Investigation of the energy barrier to the rotation of amide CN bonds in ACE inhibitors by NMR, dynamic HPLC and DFT.

The isomerizations of Enalapril, Perindopril, Enalaprilat and Lisinopril have been investigated using NMR spectroscopic, dynamic chromatographic, unified equation and DFT theoretical calculations. The thermodynamic parameters (ΔH, ΔS and ΔG) were determined by varying the temperature in the NMR experiments. At the coalescence temperature, we can evaluate the isomerization barrier to the rotation (ΔG(≠)) around the amide bond. Using dynamics chromatography and an unified equation introduced by Trap, we can determine isomerization rate constants and Gibbs activation energies. Molecular mechanics calculations also provided evidence for the presence of low energy conformers for the ACE due to restricted amide rotation. With the value of barriers (ΔE) between them of the order of (20kJmol(-1)), which is in agreement with the dynamic NMR results and DFT calculations.

Determination of Chlorophenols in Water Samples Using Solid-Phase Extraction Enrichment Procedure and Gas Chromatography Analysis.

Solid-phase extraction (SPE) procedure followed by derivatization and gas chromatography electron capture detection was evaluated for the determination of trace amounts of chlorophenols (CPs) in waters samples. Different parameters affecting extraction efficiency such as, volume of elution solvent, volume and pH of water sample, quantity of sorbent phase were studied and optimized. SPE was carried out on polystyrene-divinylbenzene (Bond Elut ENV) and high recoveries were obtained using 1000 mg of this cartridge for the treatment of 500 mL of acidified water sample. The described method was then tested on spiked tap, mineral, ground and surface water samples. The overall procedure provided limits of detection lower than 20 ng L(-1), recoveries of 70%-106% and an enrichment factor of 500 for the examined CPs in 500 mL water samples. Among the studied compounds, pentachlorophenol was detected in tap water at a concentration level of 0.06 µg L(-1).

Particulate polycyclic aromatic hydrocarbons (PAH) in the atmosphere of Bizerte city, Tunisia.

The particle-phase concentrations of polycyclic aromatic hydrocarbons (PAH) were determined in 13 air samples collected in an urban area of Bizerte (Tunisia) during 2009-2010. Atmospheric particulate samples were extracted by ultrasonic bath and analyzed by high-performance liquid chromatography with fluorescence detection. PAH were found in all the analyzed air samples and the most abundant compounds were pyrene, fluoranthene, benzo[g,h,i]perylene, benzo[b]fluoranthene, chrysene and benzo[a]pyrene. ∑14-PAH concentrations ranging from 9.38 to 44.81 ng m(-3) with mean value of 25.39 ng m(-3). PAH diagnostic ratio source analysis revealed gasoline and diesel vehicular emissions as major sources. The mean total benzo[a]pyrene toxicity equivalent calculated for samples was 3.66 ng m(-3) and the mean contribution of the carcinogenic potency of benzo[a]pyrene was determined to be 55.8 %. Concentrations of particulate PAH in Bizerte city atmosphere were approximately eight times greater than sampled at a nearby rural site.

Polychlorinated biphenyls in sediments from Ghar El Melh lagoon, Tunisia.

The concentrations of 20 Polychlorinated biphenyls (PCBs) were determined in 12 superficial sediments collected from The Ghar El Melh lagoon. Sediment samples were extracted by Soxhlet and analyzed by Gas chromatography with electron capture detector. The concentrations of PCBs, as sum of the 20 congeners, ranged from not detected to 3.987 ng/g on a dry weight basis, with a predominance of highly chlorinated (penta- and hepta-chlorobiphenyls) congeners. No significant correlation was found between the total PCB concentrations and organic carbon content suggesting that sediment organic carbon content did not play an important role in controlling the PCBs levels in the sediments. PCB levels in sediments were compared with Sediments Quality Guidelines (ERM-ERL indexes) for evaluation probable toxic effects on marine organism. The PCBs concentrations were lower than ERM and ERL values for all the collected samples.

Polycyclic aromatic hydrocarbons in superficial sediments from Ghar El Melh lagoon, Tunisia.

The concentrations of 17 polycyclic aromatic hydrocarbons (PAHs) were determined in 12 superficial sediments collected from the Ghar El Melh lagoon. Sediment samples were extracted by Soxhlet, and analyzed by Gas chromatography with flame ionisation detector (FID). PAH concentrations, ranged from 39.59 to 655.28 ng/g on a dry weight. Total PAH concentrations were not correlated with organic carbon (OC) content or grain size (% <63 microm). Special PAH compound ratios, such as Ft/Py and Ft/Ft + Py were calculated to evaluate different hydrocarbon origins and showed that PAHs are derived from pyrolytic process.

Distribution of polychlorinated biphenyls and organochlorine pesticides in human breast milk from various locations in Tunisia: levels of contamination, influencing factors, and infant risk assessment.

The concentrations of dichlorodiphenytrichloroethane and its metabolites (DDTs), hexachlorobenzene (HCB), hexachlorocyclohexane isomers (HCHs), dieldrin, and 20 polychlorinated biphenyls (PCBs) were determined in 237 human breast milk samples collected from 12 locations in Tunisia. Gas chromatography with electron capture detector (GC-ECD) was used to identify and quantify residue levels on a lipid basis of organochlorine compounds (OCs). The predominant OCs in human breast milk were PCBs, p,p'-DDE, p,p'-DDT, HCHs, and HCB. Concentrations of DDTs in human breast milk from rural areas were significantly higher than those from urban locations (p<0.05). With regard to PCBs, we observed the predominance of mid-chlorinated congeners due to the presence of PCBs with high K(ow) such as PCB 153, 138, and 180. Positive correlations were found between concentrations of OCs in human breast milk and age of mothers and number of parities, suggesting the influence of such factors on OC burdens in lactating mothers. The comparison of daily intakes of PCBs, DDTs, HCHs, and HCB to infants through human breast milk with guidelines proposed by WHO and Health Canada shows that some individuals accumulated OCs in breast milk close to or higher than these guidelines.

Organochlorine pesticide residues in human milk of mothers living in northern Tunisia.

The levels of 13 organochlorine pesticides (OCPs) were measured in breast milk from 87 Tunisian mothers throughout their lactation periods. Breast milk levels of OCP residues were determined using a validated methodology that included capillary column gas chromatography with electron-capture detection. All samples contained detectable residues of p,p'-DDE (2.421 mg/kg milk fat) and HCB (0.260 mg/kg milk fat). The other OCP residues were detected in the following order of frequency: Dieldrin 38%, beta-HCH 22.9% and gamma-HCH 6.8%. It was made an attempt to point out the relationship between some factors and the transfer of OCP residues into breast milk. In this study we found that concentrations of OCPs increased with mothers' age, these levels decreased with the number of children.

Determination of carbaryl and some organophosphorus pesticides in drinking water using on-line liquid chromatographic preconcentration techniques.

Reversed-phase high-performance liquid chromatography (HPLC) was adapted for the determination of trace concentrations of carbaryl and seven organophosphorus pesticides in drinking water. Between 100 and 300 ml of water sample is passed through a 1.5-cm precolumn, packed with C18-bonded silica or styrene-divinylbenzene copolymer (PRP-1) sorbent at a flow-rate of 3 ml/min. The HPLC system is then switched to an acetonitrile-water gradient elution programme. The analytes that have been concentrated on the precolumn are eluted and separated on a 15-cm C18 analytical column and are determined by measuring their UV absorption at 254 nm. This wavelength was selected as the optimum for the simultaneous determination of these pesticides. The preconcentration yields of the examined solutes obtained with the two types of precolumn are almost identical. Band broadening is avoided by a suitable choice of the C18 precolumn and the analytical column. With 200 ml of tap water, the recoveries for most of the examined pesticides were ca. 90%, except for carbaryl (54%). The detection limits are in the range 0.03-0.2 micrograms/l.

[High resolution gas phase chromatography-mass spectrometry of polychlorinated biphenyl congener residues in samples of biologic origin]. / Chromatographie en phase gazeuse haute résolution-spectrométrie de masse des congénères de biphényles polychlorés dans quelques échantillons d'origine biologique.

A study is performed on polychlorinated biphenyl (PCB) congener residues in samples of human blood and milk as well as in falcon and pigeon eggs. Most of the PCB congeners found in these biological samples were quantified by high-resolution gas chromatography (HRGC). A PCB technical mixture--namely, DP6 (Phenochlor)--was used for the calibration as its composition was previously determined by HRGC-mass spectrometry. The usefulness of such a congener analysis is outlined. It is the first time to the best of our knowledge that a Phenochlor mixture is used for standardization.

Organochlorine residues in the Tunisian market basket.

This paper provides preliminary findings on organochlorine residues in Tunisian foodstuffs, i.e.: butter, milk, cheese, fish, canned tuna and sardines, beef, egg yolk, chicken and beef liver. The techniques used are HPLC, MS-GC, ECD-GC.

Hexachlorobenzene in Tunisian mothers' milk, cord blood and foodstuffs.

This paper reports some preliminary results concerning hexachlorobenzene (HCB) contamination of Tunisian human milk, human cord and adult blood and foodstuffs (cows' milk, meat, eggs). The analyses were performed by gas chromatography with electron-capture detection.