Alan Jones

Corynetoxins causative agents of annual ryegrass toxicity; their identification as tunicamycin group antibiotics

The corynetoxins, formed in galled seeds of Lolium rigidum(annul ryegrass) occupied by Corynebacterium rathayi and responsible for annual ryegrass toxicity, are identified as new members of the tunicamycin group of antibiotics.

Study of the promoting influence of transition metals on the reduction of cupric oxide by temperature programmed reduction

Temperature programmed reduction (t.p.r.) has been used to study the hydrogen reduction of cupric oxide and the influence on the reduction of transition metals added to the bulk oxide. X.r.d. and X.p.s. were used to characterise the samples.For cupric oxide containing 2 mol% metal additive, three types of reduction behaviour were indicated. (i)For Cr, Mn, Fe, Co and Ni, a single reduction process some 30 K below that observed for pure CuO. (ii) For Pd and Ru, two reduction processes some 100 K below that observed for pure CuO. (iii) For Pt, Rh and Ir, complex reduction behaviour with the bulk of the reduction occurring some 100 K below that for CuO. For Ag and Au, similar complex behaviour with the main reduction some 30 K below that for CuO.A detailed study was made of the reduction of CuO containing Pd (0.05–4.0 mol%) and Pt (0.05–10 mol%).Measured activation energies were essentially independent of the metal additive indicating that rate limiting steps for the reductions involve the growth of metal nuclei.The promoting effects of metal additives are discussed in terms of their ability (i) to remain within the CuO lattice, (ii) to produce extra nucleation sites and (iii) to increase the concentration of surface hydrogen. Thus the first row transition metals produce extra copper nucleation sites by non-specific distortion of the CuO lattice. For Group VIII and Ib additives, the nucleation sites are provided by the preferential reduction of the additive ion. The Group VIII metals further promote the reduction of CuO by mechanisms involving hydrogen adsorption and spillover.

Temperature programmed reduction of copper ions in zeolites

Temperature programmed reduction (t.p.r.) has been used to study the redox behaviour of copper ions in X and Y zeolites. Two distinct CuII to CuI reduction processes are discernible in both X and Y zeolites. These two processes have been attributed to the reduction of CuII ions occupying sodalite and supercage sites; a small fraction of the CuII ions, assumed to occupy hexagonal prism sites, remain unreduced. At 773 K in nitrogen, autoreduction of both sodalite and supercage CuII occurs in X zeolite, while only supercage CuII ions are autoreduced in Y zeolite. The reductions are reversible in Y zeolite, but some CuO is formed in X which is subsequently reduced by a third process. Activation energies (kJ mol–1) were obtained as follows: CuII to CuI(sodalite cages) 84 ± 13, CuII to CuI(supercages) 64 ± 10 and CuO to Cu0(X-type zeolite) 49 ± 7.

Catalytic oxidation of hydrogen over platinum

The oxidation of hydrogen on platinum has been studied using a microcalorimetric technique. The reaction takes place by two mechanisms depending on whether the surface is in an oxidised or reduced state. On the reduced surface, hydrogen is dissociatively adsorbed and competes with adsorbed molecular oxygen for adsorption sites. The reaction rate is higher on the oxidised surface where hydrogen molecules are weakly adsorbed and react with strongly adsorbed oxygen.

Kinetics of methanol oxidation over platinum wire catalysts

The oxidation of methanol at atmospheric pressure over platinum wire catalysts has been studied over a wide range of experimental conditions (T= 310–660 K, PO2/PCH3OH= 2–100). Two experimental techniques were used. In the conventional flow-reactor experiments kinetic parameters were obtained from measurement of gas-phase concentrations, while in the microcalorimeter experiments kinetic parameters were derived from the rates of heat generation at the catalyst surface.At 373 K, for PO2/PCH3OH= 25, a point within the experimental range common to both techniques, the specific rates of oxidation determined by each method were 120 nmol s–1 cm–2(conventional flow reactor) and 100 nmol s–1 cm–2(microcalorimeter). The use of the microcalorimeter enabled kinetic measurements to be made over the full experimental range. It was found that the observed kinetics were dependent on both temperature and oxygen : methanol ratio. Thus in the general rate expression: R=kPmCH3OHPnO2 the values of m and n were found to vary between 0 and ½(PO2/PCH3OH⩽ 5, T 405 K, all ratios).Non-steady-state kinetics were also observed for PO2/PCH3OH= 5 at temperatures between 380 and 405 K.A mechanism, which is consistent with the observations, is proposed involving the interaction of gaseous methanol with adsorbed atomic oxygen to produce adsorbed methoxy species. These species react with further oxygen to produce formaldehyde or carbon dioxide.

Structure elucidation of phomopsin A, a novel cyclic hexapeptide mycotoxin produced by Phomopsis leptostromiformis

Phomopsin A, the main mycotoxin isolated from cultures of Phomopsis leptostromiformis and the cause of lupinosis disease in animals grazing infected lupins, is a cyclic hexapeptide containing 3-hydroxyisoleucine, 3,4-didehydrovaline, N-methyl-3-(3-chloro-4,5-dihydroxyphenyl)-3-hydroxyalanine, E-2,3-didehydroaspartic acid, E-2,3-didehydroisoleucine, and 3,4-didehydroproline; its 13C n.m.r. spectrum was completely assigned and the amino-acid sequence established unambiguously by extensive heteronuclear 13C-{1H} selective population inversion n.m.r. experiments.

Percutaneous valved stent repair of a failed homograft: Implications for the Ross procedure

A case of percutaneous pulmonary valve implantation following a failed homograft in the pulmonary position is reported. A 16-year-old boy developed infective endocarditis of his pulmonary homograft, which was implanted four years earlier during a Ross procedure for congenital aortic stenosis. Following successful medical therapy, the boy was symptomatic due to pulmonary stenosis and regurgitation. A 22 mm Melody valve (Medtronic, USA) was successfully implanted percutaneously. His symptoms resolved and he was discharged home one day after the procedure. Echocardiography at the six-month follow-up demonstrated a normally functioning pulmonary valve. Percutaneous pulmonary valve replacement may make the Ross procedure a more attractive option for patients with aortic stenosis, particularly in the pediatric population.

Biosynthesis of echinulin. The stereochemistry of aromatic isoprenylation

The incorporation of [1,2-13C]acetate into echinulin has shown that the aromatic isoprenylation at the 5- and 7-positions occurs without any change in stereochemistry around the double bond of the dimethyl-allyl group and chemical degradation of echinulin, obtained by feeding [5(R)-3H]- and [5(S)-3H]mevalonate, to isopentylamine and oxidation with pea seedling diamine oxidase has shown that the isoprenylation reactions at positions 5- and 7- proceed with inversion of configuration at the allylic pyrophosphate.

Oscillations of the platinum-catalysed oxidation of carbon monoxide induced by inhibitors

Isothermal oscillations in the heterogeneous oxidation of carbon monoxide on platinum have been induced in an open system by the addition of low concentrations of organophosphorus compounds to the system.