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1

Determination of the absolute configuration of vibsanin F by asymmetric synthesis via ?-allylpalladium complex  

Microsoft Academic Search

The absolute configuration of vibsanin F (1), one of the simplest 11-membered ring vibsane-type diterpene, was established to be 6R, 7S and 11S by asymmetric synthesis. A diastereomer (1a) with a 6S, 7S and 11S configuration was synthesized starting from myrcene by procedures featuring a Sharpless asymmetric epoxidation and a high diastereoselective eleven-membered ring formation between a ?-allylpalladium complex and

Hiroaki Yuasa; Gouki Makado; Yoshiyasu Fukuyama

2003-01-01

2

Hydroxamic Acids in Asymmetric Synthesis  

PubMed Central

Metal-catalyzed stereoselective reactions are a central theme in organic chemistry research. In these reactions, the stereoselection is achieved predominantly by introducing chiral ligands at the metal catalyst’s center. For decades, researchers have sought better chiral ligands for asymmetric catalysis and have made great progress. Nevertheless, to achieve optimal stereoselectivity and to catalyze new reactions, new chiral ligands are needed. Due to their high metal affinity, hydroxamic acids play major roles across a broad spectrum of fields from biochemistry to metal extraction. Dr. K. Barry Sharpless first revealed their potential as chiral ligands for asymmetric synthesis in 1977: He published the chiral vanadium-hydroxamic-acid-catalyzed, enantioselective epoxidation of allylic alcohols before his discovery of Sharpless Asymmetric Epoxidation, which uses titanium-tartrate complex as the chiral reagent. However, researchers have reported few highly enantioselective reactions using metal-hydroxamic acid as catalysts since then. This Account summarizes our research on metal-catalyzed asymmetric epoxidation using hydroxamic acids as chiral ligands. We designed and synthesized a series of new hydroxamic acids, most notably the C2-symmetric bis-hydroxamic acid (BHA) family. V-BHA-catalyzed epoxidation of allylic and homoallylic alcohols achieved higher activity and stereoselectivity than Sharpless Asymmetric Epoxidation in many cases. Changing the metal species led to a series of unprecedented asymmetric epoxidation reactions, such as (i) single olefins and sulfides with Mo-BHA, (ii) homoallylic and bishomoallylic alcohols with Zr- and Hf-BHA, and (iii) N-alkenyl sulfonamides and N-sulfonyl imines with Hf-BHA. These reactions produce uniquely functionalized chiral epoxides with good yields and enantioselectivities. PMID:23157425

Li, Zhi; Yamamoto, Hisashi

2012-01-01

3

Asymmetric synthesis of (+)-1-deoxynojirimycin and (+)-castanospermine  

Microsoft Academic Search

Asymmetric total syntheses of (+)-1-deoxynojirimycin (1) and (+)-castanospermine (2) are described. Starting from diene 3, the required absolute stereochemistry is introduced by an asymmetric hydroxylation followed by epoxidation. An intramolecular cyclization of amine 17 gives access to the corresponding tetrasubstituted piperidine 18, which is a precursor to compounds 1 and 2. (+)-Deoxynojirimicyn (1) was obtained in 36% yield over 11

Peter Somfai; Patrice Marchand; Staffan Torsell; Ulf M Lindström

2003-01-01

4

Photochirogenesis: Photochemical models on the absolute asymmetric formation of amino acids in interstellar space  

NASA Astrophysics Data System (ADS)

Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical L-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which interstellar ultraviolet (UV) circularly polarized light (CPL) induces an enantiomeric excess in chiral organic molecules in the interstellar/circumstellar media. This scenario is supported by a) the detection of amino acids in the organic residues of UV-photo-processed interstellar ice analogues, b) the occurrence of L-enantiomer-enriched amino acids in carbonaceous meteorites, and c) the observation of CPL of the same helicity over large distance scales in the massive star-forming region of Orion. These topics are of high importance in topical biophysical research and will be discussed in this review. Further evidence that amino acids and other molecules of prebiotic interest are asymmetrically formed in space comes from studies on the enantioselective photolysis of amino acids by UV-CPL. Also, experiments have been performed on the absolute asymmetric photochemical synthesis of enantiomer-enriched amino acids from mixtures of astrophysically relevant achiral precursor molecules using UV-circularly polarized photons. Both approaches are based on circular dichroic transitions of amino acids that will be highlighted here as well. These results have strong implications on our current understanding of how life's precursor molecules were possibly built and how life selected the left-handed form of proteinogenic amino acids.

Meinert, Cornelia; de Marcellus, Pierre; Le Sergeant D'Hendecourt, Louis; Nahon, Laurent; Jones, Nykola C.; Hoffmann, Søren V.; Bredehöft, Jan Hendrik; Meierhenrich, Uwe J.

2011-10-01

5

Asymmetric synthesis of tertiary thiols and thioethers  

PubMed Central

Summary Enantiomerically pure tertiary thiols provide a major synthetic challenge, and despite the importance of chiral sulfur-containing compounds in biological and medicinal chemistry, surprisingly few effective methods are suitable for the asymmetric synthesis of tertiary thiols. This review details the most practical of the methods available. PMID:21647256

MacLellan, Paul

2011-01-01

6

Combined Acid Catalysis for Asymmetric Synthesis  

E-print Network

Combined Acid Catalysis for Asymmetric Synthesis Michael T. Corbett University of North Carolina, 44, 1924­1942. Limitations of classical Brønsted/Lewis Acid catalysis: · Poor reactivity (low acidity) · Low selectivity · High catalyst loading R X R X HMLn X Lewis Acid Catalysis Brønsted Acid Catalysis X

Johnson, Jeff S.

7

Asymmetric Synthesis Metallophosphite-Induced Nucleophilic  

E-print Network

reactions. The acyl anion equivalent formed on nucleophilic addition and subsequent [1,2] BrookAsymmetric Synthesis Metallophosphite-Induced Nucleophilic Acylation of a,b-Unsaturated Amides, Justin R. Potnick, Christopher M. Yates, Peter S. White, and Jeffrey S. Johnson* Nucleophilic acylation

Baltisberger, Jay H.

8

Asymmetric Silver "Nanocarrot" Structures: Solution Synthesis and Their Asymmetric Plasmonic Resonances  

E-print Network

Asymmetric Silver "Nanocarrot" Structures: Solution Synthesis and Their Asymmetric Plasmonic the wet-chemical synthesis of asymmetric one-dimensional (1D) silver "nanocarrot" structures that exhibit of the longitudinal surface plasmon resonance peaks. The silver nanocarrots also show very high sensitivity

9

Studies Culminating in the Total Synthesis and Determination of the Absolute Configuration of (-)-Saudin  

PubMed Central

A full account of studies that culminated in the total synthesis of both antipodes and the assignment of its absolute configuration of Saudin, a hypoglycemic natural product. Two approaches are described, the first proceeding though bicyclic lactone intermediates and related second monocyclic esters. The former was obtained via asymmetric Diels-Alder cycloaddition and the latter by an asymmetric annulation protocol. Both approaches employ a Lewis acid promoted Claisen rearrangement, with the successful approach taking advantage of bidentate chelation to control the facial selectivity of the key Claisen rearrangement PMID:22523435

Boeckman, Robert K.; del Rosario Ferreira, Maria Rico; Mitchell, Lorna H.; Shao, Pengcheng; Neeb, Michael J.; Fang, Yue

2011-01-01

10

Asymmetric synthesis of aryloxypropanolamines via OsO 4-catalyzed asymmetric dihydroxylation  

Microsoft Academic Search

A simple and effective procedure for the enantioselective synthesis of several ?-adrenergic blocking agents incorporating the first asymmetric synthesis of celiprolol, is described. The key steps are (i) sharpless asymmetric dihydroxylation of aryl allyl ethers to introduce chirality into the molecules and (ii) conversion of cyclic sulfates into the corresponding epoxides using a three-step procedure.

Iliyas A. Sayyed; Vinay V. Thakur; Milind D. Nikalje; Gajanan K. Dewkar; S. P. Kotkar; A. Sudalai

2005-01-01

11

Catalytic asymmetric total synthesis of (+)-caprazol.  

PubMed

Catalytic asymmetric total synthesis of caprazol, a lipo-nucleoside antibiotic, has been accomplished employing two of the stereoselective C-C bond forming reactions as key transformations. The stereochemistries of the ?-hydroxy-?-aminoester moiety at the juncture of the uridine part and diazepanone part, and of the ?-hydroxy-?-amino acid moiety embedded in the diazepanone system, were constructed using a diastereoselective isocyanoacetate aldol reaction (dr = 88:12) and an enantioselective anti-nitroaldol reaction catalyzed by a Nd/Na-chiral amide ligand (dr = 12:1, 95% ee), respectively. PMID:24897294

Gopinath, Purushothaman; Wang, Lu; Abe, Hikaru; Ravi, Gandamala; Masuda, Takashi; Watanabe, Takumi; Shibasaki, Masakatsu

2014-06-20

12

Microscale Synthesis of Chiral Alcohols via Asymmetric Catalytic Transfer Hydrogenation  

ERIC Educational Resources Information Center

Synthesis of pure enantiomers is a key issue in industry, especially in areas connected to life sciences. Catalytic asymmetric synthesis has emerged as a powerful and practical tool. Here we describe an experiment on racemic reduction and asymmetric reduction via a catalytic hydrogen transfer process. Acetophenone and substituted acetophenones are…

Peeters, Christine M.; Deliever, Rik; De Vos, Dirk

2009-01-01

13

Asymmetric catalytic synthesis of the proposed structure of trocheliophorolide B  

PubMed Central

A concise catalytic asymmetric synthesis of the proposed structure of Trocheliophorolide B is reported. The synthetic sequence notably features an asymmetric acetaldehyde alkynylation, Ru-catalyzed alder-ene reaction and Zn-ProPhenol ynone aldol condensation. Comparison with the reported data suggests a miss-assignment of the natural product structure. PMID:22913543

Quintard, Adrien

2012-01-01

14

Asymmetric catalytic synthesis of the proposed structure of trocheliophorolide B.  

PubMed

A concise catalytic asymmetric synthesis of the proposed structure of trocheliophorolide B is reported. The synthetic sequence notably features an asymmetric acetaldehyde alkynylation, a Ru-catalyzed alder-ene reaction, and a Zn-ProPhenol ynone aldol condensation. Comparison with the reported data suggests a misassignment of the natural product structure. PMID:22913543

Trost, Barry M; Quintard, Adrien

2012-09-01

15

Asymmetric Total Synthesis of the Epoxykinamycin FL-120B’**  

PubMed Central

Turn up the heat: An asymmetric total synthesis of the epoxykinamycin FL-120B’ is reported. The synthesis establishes a route to epoxide-containing diazobenzofluorenes which could potentially serve as monomers to the dimeric lomaiviticins. Key steps include Sharpless asymmetric epoxidation, Stille coupling, and intramolecular Friedel-Crafts acylation of atropisomeric carboxylic acids at elevated temperatures to construct the FL-120B’ core structure. PMID:21953671

Scully, Stephen S.; Porco, John A.

2012-01-01

16

Synthesis and absolute configuration of demethyl (C-11) cezomycin.  

PubMed

The synthesis of (-)-demethyl (C-11) cezomycin was achieved through an efficient route that features the use of a Kulinkovich reaction to couple two multifunctionality-containing fragments and a cascade of ring opening of cyclopropanol/1,5-hydrogen shift/desilylation-oxidation. The hidden yet undeniable problem of irreproducible specific rotation for this family of compounds was solved by sufficient acidification. The absolute configuration for the natural product was thus established as the mirror image of the synthetic sample. PMID:23881716

Li, Shao-Gang; Wu, Yikang

2013-11-01

17

Assignment of Absolute Configuration to SCH 351448 via Total Synthesis?  

PubMed Central

The synthesis and absolute configuration of SCH 351448, an interesting ionophoric natural product, are reported herein. Mukaiyama aldol-Prins and segment-coupling Prins reactions were employed to construct the constituent tetrahydropyrans of SCH 351448. Efforts to assemble the C2-symmetric core of the natural product by a templated olefin metathesis strategy are described, however, a stepwise fragment assembly was ultimately utilized to complete the target molecule. PMID:18543942

Cheung, Lael L.; Marumoto, Shinji; Anderson, Christopher D.

2008-01-01

18

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines  

PubMed Central

Summary A new approach to the anticancer drug Velcade was developed by performing asymmetric borylation of an imine anchored with a chiral N-phosphinyl auxiliary. Throughout the 7-step synthesis, especially in the imine’s synthesis and in the asymmetric borylation reactions, operations and work-up were conducted in simple and easy ways without any column chromatographic purification, which defines the GAP (group-assisted purification) chemistry concept. It was found that the optically pure isomer (dr > 99:1) can be readily obtained by washing the crude mixture of the asymmetric borylation reaction with hexane; the chiral N-phosphinyl auxiliary can be easily recovered after deprotection is finished. Several other N-phosphinylimines were also investigated for the asymmetric borylation reaction. The absolute configuration of the borylation product was confirmed by single crystal X-ray diffraction analysis. PMID:24778728

Xie, Jian-bo; Luo, Jian; Winn, Timothy R; Cordes, David B

2014-01-01

19

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines.  

PubMed

A new approach to the anticancer drug Velcade was developed by performing asymmetric borylation of an imine anchored with a chiral N-phosphinyl auxiliary. Throughout the 7-step synthesis, especially in the imine's synthesis and in the asymmetric borylation reactions, operations and work-up were conducted in simple and easy ways without any column chromatographic purification, which defines the GAP (group-assisted purification) chemistry concept. It was found that the optically pure isomer (dr > 99:1) can be readily obtained by washing the crude mixture of the asymmetric borylation reaction with hexane; the chiral N-phosphinyl auxiliary can be easily recovered after deprotection is finished. Several other N-phosphinylimines were also investigated for the asymmetric borylation reaction. The absolute configuration of the borylation product was confirmed by single crystal X-ray diffraction analysis. PMID:24778728

Xie, Jian-Bo; Luo, Jian; Winn, Timothy R; Cordes, David B; Li, Guigen

2014-01-01

20

Asymmetric synthesis of vabicaserin via oxidative multicomponent annulation and asymmetric hydrogenation of a 3,4-substituted quinolinium salt.  

PubMed

An efficient, asymmetric synthesis of the 5-HT2C agonist vabicaserin in four chemical steps and 54% overall yield from commercially available benzodiazepine was achieved. The synthesis was highlighted by a novel oxidative, multicomponent reaction to affect the quinolinium ring assembly in one step followed by an unprecedented asymmetric hydrogenation of a 3,4-substituted quinolinium salt. PMID:23751116

Dragan, Vladimir; McWilliams, J Christopher; Miller, Ross; Sutherland, Karen; Dillon, John L; O'Brien, Michael K

2013-06-21

21

A Catalytic, Asymmetric Formal Synthesis of (+)-Hamigeran B  

PubMed Central

A concise asymmetric, formal synthesis of (+)-hamigeran B is reported. A Pd-catalyzed, decarboxylative allylic alkylation, employing a trifluoromethylated derivative of t-BuPHOX, is utilized as the enantioselective step to form the critical quaternary carbon center in excellent yield and enantioselectivity. The product is converted in three steps to a late-stage intermediate previously used in the synthesis of hamigeran B. PMID:21271716

Mukherjee, Herschel; McDougal, Nolan T.; Virgil, Scott C.

2011-01-01

22

Catalytic Asymmetric Synthesis of Highly Substituted Pyrrolizidines  

PubMed Central

A catalytic asymmetric double (1,3)-dipolar cycloaddition reaction has been developed. Using a chiral silver catalyst, enantioenriched pyrrolizidines can be prepared in one flask from inexpensive, commercially available starting materials. The pyrrolizidine products contain a variety of substitution patterns and as many as six stereogenic centers. PMID:23565328

Lim, Andrew D.; Codelli, Julian A.

2012-01-01

23

Pseudoephenamine: A Practical Chiral Auxiliary for Asymmetric Synthesis  

PubMed Central

Pseudoephenamine is shown to be a versatile chiral auxiliary for asymmetric synthesis. It is free from regulatory restrictions and exhibits remarkable stereocontrol in alkylation reactions, especially those that form quaternary carbon centers. Amides derived from pseudoephenamine exhibit a high propensity to be crystalline substances and provide sharp, well-defined peaks in NMR spectra. PMID:22461381

Morales, Marvin R.; Mellem, Kevin T.; Myers, Andrew G.

2013-01-01

24

First asymmetric synthesis of planar chiral [2.2]metacyclophanes.  

PubMed

A general three step asymmetric synthesis of planar chiral [2.2]metacyclophanes utilizing selective benzylic and aryl metalations is described. The final enantioselective step is achieved using a (-)-sparteine mediated aryl metalation, following which electrophile reaction gives planar chiral cyclophanes with enantiomeric ratios (er) above 90?:?10. PMID:23615867

Blangetti, Marco; Müller-Bunz, Helge; O'Shea, Donal F

2013-07-14

25

Organocatalytic asymmetric synthesis of ?(3)-amino acid derivatives.  

PubMed

?(3)-Amino acid derivatives are an essential resource for pharmaceutical production, medicinal chemistry, and biochemistry. In this article, recent developments in versatile organocatalysis, i.e., Brønsted acid catalysis, Brønsted base catalysis, Lewis acid catalysis, Lewis base catalysis, and phase-transfer catalysis, for the asymmetric synthesis of ?(3)-amino acid derivatives will be presented. PMID:23748260

Kim, Sun Min; Yang, Jung Woon

2013-08-01

26

Streamlined catalytic asymmetric synthesis of atorvastatin.  

PubMed

An efficient enantioselective synthetic route to atorvastatin was developed based on a direct catalytic asymmetric aldol reaction. The expensive chiral ligand used in the initial aldol reaction was readily recovered (91 %) and reused. Implementation of an oxy-Michael reaction for the construction of the syn-1,3-diol unit eliminated several redundant steps, allowing for rapid access to the common intermediate in six steps. PMID:23436316

Kawato, Yuji; Chaudhary, Sandeep; Kumagai, Naoya; Shibasaki, Masakatsu

2013-03-18

27

Phase-transfer-catalysed asymmetric synthesis of tetrasubstituted allenes  

NASA Astrophysics Data System (ADS)

Allenes are molecules based on three carbons connected by two cumulated carbon-carbon double bonds. Given their axially chiral nature and unique reactivity, substituted allenes have a variety of applications in organic chemistry as key synthetic intermediates and directly as part of biologically active compounds. Although the demands for these motivated many endeavours to make axially chiral, substituted allenes by exercising asymmetric catalysis, the catalytic asymmetric synthesis of fully substituted ones (tetrasubstituted allenes) remained largely an unsolved issue. The fundamental obstacle to solving this conundrum is the lack of a simple synthetic transformation that provides tetrasubstituted allenes in the action of catalysis. We report herein a strategy to overcome this issue by the use of a phase-transfer-catalysed asymmetric functionalization of 1-alkylallene-1,3-dicarboxylates with N-arylsulfonyl imines and benzylic and allylic bromides.

Hashimoto, Takuya; Sakata, Kazuki; Tamakuni, Fumiko; Dutton, Mark J.; Maruoka, Keiji

2013-03-01

28

Asymmetric synthesis of substituted NH-piperidines from chiral amines.  

PubMed

Previously, we reported an efficient asymmetric synthesis of substituted piperidines through an exocyclic chirality induced nitroalkene/amine/enone (NAE) condensation reaction. An effective protecting group strategy was developed herein to achieve enantiopure piperidines (yields up to 92%) with complete chirality retention (ee > 95%). A simple derivatization of the obtained piperidines gave thiourea catalysts, indicating the strong potential of this method for producing new amine-based dual functional organocatalysts for future development. PMID:24933675

Gautam, Lekh Nath; Su, Yijin; Akhmedov, Novruz G; Petersen, Jeffrey L; Shi, Xiaodong

2014-09-01

29

Asymmetric Synthesis of Highly Functionalized Tetrahydropyran DPP-4 Inhibitor.  

PubMed

A practical synthesis of a highly functionalized tetrahydropyran DPP-4 inhibitor is described. The asymmetric synthesis relies on three back-to-back Ru-catalyzed reactions. A Ru-catalyzed dynamic kinetic resolution (DKR) reduction establishes two contiguous stereogenic centers in one operation. A unique dihydropyran ring is efficiently constructed through a preferred Ru-catalyzed cycloisomerization. Hydroboration followed by a Ru-catalyzed oxidation affords the desired functionalized pyranone core scaffold. Finally, stereoselective reductive amination and subsequent acidic deprotection afford the desired, potent DPP-4 inhibitor in 25% overall yield. PMID:25269068

Xu, Feng; Zacuto, Michael J; Kohmura, Yoshinori; Rosen, Jon; Gibb, Andrew; Alam, Mahbub; Scott, Jeremy; Tschaen, David

2014-10-17

30

Catalytic asymmetric synthesis of allylic alcohols and derivatives and their applications in organic synthesis.  

PubMed

Allylic alcohols represent an important and highly versatile class of chiral building blocks for organic synthesis. This Review summarizes the plethora of methods developed for the catalytic asymmetric synthesis of enantioenriched allylic alcohols. These include: dynamic kinetic resolution (DKR/DKAT), nucleophilic 1,2-addition to carbonyl groups, allylic substitution, oxidation of C-H bonds, the addition of O nucleophiles to ? systems, reduction of unsaturated carbonyl compounds, and an alternative route from enantioenriched propargylic alcohols. Furthermore, these catalytic asymmetric processes are exemplified by their applications in the syntheses of complex molecules such as natural products and potential therapeutic agents. PMID:23319206

Lumbroso, Alexandre; Cooke, Michael L; Breit, Bernhard

2013-02-11

31

Asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones via enantioselective tandem Michael-aldol reaction.  

PubMed

A simple and efficient method for the asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones and related natural products was developed on the basis of the catalytic asymmetric tandem Michael-aldol reaction and simple transformations. The synthetic utility of this method was illustrated by the facile synthesis of trisubstituted ?-butyrolactone natural products. PMID:23252990

Lee, Sung Il; Jang, Jin Hee; Hwang, Geum-Sook; Ryu, Do Hyun

2013-01-18

32

Asymmetric organocatalytic synthesis of 4,6-bis(1H-indole-3-yl)-piperidine-2 carboxylates.  

PubMed

We developed an asymmetric organocatalytic synthesis of 4,6-bis(1H-indole-3-yl)-piperidine-2-carboxylates using 10 mol% of a chiral phosphoric acid. The products, which are novel bisindole-piperidine-amino acid hybrids, can be obtained in one step from 3-vinyl indoles with imino esters in dichloromethane at room temperature after 1 h of reaction time. A variety of these compounds could be synthesized in up to 70% yield and 99% ee, and they were experimentally and computationally analyzed regarding their relative and absolute stereochemistry. PMID:24733144

Zhong, Sabilla; Nieger, Martin; Bihlmeier, Angela; Shi, Min; Bräse, Stefan

2014-05-28

33

Asymmetric synthesis of l-DOPA and ( R)-selegiline via, OsO 4-catalyzed asymmetric dihydroxylation  

Microsoft Academic Search

A simple and effective procedure for the enantioselective synthesis of two important neurotransmitter drugs, that is, (S)-3,4-dihydroxyphenylalanine (l-DOPA) and (R)-N,?-dimethyl-N-2-propynylbenzeneethaneamine [(R)-selegiline], is described by employing the Sharpless asymmetric dihydroxylation (AD) as a key step to introduce chirality.

Iliyas Ali Sayyed; Arumugam Sudalai

2004-01-01

34

Chiral 1,3,2-oxazaborolidines in asymmetric synthesis: recent advances  

NASA Astrophysics Data System (ADS)

The use of chiral 1,3,2-oxazaborolidines in asymmetric organic synthesis, particularly, in enantioselective reduction of ketones, imines and oxime ethers, asymmetric Diels-Alder reactions, aldol condensation and atroposelective reduction of lactones is reviewed. Reactions of immobilised 1,3,2-oxazaborolidines are also considered.

Glushkov, Vladimir A.; Tolstikov, Alexander G.

2004-06-01

35

Asymmetric [2 + 2] cycloaddition: total synthesis of (-)-swainsonine and (+)-6-epicastanospermine.  

PubMed

[reaction: see text] An asymmetric total synthesis of (-)-swainsonine and (+)-6-epicastanospermine is described from a common intermediate, which is obtained through diastereoselective [2 + 2] cycloaddition of dichloroketene to a chiral enol ether. PMID:17020291

Ceccon, Julien; Greene, Andrew E; Poisson, Jean-François

2006-10-12

36

Asymmetric synthesis of (+)-castanospermine through enol ether metathesis-hydroboration/oxidation.  

PubMed

An asymmetric synthesis of (+)-castanospermine is presented in which enol ether metathesis-hydroboration/oxidation is used for stereoselective installation of the trans-trans hydroxyl groups on the piperidine ring of the alkaloid. PMID:19421437

Ceccon, Julien; Danoun, Grégory; Greene, Andrew E; Poisson, Jean-François

2009-05-21

37

Highly enantioselective synthesis of chiral cyclic amino alcohols and conhydrine by ruthenium-catalyzed asymmetric hydrogenation.  

PubMed

A highly efficient enantio- and diastereoselective synthesis of chiral cis-beta-N-alkyl/arylamino cyclic alcohols has been realized by asymmetric hydrogenation of racemic alpha-amino cyclic ketones via DKR catalyzed by [RuCl(2)((S)-Xyl-SDP)((R,R)-DPEN)]. The enantioselectivities of the reaction were up to 99.9% ee with 99:1 cis-selectivities. A practical catalytic asymmetric synthesis of all four isomers of conhydrine was also developed. PMID:19788265

Liu, Sheng; Xie, Jian-Hua; Li, Wei; Kong, Wei-Ling; Wang, Li-Xin; Zhou, Qi-Lin

2009-11-01

38

Phase-transfer-catalyzed asymmetric synthesis of axially chiral anilides.  

PubMed

Catalytic asymmetric synthesis of axially chiral o-iodoanilides and o-tert-butylanilides as useful chiral building blocks was achieved by means of binaphthyl-modified chiral quaternary ammonium-salt-catalyzed N-alkylations under phase-transfer conditions. The synthetic utility of axially chiral products was demonstrated in various transformations. For example, axially chiral N-allyl-o-iodoanilide was transformed to 3-methylindoline by means of radical cyclization with high chirality transfer from axial chirality to C-centered chirality. Furthermore, stereochemical information on axial chirality in o-tert-butylanilides could be used as a template to control the stereochemistry of subsequent transformations. The transition-state structure of the present phase-transfer reaction was discussed on the basis of the X-ray crystal structure of ammonium anilide, which was prepared from binaphthyl-modified chiral ammonium bromide and o-iodoanilide. The chiral tetraalkylammonium bromide as a phase-transfer catalyst recognized the steric difference between the ortho substituents on anilide to obtain high enantioselectivity. The size and structural effects of the ortho substituents on anilide were investigated, and a wide variety of axially chiral anilides that possess various functional groups could be synthesized with high enantioselectivities. This method is the only general way to access a variety of axially chiral anilides in a highly enantioselective fashion reported to date. PMID:24273122

Liu, Kun; Wu, Xiangfei; Kan, S B Jennifer; Shirakawa, Seiji; Maruoka, Keiji

2013-12-01

39

Synthesis and application of phosphinoferrocenylaminophosphine ligands for asymmetric catalysis.  

PubMed

A new class of bidentate ligands utilizing a phosphine-aminophosphine structure has been prepared on a ferrocenylethyl backbone in a straightforward and scalable fashion from acetylferrocene. The unique property of the alpha-ferrocenyl carbonium ion that allows the replacement of a variety of "leaving groups" with retention of configuration greatly facilitates the synthesis, and a number of ligands have been prepared by varying the nitrogen and phosphorus substituents on the aminophosphine. These readily prepared phosphinoferrocenylaminophosphines, known as BoPhoz ligands, show surprising hydrolytic and air stability, with no degradation after 3 years open to the air. The rhodium complexes of these ligands show exceedingly high enantioselectivities (generally >95% ee) and activities often in excess of 50,000 catalyst turnovers per hour for the asymmetric hydrogenation of a wide variety of dehydro-alpha-amino acid and itaconic acid derivatives. They also show high activity and good to excellent enantioselectivity for the hydrogenation of a number of alpha-ketoesters. PMID:15730312

Boaz, Neil W; Mackenzie, Elaine B; Debenham, Sheryl D; Large, Shannon E; Ponasik, James A

2005-03-01

40

Synthesis and absolute stereochemistry of marine nor-sesquiterpene austrodoric acid  

Microsoft Academic Search

An enantiospecific synthesis of the nor-sesquiterpene austrodoric acid 1, recently isolated from an Antarctic marine mollusk, has been achieved. The synthetic strategy was based on the ring contraction of a suitable homo-drimanic epoxide 3, easily obtained from commercial (+)-sclareolide 4. The absolute configuration of natural austrodoric acid, not determined previously, has been now established by analyzing the CD profile of

Veaceslav Kulcitki; Nicon Ungur; Margherita Gavagnin; Marianna Carbone; Guido Cimino

2004-01-01

41

Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step.  

PubMed

The first organocatalytic asymmetric synthesis of smyrindiol, by using an (S)-proline catalyzed enantioselective intramolecular aldol reaction as the key step, is described. Smyrindiol was synthesized from commercially available 2,4-dihydroxybenzaldehyde in 15 steps, with excellent stereoselectivity (de = 99%, ee = 99%). In the course of this total synthesis a new and mild coumarin assembly was developed. PMID:23019438

Enders, Dieter; Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

2012-01-01

42

Synthesis of the tetracyclic core of Illicium sesquiterpenes using an organocatalyzed asymmetric Robinson annulation  

PubMed Central

Summary An enantioselective synthesis of the core framework of neurotrophic Illicium majucin-type sesquiterpenes is described here. This strategy is based on an organocatalyzed asymmetric Robinson annulation and provides an efficient approach for a diversity-oriented synthesis of Illicium natural products that holds remarkable therapeutic potential for neurodegenerative diseases. PMID:23843905

Trzoss, Lynnie; Xu, Jing; Lacoske, Michelle H

2013-01-01

43

Chiral iminoesters derived from D-glyceraldehyde in [3 + 2] cycloaddition reactions. Asymmetric synthesis of a key intermediate in the synthesis of neuramidinase inhibitors.  

PubMed

Silver-catalyzed endo-selective and copper-catalyzed exo-selective asymmetric [3 + 2] cycloadditions of acrylates to chiral iminoesters derived from D-glyceraldehyde have been investigated. The reaction diastereoselectively provides highly functionalized pyrrolidines. This approach was used to develop the first asymmetric synthesis of a key intermediate in the synthesis of pyrrolidine influenza neuramidinase inhibitors. PMID:24143968

Gálvez, José A; Díaz-de-Villegas, María D; Alías, Miriam; Badorrey, Ramón

2013-11-15

44

Short asymmetric synthesis of phenanthroindolizidines through chiral homoallylic sulfinamines.  

PubMed

An efficient stereocontrolled preparation of chiral phenanthroindolizidines is detailed. The synthesis relies on the stereoselective indium-mediated allylation of 2-(phenanthren-9-yl)acetaldehyde derivatives with chiral tert-butylsulfinamide. Chemoselective transformations from the corresponding homoallylic sulfinamine allow the synthesis of the phenanthroindolizidines in only three synthetic operations, without any detectable racemization. Following this procedure, the synthesis of natural (-)-tylophorine was successfully accomplished. PMID:25070561

Anton-Torrecillas, Cintia; Gonzalez-Gomez, Jose C

2014-09-28

45

Concise enantioselective synthesis of duloxetine via direct catalytic asymmetric aldol reaction of thioamide.  

PubMed

Direct catalytic asymmetric aldol reaction of thioamide offers a new entry to the concise enantioselective synthesis of duloxetine. The direct aldol protocol was scalable (>20 g) to afford the aldol product in 92% ee after LiAlH(4) reduction, and 84% of the chiral ligand was recovered after recrystallization. The following four steps of transformation delivered duloxetine. PMID:22494391

Suzuki, Yuta; Iwata, Mitsutaka; Yazaki, Ryo; Kumagai, Naoya; Shibasaki, Masakatsu

2012-05-01

46

Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis of Solanapyrone D  

E-print Network

Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis the development of enantioselective catalytic variants of the Diels-Alder reaction.1 During this time, remarkable levels of enantiocontrol in the intramolecular Diels-Alder (IMDA) reaction,2,3 a notable deficiency

MacMillan, David W. C.

47

Large-scale asymmetric synthesis of the bioprotective agent JP4-039 and analogs  

PubMed Central

JP4-039 is a novel nitroxide conjugate capable of crossing lipid bilayer membranes and scavenging reactive oxygen species (ROS). An efficient and scalable one-pot hydrozirconation-transmetalation-imine addition methodology has been developed for its asymmetric preparation. Furthermore, this versatile methodology allows for the synthesis of cyclopropyl and fluorinated analogs of the parent lead structure. PMID:21452836

Frantz, Marie-Celine; Pierce, Joshua G.; Pierce, Joan M.; Kangying, Li; Qingwei, Wan; Johnson, Matthew; Wipf, Peter

2011-01-01

48

Asymmetric Catalytic Synthesis of P-Stereogenic Phosphines via a Nucleophilic Ruthenium Phosphido Complex  

E-print Network

reaction. On the basis of the strong basicity and nucleophilicity of previously reported iron and rutheniumAsymmetric Catalytic Synthesis of P-Stereogenic Phosphines via a Nucleophilic Ruthenium Phosphido@berkeley.edu; fdtoste@berkeley.edu Many reactions rely upon the activation of an electrophile via coordination

Toste, Dean

49

A new approach to asymmetric synthesis of infectocaryone.  

PubMed

A useful and flexible strategy for synthesis of (-)- and (+)-infectocaryone from commercial sugars is developed. The key step of the synthesis is a new-type Diels-Alder reaction with good chemoselectivity and stereoselectivity, in which a mixture of alkene regioisomers in a dynamic equilibrium is employed as chiral dienophiles for the first time. PMID:25141777

Liu, Xiubing; Hu, Lingling; Liu, Xiaojing; Jia, Junhao; Jiang, Lizhen; Lin, Jiangfeng; Chen, Xiaochuan

2014-10-14

50

Asymmetric multibranched conjugated molecules: synthesis, structure and photophysical properties.  

PubMed

The symmetric multibranched ?-conjugated compounds with C3 or C6 configuration have been intensively studied. The reports on asymmetric multibranched compounds are very limited. In this work, we designed and synthesized two asymmetric multibranched ?-conjugated molecules using truxene as the central core, diphenylamino and thiophenyl (or thiophenylethynyl) groups as the different branches respectively: 2,7-di(N,N-diphenylamino)-12-(2-thiophenyl)-5,5',10,10',15,15'-hexaethyltruxene and 2,7-di(N,N-diphenylamino)-12-(2-thiophenylethynyl)-5,5',10,10',15,15'-hexaethyltruxene. Their photophysical properties have been explored combining with their theoretical calculation and X-ray single-crystal structure of a key intermediate. Though their different ?-conjugation length of branches, the two title compounds exhibit almost same absorption maxima. However, their emission peaks behave a gradual red-shift with the increase of the conjugation length. The theoretical calculation results indicate that the two asymmetric compounds behave a main transition from the HOMO-1 to the LUMO or from the HOMO to the LUMO+1 upon excited. PMID:25062050

Zhao, Li; Wang, Wenji; Yuan, Mao-Sen

2015-01-25

51

A concise, asymmetric synthesis of (2R,3R)-3-hydroxyaspartic acid.  

PubMed

3-Hydroxyaspartic acid and its derivatives are found both in the free form and as peptide constituents in various microorganisms and fungi. Considering the biological importance of this amino acid and its potential utility as a multifunctional building block in organic syntheses, we have developed a short-step, asymmetric synthetic route to a strategically protected 3-hydroxyaspartic acid derivative in enantiopure form. The key steps in the synthesis involve, Sharpless asymmetric aminohydroxylation of commercially available trans-ethyl cinnamate, and, utilization of the phenyl group as a masked carboxylic acid synthon towards construction of the complete structural framework of the title compound. PMID:17914600

Khalaf, J K; Datta, A

2008-08-01

52

Inherently Chiral Calixarenes: Synthesis, Optical Resolution, Chiral Recognition and Asymmetric Catalysis  

PubMed Central

Inherently chiral calixarenes, whose chirality is based on the absence of a planar symmetry or an inversion center in the molecules as a whole through the asymmetric array of several achiral groups upon the three-dimensional calix-skeletons, are challenging and attractive chiral molecules, because of their potential in supramolecular chemistry. The synthesis and optical resolution of all varieties of inherently chiral calixarenes are systematically discussed and classified, and their applications in chiral recognition and asymmetric catalysis are thoroughly illustrated in this review. PMID:21339996

Li, Shao-Yong; Xu, Yao-Wei; Liu, Jun-Min; Su, Cheng-Yong

2011-01-01

53

Large-scale asymmetric synthesis of a cathepsin S inhibitor.  

PubMed

A potent reversible inhibitor of the cysteine protease cathepsin-S was prepared on large scale using a convergent synthetic route, free of chromatography and cryogenics. Late-stage peptide coupling of a chiral urea acid fragment with a functionalized aminonitrile was employed to prepare the target, using 2-hydroxypyridine as a robust, nonexplosive replacement for HOBT. The two key intermediates were prepared using a modified Strecker reaction for the aminonitrile and a phosphonation-olefination-rhodium-catalyzed asymmetric hydrogenation sequence for the urea. A palladium-catalyzed vinyl transfer coupled with a Claisen reaction was used to produce the aldehyde required for the side chain. Key scale up issues, safety calorimetry, and optimization of all steps for multikilogram production are discussed. PMID:20102230

Lorenz, Jon C; Busacca, Carl A; Feng, XuWu; Grinberg, Nelu; Haddad, Nizar; Johnson, Joe; Kapadia, Suresh; Lee, Heewon; Saha, Anjan; Sarvestani, Max; Spinelli, Earl M; Varsolona, Rich; Wei, Xudong; Zeng, Xingzhong; Senanayake, Chris H

2010-02-19

54

Supported liquid membrane as a novel tool for driving the equilibrium of ?-transaminase catalyzed asymmetric synthesis.  

PubMed

An attractive option to produce chiral amines of industrial importance is through asymmetric synthesis using ?-transaminase. However, reaching high yields often requires a strategy for shifting the equilibrium position. This paper describes a novel strategy for handling this problem. It involves the use of a supported liquid membrane (SLM) together with a packed bed reactor. The reactor contains Escherichia coli cells with ?-transaminase from Arthrobacter citreus, immobilized by flocculation with chitosan. The SLM consists of a hollow fibre membrane contactor in which the pores contain undecane. The system enables continuous extraction of the amine product and was used to successfully shift the equilibrium in asymmetric synthesis of (S)-?-methylbenzylamine (MBA). A conversion of 98% was reached, compared to 50% without product extraction. Moreover, a selective extraction of the produced MBA was realized. A high product concentration of 55g/l was reached after 80h, and the system showed promising potential for continuous operation. PMID:24675224

Rehn, Gustav; Adlercreutz, Patrick; Grey, Carl

2014-06-10

55

Total synthesis of (R)-sarkomycin via asymmetric rhodium-catalyzed conjugate addition.  

PubMed

(R)-Sarkomycin was prepared using a five-step total synthesis. Key steps in the enantioselective construction of the targeted scaffold were a rhodium-catalyzed asymmetric conjugate alkenyl addition with subsequent silyl trapping and a Mukaiyama aldol reaction with aqueous formaldehyde. Protection of the hydroxy group as a THP acetal and oxidative cleavage of the C,C-double bond provided a stable direct precursor to the natural product. The final liberation was carried out under slightly acidic conditions in a microwave-assisted reaction, resulting in a high yield of the "deceptive" sarkomycin. This represents the shortest enantioselective synthesis of this rather unstable compound to date and the first to employ asymmetric catalysis to introduce the stereogenic center. PMID:24079484

Westmeier, Johannes; Kress, Steffen; Pfaff, Christopher; von Zezschwitz, Paultheo

2013-11-01

56

Enantioselective synthesis of ?-aryloxycarboxylic esters via asymmetric hydrogenation of ?-aryloxy-?,?-unsaturated esters.  

PubMed

A novel synthesis of ?-aryloxycarboxylic esters via asymmetric hydrogenation of the corresponding ?-aryloxy-?,?-unsaturated esters has been demonstrated. Bis(norbornadiene)rhodium(I) tetrafluoroborate (1 mol %) and Walphos W008-1 were used to generate the saturated products with high enantioselectivity and in high yield. The tolerability of the reaction to a diverse range of substituents on the aromatic ring was also explored. PMID:23072596

Stewart, Gavin W; Shevlin, Michael; Yamagata, Adam D Gammack; Gibson, Andrew W; Keen, Stephen P; Scott, Jeremy P

2012-11-01

57

A Rapid, Asymmetric Synthesis of the Decahydrofluorene Core of the Hirsutellones  

PubMed Central

A tandem ketene-trapping/Diels–Alder cyclization sequence was the pivotal transformation in an efficient, asymmetric synthesis of a decahydrofluorene tricyclic structure possessing eight stereogenic centers and key features of the hirsutellone class of antitubercular natural products. The hirsutellone-like ?-keto ester that was fashioned by this sequence (thirteen steps; 6% overall yield) demonstrated significant inhibitory activity against Mycobacterium tuberculosis. The mechanism of action of this antitubercular compound is not yet known. PMID:19119873

Tilley, S. David; Reber, Keith P.; Sorensen, Erik J.

2010-01-01

58

Asymmetric Disulfonimide-Catalyzed Synthesis of ?-Amino-?-Ketoester Derivatives by Vinylogous Mukaiyama-Mannich Reactions.  

PubMed

An organocatalytic asymmetric synthesis of ?-amino-?-ketoester derivatives has been developed. A chiral disulfonimide (DSI) serves as a highly efficient precatalyst for a vinylogous Mukaiyama-Mannich reaction of readily available dioxinone-derived silyloxydienes with N-Boc-protected imines, delivering products in excellent yields and enantioselectivities. The synthetic utility of this reaction is illustrated in various transformations, including a new C?C bond-forming reaction, which provide useful enantioenriched building blocks. The methodology is applied in a formal synthesis of (-)-lasubin. PMID:25348924

Wang, Qinggang; van Gemmeren, Manuel; List, Benjamin

2014-12-01

59

Asymmetric synthesis of trisubstituted oxazolidinones by the thiourea-catalyzed aldol reaction of 2-isocyanatomalonate diester.  

PubMed

A new method has been developed for the synthesis of chiral 4-carboxyl oxazolidinones by the catalytic asymmetric aldol reaction of an isocyanatomalonate diester with an aldehyde in the presence of a thiourea catalyst. The resulting chiral 4-carboxyl oxazolidinones are the equivalent of ?-hydroxy-?-amino acids bearing a tri- or tetrasubstituted carbon center at their ? position. With this in mind, this procedure was successfully applied to the first total synthesis of mycestericin C, which was completed in 12 steps and represents one of the shortest reported sequences for the construction of natural products of this type. PMID:25203516

Sakamoto, Shota; Kazumi, Naoya; Kobayashi, Yusuke; Tsukano, Chihiro; Takemoto, Yoshiji

2014-09-19

60

Asymmetric synthetic access to the hetisine alkaloids: total synthesis of (+)-nominine.  

PubMed

A dual cycloaddition strategy for the synthesis of the hetisine alkaloids has been developed, illustrated by a concise asymmetric total synthesis of (+)-nominine (7). The approach relies on an early-stage intramolecular 1,3-dipolar cycloaddition of a 4-oxido-isoquinolinium betaine dipole with an ene-nitrile dipolarophile. Subsequent late-stage pyrrolidine-induced dienamine isomerization/Diels-Alder cascade allows for rapid construction of the carbon--nitrogen polycyclic skeleton within this class of C(20)-diterpenoid alkaloids. PMID:18046691

Peese, Kevin M; Gin, David Y

2008-01-01

61

Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl Heteroaryl- and Diheteroarylmethanols  

PubMed Central

Enantioenriched diaryl-, aryl heteroaryl- and diheteroarylmethanols exhibit important biological and medicinal properties. One-pot catalytic asymmetric syntheses of these compounds beginning from readily available aryl bromides are introduced. Thus, lithium-bromide exchange with commercially available aryl bromides and n-BuLi was followed by salt metathesis with ZnCl2 to generate ArZnCl. A second equivalent of n-BuLi was added to form the mixed organozinc, ArZnBu. In the presence of enantioenriched amino alcohol-based catalysts, ArZnBu adds to aldehydes to afford essentially racemic diarylmethanols. The low enantioselectivities were attributed to a LiCl-promoted background reaction. To inhibit this background reaction, the chelating diamine TEEDA (tetraethylethylene diamine) was introduced prior to aldehyde addition. Under these conditions, enantioenriched diarylmethanols were obtained with >90% ee. Arylations of enals generated allylic alcohols with 81–90% ee. This procedure was unsuccessful, however, when applied to heteraryl bromides, which was attributed to decomposition of the heteroaryl lithium under the salt metathesis conditions. To avoid this problem, the metathesis was conducted with EtZnCl, which enabled the salt metathesis to proceed at low temperatures. The resulting EtZn(ArHetero) intermediates (ArHetero=2- and 3-thiophenyl, 2-benzothiophenyl, 3-furyl, and 5-indolyl) were successfully added to aldehydes and heteroaryl aldehydes with enantioselectivities between 81–99%. These are the first examples of catalytic and highly enantioselective syntheses of diheteroarylmethanols. In a similar fashion, ferrocenyl bromide was used to generate FcZnEt and the ferrocenyl group added to benzaldehyde and heteroaromatic aldehydes to form ferrocene-based ligand precursors in 86–95% yield with 96–98% ee. It was also found that the arylation and heteroarylation of enals could be followed by diastereoselective epoxidations to provide epoxy alcohols with high enantio- and diastereoselectivities in a one-pot procedure. PMID:19653691

Salvi, Luca; Kim, Jeung Gon; Walsh, Patrick J.

2009-01-01

62

The origins of homochirality examined by using asymmetric autocatalysis.  

PubMed

Pyrimidyl alkanol was found to act as an asymmetric autocatalyst in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Asymmetric autocatalysis of 2-alkynylpyrimidyl alkanol with an extremely low enantiomeric excess (ca. 0.00005% ee) exhibits enormous asymmetric amplification to afford the same compound with >99.5% ee. This asymmetric autocatalysis with amplification of ee has been employed to examine the validity of proposed theories of the origins of homochirality. Circularly polarized light, quartz, sodium chlorate, cinnabar, chiral organic crystals and spontaneous absolute asymmetric synthesis were considered as possible candidates for the origin of chirality; each could act as a chiral source in asymmetric autocatalysis. Asymmetric autocatalysis can discriminate the isotope chirality arising from the small difference between carbon (carbon-13/carbon-12) and hydrogen (D/H) isotopes. Cryptochiral compounds were also discriminated by asymmetric autocatalysis. PMID:24449510

Soai, Kenso; Kawasaki, Tsuneomi; Matsumoto, Arimasa

2014-02-01

63

Toward a real synthesis of quantum and relativity theories: experimental evidence for absolute simultaneity  

NASA Astrophysics Data System (ADS)

We have demonstrated spatially-discontinuous quantum jumps of electrons at a distance as long as about 1cm. The effect occurs in a modified integer quantum Hall system consisted of a great number of extended Laughlin-Halperin-type states. Our observations directly contradict the no-aether Einstein's interpretation of special relativity together with the Minkowski's model of spacetime. However they are consistent with the aether-related Lorentz-Poincare's interpretation that allows absolute simultaneity. We thus strongly challenge the fundamental status of Lorentz invariance and hence break the basic argument against de Broglie-Bohm realistic quantum theory. We argue that both de Broglie-Bohm and Lorentz-Poincare theories are capable of providing a real synthesis of quantum and relativity theories. This synthesis is of such kind that quantum theory appears the most fundamental physical theory for which relativity is only a limiting case. In accordance with this hierarchy, quantum theory naturally resolves the problem of aether in Lorentz-Poincare's relativity. The role of aether could be played by a deeper Bohm-type undivided quantum pre-space, the relevance of which at any lengthscale directly follows from our observations.

Emelyanov, S. A.

2013-06-01

64

Asymmetric synthesis of cis-aminocyclopentenols, building blocks for medicinal chemistry.  

PubMed

A highly efficient one-pot multistep process involving an asymmetric Pd(II)-catalyzed Overman rearrangement and a Ru(II)-catalyzed ring-closing metathesis reaction has been developed for the preparation of (R)- or (S)-aminocyclopenta-2-enes. The rapid strategy employed and the relatively mild conditions of the one-pot process allowed the multigram synthesis of the carbocycles in high enantiomeric excess (92% ee). The synthetic utility of these compounds was demonstrated by the stereoselective incorporation of hydroxyl groups, generating cis-4- and cis-5-aminocyclopenta-2-en-1-ols, important building blocks for medicinal chemistry. PMID:24386912

Zaed, Ahmed M; Grafton, Mark W; Ahmad, Sajjad; Sutherland, Andrew

2014-02-01

65

Asymmetric total synthesis of a putative sex pheromone component from the parasitoid wasp Trichogramma turkestanica  

PubMed Central

Summary Virgin females of the parasitoid wasp Trichogramma turkestanica produce minute amounts of a sex pheromone, the identity of which has not been fully established. The enantioselective synthesis of a putative component of this pheromone, (6S,8S,10S)-4,6,8,10-tetramethyltrideca-2E,4E-dien-1-ol (2), is reported as a contribution to this identification. Catalytic asymmetric conjugate addition of methylmagnesium bromide and stereoselective Horner–Wadsworth–Emmons olefinations are used as the key steps, and 2 was obtained in 16 steps with an overall yield of 4.4%. PMID:24778730

Geerdink, Danny; Buter, Jeffrey; van Beek, Teris A

2014-01-01

66

Highly enantioselective synthesis of ?-, ?-, and ?-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)-Cu- or Pd-catalyzed cross-coupling.  

PubMed

Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (?99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (?99% ee) and catalytic synthesis of various ?- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)-Cu- or Pd-catalyzed cross-coupling. ZACA-in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ?-alkene-1-ols produced both (R)- and (S)-?,?-dioxyfunctional intermediates (3) in 80-88% ee, which were readily purified to the ?99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These ?,?-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of ?-, ?-, and ?-chiral 1-alkanols of ?99% ee. The M?NP ester analysis has been applied to the determination of the enantiomeric purities of ?- and ?-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols. PMID:24912191

Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-ichi

2014-06-10

67

Asymmetric Synthesis of anti-?-Amino-?-Hydroxy Esters via Dynamic Kinetic Resolution of ?-Amino-?-Keto Esters  

PubMed Central

A method for the asymmetric synthesis of enantioenriched anti-?-hydroxy-?-amino acid derivatives by enantioconvergent reduction of the corresponding racemic ?-keto esters is presented. The requisite ?-keto esters are prepared via Mannich addition of ethyl diazoacetate to imines followed by oxidation of the diazo group with Oxone®. Implementation of a recently-developed dynamic kinetic resolution of ?-substituted-?-keto esters via Ru(II)-catalyzed asymmetric transfer hydrogenation provides the title motif in routinely high diastereo- and enantioselectivity. PMID:23631467

Goodman, C. Guy; Do, Dung T.

2013-01-01

68

The ever-expanding role of asymmetric covalent organocatalysis in scalable, natural product synthesis.  

PubMed

Following the turn of the millennium, the role of asymmetric covalent organocatalysis has developed into a scalable, synthetic paradigm galvanizing the synthetic community toward utilization of these methods toward more practical, metal-free syntheses of natural products. A myriad of reports on asymmetric organocatalytic modes of substrate activation relying on small, exclusively organic molecules are delineating what has now become the multifaceted field of organocatalysis. In covalent catalysis, the catalyst and substrate combine to first form a covalent, activated intermediate that enters the catalytic cycle. Following asymmetric bond formation, the chiral catalyst is recycled through hydrolysis or displacement by a pendant group on the newly formed product. Amine- and phosphine-based organocatalysts are the most common examples that have led to a vast array of reaction types. This Highlight provides a brief overview of covalent modes of organocatalysis and applications of scalable versions of these methods applied to the total synthesis of natural products including examples from our own laboratory. PMID:25042097

Abbasov, Mikail E; Romo, Daniel

2014-10-01

69

Asymmetric total synthesis of (+)- and ent-(-)-yatakemycin and duocarmycin SA: evaluation of yatakemycin key partial structures and its unnatural enantiomer.  

PubMed

Complementary to studies that provided the first yatakemycin total synthesis resulting in its structure revision and absolute stereochemistry assignment, a second-generation asymmetric total synthesis is disclosed herein. Since the individual yatakemycin subunits are identical to those of duocarmycin SA (alkylation subunit) or CC-1065 (central and right-hand subunits), the studies also provide an improvement in our earlier total synthesis of CC-1065 and, as detailed herein, have been extended to an asymmetric total synthesis of (+)-duocarmycin SA. Further extensions of the studies provided key yatakemycin partial structures and analogues for comparative assessments. This included the definition of the DNA selectivity (adenine central to a five-base-pair AT sequence, e.g., 5'-AAAAA), efficiency, relative rate, and reversibility of ent-(-)-yatakemycin and its comparison with the natural enantiomer (identical selectivity and efficiency), structural characterization of the adenine N3 adduct confirming the nature of the DNA reaction, and comparisons of the cytotoxic activity of the natural product (L1210, IC50 = 5 pM) with those of its unnatural enantiomer (IC50 = 5 pM) and a series of key partial structures including those that probe the role of the C-terminus thiomethyl ester. The only distinguishing features between the enantiomers is that ent-(-)-yatakemycin alkylates DNA at a slower rate (krel = 0.13) and is reversible, whereas (+)-yatakemycin is not. Nonetheless, even ent-(-)-yatakemycin alkylates DNA at a faster rate and with a greater thermodynamic stability than (+)-duocarmycin SA, illustrating the unique characteristics of such "sandwiched" agents. PMID:17147378

Tichenor, Mark S; Trzupek, John D; Kastrinsky, David B; Shiga, Futoshi; Hwang, Inkyu; Boger, Dale L

2006-12-13

70

Total synthesis and determination of the absolute configuration of rakicidin a.  

PubMed

Rakicidin A is a cyclic depsipeptide that has exhibited unique growth inhibitory activity against chronic myelogenous leukemia stem cells. Furthermore, rakicidin A has five chiral centers with unknown stereochemical assignment, and thus, can be represented by one of 32 possible stereoisomers. To predict the most probable stereochemistry of rakicidin A, calculations and structural comparison with natural cyclic depsipeptides were applied. A total synthesis of the proposed structure was subsequently completed and highlighted by the creation of a sterically hindered ester bond (C1-C15) through trans-acylation from an easily established isomer (C1-C13). The analytic data of the synthetic target were consistent with that of natural rakicidin A, and then the absolute configuration of rakicidin A was assigned as 2S, 3S, 14S, 15S, 16R. This work suggests strategies for the determination of unknown chiral centers in other cyclic depsipeptides, such as rakicidin B, C, D, BE-43547, and vinylamycin, and facilitates the investigations of rakicidin A as an anticancer stem cell agent. PMID:25286338

Sang, Feng; Li, Dongmei; Sun, Xiaolong; Cao, Xianqiang; Wang, Liang; Sun, Jianlei; Sun, Bingxia; Wu, Lingling; Yang, Guang; Chu, Xiaoqian; Wang, Jinghan; Dong, Changming; Geng, Yan; Jiang, Hong; Long, Haibo; Chen, Sijia; Wang, Guiyan; Zhang, Shuzhong; Zhang, Quan; Chen, Yue

2014-11-01

71

Enantioselective synthesis of cyclic amides and amines through mo-catalyzed asymmetric ring-closing metathesis.  

PubMed

First, an efficient method for the synthesis of optically enriched N-fused bicyclic structures is reported. Through Mo-catalyzed desymmetrization of readily available achiral polyene substrates, 5,6-, 5,7-, and 5,8-bicyclic amides can be synthesized in up to >98% ee. The effects of catalyst structure, olefin substitution, positioning of Lewis basic functional groups and ring size are examined and discussed in detail. In the second phase of investigations, a catalytic asymmetric method for highly enantioselective (up to 97% ee) synthesis of small- and medium-ring unsaturated cyclic amines is reported; optically enriched products bear a secondary amine or a readily removable Cbz or acetamide unit. Regio- and diastereoselective functionalizations of olefins within the optically enriched amine products have been carried out. Both catalytic asymmetric methods include transformations that lead to the formation of trisubstituted as well as disubstituted cyclic alkenes. The protocols outlined herein afford various cyclic amines of high optical purity; such products are not easily accessed by alternative protocols and can be used in enantioselective total syntheses of biologically active molecules. PMID:15941288

Sattely, Elizabeth S; Cortez, G Alexander; Moebius, David C; Schrock, Richard R; Hoveyda, Amir H

2005-06-15

72

Synthesis of nitrogenated heterocycles by asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)haloimines.  

PubMed

Highly optically enriched, protected, nitrogenated heterocycles with different ring sizes have been synthesized by a very efficient methodology consisting of the asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)haloimines followed by treatment with a base to promote an intramolecular nucleophilic substitution process. N-protected aziridines, pyrrolidines, piperidines, and azepanes bearing aromatic, heteroaromatic, and aliphatic substituents have been obtained in very high yields and diastereomeric ratios up to >99:1. The free heterocycles can be easily obtained by a simple and mild desulfinylation procedure. Both enantiomers of the free heterocycles can be prepared with the same good results by changing the absolute configuration of the sulfur atom of the sulfinyl group. PMID:23952598

Pablo, Óscar; Guijarro, David; Yus, Miguel

2013-09-20

73

Nickel-catalyzed asymmetric cross-couplings of secondary allylic chlorides and planar-chiral compounds in asymmetric synthesis  

E-print Network

In Part I, nickel-catalyzed asymmetric carbon-carbon bond-forming reactions are described. A nickel/Pybox system effectively catalyzes regio- and enantioselective cross-couplings between racemic secondary allylic chlorides ...

Son, Sunghee

2008-01-01

74

Structure and Synthesis of Anhydrobisfarnesol from Euphorbia lateriflora and Asymmetric Synthesis of ( R)-Sesquilavandulol  

Microsoft Academic Search

Anhydrobisfarnesol has been isolated from the latex of Euphorbia lateriflora and assigned structure 4 on the basis of its spectroscopic properties. Its structure has been confirmed by synthesis using a photochemical isomerisation procedure. A similar approach has been used for the total synthesis of (R)-sesquilavandulol.

Sophie Faure; Joseph D. Connolly; Christopher O. Fakunle; Olivier Piva

2000-01-01

75

Enantioselective synthesis of anti- and syn-?-hydroxy-?-phenyl carboxylates via boron-mediated asymmetric aldol reaction.  

PubMed

A reagent-controlled, diastereo- and enantioselective synthesis of anti- and syn-?-hydroxy-?-phenyl carboxylates has been achieved by the proper choice of solvent, temperature, alkoxy group, and amine for the diisopinocampheylboron-mediated asymmetric enolization-aldolization of phenylacetates. The pure diastereomers can be readily separated by column chromatography. PMID:23478288

Ramachandran, P Veeraraghavan; Chanda, Prem B

2013-04-18

76

Organocatalytic Asymmetric Synthesis of Functionalized 1,3,5-Triarylpyrrolidin-2-ones via an Aza-Michael/Aldol Domino Reaction  

PubMed Central

The organocatalytic asymmetric synthesis of functionalized 1,3,5-triarylpyrrolidin-2-ones bearing three contiguous stereocenters through an aza-Michael/aldol domino reaction of ?-ketoamides with ?,?-unsaturated aldehydes is described. The domino products were further derivatized by aldehyde olefination under one-pot conditions. The reaction proceeds with excellent diastereoselectivities (>20:1) and good to excellent enantioselectivities (60–96% ee).

Joie, Celine; Deckers, Kristina; Enders, Dieter

2014-01-01

77

Nucleophilic Chiral Amines as Catalysts in Asymmetric Synthesis Stefan France, David J. Guerin, Scott J. Miller,*, and Thomas Lectka*,  

E-print Network

Perspective 2985 2. Reactions Catalyzed by Chiral Nucleophilic Amines 2987 2.1. Kinetic Resolution of Alcohols are catalyzed by chiral nucleophiles, build- ing on the vast assortment of reactions in nature in whichNucleophilic Chiral Amines as Catalysts in Asymmetric Synthesis Stefan France, David J. Guerin

Lectka, Thomas

78

Asymmetric C-C Bond Formation between Chiral N-Phosphonyl Imines and Ni(II)-Complex of Glycine Schiff Base Provides a GAP Synthesis of ?,?-syn-Diamino Acid Derivatives  

PubMed Central

The GAP asymmetric synthesis of ?,?-diamino acid derivatives has been achieved by reacting chiral N-phosphonyl imines with Ni(II)-complex of glycine ester-based enolate without the use of traditional purifications of chromatography and recrystallization. The successful control of synstereochemistry of vicinal diamino products complements our previous methods which afforded anti stereoisomers and enables all four individual isomers to be synthesized by simply changing enolate geometry. In contrast to our previous synthesis where required at least 5 equiv of glycine Schiff base enolate for complete conversion, the new synthesis only needs 1.1 equiv of glycine Schiff base enolate to give complete diastereoselectivity (>99% de) and yields (91% – 97%). The absolute stereochemistry has been unambiguously determined by X-ray structural analysis.

Sun, Hao; Zhang, Haowei; Han, Jianlin

2014-01-01

79

Stereoselective synthesis of caffeic acid amides via enzyme-catalyzed asymmetric aminolysis reaction.  

PubMed

In this study, a new method was developed to prepare enantiopure caffeic acid amides by enzyme-catalyzed asymmetric aminolysis reaction. Methoxymethyl chloride (MOMCl) was first introduced as a protective and esterified reagent to obtain the MOM-protected caffeic acid MOM ester 1d. Aminolysis reaction occurred between 1d and (R, S)-?-phenylethylamine in the presence of an immobilized lipase (Novozym 435) from Candida antarctica. Compared with the methyl-protected caffeic acid methyl ester 1c, 1d as substrate improved the lipase-catalyzed reaction rate by 5.5-fold. After Novozym 435-catalyzed aminolysis reaction was established, we evaluated the effects of synthesis parameters on the catalytic activity and enantioselectivity of Novozym 435. A reaction conversion rate of 25.5% and an E value of >100 were achieved under the following optimum conditions: reaction solvent, anhydrous isooctane; reaction temperature, 70°C; reaction time, 24h; ester-to-amine substrate molar ratio, 1:40; and enzyme additive amount, 40 mg. Kinetic and thermodynamic analyses were conducted to determine the main factors affecting enantiomeric discrimination. Novozym 435 still showed 80% of its initial activity after recycling five times. Highly optically pure caffeic acid amides with an enantiomeric excess of 98.5% were finally obtained by HCl deprotection. The established enzyme-catalyzed asymmetric aminolysis method in this study might be used to prepare other caffeic acid amides. PMID:24056082

Xiao, Peiliang; Zhang, Suoqin; Ma, Huayu; Zhang, Aijun; Lv, Xiaoli; Zheng, Liangyu

2013-12-01

80

N-silyl oxyketene imines are underused yet highly versatile reagents for catalytic asymmetric synthesis  

NASA Astrophysics Data System (ADS)

The reactions of acyl anion equivalents (d1 synthons) with carbonyl electrophiles allow for the construction of a wide range of molecules useful for the synthesis of biologically active compounds, natural products and chiral ligands. Despite their utility, significant challenges still exist for developing catalytic, enantioselective variants of these reactions. For example, the asymmetric benzoin process, arguably the most characteristic reaction of d synthetic equivalents, finds no general solution for reactions involving aliphatic acyl anions. In this Article, we introduce a new class of stable, isolable silyl ketene imines derived from protected cyanohydrins. These nucleophiles serve as acyl anion equivalents in Lewis base catalysed aldol addition reactions and allow for the preparation of cross-benzoin and glycolate-aldol products in high yield and with exceptional diastereo- and enantioselectivities.

Denmark, Scott E.; Wilson, Tyler W.

2010-11-01

81

Asymmetric Synthesis of Novel Ferrocenyl Ligands with Planar and Central Chirality.  

PubMed

A stereogenic center at the position beta to the metallocene backbone is present in ferrocenyl ligands 2, which are interesting for asymmetric catalysis. These planar-chiral compounds are accessible for the first time by a highly diastereoselective and enantioselective synthesis (de=93-97 %; ee>/=96 %) from the ferrocenyl ketones 1. A variety of donor groups (E(1)=Ph(2)P small middle dotBH(3), SMe, SiPr; E(2)=SMe, STol, SePh, Ph(2)P small middle dotBH(3), iPr(2)P small middle dotBH(3)) can be introduced as electrophiles. Tol=tolyl=CH(3)C(6)H(4). PMID:10458809

Enders; Peters; Lochtman; Raabe

1999-08-01

82

Asymmetric total synthesis of 1-deoxy-7,8-di-epi-castanospermine.  

PubMed

An efficient, stereocontrolled synthesis of (6S,7S,8S,8aR)-6,7,8-trihydroxyindolizidine (alias 1-deoxy-7,8-di-epi-castanospermine) (14) has been developed, which exploits an asymmetric vinylogous Mukaiyama aldol reaction (VMAR) between N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsilyloxy)pyrrole (1) and 2,3-O-isopropylidene-D-glyceraldehyde (2) to construct the initial pyrrolidine building block 3, and an ene-ene ring closing metathesis reaction (RCM) (9 to 10) to install the indolizidine skeleton. The synthetic sequence was 13 steps, proceeding in 19.5% overall yield. The configurational and conformational structure of 14 was ascertained unambiguously and confronted to previously published assignments of rac-14 and ent-14. PMID:20237688

Zambrano, Vincenzo; Rassu, Gloria; Roggio, Annamaria; Pinna, Luigi; Zanardi, Franca; Curti, Claudio; Casiraghi, Giovanni; Battistini, Lucia

2010-04-01

83

Thiophenyl-substituted triazolyl-thione L-alanine: asymmetric synthesis, aggregation and biological properties.  

PubMed

In this work, we report the asymmetric synthesis and characterization of an artificial amino acid based on triazolyl-thione L-alanine, which was modified with a thiophenyl-substituted moiety, as well as in vitro studies of its nucleic acid-binding ability. We found, by dynamic light scattering studies, that the synthetic amino acid was able to form supramolecular aggregates having a hydrodynamic diameter higher than 200 nm. Furthermore, we demonstrated, by UV and CD experiments, that the heteroaromatic amino acid, whose enzymatic stability was demonstrated by HPLC analysis also after 24 h of incubation in human serum, was able to bind a RNA complex, which is a feature of biomedical interest in view of innovative antiviral strategies based on modulation of RNA-RNA molecular recognition. PMID:24952728

Saghyan, Ashot S; Simonyan, Hayarpi M; Petrosyan, Satenik G; Geolchanyan, Arpine V; Roviello, Giovanni N; Musumeci, Domenica; Roviello, Valentina

2014-10-01

84

Dynamic kinetic asymmetric synthesis of five contiguous stereogenic centers by sequential organocatalytic stetter and Michael-aldol reaction: enantioselective synthesis of fully substituted cyclopentanols bearing a quaternary stereocenter.  

PubMed

A synthesis of fully substituted cyclopentanes bearing a quaternary carbon center and five contiguous stereogenic centers has been achieved by sequential organocatalyzed Stetter and Michael-Aldol reactions of heteroaromatic aldehydes, nitroalkenes, and ?,?-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with dynamic kinetic asymmetric transformation and excellent enantioselectivities (up to >99% ee). PMID:21348455

Hong, Bor-Cherng; Dange, Nitin S; Hsu, Che-Sheng; Liao, Ju-Hsiou; Lee, Gene-Hsiang

2011-03-18

85

The synthesis and applications of a biaryl-based asymmetric phosphine ligand  

E-print Network

The asymmetric biaryl backbone of a dialkylbiphenyl phosphine ligand was developed, synthesized, and resolved. The application of the chiral phosphine ligand to the asymmetric Suzuki-Miyaura cross-coupling reaction was ...

Hirai, Satoko

2005-01-01

86

Establishing the Absolute Configuration of the Asbestinins: Enantioselective Total Synthesis of 11-Acetoxy-4-deoxyasbestinin D  

E-print Network

an intramolecular Diels-Alder cycloaddition.2k The total synthesis of 11-acetoxy-4-deoxyasbestinin D (1) was undertaken with the intent of validating the intramolecular Diels-Alder approach for the synthesis of the required Diels-Alder precursor. To this end, the benzyl ether was reductively cleaved, and the resultant

87

Memory of chirality of tertiary aromatic amide: application to the asymmetric synthesis of (S)-?-methylDOPA.  

PubMed

We describe an original asymmetric synthesis of (S)-?-methylDOPA proceeding by the concept of memory of chirality, the only source of chirality being the starting D-alanine. The initial chirality of the amino acid is temporarily transferred to a dynamic axial chirality of a tertiary aromatic amide. The (S)-?-methylDOPA hydrochloride is obtained after four steps with 98% ee. PMID:22950908

Mai, Thi Thoa; Viswambharan, Baby; Gori, Didier; Kouklovsky, Cyrille; Alezra, Valérie

2012-10-01

88

Asymmetric synthesis of enantiomerically pure 1,4-di- and 1,1,4-trisubstituted tetrahydro-1 H-3-benzazepines  

Microsoft Academic Search

A four step asymmetric synthesis of 1,4-di- and 1,1,4-trisubstituted enantiomerically pure tetrahydro-3-benzazepines is described. Tricyclic oxazolobenzazepinones trans-9 and cis-10 allow the introduction of different alkyl groups (methyl, ethyl, allyl) with high diastereoselectivity (dr >99:1). The relative configuration of the new stereogenic center was determined by NOE experiments. Tricyclic lactams trans-9 and cis-10 were also used for the introduction of two

Soumya Sarkar; Dirk Schepmann; Bernhard Wünsch

2011-01-01

89

Grazing incident asymmetric X-ray diffraction of ?-FeSi 2 layers, produced by ion beam synthesis  

Microsoft Academic Search

The crystal structure of ?-FeSi2 phase, prepared by ion beam synthesis (IBS) method, followed by rapid thermal annealing (RTA) is investigated by grazing incident asymmetric X-ray diffraction (GIAXRD). The X-ray spectra, obtained at different grazing angles, indicated that the ?-FeSi2 phase is formed in the whole implantation range. From the comparison of the reflections intensities ratios, it is found that

A. Atanassov; M. Baleva; V. Darakchieva; E. Goranova

2004-01-01

90

Synthesis of 2,5-asymmetrically substituted 3,4-diaminothieno[2,3-b]thiophenes by domino reaction.  

PubMed

A convenient one pot synthesis of 2,5-asymmetrically substituted thieno[2,3-b]thiophenes is developed. The method is based on consecutive domino reactions (SN2 reaction ? Thorpe-Ziegler reaction) using malononitrile and carbon disulfide as starting materials with the generation of potassium 2,2-dicyanoethene-1,1-bis(thiolate) in a solution. The high yield of the target thienothiophenes was achieved using the Ziegler dilution effect. PMID:24028177

Zubarev, Andrey A; Larionova, Natalia A; Rodinovskaya, Lyudmila A; Mortikov, Valery Yu; Shestopalov, Anatoliy M

2013-10-14

91

Synthesis, coordination behaviour, structural features and use in asymmetric hydrogenations of bifep-type biferrocenes.  

PubMed

A protocol for the synthesis of C2- and C1-symmetric 2,2''-diarylphosphino-substituted biferrocenes (bifep-type ligands) is presented and the preparation of four representatives is described [(Sp,Sp)-2-R1(2)P-2''- R2(2)P-1,1''-biferrocene; (bifep): R1=R2=Ph; : R1=Ph, R2=Cy; : R1=R2=3,5-Me2C6H3; : R1=3,5-Me(2-)4-OMe-C6H2, R2=3,5-(CF3)2C6H3]. In addition, the synthesis of three palladium(II) complexes ([PdX2(L)], : L=, X=Cl; : L=, X=Cl; : L=, X=C6F5 and of four bifep ruthenium complexes (: [RuCl(p-cymene)()]PF6; : [RuI(p-cymene)()]PF6; : [RuCl(benzene)()]PF(6); : [RuI(p-cymene)()]I) is reported. In the solid state the biferrocene unit of complexes , and adopt either a (P)-shaped () or an (M)-shaped (, ) conformation. In solution, palladium complexes and are present as equilibrium mixtures of rapidly interconverting (P)- and (M)-shaped conformers. Rhodium- and iridium-mediated asymmetric hydrogenations of a number of olefins and one imine give products with only low to moderate enantiomeric excess, while in the ruthenium-catalyzed hydrogenation of ketones a maximum e.e. of 82% is obtained. The low enantioselectivities are assumed to be related to the conformational flexibility of bifep-type ligands. PMID:19333499

Espino, Gustavo; Xiao, Li; Puchberger, Michael; Mereiter, Kurt; Spindler, Felix; Manzano, Blanca R; Jalón, Félix A; Weissensteiner, Walter

2009-04-21

92

Mechanism of the Cobalt Oxazoline Palladacycle (COP)-Catalyzed Asymmetric Synthesis of Allylic Esters  

PubMed Central

The catalytic enantioselective SN2? displacement of (Z)-allylic trichloroacetimidates catalyzed by the palladium(II) complex [COP-OAc]2 is a broadly useful method for the asymmetric synthesis of chiral branched allylic esters. A variety of experiments aimed at elucidating the nature of the catalytic mechanism and its rate- and enantiodetermining steps are reported. Key findings include: (a) the demonstration that a variety of bridged-dipalladium complexes are present and constitute resting states of the COP catalyst, however, monomeric palladium (II) complexes are likely involved in the catalytic cycle; (b) labeling experiments establishing that the reaction proceeds in an overall antarafacial fashion; (c) secondary deuterium kinetic isotope effects that suggest substantial rehybridization at both C1 and C3 in the rate-limiting step; and (d) DFT computational studies (B3-LYP/def2-TZVP) that provide evidence for bidentate substrate-bound intermediates and an anti-oxypalladation/syn-deoxypalladation pathway. These results are consistent with a novel mechanism in which chelation of the imidate nitrogen to form a cationic palladium (II) intermediate activates the alkene for attack by external carboxylate in the enantiodetermining step. Computational modeling of the transition-state structure for the acyloxy palladation step provides a model for enantioinduction. PMID:20942424

Cannon, Jeffrey S.; Kirsch, Stefan F.; Overman, Larry E.; Sneddon, Helen F.

2010-01-01

93

Molecular Models of Reactants and Products from an Asymmetric Synthesis of a Chiral Carboxylic Acid  

NSDL National Science Digital Library

Our JCE Featured Molecules for this month come from the paper by Thomas E. Smith, David P. Richardson, George A. Truran, Katherine Belecki, and Megumi Onishi (1). The authors describe the use of a chiral auxiliary, 4-benzyl-2-oxazolidinone, in the synthesis of a chiral carboxylic acid. The majority of the molecules used in the experiment, together with several of the pharmaceuticals mentioned in the paper, have been added to our molecule collection. In many instances multiple enantiomeric and diastereomeric forms of the molecules have been included. This experiment could easily be extended to incorporate various aspects of computation for use in an advanced organic or integrated laboratory. Here are some possible exercises using the R and S forms of the 4-benzyl-2-oxazolidinone as the authors point out that both forms are available commercially. Calculation of the optimized structures and energies of the enantiomers at the HF/631-G(d) level using Gaussian03 (2) produces the results shown in Table 1. Evaluation of the vibrational frequencies results in no imaginary frequencies and the 66 real frequencies are identical for the two forms. Examination of the computed IR spectra also shows them to be identical. Additionally, the Raman and NMR spectra can be calculated for the enantiomers and compared to experimental values and spectral patterns. A tool that is becoming increasingly important for assigning absolute configuration is vibrational circular dichroism (VCD). Although the vibrational spectra of an enantiomeric pair are identical, the VCD spectra show opposite signs, as shown in Figure 1. One can imagine a synthesis, using an unknown enantiomer of the chiral auxiliary, followed by calculations of the electronic and vibrational properties of all of the intermediates and the product, and determination of absolute configuration of reactants and products by comparison of experimental and computed VCD spectra. Using a viewer capable of displaying two molecules that can be moved independently, students could more easily visualize the origin of the enantiomeric preference in the reaction between the chelated enolate and allyl iodide.

94

Asymmetric Synthesis of Spirocyclic 2-Benzopyrans for Positron Emission Tomography of ?1 Receptors in the Brain.  

PubMed

Sharpless asymmetric dihydroxylation of styrene derivative 6 afforded chiral triols (R)-7 and (S)-7, which were cyclized with tosyl chloride in the presence of Bu2SnO to provide 2-benzopyrans (R)-4 and (S)-4 with high regioselectivity. The additional hydroxy moiety in the 4-position was exploited for the introduction of various substituents. Williamson ether synthesis and replacement of the Boc protective group with a benzyl moiety led to potent ?1 ligands with high ?1/?2-selectivity. With exception of the ethoxy derivative 16, the (R)-configured enantiomers represent eutomers with eudismic ratios of up to 29 for the ester (R)-18. The methyl ether (R)-15 represents the most potent ?1 ligand of this series of compounds, with a Ki value of 1.2 nM and an eudismic ratio of 7. Tosylate (R)-21 was used as precursor for the radiosynthesis of [18F]-(R)-20, which was available by nucleophilic substitution with K[18F]F K222 carbonate complex. The radiochemical yield of [18F]-(R)-20 was 18%-20%, the radiochemical purity greater than 97% and the specific radioactivity 175-300 GBq/µmol. Although radiometabolites were detected in plasma, urine and liver samples, radiometabolites were not found in brain samples. After 30 min, the uptake of the radiotracer in the brain was 3.4% of injected dose per gram of tissue and could be reduced by coadministration of the ?1 antagonist haloperidol. [18F]-(R)-20 was able to label those regions of the brain, which were reported to have high density of ?1 receptors. PMID:24451404

Holl, Katharina; Schepmann, Dirk; Fischer, Steffen; Ludwig, Friedrich-Alexander; Hiller, Achim; Donat, Cornelius K; Deuther-Conrad, Winnie; Brust, Peter; Wünsch, Bernhard

2014-01-01

95

Asymmetric Synthesis of Spirocyclic 2-Benzopyrans for Positron Emission Tomography of ?1 Receptors in the Brain  

PubMed Central

Sharpless asymmetric dihydroxylation of styrene derivative 6 afforded chiral triols (R)-7 and (S)-7, which were cyclized with tosyl chloride in the presence of Bu2SnO to provide 2-benzopyrans (R)-4 and (S)-4 with high regioselectivity. The additional hydroxy moiety in the 4-position was exploited for the introduction of various substituents. Williamson ether synthesis and replacement of the Boc protective group with a benzyl moiety led to potent ?1 ligands with high ?1/?2-selectivity. With exception of the ethoxy derivative 16, the (R)-configured enantiomers represent eutomers with eudismic ratios of up to 29 for the ester (R)-18. The methyl ether (R)-15 represents the most potent ?1 ligand of this series of compounds, with a Ki value of 1.2 nM and an eudismic ratio of 7. Tosylate (R)-21 was used as precursor for the radiosynthesis of [18F]-(R)-20, which was available by nucleophilic substitution with K[18F]F K222 carbonate complex. The radiochemical yield of [18F]-(R)-20 was 18%–20%, the radiochemical purity greater than 97% and the specific radioactivity 175–300 GBq/µmol. Although radiometabolites were detected in plasma, urine and liver samples, radiometabolites were not found in brain samples. After 30 min, the uptake of the radiotracer in the brain was 3.4% of injected dose per gram of tissue and could be reduced by coadministration of the ?1 antagonist haloperidol. [18F]-(R)-20 was able to label those regions of the brain, which were reported to have high density of ?1 receptors. PMID:24451404

Holl, Katharina; Schepmann, Dirk; Fischer, Steffen; Ludwig, Friedrich-Alexander; Hiller, Achim; Donat, Cornelius K.; Deuther-Conrad, Winnie; Brust, Peter; Wunsch, Bernhard

2014-01-01

96

Asymmetric synthesis of protected ?-amino boronic acid derivatives with an air- and moisture-stable Cu(II) catalyst.  

PubMed

The asymmetric borylation of N-tert-butanesulfinyl imines with bis(pinacolato)diboron is achieved using a Cu(II) catalyst and provides access to synthetically useful and pharmaceutically relevant ?-amino boronic acid derivatives. The Cu(II)-catalyzed reaction is performed on the benchtop in air at room temperature using commercially available, inexpensive reagents at low catalyst loadings. A variety of N-tert-butanesulfinyl imines, including ketimines, react readily to provide ?-sulfinamido boronate esters in good yields and with high stereoselectivity. In addition, this transformation is applied to the straightforward, telescoped synthesis of ?-sulfinamido trifluoroborates. PMID:24684495

Buesking, Andrew W; Bacauanu, Vlad; Cai, Irene; Ellman, Jonathan A

2014-04-18

97

Preparation of anti-Vicinal Amino Alcohols: Asymmetric Synthesis of d-erythro-Sphinganine, (+)-Spisulosine, and d-ribo-Phytosphingosine  

PubMed Central

Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM ether-directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor d-erythro-sphinganine and the antitumor agent (+)-spisulosine, whereas the Overman rearrangement of chiral allylic trichloroacetimidates generated by the asymmetric reduction of an ?,?-unsaturated methyl ketone allowed rapid access both to d-ribo-phytosphingosine and l-arabino-phytosphingosine. PMID:23795558

2013-01-01

98

Synthesis of tertiary alkyl fluoride centers by asymmetric C?C(F) bond formation  

Microsoft Academic Search

Asymmetric alkylation of pseudoephedrine ?-fluoropropionamide (1) affords ?-alkylated products efficiently and with excellent stereocontrol at the newly formed tertiary alkyl fluoride center. Mild alkaline hydrolysis of the products provides the corresponding carboxylic acids with high enantiomeric excess.

Andrew G. Myers; Lydia McKinstry; James L. Gleason

1997-01-01

99

Phosphine-Catalyzed Formation of Carbon-Sulfur Bonds: Catalytic Asymmetric Synthesis of gamma-Thioesters  

E-print Network

A method for catalytic asymmetric ? sulfenylation of carbonyl compounds has been developed. In the presence of an appropriate catalyst, thiols not only add to the ? position of allenoates, overcoming their propensity to ...

Sun, Jianwei

100

Asymmetric reactions in continuous flow  

PubMed Central

Summary An overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed. PMID:19478913

Mak, Xiao Yin; Laurino, Paola

2009-01-01

101

Development of a concise, asymmetric synthesis of a smoothened receptor (SMO) inhibitor: enzymatic transamination of a 4-piperidinone with dynamic kinetic resolution.  

PubMed

A concise, asymmetric synthesis of a smoothened receptor inhibitor (1) is described. The synthesis features an enzymatic transamination with concurrent dynamic kinetic resolution (DKR) of a 4-piperidone (4) to establish the two stereogenic centers required in a single step. This efficient reaction affords the desired anti amine (3) in >10:1 dr and >99% ee. The title compound is prepared in only five steps with 40% overall yield. PMID:24502520

Peng, Zhihui; Wong, John W; Hansen, Eric C; Puchlopek-Dermenci, Angela L A; Clarke, Hugh J

2014-02-01

102

Asymmetric bromine-lithium exchange: application toward the synthesis of natural product.  

PubMed

Asymmetric bromine-lithium exchange has been successfully employed to synthesize bicoumarin chiral building blocks of (+)-isokotanin A and (-)-kotanin in good yields and with an excellent level of enantioselectivity. This is the first reported example of formal syntheses, using this direct methodology, leading to the single (M)-atropoisomer of (+)-isokotanin A and (-)-kotanin building blocks, without any resolution step. PMID:23919304

Graff, Julien; Debande, Thibaut; Praz, Jézabel; Guénée, Laure; Alexakis, Alexandre

2013-08-16

103

Asymmetric Total Synthesis of (-)-Isolaurallene Michael T. Crimmins* and Kyle A. Emmitte  

E-print Network

from the glycolic acid derivative as described for the antipode.12 Exposure of 4 to NaN- (SiMe3,3 ciguatoxin,4 gambieric acid A,5 the eunicellins,6 and the simpler metabolites obtusenyne,7-C13.13 The assembly of diene 3 would be completed by an asymmetric glycolate alkylation14

104

Asymmetric reduction of 4-hydroxy-2-butanone to (R)-1,3-butanediol with absolute stereochemical selectivity by a newly isolated strain of Pichia jadinii.  

PubMed

In this study, a novel strain of Pichia jadinii, HBY61, capable of the biocatalysis of 4-hydroxy-2-butanone (4H2B) to (R)-1,3-BD was isolated. HBY61 produced (R)-1,3-BD with high activity and absolute stereochemical selectivity (100 % e.e). Glucose and beef extract were found to be the key factors governing the fermentation, and their optimal concentrations were determined to be 84.2 and 43.7 g/L, respectively. The optimal bioconversion conditions of 4H2B catalyzed by HBY61 were pH 7.4, 30 °C, and 250 rpm with 6 % (v/v) glucose as the co-substrate. Accordingly, when 45 g/L of 4H2B was divided into three equal parts and added successively into the system at set time intervals, the maximum (R)-1,3-BD concentration reached 38.3 g/L with high yield (85.1 %) and strict 100 % enantioselectivity. Compared with previously reported yields for the biocatalytic production of (R)-1,3-BD, the use of strain HBY61 provided a high yield with excellent stereoselectivity. PMID:25306883

Yang, Taowei; Man, Zaiwei; Rao, Zhiming; Xu, Meijuan; Zhang, Xian; Xu, Zhenghong

2014-12-01

105

Enantiopure Narrow Bite-Angle P?OP Ligands: Synthesis and Catalytic Performance in Asymmetric Hydroformylations and Hydrogenations.  

PubMed

Herein is reported the preparation of a set of narrow bite-angle P-OP ligands the backbone of which contains a stereogenic carbon atom. The synthesis was based on a Corey-Bakshi-Shibata (CBS)-catalyzed asymmetric reduction of phosphomides. The structure of the resulting 1,1-P-OP ligands, which was selectively tuned through adequate combination of the configuration of the stereogenic carbon atom, its substituent, and the phosphite fragment, proved crucial for providing a rigid environment around the metal center, as evidenced by X-ray crystallography. These new ligands enabled very good catalytic properties in the Rh-mediated enantioselective hydrogenation and hydroformylation of challenging and model substrates (up to 99?%?ee). Whereas for asymmetric hydrogenation the optimal P-OP ligand depended on the substrate, for hydroformylation, a single ligand was the highest-performing one for almost all studied substrates: it contains an R-configured stereogenic carbon atom between the two phosphorus ligating groups, and an S-configured 3,3'-diphenyl-substituted biaryl unit. PMID:25335770

Fernández-Pérez, Héctor; Benet-Buchholz, Jordi; Vidal-Ferran, Anton

2014-11-17

106

Enantioselective Synthesis of anti- and syn-homopropargyl alcohols via Chiral Br?nsted Acid Catalyzed asymmetric Allenylboration reactions  

PubMed Central

Chiral Brønsted acid catalyzed asymmetric allenylboration reactions are described. Under optimized conditions, anti-homopropargyl alcohols 2 are obtained in high yields with excellent diastereo- and enantioselectivities from stereochemically matched aldehyde allenylboration reactions with (M)-1 catalyzed by the chiral phosphoric acid (S)-4. The syn-isomers 3 can also be obtained in good diastereoselectivities and excellent enantioselectivities from the mismatched allenylboration reactions of aromatic aldehydes using (M)-1 in the presence of the enantiomeric phosphoric acid (R)-4. The stereochemistry of the methyl group introduced into 2 and 3 is controlled by the chirality of the allenylboronate (M)-1, whereas the configuration of the new hydroxyl stereocenter is controlled by the enantioselectivity of the chiral phosphoric acid catalyst used in these reactions. The synthetic utility of this methodology was further demonstrated in triple asymmetric syntheses of a variety of anti,anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents. PMID:22731887

Chen, Ming; Roush, William R.

2012-01-01

107

Preparation of a new chiral non-racemic sulfur-containing diselenide and applications in asymmetric synthesis.  

PubMed

The synthesis of the new chiral non-racemic sulfur-containing diselenide, di-2-methoxy-6-[(1S)-1-(methylthio)ethyl]phenyl diselenide, is described. When treated with ammonium persulfate this diselenide is transformed into the corresponding selenenyl sulfate, which acts as a strong electrophilic reagent and adds to alkenes, in the presence of methanol or water, to afford the products of selenomethoxylation or selenohydroxylation, respectively, with excellent diastereoselectivities. Starting from alkenes containing internal nucleophiles, asymmetric cyclofunctionalization reactions also resulted in good chemical yields, complete regioselectivities, and high diastereoselectivities. This sulfur-containing diselenide can also be used in catalytic amounts to promote one-pot selenenylation-deselenenylation processes, from which several types of products can be obtained in high yield and with good enantiomeric excess. PMID:11891899

Tiecco, Marcello; Testaferri, Lorenzo; Santi, Claudio; Tomassini, Cristina; Marini, Francesca; Bagnoli, Luana; Temperini, Andrea

2002-03-01

108

Nickel-Catalyzed Asymmetric Transfer Hydrogenation of Olefins for the Synthesis of ?- and ?-Amino Acids.  

PubMed

The field of asymmetric (transfer) hydrogenation of prochiral olefins has been dominated by noble metal catalysts based on rhodium, ruthenium, and iridium. Herein we report that a simple nickel catalyst is highly active in the transfer hydrogenation using formic acid. Chiral ?- and ?-amino acid derivatives were obtained in good to excellent enantioselectivity. The key toward success was the use of the strongly donating and sterically demanding bisphosphine Binapine. PMID:25224466

Yang, Peng; Xu, Haiyan; Zhou, Jianrong Steve

2014-11-01

109

Efficient asymmetric synthesis of silanediol precursors from 1,5-dihydrosiloles.  

PubMed

Dihydrosiloles are easily prepared from 1,3-dienes and dichlorosilanes, even on kilogram scale. Asymmetric hydroboration of a 3-alkyl-1,5-dihydrosilole, prepared from a 2-alkyl-1,3-diene, followed by treatment with aqueous HF results in Peterson fragmentation, forming optically active 3-alkyl-4-fluorosilyl-1-butenes. The fluorosilanes are stable to moisture but very reactive toward nucleophiles. In addition, they can be converted to nucleophilic silyllithium reagents. PMID:17967032

Sen, Sushmita; Purushotham, Madhusudhan; Qi, Yingmei; Sieburth, Scott McN

2007-11-22

110

Asymmetric Synthesis of Diverse Glycolic Acid Scaffolds via Dynamic Kinetic Resolution of ?-Keto Esters  

PubMed Central

The dynamic kinetic resolution of ?-keto esters via asymmetric transfer hydrogenation has been developed as a technique for the highly stereoselective construction of structurally diverse ?-substituted-?-hydroxy carboxylic acid derivatives. Through the development of a privileged m-terphenylsulfonamide for (arene)RuCl(monosulfonamide) complexes with a high affinity for selective ?-keto ester reduction, excellent levels of chemo-, diastereo-, and enantiocontrol can be realized in the reduction of ?-aryl- and ?-chloro-?-keto esters. PMID:23186551

Steward, Kimberly M.; Corbett, Michael T.; Goodman, C. Guy; Johnson, Jeffrey S.

2012-01-01

111

Chemistry of Ethanediyl S,S-Acetals 9Asymmetric Synthesis of Chiral cis Allylic Alcohols  

Microsoft Academic Search

(2Z,1S)-1,3-diphenyl-2-propenol (3) is obtained from the chiral 5,6-dihydro-1,4-dithiin 1b in two steps and 60% enantiomeric excess. Combining our previously reported stereoselective double bond formation and this 1,4 asymmetric induction introduces a new route to chiral allylic alcohols with cis geometry from simple aldehydes and methyl ketones.

Rornualdo Caputo; Carla Ferreri; Giovanni Palumbo; Silvana Pedatella

1995-01-01

112

Synthesis of Several Cleistrioside and Cleistetroside Natural Products via a Divergent De Novo Asymmetric Approach  

PubMed Central

The de novo asymmetric syntheses of several partially acylated dodecanyl tri- and tetra-rhamnoside natural products (cleistriosides-5 & 6 and cleistetrosides-2 to 7) have been achieved (19 to 24 steps). The divergent route requires the use of three or less protecting groups. The asymmetry was derived via Noyori reduction of an acylfuran. The rhamno-stereochemistry was installed by a diastereoselective palladium-catalyzed glycosylation, ketone reduction and dihydroxylation. PMID:21038879

Wu, Bulan; Li, Miaosheng; O’Doherty, George A.

2010-01-01

113

Recent Applications of Vinyl Sulfones and Vinyl Sulfoxides in Asymmetric Synthesis  

Microsoft Academic Search

Herein we present some new synthetic applications based on the use of functionalized ?,?-unsaturated sulfones and ?,?-unsaturated sulfoxides. In particular, we have developed a stereodivergent approach to the synthesis of castanospermine stereoisomers from ?-amino-?-oxygenated-?.?-unsaturated sulfones as well as a stereoselective synthesis of substituted dihydrofurans by Pd(0) catalyzed reaction of the carbonate derivatives of ?-oxygenated-?.?-unsaturated sulfones with methylene active ketones. Additionally,

Juan C. Carretero; RamóN GóMez Arrayás; Nuria Diaz Buezo; José Luis Garrido; Inés Alonso; Javier Adrio

1999-01-01

114

Synthesis of Enantiomerically Enriched Imidazolidin-2-Ones via Asymmetric Pd-Catalyzed Alkene Carboamination Reactions  

PubMed Central

A catalyst composed of Pd2(dba)3 and (S)-Siphos-PE is effective for the enantioselective coupling of N-allyureas with aryl bromides to afford 4-substituted imidazolidin-2-ones with up to 95% ee. Added water leads to significantly improved enantioselectivities with electron-poor aryl halide substrates. The mechanism of these transformations is discussed, and evidence is presented which suggests that, in contrast to other asymmetric alkene carboaminations, C–C bond-forming reductive elimination is the enantiodetermining step of these reactions. PMID:22936415

Hopkins, Brett A.

2012-01-01

115

Asymmetric synthesis of cis-2,5-disubstituted pyrrolidine, the core scaffold of ?3-AR agonists.  

PubMed

A practical, enantioselective synthesis of cis-2,5-disubstituted pyrrolidine is described. Application of an enzymatic DKR reduction of a keto ester, which is easily accessed through a novel intramolecular N?C benzoyl migration, yields syn-1,2-amino alcohol in >99% ee and >99:1 dr. Subsequent hydrogenation of cyclic imine affords the cis-pyrrolidine in high diastereoselectivity. By integrating biotechnology into organic synthesis and isolating only three intermediates over 11 steps, the core scaffold of ?3-AR agonists is synthesized in 38% overall yield. PMID:23451898

Xu, Feng; Chung, John Y L; Moore, Jeffery C; Liu, Zhuqing; Yoshikawa, Naoki; Hoerrner, R Scott; Lee, Jaemoon; Royzen, Maksim; Cleator, Ed; Gibson, Andrew G; Dunn, Robert; Maloney, Kevin M; Alam, Mahbub; Goodyear, Adrian; Lynch, Joseph; Yasuda, Nobuyashi; Devine, Paul N

2013-03-15

116

Pd-catalyzed enantioselective C-H iodination: asymmetric synthesis of chiral diarylmethylamines.  

PubMed

An enantioselective C-H iodination reaction using a mono-N-benzoyl-protected amino acid has been developed for the synthesis of chiral diarylmethylamines. The reaction uses iodine as the sole oxidant and proceeds at ambient temperature and under air. PMID:24151991

Chu, Ling; Wang, Xiao-Chen; Moore, Curtis E; Rheingold, Arnold L; Yu, Jin-Quan

2013-11-01

117

Enantioselective synthesis of dityrosine and isodityrosine via asymmetric phase-transfer catalysis  

Microsoft Academic Search

Application of N-anthracenylmethyl cinchonidinium chloride quaternary ammonium phase-transfer catalysts to the enantio- and diastereoselective synthesis of dityrosine and isodityrosine is reported. Under liquid-liquid phase-transfer conditions the key ?-amino acid substituents are introduced with high enantioselectivity (?95%e.e.).

Barry Lygo

1999-01-01

118

Asymmetrical 2,6-bis(benzylidene)cyclohexanones: Synthesis, cytotoxic activity and QSAR study.  

PubMed

In order to develop novel anti-cancer agents, a series of asymmetrical 2,6-bis (benzylidene)cyclohexanone derivatives containing nitrobenzylidene moiety were synthesized and their cytotoxic activity were determined in vitro against MDA-MB 231, MCF-7 and SK-N-MC cell lines using MTT assay. Among the tested compounds, the highest activity against MDA-MB 231 cells was achieved by 2-(3-bromo-5-methoxy-4-propoxybenzylidene)-6-(2-nitrobenzylidene)cyclohexanone (compound 5d). Whereas, compound 5j (the 3-nitro analog of compound 5d) was the most potent compound against MCF-7 and SK-N-MC cell lines. The results indicated that the cytotoxic activity profile against different tumor cells can be optimized by desired 4-alkoxy-3-bromo-5-methoxybenzylidene scaffold. PMID:22341788

Nakhjiri, Maryam; Safavi, Maliheh; Alipour, Eskandar; Emami, Saeed; Atash, Amir Farzin; Jafari-Zavareh, Mona; Ardestani, Sussan K; Khoshneviszadeh, Mehdi; Foroumadi, Alireza; Shafiee, Abbas

2012-04-01

119

Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses  

PubMed Central

Summary Several novel chiral N-heterocyclic carbene and phosphine ligands were prepared from (S)-BINOL. Moreover, their ligated Au complexes were also successfully synthesized and characterized by X-ray crystal diffraction. A weak gold-? interaction between the Au atom and the aromatic ring in these gold complexes was identified. Furthermore, we confirmed the formation of a pair of diastereomeric isomers in NHC gold complexes bearing an axially chiral binaphthyl moiety derived from the hindered rotation around C–C and C–N bonds. In the asymmetric intramolecular hydroamination reaction most of these chiral Au(I) complexes showed good catalytic activities towards olefins tethered with a NHTs functional group to give the corresponding product in moderate yields and up to 29% ee. PMID:24204435

Sun, Yin-wei

2013-01-01

120

Asymmetric Synthesis of Functionalized Dihydro- and Tetrahydropyrans via an Organocatalytic Domino Michael-Hemiacetalization Reaction  

PubMed Central

Starting from ?-hydroxymethyl nitroalkenes and various 1,3-dicarbonyl compounds, a one-pot organocatalyzed diastereo- and enantioselective synthesis of polyfunctionalized dihydro- and tetrahydropyran derivatives via a domino Michael-hemiacetalization sequence is reported. The title compounds bearing a variety of functional groups can be synthesized in this way in good yields (59–91%) and with moderate to excellent diastereoselectivities (26–98% de) and enantioselectivities (71–99% ee).

Urbanietz, Gregor; Atodiresei, Iuliana; Enders, Dieter

2014-01-01

121

Enantioselective synthesis of bis-?-amino acid esters via asymmetric phase-transfer catalysis  

Microsoft Academic Search

Application of N-anthracenylmethyl dihydrocinchonidinium bromide quaternary ammonium phase-transfer catalysts to the enantio- and diastereoselective synthesis of a series of bis-?-amino acid esters is reported. Under liquid-liquid phase-transfer conditions the target amino acid esters are obtained with high enantiomeric excess (?95%e.e.) via alkylation of two molecules of a benzophenone-derived glycine-imine with an appropriate dibromide.

Barry Lygo; John Crosby; Justine A. Peterson

1999-01-01

122

Organocatalytic asymmetric synthesis of 3-chlorooxindoles bearing adjacent quaternary-tertiary centers.  

PubMed

A new methodology was developed for the synthesis of enantiomerically enriched 3,3-disubstituted 3-chlorooxindoles 3 via a Michael addition of 3-chloroxindoles to nitroolefins 2, catalyzed by chiral squaramide 10. Products with adjacent quaternary-tertiary centers were isolated in excellent yields (up to 99%), high diastereoselectivities (up to 11:1), and enantiomeric purities (up to 92%). This is the first example where 3-chloroxoindoles 1 have been used as nucleophiles in a highly stereoselective organocatalytic reaction. PMID:22958139

Noole, Artur; Järving, Ivar; Werner, Franz; Lopp, Margus; Malkov, Andrei; Kanger, Tõnis

2012-09-21

123

Asymmetric synthesis of congested spiro-cyclopentaneoxindoles via an organocatalytic cascade reaction.  

PubMed

Starting from simple alkylidene oxindoles and nitroketones, a highly stereoselective methodology was developed for the synthesis of spiro-cyclopentaneoxindoles with four consecutive stereogenic centers. Using an organocatalytic cascade of Michael and aldol reactions in the presence of a chiral thiourea catalyst products were obtained in moderate to high yields and excellent enantioselectivities. Nitro, ester, and hydroxyl groups were introduced to the spiro ring, which could be used to facilitate further functionalization of the products. PMID:23879690

Noole, Artur; Ilmarinen, Kaja; Järving, Ivar; Lopp, Margus; Kanger, Tõnis

2013-08-16

124

Asymmetric total synthesis of (+)-bermudenynol, a C15 Laurencia metabolite with a vinyl chloride containing oxocene skeleton, through intramolecular amide enolate alkylation.  

PubMed

A substrate-controlled asymmetric total synthesis of (+)-bermudenynol, a compact and synthetically challenging C15 Laurencia metabolite that contains several halogen atoms, is reported. The oxocene core, which contains a vinyl chloride, was constructed by an efficient and highly stereoselective intramolecular amide enolate alkylation (IAEA). This result showcases the broad utility of the IAEA methodology as a useful alternative for cases in which the ring-closing metathesis is inefficient. PMID:24227662

Kim, Gyudong; Sohn, Te-Ik; Kim, Deukjoon; Paton, Robert S

2014-01-01

125

Asymmetric synthesis of the tricyclic core of NGF-inducing cyathane diterpenes via a transition-metal-catalyzed [5 + 2] cycloaddition.  

PubMed

[reaction: see text] A concise asymmetric synthesis of the tricyclic core of cyathane diterpenes is described, based on a novel transition-metal-catalyzed intramolecular [5 + 2] cycloaddition of ynone-vinylcyclopropane 10 (assembled from commercially available (S)-(-)-limonene), which proceeds in 90% yield with >95% selectivity. This strategy provides efficient access (14 steps and 13% overall yield) to potential analogues as well as precursors of nerve growth factor (NGF)-inducing diterpenes. PMID:11418060

Wender, P A; Bi, F C; Brodney, M A; Gosselin, F

2001-06-28

126

Absolute stereochemistry of anisodorin 5  

Microsoft Academic Search

The absolute stereochemistry of the natural diterpene anisodorin 5 1, previously isolated from the marine dorid nudibranch Anisodoris fontaini, has been established by synthesis of its enantiomer ent-anisodorin 5 3.

Nicon Ungur; Margherita Gavagnin; Ernesto Mollo; Guido Cimino

1999-01-01

127

Synthesis, Annealing and Performance of Pd-Au Asymmetric Composite Membranes for Hydrogen Purification  

SciTech Connect

Composite asymmetric Pd-Au membranes, based on porous Inconel and Hastelloy tubular supports, were prepared by means of electroless deposition and galvanic displacement techniques and tested, before and after Au deposition, in pure H2 atmosphere. The final membranes, with Au average bulk composition up to 16.7 wt%, were 9 15 m thick and showed, for the entire duration of characterization, H2/He ideal selectivity in excess of 900. The annealing of the as-prepared membranes was conducted through the coating and diffusion mechanism in He and H2 atmospheres at 500 C. The annealing conditions were chosen after non-isothermal and isothermal HT-XRD studies on coupons synthetized with similar preparation methods. After the formation of the Pd-Au layer, the membranes showed steady flux and a stable Au gradient on the membrane top layer. Comparisons between permeance for Pd/Au and pure Pd membranes indicated that the membranes with an Au average bulk composition of 4.5 and 5.4 wt% had an enhancement, up to 20%, of the H2 permeability in the temperature range 250 450 C with respect to pure Pd membranes. On the other hand, the membrane having the highest Au composition, 16.7 wt%, even though characterized by a lower H2 permeability (77% of pure Pd) had a rather high surface Au composition (approximately 46 wt%), which might provide good H2S poisoning tolerance.

Ma, Yi Hua [Worcester Polytechnic Institute; Chen, Chao-Huang [Worcester Polytechnic Institute; Catalano, Jacopo [Worcester Polytechnic Institute; Guazzone, Federico [Worcester Polytechnic Institute; Payzant, E Andrew [ORNL

2013-01-01

128

Asymmetric synthesis from terminal alkenes by diboration/cross-coupling cascades  

PubMed Central

Amongst prospective starting materials for organic synthesis, terminal (monosubstituted) alkenes are ideal. In the form of ?-olefins, they are manufactured on enormous scale and they are the core product features from many organic chemical reactions. While their latent reactivity can easily enable hydrocarbon chain extension, alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these impressive attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic ?-olefins in >90% ee and, with the exception of site-controlled isotactic polymerization of ?-olefins,1 none of these processes result in chain-extending C-C bond formation to the terminal carbon.2, 3, 4, 5, 6 Herein, we describe a strategy that directly addresses this gap in synthetic methodology and present a single-flask catalytic enantioselective conversion of terminal alkenes into a range of chiral products. These reactions are enabled by an unusual neighboring group participation effect that accelerates Pd-catalyzed cross-coupling of 1,2-bis(boronates) relative to nonfunctionalized alkyl boronate analogs. In tandem with enantioselective diboration, this reactivity feature connects abundant alkene starting materials to a diverse array of chiral products. Importantly with respect to synthesis utility, the tandem diboration/cross-coupling reaction (DCC reaction) generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), employs low loadings (1–2 mol %) of commercially available catalysts and reagents, it offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology. PMID:24352229

Mlynarski, Scott N.; Schuster, Christopher H.; Morken, James P.

2013-01-01

129

De novo asymmetric synthesis of cladospolide B-D: structural reassignment of cladospolide D via the synthesis of its enantiomer.  

PubMed

The enantioselective synthesis of cladospolide B, C, and (ent)-cladospolide D has been achieved in 11-15 steps from 1-nonyne. The route relies upon an alkyne zipper reaction to relay an ynone and dienoate functional groups across a nine carbon fragment, which enables a highly enantioselective Noyori ynone reduction and a diastereo- and regioselective Sharpless dihydroxylation of a dienoate. In addition to being a flexible approach to three members of the cladospolide natural products, this route for the first time correctly established the structure for cladospolide D. PMID:19193044

Xing, Yalan; O'Doherty, George A

2009-03-01

130

From highly enantioselective catalytic reaction of 1,3-diynes with aldehydes to facile asymmetric synthesis of polycyclic compounds.  

PubMed

(S)-1,1'-Binaphth-2-ol (BINOL) in combination with ZnEt(2), Ti(O(i)Pr)(4), and biscyclohexylamine was found to catalyze the highly enantioselective (83-95% ee) addition of various 1,3-diynes to aldehydes of diverse structures. This method provides a convenient pathway to generate a number of optically active dienediynes as the acyclic precursors to polycyclic compounds. The chiral dienediynes undergo highly chemoselective Pauson-Khand (PK) cycloaddition in benzaldehyde by using [Rh(cod)Cl](2) as the catalyst in the presence of rac-BINAP. High diastereoselectivity (up to >20:1) has also been achieved with the chiral dienediyne substrates containing a bulky substituent adjacent to the chiral center. In the presence of the Grubbs II catalyst, ring-closing enyne metathesis of the PK cycloaddition products led to the formation of the desired 5,5,7- and 5,5,8-fused tricyclic compounds. Further highly diastereoselective Diels-Alder reaction of a 5,5,7-tricyclic compound with maleic anhydride produced a 5,5,7,6-polycyclic product. The asymmetric synthesis of polycyclic compounds from optically active dienediynes has established a novel and efficient synthetic route to the structural framework of many biologically significant molecules. PMID:21688803

Turlington, Mark; Du, Yuhao; Ostrum, Samuel G; Santosh, Vishaka; Wren, Kathryne; Lin, Tony; Sabat, Michal; Pu, Lin

2011-08-01

131

Absolutely relativity  

NASA Astrophysics Data System (ADS)

The light speed constancy is proved here and then it is not a principle suppose it is a proposition proved absolutely based on the Galilean transformation and simultaneity and this is a book full from new discoveries along the absolutely proof for Lorentz transformation. Even in a page I have proved Lorentz transformation by the brawer constant point based on the Galilean transformation until to show easily it is possible to generate absolutely relativity and this is not ether theorem suppose we are upon the new discoveries all mathematical and complete, not a theory.

Lutephy, Mohsen

2012-03-01

132

ASYMMETRIC SYNTHESIS OF (Rp)- AND (Sp)-2ETHYL, (Rp)-2-PENTYLOXY-, (Sp)-2-PENTYLTHIO- AND (Sp)-2-PENTYLAMINO-4H-1,3,2-BENZODIOXAPHOSPHORIN 2OXIDES  

Microsoft Academic Search

2-Substituted-4H-1,3,2-benzodioxaphosphorin 2-oxides (2-substituted-BDPOs) are potent and stereoselective inhibitors of neuropathy target esterase (NTE) when the 2-substituent is n-alkyl, n-alkyloxy, n-alkylthio or n-alkylamino with maximum potency for the C7 to C9 analogs. Asymmetric syntheses were developed to assign the absolute configurations of each type of 2-substituted-BDPO. (Sp)-O-Methyl ethylphosphonothioic acid, the chiral starting material for (Rp)- and (Sp)-2-ethyl-BDPOs, was obtained by resolution

Shao-Yong Wu; John E. Casida

1994-01-01

133

Synthesis of Bis(indole) Alkaloids from Arundo donax: The Ynindole Diels-Alder Reaction, Conformational Chirality, and Absolute Stereochemistry.  

PubMed

Bis(indole) alkaloids from Arundo donax were synthesized using the first ynindole Diels-Alder reaction. The alkaloids are chiral, having stable enantiomeric conformations with half-lives of racemization of t1/2 =4150-25100?seconds at room temperature. Their absolute stereochemistry was determined using the exciton chirality method. PMID:25200279

Chen, Jingjin; Ferreira, Andrew J; Beaudry, Christopher M

2014-10-27

134

Asymmetric synthesis from terminal alkenes by cascades of diboration and cross-coupling.  

PubMed

Terminal, monosubstituted alkenes are ideal prospective starting materials for organic synthesis because they are manufactured on very large scales and can be functionalized via a broad range of chemical transformations. Alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic ?-olefins into chiral products with an enantiomeric excess greater then 90 per cent. With the exception of site-controlled isotactic polymerization of ?-olefins, none of these catalytic enantioselective processes results in chain-extending carbon-carbon bond formation to the terminal carbon. Here we describe a strategy that directly addresses this gap in synthetic methodology, and present a single-flask, catalytic enantioselective conversion of terminal alkenes into a number of chiral products. These reactions are facilitated by a neighbouring functional group that accelerates palladium-catalysed cross-coupling of 1,2-bis(boronates) relative to non-functionalized alkyl boronate analogues. In tandem with enantioselective diboration, this reactivity feature transforms alkene starting materials into a diverse array of chiral products. We note that the tandem diboration/cross-coupling reaction generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), uses low loadings (1-2 mol per cent) of commercially available catalysts and reagents, offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology. PMID:24352229

Mlynarski, Scott N; Schuster, Christopher H; Morken, James P

2014-01-16

135

Asymmetric synthesis of the cytotoxic marine natural product (+)-awajanomycin and its C-11 epimer.  

PubMed

Full details of the convergent synthetic approach to awajanomycin, and the first total syntheses of the marine natural product (+)-awajanomycin (1) and its C-11 epimer 38 by an improved 13-step approach, are described. The key elements of the synthetic strategy resided in the use of (R)-18 as the chiral building block to construct the gamma-lactone-delta-lactam core 3 and cross-olefin metathesis as the key reaction to couple the latter with the allylic alcohol segment (R- or S-4). The efficient construction of the core 3 was realized by taking advantage of the inherent multiple reactivities of the chiral building block (R)-18. A highly diastereoselective one-pot transformation of 6 to 26 was achieved in a "one stone four birds" manner. On the other hand, enantioselective synthesis of both enantiomers of the segment 4 has been undertaken by an alternative and more efficient two-step procedure. Both awajanomycin (1) and 11-epi-awajanomycin 38 have been synthesized with overall yields of 3.8% and 3.6%, respectively. Quantum chemical calculations were undertaken to reveal the low reactivity of compound 27 toward methoxycarbonylation and to get an insight into the favored conformations of the intermediates 25-27. In addition, the geometry of the side product 39 arising from the homocoupling of the allylic alcohol moiety 4 was revised as E, and an unusual cyclopropanation reaction was discovered. PMID:20507081

Fu, Rui; Ye, Jian-Liang; Dai, Xi-Jie; Ruan, Yuan-Ping; Huang, Pei-Qiang

2010-06-18

136

Aluminum complexes incorporating symmetrical and asymmetrical tridentate pincer type pyrrolyl ligands: synthesis, characterization and reactivity study.  

PubMed

A series of aluminum complexes incorporating substituted symmetrical and asymmetrical tridentate pyrrolyl ligands are synthesized conveniently and the treatment of the derivatives with small organic molecules are analyzed. The reaction of lithiated [C4H2NH(2-CH2NH(t)Bu)(5-CH2NR1R2)], where for 1, R1 = R2 = Me; 2, R1 = H, R2 = (t)Bu, with AlCl3 in diethyl ether affords Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)]Cl2 (3) and Al[C4H2N(2,5-CH2NH(t)Bu)2]Cl2 (4), respectively, in high yields. Furthermore, subjecting 3 and 4 to reaction with one equiv. of LiNMePh in diethyl ether generates Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)][NMePh]Cl (5) and Al[C4H2N(2,5-CH2NH(t)Bu)2][NMePh]Cl (6), respectively, while eliminating one equiv. of LiCl. The reaction between compound 4 with two equiv. of LiO-Ph-4-Me in diethyl ether yields the aluminum di-phenoxide compound Al[C4H2N(2,5-CH2NH(t)Bu)2](O-Ph-4-Me)2 (7) whereas the combination of 3 and two equiv. of LiNH(t)Bu, produces Al[C4H2N(2-CH2N(t)Bu)(5-CH2NMe2)](NH(t)Bu)(NH2(t)Bu) (8). Additionally, the mixing of 1 and one equiv. of AlMe3 renders Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)]Me2 (9). Adding one more equiv. of AlMe3 with 9 affords {Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)AlMe3]Me2} (10), which can also be obtained by treating 1 with two equiv. of AlMe3 directly. The treatment of 9 with one equiv. of 2,6-dimethylphenol in diethyl ether gives the aluminum alkoxide derivative, Al[C4H2N(2-CH2NH(t)Bu)(5-CH2NMe2)](O-C6H3-2,6-Me2)Me (11). Furthermore, the reaction between 9 and one equiv. of 1-ethyl-1-phenyl ketene, initiates the aluminum dimethyl complex Al{C4H2N[2-CH2CEtPh-C(=O)-NH(t)Bu](5-CH2NMe2)}Me2 (12) with a C-N bond breakage and a C-C bond formation. All the Al-derivatives are characterized by (1)H and (13)C NMR spectroscopy and the molecular structures are determined by single crystal X-ray diffractometry in solid state. PMID:23907274

Liu, Pei-Hsin; Chuang, Fu-Jung; Tu, Cheng-Yi; Hu, Ching-Han; Lin, Tzu-Wei; Wang, Yu-Tang; Lin, Chia-Her; Datta, Amitabha; Huang, Jui-Hsien

2013-10-01

137

Clarifying the structure of granadaene: total synthesis of related analogue [2]-granadaene and confirmation of its absolute stereochemistry.  

PubMed

Streptococcus agalactiae is an important agent in the infection of neonates in the first world. One of the most extended methods for its identification is based on the detection of a characteristic red pigment in the patient samples, named [12]-granadaene (1). In this article, we present a modular and flexible approach to simple analogues of this ornithine rhamno-polyene 1 and the elucidation of the most important features of its structure: the absolute configuration at C-27, the stereochemistry of the anomeric center and the link of the amino acid ornithine to the rest of the structure. PMID:23043725

Paradas, Miguel; Jurado, Rocío; Haidour, Ali; Rodríguez Granger, Javier; Sampedro Martínez, Antonio; de la Rosa Fraile, Manuel; Robles, Rafael; Justicia, José; Cuerva, Juan M

2012-11-15

138

Total synthesis of junionone, a natural monoterpenoid from Juniperus communis L., and determination of the absolute configuration of the naturally occurring enantiomer by ROA spectroscopy.  

PubMed

Recently, we reported a novel access to 2,2-diethyl-3-[(E/Z)-prop-1-en-1-yl]cyclobutanone by an intramolecular nucleophilic substitution with allylic rearrangement (S(N)i') of (E)-6-chloro-3,3-diethylhept-4-en-2-one. The ring closure reaction was found to proceed with selective syn-displacement of the leaving group. This method was now applied to the total synthesis of junionone, an olfactorily interesting cyclobutane monoterpenoid isolated from Juniperus communis, L. S(N)i' Ring closure of the ketone enolate of (E)-3,3-dimethyl-5-[(2R,3R)-3-methyloxiran-2-yl]pent-4-en-2-one (R,R)-(E)-4' proceeded only after the epoxide moiety had been activated by Lewis acid and led to the junionone precursors (3R)- and (3S)-3-[(1E,3R)-3-hydroxybut-1-en-1-yl]-2,2-dimethylcyclobutanone (S/R,R)-(E)-3. The ratio of syn- and anti-conformers in the transitory molecular arrangement was found to depend on the nature of the Lewis acid. The absolute configuration of both the synthetic as well as the natural junionone, isolated from juniper berry oil, was determined by Raman Optical Activity (ROA) spectroscopy. Our experiments led to a novel synthetic route to both (+)- and (-)-junionone, the first determination of the absolute configuration of natural junionone, and to the development of a practical ROA procedure for measuring milligram quantities of volatile liquids. PMID:18205115

Lovchik, Martin A; Fráter, Georg; Goeke, Andreas; Hug, Werner

2008-01-01

139

Asymmetric decarboxylative 1,4-addition of malonic acid half thioesters to vinyl sulfones: highly enantioselective synthesis of 3-monofluoromethyl-3-arylpropanoic esters.  

PubMed

An asymmetric decarboxylative 1,4-addition of malonic acid half thioesters (MAHTs) to 2-aryl-substituted vinyl sulfones has been developed, yielding adducts with excellent enantioselectivity (up to 97?% ee). In view of tuning pKa values, a quinine-based benzyl-substituted thiourea was designed and demonstrated as the most efficient catalyst. The enantioselective synthesis of 3-monofluorinated analogues of 3-methyl indanone and (+)-turmerone has been accomplished from decarboxylative 1,4-addition adducts with satisfactory results. PMID:24591040

Qiao, Baokun; Liu, Qian; Liu, Hongjun; Yan, Lin; Jiang, Zhiyong

2014-05-01

140

Catalytic Asymmetric Synthesis Using Feedstocks. An Enantioselective Route to 2-Arylpropionic Acids and 1-Arylethyl Amines via Hydrovinylation of Vinyl Arenes  

PubMed Central

A three-step procedure for the synthesis of 2-arylpropionic acids (profens) from vinyl arenes in nearly enantiomerically pure form has been developed. Excellent yields (>97%), regioselectivities (>99%), and enantioselectivities (>97% ee) for the desired branched products were obtained in the asymmetric hydrovinylation reactions of vinyl arenes, and the products from these reactions were transformed into 2-arylpropionic acids via oxidative degradation. Subsequent Curtius or Schmidt rearrangements of these acids provided highly valued 1-arylethyl amines, including a prototypical primary amine with an ?-chiral tertiary N-alkyl group, in very good yields. PMID:19317393

Smith, Craig R.; RajanBabu, T. V.

2009-01-01

141

Synthesis and Application of New Ligands Derived from N-Heterocyclic Carbenes, Phosphines and Phosphites for Asymmetric Hydrogenations  

E-print Network

N-Heterocyclic carbene and phosphorus ligands have been synthesized and used for many catalytic reactions including chiral analogs of Crabtree’s catalyst for asymmetric hydrogenation. These catalysts have been studied extensively...

Khumsubdee, Sakunchai

2013-11-05

142

Asymmetric reactions in sonochemistry  

Microsoft Academic Search

Sonochemical processes involved in asymmetric synthesis are reviewed. The goal of this overview is to provide a comprehensive picture about the fields of both enantioselective and diastereoselective reactions accelerated or initiated by ultrasounds. Since the most, in many cases comparative, data are available in heterogeneous metal catalysis, the emphasis will be placed on these enantioselective hydrogenations, however, other applications such

Béla Török; Katalin Balázsik; Károly Felföldi; Mihály Bartók

2001-01-01

143

One-step synthesis of organic–inorganic hybrid asymmetric dimer particles via miniemulsion polymerization and functionalization with silver  

Microsoft Academic Search

Organic–inorganic polystyrene (PSt)–silica (SiO2) hybrid asymmetric particles were prepared in one step by a miniemulsion polymerization technique. The organic and inorganic reagents were confined in miniemulsion microreactor droplets. After the formation of PSt and SiO2, internal phase separation inside the droplets was accelerated owing to the hydrophobicity of PSt and the hydrophilicity of SiO2. Therefore, PSt–SiO2 hybrid asymmetric particles could

Wei Lu; Min Chen; Limin Wu

2008-01-01

144

A convenient asymmetric synthesis of a beta-amino ester with additional functionalization as a precursor for peptide nucleic acid (PNA) monomers.  

PubMed

We report the asymmetric synthesis of di-3-pentyl (3S,alphaS,7E)-3-N-benzyl-N-alpha-methylbenzylamino-dec-7-enedioate (9), which contains the correct functionalization to produce delta-amino acid derivatives to be used as monomers for Peptide Nucleic Acid (PNA) formation With this aim, thymine-pentanoic acid 15 and some of its ester derivatives were obtained, their reactivity was studied and the noteworthy ethyl ester 12 was quantitatively produced by transesterification of methyl ester 11, thus paving the way for the synthesis of the thymine-containing amino ester IV, which has been designed as a building block for a Nucleic-Acid analog with a chiral, flexible peptide backbone. PMID:17962776

Garrido, Narciso M; Díez, David; Domínguez, Sara H; Sánchez, M Rosa; García, Mercedes; Urones, Julio G

2006-01-01

145

One-step synthesis of organic-inorganic hybrid asymmetric dimer particles via miniemulsion polymerization and functionalization with silver.  

PubMed

Organic-inorganic polystyrene (PSt)-silica (SiO2) hybrid asymmetric particles were prepared in one step by a miniemulsion polymerization technique. The organic and inorganic reagents were confined in miniemulsion microreactor droplets. After the formation of PSt and SiO2, internal phase separation inside the droplets was accelerated owing to the hydrophobicity of PSt and the hydrophilicity of SiO2. Therefore, PSt-SiO2 hybrid asymmetric particles could be synthesized in one step. Between each pair of asymmetric particles, silane couplers act as bridges connecting the PSt and SiO2 particles. The size of PSt particles in these asymmetric particles was easily tuned either by changing the weight ratio of St/TEOS or by varying the sonication power during the miniemulsion preparation. After functionalization of the as-prepared asymmetric dimers by surface decoration with Ag particles, enhanced surface-enhanced Raman scattering (SERS) properties were observed due to electromagnetic enhancement of the added Ag colloids. PMID:18805542

Lu, Wei; Chen, Min; Wu, Limin

2008-12-01

146

Part I. Asymmetric Diels-Alder reaction of cyclic Isoimidium salts Part II. Total synthesis of a camphor derived dimer Part III. Asymmetric cyclopropanation catalyzed by chiral camphor-based Dirhodium(II) complex.  

E-print Network

??Part I. Asymmetric Diels-Alder Reaction of Cyclic Isoimidium Salts The asymmetric Diels-Alder reaction of cyclic isoimidium salts are described. The corresponding cycloadducts are obtained with… (more)

Miller, Yan (1982 - )

2010-01-01

147

One-Pot Asymmetric Nitro-Mannich/Hydroamination Cascades for the Synthesis of Pyrrolidine Derivatives: Combining Organocatalysis and Gold Catalysis  

PubMed Central

The highly enantioselective preparation of trisubstituted pyrrolidine derivatives employing a one-pot nitro-Mannich/hydroamination cascade is reported. This cascade approach utilizes an asymmetric bifunctional organocatalytic nitro-Mannich reaction followed by a gold-catalyzed allene hydroamination reaction. The products are afforded in good yields and excellent diastereo- and enantioselectivities. PMID:24563809

2014-01-01

148

Asymmetric synthesis of gem-diaryl substituted cyclic sulfamidates and sulfamides by rhodium-catalyzed arylation of cyclic ketimines.  

PubMed

Asymmetric addition of arylboronates to aryl-substituted cyclic ketimines proceeded in the presence of a rhodium catalyst coordinated with a chiral diene ligand to give high yields of sulfamidates and sulfamides with high enantioselectivity (up to 99% ee). PMID:23661175

Nishimura, Takahiro; Ebe, Yusuke; Fujimoto, Hiroto; Hayashi, Tamio

2013-06-18

149

Synthesis of novel chiral tridentate schiff-base ligands and their applications in catalytic asymmetric Henry reaction.  

PubMed

A series of chiral tridentate Schiff-bases were prepared and used as ligands in the catalytic asymmetric Henry reaction. Under the optimal conditions, a variety of arylaldehydes were smoothly converted into corresponding adducts with high yields (up to 98%) and excellent enantioselectivities (up to 97% ee). Chirality 26: 780-783, 2014. © 2014 Wiley Periodicals, Inc. PMID:25318691

Qiang, Gen-Rong; Shen, Tian-Hua; Zhou, Xiao-Cong; An, Xiao-Xia; Song, Qing-Bao

2014-12-01

150

Non-cross-linked polystyrene-supported 2-imidazolidinone chiral auxiliary: synthesis and application in asymmetric alkylation reactions  

PubMed Central

Summary Asymmetric alkylation reactions using non-cross-linked polystyrene (NCPS)-supported 2-imidazolidinone chiral auxiliaries were successfully investigated with excellent diastereocontrol (>99% de). The recovery and the recycling of this soluble polymer-supported chiral auxiliary were achieved in order to produce highly optical pure carboxylic acids. PMID:24204423

Nguyen, Quynh Pham Bao

2013-01-01

151

A gram-scale route to phlegmarine alkaloids: rapid total synthesis of (-)-cermizine B.  

PubMed

The synthesis of the Lycopodium alkaloid (-)-cermizine B (1), which establishes its absolute configuration, is achieved by combining asymmetric organocatalysis and an uninterrupted eight-step reaction sequence, followed by a final reduction step. This "pot-economy" strategy provides access to the cis-phlegmarine stereoparent embedded in 1 for the first time, rapidly and on a gram-scale. PMID:24727855

Bradshaw, Ben; Luque-Corredera, Carlos; Bonjoch, Josep

2014-07-11

152

Asymmetric Synthesis of P-Chiral Diphosphines. Steric Effects on the Palladium-Complex-Promoted Asymmetric Diels-Alder Reaction between a Dimethylphenylphosphole and (E/Z)-Methyl-Substituted Diphenylvinylphosphines.  

PubMed

The organopalladium complex containing ortho-metalated (S)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary has been used successfully to promote the asymmetric [4+2] Diels-Alder reactions between 1-phenyl-3,4-dimethylphosphole and the following coordinated dienophiles: (a) diphenylvinylphosphine; (b) (E)-diphenyl-1-propenylphosphine; (c) (Z)-diphenyl-1-propenylphosphine. Reaction a generates three carbon and one phosphorus stereogenic centers while reactions b and c each produce four carbon and one phosphorus chiral centers. In dichloromethane, all three reactions proceeded smoothly at room temperature giving the corresponding rigid diphosphines in high yields. Under similar reaction conditions, the reaction times observed for reactions a-c are 2, 3, and 50 h, respectively. Two-dimensional ROESY NMR studies confirmed that the prolonged reaction time required for reaction c is due to several major repulsive interactions between the chiral naphthylamine auxiliary and the (Z)-methyl-substituted vinylphosphine in the transition state. Nevertheless, all three reactions gave the corresponding rigid diphosphine in high yields. The absolute stereochemistries of the three bidentate phosphine ligands that were produced from the cycloaddition reactions have been assigned by 2D ROESY NMR spectroscopy. These diphosphines are powerful sequesterers of group 8 metals although they are highly air-sensitive in the free ligand form. The coordination chemistry and the absolute stereochemistry of the optically active complex [1alpha,4alpha,5alpha(S),6alpha(S),7R]-dichloro[5-(diphenylphosphino)-2,3,6-trimethy-7-phenyl-7-phosphabicyclo[2.2.1]-hept-2-ene-P(5)(),P(7)()]palladium(II) has been studied by single-crystal X-ray analysis. Crystal structure data: C(27)H(28)Cl(2)P(2)Pd, M(r) = 591.7; triclinic; space group P1; a = 8.643(3), b = 9.044(6), c = 9.058(4) Å; alpha = 102.75(4) degrees, beta = 108.59(2) degrees, gamma = 97.82(3) degrees; V = 638.0(5) Å(3); Z = 1; R(1) = 0.036. PMID:11669835

Aw, Beng-Hwee; Hor, T. S. Andy; Selvaratnam, S.; Mok, K. F.; White, Andrew J. P.; Williams, David J.; Rees, Nicholas H.; McFarlane, William; Leung, Pak-Hing

1997-05-01

153

Asymmetric synthesis of ?-chloro-?,?-diamino- and ?,?-aziridino-?-aminoacylpyrrolidines and -piperidines via stereoselective Mannich-type additions of N-(diphenylmethylene)glycinamides across ?-chloro-N-sulfinylimines  

PubMed Central

Summary The asymmetric synthesis of new chiral ?-chloro-?,?-diaminocarboxylamide derivatives by highly diastereoselective Mannich-type reactions of N-(diphenylmethylene)glycinamides across chiral ?-chloro-N-p-toluenesulfinylaldimines was developed. The resulting (S S,2S,3S)-?-chloro-?,?-diaminocarboxylamides were formed with the opposite enantiotopic face selectivity as compared to the (S S,2R,3R)-?-chloro-?,?-diaminocarboxyl esters obtained via Mannich-type addition of analogous N-(diphenylmethylene)glycine esters across a chiral ?-chloro-N-p-toluenesulfinylaldimine. Selective deprotection under different acidic reaction conditions and ring closure of the ?-chloro-?,?-diaminocarboxylamides was optimized, which resulted in N?-deprotected syn-?-chloro-?,?-diaminocarboxylamides, N-sulfinyl-?,?-aziridino-?-aminocarboxylamide derivatives, a trans-imidazolidine, and an N?,N?-deprotected syn-?-chloro-?,?-diaminocarboxylamide. PMID:23243474

Callebaut, Gert; Mangelinckx, Sven; Van der Veken, Pieter; Tornroos, Karl W; Augustyns, Koen

2012-01-01

154

Highly diastereoselective and stereodivergent dihydroxylations of acyclic allylic amines: application to the asymmetric synthesis of 3,6-dideoxy-3-amino-L-talose.  

PubMed

Aminohydroxylation of tert-butyl sorbate [tert-butyl (E,E)-hexa-2,4-dienoate] using enantiopure lithium (R)-N-benzyl-N-(?-methylbenzyl)amide and (-)-camphorsulfonyloxaziridine gives tert-butyl (R,R,R,E)-2-hydroxy-3-[N-benzyl-N-(?-methylbenzyl)amino]hex-4-enoate in >99:1 dr. Subsequent dihydroxylation under Upjohn conditions (OsO(4)/NMO) gives tert-butyl (2R,3R,4S,5S,?R)-2,4,5-trihydroxy-3-[N-benzyl-N-(?-methylbenzyl)amino]hexanoate (in 95:5 dr) while dihydroxylation under Donohoe conditions (OsO(4)/TMEDA) proceeds with antipodal diastereofacial selectivity to give the (R,R,R,R,R)-diastereoisomer (in 95:5 dr). The amino triols resulting from these dihydroxylation reactions are useful for further elaboration, as demonstrated by the asymmetric synthesis of 3,6-dideoxy-3-amino-L-talose. PMID:21488631

Csatayová, Kristína; Davies, Stephen G; Lee, James A; Roberts, Paul M; Russell, Angela J; Thomson, James E; Wilson, David L

2011-05-20

155

Catalytic Asymmetric Synthesis of Alkynyl Aziridines: Both Enantiomers of cis-Aziridines from One Enantiomer of the Catalyst.  

PubMed

Alkynyl aziridines can be obtained from the catalytic asymmetric aziridination (AZ reaction) of alkynyl imines with diazo compounds in high yields and high asymmetric inductions mediated by a chiral boroxinate or BOROX catalyst. In contrast to the AZ reaction with aryl- and alkyl-substituted imines, alkynyl imines react to give cis-substituted aziridines with both diazo esters and diazo acetamides. Remarkably, however, the two diazo compounds give different enantiomers of the cis-aziridine from the same enantiomer of the catalyst. Theoretical considerations of the possible transition states for the enantiogenic step reveal that the switch in enantiomers results from a switch from Si-face to Re-face addition to the imine, which in turn is related to a switch from reaction with an E-imine in the former and a Z-isomer of the imine in the latter. PMID:25205455

Guan, Yong; López-Alberca, Maria P; Lu, Zhenjie; Zhang, Yu; Desai, Aman A; Patwardhan, Aniruddha P; Dai, Yijing; Vetticatt, Mathew J; Wulff, William D

2014-10-20

156

One-step synthesis of graphene nanoribbon-MnO? hybrids and their all-solid-state asymmetric supercapacitors.  

PubMed

Three-dimensional (3D) hierarchical hybrid nanomaterials (GNR-MnO?) of graphene nanoribbons (GNR) and MnO? nanoparticles have been prepared via a one-step method. GNR, with unique features such as high aspect ratio and plane integrity, has been obtained by longitudinal unzipping of multi-walled carbon nanotubes (CNTs). By tuning the amount of oxidant used, different mass loadings of MnO? nanoparticles have been uniformly deposited on the surface of GNRs. Asymmetric supercapacitors have been fabricated with the GNR-MnO? hybrid as the positive electrode and GNR sheets as the negative electrode. Due to the desirable porous structure, excellent electrical conductivity, as well as high rate capability and specific capacitances of both the GNR and GNR-MnO? hybrid, the optimized GNR//GNR-MnO? asymmetric supercapacitor can be cycled reversibly in an enlarged potential window of 0-2.0 V. In addition, the fabricated GNR//GNR-MnO? asymmetric supercapacitor exhibits a significantly enhanced maximum energy density of 29.4 W h kg(-1) (at a power density of 12.1 kW kg(-1)), compared with that of the symmetric cells based on GNR-MnO? hybrids or GNR sheets. This greatly enhanced energy storage ability and high rate capability can be attributed to the homogeneous dispersion and excellent pseudocapacitive performance of MnO? nanoparticles and the high electrical conductivity of the GNRs. PMID:24608664

Liu, Mingkai; Tjiu, Weng Weei; Pan, Jisheng; Zhang, Chao; Gao, Wei; Liu, Tianxi

2014-04-21

157

LETTER 1371 An Improved Procedure for Asymmetric Aldol Additions with N-Acyl  

E-print Network

: Asymmetric aldol additions using chlorotitanium eno- lates of N-acyl oxazolidinones, oxazolidinethiones reactions, asymmetric synthesis, titanium eno- lates, imides, glycolates The chiral auxiliary mediated found increasingly wider use as an eno- lization method for asymmetric aldol reactions.10 However

158

Enantioselective synthesis of 2-methyl indolines by palladium catalysed asymmetric C(sp3)-H activation/cyclisation.  

PubMed

The first example of the enantioselective methyl C-H activation by an intramolecular ArPdX species and subsequent cyclisation was developed. Palladium catalysts using commercially available chiral diphosphines yield good ee's (up to 93% ee) in the synthesis of 2-methyl indolines from 2-halo N-isopropyl anilides. This approach was also employed for the synthesis of enantioenriched cyclohexyl fused indolines with moderate enantioselectivities. PMID:21927738

Anas, Saithalavi; Cordi, Alex; Kagan, Henri B

2011-11-01

159

Synthesis of an azido precursor to (2S,5R)-5-hydroxylysine using an asymmetric organocatalytic chlorination/reduction sequence.  

PubMed

An efficient, robust, and scalable synthesis of an azido precursor to the modified amino acid (2S,5R)-5-hydroxylysine was developed on the basis of the use of a highly stereoselective organocatalytic ?-chlorination-reduction protocol. The final Fmoc-protected (2S,5R)-6-azido-5-hydroxylysine derivative can be used in solid-phase peptide synthesis, providing access to proteins that contain large quantities of post-translationally modified lysine (e.g., collagens). PMID:24175670

Johannes, Manuel; Brimble, Margaret A

2013-12-20

160

Chiral fullerenes from asymmetric catalysis.  

PubMed

Fullerenes are among the most studied molecules during the last three decades, and therefore, a huge number of chemical reactions have been tested on these new carbon allotropes. However, the aim of most of the reactions carried out on fullerenes has been to afford chemically modified fullerenes that are soluble in organic solvents or even water in the search for different mechanical, optical, or electronic properties. Therefore, although a lot of effort has been devoted to the chemical functionalization of these molecular allotropes of carbon, important aspects in the chemistry of fullerenes have not been properly addressed. In particular, the synthesis of chiral fullerenes at will in an efficient manner using asymmetric catalysis has not been previously addressed in fullerene science. Thus, despite the fact that the chirality of fullerenes has always been considered a fundamental issue, the lack of a general stereoselective synthetic methodology has restricted the use of enantiopure fullerene derivatives, which have usually been obtained only after highly expensive HPLC isolation on specific chiral columns or prepared from a pool of chiral starting materials. In this Account, we describe the first stereodivergent catalytic enantioselective syntheses in fullerene science, which have allowed the highly efficient synthesis of enantiomerically pure derivatives with total control of the stereochemical result using metallic catalysts and/or organocatalysts under very mild conditions. Density functional theory calculations strongly support the experimental findings for the assignment of the absolute configuration of the new stereocenters, which has also been ascertained by application of the sector rule and single-crystal X-ray diffraction. The use of the curved double bond of fullerene cages as a two-?-electron component in a variety of stereoselective cycloaddition reactions represents a challenging goal considering that, in contrast to most of the substituted olefins used in these reactions, pristine fullerene is a noncoordinating dipolarophile. The aforementioned features make the study of stereoselective 1,3-dipolar cycloadditions onto fullerenes a unique scenario to shed light onto important mechanistic aspects. On the other hand, the availability of achiral starting materials as well as the use of nonexpensive asymmetric catalysts should provide access to chiral fullerenes and their further application in a variety of different fields. In this regard, in addition to biomedical applications, chiral fullerenes are of interest in less-studied areas such as materials science, organic electronics, and nanoscience, where control of the order and morphology at the nanometer scale are critical issues for achieving better device efficiencies. PMID:25080165

Maroto, Enrique E; Izquierdo, Marta; Reboredo, Silvia; Marco-Martínez, Juan; Filippone, Salvatore; Martín, Nazario

2014-08-19

161

A Double Asymmetric Hydrogenation Strategy for the Reduction of 1,1-Diaryl Olefins Applied to an Improved Synthesis of CuIPhEt, a C2-Symmetric N-Heterocyclic Carbenoid  

PubMed Central

A library of iridium and rhodium phosphine catalysts have been screened for the double asymmetric hydrogenation of 2,6-di-(1-phenylethenyl)-4-methyl aniline to produce the C2-symmetric aniline precursor of the N-heterocyclic carbenoid CuIPhEt. The best catalyst produced the desired enantiomer in 98.6% selectivity. This rare example of a highly selective hydrogenation of a 1,1-diaryl olefin enables a 4 step asymmetric synthesis of the C2-symmetric phenylethyl imidazolium ion (IPhEt) from p-toluidine and phenylacetylene, and its conversion to the hydrosilylation catalyst CuIPhEt. PMID:23383707

Spahn, Elizabeth; Albright, Abigail; Shevlin, Michael; Pauli, Larissa; Pfaltz, Andreas; Gawley, Robert E.

2013-01-01

162

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity  

PubMed Central

Despite over three decades of research into asymmetric phase transfer catalysis (APTC), a fundamental understanding of the factors that affect the rate and stereoselectivity of this important process are still obscure. This paper describes the initial stages of a long-term program aimed at elucidating the physical organic foundations of APTC employing a chemoinformatic analysis of the alkylation of a protected glycine imine with a libraries of enantiomerically enriched quaternary ammonium ions. The synthesis of the quaternary ammonium ions follows a diversity oriented approach wherein the tandem inter[4+2]/intra[3+2] cycloaddition of nitroalkenes serves as the key transformation. A two part synthetic strategy comprised of: (1) preparation of enantioenriched scaffolds and (2) development of parallel synthesis procedures is described. The strategy allows for the facile introduction of four variable groups in the vicinity of a stereogenic quaternary ammonium ion. The quaternary ammonium ions exhibited a wide range of activity and to a lesser degree enantioselectivity. Catalyst activity and selectivity are rationalized in a qualitative way based on the effective positive potential of the ammonium ion. PMID:21446721

Denmark, Scott E.; Gould, Nathan D.; Wolf, Larry M.

2011-01-01

163

Concise synthesis of 2,4-disubstituted thiazoles from ?-azido disulfides and carboxylic acids or anhydrides: asymmetric synthesis of cystothiazole C.  

PubMed

A novel and efficient method for the one-pot synthesis of 2,4-disubstituted thiazoles from carboxylic acids or anhydrides is presented. Based on this new method, the total synthesis of the bis-2,4-disubstituted bis(thiazoles) natural product cystothiazole C is also presented. PMID:25223403

Liu, Yi; Sun, Xue; Zhang, Xing; Liu, Jun; Du, Yuguo

2014-10-01

164

Total Synthesis of (-)-18-epi-peloruside A: An Alkyne Linchpin Strategy  

PubMed Central

A convergent synthetic route towards cytotoxic agent peloruside A that hinges on the use of an alkyne linchpin to assemble the natural product is described. Other highlights of this synthesis include an asymmetric desymmetrization reaction of a 1,3-diol, a one pot conversion of a dibromoolefin to a stereodefined enone, and a diastereoselective aldol condensation. Misassignment of the absolute stereochemistry of the C18 stereocenter in our synthesis provided the natural product epimeric at the C18 ethyl stereocenter. PMID:24490808

Michaelis, David J.; Malhotra, Sushant

2013-01-01

165

Synthesis and structures of hypervalent organoantimony and organobismuth chlorides containing asymmetric C,E,C-chelating (E = O, S) ligands.  

PubMed

Two asymmetric tridentate C,E,C-chelating ligand precursors, 1-Br-2-[(2'-BrC6H4CH2E)CH2]C10H6 (E = O (1), E = S (2), were prepared in good yield. Lithiation of the two precursors was achieved by a reaction with n-BuLi, and was followed by treatment with SbCl3 or BiCl3 in a 1: 1molar ratio to give four air-stable hypervalent organoantimony and organobismuth chlorides with an asymmetric C,E,C-chelating ligand (E = O, S), i.e. (C6H4CH2OCH2C10H6)SbCl (3), (C6H4CH2SCH2C10H6)SbCl (4), (C6H4CH2OCH2C10H6)BiCl (5) and (C6H4CH2SCH2C10H6)BiCl (6). These compounds were characterized by NMR spectroscopy, elemental analysis and melting point determination. X-ray structure analysis of compounds 3-6 revealed that the donor atoms (O, S) are strongly coordinated to the metal atoms (Sb, Bi). Compounds 3-6 exhibit chirality and crystallize as racemic mixtures. PMID:23661039

Tan, Nianyuan; Chen, Yi; Yin, Shuang-Feng; Qiu, Renhua; Zhou, Yongbo; Au, C T

2013-07-14

166

m-Carborane-based chiral NBN pincer-metal complexes: synthesis, structure, and application in asymmetric catalysis.  

PubMed

We have succeeded in synthesizing m-carborane-based chiral NBN-pincer ligands, 1,7-bis(oxazolinyl)-1,7-dicarba-closo-dodecaborane (Carbox) (7-9). The combination of bis(hydroxyamides) and 3 equiv of diethylaminosulfur trifluoride (DAST) is a key step for cyclization to form oxazoline rings in excellent yields. X-ray crystal structures of these ligands confirmed three donor sites, one central B and two flanking N atoms in fixed positions. The electrophilic halogenation of the Carbox pincer ligands with iodine and a catalytic amount of Lewis acid led to ring-opening of the oxazolines and afforded bis(haloamides) (13 and 14). The air- and moisture-stable Carbox pincer complexes of rhodium(III), nickel(II), and palladium(II) were synthesized by the oxidative addition of RhCl(3)·3H(2)O, Ni(COD)(2), and Pd(CH(3)CN)(4)[BF(4)](2) to the Carbox pincer ligands (7-9), respectively. The catalytic activity of the rhodium(III) complexes (18-20) was examined for the asymmetric conjugate reduction of ?,?-unsaturated esters and reductive aldol reaction. Among these catalysts, [(S,S)-Carbox-iPr]Rh(OAc)(2)·H(2)O (18) showed the highest enantioselective catalytic ability for both asymmetric conjugate reduction and reductive aldol reaction. PMID:21438543

El-Zaria, Mohamed E; Arii, Hidekazu; Nakamura, Hiroyuki

2011-05-01

167

Acylation, Diastereoselective Alkylation, and Cleavage of an Oxazolidinone Chiral Auxiliary: A Multistep Asymmetric Synthesis Experiment for Advanced Undergraduates  

ERIC Educational Resources Information Center

An introduction to the concepts and experimental techniques of diastereoselective synthesis using a chiral auxiliary is described. The 4-benzyl-2-oxazolidinone chiral auxiliary developed by Evans is acylated with propionic anhydride under mild conditions using DMAP as an acyl transfer catalyst. Deprotonation with NaN(TMS)[subscript 2] at -78…

Smith, Thomas E.; Richardson, David P.; Truran, George A.; Belecki, Katherine; Onishi, Megumi

2008-01-01

168

Application of an intramolecular dipolar cycloaddition to an asymmetric synthesis of the fully oxygenated tricyclic core of the stemofoline alkaloids  

PubMed Central

An intramolecular non-stabilized azomethine ylide dipolar cycloaddition was applied toward the first non-racemic synthesis of the fully-oxygenated bridged pyrrolizidine core (45) of (+)-stemofoline (1) in eleven steps from a commercially available starting material. PMID:18443655

Carra, Ryan J.; Epperson, Matthew T.; Gin, David Y.

2008-01-01

169

Synthesis and gene transfection activity of cyclen-based cationic lipids with asymmetric acyl-cholesteryl hydrophobic tails.  

PubMed

A series of novel 1,4,7,10-tetraazacyclododecane (cyclen)-based cationic lipids with asymmetric double hydrophobic tails (cholesteryl and long aliphatic chains) were designed and synthesized. Lysine was chosen as a linking moiety in the molecular backbone. The liposomes formed from 8 and dioleoylphosphatidylethanolamine (DOPE) could bind and condense plasmid DNA into nanoparticles under a low N/P ratio. These nano-scaled lipoplexes have low cytotoxicity, and might efficiently transfect A549 cells. In vitro transfection results revealed that all cationic lipids showed a comparable or better transfection efficiency (TE) than commercially available Lipofectamine 2000. The length and saturation degree of the aliphatic chain would affect their gene transfection performance, and the linoleic acid-containing 8e could give the best TE. PMID:24752704

Liu, Bao-Quan; Yi, Wen-Jing; Zhang, Ji; Liu, Qiang; Liu, Yan-Hong; Fan, Sheng-Di; Yu, Xiao-Qi

2014-06-01

170

Asymmetric total synthesis of paecilomycin E, 10'-epi-paecilomycin E and 6'-epi-cochliomycin C.  

PubMed

The asymmetric total syntheses of naturally occurring resorcylic acid lactone paecilomycin E and two of its structural congeners have been reported in this article. The major highlight of the synthetic venture is the application of the late stage Mitsunobu macrolactonization method (as it is difficult to achieve the desired products through the standard carboxyl activation method) of a properly functionalized seco-acid. The macrolactonization precursor was synthesized by applying an "E"-selective Julia-Kocienski olefination of a highly functionalized aromatic aldehyde and a sulphone, which constitutes all the stereocenters (C4', C5', C6' and C10'; 3S,7R,8R,9S) in the target molecule. PMID:25204742

Pal, Pratik; Jana, Nandan; Nanda, Samik

2014-11-01

171

Enantioselective synthesis of primary 1-(aryl)alkylamines by nucleophilic 1,2-addition of organolithium reagents to hydroxyoxime ethers and application to asymmetric synthesis of G-protein-coupled receptor ligands.  

PubMed

(E)-Arylaldehyde oxime ethers bearing a (1S)-2-hydroxy-1-phenylethyl or (2R)-1-hydroxy-2-phenylethyl group as a chiral auxiliary, both derived from a single precursor, methyl (R)-mandelate, underwent nucleophilic addition with organolithium reagents via six-membered chelates to give the diastereomerically enriched (R)- and (S)-adducts, respectively, which, after chiral auxiliary removal by reductive N-O bond cleavage, led to the corresponding (R)- and (S)-1-(aryl)ethylamines. This organolithium addition protocol using methyllithium was applied in an enantiodivergent fashion to the preparation of both enantiomers of 1-(2-hydroxyphenyl)ethylamine, which has been previously used as an efficient chiral auxiliary for the synthesis of natural products in this laboratory. The synthetic utility of this methodology involving diastereoselective methyl addition was demonstrated by further application to the asymmetric synthesis of a new type of calcium receptor agonist (calcimimetics), (R)-(+)-NPS R-568 and its thio analogue. Furthermore, diastereoselective vinylation was accomplished by application of the hydroxy oxime ether-based protocol using vinyllithium, which allowed the development of the enantioselective synthesis of the NK-1 receptor antagonists, (+)-CP-99,994 and (+)-CP-122,721. PMID:15307728

Atobe, Masakazu; Yamazaki, Naoki; Kibayashi, Chihiro

2004-08-20

172

A convenient synthesis of chiral succinic acid-d 2 by catalytic asymmetric reduction using a ruthenium BINAP catalyst  

Microsoft Academic Search

The synthesis of (2R,3R) and (2S,3S) dideuteriosuccinic acid in 63 ± 10% enantiomeric excess by reduction of the half acid ester of ethyl fumarate from (R) and (S) BINAP ruthenium (II) diacetate complex, respectively, is reported. (2R,3R) and (2S,3S)-Dideuteriosuccinic acid has also been prepared from (R)-BINAP ruthenium (II) dicarboxylate complex directly in similar optical purity by reversing the sequence of

Cheok N. Tam; Timothy A. Keiderling

1995-01-01

173

Asymmetric Synthesis of 1,3-anti-Diol Containing Subunits using Phosphorus-Based Tethers: Application in the Total Synthesis of Dolabelide C  

E-print Network

-854. (b) Gauthier, D. R.; Zandi, K. S.; Shea, K. J.; "Disposable Tethers in Synthetic Organic Chemistry," Tetrahedron 1998, 54, 2289-2338. (2) (a) White, J. D.; Carter R. G. In Science of Synthesis: Houben-Weyl Methods of Molecular Transformations...; Fleming, I., Ed.; Georg Thieme Verlag: New York, 2001; Vol. 4, pp 371-412 and references cited therein. (b) Evans, P. A. ; Cui, J.; Gharpure, S. J.; Polosukhin, A.; Zhang, H. R. "Enantioselective Total Synthesis of the Potent Antitumor Agent (–)-Mucocin...

Thomas, Christopher Daniel

2010-12-16

174

1: Mass asymmetric fission barriers for {sup 98}Mo; 2: Synthesis and characterization of actinide-specific chelating agents  

SciTech Connect

Excitation functions have been measured for complex fragment emission from the compound nucleus {sup 98}Mo, produced by the reaction of {sup 86}Kr with {sup 12}C. Mass asymmetric fission barriers have been obtained by fitting the excitation functions with a transition state formalism. The extracted barriers are {approximately} 5.7 MeV higher, on average, than the calculations of the Rotating Finite Range Model (RFRM). These data clearly show an isospin dependence of the conditional barriers when compared with the extracted barriers from {sup 90}Mo and {sup 94}Mo. Eleven different liquid/liquid extractants were synthesized based upon the chelating moieties 3,2-HOPO and 3,4-HOPO; additionally, two liquid/liquid extractants based upon the 1,2-HOPO chelating moiety were obtained for extraction studies. The Pu(IV) extractions, quite surprisingly, yielded results that were very different from the Fe(III) extractions. The first trend remained the same: the 1,2-HOPOs were the best extractants, followed closely by the 3,2-HOPOs, followed by the 3,4-HOPOs; but in these Pu(IV) extractions the 3,4-HOPOs performed much better than in the Fe(III) extractions. 129 refs.

Veeck, A.C. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; [Lawrence Livermore National Lab., CA (United States). Glenn T. Seaborg Inst. for Transactinium Science; [Lawrence Berkeley National Lab., CA (United States). Nuclear Science Div.

1996-08-01

175

Synthesis and characterization of mesoporous spinel NiCo2O4 using surfactant-assembled dispersion for asymmetric supercapacitors  

NASA Astrophysics Data System (ADS)

A simple and scalable process has been developed for synthesizing spinel NiCo2O4 nanocrystals through a thermal decomposition method. The introduction of hexadecyltrimethylammonium bromide (CTAB, (C16H33)N(CH3)3Br) into precursor solutions significantly enhances the homogeneity and porosity of spinel NiCo2O4. The porosity and high specific surface area of NiCo2O4 preserves the brilliant pseudo-capacitive performances due to providing smooth paths for electrolyte penetration and ion diffusion into inner active sites. Morphologies and microstructures of the active materials are examined by transmission electron microscopic (TEM) and X-ray diffraction (XRD) analyses. Thermogravimetric analysis (TGA) is used to evaluate the thermal properties of precursor solutions. The electrochemical performances of NiCo2O4 are systematically characterized by cyclic voltammetry and charge-discharge tests. Asymmetric supercapacitors are assembled with these brilliant binary oxides as the positive electrode and activated carbon as the negative electrode. The highly porous NiCo2O4 exhibits superior capacitive performances, i.e., high specific capacitance (764 F g-1 at 2 mV s-1) and long cycle life.

Hsu, Chun-Tsung; Hu, Chi-Chang

2013-11-01

176

Concise asymmetric synthesis of a (1R,2S)-1-amino- 2-vinylcyclopropanecarboxylic acid-derived sulfonamide and ethyl ester.  

PubMed

The development and demonstration of short, robust and chromatography-free sequences for the preparation of a (1R,2S)-1-amino-2-vinylcyclopropane-carboxylic acid-derived sulfonamide and ethyl ester in ?99% ee are described. Both compounds are common building blocks in multiple preparations of potent HCV NS3 protease inhibitors. The robustness of the asymmetric cyclopropanation of (E)-N-benzylideneglycine ethyl ester under phase transfer catalysis conditions is significantly improved based on a detailed mechanistic investigation that included an analysis of the catalyst decomposition pathway, a postulated model for the stereo-selectivity that was guided by calculations and rigorous quality control of the starting materials and reagents. Wet milling has been demonstrated to dramatically accelerate this phase transfer reaction. A bench stable benzylidene-protected primary 1-amino-2-vinylcyclopropane amide intermediate was isolated and its reliable enantiomeric enrichment was achieved by a controlled crystallization process. A chemical resolution procedure was identified using di-p-toluoyl-(D)-tartaric acid to access (1R,2S)-1-amino-2-vinyl-cyclopropanecarboxylic ester in high ee. PMID:24175327

Lou, Sha; Cuniere, Nicolas; Su, Bao-Ning; Hobson, Lindsay A

2013-10-21

177

Asymmetric synthesis of L-2-amino[3-11C]butyric acid, L-[3-11C]norvaline and L-[3-11C]valine.  

PubMed

The short-lived radionuclide 11C (t1/2 = 20.4 min) has been used in the asymmetric synthesis of L-2-amino[3-11C]butyric acid, L-[3-11C]-norvaline and L-[3-11C]valine. The syntheses were performed by alkylation of [(+)-2-hydroxypinanyl-3-idene]-glycine tert-butyl ester under anhydrous conditions in tetrahydrofuran/1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone with lithiated 2,2,6,6-tetramethylpiperidine as base, using the appropriate 11C-alkyl iodides prepared in a one-pot reactor from [11C]carbon dioxide. Following removal of the protecting groups, the -[3-11C]amino acids were obtained in 80-82% enantiomeric excess and in 9-25% radiochemical yields, decay corrected and calculated on the basis of the amount of [11C]carbon dioxide at the start of the syntheses within 50-55 min. PMID:3434082

Antoni, G; Långström, B

1987-08-01

178

Asymmetric synthesis of ?-amino acids via homologation of Ni(II) complexes of glycine Schiff bases; Part 1: alkyl halide alkylations.  

PubMed

Alkylations of chiral or achiral Ni(II) complexes of glycine Schiff bases constitute a landmark in the development of practical methodology for asymmetric synthesis of ?-amino acids. Straightforward, easy preparation as well as high reactivity of these Ni(II) complexes render them ready available and inexpensive glycine equivalents for preparing a wide variety of ?-amino acids, in particular on a relatively large scale. In the case of Ni(II) complexes containing benzylproline moiety as a chiral auxiliary, their alkylation proceeds with high thermodynamically controlled diastereoselectivity. Similar type of Ni(II) complexes derived from alanine can also be used for alkylation providing convenient access to quaternary, ?,?-disubstituted ?-amino acids. Achiral type of Ni(II) complexes can be prepared from picolinic acid or via recently developed modular approach using simple secondary or primary amines. These Ni(II) complexes can be easily mono/bis-alkylated under homogeneous or phase-transfer catalysis conditions. Origin of diastereo-/enantioselectivity in the alkylations reactions, aspects of practicality, generality and limitations of this methodology is critically discussed. PMID:23832533

Sorochinsky, Alexander E; Aceña, José Luis; Moriwaki, Hiroki; Sato, Tatsunori; Soloshonok, Vadim A

2013-10-01

179

Synthesis of ribo-hexopyranoside- and altrose-based azacrown ethers and their application in an asymmetric Michael addition.  

PubMed

The synthesis of four new ribo-hexopyranoside-based chiral lariat ethers of monoaza-15-crown-5 type and two altropyranoside-based crown ethers were elaborated. Our syntheses utilized the regioselective ring opening of the oxiran moiety of the 2,3-anhydro sugars by nucleophilic reagents to afford the key intermediates. The reaction of methyl-2,3-anhydro-4,6-O-benzylidene-?-D-mannopyranoside with ethanolamine is especially of interest to afford a 3-substituted altropyranoside. One of the ribo-hexopyranoside-based lariat ethers with a 4-methoxyphenyl substituent induced an enantioselectivity of 80% when used as catalyst in the Michael addition of diethyl acetamidomalonate to trans-?-nitrostyrene under phase transfer catalytic conditions. PMID:23220061

Rapi, Zsolt; Bakó, Péter; Keglevich, György; Szöll?sy, Áron; Drahos, László; Heged?s, László

2013-01-10

180

Asymmetric catalysis on the nanoscale: the organocatalytic approach to helicenes.  

PubMed

The first asymmetric organocatalytic synthesis of helicenes is reported. A novel SPINOL-derived phosphoric acid, bearing extended ?-substituents, catalyzes the asymmetric synthesis of helicenes through an enantioselective Fischer indole reaction. A variety of azahelicenes and diazahelicenes could be obtained with good to excellent yields and enantioselectivities. PMID:24737692

Kötzner, Lisa; Webber, Matthew J; Martínez, Alberto; De Fusco, Claudia; List, Benjamin

2014-05-12

181

Enhanced asymmetric induction for the copolymerization of CO2 and cyclohexene oxide with unsymmetric enantiopure salenCo(III) complexes: synthesis of crystalline CO2-based polycarbonate.  

PubMed

Enantiopure metal-complex catalyzed asymmetric alternating copolymerization of CO(2) and meso-epoxides is a powerful synthetic strategy for preparing optically active polycarbonates with main-chain chirality. The previous studies regarding chiral zinc catalysts provided amorphous polycarbonates with moderate enantioselectivity, and thus, developing highly stereoregular catalysts for this enantioselective polymerization is highly desirable. Herein, we report the synthesis of highly isotactic poly(cyclohexene carbonate)s from meso-cyclohexene oxide using dissymmetrical enantiopure salenCo(III) complexes in conjunction with bis(triphenylphosphine)iminium chloride (PPNCl) as catalyst. The presence of a chiral induction agent such as (S)-propylene oxide or (S)-2-methyltetrahydrofuran significantly improved the enantioselectivity regarding (S,S)-salenCo(III) catalyst systems. Up to 98:2 of RR:SS was observed in the resultant polycarbonates obtained from the catalyst system based on (S,S)-salenCo(III) complex 4d bearing an adamantyl group on the phenolate ortho position, in the presence of (S)-2-methyltetrahydrofuran. Primary ONIOM (DFT:UFF) calculations, which were performed to investigate the effect of the competitive coordination of (S)-induction agent versus cyclohexene oxide to Co(III) center on enantioselectivity, suggest that the (S)-C-O bond in cyclohexene oxide is more favorable for cleavage, due to the interaction between oxygen atom of (S)-induction agent and (S)-C-H of the coordinated cyclohexene oxide. The highly isotactic poly(cyclohexene carbonate) is a typical semicrystalline polymer, possessing a melting point of 216 °C and a decomposition temperature of 310 °C. PMID:22385473

Wu, Guang-Peng; Ren, Wei-Min; Luo, Yi; Li, Bo; Zhang, Wen-Zhen; Lu, Xiao-Bing

2012-03-28

182

Synthesis and determination of the absolute configuration of Armatol A through a polyepoxide cyclization cascade : revision of the proposed structures of Armatols A-F  

E-print Network

Cyclization Cascades Leading to the Tricyclic Fragment of Armatol A The synthesis of the fused 6,7,7-tricycle of armatol A was investigated. Fragments containing both a ketone and an aldehyde for subsequent fragment coupling ...

Underwood, Brian Saxton

2011-01-01

183

Revised assignment of absolute configuration of the cis- and trans-N6-deoxyadenosine adducts at C14 of (+/-)-11beta,12alpha-dihydroxy-13alpha,14alpha-epoxy-11,12,13,14-tetrahydrodibenzo[a,l]pyrene by stereoselective synthesis.  

PubMed

We have reassigned relative and absolute configurations by unambiguous stereoselective syntheses of the cis- (13s and 13R) and trans-N6-deoxyadenosine (dAdo) adduct diastereomers (14S and 14R) derived from (+/-)-11beta,12alpha-dihydroxy-13alpha,14alpha-epoxy-11,12,13,14-tetrahydrodibenzo[a,l]pyrene (DB[a,l]P DE-2), previously reported by Li et al. [(1999) Chem. Res. Toxicol. 12, 758-767]. Two stereoselective methods, asymmetric aminohydroxylation of the (+/-)-trans-11,12-dihydrodiol (3) with 3',5'-di-O-(tert -butyldimethylsilyl)-2'-deoxyadenosine (4) and the highly stereoselective cis addition of 4 to (+/-)-DB[a,l]P DE-2 in hexafluoropropan-2-ol (HFP), were employed. Both afforded a 1:1 mixture of the cis-N6-dAdo adduct diastereomers, which were separated as triacetates (5S and 5R) in comparable yields (approximately 80%). The corresponding trans adduct diastereomers (10S and 10R) were obtained by coupling the aminotriol derived from trans opening of (+/-)-DB[a,l]P DE-2 with 6-fluoro-(2'-deoxy-3,5-di-tert-butyldimethylsilyloxy-beta-D-erythro-pentafuranosyl)purine (9) and subsequent acetylation in approximately 70% yield. The cis-5S and -5R and trans-10S and -10R were separately treated with 7% HF-pyridine followed by ammonolysis in NH3-saturated MeOH to give the dAdo adducts with all hydroxyl groups free (13S, 13R, 14S, and 14R). Comparison of the 1H NMR and CD spectra of these presently synthesized dAdo adducts with spectra of the previously reported compounds revealed that the interpretation of the 1H NMR and CD spectra and assignment of the relative stereochemistry (cis/trans) and absolute configuration made by Li et al. were at variance with our results. The above highly stereoselective syntheses of (+/-)-DB[a,l]P DE-2 adducted dAdo derivatives enabled efficient preparation of each of the four possible stereoisomeric 5'-dimethoxytrityl-3'-phosphoramidites for use in oligonucleotide synthesis. PMID:19053320

Yagi, Haruhiko; Frank, Heinrich; Seidel, Albrecht; Jerina, Donald M

2008-12-01

184

Applications of organocatalytic asymmetric synthesis to drug prototypes--dual action and selective inhibitors of n-nitric oxide synthase with activity against the 5-HT1D/1B subreceptors.  

PubMed

The scope of MacMillan's organocatalytic asymmetric conjugate addition reaction of indoles and electron-rich aromatics to ?,?-unsaturated aldehydes has been extended to the use of 3-amino crotonaldehydes as substrates. The aromatics used include indoles as well as an aniline and a furan. The scope and effect of the groups on nitrogen (R, R') has also been studied. The method has been applied to the concise synthesis of an advanced precursor to S-(+)-1, a drug prototype for the treatment of migraine headaches. PMID:21271688

Hanessian, Stephen; Stoffman, Eli; Mi, Xueling; Renton, Paul

2011-03-01

185

Absolute nuclear material assay  

DOEpatents

A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

Prasad, Manoj K. (Pleasanton, CA); Snyderman, Neal J. (Berkeley, CA); Rowland, Mark S. (Alamo, CA)

2012-05-15

186

Measuring Absolute Oxygen Pressure  

NASA Technical Reports Server (NTRS)

Sensor determines absolute pressure of oxygen without reference pressure source. Absolute oxygen pressure transducer with control circuit enables measurement without reference pressure. Transducer, two part device, combines solid electrolyte membranes sensor with diffusional orifice. Device adapted for direct control of oxygen pressure in combustion mixtures.

Richter, R.

1985-01-01

187

Asymmetric Earth  

NASA Astrophysics Data System (ADS)

The net rotation, or so-called W-ward drift of the lithosphere, implies a decoupling of the plates relative to the underlying asthenosphere, and a relative "E-ward" mantle flow. This polarized flow can account for a number of asymmetries. When comparing the W-directed versus the E- to NE-directed subduction zones, as a general observation, they have the subduction hinge diverging versus converging relative to the upper plate; low versus high topography and structural elevation respectively; deep versus shallow trenches and foreland basins; shallow versus deep decollement; low versus high basement involvement; high versus low heat flow and gravity anomaly; shallow versus deep asthenosphere; etc. The western limbs of rift zones show S-waves faster in the lithosphere and slower in the asthenosphere with respect to the eastern limb. The asymmetry can be recognized when moving along the "tectonic equator", which describes the fastest flow of plates relative to the mantle, and it undulates relative to the geographic equator. In our reconstructions, the best fit for the tectonic equator has a pole of rotation at latitude -56.4° and longitude 136.7°, with an angular velocity of 1.2036°/Ma. Shear-wave splitting alignments tend to parallel the tectonic flow, apart along the subduction zones where they become orthogonal, as a flow encountering an obstacle. The tectonic equator lies close to the revolution plane of the Moon about the Earth. All these data and interpretations point for an asymmetric Earth, whose nature appears to be related to the rotation and its tidal despinning, combined with the thermal cooling of the planet. However, this model has been questioned on the basis of the high viscosity so far inferred in the asthenosphere. Preliminary modelling shows that the tidal oscillation can generate gravitational wave propagation in the lithosphere, and the wave velocity can increase with the decrease of the asthenospheric viscosity.

Doglioni, Carlo; Carminati, Eugenio; Crespi, Mattia; Cuffaro, Marco; Ismail-Zadeh, Alik; Levshin, Anatoli; Panza, Giuliano F.; Riguzzi, Federica

2010-05-01

188

Simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition for controlled synthesis of asymmetric axial ZnO nanospindles  

NASA Astrophysics Data System (ADS)

Single-component nanostructures with axial asymmetry were successfully synthesized in organic solvents via a new type of growth model. Asymmetric axial ZnO nanospindles with a hexagonal cross-section were produced by a growth model consisting of simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition. The growth process of ZnO nanospindles is explained by comprehensively characterizing and monitoring the products at different reaction time intervals. Hexagonal discs containing dislocations were first generated at a reaction time of 2.5 min. When the reaction time continued to increase, the nanodiscs grew along the <0002> direction. Half-nanospindles were formed at mid-reaction stage when the growth rate of [0001] was greater than [000-1]. Finally, the asymmetric nanospindles were obtained at 40 min. Further, the length of the asymmetric axial ZnO spindles can be precisely tuned by the adjustment of reaction temperature. Thus, the growth model presented here can synthesize a new category of one-dimensional asymmetric nanostructures.Single-component nanostructures with axial asymmetry were successfully synthesized in organic solvents via a new type of growth model. Asymmetric axial ZnO nanospindles with a hexagonal cross-section were produced by a growth model consisting of simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition. The growth process of ZnO nanospindles is explained by comprehensively characterizing and monitoring the products at different reaction time intervals. Hexagonal discs containing dislocations were first generated at a reaction time of 2.5 min. When the reaction time continued to increase, the nanodiscs grew along the <0002> direction. Half-nanospindles were formed at mid-reaction stage when the growth rate of [0001] was greater than [000-1]. Finally, the asymmetric nanospindles were obtained at 40 min. Further, the length of the asymmetric axial ZnO spindles can be precisely tuned by the adjustment of reaction temperature. Thus, the growth model presented here can synthesize a new category of one-dimensional asymmetric nanostructures. Electronic supplementary information (ESI) available: XRD pattern, TEM, and SEM images of ZnO nanospindles. See DOI: 10.1039/c4nr01888e

Yang, Hong-Jie; He, Sheng-Yan; Tuan, Hsing-Yu

2014-07-01

189

New androst-4-en-17-spiro-1,3,2-oxathiaphospholanes. Synthesis, assignment of absolute configuration and in vitro cytotoxic and antimicrobial activities.  

PubMed

The reactions of 17?-hydroxyprogesterone with Lawesson's reagent (LR) in toluene, CH(2)Cl(2) and/or CCl(4) gave, depending on the duration of the reaction, two diastereoisomeric androst-4-en-17-spiro-1,3,2-oxathiaphospholane-2-sulfide pairs 2a,b and 3a,b in approximately 7:3 ratio, differing in configuration at the phosphorus atom. A parallel analysis of heteronuclear 2D (1)H-(13)C spectra (HSQC and HMBC) and homonuclear 2D spectra (NOESY) enabled complete (1)H and (13)C assignments of each isomer. Also, analysis of NOESY correlations provided evidence for the preferred conformation. X-ray analysis of 3a confirmed the structure and absolute configuration on phosphorus. A pathway for the formation of 1,3,2-oxathiaphospholane ring was proposed. Cytotoxic activity in vitro was tested against three tumor cell lines (human cervix carcinoma HeLa cells and two human breast carcinoma MDA-MB-361 and MDA-MB-453 cells). Compound 3a and mixture 3a,b showed a moderate activity against HeLa and MDA-MB-453 cell lines while against MDA-MB-361 cell line all tested compounds exerted very weak cytotoxic effect. Antimicrobial activity against Gram-positive, Gram-negative bacteria and fungal cells, toxicity to brine shrimp Artemia salina, were evaluated. All tested compounds showed strong antifungal activity. PMID:22342468

Krsti?, Natalija M; Bjelakovi?, Mira S; Pavlovi?, Vladimir D; Robeyns, Koen; Jurani?, Zorica D; Mati?, Ivana; Novakovi?, Irena; Sladi?, Dušan M

2012-04-01

190

Phosphine-catalyzed asymmetric [4+1] annulation of activated ?,?-unsaturated ketones with Morita-Baylis-Hillman carbonates: enantioselective synthesis of spirooxindoles containing two adjacent quaternary stereocenters.  

PubMed

The asymmetric [4+1] annulation of activated ?,?-unsaturated ketones with MBH carbonates catalyzed by bifunctional thiourea-phosphine catalysts derived from an axially chiral binaphthyl scaffold has been developed, giving spirooxindoles with two adjacent quaternary stereocenters in good yields with high enantioselectivities and moderate diastereoselectivities under mild conditions. PMID:24976341

Hu, Fang-Le; Wei, Yin; Shi, Min

2014-08-18

191

Asymmetric organocatalytic desymmetrization of 4,4-disubstituted cyclohexadienones at high pressure: a new powerful strategy for the synthesis of highly congested chiral cyclohexenones.  

PubMed

A highly diastereoselective and enantioselective method for the asymmetric desymmetrization of 4,4-disubstituted cyclohexadienones using the Michael addition reaction of malonates under catalysis with the primary amine-thiourea conjugate catalyst and PPY at high pressure was developed. PMID:24887588

Miyamae, Naomu; Watanabe, Naruhisa; Moritaka, Maya; Nakano, Keiji; Ichikawa, Yoshiyasu; Kotsuki, Hiyoshizo

2014-08-21

192

Catalytic asymmetric synthesis of [2,3]-fused indoline heterocycles through inverse-electron-demand aza-Diels-Alder reaction of indoles with azoalkenes.  

PubMed

An unprecedented catalytic asymmetric inverse-electron-demand aza-Diels-Alder reaction of indoles with in?situ formed azoalkenes is reported. A diverse set of [2,3]-fused indoline heterocycles were achieved in generally good yields (up to 97?%) with high regioselectivity and diastereoselectivity (>20:1 d.r.), and with excellent enantioselectivity (up to 99?% ee). PMID:24668693

Tong, Min-Chao; Chen, Xuan; Li, Jun; Huang, Rong; Tao, Haiyan; Wang, Chun-Jiang

2014-04-25

193

Asymmetric Ashes  

NASA Astrophysics Data System (ADS)

Astronomers are reporting remarkable new findings that shed light on a decade-long debate about one kind of supernovae, the explosions that mark a star's final demise: does the star die in a slow burn or with a fast bang? From their observations, the scientists find that the matter ejected by the explosion shows significant peripheral asymmetry but a nearly spherical interior, most likely implying that the explosion finally propagates at supersonic speed. These results are reported today in Science Express, the online version of the research journal Science, by Lifan Wang, Texas A&M University (USA), and colleagues Dietrich Baade and Ferdinando Patat from ESO. "Our results strongly suggest a two-stage explosion process in this type of supernova," comments Wang. "This is an important finding with potential implications in cosmology." ESO PR Photo 44/06 ESO PR Photo 44/06 Clumpy Explosion (Artist's Impression) Using observations of 17 supernovae made over more than 10 years with ESO's Very Large Telescope and the McDonald Observatory's Otto Struve Telescope, astronomers inferred the shape and structure of the debris cloud thrown out from Type Ia supernovae. Such supernovae are thought to be the result of the explosion of a small and dense star - a white dwarf - inside a binary system. As its companion continuously spills matter onto the white dwarf, the white dwarf reaches a critical mass, leading to a fatal instability and the supernova. But what sparks the initial explosion, and how the blast travels through the star have long been thorny issues. The supernovae Wang and his colleagues observed occurred in distant galaxies, and because of the vast cosmic distances could not be studied in detail using conventional imaging techniques, including interferometry. Instead, the team determined the shape of the exploding cocoons by recording the polarisation of the light from the dying stars. Polarimetry relies on the fact that light is composed of electromagnetic waves that oscillate in certain directions. Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflected off a pond. When light scatters through the expanding debris of a supernova, it retains information about the orientation of the scattering layers. If the supernova is spherically symmetric, all orientations will be present equally and will average out, so there will be no net polarisation. If, however, the gas shell is not round, a slight net polarisation will be imprinted on the light. This is what broad-band polarimetry can accomplish. If additional spectral information is available ('spectro-polarimetry'), one can determine whether the asymmetry is in the continuum light or in some spectral lines. In the case of the Type Ia supernovae, the astronomers found that the continuum polarisation is very small so that the overall shape of the explosion is crudely spherical. But the much larger polarization in strongly blue-shifted spectral lines evidences the presence, in the outer regions, of fast moving clumps with peculiar chemical composition. "Our study reveals that explosions of Type Ia supernovae are really three-dimensional phenomena," says Dietrich Baade. "The outer regions of the blast cloud is asymmetric, with different materials found in 'clumps', while the inner regions are smooth." "This study was possible because polarimetry could unfold its full strength thanks to the light-collecting power of the Very Large Telescope and the very precise calibration of the FORS instrument," he adds. The research team first spotted this asymmetry in 2003, as part of the same observational campaign (ESO PR 23/03 and ESO PR Photo 26/05). The new, more extensive results show that the degree of polarisation and, hence, the asphericity, correlates with the intrinsic brightness of the explosion. The brighter the supernova, the smoother, or less clumpy, it is. "This has some impact on the us

2006-11-01

194

Absolute Biodiesel Potential Country Name  

E-print Network

Absolute Biodiesel Potential Country Name Production Cost ($/liter) Potential Biodiesel Volume,234 0% 0% #12;Absolute Biodiesel Potential Country Name Production Cost ($/liter) Potential Biodiesel;Absolute Biodiesel Potential Country Name Production Cost ($/liter) Potential Biodiesel Volume (liters

Wisconsin at Madison, University of

195

Gold-catalyzed asymmetric allylic substitution of free alcohols: an enantioselective approach to chiral chromans with quaternary stereocenters for the synthesis of vitamin?e and analogues.  

PubMed

The enantioselective synthesis of ?- and ?-tocopherol (the most biologically active members of vitamin?E family) and analogues has been accomplished employing a new enantioselective gold catalyzed intramolecular allylic alkylation reaction followed by an olefin cross-metathesis as key steps. The methodology proved to be applicable to different olefins highlighting its potential for the synthesis of diverse libraries. PMID:25201099

Uria, Uxue; Vila, Carlos; Lin, Ming-Yuan; Rueping, Magnus

2014-10-20

196

Application of Catalytic Dynamic Resolution of N-Boc-2-lithiopiperidine to the Asymmetric Synthesis of 2-Aryl and 2-Vinyl Piperidines  

PubMed Central

The highly enantioselective synthesis of 2-aryl- and 2-vinyl-piperidines has been accomplished through a catalytic dynamic resolution (CDR) of N-Boc-2-lithiopiperidine. The method has been applied to the synthesis of both enantiomers of the tobacco alkaloid anabasine. PMID:21174392

Beng, Timothy K.; Gawley, Robert E.

2011-01-01

197

Dynamic kinetic resolution in the stereoselective synthesis of 4,5-diaryl cyclic sulfamidates by using chiral rhodium-catalyzed asymmetric transfer hydrogenation.  

PubMed

The dynamic kinetic resolution of 4,5-diaryl cyclic sulfamidate imines was achieved via asymmetric transfer hydrogenation using a HCO(2)H/Et(3)N mixture as the hydrogen source and chiral Rh catalysts (R,R)- or (S,S)-RhCl(TsDPEN)Cp* affording the corresponding cyclic sulfamidates in good yields with up to >20 : 1 dr and up to >99% ee. PMID:21331420

Han, Juae; Kang, Soyeong; Lee, Hyeon-Kyu

2011-04-01

198

Efficient synthesis of optically pure alcohols by asymmetric hydrogen-transfer biocatalysis: application of engineered enzymes in a 2-propanol–water medium  

Microsoft Academic Search

We describe an efficient method for producing both enantiomers of chiral alcohols by asymmetric hydrogen-transfer bioreduction\\u000a of ketones in a 2-propanol (IPA)–water medium with E. coli biocatalysts expressing phenylacetaldehyde reductase (PAR: wild-type and mutant enzymes) from Rhodococcus sp. ST-10 and alcohol dehydrogenase from Leifsonia sp. S749 (LSADH). We also describe the detailed properties of mutant PARs, Sar268, and HAR1, which

Nobuya Itoh; Kentaro Isotani; Masatoshi Nakamura; Kousuke Inoue; Yasuhiro Isogai; Yoshihide Makino

199

Terminating Catalytic Asymmetric Heck Cyclizations by Stereoselective Intramolecular Capture of ?3-Allylpalladium Intermediates: Total Synthesis of (-)-Spirotryprostatin B and Three Stereoisomers  

PubMed Central

A catalytic intramolecular Heck reaction, followed by capture of the resulting ?3-allylpalladium intermediate by a tethered diketopiperazine, is the central step in a concise synthetic route to (?)-spirotryprostatin B and three stereoisomers. This study demonstrates that an acyclic, chiral ?3-allylpalladium fragment generated in a catalytic asymmetric Heck cyclization can be trapped by even a weakly nucleophilic diketopiperazine more rapidly than it undergoes diastereomeric equilibration. PMID:20725641

Overman, Larry E.; Rosen, Mark D.

2010-01-01

200

Computing Solar Absolute Fluxes  

E-print Network

Computed color indices and spectral shapes for individual stars are routinely compared with observations for essentially all spectral types, but absolute fluxes are rarely tested. We can confront observed irradiances with the predictions from model atmospheres for a few stars with accurate angular diameter measurements, notably the Sun. Previous calculations have been hampered by inconsistencies and the use of outdated atomic data and abundances. I provide here a progress report on our current efforts to compute absolute fluxes for solar model photospheres. Uncertainties in the solar composition constitute a significant source of error in computing solar radiative fluxes.

Carlos Allende Prieto

2007-09-14

201

Relative and Absolute Directions  

NSDL National Science Digital Library

The purpose of this resource is to learn about latitude and longitude while developing math skills. Students begin by asking the simple question: 'Where Am I?' Then they learn about the magnetic Earth and the use of compasses and angles. Students also learn about the difference between relative and absolute locations. Throughout this activity, students practice using a variety of math skills.

The GLOBE Program, University Corporation for Atmospheric Research (UCAR)

2003-08-01

202

ABSOLUTE WAARHEID EN TRANSCENDENTIE  

Microsoft Academic Search

The debate about the relation between science and truth is manifestly epistemological, but latently and fundamentally metaphysical. Popper's theory of verisimilitude provides us with a striking example. According to Popper, science aims at bringing us nearer to 'absolute, objective truth'; the growth of scientific knowledge is seen as a never ending realisation of that ultimate aim. This thesis of verisimilitude

A. BURMS

1982-01-01

203

Absolute ultraviolet stellar fluxes  

NASA Technical Reports Server (NTRS)

A study, made to calibrate the ultraviolet spectra of stars to within an absolute accuracy of 10%, is summarized. Data were taken by a 13 inch UVR telescope onboard several rocket flights. Calibrated and existing ground based data are in reasonable agreement. Calibrated results are presented in graphical form.

Evans, D. C.

1972-01-01

204

Improved synthesis and application of planar-chiral nucleophilic catalysts in asymmetric reactions and copper-catalyzed enantioselective N-H insertion reactions  

E-print Network

The development of an improved synthesis of nucleophilic planar-chiral catalysts is described in Chapter 1. This route is amenable to scale-up and preparative chiral HPLC is unnecessary to resolve the racemic catalysts. ...

Lee, Elaine C

2007-01-01

205

Bifunctional Asymmetric Catalysis  

PubMed Central

CONSPECTUS In the field of catalytic, asymmetric synthesis, there is a growing emphasis on multifunctional systems, in which multiple parts of a catalyst or multiple catalysts work together to promote a specific reaction. These efforts, in part, are result-driven, and they are also part of a movement toward emulating the efficiency and selectivity of nature’s catalysts, enzymes. In this Account, we illustrate the importance of bifunctional catalytic methods, focusing on the cooperative action of Lewis acidic and Lewis basic catalysts by the simultaneous activation of both electrophilic and nucleophilic reaction partners. For our part, we have contributed three separate bifunctional methods that combine achiral Lewis acids with chiral cinchona alkaloid nucleophiles, for example, benzoylquinine (BQ), to catalyze highly enantioselective cycloaddition reactions between ketene enolates and various electrophiles. Each method requires a distinct Lewis acid to coordinate and activate the electrophile, which in turn increases the reaction rates and yields, without any detectable influence on the outstanding enantioselectivities inherent to these reactions. To place our results in perspective, many important contributions to this emerging field are highlighted and our own reports are chronicled. PMID:18402470

PAULL, DANIEL H.; ABRAHAM, CIBY J.; SCERBA, MICHAEL T.; ALDEN-DANFORTH, ETHAN; LECTKA, THOMAS

2008-01-01

206

Absolute beam brightness detector  

SciTech Connect

In generally accepted emittance measurement, main attention is concentrated on emittance areas {epsilon}{sub x}, {epsilon}{sub y} occupied by desired part of ion beam in transverse phase space and shape of these areas. The absolute beam phase density (brightness) as usually is not measured directly and the average beam brightness B is calculated from a beam intensity I and the transverse emittances. In the ion source and low energy beam transport (LEBT) optimization, it is important to preserve the beam brightness because some aberration of ion optic and beam instabilities can decrease the brightness of the central part of ion beam significantly. For these brightness measurements, it is convenient to use an absolute beam brightness detector with the brightness determination from one short considered in this article.

Dudnikov, Vadim [Muons, Inc., Batavia, Illinois 60510 (United States)

2012-02-15

207

Controlled synthesis, asymmetrical transport behavior and luminescence properties of lanthanide doped ZnO mushroom-like 3D hierarchical structures.  

PubMed

Lanthanide doped ZnO mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared ZnO:Ln(3+) (Ln = Tb, Eu) samples have a hexagonal phase structure and possess a mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 ?m, and the diameters of pileus and stipe are about 0.8 ?m and 0.4 ?m, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by several radial ZnO:Ln(3+) nanorods, whereas the stipe is composed of over layered ZnO:Ln(3+) nanosheets. Moreover, asymmetrical I-V characteristic curves of ZnO:Ln(3+) mushrooms indicate that the texture composition of the 3D hierarchical morphology might lead to the asymmetrical transport behavior of electrical conductivity. Lanthanide doped ZnO samples can exhibit red or green emission under the excitation of UV light. PMID:25293373

Yue, Dan; Lu, Wei; Jin, Lin; Li, Chunyang; Luo, Wen; Wang, Mengnan; Wang, Zhenling; Hao, Jianhua

2014-10-24

208

Supernova Absolute Magnitude Distributions  

Microsoft Academic Search

We have extended the 1990 study of supernova absolute-magnitude distributions by Miller and Branch. Supernova apparent magnitudes are taken from an updated version of the Asiago Supernova Catalog. Where possible, distances are based on Cepheid variables in the SN parent galaxy or a galaxy in the same group; otherwise re-scaled distances from the Nearby Galaxies Catalog, or Hubble-Law distances (for

D. Richardson; D. Branch; D. Casebeer; J. Deaton; E. Baron

1996-01-01

209

The Direct Catalytic Asymmetric Aldol Reaction  

PubMed Central

Asymmetric aldol reactions are a powerful method for the construction of carbon-carbon bonds in an enantioselective fashion. Historically this reaction has been performed in a stoichiometric fashion to control the various aspects of chemo-, diastereo-, regio- and enantioselectivity, however, a more atom economical approach would unite high selectivity with the use of only a catalytic amount of a chiral promoter. This critical review documents the development of direct catalytic asymmetric aldol methodologies, including organocatalytic and metal-based strategies. New methods have improved the reactivity, selectivity and substrate scope of the direct aldol reaction and enabled the synthesis of complex molecular targets PMID:20419212

Brindle, Cheyenne S.

2013-01-01

210

Asymmetric Hydrogenation of Itaconic Acid and Enol Acetate Derivatives with  

E-print Network

. A variety of chiral 2-substituted succinic acids and chiral acetates have been obtained in excellent ee efficient synthesis of chiral R-amino acids via transition metal-catalyzed asymmetric hydrogenation has become one of most efficient methods for the synthesis of chiral R-amino acids, chiral -amino

Zhang, Xumu

211

Memory of chirality (MOC) concept in imino-aldol reaction: enantioselective synthesis of ?,?-diamino esters and aziridines.  

PubMed

A simple strategy for the synthesis of chiral ?,?-diamino- and ?-amino,?-hydroxy ester derivatives in high yields with moderate to high ee has been developed via asymmetric imino-aldol and aldol reactions, respectively, starting from protected aminoesters employing memory of chirality concept for chiral induction. This strategy has been extended for the enantioselective synthesis of aziridines (ee up to 92%). The absolute configuration of the imino-aldol adducts has been determined. The stereochemical outcome of the products has been explained by a suitable mechanism and supported by computational studies. PMID:23320819

Ghorai, Manas K; Ghosh, Koena; Yadav, A K; Nanaji, Y; Halder, Sandipan; Sayyad, Masthanvali

2013-03-15

212

Studies in asymmetric ?-lactone synthesis: extensions of the chiral nucleophile catalyzed aldol-lactonization (NCAL) reaction and new transformations of chlorinated ?-lactones  

E-print Network

-lactones were accomplished to further extend the utility of these products. In addition, 4-(trichloromethyl)-2-oxetanone was transformed into a variety of amino acid precursors. The first synthesis of the natural amino acid, 2-amino-5-methyl-6-hydroxyhex-4...

Tennyson, Reginald L.

2012-06-07

213

Fluorine effects in organocatalysis - asymmetric Brønsted acid assisted Lewis base catalysis for the synthesis of trifluoromethylated heterocycles exploiting the negative hyperconjugation of the CF3-group.  

PubMed

An efficient Brønsted acid assisted Lewis base catalysis protocol for the synthesis of enantiomerically pure trifluoromethylated dihydropyridazines starting from readily available hydrazones and ?,?-unsaturated aldehydes has been developed. The reaction exhibits high tolerance towards many functional groups and is applicable to various aliphatic, aromatic and hetero-aromatic ?,?-unsaturated aldehydes, and provides the products in good yields and with excellent enantioselectivities. PMID:24911934

Volla, Chandra M R; Das, Arindam; Atodiresei, Iuliana; Rueping, Magnus

2014-07-25

214

Sequential organocatalytic Stetter and Michael-Aldol condensation reaction: asymmetric synthesis of fully substituted cyclopentenes via a [1 + 2 + 2] annulation strategy.  

PubMed

A stereoselective synthesis of fully substituted cyclopentenes has been achieved by a sequential organocatalyzed Stetter and Michael-aldol condensation of aromatic aldehydes, nitroalkenes, and ?,?-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with excellent diastereoselectivities and enantioselectivities (up to >99% ee). PMID:20936853

Hong, Bor-Cherng; Dange, Nitin S; Hsu, Che-Sheng; Liao, Ju-Hsiou

2010-11-01

215

Asymmetric Ultrasonic Pulse Radiation Using Electromagnetic-Induction Transducer and PZT(Pb(Zr-Ti)O3) Transducer with Wave Synthesis Method  

NASA Astrophysics Data System (ADS)

In medical applications, especially in urology, we use a fragmentation calculus technique with shock waves. This technique is very profitable because of no abdominal surgery for a human being. Large negative sound amplitude pulses, however, can cause problems such as internal hemorrhage or pain in the human body. The final goal of this study is to develop a means to project an intense positive unipolar pulse without negative sound pressure. We improved a composite transducer consisting of an electromagnetic-induction-type (EMI) transducer and PZT (Pb(Zr-Ti)O3) transducers. An EMI transducer consisting of a metal coil and vibration membrane can project intense sound pulses into water. In order to suppress its negative sound pressure, we project a compensation pulse with PZT transducers using an inverse filtering method. An asymmetric pulse whose P+ to P- amplitude ratio was very high was projected in water.

Endoh, Nobuyuki; Yamamoto, Koji

1993-05-01

216

Palladium-N-Heterocyclic Carbene (NHC)-Catalyzed Asymmetric Synthesis of Indolines through Regiodivergent C(sp(3) )?H Activation: Scope and DFT Study.  

PubMed

Two bulky, chiral, monodentate N-heterocyclic carbene ligands were applied to palladium-catalyzed asymmetric C?H arylation to incorporate C(sp(3) )?H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans-2,3-substituted indolines. Although this CAr ?Calkyl coupling requires high temperatures (140-160?°C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The C?H activation at a tertiary center was realized only in the case of a cyclopropyl group. No C?H activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine C?H activation is used to rationalize experimentally observed regio- and enantioselectivities. PMID:25262613

Katayev, Dmitry; Larionov, Evgeny; Nakanishi, Masafumi; Besnard, Céline; Kündig, E Peter

2014-11-10

217

Zn(II), Ni(II), Cu(II) and Pb(II) complexes of tridentate asymmetrical Schiff base ligands: Synthesis, characterization, properties and biological activity  

NASA Astrophysics Data System (ADS)

New asymmetrical tridentate Schiff base ligands were synthesized using 1,2-phenylenediamine, 4-methyl-1,2-phenylenediamine, 2-hydroxy-1-napthaldehyde, 9-anthracenecarboxaldehyde. Schiff base ligands and their metal complexes were synthesised and characterized by using FT-IR, 1H NMR, 13C NMR, UV-Vis, XRD, ESR, elemental analysis and fluorescence studies. The antimicrobial activity of the ligands and their metal complexes were studied against Staphylococcus aureus ATCC 29213, S. aureus ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853. The determination of the antibacterial activity was done using the broth microdilution methods. In general, it has been determined that the studied compounds have MIC values similar to Gram-positive and Gram-negative bacteria. It has been found that Ni, Pb, Zn derivatives of HL1A and ZnL2A has lower MIC values than ampicillin for P. aeruginosa ATCC 27853 strain.

?ahin, Mustafa; Koçak, Nuriye; Erdenay, Damla; Arslan, U?ur

2013-02-01

218

Design and synthesis of a new type of ferrocene-based planar chiral DMAP analogues. A new catalyst system for asymmetric nucleophilic catalysis.  

PubMed

A new first-generation catalyst system for nucleophilic catalysis has been developed. It is based on a planar chiral ferrocene skeleton with either the potent nucleophile 4-(dimethylamino)pyridine (DMAP) or the related 4-nitropyridine N-oxide attached in either the 2- or the 3-position. The syntheses are short, efficient, and enantioselective and X-ray crystal structures of both DMAP-derived catalysts are presented. The DMAP-based catalysts were tested in asymmetric reactions and the 3-derivative 14 showed good activity and a moderate level of enantioselectivity. The sense of induction (selectivity) was studied using molecular modeling and the results pointed at new directions for future generations of catalysts based on this design. PMID:16209575

Seitzberg, Jimmi Gerner; Dissing, Carsten; Søtofte, Inger; Norrby, Per-Ola; Johannsen, Mogens

2005-10-14

219

Absolute configuration of odorine  

PubMed Central

The title compound, known as odorine or roxburghiline {systematic name: (S)-N-[(R)-1-cinnamoylpyrrolidin-2-yl]-2-methyl­butanamide}, C18H24N2O2, is a nitro­genous compound isolated from the leaves of Aglaia odorata. The absolute configuration was determined by refinement of the Flack parameter with data collected using Cu K? radiation showing positions 2 and 2? to be S and R, respectively. The pyrrolidine ring adopts an envelope conformation. In the crystal, mol­ecules are linked into chains along [010] by inter­molecular N—H?O hydrogen bonds. PMID:21588760

Fun, Hoong-Kun; Chantrapromma, Suchada; Yodsaoue, Orapun; Karalai, Chatchanok

2010-01-01

220

Absolute configuration of micromelin  

PubMed Central

The title compound {systematic name: 7-meth­oxy-6-[(1R,2R,5R)-5-methyl-4-oxo-3,6-dioxabicyclo­[3.1.0]hexan-2-yl]-2H-chromen-2-one}, C15H12O6, is a coumarin, which was isolated from the roots of Micromelum glanduliferum. There are two mol­ecules in the asymmetric unit with slight differences in bond angles. In both mol­ecules, the furan ring adopts a flattened envelope conformation. In the crystal, mol­ecules are linked by weak C—H?O inter­actions into chains along the a axis. Aromatic ?–? stacking inter­actions with centroid–centroid distances in the range 3.6995?(11)–3.8069?(11)?Å and C?O short contacts [3.030?(2)–3.171?(3)?Å] also occur. PMID:21837101

Fun, Hoong-Kun; Siridechakorn, Ittipon; Laphookhieo, Surat; Chantrapromma, Suchada

2011-01-01

221

Absolute-structure reports.  

PubMed

All the 139 noncentrosymmetric crystal structures published in Acta Crystallographica Section C between January 2011 and November 2012 inclusive have been used as the basis of a detailed study of the reporting of absolute structure. These structure determinations cover a wide range of space groups, chemical composition and resonant-scattering contribution. Defining A and D as the average and difference of the intensities of Friedel opposites, their level of fit has been examined using 2AD and selected-D plots. It was found, regardless of the expected resonant-scattering contribution to Friedel opposites, that the Friedel-difference intensities are often dominated by random uncertainty and systematic error. An analysis of data collection strategy is provided. It is found that crystal-structure determinations resulting in a Flack parameter close to 0.5 may not necessarily be from crystals twinned by inversion. Friedifstat is shown to be a robust estimator of the resonant-scattering contribution to Friedel opposites, very little affected by the particular space group of a structure nor by the occupation of special positions. There is considerable confusion in the text of papers presenting achiral noncentrosymmetric crystal structures. Recommendations are provided for the optimal way of treating noncentrosymmetric crystal structures for which the experimenter has no interest in determining the absolute structure. PMID:23907862

Flack, Howard D

2013-08-01

222

The information as Absolute  

E-print Network

This article presents and grounds (i.e. presents proof of the existence, the truth, the self-consistence and the completeness of)the informational conception ("the Information as Absolute" conception)in physics and philosophy. the conception defines the information as an ultimately common, real and fundamental concept/phenomenon - "Absolute", which exists as anabsolutely infinite set ("Information" Set) of elements (members) and informational (e.g., logical) linksbetween the elements; where any element itself is some informational structure also. Correspondingly, for example, Matter as the substence, radiation, etc., is some development or realization of informational patterns, constituting a specific - and practically infinitesimal comparing to the Set - subset of the "Information" Set. The conception allows for the resolution, or at least for a consideration on a higher level of comprehension, of the basic ontological and epistemological problems in philosophy and natural sciences; in physics it allows to suggest reasonable model, which makes more clear basic phisical notions,such as space, time, matter, etc.

Sergey V. Shevchenko; Vladimir V. Tokarevsky

2010-04-20

223

ABSOLUTE POLARIMETRY AT RHIC.  

SciTech Connect

Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy Of {Delta}P{sub beam}/P{sub beam} < 5%. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features proton-proton elastic scattering in the Coulomb nuclear interference (CNI) region. Precise measurements of the analyzing power A{sub N} of this process has allowed us to achieve {Delta}P{sub beam}/P{sub beam} = 4.2% in 2005 for the first long spin-physics run. In this report, we describe the entire set up and performance of the system. The procedure of beam polarization measurement and analysis results from 2004-2005 are described. Physics topics of AN in the CNI region (four-momentum transfer squared 0.001 < -t < 0.032 (GeV/c){sup 2}) are also discussed. We point out the current issues and expected optimum accuracy in 2006 and the future.

OKADA; BRAVAR, A.; BUNCE, G.; GILL, R.; HUANG, H.; MAKDISI, Y.; NASS, A.; WOOD, J.; ZELENSKI, Z.; ET AL.

2007-09-10

224

January 2004 Asymmetric Cell  

E-print Network

January 2004 Asymmetric Cell Division By Pamela J. Hines and Suzanne Kadereit Asymmetric cell cell" is one of the fates. In the case of the stem cell, the cell's first step must be to divide and to produce one daughter like itself, able to continue as a stem cell, and one daughter unlike itself, able

Extavour, Cassandra

225

Asymmetric cell division  

Microsoft Academic Search

Asymmetric cell division is a conserved mechanism for partitioning information during mitosis. Over the past several years, significant progress has been made in our understanding of how cells establish polarity during asymmetric cell division and how determinants, in the form of localized proteins and mRNAs, are segregated. In particular, genetic studies in Drosophila and Caenorhabditis elegans have linked cell polarity,

Fabrice Roegiers; Yuh Nung Jan

2004-01-01

226

Synthesis, crystal structures, and properties of two novel cadmium(II)-organic frameworks based on asymmetric dicarboxylate and N-donor ligands  

NASA Astrophysics Data System (ADS)

Two novel cadmium(II)-organic frameworks with asymmetric dicarboxylate and N-donor ligands, namely [Cd(cpa)(phen)]n (1) and {[Cd2(cpa)2(bpy)1.5]·0.5H2O}n (2) (H2cpa = 3-(4-benzoic)propionic acid, phen = 1,10-phenanthroline, bpy = 4,4";-bipyridine) have been hydrothermally synthesized and characterized by elemental analyses, FT-IR spectra, single-crystal X-ray diffraction analyses, TGA, powder XRD and fluorescent measurements. 1 displays a double zigzag chain structure containing 8-number and 22-number circles. 2 Shows a 6-connected 3D polymer network based on tetranuclear cadmium cluster units. The most striking feature of 2 is that a pair of identical 3D networks are interlocked with each other to the form a 2-fold interpenetrated 3D ?-Po structural topology. The diverse structures of two complexes indicate that the skeleton of N-donor ligands plays a great role in the assembly of such different frameworks. In addition, the thermal stabilities, XRD and photoluminescence properties of 1-2 were also studied.

Chen, Xiaoli; Gao, Loujun; Zhang, Xiaoge; Han, Xuhua; Wang, Yao; Sun, Rong

2014-08-01

227

Synthesis, photophysical and charge-transporting properties of a novel asymmetric indolo [3,2-b]carbazole derivative containing benzothiazole and diphenylamino moieties.  

PubMed

A novel asymmetric donor-?-donor-?-acceptor compound, 2-benzothiazolyl-8-diphenylamino-5,11-dihexylindolo[3,2-b]carbazole (BDDAICZ), has been successfully synthesized by introducing a benzothiazole moiety (as an electron-acceptor) and a diphenylamino moiety (as an electron-donor) to 2-position and 8-position of indolo[3,2-b]carbazole moiety (as a skeleton and an electron-donor), and characterized by elemental analysis, (1)H NMR, (13)C NMR and MS. The thermal, electrochemical properties of BDDAICZ were characterized by thermogravimetric analysis combined with electrochemistry. The absorption and emission spectra of BDDAICZ was experimentally determined in several solvents and computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculated absorption and emission wavelengths are coincident with the measured data. The ionization potential (IP), the electron affinity (EA) and reorganization energy of BDDAICZ were also investigated using density functional theory (DFT). Charge-transporting properties of BDDAICZ were characterized by OLEDs devices fabricated by using it as charge-transport layers. The results show that BDDAICZ has excellent thermal stability, electrochemical stability and hole-transporting properties, indicating its potential application as a hole-transporting material in OLEDs devices. PMID:24973792

Shi, Heping; Yuan, Jiandong; Dong, Xiuqing; Cheng, Fangqin

2014-12-10

228

Facile synthesis of hierarchical Co3O4@MnO2 core-shell arrays on Ni foam for asymmetric supercapacitors  

NASA Astrophysics Data System (ADS)

Hierarchical Co3O4@MnO2 core-shell arrays on Ni foam have been fabricated by a facile hydrothermal approach and further investigated as the electrode for high-performance supercapacitors. Owing to the high conductivity of the well-defined mesoporous Co3O4 nanowire arrays in combination with the large surface area provided by the ultrathin MnO2 nanosheets, the unique designed Co3O4@MnO2 core-shell arrays on Ni foam have exhibited a high specific capacitance (560 F g-1 at a current density of 0.2 A g-1), good rate capability, and excellent cycling stability (95% capacitance retention after 5000 cycles). An asymmetric supercapacitor with Co3O4@MnO2 core-shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide activated graphene (MEGO) as the negative electrode yielded an energy density of 17.7 Wh kg-1 and a maximum power density of 158 kW kg-1. The rational design of the unique core-shell array architectures demonstrated in this work provides a new and facile approach to fabricate high-performance electrode for supercapacitors.

Huang, Ming; Zhang, Yuxin; Li, Fei; Zhang, Lili; Wen, Zhiyu; Liu, Qing

2014-04-01

229

Synthesis, photophysical and charge-transporting properties of a novel asymmetric indolo [3,2-b]carbazole derivative containing benzothiazole and diphenylamino moieties  

NASA Astrophysics Data System (ADS)

A novel asymmetric donor-?-donor-?-acceptor compound, 2-benzothiazolyl-8-diphenylamino-5,11-dihexylindolo[3,2-b]carbazole (BDDAICZ), has been successfully synthesized by introducing a benzothiazole moiety (as an electron-acceptor) and a diphenylamino moiety (as an electron-donor) to 2-position and 8-position of indolo[3,2-b]carbazole moiety (as a skeleton and an electron-donor), and characterized by elemental analysis, 1H NMR, 13C NMR and MS. The thermal, electrochemical properties of BDDAICZ were characterized by thermogravimetric analysis combined with electrochemistry. The absorption and emission spectra of BDDAICZ was experimentally determined in several solvents and computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculated absorption and emission wavelengths are coincident with the measured data. The ionization potential (IP), the electron affinity (EA) and reorganization energy of BDDAICZ were also investigated using density functional theory (DFT). Charge-transporting properties of BDDAICZ were characterized by OLEDs devices fabricated by using it as charge-transport layers. The results show that BDDAICZ has excellent thermal stability, electrochemical stability and hole-transporting properties, indicating its potential application as a hole-transporting material in OLEDs devices.

Shi, Heping; Yuan, Jiandong; Dong, Xiuqing; Cheng, Fangqin

2014-12-01

230

Absolute radiometric code (ARC)  

NASA Astrophysics Data System (ADS)

The Absolute Radiometric Code (ARC) is a collection of Matlab functions tied together under a Matlab Graphical User Interface (GUI). ARC was developed as part of the Satellite Imaging Experiment conducted by the Air Force Research Laboratory at Kirtland, AFB, in order to get fast estimates of the Optical Cross Sections of various satellites. ARC uses multiple star measures to calculate the atmospheric and optical transmission of the system. The transmissions are then used to compute the optical cross section of an object. Generally, the optical transmission of a sensor system can be characterized quite well, so it serves as a sanity check on all ARC results. The atmospheric transmission changes considerably from night to night and even from hour to hour on the same night. ARC uses a collection of calibration stars at various elevation angles to determine the atmospheric transmission through the viewing times. The star calibration is generally taken several times during the experiment period.

Riker, James F.; Roark, Jon; Stogsdill, Stephen E.; DeShetler, W. Bruce; Brunson, Richard L.

1999-08-01

231

Absolute Equilibrium Entropy  

NASA Technical Reports Server (NTRS)

The entropy associated with absolute equilibrium ensemble theories of ideal, homogeneous, fluid and magneto-fluid turbulence is discussed and the three-dimensional fluid case is examined in detail. A sigma-function is defined, whose minimum value with respect to global parameters is the entropy. A comparison is made between the use of global functions sigma and phase functions H (associated with the development of various H-theorems of ideal turbulence). It is shown that the two approaches are complimentary though conceptually different: H-theorems show that an isolated system tends to equilibrium while sigma-functions allow the demonstration that entropy never decreases when two previously isolated systems are combined. This provides a more complete picture of entropy in the statistical mechanics of ideal fluids.

Shebalin, John V.

1997-01-01

232

Optical tweezers absolute calibration  

E-print Network

Optical tweezers are highly versatile laser traps for neutral microparticles, with fundamental applications in physics and in single molecule cell biology. Force measurements are performed by converting the stiffness response to displacement of trapped transparent microspheres, employed as force transducers. Usually, calibration is indirect, by comparison with fluid drag forces. This can lead to discrepancies by sizable factors. Progress achieved in a program aiming at absolute calibration, conducted over the past fifteen years, is briefly reviewed. Here we overcome its last major obstacle, a theoretical overestimation of the peak stiffness, within the most employed range for applications, and we perform experimental validation. The discrepancy is traced to the effect of primary aberrations of the optical system, which are now included in the theory. All required experimental parameters are readily accessible. Astigmatism, the dominant effect, is measured by analyzing reflected images of the focused laser spo...

Dutra, R S; Neto, P A Maia; Nussenzveig, H M

2014-01-01

233

Rh2 (S-1,2-NTTL)4 : A Novel Rh2 (S-PTTL)4 Analog With Lower Ligand Symmetry for Asymmetric Synthesis of Chiral Cyclopropylphosphonates.  

PubMed

A new series of dirhodium(II) tetracarboxylate was derived from N-1,2-naphthaloyl-(S)-amino acid ligands. In terms of enantioselectivity, Rh2 (S-1,2-NTTL)4 () derived from N-1,2-naphthaloyl-(S)-tert-leucine, was the best-performing catalyst among the new series in the enantioselective synthesis of cyclopropylphosphonate derivatives (up to >99% enantiomeric excess). A predictive model was proposed to justify the observed high enantiomeric induction exhibited by Rh2 (S-1,2-NTTL)4 with donor-acceptor phosphonate carbenoids. Chirality 26:764-774, 2014. © 2014 Wiley Periodicals, Inc. PMID:25042525

Adly, Frady G; Maddalena, Johncarlo; Ghanem, Ashraf

2014-11-01

234

Catalytic asymmetric [3+2] cycloaddition of azomethine ylides. Development of a versatile stepwise, three-component reaction for diversity-oriented synthesis.  

PubMed

We report a new catalyst system that should enhance the use of enantioselective 1,3-dipolar cycloadditions of azomethine ylides with electronic-deficient olefins in the divergent pathways of diversity-oriented synthesis (DOS). The underlying reaction is of considerable interest in DOS because its stereospecificity enables stereochemical diversification of up to four tetrahedral centers on pyrrolidine rings. This new catalyst system extends the scope and selectivity of the azomethine ylide cycloaddition and is compatible with reagents used in a one-bead/one-stock solution technology platform for DOS. PMID:12926931

Chen, Chuo; Li, Xiaodong; Schreiber, Stuart L

2003-08-27

235

Divergent total synthesis of the Lycopodium alkaloids huperzine A, huperzine B, and huperzine U.  

PubMed

Huperzine A, huperzine B, and huperzine U are congeners isolated from the Chinese herb Huperzia serrata (= Lycopodium serratum ) in minuscule amounts. The most efficient total synthesis of huperzine A, the first asymmetric total syntheses of huperzine B, and the first total synthesis of huperzine U have been achieved efficiently in overall yields of 17%, 10%, and 9%, respectively, each spanning 10-13 steps from (R)-pulegone. The featured steps include palladium-catalyzed Buchwald-Hartwig coupling and Heck cyclization reactions and an Ir-catalyzed olefin isomerization reaction. This work has established the absolute configurations of huperzine B and huperzine U and revealed that natural huperzine A, huperzine B, and huperzine U possess the same set of absolute stereochemistries, thus providing support for the potential role of huperzine B and huperzine U in the biosynthesis of huperzine A. PMID:24299147

Ding, Rui; Fu, Jian-Guo; Xu, Guang-Qiang; Sun, Bing-Feng; Lin, Guo-Qiang

2014-01-01

236

Absolute neutrino mass measurements  

SciTech Connect

The neutrino mass plays an important role in particle physics, astrophysics and cosmology. In recent years the detection of neutrino flavour oscillations proved that neutrinos carry mass. However, oscillation experiments are only sensitive to the mass-squared difference of the mass eigenvalues. In contrast to cosmological observations and neutrino-less double beta decay (0v2{beta}) searches, single {beta}-decay experiments provide a direct, model-independent way to determine the absolute neutrino mass by measuring the energy spectrum of decay electrons at the endpoint region with high accuracy.Currently the best kinematic upper limits on the neutrino mass of 2.2eV have been set by two experiments in Mainz and Troitsk, using tritium as beta emitter. The next generation tritium {beta}-experiment KATRIN is currently under construction in Karlsruhe/Germany by an international collaboration. KATRIN intends to improve the sensitivity by one order of magnitude to 0.2eV. The investigation of a second isotope ({sup 137}Rh) is being pursued by the international MARE collaboration using micro-calorimeters to measure the beta spectrum. The technology needed to reach 0.2eV sensitivity is still in the R and D phase. This paper reviews the present status of neutrino-mass measurements with cosmological data, 0v2{beta} decay and single {beta}-decay.

Wolf, Joachim [Karlsruhe Institute of Technology (KIT), IEKP, Postfach 3640, 76021 Karlsruhe (Germany)

2011-10-06

237

Absolute Zero: Science Educator's Guide  

NSDL National Science Digital Library

This guide provides recommendations for curricular modules on low temperature physics. Designed for teachers and informal educators of middle school students. this guide complements the Absolute Zero Community Education Outreach Guide. Suggestions on leading discussions, increasing student participation, and the use of inquiry are included. This material is related to a two-part public broadcasting special, Absolute Zero, produced by Meridian Productions and Windfall Films. Absolute Zero is underwritten by the National Science Foundation and the Alfred P. Sloan Foundation and is based largely on Tom Shachtmanâs acclaimed book, Absolute Zero and the Conquest of Cold.

2008-09-18

238

Asymmetric Boltzmann machines.  

PubMed

We study asymmetric stochastic networks from two points of view: combinatorial optimization and learning algorithms based on relative entropy minimization. We show that there are non trivial classes of asymmetric networks which admit a Lyapunov function L under deterministic parallel evolution and prove that the stochastic augmentation of such networks amounts to a stochastic search for global minima of L. The problem of minimizing L for a totally antisymmetric parallel network is shown to be associated to an NP-complete decision problem. The study of entropic learning for general asymmetric networks, performed in the non equilibrium, time dependent formalism, leads to a Hebbian rule based on time averages over the past history of the system. The general algorithm for asymmetric networks is tested on a feed-forward architecture. PMID:1768713

Apolloni, B; Bertoni, A; Campadelli, P; de Falco, D

1991-01-01

239

Total synthesis of Class II and Class III Galbulimima Alkaloids  

E-print Network

I. Total Synthesis of All Class III Galbulimima Alkaloids We describe the total synthesis of (+)- and (-)-galbulimima alkaloid 13, (-)-himgaline anad (-)-himbadine. The absolute stereochemistry of natural (-)-galbulimima ...

Tjandra, Meiliana

2010-01-01

240

Prediction of Multi-Target Networks of Neuroprotective Compounds with Entropy Indices and Synthesis, Assay, and Theoretical Study of New Asymmetric 1,2-Rasagiline Carbamates  

PubMed Central

In a multi-target complex network, the links (Lij) represent the interactions between the drug (di) and the target (tj), characterized by different experimental measures (Ki, Km, IC50, etc.) obtained in pharmacological assays under diverse boundary conditions (cj). In this work, we handle Shannon entropy measures for developing a model encompassing a multi-target network of neuroprotective/neurotoxic compounds reported in the CHEMBL database. The model predicts correctly >8300 experimental outcomes with Accuracy, Specificity, and Sensitivity above 80%–90% on training and external validation series. Indeed, the model can calculate different outcomes for >30 experimental measures in >400 different experimental protocolsin relation with >150 molecular and cellular targets on 11 different organisms (including human). Hereafter, we reported by the first time the synthesis, characterization, and experimental assays of a new series of chiral 1,2-rasagiline carbamate derivatives not reported in previous works. The experimental tests included: (1) assay in absence of neurotoxic agents; (2) in the presence of glutamate; and (3) in the presence of H2O2. Lastly, we used the new Assessing Links with Moving Averages (ALMA)-entropy model to predict possible outcomes for the new compounds in a high number of pharmacological tests not carried out experimentally. PMID:25255029

Romero Duran, Francisco J.; Alonso, Nerea; Caamano, Olga; Garcia-Mera, Xerardo; Yanez, Matilde; Prado-Prado, Francisco J.; Gonzalez-Diaz, Humberto

2014-01-01

241

Supernova absolute-magnitude distributions  

Microsoft Academic Search

The Asiago Supernova Catalogue and the Nearby Galaxies Catalog are used to study the absolute-magnitude distributions of supernovae. SNe Ia that appear to be subluminous are in highly inclined disk galaxies, which implies that the apparent dispersion in SN Ia absolute magnitudes is dominated by interstellar extinction in the parent galaxies, and, thus, that SNe Ia are good intrinsic standard

Douglas L. Miller; David Branch

1990-01-01

242

Absolute and Relative Grading Standards.  

ERIC Educational Resources Information Center

K. K. Waltman and D. A. Frisbie (1994) observed that teachers and parents often interpret grades given to students in both absolute and relative senses. They conclude that this sort of interpretation is illogical and may indicate misunderstandings in several areas. Absolute and relative methods of assigning letter grades are approached from…

Johanson, George A.

243

Absolute stability of a class of trilateral haptic systems.  

PubMed

Trilateral haptic systems can be modeled as three-port networks. We present a criterion for absolute stability of a general class of three-port networks. Traditionally, existing (i.e., Llewellyn's) criteria have facilitated the stability analysis of bilateral haptic systems modeled as two-port networks. If the same criteria were to be used for stability analysis of a three-port network, its third port termination would need to be assumed known for it to reduce to a two-port network. This is restrictive because, for absolute stability, all three terminations of the three-port network must be allowed to be arbitrary (while passive). Extending Llewellyn's criterion, we present closed-form necessary and sufficient conditions for absolute stability of a general class of three-port networks. We first find a symmetrization condition under which a general asymmetric impedance (or admittance) matrix Z3 × 3 has a symmetric equivalent Zeq from a network stability perspective. Then, via the equivalence of passivity and absolute stability for reciprocal networks, an absolute stability condition for the original nonreciprocal network is derived. To demonstrate the convenience and utility of using this criterion for both analysis and design, it is applied to the problem of designing stabilizing controllers for dual-user haptic teleoperation systems, with simulations and experiments validating the criterion. PMID:25248167

Li, Jian; Tavakoli, Mahdi; Huang, Qi

2014-01-01

244

Improved synthesis of structural analogues of (?)-epicatechin gallate for modulation of staphylococcal ?-lactam resistance?  

PubMed Central

The high-yielding synthesis of enantiomerically pure epicatechin gallate analogues where the A and/or B-ring hydroxylation is reduced or altered has been achieved by optimising routes to the catechin stereochemistry. The B-ring analogues were synthesised by using an electrophilic ring closure onto an enantiomerically enriched epoxide as a key step. The A and B-ring hydroxyl-deleted analogues were synthesised through a Mitsunobu cyclisation. For the B-ring analogues, the anti- (catechin) stereochemistry was converted to the syn- (epicatechin) stereochemistry by a known oxidation/reduction protocol. Absolute stereochemistry was derived from either a Sharpless epoxidation or asymmetric dihydroxylation. PMID:24876661

Anderson, James C.; Grounds, Helen; Reeves, Suzanna; Taylor, Peter W.

2014-01-01

245

Palladium-catalyzed enantioselective allylic alkylation of thiocarboxylate ions: asymmetric synthesis of allylic thioesters and memory effect/dynamic kinetic resolution of allylic esters.  

PubMed

The palladium-catalyzed allylic alkylation of KSAc and KSBz with racemic cyclic and acyclic allylic esters by using N,N'-(1R,2R)-1,2-cyclohexandiylbis[2-(diphenylphosphino)-benzamide] as ligand frequently gave the corresponding allylic thioesters with high ee values and yields. The reaction of the cyclic allylic carbonates with KSAc in the presence of H(2)O was accompanied by a partial palladium-catalyzed enantioselective "hydrolysis" of the substrates with formation of the corresponding enantioenriched allylic alcohols. The degree of the "hydrolysis" was strongly dependent on the solvent and the thiocarboxylate ion. Highly selective kinetic resolutions (KRs) were observed in the palladium-catalyzed reaction of the racemic cyclohexenyl and cycloheptenyl acetates with KSAc. While the KR of the cyclohexenyl acetate is characterized by a selectivity factor S = 72 +/- 19, that of the cycloheptenyl acetate afforded (R)-cycloheptenyl acetate of >or=99% ee in 48% yield and (S)-cycloheptenyl thioacetate of 98% ee in 50% yield. The palladium-catalyzed reaction of the racemic cyclopentenyl acetate with KSAc showed a strong "memory effect" (ME), that is, both enantiomers reacted with different enantioselectivities. The ME was probed by studying the palladium-catalyzed reactions of both the matched acetate of >or=99% ee and the mismatched acetate of >or=99% ee with KSAc. The acetates not only reacted with different enantioselectivities and rates but also suffered an unexpected and concomitant palladium-catalyzed racemization in the presence of the chiral ligand. This led in the case of the mismatched acetate to a temporary dynamic kinetic resolution (DKR) that featured a racemization of the mismatched acetate by the chiral catalyst. Studies of the palladium-catalyzed reaction of the racemic cyclopentenyl acetate, carbonate, and naphthoate with KSAc in the presence of the chiral ligand also showed the ME to be strongly dependent on the nucleofuge. This also allowed the synthesis of (S)-cyclopentenyl thioacetate of 92% ee in high yield from the racemic cyclopentenyl naphthoate. PMID:15176829

Lüssem, Bernhard J; Gais, Hans-Joachim

2004-06-11

246

Organocatalytic asymmetric fluorination of ?-chloroaldehydes involving kinetic resolution  

PubMed Central

Summary In a previous study it was shown that the enantioselective ?-fluorination of racemic ?-chloroaldehydes with a chiral organocatalyst yielded the corresponding ?-chloro-?-fluoroaldehydes with high enantioselectivity. It was also revealed that kinetic resolution of the starting aldehydes was involved in this asymmetric fluorination. This paper describes the determination of the absolute stereochemistry of a resulting ?-chloro-?-fluoroaldehyde. Some information about the substrate scope and a possible reaction mechanism are also described which shed more light on the nature of this asymmetric fluorination reaction. PMID:24605153

Okimi, Takuya; Abe, Yoshiyuki; Narayama, Akira; Nakamura, Nami; Iwasa, Seiji

2014-01-01

247

Asymmetric passive dynamic walker.  

PubMed

The objective of this research is to better understand the dynamics of gait asymmetry in humans with central nervous system damage, such as stroke, by using a model of a passive dynamic walker (PDW). By changing the mass, mass location, knee location, and leg length of one leg while leaving the parameters of the other leg unchanged, we show that stable asymmetric walking patterns exist for PDW models. The asymmetric PDW model shows several stable walking patterns that have a single, double, and quadruple repeat pattern where the step lengths between the two legs differ by over 15%. This model will allow an analysis of the passive dynamics of walking separate from the cognitive control in asymmetric human walking to test different gait rehabilitation hypotheses. PMID:22275663

Honeycutt, Craig; Sushko, John; Reed, Kyle B

2011-01-01

248

Asymmetrical field emitter  

DOEpatents

Providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure.

Fleming, James G. (Albuquerque, NM); Smith, Bradley K. (Albuquerque, NM)

1995-01-01

249

Asymmetrical field emitter  

DOEpatents

A method is disclosed for providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure. 17 figs.

Fleming, J.G.; Smith, B.K.

1995-10-10

250

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation  

E-print Network

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation Inauguraldissertation. Parts of this work have been previously published: ,,Proline-Based P,O Ligands/Iridium Complexes in Iridium-Catalyzed Asymmetric Hydrogenation: New Catalysts, Substrates and Applications in Total Synthesis

Amrhein, Valentin

251

Ordered Mesoporous Silica as Supports in the Heterogeneous Asymmetric Catalysis  

Microsoft Academic Search

Enantioselective synthesis of organic compounds has been studied by homogeneous catalysts for several years. However, these\\u000a catalysts have yet to make a significant impact on industrial scales for fine chemical synthesis. A primary reason is the\\u000a designing of a homogeneous asymmetric catalyst, which requires relatively bulky ligands and catalyst recovery and recycling\\u000a often causes problems. One of the convincing ways

Suman Sahoo; Ankur Bordoloi; S. B. Halligudi

252

Asymmetric universal entangling machine  

E-print Network

We give a definition of asymmetric universal entangling machine which entangles a system in an unknown state to a specially prepared ancilla. The machine produces a fixed state-independent amount of entanglement in exchange to a fixed degradation of the system state fidelity. We describe explicitly such a machine for any quantum system having $d$ levels and prove its optimality. We show that a $d^2$-dimensional ancilla is sufficient for reaching optimality. The introduced machine is a generalization to a number of widely investigated universal quantum devices such as the symmetric and asymmetric quantum cloners, the symmetric quantum entangler, the quantum information distributor and the universal-NOT gate.

Dmitri Horoshko; Mikhail Kolobov; Sergei Kilin

2004-12-23

253

Cryogenic, Absolute, High Pressure Sensor  

NASA Technical Reports Server (NTRS)

A pressure sensor is provided for cryogenic, high pressure applications. A highly doped silicon piezoresistive pressure sensor is bonded to a silicon substrate in an absolute pressure sensing configuration. The absolute pressure sensor is bonded to an aluminum nitride substrate. Aluminum nitride has appropriate coefficient of thermal expansion for use with highly doped silicon at cryogenic temperatures. A group of sensors, either two sensors on two substrates or four sensors on a single substrate are packaged in a pressure vessel.

Chapman, John J. (Inventor); Shams. Qamar A. (Inventor); Powers, William T. (Inventor)

2001-01-01

254

An asymmetric watermarking method  

Microsoft Academic Search

This paper presents an asymmetric watermarking method as an alternative to classical direct sequence spread spectrum and watermarking Costa (1983) schemes techniques. This new method provides a higher security level against malicious attacks threatening watermarking techniques used for a copy protection purpose. This application, which is quite different from the classical copyright enforcement issue, is extremely challenging as no public

T. Furon; P. Duhamel

2003-01-01

255

Asymmetric cell division  

Microsoft Academic Search

With the recent identification of intrinsic cell-fate determinants for asymmetric cell division in several systems, biologists have begun to gain insight into the cellular mechanisms by which these determinants are preferentially segregated into one of the two daughter cells during mitosis so that the daughter cells acquire different fates.

Yuh Nung Jan; Lily Yeh Jan

1998-01-01

256

Asymmetric Organocatalysis Andrew Satterfield  

E-print Network

Asymmetric Organocatalysis Andrew Satterfield 2 - 24 - 06 #12;Outline ·Phase Transfer Catalysis Transfer Catalysis Muroaka K. Angew. Chem. Int. Ed. 2005, 44, 1549. Andrews, B; Lygo B. Acc. Chem. Res Catalysis ·Proline and derivatives ·Imidazolidinones #12;Organocatalysis N HO N N H N O Ph N H OTMS CF3F3C

Johnson, Jeff S.

257

Catalytic asymmetric Diels-Alder reactions involving aryl vinyl ketones.  

PubMed

A catalytic asymmetric Diels-Alder reaction of an aryl vinyl ketone with 1,3-dienylcarbamate has been developed. Cyclohexenes bearing vicinal amino and aroyl groups in a cis-configuration were prepared in excellent ee (>99%) and endo (single diastereomer) selectivity. The absolute configuration of one DA product was unambiguously confirmed using XRD analysis. The transition state structure was proposed on the basis of DFT calculations. PMID:25271484

Kong, Liman; Han, Xiaoyu; Jiao, Peng

2014-10-21

258

Supernova absolute-magnitude distributions  

SciTech Connect

The Asiago Supernova Catalogue and the Nearby Galaxies Catalog are used to study the absolute-magnitude distributions of supernovae. SNe Ia that appear to be subluminous are in highly inclined disk galaxies, which implies that the apparent dispersion in SN Ia absolute magnitudes is dominated by interstellar extinction in the parent galaxies, and, thus, that SNe Ia are good intrinsic standard candles (sigma below 0.4 mag). An upper limit to the difference between SNe Ib and SNe Ia in the B band is 1.87 mag, but the bolometric difference is smaller. Due to a large intrinsic range in peak absolute magnitude (about 6 mag), the observed sample of SNe II is severely influenced by selection effects; intrinsically faint SNe II (M/B/greater than about -17 for H0 = 75 km/s per Mpc) are much more common than intrinsically bright ones. 45 refs.

Miller, D.L.; Branch, D. (Oklahoma Univ., Norman (USA))

1990-08-01

259

Multipartite Asymmetric Quantum Cloning  

E-print Network

We investigate the optimal distribution of quantum information over multipartite systems in asymmetric settings. We introduce cloning transformations that take $N$ identical replicas of a pure state in any dimension as input, and yield a collection of clones with non-identical fidelities. As an example, if the clones are partitioned into a set of $M_A$ clones with fidelity $F^A$ and another set of $M_B$ clones with fidelity $F^B$, the trade-off between these fidelities is analyzed, and particular cases of optimal $N \\to M_A+M_B$ cloning machines are exhibited. We also present an optimal $1 \\to 1+1+1$ cloning machine, which is the first known example of a tripartite fully asymmetric cloner. Finally, it is shown how these cloning machines can be optically realized.

S. Iblisdir; A. Acin; N. Gisin; J. Fiurasek; R. Filip; N. J. Cerf

2004-11-24

260

Asymmetric mineral mining plough  

SciTech Connect

A mineral mining plough for use in asymmetric ploughing, and movable to and fro alongside a conveyor, has a plough body provided with cutter means at its two ends. A first cutter means is arranged to win material when the plough is on the uphill run (That is to say when the plough moves in the opposite direction as the conveyor). A second cutter means is arranged to win material when the plough is on the downhill run. The second cutter means is mounted on the plough body for vertical movement relative to the plough body. This enables the second cutter means to be swung out of its working position (On the downhill run) to lie in a rest position (On the uphill run) in which it is in the path of travel of the first cutter means. This vertical movement of the second cutter means results in a plough of shorter length than known asymmetric ploughs.

Hauschopp, A.; Huss, H.; Rassmann, C.; Schwolow, G.

1981-07-28

261

Asymmetric synthesis of tetrahydroquinolines through supramolecular organocatalysis.  

PubMed

Functionalized chiral tetrahydroquinolines were synthesized through supramolecular organocatalysis using quinidine-NH-thiourea 3c/L-phenylalanine 4i followed by reductive amination from the simple substrates. PMID:24840771

Ramachary, Dhevalapally B; Shruthi, Kodambahalli S

2014-07-01

262

Asymmetric dipolar ring  

DOEpatents

A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field.

Prosandeev, Sergey A. (Fayetteville, AR); Ponomareva, Inna V. (Tampa, FL); Kornev, Igor A. (Ill-de-France, FR); Bellaiche, Laurent M. (Fayetteville, AR)

2010-11-16

263

Engineering asymmetric vesicles  

NASA Astrophysics Data System (ADS)

Vesicles are bilayers of lipid molecules enclosing a fixed volume of aqueous solution. Ubiquitous in cells, they can be produced in vitro to study the physical properties of biological membranes and for use in drug delivery and cosmetics. Biological membranes are, in fact, a fluid mosaic of lipids and other molecules; the richness of their chemical and mechanical properties in vivo is often dictated by an asymmetric distribution of these molecules. Techniques for vesicle preparation have been based on the spontaneous assembly of lipid bilayers, precluding the formation of such asymmetric structures. Partial asymmetry has been achieved only with chemical methods greatly restricting the study of the physical and chemical properties of asymmetric vesicles and their use in potential applications for drug delivery. Here we describe the systematic engineering of unilamellar vesicles assembled with two independently prepared monolayers; this process produces asymmetries as high as 95%. We demonstrate the versatility of our method by investigating the stability of the asymmetry. We also use it to engineer hybrid structures comprised of an inner leaflet of diblock copolymer and an independent lipid outer leaflet.

Pautot, Sophie; Frisken, Barbara J.; Weitz, D. A.

2003-09-01

264

Asymmetrically-Driven Implosions  

NASA Astrophysics Data System (ADS)

Techniques to achieve uniform, near-spherical symmetry of radiation drive on a capsule in a laser-heated hohlraum have received detailed attention in the context of ICF. However, much less attention has been paid to the understanding of the hohlraum physics in cases where the radiation drive departs significantly from spherical symmetry. In recent work at the OMEGA laser, AWE has carried out a series of experiments to study the implosion dynamics of a capsule irradiated by a deliberately asymmetric X-ray drive. The experimental data provide a sensitive test of radiation transport in which drive symmetry is modulated by the use of variable albedo layers and asymmetric laser-beam timing. Data from foam-ball and thin-shell capsule experiments are presented, together with modelling using consecutively linked Lagrangian and Eulerian, as well as single-step ALE, calculational schemes. The thin-shell capsules exhibit much stronger sensitivity to asymmetry than foam balls resulting in the formation of a well-defined polar jet. These data are shown to challenge computational modelling in this highly asymmetric, strongly convergent regime.

Vaughan, Kelly

2009-11-01

265

Asymmetrical Capacitors for Propulsion  

NASA Technical Reports Server (NTRS)

Asymmetrical Capacitor Thrusters have been proposed as a source of propulsion. For over eighty years, it has been known that a thrust results when a high voltage is placed across an asymmetrical capacitor, when that voltage causes a leakage current to flow. However, there is surprisingly little experimental or theoretical data explaining this effect. This paper reports on the results of tests of several Asymmetrical Capacitor Thrusters (ACTs). The thrust they produce has been measured for various voltages, polarities, and ground configurations and their radiation in the VHF range has been recorded. These tests were performed at atmospheric pressure and at various reduced pressures. A simple model for the thrust was developed. The model assumed the thrust was due to electrostatic forces on the leakage current flowing across the capacitor. It was further assumed that this current involves charged ions which undergo multiple collisions with air. These collisions transfer momentum. All of the measured data was consistent with this model. Many configurations were tested, and the results suggest general design principles for ACTs to be used for a variety of purposes.

Canning, Francis X.; Melcher, Cory; Winet, Edwin

2004-01-01

266

Absolute configuration of amphidinin A.  

PubMed

The absolute configurations at six stereogenic centers in amphidinin A (1), a cytotoxic linear polyketide isolated from a symbiotic marine dinoflagellate, Amphidinium sp., were elucidated to be 2R, 4R, 6S, 9R 11R, and 12S by the combination of J-based configuration analysis, modified Mosher's method, and density-functional theory calculations. PMID:24836179

Iwai, Takahiro; Kubota, Takaaki; Kobayashi, Jun'ichi

2014-06-27

267

Absolute transition probabilities of phosphorus.  

NASA Technical Reports Server (NTRS)

Use of a gas-driven shock tube to measure the absolute strengths of 21 P I lines and 126 P II lines (from 3300 to 6900 A). Accuracy for prominent, isolated neutral and ionic lines is estimated to be 28 to 40% and 18 to 30%, respectively. The data and the corresponding theoretical predictions are examined for conformity with the sum rules.-

Miller, M. H.; Roig, R. A.; Bengtson, R. D.

1971-01-01

268

The Concept of the Absolute  

E-print Network

KU ScholarWorks | The University of Kansas Pre-1923 Dissertations and Theses Collection The Concept of the Absolute; Its Historical Development 1910 by C.O. VanDyke This work was digitized by the Scholarly Communications program staff in the KU...

Van Dyke, C. O.

1910-01-01

269

Asymmetric [4+2] cycloadditions employing 1,3-dienes derived from (R)-4-t-butyldimethyl-silyloxy-2-cyclohexen-1-one  

PubMed Central

1.3-Dienes derived from (R)-4-t-butyldimethylsilyloxy-2-cyclohexen-1-one react with activated dienophiles to form predominately (or sometimes exclusively) syn/endo products. These controlled [4+2] cycloadditions increase the asymmetric complexity from one asymmetric center in the starting material to five asymmetric centers in the products in a single step, and provide a powerful approach for the asymmetric synthesis of compounds containing the bicyclo[2.2.2]octanone carbon skeleton. PMID:20161352

Hua, Zhengmao; Chen, Lei; Mei, Yan; Jin, Zhendong

2009-01-01

270

Optimal Asymmetric Quantum Cloning  

E-print Network

While the no-cloning theorem, which forbids the perfect copying of quantum states, is well-known as one of the defining features of quantum mechanics, the question of how well the theory allows a state to be cloned is yet to be completely solved. In this paper, rigorous solutions to the problem of M to N asymmetric cloning of qudits are obtained in a number of interesting cases. The central result is the solution to the 1 to N universal asymmetric qudit cloning problem for which the exact trade-off in the fidelities of the clones for every N and d is derived. Analogous results are proven for qubits when M=N-1. We also consider state-dependent 1 to N qubit cloning, providing a general parametrization in terms of a Heisenberg star Hamiltonian. In all instances, we determine the feasibility of implementing the cloning economically, i.e., without an ancilla, and determine the dimension of the ancilla when an economic implementation is not possible.

Alastair Kay; Ravishankar Ramanathan; Dagomir Kaszlikowski

2012-08-28

271

Colon Cryptogenesis: Asymmetric Budding  

PubMed Central

The process of crypt formation and the roles of Wnt and cell-cell adhesion signaling in cryptogenesis are not well described; but are important to the understanding of both normal and cancer colon crypt biology. A quantitative 3D-microscopy and image analysis technique is used to study the frequency, morphology and molecular topography associated with crypt formation. Measurements along the colon reveal the details of crypt formation and some key underlying biochemical signals regulating normal colon biology. Our measurements revealed an asymmetrical crypt budding process, contrary to the previously reported symmetrical fission of crypts. 3D immunofluorescence analyses reveals heterogeneity in the subcellular distribution of E-cadherin and ?-catenin in distinct crypt populations. This heterogeneity was also found in asymmetrical budding crypts. Singular crypt formation (i.e. no multiple new crypts forming from one parent crypt) were observed in crypts isolated from the normal colon mucosa, suggestive of a singular constraint mechanism to prevent aberrant crypt production. The technique presented improves our understanding of cryptogenesis and suggests that excess colon crypt formation occurs when Wnt signaling is perturbed (e.g. by truncation of adenomatous polyposis coli, APC protein) in most colon cancers. PMID:24205248

Tan, Chin Wee; Hirokawa, Yumiko; Gardiner, Bruce S.; Smith, David W.; Burgess, Antony W.

2013-01-01

272

Hunting Asymmetric Stops  

E-print Network

We point out that in the irreducible natural SUSY spectrum, stops have comparable branching fractions to chargino-bottom and neutralino-top in the vast bulk of parameter space, provided only that both decay modes are kinematically accessible. The total stop pair branching fractions into ttbar + MET can therefore be reduced to O(50%), while b bbar + X branching fractions are typically much smaller, O(10%), thus limiting the reach of traditional stop searches. We propose a new stop search targeting the asymmetric final state \\~t\\~t* --> t chi^0 b chi^pm, which can restore sensitivity to natural stops in the 7 and 8 TeV LHC runs. In addition we present a new variable, topness, which efficiently suppresses the dominant top backgrounds to semi-leptonic top partner searches. We demonstrate the utility of topness in both our asymmetric search channel and traditional \\~t\\~t* --> ttbar + MET searches and show that it matches or out-performs existing variables.

Michael L. Graesser; Jessie Shelton

2012-12-18

273

Colon cryptogenesis: asymmetric budding.  

PubMed

The process of crypt formation and the roles of Wnt and cell-cell adhesion signaling in cryptogenesis are not well described; but are important to the understanding of both normal and cancer colon crypt biology. A quantitative 3D-microscopy and image analysis technique is used to study the frequency, morphology and molecular topography associated with crypt formation. Measurements along the colon reveal the details of crypt formation and some key underlying biochemical signals regulating normal colon biology. Our measurements revealed an asymmetrical crypt budding process, contrary to the previously reported symmetrical fission of crypts. 3D immunofluorescence analyses reveals heterogeneity in the subcellular distribution of E-cadherin and ?-catenin in distinct crypt populations. This heterogeneity was also found in asymmetrical budding crypts. Singular crypt formation (i.e. no multiple new crypts forming from one parent crypt) were observed in crypts isolated from the normal colon mucosa, suggestive of a singular constraint mechanism to prevent aberrant crypt production. The technique presented improves our understanding of cryptogenesis and suggests that excess colon crypt formation occurs when Wnt signaling is perturbed (e.g. by truncation of adenomatous polyposis coli, APC protein) in most colon cancers. PMID:24205248

Tan, Chin Wee; Hirokawa, Yumiko; Gardiner, Bruce S; Smith, David W; Burgess, Antony W

2013-01-01

274

Asymmetric coevolutionary voter dynamics  

NASA Astrophysics Data System (ADS)

We consider a modification of the adaptive contact process that, interpreted in the context of opinion dynamics, breaks the symmetry of the coevolutionary voter model by assigning to each node type a different strategy to promote consensus: Orthodox opinion holders spread their opinion via social pressure and rewire their connections following a segregationist strategy; heterodox opinion holders adopt a proselytic strategy, converting their neighbors through personal interactions, and relax to the orthodox opinion according to its representation in the population. We give a full description of the phase diagram of this asymmetric model, using the standard pair approximation equations and assessing their performance by comparison with stochastic simulations. We find that although global consensus is favored with regard to the symmetric case, the asymmetric model also features an active phase. We study the stochastic properties of the corresponding metastable state in finite-size networks, discussing the applicability of the analytic approximations developed for the coevolutionary voter model. We find that, in contrast to the symmetric case, the final consensus state is predetermined by the system's parameters and independent of initial conditions for sufficiently large system sizes. We also find that rewiring always favors consensus, both by significantly reducing convergence times and by changing their scaling with system size.

Wieland, Stefan; Nunes, Ana

2013-12-01

275

Asymmetrical Ventricular Enlargement in Parkinson's  

E-print Network

Asymmetrical Ventricular Enlargement in Parkinson's Disease Xuemei Huang, MD, PhD,1 * Yueh Z. Lee, Chapel Hill, North Carolina, USA; 3 Department of Medicine (Neurology), Pacific Parkinson's Research, Bethesda, Maryland, USA Abstract: Parkinson's disease (PD) typically manifests with asymmetric motor

Utah, University of

276

Preparation of asymmetric porous materials  

DOEpatents

A method for preparing an asymmetric porous material by depositing a porous material film on a flexible substrate, and applying an anisotropic stress to the porous media on the flexible substrate, where the anisotropic stress results from a stress such as an applied mechanical force, a thermal gradient, and an applied voltage, to form an asymmetric porous material.

Coker, Eric N. (Albuquerque, NM)

2012-08-07

277

Asymmetrically Warped Spacetimes  

E-print Network

We investigate spacetimes in which the speed of light along flat 4D sections varies over the extra dimensions due to different warp factors for the space and the time coordinates (``asymmetrically warped'' spacetimes). The main property of such spaces is that while the induced metric is flat, implying Lorentz invariant particle physics on a brane, bulk gravitational effects will cause apparent violations of Lorentz invariance and of causality from the brane observer's point of view. An important experimentally verifiable consequence of this is that gravitational waves may travel with a speed different from the speed of light on the brane, and possibly even faster. We find the most general spacetimes of this sort, which are given by certain types of black hole spacetimes characterized by the mass and the charge of the black hole. We show how to satisfy the junction conditions and analyze the properties of these space-times.

Csáki, C

2001-01-01

278

Asymmetrically Warped Spacetimes  

E-print Network

We investigate spacetimes in which the speed of light along flat 4D sections varies over the extra dimensions due to different warp factors for the space and the time coordinates (``asymmetrically warped'' spacetimes). The main property of such spaces is that while the induced metric is flat, implying Lorentz invariant particle physics on a brane, bulk gravitational effects will cause apparent violations of Lorentz invariance and of causality from the brane observer's point of view. An important experimentally verifiable consequence of this is that gravitational waves may travel with a speed different from the speed of light on the brane, and possibly even faster. We find the most general spacetimes of this sort, which are given by certain types of black hole spacetimes characterized by the mass and the charge of the black hole. We show how to satisfy the junction conditions and analyze the properties of these space-times.

Csaba Csaki

2001-10-30

279

Asymmetrically warped spacetimes  

SciTech Connect

We investigate spacetimes in which the speed of light along flat 4D sections varies over the extra dimensions due to different warp factors for the space and the time coordinates ('asymmetrically warped' spacetimes). The main property of such spaces is that while the induced metric is flat, implying Lorentz invariant particle physics on a brane, bulk gravitational effects will cause apparent violations of Lorentz invariance and of causality from the brane observer's point of view. An important experimentally verifiable consequence of this is that gravitational waves may travel with a speed different from the speed of light on the brane, and possibly even faster. We find the most general spacetimes of this sort, which are given by certain types of black hole spacetimes characterized by the m a s and the charge of the black hole. We show how to satisfy the junction conditions and analyze the properties of these space-times.

Csaki, C. (Csaba)

2001-01-01

280

PROJECTIVE GROUP STRUCTURES AS ABSOLUTE GALOIS STRUCTURES  

E-print Network

PROJECTIVE GROUP STRUCTURES AS ABSOLUTE GALOIS STRUCTURES of a cover to a cartesioan square . . . . . . . . . . . . . . * *. 1 4. Projective groups structures of the Main Theorem . . . . . . . . . . . . . . . . . . . . 1 14. Projective group structures as absolute

281

PROJECTIVE GROUP STRUCTURES AS ABSOLUTE GALOIS STRUCTURES  

E-print Network

PROJECTIVE GROUP STRUCTURES AS ABSOLUTE GALOIS STRUCTURES. A proper profinite group structure G is projective if and only if G* * is the absolute Galois group to a cartesian square . . . . . . . . . . . . . . . * * 19 4. Projective group structures

Pop, Florian

282

Asymmetric hydrogenation of pyridinium salts with an iridium phosphole catalyst.  

PubMed

Iridium-catalyzed asymmetric hydrogenation of N-alkyl-2-alkylpyridinium salts provided 2-aryl-substituted piperidines with high levels of enantioselectivity. Simple benzyl and other alkyl groups successfully activated the challenging pyridine substrates toward hydrogenation. The use of the unusual chiral-phosphole-based MP(2) -SEGPHOS was the key to the success of this approach which provides a versatile and practical procedure for the synthesis of chiral piperidines. PMID:25297378

Chang, Mingxin; Huang, Yuhua; Liu, Shaodong; Chen, Yonggang; Krska, Shane W; Davies, Ian W; Zhang, Xumu

2014-11-17

283

Microbial asymmetric oxidation of 2-butyl-1,3-propanediol  

Microsoft Academic Search

Microbial asymmetric oxidation of 2-butyl-1,3-propanediol was investigated for an efficient synthesis of S- and R-enantiomers of 2-hydroxymethylhexanoic acid (2-HMHA). From an intensive survey of the stocked bacterial strains, Acetobacter pasteurianus IAM 12073 and Pseudomonas putida IFO 3738 were found to show the highest S- and R-2-HMHA-producing activity, respectively. Under optimized conditions, A. pasteurianus (351 mg dry cell weight) and P. putida

K. Mitsukura; T. Uno; T. Yoshida; T. Nagasawa

2007-01-01

284

Asymmetric photoredox transition-metal catalysis activated by visible light.  

PubMed

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the 'green' synthesis of non-racemic chiral molecules. PMID:25373679

Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

2014-11-01

285

Absolute MR thermometry using nanocarriers.  

PubMed

Accurate time-resolved temperature mapping is crucial for the safe use of hyperthermia-mediated drug delivery. We here propose a magnetic resonance imaging temperature mapping method in which drug delivery systems serve not only to improve tumor targeting, but also as an accurate and absolute nano-thermometer. This method is based on the temperature-dependent chemical shift difference between water protons and the protons in different groups of drug delivery systems. We show that the chemical shift of the protons in the ethylene oxide group in polyethylene glycol (PEG) is temperature-independent, whereas the proton resonance of water decreases with increasing temperature. The frequency difference between both resonances is linear and does not depend on pH and physiological salt conditions. In addition, we show that the proton resonance of the methyl group in N-(2-hydroxypropyl)-methacrylamide (HPMA) is temperature-independent. Therefore, PEGylated liposomes, polymeric mPEG-b-pHPMAm-Lac2 micelles and HPMA copolymers can provide a temperature-independent reference frequency for absolute magnetic resonance (MR) thermometry. Subsequently, we show that multigradient echo MR imaging with PEGylated liposomes in situ allows accurate, time-resolved temperature mapping. In conclusion, nanocarrier materials may serve as highly versatile tools for tumor-targeted drug delivery, acting not only as hyperthermia-responsive drug delivery systems, but also as accurate and precise nano-thermometers. PMID:24706612

Deckers, Roel; Sprinkhuizen, Sara M; Crielaard, Bart J; Ippel, Johannes H; Boelens, Rolf; Bakker, Chris J G; Storm, Gert; Lammers, Twan; Bartels, Lambertus W

2014-01-01

286

A novel predictor of restenosis and adverse cardiac events: asymmetric dimethylarginine  

Microsoft Academic Search

The aim of this study is to investigate if serum asymmetric dimethylarginine (ADMA) levels can predict restenosis and major\\u000a adverse cardiac events (MACE) in patients who undergo percutaneous coronary interventions. The most important cause of restenosis\\u000a following percutaneous coronary intervention is neointimal hyperplasia. Nitric oxide (NO) prevents the neointimal hyperplasia\\u000a growing. Asymmetric dimethylarginine is a competitive inhibitor of NO synthesis.

Hasan Ari; Selma Ari; Ercan Erdo?an; Osman Tiryakio?lu; Yasemin Üstünda?; Ka?an Huysal; Vedat Koca; Tahsin Bozat

2010-01-01

287

Development of asymmetric reactions catalyzed by chiral organotin-alkoxide reagents.  

PubMed

Asymmetric catalysis under almost-neutral reaction conditions is key for the efficient synthesis of optically active polar molecules. We have developed catalytic enantioselective reactions of acyclic or cyclic alkenyl esters by using an (S)-BINOL-derived chiral tin-dibromide reagent that possesses a bulky aryl group at the 3 or 3' position as the chiral pre-catalyst in the presence of a sodium alkoxide and an alcohol, in which a chiral tin alkoxide bromide is generated in situ and recycled with the assistance of an alcohol. In this Personal Account, we describe three types of asymmetric transformation that proceed through a chiral tin enolate: 1) The asymmetric aldol reaction of alkenyl esters or unsaturated lactones with aldehydes or isatins; 2) the asymmetric three-component Mannich-type reaction of alkenyl esters and related cycloaddition reactions; and 3) the asymmetric N-nitroso aldol reaction of unsaturated lactones with nitrosoarenes. PMID:23424074

Yanagisawa, Akira; Yoshida, Kazuhiro

2013-02-01

288

Asymmetric inheritance of cytoophidia in Schizosaccharomyces pombe  

PubMed Central

ABSTRACT A general view is that Schizosaccharomyces pombe undergoes symmetric cell division with two daughter cells inheriting equal shares of the content from the mother cell. Here we show that CTP synthase, a metabolic enzyme responsible for the de novo synthesis of the nucleotide CTP, can form filamentous cytoophidia in the cytoplasm and nucleus of S. pombe cells. Surprisingly, we observe that both cytoplasmic and nuclear cytoophidia are asymmetrically inherited during cell division. Our time-lapse studies suggest that cytoophidia are dynamic. Once the mother cell divides, the cytoplasmic and nuclear cytoophidia independently partition into one of the two daughter cells. Although the two daughter cells differ from one another morphologically, they possess similar chances of inheriting the cytoplasmic cytoophidium from the mother cell, suggesting that the partition of cytoophidium is a stochastic process. Our findings on asymmetric inheritance of cytoophidia in S. pombe offer an exciting opportunity to study the inheritance of metabolic enzymes in a well-studied model system. PMID:25361577

Zhang, Jing; Hulme, Lydia; Liu, Ji-Long

2014-01-01

289

Activation of carboxylic acids in asymmetric organocatalysis.  

PubMed

Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. Its success relies to a large extent upon the introduction of novel and generic activation modes. Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition-metal catalysis, a general and well-defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self-assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine-opening reaction with carboxylic acids as nucleophiles. PMID:24888674

Monaco, Mattia Riccardo; Poladura, Belén; Diaz de Los Bernardos, Miriam; Leutzsch, Markus; Goddard, Richard; List, Benjamin

2014-07-01

290

Tectonically Asymmetric Earth  

NASA Astrophysics Data System (ADS)

The net rotation, or so-called W-ward drift of the lithosphere, implies a decoupling of the plates relative to the underlying asthenosphere, and a relative "E-ward" mantle flow. This polarized flow can account for a number of asymmetries. When comparing the W-directed versus the E- to NE-directed subduction zones, as a general observation, they have the subduction hinge diverging versus converging relative to the upper plate; low versus high topography and structural elevation respectively; deep versus shallow trenches and foreland basins; shallow versus deep decollement; low versus high basement involvement; high versus low heat flow and gravity anomaly; shallow versus deep asthenosphere; etc. The western limbs of rift zones have in average a deeper bathymetry, and show S-waves faster in the lithosphere and slower in the asthenosphere with respect to the eastern limb. These asymmetries can be recognized when moving along the "tectonic equator", which describes the fastest flow of plates relative to the mantle, and it undulates relative to the geographic equator, with an angle of about 30°. Shear-wave splitting alignments tend to parallel the tectonic flow, apart along the subduction zones where they become orthogonal, as a flow encountering an obstacle. The estimates of the net rotation span from 0.2° to 1.2° Ma. However, only a net rotation >1° Ma is required in order to satisfy the aforementioned tectonically asymmetric Earth. In our reconstructions, the best fit for the tectonic equator has a pole of rotation at latitude 56.4° and longitude 136.7°, with an angular velocity of 1.2036°/Ma. This velocity can be obtained only if the source of the so-called volcanic trails or plumes are sourced from the middle of the low-velocity layer, at the top of the asthenosphere, i.e., within the decoupling layer of the plates relative to the underlying mantle. The tectonic equator lies close to the revolution plane of the Moon about the Earth. All these data and interpretations point for an asymmetric Earth, whose nature appears to be related to the rotation and its tidal despinning, combined with the thermal cooling of the planet.

Doglioni, C.; Carminati, E.; Crespi, M.; Cuffaro, M.; Panza, G. F.; Riguzzi, F.

2011-12-01

291

A flexible enantioselective total synthesis of diospongins A and B and their enantiomers using catalytic hetero-Diels-Alder/Rh-catalyzed 1,4-addition and asymmetric transfer hydrogenation reactions as key steps.  

PubMed

A unified enantioselective route to total synthesis of diospongins A and B and their enantiomers has been developed employing achiral starting materials. All three stereocenters were introduced by means of catalytic reactions. PMID:19817354

Kumaraswamy, Gullapalli; Ramakrishna, Gajula; Naresh, Police; Jagadeesh, Bharatam; Sridhar, Balasubramanian

2009-11-01

292

Asymmetric Bessel modes.  

PubMed

We propose a new, three-parameter family of diffraction-free asymmetric elegant Bessel modes (aB-modes) with an integer and fractional orbital angular momentum (OAM). The aB-modes are described by the nth-order Bessel function of the first kind with complex argument. The asymmetry degree of the nonparaxial aB-mode is shown to depend on a real parameter c?0: when c=0, the aB-mode is identical to a conventional radially symmetric Bessel mode; with increasing c, the aB-mode starts to acquire a crescent form, getting stretched along the vertical axis and shifted along the horizontal axis for c?1. On the horizontal axis, the aB-modes have a denumerable number of isolated intensity zeros that generate optical vortices with a unit topological charge of opposite sign on opposite sides of 0. At different values of the parameter c, the intensity zeros change their location on the horizontal axis, thus changing the beam's OAM. An isolated intensity zero on the optical axis generates an optical vortex with topological charge n. The OAM per photon of an aB-mode depends near-linearly on c, being equal to ?(n+cI1(2c)/I0(2c)), where ? is the Planck constant and In(x) is a modified Bessel function. PMID:24979002

Kotlyar, V V; Kovalev, A A; Soifer, V A

2014-04-15

293

Extremal asymmetric universal cloning machines  

E-print Network

The trade-offs among various output fidelities of asymmetric universal cloning machines are investigated. First we find out all the attainable optimal output fidelities for the 1 to 3 asymmetric universal cloning machine and it turns out that there are two kinds of extremal asymmetric cloning machines which have to cooperate in order to achieve some of the optimal output fidelities. Second we construct a family of extremal cloning machines that includes the universal symmetric cloning machine as well as an asymmetric 1 to $1+N$ cloning machine for qudits with two different output fidelities such that the optimal trade-off between the measurement disturbance and state estimation is attained in the limit of infinite $N$.

Mingming Jiang; Sixia Yu

2012-02-08

294

Extremal asymmetric universal cloning machines  

E-print Network

The trade-offs among various output fidelities of asymmetric universal cloning machines are investigated. First we find out all the attainable optimal output fidelities for the 1 to 3 asymmetric universal cloning machine and it turns out that there are two kinds of extremal asymmetric cloning machines which have to cooperate in order to achieve some of the optimal output fidelities. Second we construct a family of extremal cloning machines that includes the universal symmetric cloning machine as well as an asymmetric 1 to $1+N$ cloning machine for qudits with two different output fidelities such that the optimal trade-off between the measurement disturbance and state estimation is attained in the limit of infinite $N$.

Jiang, Mingming

2012-01-01

295

Evaluation of novel enoate reductases as potential biocatalyst for enantiomerically pure compound synthesis.  

E-print Network

??Asymmetric synthesis with biocatalyst has become an increasingly interesting and cost effective manufacturing process in fine chemicals, pharmaceuticals, and agrochemical intermediates. Enoate reductases from the… (more)

Yanto, Yanto

2011-01-01

296

Enantioselective synthesis of (+)-malbrancheamide B.  

PubMed

The asymmetric total synthesis of the chlorinated [2.2.2]-diazabicyclic indole alkaloid (+)-malbrancheamide B is reported. Key to the synthesis is a domino reaction sequence that employs an aldol condensation, alkene isomerization, and intramolecular Diels-Alder cycloaddition. Diastereofacial selection between the azadiene stereofaces is enforced with a chiral aminal auxiliary. A formal 7-step (longest linear route) synthesis of (±)-malbrancheamide B is also reported. PMID:23360221

Laws, Stephen W; Scheerer, Jonathan R

2013-03-15

297

Absolute configuration of isovouacapenol C  

PubMed Central

The title compound, C27H34O5 {systematic name: (4aR,5R,6R,6aS,7R,11aS,11bR)-4a,6-dihy­droxy-4,4,7,11b-tetra­methyl-1,2,3,4,4a,5,6,6a,7,11,11a,11b-dodeca­hydro­phenanthro[3,2-b]furan-5-yl benzoate}, is a cassane furan­oditerpene, which was isolated from the roots of Caesalpinia pulcherrima. The three cyclo­hexane rings are trans fused: two of these are in chair conformations with the third in a twisted half-chair conformation, whereas the furan ring is almost planar (r.m.s. deviation = 0.003?Å). An intra­molecular C—H?O inter­action generates an S(6) ring. The absolute configurations of the stereogenic centres at positions 4a, 5, 6, 6a, 7, 11a and 11b are R, R, R, S, R, S and R, respectively. In the crystal, mol­ecules are linked into infinite chains along [010] by O—H?O hydrogen bonds. C?O [3.306?(2)–3.347?(2)?Å] short contacts and C—H?? inter­actions also occur. PMID:21588364

Fun, Hoong-Kun; Yodsaoue, Orapun; Karalai, Chatchanok; Chantrapromma, Suchada

2010-01-01

298

Synthesis and Suzuki-Miyaura Cross-Coupling of Enantioenriched Secondary Potassium ?-Trifluoroboratoamides: Catalytic, Asymmetric Conjugate Addition of Bisboronic Acid and Tetrakis(dimethylamino)diboron to ?,?-Unsaturated Carbonyl Compounds  

PubMed Central

Enantioenriched potassium ?-trifluoroboratoamides have been synthesized via an asymmetric, copper-catalyzed 1,4-addition of tetrahydroxydiboron (BBA) and tetrakis(dimethylamino)diboron to ?,?-unsaturated amides. These dibora reagents provide access to the desired organotrifluoroborates using effective and atom economical sources of boron. The copper-catalyzed ?-boration is extended to ?,?-unsaturated ketones and esters. Desired potassium organotrifluoroborates are synthesized with yields up to 92% and enantiomeric ratios up to 98:2. The enantioenriched potassium ?-trifluoroboratoamides are successfully cross-coupled with an array of aryl and heteroaryl chlorides in high yield with complete stereochemical fidelity as the transmetalation proceeds through an SE2 mechanism via an open transition state. PMID:24741373

Wisniewski, Steven R.; Hosseini-Sarvari, Mona

2014-01-01

299

Asymmetric distances for binary embeddings.  

PubMed

In large-scale query-by-example retrieval, embedding image signatures in a binary space offers two benefits: data compression and search efficiency. While most embedding algorithms binarize both query and database signatures, it has been noted that this is not strictly a requirement. Indeed, asymmetric schemes that binarize the database signatures but not the query still enjoy the same two benefits but may provide superior accuracy. In this work, we propose two general asymmetric distances that are applicable to a wide variety of embedding techniques including locality sensitive hashing (LSH), locality sensitive binary codes (LSBC), spectral hashing (SH), PCA embedding (PCAE), PCAE with random rotations (PCAE-RR), and PCAE with iterative quantization (PCAE-ITQ). We experiment on four public benchmarks containing up to 1M images and show that the proposed asymmetric distances consistently lead to large improvements over the symmetric Hamming distance for all binary embedding techniques. PMID:24231864

Gordo, Albert; Perronnin, Florent; Gong, Yunchao; Lazebnik, Svetlana

2014-01-01

300

Asymmetric Distances for Binary Embeddings.  

PubMed

In large-scale query-by-example retrieval, embedding image signatures in a binary space offers two benefits: data compression and search efficiency. While most embedding algorithms binarize both query and database signatures, it has been noted that this is not strictly a requirement. Indeed, asymmetric schemes which binarize the database signatures but not the query still enjoy the same two benefits but may provide superior accuracy. In this work, we propose two general asymmetric distances which are applicable to a wide variety of embedding techniques including Locality Sensitive Hashing (LSH), Locality Sensitive Binary Codes (LSBC), Spectral Hashing (SH), PCA Embedding (PCAE), PCA Embedding with random rotations (PCAE-RR), and PCA Embedding with iterative quantization (PCAE-ITQ). We experiment on four public benchmarks containing up to 1M images and show that the proposed asymmetric distances consistently lead to large improvements over the symmetric Hamming distance for all binary embedding techniques. PMID:23712997

Gordo, Albert; Perronnin, Florent; Gong, Yunchao; Lazebnik, Svetlana

2013-05-21

301

Absolute Income, Relative Income, and Happiness  

ERIC Educational Resources Information Center

This paper uses data from the World Values Survey to investigate how an individual's self-reported happiness is related to (i) the level of her income in absolute terms, and (ii) the level of her income relative to other people in her country. The main findings are that (i) both absolute and relative income are positively and significantly…

Ball, Richard; Chernova, Kateryna

2008-01-01

302

Absolute Optical Metrology: Nanometers to Kilometers  

Microsoft Academic Search

We provide an overview of developments in high-accuracy absolute optical metrology with emphasis on space-based applications. Specific work on the Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor is described along with novel applications of the sensor.

S. Dubovitsky; O. P. Lay; R. D. Peters; C. C. Liebe

2005-01-01

303

Nonequilibrium equalities in absolutely irreversible processes  

NASA Astrophysics Data System (ADS)

We generalize nonequilibrium integral equalities to situations involving absolutely irreversible processes for which the forward-path probability vanishes and the entropy production diverges, rendering conventional integral fluctuation theorems inapplicable. We identify the mathematical origins of absolute irreversibility as the singularity of probability measure. We demonstrate the validity of the obtained equalities for several models.

Murashita, Yûto; Funo, Ken; Ueda, Masahito

2014-10-01

304

Absolute instability of the Gaussian wake profile  

NASA Technical Reports Server (NTRS)

Linear parallel-flow stability theory has been used to investigate the effect of viscosity on the local absolute instability of a family of wake profiles with a Gaussian velocity distribution. The type of local instability, i.e., convective or absolute, is determined by the location of a branch-point singularity with zero group velocity of the complex dispersion relation for the instability waves. The effects of viscosity were found to be weak for values of the wake Reynolds number, based on the center-line velocity defect and the wake half-width, larger than about 400. Absolute instability occurs only for sufficiently large values of the center-line wake defect. The critical value of this parameter increases with decreasing wake Reynolds number, thereby indicating a shrinking region of absolute instability with decreasing wake Reynolds number. If backflow is not allowed, absolute instability does not occur for wake Reynolds numbers smaller than about 38.

Hultgren, Lennart S.; Aggarwal, Arun K.

1987-01-01

305

Resonance in Asymmetric Warped Geometry  

E-print Network

We study the spectrum of an asymmetric warped braneworld model with different AdS curvatures on either side of the brane. In addition to the RS-like modes we find a resonance state. Its mass is proportional to the geometric mean of the two AdS curvature scales, while the difference between them determines the strength of the resonance peak. There is a complementarity between the RS zero-mode and the resonance: making the asymmetry stronger weakens the zero-mode but strengthens the resonance, and vice versa. We calculate numerically the braneworld gravitational potential and discuss the holographic correspondence for the asymmetric model.

Gregory Gabadadze; Luca Grisa; Yanwen Shang

2006-04-28

306

Studies of stereocontrolled allylation reactions for the total synthesis of phorboxazole A  

PubMed Central

A highly convergent total synthesis of the potent anticancer agent (+)-phorboxazole A (1) is accomplished. Four components (3–6) are assembled with considerations for control of absolute and relative stereochemistry. Iterative asymmetric allylation methodology addresses key stereochemical features in the preparation of the 2,6-cis- and 2,6-trans-tetrahydropyranyl rings of the C3–C19 component (3). The stereocontrolled asymmetric allylation process is also used for development of the C28–C41 fragment (4). Novel Barbier coupling reactions of ?-iodomethyl oxazoles and related thiazoles are described with samarium iodide. The convergent assembly of components 4 and 5 features formation of the fully substituted C22–C26 pyran by intramolecular capture of an allyl cation intermediate with high facial selectivity, and further efforts lead to E-C19/C20 olefination. The synthesis culminates with use of a modified Julia olefination for attachment of the C42–C46 segment and subsequent late-stage macrocyclization by installation of the (Z)-C2/C3 ?,?-unsaturated lactone. PMID:15277662

Williams, David R.; Kiryanov, Andre A.; Emde, Ulrich; Clark, Michael P.; Berliner, Martin A.; Reeves, Jonathan T.

2004-01-01

307

Asymmetrical Dimethylarginine in Renal Disease: Limits of Variation or Variation Limits?  

Microsoft Academic Search

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is increasingly recognized as a putative biomarker in cardiovascular and renal disease. Elevated plasma levels of ADMA are the consequence of increased synthesis, reduced renal clearance or reduced enzymatic degradation. Based upon the metabolic fate the highest plasma concentrations of ADMA have been reported in patients with renal failure in

Johannes Jacobi; Philip S. Tsao

2008-01-01

308

Catalytic asymmetric hydrophosphonylation of ketimines.  

PubMed

Catalytic asymmetric hydrophosphonylation of aromatic and aliphatic N-thiophosphinoyl ketimines with dialkyl phosphite was efficiently promoted by as little as 0.5 mol% of catalyst loading at ambient temperature. The catalyst can be recovered for repeated use, and facile removal of the thiophosphinoyl group allowed for ready access to the phosphonic acid analogue of enantioenriched ?,?-disubstituted ?-amino acids. PMID:23819732

Yin, Liang; Bao, Youmei; Kumagai, Naoya; Shibasaki, Masakatsu

2013-07-17

309

Y2MoSe3O12 and Y2MoTe3O12: Solid-state synthesis, structure determination, and characterization of two new quaternary mixed metal oxides containing asymmetric coordination environment  

NASA Astrophysics Data System (ADS)

Two new quaternary yttrium molybdenum selenium/tellurium oxides, Y2MoSe3O12 and Y2MoTe3O12 have been prepared by standard solid-state reactions using Y2O3, MoO3, and SeO2 (or TeO2) as reagents. Single-crystal X-ray diffraction was used to determine the crystal structures of the reported materials. Although both of the materials contain second-order Jahn-Teller (SOJT) distortive cations and are stoichiometrically similar, they reveal different structural features: while Y2MoSe3O12 shows a three-dimensional framework consisting of YO8, MoO6, and SeO3 groups, Y2MoTe3O12 exhibits a layered structure composed of YO8, MoO4, TeO3, and TeO4 polyhedra. With the Mo6+ cations in Y2MoSe3O12, a C3-type intraoctahedral distortion toward a face is observed, in which the direction of the out-of-center distortion for Mo6+ is away from the oxide ligand linked to a Se4+ cation. The Se4+ and Te4+ cations in both materials are in asymmetric coordination environment attributed to the lone pairs. Elemental analyses, infrared spectroscopy, thermal analyses, intraoctahedral distortions, and dipole moment calculations for the compounds are also presented.

Bang, Seong-eun; Pan, Zhi; Kim, Yeong Hun; Lee, Dong Woo; Ok, Kang Min

2013-12-01

310

New 'side-off' coordination asymmetric homobinuclear Ni(II) and heterobinuclear Ni(II)sbnd Zn(II) complexes as models for hydrolysis of p-nitrophenylphosphate: Synthesis, characterization and electrochemical studies  

NASA Astrophysics Data System (ADS)

A series of new phenol based coordination asymmetric side-off homobinuclear Ni(II) and heterobinuclear Ni(II)sbnd Zn(II) complexes have been synthesized and characterized by elemental analysis and spectral analysis. The electronic spectra of all the complexes show "Red shift" in LMCT band, for the ligand H2L2 having electron donating C2H5 groups as N-substituents in the free side arms compared to ligand H2L1 having relatively lower electron donating CH3 groups. Electrochemical studies of the complexes reveal that all the binuclear complexes show two irreversible one-electron transfer reduction waves in the cathodic region. There is an "anodic shift" in the first reduction potential of the complexes of the ligand H2L1 when compared to that of the complexes of the ligand H2L2 due to the presence of higher electron donating C2H5 N-substituents in the later case than the relatively lower electron donating N-substituents in the former case. Hydrolysis of p-nitrophenylphosphate using homobinuclear Ni(II) and heterobinuclear Ni(II)sbnd Zn(II) complexes as catalysts showed that the homobinuclear complexes have higher rate constant values than that of the corresponding heterobinuclear complexes. A comparison of the spectral, electrochemical and catalytic behavior of the complexes of the ligands is discussed on the basis of the electron donating nature of the N-substituents at the free side arms.

Shanmuga Bharathi, K.; Sreedaran, S.; Kalilur Rahiman, A.; Narayanan, Vengidusamy

2013-03-01

311

New 'side-off' coordination asymmetric homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes as models for hydrolysis of p-nitrophenylphosphate: synthesis, characterization and electrochemical studies.  

PubMed

A series of new phenol based coordination asymmetric side-off homobinuclear Ni(II) and heterobinuclear Ni(II)Zn(II) complexes have been synthesized and characterized by elemental analysis and spectral analysis. The electronic spectra of all the complexes show "Red shift" in LMCT band, for the ligand H(2)L(2) having electron donating C(2)H(5) groups as N-substituents in the free side arms compared to ligand H(2)L(1) having relatively lower electron donating CH(3) groups. Electrochemical studies of the complexes reveal that all the binuclear complexes show two irreversible one-electron transfer reduction waves in the cathodic region. There is an "anodic shift" in the first reduction potential of the complexes of the ligand H(2)L(1) when compared to that of the complexes of the ligand H(2)L(2) due to the presence of higher electron donating C(2)H(5) N-substituents in the later case than the relatively lower electron donating N-substituents in the former case. Hydrolysis of p-nitrophenylphosphate using homobinuclear Ni(II) and heterobinuclear Ni(II)-Zn(II) complexes as catalysts showed that the homobinuclear complexes have higher rate constant values than that of the corresponding heterobinuclear complexes. A comparison of the spectral, electrochemical and catalytic behavior of the complexes of the ligands is discussed on the basis of the electron donating nature of the N-substituents at the free side arms. PMID:23314389

Shanmuga Bharathi, K; Sreedaran, S; Kalilur Rahiman, A; Narayanan, Vengidusamy

2013-03-15

312

Stereodivergent Synthesis of Chiral Fullerenes by [3 + 2] Cycloadditions to C60  

PubMed Central

A wide range of new dipoles and catalysts have been used in 1,3-dipolar cycloadditions of N-metalated azomethine ylides onto C60 yielding a full stereodivergent synthesis of pyrrolidino[60]fullerenes with complete diastereoselectivities and very high enantioselectivities. The use of less-explored chiral ?-iminoamides as starting 1,3-dipoles leads to an interesting double asymmetric induction resulting in a matching/mismatching effect depending upon the absolute configuration of the stereocenter in the starting ?-iminoamide. An enantioselective process was also found in the retrocycloaddition reaction as revealed by mass spectrometry analysis on quasi-enantiomeric pyrrolidino[60]fullerenes. Theoretical DFT calculations are in very good agreement with the experimental data. On the basis of this agreement, a plausible reaction mechanism is proposed. PMID:24359021

2013-01-01

313

Asymmetric organocatalysis at the service of medicinal chemistry.  

PubMed

The application of the most representative and up-to-date examples of homogeneous asymmetric organocatalysis to the synthesis of molecules of interest in medicinal chemistry is reported. The use of different types of organocatalysts operative via noncovalent and covalent interactions is critically reviewed and the possibility of running some of these reactions on large or industrial scale is described. A comparison between the organo- and metal-catalysed methodologies is offered in several cases, thus highlighting the merits and drawbacks of these two complementary approaches to the obtainment of very popular on market drugs or of related key scaffolds. PMID:24971178

Ricci, Alfredo

2014-01-01

314

Asymmetric vinylogous Mannich reactions: a versatile approach to functionalized heterocycles.  

PubMed

Asymmetric vinylogous Mannich reaction (VMR) of 2-(tert-butyldimethylsilyloxy)furan (TBSOF, 1) with (R(S))- or (S(S))-t-BS-imines (3) furnished 5-aminoalkylbutenolides 7a-k in 75-87% yields with anti/syn ratios ranging from 75:25 to 97:3. Butenolides 7a-f,k were readily converted into substituted lactones 8 and 5 and 6-substituted 5-hydroxypiperidin-2-ones 11a-g, which are, in turn, key intermediates for the synthesis of many bioactive compounds. PMID:21854016

Ruan, Shu-Tang; Luo, Jie-Min; Du, Yu; Huang, Pei-Qiang

2011-09-16

315

Magnifying absolute instruments for optically homogeneous regions  

NASA Astrophysics Data System (ADS)

We propose a class of magnifying absolute optical instruments with a positive isotropic refractive index. They create magnified stigmatic images, either virtual or real, of optically homogeneous three-dimensional spatial regions within geometrical optics.

Tyc, Tomáš

2011-09-01

316

Absolute vs. intensity-based emission caps  

E-print Network

Cap-and-trade systems limit emissions to some pre-specified absolute quantity. Intensity-based limits, that restrict emissions to some pre-specified rate relative to input or output, are much more widely used in environmental ...

Ellerman, A. Denny.

317

The Simplicity Argument and Absolute Morality  

ERIC Educational Resources Information Center

In this paper the author has maintained that there is a similarity of thought to be found in the writings of Cudworth, Emerson, and Husserl in his investigation of an absolute system of morality. (Author/RK)

Mijuskovic, Ben

1975-01-01

318

A Cryogenic Radiometer for Absolute Radiometric Measurements  

Microsoft Academic Search

The adoption in 1979 of a new definition of the candela, which permitted a detector-based approach to the realization of the unit, has emphasized the importance of high-accuracy absolute radiation detectors. This paper describes a new electrical-substitution absolute radiometer operating at 5 K, based on a standard commercial helium cryostat, which has been developed at NPL for optical radiant-power measurements.

J E Martin; N P Fox; P J Key

1985-01-01

319

MSTAR: a submicrometer absolute metrology system.  

PubMed

The Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor permits absolute distance measurement with subnanometer accuracy, an improvement of 4 orders of magnitude over current techniques. The system uses fast phase modulators to resolve the integer cycle ambiguity of standard interferometers. The concept is described and demonstrated over target distances up to 1 m. The design can be extended to kilometer-scale separations. PMID:12816236

Lay, O P; Dubovitsky, S; Peters, R D; Burger, J P; Ahn, S W; Steier, W H; Fetterman, H R; Chang, Y

2003-06-01

320

Measurement of the Absolute Branching Fraction of D0-->K-pi+  

Microsoft Academic Search

We measure the absolute branching fraction for D0-->K-pi+ using partial reconstruction of B¯0-->D*+Xl-nu¯l decays, in which only the charged lepton and the pion from the decay D*+-->D0pi+ are used. Based on a data sample of 230×106 BB¯ pairs collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we obtain B(D0-->K-pi+)=(4.007±0.037±0.072)%, where the

B. Aubert; M. Bona; D. Boutigny; Y. Karyotakis; J. P. Lees; V. Poireau; X. Prudent; V. Tisserand; A. Zghiche; J. Garra Tico; E. Grauges; L. Lopez; A. Palano; G. Eigen; I. Ofte; B. Stugu; L. Sun; G. S. Abrams; M. Battaglia; D. N. Brown; J. Button-Shafer; R. N. Cahn; Y. Groysman; R. G. Jacobsen; J. A. Kadyk; L. T. Kerth; Yu. G. Kolomensky; G. Kukartsev; D. Lopes Pegna; G. Lynch; L. M. Mir; T. J. Orimoto; M. Pripstein; N. A. Roe; M. T. Ronan; K. Tackmann; W. A. Wenzel; P. Del Amo Sanchez; C. M. Hawkes; A. T. Watson; T. Held; H. Koch; B. Lewandowski; M. Pelizaeus; T. Schroeder; M. Steinke; W. N. Cottingham; D. Walker; D. J. Asgeirsson; T. Cuhadar-Donszelmann; B. G. Fulsom; C. Hearty; N. S. Knecht; T. S. Mattison; J. A. McKenna; A. Khan; M. Saleem; L. Teodorescu; V. E. Blinov; A. D. Bukin; V. P. Druzhinin; V. B. Golubev; A. P. Onuchin; S. I. Serednyakov; Yu. I. Skovpen; E. P. Solodov; K. Yu Todyshev; M. Bondioli; S. Curry; I. Eschrich; D. Kirkby; A. J. Lankford; P. Lund; M. Mandelkern; E. C. Martin; D. P. Stoker; S. Abachi; C. Buchanan; S. D. Foulkes; J. W. Gary; F. Liu; O. Long; B. C. Shen; L. Zhang; H. P. Paar; S. Rahatlou; V. Sharma; J. W. Berryhill; C. Campagnari; A. Cunha; B. Dahmes; T. M. Hong; D. Kovalskyi; J. D. Richman; T. W. Beck; A. M. Eisner; C. J. Flacco; C. A. Heusch; J. Kroseberg; W. S. Lockman; T. Schalk; B. A. Schumm; A. Seiden; D. C. Williams; M. G. Wilson; L. O. Winstrom; E. Chen; C. H. Cheng; A. Dvoretskii; F. Fang; D. G. Hitlin; I. Narsky; T. Piatenko; F. C. Porter; G. Mancinelli; B. T. Meadows; K. Mishra; M. D. Sokoloff; F. Blanc; P. C. Bloom; S. Chen; W. T. Ford; J. F. Hirschauer; A. Kreisel; M. Nagel; U. Nauenberg; A. Olivas; J. G. Smith; K. A. Ulmer; S. R. Wagner; J. Zhang; A. M. Gabareen; A. Soffer; W. H. Toki; R. J. Wilson; F. Winklmeier; Q. Zeng; D. D. Altenburg; E. Feltresi; A. Hauke; H. Jasper; J. Merkel; A. Petzold; B. Spaan; K. Wacker; T. Brandt; V. Klose; H. M. Lacker; W. F. Mader; R. Nogowski; J. Schubert; K. R. Schubert; R. Schwierz; J. E. Sundermann; A. Volk; D. Bernard; G. R. Bonneaud; E. Latour; V. Lombardo; Ch. Thiebaux; M. Verderi; P. J. Clark; W. Gradl; F. Muheim; S. Playfer; A. I. Robertson; Y. Xie; M. Andreotti; D. Bettoni; C. Bozzi; R. Calabrese; A. Cecchi; G. Cibinetto; P. Franchini; E. Luppi; M. Negrini; A. Petrella; L. Piemontese; E. Prencipe; V. Santoro; F. Anulli; R. Baldini-Ferroli; A. Calcaterra; R. de Sangro; G. Finocchiaro; S. Pacetti; P. Patteri; I. M. Peruzzi; M. Piccolo; M. Rama; A. Zallo; A. Buzzo; R. Contri; M. Lo Vetere; M. M. Macri; M. R. Monge; S. Passaggio; C. Patrignani; E. Robutti; A. Santroni; S. Tosi; K. S. Chaisanguanthum; M. Morii; J. Wu; R. S. Dubitzky; J. Marks; S. Schenk; U. Uwer; D. J. Bard; P. D. Dauncey; R. L. Flack; J. A. Nash; M. B. Nikolich; W. Panduro Vazquez; P. K. Behera; X. Chai; M. J. Charles; U. Mallik; N. T. Meyer; V. Ziegler; J. Cochran; H. B. Crawley; L. Dong; V. Eyges; W. T. Meyer; S. Prell; E. I. Rosenberg; A. E. Rubin; A. V. Gritsan; Z. J. Guo; C. K. Lae; A. G. Denig; M. Fritsch; G. Schott; N. Arnaud; J. Béquilleux; M. Davier; G. Grosdidier; A. Höcker; V. Lepeltier; F. Le Diberder; A. M. Lutz; S. Pruvot; S. Rodier; P. Roudeau; M. H. Schune; J. Serrano; V. Sordini; A. Stocchi; W. F. Wang; G. Wormser; D. J. Lange; D. M. Wright; C. A. Chavez; I. J. Forster; J. R. Fry; E. Gabathuler; R. Gamet; D. E. Hutchcroft; D. J. Payne; K. C. Schofield; C. Touramanis; A. J. Bevan; K. A. George; F. di Lodovico; W. Menges; R. Sacco; G. Cowan; H. U. Flaecher; D. A. Hopkins; P. S. Jackson; T. R. McMahon; F. Salvatore; A. C. Wren; C. L. Davis; J. Allison; N. R. Barlow; R. J. Barlow; Y. M. Chia; C. L. Edgar; G. D. Lafferty; T. J. West; J. I. Yi; J. Anderson; C. Chen; A. Jawahery; D. A. Roberts; G. Simi; J. M. Tuggle; G. Blaylock; C. Dallapiccola; S. S. Hertzbach; X. Li; T. B. Moore; E. Salvati; S. Saremi; R. Cowan; P. H. Fisher; G. Sciolla; S. J. Sekula; M. Spitznagel; F. Taylor; R. K. Yamamoto; S. E. McLachlin; P. M. Patel; S. H. Robertson; A. Lazzaro; F. Palombo; J. M. Bauer; L. Cremaldi; V. Eschenburg; R. Godang; R. Kroeger; D. A. Sanders; D. J. Summers; H. W. Zhao; S. Brunet; D. Côté; M. Simard; P. Taras; F. B. Viaud; H. Nicholson; G. de Nardo; F. Fabozzi; L. Lista; D. Monorchio; C. Sciacca; M. A. Baak; G. Raven; H. L. Snoek; C. P. Jessop; J. M. Losecco; G. Benelli; L. A. Corwin; K. K. Gan; K. Honscheid; D. Hufnagel; H. Kagan; R. Kass; J. P. Morris; A. M. Rahimi; J. J. Regensburger; R. Ter-Antonyan; Q. K. Wong; N. L. Blount; J. Brau; R. Frey; O. Igonkina; J. A. Kolb; M. Lu; R. Rahmat; N. B. Sinev; D. Strom; J. Strube; E. Torrence; N. Gagliardi; A. Gaz; M. Margoni; M. Morandin; A. Pompili; M. Posocco; M. Rotondo; F. Simonetto; R. Stroili; C. Voci; E. Ben-Haim; H. Briand; J. Chauveau; P. David; L. Del Buono; Ch. de La Vaissière; O. Hamon; B. L. Hartfiel; Ph. Leruste; J. Malclès; J. Ocariz

2008-01-01

321

A concise and stereoselective synthesis of squalamine.  

PubMed

[reaction: see text] A short and highly stereoselective synthesis of the novel steroid squalamine (1) was accomplished in nine steps from easily available methyl chenodeoxylcholanate 2. Our synthesis featured improved dehydrogenation of 4 followed by conjugate reduction to construct the trans AB-ring system and efficient asymmetric isopropylation of aldehyde 6 to introduce the C-24R-hydroxyl group. PMID:12943401

Zhang, Dong-Hui; Cai, Feng; Zhou, Xiang-Dong; Zhou, Wei-Shan

2003-09-01

322

Asymmetric fingerprinting for larger collusions  

Microsoft Academic Search

. Fingerprinting schemes deter people from illegallyredistributing digital data by enabling the original merchant ofthe data to identify the original buyer of a redistributed copy.So-called traitor-tracing schemes have the same goal for keysused to decrypt information that is broadcast in encryptedform. Recently, asymmetric fingerprinting and traitor-tracingschemes were introduced. Here, only the buyer knows thefingerprinted copy after a sale, and if

Birgit Pfitzmann; Michael Waidner

1997-01-01

323

Merging neutron stars: asymmetric systems  

E-print Network

Results of 3D, Newtonian hydrodynamic calculations of the last stages of the inspiral and the final coalescence of neutron star binary systems are described. The focus is on sligthly asymmetric systems with the asymmetry stemming either from different spins or different masses of the binary components. Implications for nucleosynthesis and gamma ray bursts are discussed. Test calculations for the used viscosity scheme are provided in the appendix.

S. Rosswog; M. B. Davies; F. -K. Thielemann; T. Piran

2000-05-29

324

Dividend Policy under Asymmetric Information  

Microsoft Academic Search

ABSTRACT We extend the standard finance model of the firm's dividend\\/investment\\/financing decisions by allowing the firm's managers,to know,more than outside investors about the true state of the firm's current earnings. The extension endogenizes the dividend (and financing) announcement,effects amply documented,in recent research. But once trading of shares is admitted to the model along with asymmetric information, the familiar Fisherian criterion

Merton H. Miller; Kevin Rock

1985-01-01

325

Asymmetric information and macroeconomic dynamics  

NASA Astrophysics Data System (ADS)

We show how macroeconomic dynamics can be derived from asymmetric information. As an illustration of the utility of this approach we derive the equilibrium density, non-equilibrium densities and the equation of motion for the response to a demand shock for productivity in a simple economy. Novel consequences of this approach include a natural incorporation of time dependence into macroeconomics and a common information-theoretic basis for economics and other fields seeking to link micro-dynamics and macro-observables.

Hawkins, Raymond J.; Aoki, Masanao; Roy Frieden, B.

2010-09-01

326

Asymmetric Wettability Directs Leidenfrost Droplets  

SciTech Connect

Leidenfrost phenomena on nano- and microstructured surfaces are of great importance for increasing control over heat transfer in high power density systems utilizing boiling phenomena. They also provide an elegant means to direct droplet motion in a variety of recently emerging fluidic systems. Here, we report the fabrication and characterization of tilted nanopillar arrays (TNPAs) that exhibit directional Leidenfrost water droplets under dynamic conditions, namely on impact with Weber numbers 40 at T 325 C. The batch fabrication of the TNPAs was achieved by glancing-angle anisotropic reactive ion etching of a thermally dewet platinum mask, with mean pillar diameters of 100 nm and heights of 200-500 nm. In contrast to previously implemented macro- and microscopic Leidenfrost ratchets, our TNPAs induce no preferential directional movement of Leidenfrost droplets under conditions approaching steady-state film boiling, suggesting that the observed droplet directionality is not a result of asymmetric vapor flow. Using high-speed imaging, phase diagrams were constructed for the boiling behavior upon impact for droplets falling onto TNPAs, straight nanopillar arrays, and smooth silicon surfaces. The asymmetric impact and directional trajectory of droplets was exclusive to the TNPAs for impacts corresponding to the transition boiling regime, revealing that asymmetric wettability upon impact is the mechanism for the droplet directionality.

Agapov, Rebecca L [ORNL] [ORNL; Boreyko, Jonathan B [ORNL] [ORNL; Briggs, Dayrl P [ORNL] [ORNL; Srijanto, Bernadeta R [ORNL] [ORNL; Retterer, Scott T [ORNL] [ORNL; Collier, Pat [ORNL] [ORNL; Lavrik, Nickolay V [ORNL] [ORNL

2014-01-01

327

Absolute and relative quantification of RNA modifications via biosynthetic isotopomers.  

PubMed

In the resurging field of RNA modifications, quantification is a bottleneck blocking many exciting avenues. With currently over 150 known nucleoside alterations, detection and quantification methods must encompass multiple modifications for a comprehensive profile. LC-MS/MS approaches offer a perspective for comprehensive parallel quantification of all the various modifications found in total RNA of a given organism. By feeding (13)C-glucose as sole carbon source, we have generated a stable isotope-labeled internal standard (SIL-IS) for bacterial RNA, which facilitates relative comparison of all modifications. While conventional SIL-IS approaches require the chemical synthesis of single modifications in weighable quantities, this SIL-IS consists of a nucleoside mixture covering all detectable RNA modifications of Escherichia coli, yet in small and initially unknown quantities. For absolute in addition to relative quantification, those quantities were determined by a combination of external calibration and sample spiking of the biosynthetic SIL-IS. For each nucleoside, we thus obtained a very robust relative response factor, which permits direct conversion of the MS signal to absolute amounts of substance. The application of the validated SIL-IS allowed highly precise quantification with standard deviations <2% during a 12-week period, and a linear dynamic range that was extended by two orders of magnitude. PMID:25129236

Kellner, Stefanie; Ochel, Antonia; Thüring, Kathrin; Spenkuch, Felix; Neumann, Jennifer; Sharma, Sunny; Entian, Karl-Dieter; Schneider, Dirk; Helm, Mark

2015-02-01

328

Jasminum flexile flower absolute from India--a detailed comparison with three other jasmine absolutes.  

PubMed

Jasminum flexile flower absolute from the south of India and the corresponding vacuum headspace (VHS) sample of the absolute were analyzed using GC and GC-MS. Three other commercially available Indian jasmine absolutes from the species: J. sambac, J. officinale subsp. grandiflorum, and J. auriculatum and the respective VHS samples were used for comparison purposes. One hundred and twenty-one compounds were characterized in J. flexile flower absolute, with methyl linolate, benzyl salicylate, benzyl benzoate, (2E,6E)-farnesol, and benzyl acetate as the main constituents. A detailed olfactory evaluation was also performed. PMID:19831037

Braun, Norbert A; Kohlenberg, Birgit; Sim, Sherina; Meier, Manfred; Hammerschmidt, Franz-Josef

2009-09-01

329

Quinap and congeners: atropos PN ligands for asymmetric catalysis.  

PubMed

Among the range of P,N-chelating ligands that have been employed in asymmetric catalysis, those relying on atropisomerism for the stability of individual enantiomers form a definable class. These APN (atropos P,N) ligands require a specific type of biaryl, with one component carrying a pendant phosphine unit, most commonly diaryl substituted, and the other bearing an sp(2)-nitrogen adjacent to the biaryl link. When substituents in the biaryl inhibit rotation about the linking bond, stable nonracemizing six-membered ring chelates can be formed. This Perspective relates the background to the initial synthesis in 1993 of Quinap, the original member of the series, and initial observations on its effectiveness in asymmetric catalysis. The current state of play in development of syntheses of this and other members of the APN ligand family is assessed, and their applications in asymmetric catalysis are presented. These include hydroboration and diboration of alkenes, 1,3-dipolar cycloadditions, alkynylation of iminium salts in a three-component (A(3)) condensation, and conjugate additions of Cu acetylides. PMID:24806741

Fernández, Elena; Guiry, Patrick J; Connole, Kieran P T; Brown, John M

2014-06-20

330

Mechanistic insights on cooperative asymmetric multicatalysis using chiral counterions.  

PubMed

Cooperative multicatalytic methods are steadily gaining popularity in asymmetric catalysis. The use of chiral Brønsted acids such as phosphoric acids in conjunction with a range of transition metals has been proven to be effective in asymmetric synthesis. However, the lack of molecular-level understanding and the accompanying ambiguity on the role of the chiral species in stereoinduction continues to remain an unresolved puzzle. Herein, we intend to disclose some novel transition state models obtained through DFT(B3LYP and M06) computations for a quintessential reaction in this family, namely, palladium-catalyzed asymmetric Tsuji-Trost allylation of aldehydes. The aldehyde is activated as an enamine by the action of a secondary amine (organocatalysis), which then adds to an activated Pd-allylic species (transition metal catalysis) generated through the protonation of allyic alcohol by chiral BINOL-phosphoric acid (Brønsted acid catalysis). We aim to decipher the nature of chiral BINOL-phosphates and their role in creating a quaternary chiral carbon atom in this triple catalytic system. The study reports the first transition state model capable of rationalizing chiral counterion-induced enantioselectivity. It is found that the chiral phosphate acts as a counterion in the stereocontrolling event rather than the conventional ligand mode. PMID:25050786

Jindal, Garima; Sunoj, Raghavan B

2014-08-15

331

Tandem Reactions for Streamlining Synthesis  

PubMed Central

CONSPECTUS In 1980 Sharpless and Katsuki introduced the asymmetric epoxidation of prochiral allylic alcohols (the Sharpless-Katsuki Asymmetric Epoxidation), which enabled the rapid synthesis of highly enantioenriched epoxy alcohols. This reaction was a milestone in the development of asymmetric catalysis because it was the first highly enantioselective oxidation reaction. Furthermore, it provided access to enantioenriched allylic alcohols that are now standard starting materials in natural product synthesis. In 1981 Sharpless and coworkers made another seminal contribution by describing the kinetic resolution (KR) of racemic allylic alcohols. This work demonstrated that small-molecule catalysts could compete with enzymatic catalysts in KRs. For these pioneering works, Sharpless was awarded the 2001 Nobel Prize with Knowles and Noyori. Despite these achievements, the Sharpless KR is not an efficient method to prepare epoxy alcohols with high enantiomeric excess (ee). First, the racemic allylic alcohol must be prepared and purified. KR of the racemic allylic alcohol must be stopped at low conversion, because the ee of the product epoxy alcohol decreases as the KR progresses. Thus, better methods to prepare epoxy alcohols containing stereogenic carbinol carbons are needed. This Account summarizes our efforts to develop one-pot methods for the synthesis of various epoxy alcohols and allylic epoxy alcohols with high enantio-, diastereo-, and chemoselectivity. Our laboratory developed titanium-based catalysts for use in the synthesis of epoxy alcohols with tertiary carbinols. The catalysts are involved in the first step, which is an asymmetric alkyl or allyl addition to enones. The resulting intermediates are then subjected to a titanium-directed diastereoselective epoxidation to provide tertiary epoxy alcohols. Similarly, the synthesis of acyclic epoxy alcohols begins with asymmetric additions to enals and subsequent epoxidation. The methods described here enable the synthesis of skeletally diverse epoxy alcohols. PMID:18710197

HUSSAIN, MAHMUD M.; WALSH, PATRICK J.

2009-01-01

332

Asymmetric gold nanoparticle reduction into polydimethylsiloxane thin films  

NASA Astrophysics Data System (ADS)

Polymer thin films embedded with plasmonic gold nanoparticles (AuNPs) are of significant interest in biomedicine, optics, photovoltaic, and nanoelectromechanical systems. Thin polydimethylsiloxane (PDMS) films containing 3-7 micron layers of AuNPs that were fabricated with a novel diffusive-reduction synthesis technique attenuated up to 85% of incoming laser light at the plasmon resonance. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior optothermal capabilities relative to thicker films in which AuNPs were reduced throughout. A photonto- heat conversion of up to 3000°C/watt was demonstrated, which represents a 3-230-fold increase over previous AuNPfunctionalized systems. Optical attenuation and thermal response increased in proportion to order of magnitude increases in tetrachloroaurate (TCA) solution concentration. Optical and thermoplasmonic responses were observed with and without an adjacent mesh support, which increased attenuation but decreased thermal response. Morphological, optical, and thermoplasmonic properties of asymmetric AuNP-PDMS films varied significantly with diffusive TCA concentration. Gold nanoparticles, networks, and conglomerates were formed via reduction as the amount of dissolved TCA increased across a log10-scale. Increasing TCA concentrations caused polymer surface cratering, leading to a larger effective surface area. This method, utilizing the diffusion of TCA into a single exposed partially cured PDMS interface, could be used to replace expensive lithographic or solution synthesis of plasmon-functionalized systems.

Dunklin, Jeremy R.; Forcherio, Gregory T.; Berry, Keith R.; Roper, D. Keith

2014-09-01

333

Signalling problem in absolutely unstable systems  

NASA Astrophysics Data System (ADS)

The dynamics of unstable systems crucially depends on the nature of the instability, either convective or absolute. The signalling problem, which is the study of the spatial response to a localized time-harmonic forcing, is generally believed to be relevant only for stable or convectively unstable systems and to be ill-posed for absolutely unstable systems, where the self-sustained perturbations grow faster than the forced harmonic response. The present investigation shows that the signalling problem may still be well posed for media displaying absolutely unstable regions. Considering weakly spatially inhomogenous systems, conditions are derived for the validity of the signalling problem. The complete spatial response to harmonic forcing is first analytically derived in terms of asymptotic approximations and then confirmed by direct numerical simulations.

Pier, Benoît

2011-06-01

334

Absolute Zero: Community Education Outreach Guide  

NSDL National Science Digital Library

This guide provides curricular resources for study of the history and science of the quest for ever colder temperature. Designed for teachers and informal educators of middle school students. this guide offers hands-on demonstrations, questions to encourage student participation, suggestions for class activities, and ways to encourage students to continue studying the science. Topics include low-temperature physics and the impact of technologies such as air conditioning, refrigeration and liquefied gases. This material is related to a two-part public broadcasting special, Absolute Zero, produced by Meridian Productions and Windfall Films. Absolute Zero is underwritten by the National Science Foundation and the Alfred P. Sloan Foundation and is based largely on Tom Shachtmanâs acclaimed book, Absolute Zero and the Conquest of Cold.

2008-09-18

335

Absolute Photoacoustic Thermometry in Deep Tissue  

PubMed Central

Photoacoustic (PA) thermography is a promising tool for temperature measurement in deep tissue. Here, we propose an absolute temperature measurement method based on the dual temperature dependences of the Grüneisen parameter and the speed of sound in tissue. By taking ratiometric measurements at two adjacent temperatures, we can eliminate the factors that are temperature irrelevant but difficult to correct for in deep tissue. To validate our method, absolute temperatures of blood-filled tubes embedded ~9 mm deep in chicken tissue were measured in a biologically relevant range from 28 °C to 46 °C. The temperature measurement accuracy was ~0.6 °C. The results suggest that our method can be potentially used for absolute temperature monitoring in deep tissue during thermotherapy. PMID:24322224

Tai, Stephen; Zhou, Yong; Wang, Lihong V.

2013-01-01

336

Absolute photoacoustic thermometry in deep tissue.  

PubMed

Photoacoustic thermography is a promising tool for temperature measurement in deep tissue. Here we propose an absolute temperature measurement method based on the dual temperature dependences of the Grüneisen parameter and the speed of sound in tissue. By taking ratiometric measurements at two adjacent temperatures, we can eliminate the factors that are temperature irrelevant but difficult to correct for in deep tissue. To validate our method, absolute temperatures of blood-filled tubes embedded ~9 mm deep in chicken tissue were measured in a biologically relevant range from 28°C to 46°C. The temperature measurement accuracy was ~0.6°C. The results suggest that our method can be potentially used for absolute temperature monitoring in deep tissue during thermotherapy. PMID:24322224

Yao, Junjie; Ke, Haixin; Tai, Stephen; Zhou, Yong; Wang, Lihong V

2013-12-15

337

Absolute distance metrology for space interferometers  

NASA Astrophysics Data System (ADS)

Space interferometers consisting of several free flying telescopes, such as the planned Darwin mission, require a complex metrology system to make all the components operate as a single instrument. Our research focuses on one of its sub-systems that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy would be in the order of 10 µm over 250 meter. To measure this absolute distance, we are currently exploring the frequency sweeping interferometry technique. Its measurement principle is to first measure a phase in the interferometer, sweep a tunable laser over a known frequency interval and finally measure a second phase. By also counting the number of fringes during the sweep it is possible to determine the absolute path length difference without ambiguities. The wavelength at the endpoints of the sweep is stabilized on a Fabry-Perot cavity. In this way the unknown distance is directly referenced to the length of the Fabry-Perot cavity.

Swinkels, Bas L.; Wendrich, Thijs J.; Bhattacharya, Nandini; Wielders, Arno A.; Braat, Joseph J.

2004-09-01

338

Precise Measurement of the Absolute Fluorescence Yield  

SciTech Connect

We present preliminary results of the absolute yield of fluorescence emission in atmospheric gases. Measurements were performed at the Fermilab Test Beam Facility with a variety of beam particles and gases. Absolute calibration of the fluorescence yield to 5% level was achieved by comparison with two known light sources - the Cherenkov light emitted by the beam particles, and a calibrated nitrogen laser. The uncertainty of the energy scale of current Ultra-High Energy Cosmic Rays experiments will be significantly improved by the AIRFLY measurement.

Ave, M.; Daumiller, K.; Keilhauer, B.; Klages, H.; Salamida, F.; Smida, R. [Karlsruhe Institute of Technology, IK, Postfach 6980, D - 76021 Karlsruhe (Germany); Bohacova, M.; Nozka, L.; Palatka, M.; Ridky, J.; Schovanek, P. [Institute of Physics of the Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Praha 8 (Czech Republic); Di Carlo, P.; Iarlori, M.; Petrera, S.; Rizi, V. [Dipartimento di Fisica dell'Universita de l'Aquila and INFN, Via Vetoio, I-67010 Coppito, Aquila (Italy); Di Giulio, C.; Verzi, V. [Dipartimento di Fisica dell'Universita di Roma Tor Vergata and Sezione INFN, Via della Ricerca Scientifica, I-00133 Roma (Italy); San Luis, P. Facal; Monasor, M.; Privitera, P. [University of Chicago, Enrico Fermi Institute and Kavli Institute for Cosmological Physics, 5640 S. Ellis Ave., Chicago, IL 60637 (United States)

2011-09-22

339

Absolute measurement of hyperspectral and angular reflection.  

PubMed

A new instrument for absolute measurement of hyperspectral and angular reflection is presented. The instrument determines absolute values of angular reflection quantities in a wavelength range from 380 to 780 nm with a 3 nm spectral resolution by using a white source and a CCD-based spectroradiometer. Through uncertainty evaluation, the measurement uncertainty is determined as 1.4%-2.9% (k=2) for white diffuse material of Spectralon. The gonioreflectometric determination and an integrating-sphere-based reflection measurement traceable to KRISS spectral reflectance scale are compared by determining hemispherical reflectance, which results in agreement in their uncertainties. PMID:25322100

Hwang, Jisoo

2014-09-20

340

LG tools for asymmetric wargaming  

NASA Astrophysics Data System (ADS)

Asymmetric operations represent conflict where one of the sides would apply military power to influence the political and civil environment, to facilitate diplomacy, and to interrupt specified illegal activities. This is a special type of conflict where the participants do not initiate full-scale war. Instead, the sides may be engaged in a limited open conflict or one or several sides may covertly engage another side using unconventional or less conventional methods of engagement. They may include peace operations, combating terrorism, counterdrug operations, arms control, support of insurgencies or counterinsurgencies, show of force. An asymmetric conflict can be represented as several concurrent interlinked games of various kinds: military, transportation, economic, political, etc. Thus, various actions of peace violators, terrorists, drug traffickers, etc., can be expressed via moves in different interlinked games. LG tools allow us to fully capture the specificity of asymmetric conflicts employing the major LG concept of hypergame. Hypergame allows modeling concurrent interlinked processes taking place in geographically remote locations at different levels of resolution and time scale. For example, it allows us to model an antiterrorist operation taking place simultaneously in a number of countries around the globe and involving wide range of entities from individuals to combat units to governments. Additionally, LG allows us to model all sides of the conflict at their level of sophistication. Intelligent stakeholders are represented by means of LG generated intelligent strategies. TO generate those strategies, in addition to its own mathematical intelligence, the LG algorithm may incorporate the intelligence of the top-level experts in the respective problem domains. LG models the individual differences between intelligent stakeholders. The LG tools make it possible to incorporate most of the known traits of a stakeholder, i.e., real personalities involved in the conflict with their specific individual style.

Stilman, Boris; Yakhnis, Alex; Yakhnis, Vladimir

2002-07-01

341

Pacific trench motions controlled by the asymmetric plate configuration  

NASA Astrophysics Data System (ADS)

We present a novel explanation for absolute trench-normal motions of slabs surrounding the Pacific. Rapid subduction-zone retreat on the eastern side of the Pacific and slow advance in the west can result from the large-scale asymmetric plate configuration. We use simple fluid dynamics to explain the mechanical background of this hypothesis, and we use the results of a simple finite difference scheme to estimate the effect on trench motion velocities. The hypothesis is based on two key assumptions. First, we follow the concept of plate-scale horizontal counterflow in the asthenosphere driven by accretion of asthenosphere into lithosphere and by plate motion. Second, we assume that horizontally wide slabs without large slab windows drift passively in the mantle flow field and do not retreat as a result of flow around the slab. If the asthenosphere transfers flow-related horizontal shear stress into deeper levels of the mantle, an asymmetry in the plate configuration leads to different net pressure forces on the two slabs and thus affects the retreat behavior. In an ocean with an asymmetric ridge position, the slab of the smaller plate should retreat faster than the slab of the large plate, which may even advance. Also, the domain of a slower moving plate should collapse faster than the domain of the faster plate. Our model explains the counterintuitive negative correlation between slab age and retreat velocity observed in the Pacific. It also accords with the topographic asymmetry of the ridge flanks along the Pacific rise.

Nagel, Thorsten J.; Ryan, William B. F.; Malinverno, Alberto; Buck, W. Roger

2008-06-01

342

Symmetric mortality and asymmetric suicide cycles.  

PubMed

In this investigation, tests were performed to determine whether mortality cycles are asymmetric. Results from an asymmetry test of U.S. time-series data from 1951 to 2005 provide no evidence that all-cause mortality or mortality caused by disease causes asymmetric cycles. However, the rate of fatalities from suicide exhibits the pattern of an asymmetric cycle. The evidence for asymmetric suicide cycles is statistically significant for men and working-age groups but not for women and non-working-age groups. PMID:20378221

Wu, Wen-Chieh; Cheng, Hui-Pei

2010-06-01

343

PROJECTIVE GROUP STRUCTURES AS ABSOLUTE GALOIS STRUCTURES  

E-print Network

PROJECTIVE GROUP STRUCTURES AS ABSOLUTE GALOIS STRUCTURES WITH BLOCK APPROXIMATION # by Dan Haran Bonn, Germany e­mail: pop@math.uni­bonn.de Abstract. A proper profinite group structure G is projective of a cover to a cartesian square . . . . . . . . . . . . . . . 19 4. Projective group structures

Pop, Florian

344

Absolute Points for Multiple Assignment Problems  

ERIC Educational Resources Information Center

An algorithm is presented to solve multiple assignment problems in which a cost is incurred only when an assignment is made at a given cell. The proposed method recursively searches for single/group absolute points to identify cells that must be loaded in any optimal solution. Unlike other methods, the first solution is the optimal solution. The…

Adlakha, V.; Kowalski, K.

2006-01-01

345

HARDCOVER JACKET COPY--FLAPS Absolutely Small  

E-print Network

salt dissolve in water, while oil does not, and much more "There are a few books that I always keep Michael D. Fayer, Ph.D. Our intuition about how things should behave is usually right in the everyday, Absolutely Small develops your intuition for the nature of things at their smallest and most intriguing level

Fayer, Michael D.

346

High-accuracy absolute distance metrology Proefschrift  

E-print Network

High-accuracy absolute distance metrology Proefschrift ter verkrijging van de graad van doctor aan-ray telescopes and synthetic aperture telescopes. For most of these, a metrology system that measures with a complex metrology system that monitors all the distances, angles and velocities in the system

347

Absolute Irreducibility of Polynomials via Newton Polytopes  

Microsoft Academic Search

A multivariable polynomial is associated with a polytope, called its Newton polytope. A polynomial is absolutely irreducible if its Newton polytope is indecomposable in the sense of Minkowski sum of polytopes. Two general constructions of indecomposable polytopes are given, and they give many simple irreducibility criteria including the well-known Eisenstein criterion. Polynomials from these criteria are over any field and

Shuhong Gao

2001-01-01

348

ASYMMETRIC SOLAR POLAR FIELD REVERSALS  

SciTech Connect

The solar polar fields reverse because magnetic flux from decaying sunspots moves toward the poles, with a preponderance of flux from the trailing spots. If there is a strong asymmetry, in the sense that most activity is in the northern hemisphere, then that excess flux will move toward the north pole and reverse that pole first. If there is more activity in the south later on, then that flux will help to reverse the south pole. In this way, two humps in the solar activity and a corresponding difference in the time of reversals develop (in the ideal case). Such a difference was originally noted in the very first observation of polar field reversal just after the maximum of the strongly asymmetric solar cycle 19, when the southern hemisphere was most active before sunspot maximum and the south pole duly reversed first, followed by the northern hemisphere more than a year later, when that hemisphere became most active. Solar cycles since then have had the opposite asymmetry, with the northern hemisphere being most active before solar maximum. We show that polar field reversals for these cycles have all happened in the north first, as expected. This is especially noteworthy for the present solar cycle 24. We suggest that the association of two or more peaks of solar activity when separated by hemispheres with correspondingly different times of polar field reversals is a general feature of the cycle, and that asymmetric polar field reversals are simply a consequence of the asymmetry of solar activity.

Svalgaard, Leif [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)] [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Kamide, Yohsuke, E-mail: leif@leif.org [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi (Japan)] [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi (Japan)

2013-01-20

349

Active Matter on Asymmetric Substrates  

E-print Network

For collections of particles in a thermal bath interacting with an asymmetric substrate, it is possible for a ratchet effect to occur where the particles undergo a net dc motion in response to an ac forcing. Ratchet effects have been demonstrated in a variety of systems including colloids as well as magnetic vortices in type-II superconductors. Here we examine the case of active matter or self-driven particles interacting with asymmetric substrates. Active matter systems include self-motile colloidal particles undergoing catalysis, swimming bacteria, artificial swimmers, crawling cells, and motor proteins. We show that a ratchet effect can arise in this type of system even in the absence of ac forcing. The directed motion occurs for certain particle-substrate interaction rules and its magnitude depends on the amount of time the particles spend swimming in one direction before turning and swimming in a new direction. For strictly Brownian particles there is no ratchet effect. If the particles reflect off the barriers or scatter from the barriers according to Snell's law there is no ratchet effect; however, if the particles can align with the barriers or move along the barriers, directed motion arises. We also find that under certain motion rules, particles accumulate along the walls of the container in agreement with experiment. We also examine pattern formation for synchronized particle motion. We discuss possible applications of this system for self-assembly, extracting work, and sorting as well as future directions such as considering collective interactions and flocking models.

C. J. Olson Reichhardt; J. Drocco; T. Mai; M. B. Wan; C. Reichhardt

2011-07-20

350

Asymmetric growth in polyelectrolyte multilayers.  

PubMed

Radioactive counterions were used to track the ratio of positive to negative polymer repeat units within a polyelectrolyte multilayer made from poly(diallyldimethylammonium chloride), PDADMAC, and poly(styrene sulfonate), PSS. For this widely employed pair of "linearly" assembled polyelectrolytes it was found that the accepted model of charge overcompensation for each layer is incorrect. In fact, overcompensation at the surface occurs only on the addition of the polycation, whereas PSS merely compensates the PDADMAC. After the assembly of about a dozen layers, excess positive sites begin to accrue in the multilayer. Treating the surface as a reaction-diffusion region for pairing of polymer charges, a model profile was constructed. It is shown that different reaction-diffusion ranges of positive and negative polyelectrolyte charge lead to a blanket of glassy, stoichiometric complex growing on top of a layer of rubbery, PDADMAC-rich complex. Though overcompensation and growth was highly asymmetric with respect to the layer number, entirely conventional "linear" assembly of the multilayer was observed. The impact of asymmetric growth on various properties of multilayers is discussed. PMID:23672490

Ghostine, Ramy A; Markarian, Marie Z; Schlenoff, Joseph B

2013-05-22

351

Scatterometry measurement of asymmetric gratings  

NASA Astrophysics Data System (ADS)

Scatterometry has been used extensively for the characterization of critical dimensions (CD) and detailed sidewall profiles of periodic structures in microelectronics fabrication processes. So far the majority of applications are for symmetric gratings. In most cases devices are designed to be symmetric although errors could occur during fabrication process and result in undesired asymmetry. The problem with conventional optical scatterometry techniques lies in the lack of capability to distinguish between left and right asymmetries. In this work we investigate the possibility of measuring grating asymmetry using Mueller matrix spectroscopic ellipsometry (MM-SE). A patterned hard disk prepared by nano-imprint technique is used for the study. The relief image on the disk sometimes has asymmetrical sidewall profile, presumably due to the uneven separation of the template from the disk. The undesired tilting resist profile causes difficulties to the downstream processes or even makes them fail. Cross-section SEM reveals that the asymmetrical resist lines are typically tilted towards the outer diameter direction. The simulation and experimental data show that certain Mueller matrix elements are proportional to the direction and amplitude of profile asymmetry, providing a direct indication to the sidewall tilting. The tilting parameter can be extracted using rigorous optical critical dimension (OCD) modeling or calibration method. We demonstrate that this technique has good sensitivity for measuring and distinguishing left and right asymmetry caused by sidewall tilting, and can therefore be used for monitoring processes, such as lithography and etch processing, for which symmetric structures are desired.

Li, Jie; Hwu, Justin J.; Liu, Yongdong; Rabello, Silvio; Liu, Zhuan; Hu, Jiangtao

2009-12-01

352

Geometry-induced asymmetric diffusion  

E-print Network

Past work has shown that ions can pass through a membrane more readily in one direction than the other. We demonstrate here in a model and an experiment that for a mixture of small and large particles such asymmetric diffusion can arise solely from an asymmetry in the geometry of the pores of the membrane. Our deterministic simulation considers a two-dimensional gas of elastic disks of two sizes diffusing through a membrane, and our laboratory experiment examines the diffusion of glass beads of two sizes through a metal membrane. In both experiment and simulation, the membrane is permeable only to the smaller particles, and the asymmetric pores lead to an asymmetry in the diffusion rates of these particles. The presence of even a small percentage of large particles can clog a membrane, preventing passage of the small particles in one direction while permitting free flow of the small particles in the other direction. The purely geometric kinetic constraints may play a role in common biological contexts such as membrane ion channels.

Robert S. Shaw; Norman Packard; Matthias Schröter; Harry L. Swinney

2007-04-28

353

Asymmetrical membranes and surface tension.  

PubMed Central

The (31)P-nuclear magnetic resonance chemical shift of phosphatidic acid in a membrane is sensitive to the lipid head group packing and can report qualitatively on membrane lateral compression near the aqueous interface. We have used high-resolution (31)P-nuclear magnetic resonance to evaluate the lateral compression on each side of asymmetrical lipid vesicles. When monooleoylphosphatidylcholine was added to the external monolayer of sonicated vesicles containing dioleoylphosphatidylcholine and dioleoylphosphatidic acid, the variation of (31)P chemical shift of phosphatidic acid indicated a lateral compression in the external monolayer. Simultaneously, a slight dilation was observed in the inner monolayer. In large unilamellar vesicles on the other hand the lateral pressure increased in both monolayers after asymmetrical insertion of monooleoylphosphatidylcholine. This can be explained by assuming that when monooleoylphosphatidylcholine is added to large unilamellar vesicles, the membrane bends until the strain is the same in both monolayers. In the case of sonicated vesicles, a change of curvature is not possible, and therefore differential packing in the two layers remains. We infer that a variation of lipid asymmetry by generating a lateral strain in the membrane can be a physiological way of modulating the conformation of membrane proteins. PMID:12202370

Traikia, Mounir; Warschawski, Dror E; Lambert, Olivier; Rigaud, Jean-Louis; Devaux, Philippe F

2002-01-01

354

Asymmetric low back loading in asymmetric lifting movements is not prevented by pelvic twist  

Microsoft Academic Search

Asymmetric lifting is associated with an increased risk of low back disorders. Especially in lifting movements, characterized by a small amount of asymmetry, it is still the question if asymmetric lumbosacral torques occur, or if subjects try to avoid asymmetric back loading by twisting their pelvis with respect to the feet. An increase of the lifting speed or the box

Idsart Kingma; Jaap H van Dieën; Michiel de Looze; Huub M Toussaint; Patricia Dolan; Chris T. M Baten

1998-01-01

355

Multipartite asymmetric quantum cloning S. Iblisdir,1  

E-print Network

Multipartite asymmetric quantum cloning S. Iblisdir,1 A. Acín,2 N. J. Cerf,3 R. Filip,4 J. Fiurásek in asymmetric settings. We introduce cloning transformations that take N identical replicas of a pure state in any dimension as input and yield a collection of clones with nonidentical fidelities. As an example

Cerf, Nicolas

356

Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach.  

PubMed

Ball-milling and pestle and mortar grinding have emerged as powerful methods for the development of environmentally benign chemical transformations. Recently, the use of these mechanochemical techniques in asymmetric organocatalysis has increased. This review highlights the progress in asymmetric organocatalytic reactions assisted by mechanochemical techniques. PMID:23243475

Chauhan, Pankaj; Chimni, Swapandeep Singh

2012-01-01

357

Defect-free ultrahigh flux asymmetric membranes  

DOEpatents

Defect-free, ultrahigh flux integrally-skinned asymmetric membranes having extremely thin surface layers (<0.2 .mu.m) comprised of glassy polymers are disclosed. The membranes are formed by casting an appropriate drope followed by forced convective evaporation of solvent to obtain a dry phase separated asymmetrical structure. The structure is then washed in a precipitation liquid and dried.

Pinnau, Ingo (Austin, TX); Koros, William J. (Austin, TX)

1990-01-01

358

Directing cell migration with asymmetric micropatterns  

E-print Network

Directing cell migration with asymmetric micropatterns Xingyu Jiang*, Derek A. Bruzewicz*, Amy P This report shows that the direction of polarization of attached mammalian cells determines the direction constrain individual cells to asymmetric geometries (for example, a teardrop); these geometries polarize

Prentiss, Mara

359

Asymmetric Reaction Functions for the Euro Area  

Microsoft Academic Search

This paper offers a preliminary evaluation of ECB conduct of monetary policy by estimating a fairly general reaction function for the euro area. The specification of the policy rule embodies a number of nonlinearities which are shown to stem from asymmetric preferences and a convex aggregate supply curve. Asymmetric preferences allow, but do not require, policy-makers to weight differently positive

Paolo Surico

2003-01-01

360

Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach  

PubMed Central

Summary Ball-milling and pestle and mortar grinding have emerged as powerful methods for the development of environmentally benign chemical transformations. Recently, the use of these mechanochemical techniques in asymmetric organocatalysis has increased. This review highlights the progress in asymmetric organocatalytic reactions assisted by mechanochemical techniques. PMID:23243475

Chauhan, Pankaj

2012-01-01

361

A stereoselective switch: enantiodivergent approach to the synthesis of isoflavanones.  

PubMed

A modular six-step asymmetric synthesis of two naturally occurring and three non-natural isoflavanones containing tertiary ?-aryl carbonyls is reported. This synthetic route, utilising a Pd-catalyzed decarboxylative asymmetric protonation, produces isoflavanones in excellent enantioselectivities from 76-97?%. A switch in the sense of stereoinduction was observed when different H(+) sources were employed, showing the first example of dual stereocontrol in an asymmetric protonation reaction. The first enantioselective synthesis of the naturally occurring isoflavanones sativanone and 3-o-methylviolanone has been accomplished. PMID:25314579

Doran, Robert; Carroll, Michael P; Akula, Ramulu; Hogan, Bryan F; Martins, Marta; Fanning, Séamus; Guiry, Patrick J

2014-11-17

362

Designing asymmetric multiferroics with strong magnetoelectric coupling  

NASA Astrophysics Data System (ADS)

Multiferroics offer exciting opportunities for electric-field control of magnetism. Single-phase multiferroics suitable for such applications at room temperature need much more study. Here, we propose the concept of an alternative type of multiferroics, namely, the "asymmetric multiferroic." In asymmetric multiferroics, two locally stable ferroelectric states are not symmetrically equivalent, leading to different magnetic properties between these two states. Furthermore, we predict from first principles that a Fe-Cr-Mo superlattice with the LiNbO3-type structure is such an asymmetric multiferroic. The strong ferrimagnetism, high ferroelectric polarization, and significant dependence of the magnetic transition temperature on polarization make this asymmetric multiferroic an ideal candidate for realizing electric-field control of magnetism at room temperature. Our study suggests that the asymmetric multiferroic may provide an alternative playground for voltage control of magnetism and find its applications in spintronics and quantum computing.

Lu, X. Z.; Xiang, H. J.

2014-09-01

363

Asymmetric vanadium catalyzed sulfide oxidation  

SciTech Connect

A vanadium based catalyst for the enantioselective sulfide oxidation was developed. In a very convenient procedure sulfides 1 can be enantioselectively oxidized to the corresponding optically active sulfoxides 2 with less than 0.1 mol% catalyst and hydrogen peroxide as oxygen source. The structure of ligand 3 was varied and special characteristics of the catalyst system were investigated. An important factor for good asymmetric induction is the primary hydroxyl group in 3. With other donors at this position, such as NHCOR, NHTs or carboxylate, racemic sulfoxides or products with moderate enantioselectivities were obtained. Another interesting feature is the ligand accelerated catalysis observed in this reaction. The current state of development and results of the oxidation of various substrates will be presented.

Bienewald, F.; Bolm, C. [Univ. of Marburg (Germany)

1995-12-31

364

Recent Developments in Asymmetric Catalysis  

NASA Astrophysics Data System (ADS)

The field of gold catalysis has experienced exponential expansion within the last 15 years [1]. The majority of gold-catalyzed reactions rely on the activation of carbon-carbon ?-bonds enhancing the electrophilicity of the unsaturated moiety and therefore favoring nucleophilic additions to the carbon-carbon bond. Rare examples employing the activation of a nucleophilic derivative have been reported. The enantioselective transformations employing gold catalysts have appeared only recently and rely mainly on gold(I) linear chiral complexes, which make the control of stereogenic centers much more difficult [2]. This situation therefore slowed the expansion of the field and made it difficult to generalize chiral systems. This chapter intends to present the seminal examples related to asymmetric catalysis focusing exclusively on the use of a chiral catalyst [3]…

Toullec, Patrick Y.; Pradal, Alexandre; Michelet, Véronique

2014-04-01

365

Absolute calibration of TFTR helium proportional countersa)  

NASA Astrophysics Data System (ADS)

The TFTR helium proportional counters are located in the central five (5) channels of the TFTR multichannel neutron collimator. These detectors were absolutely calibrated using a 14 MeV neutron generator positioned at the horizontal midplane of the TFTR vacuum vessel. The neutron generator position was scanned in centimeter steps to determine the collimator aperture width to 14 MeV neutrons and the absolute sensitivity of each channel. Neutron profiles were measured for TFTR plasmas with time resolution between 5 and 50 ms depending upon count rates. The He detectors were used to measure the burnup of 1 MeV tritons in deuterium plasmas, the transport of tritium in trace tritium experiments, and the residual tritium levels in plasmas following 50:50 DT experiments.

Strachan, J. D.; Barnes, Cris W.; Diesso, M.; Jassby, D.; Johnson, L.; Loughlin, M.; McCauley, S.; Munsat, T.; Roquemore, A. L.

1995-02-01

366

Absolute-magnitude Distributions of Supernovae  

NASA Astrophysics Data System (ADS)

The absolute-magnitude distributions of seven supernova (SN) types are presented. The data used here were primarily taken from the Asiago Supernova Catalogue, but were supplemented with additional data. We accounted for both foreground and host-galaxy extinction. A bootstrap method is used to correct the samples for Malmquist bias. Separately, we generate volume-limited samples, restricted to events within 100 Mpc. We find that the superluminous events (MB < -21) make up only about 0.1% of all SNe in the bias-corrected sample. The subluminous events (MB > -15) make up about 3%. The normal Ia distribution was the brightest with a mean absolute blue magnitude of -19.25. The IIP distribution was the dimmest at -16.75.

Richardson, Dean; Jenkins, Robert L., III; Wright, John; Maddox, Larry

2014-05-01

367

An absolute measure for a key currency  

NASA Astrophysics Data System (ADS)

It is generally considered that the US dollar and the euro are the key currencies in the world and in Europe, respectively. However, there is no absolute general measure for a key currency. Here, we investigate the 24-hour periodicity of foreign exchange markets using a recurrence plot, and define an absolute measure for a key currency based on the strength of the periodicity. Moreover, we analyze the time evolution of this measure. The results show that the credibility of the US dollar has not decreased significantly since the Lehman shock, when the Lehman Brothers bankrupted and influenced the economic markets, and has increased even relatively better than that of the euro and that of the Japanese yen.

Oya, Shunsuke; Aihara, Kazuyuki; Hirata, Yoshito

368

A Global Approach to Absolute Parallelism Geometry  

NASA Astrophysics Data System (ADS)

In this paper we provide a global investigation of the geometry of parallelizable manifolds (or absolute parallelism geometry) frequently used in applications. We discuss different linear connections and curvature tensors from a global point of view. We give an existence and uniqueness theorem for a remarkable linear connection, called the canonical connection. Different curvature tensors are expressed in a compact form in terms of the torsion tensor of the canonical connection only. Using the Bianchi identities, some interesting identities are derived. An important special fourth-order tensor, which we refer to as Wanas tensor, is globally defined and investigated. Finally a "double-view" for the fundamental geometric objects of an absolute parallelism space is established: The expressions of these geometric objects are computed in the parallelization basis and are compared with the corresponding local expressions in the natural basis. Physical aspects of some geometric objects considered are pointed out.

Youssef, Nabil L.; Elsayed, Waleed A.

2013-08-01

369

Absolute and relative dosimetry for ELIMED  

SciTech Connect

The definition of detectors, methods and procedures for the absolute and relative dosimetry of laser-driven proton beams is a crucial step toward the clinical use of this new kind of beams. Hence, one of the ELIMED task, will be the definition of procedures aiming to obtain an absolute dose measure at the end of the transport beamline with an accuracy as close as possible to the one required for clinical applications (i.e. of the order of 5% or less). Relative dosimetry procedures must be established, as well: they are necessary in order to determine and verify the beam dose distributions and to monitor the beam fluence and the energetic spectra during irradiations. Radiochromic films, CR39, Faraday Cup, Secondary Emission Monitor (SEM) and transmission ionization chamber will be considered, designed and studied in order to perform a fully dosimetric characterization of the ELIMED proton beam.

Cirrone, G. A. P.; Schillaci, F.; Scuderi, V. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic); Cuttone, G.; Candiano, G.; Musumarra, A.; Pisciotta, P.; Romano, F. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy); Carpinelli, M. [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy)] [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy); Leonora, E.; Randazzo, N. [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Presti, D. Lo [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Raffaele, L. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Tramontana, A. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Cirio, R.; Sacchi, R.; Monaco, V. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy); Marchetto, F.; Giordanengo, S. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)

2013-07-26

370

Absolute distance metrology for space interferometers  

NASA Astrophysics Data System (ADS)

Future space missions, among which the Darwin Space Interferometer, will consist of several free flying satellites. A complex metrology system is required to have all the components fly accurately in formation and have it operate as a single instrument. Our work focuses on a possible implementation of the sub-system that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy is on the order of 70 micrometer over a distance of 250 meter. We are exploring a technique called frequency sweeping interferometry, which involves interferometrically measuring a phase difference while sweeping the wavelength of a tunable laser. This phase difference is directly proportional to the absolute distance. A very high finesse Fabry-Perot cavity is used as a reference standard, to which the laser is locked at the end-points of the sweep. We will discuss our measurement scheme, our set-up and some first measurements.

Swinkels, Bas L.; Latoui, Abdelhalim; Bhattacharya, Nandini; Wielders, Arno A.; Braat, Joseph J. M.

2005-08-01

371

Absolute distance metrology for space interferometers  

NASA Astrophysics Data System (ADS)

Future space missions, among which the Darwin Space Interferometer, will consist of several free flying satellites. A complex metrology system is required to have all the components fly accurately in formation and have it operate as a single instrument. Our work focuses on a possible implementation of the sub-system that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy is on the order of 70 micrometer over a distance of 250 meter. We are exploring a technique called frequency sweeping interferometry, which involves interferometrically measuring a phase difference while sweeping the wavelength of a tunable laser. This phase difference is directly proportional to the absolute distance. A very high finesse Fabry-Perot cavity is used as a reference standard, to which the laser is locked end-points of the sweep. We will discuss the control system that drives the setup and show some first experimental results.

Swinkels, Bas L.; Bhattacharya, Nandini; Wielders, Arno A.; Braat, Joseph J. M.

2005-06-01

372

Improvement in Central Arterial Pressure Waveform during Hemodialysis Is Related to a Reduction in Asymmetric Dimethylarginine (ADMA) Levels  

Microsoft Academic Search

Background: Cardiovascular mortality is high in hemodialysis (HD) patients. Early arterial pressure wave reflections, reflecting arterial stiffness and the endogenous nitric oxide synthesis inhibitor asymmetric dimethylarginine (ADMA) levels predict mortality in HD patients. Therefore, we aimed to study changes in ADMA levels and central arterial pressure waveform during HD. Methods: Thirty-two chronic HD patients were studied before and after a

Inga Soveri; Lars Lind; Björn Wikström; Mihkel Zilmer; Kersti Zilmer; Bengt Fellström

2007-01-01

373

Redetermination and absolute configuration of pruniflorone M monohydrate  

PubMed Central

The title xanthone known as pruniflorone M (systematic name: (2R)-5,10-dihy­droxy-2-hy­droxy­methyl-1,1-dimethyl-1H-furo[2,3-c]xanthen-6-one), crystallized in a monohydrate form, C18H16O6·H2O. It was isolated from the green fruits of Cratoxylum formosum ssp. pruniflorum. The structure of the title compound has been reported previously [Boonnak et al. (2010 ?). Aust. J. Chem. 63, 1550–1556], but we report here the absolute configuration determined using Cu K? radiation. There are two crystallograpically independent mol­ecules in the asymmetric unit, which differ slightly in the bond angles. The hy­droxy­methyl substituents at position 2 of the furan rings of both pruniflorone M mol­ecules adopt R configurations. In both mol­ecules, the three rings of the xanthone skeleton are approximately coplanar, with an r.m.s. deviation of 0.0124?(2)?Å for one mol­ecule and 0.0289?(2)?Å for the other, and the furan ring adopts an envelope conformation. In the crystal, mol­ecules of pruniflorone M and water are linked into a two-dimensional network by O—H?O hydrogen bonds and weak C—H?O inter­actions. The crystal structure is further consolidated by ?–? inter­actions with centroid–centroid distances in the range 3.5987?(13)–3.7498?(14)?Å. Short C?C [3.378?(3)?Å] and O?O [2.918?(3)?Å] contacts are also observed. PMID:22090964

Fun, Hoong-Kun; Chantrapromma, Suchada; Boonnak, Nawong; Karalai, Chatchanok; Chantrapromma, Kan

2011-01-01

374

A stereodivergent strategy for the preparation of corynantheine and ipecac alkaloids, their epimers, and analogues: efficient total synthesis of (-)-dihydrocorynantheol, (-)-corynantheol, (-)-protoemetinol, (-)-corynantheal, (-)-protoemetine, and related natural and nonnatural compounds.  

PubMed

Here we present a general and common catalytic asymmetric strategy for the total and formal synthesis of a broad number of optically active natural products from the corynantheine and ipecac alkaloid families, for example, indolo[2,3-a]- and benzo[a]quinolizidines. Construction of the core alkaloid skeletons with the correct absolute and relative stereochemistry relies on an enantioselective and diastereodivergent one-pot cascade sequence followed by an additional diastereodivergent reaction step. This allows for enantio- and diastereoselective synthesis of three out of four possible epimers of the quinolizidine alkaloids that begin from common and easily accessible starting materials by using a common synthetic route. Focus has been made on excluding protecting groups and limiting isolation and purification of synthetic intermediates. This methodology is applied in the total synthesis of the natural products (-)-dihydrocorynantheol, (-)-hirsutinol, (-)-corynantheol, (-)-protometinol, (-)-dihydrocorynantheal, (-)-corynantheal, (-)-protoemetine, (-)-(15S)-hydroxydihydrocorynantheol, and an array of their nonnatural epimers. The potential of this strategy is also demonstrated in the synthesis of biologically interesting natural product analogues not accessible through synthetic elaboration of alkaloid precursors available from nature, for example, thieno[3,2-a]quinolizidine derivatives. We also report the formal synthesis of (+)-dihydrocorynantheine, (-)-emetine, (-)-cephaeline, (-)-tubulosine, and (-)-deoxytubulosine. PMID:22052788

Zhang, Wei; Bah, Juho; Wohlfarth, Andreas; Franzén, Johan

2011-12-01

375

Force on an Asymmetric Capacitor  

E-print Network

When a high voltage (~30 kV) is applied to a capacitor whose electrodes have different physical dimensions, the capacitor experiences a net force toward the smaller electrode (Biefeld-Brown effect). We have verified this effect by building four capacitors of different shapes. The effect may have applications to vehicle propulsion and dielectric pumps. We review the history of this effect briefly through the history of patents by Thomas Townsend Brown. At present, the physical basis for the Biefeld-Brown effect is not understood. The order of magnitude of the net force on the asymmetric capacitor is estimated assuming two different mechanisms of charge conduction between its electrodes: ballistic ionic wind and ionic drift. The calculations indicate that ionic wind is at least three orders of magnitude too small to explain the magnitude of the observed force on the capacitor. The ionic drift transport assumption leads to the correct order of magnitude for the force, however, it is difficult to see how ionic drift enters into the theory. Finally, we present a detailed thermodynamic treatment of the net force on an asymmetric capacitor. In the future, to understand this effect, a detailed theoretical model must be constructed that takes into account plasma effects: ionization of gas (or air) in the high electric field region, charge transport, and resulting dynamic forces on the electrodes. The next series of experiments should determine whether the effect occurs in vacuum, and a careful study should be carried out to determine the dependence of the observed force on gas pressure, gas species and applied voltage.

Thomas B. Bahder; Chris Fazi

2002-10-31

376

Absolute photoionization cross sections of atomic oxygen  

NASA Technical Reports Server (NTRS)

The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

Samson, J. A. R.; Pareek, P. N.

1985-01-01

377

Absolute photoionization cross sections of atomic oxygen  

NASA Technical Reports Server (NTRS)

The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

Samson, J. A. R.; Pareek, P. N.

1982-01-01

378

On absolute CM-periods, II  

Microsoft Academic Search

For a CM-fieldK, Shimura defined the period symbolpK by factorizing periods of abelian varieties with complex multiplication. We define the absolute period symbolgK using division values of the multiple gamma function and conjecture that pK coincides with gK up to the multiplication by algebraic numbers. Taking the action of Gal(Q Q) into account, we present a refined version of this

Hiroyuki Yoshida

1998-01-01

379

The absolute bioavailability of caffeine in man  

Microsoft Academic Search

The absolute bioavailability of orally administered caffeine was investigated in 10 healthy adult male volunteers, aged 18.8 to 30.0 years. The subjects were administered a 5 mg\\/kg dose of caffeine as either an aqueous oral solution or an intravenous infusion, on separate occasions about 1 week apart, in a randomized crossover fashion. Plasma samples were collected over the 24-h period

J. Blanchard; S. J. A. Sawers

1983-01-01

380

The absolute spectrophotometric catalog by Anita Cochran  

NASA Astrophysics Data System (ADS)

The absolute spectrophotometric catalog by Anita Cochran is presented in a machine-readable form. The catalog systematizes observations acquired at the McDonald Observatory in 1977-1978. The data are compared with other sources, in particular, the calculated broadband stellar magnitudes are compared with photometric observations by other authors, to show that the observational data given in the catalog are reliable and suitable for a variety of applications. Observations of variable stars of different types make Cochran's catalog especially valuable.

Burnashev, V. I.; Burnasheva, B. A.; Ruban, E. V.; Hagen-Torn, E. I.

2014-06-01

381

The absolute position of a resonance peak  

E-print Network

It is common practice in scattering theory to correlate between the position of a resonance peak in the cross section and the real part of a complex energy of a pole of the scattering amplitude. In this work we show that the resonance peak position appears at the absolute value of the pole's complex energy rather than its real part. We further demonstrate that a local theory of resonances can still be used even in cases previously thought impossible.

Shachar Klaiman; Nimrod Moiseyev

2010-05-26

382

Absolute distance metrology for space interferometers  

NASA Astrophysics Data System (ADS)

Space interferometers consisting of several free flying telescopes, such as the planned Darwin mission, require a complex metrology system to make all the components operate as a single instrument. This metrology system consists of various sub-systems to monitor distances, angles and speeds. Our research focuses on one of these sub-systems that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy would be in the order of 10 ?m over 250 meter. To measure this absolute distance, we are currently building a frequency sweeping interferometer. It is operated by first measuring a phase in the interferometer, sweeping a tunable laser over a known frequency interval and finally measuring a second phase. By also counting the number of fringes during the sweep it is possible to determine the absolute path length difference without ambiguities. We plan on actively stabilizing the wavelength at the endpoints of the sweep on a Fabry-Perot cavity using the Pound-Drever-Hall technique. In this way the unknown distance is directly referenced to the length of the Fabry-Perot cavity.

Swinkels, B. L.; Wendrich, T. J.; Bhattacharya, N.; Wielders, A. A.; Braat, J. J. M.

2004-06-01

383

Organocatalytic asymmetric aldol reaction of hydroxyacetone with ?,?-unsaturated ?-keto esters: facile access to chiral tertiary alcohols.  

PubMed

An efficient direct asymmetric aldol reaction between hydroxyacetone and ?,?-unsaturated ?-keto esters has been successfully developed. In the presence of 9-amino-9-deoxy-epi-cinchonine and trifluoroacetic acid, the direct aldol reaction of O-protected hydroxyacetone proceeded in a highly enantioselective manner, affording the desired adducts containing a chiral tertiary alcohol in high yields and with excellent enantioselectivities. The aldol products obtained are valuable precursors for the synthesis of 2-substituted glycerol derivatives. PMID:21902199

Liu, Chen; Dou, Xiaowei; Lu, Yixin

2011-10-01

384

A new asymmetric diamide from the seed cake of Jatropha curcas L.  

PubMed

A new asymmetric diamide (E)-N-(3-acetamidopropyl)-cinnamamide named curcamide (1) has been isolated from the ethanol extract of the seed cake of Jatropha curcas L. along with 7 known compounds identified as isoamericanin (2), isoprincepin (3), caffeoylaldehyde (4), isoferulaldehyde (5), glycerol monooleate (6), syringaldehyde (7), and ?-ethyl-d-glucopyranoside (8). The synthesis and antibacterial activity of the new compound have been also studied. PMID:22516541

Yao, Licheng; Han, Changri; Chen, Guangying; Song, Xiaoping; Chang, Yonghui; Zang, Wenxia

2012-12-01

385

Kinetic simulation of capacitively coupled plasmas driven by trapezoidal asymmetric voltage pulses  

NASA Astrophysics Data System (ADS)

A kinetic Particle-In-Cell simulation with Monte Carlo Collisions was performed of a geometrically symmetric capacitively coupled, parallel-plate discharge in argon, driven by trapezoidal asymmetric voltage pulses with a period of 200 ns. The discharge was electrically asymmetric, making the ion energy distributions at the two electrodes different from one another. The fraction of the period (?), during which the voltage was kept at a constant (top-flat) positive value, was a critical control parameter. For the parameter range investigated, as ? increased, the mean ion energy on the grounded electrode increased and the ions became more directional, whereas the opposite was found for the ions striking the powered electrode. The absolute value of the DC self-bias voltage decreased as ? increased. Plasma instabilities, promoted by local double layers and electric field reversals during the time of the positive voltage excursion, were characterized by electron plasma waves launched from the sheath edge.

Diomede, Paola; Economou, Demetre J.

2014-06-01

386

Asymmetric Dicke class states: Generation and applications  

NASA Astrophysics Data System (ADS)

Dicke class states are maximally entangled states of atoms or atom-like two-state entities involving a small number of excitations (much less than the total number of atoms). The so-called asymmetric Dicke states, which carry different relative phases for different permutations corresponding to different atomic entities being in the excited state, are more useful for quantum information processing tasks than the symmetric Dicke states. I have devised a practical conceptual proposal for generation of asymmetric Dicke states based on an existing proposal to generate symmetric Dicke states. I also show that the asymmetric Dicke-class states can be used for perfect teleportation and dense coding.

DeYoung, Daniel

387

Cell division site placement and asymmetric growth in mycobacteria.  

PubMed

Mycobacteria are members of the actinomycetes that grow by tip extension and lack apparent homologues of the known cell division regulators found in other rod-shaped bacteria. Previous work using static microscopy on dividing mycobacteria led to the hypothesis that these cells can grow and divide asymmetrically, and at a wide range of sizes, in contrast to the cell growth and division patterns observed in the model rod-shaped organisms. In this study, we test this hypothesis using live-cell time-lapse imaging of dividing Mycobacterium smegmatis labelled with fluorescent PBP1a, to probe peptidoglycan synthesis and label the cell septum. We demonstrate that the new septum is placed accurately at mid-cell, and that the asymmetric division observed is a result of differential growth from the cell tips, with a more than 2-fold difference in growth rate between fast and slow growing poles. We also show that the division site is not selected at a characteristic cell length, suggesting this is not an important cue during the mycobacterial cell cycle. PMID:22970255

Joyce, Graham; Williams, Kerstin J; Robb, Matthew; Noens, Elke; Tizzano, Barbara; Shahrezaei, Vahid; Robertson, Brian D

2012-01-01

388

Cell Division Site Placement and Asymmetric Growth in Mycobacteria  

PubMed Central

Mycobacteria are members of the actinomycetes that grow by tip extension and lack apparent homologues of the known cell division regulators found in other rod-shaped bacteria. Previous work using static microscopy on dividing mycobacteria led to the hypothesis that these cells can grow and divide asymmetrically, and at a wide range of sizes, in contrast to the cell growth and division patterns observed in the model rod-shaped organisms. In this study, we test this hypothesis using live-cell time-lapse imaging of dividing Mycobacterium smegmatis labelled with fluorescent PBP1a, to probe peptidoglycan synthesis and label the cell septum. We demonstrate that the new septum is placed accurately at mid-cell, and that the asymmetric division observed is a result of differential growth from the cell tips, with a more than 2-fold difference in growth rate between fast and slow growing poles. We also show that the division site is not selected at a characteristic cell length, suggesting this is not an important cue during the mycobacterial cell cycle. PMID:22970255

Joyce, Graham; Williams, Kerstin J.; Robb, Matthew; Noens, Elke; Tizzano, Barbara; Shahrezaei, Vahid; Robertson, Brian D.

2012-01-01

389

Asymmetric exclusion process models for translation and biological transport  

NASA Astrophysics Data System (ADS)

In the totally asymmetric simple exclusion process (TASEP), particles travel unidirectionally along a one-dimensional lattice and interact with each other by hard-core exclusion. Variants of the TASEP have been used to model the movement of molecular motors along biopolymers, including ribosomes on mRNA and various motors on cytoskeletal filaments. Ribosomes synthesize proteins as they traverse an mRNA molecule, so their motion is important in understanding the kinetics of protein production. We model protein synthesis as a TASEP with quenched disorder in the particle hopping rates. The hopping rates are determined by gene sequences and the availability of biomolecules. We use a statistical ensemble method in fitting the model to experimental data. The model is able to explain much of the nonlinear relationship between mRNA and protein levels.

Shaw, Leah

2005-03-01

390

Microbial asymmetric oxidation of 2-butyl-1,3-propanediol.  

PubMed

Microbial asymmetric oxidation of 2-butyl-1,3-propanediol was investigated for an efficient synthesis of S- and R-enantiomers of 2-hydroxymethylhexanoic acid (2-HMHA). From an intensive survey of the stocked bacterial strains, Acetobacter pasteurianus IAM 12073 and Pseudomonas putida IFO 3738 were found to show the highest S- and R-2-HMHA-producing activity, respectively. Under optimized conditions, A. pasteurianus (351 mg dry cell weight) and P. putida (642 mg dry cell weight) cells produced 12.0 g l(-1) S-2-HMHA with 89% enantiomeric excess (e.e.) at 24 h of incubation and 5.1 g l(-1) R-2-HMHA with 94% e.e. at 35 h of incubation from 2-butyl-1,3-propanediol. PMID:17453192

Mitsukura, K; Uno, T; Yoshida, T; Nagasawa, T

2007-08-01

391

Stereocontrol in Asymmetric ?-Lactam Syntheses from Imines and Cyanosuccinic Anhydrides  

PubMed Central

Computations (SCS-MP2//B3LYP) reveal that the asymmetric synthesis of highly substituted ?-lactams with three stereogenic centers, including one quaternary center, proceeds through a Mannich reaction between the enol form of the anhydride and the E-imine, followed by a transannular acylation. This new mechanistic picture accounts for both the observed reactivity and stereoselectivity. CH-O and hydrogen bonding interactions in the Mannich step and torsional steering effects in the acylation step are responsible for stereocontrol. It is demonstrated that this new mechanistic picture applies to the related reactions of homophthalic anhydrides with imines and presents new vistas for the design of a new reaction to access complex molecular architectures. PMID:24070216

Pattawong, Ommidala; Tan, Darlene Q.; Fettinger, James C.; Shaw, Jared T.; Cheong, Paul Ha-Yeon

2014-01-01

392

Achieving Climate Change Absolute Accuracy in Orbit  

NASA Technical Reports Server (NTRS)

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREO's inherently high absolute accuracy will be verified and traceable on orbit to Système Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earth's thermal infrared spectrum (5-50 micron), the spectrum of solar radiation reflected by the Earth and its atmosphere (320-2300 nm), and radio occultation refractivity from which accurate temperature profiles are derived. The mission has the ability to provide new spectral fingerprints of climate change, as well as to provide the first orbiting radiometer with accuracy sufficient to serve as the reference transfer standard for other space sensors, in essence serving as a "NIST [National Institute of Standards and Technology] in orbit." CLARREO will greatly improve the accuracy and relevance of a wide range of space-borne instruments for decadal climate change. Finally, CLARREO has developed new metrics and methods for determining the accuracy requirements of climate observations for a wide range of climate variables and uncertainty sources. These methods should be useful for improving our understanding of observing requirements for most climate change observations.

Wielicki, Bruce A.; Young, D. F.; Mlynczak, M. G.; Thome, K. J; Leroy, S.; Corliss, J.; Anderson, J. G.; Ao, C. O.; Bantges, R.; Best, F.; Bowman, K.; Brindley, H.; Butler, J. J.; Collins, W.; Dykema, J. A.; Doelling, D. R.; Feldman, D. R.; Fox, N.; Huang, X.; Holz, R.; Huang, Y.; Jennings, D.; Jin, Z.; Johnson, D. G.; Jucks, K.; Kato, S.; Kratz, D. P.; Liu, X.; Lukashin, C.; Mannucci, A. J.; Phojanamongkolkij, N.; Roithmayr, C. M.; Sandford, S.; Taylor, P. C.; Xiong, X.

2013-01-01

393

Determination of the absolute contours of optical flats  

NASA Technical Reports Server (NTRS)

Emersons procedure is used to determine true absolute contours of optical flats. Absolute contours of standard flats are determined and a comparison is then made between standard and unknown flats. Contour differences are determined by deviation of Fizeau fringe.

Primak, W.

1969-01-01

394

An absolute radius scale for Saturn's rings  

NASA Technical Reports Server (NTRS)

Radio and stellar occultation observations of Saturn's rings made by the Voyager spacecraft are discussed. The data reveal systematic discrepancies of almost 10 km in some parts of the rings, limiting some of the investigations. A revised solution for Saturn's rotation pole has been proposed which removes the discrepancies between the stellar and radio occultation profiles. Corrections to previously published radii vary from -2 to -10 km for the radio occultation, and +5 to -6 km for the stellar occultation. An examination of spiral density waves in the outer A Ring supports that the revised absolute radii are in error by no more than 2 km.

Nicholson, Philip D.; Cooke, Maren L.; Pelton, Emily

1990-01-01

395

Absolute Priority for a Vehicle in VANET  

NASA Astrophysics Data System (ADS)

In today's world, traffic jams waste hundreds of hours of our life. This causes many researchers try to resolve the problem with the idea of Intelligent Transportation System. For some applications like a travelling ambulance, it is important to reduce delay even for a second. In this paper, we propose a completely infrastructure-less approach for finding shortest path and controlling traffic light to provide absolute priority for an emergency vehicle. We use the idea of vehicular ad-hoc networking to reduce the imposed travelling time. Then, we simulate our proposed protocol and compare it with a centrally controlled traffic light system.

Shirani, Rostam; Hendessi, Faramarz; Montazeri, Mohammad Ali; Sheikh Zefreh, Mohammad

396

Note: Real-time absolute air refractometer.  

PubMed

We present a real-time absolute air refractometer benefiting from the synthetic pseudo-wavelength (SPW) method. Based on laser heterodyne interferometry, the SPW method uses three vacuum cells with specific lengths to synthesize a set of synthetic pseudo-wavelengths, by combination of which the refractive index can be determined directly without ambiguity. In addition, owing to the parallel arrangement of the vacuum cells in the optical path, the measured data can be collected simultaneously so that one measurement process can be less than 2 ms. The real-time feature makes it possible for instantaneous compensation for laser interferometers. PMID:24880432

Huang, Pei; Zhang, Jitao; Li, Yan; Wei, Haoyun

2014-05-01

397

Absolute method of measuring magnetic susceptibility  

USGS Publications Warehouse

An absolute method of standardization and measurement of the magnetic susceptibility of small samples is presented which can be applied to most techniques based on the Faraday method. The fact that the susceptibility is a function of the area under the curve of sample displacement versus distance of the magnet from the sample, offers a simple method of measuring the susceptibility without recourse to a standard sample. Typical results on a few substances are compared with reported values, and an error of less than 2% can be achieved. ?? 1959 The American Institute of Physics.

Thorpe, A.; Senftle, F.E.

1959-01-01

398

Continuum limit of electrostatic gyrokinetic absolute equilibrium  

SciTech Connect

Electrostatic gyrokinetic absolute equilibria with continuum velocity field are obtained through the partition function and through the Green function of the functional integral. The new results justify and explain the prescription for quantization/discretization or taking the continuum limit of velocity. The mistakes in the Appendix D of our earlier work [J.-Z. Zhu and G. W. Hammett, Phys. Plasmas 17, 122307 (2010)] are explained and corrected. If the lattice spacing for discretizing velocity is big enough, all the invariants could concentrate at the lowest Fourier modes in a negative-temperature state, which might indicate a possible variation of the dual cascade picture in 2D plasma turbulence.

Zhu Jianzhou [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2012-06-15

399

Absolute temperature stability of passive imaging radiometers  

NASA Astrophysics Data System (ADS)

A challenge in the development of multi-channel millimeter wave imaging radiometers is overcoming effects associated with the temperature dependence of receiver responsivity. In this paper, the stability of absolute radiation temperature measurements, made with direct and heterodyne detection radiometers, is investigated theoretically and experimentally. The agreement between theory and experiment is found to be good. Changes in measured radiation temperatures were found to be between 6 degree(s)K at 35 GHz and 145 degree(s)K at 220 GHz, for a one degree change in instrumental temperature. Suggestions are made, as to how the temperature stability of radiometers may be improved.

Salmon, Neil A.; Borrill, Jonathan R.; Gleed, David G.

1997-06-01

400

Enantioselective Total Synthesis of Ustiloxin D Hiroko Tanaka, Andrew M. Sawayama, and Thomas J. Wandless*  

E-print Network

in their synthesis include the use of a nucleophilic aromatic substitution reaction to construct the chiral tertiary alkyl- aryl ether,4b as well as Sharpless's asymmetric aminohydroxylation reaction to install the C10 reactions in the context of a total synthesis. A requirement for our synthesis was to develop a strategy

Wandless, Tom

401

Parasitism of asymmetrical pelvic phenotypes in stickleback  

E-print Network

and bilateral asymmetry of the pelvis. Seventeen percent of the fish had an asymmetrical pelvis and, of these, if the directional asymmetry of the pelvis is under genctic control, asymmetry would be favoured during early

Reimchen, Thomas E.

402

Geometrically robust perceptual fingerprinting: an asymmetric case  

E-print Network

Geometrically robust perceptual fingerprinting: an asymmetric case Oleksiy Koval, Sviatoslav investigate the impact of the fingerprint length on the error performance of these protocols relaxing. INTRODUCTION Recent advances in modern networking and multimedia technologies have open an access

Genève, Université de

403

Practical methodology for the asymmetric synthesis of organofluorine compounds  

Microsoft Academic Search

Pseudoephedrine ?-fluoroacetamide (1), a nonvolatile, crystalline solid, is alkylated efficiently and with high diastereoselectivity with reactive alkyl halides. The alkylation products can be hydrolyzed under mild basic conditions to form ?-fluoro carboxylates with high enantiomeric enrichment.

Andrew G. Myers; Lydia McKinstry; Joseph K. Barbay; James L. Gleason

1998-01-01

404

Asymmetric Methods for the Synthesis of Flavanones, Chromanones, and Azaflavanones  

PubMed Central

Flavanones, chromanones, and related structures are privileged natural products that display a wide variety of biological activities. Although flavanoids are abundant in nature, there are a limited number of available general and efficient synthetic methods for accessing molecules of this class in a stereoselective manner. Their structurally simple architectures belie the difficulties involved in installation and maintenance of the stereogenic configuration at the C2 position, which can be sensitive and can undergo epimerization under mildly acidic, basic, and thermal reaction conditions. This review presents the methods currently used to access these related structures. The synthetic methods include manipulation of the flavone/flavanone core, carbon-carbon bond formation, and carbon–heteroatom bond formation. PMID:22876166

Nibbs, Antoinette E.

2012-01-01

405

Total Synthesis of (+)-Laurencin: An Asymmetric Alkylation-Ring-Closing  

E-print Network

and marine organisms that feed on Laurencia species have produced a diverse collection of natural products, (+)-laurencin 1, was isolated from the extracts of Laurencia glandulifera by Irie and Masamune in 1965

406

Silyl Ketene Imines: Highly Versatile Nucleophiles for Catalytic, Asymmetric Synthesis  

PubMed Central

This Minireview provides an overview on the development of silyl ketene imines and their recent applications in catalytic, enantioselective reactions. The unique structure of the ketene imine allows a diverse range of reactivity patterns and provides solutions to existing challenges in the enantioselective construction of quaternary stereogenic carbon centers and cross-benzoin adducts. A variety of reactions for which silyl ketene imines have been applied are presented with an overall goal of inspiring new uses for these underutilized nucleophiles. PMID:22968901

Denmark, Scott E.; Wilson, Tyler W.

2012-01-01

407

Total Synthesis of (+)-Scholarisine A  

PubMed Central

An effective total synthesis and assignment of the absolute configuration of the architecturally challenging (+)-scholarisine A has been achieved via a 20-step sequence. Highlights include a reductive cyclization, involving a nitrile and an epoxide; a modified Fischer indole protocol; a late stage oxidative-lactonization; and an intramolecular cyclization leading to the indolenine ring system of (+)-scholarisine A. PMID:22280070

Adams, Gregory L.; Carroll, Patrick J.; Smith, Amos B.

2012-01-01

408

Symmetric and asymmetric hybridization in citrus spp.  

E-print Network

be better tolerated than the whole donor genome (Ramulu et al., 1996a,b). Asymmetric hybrids have been produced in fusing species of Medicago, tobacco, tomato, potato, tomato + potato, Arabidopsis thaliana + Brassica napus and rice + Zizania latifolia... be better tolerated than the whole donor genome (Ramulu et al., 1996a,b). Asymmetric hybrids have been produced in fusing species of Medicago, tobacco, tomato, potato, tomato + potato, Arabidopsis thaliana + Brassica napus and rice + Zizania latifolia...

Bona, Claudine M.

2009-05-15

409

Transformation of America's Military and Asymmetric War  

Microsoft Academic Search

In the post–Cold War and post–9\\/11 era, the need for broadening the focus of military transformation to include asymmetric warfare capabilities has been given lip service. The U.S. military did not feel the necessity to widen the scope, if not to change the focus, of transformation to include asymmetric warfare until 2003 and 2004. During Operation Iraqi Freedom, the Iraqi

Ehsan Ahrari

2010-01-01

410

Modeling Asymmetric Rolling Process of Mg alloys  

SciTech Connect

Asymmetric deformation during rolling can arise in various ways: difference in the radii, speeds, frictions of the top and bottom rolls. Asymmetric warm rolling processes of magnesium alloys were modeled using a lagrangian incremental approach. A constitutive equation representing flow behaviors of AZ31 magnesium alloys during warm deformation was implemented to the modeling. Various roll speed ratios were introduced to investigate deformation behaviors of the magnesium alloys. Bending and texturing of the strips were examined.

Cho, Jaehyung; Kim, Hyung-Wuk; Kang, Suk-Bong [Korea Institute of Materials Science, 66 Sangnam-dong, Changwon-city, Kyungnam, 641-010 (Korea, Republic of)

2010-06-15

411

Experimental results for absolute cylindrical wavefront testing  

NASA Astrophysics Data System (ADS)

Applications for Cylindrical and near-cylindrical surfaces are ever-increasing. However, fabrication of high quality cylindrical surfaces is limited by the difficulty of accurate and affordable metrology. Absolute testing of such surfaces represents a challenge to the optical testing community as cylindrical reference wavefronts are difficult to produce. In this paper, preliminary results for a new method of absolute testing of cylindrical wavefronts are presented. The method is based on the merging of the random ball test method with the fiber optic reference test. The random ball test assumes a large number of interferograms of a good quality sphere with errors that are statistically distributed such that the average of the errors goes to zero. The fiber optic reference test utilizes a specially processed optical fiber to provide a clean high quality reference wave from an incident line focus from the cylindrical wave under test. By taking measurements at different rotation and translations of the fiber, an analogous procedure can be employed to determine the quality of the converging cylindrical wavefront with high accuracy. This paper presents and discusses the results of recent tests of this method using a null optic formed by a COTS cylindrical lens and a free-form polished corrector element.

Reardon, Patrick J.; Alatawi, Ayshah

2014-09-01

412

Calern Observatory absolute declinations (Martin+, 1999)  

NASA Astrophysics Data System (ADS)

A regular observational programme with a photoelectric astrolabe have been performed at ``Observatoire du Calern" (Observatoire de la Cote d'Azur, OCA, ?=+43°44'55.011"; ?=-0h27m42.44s, Calern, Caussols, France) for the last twenty years. It has been almost fully automatized between 1984 and 1987. Since 1988 the photoelectric astrolabe was used without any modification. In addition to determining the daily orientation of the local vertical, the yearly analysis of the residuals permits to derive corrections to the used star catalogue Vigouroux et al. (1992A&AS...96..477V). A global reduction method was applied for the ASPHO observations. The new form of the equations Martin & Leister (1997A&AS..126..169M) give us the possibility of using the entire set of the observing program using data taken at two zenith distances (30° and 45°). The program contains about 41648 stars' transits of 269 different stars taken at ``Observatoire du Calern" (OCA). The reduction was based on the HIPPARCOS system. We discuss the possibility of computing absolute declinations through stars belonging simultaneously to the 30° and 45° zenith distances programmes. The absolute declination corrections were determined for 185 stars with precision of 0.027" and the value of the determined equator correction is -0.018"+/-0.005". The instrumental effects were also determined. The mean epoch is 1995.29. (1 data file).

Martin, V. A. F.; Leister, N. V.; Vigouroux, G.; Furia, M.; Journet, A.

1999-05-01

413

Absolute Spectrophotometry of 237 Open Cluster Stars  

NASA Astrophysics Data System (ADS)

We present absolute spectrophotometry of 237 stars in 7 nearby open clusters: Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M 39. The observations were taken using the Wampler single-channel scanner (Wampler 1966) on the Crossley 0.9m telescope at Lick Observatory from July 1973 through December 1974. 21 bandpasses spanning the spectral range 3500 Angstroms to 7780 Angstroms were observed for each star, with bandwiths ranging from 32Angstroms to 64 Angstroms. Data are standardized to the Hayes--Latham (1975) system. Our measurements are compared to filter colors on the Johnson BV, Stromgren ubvy, and Geneva U V B_1 B_2 V_1 G systems, as well as to spectrophotometry of a few stars published by Gunn, Stryker & Tinsley and in the Spectrophotometric Standards Catalog (Adelman; as distributed by the NSSDC). Both internal and external comparisons to the filter systems indicate a formal statistical accuracy per bandpass of 0.01 to 0.02 mag, with apparent larger ( ~ 0.03 mag) differences in absolute calibration between this data set and existing spectrophotometry. These data will comprise part of the spectrophotometry that will be used to calibrate the Beijing-Arizona-Taipei-Connecticut Color Survey of the Sky (see separate paper by Burstein et al. at this meeting).

Clampitt, L.; Burstein, D.

1994-12-01

414

Development of new methods in organic synthesis and their applications to the synthesis of biologically interesting natural products.  

PubMed

2,6-Dimethyl-9-Aryl-9-phosphabicyclo[3.3.1]nonanes (9-PBN and 9-NapBN) and the chiral diaminophosphine oxides (DIAPHOXs) derived from aspartic acid have been introduced as useful ligands and preligands, respectively, for transition metal-catalyzed asymmetric synthesis. anti-Selective asymmetric hydrogenation of ?-amino-?-ketoesters using Ru-, Rh-, Ir-, and Ni-catalysts through dynamic kinetic resolution have been developed for the first time, producing efficiently important anti ?-hydroxy-?-amino acids. The total synthesis of several biologically active natural products was achieved by use of the transition metal-catalyzed reaction using DIAPHOX, anti-selective asymmetric hydrogenation, and reactions developed by us. Synthesis of tangutorine, an antitumor indole alkaloid, has been enantioselectively achieved for the first time. Enantioselective synthesis of a martinelline chiral core was accomplished using the asymmetric tandem Michael-Aldol reaction as a key step developed by us. This synthesis represents the formal total synthesis of martinelline and martinellic acid. Papuamide B was synthesized through the elucidation of unknown stereostructures by using the anti-selective asymmetric hydrogenation and reactions developed by us. PMID:22223369

Hamada, Yasumasa

2012-01-01

415

Asymmetric Magnetic Reconnection in the Solar Atmosphere  

NASA Astrophysics Data System (ADS)

Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasm! oid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S. C.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

2013-12-01

416

Asymmetric Magnetic Reconnection in the Solar Atmosphere  

NASA Astrophysics Data System (ADS)

Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasmoid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

Murphy, N. A.; Miralles, M.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

2013-12-01

417

Measurement of the Absolute Branching Fraction of D0 to K- pi+  

SciTech Connect

The authors measure the absolute branching fraction for D{sup 0} {yields} K{sup -} {pi}{sup +} using partial reconstruction of {bar B}{sup 0} {yields} D*{sup +}X{ell}{sup -}{bar {nu}}{sub {ell}} decays, in which only the charged lepton and the pion from the decay D*{sup +} {yields} D{sup 0}{pi}{sup +} are used. Based on a data sample of 230 million B{bar B} pairs collected at the {Upsilon}(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC, they obtain {Beta}(D{sup 0} {yields} K{sup -}{pi}{sup +}) = (4.007 {+-} 0.037 {+-} 0.070)%, where the first error is statistical and the second error is systematic.

Aubert, B.; Bona, M.; Boutigny, D.; Karyotakis, Y.; Lees, J.P.; Poireau, V.; Prudent, X.; Tisserand, V.; Zghiche, A.; /Annecy, LAPP; Garra Tico, J.; Grauges, E.; /Barcelona U., ECM; Lopez, L.; Palano, A.; /Bari U.; Eigen, G.; Ofte, I.; Stugu, B.; Sun, L.; /Bergen U.; Abrams, G.S.; Battaglia, M.; Brown, D.N.; Button-Shafer, J.; /LBL, Berkeley

2007-04-25

418

Hydrological effects on gravity measurements at the Canadian Absolute Gravity Site  

NASA Astrophysics Data System (ADS)

The Canadian Gravity Standardization Net (CGSN), a network of primary and secondary gravity sites, provides the reference linkage for regional and local gravity surveys performed in different places and at different epochs in Canada. Maintained over the last five decades, CSGN has produced a reliable determination of the gravitational potential as well as associated temporal variations upon the Earth's surface. As part of CGSN more than 60 absolute gravity stations have been established across Canada. This network of absolute gravity sites is designed to provide absolute control for the CGSN and to continue the monitoring of temporal variations resulting from glacial isostatic adjustment, tectonic deformation and other processes. Additionally, monitoring of temporal gravity change rates at key, continuous GPS sites is an important step towards maintenance of an integrated reference system. The primary site for evaluating the stability of the absolute gravimeters for this network is the Canadian Absolute Gravity Site (CAGS), located near Ottawa at Cantley, Quebec (Lat. 45.585°N, Long. 75.807°W). CAGS is the base station for all JILA-2 and A10-003 field measurements as well as housing the Canadian Superconducting Gravimeter Installation (CSGI) which is contributing continuous data to the Global Geodynamics Project (1997-2003). Although owned by a consortium of Canadian universities, superconducting gravimeter GWR12 is operated with the assistance of the Geodetic Survey Division and provides a data stream which can be compared with frequent, repeated absolute gravity measurements. Additional CAGS/CSGI on-site data include: continuous water-level measurements from shallow (10m) and deep (120m) wells, observations from meteorological instrumentation, and continuous Global Positioning System (GPS) observations. Using the data available from the CAGS, we have begun to carry out a systematic self-consistent and complete synthesis, evaluation and interpretation of all available absolute gravity data collected over the last decade. Data from superconducting gravimeter GWR12, coupled with these absolute measurements, will be used to test models of seasonal variations in gravity at the CAGS base station due to groundwater effects identified in earlier work (e.g. Bower and Courtier, 1998).

Henton, J. A.; Liard, J. O.; Lambert, A.; Gagnon, C.; Courtier, N.

2003-04-01

419

Use of absolute and comparative performance feedback in absolute and comparative judgments and decisions  

Microsoft Academic Search

Which matters more—beliefs about absolute ability or ability relative to others? This study set out to compare the effects of such beliefs on satisfaction with performance, self-evaluations, and bets on future performance. In Experiment 1, undergraduate participants were told they had answered 20% correct, 80% correct, or were not given their scores on a practice test. Orthogonal to this manipulation,

Don A. Moore; William M. P. Klein

2008-01-01

420

Perceiving pitch absolutely: Comparing absolute and relative pitch possessors in a pitch memory task  

Microsoft Academic Search

BACKGROUND: The perceptual-cognitive mechanisms and neural correlates of Absolute Pitch (AP) are not fully understood. The aim of this fMRI study was to examine the neural network underlying AP using a pitch memory experiment and contrasting two groups of musicians with each other, those that have AP and those that do not. RESULTS: We found a common activation pattern for

Katrin Schulze; Nadine Gaab; Gottfried Schlaug

2009-01-01

421

Use of Absolute and Comparative Performance Feedback in Absolute and Comparative Judgments and Decisions  

ERIC Educational Resources Information Center

Which matters more--beliefs about absolute ability or ability relative to others? This study set out to compare the effects of such beliefs on satisfaction with performance, self-evaluations, and bets on future performance. In Experiment 1, undergraduate participants were told they had answered 20% correct, 80% correct, or were not given their…

Moore, Don A.; Klein, William M. P.

2008-01-01

422

Enantioselective synthesis of a chiral coordination polymer with circularly polarized visible laser.  

PubMed

Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL-responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL-induced enantioselective synthesis. By irradiation with either left-handed or right-handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left-handed CPL resulted in crystals with a left-handed helical structure, and right-handed CPL led to crystals with a right-handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers. PMID:25251289

Wu, Shu-Ting; Cai, Zhen-Wen; Ye, Qiao-Yan; Weng, Chen-Hao; Huang, Xi-He; Hu, Xiao-Lin; Huang, Chang-Cang; Zhuang, Nai-Feng

2014-11-17

423

Optical cryostat realizations at absolut System  

NASA Astrophysics Data System (ADS)

This paper describes two kinds of optical cryostats designed and manufactured at Absolut System. The first one makes use of pressurized LN2 for temperature control of a sample holder in the 80 K - 470 K temperature range. An optical window is implemented above the sample holder to allow for rugosity and 3D distortion of heterogeneous semicon sample assemblies on a wafer. The second one makes use of CRYOMECH remote motor type pulse tube cryocoolers for temperature control of the sample holder in the 3 K - 300 K temperature range. In this type of cryostats, particular attention has been paid to reduce the vibrations exported by the cooler. These 4 K ultra low vibration cryostats are used for characterization of samples via optical windows. Both designs will be presented and the performance reported.

Trollier, T.; Ravex, A.; Tanchon, J.

2014-01-01

424

Absolute Maximal Entanglement and Quantum Secret Sharing  

E-print Network

We study the existence of absolutely maximally entangled (AME) states in quantum mechanics and its applications to quantum information. AME states are characterized by being maximally entangled for all bipartitions of the system and exhibit genuine multipartite entanglement. With such states, we present a novel parallel teleportation protocol which teleports multiple quantum states between groups of senders and receivers. The notable features of this protocol are that (i) the partition into senders and receivers can be chosen after the state has been distributed, and (ii) one group has to perform joint quantum operations while the parties of the other group only have to act locally on their system. We also prove the equivalence between pure state quantum secret sharing schemes and AME states with an even number of parties. This equivalence implies the existence of AME states for an arbitrary number of parties based on known results about the existence of quantum secret sharing schemes.

Helwig, Wolfram; Riera, Arnau; Latorre, José I; Lo, Hoi-Kwong

2012-01-01

425

Absolute image registration for geosynchronous satellites  

NASA Technical Reports Server (NTRS)

A procedure for the absolute registration of earth images acquired by cameras on geosynchronous satellites is described. A conventional least squares process is used to estimate navigational parameters and camera pointing biases from observed minus computed landmark line and element numbers. These estimated parameters along with orbit and attitude dynamic models are used to register images, employing an automated grey-level correlation technique, inside the span represented by the landmark data. Experimental results obtained from processing the SMS-2 observation data base covering May 2, 1979 through May 20, 1979 show registration accuracies with a standard deviation of less than two pixels if the registration is within the landmark data span. It is also found that accurate registration can be expected for images obtained up to 48 hours outside of the landmark data span.

Nankervis, R.; Koch, D.; Sielski, H.; Hall, D.

1980-01-01

426

Absolute radiometric calibration of the Thematic Mapper  

NASA Technical Reports Server (NTRS)

Calibration data for the solar reflective bands of the Landsat-5 TM obtained from five in-flight absolute radiometric calibrations from July 1984-November 1985 at White Sands, New Mexico are presented and analyzed. Ground reflectance and atmospheric data were utilized to predict the spectral radiance at the entrance pupil of the TM and the average number of digital counts in each TM band. The calibration of each of the TM solar reflective bands was calculated in terms of average digital counts/unit spectral radiance for each band. It is observed that for the 12 reflectance-based measurements the rms variation from the means as a percentage of the mean is + or - 1.9 percent; for the 11 measurements in the IR bands, it is + or - 3.4 percent; and the rms variation for all 23 measurements is + or - 2.8 percent.

Slater, P. N.; Biggar, S. F.; Holm, R. G.; Jackson, R. D.; Mao, Y.

1986-01-01

427

Absolute astrometry in the next 50 years  

E-print Network

With ESA's astrometry satellite Gaia in orbit since December 2013 it is time to look at the future of fundamental astrometry and a time frame of 50 years is needed in this matter. A dozen science issues for a Gaia successor mission in twenty years are presented and in this context the possibilities for absolute astrometry with mas or sub-mas accuracies are discussed. The three powerful techniques: VLBI, the MICADO camera on the E-ELT, and the LSST are described and documented by literature references and by an extensive correspondence with leading astronomers who readily responded with all the information I needed. In brief, the two Gaia-like missions would provide an astrometric foundation for all branches of astronomy from the solar system and stellar systems to compact galaxies, quasars and dark matter by data which cannot be surpassed in the next 50 years.

Høg, Erik

2014-01-01

428

Measured and modelled absolute gravity in Greenland  

NASA Astrophysics Data System (ADS)

Present day changes in the ice volume in glaciated areas like Greenland will change the load on the Earth and to this change the lithosphere will respond elastically. The Earth also responds to changes in the ice volume over a millennial time scale. This response is due to the viscous properties of the mantle and is known as Glaical Isostatic Adjustment (GIA). Both signals are present in GPS and absolute gravity (AG) measurements and they will give an uncertainty in mass balance estimates calculated from these data types. It is possible to separate the two signals if both gravity and Global Positioning System (GPS) time series are available. DTU Space acquired an A10 absolute gravimeter in 2008. One purpose of this instrument is to establish AG time series in Greenland and the first measurements were conducted in 2009. Since then are 18 different Greenland GPS Network (GNET) stations visited and six of these are visited more then once. The gravity signal consists of three signals; the elastic signal, the viscous signal and the direct attraction from the ice masses. All of these signals can be modelled using various techniques. The viscous signal is modelled by solving the Sea Level Equation with an appropriate ice history and Earth model. The free code SELEN is used for this. The elastic signal is modelled as a convolution of the elastic Greens function for gravity and a model of present day ice mass changes. The direct attraction is the same as the Newtonian attraction and is calculated as this. Here we will present the preliminary results of the AG measurements in Greenland. We will also present modelled estimates of the direct attraction, the elastic and the viscous signals.

Nielsen, E.; Forsberg, R.; Strykowski, G.

2012-12-01

429

Absolute Abundance of Methane and Water on Mars: Spatial Maps  

NASA Astrophysics Data System (ADS)

We earlier reported ground-based detections of methane on Mars, and presented evidence for local enhancements in its mixing ratio consistent with local release. Our long-slit infrared observations (now extending over two Mars years) sample a wide range of seasons and areocentric longitudes with significant spatial coverage. By orienting the slit North-South on the planet, we obtain simultaneous spectra at many latitudes on Mars. Heretofore, we presented differential abundances using one spectrum as a standard of comparison for spectra taken at other latitudes; this approach provides excellent removal of telluric features at the expense of reducing the intensity of residual spectral lines from Mars. Our differential extractions for water agreed with simultaneous measurements acquired with TES. Our differential extractions for methane implied strong latitudinal gradients - these are contrary to predictions if photochemistry limits the lifetime of methane on Mars, but instead require local release and a much shorter lifetime. The lifetime against destruction cannot be much longer than equator-to-pole transport times imposed by the Hadley circulation (weeks). A shorter lifetime requires that estimated production rates be revised upwards commensurately. The extraction of absolute spectral signatures for Mars requires both special instrumental factors (high sensitivity, high resolving power) and an appropriate spectral synthesis technique. The telluric transmittance spectrum must be synthesized at very high resolution (approaching 100 m/sec), as otherwise the subtraction of synthetic from measured spectra produces unacceptably large residuals. This requires inclusion of mixed line-shape functions for H2O, CH4, and O3, and of pressure shift effects for CH4 and H2O. Here, we present absolute extractions of methane and water, based on such multi-layer atmospheric models for Mars and Earth. We will compare and contrast the new results with our earlier findings. Supported by Grants to MJM from NASA's Planetary Astronomy Program (344-32-51-96) and Astrobiology Program (344-53-51), and NSF RUI Grant AST-0205397 to REN. GLV was supported by the NAS-NRC under the NASA Resident Research Associateship Program.

Mumma, M. J.; Novak, R. E.; Hewagama, T.; Villanueva, G. L.; Bonev, B. P.; DiSanti, M. A.; Smith, M. D.; Dello Russo, N.

2005-08-01

430

Stereoselective Synthesis of Quaternary Proline Analogues  

PubMed Central

This review describes available methods for the diastereoselective and asymmetric synthesis of quaternary prolines. The focus is on the preparation of ?-functionalized prolines with the pyrrolidine moiety not embedded in a polycyclic frame. The diverse synthetic approaches are classified according to the bond which is formed to complete the quaternary skeleton. PMID:19655047

Calaza, M. Isabel

2009-01-01

431

Dysregulation of dimethylargininedimethylaminohydrolase/asymmetric dimethylarginine pathway in rat type II diabetic nephropathy  

PubMed Central

An impaired generation of nitric oxide has been associated with diabetic renal disease. In order to elucidate the underlying molecular mechanisms into how nitric oxide synthesis is impaired in diabetic renal disease, we examined changes in activities and expressions of some renal enzymes involved in nitric oxide production during the development of diabetic nephropathy in type II diabetic Otsuka Long-Evans Tokushima Fatty rats. Ten-week old Otsuka Long-Evans Tokushima Fatty (n = 40) and control Long-Evans Tokushima Otsuka rats (n = 20) were given drinking water containing 20% sucrose to accelerate the development of diabetic nephropathy. Otsuka Long-Evans Tokushima Fatty rats developed diabetic nephropathy in an age-dependent manner. Renal nitric oxide synthase activities in Otsuka Long-Evans Tokushima Fatty rats gradually declined with the progression of diabetic mellitus and were significantly lower than those of age-matched Long-Evans Tokushima Otsuka rats after 22 weeks of age. The lower activities of renal nitric oxide synthase in Otsuka Long-Evans Tokushima Fatty rats were correlated with relatively higher levels of renal free asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, and were also correlated with decreased activities of dimethylargininedimethylaminohydrolase which metabolizes asymmetric dimethylarginine to citrulline. These results imply that dimethylargininedimethylaminohydrolase dysregulation may play an important role in the development of diabetic nephropathy by increasing asymmetric dimethylarginine levels, which leads to inhibition of renal nitric oxide synthesis. PMID:22962534

Lai, Ying-Ling; Aoyama, Sae; Ohata, Miyuki; Otsuka, Nami; Shiokawa, Hidemi; Tomono, Susumu; Fujiwara, Yukio; Kanazawa, Hiroaki; Miyoshi, Noriyuki; Ohshima, Hiroshi

2012-01-01

432

Asymmetrically cut crystals for synchrotron radiation monochromators  

SciTech Connect

Asymmetrically cut crystals are interesting for use in synchrotron radiation monochromators because of their good energy resolution characteristics and their focusing properties. Ray tracing codes, such as SHADOW, are very efficient in the design and development of new optical devices. In order to determine the convenience of using asymmetrically cut crystals for x-ray monochromators, SHADOW has been extended to include these kinds of crystals. The physical approach to ray tracing asymmetrically cut crystals is based on the coexistence of two periodic structures. One of these is the bulk periodic structure of the Bragg planes. Such a structure determines the existence of a rocking curve near the Bragg condition, and is implemented in SHADOW following the Darwin--Prins formalism of the dynamical theory of diffraction. The second periodic structure is a one-dimensional grating on the crystal surface, formed by the truncation of the lattice planes with the surface. This grating is responsible for the focusing properties of these crystals and plays an essential role in determining the trajectory of the rays. The combination of an asymmetric crystal and a nonplanar surface can be easily achieved by bending (Johann case) to provide improved properties. More complex cases such as the ground-bent crystals (i.e., Johansson geometry) can be considered as a particular case of asymmetrical crystals in which the angle between the Bragg planes and the surface change along the crystal surface. All these cases have been implemented in SHADOW.

Sanchez del Rio, M. (European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble Cedex (France)); Cerrina, F. (Center for X-ray Lithography, 3731 Schneider Drive, Stoughton, Wisconsin 53589 (United States))

1992-01-01

433

The asymmetric gait toenail unit sign.  

PubMed

The aim of this investigation was to resolve a diagnostic problem and report toenail unit changes attributable to shoe friction that resemble onychomycosis, but that are fungus-negative, and identify common skeletal causes in patients with an asymmetric walking gait. X-ray and clinical feet inspections were performed to evaluate skeletal components that change normal foot biodynamics. Forty-nine patients, all dermatophyte-negative, were reviewed. All patients were those seen in our private practice who demonstrated skeletal and toenail unit abnormalities such as onycholysis, nail bed keratosis resembling distal subungual onychomycosis, nail plate surface abnormalities, distal toe skin keratosis, a diagnostic nail plate shape, as well as several skeletal abnormalities. The clinical abnormalities of the asymmetric gait syndrome include onycholysis, nail bed keratosis, nail plate surface abnormalities, and a diagnostic nail plate shape. By the patient's history, the skeletal findings that were present worsened with age and, in many patients, they were familial. Onychomycosis does not lead to an asymmetric gait nail problem, asymmetric gait toenail does not favor dermatophyte infection, and not all nail dystrophies are the result of an asymmetric walking gait. PMID:23008938

Zaias, Nardo; Rebell, Gerbert; Casal, German; Appel, Jason

2012-01-01

434

Total synthesis of herbimycin A.  

PubMed

Benzoquinone ansamycin antibiotic herbimycin A was synthesized in 19 linear steps and 4.2% yield. Highlighted is the design of a chiral ?-lactone as the C11-C15 synthon that enabled a facile catalytic asymmetric synthesis of the challenging C8-C20 fragment of the target molecule. The easy access to the stereogenic centers and high overall yield made the strategy applicable in the molecular editing of benzoquinone ansamycins. PMID:24911938

Yan, Rui; Bian, Chuancai; Yu, Xiaoming

2014-06-20

436

Criticality in charge-asymmetric hard-sphere ionic fluids  

NASA Astrophysics Data System (ADS)

Phase separation and criticality are analyzed in z:1 charge-asymmetric ionic fluids of equisized hard spheres by generalizing the Debye-Hückel approach combined with ionic association, cluster solvation by charged ions, and hard-core interactions, following lines developed by Fisher and Levin for the 1:1 case (i.e., the restricted primitive model). Explicit analytical calculations for 2:1 and 3:1 systems account for ionic association into dimers, trimers, and tetramers and subsequent multipolar cluster solvation. The reduced critical temperatures, Tc* (normalized by z ), decrease with charge asymmetry, while the critical densities increase rapidly with z . The results compare favorably with simulations and represent a distinct improvement over all current theories such as the mean spherical approximation, symmetric Poisson-Boltzmann theory, etc. For z?1 , the interphase Galvani (or absolute electrostatic) potential difference, ??(T) , between coexisting liquid and vapor phases is calculated and found to vanish as ?T-Tc?? when T?Tc —with, since our approximations are classical, ?=(1)/(2) . Above Tc , the compressibility maxima and so-called k -inflection loci (which aid the fast and accurate determination of the critical parameters) are found to exhibit a strong z dependence.

Aqua, Jean-Noël; Banerjee, Shubho; Fisher, Michael E.

2005-10-01

437

Reversal modes in asymmetric Ni nanowires  

NASA Astrophysics Data System (ADS)

We have investigated the evolution of the magnetization reversal mechanism in asymmetric Ni nanowires as a function of their geometry. Circular nanowires are found to reverse their magnetization by the propagation of a vortex domain wall, while in very asymmetric nanowires the reversal is driven by the propagation of a transverse domain wall. The effect of shape asymmetry of the wire on coercivity and remanence is also studied. Angular dependence of the remanence and coercivity is also addressed. Tailoring the magnetization reversal mechanism in asymmetric nanowires can be useful for magnetic logic and race-track memory, both of which are based on the displacement of magnetic domain walls. Finally, an alternative method to detect the presence of magnetic drops is proposed.

Leighton, B.; Pereira, A.; Escrig, J.

2012-11-01

438

Asymmetric Electron Distributions in the Solar Wind  

NASA Astrophysics Data System (ADS)

A plausible mechanism responsible for producing asymmetric electron velocity distribution functions in the solar wind is investigated by means of one-dimensional electrostatic particle-in-cell (PIC) simulation. A recent paper suggests that the variation in the ion-to-electron temperature ratio influences the nonlinear wave-particle dynamics such that it results in the formation of asymmetric distributions. The present PIC code simulation largely confirms this finding, but quantitative differences between the weak turbulence formalism and the present PIC simulation are also found, suggesting the limitation of the analytical method. The inter-relationship between the asymmetric electron distribution and the ion-to-electron temperature ratio may be a new useful concept for the observation.

Rha, Kicheol; Ryu, Chang-Mo; Yoon, Peter H.

2013-09-01

439

Asymmetric soft-error resistant memory  

NASA Technical Reports Server (NTRS)

A memory system is provided, of the type that includes an error-correcting circuit that detects and corrects, that more efficiently utilizes the capacity of a memory formed of groups of binary cells whose states can be inadvertently switched by ionizing radiation. Each memory cell has an asymmetric geometry, so that ionizing radiation causes a significantly greater probability of errors in one state than in the opposite state (e.g., an erroneous switch from '1' to '0' is far more likely than a switch from '0' to'1'. An asymmetric error correcting coding circuit can be used with the asymmetric memory cells, which requires fewer bits than an efficient symmetric error correcting code.

Buehler, Martin G. (inventor); Perlman, Marvin (inventor)

1991-01-01

440

Asymmetric effects on Earth's polar motion  

NASA Astrophysics Data System (ADS)

Differential equations ruling the Earth's polar motion are slightly asymmetric with respect to the pole coordinates. This is not only associated with the lack of axial symmetry around the Earth figure axis (triaxiality) but also with the longitude dependency of the pole tide (the main contribution). We propose a consistent handling of both asymmetric contributions, formulating a unique equation in the complex equatorial plane, of which we derive a general solution. Difference with respect to the usual symmetric solution is discussed and found significant in light of the present accuracy of the observed pole coordinates. For the same geophysical excitation, the prograde Chandler wobble is accompanied by a retrograde component up to 2 milliarcseconds (mas), transforming it in a slight elliptic motion. The asymmetric contribution is relatively larger in the geodetic excitation function, for Chandler wobble excitation mixes prograde and retrograde components of comparable level (1 mas).

Bizouard, Christian; Zotov, Leonid

2013-06-01

441

Asymmetric septal hypertrophy and hypothyroidism in children.  

PubMed Central

Any echocardiographic study of two children with hypothyroidism demonstrated the presence of asymmetric septal hypertrophy. One child died aged 11 months, and pronounced thickening of the interventricular septum was confirmed at necropsy. There was also hypertrophy of the left ventricular free wall. Histological examination showed only slight muscle fibre disarray, but there was striking vacuolation and hypertrophy of muscle fibres. In the second case, a child aged five years, the asymmetric septal hypertrophy disappeared after 18 months' treatment with L-thyroxine. Furthermore, other indices of myocardial function also returned to normal. The mechanism producing asymmetric septal hypertrophy in hypothyroidism is unknown. These are the youngest cases in which this association has been reported. Images PMID:2932134

Altman, D I; Murray, J; Milner, S; Dansky, R; Levin, S E

1985-01-01

442

Issues in Absolute Spectral Radiometric Calibration: Intercomparison of Eight Sources  

NASA Technical Reports Server (NTRS)

The application of atmospheric models to AVIRIS and other spectral imaging data to derive surface reflectance requires that the sensor output be calibrated to absolute radiance. Uncertainties in absolute calibration are to be expected, and claims of 92% accuracy have been published. Measurements of accurate surface albedos and cloud absorption to be used in radiative balance calculations depend critically on knowing the absolute spectral-radiometric response of the sensor. The Earth Observing System project is implementing a rigorous program of absolute radiometric calibration for all optical sensors. Since a number of imaging instruments that provide output in terms of absolute radiance are calibrated at different sites, it is important to determine the errors that can be expected among calibration sites. Another question exists about the errors in the absolute knowledge of the exoatmospheric spectral solar irradiance.

Goetz, Alexander F. H.; Kindel, Bruce; Pilewskie, Peter

1998-01-01

443

Asymmetric membrane osmotic capsules for terbutaline sulphate.  

PubMed

The aim of the present study was to design an asymmetric membrane capsule, an osmotic pump-based drug delivery system of ethyl cellulose for controlled release of terbutaline sulphate. asymmetric membrane capsules contains pore-forming water soluble additive, sorbitol in different concentrations in the capsule shell membrane, which after coming in contact with water, dissolves, resulting in an in situ formation of a microporous structure. The terbutaline sulphate is a ?-adrenoreceptor agonist widely used in the treatment of asthma. The oral dosage regimen of terbutaline sulphate is 5 mg twice or thrice daily, the plasma half-life is approximate 3-4 h and it produces GI irritation with extensive first pass metabolism. Hence, terbutaline sulphate was chosen as a model drug with an aim to develop controlled release system. Different formulations of ethyl cellulose were prepared by phase inversion technique using different concentrations of sorbitol as pore forming agent. It was found that the thickness of the prepared asymmetric membrane capsules was increased with increase in concentration of ethyl cellulose and pore forming agent, i.e. sorbitol. The dye release study in water and 10% sodium chloride solution indicates that, the asymmetric membrane capsules follow osmotic principle to release content. The pores formed due to sorbitol were confirmed by microscopic observation of transverse section of capsule membrane. Data of in vitro release study of terbutaline sulphate from asymmetric membrane capsules indicated that, the capsules prepared with 10% and 12.5% of ethyl cellulose and 25% of sorbitol released as much as 97.44% and 76.27% in 12 h, respectively with zero order release rate. Hence asymmetric membrane capsule of 10% ethyl cellulose and 25% of sorbitol is considered as optimum for controlled oral delivery of terbutaline sulphate. PMID:23204625

Gobade, N G; Koland, Marina; Harish, K H

2012-01-01

444

Positioning, alignment and absolute pointing of the ANTARES neutrino telescope  

NASA Astrophysics Data System (ADS)

A precise detector alignment and absolute pointing is crucial for point-source searches. The ANTARES neutrino telescope utilises an array of hydrophones, tiltmeters and compasses for the relative positioning of the optical sensors. The absolute calibration is accomplished by long-baseline low-frequency triangulation of the acoustic reference devices in the deep-sea with a differential GPS system at the sea surface. The absolute pointing can be independently verified by detecting the shadow of the Moon in cosmic rays.

Fehr, F.; Distefano, C.; Antares Collaboration

2010-01-01

445

Absolute luminosity measurements with the LHCb detector at the LHC  

Microsoft Academic Search

Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of

R. Aaij; B. Adeva; M. Adinolfi; C. Adrover; A. Affolder; Z. Ajaltouni; J. Albrecht; F. Alessio; M. Alexander; G. Alkhazov; P. Alvarez Cartelle; A. A. Alves Jr; S. Amato; Y. Amhis; J. Anderson; R. B. Appleby; O. Aquines Gutierrez; F. Archilli; L. Arrabito; A. Artamonov; M. Artuso; E. Aslanides; G. Auriemma; S. Bachmann; J. J. Back; D. S. Bailey; V. Balagura; W. Baldini; R. J. Barlow; C. Barschel; S. Barsuk; W. Barter; A. Bates; C. Bauer; Th. Bauer; A. Bay; I. Bediaga; K. Belous; I. Belyaev; E. Ben-Haim; M. Benayoun; G. Bencivenni; S. Benson; J. Benton; R. Bernet; M van Beuzekom; A. Bien; S. Bifani; A. Bizzeti; P. M. Bjørnstad; T. Blake; F. Blanc; C. Blanks; J. Blouw; S. Blusk; A. Bobrov; V. Bocci; A. Bondar; N. Bondar; W. Bonivento; S. Borghi; A. Borgia; T. J. V. Bowcock; C. Bozzi; T. Brambach; J. van den Brand; J. Bressieux; D. Brett; S. Brisbane; M. Britsch; T. Britton; N. H. Brook; H. Brown; A. Büchler-Germann; I. Burducea; A. Bursche; J. Buytaert; S. Cadeddu; J. M. Caicedo Carvajal; O. Callot; M. Calvi; M. Calvo Gomez; A. Camboni; P. Campana; A. Carbone; G. Carboni; R. Cardinale; A. Cardini; L. Carson; K. Carvalho Akiba; G. Casse; M. Cattaneo; M. Charles; Ph. Charpentier; N. Chiapolini; K. Ciba; X. Cid Vidal; G. Ciezarek; P. E. L. Clarke; M. Clemencic; H. V. Cliff; J. Closier; C. Coca; V. Coco; J. Cogan; P. Collins; F. Constantin; G. Conti; A. Contu; A. Cook; M. Coombes; G A Cowan; R. Currie; B. D'Almagne; C. D'Ambrosio; P. David; I. De Bonis; S. De Capua; M. De Cian; F. De Lorenzi; J. M. De Miranda; L. De Paula; P. De Simone; D. Decamp; M. Deckenhoff; H. Degaudenzi; M. Deissenroth; L. Del Buono; C. Deplano; O. Deschamps; F. Dettori; J. Dickens; H. Dijkstra; P. Diniz Batista; S. Donleavy; F. Dordei; A. Dosil Suárez; D. Dossett; A. Dovbnya; F. Dupertuis; R. Dzhelyadin; C. Eames; S. Easo; U. Egede; V. Egorychev; S. Eidelman; D. van Eijk; F. Eisele; S. Eisenhardt; R. Ekelhof; L. Eklund; Ch. Elsasser; D. G. d'Enterria; D. Esperante Pereira; L. Estève; A. Falabella; E. Fanchini; C. Färber; G. Fardell; C. Farinelli; S. Farry; V. Fave; V. Fernandez Albor; M. Ferro-Luzzi; S. Filippov; C. Fitzpatrick; M. Fontana; F. Fontanelli; R. Forty; M. Frank; C. Frei; M. Frosini; S. Furcas; A. Gallas Torreira; D. Galli; M. Gandelman; P. Gandini; Y. Gao; J. C. Garnier; J. Garofoli; J. Garra Tico; L. Garrido; C. Gaspar; N. Gauvin; M. Gersabeck; T. Gershon; Ph. Ghez; V V Gligorov; C. Göbel; D. Golubkov; A. Golutvin; A. Gomes; H. Gordon; M. Grabalosa Gándara; R. Graciani Diaz; L. A. Granado Cardoso; E. Graugés; G. Graziani; A. Grecu; S. Gregson; B. Gui; E. Gushchin; Yu. Guz; T. Gys; G. Haefeli; C. Haen; S. C. Haines; T. Hampson; S. Hansmann-Menzemer; R. Harji; N. Harnew; J. Harrison; P. F. Harrison; J. He; V. Heijne; K. Hennessy; P. Henrard; J. A. Hernando Morata; E. van Herwijnen; E. Hicks; W. Hofmann; K. Holubyev; P. Hopchev; W. Hulsbergen; P. Hunt; T. Huse; R. S. Huston; D. Hutchcroft; D. Hynds; V. Iakovenko; P. Ilten; J. Imong; R. Jacobsson; A. Jaeger; M. Jahjah Hussein; E. Jans; F. Jansen; P. Jaton; B. Jean-Marie; F. Jing; M. John; D. Johnson; C. R. Jones; B. Jost; S. Kandybei; M. Karacson; T. M. Karbach; J. Keaveney; U. Kerzel; T. Ketel; A. Keune; B. Khanji; Y. M. Kim; M. Knecht; S. Koblitz; P. Koppenburg; A. Kozlinskiy; L. Kravchuk; K. Kreplin; M. Kreps; G. Krocker; P. Krokovny; F. Kruse; K. Kruzelecki; M. Kucharczyk; S. Kukulak; R. Kumar; T. Kvaratskheliya; V. N. La Thi; D. Lacarrere; G. Lafferty; A. Lai; D. Lambert; R. W. Lambert; E. Lanciotti; G. Lanfranchi; C. Langenbruch; T. Latham; R. Le Gac; J. van Leerdam; J.-P. Lees; R. Lefèvre; A. Leflat; J. Lefrançois; O. Leroy; T. Lesiak; L. Li; L. Li Gioi; M. Lieng; M. Liles; R. Lindner; C. Linn; B. Liu; G. Liu; J. H. Lopes; E. Lopez Asamar; N. Lopez-March; J. Luisier; F. Machefert; I. V. Machikhiliyan; F. Maciuc; O. Maev; J. Magnin; S. Malde; R. M. D. Mamunur; G Mancinelli; N. Mangiafave; U. Marconi; R. Märki; J. Marks; G. Martellotti; A. Martens; L. Martin; A. Martín Sánchez; D. Martinez Santos; A. Massafferri; R. Matev; Z. Mathe; C. Matteuzzi; M. Matveev; E. Maurice; B. Maynard; A. Mazurov; G. McGregor; R. McNulty; C. Mclean; M. Meissner; M. Merk; J. Merkel; R. Messi; S. Miglioranzi; D. A. Milanes; M.-N. Minard; S. Monteil; D. Moran; P. Morawski; I. Mous; F. Muheim; K. Müller; R. Muresan; B. Muryn; M. Musy; J. Mylroie-Smith; P. Naik; T. Nakada; R. Nandakumar; J. Nardulli; I. Nasteva; M Needham; N. Neufeld; C. Nguyen-Mau; M. Nicol; S. Nies; V. Niess; N. Nikitin; A. Oblakowska-Mucha; V. Obraztsov; S. Oggero; S. Ogilvy; O. Okhrimenko; R. Oldeman; M. Orlandea; J. M. Otalora Goicochea; P. Owen; B. Pal; J. Palacios; M. Palutan; J. Panman; A. Papanestis; M. Pappagallo; C J Parkinson; G. Passaleva; G. D. Patel; M. Patel; S. K. Paterson; G. N. Patrick; C Pavel-Nicorescu; A. Pazos Alvarez; A. Pellegrino; G. Penso

2011-01-01

446

Absolute nuclear material assay using count distribution (LAMBDA) space  

DOEpatents

A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

Prasad, Manoj K. (Pleasanton, CA); Snyderman, Neal J. (Berkeley, CA); Rowland, Mark S. (Alamo, CA)

2012-06-05

447

Total absorption in asymmetric hyperbolic media  

PubMed Central

Finite-thickness slabs of hyperbolic media with tilted optical axes exhibit asymmetry properties for waves propagating upward and downward with respect to slab interfaces. Under certain conditions, asymmetric hyperbolic media acquire extreme permittivity parameters and the difference between upward and downward propagating waves becomes very large. Furthermore, both waves can be perfectly matched with the free space; such a feature makes possible the development of optically ultra thin perfect absorbers. The proposed approach is unified and allows the use of different -negative materials. Of particular interest is the asymmetric hyperbolic medium, made of silicon nanowires, since it can be directly applicable to solar cell systems. PMID:24036519

Nefedov, Igor S.; Valagiannopoulos, Constantinos A.; Hashemi, Seed M.; Nefedov, Evgeny I.

2013-01-01

448

Asymmetric Introgressive Hybridization Among Louisiana Iris Species  

PubMed Central

In this review, we discuss findings from studies carried out over the past 20+ years that document the occurrence of asymmetric introgressive hybridization in a plant clade. In particular, analyses of natural and experimental hybridization have demonstrated the consistent introgression of genes from Iris fulva into both Iris brevicaulis and Iris hexagona. Furthermore, our analyses have detected certain prezygotic and postzygotic barriers to reproduction that appear to contribute to the asymmetric introgression. Finally, our studies have determined that a portion of the genes transferred apparently affects adaptive traits. PMID:24710008

Arnold, Michael L.; Tang, Shunxue; Knapp, Steven J.; Martin, Noland H.

2010-01-01

449

Asymmetric interface temperature during vapor bubble growth  

NASA Astrophysics Data System (ADS)

We investigate the nucleation, growth, and detachment of single vapor bubbles at the interface microscale. Shear flow is used to investigate pool and convective boiling situations using visible and infrared visualizations. We determine a threshold Reynolds number for the onset of asymmetric interfacial temperatures. Below this threshold, bubble growth is geometrically and thermally symmetric, while above, bubbles no longer grow thermally symmetrically. This is explained by the dominance of convective heat transfer removal over viscous effects at the bubble interface. We experimentally demonstrate asymmetric interfacial temperature profiles that should be taken into account for future bubble growth modeling.

Diana, A.; Castillo, M.; Steinberg, T.; Brutin, D.

2013-07-01

450

Total Synthesis of Mycolactones A and B  

PubMed Central

First and second generation total syntheses of mycolactones A and B are reported. The first generation total synthesis unambiguously confirmed our earlier assignment of the relative and absolute stereochemistry of mycolactones A and B. Knowledge of the chemical properties of the mycolactones accumulated through the first generation total synthesis allowed us to implement several major improvements to the original synthesis, including: (1) optimizing the choice of protecting groups, (2) eliminating the unnecessary adjustment of protecting groups, and (3) improving the overall stereoselectivity and synthetic efficiency. The second generation total synthesis consists of 21 longest linear steps, with 8.8% overall yield. PMID:17940589

Song, Fengbin; Fidanze, Steve; Benowitz, Andrew B.; Kishi, Yoshito

2007-01-01

451

Absolute quantum energy inequalities in curved spacetime  

E-print Network

Quantum Energy Inequalities (QEIs) are results which limit the extent to which the smeared renormalised energy density of the quantum field can be negative, when averaged along a timelike curve or over a more general timelike submanifold in spacetime. On globally hyperbolic spacetimes the minimally-coupled massive quantum Klein--Gordon field is known to obey a `difference' QEI that depends on a reference state chosen arbitrarily from the class of Hadamard states. In many spacetimes of interest this bound cannot be evaluated explicitly. In this paper we obtain the first `absolute' QEI for the minimally-coupled massive quantum Klein--Gordon field on four dimensional globally hyperbolic spacetimes; that is, a bound which depends only on the local geometry. The argument is an adaptation of that used to prove the difference QEI and utilises the Sobolev wave-front set to give a complete characterisation of the singularities of the Hadamard series. Moreover, the bound is explicit and can be formulated covariantly under additional (general) conditions. We also generalise our results to incorporate adiabatic states.

Christopher J. Fewster; Calvin J. Smith

2007-02-09

452

Optimizing an Absolute Gravimeter Comparison Schedule  

NASA Astrophysics Data System (ADS)

Since 1980 various groups have executed comparisons of absolute gravimeters for the purpose of determining the accuracy of operational meters. While the final method of processing data and estimating meter accuracy has varied from comparison to comparison, one common fact has persisted - two meters can not observe gravity at both the same time and the same place. With this simple fact in mind, and despite variations in the final method of data processing, it has always been necessary to develop an efficient observation schedule for a comparison. Such a schedule must obviously depend on the number of meters in attendance and number of observing piers available. But other factors must be considered, such as how many observations each meter is required to make, how many times a meter compares to another meter and how many times a meter compares to itself - all of which effect the conditioning of the equation system. Finding the most efficient schedule with the greatest conditioning of the equation system is a problem of optimization. The number of possible combinations for even small numbers of meters and piers grows exponentially out of computational possibility if a brute force method is used. This talk discusses an efficient solution to forming such an optimized schedule, and a fast computer program which makes use of this solution.

Smith, D. A.; Saleh, J.; Eckl, M. C.

2013-12-01

453

Absolute number concentration measurement of submicrometer particles  

SciTech Connect

Condensation nuclei in the atmosphere are known to be an important factor in the development of clouds, the occurrence of rainfall, and the formation of particulate air pollutions that can cause undesirable effects on man and his environment. Condensation nuclei are invisible and numerous, and their number concentration has become the characteristic of interest and has been widely studied since the development of the first condensation nuclei counter by Aitken in 1888. A conventional nuclei counter employs the so-called condensation technique which enables the minute nuclei to grow, in a supersaturated environment, to ..mu..m-sized droplets; the number concentration of the visible droplets is then measured. Since each nucleus grows to a droplet, the number concentration of droplets and nuclei remains the same. The number of droplets is measured by (1) direct observation with a microscope (direct counter), (2) counting from photographs of the droplets (photographic counter), (3) suitably calibrated light transmission (or scattering) measurement (relative photoelectric counter). Most of the widely-used counters are relative counters in which the instrument reading must be calibrated against a direct or photographic counter. A new condensation nuclei counter is described which is designed to have the following advantages over the widely-used counters: (a) It provides an absolute concentration measurement. (b) Even a small random fluctuation of nuclei concentration can immediately be detected.

Chen, T.H.B.

1982-01-01

454

Absolute spacetime: the twentieth century ether  

E-print Network

All gauge theories need ``something fixed'' even as ``something changes.'' Underlying the implementation of these ideas all major physical theories make indispensable use of an elaborately designed spacetime model as the ``something fixed,'' i.e., absolute. This model must provide at least the following sequence of structures: point set, topological space, smooth manifold, geometric manifold, base for various bundles. The ``fine structure'' of spacetime inherent in this sequence is of course empirically unobservable directly, certainly when quantum mechanics is taken into account. This issue is at the basis of the difficulties in quantizing general relativity and has been approached in many different ways. Here we review an approach taking into account the non-Boolean properties of quantum logic when forming a spacetime model. Finally, we recall how the fundamental gauge of diffeomorphisms (the issue of general covariance vs coordinate conditions) raised deep conceptual problems for Einstein in his early development of general relativity. This is clearly illustrated in the notorious ``hole'' argument. This scenario, which does not seem to be widely known to practicing relativists, is nevertheless still interesting in terms of its impact for fundamental gauge issues.

Carl H. Brans

1998-01-09

455

Absolute radiance re-calibration of FIRST  

NASA Astrophysics Data System (ADS)

The FIRST (Far-InfraRed Spectroscopy of the Troposphere) instrument is a 10 to 100 micron spectrometer with 0.64 micron resolution designed to measure the complete mid and far-infrared radiance of the Earth's Atmosphere. FIRST has been successfully used to obtain high-quality atmospheric radiance data from the ground and from a high-altitude balloon. A Fourier transform interferometer is used to provide the spectral resolution and two on-board blackbodies are used for calibration. This paper discusses the recent re-calibration of FIRST at Space Dynamics Laboratory for absolute radiance accuracy. The calibration used the LWRICS (Long Wave Infrared Calibration Source) blackbody, which NIST testing shows to be accurate to the ~100 mK level in brightness temperature. There are several challenges to calibrating FIRST, including the large dynamic range, out of phase light, and drift in the interferogram phase. The accuracy goal for FIRST was 0.2 K over most of the 10 to 100 micron range, and results show FIRST meets this goal for a range of target temperatures.

Latvakoski, Harri; Mlynczak, Martin; Johnson, David; Cageao, Rich; Swasey, Jason; Johnson, Kendall

2012-10-01

456

Absolute and Convective Instability of a Liquid Jet  

NASA Technical Reports Server (NTRS)

The existence of absolute instability in a liquid jet has been predicted for some time. The disturbance grows in time and propagates both upstream and downstream in an absolutely unstable liquid jet. The image of absolute instability is captured in the NASA 2.2 sec drop tower and reported here. The transition from convective to absolute instability is observed experimentally. The experimental results are compared with the theoretical predictions on the transition Weber number as functions of the Reynolds number. The role of interfacial shear relative to all other relevant forces which cause the onset of jet breakup is explained.

Lin, S. P.; Hudman, M.; Chen, J. N.

1999-01-01

457

Organocatalytic cascade reactions as a new tool in total synthesis  

NASA Astrophysics Data System (ADS)

The total synthesis of natural products and biologically active compounds, such as pharmaceuticals and agrochemicals, has reached an extraordinary level of sophistication. We are, however, still far away from the 'ideal synthesis' and the state of the art is still frequently hampered by lengthy protecting-group strategies and costly purification procedures derived from the step-by-step protocols. In recent years several new criteria have been brought forward to solve these problems and to improve total synthesis: atom, step and redox economy or protecting-group-free synthesis. Over the past decade the research area of organocatalysis has rapidly grown to become a third pillar of asymmetric catalysis standing next to metal and biocatalysis, thus paving the way for a new and powerful strategy that can help to address these issues - organocatalytic cascade reactions. In this Review we present the first applications of such asymmetric organocascade reactions to the total synthesis of natural products.

Grondal, Christoph; Jeanty, Matthieu; Enders, Dieter

2010-03-01

458

An efficient route to chiral N-heterocycles bearing a C-F stereogenic center via asymmetric hydrogenation of fluorinated isoquinolines.  

PubMed

An efficient iridium-catalyzed asymmetric hydrogenation of the fluorinated isoquinoline derivatives has been successfully developed for the synthesis of chiral fluorinated tetrahydroisoquinoline derivatives with up to 93% ee. This methodology features the use of a hydrochloride salt as well as a catalytic amount of halogenated hydantoin which were vital for the reactivity, enantioselectivity, and inhibition of the hydrodefluorination pathway. PMID:23945790

Guo, Ran-Ning; Cai, Xian-Feng; Shi, Lei; Ye, Zhi-Shi; Chen, Mu-Wang; Zhou, Yong-Gui

2013-10-01

459

Orion Absolute Navigation System Progress and Challenge  

NASA Technical Reports Server (NTRS)

The absolute navigation design of NASA's Orion vehicle is described. It has undergone several iterations and modifications since its inception, and continues as a work-in-progress. This paper seeks to benchmark the current state of the design and some of the rationale and analysis behind it. There are specific challenges to address when preparing a timely and effective design for the Exploration Flight Test (EFT-1), while still looking ahead and providing software extensibility for future exploration missions. The primary onboard measurements in a Near-Earth or Mid-Earth environment consist of GPS pseudo-range and delta-range, but for future explorations missions the use of star-tracker and optical navigation sources need to be considered. Discussions are presented for state size and composition, processing techniques, and consider states. A presentation is given for the processing technique using the computationally stable and robust UDU formulation with an Agee-Turner Rank-One update. This allows for computational savings when dealing with many parameters which are modeled as slowly varying Gauss-Markov processes. Preliminary analysis shows up to a 50% reduction in computation versus a more traditional formulation. Several state elements are discussed and evaluated, including position, velocity, attitude, clock bias/drift, and GPS measurement biases in addition to bias, scale factor, misalignment, and non-orthogonalities of the accelerometers and gyroscopes. Another consideration is the initialization of the EKF in various scenarios. Scenarios such as single-event upset, ground command, and cold start are discussed as are strategies for whole and partial state updates as well as covariance considerations. Strategies are given for dealing with latent measurements and high-rate propagation using multi-rate architecture. The details of the rate groups and the data ow between the elements is discussed and evaluated.

Holt, Greg N.; D'Souza, Christopher

2012-01-01

460

Absolute determination of local tropospheric OH concentrations  

NASA Technical Reports Server (NTRS)

Long path absorption (LPA) according to Lambert Beer's law is a method to determine absolute concentrations of trace gases such as tropospheric OH. We have developed a LPA instrument which is based on a rapid tuning of the light source which is a frequency doubled dye laser. The laser is tuned across two or three OH absorption features around 308 nm with a scanning speed of 0.07 cm(exp -1)/microsecond and a repetition rate of 1.3 kHz. This high scanning speed greatly reduces the fluctuation of the light intensity caused by the atmosphere. To obtain the required high sensitivity the laser output power is additionally made constant and stabilized by an electro-optical modulator. The present sensitivity is of the order of a few times 10(exp 5) OH per cm(exp 3) for an acquisition time of a minute and an absorption path length of only 1200 meters so that a folding of the optical path in a multireflection cell was possible leading to a lateral dimension of the cell of a few meters. This allows local measurements to be made. Tropospheric measurements have been carried out in 1991 resulting in the determination of OH diurnal variation at specific days in late summer. Comparison with model calculations have been made. Interferences are mainly due to SO2 absorption. The problem of OH self generation in the multireflection cell is of minor extent. This could be shown by using different experimental methods. The minimum-maximum signal to noise ratio is about 8 x 10(exp -4) for a single scan. Due to the small size of the absorption cell the realization of an open air laboratory is possible in which by use of an additional UV light source or by additional fluxes of trace gases the chemistry can be changed under controlled conditions allowing kinetic studies of tropospheric photochemistry to be made in open air.

Armerding, Wolfgang; Comes, Franz-Josef

1994-01-01

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