Oliver W. Howarth

The glycosylceramides of the nematodeCaenorhabditis elegans contain an unusual, branched-chain sphingoid base

Caenorhabditis elegans was cultured in semi-defined medium containing yeast extract, soy peptone, glucose, hemoglobin, Tween 80, and sitosterol. Monoglycosylceramides were chromatographically purified from nematode extracts. Their structures were elucidated with mass spectrometry, nuclear magnetic resonance spectroscopy, and analysis of methanolysis products of the parent cerebrosides. The glycosylceramides were unusual in that the only long-chain sphingoid base detected was aniso-branched compound with a C-4 double bond (i.e., 15-methyl-2-aminohexadec-4-en-1,3-diol). Glucose was the only sugar moiety detected. The fatty acids consisted of a series of primarily straint-chain, saturated, 2-hydroxylated C20–C26 acids; someiso-branched analogs also occurred. The sphingomyelins ofC. elegans were also hydrolyzed, and the sameiso-branched C17 compound was the only sphingoid base detected. This is the first structural analysis of a nematode glycosphingolipid and the first report of an organism in which the long-chain sphingoid bases are entirelyiso-branched.

Speciation in vanadium bioinorganic systems. 6. Speciation study of aqueous peroxovanadates, including complexes with imidazole.

Using a combination of potentiometry (glass electrode) and quantitative 51V NMR spectroscopy, the full speciation in the vanadate-peroxide and vanadate-peroxide-imidazole systems was determined in the pH range 1-10 (0.150 M Na(Cl) medium, 25 degrees C). Using the computer program LAKE, the pKa value of imidazole and the formation constants for 10 peroxovanadate species and also for three more species where a single imidazole moiety is also bound, have been calculated. The experimental data show a good fit to the calculated speciation model, even for the less abundant species. The species are either monomeric or dimeric in vanadium, and four resonances of the dimeric species have been unambiguously assigned via 2D 51V NMR. Diperoxovanadates are the favoured species at pH 2-10, when sufficient peroxide is present. Imidazole is found to bind strongly to them at pH 6-9. The equilibrium conditions are illustrated in distribution diagrams.

Structural and materials properties of a polysulphide-modified epoxide resin

Abstract The nature of epoxy resins of the diglycidyl ether of bisphenol A modified by incorporation of 10 to 20 g phr of various linear polysulphides has been examined by 13 C n.m.r. spectroscopy (conventional and cross-polarization/magic angle spinning), transmission electron microscopy, scanning transmission electron microscopy and dynamic mechanical thermal analysis. Most, but not all, cured materials feature disperse rubber particles with diameters of μ m. The materials properties of the modified resins have been measured by tensile and impact testing: modification entails improvement but not necessarily either in proportion to the linear polysulphide content or dependent on the demonstrable presence of disperse particles.

Chemoenzymatic synthesis of ethyl 1-thio-(β-D-galactopyranosyl)-O-β-D-glycopyranosyl disaccharides using the β-galactosidase from Bacillus circulans

Abstract Different ethyl 1-thio-β-D-disaccharides have been synthesised by transgalactosylation using the β-galactosidase from Bacillus circulans as biocatalyst. This β-galactosidase shows mainly a β-1–4 specificity in the galactosyl transfer. Gal-β-(1–4)-O-β-D-GlcSEt 15 was obtained in 36% yield, Gal-β-(1ndash;4)-O-α-D-GlcSEt 19 in 30% yield, Gal-β-(1–4)-O-β-D-GalSEt 17 in 60% yield, Gal-β-(1–4)-O-β-D-GalNAcSEt 20 in 49% yield, Gal-β-(1–4)-O-β-D-Gal-β-(1–4)-O-β-D-GalNAcSEt 21 in 9% yield, Gal-β-(1–6)-O-β-D-GlcSEt 16 in 3% yield and Gal-β-(1–3)-O-β-D-XylSEt 18 in 25% yield.

Structure of the ecdysone glucoside formed by a baculovirus ecdysteroid UDP-glucosyltransferase

The egt gene of the baculovirus Autographa californica nuclear polyhedrosis virus encodes an ecdysteroid UDP-glucosyltransferase. The glucoside formed by this enzyme using ecdysone and UDP-glucose as substrates has been purified and structurally characterized by nuclear magnetic resonance spectroscopy and by fast atom bombardment mass spectrometry. These studies have identified the conjugate as ecdysone 22-O-β-d-glucopyranoside. Substrate specificity studies have confirmed that ecdysteroids lacking a hydroxyl moiety at C-22 are not substrates for the enzyme.

Protonation of the decavanadate(6–) ion: a vanadium-51 nuclear magnetic resonance study

The first protonation site of [V10O28]6– differs both from the second protonation site and from the site of preferential interaction with aqueous manganese(II) ion. It is probably an out-of-plane apex, and not a bridging oxygen as has recently been proposed. The 51V n.m.r. linewidths are almost independent of direct protonation but depend in-directly on more distant protonation.

Solid-state nuclear magnetic resonance studies of sodium and aluminium in coal

23Na MAS-n.m.r. spectra have been obtained for a variety of coals, both in their raw state and after thorough drying. These show the Na+ to be surface-bound, and hydrated in the raw state. Dehydration probably creates coordinative unsaturation in some coals, although NaCl as such is only a minor component of the dry coals. Ashing destroys the original Na+ environment showing that this is not mineral. 27Al MAS-n.m.r. spectra have also been obtained, and point to a varied clay mineral structure.

Two-dimensional silicon-29 NMR studies of aqueous silicate solutions

Abstract Two-dimensional NMR techniques have been used to study the structures of species present in an alkaline aqueous solution of potassium silicate enriched in 29 Si. Both J -resolved and shift-correlated silicon-29 spectra are reported, together with projections and cross sections. The value of combining information from these different techniques is emphasized.

Metabolism of bicyclic aza-arenes by Pseudomonas putida to yield vicinal cis-dihydrodiols and phenols.

Metabolism of the aza-arenes quinoline, isoquinoline, quinazoline, and quinoxaline by a mutant strain of the bacterium Pseudomonas putida resulted in attack at the carbocyclic ring (to yield stable cis-dihydrodiols and phenols) and at the heterocyclic ring (to yield phenols and ring cleavage products).

Novel lactones from Aspergillus versicolor

Abstract Two novel aromatic lactones were isolated from Aspergillus versicolor fermentation broth. The structures were determined mainly by 1D and 2D NMR spectroscopy.