Approaches to the liquid chromatographic determination of carboxylic acids using potentiometric detection with a metallic copper electrode

Summary A metallic copper electrode is evaluated as a potentiometric detector for carboxylic acids. The application of this device to ion-exchange chromatography is illustrated by the determination of oxalate in urine. Oxalate was selectively detected in the presence of a 100-fold excess of sulphate after separation on a low-capacity methacrylate anion-exchange column using 0.7mM potassium hydrogen phthalate at pH 7.1 as eluent. Calibration plots were linear up to 50ppm of oxalate. Potentiometric detection has also been applied to ion-exclusion chromatography using 0.005% phosphoric acid as eluent. With this method detection limits of 0.2, 2.1, 5.0 and 5.3μg were obtained for formic, acetic, propionic and iso-butyric acids, respectively.     

2,2-di(fluoroalkyl)-5,5-difluoro-1,3-dioxolan-4-ones

The condensation of fluoroacetones with oxalyl fluoride in the presence of potassium fluoride has been shown to yield 2,2-di(fluoroalkyl)-5,5-difluoro-1,3-dioxolan-4-ones.     

Elemental composition of hair and bone density measurements at diagnosis in paediatric inflammatory bowel disease

A dual energy X-ray absorptiometry (DEXA) system has been employed to measure the bone mineral density (BMD) of children with inflammatory bowel disease (IBD); Crohn's disease (CD) and ulcerative colitis (UC) at diagnosis. The results of the study indicate that even at diagnosis, a significantly reduced bone mineral density measured in terms of the Z-score, was observed in the lumbar spine and whole body of the IBD subjects. This was found to be more pronounced in Crohn's disease than in the ulcerative colitis subjects. Furthermore, the study was extended to investigate the elemental composition of hair of IBD subjects and age matched controls using instrumental neutron activation analysis (INAA). The concentrations of 11 elements; Al, Br, Ca, Cl, Cu, I, K, Mg, Mn, Na and V were determined. A significantly reduced concentration of Ca, Cu, K, Mn, and V were observed in the hair of IBD subjects as compared to the control group. This revised version was published online in August 2006 with corrections to the Cover Date.     

The absolute configuration of the dicipiene diterpenes

The absolute configuration of the decipiene diterpenes has been determined by degradation to 4R-4-(2-methoxy-4-methylphenyl)-pentanoic acid. Photolysis of 1,18-diacetoxy-13-oxodecipi-14-ene proceeds through a novel photochemical reaction, formally a [2 + 2] cycloreversion, to generate a key intermediate for the degradation.     

Evolution of structure and magnetic properties in electron-doped double perovskites, Sr2−xLaxMnWO6 (0?x?1)

Powder neutron and X-ray diffraction studies show that the double perovskites in the region 0?x?1 exhibit two crystallographic modifications at room temperature: monoclinic P2₁/n and tetragonal I4/m, with a boundary at 0.75<x<0.9. Magnetic susceptibility measurements indicate that for x=0 and 0.5 Sr_2−xLa_xMnWO₆ orders antiferromagnetically (AFM) at 15 and 25 K, respectively, for 0.75?x<1.0, a contribution of weak ferromagnetism (FM), probably due to canted-AFM order, increases with increasing x. The end point compound SrLaMnWO₆ shows the strongest FM cluster effect; however, no clear evidence of magnetic order is discernable down to 4.2 K. X-ray absorption spectroscopy (XAS) confirms Mn²⁺ and mixed-valent W^6+/5+ formal oxidation states in Sr_2−xLa_xMnWO₆.     

Structurally Divergent Lithium Catalyzed Friedel–Crafts Reactions on Oxetan‐3‐ols: Synthesis of 3,3‐Diaryloxetanes and 2,3‐Dihydrobenzofurans

The first examples of 3,3‐diaryloxetanes are prepared in a lithium‐catalyzed and substrate dependent divergent Friedel–Crafts reaction. para‐Selective Friedel–Crafts reactions of phenols using oxetan‐3‐ols afford 3,3‐diaryloxetanes by displacement of the hydroxy group. These constitute new isosteres for benzophenones and diarylmethanes. Conversely, ortho‐selective Friedel–Crafts reactions of phenols afford 3‐aryl‐3‐hydroxymethyl‐dihydrobenzofurans by tandem alkylation–ring‐opening reactions; the outcome of the reaction diverging to structurally distinct products dependent on the substrate regioselectivity. Further reactivity of the oxetane products is demonstrated, suitable for incorporation into drug discovery efforts.     

Momentum transport from nonlinear mode coupling of magnetic fluctuations

A cause of observed anomalous plasma momentum transport in a reversed-field pinch is determined experimentally. Magnetohydrodynamic theory predicts that nonlinear interactions involving triplets of tearing modes produce internal torques that redistribute momentum. Evidence for the nonlinear torque is acquired by detecting the correlation of momentum redistribution with the mode triplets, with the elimination of one of the modes in the triplet, and with the external driving of one of the modes.