Effect of cations on the structure of bilayers formed by lipopolysaccharides isolated from Pseudomonas aeruginosa PAO1

The asymmetric outer membrane of Gram-negative bacteria contains lipopolysaccharides (LPSs) which contribute significantly to the bacterium's surface properties and play a crucial role in regulating membrane permeability. We report on neutron diffraction studies performed on aligned, self-assembled bilayers of Na-, Ca-, and Mg-salt forms of LPS isolated from Pseudomonas aeruginosa PAO1. From the one-dimensional neutron scattering length density profiles we find that water penetrates Ca2+-LPS bilayers to a lesser extent than either Na+- or Mg2+-LPS bilayers. This differential water penetration could have implications as to how small molecules permeate the outer membrane of Gram-negative bacteria and, possibly, how nonlamellar phases are formed.     

Analysis of biological fluids by high-field nuclear magnetic resonance spectroscopy

The application of high-field Fourier transform nuclear magnetic resonance (NMR) spectroscopy to the analysis of biological fluids such as urine, plasma and bile is described. Applications include areas such as clinical chemistry, experimental and clinical toxicology and drug metabolism studies. In the case of proton NMR some means of attenuating or eliminating the interference due to water protons is required and suitable strategies for achieving this are discussed. The use of 2-dimensional NMR or solid-phase extraction/chromatography to enable the identification of unknowns is discussed and the potential usefulness of ¹⁹F NMR for studying the metabolism of fluorinated xenobiotics is highlighted.     

Reduction of the pertechnetate anion with bidentate phosphine ligands

The reduction of ammonium pertechnetate with bis(diphenylphosphino)methane (dppm), and with diphenyl-2-pyridyl phosphine (Ph(2)Ppy), has been investigated. The neutral Tc(II) complex, trans-TcCl(2)(dppm)(2) (1), has been isolated from the reaction of (NH(4))[TcO(4)] with excess dppm in refluxing EtOH/HCl. Chemical oxidation with ferricinium hexafluorophosphate results in formation of the cationic Tc(III) analogue, trans-[TcCl(2)(dppm)(2)](PF(6)) (2). The dppm ligands adopt the chelating bonding mode in both complexes, resulting in strained four member metallocycles. With excess PhPpy, the reduction of (NH(4))[TcO(4)] in refluxing EtOH/HCl yields a complex with one chelating Ph(2)Ppy ligand and one unidentate Ph(2)Ppy ligand, mer-TcCl(3)(Ph(2)Ppy-P,N)(Ph(2)Ppy-P) (3). The cationic Tc(III) complexes, trans-[TcCl(2)(Ph(2)P(O)py-N,O)(2)](PF(6)) (4) and trans-[TcCl(2)(dppmO-P,O)(2)](PF(6)) (5) (Ph(2)P(O)py = diphenyl-2-pyridyl phosphine monoxide and dppmO = bis(diphenylphosphino)methane monoxide), have been isolated as byproducts from the reactions of (NH(4))[TcO(4)] with the corresponding phosphine. The products have been characterized in the solid state and in solution via a combination of single-crystal X-ray crystallography and spectroscopic techniques. The solution state spectroscopic results are consistent with the retention of the bonding modes revealed in the crystal structures.     

N-α-Benzyloxyacetyl derivatives of (S)-4-benzyl-5,5-dimethyloxazolidin-2-one for the asymmetric synthesis of differentially protected α,β-dihydroxyaldehydes

α-Dibenzylamino- and α-benzyloxy- derivatives of N-acetyl-(S)-4-benzyl-5,5-dimethyloxazolidin-2-one readily undergo highly stereoselective boron mediated syn-aldol reactions with a range of aromatic and aliphatic aldehydes, generating the syn-aldol products in good to excellent yields as single diastereoisomers after purification. In the α-dibenzylamino series, deprotection of the functionalised aldol fragments to the corresponding α-amino-β-hydroxy methyl ester or α-amino-β-hydroxyaldehyde proved problematic, with a range of N- and O-protecting groups giving mixtures of products arising from endocyclic and exocyclic cleavage pathways. However, in the α-benzyloxy series, O-silyl protection of the aldol products, and subsequent DIBAL reduction gives stereoselectively the corresponding N-1′-hydroxyalkyloxazolidin-2-ones, which undergo base promoted fragmentation to the desired highly functionalised and differentially protected α,β-dihydroxyaldehydes in good yields and without loss of stereochemical integrity.     

UPLC/MS(E); a new approach for generating molecular fragment information for biomarker structure elucidation

A new approach to obtain fragmentation information in liquid chromatography/mass spectrometry (LC/MS) studies of small molecules in complex mixtures is presented using simultaneous acquisition of exact mass at high and low collision energy, MS(E). LC/MS-TOF and LC/MS/MS-TOF are powerful tools for the analysis of complex mixtures, especially those for biological fluids allowing the elucidation of elemental composition and fragmentation information. In this example the composition of rat urine was studied using this new approach, allowing the structures of several endogenous components to be confirmed in one analytical run by the simultaneous acquisition of exact mass precursor and fragment ion data. The spectral data obtained using this new approach are comparable to those obtained by conventional LC/MS/MS as exemplified by the identification of endogenous metabolites present in rat urine.     

Moderating the nucleophilicity of the sulfide ligands in the dinuclear {Pt2S2} metalloligand system using triphenylarsine

Reaction of cis-[PtCl₂(AsPh₃)₂] with excess sodium sulfide in benzene gave the triphenylarsine analogue of the well-known metalloligand [Pt₂(μ-S)₂(PPh₃)₄] as an orange solid.The compound was characterised by detailed mass spectrometry studies, and by conversion to various alkylated and metallated derivatives.The sulfide ligands in [Pt₂(μ-S)₂(AsPh₃)₄] are less basic than the triphenylphosphine analogue, and the complex gives a relatively weak [M+H]⁺ ion in the positive-ion electrospray (ESI) mass spectrum, compared with the phosphine analogue.Methylation of an equimolar mixture of [Pt₂(μ-S)₂(PPh₃)₄] and [Pt₂(μ-S)₂(AsPh₃)₄] with MeI gave the species [Pt₂(μ-S)(μ-SMe)(AsPh₃)₄]⁺ and [Pt₂(μ-SMe)₂(PPh₃)₃I]⁺, indicating a reduced tendency for the sulfide of [Pt₂(μ-S)(μ-SMe)(AsPh₃)₄]⁺ to undergo alkylation.The lability of the arsine ligands is confirmed by the reaction of an equimolar mixture of [Pt₂(μ-S)₂(PPh₃)₄] and [Pt₂(μ-S)₂(AsPh₃)₄] with n-butyl chloride, giving [Pt₂(μ-S)(μ-SBu)(EPh₃)₄]⁺ (E = P, As), which with Me₂SO₄ gave a mixture of [Pt₂(μ-SMe)(μ-SBu)(PPh₃)₄]²⁺ and [Pt₂(μ-SMe)(μ-SBu)(AsPh₃)₃Cl]⁺.Reactivity towards 1,2-dichloroethane follows a similar pattern.The formation and ESI MS detection of mixed phosphine-arsine {Pt₂S₂} species of the type[Pt₂(μ-S)₂(AsPh₃)_n(PPh₃)_4−n] is also discussed. Coordination chemistry of [Pt₂(μ-S)₂(AsPh₃)₄] towards a range of metal-chloride substrates, forming sulfide-bridged trinuclear aggregates, has also been probed using ESI MS, and found to be similar to the phosphine analogue. The X-ray crystal structure of [Pt₂(μ-S)₂(AsPh₃)₄Pt(cod)](PF₆)₂ (cod = 1,5-cyclo-octadiene) has been determined for comparison with the (previously reported) triphenylphosphine analogue. ESI MS is a powerful tool in exploring the chemistry of this system; in some cases the derivatising agent p-bromobenzyl bromide is used to convert sparingly soluble and/or poorly ionising {Pt₂S₂} species into soluble, charged derivatives for MS analysis.     

An Electron-Deficient Triosmium Cluster Containing the Thianthrene Ligand: Synthesis, Structure and Reactivity of [Os3(CO)9(μ3-η2-C12H7S2)(μ-H)]

Reaction of [Os₃(CO)₁₀(CH₃CN)₂] with thianthrene at 80 °C leads to the nonacarbonyl dihydride compound [Os₃(CO)₉(μ-3,4-η²-C₁₂H₆S₂)(μ-H)₂] (1) and the 46-electron monohydride compound [Os₃(CO)₉(μ₃-η²-C₁₂H₇S₂)(μ-H)] (2). Compound 2 reacts reversibly with CO to give the CO adduct [Os₃(CO)₁₀(μ-η²-C₁₂H₇S₂)(μ-H)] (3) whereas with PPh₃ it gives the addition product [Os₃(CO)₉)(PPh₃)(μ-η²-C₁₂H₇S₂)(μ-H)] (4) as well as the substitution product 1,2-[Os₃(CO)₁₀((PPh₃)₂] (5) Compound 2 represents a unique example of an electron-deficient triosmium cluster in which the thianthrene ring is bound to cluster by coordination of the sulfur lone pair and a three-center-two-electron bond with the C(2) carbon which bridges the same edge of the triangle as the hydride. Electrochemical and DFT studies which elucidate the electronic properties of 2 are reported. Dedicated to the memory of a great scientist, F. Albert Cotton.     

In Vivo Endoscopic Tissue Identification by Rapid Evaporative Ionization Mass Spectrometry (REIMS)

Gastrointestinal cancers are a leading cause of mortality, accounting for 23 % of cancer‐related deaths worldwide. In order to improve outcomes from these cancers, novel tissue characterization methods are needed to facilitate accurate diagnosis. Rapid evaporative ionization mass spectrometry (REIMS) is a technique developed for the in vivo classification of human tissue through mass spectrometric analysis of aerosols released during electrosurgical dissection. This ionization technique was further developed by utilizing surface induced dissociation and was integrated with an endoscopic polypectomy snare to allow in vivo analysis of the gastrointestinal tract. We tested the classification performance of this novel endoscopic REIMS method in vivo. It was shown to be capable of differentiating between healthy layers of the intestinal wall, cancer, and adenomatous polyps based on the REIMS fingerprint of each tissue type in vivo.     

Structural Studies of Some Compounds Containing C2 Fragments Attached to Various Metal‐Ligand End‐Groups

The preparation, characterisation and single‐crystal XRD molecular structure determinations of four complexes containing –CC–ML_n end‐groups, namely Ru{C≡CFc′(I)}(dppe)Cp ( 1 ), the vinylidene [Os(=C=CH₂)(PPh₃)₂Cp]PF₆ ( 2 ), trans‐Pt(C≡CC₆H₄‐4‐C≡CPh){C≡CC₆H₄‐4‐C₂Ph[Co₂(μ‐dppm)(CO)₄]}(PPh₃)₂ ( 3 ), and C₆H₄{μ₃‐C₂[AuRu₃(CO)₉(PPh₃)]}₂‐1,4 ( 4 ) are reported. In these compounds a range of –CC– environments is found, extending from the σ‐bonded alkynyl group in 1 to examples where the C₂ unit interacts with either a proton (in vinylidene 2 ), by bridging a dicobalt carbonyl moiety (in 3 ) or the AuRu₃ cluster in 4 . Changes in geometry are rationalised by considering the various bonding modes.     

Cycloauration of pyridyl sulfonamides

The pyridyl-2-alkylsulfonamides C(5)H(4)N(CH(2))(n)NHSO(2)R (n = 1,2; R = Me, Ph or p-C(6)H(4)Me) and 8-(p-tosylamino)quinoline undergo facile cycloauration reactions with H[AuCl(4)] in water, giving metallacyclic complexes coordinated through the pyridyl (or quinolyl) nitrogen atom and the deprotonated nitrogen of the sulfonamide group. The complexes have been fully characterised by NMR spectroscopy, ESI mass spectrometry and elemental analysis. The X-ray crystal structures of two derivatives reveal the presence of non-planar sulfonamide nitrogen atoms. The complexes show low activity against P388 murine leukaemia cells, possibly as a result of their ease of reduction with mild reducing agents.