Basin-internal derivation of hydrocarbons in the Witwatersrand Basin, South Africa: evidence from bulk and molecular δ13C data

Gold in the quartz-pebble conglomerates of the late Archean Witwatersrand Basin, South Africa, is often intimately associated with carbonaceous matter of organic/biogenic origin which occurs in the form of stratiform carbon seams and paragenetically late bitumen nodules. Both carbon forms are believed to be formed by solidification of migrating hydrocarbons. This paper presents bulk and molecular chemical and stable carbon isotope data for the carbonaceous matter, all of which are used to provide a clue to the source of the hydrocarbons. These data are compared with those from intra-basinal shales and overlying dolostone of the Transvaal Supergroup. The delta C-13 values of the extracts from the Witwatersrand carbonaceous material show small differences (up to 2.4 parts per thousand) compared to the associated insoluble organic matter. This suggests that the auriferous rocks were stained by mobile hydrocarbons produced by thermal and oxidative alteration of indigenous bitumens, a contribution from hydrocarbons derived from intra-basinal Witwatersrand shales cannot be excluded. Individual aliphatic hydrocarbons of the various carbonaceous materials were subjected to compound specific isotope analysis using on-line gas chromatography/combustion/stable isotope ratio mass spectrometry (GC/C/IRMS). The limited variability of the molecular parameters and uniform delta C-13 values of individual n-alkanes (-31.1 +/- 1.7 parts per thousand) and isoprenoids (-30.7 +/- 1.1 parts per thousand) in the Witwatersrand samples exclude the mixing of oils from different sources. Carbonaceous matter in the dolostones shows distinctly different bulk and molecular isotope characteristics and thus cannot have been the source of the hydrocarbons in the Witwatersrand deposits. All the various forms of Witwatersrand carbon appear indigenous to the Witwatersrand Basin, and the differences between them are explained by variable, in general probably short (centimeter- to meter-scale) hydrocarbon migration during diagenesis and subsequent hydrothermal infiltration. (C) 2001 Elsevier Science B.V. All rights reserved.

Influence of stationary phase and eluent properties on chromatographic separation of carbohydrates

In this thesis, the sorption and elastic properties of the cation-exchange resins were studied to explain the liquid chromatographic separation of carbohydrates. Na+, Ca2+ and La3+ form strong poly(styrene-co-divinylbenzene) (SCE) as well as Na+ and Ca2+ form weak acrylic (WCE) cation-exchange resins at different cross-link densities were treated within this work. The focus was on the effects of water-alcohol mixtures, mostly aqueous ethanol, and that of the carbohydrates. The carbohydrates examined were rhamnose, xylose, glucose, fructose, arabinose, sucrose, xylitol and sorbitol. In addition to linear chromatographic conditions, non-linear conditions more typical for industrial applications were studied. Both experimental and modeling aspectswere covered. The aqueous alcohol sorption on the cation-exchangers were experimentally determined and theoretically calculated. The sorption model includes elastic parameters, which were obtained from sorption data combined with elasticity measurements. As hydrophilic materials cation-exchangers are water selective and shrink when an organic solvent is added. At a certain deswelling degree the elastic resins go through glass transition and become as glass-like material. Theincreasing cross-link level and the valence of the counterion decrease the sorption of solvent components in the water-rich solutions. The cross-linkage or thecounterions have less effect on the water selectivity than the resin type or the used alcohol. The amount of water sorbed is higher in the WCE resin and, moreover, the WCE resin is more water selective than the corresponding SCE resin. Theincreased aliphatic part of lower alcohols tend to increase the water selectivity, i.e. the resins are more water selective in 2-propanol than in ethanol solutions. Both the sorption behavior of carbohydrates and the sorption differences between carbohydrates are considerably affected by the eluent composition and theresin characteristics. The carbohydrate sorption was experimentally examined and modeled. In all cases, sorption and moreover the separation of carbohydrates are dominated by three phenomena: partition, ligand exchange and size exclusion. The sorption of hydrophilic carbohydrates increases when alcohol is added into the eluent or when carbohydrate is able to form coordination complexes with the counterions, especially with multivalent counterions. Decreasing polarity of the eluent enhances the complex stability. Size exclusion effect is more prominent when the resin becomes tighter or carbohydrate size increases. On the other hand,the elution volumes between different sized carbohydrates decreases with the decreasing polarity of the eluent. The chromatographic separation of carbohydrateswas modeled, using rhamnose and xylose as target molecules. The thermodynamic sorption model was successfully implemented in the rate-based column model. The experimental chromatographic data were fitted by using only one adjustable parameter. In addition to the fitted data also simulated data were generated and utilized in explaining the effect of the eluent composition and of the resin characteristics on the carbohydrate separation.

Acylation of chiral alcohols: a simple procedure for chiral GC analysis

The use of iodine as a catalyst and either acetic or trifluoroacetic acid as a derivatizing reagent for determining the enantiomeric composition of acyclic and cyclic aliphatic chiral alcohols was investigated. Optimal conditions were selected according to the molar ratio of alcohol to acid, the reaction time, and the reaction temperature. Afterwards, chiral stability of chiral carbons was studied. Although no isomerization was observed when acetic acid was used, partial isomerization was detected with the trifluoroacetic acid. A series of chiral alcohols of a widely varying structural type were then derivatized with acetic acid using the optimal conditions. The resolution of the enantiomeric esters and the free chiral alcohols was measured using a capillary gas chromatograph equipped with a CP Chirasil-DEX CB column. The best resolutions were obtained with 2-pentyl acetates (α = 3.00) and 2-hexyl acetates (α = 1.95). This method provides a very simple and efficient experimental workup procedure for analyzing chiral alcohols by chiral-phase GC.

Toxicity of allyl esters in insect cell lines and in Spodoptera littoralis larvae

We investigated the effects of five allyl esters, two aromatic (allyl cinnamate and allyl 2-furoate) and three aliphatic (allyl hexanoate, allyl heptanoate, and allyl octanoate) in established insect cell lines derived from different species and tissues. We studied embryonic cells of the fruit fly Drosophila melanogaster (S2) (Diptera) and the beet armyworm Spodoptera exigua (Se4) (Lepidoptera), fat body cells of the Colorado potato beetle Leptinotarsa decemlineata (CPB) (Coleoptera), ovarian cells of the silkmoth Bombyx mori (Bm5), and midgut cells of the spruce budworm Choristoneura fumiferana (CF203) (Lepidoptera). Cytotoxicity was determined with use of MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] and trypan blue. In addition, we tested the entomotoxic action of allyl cinnamate against the cotton leafworm Spodoptera littoralis .The median (50%) cytotoxic concentrations (EC50s) of the five allyl esters in the MTT bioassays ranged between 0.25 and 27 mM with significant differences among allyl esters (P = 0.0012), cell lines (P < 0.0001), and the allyl estercell line interaction (P < 0.0001). Allyl cinnamate was the most active product, and CF203 the most sensitive cell line. In the trypan blue bioassays, cytotoxicity was produced rapidly and followed the same trend observed in the MTT bioassay. In first instars of S. littoralis, allyl cinnamate killed all larvae at 0.25% in the diet after 1 day, while this happened in third instars after 5 days. The LC50 in first instars was 0.08%. In addition, larval weight gain was reduced (P < 0.05) after 1 day of feeding on diet with 0.05%. In conclusion, the data provide evidence of the significant but differential cytotoxicity among allyl esters in insect cells of different species and tissues. Midgut cells show high sensitivity, indicating the insect midgut as a primary target tissue. Allyl cinnamate caused rapid toxic effects in S. littoralis larvae at low concentrations, suggesting further potential for use in pest control.

Toxicity assessment of refill liquids for electronic cigarettes.

We analyzed 42 models from 14 brands of refill liquids for e-cigarettes for the presence of micro-organisms, diethylene glycol, ethylene glycol, hydrocarbons, ethanol, aldehydes, tobacco-specific nitrosamines, and solvents. All the liquids under scrutiny complied with norms for the absence of yeast, mold, aerobic microbes, Staphylococcus aureus, and Pseudomonas aeruginosa. Diethylene glycol, ethylene glycol and ethanol were detected, but remained within limits authorized for food and pharmaceutical products. Terpenic compounds and aldehydes were found in the products, in particular formaldehyde and acrolein. No sample contained nitrosamines at levels above the limit of detection (1 μg/g). Residual solvents such as 1,3-butadiene, cyclohexane and acetone, to name a few, were found in some products. None of the products under scrutiny were totally exempt of potentially toxic compounds. However, for products other than nicotine, the oral acute toxicity of the e-liquids tested seems to be of minor concern. However, a minority of liquids, especially those with flavorings, showed particularly high ranges of chemicals, causing concerns about their potential toxicity in case of chronic oral exposure.

An integrated pharmacokinetic and pharmacodynamic study of a new drug of abuse, methylone, a synthetic cathinone sold as 'bath salts'

Material and methods. Methylone was administered to male Sprague-Dawley rats intravenously (10 mg/kg) and orally (15 and 30 mg/kg). Plasma concentrations and metabolites were characterized by LC/MS and LC-MS/MS fragmentation patterns. Locomotor activity was monitored for 180-240 min. Results. Oral administration of methylone induced a dose-dependent increase in locomotor activity in rats. The plasma concentrations after i.v. administration were described by a two-compartment model with distribution and terminal elimination phases of α = 1.95 h− 1 and β = 0.72 h− 1. For oral administration, peak methylone concentrations were achieved between 0.5 and 1 h and fitted to a flip-flop model. Absolute bioavailability was about 80% and the percentage of methylone protein binding was of 30%. A relationship between methylone brain levels and free plasma concentration yielded a ratio of 1.42 ± 0.06, indicating access to the central nervous system. We have identified four Phase I metabolites after oral administration. The major metabolic routes are N-demethylation, aliphatic hydroxylation and O-methylation of a demethylenate intermediate. Discussion. Pharmacokinetic and pharmacodynamic analysis of methylone showed a correlation between plasma concentrations and enhancement of the locomotor activity. A contribution of metabolites in the activity of methylone after oral administration is suggested. Present results will be helpful to understand the time course of the effects of this drug of abuse in humans.

An integrated pharmacokinetic and pharmacodynamic study of a new drug of abuse, methylone, a synthetic cathinone sold as 'bath salts'

Material and methods. Methylone was administered to male Sprague-Dawley rats intravenously (10 mg/kg) and orally (15 and 30 mg/kg). Plasma concentrations and metabolites were characterized by LC/MS and LC-MS/MS fragmentation patterns. Locomotor activity was monitored for 180-240 min. Results. Oral administration of methylone induced a dose-dependent increase in locomotor activity in rats. The plasma concentrations after i.v. administration were described by a two-compartment model with distribution and terminal elimination phases of α = 1.95 h− 1 and β = 0.72 h− 1. For oral administration, peak methylone concentrations were achieved between 0.5 and 1 h and fitted to a flip-flop model. Absolute bioavailability was about 80% and the percentage of methylone protein binding was of 30%. A relationship between methylone brain levels and free plasma concentration yielded a ratio of 1.42 ± 0.06, indicating access to the central nervous system. We have identified four Phase I metabolites after oral administration. The major metabolic routes are N-demethylation, aliphatic hydroxylation and O-methylation of a demethylenate intermediate. Discussion. Pharmacokinetic and pharmacodynamic analysis of methylone showed a correlation between plasma concentrations and enhancement of the locomotor activity. A contribution of metabolites in the activity of methylone after oral administration is suggested. Present results will be helpful to understand the time course of the effects of this drug of abuse in humans.

Stereoselective Synthesis of (-)-Spicigerolide

(-)-Spicigerolide was enantioselectively synthesized from a protected (S)-lactaldehyde. The synthesis of the polyacetylated framework relied on two Zn-mediated stereoselective additions of alkynes to aldehydes as well as a regiocontrolled [3,3]-sigmatropic rearrangement of an allylic acetate. The pyranone moiety was constructed via ring-closing metathesis.

The ABCG transporter PEC1/ABCG32 is required for the formation of the developing leaf cuticle in Arabidopsis.

The cuticle is an essential diffusion barrier on aerial surfaces of land plants whose structural component is the polyester cutin. The PERMEABLE CUTICLE1/ABCG32 (PEC1) transporter is involved in plant cuticle formation in Arabidopsis. The gpat6 pec1 and gpat4 gapt8 pec1 double and triple mutants are characterized. Their PEC1-specific contributions to aliphatic cutin composition and cuticle formation during plant development are revealed by gas chromatography/mass spectrometry and Fourier-transform infrared spectroscopy. The composition of cutin changes during rosette leaf expansion in Arabidopsis. C16:0 monomers are in higher abundance in expanding than in fully expanded leaves. The atypical cutin monomer C18:2 dicarboxylic acid is more prominent in fully expanded leaves. Findings point to differences in the regulation of several pathways of cutin precursor synthesis. PEC1 plays an essential role during expansion of the rosette leaf cuticle. The reduction of C16 monomers in the pec1 mutant during leaf expansion is unlikely to cause permeability of the leaf cuticle because the gpat6 mutant with even fewer C16:0 monomers forms a functional rosette leaf cuticle at all stages of development. PEC1/ABCG32 transport activity affects cutin composition and cuticle structure in a specific and non-redundant fashion.

Contribuições recentes da reação de hidroformilação na síntese de produtos farmacêuticos: parte II

The hydroformylation reaction represents one of the most important C1-chemistry area in the chemical industry. This catalytic process, which has been developed up to now mainly to the production of commodities chemicals, has shown a remarkable potential for the preparation of several categories of specialty chemicals and in particular pharmaceutical compounds. Arylpropanoic acids, various amines containing aryl groups, and intermediates for the preparation of vitamins, carbocyclic and heterocyclic compounds and many other classes of organic molecules endowed with pharmacological activity are currently accessible in good-to-high yields through hydroformylation of selected olefinic substrates. The asymmetric hydroformylation is going to reach the stage of maturity and hence to contribute in solving many troublesome synthetic problems connected with the preparation of pharmacologically active compounds with very high enantiomeric purity. The present survey emphasizes the usefulness of synthesis gas as a starting material in fine chemistry, which is expected to be important for industry.

Oxidações eletrocatalíticas de álcoois e dióis em meio bifásico utilizando metanossulfonato de CeIV como mediador

Some alcohols and diols were oxidized electrocatalytically in a biphasic system using ceriumIV methanesulphonate as mediator. A mixture of methanesulphonic acid solution and benzene was used and aldehydes, ketones and diacids were some of the principal products obtained with yield varying from 27 to 98%. In several cases selectivity was obtained.

Influência do material do alambique na composição química das aguardentes de cana-de-açúcar

This paper describes variations in the profile of the main volatile organic compounds present in Brazilian sugar cane spirits distilled in copper and stainless steel distillers. The main organic compounds: aldehydes, ketones, carboxylic acids, alcohols and esters, were determined through High Performance Liquid Chromatography (HPLC) and High Resolution Gas Cromatography (HRGC). The spirits produced in copper distillers exhibit higher contents of aldehydes with respect to the ones produced in stainless steel. The inverse is true with respect to the higher alcohol and ester contents. No significant variation has been observed for the carboxylic acids.

Fontes, reatividade e quantificação de metanol e etanol na atmosfera

In the last two decades, the use of oxygenated fuels, like methanol and ethanol, pure or in mixture with gasoline, has been growing due to benefits introduced into the air quality. In Brasil, the fraction of light duty vehicles powered by pure hydrated ethanol is estimated at about 4 million, while the remaining vehicles actually utilize a mixture (22:78 v/v) of ethanol:gasoline. As a consequence, there's a need for the availability of methods that can provide the evaluation of possible impacts of alcohol emissions in the formation of chemical species in the atmosphere, as ozone, aldehydes, carboxylic acids and so on. In this paper, methanol and ethanol are discussed in their general aspects, as well as their atmospheric sources, chemical reactivity and available methods of analysis.

Estudo calorimétrico da interação de álcoois com Saccharomyces cerevisiae a 298 K

The calorimetric experiments based on technique breaking ampoule were carried out by measuring of the heat of solution of alcohol in isotonic solution (NaCl 0.10 M) and alcohol in suspension of Sc at 298 K. From these data the enthalpy of interaction alcohol with suspension of Sc (DtrsH°) was calculate by Hess law. In this study, the results indicate that the enthalpy of interaction of aliphatic alcohol (C2-C8) with suspensions of Sc is a process exothermic and becomes more exothermic with increasing of -CH2 group of alcohol in range -1,14 to -4,0 kJ.mol-1. We concluded that enthalpy of interaction shows a linear relationship with increasing of alcohol's lipophilicity, in agreement with Traube's rule.

Fases estacionárias para cromatografia líquida de alta eficiência em fase reversa (CLAE-FR) baseadas em superfícies de óxidos inorgânicos funcionalizados

Particles of porous silica or other solvent resistent inorganic oxides can be functionalized by aliphatic (e.g., C-8 or C-18) or other groups to give stationary phases for use in reversed phase HPLC. The functionalization can be done by bonding of individual groups to the surface of the support particles, by producing an organic polymeric film from pre-polymers, or by adsorbing/immobilizing pre-formed polymers on the surfaces. These three types of functionalization are reviewed.