence of the stability constants and the results show that the thermodynamics of the complexationreactions is affected by the nature and composition of the mixed solvents and in most cases, the complexes are enthalpy destabilized but entropy stabilized.