Home About us Contact
|
Home About us Contact | ||
|
|
||
Enantiomeric Composition (enantiomeric + composition)
Selected AbstractsEnantiomeric composition of chiral polychlorinated biphenyl atropisomers in dated sediment coresENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2007Charles S. Wong Abstract ,Enantiomer fractions (EFs) of seven chiral poly chlorinated biphenyls (PCBs) were measured in dated sediment cores of Lake Hartwell (SC, USA) and Lake Ontario (USA) to detect, quantify, and gain insight regarding microbial reductive dechlorination of PCBs in lake sediments with high and low concentrations, respectively. Lake Hartwell sediments had high total PCBs (5,60 ,g/g), with significantly nonracemic EFs that generally were consistent with those from previous laboratory microcosm reductive dechlorination experiments using sediments from these sites. Thus, stereoselective reductive dechlorination had occurred in situ, including at total PCB concentrations of less than the threshold of approximately 30 to 80 ,g/g suggested as being necessary for reductive dechlorination. Enantiomer fractions of PCBs 91, 95, 132, and 136 in Lake Hartwell cores were significantly correlated both with concentrations of those individual congeners and with total PCB concentration for some sites. This result indicates that enantioselective microbial dechlorination activity increases with higher concentrations within sediments for these congeners. Enantiomer composition reversed with depth for PCBs 91, 132, and 176, suggesting that multiple microbial populations may be present within the same core that are enantioselectively dechlorinating PCBs. Such observations indicate that concentration and time are not the only factors affecting biotransformation, complicating prediction of enantioselectivity. Comparison of EFs with dates suggested biotransformation half-lives of approximately 30 years, which is on the same time scale as sequestration by burial. In contrast, Lake Ontario sediments (maximum total PCBs, 400 ng/g) had racemic or near-racemic amounts of most congeners throughout the core profile, which is consistent with achiral indicators suggesting no microbial biotransformation within Lake Ontario sediments. Thresholds for reductive dechlorination may exist, but they would be at concentrations of less than 30 to 80 ,g/g. [source] Enantiomeric composition of (E)- and (Z)-sabinene hydrate and their acetates in ,ve Origanum spp.FLAVOUR AND FRAGRANCE JOURNAL, Issue 2 2005Olga Larkov Abstract The enantiomers of (E)- and (Z)-sabinene hydrate and of (E)- and (Z)-sabinene hydrate acetate from extracts of Origanum ramonense Danin, O. dayi Post, O. majorana L., O. vulgare L. ssp. vulgare and O. syriacum L. ssp. syriacum were analysed by GC,MS with chiral and non-chiral capillary columns. The order of elution, the enantiomeric ratios and relative percentages of the four pairs of enantiomers were determined. The (1S)-enantiomers of (E)-sabinene hydrate and (E)-sabinene hydrate acetate were predominant in O. dayi, whereas in the other Origanum spp. the (1R)-enantiomers were predominant. (Z)-sabinene hydrate acetate was not detected in O. syriacum, while the (1R)-enantiomer was present in an optically pure form in O. ramonense, O. majorana and O. vulgare; in O. dayi the enantiomeric purity was 97%. The enantiomeric distributions of (E)- and (Z)-sabinene hydrate and their acetates were determined for the ,rst time in Origanum spp. Copyright © 2004 John Wiley & Sons, Ltd. [source] Pittosporum undulatum Vent. grown in Portugal: secretory structures, seasonal variation and enantiomeric composition of its essential oilFLAVOUR AND FRAGRANCE JOURNAL, Issue 1 2007Nicolau J. Ferreira Abstract Aerial parts of Pittosporum undulatum were collected fortnightly for 1 year at the Parque de Saúde de Lisboa. Collective samples of two populations were investigated, i.e. from pruned and non-pruned trees, and in addition samples from one pruned and one non-pruned individual. An SEM study of the aerial parts showed the presence of non-glandular T-shaped trichomes, and capitate trichomes with an elongated stalk and two to four round-shaped cells on the top. Numerous canals were seen at the level of the capsule wall as well as in the leaves and stems. Essential oil samples were isolated from the (deep-frozen) aerial parts by hydrodistillation to estimate the oil yields, and by distillation,extraction to determine their percentage composition, and analysed by GC and GC,MS. Monoterpenes (59,97%) were dominant in all oils, sabinene (5,58%), limonene (2,37%) and terpinen-4-ol (4,27%) being the major components, although in different relative amounts during the year of collection. Benzyl benzoate (8%) and benzyl salicylate (10%) attained high relative amounts in the oils from fully developed flowers, whereas in the oils from the other plant parts their relative amounts did not exceed 1%. The enantiomeric ratio of sabinene, limonene and terpinen-4-ol was investigated in the leaf, flower and capsule oils, showing dominance of the (+)-forms and homogeneity between all the oil samples. Copyright © 2006 John Wiley & Sons, Ltd. [source] Kinetic Enzymatic Resolution of Cyclopropane DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12 2003Jörg Pietruszka Abstract The kinetic enzymatic resolution of various cyclopropane derivatives was systematically investigated. The study focused on synthetically useful cyclopropylmethanols (e.g., 18a/j or 19a/j) as well as some rarely investigated cyclopropanols (e.g., 24/25 or 27). The combination of enantioselective catalytic or diastereoselective synthesis of enantiomerically enriched compounds with enzymatic approaches ultimately led to the most convenient route to enantiomerically pure starting materials. Again, this was especially proven for the synthesis of cyclopropanols 18a/j and 19a/j. Key to the successful investigation was to rigorously establish an analytical tool for the analysis of enantiomeric composition of reaction mixtures. [source] Enantioseparation of nuarimol by affinity electrokinetic chromatography-partial filling technique using human serum albumin as chiral selectorJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2008Maria Amparo Martínez-Gómez Abstract The present paper deals with the enantiomeric separation of nuarimol enantiomers by affinity EKC-partial filling technique using HSA as chiral selector. Firstly, a study of nuarimol interactions with HSA by CE-frontal analysis was performed. The binding parameters obtained for the first site of interaction were n1 = 0.84; K1 = 9.7 ± 0.3×103 M,1 and the protein binding percentage of nuarimol at physiological concentration of HSA was 75.2 ± 0.2%. Due to the moderate affinity of nuarimol towards HSA the possibility of using this protein as chiral selector for the separation of nuarimol using the partial filling technique was evaluated. A multivariate optimization approach of the most critical experimental variables in enantioresolution, running pH, HSA concentration and plug length was carried out. Separation of nuarimol enantiomers was obtained under the following selected conditions: electrophoretic buffer composed of 50 mM Tris at pH 7.3; 160 ,M HSA solution applied at 50 mbar for 156 s as chiral selector; nuarimol solutions in the range of 2,8×10,4 M injected hydrodynamically at 30 mbar for 2 s and the electrophoretic runs performed at 30°C applying 15 kV voltage. Resolution, accuracy, reproducibility speed and cost of the proposed method make it suitable for quality control of the enantiomeric composition of nuarimol in formulations and for further toxicological studies. The results showed a different affinity between nuarimol enantiomers towards HSA. [source] Enantiomeric purity of (+/,)-methyl jasmonate in fresh leaf samples and commercial fragrancesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2007Maria L. Ruiz del Castillo Abstract The enantiomeric purity of (+/,)-methyl jasmonate in fresh leaf material of Jasminum from different species and Rosmarinus officinalis was examined by solid-phase microextraction-GC-MS (SPME-GC-MS). For comparison with these natural products, commercial jasmine and rosemary fragrances were also studied. The extraction conditions were selected as a result of testing different values of temperature (40, 50, and 60°C) and time (2, 15, 30, and 40 min). The results obtained in this work revealed a range of enantiomeric excesses for (+/,)-methyl jasmonate varying from 13 to 95% depending on the Jasminum specie considered. In contrast, (,)-methyl jasmonate always occurred as a pure enantiomer in all R. officinalis samples studied. This implies those Jasminum species in which the enantiomeric purity of (,)-methyl jasmonate is high enough and any R. officinalis sample might be used as natural sources of pure (,)-methyl jasmonate. Concerning the commercial fragrances, those of jasmine showed enantiomeric composition of (,)-methyl jasmonate ranging from 1 to 15% whereas those of rosemary exhibited practically the pure (,)-methyl jasmonate. This fact suggests the addition and nonaddition of the racemic mixture of methyl jasmonate to the commercial jasmine and rosemary samples, respectively. [source] Enantiomeric composition studies in Lavandula species using supercritical fluidsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2005Gema Flores Abstract Characteristic aroma compounds in plants and essential oils of Lavandula from different varieties were examined. The study of the qualitative and quantitative composition of the major volatile components was faced by developing a method based on the use of supercritical fluid extraction-GC-MS (SFE-GC-MS). The optimization of a variety of parameters affecting SFE extraction enabled RSDs from three replicates lower than 2% to be achieved. Equally, recoveries of up to 59% were obtained by applying the proposed method. The use of multidimensional GC was necessary to enantiomerically resolve the target compounds. The obtained results showed enantiomeric purities >90% for all studied compounds in all varieties considered, proving the natural invariability of the enantiomeric composition of the compounds of interest. This information can be useful in authenticity studies as well as in selecting natural sources of enantiomerically pure compounds. [source] Determination of the enantiomeric excess of chiral carboxylic acids by 31P NMR with phosphorylated derivatizing agents from C2 -symmetrical diamines containing the (S)-,-phenylethyl groupCHIRALITY, Issue 6 2007Virginia M. Mastranzo Abstract The use of P(III) and P(V) organophosphorus derivatizing agents prepared from C2 symmetrical (1R,2R)- and (1S,2S)- trans - N,N,-bis-[(S)-,-phenylethyl]-cyclohexane-1,2-diamines 1 and 2, as well as (1R,2R)- and (1S,2S)- trans - N,N,-bis-[(S)-,-phenylethyl]-4-cyclohexene-1,2-diamines 3 and 4 for the determination of enantiomeric composition of chiral carboxylic acids by 31P NMR, is described. Chirality, 2007. © 2007 Wiley-Liss, Inc. [source] | ||||||||||