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1

Enantioselective Synthesis of Apoptolidin Sugars  

E-print Network

Enantioselective Synthesis of Apoptolidin Sugars Michael T. Crimmins* and Alan Long Venable synthesis of the C9 and C27 sugar subunits (2) and (3), respectively, of the potent antitumor agent of the aldol adducts efficiently provided the three sugar units. A -selective glycosidation completed

2

Enantioselective synthesis of helical polydiacetylene by application of linearly polarized light and magnetic field.  

PubMed

Magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic field, causes the difference in absorption coefficients of left and right circularly polarized light and has the potential for magnetically induced enantioselectivity in chemical reactions. Compared with the well-established technique with circularly polarized light, there are few reports on the production of helical conjugated polymers in a photochemical reaction based on above magnetochiral anisotropy mechanism. Herein, we demonstrate experimentally that the enantioselective polymerization of diacetylene derivative can be achieved in the liquid crystal phase by application of linearly polarized light under a parallel or antiparallel magnetic field. The screw direction of predominant helical polydiacetylene chain can be rigorously controlled with the relative orientation of linearly polarized light and the magnetic field. Moreover, the prepared helical polydiacetylene assemblies can serve as a direct visual probe for the enantioselective recognition of D- or L-lysine. PMID:25247276

Xu, Yangyang; Yang, Guang; Xia, Hongyan; Zou, Gang; Zhang, Qijin; Gao, Jiangang

2014-01-01

3

Enantioselective Synthesis of SNAP-7941  

PubMed Central

An enantioselective synthesis of SNAP-7941, a potent melanin concentrating hormone receptor antagonist, was achieved using two organocatalytic methods. The first method utilized to synthesize the enantioenriched dihydropyrimidone core was the Cinchona alkaloid-catalyzed Mannich reaction of ?-keto esters to acyl imines and the second was chiral phosphoric acid-catalyzed Biginelli reaction. Completion of the synthesis was accomplished via selective urea formation at the N3 position of the dihydropyrimidone with the 3-(4-phenylpiperidin-1-yl)propyl amine side chain fragment. The synthesis of SNAP-7921 highlights the utility of asymmetric organocatalytic methods in the construction of an important class of chiral heterocycles. PMID:18767801

Goss, Jennifer M.; Schaus, Scott E.

2009-01-01

4

Enantioselective synthesis of pentacycloanammoxic acid.  

PubMed

A highly effective enantioselective synthesis of pentacycloanammoxic acid (1), an unusual naturally occurring fatty acid from Candidatus Brocadia anammoxidans, has been accomplished. The C20-structure of 1 was assembled with stereocontrol from four building blocks, cyclobutene, 2-cyclopentenone, the chiral silylcyclopentenone 6, and 7-bromoheptanoic acid. Both 1 and its enantiomer are now available in quantities that should facilitate future studies on the mode of biosynthesis which appears to be unprecedented. PMID:16522072

Mascitti, Vincent; Corey, E J

2006-03-15

5

Enantioselective Total Synthesis of (?)-Acylfulvene and (?)- Irofulven  

E-print Network

We report our full account of the enantioselective total synthesis of (?)-acylfulvene (1) and (?)-irofulven (2), which features metathesis reactions for the rapid assembly of the molecular framework of these antitumor ...

Movassaghi, Mohammad

6

First enantioselective total synthesis of (-)-tejedine.  

PubMed

[structure: see text] The first enantioselective total synthesis of (-)-tejedine (1) is reported. Tejedine is a seco-bisbenzyltetrahydroisoquinoline isolated in 1998 as a minor component from Berberis vulgaris. The synthesis was achieved using a strategy employing four key steps, including a chiral auxiliary-assisted diastereoselective Bischler-Napieralski cyclization. PMID:12153207

Wang, You-Chu; Georghiou, Paris E

2002-08-01

7

Enantioselective total synthesis of (-)-maoecrystal v.  

PubMed

The enantioselective synthesis of maoecrystal V, a cytotoxic polycyclic diterpene, is described. Key reactions in the synthesis include an intramolecular Heck reaction, an oxidative cycloetherification, and an intermolecular Diels-Alder reaction to forge the carbocyclic core in a concise and stereoselective manner. Late-stage amine and C-H oxidation is used to install the final functional groups required to complete the synthesis. PMID:25495370

Zheng, Changwu; Dubovyk, Igor; Lazarski, Kiel E; Thomson, Regan J

2014-12-24

8

Studies on the Enantioselective Synthesis of Isofagomine  

Microsoft Academic Search

Glycosidase inhibitors have recently shown promise as potential medicines in the treatment of AIDS and diabetes. We propose a novel enantioselective synthesis of glycosidase inhibitor isofagomine that features both enzyme and organometallic catalysis. Crotonaldehyde, the starting material is first reacted with HCN in the presence of the enzyme oxynitrilase to form the (R)-cyanohydrin in greater than 99% enantiomeric excess. Treatment

Mark Paulsen

2008-01-01

9

Expedient enantioselective synthesis of cermizine D.  

PubMed

An efficient enantioselective synthesis of cermizine D has been developed that exploits the use of a common intermediate to access over 85% of the carbon backbone. Key steps include an organocatalyzed heteroatom Michael addition, a diastereoselective alkylation with ?-iodomethyl phenyl sulfide, a conjugate addition to a vinyl sulfone species, and a sulfone coupling/desulfurization sequence to join the two major subunits. PMID:22372610

Veerasamy, Nagarathanam; Carlson, Erik C; Carter, Rich G

2012-03-16

10

An enantioselective access to 1-alkyl-1,2,3,4-tetrahydroisoquinolines. Application to a new synthesis of (-)-argemonine.  

PubMed

Potassium ferricyanide oxidation of salt 1 gave isoquinolinone 7 whose treatment with Grignard reagents resulted in a high-yield formation of substituted isoquinolinium salts 5. The selectivity of the reduction of these salts to give derivatives 6 has been studied. Particularly good selectivities (82-84%) were observed when R is a benzylic group. On the basis of these results, a practical and enantioselective synthesis of the natural alkaloid (-)-argemonine is presented. PMID:15074921

Youte, Jean-Jacques; Barbier, Denis; Al-Mourabit, Ali; Gnecco, Dino; Marazano, Christian

2004-04-16

11

Pd-Catalyzed Enantioselective Aerobic Oxidation of Secondary Alcohols: Applications to the Total Synthesis of Alkaloids  

PubMed Central

Enantioselective syntheses of the alkaloids (?)-aurantioclavine, (+)-amurensinine, (?)-lobeline, and (?)- and (+)-sedamine are described. The syntheses demonstrate the effectiveness of the Pd-catalyzed asymmetric oxidation of secondary alcohols in diverse contexts and the ability of this methodology to set the absolute configuration of multiple stereocenters in a single operation. The utility of an aryne C–C insertion reaction in accessing complex polycyclic frameworks is also described. PMID:18798630

Krishnan, Shyam; Bagdanoff, Jeffrey T.; Ebner, David C.; Ramtohul, Yeeman K.; Tambar, Uttam K.; Stoltz, Brian M.

2008-01-01

12

Enantioselective synthesis of ( R)- and ( S)- N-Boc-morpholine-2-carboxylic acids by enzyme-catalyzed kinetic resolution: application to the synthesis of reboxetine analogs  

Microsoft Academic Search

The (R)- and (S)-N-Boc-morpholine-2-carboxylic acids 9 and 10 were prepared using an enantioselective synthesis employing a highly selective enzyme-catalyzed kinetic resolution of racemic n-butyl 4-benzylmorpholine-2-carboxylate (11) as the key step. Acids 9 and 10 were then converted efficiently and stereoselectively to reboxetine analogs 3 and 4.

Paul V. Fish; Malcolm Mackenny; Gerwyn Bish; Timothy Buxton; Russell Cave; David Drouard; David Hoople; Alan Jessiman; Duncan Miller; Christelle Pasquinet; Bhairavi Patel; Keith Reeves; Thomas Ryckmans; Melanie Skerten; Florian Wakenhut

2009-01-01

13

Enantioselective synthesis of 12-amino alkylidenecyclopentenone prostaglandins.  

PubMed

An enantioselective synthesis of new 12-amino alkylidenecyclopentenone prostaglandins is reported. The key step of the synthesis involved a [3.3] sigmatropic rearrangement of an asymmetric allylic cyanate to elaborate an asymmetric 5-amino-1,6-diene which was further transformed into cyclopentenone by successive ring-closing metathesis reaction catalyzed by the Grubbs reagent and one-pot oxidation. A palladium-catalyzed cross-coupling reaction on a 5-iodo-1,5-diene allowed the synthesis of prostanoids with variable Rw side chains. These new compounds exhibit high cytotoxic activities. PMID:12076134

Roulland, Emmanuel; Monneret, Claude; Florent, Jean-Claude; Bennejean, Caroline; Renard, Pierre; Léonce, Stéphane

2002-06-28

14

Enantioselective Synthesis of Pactamycin, a Complex Antitumor Antibiotic  

PubMed Central

Medicinal application of many complex natural products is precluded by the impracticality of their chemical synthesis. Pactamycin, the most structurally-intricate aminocyclopentitol antibiotic, displays potent anti-prolific properties across multiple phylogenetic domains, but is highly cytotoxic. A limited number of analogs produced by genetic engineering technologies show reduced cytotoxicity against mammalian cells, renewing promise for therapeutic applications. For decades, an efficient synthesis of pactamycin amenable to analog derivatizations has eluded researchers. Herein, we present a short asymmetric total synthesis of pactamycin. An enantioselective Mannich reaction/symmetry-breaking reduction sequence was designed to enable assembly of the entire carbon core skeleton in under five steps and control critical three-dimensional (stereochemical) functional group relationships. This modular route totals fifteen steps and is immediately amenable for structural analog synthesis. PMID:23580525

Malinowski, Justin T.; Sharpe, Robert J.; Johnson, Jeffrey S.

2014-01-01

15

Enantioselective synthesis of stephacidin B.  

PubMed

We describe an enantioselective synthetic route to the antiproliferative alkaloid stephacidin B (1) proceeding in 18 steps and 4.0% yield from 4,4-(ethylenedioxy)-2,2-dimethylcyclohexanone (3). Key features of the synthetic sequence include the use of the Corey-Bakshi-Shibata (CBS) reduction to introduce asymmetry early in the synthetic route, use of the novel electrophile N-(tert-butoxycarbonyl)-5-(isopropylsulfonyloxymethyl)-2,3-dihydropyrrole in a stereoselective enolate alkylation, a diastereoselective Strecker-type addition of hydrogen cyanide to an N-Boc enamine substrate in the solvent hexafluoroisopropanol, platinum-catalyzed nitrile hydrolysis under neutral conditions, cyclization of an acylamino radical intermediate to form the diketopiperazine core of stephacidin B, and implementation of a convergent procedure for introduction of the key 3-alkylidene-3H-indole 1-oxide functional group in the final stage of the route to prepare the structure 2, previously proposed to be the fungal metabolite avrainvillamide (17 steps, 4.2% yield). We observed that synthetic (-)-2 dimerized in the presence of triethylamine to form (+)-stephacidin B (>95%). We also obtained evidence that 2 can form 1 under mild conditions, and that 2 reacts with nucleophiles, such as methanol, by conjugate addition. PMID:15826171

Herzon, Seth B; Myers, Andrew G

2005-04-20

16

Catalytic enantioselective synthesis of quaternary carbon stereocentres  

NASA Astrophysics Data System (ADS)

Quaternary carbon stereocentres--carbon atoms to which four distinct carbon substituents are attached--are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials.

Quasdorf, Kyle W.; Overman, Larry E.

2014-12-01

17

Catalytic enantioselective synthesis of quaternary carbon stereocentres.  

PubMed

Quaternary carbon stereocentres-carbon atoms to which four distinct carbon substituents are attached-are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials. PMID:25503231

Quasdorf, Kyle W; Overman, Larry E

2014-12-11

18

Synthesis of tunable diamine ligands with spiro indane-2,2?-pyrrolidine backbone and their applications in enantioselective Henry reaction.  

PubMed

Novel diamine ligands with spiro indane-2,2?-pyrrolidine scaffold were synthesized starting from Seebach’s oxazolidinone 6 and were subsequently employed in asymmetric Henry reaction. Following the initial experimental findings, further synthesis resulted in two types of spiro diamines, with varying substituents at both nitrogen atoms. Ligands of type A, containing a small substituent at N-1? atom, and a large group at N-1 atom gave predominantly the S-configured ?-nitroalcohol, while ligands of type B, with the reversed location of small and large substituents furnished the R-configured product. Both types of ligands turned out to be versatile catalysts for the Henry reaction between nitromethane and an assortment of aryl as well as alkyl aldehydes offering either S- (lig. A) or R-configured (lig. B) nitroalcohols in a good to high chemical yield and an excellent enantioselectivity up to 99% ee. PMID:24437641

?wiek, Rafa?; Niedziejko, Piotr; Ka?u?a, Zbigniew

2014-02-01

19

An enantioselective total synthesis of helioporins C and E.  

PubMed

A short and enantioselective total synthesis of helioporins C and E, which are bioactive marine diterpenes containing a serrulatane or amphilectane skeleton, was elaborated. The chirogenic step, i.e. a Cu(I)-catalyzed allylic alkylation of a cinnamyl chloride with methylmagnesium bromide, proceeded with virtually complete enantioselectivity (99% ee) in the presence of a chiral phosphine-phosphite ligand. The other stereocenters were diastereoselectively established through Me(2)AlCl-mediated cationic cyclization and Ir-catalyzed hydrogenation. PMID:23148527

Lölsberg, Wibke; Werle, Susen; Neudörfl, Jörg-Martin; Schmalz, Hans-Günther

2012-12-01

20

Biomimetic synthesis and studies toward enantioselective synthesis of flindersial alkaloids.  

PubMed

A strategy allowing both stereocontrol and control over structural isomer formation has been defined for the antimalarial flindersial alkaloids. The recently reported flinderoles were demonstrated to be derived from the natural product borrerine. The structural isomers of flinderoles, the borreverines, were also produced in vitro along with the flinderoles through the dimerization of borrerine in acidic conditions. This result is thought to replicate the biosynthesis of these compounds. Flinderoles A, B, and C, desmethylflinderole C, isoborreverine, and dimethylisoborreverine can each be synthesized in three steps from tryptamine. Furthermore, progress toward a concise enantioselective synthesis of flinderoles A, B, and C is described. This work includes enantioselective conjugate addition to an unprotected indole-appended enone. Chirality 27:14-17, 2015. © 2013 Wiley Periodicals, Inc. PMID:23529894

Vallakati, Ravikrishna; Lundy, Brian J; Jansone-Popova, Santa; May, Jeremy A

2015-01-01

21

Catalytic Enantioselective 1,3-Dipolar Cycloadditions of Azomethine Ylides for Biology-Oriented Synthesis  

PubMed Central

Conspectus Cycloaddition reactions are among the most powerful methods for the synthesis of complex compounds. In particular, the development and application of the 1,3-dipolar cycloaddition, an important member of this reaction class, has grown immensely due to its powerful ability to efficiently build various five-membered heterocycles. Azomethine ylides are commonly used as dipoles for the synthesis of the pyrrolidine scaffold, which is an important motif in natural products, pharmaceuticals, and biological probes. The reaction between azomethine ylides and cyclic dipolarophiles allows access to polycyclic products with considerable complexity. The extensive application of the 1,3-dipolar cycloaddition is based on the fact that the desired products can be obtained with high yield in a regio- and stereocontrolled manner. The most attractive feature of the 1,3-dipolar cycloaddition of azomethine ylides is the possibility to generate pyrrolidines with multiple stereocenters in a single step. The development of enantioselective cycloadditions became a subject of intensive and impressive studies in recent years. Among many modes of stereoinduction, the application of chiral metal–ligand complexes has emerged as the most viable option for control of enantioselectivity. In chemical biology research based on the principle of biology-oriented synthesis (BIOS), compound collections are prepared inspired by natural product scaffolds. In BIOS, biological relevance is employed as the key criterion to generate hypotheses for the design and synthesis of focused compound libraries. In particular, the underlying scaffolds of natural product classes provide inspiration for BIOS because they define the areas of chemical space explored by nature, and therefore, they can be regarded as “privileged”. The scaffolds of natural products are frequently complex and rich in stereocenters, which necessitates the development of efficient enantioselective methodologies. This Account highlights examples, mostly from our work, of the application of 1,3-dipolar cycloaddition reactions of azomethine ylides for the catalytic enantioselective synthesis of complex products. We successfully applied the 1,3-dipolar cycloaddition in the synthesis of spiro-compounds such as spirooxindoles, for kinetic resolution of racemic compounds in the synthesis of an iridoid inspired compound collection and in the synthesis of a nitrogen-bridged bicyclic tropane scaffold by application of 1,3-fused azomethine ylides. Furthermore, we performed the synthesis of complex molecules with eight stereocenters using tandem cycloadditions. In a programmable sequential double cycloaddition, we demonstrated the synthesis of both enantiomers of complex products by simple changes in the order of addition of chemicals. Complex products were obtained using enantioselective higher order [6 + 3] cycloaddition of azomethine ylides with fulvenes followed by Diels–Alder reaction. The bioactivity of these compound collections is also discussed. PMID:24730692

2014-01-01

22

Diastereo- and enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine: mechanistic insight into sequential nitroso Aldol/Michael reaction and application for optically pure 1-amino-3,4-diol synthesis.  

PubMed

This article presents complete diastereo- and highly enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine. With the hydrogen bonding of two hydroxyls in the bulky binaphthol 1c, high enantioselectivities and complete diastereoselectivity are realized in 2-oxa-3-aza-bicycloketone synthesis. On the other hand, alpha,beta-unsaturated ketone can be employed as diene precursor, utilizing readily available tetrazole catalyst 3b, to provide the 3-oxa-2-aza-bicycloketones in moderate yields with complete enantioselectivities. Investigation into the reaction utilizing 2-morpholino-4,4-diphenylcyclohexadiene 2d clearly indicated that cyclization with the bulky binaphthol 1c is involved in the sequential process, the N-nitroso aldol reaction, followed by Michael addition. In addition, optically pure 1-amino-3,4-diol is synthesized from 2-oxa-3-aza-bicycloketones. Use of p-phenoxynitrosobenzene allows access to protected amino diol via cleavage of the N-Ph bond. PMID:17263400

Momiyama, Norie; Yamamoto, Yuhei; Yamamoto, Hisashi

2007-02-01

23

Organocatalytic Highly Enantioselective Synthesis of Secondary ?-Hydroxyphosphonates†  

PubMed Central

The first organocatalytic cross aldol reaction of ketones and diethyl formylphosphonate hydrate has been realized by using readily available L-prolinamide as the catalyst. Secondary ?-hydroxyphosphonates have been synthesized in high enantioselective (up to >99% ee) and good diastereoselectivity. PMID:17020334

Dodda, Rajasekhar; Cong-Gui, Zhao

2008-01-01

24

Enantioselective total synthesis of callipeltoside A: two approaches to the macrolactone fragment  

PubMed Central

The enantioselective total synthesis of callipeltoside A is described. Two syntheses of the macrolactone subunit are included: the first relies upon an Ireland–Claisen rearrangement to generate the trisubstituted olefin geometry and the second utilizes an enantioselective vinylogous aldol reaction for this purpose. Enantioselective syntheses of the sugar and chlorocyclopropane side chain fragments are also disclosed. The relative and absolute stereochemistry of this natural product was determined by fragment coupling with the two enantiomers of the side chain fragment. PMID:22859865

Evans, David A.; Burch, Jason D.; Hu, Essa; Jaeschke, Georg

2012-01-01

25

Enantioselective Synthesis of ?-Quaternary Mannich Adducts by Palladium-Catalyzed Allylic Alkylation: Total Synthesis of (+)-Sibirinine.  

PubMed

A catalytic enantioselective method for the synthesis of ?-quaternary Mannich-type products is reported. The two-step sequence of (1) Mannich reaction followed by (2) decarboxylative enantioselective allylic alkylation serves as a novel strategy to in effect access asymmetric Mannich-type products of "thermodynamic" enolates of substrates possessing additional enolizable positions and acidic protons. Palladium-catalyzed decarboxylative allylic alkylation enables the enantioselective synthesis of five-, six-, and seven-membered ketone, lactam, and other heterocyclic systems. The mild reaction conditions are notable given the acidic free N-H groups and high functional group tolerance in each of the substrates. The utility of this method is highlighted in the first total synthesis of (+)-sibirinine. PMID:25578104

Numajiri, Yoshitaka; Pritchett, Beau P; Chiyoda, Koji; Stoltz, Brian M

2015-01-28

26

Scalable enantioselective total synthesis of taxanes  

NASA Astrophysics Data System (ADS)

Taxanes form a large family of terpenes comprising over 350 members, the most famous of which is Taxol (paclitaxel), a billion-dollar anticancer drug. Here, we describe the first practical and scalable synthetic entry to these natural products via a concise preparation of (+)-taxa-4(5),11(12)-dien-2-one, which has a suitable functional handle with which to access more oxidized members of its family. This route enables a gram-scale preparation of the ‘parent’ taxane—taxadiene—which is the largest quantity of this naturally occurring terpene ever isolated or prepared in pure form. The characteristic 6-8-6 tricyclic system of the taxane family, containing a bridgehead alkene, is forged via a vicinal difunctionalization/Diels-Alder strategy. Asymmetry is introduced by means of an enantioselective conjugate addition that forms an all-carbon quaternary centre, from which all other stereocentres are fixed through substrate control. This study lays a critical foundation for a planned access to minimally oxidized taxane analogues and a scalable laboratory preparation of Taxol itself.

Mendoza, Abraham; Ishihara, Yoshihiro; Baran, Phil S.

2012-01-01

27

Rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles by enantioselective [2+2+2] cycloaddition.  

PubMed

A rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles has been developed through a [2+2+2] cycloaddition of silicon-containing prochiral triynes with internal alkynes. High yields and enantioselectivities have been achieved by employing an axially chiral monophosphine ligand, and the present catalysis is also applicable to the asymmetric synthesis of a germanium-stereogenic dibenzogermole. Preliminary studies on the optical properties of these compounds are also described. PMID:25491349

Shintani, Ryo; Takagi, Chihiro; Ito, Tomoaki; Naito, Masanobu; Nozaki, Kyoko

2015-01-26

28

Enamine/Carbene Cascade Catalysis in the Diastereo- and Enantioselective Synthesis of Functionalized Cyclopentanones  

PubMed Central

Herein we report an enantioselective synthesis of complex cyclopentanones using aliphatic aldehydes and activated enones. With the combination of a chiral secondary amine and a chiral triazolium catalyst, high diastereoselectivity and excellent enantioselectivity can be achieved. We present evidence of a clear cooperative effect when these two catalysts are present simultaneously in the system. PMID:21927711

Ozboya, Kerem E.

2011-01-01

29

Asymmetric synthesis of trifluoromethylated amines via catalytic enantioselective isomerization of imines.  

PubMed

A new approach toward the asymmetric synthesis of optically active trifluoromethylated amines was enabled by an unprecedented, highly enantioselective catalytic isomerization of trifluoromethyl imines with a new chiral organic catalyst. Not only aryl but also alkyl trifluoromethylated amines could be obtained in high enantioselectivities. PMID:22906148

Wu, Yongwei; Deng, Li

2012-09-01

30

Development of Ruthenium Catalysts for the Enantioselective Synthesis of P-Stereogenic Phosphines via Nucleophilic  

E-print Network

Development of Ruthenium Catalysts for the Enantioselective Synthesis of P-Stereogenic Phosphines the development of ruthenium(II) catalysts for the enantioselective alkylation of chiral racemic secondary asymmetric environment around the ruthenium center. The (R)-MeO- BiPHEP/dmpe (dmpe ) 1,2-bis

Toste, Dean

31

Enantioselective synthesis of arylglycine derivatives by direct C-H oxidative cross-coupling.  

PubMed

A new method for the synthesis of chiral ?-amino acid derivatives by enantioselective C-H arylation of N-aryl glycine esters with aryl boric acids in the presence of a chiral Pd(ii)-catalyst has been developed. This work successfully integrates the direct C-H oxidation with asymmetric arylation and exhibits excellent enantioselectivity. PMID:25348347

Wei, Xiao-Hong; Wang, Gang-Wei; Yang, Shang-Dong

2015-01-18

32

Enantioselective Total Synthesis of Plectosphaeroic Acid B  

PubMed Central

The first total synthesis of a member of the plectosphaeroic acid family of fungal natural products is reported. Key steps include the late-stage formation of the hindered N6–C9? bond and stereoselective introduction of the two methylthio substituents. PMID:23452064

Jabri, Salman Y.; Overman, Larry E.

2013-01-01

33

Enantioselective synthesis of a chiral nitrogen-doped buckybowl.  

PubMed

Bowl-shaped aromatic compounds, namely buckybowls constitute a family of curved polycyclic aromatic carbons along with fullerenes and carbon nanotubes. Doping of heteroatoms to the carbon frameworks of such aromatic compounds drastically modulates their physical and chemical properties. In contrast to nitrogen-doped azafullerenes or carbon nanotubes, synthesis of azabuckybowls, nitrogen-doped buckybowls, remains an unsolved challenging task. Here we report the first enantioselective synthesis of a chiral azabuckybowl, triazasumanene. X-ray crystallographic analysis confirmed that the doping of nitrogen induces a more curved and deeper bowl structure than in all-carbon buckybowls. As a result of the deeper bowl structure, the activation energy for the bowl inversion (thermal flipping of the bowl structure) reaches an extraordinarily high value (42.2?kcal per mol). As the bowl inversion corresponds to the racemization process for chiral buckybowls, this high bowl inversion energy leads to very stable chirality of triazasumanene. PMID:22692534

Tan, Qitao; Higashibayashi, Shuhei; Karanjit, Sangita; Sakurai, Hidehiro

2012-01-01

34

Enantioselective Synthesis of Tetrahydroprotoberberines and Bisbenzylisoquinoline Alkaloids from a Deprotonated -Aminonitrile  

E-print Network

Enantioselective Synthesis of Tetrahydroprotoberberines and Bisbenzylisoquinoline Alkaloids from for the preparation of various alkaloids. Here, the preparation of the benzylisoquinolines (+)-laudanidine and (-)-tetrahydropseudoepiberberine using Noyori's asymmetric transfer hydrogenation are described. The dimeric alkaloids (+)-O

Lawson, Catherine L.

35

Enantioselective synthesis of PPAR (peroxisome proliferator-activated receptors) agonists and antagonists.  

PubMed

This review deals with stereoselective issues in PPAR ligands some of which are in clinical use for treating certain metabolic disorders. After a short introduction of these nuclear receptor and their agonists, some cases of enantioselective separations are reported. The main part concerns stereoselective synthesis first starting with asymmetric synthesis from chiral precursors followed by what we refer to as "true" enantioselective methods. Some examples are discussed in detail for each particular heading. PMID:24758429

Goya, Pilar; Perez-Fernandez, Ruth; Gonzalez-Muniz, Rosario; Elguero, Jose

2014-01-01

36

Enantioselective synthesis of triarylmethanes by chiral imidodiphosphoric acids catalyzed Friedel-Crafts reactions.  

PubMed

The first enantioselective synthesis of pyrrolyl-substituted triarylmethanes has been accomplished using a novel imidodiphosphoric acid catalyst, which is derived from two (R)-BINOL frameworks with different 3,3'-substituents. This strategy was also expanded to the synthesis of bis(indolyl)-substituted triarylmethanes with high enantioselectivities, which could only be obtained with moderate ee values in previous reports. These two efficient Friedel-Crafts alkylation processes feature low catalyst loading, broad functional group compatibilities, and the potential to provide practical pathways for the synthesis of enantioenriched bioactive triarylmethanes. PMID:24490630

Zhuo, Ming-Hua; Jiang, Yi-Jun; Fan, Yan-Sen; Gao, Yang; Liu, Song; Zhang, Suoqin

2014-02-21

37

Enantioselective Total Synthesis of (?)-Nardoaristolone B via a Gold(I)-Catalyzed Oxidative Cyclization  

PubMed Central

The first enantioselective total synthesis of (?)-nardoaristolone B is accomplished by the implementation of an enantio- and diastereoselective copper(I)-catalyzed conjugate addition/enolate trapping sequence and a gold(I)-catalyzed oxidative cyclization (intermolecular oxidant), employed for the first time in total synthesis. PMID:25563976

2015-01-01

38

Highly enantioselective synthesis of tetrahydrocarbolines via iridium-catalyzed intramolecular Friedel-Crafts type allylic alkylation reactions.  

PubMed

A highly enantioselective synthesis of substituted tetrahydrocarbolines via Ir-catalyzed Friedel-Crafts type intramolecular asymmetric allylic alkylation of 2-indolyl allyl carbonates has been developed. This strategy features excellent chemoselectivity and enantioselectivity, mild reaction conditions, and an easily accessed chiral ligand. PMID:24215126

Xu, Qing-Long; Zhuo, Chun-Xiang; Dai, Li-Xin; You, Shu-Li

2013-12-01

39

Chiral phosphoramide-catalyzed enantioselective synthesis of 2,3'-diindolylarylmethanes from indol-2-yl carbinols and indoles.  

PubMed

We present the first asymmetric reaction of indol-2-yl carbinols with indole derivatives catalyzed by chiral phosphoramides for the enantioselective synthesis of 2,3'-diindolylarylmethanes in excellent yields of over 90% as well as high enantioselectivity of up to 96% ee. PMID:24958365

Qi, Shuai; Liu, Chao-You; Ding, Jin-Ying; Han, Fu-She

2014-08-11

40

Enantioselective synthesis of Amaryllidaceae alkaloids (+)-vittatine, (+)-epi-vittatine, and (+)-buphanisine.  

PubMed

Cat. on a hot tin roof: Enantioselective catalytic Michael addition of ?-cyanoketones to acrylates under bifunctional organocatalysis was used to construct the unique arylic all-carbon quaternary stereocenter, which is synthetically crucial in the chemical synthesis of optically pure cis-aryl hydroindole alkaloids. The protocol offers an asymmetric route to (+)-vittatine, (+)-epi-vittatine, and (+)-buphanisine. PMID:23788411

Wei, Meng-Xue; Wang, Cheng-Tao; Du, Ji-Yuan; Qu, Hu; Yin, Pei-Rong; Bao, Xu; Ma, Xiao-Yan; Zhao, Xian-He; Zhang, Guo-Biao; Fan, Chun-An

2013-09-01

41

Toward the Synthesis of Cobyric Acid. Enantioselective Syntheses of Completely Differentiated Ring D Synthons  

PubMed Central

Alkyne acids 11 were prepared in an enantioselective fashion from allylic ester derivatives 18 or 20 by Ireland-Claisen rearrangement, followed by Si-assisted elimination of HBr. The title compounds are attractive ring D synthons for an ongoing synthesis of cobyric acid. PMID:18537250

Wang, Hui; Tassa, Carlos; Jacobi, Peter A.

2008-01-01

42

Toward the synthesis of cobyric acid. Enantioselective syntheses of completely differentiated ring D synthons.  

PubMed

Alkyne acids 11 were prepared in an enantioselective fashion from allylic ester derivatives 18 or 20 by Ireland-Claisen rearrangement, followed by Si-assisted elimination of HBr. The title compounds are attractive ring D synthons for an ongoing synthesis of cobyric acid. PMID:18537250

Wang, Hui; Tassa, Carlos; Jacobi, Peter A

2008-07-01

43

Asymmetric epoxidation of cis-alkenes mediated by iminium salts: highly enantioselective synthesis of levcromakalim.  

PubMed

[reaction: see text] A range of cis-substituted olefins has been epoxidized with a new dihydroisoquinolinium salt catalyst, using tetraphenylphosphonium monoperoxysulfate as the stoichiometric oxidant, giving ee's of up to 97%. The reaction has been used as the key step in an enantioselective synthesis of the antihypertensive agent levcromakalim. PMID:15673243

Page, Philip C Bulman; Buckley, Benjamin R; Heaney, Harry; Blacker, A John

2005-02-01

44

A Green, Enantioselective Synthesis of Warfarin for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

The enantioselective synthesis of drugs is of fundamental importance in the pharmaceutical industry. In this experiment, students synthesize either enantiomer of warfarin, a widely used anticoagulant, in a single step from inexpensive starting materials. Stereoselectivity is induced by a commercial organocatalyst, ("R","R")- or…

Wong, Terence C.; Sultana, Camille M.; Vosburg, David A.

2010-01-01

45

Synthesis of ?-Amino Acid Derivatives and Peptides via Enantioselective Addition of Masked Acyl Cyanides to Imines.  

PubMed

A general, asymmetric synthesis of amino acid derivatives is reported. Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselective additions to N-Boc-aldimines. The reactions are catalyzed by a modified cinchona alkaloid, which can function as a bifunctional, hydrogen bonding catalyst, and afford adducts in excellent yields (90-98%) and high enantioselectivities (up to 97.5:2.5 er). Unmasking the addition products gives acyl cyanide intermediates that are intercepted by a variety of nucleophiles to afford ?-amino acid derivatives. Notably, the methodology provides an alternative method for peptide bond formation. PMID:25366558

Yang, Kin S; Rawal, Viresh H

2014-11-19

46

Enantioselective synthesis of beta-trifluoromethyl-beta-lactones via NHC-catalyzed ketene-ketone cycloaddition reactions.  

PubMed

The highly diastereo- and enantioselective synthesis of beta-trifluoromethyl-beta-lactones bearing two contiguous stereocenters was realized by chiral N-heterocyclic carbene-catalyzed formal cycloaddition reaction of alkyl(aryl)ketenes and trifluoromethyl ketones. PMID:19681591

Wang, Xiao-Na; Shao, Pan-Lin; Lv, Hui; Ye, Song

2009-09-17

47

Synthetic Studies on Norrisolide: Enantioselective Synthesis of the  

E-print Network

), efficient, and enantioselective. Norrisolide (1) is a marine natural product, initially isolated by Faulkner be attributed to their initially reported poor antimicrobial activity.2b Recent studies, however, have indicated Among the few natural products known to affect the Golgi organization, 1 distinguishes itself as being

Theodorakis, Emmanuel

48

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

E-print Network

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

Lee, Elaine C

2007-01-01

49

Phosphathiahelicenes: synthesis and uses in enantioselective gold catalysis.  

PubMed

Enantiomerically pure thiahelicenes displaying a terminal phosphole unit and a stereogenic phosphorus center have been prepared by oxidative photocyclization of a diaryl-olefin precursor. Starting from one of these phosphathiahelicene oxides, the corresponding trivalent phosphine-Au(I) complex is obtained with complete diastereoselectivity. It affords a new, excellent precatalyst for the enantioselective cycloisomerization of N-tethered enynes (up to 96?% ee). PMID:25113927

Aillard, Paul; Voituriez, Arnaud; Dova, Davide; Cauteruccio, Silvia; Licandro, Emanuela; Marinetti, Angela

2014-09-22

50

Enantioselective Total Synthesis of Guanacastepene N Using an Uncommon 7-Endo Heck Cyclization as a Pivotal Step  

PubMed Central

A convergent, enantioselective total synthesis of (+)-guanacastepene N was developed that features a 7-endo Heck cyclization as the key step. In the course of this synthesis, short syntheses of the enantiomerically pure cyclopentenone and cyclohexene building blocks 5 and 6, which constitute A and C ring fragments of guanacastepene N, were developed. These fragments were linked by a challenging conjugate addition reaction that also generated the C11 quaternary carbon stereocenter. Regioselective 7-endo Heck cyclization gave rise to a tricyclic intermediate, which was elaborated to complete the first total synthesis of guanacastepene N and the second enantioselective total synthesis of a guanacastepene natural product. PMID:17017789

Iimura, Shin; Paulini, Ralph; Zakarian, Armen

2013-01-01

51

Enantioselective total syntheses of acylfulvene, irofulven, and the agelastatins  

E-print Network

I. Enantioselective Total Synthesis of (-)-Acylfulvene, and (-)-Irofulven We report the enantioselective total synthesis of (-)-acylfulvene and (-)-irofulven, which features metathesis reactions for the rapid assembly of ...

Siegel, Dustin S. (Dustin Scott), 1980-

2010-01-01

52

Highly efficient, enantioselective synthesis of (+)-grandisol from a C2-symmetric bis(alpha,beta-butenolide).  

PubMed

[reaction: see text] A new, very efficient, enantioselective synthesis of the sexual attracting insect pheromone (+)-grandisol has been developed, in which the key step is the double [2 + 2] photocycloaddition of ethylene to a bis(alpha,beta-butenolide) readily available from D-mannitol. The C2 symmetry of the substrate and the appropriate protection of the central diol unit are the crucial features for the high diastereofacial discrimination during the cycloaddition process. PMID:10814272

de March, P; Figueredo, M; Font, J; Raya, J

2000-01-27

53

Determination by enantioselective synthesis of the absolute configuration of CPE, a potential intermediate in coronatine biosynthesis.  

PubMed

The first enantioselective synthesis of the methyl ester of CPE, a potential intermediate in coronatine (COR) biosynthesis, is described. Comparison of the specific rotation of the synthetic ester with that of the methyl ester of natural CPE established that the latter possesses the (R) configuration. This configuration is the same as that found at the corresponding asymmetric center of coronatine. Structure: see text. PMID:11554839

Tao, T; Parry, R J

2001-09-20

54

Enantioselective total synthesis of isishippuric acid B via intramolecular Michael reaction.  

PubMed

The first enantioselective total synthesis of isishippuric acid B bearing a novel 4,5-seco-6-norquadrane skeleton was accomplished from (R)-citronellal with use of a Diels-Alder cycloaddition and an intramolecular Michael addition as the ring-forming steps. Comparison of the optical rotation of the synthetic material with that of the natural product confirmed the absolute configuration of isishippuric acid B to be 1R, 2R, 8R, and 11R. PMID:17539655

Torihata, Munefumi; Nakahata, Takashi; Kuwahara, Shigefumi

2007-06-21

55

Synthesis of isohasubanan alkaloids via enantioselective ketone allylation and discovery of an unexpected rearrangement.  

PubMed

A synthesis of the hasubanan alkaloids hasubanonine, runanine, and aknadinine via a unified route was attempted. Construction of key phenanthrene intermediates by a Suzuki coupling-Wittig olefination-ring-closing metathesis sequence allowed a convergent and flexible approach. Conversion of the phenanthrenes into the target structures was projected to involve six steps including phenolic oxidation, ketone allylation, anionic oxy-Cope rearrangement, and acid-promoted cyclization. The final step was thwarted by a pinacol-like rearrangement that delivered the unnatural isohasubanan alkaloid skeleton. The structures of the products were established by exhaustive NMR experiments and confirmed by GIAO (13)C NMR calculations of runanine, isorunanine, and three other isomers. These computations revealed some inconsistencies with the benzene solvent correction which suggest that caution should be used in employing this algorithm. The racemic synthesis of isohasubanonine was transformed into an enantioselective synthesis by the discovery that Nakamura's chiral bisoxazoline-ligated allylzinc reagent mediates the enantioselective allylation of ketone 19 in 93% ee. This method could be extended to three other structurally related ketones (92-96% ee), and the enantioselective syntheses of two other isohasubanan alkaloids, isorunanine and isoaknadinine, were accomplished. Racemic isohasubanonine was found to be an ineffective analgesic agent. PMID:19072324

Nielsen, Daniel K; Nielsen, Laura L; Jones, Spencer B; Toll, Lawrence; Asplund, Matthew C; Castle, Steven L

2009-02-01

56

From racemic to enantioselective total synthesis of trigonoliimines via development of an organocatalytic enantioselective Michael addition of ?-aryl-?-isocyanoacetate to vinyl phenyl selenone.  

PubMed

Trigonoliimines are hexacyclic bisindole alkaloids isolated recently by Hao and co-workers. A synthesis of (±)-trigonoliimine B was accomplished in seven steps from simple starting materials featuring the Bischler-Napieralski reaction for closing the seven-membered ring with concomitant formation of an exoimine. Sulfolane was found to be the solvent of choice for this unprecedented transformation. An organocatalytic enantioselective synthesis of ?,?'-disubstituted ?-amino acids was subsequently developed using methyl ?-aryl-?-isocyanoacetates as glycine templates and vinyl phenyl selenone as a Michael acceptor. Using one of this Michael adducts as a starting material, total synthesis of both (+)- and (-)-trigonoliimine A was subsequently realized. PMID:24983599

Buyck, Thomas; Wang, Qian; Zhu, Jieping

2014-01-01

57

Catalytic, Enantioselective Alkylation of r-Imino Esters: The Synthesis of Nonnatural r-Amino Acid Derivatives  

E-print Network

Catalytic, Enantioselective Alkylation of r-Imino Esters: The Synthesis of Nonnatural r-Amino Acid, 2001 Abstract: Methodology for the practical synthesis of nonnatural amino acids has been developed (up to 25:1/anti:syn), are protected nonnatural amino acids that represent potential precursors

Lectka, Thomas

58

Highly enantioselective catalytic asymmetric synthesis of a (R)-sibutramin precursor.  

PubMed

The first highly enantioselective, catalytic asymmetric synthesis of di-des-methylsibutramine 3 is described. Dienamide 10, prepared by acetic acid anhydride quenching of the condensation product of nitrile 4 with a methallyl magnesium chloride, proved to be an excellent substrate for ruthenium-catalyzed asymmetric hydrogenation with atropisomeric diphosphine ligands. Hydrogenation with a ruthenium/(R)- MeOBiPheP catalyst at S/C = 500, gave the chiral amide (R)-9 in 98.5% ee in almost quantitative yield. After acidic amide hydrolysis the desired amine (R)-3 was obtained without erosion of enantioselectivity. It is anticipated that the overall process will be amenable to large-scale production. PMID:21137687

Berens, Ulrich; Hafner, Andreas; Dosenbach, Oliver; Tritschler, Tanja; Schwarzenbach, Franz; Kirner, Hans-Jörg; Malan, Christophe; Mai-Huynh, Oanh

2010-01-01

59

Asymmetric Total Synthesis of (?)-Plicatic Acid via a Highly Enantioselective and Diastereoselective Nucleophilic Epoxidation of Acyclic Trisubstitued Olefins  

PubMed Central

The first total synthesis of (?)-plicatic acid has been achieved by a concise and enantioselective route. In this synthesis, a conceptually new strategy featuring an asymmetric epoxidation-intramolecular epoxy-ring-opening Friedel-Crafts reaction sequence was developed for the stereoselective construction of the 2,7’-cyclolignane skeleton bearing contiguous quaternary-quaternary-tertiary stereocenters. The implementation of this strategy was enabled by the development of a modified protocol for the Seebach epoxidation with TADOOH, which affords an unprecedented, highly enantioselective and diastereoselective epoxidation with a range of ?-carbonyl-?-substituted acrylates 3. PMID:19601599

Sun, Bing-Feng; Hong, Ran; Kang, Yan-Biao; Deng, Li

2009-01-01

60

Enantioselective total Synthesis of the agelastatin and trigonoliimine alkaloids  

E-print Network

I. Total Synthesis of the (-)-Agelastatin Alkaloids The pyrrole-imidazole family of marine alkaloids, derived from linear clathrodin-like precursors, constitutes a diverse array of structurally complex natural products. ...

Han, Sunkyu, 1982-

2012-01-01

61

A General, Highly Enantioselective Method for the Synthesis of D and L r-Amino Acids and Allylic Amines  

E-print Network

A General, Highly Enantioselective Method for the Synthesis of D and L r-Amino Acids and Allylic of amino acids is a subject of intense interest in the field of asymmetric catalysis. Traditionally. In this paper, we report on a different approach to amino acids based on an expeditious route to enantiopure

Walsh, Patrick J.

62

Enantioselective total synthesis of (-)-minovincine in nine chemical steps: an approach to ketone activation in cascade catalysis.  

PubMed

Dressed to the nines: The first enantioselective total synthesis of (-)-minovincine has been accomplished in nine chemical steps and 13?% overall yield. A novel, one-step Diels-Alder/?-elimination/conjugate addition organocascade sequence allowed rapid access to the central tetracyclic core in an asymmetric manner. Boc=tert-butoxycarbonyl, LG=leaving group, PMB=para-methoxybenzyl. PMID:24000234

Laforteza, Brian N; Pickworth, Mark; Macmillan, David W C

2013-10-18

63

Enantioselective Total Synthesis of (?)-Minovincine in Nine Chemical Steps: An Approach to Ketone Activation in Cascade Catalysis  

PubMed Central

More cycling–fewer steps The first enantioselective total synthesis of (?)-minovincine has been accomplished in nine chemical steps and 13% overall yield. A novel, one-step Diels–Alder/?-elimination/conjugate addition organocascade sequence allowed rapid access to the central tetracyclic core in an asymmetric manner. PMID:24000234

Laforteza, Brian N.; Pickworth, Mark

2014-01-01

64

Effect of high pressure on the organocatalytic asymmetric Michael reaction: highly enantioselective synthesis of ?-nitroketones with quaternary stereogenic centers.  

PubMed

The significant effect of hydrostatic pressure on the difficult organocatalytic 1,4-conjugate addition of nitroalkanes to prochiral sterically congested ?,?-disubstituted enones is demonstrated. This approach allows for the synthesis of ?-nitroketones containing quaternary stereogenic centers with good yields, excellent enantioselectivity, and low loading (1-5 mol %) of simple chiral primary amine catalysts. PMID:21671564

Kwiatkowski, Piotr; Dudzi?ski, Krzysztof; ?y?wa, Dawid

2011-07-15

65

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

PubMed

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

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

2005-06-15

66

New oxazoline-based ligands for application in asymmetric synthesis  

Microsoft Academic Search

Asymmetric catalysis is a powerful tool in the synthesis of optically pure compounds by providing excellent possibilities to introduce enantioselectivity using small amounts of an enantiomerically pure catalyst. Among the large variety of asymmetric ligands that have emerged since the start of aymmetric catalysis, enantiopure C2-symmetric bisoxazoline ligands have been identified as a 'privileged' class of ligands with applications in

H. L. van Lingen

2005-01-01

67

Organocatalytic asymmetric cascade reactions of 7-vinylindoles: diastereo- and enantioselective synthesis of c7-functionalized indoles.  

PubMed

The first catalytic asymmetric cascade reaction of 7-vinylindoles has been established by the rational design of such substrates. Cascade reactions with isatin-derived 3-indolylmethanols in the presence of a chiral phosphoric acid derivative allow the diastereo- and enantioselective synthesis of C7-functionalized indoles as well as the construction of cyclopenta[b]indole and spirooxindole frameworks (all >95:5 d.r., 94->99?% ee). This approach not only addresses the great challenge of the catalytic asymmetric synthesis of C7-functionalized indoles, but also provides an efficient method for constructing biologically important cyclopenta[b]indole and spirooxindole scaffolds with excellent optical purity. Investigation of the reaction pathway and activation mode has suggested that this cascade reaction proceeds through a vinylogous Michael addition/Friedel-Crafts process, in which dual H-bonding activation of the two reactants plays a crucial role. PMID:25521722

Shi, Feng; Zhang, Hong-Hao; Sun, Xiao-Xue; Liang, Jing; Fan, Tao; Tu, Shu-Jiang

2015-02-16

68

Phormidolides B and C, cytotoxic agents from the sea: enantioselective synthesis of the macrocyclic core.  

PubMed

New cytotoxic polyketide macrolides named phormidolides?B and C were isolated from a marine sponge of the Petrosiidae family collected off the coast of Pemba (Tanzania). The isolation, structure elucidation, and enantioselective synthesis of three diastereomers of the macrocyclic core is described herein. The described synthetic methodology started from 2-deoxy-D-ribose or 2-deoxy-L-ribose and afforded the desired macrocycles with high enantiomeric purity. The key step of the synthesis is the formation of the Z-trisubstituted double bond using a Julia-Kocienski olefination. The versatility of the synthetic methodology may provide access to other enantiopure macrocycles by making changes in the starting materials or chiral inductors. PMID:25359690

Lorente, Adriana; Gil, Alejandro; Fernández, Rogelio; Cuevas, Carmen; Albericio, Fernando; Álvarez, Mercedes

2015-01-01

69

Enantioselective synthesis of (-)-maoecrystal v by enantiodetermining C-h functionalization.  

PubMed

The evolution of a program directed at the enantioselective total synthesis of maoecrystal V, a highly modified ent-kauranoid, is described. An early stage chiral auxiliary-directed asymmetric C-H functionalization for the construction of a key benzofuran intermediate enabled the first asymmetric synthesis of the natural enantiomer of maoecrystal V, confirming the assigned stereochemistry. A divergent course of the central intramolecular Diels-Alder reaction, which is dependent on the nature of the dienophile, initially led to the development of an unanticipated and previously unknown isomer of maoecrystal V, which we named maoecrystal ZG. In light of the reported selective and potent cytotoxic activity of maoecrystal V, the cytotoxic properties of maoecrystal ZG were also investigated. PMID:25409033

Lu, Ping; Mailyan, Artur; Gu, Zhenhua; Guptill, David M; Wang, Hengbin; Davies, Huw M L; Zakarian, Armen

2014-12-24

70

Developing novel organocatalyzed aldol reactions for the enantioselective synthesis of biologically active molecules  

PubMed Central

Aldol reaction is one of the most important methods for the formation of carbon-carbon bonds. Because of its significance and usefulness, asymmetric versions of this reaction have been realized with different approaches in the past. Over the last decade, the area of organocatalysis has made significant progresses. As one of most studied reactions in organocatalyses, organocatalyzed aldol reaction has emerged as a powerful tool for the synthesis of a large number of useful products in optically enriched forms. In this review, we summarize our efforts on the development of novel organocatalyzed aldol reactions for the enantioselective synthesis of biological active molecules. Literatures closely related to our studies are also covered. PMID:21918584

Bhanushali, Mayur; Zhao, Cong-Gui

2011-01-01

71

Highly enantioselective Friedel-Crafts alkylation reaction catalyzed by rosin-derived tertiary amine-thiourea: synthesis of modified chromanes with anticancer potency.  

PubMed

We present herein for the first time the synthesis and preliminary biological evaluation of various modified chromanes via a rosin-derived tertiary amine-thiourea-catalyzed highly enantioselective Friedel-Crafts alkylation reaction. PMID:22080190

Jiang, Xianxing; Wu, Lipeng; Xing, Yanhong; Wang, Long; Wang, Shoulei; Chen, Zongyao; Wang, Rui

2012-01-11

72

Enantioselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes. Synthesis of amphidinolides T1 and T4 via catalytic, stereoselective macrocyclizations  

E-print Network

I. Enantioselective Nickel-Catalyzed Reductive Couplings of Alkynes and Aldehydes Allylic alcohol synthesis via a nickel-catalyzed reductive coupling reaction of alkylsubstituted alkynes and aldehydes was studied for ligand ...

Colby Davie, Elizabeth A. (Elizabeth Anne)

2005-01-01

73

Highly enantioselective total synthesis of natural epoxydictymene. An alkoxy-directed cyclization route to highly strained trans-oxabicyclo[3.3.0]octanes  

Microsoft Academic Search

An enantioselective synthesis of (+)-epoxydictymene, which involves efficient construction of the strained oxabicyclo[3.3.0]octane subunit by irradiation with iodosobenzene diacetate and iodine in cyclohexane solution, is reported.

Leo A. Paquette; Li-Qiang Sun; Dirk Friedrich; Paul B. Savage

1997-01-01

74

Absolute asymmetric synthesis in enantioselective autocatalytic reaction networks: theoretical games, speculations on chemical evolution and perhaps a synthetic option.  

PubMed

The Soai reaction and the Viedma deracemization of racemic conglomerate crystal mixtures are experimental pieces of evidence of the ability of enantioselective autocatalytic coupled networks to yield absolute asymmetric synthesis. Thermodynamically open systems or systems with non-uniform energy distributions may lead to chiral final states and, in systems able to come into thermodynamic equilibrium with their surroundings, to kinetically controlled absolute asymmetric synthesis. The understanding of network parameters and of the thermodynamic scenarios that may lead to spontaneous mirror symmetry breaking (SMSB) could assist in the development of new methods for asymmetric synthesis and enantioselective polymerizations (e.g., replicators), and to frame reasonable speculations on the origin of biological homochirality. PMID:25352056

Ribó, Josep M; Blanco, Celia; Crusats, Joaquim; El-Hachemi, Zoubir; Hochberg, David; Moyano, Albert

2014-12-22

75

Enantioselective Synthesis of (+)-Chamaecypanone C, a Novel Microtubule Inhibitor**  

PubMed Central

A number of bicyclo[2.2.2]octenone-containing natural products have been isolated from the heartwood of Chamaecyparis obtusa var. formosana (Figure 1) including the Diels-Alder adducts[1] obtunone (1),[2] chamaecypanone C (2),[3] and the [4+2] dimer (+)-3.[2],[4] Compound (+)-2 was shown to exhibit potent cytotoxicity against several human cancer cells including human oral epidermoid carcinoma (KB) (IC50 = 190 nM).[3] The biosynthesis of 2 was proposed[3] to occur via endo [4+2] cycloaddition between 1-hydroxymentha-3,5-dien-2-one 4 (Figure 2) and 1,3-bis-arylcyclopenta-1,3-diene 5, followed by oxidation to an enone in accord with literature reports of cyclopentadienes as biosynthetic precursors to natural products.[1b] An alternative possibility involving the corresponding cyclopentadienone 6 as dienophile may also be considered in light of known biosyntheses involving reactive cyclopentadienones.[5] Herein, we report a concise synthesis of both enantiomers of chamaecypanone C involving a retro-DA/DA cascade of dimer 3, obtained utilizing copper-mediated asymmetric oxidative dearomatization,[6] as well as biological studies documenting that the cytotoxic action of (+)-2 involves mitotic arrest as a consequence of its binding in the colchicine site of tubulin. PMID:19140149

Dong, Suwei; Hamel, Ernest; Bai, Ruoli; Covell, David G.; Beutler, John A.; Porco, John A.

2009-01-01

76

Enantioselective synthesis of 1-methoxy- and 1-deoxy-2?-methyl-? 8-tetrahydrocannabinols: New selective ligands for the CB 2 receptor  

Microsoft Academic Search

Two new series of cannabinoids were prepared and their affinities for the CB1 and CB2 receptors were determined. These series are the (2?R)- and (2?S)-1-methoxy- and 1-deoxy-3-(2?-methylalkyl)-?8-tetrahydrocannabinols, with alkyl side chains of three to seven carbon atoms. These compounds were prepared by a route that employed the enantioselective synthesis of the resorcinol precursors to the cannabinoid ring system. All of

John W. Huffman; Simon M. Bushell; Sudhir N. Joshi; Jenny L. Wiley; Billy R. Martin

2006-01-01

77

Development of ProPhenol Ligands for the Diastereo- and Enantioselective Synthesis of ?-Hydroxy-?-amino Esters  

PubMed Central

A zinc–ProPhenol-catalyzed direct asymmetric aldol reaction between glycine Schiff bases and aldehydes is reported. The design and synthesis of new ProPhenol ligands bearing 2,5-trans-disubstituted pyrrolidines was essential for the success of this process. The transformation operates at room temperature and affords syn ?-hydroxy-?-amino esters in high yields with good to excellent levels of diastereo- and enantioselectivity. PMID:24502188

2015-01-01

78

Enantioselective one-pot synthesis of ring-fused tetrahydroquinolines via aerobic oxidation and 1,5-hydride transfer/cyclization sequences.  

PubMed

Enantioselective organocatalytic synthesis of tetrahydroquinolines has been achieved via an aerobic oxidation and a 1,5-hydride transfer/cyclization sequence. The feature of this research is a one-pot transformation of 3-arylprop-2-en-1-ol derivatives into tetrahydroquinolines using a Ru(VII)-catalyzed aerobic oxidation and highly efficient internal redox reactions. The synthetically useful ring-fused tetrahydroquinoline derivatives are obtained in moderate yields and high levels of enantioselectivity. PMID:25280134

Suh, Chang Won; Kim, Dae Young

2014-10-17

79

A Concise Enantioselective Synthesis and Cytotoxic Evaluation of the Anticancer Rotenoid Deguelin Enabled by a Tandem Knoevenagel/Conjugate Addition/Decarboxylation Sequence  

PubMed Central

(?)-Deguelin is a rotenoid natural product that possesses significant potential as a chemopreventive and chemotherapeutic agent. While several racemic syntheses of deguelin have been reported, a formal evaluation of the anticancer activity of both the natural and unnatural enantiomers remains lacking. We describe herein the successful application of a flexible and selective thiourea-catalyzed cyclization strategy toward the enantioselective total synthesis of deguelin, which allows access to either stereoisomer for biological studies. The synthesis was completed in six steps (longest linear) with no protecting groups. The evaluation of both enantiomers of the natural product demonstrated potent inhibition of several cancer cell lines by these compounds, but interestingly showed that the unnatural (+)-deguelin preferentially inhibited the growth of MCF-7 breast cancer and HepG2 liver carcinoma cells when compared to the natural product. PMID:24101971

Farmer, Rebecca L.

2013-01-01

80

Enantioselective synthesis of tatanans A–C and reinvestigation of their glucokinase-activating properties  

PubMed Central

The tatanans are members of a novel class of complex sesquilignan natural products recently isolated from the rhizomes of Acorus tatarinowii Schott plants. Tatanans A, B and C have previously been reported to have potent glucokinase-activating properties that exceed the in vitro activity of known synthetic antidiabetic agents. Here, using a series of sequential [3,3]-sigmatropic rearrangements, we report the total synthesis of tatanan A in 13 steps and 13% overall yield. We also complete a concise enantioselective total synthesis of more complex, atropisomeric tatanans B and C via a distinct convergent strategy based on a palladium-catalysed diastereotopic aromatic group differentiation (12 steps, 4% and 8% overall yield, respectively). A plausible biosynthetic relationship between acyclic tatanan A and spirocyclic tatanans B and C is proposed and probed experimentally. With sufficient quantities of the natural products in hand, we undertake a detailed functional characterization of the biological activities of tatanans A–C. Contrary to previous reports, our assays utilizing pure recombinant human enzyme demonstrate that tatanans do not function as allosteric activators of glucokinase. PMID:23609092

Xiao, Qing; Jackson, Jeffrey J.; Basak, Ashok; Bowler, Joseph M.; Miller, Brian G.; Zakarian, Armen

2014-01-01

81

Enantioselective Synthesis of Angularly Substituted 1-Azabicylic Rings: Coupled Dynamic Kinetic Epimerization and Chirality Transfer  

PubMed Central

A new strategy for enantioselective synthesis of azacyclic molecules in which dynamic kinetic equilibration of diastereomeric iminium ions precedes a stereochemistry-determining sigmatropic rearrangement is reported. The method is illustrated by the synthesis in high enantiomeric purity (generally 95–99% ee) of a variety of 1-azabicyclic molecules containing angular allyl or 3-substituted 2-propenyl side chains adjacent to nitrogen and up to three stereogenic centers. In these products, the size of the carbocyclic ring is varied widely (5–12 membered), however useful yields are obtained in forming 1-azabicyclic products containing only fused pyrrolidine and piperidine rings. Chi-rality transfer from substituents at carbons 1 and 2 of the 3-butenylamine fragment of the starting material is investigated, with methyl and phenyl substituents at the allylic position shown to provide exquisite stereocontrol (generally 98–99% chirality transfer). An attractive feature of the method is the ability to carry out the key transformation in the absence of solvent. Illustrated also is the high yielding conversion of four such products to a new family of bicyclic ?-amino acids of high enantiomeric purity. PMID:24090405

Aron, Zachary D.; Ito, Tatsuya; May, Tricia L.; Overman, Larry E.; Wang, Jocelyn

2013-01-01

82

Synthesis and studies of polypeptide materials: Enantioselective polymerization of gamma-benzyl glutamate-N-carboxyanhydride and synthesis of optically active poly(beta-peptides)  

NASA Astrophysics Data System (ADS)

A class of zero-valent transition metal complexes have been developed by Deming et al for the controlled polymerization of alpha-aminoacid-N-carboxyanhydrides (alpha-NCAs). This discovery provided a superior starting point for the development of enantioselective polymerizations of racemic alpha-NCAs. Bidentate chiral ligands were synthesized and tested for their abilities to induce enantioselective polymerization of gamma-benzyl-glutamate NCA (Glu NCA) when they were coordinated to zero-valent nickel complexes. When optically active 2-pyridinyl oxazoline ligands were mixed with bis(1,5-cyclooctadiene)nickel in THF, chiral nickel complexes were formed that selectively polymerized one enantiomer of Glu NCA over the other. The highest selectivity was observed with the nickel complex of (S)-4-tert-butyl-2-pyridinyl oxazoline, which gave a ratio of enantiomeric polymerization rate constants (kD/kL) of 5.2. It was found that subtle modification of this ligand by incorporation of additional substituents had a substantial impact on initiator enantioselectivities. In separate efforts, methodology was developed for the general synthesis of optically active beta-aminoacid-N-carboxyanhydrides (beta-NCAs) via cyclization of Nbeta-Boc- or Nbeta-Cbz-beta-amino acids using phosphorus tribromide. The beta-NCA molecules could be polymerized in good yields using strong bases or transition metal complexes to give optically active poly(beta-peptides) bearing proteinogenic side chains. The resulting poly(beta-peptides), which have moderate molecular weights, adopt stable helical conformations in solution. Poly(beta-homoglutamate and poly(beta-homolysine), the side-chain deprotected polymers, were found to display pH dependent helix-coil conformation transitions in aqueous solution, similar to their alpha-analogs. A novel method for poly(beta-aspartate) synthesis was developed via the polymerization of L-aspartate alkyl ester beta lactams using metal-amido complexes. Poly(beta-aspartates) bearing short ethylene glycol side chains were obtained with controlled molecular weights and narrow molecular weight distributions when Sc(N(TMS)2)3 was used as initiator for the beta-lactam polymerizations. Polymer chain lengths could be controlled by both stoichiometry and monomer conversion, characteristic of a living polymerization system. Di- and tri-block copoly(beta-peptides) with desired chain lengths were also synthesized using this method. It was found that these techniques were generally applicable for the synthesis of poly(beta-peptides), bearing other proteinogetic side chains. Synthesis and studies of polypeptide materials were extended to unexplored areas by incorporation of both alpha- and beta-amino acid residues into single polymer chains. Two sequence specific polypeptides bearing alternating beta-alpha, or beta-alpha-alpha amino acid residues were synthesized. Both polymers were found to adopt unprecedented stable conformations in solution.

Cheng, Jianjun

83

Enantioselective synthesis of ?-benzylated lanthionines and related tripeptides for biological incorporation into E. coli peptidoglycan.  

PubMed

The synthesis of modified tripeptides (S)-Ala-?-(R)-Glu-X, where X = (R,S) or (R,R) diastereomers of ?-benzyl or ?-(4-azidobenzyl)lanthionine, was carried out. The chemical strategy involved the enantioselective alkylation of a 4-MeO-phenyloxazoline. The reductive opening of the alkylated oxazolines, followed by cyclization and oxidation, led to four PMB-protected sulfamidates. Subsequent PMB removal, Boc protection and regioselective opening with cysteine methyl ester led to protected lanthionines. These compounds were further converted in a one pot process to the corresponding protected tripeptides. After ester and Boc deprotection, the four tripeptides were evaluated as potential analogues of the natural tripeptide (S)-Ala-?-(R)-Glu-meso-A2pm. These compounds were evaluated for introduction, by means of the biosynthetic recycling pathway, into the peptidoglycan of Escherichia coli. A successful in vitro biosynthesis of UDP-MurNAc-tripeptides from the tripeptides containing ?-benzyl lanthionine was achieved using purified murein peptide ligase (Mpl). Bioincorporation into E. coli W7 did not occur under different tested conditions probably due to the bulky benzyl group at the C? carbon of the C-terminal amino acid. PMID:25355616

Denoël, Thibaut; Zervosen, Astrid; Lemaire, Christian; Joris, Bernard; Hervé, Mireille; Blanot, Didier; Zaragoza, Guillermo; Luxen, André

2014-12-28

84

Synthesis of chiral 3-substituted phthalides by a sequential organocatalytic enantioselective aldol-lactonization reaction. Three-step synthesis of (S)-(-)-3-butylphthalide.  

PubMed

The development of efficient methods for the facile construction of important molecular frameworks is an important goal in organic synthesis. Chiral 3-substituted phthalides are widely distributed in a large collection of natural products with broad, potent, and potentially path-pointing biological activities. In this investigation, we have uncovered an unprecedented organocatalytic asymmetric aldol-lactonization reaction of 2-formylbenzoic esters with ketones/aldehydes for convenient construction of the enantioenriched "privileged" scaffold. As a result of the sensitive nature of substrate structures of an organocatalytic enantioselective aldol reaction, after extensive optimization of reaction conditions, catalyst L-prolinamide alcohol IV is identified as the best promoter. Interestingly, it is found that in this reaction, addition of an acid additive PhCO(2)H can significantly enhance reaction efficiency with use of only as low as 2.5 mol % IV for the process. Moreover, due to the sensitivity of reaction conditions toward a sequential aldol-lactonization process without affecting enantioselectivity and racemization, it is essential to remove the catalyst for the subsequent facile lactonization reaction in the presence of K(2)CO(3). The aldol-lactonization processes serve as a powerful approach to the preparation of synthetically and biologically important 3-substituted phthalides with a high level of enantioselectivities. A 3-step catalytic asymmetric synthesis of the natural product of 3-butylphthalide is reported. PMID:20000698

Zhang, Haoyi; Zhang, Shilei; Liu, Lu; Luo, Guangshun; Duan, Wenhu; Wang, Wei

2010-01-15

85

Enantioselective nucleophile-catalyzed cycloadditions  

E-print Network

Chapter 1 describes the development of an asymmetric nucleophile-catalyzed [2+2] cycloaddition of ketenes with aldehydes. This is the first report of a catalytic enantioselective synthesis of trisubstituted [beta]-lactones. ...

Wilson, Jonathan E., Ph. D. Massachusetts Institute of Technology

2007-01-01

86

Enantioselective Friedel-Crafts alkylation for synthesis of 2-substituted indole derivatives.  

PubMed

An efficient catalytic asymmetric intermolecular C2 Friedel-Crafts alkylation reaction between N-methyl skatole and ?,?-unsaturated ?-ketoesters has been realized by a chiral N,N'-dioxide-Ni(II) complex. The corresponding indole derivatives were obtained in good yield (up to 96%) with excellent enantioselectivities (up to 99% ee) under mild reaction conditions. PMID:24158312

Zhang, Yulong; Liu, Xiaohua; Zhao, Xiaohu; Zhang, Jianlin; Zhou, Lin; Lin, Lili; Feng, Xiaoming

2013-12-14

87

Photoredox Activation and Anion Binding Catalysis in the Dual Catalytic Enantioselective Synthesis of ?-Amino Esters  

PubMed Central

The enantioselective oxidative C-H functionalization of tetrahydroisoquinoline derivatives is achieved through the merger of photoredox and asymmetric anion-binding catalysis. This combination of two distinct catalysis concepts introduces a potentially general approach to asymmetric transformations in oxidative photocatalysis. PMID:24294480

Bergonzini, Giulia; Schindler, Corinna S.; Wallentin, Carl-Johan

2013-01-01

88

Enantioselective microbial synthesis of the indigenous natural product (-)-?-bisabolol by a sesquiterpene synthase from chamomile (Matricaria recutita).  

PubMed

(-)-?-Bisabolol, a sesquiterpene alcohol, is a major ingredient in the essential oil of chamomile (Matricaria recutita) and is used in many health products. The current supply of (-)-?-bisabolol is mainly dependent on the Brazilian candeia tree (Eremanthus erythropappus) by distillation or by chemical synthesis. However, the distillation method using the candeia tree is not sustainable, and chemical synthesis suffers from impurities arising from undesirable ?-bisabolol isomers. Therefore enzymatic synthesis of (-)-?-bisabolol is a viable alternative. In the present study, a cDNA encoding (-)-?-bisabolol synthase (MrBBS) was identified from chamomile and used for enantioselective (-)-?-bisabolol synthesis in yeast. Chamomile MrBBS was identified by Illumina and 454 sequencing, followed by activity screening in yeast. When MrBBS was expressed in yeast, 8 mg of ?-bisabolol was synthesized de novo per litre of culture. The structure of purified ?-bisabolol was elucidated as (S,S)-?-bisabolol [or (-)-?-bisabolol]. Although MrBBS possesses a putative chloroplast-targeting peptide, it was localized in the cytosol, and a deletion of its N-terminal 23 amino acids significantly reduced its stability and activity. Recombinant MrBBS showed kinetic properties comparable with those of other sesquiterpene synthases. These data provide compelling evidence that chamomile MrBBS synthesizes enantiopure (-)-?-bisabolol as a single sesquiterpene product, opening a biotechnological opportunity to produce (-)-?-bisabolol. PMID:25048207

Son, Young-Jin; Kwon, Moonhyuk; Ro, Dae-Kyun; Kim, Soo-Un

2014-10-15

89

Enantioselective synthesis of piperidines through the formation of chiral mixed phosphoric acid acetals: experimental and theoretical studies.  

PubMed

An enantioselective intramolecular chiral phosphoric acid-catalyzed cyclization of unsaturated acetals has been utilized for the synthesis of functionalized chiral piperidines. The chiral enol ether products of these cyclizations undergo subsequent in?situ enantioenrichment through acetalization of the minor enantiomer. A new computational reaction exploration method was utilized to elucidate the mechanism and stereoselectivity of this transformation. Rather than confirming the originally postulated cyclization proceeding directly through a vinyl oxocarbenium ion, simulations identified an alternative two-step mechanism involving the formation of a mixed chiral phosphate acetal, which undergoes a concerted, asynchronous S(N)2'-like displacement to yield the product with stereoselectivity in agreement with experimental observations. PMID:25196818

Sun, Zhankui; Winschel, Grace A; Zimmerman, Paul M; Nagorny, Pavel

2014-10-13

90

Catalytic enantioselective synthesis of atropisomeric biaryls: a cation-directed nucleophilic aromatic substitution reaction.  

PubMed

A catalytic enantioselective nucleophilic aromatic substitution reaction which yields axially chiral biaryl derivatives in excellent yields with e.r.?values of up to 97:3 has been developed. This process uses a chiral counterion to direct the addition of thiophenolate to a prochiral dichloropyrimidine by a tandem desymmetrization/kinetic resolution mechanism. The products can be derivatized to a range of atropisomeric structures without any reduction in enantioenrichment, thus offering access to unexplored chiral biaryl architectures. PMID:25257677

Armstrong, Roly J; Smith, Martin D

2014-11-17

91

Co(III)(salen)-catalyzed HKR of two stereocentered alkoxy- and azido epoxides: a concise enantioselective synthesis of (S,S)-reboxetine and (+)-epi-cytoxazone.  

PubMed

The HKR of racemic syn- or anti- alkoxy- and azido epoxides catalyzed by Co(salen) complex affords a practical access to a series of enantioenriched syn- or anti- alkoxy- and azido epoxides and the corresponding 1,2-diols. This strategy has been successfully employed in the concise, enantioselective synthesis of bioactive molecules such as (S,S)-reboxetine and (+)-epi-cytoxazone. PMID:20526501

Reddy, R Santhosh; Chouthaiwale, Pandurang V; Suryavanshi, Gurunath; Chavan, Vilas B; Sudalai, Arumugam

2010-07-21

92

Towards the enantioselective synthesis of (-)-euonyminol--preparation of a fully functionalised lower-rim model.  

PubMed

The development of a stereoselective total synthesis of ?-dihydroagarofuran 4 is described. This compound contains the same oxygenation pattern on its 'lower-rim' as found in the natural sesquiterpene (-)-euonyminol (1) and it is expected that the route described should be applicable to the synthesis of that complex natural product. (-)-Euonyminol is found as the core scaffold of a series of complex macrodilactone sesquiterpenoids isolated from the Celastraceae which possess interesting biological activities (e.g. anti-HIV activity). The synthetic route builds upon an epoxidative asymmetric desymmetrisation of meso-diallylic alcohol 10 that we have reported previously. It features a lactate Ireland-Claisen rearrangement to establish the quaternary stereocentre at C11 (27?28a) and an unusual dealkylative intramolecular epoxide-opening by the C11 methyl ether to establish the tetrahydrofuranyl C-ring of the ?-dihydroagarofuran skeleton (35?36). PMID:23443742

Webber, Matthew J; Warren, Sarah A; Grainger, Damian M; Weston, Matthew; Clark, Stacy; Woodhead, Steven J; Powell, Lyn; Stokes, Stephen; Alanine, Alexander; Stonehouse, Jeffrey P; Frampton, Christopher S; White, Andrew J P; Spivey, Alan C

2013-04-21

93

Unprecedented 8,9'-neolignans: enantioselective synthesis of possible stereoisomers for structural determination.  

PubMed

(+)-Wutaienin (3) and its C-7 methyl ether (4), isolated from Zanthoxylum wutaiense, were found to be unprecedented 8,9'-neolignans containing an (S)-2-(1,1-dimethyl-1-hydroxymethyl)-7-methoxydihydrobenzofuran skeleton. Wutaienin (3) was present in the plant as an inseparable 1:1 mixture of the (7,8)-syn-diastereoisomers. The diastereoisomeric mixture was characterized by comparison with four possible diastereoisomers, which were enantioselectively synthesized from (S)-5-bromo-(1,1-dimethyl-1-hydroxymethyl)-7-methoxydihydrobenzofuran using Evans' oxazolidinone-assisted asymmetric aldol condensation to install the chiral centers at the C-7 and C-8 positions. PMID:25427159

Takahashi, Masato; Suzuki, Noriyuki; Ishikawa, Tsutomu; Huang, Hung-Yi; Chang, Hsun-Shuo; Chen, Ih-Sheng

2014-12-26

94

Design and enantioselective synthesis of cashmeran odorants by using "enol catalysis".  

PubMed

Novel Cashmeran odorants were designed by molecular modeling. Their short syntheses involve a novel asymmetric Brønsted acid catalyzed Michael addition of unactivated ?-substituted ketones. This key transformation was realized by utilizing a new type of enol activation catalysis and affords different cyclic ketones bearing ?-quaternary stereocenters in good to excellent yields and with high enantioselectivity. Subsequent McMurry coupling and Saegusa-Ito oxidation furnished the enantiopure target odorants, one enantiomer of which indeed possesses the typical olfactory aspects of Cashmeran. PMID:25573140

Felker, Irene; Pupo, Gabriele; Kraft, Philip; List, Benjamin

2015-02-01

95

Enantioselective Protonation  

PubMed Central

Enantioselective protonation is a common process in biosynthetic sequences. The decarboxylase and esterase enzymes that effect this valuable transformation are able to control both the steric environment around the proton acceptor (typically an enolate) and the proton donor (typically a thiol). Recently, several chemical methods to achieve enantioselective protonation have been developed by exploiting various means of enantiocontrol in different mechanisms. These laboratory transformations have proven useful for the preparation of a number of valuable organic compounds. PMID:20428461

Mohr, Justin T.; Hong, Allen Y.; Stoltz, Brian M.

2010-01-01

96

Asymmetric catalytic Mannich reactions catalyzed by urea derivatives: enantioselective synthesis of beta-aryl-beta-amino acids.  

PubMed

Highly enantioselective addition reactions between silyl ketene acetals and N-Boc aldimines are catalyzed by the thiourea-based catalyst 1c. Extraordinary scope is observed in this methodology with regard to the imine substrate, with aryl and heteroaromatic derivatives generally affording nearly quantitative yields of beta-amino ester product in up to 98% enantioselectivity. PMID:12405820

Wenzel, Anna G; Jacobsen, Eric N

2002-11-01

97

Simple strategy for synthesis of optically active allylic alcohols and amines by using enantioselective organocatalysis  

PubMed Central

A simple organocatalytic one-pot protocol for the construction of optically active allylic alcohols and amines using readily available reactants and catalyst is presented. The described reaction is enabled by an enantioselective enone epoxidation/aziridination-Wharton-reaction sequence affording two highly privileged and synthetically important classes of compounds in an easy and benign way. The advantages of the described sequence include easy generation of stereogenic allylic centers, also including quaternary stereocenters, with excellent enantio- and diastereomeric-control and high product diversity. Furthermore, using monosubstituted enones as substrates, having moderate enantiomeric excess, the one-pot reaction sequence proceeds with an enantioenrichment of the products and high diastereoselectivity was achieved. PMID:20547884

Jiang, Hao; Holub, Nicole; Anker Jørgensen, Karl

2010-01-01

98

Highly enantioselective synthesis of alpha,beta-diaminopropanoic acid derivatives using a catalytic asymmetric hydrogenation approach.  

PubMed

Rh-DuPhos-catalyzed asymmetric hydrogenation of alpha,beta-diamidoacrylates provides a highly efficient and enantioselective route to chiral alpha,beta-diaminopropanoic acid derivatives. The mechanistic course of the hydrogenation was studied using isotopically enriched enamide complexes and phosphorus and carbon NMR. Addition of methyl alpha-N-benzoyl-beta-N-acetyl-diaminopropenoate to the solvated catalyst gave a single 1:1 enamide complex and demonstrated the binding of the olefin and alpha-amide carbonyl group; the carboxylate and beta-N-acyl groups did not bind to the metal. Changes to the electronic and steric properties of the beta-N-acyl group were well tolerated; however, small changes to the binding alpha-N-acyl group were found to significantly affect hydrogenation yields. PMID:11397145

Robinson, A J; Lim, C Y; He, L; Ma, P; Li, H Y

2001-06-15

99

Palladium(II)-Catalyzed Enantioselective Synthesis of 2-Vinyl Oxygen Heterocycles  

PubMed Central

2-Vinylchromanes (1), 2-vinyl-1,4-benzodioxanes (2), and 2,3-dihydro-2-vinyl-2H-1,4-benzoxazines (3) can be prepared in high yields (90–98%) and excellent enantiomeric purities (87–98% ee) by [COP-OAc]2-catalyzed cyclization of phenolic (E)-allylic trichloroacetimidate precursors. Deuterium-labeling and computational experiments are consistent with these cyclization reactions taking place by an anti-oxypalladation/syn-deoxypalladation mechanism. 2-Vinylchromanes can be prepared also in good yields and high enantiomeric purities from analogous (E)-allylic acetate precursors, which constitutes the first report that acetate is a competent leaving group in COP-catalyzed enantioselective SN2? substitution reactions. PMID:22316285

Cannon, Jeffrey S.; Olson, Angela C.; Overman, Larry E.; Solomon, Nicole S.

2012-01-01

100

Cooperative dual catalysis: application to the highly enantioselective conjugate cyanation of unsaturated imides.  

PubMed

Cooperative heterobimetallic catalysis was used as a design principle to achieve a highly reactive system for the enantioselective conjugate addition of cyanide to alpha,beta-unsaturated imides. A dual-catalyst pathway involving chiral (salen)Al complex 1b and chiral (pybox)Er complex 4b provides measurable improvements in rates and enantioselectivities relative to single-catalyst systems. Mechanistic studies point to a cooperative bimetallic mechanism involving activation of the imide by the Al complex and activation of cyanide by the Er complex. PMID:15303860

Sammis, Glenn M; Danjo, Hiroshi; Jacobsen, Eric N

2004-08-18

101

Simple Organic Molecules as Catalysts for Enantioselective Synthesis of Amines and Alcohols  

PubMed Central

The discovery of new catalysts that can generate complex organic compounds via enantioselective transformations is central to advances in the life sciences;i for this reason, many chemists try to discover catalysts that can be used to produce chiral molecules with a strong preference for one mirror image isomer.ii The ideal catalyst should be devoid of precious elementsiii and should bring reactions to completion in a few hours using operationally simple procedures. In this manuscript, we introduce a set of small organic molecules that can catalyze reactions of unsaturated organoboron reagents with imines and carbonyls; the products of the reactions are enantiomerically pure amines and alcohols, which can be used to synthesize more complex, biologically active molecules. A distinguishing feature of this new catalyst class is the presence of a 'key' proton embedded within their structure. The catalyst is derived from the abundant amino acid valine and was prepared in large quantities in four steps using inexpensive reagents. Reactions are scalable, do not demand stringent conditions, and can be performed with as little as 0.25 mol % catalyst in less than six hours at room temperature to generate products in >85% yield and ?97:3 enantiomeric ratio. The efficiency, selectivity and operational simplicity of the transformations and the range of boron-based reagents render this advance vital to future progress in chemistry, biology and medicine. PMID:23407537

Silverio, Daniel L.; Torker, Sebastian; Pilyugina, Tatiana; Vieira, Erika M.; Snapper, Marc L.; Haeffner, Fredrik; Hoveyda, Amir H.

2012-01-01

102

Enantioselective Synthesis of the C(1)–C(11) Fragment of Tedanolide C  

PubMed Central

A convergent synthesis of the protected C(1)–C(11) fragment 6 of the targeted enantiomer of tedanolide C is described. The key step of the synthesis is the Felkin-Ahn addition of vinyl iodide 7 to aldehyde 8 that proceeds in 80% yield with 4:1 diastereoselectivity. PMID:23249423

Geist, Julie G.; Barth, Roland

2012-01-01

103

Enantioselective synthesis of tetrahydroisoquinolines via iridium-catalyzed intramolecular Friedel-Crafts-type allylic alkylation of phenols.  

PubMed

An efficient iridium-catalyzed intramolecular Friedel-Crafts-type allylic alkylation reaction of phenols was developed, affording tetrahydroisoquinolines with moderate to excellent yields, enantioselectivity, and good regioselectivity. PMID:22540154

Xu, Qing-Long; Dai, Li-Xin; You, Shu-Li

2012-05-18

104

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

PubMed Central

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

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

2009-01-01

105

Enantioselective synthesis of benzoindolizidine derivatives using chiral phase-transfer catalytic intramolecular domino aza-Michael addition/alkylation.  

PubMed

An efficient and enantioselective strategy to synthesize benzoindolizidines from ?,?-unsaturated amino ketones via domino intramolecular aza-Michael addition/alkylation was developed. These reactions were enabled by cinchona alkaloid-derived quaternary ammonium salts as the phase-transfer catalyst. A variety of benzoindolizidines were prepared in good yields (up to 93%) and enantioselectivities (up to 92.8?:?7.2 er). PMID:25428596

Guo, Jiajia; Yu, Shouyun

2015-01-28

106

Enantioselective Total Synthesis and Biological Evaluation of (+)-Kibdelone A and a Tetrahydroxanthone Analogue  

PubMed Central

The total synthesis of kibdelone A has been accomplished using In(III)-catalyzed arylation of a heterocyclic quinone monoketal and iodine-mediated oxidative photochemical electrocyclization for construction of the ABCD ring moiety. Enzymatic dihydroxylation of methyl 2-halobenzoate substrates was employed for synthesis of activated 2-halo-cyclohexene F-ring fragments. A one pot oxa-Michael-Friedel-Crafts process allowed access to the first simplified analogues of the kibdelones PMID:23834060

Winter, Dana K.; Endoma-Arias, Mary Ann; Hudlicky, Tomas; Beutler, John A.; Porco, John A.

2013-01-01

107

Enantioselective total synthesis of (+)-brefeldin A and 7-epi-brefeldin A.  

PubMed

A convergent enantioselective route to brefeldin A (BFA) and 7-epi-BFA was developed. The key C-4/C-5 chiral centers were established by using chiral auxiliary induced intermolecular asymmetric aldolization in the presence of TiCl(4) and TMEDA. The results with the thiazolidinethione/TiCl(4) mediated intermolecular asymmetric aldolization added some new information about the scope and limitations to the existing knowledge of that type of reactions (which so far was essentially limited to the reactions with N-propionyl thiazolidinethiones). During the course a method for protecting the liable aldol hydroxyl groups by using inexpensive TBSCl in DMF with 2,6-lutidine as the base was developed to replace the otherwise unavoidable TBSOTf procedure. Due to the excessive steric hindrance, removal of the auxiliary was much more difficult than most literature cases. Cleavage of the oxazolidinone by reduction was almost impossible. The thiazolidinethione auxiliary was relatively easier to remove. However, several reactions reported for facile removal of thiazolidinethione auxiliaries in the literature still failed. Reductive removal of the thiazolidinethione auxiliary was most effectively realized with LiBH(4) in diethyl ether in the presence of 1 equiv of MeOH (a modification of a literature procedure for removal of oxazolidinone auxiliaries in less hindered substrates). Apart from the auxiliary removal, oxidation of the alcohol into aldehyde and the deprotection of the dithiolane protecting group were also rather difficult in the present context. A range of methods were screened before final solutions were found. The five-membered ring was constructed by employing an intramolecular Mukaiyama reaction after many attempts with the intramolecular aldolization under a variety of conditions failed. The rate of elimination of the alkoxyl to form the alpha,beta-double bond of the key intermediate cyclopentenone 49 with DBU was highly solvent dependent (very sluggish in CH(2)Cl(2) but rather fast in MeOH). Introduction of the lower chain (which was synthesized by using a Jacobsen KHR to establish the C-15 chirality) was achieved through a Michael addition similar to the precedents in the literature. It has not been noticed before that the yield of this Michael reaction could be dramatically raised by using 3 equiv of the copper-lithium reagent 55. Reduction of the C-7 carbonyl was apparently more difficult than similar cases in the literature. After examination of many reagents under various conditions, it was found that the best reagent for yielding the alpha-isomer was (S)-2-methyl-CBS-borolidine/BH(3) and that for the beta-isomer was L-Selectride. The alpha- and beta-isomers were then further elaborated into (+)-brefeldin A and 7-epi-BFA, respectively. An unexpected yet very interesting solubility difference between BFA and 7-epi-BFA was also observed. PMID:15153019

Wu, Yikang; Shen, Xin; Yang, Yong-Qing; Hu, Qi; Huang, Jia-Hui

2004-05-28

108

Enantioselective Synthesis of Tetrahydroquinolines, Tetrahydroquinoxalines, and Tetrahydroisoquinolines via Pd-Catalyzed Alkene Carboamination Reactions.  

PubMed

A catalyst composed of Pd2(dba)3 and (S)-Siphos-PE provides excellent results in Pd-catalyzed alkene carboamination reactions between aniline derivatives bearing pendant alkenes and aryl or alkenyl halides. These transformations generate tetrahydroquinolines and tetrahydroquinoxalines that contain quaternary carbon stereocenters with high levels of asymmetric induction. In addition this catalyst also effects the asymmetric synthesis of tetrahydroisoquinolines via related transformations of 2-allylbenzylamines. In contrast to most other approaches to the asymmetric synthesis of these compounds, which frequently involve functional group interconversion or a single C-C or C-N bond-forming event, the carboamination reactions generate both a C-N bond, a C-C bond, and a stereocenter. PMID:25431650

Hopkins, B A; Wolfe, J P

2014-12-01

109

Enantioselective Synthesis of ?-Aminosilanes by Copper-Catalyzed Hydroamination of Vinylsilanes.  

PubMed

The synthesis of ?-aminosilanes by a highly enantio- and regioselective copper-catalyzed hydroamination of vinylsilanes is reported. The system employs Cu-DTBM-SEGPHOS as the catalyst, diethoxymethylsilane as the stoichiometric reductant, and O-benzoylhydroxylamines as the electrophilic nitrogen source. This hydroamination reaction is compatible with differentially substituted vinylsilanes, thus providing access to amino acid mimics and other valuable chiral organosilicon compounds. PMID:25475991

Niljianskul, Nootaree; Zhu, Shaolin; Buchwald, Stephen L

2015-01-26

110

Catalysis-based enantioselective total synthesis of the macrocyclic spermidine alkaloid isooncinotine  

PubMed Central

A concise and efficient total synthesis of the spermidine alkaloid (-)-isooncinotine (1) incorporating a 22-membered lactam ring is outlined. The approach is largely catalysis-based, involving a selective iron-catalyzed alkyl–aryl cross-coupling reaction of a difunctionalized pyridine substrate, a heterogeneous asymmetric hydrogenation step to set the chiral center of the target, and a highly integrated ring-closing metathesis/hydrogenation sequence to forge the saturated macrocyclic edifice in a single operation. PMID:15141085

Scheiper, Bodo; Glorius, Frank; Leitner, Andreas; Fürstner, Alois

2004-01-01

111

Organocatalyzed cyclopropanation of alpha-substituted alpha,beta-unsaturated aldehydes: enantioselective synthesis of cyclopropanes bearing a chiral quaternary center.  

PubMed

An enantioselective cyclopropanation of alpha-substituted alpha,beta-unsaturated aldehydes with bromomalonate has been successfully developed through a domino Michael/alpha-alkylation strategy. The method allows the efficient formation of cyclopropanes bearing a quaternary carbon stereocenter at the alpha-position of the aldehydes by using iminium/enamine catalysis and gives a nice extension on the organocatalytic cyclopropanation of bromomalonate and alpha,beta-unsaturated aldehydes previously reported by other groups. Very good yields (up to 81%) and enantioselectivities (up to 97% ee) have been obtained. The optically active cyclopropane derivatives are of high synthetic interest as useful targets for further elaboration into more complex structures. PMID:20512823

Terrasson, Vincent; van der Lee, Arie; de Figueiredo, Renata Marcia; Campagne, Jean Marc

2010-07-12

112

Application of microorganisms towards synthesis of chiral terpenoid derivatives.  

PubMed

Biotransformations are a standard tool of green chemistry and thus are following the rules of sustainable development. In this article, we describe the most common types of reactions conducted by microorganisms applied towards synthesis of chiral terpenoid derivatives. Potential applications of obtained products in various areas of industry and agriculture are shown. We also describe biological activity of presented compounds. Stereoselective hydroxylation, epoxidation, Baeyer-Villiger oxidation, stereo- and enantioselective reduction of ketones, and various kinetic resolutions carried out by bacteria and fungi have been reviewed. Mechanistic considerations regarding chemical and enzymatic reactions are presented. We also briefly describe modern approaches towards enhancing desired enzymatic activity in order to apply modified biocatalysts as an efficient tool and green alternative to chemical catalysts used in industry. PMID:22846902

Kuriata-Adamusiak, Renata; Strub, Daniel; Lochy?ski, Stanis?aw

2012-09-01

113

An efficient organocatalytic method for highly enantioselective Michael addition of malonates to enones catalyzed by readily accessible primary amine-thiourea.  

PubMed

A practical and highly enantioselective Michael addition of malonates to enones catalyzed by simple and readily available bifunctional primary amine-thiourea derived from 1,2-diaminocyclohexane is reported. The addition of weak acids and elevated temperature (ca. 50 °C) improved the efficiency of the Michael reaction. This approach enables the efficient synthesis of 1,5-ketoesters with good yields, excellent enantioselectivities (up to 99% ee), and low loading (0.5-5 mol %) of simple chiral primary amine-thiourea catalysts, and is applicable in multigram scale synthesis. PMID:22873407

Dudzi?ski, Krzysztof; Pakulska, Anna M; Kwiatkowski, Piotr

2012-08-17

114

Asymmetric synthesis of P-stereogenic diarylphosphinites by palladium-catalyzed enantioselective addition of diarylphosphines to benzoquinones.  

PubMed

The reaction of phenyl(2,4,6-trimethylphenyl)phosphine with a substituted benzoquinone in the presence of a chiral phosphapalladacycle complex as a catalyst and triethylamine in chloroform at -45 °C proceeded in a new type of addition manner to give a high yield of a 4-hydroxyphenyl phenyl(2,4,6-trimethylphenyl)phosphinite with 98% enantioselectivity, which is a versatile intermediate readily convertible into various phosphines and their derivatives with high enantiomeric purity. PMID:24635477

Huang, Yinhua; Li, Yongxin; Leung, Pak-Hing; Hayashi, Tamio

2014-04-01

115

Biomimetic superhelical conducting microfibers with homochirality for enantioselective sensing.  

PubMed

Chiral amplification and discrimination are great challenges in both scientific and technological research fields such as chemical synthesis, chiral catalysis, and biomedicine. By mimicking protein superstructures in nature, chiral conducting polyaniline (PANI) molecules induced by chiral dopants were self-assembled to ultra-ordered superhelical microfibers. The induced homochirality is observed to be amplified into different hierarchies, from chiral molecules to helical nanostructures, and to superhelical microstructures. Furthermore, both experimental and theoretical results indicated that the gas sensor made from a single PANI helical microfiber showed enantioselective discrimination to chiral aminohexane, giving it great potential for applications in online chiral discrimination. PMID:24370236

Zou, Wenjun; Yan, Yong; Fang, Jin; Yang, Yang; Liang, Jie; Deng, Ke; Yao, Jianlin; Wei, Zhixiang

2014-01-15

116

Asymmetric triple relay catalysis: enantioselective synthesis of spirocyclic indolines through a one-pot process featuring an asymmetric 6? electrocyclization.  

PubMed

A rare example of a one-pot process that involves asymmetric triple relay catalysis is reported. The key step is an asymmetric [1,5] electrocyclic reaction of functionalized ketimines. The substrates for this process were obtained in?situ in a two-step process that involved the hydrogenation of nitroarenes with a Pd/C catalyst to yield aryl amines and their subsequent coupling with isatin derivatives in a Brønsted acid catalyzed ketimine formation reaction. The electrocyclization was catalyzed by a bifunctional chiral Brønsted base/hydrogen bond donor catalyst. The one-pot process gave the desired products in good yields and with excellent enantioselectivity. PMID:25313907

Yin, Xiao-Ping; Zeng, Xing-Ping; Liu, Yun-Lin; Liao, Fu-Min; Yu, Jin-Sheng; Zhou, Feng; Zhou, Jian

2014-12-01

117

Diastereomeric aziridine carbinol catalyzed enantioselective arylation reaction: toward the asymmetric synthesis of both enantiomers of chiral 3-aryl phthalide.  

PubMed

The diastereomeric aziridine carbinols are applied, respectively, as efficient chiral ligand in the catalysis of asymmetric arylation and sequential arylation-lactonization cascade. The two diastereomers, which are facilely synthesized from the same chiral source, function as pseudo enantiomers in arylation of aromatic aldehydes providing the different enantiomers of the diarylmethanols with almost the same excellent enantioselectivities. The arylation method is also carried out in tandem with lactonization process to afford a concise synthetic approach to both enantiomers of optically active 3-aryl phthalide. PMID:24912109

Song, Xixi; Hua, Yuan-Zhao; Shi, Jing-Guo; Sun, Ping-Ping; Wang, Min-Can; Chang, Junbiao

2014-07-01

118

Asymmetric synthesis and catalytic activity of 3-methyl-?-proline in enantioselective anti-Mannich-type reactions.  

PubMed

Enantiomerically pure 3-methyl-?-proline was synthesized using an asymmetric phase-transfer-catalyzed alkylation of a cyanopropanoate to establish the all-carbon stereogenic center. The catalytic activity of 3-methyl-?-proline in the Mannich-type reaction between a glyoxylate imine and ketones/aldehydes was subsequently investigated. The catalyst was designed and found to be more soluble in nonpolar organic solvents relative to the unsubstituted ?-proline catalyst, and as a result allowed for added flexibility during optimization efforts. This work culminated in the development of a highly anti-diastereo- and enantioselective process employing low catalyst loading. PMID:23808600

Nagata, Kazuhiro; Kuga, Yasushi; Higashi, Akinori; Kinoshita, Atsushi; Kanemitsu, Takuya; Miyazaki, Michiko; Itoh, Takashi

2013-07-19

119

Synthesis of catalytically active polymer-bound Mn(III) salen complexes for enantioselective epoxidation of styrene derivatives  

Microsoft Academic Search

Catalytically active metal-complexing polymer-containing chiral Mn(III) salen moieties derived from (1R, 2R)-(?)-diphenylethylenediamine, (1S, 2S)-(+)-cyclohexanediamine, and (S)-(+)-diaminopropane with ?-naphthyl salicylaldehyde anchored to the polymeric matrix obtained from styrene-4-vinyl pyridine-divinyl benzene (PVPD) have been synthesised. These catalysts were used for enantioselective epoxidation of styrene and substituted styrenes, viz. 4-chloro-, 4-methyl and4-nitrostyrene using iodosyl benzene as terminal oxidant by GLC. The enantiomeric excess

R. I. Kureshy; N. H. Khan; S. H. R. Abdi; P. Iyer

1997-01-01

120

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

PubMed Central

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

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

2014-01-01

121

Recent advances in transition metal-catalyzed enantioselective hydrogenation of unprotected enamines.  

PubMed

Transition metal-catalyzed enantioselective hydrogenation of enamines is undoubtedly a useful and environment-friendly method for the preparation of optically pure chiral amines and amine derivatives. Over the last few decades, the use of transition metal catalysts containing chiral phosphorus or phosphine-oxazoline ligands attracted much attention for the hydrogenation of unprotected enamines. A number of efficient chiral catalysts have been developed, and some of them have shown high potential for the application in the synthesis of optical chiral amines in both laboratory and industry. This tutorial review focuses on the contributions concerning the transition metal-catalyzed enantioselective hydrogenation of unprotected enamines for the synthesis of chiral amines and amine derivatives. PMID:22509499

Xie, Jian-Hua; Zhu, Shou-Fei; Zhou, Qi-Lin

2012-06-01

122

Enantioselective analysis of triazole fungicide myclobutanil in cucumber and soil under different application modes by chiral liquid chromatography/tandem mass spectrometry.  

PubMed

A sensitive and enantioselective method was developed and validated for the determination of myclobutanil enantiomers by chiral liquid chromatography coupled with tandem mass spectrometry. The separation and determination were performed using reversed-phase chromatography on a Chiralcel OD-RH column, with ACN-water (70/30, v/v) as the mobile phase under isocratic conditions at 0.5 mL/min flow rate. The matrix effect, linearity, precision, accuracy, and stability were evaluated. The proposed method then was successfully applied to the study of enantioselective degradation of rac-myclobutanil in cucumber and soil under different application modes. The results showed that the preferential degradation of (+)-myclobutanil resulted in an enrichment of the (-)-myclobutanil residue in plant and soil. Moreover, in cucumber, the stereoselective intensity of myclobutanil under root douche treatment was stronger than that under foliar spraying treatment, whereas in soil, the intensity was exactly opposite. The probable reasons underlying these enantioselective effects were also discussed. This study highlighted the importance of examining the fate of both enantiomers in the greenhouse system for the correct use of chiral pesticides. PMID:22288843

Dong, Fengshou; Cheng, Li; Liu, Xingang; Xu, Jun; Li, Jing; Li, Yuanbo; Kong, Zhiqiang; Jian, Qiu; Zheng, Yongquan

2012-02-29

123

Direct amino acid-catalyzed cascade biomimetic reductive alkylations: application to the asymmetric synthesis of Hajos-Parrish ketone analogues.  

PubMed

A direct amino acid-catalyzed chemo- and enantioselective process for the double cascade synthesis of highly substituted 2-alkyl-cyclopentane-1,3-diones, 2-alkyl-3-methoxy-cyclopent-2-enones and Hajos-Parrish (H-P) ketone analogs is presented via reductive alkylation chemistry. For the first time, we have developed a single-step alkylation of cyclopentane-1,3-dione with aldehydes/ketones and a Hantzsch ester through an organocatalytic reductive alkylation strategy. A direct combination of amino acid-catalyzed cascade olefination-hydrogenation and cascade Robinson annulations of cyclopentane-1,3-dione, aldehydes/ketones, a Hantzsch ester and methyl vinyl ketone furnished the highly functionalized H-P ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products have shown direct applications in pharmaceutical chemistry. PMID:18972048

Ramachary, Dhevalapally B; Kishor, Mamillapalli

2008-11-21

124

Catalytic enantioselective Conia-ene reaction.  

PubMed

An enantioselective intramolecular Conia-ene reaction of beta-dicarbonyl compounds and alkynes to afford methylene cyclopentanes is described. The reaction employs a DTBMSegphos-Pd(II)/Yb(III) dual catalyst system that allows for the asymmetric synthesis of all-carbon quaternary centers and generates a product containing an alkene that can be further manipulated. PMID:16332048

Corkey, Britton K; Toste, F Dean

2005-12-14

125

Total synthesis and study of myrmicarin alkaloids  

E-print Network

I. Enantioselective Total Synthesis of Tricyclic Myrmicarin Alkaloids An enantioselective gram-scale synthesis of a key dihydroindolizine intermediate for the preparation of myrmicarin alkaloids is described. Key transformations ...

Ondrus, Alison Evelynn, 1981-

2009-01-01

126

Enantioselective Synthesis of (2R, 3S)- and (2S, 3R)-4,4,4-trifluoro-N-Fmoc-O-tert-butyl-threonine and their Racemization-free Incorporation into Oligopeptides via Solid-phase Synthesis  

PubMed Central

An efficient method for the enantioselective synthesis of (2R, 3S)- and (2S, 3R)-4,4,4-trifluoro-N-Fmoc-O-tert-butyl-threonine (tfT) on multi-gram scales was developed. Absolute configurations of the two stereoisomers were ascertained by X-ray crystallography. Racemization-free coupling conditions for the incorporation of tfT into oligopeptides were then explored. For solution-phase synthesis, tfT racemization was not an issue under conventional coupling conditions. For solid-phase synthesis, the following conditions were identified to achieve racemization-free synthesis: if tfT (3.0 eq.) was not the first amino acid to be linked to the resin (1.0 eq.), the condition is: 2.7 eq. DIC/3.0 eq. HOBt as the coupling reagent at 0 °C for 20 h; if tfT (3.0 eq.) was the first amino acid to be linked to the resin (1.0 eq.), then 1.0 eq. of CuCl2 needs to be added to the coupling reagent. PMID:17702025

Xiao, Nu; Jiang, Zhong-Xing; Yu, Y. Bruce

2010-01-01

127

Expression of a lipase on the cell-surface of Escherichia coli using the OmpW anchoring motif and its application to enantioselective reactions.  

PubMed

Microbial-surface display is the expression of proteins or peptides on the surface of cells by fusing an appropriate protein as an anchoring motif. Here, the outer membrane protein W (OmpW) was selected as a fusion partner for functional expression of Pseudomonas fluorescence SIK W1 lipase (TliA) on the cell-surface of Escherichia coli. Localization of the truncated OmpW-TliA fusion protein on the cell-surface was confirmed by immunoblotting and functional assay of lipase activity. Enantioselective hydrolysis of rac-phenylethyl butanoate by the displayed lipase resulted in optically active (R)-phenyl ethanol with 96% enantiomeric excess and 44% of conversion in 5 days. Thus, a small outer membrane protein OmpW, is a useful anchoring motif for displaying an active enzyme of ~50 kDa on the cell-surface and the surface-displayed lipase can be employed as an enantioselective biocatalyst in organic synthesis. PMID:23881313

Lee, Hyuk; Park, Si Jae; Han, Mee-Jung; Eom, Gyeong Tae; Choi, Min-Jung; Kim, Seong Ho; Oh, Young Hoon; Song, Bong Keun; Lee, Seung Hwan

2013-10-01

128

Enantioselective Decarboxylative Alkylation Reactions: Catalyst Development, Substrate Scope, and Mechanistic Studies  

PubMed Central

?-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursors: enol carbonates, enol silanes, and racemic ?-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center. PMID:22083969

Behenna, Douglas C.; Mohr, Justin T.; Sherden, Nathaniel H.; Marinescu, Smaranda C.; Harned, Andrew M.; Tani, Kousuke; Seto, Masaki; Ma, Sandy; Novák, Zoltán; Krout, Michael R.; McFadden, Ryan M.; Roizen, Jennifer L.; Enquist, John A.; White, David E.; Levine, Samantha R.; Petrova, Krastina V.; Iwashita, Akihiko; Virgil, Scott C.; Stoltz, Brian M.

2012-01-01

129

Catalytic enantioselective conjugate additions with ?,?-unsaturated sulfones  

PubMed Central

We describe the development of a highly efficient catalytic asymmetric conjugate addition to ?,?-unsaturated sulfones. Utilizing practical bifunctional organic catalysts and involving air- and moisture-tolerant conditions, conjugate additions of a wide range of Michael donors to ?,?-unsaturated sulfones proceeded in excellent enantioselectivity/diastereoselectivity and high yield. This efficient and operationally simple new catalytic asymmetric reaction should provide a versatile approach for the asymmetric synthesis of chiral sulfones bearing all-carbon quaternary stereocenters. PMID:20161246

Li, Hongming; Song, Jun; Deng, Li

2009-01-01

130

A three-step, highly enantioselective synthesis of ( R)-2-methyl tryptophane ethyl ester: Comparison with chemical resolution  

Microsoft Academic Search

(R)-2-Methyltryptophan ethyl ester, (R)-2, having an enantiomeric purity >,=96% was obtained in 3 steps and using (SSS)-hydroxypinanone, 1, as the recoverable chiral auxiliary. The synthesis of the alkylating agent, 5a, was improved (to a reproduceble 55% overall yield from 2,3-dimethylindole). The resolution of racemic-2 through chromatographic separation of the corresponding iminoester derived from (RRR)-1 also proved to be easy and

Arlette Solladié-Cavallo; Johanes Schwarz; Cyrille Mouza

1998-01-01

131

Highly enantioselective and efficient synthesis of flavanones including pinostrobin through the rhodium-catalyzed asymmetric 1,4-addition.  

PubMed

An efficient synthesis of bioactive chiral flavanones (1) was achieved through the Rh-catalyzed asymmetric 1,4-addition of arylboronic acid to chromone. The reaction in toluene proceeded smoothly at room temperature in the presence of 0.5% Rh catalyst with electron-poor chiral diphosphine MeO-F(12)-BIPHEP. In this reaction, the 1,2-addition to (S)-1 frequently occurred to yield (2S,4R)-2,4-diaryl-4-chromanol as a byproduct, which could be reduced by changing the reaction solvent to CH(2)Cl(2) to deactivate the Rh catalyst (3% required). PMID:21413690

Korenaga, Toshinobu; Hayashi, Keigo; Akaki, Yusuke; Maenishi, Ryota; Sakai, Takashi

2011-04-15

132

Enantioselective Synthesis of 3,4-Dihydro-1,2-oxazepin-5(2H)-ones and 2,3-Dihydropyridin-4(1H)-ones from ?-Substituted ?-Hydroxyaminoaldehydes  

PubMed Central

The synthesis of 3,4-dihydro-1,2-oxazepin-5(2H)-ones and 2,3-dihydropyridin-4(1H)-ones from ?-substituted ?-hydroxyaminoaldehydes is reported. The ?-hydroxyaminoaldehydes were prepared by enantioselective organocatalytic 1,4-addition of N-tert-butyl (tert-butyldimethylsilyl)oxycarbamate to ?,?-unsaturated aldehydes (MacMillan protocol). Alkyne addition to the aldehydes followed by alcohol oxidation furnished N-Boc O-TBS-protected ?-aminoynones. Removal of the TBS protecting group initiated a 7-endo-dig cyclization to yield previously unknown 3,4-dihydro-1,2-oxazepin-5(2H)-ones. Reductive cleavage of the N–O bond of the oxazepinones and Boc-deprotection provided 2-substituted 2,3-dihydropyridin-4(1H)-ones via 6-endo-trig cyclization. 2,3-Dihydropyridin-4(1H)-ones are versatile intermediates that have been used for the synthesis of many alkaloids. The new protocol allows the synthesis of 3-dihydropyridin-4(1H)-ones carrying an array of substituents at C2 that cannot be prepared from commercial ?-amino acids or by one-carbon homologation of proteinogenic amino acids. The use of readily available ?-hydroxylaminoaldehydes expands the utility of our previously reported method to prepare 2,3-dihydropyridin-4(1H)-ones from ?-amino acids as the source of diversity and chirality. A broad substrate scope is possible because ?-aminoaldehydes can be prepared from ?,?-unsaturated aldehydes by an enantioselective organocatalytic process. PMID:24785413

2015-01-01

133

Enantioselective Approach to Quinolizidines: Total Synthesis of Cermizine D and Formal Syntheses of Senepodine G & Cermizine C  

PubMed Central

The formal total syntheses of C5-epi-senepodine G and C5-epi-cermizine C have been accomplished through a novel diastereoselecetive, intramolecular amide Michael addition process. The total synthesis of cermizine D has been achieved through use of an organocatalyzed, heteroatom Michael addition to access a common intermediate. Additional key steps of this sequence include a matched, diastereoselective alkylation with an iodomethylphenyl sulfide and sulfone-aldehyde coupling/reductive desulfurization sequence to combine the major subunits. The utility of a Hartwig-style C-N coupling has been explored on functionally dense coupling partners. Diastereoselective conjugate additions to ?,?-unsaturated sulfones has been investigated which provided the key sulfone intermediate in just six steps from commercially available starting materials. The formal syntheses of senepodine G and cermizine C have been accomplished through an intramolecular cyclization process of a N-Boc protected piperidine sulfone. PMID:23627426

Veerasamy, Nagarathanam; Carlson, Erik C.; Collett, Nathan D.; Saha, Mrinmoy

2013-01-01

134

Enamino Ester Reduction: A Short Enantioselective Route to Pyrrolizidine and Indolizidine Alkaloids. Synthesis of (+)-Laburnine, (+)-Tashiromine, and (-)-Isoretronecanol.  

PubMed

Various chiral pyrrolidine tetrasubstituted beta-enamino esters were reduced catalytically or chemically with good to moderate diastereoselectivity owing to a chiral induction originated from (S)-alpha-methylbenzylamine. With endocyclic double bond compounds, the best result was obtained using PtO(2) as hydrogenation catalyst and led to a major syn addition product (e.d. 90%). In the case of exocyclic double bond compounds, hydrogenation over Pd/C gave rise to the higher diastereoselectivity and mainly afforded the unexpected anti addition product (e.d. 84%). The scope of these reductions has been extended to the synthesis of three pyrrolizidine or indolizidine alkaloids: (+)-tashiromine, (+)-laburnine, and (-)-isoretronecanol. Syntheses of these natural products, starting from chiral beta-enamino diesters, were achieved in a short and convenient manner, leading to enantiopure compounds in good overall yields. PMID:11674411

David, Olivier; Blot, Jérôme; Bellec, Christian; Fargeau-Bellassoued, Marie-Claude; Haviari, Gjergj; Célérier, Jean-Pierre; Lhommet, Gérard; Gramain, Jean-Claude; Gardette, Daniel

1999-04-30

135

Lithiation-borylation methodology and its application in synthesis.  

PubMed

Developing new methods that enable the synthesis of new and complex molecules with complete control of their 3-D shape is central to the advancement of synthetic chemistry with applications spanning from medicine to materials. Our approach consists of the iterative combination of small building blocks through the use of boron chemistry to essentially "grow" molecules. This approach, which we term assembly-line synthesis (ALS), resembles the way that nature assembles natural products (e.g., the polyketide synthase machinery) and has the advantage that many structural variations can be easily introduced and the products can be evaluated in structural or biological contexts. Chiral boronic esters have been recognized as valuable building blocks due to their unique chemical properties. They are both chemically and configurationally stable, and they can be prepared with very high levels of enantioselectivity. Additionally they undergo a broad array of transformations that lead to the stereocontrolled formation of C-C and C-X (X = heteroatom) bonds. This versatility makes boronic acids ideal building blocks for iterative molecular assembly. A powerful reaction platform for chemical diversification using chiral boronic esters is their homologation using lithium carbenoids via 1,2-metalate rearrangement. In the 1980s, Matteson described the use of boronic esters bearing a chiral diol in a two-step homologation process with dichloromethyl lithium and Grignard reagents (substrate-controlled approach). We have focused on reagent control and have found that Hoppe's chiral lithiated carbamates can be used as carbenoid equivalents in conjunction with achiral boronic esters. This reagent-controlled process offers many advantages due to the easy access of both the chiral lithiated carbamates and stable boronic esters. The carbamates can be derived from primary or secondary alcohols, and a broad range of functionalized boronic esters and boranes can be employed. Multiple homologations can be carried out in a one-pot sequence thereby streamlining the process to a single operation. This methodology has enabled the synthesis of many molecules containing multiple contiguous stereogenic centers with exquisite 3-D control. In this Account, we trace our own studies to establish the lithiation-borylation methodology and describe selected synthetic applications. PMID:25262745

Leonori, Daniele; Aggarwal, Varinder K

2014-10-21

136

Enantioselective Synthesis of Homoallylic Amines through Reactions of (Pinacolato)allylborons with Aryl-, Heteroaryl-, Alkyl- or Alkene-Substituted Aldimines Catalyzed by Chiral C1-Symmetric NHC–Cu Complexes  

PubMed Central

A catalytic method for enantioselective synthesis of homoallylamides through Cu-catalyzed reactions of stable and easily accessible (pinacolato)allylborons with aryl-, heteroaryl-,alkyl- or alkenyl-substituted N-phosphinoylimines is disclosed. Transformations are promoted by 1–5 mol % of readily accessible NHC–Cu complexes, derived from C1-symmetric imidazolinium salts, which can be prepared in multi-gram quantities in four steps from commercially available materials. Allyl additions deliver the desired products in up to quantitative yield and 98.5:1.5 enantiomeric ratio and are amenable to gram-scale operations. A mechanistic model accounting for the observed selectivity levels and trends is proposed. PMID:21341657

Vieira, Erika M.; Snapper, Marc L.; Hoveyda, Amir H.

2011-01-01

137

Chiral functionalization of graphene oxide by optically active helical-substituted polyacetylene chains and its application in enantioselective crystallization.  

PubMed

This article reports an original, versatile strategy to chirally functionalize graphene oxide (GO) with optically active helical-substituted polyacetylene. GO was first converted into alkynyl-GO containing polymerizable -C?C moieties, which took part in the polymerization of another chiral acetylenic monomer, yielding the expected GO hybrid covalently grafted with chiral helical polyacetylene chains. Transmission electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analyses verified the successful attachment of substituted polyacetylene chains on GO by covalent chemical bonding. Moreover, circular dichroism effects and UV-vis absorption demonstrated that the GO hybrid possessed fascinating optical activity. It also largely improved the dispersibility of GO in tetrahydrofuran. The GO-derived hybrid was further used as a chiral inducer toward enantioselective crystallization of alanine enantiomers. l-Alanine was preferably induced to crystallize, forming rodlike crystals. PMID:24902050

Li, Weifei; Liang, Junya; Yang, Wantai; Deng, Jianping

2014-06-25

138

Nanostructures for Energy Application: Synthesis, Characterization and Advanced Applications  

E-print Network

Nanostructures for Energy Application: Synthesis, Characterization and Advanced Applications The primary focus of our research activity is development of novel nanostructures for optical, electrical and characterizing metal, semiconductor, magnetic, insulating inorganic nanostructures, and multi

Vardi, Amichay

139

Valence Tautomerism in Titanium Enolates: Catalytic Radical Haloalkylation and Application in the Total Synthesis of Neodysidenin  

PubMed Central

A direct ruthenium-catalyzed radical chloroalkylation of N-acyl oxazolidinones capitalizing on valence tautomerism of titanium enolates has been developed. The chloroalkylation method served as the centerpiece in the enantioselective total synthesis of trichloroleucine-derived marine natural product neodysidenin. PMID:20078122

Beaumont, Stéphane; Ilardi, Elizabeth A.; Monroe, Lucas R.; Zakarian, Armen

2010-01-01

140

Enantioselective deprotonation of the 8-oxabicyclo[3.2.1]octan-3-one: Synthesis of 8-oxa-norcocaines and 8-oxa-pseudonorcocaines  

Microsoft Academic Search

The enantioselective deprotonation of the 8-oxabicyclo[3.2.1]octan-3-one with chiral lithium amides 5 and 6, in the presence of LiCl, gave the chiral lithium enolates which were in turn reacted with methyl cyanoformate. The resulting chiral ?-keto esters were reduced with sodium amalgam to afford the 8-oxa-ecgonine- and 8-oxa-pseudoecgonine-like derivatives which allowed facile preparation of the (+)- and (?)-8-oxa-norcocaines and (+)- and

Daniele Simoni; Marinella Roberti; Riccardo Rondanin; Alan P. Kozikowski

1999-01-01

141

Dynamic kinetic resolution based asymmetric transfer hydrogenation of ?-alkoxy-?-ketophosphonates. Diastereo- and enantioselective synthesis of monoprotected 1,2-dihydroxyphosphonates.  

PubMed

Dynamic kinetic resolution driven, asymmetric transfer hydrogenation reactions of a wide range of 2-substituted ?-alkoxy-?-ketophosphonates 3 were observed to proceed efficiently to give the corresponding 2-substituted ?-alkoxy-?-hydroxy phosphonates 4 with excellent levels of diastereo- and enantioselectivity. These processes are promoted by using well-defined, commercially available, chiral transition metal catalysts and a 0.2:1 mixture of formic acid and triethylamine as the hydrogen source and solvent. PMID:24568588

Son, Se-Mi; Lee, Hyeon-Kyu

2014-03-21

142

Enantioselective synthesis of phenylacetamides in the presence of high organic cosolvent concentrations catalyzed by stabilized penicillin G acylase. Effect of the acyl donor.  

PubMed

Immobilization of penicillin G acylase on glyoxyl agarose and its further hydrophilization by physicochemical modification with ionic polymers has made it possible to perform the direct condensation between (+/-)-2-hydroxy-2-phenylethylamine [(+/-)-1] and different acyl donors in the presence of high concentrations of organic cosolvent (up to 90%) in the reaction medium. Using 50 mM phenyl acetic acid and these drastic reaction conditions, too harsh for any other PGA preparation, we have achieved an almost quantitative transformation (more than 99%) of 10 mM (+/-)-1 into the corresponding amide. Remarkably, the enantioselectivity of the enzyme immobilized on the amine was strongly dependent on the acyl donor employed. Thus, using phenylacetic acid (2), the enantioselectivity was almost negligible (1.3 favoring the S isomer), whereas using S-mandelic acid [(S)-4], the E factor reached a value of 21 (also favoring the S isomer). By using R-mandelic acid [(R)-4], we observed a different enantioselectivity (E was 3.6 favoring the R). At 4 degrees C, the E value reached a value higher than 100 when (S)-4 was used as the acyl donor. The reaction performed under these conditions allowed us to produce (2S,2'S)-N-2'-hydroxy-2'-phenyl)-2-hydroxyphenylacetamide [(2S,2'S)-7] with a diasteromeric excess higher than 98%. PMID:15176909

Abian, Olga; Mateo, César; Palomo, José M; Fernández-Lorente, Gloria; Guisán, José M; Fernández-Lafuente, Roberto

2004-01-01

143

Chiral linear polymers bonded alternatively with salen and 1,4-dialkoxy-2,6-diethynylbenzene: synthesis and application to diethylzinc addition to aldehydes  

Microsoft Academic Search

The synthesis of chiral polymers 1 bonded alternatively with salen and 1,4-dialkoxy-2,6-diethynylbenzene was accomplished. These polymers are recyclable and catalyze the Et2Zn addition to aldehydes with good enantioselectivity.

Suribabu Jammi; Laxmidhar Rout; Tharmalingam Punniyamurthy

2007-01-01

144

Enantioselective [4 + 2] cycloadditions of iminoacetonitriles : application to the total synthesis of (-)-quinolizidine 2071  

E-print Network

Iminoacetonitriles participate as reactive dienophiles in intramolecular Diels-Alder cycloadditions affording quinolizidines and indolizidines. The resulting a-amino nitrile cycloadducts are versatile intermediates that ...

Fontaine, Shaun D. (Shaun David)

2011-01-01

145

Chemoenzymatic synthesis of the chiral side-chain of statins: application of an alcohol dehydrogenase catalysed ketone reduction on a large scale.  

PubMed

The chemoenzymatic synthesis of the tert-butyl (S)-6-chloro-5-hydroxy-3-ketohexanoate is described. Our approach relies on a highly regio- and enantioselective reduction of a beta,delta-diketohexanoate ester catalysed by NADP(H)-dependent alcohol dehydrogenase of Lactobacillus brevis (LBADH). A detailed description of the scale-up of the enzymatic synthesis of the hydroxyketo ester is given which includes a scale-up of the substrate synthesis as well, i.e. the preparation of diketo ester on a 100 g scale. Furthermore, studies directed towards improving the co-catalyst [NADP(H)] consumption of the enzymatic key step by kinetic studies and application of a biphasic reaction medium were performed. PMID:18288496

Wolberg, Michael; Filho, Murillo Villela; Bode, Silke; Geilenkirchen, Petra; Feldmann, Ralf; Liese, Andreas; Hummel, Werner; Müller, Michael

2008-04-01

146

Enantioselective synthesis of dihydrocoumarin derivatives by chiral scandium(iii)-complex catalyzed inverse-electron-demand hetero-Diels-Alder reaction.  

PubMed

An asymmetric inverse-electron-demand hetero-Diels-Alder reaction between o-quinone methides and azlactones to generate potentially pharmacological active dihydrocoumarins has been achieved efficiently by using a chiral N,N'-dioxide-Sc(iii) complex as the catalyst. The desired products were obtained in high yields with excellent enantioselectivities and diastereoselectivities (up to 94% yield, 96% ee and >19?:?1 dr) under mild reaction conditions. A concerted reaction pathway was confirmed by Operando IR and control experiments. PMID:25649623

Hu, Haipeng; Liu, Yangbin; Guo, Jing; Lin, Lili; Xu, Yali; Liu, Xiaohua; Feng, Xiaoming

2015-02-17

147

Enantioselective Synthesis of 5,7-Bicyclic Ring Systems from Axially Chiral Allenes Using a Rh(I)-Catalyzed Cyclocarbonylation Reaction  

PubMed Central

A transfer of chirality in an intramolecular Rh(I)-catalyzed allenic Pauson-Khand reaction (APKR) to access tetrahydroazulenones, tetrahydrocyclopenta[c]azepinones and dihydrocyclopenta[c]oxepinones enantioselectively (22 – 99% ee) is described. The substitution pattern of the allene affected the transfer of chiral information. Complete transfer of chirality was obtained for all trisubstituted allenes, but loss of chiral information was observed for disubstituted allenes. This work constitutes the first demonstration of a transfer of chiral information from an allene to the 5-position of a cyclopentenone using a cyclocarbonylation reaction. The absolute configuration of the corresponding cyclocarbonylation product was also established, something that is rarely done. PMID:23485149

Grillet, Francois; Brummond, Kay M.

2013-01-01

148

Organocatalytic sequential one-pot double cascade asymmetric synthesis of Wieland-Miescher ketone analogues from a Knoevenagel/hydrogenation/Robinson annulation sequence: scope and applications of organocatalytic biomimetic reductions.  

PubMed

A practical and novel organocatalytic chemo- and enantioselective process for the cascade synthesis of highly substituted 2-alkyl-cyclohexane-1,3-diones and Wieland-Miescher (W-M) ketone analogs is presented via reductive alkylation as a key step. First time, we developed the one-step alkylation of dimedone and 1,3-cyclohexanedione with aldehydes and Hantzsch ester through an organocatalytic reductive alkylation strategy. Direct combination of l-proline-catalyzed cascade Knoevenagel/hydrogenation and cascade Robinson annulation of CH acids (dimedone and 1,3-cyclohexanedione), aldehydes, Hantzsch ester, and methyl vinyl ketone furnished the highly functionalized W-M ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products show a direct application in pharmaceutical chemistry. PMID:17552564

Ramachary, Dhevalapally B; Kishor, Mamillapalli

2007-07-01

149

Highly Enantioselective Intramolecular 1,3-Dipolar Cycloaddition: A Route to Piperidino-Pyrrolizidines.  

PubMed

Enantioselective catalytic intermolecular 1,3-dipolar cycloadditions are powerful methods for the synthesis of heterocycles. In contrast, intramolecular enantioselective 1,3-dipolar cycloadditions are virtually unexplored. A highly enantioselective synthesis of natural-product-inspired pyrrolidino-piperidines by means of an intramolecular 1,3-dipolar cycloaddition with azomethine ylides is now reported. The method has a wide scope and yields the desired cycloadducts with four tertiary stereogenic centers with up to 99?% ee. Combining the enantioselective catalytic intramolecular 1,3-dipolar cycloaddition with a subsequent diastereoselective intermolecular 1,3-dipolar cycloaddition yielded complex piperidino-pyrrolizidines with very high stereoselectivity in a one-pot tandem reaction. PMID:25393926

Vidadala, Srinivasa Rao; Golz, Christopher; Strohmann, Carsten; Daniliuc, Constantin-G; Waldmann, Herbert

2014-11-12

150

Enantioselective hydrogenation of ?,?-disubstituted nitroalkenes.  

PubMed

The first highly chemo- and enantioselective hydrogenation of ?,?-disubstituted nitroalkenes was accomplished with rhodium/JosiPhos-J2 as a catalyst, with the yield and enantioselectivity of up to 95% and 94%, respectively. The ?-chiral nitroalkanes will provide an entry to valuable chiral amphetamines which are otherwise not so easily accessed. PMID:24970566

Li, Shengkun; Huang, Kexuan; Zhang, Xumu

2014-08-18

151

A photoisomerization-coupled asymmetric Stetter reaction: application to the total synthesis of three diastereomers of (?)-cephalimysin A  

PubMed Central

The total synthesis of 8-epi, 8,9-epi, and 9-epi-(?)-cephalimysin A is described. Our catalytic enantioselective synthesis takes advantage of a novel tandem photoisomerization/Stetter reaction. The approach provides rapid access to the desired spirofuranone lactam core in good yield and excellent enantioselectivity. A late stage oxidation strategy allows for flexible access to three of the four diastereomers of cephalimysin A. Access to the epimers provides further support for the correction of the initially proposed relative stereochemistry of cephalimysin A. PMID:24224080

Lathrop, Stephen P.

2013-01-01

152

Direct enantioselective conjugate addition of carboxylic acids with chiral lithium amides as traceless auxiliaries.  

PubMed

Michael addition is a premier synthetic method for carbon-carbon and carbon-heteroatom bond formation. Using chiral dilithium amides as traceless auxiliaries, we report the direct enantioselective Michael addition of carboxylic acids. A free carboxyl group in the product provides versatility for further functionalization, and the chiral reagent can be readily recovered by extraction with aqueous acid. The method has been applied in the enantioselective total synthesis of the purported structure of pulveraven B. PMID:25562717

Lu, Ping; Jackson, Jeffrey J; Eickhoff, John A; Zakarian, Armen

2015-01-21

153

Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation  

PubMed Central

Summary Pd-catalyzed enantioselective alkylation in conjunction with further synthetic elaboration enables the formal total syntheses of a number of “classic” natural product target molecules. This publication highlights recent methods for setting quaternary and tetrasubstituted tertiary carbon stereocenters to address the synthetic hurdles encountered over many decades across multiple compound classes spanning carbohydrate derivatives, terpenes, and alkaloids. These enantioselective methods will impact both academic and industrial settings, where the synthesis of stereogenic quaternary carbons is a continuing challenge. PMID:25383121

Liu, Yiyang; Liniger, Marc; McFadden, Ryan M; Roizen, Jenny L; Malette, Jacquie; Reeves, Corey M; Behenna, Douglas C; Seto, Masaki; Kim, Jimin; Mohr, Justin T; Virgil, Scott C

2014-01-01

154

Synthesis, properties, and applications of nanophase materials  

SciTech Connect

Work on the synthesis, properties, and applications of nanophase materials has developed rapidly during the past decade. A wide variety of methods now exist for their production, including several plasma-based processes. The possibilities for engineering new materials with unique or improved properties for a number of applications is now evident from the extant research results. A brief review is presented here along with some examples of useful application areas and some thoughts for the future of this field.

Siegel, R.W. [Max-Planck-Institut fuer Mikrostrukturphysik, Halle/Saale (Germany)]|[Argonne National Lab., IL (United States)

1995-04-01

155

Enantioselective separation and phytotoxicity on rice seedlings of paclobutrazol.  

PubMed

The environmental significance of enantioselectivity in chiral insecticides and herbicides has been widely studied. However, little information is currently available on the enantioselective behavior of chiral plant growth regulators. In this study, paclobutrazol enantiomers were resolved and prepared by chiral high-performance liquid chromatography with a Sino-chiral OJ column. The relationship among absolute configuration, optical activity and circular dichroism of paclobutrazol enantiomers was established. The enantioselective behavior of paclobutrazol, including enantioselective effect of paclobutrazol on the growth of rice seedlings and cyanobacteria and enantioselective loss of paclobutrazol in rice seedling growth media, in rice culture system was studied. The (2S,3S)-(-)-enantiomer was almost 3.1 times more active than the (2R,3R)-(+)-enantiomer toward shoot growth as measured by 7 day EC50 values. Enantioselectivity could not be determined with respect to root growth of rice seedlings because a typical dosage response was not observed in the range of the concentrations studied. The dissipation of paclobutrazol in rice growth medium is not enantioselective. Enantiomers and diastereoisomer of paclobutrazol all facilitated the growth of cyanobacteria, which increase the effectiveness of rice biofertilizers. The (2S,3S)-(-)-enantiomer showed stronger stimulatory activity on Microcystis aeruginosa cyanobacteria than the (2R,3R)-(+)-enantiomer, whereas the latter was a more potent stimulator of Anabaena sp. growth. These observations indicate that application of the (2S,3S)-(-)-enantiomer of paclobutrazol and Microcystis aeruginosa in rice cultivation is a good strategy for improving rice seedling performance. PMID:21395310

Zhang, Anping; Xie, Xuemei; Liu, Weiping

2011-04-27

156

Enantioselectivity in the phytotoxicity of herbicide imazethapyr.  

PubMed

Chiral compounds usually behave enantioselectively in phyto-biochemical processes. With the increasing application of chiral herbicides, their enantioselective phytotoxicity to plants merits further study, and little information is available in this area. The purpose of this study was to examine the enantioselective phytotoxicity of the herbicide imazethapyr (IM) on the roots of maize (Zea mays L.) seedlings. Enantiomers of IM were separated by HPLC, and their absolute configurations were confirmed as S-(+)-IM and R-(-)-IM by the octant rule. Plant growth measurements and morphological, microscopic, and ultrastructural observations were conducted after treatment with individual IM enantiomers and the racemate. Observations of root morphology showed that the root diameter significantly increased, whereas the root volume, surface area, and number of root tips decreased significantly. IM enantiomers selectively damaged root hair growth and significantly reduced the sloughing of border cells from the tips. IM also had adverse effects on cell organelles, such as statocytes, mitochondria, dictyosomes, and endoplasmic reticulum in maize roots. Moreover, cell membranes and cell walls were thicker than usual after IM treatment. All of the results showed the same trend that the R-(-)-IM affected the root growth of maize seedlings more severely than the S-(+)-IM. The inhibition abilities of (+/-)-IM was between S-(+)- and R-(-)-IM. The behavior of the active enantiomer, instead of just the racemate, may have more relevance to the herbicidal effects and ecological safety of IM. Therefore, enantiomeric differences should be considered when evaluating the bioavailability of the herbicide IM. PMID:19199589

Zhou, Qingyan; Xu, Chao; Zhang, Yongsong; Liu, Weiping

2009-02-25

157

Synthesis of chiral N-phosphoryl aziridines through enantioselective aziridination of alkenes with phosphoryl azide via Co(II)-based metalloradical catalysis  

PubMed Central

Summary The Co(II) complex of a new D 2-symmetric chiral porphyrin 3,5-DiMes-QingPhyrin, [Co(P6)], can catalyze asymmetric aziridination of alkenes with bis(2,2,2-trichloroethyl)phosphoryl azide (TcepN3) as a nitrene source. This new Co(II)-based metalloradical aziridination is suitable for different aromatic olefins, producing the corresponding N-phosphorylaziridines in good to excellent yields (up to 99%) with moderate to high enantioselectivities (up to 85% ee). In addition to mild reaction conditions and generation of N2 as the only byproduct, this new metalloradical catalytic system is highlighted with a practical protocol that operates under neutral and non-oxidative conditions. PMID:24991280

Tao, Jingran; Jin, Li-Mei

2014-01-01

158

Synthesis Techniques, Properties, and Applications of Nanodiamonds  

Microsoft Academic Search

Synthesis methods (ion and laser bombarding, CVD, hydrothermal, ultrasonic, electrochemical, and detonation techniques) for obtaining various forms of nanodiamonds (NDs) are generalized. Structure, physical and chemical properties, functionalization of NDs and composites on its basis are discussed, as well as their applications in medicine, electrochemistry, materials chemistry and technology.

Boris I. Kharisov; Oxana V. Kharissova; Leonardo Chávez-Guerrero

2010-01-01

159

An overview of quantumquantum dotdot synthesis, applications  

E-print Network

An overview of quantumquantum dotdot synthesis, applications and safety Nastassja Lewinski Department of Bioengineering nal@rice.edu #12;What are "Quantum Dots"? II-VI: ZnS, ZnSe, CdSe, CdTe, CdS, Hg et al. Sensors, 6, 2006 Parungo et al. JTCS, 129, 2005 #12;Tumor Tissue Margin Detection #12;NIR

160

Enantioselective Gas Chromatographic Separation of Racemic N-alkylated Barbiturates: Application of C11-Chirasil-Dex as Chiral Stationary Phase in GC  

PubMed Central

Chirasil-?-Dex containing an undecamethylene spacer (C11-Chirasil-Dex) was synthesized and used as chiral stationary phase (CSP) in enantioselective gas chromatography (GC). The versatility of the new stationary phase in the simultaneous enantiomeric separation of a set of N-alkylated barbiturates is demonstrated. PMID:19662180

Ghanem, Ashraf

2007-01-01

161

Enantioselective synthesis and antioxidant activity of 3-(3,4-dihydroxyphenyl)-glyceric acid--basic monomeric moiety of a biologically active polyether from Symphytum asperum and S. caucasicum.  

PubMed

The racemic and enantioselective synthesis of a novel glyceric acid derivative, namely, 2,3-dihydroxy-3-(3,4-dihydroxyphenyl)-propionic acid as well as the antioxidant activities is described. The virtually pure enantiomers, (+)-(2R,3S)-2,3-dihydroxy-3-(3,4-dihydroxyphenyl)-propionic acid and (-)-(2S,3R)-2,3-dihydroxy-3-(3,4-dihydroxyphenyl)-propionic acid were synthesized for the first time via Sharpless asymmetric dihydroxylation of trans-caffeic acid derivatives using the enantiocomplementary catalysts, (DHQD)(2)-PHAL and (DHQ)(2)-PHAL. The determination of enantiomeric purity of the novel chiral glyceric acid derivatives was performed by high-performance liquid chromatographic techniques on the stage of their alkylated precursors. The novel glyceric acid derivatives show strong antioxidant activity against hypochlorite and N,N-diphenyl-N-picryl-hydrazyl free radical. Their antioxidant activity is about 40-fold higher than that of the corresponding natural polyether and three-fold higher of trans-caffeic acid itself. PMID:20143412

Merlani, Maia; Barbakadze, Vakhtang; Amiranashvili, Lela; Gogilashvili, Lali; Yannakopoulou, Elina; Papadopoulos, Kyriakos; Chankvetadze, Bezhan

2010-08-01

162

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

PubMed

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

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

2014-07-25

163

EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology  

E-print Network

the Fourth Biennial Emergy Conference, Gainesville, Florida Edited by Mark T. Brown University of Floridaii EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology Proceedings from Emergy Database for Standardized National Emergy Synthesis Sharlynn Sweeney, Matthew J. Cohen, Danielle

Slatton, Clint

164

MICROWAVE TECHNOLOGY CHEMICAL SYNTHESIS APPLICATIONS  

EPA Science Inventory

Microwave-accelerated chemical syntheses in various solvents as well as under solvent-free conditions have witnessed an explosive growth. The technique has found widespread application predominantly exploiting the inexpensive unmodified household microwave (MW) ovens although th...

165

Enantioselective Synthesis of Axially Chiral Biaryls by the Pd-Catalyzed Suzuki-Miyaura Reaction: Substrate Scope and Quantum Mechanical Investigations  

PubMed Central

We report efficient syntheses of axially chiral biaryl amides in yields ranging from 80–92%, and with enantioselectivity in the range 88–94% ee employing an asymmetric Suzuki-Miyaura process with Pd(OAc)2 and KenPhos as ligand. These studies demonstrate that electron-rich and electron-deficient o-halobenzamides can be efficiently coupled with 2-methyl-1-naphthylboronic acid and 2-ethoxy-1-naphthylboronic acid. The yields and selectivities of the reactions are independent of the nature of halogen substituent on the benzamide coupling partner. Our investigations demonstrate that axially chiral heterocyclic and biphenyl compounds can also be synthesized with this methodology. We also report computational studies used to determine the origin of stereoselectivity during the selectivity-determining reductive elimination step of the related coupling of tolyl boronic acid with naphthylphosphonate bromide that was reported in a previous publication (J. Am. Chem. Soc. 2000, 122, 12051–12052). These studies indicate that the stereoselectivity arises from a combination of weak -(C)H•••O interactions as well as steric interactions between the tolyl and naphthylphosphonate addends in the transition state for C-C coupling. PMID:20698695

Shen, Xiaoqiang; Jones, Gavin O.; Watson, Donald A.; Bhayana, Brijesh; Buchwald, Stephen L.

2010-01-01

166

Ethylene glycol: properties, synthesis, and applications.  

PubMed

Ethylene glycol (EG) is an important organic compound and chemical intermediate used in a large number of industrial processes (e.g. energy, plastics, automobiles, and chemicals). Indeed, owing to its unique properties and versatile commercial applications, a variety of chemical systems (e.g., catalytic and non-catalytic) have been explored for the synthesis of EG, particularly via reaction processes derived from fossil fuels (e.g., petroleum, natural gas, and coal) and biomass-based resources. This critical review describes a broad spectrum of properties of EG and significant advances in the prevalent synthesis and applications of EG, with emphases on the catalytic reactivity and reaction mechanisms of the main synthetic methodologies and applied strategies. We also provide an overview regarding the challenges and opportunities for future research associated with EG. PMID:22488259

Yue, Hairong; Zhao, Yujun; Ma, Xinbin; Gong, Jinlong

2012-06-01

167

Enol Ethers as Substrates for Efficient Z- and Enantioselective Ring-Opening/Cross-Metathesis Reactions Promoted by Stereogenic-at-Mo Complexes: Utility in Chemical Synthesis and Mechanistic Attributes  

E-print Network

The first examples of catalytic enantioselective ring-opening/cross-metathesis (EROCM) reactions that involve enol ethers are reported. Specifically, we demonstrate that catalytic EROCM of several oxa- and azabicycles, ...

Yu, Miao

168

Synthesis and Applications of Imogolite Nanotubes  

NASA Astrophysics Data System (ADS)

Imogolite is a naturally occurring nanotube aluminum silicate. It is classified as a clay mineral, with tube dimensions of about 2 nm in outside diameter, 1 nm in inside diameter, and lengths ranging from tens of nanometers to several micrometers. Imogolite is remarkable not only for its nanoscale fibrous microstructure and its high surface area but also in its ability to adsorb water. So it can be expected to find a wide range of applications. In this chapter, synthesis method for imogolite and applications for anti-dewing materials and heat exchange material in adsorption-type heat pump systems are described.

Suzuki, Masaya; Inukai, Keiichi

169

Amphiphilic conetworks: Definition, synthesis, applications  

Microsoft Academic Search

The emerging field of amphiphilic conetworks (APCNs) is critically reviewed. A definition of APCNs is proposed and discussed in depth. The field of APCN science, born in 1988, is delineated and differentiated from similar constructs (e.g. interpenetrating networks, grafted networks). Among the justifications for sustained scientific\\/technological interest in APCNs are hosts of high-technology applications, some in commercial use and some

Gabor Erdodi; Joseph P. Kennedy

2006-01-01

170

Germanium nanocrystals: Synthesis, characterization, and applications  

NASA Astrophysics Data System (ADS)

The aim of this work was to demonstrate a simple synthesis route of Ge nanostructures (nanoparticles and nanowires), to characterize the physical and optical properties of Ge nanocrystal, and to demonstrate their biological and optoelectronics applications. The appropriate organometallic Ge 2+ precursors for the synthesis of Ge nanocrystals were identified. These precursors were used to develop a simple route that produced high quality Ge nanocrystals in high yield under mild conditions without using potentially contaminating catalysts and forming byproducts. The particle size was varied from 1 to 10 nm, depending on the reaction parameters. The relatively low-temperature, low-pressure nanocrystal synthesis condition allowed the use of organic solvents and surfactants. We also demonstrated morphological control over Ge nanocrystals via Ge2+ precursor reactivity modification. During synthesis, the surfactants passivate the nanocrystal surface and minimize surface oxidation. This synthesis method allowed optical characterization of Ge nanocrystals decoupled from contamination and oxidation. When excited with photons, Ge nanoparticles exhibit quantum confinement effect in both infrared and ultraviolet regions, as well as optical nonlinearity by the presence of two-photon absorption. These free-standing Ge nanocrystals could be further become integral elements in various optoelectronic devices. Herein, the production of water-soluble Ge nanoparticles was demonstrated as a proof of the effectiveness of our synthesis method. Addition of secondary layer surfactants such as cationic cetyltrimethylammonium bromide (CTAB) or functionalized polyethylene glycol (PEG), transforms the Ge nanoparticles to become water-soluble. The biocompatible, functionalized, water-soluble Ge nanoparticles were bound to extracellular receptors and also incorporated into the cells as a proof-of-concept demonstration for potential biomarker applications. In expectation of forming a 3-D superlattice of Ge nanocrystals within a SiO2 matrix, the real-time monitoring of ordered mesoporous SiO 2 structure formation via evaporation induced self assembly was also conducted to understand the structural ordering inside the silica matrix. The mesoporous film was then used for in situ and real-time study of profile evolution during plasma etching using attenuated total reflection Fourier transform infrared spectroscopy. We envision that the patterned 3-D superlattice of Ge nanocrystals will lead to advanced materials applications, such as coherent phonon generator and high-sensitivity biosensor.

Gerung, Henry

171

Total synthesis of (+)-angelmarin.  

PubMed

An efficient 8-step enantioselective total synthesis of (+)-angelmarin, starting from commercially available umbelliferone, has been achieved. Key reactions include olefin cross-metathesis and a Shi epoxidation-cyclization sequence. PMID:19459593

Magolan, Jakob; Coster, Mark J

2009-07-17

172

APPLICATIONS OF CAPILLARY ELECTROPHORESIS TO THE STUDY OF CHIRAL ENVIRONMENTAL POLLUTANTS: ENANTIOMER SEPARATION AND MEASUREMENTS OF ENANTIOSELECTIVITY  

EPA Science Inventory

CE is rarely used for routine environmental analysis of organic pollutants -- certainly not to the extent of gas chromatography or high pressure liquid chromatography. There are advantages to CE, however, that belie this lack of application. For example, CE is preferred over GC f...

173

Bidentate urea-based chiral selectors for enantioselective high performance liquid chromatography: synthesis and evaluation of "Crab-like" stationary phases.  

PubMed

A rational approach for the design and preparation of two new "Crab-like" totally synthetic, brush-type chiral stationary phases is presented. Enantiopure diamines, namely 1,2-diaminocyclohexane and 1,2-diphenyl-1,2-ethylene-diamine were treated with 3-(triethoxysilyl)propyl isocyanate, to yield reactive ureido selectors that were eventually attached to unmodified silica particles through a stable, bidentate tether, through a facile two-step one-pot procedure. A full chemical characterization of the new materials has been obtained through solid-state NMR (both (29)Si and (13)C CPMAS) spectroscopy. Columns packed with the two Crab-like chiral stationary phases allow for different mechanisms of separation: normal phase liquid chromatography, reversed phase liquid chromatography and polar organic mode and show a high stability at basic pH values. In particular, the Crab-like column containing the 1,2-diphenyl-1,2-ethylene-diamine selector proved a promising candidate for the resolution of a wide range of racemates (including benzodiazepines, N-derivatized amino acids, and free carboxylic acids) both in normal phase and polar organic mode. An Hmin of 9.57 at a ?sf of 0.80mm/s (corresponding to 0.8mL/min) was obtained through van Deemter analysis, based on toluene, for the Crab-like column with the 1,2-diphenyl-1,2-ethylene-diamine selector (250mm×4.6mm I.D.), with a calculated reduced height equivalent to a theoretical plate (h) of only 1.91. Finally, comparative studies were performed with a polymeric commercially available P-CAP-DP column in order to evaluate enantioselectivity and resolution of the Crab-like columns. PMID:23726086

Kotoni, Dorina; Villani, Claudio; Bell, David S; Capitani, Donatella; Campiglia, Pietro; Gasparrini, Francesco

2013-07-01

174

C-C bond fragmentation by Grob/Eschenmoser reactions, applications in dendrimer synthesis.  

PubMed

C-C bond fragmentation of structurally diverse carbocycles has been applied to the divergent synthesis of dendrimers. The fragmentation has been paired to deprotection or thio-Michael reaction, allowing the preparation of a fourth generation dendrimer of narrow molecular weight distribution. Methodologies to increase water solubility have been examined using appended carboxylic acid or oligoether moieties. In addition, incorporation of chiral prolinol derivatives has resulted in the synthesis of dendrimers that have been shown to catalyse the ?-amination of aldehydes in good yield and modest enantioselectivity. PMID:23925375

Hierold, Judith; Lupton, David W

2013-09-28

175

Dendrimers: synthesis, applications, and properties  

PubMed Central

Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell. Their three traditional macromolecular architectural classes are broadly recognized to generate rather polydisperse products of different molecular weights. A variety of dendrimers exist, and each has biological properties such as polyvalency, self-assembling, electrostatic interactions, chemical stability, low cytotoxicity, and solubility. These varied characteristics make dendrimers a good choice in the medical field, and this review covers their diverse applications. PMID:24994950

2014-01-01

176

DNA Oligonucleotide Synthesis in Mesoporous Silicon for Biosensing Applications  

E-print Network

DNA Oligonucleotide Synthesis in Mesoporous Silicon for Biosensing Applications Jenifer L. Lawrie for improving the sensitivity of label-free optical biosensors based on in-situ synthesis of DNA probes within was utilized as the sensor structure. Synthesis of DNA probe, as well as sensing of target DNA, was verified

Weiss, Sharon

177

Enzyme Mimic to Develop Antioxidant Nanoreactors: From Synthesis to Application  

E-print Network

Enzyme Mimic to Develop Antioxidant Nanoreactors: From Synthesis to Application.................................................................................................................20 1.10.1. Administration of antioxidant enzymes................................................................................20 1.10. 2. Administration of enzyme mimics

Amrhein, Valentin

178

Synthesis, characterization and applications of magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

In the past few years, the synthesis of magnetic nanoparticles has received considerable attention due to their potential use in clinical applications. Since the properties of these nanoparticles depend strongly on their size, shape and crystallinity, there is a need for a general method to produce these particles with a controlled size, shape and crystal type. Of the many magnetic materials (Co, Ni, and Fe), the magnetite (Fe3O 4) is least toxic and hence most promising for applications in medical diagnostics. Microemulsion-based synthesis utilizes the local aqueous environment within a reverse micelle as a nano-scale reactor and allows synthesizing nanoparticles with a hydrophilic surface for subsequent functionalization. By controlling the water-to-surfactant ratio, the type of surfactants, and the ionic strength of the aqueous core, one can control the size and shape of the resulting particles. We developed such a system that allows the multi-step synthesis of surface-functionalized, magnetic nanoparticles in a one-pot synthesis reaction. By altering the system chemistry, we were further able to produce either spheres or cylinders of controlled dimension in the size range of 5 nm to 30 nm. Using standard bio-conjugation techniques, we successfully immobilized an enzyme onto the nanoparticles. We also developed a theoretical model for the separation and fractionation of nanoparticles based on their size and magnetic properties. Using the multiphysics and finite element modeling capabilities of FEMLAB(TM), we solved the coupled system of PDEs describing the interaction of magnetic particles within a magnetic field for either static (cylindrical beaker) or convective flow (capillary) conditions. A net retention time as high as 310 s is achieved for 200 nm particles at field strength of 1250 kA/m. The model allows the design of a magnetic, field-flow fractionation (MFFF) system to separate nanoparticles by size.

Kanmukhla, Vikram Kumar

179

Highly enantioselective Michael addition promoted by a new diterpene-derived bifunctional thiourea catalyst: a doubly stereocontrolled approach to chiral succinimide derivatives.  

PubMed

A doubly stereocontrolled organocatalytic asymmetric Michael addition to the synthesis of substituted succinimides is described. Starting from aldehydes and maleimides, both enantiomers of the succinimides could be obtained in high to excellent yields (up to 98%) and enantioselectivities (up to 99%) when one of the two special chiral diterpene-derived bifunctional thioureas was individually used as a catalyst. Moreover, these catalysts can be efficiently used in large-scale catalytic synthesis with the same level of yield and enantioselectivity. PMID:24420919

Song, Zhong-Tai; Zhang, Tao; Du, Hai-Long; Ma, Zhi-Wei; Zhang, Chang-Hua; Tao, Jing-Chao

2014-02-01

180

Widely Applicable Synthesis of Enantiomerically Pure (?99% ee) Tertiary Alkyl-containing 1-Alkanols via ZACA–Pd- or Cu-Catalyzed Cross-Coupling  

PubMed Central

A highly enantioselective and widely applicable method for the synthesis of various chiral 2-alkyl-1-alkanols, especially those of feeble chirality, has been developed. It consists of zirconium-catalyzed asymmetric carboalumination of alkenes (ZACA) – lipase-catalyzed acetylation – Pd- or Cu-catalyzed cross-coupling. By virtue of the high selectivity factor (E) associated with iodine, either (S)- or (R)-enantiomer of 3-iodo-2-alkyl-1-alkanols (1), prepared by ZACA reaction of allyl alcohol, can be readily purified to the level of ?99% ee by lipase-catalyzed acetylation. A variety of chiral tertiary alkyl-containing alcohols, including those that have been otherwise difficult to prepare, can now be synthesized in high enantiomeric purity by Pd- or Cu-catalyzed cross-coupling of (S)-1 or (R)-2 for introduction of various primary, secondary and tertiary carbon groups with retention of all carbon skeletal features. These chiral tertiary alkyl-containing alcohols can be further converted to the corresponding acids with full retention of the stereochemistry. The synthetic utility of this method has been demonstrated in the highly enantioselective (?99% ee) and efficient syntheses of (R)-2-methyl-1-butanol, (R)- and (S)-arundic acids. PMID:23670801

Xu, Shiqing; Lee, Ching-Tien; Wang, Guangwei

2013-01-01

181

Synthesis, characterization and applications of different nanostructures  

NASA Astrophysics Data System (ADS)

There has been a growing interest in the field of nanoscience for the last several decades including the use in optical, electrical, biological and medicinal applications. This thesis focuses on the synthesis of different nanoparticles for their potential uses in drug delivery and antimicrobial agents as well as porous alumina membranes as surface enhanced Raman scattering or SERS substrates. The synthesis of nanocomposites (NCs) composed of silica and poly(4-vinyl pyridine) (P4VP) in a basic ethanol solution is presented in chapter 2. The composition of the NCs appears to be homogenous after synthesis and is greatly affected by heat and pH changes. When the NCs are heated, a core-shell nanostructure is produced with silica forming a shell around a P4VP core. At lower pHs, the NCs form a silica core with a P4VP shell while at higher pHs the silica is etched away causing the NC to decompose. A novel synthesis method of growing stable copper oxide nanoparticles with poly(acrylic acid) (PAA) is presented in chapter 3. Insoluble copper (I) oxide is dissolved with ammonium hydroxide and reduced using sodium borohydride to form metallic copper nanoparticles that oxidize overtime to form copper oxide nanoparticles stable in an aqueous environment. In addition to copper oxide nanoparticles, copper (I) iodide and copper (II) sulfide particles were also synthesized in the presence of PAA. In chapter 4, alumina membranes with 100nm and 200nm pores were coated with silver and used as SERS substrates to detect small molecules. The alumina membranes are coated with silver by reducing silver (I) oxide with ethanol. The thickness of the silver layer depends primarily on the length of time the substrate comes into contact with the Ag2O in solution with longer exposure times producing thicker films. Raman scattering of 10-100nM adenine concentrations were collected.

Snyder, Whitney Elaine

182

Highly enantioselective synthesis of chiral secondary amines by gold(I)/chiral Brønsted acid catalyzed tandem intermolecular hydroamination and transfer hydrogenation reactions.  

PubMed

A method for the synthesis of enantiomerically enriched secondary amines with excellent ee values through the tandem intermolecular hydroamination/transfer hydrogenation of alkynes using a "gold(I) complex-chiral Brønsted acid" protocol is developed. The catalysis works for a wide variety of aryl, alkenyl, and aliphatic alkynes as well as anilines with different electronic properties. PMID:19678678

Liu, Xin-Yuan; Che, Chi-Ming

2009-09-17

183

Synthesis of complex fluorides for optical applications  

NASA Astrophysics Data System (ADS)

Large single crystals of alkali metal fluorides are desirable for many reasons. Fluoride laser crystals have a wide transmission range and on account of their low phonon energies, many efficient laser emissions have been obtained from 285 nm to 4.34 microm.1,2 Inorganic fluoride single crystals feature large bandgaps, very wide optical transmittance ranges from vacuum-ultraviolet (VUV) to mid-IR wavelength regions, lower refractive indices than those of oxides, and typically lower phonon energies (which drastically reduce multiphonon relaxation rates of rare earth ions).3 The main goal of this work was to investigate the hydrothermal synthesis of alkali metal fluorides. Melt techniques have been used thoroughly to research a variety of fluoride systems and showed many phases that were inaccessible due to incongruent melting or phase stability. The existence of these phases was shown but never characterized or grown as a crystalline material. Solution growth in supercritical water was an ideal way to attempt the synthesis of novel compounds and phases. New synthetic routes to known phases and compounds also arose as a part of this work. Optically clear colorless crystals of K2BeF4 were synthesized up to 2 mm in size, and showed no phase transitions up to 1029 K, which suggests paraelectricitys at room temperature, contradicting previous reports.4 Attempts to incorporate a rare earth ion into the fluoroberyllate lattice proved unsuccessful however reactions between beryllium fluoride and lanthanide fluorides could be exploited as a synthetic route to single crystal rare earth fluorides. Hydrothermal reactions with KF produced crystals of three different phases: hexagonal KY2F7, trigonal KYF4 and orthorhombic K2YF5. All were optically clear, colorless crystals, with the K2YF5 crystals growing the largest. This compound is beneficial due to its application as a radiation dosimeter and laser host. 5,6 Optical quality colorless crystals of RbY2F7 and CsY2F7 up to 4 mm in size were produced, and many spectroscopically active rare earth elements were doped into both hosts. A novel synthetic pathway to the hexagonal beta-RbGd3F 10, was discovered which led to the novel compound, beta-RbHo 3F10. The hydrothermal synthesis of hexafluoroelpasolites and lanthanide sesquioxides is also investigated. The hydrothermal synthesis described in this work has furthered the study of complex fluorides for optical applications. Novel synthetic pathways were discovered to known optical materials. Novel materials were also discovered. 1Takashima, M. In Advanced Inorganic Fluorides: Synthesis, Characterization and Applications, Nakajima, T.; Zemva, B.; Tressaud, A.; Elsevier: Amsterdam, The Netherlands, 2000, 176. 2Fouassier, C. In Advanced Inorganic Fluorides: Synthesis, Characterization and Applications, Nakajima, T.; Zemva, B.; Tressaud, A.; Elsevier: Amsterdam, The Netherlands, 2000, 316. 3Capper, P. In Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials, John Wiley and Sons: Great Britain, 2005. 4Solans, X.; Gonzalez-Silgo, C.; Calvet, T.; Ruiz-Perez, C.; Martinez-Sarrion, M. L.; Mestres, L. Phys. Rev. B 1998, 57(9), 5122-5125. 5Azorin-Nieto, J.; Khaidukov, N.M.; Sanchez-Rodriguez, A.; Azorin-Vega, J.C. Nuclear Instruments and Methods in Physics Research, 2007, B263, 36-40. 6Wang, D.; Min, Y.; Xia, S.; Makhov, V.N.; Khaidukov, N.M.; J.C. Krupa, J.C. Journal of Alloys and Compounds, 2003, 361, 294-298.

Stepleton, Seth Eugene

184

Chiral Brønsted acid-catalyzed Friedel-Crafts alkylation of electron-rich arenes with in situ-generated ortho-quinone methides: highly enantioselective synthesis of diarylindolylmethanes and triarylmethanes.  

PubMed

We disclose herein a highly enantioselective protocol for the Brønsted acid-catalyzed addition of indoles and phenols to in situ-generated ortho-quinone methides which deliver broadly substituted diarylindolylmethanes and triarylmethanes, respectively, in a one-pot reaction under very mild conditions. A chiral phosphoric acid catalyst has been developed for this process serving to convert the starting ortho-hydroxybenzhydryl alcohols into the reactive ortho-quinone methides and to control the enantioselectivity of the carbon-carbon bond-forming event via hydrogen-bonding. PMID:25493449

Saha, Satyajit; Alamsetti, Santosh Kumar; Schneider, Christoph

2015-01-01

185

Enantioselective Allylic Hydroxylation of ?-Alkenoic Acids and Esters by P450 BM3 Monooxygenase.  

PubMed

Chiral allylic alcohols of ?-alkenoic acids and derivatives thereof are highly important building blocks for the synthesis of biologically active compounds. The direct enantioselective C?H oxidation of linear terminal olefins offers the shortest route toward these compounds, but known synthetic methods are limited and suffer from low selectivities. Described herein is an enzymatic approach using the P450 BM3 monooxygenase mutant A74G/L188Q, which catalyzes allylic hydroxylation with high to excellent chemo- and enantioselectivities providing the desirable secondary alcohols. PMID:25164074

Neufeld, Katharina; Henßen, Birgit; Pietruszka, Jörg

2014-11-24

186

Palladium-catalyzed enantioselective decarboxylative cycloaddition of vinylethylene carbonates with isocyanates.  

PubMed

An efficient method for the enantioselective construction of ?-substituted ?-vinylglycinol derivatives through palladium-catalyzed decarboxylative cycloaddition of vinylethylene carbonates with isocyanates was developed. By using a palladium complex generated in situ from [Pd2 (dba)3 ]?CHCl3 (dba=dibenzylideneacetone) and (S)-Segphos as a catalyst under mild reaction conditions, the process provided 4-substituted-4-vinyloxazolidin-2-ones in high yields with a high level of enantioselectivity. The stereochemical outcome of the reaction was explained by DFT calculations and the synthetic utility of the process was demonstrated by the gram-scale transformation and formal synthesis of MK-0731 as a kinesin spindle protein inhibitor. PMID:25400207

Khan, Ajmal; Xing, Juxiang; Zhao, Jingming; Kan, Yuhe; Zhang, Wanbin; Zhang, Yong Jian

2015-01-01

187

Squaramide-Catalyzed Enantioselective Michael Addition of Masked Acyl Cyanides to Substituted Enones  

PubMed Central

Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselective Michael addition to substituted enones. The reactions are catalyzed by chiral squaramides and afford adducts in high yields (90–99%) and with excellent enantioselectivities (85–98%). The addition products are unmasked to produce dicyanohydrins that, upon treatment with a variety of nucleophiles, provide ?-keto acids, esters, and amides. The use of this umpolung synthon has enabled, in enantiomerically enriched form, the first total synthesis of the prenylated polyphenol (+)-fornicin C. PMID:24090310

Yang, Kin S.; Nibbs, Antoinette E.; Türkmen, Yunus E.; Rawal, Viresh H.

2014-01-01

188

Enantioselective construction of quaternary N-heterocycles by palladium-catalysed decarboxylative allylic alkylation of lactams  

NASA Astrophysics Data System (ADS)

The enantioselective synthesis of nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines, including the total synthesis of natural products and medicinal chemistry. In this Article, we describe the highly enantioselective palladium-catalysed decarboxylative allylic alkylation of readily available lactams to form 3,3-disubstituted pyrrolidinones, piperidinones, caprolactams and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envisage that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously used in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures.

Behenna, Douglas C.; Liu, Yiyang; Yurino, Taiga; Kim, Jimin; White, David E.; Virgil, Scott C.; Stoltz, Brian M.

2012-02-01

189

Enantioselective Construction of Quaternary N-Heterocycles by Palladium-Catalyzed Decarboxylative Allylic Alkylation of Lactams  

PubMed Central

The enantioselective synthesis of Nitrogen-containing heterocycles (N-heterocycles) represents a substantial chemical research effort and resonates across numerous disciplines including the total synthesis of natural products and medicinal chemistry. In this manuscript, we describe the highly enantioselective palladium-catalyzed decarboxylative allylic alkylation of readily available lactams to form 3,3,-disubstituted pyrrolidinones, piperidinones, caprolactams, and structurally related lactams. Given the prevalence of quaternary N-heterocycles in biologically active alkaloids and pharmaceutical agents, we envision that our method will provide a synthetic entry into the de novo asymmetric synthesis of such structures. As an entry for these investigations we demonstrate how the described catalysis affords enantiopure quaternary lactams that intercept synthetic intermediates previously employed in the synthesis of the Aspidosperma alkaloids quebrachamine and rhazinilam, but that were previously only available by chiral auxiliary approaches or as racemic mixtures. PMID:22270628

Behenna, Douglas C.; Liu, Yiyang; Yurino, Taiga; Kim, Jimin; White, David E.; Virgil, Scott C.; Stoltz, Brian M.

2011-01-01

190

Studies toward the total synthesis of dumsin. 2. A second generation approach resulting in enantioselective construction of a functionalized ABC subunit of the tetranortriterpenoid insect antifeedant.  

PubMed

A synthesis of the ABC framework of dumsin is described. The optically active intermediate 9b, which is expeditiously assembled from 5-oxobornyl pivalate by the sequential implementation of an oxy-Cope rearrangement and an intramolecular ene reaction, proved to be suitably functionalized for ultimate conversion to 5. The synthesis plan relies on two approaches to this targeted intermediate. In the first, the exocyclic double bond introduced during EtAlCl2-promoted closure of aldehyde 10b is cleaved to leave a carbonyl group that is amenable to hydride reduction and elimination of water. Cleavage of the resulting double bond with ruthenium tetroxide provided the seco ketoacid. The same advanced intermediate was obtained by initially positioning the double bond internal to the five-membered ring in advance of transient ring expansion via diketone formation and intramolecular aldolization. Both of these approaches bypass the complications arising from the substantial steric congestion prevailing in these structural networks. The task of covalently positioning an oxygen atom adjacent to the gem-dimethyl-substituted carbon in 5 was properly realized by oxidative decarboxylation. The stereochemical assignments to many of the intermediates were confirmed by an X-ray crystallographic analysis of 43. PMID:17194102

Paquette, Leo A; Hu, Yang; Luxenburger, Andreas; Bishop, Raynauld L

2007-01-01

191

Nanostructured metal foams: synthesis and applications  

SciTech Connect

Fabrication of monolithic metallic nanoporous materials is difficult using conventional methodology. Here they report a relatively simple method of synthesizing monolithic, ultralow density, nanostructured metal foams utilizing self-propagating combustion synthesis of novel metal complexes containing high nitrogen energetic ligands. Nanostructured metal foams are formed in a post flame-front dynamic assembly with densities as low as 0.011 g/cc and surface areas as high as 270 m{sup 2}/g. They have produced metal foams via this method of titanium, iron, cobalt, nickel, zirconium, copper, palladium, silver, hafnium, platinum and gold. Microstructural features vary as a function of composition and process parameters. Applications for the metal foams are discussed including hydrogen absorption in palladium foams. A model for the sorption kinetics of hydrogen in the foams is presented.

Luther, Erik P [Los Alamos National Laboratory; Tappan, Bryce [Los Alamos National Laboratory; Mueller, Alex [Los Alamos National Laboratory; Mihaila, Bogdan [Los Alamos National Laboratory; Volz, Heather [Los Alamos National Laboratory; Cardenas, Andreas [Los Alamos National Laboratory; Papin, Pallas [Los Alamos National Laboratory; Veauthier, Jackie [Los Alamos National Laboratory; Stan, Marius [Los Alamos National Laboratory

2009-01-01

192

Highly enantioselective [4 + 2] cycloaddition reactions catalyzed by a chiral N-methyl-oxazaborolidinium cation.  

PubMed

The reaction of lithium aryl borohydrides with salts of beta-amino alcohols provides a new route for the synthesis of oxazaborolidines. This method also leads to the first synthesis of hitherto elusive N-methyl oxazaborolidine cations, specifically the cationic proline derivative 3. Compound 3 is a strong chiral Lewis acid which is very effective for catalysis of [4 + 2]-cycloaddition reactions in good yield and with high enantioselectivity. Several diverse examples illustrate the scope of these catalytic reactions. PMID:18582066

Canales, Eda; Corey, E J

2008-08-01

193

Enantioselective syntheses of the proposed structures of cytotoxic macrolides iriomoteolide-1a and -1b.  

PubMed

Enantioselective total syntheses of the proposed structures of macrolide cytotoxic agents iriomoteolide-1a and -1b have been accomplished. The synthesis was carried out in a convergent and stereoselective manner. However, the present work suggests that the reported structures have been assigned incorrectly. The synthesis features Julia-Kocienski olefination, Sharpless asymmetric epoxidation, Brown asymmetric crotylboration, a Sakurai reaction, an aldol reaction, and enzymatic resolution as the key steps. PMID:20560539

Ghosh, Arun K; Yuan, Hao

2010-07-16

194

Synthesis, Characterization and Catalytic Applications of Organized Mesoporous Aluminas  

Microsoft Academic Search

The synthesis of organized mesoporous aluminas has opened a very interesting area for application of this type of materials, particularly as catalysts or catalyst supports. This review focuses on the individual synthesis routes to produce organized mesoporous aluminas with large surface areas and narrow pore size distributions, and on the evaluation of their textural, chemical and thermal properties and outlines

Nad?žda Žilková; Ji?í ?ejka

2008-01-01

195

The fractional - order controllers: Methods for their synthesis and application  

Microsoft Academic Search

This paper deals with fractional-order controllers. We outline mathematical description of fractional controllers and methods of their synthesis and application. Synthesis method is a modified root locus method for fractional-order systems and fractional-order controllers. In the next section we describe how to apply the fractional controller on control systems.

Ivo Petras

2000-01-01

196

Enantioselective recognition at mesoporous chiral metal surfaces  

PubMed Central

Chirality is widespread in natural systems, and artificial reproduction of chiral recognition is a major scientific challenge, especially owing to various potential applications ranging from catalysis to sensing and separation science. In this context, molecular imprinting is a well-known approach for generating materials with enantioselective properties, and it has been successfully employed using polymers. However, it is particularly difficult to synthesize chiral metal matrices by this method. Here we report the fabrication of a chirally imprinted mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and chiral template molecules. The porous platinum retains a chiral character after removal of the template molecules. A matrix obtained in this way exhibits a large active surface area due to its mesoporosity, and also shows a significant discrimination between two enantiomers, when they are probed using such materials as electrodes. PMID:24548992

Wattanakit, Chularat; Côme, Yémima Bon Saint; Lapeyre, Veronique; Bopp, Philippe A.; Heim, Matthias; Yadnum, Sudarat; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

2014-01-01

197

Chiral Brønsted acid from a cationic gold(I) complex: catalytic enantioselective protonation of silyl enol ethers of ketones.  

PubMed

A chiral Brønsted acid has been developed from a cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to the enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities, including cyclic ketones bearing aliphatic substrates at the ?-position. Furthermore, the application of this Brønsted acid was extended to the first Brønsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio. PMID:21815666

Cheon, Cheol Hong; Kanno, Osamu; Toste, F Dean

2011-08-31

198

Chiral Brønsted Acid from a Cationic Gold(I) Complex: Catalytic Enantioselective Protonation of Silyl Enol Ethers of Ketones  

PubMed Central

A chiral Brønsted acid has been developed from cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities including cyclic ketones bearing aliphatic substrates at the ?-position. Furthermore, the application of this Brønsted acid was extended to the first Brønsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio. PMID:21815666

Cheon, Cheol Hong; Kanno, Osamu; Toste, F. Dean

2011-01-01

199

Enantioselective Homocrotylboration of Aliphatic Aldehydes  

PubMed Central

A practical route to optically pure syn-homocrotylation reagents is described, including highly diastereo-and enantioselective preparation of numerous syn-homocrotyl products, as well as several matched mismatched pairs. NMR experiments suggest that the active homocrotylating species is a cyclopropylcarbinyldichloroborane generated by chloride exchange from the PhBCl2 activator. Computational studies support the intermediacy of chloroboranes, and suggest that homoal-lyl/homocrotyl transfers occur through Zimmerman-Traxler transition states. PMID:23256566

Lin, Hongkun; Pei, Wenbo; Wang, Hao

2013-01-01

200

Concise total synthesis of (+)-gliocladins B and C  

E-print Network

The first total synthesis of (+)-gliocladin B is described. Our concise and enantioselective synthesis takes advantage of a new regioselective Friedel–Crafts-based strategy to provide an efficient multigram-scale access ...

Movassaghi, Mohammad

201

Studies toward the total synthesis of glycinoeclepin A  

E-print Network

Studies directed toward the synthesis of the A-ring portion of glycinoeclepin A are described. The enantioselective synthesis of key diketone intermediate 128 in four steps from 2,2-dimethyl-1,3-cyclohexanedione (5) has ...

Thongsornkleeb, Charnsak

2006-01-01

202

Synthesis of chiral ?- substituted ?-hydroxy acid derivatives on solid support  

Microsoft Academic Search

Enantioselective aldol condensation using solid supported chiral auxiliary was used for the synthesis of ?-substituted-?-hydroxy acid and ester. The solid phase synthesis proceeded with high degree of enatioselectivity, as is observed in solution chemistry.

Ashok V Purandare; Sesha Natarajan

1997-01-01

203

Efficient synthesis of ?-extended phenazasilines for optical and electronic applications.  

PubMed

The rhodium-catalyzed synthesis of phenazasilines from readily achievable biarylhydrosilanes is presented. This highly efficient method offers opportunities for preparing ?-extended phenazasilines with enhanced optoelectronic properties for device applications in organic electronics. PMID:25370829

Li, Huanhuan; Wang, Yang; Yuan, Kai; Tao, Ye; Chen, Runfeng; Zheng, Chao; Zhou, Xinhui; Li, Junfeng; Huang, Wei

2014-12-25

204

Synthesis of highly quenching fullerene derivatives for biosensor applications  

E-print Network

This dissertation examines the synthesis of fullerene-based fluorescence quenchers for numerous biosensor applications. The Introduction describes the need for biosensors in our society, what they are and various biosensing ...

Pérez, Vanessa Virginia, 1981-

2004-01-01

205

One-pot organocatalytic enantioselective Michael-Michael-aldol-Henry reaction cascade. A facile entry to the steroid system with six contiguous stereogenic centers.  

PubMed

An expedited method has been developed for the enantioselective synthesis of highly functionalized steroid systems containing six contiguous stereogenic centers with high enantioselectivities (99% ee). The one-pot methodology comprises a cascade of organocatalytic Michael-Michael-aldol-Henry reactions of 7-nitrohept-3-en-2-one and 5-(1-methyl-2,5-dioxocyclopentyl)pent-2-enal. The structure and absolute configuration of the products were confirmed by X-ray analyses of appropriate products. PMID:24796861

Jhuo, Dai-Huei; Hong, Bor-Cherng; Chang, Chun-Wei; Lee, Gene-Hsiang

2014-05-16

206

Synthesis and characterization of advanced materials for Navy applications  

NASA Technical Reports Server (NTRS)

The synthesis of ceramics and ceramic coatings through the sol-gel process has extensive application with the United States Navy and a broad range of potential commercial applications as well. This paper surveys seven specific applications for which the Navy is investigating these advanced materials. For each area, the synthetic process is described and the characteristics of the materials are discussed.

Covino, J.; Lee, I.

1994-01-01

207

Enantioselective Diels–Alder reactions catalyzed by hydrogen bonding  

PubMed Central

Like molecules of life (e.g., proteins and DNA), many pharmaceutical drugs are also asymmetric (chiral); they are not superimposable on their mirror images. One mirror image form (enantiomer) of a drug can have desirable activity, the other not. Consequently, the development of methods for the selective synthesis of one enantiomer is of great scientific and economic importance. We report here that a simple, commercially available chiral alcohol, ?,?,??,??-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL), catalyzes the all-carbon Diels–Alder reactions of aminosiloxydienes and substituted acroleins to afford the products in good yields and high enantioselectivities (up to 92% enantiomeric excess). It is remarkable that the reactions are promoted by hydrogen bonding, the ubiquitous “glue” that helps to keep water molecules together and holds up the 3D structures of proteins. Hydrogen bond catalysis is little used in chemical synthesis, wherein most reactions are promoted by complexes of Lewis acidic metal salts coordinated to chiral ligands. As it does for enzymes, hydrogen bonding not only organizes TADDOL into a well defined conformation, but, functioning as a Brønsted acid catalyst, it also activates the dienophile toward reaction with the diene. The gross structure of the TADDOL has been found to have a profound influence on both the rate and the enantioselectivity of the cycloadditions. These structure–function effects are rationalized by evaluating the conformation adopted by the TADDOLs in the crystal state. It is suggested that ?,?-stacking plays an central role in the overall catalytic cycle, in particular, the enantioselective step. PMID:15069185

Thadani, Avinash N.; Stankovic, Ana R.; Rawal, Viresh H.

2004-01-01

208

Silver nanoparticles: Synthesis methods, bio-applications and properties.  

PubMed

Abstract Silver nanoparticles size makes wide range of new applications in various fields of industry. Synthesis of noble metal nanoparticles for applications such as catalysis, electronics, optics, environmental and biotechnology is an area of constant interest. Two main methods for Silver nanoparticles are the physical and chemical methods. The problem with these methods is absorption of toxic substances onto them. Green synthesis approaches overcome this limitation. Silver nanoparticles size makes wide range of new applications in various fields of industry. This article summarizes exclusively scalable techniques and focuses on strengths, respectively, limitations with respect to the biomedical applicability and regulatory requirements concerning silver nanoparticles. PMID:24937409

Abbasi, Elham; Milani, Morteza; Fekri Aval, Sedigheh; Kouhi, Mohammad; Akbarzadeh, Abolfazl; Tayefi Nasrabadi, Hamid; Nikasa, Parisa; Joo, San Woo; Hanifehpour, Younes; Nejati-Koshki, Kazem; Samiei, Mohammad

2014-06-17

209

Synthesis and applications of metal oxide nanowires  

NASA Astrophysics Data System (ADS)

The one-dimensional nanostructured materials have attracted much attention because of their superior properties from the deducing size in the nanometer range. Among them, metal oxide materials provide a wide diversity and functionality in both theoretical study and applications. This work focused on the synthesis of metal oxide nanowires, and further investigated possible applications of nanostructured metal oxide materials. High quality ZnO nanowires have been synthesized by catalyst-assisted molecular beam epitaxy. The control of initial Au or Ag film thickness and subsequent annealing conditions is shown to provide an effective method for controlling the size and density of nucleation sites for catalyst-driven growth of ZnO nanowires. For gas sensing applications, it is found that the sensitivity for detecting hydrogen is greatly enhanced by sputter-depositing metal catalysts (Pt and Pt) on surface. The sensors are shown to detect ppm hydrogen at room temperature using <0.4 mW of power when using multiple nanowires. A comparison study of the hydrogen-sensing characteristics of ZnO thin films with different thickness and ZnO nanowires was studied. The Pt-coated single nanowires show a current response by approximately a factor of 3 larger at room temperature. Both types of sensors are shown to be capable of the detection of ppm hydrogen at room temperature with nW power levels, but the nanowires show different recovery characteristics, consistent with the expected higher surface coverage of adsorbed hydrogen. The feasibility of a number of metal oxide nanowires has been synthesized by a high-pressure assisted pulsed laser deposition. The high density well-aligned metal oxide nanowires can be directly grown on substrate without metal catalysts. The results suggest the possibility of growing complex metal oxide nanostructures, including tailored heterostructures and aligned heterojunction arrays with PLD technique. The growth of epitaxial SnO2 on c-sapphire using pulsed laser deposition is examined. X-ray diffraction analysis shows that the films are highly a-axis oriented SnO2 with the rutile structure. The effects of Ga doping on SnO2 films were studied. The Hall data showed p-type behavior occurs only at specific growth condition, but converted back to n-type and degraded as time proceeds.

Tien, Li-Chia

210

A Lewis acid activated reaction of Zn with EtI to promote highly enantioselective alkyne additions to aldehydes.  

PubMed

An easily available BINOL-Ti(O(i)Pr)4 catalyst system is found to activate the reaction of Zn powder with EtI for the asymmetric alkyne addition to aldehydes at room temperature. It allows the synthesis of a number of synthetically useful chiral propargylic alcohols with both high yields and high enantioselectivity (up to >96% ee). PMID:25407055

Chen, Shan-Yong; Liu, Winnie; Wu, Xuedan; Ying, Jun; Yu, Xiaoqi; Pu, Lin

2015-01-01

211

Enantioselective desymmetrisation of citric acid catalysed by the substrate-tolerant petrobactin biosynthetic enzyme AsbA.  

PubMed

AsbA catalyses the highly enantioselective desymmetrisation of citric acid via ATP-dependent condensation with spermidine, as well as the condensation of citric acid with several spermidine analogues and the condensation of the citric acid analogue tricarballylic acid with spermidine, suggesting that it may be a useful biocatalyst for asymmetric synthesis. PMID:19259597

Oves-Costales, Daniel; Song, Lijiang; Challis, Gregory L

2009-03-21

212

Synthesis, characterisation, and applications of Mn-Zn ferrite nanoparticles  

Microsoft Academic Search

This paper deals with the synthesis, characterization, and some applications of Mn-Zn ferrite nanoparticles. The Mn-Zn ferrite was prepared from metallic nitrates, iron citrate and citric acid with the co-precipitation method with different pH values and it was further used to synthesis Mn-Zn ferrite with polariser i.e. H2O2 (Hydrogen peroxide). The X-ray diffraction pattern shows the single phase spinel structure

Madan Lal; D. K. Sharma; M. Singh

2006-01-01

213

Total synthesis and study of myrmicarin alkaloids  

E-print Network

The myrmicarins are a family of air- and temperature-sensitive alkaloids that possess unique structural features. Our concise enantioselective synthesis of the tricyclic myrmicarins enabled evaluation of a potentially ...

Ondrus, Alison E.

214

Organocatalytic Enantioselective Synthesis of ?-Hydroxy Phosphonates  

PubMed Central

Tertiary ?-hydroxy phosphonates have been synthesized in good yields and high enantiomeric purity (up to 99% ee) through a novel L-proline-catalyzed cross aldol reaction of ?-keto phosphonates and ketones. PMID:16756289

Samanta, Sampak; Zhao, Cong-Gui

2008-01-01

215

ENANTIOSELECTIVITY IN THE BIODEGRADATION OF PCB ATROPISOMERS  

EPA Science Inventory

Microcosms inoculated with sediment from two locations in a contaminated reservoir, Lake Hartwell, SC, USA, degraded certain PCB atropisomers enantioselectively while other atropisomers were degraded in racemic proportions. The microcosms were spiked with either 234-236 PCB (PCB...

216

Catalytic enantioselective bromoamination of allylic alcohols.  

PubMed

An enantioselective bromoamination of allylic alcohols has been developed for the first time using a newly designed cinchona-derived thiourea as the catalyst and N,N-dibromo-4-nitrobenzenesulfonamide as a bromine and amine source. PMID:25259372

Qi, Juan; Fan, Guo-Tao; Chen, Jie; Sun, Ming-Hui; Dong, Yu-Ting; Zhou, Ling

2014-11-18

217

Enantioselective Sensing by Luminescence  

Microsoft Academic Search

\\u000a \\u000a Abstract  Enantiomeric analysis is one of the crucial points for the sensor technology, due to the increasing importance that enantiomerically\\u000a pure compounds and drugs have in pharmaceutic and agrochemical applications. Enantiomeric luminescent sensors give different\\u000a responses by interaction or reaction with chiral molecules, allowing one to assess their optical purity by spectroscopic measurements.\\u000a Moreover, chemosensors have been developed to perform enantiomeric

Alessandro Accetta; Roberto Corradini; Rosangela Marchelli

218

Enantioselective Cycloaddition of Münchnones onto [60]Fullerene: Organocatalysis versus Metal Catalysis  

PubMed Central

Novel chiral catalytic systems based on both organic compounds and metal salts have been developed for the enantioselective [3 + 2] cycloaddition of münchnones onto fullerenes and olefins. These two different approaches proved to be efficient and complementary in the synthesis of optically active pyrrolino[3,4:1,2][60]fullerenes with high levels of enantiomeric excess and moderate to good conversions. Further functionalization of the pyrrolinofullerene carboxylic acid derivatives has been carried out by esterification and amidation reactions. PMID:24483247

2014-01-01

219

Enantioselective Functionalization of Allylic C-H Bonds Following a Strategy of Functionalization and Diversification  

PubMed Central

We report the enantioselective functionalization of allylic C-H bonds in terminal alkenes by a strategy involving the installation of a temporary functional group at the terminal carbon atom by C-H bond functionalization, followed by diversification of this intermediate with a broad scope of reagents. The method consists of a one-pot sequence of palladium-catalyzed allylic C-H bond oxidation under neutral conditions to form linear allyl benzoates, followed by iridium-catalyzed allylic substitution. This overall transformation forms a variety of chiral products containing a new C-N, C-O, C-S or C-C bond at the allylic position in good yield with high branched-to-linear selectivity and excellent enantioselectivity (ee ? 97%). The broad scope of the overall process results from separating the oxidation and functionalization steps; by doing so, the scope of nucleophile encompasses those sensitive to direct oxidative functionalization. The high enantioselectivity of the overall process is achieved by developing an allylic oxidation that occurs without acid to form the linear isomer with high selectivity. These allylic functionalization processes are amenable to an iterative sequence leading to (1,n)-functionalized products with catalyst-controlled diastereo- and enantioselectivity. The utility of the method in the synthesis of biologically active molecules has been demonstrated. PMID:24156776

Sharma, Ankit; Hartwig, John F.

2013-01-01

220

NSF/Tokyo Report: US-Japan Workshop: Nanoparticle Synthesis and Applications  

NSF Publications Database

... 97-19 NSF/Tokyo Report: US-Japan Workshop: Nanoparticle Synthesis and Applications Date: 5/21/97 The ... #97-13 (May 12, 1997) US-Japan Workshop: Nanoparticle Synthesis and Applications The following ...

221

The role of electrostatic interactions in enantioselective separation was demonstrated. Enantioselective separation of N-  

E-print Network

The role of electrostatic interactions in enantioselective separation was demonstrated that has not been addressed yet in the Pirkle-type host­guest interaction is the electrostatic interaction of conditions affecting the electrostatic interaction could improve enantioselectivity.4 In this letter, we

Goddard III, William A.

222

Design and synthesis of mixed oxides nanoparticles for biofuel applications  

SciTech Connect

The work in this dissertation presents the synthesis of two mixed metal oxides for biofuel applications and NMR characterization of silica materials. In the chapter 2, high catalytic efficiency of calcium silicate is synthesized for transesterfication of soybean oil to biodisels. Chapter 3 describes the synthesis of a new Rh based catalyst on mesoporous manganese oxides. The new catalyst is found to have higher activity and selectivity towards ethanol. Chapter 4 demonstrates the applications of solid-state Si NMR in the silica materials.

Chen, Senniang

2010-05-15

223

Synthesis and Applications of Mixed Oxide Nanotubes  

NASA Astrophysics Data System (ADS)

Metal oxide nanotube is one of the nanostructured materials. Templates method, which is the technique in which templates are covered with metal oxides and the templates were removed to form metal oxide nanotubes, is a typical synthesis method for metal oxide nanotubes. In this section, synthesis of mixed oxide nanotubes using carbon nanofibers (CNFs) as templates is described. Because CNFs with various shapes were used as templates, oxide nanotubes with various shapes such as straight and helical were formed. Successive adsorption of metal oxide precursors on CNFs resulted in the formation of mixed oxide nanotubes with specific composition. In addition, a nano-macrostructured material, silica fiber-immobilized nanofibrous LaMnO3, was fabricated using this template process. In propane oxidation, the nano-macrostructured material showed superior activity to the conventional powder catalysts.

Ogihara, Hitoshi; Sadakane, Masahiro; Ueda, Wataru

224

Gold nanorods: Synthesis, characterization and applications  

Microsoft Academic Search

This article provides an overview of current research into the synthesis and properties of gold nanorods. Interest in rod-shaped nanoparticles stems from their unique optical properties, which can be approximated by Mie–Gans theory. We begin by outlining briefly the origin of the shape-dependent optical properties of rods. The different synthetic strategies that have been developed to achieve decent yields and

Jorge Pérez-Juste; Isabel Pastoriza-Santos; Luis M. Liz-Marzán; Paul Mulvaney

2005-01-01

225

MATConcat: An Application for Exploring Concatenative Sound Synthesis Using MATLAB  

Microsoft Academic Search

MATConcat is a MATLAB application for exploring con- catenative sound synthesis. Using this program a sound or composition can be concatenatively synthesized with audio segments from a database of other sounds. The algorithm matches segments based on similarity of specified feature vec- tors, currently consisting of six independent elements. Us- ing MATConcat a recording of Mahler can be synthesized us-

Bob L. Sturm

2004-01-01

226

EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology  

E-print Network

the Fourth Biennial Emergy Conference, Gainesville, Florida Edited by Mark T. Brown University of Floridaii EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology Proceedings from basis. Converting each flow to macroeconomic flows (using the global emergy money ratio) suggests

Slatton, Clint

227

EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology  

E-print Network

the Fourth Biennial Emergy Conference, Gainesville, Florida Edited by Mark T. Brown University of Floridaii EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology Proceedings from-renewable emergy use per capita, were compared to social, political, economic, and environmental indicators

Slatton, Clint

228

Group IV clathrates: synthesis, optoelectonic properties, and photovoltaic applications  

NASA Astrophysics Data System (ADS)

Group IV clathrates are a unique class of guest/framework type compounds that are considered potential candidates for a wide range of applications (superconductors to semiconductors). To date, most of the research on group IV clathrates has focused heavily on thermoelectric applications. Recently, these materials have attracted attention as a result of their direct, wide band gaps for possible use in photovoltaic applications. Additionally, framework alloying has been shown to result in tunable band gaps. In this review, we discuss the current work and future opportunities concerning the synthesis and optical characterization of group IV clathrates for optoelectronics applications.

Krishna, Lakshmi; Martinez, Aaron D.; Baranowski, Lauryn L.; Brawand, Nicholas P.; Koh, Carolyn A.; Stevanovi?, Vladan; Lusk, Mark T.; Toberer, Eric S.; Tamboli, Adele C.

2014-03-01

229

Aerosol synthesis and application of folded graphene-based materials  

NASA Astrophysics Data System (ADS)

Graphene oxide colloid has been widely used in the synthesis of various graphene-based materials. Graphene oxide sheets, with a low bending rigidity, can be folded when assembled in aqueous phase. A simple but industrial scalable way, aerosol processing, can be used to fabricate folded graphene-based materials. These folded materials can carry various cargo materials and be used in different applications such as time-controlled drug release, medical imaging enhancement, catalyst support and energy related areas. The aerosol synthesis of folded graphene-based materials can also be easily extended to fabricate hybrid nanomaterials without any complicated chemistries.

Chen, Yantao; Wang, Zhongying; Qiu, Yang

2015-12-01

230

Synthesis and Characterization of Polymers for Fuel Cells Application  

NASA Technical Reports Server (NTRS)

The goal of this summer research is to prepare Polymer Exchange Membranes (PEM s) for fuel cell application. Several high temperature polymers such as polybenzimidazoles and polyether ketones were known to possess good high temperature stability and had been investigated by post-sulfonation to yield sulfonated polymers. The research project will involve two approaches: 1. Synthesis of polybenzimidazoles and then react with alkyl sultonse to attach an aliphatic sulfonic groups. 2. Synthesis of monomers containing sulfonic acid units either on a aromatic ring or on an aliphatic chain and then polymerize the monomers to form high molecular weight sulfonate polymers.

Tytko, Stephen F.

2003-01-01

231

Naphthodithiophenediimide (NDTI): synthesis, structure, and applications.  

PubMed

A straightforward synthesis of ?,?-unsubstituted and ?-halogenated naphtho[2,3-b:6,7-b']dithiophenediimides (NDTIs) is described. Electrochemical and optical studies of N,N-dioctyl-NDTI demonstrate that the compound has a low-lying LUMO energy level (4.0 eV below the vacuum level) and a small HOMO-LUMO gap (~2.1 eV). With its interesting electronic and optical properties, in addition to its planar structure, NDTI is a promising building block for the development of novel ?-functional materials. In fact, it afforded n-channel, p-channel, and ambipolar materials, depending on the molecular modification. PMID:23879366

Fukutomi, Yuta; Nakano, Masahiro; Hu, Jian-Yong; Osaka, Itaru; Takimiya, Kazuo

2013-08-01

232

Enantioselective cyclopropanation of indoles: construction of all-carbon quaternary stereocenters.  

PubMed

The first enantioselective copper-catalyzed cyclopropanation of N-acyl indoles is described. Using carbohydrate-based bis(oxazoline) ligands (glucoBox), the products were obtained in up to 72% ee. Cyclopropanation of N-Boc 3-methyl indole yielded a product with an all-carbon quaternary stereocenter, which is a valuable building block for the synthesis of indole alkaloids: Deprotection and rearrangement gave a tricyclic hemiaminal ester in 96% ee, which was subsequently employed as a key intermediate for the synthesis of (-)-desoxyeseroline. PMID:23009104

Özüduru, Gülsüm; Schubach, Thea; Boysen, Mike M K

2012-10-01

233

Nanoparticles: synthesis and applications in life science and environmental technology  

NASA Astrophysics Data System (ADS)

This work focuses on the synthesis, functionalization, and application of gold and silver nanoparticles, magnetic nanoparticles Fe3O4, combination of 4-ATP-coated silver nanoparticles and Fe3O4 nanoparticles. The synthesis methods such as chemical reduction, seeding, coprecipitation,and inverse microemulsion will be outlined. Silica- and amino-coated nanoparticles are suitable for several applications in biomedicine and the environment. The applications of the prepared nanoparticles for early detection of breast cancer cells, basal cell carcinoma, antibacterial test, arsenic removal from water, Herpes DNA separation, CD4+ cell separation and isolation of DNA of Hepatitis virus type B (HBV) and Epstein–Barr virus (EBV) are discussed. Finally, some promising perspectives will be pointed out. Invited talk at the 7th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2014, 2-6 November, 2014, Ha Long, Vietnam.

Luong Nguyen, Hoang; Nguyen, Hoang Nam; Hai Nguyen, Hoang; Quynh Luu, Manh; Hieu Nguyen, Minh

2015-03-01

234

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications  

PubMed Central

Bridged bicyclic sulfide 1 was originally found to provide high levels of asymmetric induction in sulfur ylide-mediated epoxidations. This sulfide possesses chirality in the [2.2.1] thioether moiety and the [2.2.1] camphor-derived carbocyclic moiety. To determine whether the optimal sulfide had been used, a diastereomer of sulfide 1 in which the stereochemistry of the [2.2.1] carbocycle was reversed (sulfide 5) was prepared and studied as an epoxidation catalyst. This diastereomer gave considerably lower levels of asymmetric induction than the original sulfide 1. From computational and x-ray studies it was found that sulfide 5 gave rise to a more hindered ylide, which reacted more reversibly with aldehydes leading to lower enantioselectivity. Conditions that reduced reversibility were also tested and high enantioselectivities were returned for sulfide 5 (similar to sulfide 1). The implications for the synthesis of chiral sulfides for asymmetric epoxidations are discussed. PMID:15034181

Aggarwal, Varinder K.; Charmant, Jonathan; Dudin, Leo; Porcelloni, Marina; Richardson, Jeffery

2004-01-01

235

Synthesis of boron nitride nanotubes and their applications  

PubMed Central

Summary Boron nitride nanotubes (BNNTs) have been increasingly investigated for use in a wide range of applications due to their unique physicochemical properties including high hydrophobicity, heat and electrical insulation, resistance to oxidation, and hydrogen storage capacity. They are also valued for their possible medical and biomedical applications including drug delivery, use in biomaterials, and neutron capture therapy. In this review, BNNT synthesis methods and the surface modification strategies are first discussed, and then their toxicity and application studies are summarized. Finally, a perspective for the future use of these novel materials is discussed. PMID:25671154

Kalay, Saban; Yilmaz, Zehra; Sen, Ozlem; Emanet, Melis; Kazanc, Emine

2015-01-01

236

Application of optimality criteria in structural synthesis  

NASA Technical Reports Server (NTRS)

The rational use of optimality criteria was investigated for a class of structural synthesis problems where materials, configuration and applied load conditions are specified, and the minimum weight design is to be determined. The potential of hybrid methods of structural optimization for dealing with relatively large design problems involving practical complexity was explored. The reduced basis concept in design space was used to decrease the number of generalized design variables dealt with by the mathematical programming algorithm. Optimality criteria methods for obtaining design vectors associated with displacement, system buckling and natural frequency constraints are presented. A stress ratio method was used to generate a basis design vector representing the stress constraints. The finite element displacement method was used as the basic structural analysis tool. Results for several examples of truss systems subject to stress, displacement and minimum size constraints are presented. An assessment of these results indicates the effectiveness of the hybrid method developed.

Terai, K.

1974-01-01

237

Ordered mesoporous metal oxides: synthesis and applications.  

PubMed

Great progress has been made in the preparation and application of ordered mesoporous metal oxides during the past decade. However, the applications of these novel and interesting materials have not been reviewed comprehensively in the literature. In the current review we first describe different methods for the preparation of ordered mesoporous metal oxides; we then review their applications in energy conversion and storage, catalysis, sensing, adsorption and separation. The correlations between the textural properties of ordered mesoporous metal oxides and their specific performance are highlighted in different examples, including the rate of Li intercalation, sensing, and the magnetic properties. These results demonstrate that the mesoporosity has a direct impact on the properties and potential applications of such materials. Although the scope of the current review is limited to ordered mesoporous metal oxides, we believe that the information may be useful for those working in a number of fields. PMID:22653082

Ren, Yu; Ma, Zhen; Bruce, Peter G

2012-07-21

238

Synthesis of plasmonic nanocomposites for diverse applications.  

PubMed

We report the synthesis of gold and silver nanostructures embedded in different dielectric matrices by atom beam co-sputtering, a novel technique. We have synthesized gold-silicon core shell nanostructures and Au-ZnO nanocomposite with tunable surface plasmon resonance (SPR) by atom beam co-sputtering and subsequent annealing. The Au-ZnO nanocomposite shows significant enhancement in intensity of Raman modes of fullerene molecules and therefore can help in surface enhanced Raman spectroscopy investigation of organic molecules. The synthesized Ag-polymer nanocomposite thin films show excellent features of broad SPR absorption extending upto IR region and a narrow transmission of light in UV region approximately 320 nm which could be of technological interest in solar absorbers and UV light filters respectively. The Ag-silica nanocomposite thin films show their utility in glucose sensing. The gold-silica nanocomposite thin films exhibit their possible use in detection of human ovarian cancer cells in a preliminary study. The shift in SPR peak of Au nanoparticles (NPs) present at the surface of silica synthesized by thermal evaporation and annealing, after attachment of biological molecules like proteins has been studied. PMID:20355488

Avasthi, D K; Mishra, Y K; Singhal, R; Kabiraj, D; Mohapatra, S; Mohanta, B; Gohil, Nivedita K; Singh, N

2010-04-01

239

Synthesis of software programs for embedded control applications  

Microsoft Academic Search

Software components for embedded reactive real-time applications must satisfy tight code size and run- time constraints. Cooperating finite state machines provide a convenient intermediate format for embedded system co-synthesis, between high-level specification languages and software or hardware implementations. We propose a software generation methodology that takes advantage of a restricted class of specifications and allows for tight control over the

Felice Balarin; Massimiliano Chiodo; Paolo Giusto; Harry Hsieh; Attila Jurecska; Luciano Lavagno; Alberto L. Sangiovanni-vincentelli; Ellen M. Sentovich; Kei Suzuki

1999-01-01

240

Shape-controlled synthesis and catalytic application of ceria nanomaterials.  

PubMed

Because of their excellent properties and extensive applications, ceria nanomaterials have attracted much attention in recent years. This perspective provides a comprehensive review of current research activities that focus on the shape-controlled synthesis methods of ceria nanostructures. We elaborate on the synthesis strategies in the following four sections: (i) oriented growth directed by the crystallographic structure of cerium-based materials; (ii) oriented growth directed by the use of an appropriate capping reagent; (iii) growth confined or dictated by various templates; (iv) other potential methods for generating CeO(2) nanomaterials. In this perspective, we also discuss the catalytic applications of ceria nanostructures. They are often used as active components or supports in many catalytic reactions and their catalytic activities show morphology dependence. We review the morphology dependence of their catalytic performances in carbon monoxide oxidation, water-gas shift, nitric oxide reduction, and reforming reactions. At the end of this review, we give a personal perspective on the probable challenges and developments of the controllable synthesis of CeO(2) nanomaterials and their catalytic applications. PMID:23027607

Zhang, Dengsong; Du, Xianjun; Shi, Liyi; Gao, Ruihua

2012-12-28

241

Plasma Synthesis of Nanoparticles for Nanocomposite Energy Applications  

SciTech Connect

The nanocomposite energy applications for plasma reactor produced nanoparticles are reviewed. Nanoparticles are commonly defined as particles less than 100 nm in diameter. Due to this small size, nanoparticles have a high surface-to-volume ratio. This increases the surface energy compared to the bulk material. The high surface-to-volume ratio and size effects (quantum effects) give nanoparticles distinctive chemical, electronic, optical, magnetic and mechanical properties from those of the bulk material. Nanoparticles synthesis can be grouped into 3 broad approaches. The first one is wet phase synthesis (sol-gel processing), the second is mechanical attrition, and the third is gas-phase synthesis (aerosol). The properties of the final product may differ significantly depending on the fabrication route. Currently, there are no economical large-scale production processes for nanoparticles. This hinders the widespread applications of nanomaterials in products. The Idaho National Laboratory (INL) is engaging in research and development of advanced modular hybrid plasma reactors for low cost production of nanoparticles that is predicted to accelerate application research and enable the formation of technology innovation alliances that will result in the commercial production of nanocomposites for alternative energy production devices such as fuel cells, photovoltaics and electrochemical double layer capacitors.

Peter C. Kong; Alex W. Kawczak

2008-09-01

242

Nitroderivatives of catechol: from synthesis to application.  

PubMed

Nitroderivatives of catechol (NDCs) are reviewed with special emphasis on their complexes and applications. Binary, ternary and quaternary NDC complexes with more than 40 elements (aluminum, arsenic, boron, beryllium, calcium, cobalt, copper, iron, gallium, germanium, magnesium, manganese, molybdenum, niobium, rare earth elements, silicon, tin, strontium, technetium, thallium, titanium, uranium, vanadium, tungsten, zinc and zirconium) are discussed and the key characteristics of the developed analytical procedures - tabulated. The bibliography includes 206 references. PMID:24061167

Gavazov, Kiril B

2012-03-01

243

Titanium-Catalyzed Enantioselective Additions of  

E-print Network

Titanium-Catalyzed Enantioselective Additions of Alkyl Groups to Aldehydes: Mechanistic Studies by zinc- or titanium- based catalysts. While the mechanism of the zinc/amino alcohol catalysts has received significant attention, the titanium-based catalysts have been less studied. This Account

Walsh, Patrick J.

244

Enantioselective Construction of Cyclic Quaternary Centers: (-)-Mesembrine  

E-print Network

Enantioselective Construction of Cyclic Quaternary Centers: (-)-Mesembrine Douglass F. Taber next needed a dehydration method that would give predominantly the (E)-R, -unsaturated ester from) Gericke, N. P.; Van Wyk, B. E. World Patent 9746234, 1997. (2) For leading references to previous

Taber, Douglass

245

Enantioselective Analysis in instruments onboard ROSETTA/PHILAE and ExoMars  

NASA Astrophysics Data System (ADS)

It has been suggested a number of times in the past, to look for chirality as a biomarker. So far, for lack of appropriate instrumentation, space missions have never included enantioselective analysis. The distinction between enantiomers is of crucial importance to the question of the origin of the very first (pre)biotic molecules. If molecules detected in situ on another celestial body were found to exhibit a chiral bias, this would mean that at least partial asymmetric synthesis could take place abiotically. If this chiral bias should be found to be near 100For the currently flying ESA mission ROSETTA an enantioselective instrument was built, to try for the first time to detect and separate chiral molecules in situ. This instrument is COSAC, the Cometary Sampling and Acquisition Experiment, an enantioselective GCMS device[1,2], which is included in the lander PHLIAE that will eventually in 2014 land on the nucleus of comet 67P/Churyumov-Gerasimenko. A similar but even more powerful type of enantioselective GC-MS is in preparation for ESA's ExoMars mission. This instrument is part of MOMA, the Mars Organic Molecules Analyser. It has the objective of identifying and quantifying chiral organic molecules in surface and subsurface samples of Mars. Currently ExoMars is scheduled for 2018. The newly developed enantioselective technique utilized by both COSAC and MOMA will be described, including sample acquisition, derivatization, and separation in space-resistant chiral stationary capillary columns with time-of-flight mass spectrometric detection. Results of enantioselective analyses of representative test samples with special emphasis on amino acids[3], the building blocks of protein polymers, will be presented and we will discuss potential results of space missions Rosetta and ExoMars. [1] Thiemann W.H.-P., Meierhenrich U.: ESA Mission ROSETTA Will Probe for Chirality of Cometary Amino Acids. Origins of Life and Evolution of Biospheres 31 (2001), 199-210. [2] Goesmann F., Rosenbauer H., Roll R., Szopa C., Raulin F., Sternberg R., Israel G., Meier-henrich U., Thiemann W., Muñoz Caro G.M.: COSAC, The cometary sampling and composi-n tion experiment on Philae. Space Science Reviews 128 (2007), 257-280. [3] Meierhenrich U.J.: Amino Acids and the Asymmetry of Life -Caught in the Act of Forma-tion. Springer, Heidelberg Berlin New York (2008).

Hendrik Bredehöft, Jan; Thiemann, Wolfram; Meierhenrich, Uwe; Goesmann, Fred

246

Synthesis and applications of several curved polycyclic aromatic hydrocarbons  

NASA Astrophysics Data System (ADS)

This thesis describes the synthesis and applications of two curved polycyclic aromatic hydrocarbons, hexabenzocoronene (HBC) and pentabenzocoronene (PBC). In Chapter 2, a monolayer of a carboxylic acid functionalized HBC is incorporated into an ultra small nanotube junction (˜ 2 to 6 nm). The junction is formed by cutting a single carbon nanotube using both electron beam lithography and oxygen plasma. These HBC-filled junctions are effective organic field effect transistor devices when the two ends of the nanotube are used as electrodes. As the molecules are exposed, they are sensitive to the environment and are capable of detecting electron deficient aromatic compounds such as TCNQ. In Chapter 3, the synthesis of PBC and several of its derivatives is described. The application of alkoxylated derivatives of PBC as discotic liquid crystals and as n-type organic field effect transistors is discussed. In Chapter 4, possible methods for incorporating HBC and PBC into the templated growth of carbon nanotubes are described. If successful, this would allow for the synthesis of carbon nanotubes samples with a single chiral index. For accurate spectroscopic characterization of single carbon nanotubes, unbundled carbon nanotubes are desired. Nanoparticle size has a strong correlation to carbon nanotube diameter. As such, for this project, well separated and uniformly sized nanoparticles are necessary. Arrays of catalyst nanoparticles have been synthesized using diblock copolymer templates, which allow the size and separation to be tuned. The stability and carbon nanotube growth activity of copper, ruthenium and cobalt nanoparticle arrays are presented.

Myers, Matthew

2008-07-01

247

Engineering and Applications of fungal laccases for organic synthesis  

PubMed Central

Laccases are multi-copper containing oxidases (EC 1.10.3.2), widely distributed in fungi, higher plants and bacteria. Laccase catalyses the oxidation of phenols, polyphenols and anilines by one-electron abstraction, with the concomitant reduction of oxygen to water in a four-electron transfer process. In the presence of small redox mediators, laccase offers a broader repertory of oxidations including non-phenolic substrates. Hence, fungal laccases are considered as ideal green catalysts of great biotechnological impact due to their few requirements (they only require air, and they produce water as the only by-product) and their broad substrate specificity, including direct bioelectrocatalysis. Thus, laccases and/or laccase-mediator systems find potential applications in bioremediation, paper pulp bleaching, finishing of textiles, bio-fuel cells and more. Significantly, laccases can be used in organic synthesis, as they can perform exquisite transformations ranging from the oxidation of functional groups to the heteromolecular coupling for production of new antibiotics derivatives, or the catalysis of key steps in the synthesis of complex natural products. In this review, the application of fungal laccases and their engineering by rational design and directed evolution for organic synthesis purposes are discussed. PMID:19019256

Kunamneni, Adinarayana; Camarero, Susana; García-Burgos, Carlos; Plou, Francisco J; Ballesteros, Antonio; Alcalde, Miguel

2008-01-01

248

Phosphine-catalyzed enantioselective ?-addition of 3-substituted oxindoles to 2,3-butadienoates and 2-butynoates: use of prochiral nucleophiles.  

PubMed

The first phosphine-catalyzed enantioselective ?-addition with prochiral nucleophiles and 2,3-butadienoates as the reaction partners has been developed. Both 3-alkyl- and 3-aryl-substituted oxindoles could be employed in this process, which is catalyzed by a chiral phosphine that is derived from an amino acid, thus affording oxindoles that bear an all-carbon quaternary center at the 3-position in high yields and excellent enantioselectivity. The synthetic value of these ?-addition products was demonstrated by the formal total synthesis of two natural products and by the preparation of biologically relevant molecules and structural scaffolds. PMID:24520067

Wang, Tianli; Yao, Weijun; Zhong, Fangrui; Pang, Guo Hao; Lu, Yixin

2014-03-10

249

Application of global sensitivity equations in multidisciplinary aircraft synthesis  

NASA Technical Reports Server (NTRS)

The present paper investigates the applicability of the Global Sensitivity Equation (GSE) method in the multidisciplinary synthesis of aeronautical vehicles. The GSE method provides an efficient approach for representing a large coupled system by smaller subsystems and accounts for the subsystem interactions by means of first-order behavior sensitivities. This approach was applied in an aircraft synthesis problem with performance constraints stemming from the disciplines of structures, aerodynamics, and flight mechanics. Approximation methods were considered in an attempt to reduce problem dimensionality and to improve the efficiency of the optimization process. The influence of efficient constraint representations, the choice of design variables, and design variable scaling on the conditioning of the system matrix was also investigated.

Hajela, P.; Bloebaum, C. L.; Sobieszczanski-Sobieski, Jaroslaw

1990-01-01

250

Synthesis and catalytic applications of combined zeolitic/mesoporous materials  

PubMed Central

Summary In the last decade, research concerning nanoporous siliceous materials has been focused on mesoporous materials with intrinsic zeolitic features. These materials are thought to be superior, because they are able to combine (i) the enhanced diffusion and accessibility for larger molecules and viscous fluids typical of mesoporous materials with (ii) the remarkable stability, catalytic activity and selectivity of zeolites. This review gives an overview of the state of the art concerning combined zeolitic/mesoporous materials. Focus is put on the synthesis and the applications of the combined zeolitic/mesoporous materials. The different synthesis approaches and formation mechanisms leading to these materials are comprehensively discussed and compared. Moreover, Ti-containing nanoporous materials as redox catalysts are discussed to illustrate a potential implementation of combined zeolitic/mesoporous materials. PMID:22259762

Vernimmen, Jarian; Cool, Pegie

2011-01-01

251

Zirconium-Catalyzed Desymmetrization of Aminodialkenes and Aminodialkynes through Enantioselective Hydroamination.  

PubMed

The catalytic addition of alkenes and amines (hydroamination) typically provides ?- or ?-amino stereocenters directly through C-N or C-H bond formation. Alternatively, desymmetrization reactions of symmetrical aminodialkenes or aminodialkynes provide access to stereogenic centers with the position controlled by the substrate's structure. In the present study of an enantioselective zirconium-catalyzed hydroamination, stereocenters resulting from C-N bond formation and desymmetrization of a prochiral quaternary center are independently controlled by the catalyst and reaction conditions. Using a single catalyst, the method provides selective access to either diastereomer of optically enriched five-, six-, and seven-membered cyclic amines from aminodialkenes and enantioselective synthesis of five-, six-, and seven-membered cyclic imines from aminodialkynes. Experiments on hydroamination of aminodialkenes testing the effects of the catalyst:substrate ratio, the absolute concentration of the catalyst, and the absolute initial concentration of the primary amine substrate show that the latter parameter strongly influences the stereoselectivity of the desymmetrization process, whereas the absolute configuration of the ?-amino stereocenter generated by C-N bond formation is not affected by these parameters. Interestingly, isotopic substitution (H2NR vs D2NR) of the substrate enhances the stereoselectivity of the enantioselective and diastereoselective processes in aminodialkene cyclization and the peripheral stereocenter in aminodialkyne desymmetrization/cyclization. PMID:25560913

Manna, Kuntal; Eedugurala, Naresh; Sadow, Aaron D

2015-01-14

252

Boron nitride nanotube: synthesis and applications  

NASA Astrophysics Data System (ADS)

Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA/JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800°C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.

Tiano, Amanda L.; Park, Cheol; Lee, Joseph W.; Luong, Hoa H.; Gibbons, Luke J.; Chu, Sang-Hyon; Applin, Samantha; Gnoffo, Peter; Lowther, Sharon; Kim, Hyun Jung; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Kang, Jin Ho; Sauti, Godfrey; Thibeault, Sheila A.; Yamakov, Vesselin; Wise, Kristopher E.; Su, Ji; Fay, Catharine C.

2014-04-01

253

Conjugated microporous polymers: design, synthesis and application.  

PubMed

Conjugated microporous polymers (CMPs) are a class of organic porous polymers that combine ?-conjugated skeletons with permanent nanopores, in sharp contrast to other porous materials that are not ?-conjugated and with conventional conjugated polymers that are nonporous. As an emerging material platform, CMPs offer a high flexibility for the molecular design of conjugated skeletons and nanopores. Various chemical reactions, building blocks and synthetic methods have been developed and a broad variety of CMPs with different structures and specific properties have been synthesized, driving the rapid growth of the field. CMPs are unique in that they allow the complementary utilization of ?-conjugated skeletons and nanopores for functional exploration; they have shown great potential for challenging energy and environmental issues, as exemplified by their excellent performance in gas adsorption, heterogeneous catalysis, light emitting, light harvesting and electrical energy storage. This review describes the molecular design principles of CMPs, advancements in synthetic and structural studies and the frontiers of functional exploration and potential applications. PMID:23846024

Xu, Yanhong; Jin, Shangbin; Xu, Hong; Nagai, Atsushi; Jiang, Donglin

2013-10-21

254

Biomedical Nanocrystal Agents: Design, Synthesis, and Applications  

NASA Astrophysics Data System (ADS)

In these days, nanomaterials are applied in a variety of biomedical applications including magnetic resonance imaging (MRI), cell imaging, drug delivery, and cell separation. Most MRI contrast agents affect the longitudinal relaxation time (T1) and transverse relaxation time (T2 ) of water protons in the tissue and result in increased positive or negative contrast. Here, we report the optimization of r1 (1/T 1) or r2 (1/T2) relaxivity dynamics with diameter controlled gadolinium oxide nanocrystals (2˜22 nm) and iron based magnetic nanocrystals (4 ˜33 nm). The r1 and r2 MR relaxivity values of hydrated nanocrystals were optimized and examined depending on their core diameter, surface coating, and compositions; the high r1 value of gadolinium oxide was 40-60 S-1mM-1, which is 10-15 fold higher than that of commercial Gd (III) chelates (4.3˜4.6 S-1mM-1). Moreover, in vitro toxicological studies revealed that polymer coated nanocrystals suspensions had no significant effect on human dermal fibroblast (HDF) cells even at high concentration. Towards multimodal imaging or multifunctional ability, we developed the iron oxide/QDs complexes, which consist of cores of iron oxide that act as nucleation sites for fluorescent QDs. The choice of variable QDs helped to visualize and remove large iron oxide materials in a magnetic separation. Additionally, diluted materials concentrated on the magnet could be fluorescently detected even at very low concentration. The designed MRI or multifunctional nanomaterials will give great and powerful uses in biomedical applications.

Cho, Minjung

255

Bismuth-based oxide semiconductors: Mild synthesis and practical applications  

NASA Astrophysics Data System (ADS)

In this dissertation study, bismuth based oxide semiconductors were prepared using 'mild' synthesis techniques---electrodeposition and solution combustion synthesis. Potential environmental remediation and solar energy applications of the prepared oxides were evaluated. Bismuth vanadate (BiVO4) was prepared by electrodeposition and solution combustion synthesis. A two step electrosynthesis strategy was developed and demonstrated for the first time. In the first step, a Bi film was first electrodeposited on a Pt substrate from an acidic BiCl3 medium. Then, this film was anodically stripped in a medium containing hydrolyzed vanadium precursor, to generate Bi3+, and subsequent BiVO4 formation by in situ precipitation. The photoelectrochemical data were consistent with the in situ formation of n-type semiconductor films. In the solution combustion synthesis procedure, BiVO4 powders were prepared using bismuth nitrate pentahydrate as the bismuth precursor and either vanadium chloride or vanadium oxysulfate as the vanadium precursor. Urea, glycine, or citric acid was used as the fuel. The effect of the vanadium precursor on the photocatalytic activity of combustion synthesized BiVO 4 was evaluated in this study. Methyl orange was used as a probe to test the photocatalytic attributes of the combustion synthesized (CS) samples, and benchmarked against a commercial bismuth vanadate sample. The CS samples showed superior activity to the commercial benchmark sample, and samples derived from vanadium chloride were superior to vanadium oxysulfate counterparts. The photoelectrochemical properties of the various CS samples were also studied and these samples were shown to be useful both for environmental photocatalytic remediation and water photooxidation applications. Silver bismuth tungstate (AgBiW2O8) nanoparticles were prepared for the first time by solution combustion synthesis by using silver nitrate, bismuth nitrate, sodium tungstate as precursors for Ag, Bi, and W respectively and urea as the fuel. The photocatalytic activity of these nanoparticles was superior to a sample prepared by solid-state synthesis. The combustion-synthesized particles were subsequently modified with Pt catalyst islands using a photodeposition technique and then used for the photo-generation of syngas (CO + H2). Formic acid was used in these experiments for in situ generation of CO2 and its subsequent reduction to CO. In the absence of Pt modification, H2 was not obtained. These results were compared with those obtained with acetic acid in place of formic acid, and finally the mechanistic pathways for syngas and methane photogeneration are presented.

Timmaji, Hari Krishna

256

Functional Metal Oxide Nanostructures: Their Synthesis, Characterization, and Energy Applications  

NASA Astrophysics Data System (ADS)

This research focuses on studying metal oxides (MnO 2, Co3O4, MgO, Y2O3) for various applications including water oxidation and photocatalytic oxidation, developing different synthesis methodologies, and presenting detailed characterization studies of these metal oxides. This research consists of three major parts. The first part is studying novel applications and developing a synthesis method for manganese oxide nanomaterials. Manganese oxide materials were studied for renewable energy applications by using them as catalysts for water oxidation reactions. In this study, various crystallographic forms of manganese oxides (amorphous, 2D layered, 1D 2 x 2 tunnel structures) were evaluated for water oxidation catalysis. Amorphous manganese oxides (AMO) were found to be catalytically active for chemical and photochemical water oxidation compared to cryptomelane type tunnel manganese oxides (2 x 2 tunnels; OMS2) or layered birnessite (OL-1) materials. Detailed characterization was done to establish a correlation between the properties of the manganese oxide materials and their catalytic activities in water oxidation. The gas phase photocatalytic oxidation of 2-propanol under visible light was studied using manganese oxide 2 x 2 tunnel structures (OMS-2) as catalysts (Chapter 3). The reaction is 100% selective to acetone. As suggested by the photocatalytic and characterization data, important factors for the design of active OMS-2 photocatalysts are synthesis methodology, morphology, mixed valency and the release of oxygen from the OMS-2 structure. Manganese oxide octahedral molecular sieves (2 x 2 tunnels; OMS-2) with self-assembled dense or hollow sphere morphologies were fabricated via a room temperature ultrasonic atomization assisted synthesis (Chapter 4). The properties and catalytic activities of these newly developed materials were compared with that of OMS-2 synthesized by conventional reflux route. These materials exhibit exceptionally high catalytic activities in oxidation reactions and adsorption of heavy metal. Spontaneous formation of OMS-2 nanospheres was possible by tuning reaction parameters in the ultrasonic atomization process. In the second part, a microwave-hydrothermal route has been developed for the synthesis of 1D cobalt compounds (Chapter 5). These compounds are transformed to spinel type Co3O4 nanorods. The effects of solvents, cobalt sources, and microwave radiation time in the formation of 1D cobalt oxide nanostructures were studied in detail. These materials are catalytically active for CO oxidation and styrene oxidation reactions. Magnesia-yttria nanocomposites with controlled nanoscale grain sizes and homogenous microstructures are useful as IR transparent materials. A simple cost-effective sucrose based sol-gel route was devised for making MgO-Y 2O3 nanocomposites. Grain growth in these nanocomposites was systematically evaluated using transmission electron microscopy studies.

Iyer, Aparna

257

Enantioselective Total Syntheses of Plectosphaeroic Acids B and C  

PubMed Central

Evolution of the synthetic strategy that culminated in the first total syntheses of the structurally unique plectosphaeroic acids B (2) and C (3) is described. The successful enantioselective route to (+)-2 and (+)-3 proceeds in 6 and 11 steps from the known hexahydro-2H-pyrazinopyrrolo[2,3-b]indole-1,4-dione 39, which in turn are available in enantiomerically pure form by chemical synthesis. The central challenge in this synthesis endeavor was uniting the hexahydro-2H-pyrazinopyrrolo[2,3-b]indole-1,4-dione and cinnabarinic acid fragments of these marine alkaloids. Critical for achieving this successful C–N bond formation was the use of an iodocinnabarinic acid diester in which the amino group was masked with two Boc substituents, a Cu(I) carboxylate complex, and the weak base KOAc. The highly congested C–N bond generated in this coupling, in conjunction with the delicate nature of the densely functionalized coupling partners, provide striking testament to the power of modern copper-mediated amination methods. Two approaches, one stereoselective, for introducing the methylthio substituents of (+)-plectosphaeroic acid B were developed. The epitrisulfide ring of (+)-plectosphaeroic acid C was formed by ring expansion of an epidisulfide precursor. PMID:24007470

Jabri, Salman Y.

2013-01-01

258

One-pot asymmetric synthesis of seven-membered carbocycles cyclohepta[b]indoles via a sequential organocatalytic Michael/double Friedel-Crafts alkylation reaction.  

PubMed

A new method has been developed for the enantioselective synthesis of highly functionalized cyclohepta[b]indoles with high enantioselectivity (up to 96% ee). The process combines an enantioselective organocatalytic Michael addition and a highly efficient double Friedel-Crafts reaction sequence in one pot with good yields and stereoselectivity. The structures and absolute configurations of the products were confirmed by X-ray analysis. PMID:23848568

Dange, Nitin S; Hong, Bor-Cherng; Lee, Chih-Ching; Lee, Gene-Hsiang

2013-08-01

259

Synthesis and functionalisation of magnetic nanoparticles for hyperthermia applications.  

PubMed

A summary of recent developments in the synthesis, stabilisation and coating of magnetic iron oxide nanoparticles for hyperthermia applications is presented. Methods for synthesis in aqueous, organic and microemulsion systems are reviewed together with the resulting heating rates of the nanoparticles. Different stabilisation mechanisms for iron oxide nanoparticles from aqueous and organic media are discussed as intermediates for further coating and functionalisation. Coating with silica and/or polysaccharides is mainly used for design of nanoparticles especially for targeted hyperthermia application. These coatings permit versatile functionalisation as a basis for conjugating biomolecules, e.g. antibodies or peptides. Various strategies to conjugate biomolecules on the particle surface are discussed, with emphasis on methods that preserve biofunctionality after immobilisation. The efficiency of established methods such as carbodiimide coupling and oriented conjugation strategies is compared with new developments such as the bioorthogonal approaches that are based on the cycloaddition of strain-promoted alkynes with azides or nitrones. For targeted hyperthermia applications the study of the formation of a protein corona around nanoparticles with site-specific biomolecules on the surface is essential to achieve improved circulation times in the blood and reduced non-specific uptake by non-targeted organs for a high specific accumulation in the target tissue. PMID:24099465

Grüttner, Cordula; Müller, Knut; Teller, Joachim; Westphal, Fritz

2013-12-01

260

Hierarchical layered double hydroxide nanocomposites: structure, synthesis and applications.  

PubMed

Layered double hydroxide (LDH)-based nanocomposites, constructed by interacting LDH nanoparticles with other nanomaterials (e.g. silica nanoparticles and magnetic nanoparticles) or polymeric molecules (e.g. proteins), are an emerging yet active area in healthcare, environmental remediation, energy conversion and storage. Combining advantages of each component in the structure and functions, hierarchical LDH-based nanocomposites have shown great potential in biomedicine, water purification, and energy storage and conversion. This feature article summarises the recent advances in LDH-based nanocomposites, focusing on their synthesis, structure, and application in drug delivery, bio-imaging, water purification, supercapacitors, and catalysis. PMID:25562489

Gu, Zi; Atherton, John James; Xu, Zhi Ping

2015-02-01

261

Enantioselective behavior of lipases from Aspergillus niger immobilized in different supports  

Microsoft Academic Search

Considering the extraordinary microbial diversity and importance of fungi as enzyme producers, the search for new biocatalysts\\u000a with special characteristics and possible applications in biocatalysis is of great interest. Here, we report the performance\\u000a in the resolution of racemic ibuprofen of a native enantioselective lipase from Aspergillus niger, free and immobilized in five types of support (Accurel EP-100, Amberlite MB-1,

Vania Castriani Fernandes da Silva; Fabiano Jares Contesini; Patrícia de Oliveira Carvalho

2009-01-01

262

Enantioselective oxidative gold catalysis enabled by a designed chiral p,n-bidentate ligand.  

PubMed

A newly developed P,N-bidentate ligand enables enantioselective intramolecular cyclopropanation by a reactive ?-oxo gold carbene intermediate generated in situ. The ligand design is based on our previously proposed structure (with a well-organized triscoordinated gold center) of the carbene intermediate in the presence of a P,N-bidentate ligand. A C2 -symmetric piperidine ring was incorporated in the ligand as the nitrogen-containing moiety. A range of racemic transformations of ?-oxo gold carbene intermediates have been developed recently, and this new class of chiral ligands could enable their modification for asymmetric synthesis, as demonstrated in this study. PMID:25431180

Ji, Kegong; Zheng, Zhitong; Wang, Zhixun; Zhang, Liming

2015-01-19

263

Enantioselective ring opening of epoxides by fluoride anion promoted by a cooperative dual-catalyst system.  

PubMed

An enantioselective method for the synthesis of beta-fluoroalcohols by catalytic nucleophilic fluorination of epoxides is described. Mild reaction conditions and high selectivity are made possible by the use of benzoyl fluoride as a soluble, latent source of fluoride anion. A chiral amine and chiral Lewis acid serve as cooperative catalysts for desymmetrizations of five- through eight-membered cyclic epoxides, affording products in up to 95% ee. The cocatalytic protocol is also effective for kinetic resolutions of racemic terminal epoxides, which proceed with k(rel) values as high as 300. PMID:20163118

Kalow, Julia A; Doyle, Abigail G

2010-03-17

264

Synthesis and catalytic applications of novel mesoporous aluminosilicate molecular sieves  

SciTech Connect

This paper reports on the synthesis of 4 series of mesoporous aluminosilicate molecular sieves (Al-MCM-41) and their catalytic applications. Four different Al compounds were examined as Al source in the hydrothermal synthesis, including pseudo boehmite (alumina), Al sulfate, Al isopropoxide, and Na aluminate. Each Al source was examined at 3 different feed Si/Al ratios in the synthesis. XRD results show that there are differences in the d{sub 100}-spacings for the samples prepared with different Al sources: Na aluminate > Al isopropoxide < Na aluminate. XRD also indicates that the synthesized Al-MCM-41 samples have different crystallinity. {sup 27}Al NMR and {sub 29}Si NMR reveal that most of the Al species in the samples prepared with pseudo boehmite were present in octahedral coordination, whereas in other samples nearly all the Al species are tetrahedral (in the framework). The acid characteristics of the synthesized molecular sieves were characterized by temperature-programmed desorption of n-butylamine, and by using 1,3,5-triisopropylbenzene hydrocracking as probe reaction. The results of TPD and probe reaction clearly indicate that the Al source used for synthesis has a major impact on the acidic and catalytic properties of Al-MCM-41. The samples prepared with Al isopropoxide and Na aluminate are better as catalysts than those with Al sulfate and pseudo boehmite. They also explored the potential of mesoporous molecular sieves as support for noble metal hydrogenation catalysts and metal sulfide-based hydrotreating catalysts. Pd and Pt-loaded mesoporous molecular sieves were prepared and applied for hydrogenation of naphthalene and phenanthrene. The results show that mesoporous molecular sieve-supported catalysts are much more active than alumina- and titania-supported catalysts. The data for dibenzothiophene hydrodesulfurization suggest that Al-MCM-41 supported Co-Mo may be effective for deep desulfurization of distillate fuels.

Reddy, K.M.; Song, C. [Pennsylvania State Univ., University Park, PA (United States)

1997-12-31

265

Perfluorophenyl Azides: New Applications in Surface Functionalization and Nanomaterial Synthesis  

PubMed Central

Conspectus A major challenge in materials science is the ongoing search for coupling agents that are readily synthesized, capable of versatile chemistry, able to easily functionalize materials and surfaces, and efficient in covalently linking organic and inorganic entities. A decade ago, we began a research program investigating perfluorophenylazides (PFPAs) as the coupling agents in surface functionalization and nanomaterial synthesis. The p-substituted PFPAs are attractive heterobifunctional coupling agents because of their two distinct and synthetically distinguishable reactive centers: (i) the fluorinated phenylazide, which is capable of forming stable covalent adducts, and (ii) the functional group R, which can be tailored through synthesis. Two approaches have been undertaken for material synthesis and surface functionalization. The first method involves synthesizing PFPA bearing the first molecule or material with a functional linker R, and then attaching the resulting PFPA to the second material by activating the azido group. In the second approach, the material surface is first functionalized with PFPA via functional center R, and coupling of the second molecule or material is achieved with the surface azido groups. In this Account, we review the design and protocols of the two approaches, providing examples in which PFPA derivatives were successfully used in material surface functionalization, ligand conjugation, and the synthesis of hybrid nanomaterials. The methods developed have proved to be general and versatile, and they are applicable to a wide range of materials (especially those that lack reactive functional groups or are difficult to derivatize) and to various substrates of polymers, oxides, carbon materials, and metal films. The coupling chemistry can be initiated by light, heat, and electrons. Patterned structures can be generated by selectively activating the areas of interest. Furthermore, the process is easy to perform, and light activation occurs in minutes, greatly facilitating the efficiency of the reaction. PFPAs indeed demonstrate many benefits as versatile surface coupling agents and offer opportunities for further exploration. PMID:20690606

Liu, Li-Hong; Yan, Mingdi

2010-01-01

266

Vancomycin Molecular Interactions: Antibiotic and Enantioselective Mechanisms  

NASA Astrophysics Data System (ADS)

Medical studies established that vancomycin and other related macrocyclic antibiotics have an enhanced antimicrobial activity when they are associated as dimers. The carbohydrate units attached to the vancomycin basket have an essential role in the dimerization reaction. Covalently synthesized dimers were found active against vancomycin-resistant bacterial strains. A great similarity between antibiotic potential and enantioselectivity was established. A covalent vancomycin dimer was studied in capillary electrophoresis producing excellent chiral separation of dansyl amino acids. Balhimycin is a macrocyclic glycopeptide structurally similar to vancomycin. The small differences are, however, responsible for drastic differences in enantioselectivity in the same experimental conditions. Contributions from studies examining vancomycin's mechanism for antimicrobial activity have substantially aided our understanding of its mechanism in chiral recognition.

Ward, Timothy J.; Gilmore, Aprile; Ward, Karen; Vowell, Courtney

267

Acetic acid bacteria as enantioselective biocatalysts  

Microsoft Academic Search

Acetic acid bacteria (five strains of Acetobacter and five strains of Gluconobacter) were used for the biotransformation of different primary alcohols (2-chloropropanol and 2-phenylpropanol) and diols (1,3-butandiol, 1,4-nonandiol and 2,3-butandiol). Most of the tested strains efficiently oxidized the substrates. 2-Chloropropanol and 1,3-butandiol were oxidized with good rates and low enantioselectivity (enantiomeric excess=18–46% of the S-acid), while microbial oxidation of 2-phenylpropanol

A Romano; R Gandolfi; P Nitti; M Rollini; F Molinari

2002-01-01

268

Highly enantioselective organocatalytic ?-sulfenylation of azlactones.  

PubMed

The first asymmetric ?-sulfenylation of azlactones with N-(sulfanyl)succinimides has been developed by using cinchona alkaloid-derived squaramide as a catalyst and 4 Å molecular sieves as an additive. The reaction conditions were suitable to 4-alkyl and benzyl-substituted azlactones as well as N-(benzyl/alkyl/arylthio)succinimides, affording adducts with high enantioselectivities (81-94% ee). PMID:24432722

Qiao, Baokun; Liu, Xinfei; Duan, Shaobo; Yan, Lin; Jiang, Zhiyong

2014-02-01

269

Utilization of maltodextrin based enantioselective, potentiometric membrane electrodes for the enantioselective assay of S-perindopril.  

PubMed

Enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with different maltodextrins {dextrose equivalent (DE) 4.0-7.0 (I), 13.0-17.0 (II) and 16.5-19.5 (III)} as chiral selectors for the assay of S-perindopril is described. The proposed electrodes could be reliably employed in the assay of S-perindopril raw material and from its pharmaceutical formulation, Coversyl((R)) tablets. The electrode based on maltodextrin (I) showed the best enantioselectivity and time-stability. The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper. PMID:18969348

Ozoemena, Kenneth I; Stefan, Raluca-Ioana; van Staden, Jacobus F; Aboul-Enein, Hassan Y

2004-03-10

270

Nanocrystals-Related Synthesis, Assembly, and Energy Applications  

SciTech Connect

During the past decades, nanocrystals have attracted broad attention due to their unique shape- and size-dependent physical and chemical properties that differ drastically from their bulk counterparts. Hitherto, much effort has been dedicated to achieving rational controlling over the morphology, assembly, and related energy applications of the nanomaterials. Therefore, the ability to manipulate the morphology, size, and size distribution of inorganic nanomaterials is still an important goal in modern materials physics and chemistry. Especially, the world s demand for energy supply is causing a dramatic escalation of social and political unrest. Likewise, the environmental impact of the global climate change due to the combustion of fossil fuel is becoming increasingly alarming. These problems compel us to search for effective routes to build devices that can supply sustainable energy, with not only high efficiency but also environmental friendship. One of ways to relieve the energy crisis is to exploit devices based on renewable energy sources, such as solar energy and water power. Aiming at this exploration, the primary stage requires the design of appropriate strategies for the synthesis of high-quality nanocrystals with respect to size uniformity and superior electrochemical performances. As a consequence, we organize the current special issue for Journal of Nanomaterials to provide the authors with a platform and readers with the latest achievements of nanocrystals-related synthesis, assembly, and energy applications.

Zou, Bo [Jilin University, Changchun; Yu, Williams [Worcester Polytechnic Institute; Seo, Jaetae [Hampton University; Zhu, Ting [Philips Lumileds Lighting Company; Hu, Michael Z. [ORNL

2012-01-01

271

Semiconducting black phosphorus: synthesis, transport properties and electronic applications.  

PubMed

Phosphorus is one of the most abundant elements preserved in earth, and it comprises a fraction of ?0.1% of the earth crust. In general, phosphorus has several allotropes, and the two most commonly seen allotropes, i.e. white and red phosphorus, are widely used in explosives and safety matches. In addition, black phosphorus, though rarely mentioned, is a layered semiconductor and has great potential in optical and electronic applications. Remarkably, this layered material can be reduced to one single atomic layer in the vertical direction owing to the van der Waals structure, and is known as phosphorene, in which the physical properties can be tremendously different from its bulk counterpart. In this review article, we trace back to the research history on black phosphorus of over 100 years from the synthesis to material properties, and extend the topic from black phosphorus to phosphorene. The physical and transport properties are highlighted for further applications in electronic and optoelectronics devices. PMID:25307017

Liu, Han; Du, Yuchen; Deng, Yexin; Ye, Peide D

2014-10-13

272

A carbohydrate approach for the formal total synthesis of (?)-aspergillide C  

PubMed Central

Summary An enantioselective formal total synthesis of aspergillide C is accomplished using commercially available tri-O-acetyl-D-galactal employing a Ferrier-type C-glycosylation, utilizing a Trost hydrosilylation and protodesilylation as key reactions.

Hari Krishna, Namballa; Sridhar, Ydhyam; Kamal, Ahmed

2014-01-01

273

Aerosol Route Synthesis and Applications of Doped Nanostructured Materials  

NASA Astrophysics Data System (ADS)

Nanotechnology presents an attractive opportunity to address various challenges in air and water purification, energy, and other environment issues. Thus, the development of new nanoscale materials in low-cost scalable synthesis processes is important. Furthermore, the ability to independently manipulate the material properties as well as characterize the material at different steps along the synthesis route will aide in product optimization. In addition, to ensure safe and sustainable development of nanotechnology applications, potential impacts need to be evaluated. In this study, nanomaterial synthesis in a single-step gas phase reactor to continuously produce doped metal oxides was demonstrated. Copper-doped TiO2 nanomaterial properties (composition, size, and crystal phase) were independently controlled based on nanoparticle formation and growth mechanisms dictated by process control parameters. Copper dopant found to significantly affect TiO2 properties such as particle size, crystal phase, stability in the suspension, and absorption spectrum (shift from UV to visible light absorption). The in-situ charge distribution characterization of the synthesized nanomaterials was carried out by integrating a tandem differential mobility analyzer (TDMA) set up with the flame reactor synthesis system. Both singly- and doubly- charged nanoparticles were measured, with the charged fractions dependent on particle mobility and dopant concentration. A theoretical calculation was conducted to evaluate the relative importance of the two charging mechanisms, diffusion and thermo-ionization, in the flame. Nanoparticle exposure characterization was conducted during synthesis as a function of operating condition, product recovery and handling technique, and during maintenance of the reactors. Strategies were then indentified to minimize the exposure risk. The nanoparticle exposure potential varied depending on the operating conditions such as precursor feed rate, working conditions of the fume hood, ventilation system, and distance from the reactors. Nanoparticle exposure varied during product recovery and handling depending on the quantity of nanomaterial handled. Most nanomaterial applications require nanomaterials to be in solution. Thus, the role of nanomaterial physio-chemical properties (size, crystal phase, dopant types and concentrations) on dispersion properties was investigated based on hydrodynamic size and surface charge. Dopant type and concentration were found to significantly affect iso-electric point (IEP)-shifting the IEP to a high or lower pH value compared to pristine TiO2 based on the oxidation state of the dopant. The microbial inactivation effectiveness of as-synthesized nanomaterials was investigated under different light irradiation conditions. Microbial inactivation was found to strongly depend on the light irradiation condition as well as on material properties such chemical composition, crystal phase, and particle size. The potential interaction mechanisms of copper-doped TiO2 nanomaterial with microbes were also explored. The studies conducted as part of this dissertation addressed issues in nanomaterial synthesis, characterization and their potential environmental applications.

Sahu, Manoranjan

274

Enantioselective Biotransformation of Chiral PCBs in Whole Poplar Plants  

PubMed Central

Chiral PCBs have been used as molecular probes of biological metabolic processes due to their special physical, chemical and biological properties. Many animal studies showed the enantioselective biotransformation of chiral PCBs, but it is unclear whether plants can enantioselectively biotransform chiral PCBs. In order to explore the enantioselectivity of chiral PCBs in whole plants, poplars (Populus deltoides × nigra, DN34), a model plant with complete genomic sequence, were hydroponically exposed to 2,2?,3,5?,6-pentachlorobiphenyl (PCB95) and 2,2?,3,3?,6,6?-hexachlorobiphenyl (PCB136) for 20 days. PCB95 and PCB136 were shown to be absorbed, taken-up and translocated in whole poplars, and they were detected in various tissues of whole poplars. However, the enantioselectivity of poplar for PCB95 and PCB136 proved to be quite different. The first eluting enantiomer of PCB95 was enantioselectively removed in whole poplar, especially in the middle and bottom xylem. It was likely enantioselectively metabolized inside poplar tissues, in contrast to racemic mixtures of PCB95 remaining in hydroponic solutions in contact with plant roots of whole and dead poplars. Unlike PCB95, PCB136 remained nearly racemic in most parts of whole poplars after 20 days exposure. These results suggest that PCB136 is more difficult to be enantioslectively biotransformed than PCB95 in whole poplars. This is the first evidence of enantioselectivity of chiral PCBs in whole plants, and suggests that poplars can enantioselectively biotransform at least one chiral PCB. PMID:21329345

Zhai, Guangshu; Hu, Dingfei; Lehmler, Hans-Joachim; Schnoor, Jerald L.

2011-01-01

275

Enantioselective biotransformation of chiral PCBs in whole poplar plants.  

PubMed

Chiral PCBs have been used as molecular probes of biological metabolic processes due to their special physical, chemical, and biological properties. Many animal studies showed the enantioselective biotransformation of chiral PCBs, but it is unclear whether plants can enantioselectively biotransform chiral PCBs. In order to explore the enantioselectivity of chiral PCBs in whole plants, poplars (Populus deltoides × nigra, DN34), a model plant with complete genomic sequence, were hydroponically exposed to 2,2',3,5',6-pentachlorobiphenyl (PCB95) and 2,2',3,3',6,6'-hexachlorobiphenyl (PCB136) for 20 days. PCB95 and PCB136 were shown to be absorbed, taken-up and translocated in whole poplars, and they were detected in various tissues of whole poplars. However, the enantioselectivity of poplar for PCB95 and PCB136 proved to be quite different. The first eluting enantiomer of PCB95 was enantioselectively removed in whole poplar, especially in the middle and bottom xylem. It was likely enantioselectively metabolized inside poplar tissues, in contrast to racemic mixtures of PCB95 remaining in hydroponic solutions in contact with plant roots of whole and dead poplars. Unlike PCB95, PCB136 remained nearly racemic in most parts of whole poplars after 20 days exposure. These results suggest that PCB136 is more difficult to be enantioslectively biotransformed than PCB95 in whole poplars. This is the first evidence of enantioselectivity of chiral PCBs in whole plants, and suggests that poplars can enantioselectively biotransform at least one chiral PCB. PMID:21329345

Zhai, Guangshu; Hu, Dingfei; Lehmler, Hans-Joachim; Schnoor, Jerald L

2011-03-15

276

Highly enantioselective hydrogenation of enamides catalyzed by chiral phosphoric acids.  

PubMed

A highly enantioselective hydrogenation of enamides catalyzed by a dual chiral-achiral acid system was developed. By employing a substoichiometric amount of a chiral phosphoric acid and acetic acid, catalyst loadings as low as 1 mol % of the chiral catalyst were sufficient to provide excellent yield and enantioselectivity of the reduction product. PMID:19199770

Li, Guilong; Antilla, Jon C

2009-03-01

277

Dual catalysis in enantioselective oxidopyrylium-based [5 + 2] cycloadditions.  

PubMed

A new method for effecting catalytic enantioselective intramolecular [5 + 2] cycloadditions based on oxidopyrylium intermediates is reported. The dual catalyst system consists of a chiral primary aminothiourea and a second achiral thiourea. Experimental evidence points to a new type of cooperative catalysis with each species being necessary to generate a reactive pyrylium ion pair that undergoes subsequent cycloaddition with high enantioselectivity. PMID:21848300

Burns, Noah Z; Witten, Michael R; Jacobsen, Eric N

2011-09-21

278

Enantioselective artificial metalloenzymes based on a bovine pancreatic polypeptide scaffold.  

PubMed

Site creation: Enantioselective artificial metalloenzymes have been created by grafting a new active site onto bovine pancreatic polypeptide through the introduction of an amino acid capable of coordinating a copper(II) ion. This hybrid catalyst gave good enantioselectivities in the Diels-Alder and Michael addition reactions in water (see scheme) and displayed a very high substrate selectivity. PMID:19557756

Coquière, David; Bos, Jeffrey; Beld, Joris; Roelfes, Gerard

2009-01-01

279

Supercritical fluid chromatography as a tool for enantioselective separation; a review.  

PubMed

Supercritical fluid chromatography (SFC) has become popular in the field of enantioselective separations. Many works have been reported during the last years. This review covers the period from 2000 till August 2013. The article is divided into three main chapters. The first one comprises a basic introduction to SFC. The authors provide a brief explanation of general principles and possibilities of this method. The advantages and drawbacks are also listed. Next part deals with chiral separation systems available in SFC, namely with the commonly used chiral stationary phases. Properties and interaction possibilities of the chiral separation systems are described. Recent theoretical papers are emphasized in this chapter. The last part of the paper gives an overview of applications of enantioselective SFC in analytical chemistry, in both analytical and preparative scales. Separation systems and conditions are summed up in tables so that they provide a helpful tool for analysts who search for a particular method of analysis. PMID:24703210

Kalíková, Kv?ta; Slechtová, Tereza; Vozka, Ji?í; Tesa?ová, Eva

2014-04-22

280

Enantioselective quantitative analysis of amphetamine in human plasma by liquid chromatography/high-resolution mass spectrometry.  

PubMed

A method for the quantitative enantioselective analysis of amphetamine in human plasma by LC-HRMS is presented. High-resolution detection, alone and in combination with targeted MS/MS, was validated and compared to a highly sensitive GC-NICI-Method. Derivatization with (S)-N-(heptafluorobutyryl)-prolyl chloride was accomplished to yield derivatives suitable for enantioselective analysis of amphetamine on a nonchiral reversed phase column with MS-compatible mobile phase. Equal analytical performance was observed for the methods presented and the GC-NICI-MS method. A dynamic range of 4,000 was found for the established calibration curves. A fivefold deuterated analogue of both enantiomeres was used as an internal standard. Full validation data are given to demonstrate the usefulness of the assay, including specificity, linearity, accuracy and precision, autosampler stability, matrix effect, and prospective analytical batch size accuracy. The method has been successfully applied to pharmacokinetic profiling of the drug after oral application. PMID:24825764

Leis, Hans J; Fauler, Günter; Windischhofer, Werner

2014-07-01

281

Synthesis and Applications of Non-spherical Dimer Colloids  

NASA Astrophysics Data System (ADS)

Colloids are promising building blocks in material synthesis because of their controllability of size and surface properties. The synthesis of chemically and/or geometrically anisotropic colloidal particles has received attentions with the expectation of building blocks for complex structures. However, the synthesis of anisotropic colloidal particles is by far more difficult than the synthesis of spherical colloidal particles. Lack of monodispersity and productivity of many anisotropic particles often limits their applications as a building block for complex structures. Thus, it is highly desirable to develop methods which can produce a large amount of monodisperse non-spherical particles with controllable asymmetric surface properties. This dissertation details the work for developing such a method. The major result of this dissertation is a synthetic method to produce monodisperse non-spherical colloids with anisotropic surface property in a large quantity. The anisotropic colloid, which we call it as Dimer particle, has two fused lobes like a dumbbell and each lobe's size can be independently controlled. We present a novel method to synthesize sub-micron size Dimer particles. This method can produce a large amount of submicron-sized Dimer particles with good monodispersity and well-controlled shape. Submicron-sized Dimer particles have been highly desired since they can be used as a building block for self assembly using Brownian motion, colloidal surfactant for Pickering emulsion, and photonic materials. To fully take advantage of the anisotropy of the particles, we develop a facile method to tailor the surface property of each lobe independently by asymmetrically coating the particles with gold nanoparticles. This method doesn't need the arrangement of particles onto any type of interfaces. Asymmetric coating of gold nanoparticles can be carried out simply by mixing Dimer particles with gold nanoparticles. The formation mechanism of the submicron-sized Dimer particles is explained with evidences. Finally, we illustrate that Dimer particles show rich phase behavior under electric fields and explain the behavior by considering various interactions involved in the system. Our investigation shows that electric field can effectively control the orientation and assembled structure of Dimer particles. In conclusion, these asymmetrically functionalized Dimer particles are promising building blocks to generate suprastructures that will be useful in photonic, electronic and diagnostic applications.

Yoon, Kisun

282

Chiral separation by enantioselective liquid-liquid extraction.  

PubMed

The literature on enantioselective liquid-liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid-liquid extraction is a technology of interest for a wide range of chemists and chemical engineers in the fields of fine chemicals, pharmaceuticals, agrochemicals, fragrances and foods. In this review the principles and advances of resolution through enantioselective liquid-liquid extraction are discussed, starting with an introduction on the principles of enantioselective liquid-liquid extraction including host-guest chemistry, extraction and phase transfer mechanisms, and multistage liquid-liquid extraction processing. Then the literature on enantioselective liquid-liquid extraction systems is reviewed, structured on extractant classes. The following extractant classes are considered: crown ether based extractants, metal complexes and metalloids, extractants based on tartrates, and a final section with all other types of chiral extractants. PMID:21107491

Schuur, Boelo; Verkuijl, Bastiaan J V; Minnaard, Adriaan J; de Vries, Johannes G; Heeres, Hero J; Feringa, Ben L

2011-01-01

283

Catalytic asymmetric assembly of octahydroindolones: divergent synthesis of lycorine-type amaryllidaceae alkaloids (+)-?-lycorane and (+)-lycorine.  

PubMed

We report the first catalytic asymmetric approach to octahydroindolones and a divergent enantioselective synthesis of perhydroindole alkaloids, as exemplified by lycorine-type Amaryllidaceae alkaloids (+)-?-lycorane and (+)-lycorine, from a common intermediate by using a highly concise route. The assembly of octahydroindolones employs a catalytic enantioselective 1,4-conjugate addition of nitro dienynes, followed by a TsOH-catalyzed cascade synthesis of highly functionalized enones, and a diastereoselective intramolecular Michael addition. PMID:24700723

Sun, Zhongwen; Zhou, Mingtao; Li, Xiang; Meng, Xueling; Peng, Fangzhi; Zhang, Hongbin; Shao, Zhihui

2014-05-12

284

Carbon nanotubes and tungsten oxide nanorods: Synthesis and applications  

NASA Astrophysics Data System (ADS)

Synthesis and applications of two types of one-dimensional nanomaterials, carbon nanotubes (CNTs) and tungsten oxide nanorods, are investigated in this dissertation. Multi-walled CNTs have been successfully synthesized using two types of chemical vapor deposition (CVD) methods: microwave plasma enhanced CVD and atmospheric pressure thermal CVD. CNTs and their synthesis processes are characterized with various analysis techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and optical emission spectroscopy. Ultra-thin and high quality multi-walled CNTs are discovered in CNT films produced by MPCVD, which exhibit good field emission performance that is found to be dependent on the synthesis conditions, like the growth time and CH4/H2 flow ratio. CNTs grown by thermal CVD have similar field emission performance. Based on silicon surface micromachining techniques and thermal CVD method, a self-aligned method has been developed to fabricate CNT based gated field emitter arrays (FEAs) which demonstrate low turn-on voltage and good emission current. Tungsten oxide nanorods have been synthesized on various tungsten substrates via thermal annealing in argon at atmospheric pressure. Nanorod growth mechanism is proposed based on thermal oxidation of tungsten in gas ambient with a very low partial pressure of oxygen as well as the self-catalytic effect on tungsten surface. The lattice structure and composition of the tungsten oxide nanorods are observed and analyzed using high resolution TEM, selected area electron diffraction (SAD), and energy dispersive X-ray spectroscopy (EDXS). The analysis results reveal that the lattice structure of the tungsten oxide nanorods is closest to that of the monoclinic WO3 crystal. Tungsten oxide nanorods have been successfully grown on tungsten tips for use in scanning tunneling microscope (STM) as probes which readily produce atomic resolution images on sample surface. Nanorod based FEAs are also successfully fabricated using similar techniques as those for fabricating CNTs based FEAs. Low turn-on voltage and low gate current are achieved.

Xiao, Bing

285

Applications of ultrasound to the synthesis of nanostructured materials.  

PubMed

Recent advances in nanostructured materials have been led by the development of new synthetic methods that provide control over size, morphology, and nano/microstructure. The utilization of high intensity ultrasound offers a facile, versatile synthetic tool for nanostructured materials that are often unavailable by conventional methods. The primary physical phenomena associated with ultrasound that are relevant to materials synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive collapse of bubbles in a liquid) creates extreme conditions inside the collapsing bubble and serves as the origin of most sonochemical phenomena in liquids or liquid-solid slurries. Nebulization (the creation of mist from ultrasound passing through a liquid and impinging on a liquid-gas interface) is the basis for ultrasonic spray pyrolysis (USP) with subsequent reactions occurring in the heated droplets of the mist. In both cases, we have examples of phase-separated attoliter microreactors: for sonochemistry, it is a hot gas inside bubbles isolated from one another in a liquid, while for USP it is hot droplets isolated from one another in a gas. Cavitation-induced sonochemistry provides a unique interaction between energy and matter, with hot spots inside the bubbles of approximately 5000 K, pressures of approximately 1000 bar, heating and cooling rates of >10(10) K s(-1); these extraordinary conditions permit access to a range of chemical reaction space normally not accessible, which allows for the synthesis of a wide variety of unusual nanostructured materials. Complementary to cavitational chemistry, the microdroplet reactors created by USP facilitate the formation of a wide range of nanocomposites. In this review, we summarize the fundamental principles of both synthetic methods and recent development in the applications of ultrasound in nanostructured materials synthesis. PMID:20401929

Bang, Jin Ho; Suslick, Kenneth S

2010-03-12

286

Synthesis, characterisation, and applications of Mn-Zn ferrite nanoparticles  

NASA Astrophysics Data System (ADS)

This paper deals with the synthesis, characterization, and some applications of Mn-Zn ferrite nanoparticles. The Mn-Zn ferrite was prepared from metallic nitrates, iron citrate and citric acid with the co-precipitation method with different pH values and it was further used to synthesis Mn-Zn ferrite with polariser i.e. H IIO II (Hydrogen peroxide). The X-ray diffraction pattern shows the single phase spinel structure of the ferrites. The effect of pH and the oxidizing agent on the electrical properties of Mn-Zn ferrite was studied. The d.c. resistivity is improved with the pH value and further improved by the addition of H IIO II (Hydrogen peroxide), which acts as a strong oxidizing agent. The dielectric constant decreases with increasing pH value; at the same time the dielectric loss also decreases. Further the decrease in dielectric properties by addition of oxidizing agent are justified by inverse proportionality between resistivity and dielectric constant.

Lal, Madan; Sharma, D. K.; Singh, M.

2006-03-01

287

Nanoparticles for hyperthermic therapy: synthesis strategies and applications in glioblastoma.  

PubMed

Glioblastoma multiforme (GBM) is the most common and most aggressive malignant primary brain tumor in humans. Current GBM treatment includes surgery, radiation therapy, and chemotherapy, sometimes supplemented with novel therapies. Despite recent advances, survival of GBM patients remains poor. Major challenges in GBM treatment are drug delivery across the blood-brain barrier, restriction of damage to healthy brain tissues, and limitation of resistance to therapies. This article reviews recent advances in the application of magnetic nanoparticles (MNPs), gold nanorods (GNRs), and carbon nanotubes (CNTs) for hyperthermia ablation of GBM. First, the article introduces GBM, its current treatment, and hyperthermia as a potential modality for the management of GBM. Second, it introduces MNPs, GNRs, and CNTs as inorganic agents to induce hyperthermia in GBM. Third, it discusses different methodologies for synthesis of each inorganic agent. Finally, it reviews in vitro and in vivo studies in which MNPs, GNRs, and CNTs have been applied for hyperthermia ablation and drug delivery in GBM. PMID:24959075

Verma, Jyoti; Lal, Sumit; Van Noorden, Cornelis J F

2014-01-01

288

Nanoparticles for hyperthermic therapy: synthesis strategies and applications in glioblastoma  

PubMed Central

Glioblastoma multiforme (GBM) is the most common and most aggressive malignant primary brain tumor in humans. Current GBM treatment includes surgery, radiation therapy, and chemotherapy, sometimes supplemented with novel therapies. Despite recent advances, survival of GBM patients remains poor. Major challenges in GBM treatment are drug delivery across the blood–brain barrier, restriction of damage to healthy brain tissues, and limitation of resistance to therapies. This article reviews recent advances in the application of magnetic nanoparticles (MNPs), gold nanorods (GNRs), and carbon nanotubes (CNTs) for hyperthermia ablation of GBM. First, the article introduces GBM, its current treatment, and hyperthermia as a potential modality for the management of GBM. Second, it introduces MNPs, GNRs, and CNTs as inorganic agents to induce hyperthermia in GBM. Third, it discusses different methodologies for synthesis of each inorganic agent. Finally, it reviews in vitro and in vivo studies in which MNPs, GNRs, and CNTs have been applied for hyperthermia ablation and drug delivery in GBM. PMID:24959075

Verma, Jyoti; Lal, Sumit; Van Noorden, Cornelis JF

2014-01-01

289

Enantioselective total syntheses of manzamine a and related alkaloids.  

PubMed

As a prelude to undertaking the total syntheses of the complex manzamine alkaloids, a series of model studies were conducted to establish the scope and limitations of intramolecular [4 + 2] cycloadditions of N-acylated vinylogous ureas with the trienic substrates 17a,b, 28a,b, and 34. These experiments clearly demonstrated that the geometry of the internal double bond and the presence of an electron-withdrawing group on the diene moiety were essential for the facile and stereoselective formation of the desired cycloadducts. The enantioselective syntheses of the manzamine alkaloids ircinol A (75), ircinal A (5), and manzamine A (1) were then completed by employing a convergent strategy that featured a novel domino Stille/Diels-Alder reaction to construct the tricyclic ABC ring core embodied in these alkaloids. Thus, the readily accessible chiral dihydropyrrole 58 was first converted in a single chemical operation into the key tricyclic intermediate 60. Two ring-closing metathesis reactions were then used to form the 13- and 8-membered rings leading to Z-72 and 74, the latter of which was quickly elaborated into ircinal A (5) via ircinol A (75). The synthetic 5 thus obtained was converted into manzamine A (1) following literature precedent. This concise synthesis of ircinal A required a total of 24 operations from commercially available starting materials with the longest linear sequence being 21 steps. PMID:12121099

Humphrey, John M; Liao, Yusheng; Ali, Amjad; Rein, Tobias; Wong, Yue-Ling; Chen, Hui-Ju; Courtney, Anne K; Martin, Stephen F

2002-07-24

290

DNA-based hybrid catalysts for asymmetric organic synthesis.  

PubMed

Stereoselective hybrid systems based on metal-assisted catalysis with a chiral biomacromolecule form an attractive research area for the synthesis of enantiomerically pure compounds. Although various methods are available for this purpose, most rely on the use of enzymes, proteins, or RNA. The application of DNA-based hybrid catalysts for enantioselective synthesis emerged only a few years ago. DNA-based hybrid catalysts have been self-assembled from DNA and a metal complex with a specific ligand through supramolecular or covalent anchoring strategies and have demonstrated high stereoselectivity and rate enhancement in Lewis acid catalyzed reactions, such as Diels-Alder, Michael addition, and Friedel-Crafts reactions. For these reactions, cheap and commercially available salmon testes DNA has generally been used. In this Minireview, we summarize recent developments in the area of asymmetric catalysis with DNA-based hybrid catalysts. PMID:20455226

Park, Soyoung; Sugiyama, Hiroshi

2010-05-25

291

Synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles.  

PubMed

In this article we describe the synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles (DENs). These materials are synthesized by a template approach in which metal ions are extracted into the interior of dendrimers and then subsequently chemically reduced to yield nearly size-monodisperse particles having dimensions of less than 3 nm. Monometallic, bimetallic (including core/shell), and semiconductor nanoparticles have been prepared by this route. The dendrimer component of these composites serves not only as a template for preparing the nanoparticle replica but also to stabilize the nanoparticle, makes it possible to tune solubility, and provides a means for immobilization of the nanoparticle on solid supports. These materials have a number of potential applications, but the focus here is on catalysis. Homogeneous catalytic reactions, including hydrogenations, Heck coupling, and Suzuki reactions, in water, organic solvents, biphasic fluorous/organic solvents, and liquid and supercritical CO2 are discussed. In many cases it is easy to recycle catalytic DENs. DENs can also be immobilized on supports, such as silica and titania, and used for heterogeneous catalysis. Bimetallic DENs are shown to have particularly interesting catalytic properties. In addition to a discussion of current progress in this field, a number of intriguing questions related to the properties and potential applications of these materials are examined. PMID:16866429

Scott, Robert W J; Wilson, Orla M; Crooks, Richard M

2005-01-20

292

Solution synthesis, optical properties, and bioimaging applications of silicon nanocrystals.  

PubMed

Understanding and unlocking the potential of semiconductor nanocrystals (NCs) is important for future applications ranging from biomedical imaging contrast agents to the next generation of solar cells and LEDs. Silicon NCs (Si NCs) have key advantages compared with other semiconductor NCs due to silicon's high natural abundance, low toxicity and strong biocompatibility, and unique size, and surface dependent optical properties. In this Account, we review and discuss the synthesis, surface modification, purification, optical properties, and applications of Si NCs. The synthetic methods used to make Si NCs have improved considerably in the last 5-10 years; highly monodisperse Si NCs can now be produced on the near gram scale. Scaled-up syntheses have allowed scientists to drive further toward the commercial utilization of Si NCs. The synthesis of doped Si NCs, through addition of a simple elemental precursor to a reaction mixture or by the production of a single source precursor, has shown great promise. Doped Si NCs have demonstrated unique or enhanced properties compared with pure Si NCs, for example, magnetism due to the presence of magnetic metals like Fe and Mn. Surface reactions have reached a new level of sophistication where organic (epoxidation and diol formation) and click (thiol based) chemical reactions can be carried out on attached surface molecules. This has led to a wide range of biocompatible functional groups as well as a degree of emission tuneability. The purification of Si NCs has been improved through the use of size separation columns and size selective precipitation. These purification approaches have yielded highly monodisperse and pure Si NCs previously unachieved. This has allowed scientists to study the size and surface dependent properties and toxicity and enabled the use of Si NCs in biomedical applications. The optical properties of Si NCs are complex. Using a combination of characterization techniques, researchers have explored the relation between the optical properties and the size, surface functionalization, and preparation method. This work has led to a greater fundamental understanding of the unique optical properties of Si NCs. Si NCs are being studied for a wide range of important applications, including LEDS with tunable electroluminescence ranging from NIR to yellow, the encapsulation of Si NCs within micelles terminated with proteins to allow targeted in vivo imaging of cells, Si NC-polymer hybrid solar cells, and the use of Si NCs in battery anodes with high theoretical capacity and good charge retention. PMID:25252604

McVey, Benjamin F P; Tilley, Richard D

2014-10-21

293

Total syntheses of ?-lactone containing natural products: I. total synthesis of belactosin C II. synthetic studies toward spongiolactone  

E-print Network

The recently isolated bacterial metabolites, belactosins A-C from a fermentation broth of Streptomyces sp. UCK14, uniquely contain a ?-lactone dipeptide motif and exhibit anticancer activities. The enantioselective synthesis of (-)-belactosin C...

Cho, Sung Wook

2009-05-15

294

Application of -Synthesis based H-Control for Adaptive Optics in Laser Material Processing  

E-print Network

, adaptive optics (short AO) are considered appropriate means for a real-time compensation of the disApplication of µ-Synthesis based H-Control for Adaptive Optics in Laser Material Processing Steffen-- adaptive optics, robust control, H-control, material processing, µ-synthesis I. INTRODUCTION As the costs

Knobloch,Jürgen

295

Alphabetic Trees: Theory and Applications in Layout-Driven Logic Synthesis  

E-print Network

Alphabetic Trees: Theory and Applications in Layout-Driven Logic Synthesis Revision of TCAD synthesis which relies on alphabetic tree construction is presented. Alphabetic trees are trees which any internal edge crossing. First, a mechanism for generating all alphabetic trees on a given number

Pedram, Massoud

296

APPLICATION OF THE RATE OF NUCLEIC ACID SYNTHESIS TO THE STUDY OF MICROBIAL GROWTH  

E-print Network

APPLICATION OF THE RATE OF NUCLEIC ACID SYNTHESIS TO THE STUDY OF MICROBIAL GROWTH AND PRODUCTION. Stroup Tom Humphreys #12;ABSTRACT The rate of nucleic acid synthesis was used as a measure of growth grown under controlled conditions. These studies demonstrated that accurate rates of nucleic acid

Luther, Douglas S.

297

Application of ASP for Automatic Synthesis of Flexible Multiprocessor Systems from Parallel Programs  

E-print Network

Application of ASP for Automatic Synthesis of Flexible Multiprocessor Systems from Parallel. However, as the synthesis problem usually exhibits structure, Answer Set Programming (ASP), for which be effectively employed. This pa- per presents a design flow based on ASP that uses the solver clasp as back

Schaub, Torsten

298

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules  

NASA Astrophysics Data System (ADS)

A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules.

Ben-Moshe, Assaf; Wolf, Sharon Grayer; Sadan, Maya Bar; Houben, Lothar; Fan, Zhiyuan; Govorov, Alexander O.; Markovich, Gil

2014-07-01

299

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules.  

PubMed

A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules. PMID:25001884

Ben-Moshe, Assaf; Wolf, Sharon Grayer; Bar Sadan, Maya; Houben, Lothar; Fan, Zhiyuan; Govorov, Alexander O; Markovich, Gil

2014-01-01

300

Enantioselective esterification of racemic naproxen by lipases in organic solvent.  

PubMed

Enantioselective esterification of naproxen, 2-(6-methoxy-2-naphthyl) propionic acid, was attempted by lipases in nearly anhydrous isooctane. The nature of the alcohol affects the reactivity and enantioselectivity of the lipase from Candida cylindracea. Alcohols containing a trimethylsilyl group are highly reactive and enantioselective to the S-isomer of the acid. An optimal temperature around 65 degrees C and an enzyme concentration less than 7 mg ml-1 were proposed to resolve the racemate, with trimethylsilyl methanol as nucleophile, from a consideration of the enantiomeric ratio, the ester formation, and the resistance of mass transfer for the substrate. PMID:7764635

Tsai, S W; Wei, H J

1994-04-01

301

Diastereoselective bromination of compounds bearing a cyclohex-3-enol moiety: application to the enantioselective synthesis of (1R)-cis-deltamethrinic acid.  

PubMed

(1R)-cis-chrysanthemic acid has been prepared in a few steps with complete control of the relative and absolute stereochemistry. Some mechanistic aspect of the addition of bromine to the C,C double bond of 2,2,5,5-tetramethylcyclohex-3-enol is disclosed. PMID:19007137

Krief, Alain; Jeanmart, Stephane; Kremer, Adrian

2008-12-19

302

Synthesis of internally functionalized silica nanoparticles for theranostic applications  

NASA Astrophysics Data System (ADS)

This thesis addresses the synthesis and characterization of novel inorganic silica nanoparticle hybrids. It focuses in large part on their potential applications in the medical field. Silica acts as a useful carrier for a variety of compounds and this thesis silica will demonstrate its use as a carrier for boron or gadolinium. Boron-10 and gadolinium-157 have been suggested for the radiological treatment of tumor cells through the process called neutron capture therapy (NCT). Gadolinium is also commonly used as a Magnetic Resonance Imaging (MRI) contrast agent. Particles that carry it have potential theranostic applications of both imaging and treating tumors. Chapter 1 presents a background on synthetic strategies and usages of silica nanoparticles, and NCT theory. Chapter 2 describes a procedure to create mesoporous metal chelating silica nanoparticles, mDTTA. This is achieved via a co-condensation of tetraethoxysilane (TEOS) and 3-trimethoxysilyl-propyl diethylenetriamine (SiDETA) followed by a post-synthesis modification step with bromoacetic acid (BrAA). These particles have a large surface area and well-defined pores of ~2 nm. The mDTTA nanoparticles were used to chelate the copper(II), cobalt(II) and gadolinium(III). The chelating of gadolinium is the most interesting since it can be used as a MRI contrast agent and a neutron capture therapeutic. The synthetic procedure developed also allows for the attachment of a fluorophore that gives the gadolinium chelating mDTTA nanoparticles a dual imaging modality. Chapter 3 presents the synthetic method used to produce two classes of large surface area organically modified silica (ORMOSIL) nanoparticles. Condensating the organosilane vinyltrimethoxysilane in a micellar solution results in nanoparticles that are either surface rough (raspberry-like) or mesoporous nanoparticles, which prior to this thesis has not been demonstrated in ORMOSIL chemistry. Furthermore, the vinyl functionalities are modified, using hydroboration, to make the nanoparticles into water-dispersible boron carriers that also have potential boron neutron capture therapy (BNCT) applications. Lastly, Chapter 4 provides a general description of NCT, specifically that involving boron-10 and gadolinium-157. It further describes the synthetic methodology used in producing fatty acid coated boron nanoparticles (BNPs). The BNPs are encapsulated with silica to add a hydrophilic shell so that they can potentially be used in biological systems as BNCT agents. The silica shell is also modified with a fluorophore, dansyl chloride, so that the particle hybrid could be imaged during cell studies.

Walton, Nathan Isaac

303

Green synthesis and applications of Au-Ag bimetallic nanoparticles  

NASA Astrophysics Data System (ADS)

This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenol < k2-nitrophenol < k3-nitrophenol. Thermal conductivity is measured as a function of volume fraction and it is observed that the incorporation of the alloy nanoparticles enhances the thermal conductivity of the base fluid (water) showing nanofluid application. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field.

Meena Kumari, M.; Jacob, John; Philip, Daizy

2015-02-01

304

Synthesis, characterization and biosensing application of photon upconverting nanoparticles  

NASA Astrophysics Data System (ADS)

Phosphor/fluorescent molecules/particles have been widely used in various applications for quite some time. Typically, light with longer wavelength(s) is emitted when excited by shorter wavelength light. The opposite effect also exists, where a phosphor particle is excited with an infrared or red light and emits color(s) of shorter wavelengths, a process called up-conversion. Materials with upconverting properties have narrower absorption and line emission spectra than their down-converting counterparts. Because most non-target materials in a complex mixture do not possess such photon up-conversion properties, a dramatically improved S/N ratio is expected in sensing and luminescence reporting applications. This makes photon upconverting materials ideal for identification of trace amounts of target molecules. Here we report the synthesis, characterization and DNA detection application based on NaYF4:Yb3+, Er3+ photon upconverting nanoparticles. The design of a nucleotide sensor for the detection of point mutation associated with sickle cell disease is described. The underlying principle for the detection is luminescence resonance energy transfer (LRET), with the photon upconverting nanoparticle as the donor and a dye, N,N,N',N'-tetramethyl-6-carboxyrhodamine (TAMRA), as the acceptor. The detection scheme is based on a sandwich-type hybridization format. The presence of the target DNA is indicated by the increase of the normalized acceptor's emission. Based on photon upconverting nanoparticles, which display high S/N ratio and no photobleaching, the DNA sensor demonstrates high sensitivity and specificity. The results demonstrate great potential of such nanomaterials as oligonucleotide sensors.

Kumar, Manoj; Zhang, Peng

2009-02-01

305

Sustainable synthesis, characterization, and applications of metal oxide nanostructures  

NASA Astrophysics Data System (ADS)

Nanomaterials have attracted significant research focus due to their advantageous and unique properties (i.e. electronic, magnetic, optical, and mechanical) as compared with the bulk. Metal oxide nanostructures are of particular interest, as they are very robust and display high chemical and thermal stability, while offering a diverse array of fascinating properties. By reliably controlling the size, morphology, composition, and crystallinity of these nanostructures, their properties can be tuned for a specific purpose. These advantageous tailorable properties render them as ideal candidates for many applications such as catalysis, sensing, electronics, optoelectronics, energy storage, and even medicine. Driven by their increased popularity and potential applications, efforts to synthesize nanomaterials have moved toward environmentally-friendly methodologies, such as wet-chemical, molten-salt, hydrothermal, and sol-gel methods. We will discuss the green synthesis of strontium ruthenate (SrRuO 3), the yttrium manganese oxides (YMnO3 and YMn2O 5), and the magnetic spinel ferrites (MFe2O4 where 'M' is Mg, Fe, Co, Ni, Cu, and Zn) and our ability to reliably tune their properties for various applications. The effects of the molten salt parameters on the resulting particle size and morphology were explored for SrRuO 3 and the yttrium manganese oxides. For example, rapid cooling rates and the use of surfactants allowed us to produced faceted octahedra of SrRuO 3, which resulted in a 4-fold enhancement of their activity towards methanol oxidation with respect to smooth rounded particles. Similarly, using the hydrothermal method, we generated ferrite nanoparticles of different compositions and sizes. We investigated their potential as contrast agents for magnetic resonance imaging (MRI) and as photocatalysts, and observed significant differences as a function of both size and composition. Similarly, we will also examine surface and structural effects upon the electronic properties of V2O 3 nanowires.

Tiano, Amanda Lyn

306

BIOACCUMULATION AND ENANTIOSELECTIVE BIOTRANSFORMATION OF FIPRONIL AND SELECTED CONAZOLE FUNGICIDES  

EPA Science Inventory

In this research, dietary accumulation and enantioselective biotransformation were determined for rainbow trout (Oncorhynchus mykiss) exposed separately to the phenylpyrazole insecticide fipronil and to a series of selected conazole fungicides. Bioaccumulation of each pesticide ...

307

Target-directed synthesis of antibacterial drug candidate GSK966587.  

PubMed

An efficient enantioselective total synthesis of the potent antibiotic GSK966587 was accomplished. Highlights of the synthesis include two innovative Heck reactions, a highly selective zincate base directed ortho-metalation, Sharpless asymmetric epoxidation, and a fully convergent final step fragment coupling. PMID:20670007

Voight, Eric A; Yin, Hao; Downing, Susan V; Calad, Stacie A; Matsuhashi, Hayao; Giordano, Ilaria; Hennessy, Alan J; Goodman, Richard M; Wood, Jeffery L

2010-08-01

308

Catalytic Enantioselective Epoxidation of Tertiary Allylic- and Homoallylic Alcohols  

PubMed Central

An efficient and versatile method for the enantioselective epoxidation of both tertiary allylic- and homoallylic alcohols catalyzed by Hf(IV)-bishydroxamic acid (BHA) complexes is described. Asymmetric epoxidation, kinetic resolution, and desymmetrization have been developed demonstrating the flexible nature of the system, Hf(IV)-BHA. This is the first report in which these substrates were obtained with enantioselectivities up to 99%. PMID:23406082

Olivares-Romero, José Luis; Li, Zhi

2013-01-01

309

Salen Promoted Enantioselective Nazarov Cyclizations of Activated and Unactivated Dienones  

PubMed Central

A novel class of chiral 5,5?-di(2,4,6-trialkyl)aryl salen-metal complexes have been developed and shown to catalyze highly enantioselective Nazarov cyclization reactions, giving rise to cyclopentenoids in 90:10–98:2 er. Significantly, the catalysts also promote, for the first time, highly enantioselective Nazarov reactions of “unactivated” dienones, producing hydrindenone products having in place three contiguous chiral centers. PMID:23506509

Hutson, Gerri E.; Türkmen, Yunus E.; Rawal, Viresh H.

2014-01-01

310

Chiral bicyclic guanidine-catalyzed enantioselective reactions of anthrones.  

PubMed

Chiral bicyclic guanidine 1 was found to be an excellent catalyst for reactions between anthrones and various dienophiles. The catalyst can tolerate a range of substituents and substitution patterns, making several anthrone derivatives suitable for this reaction. Both Diels-Alder and Michael adducts were obtained in excellent yields, high regioselectivities, and high enantioselectivities. This is the first case of a highly enantioselective base-catalyzed anthrone Diels-Alder reaction. PMID:17044689

Shen, Juan; Nguyen, Thanh Truc; Goh, Yong-Peng; Ye, Weiping; Fu, Xiao; Xu, Junye; Tan, Choon-Hong

2006-10-25

311

Low dimensional silver nanostructures : synthesis, growth mechanism, properties and applications.  

E-print Network

??Synthesis of metal nanoparticles has recently attracted extensive research interest because of the importance of these materials' specific properties such as optical, electronic, magnetic, mechanical,… (more)

Xiong, Shixian

2011-01-01

312

New Applications of Boron Dihalides and Organotrifluoroborates in Organic Synthesis.  

E-print Network

??This dissertation summarizes research focused on the use of boron dihalides and organotrifluoroborates in organic synthesis. The boron dihalide mediated aryl propargyl ether cleavage reactions… (more)

Hall, Kelly Elizabeth

2013-01-01

313

Silver nanoparticles: synthesis, properties, toxicology, applications and perspectives  

NASA Astrophysics Data System (ADS)

In recent years the outbreak of re-emerging and emerging infectious diseases has been a significant burden on global economies and public health. The growth of population and urbanization along with poor water supply and environmental hygiene are the main reasons for the increase in outbreak of infectious pathogens. Transmission of infectious pathogens to the community has caused outbreaks of diseases such as influenza (A/H5N1), diarrhea (Escherichia coli), cholera (Vibrio cholera), etc throughout the world. The comprehensive treatments of environments containing infectious pathogens using advanced disinfectant nanomaterials have been proposed for prevention of the outbreaks. Among these nanomaterials, silver nanoparticles (Ag-NPs) with unique properties of high antimicrobial activity have attracted much interest from scientists and technologists to develop nanosilver-based disinfectant products. This article aims to review the synthesis routes and antimicrobial effects of Ag-NPs against various pathogens including bacteria, fungi and virus. Toxicology considerations of Ag-NPs to humans and ecology are discussed in detail. Some current applications of Ag-NPs in water-, air- and surface- disinfection are described. Finally, future prospects of Ag-NPs for treatment and prevention of currently emerging infections are discussed.

Tran, Quang Huy; Quy Nguyen, Van; Le, Anh-Tuan

2013-09-01

314

Surfactantless synthesis of silver nanoplates and their application in SERS.  

SciTech Connect

Silver nanoplates with thicknesses of 50-70 nm and edge lengths ranging from 200 nm to 1 mm are grown on semiconductor waters at room temperature through a simple galvanic reaction between an aqueous solution of silver nitrate and n-type GaAs. The as-grown silver structures have chemically clean surfaces because no surfactant or coordinating molecules are involved in the synthesis. Electron microscopy characterization indicates that each silver plate has rough surfaces and a half-moon morphology with one straight edge and on arclike edge. Systematic studies on varying reaction conditions reveal that the oxide (i.e., Ga{sub 2}O{sub 3} and As{sub 2}O{sub 3}) layers of GaAs, generated in situ in the reactions, play an important role in assisting the growth of anisotropic nanoplates. The cleanliness of the surfaces of the silver nanoplates is beneficial to attachment of interesting molecules on their surfaces for various applications, such as plasmonic-enhanced photophysical and photochemical processes and surface-enhanced spectroscopies.

Sun, Y.; Wiederrecht, G.; Center for Nanoscale Materials

2007-11-01

315

Synthesis and applications of quantum dots and magnetic quantum dots  

NASA Astrophysics Data System (ADS)

We have developed a new synthetic method for producing high-quality quantum dots (QDs) in aqueous solution for biological imaging applications. The glutathione-capped CdTe, ZnSe and Zn 1-xCd xSe alloyed QDs derived are tunable in fluorescence emissions between 360 nm and 700 nm. They show high quantum yields (QYs) of up to 50%, with narrow bandwidths of 19-55 nm. The synthesis of glutathione-capped QDs is simple and cost-effective compared to the conventional organometallic approaches. It can be easily scaled up for the commercial production of alloyed nanocrystals of various compositions. We have also demonstrated the fabrication of magnetic quantum dots (MQDs) through a seed-mediated approach. The formation and assembly of these bifunctional nanocomposites have been elucidated by high-resolution transmission electron microscopy (HRTEM). The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components in this hybrid system. We have created biocompatible silica-coated MQDs that effectively target the cell membranes.

Ying, Jackie Y.; Zheng, Yuangang; Selvan, S. Tamil

2008-02-01

316

Synthesis and Characterization of Dyes with Solar Energy Applications  

NASA Astrophysics Data System (ADS)

The sun provides Earth with a virtually limitless source of energy capable of sustaining all of humanity's needs. Photosynthetic organisms have exploited this energy for eons. However, efficiently converting solar radiation into a readily available and easily transportable form is complex. New materials with optimized physical, electrochemical, and photophysical properties are at the forefront of organic solar energy conversion research. In the work presented herein, porphyrin and organometallic dyes with widely-varied properties were studied for solar energy applications. In one project, porphyrins and porphyrin-fullerene dyads with aniline-like features were polymerized via electrochemical methods into semiconductive thin films. These were shown to have high visible light absorption and stable physical and electrochemical properties. However, experimentation using porphyrin polymer films as both the light absorber and semiconductor in a photoelectrochemical cell showed relatively low efficiency of converting absorbed solar energy into electricity. In separate work, tetra-aryl porphyrin derivatives were examined in conjunction with wide-bandgap semiconductive oxides TiO2 and SnO2. Carboxylic acid-, phosphonic acid-, and silatrane-functionalized porphyrins were obtained or synthesized for attachment to the metal oxide species. Electrochemical, photophysical, photoelectrochemical, and surface stability studies of the porphyrins were performed for comparative purposes. The order of surface linkage stability on TiO2 in alkaline conditions, from most stable to least, was determined to be siloxane > phosphonate > carboxylate. Finally, porphyrin dimers fused via their meso and beta positions were synthesized using a chemical oxidative synthesis with a copper(II) oxidant. The molecules exhibit strong absorption in the visible and near-infrared spectral regions as well as interesting electrochemical properties suggesting possible applications in light harvesting and redox catalysis.

Brennan, Bradley J.

317

Synthesis, characterizations, and applications of carbon nanotubes and silicon nanowires  

NASA Astrophysics Data System (ADS)

Carbon nanotubes (CNTs) have received great attention because of their unique structure and promising applications in microelectronic devices such as field electron emitters. Silicon nanowires (SiNWs) are also very popular because Si is a well established electronic material. This thesis will present my effort on synthesis, characterizations, and applications of CNTs and SiNWs by thermal chemical vapor deposition (CVD) method. For CNTs growth, block copolymer micelles were used as a template to create large area arrays of metal nanoclusters as catalysts for patterned arrays, and Fe/Al/Fe sandwich film on single crystal magnesium oxide (MgO) substrate was used as the catalyst for growth of long length aligned CNTs by CVD. The factors that affect the structure and length of CNTs have been investigated. CNTs were also grown on etched Si substrate by PECVD method. Continuous dropwise condensation was achieved on a biomimetic two-tier texture with short CNTs deposited on micromachined pillars. Superhydrophobic condensation model was studied. For SiNWs growth, hydrogen gold tetrachloride was uniformly mixed into the salt and decomposed into gold nanoparticles at the growth temperature and acted as the catalyst particles to start the growth of Si nanowires. The as-grown Si nanowires are about 70--90 nm in diameter and up to 200 micrometers long. The salt was completely removed by water rinse after growth. Field emission of aligned CNTs grown on Si substrates and SiNWs on Si substrates and carbon clothes has been studied. A post growth annealing procedure has been found to drastically improve the field emission performance of these CNTs and SiNWs.

Xiong, Guangyong

318

Synthesis and characterization of advanced nanomaterials for energy applications  

NASA Astrophysics Data System (ADS)

Energy is essential for life. It is thus important to continue understanding how to reduce energy consumption, and increase energy generation. The use of nanoscale materials (nanomaterials) are expected to reduce resources and energy needed in fabricating electrical and electronic devices and help in reducing energy consumption. For example, boron nitride nanotubes (BNNTs) which have uniform band structures, are expected to find application in nanoscale electronic and optoelectronic devices. These devices will have smaller dimension, cost fewer resources and less energy to fabricate, and consume less energy due to minimum electron scattering in their ideally defect-free tubular structures. On the other hand, nanomaterials are also expected to improve the performance of thermoelectric devices that can convert heat into energy. In this thesis, we first investigated low-temperature synthesis of BNNTs (Chapter 1). Effects of substrate temperatures, bias voltages, and catalysts are discussed and a selective-phase growth model is proposed. During the course of this investigation, we discovered Si nanotubes (SiNTs) by catalytic plasma treatment (Chapter 2). The detailed growth parameters and characterizations are presented and a modified growth model is discussed. In addition, electronic properties are measured by AFM. Since Si has exceptional thermoelectric properties, the newly discovered SiNTs are prospects for related applications. We have thus evaluated the potential conversion efficiency and production cost of various nanostructured thermoelectric materials (Chapter 3 and 4). Based on state-of-the-art dish-stirling systems, we evaluate the feasibility of replacing stirling engines by thermoelectric modules. Finally, we have decided to investigate the properties of boron-nanocarbon ensembles (Chapter 5 and 6) as prospective thermoelectric materials. Detailed characterizations includes SEM, HRTEM, Raman, XRD are presented. Seebeck coefficient and electrical conductivity are both measured with various temperatures. Induction quenching confirms that boron-doping help improve power factor of nanocarbon ensembles.

Xie, Ming

319

Synthesis, assembly, and applications of single-walled carbon nanotube  

NASA Astrophysics Data System (ADS)

This dissertation presents the synthesis and assembly of aligned carbon nanotubes, and their applications in both nano-electronics such as transistor and integrated circuits and macro-electronics in energy conversion devices as transparent conducting electrodes. Also, the high performance chemical sensor using metal oxide nanowire has been demonstrated. Chapter 1 presents a brief introduction of carbon nanotube, followed by discussion of a new synthesis technique using nanosphere lithography to grow highly aligned single-walled carbon nanotubes atop quartz and sapphire substrates. This method offers great potential to produce carbon nanotube arrays with simultaneous control over the nanotube orientation, position, density, diameter and even chirality. Chapter 3 introduces the wafer-scale integration and assembly of aligned carbon nanotubes, including full-wafer scale synthesis and transfer of massively aligned carbon nanotube arrays, and nanotube device fabrication on 4 inch Si/SiO2 wafer to yield submicron channel transistors with high on-current density ˜ 20 muA/mum and good on/off ratio and CMOS integrated circuits. In addition, various chemical doping methods for n-type nanotube transistors are studied to fabricate CMOS integrated nanotube circuits such as inverter, NAND and NOR logic devices. Furthermore, defect-tolerant circuit design for NAND and NOR is proposed and demonstrated to guarantee the correct operation of logic circuit, regardless of the presence of mis-aligned or mis-positioned nanotubes. Carbon nanotube flexible electronics and smart textiles for ubiquitous computing and sensing are demonstrated in chapter 4. A facile transfer printing technique has been introduced to transfer massively aligned single-walled carbon nanotubes from the original sapphire/quartz substrates to virtually any other substrates, including glass, silicon, polymer sheets, and even fabrics. The characterization of transferred nanotubes reveals that the transferred nanotubes are highly conductive, transparent, and flexible as well. Based on transferred nanotube arrays on fabric, we have successfully demonstrated nanotube transistors with on/off ratios ˜ 105, and chemical sensors for low-concentration NO2 and 2,4,6-trinitrotoluene (TNT). In Chapter 5, I present the study of transparent conductive thin films made with two kinds of commercial carbon nanotubes: HiPCO and arc-discharge nanotubes. These films have been further exploited as hole-injection electrodes for organic light emitting diodes (OLEDs) on both rigid glass and flexible substrates. Our experiments reveal that films based on arc discharge nanotubes are overwhelmingly better than HiPCO-nanotube-based films in all the critical aspects, including the surface roughness, sheet resistance, and transparency. The optimized films show a typical sheet resistance of ˜160O/? at 87% transparency and have been successfully used to make OLEDs with high stability and long lifetime. Lastly, I present the fast and scalable integration of nanowire chemical sensors with micromachined hotplates built on SiN membranes. These hotplates allowed nanowire chemical sensors to operate at elevated temperatures in order to enhance the sensitivity of chemical sensors to target gases. By applying different current through the platinum heating filament, we can easily vary the device temperature from room temperature to 350°C. These nanosensors with integrated hot plates have been exploited for the detection of ethanol, CO and hydrogen down to concentrations of 1 ppm, 10 ppm and 50 ppm, respectively.

Ryu, Koungmin

320

Evaluation of achiral templates with fluxional brønsted basic substituents in enantioselective conjugate additions.  

PubMed

Enantioselective conjugate addition of malononitrile to pyrazolidinone-derived enoates proceeds in excellent yields and high enantioselectivities. A comparison of fluxional substituents with and without a Brønsted basic site and their impact on selectivity is detailed. Molecular sieves as an additive were found to be essential to achieve high enantioselectivity. PMID:25490703

Adachi, Shinya; Takeda, Norihiko; Sibi, Mukund P

2014-12-19

321

[2+2] Photocycloaddition of 3-alkenyloxy-2-cycloalkenones: enantioselective Lewis acid catalysis and ring expansion.  

PubMed

By application of substoichiometric amounts (50?mol?%) of a chiral Lewis acid, the intramolecular [2+2] photocycloaddition of the title compounds was achieved with high enantioselectivity (up to 94?%?ee). Upon cleavage of the cyclobutane ring the resulting tricyclic products underwent ring-expansion reactions under acidic conditions and formed anellated seven- or eight-membered-ring systems without racemization. The ring expansion could be combined with a diastereoselective reduction (triethylsilane) or allylation (allyltrimethylsilane) upon BF3 catalysis (48-87?% yield). PMID:25251714

Brimioulle, Richard; Bach, Thorsten

2014-11-17

322

Enantioselective disposition of clenbuterol in rats.  

PubMed

Clenbuterol is a long-acting ?2-adrenoceptor agonist and bronchodilator that is used for the treatment of asthma, but the desired activities reside almost exclusively in the (-)-R-enantiomer. This study examined enantioselectivity in the disposition of clenbuterol following administration of clenbuterol racemate to rats. Concentrations of clenbuterol enantiomers in plasma, urine and bile were determined by LC-MS/MS assay with a Chirobiotic T column. This method was confirmed to show high sensitivity, specificity and precision, and clenbuterol enantiomers in 0.1 ml volumes of plasma were precisely quantified at concentrations as low as 0.25 ng/ml. The pharmacokinetic profiles of clenbuterol enantiomers following intravenous and intraduodenal administration of clenbuterol racemate (2 mg/kg) in rats were significantly different. The distribution volume of (-)-R-clenbuterol (9.17 l/kg) was significantly higher than that of (+)-S-clenbuterol (4.14 l/kg). The total body clearance of (-)-R-clenbuterol (13.5 ml/min/kg) was significantly higher than that of the (+)-S-enantiomer (11.5 ml/min/kg). An in situ absorption study in jejunal loops showed no difference in the residual amount between the (-)-R- and (+)-S-enantiomers. Urinary clearance was the same for the two enantiomers, but biliary excretion of (-)-R-clenbuterol was higher than that of the (+)-S-enantiomer. The fractions of free (non-protein-bound) (-)-R- and (+)-S-clenbuterol in rat plasma were 48.8% and 33.1%, respectively. These results indicated that there are differences in the distribution and excretion of the clenbuterol enantiomers, and these may be predominantly due to enantioselective protein binding. PMID:24323748

Hirosawa, Iori; Ishikawa, Mai; Ogino, Mio; Ito, Hiroshi; Hirao, Takuya; Yamada, Harumi; Asahi, Mariko; Kotaki, Hajime; Sai, Yoshimichi; Miyamoto, Ken-Ichi

2014-05-01

323

(I) Novel Perfluorinated Aromatic Amino Acids: Synthesis and Applications (II) Thioflavin T Dimers as Novel Amyloid Ligands.  

E-print Network

??This thesis includes two projects: "Novel perfluorinated aromatic amino acids: synthesis and applications" and "Thioflavin T dimers as novel amyloid ligands". I) Novel perfluorinated aromatic… (more)

Qin, Luoheng

2012-01-01

324

Stereoselective synthesis of both enantiomers of rugulactone.  

PubMed

The stereoselective total synthesis of both enantiomers of rugulactone 1 has been completed by applying enantioselective allyl additions as key steps. Two different strategies based on highly stable and enantiomerically pure ?-substituted allylboronic esters 2 and 3 were performed starting from boronic ester 4. PMID:21434691

Böse, Dietrich; Fernández, Enrique; Pietruszka, Jörg

2011-05-01

325

PDMS based microfluidic chips and their application in material synthesis  

NASA Astrophysics Data System (ADS)

Microfluidics is a highly interdisciplinary science which is to deal with the behavior, control and manipulation of fluids that are constrained to sub-milimeter scale. It incorporates the knowledge and technique intersecting physics, chemistry, mechanics, nanoscience and biotechnology, with practical applications to the design of systems in which small volumes of fluids will be used. In this thesis, we started our research from GER fluid synthesis which then is applied to designing different functions of microfluidic devices, valve, pump, and mixer. We built a way to correlate mechanical signal with electric signal by soft matter. The mechanical devices based GER fluid had good operating stability and mechanical performance. We studied how to improve the performance of GER fluid by increasing the yield stress while avoiding the sendimentation of nanoparticles in GER suspension. The meaning of this work is to enhance the stability and mechanical strength of GER fluid when it is applyed to the microfluidc channels. We tried different oils and studied the particle size for the GER effect. The largest yield stress which amounts to 300 kPa is achievable compared to previous GER fluid with 100 kPa. Microfluidic reactor, directing the flow of microliter volumes along microscale channels, offers the advantages of precise control of reagent loading, fast mixing and an enhanced reaction rate, cessation of the reaction at specific stages, and more. Basically, there are two microfluidic flow regimes, continuous flow and segmented flow (suspended droplets, channel-spanning slug, and wall-wetting films). Both flow regimes offer chemical reaction applications, e.g., continuous flow formation of polymer nanospheres and inorganic nanoparticles, size- and shape-control synthesis by segmented flow, and precipitate-forming reactions in droplets, wherein the segmented flow has gained more popularity in that area. The compartmentalization of segmented flow offers advantages to chemical reactions. Here, we report the microfluidic fabrication of magnetically responsive microsphere, macroporous polymer microspheres and hollow titania microspheres. To prepare magnetically responsive microsphere, we introduced magnetic particles into liquid shell and drug into liquid core. After cross-linking reaction of the shell, we studied the magnetic contraction and extention behavior which induced the drug release efficiency. To prepare porous polymer, the H 2O2 solution was encapsulated in polymer precursor, after which we investigated its decomposition under UV irradiation, which simultaneously induces the polymerization of the encapsulating shell. Because the H 2O2 decomposition leads to the release of oxygen, porous microspheres were obtained from a combined H2O2-decomposition/polymer precursor polymerization reaction. To prepare hollow titanium gel microspheres, water droplets were first formed by the flow focusing geometry in microfluidic chip and used as a soft template. Then hydrolysis and gelation of titanium alkoxide on the droplet's surface were induced in following serpentine channels, controlled by interface water diffusion. The water diffusion process can be controlled by the amount of the "dewetting" reagent butanol, by which the surface morphology of the titania microspheres can be tuned.

Gong, Xiuqing

326

Perspective view of GSC: How to realize the industrial application of artificial photo synthesis?  

NASA Astrophysics Data System (ADS)

Artificial photo synthesis is one of the dream reactions, which can contribute to the industrial application from a view point of green sustainable chemistry. Considering the hardness of subjects to obtain the enough performance on artificial photo synthesis and the difference between the current infrastructure and required ones, which can fit to this application, we have to solve these subjects one by one from a strategic view point. Diversification of chemical resource and compatibility of process technologies will be the keys for industrial application.

Setoyama, T.

2013-12-01

327

Rational control of hydrothermal nanowire synthesis and its applications  

E-print Network

Hydrothermal nanowire synthesis is a rapidly emerging nanowire discipline that enables low temperature growth and batch process. It has a major impact on the development of novel energy conversion devices, high density ...

Joo, Jaebum

2010-01-01

328

Biogenic synthesis of metal nanoparticles from actinomycetes: biomedical applications and cytotoxicity.  

PubMed

Biogenic synthesis of metal nanoparticles has been well proved by using bacteria, fungi, algae, actinomycetes, plants, etc. Among the different microorganisms used for the synthesis of metal nanoparticles, actinomycetes are less known. Although, there are reports, which have shown that actinomycetes are efficient candidates for the production of metal nanoparticles both intracellularly and extracellularly. The nanoparticles synthesized by the members of actinomycetes present good polydispersity and stability and possess significant biocidal activities against various pathogens. The present review focuses on biological synthesis of metal nanoparticles and their application in medicine. In addition, the toxicity of these biogenic metal nanoparticles to human beings and environment has also been discussed. PMID:25158833

Golinska, Patrycja; Wypij, Magdalena; Ingle, Avinash P; Gupta, Indarchand; Dahm, Hanna; Rai, Mahendra

2014-10-01

329

Synthesis of Distributed Execution Platforms for Cyber-Physical Systems with Applications to  

E-print Network

Synthesis of Distributed Execution Platforms for Cyber-Physical Systems with Applications to High for high-performance building applications. This is an example of a class of cyber- physical systems where Terms--Cyber­Physical Systems; CAD; Sythesis; I. INTRODUCTION Aircraft, cars, buildings, factories

Carloni, Luca

330

High-level synthesis and codesign methods: An application to a Videophone Codec  

Microsoft Academic Search

This paper describes a high-level multi-HDL design process applied to an industrial design of a single chip Videophone Codec. It makes use of many state-of-the-art design tools and methods: Behavioural VHDL control path synthesis for the controller of the Codec motion estimator; behavioural DSP synthesis from Silage to generate an application-specific calculation unit that performs vector prediction for the motion

Pierre Paulin; J. Frehel; Michel Harrand; Elisabeth Berrebi; Clifford Liem; F. Nacabul; Jean-Claude Herluison

1995-01-01

331

Synthesis, self-assembly and potential applications of cobalt-based nanoparticles with tailored magnetic properties  

Microsoft Academic Search

This dissertation includes a comprehensive study of the wide range of issues involving the synthesis, self-assembly, magnetic behavior and bio-sensing applications of cobalt and related binary-element nanoparticles. We began with the development of a robust chemical method for the reproducible synthesis of monodispersed, metallic cobalt nanoparticles with good size control, narrow size distribution and well-defined shapes, including spheres and anisotropic

Yuping Bao

2006-01-01

332

n-Type conjugated polymers: advances in synthesis, photophysics, charge transport, and device applications  

Microsoft Academic Search

Our recent studies in the synthesis, photophysics, charge transport, and optoelectronic and electronic device applications of n-type conjugated polymers and oligomers will be presented. Recent synthesis of organic-solvent soluble polyquinolines has facilitated studies of their solution and solid photophysics and fabrication of more efficient light-emitting diodes. For example, large improvements in external efficiencies (2.5 2300 cd\\/m2), and ambient air stability

Samson A. Jenekhe

2002-01-01

333

Enantioselective HPLC-DAD method for the determination of etodolac enantiomers in tablets, human plasma and application to comparative pharmacokinetic study of both enantiomers after a single oral dose to twelve healthy volunteers.  

PubMed

An enantioselective high performance liquid chromatographic method with diode array detection (HPLC-DAD) was developed and validated for the determination of etodolac enantiomers in tablets and human plasma. Enantiomeric separation was achieved on a Kromasil Cellucoat chiral column (250 mm × 4.6mm i.d., 5 µm particle size) using a mobile phase consisting of hexane: isopropanol: triflouroacetic acid (90:10:0.1 v/v/v) at a flow rate of 1.0 mL min(-1). The chromatographic system enables the separation of the two enantiomers and the internal standard within a cycle time of 8 min. The resolution between the two enantiomers was 4.25 and the resolution between each enantiomer and the internal standard was more than 2.0. Detection was carried out at 274 nm, and the purity assessment was performed using a photodiode array detector. Solid phase extraction technique using C-18 cartridge was applied to extract the analytes from the plasma samples, and the percentage recovery was more than 95% for the lower quantification limit. The method has been validated with respect to selectivity, linearity, accuracy and precision, robustness, limit of detection and limit of quantification. The validation acceptance criteria were met in all cases. The linearity range for the determination of each enantiomer in human plasma was 0.4-30.0 µg mL(-1) and the limits of quantification of R-etodolac and S-etodolac were 0.20 and 0.19 µg mL(-1), respectively. The validated method was successfully applied to the determination of etodolac enantiomers in tablets and to a comparative pharmacokinetic study of the two enantiomers after the administration of 300 mg single oral dose etodolac racemate tablets to twelve healthy volunteers. PMID:25159440

Hewala, Ismail I; Moneeb, Marwa S; Elmongy, Hatem A; Wahbi, Abdel-Aziz M

2014-12-01

334

Interspecies differences in the enantioselectivity of epoxide hydrolases in Cryptococcus laurentii (Kufferath) C.E. Skinner and Cryptococcus podzolicus (Bab'jeva & Reshetova) Golubev.  

PubMed

Isolates representing Cryptococcus laurentii and Cryptococcus podzolicus, originating from soil of a heathland indigenous to South Africa, were screened for the presence of enantioselective epoxide hydrolases for 2,2-disubstituted epoxides. Epoxide hydrolase activity for the 2,2-disubstituted epoxide (+/-)-2-methyl-2-pentyl oxirane was found to be abundantly present in all isolates. The stereochemistry of the products formed by the epoxide hydrolase enzymes from isolates belonging to the two species (11 isolates representing C. laurentii and 23 isolates representing C. podzolicus) was investigated. The enantiopreferences of the epoxide hydrolases for 2,2-disubstituted epoxides of these two species were found to be opposite. All strains of C. laurentii preferentially hydrolysed the (S)-epoxides while all C. podzolicus isolates preferentially hydrolysed the (R)-epoxides of (+/-)-2,2-disubstituted epoxides. These findings indicate that the stereochemistry of the products formed from 2,2-disubstituted epoxides by the epoxide hydrolase enzymes of these yeasts should be evaluated as additional taxonomic criterion within the genus Cryptococcus. Also, the selectivity of some epoxide hydrolases originating from isolates of C. podzolicus was high enough to be considered for application in biotransformations for the synthesis of enantiopure epoxides and vicinal diols. PMID:15709362

Botes, Adriana L; Lotter, Jeanette; Rhode, Owen H J; Botha, Alfred

2005-01-01

335

Enantioselective organocatalytic indole alkylations. Design of a new and highly effective chiral amine for iminium catalysis.  

PubMed

The indole framework has become widely identified as a "privileged" structure with representation in over 3000 natural isolates and 40 medicinal agents of diverse therapeutic action. A new strategy for asymmetric access to this important pharmacaphore has been accomplished that involves the amine catalyzed alkylation of indoles with alpha,beta-unsaturated aldehydes. Central to these studies has been the design of a new chiral amine catalyst that exhibits improved reactivity and selectivity for iminium catalysis. This new (2S,5S)-5-benzyl-2-tert-butyl-imidazolidinone catalyst has enabled the conjugate addition of a variety of indole systems to a diverse range of alpha,beta-unsaturated aldehydes in high yield and with excellent levels of enantiocontrol (70-97% yield, 84-97% ee). A demonstration of the utility of this new organocatalytic alkylation for the rapid construction of biomedically relevant molecules is presented in the enantioselective synthesis of an indolobutyric acid COX-2 inhibitor. PMID:11841277

Austin, Joel F; MacMillan, David W C

2002-02-20

336

Enantioselective Syntheses and Sensory Properties of 2-Methyl-tetrahydrofuran-3-thiol Acetates.  

PubMed

The enantioselective synthesis of four stereoisomers of 2-methyl-tetrahydrofuran-3-thiol acetate was achieved. The two enantiomers of the important intermediate cis-2-methyl-3-hydroxy-tetrahydrofuran were obtained by Sharpless asymmetric dihydroxylation (AD), whereas the two enantiomers of trans-2-methyl-3-hydroxy-tetrahydrofuran were derived from the corresponding optically active cis-isomers by Mitsunobu reaction. Each stereoisomer of 2-methyl-3-hydroxy-tetrahydrofuran went through mesylation and nucleophilic substitution to afford the corresponding product with specific configuration. (2R,3S)- and (2R,3R)-2-methyl-tetrahydrofuran-3-thiol acetate were obtained in 80% ee, whereas the (2S,3R)- and (2S,3S)-isomers were in 62% ee. The odor properties of the synthesized four stereoisomers were evaluated by gas chromatography-olfactometry (GC-O), which revealed perceptible differences among stereoisomers both in odor features and in intensities. PMID:25560460

Dai, Yifeng; Shao, Junqiang; Yang, Shaoxiang; Sun, Baoguo; Liu, Yongguo; Ning, Ting; Tian, Hongyu

2015-01-21

337

Manganese-Substituted ?-Carbonic Anhydrase as an Enantioselective Peroxidase  

NASA Astrophysics Data System (ADS)

Carbonic anhydrase binds a zinc ion in a hydrophobic active site using the imidazole groups of three histidine residues. The natural role of carbonic anhydrase is to catalyze the reversible hydration of carbon dioxide to bicarbonate, but it also catalyzes hydrolysis of esters with moderate enantioselectivity. Replacing the active-site zinc with manganese yielded manganese-substituted carbonic anhydrase (CA[Mn]), which shows peroxidase activity with a bicarbonate-dependent mechanism. In the presence of bicarbonate and hydrogen peroxide, CA[Mn] catalyzed the efficient oxidation of o-dianisidine with k cat /K M = 1.4 × 106 M-1s-1, which is comparable to that for horseradish peroxidase, k cat /K M = 57 × 106 M-1s-1. CA[Mn] also catalyzed the moderately enantioselective epoxidation of olefins to epoxides (E = 5 for p-chlorostyrene). This enantioselectivity is similar to that for natural heme-based peroxidases, but has the advantage that CA[Mn] avoids formation of aldehyde side products. CA[Mn] degrades during the epoxidation, limiting the yield of the epoxidations to <12%. Replacement of active-site residues Asn62, His64, Asn67, Gln92, or Thr200 with alanine by site-directed mutagenesis decreased the enantioselectivity showing that the active site controls enantioselectivity of the epoxidation.

Jing, Qing; Okrasa, Krzysztof; Kazlauskas, Romas J.

338

Enantioselective direct aldol reactions catalyzed by L-prolinamide derivatives.  

PubMed

l-Prolinamides 2, prepared from l-proline and simple aliphatic and aromatic amines, have been found to be active catalysts for the direct aldol reaction of 4-nitrobenzaldehyde with neat acetone at room temperature. They give moderate enantioselectivities of up to 46% enantiomeric excess (ee). The enantioselectivity increases as the amide N-H becomes a better hydrogen bond donor. l-Prolinamides 3, derived from the reaction of l-proline with alpha,beta-hydroxyamines such that there is a terminal hydroxyl group, show more efficient catalysis and higher enantioselectivities. In particular, catalyst 3h, prepared from l-proline and (1S,2S)-diphenyl-2-aminoethanol, exhibits high enantioselectivities of up to 93% ee for aromatic aldehydes and up to >99% ee for aliphatic aldehydes under -25 degrees C. Model reactions of benzaldehyde with three enamines derived from the condensation of prolinamides with acetone have been studied by quantum mechanics calculations. The calculations reveal that the amide N-H and the terminal hydroxyl groups form hydrogen bonds with the benzaldehyde substrate. These hydrogen bonds reduce the activation energy and cause high enantioselectivity. Our results suggest a new strategy in the design of new organic catalysts for direct asymmetric aldol reactions and related transformations. PMID:15079057

Tang, Zhuo; Jiang, Fan; Cui, Xin; Gong, Liu-Zhu; Mi, Ai-Qiao; Jiang, Yao-Zhong; Wu, Yun-Dong

2004-04-20

339

Total Synthesis of the Hsp90 Inhibitor Geldanamycin  

PubMed Central

An enantioselective synthesis of the Hsp90 inhibitor geldanamycin was achieved in 20 linear steps and 2.0% overall yield from 2-methoxyhydroquinone. The synthesis is highlighted by a regio- and stereoselective hydroboration reaction; a Sc(OTf)3/Et3SiH-mediated pyran ring-opening reaction; an enantioselective crotylation to simultaneously install the C8–C9 (E)-trisubstituted olefin, the C10 and C11 stereocenters; a chelation-controlled asymmetric metallated acetylide addition; and an intramolecular copper(I)-mediated aryl amidation reaction to close the 19-membered macrolactam. PMID:18489177

Qin, Hua-Li; Panek, James S.

2008-01-01

340

Synthesis and applications of bioinspired inorganic nanostructured materials  

NASA Astrophysics Data System (ADS)

Although the study of biominerals may be traced back many centuries, it is only recently that biological principles have been applied to synthetic systems in processes termed "biomimetic" and "bioinspired" to yield materials syntheses that are otherwise not possible and may also reduce the expenditure of energy and/or eliminate toxic byproducts. Many investigators have taken inspiration from interesting and unusual minerals formed by organisms, in a process termed biomineralisation, to tailor the nanostructure of inorganic materials not necessarily found biogenically. However, the fields of nanoparticle synthesis and biomineralisation remain largely separate, and this thesis is an attempt to apply new studies on biomineralisation to nanomaterials science. Principally among the proteins that influence biomineralisation is a group comprised largely of negatively charged aspartic acid residues present in serum. This study is an investigation determining the ability of these serum proteins and other anolagous biomolecules to stabilise biologically relevant amorphous minerals and influence the formation of a variety of materials at the nanoscale. Three different materials were chosen to demonstrate this effect; gold was templated into nanosized single crystals by the action of bioorganic molecules, and the utility of these nanoparticles as a biosensor was explored. The influence of bioorganic molecules on the phase selection and crystal size restriction of titanium dioxide, an important semiconductor with many applications, was explored. The use of bioorganically derived nanoparticles of titanium dioxide was then demonstrated as a highly efficient photocatalyst. Finally, calcium carbonate, a prevalent biomineral was shown to form highly ordered structures over a variety of length scales and different crystalline polymorphs under the influence of a templating protein. In addition, an alternative route to producing calcium phosphate nanoparticle dispersions by mechanical filtration was explored and use as a transfection vector was optimised in two cell lines. Several significant achievements are presented: (i) the assessment of the relative ability of serum, serum derived proteins and their analogues to stabilize the amorphous state, (ii) the formation of single crystalline gold templated by an antibody, (iii) the formation of highly photocatalytically active nanoparticulate anatase by a phosphorylated cyclic esther, (iv) the formation of conical structures at the air liquid interface by the templating ability of a protein and (v) the optimisation of calcium phosphate nanoparticle mediated transfection in two cell lines by mechanical filtration.

Bassett, David C.

2011-12-01

341

Chemically functionalized gold nanoparticles: Synthesis, characterization, and applications  

NASA Astrophysics Data System (ADS)

This thesis focuses on the development and application of gold nanoparticle based detection systems and biomimetic structures. Each class of modified nanoparticle has properties that are defined by its chemical moieties that interface with solution and the gold nanoparticle core. In Chapter 2, a comparison of the biomolecular composition and binding properties of various preparations of antibody oligonucleotide gold nanoparticle conjugates is presented. These constructs differed significantly in terms of their structure and binding properties. Chapter 3 reports the use of electroless gold deposition as a light scattering signal enhancer in a multiplexed, microarray-based scanometric immunoassay using the gold nanoparticle probes evaluated in Chapter 2. The use of gold development results in greater signal enhancement than the typical silver development, and multiple rounds of metal development were found to increase the resulting signal compared to one development. Chapter 4 describes an amplified scanometric detection method for human telomerase activity. Gold nanoparticles functionalized with specific oligonucleotide sequences can efficiently capture telomerase enzymes and subsequently be elongated. Both the elongated and unmodified oligonucleotide sequences are simultaneously measured. At low telomerase concentrations, elongated strands cannot be detected, but the unmodified sequences, which come from the same probe particles, can be detected because their concentration is higher, providing a novel form of amplification. Chapter 5 reports the development of a novel colorimetric nitrite and nitrate ion assay based upon gold nanoparticle probes functionalized with Griess reaction reagents. This assay takes advantage of the distance-dependent plasmonic properties of the gold nanoparticles and the ability of nitrite ion to facilitate the cross coupling of novel nanoparticle probes. The assay works on the concept of a kinetic end point and can be triggered at the EPA limit for this ion in drinking water. Finally, Chapter 6 describes the synthesis of high density lipoprotein biomimetic nanoparticles capable of binding cholesterol. These structures use a gold nanoparticle core to template the assembly of a mixed phospholipid layer and the adsorption of apolipoprotein A-I. These synthesized structures have the general size and surface composition of natural HDL and bind free cholesterol with a Kd of 4 nM.

Daniel, Weston Lewis

342

Enantioselective Cyclizations of Silyloxyenynes Catalyzed by Cationic Metal Phosphine Complexes  

PubMed Central

The discovery of complementary methods for enantioselective transition-metal-catalyzed cyclization with silyloxyenynes has been accomplished using chiral phosphine ligands. Under palladium catalysis, 1,6-silyloxyenynes bearing a terminal alkyne led to the desired 5-membered ring with high enantioselectivities (up to 91% ee). As for reactions under cationic gold catalysis, 1,6- and 1,5-silyloxyenynes bearing an internal alkyne furnished the chiral cyclopentane derivatives with excellent enantiomeric excess (up to 94% ee). Modification of the substrate by incorporating an ?,?-unsaturation led to the discovery of a tandem cyclization. Remarkably, using silyloxy-1,3-dien-7-ynes under gold catalysis conditions provided the bicyclic derivatives with excellent diastereo- and enantioselectivities (up to >20:1 dr and 99% ee). PMID:22296571

Brazeau, Jean-François; Zhang, Suyan; Colomer, Ignacio; Corkey, Britton K.; Toste, F. Dean

2012-01-01

343

?-Conjugated Aromatics Based on Truxene: Synthesis, Self-Assembly, and Applications.  

PubMed

Recently, many efforts have been devoted to developing novel polycyclic aromatics due to their unique optical and electronic properties and broad applications, such as in organic field-effect transistors, organic photovoltaics, and organic light-emitting diodes. Among various ?-conjugated molecules, many truxene derivatives have interesting characteristics such as C3 -symmetry, strong blue emission, and a planar rigid structure. Moreover, compared with many other ?-conjugated aromatics, the synthesis and modification of truxene are particularly facile and diverse. In this account, we summarize investigations into truxene derivatives from synthesis and physical properties to applications in organic electronics. PMID:25474741

Shi, Ke; Wang, Jie-Yu; Pei, Jian

2015-02-01

344

Synthesis of Enantiomerically Pure Anthracyclinones  

NASA Astrophysics Data System (ADS)

The anthracycline antibiotics are among the most important clinical drugs used in the treatment of human cancer. The search for new agents with improved therapeutic efficacy and reduced cardiotoxicity stimulated considerable efforts in the synthesis of new analogues. Since the biological activity of anthracyclines depends on their natural absolute configuration, various strategies for the synthesis of enantiomerically pure anthracyclinones (aglycones) have been developed. They comprise: resolution of racemic intermediate, incorporation of a chiral fragment derived from natural and non-natural chiral pools, asymmetric synthesis with the use of a chiral auxiliary or a chiral reagent, and enantioselective catalysis. Synthetic advances towards enantiopure anthracyclinones reported over the last 17 years are reviewed.

Achmatowicz, Osman; Szechner, Barbara

345

Synthesis, functionalisation and characterisation of mesoporous materials and sol–gel glasses for applications in catalysis, adsorption and photonics  

Microsoft Academic Search

In this review, synthesis and functionalisation approaches for ordered mesoporous materials and sol–gel glasses are described. Catalytic and adsorption applications are emphasised for the ordered mesoporous materials, while optical applications are the focus for sol–gel glasses.

Gisle Øye; Wilhelm R. Glomm; Torbjørn Vrålstad; Sondre Volden; Heléne Magnusson; Michael Stöcker; Johan Sjöblom

2006-01-01

346

Synthesis of Ag nanorods and application to soft die attaching  

Microsoft Academic Search

In this paper, we report the synthesis of Ag nanoparticles paste, a new bonding agent using between chips and substrates in semiconductor devices. Ag nanorods with varied yield have been successfully synthesized by simply adjusting the concentration of additive salt, the moral ratio of capping agent to AgNO3. The Ag nanoparticles can be sintered to form porous die attach layer

Jinting Jiu; Keiichi Murai; Keunsoo Kim; Katsuaki Suganuma

2008-01-01

347

Direct digital RF synthesis and modulation for MSAT mobile applications  

NASA Technical Reports Server (NTRS)

A practical method of performing direct digital RF synthesis using the Hilbert transform single sideband (SSB) technique is described. It is also shown that amplitude and phase modulation can be achieved directly at L-band with frequency stability and spurii performance exceeding stringent MSAT system requirements.

Crozier, Stewart; Datta, Ravi; Sydor, John

1993-01-01

348

Applications of Ultrasound to the Synthesis of Nanostructured Materials  

E-print Network

Cavitation Chemistry deals with the interaction between energy and matter, and chemical reactions require some form of energy (e.g., heat, REVIEW www.MaterialsViews.com www.advmat.de [*] Prof. K. S. Suslick synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive

Suslick, Kenneth S.

349

Enantioselective Iodolactonization of Disubstituted Olefinic Acids Using a Bifunctional Catalyst  

PubMed Central

The enantioselective iodolactonizations of a series of diversely-substituted olefinic carboxylic acids are promoted by a BINOL-derived, bifunctional catalyst. Reactions involving 5-alkyl- and 5-aryl-4(Z)-pentenoic acids and 6-alkyl- and 6-aryl-5(Z)-hexenoic acids provide the corresponding ?- and ?-lactones having stereogenic C–I bonds in excellent yields and >97:3 er. Significantly, this represents the first organocatalyst that promotes both bromo- and iodolactonization with high enantioselectivities. The potential of this catalyst to induce kinetic resolutions of racemic unsaturated acids is also demonstrated. PMID:23199100

Fang, Chao; Paull, Daniel H.; Hethcox, J. Caleb; Shugrue, Christopher R.; Martin, Stephen F.

2012-01-01

350

Enantioselective synthesis of L-(-)-4- boronophenylalanine (L-BPA)  

DOEpatents

A method of making substantially pure L-BPA is disclosed. The method includes the steps of reacting 4-bromobenzaldehyde with ethylene glycol to form 4-bromobenzaldehyde ethylene glycol acetal, sequentially reacting 4-bromobenzaldehyde ethyleneglycol acetal with Mg to produce the Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, reacting 4-boronobenzaldehyde with diethanol amine to form 4-boronobenzaldehyde diethanolamine ester, condensing the 4-boronobenzaldehyde diethanolamine ester with 2-phenyl-2-oxazolin-5-one to form an azlactone, reacting the azlactone with an alkali metal hydroxide to form z-.alpha.-benzoylamino-4-boronocinnamic acid, asymmetrically hydrogenating the z-.alpha.-benzoylamino-4-boronocinnamic acid in the presence of a catalyst of a cheltate complex of rhodium (I) with chiral bisphosphines to form L-(+)-N-benzoyl-4-boronophenylalanine, and thereafter acidifying the L-(+)-N-benzoyl-4-boronophenylalanine in an organic medium to produce L-BPA.

Samsel, Edward G. (Baton Rouge, LA)

1992-01-01

351

Enantioselective synthesis of L-(-)-4- boronophenylalanine (L-BPA)  

DOEpatents

A method of making substantially pure L-BPA is disclosed. The method includes the steps of reacting 4-bromobenzaldehyde with ethylene glycol to form 4-bromobenzaldehyde ethylene glycol acetal, sequentially reacting 4-bromobenzaldehyde ethyleneglycol acetal with Mg to produce the Grignard reagent and thereafter reacting with tributyl borate and then converting to an acid environment to form 4-boronobenzaldehyde, reacting 4-boronobenzaldehyde with diethanol amine to form 4-boronobenzaldehyde diethanolamine ester, condensing the 4-boronobenzaldehyde diethanolamine ester with 2-phenyl-2-oxazolin-5-one to form an azlactone, reacting the azlactone with an alkali metal hydroxide to form z-[alpha]-benzoylamino-4boronocinnamic acid, asymmetrically hydrogenating the z-[alpha]-benzoylamino-4-boronocinnamic acid in the presence of a catalyst of a cheltate complex of rhodium (I) with chiral bisphosphines to form L-(+)-N-benzoyl-4-boronophenylalanine, and thereafter acidifying the L-(+)-N-benzoyl-4-boronophenylalanine in an organic medium to produce L-BPA. 3 figs.

Samsel, E.G.

1992-10-20

352

Enantioselective Synthesis of ()-Jiadifenin, a Potent Neurotrophic Modulator  

E-print Network

instrument or a 500 MHz JEOL instrument. CDCl3 was treated with flame dried K2CO3, chemical shifts sulfurane, THF 2. H2, Pd/C, MeOH O O OH O O 10 Compound 10: To a solution of alcohol 4[1] (420 mg, 1.5 mmol

Theodorakis, Emmanuel

353

Synthetic studies on the icetexones: enantioselective formal syntheses of icetexone and epi-icetexone  

PubMed Central

Two strategies for the synthesis of the icetexane diterpenoids icetexone and epi-icetexone that rely on Ga(III)-catalyzed cycloisomerization of alkynyl indene substrates to yield fused [6-7-6] tricycles have been explored. In the first approach, access to a tricycle bearing a gem-dimethyl group paved the way for explorations of C–H functionalization of one of the methyl groups in close proximity to a hydroxyl-directing group. This approach was ultimately unsuccessful and led only to ring cleaved products. In the second approach, an alkynyl indene substrate bearing a cyano substituent was utilized, which was effective in providing a functional handle to access the icetexone subclass of diterpenoids. A key epoxide opening/diazene rearrangement sequence was utilized to complete a formal synthesis of icetexone and epi-icetexone, which is discussed in detail. Furthermore, the cyano-containing substrate has been prepared in enantioenriched form using a Rh-catalyzed conjugate addition reaction, which now provides a route to the enantioselective synthesis of these natural products. PMID:24249921

de Jesus Cortez, Felipe; Lapointe, David; Hamlin, Amy M.; Simmons, Eric M.; Sarpong, Richmond

2013-01-01

354

Asymmetric catalytic conjugate addition of acetaldehyde to nitrodienynes/nitroenynes: applications to the syntheses of (+)-?-lycorane and chiral ?-alkynyl acids.  

PubMed

The catalytic enantioselective conjugate addition of acetaldehyde to polyconjugated substrates, nitrodienynes and nitroenynes, has been accomplished using organocatalysis. Various functionalized 1,3-enynes and propargylic compounds were obtained in moderate to good yields with high enantioselectivity. The synthetic utilities of the conjugate addition reactions have been highlighted in the concise total synthesis of (+)-?-lycorane and the metal-free synthesis of chiral ?-alkynyl acids. PMID:24811051

Meng, Xue-Ling; Liu, Teng; Sun, Zhong-Wen; Wang, Jin-Chen; Peng, Fang-Zhi; Shao, Zhi-Hui

2014-06-01

355

Total Synthesis of Apoptolidin A  

PubMed Central

A highly convergent, enantioselective total synthesis of the potent antitumor agent apoptolidin A, has been completed. The key transformations include highly selective glycosylations to attach the C27 disaccharide and the C9 6?-deoxy-l-glucose, a cross metathesis to incorporate the C1-C10 trienoate unit, and a Yamaguchi macrolactonization to complete the macrocycle. Twelve stereocenters in the polypropionate segments and sugar units were established through diastereoselective chlorotitanium enolate aldol reactions. PMID:19199767

Crimmins, Michael T.; Christie, Hamish S.; Long, Alan; Chaudhary, Kleem

2009-01-01

356

Aryl bromides as inexpensive starting materials in the catalytic enantioselective arylation of aryl aldehydes: the additive TMEDA enhances the enantioselectivity.  

PubMed

We used aryl bromides as inexpensive starting materials to enantioselectively arylate aldehydes in one pot. Aryl bromides readily transfer aryls to aryllithiums with n-butyllithium, successively to triarylaluminums with aluminum chloride, and then to aryltitaniums with titanium isopropoxide. Finally aryltitaniums arylate aldehydes catalyzed by (S)-H8-BINOL-Ti(Oi-Pr)2 in excellent yields and enantioselectivities. The additive TMEDA evidently suppresses the racemic background reaction promoted by LiCl generated from salt metathesis. This procedure represents a cost-effective and operationally convenient method for enantioenriched diarylmethanols. PMID:25279967

Yang, Yong-Xin; Liu, Yue; Zhang, Lei; Jia, Yan-E; Wang, Pei; Zhuo, Fang-Fang; An, Xian-Tao; Da, Chao-Shan

2014-11-01

357

Chiral phosphane alkenes (PALs): simple synthesis, applications in catalysis, and functional hemilability.  

PubMed

A simple synthesis of a chiral phosphane alkene (PAL) involves: 1) palladium-catalyzed Suzuki coupling of 10-bromo-5H-dibenzo[a,d]cyclohepten-5-ol (1) with phenylboronic acid to give quantitatively 10-phenyl-5H-dibenzo[a,d]cyclohepten-5-ol (2); 2) reaction of 2 with Ph(2)PCl under acidic conditions to give a racemic mixture of the phosphane oxide (10-phenyl-5H-dibenzo[a,d]cyclohepten-5-yl)diphenylphosphane oxide ((Ph)troppo(Ph), 3), which is separated into enantiomers by using high-pressure liquid chromatography (HPLC) on a chiral column; 3) reduction with trichlorosilane to give the enantiomerically pure phosphanes (R)- and (S)-(10-phenyl-5H-dibenzo[a,d]cyclohepten-5-yl)diphenylphosphane ((Ph)tropp(Ph), 4). This highly rigid, concave-shaped ligand serves as a bidentate ligand in Rh(I) and Ir(I) complexes. Catalysts prepared from [Rh(2)(mu(2)-Cl)(2)(C(2)H(4))(4)] and (S)-4 have allowed the efficient enantioselective 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyls (Hayashi-Miyaura reaction) (5-0.1 mol % catalyst, up to 95% ee). The iridium complex (S,S)-[Ir((Ph)tropp(Ph))(2)]OTf ((S,S)-6; OTf=SO(3)CF(3)) has been used as a catalyst in the hydrogenation of various nonfunctionalized and functionalized olefins (turnover frequencies (TOFs) of up to 4000 h(-1)) and moderate enantiomeric excesses have been achieved (up to 67% ee). [Ir((Ph)tropp(Ph))(2)]OTf reversibly takes up three equivalents of H(2). The highly reactive octahedral [Ir(H)(2)(OTf)(CH(2)Cl(2))(H(2)-(Ph)tropp(Ph))(2)] could be isolated and contains two hydrogenated monodentate H(2)-(Ph)tropp(Ph) phosphanes, one CH(2)Cl(2) molecule, one triflate anion, and two hydrides. Based on this structure and extensive NMR spectroscopic studies, a mechanism for the hydrogenation reactions is proposed. PMID:16718725

Piras, Elisabetta; Läng, Florian; Rüegger, Heinz; Stein, Daniel; Wörle, Michael; Grützmacher, Hansjörg

2006-07-24

358

652 J.Org.Chem. 1988,53,652-657 Total Synthesis of Milbemycin &  

E-print Network

& was reported by Smith6 in 1982 followed shortly thereafter by the first enantioselective synthesis by Williams.; Bloom,J.D.; Thompson, A. S.;Winzenberg,K. N.; Smith,A. B., 1111Ibid. 1986,108,2662. (7)Williams,D. R prepared by Williams is intercepted to constitutea total synthesis. The milbemycins are a class

359

Stiffness coupling application to modal synthesis program, users guide  

NASA Technical Reports Server (NTRS)

A FORTRAN IV computer program used to perform modal synthesis of structures by stiffness coupling, using the dynamic transformation method is described. The program was named SCAMP (Stiffness Coupling Approach Modal-Synthesis Program). The program begins with the entry of a substructure's physical mode shapes and eigenvalues or a substructure's mass and stiffness matrix. If the mass and stiffness matrices are entered, the eigen problem for the individual substructure is solved. Provisions are included for a maximum of 20 substructures which are coupled by stiffness matrix springs. Each substructure has a number degrees of freedom (DOF), except that for DOF greater than 100; vector sets having maximum row and column size of 100 were generated prior to entering SCAMP. The substructures are then coupled together via coupling springs, and the dynamic transformation is used to reduce the size of the eigen problem.

Kuhar, E. J.

1976-01-01

360

Synthesis of high purity metal oxide nanoparticles for optical applications  

NASA Astrophysics Data System (ADS)

In this paper we present our recent research results in synthesizing various metal oxide nanoparticles for use as laser gain media (solid state as well as fiber lasers) and transparent ceramic windows via two separate techniques, co-precipitation and flame spray pyrolysis. The nanoparticles were pressed into ceramic discs that exhibited optical transmission approaching the theoretical limit and showed very high optical-to-optical lasing slope efficiency. We have also synthesized sesquioxide nanoparticles using a Flame Spray Pyrolysis (FSP) technique that leads to the synthesis of a metastable phase of sesquioxide which allows fabricating excellent optical quality transparent windows with very fine grain sizes. Finally, we present our research in the synthesis of rare earth doped boehmite nanoparticles where the rareearth ion is encased in a cage of aluminum and oxygen to prevent ion-ion proximity and energy transfer. The preforms have been drawn into fibers exhibiting long lifetimes and high laser efficiencies.

Baker, C.; Kim, W.; Friebele, E. J.; Villalobos, G.; Frantz, J.; Shaw, L. B.; Sadowski, B.; Fontana, J.; Dubinskii, M.; Zhang, J.; Sanghera, J.

2014-09-01

361

Silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications, and toxicity effects  

NASA Astrophysics Data System (ADS)

Silver nanoparticles are nanoparticles of silver which are in the range of 1 and 100 nm in size. Silver nanoparticles have unique properties which help in molecular diagnostics, in therapies, as well as in devices that are used in several medical procedures. The major methods used for silver nanoparticle synthesis are the physical and chemical methods. The problem with the chemical and physical methods is that the synthesis is expensive and can also have toxic substances absorbed onto them. To overcome this, the biological method provides a feasible alternative. The major biological systems involved in this are bacteria, fungi, and plant extracts. The major applications of silver nanoparticles in the medical field include diagnostic applications and therapeutic applications. In most of the therapeutic applications, it is the antimicrobial property that is being majorly explored, though the anti-inflammatory property has its fair share of applications. Though silver nanoparticles are rampantly used in many medical procedures and devices as well as in various biological fields, they have their drawbacks due to nanotoxicity. This review provides a comprehensive view on the mechanism of action, production, applications in the medical field, and the health and environmental concerns that are allegedly caused due to these nanoparticles. The focus is on effective and efficient synthesis of silver nanoparticles while exploring their various prospective applications besides trying to understand the current scenario in the debates on the toxicity concerns these nanoparticles pose.

Prabhu, Sukumaran; Poulose, Eldho K.

2012-10-01

362

The application of green chemistry methods in organophosphorus synthesis  

NASA Astrophysics Data System (ADS)

Data concerning the synthesis of organophosphorus compounds in ionic liquids, in water and under solvent-free conditions are considered and summarized. It is shown that this strategy, which complies with the definition of green chemistry, has advantages in terms of the rate of the process and the yields of target products as compared with syntheses in common organic solvents. The Wittig, Horner-Wadsworth-Emmons, Kabachnik-Fields, Arbuzov and Michaelis reactions are considered as examples. The bibliography includes 178 references.

Odinets, Irina L.; Matveeva, E. V.

2012-03-01

363

Synthesis of software programs for embedded control application  

Microsoft Academic Search

Software components for embedded reactive real-time appli- cations must satisfy tight code size and run-time constraints. Cooperating Finite State Machines provide a convenient in- termediate format for embedded system co-synthesis, between high-level specification languages and software or hardware implementations. We propose a software generation method- ology that takes advantage of the very restricted class of spec- ifications and allows for

Massimiliano Chiodo; Paolo Guisto; Attila Jurecska; Luciano Lavagno; Ellen Sentovich; Harry Hsieh; Kei Suzuki

1995-01-01

364

Applications of helical-chiral pyridines as organocatalysts in asymmetric synthesis.  

PubMed

A new family of chiral pyridines has been designed and synthesized for use in asymmetric organocatalysis. Thus, helical-chiral pyridines induce high enantioselectivity in a range of mechanistically unrelated, synthetically significant transformations, including Friedel-Crafts alkylation with nitroalkenes, periselective Diels-Alder reactions with nitroalkenes, the ring-opening of epoxides with a chloride nucleophile, and the propargylation of aldehydes. PMID:23172849

Peng, Zhili; Takenaka, Norito

2013-02-01

365

Synthesis and application of melamine-based dendrimer/sba-15 hybrid materials  

E-print Network

-Eder-Sauer-Wiechert reaction. It went virtually forgotten until recently when Benjamin List et al. studied it as a potential class I aldolase mimic. 46 They showed that it could be used as an enantioselective catalyst in aldol reactions including that shown...

Lunn, Jonathan David

2007-09-17

366

Synthesis, Characterization, and Applications of Hemifluorinated Dibranched Amphiphiles  

PubMed Central

Here we describe the synthesis, the physicochemical and preliminary pharmaceutical assessment of a novel class of hemifluorinated dibranched derivatives (M1diHxFy). These novel compounds have the remarkable ability of completely stopping the Ostwald ripening commonly associated with nanoemulsions. The developed synthesis is modular and it allows easy incremental structural variations in the fluorophilic (fluorous chains)-, lipophilic (alkyl spacer head)- and hydrophilic (polar head) domains. Furthermore, the synthesis can be easily scaled-up and highly pure compounds can be readily obtained through silica gel and fluoro-silica gel column chromatography, without any need to use HPLC or other time-consuming techniques. Surface properties like micelle formation, critical aggregation concentration (CAC) and emulsion stability studies demonstrated the different behavior of dibranched hemifluorinated surfactant (M1diHxFy) with respect to that of single chain semifluorinated analogues (MzFy). Remarkably, the new polymer M1diH3F8 drastically slowed the ripening of nanoemulsions of the commonly used fluorinated anesthetic sevoflurane over a period of more than one year. During this time, the nanodroplet size did not increase to more than 400 nm. This result is very promising for inducing and maintaining general anesthesia through intravenous delivery of volatile anesthetics, eliminating the need for the use of large and costly vaporizers in the operating room. PMID:21736353

Parlato, Maria Cristina; Jee, Jun-Pil; Teshite, Motti; Mecozzi, Sandro

2011-01-01

367

M-type barium hexaferrite synthesis and characterization for phase shifter applications  

E-print Network

M-type barium hexaferrite synthesis and characterization for phase shifter applications A. T. Wise; published online 13 April 2011) M-type barium hexaferrite films have been grown by liquid phase epitaxy half a percent. VC 2011 American Institute of Physics. [doi:10.1063/1.3559471] Since M-type barium

McHenry, Michael E.

368

M-type barium hexaferrite synthesis and characterization for phase shifter applications  

E-print Network

M-type barium hexaferrite synthesis and characterization for phase shifter applications A. T. Wise subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions #12;M-type barium-type barium hexaferrite films have been grown by liquid phase epitaxy and examined by x-ray diffraction

Laughlin, David E.

369

Automatic Synthesis of High-Performance Codes for Quantum Chemistry Applications  

E-print Network

for a class of scientific computations encountered in chemistry and physics. We focus on electronic structure of semiconductors and metals, and in computational chemistry codes such as ACES II, GAMESS, Gaussian, NWChem[8], #12Automatic Synthesis of High-Performance Codes for Quantum Chemistry Applications£ Gerald

Baumgartner, Gerald

370

An electrochemical method for the synthesis of few layer graphene sheets for high temperature applications.  

PubMed

We demonstrate an electrochemical technique for the large scale synthesis of high quality few layer graphene sheets (FLGS) directly from graphite using oxalic acid (a weak acid) as the electrolyte. One of the interesting observations is that the FLGS are stable at least up to 800 °C and hence have potential application in solid oxide fuel cells as a gas diffusion layer. PMID:24667902

Mahanandia, Pitamber; Simon, Frank; Heinrich, Gert; Nanda, Karuna Kar

2014-05-01

371

Advances in hypersonic vehicle synthesis with application to studies of advanced thermal protection system  

NASA Technical Reports Server (NTRS)

This report summarizes the work entitled 'Advances in Hypersonic Vehicle Synthesis with Application to Studies of Advanced Thermal Protection Systems.' The effort was in two areas: (1) development of advanced methods of trajectory and propulsion system optimization; and (2) development of advanced methods of structural weight estimation. The majority of the effort was spent in the trajectory area.

Ardema, Mark D.

1995-01-01

372

Shape Memory RGD-Containing Networks: Synthesis, Characterization, and Application in Cell Culture  

E-print Network

Shape Memory RGD-Containing Networks: Synthesis, Characterization, and Application in Cell Culture for more than a decade that hydrogels can be designed to exhibit shape memory functionality­--the ability to change from one defined shape to another when triggered by a defined stimulus­-- shape memory hydrogels

Mather, Patrick T.

373

Qualitative Analysis of Distributed Physical Systems with Applications to Control Synthesis \\Lambda  

E-print Network

Qualitative Analysis of Distributed Physical Systems with Applications to Control Synthesis \\Lambda fields. Analyzing and controlling these physical processes and systems are common tasks in many and controllability. This paper develops an ontological abstraction and a structure­based design mechanism

Bailey-Kellogg, Chris

374

Total Synthesis of (±)-Hirsutine: Application of Phosphine-Catalyzed Imine–Allene [4 + 2] Annulation  

PubMed Central

The total synthesis of the indole alkaloid hirsutine has been achieved, with a key step being the application of our phosphine-catalyzed [4 + 2] annulation of an imine with ethyl ?-methylallenoate. From commercially available indole-2-carboxaldehyde, the target was synthesized in 14 steps and 6.7% overall yield. PMID:22920858

Villa, Reymundo A.; Xu, Qihai; Kwon, Ohyun

2012-01-01

375

Invariant Synthesis for Verification of Parameterized Cyber-Physical Systems with Applications to  

E-print Network

Invariant Synthesis for Verification of Parameterized Cyber-Physical Systems with Applications for synthesizing inductive invariants for cyber- physical aerospace systems that are parameterized on the number in virtually any cyber-physical aerospace system. A variety of techniques for verifying aerospace systems have

Liberzon, Daniel

376

The Enantioselective Addition of Alkyne Nucleophiles to Carbonyl Groups  

PubMed Central

Over the past decade, large strides have been achieved in the invention of methods for the direct enantioselective addition of alkynes and metal alkynylide nucleophiles into prochiral aldehydes, ketones, and imines. This review highlights and compares the available methods for these transformations. PMID:24353484

Trost, Barry M.; Weiss, Andrew H.

2013-01-01

377

Catalytic, Enantioselective, Intramolecular Carbosulfenylation of Olefins. Preparative and Stereochemical Aspects  

PubMed Central

The first catalytic, enantioselective, intramolecular carbosulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenylsulfenylphthalimide, a chiral selenophosphoramide derived from BINAM, and ethanesulfonic acid as a co-catalytic Brønsted acid induced an efficient and selective cyclofunctionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylenedioxyphenyl ring. Under these conditions, 6-phenylthio-5,6,7,8-tetrahydronaphthalenes are formed diastereospecifically in good yields (50–92%) and high enantioselectivities (71:29 – 97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron deficient alkenes. The Brønsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with mono-activated arene nucleophiles. PMID:24328051

Denmark, Scott E.; Jaunet, Alex

2014-01-01

378

A Hybrid Phosphorus Ligand for Highly Enantioselective Asymmetric Hydroformylation  

E-print Network

A Hybrid Phosphorus Ligand for Highly Enantioselective Asymmetric Hydroformylation Yongjun Yan phosphorus ligand has been prepared starting from chiral NOBIN (2-amino-2- hydroxy-1,1-binaphthyl). Excellent phosphorus ligands bearing two different phosphorus groups are effective in asymmetric hydroformylation.2a

Zhang, Xumu

379

Cation-? interactions in iminium ion activation: correlating quadrupole moment & enantioselectivity.  

PubMed

A linear correlation between quadrupole moment (Qzz) and enantioselectivity (es) advocates the notion that a cation-? interaction is a contributing factor in the addition of uncharged nucleophiles to iminium salts derived from MacMillan's 1st generation catalyst. The quadrupole moment of the aryl shielding group is a useful qualitative parameter for predicting selectivity (Qzz < 0 ? high es). PMID:25434331

Holland, M C; Metternich, J B; Mück-Lichtenfeld, C; Gilmour, R

2014-12-01

380

Chiral phosphoric acid-catalyzed enantioselective and diastereoselective spiroketalizations.  

PubMed

Catalytic enantioselective and diastereoselective spiroketalizations with BINOL-derived chiral phosphoric acids are reported. The chiral catalyst can override the inherent preference for the formation of thermodynamic spiroketals, and highly selective formation of nonthermodynamic spiroketals could be achieved under the reaction conditions. PMID:22545651

Sun, Zhankui; Winschel, Grace A; Borovika, Alina; Nagorny, Pavel

2012-05-16

381

Synthesis and application of a new fluorous-tagged ammonia equivalent.  

PubMed

A novel fluorous-tagged ammonia equivalent has been developed. It is based on a nitrogen-oxygen bond, which can be cleaved in a traceless manner by a molybdenum complex or samarium diiodide. The application in the synthesis of ureas, amides, sulfonamides, and carbamates is described. The scope of the fluorous N-O linker is exemplified by the synthesis of itopride, a drug used for the treatment of functional dyspepsia. Itopride was synthesized with the aid of fluorous purification methods and the product was isolated in good overall yield, with high purity. PMID:20333716

Nielsen, Simon D; Smith, Garrick; Begtrup, Mikael; Kristensen, Jesper L

2010-04-19

382

Application of advanced multidisciplinary analysis and optimization methods to vehicle design synthesis  

NASA Technical Reports Server (NTRS)

Advanced multidisciplinary analysis and optimization methods, namely system sensitivity analysis and non-hierarchical system decomposition, are applied to reduce the cost and improve the visibility of an automated vehicle design synthesis process. This process is inherently complex due to the large number of functional disciplines and associated interdisciplinary couplings. Recent developments in system sensitivity analysis as applied to complex non-hierarchic multidisciplinary design optimization problems enable the decomposition of these complex interactions into sub-processes that can be evaluated in parallel. The application of these techniques results in significant cost, accuracy, and visibility benefits for the entire design synthesis process.

Consoli, Robert David; Sobieszczanski-Sobieski, Jaroslaw

1990-01-01

383

[3,3]-Sigmatropic rearrangements: recent applications in the total synthesis of natural products†  

PubMed Central

Among the fundamental chemical transformations in organic synthesis, the [3,3]-sigmatropic rearrangement occupies a unique position as a powerful, reliable, and well-defined method for the stereoselective construction of carbon–carbon or carbon–heteroatom bonds. While many other reactions can unite two subunits and create a new bond, the strengths of sigmatropic rearrangements derive from their ability to enable structural reorganization with unmatched build-up of complexity. Recent applications that illustrate [3,3]-sigmatropic processes as a key concept in the synthesis of complex natural products are described in this tutorial review, covering literature from about 2001 through early 2009. PMID:19847347

Ilardi, Elizabeth A.; Stivala, Craig E.

2014-01-01

384

Application of Modified Least Squares Method to a Space Curve Generating Mechanism for Optimum Synthesis  

NASA Astrophysics Data System (ADS)

Synthesis of mechanisms for generation of space curve is a challenging task for designers of the mechanical systems. Least squares method (LSM) has been extensively used for optimization of both planar and spatial mechanisms. Modified least squares method is applied for optimum synthesis of a slotted link mechanism with flexibly attached slider for space curve generation to show the scope of the modified method for optimum design. An example problem is included to illustrate the application of the method. Results are compared with conventional LSM.

Baishya, N. J.; Sharma, D.; Dixit, U. S.

2014-11-01

385

Enantioselective stable isotope analysis (ESIA) of polar Herbicides  

NASA Astrophysics Data System (ADS)

The complexity of aquatic systems makes it challenging to assess the environmental fate of chiral micropolutants. As an example, chiral herbicides are frequently detected in the environment (Buser and Muller, 1998); however, hydrological data is needed to determine their degradability from concentration measurements. Otherwise declining concentrations cannot unequivocally be attributed to degradation, but could also be caused by dilution effects. In contrast, isotope ratios or enantiomeric ratios are elegant alternatives that are independent of dilution and can even deliver insights into reaction mechanisms. To combine the advantages of both approaches we developed an enatioselective stable isotope analysis (ESIA) method to investigate the fate of the chiral herbicides 4-CPP ((RS)-2-(4-chlorophenoxy)-propionic acid), mecoprop (2-(4-Chloro-2-methylphenoxy)-propionic acid) and dichlorprop (2-(2,4-Dichlorophenoxy)-propionic acid). After testing the applicable concentration range of the method, enantioselective isotope fractionation was investigated by microbial degradation using dichlorprop as a model compound. The method uses enantioselective gas-chromatography (GC) to separate enantiomers. Subsequently samples are combusted online to CO2 and carbon isotope ratios are determined for each enantiomer by isotope-ratio-mass-spectrometry (IRMS). Because the analytes contain a polar carboxyl-group, samples were derivatised prior to GC-IRMS analysis with methanolic BF3 solution. Precise carbon isotope analysis (2? ?0.5‰) was achieved with a high sensitivity of ? 7 ng C that is needed on column for one analysis. Microbial degradation of the model compound dichlorprop was conducted with Delftia acidovorans MC1 and pronounced enantiomer fractionation, but no isotope fractionation was detected. The absence of isotope fractionation can be explained by two scenarios: either the degrading enzyme has no isotopic preference, or another step in the reaction without an isotopic preference was rate determining. Our findings are in contrast to previously reported results for the degradation of ?-hexachlorocyclohexane (Badea et al., 2012), where isotope fractionation, but no enantiomeric fractionation was observed. Hence the two lines of evidence seem to be independent of each other. Enhanced insight maybe provided when both effects appear simultaneously, as shown downstream of a landfill site under anaerobic conditions for the chiral herbicide 4-CPP (Milosevic et al., 2013). Buser HR, Muller MD (1998): Occurrence and transformation reactions of chiral and achiral phenoxyalkanoic acid herbicides in lakes and rivers in Switzerland. Environmental Science & Technology 32 (5):626-633. Badea S-L, Vogt C, Gehre M, Fischer A, Danet A-F, Richnow H-H (2011): Development of an enantiomer-specific stable carbon isotope analysis (ESIA) method for assessing the fate of alpha-hexachlorocyclohexane in the environment. Rapid Communications in Mass Spectrometry 25 (10):1363-1372. Milosevic N, Qiu S, Elsner M, Einsiedl F, Maier MP, Bensch HKV, Albrechtsen HJ, Bjerg PL (2013): Combined isotope and enantiomer analysis to assess the fate of phenoxy acids in a eterogeneous geologic setting at an old landfill. Water Research 47 (2): 637-649.

Maier, Michael; Qiu, Shiran; Elsner, Martin

2013-04-01

386

Application of Chemoenzymatic Hydrolysis in the Synthesis of 2-Monoacylglycerols  

PubMed Central

The selective biocatalyzed synthesis of 2-monoacylglycerols (2-MAGs) through the use of commercially available immobilized Candida antarctica (Novozym435) and Rhizomucor miehei is explored. Reactions at room temperature result in the formation of a 2-MAG and a corresponding ethyl ester of the fatty acid with immobilized Candida antarctica within 2h with yields ranging from 36%–83%. Similar reaction conditions with immobilized Rhizomucor miehei yielded exclusively the 2-MAG after 24h with yields ranging from 37% to 88%. Yields vary on the acyl group at the sn-2 position and choice of enzyme involved. PMID:22822273

Whitten, Kyle M.; Makriyannis, Alexandros; Vadivel, Subramanian K.

2012-01-01

387

Applications of Ultrasound to the Synthesis of Nanostructured Materials  

Microsoft Academic Search

Recent advances in nanostructured materials have been led by the\\u000a development of new synthetic methods that provide control over size,\\u000a morphology, and nano\\/microstructure. The utilization of high intensity\\u000a ultrasound offers a facile, versatile synthetic tool for nanostructured\\u000a materials that are offers a facile, by conventional methods. The primary\\u000a physical phenomena associated with ultrasound that are relevant to\\u000a materials synthesis are

Jin Ho Bang; Kenneth S. Suslick

2010-01-01

388

Crystal structures of two Bacillus carboxylesterases with different enantioselectivities.  

PubMed

Naproxen esterase (NP) from Bacillus subtilis Thai I-8 is a carboxylesterase that catalyzes the enantioselective hydrolysis of naproxenmethylester to produce S-naproxen (E>200). It is a homolog of CesA (98% sequence identity) and CesB (64% identity), both produced by B. subtilis strain 168. CesB can be used for the enantioselective hydrolysis of 1,2-O-isopropylideneglycerol (solketal) esters (E>200 for IPG-caprylate). Crystal structures of NP and CesB, determined to a resolution of 1.75Å and 2.04Å, respectively, showed that both proteins have a canonical ?/? hydrolase fold with an extra N-terminal helix stabilizing the cap subdomain. The active site in both enzymes is located in a deep hydrophobic groove and includes the catalytic triad residues Ser130, His274, and Glu245. A product analog, presumably 2-(2-hydroxyethoxy)acetic acid, was bound in the NP active site. The enzymes have different enantioselectivities, which previously were shown to result from only a few amino acid substitutions in the cap domain. Modeling of a substrate in the active site of NP allowed explaining the different enantioselectivities. In addition, Ala156 may be a determinant of enantioselectivity as well, since its side chain appears to interfere with the binding of certain R-enantiomers in the active site of NP. However, the exchange route for substrate and product between the active site and the solvent is not obvious from the structures. Flexibility of the cap domain might facilitate such exchange. Interestingly, both carboxylesterases show higher structural similarity to meta-cleavage compound (MCP) hydrolases than to other ?/? hydrolase fold esterases. PMID:24418394

Rozeboom, Henriëtte J; Godinho, Luis F; Nardini, Marco; Quax, Wim J; Dijkstra, Bauke W

2014-03-01

389

Cysteine functionalized copper organosol: synthesis, characterization and catalytic application  

NASA Astrophysics Data System (ADS)

We herein report a facile one-pot synthesis, stabilization, redispersion and Cu-S interaction of L-cysteine and dodecanethiol (DDT) protected copper organosol in toluene from precursor copper stearate using sodium borohydride in toluene under a nitrogen atmosphere. Surface modification of the synthesized copper organosol with an amino acid L-cysteine and an alkanethiol (dodecanethiol, DDT) is accomplished by a thiolate bond between the used ligands and nanoparticle surface. The cysteine molecule binds the copper surface via a thiolate and amine linkage but not through electrostatic interaction with the carboxylate group due to the solvent polarity and dielectric medium. Fourier transform infrared (FTIR) analysis was performed to confirm the surface functionalization of the amino acid and DDT to the copper surface. Copper organosol has been characterized by optical spectroscopy (UV/vis), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). The as-synthesized particles are spherical in shape and exhibit a Mie scattering profile with an absorption maxima in the visible range. Copper nanoparticles capped by cysteine and/or DDT in non-aqueous media are found to represent an interesting catalytic approach for the synthesis of octylphenyl ether.

Panigrahi, Sudipa; Kundu, Subrata; Basu, Soumen; Praharaj, Snigdhamayee; Jana, Subhra; Pande, Surojit; Ghosh, Sujit Kumar; Pal, Anjali; Pal, Tarasankar

2006-11-01

390

Triaxial Burke-Schumann Flames with Applications to Flame Synthesis  

NASA Technical Reports Server (NTRS)

The problem of a flame generated by three coaxial flows is solved by extending the Burke-Schumann methodology to include a third stream. The solution is particularly relevant to flame synthesis wherein multiple tubes are often employed either to introduce inert as a diffusion barrier or to introduce more than two reactants. The general problem is solved where the inner and outer tubes contain reactants and the middle tube contains either an inert or a third reactant. Relevant examples are considered and the results show that the triaxial Burke-Schumann flame can be substantially more complicated than the traditional Burke-Schumann flame. When the middle flow is inert the flame temperature is no longer constant but increases axially, reaching a maximum at the flame centerline. At the exit the flame does not sit on the tube exit but instead resides between the inner and outer tubes, resulting in an effective barrier for particle build-up on the burner rim. For the case of a third reactant in the middle flow, synthesis chemistry where the inner reaction is endothermic and the outer reaction is exothermic is considered. In addition to showing the flame temperature and flame shape, the results identify conditions wherein reaction is not possible due to insufficient heat transfer from the outer flame to support the inner flame reaction.

Chao, B. H.; Axelbaum, R. L.; Gokoglu, Suleyman (Technical Monitor)

2000-01-01

391

Nano-engineered materials based on fullerenes: synthesis and biomedical applications  

NASA Astrophysics Data System (ADS)

The nanoengineering of various materials for biomedical application has became in the last decade one of the most important research areas, due to the continuous struggle to find new and more efficient instruments for the therapy of cancer and other diseases. Attempts to obtain functionalized derivatives of fullerene seek the synthesis of watersoluble materials, in order to investigate their effects in physiological conditions. International studies on the biological properties of fullerenes and their derivatives, are now targeted towards anti-tumor effects, pharmacology and their involvement in oxidative stress. Their toxicity, demonstrated both in vitro and in vivo is important for characterization and selection of applications. Phototoxicity of some molecules of fullerenes has been identified as future therapeutic tool. The present paper describes the synthesis, characterization and some biomedical applications of some nanomaterials based on fullerenes.

Fierascu, Radu Claudiu; Dumitriu, Irina; Ion, Rodica Mariana; Neagu, Monica; Constantin, Carolina; Stavaru, Crina

2010-11-01

392

When gold meets chiral Brønsted acid catalysts: extending the boundaries of enantioselective gold catalysis.  

PubMed

This review describes the development in the use of Au(I)/Brønsted acid binary catalytic systems to enable an enantioselective transformation in one-pot that cannot be achieved by gold catalysts alone. The examples discussed herein are promising since apart from using chiral ligands there exists a possibility of using chiral Brønsted acids. Clearly, the horizon for enantioselective gold catalysis has been expanded as more options to make the gold-catalyzed reactions enantioselective have become available. PMID:25177929

Inamdar, Suleman M; Konala, Ashok; Patil, Nitin T

2014-12-14

393

An Overview of Stereoselective Synthesis of ?-Aminophosphonic Acids and Derivatives  

PubMed Central

An overview of all methodologies published during the last few years focused to the stereoselective (diastereoselective or enantioselective) synthesis of ?-aminophosphonic acids and derivatives is reported. The procedures have been classified according a retrosynthetic strategy and taking into account the formation of each one of the bonds connected to the chiral centre. PMID:20871799

Ordóñez, Mario; Rojas-Cabrera, Haydée; Cativiela, Carlos

2009-01-01

394

Efficient, Divergent Synthesis of Cryptophycin Unit A Analogues  

PubMed Central

A flexible and divergent synthesis of cryptophycin unit A analogues is described. This method relies on iridium-catalysed stereo- and enantioselective crotylation and chemoselective one-pot oxidative olefination to access common intermediate 8. Heck, cross metathesis, and Suzuki-Miyaura reactions are illustrated for the generation of methyl ester unit A analogues 10a-d. PMID:22617820

Bolduc, Kyle L.; Larsen, Scott D.; Sherman, David H.

2012-01-01

395

The first asymmetric total synthesis of (+)-coriandrone A and B.  

PubMed

The first enantioselective total synthesis of (+)-coriandrone A and B, two bioactive natural products, has been achieved in 10 steps and 11 steps starting from commercially available methyl 2-hydroxy-4-methoxybenzoate. Key reactions include a Claison rearrangement, a Shi-type epoxidation-cyclization sequence and ortho-metallation of t-butylbenzamides with (S)-(-)-propylene oxide reaction. PMID:23986305

Wang, Wenjing; Xue, Jijun; Tian, Tian; Jiao, Yingdong; Li, Ying

2013-10-21

396

Synthesis of anisotropic silver nanoparticles using novel strain, Bacillus flexus and its biomedical application.  

PubMed

Synthesis of metallic nanoparticles has attracted by bacterial based production and alternative to physical and chemical approaches. The present work was focused to nominate a bacterial strain for synthesis of potential silver nanoparticles. The target was achieved by screening of 127 isolates from silver mining wastes. A strain designated S-27 found to be a potential candidate for rapid synthesis of silver nanoparticles among tested microorganisms. It was subjected to molecular characterization by 16S rDNA sequence analysis. It was found that S-27 belonging to Bacillus flexus. Synthesis of silver nanoparticles was achieved by addition of culture supernatants with aqueous silver nitrate solution, immediately it turns to brown colour solution showed a peak at 420 nm corresponding to the plasmon absorbance of silver nanoparticles by UV-vis spectroscopy. Various instrumentation techniques, such as AFM, FESEM, XRD and FTIR, were adopted to characterize the synthesized nanoparticles. Anisotropic nanoparticles, such as spherical and triangular shaped nanoparticles, have been synthesized and sizes were found to be 12 and 65 nm, respectively. It was stable in aqueous solution in five months period of storage at room temperature in the dark. Synthesized nanoparticles showed efficacy on antibacterial property against clinically isolated multi-drug resistant (MDR) microorganisms. It is suggested that biogenic synthesis of nanoparticles have wide-application in medicine and physical chemistry and it can produce with eco-friendly, easy downstream processing and rapid scale-up processing. PMID:23018021

Priyadarshini, S; Gopinath, V; Meera Priyadharsshini, N; MubarakAli, D; Velusamy, P

2013-02-01

397

Structural effects on the enantioselective acetylation of 4-hydroxychromans catalyzed by microbial lipases  

Microsoft Academic Search

Kinetic resolutions of a series of racemic 4-hydroxychromans by the Candida cylindracea lipase catalysed acetylation are described. Correlation between structure (conformation) and enantioselectivity is discussed.

Maja Majeri?; Mirjana Gelo-Puji?; Vitomir Šunji?; Albert Lévai; Peter Sebök; Tibor Timàr

1995-01-01

398

Synthesis, NMR Characterization, and a Simple Application of Lithium Borotritide.  

PubMed

LiBH(4) is a powerful and selective reagent for regiospecific reduction reactions. A simple synthesis of LiB(3)H(4) at near theoretical specific radioactivity is reported. We have treated Li(3)H synthesized from tritium gas ((3)H(2), approximately 98%) with BBr(3) to produce LiB(3)H(4) (specific activity = 4120 GBq/mmol = 110 Ci/mmol. The maximum theoretical specific activity of LiB(3)H(4) is 4252 GBq/mmol = 115.04 Ci/mmol; 1 matom of (3)H = 1063 GBq = 28.76 Ci.) The tritium labeling performance of the reagent was tested by an exemplary reduction of 2-naphthaldehyde to 2-naphthalenemethanol. LiB(3)H(4) and the reduction products were characterized by a combination of (1)H, (3)H, and (11)B NMR techniques, as appropriate. PMID:11667852

Than, Chit; Morimoto, Hiromi; Andres, Hendrik; Williams, Philip G.

1996-12-13

399

Synthesis of eukaryotic translation elongation inhibitor lactimidomycin via Zn(II)-mediated Horner-Wadsworth-Emmons macrocyclization.  

PubMed

An enantioselective synthesis of potent eukaryotic translation elongation inhibitor lactimidomycin has been accomplished in 21 linear steps. This synthesis features a Zn(II)-mediated Horner-Wadsworth-Emmons reaction that could be executed on a large scale to provide the highly strained 12-membered lactimidomycin macrolactone. PMID:23731327

Larsen, Brian J; Sun, Zhankui; Nagorny, Pavel

2013-06-21

400

Development of catalysts and ligands for enantioselective gold catalysis.  

PubMed

During the past decade, the use of Au(I) complexes for the catalytic activation of C-C ?-bonds has been investigated intensely. Over this time period, the development of homogeneous gold catalysis has been extraordinarily rapid and has yielded a host of mild and selective methods for the formation of carbon-carbon and carbon-heteroatom bonds. The facile formation of new bonds facilitated by gold naturally led to efforts toward rendering these transformations enantioselective. In this Account, we survey the development of catalysts and ligands for enantioselective gold catalysis by our research group as well as related work by others. We also discuss some of our strategies to address the challenges of enantioselective gold(I) catalysis. Early on, our work with enantioselective gold-catalyzed transformations focused on bis(phosphinegold) complexes derived from axially chiral scaffolds. Although these complexes were highly successful in some reactions like cyclopropanation, the careful choice of the weakly coordinating ligand (or counterion) was necessary to obtain high levels of enantioselectivity for the case of allene hydroamination. These counterion effects led us to use the anion itself as a source of chirality, which was successful in the case of allene hydroalkoxylation. In general, these tactics enhance the steric influence around the reactive gold center beyond the two-coordinate ligand environment. The use of binuclear complexes allowed us to use the second gold center and its associated ligand (or counterion) to exert a further steric influence. In a similar vein, we employed a chiral anion (in place of or in addition to a chiral ligand) to move the chiral information closer to the reactive center. In order to expand the scope of reactions amenable to enantioselective gold catalysis to cycloadditions and other carbocyclization processes, we also developed a new class of mononuclear phosphite and phosphoramidite ligands to supplement the previously widely utilized phosphines. However, we needed to judiciously design the steric environment to create "walls" that enclose the gold center. We also successfully applied these same considerations to the development of binuclear carbene ligands for gold. Finally, we describe the design of bifunctional urea-monophosphine ligands used in a gold-catalyzed three-component coupling. PMID:24228794

Wang, Yi-Ming; Lackner, Aaron D; Toste, F Dean

2014-03-18

401

Synthesis and applications of electron deficient conjugated polymers  

E-print Network

Chapter 1. In this introductory chapter, we present the general properties of conjugated polymers for sensory and electronic applications, with a special emphasis placed on electron-deficient materials. Chapter 2. In this ...

Kim, Youngmi, Ph. D

2005-01-01

402

Design and synthesis of nanocrystal heterostructures for optoelectronic applications  

E-print Network

Colloidal semiconductor nanocrystals can be used for a variety of optoelectronic applications including light emitting devices (LEDs) and photovoltaics. Their narrow emission spectra make them excellent fluorophors for use ...

Halpert, Jonathan E

2008-01-01

403

Synthesis and Characterization of Polymer Nanocomposites for Energy Applications  

E-print Network

Polymer nanocomposites are used in a variety of applications due to their good mechanical properties. Specifically, better performance of lithium ion batteries and thermal interface material can be obtained by using conductive materials and polymer...

Park, Wonchang

2011-10-21

404

Synthesis and application of new polymer bound catalysts  

SciTech Connect

Nitric acid has been shown to be a weak acid in acetonitrile. It is conceivable that a nitrate salt of a weakly Lewis acidic cation could furnish a ''naked'' nitrate anion as a basic catalyst in a variety of reactions in non-aqueous solvents. Such a nitrate salt could also be bound to a polymeric support via the cation, thereby allowing for reclamation and recycling of the nitrate ion. This subject is dealt with in Chapter 2, wherein my contributions consisted of performing all the reactions with the polymer supported catalyst and carrying out the experiments necessary to shed light on the reaction mechanisms. Chapter 3 contains a description of the structure and catalytic properties of an azidoproazaphosphatrane. This compound is an air-stable versatile catalyst that has proven useful not only homogeneously, but also when bound to a solid support. The synthesis of a polymer bound proazaphosphatrane containing a trivalent phosphorus is presented in Chapter 4. Such a compound has been sought after by our group for a number of years. Not only does the synthesis I have accomplished for it allow for easier separation of proazaphosphatrane catalysts from reaction mixtures, but recycling of the base is made much simpler. Proazaphosphatranes are useful homogeneous catalysts that activate atoms in other reagents, thus enhancing their reactivity. The next chapters deal with two such reactions with aldehydes and ketones, namely silylcyanations with trialkylsilylcyanides (Chapters 5 and 6) and reductions with poly(methylhydrosiloxane), in Chapter 7. In Chapter 5, Zhigang Wang performed the initial optimization and scoping of the reaction, while repetitions of the scoping experiments for reproducibility, determination of diastereomeric ratios, and experiments aimed at elucidating aspects of the mechanism were performed by me. The proazaphosphatrane coordinates to the silicon atom in both cases, thereby allowing the aforementioned reactions to proceed under much milder conditions. Proazaphosphatranes are also effective Broensted-Lowry bases. This is illustrated in Chapter 8 wherein a wide variety of conjugate addition reactions are catalyzed by proazaphosphatranes. In that chapter, repetitions of the nitroalkane addition reactions for reproducibility, improved spectral data for the products and comparisons of literature yields of all reactions were performed by the author.

Fetterly, Brandon Michael

2005-08-01

405

Quinones as dienophiles in the Diels-Alder reaction: history and applications in total synthesis.  

PubMed

In the canon of reactions available to the organic chemist engaged in total synthesis, the Diels-Alder reaction is among the most powerful and well understood. Its ability to rapidly generate molecular complexity through the simultaneous formation of two carbon-carbon bonds is almost unrivalled, and this is reflected in the great number of reported applications of this reaction. Historically, the use of quinones as dienophiles is highly significant, being the very first example investigated by Diels and Alder. Herein, we review the application of the Diels-Alder reaction of quinones in the total synthesis of natural products. The highlighted examples span some 60?years from the landmark syntheses of morphine (1952) and reserpine (1956) by Gates and Woodward, respectively, through to the present day examples, such as the tetracyclines. PMID:24446164

Nawrat, Christopher C; Moody, Christopher J

2014-02-17

406

Synthesis of chiral sulfoximine-based thioureas and their application in asymmetric organocatalysis  

PubMed Central

Summary For the first time, chiral sulfoximine derivatives have been applied as asymmetric organocatalysts. In combination with a thiourea-type backbone the sulfonimidoyl moiety leads to organocatalysts showing good reactivity in the catalytic desymmetrization of a cyclic meso-anhydride and moderate enantioselectivity in the catalytic asymmetric Biginelli reaction. Straightforward synthetic routes provide the newly designed thiourea-sulfoximine catalysts in high overall yields without affecting the stereohomogeneity of the sulfur-containing core fragment. PMID:23019479

Frings, Marcus; Thomé, Isabelle

2012-01-01

407

Synthesis, NMR characterization, and a simple application of lithium borotritide  

SciTech Connect

LiBH{sub 4} is a powerful and selective reagent for regiospecific reduction reactions. A simple synthesis of LiB{sup 3}H{sub 4} at near theoretical specific radioactivity is reported. The authors have treated Li{sup 3}H synthesized from tritium gas ({sup 3}H{sub 2}, {approximately}98%) with BBr{sub 3} to produce LiB{sup 3}H{sub 4} (specific activity = 4120 GBq/mmol = 110 Ci/mmol. The maximum theoretical specific activity of LiB{sup 3}H{sub 4} is 4252 GBq/mmol = 115.04 Ci/mmol; 1 matom of {sup 3}H = 1063 GBq = 28.76 Ci.) The tritium labeling performance of the reagent was tested by an exemplary reduction of 2-naphthaldehyde to 2-naphthalenemethanol. LiB{sup 3}H{sub 4} and the reduction products were characterized by a combination of {sup 1}H, {sup 3}H, and {sup 11}B NMR techniques, as appropriate. 35 refs., 1 fig.

Than, Chit; Morimoto, Hiromi [Lawrence Berkeley National Lab., CA (United States)] [Lawrence Berkeley National Lab., CA (United States); Andres, H. [Sandoz Pharma Ltd., Basle (Switzerland)] [and others] [Sandoz Pharma Ltd., Basle (Switzerland); and others

1996-12-13

408

Synthesis and application of dye-ligand affinity adsorbents.  

PubMed

Dye-ligand affinity chromatography is a widely used technique in protein purification. The utility of the reactive dyes as affinity ligands results from their unique chemistry, which confers wide specificity towards a large number of proteins. They are commercially available, are inexpensive, and can easily be immobilized. Important factors that contribute to the successful operation of a dye-ligand chromatography include adsorbent properties, such as matrix type and ligand concentration, the buffer conditions used in the adsorption and elution stages, and contacting parameters like flow rate and column geometry. In general, with dye-ligand affinity chromatography, the specificity is provided by the adsorption and elution conditions employed in a particular purification, and these must often be worked out by trial and error. The present chapter provides protocols for the synthesis of dye-ligand affinity adsorbents as well as protocols for screening, selection, and optimization of a dye-ligand purification step. The purification of the glutathione transferases from Phaseolus vulgaris crude extract on Cibacron Blue 3GA-Sepharose is given as an example. PMID:24648082

Chronopoulou, Evangelia; Labrou, Nikolaos E

2014-01-01

409

Synthesis and properties of multipod-shaped ZnO nanorods for gas-sensor applications  

Microsoft Academic Search

We reported the synthesis and optical properties of ZnO nanorods with multipod shapes, and their applications as gas sensors. The multipod-shaped ZnO (M-ZnO ) nanorods, having tens of needle-like nanorods united at a common junction, exhibited different structural and optical characters from those of the tetrapod-shaped ZnO (T-ZnO) nanorods. Employing the M-ZnO and the T-ZnO nanorods, respectively, gas sensors were

T. Gao; T. H. Wang

2005-01-01

410

Silica-based nanocapsules: synthesis, structure control and biomedical applications.  

PubMed

Synergistically combining the merits of silica (e.g., mechanical robustness, biocompatibility and great versatility in surface functionalization) and capsular configurations (e.g., a large inner cavity, low density and favourable colloidal properties), silica-based nanocapsules (SNCs) with a size cutoff of ?100 nm have gained growing interest in encapsulating bioactive molecules for bioimaging and controlled delivery applications. Within this context, this review provides a comprehensive overview of the synthetic strategies, structural control and biomedical applications of SNCs. Special emphasis is placed on size control at the nanoscale and material composition manipulation of each strategy and the newly emerging synthetic strategies. The applications of SNCs in bioimaging/diagnosis and drug delivery/therapy and the structure engineering that is critically important for the bio-performance of SNCs are also addressed in this review. PMID:25310644

Zhang, Yu; Hsu, Benedict You Wei; Ren, Changliang; Li, Xu; Wang, John

2015-01-01

411

Engineering chiral porous metal-organic frameworks for enantioselective adsorption and separation  

NASA Astrophysics Data System (ADS)

The separation of racemic molecules is of substantial significance not only for basic science but also for technical applications, such as fine chemicals and drug development. Here we report two isostructural chiral metal-organic frameworks decorated with chiral dihydroxy or -methoxy auxiliares from enantiopure tetracarboxylate-bridging ligands of 1,1?-biphenol and a manganese carboxylate chain. The framework bearing dihydroxy groups functions as a solid-state host capable of adsorbing and separating mixtures of a range of chiral aromatic and aliphatic amines, with high enantioselectivity. The host material can be readily recycled and reused without any apparent loss of performance. The utility of the present adsorption separation is demonstrated in the large-scale resolution of racemic 1-phenylethylamine. Control experiments and molecular simulations suggest that the chiral recognition and separation are attributed to the different orientations and specific binding energies of the enantiomers in the microenvironment of the framework.

Peng, Yongwu; Gong, Tengfei; Zhang, Kang; Lin, Xiaochao; Liu, Yan; Jiang, Jianwen; Cui, Yong

2014-07-01

412

Metallic nanoparticles: microbial synthesis and unique properties for biotechnological applications, bioavailability and biotransformation.  

PubMed

Abstract The impact of nanotechnology in all areas of science and technology is evident. The expanding availability of a variety of nanostructures with properties in the nanometer size range has sparked widespread interest in their use in biotechnological systems, including the field of environmental remediation. Nanomaterials can be used as catalysts, adsorbents, membranes, water disinfectants and additives to increase catalytic activity and capability due to their high specific surface areas and nanosize effects. Thus, nanomaterials appear promising for new effective environmental technologies. Definitely, nanotechnology applications for site remediation and wastewater treatment are currently in research and development stages, and new innovations are underway. The synthesis of metallic nanoparticles has been intensively developed not only due to its fundamental scientific interest but also for many technological applications. The use of microorganisms in the synthesis of nanoparticles is a relatively new eco-friendly and promising area of research with considerable potential for expansion. On the other hand, chemical synthesis occurs generally under extreme conditions (e.g. pH, temperature) and also chemicals used may have associated environmental and human health impacts. This review is an overview of current research worldwide on the use of microorganisms during the biosynthesis of metallic nanoparticles and their unique properties that make them good candidates for many applications, including in biotechnology. PMID:23937251

Pereira, Luciana; Mehboob, Farrakh; Stams, Alfons J M; Mota, Manuel M; Rijnaarts, Huub H M; Alves, M Madalena

2015-03-01

413

One-dimensional CdS nanostructures: synthesis, properties, and applications  

NASA Astrophysics Data System (ADS)

One-dimensional (1D) semiconductor nanostructures are of prime interest due to their potential in investigating the size and dimensionality dependence of the materials' physical properties and constructing nanoscale electronic and optoelectronic devices. Cadmium sulfide (CdS) is an important semiconductor compound of the ii-vi group, and its synthesis and properties have been of growing interest owing to prominent applications in several fields. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, novel properties and unique applications of 1D CdS nanostructures in nanotechnology. It begins with the rational design and synthesis of 1D CdS nanostructures, and then highlights a range of unique properties and applications (e.g. photoluminescence, cathodoluminescence, electrochemiluminescence, photocatalysis, lasers, waveguides, modulators, solar cells, field-effect transistors, photodetectors, field-emitters, and nanogenerators) associated with them. Finally, the review is concluded with the author outlook of the perspectives with respect to future research on 1D CdS nanostructures.

Zhai, Tianyou; Fang, Xiaosheng; Li, Liang; Bando, Yoshio; Golberg, Dmitri

2010-02-01

414

Transition metal-catalyzed enantioselective hydrogenation of enamides and enamines.  

PubMed

Transition metal-catalyzed enantioselective hydrogenation of enamides and enamines is one of the most important methods for the preparation of optically active amines. This review describes the recent developments of highly efficient catalytic asymmetric hydrogenation of enamides, and enamines. It specifically focuses on the substrates because hydrogenation of enamides and enamines is highly dependent on the substrates although the chiral metal catalysts play a significant role. PMID:24595741

Zhou, Qi-Lin; Xie, Jian-Hua

2014-01-01

415

Enantioselective hydrolyzation and photolyzation of dufulin in water  

PubMed Central

Background Dufulin is a novel, highly effective antiviral agent that activatives systemic acquired resistance of plants. This compound is widely used in China to prevent and control viral diseases in tobacco, vegetable and rice. Dufulin can treat plants infected by the tobacco mosaic virus and the cucumber mosaic virus. However, the achiral analysis and residue determination of dufulin remain underdeveloped because of its high enantioselectivity rates and high control costs. The enantioselectivity of an antiviral compound is an important factor that should be considered when studying the effect of chiral pesticides on the environment. The enantioselective degradation of dufulin in water remains an important objective in pesticide science. Results The configuration of dufulin enantiomers was determined in this study based on its circular dichroism spectra. The S-(+)-dufulin and R-(?)-dufulin enantiomers were separated and identified using an amylose tris-(3,5-dimethylphenylcarbamate) chiral column by normal phase high-performance liquid chromatography. The degradation of the rac-dufulin racemate and its separate enantiomers complied with first-order reaction kinetics and demonstrated acceptable linearity. The enantioselective photolysis of rac-dufulin allowed for the faster degradation of R-(?)-dufulin, as compared with S-(+)-dufulin. However, S-(+)-dufulin was hydrolyzed faster than its antipode. Conclusion The photolysation and hydrolyzation of dufulin in water samples normally complied with the first-order kinetics and demonstrated acceptable linearity (R2>0.66). A preferential photolysation of the R-(?)-enantiomer was observed in water samples. Moreover, the S-(+)-enantiomer was hydrolyzed faster than its antipode. PMID:23680125

2013-01-01

416

Synthesis and application of mesoporous and macroporous particles  

NASA Astrophysics Data System (ADS)

Phosphine and amine functionalized mesoporous silica materials were metallated with Rh(CO)2(i-Pr2NH)Cl or Rh2 (CO)4Cl2, respectively to yield catalysts containing the Rh(PPh2R)2(CO)Cl or Rh(CO)2(NH2 R)Cl, where R is a propyl chain bonded to the silica surface, reactive centers. In order to ascertain the effect of pore size on rates of hydroformylation catalysis both 35 A and 45 A pore size materials were used. Using the hydroformylation of octene as a reference reaction, the phosphine based, 45 A catalysts were 1.5 to 1.3 times faster than the amine based, 45 A catalysts, and the 45 A materials were 2.6 to 2.1 times faster than the 35 A materials. The ability of the surface bound phosphine catalysts to affect hydroformylation was strongly influenced by the steric constraints of the substrate. Terminal alkenes were readily hydroformylated and norbornene was slowly hydroformylated, but pinene, trans-cyclododecene, cyclohexene and cholesterol were completely unaffected. Hollow porous microspheres can be created for use as electrolyte storage within the active material of the battery electrode. Synthesis of porous hollow glass microspheres (HGMs) has been accomplished by pyrolyzing a mixture of cobalt, titanium, and colloidal silica. The porous HGMs are generated by spray flame pyrolysis of a solution of cobalt, titanium, and silica into a 7000 tube furnace. A phase separation condenses the cobalt to the center of the sphere where it can be etched as well as titanium. Other etching techniques include using HF to etch commercial hollow glass microspheres, and sodium diffusion.

Newell, J. David

417

Synthesis and characterization of polymers for light waveguide applications  

NASA Astrophysics Data System (ADS)

The overall goal of this research was to prepare organo- soluble polymers that display low birefringence, low optical loss, and high thermal stability for use in light waveguide devices. Thus, two series of thermally stable polymers, i.e., aromatic polyimides and perfluorocyclobutane-containing poly(aryl ethers), were synthesized and characterized. The approach to the aromatic polyimides involved the synthesis of a new series of 4,4'-(9- fluorenylidene)dianilines containing large polarizable substituents. The diamines were polymerized with 2,2'-bis[4-(3,4- dicarboxyphenoxy)phenyl]propane dianhydride (BisA-DA) and 2,2'-bis(3,4- dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) in refluxing m-cresol containing a catalytic amount of isoquinoline. The polyimides were soluble in common organic solvents such as N-methyl-2- pyrrolidinone (NMP), tetrahydrofuran (THF), chloroform (CHCl3), and cyclopentanone and could be solution cast into tough films. Thin films of the new cardo polyimides displayed birefringences that ranged from -0.0042 to 0.0074. In the second part of this work, a series of new difunctional and trifunctional trifluorovinylether-containing monomers was synthesized and polymerized via the thermal cyclodimerization of the vinyl groups. The number of carbon-hydrogen bonds was minimized in these systems in order to minimize the optical loss. A tough, transparent film was made from a polymer prepared from a trifunctional monomer, 1,1,1- trifluoro-2,2,2-tris(4-trifluorovinyloxyphenyl)ethane, which had a birefringence of 0.0008. The film showed negligible absorption at 1550 nm in the near-IR region. The polymer was also very thermally stable. Most of the linear polymers were soluble in common organic solvents such as NMP, THF, chloroform and cyclopentanone and could be solution cast into thin films, which displayed birefringences that ranged from -0.0005 to 0.0048.

Li, Bo

418

Dearomatization Strategies in the Synthesis of Complex Natural Products  

PubMed Central

Evolution in the field of the total synthesis of natural products has led to exciting developments over the last decade. Numerous chemo-selective and enantioselective methodologies have emerged from total syntheses, resulting in efficient access to many important natural product targets. This Review highlights recent developments concerning dearomatization, a powerful strategy for the total synthesis of architecturally complex natural products wherein planar, aromatic scaffolds are converted to three-dimensional molecular architectures. PMID:21506209

Roche, Stéphane P.; Porco, John A.

2014-01-01

419

Cyclodextrin Derivatives as Chiral Supramolecular Receptors for Enantioselective Sensing  

PubMed Central

In view of the chiral nature of many bio-molecules (and all bio-macromolecules), most of therapeutically active compounds which target these molecules need to be chiral and “good handed” to be effective. In addition to asymmetric synthetic and separation methodologies, enantioselective chemical sensors, able to distinguish between two enantiomers of the same molecule, are of relevance. In order to design these sensing tools, two major classes of enantioselective layers have been developed. The first is based on molecularly imprinted polymers which are produced (polymerized) in the presence of their target, thus the polymeric material keep in “memory” the size and the shape of this molecule and the system could be used for sensing (not reviewed here). The second approach makes use of sensitive layers containing chiral macrocyclic receptors able of stereoselective molecular recognition; these receptors are mainly based on cyclodextrins. In this contribution, are reviewed achievements in the use of native or chemically modified cyclodextrins for chiral sensing purposes (at interfaces). Potentialities of other chiral macrocycles based on calixarenes, calix-resorcinarenes or crown-ethers as supramolecular receptors for enantioselective sensing are discussed.

Shahgaldian, Patrick; Pieles, Uwe

2006-01-01

420

Enantiomerization and enantioselective bioaccumulation of metalaxyl in Tenebrio molitor larvae.  

PubMed

The enantiomerization and enantioselective bioaccumulation of metalaxyl by a single dose of exposure to Tenebrio molitor larvae under laboratory condition were studied by high-performance liquid chromatography tandem mass spectroscopy (HPLC-MS/MS) based on a ChiralcelOD-3R [cellulosetris-tris-(3, 5-dichlorophenyl-carbamate)] column. Exposure of enantiopure R-metalaxyl and S-metalaxyl in Tenebrio molitor larvae exhibited significant enantiomerization, with formation of the R enantiomers from the S enantiomers, and vice versa, which might be attributed to the chiral pesticide catalyzed by a certain enzyme in Tenebrio molitor larvae. Enantiomerization was not observed in wheat bran during the period of 21 d. In addition, bioaccumulation of rac-metalaxyl in Tenebrio molitor larvae was enantioselective with a preferential accumulation of S-metalaxyl. These results showed that enantioselectivity was caused not only by actual degradation and metabolism but also by enantiomerization, which was an important process in the environmental fate and behavior of metalaxyl enantiomers. PMID:24302540

Gao, Yongxin; Wang, Huili; Qin, Fang; Xu, Peng; Lv, Xiaotian; Li, Jianzhong; Guo, Baoyuan

2014-02-01

421

Non-aqueous microgel particles: synthesis, properties and applications.  

PubMed

Microgels are cross-linked polymer latex particles that can form stable colloidal dispersions. Their typical sizes range from 10 to 1000 nm and they can swell in response to their external environment (pH, temperature and solvency). This swelling behaviour is central to many potential applications for microgels. The existing literature is dominated by studies of the properties of aqueous microgel dispersions. In contrast, this review focusses on the development of microgel particles in non-aqueous systems, looking at the challenges of studying these particles as well as their swelling behaviour. The five main mechanisms of producing microgel particles will be discussed and examples of materials used for microgels that swell in non-aqueous solvents will be given. Finally some examples of applications for non-aqueous microgels are given. PMID:25347219

Bonham, J A; Faers, M A; van Duijneveldt, J S

2014-12-21

422

Catalytic Enantioselective Diboration of Cyclic Dienes. A Modified Ligand with General Utility  

PubMed Central

The enantioselective 1,4-diboration of cyclic dienes with a new taddol-derived phosphonite ligand occurs with excellent enantioselectivity. Oxidation delivers the derived 1,4 diol whereas homologation can be used to deliver a chiral 1,6 diol. PMID:21932816

Hong, Kai; Morken, James P.

2011-01-01

423

Enantioselective Carbonyl-Ene Reactions Catalyzed by Chiral Cationic Dirhodium(II,III) Carboxamidates.  

PubMed

An enantioselective carbonyl-ene reaction of glyoxylate esters with 1,1-disubstituted alkenes catalyzed by chiral cationic dirhodium(II,III) carboxamidates is described. The paddlewheel dirhodium(II,III) carboxamidates having one open coordination site at each rhodium smoothly catalyze the carbonyl-ene reaction to afford homoallylic alcohol products in good isolated yields with high enantioselectivities. PMID:25084486

Xu, Xichen; Wang, Xiaochen; Liu, Yuxiao; Doyle, Michael P

2014-12-19

424

Organocatalytic enantioselective Friedel–Crafts alkylation of simple phenols with trifluoropyruvate  

Microsoft Academic Search

Enantioselective Friedel–Crafts alkylation of simple phenols (4a–j) with 3,3,3-trifluoropyruvate (3) was accomplished by using chiral cinchona alkaloid catalyst 2h (10mol%). High yields and enantioselectivities (71–94% ee) of the Friedel–Crafts alkylation products were obtained.

Jun-Ling Zhao; Li Liu; Chun-Ling Gu; Dong Wang; Yong-Jun Chen

2008-01-01

425

New Strategies in Organic Catalysis: The First Enantioselective Organocatalytic Friedel-Crafts  

E-print Network

of aromatic substrates to electron deficient - and -systems, commonly known as Friedel-Crafts alkylation,1 has is also amenable to the enantioselective Friedel-Crafts alkylation of pyrroles with R, -unsaturated in the carbon-carbon bond forming event. Our enantioselective catalytic Friedel-Crafts alkylation was first

MacMillan, David W. C.

426

Highly enantioselective hydrogenation of N-phthaloyl enamides Qin Yang,a,b  

E-print Network

. Although high catalytic activities and enantioselectivities can be achieved in a number of catalytic-TangPhos complex, [Rh(Tang- Phos)(NBD)]SbF6, has exhibited high catalytic activities and enantioselectivities-acyl enamides (Table 1, entry 1). To address the reactivity issue, the effect of hydrogen pressure

Zhang, Xumu

427

NHC-Catalyzed/Titanium(IV);#8722;Mediated Highly Diastereo- and Enantioselective Dimerization of Enals  

SciTech Connect

An NHC-catalyzed, diastereo- and enantioselective dimerization of enals has been developed. The use of Ti(Oi-Pr){sub 4} is a key element for the reactivity and selectivity of this process. The cyclopentenes are obtained with high levels of diastereo- and enantioselectivity and their synthetic utility is demonstrated by functionalization of the product alkene.

Cohen, Daniel T.; Cardinal-David, Benoit; Roberts, John M.; Sarjeant, Amy A.; Scheidt, Karl A. (NWU)

2012-05-09

428

Enantioselective Selenocyclization via Dynamic Kinetic Resolution of Seleniranium Ions by Hydrogen-Bond Donor Catalysts.  

PubMed

Highly enantioselective selenocyclization reactions are promoted by the combination of a new chiral squaramide catalyst, a mineral acid, and an achiral Lewis base. Mechanistic studies reveal that the enantioselectivity originates from the dynamic kinetic resolution of seleniranium ions through anion-binding catalysis. PMID:25380129

Zhang, Hu; Lin, Song; Jacobsen, Eric N

2014-11-26

429

Enantioselective Functionalization of Radical Intermediates in Redox Catalysis: Copper-Catalyzed Asymmetric Oxytrifluoromethylation of Alkenes**  

PubMed Central

A method for the efficient enantioselective oxytrifluoromethylation of alkenes has been developed using a copper catalyst system. Mechanistic studies are consistent with a metal-catalyzed redox radical addition mechanism, in which a C–O bond is formed via the copper-mediated enantioselective trapping of a prochiral alkyl radical intermediate derived from the initial trifluoromethyl radical addition. PMID:24133010

Zhu, Rong

2013-01-01

430

Regio-and Enantioselective Alkane Hydroxylation with Engineered Cytochromes P450 BM-3  

E-print Network

Regio- and Enantioselective Alkane Hydroxylation with Engineered Cytochromes P450 BM-3 Matthew W alkanes regio- and enantioselectively using atmospheric dioxygen as an oxidant. BM-3 variant 9-10A-A328V alkanes larger than hexane primarily at the 2-position but forms R-2-alcohols (40-55% ee

Arnold, Frances H.

431

Copper-catalyzed enantioselective Friedel-Crafts alkylation of pyrrole with isatins.  

PubMed

The highly enantioselective Friedel-Crafts alkylation of pyrrole with isatins catalyzed by the tridentate Schiff base/Cu catalyst was developed. Hexafluoroisopropanol (HFIP) was used as a crucial additive to improve the enantioselectivity. In the case of N-unprotected isatins, an innovative substrate slow-releasing strategy was applied by virtue of a Henry/retro-Henry reaction. PMID:24912009

Li, Chong; Guo, Fengfeng; Xu, Kun; Zhang, Sheng; Hu, Yanbin; Zha, Zhenggen; Wang, Zhiyong

2014-06-20

432

Synthesis and device applications of doped perovskite manganite nanowires  

Microsoft Academic Search

Doped perovskite manganite films such as LaCaMnO3 and LaSrMnO3 have been studied intensively over the past years due to their colossal magnetoresistance (CMR) properties. It is expected that these doped manganite in the form of nanowires may offer great opportunities to explore intriguing physics and also practical applications in the emerging field of spintronics. We have developed a ``nanocasting'' technique

Bo Lei

2005-01-01

433

Synthesis of Graphene and Its Applications: A Review  

Microsoft Academic Search

Graphene, one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbed appreciable attention due to its exceptional electronic and optoelectronic properties. The reported properties and applications of this two-dimensional form of carbon structure have opened up new opportunities for the future devices and systems. Although graphene is known as one of the best electronic materials,

Wonbong Choi; Indranil Lahiri; Raghunandan Seelaboyina; Yong Soo Kang

2010-01-01

434

Recent advances in carbon nanodots: synthesis, properties and biomedical applications  

NASA Astrophysics Data System (ADS)

Herein, a mini review is presented concerning the most recent research progress of carbon nanodots, which have emerged as one of the most attractive photoluminescent materials. Different synthetic methodologies to achieve advanced functions and better photoluminescence performances are summarized, which are mainly divided into two classes: top-down and bottom-up. The inspiring properties, including photoluminescence emission, chemiluminescence, electrochemical luminescence, peroxidase-like activity and toxicity, are discussed. Moreover, the biomedical applications in biosensing, bioimaging and drug delivery are reviewed.

Miao, Peng; Han, Kun; Tang, Yuguo; Wang, Bidou; Lin, Tao; Cheng, Wenbo

2015-01-01

435

Polymers containing phosphorus groups and polyethers: from synthesis to application  

PubMed Central

Background Phosphorus-containing high performance polymers have aroused wide interest, mainly due to good mechanical properties and their excellent fire resistance. The flexibility of synthetic polyphosphoesters allows the development of polymers in order to obtain solid polymer electrolytes for rechargeable lithium batteries based on solid films with superior fire resistance. Results Novel linear Phosphonate-PEG polymers were synthesized by solution polycondensation of 4-chlorophenyldichlorophosphonate as a linking agent and poly(ethylene glycol)s with different molecular weights in the presence of triethylamine or 1-methylimidazole as acid scavenger. The yields were between 54% and 88% and inherent viscosity between 0.18-0.48 dl/g. Molar masses, Mn were about 26300 g/mol for polyphosphonates with PEG 2000 and 4600 g/mol for polyphosphonates with PEG 200. The LOI values for these polymers and membranes are in the range of 26–29. The membranes based on polyphosphonate with PEG 200 and 2000 showed conductivity between 6 × 10-8 S.cm-1 and 6 × 10-7 S.cm-1 at room temperature and total ionic transference number between 0.87- 0.96. The evolution of conductivity vs. temperature is linear. Conclusions 1-methylimidazole was found to be better HCl scavenger than triethylamine, and allowed higher yields and more eco-friendly synthesis of the Phosphonate-PEG polymers for SPE. These polymers and membranes based on these polymers showed good LOI values and indicate an improvement of the safety of lithium batteries. The membranes present conductivities around 6 × 10-7 S.cm-1at room temperature and total ionic transference number is higher for membranes based on polymers with high EG unit content. Best results yield 88%, inherent viscosities 0.48 dl/g and Mn 26000 were obtained with 1-methylimidazole and PEG 2000. These membranes based on these polymers showed good LOI values (in the range 26-29%) and indicate an improvement of the safety of lithium batteries. PMID:23134834

2012-01-01

436

Synthesis, morphologies and applications of polyoxometalate-containing diblock copolymers  

NASA Astrophysics Data System (ADS)

Block copolymers by virtue of their ability to self assemble and microphase-separation due to the contrast in chemical and physical properties of the covalently linked blocks constitute the essential building blocks towards various nano or micro sized architectures. Polyoxometalates (POM), on the other hand, being an interesting class of metal-oxygen nanometer-sized anionic clusters, are regarded highly due to their excellent electron accepting capability. Combining POM clusters with diblock copolymers can lead to a fascinating class of hybrid materials where the POM cluster not only affect the self-assembly process of various diblock copolymers but also brings its unique electronic properties into the hybrid system. Herein we report the detailed synthesis and characterizations of two hybrid coil-coil diblock copolymers along with two hybrid rod-coil diblock copolymers through polymerization-hybridization approach. The coil-coil diblocks were synthesized via atom transfer radial polymerization (ATRP) of styryl-type monomers and 4-vinylpyridine in sequence. For rod-coil diblock copolymers, the coil block was synthesized through ATRP, followed by the conversion of the terminal bromide to an azide. Ethynyl terminated poly (p-phenylenevinylene) (PPV) and poly (3-hexylthiophene) (P3HT) were prepared separately as the rod blocks. The rod block and the coil block were connected through click chemistry to yield rod-coil diblock copolymers. After removing the phthalimide protecting groups to regenerate aryl amines, POM clusters were finally linked to the coil block of all diblock copolymers to yield the targeted hybrid diblock copolymers. The covalent cluster attachment was confirmed by UV-Vis spectroscopy, FTIR and cyclovoltammetry measurements. The structures, solution and film optical properties, self-assembled morphologies and solar cell performances of these hybrids have been studied. It has been found that solar cell devices based on hybrid P3HT exhibited rather poor performances. Fluorescence dynamic studies indicate that the photoinduced electron transfer process from the rod block to pendant POMs is quite inefficient which may account for the poor device performance. Though the self-assembly process of these hybrid diblock copolymers and the preliminary morphologies has been demonstrated, detailed and systematic study of morphological control requires further extensive research.

Chakraborty, Sanjiban

437

Transition-Metal Catalyzed Synthesis of Aspergillide B: An Alkyne Addition Strategy  

PubMed Central

A catalytic enantioselective formal total synthesis of aspergillide B is reported. This linchpin synthesis was enabled by the development of new conditions for Zn-ProPhenol catalyzed asymmetric alkyne addition. This reaction was used in conjunction with ruthenium-catalyzed trans-hydrosilylation to affect the rapid construction of a late-stage synthetic intermediate of aspergillide B to complete a formal synthesis of aspergillide B in a highly efficient manner. PMID:22356535

Bartlett, Mark J.

2012-01-01

438

Functional Group Tolerant Nickel-Catalyzed Cross-Coupling Reaction for Enantioselective Construction of 30 Methyl-Bearing Stereocenters  

PubMed Central

The first Negishi nickel-catalyzed stereospecific cross-coupling reaction of secondary benzylic esters is reported. A series of traceless directing groups are evaluated for ability to promote cross-coupling with dimethylzinc. Esters with a chelating thioether derived from commercially-available 2-(methylthio)acetic acid are most effective. The products are formed in high yield and with excellent stereospecificity. A variety of functional groups are tolerated in the reaction including alkenes, alkynes, esters, amines, imides, and O-, S-, and N-heterocycles. The utility of this transformation is highlighted in the enantioselective synthesis of a retinoic acid receptor (RAR) agonist and a fatty acid amide hydrolase (FAAH) inhibitor. PMID:23751004

Wisniewska, Hanna M.; Swift, Elizabeth C.; Jarvo, Elizabeth R.

2013-01-01

439

Synthesis of nanostructured materials in inverse miniemulsions and their applications  

NASA Astrophysics Data System (ADS)

Polymeric nanogels, inorganic nanoparticles, and organic-inorganic hybrid nanoparticles can be prepared via the inverse miniemulsion technique. Hydrophilic functional cargos, such as proteins, DNA, and macromolecular fluoresceins, may be conveniently encapsulated in these nanostructured materials. In this review, the progress of inverse miniemulsions since 2000 is summarized on the basis of the types of reactions carried out in inverse miniemulsions, including conventional free radical polymerization, controlled/living radical polymerization, polycondensation, polyaddition, anionic polymerization, catalytic oxidation reaction, sol-gel process, and precipitation reaction of inorganic precursors. In addition, the applications of the nanostructured materials synthesized in inverse miniemulsions are also reviewed.

Cao, Zhihai; Ziener, Ulrich

2013-10-01

440

New materials graphyne, graphdiyne, graphone, and graphane: review of properties, synthesis, and application in nanotechnology.  

PubMed

Plenty of new two-dimensional materials including graphyne, graphdiyne, graphone, and graphane have been proposed and unveiled after the discovery of the "wonder material" graphene. Graphyne and graphdiyne are two-dimensional carbon allotropes of graphene with honeycomb structures. Graphone and graphane are hydrogenated derivatives of graphene. The advanced and unique properties of these new materials make them highly promising for applications in next generation nanoelectronics. Here, we briefly review their properties, including structural, mechanical, physical, and chemical properties, as well as their synthesis and applications in nanotechnology. Graphyne is better than graphene in directional electronic properties and charge carriers. With a band gap and magnetism, graphone and graphane show important applications in nanoelectronics and spintronics. Because these materials are close to graphene and will play important roles in carbon-based electronic devices, they deserve further, careful, and thorough studies for nanotechnology applications. PMID:24808721

Peng, Qing; Dearden, Albert K; Crean, Jared; Han, Liang; Liu, Sheng; Wen, Xiaodong; De, Suvranu

2014-01-01

441

New materials graphyne, graphdiyne, graphone, and graphane: review of properties, synthesis, and application in nanotechnology  

PubMed Central

Plenty of new two-dimensional materials including graphyne, graphdiyne, graphone, and graphane have been proposed and unveiled after the discovery of the “wonder material” graphene. Graphyne and graphdiyne are two-dimensional carbon allotropes of graphene with honeycomb structures. Graphone and graphane are hydrogenated derivatives of graphene. The advanced and unique properties of these new materials make them highly promising for applications in next generation nanoelectronics. Here, we briefly review their properties, including structural, mechanical, physical, and chemical properties, as well as their synthesis and applications in nanotechnology. Graphyne is better than graphene in directional electronic properties and charge carriers. With a band gap and magnetism, graphone and graphane show important applications in nanoelectronics and spintronics. Because these materials are close to graphene and will play important roles in carbon-based electronic devices, they deserve further, careful, and thorough studies for nanotechnology applications. PMID:24808721

Peng, Qing; Dearden, Albert K; Crean, Jared; Han, Liang; Liu, Sheng; Wen, Xiaodong; De, Suvranu

2014-01-01

442

Synthesis of polyhydroxyalkanoate from palm oil and some new applications.  

PubMed

Polyhydroxyalkanoate (PHA) is a potential substitute for some petrochemical-based plastics. This biodegradable plastic is derived from microbial fermentation using various carbon substrates. Since carbon source has been identified as one of the major cost-absorbing factors in PHA production, cheap and renewable substrates are currently being investigated as substitutes for existing sugar-based feedstock. Plant oils have been found to result in high-yield PHA production. Malaysia, being the world's second largest producer of palm oil, is able to ensure continuous supply of palm oil products for sustainable PHA production. The biosynthesis and characterization of various types of PHA using palm oil products have been described in detail in this review. Besides, by-products and waste stream from palm oil industry have also demonstrated promising results as carbon sources for PHA biosynthesis. Some new applications in cosmetic and wastewater treatment show the diversity of PHA usage. With proper management practices and efficient milling processes, it may be possible to supply enough palm oil-based raw materials for human consumption and other biotechnological applications such as production of PHA in a sustainable manner. PMID:21279347

Sudesh, Kumar; Bhubalan, Kesaven; Chuah, Jo-Ann; Kek, Yik-Kang; Kamilah, Hanisah; Sridewi, Nanthini; Lee, Yan-Fen

2011-03-01

443

Immobilized Candida antarctica lipase B: Hydration, stripping off and application in ring opening polyester synthesis.  

PubMed

This work reviews the stripping off, role of water molecules in activity, and flexibility of immobilized Candida antarctica lipase B (CALB). Employment of CALB in ring opening polyester synthesis emphasizing on a polylactide is discussed in detail. Execution of enzymes in place of inorganic catalysts is the most green alternative for sustainable and environment friendly synthesis of products on an industrial scale. Robust immobilization and consequently performance of enzyme is the essential objective of enzyme application in industry. Water bound to the surface of an enzyme (contact class of water molecules) is inevitable for enzyme performance; it controls enzyme dynamics via flexibility changes and has intensive influence on enzyme activity. The value of pH during immobilization of CALB plays a critical role in fixing the active conformation of an enzyme. Comprehensive selection of support and protocol can develop a robust immobilized enzyme thus enhancing its performance. Organic solvents with a log P value higher than four are more suitable for enzymatic catalysis as these solvents tend to strip away very little of the enzyme surface bound water molecules. Alternatively ionic liquid can work as a more promising reaction media. Covalent immobilization is an exclusively reliable technique to circumvent the leaching of enzymes and to enhance stability. Activated polystyrene nanoparticles can prove to be a practical and economical support for chemical immobilization of CALB. In order to reduce the E-factor for the synthesis of biodegradable polymers; enzymatic ring opening polyester synthesis (eROPS) of cyclic monomers is a more sensible route for polyester synthesis. Synergies obtained from ionic liquids and immobilized enzyme can be much effective eROPS. PMID:22041165

Idris, Ani; Bukhari, Attaullah

2012-01-01

444

Graphene-like single-layered covalent organic frameworks: synthesis strategies and application prospects.  

PubMed

Two-dimensional (2D) nanomaterials, such as graphene and transition metal chalcogenides, show many interesting dimension-related materials properties. Inspired by the development of 2D inorganic nanomaterials, single-layered covalent organic frameworks (sCOFs), featuring atom-thick sheets and crystalline extended organic structures with covalently bonded building blocks, have attracted great attention in recent years. With their unique graphene-like topological structure and the merit of structural diversity, sCOFs promise to possess novel and designable properties. However, the synthesis of sCOFs with well-defined structures remains a great challenge. Herein, the recent development of the bottom-up synthesis methods of 2D sCOFs, such as thermodynamic equilibrium control methods, growth-kinetics control methods, and surface-assisted covalent polymerization methods, are reviewed. Finally, some of the critical properties and application prospects of these materials are outlined. PMID:24585497

Liu, Xuan-He; Guan, Cui-Zhong; Wang, Dong; Wan, Li-Jun

2014-10-29

445

Design, synthesis, conformational analysis and application of indolizidin-2-one dipeptide mimics.  

PubMed

Growth in the field of peptide mimicry over the past few decades has resulted in the synthesis of many new compounds and the investigation of novel pharmacological agents. Azabicyclo[X.Y.0]alkanone amino acids are among the attractive classes of constrained mimics, because they can create rigid peptide structures for probing the conformation and roles of natural motifs in recognition events important for biological activity. Herein, we review the last ten years of the synthesis, conformational analysis and activity of analogs of the azabicyclo[4.3.0]alkan-2-one amino acid subclass, so-called indolizidin-2-one amino acids, with particular attention on their employment as inputs for biological applications. PMID:24899358

Khashper, Arkady; Lubell, William D

2014-07-28

446

Ionic Liquid-assisted Synthesis of Polyaniline/Gold Nanocomposite and Its Biocatalytic Application  

PubMed Central

In this report, a novel chemical synthesis of polyaniline/gold nanocomposite is explored using ionic liquid (IL) 1-Butyl-3-methylimidazolium hexafluorophosphate. The direct chemical synthesis of polyaniline/gold nanocomposite was initiated via the spontaneous oxidation of aniline by AuCl4?in IL. A nearly uniform dispersion of polyaniline/Au particles with a diameter of 450 ± 80 nm was produced by this method, which indicates that this method is more suitable for controlling particle dimensions. It was also found that the electrical conductivity of the polyaniline/gold nanocomposite was more than 100 times higher than that of the pure polyaniline nanoparticles. The polyaniline/gold nanocomposite displays superior function in the biocatalytic activation of microperoxidase-11 because of the high surface area of the assembly and the enhanced charge transport properties of the composite material. We also report the possible application of polyaniline/gold nanocomposite as a H2O2biosensor. PMID:21350593

2008-01-01

447

Combustion synthesis and engineering of nanoparticles for electronic, structural and superconductor applications  

SciTech Connect

Fully dense, nanocrystalline ceramic articles were prepared by the new nanofabrication process. The process consists of two steps: synthesis of ceramic nanoparticles and fabrication of dense, nanocrystalline ceramic parts. The synthesis step produced 10-nanometer-diameter crystallites, and is capable of being scaled up to kilogram/hour production rates. The fabrication step produced dense parts at significantly reduced sintering temperatures and times -- representing a factor of 10--100 reduction in process energy requirements. The process was demonstrated by producing ultrafine-grained yttria-stabilized ZrO[sub 2], an important material with a variety of energy-related applications (solid electrolytes, oxygen sensors, electrode materials, thermal barrier coatings, etc.). Results from this period clearly illustrate the capabilities of this energy-efficient and directly commercializable process for producing dense, nanocrystalline, multicomponent oxide ceramics.

Stangle, G.C.; Amarakoon, V.R.W.; Schulze, W.A.

1993-05-28

448

Organic Light Emitting Devices: Synthesis, Properties and Applications  

NASA Astrophysics Data System (ADS)

This high-class book reflects a decade of intense research, culminating in excellent successes over the last few years. The contributions from both academia as well as the industry leaders combine the fundamentals and latest research results with application know-how and examples of functioning displays. As a result, all the four important aspects of OLEDs are covered: - syntheses of the organic materials - physical theory of electroluminescence and device efficiency - device conception and construction - characterization of both materials and devices. The whole is naturally rounded off with a look at what the future holds in store. The editor, Klaus Muellen, is director of the highly prestigious MPI for polymer research in Mainz, Germany, while the authors include Nobel Laureate Alan Heeger, one of the most notable founders of the field, Richard Friend, as well as Ching Tang, Eastman Kodak's number-one OLED researcher, known throughout the entire community for his key publications.

Mullen, Klaus; Scherf, Ullrich

2006-02-01

449

Novel and Recent Synthesis and Applications of ?-Lactams  

NASA Astrophysics Data System (ADS)

In this chapter, a comprehensive overview of the most significant and interesting contributions published from 2000 until now, concerning the preparation of novel ?-lactam structures is presented. Among the different synthetic strategies available, either novel or already known but efficient and versatile methodologies are covered. The simple modifications of one or more substituents linked to the nitrogen N-1, the C-3, and the C-4 carbon atoms of the ?-lactam nucleus were considered as an alternative synthetic protocol of more complex and polyfunctionalized molecules. Indeed, it is well known and extensively reviewed that the biological activity of this strained four-membered heterocycle is strictly dependent on the nature of the substituent groups that affect the reactivity towards the molecular active sites, increasing or lowering the possibility of interaction with the substrates. Finally, a synthetic survey of the most significant biological and pharmacological applications of the 2-azetidinones is reported.

Troisi, Luigino; Granito, Catia; Pindinelli, Emanuela

450

Synthesis and Application of Titanium Oxide Nanohole Arrays  

NASA Astrophysics Data System (ADS)

A titania nanohole array, consisting of an assembly of titania tubes with inner diameters of 200 nm and wall thicknesses of 30 nm, was successfully prepared by a liquid phase deposition method. Heat treatment at 900°C results in a titania nanohole array that consists of highly crystalline anatase and has good photocatalytic properties. It was found that dissolution of anodic alumina and the deposition of titania took place simultaneously, and alumina functioned as the nanostructure template as well as a fluoride ion scavenger. A titania nanohole array with one end closed was used as a positive electrode for a lithium ion battery, in which an electric capacity close to 300 mAh/g was obtained. In addition to titania, this preparation method is applicable to various oxides such as tin oxide, zirconium oxide, indium oxide, and iron oxide.

Yamanaka, Shinsuke; Uno, Masayoshi

451

Crystallographically oriented mesoporous WO3 films: synthesis, characterization, and applications.  

PubMed

Mesoporous semiconducting films consisting of preferentially orientated monoclinic-phase nanocrystals of tungsten trioxide have been prepared using a novel version of the sol-gel method. Transformations undergone by a colloidal solution of tungstic acid, stabilized by an organic additive such as poly(ethylene glycol) (PEG) 300, as a function of the annealing temperature have been followed by means of a confocal Raman microscope. The shape and size of WO3 nanoparticles, the porosity, and the properties of the films depend critically on preparation parameters, such as the tungstic acid/PEG ratio, the PEG chain length, and the annealing conditions. Well-crystallized WO3 films combine excellent photoresponse to the blue region of the solar spectrum, up to 500 nm, with good transparency at wavelengths larger than 550 nm. Particular applications of these nanocrystalline WO3 films include photoelectrochemical and electrochromic devices. PMID:11673995

Santato, C; Odziemkowski, M; Ulmann, M; Augustynski, J

2001-10-31

452

Targeted synthesis and environmental applications of oxide nanomaterials.  

PubMed

Oxide nanomaterials are indispensable building blocks for a future nanotechnology, because they offer an infinite variety of structural motifs that lead to their widespread technical application. Therefore, flexible and tunable preparative strategies are required to convert this large family of materials onto the nanoscale. Although hydrothermal syntheses have proven especially suitable for this purpose, their reaction pathways and mechanisms often remain unknown so that they can be difficult to control. In the following, we summarize our comprehensive approach towards nanostructured functional oxides that is based on synthetic parameter optimizations, mechanistic in situ investigations and the characterization of environmentally relevant properties, e.g. in photocatalysis or sensor technology. The connection between preparative morphology control and the resulting materials properties is demonstrated for selected tungstate systems and bismuth-containing oxides. Furthermore, different methods for the in situ monitoring of hydrothermal processes are discussed. PMID:21138192

Zhou, Ying; Patzke, Greta R

2010-01-01

453

Synthesis and chemical modification of carbon nanostructures for materials applications  

NASA Astrophysics Data System (ADS)

This dissertation explores the structure, chemical reactivities, electromagnetic response, and materials properties of various carbon nanostructures, including single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphite, and graphene nanoribbons (GNRs). Efficient production and modification of these unique structures, each with their own distinct properties, will make them more accessible for applications in electronics, materials, and biology. A method is reported for controlling the permittivity from 1--1000 MHz of SWCNT-polymer composites (0.5 wt%) for radio frequency applications including passive RF antenna structures and EMI shielding. The magnitude of the real permittivity varied between 20 and 3.3, decreasing as higher fractions of functionalized-SWCNTs were added. The microwave absorbing properties and subsequent heating of carbon nanotubes were used to rapidly cure ceramic composites. With less than 1 wt% carbon nanotube additives and 30--40 W of directed microwave power (2.45 GHz), bulk composite samples reached temperatures above 500°C within 1 min. Graphite oxide (GO) polymer nanocomposites were developed at 1, 5, and 10 wt% for the purpose of evaluating the flammability reduction and materials properties of the resulting systems. Microscale oxygen consumption calorimetry revealed that addition of GO reduced the total heat release in all systems, and GO-polycarbonate composites demonstrated very fast self-extinguishing times in vertical open flame tests. A simple solution-based oxidative process using potassium permanganate in sulfuric acid was developed for producing nearly 100% yield of graphene nanoribbons (GNRs) by lengthwise cutting and unraveling of MWCNT sidewalls. Subsequent chemical reduction of the GNRs resulted in restoration of electrical conductivity. The GNR synthetic conditions were investigated in further depth, and an improved method which utilized a two-acid reaction medium was found to produce GNRs with fewer defects and/or holes on the basal plane and higher aspect ratio. Two different covalent functionalization methods for GNRs based on diazonium chemistry were developed. The resulting functionalized GNRs (f-GNRs) are readily soluble in organic solvents which increase their solution processability. The f-GNRs were also found to be in a reduced state, with minimal sp2 carbon disruption, while also keeping the ribbon shape.

Higginbotham, Amanda Lynn

454

Synthesis and characterization of mesoporous semiconductors and their energy applications  

NASA Astrophysics Data System (ADS)

In this dissertation, we examine the structure and physical properties of mesoporous group IV materials. Two different synthetic routes were developed to synthesize mesoporous germanium powder and thin film mesoporous silicon. The structural of these materials was confirmed by various analytical techniques. The electrochemical behavior of mesoporous silicon was further explored for applications as anodes in lithium ion batteries. The thermal conductivity was also measured and the electrical conductivity was tuned for potential applications as thermoelectrics. Ordered nanostructured germanium composite materials were produced using solution-phase surfactant templating methods. Anionic germanium/surfactand frameworks with a 2-D hexagonal structure were prepared and then condensed to form zero-valent porous germanium using oxidative coupling. The majority of the cationic surfactant inside the pores can be removed, resulting in mesoporous germanium with surface areas up to 500 m2/g. Thin film of mesoporous silicon was produced from polymer template porous silica films at relatively low temperature (<700 C) using magnesium vapor as reducing agent. The final porous silicon retains its ordered cubic mesoporosity. The lithium ion cycling performance of mesoporous silicon anodes was then examined. Mesoporous silicon films formed directly on a metal current collector showed stable cycling with excellent coulomb efficiency over 3000 cycles with capacities up to 3000 mAh/g at cycling rates between 1C to 20C. The results indicate porous silicon material in this size scale can accommodate the volume expansion associated with Li alloying without cracking or loosing contact with the current collector. The thermal conductivity of mesoporous silicon was also measured using the 3 omega method. Periodic pores and grain boundaries enhance phonon scattering to dissipate thermal energy throughout the material, resulting in a decrease in the thermal conductivity by 3-5 orders of magnitude (as low as 0.01 W/m*K) from the bulk value (150 W/m*K). As thermal conductivity of mesostructured silicon decreased, its electrical conductivity decreased as well. To overcome the high overall resistance, several dopoing methods were developed to decrease the internal resistance of silicon grains. The internal resistivity decreased from 25ohm?cm for as-prepared mesoporous silicon to as low as 0.16 ohm?cm for samples optimally doped with boron.

Kang, Chris Byung-hwa

455

Synthesis and application of peptides as drug carriers.  

PubMed

An efficient cellular drug delivery is a severe problem due to the charge, the hydrophilic character or the size of many therapeutic agents. High-drug doses, necessary to compensate the reduced bioavailability, often cause strong adverse effects. Synthetic drug delivery vectors will solve this problem, if limitations like low-cellular uptake efficiency or cytotoxicity can be overcome. Among these synthetic vectors, so-called cell-penetrating peptides (CPP) have proven their applicability as drug carriers. The ability to penetrate cellular membranes without the help of any receptor or transporter molecule was also found for derivatives of the native peptide hormone human calcitonin (hCT). We have shown that truncated hCT analogs with a branched peptide design and oligocationic side chain sequences - hCT(18-32)-k 7 and hCT(9-32)-2 br - are very interesting candidates as carrier peptides for drug delivery. Both peptides were found to efficiently shuttle covalently linked small molecules and non-covalently complexed DNA and RNA inside human embryonic kidney cells (HEK 293). PMID:19377983

Rennert, Robert; Neundorf, Ines; Beck-Sickinger, Annette G

2009-01-01

456

Synthesis, functionalization and bioimaging applications of highly fluorescent carbon nanoparticles  

NASA Astrophysics Data System (ADS)

Highly fluorescent crystalline carbon nanoparticles (CNPs) have been synthesized by one step microwave irradiation of sucrose with phosphoric acid at 100 W for 3 min 40 s. This method is very simple, rapid and economical and hence can be used for large scale applications. The average particle sizes are 3 to 10 nm and they emit bright green fluorescence under the irradiation of UV-light. Therefore, the particles can be used as a unique material for bioimaging as well as drug delivery. To further increase the fluorescence property of the synthetic carbon nanoparticles we simply functionalized them by using different organic dyes, such as fluorescein, rhodamine B and ?-naphthylamine the maximum fluorescence intensity was observed for the particles functionalized with fluorescein. It is very interesting to note that all of those compounds show maximum fluorescence intensity at 225 nm excitation wavelength and for any excitation wavelength the peak positions are exactly same the position as that of CNPs itself, which is completely different from the individual precursors (dyes). All of the above compounds, including CNPs, have also been successfully introduced into the erythrocyte enriched fraction of healthy human blood cells with minimum cytotoxicity.

Chandra, Sourov; Das, Pradip; Bag, Sourav; Laha, Dipranjan; Pramanik, Panchanan

2011-04-01

457

Contrasting enantioselective DNA preference: chiral helical macrocyclic lanthanide complex binding to DNA  

PubMed Central

There is great interest in design and synthesis of small molecules which selectively target specific genes to inhibit biological functions in which particular DNA structures participate. Among these studies, chiral recognition has been received much attention because more evidences have shown that conversions of the chirality and diverse conformations of DNA are involved in a series of important life events. Here, we report that a pair of chiral helical macrocyclic lanthanide (III) complexes, (M)-Yb[LSSSSSS]3+ and (P)-Yb[LRRRRRR]3+, can enantioselectively bind to B-form DNA and show remarkably contrasting effects on GC-rich and AT-rich DNA. Neither of them can influence non-B-form DNA, nor quadruplex DNA stability. Our results clearly show that P-enantiomer stabilizes both poly(dG-dC)2 and poly(dA-dT)2 while M-enantiomer stabilizes poly(dA-dT)2, however, destabilizes poly(dG-dC)2. To our knowledge, this is the best example of chiral metal compounds with such contrasting preference on GC- and AT-DNA. Ligand selectively stabilizing or destabilizing DNA can interfere with protein–DNA interactions and potentially affect many crucial biological processes, such as DNA replication, transcription and repair. As such, bearing these unique capabilities, the chiral compounds reported here may shed light on the design of novel enantiomers targeting specific DNA with both sequence and conformation preference. PMID:22675072

Zhao, Chuanqi; Ren, Jinsong; Gregoli?ski, Janusz; Lisowski, Jerzy; Qu, Xiaogang

2012-01-01

458

Self-templating synthesis of hollow mesoporous silica and their applications in catalysis and drug delivery  

NASA Astrophysics Data System (ADS)

Hollow mesoporous silica materials have been intensively pursued because of their unique properties for various applications. Yolk/shell structured hollow mesoporous silica with functional cores inside their hollow interior can further broaden the applications of hollow mesoporous silica. The self-templating strategy has been developed as one of the most important strategies to effectively fabricate hollow mesoporous silicas and their yolk/shell counterparts. In this feature article, we provide an overview of advances in the self-templating synthesis of hollow mesoporous silica based on the following three strategies: surface-protected etching, structural difference-based selective etching, and cationic surfactant assisted self-templating. We then discuss some important applications of these self-templating strategy-derived hollow mesoporous silicas, such as nanoreactors for confined catalysis and multifunctional platforms for combined therapy. Finally, some perspectives for the future development of this active research field are provided.

Fang, Xiaoliang; Zhao, Xiaojing; Fang, Weijun; Chen, Cheng; Zheng, Nanfeng

2013-02-01

459

Noble metal aerogels-synthesis, characterization, and application as electrocatalysts.  

PubMed

Conspectus Metallic and catalytically active materials with high surface area and large porosity are a long-desired goal in both industry and academia. In this Account, we summarize the strategies for making a variety of self-supported noble metal aerogels consisting of extended metal backbone nanonetworks. We discuss their outstanding physical and chemical properties, including their three-dimensional network structure, the simple control over their composition, their large specific surface area, and their hierarchical porosity. Additionally, we show some initial results on their excellent performance as electrocatalysts combining both high catalytic activity and high durability for fuel cell reactions such as ethanol oxidation and the oxygen reduction reaction (ORR). Finally, we give some hints on the future challenges in the research area of metal aerogels. We believe that metal aerogels are a new, promising class of electrocatalysts for polymer electrolyte fuel cells (PEFCs) and will also open great opportunities for other electrochemical energy systems, catalysis, and sensors. The commercialization of PEFCs encounters three critical obstacles, viz., high cost, insufficient activity, and inadequate long-term durability. Besides others, the sluggish kinetics of the ORR and alcohol oxidation and insufficient catalyst stability are important reasons for these obstacles. Various approaches have been taken to overcome these obstacles, e.g., by controlling the catalyst particle size in an optimized range, forming multimetallic catalysts, controlling the surface compositions, shaping the catalysts into nanocrystals, and designing supportless catalysts with extended surfaces such as nanostructured thin films, nanotubes, and porous nanostructures. These efforts have produced plenty of excellent electrocatalysts, but the development of multisynergetic functional catalysts exhibiting low cost, high activity, and high durability still faces great challenges. In this Account, we demonstrate that the sol-gel process represents a powerful "bottom-up" strategy for creating nanostructured materials that tackles the problems mentioned above. Aerogels are unique solid materials with ultralow densities, large open pores, and ultimately high inner surface areas. They magnify the specific properties of nanomaterials to the macroscale via self-assembly, which endow them with superior properties. Despite numerous investigations of metal oxide aerogels, the investigation of metal aerogels is in the early stage. Recently, aerogels including Fe, Co, Ni, Sn, and Cu have been obtained by nanosmelting of hybrid polymer-metal oxide aerogels. We report here exclusively on mono-, bi- and multimetallic noble metal aerogels consisting of Ag, Au, Pt, and Pd and their application as electrocatalysts. PMID:25611348

Liu, Wei; Herrmann, Anne-Kristin; Bigall, Nadja C; Rodriguez, Paramaconi; Wen, Dan; Oezaslan, Mehtap; Schmidt, Thomas J; Gaponik, Nikolai; Eychmüller, Alexander

2015-02-17

460

Green synthesis and characterization of novel gold nanocomposites for electrochemical sensing applications.  

PubMed

Synthesis, characterization and application of Au-PANI-Calix and Au-PANI-Nap nanocomposites, is reported herein. An easy template free green synthesis is proposed and discussed for easy expediency. A variety of analytical techniques were used to characterize the nanocomposites: UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Dynamic light scattering (DLS), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were used to characterize the nanocomposites. Surface morphology was studied by transmission electron microscopy (TEM). The nanocomposites were immobilized on screen-printed electrode and showed electroactivity in neutral pH, making them promising candidates for various analytical applications. A sensitive and selective detection of Cu(2+) was perceived on the Au-PANI-Calix modified electrode with no interference from ions K(+), Ni(2+), Co(2+), Pb(2+), Cr(3+) with a detection limit of 10nM. The copper detection is facilitated for accessible ligation with 4-sulfocalix[4]arene, so as the Cu(II)-Calix complex formed. The electrode modified with Au-PANI-Nap showed sensing application towards H2O2 with a detection limit of 1 ?M. The modified electrodes were reproducible and stable for 2 months. PMID:24209352

Tanwar, Shivani; Ho, Ja-an Annie; Magi, Emanuele

2013-12-15

461

Synthesis methods to prepare single- and multi-core iron oxide nanoparticles for biomedical applications.  

PubMed

We review current synthetic routes to magnetic iron oxide nanoparticles for biomedical applications. We classify the different approaches used depending on their ability to generate magnetic particles that are either single-core (containing only one magnetic core, i.e. a single domain nanocrystal) or multi-core (containing several magnetic cores, i.e. single domain nanocrystals). The synthesis of single-core magnetic nanoparticles requires the use of surfactants during the particle generation, and careful control of the particle coating to prevent aggregation. Special attention has to be paid to avoid the presence of any toxic reagents after the synthesis if biomedical applications are intended. Several approaches exist to obtain multi-core particles based on the coating of particle aggregates; nevertheless, the production of multi-core particles with good control of the number of magnetic cores per particle, and of the degree of polydispersity of the core sizes, is still a difficult task. The control of the structure of the particles is of great relevance for biomedical applications as it has a major influence on the magnetic properties of the materials. PMID:25564784

Gutiérrez, L; Costo, R; Grüttner, C; Westphal, F; Gehrke, N; Heinke, D; Fornara, A; Pankhurst, Q A; Johansson, C; Veintemillas-Verdaguer, S; Morales, M P

2015-02-01

462

Synthesis and characterization of a photosensitive polyimide precursor and its photocuring behavior for lithography applications  

NASA Astrophysics Data System (ADS)

Photosensitive polyimide (PSPI) is of great interest, especially in microelectronic industry and potentially in the photonics and MEMS applications. Here we report on our studies for optimization of synthesis conditions for a PSPI which can be used in lithography. The direct polymerization method using phenyl phosphonic dichloride (PPD) as an activator was used to synthesize poly(amic ester) (PAE) from pyromellitic dianhydride (PMDA), 4,4'-oxydianiline (ODA) and 2-hydroxyethylmethacrylate (HEMA). Main parameters of the synthesis procedure were investigated by differential scanning calorimetry (DSC) analyses. From that, synthesis conditions were determined. Characteristics of the synthesized PAE and the imidized film were studied by the means of DSC, thermalgravimetric analyses (TGA) and Fourier transform infrared spectroscopy (FTIR). The glass transition temperature and the thermal stability of the imidized film were determined. Additionally, formulations of photo-PAE and the Irgacure 369 as photoinitiator were prepared and photocuring was tested by lithography. The results show that the images can be transferred to the PAE film by selective exposure.

Nguyen, Le Thu T.; Nguyen, Huu Nieu; La, Thai Ha T.

2007-02-01

463

Image based hair segmentation algorithm for the application of automatic facial caricature synthesis.  

PubMed

Hair is a salient feature in human face region and are one of the important cues for face analysis. Accurate detection and presentation of hair region is one of the key components for automatic synthesis of human facial caricature. In this paper, an automatic hair detection algorithm for the application of automatic synthesis of facial caricature based on a single image is proposed. Firstly, hair regions in training images are labeled manually and then the hair position prior distributions and hair color likelihood distribution function are estimated from these labels efficiently. Secondly, the energy function of the test image is constructed according to the estimated prior distributions of hair location and hair color likelihood. This energy function is further optimized according to graph cuts technique and initial hair region is obtained. Finally, K-means algorithm and image postprocessing techniques are applied to the initial hair region so that the final hair region can be segmented precisely. Experimental results show that the average processing time for each image is about 280?ms and the average hair region detection accuracy is above 90%. The proposed algorithm is applied to a facial caricature synthesis system. Experiments proved that with our proposed hair segmentation algorithm the facial caricatures are vivid and satisfying. PMID:24592182

Shen, Yehu; Peng, Zhenyun; Zhang, Yaohui

2014-01-01

464

The synthesis, characterization, and application of multifunctional magnetic nanoparticles  

NASA Astrophysics Data System (ADS)

In recent years, the field of nanotechnology has been one of extreme activity. Among other things, this activity is driven by the push for consumer technologies that are lighter, stronger, and most importantly smaller. With this push from the everyday consumer, the need for a basic understanding of the underlying physics of nanoscale materials has never been more evident. In this dissertation, the author investigates the many physical differences, in particular the differences in the magnetic properties, between nanoscale materials and their bulk counterparts. Starting out with a brief overview of magnetism, the author sets out to explore the fantastic changes in the magnetic properties of materials that occur when the physical dimensions of the materials become smaller than typical magnetic length scales. Among the first differences noticed arises when nanoscale ferromagnets are investigated. While the magnetic properties of bulk ferromagnets are governed by magnetic domain dynamics, when a material becomes small enough that only one domain is possible, a new type of magnetic behavior known as superparamagnetism arises. While this superparamagnetic behavior is well understood in terms of thermally activated spin reversal through an energy barrier, many factors, such as interactions between separate nanoparticles, cause deviations from this simple picture. The effects of these factors are investigated. In addition to the effects of interactions, the relation of nanoscale magnetics and its coupling to the dielectric properties of nanoparticles is investigated. This investigation, motivated by recent research focusing on the search for materials whose magnetic and electronic properties are influenced by each other, shows that nanomaterials can show a coupling between these properties that isn't necessarily the intrinsic coupling of the two properties, but an effect from the surface layers of nanoparticles, which are generally ignored in bulk systems due to the fact that they make up such a small percentage of the overall material. However, in nanoscale systems, the surface layers become much more involved in the determination of the overall behavior of the system as they are no longer a small percentage of the overall system, and cannot be ignored. A third investigation looks at magnetodielectric coupling that occurs in bulk Mn3O4 as a result of spin-lattice coupling with the lattice and the long-range magnetic order that develops in the system at low temperature. The motivation to study this bulk system becomes evident to the general theme of this dissertation when one asks the question, can this long-range order (extending over many unit cells of the lattice) occur in nanoscale systems (where only a few unit cells of material are present)? Preliminary data suggests that these long-range orders that occur in the bulk are not feasible in the nanoscale material. Finally, as consumer driven technology grows, the need for a single material that can be altered for use in a wide variety of applications becomes increasingly more evident. It is with this motivation that the author investigates the ability to tune the blocking temperature of an Fe3O4 nanoparticle system through cobalt doping, effectively changing the magnetocrystalline anisotropy of the system. The author finds that up to small cobalt concentrations, the magnetocrystalline anisotropy was able to be linearly increased by increasing the amount of cobalt in the system, thus providing a nanoparticle system whose blocking temperature is effectively tunable. In addition to this tuning using the cobalt doping to change the anisotropy, it was found that altering the size of the nanoparticles was also an effective way to controllably tune the blocking temperature of a nanoparticle system. In addition to the author's main research aimed at this dissertation, the author provides a small outline of some work that was done outside of the scope of his dissertation research. It is shown that while this work did not directly contribute to the dissertation topic, it did broaden th

Tackett, Ronald J.

465

Recent Applications of Acyclic (Diene)iron Complexes and (Dienyl)iron Cations in Organic Synthesis  

PubMed Central

Complexation of (tricarbonyl)iron to an acyclic diene serves to protect the ligand against oxidation, reduction and cycloaddition reactions while the steric bulk of this adjunct serves to direct the approach reagents to unsaturated groups attached to the diene onto the face opposite to iron. Furthermore, the Fe(CO)3 moiety can serve to stabilize carbocation centers adjacent to the diene (i.e. pentadienyl-iron cations). Recent applications of these reactivities to the synthesis of polyene, cyclopropane, cycloheptadiene and cyclohexenone containing natural products or analogs will be presented. PMID:21709767

Chaudhury, Subhabrata

2009-01-01

466

Acetate/acetyl-CoA metabolism associated with cancer fatty acid synthesis: overview and application.  

PubMed

Understanding cancer-specific metabolism is important for identifying novel targets for cancer diagnosis and therapy. Induced acetate/acetyl CoA metabolism is a notable feature that is related to fatty acid synthesis supporting tumor growth. In this review, we focused on the recent findings related to cancer acetate/acetyl CoA metabolism. We also introduce [1-¹¹C]acetate positron emission tomography (PET), which is a useful tool to visualize up-regulation of acetate/acetyl CoA metabolism in cancer, and discuss the utility of [1-¹¹C]acetate PET in cancer diagnosis and its application to personalized medicine. PMID:24569091

Yoshii, Yukie; Furukawa, Takako; Saga, Tsuneo; Fujibayashi, Yasuhisa

2015-01-28

467

Synthesis and Characterization of Ordered Mesoporous Silica with Controlled Macroscopic Morphology for Membrane Applications  

NASA Astrophysics Data System (ADS)

Ordered mesoporous materials have tunable pore sizes between 2 and 50 nm and are characterized by ordered pore structures and high surface areas (~1000 m2/g). This makes them particularly favorable for a number of membrane applications such as protein separation, polymer extrusion, nanowire fabrication and membrane reactors. These membranes can be fabricated as top-layers on macroporous supports or as embedded membranes in a dense matrix. The first part of the work deals with the hydrothermal synthesis and water-vapor/oxygen separation properties of supported MCM-48 and a new Al-MCM-48 type membrane for potential use in air