George W. Francis

Alkylthiolation for the determination of double-bond positions in linear alkenes

Abstract The iodine-catalysed addition of dimethyl disulphide to linear alkenes leads smoothly to α,β-bis(methylthio)alkanes. These derivatives are stable to gas chromatographic conditions and provide readily recognizable fragments on electron bombardment. This single-step derivatization procedure is thus eminently suitable for the determination of double-bond positions in linear alkenes.

Alkylthiolation for the determination of double-bond position in unsaturated fatty acid esters

Abstract The methyl esters of some mono-unsaturated fatty acids have been methylthiolated by the iodine-catalysed addition of dimethyl disulfide across the double bond. The resulting derivatives are suitable for gas chromatography. The fragmentation of the derivatives on electron impact yields mass spectra which allow immediate recognition of the position of the original double bond.

Syringetin 3-O-(6″-acetyl)-β-glucopyranoside and other flavonols from needles of norway spruce, Picea abies

Abstract The novel flavonol, syringetin 3- O -(6″-acetyl)- β -glucopyranoside, has been isolated from needles of Norway spruce ( Picea abies ) together with the 3- O -(6″-acetyl)- β -glucopyranosides of isorhamnetin and kaempferol, the 3- O -(6″- α -rhamnopyranosyl)- β -glucopyranosides of laricitrin, isorhamnetin, myricetin, quercetin and kaempferol and the 3- O - β -glucopyranosides of laricitrin, isorhamnetin, myricetin, quercetin and kaempferol. Most of the flavonols have been isolated for the first time from Norway spruce. Kaempferol 3- O -(6″-acetyl)- β -glucopyranoside has previously been isolated from Senecio aureus , but without determination of the binding site of the acetyl group. Structure determination of the flavonols was achieved from TLC, 1 H NMR and UV shift reagent data, and, in most cases, 13 C NMR and MS.

New carotenoid glycosides from oscillatoria limosa

Abstract The carotenoid composition of Oscillatoria limosa has been studied in a quantitative manner. In addition to β-carotene, cryptoxanthin, echinenone, canthaxanthin and a zeaxanthin-like carotenoid, three new glycosidic carotenoids were encountered. These were assigned the gross structures myxol-2′- O -methylmethylpentoside (I), oscillol-2,2′-di-( O -methyl-methylpentoside) (IX) and 4-keto-myxol-2′-methylpentoside (XIII) on the basis of chemical and spectral evidence. The mass spectra of the acetylated glycosides were particularly informative.

Variations in the carotenoid content of Chlamydomonas reinhardii throughout the cell cycle

Synchronous cultures of Chlamydomonas reinhardii have been examined for the total amounts of carotenoid and chlorophyll present throughout a 12 hrs light–4 hrs dark life cycle. Variations in the carotenoid distribution at different points within the cell cycle have been found. During the greater part of the light period all major carotenoids increased at a proportionally similar rate. However, the increases in lutein and violaxanthin preceded those in β-carotene and neoxanthin by some 2 hrs and that in loroxanthin, an algal xanthophyll, by about 3 hrs. A marked drop in total carotenoid accumulation, corresponding to similar temporary falling away in the accumulation of β-carotene, lutein and violaxanthin occurred at 9 hrs. The correspondence of this with the established drop in RNA accumulation and the break-up of the nucleolus was pointed out. Considerable redistribution among the carotenoids occurred during the dark period, notably the amount of β-carotene increased relative to the total xanthophylls. The full significance of these results can not be estimated in the absence of comparative data on related organisms.

Volatile compounds in crude Salvadora persica extracts

Miswak is a widely used chewing stick in Middle Eastern and African cultures that is prepared from twigs and roots of the plant Salvadora persica L. It has been reported to inhibit dental diseases. Crude extracts of S. persica twigs and roots have demonstrated in vitro antimicrobial effects. The aim of the present study was to study the chemical composition of such extracts. Chloroform and ethanol Soxhlet extracts were investigated by gas chromatography-mass spectrometry in order to identify volatile organic components. This study is the first to report the presence of oleic, linolic and stearic acids in this plant. This work has led to the identification of a variety of low molecular weight compounds most of which are simple secondary metabolites. Among the compounds identified are esters of fatty acids and of aromatic acids, and some terpenoids. Storage of S. persica twigs for two years prior to extraction did not seem to affect the result of the chemical analysis greatly.

The use of lightweight expanded clay aggregate (LECA) as sorbent for PAHs removal from water.

Lightweight expanded clay aggregate (LECA) has been explored as a sorbent for the removal of PAHs (phenanthrene, fluoranthene and pyrene) from water. The efficacy of LECA as a sorbent for PAHs was assessed using contact time, mass of sorbent and sorption isotherms in a series of batch experiments. Maximum (optimum) sorption was reached at 21 h after which the amount of PAHs sorbed remained almost constant. Batch experiments were conducted by shaking a 100ml solution mixture of individual PAHs (containing 0.02 mg/L) with LECA. The maximum sorption was 70.70, 70.82 and 72.12%, respectively for phenanthrene, fluoranthene and pyrene when a mass of 0.2 g of sorbent was used. There was an increase in sorption as a result of an increase in mass of sorbent until a maximum was reached at a mass of 4.0 g LECA with 92.61, 93.91 and 94.15% sorption of phenanthrene, fluoranthene and pyrene respectively. Sorption data were fitted to the linearised forms of the Freundlich and Langmuir isotherm models to determine the water-LECA partitioning coefficient. Physical sorption caused by the aromatic nature of the compounds was the main mechanism that governed the removal process while the hydrophobicity of the PAHs also influenced the sorption capacity. LECA can be used as an alternative method for aqueous PAHs removal.

Determination of double-bond position in linear alkenes by oxyselenation and gas chromatography-mass spectrometry

Abstract A series of alkenes having different positions of the double bond has been subjected to single-stage conversion into mixed ethers containing oxygen and selenium. The products show characteristic mass-spectral fragmentation, which allows immediate recognition of the original position of the double bond, and are suitable derivatives for gas chromatography-mass spectrometry.

Ampelopsin 7-glucoside and other dihydroflavonol 7-glucosides from needles of Picea abies

Abstract The 7- O -β-glucopyranoside of ampelopsin (5,7,3′,4′,5′-pentahydroxydihydroflavonol), a novel dihydroflavonol, together with the 7- O -β-glucopyranosides of taxifolin (5,7,3′,4′-tetrahydroxydihydroflavonol) and aromadendrin 5,7,4′-trihydroxydihydroflavonol have been isolated from needles of Norway spruce ( Picea abies ). The structures were established on the basis of acid hydrolysis, TLC and spectral data (UV, 1 H and 13 C NMR).

Droplet counter current chromatography of the carotenoids of parsleyPetroselinum crispum

SummaryThe application of droplet counter current chromatography to the separation of the carotenoids of parsley, β-carotene, lutein, violaxanthin and neoxanthin, is described. The solvent system consists of petroleum spirit bp 40–60°C: acetonitrile: methanol in the proportions 50∶10∶40. The upper layer is used as the mobile phase and the lower layer as the stationary phase.