Promotion of phosphaalkyne cyclooligomerisation by a Sb(v) to Sb(iii) redox process

A high yield of the tetraphosphaladderene, anti-tetraphosphatricyclo[4.2.0.0(2,5)]octa-3,7-diene, is obtained from reaction of the zirconocene 1,3-diphosphabicyclo[1.1.0]butane with Ph(2)SbCl(3) in THF or CH(2)Cl(2). Exploration of the reaction pathway using density functional theory suggests that an envelope-type adduct of Ph(2)SbCl and 1,3-diphosphabicyclo[1.1.0]butane plays a pivotal role in the reaction. The zwitterionic character of this intermediate species allows it to act simultaneously as both an ene and an eneophile, and a symmetry-allowed bimolecular reaction leads to the tetraphosphaladderene species via a spirocyclic intermediate.     

Cation effect on anion separations by aza-crown ligands in liquid membranes

New carriers have been prepared based on the aza-18-crown-6 structure to facilitate membrane transport of ions. One of these incorporates four aza-18-crown-6 molecules bonded to a resorcinarene ring. The other, aza-18-crown-6 bonded to an undecyl chain, was studied as a monomeric analog. These carriers have been included in dichloromethane bulk liquid membranes (BLMs) to assess cation influence on competitive transport among anions (ReO₄⁻, NO₃⁻, ClO₄⁻). ReO₄⁻ was investigated as a non-radioactive analog of the pertechnetate anion, which is of interest in nuclear waste separations. The permeability values and selectivity for ReO₄⁻ and ClO₄⁻ were the greatest when neutral source and receiving phases were used with K⁺ as the co-transported cation. The carriers also showed selectivity for ReO₄⁻ and ClO₄⁻ over NO₃⁻ with K⁺ and Na⁺ as the co-transported cations using neutral and basic aqueous phase solutions. It was also found that some cations inhibit anion transport.     

Two‐sided Group Digraphs and Graphs

We study a family of digraphs (directed graphs) that generalises the class of Cayley digraphs. For nonempty subsets of a group G, we define the two‐sided group digraph to have vertex set G, and an arc from x to y if and only if for some and . In common with Cayley graphs and digraphs, two‐sided group digraphs may be useful to model networks as the same routing and communication scheme can be implemented at each vertex. We determine necessary and sufficient conditions on L and R under which may be viewed as a simple graph of valency , and we call such graphs two‐sided group graphs. We also give sufficient conditions for two‐sided group digraphs to be connected, vertex‐transitive, or Cayley graphs. Several open problems are posed. Many examples are given, including one on 12 vertices with connected components of sizes 4 and 8.     

On the maximal number of coprime subdegrees in finite primitive permutation groups

We compute the divisor class group of the general hypersurface Y of a complex projective normal variety X of dimension at least four containing a fixed base locus Z. We deduce that completions of normal local complete intersection domains of finite type over C of dimension ≥ 4 are completions of UFDs of finite type over C.     

Evidence for a SN2-type pathway for phosphine exchange in phosphine-phosphenium cations, [R2P--PR'3]+

Abstraction of a Cl(-) ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the P--P bonded cations [R4C4P--P(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl(2)) of [Et4C4P-(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P-(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with DeltaS( not equal)=(-106.3+/-6.7) J mol(-1) K(-1), DeltaH( not equal)=(14.9+/-1.6) kJ mol(-1) and DeltaG( not equal) (298.15 K)=(46.6+/-2.6) kJ mol(-1), values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (S(N)1-type) pathway reported for the analogous exchange reactions of the [ArNCH2CH2N(Ar)P(PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [ArNCH2CH2N(Ar)P(PMe3)](+) is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong pi-pi interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective pi-donation from the amide groups reduces the intrinsic electrophilicity of [ArNCH2CH2N(Ar)P]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway.     

Development of a rapid,multi-class method for the confirmatory analysis of anti-inflammatory drugs in bovine milk using liquid chromatography tandem mass spectrometry

A rapid liquid chromatography tandem mass spectrometry (LC–MS/MS) method has been developed and validated for the simultaneous identification, confirmation and quantitation of seven licensed anti-inflammatory drugs (AIDs) in bovine milk. The method was validated in accordance with the criteria defined in Commission Decision 2002/657/EC. Two classes of AIDs were investigated, corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs). The developed method is capable of detecting and confirming dexamethasone (DXM), betamethasone (BTM), prednisolone (PRED), tolfenamic acid (TLF), 5-hydroxy flunixin (5-OH-FLU), meloxicam (MLX) and 4-methyl amino antipyrine (4-MAA) at their associated maximum residue limits (MRLs). These compounds represent all the corticosteroids and NSAIDs licensed for use in bovine animals producing milk for human consumption. These compounds have never been analysed before in the same method and also 4-methyl amino antipyrine has never been analysed with the other licensed NSAIDs. The method can be considered rapid as permits the analysis of up to 30 samples in one day. Milk samples are extracted with acetonitrile; sodium chloride is added to aid partition of the milk and acetonitrile mixture. The acetonitrile extract is then subjected to liquid–liquid purification by the addition of hexane. The purified extract is finally evaporated to dryness and reconstituted in a water/acetonitrile mixture and determination is carried out by LC–MS/MS. Decision limit (CCα) values and detection capability (CCβ) values have been established for each compound.     

Evaluation of the separation characteristics of application-specific (pesticides and dioxins) open-tubular columns for gas chromatography

The solvation parameter model is used to characterize the retention properties of four application-specific open-tubular columns (Rtx-CLPesticides, Rtx-OPPesticides, Rtx-Dioxin and Rtx-Dioxin2) at five equally spaced temperatures over the range 60-140 degrees C. Cluster analysis is used to compare the system constants to a database of forty open-tubular columns characterized according to the same method. System constants differences and retention factor correlation plots are then used to determine selectivity differences between the application-specific columns and their nearest neighbors identified by cluster analysis. The Rtx-CLPesticides and Rtx-OPPesticides columns are shown to belong to the selectivity group containing poly(dimethylmethyltrifluoroprpylsiloxane) stationary phases with Rtx-OPPesticides having a similar selectivity to a poly(dimethylmethyltrifluoropropylsiloxane) stationary phase containing 20% methyltrifluoropropylsiloxane monomer (DB-200) and Rtx-CLPesticides separation properties for a stationary phase containing less than 20% methyltrifluoropropylsiloxane monomer. The Rtx-Dioxin and Rtx-Dioxin2 columns are located in the selectivity group dominated by the poly(dimethyldiphenylsiloxane) stationary phases containing less than 20% diphenylsiloxane monomer. The Rtx-Dioxin and Rtx-Dioxin2 columns are shown to be selectivity equivalent to a (5% phenyl) carborane-siloxane copolymer stationary phase (Stx-500) and a second generation silarylene-siloxane copolymer stationary phase containing dimethylsiloxane and diphenylsiloxane monomers (DB-XLB), respectively.