946 resultados para CHIRAL SYMMETRY-BREAKING


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Once a country allergic to any type of preferential treatment or quota measure for women, France has become a country that applies gender quotas to regulate women's presence and representation in politics, the business sector, public bodies, public administration, and even some civil society organizations. While research has concentrated on the adoption of electoral gender quotas in many countries and their international diffusion, few studies focus on explaining the successful diffusion of gender quotas from politics to other domains in the same country. This paper proposes to fill this gap by studying the particularly puzzling case of a country that at one point strongly opposed the adoption of gender quotas in politics, but, in less than a decade, transformed into one of the few countries applying gender quotas across several policy domains. This paper argues that the legal entrenchment of the parity principle, the institutionalization of parity in several successive women's policy agencies, and key players in these newly created agencies are mainly responsible for this unexpected development. The diffusion of gender quotas in France thus offers an illuminating example of under which conditions women's policy agencies can act autonomously to diffuse and impose a new tool for gender equality

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A rapid, expedient and enantioselective method for the synthesis of beta-hydroxy amines and monosubstituted aziridines in up to 99% e.e., via asymmetric transfer hydrogenation of a-amino ketones and cyclisation through treatment with tosyl chloride and base, is described. (1R,2R)-N-(para-toluenesulfonyl)-1,2-ethylenediamine with formic acid has been utilised as a ligand for the Ruthenium (II) catalysed enantioselective transfer hydrogenation of the ketones.The chiral 2-methyl aziridine, which is a potentially more efficient bonding agent for Rocket Solid Propellant has been successfully achieved.

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We study how the combination of long and short laser pulses can be used to induce torsion in an axially chiral biphenyl derivative (3,5-difluoro-3 ,5 -dibromo-4 -cyanobiphenyl). A long, with respect to the molecular rotational periods, elliptically polarized laser pulse produces 3D alignment of the molecules, and a linearly polarized short pulse initiates torsion about the stereogenic axis. The torsional motion is monitored in real-time by measuring the dihedral angle using femtosecond time-resolved Coulomb explosion imaging. Within the first 4 picoseconds (ps), torsion occurs with a period of 1.25 ps and an amplitude of 3◦ in excellent agreement with theoretical calculations. At larger times, the quantum states of the molecules describing the torsional motion dephase and an almost isotropic distribution of the dihedral angle is measured.We demonstrate an original application of covariance analysis of two-dimensional ion images to reveal strong correlations between specific ejected ionic fragments from Coulomb explosion. This technique strengthens our interpretation of the experimental data

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The stereoselective addition of the titanium (IV) enolates derived from (S)-4-isopropyl-N-4-chlorobutyryl-1,3-thiazolidine-2-thione (8) and from (S)-4-isopropyl-N-4-chloropentanoyl-1,3-thiazolidine-2-thione (9) to N-Boc-2-methoxypyrrolidine (5b) afforded the addition products (+)-10 and (+)-11 in 84% yield in both cases, as 8.6:1 and 10:1 diastereoisomeric mixtures, respectively. A three-step sequence allowed to convert these adducts to (+)-isoretronecanol (1) and (+)-5-epi-tashiromine (2) in 43% and 49% overall yield, respectively.

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Styrene is used in a variety of chemical industries. Environmental and occupational exposures to styrene occur predominantly through inhalation. The major metabolite of styrene is present in two enantiomeric forms, chiral R- and S- hydroxy-1-phenyl-acetic acid (R-and S-mandelic acid, MA). Thus, the concentration of MA, particularly of its enantiomers, has been used in urine tests to determine whether workers have been exposed to styrene. This study describes a method of analyzing mandelic acid using molecular imprinting techniques and HPLC detection to perform the separation of diastereoisomers of mandelic acid. The molecularly imprinted polymer (MIP) was prepared by non-covalent molecular imprinting using (+) MA, (-) MA or (+) phenylalanine, (-) phenylalanine as templates. Methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were copolymerized in the presence of the template molecules. The bulk polymerization was carried out at 4ºC under UV radiation. The resulting MIP was grounded into 25~44¼m particles, which were slurry packed into analytical columns. After the template molecules were removed, the MIP-packed columns were found to be effective for the chromatographic resolution of (±)-mandelic acid. This method is simpler and more convenient than other chromatographic methods.

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Soitinnus: piano.

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Soil tillage is a process that accelerates soil organic matter decomposition transferring carbon to atmosphere, mainly in the CO2 form. In this study, the effect of rotary tillage on soil CO2 emission was investigated, including the presence of crop residues on the surface.Emissions were evaluated during 15 days after tillage in 3 plots: 1) non-tilled and without crop residues on soil surface (NTwo), 2) rotary tiller without the presence of crop residues on soil surface (RTwo), and 3) rotary tiller with the presence of crop residues in soil surface (RTw). Emissions from the RTw plot were higher than the other plots, (0.777 g CO2 m-2 h-1), with the lowest emissions recorded in the NTwo plot (0.414 g CO2 m-2 h-1). Total emission indicates that the difference of C-CO2 emitted to atmosphere corresponds to 3% of the total additional carbon in the crop residues in the RTw plot compared to RTwo. The increase in the RTwo emission in comparison to NTwo was followed by changes in the aggregate size distribution, especially those with average diameter lower than 2 mm. The increase in emission from the RTw plot in relation to RTwo was related to a decrease in crop residue mass on the surface, and its higher fragmentation and incorporation in soil. When the linear correlation between soil CO2 emission, and soil temperature and soil moisture is considered, only the RTw treatment showed significant correlation (p<0.05) with soil moisture.

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ABSTRACT Understanding the mechanisms involved in releasing seed dormancy is crucial for effective plant management and renewal of species in the arid zone. Zaleya pentandra is an emerging invasive weed of the arid areas of Pakistan. We investigated the effects of different dormancy breaking treatments on the germination of Z. pentandra seeds. Seeds were treated with hot water (by placing them in boiling water for 5, 15, 30, 60, 90, 120, and 150 min), dry heat (by placing them in a preheated oven at 70 oC for 1, 2, and 4 hours; at 70 oC for 1, 2, 3, and 4 days, and at 200 oC for 5, 10, 15, 30, and 45 min) and stratification (by placing them at 2-5 ºC in a refrigerator for 5, 10, 30, and 60 min; for 3, 6, and 12 hours, and for 1, 2, 4, 8, 15, and 30 days). Seeds also were soaked in thiourea ([(NH2)2CS] (0, 2,500, 5,000, 7,500, and 10,000 mg L-1 for 24 h at 30 oC) and in KNO3 (0, 10,000, 20,000, 30,000, 40,000, 50,000, and 60,000 mg L-1 for 24 h at 30 oC). Additionally, seeds were scarified with HCl (for 3, 6, 9, 12, 15, 18, and 21 h), HNO3 (for 3, 6, 9, 12, 15, 18, and 21 h), and H2SO4 (for 20, 40, 60, 80, 100, and 120 min at 30 oC) and also mechanically scarified with sandpaper. Zaleya pentandra seeds showed typical signs of hard seed coat dormancy. Mechanical scarification and acid treatments promoted seed germination to a varying degree. Seed scarification with HNO3 for 12 to 18 h as well as with HCl for 12 h and 15 h was efficient in breaking dormancy of Z. pentandra seeds, providing germination up to 92.5%. Seed scarification with H2SO4 from 20 to 120 min showed little effect, whereas hot water, dry heat, stratification and various concentrations of thiourea and KNO3 were ineffective in breaking Z. pentandra seed dormancy.

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Presentation at Open Repositories 2014, Helsinki, Finland, June 9-13, 2014

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The implementation of chiral centres within biologically active compounds has been a perplexing yet motivational force in chemistry. This work presents the attempted formation of a concurrent or sequential tandem catalyzed methodology of enantioselective nucleophilic addition and electrophilic cyclization. The 2'- arylalkynyl- aldehyde, ketone, and imine substrates used within were adeptly chosen with a dually activated structure; 1) for nucleophilic addition to the electrophilic substituents; and 2) for carbophilic activation of the alkyne substituent to undergo cyclization. To accomplish the nucleophilic addition, two distinct allylation methodologies were pursued: (/?)-BINOL catalyzed-allylboration and (5)- BINAP-AgF catalyzed-allylsilylation. BINAP catalyzed enantioselective allylation of 2'-arylalkynyl-aldehydes, to form chiral homoallylic alcohols, was successful. Homoallylic alcohols were isolated with high enantio-purity (>80%), which then underwent sequential cyclization to form chiral allylic phthalans, in moderate yields. An application of this methodology towards the construction of biologically active compounds was included with the partial synthesis of the natural product and H. pylori inhibitor, (+)-Spirolaxine methyl ether.

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A^-heterocyclic carbenes (NHCs) have become the focus of much interest as ancillary ligands for transition metal catalysts in recent years. Their structural variability and strong cy-donation properties have led to the preparation of demonstrably useful organometallic catalysts. Among the three general structural types of NHCs (imidazolylidenes, imidazolinylidenes, and benzimidazolylidenes), benzimidazolylidenes are the least investigated because of the limitation of current synthetic approaches. The preparation of chiral analogues is even more challenging. Previously, our group has demonstrated an alternative approach to synthesizing benzimidazolylidenes with a tetracyclic framework in three steps from 1,10-phenanthroline. This thesis is focused on approaches to chiral benzimidazolylidenes derived from substituted 1,10-phenanthrolines. A key step in the preparation of these ligands involves a reduction of the pyridyl rings in 1,10-phenanthrolines. Chirality can be introduced to phenanthrolines before, during, or after the reduction as illustrated by three approaches: 1) de novo construction of the phenanthroline from chiral ketones with endo and exo faces to provide a degree of diastereoselectivity during subsequent reduction; 2) introduction of substituents into the 2- and 2,9- position of phenanthroline by nucleophilic aromatic substitution, followed by a reduction-resolution sequence; and 3) use of the protected octahydrophenanthroline as a substrate for chiral induction a to nitrogen.

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This research work has been planned with the intention of synthesizing optically active bicyclo[3,l,0]-hexan-2-one using chiral carbodiimides. Several carbodiimides have been prepared for practice and for attempts at asymmetric induction. The total synthesis of dibenzo[e,g]- (l:3)diazonine and the partial synthesis of l:13-dimethyldibenzo[e,g]- (l:3)diazonine are reported. Attempts to resolve 6,6f-dimethyl-2,2t-diphenic acid were not successful. The NMR spectra of carbodiimides and the related thioureas are compared. The reaction transition state of the 4-hydroxycyclohexanone with optically pure R,R(+)-di(a-phenylethyl)-carbodiimide has been considered. The ORD application to chiral cyclohexanones is discussed.

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Four officials with shovel at the groundbreaking ceremony for West Hall, renamed Braden Hall, Chapman College, Orange, California, 1959. Partially identified, left to right: Randolph Cutlip; Colleen Richardson; Ellis Steiner; Rod ___. The men's dormitory was demolished in 2007.

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Compounds containing the pyrrolidine moiety are key substructures of compounds with biological activity and organocatalysts. In particular, annulated chiral pyrrolidines with alpha stereogenic centers have aldostereone synthase inhibition activity. In addition, 5-substituted pyrroloimidazol(in)ium salts precursors to N-heterocyclic carbene (NHC) precatalysts are rare due to a lack of convenient synthetic routes to access them. In this thesis is described a rapid synthesis of NHC precursors and a possible route to 5-substituted pyrroloimidazole biologically active compounds. The method involves the preparation of chiral saturated and achiral unsaturated pyrrolo[I,2- c]imidazol-3-ones from N-Cbz-protected t-Butyl proline carboxamide. The resulting starting materials may be used to prepare the target chiral annulated imidazol(in)ium products by a two-step sequence involving first stereoselective lithiation-substitution, followed by POCh induced salt formation.