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1

Stable Cyclic Carbenes and Related Species beyond Diaminocarbenes  

PubMed Central

The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong ?-donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus-based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon-based ligands (which are not NHCs), and which feature even stronger ?-donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made. PMID:20836099

Melaimi, Mohand; Soleilhavoup, Michèle

2011-01-01

2

Highly stable water-soluble platinum nanoparticles stabilized by hydrophilic N-heterocyclic carbenes.  

PubMed

Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N-heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt?complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high-resolution TEM, and spectroscopic techniques. Solid-state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a (13) C-(195) Pt?coupling constant for the first time in a nanosystem (940?Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle. PMID:25267410

Baquero, Edwin A; Tricard, Simon; Flores, Juan Carlos; de Jesús, Ernesto; Chaudret, Bruno

2014-11-24

3

Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold.  

PubMed

Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts. This increased stability is related to the increased strength of the gold-carbon bond relative to that of a gold-sulfur bond, and to a different mode of bonding in the case of the carbene ligand. Once bound to gold, NHCs are not displaced by thiols or thioethers, and are stable to high temperatures, boiling water, organic solvents, pH extremes, electrochemical cycling above 0 V and 1% hydrogen peroxide. In particular, benzimidazole-derived carbenes provide films with the highest stabilities and evidence of short-range molecular ordering. Chemical derivatization can be employed to adjust the surface properties of NHC-based SAMs. PMID:24755592

Crudden, Cathleen M; Horton, J Hugh; Ebralidze, Iraklii I; Zenkina, Olena V; McLean, Alastair B; Drevniok, Benedict; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J; Seki, Tomohiro; Keske, Eric C; Leake, Joanna D; Rousina-Webb, Alexander; Wu, Gang

2014-05-01

4

Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold  

NASA Astrophysics Data System (ADS)

Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts. This increased stability is related to the increased strength of the gold-carbon bond relative to that of a gold-sulfur bond, and to a different mode of bonding in the case of the carbene ligand. Once bound to gold, NHCs are not displaced by thiols or thioethers, and are stable to high temperatures, boiling water, organic solvents, pH extremes, electrochemical cycling above 0 V and 1% hydrogen peroxide. In particular, benzimidazole-derived carbenes provide films with the highest stabilities and evidence of short-range molecular ordering. Chemical derivatization can be employed to adjust the surface properties of NHC-based SAMs.

Crudden, Cathleen M.; Horton, J. Hugh; Ebralidze, Iraklii I.; Zenkina, Olena V.; McLean, Alastair B.; Drevniok, Benedict; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J.; Seki, Tomohiro; Keske, Eric C.; Leake, Joanna D.; Rousina-Webb, Alexander; Wu, Gang

2014-05-01

5

Syntheses of sterically shielded stable carbenes of the 1,2,4-triazole series and their corresponding palladium complexes: efficient catalysts for chloroarene hydrodechlorination.  

PubMed

The new sterically shielded 1,3,4-trisubstituted 1,2,4-triazol-5-ylidenes were synthesized by a three step method starting from 2-phenyl-1,3,4-oxadiazole. The syntheses of palladium complexes and (including the sterically shielded derivatives and ) were carried out via the reactions of the stable carbenes with palladium halogenide salts in THF or toluene solution. Complexes and were found to be excellent catalysts for the reductive dechlorination (hydrodechlorination) of p-dichlorobenzene. The structures of , , and were determined by single-crystal X-ray diffraction. PMID:25030067

Glinyanaya, Nataliya V; Saberov, Vagiz Sh; Korotkikh, Nikolai I; Cowley, Alan H; Butorac, Rachel R; Evans, Daniel A; Pekhtereva, Tatyana M; Popov, Anatolii F; Shvaika, Oles P

2014-10-14

6

Palladium-catalyzed carbene migratory insertion using conjugated ene-yne-ketones as carbene precursors.  

PubMed

Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, ?-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate, which is supported by DFT calculations. The palladium carbene character of the key intermediate is validated by three aspects, including bond lengths, Wiberg bond order indices, and molecular orbitals, by comparison to those reported for stable palladium carbene species. Computational studies also revealed that the rate-limiting step is ene-yne-ketone cyclization, which leads to the formation of the palladium (2-furyl)carbene, while the subsequent carbene migratory insertion is a facile process with a low energy barrier (<5 kcal/mol). PMID:23947689

Xia, Ying; Qu, Shuanglin; Xiao, Qing; Wang, Zhi-Xiang; Qu, Peiyuan; Chen, Li; Liu, Zhen; Tian, Leiming; Huang, Zhongxing; Zhang, Yan; Wang, Jianbo

2013-09-11

7

Shape-Controllable Formation of Poly-imidazolium Salts for Stable Palladium N-Heterocyclic Carbene Polymers  

NASA Astrophysics Data System (ADS)

The imidazolium-based main-chain organic polymers are one of promising platforms in heterogeneous catalysis, the size and outer morphology of polymer particles are known to have important effects on their physical properties and catalytic applications, but main-chain ionic polymers usually generate amorphous or spherical particles. Herein, we presented a versatile and facile synthetic route for size- and shape-controllable synthesis of main-chain poly-imidazolium particles. The wire-shaped, spherical and ribbon-shaped morphologies of poly-imidazolium particles were readily synthesized through quaternization of bis-(imidazol-1-yl)methane and 2,4,6-tris(4-(bromomethyl)phenyl)-1,3,5-triazine, and the modification of their size and morphology were realized through adjusting solvent polarity, solubility, concentration and temperatures. The direct complexation of the particles with Pd(OAc)2 produced ionic polymers containing palladium N-heterocyclic carbene units (NHCs) with intactness of original morphologies. The particle morphologies have a significant effect on catalytic performances. Wire-shaped palladium-NHC polymer shows excellent catalytic activity and recyclabilty in heterogeneous Suzuki-Miyaura cross-coupling reaction.

Zhao, Huaixia; Li, Liuyi; Wang, Yangxin; Wang, Ruihu

2014-06-01

8

Carbenes and Nitrenes  

ERIC Educational Resources Information Center

Summarizes the general methods for carbene and nitrene formation and the reactions in which carbenes and nitrenes are involved such as their reactions with transition metal atoms, alkenes of aromatic compounds, and uncharged oxygen or nitrogen nucleophiles. (CC)

Coyle, J. D.

1974-01-01

9

Carbene generation by cytochromes and electronic structure of heme-iron-porphyrin-carbene complex: a quantum chemical study.  

PubMed

Carbene-heme-iron-porphyrin complexes generated from cytochrome P450 (CYP450)-mediated metabolism of compounds containing methylenedioxyphenyl (MDP) moiety lead to the mechanism-based inhibition (MBI) of CYPs. This coordination complex is termed as the metabolic-intermediate complex (MIC). The bioinorganic chemistry of MDP carbenes has been studied using quantum chemical methods employing density functional theory (B3LYP functional with implicit solvent corrections) to (i) analyze the characteristics of MDP-carbene in terms of singlet-triplet energy difference, protonation, and dimerization energies, etc.; (ii) determine the electronic structure and analyze the Fe-carbene interactions; and (iii) elucidate the potential reaction pathways for the generation of carbene, using Cpd I (iron(IV)-oxo-porphine with SH(-) as the axial ligand) as the model oxidant to mimic the activity of CYP450. The results show that MDP-carbenes are sufficiently stable and nucleophilic, leading to the formation of stable MIC (-40.35 kcal/mol) on the doublet spin state, formed via interaction between ?(LP) of carbene and empty dz(2) orbital of heme-iron. This was aided by the back-bonding between filled d(xz) orbital of heme-iron and the empty p orbital of carbene. The mechanistic pathway proposed in the literature for the generation of MDP-carbene (CH hydroxylation followed by water elimination) was studied, and observed to be unfavorable, owing to the formation of highly stable hydroxylated product (-57.12 kcal/mol). An intriguing pathway involving hydride ion abstraction and proton transfer followed by water elimination step was observed to be the most probable pathway. PMID:23560646

Taxak, Nikhil; Patel, Bhargav; Bharatam, Prasad V

2013-05-01

10

Air-stable, convenient to handle Pd based PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation) themed precatalysts of N\\/O-functionalized N-heterocyclic carbenes and its utility in Suzuki–Miyaura cross-coupling reaction  

Microsoft Academic Search

Several new air-stable, convenient to handle and easily synthesized Pd based PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) type precatalysts supported over N\\/O-functionalized N-heterocyclic carbenes (NHC) namely, trans-(1-(benzyl)-3- (N-t-butylacetamido)imidazol-2-ylidene)Pd(pyridine)Cl2 (2), trans-(1-(2-hydroxy-cyclohexyl)-3- (benzyl)imidazol-2-ylidene)Pd(pyridine)Cl2 (3 )a ndtrans-(1-(o-methoxybenzyl)-3-(t-butyl)imidazol-2- ylidene)Pd(pyridine)Br2 (4), have been designed. Specifically, the Pd-NHC complexes, 2, 3 and 4 ,w ere conveniently synthesized from their respective imidazolium halide salts by

Lipika Ray; Mobin M. Shaikh; Prasenjit Ghosh

2007-01-01

11

Carbene-Stabilized Main Group Radicals and Radical Ions  

PubMed Central

Shortly after their discovery at the end of the 80s, stable singlet carbenes have been recognized as excellent ligands for transition metal based catalysts, and as organo-catalysts in their own right. At the end of the 2000s, it has been shown that they can coordinate main group elements in their zero oxidation state, and even activate small molecules. This review covers examples in the literature dealing with the most recent application of stable singlet carbenes, namely their use to stabilize radicals and radical ions that are otherwise unstable. PMID:23878717

Martin, Caleb D.; Soleilhavoup, Michele; Bertrand, Guy

2013-01-01

12

Synthesis and Properties of Chelating N-Heterocyclic Carbene Rhodium(I) Complexes: Synthetic Experiments in Current Organometallic Chemistry  

ERIC Educational Resources Information Center

The preparation and characterization of two air-stable Rh(I) complexes bearing a chelating N-heterocyclic carbene (NHC) ligand is described. The synthesis involves the preparation of a Ag(I)-NHC complex and its use as carbene transfer agent to a Rh(I) precursor. The so obtained complex can be further reacted with carbon monoxide to give the…

Mata, Jose A.; Poyatos, Macarena; Mas-Marza, Elena

2011-01-01

13

Synthesis, characterization and biological evaluation of some novel P-heterocyclic androst-4-ene derivatives.  

PubMed

The reactions of 21-hydroxyprogesterone with Lawesson's reagent in toluene or [Formula: see text] gave four P-heterocyclic androst-4-ene derivatives (two tautomeric pairs): 4-(3-thioxoandrost-4-en-17[Formula: see text]-yl)-1,3,2-oxathiaphosphole-2- sulfide (2), 4-(3-thioxoandrost-4-en-17[Formula: see text]-ylidene)-1,3,2-oxathiaphospholane-2-sulfide (3), 4-(3-oxoandrost-4-en-17[Formula: see text]-yl)-1,3,2-oxathiaphosphole-2-sulfide (4), and 4-(3-oxoandrost-4-en-17[Formula: see text]-ylidene)-1,3,2- oxathiaphospholane-2-sulfide (5). The structures of all novel 17-substituted steroids were elucidated from their analytic and spectral data (HRMS, IR, 1D NMR and 2D NMR-HSQC, HMBC, NOESY, COSY). The detailed NMR analysis for all compounds revealed the presence of two pairs of signals in approx. 8:2 ratio indicating the existence of two diastereoisomers (a and b) with different configurations at the phosphorus atom. A parallel analysis of heteronuclear 2D [Formula: see text]-[Formula: see text] spectra (HSQC and HMBC) and homonuclear 2D spectra (NOESY and COSY) enabled complete [Formula: see text] and [Formula: see text] assignments of each isomer and provided evidence for the preferred configuration on phosphorus atom. Cytotoxic activity in vitro was tested against four tumor cell lines (human cervix carcinoma HeLa cells, chronic myelogenous leukemia K-562 and two human breast carcinoma MDA-MB-361 and MDA-MB-453 cells). Compounds 3a,b and 4a,b showed a poor activity against HeLa and MDA-MB-453 cell lines, while against MDA-MB-361 cell line, all tested compounds exerted very weak cytotoxic effect. All compounds exerted moderate activity against K562 cells. Antimicrobial activity against Gram-positive, Gram-negative bacteria and fungal cells, and toxicity to brine shrimp Artemia salina were evaluated. All tested compounds showed strong antifungal activity. PMID:23748368

Krsti?, Natalija M; Pavlovi?, Vladimir D; Novakovi?, Irena T; Mati?, Ivana Z; Sladi?, Dušan M

2013-08-01

14

Planar tris-N-heterocyclic carbenes.  

PubMed

To further explore the coordination chemistry of poly-carbene complexes, two triphenylene-based planar tridentate N-heterocyclic carbenes and their corresponding tri-gold complexes were synthesized. Molecular structures of the tert-butyl substituted tritopic free carbene and the tri-nuclear gold complex were determined experimentally. A silver-dicarbene organometallic polymer was also prepared with the newly synthesized tris-NHC. PMID:23846191

Wang, Yun-Ting; Chang, Meng-Ting; Lee, Gene-Hsiang; Peng, Shie-Ming; Chiu, Ching-Wen

2013-08-21

15

Ruthenium Vinyl Carbene Intermediates in Enyne Metathesis  

PubMed Central

This review provides an overview of ruthenium vinyl carbene reactivity as it relates to enyne metathesis. Methods for the synthesis of metathesis-active and metathesis-inactive complexes are also summarized. Some of the early hypotheses about vinyl carbene intermediates in enyne metatheses were tested in the arena of synthetic chemistry and subsequently led to mechanistic studies. In these two areas, studies from the author's labs are described. There are still many unresolved questions in enyne metathesis that trace back to vinyl carbene reactivity. Hopefully this review will stimulate further investigation into vinyl carbene reactivity which should further refine our understanding of catalytic enyne metathesis. PMID:19590747

Diver, Steven T.

2009-01-01

16

Hydroboration of arynes with N-heterocyclic carbene boranes.  

PubMed

Arynes were generated in situ from ortho-silyl aryl triflates and fluoride ions in the presence of stable N-heterocyclic carbene boranes (NHC?BH3 ). Spontaneous hydroboration ensued to provide stable B-aryl-substituted NHC-boranes (NHC?BH2 Ar). The reaction shows good scope in terms of both the NHC-borane and aryne components and provides direct access to mono- and disubstituted NHC-boranes. The formation of unusual ortho regioisomers in the hydroboration of arynes with an electron-withdrawing group supports a hydroboration process with hydride-transfer character. PMID:25346015

Taniguchi, Tsuyoshi; Curran, Dennis P

2014-11-24

17

Carbenes:.ASlody in Quantitative and Qualitative Theory  

E-print Network

XCVCarbeneAngleandtheSinglet-TripietGap:Models,Mnemonics,and Correlatives.. ......... 4. Introductionto theOuantitative . . . . . 5.CarbeneOrbitals ......... 6. CarbeneElectronicConfigurations interesting carbene phenomena to be shown by the 3 atom, 6 valence ciectron, and 8 all electron level ofthe. .. . . . .. . . . .. 7. ConfigurationInteractioninCarbenes:Fundamentais.. . . 8. Configuration

Simons, Jack

18

Exotic noble gas carbene-like ions  

NASA Astrophysics Data System (ADS)

Using a combination of theoretical techniques, this work studies the Kr2C2+ species, which has electronic, structural, and some typical chemical characteristics of carbenes, and whose ground state is singlet. Similarly to the case of traditional carbenes, Kr2C2+ is metastable and appears to be a candidate for a reactive intermediate.

Echeverri, Andrea; Moreno, Norberto; Restrepo, Albeiro; Hadad, C. Z.

2014-11-01

19

N-Heterocyclic Carbene-Catalyzed Alcohol Acetylation: An Organic Experiment Using Organocatalysis  

ERIC Educational Resources Information Center

Undergraduate students in the teaching laboratory have successfully used N-heterocyclic carbenes (NHCs) as organocatalysts for the acetylation of primary alcohols, despite the high water sensitivity of uncomplexed ("free") NHCs. The free NHC readily reacted with chloroform, resulting in an air- and moisture-stable adduct that liberates…

Morgan, John P.; Shrimp, Jonathan H.

2014-01-01

20

A Three-Step Laboratory Sequence to Prepare a Carbene Complex of Silver(I) Chloride  

ERIC Educational Resources Information Center

We have developed a multistep inorganic synthesis experiment for our second-year undergraduate teaching laboratory that introduces students to modern organometallic chemistry. The ligands are prepared in two simple steps and the preparation of an air-stable silver carbene complex is accomplished in the third step. The students are introduced to…

Canal, John P.; Ramnial, Taramatee; Langlois, Lisa D.; Abernethy, Colin D.; Clyburne, Jason A. C.

2008-01-01

21

N-Heterocyclic carbene boranes are good hydride donors.  

PubMed

The nucleophilicity parameters (N) of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene borane and 1,3-dimethylimidazol-2-ylidene borane are 9.55 and 11.88. This places N-heterocyclic carbene boranes (NHC-boranes) among the most nucleophilic classes of neutral hydride donors. Reductions of highly electron-poor C?N and C?C bonds provide hydrogenation products along with new, stable borylated products. The results suggest that NHC-boranes have considerable untapped potential as neutral organic reductants. PMID:22149270

Horn, Markus; Mayr, Herbert; Lacôte, Emmanuel; Merling, Everett; Deaner, Jordan; Wells, Sarah; McFadden, Timothy; Curran, Dennis P

2012-01-01

22

An overview of N-heterocyclic carbenes  

NASA Astrophysics Data System (ADS)

The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

Hopkinson, Matthew N.; Richter, Christian; Schedler, Michael; Glorius, Frank

2014-06-01

23

?-Silyl-substituted norbornyl carbocations and carbenes.  

PubMed

endo-2-Trimethylsilyl-anti-7-norbornyl triflate undergoes solvolysis reactions 1.8 × 10(4) faster than 7-norbornyl triflate in CD3CO2D and 1.3 × 10(5) times faster in CF3CH2OH. The exclusive substitution products with retained stereochemistry point to a significantly stabilized ?-trimethylsilyl carbocation intermediate. The endo-2-trimethylsilyl-7-norbornyl carbene gives a major rearrangement product where the trimethylsilyl-activated hydrogen migrates to the carbenic center. This rearrangement product implies stabilization of the carbene by the ?-trimethylsilyl group. Isodesmic computational studies (M062X/6-311+G**) indicate that the endo-2-trimethylsilyl-7-norbornyl cation is stabilized by 16.2 kcal/mol and that the endo-2-trimethylsilyl-7-norbornyl carbene is stabilized by a smaller factor of 1.8 kcal/mol. By way of contrast, anti-7-trimethylsilyl-endo-2-norbornyl mesylate undergoes solvolysis in CD3CO2D only 2.6 times faster than endo-2-norbornyl mesylate and 9.4 times faster in CF3CH2OH. The substitution products have only partially retained stereochemistry, and significant rearrangements are observed. The anti-7-trimethylsilyl-2-norbornyl carbene gives a rearrangement product via 1,3-hydrogen migration of the C6 hydrogen, which is completely analogous to the behavior of the unsubstituted 2-norbornyl carbene. Isodesmic calculations show that the anti-7-trimethylsilyl-2-norbornyl cation is stabilized by only 3.2 kcal/mol relative to the 2-norbornyl cation, and the corresponding anti-7-trimethylsilyl-2-norbornyl carbene is stabilized by a negligible 0.9 kcal/mol. PMID:24548109

Creary, Xavier; Heffron, Anna

2014-03-21

24

Carbene based photochemical molecular assemblies for solar driven hydrogen generation.  

PubMed

Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging ligands have been prepared and structurally and photophysically characterised. The identity of the NHC-unit of the bridging ligand was established unambiguously by means of X-ray structural analysis of a heterodinuclear ruthenium-silver complex. The photophysical data indicate ultrafast intersystem crossing into an emissive and a non-emissive triplet excited state after excitation of the ruthenium centre. Exceptionally high luminescence quantum yields of up to 39% and long lifetimes of up to 2 ?s are some of the triplet excited state characteristics. Preliminary studies into the visible light driven photocatalytic hydrogen formation show no induction phase and constant turnover frequencies that are independent on the concentration of the photocatalyst. In conclusion this supports the notion of a stable assembly under photocatalytic conditions. PMID:25100041

Peuntinger, Katrin; Pilz, T David; Staehle, Robert; Schaub, Markus; Kaufhold, Simon; Petermann, Lydia; Wunderlin, Markus; Görls, Helmar; Heinemann, Frank W; Li, Jing; Drewello, Thomas; Vos, Johannes G; Guldi, Dirk M; Rau, Sven

2014-09-28

25

The synthesis of ?-alkoxy and ?-aminostannanes as precursors to Novel Chromium Fischer Carbenes.  

E-print Network

??The present study involves the use of main group organometallics: organostannanes and organolithiums as precursors to chromium Fischer carbene complexes. Fischer carbenes are well stabilized… (more)

Meyer, Annalene

2012-01-01

26

Early metal bis(phosphorus-stabilised)carbene chemistry.  

PubMed

Since the discovery of covalently-bound mid- and late-transition metal carbenes there has been a spectacular explosion of interest in their chemistry, but their early metal counterparts have lagged behind. In recent years, bis(phosphorus-stabilised)carbenes have emerged as valuable ligands for metals across the periodic table, and their use has in particular greatly expanded covalently-bound early metal carbene chemistry. In this tutorial review we introduce the reader to bis(phosphorus-stabilised)carbenes, and cover general preparative methods, structure and bonding features, and emerging reactivity studies of early metal derivatives (groups 1-4 and the f-elements). PMID:21321726

Liddle, Stephen T; Mills, David P; Wooles, Ashley J

2011-05-01

27

Isolation of a neutral boron-containing radical stabilized by a cyclic (alkyl)(amino)carbene.  

PubMed

Utilizing a cyclic (alkyl)(amino)carbene (CAAC) as a ligand, neutral CAAC-stabilized radicals containing a boryl functionality could be prepared by reduction of the corresponding haloborane adducts. The radical species with a duryl substituent was fully characterized by single-crystal X-ray structural analysis, EPR spectroscopy, and DFT calculations. Compared to known neutral boryl radicals, the isolated radical species showed larger spin density on the boron atom. Furthermore, the compound that was isolated is extraordinarily stable to high temperatures under inert conditions, both in solution and in the solid state. Electrochemical investigations of the radical suggest the possibility to generate a stable formal boryl anion species. PMID:24917474

Bissinger, Philipp; Braunschweig, Holger; Damme, Alexander; Krummenacher, Ivo; Phukan, Ashwini K; Radacki, Krzysztof; Sugawara, Shun

2014-07-01

28

On the organocatalytic activity of N-heterocyclic carbenes: role of sulfur in thiamine.  

PubMed

The reaction energy profiles of the benzoin condensation from three aldehydes catalyzed by imidazol-2-ylidene, triazol-3-ylidene, and thiazol-2-ylidene have been investigated computationally. The barriers for all steps of all investigated reactions have been found to be low enough to indicate the viability of the mechanism proposed by Breslow in the 1950s. The most remarkable difference in the catalytic cycles has been the increased stability of the Breslow intermediate in case of thiazol-2-ylidene (by ca. 10 kcal/mol) compared to the other two carbenes, which results in lower energy for the coupling of the second aldehyde molecule, thus, increasing the reversibility of the reaction. Since the analogous transketolase reaction, being involved in the carbohydrate metabolism of many organisms, requires an initial decoupling-a reverse benzoin condensation-this difference provides a reasonable explanation for the presence of a thiazolium ring in thiamine instead of the otherwise generally more available imidazole derivatives. The "resting intermediate" found by Berkessel and co-workers for a triazole-based catalyst was found more stable than the Breslow intermediate for all of the systems investigated. The (gas phase) proton affinities of several carbenes were compared, the relative trends being in agreement with the available (in aqueous solution) data. The hydrolytic ring-opening reaction of the thiazole-based carbene was shown to be different from that of imidazole-2-ylidenes. PMID:22731396

Hollóczki, Oldamur; Kelemen, Zsolt; Nyulászi, László

2012-07-20

29

Evidence for Nonstatistical Dynamics in the Wolff Rearrangement of a Carbene  

PubMed Central

Two 13C-labeled isomers of the formal Diels?Alder adduct of acetylmethyloxirene to tetramethyl 1,2,4,5-benzenetetracarboxylate have been synthesized. Flash vacuum thermolysis of these adducts leads to various isotopic isomers of acetylmethylketene, the ratios of which have been determined by NMR. The surprising finding that the principal product comes from methylpyruvoyl carbene rather than its more stable isomer diacetylcarbene is explained by MPWB1K density functional calculations, which show that the reactant probably undergoes a unimolecular rearrangement to a norcaradiene derivative prior to its fragmentation. Coupled-cluster calculations on the methylpyruvoyl carbene show that it is capable of undergoing three unimolecular isomerizations. The fastest is 1,2-acetyl migration to give acetylmethylketene directly. The next is rearrangement via acetylmethyloxirene to diacetylcarbene and thence by Wolff rearrangement to acetylmethylketene. The least-favorable reaction is degenerate rearrangement via 1,3-dimethyl-2-oxabicyclo[1.1.0]butan-4-one (the epoxide of dimethylcyclopropenone). The combined experimental and computational results indicate that Wolff rearrangement of the diacetylcarbene occurs with a 2.5:1 ratio of the methyl groups despite the fact that they are related by a twofold axis of symmetry in the carbene. Preliminary molecular dynamics simulations are consistent with this conclusion. Taken together, the results suggest that the Wolff rearrangement is subject to the same kind of nonstatistical dynamical effects detected for other kinds of thermally generated reactive intermediates. PMID:18700757

2008-01-01

30

Reactions of diaryldibromodisilenes with N-heterocyclic carbenes: formation of formal bis-NHC adducts of silyliumylidene cations.  

PubMed

Reactions of stable 1,2-dibromodisilenes ((E)-Ar(Br)Si=Si(Br)Ar) with N-heterocyclic carbenes (NHC) afforded NHC-arylbromosilylene adducts or bromide salts of the corresponding bis-NHC adducts of the formal arylsilyliumylidene cations ([ArSi:](+)). In some cases, an NHC was able to replace a bromide anion in the coordination sphere of the arylbromosilylene-NHC adduct. PMID:25043690

Agou, Tomohiro; Hayakawa, Naoki; Sasamori, Takahiro; Matsuo, Tsukasa; Hashizume, Daisuke; Tokitoh, Norihiro

2014-07-21

31

Protonolysis and thermolysis reactions of functionalised NHC-carbene boranes and borates.  

PubMed

A set of ?-ketoimidazolium and ?-ketoimidazolinium salts of the general formula [R(1)C(O)CH2{CH[NCR(3)CR(3)N(R(2))]}]X (R(1) = (t)Bu, naphth; R(2) = (i)Pr, Mes, (t)Bu; R(3) = H, Me, (H)2; X = Cl, Br) show contrasting reactivity with superhydride bases MHBEt3; two are reduced to chiral ?-alcohol carbene-boranes R(1)CH(OH)CH2{C(BEt3)[NCR(3)CR(3)N(R(2))]} (R(1) = (t)Bu; R(2) = (i)Pr, Mes; R(3) = H), two with bulky R(2) substituents are reduced to chiral ?-borate imidazolium salts [R(1)CH(OBEt3)CH2{CH[NCR(3)CR(3)N(R(2))]}]X (R(1) = (t)Bu, naphth; R(2) = Mes, (t)Bu; R(3) = H, Me; X = Cl, Br), and the two saturated heterocycle derivatives remain unreduced but form carbene-borane adducts R(1)C(O)CH2{C(BEt3)[NCR(3)CR(3)N(R(2))]} (R(1) = (t)Bu, naphth; R(2) = Mes; R(3) = (H)2). Heating solutions of the imidazolium borates results in the elimination of ethane, in the first example of organic borates functioning as Brønsted bases and forming carbene boranes R(1)CH(OBEt2)CH2{C[NCR(3)CR(3)N(R(2))]} (R(1) = naphth; R(2) = Mes; R(3) = Me). The 'abnormal' carbene borane of the form R(1)CH(OH)CH2{CH[NC(BEt3)CR(3)N(R(2))]} (R(1) = (t)Bu; R(2) = (t)Bu; R(3) = H), is also accessible by thermolysis of , suggesting that the carbene-borane alcohol is a more thermodynamically stable combination than the zwitterionic imidazolium borate. High-temperature thermolysis also can result in complete cleavage of the alcohol arm, eliminating tert-butyloxirane and forming the B-N bound imidazolium borate . The strong dependence of reaction products on the steric and electronic properties of each imidazole precursor molecule is discussed. PMID:25188908

Arnold, Polly L; Bell, Nicola L; Marr, Isobel H; She, Siyi; Hamilton, Jonathan; Fraser, Craig; Wang, Kai

2014-09-30

32

New N-Heterocyclic Carbene Ligands in Grubbs and Hoveyda-Grubbs Catalysts  

NASA Astrophysics Data System (ADS)

A series of N-heterocyclic carbene (NHC) ligands bearing aliphatic amino side groups were synthesized and reacted with the Grubbs first generation catalyst. Reactions involving symmetrical, aliphatic NHCs did not allow the isolation of any pure NHC substituted complexes due to their instability. Unsymmetrical NHCs having a planar mesityl group on one amino side reacted with Grubbs catalyst in a favorable manner, and the resulting complexes were stable enough to be isolated. X-ray crystallographic analysis demonstrated that the mesityl group is co-planar with the phenyl ring of the benzylidene, which indicates that a ?-? interaction between the mesityl arm and the benzylidene moiety might constitute an important structural element. Catalysts substituted with an NHC derived from a primary or secondary amino-group were found to surpass the parent-complex for the ROMP of cycloocta-1,5-diene. The catalyst substituted with an NHC derived from tBu-NH2 was considerably less metathesis active. Also new N-alkyl-N'-(2,6-diisopropylphenyl) heterocyclic carbenes were synthesized. These NHC ligands revealed a different reactivity towards Grubbs complexes than the hitherto reported imidazolinylidenes: (i) facile bis(NHC) coordination was found, and (ii) both NHCs on the bis(NHC) complexes can be exchanged with a phosphine, thereupon regenerating the Grubbs first generation complex. Furthermore, a comparison between the classical Hoveyda-Grubbs complexes and complexes substituted with N-alkyl-N'-(aryl) heterocyclic carbenes demonstrates that the introduction of one aliphatic group into the NHC framework does not improve the catalytic activity in any of the tested metathesis reactions. The introduction of two aliphatic amino side groups enhances the reactivity in the ROMP reaction while the increase of steric interactions lowers the CM activity. The lower activity of the N-alkyl-N'-(2,6-diisopropylphenyl) heterocyclic carbene complexes compared with the N-alkyl-N'-mesityl heterocyclic carbene complexes, may analogously be attributed to a more demanding steric environment. While small differences in donor capacities might cause a significantly different catalytic behavior, it is thus plausible that subtle steric differences exert a more determining influence on the activity of the catalysts. In addition, the obtained results confirm that the NHC's amino side groups play a pivotal role in determining the reactivity, selectivity as well as the stability of the corresponding catalysts.

Monsaert, Stijn; Ledoux, Nele; Drozdzak, Renata; van der Voort, Pascal; Verpoort, Francis

33

An ab initio investigation of fluorobromo carbene.  

PubMed

Fluorobromo carbene, an important halogenated carbene in the stratospheric ozone depletion, has long been received considerable interest. However, the energy, structure, and dynamics of even the lowest excited states have not been well understood. In this paper, we performed a detail ab initio study on CFBr using complete active space second-order perturbation (CASPT2) and multireference configuration interaction (MRCI) method. We investigated the effect of basis set on the CASPT2 results of the ground X(1)A' state and the first excited singlet A(1)A" state. The potential energy surface (PES) of the A(1)A" state along C-Br bond distance was carefully examined at CASPT2/cc-pV5Z level, by optimizing C-F bond and F-C-Br angle at every C-Br bond length in contrast to fix them at the equilibrium values. On the basis of the PES, a reliable barrier height of the A(1)A" state was obtained from CASPT2 and MRCI+Q calculations with different basis sets, considering the scalar relativistic effect, spin-orbit coupling, and core-valence correlation. Finally, we carried out the first theoretical study on higher excited state with energy up to 7 eV. The present calculated results were compared with previous experimental and theoretical results where available. Our results will add some understanding and shed more light on the structure and dynamics of electronic states of CFBr radical. PMID:23004933

Sun, Erping; Li, Rui; Sun, Qixiang; Wei, Changli; Xu, Haifeng; Yan, Bing

2012-10-25

34

Poly(fluoroalkyl acrylate)-bound ruthenium carbene complex: a fluorous and recyclable catalyst for ring-closing olefin metathesis.  

PubMed

The synthesis of a fluorous olefin metathesis catalyst derived from the Grubbs second-generation ruthenium carbene complex is described. The air stable fluorous polymer-bound ruthenium carbene complex 1 shows high reactivity in effecting the ring-closing metathesis of a broad spectrum of diene and enyne substrates leading to the formation of di-, tri-, and tetrasubstituted cyclic olefins in minimally fluorous solvent systems (PhCF3/CH2Cl2, 1:9-1:49 v/v). The catalyst can be readily separated from the reaction mixture by fluorous extraction with FC-72 and repeatedly reused. The practical advantage offered by the fluorous catalyst is demonstrated by its sequential use in up to five different metathesis reactions. PMID:14709066

Yao, Qingwei; Zhang, Yiliang

2004-01-14

35

1,2-Migration in Rhodium(II) Carbene Transfer Reaction: Remarkable Steric Effect on  

E-print Network

1,2-Migration in Rhodium(II) Carbene Transfer Reaction: Remarkable Steric Effect on Migratory the steric effect in 1,2-migration reaction of rhodium(II) carbene. Through the investigation on the diazo effect of the substituent. 1,2-Migration represents a fundamental reaction pathway for both free carbenes

Wang, Jianbo

36

Reversible insertion of carbenes into ruthenium-silicon bonds.  

PubMed

The five-coordinate carbene complexes [Ru{?P,P,Si-Si(Me)(C6H4-2-PiPr2)2}Cl(?CHR)] (2, R = Ph; 3, R = SiMe3), analogues of the Grubbs catalyst, were prepared from the dimer [Ru(?-Cl){?P,P,Si-Si(Me)(C6H4-2-PiPr2)2}]2 (1) and the corresponding diazoalkane N2CHR. The particular structural features that result from the presence of a strongly trans directing silyl group at the pincer ligand of these complexes are discussed on the basis of NMR information and the crystal structure of the vinylidene analogue [Ru{?P,P,Si-Si(Me)(C6H4-2-PiPr2)2}Cl(?C?CHPh)] (4), which was also obtained from 1 and phenylacetylene. The reactions of 3 with reagents such as P(OMe)3, CO, NCMe, and K(acac) illustrate that the first response of these carbene complexes to an increase of the coordination number around ruthenium is the insertion of the carbene ligand into the Ru-Si bond. These reactions also indicate that the insertion process is reversible and allows typical transformations of carbene ligands such as C-H functionalizations via carbene insertion (in the acac ligand) or the formation of ketene from CO. In addition, the reactions of 3 with terminal alkynes such as phenylacetylene or 3,3-dimethyl-1-butyne show that the inserted carbenes can also undergo reactions typical of metal-bound alkyls such as alkyne insertion and C-H reductive elimination. PMID:24289787

Bernal, María J; Torres, Olga; Martín, Marta; Sola, Eduardo

2013-12-18

37

Carbene Rearrangements in Three-Coordinate N-Heterocyclic Carbene Complexes of Cobalt(II) Bis(trimethylsilyl)amide.  

PubMed

The synthesis and molecular structures of the cobalt(II) N-heterocyclic carbene (NHC) complexes [(NHC)Co{N(SiMe3)2}2], where NHC = 1,3-bis(diisopropylphenyl)imidazolylidene (IPr) (6), 1,3-bis(mesityl)imidazolylidene (IMes) (7), and 1,3-bis(tert-butyl)imidazol-2-ylidene (I(t)Bu) (8), are reported. Complexes 6-8 are rare examples of three-coordinate cobalt NHC complexes. The steric congestion within the coordination environments of the cobalt(II) centers in 6 and 7 results in the longest Co-C(NHC) distances currently known. Investigating the thermal stability of 6-8, we have found that the steric congestion in 6 is such that heating the complex to reflux in toluene prompts a rearrangement from the normal, C2-bonding mode of the IPr ligand to the corresponding "abnormal" or mesoionic bonding mode. The rearrangement results in formation of [(aIPr)Co{N(SiMe3)2}2] (9), which is the first cobalt complex of an abnormal NHC ligand. The Co-C bond in 9 is 0.06 Å shorter than the analogous bond in 6, suggesting that, although the rearrangement occurs due to the spatial demands of the IPr ligand, there is also a thermodynamic driving force in terms of the Co-C bond. In contrast to the case for 6, complex 7 is stable with respect to the normal-to-abnormal rearrangement. Refluxing complex 8 in toluene results in activation of a tert-butyl substituent, which is eliminated as isobutene, followed by formation of the 1-tert-butylimidazole complex [((t)BuIm)Co{N(SiMe3)2}2] (10). PMID:25203858

Day, Benjamin M; Pal, Kuntal; Pugh, Thomas; Tuck, Jessica; Layfield, Richard A

2014-10-01

38

CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF? and BH?.  

PubMed

In situ formation of two cyclic (alkyl) (amino) carbenes (CAACs) followed by addition of BF?•Et?O provided the first two examples of CAAC-BF? complexes: 1-(2,6-diisopropylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene trifluoroborane, and 2-(2,6-diisopropylphenyl)-3,3-dimethyl-2-azaspiro[4.5]decan-1-ylidene trifluoroborane. These CAAC-BF? complexes are robust compounds that are stable to ambient laboratory conditions and silica gel chromatography. They were characterized by spectroscopy and X-ray crystallography. In contrast, a CAAC complex with borane (BH?) was readily formed in situ according to ¹H and ¹¹B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes. PMID:20978616

Monot, Julien; Fensterbank, Louis; Malacria, Max; Lacôte, Emmanuel; Geib, Steven J; Curran, Dennis P

2010-01-01

39

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals  

SciTech Connect

Highly reactive carbenes and carbon-chain radicals are studied at millimeter wavelengths by observing their rotational spectra. The purpose is to provide definitive spectroscopic identification, accurate spectroscopic constants in the lowest vibrational states, and reliable structures of the key intermediates in reactions leading to aromatic hydrocarbons and soot particles in combustion.

Gottlieb, C.A.; Thaddeus, P. [Harvard Univ., Cambridge, MA (United States)

1993-12-01

40

Unexpected C(carbene)-X (X: I, Br, Cl) Reductive Elimination From N-Heterocyclic Carbene Copper Halide Complexes Under Oxidative Conditions.  

PubMed

The non-innocent behaviors of NHC ligands have attracted wide attention due to their important implications for catalyst designs and reaction mechanisms. Herein, we report facile C(carbene)-halogen reductive eliminations from NHC copper halide complexes at RT under oxidative conditions. Density functional calculations on a simplified model system suggest that the reactions occur through oxidation of Cu(I) to Cu(III) species followed by C(carbene)-halogen reductive eliminations from NHC Cu(III) halide complexes. Remarkably short C(carbene)-chloride contacts and rare interactions between the chloride lone pair electrons and the C(carbene)p(?) orbital were found for the calculated NHC Cu(III) chlorides. The facile C(carbene)-X reductive elimination reported here warrants consideration as a potential decomposition pathway in reactions involving NHC-supported high-valent metal complexes, especially with late transition metals. PMID:21116469

Lin, Bo-Lin; Kang, Peng; Stack, T Daniel P

2010-09-13

41

Communications to the Editor Carbenic Rearrangement and Fragmentationof  

E-print Network

8261 Communications to the Editor Carbenic Rearrangement and Fragmentationof Bicyclo[4.2.2]deca-2 and photochemical properties of bicyclo[4.2.2]deca-2,4,9-trien-7-ylidene(1) and elaborate further the intramolecular. Isomerization of 1 at 220 O C , as generated from 7-diazo- bicyclo[4.2.2]deca-2,4,9-triene(2) by pyrolysis

RajanBabu, T. V. "Babu"

42

Cyclization of ?(3)-Benzylpalladium Intermediates Derived from Carbene Insertion.  

PubMed

Migratory insertion of benzylidene carbene ligands into arylpalladium(II) species generates ?(3)-benzylpalladium intermediates that can cyclize to generate five- and six-membered rings with new sp(3) centers. The reaction tolerates a range of arene functional groups and stabilized enolates. The products generated through this reaction are 1-arylindanes and 1-aryltetralins that are common to a range of natural products. PMID:25279856

Gutman, Eugene S; Arredondo, Vanessa; Van Vranken, David L

2014-10-17

43

The Depolymerization of Poly(Ethylene Terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids  

ERIC Educational Resources Information Center

The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic…

Kamber, Nahrain E.; Tsujii, Yasuhito; Keets, Kate; Waymouth, Robert M.; Pratt, Russell C.; Nyce, Gregory W.; Hedrick, James L.

2010-01-01

44

Volume 123, number 4 CHEMICAL PHYSICS LETTERS 17 January 1986 ELECTRONIC STATES OF CHROMIUM CARBENE IONS  

E-print Network

Volume 123, number 4 CHEMICAL PHYSICS LETTERS 17 January 1986 ELECTRONIC STATES OF CHROMIUM CARBENE,4] that the chromium carbene ion, CrCg, can be generated by reaction of electronically excited Cr+ with methane: Cr. Chromium ions are formed from 150 eV electron impact ionization of Cr(CD),. Reaction of excited-state Cr

Goddard III, William A.

45

1,2-migration in N-phosphano functionalized N-heterocyclic carbenes.  

PubMed

1,2-Migration of the phosphano-group to the carbene center in N-phosphano functionalized N-heterocyclic carbenes has been studied by density functional theory (DFT) calculations. An intramolecular mechanism with a three-center transition state structure seems to be most plausible for the isolated carbenes, while an intermolecular pathway catalyzed by azolium salts may be preferable for a migration proceeding in the course of generating the carbenes in situ. Our calculations show that amino-substitution at the phosphorus atom and an enhanced nucleophilicity of the heterocycle scaffold facilitate the phosphorus shift. Calculated singlet-triplet energy gaps do not correlate with thermodynamic stability of the studied carbenes and their disposition toward the 1,2-rearrangement. © 2014 Wiley Periodicals, Inc. PMID:25363134

Kirilchuk, Andrey A; Yurchenko, Aleksandr A; Kostyuk, Aleksandr N; Rozhenko, Alexander B

2015-01-01

46

CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF3 and BH3  

PubMed Central

Summary In situ formation of two cyclic (alkyl) (amino) carbenes (CAACs) followed by addition of BF3•Et2O provided the first two examples of CAAC–BF3 complexes: 1-(2,6-diisopropylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene trifluoroborane, and 2-(2,6-diisopropylphenyl)-3,3-dimethyl-2-azaspiro[4.5]decan-1-ylidene trifluoroborane. These CAAC–BF3 complexes are robust compounds that are stable to ambient laboratory conditions and silica gel chromatography. They were characterized by spectroscopy and X-ray crystallography. In contrast, a CAAC complex with borane (BH3) was readily formed in situ according to 1H and 11B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes. PMID:20978616

Monot, Julien; Geib, Steven J

2010-01-01

47

Cyclometalated mono- and dinuclear Ir(III) complexes with "click"-derived triazoles and mesoionic carbenes.  

PubMed

Orthometalation at Ir(III) centers is usually facile, and such orthometalated complexes often display intriguing electronic and catalytic properties. By using a central phenyl ring as C-H activation sites, we present here mono- and dinuclear Ir(III) complexes with "click"-derived 1,2,3-triazole and 1,2,3-triazol-5-ylidene ligands, in which the wingtip phenyl groups in the aforementioned ligands are additionally orthometalated and bind as carbanionic donors to the Ir(III) centers. Structural characterization of the complexes reveal a piano stool-type of coordination around the metal centers with the "click"-derived ligands bound either with C^N or C^C donor sets to the Ir(III) centers. Furthermore, whereas bond localization is observed within the 1,2,3-triazole ligands, a more delocalized situation is found in their 1,2,3-triazol-5-ylidene counterparts. All complexes were subjected to catalytic tests for the transfer hydrogenation of benzaldehyde and acetophenone. The dinuclear complexes turned out to be more active than their mononuclear counterparts. We present here the first examples of stable, isomer-pure, dinuclear cyclometalated Ir(III) complexes with poly-mesoionic-carbene ligands. PMID:25044321

Maity, Ramananda; Hohloch, Stephan; Su, Cheng-Yong; van der Meer, Margarethe; Sarkar, Biprajit

2014-08-01

48

GEOMETRY AND ELECTRONIC STRUCTURE OF (CO)3N1CH2. A MODEL TRANSITION METAL CARBENE  

SciTech Connect

The first application of nonempirical molecular electronic structure theory to a realistic transition metal carbene complex is reported. The system chosen was (CO){sub 3}NiCH{sub 2}, methylene (tricarbonyl) nickel(0). All studies were carried out at the self-consistent-field (SCF) level. A large and flexibly contracted basis set was chosen, labeled Ni(15s 11p 6d/11s 8p 3d); C,O(9s 5p/4s 2p); H(5s/3s). In addition, the importance of methylene carbon d functions was investigated. The critical predicted equilibrium geometrical parameters were R [Ni-C (methylene)]=1.83 {Angstrom}, {theta}(HCH)=108°. The sixfold barrier to rotation about the Ni-C (methylene) axis is small, ~o.2 kcal. The electronic structure of (CO){sub 3}NiCH{sub 2} is discussed and compared with those of the "naked" complex NiCH{sub 2} and the stable Ni(CO){sub 4} molecule.

Spangler, Dale; Wendoloski, John J.; Dupuis, Michel; Chen, Maynard M.L.; Schaefer III, Henry F.

1980-04-01

49

Characterization of Tunable Radical Metal-Carbenes: Key Intermediates in Catalytic Cyclopropanation  

PubMed Central

A new class of radical metal-carbene complex has been characterized as having Fischer-like orbital interactions and adjacent ? acceptor stabilization. Density Functional Theory (DFT) along with Natural Bond Orbital (NBO) analysis and Charge Decomposition Analysis (CDA) has given insight into the electronics of this catalytic intermediate in an open-shell cobalt-porphyrin, [Co(Por)], system. The complex has a single bond from the metal to the carbene and has radical character with localized spin density on the carbene carbon. In addition, the carbene carbon is found to be nucleophilic and “tunable” through the introduction of different ?-carbon substituents. Finally, based on these findings, rational design strategies are proposed which should lead to the enhancement of catalytic activity. PMID:21643517

Belof, Jonathan L.; Cioce, Christian R.; Xu, Xue; Zhang, X. Peter; Space, Brian; Woodcock, H. Lee

2011-01-01

50

Synthetic and catalytic studies of Group 11 N-heterocyclic carbene complexes  

E-print Network

This thesis presents the synthesis, structure and reactivity of two-coordinate Group 11 metal complexes, supported by N-heterocyclic carbene (NHC) ligands. The NHC ligand was found to stabilize monomeric, terminal fluoride ...

Laitar, David S. (David Stephen)

2006-01-01

51

Design and Synthesis of C2-Symmetric N-Heterocyclic Carbene Precursors and Metal Carbenoids  

PubMed Central

Chiral, C2-symmetric imidazolium and imidazolinium ions, as well as the corresponding copper or silver bound carbenoids, have been prepared. Structural study of these compounds by X-ray crystallography reveals a chiral pocket that surrounds the putative carbene site or the metal-carbene bond, at carbon 2, in three of the four ligands prepared. Preliminary investigation into the application of these complexes has shown one of them to be highly enantioselective in the hydrosilylation of acetophenone. PMID:21823580

Albright, Abigail; Eddings, Daniel; Black, Regina; Welch, Christopher J.; Gerasimchuk, Nikolay N.; Gawley, Robert E.

2011-01-01

52

Quantitative description of structural effects on the stability of gold(i) carbenes.  

PubMed

The gas-phase bond-dissociation energies of a SO2 -imidazolylidene leaving group of three gold(I) benzyl imidazolium sulfone complexes are reported (E0 =46.6±1.7, 49.6±1.7, and 48.9±2.1?kcal?mol(-1) ). Although these energies are similar to each other, they are reproducibly distinguishable. The energy-resolved collision-induced dissociation experiments of the three [L]-gold(I) (L=ligand) carbene precursor complexes were performed by using a modified tandem mass spectrometer. The measurements quantitatively describe the structural and electronic effects a p-methoxy substituent on the benzyl fragment, and trans [NHC] and [P] gold ligands, have towards gold carbene formation. Evidence for the formation of the electrophilic gold carbene in solution was obtained through the stoichiometric and catalytic cyclopropanation of olefins under thermal conditions. The observed cyclopropane yields are dependent on the rate of gold carbene formation, which in turn is influenced by the ligand and substituent. The donation of electron density to the carbene carbon by the p-methoxy benzyl substituent and [NHC] ligand stabilizes the gold carbene intermediate and lowers the dissociation barrier. Through the careful comparison of gas-phase and solution chemistry, the results suggest that even gas-phase leaving-group bond-dissociation energy differences of 2-3?kcal?mol(-1) enormously affect the rate of gold carbene formation in solution, especially when there are competing reactions. The thermal decay of the gold carbene precursor complex was observed to follow first-order kinetics, whereas cyclopropanation was found to follow pseudo-first-order kinetics. Density-functional-theory calculations at the M06-L and BP86-D3 levels of theory were used to confirm the observed gas-phase reactivity and model the measured bond-dissociation energies. PMID:25236486

Ringger, David H; Kobylianskii, Ilia J; Serra, Daniel; Chen, Peter

2014-10-27

53

N-heterocyclic carbene-main-group chemistry: a rapidly evolving field.  

PubMed

This Award Article targets the evolving, yet surprisingly fruitful, chemistry of N-heterocyclic carbenes with low-oxidation-state main-group elements. Specifically, the chemistry of carbene-stabilized diatomic allotropes, diborenes, gallium octahedra, beryllium borohydride, and a host of related compounds will be presented. Providing a valuable historical perspective, the foundational work concerning the organometallic chemistry of gallium with sterically demanding m-terphenyl ligands from this laboratory will also be discussed. PMID:25343222

Wang, Yuzhong; Robinson, Gregory H

2014-11-17

54

Protonolysis of a Ruthenium-Carbene Bond and Applications in Olefin Metathesis  

PubMed Central

The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicate a rate-determining protonation step to generate the metathesis active species. The NHC/MIC catalyst was found to have activity exceeding current commercial ruthenium catalysts. PMID:21574621

Keitz, Benjamin K.; Bouffard, Jean; Bertrand, Guy; Grubbs, Robert H.

2011-01-01

55

How Stable Is Stable?  

ERIC Educational Resources Information Center

Provides a problem where students are asked to find the point at which a soda can floating in some liquid changes its equilibrium between stable and unstable as the soda is removed from the can. Requires use of Newton's first law, center of mass, Archimedes' principle, stable and unstable equilibrium, and buoyant force position. (MVL)

Baehr, Marie

1994-01-01

56

Diastereoselective cyclopropanation of ketone enols with Fischer carbene complexes.  

PubMed

Treatment of aryl/heteroaryl methoxycarbene complexes of chromium with -substituted ketone lithium enolates between -78 degrees C and room temperature resulted in the diastereoselective synthesis of 1,2,2,3-tetrasubstituted cyclopropanols. An exception has been observed in the reaction with cyclohexanone lithium enolate that yielded a bicyclic 2-buten-4-olide. 1,2-Dimethoxycyclopropanes and 1-methoxy-2-trimethylsilyloxycyclopropanes were isolated by quenching the reactions with MeOTf or Me3SiCl, respectively. This novel cyclopropanation process involves formation of lithium (3-oxoalkyl)pentacarbonylchromate intermediates which on warming undergo intramolecular addition to the carbonyl group. This cyclization is equivalent to the cyclopropanation in smooth conditions of electron-rich alkenes with Fischer carbene complexes. PMID:18257560

Barluenga, José; Suero, Marcos G; Pérez-Sanchez, Ivan; Flórez, Josefa

2008-03-01

57

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts  

PubMed Central

Summary Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II) catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh3). Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction. PMID:23400639

Tubaro, Cristina; Baron, Marco; Basato, Marino

2013-01-01

58

N-Heterocyclic carbene metal complexes: photoluminescence and applications.  

PubMed

This review covers the advances made in the synthesis of luminescent transition metal complexes containing N-heterocyclic carbene (NHC) ligands. The presence of a high field strength ligand such as an NHC in the complexes gives rise to high energy emissions, and consequently, to the desired blue colour needed for OLED applications. Furthermore, the great versatility of NHC ligands for structural modifications, together with the use of other ancillary ligands in the complex, provides numerous possibilities for the synthesis of phosphorescent materials, with emission colours over the entire visible spectra and potential future applications in fields such as photochemical water-splitting, chemosensors, dye-sensitised solar cells, oxygen sensors, and medicine. PMID:24604135

Visbal, Renso; Gimeno, M Concepción

2014-05-21

59

High-resolution mapping of carbene-based protein footprints.  

PubMed

Carbene chemistry has been used recently in structural mass spectrometry as a labeling method for mapping protein surfaces. The current study presents a method for quantitating label distribution at the amino acid level and explores the nature and basis for an earlier observation of labeling bias. With the use of a method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) applied to digests of holo-calmodulin, we developed a quantitation strategy to map site-specific incorporation of carbene, generated from photolysis of ionic label precursors 2-amino-4,4-azipentanoic acid and 4,4-azipentanoic acid. The approach provides reliable incorporation data for fragments generated by electron-transfer dissociation, whereas high-energy collisional dissociation leads to energy and sequence-dependent loss of the label as a neutral. However, both can produce data suitable for mapping residues in the interaction of holo-calmodulin with M13 peptide ligand. Site-specific labeling was monitored as a function of reagent, ionic strength, and temperature, demonstrating that electrostatic interactions at the protein surface can "steer" the distribution of label precursors to sites of surface charge and favor label insertion into residues in the vicinity of the surface charge. A further preference for insertion into carboxylates was observed, based on chemical reactivity. We suggest that decoupling surface partitioning from the chemistry of insertion offers a flexible, tunable labeling strategy for structural mass spectrometry that can be applied to a broad range of protein surface compositions and promotes the design of reagents to simplify the workflow. PMID:22480364

Jumper, Chanelle C; Bomgarden, Ryan; Rogers, John; Etienne, Chris; Schriemer, David C

2012-05-15

60

Synthesis of the first radiolabeled 188Re N-heterocyclic carbene complex and initial studies on its potential use in radiopharmaceutical applications.  

PubMed

A novel approach towards the synthesis of radiolabeled organometallic rhenium complexes is presented. We successfully synthesized and analyzed the first (188)Re-labeled N-heterocyclic biscarbene complex, trans-dioxobis(1,1'-methylene-bis(3,3'-diisopropylimidazolium-2-ylidene))(188)rhenium(V) hexafluorophosphate ((188)Re-4) via transmetalation using an air-stable and moisture-stable silver(I) biscarbene complex. In order to assess the viability of this complex as a potential lead structure for in vivo applications, the stability of the (188)Re-NHC complex was tested in physiologically relevant media. Ultimately, our studies illustrate that the complex we synthesized dissociates rapidly and is therefore unsuitable for use in radiopharmaceuticals. However, it is clear that the transmetalation approach we have developed is a rapid, robust, and mild method for the synthesis of new (188)Re-labeled carbene complexes. PMID:24889257

Wagner, Thomas; Zeglis, Brian M; Groveman, Sam; Hille, Claudia; Pöthig, Alexander; Francesconi, Lynn C; Herrmann, Wolfgang A; Kühn, Fritz E; Reiner, Thomas

2014-06-15

61

Chelation assistance as a tool for the selective preparation of an imidazole-based mesoionic palladium carbene complex.  

PubMed

A C(4)-bound palladium-N-heterocyclic carbene (4) was selectively obtained from the C(2)-unsubstituted imidazolium salt 3. The higher stability of the C(4) versus the C(2)-bound carbene complex due to pyridine chelation assistance allowed this mesoionic compound to be obtained. PMID:25347320

Juzgado, Arturo; Lorenzo-García, M Mercedes; Barrejón, Myriam; Rodríguez, Ana M; Rodríguez-López, Julián; Merino, Sonia; Tejeda, Juan

2014-12-18

62

Helicene-grafted vinyl-and carbene-osmium complexes: an example of acid-base chiroptical switching  

E-print Network

| 1 Helicene-grafted vinyl- and carbene-osmium complexes: an example of acid-base chiropticalAutschbach,*,d R�gisR�au,a and JeanneCrassous,*,a The first helicene-based carbene osmium complex has been prepared from a vinyl-osmium derivative and this system has been shown to behave as a potential acid

Boyer, Edmond

63

Stabilization of a cobalt-cobalt bond by two cyclic alkyl amino carbenes.  

PubMed

(Me2-cAAC:)2Co2 (2, where Me2-cAAC: = cyclic alkyl amino carbene, :C(CH2)(CMe2)2N-2,6-iPr2C6H3)) was synthesized via the reduction of precursor (Me2-cAAC:Co(II)(?-Cl)Cl)2 (1) with KC8. 2 contains two cobalt atoms in the formal oxidation state zero. Magnetic measurement revealed that 2 has a singlet spin ground state S = 0. The cyclic voltammogram of 2 exhibits both one-electron oxidation and reduction, indicating the possible synthesis of stable species containing 2(•-) and 2(•+) ions. The latter was synthesized via reduction of 1 with required equivalents of KC8 and characterized as [(Me2-cAAC:)2Co2](•+)OTf(-) (2(•+)OTf(-)). Electron paramagnetic resonance spectroscopy of 2(•+) reveals the coupling of the electron spin with 2 equiv (59)Co isotopes, leading to a (Co(0.5))2 state. The experimental Co1-Co2 bond distances are 2.6550(6) and 2.4610(6) Å for 2 and 2(•+)OTf(-), respectively. Theoretical investigation revealed that both 2 and 2(•+)OTf(-) possess a Co-Co bond with an average value of 2.585 Å. A slight increase of the Co-Co bond length in 2 is more likely to be caused by the strong ?-accepting property of cAAC. 2(•+) is only 0.8 kcal/mol higher in energy than the energy minimum. The shortening of the Co-Co bond of 2(•+) is caused by intermolecular interactions. PMID:24437683

Mondal, Kartik Chandra; Samuel, Prinson P; Roesky, Herbert W; Carl, Elena; Herbst-Irmer, Regine; Stalke, Dietmar; Schwederski, Brigitte; Kaim, Wolfgang; Ungur, Liviu; Chibotaru, Liviu F; Hermann, Markus; Frenking, Gernot

2014-02-01

64

Photochemistry of group 6 Fischer carbene complexes: beyond the photocarbonylation reaction.  

PubMed

The seminal report by Hegedus in 1982, showing that alkoxychromium(0) carbenes reacted with imines under bright Colorado sunlight to yield ?-lactams, marked the beginning of a key reaction in organometallic chemistry. Very little was known about the mechanism of this reaction. In fact, Hegedus proposed the reversible generation of a chromium-coordinated ketene, which would react with nucleophiles. This coordinated species would show all the advantages of ketenes without their shortcomings, namely, dimerization, formation of undesired adducts, and so forth. The quest for the detection of these species and the pursuit of the mechanism of the photocarbonylation (a reaction exclusive to Cr(0) and Mo(0) carbene complexes, not W(0) carbene complexes) remained unabated over the next 15 years. In fact, all attempts to experimentally determine the mechanism of this useful reaction have been fruitless. At the same time, the photocarbonylation of Cr(0) carbenes matured into a valuable synthetic reaction, allowing access to several families of organic compounds. Unfortunately, reactions other than photocarbonylation remained elusive. We used a combination of experimental and computational methodologies to study the photocarbonylation of Cr(0) carbene complexes and the subsequent reaction of the photogenerated ketenes with nucleophiles. In parallel, we discovered new photochemical processes and succeeded in making photoreactive the so-called "unreactive" W(0) carbene complexes. In this Account, we discuss the disentangling of the mechanisms of these transformations, thereby shedding some light onto the photochemistry of group 6 metal (Fischer) carbene complexes. The original designation of the electronic transitions of group 6 carbene complexes was reassigned, and the photocarbonylation step was analyzed again, resulting in the sequence S(0)-T(1)-S(0), which is far removed from conventional organic photochemistry. The T(1) species is a chromacyclopropanone; its unpaired electrons are primarily localized in the metal fragment and in the former carbene carbon atom. The T(1)-S(0) intersystem crossing occurs with the participation of the solvent through an unusual loose-bolt radiationless mechanism. The photogenerated S(0) species reacts with imines to form the final ?-lactams in a mechanism that resembles the organic Staudinger reaction, but here the metal is present during the entire reaction coordinate. The selectivity of these reactions is defined by the nucleophilic attack on the O-bonded metallaketene instead of the subsequent conrotatory ring closure, a distinct departure from the organic reaction. Appropriate modification of the substituents of the carbene ligand or in the coordination sphere of the complex results in new photoprocesses; these include 1,2-metalladyotropic rearrangements as well as ?-fragmentations in which W(0) carbene complexes become photoreactive. Moreover, the inclusion of additional metal centers usually results in new reactions, such as the formation of fulvenes by ?(5)? ?(3) photoslippage, or in the complete inhibition of the photoreactivity. The photochemistry of group 6 metal-carbene complexes thus offers unexplored territory for pursuing new reactions and reaction mechanisms. PMID:21517052

Fernández, Israel; Cossío, Fernando P; Sierra, Miguel A

2011-07-19

65

A Diruthenium ?-Carbido Complex That Shows Singlet-Carbene-like Reactivity.  

PubMed

Low-temperature deprotonation of the cationic ?-methylidyne complex [(Cp*Ru)2(?-NPh)(?-CH)][BF4] (Cp* = ?(5)-C5Me5) with KN(SiMe3)2 affords a thermally unstable ?-carbido complex [(Cp*Ru)2(?-NPh)(?-C)] (2), as evidenced by trapping experiments with elemental S or Se and (13)C NMR spectroscopic observation. The reactivity of 2 toward CO2, Ph2S(+)CH2(-), EtOH, and an intramolecular C-H bond indicates that the ?-carbido carbon in 2 has an ambiphilic (nucleophilic and electrophilic) nature consistent with the formulation of 2 as the first example of a transition-metal-substituted singlet carbene. DFT study suggests that the Ru substituents in 2 are stronger ?-donor and weaker ?-donor to the carbene center than amino substituents in N-heterocyclic carbenes. PMID:25365114

Takemoto, Shin; Ohata, Jun; Umetani, Kento; Yamaguchi, Masahiro; Matsuzaka, Hiroyuki

2014-11-12

66

A non-diazo approach to ?-oxo gold carbenes via gold-catalyzed alkyne oxidation.  

PubMed

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, ?-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C-H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate ?-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous ?-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile ?-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of ?-oxo gold carbene intermediates. The intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C-C triple bond a surrogate of an ?-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the ?-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The ?-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of "gold rush". PMID:24428596

Zhang, Liming

2014-03-18

67

Correlation between thermal and mass spectral techniques for the characterization of allenylidene and carbene complexes  

NASA Astrophysics Data System (ADS)

The fragmentation pathways of allenylidene and carbene complexes have been studied using FAB mass spectrometry in comparison with thermal analyses (TGA, DrTG and DTA). Both the decomposition modes are investigated and the possible fragmentation pathways are suggested. The use of mass and thermal analyses (TGA and DTA) in the analyses of allenylidene and carbene complexes allowed the characterization of the fragmentation pathways in MS. The major pathway includes successive loss of carbon monoxide followed by fragmentation of the organic part of the allenylidene or carbene molecules. This is also confirmed by thermogravimetric analysis (TGA) where the first step involves the loss of carbon monoxide followed by the organic ligand. The nature of each step; exothermic or endothermic, is also studied using DTA technique. The kinetic parameters of the thermal decomposition are also studied using the Coates-Redfern method.

Mohamed, Gehad G.; Szesni, Normen; Fischer, Helmut

2008-11-01

68

{alpha},{beta}-Unsaturated Fischer carbene complexes as chemical multitalents  

SciTech Connect

The well established reaction of {alpha},{beta}-unsaturated Fischer carbenechromium complexes 6(R{sup 1} = H) with alkynes normally proceeds with carbonyl insertion to yield 4-alkoxyphenols 9. Led by the incidental formation of a cyclopentadiene 3 from certain {beta}-aminosubstituted complexes 6(X = NR{sub 2}{sup 3}, R{sup 1} = cPr) the authors have studied the influences of the nature of substituents (R{sup 1}, X on 6; R{sub L}, R{sub S} in the alkyne; R{sup 3} in the amino group), solvents, and temperature on the outcome of the reaction. Imino substitution on complexes 6 leads to 2H-pyrroles 1, a free primary amino group (X = NH{sub 2}) to pyridines 5, and bulky substituents R{sup 1} to cyclopenta[b]pyrans 8 with double insertion of an alkyne. Eventually, appropriate conditions have been developed which permit to selectively prepare either 3-alkoxy-5-(dialkylamino)cyclopentadienes 3 (as synthetic equivalents of cyclopentenones 4), 5-(dialkylaminomethylene)cyclopent-2-enones 7, 3-alkoxy-2-(1{prime}-morpholino-1{prime}-alkenyl)cyclopent-2-enones 10, and 2-acyl-3-(dialkylamino)cyclopent-2-enones 11 from easily accessible carbene complexes 6 (X = NR{sub 2}{sup 3}) in high yields. Mechanistic aspects and implications of these novel transformations will be discussed.

Meijere, A. de [Institut fuer Organische Chemie der George-August-Universitaet Goettingen (Germany)

1995-12-31

69

Group 7 transition metal complexes with N-heterocyclic carbenes.  

PubMed

This tutorial review summarizes all works and highlights recent advances published in the growing field of group 7 N-heterocyclic carbene (NHC) complexes. It provides a valuable source for all scientists that are interested in conducting research with new compounds bearing these metals. The article provides an overview of all manganese NHC complexes that are known to date. There are a lot of examples where manganese NHC complexes show unpredicted behaviour during synthesis, very different from other transition metal NHC complexes and their higher homologues rhenium and technetium. These differences are depicted and discussed. Furthermore, the chemistry of technetium NHC compounds and their chemical behaviour are discussed. To date published work on technetium NHC chemistry has been restricted to the oxidation state +v. It was found that such compounds are very reactive but show great stability in dry air. Their radioactivity makes such compounds interesting candidates for radiochemical applications. Since most group 7 NHC chemistry was conducted on rhenium NHC complexes, this tutorial review highlights the chemical behaviour of such compounds. Rhenium(i) complexes reveal luminescent properties, making them interesting candidates for applications ranging from biological markers to organic light-emitting diodes (OLEDs). Another interesting feature is the radioactivity of some compounds, which makes them excellent candidates for radiopharmaceutical research; hence their synthesis and reactivity are discussed. PMID:23475206

Hock, Sebastian J; Schaper, Lars-Arne; Herrmann, Wolfgang A; Kühn, Fritz E

2013-06-21

70

Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes For Olefin Metathesis  

NASA Astrophysics Data System (ADS)

In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(m-Cl)3RuCl (h2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a nonselective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

71

Fast transfer hydrogenation using a highly active orthometalated heterocyclic carbene ruthenium catalyst  

Microsoft Academic Search

The free carbene 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene reacts with trans,cis-RuHCl(PPh3)2(ampy) (ampy=2-(aminomethyl)pyridine) affording an orthometalated N-heterocyclic carbene complex characterized by an X-ray diffraction study. This compound in presence of NaOH shows very high catalytic activity for the transfer hydrogenation of several ketones to alcohols using 2-propanol as hydrogen source, affording TOF values up to 120,000h?1 (at 50% conversion).

Walter Baratta; Jan Schütz; Eberhardt Herdtweck; Wolfgang A. Herrmann; Pierluigi Rigo

2005-01-01

72

Sterically driven synthesis of ruthenium and ruthenium-silver N-heterocyclic carbene complexes.  

PubMed

A straightforward and efficient synthetic route to novel Ru N-heterocyclic carbene (NHC) complexes by transmetallation of non-bulky silver NHC to ruthenium dicarbonyl tetraarylcyclopentadienone is described. The same procedure with sterically demanding NHC leads to unprecedented heterobimetallic Ru-Ag(NHC) complexes. PMID:25338159

Cesari, C; Conti, S; Zacchini, S; Zanotti, V; Cassani, M C; Mazzoni, R

2014-11-01

73

N-heterocyclic carbene-catalyzed enantioselective annulation of indolin-3-ones with bromoenals.  

PubMed

N-Heterocyclic carbene-catalyzed reactions of indolin-3-ones with 2-bromoenals opened an asymmetric access to 3,4-dihydropyrano[3,2-b]indol-2(5?H)-ones in good yields and with good to excellent enantioselectivities. This protocol tolerates a broad substrate scope. In addition, a possible mechanism for the annulation reaction is presented. PMID:24729588

Ni, Qijian; Song, Xiaoxiao; Raabe, Gerhard; Enders, Dieter

2014-06-01

74

2009 Macmillan Publishers Limited. All rights reserved. A bonding model for gold(I) carbene complexes  

E-print Network

by electrophilic gold complexes. Although proposed mechanisms often invoke the intermediacy of gold© 2009 Macmillan Publishers Limited. All rights reserved. A bonding model for gold(I) carbene complexes Diego Benitez1, Nathan D. Shapiro2, Ekaterina Tkatchouk1, Yiming Wang2, William A. Goddard III1

Goddard III, William A.

75

Olefin Cyclopropanation and Carbon-Hydrogen Amination via Carbene and Nitrene  

E-print Network

Olefin Cyclopropanation and Carbon- Hydrogen Amination via Carbene and Nitrene Transfers Catalyzed ACKNOWLEDGEMENTS To my mentor and role model, Frances Arnold, whose career is proof that novel and useful research stages of this research project. To my parents and my brothers for their unconditional support. To Renata

Winfree, Erik

76

Catalytic dynamic kinetic resolutions with N-heterocyclic carbenes: asymmetric synthesis of highly substituted ?-lactones.  

PubMed

New DKR type: An N-heterocyclic carbene (NHC)-catalyzed dynamic kinetic resolution of racemic ?-substituted ?-keto esters has been developed. This method relies on the epimerization of an NHC-enol intermediate before subsequent aldol/acylation events. Highly substituted ?-lactones are produced in good yield with good to excellent selectivities (see scheme). PMID:22700327

Cohen, Daniel T; Eichman, Chad C; Phillips, Eric M; Zarefsky, Emily R; Scheidt, Karl A

2012-07-16

77

N-heterocyclic carbene-catalyzed internal redox reaction of alkynals: an efficient synthesis of allenoates.  

PubMed

An efficient N-heterocyclic carbene (NHC)-catalyzed internal redox reaction of alkynals that bear a ? leaving group has been developed. This process provides a new access to a range of allenoates in good yields. Preliminary results demonstrate that the enantioselective variant can also be achieved. PMID:22352302

Zhao, Yu-Ming; Tam, Yik; Wang, Yu-Jie; Li, Zigang; Sun, Jianwei

2012-03-16

78

Abstraction of methyl from neutral Fischer-type carbene complexes: A new site for nucleophilic attack  

SciTech Connect

Reactions of Fischer-type carbene complexes, M(CO){sub 5}(C(OMe)pH) (M = Cr, W), with metal carbonyl anions (M`{sup -} = CpFe(CO){sub 2}{sup -@}, Re(CO){sub 5}{sup -}, Mn(CO){sub 4}PPh{sub 3}{sup -}, Co(CO){sub 3}PPh{sub 3}{sup -}, Cp{sup *}Cr(CO){sub 3}{sup -}, CpMo(CO){sub 3}{sup -}) result in demethylation of the carbene complexes. The products are M(CO){sub 5}C(O)Ph{sup -} and M`-Me, characterized by infrared and NMR spectroscopy. A slower rate for reaction with W(CO){sub 5}(C(OEt)Ph) in comparison to the methyl analogue is consistent with nucleophilic attack of the metal carbonyl anion on the methyl of the methoxy group of the carbene. This is a new type of nucleophilic attack of a Fischer-type carbene. 22 refs., 1 fig., 1 tab.

Toomey, L.M.; Atwood, J.D. [State Univ. of New York, Buffalo, NY (United States)] [State Univ. of New York, Buffalo, NY (United States)

1997-02-04

79

Helicene-grafted vinyl- and carbene-osmium complexes: an example of acid-base chiroptical switching.  

PubMed

The first helicene-based carbene-osmium complex has been prepared from a vinyl-osmium derivative and this system has been shown to behave as a potential acid-base triggered chiroptical switch. PMID:24322581

Anger, Emmanuel; Srebro, Monika; Vanthuyne, Nicolas; Roussel, Christian; Toupet, Loïc; Autschbach, Jochen; Réau, Régis; Crassous, Jeanne

2014-03-18

80

Luminescent goldI carbenes from 2-pyridylisocyanide complexes: structural consequences of intramolecular versus intermolecular hydrogen-bonding interactions.  

PubMed

Isocyanide [AuX(CNPy-2)] (X = Cl, C6F5, fluoromesityl, 1/2 octafluorobiphenyl) and carbene [AuX{C(NR1R2)(NHPy-2)}] (R1R2NH = primary or secondary amines or 1/2 primary diamine) gold(I) complexes have been synthesized and characterized. For X = Cl, the carbene complexes show aurophilic interactions. The fragment NHPy-2, formed in the carbenes, can give rise to intra- (for primary amines) or intermolecular (for secondary amines) hydrogen bonds, depending on the amine used. These bonds and contacts have been studied in the solid state and in solution. The intermolecular hydrogen bonds are split in an acetone solution, but the intramolecular ones, which close a six-membered ring, survive in solution. Except for the fluoromesityl derivatives, the carbene complexes display luminescent properties. PMID:18237121

Bartolomé, Camino; Carrasco-Rando, Marta; Coco, Silverio; Cordovilla, Carlos; Martín-Alvarez, Jose M; Espinet, Pablo

2008-03-01

81

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

82

Synthesis, characterization and catalytic activity of saturated and unsaturated N-heterocyclic carbene iridium(i) complexes.  

PubMed

Both saturated and unsaturated N-benzyl substituted heterocyclic carbene (NHC) iridum(i) complexes were synthesized. The unsaturated carbene complex [(un-NHC-Bn)Ir(CO)(2)Cl] in the cis form was prepared via the carbene transfer from the corresponding silver complex to [Ir(COD)(2)Cl](2) followed by ligand substitution with CO, whereas the saturated complex was obtained via the transfer from (sat-NHC-Bn)W(CO)(5). The treatment of phosphines with (NHC)Ir(CO)(2)Cl complexes yielded the products with the phosphine ligand trans to the carbene moiety via substitution. X-Ray structural determination shows that distances of Ir-C((carbene)) in both (un-NHC-Bn)Ir(CO)(PR(3))Cl and (un-NHC-Bn)Ir(CO)(PR(3))Cl are essentially the same. Analyses of spectroscopic and crystal structural data of iridium complexes [(NHC)Ir(CO)(PR(3))Cl] and Vaska's complex show similar corresponding data in both types of complexes, suggesting that the studied NHC ligands and phosphines have similar bonding with Ir(i) metal center. All iridium complexes studied in this work illustrated their catalytically activity on N-alkylation of amine with alcohol via hydrogen transfer reduction. It appears no dramatic difference on the catalytic activity among these iridium carbene complexes; but the saturated carbene complex (sat-NHC-Bn)Ir(CO)(PR(3))Cl appears to be slightly more active. For example, the reaction of benzyl alcohol with aniline in the presence of catalyst (1 mol%) under basic conditions at 100 degrees C provided the secondary amine (N-benzylaniline) in 96% yield. PMID:19156280

Chang, Yung-Hung; Fu, Ching-Feng; Liu, Yi-Hong; Peng, Shei-Ming; Chen, Jwu-Ting; Liu, Shiuh-Tzung

2009-02-01

83

Mitochondrial permeability transition induced by dinuclear gold(I)–carbene complexes: potential new antimitochondrial antitumour agents  

Microsoft Academic Search

Seven dinuclear gold(I) complexes of bidentate N-heterocyclic carbene ligands have been evaluated for their ability to induce mitochondrial membrane permeabilisation (MMP) in isolated rat liver mitochondria. Six of the compounds, at concentrations of 10 ?M, induced Ca2+-sensitive MMP as evidenced by mitochondrial swelling. In the absence of low concentrations of exogenous Ca2+, the compounds were either inactive or their activity

Peter J. Barnard; Murray V. Baker; Susan J. Berners-Price; David A. Day

2004-01-01

84

Alkyne-Azide Cycloaddition Catalyzed by Silver Chloride and “Abnormal” Silver N-Heterocyclic Carbene Complex  

PubMed Central

A library of 1,2,3-triazoles was synthesized from diverse alkynes and azides using catalytic amounts of silver chloride instead of copper compounds. In addition, a novel “abnormal” silver N-heterocyclic carbene complex was tested as catalyst in this process. The results suggest that the reaction requires only 0.5% of silver complex, affording 1,2,3-triazoles in good yields. PMID:24307866

Ortega-Arizmendi, Aldo I.; Aldeco-Pérez, Eugenia; Cuevas-Yañez, Erick

2013-01-01

85

Femtosecond study of the rise and decay of carbenes in solution  

NASA Astrophysics Data System (ADS)

The ultrafast production and decay of carbenes from the diphenyldiazomethane precursor in isooctane has been investigated by femtosecond transient absorption spectroscopy. Diphenylcarbene is produced in less than 300 fs in a singlet state. It then undergoes an ultrafast (˜300 fs) internal conversion followed by an intermediate step of a few picoseconds, which we attribute to a conformational change between its C 1 and C 2v geometries. Finally, intersystem crossing from S 1 to the triplet ground state occurs in ˜100 ps.

Portella-Oberli, Marcia T.; Jeannin, Catherine; Soep, Benoit; Zerza, Gerald; Chergui, Majed

1998-11-01

86

Catalytic Dynamic Kinetic Resolutions with N-Heterocyclic Carbenes: Asymmetric Synthesis of Highly Substituted ?-Lactones  

PubMed Central

An N-heterocyclic carbene (NHC)-catalyzed dynamic kinetic resolution of racemic ?-substituted ?-keto esters has been developed. This method relies on the epimerization of an NHC-enol intermediate before subsequent aldol/acylation events. Highly substituted ?-lactones are produced in good yield (50–88%) with good to excellent diastereoselectivity (5:1 to 20:1 dr) and excellent enantioselectivity (up to 99% ee). PMID:22700327

Cohen, Daniel T.; Eichman, Chad C.; Phillips, Eric M.; Zarefsky, Emily R.

2012-01-01

87

Supported ruthenium-carbene catalyst on ionic magnetic nanoparticles for olefin metathesis.  

PubMed

The Grubbs-Hoveyda ruthenium-carbene complex has been covalently immobilized on ionic magnetic nanoparticles utilizing an imidazolium salt linker. The supported catalyst exhibited excellent catalytic activity for ring-closing metathesis (RCM) and cross-metathesis (CM) in the presence of less than 1 mol % of ruthenium. The catalysts can easily be recovered magnetically and reused up to seven times with minimal leaching of ruthenium species. PMID:25215600

Chen, Shu-Wei; Zhang, Zhi-Cheng; Ma, Miaofeng; Zhong, Chong-Min; Lee, Sang-gi

2014-10-01

88

A Carbene-Stabilized Gold(I) Fluoride: Synthesis and David S. Laitar, Peter Muller, Thomas G. Gray,* and Joseph P. Sadighi*  

E-print Network

A Carbene-Stabilized Gold(I) Fluoride: Synthesis and Theory David S. Laitar, Peter Mu¨ller, Thomas, 2005 Summary: The first isolable gold(I) fluoride complex, stabilized by an N-heterocyclic carbene (NHC/d interactions between fluoride and gold(I) and indicate a substantial negative charge on fluorine. Fluoride

Müller, Peter

89

Fascinating frontiers of N/O-functionalized N-heterocyclic carbene chemistry: from chemical catalysis to biomedical applications.  

PubMed

The in vogue N-heterocyclic carbenes (NHCs) have attracted attention largely for its new found popularity in chemical catalysis and also for displaying promising traits in biomedical applications. The current perspective provides an account of our efforts in exploring the utility of N/O-functionalized N-heterocyclic carbenes in these two areas. On the catalysis front, we have employed the N/O-functionalized N-heterocyclic carbene based precatalysts for the C-C and C-N bond forming reactions like the Suzuki-Miyaura, Sonogashira and Hiyama cross-couplings, the base-free Michael addition, the alkene and alkyne hydroamination reactions and the ring-opening polymerization (ROP) of L-lactides that produce biodegradable polylactide polymers while on the biomedical application front, the anticancer and antimicrobial properties of these N/O-functionalized N-heterocyclic carbene complexes were evaluated. Towards this objective, the N-heterocyclic carbene chemistry of a variety of transition metals like Ag, Au, Ni and Pd has been investigated. PMID:20495733

John, Alex; Ghosh, Prasenjit

2010-08-21

90

Cationic Bis-N-Heterocyclic Carbene (NHC) Ruthenium Complex: Structure and Application as Latent Catalyst in Olefin Metathesis.  

PubMed

An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2?a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2 -NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2?a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions. PMID:25212827

Rouen, Mathieu; Queval, Pierre; Falivene, Laura; Allard, Jessica; Toupet, Loïc; Crévisy, Christophe; Caijo, Frédéric; Baslé, Olivier; Cavallo, Luigi; Mauduit, Marc

2014-10-13

91

Oxyanion steering and CH-? interactions as key elements in an N-heterocyclic carbene-catalyzed [4 + 2] cycloaddition.  

PubMed

The N-heterocyclic carbene catalyzed [4 + 2] cycloaddition has been shown to give ?,?-unsaturated ?-lactones in excellent enantio- and diastereoselectivity. However, preliminary computational studies of the geometry of the intermediate enolate rendered ambiguous both the origins of selectivity and the reaction pathway. Here, we show that a concerted, but highly asynchronous, Diels-Alder reaction occurs rather than the stepwise Michael-type or Claisen-type pathways. In addition, two crucial interactions are identified that enable high selectivity: an oxyanion-steering mechanism and a CH-? interaction. The calculations accurately predict the enantioselectivity of a number of N-heterocyclic carbene catalysts in the hetero-Diels-Alder reaction. PMID:22765294

Allen, Scott E; Mahatthananchai, Jessada; Bode, Jeffrey W; Kozlowski, Marisa C

2012-07-25

92

Thermally Stable, Latent Olefin Metathesis Catalysts.  

PubMed

Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures. PMID:22282652

Thomas, Renee M; Fedorov, Alexey; Keitz, Benjamin K; Grubbs, Robert H

2011-12-26

93

Thermally Stable, Latent Olefin Metathesis Catalysts  

PubMed Central

Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures. PMID:22282652

Thomas, Renee M.; Fedorov, Alexey; Keitz, Benjamin K.

2011-01-01

94

Theoretical studies of mechanisms of cycloaddition reaction between difluoromethylene carbene and acetone  

NASA Astrophysics Data System (ADS)

Mechanisms of the cycloaddition reaction between singlet difluoromethylene carbene and acetone have been investigated with the second-order Møller-Plesset (MP2)/6-31G* method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface (PES) are corrected by zero-point energy (ZPE) and CCSD(T)/6-31G* single-point calculations. From the PES obtained with the CCSD(T)//MP2/6-31G* method for the cycloaddition reaction between singlet difluoromethylene carbene and acetone, it can be predicted that path B of reactions 2 and 3 should be two competitive leading channels of the cycloaddition reaction between difluoromethylene carbene and acetone. The former consists of two steps: (i) the two reactants first form a four-membered ring intermediate, INT2, which is a barrier-free exothermic reaction of 97.8 kJ/mol; (ii) the intermediate INT2 isomerizes to a four-membered product P2b via a transition state TS2b with an energy barrier of 24.9 kJ/mol, which results from the methyl group transfer. The latter proceeds in three steps: (i) the two reactants first form an intermediate, INT1c, through a barrier-free exothermic reaction of 199.4 kJ/mol; (ii) the intermediate INT1c further reacts with acetone to form a polycyclic intermediate, INT3, which is also a barrier-free exothermic reaction of 27.4 kJ/mol; and (iii) INT3 isomerizes to a polycyclic product P3 via a transition state TS3 with an energy barrier of 25.8 kJ/mol.

Lu, Xiu Hui; Yu, Hai Bin; Wu, Wei Rong; Xu, Yue Hua

95

Mechanistic studies of carbon monoxide insertion into metal-nitrene and metal-carbene bonds  

SciTech Connect

Work this quarter continued in the following areas: halide-promoted insertion of carbon monoxide into iron-{mu}-carbene bonds; ferra-pyrrolinone and ferra-azetine complexes formed from the reaction of Fe{sub 2}(CO){sub 8}({mu}-CH{sub 2}) with phosphinimines; fluorine substituted ferra-cyclopentadiene complexes with an unprecedented fluorine atom bridge between boron and carbon; synthesis of substituted pyrridinones from the combination of Fe{sub 2}({mu}-CH{sub 2})(CO{sub 8}) with phosphinimines and alkynes; and new addition and cycloaddition reactions with highly nucleophilic and chiral manganese acetylide complexes. (CBS)

Geoffroy, G.L.

1989-01-01

96

Enantioselective C-H carbene insertions with homogeneous and immobilized copper complexes.  

PubMed

The efficiency of chiral bis(oxazoline)- and azabis(oxazoline)-copper complexes in the enantioselective carbene insertion into C-H bonds of cyclic ethers in homogeneous phase strongly depends on the structure of the substrate. The immobilization on laponite clay by electrostatic interactions not only allows the recovery and reuse of the heterogeneous catalysts, but in some cases also improves enantioselectivity and overall chemoselectivity, making possible reactions that do not take place or lead to low yields in solution, even with the commonly used Rh(2)[S-DOSP](4) catalyst. PMID:21750830

Fraile, José M; López-Ram-de-Viu, Pilar; Mayoral, José A; Roldán, Marta; Santafé-Valero, Jorge

2011-09-01

97

Activation of the C-N bond of N-heterocyclic carbenes by inorganic elements.  

PubMed

N-heterocyclic carbenes (NHCs) are generally considered to be extremely robust, ideal spectator ligands. However, in the past two years there have been several reports of the activation of the endocyclic C-N bond with subsequent insertion into element-hydrogen and element-carbon bonds. The new reaction pathway casts the reactivity of the NHC heterocyclic ring into a new light, especially in the context of potential catalyst decomposition. The synthetic reports and theoretical studies in this rapidly developing area are summarized here. PMID:24763715

Iversen, Kalon J; Wilson, David J D; Dutton, Jason L

2014-09-14

98

Synthesis of new copper(I) complexes with tris(2-pyridyl) ligands. Applications to carbene and nitrene transfer reactions.  

PubMed

New copper(I) complexes with tris(2-pyridyl)methane (TPC), tris(2-pyridyl)methoxymethane (TPM) and tris(2-pyridyl)amine (TPN) ligands have been synthesized and characterized, including structural determinations by X-ray diffraction of some examples. Their activity as catalysts in carbene and nitrene transfer reactions was studied. PMID:19089020

Pérez, Julio; Morales, Dolores; García-Escudero, Luis A; Martínez-García, Héctor; Miguel, Daniel; Bernad, Pablo

2009-01-14

99

Correlation between Functionality Preference of Ru Carbenes and exo/endo Product Selectivity for Clarifying the Mechanism of Ring-  

E-print Network

outcome. The correlation between function- ality preference and exo/endo product ratio offers a solutionCorrelation between Functionality Preference of Ru Carbenes and exo/endo Product Selectivity the outcome of the reaction. The Ru catalyst favoring alkyne over alkene provides more endo product

Ihee, Hyotcherl

100

Optimized Syntheses of Cyclopentadienyl Nickel Chloride Compounds Containing "N"-Heterocyclic Carbene Ligands for Short Laboratory Periods  

ERIC Educational Resources Information Center

Experiments are described for the preparation of imidazolium chloride precursors to "N"-heterocyclic carbenes and their cyclopentadienyl nickel chloride derivatives. The syntheses have been optimized for second- and third-year undergraduate laboratories that have a maximum programmed length of three hours per week. The experiments are flexible and…

Cooke, Jason; Lightbody, Owen C.

2011-01-01

101

Synthesis, Characterization, and Reactivity of Furan- and Thiophene-Functionalized Bis(N-heterocyclic carbene) Complexes of Iron(II).  

PubMed

The synthesis of iron(II) complexes bearing new heteroatom-functionalized methylene-bridged bis(N-heterocyclic carbene) ligands is reported. All complexes are characterized by single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (2a) and tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenethiophene)methane]iron(II) hexafluorophosphate (2b) were obtained by aminolysis of [Fe{N(SiMe3)2}2(THF)] with furan- and thiophene-functionalized bis(imidazolium) salts 1a and 1b in acetonitrile. The SC-XRD structures of 2a and 2b show coordination of the bis(carbene) ligand in a bidentate fashion instead of a possible tetradentate coordination. The four other coordination sites of these distorted octahedral complexes are occupied by acetonitrile ligands. Crystallization of 2a in an acetone solution by the slow diffusion of Et2O led to the formation of cis-diacetonitriledi[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (3a) with two bis(carbene) ligands coordinated in a bidentate manner and two cis-positioned acetonitrile molecules. Compounds 2a and 2b are the first reported iron(II) carbene complexes with four coordination sites occupied by solvent molecules, and it was demonstrated that those solvent ligands can undergo ligand-exchange reactions. PMID:25188636

Rieb, Julia; Raba, Andreas; Haslinger, Stefan; Kaspar, Manuel; Pöthig, Alexander; Cokoja, Mirza; Basset, Jean-Marie; Kühn, Fritz E

2014-09-15

102

Pd-N-Heterocyclic Carbene (NHC) Organic Silica: Synthesis and Application in Carbon-Carbon Coupling Reactions  

EPA Science Inventory

The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica was prepared using sol-gel method and its application in Heck and Suzuki reaction were demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wi...

103

Coordination Chemistry of Highly Hemilabile Bidentate Sulfoxide N-Heterocyclic Carbenes with Palladium(II).  

PubMed

Imidazolium salts, [RS(O)?CH2 (C3 H3 N2 )Mes]Cl (R=Me (L1?a), Ph (L1?b)); Mes=mesityl), make convenient carbene precursors. Palladation of L1?a affords the monodentate dinuclear complex, [(PdCl2 {MeS(O)CH2 (C3 H2 N2 )Mes})2 ] (2?a), which is converted into trans-[PdCl2 (NHC)2 ] (trans-4?a; N-heterocyclic carbene) with two rotamers in anti and syn configurations. Complex trans-4?a can isomerize into cis-4?a(anti) at reflux in acetonitrile. Abstraction of chlorides from 4?a or 4?b leads to the formation of a new dication: trans-[Pd{RS(O)CH2 (C3 H2 N2 )Mes}2 ](PF6 )2 (R=Me (5?a), Ph (5?b)). The X-ray structure of 5?a provides evidence that the two bidentate SO?NHC ligands at palladium(II) are in square-planar geometry. Two sulfoxides are sulfur- and oxygen-bound, and constitute five- and six-membered chelate rings with the metal center, respectively. In acetonitrile, complexes 5?a or 5?b spontaneously transform into cis-[Pd(NHC)2 (NCMe)2 ](PF6 )2 . Similar studies of thioether-NHCs have also been examined for comparison. The results indicate that sulfoxides are more labile than thioethers. PMID:25263615

Yu, Kuo-Hsuan; Wang, Chia-Ching; Chang, I-Hsin; Liu, Yi-Hung; Wang, Yu; Elsevier, Cornelis J; Liu, Shiuh-Tzung; Chen, Jwu-Ting

2014-12-01

104

Alkynyl Fischer carbene complex as a traceless directing group for the regioselective cycloaddition of dithiolethiones to arylacetylene: synthesis of E-dithiafulvene thione and dithioesters.  

PubMed

A phenylethynyl Fischer carbene complex was used as a traceless directing group for the regioselective cycloaddition of dithiolethiones to arylacetylene, which constitutes the first synthesis of E-dithiafulvene thione or dithioesters. PMID:18188475

Granados, Alejandro M; Fracaroli, Alejandro M; de Rossi, Rita H; Fuertes, Pedro; Torroba, Tomás

2008-01-28

105

Synthesis of 1,3-dithiin dithioortho esters from the reaction of Fischer carbenes and 3H-1,2-dithiole-3-thiones.  

PubMed

[reaction: see text] Tricyclic 4-ethyl-5-thioxo-3H,5H-bis[1,2]dithiolo[3,4-d][4,3-b]pyrrol-3-one and monocyclic 3H-1,2-dithiole-3-thione derivatives reacted with Fischer carbene complexes, giving 1,3-dithiin dithioortho esters through insertion of the carbenic carbon into the S-S bond next to the thiocarbonyl function of the substrate. PMID:16408999

Granados, Alejandro M; Kreiker, Jeronimo; de Rossi, Rita H; Fuertes, Pedro; Torroba, Tomás

2006-01-20

106

Changing reaction pathways of the dimerization of 2-formylcinnamates by N-heterocyclic carbene/lewis Acid cooperative catalysis: an unusual cleavage of the carbon-carbon bond.  

PubMed

Catalyzed by a triazole carbene, the dimerization of 2-formylcinnamates underwent benzoin condensation followed by intramolecular oxa-Michael addition to afford isochromeno[4,3-c]isochromene products. Under the catalysis of a combination of triazole carbene and Ti(OPr-i)4 catalysts, the dimerization reaction of 2-formylcinnamates proceeded through a completely different route to furnish the formation of isochromenone derivatives with the elimination of an acetate moiety. PMID:25329247

Dang, Hai-Yan; Wang, Zi-Tian; Cheng, Ying

2014-11-01

107

Highly stereoselective synthesis of cyclopentanes bearing four stereocentres by a rhodium carbene-initiated domino sequence.  

PubMed

Stereoselective synthesis of a cyclopentane nucleus by convergent annulation constitutes a significant challenge for synthetic chemists. Although a number of biologically relevant cyclopentane natural products are known, more often than not, the cyclopentane core is assembled in a stepwise manner because of the lack of efficient annulation strategies. Here we report the rhodium-catalysed reactions of vinyldiazoacetates with (E)-1,3-disubstituted 2-butenols generate cyclopentanes, containing four new stereogenic centres with very high levels of stereoselectivity (99% ee, >97: 3 dr). The reaction proceeds by a carbene-initiated domino sequence consisting of five distinct steps: rhodium-bound oxonium ylide formation, [2,3]-sigmatropic rearrangement, oxy-Cope rearrangement, enol-keto tautomerization and finally an intramolecular carbonyl ene reaction. A systematic study is presented detailing how to control chirality transfer in each of the four stereo-defining steps of the cascade, consummating in the development of a highly stereoselective process. PMID:25082301

Parr, Brendan T; Davies, Huw M L

2014-01-01

108

Cooperative catalysis by carbenes and Lewis acids in a highly stereoselective route to ?-lactams  

NASA Astrophysics Data System (ADS)

Enzymes are a continuing source of inspiration for the design of new chemical reactions that proceed with efficiency, high selectivity and minimal waste. In many biochemical processes, different catalytic species, such as Lewis acids and bases, are involved in precisely orchestrated interactions to activate reactants simultaneously or sequentially. This type of `cooperative catalysis', in which two or more catalytic cycles operate concurrently to achieve one overall transformation, has great potential in enhancing known reactivity and driving the development of new chemical reactions with high value. In this disclosure, a cooperative N-heterocyclic carbene/Lewis acid catalytic system promotes the addition of homoenolate equivalents to hydrazones, generating highly substituted ?-lactams in moderate to good yields and with high levels of diastereo- and enantioselectivity.

Raup, Dustin E. A.; Cardinal-David, Benoit; Holte, Dane; Scheidt, Karl A.

2010-09-01

109

Isolation of an Imino-N-heterocyclic Carbene/Germanium(0) Adduct: A Mesoionic Germylene Equivalent.  

PubMed

An autoionization of germanium dichloride/dioxane complex with an imino-N-heterocyclic carbene ligand (L) afforded a novel germyliumylidene ion, [(L)GeCl](+) [GeCl3 ](-) , which was fully characterized. Reduction of the germyliumylidene ion with potassium graphite produced a cyclic species [(L)Ge], which can be viewed as both a Ge(0) species and a mesoionic germylene. X-ray diffraction analysis and computational studies revealed one of the lone pairs on the Ge atom is involved in the ??system on the GeC2 N2 five-membered ring. It was also confirmed that the nucleophilic behavior of [(L)Ge] as a two lone-pair donor. PMID:25283638

Su, Bochao; Ganguly, Rakesh; Li, Yongxin; Kinjo, Rei

2014-11-24

110

Tuning the electronic and ligand properties of remote carbenes: a theoretical study.  

PubMed

The effect of annulation and carbonylation on the electronic and ligating properties of remote N-heterocyclic carbenes (rNHCs) has been studied quantum-chemically. The thermodynamic stability of these complexes has been assessed on the basis of their hydrogenation and stabilization energies, while HOMO-LUMO gaps are used to measure the kinetic stabilities. Annulated/carbonylated rNHCs are found to be weaker ? donors but better ? acceptors compared with the parent rNHCs. The reactivity of these rNHCs has been studied by evaluating their nucleophilicity and electrophilicity indices. The nucleophilicity values are in good agreement with the ? basicities of all of the rNHCs. The (31)P NMR chemical shifts of the corresponding rNHC-phosphinidene adducts have been calculated and found to correlate well with the ? acidities of these rNHCs. PMID:25340967

Borthakur, Bitupon; Rahman, Taskia; Phukan, Ashwini K

2014-11-21

111

Abnormal N-heterocyclic carbene main group organometallic chemistry: a debut to the homogeneous catalysis.  

PubMed

Abnormal N-heterocyclic carbene (aNHC) adducts of zinc(II) (1) and aluminum(III) (2) were synthesized. The compounds were characterized by NMR spectroscopy and elemental analysis. The solid state structures of these complexes (1 and 2) were determined by single crystal X-ray study. Furthermore, these organozinc and organoaluminum adducts (1 and 2) were tested for the ring opening polymerization of cyclic esters. These adducts were found to be quite efficient catalysts for the polymerization of cyclicesters such as rac-lactide (rac-LA), ?-caprolactone (?-CL), and ?-valerolactone (?-VL). Furthermore, aNHC zinc adduct has been used as catalyst for the synthesis of a tri-block copolymer. PMID:23945705

Sen, Tamal K; Sau, Samaresh Chandra; Mukherjee, Arup; Hota, Pradip Kumar; Mandal, Swadhin K; Maity, Bholanath; Koley, Debasis

2013-10-21

112

Tungsten(VI) N-Heterocyclic Carbene Complexes: Synthetic, Structural, and Computational Study  

PubMed Central

The reaction of WOCl4 with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Idipp) leads to an orange solid whose spectroscopic data are consistent with the 1:1 adduct [WOCl4(Idipp)]. Computational studies at the DFT level further support this formulation. Exposure of this compound to the atmosphere results in rapid hydrolysis to various imidazolium salts. If air diffuses very slowly into solutions of [WOCl4(Idipp)], it also undergoes slow hydrolysis to form [WO2Cl2(Idipp)]. This has been crystallographically characterized and is the first five-coordinate, 1:1 adduct of WO2Cl2. This complex has also been subject to DFT calculations, and its metal–ligand bonding has been explored. The carbene–metal interaction is primarily ?-donor in nature. The mechanism of the hydrolysis has also been probed by computational methods, revealing a plausible, low-energy reaction pathway. PMID:24882916

2011-01-01

113

Cooperative Catalysis by Carbenes and Lewis Acids in a Highly Stereoselective Route to ?-Lactams  

PubMed Central

Enzymes are a continuing source of inspiration for the design of new chemical reactions that proceed with efficiency, high selectivity and minimal waste. In many biochemical processes, different catalytic species, such as Lewis acids and bases, are involved in precisely orchestrated interactions to activate reactants simultaneously or sequentially. Employing this type of cooperative catalysis, in which two or more catalytic cycles operate concurrently to achieve one overall transformation, has great potential to enhance known reactivity and drive the development of new chemical reactions with high value. In this disclosure, a cooperative N-heterocyclic carbene/Lewis acid catalytic system promotes the addition of homoenolate equivalents to hydrazones generating highly substituted ?-lactams in moderate to good yields and high levels of diastereo- and enantioselectivity. PMID:20729898

Raup, Dustin E. A.; Cardinal-David, Benoit; Holte, Dane; Scheidt, Karl A.

2010-01-01

114

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles  

PubMed Central

Summary Deprotonation of indazolium salts at low temperatures gives N-heterocyclic carbenes of indazoles (indazol-3-ylidenes) which can be trapped as rhodium complexes (X-ray analysis). In the absence of Rh, the indazol-3-ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole–indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazole–indole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis). Results of DFT calculations are presented. PMID:24778738

Guan, Zong; Namyslo, Jan C; Drafz, Martin H H; Nieger, Martin

2014-01-01

115

?-Carbon activation of saturated carboxylic esters through N-heterocyclic carbene organocatalysis  

NASA Astrophysics Data System (ADS)

The activation of the ?-carbons of carboxylic esters and related carbonyl compounds to generate enolate equivalents as nucleophiles is one of the most powerful strategies in organic synthesis. We reasoned that the horizons of chemical synthesis could be greatly expanded if the typically inert ?-carbons of saturated esters could be used as nucleophiles. However, despite the rather significant fundamental and practical values, direct use of the ?-carbons of saturated carbonyl compounds as nucleophiles remains elusive. Here we report the catalytic activation of simple saturated ester ?-carbons as nucleophiles (?-carbon activation) using N-heterocyclic carbene organocatalysts. The catalytically generated nucleophilic ?-carbons undergo enantioselective reactions with electrophiles such as enones and imines. Given the proven rich chemistry of ester ?-carbons, we expect this catalytic activation mode for saturated ester ?-carbons to open a valuable new arena for new and useful reactions and synthetic strategies.

Fu, Zhenqian; Xu, Jianfeng; Zhu, Tingshun; Leong, Wendy Wen Yi; Chi, Yonggui Robin

2013-10-01

116

Borenium Ion Catalyzed Hydroboration of Alkenes with N-Heterocyclic Carbene Boranes  

PubMed Central

Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-1-butene with the N-heterocyclic carbene-derived borane 2 and catalytic HNTf2 effects hydroboration at room temperature. With 3-hexene, surprisingly facile migration of the boron atom from C3 of the hexyl group to C2 was observed over a time scale of minutes to hours. Oxidative workup gave a mixture of alcohols containing 2-hexanol as the major product. A similar preference for the C(2) alcohol was observed after oxidative workup of the 3-octene, and 1-cyclohexyl-1-butene hydroborations. NHC-borenium cations (or functional equivalents) are postulated as the species that accomplish the hydroborations, and the C(2) selective migrations are attributed to the 4-center inter-conversion of borenium cations with cationic NHC-borane olefin ?-complexes. PMID:22713106

Prokofjevs, Aleksandrs; Boussonniere, Anne; Li, Linfeng; Bonin, Helene; Lacote, Emmanuel; Curran, Dennis P.; Vedejs, Edwin

2012-01-01

117

Photophysical properties of trans-platinum acetylide complexes featuring N-heterocyclic carbene ligands.  

PubMed

A series of trans-N-heterocyclic carbene (NHC) platinum(ii) acetylide complexes of the form (ICy)2Pt(R)2 (where ICy = 1,3-bis-(cyclohexyl)imidazol-2-ylidene and R = 1-Ethynyl-4-(phenylethynyl)benzene (PE2), 2-(9,9-Diethyl-9H-fluoren-7-yl)benzo[d]thiazole (BTF), and 9,9-Diethyl-7-ethynyl-N,N-diphenyl-9H-fluoren-2-amine (DPAF), respectively), were synthesized via Hagihara reaction of the unprotected aryl-acetylide ligands with trans-(ICy)2PtCl2 () in 47-73% yield. Precursor was generated in a one-pot synthesis via formation of a silver carbene precursor followed by transmetallation, and was obtained in high yield (95%). The single-crystal X-ray structures of , were determined and analyzed. The photophysical properties of were compared to their respective tributyl phosphine (PBu3) analogues. The optical properties of the series were studied by UV-Vis spectroscopy, photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, and open aperture nanosecond z-scan. Coupling of the organic chromophores to the platinum center affords efficient intersystem crossing as concluded by the complexes' low fluorescence quantum yields, efficient phosphorescence and intense T1 - Tn absorption. Open aperture z-scan with 606 nm, 10 ns laser pulses showed comparable optical attenuation relative to a standard sample of (PBu3)2Pt(DPAF)2 (). Pulse limiting was achieved via a dual-mechanism of two-photon absorption (2PA) coupled with excited-state absorption (ESA). TD-DFT Computations were also employed for to give greater insight into the nature of the singlet-singlet electronic transitions. PMID:25019204

Winkel, Russell W; Dubinina, Galyna G; Abboud, Khalil A; Schanze, Kirk S

2014-11-12

118

A search for thermal isomerization of olefins to carbenes: Thermal generations of the silicon-nitrogen double bond  

SciTech Connect

The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.

Zhang, Xianping.

1990-09-21

119

Zirconium complexes of the tridentate bis(aryloxide)- N-heterocyclic-carbene ligand: Chloride and alkyl functionalized derivatives  

Microsoft Academic Search

The disodium salt of a bis(aryloxide)-N-heterocyclic-carbene dianionic ligand, Na2[L], was prepared by reaction of 1,3-bis(4,6-di-tert-butyl-2-hydroxybenzyl)imidazolium bromide [H3L]Br with 3 equiv. of NaN(SiMe3)2. Reaction of ZrCl4(thf)2 with 1 equiv. of Na2[L] gave a mixture of [L]ZrCl2(thf) (1) and [L]2Zr (2). When the amount of Na2[L] was increased to 2 equiv., the bis(bis(aryloxide)-N-heterocyclic-carbene) complex 2 was obtained in good yield. The dichloro

Dao Zhang; Hidenori Aihara; Takahito Watanabe; Tsukasa Matsuo; Hiroyuki Kawaguchi

2007-01-01

120

Luminescence Studies of the Intracellular Distribution of a Dinuclear Gold(I) N-Heterocyclic Carbene Complex  

SciTech Connect

A bidentate cyclophane N-heterocyclic carbene ligand has been used to synthesize a new dinuclear Au{sup I} complex of the formula [Au{sub 2}L{sub 2}]{sup 2+}. The short Au {hor_ellipsis} Au distance imposed by the rigid cyclophane ligand leads to a red-shifted luminescence profile that enables the complex to be used as a luminescent probe for distribution studies in single living cancer cells.

Barnard, Peter J.; Wedlock, Louise E.; Baker, Murray V.; Berners-Price, Susan J.; Joyce, David A.; Skelton, Brian W.; Steer, James H. (UWA)

2008-10-03

121

Preparation of a N-Heterocyclic Carbene Nickel(II) Complex: Synthetic Experiments in Current Organic and Organometallic Chemistry  

ERIC Educational Resources Information Center

A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro-nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes[middle dot]HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with…

Ritleng, Vincent; Brenner, Eric; Chetcuti, Michael J.

2008-01-01

122

N-Heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed Mizoroki-Heck reaction of aryl chlorides with styrenes  

PubMed Central

Summary A well-defined N-heterocyclic carbene–palladium(II)-1-methylimidazole [NHC-Pd(II)-Im] complex 1 was found to be an effective catalyst for the Mizoroki–Heck reaction of a variety of aryl chlorides with styrenes. Both activated and deactivated aryl chlorides work well to give the corresponding coupling products in good to excellent yields by using tetrabutylammonium bromide (TBAB) as the ionic liquid. PMID:23209531

Gao, Ting-Ting; Jin, Ai-Ping

2012-01-01

123

Synthesis and structural investigation of R2Si (R = Me, Ph) bridged di-N-heterocyclic carbenes.  

PubMed

Functionalization of the C4 carbon of an imidazol-derived N-heterocyclic carbene (NHC) may allow fine-tuning of the electronic and steric properties of the C2 carbene center. A facile route to silyl-functionalized di-N-heterocyclic carbenes (Di-NHCs) is described. Treatment of the polymeric lithiated NHC, {Li(IPrH)}n (1) (Li(IPrH) = {(N-2,6-iPr2C6H3)2CHCLi}C:) with a dichlorosilane affords monomeric silyl-functionalized Di-NHCs, R2Si(IPrH)2 (R = Ph, 2; Me, 3). Interestingly, silyl-functionalized mono-NHC, Ph2(Cl)Si(IPrH) (4) with a pendant chloro-substituent can also be exclusively isolated maintaining the reactants 1 and Ph2SiCl2 ratio. NHCs 2 and 4 readily form copper complexes, Ph2Si{(IPrH)CuCl}2 (5) and Ph2(Cl)Si{(IPrH)CuCl} (6), on reaction with CuCl. Straightforward conversion of an NHC to a Di-NHC (2 or 3) via C4 functionalization is reported for the first time. Molecular structures of 2, 4, 5 and 6 have been established by single crystal X-ray diffraction studies. PMID:25101953

Ghadwal, Rajendra S; Reichmann, Sven O; Carl, Elena; Herbst-Irmer, Regine

2014-09-28

124

Central-to-Axial Chirality Transfer in the Benzannulation Reaction of Optically Pure Fischer Carbene Complexes in the Synthesis of Allocolchicinoids  

PubMed Central

A method for the synthesis of allocolchicinoids is explored that involves the benzannulation reaction of Fischer chromium carbene complexes with alkynes. The benzannulation reaction is employed to install the aromatic C-ring via the reaction of an ?,?-unsaturated carbene complex in which the carbene complex is attached to a seven-membered ring that is to become the B-ring of the allocolchicinoids. Two different regioisomeric series can be accessed depending on which position the carbene complex is on the seven membered ring. A key issue that is addressed is the stereochemistry of the newly formed axis of chirality that results from a stereo-relay from an existing chiral center on the seven membered ring at the position destined to be C(7) in the allocolchicinoids. The level of stereochemistry is dependent on the position of the carbene complex on the seven membered ring. A mechanism is proposed to account for this stereochemical dependence and to account for the observed effects of temperature and solvent on the stereoselectivity. Finally, the benzannulation reactions of optically pure complexes are examined and quite surprisingly one, but not both, of the diastereomeric products is racemized. The racemization can be prevented with the proper choice of solvent and temperature. A mechanism is proposed to account for the racemization of only one of the diastereomers of the product that involves the intermediacy of an ortho-quinone methide chromium tricarbonyl complex. PMID:19180172

Vorogushin, Andrei V.; Wulff, William D.; Hansen, Hans-Jurgen

2008-01-01

125

Methandiide as a non-innocent ligand in carbene complexes: from the electronic structure to bond activation reactions and cooperative catalysis.  

PubMed

The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a Ru-C single bond with additional electrostatic interactions and a Ru=C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (O-H, H-H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis. PMID:25047390

Becker, Julia; Modl, Tanja; Gessner, Viktoria H

2014-09-01

126

Synthesis, structural characterization and properties of new N-heterocyclic carbene Ag(I) complexes  

NASA Astrophysics Data System (ADS)

The syntheses and properties of new N-heterocyclic carbene complexes [{1-(2,3,5,6-tetra methyl benzyl)-3-benzylbimy}AgCl] (2a), [{1-(benzyl)-3-benzylbimy}2Ag][BF4] (2b), [{1-(benzyl)-3-butylbimy}AgBr]2 (2c), [{1-(benzyl)-3-(4-nitro-benzyl)bimy}AgBr] (2d), [{1-(benzyl)-3-(4-bromo-benzyl)bimy}AgBr] (2e), [{1-(benzyl)-3-(4-nitro-benzyl)bimy}2Ag][BF4] (2f), [{1-(benzyl)-3-(4-bromo-benzyl)bimy}2Ag][BF4] (2g) (bimy = benzimidazol-2-ylidene), and [{1-(10-bromo-9-anthracenylmethyl)-3-butylimy}AgBr] (2h) (imy = imidazol-2-ylidene) have been described. Compounds 2a-2h have been characterized by 1H NMR-, UV-vis- LC/MS-spectral studies and elemental analysis. Compounds 2a-2c and 2h are unambiguously characterized by single crystal X-ray crystallography. Compound 2h shows solution emission at room temperature.

Kishore, Ravada; Das, Samar K.

2013-12-01

127

The photochemistry of rhenium(I) tricarbonyl N-heterocyclic carbene complexes.  

PubMed

The photophysical and photochemical properties of the new tricarbonyl rhenium(I) complexes bound to N-heterocyclic carbene ligands (NHC), fac-[Re(CO)3(N^C)X] (N^C = 1-phenyl-3-(2-pyridyl)imidazole or 1-quinolinyl-3-(2-pyridyl)imidazole; X = Cl or Br), are reported. The photophysics of these complexes highlight phosphorescent emission from triplet metal-to-ligand ((3)MLCT) excited states, typical of tricarbonyl rhenium(I) complexes, with the pyridyl-bound species displaying a ten-fold shorter excited state lifetime. On the other hand, these pyridyl-bound species display solvent-dependent photochemical CO dissociation following what appear to be two different mechanisms, with a key step being the formation of cationic tricarbonyl solvato-complexes, being themselves photochemically active. The photochemical mechanisms are illustrated with a combination of NMR, IR, UV-Vis, emission and X-ray structural characterization techniques, clearly demonstrating that the presence of the NHC ligand is responsible for the previously unobserved photochemical behavior in other photoactive tricarbonyl rhenium(I) species. The complexes bound to the quinolinyl-NHC ligand (which possess a lower-energy (3)MLCT) are photostable, suggesting that the photoreactive excited state is not any longer thermally accessible. The photochemistry of the pyridyl complexes was investigated in acetonitrile solutions and also in the presence of triethylphosphite, showing a competing and bifurcated photoreactivity promoted by the trans effect of both the NHC and phosphite ligands. PMID:23939232

Vaughan, Jamila G; Reid, Brodie L; Ramchandani, Sushil; Wright, Phillip J; Muzzioli, Sara; Skelton, Brian W; Raiteri, Paolo; Brown, David H; Stagni, Stefano; Massi, Massimiliano

2013-10-21

128

All-electron relativistic multireference configuration interaction investigation of fluoroiodo carbene.  

PubMed

We present herein the first all-electron relativistic internally contracted multireference configuration interaction with Davidson correction (icMRCI+Q) study on the low-lying states of fluoroiodo carbene, CFI, which contains the most electronegative element (fluorine) and the heavy halogen (iodine). The potential energy surface (PES) of the first excited singlet state (Ã(1)A?) of CFI was carefully examined along the C-I bond distance at the icMRCI+Q/ANO-RCC level, while the other two geometric parameters were optimized at every C-I bond length in contrast to fixing them at the equilibrium values. A reliable barrier height of the Ã(1)A? state was determined to be 625 cm(-1) by our high-level icMRCI+Q calculations with large ANO-RCC basis set and with inclusion of the spin-orbit coupling, core-valence correlation, and zero-point-energy. Finally, the electronic states of CFI with vertical transition energy up to 6 eV were studied. The calculation presented here will provide more comprehensive results about the structure and behavior of electronic states of CFI radical. PMID:24611930

Sun, Erping; Lv, Hang; Shi, Dandan; Wei, Changli; Xu, Haifeng; Yan, Bing

2014-04-01

129

Iron porphyrin carbenes as catalytic intermediates: structures, Mössbauer and NMR spectroscopic properties, and bonding.  

PubMed

Iron porphyrin carbenes (IPCs) are thought to be intermediates involved in the metabolism of various xenobiotics by cytochrome P450, as well as in chemical reactions catalyzed by metalloporphyrins and engineered?P450s. While early work proposed IPCs to contain Fe(II), more recent work invokes a double-bond description of the iron-carbon bond, similar to that found in Fe(IV) porphyrin oxenes. Reported herein is the first quantum chemical investigation of IPC Mössbauer and NMR spectroscopic properties, as well as their electronic structures, together with comparisons to ferrous heme proteins and an Fe(IV) oxene model. The results provide the first accurate predictions of the experimental spectroscopic observables as well as the first theoretical explanation of their electrophilic nature, as deduced from experiment. The preferred resonance structure is Fe(II)?{:C(X)Y}(0) and not Fe(IV)={C(X)Y}(2-), a result that will facilitate research on IPC reactivities in various chemical and biochemical systems. PMID:24910004

Khade, Rahul L; Fan, Wenchao; Ling, Yan; Yang, Liu; Oldfield, Eric; Zhang, Yong

2014-07-14

130

N-heterocyclic carbene boryl radicals: a new class of boron-centered radical.  

PubMed

Reduction of xanthates by N-heterocyclic carbene boranes (NHC-boranes) has been suggested to occur by a radical chain mechanism involving heretofore unknown NHC-boryl radicals. In support of this suggestion, both the expected borane dithiocarbonate product and an unexpected borane xanthate product have now been isolated. These are the first NHC-boranes with boron-sulfur bonds, and their structures have been secured by spectroscopic and crystallographic means. The first rate constants for H-atom transfer from an NHC borane complex were determined by using the ring opening of a substituted cyclobutylcarbinyl radical as a clock reaction. The rate constant for reaction of the NHC-borane with a secondary alkyl radical at ambient temperature is 4 x 10(4) M(-1) s(-1), and the Arrhenius function displayed an entropic term (log A term) that was typical for a bimolecular reaction. The B-H bond dissociation energy of an NHC-borane complex has been estimated at 88 kcal/mol. The putative NHC-boryl radical in these transformations has been detected by EPR spectroscopy. Spectral analysis suggests that it is a pi-radical, analogous to the benzyl radical. PMID:19606860

Ueng, Shau-Hua; Solovyev, Andrey; Yuan, Xinting; Geib, Steven J; Fensterbank, Louis; Lacôte, Emmanuel; Malacria, Max; Newcomb, Martin; Walton, John C; Curran, Dennis P

2009-08-12

131

Optimizing P,N-Bidentate Ligands for Oxidative Gold Catalysis: Highly Efficient Intermolecular Trapping of ?-Oxo Gold Carbenes by Carboxylic Acids  

PubMed Central

Steric Bulk or Conformation Control? Optimization of P,N-bidentate ligands reveals the importance of conformation control in the development of highly efficient intermolecular trapping of reactive ?-oxo gold carbene intermediates. While a pendant piperidine ring offers suitable steric bulk, fixing its conformation to provide better shielding to the highly electrophilic carbene center turned out to be crucial for the excellent reaction efficiency. A generally highly efficient and broadly applicable synthesis of carboxymethyl ketones from readily available carboxylic acids and terminal alkynes is developed under exceptionally mild reaction conditions. PMID:23640818

Ji, Kegong; Zhao, Yulong; Zhang, Liming

2013-01-01

132

N-heterocyclic carbene catalyzed carba-, sulfa-, and phospha-Michael additions with NHC·CO? adducts as precatalysts.  

PubMed

N-heterocyclic carbene catalyzed Michael additions have been revisited with 1,3-dialkyl- or 1,3-diarylimidazol(in)ium-2-carboxylates, that is, NHC·CO2 adducts, as the source of the free NHC catalysts in solution. Using these precatalysts, a number of efficient carba-, sulfa-, and phospha-Michael additions were achieved very conveniently, without the need for an external strong base to generate the NHC by deprotonation of an azolium salt. To further expand the scope of the procedure, some NHC-catalyzed sulfa-Michael/aldol organocascades were also investigated. PMID:24568358

Hans, Morgan; Delaude, Lionel; Rodriguez, Jean; Coquerel, Yoann

2014-03-21

133

Structurally Characterized Cationic Silver(I) and Ruthenium(II)carbene complexes of 1,2,3-Triazol-5-ylidenes.  

PubMed

A novel 1,3,4-substituted 1,2,3-triazolium salt was found to function as an effective precursor for the synthesis of the first structurally characterized cationic silver(I) and ruthenium(II)carbene complexes of overall 1:2 ligand-to-metal stoichiometry. The Ag(I) complex crystallized in the form of an eight silver atom-containing cluster, whereas the Ru(II) complex proved to be a discrete species and was found to be capable of initiating the ring-opening metathesis polymerization of norbornene upon activation with (trimethylsilyl)diazomethane. PMID:22140293

Cai, Jiajia; Yang, Xiaoping; Arumugam, Kuppuswamy; Bielawski, Christopher W; Sessler, Jonathan L

2011-09-26

134

Structurally Characterized Cationic Silver(I) and Ruthenium(II)carbene complexes of 1,2,3-Triazol-5-ylidenes  

PubMed Central

A novel 1,3,4-substituted 1,2,3-triazolium salt was found to function as an effective precursor for the synthesis of the first structurally characterized cationic silver(I) and ruthenium(II)carbene complexes of overall 1:2 ligand-to-metal stoichiometry. The Ag(I) complex crystallized in the form of an eight silver atom-containing cluster, whereas the Ru(II) complex proved to be a discrete species and was found to be capable of initiating the ring-opening metathesis polymerization of norbornene upon activation with (trimethylsilyl)diazomethane. PMID:22140293

Cai, Jiajia; Yang, Xiaoping; Arumugam, Kuppuswamy

2011-01-01

135

N,N'-dialkyl- and N-alkyl-N-mesityl-substituted N-heterocyclic carbenes as ligands in Grubbs catalysts.  

PubMed

Various symmetrically and asymmetrically substituted N-heterocyclic carbene (NHC) ligands bearing aliphatic nitrogen-containing side groups have been synthesised. In our attempts to isolate the corresponding second-generation Grubbs catalysts, we were unsuccessful when using the symmetrical aliphatic NHC ligands. For the asymmetrical ligands bearing an aliphatic moiety on one side and an aromatic mesityl group on the other side, substitution of a phosphine ligand was achieved. The performance of a so-formed series of Ru-based metathesis initiators has been evaluated for the ring-opening metathesis polymerisation (ROMP) of cycloocta-1,5-diene and the ring-closing metathesis (RCM) of diethyl diallylmalonate. PMID:16538690

Ledoux, Nele; Allaert, Bart; Pattyn, Siegfried; Vander Mierde, Hans; Vercaemst, Carl; Verpoort, Francis

2006-06-01

136

Imidazolium-salt-functionalized ionic-CNT-supported Ru-carbene/palladium nanoparticles for recyclable tandem metathesis/hydrogenation reactions in ionic liquids.  

PubMed

NP and tuck: Two different catalysts, a Ru-carbene complex and palladium nanoparticles, were immobilized onto the same imidazolium-salt-functionalized ionic CNTs. These supported dual-function catalysts showed excellent catalytic activity in tandem metathesis/hydrogenation reactions in an ionic liquid and could be recovered and reused four times. RCM = ring-closing metathesis. PMID:23757260

Lee, Sujin; Shin, Ju Yeon; Lee, Sang-gi

2013-09-01

137

N-heterocyclic carbene catalyzed formal [3+2] annulation reaction of enals: an efficient enantioselective access to spiro-heterocycles.  

PubMed

A highly enantioselective N-heterocyclic carbene (NHC) catalyzed formal [3+2] annulation of ?,?-unsaturated aldehydes with azaaurones or aurone generating spiro-heterocycles has been developed. The protocol represents a unique NHC-activation-based approach to access spiro-heterocyclic derivatives bearing a quaternary stereogenic center with high optical purity (up to 95%?ee). PMID:25130870

Guo, Chang; Schedler, Michael; Daniliuc, Constantin G; Glorius, Frank

2014-09-15

138

Controlled CO release using photochemical, thermal and electrochemical approaches from the amino carbene complex [(CO)5CrC(NC4H8)CH3].  

PubMed

Multimodal photo, thermal and electrochemical approaches toward CO release from the amino carbene complex [(CO)5CrC(NC4H8)CH3] is reported. Picosecond time resolved infrared spectroscopy was used to probe the photo-induced early state dynamics leading to CO release, and DFT calculations confirmed that CO release occurs from a singlet excited state. PMID:25188765

McMahon, Suzanne; Rochford, Jonathan; Halpin, Yvonne; Manton, Jennifer C; Harvey, Emma C; Greetham, Gregory M; Clark, Ian P; Rooney, A Denise; Long, Conor; Pryce, Mary T

2014-10-21

139

Synthesis of Pd-N-heterocyclic carbene Pd-catalyst and its application in MW-assisted Heck and Suzuki reaction  

EPA Science Inventory

The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica is prepared using sol-gel method and its application in Heck and Suzuki reactions are demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wit...

140

Theoretical insight into electronic spectra of carbon chain carbenes H2Cn (n = 3-10)  

NASA Astrophysics Data System (ADS)

Ground-state geometries of carbenes H2Cn (n = 3-10) have been fully optimized with the C2?-symmetry constraint at the density functional theory and restricted-spin coupled-cluster single-double plus perturbative triple excitation levels of theory, respectively. Comparison of structures corresponding to the X1A1 and B1B1 electronic states has been made by the complete active space self-consistent field calculations. Parity alternation effect on various properties of the ground-state geometries has been discovered in the present study, which generally gives illustration for the relative stabilities of the titled carbon chains. Further calculations on their electronic spectra have been carried out by means of the complete active space second-order perturbation theory method along with the cc-pVTZ basis set. It is found that the vertical excitation energies of the dipole-allowed B1B1 ? X1A1 transition in the gas phase are 2.28, 4.75, 1.69, 3.66, 1.30, 2.94, 1.12, and 2.49 eV, respectively, which agree very well with the available experimental result for H2C3 (2.27 eV). In addition, the vertical excitation energies for both transitions B1B1 ? X1A1 and A1A2 ? X1A1 are found to obey a nonlinear ?E-n relationship as a function of chain size by performing curves fitting.

Zhang, Yanxin; Wang, Li; Li, Yuanyuan; Zhang, Jinglai

2013-05-01

141

Rhenium and technetium tricarbonyl complexes of N-heterocyclic carbene ligands.  

PubMed

A strategy for the conjugation of N-heterocyclic carbene (NHC) ligands to biomolecules via amide bond formation is described. Both 1-(2-pyridyl)imidazolium or 1-(2-pyridyl)benzimidazolium salts functionalized with a pendant carboxylic acid group were prepared and coupled to glycine benzyl ester using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. A series of 10 rhenium(I) tricarbonyl complexes of the form [ReX(CO)3(?N)] (?N is a bidentate NHC ligand, and X is a monodentate anionic ligand: Cl(-), RCO2(-)) were synthesized via a Ag2O transmetalation protocol from the Re(I) precursor compound Re(CO)5Cl. The synthesized azolium salts and Re(I) complexes were characterized by elemental analysis and by (1)H and (13)C NMR spectroscopy, and the molecular structures for one imidazolium salt and seven Re(I) complexes were determined by single-crystal X-ray diffraction. (1)H NMR and mass spectrometry studies for an acetonitrile-d3 solution of [ReCl(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)] show that the monodentate chloride ligand is labile and exchanges with this solvent yielding a cationic acetonitrile adduct. For the first time the labeling of an NHC ligand with technetium-99m is reported. Rapid Tc-99m labeling was achieved by heating the imidazolium salt 1-(2-pyridyl)-3-methylimidazolium iodide and Ag2O in methanol, followed by the addition of fac-[(99m)Tc(OH2)3(CO)3](+). To confirm the structure of the (99m)Tc-labeled complex, the equivalent (99)Tc complex was prepared, and mass spectrometric studies showed that the formed Tc complexes are of the form [(99m/99)Tc(CH3CN)(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)](+) with an acetonitrile molecule coordinated to the metal center. PMID:25280253

Chan, Chung Ying; Pellegrini, Paul A; Greguric, Ivan; Barnard, Peter J

2014-10-20

142

Electrochemiluminescent ruthenium(II) N-heterocyclic carbene complexes: a combined experimental and theoretical study.  

PubMed

A series of four Ru(II) complexes of the form [Ru(bpy)2(C(^)N)](2+) (where C(^)N is a bidentate pyridine-functionalized imidazolylidene- or benzimidazolylidene-based N-heterocyclic carbene (NHC) ligand and bpy is 2,2'-bipyridine) have been synthesized using a Ag(I) transmetalation protocol from the Ru(II) precursor compound, Ru(bpy)2Cl2. The synthesized azolium salts and Ru(II) complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, cyclic voltammetry, and electronic absorption and emission spectroscopy. The molecular structures for two benzimidazolium salts and three Ru(II) complexes were determined by single crystal X-ray diffraction. The complexes display photoluminescence within the range 611-629 nm, with the emission wavelength of the benzimidazolylidene containing structures, slightly blue-shifted relative to the imidazolylidene containing complexes. All complexes exhibited a reversible, one-electron oxidation, which is assigned to the Ru(2+/3+) redox couple. When compared to [Ru(bpy)3](2+), complexes of imidazolylidene containing ligands were oxidized at more negative potentials, while those of the benzimidazolylidene containing ligands were oxidized at more positive potentials. All four complexes exhibited moderately intense electrochemiluminescence (ECL) with the obtained ECL spectra closely resembling the photoluminescence spectra. The ability to predictably fine-tune the highest occupied molecular orbital (HOMO) level of the Ru(II) complexes via the flexible synthetic strategy offered by NHCs is valuable for the design of ECL-based multiplexed detection strategies. PMID:23772555

Barbante, Gregory J; Francis, Paul S; Hogan, Conor F; Kheradmand, Peyman R; Wilson, David J D; Barnard, Peter J

2013-07-01

143

Twisted stable homotopy theory  

E-print Network

There are two natural interpretations of a twist of stable homotopy theory. The first interpretation of a twist is as a nontrivial bundle whose fibre is the stable homotopy category. This kind of radical global twist forms ...

Douglas, Christopher L

2005-01-01

144

Solvent influence in the formation of normal and abnormal carbene complexes in reactions of imidazolium salts with [Ir(H)2(PPh3)2(OCMe2)2]BF4  

E-print Network

: Abnormal Normal Carbene Iridium compounds Tetrahydrofuran Dichloromethane a b s t r a c t Abnormal)2(OCMe2)2]BF4 at room temperature in tetrahydrofuran (THF) or dichloromethane (CH2Cl2). Reactions in THF

Baltisberger, Jay H.

145

Statistics of stable marriages  

NASA Astrophysics Data System (ADS)

In the stable marriage problem N men and N women have to be matched by pairs under the constraint that the resulting matching is stable. We study the statistical properties of stable matchings in the large N limit using both numerical and analytical methods. Generalizations of the model including singles and unequal numbers of men and women are also investigated.

Dzierzawa, Michael; Oméro, Marie-José

2000-11-01

146

Photophysical and photochemical trends in tricarbonyl rhenium(I) N-heterocyclic carbene complexes.  

PubMed

A family of tricarbonyl Re(I) complexes of the formulation fac-[Re(CO)3(NHC)L] has been synthesized and characterized, both spectroscopically and structurally. The NHC ligand represents a bidentate N-heterocyclic carbene species where the central imidazole ring is substituted at the N3 atom by a butyl, a phenyl, or a mesityl group and substituted at the N1 atom by a pyridyl, a pyrimidyl, or a quinoxyl group. On the other hand, the ancillary L ligand alternates between chloro and bromo. For the majority of the complexes, the photophysical properties suggest emission from the lowest triplet metal-to-ligand charge transfer states, which are found partially mixed with triplet ligand-to-ligand charge transfer character. The nature and relative energy of the emitting states appear to be mainly influenced by the identity of the substituent on the N3 atom of the imidazole ring; thus, the pyridyl complexes have blue-shifted emission in comparison to the more electron deficient pyrimidyl complexes. The quinoxyl complexes show an unexpected blue-shifted emission, possibly occurring from ligand-centered excited states. No significant variations were found upon changing the substituent on the imidazole N3 atom and/or the ancillary ligand. The photochemical properties of the complexes have also been investigated, with only the complexes bound to the pyridyl-substituted NHC ligands showing photoinduced CO dissociation upon excitation at 370 nm, as demonstrated by the change in the IR and NMR spectra as well as a red shift in the emission profile after photolysis. Temperature-dependent photochemical experiments show that CO dissociation occurs at temperatures as low as 233 K, suggesting that the Re-C bond cleaves from excited states of metal-to-ligand charge transfer nature rather than thermally activated ligand field excited states. A photochemical mechanism that takes into account the reactivity of the complexes bound to the pyridyl-NHC ligand as well as the stability of those bound to the pyrimidyl- and quinoxyl-NHC ligands is proposed. PMID:24665819

Vaughan, Jamila G; Reid, Brodie L; Wright, Phillip J; Ramchandani, Sushil; Skelton, Brian W; Raiteri, Paolo; Muzzioli, Sara; Brown, David H; Stagni, Stefano; Massi, Massimiliano

2014-04-01

147

Unexpected Anion Effect in the Alkoxylation of Alkynes Catalyzed by N-Heterocyclic Carbene (NHC) Cationic Gold Complexes.  

PubMed

The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N-heterocyclic carbene-based gold catalyst, [(NHC)AuX] (X=BARF(-) , BF4 (-) , OTf(-) , OTs(-) , TFA(-) , or OAc(-) ) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs(-) anion provides the best compromise to achieve efficient catalysis. PMID:25263571

Biasiolo, Luca; Trinchillo, Marina; Belanzoni, Paola; Belpassi, Leonardo; Busico, Vincenzo; Ciancaleoni, Gianluca; D'Amora, Angela; Macchioni, Alceo; Tarantelli, Francesco; Zuccaccia, Daniele

2014-11-01

148

Main-chain organometallic microporous polymers bearing triphenylene-tris(N-heterocyclic carbene)-gold species: catalytic properties.  

PubMed

Two triphenylene-based tris(N-heterocyclic carbene)-gold-acetylide main-chain organometallic microporous polymers (MOMPs) were obtained and fully characterized. Both materials show spherical shapes, and their size is highly dependent on the type of acetylene used in the synthetic protocol. The new solids were tested in the catalytic reduction of nitroarenes with NaBH4 and in the three-component Strecker reaction for the synthesis of ?-aminonitriles, and showed high activity in both processes. Whereas the activity of the solids in the reduction of nitroarenes may be attributed to the formation of Au nanoparticles due to the use of NaBH4 as reducing agent, the activity in the Strecker reaction may originate from the Lewis acidic activation of the ketone or imine on coordination to Au. PMID:24668881

Gonell, Sergio; Poyatos, Macarena; Peris, Eduardo

2014-05-01

149

Gold(I) N-heterocyclic carbene complexes with naphthalimide ligands as combined thioredoxin reductase inhibitors and DNA intercalators.  

PubMed

Organometallic conjugates consisting of a gold(I) N-heterocyclic carbene (NHC) moiety and a naphthalimide were prepared and investigated as cytotoxic agents that interact with both DNA and the disulfide reductase enzyme thioredoxin reductase (TrxR). The complexes were potent DNA intercalators related to their naphthalimide partial structure, inhibited TrxR as a consequence of the incorporation of the gold(I) moiety, and triggered efficient cytotoxic effects in MCF-7 breast and HT-29 colon adenocarcinoma cells. Strong effects on tumor cell metabolism were noted for the most cytotoxic complex, chlorido[1-(3'-(4''-ethylthio-1'',8''-naphthalimid-N''-yl))-propyl-3-methyl-imidazol-2-ylidene]gold(I) (4?d). In conclusion, the conjugation of naphthalimides with gold(I) NHC moieties provided a useful strategy for the design of bioorganometallic anticancer agents with multiple modes of action. PMID:24803348

Meyer, Andreas; Oehninger, Luciano; Geldmacher, Yvonne; Alborzinia, Hamed; Wölfl, Stefan; Sheldrick, William S; Ott, Ingo

2014-08-01

150

Electronic structure and slow magnetic relaxation of low-coordinate cyclic alkyl(amino) carbene stabilized iron(I) complexes.  

PubMed

Cyclic alkyl(amino) carbene stabilized two- and three-coordinate Fe(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe][B(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet of analytical techniques as well as theoretical calculations. Magnetic susceptibility and Mössbauer spectroscopy reveal the +1 oxidation state and S = 3/2 spin ground state of iron in both compounds. 2 and 3 show slow magnetic relaxation typical for single molecule magnets under an applied direct current magnetic field. The high-frequency EPR measurements confirm the S = 3/2 ground state with a large, positive zero-field splitting (?20.4 cm(-1)) and reveal easy plane anisotropy for compound 2. CASSCF/CASPT2/RASSI-SO ab initio calculations using the MOLCAS program package support the experimental results. PMID:25072104

Samuel, Prinson P; Mondal, Kartik Chandra; Amin Sk, Nurul; Roesky, Herbert W; Carl, Elena; Neufeld, Roman; Stalke, Dietmar; Demeshko, Serhiy; Meyer, Franc; Ungur, Liviu; Chibotaru, Liviu F; Christian, Jonathan; Ramachandran, Vasanth; van Tol, Johan; Dalal, Naresh S

2014-08-27

151

Random stable matchings  

NASA Astrophysics Data System (ADS)

The stable matching problem is a prototype model in economics and social sciences where agents act selfishly to optimize their own satisfaction, subject to mutually conflicting constraints. A stable matching is a pairing of adjacent vertices in a graph such that no unpaired vertices prefer each other to their partners under the matching. The problem of finding stable matchings is known as the stable marriage problem (on bipartite graphs) or as the stable room-mates problem (on the complete graph). It is well known that not all instances on non-bipartite graphs admit a stable matching. Here we present numerical results for the probability that a graph with n vertices and random preference relations admits a stable matching. In particular we find that this probability decays algebraically on graphs with connectivity ?(n) and exponentially on regular grids. On finite connectivity Erdös-Rényi graphs the probability converges to a value larger than zero. On the basis of the numerical results and some heuristic reasoning we formulate five conjectures on the asymptotic properties of random stable matchings.

Mertens, Stephan

2005-10-01

152

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

PubMed

Invited for the cover of this issue is the group of E.?Peter Kündig at the University of Geneva. The cover illustrates the regiodivergent reaction taken by two enantiomers when subjected to a chiral Pd(N-heterocyclic carbene) catalyst. The combination of a divergent reaction with an enantioselective C?H functionalization makes for fascinating chemistry. Read the full text of the article at 10.1002/chem.201403985. PMID:25250507

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

2014-11-10

153

Exploring a unique reactivity of N-heterocyclic carbenes (NHC) in rhodium(iii)-catalyzed intermolecular C-H activation/annulation.  

PubMed

Disclosed herein is the unique conjugative role of N-heterocyclic carbene (NHC) ligands as a directing group in aromatic C-H activation, coupled with a facile NHC-alkenyl annulative reductive elimination which guided the Rh(III)-catalyzed intermolecular annulations of imidazolium salts and alkynes under ambient conditions leading to structurally important imidazo[1,2-a]quinolinium motifs. PMID:25331451

Ghorai, Debasish; Choudhury, Joyanta

2014-11-01

154

Coinage-metal mediated ring opening of cis-1,2-dimethoxycyclopropane: trends from the gold, copper, and silver Fischer carbene bond strength.  

PubMed

N-heterocyclic carbene (NHC) supported coinage metal cations proved to react in the gas phase with the electron-rich cis-1,2-dimethoxycyclopropane. Upon Collision Induced Dissociation (CID), several spectrometric fragment-ion signals were observed, one corresponding to the recovery of the bare cation IMes-M(+) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and the second to the methoxymethylidene metal complex IMes-M-[HCOCH3](+). The gold and copper complexes appear to stabilize the carbene sufficiently enough to promote the latter channel. On the contrary, the silver complex binds weakly to the methoxymethylidene moiety as observed by the predominance of the bare cation IMes-M(+) channel. Density Functional Theory (DFT) investigations of the Potential Energy Surface and Bond Energy Decomposition Analyses provided results that correlate well with the experimental data. In the case of the bare cation channel, two distinct reaction pathways were found: a straightforward decoordination of the cyclopropane and a cationic rearrangement of the three-membered ring into a dimethoxypropylene isomer before dissociation. However, for the abstraction of the methoxymethylidene moiety by the metal cation, only one pathway was found. In analogy to earlier studies by other groups, we found the trend Au > Cu > Ag for the metal-carbene bond strength. PMID:24911627

Batiste, Laurent; Chen, Peter

2014-07-01

155

Synthesis and in vitro antitumor activity of water soluble sulfonate- and ester-functionalized silver(I) N-heterocyclic carbene complexes.  

PubMed

The novel N-heterocyclic carbene ligand precursor NaHIm(PrSO3) (sodium 3,3'-(1H-imidazole-3-ium-1,3-diyl)dipropane-1-sulfonate) and the related silver carbene complex [Na4(Im(PrSO3))2]AgCl have been synthesized and characterized. Recrystallization of the analogous [Im(AcEt)]AgCl complex allowed the development of X-ray analysis which led to achieve relevant structural information concerning this silver(I) derivative. Both sulfonate- and ester-functionalized silver(I) N-heterocyclic carbenes (NHCs) were evaluated for their antiproliferative activities in a wide panel of human cancer cells. Complex [Na4(Im(PrSO3))2]AgCl showed a significant in vitro antiproliferative activity that was correlated with its strong ability to inhibit thioredoxin reductase. The inhibition of this selenoenzyme determined an alteration of the cellular redox environment thus leading to the induction of the apoptotic cell death through the activation of the ASK-1 pathway. PMID:24121303

Gandin, Valentina; Pellei, Maura; Marinelli, Marika; Marzano, Cristina; Dolmella, Alessandro; Giorgetti, Marco; Santini, Carlo

2013-12-01

156

[3,3]-Sigmatropic Rearrangement vs. Carbene Formation in Gold-Catalyzed Transformations of Alkynyl Aryl Sulfoxides: Mechanistic Studies and Expanded Reaction Scope  

PubMed Central

Gold-catalyzed intramolecular oxidation of terminal alkynes with an arenesulfinyl group as the tethered oxidant is a reaction in gold chemistry of high impact, as it introduced to the field the highly-valued concept of gold carbene generation via alkyne oxidation. The proposed intermediacy of ?-oxo gold carbenes in these reactions, however, has never been substantiated. Detailed experimental studies suggest that the involvement of such reactive intermediates in the formation of dihydrobenzothiepinones is highly unlikely. Instead, a [3,3]-sigmatropic rearrangement of the initial cyclization intermediate offers a reaction path that can readily explain the high reaction efficiency and the lack of sulfonium formation. With internal alkyne substrates, however, the generation of a gold carbene species becomes competitive with the [3,3]-sigmatropic rearrangement. This reactive intermediate, nevertheless, does not proceed to afford the Friedel-Crafts type cyclization product. Extensive Density Functional Theory studies support the mechanistic conclusion that the cyclized product is formed via an intramolecular [3,3]-sigmatropic rearrangement instead of the previously proposed Friedel-Crafts type cyclization. With the new mechanistic insight, the product scope of this versatile formation of mid-sized sulfur-containing cycloalkenones has been expanded readily to various dihydrobenzothiocinones, a tetrahydrobenzocyclononenone, and even those without the entanglement of a fused benzene ring. Besides gold, Hg(OTf)2 can be an effective catalyst, thereby offering a cheap alternative for this intramolecular redox reaction. PMID:23731178

Lu, Biao; Li, Yuxue; Wang, Youliang; Aue, Donald H.; Luo, Yingdong; Zhang, Liming

2013-01-01

157

Cooperativity of anion⋯? and ?⋯? interactions regulates the self-assembly of a series of carbene proligands: Towards quantitative analysis of intermolecular interactions with Hirshfeld surface  

NASA Astrophysics Data System (ADS)

The cooperative effect of weak non-covalent forces between anions and electron deficient aromatics by ?⋯? stacking of a series of carbene proligands (1-3) have been thoroughly explored by crystallographic studies. Structural analysis revealed that the anion⋯? and ?⋯? interactions along with intermolecular hydrogen bonding mutually cooperate to facilitate the assembling of the supramolecular framework. The ?⋯? and corresponding anion⋯? interactions have been investigated in the title carbene proligands despite their association with counter ions. The presence of the anion in the vicinity of the ?-system leads to the formation of anion⋯?/?⋯?/?⋯anion network for an inductive stabilization of the assemblies. To assess the dimensionality of the supramolecular framework consolidated by cooperative anion⋯?/?⋯? interactions and hydrogen bonding, different substituent effects in the carbene backbone have been considered to tune these interactions. These facts show that the supramolecular framework based on these cooperative weak forces may be robust enough for application in molecular recognition. The investigation of close intermolecular interactions between the molecules via Hirshfeld surface analyses is presented in order to reveal subtle differences and similarities in the crystal structures. The decomposition of the fingerprint plot area provides a percentage of each intermolecular interaction, allowing for a quantified analysis of close contacts within each crystal.

Samanta, Tapastaru; Dey, Lingaraj; Dinda, Joydev; Chattopadhyay, Shyamal Kumar; Seth, Saikat Kumar

2014-06-01

158

[3 + 2]-dipolar cycloaddition reactions of an N-heterocyclic carbene boryl azide.  

PubMed

Thermal 1,3-dipolar cycloaddition reactions of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene dihydridoboron azide occur smoothly with alkynes, nitriles, and alkenes bearing electron-withdrawing groups. New, stable NHC-boryl-substituted triazoles, tetrazoles, and triazolidines are formed in good to excellent yields. PMID:22616557

Merling, Everett; Lamm, Vladimir; Geib, Steven J; Lacôte, Emmanuel; Curran, Dennis P

2012-06-01

159

Copolymerization of ethylene with norbornene catalyzed by cationic rare earth metal fluorenyl functionalized N-heterocyclic carbene complexes.  

PubMed

Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene (NHC) (Flu-NHC)Ln(CH(2)SiMe(3))(2) (Flu-NHC = (C(13)H(8)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6); Ln = Sc (2a); Y (2b); Ho (2c); Lu (2d)), ((tBu)Flu-NHC)Ln(CH(2)SiMe(3))(2) ((tBu)Flu-NHC = 2,7-(t)Bu(2)C(13)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (1a); Lu (1d)) and attached by indenyl modified N-heterocyclic carbene (Ind-NHC)Ln(CH(2)SiMe(3))(2) (Ind-NHC = C(9)H(6)CH(2)CH(2)(NCHCCHN)C(6)H(2)Me(3)-2,4,6; Ln = Sc (3a); Lu (3d)), under the activation of Al(i)Bu(3) and [Ph(3)C][B(C(6)F(5))(4)], showed varied catalytic activities toward homo- and copolymerization of ethylene and norbornene. Among which the scandium complexes, in spite of ligand type, exhibited medium to high catalytic activity for ethylene polymerization (10(5) g mol(Sc)(-1) h(-1) atm(-1)), but all were almost inert to norbornene polymerization. Remarkably, higher activity was found for the copolymerization of ethylene and norbornene when using Sc based catalytic systems, which reached up to 5 x 10(6) g mol(Sc)(-1) h(-1) atm(-1) with 2a. The composition of the isolated copolymer was varying from random to alternating according to the feed ratio of the two monomers (r(E) = 4.1, r(NB) = 0.013). The molecular structure of complex 1d was characterized by X-ray analysis. The influences of structural factors of complexes and polymerization conditions on both the catalytic activity and the norbornene content in the copolymer were discussed. PMID:19826729

Wang, Baoli; Tang, Tao; Li, Yuesheng; Cui, Dongmei

2009-11-01

160

Experimental and computational studies on the mechanism of zwitterionic ring-opening polymerization of ?-valerolactone with N-heterocyclic carbenes.  

PubMed

Experimental and computational investigations of the zwitterionic ring-opening polymerization (ZROP) of ?-valerolactone (VL) catalyzed by the N-heterocyclic carbenes (NHC) 1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene (1) and 1,3,4,5-tetramethyl-imidazol-2-ylidene (2) were carried out. The ZROP of ?-valerolactone generates cyclic poly(valerolactone)s whose molecular weights are higher than predicted from [VL]0/[NHC]0. Kinetic studies reveal the rate of polymerization is first order in [VL] and first order in [NHC]. Density functional theory (DFT) calculations were carried out to elucidate the key steps involved in the ring-opening of ?-valerolactone and its subsequent oligomerization. These studies have established that the initial steps of the mechanism involve nucleophilic attack of the NHC on ?-valerolactone to form a zwitterionic tetrahedral intermediate. DFT calculations indicate that the highest activation barrier of the entire mechanism is associated with the ring-opening of the tetrahedral intermediate formed from the NHC and ?-valerolactone, a result consistent with inefficient initiation to generate reactive zwitterions. The large barrier in this step is due to the fact that ring-opening requires a partial positive charge to develop next to the directly attached NHC moiety which already bears a delocalized positive charge. PMID:24702523

Acharya, Ashwin K; Chang, Young A; Jones, Gavin O; Rice, Julia E; Hedrick, James L; Horn, Hans W; Waymouth, Robert M

2014-06-19

161

Non-covalent interactions in coinage metal complexes of 1,2,4-triazole-based N-heterocyclic carbenes.  

PubMed

Seven coinage metal(I) complexes bearing two different triazole-based N-heterocyclic carbene (NHC) ligands, [1-tert-butyl-4-{2-[(N,N-dimethylamino)methyl]phenyl}-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide and 1-tert-butyl-4-(4-methylphenyl)-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide], were synthesized and fully characterized in solution by NMR spectroscopy as well as in the solid state by X-ray diffraction techniques. Furthermore, the XRD analysis showed that the bidentate coordination of the amino group substituted NHC ligand, previously observed for rhodium and palladium complexes, does not take place in the solid state structure of Au(I) complexes with various halide ligands. Nevertheless, the formation of sets of two head-to-tail oriented monomers aggregated via a weak metallophilic contact was revealed for both NHC ligands as well as for all three coinage metals with different halides. These experimental data correlate quite well with the previously published theoretical study on related complexes. PMID:25189129

Turek, Jan; Panov, Illia; Švec, Petr; R?ži?ková, Zde?ka; R?ži?ka, Aleš

2014-11-01

162

Traditional and ion-pair halogen-bonded complexes between chlorine and bromine derivatives and a nitrogen-heterocyclic carbene.  

PubMed

A theoretical study of the halogen-bonded complexes (A-X···C) formed between halogenated derivatives (A-X; A = F, Cl, Br, CN, CCH, CF3, CH3, H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC) has been performed using MP2/aug'-cc-pVDZ level of theory. Two types of A-X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C-X distances and small binding energies (8-54 kJ·mol(-1)). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C-X distances and large binding energies (148-200 kJ·mol(-1)), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A(-) and (+)[X-CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the ?* orbital of C-X bond is also identified as a significant stabilizing interaction in type-II complexes. PMID:25188812

Donoso-Tauda, Oscar; Jaque, Pablo; Elguero, José; Alkorta, Ibon

2014-10-01

163

Synthesis, photo-, and electrochemistry of ruthenium bis(bipyridine) complexes comprising a N-heterocyclic carbene ligand.  

PubMed

Analogues of [Ru(bpy)3](2+) were prepared in which one pyridine ligand site is substituted by a N-heterocyclic carbene (NHC) ligand, that is, either by an imidazolylidene with a variable wingtip group R (R = Me, 3a; R = Et, 3b; R = iPr, 3c), or by a benzimidazolylidene (Me wingtip group, 3d), or by a 1,2,3-triazolylidene (Me wingtip group, 3e). All complexes were characterized spectroscopically, photophysically, and electrochemically. An increase of the size of the wingtip groups from Me to Et or iPr groups distorts the octahedral geometry (NMR spectroscopy) and curtails the reversibility of the ruthenium oxidation. NHC ligands with methyl wingtip groups display reversible ruthenium oxidation at a potential that reflects the donor properties of the NHC ligand (triazolylidene > imidazolylidene > benzimidazolylidene). The most attractive properties were measured for the triazolylidene ruthenium complex 3e, featuring the smallest gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the series (2.41 eV), a slightly red-shifted absorption profile, and reasonable excited-state lifetime (188 ns) when compared to [Ru(bpy)3](2+). These features demonstrate the potential utility of triazolylidene ruthenium complexes as photosensitizers for solar energy conversion. PMID:23594091

Leigh, Vivienne; Ghattas, Wadih; Lalrempuia, Ralte; Müller-Bunz, Helge; Pryce, Mary T; Albrecht, Martin

2013-05-01

164

Pyridine-enhanced head-to-tail dimerization of terminal alkynes by a rhodium-N-heterocyclic-carbene catalyst.  

PubMed

A general regioselective rhodium-catalyzed head-to-tail dimerization of terminal alkynes is presented. The presence of a pyridine ligand (py) in a Rh-N-heterocyclic-carbene (NHC) catalytic system not only dramatically switches the chemoselectivity from alkyne cyclotrimerization to dimerization but also enhances the catalytic activity. Several intermediates have been detected in the catalytic process, including the ?-alkyne-coordinated Rh(I) species [RhCl(NHC)(?(2)-HC?CCH2Ph)(py)] (3) and [RhCl(NHC){?(2)-C(tBu)?C(E)CH=CHtBu}(py)] (4) and the Rh(III)-hydride-alkynyl species [RhClH{-C?CSi(Me)3}(IPr)(py)2] (5). Computational DFT studies reveal an operational mechanism consisting of sequential alkyne C-H oxidative addition, alkyne insertion, and reductive elimination. A 2,1-hydrometalation of the alkyne is the more favorable pathway in accordance with a head-to-tail selectivity. PMID:24114872

Rubio-Pérez, Laura; Azpíroz, Ramón; Di Giuseppe, Andrea; Polo, Victor; Castarlenas, Ricardo; Pérez-Torrente, Jesús J; Oro, Luis A

2013-11-01

165

Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki-Miyaura cross-coupling.  

PubMed

The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxy-calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b) have been synthesised. Reaction of 2 in dioxane with PdCl(2) in the presence of CsCO(3) and KBr (80 °C, 24 h) gives the carbene complex trans-[PdBr(2)(calix-monocarbene)(2)] (14), containing two N-heterocyclic carbene ligands derived from 2 (yield: 63%). Repeating the reaction in pyridine instead of dioxane gives the mixed pyridine-carbene complex trans-[PdBr(2)(calix-carbene)(pyridine)] (15) in 75% yield. Treatment of the bis-imidazolium salt 3a with [Pd(OAc)(2)] affords a chelate complex, trans-[PdI(2){calix-bis(carbene)}] (16), in which a metallo-(bis-carbene) fragment caps the upper rim of the calixarene basket. Complex 16, as well as its analogue 17, obtained from 3b, display apparent C(s)-symmetry in solution. This is not the case in the solid state, a single X-ray diffraction study carried out for 16 revealing a pinced cone structure for the calixarene skeleton, which reduces the symmetry to C(1). The chelate complex 17 shows poor activity in Suzuki-Miyaura cross-coupling of phenyl boronic acid and p-tolyl halides, an observation that suggests the presence of a strained metallocyclic unit preventing easy stereochemical rearrangement to an active species. Unlike 17, complexes 14 and 15 show good activities in cross-coupling. A comparative study using the carbene precursor 1-butyl-3-(2,6-diisopropylphenyl)imidazolium bromide (18), which is devoid of the receptor fragment, strongly suggests that the carbene ligands of 14 and 15 operate typically as bulky NHC-ligands. PMID:21879086

Brenner, Eric; Matt, Dominique; Henrion, Mickaël; Teci, Matthieu; Toupet, Loïc

2011-10-14

166

Stable isotope studies  

SciTech Connect

The research has been in four general areas: (1) correlation of isotope effects with molecular forces and molecular structures, (2) correlation of zero-point energy and its isotope effects with molecular structure and molecular forces, (3) vapor pressure isotope effects, and (4) fractionation of stable isotopes. 73 refs, 38 figs, 29 tabs.

Ishida, T.

1992-01-01

167

Stable Coulomb bubbles ?  

E-print Network

Coulomb bubbles, though stable against monopole displacement, are unstable at least with respect to quadrupole and octupole distortions. We show that there exists a temperature at which the pressure of the vapor filling the bubble stabilizes all the radial modes. In extremely thin bubbles, the crispation modes become unstable due to the surface-surface interaction.

L. G. Moretto; K. Tso; G. J. Wozniak

1996-12-12

168

Stable cartels revisited  

Microsoft Academic Search

Summary. This paper analyzes cartel stability when firms are farsighted. It studies a price leadership model á la D’ Aspremont et al. (1983), where the dominant cartel acts as a leader by determining the market price, while the fringe behaves competitively. According to D’ Aspremont et al. ‘s (1983) approach a cartel is stable if no firm has an incentive to either

Effrosyni Diamantoudi

2005-01-01

169

Expanded-ring N-heterocyclic carbenes efficiently stabilize gold(I) cations, leading to high activity in ?-acid-catalyzed cyclizations.  

PubMed

A series of six- and seven-membered expanded-ring N-heterocyclic carbene (er-NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er-NHC)AuX] (X(-) = BF4(-), NTf2(-), OTf(-)) were generated in solution. According to their (13)C?NMR spectra, the ionic character of the complexes increases in the order X(-) = Cl(-) < NTf2(-) < OTf(-) < BF4(-). Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er-NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au(+)] cations. A comparative study has been carried out of the catalytic activities of five-, six-, and seven-membered carbene complexes [(NHC)AuX], [(Ph3 P)AuX], [(Me2S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD-Dipp)Au]BF4 (1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetrahydrodiazepin-2-ylidene gold(I) tetrafluoroborate) catalyst bearing seven-membered-ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1?mol?% catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations. PMID:24682976

Morozov, Oleg S; Lunchev, Andrey V; Bush, Alexander A; Tukov, Aleksandr A; Asachenko, Andrey F; Khrustalev, Victor N; Zalesskiy, Sergey S; Ananikov, Valentine P; Nechaev, Mikhail S

2014-05-12

170

Detailed analysis of pro-apoptotic signaling and metabolic adaptation triggered by a N-heterocyclic carbene-gold(I) complex.  

PubMed

Due to their broad spectrum of biological activity and antiproliferative effect on different human cancer cell lines, gold compounds have been in the focus of drug research for many years. Gold(I)-N-heterocyclic carbene complexes are of particular interest, because of their stability, ease of derivatization and clear cytotoxicity in cancer cells. To obtain a more detailed view of the molecular mechanisms underlying their cellular activity, we used a novel gold(I)-N-heterocyclic carbene complex, [triphenylphosphane-(1,3-diethyl-5-methoxy-benzylimidazol-2-ylidene)]gold(I) iodide and investigated changes in cellular signaling pathways using quantitative signal transduction protein microarray analysis. We also analyzed changes in cell metabolism in a time-dependent manner by on-line metabolic measurements and used isolated mitochondria to elucidate the direct effects on this cell organelle. We found strong cytotoxic effects in cancer cells, accompanied by an immediate and irreversible loss of mitochondrial respiration as well as by a crucial imbalance of the intracellular redox state, resulting in apoptotic cell death. ELISA microarray analysis of signal transduction pathways revealed a time-dependent up-regulation of pro-apoptotic signaling proteins, e.g. p38 and JNK, whereas pro-survival signals that are directly linked to the thioredoxin system were down-regulated, which pinpoints to thioredoxin reductase as a central target of the compound. Further results suggest that DNA is an indirect target of the compound. Based on our findings, we outline a signaling model for the molecular mechanism underlying the antiproliferative activity of the gold(I)-N-heterocyclic carbene complex investigated, which provides a good general model for the known pattern of cell death induced by this class of substances. PMID:24777153

Holenya, Pavlo; Can, Suzan; Rubbiani, Riccardo; Alborzinia, Hamed; Jünger, Anja; Cheng, Xinlai; Ott, Ingo; Wölfl, Stefan

2014-09-01

171

Stable local oscillator module.  

SciTech Connect

This report gives a description of the development of a Stable Local Oscillator (StaLO) multi-chip module (MCM). It is a follow-on report to SAND2006-6414, Stable Local Oscillator Microcircuit. The StaLO accepts a 100MHz input signal and produces output signals at 1.2, 3.3, and 3.6 GHz. The circuit is built as a multi-chip module (MCM), since it makes use of integrated circuit technologies in silicon and lithium niobate as well as discrete passive components. This report describes the development of an MCM-based version of the complete StaLO, fabricated on an alumina thick film hybrid substrate.

Brocato, Robert Wesley

2007-11-01

172

Trinuclear gold clusters supported by cyclic (alkyl)(amino)carbene ligands: mimics for gold heterogeneous catalysts.  

PubMed

The synthesis of air- and moisture-stable trinuclear mixed-valence gold(I)/gold(0) clusters is described. They promote the catalytic carbonylation of amines under relatively mild conditions. The synthetic route leading to the trinuclear clusters involves a simple ligand exchange from the readily available ?(3)-oxo-[(Ph3 PAu)3O](+) complex. This synthetic method paves the way for the preparation of a variety of mixed-valence gold(I)/gold(0) polynuclear clusters. Moreover, the well-defined nature of the complexes demonstrates that the catalytic process involves a rare example of a definite change of oxidation state of gold from Au(0)2Au(I) to Au(I)3. PMID:24985149

Jin, Liqun; Weinberger, David S; Melaimi, Mohand; Moore, Curtis E; Rheingold, Arnold L; Bertrand, Guy

2014-08-18

173

Synthesis of Well-Defined Copper "N"-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment that Emphasizes the Role of Catalysis in Green Chemistry  

ERIC Educational Resources Information Center

A multistep experiment for an advanced synthesis lab course that incorporates topics in organic-inorganic synthesis and catalysis and highlights green chemistry principles was developed. Students synthesized two "N"-heterocyclic carbene ligands, used them to prepare two well-defined copper(I) complexes and subsequently utilized the complexes as…

Ison, Elon A.; Ison, Ana

2012-01-01

174

The photochemistry of 4-chlorophenol in water revisited: the effect of cyclodextrins on cation and carbene reactions.  

PubMed

The photochemistry of 4-chlorophenol (1) in water and in the presence of cyclodextrins has been studied by means of steady-state and time-resolved experiments. These have shown that 1 undergoes photoheterolysis of the C--Cl bond in the triplet state to yield the 4-hydroxyphenyl cation (3)2 in equilibrium with 4-oxocyclohexa-2,5-dienylidene, (3)3. These triplet intermediates scarcely react with a n nucleophile, such as water, nor abstract hydrogen from this solvent, thus they are long-lived (approximately 1 micros). Specific trapping of both intermediates has been achieved. The cation adds to 2-propenol, k(add) approximately 1.3 x 10(8) m(-1) s(-1), to form the long-lived phenonium ion 11 (with lambda(max) = 290 nm), which then converts to 3-(4-hydroxyphenyl)propane-1,2-diol (10). Carbene (3)3 is trapped by oxygen to give benzoquinone and is reduced by D-glucose (k(q) = 8.5 x 10(6) m(-1) s(-1)) to give the phenoxyl radical (8) and phenol (9). Cyclodextrins have been found to trap the intermediates much more efficiently (k(q) = 9.4 x 10(8) m(-1) s(-1) with beta-CD), which indicates that inclusion is involved. Ground state 1 forms inclusion complexes with 1:1 stoichiometry and association constants of 140 and 300 M(-1) with alpha- and beta-CD, respectively. Complexation does not change the efficiency or the mode of photofragmentation of 1; however, it does influence the course of the reaction because the major portion of the intermediates are reduced to phenol within the cavity (k'(red)> or = 5 x 10(7) s(-1)) either via a radical 8 or via a radical cation 9(+)(.). Under these conditions, neither 2-propenol nor oxygen trap the intermediates to a significant extent. PMID:15861376

Manet, Ilse; Monti, Sandra; Bortolus, Pietro; Fagnoni, Maurizio; Albini, Angelo

2005-07-01

175

Stable cosmic vortons.  

PubMed

We present solutions in the gauged U(1)×U(1) model of Witten describing vortons-spinning flux loops stabilized against contraction by the centrifugal force. Vortons were heuristically described many years ago; however, the corresponding field theory solutions were not obtained and so the stability issue remained open. We construct explicitly a family of stationary vortons characterized by their charge and angular momentum. Most of them are unstable and break in pieces when perturbed. However, thick vortons with a small radius preserve their form in the 3+1 nonlinear dynamical evolution. This gives the first ever evidence of stable vortons and impacts several branches of physics where they could potentially exist. These range from cosmology, since vortons could perhaps contribute to dark matter, to QCD and condensed matter physics. PMID:24206476

Garaud, Julien; Radu, Eugen; Volkov, Mikhail S

2013-10-25

176

Stable superstring relics  

SciTech Connect

The authors investigate the cosmological constraints on exotic stable matter states which arise in realistic free fermionic superstring models. These states appear in the superstring models due to a ``Wilson-line`` breaking of the unifying non-Abelian gauge symmetry. In the models that they consider the unifying SO(10) gauge symmetry is broken at the string level to SO(6) x SO(4), SU(5) x U(1) or SU(3) x SU(2) x U(1). The exotic matter states are classified according to the patterns of the SO(10) symmetry breaking. In SO(6) x XO(4) and SU(5) x U(1) type models one obtains fractionally charged states with Q{sub e.m.} = {+-}1/2. In SU(3) x SU(2) x U(1) type models one also obtains states with the regular charges under the Standard Model gauge group but with ``fractional`` charges under the U(1){sub z{prime}} symmetry. These states include down-like color triplets and electroweak doublets, as well as states which are Standard Model singlets. By analyzing the renormalizable and nonrenormalizable terms of the superpotential in a specific superstring model, the authors show that these exotic states can be stable. They investigate the cosmological constraints on the masses and relic density of the exotic states. They propose that, while the abundance and the masses of the fractionally charged states are highly constrained, the Standard Model-like states, and in particular the Standard Model singlet, are good dark matter candidates.

Chang, S.; Coriano, C. [Florida Univ., Gainesville, FL (United States). Inst. for Fundamental Theory; Faraggi, A.E. [Florida Univ., Gainesville, FL (United States). Inst. for Fundamental Theory]|[Inst. for Advanced Study, Princeton, NJ (United States). School of Natural Sciences

1996-05-15

177

Construct validity of Stable-2000 and Stable-2007 scores.  

PubMed

We addressed the construct validity of Stable-2000 and Stable-2007 scores by examining correlations between selected items and validated independent measures of relevant constructs in samples of convicted sex offenders. In Study 1, the Child Molester Attitudes item of the Stable-2000 shared 23% of the variance with a self-report measure of beliefs supportive of child molestation, r(19) = .48. The Deviant Sexual Interests items of the Stable-2000 and Stable-2007 shared 7% to 66% of the variance, respectively, with an offense-history-based measure of pedophilic interests, r(18) = .27 for the Stable-2000 and r(11) = .81 for the Stable-2007. In Study 2, the Lovers/Intimate Partners, General Social Rejection/Loneliness, Rapist Attitudes, and Child Molester Attitudes items of the Stable-2000 shared 4% to 19% of the variance with self-report measures of, respectively, intimacy, r(90) = -.44; loneliness, r(88) = .34; beliefs supportive of rape, r(72) = .21; and beliefs supportive of child molestation, r(78) = .36. The results generally suggest that the Stable items examined are associated with measures of similar constructs; however, the degree of convergence was lower than expected. More systematic and comprehensive research is needed to examine convergence of the Stable items with other relevant measures and additional aspects of construct validity. Such efforts will provide a clearer understanding of dynamic risk factors, appropriate areas of focus for treatment efforts, and, more generally, why some sex offenders recidivate. PMID:21543623

Nunes, Kevin L; Babchishin, Kelly M

2012-02-01

178

Stable isotope laser spectroscopy  

NASA Technical Reports Server (NTRS)

Recent advances in semiconductor laser technology have produced a reliable lightweight device ideally suited for a spacecraft high resolution molecular spectrometer. Lead-salt tunable diode lasers (TDL) emit in several spectral modes, each with a very narrow linewidth of -0.0003/cm. This spectral resolution is much narrower than typical Doppler broadened molecular linewidths in the mid-IR range. Thus it is possible to detect individual rotational lines within the vibrational band and measure their intensity, which can be used to determine gas concentration. The narrow spectral lines of any impurity gas tend to lie between the narrow lines of the gas of interest. This represents a major advantage over the accepted gas chromatograph mass spectrometer (GCMS) technique for measuring gas concentrations and isotope ratios. The careful and extensive gas purification procedures required to remove impurities for reliable GCMS measurements will not be required for an IR laser gas analysis. The infrared laser gas analysis technique is being developed to measure stable isotopic ratios of gases such as CO2, CH4, N2O, and NH3. This will eventually lead to development of instruments capable of in situ istopic measurements on planets such as Mars. The carbon (C-12, C-13) isotope ratio is indicative of the type of carbon fixation mechanisms (e.g., photosynthesis, respiration) in operation on a planet, while the nitrogen (N-14, N-15) isotope ratio can probably be used to date nitrogen-bearing Martian samples. The absorbance ratio of two adjacent lines of CO2 in the 2300/cm (4.3 micron) region of the spectrum was measured. The precision of the measurement is presently better than 1 percent and significant improvement is anticipated as rapid sweep-integration techniques and computer controlled data acquistion capabilities are incorporated.

Becker, J. F.; Yaldaei, Ramil; Mckay, Christopher P.

1989-01-01

179

Do stable atmospheric layers exist?  

NASA Astrophysics Data System (ADS)

The notion of stable atmospheric layers is a classical idealization used for understanding atmospheric dynamics and thermodynamics. Using state of the art drop sonde data and using conditional, dynamical and convective stability criteria we show that apparently stable layers are typically composed of a hierarchy of unstable layers themselves with embedded stable sublayers, and unstable sub-sub layers etc. i.e. in a Russian Matryoshka doll-like fractal hierarchy. We therefore argue that the notion of stable atmospheric layers is untenable and must be replaced by modern scaling notions.

Lovejoy, S.; Tuck, A. F.; Hovde, S. J.; Schertzer, D.

2008-01-01

180

Ruthenium(II) carbonyl complexes bearing CCC-pincer bis-(carbene) ligands: synthesis, structures and activities toward recycle transfer hydrogenation reactions.  

PubMed

A new series of ruthenium(II) carbonyl complexes with benzene-based CCC-pincer bis-(carbene) ligands, [((R)CCC(R))Ru(CO)2(X)](0/+) and [((R)CCC(R))Ru(CO)(NN)](+) ((R)CCC(R) = 2,6-bis-(1-alkylimidazolylidene)benzene, R = Me or (n)Bu; X = I, Br, CH3CN, or 6-(aminomethyl)pyridine (ampy); NN = 2·CH3CN, or chelating ampy or bipyridine), was synthesized and fully characterized. X-Ray structure determinations revealed that these eight complexes have pseudo-octahedral configurations around the ruthenium center with the pincer ligand occupying three meridional sites. These complexes prove to be efficient precatalysts demonstrating very good activity and reusability for the transfer hydrogenation of ketones. PMID:23880878

Naziruddin, Abbas Raja; Huang, Zhao-Jiunn; Lai, Wei-Chih; Lin, Wan-Jung; Hwang, Wen-Shu

2013-09-28

181

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

182

Synthesis and structure of V(V) and Mn(III) NHC complexes supported by a tridentate bis-aryloxide-N-heterocyclic carbene ligand  

Microsoft Academic Search

Vanadium (V) and manganese (III) metal complexes (2, [tBu(OCO)]V(O)Cl; 3, [tBu(OCO)]Mn(acac)), which are supported by a tridentate bis-aryloxide-N-heterocyclic carbene ligand ([tBu(OCO)]2?[?3-O,C,O-{(3,5-di-tert-butyl-C6H2O)2N2C3H4}]2?) have been prepared and structurally characterized. Both complexes were efficiently synthesized in a straightforward and smooth manner involving the direct reaction of the imidazolinium proligand 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride 1, easily accessible in a two-step synthesis with an overall good yield,

Stéphane Bellemin-Laponnaz; Richard Welter; Lydia Brelot; Samuel Dagorne

2009-01-01

183

Solvent-dependent switch of ligand donor ability and catalytic activity of ruthenium(II) complexes containing pyridinylidene amide (PYA) N-heterocyclic carbene hybrid ligands.  

PubMed

Chelating ligands incorporating both N-[1-alkylpyridin-4(1H)-ylidene]amide (PYA) and N-heterocyclic carbene (NHC) donor sites were prepared and used for the synthesis of ruthenium(II) complexes. Cyclic voltammetry, NMR, and UV-vis spectroscopy of the complexes indicate a solvent-dependent contribution of the limiting resonance structures associated with the ligand in solution. The neutral pyridylidene imine structure is more pronounced in apolar solvents (CH2Cl2), while the mesoionic pyridinium amide form is predominant in polar solvents (MeOH, DMSO). The distinct electronic properties of these hybrid PYA-NHC ligands in different solvents have a direct influence on the catalytic activity of the ruthenium center, e.g., in the dehydrogenation of benzyl alcohol to benzaldehyde. The activity in different solvents qualitatively correlates with the solvent permittivity. PMID:25046249

Leigh, Vivienne; Carleton, Daniel J; Olguin, Juan; Mueller-Bunz, Helge; Wright, L James; Albrecht, Martin

2014-08-01

184

Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene-Isoquinoline Complex  

SciTech Connect

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni(Prbimiq1)]2+ (1c, where Prbimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (Ecat = 1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s1, respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

Thoi, VanSara; Kornienko, Nick; Margarit, C; Yang, Peidong; Chang, Christopher

2013-06-07

185

A Stable Massive Charged Particle  

E-print Network

We consider the possibility of the existence of a stable massive charged particle by a minimal extension of the standard model particle content. Absolute stability in the case of singly charged particle is not possible if the usual doublet Higgs exists, unless a discrete symmetry is imposed.But a doubly charged particle is absolutely stable.

G. Rajasekaran

2011-05-26

186

Tris(carbene)borate ligands featuring imidazole-2-ylidene, benzimidazol-2-ylidene and 1,3,4-triazol-2-ylidene donors. Evaluation of donor properties in four-coordinate {NiNO}10 complexes  

PubMed Central

The synthesis and characterization of new tris(carbene)borate ligand precursors containing substituted benzimidazol-2-ylidene and 1,3,4-triazol-2-ylidene donor groups, as well as a new tris(imidazol-2-ylidene)borate ligand precursor are reported. The relative donor strength of the tris(carbene)borate ligands have been evaluated by the position of ?(NO) in four-coordinate {NiNO}10 complexes, and follows the order: imidazol-2-ylidene > benzimidazol-2-ylidene > 1,3,4-triazol-2-ylidene. There is a large variation in ?(NO), suggesting these ligands to have a wide range of donor strengths while maintaining a consistent ligand topology. All ligands are stronger donors than Tp* and Cp*. PMID:23140462

Munoz, Salvador B.; Foster, Wallace K.; Lin, Hsiu-Jung; Margarit, Charles G.; Dickie, Diane A.

2012-01-01

187

Synthesis and characterization of heterobimetallic complexes with direct cu-m bonds (m = cr, mn, co, mo, ru, w) supported by N-heterocyclic carbene ligands: a toolkit for catalytic reaction discovery.  

PubMed

Building upon the precedent of catalytically active (NHC)Cu-FeCp(CO)2 complexes, a series of (NHC)Cu-[M] complexes were synthesized via the addition of Na(+)[M](-) reagents to (NHC)CuCl synthons. The different [M](-) anions used span a range of 7 × 10(7) relative nucleophilicity units, allowing for controlled variation of nucleophile/electrophile pairing in the heterobimetallic species. Direct Cu-M bonds (M = Cr, Mn, Co, Mo, Ru, W) formed readily when the bulky IPr carbene was used as a support. Crystallographic characterization and computational examination of these complexes was conducted. For the smaller IMes carbene, structural isomerism was observed when using the weakest [M](-) nucleophiles, with (IMes)Cu-[M] and {(IMes)2Cu}{Cu[M]2} isomers being observed in equilibrium. Collectively, the series of complexes provides a toolbox for catalytic reaction discovery with precise control of structure-function relationships. PMID:25275927

Banerjee, Suparna; Karunananda, Malkanthi K; Bagherzadeh, Sharareh; Jayarathne, Upul; Parmelee, Sean R; Waldhart, Greyson W; Mankad, Neal P

2014-10-20

188

DMF as a source of oxygen and aminomethine: stereoselective 1,2-insertion of rhodium(II) azavinyl carbenes into the C?O bond of formamides for the synthesis of cis-diamino enones.  

PubMed

A new catalytic reaction in which all the atoms of a formamide are incorporated into the product through a formal stereoselective 1,2-insertion of rhodium(II) azavinyl carbenes, generated in situ from readily available N-sulfonylated 1,2,3-triazoles, into the C?O bond of DMF and other N,N-disubstituted formamides to afford cis-diamino enones is described. PMID:24708029

Jung, Da Jung; Jeon, Hyun Ji; Kim, Ju Hyun; Kim, Youngmee; Lee, Sang-gi

2014-04-18

189

Tempering the Reactivities of Postulated ?-Oxo Gold Carbenes by Bidentate Ligands: Implication of Tricoordinated Gold Intermediates and the Development of an Expedient Bimolecular Assembly of 2,4-Disubstituted Oxazoles  

PubMed Central

2,4-Oxazole is an important structural motif in various natural products. An efficient modular synthesis of this structure is achieved via a [3+2] annulation between a terminal alkyne and a carboxamide by using a gold-catalyzed oxidation strategy. The postulated reactive intermediate, a terminal ?-oxo gold carbene, previously known to be highly electrophilic and hence impropable to be trapped by stoichiometric external nucleophiles, is coerced to react smoothly with a carboxamide en route to the oxazole ring by a P,N- or P,S-bidentate ligand such as Mor-DalPhos; in stark contrast, often used ligands including monodentate phosphines and NHCs are totally ineffective. The role of these bidentate phosphines in this reaction is attributed to the formation of a tricoordinated gold carbene intermediate, which is less electrophilic and hence more chemoselective when reacting with nucleophiles. The success in using bidentate phosphine ligands to temper the reactivities of in-situ generated gold carbenes would likely open many new opportunities to apply the oxidative gold catalysis to the development of novel methods, and the implication of tricoordinated gold intermediates in homogeneous gold catalysis should stimulate further advance in gold catalysis. PMID:23039251

Luo, Yingdong; Ji, Kegong; Li, Yuxue

2012-01-01

190

Stable plastid transformation of petunia.  

PubMed

Petunia hybrida is a commercial ornamental plant and is also an important model species for genetic analysis and transgenic research. Here we describe the steps required to isolate stable plastid transformants in P. hybrida using the commercial Pink Wave cultivar. Wave cultivars are popular spreading Petunias sold as ground cover and potted plants. Transgenes introduced into P. hybrida plastids exhibit stable expression over many generations. The development of plastid transformation in P. hybrida provides an enabling technology to bring the benefits of plastid engineering, including maternal inheritance and stable expression of performance-enhancing trait genes, to the important floriculture and horticulture industries. PMID:24599860

Avila, Elena Martin; Day, Anil

2014-01-01

191

Stable Spheromaks with Profile Control  

SciTech Connect

A spheromak equilibrium with zero edge current is shown to be stable to both ideal MHD and tearing modes that normally produce Taylor relaxation in gun-injected spheromaks. This stable equilibrium differs from the stable Taylor state in that the current density j falls to zero at the wall. Estimates indicate that this current profile could be sustained by non-inductive current drive at acceptable power levels. Stability is determined using the NIMROD code for linear stability analysis. Non-linear NIMROD calculations with non-inductive current drive could point the way to improved fusion reactors.

Fowler, T K; Jayakumar, R

2008-01-29

192

Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer.  

PubMed

The desorption of dihydrogen from magnesium(II) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L=?-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(µ-H)2MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(µ-H)2MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)2Al}2] (IPr=:C[{(C6H3-i-Pr(2)-2,6)NCH}2]), is an N-heterocyclic carbene adduct of the elusive parent dialane4 (Al2H4). A computational analysis of this compound is presented. PMID:20861903

Bonyhady, Simon J; Collis, David; Frenking, Gernot; Holzmann, Nicole; Jones, Cameron; Stasch, Andreas

2010-10-01

193

STABLE ISOTOPES AND COURTS James R. Ehleringer*  

E-print Network

STANDARDS AND STABLE ISOTOPE RATIO ANALYSIS...........398 A. The Federal Rules and Daubert .................................................................................................411 B. Application of Evidence Rules to Stable Isotope Ratio Analysis ................411 1 .................................................................435 C. DNA Profiling and Stable Isotope Ratio Analysis......................................436 1

Ehleringer, Jim

194

Multi-stable cylindrical lattices  

NASA Astrophysics Data System (ADS)

We present a cylindrical lattice structure that mimics the behaviour of the virus bacteriophage T4 in having two (or more) stable states which differ in their radii and length. While the virus achieves bistability through molecular mechanisms we use composite materials to exploit the interplay between pre-stress, material properties and structural geometry. We demonstrate (computationally) that multi-stability is a robust phenomenon. We also show (analytically) that it is possible to choose the design variables so that the energy is independent of the radius, thus resulting in every state of the structure being stable.

Pirrera, Alberto; Lachenal, Xavier; Daynes, Stephen; Weaver, Paul M.; Chenchiah, Isaac V.

2013-11-01

195

Short communication Corticosterone and stable  

E-print Network

behaviour prior to the breeding season can influence egg mass in Atlantic Puffins Fratercula arctica, the Atlantic Puffin Fratercula arctica. To do this, we measured d15 N values, which gauge the relative trophicShort communication Corticosterone and stable isotopes in feathers predict egg size in Atlantic

196

On the mechanism of cyclization of 5-hexenylchromate intermediates in the reactions of Fischer carbene complexes with a lithium enolate and allylmagnesium bromide.  

PubMed

The mechanisms for the evolution of pentacarbonyl-5-hexenylchromate complexes, unsubstituted and methyl substituted at C2, formed from a pentacarbonyl(alkoxy)carbene complex of chromium, the corresponding ketone lithium enolate, and allylmagnesium bromide, were theoretically investigated by using DFT (Density Functional Theory) at the B3PW91/6-31G* level (LANL2DZ for Cr and Br) taking into account the effect of THF solvent through the PCM model (Polarizable Continuum Model). Methyl substitution at C2 provokes a shortening of about 5 degrees in the C1-C2-C3 angle that favors the formation of the pentacyclic product. Also, the presence of this methyl substituent at C2 sterically disfavors the formation of the hexacyclic product. Thus, our results yield the hexacyclic system as the most favored product for the evolution of the unsubstituted alkylpentacarbonylchromate complex, and the pentacyclic product in the case of the substituted system, in good agreement with the experimental findings. The stereochemistry of the products experimentally observed is determined at the transition state for the migration of the Cr(CO)(5) fragment from C1 to C6 and the conformational rearrangement of the C1-C6 skeleton. Amine molecules, present in the reaction medium, can play a catalytic role by assisting the 1,2-H migration in the last step for the formation of hexacyclic products. PMID:19689118

Campomanes, Pablo; Flórez, Josefa; Pérez-Sánchez, Iván; Suero, Marcos G; Sordo, Tomás L; Menéndez, M Isabel

2009-09-18

197

Total Syntheses of the Histone Deacetylase Inhibitors Largazole and 2-epi-Largazole: Application of N-Heterocyclic Carbene Mediated Acylations in Complex Molecule Synthesis  

PubMed Central

Details of the evolution of strategies toward convergent assembly of the histone deacetylase inhibiting natural product largazole exploiting ?,?-unsaturated-?,?-epoxy-aldehydes and a thiazole-thiazoline containing ?-amino-acid are described. The initial N-heterocyclic carbene mediated redox amidation exploying these two types of building blocks representing largazole’s structural domains of distinct biosynthetic origin directly afforded the seco-acid of largazole. This was accomplished without any protecting groups resident upon either thioester bearing epoxy-aldehyde or the tetrapeptide. However, the ineffective production of largazole via the final macrolactonization led to an alternative intramolecular esterification/macrolactamization strategy employing the established two building blocks. This provided largazole along with its C2-epimer via an unexpected inversion of the ?-stereocenter at the valine residue. The biological evaluation demonstrated that both largazole and 2-epi-largazole led to dose-dependent increases of acetylation of histone H3, indicating their potencies as class I histone deacetylase selective inhibitiors. Enhanced p21 expression was also induced by largazole and its C2 epimer. In addition, 2-epi-largazole displayed more potent activity than largazole in cell viability assays against PC-3 and LNCaP prostate cancer cell lines. PMID:21244075

Wang, Bo; Huang, Po-Hsien; Chen, Ching-Shih

2014-01-01

198

Water-soluble luminescent cyclometalated gold(III) complexes with cis-chelating bis(N-heterocyclic carbene) ligands: synthesis and photophysical properties.  

PubMed

A new class of cyclometalated Au(III) complexes containing various bidentate C-deprotonated C^N and cis-chelating bis(N-heterocyclic carbene) (bis-NHC) ligands has been synthesized and characterized. These are the first examples of Au(III) complexes supported by cis-chelating bis-NHC ligands. [Au(C^N)(bis-NHC)] complexes display emission in solutions under degassed condition at room temperature with emission maxima (?max ) at 498-633?nm and emission quantum yields of up to 10.1?%. The emissions are assigned to triplet intraligand (IL) ???* transitions of C^N ligands. The Au(III) complex containing a C^N (C-deprotonated naphthalene-substituted quinoline) ligand with extended ?-conjugation exhibits prompt fluorescence and phosphorescence of comparable intensity with ?max at 454 and 611?nm respectively. With sulfonate-functionalized bis-NHC ligand, four water-soluble luminescent Au(III) complexes, including those displaying both fluorescence and phosphorescence, were prepared. They show similar photophysical properties in water when compared with their counterparts in acetonitrile. The long phosphorescence lifetime of the water-soluble AuIII complex with C-deprotonated naphthalene-substituted quinoline ligand renders it to function as ratiometric sensor for oxygen. Inhibitory activity of one of these water-soluble Au(III) complexes towards deubiquitinase (DUB) UCHL3 has been investigated; this complex also displayed a significant inhibitory activity with IC50 value of 0.15??M. PMID:24957269

Hung, Faan-Fung; To, Wai-Pong; Zhang, Jing-Jing; Ma, Chensheng; Wong, Wai-Yeung; Che, Chi-Ming

2014-07-01

199

Ruthenium(II) and osmium(II) 1,2,3-triazolylidene organometallics: a preliminary investigation into the biological activity of 'click' carbene complexes.  

PubMed

Taking advantage of the facile and versatile synthetic properties of 'click' 1,2,3-triazolylidene N-heterocyclic carbenes (tzNHC's), a range of new organometallic Ru(II) and Os(II) arene complexes containing functionalised tzNHC ligands, [M(?(6)-p-cymene)(tzNHC)Cl2] [M = Ru(II), Os(II)], have been synthesised and fully characterised, including the X-ray crystal structure of one of the Os(II) complexes. The tzNHC ligands remain coordinated to the metal centres under relevant physiological conditions, and following binding to the model protein, ubiquitin. The in vitro cytotoxicity of the compounds towards human ovarian cancer cells is dependent on the substituent on the tzNHC ligand but is generally <50 ?M and in some cases <1 ?M, whilst still retaining a high degree of selectivity towards cancer cells over healthy cells (1.85 ?M in A2780 ovarian cancer cells versus 435 ?M in human embryonic kidney cells in one case). PMID:24201979

Kilpin, Kelly J; Crot, Stéphanie; Riedel, Tina; Kitchen, Jonathan A; Dyson, Paul J

2014-01-21

200

Synthesis, characterization, and photophysical study of luminescent rhenium(I) diimine complexes with various types of N-heterocyclic carbene ligands.  

PubMed

A series of luminescent Re(I) diimine complexes with various types of N-heterocyclic carbene (NHC) ligands has been synthesized through the reaction between isocyano Re(I) diimine complexes with different nucleophiles. These Re(I) NHC complexes were characterized by (1)H and (13)C NMR and IR spectroscopy, mass spectrometry, and elemental analysis. One of the precursor complexes fac-{Re(CO)3[CN(H)C6H4-2-O]2Br} and five of the Re(I) diimine complexes with different types of NHC ligands were also structurally characterized by X-ray crystallography. In the preparation of these Re(I) NHC complexes, it is found that the reactivity of the isocyanide ligands in the synthetic complex precursors is significantly affected by the electronic nature of the trans ligand. All these complexes displayed (3)MLCT [d?(Re) ? ?*(N-N)] phosphorescence in degassed CH2Cl2 and CH3CN solutions at room temperature. Through the study of the photophysical and electrochemical properties of these Re(I) NHC complexes, the electronic properties of different types of NHC ligands were investigated. PMID:24592975

Ng, Chi-On; Yiu, Shek-Man; Ko, Chi-Chiu

2014-03-17

201

Theoretical study on the effect of annelation and carbonylation on the electronic and ligand properties of N-heterocyclic silylenes and germylenes: carbene comparisons begin to break down.  

PubMed

Quantum chemical calculations have been carried out to investigate the effect of annelation and carbonylation on the electronic and ligand properties of N-heterocyclic silylenes and germylenes. The thermodynamic stability of these ligands has been found to increase with annelation, while the reverse is true for carbonylation. This is in sharp contrast to N-heterocyclic carbenes (NHCs) where annelation leads to a decrease in their thermodynamic stabilities. Compared to nonannelated derivatives, annelated and carbonylated ones are found to be weaker ? donors but better ? acceptors. The effect of carbonylation is more pronounced than annelation toward increasing the ? acidity of these ligands. Carbonylation at the ?-position with respect to the N atom attached to the Si/Ge center has been found to be the most effective way of enhancing the ? acidity of these ligands. The computed natural charges reveal that electrophilicity increases upon both annelation and carbonylation. The calculated values of (31)P NMR chemical shifts of corresponding phosphinidene adducts of these ligands have been found to correlate well with the ? acidity of these Si/Ge centers. PMID:24738711

Guha, Ankur Kanti; Phukan, Ashwini K

2014-05-01

202

A large perturbation on electronic and photophysical properties of Ir(III) carbene complexes caused by the variation of N-substitution in N,N?-heteroaromatic ligands  

NASA Astrophysics Data System (ADS)

DFT/TDDFT investigation was performed on the electronic and photophysical properties of blue-emitting Ir(III) carbene complexes (fpmi)3-xIr(N^N?)x (x = 1, 2) [fpmi = 1-(4-fluorophenyl)-3-methylimidazolin-2-ylidene-C,C2?, N^N? = 2-(1H-pyrazol-5-yl)pyridinato (1a(x = 1)/1a?(x = 2)); 2-(1H-imidazol-5-yl)pyridinato (1b/1b?); 2-(1H-imidazol-2-yl)pyridinato (1c/1c?); 2-(1H-1,2,4-triazol-5-yl)pyridinato (2a/2a?); 2-(1H-1,2,3-triazol-5-yl)pyridinato (2b/2b?); 2-(4H-1,2,4-triazol-3-yl)pyridinato (2c/2c?)]. The absorption intensities and band positions are obviously affected by the variation of N substitution in N^N? ligand. The emission properties show an apparent dependence on the solvent effects, and the N^N? ligand plays an important role in governing the emissive state. The pyrazolyl-pyridyl-based N^N? ligand is considered to be more beneficial for blue OLEDs emitters.

Liu, Yuqi; Si, Yanling; Wang, Ying; Wu, Zhijian

2014-08-01

203

Copper- and copper-N-heterocyclic carbene-catalyzed C-H activating carboxylation of terminal alkynes with CO2 at ambient conditions  

PubMed Central

The use of carbon dioxide as a renewable and environmentally friendly source of carbon in organic synthesis is a highly attractive approach, but its real world applications remain a great challenge. The major obstacles for commercialization of most current protocols are their low catalytic performances, harsh reaction conditions, and limited substrate scope. It is important to develop new reactions and new protocols for CO2 transformations at mild conditions and in cost-efficient ways. Herein, a copper-catalyzed and copper–N-heterocyclic carbene-cocatalyzed transformation of CO2 to carboxylic acids via C?H bond activation of terminal alkynes with or without base additives is reported. Various propiolic acids were synthesized in good to excellent yields under ambient conditions without consumption of any organometallic or organic reagent additives. This system has a wide scope of substrates and functional group tolerances and provides a powerful tool for the synthesis of highly functionalized propiolic acids. This catalytic system is a simple and economically viable protocol with great potential in practical applications. PMID:21059950

Yu, Dingyi; Zhang, Yugen

2010-01-01

204

Synthesis of Tridentate 2,6-Bis(imino)pyridyl Ruthenium(II) Complexes with N-Heterocyclic Carbene Ligands: Activation of Imidazolium Salts.  

PubMed

Low-valent Ru(0) complexes, [?(2)-N3]Ru(?(6)-Ar) (1) or {[N3]Ru}2(?-N2) (2), where Ar = C6H6 or C6H5Me, and [N3] = 2,6-(2,4,6-(CH3)3C6H2N?CCH3)2C5H3N, activate C-H bonds in imidazolium salts to produce bis(imino)pyridyl ruthenium-(imidazolidin-2-ylidene) complexes, [N3]Ru(H)(X)(NHC) (4) (X = halides and tosylate). Formation of 4 is most likely to proceed via C-H oxidative addition, followed by anion coordination, which is expected to be a useful pathway in synthesizing new complexes with both N-heterocyclic carbene (NHC) and hydride ligands. A zwitterionic ruthenium complex with an ylidic ligand, bis(imino)pyridyl ruthenium-(2-methyleneimidazoline) complex, 7, was also successfully isolated and fully characterized. The (1)H NMR spectra and the solid-state structure confirm that complex 7 is an ylidic transition-metal complex with both NHC and hydride ligands, which was formed through the activation of imidazolium salts. PMID:25337998

Yoo, Hyojong; Berry, Donald H

2014-11-01

205

How Stable Is Stable? Function versus Community Composition  

Microsoft Academic Search

The microbial community dynamics of a functionally stable, well-mixed, methanogenic reactor fed with glucose were analyzed over a 605-day period. The reactor maintained constant pH and chemical oxygen demand removal during this period. Thirty-six rrn clones from each of seven sampling events were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) for the Bacteria and Archaea domains and by sequence

ANA FERNANDEZ; SUIYING HUANG; SHERRY SESTON; JIAN XING; ROBERT HICKEY; CRAIG CRIDDLE; JAMES TIEDJE

1999-01-01

206

WEIGHTED GRASSMANNIANS AND STABLE HYPERPLANE ARRANGEMENTS  

E-print Network

generalization of (1) Hassett's weighted stable curves, and (2) Hacking-Keel-Tevelev's stable hyperplane's moduli M0, of weighted stable n-pointed curves [Has03], and (2) Hacking-Keel-Tevelev's moduli M(r, n The moduli space M0,n of stable n-pointed rational curves has many generaliza- tions, beginning of course

Alexeev, Valery

207

Stable phases of boson stars  

NASA Astrophysics Data System (ADS)

We analyze the physical properties of boson stars, which possess counterparts in flat space-time, Q-balls. Applying a stability analysis via catastrophe theory, we show that the families of rotating and nonrotating boson stars exhibit two stable regions, separated by an unstable region. Analogous to the case of white dwarfs and neutron stars, these two regions correspond to compact stars of lower and higher densities. Moreover, the high density phase ends when the black hole limit is approached. Here another unstable phase is encountered, exhibiting the typical spiralling phenomenon close to the black hole limit. When the interaction terms in the scalar field potential become negligible, the properties of mini-boson stars are recovered, which possess only a single stable phase.

Kleihaus, Burkhard; Kunz, Jutta; Schneider, Stefanie

2012-01-01

208

Phase stable RF transport system  

DOEpatents

An RF transport system delivers a phase-stable RF signal to a load, such as an RF cavity of a charged particle accelerator. A circuit generates a calibration signal at an odd multiple frequency of the RF signal where the calibration signal is superimposed with the RF signal on a common cable that connects the RF signal with the load. Signal isolating diplexers are located at both the RF signal source end and load end of the common cable to enable the calibration to be inserted and extracted from the cable signals without any affect on the RF signal. Any phase shift in the calibration signal during traverse of the common cable is then functionally related to the phase shift in the RF signal. The calibration phase shift is used to control a phase shifter for the RF signal to maintain a stable RF signal at the load.

Curtin, Michael T. (Los Alamos, NM); Natter, Eckard F. (San Francisco, CA); Denney, Peter M. (Los Alamos, NM)

1992-01-01

209

Stable Carbon and Nitrogen Isotopic  

Microsoft Academic Search

The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate organic matter (POM) and benthic organic matter (BOM) within the

Jennifer Lawson; PETER T. DORAN; Fabien Kenig; DAVID J. DES MARAIS; JOHN C. PRISCU

2004-01-01

210

Fractal Clusters and Stable Distribution  

Microsoft Academic Search

Size distribution of fractal clusters is shown to follow a one-sided stable distribution. Its characteristic exponent alpha is determined by the fractal relation between the cluster's surface (S) and volume (N) under the scale change: S-->aS, N-->a1\\/alphaN. This result means that an asymptotic power law size distribution p(N){\\\\propto}N-alpha-1 is deduced from the above geometrical fractal relation.

Hideki Takayasu

1988-01-01

211

Stable algorithms for link analysis  

Microsoft Academic Search

The Kleinberg HITS and the Google PageRank algorithms are eigenvector methods for identifying ``authoritative'' or ``influential'' articles, given hyperlink or citation information. That such algorithms should give reliable or consistent answers is surely a desideratum, and in~\\\\cite{ijcaiPaper}, we analyzed when they can be expected to give stable rankings under small perturbations to the linkage patterns. In this paper, we extend

Andrew Y. Ng; Alice X. Zheng; Michael I. Jordan

2001-01-01

212

Thermally stable emulsion explosive composition  

SciTech Connect

A thermally stable, cap-sensitive, water-in-oil emulsion explosive composition is described which has a discontinuous aqueous oxidizer salt solution phase containing calcium nitrate, a continuous oil or water-immiscible liquid or organic phase, an emulsifier, and a density reducing agent. The salt solution contains calcium nitrate in an amount of at least 20% by weight based on the total composition. 9 claims.

Sudweeks, W.B.; Lawrence, L.D.

1982-03-30

213

Towards stable acceleration in LINACS  

E-print Network

Ultra-stable and -reproducible high-energy particle beams with short bunches are needed in novel linear accelerators and, in particular, in the Compact Linear Collider CLIC. A passive beam phase stabilization system based on a bunch compression with a negative transfer matrix element R56 and acceleration at a positive off-crest phase is proposed. The motivation and expected advantages of the proposed scheme are outlined.

Dubrovskiy, A D

2014-01-01

214

Spin Contamination Error in Optimized Geometry of Singlet Carbene (1A1) by Broken-Symmetry Method  

NASA Astrophysics Data System (ADS)

Spin contamination errors of a broken-symmetry (BS) method in optimized structural parameters of the singlet methylene (1A1) molecule are quantitatively estimated for the Hartree-Fock (HF) method, post-HF methods (CID, CCD, MP2, MP3, MP4(SDQ)), and a hybrid DFT (B3LYP) method. For the purpose, the optimized geometry by the BS method is compared with that of an approximate spin projection (AP) method. The difference between the BS and the AP methods is about 10-20° in the HCH angle. In order to examine the basis set dependency of the spin contamination error, calculated results by STO-3G, 6-31G*, and 6-311++G** are compared. The error depends on the basis sets, but the tendencies of each method are classified into two types. Calculated energy splitting values between the triplet and the singlet states (ST gap) indicate that the contamination of the stable triplet state makes the BS singlet solution stable and the ST gap becomes small. The energy order of the spin contamination error in the ST gap is estimated to be 10-1 eV.

Kitagawa, Yasutaka; Saito, Toru; Nakanishi, Yasuyuki; Kataoka, Yusuke; Matsui, Toru; Kawakami, Takashi; Okumura, Mitsutaka; Yamaguchi, Kizashi

2009-10-01

215

Reactivity of coordinatively unsaturated bis(N-heterocyclic carbene) Pt(II) complexes toward H(2). Crystal structure of a 14-electron Pt(II) hydride complex.  

PubMed

The reactivity toward H2 of coordinatively unsaturated Pt(II) complexes, stabilized by N-heterocyclic carbene (NHC) ligands, is herein analyzed. The cationic platinum complexes [Pt(NHC')(NHC)](+) (where NHC' stands for a cyclometalated NHC ligand) react very fast with H2 at room temperature, leading to hydrogenolysis of the Pt-CH2 bond and concomitant formation of hydride derivatives [PtH(NHC)2](+) or hydrido-dihydrogen complexes [PtH(H2)(NHC)2](+). The latter species release H2 when these compounds are subjected to vacuum. The X-ray structure of complex [PtH(IPr)2][SbF6] revealed its unsaturated nature, exhibiting a true T-shaped structure without stabilization by agostic interactions. Density functional theory calculations indicate that the binding and reaction of H2 in complexes [PtH(H2)(NHC)2](+) is more favored for derivatives bearing aryl-substituted NHCs (IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and IMes = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) than for those containing tert-butyl groups (I(t)Bu). This outcome is related to the higher close-range steric effects of the I(t)Bu ligands. Accordingly, H/D exchange reactions between hydrides [PtH(NHC)2](+) and D2 take place considerably faster for IPr and IMes* derivatives than for I(t)Bu ones. The reaction mechanisms for both H2 addition and H/D exchange processes depend on the nature of the NHC ligand, operating through oxidative addition transition states in the case of IPr and IMes* or by a ?-complex assisted-metathesis mechanism in the case of I(t)Bu. PMID:24716606

Rivada-Wheelaghan, Orestes; Roselló-Merino, Marta; Ortuño, Manuel A; Vidossich, Pietro; Gutiérrez-Puebla, Enrique; Lledós, Agustí; Conejero, Salvador

2014-04-21

216

Stable transformation of petunia plastids.  

PubMed

Plastid transformation results in stably expressed foreign genes, which for most Angiosperms are largely excluded from sperm cells, thereby greatly reducing the risk of foreign gene spread through pollen. Prior to this work, fertile plastid transformants were restricted to tobacco, tomato and Lesquerella. Application of plastid engineering in the important floriculture industry requires the development of stable plastid transformation in a major ornamental plant species such as Petunia hybrida. Here we describe the successful isolation of fertile and stable plastid transformants in a commercial cultivar of P. hybrida (var. Pink Wave). Plastid targeting regions from tobacco were used to integrate aadA and gusA between the accD and rbcL genes of P. hybrida plastid DNA following particle bombardment of leaves. For three spectinomycin and streptomycin resistant lines, DNA blot analysis confirmed transgene integration into plastid DNA and homoplasmy. Maternal inheritance and homoplasmy resulted in 100% transmission of spectinomycin resistance to progeny after selfing. Plastid transformants expressed the gusA gene uniformly within leaves and to comparable levels in all three lines. Insertion of trait genes in place of gusA coding sequences enables immediate applications of our plastid transformation vector. Establishment of plastid transformation in P. hybrida facilitates a safe and reliable use of this important ornamental plant for research and plant biotechnology. PMID:15672833

Zubkot, Mikhajlo K; Zubkot, Elena I; van Zuilen, Karen; Meyer, Peter; Day, Anil

2004-12-01

217

Stable Imaging for Astronomy (SIA)  

NASA Astrophysics Data System (ADS)

One of the most challenging fields of astronomical instrumentation is probably high-contrast imaging since it ultimately combines ultra-high sensitivity at low flux and the ability to cope with photon flux contrasts of several hundreds of millions or even more. These two aspects implicitly require that high-contrast instruments should be highly stable in the sense of the reproducibility of their measurements at different times, but also, continuously stable over time. In most high contrast instruments or experiments, their sensitivity is broken after at most tens of minutes of operation due to uncontrolled and unknown behaviour of the whole experiment regarding the environmental conditions. In this paper, we introduce a general approach of an exhaustive stability study for high-contrast imaging that has been initiated at Lagrange Laboratory, Observatoire de la Côte d'Azur (OCA). On a practical ground, one of the fundamental issues of this study is the metrology, which is the basis of all reproducible measurements. We describe a small experiment designed to understand the behaviour of one of our ultra-precise metrology tools (a commercial sub-nanometric 3-way interferometer) and derive the conditions under which its operation delivers reliable results. The approach will apply to the high-contrast imaging test-bench SPEED, under development at OCA.

Beaulieu, Mathilde; Ottogalli, Sebastien; Preis, Olivier; Bresson, Yves; Rivet, Jean-Pierre; Abe, Lyu; Vakili, Farrokh

2014-07-01

218

Stable reflexive sheaves and localization  

E-print Network

We study moduli spaces $\\N$ of rank 2 stable reflexive sheaves on $\\PP^3$. Fixing Chern classes $c_1$, $c_2$, and summing over $c_3$, we consider the generating function $G^{refl}(q)$ of Euler characteristics of such moduli spaces. The action of the dense open torus $T$ on $\\PP^3$ lifts to $\\N$ and we classify all sheaves in $\\N^T$. This leads to an explicit expression for $G^{refl}(q)$. Since $c_3$ is bounded below and above, $G^{refl}(q)$ is a polynomial. For $c_1=-1$, we show its leading term is $12c_2 q^{c_{2}^{2}}$. Next, we study moduli spaces of rank 2 stable torsion free sheaves on $\\PP^3$ and consider the generating function $G(q)$ of Euler characteristics of such moduli spaces. We give an expression for this generating function in terms of $G^{refl}(q)$ and Euler characteristics of Quot schemes of certain $T$-equivariant reflexive sheaves. These Quot schemes and their fixed point loci are studied in a sequel with B. Young. The components of these fixed point loci are products of $\\PP^1$'s and give r...

Gholampour, Amin

2013-01-01

219

Palladium complexes of abnormal N-heterocyclic carbenes as precatalysts for the much preferred Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium.  

PubMed

A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC)PdI2(pyridine) type precatalysts, 1b-4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b-4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a]pyridinium iodide salts, 1a-4a, with PdCl2 in pyridine in the presence of K2CO3 as a base while the imidazo[1,2-a]pyridinium iodide salts, 1a-4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a]pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a]pyridine derived abnormal carbenes are strongly sigma-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b-4b. PMID:20023883

John, Alex; Shaikh, Mobin M; Ghosh, Prasenjit

2009-12-21

220

Paleoproxies: Heavy Stable Isotope Perspectives  

NASA Astrophysics Data System (ADS)

Recent advances in isotope ratio mass spectrometry, namely multiple collector ICP-MS and refined TIMS techniques, will significantly enhance the ability to measure heavy stable isotope fractionation, which will lead to the development of a wide array of process-identifying (bio)-geochemical tools. Thus far research in this area is not easily assessable to scientists outside the isotope field. This is due to the fact that analyzing heavy stable isotopes does not provide routine numbers which are per se true (the preciser the truer) but is still a highly experimental field. On the other hand resolving earth science problems requires specialists familiar with the environment being studied. So what is in there for paleoceanographers? In a first order approach, relating isotope variations to physical processes is straightforward. A prominent example are oxygen isotope variations with temperature. The total geological signal is of course far more complicated. At low temperatures, heavy stable isotopes variations have been reported for e.g. Ca, Cr, Fe, Cu, Zn, Mo and Tl. Fractionation mechanisms and physical parameters responsible for the observed variations are not yet resolved for most elements. Significant equilibrium isotope fractionation is expected from redox reactions of transition metals. However a difference in coordination number between two coexisting speciations of an element in the same oxidation state can also cause fractionation. Protonation of dissolved Mo is one case currently discussed. For paleoceanography studies, a principal distinction between transition metals essential for life (V to Zn plus Mo) or not will be helpful. In case of the former group, distinction between biogenic and abiogenic isotope fractionation will remain an important issue. For example, abiotic Fe redox reactions result in isotope fractionations indistinguishable in direction and magnitude from microbial effects. Only a combination of different stable isotope systems bears the potential to solve this problem for a given set of samples and thus to model the ocean system more accurately in different scales. Besides all complications some important applications of heavy stable isotopes as paleoproxies already emerge. Pilot studies indicate that Mo isotopes may present a proxy for the extend of anoxic condition in past oceans. On a finer scale the same system appears to provide a measure of (bio)-chemical redox-changes related to diagenesis. The Ca isotope system may complement more classical sea surface temperature proxies in particular environments. Promising results exist for polar waters (N. pachy left), as well as indications on the seasonality under global greenhouse conditions ~110-50 Ma ago. However, the heavily species dependent Ca isotope fractionation can not be interpreted by just adopting concepts and findings from the oxygen system. While a complication to the ease of use as SST proxy, this species dependence offers pathways to unravel different modes of bio-calcifications. Given the complexity of the matter, collaboration of specialists of different fields will be needed to develop successful process-related hypotheses and diagnostic tools.

Nagler, T. F.; Hippler, D.; Siebert, C.; Kramers, J. D.

2002-12-01

221

Scaling Behavior in the Stable Marriage Problem  

NASA Astrophysics Data System (ADS)

We study the optimization of the stable marriage problem. All individuals attempt to optimize their own satisfaction, subject to mutually conflicting constraints. We find that the stable solutions are generally not the globally best solution, but reasonably close to it. All the stable solutions form a special sub-set of the meta-stable states, obeying interesting scaling laws. Both numerical and analytical tools are used to derive our results.

Oméro, Marie-José; Dzierzawa, Michael; Marsili, Matteo; Zhang, Yi-Cheng

1997-12-01

222

Uses of stable isotopes in fish ecology  

EPA Science Inventory

Analyses of fish tissues (other than otoliths) for stable isotope ratios can provide substantial information on fish ecology, including physiological ecology. Stable isotopes of nitrogen and carbon frequently are used to determine the mix of diet sources for consumers. Stable i...

223

Substitution reactions at tetracoordinate boron: synthesis of N-heterocyclic carbene boranes with boron-heteroatom bonds.  

PubMed

Boryl halide, carboxylate and sulfonate complexes of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (dipp-Imd-BH(2)X, X = halide or sulfonate) have been prepared from the parent borane dipp-Imd-BH(3) by (1) substitution reactions with R-X (X = halide or sulfonate), (2) reactions with electrophiles (like I(2) or NIS), or (3) acid/base reactions with HX (provided that HX has a pK(a) of about 2 or less). Dipp-Imd-BH(2)I is most conveniently prepared by reaction with diiodine while dipp-Imd-BH(2)OTf is best prepared by reaction with triflic acid. These and other less reactive complexes behave as electrophiles and can be substituted by a wide range of heteroatom nucleophiles including halides, thiolates and other sulfur-based nucleophiles, isocyanate, azide, nitrite, and cyanide. The resulting products are remarkably stable, and many have been characterized by X-ray crystallography. Several are members of very rare classes of functionalized boron compounds (boron azide, nitro compound, nitrous ester, etc.). PMID:20886852

Solovyev, Andrey; Chu, Qianli; Geib, Steven J; Fensterbank, Louis; Malacria, Max; Lacôte, Emmanuel; Curran, Dennis P

2010-10-27

224

Stable density stratification solar pond  

NASA Technical Reports Server (NTRS)

A stable density-stratification solar pond for use in the collection and storage of solar thermal energy including a container having a first section characterized by an internal wall of a substantially cylindrical configuration and a second section having an internal wall of a substantially truncated conical configuration surmounting the first section in coaxial alignment therewith, the second section of said container being characterized by a base of a diameter substantially equal to the diameter of the first section and a truncated apex defining a solar energy acceptance opening is discussed. A body of immiscible liquids is disposed within the container and comprises a lower portion substantially filling the first section of the container and an upper portion substantially filling the second section of the container, said lower portion being an aqueous based liquid of a darker color than the upper portion and of a greater density. A protective cover plate is removably provided for covering the acceptance opening.

Lansing, F. L. (inventor)

1985-01-01

225

Stable reflexive sheaves and localization  

E-print Network

We study moduli spaces $\\N$ of rank 2 stable reflexive sheaves on $\\PP^3$. Fixing Chern classes $c_1$, $c_2$, and summing over $c_3$, we consider the generating function $G^{refl}(q)$ of Euler characteristics of such moduli spaces. The action of the dense open torus $T$ on $\\PP^3$ lifts to $\\N$ and we classify all sheaves in $\\N^T$. This leads to an explicit expression for $G^{refl}(q)$. Since $c_3$ is bounded below and above, $G^{refl}(q)$ is a polynomial. For $c_1=-1$, we show its leading term is $12c_2 q^{c_{2}^{2}}$. Next, we study moduli spaces of rank 2 stable torsion free sheaves on $\\PP^3$ and consider the generating function $G(q)$ of Euler characteristics of such moduli spaces. We give an expression for this generating function in terms of $G^{refl}(q)$ and Euler characteristics of Quot schemes of certain $T$-equivariant reflexive sheaves. These Quot schemes and their fixed point loci are studied in a sequel with B. Young. The components of these fixed point loci are products of $\\PP^1$'s and give rise non-trivial combinatorics. For $c_1=-1$ and $c_2=1$, we obtain $G(q) = 4(1+q) M(q^{-1})^8$, where $M(q)$ is the MacMahon function. Many techniques of this paper apply to any toric 3-fold. In general, $G^{refl}(q)$ depends on the choice of polarization which leads to wall-crossing phenomena. We briefly illustrate this in the case of $\\PP^2 \\times \\PP^1$.

Amin Gholampour; Martijn Kool

2013-08-16

226

On Nonstable and Stable Population Momentum  

PubMed Central

This article decomposes total population momentum into two constituent and multiplicative parts: “nonstable” momentum and “stable” momentum. Nonstable momentum depends on deviations between a population’s current age distribution and its implied stable age distribution. Stable momentum is a function of deviations between a population’s implied stable and stationary age distributions. In general, the factorization of total momentum into the product of nonstable and stable momentum is a very good approximation. The factorization is exact, however, when the current age distribution is stable or when observed fertility is already at replacement. We provide numerical illustrations by calculating nonstable, stable, and total momentum for 176 countries, the world, and its major regions. In short, the article brings together disparate strands of the population momentum literature and shows how the various kinds of momentum fit together into a single unifying framework. PMID:21948106

Olgiati, Analia S.; Levin, Simon A.

2014-01-01

227

Mechanism of Ni N-heterocyclic carbene catalyst for C-O bond hydrogenolysis of diphenyl ether: a density functional study.  

PubMed

Catalysts for aromatic C-O bond activation can potentially be used for the lignin degradation process. We investigated the mechanisms of C-O bond hydrogenolysis of diphenyl ether (PhOPh) by the nickel N-heterocyclic carbene (Ni-SIPr) complex to produce benzene and phenol as products. Our calculations revealed that diphenyl ether is not only a substrate, but also serves as a ligand to stabilize the Ni-SIPr complex. The Ni(SIPr)(?(6)-PhOPh) complex is initially formed before rearranging to Ni(SIPr)(?(2)-PhOPh), the active species for C-O bond activation. The catalytic reaction has three steps: (i) oxidative addition of Ni(SIPr)(?(2)-PhOPh) to form [Ni(SIPr)(OPh)(Ph)](0), (ii) ?-complex-assisted metathesis, in which H2 binds to the nickel to form [Ni(SIPr)(OPh)(Ph)(H2)](0), and then benzene (or phenol) is eliminated, and (iii) reductive elimination of phenol (or benzene) and the binding of PhOPh to regenerate Ni(SIPr)(?(2)-PhOPh). As the rate determining step is the oxidative addition step (+24 kcal mol(-1)), we also calculated the free energy barriers for the oxidative addition of diaryl ether containing a trifluoromethyl electron withdrawing group (PhOC6H4CF3) and found that C-O bond activation at the carbon adjacent to the aryl ring that contains the electron withdrawing substituent is preferred. This is in agreement with the experimental results, in that the major products are phenol and trifluoromethylbenzene. Moreover, the hydrogenation of benzene via Ni(SIPr)(?(2)-C6H6) requires a high energy barrier (+39 kcal mol(-1)); correspondingly, the hydrogenation products, e.g. cyclohexane and cyclohexadiene, were not observed in the experiment. Understanding the reaction mechanisms of the nickel catalysts for C-O bond hydrogenolysis of diphenyl ether will guide the development of catalytic systems for aromatic C-O bond activation to achieve the highest possible selectivity and efficiency. PMID:25355042

Sawatlon, Boodsarin; Wititsuwannakul, Taveechai; Tantirungrotechai, Yuthana; Surawatanawong, Panida

2014-11-18

228

Cyclometalated N-heterocyclic carbene complexes of ruthenium for access to electron-rich silylene complexes that bind the Lewis acids CuOTf and AgOTf.  

PubMed

The synthesis of the cyclometalated complexes Cp*Ru(IXy-H) (2) [IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene; IXy-H = 1-(2-CH2C6H3-6-methyl)-3-(2,6-dimethylphenyl)imidazol-2-ylidene-1-yl (the deprotonated form of IXy); Cp* = ?(5)-C5Me5] and Cp*Ru(IXy-H)(N2) (3) was achieved by dehydrochlorination of Cp*Ru(IXy)Cl (1) with KCH2Ph. Complexes 2 and 3 activate primary silanes (RSiH3) to afford the silyl complexes Cp*(IXy-H)(H)RuSiH2R [R = p-Tol (4), Mes (5), Trip (6)]. Density functional theory studies indicated that these complexes are close in energy to the corresponding isomeric silylene species Cp*(IXy)(H)Ru?SiHR. Indeed, reactivity studies indicated that various reagents trap the silylene isomer of 6, Cp*(IXy)(H)Ru?SiHTrip (6a). Thus, benzaldehyde reacts with 6 to give the [2 + 2] cycloaddition product 7, while 4-bromoacetophenone reacts via C-H bond cleavage and formation of the enolate Cp*(IXy)(H)2RuSiH[OC(?CH2)C6H4Br]Trip (8). Addition of the O-H bond of 2,6-dimethylphenol across the Ru?Si bond of 6a gives Cp*(IXy)(H)2RuSiH(2,6-Me2C6H3O)Trip (9). Interestingly, CuOTf and AgOTf also react with 6 to provide unusual Lewis acid-stabilized silylene complexes in which MOTf bridges the Ru-Si bond. The AgOTf complex, which was crystallographically characterized, exhibits a structure similar to that of [Cp*((i)Pr3P)Ru(?-H)2SiHMes](+), with a three-center, two-electron Ru-Ag-Si interaction. Natural bond orbital analysis of the MOTf complexes supported this type of bonding and characterized the donor interaction with Ag (or Cu) as involving a delocalized interaction with contributions from the carbene, silylene, and hydride ligands of Ru. PMID:25050912

Liu, Hsueh-Ju; Raynaud, Christophe; Eisenstein, Odile; Tilley, T Don

2014-08-13

229

Liquids more stable than crystals  

E-print Network

All liquids (except helium due to quantum effects) crystallize at low temperatures, forming ordered structures. The competition between disorder, which stabilizes the liquid phase, and energy, which favors the ordered crystalline structure, inevitably turns in favor of the latter when temperature is lowered and the entropic contribution to the free energy becomes progressively less and less relevant. The "liquid" state survives at low temperatures only as a glass, an out-of-equilibrium arrested state of matter. This textbook description holds inevitably for atomic and molecular systems, where the interaction between particles is set by quantum mechanical laws. The question remains whether the same physics hold for colloidal particles, where inter-particle interactions are usually short-ranged and tunable. Here we show that for patchy colloids with limited valence, conditions can be found for which the disordered liquid phase is stable all the way down to the zero-temperature limit. Our results offer interesting cues for understanding the stability of gels and the glass forming ability of atomic and molecular network glasses.

Frank Smallenburg; Francesco Sciortino

2013-07-07

230

Suppression of Stable Flies on Cattle  

E-print Network

. Management To suppress stable fly populations efficient- ly, producers should use an integrated pest management (IPM) approach. IPM relies on Figure 1. Adult stable fly (Photo courtesy of Bart Drees, Texas Cooperative Extension). E-212 7/04 three tactics... and pupa (Photo courtesy of Bart Drees, Texas Cooperative Extension). Figure 3. Remnants of hay bales can become breeding sites for stable flies. Backrubs, which use compounds such as Co- Ral 11.6% EC (coumaphos) or Atroban 11% EC (permethrin), also can...

Tomberlin, Jeffery K.

2004-07-01

231

Ultraviolet and thermally stable polymer compositions  

NASA Technical Reports Server (NTRS)

Copolymers, produced from aromatic substituted aromatic azine-siloxane compositions, are thermally stable, solar ultraviolet light non-degradable by wavelengths shorter than those reaching earth surface.

Adamson, M. J.; Gloria, H. R.; Goldsberry, R. E.; Reinisch, R. F.

1972-01-01

232

Helical metal cage of silver(I) and mercury(II)-N-heterocyclic carbene complexes of 1,4-phenylene-bis{imidazo[1,5-a]pyridine-4-iumhexaflurophosphate}  

NASA Astrophysics Data System (ADS)

Novel N-heterocyclic carbene (NHC) architecture of 1,4-phenylene-bis{imidazo[1,5-a]pyridine-4 iumhexaflurophosphate}, [1(HPF6)2] has been synthesized in two steps from commercially available starting materials. The p-phylene bridged free annulated imidazolium salt has been synthesized and characterized both in solution and solid-state and has been used to synthesize silver(I) and mercury(II)-NHC complexes using the basic metal precursors. The [Ag2(1)2][PF6]2 (2) was synthesized using [1(HPF6)2] by Ag2O method in acceptable yield. The dinuclear Hg(II) complex [Hg2(1)2][PF6]4 (3) consisting of two biscarbene ligand has been synthesized from Hg(OAc)2 and [1(HPF6)2]. The helical nature of Hg(II)-NHC (3) has been established from solid state X-ray structure.

Rana, Bidyut Kumar; Bertolasi, Valerio; Pal, Satyanarayan; Mitra, Partha; Dinda, Joydev

2013-10-01

233

Unconditionnally stable scheme for Riccati equation  

E-print Network

Unconditionnally stable scheme for Riccati equation Fran¸cois Dubois a and Abdelkader Sa¨idi b of matrix Riccati equation used in control problems. The scheme is unconditionnally stable and the solution for Riccati equation 3 · We observe that the differential system (1)(6) together with the initial condition (2

Boyer, Edmond

234

Bone stable isotope studies in archaeology  

Microsoft Academic Search

Stable isotope ratios of carbon and nitrogen in bone have become increasingly frequent inclusions in archaeological reports over the past few decades. The majority of such studies has been done in North America, where the use of marine foods and the introduction of maize have been monitored. Similar questions have been addressed in Mesoamerica and South America. In Europe, stable

Margaret J. Schoeninger; Katherine Moore

1992-01-01

235

Stable Layers in the Atmospheric Boundary Layer  

NASA Astrophysics Data System (ADS)

Field experimental studies on the establishment and growth of the nocturnal stable layer near the ground were made in January, 1998 using a tethered balloon at a site in Phoenix, Arizona. Days and nights with clear skies and light surface winds were of particular interest because small particle and carbon monoxide concentrations can be high during such times. Closest to the ground a shallow stable layer 20 meters deep with a buoyancy frequency (N) of 0.05 1/s rapidly developed before sundown. The height of this layer and N remained constant throughout the night. Above the 20-meter level, there was a transition layer which was also stable with N = 0.025 1/s. This transition layer grew throughout the night and reached 120 meters by dawn. Above the transition layer was a neutrally stable (residual) layer left over from the previous day. An unsteady layer 10 to 100 m thick with N = 0.025 1/s was also found at the top of the troposphere with the neutrally stable troposphere below and the stable stratosphere above. The growth and/or decay of turbulence in such stable layers will be discussed in light of recent theoretical developments.

Mahalov, A.; Berman, N. S.; Fernando, H. J. S.; Yu, F.; Pardyjak, E.

1998-11-01

236

Bi-stable optical element actuator device  

DOEpatents

The present invention is a bistable optical element actuator device utilizing a powered means to move an actuation arm, to which an optical element is attached, between two stable positions. A non-powered means holds the actuation arm in either of the two stable positions. The optical element may be a electromagnetic (EM) radiation or particle source, an instrument, or EM radiation or particle transmissive reflective or absorptive elements. A bearing is used to transfer motion and smoothly transition the actuation arm between the two stable positions.

Holdener, Fred R. (Tracy, CA); Boyd, Robert D. (Livermore, CA)

2002-01-01

237

Applications of stable isotopes in clinical pharmacology  

PubMed Central

This review aims to present an overview of the application of stable isotope technology in clinical pharmacology. Three main categories of stable isotope technology can be distinguished in clinical pharmacology. Firstly, it is applied in the assessment of drug pharmacology to determine the pharmacokinetic profile or mode of action of a drug substance. Secondly, stable isotopes may be used for the assessment of drug products or drug delivery systems by determination of parameters such as the bioavailability or the release profile. Thirdly, patients may be assessed in relation to patient-specific drug treatment; this concept is often called personalized medicine. In this article, the application of stable isotope technology in the aforementioned three areas is reviewed, with emphasis on developments over the past 25 years. The applications are illustrated with examples from clinical studies in humans. PMID:21801197

Schellekens, Reinout C A; Stellaard, Frans; Woerdenbag, Herman J; Frijlink, Henderik W; Kosterink, Jos G W

2011-01-01

238

Stable vector bundles and string theory  

SciTech Connect

In [4], Braun, He, Ovrut and Pantev proposed a model of string theory (based on the Calabi-Yau 3-fold X) whose low energy limit predicts certain properties of the Standard Model of particle Physics. This model depends on two vector bundles that have to be stable. We calculate the ample cone of X, and prove that one of them is stable, and the other one is not.

Gomez, Tomas L.; Sols, Ignacio [ICMAT (CSIC-UAM-UC3M-UCM), Serrano 113bis, 28006 Madrid (Spain); Facultad de Ciencias Matematicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Lukic, Sergio [Mathematics Department, Imperial College, London SW7 (United Kingdom)

2009-05-06

239

Aggressive Fibromatosis: Evidence for a Stable Phase  

PubMed Central

Purpose. Aggressive fibromatosis (AF) is an uncommon locally infiltrating benign disease of soft tissue for which treatment comprises complete surgical resection. Radiotherapy can be given postoperatively if the margin is incompletely resected. If the tumour is inoperable radiotherapy provides an alternative treatment. Hormone therapy and cytotoxic chemotherapy have also been used for unresectable or recurrent disease. All treatment modalities carry an associated morbidity. We believe that the natural history of aggressive fibromatosis may include a period of stable disease without progression, during which time, treatment is not always necessary. Patients and methods. We present a retrospective review of 42 patients referred to the Royal Marsden Hospital between 1988 and 1995 with aggressive fibromatosis. Evidence of periods of stable disease and the relationship to delivered treatment was obtained from the case notes, including the natural history prior to referral to our institution. Stable disease was defined as a period of no objective progression for 6 months or longer. Results. Seventeen patients could be assessed for stable disease and all (100%) experienced at least one episode of stable disease, eight of whom whilst receiving hormonal or cytotoxic therapy. Of the 23 patients who could not be assessed for stable disease, as they underwent surgery at presentation or recurrence of disease, only 2 had persisting disease at last follow-up. Both of these patients had had positive surgical resection margins. Discussion. This study demonstrates the variable natural history of AF, which can include a substantial period of stable disease in a significant number of patients. A less aggressive approach to the management of AF may therefore be appropriate, particularly if a subgroup of patients who are likely to experience a period of stable disease can be identified. PMID:18521247

Thomas, J. Meirion; Harmer, Clive L.

1998-01-01

240

A Tungsten Complex with a Bidentate, Hemilabile N-Heterocyclic Carbene Ligand, Facile Displacement of the Weakly Bound W-(C=C) Bond, and the Vulnerability of the NHC Ligand Towards Catalyst Deactivation During Ketone Hydrogenation  

SciTech Connect

The initial reaction observed between the N-heterocyclic carbene IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO){sub 2}(PPh{sub 3})H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMes)H]{sup +}[CpM(CO){sub 2}(PPh{sub 3})]{sup -}. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO){sub 2}(PR{sub 3})H (M = Mo, W; R = Me, Ph) produces CpM(CO){sub 2}(IMes)H. Hydride transfer from CpW(CO)2(IMes)H to Ph{sub 3}C{sub +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H{sub 2}, THF, ketones, or alcohols. Reaction of CpW(CO){sub 2}(IMes){sup +} with H{sub 2} gives the dihydride complex [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +}. Addition of Et{sub 2}CH-OH to CpW(CO){sub 2}(IMes){sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -} gives the alcohol complex [CpW(CO){sub 2}(IMes)(Et{sub 2}CH-OH)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H{sub 2} to the ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -} produces an equilibrium with the dihydride [CpW(CO){sub 2}(IMes)(H){sub 2}]{sup +} (K{sub eq} = 1.1 x 10{sup 3} at 25 {sup o}C). The tungsten ketone complex [CpW(CO){sub 2}(IMes)(Et{sub 2}C=O)]{sup +}[B(C{sub 6}F{sub 5}){sub 4}]{sup -}- serves as a modest catalyst for hydrogenation of Et{sub 2}C=O to Et{sub 2}CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]{sup +}B(C{sub 6}F{sub 5}){sub 4}{sup -}, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

Wu,F.; Dioumaev, V.; Szalda, D.; Hanson, J.; Bullock, R.

2007-01-01

241

Accelerator probes for new stable quarks  

E-print Network

The nonbaryonic dark matter of the Universe can consist of new stable double charged particles $O^{--}$, bound with primordial helium in heavy neutral O-helium (OHe)"atoms" by ordinary Coulomb interaction. O-helium dark atoms can play the role of specific nuclear interacting dark matter and provide solution for the puzzles of dark matter searches. The successful development of composite dark matter scenarios appeals to experimental search for the charged constituents of dark atoms. If $O^{--}$ is a "heavy quark cluster" $\\bar U \\bar U \\bar U$, its production at accelerators is virtually impossible and the strategy of heavy quark search is reduced to search for heavy stable hadrons, containing only single heavy quark (or antiquark). Estimates of production cross section of such particles at LHC are presented and the experimental signatures for new stable quarks are outlined.

Konstantin M. Belostky; Maxim Yu. Khlopov; Konstantin I. Shibaev

2011-11-15

242

Concentration of stable elements in food products  

SciTech Connect

Food samples were taken from commercial markets and analyzed for stable element content. The concentrations of most stable elements (Ag, Al, As, Au, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Cu, Fe, Hf, I, K, La, Mg, Mn, Mo, Na, Rb, Sb, Sc, Se, Sr, Ta, Th, Ti, V, Zn, Zr) were determined using multiple-element neutron activation analysis, while the concentrations of other elements (Cd, Hg, Ni, Pb) were determined using atomic absorption. The relevance of the concentrations found are noted in relation to other literature values. An earlier study was extended to include the determination of the concentration of stable elements in home-grown products in the vicinity of the Oak Ridge National Laboratory. Comparisons between the commercial and local food-stuff values are discussed.

Montford, M.A.; Shank, K.E.; Hendricks, C.; Oakes, T.W.

1980-01-01

243

High-Order Energy Stable WENO Schemes  

NASA Technical Reports Server (NTRS)

A new third-order Energy Stable Weighted Essentially NonOscillatory (ESWENO) finite difference scheme for scalar and vector linear hyperbolic equations with piecewise continuous initial conditions is developed. The new scheme is proven to be stable in the energy norm for both continuous and discontinuous solutions. In contrast to the existing high-resolution shock-capturing schemes, no assumption that the reconstruction should be total variation bounded (TVB) is explicitly required to prove stability of the new scheme. A rigorous truncation error analysis is presented showing that the accuracy of the 3rd-order ESWENO scheme is drastically improved if the tuning parameters of the weight functions satisfy certain criteria. Numerical results show that the new ESWENO scheme is stable and significantly outperforms the conventional third-order WENO finite difference scheme of Jiang and Shu in terms of accuracy, while providing essentially nonoscillatory solutions near strong discontinuities.

Yamaleev, Nail K.; Carpenter, Mark H.

2008-01-01

244

Stable Isotope Enrichment Capabilities at ORNL  

SciTech Connect

The Oak Ridge National Laboratory (ORNL) and the US Department of Energy Nuclear Physics Program have built a high-resolution Electromagnetic Isotope Separator (EMIS) as a prototype for reestablishing a US based enrichment capability for stable isotopes. ORNL has over 60 years of experience providing enriched stable isotopes and related technical services to the international accelerator target community, as well as medical, research, industrial, national security, and other communities. ORNL is investigating the combined use of electromagnetic and gas centrifuge isotope separation technologies to provide research quantities (milligram to several kilograms) of enriched stable isotopes. In preparation for implementing a larger scale production facility, a 10 mA high-resolution EMIS prototype has been built and tested. Initial testing of the device has simultaneously collected greater than 98% enriched samples of all the molybdenum isotopes from natural abundance feedstock.

Egle, Brian [ORNL; Aaron, W Scott [ORNL; Hart, Kevin J [ORNL

2013-01-01

245

Nonlinearly stable compact schemes for shock calculations  

NASA Technical Reports Server (NTRS)

The applications of high-order, compact finite difference methods in shock calculations are discussed. The main concern is to define a local mean which will serve as a reference for introducing a local nonlinear limiting to control spurious numerical oscillations while maintaining the formal accuracy of the scheme. For scalar conservation laws, the resulting schemes can be proven total-variation stable in one space dimension and maximum-norm stable in multiple space dimensions. Numerical examples are shown to verify accuracy and stability of such schemes for problems containing shocks. These ideas can also be applied to other implicit schemes such as the continuous Galerkin finite element methods.

Cockburn, Bernardo; Shu, Chi-Wang

1992-01-01

246

Development of thermally stable polymer concrete  

SciTech Connect

This work pertains to the development of a polymer concrete type that is thermally stable under working temperatures of 200{degree} to 300{degree}F. This material is highly durable and thermally stable with high flexural strength and ductility. Its consistency, while fresh, is suitable for both casting in place or precasting techniques. Several optimization stages were applied ranging from mixing ratios and type of aggregate to resin formulation itself. An optimized range of mixing ratios is developed along with optimized mix ingredients, relating mechanical performance to elevated temperature at various degrees of workability.

Megahed, T.N.E.D., Kukacka, L.E.; Fontana, J.J.

1989-10-01

247

Level Statistics of Stable and Radioactive Nuclei  

E-print Network

The spectral statistics of nuclei undergo through the major forms of radioactive decays ((\\alpha)(\\beta^-), and(\\beta^+) (or EC)) and also stable nuclei are investigated. With employing the MLE technique in the nearest neighbor spacing framework, the chaoticity parameters are estimated for sequences prepared by all the available empirical data. The ML-based estimated values propose a deviation to more regular dynamics in sequences constructed by stable nuclei in compare to unstable ones. In the same mass regions, nuclei transmitted through (\\alpha)decay explore less regularity in their spectra in compare to other radioactive nuclei.

M. A. Jafarizadeh; N. Fouladi; H. Sabri; B. Rashidian Maleki

2012-02-28

248

Clinically stable angina pectoris is not necessarily associated with histologically stable atherosclerotic plaques  

Microsoft Academic Search

OBJECTIVE: To investigate the extent of plaque inflammation in culprit lesions of patients with chronic stable angina. DESIGN: Retrospective study. SETTING: Amsterdam reference centre. SUBJECTS: 89 consecutive patients who underwent directional coronary atherectomy, 58 of whom met the following inclusion criteria: chronic stable angina (Canadian Cardiovascular Society classification 1-3 (group 1, n = 28)); unstable angina (Braunwald class II (group

A. C. van der Wal; A. E. Becker; K. T. Koch; J. J. Piek; P. Teeling; C. M. van der Loos; G. K. David

1996-01-01

249

GEOMETRY OF CHAOTIC AND STABLE DISCUSSIONS  

Microsoft Academic Search

Abstract: This paper addresses deliberations by discussing a branch of voting theory whereEuclidean geometry models an "issue space." When describing how it is possible to unintentionallymake inferior choices, we will encounter mathematical behaviors remarkablysimilar to "attractors" and "chaotic dynamics" from dynamical systems. Sincethe coexistence of chaotic and stable behavior is common in the Newtonian N -bodyproblem and dynamical systems, it

DONALD G. SAARI

2003-01-01

250

Conditional flux analysis and stable isotopes  

NASA Astrophysics Data System (ADS)

We propose to investigate to what extend conditional flux analysis can benefit from the addition of stable isotope information. Stable isotopes have been recognized for their potential as process tracer, and could add an extra dimension to the conditional flux concept, which aims at directly quantifying component fluxes and identifying their sources. Differences in 13C abundance in carbon dioxide can be used to distinguish assimilation or respiration sources, whereas the 18O abundance expresses differences in water exchange, for instance between canopy and soil. Lending to recent advances in measurement technology, stable isotopes can now be measured at high temporal resolutions (10Hz) required for commonly applied micrometeorological methods such as the eddy-covariance technique, or related conditional flux methods. We will present current ideas on how the conditional flux method, as recently proposed and evaluated by Thomas et al. (2008), Scanlon & Sahu (2008), to perform daytime flux partitioning at the ecosystem level, can be refined by stable isotope analysis (13C and 18O) of carbon dioxide as additional dimension for identification of fluxes.

Zeeman, M. J.; Knohl, A.; Sturm, P.; Buchmann, N. C.; Thomas, C. K.

2009-12-01

251

Stable marriage problems with quantitative preferences  

E-print Network

to women so that no man and woman, who are not married to each other, both prefer each other., woman) provides a score for each woman (resp., man). Such problems are more expressive than each man (resp., woman) provides a score for each woman (resp., man). Stable marriage problems

Walsh, Toby

252

Can Quality Certification Lead to Stable Cartels?  

Microsoft Academic Search

Cartel stability is investigated in a context of adverse selection whereconsumers are imperfectly informed about product quality. Producer collusionmay be necessary to signal quality via third-party certification. Whileexamining different cost structures for third-party certification, we showthat a stable cartel that provides information about product quality mayimprove overall welfare even if producers collude to reduce competition.

Stéphan Marette; John M. Crespi

2003-01-01

253

STABLE PLASMA JET FOR EXCITATION OF SOLUTIONS  

Microsoft Academic Search

A plasma jet, as adapted for the spectrochemical excitation of solutions ; and used with a photoelectric spectrometer to measure light intenslties, is ; described. Included is the design, construction, part specifications, operation, ; and performanoe of the stable plasma jot. The jet has a tungsten rod as an ; external, yet integral, cathodic electrode. The stabilized jet promises full

Louis E. Owen

1961-01-01

254

Alternative stable states and regional community structure  

Microsoft Academic Search

Many models of local species interactions predict the occurrence of priority effects due to alternative stable equilibria (ASE). However, few empirical examples of ASE have been shown. One possible explanation for the disparity is that local ASE are difficult to maintain regionally in patch dynamic models. Here we examine two possible mechanisms for regional coexistence of species engaged in local

Jonathan B. Shurina; Priyanga Amarasekare; Jonathan M. Chase; Robert D. Holt; Martha F. Hoopese; Mathew A. Leibold

255

SPOT multitemporal calibration over stable desert areas  

Microsoft Academic Search

SPOT absolute and multitemporal calibration is achieved using the on-board lamp plus regular checks over White Sands or other test sites which radiance is derived from ground measurements during the satellite overpass. In order to develop another independent method to monitor the long term evolution of the cameras sensitivity, systematic acquisitions of stable desert areas have been decided. The choice

Patrice J. Henry; Magdeleine C. Dinguirard; Madeleine Bodilis

1993-01-01

256

Substitution of stable isotopes in Chlorella  

NASA Technical Reports Server (NTRS)

Replacement of biologically important isotopes in the alga Chlorella by corresponding heavier stable isotopes produces increasingly greater deviations from the normal cell size and changes the quality and distribution of certain cellular components. The usefulness of isotopically altered organisms increases interest in the study of such permuted organisms.

Flaumenhaft, E.; Katz, J. J.; Uphaus, R. A.

1969-01-01

257

Rapid, stable fluid dynamics for computer graphics  

Microsoft Academic Search

We present a new method for animating water based on a simple, rapid and stable solution of a set of partial differential equations resulting from an approximation to the shallow water equations. The approximation gives rise to a version of the wave equation on a height-field where the wave velocity is proportional to the square root of the depth of

Michael Kass; Gavin S. P. Miller

1990-01-01

258

Of Prancing Horses and Bolted Stable Doors  

E-print Network

Of Prancing Horses and Bolted Stable Doors: Financial Crisis Recession and PolicyFinancial Crisis The evolution of economic thinking can be illustrated through the experience of successive generations: · Today's young adults "the return of depression economics" (2007??) · Their parents "the end of history" (1979

Kim, Tae-Kyun

259

First order and stable relativistic dissipative hydrodynamics  

E-print Network

Relativistic thermodynamics is derived from kinetic equilibrium in a general frame. Based on a novel interpretation of Lagrange multipliers in the equilibrium state we obtain a generic stable but first order relativistic dissipative hydrodynamics. Although this was believed to be impossible, we circumvent this difficulty by a specific handling of the heat flow.

P. Ván; T. S. Biró

2011-09-05

260

Stable Continental Region Earthquakes in South China  

Microsoft Academic Search

This paper reviews some remarkable characteristics of earthquakes in a Stable Continental Region (SCR) of the South China Block (SCB). The kernel of the SCB is the Yangtze platform solidified in late Proterozoic time, with continental growth to the southeast by a series of fold belts in Paleozoic time. The facts that the deviatoric stress is low, the orientations of

L. Liu

2001-01-01

261

Dynamically stable magnetic suspension/bearing system  

DOEpatents

A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw's Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements.

Post, Richard F. (Walnut Creek, CA)

1996-01-01

262

Dynamically stable magnetic suspension/bearing system  

DOEpatents

A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw`s Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements. 32 figs.

Post, R.F.

1996-02-27

263

PERTURBATION OF A GLOBALLY STABLE STEADY STATE  

Microsoft Academic Search

It is shown that within a parameterized family of semi-dynamical systems enjoying a mild uniform dissipative condition, the property that a locally asymptotically stable steady state is globally attracting is an open condition in the parameters. The ultimate goal in the analysis of most dynamical systems arising in applica- tions is to determine the asymptotic behavior of its solutions. In

H. L. SMITH; P. WALTMAN

264

Are two modes of thermohaline circulation stable?  

Microsoft Academic Search

The standard version of the coupled ocean atmosphere model developed at the Geophysical Fluid Dynamics Laboratory (GFDL) of NOAA has at least two stable equilibria. One has a realistic and active thermohaline circulation (THC) with sinking regions in the northern North Atlantic Ocean. The other has a reverse THC with extremely weak upwelling in the North Atlantic and sinking in

Syukuro Manabe; Ronald J. Stouffer

1999-01-01

265

High Temperature and Alkaline Stable Catalase.  

National Technical Information Service (NTIS)

The invention relates to thermal and pH stable catalases. One catalase of the invention was purified and characterized from Thermus brockianus. As a part of the characterization, the enzyme was compared to typical catalases from commercial sources and fou...

K. D. Schaller, V. Thompson, W. A. Apel

2004-01-01

266

Evolutionarily stable strategies in quantum games  

Microsoft Academic Search

Evolutionarily stable strategy (ESS) in classical game theory is a refinement of Nash equilibrium concept. We investigate the consequences when a small group of mutants using quantum strategies try to invade a classical ESS in a population engaged in symmetric bimatrix game of prisoner's dilemma. Secondly we show that in an asymmetric quantum game between two players an ESS pair

A. Iqbal; A. H. Toor

2001-01-01

267

Sugar feeding in adult stable flies.  

PubMed

Adult stable flies (Stomoxys calcitrans L.) are known to feed readily on sugars in the laboratory. However, little is known concerning the extent of stable fly sugar feeding in wild populations. We examined the frequency of sugar feeding in stable flies collected on Alsynite sticky traps in rural and urban environments. In addition, stable flies were visually examined to determine whether blood was present in the gut. In laboratory studies, sugars were detectable with the anthrone technique in stable flies for approximately 3 d after being imbibed, and blood could be visually detected in the gut for 24-48 h after feeding. Twelve percent of the field-collected flies had detectable sugar with a higher percentage of the urban flies having sugar fed than the rural flies, 21 and 8%, respectively. Female flies sugar fed at a slightly higher rate than males, 13 versus 11%, respectively. Less than 1% of the field-collected flies had blood in their guts. The frequency of observable blood was slightly higher in flies collected in an urban environment compared with those collected in a rural environment and did not differ between male and female flies. The number of flies with both blood and sugar was slightly higher than would be expected based on the frequencies of each alone. Seasonal patterns of both sugar feeding and blood feeding were similar in the rural and urban environments; both peaked in the early summer, May to mid-June, and dropped through the summer and fall. Sugar feeding in the urban environment increased again in October. PMID:18559167

Taylor, David B; Berkebile, Dennis R

2008-06-01

268

Directional properties of fluorenylidene moieties in unsymmetrically substituted N-heterocyclic carbenes. Unexpected CH activation of a methylfluorenyl group with palladium. Use in palladium catalysed Suzuki-Miyaura cross coupling of aryl chlorides.  

PubMed

Benzimidazolium salts having their two nitrogen atoms substituted by different 9-alkylfluorenyl groups ( and , alkyl(1)/alkyl(2) = Me/Et, Me/Pr, Me/n-Bu, Me/i-Pr, Me/Bn, Me/CH2SMe have been synthesised in high yields in two or three steps from N,N'-bis(9H-fluoren-9-ylidene)benzene-1,2-diamine (). The imidazolium salts were converted readily into the corresponding PEPPSI-type palladium complexes (PEPPSI = pyridine-enhanced precatalyst preparation stabilisation and initiation), while reaction of the methylthioether-substituted salt with PdCl2/K2CO3/pyridine afforded the palladacycle resulting from metallation of the methyl group attached to the fluorenylidene moiety. NMR and X-ray diffraction studies revealed that the carbene ligands in behave as clamp-like ligands, the resulting metal confinement arising from a combination of the orientational properties of the fluorenylidene moieties that push the alkyl groups towards the metal centre and attractive anagostic interactions involving CH2(fluorenyl) groups. Complexes were assessed in Suzuki-Miyaura cross-coupling reactions. Like their symmetrical analogues they displayed high activity in the coupling of phenyl boronic acid with p-tolylchloride but their performance remained slightly inferior to that of the related, symmetrical Et/Et complex . PMID:24927082

Teci, Matthieu; Brenner, Eric; Matt, Dominique; Gourlaouen, Christophe; Toupet, Loïc

2014-08-28

269

C(sp3)-H activation without a directing group: regioselective synthesis of N-ylide or N-heterocyclic carbene complexes controlled by the choice of metal and ligand.  

PubMed

N-Ylide complexes of Ir have been generated by C(sp(3))-H activation of ?-pyridinium or ?-imidazolium esters in reactions with [Cp*IrCl2]2 and NaOAc. These reactions are rare examples of C(sp(3))-H activation without a covalent directing group, which-even more unusually-occur ? to a carbonyl group. For the reaction of the ?-imidazolium ester [3H]Cl, the site selectivity of C-H activation could be controlled by the choice of metal and ligand: with [Cp*IrCl2]2 and NaOAc, C(sp(3))-H activation gave the N-ylide complex 4; in contrast, with Ag2O followed by [Cp*IrCl2]2, C(sp(2))-H activation gave the N-heterocyclic carbene complex 5. DFT calculations revealed that the N-ylide complex 4 was the kinetic product of an ambiphilic C-H activation. Examination of the computed transition state for the reaction to give 4 indicated that unlike in related reactions, the acetate ligand appears to play the dominant role in C-H bond cleavage. PMID:25164979

Cross, Warren B; Razak, Sunnah; Singh, Kuldip; Warner, Andrew J

2014-10-01

270

Arithmetic Brownian motion subordinated by tempered stable and inverse tempered stable processes  

NASA Astrophysics Data System (ADS)

In the last decade the subordinated processes have become popular and have found many practical applications. Therefore in this paper we examine two processes related to time-changed (subordinated) classical Brownian motion with drift (called arithmetic Brownian motion). The first one, so called normal tempered stable, is related to the tempered stable subordinator, while the second one-to the inverse tempered stable process. We compare the main properties (such as probability density functions, Laplace transforms, ensemble averaged mean squared displacements) of such two subordinated processes and propose the parameters’ estimation procedures. Moreover we calibrate the analyzed systems to real data related to indoor air quality.

Wy?oma?ska, Agnieszka

2012-11-01

271

ORIGINAL PAPER North American transect of stable hydrogen and oxygen  

E-print Network

application of d18 O and dD in palaeoclimatology, including the stable isotope analysis of various compoundsORIGINAL PAPER North American transect of stable hydrogen and oxygen isotopes in water beetles from. Chitinous remains of insects such as beetles (Coleoptera) are chemically stable and their stable isotope

Bern, Universität

272

Sourcing drugs with stable isotopes James R. Ehleringer  

E-print Network

and trafficking information. These stable isotope ratio measurements are conducted on an isotope ratioing massSourcing drugs with stable isotopes James R. Ehleringer Stable Isotope Ratio Facility@erols.com Michael J. Lott Stable Isotope Ratio Facility for Environmental Research (SIRFER) Department of Biology

Ehleringer, Jim

273

Stable, free-standing Ge nanocrystals  

SciTech Connect

Free-standing Ge nanocrystals that are stable under ambient conditions have been synthesized in a two-step process. First, nanocrystals with a mean diameter of 5 nm are grown in amorphous SiO{sub 2} by ion implantation followed by thermal annealing. The oxide matrix is then removed by selective etching in diluted HF to obtain free-standing nanocrystals on a Si wafer. After etching, nanocrystals are retained on the surface and the size distribution is not significantly altered. Free-standing nanocrystals are stable under ambient atmospheric conditions, suggesting formation of a self-limiting native oxide layer. For free-standing as opposed to embedded Ge nanocrystals, an additional amorphous-like contribution to the Raman spectrum is observed and is assigned to surface reconstruction-induced disordering of near-surface atoms.

Sharp, I.D.; Xu, Q.; Liao, C.Y.; Yi, D.O.; Beeman, J.W.; Liliental-Weber, Z.; Yu, K.M.; Zakharov, D.N.; Ager III, J.W.; Chrzan,D.C.; Haller, E.E.

2005-01-28

274

Stable chaos in fluctuation driven neural circuits  

E-print Network

We study the dynamical stability of pulse coupled networks of leaky integrate-and-fire neurons against infinitesimal and finite perturbations. In particular, we compare current versus fluctuations driven networks, the former (latter) is realized by considering purely excitatory (inhibitory) sparse neural circuits. In the excitatory case the instabilities of the system can be completely captured by an usual linear stability (Lyapunov) analysis, on the other hand the inhibitory networks can display the coexistence of linear and nonlinear instabilities. The nonlinear effects are associated to finite amplitude instabilities, which have been characterized in terms of suitable indicators. For inhibitory coupling one observes a transition from chaotic to non chaotic dynamics by decreasing the pulse width. For sufficiently fast synapses the system, despite showing an erratic evolution, is linearly stable, thus representing a prototypical example of Stable Chaos.

David Angulo-Garcia; Alessandro Torcini

2014-03-03

275

Unexpected Stable Stoichiometries of Sodium Chlorides  

NASA Astrophysics Data System (ADS)

Sodium chloride (NaCl), or rocksalt, is well characterized at ambient pressure. As a result of the large electronegativity difference between Na and Cl atoms, it has highly ionic chemical bonding (with 1:1 stoichiometry dictated by charge balance) and B1-type crystal structure. By combining theoretical predictions and diamond anvil cell experiments, we found that new materials with different stoichiometries emerge at high pressures. Compounds such as Na3Cl, Na2Cl, Na3Cl2, NaCl3, and NaCl7 are theoretically stable and have unusual bonding and electronic properties. To test this prediction, we synthesized cubic and orthorhombic NaCl3 and two-dimensional metallic tetragonal Na3Cl. These experiments establish that compounds violating chemical intuition can be thermodynamically stable even in simple systems at nonambient conditions.

Zhang, Weiwei; Oganov, Artem R.; Goncharov, Alexander F.; Zhu, Qiang; Boulfelfel, Salah Eddine; Lyakhov, Andriy O.; Stavrou, Elissaios; Somayazulu, Maddury; Prakapenka, Vitali B.; Konôpková, Zuzana

2013-12-01

276

Stable magnetic fields in stellar interiors  

NASA Astrophysics Data System (ADS)

We investigate the 50-year old hypothesis that the magnetic fields of the Ap stars are stable equilibria that have survived in these stars since their formation. With numerical simulations we find that stable magnetic field configurations indeed appear to exist under the conditions in the radiative interior of a star. Confirming a hypothesis by Prendergast (1956, ApJ, 123, 498), the configurations have roughly equal poloidal and toroidal field strengths. We find that tori of such twisted fields can form as remnants of the decay of an unstable random initial field. In agreement with observations, the appearance at the surface is an approximate dipole with smaller contributions from higher multipoles, and the surface field strength can increase with the age of the star. The results of this paper were summarised by Braithwaite & Spruit (2004, Nature, 431, 891).

Braithwaite, J.; Nordlund, Å.

2006-05-01

277

Overview and first results from project STABLE (STAble Boundary Layer Experiment)  

SciTech Connect

The STABLE project (STAble Boundary Layer Experiment) is a multiyear research effort conceived in 1984 by the Savannah River Laboratory (SRL) and planned by several research groups to study turbulence and diffusion in the stable boundary layer (SBL). The program was jointly planned by Department of Energy (DOE) affiliated laboratories and universities including SRL, Atmospheric Turbulence and Diffusion Division (ATDD) of the National Oceanic and Atmospheric Administration (NOAA), Argonne National Laboratory (ANL), North Carolina State University (NCSU), and The Pennsylvania State University. STABLE's goals are to determine the spatial and temporal distribution of turbulent events during the nighttime, to determine the validity of present models and theories in describing the structure and evolution of the SBL, to determine the role of waves and intermittent turbulence in dispersing chemicals, and to determine better parameterization for describing the mean state and intermittent events in the SBL. By taking advantage of special facility, the program seeks to economize effort and cost. 1 ref., 7 figs.

Weber, A.H.; Kurzeja, R.J.

1988-01-01

278

Thermally Stable and Flame Retardant Elastomeric Nanocomposites  

Microsoft Academic Search

\\u000a This chapter is dedicated to thermally stable and flame retardant elastomeric composites. Two approaches are considered: the\\u000a synthesis of elastomeric nanocomposites, where the nanoparticles are dispersed at the nanoscale, and the incorporation of\\u000a nanofillers at high loadings where agglomerate of nanoparticles are observed in the elastomeric matrix. The chapter is mainly\\u000a focused on the key parameter influencing the flame retardancy,

O. Cerin; G. Fontaine; S. Duquesne; S. Bourbigot

279

Stable localized patterns in thin liquid films  

NASA Technical Reports Server (NTRS)

We study a 2-D nonlinear evolution equation which describes the 3-D spatiotemporal behavior of the air-liquid interface of a thin liquid film lying on the underside of a cooled horizontal plate. We show that the Marangoni effect can stabilize the destabilizing effect of gravity (the Rayleigh-Taylor instability) allowing for the existence of stable localized axisymmetric solutions for a wide range of parameter values. Various properties of these structures are discussed.

Deissler, Robert J.; Oron, Alexander

1991-01-01

280

Uncertainty in source partitioning using stable isotopes  

Microsoft Academic Search

Stable isotope analyses are often used to quan- tify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, or C3 and C4 plant inputs to soil organic carbon. Linear mixing models can be used to partition two sources with a single isotopic signature (e.g., ?13C) or three sources with a second

Donald L. Phillips; Jillian W. Gregg

2001-01-01

281

Multiplicity of stable states in freshwater systems  

Microsoft Academic Search

It is shown with the use of minimal models that several ecological relationships in freshwater systems potentially give rise\\u000a to the existence of alternative equilibria over a certain range of nutrient values. The existence of alternative stable states\\u000a has some implications for the management of such systems. An important consequence is that signs of eutrophication are only\\u000a apparent after the

Marten Scheffer

1990-01-01

282

More on Meta-Stable Brane Configuration  

E-print Network

We describe the intersecting brane configuration of type IIA string theory corresponding to the meta-stable nonsupersymmetric vacua in four dimensional N=1 supersymmetric SU(N_c) gauge theory with an antisymmetric flavor, a conjugate symmetric flavor, eight fundamental flavors, m_f fundamental flavors and m_f antifundamental flavors. This is done by analyzing the N=1 supersymmetric SU(2m_f-N_c+4) magnetic gauge theory with dual matters and the corresponding dual superpotential.

Changhyun Ahn

2007-02-06

283

Stable Spheromaks Sustained by Neutral Beam Injection  

SciTech Connect

It is shown that spheromak equilibria, stable at zero-beta but departing from the Taylor state, could be sustained by non-inductive current drive at acceptable power levels. Stability to both ideal MHD and tearing modes is verified using the NIMROD code for linear stability analysis. Non-linear NIMROD calculations with non-inductive current drive and pressure effects could point the way to improved fusion reactors.

Fowler, T K; Jayakumar, R; McLean, H S

2008-05-14

284

Stable Isotopes in Dendroclimatology: Moving Beyond ‘Potential’  

Microsoft Academic Search

\\u000a When trees grow, they assimilate carbon from atmospheric carbon dioxide, and hydrogen and oxygen from soil water. The stable\\u000a isotope ratios of these three elements carry signals that can be interpreted in terms of past climate because isotope ratios\\u000a are climatically controlled by the tree’s water and gas exchange budgets. The traditional tree-ring proxies form the most\\u000a widespread and arguably

Mary Gagen; Danny McCarroll; Neil J. Loader; Iain Robertson

285

Detonation of Meta-stable Clusters  

SciTech Connect

We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

2008-05-31

286

Charge Radii of beta-Stable Nuclei  

E-print Network

In previous work it was shown that the radius of nucleus R is determined by the alpha-cluster structure and can be estimated on the number of alpha-clusters disregarding to the number of excess neutrons. A hypothesis also was made that the radius R_m of a beta-stable isotope, which is actually measured at electron scattering experiments, is determined by the volume occupied by the matter of the core plus the volume occupied by the peripheral alpha-clusters. In this paper it is shown that the condition R_m = R restricts the number of excess neutrons filling the core to provide the beta-stability. The number of peripheral clusters can vary from 1 to 5 and the value of R for heavy nuclei almost do not change, whereas the number of excess neutrons should change with the number of peripheral clusters to get the value of R_m close to R. It can explain the path of the beta-stability and its width. The radii R_m of the stable isotopes with 12 =< Z =< 83 and the alpha-decay isotopes with 84 =< Z =< 116 that are stable to beta-decay have been calculated.

G. K. Nie

2005-12-07

287

Stable magnetic field configurations in stars  

NASA Astrophysics Data System (ADS)

Long-lived, large-scale magnetic field configurations with similar total fluxes exist in at least three very different, although related kind of stars: upper main sequence stars, white dwarfs, and neutron stars (e.g. Reisenegger 2001). Much or all of the volume of these stars is stably stratified, so there is no convection that could maintain these fields through dynamo processes (except in the cores of upper main sequence stars). Magnetohydrodynamic simulations of stably stratified stars (Braithwaite & Spruit 2004, 2006; Braithwaite & Nordlund 2006) suggest that configurations with linked poloidal and toroidal fields get spontaneously established and might be stable over long times. Physical arguments show that such configurations are in fact natural and that the stable stratification is likely to play a crucial role in their stability. Thus, contrary to assumptions in recent papers, the field is not force-free, and the fluid cannot be taken to be barotropic. Work is in progress to represent these fields analytically and investigate the conditions for their stability. In the case of neutron stars with strong enough fields, the stable stratification can be overcome by long-term, dissipative processes such as beta decays and ambipolar diffusion (Goldreich & Reisenegger 1992; Reisenegger et al. 2005), leading to the release of magnetic energy and potentially explaining the energy source for the "magnetar" phenomenon (Thompson & Duncan 1993, 1996).

Reisenegger, Andreas; Munoz, Francisco; Santos, Raul

288

Stable isotopic analyses in paleoclimatic reconstruction  

SciTech Connect

Most traditional paleoclimatic proxy data have inherent time lags between climatic input and system response that constrain their use in accurate reconstruction of paleoclimate chronology, scaling of its variability, and the elucidation of the processes that determine its impact on the biotic and abiotic environment. With the exception of dendroclimatology, and studies of short-lived organisms and pollen recovered from annually varved lacustrine sediments, significant periods of time ranging from years, to centuries, to millennia may intervene between climate change and its first manifestation in paleoclimatic proxy data records. Reconstruction of past climate through changes in plant community composition derived from pollen sequences and plant remains from ancient woodrat middens, wet environments and dry caves all suffer from these lags. However, stable isotopic analyses can provide more immediate indication of biotic response to climate change. Evidence of past physiological response of organisms to changes in effective precipitation as climate varies can be provided by analyses of the stable isotopic content of plant macrofossils from various contexts. These analyses consider variation in the stable isotopic (hydrogen, oxygen and carbon) content of plant tissues as it reflects (1) past global or local temperature through changes in meteoric (rainfall) water chemistry in the case of the first two isotopes, and (2) plant stress through changes in plant respiration/transpiration processes under differing water availability, and varying atmospheric CO, composition (which itself may actually be a net result of biotic response to climate change). Studies currently being conducted in the Intermountain West indicate both long- and short-term responses that when calibrated with modem analogue studies have the potential of revealing not only the timing of climate events, but their direction, magnitude and rapidity.

Wigand, P.E. [Univ. and Community College System of Nevada, Reno, NV (United States)

1995-09-01

289

Isotropic turbulence, stable layers: facts or fictions?  

NASA Astrophysics Data System (ADS)

Using state of the art drop sonde data (from 237 sondes over the Pacific) we examine two classical and fundamental idealizations of atmospheric science showing that they are untenable in the light of the vertical structure. The first is the notion of stable atmospheric layers. This is used for understanding atmospheric dynamics and thermodynamics, including the most advanced dynamical meteorological notions such as potential vorticity. Using the drop sonde data, we show that each apparently stable layer is actually composed of a hierarchy of unstable layers themselves with embedded stable sublayers, each with unstable sub-sub layers etc. i.e. in a Russian doll-like fractal hierarchy whose dimension we estimate. We therefore argue that the notion is untenable and must be replaced by modern scaling notions. The second idealization we examine is the turbulence assumption of isotropy. If we include intermittency, Kolmorogov's landmark proposal that fully developed turbulence has an "inertial subrange" with isotropic energy spectrum E(k)=k**-beta with beta=5/3 has apparently been spectacularly confirmed in both the horizontal direction and in the time domain (k is a wavenumber). For gradients over a horizontal distance deltax this implies deltav=deltaz**Hh (Hh=1/3 corresponds to beta=5/3). Remarkably, Hv for gradients over vertical distances deltaz (deltav=deltaz**Hv) has not been seriously investigated. Using drop sonde data of horizontal wind, we find that from scales of 5 m to 10 km from the surface layer through to the top of the troposphere, Hv is close to (or larger) than the Bolgiano-Obukhov value 3/5. Hv greater than Hh implies that a) the atmosphere becomes progressively less stratified at smaller scales although in a scaling way; b) that at most a single (roughly) isotropic "sphero- scale" exists (often in the range 1-100 cm).

Lovejoy, S.; Tuck, A.; Hovde, S.; Schertzer, D.

2007-05-01

290

Stable parallel elimination for boundary valve ODEs  

SciTech Connect

A parallelizable and vectorizable algorithm for solving linear algebraic systems arising from two-point boundary value ODEs is described. The method is equivalent to Gaussian elimination, with row partial pivoting, applied to a certain row- and column-reordered version of the usual almost block-diagonal coefficient matrix. Analytical and numerical evidence is presented to show that the algorithm is stable. Results from implementation on a shared-memory multiprocessor and a vector processor are given. The approach can be extended to handle problems with multipoint and integral conditions or algebraic parameters.

Wright, S.J.

1991-04-01

291

Stable Elliptical Vortices in a Cylindrical Geometry  

Microsoft Academic Search

We show that, in a two-dimensional (2d) ideal fluid (also applies to a column\\u000aof quasi-2d non-neutral plasma in an axial magnetic field), large elliptical\\u000avortices in a finite disk are stable. The stability is established by\\u000acomparison between energy of elliptical and symmetrical states to satisfy a\\u000asufficient condition, without dynamical eigen-analysis. Analytical small\\u000aellipticity expansion of energy and

Peilong Chen

1998-01-01

292

Stable metallization for diamond and other materials  

NASA Technical Reports Server (NTRS)

An adherent and metallurgically stable metallization system for diamond is presented. The big improvement in metallurgical stability is attributed to the use of a ternary, amorphous Ti--Si--N diffusion barrier. No diffusion between the layers and no delamination of the metallization was observed after annealing the schemes at 400.degree. C. for 100 hours and at 900.degree. C. for 30 minutes. Thermal cycling experiments in air from -65 to 155.degree. C. and adhesion tests were performed. Various embodiments are disclosed.

Bachli, Andreas (Inventor); Kolawa, Elzbieta (Inventor); Nicolet, Marc-Aurele (Inventor); Vandersande, Jan W. (Inventor)

2000-01-01

293

Rapid mixing renders quantum dissipative systems stable  

E-print Network

The physics of many materials is modeled by quantum many-body systems with local interactions. If the model of the system is sensitive to noise from the environment, or small perturbations to the original interactions, it will not model properly the robustness of the real physical system it aims to describe, or be useful when engineering novel systems for quantum information processing. We show that local observables and correlation functions of local Liouvillians are stable to local perturbations if the dynamics is rapidly mixing and has a unique fixed point. No other condition is required.

Angelo Lucia; Toby S. Cubitt; Spyridon Michalakis; David Pérez-García

2014-09-27

294

Color stable manganese-doped phosphors  

DOEpatents

A process for preparing color stable Mn.sup.+4 doped phosphors includes providing a phosphor of formula I; A.sub.x[MF.sub.y]:Mn.sup.+4 I and contacting the phosphor in particulate form with a saturated solution of a composition of formula II in aqueous hydrofluoric acid; A.sub.x[MF.sub.y]; II wherein A is Li, Na, K, Rb, Cs, NR.sub.4 or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; R is H, lower alkyl, or a combination thereof; x is the absolute value of the charge of the [MF.sub.y] ion; and y is 5, 6 or 7. In particular embodiments, M is Si, Ge, Sn, Ti, Zr, or a combination thereof. A lighting apparatus capable of emitting white light includes a semiconductor light source; and a phosphor composition radiationally coupled to the light source, and which includes a color stable Mn.sup.+4 doped phosphor.

Lyons, Robert Joseph (Burnt Hills, NY); Setlur, Anant Achyut (Niskayuna, NY); Deshpande, Anirudha Rajendra (Twinsburg, OH); Grigorov, Ljudmil Slavchev (Sofia, BG)

2012-08-28

295

Hygrothermally stable laminated composites with optimal coupling  

NASA Astrophysics Data System (ADS)

This work begins by establishing the necessary and sufficient conditions for hygrothermal stability of composite laminates. An investigation is performed into the range of coupling achievable from within all hygrothermally stable families. The minimum number of plies required to create an asymmetric hygrothermally stable stacking sequence is found to be five. Next, a rigorous and general approach for determining designs corresponding to optimal levels of coupling is established through the use of a constrained optimization procedure. Couplings investigated include extension-twist, bend-twist, extension-bend, shear-twist, and anticlastic. For extension-twist and bend-twist coupling, specimens from five- through ten-ply laminates are manufactured and tested to demonstrate hygrothermal stability and achievable levels of coupling. Nonlinear models and finite element analysis are developed, and predictions are verified through comparison with test results. Sensitivity analyses are performed to demonstrate the robustness of the hygrothermal stability and couplings to deviations in ply angle, typical of manufacturing tolerances. Comparisons are made with current state-of-the-art suboptimal layups, and significant increases in coupling over previously known levels are demonstrated.

Haynes, Robert Andrew

296

Verification of a Dimensionally Stable Space Structure  

NASA Astrophysics Data System (ADS)

In a parallel paper of IAF97 congress, the development of a dimensionally very stable carbon/carbon telescope is presented. The present paper focuses on the verification of this structure. In order to check the stability of the telescope, the following performances were assessed: — mechanical resonance frequencies and damping, — dimensional stability after a series of thermal cycles, — gravity load deformation, — elastic deformation under static stresses simulating launch loads, — residual deformation after launch loading, — thermal expansion under uniform heating, — deformation under nonuniform heating, — stability with time under stress. The total deformations which were expected in the worse case for this long structure (565 mm were very small: defocus <1.5 ?m; decentre < a few ?m; tilt <10 ?rad. All the independent contributors to the total deformation were of course smaller and had to be assessed. The requests for accuracy of the measurement techniques were then very high. Several techniques were used in this verification, the most interesting of which were: — evaluation of geometrical stability by comparison with a Zerodur reference structure equipped with capacitive sensors, — vacuum interferometry with a very stable differential interferometer, — holographic interferometry. The measurement problems are discussed and the main results are summarised.

Kornmann, M.; Genet, M.; Jacquot, P.; Spalinger, E.; Bailly, B.; Pradier, A.

297

Stable isotope enrichment using a plasma centrifuge  

NASA Astrophysics Data System (ADS)

A primary goal of the Department of Energy's Isotope Development and Production for Research and Applications Program (Isotope Program) within the Office of Nuclear Physics (NP) is to produce isotopes that are in short supply in the U.S. and of which there exists no or insufficient domestic commercial production capability. A vacuum arc plasma centrifuge is a rigid rotor column of metal plasma in which centrifugal forces re-distribute ions radially according to their mass/charge ratio. Early work demonstrated rotation at 2 million rpm and separation of various stable isotopes. The spinning plasma column had a Gaussian flux profile, peaked on the rigid rotor axis. This work adopts a more efficient approach, with the plasma created as a hollow column, wherein the flux is concentrated at larger radii where the centrifugal action is highest. By tailoring the vacuum arc discharge geometry, the rotation rate can also be increased to ˜10 million rpm. Data from Cu, Al and other metal plasmas will be presented and discussed in light of enriched stable isotopes needed for research and medicine.

Krishnan, Mahadevan; Bures, Brian; Madden, Robert

2012-10-01

298

VIEW OF STABLE, SLAUGHTERHOUSE, AND STORE (THE TWOSTORY BRICK BUILDING ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

VIEW OF STABLE, SLAUGHTERHOUSE, AND STORE (THE TWO-STORY BRICK BUILDING BEYOND THE STABLE), LOOKING NORTH (See also WINDBER, TOWN OF, HAER No. PA-322) - Town of Eureka No. 42, Northeast of Windber, Windber, Somerset County, PA

299

Stable strontium isotope fractionation in synthetic barite  

NASA Astrophysics Data System (ADS)

The mineral barite (BaSO4) accommodates strontium (Sr) in its crystal structure, providing an archive of Sr-isotopes (87Sr/86Sr and ?88/86Sr) in the highly stable sulfate mineral. We investigated mass dependent stable Sr-isotope fractionation (?88/86Sr = ?88/86Srsolid - ?88/86Srsolution) during inorganic precipitation of barite from a barium-rich solution by addition of sulfate under controlled conditions and compared this to equilibrium isotopic fractionation calculated using Density Functional Theory modeling. Sr-substituted barite is predicted to have lower 88Sr/86Sr than any other studied species, and at 25 °C will be about 0.6-0.7‰ lower than the two modeled Sr(H2O)82+-bearing salts that could approximate aqueous Sr2+. This agrees in direction and order of magnitude with experimental results that estimate equilibrium Sr-isotope fractionation in barite to be 0.3‰ lower than aqueous Sr2+ at ?20 °C. The high ionic strength of some of the precipitating solutions (up to 1 M) and potential differences in the average coordination number of aqueous Sr2+ add to uncertainty in a direct comparison of the calculated equilibrium isotopic fractionation values with the experimental results. Stable Sr-isotope fractionation varied along with the distribution coefficient of Sr [Kd(Sr) = [Sr/Ba]barite/[Sr/Ba]solution], which is a function of both temperature and barite saturation state. However the relationship between mass dependent isotopic fractionation and Kd(Sr) is different for conditions of changing temperature versus barite saturation state. With increasing temperature (from 5 to 40 °C), the barite phase became isotopically lighter (?88/86Sr = -0.29‰ to -0.41‰). Conversely, with increasing saturation state (saturation index of barite = 3.0-4.3) the barite phase became isotopically heavier (?88/86Sr = -0.25‰ to -0.10‰). These observations suggest chemical kinetic effects control isotopic fractionation rather than equilibrium temperature effects. The relationship with saturation state indicates the potential presence of a diffusive boundary layer. Barite crystal morphology appears to be affected by the diffusion rate of solute (sulfate) to the growing crystal surface relative to the overall growth rate of barite crystals during precipitation.

Widanagamage, Inoka H.; Schauble, Edwin A.; Scher, Howie D.; Griffith, Elizabeth M.

2014-12-01

300

Isotropic turbulence, stable layers: atmospheric fictions  

NASA Astrophysics Data System (ADS)

Using state of the art drop sonde data (from 237 sondes over the Pacific) we examine two classical and fundamental idealizations of atmospheric science showing that they are untenable in the light of the vertical structure. The first is the notion of stable atmospheric layers. This is used for understanding atmospheric dynamics and thermodynamics, including notions such as potential vorticity. Using the drop sonde data, we show that each apparently stable layer is actually composed of a hierarchy of unstable layers themselves with embedded stable sublayers, each with unstable sub-sub layers etc. i.e. in a Russian doll-like fractal hierarchy whose dimension we estimate. We therefore argue that the notion is untenable and must be replaced by modern scaling notions. Although the same basic conclusion follows for conditional, dynamical and convective stability, we showed that their correlation exponent (quantifying their sparsenesses) were 0.36±0.056, 0.22±0.037, 0.15±0.016 respectively. The second idealization we examine is the turbulence assumption of isotropy. If we include intermittency, Kolmorogov's landmark proposal that fully developed turbulence has an "inertial subrange" with isotropic energy spectrum E(k) ? k**-? with ??5/3 has apparently been spectacularly confirmed in both the horizontal direction and in the time domain (k is a wavenumber). For gradients over a horizontal distance ?x this implies ?v??z**Hh (Hh=1/3 corresponds to ?=5/3; "<.>" indicates ensemble averaging). Remarkably, Hv for gradients over vertical distances ?z (?v??z**Hv) has not been seriously investigated. Using drop sonde data of horizontal wind, we find that from scales of 5 m to >10 km from the surface layer through to the top of the troposphere, Hv is close to (or larger) than the Bolgiano-Obukhov value 3/5. Hv>Hh implies that a) the atmosphere becomes progressively less stratified at smaller scales although in a scaling way; b) that at most a single (roughly) isotropic "sphero-scale" exists (often in the range 1- 100 cm).

Lovejoy, S.; Tuck, A.; Hovde, S.; Schertzer, D.

2007-12-01

301

Quantifying intrapopulation variability in stable isotope data for Spotted Seatrout  

E-print Network

stable isotope (SI) analysis, have been widely ap- plied to fish populations as a method111 Quantifying intrapopulation variability in stable isotope data for Spotted Seatrout (Cynoscion of the National Marine Fisheries Service, NOAA. Abstract--Stable isotope (SI) values of carbon (13C) and nitrogen

302

Assessing Transformation Processes of Organic Compounds Using Stable  

E-print Network

A S C O N I Swiss Federal Institute of Technology (ETH) Zurich Compound-specific stable isotope analysis signatures Compound-specific stable isotope analysis (CSIA) at natural abundance isotope levels opens newAssessing Transformation Processes of Organic Compounds Using Stable Isotope Fractionation T H O M

Gilli, Adrian

303

Stable Isotopes Confirm Community Patterns in Foraging Among Hawaiian Procellariiformes  

E-print Network

, Ontario, K7L 3N6, Canada *Corresponding author; E-mail: mgreg@sun.ac.za Abstract.--Stable-isotope analysis was to compare community foraging patterns as determined by stable-isotope analysis with tradi- tional studies50 Stable Isotopes Confirm Community Patterns in Foraging Among Hawaiian Procellariiformes

Jones, Ian L.

304

SINCERE STABLE TUBES I. REITEN AND A. SKOWRO '  

E-print Network

SINCERE STABLE TUBES I. REITEN AND A. SKOWRO ' NSKI Introduction The purpose of this paper with an identity) over an algebraically closed field k: If the AR­quiver of \\Lambda has a sincere family of stable. It is then a consequence that if the AR­quiver of \\Lambda has a sincere stable tube C such that there is no sequence X ! Y

Bielefeld, University of

305

Stable Games Josef Hofbauer and William H. Sandholm  

E-print Network

Stable Games Josef Hofbauer and William H. Sandholm Abstract-- We introduce a new class of population games called stable games. These games are characterized by self- defeating externalities: when are aban- doning. Stable games subsume many well-known classes of examples, including zero-sum games, games

Hofbauer, Josef

306

Population games, stable games, and passivity Michael J. Fox  

E-print Network

Population games, stable games, and passivity Michael J. Fox Jeff S. Shamma March 31, 2013 July 23, 2013 (revised) September 2, 2013 (revised) Abstract The class of "stable games", introduced by Hofbauer evolutionary dynamics. We show that stable games can be identified as a special case of the feedback

Shamma, Jeff S.

307

Perceptual Learning Immediately Yields New Stable Motor Coordination  

ERIC Educational Resources Information Center

Coordinated rhythmic movement is specifically structured in humans. Movement at 0[degrees] mean relative phase is maximally stable, 180[degrees] is less stable, and other coordinations can, but must, be learned. Variations in perceptual ability play a key role in determining the observed stabilities so we investigated whether stable movements can…

Wilson, Andrew D.; Snapp-Childs, Winona; Bingham, Geoffrey P.

2010-01-01

308

Ultra-stable oscillator with complementary transistors  

NASA Technical Reports Server (NTRS)

A high frequency oscillator, having both good short and long term stability, is formed by including a piezoelectric crystal in the base circuit of a first bi-polar transistor circuit, the bi-polar transistor itself operated below its transitional frequency and having its emitter load chosen so that the input impedance, looking into the base thereof, exhibits a negative resistance in parallel with a capacitive reactance. Combined with this basic circuit is an auxiliary, complementary, second bi-polar transistor circuit of the same form with the piezoelectric crystal being common to both circuits. By this configuration small changes in quiescent current are substantially cancelled by opposite variations in the second bi-polar transistor circuit, thereby achieving from the oscillator a signal having its frequency of oscillation stable over long time periods as well as short time periods.

Kleinberg, L. L. (inventor)

1974-01-01

309

Asystole following regadenoson infusion in stable outpatients.  

PubMed

Regadenoson is a selective A2A receptor agonist approved for use as a pharmacologic stress agent for myocardial perfusion imaging after several multicenter trials demonstrated its equivalence in diagnostic accuracy for the detection of coronary artery disease and a decreased incidence of serious side effects as compared to adenosine. Recently, the FDA released a safety announcement advising of the rare but serious risk of heart attack and death associated with regadenoson and adenosine in cardiac stress testing, particularly in patients with unstable angina or cardiovascular instability. We report two cases of asystole with hemodynamic collapse in stable outpatients soon after receiving a standard regadenoson injection. The prevalence of potentially life threatening bradycardia, including asystole, associated with the use of regadenoson may be greater than previously expected. These cases highlight the need for cardiac stress labs to anticipate the potential for serious side effects with all patients during the administration of coronary vasodilators. PMID:24879452

Rosenblatt, Jeffrey; Mooney, Deirdre; Dunn, Timothy; Cohen, Mylan

2014-10-01

310

Towards stable silicon nanoarray hybrid solar cells  

PubMed Central

Silicon nanoarray hybrid solar cells benefit from the ease of fabrication and the cost-effectiveness of the hybrid structure, and represent a new research focus towards the utilization of solar energy. However, hybrid solar cells composed of both inorganic and organic components suffer from the notorious stability issue, which has to be tackled before the hybrid solar cells could become a viable alternative for harvesting solar energy. Here we show that Si nanoarray/PEDOT:PSS hybrid solar cells with improved stability can be fabricated via eliminating the water inclusion in the initial formation of the heterojunction between Si nanoarray and PEDOT:PSS. The Si nanoarray hybrid solar cells are stable against rapid degradation in the atmosphere environment for several months without encapsulation. This finding paves the way towards the real-world applications of Si nanoarray hybrid solar cells. PMID:24430057

He, W. W.; Wu, K. J.; Wang, K.; Shi, T. F.; Wu, L.; Li, S. X.; Teng, D. Y.; Ye, C. H.

2014-01-01

311

Modelling of the Evolving Stable Boundary Layer  

NASA Astrophysics Data System (ADS)

A single-column model of the evolving stable boundary layer (SBL) is tested for self-similar properties of the flow and effects of ambient forcing. The turbulence closure of the model is diagnostic, based on the K-theory approach, with a semi-empirical form of the mixing length, and empirical stability functions of the Richardson number. The model results, expressed in terms of local similarity scales, are universal functions, satisfied in the entire SBL. Based on similarity expression, a realizability condition is derived for the minimum allowable turbulent heat flux in the SBL. Numerical experiments show that the development of "horse-shoe" shaped, fixed-elevation hodographs in the interior of the SBL around sunrise is controlled by effects imposed by surface thermal forcing.

Sorbjan, Zbigniew

2014-06-01

312

Electromagnetic moments of quasi-stable baryons  

SciTech Connect

We address electromagnetic properties of quasi-stable baryons in the context of chiral extrapolations of lattice QCD results. For particles near their decay threshold we show that an application of a small external magnetic field changes the particle's energy in a non-analytic way. The conventional electromagnetic moments are only well-defined when the background field B satisfies |eB|/2M{sub *}<<|M{sub *}-M-m| where M{sub *} is the mass of the resonance and M, m the masses of the decay products. A direct application of this situation is the chiral extrapolation of the {Delta}(1232)-isobar electromagnetic properties. We discuss such an extrapolation of the {Delta}(1232)-isobar magnetic dipole, electric quadrupole and magnetic octupole moments by a covariant chiral effective field theory.

Ledwig, T.; Pascalutsa, V.; Vanderhaeghen, M. [Institut fuer Kernphysik, Universitaet Mainz, D-55099 Mainz (Germany); Martin-Camalich, J. [Departamento de Fisica Teorica and IFIC, Universidad de Valencia-CSIC (Spain)

2011-10-24

313

How structurally stable are global socioeconomic systems?  

E-print Network

The stability analysis of socioeconomic systems has been centered on answering whether small perturbations when a system is in a given quantitative state will push the system permanently to a different quantitative state. However, typically the quantitative state of socioeconomic systems is subject to constant change. Therefore, a key stability question that has been under-investigated is how strong the conditions of a system itself can change before the system moves to a qualitatively different behavior, i.e., how structurally stable the systems is. Here, we introduce a framework to investigate the structural stability of socioeconomic systems formed by the network of interactions among agents competing for resources. We measure the structural stability of the system as the range of conditions in the distribution and availability of resources compatible with the qualitative behavior in which all the constituent agents can be self-sustained across time. To illustrate our framework, we study an empirical repre...

Saavedra, Serguei; Gilarranz, Luis J; Bascompte, Jordi

2014-01-01

314

SPH as a stable, accurate CFD method.  

NASA Astrophysics Data System (ADS)

SPH has previously been employed in solving high rate CFD problems but with limited success because of tension instability and low accuracy associated with it. General Dynamics OTS has recently developed a SPH code that is suitable to solve general problems in material interactions. With the MLSPH methodology, a MLS rezoner, and a proper employment of phantom particles, this simulator is stable, accurate to the second order in space. The rezoner provides locally uniform distribution of particles for higher accuracy, less instability and larger time steps. It also ensures smooth boundaries and higher boundary resolution. Furthermore it provides a natural link between Euler, Lagrange, and SPH systems. SPH particles are Lagrange interpolation points. Phantom particles can be considered as additional interpolation points that provide stability and proper treatment of boundary conditions. The use of SPH phantom particles eliminates the instability growth factor and provides environmental conditions. We are going to show several calculations done with our MLSPH simulator.

Yao, J.; Gunger, Michael E.; Matuska, Daniel A.; General Dynamics Team

2001-11-01

315

Stable quarks of the 4th family?  

E-print Network

Existence of metastable quarks of new generation can be embedded into phenomenology of heterotic string together with new long range interaction, which only this new generation possesses. We discuss primordial quark production in the early Universe, their successive cosmological evolution and astrophysical effects, as well as possible production in present or future accelerators. In case of a charge symmetry of 4th generation quarks in Universe, they can be stored in neutral mesons, doubly positively charged baryons, while all the doubly negatively charged "baryons" are combined with He-4 into neutral nucleus-size atom-like states. The existence of all these anomalous stable particles may escape present experimental limits, being close to present and future experimental test. Due to the nuclear binding with He-4 primordial lightest baryons of the 4th generation with charge +1 can also escape the experimental upper limits on anomalous isotopes of hydrogen, being compatible with upper limits on anomalous lithium. While 4th quark hadrons are rare, their presence may be nearly detectable in cosmic rays, muon and neutrino fluxes and cosmic electromagnetic spectra. In case of charge asymmetry, a nontrivial solution for the problem of dark matter (DM) can be provided by excessive (meta)stable anti-up quarks of 4th generation, bound with He-4 in specific nuclear-interacting form of dark matter. Such candidate to DM is surprisingly close to Warm Dark Matter by its role in large scale structure formation. It catalyzes primordial heavy element production in Big Bang Nucleosynthesis and new types of nuclear transformations around us.

K. Belotsky; M. Khlopov; K. Shibaev

2008-06-05

316

Characterising the Terrestrial Stable Cr Isotope Cycle  

NASA Astrophysics Data System (ADS)

Cr isotopes were shown to present a sensitive tracer of redox changes in aqueous solutions [1,2]. Here, the potential of stable Cr isotope fractionation in the environment was further investigated by high-precision double- spike MC-ICP-MS measurements. Reduction experiments of Cr(VI) to Cr(III) in aqueous solutions on ion exchange columns confirmed the mass-dependent Cr isotope fractionation of -3.4‰ per atomic mass unit reported by Ellis et al. [1]. Furthermore, these experiments revealed that the fractionation associated with adsorption is minor. This is shown by a very small preferential adsorption of isotopically heavy chromium of most likely Cr(III) species on the anion resin. A similar observation was made for Cr(III) species on cation resin. This is in line with the negligible fractionation effects that have been reported for adsorption of Cr(VI) onto ?-Al2O3 and goethite surfaces [2], respectively. Thus, the large Cr isotope fractionation that accompanies Cr reduction and the small sorption effects of both Cr(VI) and Cr(III) species make stable Cr isotopes a sensitive tracer to detect and quantify redox changes in a variety of geochemical reservoirs. The stable Cr isotope compositions of the principle silicic igneous reservoirs of the Earth do not show measurable variations. ?^{53}Cr/^{52}Cr values (relative to SRM3112a) of six mantle lherzolites (- 0.014±0.083‰; 2 SD), six ultramafic cumulate rocks (-0.034±0.094‰) and five continental and oceanic basalts that represent partial mantle melts (-0.044±0.089‰) are indistinguishable within uncertainties. Thus, unlike as was suggested for Fe isotopes [3], partial mantle melting appears not to fractionate Cr isotopes. Cr(III)-bearing uvarovite and fuchsite minerals from amphibolite facies metamorphic rocks are also equal to those of igneous rock reservoirs. These observations are not unexpected, because there is no apparent redox change of Cr involved during partial mantle melting or metamorphism. Also the fractionation effects caused by potential ligand changes of Cr between solids, and solids and melt are too small to be detected at high-temperatures. Large Cr isotope fractionations with ?^{53}Cr/^{52}Cr values of +0.672 to +1.093‰ were observed for crocoite (PbCr(VI)O4), a mineral that forms in oxidising zones of medium- to high- temperature hydrothermal systems. It has yet to be investigated whether Cr isotopes fractionate during the oxidation of Cr(III) to Cr(VI). It is, however, likely, that Cr behaves like its chemical twin Se that only fractionates during reduction [4]. In this case the observed heavy Cr isotope compositions of crocoites are the result of partial Cr(VI) reduction from the hydrothermal fluid, allowing to quantify changes in redox conditions along the hydrothermal pathway. [1] Ellis, A.S. et al. (2002), Science 295, 2060-2062, [2] Ellis, A.S. et al. (2004), Eniron. Sci. Technol. 38, 3604-3607, [3] Weyer, S. et al. (2005), Earth and Planet. Sci. Letters 240, 251-264, [4] Johnson, T.M. and Bullen, T.D. (2004), Reviews in Mineralogy & Geochemistry 55, 289-317.

Schoenberg, R.; Zink, S.; Staubwasser, M.; von Blanckenburg, F.

2006-12-01

317

Stable nuclear transformation of Pandorina morum  

PubMed Central

Background Volvocine green algae like Pandorina morum represent one of the most recent inventions of multicellularity diverged from their unicellular relatives. The 8–16 celled P. morum alga and its close multicellular relatives constitute a model lineage for research into cellular differentiation, morphogenesis and epithelial folding, sexual reproduction and evolution of multicellularity. Pandorina is the largest and most complex organism in the volvocine lineage that still exhibits isogamous sexual reproduction. So far, molecular-biological investigations in P. morum were constricted due to the absence of methods for transformation of this species, which is a prerequisite for introduction of reporter genes and (modified) genes of interest. Results Stable nuclear transformation of P. morum was achieved using chimeric constructs with a selectable marker, a reporter gene, promoters and upstream and downstream flanking sequences from heterologous sources. DNA was introduced into the cells by particle bombardment with plasmid-coated gold particles. The aminoglycoside 3?-phosphotransferase VIII (aphVIII) gene of Streptomyces rimosus under control of an artificial, heterologous promoter was used as the selectable marker. The artificial promoter contained a tandem arrangement of the promoter of both the heat shock protein 70A (hsp70A) and the ribulose-1,5-bisphosphat-carboxylase/-oxygenase S3 (rbcS3) gene of Volvox carteri. Due to the expression of aphVIII, transformants gained up to 333-fold higher resistance to paromomycin in comparison to the parent wild-type strain. The heterologous luciferase (gluc) gene of Gaussia princeps, which was previously genetically engineered to match the nuclear codon usage of Chlamydomonas reinhardtii, was used as a co-transformed, unselectable reporter gene. The expression of the co-bombarded gluc gene in transformants and the induction of gluc by heat shock were demonstrated through bioluminescence assays. Conclusion Stable nuclear transformation of P. morum using the particle bombardment technique is now feasible. Functional expression of heterologous genes is achieved using heterologous flanking sequences from Volvox carteri and Chlamydomonas reinhardtii. The aphVIII gene of the actinobacterium S. rimosus can be used as a selectable marker for transformation experiments in the green alga P. morum. The gluc gene of the marine copepod G. princeps, expressed under control of heterologous promoter elements, represents a suitable reporter gene for monitoring gene expression or for other applications in P. morum. PMID:25031031

2014-01-01

318

Stable nuclear transformation of Gonium pectorale  

PubMed Central

Background Green algae of the family Volvocaceae are a model lineage for studying the molecular evolution of multicellularity and cellular differentiation. The volvocine alga Gonium is intermediate in organizational complexity between its unicellular relative, Chlamydomonas, and its multicellular relatives with differentiated cell types, such as Volvox. Gonium pectorale consists of ~16 biflagellate cells arranged in a flat plate. The detailed molecular analysis of any species necessitates its accessibility to genetic manipulation, but, in volvocine algae, transformation procedures have so far only been established for Chlamydomonas reinhardtii and Volvox carteri. Results Stable nuclear transformation of G. pectorale was achieved using a heterologous dominant antibiotic resistance gene, the aminoglycoside 3'-phosphotransferase VIII gene (aphVIII) of Streptomyces rimosus, as a selectable marker. Heterologous 3'- and 5'-untranslated flanking sequences, including promoters, were from Chlamydomonas reinhardtii or from Volvox carteri. After particle gun bombardment of wild type Gonium cells with plasmid-coated gold particles, transformants were recovered. The transformants were able to grow in the presence of the antibiotic paromomycin and produced a detectable level of the AphVIII protein. The plasmids integrated into the genome, and stable integration was verified after propagation for over 1400 colony generations. Co-transformants were recovered with a frequency of ~30–50% when cells were co-bombarded with aphVIII-based selectable marker plasmids along with unselectable plasmids containing heterologous genes. The transcription of the co-transformed, unselectable genes was confirmed. After heterologous expression of the luciferase gene from the marine copepod Gaussia princeps, which was previously engineered to match the codon usage in C. reinhardtii, Gonium transformants show luciferase activity through light emission in bioluminescence assays. Conclusion Flanking sequences that include promoters from C. reinhardtii and from V. carteri work in G. pectorale and allow the functional expression of heterologous genes, such as the selectable marker gene aphVIII of S. rimosus or the co-transformed, codon-optimized G. princeps luciferase gene, which turned out to be a suitable reporter gene in Gonium. The availability of a method for transformation of Gonium makes genetic engineering of this species possible and allows for detailed studies in molecular evolution using the unicellular Chlamydomonas, the 16-celled Gonium, and the multicellular Volvox. PMID:19591675

Lerche, Kai; Hallmann, Armin

2009-01-01

319

Stable nuclear transformation of Eudorina elegans  

PubMed Central

Background A fundamental step in evolution was the transition from unicellular to differentiated, multicellular organisms. Volvocine algae have been used for several decades as a model lineage to investigate the evolutionary aspects of multicellularity and cellular differentiation. There are two well-studied volvocine species, a unicellular alga (Chlamydomonas reinhardtii) and a multicellular alga with differentiated cell types (Volvox carteri). Species with intermediate characteristics also exist, which blur the boundaries between unicellularity and differentiated multicellularity. These species include the globular alga Eudorina elegans, which is composed of 16–32 cells. However, detailed molecular analyses of E. elegans require genetic manipulation. Unfortunately, genetic engineering has not yet been established for Eudorina, and only limited DNA and/or protein sequence information is available. Results Here, we describe the stable nuclear transformation of E. elegans by particle bombardment using both a chimeric selectable marker and reporter genes from different heterologous sources. Transgenic algae resistant to paromomycin were achieved using the aminoglycoside 3?-phosphotransferase VIII (aphVIII) gene of Streptomyces rimosus, an actinobacterium, under the control of an artificial promoter consisting of two V. carteri promoters in tandem. Transformants exhibited an increase in resistance to paromomycin by up to 333-fold. Co-transformation with non-selectable plasmids was achieved with a rate of 50 - 100%. The luciferase (gluc) gene from the marine copepod Gaussia princeps, which previously was engineered to match the codon usage of C. reinhardtii, was used as a reporter gene. The expression of gluc was mediated by promoters from C. reinhardtii and V. carteri. Heterologous heat shock promoters induced an increase in luciferase activity (up to 600-fold) at elevated temperatures. Long-term stability and both constitutive and inducible expression of the co-bombarded gluc gene was demonstrated by transcription analysis and bioluminescence assays. Conclusions Heterologous flanking sequences, including promoters, work in E. elegans and permit both constitutive and inducible expression of heterologous genes. Stable nuclear transformation of E. elegans is now routine. Thus, we show that genetic engineering of a species is possible even without the resources of endogenous genes and promoters. PMID:23402598

2013-01-01

320

Magneto-hydrodynamically stable axisymmetric mirrors  

SciTech Connect

Making axisymmetric mirrors magnetohydrodynamically (MHD) stable opens up exciting opportunities for using mirror devices as neutron sources, fusion-fission hybrids, and pure-fusion reactors. This is also of interest from a general physics standpoint (as it seemingly contradicts well-established criteria of curvature-driven instabilities). The axial symmetry allows for much simpler and more reliable designs of mirror-based fusion facilities than the well-known quadrupole mirror configurations. In this tutorial, after a summary of classical results, several techniques for achieving MHD stabilization of the axisymmetric mirrors are considered, in particular: (1) employing the favorable field-line curvature in the end tanks; (2) using the line-tying effect; (3) controlling the radial potential distribution; (4) imposing a divertor configuration on the solenoidal magnetic field; and (5) affecting the plasma dynamics by the ponderomotive force. Some illuminative theoretical approaches for understanding axisymmetric mirror stability are described. The applicability of the various stabilization techniques to axisymmetric mirrors as neutron sources, hybrids, and pure-fusion reactors are discussed; and the constraints on the plasma parameters are formulated.

Ryutov, D. D.; Cohen, B. I.; Molvik, A. W. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Berk, H. L. [University of Texas, Austin, Texas 78712 (United States); Simonen, T. C. [University of California, Berkeley, California 94720 (United States)

2011-09-15

321

Stable normal forms for polynomial system solving  

E-print Network

This paper describes and analyzes a method for computing border bases of a zero-dimensional ideal $I$. The criterion used in the computation involves specific commutation polynomials and leads to an algorithm and an implementation extending the one provided in [MT'05]. This general border basis algorithm weakens the monomial ordering requirement for \\grob bases computations. It is up to date the most general setting for representing quotient algebras, embedding into a single formalism Gr\\"obner bases, Macaulay bases and new representation that do not fit into the previous categories. With this formalism we show how the syzygies of the border basis are generated by commutation relations. We also show that our construction of normal form is stable under small perturbations of the ideal, if the number of solutions remains constant. This new feature for a symbolic algorithm has a huge impact on the practical efficiency as it is illustrated by the experiments on classical benchmark polynomial systems, at the end o...

Mourrain, Bernard; 10.1016/j.tcs.2008.09.004

2008-01-01

322

Organized polysaccharide fibers as stable drug carriers  

PubMed Central

Many challenges arise during the development of new drug carrier systems, and paramount among them are safety, solubility and controlled release requirements. Although synthetic polymers are effective, the possibility of side effects imposes restrictions on their acceptable use and dose limits. Thus, a new drug carrier system that is safe to handle and free from side effects is very much in need and food grade polysaccharides stand tall as worthy alternatives. Herein, we demonstrate for the first time the feasibility of sodium iota-carrageenan fibers and their distinctive water pockets to embed and release a wide variety of drug molecules. Structural analysis has revealed the existence of crystalline network in the fibers even after encapsulating the drug molecules, and iota-carrageenan maintains its characteristic and reproducible double helical structure suggesting that the composites thus produced are reminiscent of cocrystals. The melting properties of iota-carrageenan:drug complexes are distinctly different from those of either drug or iota-carrageenan fiber. The encapsulated drugs are released in a sustained manner from the fiber matrix. Overall, our research provides an elegant opportunity for developing effective drug carriers with stable network toward enhancing and/or controlling bioavailability and extending shelf-life of drug molecules using GRAS excipients, food polysaccharides, that are inexpensive and non–toxic. PMID:23544530

Janaswamy, Srinivas; Gill, Kristin L.; Campanella, Osvaldo H.; Pinal, Rodolfo

2013-01-01

323

Stable spatial solitons in semiconductor optical amplifiers  

NASA Astrophysics Data System (ADS)

A spatial soliton is a shape invariant self guided beam of light or a self induced waveguide. Spatial solitons appear as a result of the balance of diffraction and nonlinear focusing in a system. They have been observed in many different conservative media in the last couple of years. Solitons are ubiquitous, because of the probability of using their interactions in optical data processing, communications etc. Up to now due to the power required to generate the solitons, and the response times of the soliton supporting media, these special waves of nature could not penetrate the applications arena. Semiconductors, with their resonant nonlinearities, are thought to be ideal candidates for fast switching, low power spatial solitons. In this dissertation it is shown theoretically and experimentally that it is possible to observe stable spatial solitons in a periodically patterned semiconductor optical amplifier (PPSOA). The solitons have unique beam profiles that change only with system parameters, like pumping current, etc. Their coherent and incoherent interactions which could lead to all optical devices have been investigated experimentally and theoretically. The formation of filaments or modulational instability has been studied theoretically and yielded analytical formulae for evaluating the filament gain and the maximum spatial frequencies in PPSOA devices. Furthermore, discrete array amplifiers have been analyzed numerically for discrete solitons, and the prospect of using multi peak discrete solitons as laser amplifiers is discussed.

Ultanir, Erdem

2004-11-01

324

Stable learning in stochastic network states.  

PubMed

The mammalian cerebral cortex is characterized in vivo by irregular spontaneous activity, but how this ongoing dynamics affects signal processing and learning remains unknown. The associative plasticity rules demonstrated in vitro, mostly in silent networks, are based on the detection of correlations between presynaptic and postsynaptic activity and hence are sensitive to spontaneous activity and spurious correlations. Therefore, they cannot operate in realistic network states. Here, we present a new class of spike-timing-dependent plasticity learning rules with local floating plasticity thresholds, the slow dynamics of which account for metaplasticity. This novel algorithm is shown to both correctly predict homeostasis in synaptic weights and solve the problem of asymptotic stable learning in noisy states. It is shown to naturally encompass many other known types of learning rule, unifying them into a single coherent framework. The mixed presynaptic and postsynaptic dependency of the floating plasticity threshold is justified by a cascade of known molecular pathways, which leads to experimentally testable predictions. PMID:22219282

El Boustani, Sami; Yger, Pierre; Frégnac, Yves; Destexhe, Alain

2012-01-01

325

Geometrical families of mechanically stable granular packings  

NASA Astrophysics Data System (ADS)

We enumerate and classify nearly all of the possible mechanically stable (MS) packings of bidipserse mixtures of frictionless disks in small sheared systems. We find that MS packings form continuous geometrical families, where each family is defined by its particular network of particle contacts. We also monitor the dynamics of MS packings along geometrical families by applying quasistatic simple shear strain at zero pressure. For small numbers of particles (N<16) , we find that the dynamics is deterministic and highly contracting. That is, if the system is initialized in a MS packing at a given shear strain, it will quickly lock into a periodic orbit at subsequent shear strain, and therefore sample only a very small fraction of the possible MS packings in steady state. In studies with N>16 , we observe an increase in the period and random splittings of the trajectories caused by bifurcations in configuration space. We argue that the ratio of the splitting and contraction rates in large systems will determine the distribution of MS-packing geometrical families visited in steady state. This work is part of our long-term research program to develop a master-equation formalism to describe macroscopic slowly driven granular systems in terms of collections of small subsystems.

Gao, Guo-Jie; Blawzdziewicz, Jerzy; O'Hern, Corey S.

2009-12-01

326

Stable Generalized Finite Element Method (SGFEM)  

E-print Network

The Generalized Finite Element Method (GFEM) is a Partition of Unity Method (PUM), where the trial space of standard Finite Element Method (FEM) is augmented with non-polynomial shape functions with compact support. These shape functions, which are also known as the enrichments, mimic the local behavior of the unknown solution of the underlying variational problem. GFEM has been successfully used to solve a variety of problems with complicated features and microstructure. However, the stiffness matrix of GFEM is badly conditioned (much worse compared to the standard FEM) and there could be a severe loss of accuracy in the computed solution of the associated linear system. In this paper, we address this issue and propose a modification of the GFEM, referred to as the Stable GFEM (SGFEM). We show that the conditioning of the stiffness matrix of SGFEM is not worse than that of the standard FEM. Moreover, SGFEM is very robust with respect to the parameters of the enrichments. We show these features of SGFEM on se...

Babuska, I

2011-01-01

327

Stable Isotope Database: present and past archives  

NASA Astrophysics Data System (ADS)

Paleoclimate data provide benchmarks against which the realism of the processes simulated by climate models can be assessed. Within this framework, it is essential to avoid introducing uncertainties associated with transfer functions and therefore to operate with robust proxies. The implementation of stable isotopes of water or carbon inside climate models motivates a synthesis of available data. Supported by the LABEX L-IPSL and involving a team of climate modelers and paleoclimatologists, this project aims to establish a worldwide database of ?18O, ?D ?17O and ?13C from oceanic microfossils, corals, ice cores, cave speleothems, lakes, tree rings, and vegetation leaves wax. The aim is to provide a global vision of the hydrological cycle during the LGM and other selected key periods (last 2000 years, Mid-Holocene, Dansgaard-Oeschger events, and the Eemian). It requires screening through hundreds of published oceanic and continental records, validating the selection of the data based on resolution and chronological information. We extracted ~900 dated ?18O records from 650 marine sediment cores, 65 ?18O records from 50 ice cores, ~200 ?18O speleothems records from 60 caves, and 540 ?13C records from 290 marine sediment cores. An additional aspect of this project consists in the construction of an online portal providing an intuitive and interactive platform allowing selecting, visualizing, and downloading of the records included in this database, thus improving the distribution and comparison of paleoclimatic records from various sites.

Bolliet, Timothé

2014-05-01

328

Embryotoxicity of stable isotopes and use of stable isotopes in studies of teratogenetic mechanisms  

SciTech Connect

Experiments on teratogenic effects of stable isotopes from our own and other laboratories are evaluated. In the first series of investigations, the enrichment of the stable isotope /sup 13/C derived from U-/sup 13/C-glucose was studied in mouse embryos at various stages of development, including limb buds in organ culture. Preimplantation mouse embryos incubated in vitro in /sup 13/C-enriched medium for 48 hours showed normal development during subsequent differentiation in vitro and also in vivo after embryo transfer to faster mothers. These embryos were 15% to 20% enriched in /sup 13/C. Administration of U-13-C-glucose to pregnant mice during organogenesis led to an increase of the absolute /sup 13/C content of the embryo for several days after the end of isotope administration, whereas the enrichment in maternal tissue decreased. No alterations of embryonic development were detected due to stable isotope enrichment. Development of cultured mouse limb buds was unaffected by incubation with 82 mol% U-/sup 13/C-glucose as judged from morphologic and biochemical criteria. The second part of the article describes the value of deuterium-labeled drugs as probes into the mechanism of activation of teratogenic metabolites. A comparison of the pharmacokinetics as well as the teratogenicity between cyclophosphamide and some specific deuterium-labeled analogues showed that the isotope effect observed can be related to a particular metabolic pathway crucial for teratogenic activation by this drug.

Spielmann, H.; Nau, H.

1986-07-01

329

Stable Vanadium Isotope Fractionation at High Temperatures  

NASA Astrophysics Data System (ADS)

Vanadium is a redox sensitive transition metal existing in multiple valence states at terrestrial conditions. Stable vanadium isotopes (reported as ?51V in % relative to an Alfa Aesar standard [1]) are a potentially powerful tracer of oxidation-reduction processes. However, the determination of ?51V is analytically challenging, primarily due to the extreme abundance ratio between the only two stable isotopes (51V/50V ~ 400) and, also, significant isobaric interferences of 50Ti and 50Cr on the minor 50V isotope. We have developed the first method able to determine ?51V to a precision (2 s.d. ~ 0.15%, [1,2]) that enables application of this isotope system to geological processes. To usefully investigate high temperature processes using vanadium isotopes, knowledge of the isotope composition and range of values present in the ambient mantle is required. Here we discuss the first ?51V measured in igneous materials encompassing peridotites, MORB, and primitive mantle-derived melts such as picrites. This first dataset provides a preliminary reconnaissance of the magnitude of natural fractionation. We find little isotope fractionation in suites of peridotites and MORB (< 0.5 %). However, the small but analytically significant variation appears to be related to secondary processes, with extremely altered peridotites consistently displaying slightly heavier isotope compositions. We find no resolvable ?51V variation between fresh MORB glass and fresh peridotite. Intriguingly, a suite of subduction-related peridotites from the Mariana forearc, previously characterized for fO2 [3], do not display the predicted co-variation between ?51V and fO2, but instead also have compositions identical to MORB glass. This nominally supports recent indications that there is limited difference in the oxygen fugacity of the MORB source and the subarc mantle wedge [e.g., 4, 5]. Finally, we observe large ?51V variations (~ 2 %) in a suite of evolving lavas from Hekla volcano, Iceland, which produces eruptive material with a wide range of SiO2 from a cogenetic source. The ?51V of Hekla lavas are well correlated with indices of differentiation such as MgO and SiO2, suggesting that processes such as fractional crystallization may be a fundamental cause of high temperature ?51V fractionation. This nascent dataset provides a first glimpse into the magnitude of vanadium isotope fractionation that may be expected at high temperatures. The presence of significant isotope variation outside of analytical precision in these materials bodes well for the use of ?51V to address a variety of broad scale questions in high temperature planetary processes. [1] Nielsen, S.G., Prytulak, J., Halliday, A.N. 2011. Geost. Geoanal. Res., in press. [2] Prytulak, J., Nielsen, S.G., Halliday, A.N. 2011. Geost. Geoanal. Res., in press. [3] Parkinson and Pearce, 1998. Journal of Petrology, 39, 1577-1618. [4] Lee et al., 2005. Journal of Petrology, 46, 2313-2336. [5] Cottrell and Kelley, 2011. Earth and Planetary Sciences Letters, 305, 270-282.

Prytulak, J.; Parkinson, I. J.; Savage, P. S.; Nielsen, S. G.; Halliday, A. N.

2011-12-01

330

Tritium and stable isotopes of magmatic waters  

NASA Astrophysics Data System (ADS)

To investigate the isotopic composition and age of water in volcanic gases and magmas, we analyzed samples from 11 active volcanoes ranging in composition from tholeiitic basalt to rhyolite: Mount St. Helens (USA), Kilauea (USA), Pacaya (Guatemala), Galeras (Colombia), Satsuma Iwo-Jima (Japan), Sierra Negra and Alcedo (Ecuador), Vulcano (Italy), Par?´cutin (Mexico), Kudryavy (Russia), and White Island (New Zealand). Tritium at relatively low levels (0.1-5 T.U.) is found in most emissions from high-temperature volcanic fumaroles sampled, even at discharge temperatures >700°C. Although magmatic fluids sampled from these emissions usually contain high CO 2, S total, HCl, HF, B, Br, 3He R/ RA, and low contents of air components, stable isotope and tritium relations of nearly all such fluids show mixing of magmatic volatiles with relatively young meteoric water (model ages?75 y). Linear ?D/ ?18O and 3H/ ?18O mixing trends of these two end-members are invariably detected at arc volcanoes. Tritium is also detected in fumarole condensates at hot spot basalt volcanoes, but collecting samples approaching the composition of end-member magmatic fluid is exceedingly difficult. In situ production of 3H, mostly from spontaneous fission of 238U in magmas is calculated to be <0.001 T.U., except for the most evolved compositions (high U, Th, and Li and low H 2O contents). These values are below the detection limit of 3H by conventional analytical techniques (about 0.01 T.U. at best). We found no conclusive evidence that natural fusion in the Earth produces anomalous amounts of detectable 3H (>0.05 T.U.).

Goff, F.; McMurtry, G. M.

2000-04-01

331

15 CFR 971.605 - Stable Reference Areas. [Reserved  

Code of Federal Regulations, 2010 CFR

...DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR COMMERCIAL RECOVERY PERMITS Environmental Effects § 971.605 Stable Reference Areas....

2010-01-01

332

15 CFR 971.605 - Stable Reference Areas. [Reserved  

...DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR COMMERCIAL RECOVERY PERMITS Environmental Effects § 971.605 Stable Reference Areas....

2014-01-01

333

HUNT STABLE COMPLEX LOOKING NORTHWEST TOWARD DOG KENNEL RUINS ACROSS ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

HUNT STABLE COMPLEX LOOKING NORTHWEST TOWARD DOG KENNEL RUINS ACROSS THE GREAT CIRCUS - Overhills, Fort Bragg Military Reservation, Approximately 15 miles NW of Fayetteville, Overhills, Harnett County, NC

334

Meta-Stable Brane Configurations by Higher Order Polynomial Superpotential  

E-print Network

We construct the type IIA nonsupersymmetric meta-stable brane configuration consisting of (2k+1) NS5-branes and D4-branes where the electric gauge theory superpotential has an order (2k+2) polynomial for the bifundamentals. We find a rich pattern of nonsupersymmetric meta-stable states as well as the supersymmetric stable ones. By adding the orientifold 4-plane to this brane configuration, we also describe the intersecting brane configuration of type IIA string theory corresponding to the meta-stable nonsupersymmetric vacua of corresponding gauge theory.

Changhyun Ahn

2008-02-01

335

Stable isotope analysis of breath using the optogalvanic effect  

Microsoft Academic Search

A new technique based on the optogalvanic effect has been developed for the measurement of stable isotope ratios in the carbon dioxide of exhaled breath. Data obtained before and after ingestion of harmless stable isotope labeled compounds, metabolized to carbon dioxide, can be used for sensitive noninvasive diagnostics of various disease conditions. The technique uses the specificity of laser resonance

Daniel E. Murnick; M. J. Colgan; H. P. Lie; D. Stoneback

1996-01-01

336

A TRIPTYCH OF DISCRETE DISTRIBUTIONS RELATED TO THE STABLE LAW  

E-print Network

is uniform [0; 1] and independent of E. 2. The discrete Linnik distribution. Pakes (1993) studiesA TRIPTYCH OF DISCRETE DISTRIBUTIONS RELATED TO THE STABLE LAW Luc Devroye School of Computer uniformly fast random variate generators. Keywords and phrases. Discrete stable distribution. Random variate

Devroye, Luc

337

Peer Reviewed Temporal Variation in Stable Carbon and Nitrogen  

E-print Network

to distinguish among seasonal assimilated diets of grizzly bears (Ursus arctos) by comparing the isotopic values, nitrogen, stable isotope, technique, Ursus arctos. Traditional methods of examining the diet of animals, Robbins et al. 2004). Specifically in bears (Ursus spp.), the stable isotopes of carbon (13 C/12 C

Gillingham, Michael

338

Stable isotopes as one of nature's ecological recorders  

E-print Network

of the natural variation in stable isotopes of components of ecological systems have provided new insights ecological activi- ties. Among the many examples, carbon isotope ratios (d13 C) of plant organic matterStable isotopes as one of nature's ecological recorders Jason B. West1 , Gabriel J. Bowen2 , Thure

Ehleringer, Jim

339

Identification of Stable Genetic Networks using Convex Programming  

E-print Network

develops a novel algorithm that identifies a sparse stable genetic network that explains noisy geneticIdentification of Stable Genetic Networks using Convex Programming Michael M. Zavlanos, A. Agung between genes and other cell substances, resulting in various models for the fundamental biological

Pappas, George J.

340

Stable isotopes in fish as indicators of habitat use  

EPA Science Inventory

In our isotopic studies of fish in Oregon Coast Range streams we have found stable isotopes of carbon, oxygen and sulfur to be surprisingly useful in identifying and discriminating specific habitat or tributary use by a variety of fish species. Stable isotopes of carbon can be u...

341

Treatment of stable vitiligo with autologous epidermal grafting and PUVA  

Microsoft Academic Search

Background: Previous reports have shown the benefits of epidermal grafting for vitiligo.Objective: Our purpose was to evaluate the effectiveness and complications of epidermal grafting in combination with PUVA on stable vitiligo refractory to conventional treatments.Methods: In 100 patients with stable refractory vitiligo we performed epidermal grafting with suction blisters followed by PUVA treatment. The grafted sites were examined for repigmentation

Seung Kyung Hann; Sungbin Im; Ha Wook Bong; Yoon-Kee Park

1995-01-01

342

1. Historic American Buildings Survey 'The Stable' EXTERIOR FROM SOUTHEAST. ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. Historic American Buildings Survey 'The Stable' EXTERIOR FROM SOUTHEAST. Photocopy of Plate No. XXVIII From: American Institute of Architects Building Committee The Octagon: An Historic Residence of the Year 1800, Washington 1927 - Octagon House, Stable, 1799 New York Avenue Northwest, Washington, District of Columbia, DC

343

Multivariate Survival Analysis with Positive Stable Zuqiang Qiou  

E-print Network

ratio between unrelated subjects (i.e., with di erent frailties) is always less than its conditional eMultivariate Survival Analysis with Positive Stable Frailties Zuqiang Qiou Palisades Research, Inc data using positive stable frailty distributions. A exible baseline hazard formula- tion using

Ravishanker, Nalini

344

A VIEW OF THE STABLES LOOKING TO THE SOUTH, TOWARD ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

A VIEW OF THE STABLES LOOKING TO THE SOUTH, TOWARD THE HUACHUCA MOUNTAINS, CIRCA 1910. HORSES ARE TIED TO THE EXTERIOR OF ONE OF THE PADDOCK CORRALS (FORT HUACHUCA HISTORICAL MUSEUM, PHOTOGRAPH 1918.00.00.126, PHOTOGRAPHER UNIDENTIFIED, CREATED BY AND PROPERTY OF THE UNITED STATES ARMY) - Fort Huachuca, Cavalry Stables, Clarkson Road, Sierra Vista, Cochise County, AZ

345

Lancifodilactone G: Insights about an Unusually Stable Enol  

E-print Network

lancifodilactone G is stable over the keto form (by 2.6 kcal/mol in water), the only known stable aliphatic enol catalysis exhibiting the most profound effect on the barrier.2 From a simple analysis of bond dissociation dissociation energy of ethylene is worth 174.1 kcal/mol while the CdO bond dissociation energy of formaldehyde

Goddard III, William A.

346

Selection of Drug Therapy in Stable Angina Pectoris  

Microsoft Academic Search

Drug therapy in stable angina has two aims: the prevention of major cardiac events (such as unstable angina, myocardial infarction, or death) and the control of chest pain and transient myocardial ischemia. Given the low incidence of major cardiac events in patients with stable angina, primary preventive studies are scarce because they require a large sample size and long-term follow-up.

Stefano Savonitto; Diego Ardissino

1998-01-01

347

ASYMPTOTICALLY STABLE DYNAMIC RISK ASSESSMENTS KARL-THEODOR EISELE  

E-print Network

ASYMPTOTICALLY STABLE DYNAMIC RISK ASSESSMENTS KARL-THEODOR EISELE AND MICHAEL KUPPER Abstract]. While first simple or dynamic risk assessments of random variables have been studied, the focus of asymptotically stable risk assessments is presented in the Section 3. In Section 4 we construct dynamic risk

Franchi, Jacques

348

APPROACHES FOR MEASURING STABLE CARBON AND NITROGEN ISOTOPES IN BACTERIA  

EPA Science Inventory

Stable isotopes have been used successfully over the past three decades to trace through aquatic food chairs. his technique, however, has only recently been used to examine aquatic microbial roles in elemental cycling. he major obstacle to measuring stable isotope compositions in...

349

Synthesis of stable derivatives of cycloprop-2-ene carboxylic acid.  

PubMed

Large-scale syntheses of 3-(cycloprop-2-en-1-oyl)oxazolidinones from acetylene and ethyl diazoacetate are described. Unlike other cyclopropenes that bear a single substitutent at C-3, these compounds are stable to long-term storage. Although the cyclopropene derivatives are unusually stable, they are reactive toward cyclic and acyclic dienes in stereoselective Diels-Alder reactions. PMID:18452335

Yan, Ni; Liu, Xiaozhong; Pallerla, Mahesh K; Fox, Joseph M

2008-06-01

350

[Stable isotopes of carbon and nitrogen in soil ecological studies].  

PubMed

The development of stable isotope techniques is one of the main methodological advances in ecology of the last decades of the 20th century. Many biogeochemical processes are accompanied by changes in the ratio between stable isotopes of carbon and nitrogen (12C/13C and 14N/15N), which allows different ecosystem components and different ecosystems to be distinguished by their isotopic composition. Analysis of isotopic composition makes it possible to trace matter and energy flows through biological systems and to evaluate the rate of many ecological processes. The main concepts and methods of stable isotope ecology and patterns of stable isotope fractionation during organic matter decomposition are considered with special emphasis on the fractionation of isotopes in food chains and the use of stable isotope studies of trophic relationships between soil animals in the field. PMID:17966909

Tiunov, A V

2007-01-01

351

Compact, Highly Stable Ion Atomic Clock  

NASA Technical Reports Server (NTRS)

A mercury-ion clock now at the breadboard stage of development (see figure) has a stability comparable to that of a hydrogen-maser clock: In tests, the clock exhibited an Allan deviation of between 2 x 10(exp -13) and 3 x 10(exp -13) at a measurement time of 1 second, averaging to about 10(exp -15) at 1 day. However, the clock occupies a volume of only about 2 liters . about a hundredth of the volume of a hydrogen-maser clock. The ion-handling parts of the apparatus are housed in a sealed vacuum tube, wherein only a getter pump is used to maintain the vacuum. Hence, this apparatus is a prototype of a generation of small, potentially portable high-precision clocks for diverse ground- and space-based navigation and radio science applications. Furthermore, this new ion-clock technology is about 100 times more stable and precise than the rubidium atomic clocks currently in use in the NAV STAR GPS Earth-orbiting satellites. In this clock, mercury ions are shuttled between a quadrupole and a 16-pole linear radio-frequency trap. In the quadrupole trap, the ions are tightly confined and optical state selection from a Hg-202 radio-frequency-discharge ultraviolet lamp is carried out. In the 16-pole trap, the ions are more loosely confined and atomic transitions resonant at frequency of about 40.507 GHz are interrogated by use of a microwave beam at that frequency. The trapping of ions effectively eliminates the frequency pulling caused by wall collisions inherent to gas-cell clocks. The shuttling of the ions between the two traps enables separation of the state-selection process from the clock microwave- resonance process, so that each of these processes can be optimized independently of the other. The basic ion-shuttling, two-trap scheme as described thus far is not new: it has been the basis of designs of prior larger clocks. The novelty of the present development lies in major redesigns of its physics package (the ion traps and the vacuum and optical subsystems) to effect the desired reduction of size to a volume of no more than a couple of liters. The redesign effort has included selection of materials for the vacuum tube, ion trap, and ultraviolet windows that withstand bakeout at a temperature of approx.450 C in preparation for sealing the tube to contain the vacuum. This part of the redesign effort follows the approach taken in the development of such other vacuum-tube electronic components as flight traveling- wave-tube amplifiers having operational and shelf lives as long as 15 years. The redesign effort has also included a thorough study of residual-gas-induced shifts of the ion-clock frequency and a study of alternative gases as candidates for use as a buffer gas within the sealed tube. It has been found that neon is more suitable than is helium, which has been traditionally used for this purpose, in that the pressure-induced frequency pulling by neon is between a third and a half of that of helium. In addition, because neon diffuses through solids much more slowly than does helium, the loss of neon by diffusion over the operational lifetime is expected to be negligible.

Prestage, John

2008-01-01

352

Continuous operation of spectroscopy instruments for stable isotope analysis  

NASA Astrophysics Data System (ADS)

Routine Application of Novel Stable Isotope Spectroscopy Instruments; Berkeley, California, 12 December 2010 ; Stable isotopes provide a tracer for biogeochemical processes and for exchange between the biosphere and atmosphere at local to global scales. Recent developments in laser spectroscopy now offer the ability to measure stable isotopes in small molecules such as water vapor and carbon dioxide in unprecedented temporal resolution (up to 10 hertz). In a meeting organized with support from the U.S. National Science Foundation-funded Biogeosphere-Atmosphere Stable Isotope Network (BASIN), an international group consisting of researchers and manufacturers' representatives discussed the challenges of daily use of absorption spectroscopy instruments for stable isotope analysis in continuous field operation. Technological advancement in absorption spectroscopy analysis techniques tied to increased availability of affordable instruments has opened the door to new scientific opportunities and facilitates the use of stable isotope analysis by a larger group of researchers. Despite technological progress, though, stable isotope analysis still requires delicate treatment of samples and setup. Meeting participants tried to identify the key responsibilities for individual labs and the scientific community to help ensure comparability of results and prepare for future regional to global collaborative research efforts. The meeting was concluded with the recommendations below.

Zeeman, Matthias J.; Tu, Kevin P.; Knohl, Alexander

2011-06-01

353

Use of stable isotopes in mineral nutrition research  

SciTech Connect

Stable isotopes are valuable tools for research on mineral bioavailability and metabolism. They can be used as tracers with no exposure to radiation and they do not decay over time. Attempts to use stable isotopes of minerals as metabolic tracers were first described only 25 years ago. There were relatively few reports of their use over the next 15 years, but interest in stable isotopes has expanded markedly in the last 10 years. The advantages of stable isotope tracers are so great that scientists have been willing to accept the laborious and costly nature of mineral isotope analysis, and substantial progress has been made in the field. New applications for stable isotopes and new analytical methods have been introduced recently. However, limitations to the approach and methodological problems remain to be resolved. This review describes early work in the field and discusses the advantages and disadvantages of stable isotope tracers and of the various methods of analysis. Information discovered with stable isotopes is reviewed, and probable future applications are discussed.69 references.

Turnlund, J.R.

1989-01-01

354

Applications of stable isotope analysis in mammalian ecology.  

PubMed

In this editorial, we provide a brief introduction and summarize the 10 research articles included in this Special Issue on Applications of stable isotope analysis in mammalian ecology. The first three articles report correction and discrimination factors that can be used to more accurately estimate the diets of extinct and extant mammals using stable isotope analysis. The remaining seven applied research articles use stable isotope analysis to address a variety of wildlife conservation and management questions from the oceans to the mountains. PMID:25013986

Walter, W David; Kurle, Carolyn M; Hopkins, John B

2014-01-01

355

A Model Describing Stable Coherent Synchrotron Radiation in Storage Rings  

NASA Astrophysics Data System (ADS)

We present a model describing high power stable broadband coherent synchrotron radiation (CSR) in the terahertz frequency region in an electron storage ring. The model includes distortion of bunch shape from the synchrotron radiation (SR), which enhances higher frequency coherent emission, and limits to stable emission due to an instability excited by the SR wakefield. It gives a quantitative explanation of several features of the recent observations of CSR at the BESSYII storage ring. We also use this model to optimize the performance of a source for stable CSR emission.

Sannibale, F.; Byrd, J. M.; Loftsdóttir, Á.; Venturini, M.; Abo-Bakr, M.; Feikes, J.; Holldack, K.; Kuske, P.; Wüstefeld, G.; Hübers, H.-W.; Warnock, R.

2004-08-01

356

A Stable Magnetic Background in SU(2) QCD  

E-print Network

Motivated by the instability of the Savvidy-Nielsen-Olesen (SNO) vacuum we make a systematic search for a stable magnetic background in pure SU(2) QCD. It is shown that Wu-Yang monopole-antimonopole pair is unstable under vacuum fluctuations. However, it is shown that a pair of axially symmetric monopole-antimonopole string configuration is stable, provided the distance between the two strings is small enough (less than a critical value). The existence of a stable monopole-antimonopole string background strongly supports that a magnetic condensation of monopole-antimonopole pairs can indeed generate a dynamical symmetry breaking, and thus a desired magnetic confinement of color, in QCD.

Y. M. Cho; D. G. Pak

2005-10-24

357

High-Order Entropy Stable Formulations for Computational Fluid Dynamics  

NASA Technical Reports Server (NTRS)

A systematic approach is presented for developing entropy stable (SS) formulations of any order for the Navier-Stokes equations. These SS formulations discretely conserve mass, momentum, energy and satisfy a mathematical entropy inequality. They are valid for smooth as well as discontinuous flows provided sufficient dissipation is added at shocks and discontinuities. Entropy stable formulations exist for all diagonal norm, summation-by-parts (SBP) operators, including all centered finite-difference operators, Legendre collocation finite-element operators, and certain finite-volume operators. Examples are presented using various entropy stable formulations that demonstrate the current state-of-the-art of these schemes.

Carpenter, Mark H.; Fisher, Travis C.

2013-01-01

358

More Meta-Stable Brane Configurations without D6-Branes  

E-print Network

We describe the intersecting brane configurations, consisting of NS-branes, D4-branes(and anti-D4-branes), in type IIA string theory corresponding to the meta-stable nonsupersymmetric vacua of N=1 SU(N_c) x SU(N_c') x SU(N_c'') gauge theory with bifundamentals. By adding the orientifold 4-plane to these brane configurations, we also discuss the meta-stable brane configurations for other gauge theory with bifundamentals. Furthermore, we study the intersecting brane configurations corresponding to the nonsupersymmetric meta-stable vacua of other gauge theory with bifundamentals, by adding the orientifold 6-plane.

Changhyun Ahn

2007-07-01

359

Stable superhydrophobic surfaces over a wide pH range  

NASA Astrophysics Data System (ADS)

A stable superhydrophobic surface was fabricated by solidifying poly(epoxy-terminated polydimethylsiloxane- co-bisphenol A) [P(ETPDMS- co-BPA)] copolymer on a rough substrate. The low surface energy of the copolymer and the geometric structure at micrometer scale of the surface contribute to the superhydrophobic property. The as-prepared surface shows stable superhydrophobicity over a wide pH range (1-14) and the wettability is excellent stable to heating, water, corrosive solution and organic solvent treatments. The procedure is simple and time-saving as well as utilizing non-fluorine-containing compounds.

Guo, Li; Yuan, Wenfang; Li, Junping; Zhang, Zhijie; Xie, Zemin

2008-01-01

360

Colloidal Manipulation of Nanostructures: Stable Dispersion and Self-assembly  

E-print Network

This dissertation work addresses two important aspects of nanotechnology - stable dispersion and self-assembly of colloidal nanostructures. Three distinctly different types of nano-scaled materials have been studied: 0-dimensional ZnO quantum dots...

Sun, Dazhi

2013-12-16

361

An Efficient and Stable Spectral Method for Electromagnetic ...  

E-print Network

Nov 6, 2011 ... focuses upon the stable and high–order numerical simulation of the ... In this work we describe a Boundary Perturbation Method (BPM) for the numerical ... depend upon strong cancellations (e.g., differences of extremely large ...

2011-11-14

362

Stable isotope views on ecosystem function: challenging or challenged?  

PubMed Central

Stable isotopes and their potential for detecting various and complex ecosystem processes are attracting an increasing number of scientists. Progress is challenging, particularly under global change scenarios, but some established views have been challenged. The IX meeting of the Spanish Association of Terrestrial Ecology (AAET, Úbeda, 18–22 October 2009) hosted a symposium on the ecology of stable isotopes where the linear mixing model approach of partitioning sinks and sources of carbon and water fluxes within an ecosystem was challenged, and new applications of stable isotopes for the study of plant interactions were evaluated. Discussion was also centred on the need for networks that monitor ecological processes using stable isotopes and key ideas for fostering future research with isotopes. PMID:20015858

Resco, Victor; Querejeta, Jose I.; Ogle, Kiona; Voltas, Jordi; Sebastia, Maria-Teresa; Serrano-Ortiz, Penelope; Linares, Juan C.; Moreno-Gutierrez, Cristina; Herrero, Asier; Carreira, Jose A.; Torres-Canabate, Patricia; Valladares, Fernando

2010-01-01

363

Recovery of enriched stable isotopes in radionuclide production  

SciTech Connect

The wide application of radionuclides in different fields of science and industry demanded an increase of their production. One of the ways to increase the radionuclide production on present cyclotrons is the use of the targets from enriched stable isotopes. This allows one to raise the productivity in some cases by two or more times and to increase radionuclidic purity. It should be noted, however, that enriched stable isotopes are very expensive. Therefore it is advisable to use such raw materials more than once. In the last ten years, The authors have used stable isotopes extensively for making of targets. Zinc-67 and zinc-68, cadmium-111 and cadmium-112, nickel-58, silver-109, thallium-203 have been employed for the production of gallium-67, indium-111, cobalt-57, cadmium-109 and thallium-201, respectively. The technique for the recovery of enriched stable isotopes has been developed. In this report the schemes of the recovering processes are presented.

Razbash, A.A.; Sevastyanov, Yu.G.; Polyakov, O.N.; Krasnov, N.N.; Konyakhin, N.A.; Tolstouhov, Yu.V.; Maklachkov, A.G. [Cyclotron Co. Ltd., Obninsk (Russian Federation)

1994-12-31

364

Stable, inflatable life raft for high seas rescue operations  

NASA Technical Reports Server (NTRS)

Raft is easily deployed and highly maneuverable in water. It has false bottom of water ballast containers attached to underside, making it exceptionally stable platform from which swimmers can operate. Raft is attachable to external moorings.

Barnett, J. H., Jr.; Harrison, F.; Marak, R.; Radnofsky, M. I.

1971-01-01

365

The Synthesis of Stable Force-Closure Grasps  

E-print Network

This thesis addresses the problem of synthesizing grasps that are force-closure and stable. The synthesis of force-closure grasps constructs independent regions of contact for the fingertips, such that the motion of ...

Nguyen

1986-07-01

366

AIAA 2002--0227 On Constructing Stable Perfectly  

E-print Network

for Euler Equations Fang Q. Hu Department of Mathematics and Statistics Old Dominion University, Norfolk Dominion University, Norfolk, Virginia 23529 In a recent work, a stable Perfectly Matched Layer (PML

Hu, Fang Q.

367

9 CFR 108.10 - Outer premises and stables.  

Code of Federal Regulations, 2013 CFR

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2013-01-01

368

9 CFR 108.10 - Outer premises and stables.  

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2014-01-01

369

9 CFR 108.10 - Outer premises and stables.  

Code of Federal Regulations, 2010 CFR

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2010-01-01

370

9 CFR 108.10 - Outer premises and stables.  

Code of Federal Regulations, 2012 CFR

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2012-01-01

371

9 CFR 108.10 - Outer premises and stables.  

Code of Federal Regulations, 2011 CFR

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2011-01-01

372

Speed of light as measured by two terrestrial stable clocks  

NASA Technical Reports Server (NTRS)

Despite the recent criticism within the special theory of relativity, there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously.

Hsu, J. P.; Sherry, T. N.; Chiu, C. B.

1977-01-01

373

Dark Atoms of Dark Matter and their Stable Charged Constituents  

E-print Network

Direct searches for dark matter lead to serious problems for simple models with stable neutral Weakly Interacting Massive Particles (WIMPs) as candidates for dark matter. A possibility is discussed that new stable quarks and charged leptons exist and are hidden from detection, being bound in neutral dark atoms of composite dark matter. Stable -2 charged particles $O^{--}$ are bound with primordial helium in O-helium (OHe) atoms, being specific nuclear interacting form of composite dark matter. The positive results of DAMA experiments can be explained as annual modulation of radiative capture of O-helium by nuclei. In the framework of this approach test of DAMA results in detectors with other chemical content becomes a nontrivial task, while the experimental search of stable charged particles at LHC or in cosmic rays acquires a meaning of direct test for composite dark matter scenario.

Maxim Yu. Khlopov

2011-11-11

374

2. QUARTERMASTER STOREHOUSE (Bldg. No. 915) IN FOREGROUND WITH STABLES ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

2. QUARTERMASTER STOREHOUSE (Bldg. No. 915) IN FOREGROUND WITH STABLES (Bldg. Nos. 916 and 917) BEHIND AND TO LEFT OF Bldg. No. 915, TAKEN FROM SOUTHEAST. - Fort Lawton, Discovery Park, Seattle, King County, WA

375

Stable isotope sales: Mound customer and shipment summaries. FY 1989.  

National Technical Information Service (NTIS)

This report lists Mound's sales of stable isotopes of noble gases, carbon, oxygen, nitrogen, chlorine, bromine, and sulfur for fiscal year 1989. Purchasers are listed alphabetically and are divided into domestic and foreign groups. Cross-reference indexes...

K. A. Flayler

1991-01-01

376

New York City Ebola Patient in Stable Condition  

MedlinePLUS

... this page, please enable JavaScript. New York City Ebola Patient in Stable Condition Three contacts of Dr. ... 2015) Friday, October 24, 2014 Related MedlinePlus Page Ebola FRIDAY, Oct. 24, 2014 (HealthDay News) -- A New ...

377

Error Analysis of Space-Stable Inertial Navigation Systems  

Microsoft Academic Search

The error equations for a space-stable inertial navigation system are derived. This is done by directly perturbing the mechanization equations in the inertial frame and then transforming in open-loop fashion to the local-level frame. A rotating inertial platform and velocity and altitude damping are considered. The relations between errors in space-stable and local-level systems are noted. Numerical results are presented

Stephen Levine; Kenneth Roy

1971-01-01

378

Diagnosing subsynchronous vibrations in turbomachinery - stable or unstable  

E-print Network

DIAGNOSING SUBSYNCHRONOUS VIBRATIONS IN TURBOMACHINERY ? STABLE OR UNSTABLE A Thesis by VINAYAKA NARAYANAN RAJAGOPALAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE August 2007 Major Subject: Mechanical Engineering DIAGNOSING SUBSYNCHRONOUS VIBRATIONS IN TURBOMACHINERY ? STABLE OR UNSTABLE A Thesis by VINAYAKA NARAYANAN RAJAGOPALAN Submitted to the Office of Graduate...

Rajagopalan, Vinayaka Narayanan

2009-05-15

379

Chlorine stable isotopes in sedimentary systems: does size matter?  

NASA Technical Reports Server (NTRS)

Stable isotope abundances vary because of size differences. The chlorine stable isotope system was one of the first described theoretically, but had a slow, disappointment strewn development, relative to other elements. Method improvement gave only small, but significant, differences in compositions of geological materials. Eventually, brines and groundwater chlorides gave larger differences. Physical processes like diffusion and adsorption, probably are the main controls of groundwater compositions. Recent work on anthropogenic groundwater contaminants shows variations resulting from manufacturing processes; implying possibilities of tracing sources.

Coleman, Max

2004-01-01

380

Ultra-Stable Oscillators for Probe Radio Science Investigations  

NASA Technical Reports Server (NTRS)

An Ultra-Stable Oscillator (USO) is: A frequency reference, and A clock It is stable, small, and sensitive. It is a science and an art form. It is flown on spacecraft/probes. It]is utilized at ground stations alone or as a cleanup loop. It eliminates lock-up time on uplink for occultation egress & effect of media on uplink signal. It has enabled significant planetary science investigations.

Asmar, Sami

2012-01-01

381

Does avian malaria infection affect feather stable isotope signatures?  

Microsoft Academic Search

It is widely accepted that stable isotope ratios in inert tissues such as feather keratin reflect the dietary isotopic signature\\u000a at the time of the tissue synthesis. However, some elements such as stable nitrogen isotopes can be affected by individual\\u000a physiological state and nutritional stress. Using malaria infection experiment protocols, we estimated the possible effect\\u000a of malaria parasite infections on

Elizabeth Yohannes; Vaidas Palinauskas; Gediminas Valki?nas; Raymond W. Lee; Casimir V. Bolshakov; Staffan Bensch

382

Loneliness and stable friendship in rejected and nonrejected preschoolers  

Microsoft Academic Search

The purpose of this study was to examine the relationship of stable mutual friendship to self-reports of loneliness in preschoolers who had been nominated as rejected or nonrejected by their peers. Ninety-four 4- and 5-year-olds were classified into five peer status groups: controversial, neglected, average, popular, and rejected. In addition, the children were classified as having a stable mutual friendship,

Michael Siegal

1995-01-01

383

Stable silver colloidal dispersions using short chain polyethylene glycol  

Microsoft Academic Search

Herein we report a ‘one pot’ facile method for environmentally benign production of stable Ag colloids, using short chain polyethylene glycol as solvent, reducing agent and stabilizer. Stable spherical metal particles 15–30nm in diameter with a well-crystallized structure were obtained at 30°C. Heating to 60°C resulted in increased spherical sizes, and heating over 90°C led to a mixture of shapes:

Monica Popa; Trinitat Pradell; Daniel Crespo; José M. Calderón-Moreno

2007-01-01

384

Formation of a Coalition-Proof Stable Cartel  

Microsoft Academic Search

Formation of coalitions in oligopolies is modeled as a noncooperative game in which firms' strategies have a binary form (to cooperate or not). The author demonstrates a one-to-one correspondence between stable cartels defined by C. d'Aspremont et al. (1983) and the Nash equilibria of this game. Using a 'coalition-proof Nash equilibrium,' they define the concept of a coalition-proof stable cartel

Sylvie Thoron

1998-01-01

385

Quantification of Biochar's 'Stable' Carbon on Centennial Timescales  

NASA Astrophysics Data System (ADS)

A basic requirement for any biochar offset methodology is for the carbon in biochar to be stable and remain sequestered on centennial timescales. It is well known that a variable component of most biochar is labile (degradable on annual/decadal timescales) and hence only a proportion of total carbon in biochar provides long-term carbon sequestration. This stable fraction of biochar is in the form of polycyclic aromatic carbon (PAC) but small ring size compounds (

McBeath, Anna; Bird, Michael

2014-05-01

386

The use of stable isotopes to study ecosystem gas exchange  

Microsoft Academic Search

Stable isotopes are a powerful research tool in environmental sciences and their use in ecosystem research is increasing.\\u000a In this review we introduce and discuss the relevant details underlying the use of carbon and oxygen isotopic compositions\\u000a in ecosystem gas exchange research. The current use and potential developments of stable isotope measurements together with\\u000a concentration and flux measurements of CO2

D. Yakir; L. da S. L. Sternberg

2000-01-01

387

7. OVERALL VIEW OF ROOM 110 (STABLES), LOOKING EAST. THE ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

7. OVERALL VIEW OF ROOM 110 (STABLES), LOOKING EAST. THE LONG, LOW SPACE IS DIVIDED INTO AISLES BY EXPOSED POSTS AND BEAMS; POSTS ARE PAINTED. CEILING TREATMENT CHANGES FROM GYPSUM BOARD TO WOOD PLANKS IN THE CENTER AISLE. THE CONCRETE SLAB FLOOR IS SLOPED FROM CENTER FOR DRAINAGE PURPOSES. SMALL, HIGH WINDOWS LINE THE NORTHEAST AND SOUTHWEST WALLS. - Presidio of San Francisco, Cavalry Stables, Cowles Street, between Lincoln Boulevard & McDowell Street, San Francisco, San Francisco County, CA

388

Meta-Stable Brane Configurations by Quartic Superpotential for Bifundamentals  

E-print Network

The type IIA nonsupersymmetric meta-stable brane configuration consisting of three NS5-branes, D4-branes and anti-D4-branes where the electric gauge theory superpotential has a quartic term for the bifundamentals besides a mass term is constructed. By adding the orientifold 4-plane and 6-plane to this brane configuration, we also describe the intersecting brane configurations of type IIA string theory corresponding to the meta-stable nonsupersymmetric vacua of corresponding gauge theories.

Changhyun Ahn

2008-01-04

389

The $G$-stable pieces of the wonderful compactification  

Microsoft Academic Search

Let $G$ be a connected, simple algebraic group over an algebraically closed\\u000afield. There is a partition of the wonderful compactification $\\\\bar{G}$ of $G$\\u000ainto finite many $G$-stable pieces, which were introduced by Lusztig. In this\\u000apaper, we will investigate the closure of any $G$-stable piece in $\\\\bar{G}$. We\\u000awill show that the closure is a disjoint union of some

Xuhua He

2007-01-01

390

Asynchronous pupation of univoltine insects as evolutionarily stable phenology  

Microsoft Academic Search

Summary  Evolutionarily stable seasonal timing of larval feeding stages is studied theoretically for univoltine insects. In the evolutionarily\\u000a stable (or ESS) population, each individual maximizes its own lifetime reproductive success by choosing the hatching and pupation\\u000a dates, given the resource availability curve with a peak in the middle of a year, a higher daily mortality in the feeding\\u000a stages, and the

Yoh Iwasa

1991-01-01

391

Generalization of symmetric ?-stable Lévy distributions for q >1  

NASA Astrophysics Data System (ADS)

The ?-stable distributions introduced by Lévy play an important role in probabilistic theoretical studies and their various applications, e.g., in statistical physics, life sciences, and economics. In the present paper we study sequences of long-range dependent random variables whose distributions have asymptotic power-law decay, and which are called (q,?)-stable distributions. These sequences are generalizations of independent and identically distributed ?-stable distributions and have not been previously studied. Long-range dependent (q,?)-stable distributions might arise in the description of anomalous processes in nonextensive statistical mechanics, cell biology, finance. The parameter q controls dependence. If q =1 then they are classical independent and identically distributed with ?-stable Lévy distributions. In the present paper we establish basic properties of (q,?)-stable distributions and generalize the result of Umarov et al. [Milan J. Math. 76, 307 (2008)], where the particular case ? =2,q?[1,3) was considered, to the whole range of stability and nonextensivity parameters ? ?(0,2] and q ?[1,3), respectively. We also discuss possible further extensions of the results that we obtain and formulate some conjectures.

Umarov, Sabir; Tsallis, Constantino; Gell-Mann, Murray; Steinberg, Stanly

2010-03-01

392

Equilibrium contact angle or the most-stable contact angle?  

PubMed

It is well-established that the equilibrium contact angle in a thermodynamic framework is an "unattainable" contact angle. Instead, the most-stable contact angle obtained from mechanical stimuli of the system is indeed experimentally accessible. Monitoring the susceptibility of a sessile drop to a mechanical stimulus enables to identify the most stable drop configuration within the practical range of contact angle hysteresis. Two different stimuli may be used with sessile drops: mechanical vibration and tilting. The most stable drop against vibration should reveal the changeless contact angle but against the gravity force, it should reveal the highest resistance to slide down. After the corresponding mechanical stimulus, once the excited drop configuration is examined, the focus will be on the contact angle of the initial drop configuration. This methodology needs to map significantly the static drop configurations with different stable contact angles. The most-stable contact angle, together with the advancing and receding contact angles, completes the description of physically realizable configurations of a solid-liquid system. Since the most-stable contact angle is energetically significant, it may be used in the Wenzel, Cassie or Cassie-Baxter equations accordingly or for the surface energy evaluation. PMID:24140073

Montes Ruiz-Cabello, F J; Rodríguez-Valverde, M A; Cabrerizo-Vílchez, M A

2014-04-01

393

Manipulation and gender neutrality in stable marriage procedures  

E-print Network

The stable marriage problem is a well-known problem of matching men to women so that no man and woman who are not married to each other both prefer each other. Such a problem has a wide variety of practical applications ranging from matching resident doctors to hospitals to matching students to schools. A well-known algorithm to solve this problem is the Gale-Shapley algorithm, which runs in polynomial time. It has been proven that stable marriage procedures can always be manipulated. Whilst the Gale-Shapley algorithm is computationally easy to manipulate, we prove that there exist stable marriage procedures which are NP-hard to manipulate. We also consider the relationship between voting theory and stable marriage procedures, showing that voting rules which are NP-hard to manipulate can be used to define stable marriage procedures which are themselves NP-hard to manipulate. Finally, we consider the issue that stable marriage procedures like Gale-Shapley favour one gender over the other, and we show how to us...

Pini, Maria; Venable, Brent; Walsh, Toby

2009-01-01

394

Medieval horse stable; the results of multi proxy interdisciplinary research.  

PubMed

A multi proxy approach was applied in the reconstruction of the architecture of Medieval horse stable architecture, the maintenance practices associated with that structure as well as horse alimentation at the beginning of 13th century in Central Europe. Finally, an interpretation of the local vegetation structure along Morava River, Czech Republic is presented. The investigated stable experienced two construction phases. The infill was well preserved and its composition reflects maintenance practices. The uppermost part of the infill was composed of fresh stabling, which accumulated within a few months at the end of summer. Horses from different backgrounds were kept in the stable and this is reflected in the results of isotope analyses. Horses were fed meadow grasses as well as woody vegetation, millet, oat, and less commonly hemp, wheat and rye. Three possible explanations of stable usage are suggested. The stable was probably used on a temporary basis for horses of workers employed at the castle, courier horses and horses used in battle. PMID:24670874

Dejmal, Miroslav; Lisá, Lenka; Fišáková Nývltová, Miriam; Bajer, Aleš; Petr, Libor; Ko?ár, Petr; Ko?árová, Romana; Nejman, Ladislav; Rybní?ek, Michal; S?vová, Zdenka; Culp, Randy; Vavr?ík, Hanuš

2014-01-01

395

The stable problem in the Rindler space-time  

E-print Network

We carefully study the stable problem of the Rindler space time by the scalar wave perturbation. Using the two different coordinate systems, the scalar wave equation is investigated. The results are different in these two cases. They are analyzed and compared in detail. The conclusions are: (a) the Rindler space time as a whole is not stable; (b) the Rindler space time could exist stably only as a part of the Minkowski space time, and the Minkowski space time could be a real entity independently; (c) there are some defects for the scalar wave equation written by the Rindler coordinates, and it is unsuitable for investigation of the stable properties of the Rindler space time. All these results might shed some lights on the stable properties of the Schwarzschild black hole. It is natural and not unreasonable for one to infer that: (a) perhaps the Regge-Wheeler equation is not sufficient to decide the stable properties; (b) the Schwarzschild black hole as a whole might be really unstable; (c) the Kruskal space time is stable and can exist as a real physical entity ; whereas the Schwarzschild black hole could occur only as part of the Kruskal space time.

Tian Gui-hua; Shi-kun Wang; Shuquan Zhong

2006-08-09

396

Medieval Horse Stable; The Results of Multi Proxy Interdisciplinary Research  

PubMed Central

A multi proxy approach was applied in the reconstruction of the architecture of Medieval horse stable architecture, the maintenance practices associated with that structure as well as horse alimentation at the beginning of 13th century in Central Europe. Finally, an interpretation of the local vegetation structure along Morava River, Czech Republic is presented. The investigated stable experienced two construction phases. The infill was well preserved and its composition reflects maintenance practices. The uppermost part of the infill was composed of fresh stabling, which accumulated within a few months at the end of summer. Horses from different backgrounds were kept in the stable and this is reflected in the results of isotope analyses. Horses were fed meadow grasses as well as woody vegetation, millet, oat, and less commonly hemp, wheat and rye. Three possible explanations of stable usage are suggested. The stable was probably used on a temporary basis for horses of workers employed at the castle, courier horses and horses used in battle. PMID:24670874

Dejmal, Miroslav; Lisa, Lenka; Fisakova Nyvltova, Miriam; Bajer, Ales; Petr, Libor; Kocar, Petr; Kocarova, Romana; Nejman, Ladislav; Rybnicek, Michal; Suvova, Zdenka; Culp, Randy; Vavrcik, Hanus

2014-01-01

397

Carbene reactions produced by recoil excitation methods  

E-print Network

and CTCT. Reactions of CTF with 1, 3-butadiene, aliene, and cyclohexene were studied. Also, products of the Diels-Alder retrogression reaction of cyclohexene were observed when high energy tritium atoms reacted with cyclohexene. A qualitative discussion.... Experimental III. 'Reaction of Tritium-Labeled Monofluorocarbene with Higher Olefins 31 IV. Reactions of F -La'baled Monofluorocarbene V. Formation of Monochlorocarbene-Clgg VI. Formation of Monobromoc"rbene-Br VII. Diels-Alder Retrogression Reaction...

Lowery, Kirby

2012-06-07

398

N-heterocyclic carbene catalysis: expansion of  

E-print Network

Asymmetric hydrogenation as a general route to polypropionates has been explored for allylic alcohols, acids, and derivatives, which has led to the generation of 2,4-dimethylated hexane derivatives. Quantitative yields in most cases...

Ogle, James William

2009-05-15

399

Multi-stable perception balances stability and sensitivity  

PubMed Central

We report that multi-stable perception operates in a consistent, dynamical regime, balancing the conflicting goals of stability and sensitivity. When a multi-stable visual display is viewed continuously, its phenomenal appearance reverses spontaneously at irregular intervals. We characterized the perceptual dynamics of individual observers in terms of four statistical measures: the distribution of dominance times (mean and variance) and the novel, subtle dependence on prior history (correlation and time-constant). The dynamics of multi-stable perception is known to reflect several stabilizing and destabilizing factors. Phenomenologically, its main aspects are captured by a simplistic computational model with competition, adaptation, and noise. We identified small parameter volumes (~3% of the possible volume) in which the model reproduced both dominance distribution and history-dependence of each observer. For 21 of 24 data sets, the identified volumes clustered tightly (~15% of the possible volume), revealing a consistent “operating regime” of multi-stable perception. The “operating regime” turned out to be marginally stable or, equivalently, near the brink of an oscillatory instability. The chance probability of the observed clustering was <0.02. To understand the functional significance of this empirical “operating regime,” we compared it to the theoretical “sweet spot” of the model. We computed this “sweet spot” as the intersection of the parameter volumes in which the model produced stable perceptual outcomes and in which it was sensitive to input modulations. Remarkably, the empirical “operating regime” proved to be largely coextensive with the theoretical “sweet spot.” This demonstrated that perceptual dynamics was not merely consistent but also functionally optimized (in that it balances stability with sensitivity). Our results imply that multi-stable perception is not a laboratory curiosity, but reflects a functional optimization of perceptual dynamics for visual inference. PMID:23518509

Pastukhov, Alexander; Garcia-Rodriguez, Pedro E.; Haenicke, Joachim; Guillamon, Antoni; Deco, Gustavo; Braun, Jochen

2013-01-01

400

STABLE BEHAVIORAL INHIBITION AND GLUCOCORTICOID PRODUCTION AS PREDICTORS OF LONGEVITY  

PubMed Central

Several personality/temperament traits have been linked to health outcomes in humans and animals but underlying physiological mechanisms for these differential outcomes are minimally understood. In this paper, we compared the strength of a behavioral trait (behavioral inhibition) and an associated physiological trait (glucocorticoid production) in predicting life span. In addition, we examined the relative stability of both the behavioral and physiological trait within individuals over a significant portion of adulthood, and tested the hypothesis that a stable behavioral trait is linked with a stable physiological bias. In a sample of 60 Sprague-Dawley male rats, we found that stable inhibition/neophobia was a stronger predictor of life span than stably elevated glucocorticoid production. In addition, these predictors appeared to have an additive influence on life span in that males with both risk factors (stable inhibition and consistently high glucocorticoid production) had the shortest life spans of all, suggesting both traits are important predictors of life span. Across a 4-month period in young adulthood, inhibition and glucocorticoid reactivity were relatively stable traits, however these two traits were not highly correlated with one another. Interestingly, baseline glucocorticoid production was a better predictor of life span than reactivity levels. The results indicate that glucocorticoid production in young adulthood is an important predictor of life span, although not as strong a predictor as inhibition, and that other physiological processes may further explain the shortened life span in behaviorally-inhibited individuals. PMID:19477191

Cavigelli, Sonia A.; Ragan, Christina M.; Michael, Kerry C.; Kovacsics, Colleen E.; Bruscke, Alexander P.

2009-01-01

401

Development of Stable Influenza Vaccine Powder Formulations: Challenges and Possibilities  

PubMed Central

Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine. PMID:18338241

Amorij, J-P.; Huckriede, A.; Wilschut, J.; Frijlink, H. W.

2008-01-01

402

Stable Isotope Ratios and the Forensic Analysis of Microorganisms  

SciTech Connect

In the aftermath of the anthrax letters of 2001, researchers have been exploring various analytical signatures for the purpose of characterizing the production environment of microorganisms. One such signature is stable isotope ratios, which in heterotrophs are a function of nutrient and water sources. Here we discuss the use of stable isotope ratios in microbe forensics, using as a database the carbon, nitrogen, oxygen and hydrogen stable isotope ratios of 247 separate cultures of B. subtilis 6051 spores produced on a total of 32 different culture media. In the context of using stable isotope ratios as a signature for sample matching, we present an analysis of variation between individual samples, between cultures produced in tandem, and between cultures produced in the same medium but at different times. Additionally, we correlate the stable isotope ratios of carbon, nitrogen, oxygen, and hydrogen for growth medium nutrients or water with those of spores and show examples of how these relationships can be used to exclude nutrient or water samples as possible growth substrates for specific cultures.

Kreuzer-Martin, Helen W.; Jarman, Kristin H.

2007-06-01

403

Longwall mining installation having stable-hole plough  

SciTech Connect

A longwall mineral mining installation has a longwall conveyor, a plough guide attached to the face-side of the conveyor, and a main plough movable to and fro along the guide. A respective stable-hole plough is movable to and fro along portions of the plough guide adjacent to each end of the conveyor. Each stablehole plough is driven by means of a respective endless drive chain which passes round two end sprockets. One end sprocket of each stable-hole plough is positioned at the face-side of the conveyor part way therealong. The other end sprocket of each stable-hole plough is positioned at the adjacent end of the conveyor on the goaf-side thereof. Each drive chain passes round a direction-changing unit positioned at the adjacent end of the conveyor.

Hauschopp, A.

1981-07-21

404

Electro-optical frequency division and stable microwave synthesis.  

PubMed

Optical frequency division by using frequency combs has revolutionized time keeping and the generation of stable microwave signals. We demonstrate optical frequency division and microwave generation by using a tunable electrical oscillator to create dual combs through phase modulation of two optical signals that have a stable difference frequency. Phase-locked control of the electrical oscillator by means of optical frequency division produces stable microwaves. Our approach transposes the oscillator and frequency reference of a conventional microwave frequency synthesizer. In this way, the oscillator experiences large phase noise reduction relative to the frequency reference. The electro-optical approach additionally relaxes the need for highly linear photodetection of the comb mode spacing. As well as simplicity, the technique is also tunable and scalable to higher division ratios. PMID:25035489

Li, Jiang; Yi, Xu; Lee, Hansuek; Diddams, Scott A; Vahala, Kerry J

2014-07-18

405

A Note on (Meta)stable Brane Configurations in MQCD  

E-print Network

We examine the M-theory version of SQCD which is known as MQCD. In the IIA limit, this theory appears to have a supersymmetry-breaking brane configuration which corresponds to the meta-stable state of N=1 SU(Nc) SQCD. However, the behavior at infinity of this non-supersymmetric brane construction differs from that of the supersymmetric ground state of MQCD. We interpret this to mean that it is not a meta-stable state in MQCD, but rather a state in another theory. This provides a concrete example of the fact that, while MQCD accurately describes the supersymmetric features of SCQD, it fails to reproduce its non-supersymmetric features (such as meta-stable states) not only quantitatively but also qualitatively.

I. Bena; E. Gorbatov; S. Hellerman; N. Seiberg; D. Shih

2006-08-22

406

Intermittent Turbulence in the Very Stable Ekman Layer  

SciTech Connect

INTERMITTENT TURBULENCE IN THE VERY STABLE EKMAN LAYER This study describes a Direct Numerical Simulation (DNS) of a very stable Ekman layer in which a constant downward heat flux is applied at the lower boundary, thus cooling the fluid above. Numerical experiments were performed in which the strength of the imposed heat flux was varied. For downward heat fluxes above a certain critical value the turbulence becomes intermittent and, as the heat flux increases beyond this value, the flow tends to relaminarize because of the very strong ambient stratification. We adopt Mahrt?s (1999) definition of the very stable boundary layer as a boundary layer in which intermittent, rather than continuous turbulence, is observed. Numerical experiments were used to test various hypothesis of where in ?stability parameter space? the very stable boundary layer is found. These experiments support the findings of Howell and Sun (1999) that the boundary layer will exhibit intermittency and therefore be categorized as ?very stable?, when the stability parameter, z/L, exceeds unity. Another marker for the very stable boundary layer, Derbyshire?s (1990) maximum heat flux criterion, was also examined. Using a case study drawn from the simulations where turbulence intermittency was observed, the mechanism that causes the intermittence was investigated. It was found that patchy turbulence originates from a vigorous inflectional, Ekman-like instability -- a roll cell -- that lifts colder air over warmer air. The resulting convective instability causes an intense burst of turbulence. This turbulence is short-lived because the lifting motion of the roll cell, as well as the roll cell itself, is partially destroyed after the patchy turbulence is generated. Examples of intermittent turbulence obtained from the simulations appear to be consistent with observations of intermittency even though the Reynolds number of the DNS is relatively low (400).

Barnard, James C.

2001-01-05

407

Life-satisfaction is a momentary judgment and a stable personality characteristic: the use of chronically accessible and stable sources.  

PubMed

Social cognition research indicates that life-satisfaction judgments are based on a selected set of relevant information that is accessible at the time of the life-satisfaction judgment. Personality research indicates that life-satisfaction judgments are quite stable over extended periods of time and predicted by personality traits. The present article integrates these two research traditions. We propose that people rely on the same sources to form repeated life-satisfaction judgments over time. Some of these sources (e.g., memories of emotional experiences, academic performance) provide stable information that explains the stability in life-satisfaction judgments. Second, we propose that the influence of personality traits on life satisfaction is mediated by the use of chronically accessible sources because traits produce stability of these sources. Most important, the influence of extraversion and neuroticism is mediated by use of memories of past emotional experiences. To test this model, participants repeatedly judged life-satisfaction over the course of a semester. After each assessment, participants reported sources that they used for these judgments. Changes in reported sources were related to changes in life-satisfaction judgments. A path model demonstrated that chronically accessible and stable sources are related to stable individual differences in life-satisfaction. Furthermore, the model supported the hypothesis that personality effects were mediated by chronically accessible and stable sources. In sum, the results are consistent with our theory that life-satisfaction judgments are based on chronically accessible sources. PMID:12049164

Schimmack, Ulrich; Diener, Ed; Oishi, Shigehiro

2002-06-01

408

Metal stable isotopes in low-temperature systems: A primer  

USGS Publications Warehouse

Recent advances in mass spectrometry have allowed isotope scientists to precisely determine stable isotope variations in the metallic elements. Biologically infl uenced and truly inorganic isotope fractionation processes have been demonstrated over the mass range of metals. This Elements issue provides an overview of the application of metal stable isotopes to low-temperature systems, which extend across the borders of several science disciplines: geology, hydrology, biology, environmental science, and biomedicine. Information on instrumentation, fractionation processes, data-reporting terminology, and reference materials presented here will help the reader to better understand this rapidly evolving field.

Bullen, T.D.; Eisenhauer, A.

2009-01-01

409

[Ranolazine--new treatment of chronic stable angina pectoris].  

PubMed

Ranolazine sustained-release tablets were recently approved in the EU for chronic stable angina as add-on therapy when symptoms are not controlled with first-line agents. The mechanism of action is thought to involve inhibition of late sodium influx in the heart, which can reduce abnormalities of contractility and repolarisation associated with ischaemia. Ranolazine increases the exercise capacity, reduces angina, and diminishes the use of nitroglycerine. The drug has an excellent safety profile and may be a valuable addition to the treatment of chronic stable angina. PMID:20003868

Ahlehoff, Ole; Hansen, Peter Riis

2009-12-01

410

On the existence of stable seasonally varying Arctic sea ice  

E-print Network

Within the framework lower order thermodynamic theories for the climatic evolution of Arctic sea ice we isolate the conditions required for the existence of stable seasonally-varying ice states. This is done by constructing a two-season model from the continuously evolving theory of Eisenman and Wettlaufer (2009) and showing that the necessary and sufficient condition for stable seasonally-varying states resides in the relaxation of the constant annual average short-wave radiative forcing. This forcing is examined within the scenario of greenhouse gas warming, as a function of which stability conditions are discerned.

Moon, W

2012-01-01

411

Example of a stable wormhole in general relativity  

NASA Astrophysics Data System (ADS)

We study a static, spherically symmetric wormhole model whose metric coincides with that of the so-called Ellis wormhole but the material source of gravity consists of a perfect fluid with negative density and a source-free radial electric or magnetic field. For a certain class of fluid equations of state, it has been shown that this wormhole model is linearly stable under both spherically symmetric perturbations and axial perturbations of arbitrary multipolarity. A similar behavior is predicted for polar nonspherical perturbations. It thus seems to be the first example of a stable wormhole model in the framework of general relativity (at least without invoking phantom thin shells as wormhole sources).

Bronnikov, K. A.; Lipatova, L. N.; Novikov, I. D.; Shatskiy, A. A.

2013-10-01

412

Stable chromosome aberrations 25 years after severe accidental radiation exposure.  

PubMed

A thorough cytogenetic analysis using G-banding was performed on 100 peripheral blood lymphocytes from an individual who had been accidentally exposed to radiation more than 25 years previously. More than 60% of the analysed cells were found to possess one or more stable chromosome aberrations (e.g. reciprocal translocations). Chromosomes 1 and 11 were more involved in these aberrations than would be expected from the relative chromosome lengths. No identical stable aberrations were found, suggesting that, 25 years after near-lethal exposure, haemopoietic stem cells display substantial diversity. PMID:8310126

Maes, A; Hilali, A; Léonard, E D; Léonard, A; Verschaeve, L

1993-01-01

413

Stable polarization-encoded quantum key distribution in fiber  

E-print Network

Polarizations of single-photon pulses have been controlled with long-term stability of more than 10 hours by using an active feedback technique for auto-compensation of unpredictable polarization scrambling in long-distance fiber. Experimental tests of long-term operations in 50, 75 and 100 km fibers demonstrated that such a single-photon polarization control supported stable polarization encoding in long-distance fibers to facilitate stable one-way fiber system for polarization-encoded quantum key distribution, providing quantum bit error rates below the absolute security threshold.

Guang Wu; Jie Chen; Yao Li; Heping Zeng

2006-06-13

414

Remarks on search methods for stable, massive, elementary particles  

NASA Astrophysics Data System (ADS)

This paper was presented at the 69th birthday celebration of Professor Eugene Commins, honoring his research achievements. These remarks are about the experimental techniques used in the search for new stable, massive particles, particles at least as massive as the electron. A variety of experimental methods such as accelerator experiments, cosmic ray studies, searches for halo particles in the galaxy and searches for exotic particles in bulk matter are described. A summary is presented of the measured limits on the existence of new stable, massive particle. .

Perl, Martin L.

2001-11-01

415

Fiber Optic Cable Thermal Preparation to Ensure Stable Operation  

NASA Technical Reports Server (NTRS)

Fiber optic cables are widely used in modern systems that must provide stable operation during exposure to changing environmental conditions. For example, a fiber optic cable on a satellite may have to reliably function over a temperature range of -50 C up to 125 C. While the system requirements for a particular application will dictate the exact method by which the fibers should be prepared, this work will examine multiple ruggedized fibers prepared in different fashions and subjected to thermal qualification testing. The data show that if properly conditioned the fiber cables can provide stable operation, but if done incorrectly, they will have large fluctuations in transmission.

Thoames Jr, William J.; Chuska, Rick F.; LaRocca, Frank V.; Switzer, Robert C.; Macmurphy, Shawn L.; Ott, Melanie N.

2008-01-01

416

Meta-stable States in Quark-Gluon Plasma  

E-print Network

We study the meta-stable states in high temperature phase of QCD characterised by nonzero expectation values for the imaginary part of the Polyakov loop. We consider $N_f= 2, 3$ dynamical staggered quarks, and carry out simulations at various values of the coupling $\\beta$ to observe these states. In particular, we find the value of the coupling ($\\beta_m$) above which the meta-stable states appear. The resulting value of $\\beta_m$ corresponds to temperature $T_m \\gtrsim 750$MeV for $N_f=2$.

Mridupawan Deka; Sanatan Digal; Ananta P. Mishra

2010-09-03

417

Formation of stable radicals in the radiolysis of hexafluoropropylene  

SciTech Connect

The radiolysis of the dimer (perfluoro-4-methyl-2-pentene) and trimer (perfluoro-2,4-dimethyl-3-ethyl-2-pentene) of hexafluoropropylene (HFP) gives thermally stable perfluoroalkyl radicals. The stability of these radicals is apparently related to the steric isolation of the unpaired electron. The formation of a growing oligomer chain perfluoroalkyl radical which is stable in the liquid phase is observed upon the radiolysis of hexafluoropropylene. The radio-chemical yield of such a radical G approx. 0.05 x 10/sup -2/ eV. The low capacity of hexafluoropropylene to undergo homopolymerization is related to the formation of similar inactive radicals.

Allayarov, S.R.; Barkalov, I.M.; Lebedeva, M.Yu.; Loginova, N.N.; Mikhailov, A.I.

1986-08-20

418

Stable Isotopic Tracing--A Way Forward for Nanotechnology  

PubMed Central

Numerous publications and reports have expressed health and safety concerns about the production and use of nanoparticles, especially in areas of exposure monitoring, personal use, and environmental fate and transport. We suggest that stable isotopic tracers, which have been used widely in the earth sciences and in metabolic and other health-related studies for several decades, could be used to address many of these issues. One such example we are pursuing is the use of stable isotopes to monitor dermal absorption of zinc and titanium oxides in sunscreen preparations and other personal care products. Other potential applications of this tracing approach are discussed. PMID:17035130

Gulson, Brian; Wong, Herbert

2006-01-01

419

STABLE ISOTOPE DYNAMICS IN SUMMER FLOUNDER TISSUES, WITH APPLICATION TO DIETARY ASSESSMENTS IN CHESAPEAKE BAY  

E-print Network

STABLE ISOTOPE DYNAMICS IN SUMMER FLOUNDER TISSUES, WITH APPLICATION TO DIETARY ASSESSMENTS Growth rates........................................................................18 Isotopic turnover 2: STABLE ISOTOPE ANALYSIS OF SUMMER FLOUNDER DIETS IN CHESAPEAKE BAY

Newman, Michael C.

420

Stoichiometry effect on stable isotope analysis of dolomite  

Microsoft Academic Search

Dolomite admixed with calcite in partially dolomitized limestones is often nonstoichiometric. Precise stable isotope compositions of these two minerals in such samples are difficult to determine. Differential acid extraction and weak-acid leaching are the two common methods used. In the present study, we evaluate the validity of these methods. Our results show that the reaction rate between dolomite and phosphoric

Tzen-Fu Yui; Shou-Yeh Gong

2003-01-01

421

Stable isotope analysis of nutrient pathways leading to Atlantic salmon  

Microsoft Academic Search

The relative contribution of terrestrial and aquatic primary energy sources in food webs along a stream continuum in the Miramichi River system, New Brunswick, was investigated through the use of stable carbon and nitrogen isotope ratios. In sites where these primary energy sources were isotopically distinct, quantitative mixing models were used to identify the relative importance of allochthonous carbon in

Richard R. Doucett; G. Power; D. R. Barton; R. J. Drimmie; R. A. Cunjak

1996-01-01

422

Egalitarian Stable Matching for VM Migration in Cloud Computing  

E-print Network

Egalitarian Stable Matching for VM Migration in Cloud Computing Hong Xu, Baochun Li Department--Virtual machine migration represents a new chal- lenge to design efficient and practical migration algorithms acceptance. In this paper, we apply this framework to the VM migration problem, and propose an egalitarian

Li, Baochun

423

Carbon dioxide sequestration as stable carbonate minerals - environmental barriers  

Microsoft Academic Search

This paper considers the major environmental impacts associated with industrial-scale carbon dioxide sequestration as stable carbonate minerals, material resulting from a study undertaken by CSMA Consultants Ltd. in 1999. The chemical bonding of carbon dioxide, through reaction of two or more products to produce magnesium or calcium carbonate has been suggested as a means to mitigate CO2 from fossil fuel

H. Haywood; J. Eyre; H. Scholes

2001-01-01

424

Carbon Stable Isotopes as Indicators of Coastal Eutrophication  

EPA Science Inventory

Coastal ecologists and managers have frequently used nitrogen stable isotopes (?15N) to trace and monitor anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of ?15N data can often be challenging, if not confounding, as the isotope values fr...

425

Stable Isotope Tracers of Process in Great Lakes Food Webs  

EPA Science Inventory

Stable isotope analyses of biota are now commonly used to discern trophic pathways between consumers and their foods. However, those same isotope data also hold information about processes that influence the physicochemical setting of food webs as well as biological processes ope...

426

Critical conditions for stable dipole-bound dianions Alejandro Ferrna  

E-print Network

Critical conditions for stable dipole-bound dianions Alejandro Ferróna and Pablo Serrab Facultad de size scaling calculations of the critical parameters for binding two electrons to a finite linear dipole field. This approach gives very accurate results for the critical parameters by using a systematic

Kais, Sabre

427

Characterizations of the Disjunctive Stable Semantics by Partial Evaluation  

Microsoft Academic Search

There are three most prominent semantics defined for certain subclasses of disjunctive logic programs: GCWA (for positive programs), PERFECT (for stratified programs), and STABLE (defined for the whole class of all disjunctive programs). While there are various competitors based on 3-valued models, notably WFS and its disjunctive counterparts, there are no other semantics consisting of two-valued models. We argue that

Stefan Brass; Jürgen Dix

1997-01-01

428

Method of producing a dimensionally stable battery separator  

Microsoft Academic Search

A method is disclosed for producing a dimensionally stable battery separator characterized by grafting acrylic acid and\\/or methacrylic acid onto a polyethylene film, treating the resulting membrane with an aqueous alkaline solution, and drying the treated membrane under application of tension.

I. Ishigaki; S. Machi; K. Murata; K. Senoo; T. Sugo; S. Tanso

1981-01-01

429

BMJ Publishing Group http://www.jstor.org/stable/27726393  

E-print Network

BMJ Publishing Group http://www.jstor.org/stable/27726393 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission

Ahmad, Sajjad

430

BMJ Publishing Group http://www.jstor.org/stable/27727279  

E-print Network

BMJ Publishing Group http://www.jstor.org/stable/27727279 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission

Ahmad, Sajjad

431

Sleeping Our Way to Weight Normalization and Stable Learning  

E-print Network

Sleeping Our Way to Weight Normalization and Stable Learning Thomas J. Sullivan1 & Virginia R. de Jolla, California Abstract The functions of sleep have been an enduring mystery. Recently, Tononi and Cirelli hypothesized that one of the functions of slow-wave sleep is to scale down synapses in the cortex

Zhou, Yuanyuan

432

Stable Sleeping in DSL Broadband Access: Feasibility and Tradeoffs  

E-print Network

1 Stable Sleeping in DSL Broadband Access: Feasibility and Tradeoffs Ioannis Kamitsos1,Paschalis means to obtain energy savings is the use of low power "sleep modes", putting DSL modems to sleep when they are not used. Executing the optimal sleeping policies is, however, not straightforward since turning the modem

433

f-beta Power Spectrum and Stable Distribution  

Microsoft Academic Search

The fractional integral of white noise produces a fractal fluctuation with a f-beta power spectrum. By generalizing Holtzmark's method, we can exactly calculate the distribution function of the fluctuation. The obtained distribution is the Levy's stable distribution of which the characteristic exponent is a simple function of beta. This result may give a new insight to the basic study of

Hideki Takayasu

1987-01-01

434

Stable isotope ecology in the Omo-Turkana Basin.  

PubMed

Stable isotopes provide an independent assessment of paleoenvironments in the Omo-Turkana Basin. Stable isotopes track the flow of oxygen and carbon through ecosystems and accordingly are not directly related to changes in mammalian faunal composition or sedimentology. Therefore, isotope studies give insight into the paleoenvironmental conditions in which human evolutionary trends have been recorded. The development of stable isotopes as indicators of continental environmental conditions has proceeded in parallel with questions about the conditions of human environment. What was the vegetation? How hot was it? How dry? What were the diets of animals living among early humans? And most persistently, how important were "savannas" to early hominids? In this review, we take the opportunity to provide extensive background on the use of isotopes in anthropological sites. The application of stable isotope ecology to anthropological sites in the Turkana Basin has a long history, but in many ways the Omo-Turkana Basin has been a proving ground for the development of new proxy methods for understanding tropical terrestrial environments in the Neogene and Quaternary. For that reason, we also describe some of the fundamental aspects of isotope ecology that developed outside the field of paleoanthropology. PMID:22170692

Cerling, Thure E; Levin, Naomi E; Passey, Benjamin H

2011-01-01

435

Male optimal and unique stable marriages with partially ordered preferences  

E-print Network

men and women express a strict order over the members of the other sex. Here we consider a more of the opposite sex, the problem is to match the men to the women so that there are no two people of opposite sex students to secondary schools [12], as well as in market trading. #12;In the classical stable marriage

Rossi, Francesca

436

APPLICATION OF STABLE ISOTOPE TECHNIQUES TO AIR POLLUTION RESEARCH  

EPA Science Inventory

Stable isotope techniques provide a robust, yet under-utilized tool for examining pollutant effects on plant growth and ecosystem function. Here, we survey a range of mixing model, physiological and system level applications for documenting pollutant effects. Mixing model examp...

437

Stable multivariate Eulerian polynomials and generalized Stirling permutations  

E-print Network

Stable multivariate Eulerian polynomials and generalized Stirling permutations J. Haglund, Mirk Abstract We study Eulerian polynomials as the generating polynomials of the descent statistic over Stirling Eulerian polyno- mial for permutations, and extends naturally to r-Stirling and generalized Stirling

Haglund, Jim

438

Robust multiuser detection in ?-stable distribution non-Gaussian noise  

E-print Network

-direction slowest-decent-search technique is still effective. The subspace-based technique for blind adaptive robust multiuser detectors, however, doesn't work very well when the ambient non Gaussian noise is ?-stable distribution. In the last chapter, we...

Zhang, Jing

2012-06-07

439

Broken Homes: Stable Risk, Changing Reasons, Changing Forms.  

ERIC Educational Resources Information Center

Cohort membership and two measures of social disadvantage were used as explanatory variables in analysis of the risk of growing up in a broken home and of the living arrangements of children with broken homes. The risk of a broken home by age 16 proved to be stable across cohorts and greater for those from disadvantaged homes. (Author/BL)

Sweetser, Dorrian Apple

1985-01-01

440

A biomarker based on the stable isotopes of nickel  

PubMed Central

The new stable isotope systems of transition metals are increasingly used to understand and quantify the impact of primitive microbial metabolisms on the modern and ancient Earth. To date, little effort has been expended on nickel (Ni) isotopes but there are good reasons to believe that this system may be more straightforward, and useful in this respect, than some others. Here, we present Ni stable isotope data for abiotic terrestrial samples and pure cultures of methanogens. The dataset for rocks reveals little isotopic variability and provides a lithologic baseline for terrestrial Ni isotope studies. In contrast, methanogens assimilate the light isotopes, yielding residual media with a complementary heavy isotopic enrichment. Methanogenesis may have evolved during or before the Archean, when methane could have been key to Earth's early systems. Our data suggest significant potential in Ni stable isotopes for identifying and quantifying methanogenesis on the early planet. Additionally, Ni stable isotope fractionation may well prove to be the fundamental unambiguous trace metal biomarker for methanogens. PMID:19553218

Cameron, Vyllinniskii; Vance, Derek; Archer, Corey; House, Christopher H.

2009-01-01

441

Stresses and Strains within the "Stable" North American Plate  

NASA Technical Reports Server (NTRS)

This paper presents a final report on "Stresses and Strains within the "Stable" North American Plate". The topics include: 1) Strain rates near the New Madrid seismic zone; 2) Signal Processing of intermediate term data; and 3) Transform fault stresses and strains. The paper also includes graphs of the stress and strain distributions.

Engeln, Joe

1995-01-01

442

Microbiological fractionation of stable sulfur isotopes: A review and critique  

Microsoft Academic Search

Microbiological transformations of sulfur compounds discriminate to various degrees between the stable sulfur isotopes S and S. Comparatively little is known on isotopic effects associated with sulfur?oxidizing organisms, and the interpretation of results is complicated since the sulfur pathways are poorly defined and compounds containing two or more sulfur atoms at different oxidation states may be involved. Dissimilatory reduction of

L. A. Chambers; P. A. Trudinger

1979-01-01

443

Bialaphos selection of stable transformants from maize cell culture  

Microsoft Academic Search

Stable transformed Black Mexican Sweet (BMS) maize callus was recovered from suspension culture cells bombarded with plasmid DNA that conferred resistance to the herbicide bialaphos. Suspension culture cells were bombarded with a mixture of two plasmids. One plasmid contained a selectable marker gene, bar, which encoded phosphinothricin acetyl transferase (PAT), and the other plasmid encoded a screenable marker for ß-glucuronidase

T. M. Spencer; W. J. Gordon-Kamm; R. J. Daines; W. G. Start; P. G. Lemaux

1990-01-01

444

A biomarker based on the stable isotopes of nickel.  

PubMed

The new stable isotope systems of transition metals are increasingly used to understand and quantify the impact of primitive microbial metabolisms on the modern and ancient Earth. To date, little effort has been expended on nickel (Ni) isotopes but there are good reasons to believe that this system may be more straightforward, and useful in this respect, than some others. Here, we present Ni stable isotope data for abiotic terrestrial samples and pure cultures of methanogens. The dataset for rocks reveals little isotopic variability and provides a lithologic baseline for terrestrial Ni isotope studies. In contrast, methanogens assimilate the light isotopes, yielding residual media with a complementary heavy isotopic enrichment. Methanogenesis may have evolved during or before the Archean, when methane could have been key to Earth's early systems. Our data suggest significant potential in Ni stable isotopes for identifying and quantifying methanogenesis on the early planet. Additionally, Ni stable isotope fractionation may well prove to be the fundamental unambiguous trace metal biomarker for methanogens. PMID:19553218

Cameron, Vyllinniskii; Vance, Derek; Archer, Corey; House, Christopher H

2009-07-01

445

Possible Potentials Responsible for Stable Circular Relativistic Orbits  

ERIC Educational Resources Information Center

Bertrand's theorem in classical mechanics of the central force fields attracts us because of its predictive power. It categorically proves that there can only be two types of forces which can produce stable, circular orbits. In this paper an attempt has been made to generalize Bertrand's theorem to the central force problem of relativistic…

Kumar, Prashant; Bhattacharya, Kaushik

2011-01-01

446

Stable DNA Aggregation by Removal of Counterions Michael U. Musheev,  

E-print Network

, when deprived of counterions, DNA precipitated from the solution into amorphous aggregates of counterions is a critical step in purification and concentration of DNA through ethanol precipitation.13Stable DNA Aggregation by Removal of Counterions Michael U. Musheev, Mirzo Kanoatov, Caroline Retif

Krylov, Sergey

447

A Stable Marriage Framework for Distributed Virtual MIMO Coalition Formation  

E-print Network

A Stable Marriage Framework for Distributed Virtual MIMO Coalition Formation Rodrigo A. Vaca Ram Multiple-input Multiple-output (MIMO) coalition formation is proposed. We model cooperation as a game. INTRODUCTION Multi-antenna systems have emerged as an effective way to improve capacity and energy efficiency

Paris-Sud XI, Université de

448

Weights in stable marriage problems increase manipulation opportunities  

E-print Network

is a well-known problem of matching men to women so that no man and woman, who are not married to each other with weighted preferences: each man (resp., woman) provides a score for each woman (resp., man). In this context (SMWs). In such problems, each man (resp., woman) provides a score for each woman (resp., man). Stable

Rossi, Francesca

449

Dynamically stable collision avoidance for tensegrity based robots  

Microsoft Academic Search

Tensegrity structures appeared in the science community about half a century ago, but they have already been applied to several heterogeneous research fields, such as architecture, civil engineering, space and even biology. Such structures keep a stable volume in space due to an intricate balance of forces between a disjoint set of rigid elements (bars) and a continuous set of

Sergi Hernandez Juan; Robert E. Skelton; Josep M. Mirats Tur

2009-01-01

450

A LOW-VOLTAGE TEMPERATURE-STABLE MICROMECHANICAL PIEZOELECTRIC OSCILLATOR  

E-print Network

A LOW-VOLTAGE TEMPERATURE-STABLE MICROMECHANICAL PIEZOELECTRIC OSCILLATOR Reza Abdolvand, Hossein). By employing the buried oxide layer of the SOI substrate as a part of the structural stack of the composite-zero-TCF devices, provided the thickness of the layers in the composite stack is adequately controlled. These low

Ayazi, Farrokh

451

Stable Metal Isotopes Reveal Copper Accumulation and Loss  

E-print Network

Stable Metal Isotopes Reveal Copper Accumulation and Loss Dynamics in the Freshwater Bivalve unidirectional fluxes. However, complicated logistics, handling, and waste issues limit.g., refs 15 and 16). None have dealt with freshwater organisms. Here we present a simple method

452

Design of Hard Water Stable Emulsifier Systems for Petroleum-  

E-print Network

Design of Hard Water Stable Emulsifier Systems for Petroleum- and Bio-based Semi for petroleum and bio-based MWFs that improve fluid lifetime by providing emulsion stability under hard water. The newly developed petroleum and bio-based formulations with improved hard water stability are competitive

Clarens, Andres

453

RFID tag antennas with stable impedance to mounted material  

Microsoft Academic Search

The following study presents two UHF RFID tag antennas for the identification of mass retailing produces. The antenna is composed of two elements, a planar dipole based antenna matched with a small inductive coil. These tags have the particularity to have stable performances to mounted material. Simulations studied the performance of tag antennas depending on the permittivity and thickness of

T. Deleruyelle; P. Pannier; J. Alarcon; M. Egels; E. Bergeret

2010-01-01

454

Fire Feedbacks with Vegetation and Alternative Stable States  

E-print Network

Fire Feedbacks with Vegetation and Alternative Stable States Brian Beckage* Chris Ellingwood.Beckage@uvm.edu Positive feedbacks between vegetation and fire disturbance may lead to nonlinear ecosystem responses to variation in fire regime. We used a cellular automaton model of fire|vegetation dynamics based on pine

Beckage, Brian

455

Stable and Unstable Operations in Algebraic Cobordism Alexander Vishik  

E-print Network

-theory, it starts with the crucial use of Milnor's operations in motivic cohomology by V.Voevodsky in his proofStable and Unstable Operations in Algebraic Cobordism Alexander Vishik Abstract We describe additive (unstable) operations from a theory A obtained from Algebraic Cobordism of M

Vishik, Alexander

456

Stable force controller design based on frequency response identification  

Microsoft Academic Search

Proposes a method of stable force controller design for robotic manipulators based on frequency response identification. The force controller described falls into the hybrid controller category. Force control loops are added to a popular position controller, enabling position control loops and force control loops to be designed independently. The proposed method does not require a detailed model of manipulator and

Junji Oaki

1991-01-01

457

Stable Isotopes James R Ehleringer and Thure E Cerling  

E-print Network

for introduction into the mass spectrometer. The most commonly used approaches involve introducing hydrogen as H2 rationing mass spectrometer. The mass spectrometer consists of a source to ionize the gas, a flight tube which are stable and that do not decay through radioactive pro- cesses over time. Most elements consist

Ehleringer, Jim

458

Original article Are stable flies (Diptera: Stomoxyinae) vectors of  

E-print Network

studies have revealed that the usual cyclic transmission by the tsetse fly Glossina fuscipes fuscipesOriginal article Are stable flies (Diptera: Stomoxyinae) vectors of Trypanosoma vivax flies (Diptera: Stomoxyinae) were also vectors of this trypanosome species in a non-cyclic way. Previous

Paris-Sud XI, Université de

459

Numerical Modeling of the Evolving Stable Boundary Layer  

NASA Astrophysics Data System (ADS)

A single-column model of the evolving stable boundary layer is tested for the consistency of turbulence parameterization, self-similar properties of the flow, and effects of ambient forcing. The turbulence closure of the model is based on the K-theory approach, with stability functions based on empirical data, and a semi-empirical form of the mixing length. The model has one internal, governing stability parameter, the Richardson number Ri, which dynamically adjusts to the boundary conditions and to external forcing. Model results, expressed in terms of local similarity scales, are universal functions of the Richardson number, i.e. they are satisfied in the entire stable boundary layer, for all instants of time, and all kinds of external forcing. Based on similarity expression, a realizability condition is derived for the minimum turbulent heat flux in the stable boundary layer. Numerical experiments show that the development of 'horse-shoe' shaped, 'fixed-elevation' wind hodographs in the interior of the stable boundary layer are solely caused by effects imposed by surface thermal forcing, and are not related to the inertial oscillation mechanism.

Sorbjan, Z.

2013-12-01

460

A STABLE HIGH-ORDER METHOD FOR TWO-DIMENSIONAL ...  

E-print Network

The purpose of the current research is to extend the work of Nicholls and ... highly efficient and accurate since it takes advantage of the fact that the DNO, al .... coupled to the FE design philosophy leads to a stable, high-order boundary ...... are quite generic as a function of profile size (?) and shape (f), the quantitative details.

SIAM (#1) 1035 2001 Apr 10 12:32:38

2006-08-10

461

Stable nitrogen isotopes in Angola Basin surface sediments  

Microsoft Academic Search

Sedimentary ?15N contains a record of biogeochemical processes occurring in the water column. Stable nitrogen isotopes were measured in the bulk sedimentary matter of 18 surface sediment samples collected in three transects in the eastern Angola Basin, perpendicular to the coast, at 6 °S, 12 °S and 17 °S and two samples from the Zaire estuary. Relative enrichment in 15N

M. Elizabeth Holmes; Peter J. Müller; Ralph R. Schneider; Monika Segl; Jürgen Pätzold; Gerold Wefer

1996-01-01

462

Meta-Stable Supersymmetry Breaking Vacua on Intersecting Branes  

E-print Network

We identify configurations of intersecting branes that correspond to the meta-stable supersymmetry breaking vacua in the four-dimensional N=1 supersymmetric Yang-Mills theory coupled to massive flavors. We show how their energies, the stability properties, and the decay processes are described geometrically in terms of the brane configurations.

Hirosi Ooguri; Yutaka Ookouchi

2006-07-24

463

Finite size mass shift formula for stable particles revisited  

E-print Network

Luescher's finite size mass shift formula in a periodic finite volume, involving forward scattering amplitudes in the infinite volume, is revisited for the two stable distinguishable particle system. The generalized mass shift formulae for the boson and fermion are derived in the boson-boson and fermion-boson systems, respectively. The nucleon mass shift is discussed in the nucleon-pion system.

Koma, Y; Koma, Yoshiaki; Koma, Miho

2004-01-01

464

How to ensure stable motion of suspended wheeled mobile robots  

Microsoft Academic Search

Purpose – A suspended wheeled mobile robot (SWMR) that consists of one or more manipulators can be exploited in various environmental conditions such as uneven surfaces. The purpose of this paper is to discuss the requirements for stable motion planning of such robotic systems to perform heavy object manipulation tasks. Design\\/methodology\\/approach – First, a systematic procedure for dynamics modelling of

Khalil Alipour; S. Ali A. Moosavian

2011-01-01

465

Standards for stable isotope measurements in natural compounds  

Microsoft Academic Search

RESEARCH based on stable isotope variations in natural compounds is expanding in scientific fields such as geochemistry, hydrology, environmental studies and biochemistry. However, intercomparison of results obtained in different laboratories is often not fully reliable and therefore to improve the intercalibration of deuterium and 18O measurements in natural waters, two water standards have been distributed by the International Atomic Energy

R. Gonfiantini

1978-01-01

466

Two Stable Equilibria of a Coupled Ocean-Atmosphere Model  

Microsoft Academic Search

Two stable equilibria have been obtained from a global model of the coupled ocean-atmosphere system developed at the Geophysical Fluid Dynamics Laboratory of NOAA. The model used for this study consists of general circulation models of the atmosphere and the world oceans and a simple model of land surface. Starting from two different initial conditions, `asynchronous' time integrations of the

S. Manabe; R. J. Stouffer

1988-01-01

467

Stable periodic billiard paths in obtuse isosceles triangles  

E-print Network

Stable periodic billiard paths in obtuse isosceles triangles W. Patrick Hooper March 27, 2006 Can you place a small billiard ball on a frictionless triangular pool table and hit it so that it comes dynamics s # of a periodic billiard path # is the bi­infinite sequence of edges the billiard path hits

Hooper, Patrick

468

Stable periodic billiard paths in obtuse isosceles triangles  

E-print Network

Stable periodic billiard paths in obtuse isosceles triangles W. Patrick Hooper March 27, 2006 Can you place a small billiard ball on a frictionless triangular pool table and hit it so that it comes dynamics s of a periodic billiard path is the bi-infinite sequence of edges the billiard path hits, which

Hooper, Patrick

469

Neutron Stimulated Emission Computed Tomography of Stable Isotopes  

E-print Network

Analysis (NAA) also known as Instrumental Neutron Activation Analysis (INAA). The latter terms usually to previous work. It will be helpful to distinguish the physical principal of NSECT from Neutron ActivationNeutron Stimulated Emission Computed Tomography of Stable Isotopes Carey E. Floyd Jr.*ab , Calvin

470

A stable tracking control method for an autonomous mobile robot  

Microsoft Academic Search

A stable tracking control rule is proposed for nonholonomic vehicles. The stability of the rule is proved through the use of a Liapunov function. Inputs to the vehicle are a reference posture (x r, yr, ?r)t and reference velocities (?r, ?r) t. The major objective of this study is to propose a control rule to find reasonable target linear and

Yutaka Kanayama; Yoshihiko Kimura; Fumio Miyazaki; Tetsuo Noguchi

1990-01-01

471

A Converse Liapunov Theorem for Uniformly Locally Exponentially Stable  

E-print Network

A Converse Liapunov Theorem for Uniformly Locally Exponentially Stable Systems Admitting Carath´eodory Solutions Jochen Trumpf Robert Mahony School of Engineering, Australian National University, ACT, 0200, Australia. (e-mail: Jochen.Trumpf@anu.edu.au) School of Engineering, Australian National University, ACT

Trumpf, Jochen

472

SYNTHESIS Elucidating the nutritional dynamics of fungi using stable isotopes  

E-print Network

). The formation of macroscopic sporocarps (mushrooms) by many ECM and SAP fungi allows for experimentalREVIEW AND SYNTHESIS Elucidating the nutritional dynamics of fungi using stable isotopes Jordan R (SAP) fungi are essential to terrestrial element cycling due to their uptake of mineral nutrients

Henkel, Terry

473

SYNTHESES Elucidating the nutritional dynamics of fungi using stable isotopes  

E-print Network

). The formation of macroscopic sporocarps (mushrooms) by many ECM and SAP fungi allows for experimentalREVIEW AND SYNTHESES Elucidating the nutritional dynamics of fungi using stable isotopes Jordan R (SAP) fungi are essential to terrestrial element cycling due to their uptake of mineral nutrients

Bruns, Tom

474

The myth of Earth's stable axis David Waltham  

E-print Network

The myth of Earth's stable axis David Waltham Citation: Phys. Today 64(12), 12 (2011); doi: 10 (mshapiro@chem.ubc.ca) University of British Columbia Vancouver, British Columbia, Canada The myth of Earth, page 12) was slightly marred by the opening paragraph, which repeated the myth that Earth, unlike Mars

Sheldon, Nathan D.

475