QUENCHING OF THE EXCITED STATES OF 2-PHENYLBENZOXAZOLE BY AZIDE ANION. FLUORESCENCE AND ESR STUDY

Electron spin resonance, spin-trapping and fluorescence techniques demonstrate that 2-phenylbenzoxazole (P) participates in photo-induced reactions with alcohols and electron donors like the azide ion. Irradiation of Pat 300 nm in deaerated ethanol produces ethoxyl and hydroxyethyl radicals which can be detected with the spin trap, 5,5-dimethyl-l-pyrroline-l-oxide (DMPO). However, irradiation of P in the presence of N^-₃ leads to the appearance of the azide radical, N^-₃, which also reacts with DMPO. Studies with the nitroxyl radical, 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO), suggest that electron transfer from the azide anion to an excited state of P yields the semi-reduced sensitizer, P^-, which in turn reacts with TEMPO. The effect of sodium azide upon the fluorescence intensity and lifetime of P in aqueous ethanol has also been studied.     

A novel route for the synthesis of nanocomposite tungsten carbide–cobalt using a biopolymer as a carbon source

A new synthetic route to nanoparticulate tungsten carbide–cobalt is demonstrated, using a sol–gel approach in an aqueous solution containing a biopolymer. On calcination, the biopolymer was found to act both as a source of carbon and also as an anti-sintering, structure-directing template. By keeping the tungsten carbide phase nanoparticulate, the hardness was found to be commensurate with that seen in more traditional ‘heat and beat’ syntheses. This research was supported by the Royal Society through their University Research Fellowship scheme.     

Iron-catalysed Suzuki coupling? A cautionary tale

In our hands, Fe(II) or (III) pyridine complexes show no activity in Suzuki biaryl cross-coupling reactions, except in one irreproducible instance when complete conversion was observed. A comparison with palladium acetate under the same conditions showed that complete conversion can be obtained in a S:C ratio of 1,000,000:1 and therefore extreme caution must be exercised to prevent ‘false-positives’ arising from trace Pd-contaminants.     

Convective heat transfer and fluid flow physics in some ribbed ducts using liquid crystal thermography and PIV measuring techniques

Enhancement of forced convection is important in several engineering applications. Surface modifications like rib-roughening are commonly used in applications such as compact heat exchangers and internal cooling of gas turbine blades and vanes. This paper gives a brief summary of convective heat transfer and fluid flow in some ribbed ducts using liquid crystal thermography and PIV measuring techniques. Details of the flow pattern and the influence of rib configuration and arrangement on the heat transfer are presented. Nevertheless, the understanding of the flow and thermal physics in ribbed ducts is not yet complete and further studies are needed.     

Synthesis of CF3-substituted sulfoximines from sulfonimidoyl fluorides

N-Protected trifluoromethyl-substituted sulfoximines have been prepared by treatment of sulfonimidoyl fluorides with a combination of the Ruppert-Prakash reagent (TMSCF(3)) and tetrabutyl ammonium fluoride (TBAF). The starting materials were accessed following two synthetic routes, and for each reaction sequence the substrate scope was evaluated. Accordingly, a wide variety of aryl-substituted products were obtained in moderate to good yield.     

Factors influencing mononuclear versus multinuclear coordination in a series of potentially hexadentate acyclic N6 ligands: the roles of flexibility and chelate ring size

The synthesis of the new potentially hexadentate ligands N,N'-bis(2,2'-bipyridin-6-ylmethyl)butane-1,4-diamine (bmbu), N,N'-bis(2,2'-bipyridin-6-ylmethyl)pentane-1,5-diamine (bmpt) and N,N'-bis(2,2'-bipyridin-6-ylmethyl)octane-1,8-diamine (bmot) from the condensation of 2,2'-bipyridine-6-carbaldehyde with the appropriate diamine (butane-1,4-diamine, pentane-1,5-diamine and octane-1,8-diamine, respectively) and subsequent reduction, is reported. Bmet, bmpp and bmbu all form mononuclear complexes with first-row transition metal ions (Co(3+), Fe(2+), Ni(2+), Mn(2+)), and X-ray structures of [Mn(bmet)](ClO(4))(2), [Ni(bmet)](ClO(4))(2), [Fe(bmet)](ClO(4))(2), [Mn(bmpp)](ClO(4))(2)·2MeCN and [Co(bmpp)](ClO(4))(3)·H(2)O are reported. As the aliphatic methylene chain increases in length, formation of dinuclear, and in some cases trinuclear, complexes becomes more pronounced, as evidenced by mass spectral analysis of solutions containing Ni(2+) and bmpt, and Ni(2+), Fe(2+) and Mn(2+) with bmot. The increasing preference for multinuclear complexes with increasing chain length is ascribed to the difficulty of incorporating a medium-sized (8 to 13-membered) chelate ring in a mononuclear complex.     

Synthesis and evaluation of fluorogenic 2-amino-1,8-naphthyridine derivatives for the detection of bacteria

Several novel fluorogenic N-aminoacylnaphthyridine substrates were synthesized in good yield and tested for their ability to detect pathogenic bacteria in agar-based cell culture. Simple 2-N-(β-alanyl)amino-5,7-dialkylnaphthyridine substrates were selectively hydrolysed by β-alanylaminopeptidase expressing bacteria, but were subject to diffusion in the agar medium. Diffusion was reduced in the 2-N-(β-alanyl)amino-7-alkylnaphthyridine substrates with longer alkyl chains, but inhibition of growth was increased. 2-N-(β-Alanyl)amino-7-octylnaphthyridine inhibited the growth of all species tested, except for strains resistant to colistin/polymyxin, providing a rationale for the development of substrates for the selective detection of drug resistant species in clinical samples.     

Field Effects in Condensed Media on Polarized Absorption

The existence of anisotropic local field perturbation on electronic absorption is proved by non-zero linear dichroism of isotropic chromophores (Mo(CO)₆) in anisotropic environment. Two sources of such effects are possible: a) perturbation of the electronic energy levels in the chromophore by the static electric solvent field (= Stark effect) or, in case of anisotropic polarizable or dipolar molecules, similar effects involving molecular orientation, and b) dielectric effects on the effective radiation field. The latter effect was considered by various models: The Lorentz field model predicts an effect with wrong sign, it also yields too large a magitude if the anisotropy of the field is considered. If no local field correction is made and the anisotropy only operates in the radiation intensity a result more in agreement with experiment is obtained. By using the Onsager-Böttcher model one may take into account specific properties of the absorbing molecule, like anisotropy in α/r³ where α is its polarizability and r its Onsager radius.     

Evaluation of Carbon Rod Atomizer for Routine Analysis of Vanadium in Crude Oil by Atomic Absorption Spectroscopy

Abstract

The Carbon Rod Atomizer (CRA) was evaluated for routine trace analysis of vanadium in crude oil by atomic absorption spectroscopy with a carbon (graphite) tube as a micro-furnace. Two crude oil samples were analyzed, both by standard addition and standard working curve methods, and the results confirmed by analysis with flame atomic absorption spectroscopy using a fuel-rich nitrous oxide-acetylene flame. Because of the relative involatility of vanadium at the temperature of the CRA, quantitative recoveries of vanadium in crude oil occur only when the vanadium content of the sample injected into the CRA does not exceed the limit of about 1 × 10^?8 g. A sensitivity (weight/1% absorption) of 7.0 × 10^?11 g and detection limit (signal-to-root-mean-square-noise equal to two) of 6.9 × 10^?12 are reported.