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1

Enzyme-catalyzed acylation of homoserine: mechanistic characterization of the Haemophilus influenzae met2-encoded homoserine transacetylase.  

PubMed

The first unique step in bacterial and plant methionine biosynthesis involves the acylation of the gamma-hydroxyl of homoserine. In Haemophilus influenzae, acylation is accomplished via an acetyl-CoA-dependent acetylation catalyzed by homoserine transacetylase. The activity of this enzyme regulates flux of homoserine into multiple biosynthetic pathways and, therefore, represents a critical control point for cell growth and viability. We have cloned homoserine transacetylase from H. influenzae and present the first detailed enzymatic study of this enzyme. Steady-state kinetic experiments demonstrate that the enzyme utilizes a ping-pong kinetic mechanism in which the acetyl group of acetyl-CoA is initially transferred to an enzyme nucleophile before subsequent transfer to homoserine to form the final product, O-acetylhomoserine. The maximal velocity and V/K(homoserine) were independent of pH over the range of values tested, while V/K(acetyl)(-)(CoA) was dependent upon the ionization state of a single group exhibiting a pK value of 8.6, which was required to be protonated. Solvent kinetic isotope effect studies yielded inverse effects of 0.75 on V and 0.74 on V/K(CoA) on the reverse reaction and effects of 1.2 on V and 1.7 on V/K(homoserine) on the forward reaction. Direct evidence for the formation of an acetyl-enzyme intermediate was obtained using rapid-quench labeling studies. On the basis of these observations, we propose a chemical mechanism for this important member of the acyltransferase family and contrast its mechanism with that of homoserine transsuccinylase. PMID:10913262

Born, T L; Franklin, M; Blanchard, J S

2000-07-25

2

Purification and properties of homoserine transacetylase from Bacillus polymyxa.  

PubMed

Homoserine transacetylase (EC 2.3.1.31), the first enzyme of methionine biosynthesis, has been purified to near homogeneity from extracts of a methionine auxotroph of Bacillus polymyxa. The enzyme is subject to rapid irreversible inactivation. Its half-life at 0 degrees is 15 min and much less at higher temperatures, but ethylene glycol affords some protection. In addition, Zn2+ reversibly inhibits the enzyme with a K-I of 3 muM. The enzyme has a molecular weight of about 40,000 and consists of a single polypeptide chain. Besides catalyzing the acetyl transfer from acetyl-CoA to L-homoserine, homoserine transacetylase promotes a homoserine-O-acetylhomoserine exchange reaction in the absence of CoA, suggesting the formation of an acetyl-enzyme intermediate. The results of kinetic studies are consistent with a ping-pong mechanism. Homoserine transacetylase is subject to multivalent feedback inhibition by L-methionine and S-adenosylmethionine. Analysis of the inhibition data and specificity studies suggest that the inhibitors bind to separate sites on the enzyme which are distinct from the active site. Inhibition is competitive with respect to both substrates, and the saturation curves for the inhibitors, as well as substrate saturation curves in the absence or presence of the inhibitors, are hyperbolic. The absence of cooperativity is, in fact, a property which would be expected in a monomeric allosteric enzyme such as homoserine transacetylase. PMID:1126938

Wyman, A; Paulus, H

1975-05-25

3

Catalytic mechanism of fungal homoserine transacetylase.  

PubMed

Homoserine transacetylase is a required catalyst in the biochemical pathway that metabolizes Asp to Met in fungi. The enzyme from the yeast Schizosaccharomyces pombe activates the hydroxyl group of L-homoserine by acetylation from acetyl coenzyme A. This enzyme is unique to fungi and some bacteria and presents an important new target for drug discovery. Steady-state kinetic parameters provide evidence that this enzyme follows a ping-pong mechanism. Proton inventory was consistent with a single-proton transfer, and pH studies suggested the participation of at least one residue with a pKa value of 6.4-6.6, possibly a His or Asp/Glu in catalysis. Protein sequence alignments indicate that this enzyme belongs to the alpha/beta-hydrolase fold superfamily of enzymes, indicating the involvement of an active-site nucleophile and possibly a canonical catalytic triad. We constructed site-specific mutants and identified Ser163, Asp403, and His432 as the likely active-site residues of a catalytic triad based on steady-state kinetics and genetic complementation of a yeast null mutant. Moreover, unlike the wild-type enzyme, inactive site mutants were not capable of producing an acetyl-enzyme intermediate. Homoserine transacetylase therefore catalyzes the acetylation of L-homoserine via a covalent acyl-enzyme intermediate through an active-site Ser. These results form the basis of future exploitation of this enzyme as an antimicrobial target. PMID:16216079

Nazi, Ishac; Wright, Gerard D

2005-10-18

4

Purification and characterization of Thermotoga maritima homoserine transsuccinylase indicates it is a transacetylase  

Microsoft Academic Search

The methionine biosynthetic pathway found in bacteria is controlled at the first step, acylation of the ?-hydroxyl of homoserine. This reaction is catalyzed by one of two unique enzymes, homoserine transacetylase or homoserine transsuccinylase, which have no amino acid sequence similarity. We cloned, expressed, and purified homoserine transsuccinylase from the thermophilic bacterium Thermotoga maritima. Substrate specificity experiments demonstrated that acetyl-coenzyme A

Maryam Goudarzi; Timothy L. Born

2006-01-01

5

?-Lactone natural products and derivatives inactivate homoserine transacetylase, a target for antimicrobial agents  

Microsoft Academic Search

Homoserine transacetylase (HTA) catalyzes the transfer of an acetyl group from acetyl-CoA to the hydroxyl group of homoserine. This is the first committed step in the biosynthesis of methionine (Met) from aspartic acid in many fungi, Gram-positive and some Gram-negative bacteria. The enzyme is absent in higher eukaryotes and is important for microorganism growth in Met-poor environments, such as blood

Gianfranco De Pascale; Ishac Nazi; Paul H M Harrison; Gerard D Wright

2011-01-01

6

Calreticulin Induces Dilated Cardiomyopathy  

PubMed Central

Background Calreticulin, a Ca2+-buffering chaperone of the endoplasmic reticulum, is highly expressed in the embryonic heart and is essential for cardiac development. After birth, the calreticulin gene is sharply down regulated in the heart, and thus, adult hearts have negligible levels of calreticulin. In this study we tested the role of calreticulin in the adult heart. Methodology/Principal Findings We generated an inducible transgenic mouse in which calreticulin is targeted to the cardiac tissue using a Cre/loxP system and can be up-regulated in adult hearts. Echocardiography analysis of hearts from transgenic mice expressing calreticulin revealed impaired left ventricular systolic and diastolic function and impaired mitral valve function. There was altered expression of Ca2+ signaling molecules and the gap junction proteins, Connexin 43 and 45. Sarcoplasmic reticulum associated Ca2+-handling proteins (including the cardiac ryanodine receptor, sarco/endoplasmic reticulum Ca2+-ATPase, and cardiac calsequestrin) were down-regulated in the transgenic hearts with increased expression of calreticulin. Conclusions/Significance We show that in adult heart, up-regulated expression of calreticulin induces cardiomyopathy in vivo leading to heart failure. This is due to an alternation in changes in a subset of Ca2+ handling genes, gap junction components and left ventricle remodeling.

Lee, Dukgyu; Oka, Tatsujiro; Hunter, Beth; Robinson, Alison; Papp, Sylvia; Nakamura, Kimitoshi; Srisakuldee, Wattamon; Nickel, Barbara E.; Light, Peter E.; Dyck, Jason R. B.; Lopaschuk, Gary D.; Kardami, Elissavet; Opas, Michal; Michalak, Marek

2013-01-01

7

Chaperone properties of calreticulin.  

PubMed

Calreticulin is a highly conserved protein with a relative molecular weight of 46,000, and is mainly located in the endoplasmic reticulum. Calreticulin was first characterized as a calcium-binding protein in the endoplasmic reticulum, but since then other functions of calreticulin have been characterized, including chaperone and lectin properties, and regulation of integrin and nuclear hormone receptor activity. We have investigated the interactions between purified human placental calreticulin and native and denatured proteins. Our results show that calreticulin binds to denatured proteins in a time- and pH-dependent manner, which at physiological pH is dependent on divalent cations. The binding was dependent on the state of the denatured protein, and was highly sensitive to the ionic composition of the environment, being strongly inhibited by phosphate-containing compounds. Calreticulin did not seem to distinguish between denatured glycosylated and non-glycosylated proteins, and was found to bind to native basic proteins, presumably by sheer electrostatic forces. PMID:9661269

Svaerke, C; Houen, G

1998-07-01

8

Purification and characterization of Thermotoga maritima homoserine transsuccinylase indicates it is a transacetylase.  

PubMed

The methionine biosynthetic pathway found in bacteria is controlled at the first step, acylation of the gamma-hydroxyl of homoserine. This reaction is catalyzed by one of two unique enzymes, homoserine transacetylase or homoserine transsuccinylase, which have no amino acid sequence similarity. We cloned, expressed, and purified homoserine transsuccinylase from the thermophilic bacterium Thermotoga maritima. Substrate specificity experiments demonstrated that acetyl-coenzyme A (CoA) is the preferred acyl donor and is used at least 30-fold more efficiently than succinyl-CoA. Steady-state kinetic experiments confirm that the enzyme utilizes a ping-pong kinetic mechanism in which the acetate group of acetyl-CoA is initially transferred to an enzyme nucleophile before subsequent transfer to homoserine. The maximal velocity, V/K (acetyl-CoA) and V/K (homoserine), all exhibited bell-shaped pH curves with apparent pKs of 6.0-6.9 and 8.2-8.8. The enzyme was inactivated by iodoacetamide in a pH-dependent manner, with an apparent pK of 6.3, suggesting the presence of an active-site cysteine residue which forms an acetyl-enzyme thioester intermediate during catalytic turnover, similar to observations with other transsuccinylases. In addition, the enzyme is highly stable at elevated temperatures, maintaining full activity at 70 degrees C. Taken together, these data suggest that the T. maritima enzyme functions biochemically as a transacetylase, despite having the sequence of a transsuccinylase. PMID:16708165

Goudarzi, Maryam; Born, Timothy L

2006-10-01

9

?-Lactone natural products and derivatives inactivate homoserine transacetylase, a target for antimicrobial agents.  

PubMed

Homoserine transacetylase (HTA) catalyzes the transfer of an acetyl group from acetyl-CoA to the hydroxyl group of homoserine. This is the first committed step in the biosynthesis of methionine (Met) from aspartic acid in many fungi, Gram-positive and some Gram-negative bacteria. The enzyme is absent in higher eukaryotes and is important for microorganism growth in Met-poor environments, such as blood serum, making HTA an attractive target for new antimicrobial agents. HTA catalyzes acetyl transfer via a double displacement mechanism facilitated by a classic Ser-His-Asp catalytic triad located at the bottom of a narrow actives site tunnel. We explored the inhibitory activity of several ?-lactones to block the activity of HTA. In particular, the natural product ebelactone A, a ?-lactone with a hydrophobic tail was found to be a potent inactivator of HTA from Haemophilus influenzae. Synthetic analogs of ebelactone A demonstrated improved inactivation characteristics. Covalent modification of HTA was confirmed by mass spectrometry, and peptide mapping identified Ser143 as the modified residue, consistent with the known structure and mechanism of the enzyme. These results demonstrate that ?-lactone inhibitors are excellent biochemical probes of HTA and potential leads for new antimicrobial agents. PMID:21522158

De Pascale, Gianfranco; Nazi, Ishac; Harrison, Paul H M; Wright, Gerard D

2011-07-01

10

Immunocytochemical localisation of calreticulin in Trypanosoma cruzi  

Microsoft Academic Search

Calreticulin, a Ca 2+ chaperone, is found in many different locations in various eukaryotic cells, including lumen of the endoplasmic reticulum, the cell surface, perinuclear areas and cytosolic granules. In the present study, a polyclonal antibody against calreticulin was used for the immunocytochemical localisation of the protein in Trypanosoma cruzi. Labelling was observed in the endoplasmic reticulum, Golgi complex, reservosomes,

Thaïs Souto-Padrón; Carlos A. Labriola; Wanderley de Souza

2004-01-01

11

The interactions of calreticulin with immunoglobulin G and immunoglobulin Y  

Microsoft Academic Search

Calreticulin is a chaperone of the endoplasmic reticulum (ER) assisting proteins in achieving the correctly folded structure. Details of the binding specificity of calreticulin are still a matter of debate. Calreticulin has been described as an oligosaccharide-binding chaperone but data are also accumulating in support of calreticulin as a polypeptide binding chaperone. In contrast to mammalian immunoglobulin G (IgG), which

Karen Mai Møllegaard; Karen Duus; Sofie Dietz Træholt; Morten Thaysen-Andersen; Yan Liu; Angelina S. Palma; Ten Feizi; Paul R. Hansen; Peter Højrup; Gunnar Houen

2011-01-01

12

Peptide binding specificity of the chaperone calreticulin.  

PubMed

Calreticulin is a molecular chaperone with specificity for polypeptides and N-linked monoglucosylated glycans. In order to determine the specificity of polypeptide binding, the interaction of calreticulin with polypeptides was investigated using synthetic peptides of different length and composition. A large set of available synthetic peptides (n=127) was tested for binding to calreticulin and the results analysed by multivariate data analysis. The parameter that correlated best with binding was hydrophobicity while beta-turn potential disfavoured binding. Only hydrophobic peptides longer than 5 amino acids showed binding and a clear correlation with hydrophobicity was demonstrated for oligomers of different hydrophobic amino acids. Insertion of hydrophilic amino acids in a hydrophobic sequence diminished or abolished binding. In conclusion our results show that calreticulin has a peptide-binding specificity for hydrophobic sequences and delineate the fine specificity of calreticulin for hydrophobic amino acid residues. PMID:17499031

Sandhu, Noreen; Duus, Karen; Jørgensen, Charlotte S; Hansen, Paul R; Bruun, Susanne W; Pedersen, Lars Ø; Højrup, Peter; Houen, Gunnar

2007-06-01

13

Characterization of the autoantigen calreticulin.  

PubMed

Anti-Ro/SS-A antibodies are commonly found in the sera of patients with Sjögren's syndrome and SLE. These antibodies also occur in the mothers of children with neonatal lupus and congenital heart block. Ro/SS-A is a ribonucleoprotein complex whose cellular function remains unknown. To study its cellular function and to characterize its immunoreactivity, we have used an oligonucleotide designed after the published amino terminal sequence of a putative 60-kDa Ro/SS-A autoantigen to isolate its cDNA. This cDNA encodes a polypeptide that is the human homologue of calreticulin, a calcium binding protein of the endoplasmatic reticulum. The encoded polypeptide also shows a 64.4% identity with RAL-1, an Ag of the river blindness pathogen Onchocerca volvulus. Contrary to the data published by other authors, our results indicate that calreticulin is not a Ro/SS-A autoantigen. Moreover, we show that anticalreticulin autoantibodies occur in the sera of patients with SLE and patients with onchocerciasis. PMID:1919005

Rokeach, L A; Haselby, J A; Meilof, J F; Smeenk, R J; Unnasch, T R; Greene, B M; Hoch, S O

1991-11-01

14

Calreticulin: one protein, one gene, many functions.  

PubMed Central

The endoplasmic reticulum (ER) plays a critical role in the synthesis and chaperoning of membrane-associated and secreted proteins. The membrane is also an important site of Ca(2+) storage and release. Calreticulin is a unique ER luminal resident protein. The protein affects many cellular functions, both in the ER lumen and outside of the ER environment. In the ER lumen, calreticulin performs two major functions: chaperoning and regulation of Ca(2+) homoeostasis. Calreticulin is a highly versatile lectin-like chaperone, and it participates during the synthesis of a variety of molecules, including ion channels, surface receptors, integrins and transporters. The protein also affects intracellular Ca(2+) homoeostasis by modulation of ER Ca(2+) storage and transport. Studies on the cell biology of calreticulin revealed that the ER membrane is a very dynamic intracellular compartment affecting many aspects of cell physiology.

Michalak, M; Corbett, E F; Mesaeli, N; Nakamura, K; Opas, M

1999-01-01

15

Post-translational arginylation of calreticulin: a new isospecies of calreticulin component of stress granules.  

PubMed

Post-translational arginylation consists of the covalent union of an arginine residue to a Glu, Asp, or Cys amino acid at the N-terminal position of proteins. This reaction is catalyzed by the enzyme arginyl-tRNA protein transferase. Using mass spectrometry, we have recently demonstrated in vitro the post-translational incorporation of arginine into the calcium-binding protein calreticulin (CRT). To further study arginylated CRT we raised an antibody against the peptide (RDPAIYFK) that contains an arginine followed by the first 7 N-terminal amino acids of mature rat CRT. This antibody specifically recognizes CRT obtained from rat soluble fraction that was arginylated in vitro and also recognizes endogenous arginylated CRT from NIH 3T3 cells in culture, indicating that CRT arginylation takes place in living cells. Using this antibody we found that arginylation of CRT is Ca2+-regulated. In vitro and in NIH 3T3 cells in culture, the level of arginylated CRT increased with the addition of a Ca2+ chelator to the medium, whereas a decreased arginine incorporation into CRT was found in the presence of Ca2+. The arginylated CRT was observed in the cytosol, in contrast to the non-arginylated CRT that is in the endoplasmic reticulum. Under stress conditions, arginylated CRT was found associated to stress granules. These results suggest that CRT arginylation occurs in the cytosolic pool of mature CRT (defined by an Asp acid N-terminal) that is probably retrotranslocated from the endoplasmic reticulum. PMID:17197444

Decca, María B; Carpio, Marcos A; Bosc, Christophe; Galiano, Mauricio R; Job, Didier; Andrieux, Annie; Hallak, Marta E

2007-03-16

16

Subunit structure of dihydrolipoyl transacetylase component of pyruvate dehydrogenase complex from Escherichia coli  

PubMed Central

Limited tryptic digestion of the pyruvate dehydrogenase complex of Escherichia coli or its dihydrolipoyl transacetylase core cleaves the trypsin-sensitive transacetylase subunits into two large fragments, A (lipoyl domain) and D (subunit binding domain). Release of fragments A from the complex does not significantly affect its sedimentation coefficient or its appearance in the electron microscope. Fragment A contains the lipoyl moieties (3H-labeled), is acidic with an apparent isoelectric point of about 4.0, has a Mr of 31,600 as determined by sedimentation equilibrium analysis, and has a swollen or extended structure (f/fo = 1.78). Fragment A exhibits anomalous properties, probably due to its acidic nature. It is resistant to staining with Coomassie blue and it migrates on sodium dodecyl sulfate/polyacrylamide gels as if it had a Mr of 46,000-48,000. Further tryptic digestion converts fragment A into a lipoyl-containing fragment of Mr 20,000 (fragment B) and eventually into an apparently stable product of estimated Mr about 10,000 (fragment C). Fragment D has a compact structure of Mr about 29,600 as determined by sedimentation equilibrium analysis in 6 M guanidinium chloride, and it possesses the intersubunit binding sites of the transacetylase, the binding sites for pyruvate dehydrogenase and dihydrolipoyl dehydrogenase, and the catalytic site for transacetylation. The assemblage of fragments D is responsible for the cube-like appearance of the transacetylase in the electron microscope. High-resolution electron micrographs of the transacetylase show fiber-like extensions, apparently corresponding to tryptic fragment A, surrounding the cube-like core. Images

Bleile, Dennis M.; Munk, Peter; Oliver, Robert M.; Reed, Lester J.

1979-01-01

17

Calreticulin modulates cell adhesiveness via regulation of vinculin expression  

Microsoft Academic Search

Calreticulin is an ubiquitous and highly con- served high capacity Ca2+-binding protein that plays a major role in Ca 2÷ storage within the lumen of the ER. Here, using L fibroblast cell lines expressing different levels of calreticulin, we show that calreticulin plays a role in the control of cell adhesiveness via regulation of expression of vinculin, a cytoskeletal protein

Michal Opas; Greta K. Jass; Nasrin Mesaeli; Marek Michalak

1996-01-01

18

Calreticulin in the immune system: ins and outs  

PubMed Central

Calreticulin is a calcium-binding chaperone that has several functions in the immune response. In the endoplasmic reticulum (ER), calreticulin facilitates the folding of major histocompatibility complex (MHC) class I molecules and their assembly factor tapasin, thereby influencing antigen presentation to cytotoxic T cells. Although calreticulin is normally ER-resident, it is found at the cell surface of living cancer cells and dying cells. Here, calreticulin promotes cellular phagocytic uptake. In tumor vaccine models, drugs that induce cell-surface calreticulin confer enhanced tumor protection in an extracellular calreticulin-dependent manner. Much remains to be understood about the roles of calreticulin in these distinct functions. Further investigations are important towards advancing basic knowledge of glycoprotein folding pathways, and towards developing new cancer therapeutic strategies.

Raghavan, Malini; Wijeyesakere, Sanjeeva J.; Peters, Larry Robert; Del Cid, Natasha

2014-01-01

19

Post-translational arginylation of calreticulin: a new isospecies of calreticulin component of stress granules  

PubMed Central

Post-translational arginylation consists in the covalent union of an arginine residue to a Glu, Asp or Cys amino acid at the N-terminal position of proteins. This reaction is catalyzed by the enzyme arginyl-tRNA protein transferase. Using mass spectrometry, we have recently demonstrated in vitro the posttranslational incorporation of arginine into the calcium-binding protein calreticulin (CRT). To further study arginylated-CRT we raised an antibody against the peptide (RDPAIYFK), which contains an arginine followed by the first 7 N-terminal amino acids of mature rat CRT. This antibody specifically recognizes CRT obtained from rat soluble fraction that was arginylated in vitro and also recognizes endogenous arginylated CRT from NIH 3T3 cells in culture, indicating that CRT arginylation takes place in living cells. Using this antibody we found that arginylation of CRT is Ca2+-regulated. In vitro and in NIH 3T3 cells in culture, the level of arginylated-CRT increased with the addition of a Ca2+ chelator to the medium, whereas a decreased arginine incorporation into CRT was found in the presence of Ca2+. The arginylated-CRT was observed in the cytosol, in contrast to the non arginylated CRT which is in the endoplasmic reticulum (ER). Under stress conditions, arginylated-CRT was found associated to stress granules. These results suggest that CRT arginylation occurs in the cytosolic pool of mature CRT (defined by an Asp acid N-terminal) which is probably retro-translocated from the ER.

Decca, Maria B.; Carpio, Marcos A.; Bosc, Christophe; Galiano, Mauricio R.; Job, Didier; Andrieux, Annie; Hallak, Marta E.

2007-01-01

20

Constitutive expression of calreticulin in osteoblasts inhibits mineralization  

PubMed Central

Recent studies have shown that the multifunctional protein calreticulin can localize to the cell nucleus and regulate gene transcription via its ability to bind a protein motif in the DNA-binding domain of nuclear hormone receptors. A number of known modulators of bone cell function, including vitamin D, act through this receptor family, suggesting that calreticulin may regulate their action in bone cells. We have used a gain-of-function strategy to examine this putative role of calreticulin in MC3T3-E1 osteoblastic cells. Purified calreticulin inhibited the binding of the vitamin D receptor to characterized vitamin D response elements in gel retardation assays. This inhibition was due to direct protein-protein interactions between the vitamin D receptor and calreticulin. Expression of calreticulin transcripts declined during MC3T3-E1 osteoblastic differentiation. MC3T3-E1 cells were transfected with calreticulin expression vectors; stably transfected cell lines overexpressing recombinant calreticulin were established and assayed for vitamin D-induced gene expression and the capacity to mineralize. Constitutive calreticulin expression inhibited basal and vitamin D-induced expression of the osteocalcin gene, whereas osteopontin gene expression was unaffected. This pattern mimicked the gene expression pattern observed in parental cells before down- regulation of endogenous calreticulin expression. In long-term cultures of parental or vector-transfected cells, 1 alpha,25-dihydroxyvitamin D3 (1,25[OH]2D3) induced a two- to threefold stimulation of 45Ca accumulation into the matrix layer. Constitutive expression of calreticulin inhibited the 1,25(OH)2D3-induced 45Ca accumulation. This result correlated with the complete absence of mineralization nodules in long-term cultures of calreticulin-transfected cells. These data suggest that calreticulin can regulate bone cell function by interacting with specific nuclear hormone receptor-mediated pathways.

1995-01-01

21

Interaction of calreticulin with amyloid beta peptide 1-42.  

PubMed

The interaction of calreticulin with amyloid beta (Abeta) was investigated using solid phase and solution binding assays. Calreticulin bound Abeta 1-42 in a time and concentration dependent fashion. The binding was optimal at pH 5 and was stimulated by Ca2+ and inhibited by Zn2+ at pH 7. Interaction took place through the hydrophobic C-terminus of Abeta 1-42 and the polypeptide binding site of calreticulin. The results are discussed in the light of a reported role of calreticulin as a cell surface scavenger receptor. PMID:18221019

Duus, K; Hansen, P R; Houen, G

2008-01-01

22

Distinct clinical characteristics of myeloproliferative neoplasms with calreticulin mutations.  

PubMed

Somatic insertions/deletions in the calreticulin gene have recently been discovered to be causative alterations in myeloproliferative neoplasms. A combination of qualitative and quantitative allele-specific polymerase chain reaction, fragment-sizing, high resolution melting and Sanger-sequencing was applied for the detection of three driver mutations (in Janus kinase 2, calreticulin and myeloproliferative leukemia virus oncogene genes) in 289 cases of essential thrombocythemia and 99 cases of primary myelofibrosis. In essential thrombocythemia, 154 (53%) Janus kinase 2 V617F, 96 (33%) calreticulin, 9 (3%) myeloproliferative leukemia virus oncogene gene mutation-positive and 30 triple-negative (11%) cases were identified, while in primary myelofibrosis 56 (57%) Janus kinase 2 V617F, 25 (25%) calreticulin, 7 (7%) myeloproliferative leukemia virus oncogene gene mutation-positive and 11 (11%) triple-negative cases were identified. Patients positive for the calreticulin mutation were younger and had higher platelet counts compared to Janus kinase 2 mutation-positive counterparts. Calreticulin mutation-positive patients with essential thrombocythemia showed a lower risk of developing venous thrombosis, but no difference in overall survival. Calreticulin mutation-positive patients with primary myelofibrosis had a better overall survival compared to that of the Janus kinase 2 mutation-positive (P=0.04) or triple-negative cases (P=0.01). Type 2 calreticulin mutation occurred more frequently in essential thrombocythemia than in primary myelofibrosis (P=0.049). In essential thrombocythemia, the calreticulin mutational load was higher than the Janus kinase 2 mutational load (P<0.001), and increased gradually in advanced stages. Calreticulin mutational load influenced blood counts even at the time point of diagnosis in essential thrombocythemia. We confirm that calreticulin mutation is associated with distinct clinical characteristics and explored relationships between mutation type, load and clinical outcome. PMID:24895336

Andrikovics, Hajnalka; Krahling, Tunde; Balassa, Katalin; Halm, Gabriella; Bors, Andras; Koszarska, Magdalena; Batai, Arpad; Dolgos, Janos; Csomor, Judit; Egyed, Miklos; Sipos, Andrea; Remenyi, Peter; Tordai, Attila; Masszi, Tamas

2014-07-01

23

Distinct clinical characteristics of myeloproliferative neoplasms with calreticulin mutations  

PubMed Central

Somatic insertions/deletions in the calreticulin gene have recently been discovered to be causative alterations in myeloproliferative neoplasms. A combination of qualitative and quantitative allele-specific polymerase chain reaction, fragment-sizing, high resolution melting and Sanger-sequencing was applied for the detection of three driver mutations (in Janus kinase 2, calreticulin and myeloproliferative leukemia virus oncogene genes) in 289 cases of essential thrombocythemia and 99 cases of primary myelofibrosis. In essential thrombocythemia, 154 (53%) Janus kinase 2 V617F, 96 (33%) calreticulin, 9 (3%) myeloproliferative leukemia virus oncogene gene mutation-positive and 30 triple-negative (11%) cases were identified, while in primary myelofibrosis 56 (57%) Janus kinase 2 V617F, 25 (25%) calreticulin, 7 (7%) myeloproliferative leukemia virus oncogene gene mutation-positive and 11 (11%) triple-negative cases were identified. Patients positive for the calreticulin mutation were younger and had higher platelet counts compared to Janus kinase 2 mutation-positive counterparts. Calreticulin mutation-positive patients with essential thrombocythemia showed a lower risk of developing venous thrombosis, but no difference in overall survival. Calreticulin mutation-positive patients with primary myelofibrosis had a better overall survival compared to that of the Janus kinase 2 mutation-positive (P=0.04) or triple-negative cases (P=0.01). Type 2 calreticulin mutation occurred more frequently in essential thrombocythemia than in primary myelofibrosis (P=0.049). In essential thrombocythemia, the calreticulin mutational load was higher than the Janus kinase 2 mutational load (P<0.001), and increased gradually in advanced stages. Calreticulin mutational load influenced blood counts even at the time point of diagnosis in essential thrombocythemia. We confirm that calreticulin mutation is associated with distinct clinical characteristics and explored relationships between mutation type, load and clinical outcome.

Andrikovics, Hajnalka; Krahling, Tunde; Balassa, Katalin; Halm, Gabriella; Bors, Andras; Koszarska, Magdalena; Batai, Arpad; Dolgos, Janos; Csomor, Judit; Egyed, Miklos; Sipos, Andrea; Remenyi, Peter; Tordai, Attila; Masszi, Tamas

2014-01-01

24

Differential modulation of SERCA2 isoforms by calreticulin.  

PubMed

In Xenopus laevis oocytes, overexpression of calreticulin suppresses inositol 1,4,5-trisphosphate-induced Ca2+ oscillations in a manner consistent with inhibition of Ca2+ uptake into the endoplasmic reticulum. Here we report that the alternatively spliced isoforms of the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA)2 gene display differential Ca2+ wave properties and sensitivity to modulation by calreticulin. We demonstrate by glucosidase inhibition and site-directed mutagenesis that a putative glycosylated residue (N1036) in SERCA2b is critical in determining both the selective targeting of calreticulin to SERCA2b and isoform functional differences. Calreticulin belongs to a novel class of lectin ER chaperones that modulate immature protein folding. In addition to this role, we suggest that these chaperones dynamically modulate the conformation of mature glycoproteins, thereby affecting their function. PMID:9722609

John, L M; Lechleiter, J D; Camacho, P

1998-08-24

25

Vasostatin, a Calreticulin Fragment, Inhibits Angiogenesis and Suppresses Tumor Growth  

Microsoft Academic Search

Summary An endothelial cell inhibitor was purified from supernatant of an Epstein-Barr virus-immortal- ized cell line and identified as fragments of calreticulin. The purified recombinant NH 2 -termi- nal domain of calreticulin (amino acids 1-180) inhibited the proliferation of endothelial cells, but not cells of other lineages, and suppressed angiogenesis in vivo. We have named this NH 2 - terminal

Sandra E. Pike; Lei Yao; Karen D. Jones; Barry Cherney; Ettore Appella; Kazuyasu Sakaguchi; Hira Nakhasi; Julie Teruya-Feldstein; Peter Wirth; Ghanshyam Gupta; Giovanna Tosato

2010-01-01

26

ERp57 Does Not Require Interactions with Calnexin and Calreticulin to Promote Assembly of Class I Histocompatibility Molecules, and It Enhances Peptide Loading Independently of Its Redox Activity*  

PubMed Central

ERp57 is a thiol oxidoreductase that catalyzes disulfide formation in heavy chains of class I histocompatibility molecules. It also forms a mixed disulfide with tapasin within the class I peptide loading complex, stabilizing the complex and promoting efficient binding of peptides to class I molecules. Since ERp57 associates with the lectin chaperones calnexin and calreticulin, it is thought that ERp57 requires these chaperones to gain access to its substrates. To test this idea, we examined class I biogenesis in cells lacking calnexin or calreticulin or that express an ERp57 mutant that fails to bind to these chaperones. Remarkably, heavy chain disulfides formed at the same rate in these cells as in wild type cells. Moreover, ERp57 formed a mixed disulfide with tapasin and promoted efficient peptide loading in the absence of interactions with calnexin and calreticulin. These findings suggest that ERp57 has the capacity to recognize its substrates directly in addition to being recruited through lectin chaperones. We also found that calreticulin could be recruited into the peptide loading complex in the absence of interactions with both ERp57 and substrate oligosaccharides, demonstrating the importance of its polypeptide binding site in substrate recognition. Finally, by inactivating the redox-active sites of ERp57, we demonstrate that its enzymatic activity is dispensable in stabilizing the peptide loading complex and in supporting efficient peptide loading. Thus, ERp57 appears to play a structural rather than catalytic role within the peptide loading complex.

Zhang, Yinan; Kozlov, Guennadi; Pocanschi, Cosmin L.; Brockmeier, Ulf; Ireland, Breanna S.; Maattanen, Pekka; Howe, Chris; Elliott, Tim; Gehring, Kalle; Williams, David B.

2009-01-01

27

Role of homoserine transacetylase as a new target for antifungal agents.  

PubMed

Microbial amino acid biosynthesis is a proven yet underexploited target of antibiotics. The biosynthesis of methionine in particular has been shown to be susceptible to small-molecule inhibition in fungi. The first committed step in Met biosynthesis is the acylation of homoserine (Hse) by the enzyme homoserine transacetylase (HTA). We have identified the MET2 gene of Cryptococcus neoformans H99 that encodes HTA (CnHTA) by complementation of an Escherichia coli metA mutant that lacks the gene encoding homoserine transsuccinylase (HTS). We cloned, expressed, and purified CnHTA and determined its steady-state kinetic parameters for the acetylation of L-Hse by acetyl coenzyme A. We next constructed a MET2 mutant in C. neoformans H99 and tested its growth behavior in Met-deficient media, confirming the expected Met auxotrophy. Furthermore, we used this mutant in a mouse inhalation model of infection and determined that MET2 is required for virulence. This makes fungal HTA a viable target for new antibiotic discovery. We screened a 1,000-compound library of small molecules for HTA inhibitors and report the identification of the first inhibitor of fungal HTA. This work validates HTA as an attractive drug-susceptible target for new antifungal agent design. PMID:17353245

Nazi, Ishac; Scott, Adam; Sham, Anita; Rossi, Laura; Williamson, Peter R; Kronstad, James W; Wright, Gerard D

2007-05-01

28

Role of Homoserine Transacetylase as a New Target for Antifungal Agents?  

PubMed Central

Microbial amino acid biosynthesis is a proven yet underexploited target of antibiotics. The biosynthesis of methionine in particular has been shown to be susceptible to small-molecule inhibition in fungi. The first committed step in Met biosynthesis is the acylation of homoserine (Hse) by the enzyme homoserine transacetylase (HTA). We have identified the MET2 gene of Cryptococcus neoformans H99 that encodes HTA (CnHTA) by complementation of an Escherichia coli metA mutant that lacks the gene encoding homoserine transsuccinylase (HTS). We cloned, expressed, and purified CnHTA and determined its steady-state kinetic parameters for the acetylation of L-Hse by acetyl coenzyme A. We next constructed a MET2 mutant in C. neoformans H99 and tested its growth behavior in Met-deficient media, confirming the expected Met auxotrophy. Furthermore, we used this mutant in a mouse inhalation model of infection and determined that MET2 is required for virulence. This makes fungal HTA a viable target for new antibiotic discovery. We screened a 1,000-compound library of small molecules for HTA inhibitors and report the identification of the first inhibitor of fungal HTA. This work validates HTA as an attractive drug-susceptible target for new antifungal agent design.

Nazi, Ishac; Scott, Adam; Sham, Anita; Rossi, Laura; Williamson, Peter R.; Kronstad, James W.; Wright, Gerard D.

2007-01-01

29

Calreticulin Is a Thermostable Protein with Distinct Structural Responses to Different Divalent Cation Environments*  

PubMed Central

Calreticulin is a soluble calcium-binding chaperone of the endoplasmic reticulum (ER) that is also detected on the cell surface and in the cytosol. Calreticulin contains a single high affinity calcium-binding site within a globular domain and multiple low affinity sites within a C-terminal acidic region. We show that the secondary structure of calreticulin is remarkably thermostable at a given calcium concentration. Rather than corresponding to complete unfolding events, heat-induced structural transitions observed for calreticulin relate to tertiary structural changes that expose hydrophobic residues and reduce protein rigidity. The thermostability and the overall secondary structure content of calreticulin are impacted by the divalent cation environment, with the ER range of calcium concentrations enhancing stability, and calcium-depleting or high calcium environments reducing stability. Furthermore, magnesium competes with calcium for binding to calreticulin and reduces thermostability. The acidic domain of calreticulin is an important mediator of calcium-dependent changes in secondary structure content and thermostability. Together, these studies indicate interactions between the globular and acidic domains of calreticulin that are impacted by divalent cations. These interactions influence the structure and stability of calreticulin, and are likely to determine the multiple functional activities of calreticulin in different subcellular environments.

Wijeyesakere, Sanjeeva J.; Gafni, Ari A.; Raghavan, Malini

2011-01-01

30

High-level bacterial expression, purification and characterization of human calreticulin.  

PubMed

To investigate its cellular function and role in autoimmune disease pathogenesis, we have bacterially expressed human calreticulin, a major calcium-binding protein in the endoplasmic reticulum and a human autoantigen. This is the first report describing the heterologous expression of calreticulin from any source. The recombinant calreticulin constituted approximately 32% of the soluble Escherichia coli proteins, and was purified to apparent homogeneity by ion exchange and hydrophobic liquid chromatography. As does the bona fide protein, the recombinant calreticulin binds calcium and undergoes changes in its conformation upon Zn2+ binding. We take this as a strong indication that the folding of the E.coli-expressed calreticulin is very similar, if not identical, to that of the authentic protein. Moreover, the bacterially expressed calreticulin readily reacted with anti-human and anti-rabbit antibodies, and the anti-recombinant calreticulin antibodies immunoreacted with HeLa calreticulin. The availability of this expression system will allow us to carry out site-specific and deletion mutagenesis analysis in structure--function studies of calreticulin. PMID:1817262

Rokeach, L A; Haselby, J A; Hoch, S O

1991-12-01

31

Ultrastructural analysis of development of myocardium in calreticulin-deficient mice  

PubMed Central

Background Calreticulin is a Ca2+ binding chaperone of the endoplasmic reticulum which influences gene expression and cell adhesion. The levels of both vinculin and N-cadherin are induced by calreticulin expression, which play important roles in cell adhesiveness. Cardiac development is strictly dependent upon the ability of cells to adhere to their substratum and to communicate with their neighbours. Results We show here that the levels of N-cadherin are downregulated in calreticulin-deficient mouse embryonic hearts, which may lead to the disarray and wavy appearance of myofibrils in these mice, which we detected at all investigated stages of cardiac development. Calreticulin wild type mice exhibited straight, thick and abundant myofibrils, which were in stark contrast to the thin, less numerous, disorganized myofibrils of the calreticulin-deficient hearts. Interestingly, these major differences were only detected in the developing ventricles while the atria of both calreticulin phenotypes were similar in appearance at all developmental stages. Glycogen also accumulated in the ventricles of calreticulin-deficient mice, indicating an abnormality in cardiomyocyte metabolism. Conclusion Calreticulin is temporarily expressed during heart development where it is required for proper myofibrillogenesis. We postulate that calreticulin be considered as a novel cardiac fetal gene.

Lozyk, Mira D; Papp, Sylvia; Zhang, Xiaochu; Nakamura, Kimitoshi; Michalak, Marek; Opas, Michal

2006-01-01

32

Differential Modulation of SERCA2 Isoforms by Calreticulin  

Microsoft Academic Search

In Xenopus laevis oocytes, overexpression of calreticulin suppresses inositol 1,4,5-trisphosphate- induced Ca 2 1 oscillations in a manner consistent with inhibition of Ca 2 1 uptake into the endoplasmic reticu- lum. Here we report that the alternatively spliced iso- forms of the sarcoendoplasmic reticulum Ca 2 1 -ATPase (SERCA)2 gene display differential Ca 2 1 wave proper- ties and sensitivity

Linu M. John; James D. Lechleiter; Patricia Camacho

1998-01-01

33

Modes of Calreticulin Recruitment to the Major Histocompatibility Complex Class I Assembly Pathway*  

PubMed Central

Major histocompatibility complex (MHC) class I molecules are ligands for T-cell receptors of CD8+ T cells and inhibitory receptors of natural killer cells. Assembly of the heavy chain, light chain, and peptide components of MHC class I molecules occurs in the endoplasmic reticulum (ER). Specific assembly factors and generic ER chaperones, collectively called the MHC class I peptide loading complex (PLC), are required for MHC class I assembly. Calreticulin has an important role within the PLC and induces MHC class I cell surface expression, but the interactions and mechanisms involved are incompletely understood. We show that interactions with the thiol oxidoreductase ERp57 and substrate glycans are important for the recruitment of calreticulin into the PLC and for its functional activities in MHC class I assembly. The glycan and ERp57 binding sites of calreticulin contribute directly or indirectly to complexes between calreticulin and the MHC class I assembly factor tapasin and are important for maintaining steady-state levels of both tapasin and MHC class I heavy chains. A number of destabilizing conditions and mutations induce generic polypeptide binding sites on calreticulin and contribute to calreticulin-mediated suppression of misfolded protein aggregation in vitro. We show that generic polypeptide binding sites per se are insufficient for stable recruitment of calreticulin to PLC substrates in cells. However, such binding sites could contribute to substrate stabilization in a step that follows the glycan and ERp57-dependent recruitment of calreticulin to the PLC.

Del Cid, Natasha; Jeffery, Elise; Rizvi, Syed Monem; Stamper, Ericca; Peters, Larry Robert; Brown, William Clay; Provoda, Chester; Raghavan, Malini

2010-01-01

34

Estradiol Differentially Regulates Calreticulin: A Potential Link with Abnormal T Cell Function in Systemic Lupus Erythematosus?  

PubMed Central

Objective Systemic lupus erythematosus (SLE) is an autoimmune disease that affects women nine times more often than men. The present study investigates estradiol-dependent control of the calcium buffering protein, calreticulin, to gain further insight into the molecular basis of abnormal T cell signaling in SLE T cells. Methods T cells were purified from blood samples obtained from healthy females and SLE patients. Calreticulin expression was quantified by real time polymerase chain amplification. Calreticulin and estrogen receptor-? were co-precipitated and analyzed by Western blotting to determine if the proteins associate in T cells. Results Calreticulin expression increased (p= 0.034)in activated control T cells, while estradiol decreased (p = 0.044) calreticulin in resting T cells. Calreticulin expression decreased in activated SLE T cell samples and increased in approximately 50% of resting T cell samples. Plasma estradiol was similar (p > 0.05) among SLE patients and control volunteers. Estrogen receptor-?and calreticulin co-precipitated from nuclear and cytoplasmic T cell compartments. Conclusions The results indicate that estradiol tightly regulates calreticulin expression in normal human T cells and the dynamics are different between activated and resting T cells. The absence of this tight regulation in SLE T cells could contribute to abnormal T cell function.

Ward, Julie M.; Rider, Virginia; Abdou, Nabih I.; Kimler, Bruce

2014-01-01

35

The Polypeptide Binding Conformation of Calreticulin Facilitates Its Cell-surface Expression under Conditions of Endoplasmic Reticulum Stress*  

PubMed Central

We define two classes of calreticulin mutants that retain glycan binding activity; those that display enhanced or reduced polypeptide-specific chaperone activity, due to conformational effects. Under normal conditions, neither set of mutants significantly impacts the ability of calreticulin to mediate assembly and trafficking of major histocompatibility complex class I molecules, which are calreticulin substrates. However, in cells treated with thapsigargin, which depletes endoplasmic reticulum calcium, major histocompatibility complex class I trafficking rates are accelerated coincident with calreticulin secretion, and detection of cell-surface calreticulin is dependent on its polypeptide binding conformations. Together, these findings identify a site on calreticulin that is an important determinant of the induction of its polypeptide binding conformation and demonstrate the relevance of the polypeptide binding conformations of calreticulin to endoplasmic reticulum stress-induced interactions.

Jeffery, Elise; Peters, Larry Robert; Raghavan, Malini

2011-01-01

36

Comparison of Protein Acetyltransferase Action of CRTAase with the Prototypes of HAT  

PubMed Central

Our laboratory is credited for the discovery of enzymatic acetylation of protein, a phenomenon unknown till we identified an enzyme termed acetoxy drug: protein transacetylase (TAase), catalyzing the transfer of acetyl group from polyphenolic acetates to receptor proteins (RP). Later, TAase was identified as calreticulin (CR), an endoplasmic reticulum luminal protein. CR was termed calreticulin transacetylase (CRTAase). Our persistent study revealed that CR like other families of histone acetyltransferases (HATs) such as p300, Rtt109, PCAF, and ESA1, undergoes autoacetylation. The autoacetylated CR was characterized as a stable intermediate in CRTAase catalyzed protein acetylation, and similar was the case with ESA1. The autoacetylation of CR like that of HATs was found to enhance protein-protein interaction. CR like HAT-1, CBP, and p300 mediated the acylation of RP utilizing acetyl CoA and propionyl CoA as the substrates. The similarities between CRTAase and HATs in mediating protein acylation are highlighted in this review.

Ponnan, Prija; Kumar, Ajit; Singh, Prabhjot; Gupta, Prachi; Joshi, Rini; Saso, Luciano; Prasad, Ashok K.; Rastogi, Ramesh C.; Parmar, Virinder S.; Raj, Hanumantharao G.

2014-01-01

37

NMR structure of the calreticulin P-domain  

PubMed Central

The NMR structure of the rat calreticulin P-domain, comprising residues 189–288, CRT(189–288), shows a hairpin fold that involves the entire polypeptide chain, has the two chain ends in close spatial proximity, and does not fold back on itself. This globally extended structure is stabilized by three antiparallel ?-sheets, with the ?-strands comprising the residues 189–192 and 276–279, 206–209 and 262–265, and 223–226 and 248–251, respectively. The hairpin loop of residues 227–247 and the two connecting regions between the ?-sheets contain a hydrophobic cluster, where each of the three clusters includes two highly conserved tryptophyl residues, one from each strand of the hairpin. The three ?-sheets and the three hydrophobic clusters form a repeating pattern of interactions across the hairpin that reflects the periodicity of the amino acid sequence, which consists of three 17-residue repeats followed by three 14-residue repeats. Within the global hairpin fold there are two well-ordered subdomains comprising the residues 219–258, and 189–209 and 262–284, respectively. These are separated by a poorly ordered linker region, so that the relative orientation of the two subdomains cannot be precisely described. The structure type observed for CRT(189–288) provides an additional basis for functional studies of the abundant endoplasmic reticulum chaperone calreticulin.

Ellgaard, Lars; Riek, Roland; Herrmann, Torsten; Guntert, Peter; Braun, Daniel; Helenius, Ari; Wuthrich, Kurt

2001-01-01

38

Calreticulin: non-endoplasmic reticulum functions in physiology and disease  

PubMed Central

Calreticulin (CRT), when localized to the endoplasmic reticulum (ER), has important functions in directing proper conformation of proteins and glycoproteins, as well as in homeostatic control of cytosolic and ER calcium levels. There is also steadily accumulating evidence for diverse roles for CRT localized outside the ER, including data suggesting important roles for CRT localized to the outer cell surface of a variety of cell types, in the cytosol, and in the extracellular matrix (ECM). Furthermore, the addition of exogenous CRT rescues numerous CRT-driven functions, such as adhesion, migration, phagocytosis, and immunoregulatory functions of CRT-null cells. Recent studies show that topically applied CRT has diverse and profound biological effects that enhance cutaneous wound healing in animal models. This evidence for extracellular bioactivities of CRT has provided new insights into this classically ER-resident protein, despite a lack of knowledge of how CRT exits from the ER to the cell surface or how it is released into the extracellular milieu. Nonetheless, it has become clear that CRT is a multicompartmental protein that regulates a wide array of cellular responses important in physiological and pathological processes, such as wound healing, the immune response, fibrosis, and cancer.—Gold, L. I., Eggleton, P., Sweetwyne, M. T., Van Duyn, L. B., Greives, M. R., Naylor, S.-M., Michalak, M., Murphy-Ullrich, J. E. Calreticulin: non-endoplamic reticulum functions in physiology and disease.

Gold, Leslie I.; Eggleton, Paul; Sweetwyne, Mariya T.; Van Duyn, Lauren B.; Greives, Matthew R.; Naylor, Sara-Megumi; Michalak, Marek; Murphy-Ullrich, Joanne E.

2010-01-01

39

Molecular cloning and characterization of a calreticulin cDNA from the pinewood nematode Bursaphelenchus xylophilus.  

PubMed

The cloning and characterization of a cDNA encoding a calreticulin from the pinewood nematode Bursaphelenchus xylophilus is described herein. The full-length cDNA (Bx-crt-1) contained a 1200 bp open reading frame that could be translated to a 399 amino acid polypeptide. The deduced protein contained highly conserved regions of a calreticulin gene and had 66.2-70.1% amino acid sequence identity to other calreticulin sequences from nematodes. RNAi, RT-PCR amplification, and southern blot suggest that Bx-crt-1 may be important for the development of B. xylophilus. PMID:21371475

Li, Xundong; Zhuo, Kan; Luo, Mei; Sun, Longhua; Liao, Jinling

2011-06-01

40

Modulation of gene expression by calreticulin binding to the glucocorticoid receptor  

Microsoft Academic Search

CALRETICULIN is a multifunctional protein that acts as a major Ca2+-binding (storage) protein in the lumen of the endoplasmic reticulum1. It is also found in the nucleus2, suggesting that it may have a role in transcription regulation. Calreticulin has been reported to bind to the synthetic peptide KLGFFKR3, which is almost identical to an amino-acid sequence in the DNA-binding domain

Kimberly Burns; Brenda Duggan; Eric A. Atkinson; Konrad S. Famulski; Mona Nemer; R. Chris Bleackley; Marek Michalak

1994-01-01

41

Disrupted WNT signaling in mouse embryonic stem cells in the absence of calreticulin.  

PubMed

The role of endoplasmic reticulum (ER) homeostasis and protein quality control in the regulation of WNT signaling is not understood. Here we provide evidence for a role of calreticulin in the regulation of WNT signaling. We show that a deficiency in calreticulin disrupted WNT signaling, and prevented cell cycle progression via the miR-302 microRNA family. These effects were dependent on the Ca(2+) buffering capacity of calreticulin, as the protein is important in regulating ER Ca(2+) release and activation of Ca(2+)-dependent kinase and phosphatase cascades (including c-Src, Akt, and PTP1B). We also show that calreticulin plays a role in the secretion and ER retention of WNT3a, thereby affecting downstream WNT signaling. In calreticulin-deficient ES cells, the WNT and miR-302 dependent maintenance of the naïve ES cell state and the transition to primed pluripotency transition were lost, preventing cells from undergoing accurate differentiation. Together, these findings demonstrate unexpected roles of calreticulin and ER Ca(2+) homeostasis/signaling in the canonical WNT signaling pathway. PMID:24415131

Groenendyk, Jody; Michalak, Marek

2014-04-01

42

Regulation of peripheral T cell activation by calreticulin  

PubMed Central

Regulated expression of positive and negative regulatory factors controls the extent and duration of T cell adaptive immune response preserving the organism's integrity. Calreticulin (CRT) is a major Ca2+ buffering chaperone in the lumen of the endoplasmic reticulum. Here we investigated the impact of CRT deficiency on T cell function in immunodeficient mice reconstituted with fetal liver crt?/? hemopoietic progenitors. These chimeric mice displayed severe immunopathological traits, which correlated with a lower threshold of T cell receptor (TCR) activation and exaggerated peripheral T cell response to antigen with enhanced secretion of inflammatory cytokines. In crt?/? T cells TCR stimulation induced pulsatile cytosolic elevations of Ca2+ concentration and protracted accumulation of nuclear factor of activated T cells in the nucleus as well as sustained activation of the mitogen-activated protein kinase pathways. These observations support the hypothesis that CRT-dependent shaping of Ca2+ signaling critically contributes to the modulation of the T cell adaptive immune response.

Porcellini, Simona; Traggiai, Elisabetta; Schenk, Ursula; Ferrera, Denise; Matteoli, Michela; Lanzavecchia, Antonio; Michalak, Marek; Grassi, Fabio

2006-01-01

43

Interaction of calreticulin with CD40 ligand, TRAIL and Fas ligand.  

PubMed

The molecular chaperone calreticulin has been shown to bind C1q and mannan-binding lectin (MBL), which are constituents of the innate immune defence system. C1q and MBL do not share a large sequence identity but have a similar overall molecular architecture: an N-terminal triple-helical collagen-like domain and a C-terminal globular domain with ligand-binding properties. C1q is a hetero-trimer, while MBL is a homo-trimer, but due to the presence of N-terminal cysteines they both form higher order oligomers of trimers, which are the mature functional molecules. The same molecular architecture is utilized by many other functionally diverse molecules and in this work the interaction of calreticulin with C1q and structurally similar molecules was investigated. In addition to C1q and MBL, CD40 ligand (CD40L), tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL) were found to bind calreticulin strongly. A low level or no binding was observed for adiponectin, tumour necrosis factor-alpha (TNF-alpha), CD30L, surfactant protein-A and -D and collagen VIII. The interaction with calreticulin required a conformational change in CD40L, TRAIL and FasL and showed the same characteristics as calreticulin's interaction with C1q and MBL: a time-dependent saturable binding to immobilized protein, which was initially sensitive to salt but gradually developed into a salt-insensitive interaction. Thus, the interaction requires a structural change in the interaction partner and leads to a conformational change in calreticulin itself. The implications of these results are that calreticulin may function as a general response modifier for a whole group of immunologically important proteins. PMID:17953526

Duus, K; Pagh, R T; Holmskov, U; Højrup, P; Skov, S; Houen, G

2007-11-01

44

lac operon induction in Escherichia coli: Systematic comparison of IPTG and TMG induction and influence of the transacetylase LacA.  

PubMed

Most commonly used expression systems in bacteria are based on the Escherichia coli lac promoter. Furthermore, lac operon elements are used today in systems and synthetic biology. In the majority of the cases the gratuitous inducers IPTG or TMG are used. Here we report a systematic comparison of lac promoter induction by TMG and IPTG which focuses on the aspects inducer uptake, population heterogeneity and a potential influence of the transacetylase, LacA. We provide induction curves in E. coli LJ110 and in isogenic lacY and lacA mutant strains and we show that both inducers are substrates of the lactose permease at low inducer concentrations but can also enter cells independently of lactose permease if present at higher concentrations. Using a gfp reporter strain we compared TMG and IPTG induction at single cell level and showed that bimodal induction with IPTG occurred at approximately ten-fold lower concentrations than with TMG. Furthermore, we observed that lac operon induction is influenced by the transacetylase, LacA. By comparing two Plac-gfp reporter strains with and without a lacA deletion we could show that in the lacA(+) strain the fluorescence level decreased after few hours while the fluorescence further increased in the lacA(-) strain. The results indicate that through the activity of LacA the IPTG concentration can be reduced below an inducing threshold concentration-an influence that should be considered if low inducer amounts are used. PMID:22079752

Marbach, Anja; Bettenbrock, Katja

2012-01-01

45

Structural and functional relationships between the lectin and arm domains of calreticulin.  

PubMed

Calreticulin and calnexin are key components in maintaining the quality control of glycoprotein folding within the endoplasmic reticulum. Although their lectin function of binding monoglucosylated sugar moieties of glycoproteins is well documented, their chaperone activity in suppressing protein aggregation is less well understood. Here, we use a series of deletion mutants of calreticulin to demonstrate that its aggregation suppression function resides primarily within its lectin domain. Using hydrophobic peptides as substrate mimetics, we show that aggregation suppression is mediated through a single polypeptide binding site that exhibits a K(d) for peptides of 0.5-1 ?M. This site is distinct from the oligosaccharide binding site and differs from previously identified sites of binding to thrombospondin and GABARAP (4-aminobutyrate type A receptor-associated protein). Although the arm domain of calreticulin was incapable of suppressing aggregation or binding hydrophobic peptides on its own, it did contribute to aggregation suppression in the context of the whole molecule. The high resolution x-ray crystal structure of calreticulin with a partially truncated arm domain reveals a marked difference in the relative orientations of the arm and lectin domains when compared with calnexin. Furthermore, a hydrophobic patch was detected on the arm domain that mediates crystal packing and may contribute to calreticulin chaperone function. PMID:21652723

Pocanschi, Cosmin L; Kozlov, Guennadi; Brockmeier, Ulf; Brockmeier, Achim; Williams, David B; Gehring, Kalle

2011-08-01

46

Calreticulin Enhances Porcine Wound Repair by Diverse Biological Effects  

PubMed Central

Extracellular functions of the endoplasmic reticulum chaperone protein calreticulin (CRT) are emerging. Here we show novel roles for exogenous CRT in both cutaneous wound healing and diverse processes associated with repair. Compared with platelet-derived growth factor-BB-treated controls, topical application of CRT to porcine excisional wounds enhanced the rate of wound re-epithelialization. In both normal and steroid-impaired pigs, CRT increased granulation tissue formation. Immunohistochemical analyses of the wounds 5 and 10 days after injury revealed marked up-regulation of transforming growth factor-?3 (a key regulator of wound healing), a threefold increase in macrophage influx, and an increase in the cellular proliferation of basal keratinocytes of the new epidermis and of cells of the neodermis. In vitro studies confirmed that CRT induced a greater than twofold increase in the cellular proliferation of primary human keratinocytes, fibroblasts, and microvascular endothelial cells (with 100 pg/ml, 100 ng/ml, and 1.0 pg/ml, respectively). Moreover, using a scratch plate assay, CRT maximally induced the cellular migration of keratinocytes and fibroblasts (with 10 pg/ml and 1 ng/ml, respectively). In addition, CRT induced concentration-dependent migration of keratinocytes, fibroblasts macrophages, and monocytes in chamber assays. These in vitro bioactivities provide mechanistic support for the positive biological effects of CRT observed on both the epidermis and dermis of wounds in vivo, underscoring a significant role for CRT in the repair of cutaneous wounds.

Nanney, Lillian B.; Woodrell, Christopher D.; Greives, Mathew R.; Cardwell, Nancy L.; Pollins, Alonda C.; Bancroft, Tara A.; Chesser, Adrianne; Michalak, Marek; Rahman, Mohammad; Siebert, John W.; Gold, Leslie I.

2008-01-01

47

Immune response to Schistosoma mansoni calreticulin in schistosomiasis resistant individuals.  

PubMed

The major strategy to reduce the impact of schistosomiasis is the development of a defined antigen vaccine. It has recently been reported that the 62-kDa antigen known as S. mansoni calreticulin (SmCaR), is a good T- and B-cell antigen and represents a potential vaccine candidate. In the present study the immune response to SmCaR was evaluated in individuals resistant to schistosomiasis. Lymphoproliferative response and cytokine production to SmCaR was assessed in 30 schistosomiasis resistant and healthy individuals. Only 10% of the schistosomiasis resistant individuals showed significant proliferative response to SmCaR while all of them showed significant proliferative response to soluble adult warm antigen (SAWA). On the other hand, 20-30% of the schistosomiasis resistant individuals showed detectable levels of IL-2, IL-4 and IFN-gamma after stimulation with SmCaR, and 59% of them showed had anti SmCaR IgM specific antibodies. These findings suggest that SmCaR might be a potential vaccine antigen. PMID:16734116

El Naglaa, Gengihi; Zada, Suher; El Demellawy, Maha A

2004-01-01

48

Calreticulin Couples Calcium Release and Calcium Influx in Integrin-mediated Calcium Signaling  

PubMed Central

The engagement of integrin ?7 in E63 skeletal muscle cells by laminin or anti-?7 antibodies triggered transient elevations in the intracellular free Ca2+ concentration that resulted from both inositol triphosphate-evoked Ca2+ release from intracellular stores and extracellular Ca2+ influx through voltage-gated, L-type Ca2+ channels. The extracellular domain of integrin ?7 was found to associate with both ectocalreticulin and dihydropyridine receptor on the cell surface. Calreticulin appears to also associate with cytoplasmic domain of integrin ?7 in a manner highly dependent on the cytosolic Ca2+ concentration. It appeared that intracellular Ca2+ release was a prerequisite for Ca2+ influx and that calreticulin associated with the integrin cytoplasmic domain mediated the coupling of between the Ca2+ release and Ca2+ influx. These findings suggest that calreticulin serves as a cytosolic activator of integrin and a signal transducer between integrins and Ca2+ channels on the cell surface.

Kwon, Min Seong; Park, Chun Shik; Choi, Kyeong-rock; Park, Chul-Seung; Ahnn, Joohong; Kim, Jae Il; Eom, Soo Hyun; Kaufman, Stephen J.; Song, Woo Keun

2000-01-01

49

Structural Insight into the Role of Thrombospondin-1 Binding to Calreticulin in Calreticulin-Induced Focal Adhesion Disassembly†  

PubMed Central

Thrombospondin-1 (TSP1) binding to calreticulin (CRT) on the cell surface stimulates association of CRT with LDL receptor-related protein (LRP1) to signal focal adhesion disassembly and engagement of cellular activities. The structural basis for this phenomenon is unknown. We studied the binding thermodynamics of the TSP1–CRT complex and the conformational changes in CRT induced by binding to TSP1 with combined binding free energy analysis, molecular dynamics simulation, and anisotropic network model restrained molecular dynamics simulation. Results showed that mutations of Lys 24 and Lys 32 in TSP1 to Ala and of amino acids 24–26 and 32–34 in CRT to Ala significantly weakened the binding of TSP1 and CRT, which is consistent with experimental results. Upon validation of the calculated binding affinity changes of the TSP1–CRT complex by mutations in key residues in TSP1 and CRT with the experimental results, we performed conformational analyses to understand the role of TSP1 binding to CRT in the induction of conformational changes in CRT. Conformational analyses showed that TSP1 binding to CRT resulted in a more “open” conformation and a significant rotational change for the CRT N-domain with respect to the CRT P-domain, which could expose the potential binding site(s) in CRT for binding to LRP1 to signal focal adhesion disassembly. Results offer structural insight into the role of TSP1 binding to CRT in CRT-induced focal adhesion disassembly.

Yan, Qi; Murphy-Ullrich, Joanne E.; Song, Yuhua

2010-01-01

50

Calreticulin Regulates Transforming Growth Factor-?-stimulated Extracellular Matrix Production*  

PubMed Central

Endoplasmic reticulum (ER) stress is an emerging factor in fibrotic disease, although precise mechanisms are not clear. Calreticulin (CRT) is an ER chaperone and regulator of Ca2+ signaling up-regulated by ER stress and in fibrotic tissues. Previously, we showed that ER CRT regulates type I collagen transcript, trafficking, secretion, and processing into the extracellular matrix (ECM). To determine the role of CRT in ECM regulation under fibrotic conditions, we asked whether CRT modified cellular responses to the pro-fibrotic cytokine, TGF-?. These studies show that CRT?/? mouse embryonic fibroblasts (MEFs) and rat and human idiopathic pulmonary fibrosis lung fibroblasts with siRNA CRT knockdown had impaired TGF-? stimulation of type I collagen and fibronectin. In contrast, fibroblasts with increased CRT expression had enhanced responses to TGF-?. The lack of CRT does not impact canonical TGF-? signaling as TGF-? was able to stimulate Smad reporter activity in CRT?/? MEFs. CRT regulation of TGF-?-stimulated Ca2+ signaling is important for induction of ECM. CRT?/? MEFs failed to increase intracellular Ca2+ levels in response to TGF-?. NFAT activity is required for ECM stimulation by TGF-?. In CRT?/? MEFs, TGF-? stimulation of NFAT nuclear translocation and reporter activity is impaired. Importantly, CRT is required for TGF-? stimulation of ECM under conditions of ER stress, as tunicamycin-induced ER stress was insufficient to induce ECM production in TGF-? stimulated CRT?/? MEFs. Together, these data identify CRT-regulated Ca2+-dependent pathways as a critical molecular link between ER stress and TGF-? fibrotic signaling.

Zimmerman, Kurt A.; Graham, Lauren V.; Pallero, Manuel A.; Murphy-Ullrich, Joanne E.

2013-01-01

51

Fine specificity of autoantibodies to calreticulin: epitope mapping and characterization  

PubMed Central

Extracellular calreticulin (CRT) as well as anti-CRT antibodies have been reported in patients with various autoimmune disorders and CRT has been implicated in ‘epitope spreading’ to other autoantigens such as the Ro/SS-A complex. In addition, antibodies against parasite forms of the endoplasmic reticulum chaperone, CRT, have been found in patients suffering from onchocerciasis and schistosomiasis. In this study, we screened sera for anti-CRT antibodies from patients with active and inactive systemic lupus ertythematosus (SLE) and primary or secondary Sjögren's syndrome. Approximately 40% of all SLE patients were positive for anti-CRT antibodies. The antigenic regions of CRT were determined using full length CRT and fragments of CRT prepared in yeast and Escherichia coli, respectively. Synthetic 15mer peptides corresponding to the major autoantigenic region of CRT (amino acids 1–289), each one overlapping by 12 amino acids, were used to map the B cell epitopes on the CRT protein recognized by autoimmune sera. Major antigenic epitopes were found to be associated with the N-terminal half of the protein in 69% of the SLE sera from active disease patients, while the C-domain was not antigenic. Major epitopes were found to be reactive with antibodies in sera from SLE patients with both active and inactive disease, spanning different regions of the N and P-domains. Sera from both healthy and disease controls and primary Sjögren's syndrome patients were non-reactive to these sequences. Limited proteolysis of CRT with two major leucocyte serine proteases, elastase and cathepsin G, demonstrated that an N-terminal region of CRT is resistant to digestion. Interestingly, some of the epitopes with the highest reactivity belong to the fragments of the protein which bind to C1q and inhibit complement activation. Whether C1q association with CRT is a pathological or protective interaction between these two proteins is currently under investigation.

Eggleton, P; Ward, F J; Johnson, S; Khamashta, M A; Hughes, G R V; Hajela, V A; Michalak, M; Corbett, E F; Staines, N A; Reid, K B M

2000-01-01

52

Generation of Amyloid-? Is Reduced by the Interaction of Calreticulin with Amyloid Precursor Protein, Presenilin and Nicastrin  

PubMed Central

Dysregulation of the proteolytic processing of amyloid precursor protein by ?-secretase and the ensuing generation of amyloid-? is associated with the pathogenesis of Alzheimer's disease. Thus, the identification of amyloid precursor protein binding proteins involved in regulating processing of amyloid precursor protein by the ?-secretase complex is essential for understanding the mechanisms underlying the molecular pathology of the disease. We identified calreticulin as novel amyloid precursor protein interaction partner that binds to the ?-secretase cleavage site within amyloid precursor protein and showed that this Ca2+- and N-glycan-independent interaction is mediated by amino acids 330–344 in the C-terminal C-domain of calreticulin. Co-immunoprecipitation confirmed that calreticulin is not only associated with amyloid precursor protein but also with the ?-secretase complex members presenilin and nicastrin. Calreticulin was detected at the cell surface by surface biotinylation of cells overexpressing amyloid precursor protein and was co-localized by immunostaining with amyloid precursor protein and presenilin at the cell surface of hippocampal neurons. The P-domain of calreticulin located between the N-terminal N-domain and the C-domain interacts with presenilin, the catalytic subunit of the ?-secretase complex. The P- and C-domains also interact with nicastrin, another functionally important subunit of this complex. Transfection of amyloid precursor protein overexpressing cells with full-length calreticulin leads to a decrease in amyloid-?42 levels in culture supernatants, while transfection with the P-domain increases amyloid-?40 levels. Similarly, application of the recombinant P- or C-domains and of a synthetic calreticulin peptide comprising amino acid 330–344 to amyloid precursor protein overexpressing cells result in elevated amyloid-?40 and amyloid-?42 levels, respectively. These findings indicate that the interaction of calreticulin with amyloid precursor protein and the ?-secretase complex regulates the proteolytic processing of amyloid precursor protein by the ?-secretase complex, pointing to calreticulin as a potential target for therapy in Alzheimer's disease.

Ploger, Frank; Loers, Gabriele; Lutz, David; Buck, Friedrich; Michalak, Marek; Schachner, Melitta; Kleene, Ralf

2013-01-01

53

A comparative proteomic study identified calreticulin and prohibitin up-regulated in adrenocortical carcinomas  

PubMed Central

Background Identifying novel tumor biomarkers to develop more effective diagnostic and therapeutic strategies for patients with ACC is urgently needed. The aim of the study was to compare the proteomic profiles between adrenocortical carcinomas (ACC) and normal adrenocortical tissues in order to identify novel potential biomarkers for ACC. Methods The protein samples from 12 ACC tissues and their paired adjacent normal adrenocortical tissues were profiled with two-dimensional electrophoresis; and differentially expressed proteins were identified by mass spectrometry. Expression patterns of three differently expressed proteins calreticulin, prohibitin and HSP60 in ACC, adrenocortical adenomas (ACA) and normal adrenocortical tissues were further validated by immunohistochemistry. Results In our proteomic study, we identified 20 up-regulated and 9 down-regulated proteins in ACC tissues compared with paired normal controls. Most of the up-regulated proteins were focused in protein binding and oxidoreductase activity in Gene Ontology (GO) molecular function classification. By immunohistochemistry, two biomarkers calreticulin and prohibitin were validated to be overexpressed in ACC compared with adrenocortical adenomas (ACA) and normal tissues, but also calreticulin overexpression was significantly associated with tumor stages of ACC. Conclusion For the first time, calreticulin and prohibitin were identified to be novel candidate biomarkers for ACC, and their roles during ACC carcinogenesis and clinical significance deserves further investigation. Virtual slides The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1897372598927465

2013-01-01

54

Transient dissociation of polyribosomes and concurrent recruitment of calreticulin and calmodulin transcripts in gravistimulated maize pulvini  

NASA Technical Reports Server (NTRS)

The dynamics of polyribosome abundance were studied in gravistimulated maize (Zea mays) stem pulvini. During the initial 15 min of gravistimulation, the amount of large polyribosomes transiently decreased. The transient decrease in polyribosome levels was accompanied by a transient decrease in polyribosome-associated mRNA. After 30 min of gravistimulation, the levels of polyribosomes and the amount of polyribosome-associated mRNA gradually increased over 24 h up to 3- to 4-fold of the initial value. Within 15 min of gravistimulation, total levels of transcripts coding for calreticulin and calmodulin were elevated 5-fold in maize pulvinus total RNA. Transcripts coding for calreticulin and calmodulin were recruited into polyribosomes within 15 min of gravistimulation. Over 4 h of gravistimulation, a gradual increase in the association of calreticulin and calmodulin transcripts with polyribosomes was seen predominantly in the lower one-half of the maize pulvinus; the association of transcripts for vacuolar invertase with polyribosomes did not change over this period. Our results suggest that within 15 min of gravistimulation, the translation of the majority of transcripts associated with polyribosomes decreased, resembling a general stress response. Recruitment of calreticulin and calmodulin transcripts into polyribosomes occurred predominantly in the lower pulvinus one-half during the first 4 h when the presentation time for gravistimulation in the maize pulvinus is not yet complete.

Heilmann, I.; Shin, J.; Huang, J.; Perera, I. Y.; Davies, E.

2001-01-01

55

Confirmation of Tick Bite by Detection of Antibody to Ixodes Calreticulin Salivary Protein?  

PubMed Central

Ticks introduce a variety of pharmacologically active molecules into their host during attachment and feeding in order to obtain a blood meal. People who are repeatedly exposed to ticks may develop an immune response to tick salivary proteins. Despite this response, people usually are unaware of having been bitten, especially if they are not repeatedly exposed to ticks. In order to develop a laboratory marker of tick exposure that would be useful in understanding the epidemiology of tick-borne infection and the immune response to tick bite, we developed an enzyme-linked immunosorbent assay (ELISA) to detect antibody to a recombinant form of calreticulin protein found in the salivary glands of Ixodes scapularis, a member of a complex of Ixodes ticks that serve as the vectors for Lyme disease, human babesiosis, and human granulocytic anaplasmosis. Using this assay, we tested sera obtained from C3H/HeN and BALB/c mice before and after experimental deer tick infestation. These mice developed antibody to Ixodes calreticulin antigen after infestation. We then used the same assay to test sera obtained from people before and after they experienced deer tick bite(s). People experiencing deer tick bite(s) developed Ixodes calreticulin-specific antibody responses that persisted for up to 17 months. This Ixodes recombinant calreticulin ELISA provides objective evidence of deer tick exposure in people.

Alarcon-Chaidez, Francisco; Ryan, Raymond; Wikel, Stephen; Dardick, Kenneth; Lawler, Caroline; Foppa, Ivo M.; Tomas, Patricio; Cushman, Alexis; Hsieh, Ann; Spielman, Andrew; Bouchard, Keith R.; Dias, Filiciano; Aslanzadeh, Jaber; Krause, Peter J.

2006-01-01

56

Enolase 1 and calreticulin regulate the differentiation and function of mouse mast cells.  

PubMed

It has become widely accepted that the role of mast cells is not restricted to allergic processes. Thus, mast cells play an important role in innate and adaptive immune responses, but study of proteins related to differentiation of mast cells has not been done yet. Enolase 1 is a glycolytic enzyme expressed in most tissues and calreticulin, known as endoplasmic reticulum (ER) resident chaperon, has multifunctional responses. This study aimed to investigate the effects of these proteins on the differentiation and functions of mouse bone marrow-derived mast cells (BMMCs). To identify the target proteins related to the differentiation of BMMCs, we examined the protein expression pattern of BMMCs using 2-dimensional electrophoresis (2-DE) and MALDI-TOF analysis. Expressions of Fc?RI?, surface molecules (c-kit, CD40, CD40L, VCAM-1), tryptase, and cytokines were examined in BMMCs using FACS analysis, Western blot, and RT-PCR respectively. Enolase 1 and calreticulin were transfected into BMMCs, and [Ca(2+)]i levels were determined by confocal microscope, while amounts of TNF-? and LTs were measured by ELISA. Eight proteins were identified by proteomic analysis. Enolase and calreticulin siRNA transfection inhibited the expressions of Fc?RI?, surface molecules, tryptase, and cytokine mRNA, which are gradually enhanced during culture periods of BMMCs. Enolase 1 and calreticulin siRNA reduced the [Ca(2+)]i levels, amounts of total TNF-?, and the release of TNF-? and leukotrienes, all of which are increased in the BMMCs activated with antigen/antibody reaction. The data suggest that enolase 1 and calreticulin are important proteins in regulating the differentiation and functions of BMMCs. PMID:21803152

Ryu, Su Youn; Hong, Gwan Ui; Kim, Dae Yong; Ro, Jai Youl

2012-01-01

57

Over-expression of Chinese Cabbage Calreticulin 1, BrCRT1 , Enhances Shoot and Root Regeneration, But Retards Plant Growth in Transgenic Tobacco  

Microsoft Academic Search

Calreticulin (CRT) is a ubiquitously expressed, high capacity Ca2+-binding protein that is involved in intracellular Ca2+ homeostasis and molecular chaperoning in the endoplasmic reticulum (ER). A cDNA encoding a calreticulin, BrCRT1 (Brassica rapa Calreticulin 1), has been isolated from Chinese cabbage (B. rapa subsp. pekinensis) flower bud. Constitutive over-expression of the BrCRT1 gene promotes robust shoot production and root formation

Zheng-Lu Jin; Joon Ki Hong; Kyung Ae Yang; Ja Choon Koo; Young Ju Choi; Woo Sik Chung; Dae-Jin Yun; Sang Yeol Lee; Moo Je Cho; Chae Oh Lim

2005-01-01

58

Calreticulin enriched as an early-stage encapsulation protein in wax moth Galleria mellonella larvae  

Microsoft Academic Search

To investigate the molecular mechanism of the early-stage encapsulation reaction in insects, we purified a 47kDa protein from injected beads into Galleria mellonella larvae. When a cDNA clone was isolated, the 47kDa protein showed high homology with Drosophila and human calreticulin. Western blotting analysis showed that the 47kDa protein was present in the hemocytes, but not in the plasma. When

J. Y. Choi; M. M. A. Whitten; M. Y. Cho; K. Y. Lee; M. S. Kim; N. A. Ratcliffe; B. L. Lee

2002-01-01

59

Immunocytochemical evidence of calreticulin-like protein in pollen tubes and styles of Petunia hybrida Hort  

Microsoft Academic Search

Summary.   With a polyclonal antibody raised against calreticulin (CRT) the locations where the protein occurs in unpollinated and pollinated\\u000a styles of Petunia hybrida were localized. The epitopes binding the CRT antibody were immunolocalized preferentially in pollen tubes. In transmitting\\u000a tract cells, both before and after pollination, the level of CRT was low. The protein was mainly localized in the cytosol

M. Lenartowska; K. Kara?; J. Marshall; R. Napier; E. Bednarska

2002-01-01

60

Characterization of a histidine- and alanine-rich protein showing interaction with calreticulin in rice  

Microsoft Academic Search

Calreticulin (CRT) is a major calcium-sequestering protein in the endoplasmic reticulum and has been implicated in a variety\\u000a of cellular functions. To analyze the function of CRT in rice, a yeast two-hybrid protein interaction assay was used for identifying\\u000a interacting proteins. Fourteen of 17 interacting cDNA clones found coded for a novel histidine- and alanine-rich protein (OsHARP)\\u000a of 342 amino

Setsuko Komatsu; Asad Jan; Yasunori Koga

2009-01-01

61

A mathematical model predicts that calreticulin interacts with the endoplasmic reticulum Ca(2+)-ATPase.  

PubMed Central

A robust mathematical model developed from single cell calcium (Ca(2+)) dynamics has enabled us to predict the consequences of over-expression of endoplasmic reticulum-located chaperones. Model predictions concluded that calreticulin interacts with the lumenal domain of the sarcoplasmic and endoplasmic reticulum Ca(2+)-activated ATPase (SERCA) pump, altering pump affinity for Ca(2+) (K(1/2) switches from 247 to 431 nM) and hence generating Ca(2+) oscillations. Expression of calreticulin in the ER generated an average of six transient-decline oscillations during the Ca(2+) recovery phase, upon exposure to maximal levels of the agonist ATP. In contrast, normal cells produced a single Ca(2+) transient with few or no oscillations. By conditioning the model to experimental data, parameters for generation and decay of IP(3) and SERCA pump kinetics were determined. To elucidate the possible source of the oscillatory behavior three possible oscillators, 1) IP(3), 2) IP(3)R, and 3) SERCA pump, were investigated and parameters constrained by experimental data to produce the best candidate. Each of the three oscillators generated very good fits with experimental data. However, converting a normal exponential recovery to a transient-decline oscillator predicted that the SERCA pump is the most likely candidate for calreticulin-mediated Ca(2+) release, highlighting the role of this chaperone as a signal protein within the endoplasmic reticulum.

Baker, Helen L; Errington, Rachel J; Davies, Sally C; Campbell, Anthony K

2002-01-01

62

Calreticulin binds preferentially with B cell linear epitopes of Ro60 kD autoantigen, enhancing recognition by anti-Ro60 kD autoantibodies  

PubMed Central

Calreticulin is a molecular chaperone to newly synthesized polypeptides. Previous studies suggested that calreticulin is probably a protein member of the Ro/La RNP complex. The aims of this study were (a) to investigate whether linear B cell epitopes of the Ro/La RNP complex are bound to calreticulin and (b) if the complex peptide–calreticulin is recognized specifically by anti-Ro autoantibodies. Calreticulin was isolated from either human or pig spleen using a multi-step purification method and found to interact preferentially with biotinylated peptides derived from the sequence of the Ro60 kD 175–184aa(10p) and 216–232aa(17p). The interaction of the peptide–calreticulin complex was favoured by the combination of heat treatment, divalent cations and ATP. La/SSB epitopes did not react with calreticulin. Peptides corresponding to La/SSB epitopes as well as the common epitope of Sm did not interact with calreticulin. Thirty-eight anti-Ro60 KD positive and 23 anti-Ro60 kD negative sera of patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) were tested. All anti-Ro60 kD positive sera bound the complex calreticulin-17p, while 95% of the same sera had activity against the complex calreticulin ?10p. Tested individually, calreticulin, pep10p and pep17p presented very low reactivity (8%, 11% and 29%, respectively) against anti-Ro60 kD positive sera. Anti-Ro60 KD negative sera did not exhibit significant reactivity either with calreticulin, 10? and 17? or with the complexes calreticulin ?10p and calreticulin-17p (<5%). These results suggest that calreticulin can induce conformation-dependent recognition of the Ro60 kD epitopes, leading eventually to their recognition by autoantibodies. This is the first time that such a relationship is shown between a chaperone protein and fragments of an intracellular autoantigen. This work also provides insights into the understanding of mechanisms for autoantibody production. Furthermore, this association can be proved useful for the development of new sensitive assays for autoantibody detection.

STAIKOU, E V; ROUTSIAS, J G; MAKRI, A A; TERZOGLOU, A; SAKARELLOS-DAITSIOTIS, M; SAKARELLOS, C; PANAYOTOU, G; MOUTSOPOULOS, H M; TZIOUFAS, A G

2003-01-01

63

The chaperone and potential mannan-binding lectin (MBL) co-receptor calreticulin interacts with MBL through the binding site for MBL-associated serine proteases.  

PubMed

The chaperone calreticulin has been suggested to function as a C1q and collectin receptor. The interaction of calreticulin with mannan-binding lectin (MBL) was investigated by solid-phase binding assays. Calreticulin showed saturable and time-dependent binding to recombinant MBL, provided that MBL was immobilized on a solid surface or bound to mannan on a surface. The binding was non-covalent and biphasic with an initial salt-sensitive phase followed by a more stable salt-insensitive interaction. For plasma-derived MBL, known to be complexed with MBL-associated serine proteases (MASPs), no binding was observed. Interaction of calreticulin with recombinant MBL was fully inhibited by recombinant MASP-2, MASP-3 and MAp19, but not by the MASP-2 D105G and MAp19 Y59A variants characterized by defective MBL binding ability. Furthermore, MBL point mutants with impaired MASP binding showed no interaction with calreticulin. Comparative analysis of MBL with complement component C1q, its counterpart of the classical pathway, revealed that they display similar binding characteristics for calreticulin, providing further indication that calreticulin is a common co-receptor/chaperone for both proteins. In conclusion, the potential MBL co-receptor calreticulin binds to MBL at the MASP binding site and the interaction may involve a conformational change in MBL. PMID:18177377

Pagh, Rasmus; Duus, Karen; Laursen, Inga; Hansen, Paul R; Mangor, Julie; Thielens, Nicole; Arlaud, Gérard J; Kongerslev, Leif; Højrup, Peter; Houen, Gunnar

2008-02-01

64

Inhibition of host cell encapsulation through inhibiting immune gene expression by the parasitic wasp venom calreticulin.  

PubMed

Parasitoid wasps inject venom into the host to protect their offspring against host immune responses. In our previous study, we identified a calreticulin (CRT) in Pteromalus puparum venom. In this study, we expressed the wild-type and the coiled-coil domain deletion mutant P. puparum calreticulins (PpCRTs) in Escherichia coli and prepared polyclonal antibody in rabbit against PpCRT. Western blot analysis showed that PpCRT protein was not only present in the venom but also in all the tissues tested. Real time PCR results indicated that PpCRT mRNA was highly expressed in the venom gland. The transcript level of PpCRT in the venom gland was peaked at 2 days post-eclosion, while the PpCRT protein in the venom was maintained at a constant level. Both recombinant wild-type and mutant PpCRT proteins could bind to the surface of P. puparum eggs. Recombinant PpCRT inhibited hemocyte spreading and cellular encapsulation of the host Pieris rapae in vitro, and the coiled-coil domain is important for the inhibitory function of PpCRT. Immunocytochemistry results showed that PpCRT entered P. rapae hemocytes, and the coiled-coil domain played a role in this process. After injection of recombinant PpCRT into P. rapae pupae, real time PCR results showed that PpCRT inhibited transcript levels of host encapsulation-related genes, including calreticulin and scavenger receptor genes. In conclusion, our results suggest that P. puparum venom protects its offspring against host cellular immune responses via its functional component PpCRT to inhibit the expression of host cellular response-related genes. PMID:23933213

Wang, Lei; Fang, Qi; Qian, Cen; Wang, Fei; Yu, Xiao-Qiang; Ye, Gongyin

2013-10-01

65

Interaction between the individual isoenzymes of pyruvate dehydrogenase kinase and the inner lipoyl-bearing domain of transacetylase component of pyruvate dehydrogenase complex.  

PubMed Central

Protein-protein interactions play an important role in the regulation of enzymic activity of pyruvate dehydrogenase kinase (PDK). It is generally believed that the binding of PDK to the inner lipoyl-bearing domain L2 of the transacetylase component E2 of pyruvate dehydrogenase complex largely determines the level of kinase activity. In the present study, we characterized the interaction between the individual isoenzymes of PDK (PDK1-PDK4) and monomeric L2 domain of human E2, as well as the effect of this interaction on kinase activity. It was found that PDK isoenzymes are markedly different with respect to their affinities for L2. PDK3 demonstrated a very tight binding, which persisted during isolation of PDK3-L2 complexes using size-exclusion chromatography. Binding of PDK1 and PDK2 was readily reversible with the apparent dissociation constant of approx. 10 microM for both isoenzymes. PDK4 had a greatly reduced capacity for L2 binding (relative order PDK3>PDK1=PDK2>PDK4). Monomeric L2 domain alone had very little effect on the activities of either PDK1 or PDK2. In contrast, L2 caused a 3-fold increase in PDK3 activity and approx. 37% increase in PDK4 activity. These results strongly suggest that the interactions between the individual isoenzymes of PDK and L2 domain are isoenzyme-specific and might be among the major factors that determine the level of kinase activity of particular isoenzyme towards the pyruvate dehydrogenase complex.

Tuganova, Alina; Boulatnikov, Igor; Popov, Kirill M

2002-01-01

66

Novel mutations in the calreticulin gene core promoter and coding sequence in schizoaffective disorder.  

PubMed

We have recently reported the first case of mutation in the core promoter sequence of the human calreticulin gene in a family case of schizoaffective disorder. Remarkably, this gene coincides with a region of suggested linkage at 19p13.2, identified in a whole genome scan [Hamshere et al. (2005); Arch Gen Psychiatry 62;1081-1088]. The identified mutation was located at the conserved position -48 from the transcription start site, and was shown to be of functional effect, resulting in the aberrant expression of the gene. Following screening of the gene in 60 independent cases of schizoaffective disorder, we report novel germ-line mutations at positions -205 C > T and the conserved exon 5 (c: 682 C > T, pro228ser) in two unrelated cases of schizoaffective disorder. These mutations were disease-specific, and as for the -48 G > C mutation, neither was detected in a control population of 370 individuals, indicating a contribution of 3.17% in this sample series. To our knowledge, this is the first instance of disease-specific mutations in schizoaffective disorder, which warrants systematic screening of the regulatory and coding regions of the calreticulin gene in this disorder. PMID:19760677

Nabi, M Olad; Mirabzadeh, A; Feizzadeh, G; Khorshid, H R Khorram; Karimlou, M; Yeganeh, M Zarif; Asgharian, A M; Najmabadi, H; Ohadi, M

2010-03-01

67

Adiponectin modulates inflammatory reactions via calreticulin receptor-dependent clearance of early apoptotic bodies  

PubMed Central

Obesity and type 2 diabetes are associated with chronic inflammation. Adiponectin is an adipocyte-derived hormone with antidiabetic and antiinflammatory actions. Here, we demonstrate what we believe to be a previously undocumented activity of adiponectin, facilitating the uptake of early apoptotic cells by macrophages, an essential feature of immune system function. Adiponectin-deficient (APN-KO) mice were impaired in their ability to clear apoptotic thymocytes in response to dexamethasone treatment, and these animals displayed a reduced ability to clear early apoptotic cells that were injected into their intraperitoneal cavities. Conversely, adiponectin administration promoted the clearance of apoptotic cells by macrophages in both APN-KO and wild-type mice. Adiponectin overexpression also promoted apoptotic cell clearance and reduced features of autoimmunity in lpr mice whereas adiponectin deficiency in lpr mice led to a further reduction in apoptotic cell clearance, which was accompanied by exacerbated systemic inflammation. Adiponectin was capable of opsonizing apoptotic cells, and phagocytosis of cell corpses was mediated by the binding of adiponectin to calreticulin on the macrophage cell surface. We propose that adiponectin protects the organism from systemic inflammation by promoting the clearance of early apoptotic cells by macrophages through a receptor-dependent pathway involving calreticulin.

Takemura, Yukihiro; Ouchi, Noriyuki; Shibata, Rei; Aprahamian, Tamar; Kirber, Michael T.; Summer, Ross S.; Kihara, Shinji; Walsh, Kenneth

2007-01-01

68

Assembly and Antigen-Presenting Function of MHC Class I Molecules in Cells Lacking the ER Chaperone Calreticulin  

Microsoft Academic Search

MHC class I molecules expressed in a calreticulin-deficient cell line (K42) assembled with ? 2-microglobulin (?2-m) normally, but their subsequent loading with optimal peptides was defective. Suboptimally loaded class I molecules were released into the secretory pathway. This occurred despite the ability of newly synthesized class I to interact with the transporter associated with antigen processing (TAP) loading complex. The

Bin Gao; Raju Adhikari; Mark Howarth; Kimitoshi Nakamura; Marielle C Gold; Ann B Hill; Rai Knee; Marek Michalak; Tim Elliott

2002-01-01

69

Nematode pyruvate dehydrogenase kinases: role of the C-terminus in binding to the dihydrolipoyl transacetylase core of the pyruvate dehydrogenase complex.  

PubMed Central

Pyruvate dehydrogenase kinases (PDKs) from the anaerobic parasitic nematode Ascaris suum and the free-living nematode Caenorhabditis elegans were functionally expressed with hexahistidine tags at their N-termini and purified to apparent homogeneity. Both recombinant PDKs (rPDKs) were dimers, were not autophosphorylated and exhibited similar specific activities with the A. suum pyruvate dehydrogenase (E1) as substrate. In addition, the activities of both PDKs were activated by incubation with PDK-depleted A. suum muscle pyruvate dehydrogenase complex (PDC) and were stimulated by NADH and acetyl-CoA. However, the recombinant A. suum PDK (rAPDK) required higher NADH/NAD+ ratios for half-maximal stimulation than the recombinant C. elegans PDK (rCPDK) or values reported for mammalian PDKs, as might be predicted by the more reduced microaerobic mitochondrial environment of the APDK. Limited tryptic digestion of both rPDKs yielded stable fragments truncated at the C-termini (trPDKs). The trPDKs retained their dimeric structure and exhibited substantial PDK activity with the A. suum E1 as substrate, but PDK activity was not activated by incubation with PDK-depleted A. suum PDC or stimulated by elevated NADH/NAD+ or acetyl-CoA/CoA ratios. Direct-binding assays demonstrated that increasing amounts of rCPDK bound to the A. suum PDK-depleted PDC. No additional rCPDK binding was observed at ratios greater than 20 mol of rCPDK/mol of PDC. In contrast, the truncated rCPDK (trCPDK) did not exhibit significant binding to the PDC. Similarly, a truncated form of rCPDK, rCPDK1-334, generated by mutagenesis, exhibited properties similar to those observed for trCPDK. These results suggest that the C-terminus of the PDK is not required for subunit association of the homodimer or catalysis, but instead seems to be involved in the binding of the PDKs to the dihydrolipoyl transacetylase core of the complex.

Chen, W; Komuniecki, P R; Komuniecki, R

1999-01-01

70

Calreticulin contributes to C1q-dependent recruitment of microglia in the leech Hirudo medicinalis following a CNS injury  

PubMed Central

Background The medicinal leech is considered as a complementary and appropriate model to study immune functions in the central nervous system (CNS). In a context in which an injured leech’s CNS can naturally restore normal synaptic connections, the accumulation of microglia (immune cells of the CNS that are exclusively resident in leeches) has been shown to be essential at the lesion to engage the axonal sprouting. HmC1q (Hm for Hirudo medicinalis) possesses chemotactic properties that are important in the microglial cell recruitment by recognizing at least a C1q binding protein (HmC1qBP alias gC1qR). Material/Methods Recombinant forms of C1q were used in affinity purification and in vitro chemotaxis assays. Anti-calreticulin antibodies were used to neutralize C1q-mediated chemotaxis and locate the production of calreticulin in leech CNS. Results A newly characterized leech calreticulin (HmCalR) has been shown to interact with C1q and participate to the HmC1q-dependent microglia accumulation. HmCalR, which has been detected in only some microglial cells, is consequently a second binding protein for HmC1q, allowing the chemoattraction of resident microglia in the nerve repair process. Conclusions These data give new insight into calreticulin/C1q interaction in an immune function of neuroprotection, suggesting another molecular target to use in investigation of microglia reactivity in a model of CNS injury.

Le Marrec-Croq, Francoise; Bocquet-Garcon, Annelise; Vizioli, Jacopo; Vancamp, Christelle; Drago, Francesco; Franck, Julien; Wisztorski, Maxence; Salzet, Michel; Sautiere, Pierre-Eric; Lefebvre, Christophe

2014-01-01

71

Expression of the high capacity calcium-binding domain of calreticulin increases bioavailable calcium stores in plants  

NASA Technical Reports Server (NTRS)

Modulation of cytosolic calcium levels in both plants and animals is achieved by a system of Ca2+-transport and storage pathways that include Ca2+ buffering proteins in the lumen of intracellular compartments. To date, most research has focused on the role of transporters in regulating cytosolic calcium. We used a reverse genetics approach to modulate calcium stores in the lumen of the endoplasmic reticulum. Our goals were two-fold: to use the low affinity, high capacity Ca2+ binding characteristics of the C-domain of calreticulin to selectively increase Ca2+ storage in the endoplasmic reticulum, and to determine if those alterations affected plant physiological responses to stress. The C-domain of calreticulin is a highly acidic region that binds 20-50 moles of Ca2+ per mole of protein and has been shown to be the major site of Ca2+ storage within the endoplasmic reticulum of plant cells. A 377-bp fragment encoding the C-domain and ER retention signal from the maize calreticulin gene was fused to a gene for the green fluorescent protein and expressed in Arabidopsis under the control of a heat shock promoter. Following induction on normal medium, the C-domain transformants showed delayed loss of chlorophyll after transfer to calcium depleted medium when compared to seedlings transformed with green fluorescent protein alone. Total calcium measurements showed a 9-35% increase for induced C-domain transformants compared to controls. The data suggest that ectopic expression of the calreticulin C-domain increases Ca2+ stores, and that this Ca2+ reserve can be used by the plant in times of stress.

Wyatt, Sarah E.; Tsou, Pei-Lan; Robertson, Dominique; Brown, C. S. (Principal Investigator)

2002-01-01

72

Sumoylation regulates ER stress response by modulating calreticulin gene expression in XBP-1-dependent mode in Caenorhabditis elegans.  

PubMed

Excessive accumulation of unfolded proteins in the endoplasmic reticulum (ER) lumen causes ER stress, which induces a set of genes, including those encoding ER-resident chaperones, to relieve the detrimental effects and recover homeostasis. Calreticulin is a chaperone that facilitates protein folding in the ER lumen, and its gene expression is induced by ER stress in Caenorhabditis elegans. Sumoylation conjugates small ubiquitin-like modifier (SUMO) proteins with target proteins to regulate a variety of biological processes, such as protein stability, nuclear transport, DNA binding, and gene expression. In this study, we showed that C. elegans X-box-binding protein 1 (Ce-XBP-1), an ER stress response transcription factor, interacts with the SUMO-conjugating enzyme UBC-9 and a SUMOylation target. Our results indicated that abolishing sumoylation enhanced calreticulin expression in an XBP-1-dependent manner, and the resulting increase in calreticulin counteracted ER stress. Furthermore, sumoylation was repressed in C. elegans undergoing ER stress. Finally, RNAi against ubc-9 mainly affected the expression of genes associated with ER functions, such as lipid and organic acid metabolism. Our results suggest that sumoylation plays a regulatory role in ER function by controlling the expression of genes required for ER homeostasis in C. elegans. PMID:24933177

Lim, Yunki; Lee, Dukgyu; Kalichamy, Karunambigai; Hong, Seong-Eui; Michalak, Marek; Ahnn, Joohong; Kim, Do Han; Lee, Sun-Kyung

2014-08-01

73

Ligand-specific, transient interaction between integrins and calreticulin during cell adhesion to extracellular matrix proteins is dependent upon phosphorylation/dephosphorylation events.  

PubMed Central

As transmembrane heterodimers, integrins bind to both extracellular ligands and intracellular proteins. We are currently investigating the interaction between integrins and the intracellular protein calreticulin. A prostatic carcinoma cell line (PC-3) was used to demonstrate that calreticulin can be found in the alpha3 immunoprecipitates of cells plated on collagen type IV, but not when plated on vitronectin. Conversely, alphav immunoprecipitates contained calreticulin only when cells were plated on vitronectin, i. e. not when plated on collagen IV. The interactions between these integrins and calreticulin were independent of actin cytoskeleton assembly and were transient, being maximal approx. 10-30 min after the cells came into contact with the substrates prior to complete cell spreading and formation of firm adhesive contacts. We demonstrate that okadaic acid, an inhibitor of intracellular serine/threonine protein phosphatases, inhibited the alpha3beta1-mediated adhesion of PC-3 cells to collagen IV and the alpha2beta1-mediated attachment of Jurkat cells to collagen I. This inhibition by okadaic acid was accompanied by inhibition of the ligand-specific interaction of calreticulin with the respective integrins in the two cell types. Additionally, we found that pharmacological inhibition of mitogen-activated protein kinase kinase (MEK) resulted in prolongation of the calreticulin-integrin interaction, and enhancement of PC-3 cell attachment to collagen IV. We conclude that calreticulin interacts transiently with integrins during cell attachment and spreading. This interaction depends on receptor occupation, is ligand-specific, and can be modulated by protein phosphatase and MEK activity.

Coppolino, M G; Dedhar, S

1999-01-01

74

Calnexin and calreticulin bind to enzymically active tissue-type plasminogen activator during biosynthesis and are not required for folding to the native conformation.  

PubMed Central

The roles of the endoplasmic-reticulum lectins calnexin and calreticulin in the folding of tissue-type plasminogen activator (tPA) have been investigated using an in vitro translation system that reconstitutes these processes as they would occur in the intact cell. Using co-immunoprecipitation of newly synthesized tPA with antibodies to calnexin and calreticulin, it was demonstrated that the interaction of tPA with both lectins was dependent upon tPA glycosylation and glucosidase trimming. When tPA was synthesized in the presence of semi-permeabilized cells under conditions preventing complex formation with calnexin and calreticulin, the translation product had a specific plasminogenolytic activity identical with that when synthesized under conditions permitting interactions with both lectins. Furthermore, complexes of tPA bound to calnexin and calreticulin were shown to be enzymically active. These results demonstrate that calnexin and calreticulin can form a stable interaction with correctly folded tPA; however, such interactions are not required for the synthesis of enzymically active tPA.

Allen, S; Bulleid, N J

1997-01-01

75

Plasmodesmata without callose and calreticulin in higher plants - open channels for fast symplastic transport?  

PubMed

Plasmodesmata (PD) represent membrane-lined channels that link adjacent plant cells across the cell wall. PD of higher plants contain a central tube of endoplasmic reticulum (ER) called desmotubule. Membrane and lumen proteins seem to be able to move through the desmotubule, but most transport processes through PD occur through the cytoplasmic annulus (Brunkard etal., 2013). Calreticulin (CRT), a highly conserved Ca(2+)-binding protein found in all multicellular eukaryotes, predominantly located in the ER, was shown to localize to PD, though not all PD accumulate CRT. In nitrogen-fixing actinorhizal root nodules of the Australian tree Casuarina glauca, the primary walls of infected cells containing the microsymbiont become lignified upon infection. TEM analysis of these nodules showed that during the differentiation of infected cells, PD connecting infected cells, and connecting infected and adjacent uninfected cells, were reduced in number as well as diameter (Schubert etal., 2013). In contrast with PD connecting young infected cells, and most PD connecting mature infected and adjacent uninfected cells, PD connecting mature infected cells did not accumulate CRT. Furthermore, as shown here, these PD were not associated with callose, and based on their diameter, they probably had lost their desmotubules. We speculate that either this is a slow path to PD degradation, or that the loss of callose accumulation and presumably also desmotubules leads to the PD becoming open channels and improves metabolite exchange between cells. PMID:24634671

Demchenko, Kirill N; Voitsekhovskaja, Olga V; Pawlowski, Katharina

2014-01-01

76

Impact of calreticulin mutations on clinical and hematological phenotype and outcome in essential thrombocythemia.  

PubMed

Mutations in the calreticulin (CALR) gene were recently discovered in patients with essential thrombocythemia (ET) lacking the JAK2V617F and MPLW515 mutations, but no information is available on the clinical correlates. In this series, CALR mutations were found in 15.5% of 576 World Health Organization-defined ET patients, accounting for 48.9% of JAK2 and MPL wild-type (wt) patients. CALR-mutated patients were preferentially male and showed higher platelet count and lower hemoglobin and leukocyte count compared with JAK2- and MPL-mutated patients. Patients carrying the CALR mutation had a lower risk of thrombosis than JAK2- and MPL-mutated patients; of interest, their risk was superimposable to patients who were wt for the above mutations. CALR mutation had no impact on survival or transformation to post-ET myelofibrosis. Genotyping for CALR mutations represents a novel useful tool for establishing a clonal myeloproliferative disorder in JAK2 and MPL wt patients with thrombocytosis and may have prognostic and therapeutic relevance. PMID:24371211

Rotunno, Giada; Mannarelli, Carmela; Guglielmelli, Paola; Pacilli, Annalisa; Pancrazzi, Alessandro; Pieri, Lisa; Fanelli, Tiziana; Bosi, Alberto; Vannucchi, Alessandro M

2014-03-01

77

Calreticulin activates ?1 integrin via fucosylation by fucosyltransferase 1 in J82 human bladder cancer cells.  

PubMed

Fucosylation regulates various pathological events in cells. We reported that different levels of CRT (calreticulin) affect the cell adhesion and metastasis of bladder cancer. However, the precise mechanism of tumour metastasis regulated by CRT remains unclear. Using a DNA array, we identified FUT1 (fucosyltransferase 1) as a gene regulated by CRT expression levels. CRT regulated cell adhesion through ?1,2-linked fucosylation of ?1 integrin and this modification was catalysed by FUT1. To clarify the roles for FUT1 in bladder cancer, we transfected the human FUT1 gene into CRT-RNAi stable cell lines. FUT1 overexpression in CRT-RNAi cells resulted in increased levels of ?1 integrin fucosylation and rescued cell adhesion to type-I collagen. Treatment with UEA-1 (Ulex europaeus agglutinin-1), a lectin that recognizes FUT1-modified glycosylation structures, did not affect cell adhesion. In contrast, a FUT1-specific fucosidase diminished the activation of ?1 integrin. These results indicated that ?1,2-fucosylation of ?1 integrin was not involved in integrin-collagen interaction, but promoted ?1 integrin activation. Moreover, we demonstrated that CRT regulated FUT1 mRNA degradation at the 3'-UTR. In conclusion, the results of the present study suggest that CRT stabilized FUT1 mRNA, thereby leading to an increase in fucosylation of ?1 integrin. Furthermore, increased fucosylation levels activate ?1 integrin, rather than directly modifying the integrin-binding sites. PMID:24593306

Lu, Yi-Chien; Chen, Chiung-Nien; Chu, Chia-Ying; Lu, Jenher; Wang, Bo-Jeng; Chen, Chia-Hua; Huang, Min-Chuan; Lin, Tsui-Hwa; Pan, Chin-Chen; Chen, Swey-Shen Alex; Hsu, Wen-Ming; Liao, Yung-Feng; Wu, Pei-Yi; Hsia, Hsin-Yi; Chang, Cheng-Chi; Lee, Hsinyu

2014-05-15

78

Use of recombinant calreticulin and cercarial transformation fluid (CTF) in the serodiagnosis of Schistosoma mansoni.  

PubMed

Schistosomiasis is traditionally diagnosed by microscopic detection of ova in stool samples, but this method is labour intensive and its sensitivity is limited by low and variable egg secretion in many patients. An alternative is an ELISA using Schistosoma mansoni soluble egg antigen (SEA) to detect anti-schistosome antibody in patient samples. SEA is a good diagnostic marker in non-endemic regions but is of limited value in endemic regions, mainly because of its high cost and limited specificity. Here we assess seven novel antigens for the detection of S. mansoni antibody in an endemic region (the Northern Nile Delta). Using recombinant S. mansoni calreticulin (CRT) and fragments thereof, anti-CRT antibodies were detected in the majority of 97 patients sera. The diagnostic value of some of these antigens was, however, limited by the presence of cross-reacting antibody in the healthy controls, even those recruited in non-endemic areas. Cercarial transformation fluid (CTF), a supernatant that contains soluble material released by the cercariae upon transformation to the schistosomula, is cheaper and easier to produce than SEA. An ELISA using CTF as the detection antigen had a sensitivity of 89.7% and an estimated specificity of 100% when used in non-endemic regions, matching the performance of the established SEA ELISA. CTF was substantially more specific than SEA for diagnosis in the endemic region, and less susceptible than SEA to cross-reacting antibody in the sera of controls with other protozoan and metazoan infections. PMID:20691496

El Aswad, Bahaa El Deen Wade; Doenhoff, Michael J; El Hadidi, Abeer Shawky; Schwaeble, Wilhelm J; Lynch, Nicholas J

2011-03-01

79

Trypanosoma cruzi calreticulin inhibits the complement lectin pathway activation by direct interaction with L-Ficolin.  

PubMed

Trypanosoma cruzi, the agent of Chagas' disease, the sixth neglected tropical disease worldwide, infects 10-12 million people in Latin America. Differently from T. cruzi epimastigotes, trypomastigotes are complement-resistant and infective. CRPs, T-DAF, sialic acid and lipases explain at least part of this resistance. In vitro, T. cruzi calreticulin (TcCRT), a chaperone molecule that translocates from the ER to the parasite surface: (a) Inhibits the human classical complement activation, by interacting with C1, (b) As a consequence, an increase in infectivity is evident and, (c) It inhibits angiogenesis and tumor growth. We report here that TcCRT also binds to the L-Ficolin collagenous portion, thus inhibiting approximately between 35 and 64% of the human complement lectin pathway activation, initiated by L-Ficolin, a property not shared by H-Ficolin. While L-Ficolin binds to 60% of trypomastigotes and to 24% of epimastigotes, 50% of the former and 4% of the latter display TcCRT on their surfaces. Altogether, these data indicate that TcCRT is a parasite inhibitory receptor for Ficolins. The resulting evasive activities, together with the TcCRT capacity to inhibit C1, with a concomitant increase in infectivity, may represent T. cruzi strategies to inhibit important arms of the innate immune response. PMID:24769495

Sosoniuk, Eduardo; Vallejos, Gerardo; Kenawy, Hany; Gaboriaud, Christine; Thielens, Nicole; Fujita, Teizo; Schwaeble, Wilhelm; Ferreira, Arturo; Valck, Carolina

2014-07-01

80

Calsequestrin 2 (CASQ2) mutations increase expression of calreticulin and ryanodine receptors, causing catecholaminergic polymorphic ventricular tachycardia  

PubMed Central

Catecholamine-induced polymorphic ventricular tachycardia (CPVT) is a familial disorder caused by cardiac ryanodine receptor type 2 (RyR2) or calsequestrin 2 (CASQ2) gene mutations. To define how CASQ2 mutations cause CPVT, we produced and studied mice carrying a human D307H missense mutation (CASQ307/307) or a CASQ2-null mutation (CASQ?E9/?E9). Both CASQ2 mutations caused identical consequences. Young mutant mice had structurally normal hearts but stress-induced ventricular arrhythmias; aging produced cardiac hypertrophy and reduced contractile function. Mutant myocytes had reduced CASQ2 and increased calreticulin and RyR2 (with normal phosphorylated proportions) but unchanged calstabin levels, as well as reduced total sarcoplasmic reticulum (SR) Ca2+, prolonged Ca2+ release, and delayed Ca2+ reuptake. Stress further diminished Ca2+ transients, elevated cytosolic Ca2+, and triggered frequent, spontaneous SR Ca2+ release. Treatment with Mg2+, a RyR2 inhibitor, normalized myocyte Ca2+ cycling and decreased CPVT in mutant mice, indicating RyR2 dysfunction was critical to mutant CASQ2 pathophysiology. We conclude that CPVT-causing CASQ2 missense mutations function as null alleles. In the absence of CASQ2, calreticulin, a fetal Ca2+-binding protein normally downregulated at birth, remains a prominent SR component. Adaptive changes to CASQ2 deficiency (increased posttranscriptional expression of calreticulin and RyR2) maintained electrical-mechanical coupling, but increased RyR2 leakiness, a paradoxical response further exacerbated by stress. The central role of RyR2 dysfunction in CASQ2 deficiency unifies the pathophysiologic mechanism underlying CPVT due to RyR2 or CASQ2 mutations and suggests a therapeutic approach for these inherited cardiac arrhythmias.

Song, Lei; Alcalai, Ronny; Arad, Michael; Wolf, Cordula M.; Toka, Okan; Conner, David A.; Berul, Charles I.; Eldar, Michael; Seidman, Christine E.; Seidman, J.G.

2007-01-01

81

Overexpression of calreticulin contributes to the development and progression of pancreatic cancer.  

PubMed

We studied the clinicopathological significance for Calreticulin (CRT) expression in pancreatic cancer (PC), and its functional relationship with other signaling genes (especially with p53) in regulating the biological behavior of PC cells. IHC, IF, IB, and real-time PCR were used to detect CRT expression in PC, while transfection and drug intervention were used to investigate the functional relationship of CRT with other signaling genes. IHC showed both CRT and p53 expression was significantly increased in PC, compared to that in paired non-cancerous pancreatic tissues (P?

Sheng, Weiwei; Chen, Chuanping; Dong, Ming; Zhou, Jianping; Liu, Qingfeng; Dong, Qi; Li, Feng

2014-07-01

82

Helper component-proteinase (HC-Pro) protein of Papaya ringspot virus interacts with papaya calreticulin.  

PubMed

Potyviral helper component-proteinase (HC-Pro) is a multifunctional protein involved in plant-virus interactions. In this study, we constructed a Carica papaya L. plant cDNA library to investigate the host factors interacting with Papaya ringspot virus (PRSV) HC-Pro using a Sos recruitment two-hybrid system (SRS). We confirmed that the full-length papaya calreticulin, designated PaCRT (GenBank accession no. FJ913889), interacts specifically with PRSV HC-Pro in yeast, in vitro and in plant cells using SRS, in vitro protein-binding assay and bimolecular fluorescent complementation assay, respectively. SRS analysis of the interaction between three PaCRT deletion mutants and PRSV HC-Pro demonstrated that the C-domain (residues 307-422), with a high Ca(2+)-binding capacity, was responsible for binding to PRSV HC-Pro. In addition, quantitative real-time reverse transcriptase-polymerase chain reaction assay showed that the expression of PaCRT mRNA was significantly upregulated in the primary stage of PRSV infection, and decreased to near-basal expression levels in noninoculated (healthy) papaya plants with virus accumulation inside host cells. PaCRT is a new calcium-binding protein that interacts with potyviral HC-Pro. It is proposed that the upregulated expression of PaCRT mRNA may be an early defence-related response to PRSV infection in the host plant, and that interaction between PRSV HC-Pro and PaCRT may be involved in plant calcium signalling pathways which could interfere with virus infection or host defence. PMID:20447282

Shen, Wentao; Yan, Pu; Gao, Le; Pan, Xueying; Wu, Jinyan; Zhou, Peng

2010-05-01

83

Protein Recycling from the Golgi Apparatus to the Endoplasmic Reticulum in Plants and Its Minor Contribution to Calreticulin Retention  

PubMed Central

Using pulse–chase experiments combined with immunoprecipitation and N-glycan structural analysis, we showed that the retrieval mechanism of proteins from post–endoplasmic reticulum (post-ER) compartments is active in plant cells at levels similar to those described previously for animal cells. For instance, recycling from the Golgi apparatus back to the ER is sufficient to block the secretion of as much as 90% of an extracellular protein such as the cell wall invertase fused with an HDEL C-terminal tetrapeptide. Likewise, recycling can sustain fast retrograde transport of Golgi enzymes into the ER in the presence of brefeldin A. However, on the basis of our data, we propose that this retrieval mechanism in plants has little impact on the ER retention of a soluble ER protein such as calreticulin. Indeed, the latter is retained in the ER without any N-glycan–related evidence for a recycling through the Golgi apparatus. Taken together, these results indicate that calreticulin and perhaps other plant reticuloplasmins are possibly largely excluded from vesicles exported from the ER. Instead, they are probably retained in the ER by mechanisms that rely primarily on signals other than H/KDEL motifs.

Pagny, Sophie; Cabanes-Macheteau, Marion; Gillikin, Jeffrey W.; Leborgne-Castel, Nathalie; Lerouge, Patrice; Boston, Rebecca S.; Faye, Loic; Gomord, Veronique

2000-01-01

84

Radiation-induced immunogenic modulation of tumor enhances antigen processing and calreticulin exposure, resulting in enhanced T-cell killing.  

PubMed

Radiation therapy (RT) is used for local tumor control through direct killing of tumor cells. Radiation-induced cell death can trigger tumor antigen-specific immune responses, but these are often noncurative. Radiation has been demonstrated to induce immunogenic modulation (IM) in various tumor types by altering the biology of surviving cells to render them more susceptible to T cell-mediated killing. Little is known about the mechanism(s) underlying IM elicited by sub-lethal radiation dosing. We have examined the molecular and immunogenic consequences of radiation exposure in breast, lung, and prostate human carcinoma cells. Radiation induced secretion of ATP and HMGB1 in both dying and surviving tumor cells. In vitro and in vivo tumor irradiation induced significant upregulation of multiple components of the antigen-processing machinery and calreticulin cell-surface expression. Augmented CTL lysis specific for several tumor-associated antigens was largely dictated by the presence of calreticulin on the surface of tumor cells and constituted an adaptive response to endoplasmic reticulum stress, mediated by activation of the unfolded protein response. This study provides evidence that radiation induces a continuum of immunogenic alterations in tumor biology, from immunogenic modulation to immunogenic cell death. We also expand the concept of immunogenic modulation, where surviving tumor cells recovering from radiation-induced endoplasmic reticulum stress become more sensitive to CTL killing. These observations offer a rationale for the combined use of radiation with immunotherapy, including for patients failing RT alone. PMID:24480782

Gameiro, Sofia R; Jammeh, Momodou L; Wattenberg, Max M; Tsang, Kwong Y; Ferrone, Soldano; Hodge, James W

2014-01-30

85

Reversion of the human calreticulin gene promoter to the ancestral type as a result of a novel psychosis-associated mutation  

Microsoft Academic Search

Development-dependent, tissue-specific expression of the calreticulin (CALR) gene in the gray matter coincides with the expression of psychoses phenotypes. We have recently reported instances of mutations within the core promoter sequence of the gene in schizoaffective disorder. In view of the mounting evidence on the genetic overlap in the psychiatric spectrum, we investigated this gene in a spectrum of patients

T. Farokhashtiani; A. Mirabzadeh; M. Olad Nabi; Z. Ghaem Magham; H. R. Khorram Khorshid; H. Najmabadi; M. Ohadi

2011-01-01

86

Human Survivin and Trypanosoma cruzi Calreticulin Act in Synergy against a Murine Melanoma In Vivo  

PubMed Central

Immune-based anti-tumor or anti-angiogenic therapies hold considerable promise for the treatment of cancer. The first approach seeks to activate tumor antigen-specific T lymphocytes while, the second, delays tumor growth by interfering with blood supply. Tumor Associated Antigens are often employed to target tumors with therapeutic drugs, but some are also essential for tumor viability. Survivin (Surv) is a member of the inhibitor of apoptosis protein family that is considered a Tumor Associated Antigen important for cancer cell viability and proliferation. On the other hand, Trypanosoma cruzi (the agent of Chagas’ disease) calreticulin (TcCRT) displays remarkable anti-angiogenic properties. Because these molecules are associated with different tumor targets, we reasoned that immunization with a Surv-encoding plasmid (pSurv) and concomitant TcCRT administration should generate a stronger anti-tumor response than application of either treatment separately. To evaluate this possibility, C57BL/6 mice were immunized with pSurv and challenged with an isogenic melanoma cell line that had been pre-incubated with recombinant TcCRT (rTcCRT). Following tumor cell inoculation, mice were injected with additional doses of rTcCRT. For the combined regimen we observed in mice that: i). Tumor growth was impaired, ii). Humoral anti-rTcCRT immunity was induced and, iii). In vitro rTcCRT bound to melanocytes, thereby promoting the incorporation of human C1q and subsequent macrophage phagocytosis of tumor cells. These observations are interpreted to reflect the consequence of the following sequence of events: rTcCRT anti-angiogenic activity leads to stress in tumor cells. Murine CRT is then translocated to the external membrane where, together with rTcCRT, complement C1 is captured, thus promoting tumor phagocytosis. Presentation of the Tumor Associated Antigen Surv induces the adaptive anti-tumor immunity and, independently, mediates anti-endothelial cell immunity leading to an important delay in tumor growth.

Aguilar-Guzman, Lorena; Lobos-Gonzalez, Lorena; Rosas, Carlos; Vallejos, Gerardo; Falcon, Cristian; Sosoniuk, Eduardo; Coddou, Francisca; Leyton, Lisette; Lemus, David; Quest, Andrew F. G.; Ferreira, Arturo

2014-01-01

87

Calreticulin and other components of endoplasmic reticulum stress in rat and human inflammatory demyelination  

PubMed Central

Background Calreticulin (CRT) is a chaperone protein, which aids correct folding of glycosylated proteins in the endoplasmic reticulum (ER). Under conditions of ER stress, CRT is upregulated and may be displayed on the surface of cells or be secreted. This ‘ecto-CRT’ may activate the innate immune response or it may aid clearance of apoptotic cells. Our and other studies have demonstrated upregulation of ER stress markers CHOP, BiP, ATF4, XBP1 and phosphorylated e-IF2 alpha (p-eIF2 alpha) in biopsy and post-mortem human multiple sclerosis (MS) samples. We extend this work by analysing changes in expression of CRT, BiP, CHOP, XBP1 and p-eIF2 alpha in a rat model of inflammatory demyelination. Demyelination was induced in the spinal cord by intradermal injection of recombinant mouse MOG mixed with incomplete Freund’s adjuvant (IFA) at the base of the tail. Tissue samples were analysed by semi-quantitative scoring of immunohistochemically stained frozen tissue sections. Data generated following sampling of tissue from animals with spinal cord lesions, was compared to that obtained using tissue derived from IFA- or saline-injected controls. CRT present in rat serum and in a cohort of human serum derived from 14 multiple sclerosis patients and 11 healthy controls was measured by ELISA. Results Stained tissue scores revealed significantly (p<0.05) increased amounts of CRT, CHOP and p-eIF2 alpha in the lesion, lesion edge and normal-appearing white matter when compared to controls. CHOP and p-eIF2 alpha were also significantly raised in regions of grey matter and the central canal (p<0.05). Immunofluorescent dual-label staining confirmed expression of these markers in astrocytes, microglia or neurons. Dual staining of rat and human spinal cord lesions with Oil Red O and CRT antibody showed co-localisation of CRT with the rim of myelin fragments. ELISA testing of sera from control and EAE rats demonstrated significant down-regulation (p<0.05) of CRT in the serum of EAE animals, compared to saline and IFA controls. This contrasted with significantly increased amounts of CRT detected in the sera of MS patients (p<0.05), compared to controls. Conclusion This data highlights the potential importance of CRT and other ER stress proteins in inflammatory demyelination.

2013-01-01

88

Anti-C1q receptor/calreticulin autoantibodies in patients with systemic lupus erythematosus (SLE)  

PubMed Central

SLE is a disease characterized by the presence of multiple autoantibodies and high levels of circulating immune complexes. We studied the presence and functional relevance of autoantibodies directed against a receptor for the collagen-like stalks of the first subcomponent of complement, also known as calreticulin (cC1qR/CaR), in patients with SLE. In a cross-sectional study it was found that higher titres of antibodies against cC1qR/CaR are present in sera of SLE patients compared with normal donors. No association between anti-cC1qR/CaR titres and SLE disease activity was found. Following gel filtration of SLE serum it was found that anti-cC1qR/CaR reactivity is associated with the peak of monomeric IgG. Purified IgG from patients was able to specifically immunoprecipitate cC1qR/CaR. Since we have shown previously that cC1qR/CaR is able to inhibit the haemolytic activity of C1q, we determined a possible pathogenic role for anti-cC1qR/CaR on complement regulation. IgG derived from SLE serum reversed the inhibitory capacity of cC1qR/CaR in a dose-dependent fashion up to 63%, whereas IgG from normal donors had no significant effect. With respect to the capacity of anti-cC1qR/CaR antibodies to activate neutrophils, it was found that incubation of normal neutrophils with F(ab?)2 anti-cC1qR/CaR resulted in a very limited oxidative burst. However, cross-linking of F(ab?)2 anti-cC1qR/CaR on the neutrophils clearly induced neutrophil activation. Pre-incubation of the SLE-derived F(ab?)2 with cC1qR/CaR prevented activation of neutrophils up to 81 ± 5%. These results suggest that the presence of anti-cC1qR/CaR antibodies in patients with SLE may modulate complement and neutrophil activation.

Van Den Berg, R H; Siegert, C E H; Faber-Krol, M C; Huizinga, T W J; Van ES, L A; Daha, M R

1998-01-01

89

Human survivin and Trypanosoma cruzi calreticulin act in synergy against a murine melanoma in vivo.  

PubMed

Immune-based anti-tumor or anti-angiogenic therapies hold considerable promise for the treatment of cancer. The first approach seeks to activate tumor antigen-specific T lymphocytes while, the second, delays tumor growth by interfering with blood supply. Tumor Associated Antigens are often employed to target tumors with therapeutic drugs, but some are also essential for tumor viability. Survivin (Surv) is a member of the inhibitor of apoptosis protein family that is considered a Tumor Associated Antigen important for cancer cell viability and proliferation. On the other hand, Trypanosoma cruzi (the agent of Chagas' disease) calreticulin (TcCRT) displays remarkable anti-angiogenic properties. Because these molecules are associated with different tumor targets, we reasoned that immunization with a Surv-encoding plasmid (pSurv) and concomitant TcCRT administration should generate a stronger anti-tumor response than application of either treatment separately. To evaluate this possibility, C57BL/6 mice were immunized with pSurv and challenged with an isogenic melanoma cell line that had been pre-incubated with recombinant TcCRT (rTcCRT). Following tumor cell inoculation, mice were injected with additional doses of rTcCRT. For the combined regimen we observed in mice that: i). Tumor growth was impaired, ii). Humoral anti-rTcCRT immunity was induced and, iii). In vitro rTcCRT bound to melanocytes, thereby promoting the incorporation of human C1q and subsequent macrophage phagocytosis of tumor cells. These observations are interpreted to reflect the consequence of the following sequence of events: rTcCRT anti-angiogenic activity leads to stress in tumor cells. Murine CRT is then translocated to the external membrane where, together with rTcCRT, complement C1 is captured, thus promoting tumor phagocytosis. Presentation of the Tumor Associated Antigen Surv induces the adaptive anti-tumor immunity and, independently, mediates anti-endothelial cell immunity leading to an important delay in tumor growth. PMID:24755644

Aguilar-Guzmán, Lorena; Lobos-González, Lorena; Rosas, Carlos; Vallejos, Gerardo; Falcón, Cristián; Sosoniuk, Eduardo; Coddou, Francisca; Leyton, Lisette; Lemus, David; Quest, Andrew F G; Ferreira, Arturo

2014-01-01

90

Epitopes of the Onchocerca volvulus RAL1 antigen, a member of the calreticulin family of proteins, recognized by sera from patients with onchocerciasis.  

PubMed

RAL1 is an antigen (Ag) encoded by the filarial nematode Onchocerca volvulus, the parasite causing onchocerciasis (river blindness). RAL1 shares 64.4% identity with the autoantigen calreticulin. The striking similarity of the parasite Ag and the human autoantigen has led to the hypothesis that RAL1 may induce a cross-reactive immune response to calreticulin, which in turn may be involved in the pathogenesis of onchocerciasis. To test this hypothesis, we explored the immune response to RAL1 recombinant Ag (RAL1 rAg) and human calreticulin in patients with O. volvulus infection. A total of 86% of the O. volvulus-infected individuals produced antibodies recognizing RAL1 rAg. Antibody reactivity to RAL1 rAg in patient sera was confined primarily to the central and carboxyl-terminal parts of the molecule. No significant correlations were found to associate recognition of RAL1 rAg, or any particular portion thereof, with a particular disease state. Antibodies against RAL1 thus appear to be produced as a general immune reaction to O. volvulus infection and do not necessarily lead to a cross-reacting response with the host protein. In contrast, 33% of the patient sera tested bound recombinant human calreticulin. All of these sera also recognized a polypeptide encompassing the carboxyl-terminal portion of the RAL1 rAg. These results suggest that recognition of an epitope encoded in the carboxyl-terminal portion of RAL1 is at least in part responsible for inducing a cross-reacting immune response to the host protein. PMID:7520419

Rokeach, L A; Zimmerman, P A; Unnasch, T R

1994-09-01

91

Over-expression of calcium-dependent protein kinase 13 and calreticulin interacting protein 1 confers cold tolerance on rice plants  

Microsoft Academic Search

Calcium is a ubiquitous signaling molecule and changes in cytosolic calcium concentration are involved in plant responses\\u000a to various stimuli. The rice calcium-dependent protein kinase 13 (CDPK13) and calreticulin interacting protein 1 (CRTintP1)\\u000a have previously been reported to be involved in cold stress response in rice. In this study, rice lines transformed with sense\\u000a CDPK13 or CRTintP1 constructs were produced

Setsuko Komatsu; Guangxiao Yang; Monowar Khan; Haruko Onodera; Seiichi Toki; Masayuki Yamaguchi

2007-01-01

92

Epitopes of the Onchocerca volvulus RAL1 antigen, a member of the calreticulin family of proteins, recognized by sera from patients with onchocerciasis.  

PubMed Central

RAL1 is an antigen (Ag) encoded by the filarial nematode Onchocerca volvulus, the parasite causing onchocerciasis (river blindness). RAL1 shares 64.4% identity with the autoantigen calreticulin. The striking similarity of the parasite Ag and the human autoantigen has led to the hypothesis that RAL1 may induce a cross-reactive immune response to calreticulin, which in turn may be involved in the pathogenesis of onchocerciasis. To test this hypothesis, we explored the immune response to RAL1 recombinant Ag (RAL1 rAg) and human calreticulin in patients with O. volvulus infection. A total of 86% of the O. volvulus-infected individuals produced antibodies recognizing RAL1 rAg. Antibody reactivity to RAL1 rAg in patient sera was confined primarily to the central and carboxyl-terminal parts of the molecule. No significant correlations were found to associate recognition of RAL1 rAg, or any particular portion thereof, with a particular disease state. Antibodies against RAL1 thus appear to be produced as a general immune reaction to O. volvulus infection and do not necessarily lead to a cross-reacting response with the host protein. In contrast, 33% of the patient sera tested bound recombinant human calreticulin. All of these sera also recognized a polypeptide encompassing the carboxyl-terminal portion of the RAL1 rAg. These results suggest that recognition of an epitope encoded in the carboxyl-terminal portion of RAL1 is at least in part responsible for inducing a cross-reacting immune response to the host protein. Images

Rokeach, L A; Zimmerman, P A; Unnasch, T R

1994-01-01

93

Molecular cloning of a new wheat calreticulin gene TaCRT1 and expression analysis in plant defense responses and abiotic stress resistance.  

PubMed

Calreticulin proteins play essential roles in regulating various metabolic processes and in molecular signal transduction in animals and plants. Using homologous PCR, we screened a cDNA library of the wheat resistance gene Yr5 from a near-isogenic line in the susceptible common wheat variety Taichung 29, which was inoculated with an incompatible race CYR32 of Puccinia striiformis. We isolated a novel full-length cDNA encoding calreticulin protein, which we named TaCRT1. Sequence analyses indicated that TaCRT1 contains an open reading frame of 1287 bp in length; it was deduced to encode 428 amino acids. Clustering analysis showed that TaCRT1 belongs to group III of the calreticulin protein family. Semi-quantitative RT-PCR was used to analyze expression profiles of the isolated gene under biotic and abiotic stresses. Expression of TaCRT1 was suppressed by exogenous application of phytohormones, such as abscisic acid and methyl jasmonate, and by dehydration; but it was induced by CYR32 infection and cold treatment. Based on the expression patterns, we propose that TaCRT1 participates in regulatory processes involved in defense responses and stress resistance in wheat. PMID:22095480

An, Y Q; Lin, R M; Wang, F T; Feng, J; Xu, Y F; Xu, S C

2011-01-01

94

A panel of tumor markers, calreticulin, annexin A2, and annexin A3 in upper tract urothelial carcinoma identified by proteomic and immunological analysis  

PubMed Central

Background Upper tract urothelial carcinoma (UTUC) is a tumor with sizable metastases and local recurrence. It has a worse prognosis than bladder cancer. This study was designed to investigate the urinary potential tumor markers of UTUC. Methods Between January 2008 and January 2009, urine was sampled from 13 patients with UTUC and 20 healthy adults. The current study identified biomarkers for UTUC using non-fixed volume stepwise weak anion exchange chromatography for fractionation of urine protein prior to two-dimensional gel electrophoresis. Results Fifty five differential proteins have been determined by comparing with the 2-DE maps of the urine of UTUC patients and those of healthy people. Western blotting analysis and immunohistochemistry of tumor tissues and normal tissues from patients with UTUC were carried out to further verify five possible UTUC biomarkers, including zinc-alpha-2-glycoprotein, calreticulin, annexin A2, annexin A3 and haptoglobin. The data of western blot and immunohistochemical analysis are consistent with the 2-DE data. Combined the experimental data in the urine and in tumor tissues collected from patients with UTUC, the crucial over-expressed proteins are calreticulin, annexin A2, and annexin A3. Conclusions Calreticulin, annexin A2, and annexin A3 are very likely a panel of biomarkers with potential value for UTUC diagnosis.

2014-01-01

95

The Interaction of Classical Complement Component C1 with Parasite and Host Calreticulin Mediates Trypanosoma cruzi Infection of Human Placenta  

PubMed Central

Background 9 million people are infected with Trypanosoma cruzi in Latin America, plus more than 300,000 in the United States, Canada, Europe, Australia, and Japan. Approximately 30% of infected individuals develop circulatory or digestive pathology. While in underdeveloped countries transmission is mainly through hematophagous arthropods, transplacental infection prevails in developed ones. Methodology/Principal Findings During infection, T. cruzi calreticulin (TcCRT) translocates from the endoplasmic reticulum to the area of flagellum emergence. There, TcCRT acts as virulence factor since it binds maternal classical complement component C1q that recognizes human calreticulin (HuCRT) in placenta, with increased parasite infectivity. As measured ex vivo by quantitative PCR in human placenta chorionic villi explants (HPCVE) (the closest available correlate of human congenital T. cruzi infection), C1q mediated up to a 3–5-fold increase in parasite load. Because anti-TcCRT and anti-HuCRT F(ab?)2 antibody fragments are devoid of their Fc-dependent capacity to recruit C1q, they reverted the C1q-mediated increase in parasite load by respectively preventing its interaction with cell-bound CRTs from both parasite and HPCVE origins. The use of competing fluid-phase recombinant HuCRT and F(ab?)2 antibody fragments anti-TcCRT corroborated this. These results are consistent with a high expression of fetal CRT on placental free chorionic villi. Increased C1q-mediated infection is paralleled by placental tissue damage, as evidenced by histopathology, a damage that is ameliorated by anti-TcCRT F(ab?)2 antibody fragments or fluid-phase HuCRT. Conclusions/Significance T. cruzi infection of HPCVE is importantly mediated by human and parasite CRTs and C1q. Most likely, C1q bridges CRT on the parasite surface with its receptor orthologue on human placental cells, thus facilitating the first encounter between the parasite and the fetal derived placental tissue. The results presented here have several potential translational medicine aspects, specifically related with the capacity of antibody fragments to inhibit the C1q/CRT interactions and thus T. cruzi infectivity.

Castillo, Christian; Ramirez, Galia; Valck, Carolina; Aguilar, Lorena; Maldonado, Ismael; Rosas, Carlos; Galanti, Norbel; Kemmerling, Ulrike; Ferreira, Arturo

2013-01-01

96

Muon-catalyzed fusion  

Microsoft Academic Search

Great progress achieved in muon-catalyzed fusion research in the past decade now makes it possible to review careful quantitative calculations and measurements. The major experimental surprises have doubled the fusion yields, but direct energy production would appear to be excluded without a significant breakthrough.(AIP)

W. H. Breunlich; P. Kammel; J. S. Cohen; M. Leon

1989-01-01

97

Catalyzed sodium chlorate candles  

NASA Technical Reports Server (NTRS)

The catalytic effect of cobalt powder on chlorate decomposition has been confirmed. Catalysis is enhanced by oxidation of the metal during burning. Catalysts other than cobalt compounds should also be effective; the complete elimination of fuel has shown that the oxidation of cobalt during decomposition is not a vital factor in the improved performance of catalyzed candles.

Malich, C. W.; Wydeven, T.

1972-01-01

98

Abundant accumulation of the calcium-binding molecular chaperone calreticulin in specific floral tissues of Arabidopsis thaliana.  

PubMed Central

Calreticulin (CRT) is a calcium-binding protein in the endoplasmic reticulum (ER) with an established role as a molecular chaper-one. An additional function in signal transduction, specifically in calcium distribution, is suggested but not proven. We have analyzed the expression pattern of Arabidopsis thaliana CRTs for a comparison with these proposed roles. Three CRT genes were expressed, with identities of the encoded proteins ranging from 54 to 86%. Protein motifs with established functions found in CRTs of other species were conserved. CRT was found in all of the cells in low amounts, whereas three distinct floral tissues showed abundant expression: secreting nectaries, ovules early in development, and a set of subepidermal cells near the abaxial surface of the anther. Localization in the developing endosperm, which is characterized by high protein synthesis rates, can be reconciled with a specific chaperone function. Equally, nectar production and secretion, a developmental stage marked by abundant ER, may require abundant CRT to accommodate the traffic of secretory proteins through the ER. Localization of CRT in the anthers, which are degenerating at the time of maximum expression of CRT, cannot easily be reconciled with a chaperone function but may indicate a role for CRT in anther maturation or dehiscence.

Nelson, D E; Glaunsinger, B; Bohnert, H J

1997-01-01

99

Calreticulin exposure on malignant blasts predicts a cellular anticancer immune response in patients with acute myeloid leukemia  

PubMed Central

Experiments performed in mice revealed that anthracyclines stimulate immunogenic cell death that is characterized by the pre-apoptotic exposure of calreticulin (CRT) on the surface of dying tumor cells. Here, we determined whether CRT exposure at the cell surface (ecto-CRT) occurs in human cancer in response to anthracyclines in vivo, focusing on acute myeloid leukemia (AML), which is currently treated with a combination of aracytine and anthracyclines. Most of the patients benefit from the induction chemotherapy but relapse within 1–12 months. In this study, we investigated ecto-CRT expression on malignant blasts before and after induction chemotherapy. We observed that leukemic cells from some patients exhibited ecto-CRT regardless of chemotherapy and that this parameter was not modulated by in vivo chemotherapy. Ecto-CRT correlated with the presence of phosphorylated eIF2? within the blasts, in line with the possibility that CRT exposure results from an endoplasmic reticulum stress response. Importantly, high levels of ecto-CRT on malignant myeloblasts positively correlated with the ability of autologous T cells to secrete interferon-? on stimulation with blast-derived dendritic cell. We conclude that the presence of ecto-CRT on leukemia cells facilitates cellular anticancer immune responses in AML patients.

Wemeau, M; Kepp, O; Tesniere, A; Panaretakis, T; Flament, C; De Botton, S; Zitvogel, L; Kroemer, G; Chaput, N

2010-01-01

100

Over-expression of calcium-dependent protein kinase 13 and calreticulin interacting protein 1 confers cold tolerance on rice plants.  

PubMed

Calcium is a ubiquitous signaling molecule and changes in cytosolic calcium concentration are involved in plant responses to various stimuli. The rice calcium-dependent protein kinase 13 (CDPK13) and calreticulin interacting protein 1 (CRTintP1) have previously been reported to be involved in cold stress response in rice. In this study, rice lines transformed with sense CDPK13 or CRTintP1 constructs were produced and used to investigate the function of these proteins. When the plants were incubated at 5 degrees C for 3 days, leaf blades of both the sense transgenic and vector control rice plants became wilted and curled. When the plants were transferred back to non-stress conditions after cold treatment, the leaf blades died, but the sheaths remained green in the sense transgenic rice plants. Expression of CDPK13 or CRTintP1 was further examined in several rice varieties including cold-tolerant rice varieties. Accumulation of these proteins in the cold-tolerant rice variety was higher than that in rice varieties that are intermediate in their cold tolerance. To examine whether over-expression of CDPK13 and CRTintP1 would have any effect on the proteins or not, sense transgenic rice plants were analyzed using proteomics. The 2D-PAGE profiles of proteins from the vector control were compared with those of the sense transgenic rice plants. Two of the proteins that differed between these lines were calreticulins. The results suggest that CDPK13, calreticulin and CRTintP1 might be important signaling components for response to cold stress in rice. PMID:17318583

Komatsu, Setsuko; Yang, Guangxiao; Khan, Monowar; Onodera, Haruko; Toki, Seiichi; Yamaguchi, Masayuki

2007-06-01

101

Endoplasmic reticulum chaperones GRP78 and calreticulin prevent oxidative stress, Ca2+ disturbances, and cell death in renal epithelial cells.  

PubMed

Activation of stress response genes can impart cellular tolerance to environmental stress. Iodoacetamide (IDAM) is an alkylating toxicant that up-regulates expression of hsp70 (Liu, H., Lightfoot, D. L., and Stevens, J. L. (1996) J. Biol. Chem. 271, 4805-4812) and grp78 in LLC-PK1 renal epithelial cells. Therefore, we used IDAM to determine the role of these genes in tolerance to toxic chemicals. Prior heat shock did not protect cells from IDAM but pretreatment with trans-4,5-dihydroxy-1,2-dithiane (DTTox), thapsigargin, or tunicamycin enhanced expression of the endoplasmic reticulum (ER) chaperones GRP78 and GRP94 and rendered cells tolerant to IDAM. Cells expressing a 524-base pair antisense grp78 fragment (pkASgrp78) had a diminished capacity to up-regulate grp78 and grp94 expression after ER stress. Protection against IDAM due to prior ER stress was also attenuated in pkASgrp78 cells suggesting that ER chaperones of the GRP family are critical for tolerance. Covalent binding of IDAM to cellular macromolecules and depletion of cellular thiols was similar in tolerant and naïve cells. However, DTTox pretreatment blocked the increases in cellular Ca2+ and lipid peroxidation observed after IDAM treatment. Overexpressing the ER Ca2+-binding protein calreticulin prevented IDAM-induced cell death, the rise in cytosolic Ca2+, and oxidative stress. Although activation of the ER stress response did not prevent toxicity due to Ca2+ influx, EGTA-AM and ruthenium red both blocked cell death suggesting that redistribution of intracellular Ca2+ to the mitochondria may be important in toxicity. The data support a model in which induction of ER stress proteins prevents disturbances of intracellular Ca2+ homeostasis, thus uncoupling toxicant exposure from oxidative stress and cell death. Multiple ER stress proteins are likely to be involved in this tolerance response. PMID:9268304

Liu, H; Bowes, R C; van de Water, B; Sillence, C; Nagelkerke, J F; Stevens, J L

1997-08-29

102

Whole-cell vaccine coated with recombinant calreticulin enhances activation of dendritic cells and induces tumour-specific immune responses.  

PubMed

It has been reported that calreticulin (CRT) plays an important role in mediating immunogenic tumour cell death. In the process of tumour cell apoptosis induced by specific stimuli, CRT is quickly transferred from the endoplasmic reticulum to the cell membrane. As a specific ligand, CRT on the surface of apoptotic tumour cells could mediate the recognition and clearance of apoptotic tumour cells by professional and non-professional phagocytes. In our previous studies, we used B16-F1 mouse melanoma cells coated with mCRT-vGPCR (a recombinant fusion protein of mouse CRT and virus G-protein-coupled receptor) as a whole-cell tumour vaccine to immunise experimental animals and found that this whole-cell vaccine could strongly inhibit the growth of homologous tumours. In this study, we further evaluated immune responses induced by this mCRT-vGPCR-coated whole-cell vaccine both in vivo and in vitro. An in vitro phagocytosis assay showed that the mCRT-vGPCR on the cell surface greatly enhanced the engulfment of B16-F1 cells by dendritic cells (DCs). The specific antitumour immune response was observed when the mCRT-vGPCR-coated B16-F1 cells were used as a whole-cell tumour vaccine to immune mice, which included significantly enhanced cytotoxic T lymphocyte (CTL) activities and increased the number of IFN-?-producing T cells. These results indicate that the mCRT-vGPCR-coated whole-cell vaccine can induce specific antitumour immunity though the activation of DCs. These results may provide an experimental basis for the development of new tumour vaccines. PMID:23166014

Wu, Hongyan; Han, Yu; Qin, Ye; Cao, Chunyu; Xia, Yan; Liu, Changbai; Wang, Yanlin

2013-02-01

103

The Ca(2+) status of the endoplasmic reticulum is altered by induction of calreticulin expression in transgenic plants  

NASA Technical Reports Server (NTRS)

To investigate the endoplasmic reticulum (ER) Ca(2+) stores in plant cells, we generated tobacco (Nicotiana tabacum; NT1) suspension cells and Arabidopsis plants with altered levels of calreticulin (CRT), an ER-localized Ca(2+)-binding protein. NT1 cells and Arabidopsis plants were transformed with a maize (Zea mays) CRT gene in both sense and antisense orientations under the control of an Arabidopsis heat shock promoter. ER-enriched membrane fractions from NT1 cells were used to examine how altered expression of CRT affects Ca(2+) uptake and release. We found that a 2.5-fold increase in CRT led to a 2-fold increase in ATP-dependent (45)Ca(2+) accumulation in the ER-enriched fraction compared with heat-shocked wild-type controls. Furthermore, after treatment with the Ca(2+) ionophore ionomycin, ER microsomes from NT1 cells overproducing CRT showed a 2-fold increase in the amount of (45)Ca(2+) released, and a 2- to 3-fold increase in the amount of (45)Ca(2+) retained compared with wild type. These data indicate that altering the production of CRT affects the ER Ca(2+) pool. In addition, CRT transgenic Arabidopsis plants were used to determine if altered CRT levels had any physiological effects. We found that the level of CRT in heat shock-induced CRT transgenic plants correlated positively with the retention of chlorophyll when the plants were transferred from Ca(2+)-containing medium to Ca(2+)-depleted medium. Together these data are consistent with the hypothesis that increasing CRT in the ER increases the ER Ca(2+) stores and thereby enhances the survival of plants grown in low Ca(2+) medium.

Persson, S.; Wyatt, S. E.; Love, J.; Thompson, W. F.; Robertson, D.; Boss, W. F.; Brown, C. S. (Principal Investigator)

2001-01-01

104

The Ca(2+) status of the endoplasmic reticulum is altered by induction of calreticulin expression in transgenic plants.  

PubMed

To investigate the endoplasmic reticulum (ER) Ca(2+) stores in plant cells, we generated tobacco (Nicotiana tabacum; NT1) suspension cells and Arabidopsis plants with altered levels of calreticulin (CRT), an ER-localized Ca(2+)-binding protein. NT1 cells and Arabidopsis plants were transformed with a maize (Zea mays) CRT gene in both sense and antisense orientations under the control of an Arabidopsis heat shock promoter. ER-enriched membrane fractions from NT1 cells were used to examine how altered expression of CRT affects Ca(2+) uptake and release. We found that a 2.5-fold increase in CRT led to a 2-fold increase in ATP-dependent (45)Ca(2+) accumulation in the ER-enriched fraction compared with heat-shocked wild-type controls. Furthermore, after treatment with the Ca(2+) ionophore ionomycin, ER microsomes from NT1 cells overproducing CRT showed a 2-fold increase in the amount of (45)Ca(2+) released, and a 2- to 3-fold increase in the amount of (45)Ca(2+) retained compared with wild type. These data indicate that altering the production of CRT affects the ER Ca(2+) pool. In addition, CRT transgenic Arabidopsis plants were used to determine if altered CRT levels had any physiological effects. We found that the level of CRT in heat shock-induced CRT transgenic plants correlated positively with the retention of chlorophyll when the plants were transferred from Ca(2+)-containing medium to Ca(2+)-depleted medium. Together these data are consistent with the hypothesis that increasing CRT in the ER increases the ER Ca(2+) stores and thereby enhances the survival of plants grown in low Ca(2+) medium. PMID:11457960

Persson, S; Wyatt, S E; Love, J; Thompson, W F; Robertson, D; Boss, W F

2001-07-01

105

Molecular responses of calreticulin gene to Vibrio anguillarum and WSSV challenge in the ridgetail white prawn Exopalaemon carinicauda.  

PubMed

Calreticulin (CRT), as a highly conserved endoplasmic reticulum luminal resident protein, plays important roles in Ca(2+) homeostasis, molecular chaperoning and response to viral infection. In this study, a full-length cDNA of CRT (designated EcCRT) was cloned from hemocytes of the ridgetail white prawn Exopalaemon carinicauda by using rapid amplification of cDNA ends (RACE) approaches. The full-length cDNA of EcCRT was 1725 bp, which contains a 5'-untranslated region (UTR) of 57 bp, 3'-UTR of 453 bp with a poly (A) tail, an open reading frame (ORF) of 1215 bp, encoding a 404 amino-acid polypeptide with the predicted molecular weight of 46.51 kDa and estimated isoelectric point of 4.32. The deduced amino acid sequence of EcCRT shared high identity (82%-85%) with that of other crustaceans. Phylogenetic analysis showed that EcCRT of E. carinicauda was clustered together with CRT of other shrimps, indicating that EcCRT should be a member of the CRT family. Quantitative real-time RT-qPCR analysis indicated that EcCRT was expressed in hemocytes, gill, hepatopancreas, muscle, ovary, intestine, stomach and eyestalk, with the highest expression level in hemocytes. After Vibrio anguillarum and WSSV challenge, the expression level of EcCRT transcripts both in the hemocytes and hepatopancreas of E. carinicauda were up-regulated in the first 6 h, respectively. The results suggested that EcCRT might be associated with the immune defenses to V. anguillarum and WSSV in E. carinicauda. PMID:24188748

Duan, Yafei; Liu, Ping; Li, Jitao; Wang, Yun; Li, Jian; Chen, Ping

2014-01-01

106

Entamoeba histolytica and E. dispar Calreticulin: Inhibition of Classical Complement Pathway and Differences in the Level of Expression in Amoebic Liver Abscess  

PubMed Central

The role of calreticulin (CRT) in host-parasite interactions has recently become an important area of research. Information about the functions of calreticulin and its relevance to the physiology of Entamoeba parasites is limited. The present work demonstrates that CRT of both pathogenic E. histolytica and nonpathogenic E. dispar species specifically interacted with human C1q inhibiting the activation of the classical complement pathway. Using recombinant EhCRT protein, we demonstrate that CRT interaction site and human C1q is located at the N-terminal region of EhCRT. The immunofluorescence and confocal microscopy experiments show that CRT and human C1q colocalize in the cytoplasmic vesicles and near to the surface membrane of previously permeabilized trophozoites or are incubated with normal human serum which is known to destroy trophozoites. In the presence of peripheral mononuclear blood cells, the distribution of EhCRT and C1q is clearly over the surface membrane of trophozoites. Nevertheless, the level of expression of CRT in situ in lesions of amoebic liver abscess (ALA) in the hamster model is different in both Entamoeba species; this molecule is expressed in higher levels in E. histolytica than in E. dispar. This result suggests that EhCRT may modulate some functions during the early moments of the host-parasite relationship.

Ximenez, Cecilia; Gonzalez, Enrique; Nieves, Miriam E.; Silva-Olivares, Angelica; Shibayama, Mineko; Galindo-Gomez, Silvia; Escobar-Herrera, Jaime; Garcia de Leon, Ma del Carmen; Moran, Patricia; Valadez, Alicia; Rojas, Liliana; Hernandez, Eric G.; Partida, Oswaldo; Cerritos, Rene

2014-01-01

107

Hydroxide-catalyzed bonding  

NASA Technical Reports Server (NTRS)

A method of bonding substrates by hydroxide-catalyzed hydration/dehydration involves applying a bonding material to at least one surface to be bonded, and placing the at least one surface sufficiently close to another surface such that a bonding interface is formed between them. A bonding material of the invention comprises a source of hydroxide ions, and may optionally include a silicate component, a particulate filling material, and a property-modifying component. Bonding methods of the invention reliably and reproducibly provide bonds which are strong and precise, and which may be tailored according to a wide range of possible applications. Possible applications for bonding materials of the invention include: forming composite materials, coating substrates, forming laminate structures, assembly of precision optical components, and preparing objects of defined geometry and composition. Bonding materials and methods of preparing the same are also disclosed.

Gwo, Dz-Hung (Inventor)

2003-01-01

108

Wogonin Induced Calreticulin/Annexin A1 Exposure Dictates the Immunogenicity of Cancer Cells in a PERK/AKT Dependent Manner  

PubMed Central

In response to ionizing irradiation and certain chemotherapeutic agents, dying tumor cells elicit a potent anticancer immune response. However, the potential effect of wogonin (5,7-dihydroxy-8-methoxyflavone) on cancer immunogenicity has not been studied. Here we demonstrated for the first time that wogonin elicits a potent antitumor immunity effect by inducing the translocation of calreticulin (CRT) and Annexin A1 to cell plasma membrane as well as the release of high-mobility group protein 1 (HMGB1) and ATP. Signal pathways involved in this process were studied. We found that wogonin-induced reactive oxygen species (ROS) production causes an endoplasmic reticulum (ER) stress response, including the phosphorylation of PERK (PKR-like endoplasmic reticulum kinase)/PKR (protein kinase R) and eIF2? (eukaryotic initiation factor 2?), which served as upstream signal for the activation of phosphoinositide 3-kinase (PI3K)/AKT, inducing calreticulin (CRT)/Annexin A1 cell membrane translocation. P22/CHP, a Ca2+-binding protein, was associated with CRT and was required for CRT translocation to cell membrane. The releases of HMGB1 and ATP from wogonin treated MFC cells, alone or together with other possible factors, activated dendritic cells and induced cytokine releases. In vivo study confirmed that immunization with wogonin-pretreated tumor cells vaccination significantly inhibited homoplastic grafted gastric tumor growth in mice and a possible inflammatory response was involved. In conclusion, the activation of PI3K pathway elicited by ER stress induced CRT/Annexin A1 translocation (“eat me” signal) and HMGB1 release, mediating wogonin-induced immunity of tumor cell vaccine. This indicated that wogonin is a novel effective candidate of immunotherapy against gastric tumor.

Yang, Yong; Li, Xian-Jing; Chen, Zhen; Zhu, Xuan-Xuan; Wang, Jing; Zhang, Lin-bo; Qiang, Lei; Ma, Yan-jun; Li, Zhi-yu; Guo, Qing-Long; You, Qi-Dong

2012-01-01

109

Cold fusion catalyzed by muons and electrons.  

National Technical Information Service (NTIS)

Two alternative methods have been suggested to produce fusion power at low temperature. The first, muon catalyzed fusion or MCF, uses muons to spontaneously catalyze fusion through the muon mesomolecule formation. Unfortunately, this method fails to gener...

R. M. Kulsrud

1990-01-01

110

Iridium-Catalyzed Allylic Substitution  

Microsoft Academic Search

Iridium-catalyzed asymmetric allylic substitution has become a valuable method to prepare products from the addition of nucleophiles at the more substituted carbon of an allyl unit. The most active and selective catalysts contain a phosphoramidite ligand possessing at least one arylethyl substituent on the nitrogen atom of the ligand. In these systems, the active catalyst is generated by a base-induced

John F. Hartwig; Mark J. Pouy

2011-01-01

111

Reversion of the human calreticulin gene promoter to the ancestral type as a result of a novel psychosis-associated mutation.  

PubMed

Development-dependent, tissue-specific expression of the calreticulin (CALR) gene in the gray matter coincides with the expression of psychoses phenotypes. We have recently reported instances of mutations within the core promoter sequence of the gene in schizoaffective disorder. In view of the mounting evidence on the genetic overlap in the psychiatric spectrum, we investigated this gene in a spectrum of patients afflicted with schizophrenia, schizoaffective disorder and major affective disorder. We found that a unique mutation at nucleotide -220 from the transcription start site, located at a conserved genomic block in the promoter region of the gene, co-occurs with the spectrum of psychoses (p<0.005). This mutation reverts the human promoter sequence to the ancestral type observed in chimpanzee, mouse, and several other species, implying that the genomic block harboring nucleotide -220 may be involved in the evolution of human-specific higher-order functions of the brain (e.g. language, conceptual thinking, and judgment), that are ubiquitously impaired in psychoses. We propose that CALR is not only a promising candidate in the spectrum of psychoses, but also, a gene that may be important in the human-unique brain processes. PMID:21182888

Farokhashtiani, T; Mirabzadeh, A; Olad Nabi, M; Magham, Z Ghaem; Khorshid, H R Khorram; Najmabadi, H; Ohadi, M

2011-03-30

112

The n3-polyunsaturated fatty acid docosahexaenoic acid induces immunogenic cell death in human cancer cell lines via pre-apoptotic calreticulin exposure.  

PubMed

Some anticancer chemotherapeutics, such as anthracyclines and oxaliplatin, elicit immunogenic apoptosis, meaning that dying cancer cells are engulfed by dendritic cells and tumor antigens are efficiently presented to CD8+ T cells, which control residual tumor cells. Immunogenic apoptosis is characterized by pre-apoptotic cell surface exposure of calreticulin (CRT), which usually resides into the endoplasmic reticulum. We investigated the ability of the n3-polyunsaturated fatty acid docosahexaenoic acid (22:6n3, DHA) to induce pre-apoptotic CRT exposure on the surface of the human PaCa-44 pancreatic and EJ bladder cancer cell lines. Cells were treated with 150 ?M DHA for different time periods, and, by immunoblot and immunofluorescence, we showed that DHA induced CRT exposure, before the apoptosis-associated phosphatidylserine exposure. As for the known immunogenic compounds, CRT exposure was inhibited by the antioxidant GSH, the pan-caspase zVAD-FMK, and caspase-8 IETD-FMK inhibitor. We provide the first evidence that DHA induces CRT exposure, representing thus a novel potential anticancer immunogenic chemotherapeutic agent. PMID:21779875

Molinari, Romina; D'Eliseo, Donatella; Manzi, Laura; Zolla, Lello; Velotti, Francesca; Merendino, Nicolò

2011-10-01

113

Soluble Calreticulin Induces Tumor Necrosis Factor-? (TNF-?) and Interleukin (IL)-6 Production by Macrophages through Mitogen-Activated Protein Kinase (MAPK) and NF?B Signaling Pathways  

PubMed Central

We have recently reported that soluble calreticulin (CRT) accumulates in the sera of patients with rheumatoid arthritis or systemic lupus erythematosus. Moreover, following self-oligomerization, soluble recombinant CRT (rCRT) polypeptides exhibit potent immunostimulatory activities including macrophage activation in vitro and antibody induction in vivo. This study was designed to further investigate the underlying molecular mechanisms for soluble CRT-induced macrophage activation. Treatment of murine macrophages with oligomerized rCRT (OrCRT) led to (i) TNF-? and IL-6 transcription and protein expression without affecting intracellular mRNA stability; and (ii) I?B? degradation, NF?B phosphorylation and sustained MAPK phosphorylation in cells. Inhibition of IKK and JNK in macrophages substantially abrogated production of TNF-? and IL-6 induced by OrCRT, while ERK suppression only reduced IL-6 expression in parallel experiments. In vitro, fucoidan, a scavenger receptor A (SRA)-specific ligand, significantly reduced the uptake of FITC-labeled OrCRT by macrophages and subsequent MAPK and NF?B activation, thereby suggesting SRA as one of the potential cell surface receptors for soluble CRT. Together, these data indicate that soluble CRT in oligomerized form could play a pathogenic role in autoimmune diseases through induction of pro-inflammatory cytokines (e.g., TNF-? and IL-6) by macrophages via MAPK-NF?B signaling pathway.

Duo, Cui-Cui; Gong, Fang-Yuan; He, Xiao-Yan; Li, Yan-Mei; Wang, Jun; Zhang, Jin-Ping; Gao, Xiao-Ming

2014-01-01

114

Iridium-Catalyzed Allylic Substitution  

Microsoft Academic Search

\\u000a \\u000a Abstract  Iridium-catalyzed asymmetric allylic substitution has become a valuable method to prepare products from the addition of nucleophiles\\u000a at the more substituted carbon of an allyl unit. The most active and selective catalysts contain a phosphoramidite ligand\\u000a possessing at least one arylethyl substituent on the nitrogen atom of the ligand. In these systems, the active catalyst is\\u000a generated by a base-induced

John F. Hartwig; Mark J. Pouy

115

Catalyzed oxidation for nanowire growth.  

PubMed

A simple, low-cost and scalable route to substrate-supported nanowire growth is reported based on catalyzed oxidation. The process shares common features with popular catalyzed nanowire growth techniques such as vapor-liquid-solid (VLS), vapor-solid-solid (VSS), or vapor-quasi-solid (VQS) that use catalyst nanoparticles to direct the deposition of reactants from the vapor phase. Catalyzed oxidation for nanowire growth (CONG) utilizes catalyzed anion (e.g. O2) reduction from the vapor phase and metal (e.g. Fe) oxidation from the substrate to produce oxide nanowires (e.g. Fe3O4). The approach represents a new class of nanowire growth methodology that may be applied to a broad range of systems. CONG does not require expensive chemical vapor deposition or physical vapor deposition equipment and can be implemented at intermediate temperatures (400-600?°C) in a standard laboratory furnace. This work also demonstrates a passive approach to catalyst deposition that allows the process to be implemented simply with no lithography or physical vapor deposition steps. This effort validates the general approach by synthesizing MnO, Fe3O4, WO3, MgO, TiO2, ZnO, ReO3, and NiO nanowires via CONG. The process produces single crystalline nanowires that can be grown to high aspect ratio and as high-density nanowire forests. Applications of the as-grown Fe3O4 and ReO3 nanowires for lithium ion battery systems are demonstrated to display high areal energy density and power. PMID:24633154

Tai, Kaiping; Sun, Ke; Huang, Bo; Dillon, Shen J

2014-04-11

116

Thermodynamics of Enzyme-Catalyzed Reactions Database  

National Institute of Standards and Technology Data Gateway

SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

117

Nicotiana benthamiana calreticulin 3a is required for the ethylene-mediated production of phytoalexins and disease resistance against oomycete pathogen Phytophthora infestans.  

PubMed

Mature Nicotiana benthamiana shows strong resistance to the potato late blight pathogen Phytophthora infestans. By screening using virus-induced random gene silencing, we isolated a gene for plant-specific calreticulin NbCRT3a as a required gene for resistance of N. benthamiana against P. infestans. NbCRT3a encodes an endoplasmic reticulum quality-control (ERQC) chaperone for the maturation of glycoproteins, including glycosylated cell-surface receptors. NbCRT3a-silenced plants showed no detectable growth defects but resistance to P. infestans was significantly compromised. Defense responses induced by the treatment with INF1 (a secretory protein of P. infestans), such as production of reactive oxygen species and accumulation of phytoalexins, were suppressed in NbCRT3a-silenced N. benthamiana. Expression of an ethylene-regulated gene for phytoalexin biosynthesis, NbEAS, was reduced in NbCRT3a-silenced plants, whereas the expression of salicylic acid-regulated NbPR-1a was not affected. Consistently, induction of ethylene production by INF1 was suppressed in NbCRT3a-silenced plants. Resistance reactions induced by a hyphal wall components elicitor prepared from P. infestans were also impaired in NbCRT3a-silenced plants. However, cell death induced by active mitogen-activated protein kinase kinase (NbMEK2(DD)) was not affected by the silencing of NbCRT3a. Thus, NbCRT3a is required for the initiation of resistance reactions of N. benthamiana in response to elicitor molecules derived from P. infestans. PMID:23617417

Matsukawa, Mizuki; Shibata, Yusuke; Ohtsu, Mina; Mizutani, Aki; Mori, Hitoshi; Wang, Ping; Ojika, Makoto; Kawakita, Kazuhito; Takemoto, Daigo

2013-08-01

118

Iridium-Catalyzed Allylic Substitution  

NASA Astrophysics Data System (ADS)

Iridium-catalyzed asymmetric allylic substitution has become a valuable method to prepare products from the addition of nucleophiles at the more substituted carbon of an allyl unit. The most active and selective catalysts contain a phosphoramidite ligand possessing at least one arylethyl substituent on the nitrogen atom of the ligand. In these systems, the active catalyst is generated by a base-induced cyclometalation at the methyl group of this substituent to generate an iridium metalacycle bound by the COD ligand of the [Ir(COD)Cl]2 precursor and one additional labile dative ligand. Such complexes catalyze the reactions of linear allylic esters with alkylamines, arylamines, phenols, alcohols, imides, carbamates, ammonia, enolates and enolate equivalents, as well as typical stabilized carbon nucleophiles generated from malonates and cyanoesters. Iridium catalysts for enantioselective allylic substitution have also been generated from phosphorus ligands with substituents bound by heteroatoms, and an account of the studies of such systems, along with a description of the development of iridium catalysts is included.

Hartwig, John F.; Pouy, Mark J.

119

Sequence similarity of calreticulin with a Ca2(+)-binding protein that co-purifies with an Ins(1,4,5)P3-sensitive Ca2+ store in HL-60 cells.  

PubMed

HL-60 cells possess a 60 kDa Ca2(+)-binding protein that is contained in a discrete subcellular compartment, referred to as calciosomes. Subcellular fractionation studies have suggested that, in HL-60 cells, this intracellular compartment is an Ins(1,4,5)P3-sensitive Ca2+ store. In order to investigate the structural relationship of the 60 kDa Ca2(+)-binding protein of HL-60 cells to other Ca2(+)-binding proteins, we have purified the protein by ammonium sulphate extraction, acid precipitation, and DEAE-cellulose and phenyl-Sepharose column chromatography. The N-terminal sequence of the protein shows 93% identity with rabbit muscle calreticulin, a recently cloned sarcoplasmic reticulum Ca2(+)-binding protein. No amino acid sequence similarity with calsequestrin was found, although the purified protein cross-reacted with anti-calsequestrin antibodies. The calreticulin-related protein of HL-60 cells might play a role as an intravesicular Ca2(+)-binding protein of an Ins(1,4,5)P3-sensitive Ca2+ store. PMID:2400400

Krause, K H; Simmerman, H K; Jones, L R; Campbell, K P

1990-09-01

120

Oxidations catalyzed by fungal peroxygenases.  

PubMed

The enzymatic oxyfunctionalization of organic molecules under physiological conditions has attracted keen interest from the chemical community. Unspecific peroxygenases (EC 1.11.2.1) secreted by fungi represent an intriguing enzyme type that selectively transfers peroxide-borne oxygen with high efficiency to diverse substrates including unactivated hydrocarbons. They are glycosylated heme-thiolate enzymes that form a separate superfamily of heme proteins. Among the catalyzed reactions are hydroxylations, epoxidations, dealkylations, oxidations of organic hetero atoms and inorganic halides as well as one-electron oxidations. The substrate spectrum of fungal peroxygenases and the product patterns show similarities both to cytochrome P450 monooxygenases and classic heme peroxidases. Given that selective oxyfunctionalizations are among the most difficult to realize chemical reactions and that respectively transformed molecules are of general importance in organic and pharmaceutical syntheses, it will be worth developing peroxygenase biocatalysts for industrial applications. PMID:24607599

Hofrichter, Martin; Ullrich, René

2014-04-01

121

Iron-catalyzed intermolecular hydroamination of styrenes.  

PubMed

An iron-catalyzed formal hydroamination of alkenes has been developed. It features O-benzoyl-N,N-dialkylhydroxylamines as the electrophilic nitrogen source and cyclopentylmagnesium bromide as the reducing agent for intermolecular hydroamination of styrene and derivatives with good yield and excellent Markovnikov regioselectivity. The reaction presumably proceeds through the iron-catalyzed hydrometalation of styrene followed by electrophilic amination with the electrophilic O-benzoylhydroxylamine. PMID:24983840

Huehls, C Bryan; Lin, Aijun; Yang, Jiong

2014-07-18

122

Enantioselective, Iridium-Catalyzed Monoallylation of Ammonia  

PubMed Central

Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations.

Pouy, Mark J.; Stanley, Levi M.; Hartwig, John F.

2009-01-01

123

Palladium catalyzed hydrogenation of bio-oils and organic compounds  

DOEpatents

The invention provides palladium-catalyzed hydrogenations of bio-oils and certain organic compounds. Experimental results have shown unexpected and superior results for palladium-catalyzed hydrogenations of organic compounds typically found in bio-oils.

Elliott, Douglas C [Kennewick, WA; Hu, Jianli [Richland, WA; Hart,; Todd, R [Kennewick, WA; Neuenschwander, Gary G [Burbank, WA

2011-06-07

124

Microorganisms detected by enzyme-catalyzed reaction  

NASA Technical Reports Server (NTRS)

Enzymes detect the presence of microorganisms in soils. The enzyme lysozymi is used to release the enzyme catalase from the microorganisms in a soil sample. The catalase catalyzes the decomposition of added hydrogen peroxide to produce oxygen which is detected manometrically. The partial pressure of the oxygen serves as an index of the samples bacteria content.

Vango, S. P.; Weetall, H. H.; Weliky, N.

1966-01-01

125

Copper-Catalyzed Oxytrifluoromethylation of Unactivated Alkenes  

PubMed Central

A mild, versatile and convenient method for the efficient oxytrifluoromethylation of unactivated alkenes has been developed based on a copper-catalyzed oxidative difunctionalization strategy. This methodology provides access to a variety of classes of synthetically useful CF3-containing building blocks from simple starting materials.

Zhu, Rong; Buchwald, Stephen L.

2012-01-01

126

Palladium-Catalyzed Arylation of Cyanamides  

PubMed Central

The cross-coupling of alkyl cyanamides with a number of aryl, heteroaryl, and vinyl halide and pseudohalide coupling partners has been developed via a modification of Pd-catalyzed amidation methods. The reactions proceed selectively under mild conditions with reasonable reaction times in moderate to excellent yields.

Stolley, Ryan M.; Guo, Wenxing; Louie, Janis

2014-01-01

127

Organic acids tunably catalyze carbonic Acid decomposition.  

PubMed

Density functional theory calculations predict that the gas-phase decomposition of carbonic acid, a high-energy, 1,3-hydrogen atom transfer reaction, can be catalyzed by a monocarboxylic acid or a dicarboxylic acid, including carbonic acid itself. Carboxylic acids are found to be more effective catalysts than water. Among the carboxylic acids, the monocarboxylic acids outperform the dicarboxylic ones wherein the presence of an intramolecular hydrogen bond hampers the hydrogen transfer. Further, the calculations reveal a direct correlation between the catalytic activity of a monocarboxylic acid and its pKa, in contrast to prior assumptions about carboxylic-acid-catalyzed hydrogen-transfer reactions. The catalytic efficacy of a dicarboxylic acid, on the other hand, is significantly affected by the strength of an intramolecular hydrogen bond. Transition-state theory estimates indicate that effective rate constants for the acid-catalyzed decomposition are four orders-of-magnitude larger than those for the water-catalyzed reaction. These results offer new insights into the determinants of general acid catalysis with potentially broad implications. PMID:24933150

Kumar, Manoj; Busch, Daryle H; Subramaniam, Bala; Thompson, Ward H

2014-07-10

128

Ester synthesis in lipase-catalyzed reactions  

Microsoft Academic Search

This review discusses the myriad of reaction systems employed in ester production catalyzed by lipases. Enzyme behavior in reaction systems is a consequence of certain structural patterns typical of lipases. Water has a profound effect on the lipase behavior either directly by affecting the hydration of the enzyme or indirectly by changing the nature of the reaction media and\\/or enzyme

Ahmad R. M Yahya; William A Anderson; Murray Moo-Young

1998-01-01

129

Enantioselective iridium-catalyzed allylic arylation.  

PubMed

We describe herein the development of the first iridium-catalyzed allylic substitution using arylzinc nucleophiles. High enantioselectivities were obtained from the reactions, which used commercially available Grignard reagents as the starting materials. This methodology was also shown to be compatible with halogen/metal exchange reactions. Its synthetic potential is demonstrated by its application towards the formal synthesis of (+)-sertraline. PMID:19072966

Polet, Damien; Rathgeb, Xavier; Falciola, Caroline A; Langlois, Jean-Baptiste; El Hajjaji, Samir; Alexakis, Alexandre

2009-01-01

130

Direct conversion of muon catalyzed fusion energy.  

National Technical Information Service (NTIS)

In this paper a method of direct conversion of muon catalyzed fusion (MCF) energy is proposed in order to reduce the cost of muon production. This MCF concept is based on a pellet composed of many thin solid deuterium-tritium (DT) rods encircled by a meta...

T. Tajima S. Eliezer R. M. Kulsrud

1990-01-01

131

Palladium-catalyzed amination of aryl nonaflates.  

PubMed

The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of ligands 2-4 and 6 allows for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. With use of Xantphos 5, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkylamine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions. PMID:14656080

Anderson, Kevin W; Mendez-Perez, Maria; Priego, Julian; Buchwald, Stephen L

2003-12-12

132

Heterogeneously-Catalyzed Conversion of Carbohydrates  

NASA Astrophysics Data System (ADS)

Polyfunctionality of carbohydrates and their low solubility in conventional organic solvents make rather complex their conversion to higher value added chemicals. Therefore, innovative processes are now strongly needed in order to increase the selectivity of these reactions. Here, we report an overview of the different heterogeneously-catalyzed processes described in the literature. In particular, hydrolysis, dehydration, oxidation, esterification, and etherification of carbohydrates are presented. We shall discuss the main structural parameters that need to be controlled and that permit the conversion of carbohydrates to bioproducts with good selectivity. The conversion of monosaccharides and disaccharides over solid catalysts, as well as recent advances in the heterogeneously-catalyzed conversion of cellulose, will be presented.

Vigier, Karine De Oliveira; Jérôme, François

133

Antiproton catalyzed microfission/fusion propulsion  

NASA Technical Reports Server (NTRS)

Inertial confinement fusion (ICF) utilizing an antiproton catalyzed hybrid fission/fusion target is discussed as a potential energy source for interplanetary propulsion. A proof-of-principle experiment underway at Phillips Laboratory, Kirtland AFB and antiproton trapping experiments at CERN, Geneva, Switzerland, are presented. The ICAN propulsion concept is described and results of performance analyses are reviewed. Future work to further define the ICAN concept is outlined.

Chiang, Pi-Ren; Lewis, Raymond A.; Smith, Gerald A.; Newton, Richard; Dailey, James; Werthman, W. Lance; Chakrabarti, Suman

1994-01-01

134

Enzyme-Catalyzed Processes in Organic Solvents  

Microsoft Academic Search

Three different lipases (porcine pancreatic, yeast, and mold) can vigorously act as catalysts in a number of nearly anhydrous organic solvents. Various transesterification reactions catalyzed by porcine pancreatic lipase in hexane obey Michaelis-Menten kinetics. The dependence of the catalytic activity of the enzyme in organic media on the pH of the aqueous solution from which it was recovered is bell-shaped,

Aleksey Zaks; Alexander M. Klibanov

1985-01-01

135

Gold(I)-catalyzed enantioselective cycloaddition reactions  

PubMed Central

Summary In recent years there have been extraordinary developments of gold(I)-catalyzed enantioselective processes. This includes progress in the area of cycloaddition reactions, which are of particular interest due to their potential for the rapid construction of optically active cyclic products. In this article we will summarize some of the most remarkable examples, emphasizing reaction mechanisms and key intermediates involved in the processes.

2013-01-01

136

Rhodium Catalyzed Direct Arylation of ?-Diazoimines.  

PubMed

An efficient rhodium catalyzed direct arylation of ?-diazoimines, generated from readily accessible 1,2,3-triazole, has been accomplished for the synthesis of 2,2-diaryl enamides. The reaction involves the chemo- and regioselective insertion of rhodium azavinyl carbene into aromatic C(sp(2))-H bonds. Utility of the developed methodology was demonstrated in the synthesis of indole and tetrahydroisoquinoline frameworks. PMID:24724575

Yadagiri, Dongari; Anbarasan, Pazhamalai

2014-05-01

137

Iron-catalyzed asymmetric haloamination reactions.  

PubMed

The first iron(III)/N,N'-dioxide-catalyzed asymmetric haloamination of 3-alkylidene- and 3-arylidene-indolin-2-ones was developed, affording the corresponding chiral oxindole derivatives bearing vicinal haloamine substituents with excellent results (up to 99% yield, 99% ee, >19?:?1 dr). This iron catalyst also exhibits perfect enantioselectivity for chalcone derivatives. The cooperative activation of the substrate and the reagent in concert guarantees the high stereoselectivity. PMID:23903004

Cai, Yunfei; Liu, Xiaohua; Zhou, Pengfei; Kuang, Yulong; Lin, Lili; Feng, Xiaoming

2013-09-21

138

Copper-catalyzed intermolecular aminoazidation of alkenes.  

PubMed

Copper-catalyzed intermolecular aminoazidation of alkenes is described. This novel methodology provides an efficient approach to vicinal amino azides which can easily be transformed into other valuable amine derivatives. The commercially available N-fluorobenzenesulfonimide (NFSI) is used as a nitrogen-radical precursor and TMSN3 as the N3 source. Yields are moderate to excellent, and for internal alkenes aminoazidation occurs with excellent diastereoselectivity. PMID:24588747

Zhang, Bo; Studer, Armido

2014-03-21

139

Palladium-catalyzed oxidative carbonylation reactions.  

PubMed

Palladium-catalyzed coupling reactions have become a powerful tool for advanced organic synthesis. This type of reaction is of significant value for the preparation of pharmaceuticals, agrochemicals, as well as advanced materials. Both, academic as well as industrial laboratories continuously investigate new applications of the different methodologies. Clearly, this area constitutes one of the major topics in homogeneous catalysis and organic synthesis. Among the different palladium-catalyzed coupling reactions, several carbonylations have been developed and widely used in organic syntheses and are even applied in the pharmaceutical industry on ton-scale. Furthermore, methodologies such as the carbonylative Suzuki and Sonogashira reactions allow for the preparation of interesting building blocks, which can be easily refined further on. Although carbonylative coupling reactions of aryl halides have been well established, palladium-catalyzed oxidative carbonylation reactions are also interesting. Compared with the reactions of aryl halides, oxidative carbonylation reactions offer an interesting pathway. The oxidative addition step could be potentially avoided in oxidative reactions, but only few reviews exist in this area. In this Minireview, we summarize the recent development in the oxidative carbonylation reactions. PMID:23307763

Wu, Xiao-Feng; Neumann, Helfried; Beller, Matthias

2013-02-01

140

Interactive Muon Catalyzed and Inertial Confinement Fusion  

NASA Astrophysics Data System (ADS)

Energetic viability calculations of nuclear fusion energy systems based on two distinct approaches to a symbiotic combination of Muon Catalyzed Fusion (mu CF) and Inertial Confinement Fusion (ICF) have been performed. The first approach involves a deuterium-tritium ICF pellet ignited by muon catalyzed fusion heating; the second approach is based on the energy generated by muCF reactions in deuterium-tritium compressed to high density. Viability evaluations rely upon modelling of identified critical energy gain parameters for energy systems based upon each of the muCF-ICF approaches. Analysis leading to viability evaluation consists of outlining the general technological requirements of an interactive muCF-ICF system and developing muon catalyzed reaction models in conditions found in high density compressions. An energy system based on muCF in compressed deuterium-tritium was found to be non-viable due primarily to the sharp decrease in the muon induced fusion rate for temperatures greater than 40 eV. The viability of a fusion energy system based on the mu CF triggered spark ignition is favourable provided that technology can be developed which allows for the deposition of sufficient quantities of muons into a very small volume within a very short duration.

Cripps, Gregory Ronald

141

Mechanistic considerations of guanidine-catalyzed reactions.  

PubMed

This feature article discusses the various mechanistic aspects of guanidine-catalyzed reactions. Guanidines are well known as strong organic bases; however, in the first section, three most common commercially available guanidines, TMG, TBD and MTBD, will be used to illustrate the use of guanidines as nucleophilic catalysts. In the second section, different modes of hydrogen bonding interactions of the conjugate acid of guanidine, the guanidinium, are discussed. Particularly interesting are the possibilities of mono-functional or bifunctional activation of a nucleophile and an electrophile by guanidinium. PMID:21541409

Fu, Xiao; Tan, Choon-Hong

2011-08-01

142

Ligand Intermediates in Metal-Catalyzed Reactions  

SciTech Connect

The longest-running goal of this project has been the synthesis, isolation, and physical chemical characterization of homogeneous transition metal complexes containing ligand types believed to be intermediates in the metal-catalyzed conversion of CO/H{sub 2}, CO{sub 2}, CH{sub 4}, and similar raw materials to organic fuels, feedstocks, etc. In the current project period, complexes that contain unusual new types of C{sub x}(carbide) and C{sub x}O{sub y} (carbon oxide) ligands have been emphasized. A new program in homogeneous fluorous phase catalysis has been launched as described in the final report.

Gladysz, John A.

1999-07-31

143

Palladium-catalyzed direct arylation of selenophene.  

PubMed

An efficient and convenient method was developed for the regioselective formation of 2-aryl- or 2,5-diarylselenophenes via a palladium-catalyzed direct arylation. This protocol is suitable for a wide range of aryl halides containing different functional groups. The 2-arylated substrates can undergo an additional regioselective direct arylation event furnishing symmetrical or unsymmetrical 2,5-diaryl selenophenes in good yield. Competition experiments and the role of the acid additive are in agreement with a concerted metalation deprotonation (CMD) pathway. PMID:24893620

Rampon, Daniel S; Wessjohann, Ludger A; Schneider, Paulo H

2014-07-01

144

Biginelli Reaction Catalyzed by Copper Nanoparticles  

PubMed Central

We recently reported a novel synthesis of copper nanoparticles from copper sulphate utilizing the charge-compensatory effect of ionic liquid [bmim]BF4 and ethylene glycol. The nanoparticles were characterized and found to be stable for one year. Here we hypothesize that the stabilized nanoparticles should be able to catalyze one-pot multicomponent organic reactions. We show that the nanoparticles catalyzed Biginelli reaction at room temperature to give the product 3,4-dihydopyrimidinone (>90% yield in ?15 minutes) from aldehydes, ?-diketoester (ethylacetoacetate) and urea (or thiourea). ). Remarkably, such high yields and rapid kinetics was found to be independent of the electronic density on the reactant aryl-aldehyde. This was probably because even the surface-active particles reacted faster in the presence of ionic liquid as compared to conventional methods. The heterocyclic dihydropyrimidinones (DHPMs) and their derivatives are widely used in natural and synthetic organic chemistry due to their wide spectrum of biological and therapeutic properties (resulting from their antibacterial, antiviral, antitumor and anti-inflammatory activities. Our method has an easy work-up procedure and the nanoparticles could be recycled with minimal loss of efficiency.

Dewan, Manika; Kumar, Ajeet; Saxena, Amit; De, Arnab; Mozumdar, Subho

2012-01-01

145

Antibody-catalyzed anaerobic destruction of methamphetamine  

PubMed Central

Methamphetamine [(+)-2] abuse has emerged as a fast-rising global epidemic, with immunopharmacotherapeutic approaches being sought for its treatment. Herein, we report the generation and characterization of a monoclonal antibody, YX1-40H10, that catalyzes the photooxidation of (+)-2 into the nonpsychoactive compound benzaldehyde (14) under anaerobic conditions in the presence of riboflavin (6). Studies have revealed that the antibody facilitates the conversion of (+)-2 into 14 by binding the triplet photoexcited state of 6 in proximity to (+)-2. The antibody binds riboflavin (Kd = 180 ?M), although this was not programmed into hapten design, and the YX1-40H10-catalyzed reaction is inhibited by molecular oxygen via the presumed quenching of the photoexcited triplet state of 6. Given that this reaction is another highlight in the processing of reactive intermediates by antibodies, we speculate that this process may have future significance in vivo with programmed immunoglobulins that use flavins as cofactors to destroy selectable molecular targets under hypoxic or even anoxic conditions.

Xu, Yang; Hixon, Mark S.; Yamamoto, Noboru; McAllister, Laura A.; Wentworth, Anita D.; Wentworth, Paul; Janda, Kim D.

2007-01-01

146

Tax posttranslational modifications and interaction with calreticulin in MT-2 cells and human peripheral blood mononuclear cells of human T cell lymphotropic virus type-I-associated myelopathy/tropical spastic paraparesis patients.  

PubMed

The human retrovirus human T cell lymphotropic virus type-I (HTLV-1) is the etiologic agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Axonal degeneration in HAM/TSP patients occurs without neuron infection, with the secreted viral Tax protein proposed to be involved. We previously found that Tax secreted into the culture medium of MT-2 cells (HTLV-1-infected cell line) produced neurite retraction in neuroblastoma cells differentiated to neuronal type. To assess the relevance of Tax posttranslational modifications on this effect, we addressed the question of whether Tax secreted by MT-2 cells and peripheral blood mononuclear cells (PBMCs) of HTLV-1-infected subjects is modified. The interaction of Tax with calreticulin (CRT) that modulates intracellular Tax localization and secretion has been described. We studied Tax localization and modifications in MT-2 cells and its interaction with CRT. Intracellular Tax in MT-2 cells was assessed by flow cytometry, corresponding mainly to a 71-kDa protein followed by western blot. This protein reported as a chimera with gp21 viral protein-confirmed by mass spectrometry-showed no ubiquitination or SUMOylation. The Tax-CRT interaction was determined by confocal microscopy and coimmunoprecipitation. Extracellular Tax from HAM/TSP PBMCs is ubiquitinated according to western blot, and its interaction with CRT was shown by coimmunoprecipitation. A positive correlation between Tax and CRT secretion was observed in HAM/TSP PBMCs and asymptomatic carriers. For both proteins inhibitors and activators of secretion showed secretion through the endoplasmic reticulum-Golgi complex. Tax, present in PBMC culture medium, produced neurite retraction in differentiated neuroblastoma cells. These results suggest that Tax, whether ubiquitinated or not, is active for neurite retraction. PMID:24321043

Medina, Fernando; Quintremil, Sebastian; Alberti, Carolina; Barriga, Andres; Cartier, Luis; Puente, Javier; Ramírez, Eugenio; Ferreira, Arturo; Tanaka, Yuetsu; Valenzuela, Maria Antonieta

2014-04-01

147

Recombinant murine calreticulin fragment 39-272 expands CD1d(hi)CD5+ IL-10-secreting B cells that modulate experimental autoimmune encephalomyelitis in C57BL/6 mice.  

PubMed

Calreticulin (CRT) is a Ca²? binding molecular chaperone in the endoplasmic reticulum, but can also accumulate in soluble form in serum and/or synovial fluid of patients with rheumatic disorders. We have recently shown that a prokaryotically expressed recombinant CRT fragment 39-272 (rCRT/39-272) exhibited potent stimulatory activities against macrophages and B cells. However, intraperitoneal (i.p.) administration of rCRT/39-272 effectively suppressed delayed-type hypersensitivity in mice, attributable to production of anti-CRT Abs favoring Th2 cell differentiation. In this study, we further demonstrate that i.p. injection of rCRT/39-272 reduced disease severity in mouse model of experimental autoimmune encephalomyelitis (EAE), by inhibiting autoantigen-specific Th1 differentiation in vivo. Interestingly, the EAE-modulating effect of rCRT/39-272 was attributed to activation/expansion of CD1d(hi)CD5? IL-10-secreting B (B10) cells rather than induction of CRT-specific antibodies in mice. In vitro, rCRT/39-272 could activate and expand murine splenic B10 cells through a Toll like receptor 4 (TLR4)-dependent pathway. The rCRT-activated B10 cells were able to not only enhance Th2 cell differentiation in vitro but also reduce EAE scores of recipient animals in passive transfer experiments. These results revealed soluble CRT, likely released by tissue cells under stress conditions, as a potentially important multi-faced player in immunoregulation and immunopathological responses. PMID:23523122

Hong, Chao; Zhang, Tengteng; Gao, Xiao-Ming

2013-10-01

148

Melanoma B16-F1 cells coated with fusion protein of mouse calreticulin and virus G-protein coupled receptor induced the antitumor immune response in Balb/C mice.  

PubMed

In apoptotic progress of tumor cells stimulated by special agents, the calreticulin (CRT) was relocated from endoplasmic reticulum onto the cell surface. When used as cellular antigen to immunize experimental animals, these CRT-coated apoptotic tumor cells could initiate effective anti-tumor immunoresponse against homologous tumor cells, indicating the value of CRT in anti-tumor immunotherapy. In order to develop an universal technique that could make CRT-coating more efficiently in the tumor cells, in this study, a mouse CRT recombinant gene with virus G-protein coupled receptor (vGPCR) was constructed and cloned into vector pcDNA3.1(+). When resulted plasmid pcDNA3.1(+)-mCRT/ vGPCR was stably transfected into the mouse melanoma B16-F1 cells, the mCRT-vGPCR recombinant protein was synthesized. With the membrane-locating ability of vGPCR in the recombinant protein, mCRT-vGPCR was carried onto the surface of B16-F1 cells efficiently. Overexpression of mCRT-vGPCR on the cell surface could enhance the phagocytosis of B16-F1 by macrophages in vitro. When mCRT-vGPCR coated B16-F1 cells were used as a cell-antigen to immunize mice, the specific anti-tumor immune response against the homologous tumor cells was initiated efficiently. Our data in this study may provide a new possibility for CRT-mediated tumor immune prevention and treatment. PMID:21270533

Qin, Yi; Han, Yu; Cao, Chunyu; Ren, Yushan; Li, Chunhong; Wang, Yanlin

2011-03-15

149

Mammalian Tyrosinase Catalyzes Three Reactions in the Biosynthesis of Melanin  

Microsoft Academic Search

The biosynthesis of melanin is initiated by the catalytic oxidation of tyrosine to dopa by tyrosinase in a reaction that requires dopa as a cofactor. Tyrosinase then catalyzes the dehydrogenation of dopa to dopaquinone. The subsequent reactions can proceed spontaneously in vitro. Tyrosinase, purified from murine melanomas and the skins of brown mice, has now been shown to catalyze a

Ann Korner; John Pawelek

1982-01-01

150

Representing Rate Equations for Enzyme-Catalyzed Reactions  

ERIC Educational Resources Information Center

Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

Ault, Addison

2011-01-01

151

Acylative Dimerization of Tetrahydrofuran Catalyzed by Rare?Earth Triflates  

Microsoft Academic Search

Ytterbium, scandium, and lanthanum triflates catalyze the cleavage reactions of cyclic ethers to give various products. Most notable was the acylative cleavage of tetrahydrofuran with acetic anhydride catalyzed by Yb(triflate)3 to give the dimeric compound CH3CO2(CH2)4O(CH2)4OCOCH3 in 69% yield.

William H. Miles; Daniel A. Ruddy; Samira Tinorgah; Rebecca L. Geisler

2004-01-01

152

Acid-Catalyzed Isomerization of Carvone to Carvacrol  

ERIC Educational Resources Information Center

The acid-catalyzed isomerization of carvone to carvacrol, first reported by Ritter and Ginsburg, is especially well suited with a permanent-magnet FT instrument. The acid-catalyzed isomerization of carvone to carvacrol produced a 61% yield after a three hour reflux with 30% aqueous sulfuric acid.

Kjonaas, Richard A.; Mattingly, Shawn P.

2005-01-01

153

Enzyme-catalyzed synthesis of aliphatic-aromatic oligoamides.  

PubMed

Enzymatically catalyzed polycondensation of p-xylylenediamine and diethyl sebacate resulted in oligo(p-xylylene sebacamide) with high melting temperatures (223-230 °C) and the enzymatic polycondensation of dimethyl terephthalate and 1,8-diaminooctane leads to oligo(octamethylene terephthalamide) with two melting temperatures at 186 and 218 °C. No oligoamides, but products 1 and 2, were formed from the enzymatic reaction of dimethyl terephthalate and p-xylylenediamine. All reactions were catalyzed by CAL-B, icutinase, or CLEA cutinase. All reactions catalyzed by CAL-B show higher conversion than reactions catalyzed by icutinase or CLEA cutinase. The highest DPmax of 15 was achieved in a one-step and two-step synthesis of oligo(p-xylylene sebacamide) catalyzed by CLEA cutinase. PMID:23544613

Stavila, E; Alberda van Ekenstein, G O R; Loos, K

2013-05-13

154

Transition metal catalyzed synthesis of aryl sulfides.  

PubMed

The presence of aryl sulfides in biologically active compounds has resulted in the development of new methods to form carbon-sulfur bonds. The synthesis of aryl sulfides via metal catalysis has significantly increased in recent years. Historically, thiolates and sulfides have been thought to plague catalyst activity in the presence of transition metals. Indeed, strong coordination of thiolates and thioethers to transition metals can often hinder catalytic activity; however, various catalysts are able to withstand catalyst deactivation and form aryl carbon-sulfur bonds in high-yielding transformations. This review discusses the metal-catalyzed arylation of thiols and the use of disulfides as metal-thiolate precursors for the formation of C-S bonds. PMID:21242940

Eichman, Chad C; Stambuli, James P

2011-01-01

155

Fabrication of catalyzed ion transport membrane systems  

DOEpatents

Process for fabricating a catalyzed ion transport membrane (ITM). In one embodiment, an uncatalyzed ITM is (a) contacted with a non-reducing gaseous stream while heating to a temperature and for a time period sufficient to provide an ITM possessing anion mobility; (b) contacted with a reducing gaseous stream for a time period sufficient to provide an ITM having anion mobility and essentially constant oxygen stoichiometry; (c) cooled while contacting the ITM with the reducing gaseous stream to provide an ITM having essentially constant oxygen stoichiometry and no anion mobility; and (d) treated by applying catalyst to at least one of (1) a porous mixed conducting multicomponent metallic oxide (MCMO) layer contiguous with a first side of a dense layer of MCMO and (2) a second side of the dense MCMO layer. In another embodiment, these steps are carried out in the alternative order of (a), (d), (b), and (c).

Carolan, Michael Francis; Kibby, Charles Leonard

2013-06-04

156

Direct conversion of muon catalyzed fusion energy  

SciTech Connect

In this paper a method of direct conversion of muon catalyzed fusion (MCF) energy is proposed in order to reduce the cost of muon production. This MCF concept is based on a pellet composed of many thin solid deuterium-tritium (DT) rods encircled by a metallic circuit immersed in a magnetic field. The direct energy conversion is the result of the heating of the pellet by beam injection and fusion alphas. The expanding DT rods causes the change of magnetic flux linked by the circuit. Our calculation shows that the direct conversion method reduces the cost of one muon by a factor of approximately 2.5 over the previous methods. The present method is compatible with a reactor using the pellet concept, where the muon sticking is reduced by the ion cyclotron resonance heating and the confinement of the exploding pellet is handled by magnetic fields and the coronal plasma. 17 refs., 6 figs.

Tajima, T. (Texas Univ., Austin, TX (USA). Inst. for Fusion Studies); Eliezer, S. (Israel Atomic Energy Commission, Yavne (Israel). Soreq Nuclear Research Center); Kulsrud, R.M. (Institute for Advanced Study, Princeton, NJ (USA) Princeton Univ., NJ (USA). Plasma Physics Lab.)

1990-03-01

157

Density Functional Study of Mo-Carbonyl-Catalyzed Alkynol Cycloisomerization: Comparison with W-Catalyzed Reaction  

PubMed Central

Mo-catalyzed endo-cycloisomerizations of alkynes tethered to alcohols have been studied using density functional theory, and comparisons were made with the W-catalyzed reaction. The cycloisomerization is initiated with the formation of metal alkyne ? complex and is followed by the rate-determining step, which transforms the ? complex to a vinylidene carbene complex, considered to be critical for endo-mode cyclization. Several different alkynols have been selected to investigate five- and six-membered ring endo-cycloisomerizations in the presence of Mo(CO)5 catalyst. The energy barriers calculated for five- and six-membered ring cycloisomerizations are within a range of 25–30 kcal/mol for most cases studied, showing no significant energy difference between the two metals. The stabilization effect of THF and Et3N solvents and the substitution reaction of THF by alkynol substrates in the reaction process with Mo and W complexes are studied as well. The principal difference between Mo- and W-catalyzed cycloisomerization processes appears to be the initial formation of a ? complex, which is more stabilizing for formation of the W-alkyne vs Mo-alkyne complexes.

Nowroozi-Isfahani, Taraneh; Musaev, Djamaladdin G.; McDonald, Frank E.; Morokuma, Keiji

2006-01-01

158

The Structural Basis of Ribozyme-Catalyzed RNA Assembly  

SciTech Connect

Life originated, according to the RNA World hypothesis, from self-replicating ribozymes that catalyzed ligation of RNA fragments. We have solved the 2.6 angstrom crystal structure of a ligase ribozyme that catalyzes regiospecific formation of a 5' to 3' phosphodiester bond between the 5'-triphosphate and the 3'-hydroxyl termini of two RNA fragments. Invariant residues form tertiary contacts that stabilize a flexible stem of the ribozyme at the ligation site, where an essential magnesium ion coordinates three phosphates. The structure of the active site permits us to suggest how transition-state stabilization and a general base may catalyze the ligation reaction required for prebiotic RNA assembly.

Robertson, M.P.; Scott, W.G.; /UC, Santa Cruz

2007-07-12

159

Thioglycoside hydrolysis catalyzed by {beta}-glucosidase  

SciTech Connect

Sweet almond {beta}-glucosidase (EC 3.2.1.21) has been shown to have significant thioglycohydrolase activity. While the K{sub m} values for the S- and O-glycosides are similar, the k{sub cat} values are about 1000-times lower for the S-glycosides. Remarkably, the pH-profile for k{sub cat}/K{sub m} for hydrolysis of p-nitrophenyl thioglucoside (pNPSG) shows the identical dependence on a deprotonated carboxylate (pK{sub a} 4.5) and a protonated group (pK{sub a} 6.7) as does the pH-profile for hydrolysis of the corresponding O-glycoside. Not surprisingly, in spite of the requirement for the presence of this protonated group in catalytically active {beta}-glucosidase, thioglucoside hydrolysis does not involve general acid catalysis. There is no solvent kinetic isotope effect on the enzyme-catalyzed hydrolysis of pNPSG.

Shen Hong [Department of Chemistry, Tulane University, New Orleans, LA 70118 (United States); Byers, Larry D. [Department of Chemistry, Tulane University, New Orleans, LA 70118 (United States)], E-mail: byers@tulane.edu

2007-10-26

160

Toluene Monooxygenase-Catalyzed Epoxidation of Alkenes  

PubMed Central

Several toluene monooxygenase-producing organisms were tested for their ability to oxidize linear alkenes and chloroalkenes three to eight carbons long. Each of the wild-type organisms degraded all of the alkenes that were tested. Epoxides were produced during the oxidation of butene, butadiene, and pentene but not hexene or octadiene. A strain of Escherichia coli expressing the cloned toluene-4-monooxygenase (T4MO) of Pseudomonas mendocina KR1 was able to oxidize butene, butadiene, pentene, and hexene but not octadiene, producing epoxides from all of the substrates that were oxidized. A T4MO-deficient variant of P. mendocina KR1 oxidized alkenes that were five to eight carbons long, but no epoxides were detected, suggesting the presence of multiple alkene-degrading enzymes in this organism. The alkene oxidation rates varied widely (ranging from 0.01 to 0.33 ?mol of substrate/min/mg of cell protein) and were specific for each organism-substrate pair. The enantiomeric purity of the epoxide products also varied widely, ranging from 54 to >90% of a single epoxide enantiomer. In the absence of more preferred substrates, such as toluene or alkenes, the epoxides underwent further toluene monooxygenase-catalyzed transformations, forming products that were not identified.

McClay, Kevin; Fox, Brian G.; Steffan, Robert J.

2000-01-01

161

Biotransformations catalyzed by the genus rhodococcus  

SciTech Connect

Rhodococci display a diverse range of metabolic capabilities and they are a ubiquitous feature of many environments. They are able to degrade short-chain, long-chain, and halogenated hydrocarbons, and numerous aromatic compounds, including halogenated and other substituted aromatics, heteroaromatics, hydroaromatics, and polycyclic aromatic hydrocarbons. They possess a wide variety of pathways for degrading and modifying aromatic compounds, including dioxygenase and monooxygenase ring attack, and cleavage of catechol by both ortho- and meta-routes, and some strains posses a modified 3-oxoadipate pathway. Biotransformations catalyzed by rhodococci include steroid modification, enantioselective synthesis, and the transformation of nitriles to amides and acids. Tolerance of rhodococci to starvation, their frequent lack of catabolite repression, and their environmental persistence make them excellent candidates for bioremediation treatments. Some strains can produce poly(3-hydroxyalkanoate)s, others can accumulate cesium, and still others are the source of useful enzymes such as phenylalanine dehydrogenase and endoglycosidases. Other actual or potential applications of rhodococci include desulfurization of coal, bioleaching, use of their surfactants in enhancement of oil recovery and as industrial dispersants, and the construction of biosensors.

Warhurst, A.M.; Fewson, C.A. (Univ. of Glasgow (United Kingdom). Dept. of Biochemistry)

1994-01-01

162

Hypervalent iodine-catalyzed oxylactonization of ketocarboxylic acids to ketolactones.  

PubMed

The hypervalent iodine-catalyzed oxylactonization of ketocarboxylic acids to ketolactones was achieved in the presence of iodobenzene (10 mol%), p-toluenesulfonic acid monohydrate (20 mol%) and meta-chloroperbenzoic acid as a stoichiometric co-oxidant. PMID:19376702

Uyanik, Muhammet; Yasui, Takeshi; Ishihara, Kazuaki

2009-07-15

163

ENVIRONMENTAL ASSESSMENT OF THE BASE CATALYZED DECOMPOSITION (BCD) PROCESS  

EPA Science Inventory

This report summarizes laboratory-scale, pilot-scale, and field performance data on BCD (Base Catalyzed Decomposition) and technology, collected to date by various governmental, academic, and private organizations....

164

Pd-catalyzed arylation of chlorotrifluoroethylene using arylboronic acids.  

PubMed

The palladium-catalyzed cross-coupling of chlorotrifluoroethylene and arylboronic acids proceeds in the presence of a base and H(2)O to provide ?,?,?-trifluorostyrene derivatives in satisfactory yields. PMID:22691065

Yamamoto, Tetsuya; Yamakawa, Tetsu

2012-07-01

165

Palladium-catalyzed asymmetric hydrogenation of 3-phthalimido substituted quinolines.  

PubMed

Homogeneous Pd-catalyzed asymmetric hydrogenation of 3-phthalimido substituted quinolines was successfully developed, providing facile access to chiral substituted tetrahydroquinolines bearing two contiguous stereogenic centers with up to 90% ee. PMID:25014777

Cai, Xian-Feng; Huang, Wen-Xue; Chen, Zhang-Pei; Zhou, Yong-Gui

2014-07-24

166

Recent developments in gold-catalyzed cycloaddition reactions  

PubMed Central

Summary In the last years there have been extraordinary advances in the development of gold-catalyzed cycloaddition processes. In this review we will summarize some of the most remarkable examples, and present the mechanistic rational underlying the transformations.

2011-01-01

167

Palladium-Catalyzed Synthesis of N-tert-Prenylindoles  

PubMed Central

Palladium-catalyzed N-tert-prenylation of indoles, tricarbonylchromium-activated indoles, and indolines that occur in high yields (up to 94%) with high tert-prenyl-to-n-prenyl selectivity (up to 12:1) are reported.

Johnson, Kirsten F.; Van Zeeland, Ryan

2013-01-01

168

Muon Catalyzed Fusion - Fission Reactor Driven by a Recirculating Beam.  

National Technical Information Service (NTIS)

The recent experimentally inferred value of multiplicity of fusion of deuterium and tritium catalyzed by muons has rekindled interest in its application to reactors. Since the main energy expended is in pion (and consequent muon) productions, we try to mi...

M. N. Rosenbluth S. Eliezer T. Tajima

1986-01-01

169

Lipase-catalyzed synthesis of aliphatic polyesters and properties characterization  

Microsoft Academic Search

A novel lipase-catalyzed synthesis of aliphatic polyesters has been achieved successfully by using Candida sp.99-125 with diethyl sebacate and 1,4-butanediol as starting substrates in absence of organic solvents. The lipase from Candida sp.99-125 was employed for the first time to catalyze synthesis of poly(butylene sebacate) and showed high catalytic activity for bulkpolymerization under mild reaction conditions. The eco-friendly processes, without

Wenhui Liu; Biqiang Chen; Fang Wang; Tianwei Tan; Li Deng

2011-01-01

170

Acid and Base-Catalyzed D-Glucosylurea Anomerization  

Microsoft Academic Search

The D-glucosylureas have been found to undergo both acid- and base-catalyzed anomerization. Water was not an effective catalyst for the transformation but the addition of either an acid or base resulted in the formation of an equilibrium mixture. Kinetic investigations of the acid-catalyzed reaction indicated that the key intermediate step was die formation of an iminium ion. A deuterium isotope

Richard F. Helm; Joseph J. Karchesy

1993-01-01

171

Highly efficient gold-catalyzed synthesis of dibenzocycloheptatrienes.  

PubMed

Dibenzocycloheptatrienes are obtained by a gold-catalyzed 7-exo-dig hydroarylation protocol in a highly efficient manner. The gold-catalyzed reaction usually gives the products in high yields and excellent selectivity. This procedure provides an easy and efficient access to dibenzocycloheptanoids, which are an interesting and unique class of natural products. This was underlined by the first total synthesis of reticuol. PMID:24771698

Pflästerer, Daniel; Rettenmeier, Eva; Schneider, Severin; de Las Heras Ruiz, Edgar; Rudolph, Matthias; Hashmi, A Stephen K

2014-05-26

172

Mechanism of enzyme-catalyzed phospho group transfer  

SciTech Connect

To understand more fully the mechanism of enzyme-catalyzed phospho group transfer, the stereochemical course at phosphorus of four enzymes has been determined. First, using adenosine (..gamma..-(S)-/sup 16/O, /sup 17/O, /sup 18/O)triphosphate as the substrate, the reaction catalyzed by creatine kinase has been found to proceed with overall inversion of configuration at phosphorus. Second, using adenosine (..beta..-(S)-/sup 16/O, /sup 17/O, /sup 18/O)diphosphate as the substrate, the reaction catalyzed by adenylate kinase has been found also to proceed with overall inversion. Third, the reaction catalyzed by phosphoenolpyruvate carboxylase has been studied using ((S/sub p/)-/sup 16/O, /sup 17/O)thiophospoenolpyruvate as the substrate in H/sub 2/ /sup 18/O. Fourth, using adenosine 5'-O-((..gamma..S/sub p/)-..beta gamma..-/sup 17/O,..gamma..-/sup 17/O,/sup 18/O)(3-thiotriphosphate) as the substrate, the reaction catalyzed by pyruvate carboxylase has been shown to proceed with inversion at phosphorus. This results rules out the chemically and enzymatically precendented composite mechanism that had been proposed for this enzyme and supports a stepwise pathway again involving the intermediacy of carboxyphosphate. The first pair of results supports the growing body of evidence that enzyme-catalyzed phospho group transfer proceeds by an in-line associative mechanism. The second pair of results eliminate mechanistic suggestions of concerted electrocyclic processes in bicarbonate dependent carboxylation reactions.

Hansen, D.E.

1986-01-01

173

Nitroreductase catalyzed biotransformation of CL-20.  

PubMed

Previously, we reported that a salicylate 1-monooxygenase from Pseudomonas sp. ATCC 29352 biotransformed CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-isowurtzitane) (C(6)H(6)N(12)O(12)) and produced a key metabolite with mol. wt. 346 Da corresponding to an empirical formula of C(6)H(6)N(10)O(8) which spontaneously decomposed in aqueous medium to produce N(2)O, NH(4)(+), and HCOOH [Appl. Environ. Microbiol. (2004)]. In the present study, we found that nitroreductase from Escherichia coli catalyzed a one-electron transfer to CL-20 to form a radical anion (CL-20(-)) which upon initial N-denitration also produced metabolite C(6)H(6)N(10)O(8). The latter was tentatively identified as 1,4,5,8-tetranitro-1,3a,4,4a,5,7a,8,8a-octahydro-diimidazo[4,5-b:4',5'-e]pyrazine [IUPAC] which decomposed spontaneously in water to produce glyoxal (OHCCHO) and formic acid (HCOOH). The rates of CL-20 biotransformation under anaerobic and aerobic conditions were 3.4+/-0.2 and 0.25+/-0.01 nmol min(-1)mg of protein(-1), respectively. The product stoichiometry showed that each reacted CL-20 molecule produced about 1.8 nitrite ions, 3.3 molecules of nitrous oxide, 1.6 molecules of formic acid, 1.0 molecule of glyoxal, and 1.3 ammonium ions. Carbon and nitrogen products gave mass-balances of 60% and 81%, respectively. A comparative study between native-, deflavo-, and reconstituted-nitroreductase showed that FMN-site was possibly involved in the biotransformation of CL-20. PMID:15313201

Bhushan, Bharat; Halasz, Annamaria; Hawari, Jalal

2004-09-10

174

Anodophilic biofilm catalyzes cathodic oxygen reduction.  

PubMed

Poor cathodic oxygen reduction and the detrimental buildup of a pH gradient between anode and cathode are the major hurdles in the development of sustainable microbial fuel cells (MFCs). This article describes and tests a concept that can help overcoming both of these limitations, by inverting the polarity of the MFC repeatedly, allowing anodic and cathodic reactions to occur alternately in the same half-cell and hence neutralizing its respective pH effects. For simplicity, we studied polarity inversion exclusively in one half-cell, maintaining its potential at -300 mV (vs Ag/AgCl) by a potentiostat. An alternating supply of acetate and dissolved oxygen to the biofilm resulted in the tested half-cell repeatedly changing from an anode to a cathode and vice versa. This repeated inversion of current direction avoided the detrimental drifting of the electrolyte pH. Control runs without current inversion ceased to produce current, as a result of anode acidification. The presence of the anodophilic biofilm survived the intermittent oxygen exposure and could measurably facilitate the cathodic reaction by reducing the apparent oxygen overpotential. It enabled cathodic oxygen reduction at about -150 mV (vs Ag/AgCl) compared to -300 mV (vs Ag/AgCl) for the same electrode material (granular graphite) without biofilm. Provided that a suitable cathodic potential was chosen, the presence of "anodophilic bacteria" at the cathode could enable a 5-fold increase in power output. Overall, the ability of an electrochemically active biofilm to catalyze both substrate oxidation and cathodic oxygen reduction in a single bioelectrochemical system has been documented. This property could be useful to alleviate both the cathodic oxygen reduction and the detrimental drifting of electrolyte pH in an MFC system. Further research is warranted to explore the application of such bidirectional microbial catalytic properties for sustainable MFC processes. PMID:19954225

Cheng, Ka Yu; Ho, Goen; Cord-Ruwisch, Ralf

2010-01-01

175

Gold-catalyzed rearrangements and beyond.  

PubMed

Cycloisomerizations of enynes are probably the most representative carbon-carbon bond forming reactions catalyzed by electrophilic metal complexes. These transformations are synthetically useful because chemists can use them to build complex architectures under mild conditions from readily assembled starting materials. However, these transformations can have complex mechanisms. In general, gold(I) activates alkynes in the presence of any other unsaturated functional group by forming an (?(2)-alkyne)-gold complex. This species reacts readily with nucleophiles, including electron-rich alkenes. In this case, the reaction forms cyclopropyl gold(I) carbene-like intermediates. These can come from different pathways depending on the substitution pattern of the alkyne and the alkene. In the absence of external nucleophiles, 1,n-enynes can form products of skeletal rearrangement in fully intramolecular reactions, which are mechanistically very different from metathesis reactions initiated by the [2 + 2] cycloaddition of a Grubbs-type carbene or other related metal carbenes. In this Account, we discuss how cycloisomerization and addition reactions of substituted enynes, as well as intermolecular reactions between alkynes and alkenes, are best interpreted as proceeding through discrete cationic intermediates in which gold(I) plays a significant role in the stabilization of the positive charge. The most important intermediates are highly delocalized cationic species that some chemists describe as cyclopropyl gold(I) carbenes or gold(I)-stabilized cyclopropylmethyl/cyclobutyl/homoallyl carbocations. However, we prefer the cyclopropyl gold(I) carbene formulation for its simplicity and mnemonic value, highlighting the tendency of these intermediates to undergo cyclopropanation reactions with alkenes. We can add a variety of hetero- and carbonucleophiles to the enynes in the presence of gold(I) in intra- or intermolecular reactions, leading to the corresponding adducts with high stereoselectivity through stereospecific anti-additions. We have also developed stereospecific syn-additions, which probably occur through similar intermediates. The attack of carbonyl groups at the cyclopropyl carbons of the intermediate cyclopropyl gold(I) carbenes initiates a particularly interesting group of reactions. These trigger a cascade transformation that can lead to the formation of two C-C and one C-O bonds. In the fully intramolecular process, this stereospecific transformation has been applied for the synthesis of natural sesquiterpenoids such as (+)-orientalol F and (-)-englerin A. Intra- and intermolecular trapping of cyclopropyl gold(I) carbenes with alkenes leads to the formation of cyclopropanes with significant increase in the molecular complexity, particularly in cases in which this process combines with the migration of propargylic alkoxy and related OR groups. We have recently shown this in the stereoselective total synthesis of the antiviral sesquiterpene (+)-schisanwilsonene by a cyclization/1,5-acetoxy migration/intermolecular cyclopropanation. In this synthesis, the cyclization/1,5-acetoxy migration is faster than the alternative 1,2-acyloxy migration that would result in racemization. PMID:24175907

Obradors, Carla; Echavarren, Antonio M

2014-03-18

176

Gold-Catalyzed Rearrangements and Beyond  

PubMed Central

Cycloisomerizations of enynes are probably the most representative carbon–carbon bond forming reactions catalyzed by electrophilic metal complexes. These transformations are synthetically useful because chemists can use them to build complex architectures under mild conditions from readily assembled starting materials. However, these transformations can have complex mechanisms. In general, gold(I) activates alkynes in the presence of any other unsaturated functional group by forming an (?2-alkyne)–gold complex. This species reacts readily with nucleophiles, including electron-rich alkenes. In this case, the reaction forms cyclopropyl gold(I) carbene-like intermediates. These can come from different pathways depending on the substitution pattern of the alkyne and the alkene. In the absence of external nucleophiles, 1,n-enynes can form products of skeletal rearrangement in fully intramolecular reactions, which are mechanistically very different from metathesis reactions initiated by the [2 + 2] cycloaddition of a Grubbs-type carbene or other related metal carbenes. In this Account, we discuss how cycloisomerization and addition reactions of substituted enynes, as well as intermolecular reactions between alkynes and alkenes, are best interpreted as proceeding through discrete cationic intermediates in which gold(I) plays a significant role in the stabilization of the positive charge. The most important intermediates are highly delocalized cationic species that some chemists describe as cyclopropyl gold(I) carbenes or gold(I)-stabilized cyclopropylmethyl/cyclobutyl/homoallyl carbocations. However, we prefer the cyclopropyl gold(I) carbene formulation for its simplicity and mnemonic value, highlighting the tendency of these intermediates to undergo cyclopropanation reactions with alkenes. We can add a variety of hetero- and carbonucleophiles to the enynes in the presence of gold(I) in intra- or intermolecular reactions, leading to the corresponding adducts with high stereoselectivity through stereospecific anti-additions. We have also developed stereospecific syn-additions, which probably occur through similar intermediates. The attack of carbonyl groups at the cyclopropyl carbons of the intermediate cyclopropyl gold(I) carbenes initiates a particularly interesting group of reactions. These trigger a cascade transformation that can lead to the formation of two C–C and one C–O bonds. In the fully intramolecular process, this stereospecific transformation has been applied for the synthesis of natural sesquiterpenoids such as (+)-orientalol F and (?)-englerin A. Intra- and intermolecular trapping of cyclopropyl gold(I) carbenes with alkenes leads to the formation of cyclopropanes with significant increase in the molecular complexity, particularly in cases in which this process combines with the migration of propargylic alkoxy and related OR groups. We have recently shown this in the stereoselective total synthesis of the antiviral sesquiterpene (+)-schisanwilsonene by a cyclization/1,5-acetoxy migration/intermolecular cyclopropanation. In this synthesis, the cyclization/1,5-acetoxy migration is faster than the alternative 1,2-acyloxy migration that would result in racemization.

2013-01-01

177

N-Heterocyclic Carbene-Catalyzed Conjugate Additions of Alcohols  

PubMed Central

An efficient intermolecular conjugate addition of alcohols to activated alkenes catalyzed by N-heterocyclic carbenes has been developed. With 5 mol % of the free carbene derived from IMes•HCl, unsaturated ketones and esters are competent substrates and a variety of primary and secondary alcohols can be employed as the nucleophile. No oligomerization is observed under these mild conditions for effective hydroalkoxylation. In addition to reactions with activated alkenes, IMes catalyzes the formation of vinyl ethers through the 1,4-addition of alcohols to ynones and promotes tandem conjugate addition/Michael cascade reactions. Preliminary data supports a Brønsted base mechanism with the free carbene.

Phillips, Eric M.; Riedrich, Matthias; Scheidt, Karl A.

2010-01-01

178

New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles  

SciTech Connect

The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I{sub 2}, ICl, PhSeCl, PhSCl and p-O{sub 2}NC{sub 6}H{sub 4}SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellent yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these palladium-catalyzed C-H activation reactions parallel electrophilic aromatic substitution. A relatively efficient synthesis of cyclopropanes has been developed using palladium-catalyzed C-H activation chemistry, in which two new carbon-carbon bonds are formed in a single step. This method involves the palladium-catalyzed activation of relatively unreactive C-H bonds, and provides a very efficient way to synthesize cyclopropapyrrolo[1,2-a]indoles, analogues of the mitomycin antibiotics.

Qinhua Huang

2004-12-19

179

The mechanism of Fe (III)-catalyzed ozonation of phenol.  

PubMed

Fe (III)-catalyzed ozonation yielded better degradation rate and extent of COD (Chemical Oxygen Demand) or oxalic acid as compared with oxidation by ozone alone. Two parameters with strong effects on the efficiency of ozonation are pH of the solution and the catalyst (Fe(3+)) dosage. The existence of a critical pH value determining the catalysis of Fe (III) in acid conditions was observed in phenol and oxalic acid systems. The best efficiency of catalysis was obtained at a moderate concentration of the catalyst. A reasonable mechanism of Fe (III)-catalyzed ozonation of phenol was obtained based on the results and literature. PMID:15547962

Zhu, Xiang-Feng; Xu, Xin-Hua

2004-12-01

180

3-Hydroxylaminophenol Mutase From Ralstonia eutropha JMP134 Catalyzes a Bamberger Rearrangement.  

National Technical Information Service (NTIS)

3-Hydroxylaminophenol mutase from Ralstonia eutropha JMP134 is involved in the degradative pathway of 3-nitrophenol, in which it catalyzes the conversion of 3-hydroxylaminophenol to aminohydroquinone. To show that the reaction was really catalyzed by a si...

A. Schenzle H. Lenke J. C. Spain H. Knackmuss

1999-01-01

181

Combination of stereospecific dihydroxylation and enzyme catalyzed enantioselective resolution for synthesis of enantiopure vicinal diols  

Microsoft Academic Search

By employing a combination of stereospecific osmium catalyzed dihydroxylation of selected alkenes, and enantioselective lipase catalyzed kinetic resolution, nine alkenes were converted into nine enantiopure vicinal diols and nine enantiopure hydroxy butanoates.

Anders Riise Moen; Kjersti Ruud; Thorleif Anthonsen

2008-01-01

182

Amberlyst-15 Catalyzed Addition of Phenols to ?,?-Unsaturated Ketones  

Microsoft Academic Search

Amberlyst-15 has been used to catalyze regioselective additions of phenols to ?,?-unsaturated ketones in yields of 20–90%. The reaction is superior to the analogous reaction employing concentrated sulfuric acid in affording greater yields and purer products with a minimum of laboratory operations.

Richard A. Bunce; Henry D. Reeves

1989-01-01

183

Kinetics of acid-catalyzed cleavage of cumene hydroperoxide  

Microsoft Academic Search

The cleavage of cumene hydroperoxide, in the presence of sulfuric acid, to form phenol and acetone has been examined by adiabatic calorimetry. As expected, acid can catalyze cumene hydroperoxide reaction at temperatures below that of thermally-induced decomposition. At elevated acid concentrations, reactivity is also observed at or below room temperature. The exhibited reactivity behavior is complex and is significantly affected

M. E. Levin; N. O. Gonzales; L. W. Zimmerman; J. Yang

2006-01-01

184

Squaramide-catalyzed enantioselective Michael addition of malononitrile to chalcones.  

PubMed

A highly enantioselective Michael addition of malononitrile to chalcones catalyzed by a chiral quinine-derived squaramide catalyst has been developed. This organocatalytic reaction at a very low catalyst loading (0.5 mol%) led to chiral ?-cyano carbonyl compounds in good yields with high enantioselectivities (up to 96% ee) under mild reaction conditions. PMID:22071519

Yang, Wen; Jia, Yang; Du, Da-Ming

2012-01-14

185

Catalyzed Steam Gasification of Biomass. Phase II. Final Research Report.  

National Technical Information Service (NTIS)

The Wright-Malta gasification process is characterized by low-temperature, catalyzed steam gasification in a pressurized rotary kiln. Fresh biomass moves slowly and continuously through the kiln, where it is gradually heated to around 1200 exp 0 F in an a...

R. H. Hooverman

1979-01-01

186

Gold(I)-catalyzed macrocyclization of 1,n-enynes.  

PubMed

The gold(I)-catalyzed [2 + 2] cycloaddition of large 1,n-enynes (n = 10-16) provides access to 9- to 15-membered ring macrocycles incorporating a cyclobutene moiety. The reaction requires the use of a gold(I) catalyst bearing a sterically hindered biphenylphosphine ligand. PMID:23485064

Obradors, Carla; Leboeuf, David; Aydin, Juhanes; Echavarren, Antonio M

2013-04-01

187

Asymmetric NHC-catalyzed redox ?-amination of ?-aroyloxyaldehydes.  

PubMed

Asymmetric ?-amination through an N-heterocyclic carbene (NHC)-catalyzed redox reaction of ?-aroyloxyaldehydes with N-aryl-N-aroyldiazenes to form ?-hydrazino esters with high enantioselectivity (up to 99% ee) is reported. The hydrazide products are readily converted into enantioenriched N-aryl amino esters through samarium(II) iodide mediated N-N bond cleavage. PMID:24215115

Taylor, James E; Daniels, David S B; Smith, Andrew D

2013-12-01

188

Glucose Oxidase Catalyzed Self-Assembly of Bioelectroactive Gold Nanostructures.  

National Technical Information Service (NTIS)

Glucose oxidase catalyzes the formation of metallic gold particles in immediate proximity of the protein from gold (III) chloride in the absence of any other catalytic or reductive substrates. The protein-mediated gold reduction reaction leads to size-con...

D. Ivnitski G. R. Johnson H. R. Luckarift P. Atanassov R. Rincon

2010-01-01

189

Cu(II) - Catalyzed Hydrazine Reduction of Ferrous Nitrate  

SciTech Connect

This report discusses the results of a study of catalyzed hydrazine reduction of ferrous nitrate. It is apparent that there is a substantial reaction between hydrazine and nitrate ion (or nitric acid) to produce HN3 during both the reduction of Fe(III) and during storage at room temperature.

Karraker, D.G.

2001-10-15

190

Rhodium(II)-catalyzed stereoselective synthesis of allylsilanes.  

PubMed

The rhodium-catalyzed decomposition of 2-(triisopropylsilyl)ethyl aryl- and vinyldiazoacetates results in the stereoselective formation of Z-allylsilanes. The transformation is considered to proceed by silyl-directed intramolecular C-H functionalization to form a ?-lactone intermediate followed by a silyl-activated extrusion of carbon dioxide. PMID:24283585

Guptill, David M; Cohen, Carolyn M; Davies, Huw M L

2013-12-20

191

Transition-Metal-Catalyzed Carbonylation of Methyl Acetate.  

ERIC Educational Resources Information Center

Presents a study of the rhodium-catalyzed, ioding-promoted carbonylation of methyl acetate. This study provides an interesting contrast between the carbonylation of methyl acetate and the carbonylation of methanol when similar rhodium/iodine catalyst systems are used. (JN)

Polichnowski, S. W.

1986-01-01

192

Gold-catalyzed propargylic substitutions: Scope and synthetic developments.  

PubMed

This personal account summarizes our recent developments in gold-catalyzed direct substitutions on propargylic (allylic, benzylic) alcohols, with various nucleophiles (and bi-nucleophiles) based on the ?- and/or ?-acidity of gold(III) complexes. Synthetic developments are also briefly described. PMID:21804883

Debleds, Olivier; Gayon, Eric; Vrancken, Emmanuel; Campagne, Jean-Marc

2011-01-01

193

Platinum-catalyzed oxoarylations of ynamides with nitrones.  

PubMed

A new platinum-catalyzed oxoarylation of ynamides with nitrones is reported. Cascade sequences for the synthesis of indolin-2-ones via NaBH(3)CN reduction in situ of the initially formed oxoarylation products are also developed. PMID:23088158

Bhunia, Sabyasachi; Chang, Chin-Jung; Liu, Rai-Shung

2012-11-01

194

Gold-catalyzed 1,3-transposition of ynones.  

PubMed

An efficient, regioselective gold-catalyzed 1,3-transposition reaction of ynones and diynones has been developed. It was found that stereoelectronic (interrupted conjugation) and electronic (extended conjugation) factors could efficiently govern the regioselectivity of this thermodynamically controlled transformation. The produced conjugated diynones were efficiently transformed into diverse alkyne-substituted five- and six-membered heterocycles. PMID:24971528

Kazem Shiroodi, Roohollah; Soltani, Mohammad; Gevorgyan, Vladimir

2014-07-16

195

Iron-catalyzed reductive cyclization of 1,6-enynes.  

PubMed

A precatalyst of FeCl2 and iminopyridine was activated in situ by a combination of diethylzinc and magnesium bromide etherate; it catalyzed the reductive cyclization of 1,6-enynes to give pyrrolidine and tetrahydrofuran derivatives from N- and O-tethered 1,6-enynes. The scope of the transformation was explored. PMID:24369926

Lin, Aijun; Zhang, Zhi-Wei; Yang, Jiong

2014-01-17

196

Acid-catalyzed dehydrogenation of amine-boranes  

DOEpatents

A method of dehydrogenating an amine-borane using an acid-catalyzed reaction. The method generates hydrogen and produces a solid polymeric [R.sup.1R.sup.2B--NR.sup.3R.sup.4].sub.n product. The method of dehydrogenating amine-boranes may be used to generate H.sub.2 for portable power sources.

Stephens, Frances Helen (Santa Fe, NM) [Santa Fe, NM; Baker, Ralph Thomas (Los Alamos, NM) [Los Alamos, NM

2010-01-12

197

Strictosidine Synthase: Mechanism of a Pictet-Spengler Catalyzing Enzyme  

PubMed Central

The Pictet–Spengler reaction, which yields either a ?-carboline or a tetrahydroquinoline product from an aromatic amine and an aldehyde, is widely utilized in plant alkaloid biosynthesis. Here we deconvolute the role that the biosynthetic enzyme strictosidine synthase plays in catalyzing the stereoselective synthesis of a ?-carboline product. Notably, the rate-controlling step of the enzyme mechanism, as identified by the appearance of a primary kinetic isotope effect (KIE), is the rearomatization of a positively charged intermediate. The KIE of a nonenzymatic Pictet–Spengler reaction indicates that rearomatization is also rate-controlling in solution, suggesting that the enzyme does not significantly change the mechanism of the reaction. Additionally, the pH dependence of the solution and enzymatic reactions provides evidence for a sequence of acid–base catalysis steps that catalyze the Pictet–Spengler reaction. An additional acid-catalyzed step, most likely protonation of a carbinolamine intermediate, is also significantly rate controlling. We propose that this step is efficiently catalyzed by the enzyme. Structural analysis of a bisubstrate inhibitor bound to the enzyme suggests that the active site is exquisitely tuned to correctly orient the iminium intermediate for productive cyclization to form the diastereoselective product. Furthermore, ab initio calculations suggest the structures of possible productive transition states involved in the mechanism. Importantly, these calculations suggest that a spiroindolenine intermediate, often invoked in the Pictet–Spengler mechanism, does not occur. A detailed mechanism for enzymatic catalysis of the ?-carboline product is proposed from these data.

Maresh, Justin J.; Giddings, Lesley-Ann; Friedrich, Anne; Loris, Elke A.; Panjikar, Santosh; Trout, Bernhardt L.

2010-01-01

198

Nickel-catalyzed coupling of allyl chlorides and enynes.  

PubMed

The Ni-catalyzed coupling of allyl chlorides and enynes has been developed; the cyclization of enynes was triggered by the addition of pi-allylnickel species to the alkyne part, followed by the incorporation of the alkene part. PMID:16493836

Ikeda, Shin-ichi; Suzuki, Kaori; Odashima, Kazunori

2006-01-28

199

Copper-catalyzed regioselective fluorination of allylic halides.  

PubMed

Group activity: A novel copper-catalyzed fluorination of internal allylic bromides and chlorides has been developed by using Et3N?3?HF as the fluorine source. A functional group (FG) within the substrate is required to achieve the allylic fluorination, and a variety of secondary allylic fluoride compounds can be accessed in good yield with excellent regioselectivity. PMID:23775917

Zhang, Zuxiao; Wang, Fei; Mu, Xin; Chen, Pinhong; Liu, Guosheng

2013-07-15

200

Palladium-catalyzed direct arylation of indoles with cyclohexanones.  

PubMed

A novel palladium catalyzed approach to 3-arylindoles was developed from indoles and cyclohexanones. Various cyclohexanones acted as aryl sources via an alkylation and dehydrogenation sequence using molecular oxygen as the hydrogen acceptor. This method showed good regioselectivity and afforded 3-arylindoles as the sole products. PMID:24597845

Chen, Shanping; Liao, Yunfeng; Zhao, Feng; Qi, Hongrui; Liu, Saiwen; Deng, Guo-Jun

2014-03-21

201

Chiral Brønsted acid catalyzed enantioselective intermolecular allylic aminations.  

PubMed

This paper describes an enantioselective intermolecular allylic amination catalyzed by a chiral Brønsted acid via a possible chiral contact ion pair intermediate. A variety of symmetrical or unsymmetrical allylic alcohols can be smoothly aminated to afford the desired products in moderate to high yields with good enantioselectivities and/or regioselectivities. PMID:24872122

Zhuang, Minyang; Du, Haifeng

2014-06-11

202

Novobiocin and Coumermycin Inhibit DNA Supercoiling Catalyzed by DNA Gyrase  

Microsoft Academic Search

Novobiocin and coumermycin are known to inhibit the replication of DNA in Escherichia coli. We show that these drugs inhibit the supercoiling of DNA catalyzed by E. coli DNA gyrase, a recently discovered enzyme that introduces negative superhelical turns into covalently circular DNA. The activity of DNA gyrase purified from a coumermycin-resistant mutant strain is resistant to both drugs. The

Martin Gellert; Mary H. O'Dea; Tateo Itoh; Jun-Ichi Tomizawa

1976-01-01

203

Catalyzing Graduate Teaching Assistants' Laboratory Teaching through Design Research  

ERIC Educational Resources Information Center

We report on a study of a laboratory teaching apprenticeship program designed to improve graduate teaching assistant (GTA) performance. To catalyze GTAs as laboratory teachers we constructed learning goals, synthesized previous literature into a design model and a developmental path, and built two instruments to measure 12 strategic pedagogical…

Bond-Robinson, Janet; Rodriques, Romola A. Bernard

2006-01-01

204

Palladium-Catalyzed Coupling Reactions of Aryl Chlorides  

Microsoft Academic Search

Collectively, palladium-catalyzed cou- pling reactions represent some of the most powerful and versatile tools avail- able to synthetic organic chemists. Their widespread popularity stems in part from the fact that they are gen- erally tolerant to a large number of functional groups, which allows them to be employed in a wide range of applications. However, for many years a major

Adam F. Littke; Gregory C. Fu

2002-01-01

205

Pd(0)-Catalyzed radical aryldifluoromethylation of activated alkenes.  

PubMed

A Pd(0)-catalyzed intramolecular aryldifluoromethylation of activated alkenes under mild reaction conditions has been developed. This reaction provides a new method for construction of a variety of difluoromethylated oxindoles. Mechanistic investigations indicate that a difluoromethyl radical, which was triggered by Pd(0), initiated the cascade sequence through an addition to the alkene. PMID:24622897

Wang, Jian-Yong; Su, Yi-Ming; Yin, Feng; Bao, Yan; Zhang, Xin; Xu, Yue-Ming; Wang, Xi-Sheng

2014-04-21

206

4-Dimenthylaminopyridine or Acid-Catalyzed Synthesis of Esters: A Comparison  

ERIC Educational Resources Information Center

A set of highly atom-economic experiments was developed to highlight the differences between acid- and base-catalyzed ester syntheses and to introduce the principles of atom economy. The hydrochloric acid-catalyzed formation of an ester was compared with the 4-dimethylaminopyradine-catalyzed ester synthesis.

van den Berg, Annemieke W. C.; Hanefeld, Ulf

2006-01-01

207

Cholera toxin can catalyze ADP-ribosylation of cytoskeletal proteins  

SciTech Connect

Cholera toxin catalyzes transfer of radiolabel from (/sup 32/P)NAD/sup +/ to several peptides in particulate preparations of human foreskin fibroblasts. Resolution of these peptides by two-dimensional gel electrophoresis allowed identification of two peptides of M/sub r/ = 42,000 and 52,000 as peptide subunits of a regulatory component of adenylate cyclase. The radiolabeling of another group of peptides (M/sub r/ = 50,000 to 65,000) suggested that cholera toxin could catalyze ADP-ribosylation of cytoskeletal proteins. This suggestion was confirmed by showing that incubation with cholera toxin and (/sup 32/P)NAD/sup +/ caused radiolabeling of purified microtubule and intermediate filament proteins.

Kaslow, H.R.; Groppi, V.E.; Abood, M.E.; Bourne, H.R.

1981-11-01

208

Gold-catalyzed C(sp(3))-H bond functionalization.  

PubMed

C-H bonds are ubiquitous in organic molecules. Homogenous gold-catalyzed direct functionalization of unsaturated C-H bonds has emerged as a powerful method in our synthetic toolbox. However, Csp(3)-H bonds have larger dissociation energy and lower proton acidity, and thus the efficient and exquisitely selective cleavage of this kind of chemical bonds for the formation of new carbon-carbon and carbon-heteroatom bonds is still a great challenge. In this tutorial review, we will highlight the recent achievements of gold-catalyzed oxidative and redox-neutral Csp(3)-H bond functionalization, which opens new avenues for economical and sustainable construction of fine chemicals. PMID:24853478

Xie, Jin; Pan, Changduo; Abdukader, Ablimit; Zhu, Chengjian

2014-07-01

209

Rearrangement reactions catalyzed by cytochrome P450s.  

PubMed

Cytochrome P450s promote a variety of rearrangement reactions both as a consequence of the nature of the radical and other intermediates generated during catalysis, and of the neighboring structures in the substrate that can interact either with the initial radical intermediates or with further downstream products of the reactions. This article will review several kinds of previously published cytochrome P450-catalyzed rearrangement reactions, including changes in stereochemistry, radical clock reactions, allylic rearrangements, "NIH" and related shifts, ring contractions and expansions, and cyclizations that result from neighboring group interactions. Although most of these reactions can be carried out by many members of the cytochrome P450 superfamily, some have only been observed with select P450s, including some reactions that are catalyzed by specific endoperoxidases and cytochrome P450s found in plants. PMID:20971058

Ortiz de Montellano, Paul R; Nelson, Sidney D

2011-03-01

210

Rearrangement Reactions Catalyzed by Cytochrome P450s  

PubMed Central

Cytochrome P450s promote a variety of rearrangement reactions both as a consequence of the nature of the radical and other intermediates generated during catalysis, and of the neighboring structures in the substrate that can interact either with the initial radical intermediates or with further downstream products of the reactions. This article will review several kinds of previously published cytochrome P450-catalyzed rearrangement reactions, including changes in stereochemistry, radical clock reactions, allylic rearrangements, “NIH” and related shifts, ring contractions and expansions, and cyclizations that result from neighboring group interactions. Although most of these reactions can be carried out by many members of the cytochrome P450 superfamily, some have only been observed with select P450s, including some reactions that are catalyzed by specific endoperoxidases and cytochrome P450s found in plants.

Ortiz de Montellano, Paul R.; Nelson, Sidney D.

2010-01-01

211

Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.  

PubMed Central

The negative strand of the satellite RNA of tobacco ringspot virus (sTobRV(-)) contains a hairpin catalytic domain that shows self-cleavage and self-ligation activities in the presence of magnesium ions. We describe here that the minimal catalytic domain can catalyze a cross-ligation reaction between two kinds of substrates in trans. The cross-ligated product increased when the reaction temperature was decreased during the reaction from 37 degrees C to 4 degrees C. A two-stranded hairpin ribozyme, divided into two fragments between G45 and U46 in a hairpin loop, showed higher ligation activity than the nondivided ribozyme. The two stranded ribozyme also catalyzed an exchange reaction of the 3'-portion of the cleavage site. Images

Komatsu, Y; Koizumi, M; Sekiguchi, A; Ohtsuka, E

1993-01-01

212

Ruthenium-catalyzed cascade C-H functionalization of phenylacetophenones.  

PubMed

Three orthogonal cascade C?H functionalization processes are described, based on ruthenium-catalyzed C?H alkenylation. 1-Indanones, indeno indenes, and indeno furanones were accessed through cascade pathways by using arylacetophenones as substrates under conditions of catalytic [{Ru(p-cymene)Cl2 }2 ] and stoichiometric Cu(OAc)2 . Each transformation uses C?H functionalization methods to form C?C bonds sequentially, with the indeno furanone synthesis featuring a C?O bond formation as the terminating step. This work demonstrates the power of ruthenium-catalyzed alkenylation as a platform reaction to develop more complex transformations, with multiple C?H functionalization steps taking place in a single operation to access novel carbocyclic structures. PMID:24453063

Mehta, Vaibhav P; García-López, José-Antonio; Greaney, Michael F

2014-02-01

213

Copper-catalyzed annulation of amidines for quinazoline synthesis.  

PubMed

An efficient Cu-catalyzed synthesis of quinazolines via the C-N bond formation reactions between N-H bonds of amidines and C(sp(3))-H bonds adjacent to sulfur or nitrogen atoms in the commonly used solvents, such as DMSO, DMF, DMA, NMP or TMEDA, followed by intramolecular C-C bond formation reactions was developed for the first time. PMID:23756495

Lv, Yunhe; Li, Yan; Xiong, Tao; Pu, Weiya; Zhang, Hongwei; Sun, Kai; Liu, Qun; Zhang, Qian

2013-07-21

214

Carboxypeptidase Y catalyzed C-terminal modifications of peptides  

Microsoft Academic Search

It is demonstrated that carboxypeptidase Y catalyzes the exchange of C-terminal amino acid residues in peptides for various\\u000a other groups. Using N-blocked dipeptides as substrates and alcohols, ammonia, glycine, glycine amide and glycine methyl ester\\u000a as nucleophiles, it is shown that peptides can be converted to peptide esters, peptide amides and to peptides with altered\\u000a C-terminal amino acid residues. The

Klaus Breddam; Fred Widmer; Jack T. Johansen

1981-01-01

215

Synthesis of delicious peptide fragments catalyzed by immobilized proteases  

Microsoft Academic Search

The synthesis of benzyloxycarbonyl-lysine-glycine methyl ester (CBZ-Lys-Gly-OMe) and benzyloxycarbonyl-serine-leucine methyl ester (CBZ-Ser-Leu-OMe) have been carried out in aqueous organic systems catalyzed by immobilized trypsin and thermolysin respectively. The dipeptides orginated by the elimination of benzyloxycarbonyl and methoxy groups are two fragments of the delicious peptide, which is an octapeptide of industrial interest with a taste profile umami\\/sour. In both synthesis

M. D. Romero; J. Aguado; M. J. Guerra; G. Alvaro; R. Navarro; E. Rubio

1997-01-01

216

Nickel-Catalyzed ?-Arylation of Ketones with Phenol Derivatives.  

PubMed

The nickel-catalyzed ?-arylation of ketones with readily available phenol derivatives (esters and carbamates) provides access to useful ?-arylketones. For this transformation, 3,4-bis(dicyclohexylphosphino)thiophene (dcypt) was identified as a new, enabling, air-stable ligand for this transformation. The intermediate of an assumed C?O oxidative addition was isolated and characterized by X-ray crystal-structure analysis. PMID:24845077

Takise, Ryosuke; Muto, Kei; Yamaguchi, Junichiro; Itami, Kenichiro

2014-06-23

217

Palladium-Catalyzed ?-Arylation of 2-Chloroacetates and 2-Chloroacetamides  

PubMed Central

A method has been developed for the Pd-catalyzed synthesis of ?-(hetero)aryl esters and amides through a Suzuki–Miyaura cross-coupling reaction. This method avoids the use of strong base, does not necessitate inert or low temperature formation of reagents, and does not require the use of a large excess of organometallic reagent. Utilization of organotrifluoroborate salts as nucleophilic partners allows a variety of functional groups and heterocyclic compounds to be tolerated.

Traister, Kaitlin M.; Barcellos, Thiago

2013-01-01

218

Asymmetric cyclopropanation catalyzed by C 2-symmetric bi(oxazolines)  

Microsoft Academic Search

C2-symmetric bi(oxazolines) 3a–e were prepared in three steps based on a tartaric-derived vicinal diamine as common precursor. These chiral ligands were studied with respect to their directive influence on the enantioselective copper catalyzed cyclopropanation of 1,1-diphenylethylene and styrene. The highest enantioselectivities (79% ee) were achieved with bi(oxazoline) 3e, bearing bulky adamantyl groups even using commercial CuOTf. The presence of desiccants

Rachel Boulch; Andreas Scheurer; Paul Mosset; Rolf W Saalfrank

2000-01-01

219

Asymmetric synthesis of ?-alkyl ?-selenocarbonyl compounds catalyzed by bifunctional organocatalysts.  

PubMed

A new organocatalytic approach for the synthesis of a variety of ?-alkyl, ?-phenylselenyl ketones as well as their corresponding esters and amides, by the addition of ?-selenocarbonyl derivatives to nitroalkenes catalyzed by thiourea or squaramide cinchona catalysts, is presented. This catalytic system allows the preparation in high yields of enantiomerically enriched selenocarbonyl derivatives bearing two chiral centers with excellent ee's and dr's by using catalytic loadings of 3 mol%. PMID:21591622

Marcos, Vanesa; Alemán, Jose; Ruano, Jose L Garcia; Marini, Francesca; Tiecco, Marcello

2011-06-17

220

Experimental investigation of muon-catalyzed d-t fusion  

Microsoft Academic Search

Measurements of the absolute neutron yield and the time dependence of the appearance of neutrons resulting from muon-catalyzed fusion have been carried out in high-density deuterium-tritium mixtures. The temperature dependence of the resonant dt..mu..-molecular formation process has been determined in the range 100 to 540 K. Mesomolecular formation is found to be resonant for DT as well as D target

S. E. Jones; A. N. Anderson; A. J. Caffrey; J. B. Walter; K. D. Watts; J. N. Bradbury; P. A. M. Gram; M. Leon; H. R. Maltrud; M. A. Paciotti

1983-01-01

221

Synthesis of thiazolines by copper catalyzed aminobromination of thiohydroximic acids.  

PubMed

A copper catalyzed aminobromination of alkene tethered thiohydroximic acids is described, providing a rapid approach to unnatural thiazoline scaffolds not readily available via existing methods. Moderate to high yields of bromothiazolines are obtained with alkyl- and aryl-substituted thiohydroximic acid building blocks containing mono-, di-, and trisubstituted alkenes. The reaction provides high levels of 5-exo selectivity, and terminally monosubstituted alkenes result in predominant syn-diastereoselectivity. PMID:24645640

Lemercier, Bérénice C; Pierce, Joshua G

2014-04-01

222

Palladium-Catalyzed Synthesis of N-Aryl Carbamates  

PubMed Central

An efficient synthesis of aryl carbamates was achieved by introducing alcohols into the reaction of palladium-catalyzed cross-coupling of ArX (X = Cl, OTf) with sodium cyanate. The use of aryl triflates as electrophilic components in this transformation allowed for an expanded substrate scope for direct synthesis of aryl isocyanates. This methodology provides direct access to major carbamate protecting groups, S-thiocarbamates, and diisocyanate precursors to polyurethane materials.

Vinogradova, Ekaterina V.; Park, Nathaniel H.; Fors, Brett P.; Buchwald, Stephen L.

2013-01-01

223

Phase Transfer Catalyzed Fluoroalkoxylation of Haloaromatic and Haloheteroaromatic Systems  

Microsoft Academic Search

A series of neutral and ionic phase transfer catalysts have been investigated with regard to catalyzing the fluoroalkoxylation of haloaromatic and haloheteroaromatic systems. Poly(ethyleneglycol)8000 and tetrabutylphosphonium bromide were found to be the most effective catalysts.In previous papers we have described the fluoroalkoxylation of monohalo and dihaloaromatic and heteroaromatic substrates. Our interest in this reaction stemmed from the need to prepare

John T. Gupton; Joe Coury; Martin Moebus; John P. Idoux

1985-01-01

224

A novel palladium-catalyzed intramolecular redox reaction.  

PubMed

[reaction: see text] A new type of palladium-catalyzed redox reaction is described, forming enones from 2-(2-bromobenzyl)-ketones with an overall loss of HBr. The scope and limitations of the reaction are demonstrated by a series of cyclic and acyclic substrates. The mechanism most probably involves the formation of an intramolecular arylpalladium enolate and is related to the oxidation of silyl enol ethers with palladium acetate. PMID:11388850

Högenauer, K; Mulzer, J

2001-05-17

225

Active target production of muons for muon-catalyzed fusion  

SciTech Connect

Using a Monte Carlo method, we study the energy efficiency of muon production by a high-energy beam of deuterons, i.e., protons and neutrons, injected into infinite deuterium-tritium targets. We present detailed results for the dependence on target density and beam energy. The key role of secondary (shower) production of muons is demonstrated. Constraints on the possibility of muon catalyzed fusion power reactors are established.

Jandel, M.; Danos, M.; Rafelski, J.

1988-01-01

226

Copper-catalyzed aerobic oxidative synthesis of aromatic carboxylic acids.  

PubMed

A simple, practical and efficient copper-catalyzed method for synthesis of aromatic carboxylic acids has been developed. The protocol uses inexpensive CuI/L-proline as the catalyst/ligand, and readily available aryl halides and malononitrile as the starting materials, and the corresponding aromatic carboxylic acids were obtained in moderate to good yields. The method is of tolerance towards functional groups in the substrates. PMID:21152586

Yang, Daoshan; Yang, Haijun; Fu, Hua

2011-02-28

227

Biaryl Phosphine Ligands in Palladium-Catalyzed Amination  

PubMed Central

Palladium-catalyzed amination of aryl halides has undergone rapid development in the last 12 years. This has been largely driven by implementation of new classes of ligands. Biaryl phosphines have proven to provide especially active catalysts in this context. This review discusses the applications that these catalysts have found in C-N cross-coupling in heterocycle synthesis, pharmaceuticals, materials science and natural product synthesis.

Surry, David S.

2012-01-01

228

Catalyzed steam gasification of biomass. Phase II. Final research report  

Microsoft Academic Search

The Wright-Malta gasification process is characterized by low-temperature, catalyzed steam gasification in a pressurized rotary kiln. Fresh biomass moves slowly and continuously through the kiln, where it is gradually heated to around 1200°F in an atmosphere of 300 psi steam. During its traverse, pyrolysis and reaction of steam with the nascent char convert nearly all of the organic solids to

Hooverman

1979-01-01

229

A simple strategy for glycosyltransferase-catalyzed aminosugar nucleotide synthesis.  

PubMed

A set of 2-chloro-4-nitrophenyl glucosamino-/xylosaminosides were synthesized and assessed as potential substrates in the context of glycosyltransferase-catalyzed formation of the corresponding UDP/TDP-?-D-glucosamino-/xylosaminosugars and in single-vessel model transglycosylation reactions. This study highlights a robust platform for aminosugar nucleotide synthesis and reveals OleD Loki to be a proficient catalyst for U/TDP-aminosugar synthesis and utilization PMID:24677528

Zhang, Jianjun; Singh, Shanteri; Hughes, Ryan R; Zhou, Maoquan; Sunkara, Manjula; Morris, Andrew J; Thorson, Jon S

2014-03-21

230

Gold-catalyzed cyclization of allenyl acetal derivatives  

PubMed Central

Summary The gold-catalyzed transformation of allenyl acetals into 5-alkylidenecyclopent-2-en-1-ones is described. The outcome of our deuterium labeling experiments supports a 1,4-hydride shift of the resulting allyl cationic intermediates because a complete deuterium transfer is observed. We tested the reaction on various acetal substrates bearing a propargyl acetate, giving 4-methoxy-5-alkylidenecyclopent-2-en-1-ones 4 via a degradation of the acetate group at the allyl cation intermediate.

Vasu, Dhananjayan; Pawar, Samir Kundlik

2013-01-01

231

On the Brønsted acid-catalyzed homogeneous hydrolysis of furans.  

PubMed

Furan affairs: Electronic structure calculations of the homogeneous Brønsted acid-catalyzed hydrolysis of 2,5-dimethylfuran show that proton transfer to the ?-position is rate-limiting and provides support that the hydrolysis follows general acid catalysis. By means of projected Fukui indices, we show this to be the case for unsubstituted, 2-, and 2,5-substituted furans with electron-donating groups. PMID:24006230

Nikbin, Nima; Caratzoulas, Stavros; Vlachos, Dionisios G

2013-11-01

232

Dehalogenation of Monohalopyridines Catalyzed by Group 4 Metallocene Reagent  

Microsoft Academic Search

The Cp'2MCl2\\/hydride (Cp' = Cp or Cp*: Cp = ?5-C5H5, Cp* = ?5-C5Me5; M = Ti, Zr, Hf) reagent catalyzes the dehalogenation of monohalopyridines at room temperature to give pyridine. The catalytic activity decreases in the order of M = Ti > Zr > Hf: M-F ? M-Cl ? M-Br ? M-I; Cp2M > CpCp* M>C p *2M; Red-Al >

Bo-Hye Kim; Hee-Gweon Woo; Whan-Gi Kim; Sock-Sung Yun; Taek-Sung Hwang

233

Asymmetric synthesis catalyzed by chiral ferrocenylphosphine-metal complexes  

Microsoft Academic Search

Optically active ferrocenylphosphines containing, on the side chain, hydroxy group appropriately distant from the ferrocene nucleus have been found to be effective ligands for the palladium-catalyzed asymmetric allylic alkylation of 1,3-disubstituted 2-propenyl acetates with sodium acetylacetonate and related soft carbon nucleophiles to give the alkylation products of up to 96% ee. chiral ferrocenylphosphines which have tertiary amines on the side

Tamio Hayashi

1988-01-01

234

Studies in Chain Transfer. II. Catalyzed Polymerization of Methyl Methacrylate  

Microsoft Academic Search

The chain-transfer reaction between growing methyl methacrylate (M) polymer radical and toluene (S) when catalyzed by varying quantities of benzoyl peroxide (B) at 80 and 60 degrees C and p-nitrobenzoyl peroxide at 80 degrees C has been studied. It has been established that the transfer constant calculated from the slope of 1\\/{P} against S\\/M curve at constant B\\/M is not

Sadhan Basu; Jyotirindra Nath Sen; Santi R. Palit

1952-01-01

235

Palladium catalyzed intramolecular acylcyanation of alkenes using ?-iminonitriles.  

PubMed

Reported here is a palladium catalyzed intramolecular acylcyanation of alkenes using ?-iminonitriles. Through this method, highly functionalized indanones are synthesized in moderate to high yields using Pd(PPh3)4, without need for any additional ligands, and a common Lewis acid (ZnCl2). Additionally, the reaction tolerates substitution at various positions on the aromatic ring including electron donating and electron withdrawing groups. PMID:24980625

Rondla, Naveen R; Ogilvie, Jodi M; Pan, Zhongda; Douglas, Christopher J

2014-07-15

236

Reductive hydrogenation of polycyclic aromatic hydrocarbons catalyzed by metalloporphyrins  

Microsoft Academic Search

The hydrogenation of polycyclic aromatic hydrocarbons (PAHs) (naphthalene, anthracene, and phenanthrene) catalyzed by metalloporphyrins based on cobalt, nickel or iron was studied in aqueous solutions at room temperature and ambient pressure. Nickel porphyrin (P1) activated by nanosized zero-valent iron (nano-ZVI) and cobalt porphyrins (P2) and (P4) activated by titanium(III) citrate as the electron donor were demonstrated to be promising catalysts

Elza Nelkenbaum; Ishai Dror; Brian Berkowitz

2007-01-01

237

Myeloperoxidase-Catalyzed Oxidation of Melatonin by Activated Neutrophils  

Microsoft Academic Search

In the presence of hydrogen peroxide, horseradish peroxidase (HRP) catalyzes the production of N1-acetyl-N2-formyl-5-methoxykynuramine from melatonin. This reaction consumes oxygen and exhibits chemiluminescence in the 440–540 nm region. The excited cleavage product derived from the thermolysis of an intermediate dioxetane is suggested to be the emitting species. Chemiluminescence and the indole ring cleavage product were also observed when HRP\\/H2O2 was

Sueli de Oliveira Silva; Valdecir F. Ximenes; Luiz Henrique Catalani; Ana Campa

2000-01-01

238

Enzyme-catalyzed biocathode in a photoelectrochemical biofuel cell  

NASA Astrophysics Data System (ADS)

A novel double-enzyme photoelectrochemical biofuel cell (PEBFC) has been developed by taking glucose dehydrogenase (GDH) and horseradish peroxidase (HRP) as the enzyme of the photoanode and biocathode to catalyze the oxidation of glucose and the reduction of oxygen. A H2-mesoporphyrin IX is used as a dye for a TiO2 film electrode to fabricate a photoanode. The horseradish peroxidase (HRP) is immobilized on a glassy carbon (GC) electrode to construct a biocathode which is used to catalyze the reduction of oxygen in the PEBFC for the first time. The biocathode exhibits excellent electrocatalytic activity in the presence of O2. The performances of the PEBFC are obtained by current-voltage and power-voltage curves. The short-circuit current density (Isc), the open-circuit voltage (Voc), maximum power density (Pmax), fill factor (FF) and energy conversion efficiency (?) are 439 ?A cm-2, 678 mV, 79 ?W cm-2, 0.39 and 0.016%, respectively, and the incident photon-to-collected electron conversion efficiency (IPCE) is 32% at 350 nm. The Isc is higher than that of the PEBFC with Pt cathode, and the Voc is higher than that of the dye-sensitized solar cell or the enzyme-catalyzed biofuel cell operating individually, which demonstrates that the HRP is an efficient catalyst for the biocathode in the PEBFC.

Yang, Jing; Hu, Donghua; Zhang, Xiaohuan; Wang, Kunqi; Wang, Bin; Sun, Bo; Qiu, Zhidong

2014-12-01

239

Asymmetric Additions to Dienes Catalyzed by a Dithiophosphoric Acid  

PubMed Central

Chiral Brønsted acids have become an invaluable tool for achieving a variety of asymmetric chemical transformations under catalytic conditions while avoiding the use of toxic and expensive metals1–8. While the catalysts developed so far are remarkably effective at activating polarized functional groups, chemists have not yet been able to use organic Brønsted acids to catalyze highly enantioselective transformations of unactivated carbon-carbon multiple bonds. This deficiency persists despite the fact that racemic acid-catalyzed “Markovnikov” additions to olefins are a well-established part of the chemist’s toolbox. Here we show that chiral dithiophosphoric acids catalyze the intramolecular hydroamination and hydroarylation of dienes and allenes to generate heterocyclic products in exceptional yield and enantiomeric excess. To help rationalize the unique success of this catalytic system, we present a mechanistic hypothesis that involves the addition of the acid catalyst to the diene followed by SN2? displacement of the resulting dithiophosphate intermediate. Mass spectrometry and deuterium labelling studies are presented in support of the proposed mechanism. The catalysts and concepts revealed in this study should prove applicable to other asymmetric functionalizations of unsaturated systems.

Shapiro, Nathan D.; Rauniyar, Vivek; Hamilton, Gregory L.; Wu, Jeffrey; Toste, F. Dean

2011-01-01

240

Protection of wood from microorganisms by laccase-catalyzed iodination.  

PubMed

In the present work, Norway spruce wood (Picea abies L.) was reacted with a commercial Trametes versicolor laccase in the presence of potassium iodide salt or the phenolic compounds thymol and isoeugenol to impart an antimicrobial property to the wood surface. In order to assess the efficacy of the wood treatment, a leaching of the iodinated and polymerized wood and two biotests including bacteria, a yeast, blue stain fungi, and wood decay fungi were performed. After laccase-catalyzed oxidation of the phenols, the antimicrobial effect was significantly reduced. In contrast, the enzymatic oxidation of iodide (I(-)) to iodine (I(2)) in the presence of wood led to an enhanced resistance of the wood surface against all microorganisms, even after exposure to leaching. The efficiency of the enzymatic wood iodination was comparable to that of a chemical wood preservative, VP 7/260a. The modification of the lignocellulose by the laccase-catalyzed iodination was assessed by the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. The intensities of the selected lignin-associated bands and carbohydrate reference bands were analyzed, and the results indicated a structural change in the lignin matrix. The results suggest that the laccase-catalyzed iodination of the wood surface presents an efficient and ecofriendly method for wood protection. PMID:22865075

Schubert, M; Engel, J; Thöny-Meyer, L; Schwarze, F W M R; Ihssen, J

2012-10-01

241

Acid-Catalyzed Preparation of Biodiesel from Waste Vegetable Oil: An Experiment for the Undergraduate Organic Chemistry Laboratory  

ERIC Educational Resources Information Center

This undergraduate organic laboratory exercise involves the sulfuric acid-catalyzed conversion of waste vegetable oil into biodiesel. The acid-catalyzed method, although inherently slower than the base-catalyzed methods, does not suffer from the loss of product or the creation of emulsion producing soap that plagues the base-catalyzed methods when…

Bladt, Don; Murray, Steve; Gitch, Brittany; Trout, Haylee; Liberko, Charles

2011-01-01

242

Enantioselective Total Syntheses of (-)-Taiwaniaquinone H and (-)-Taiwaniaquinol B by Iridium-Catalyzed Borylation and Palladium-Catalyzed Asymmetric ?-Arylation  

PubMed Central

We report a concise, enantioselective total synthesis of (?)-taiwaniaquinone H and the first enantioselective total synthesis of (?)-taiwaniaquinol B by a route that includes enantioselective, palladium-catalyzed ?-arylation of a ketone with an aryl bromide that was generated by sterically controlled halogenation via iridium-catalyzed C–H borylation. This asymmetric ?-arylation creates the benzylic, quaternary stereogenic center present in the taiwaniaquinoids. The synthesis was completed efficiently by developing a Lewis acid-promoted cascade to construct the [6,5,6] tricyclic core of an intermediate common to the synthesis of a number of taiwaniaquinoids. Through the preparation of these compounds, we demonstrate the utility of constructing benzylic, quaternary, stereogenic centers, even those lacking a carbonyl group in the ?-position, by asymmetric ?-arylation.

Liao, Xuebin; Stanley, Levi M.; Hartwig, John F.

2011-01-01

243

Growth and characterization of gold catalyzed SiGe nanowires and alternative metal-catalyzed Si nanowires  

Microsoft Academic Search

The growth of semiconductor (SC) nanowires (NW) by CVD using Au-catalyzed VLS process has been widely studied over the past\\u000a few years. Among others SC, it is possible to grow pure Si or SiGe NW thanks to these techniques. Nevertheless, Au could deteriorate\\u000a the electric properties of SC and the use of other metal catalysts will be mandatory if NW

Alexis Potié; Thierry Baron; Florian Dhalluin; Guillaume Rosaz; Bassem Salem; Laurence Latu-Romain; Martin Kogelschatz; Pascal Gentile; Fabrice Oehler; Laurent Montès; Jens Kreisel; Hervé Roussel

2011-01-01

244

First evidence for the use of organosilver compounds in Pd-catalyzed coupling reactions; a mechanistic rationale for the Pd/Ag-catalyzed enyne synthesis?  

PubMed

Silver acetylides have been prepared and used in Pd-catalyzed coupling reactions. Enynes have thus been obtained in good yields. This work demonstrates that organosilver compounds could enter the Pd catalytic cycle; it also supports the role of silver acetylides as intermediates in the new Pd/Ag-catalyzed coupling reaction. PMID:11405680

Dillinger, S; Bertus, P; Pale, P

2001-05-31

245

Gold-catalyzed cyclization reactions of allenol and alkynol derivatives.  

PubMed

Although gold is chemically inert as a bulk metal, the landmark discovery that gold nanoparticles can be effective catalysts has opened up new and exciting research opportunities in the field. In recent years, there has been growth in the number of reactions catalyzed by gold complexes [gold(I) and gold(III)], usually as homogeneous catalysts, because they are soft Lewis acids. In addition, alkynes and allenes have interesting reactivities and selectivities, notably their ability to produce complex structures in very few steps. In this Account, we describe our work in gold catalysis with a focus on the formation of C-C and C-O bonds using allenes and alkynes as starting materials. Of these, oxa- and carbo-cyclizations are perhaps the best known and most frequently studied. We have divided those contributions into sections arranged according to the nature of the starting material (allene versus alkyne). Gold-catalyzed carbocyclizations in allenyl C2-linked indoles, allenyl-?-lactams, and allenyl sugars follow different mechanistic pathways. The cyclization of indole-tethered allenols results in the efficient synthesis of carbazole derivatives, for example. However, the compound produced from gold-catalyzed 9-endo carbocyclization of (aryloxy)allenyl-tethered 2-azetidinones is in noticeable contrast to the 5-exo hydroalkylation product that results from allenyl sugars. We have illustrated the unusual preference for the 4-exo-dig cyclization in allene chemistry, as well as the rare ?-hydride elimination reaction, in gold catalysis from readily available ?-allenols. We have also observed in ?-allenols that a (methoxymethyl)oxy protecting group not only masks a hydroxyl functionality but also exerts directing effects as a controlling unit in a gold-catalyzed regioselectivity reversal. Our recent work has also led to a combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled products) and 1,3-oxazin-2-one derivatives (thermodynamically favored) from easily accessible allenic carbamates. In addition, we discuss the direct gold-catalyzed cycloketalization of alkynyldioxolanes, as well as aminoketalization of alkynyloxazolidines. We performed labeling studies and density functional calculations to gain insight into the mechanisms of the bis-heterocyclization reactions. We also describe the controlled gold-catalyzed reactions of primary and secondary propargylic hydroperoxides with a variety of nucleophiles including alcohols and phenols, allowing the direct synthesis of ?-functionalized ketones. Through computations and (18)O-labeling experiments, we discovered various aspects of the controlled reactivity of propargylic hydroperoxides with external nucleophiles under gold catalysis. The mechanism resembles a Meyer-Schuster rearrangement, but notably, the presence and geometry characteristics of the OOH functional group allow a new pathway to happen, which cannot apply to propargylic alcohols. PMID:24428670

Alcaide, Benito; Almendros, Pedro

2014-03-18

246

A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes  

SciTech Connect

Known SABATH methyltransferases, all of which were identified from seed plants, catalyze methylation of either the carboxyl group of a variety of low molecular weight metabolites or the nitrogen moiety of precursors of caffeine. In this study, the SABATH family from the bryophyte Physcomitrella patens was identified and characterized. Four SABATH-like sequences (PpSABATH1, PpSABATH2, PpSABATH3, and PpSABATH4) were identified from the P. patens genome. Only PpSABATH1 and PpSABATH2 showed expression in the leafy gametophyte of P. patens. Full-length cDNAs of PpSABATH1 and PpSABATH2 were cloned and expressed in soluble form in Escherichia coli. Recombinant PpSABATH1 and PpSABATH2 were tested for methyltransferase activity with a total of 75 compounds. While showing no activity with carboxylic acids or nitrogen-containing compounds, PpSABATH1 displayed methyltransferase activity with a number of thiols. PpSABATH2 did not show activity with any of the compounds tested. Among the thiols analyzed, PpSABATH1 showed the highest level of activity with thiobenzoic acid with an apparent Km value of 95.5 lM, which is comparable to those of known SABATHs. Using thiobenzoic acid as substrate, GC MS analysis indicated that the methylation catalyzed by PpSABATH1 is on the sulfur atom. The mechanism for S-methylation of thiols catalyzed by PpSABATH1 was partially revealed by homology-based structural modeling. The expression of PpSABATH1 was induced by the treatment of thiobenzoic acid. Further transgenic studies showed that tobacco plants overexpressing PpSABATH1 exhibited enhanced tolerance to thiobenzoic acid, suggesting that PpSABATH1 have a role in the detoxification of xenobiotic thiols.

Zhao, Nan [ORNL; Ferrer, Jean-Luc [Universite Joseph Fourier, France; Moon, Hong S [Department of Plant Sciences, University of Tennessee; Kapteyn, Jeremy [Institute of Biological Chemistry, Washington State University; Zhuang, Xiaofeng [Department of Plant Sciences, University of Tennessee; Hasebe, Mitsuyasu [Laboratory of Evolutionary Biology, National Institute for Biology, 38 Nishigounaka; Stewart, Neal C. [Department of Plant Sciences, University of Tennessee; Gang, David R. [Institute of Biological Chemistry, Washington State University; Chen, Feng [University of Tennessee, Knoxville (UTK)

2012-01-01

247

Stereoselective Isoxazolidine Synthesis Via Copper-Catalyzed Alkene Aminooxygenation  

PubMed Central

Isoxazolidines are useful in organic synthesis, drug discovery and chemical biology endeavors. A new stereoselective synthesis of methyleneoxy-substituted isoxazolidines is disclosed. The method involves copper-catalyzed aminooxygenation/cyclization of N-sulfonyl-O-butenyl hydroxylamines in the presence of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl radical (TEMPO) and O2, and provides substituted isoxazolidines in excellent yields and diastereoselectivities. We also demonstrate selective mono N-O reduction followed by oxidation of the remaining N-O bond to reveal a 2-amino-?-lactone. Reduction of the ?-lactone reveals the corresponding aminodiol.

Karyakarte, Shuklendu D.; Smith, Thomas P.

2012-01-01

248

Synthesis of Dihydrobenzofurans via Palladium-Catalyzed Heteroannulations  

SciTech Connect

Palladium-catalyzed heteroannulation of 1,3-dienes with 3-iodo-2-alkenols, and 2-iodo-2-alkenols, as well as their amino analogs, affords the corresponding cyclic ethers and amines respectively. The presence of a {beta}-hydrogen in the vinylic halide results in {beta}-hydride elimination giving the corresponding alkyne. The presence of a bulky group in the {alpha}-position of the vinylic halide results in failure or reduced amounts of annulation products. A chloride source, pyridine base and electron-rich phosphine are essential for this reaction.

Roman Vladimirovich Rozhkov

2004-12-19

249

Palladium-catalyzed oxidation of unsaturated hydrocarbons using molecular oxygen.  

PubMed

Oxidation reactions are central components of organic chemistry, and modern organic synthesis increasingly requires selective and mild oxidation methods. Although researchers have developed new organic oxidation methods in recent years, the chemistry community faces continuing challenges to use "green" reagents and maximize atom economy. Undoubtedly, with its low cost and lack of environmentally hazardous byproducts, molecular oxygen (O(2)) is an ideal oxidant. However, relatively limited methodologies are available that use O(2) efficiently in selective organic transformations. Recently, the use of metal catalysts coupled with the reduction of O(2) has become an attractive approach for aerobic oxidation. In particular, Pd complexes have shown great potential for the development of versatile aerobic reactions because of their ability to directly couple O(2) reduction. As a result, these complexes have attracted tremendous research attention and afford new opportunities for selective oxidation chemistry. In this Account we highlight some of our progress toward the synthetic goal to functionalize the unsaturated hydrocarbons largely through the appropriate choice of Pd catalysts and O(2). We have focused on developing simple and efficient methods to construct new carbon-carbon and carbon-heteroatom bonds with O(2) as the oxidant and/or reactant. We have demonstrated Pd-catalyzed oxidation of carbon-carbon double bonds, Pd-catalyzed oxidation of carbon-carbon triple bonds, and Pd-catalyzed oxidative cross-coupling reactions of alkenes and/or alkynes with high selectivity. O(2) plays a critical role in the success of these transformations. Most of the reactions can tolerate a range of functional groups, and some can occur under aqueous conditions. Depending on the specific process, we propose several mechanistic scenarios that describe the in situ generation of different intermediates and discuss the plausible reaction pathways. These methods provide new strategies for the green synthesis of diverse 1,2-diols, carbonyls, lactones, conjugated dienes, trienes, and aromatic rings. These products have potential applications in natural product synthesis, materials science, and bioorganic chemistry. Given our new mechanistic understanding, we are optimistic that additional Pd-catalyzed aerobic oxidative transformations will be developed that are both more economical and environmentally friendly. PMID:22839752

Wu, Wanqing; Jiang, Huanfeng

2012-10-16

250

Muon catalyzed fusion in deuterium at 3 K  

SciTech Connect

Muon catalyzed fusion in deuterium has traditionally been studied in gaseous and liquid targets. The TRIUMF solid hydrogen layer target system has been used to study the fusion reaction rates in the solid phase at a target temperature of 3 K. Both branches of the cycle were observed; neutrons by a liquid organic scintillator, and protons by a silicon detector located inside the target system. The effective molecular formation rate from the upper hyperfine state and the spin exchange rate have been measured, and information on the branching ratio parameters has been extracted.

Knowles, P.E.; Beer, G.A. [Univ. of Victoria, British Columbia (Canada); Bailey, J.M. [Chester Technology (United Kingdom)] [and others

1995-12-01

251

Base-Catalyzed Depolymerization of Lignin: Separation of Monomers  

SciTech Connect

In our quest for fractionating lignocellulosic biomass and valorizing specific constitutive fractions, we have developed a strategy for the separation of 12 added value monomers generated during the hydrolytic based-catalyzed depolymerization of a Steam Exploded Aspen Lignin. The separation strategy combines liquid-liquid-extraction (LLE), followed by vacuum distillation, liquid chromatography (LC) and crystallization. LLE, vacuum distillation and flash LC were tested experimentally. Batch vacuum distillation produced up to 4 fractions. Process simulation confirmed that a series of 4 vacuum distillation columns could produce 5 distinct monomer streams, 3 of which require further chromatography and crystallization for purification.

Vigneault, A.; Johnson, D. K.; Chornet, E.

2007-12-01

252

Probing the Regiospecificity of Enzyme-Catalyzed Steroid Glycosylation  

PubMed Central

The potential of a uniquely permissive engineered glycosyltransferase (OleD ASP) as a catalyst for steroid glycosylation is highlighted. The ability of OleD ASP to glucosylate a range of cardenolides and bufadienolides was assessed using a rapid LC-UV/MS-SPE-NMR analytical platform. While a bias toward OleD-catalyzed C3 mono-glucosylation was observed, subtle alterations of the steroidal architecture in some cases, invoked diglucosylation or, in one case (digoxigenin), C12 glucosylation. This latter case represents the first, and highly efficient, synthesis of digoxigenin 12-O-?-D-glucoside.

Zhou, Maoquan; Hou, Yanpeng; Hamza, Adel; Zhan, Chang-Guo; Bugni, Tim S.; Thorson, Jon S.

2012-01-01

253

Complex Biotransformations Catalyzed by Radical S-Adenosylmethionine Enzymes*  

PubMed Central

The radical S-adenosylmethionine (AdoMet) superfamily currently comprises thousands of proteins that participate in numerous biochemical processes across all kingdoms of life. These proteins share a common mechanism to generate a powerful 5?-deoxyadenosyl radical, which initiates a highly diverse array of biotransformations. Recent studies are beginning to reveal the role of radical AdoMet proteins in the catalysis of highly complex and chemically unusual transformations, e.g. the ThiC-catalyzed complex rearrangement reaction. The unique features and intriguing chemistries of these proteins thus demonstrate the remarkable versatility and sophistication of radical enzymology.

Zhang, Qi; Liu, Wen

2011-01-01

254

Acid-catalyzed isomerization of fucosterol and ? 5 -avenasterol  

Microsoft Academic Search

This work shows that fucosterol, ?5-avenasterol, and similar ethylidene-side chain sterols can undergo acid-catalyzed isomerization to give a mixture of five\\u000a isomers. Four isomers formed from fucosterol were analyzed, using gas chromatography-mass spectrometry, and were characterized\\u000a as ?5-avenasterol two ?5,23-stigmastadienols, and ?5,24(250)-stigmastadienol. When the unsaponifiables fraction from oat oil was subjected to acid hydrolysis, the two ?5,23-stigmastadienol isomers and ?5,24(25)-stigmastadienol

Afaf Kamal-Eldin; Kaisu Määttä; Jari Toivo; Anna-Maija Lampi; Vieno Piironen

1998-01-01

255

Laser-Catalyzed Domain Formation in Spinor-1 Bose Condensates  

NASA Astrophysics Data System (ADS)

We show theoretically that it is possible to optically control domain formation in a spinor-1 87Rb gas. A model is proposed to include the photoassociation (PA) interaction characterizing the symmetry breaking of MF = ±1 ferromagnetic condensate. We find that the dynamical process of the domain formation can be greatly controlled by the PA field. The PA field can enhance or suppress the spatial separation of domains, which can provide a flexible tool to modulate the domain structure and indicate an interesting research field of laser-catalyzed in spinor condensate.

Jiang, Ya-Jing; Sun, Jing-Xin; Jing, Hui

2012-11-01

256

Palladium- and nickel-catalyzed alkenylation of enolates.  

PubMed

Transition-metal-catalyzed alkenylation of enolates provides a direct method to synthesize broadly useful ?,?-unsaturated carbonyl compounds from the corresponding carbonyl compound and alkenyl halides. Despite being reported in the early seventies, this reaction class saw little development for many years. In the past decade, however, efforts to develop this reaction further have increased considerably, and many research groups have reported efficient coupling protocols, including enantioselective versions. These reactions most commonly employ palladium catalysts, but there are also some important reports using nickel. There are many examples of this powerful transformation being used in the synthesis of complex natural products. PMID:23325616

Ankner, Tobias; Cosner, Casey C; Helquist, Paul

2013-02-01

257

Palladium pincer complex-catalyzed allylic stannylation with hexaalkylditin reagents.  

PubMed

Palladium pincer complex (1)-catalyzed stannylation of allyl chloride, phosphonate, and epoxide substrates (4a-h) could be performed with hexaalkylditin reagents (3) under mild neutral reaction conditions. This catalytic reaction proceeds via palladium(II) intermediates without involvement of allyl-palladium complexes, and therefore the allylstannane product does not interfere with the palladium catalyst. Use of a combined catalytic system (1 + 2) allowed the development of an effective one-pot procedure for allylation of aldehyde and imine electrophiles. [reaction: see text] PMID:15151425

Wallner, Olov A; Szabó, Kálmán J

2004-05-27

258

Can Chlorine Anion Catalyze the Reaction fo HOCl with HCl?  

NASA Technical Reports Server (NTRS)

The reaction of HOCl + HCl -> Cl2 + H20 in the presence of Cl has been studied using ab initio methods. This reaction has been shown to have a high activation barrier of 46.5 kcal/mol. The chlorine anion, Cl- is found to catalyze the reaction, viz. two mechanisms. The first involves Cl- interacting through the concerted four-center transition state of the neutral reaction. The other mechanism involves the formation of a HCl-HOCl-Cl- intermediate which dissociates into Cl2 + Cl- + H20. The steps are found to have no barriers. The overall exothermicity is 15.5 kcal/mol.

Richardson, S. L.; Francisco, J. S.; Mebel, A. M.; Morokuma, K.

1997-01-01

259

Enantioselective copper-catalyzed carboetherification of unactivated alkenes.  

PubMed

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein reported is a highly efficient copper-catalyzed cyclization of ?-unsaturated pentenols which terminates in C?C bond formation, a net alkene carboetherification. Both intra- and intermolecular C?C bond formations are demonstrated, thus yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition-state calculations support a cis-oxycupration stereochemistry-determining step. PMID:24798697

Bovino, Michael T; Liwosz, Timothy W; Kendel, Nicole E; Miller, Yan; Tyminska, Nina; Zurek, Eva; Chemler, Sherry R

2014-06-16

260

Direct metal-catalyzed regioselective functionalization of enamides.  

PubMed

Enamides are stable enamine surrogates and provide key intermediates for the synthesis of small but complex nitrogen-containing compounds. Metal-catalyzed regioselective functionalization of enamides provides a rapid method to synthesize useful nitrogen containing heterocycles. This review discloses the recent progress made in the development of the C?H functionalization of enamides involving efficient and atom-economical routes. Syntheses of different heterocycles are classified based on the site reactivity of enamides and key mechanistic insights are given for each transformation. PMID:24862089

Gigant, Nicolas; Chausset-Boissarie, Laëtitia; Gillaizeau, Isabelle

2014-06-16

261

Palladium-catalyzed carbonylation of aryl tosylates and mesylates.  

PubMed

A general protocol for the palladium-catalyzed carbonylation of aryl tosylates and mesylates to form esters has been developed using a catalyst system derived from Pd(OAc)2 and the bulky, bidentate dcpp ligand. The system operates under mild conditions: atmospheric CO pressure and temperatures of 80-110 degrees C. A broad substrate scope has been demonstrated allowing carbonylation of electron-rich, electron-poor, and heterocyclic tosylates and mesylates, and the reaction shows wide functional group tolerance. PMID:18257577

Munday, Rachel H; Martinelli, Joseph R; Buchwald, Stephen L

2008-03-01

262

Cyclohexane oxidation catalyzed by mononuclear iron(III) complexes  

Microsoft Academic Search

In this work, we present the oxidation of cyclohexane catalyzed by a family of mononuclear iron(III) complexes: [Fe(BMPA)Cl3] 1, [Fe(MPBMPA)Cl3] 2, [Fe(PBMPA)Cl2] 3 and [Fe(PABMPA)Cl2](ClO4) 4 using hydrogen peroxide or tert-butyl hydroperoxide as oxidant, in acetonitrile solution. These complexes were able to oxidize the cyclohexane into cyclohexanol and cyclohexanone with good yields. It was also possible to characterize by gas

Nakédia M. F. Carvalho; Adolfo Horn; O. A. C. Antunes

2006-01-01

263

Palladium(II)-catalyzed direct intermolecular alkenylation of chromones.  

PubMed

A new efficient method for the direct alkenylation of chromones via a palladium(II)-catalyzed C-H functionalization reaction was developed. The use of pivalic acid with Cu(OAc)(3)/Ag(2)CO(3) provided superior reactivity in the cross-coupling of chromones with alkene partners. This approach represents a significant advance over the existing two-step method and afforded various 3-vinylchromone derivatives, which are privileged structures in many biologically active compounds and versatile synthetic building blocks. PMID:21797199

Kim, Donghee; Hong, Sungwoo

2011-08-19

264

Diversity synthesis using the complimentary reactivity of rhodium(II)- and palladium(II)-catalyzed reactions.  

PubMed

Rhodium(II)-catalyzed reactions of aryldiazoacetates can be conducted in the presence of iodide, triflate, organoboron, and organostannane functionality, resulting in the formation of a variety of cyclopropanes or C-H insertion products with high stereoselectivity. The combination of the rhodium(II)-catalyzed reaction with a subsequent palladium(II)-catalyzed Suzuki coupling offers a novel strategy for diversity synthesis. PMID:16839138

Ni, Aiwu; France, Jessica E; Davies, Huw M L

2006-07-21

265

Role of Homoserine Transacetylase as a New Target for Antifungal Agents  

Microsoft Academic Search

Microbial amino acid biosynthesis is a proven yet underexploited target of antibiotics. The biosynthesis of methionine in particular has been shown to be susceptible to small-molecule inhibition in fungi. The first committed step in Met biosynthesis is the acylation of homoserine (Hse) by the enzyme homoserine transacety- lase (HTA). We have identified the MET2 gene of Cryptococcus neoformans H99 that

Ishac Nazi; Adam Scott; Anita Sham; Laura Rossi; Peter R. Williamson; James W. Kronstad; Gerard D. Wright

2007-01-01

266

Genetic and biochemical investigation into the role and mechanism of fungal homoserine transacetylase  

Microsoft Academic Search

In an era of increasing fungal infections, we are encountering a significant challenge due to a simultaneous rise in drug resistant pathogenic fungi. The number of antifungal drugs is limited as are the targets they inhibit, which presents an additional obstacle for medical sciences. The limited number of drugs and targets that have been successfully exploited in antifungal drug discovery

Ishac Nazi

2006-01-01

267

Aldose Reductase-catalyzed Reduction of Aldehyde Phospholipids  

PubMed Central

SUMMARY Oxidation of unsaturated phospholipids results in the generation of aldehyde side chains that remain esterified to the phospholipid backbone. Such “core” aldehydes elicit immune responses and promote inflammation. However, the biochemical mechanisms by which phospholipid aldehydes are metabolized or detoxified are not well understood. In the studies reported here, we examined whether aldose reductase (AR), which reduces hydrophobic aldehydes, metabolizes phospholipid aldehydes. Incubation with AR led to the reduction of 5-oxovaleroyl, 7-oxo-5-heptenoyl, 5-hydroxy-6-oxo-caproyl, and 5-hydroxy-8-oxo-6-octenoyl phospholipids generated upon oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC). The enzyme also catalyzed the reduction of phospholipid aldehydes generated from the oxidation of 1-alkyl, and 1-alkenyl analogs of PAPC, and 1-palmitoyl-2-arachidonoyl phosphatidic acid or phosphoglycerol. Aldose reductase catalyzed the reduction of chemically synthesized 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphatidylcholine (POVPC) with a Km of 10 ?M. Addition of POVPC to the culture medium led to incorporation and reduction of the aldehyde in COS-7 and THP-1 cells. Reduction of POVPC in these cells was prevented by the AR inhibitors sorbinil and tolrestat and was increased in COS-7 cells overexpressing AR. Together, these observations suggest that AR may be a significant participant in the metabolism of several structurally diverse phospholipid aldehydes. This metabolism may be a critical regulator of the pro-inflammatory and immunogenic effects of oxidized phospholipids.

Srivastava, Sanjay; Spite, Matthew; Trent, John O.; West, Matthew B.; Ahmed, Yonis; Bhatnagar, Aruni

2012-01-01

268

Porous silicon formation during Au-catalyzed etching  

NASA Astrophysics Data System (ADS)

The formation of "black" nano-textured Si during the Au-catalyzed wet-chemical etch process was investigated with respect to photovoltaic applications. Cross-sectional scanning electron microscopy (SEM) images recorded at different stages of the etch process exhibit an evolution of a two-layer structure, consisting of cone-like Si hillocks covered with a nano-porous Si (np-Si) layer. Optical measurements confirm the presence of a np-Si phase which appears after the first ˜10 s of the etch process and continuously increases with the etch time. Furthermore, the etch process was investigated on Si substrates with different doping levels (˜0.01-100 ? cm). SEM images show a transition from the two-layer morphology to a structure consisting entirely of np-Si for higher doping levels (<0.1 ? cm). The experimental results are discussed on the basis of the model of a local electrochemical etch process. A better understanding of the metal-catalyzed etch process facilitates the fabrication of "black" Si on various Si substrates, which is of significant interest for photovoltaic applications.

Algasinger, Michael; Bernt, Maximilian; Koynov, Svetoslav; Stutzmann, Martin

2014-04-01

269

AID from bony fish catalyzes class switch recombination  

PubMed Central

Class switch recombination was the last of the lymphocyte-specific DNA modification reactions to appear in the evolution of the adaptive immune system. It is absent in cartilaginous and bony fish, and it is common to all tetrapods. Class switching is initiated by activation-induced cytidine deaminase (AID), an enzyme expressed in cartilaginous and bony fish that is also required for somatic hypermutation. Fish AID differs from orthologs found in tetrapods in several respects, including its catalytic domain and carboxy-terminal region, both of which are essential for the switching reaction. To determine whether evolution of class switch recombination required alterations in AID, we assayed AID from Japanese puffer and zebra fish for class-switching activity in mouse B cells. We find that fish AID catalyzes class switch recombination in mammalian B cells. Thus, AID had the potential to catalyze this reaction before the teleost and tetrapod lineages diverged, suggesting that the later appearance of a class-switching reaction was dependent on the evolution of switch regions and multiple constant regions in the IgH locus.

Barreto, Vasco M.; Pan-Hammarstrom, Qiang; Zhao, Yaofeng; Hammarstrom, Lennart; Misulovin, Ziva; Nussenzweig, Michel C.

2005-01-01

270

Enzyme catalyzed electricity-driven water softening system.  

PubMed

Hardness in water, which is caused by divalent cations such as calcium and magnesium ions, presents a major water quality problem. Because hard water must be softened before use in residential applications, there is great interest in the saltless water softening process because, unlike ion exchange softeners, it does not introduce additional ions into water. In this study, a saltless hardness removal driven by bioelectrochemical energy produced through enzymatic oxidation of glucose was proposed and investigated. Glucose dehydrogenase was coated on a carbon electrode to catalyze glucose oxidation in the presence of NAD? as a cofactor/mediator and methylene green as an electrocatalyst. The results showed that electricity generation stimulated hardness removal compared with non-electricity conditions. The enzymatic water softener worked upon a 6h batch operation per day for eight days, and achieved an average hardness removal of 46% at a high initial concentration of 800 mg/L as CaCO?. More hardness was removed at a lower initial concentration. For instance, at 200mg/L as CaCO? the enzymatic water softener removed 76.4±4.6% of total hardness. The presence of magnesium ions decreased hardness removal because of its larger hydrated radius than calcium ions. The enzymatic water softener removed 70-80% of total hardness from three actual hard water samples. These results demonstrated a proof-of-concept that enzyme catalyzed electricity generation can be used to soften hard water. PMID:23040397

Arugula, Mary A; Brastad, Kristen S; Minteer, Shelley D; He, Zhen

2012-12-10

271

Lipase-catalyzed polyester synthesis - A green polymer chemistry  

PubMed Central

This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemo-enzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting ‘green polymer chemistry’.

Kobayashi, Shiro

2010-01-01

272

A new concept for muon catalyzed fusion reactor  

NASA Astrophysics Data System (ADS)

A new concept for a muon catalyzed pure fusion reactor is considered. To our best knowledge this constitutes a first plausible configuration to make energy gain without resorting to fissile matter breeding by fusion neutrons, although a number of crucial physical and engineering questions as well as details have yet to be resolved. A bundle of DT ice ribbons (with a filling factor f) is immersed in the magnetic field. The overall magnetic field in the mirror configuration confines pions created by the injected high energy deuterium (or tritium) beam. The DT materials is long enough to be inertially confined along the axis of mirror. The muon catalyzed mesomolecule formation and nuclear fusion take place in the DT target, leaving ?++ and occasionally (??)+ (muon sticking). The stuck muons are stripped fast enough in the target, while they are accelerated by ion cyclotron resonance heating when they circulate in the vaccum (or dilute plasma). The ribbon is (eventually) surrounded and pressure-confined by this coronal plasma, whereas the corona is magnetically confined. The overall bundle of ribbons (a pellet) is inertially confined. This configuration may also be of use for stripping stuck muons via the plasma mechanism of Menshikov and Ponomarev.

Tajima, T.; Eliezer, S.; Kulsrud, R. M.

1988-12-01

273

Search for muon catalyzed d 3He-fusion  

NASA Astrophysics Data System (ADS)

We report on the results of an experiment aimed at observing muon-catalyzed d 3He-fusion with a setup previously used for studies of the muon-catalyzed dd-fusion. The basic element of the setup is a high pressure ionization chamber operating as an active target. In this experiment the chamber was filled with an HD + 3He (5.6%) gas mixture at 13.2 bar pressure and 50 K temperature. These conditions were chosen as optimal for formation of the 3He?d-molecules with a low level of background from the d-?-d fusion. The chamber was exposed to the negative muon beam at PSI. During a 3-week data-taking period, 9.7 × 108 muon stops have been selected. The analysis of the data was able to determine a new upper limit for the d 3He-fusion rate in the 3He?d-molecule (?f? 6× 104 s-1), which is more than three orders of magnitude lower than the previously existed limit.

Maev, E. M.; Balin, D. V.; Case, T.; Crowe, K. M.; Del Rosso, A.; Ganzha, V. A.; Hartmann, F. J.; Kozlov, S. M.; Lauss, B.; Maev, O. E.; Mühlbauer, M.; Mulhauser, F.; Petitjean, C.; Petrov, G. E.; Sadetsky, S. M.; Schapkin, G. N.; Schott, W.; Semenchuk, G. G.; Smirenin, Yu. V.; Soroka, M. A.; Vasiliev, A. A.; Vorobyov, A. A.; Voropaev, N. I.; Zmeskal, J.

1999-06-01

274

Self-regulated pulsed nucleation in catalyzed nanowire growth  

NASA Astrophysics Data System (ADS)

We present a theoretical analysis of catalyzed nanowire growth based on the material balance in a droplet within one monolayer growth cycle. Pulsed supersaturation and nucleation probability density are shown to originate from the material balance under rather general assumptions. We calculate explicitly the time-dependent nucleation probability as a function of nanowire radius and growth conditions. For small nanowire radii, the timescale hierarchy of different growth steps is demonstrated, leading to a temporal anticorrelation of nucleation events. Numerical analysis is performed in the case of Au-catalyzed GaAs nanowires, where the nucleation probabilities are mapped out as functions of nanowire radius at different conditions. The transition from deltalike to Poissonian temporal distribution of nucleation events is discussed depending on relevant parameters. We speculate that the self-regulated narrowing of nucleation probabilities suppresses random broadening of nanowire length distributions. This focusing effect is specific for nucleation in nanovolumes and might be used for tailoring the size spectra of different nano-objects.

Dubrovskii, V. G.

2013-05-01

275

Electrostatic effects on the rates of DNA-catalyzed reactions  

NASA Astrophysics Data System (ADS)

Diol-epoxide metabolites of many genotoxic polycyclic aromatic hydrocarbons are hydrolyzed to tetraols in a detoxification reaction. The hydrolysis reaction has both spontaneous and acid-catalyzed components; moreover, the reaction rate increases in the presence of DNA. The best studied of these diol epoxide metabolites are the trans 7,8 diol-9,10 epoxides of benzo[a]pyrene: anti-BPDE, the proximate carcinogen, in which the oxirane ring is anti with respect to the 7-hydroxyl group, and its syn diastereomer, syn-BPDE. Jerina and coworkers have studied the kinetics of the hydrolysis of syn- and anti-BPDE as a function of pH and DNA concentration and have measured the equilibrium constant for the formation of a noncovalent complex with DNA. They constructed a two-state model in which the diol epoxide is either free or statically bound: the free fraction is hydrolyzed with the same kinetics as it exhibits in solution without DNA; the bound diol epoxide reacts at faster rates. In this model, the dependence of the observed hydrolysis rates on both DNA concentration and pH is explained by using the rate constants, k0 and kH, for reactions of the free diol epoxide, the rate constants, kcat0 and kcatH, for the bound molecule, and the binding constant, Keq. The present work uses an acidic-domain interpretation of the two-state model to explain the catalytic effect of DNA on the acid-catalyzed hydrolysis of syn- and anti-BPDE. Postulating that the rate enhancement is a result of acidic domains at the DNA surface, we assumed the relationship k catH = k H [H +] b, where [H +] b is the hydrogen ion concentration near the bound molecule. Using numerical solutions to the Poisson-Boltzmann equation, the pH dependence of acidic domains at the surface of the polyelectrolyte, DNA, was calculated. Energy-minimization calculations were used to estimate the conformations of diol epoxide-DNA intercalation complexes. Poisson-Boltzmann (PB) calculations on these structures yielded hydrogen-ion concentrations near the epoxide group consistent with the k catH/k H ratio over a range of added-salt concentrations. The results strongly suggest that DNA catalysis of diol-epoxide hydrolysis is a polyelectrolyte effect. The mechanisms and rate constants observed for the acid-catalyzed hydrolysis in the absence of DNA are consistent with the increase in the rate constant induced by DNA. It may be concluded that the catalysis is primarily an effect of the acidic domains in the surface grooves of the nucleic acid.

Pack, George R.; Wong, Linda

1996-04-01

276

Montmorillonite Clay-Catalyzed Synthesis of RNA Oligomers  

NASA Astrophysics Data System (ADS)

It is proposed that catalysis had a central role in the origins of life. This will be illustrated using the montmorillonite clay-catalyzed synthesis of oligomers of RNA from activated monomers, (Ferris and Ertem, 1993) a possible step in the origin of the RNA world (Ferris, 2005). Structural analysis of oligomers formed in the reaction of the activated monomer of 5'-AMP with that of 5'-CMP demonstrated that the oligomers formed were not produced by random synthesis but rather the sequences observed were directed by the montmorillonite catalyst (Miyakawa and Ferris, 2003). RNA oligomers containing up to 40 mers have been synthesized in reactions performed in water at 25 oC in the presence of montmorillonite (Huang and Ferris, 2003). Analysis of the structure elements in these oligomers from the 7 to 39 mers showed that they did not vary. Reaction of D, L-mixtures of the activated monomers of A and U resulted in the formation of greater amounts of the homochiral amounts of dimers and trimers of A than would be expected if there was no selectivity in the reaction. A limited number of the dimers and trimers of U were also formed but here the selectivity was for the formation of an excess of heterochiral products (Joshi et al., 2000). A postulate that explains why homochiral trimers of U are not formed and the significance of catalysis in prebiotic synthesis will be discussed. Ferris, J.P. (2005) Origins of life, molecular basis of. In R.A. Meyers, Ed. Encyclopedia of Molecular Cell Biology and Molecular Medicine, 10. Wiley-VCH Verlag, Weinheim, Germany. Ferris, J.P., and Ertem, G. (1993) Montmorillonite catalysis of RNA oligomer formation in aqueous solution. A model for the prebiotic formation of RNA. J. Am. Chem. Soc., 115, 12270-12275. Huang, W., and Ferris, J.P. (2003) Synthesis of 35-40 mers of RNA oligomers from unblocked monomers. A simple approach to the RNA world. Chem. Commun., 1458-1459. Joshi, P.C., Pitsch, S., and Ferris, J.P. (2000) Homochiral selection in the montmorillonite-catalyzed and uncatalyzed prebiotic synthesis of RNA. Chem. Commun., 2497-2498. Miyakawa, S., and Ferris, J.P. (2003) Sequence- and Regioselectivity in the montmorillonite-catalyzed synthesis of RNA. J. Am. Chem. Soc., 125, 8202-8208.

Ferris, J. P.; Miyakawa, S.; Huang, W.; Joshi, P.

2005-12-01

277

Utilization of peroxide and its relevance in oxygen insertion reactions catalyzed by chloroperoxidase  

Microsoft Academic Search

Chloroperoxidase (CPO) catalyzed oxygen insertions are highly enantioselective and hence of immense biotechnological potential. A peroxide activation step is required to give rise to the compound I species that catalyzes this chiral reaction. A side reaction, a catalase type peroxide dismutation, is another feature of CPO’s versatility. This work systematically investigates the utilization of different peroxides for the two reactions,

Kelath Murali Manoj; Lowell P. Hager

2001-01-01

278

Palladium-Catalyzed Carbonylation of o-Iodoanilines for Synthesis of Isatoic Anhydrides.  

PubMed

A novel palladium-catalyzed oxidative double carbonylation of o-iodoanilines for the synthesis of isatoic anhydrides has been developed. The reaction employs readily available o-iodoanilines as the starting materials and proceeds under mild conditions. For extension, palladium-catalyzed oxidative carbonylation of anthranilic acids was developed for the synthesis of substituted isatoic anhydrides in high to excellent yields. PMID:24720706

Gao, Sha; Chen, Ming; Zhao, Mi-Na; Du, Wei; Ren, Zhi-Hui; Wang, Yao-Yu; Guan, Zheng-Hui

2014-05-01

279

Palladium-catalyzed benzylation of arylboronic acids with n,n-ditosylbenzylamines.  

PubMed

The palladium-catalyzed coupling of N,N-ditosylbenzylamines with arylboronic acids has been investigated, and the resulting diarylmethanes were obtained in high yields. Conversion of the amine to a N,N-ditosylimide group provided an efficient leaving group for the Pd-catalyzed benzylation of arylboronic acids. PMID:24724961

Yoon, Sangeun; Hong, Myeng Chan; Rhee, Hakjune

2014-05-01

280

Mechanism of Xanthine Oxidase Catalyzed Biotransformation of HMX Under Anaerobic Conditions.  

National Technical Information Service (NTIS)

Enzyme catalyzed biotransformation of the energetic chemical octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetrazocine (HMX) is not known. The present study describes a xanthine oxidase (XO) catalyzed biotransformation of HMX to provide insight into the biodegrad...

A. Halasz B. Bhushan J. Hawari J. C. Spain L. Paquet

2003-01-01

281

Hg(OTf)2-catalyzed vinylogous semi-pinacol rearrangement leading to 1,4-dihydroquinolines.  

PubMed

An efficient method for the construction of dihydroquinoline derivatives possessing a quaternary carbon center is developed by an application of Hg(OTf)(2)-catalyzed vinylogous semi-pinacol-type rearrangement. The reaction was found to be specifically catalyzed by mercury salt and to proceed via a bicyclic aminal. PMID:22339178

Namba, Kosuke; Kanaki, Michika; Suto, Hiroki; Nishizawa, Mugio; Tanino, Keiji

2012-03-01

282

Synthesis of Functionalized Cyclohexenone Core of Welwitindolinones via Rhodium- Catalyzed [5+1] Cycloaddition  

PubMed Central

The cyclohexenone core of welwitindolinones was synthesized by a Rh(I)-catalyzed [5+1]-cycloaddition of an allenylcyclopropane with CO. A penta-substituted cyclopropane was prepared successfully by a Rh(II)-catalyzed intramolecular cyclopropanation of alkenes with chlorodiazoacetates.

Zhang, Min

2012-01-01

283

Copper-catalyzed bis-arylations of alkenes leading to oxindole derivatives.  

PubMed

A simple and practical copper-catalyzed approach to oxindole derivatives by copper-catalyzed bis-arylation of N-alkyl-N-phenylacrylamides with diaryliodonium triflates has been developed under mild conditions, and the method is of tolerance towards some functional groups in the substrates. PMID:24817255

Shi, Liangliang; Wang, Yuyuan; Yang, Haijun; Fu, Hua

2014-06-28

284

Lipase-catalyzed synthesis of fattythioic acids from palm oil.  

PubMed

The present work focuses on the synthesis of fattythioic acids (FTAs) by a one-step lipase catalyzed reaction of palm oil with carbonothioic S,S-acid using Lipozyme. The product was characterized using Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance ((1)H NMR) technique and elemental analysis. The effects of various reaction parameters such as reaction time, temperature, amount of enzyme, molar ratio of substrates, and various organic solvents of the reaction system were investigated. The optimum conditions to produce FTAs were respectively, incubation time, 20 h, temperature, 40°C, amount of enzyme, 0.05 g and molar ratio of carbonothioic S,S-acid to palm oil, 5.0:1.0. Hexane was the best solvent for this reaction. The conversion of the products at optimum conditions was around 91%. PMID:21178316

Al-Mulla, Emad A Jaffar

2011-01-01

285

Synthesis of Rosin Acid Starch Catalyzed by Lipase  

PubMed Central

Rosin, an abundant raw material from pine trees, was used as a starting material directly for the synthesis of rosin acid starch. The esterification reaction was catalyzed by lipase (Novozym 435) under mild conditions. Based on single factor experimentation, the optimal esterification conditions were obtained as follows: rosin acid/anhydrous glucose unit in the molar ratio 2?:?1, reaction time 4?h at 45°C, and 15% of lipase dosage. The degree of substitution (DS) reaches 0.098. Product from esterification of cassava starch with rosin acid was confirmed by FTIR spectroscopy and iodine coloration analysis. Scanning electron microscopy and X-ray diffraction analysis showed that the morphology and crystallinity of the cassava starch were largely destroyed. Thermogravimetric analysis indicated that thermal stability of rosin acid starch decreased compared with native starch.

Lin, Rihui; Li, He; Long, Han; Su, Jiating; Huang, Wenqin

2014-01-01

286

Homogeneously catalyzed oxidation for the destruction of aqueous organic wastes  

SciTech Connect

Several organic species, specifically atrazine, 2,4-dichlorophenozyacetic acid, and biphenyl, were converted to CO{sub 2} and other non-harmful gases through oxidation catalyzed by inorganic acid. Nearly complete conversion was obtained through homogeneous liquid-phase oxidation with ammonium nitrate. The kinetics of reaction have been investigated and indicate parallel oxidation and thermal degradation of the oxidant. This results in a maximum conversion at an intermediate temperature. Increasing oxidant concentration accelerates the rate of conversion and shifts the location of the optimum temperature. Reaction at varying acid concentration revealed that conversion increased with an approximately linear relationship as the pH of the solution was increased. Conversion was increased to greater than 99% through the addition of small amounts of transition metal salts demonstrating the suitability of a treatment process based on this technology for wastestreams containing small quantities of heavy metals.

Leavitt, D.D.; Horbath, J.S.; Abraham, M.A. (Univ. of Tulsa, OK (USA))

1990-11-01

287

Structural control of cytochrome P450-catalyzed ?-hydroxylation.  

PubMed

The regiospecific or preferential ?-hydroxylation of hydrocarbon chains is thermodynamically disfavored because the ease of C-H bond hydroxylation depends on the bond strength, and the primary C-H bond of a terminal methyl group is stronger than the secondary or tertiary C-H bond adjacent to it. The hydroxylation reaction will therefore occur primarily at the adjacent secondary or tertiary C-H bond unless the protein structure specifically enforces primary C-H bond oxidation. Here we review the classes of enzymes that catalyze ?-hydroxylation and our current understanding of the structural features that promote the ?-hydroxylation of unbranched and methyl-branched hydrocarbon chains. The evidence indicates that steric constraints are used to favor reaction at the ?-site rather than at the more reactive (?-1)-site. PMID:20727847

Johnston, Jonathan B; Ouellet, Hugues; Podust, Larissa M; Ortiz de Montellano, Paul R

2011-03-01

288

Structural control of cytochrome P450-catalyzed ?-hydroxylation  

PubMed Central

The regiospecific or preferential ?-hydroxylation of hydrocarbon chains is thermodynamically disfavored because the ease of C-H bond hydroxylation depends on the bond strength, and the primary C-H bond of a terminal methyl group is stronger than the secondary or tertiary C-H bond adjacent to it. The hydroxylation reaction will therefore occur primarily at the adjacent secondary or tertiary C-H bond unless the protein structure specifically enforces primary C-H bond oxidation. Here we review the classes of enzymes that catalyze ?-hydroxylation and our current understanding of the structural features that promote the ?-hydroxylation of unbranched and methyl-branched hydrocarbon chains. The evidence indicates that steric constraints are used to favor reaction at the ?-site rather than at the more reactive (?-1)-site.

Johnston, Jonathan B.; Ouellet, Hugues; Podust, Larissa M.; Ortiz de Montellano, Paul R.

2010-01-01

289

The pyrite iron cycle catalyzed by Acidithiobacillus ferrooxidans.  

PubMed

In this paper, we study a model of the biotic pyrite iron cycle catalyzed by bacteria Acidithiobacillus ferrooxidans, in mining activity sites waste dumps. Chemical reactions, reaction rates and the population growth model are mostly taken from the existing literature. Analysis of the corresponding dynamical system shows the existence of up to four non-trivial steady state solutions. The stability of the equilibria solutions is determined, finding up to two coexisting stable solutions. Two Hopf bifurcations and a region of parameter space in which there are stable periodic solutions are found. In addition, we find a homoclinic bifurcation which gives rise to a stable periodic orbit of large period. The existence of these stable oscillatory solutions gives a possible explanation for the oscillations of bacteria concentration and pH for the iron cycle, described in Jaynes et al. (Water Resour Res 20:233-242, 1984). PMID:23852143

Dumett, Miguel A; Keener, James P

2014-08-01

290

Engineering entropy-driven reactions and networks catalyzed by DNA.  

PubMed

Artificial biochemical circuits are likely to play as large a role in biological engineering as electrical circuits have played in the engineering of electromechanical devices. Toward that end, nucleic acids provide a designable substrate for the regulation of biochemical reactions. However, it has been difficult to incorporate signal amplification components. We introduce a design strategy that allows a specified input oligonucleotide to catalyze the release of a specified output oligonucleotide, which in turn can serve as a catalyst for other reactions. This reaction, which is driven forward by the configurational entropy of the released molecule, provides an amplifying circuit element that is simple, fast, modular, composable, and robust. We have constructed and characterized several circuits that amplify nucleic acid signals, including a feedforward cascade with quadratic kinetics and a positive feedback circuit with exponential growth kinetics. PMID:18006742

Zhang, David Yu; Turberfield, Andrew J; Yurke, Bernard; Winfree, Erik

2007-11-16

291

Acid-catalyzed isomerization of fucosterol and delta5-avenasterol.  

PubMed

This work shows that fucosterol, delta5-avenasterol, and similar ethylidene-side chain sterols can undergo acid-catalyzed isomerization to give a mixture of five isomers. Four isomers formed from fucosterol were analyzed, using gas chromatography-mass spectrometry, and were characterized as delta5-avenasterol, two delta5,23-stigmastadienols, and delta5,24(25)-stigmastadienol. When the unsaponifiables fraction from oat oil was subjected to acid hydrolysis, the two delta5,23-stigmastadienol isomers and delta5,24(25)-stigmastadienol were detected while fucosterol coeluted with sitosterol. Interisomerization of ethylidene-side chain sterols represents a limitation to the use of the acid hydrolysis method in the determination of sterols in food and other plant materials rich in these sterols, e.g., oat lipids. PMID:9870901

Kamal-Eldin, A; Määttä, K; Toivo, J; Lampi, A M; Piironen, V

1998-11-01

292

Oxidation products of quercetin catalyzed by mushroom tyrosinase.  

PubMed

Quercetin was oxidized as a substrate catalyzed by mushroom tyrosinase to the corresponding o-quinone and subsequent isomerization to p-quinone methide type intermediate; followed by the addition of water on C-2 yielding a relatively stable intermediate, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone. In the presence of a catalytic amount of l-DOPA as a cofactor, the rate of this oxidation was enhanced. Fisetin, which lacks the C-5 hydroxyl group, was also oxidized but the rate of oxidation was faster than that of quercetin, indicating that the C-5 hydroxyl group is not essential but is associated with the activity. PMID:15388161

Kubo, Isao; Nihei, Ken-ichi; Shimizu, Kuniyoshi

2004-10-15

293

WILDCAT: a catalyzed D-D tokamak reactor  

SciTech Connect

WILDCAT is a conceptual design of a catalyzed D-D, tokamak, commercial, fusion reactor. WILDCAT utilizes the beneficial features of no tritium breeding, while not extrapolating unnecessarily from existing D-T designs. The reactor is larger and has higher magnetic fields and plasma pressures than typical D-T devices. It is more costly, but eliminates problems associated with tritium breeding and has tritium inventories and throughputs approximately two orders of magnitude less than typical D-T reactors. There are both a steady-state version with Alfven-wave current drive and a pulsed version. Extensive comparison with D-T devices has been made, and cost and safety analyses have been included. All of the major reactor systems have been worked out to a level of detail appropriate to a complete, conceptual design.

Evans, K. Jr.; Baker, C.C.; Brooks, J.N.

1981-11-01

294

The PSI experiments on muon-catalyzed pt fusion  

NASA Astrophysics Data System (ADS)

The experiments on pt fusion performed at Paul Scherrer Institut, Villigen, Switzerland, are described. Liquid triple mixtures of protium, deuterium and tritium with low concentrations on deuterium and tritium were used. Gamma rays, X-rays, neutrons and, for the first time, conversion muons, were measured. Preliminary results are: Rate for spin flip from the triplet to the singlet state of t?(1s), ?10=(1.0±0.2) × 103?s-1; rate for muon-catalyzed pt fusion from the ( I=1) nuclear-spin state, ?{pt/f}( I=1)=0.07±0.01?s-1; and the molecular formation rate, ?{pt/m}=(7.5±1.3)?s-1 (all normalized to liquid hydrogen density).

Hartmann, F. J.; Baumann, P.; Daniel, H.; von Egidy, T.; Grunewald, S.; Lipowsky, R.; Moser, E.; Schott, W.; Ackerbauer, P.; Breunlich, W. H.; Fuchs, M.; Jeitler, M.; Kammel, P.; Marton, J.; Nägele, N.; Werner, J.; Zmeskal, J.; Bossy, H.; Crowe, K. M.; Sherman, R. H.; Lou, K.; Petitjean, C.; Markushin, V. E.

1993-03-01

295

Mechanistic investigations of the rhodium catalyzed propargylic CH activation.  

PubMed

Previously we reported the redox-neutral atom economic rhodium catalyzed coupling of terminal alkynes with carboxylic acids using the DPEphos ligand. We herein present a thorough mechanistic investigation applying various spectroscopic and spectrometric methods (NMR, in situ-IR, ESI-MS) in combination with DFT calculations. Our findings show that in contrast to the originally proposed mechanism, the catalytic cycle involves an intramolecular protonation and not an oxidative insertion of rhodium in the OH bond of the carboxylic acid. A ?-allyl complex was identified as the resting state of the catalytic transformation and characterized by X-ray crystallographic analysis. By means of ESI-MS investigations we were able to detect a reactive intermediate of the catalytic cycle. PMID:24377792

Gellrich, Urs; Meißner, Antje; Steffani, Alberto; Kähny, Matthias; Drexler, Hans-Joachim; Heller, Detlef; Plattner, Dietmar A; Breit, Bernhard

2014-01-22

296

Laccase-catalyzed oxidative polymerization of phenolic compounds.  

PubMed

Enzymatic polymerization of phenolic compounds (catechol, resorcinol, and hydroquinone) was carried out using laccase. The mechanism of polymerization and the structures of the polymers were evaluated in terms of UV-Vis and Fourier transform infrared spectroscopy. The molecular weights of the produced polyphenols were determined with GPC. The results showed that the phenolic monomers firstly turned into quinone intermediates by laccase catalysis. Through further oxidation, the intermediates formed covalent bonds. Finally, catechol units were linked together with ether bonds, and both resorcinol and hydroquinone units were linked together with C-C bonds. The number-average molecular weights of the polyphenols ranged from 1,000 to 1,400 Da (corresponding to the degree of polymerization that varied from 10 to 12) with a lower polydispersity value of about 1.10, showing selective polymerization of phenolic compounds catalyzed by laccase. PMID:23996120

Sun, Xuejiao; Bai, Rubing; Zhang, Ya; Wang, Qiang; Fan, Xuerong; Yuan, Jiugang; Cui, Li; Wang, Ping

2013-12-01

297

Cytochromes P450 Catalyze the Reduction of ?,?-Unsaturated Aldehydes  

PubMed Central

The metabolism of ?,?-unsaturated aldehydes, e.g. 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O2, and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ? P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 & rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions, but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and ?-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of reduction of ?,?-unsaturated aldehydes in liver.

Amunom, Immaculate; Dieter, Laura J.; Tamasi, Viola; Cai, Jan; Conklin, Daniel J.; Srivastava, Sanjay; Martin, Martha V.; Guengerich, F. Peter; Prough, Russell A.

2011-01-01

298

Multimethylation of Rickettsia OmpB catalyzed by lysine methyltransferases.  

PubMed

Methylation of rickettsial OmpB (outer membrane protein B) has been implicated in bacterial virulence. Rickettsial methyltransferases RP789 and RP027-028 are the first biochemically characterized methyltransferases to catalyze methylation of outer membrane protein (OMP). Methylation in OMP remains poorly understood. Using semiquantitative integrated liquid chromatography-tandem mass spectroscopy, we characterize methylation of (i) recombinantly expressed fragments of Rickettsia typhi OmpB exposed in vitro to trimethyltransferases of Rickettsia prowazekii RP027-028 and of R. typhi RT0101 and to monomethyltransferases of R. prowazekii RP789 and of R. typhi RT0776, and (ii) native OmpBs purified from R. typhi and R. prowazekii strains Breinl, RP22, and Madrid E. We found that in vitro trimethylation occurs at relatively specific locations in OmpB with consensus motifs, KX(G/A/V/I)N and KT(I/L/F), whereas monomethylation is pervasive throughout OmpB. Native OmpB from virulent R. typhi contains mono- and trimethyllysines at locations well correlated with methylation in recombinant OmpB catalyzed by methyltransferases in vitro. Native OmpBs from highly virulent R. prowazekii strains Breinl and RP22 contain multiple clusters of trimethyllysine in contrast to a single cluster in OmpB from mildly virulent R. typhi. Furthermore, OmpB from the avirulent strain Madrid E contains mostly monomethyllysine and no trimethyllysine. The native OmpB from Madrid E was minimally trimethylated by RT0101 or RP027-028, consistent with a processive mechanism of trimethylation. This study provides the first in-depth characterization of methylation of an OMP at the molecular level and may lead to uncovering the link between OmpB methylation and rickettsial virulence. PMID:24497633

Abeykoon, Amila; Wang, Guanghui; Chao, Chien-Chung; Chock, P Boon; Gucek, Marjan; Ching, Wei-Mei; Yang, David C H

2014-03-14

299

Cathodic oxygen reduction catalyzed by bacteria in microbial fuel cells.  

PubMed

Microbial fuel cells (MFCs) have the potential to combine wastewater treatment efficiency with energetic efficiency. One of the major impediments to MFC implementation is the operation of the cathode compartment, as it employs environmentally unfriendly catalysts such as platinum. As recently shown, bacteria can facilitate sustainable and cost-effective cathode catalysis for nitrate and also oxygen. Here we describe a carbon cathode open to the air, on which attached bacteria catalyzed oxygen reduction. The bacteria present were able to reduce oxygen as the ultimate electron acceptor using electrons provided by the solid-phase cathode. Current densities of up to 2.2 A m(-2) cathode projected surface were obtained (0.303+/-0.017 W m(-2), 15 W m(-3) total reactor volume). The cathodic microbial community was dominated by Sphingobacterium, Acinetobacter and Acidovorax sp., according to 16S rRNA gene clone library analysis. Isolates of Sphingobacterium sp. and Acinetobacter sp. were obtained using H(2)/O(2) mixtures. Some of the pure culture isolates obtained from the cathode showed an increase in the power output of up to three-fold compared to a non-inoculated control, that is, from 0.015+/-0.001 to 0.049+/-0.025 W m(-2) cathode projected surface. The strong decrease in activation losses indicates that bacteria function as true catalysts for oxygen reduction. Owing to the high overpotential for non-catalyzed reduction, oxygen is only to a limited extent competitive toward the electron donor, that is, the cathode. Further research to refine the operational parameters and increase the current density by modifying the electrode surface and elucidating the bacterial metabolism is warranted. PMID:18288216

Rabaey, Korneel; Read, Suzanne T; Clauwaert, Peter; Freguia, Stefano; Bond, Philip L; Blackall, Linda L; Keller, Jurg

2008-05-01

300

New metal catalyzed syntheses of nanostructured boron nitride and alkenyldecaboranes  

NASA Astrophysics Data System (ADS)

The goals of the research described in this dissertation were two-fold. The first goal was to develop new methods, employing metal-catalyzed chemical vapor deposition reactions of molecular polyborane precursors, for the production of boron nitride nanostructured materials, including both boron nitride nanotubes (BNNTs) and boron nitride nanosheets (BNNS). The second goal was to develop new systematic metal-catalyzed reactions for polyboranes that would facilitate their functionalization for possible biomedical and/or materials applications. The syntheses of multi- and double-walled BNNTs were achieved with the aid of a floating nickel catalyst via the catalytic chemical vapor deposition (CCVD) of borazine (B3N3H6) or decaborane (B10H14) molecular precursors in ammonia atmospheres, with each precursor having its own advantages. While borazine is a single-source precursor containing both boron and nitrogen, the decaborane-based syntheses required the additional step of reaction with ammonia. However, the higher observed BNNT yields and the ease of handling and commercial availability of decaborane are distinct advantages. The BNNTs derived from both precursors were crystalline with highly ordered structures. The BNNTs grown at 1200 ºC from borazine were mainly double walled, with lengths up to 0.2 µm and ˜2 nm diameters. The BNNTs grown at 1200-1300 ºC from decaborane were double- and multi-walled, with the double-walled nanotubes having ˜2 nm inner diameters and the multi-walled nanotubes (˜10 walls) having ˜4-5 nm inner diameters and ˜12-14 nm outer diameters. BNNTs grown from decaborane at 1300 ºC were longer, averaging ˜0.6 µm, whereas those grown at 1200 ºC had average lengths of ˜0.2 µm. The BNNTs were characterized using scanning and transmission electron microscopies (SEM and TEM), and electron energy loss spectroscopy (EELS). This floating catalyst method now provides a catalytic and potentially scalable route to BNNTs with low defect density from safe and commercially available precursor compounds. A catalytic CVD method, employing the thermally induced reactions of ammonia with decaborane on polycrystalline nickel and copper foils, was also successfully developed for the production of BNNS. The metals were readily etched and the BNNS transferred to other substrates. The EELS and Raman spectra and the electron diffraction patterns of the BNNS confirmed the formation of h-BN and their optical, AFM and TEM characterizations showed BNNS with large micron-scale areas with some crumpling and folding. Most of the BNNS deposited on Ni were two- or three-layered; however, some regions were thicker containing up to six BN sheets. The films on Cu also contained two- and three-layered BNNS, but had large amorphous BN regions. Many of the BNNS grown on Ni exhibited well-defined angular edges, with near regular angles of 30º, 60º or 90º, suggesting that with a fine-tuning of the decaborane/ammonia pressure and growth conditions, controlled growth of regular polygonal BNNS structures can be achieved. To achieve the second goal, transition-metal-catalyzed decaborane-alkyne hydroboration reactions were developed that provide high-yield routes to the previously unknown di- and monoalkenyldecaboranes. An unusual catalyst product selectivity was observed, with the reactions catalyzed by the [RuCl2 (p-cymene)]2 and [Cp*IrCl2]2 complexes giving the ?-E alkenyldecaboranes and the corresponding reactions with the [RuI2(p-cymene)]2 complex giving the ?-alkenyldecaborane isomers. These product selectivities coupled with the differences observed in NMR studies of catalyzed reactions in progress, suggest quite distinct mechanistic steps for the different catalysts. It was further demonstrated that the new alkenyldecaboranes could be easily modified with the aid of metal-catalyzed hydroborations and homo and cross metathesis reactions to yield both linked cage and chemically active derivatives. These results demonstrate that the alkenyldecaboranes could serve as important materials for many potential polyborane biomedica

Chatterjee, Shahana

301

Iron catalyzed polyethylene chain growth on zinc: a study of the factors delineating chain transfer versus catalyzed chain growth in zinc and related metal alkyl systems.  

PubMed

The bis(imino)pyridine iron complex, [[2,6-(MeC=N-2,6-iPr2C6H3)2C5H)N]FeCl2] (1), in combination with MAO and ZnEt2 (> 500 equiv.), is shown to catalyze polyethylene chain growth on zinc. The catalyzed chain growth process is characterized by an exceptionally fast and reversible exchange of the growing polymer chains between the iron and zinc centers. Upon hydrolysis of the resultant ZnR2 product, a Poisson distribution of linear alkanes is obtained; linear alpha-olefins with a Poisson distribution can be generated via a nickel-catalyzed displacement reaction. Other dialkylzinc reagents such as ZnMe2 and ZniPr2 also show catalyzed chain growth; in the case of ZnMe2 a slight broadening of the product distribution is observed. The products obtained from Zn(CH2Ph)2 show evidence for chain transfer but not catalyzed chain growth, whereas ZnPh2 shows no evidence for chain transfer. The Group 13 metal alkyl reagents AlR3 (R = Me, Et, octyl, IBu) and GaR3 (R = Et, nBu) act as highly efficient chain transfer agents, whereas GaMe3 exhibits behavior close to catalyzed chain growth. LinBu, MgnBu2 and BEt3 result in very low activity catalyst systems. SnMe4 and PbEt4 give active catalysts, but with very little chain transfer to Sn or Pb. The remarkably efficient iron catalyzed chain growth reaction for ZnEt2 compared to other metal alkyls can be rationalized on the basis of: (1) relatively low steric hindrance around the zinc center, (2) their monomeric nature in solution, (3) the relatively weak Zn-C bond, and (4) a reasonably close match in Zn-C and Fe-C bond strengths. PMID:15327329

Britovsek, George J P; Cohen, Steven A; Gibson, Vernon C; Van Meurs, Martin

2004-09-01

302

Study of Silicidation Process of Tungsten Catalyzer during Silicon Film Deposition in Catalytic Chemical Vapor Deposition  

NASA Astrophysics Data System (ADS)

In catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD, source gases are decomposed by catalytic cracking reactions with heated catalyzing metal wires. In the case of silicon (Si) film deposition, such metal wires are often converted to silicide, which shortens the lifetime of catalyzing wires. As a catalyzer, tungsten (W) is widely used. Thus, the process of silicidation of a W catalyzer at temperatures over 1650 °C, which is the temperature used in Cat-CVD for Si film deposition, was studied extensively in various experiments. It is found that two phases of tungsten-silicide, WSi2 and W5Si3, are formed at this temperature, and that the radiation emissivity of WSi2 is 1.2 to 1.7 times higher than that of W5Si3 and pure W. The increase of surface emissivity due to the formation of WSi2 decreases the catalyzer surface temperature which induces further growth of the tungsten-silicide layer. It is also found that the suppression of WSi2 formation by elevating catalyzer temperatures over 1750 °C is a key to extending the lifetime of the W catalyzer in Cat-CVD.

Honda, Kazuhiro; Ohdaira, Keisuke; Matsumura, Hideki

2008-05-01

303

High power density yeast catalyzed microbial fuel cells  

NASA Astrophysics Data System (ADS)

Microbial fuel cells leverage whole cell biocatalysis to convert the energy stored in energy-rich renewable biomolecules such as sugar, directly to electrical energy at high efficiencies. Advantages of the process include ambient temperature operation, operation in natural streams such as wastewater without the need to clean electrodes, minimal balance-of-plant requirements compared to conventional fuel cells, and environmentally friendly operation. These make the technology very attractive as portable power sources and waste-to-energy converters. The principal problem facing the technology is the low power densities compared to other conventional portable power sources such as batteries and traditional fuel cells. In this work we examined the yeast catalyzed microbial fuel cell and developed methods to increase the power density from such fuel cells. A combination of cyclic voltammetry and optical absorption measurements were used to establish significant adsorption of electron mediators by the microbes. Mediator adsorption was demonstrated to be an important limitation in achieving high power densities in yeast-catalyzed microbial fuel cells. Specifically, the power densities are low for the length of time mediator adsorption continues to occur. Once the mediator adsorption stops, the power densities increase. Rotating disk chronoamperometry was used to extract reaction rate information, and a simple kinetic expression was developed for the current observed in the anodic half-cell. Since the rate expression showed that the current was directly related to microbe concentration close to the electrode, methods to increase cell mass attached to the anode was investigated. Electrically biased electrodes were demonstrated to develop biofilm-like layers of the Baker's yeast with a high concentration of cells directly connected to the electrode. The increased cell mass did increase the power density 2 times compared to a non biofilm fuel cell, but the power density increase was shown to quickly saturate with cell mass attached on the electrode. Based on recent modelling data that suggested that the electrode currents might be limited by the poor electrical conductivity of the anode, the power density versus electrical conductivity of a yeast-immobilized anode was investigated. Introduction of high aspect ratio carbon fiber filaments to the immobilization matrix increased the electrical conductivity of the anode. Although a higher electrical conductivity clearly led to an increase in power densities, it was shown that the principal limitation to power density increase was coming from proton transfer limitations in the immobilized anode. Partial overcoming of the gradients lead a power density of ca. 250 microW cm-2, which is the highest reported for yeast powered MFCs. A yeast-catalyzed microbial fuel cell was investigated as a power source for low power sensors using raw tree sap. It was shown that yeast can efficiently utilize the sucrose present in the raw tree sap to produce electricity when excess salt is added to the medium. Therefore the salinity of a potential energy source is an important consideration when MFCs are being considered for energy harvesting from natural sources.

Ganguli, Rahul

304

Rh(I)-Catalyzed Direct Arylation of Pyridines and Quinolines  

SciTech Connect

The pyridine and quinoline nuclei are privileged scaffolds that occupy a central role in many medicinally relevant compounds. Consequently, methods for their expeditious functionalization are of immediate interest. However, despite the immense importance of transition-metal catalyzed cross-coupling for the functionalization of aromatic scaffolds, general solutions for coupling 2-pyridyl organometallics with aryl halides have only recently been presented. Direct arylation at the ortho position of pyridine would constitute an even more efficient approach because it eliminates the need for the stoichiometric preparation and isolation of 2-pyridyl organometallics. Progress towards this goal has been achieved by activation of the pyridine nucleus for arylation via conversion to the corresponding pyridine N-oxide or N-iminopyridinium ylide. However, this approach necessitates two additional steps: activation of the pyridine or quinoline starting material, and then unmasking the arylated product. The use of pyridines directly would clearly represent the ideal situation both in terms of cost and simplicity. We now wish to document our efforts in this vein, culminating in an operationally simple Rh(I)-catalyzed direct arylation of pyridines and quinolines. We recently developed an electron-rich Rh(I) system for catalytic alkylation at the ortho position of pyridines and quinolines with alkenes. Therefore, we initially focused our attention on the use of similarly electron-rich Rh(I) catalysts for the proposed direct arylation. After screening an array of electron-rich phosphine ligands and Rh(I) salts, only marginal yields (<20%) of the desired product were obtained. Much more efficient was an electron-poor Rh(I) system with [RhCl(CO){sub 2}]{sub 2} as precatalyst (Table 1). For the direct arylation of picoline with 3,5-dimethyl-bromobenzene, addition of P(OiPr){sub 3} afforded a promising 40% yield of the cross coupled product 1a (entry 1). The exclusion of phosphite additive proved even more effective, with the yield of 1a improving to 61% (entry 2). Further enhancement in yield was not observed upon the inclusion of other additives such as MgO (entry 3), various organic bases (entries 4, 5), or a protic acid source (entry 6). Absolute concentration proved very important, with the best results being obtained at relatively high concentrations of the aryl bromide (compare entries 7 and 8). A marginal improvement was observed upon running the reaction with 6 equivalents of 2-methyl pyridine (entry 9). The reaction temperature could also be increased to 175 or 190 C while maintaining reaction yield, to enable the reaction time to be reduced to 24 h (entries 10 and 11). In summary, we have developed a Rh(I)-catalyzed strategy for the direct arylation of pyridines and quinolines. The heterocycle is used without the need for prefunctionalization, and all reaction components are inexpensive and readily available. The strategy represents an expeditious route to an important class of bis(hetero)aryls and should be of broad utility.

Berman, Ashley; Lewis, Jared; Bergman, Robert; Ellman, Jonathan

2008-07-29

305

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

PubMed

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

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

2014-06-10

306

Ru-catalyzed hydroamidation of alkenes and cooperative aminocarboxylation procedure with chelating formamide.  

PubMed

[reaction: see text] A strategy of chelation-assisted activation of formamide was employed to achieve hydroamidation of alkenes to generate one-carbon-elongated amides in moderate to good selectivity and yields. Also reported is the two-metal-catalyzed cooperative aminocarboxylation of aryl iodides, in which Ru is presumed to catalyze decarbonylation of formamide to release carbon monoxide and amine for the subsequent Pd-catalyzed aminocarboxylation routes, thus enabling the net transformation to be performed in the absence of external CO pressure. PMID:12868890

Ko, Sangwon; Han, Hoon; Chang, Sukbok

2003-07-24

307

Evaluating Transition-Metal Catalyzed Transformations for the Synthesis of Laulimalide  

PubMed Central

Laulimalide is a structurally unique 20-membered marine macrolide displaying microtubule stabilizing activity similar to that of paclitaxel and the epothilones. The use of atom economical transformations such as a rhodium-catalyzed cycloisomerization to form the endocyclic dihydropyran, a dinuclear zinc-catalyzed asymmetric glycolate aldol to prepare the syn 1,2-diol and an intramolecular ruthenium-catalyzed alkene-alkyne coupling to build the macrocycle enabled us to synthesize laulimalide via an efficient and convergent pathway. The designed synthetic route also allowed us to prepare an analogue of the natural product that possesses significant cytotoxic activity.

Trost, Barry M.; Amans, Dominique; Seganish, W. Michael; Chung, Cheol K.

2009-01-01

308

The isolation and characterization of a rhodacycle intermediate implicated in metal-catalyzed reactions of alkylidenecyclopropanes.  

PubMed

The isolation and characterization of a rhodacycle intermediate implicated in rhodium-catalyzed reactions of alkylidenecyclopropanes (ACPs) is described. The structure of the metallacycle was unambiguously determined by X-ray crystallography and is catalytically competent in the rhodium-catalyzed carbocyclization and ene-cycloisomerization reactions of ACPs. This work represents a rare example of the isolation of a metallacycle in a metal-catalyzed higher-order carbocyclization reaction and thereby provides important insight into the ligand requirements for the insertion of ?-components. Furthermore, it serves as a convenient synthon for the development of challenging higher-order carbocyclization reactions, as exemplified by the reaction with an activated allene. PMID:24616050

Inglesby, Phillip A; Bacsa, John; Negru, Daniela E; Evans, P Andrew

2014-04-01

309

Pd/C catalyzed Suzuki-Miyaura cross coupling reaction: Is it heterogeneous or homogeneous?  

NASA Astrophysics Data System (ADS)

The Suzuki-Miyaura cross-coupling reaction is a popular industrial method of creating covalent bonds between two carbons. This reaction can be catalyzed by a myriad of palladium catalyst including heterogeneous and homogeneous. The objective of this research is to study whether the Suzuki cross coupling reaction catalyzed by solid supported palladium catalysts is truly heterogeneous in nature (i.e. does the reaction occurs on the surface of the catalyst or does palladium leach from the solid support and catalyze the reaction in a homogenous manner).

Hoang, Tony Phuc

310

STM tip catalyzed adsorption of thiol molecules at the nanometer scale.  

PubMed

The tungsten oxide covered tungsten (W) tip of a scanning tunneling microscope was found to act as a catalyst to catalyze the S-H dissociative adsorption of phenylthiol and 1-octanethiol molecules onto a Ge(100) surface. By varying the distance between the tip and the surface, the area of the tip-catalyzed adsorption could be controlled. We have found that the thiol headgroup is the critical functional group for this catalysis and the catalytic material is the tungsten oxide layer of the tip. This local tip-catalyzed adsorption may be used in positive lithographic methods to produce nanoscale patterning on semiconductor substrates. PMID:20536126

Min, Young Hwan; Jung, Soon Jung; Youn, Young-Sang; Kim, Do Hwan; Kim, Sehun

2010-07-01

311

Structural Analysis of ATP Analogs Compatible with Kinase-Catalyzed Labeling  

PubMed Central

Kinase-catalyzed protein phosphorylation is an important biochemical process involved in cellular functions. We recently discovered that kinases promiscuously accept ?-modified ATP analogs as cosubstrates and used several ATP analogs as tools for studying protein phosphorylation. Herein, we explore the structural requirements of ?-modified ATP analogs for kinase compatibility. To understand the influence of linker length and composition, a series of ATP analogs was synthesized and the efficiency of kinase-catalyzed labeling was determined by quantitative mass spectrometry. This study on factors influencing kinase cosubstrate promiscuity will enable design of ATP analogs for a variety of kinase-catalyzed labeling reactions.

Suwal, Sujit; Senevirathne, Chamara; Garre, Satish; Pflum, Mary Kay H.

2012-01-01

312

Palladium-catalyzed regioselective azidation of allylic C-H bonds under atmospheric pressure of dioxygen.  

PubMed

A palladium-catalyzed allylic azidation of alkenes with sodium azide under atmospheric pressure of dioxygen was developed. This methodology provides a new efficient and simple route for accessing allylic azides. Furthermore, the one-pot process consisting of Pd-catalyzed allylic azidation of alkenes and Cu-catalyzed 1,3-dipolar cycloaddition led directly to the 1,2,3-triazole from the alkene. The formed allylic azide can be also in situ reduced to the allylic amine or oxidized to the alkenyl nitrile. PMID:24733286

Chen, Huoji; Yang, Wanfei; Wu, Wanqing; Jiang, Huanfeng

2014-06-01

313

Bonding by Hydroxide-Catalyzed Hydration and Dehydration  

NASA Technical Reports Server (NTRS)

A simple, inexpensive method for bonding solid objects exploits hydroxide-catalyzed hydration and dehydration to form silicate-like networks in thin surface and interfacial layers between the objects. The method can be practiced at room temperature or over a wide range of temperatures. The method was developed especially to enable the formation of precise, reliable bonds between precise optical components. The bonds thus formed exhibit the precision and transparency of bonds formed by the conventional optical-contact method and the strength and reliability of high-temperature frit bonds. The method also lends itself to numerous non-optical applications in which there are requirements for precise bonds and/or requirements for bonds, whether precise or imprecise, that can reliably withstand severe environmental conditions. Categories of such non-optical applications include forming composite materials, coating substrates, forming laminate structures, and preparing objects of defined geometry and composition. The method is applicable to materials that either (1) can form silicate-like networks in the sense that they have silicate-like molecular structures that are extensible into silicate-like networks or (2) can be chemically linked to silicate-like networks by means of hydroxide-catalyzed hydration and dehydration. When hydrated, a material of either type features surface hydroxyl (-OH) groups. In this method, a silicate-like network that bonds two substrates can be formed either by a bonding material alone or by the bonding material together with material from either or both of the substrates. Typically, an aqueous hydroxide bonding solution is dispensed and allowed to flow between the mating surfaces by capillary action. If the surface figures of the substrates do not match precisely, bonding could be improved by including a filling material in the bonding solution. Preferably, the filling material should include at least one ingredient that can be hydrated to have exposed hydroxyl groups and that can be chemically linked, by hydroxide catalysis, to a silicate-like network. The silicate-like network could be generated in situ from the filling material and/or substrate material, or could be originally present in the bonding material.

Gwo, Dz-Hung

2008-01-01

314

Acid-catalyzed Heterogeneous Reactions in SOA Formation  

NASA Astrophysics Data System (ADS)

The importance of heterogeneous reactions in secondary organic aerosol (SOA) formation has recently excited a great deal of interest in the aerosol community. Jang and Kamens (2001) showed enhanced aerosol yield from aldehydes, which can be produced by atmospheric photochemical reactions, in the presence of acidic seed. They suggest that the carbonyl functional groups of the aldehydes further react in the aerosol phase via hydration, polymerization, and hemiacetal/acetal formation with alcohols at an accelerated rate in the presence of acid. Jang et al. (2003) demonstrated similar results using a flow reactor and Czoschke et al. (in press) qualitatively showed increased yields for isoprene and alpha-pinene ozonolysis in the presence of acidic seed. While these findings are intriguing and important, the conditions under which the experiments were carried out were atmospherically unrealistic. A series of SOA formation experiments have been carried out in the Caltech Indoor Chamber Facility, which is comprised of dual 28 m3 FEP Teflon chambers, with the flexibility to carry out both dark ozonolysis and photochemical OH oxidation reactions. Cycloheptene and alpha-pinene were oxidized in the presence of neutral seed under dry (<10% RH) and humid (50% RH) conditions and in the presence of acidic seed under humid (50% RH) conditions. The SOA yields for these experiments will be presented, and the extent of the influence of acid-catalyzed reactions on SOA yield will be discussed. Reference List 1. Cocker, D. R. III. and R. C. Flagan and J. H. Seinfeld, State-of-the-art chamber facility for studying atmospheric aerosol chemistry, Environmental Science and Technology, 35, 2594-2601, 2001. 2. Czoschke, N. M., M. Jang, and R. M. Kamens, Effect of acid seed on biogenic sceondary organic aerosol growth, Atmospheric Environment, In press. 3. Jang, M., S. Lee, and R. M. Kamens, Organic aerosol growth by acid-catalyzed heterogeneous reactions of octanal in a flow reactor, Atmospheric Environment, 37, 2125-2138, 2003. 4. Jang, M. S. and R. M Kamens, Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst. Environmental Science and Technology, 35, 4758-4766,2001.

Ng, N.; Keywood, M.; Varutbangkul, V.; Gao, S.; Loewer, E.; Surratt, J.; Richard, F. C.; John, S. H.

2003-12-01

315

Exploring chain length selectivity in HIC-catalyzed polycondensation reactions.  

PubMed

Polyester synthesis activity of immobilized Humicola insolens (HiC) was systematically studied with three-series of substrates varying in (i) omega-hydroxyalkanoic acid (omegaHA), (ii) alpha,omega-n-alkane diol, and (iii) alpha,omega-n-alkane diacid chain length. Covalent immobilization of HiC on Amberzyme oxirane (AO) resin (i.e., AO-HiC) was prepared. HiC-AO's activity for omegaHA substrates with 6, 10, 12, and 16 carbons was C16 > C12, where C10-omegaHA and C6-omegaHA were not polymerized. In contrast, N435's activity for omegaHA substrates was C16 = C12 > C10, where C6-omegaHA was not polymerized. HiC-AO activity for copolymerization of sebacic acid (C10-diacid) with alpha,omega-n-alkane diols with 3-, 4-, 5-, 6-, and 8-carbon chain lengths was C8 > C6, where C3, C4, and C5 diols were not polymerized. N435's relative activity for diol substrates was C8 = C6 = C5 > C4 > C3. HiC-AO activity for copolymerizations of 1,8-octanediol with alpha,omega-n-alkane diacids with 6-, 8-, 9-, 10-, and 13-carbon chain lengths was C13 = C10, where HiC showed little activity for C6, C8, and C9 diacid copolymerization. N435 displayed similar activity for all these diacid chain lengths. Thus, N435 has a broader substrate promiscuity than HiC-AO. This is most apparent for shorter chain length omegaHA, diol, and diacid monomers. These trends were similarly observed for a series of small molecule esterification reactions. Comparison of HiC-AO- and N435-catalyzed C16-HA homopolymerization at 8 h gave polymers with M(n) 40.4 and 25.5 kg/mol, respectively. Furthermore, HiC-AO- and N435-catalyzed copolymerization of 1,8-octanediol/C13-diacid polymerizations at 8 h gave polymers with M(n) of 11.0 and 9.6 kg/mol, respectively. PMID:20095578

Feder, David; Gross, Richard A

2010-03-01

316

Pressure catalyzed bond dissociation in an anthracene cyclophane photodimer.  

PubMed

The anthracene cyclophane bis-anthracene (BA) can undergo a [4 + 4] photocycloaddition reaction that results in a photodimer with two cyclobutane rings. We find that the subsequent dissociation of the dimer, which involves the rupture of two carbon-carbon bonds, is strongly accelerated by the application of mild pressures. The reaction kinetics of the dimer dissociation in a Zeonex (polycycloolefin) polymer matrix were measured at various pressures and temperatures. Biexponential reaction kinetics were observed for all pressures, consistent with the presence of two different isomers of bis(anthracene). One of the rates showed a strong dependence on pressure, yielding a negative activation volume for the dissociation reaction of ?V(++) = -16 Å(3). The 93 kJ/mol activation energy for the dissociation reaction at ambient pressure is lowered by more than an order of magnitude from 93 to 7 kJ/mol with the application of modest pressure (0.9 GPa). Both observations are consistent with a transition state that is stabilized at higher pressures, and a mechanism for this is proposed in terms of a two-step process where a flattening of the anthracene rings precedes rupture of the cyclobutane rings. The ability to catalyze covalent bond breakage in isolated small molecules using compressive forces may present opportunities for the development of materials that can be activated by acoustic shock or stress. PMID:22486461

Jezowski, Sebastian R; Zhu, Lingyan; Wang, Yaobing; Rice, Andrew P; Scott, Gary W; Bardeen, Christopher J; Chronister, Eric L

2012-05-01

317

Kinetics of acid base catalyzed transesterification of Jatropha curcas oil.  

PubMed

Out of various non-edible oil resources, Jatropha curcas oil (JCO) is considered as future feedstock for biodiesel production in India. Limited work is reported on the kinetics of transesterification of high free fatty acids containing oil. The present study reports the results of kinetic study of two-step acid base catalyzed transesterification process carried out at an optimum temperature of 65 °C and 50 °C for esterification and transesterification respectively under the optimum methanol to oil ratio of 3:7 (v/v), catalyst concentration 1% (w/w) for H?SO? and NaOH. The yield of methyl ester (ME) has been used to study the effect of different parameters. The results indicate that both esterification and transesterification reaction are of first order with reaction rate constant of 0.0031 min?¹ and 0.008 min?¹ respectively. The maximum yield of 21.2% of ME during esterification and 90.1% from transesterification of pretreated JCO has been obtained. PMID:20570507

Jain, Siddharth; Sharma, M P

2010-10-01

318

Lipase catalyzed esterification of glycidol in organic solvents.  

PubMed

We studied the resolution of racemic glycidol through esterification with butyric acid catalyzed by porcine pancreatic lipase in organic media. A screening of seven solvents (log P values between 0.49 and 3.0, P being the n-octanol-water partition coefficient of the solvent) showed that neither log P nor the logarithm of the molar solubility of water in the solvent provides good correlations between enantioselectivity and the properties of the organic media. Chloroform was one of the best solvents as regards the enantiomeric purity (e. p.) of the ester produced. In this solvent, the optimum temperature for the reaction was determined to be 35 degrees C. The enzyme exhibited maximum activity at a water content of 13 +/- 2% (w/w). The enantiomeric purity obtained was 83 +/- 2% of (S)-glycidyl butyrate and did not depend on the alcohol concentration or the enzyme water content for values of these parameters up to 200 mM and 25% (w/w), respectively. The reaction was found to follow a BiBi mechanism. PMID:18613050

Martins, J F; Da Ponte, M N; Barreiros, S

1993-08-01

319

Temperature dependences of rate coefficients for electron catalyzed mutual neutralization  

SciTech Connect

The flowing afterglow technique of variable electron and neutral density attachment mass spectrometry (VENDAMS) has recently yielded evidence for a novel plasma charge loss process, electron catalyzed mutual neutralization (ECMN), i.e., A{sup +}+ B{sup -}+ e{sup -}{yields} A + B + e{sup -}. Here, rate constants for ECMN of two polyatomic species (POCl{sub 3}{sup -} and POCl{sub 2}{sup -}) and one diatomic species (Br{sub 2}{sup -}) each with two monatomic cations (Ar{sup +}and Kr{sup +}) are measured using VENDAMS over the temperature range 300 K-500 K. All rate constants show a steep negative temperature dependence, consistent with that expected for a three body process involving two ions and an electron. No variation in rate constants as a function of the cation type is observed outside of uncertainty; however, rate constants of the polyatomic anions ({approx}1 x 10{sup -18} cm{sup 6} s{sup -1} at 300 K) are measurably higher than that for Br{sub 2}{sup -}[(5.5 {+-} 2) x 10{sup -19} cm{sup 6} s{sup -1} at 300 K].

Shuman, Nicholas S.; Miller, Thomas M.; Friedman, Jeffrey F.; Viggiano, Albert A. [Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117 (United States); Maeda, Satoshi; Morokuma, Keiji [Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322 (United States)

2011-07-14

320

ATP-Independent Hydrocarbon Formation Catalyzed by Isolated Nitrogenase Cofactors  

PubMed Central

Nitrogenase is a highly complex and uniquely versatile metalloenzyme that is capable of reducing a broad spectrum of substrates, such as dinitrogen (N2), carbon monoxide (CO) and cyanide (CN-), under ambient conditions.[1-4] The molybdenum (Mo)- and vanadium (V)-nitrogenases are two homologous members of this enzyme family, both utilizing a specific reductase (Fe protein) to donate electrons to the cofactor site (FeMoco or FeVco) of a catalytic component (MoFe or VFe protein) during catalysis. The buried location of cofactor poses a challenge to electron transfer in this process, rendering it strictly dependent on ATP-assisted formation of an electron transport chain—within a complex between the reductase and the catalytic component—that extends all the way from the [Fe4S4] cluster of the former, via the P-cluster, to the cofactor site of the latter.[5] On the other hand, both FeMoco and FeVco can be extracted as intact entities into organic solvents,[6-8] spurring interest in seeking an ATP-independent reaction system, in which electrons can be directly delivered to the isolated cofactors for substrate reduction. In particular, the recent discovery that nitrogenases can reduce CO to hydrocarbons[3,4] makes it an attractive task to explore the capacity of cofactors to directly catalyze the formation of hydrocarbons from CO, as well as CN-—another carbonaceous molecule that is isoelectronic to CO.

Lee, Chi Chung; Hu, Yilin; Ribbe, Markus W.

2012-01-01

321

DNA damage by sulfite autoxidation catalyzed by cobalt complexes.  

PubMed

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 microM) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O2, DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO3 -, HO and H radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex. PMID:18854902

Alipázaga, María V; Moreno, Ruben G M; Linares, Edlaine; Medeiros, Marisa H G; Coichev, Nina

2008-11-01

322

Nanocrystalline TiO?-catalyzed photoreversible color switching.  

PubMed

We report a novel photoreversible color switching system based on the photocatalytic activity of TiO2 nanocrystals and the redox-driven color switching property of methylene blue (MB). This system rapidly changes from blue to colorless under UV irradiation and recovers its original blue color under visible light irradiation. We have identified four major competing reactions that contribute to the photoreversible switching, among which two are dominant: the decoloration process is mainly driven by the reduction of MB to leuco MB by photogenerated electrons from TiO2 nanocrystals under UV irradiation, and the recoloration process operates by the TiO2-induced self-catalyzed oxidation of LMB under visible irradiation. Compared with the conventional color switching systems based on photoisomerization of chromophores, our system has not only low toxicity but also significantly improved switching rate and cycling performance. It is envisioned that this photoreversible system may promise unique opportunities for many light-driven actuating or color switching applications. PMID:24555513

Wang, Wenshou; Ye, Miaomiao; He, Le; Yin, Yadong

2014-03-12

323

Stereochemistry and mechanism of reactions catalyzed by tryptophanase Escherichia coli.  

PubMed

Several beta replacement and alpha,beta elimination reactions catalyzed by tryptophanase from Escherichia coli are shown to proceed stereospecifically with retention of configuration. These conversions include synthesis of tryptophan from (2S,3R)- and (2s,3s)-[3(-3H)]serine in the presence of indole, deamination of these serines in D2O to pyruvate and ammonia, and cleavage of (2S,3R)-and (2S,3S)-[3(-3H)]tryptophan in D2O to indole, pyruvate, and ammonia. A coupled reaction with lactate dehydrogenase was used to trap the stereospecifically labeled [3-H,2H,3H]pryuvates as lactate, which was oxidized to acetate for chirality analysis of the methyl group. During deamination of tryptophan there is significant intramolecular transfer of the alpha proton of the amino acid to C-3 of indole. To determine the exposed face of the cofactor.substrate complex on the enzyme surface and to analyze its conformational orientation, sodium boro[3H]hydride was used to reduce tryptophanase-bound alaninepyridoxal phosphate Schiff's base. Degradation of the resulting pyridoxylalanine to (2S)-[2(-3H)]alanine and (4'S)-[4'(-3H)]pyridoxamine demonstrates that reduction occurs from the exposed si face at C-4' of the complex and that the ketimine double bond is trans. PMID:353050

Vederas, J C; Schleicher, E; Tsai, M D; Floss, H G

1978-08-10

324

Feasibility of an antiproton catalyzed fission fragment rocket  

SciTech Connect

The purpose of this project was to investigate the feasibility of an antiproton catalyzed fission fragment rocket (FFR). The FFR is characterized by the extraction of fission fragments from the fissile fuel, and the utilization of their kinetic energy for thrust generation. A significant drawback to previous FFR designs was the requirement to maintain a critical nuclear pile as the fission fragment source. The author examined the possibility of replacing the critical pile with a sub-critical pile driven by antiprotons. Recent experiments have revealed that antiprotons stimulate highly energetic fissions in {sup 238}U, with a neutron multiplicity of 13.7 neutrons per fission. This interaction was used as a throttled neutron source. The pile consisted of layers of fissile coated fibers which are designed to allow fission fragments to escape them, where the fragments collide with a fluid. The heated fluid is then ejected from the rocket to provide thrust. The calculations performed indicate that each antiproton injected into the pile can stimulate 8 or more fissions while maintaining a neutron multiplication of less than 0.4. Based on the results seen, the engine design presented is inadequate. Limitations introduced by the reaction fluid far outweigh the simplicity-of-design gained. Despite this, the basic idea of using the antiproton-U interaction as a source of spacecraft propulsion warrants further study.

Hdinger, D.S.

1992-03-01

325

A Personal Adventure in Muon-Catalyzed Fusion  

NASA Astrophysics Data System (ADS)

Luis Alvarez and colleagues discovered muon-catalyzed fusion of hydrogen isotopes by chance in late 1956. On sabbatical leave at Princeton University during that year, I read the first public announcement of the discovery at the end of December in that well-known scientific journal, The New York Times. A nuclear theorist by prior training, I was intrigued enough in the phenomenon to begin some calculations. I describe my work here, my interaction with Alvarez, and a summary of the surprising developments, both before and after Alvarez’s discovery. The rare proton-deuteron ( p-d) fusion events in Alvarez’s liquid-hydrogen bubble chamber occurred only because of the natural presence of a tiny amount of deuterium (heavy hydrogen). Additionally, the fusion rate, once the proton-deuteron-muon ( pd? - ) molecular ion has been formed, is sufficiently slow that only rarely does an additional catalytic act occur. A far different situation occurs for muons stopping in pure deuterium or a deuterium-tritium ( d- t) mixture where the fusion rates are many orders of magnitude larger and the molecular-formation rates are large compared to the muon’s decay rate. The intricate interplay of atomic, molecular, and nuclear science, together with highly fortuitous accidents in the molecular dynamics and the hope of practical application, breathed life into a seeming curiosity. A small but vigorous worldwide community has explored these myriad phenomena in the past 50 years.

Jackson, John David

2010-03-01

326

Broadening the scope of glycosyltransferase-catalyzed sugar nucleotide synthesis  

PubMed Central

We described the integration of the general reversibility of glycosyltransferase-catalyzed reactions, artificial glycosyl donors, and a high throughput colorimetric screen to enable the engineering of glycosyltransferases for combinatorial sugar nucleotide synthesis. The best engineered catalyst from this study, the OleD Loki variant, contained the mutations P67T/I112P/T113M/S132F/A242I compared with the OleD wild-type sequence. Evaluated against the parental sequence OleD TDP16 variant used for screening, the OleD Loki variant displayed maximum improvements in kcat/Km of >400-fold and >15-fold for formation of NDP–glucoses and UDP–sugars, respectively. This OleD Loki variant also demonstrated efficient turnover with five variant NDP acceptors and six variant 2-chloro-4-nitrophenyl glycoside donors to produce 30 distinct NDP–sugars. This study highlights a convenient strategy to rapidly optimize glycosyltransferase catalysts for the synthesis of complex sugar nucleotides and the practical synthesis of a unique set of sugar nucleotides.

Gantt, Richard W.; Peltier-Pain, Pauline; Singh, Shanteri; Zhou, Maoquan; Thorson, Jon S.

2013-01-01

327

Production of Chemoenzymatic Catalyzed Monoepoxide Biolubricant: Optimization and Physicochemical Characteristics  

PubMed Central

Linoleic acid (LA) is converted to per-carboxylic acid catalyzed by an immobilized lipase from Candida antarctica (Novozym 435). This per-carboxylic acid is only intermediate and epoxidized itself in good yields and almost without consecutive reactions. Monoepoxide linoleic acid 9(12)-10(13)-monoepoxy 12(9)-octadecanoic acid (MEOA) was optimized using D-optimal design. At optimum conditions, higher yield% (82.14) and medium oxirane oxygen content (OOC) (4.91%) of MEOA were predicted at 15??L of H2O2, 120?mg of Novozym 435, and 7?h of reaction time. In order to develop better-quality biolubricants, pour point (PP), flash point (FP), viscosity index (VI), and oxidative stability (OT) were determined for LA and MEOA. The results showed that MEOA exhibited good low-temperature behavior with PP of ?41°C. FP of MEOA increased to 128°C comparing with 115°C of LA. In a similar fashion, VI for LA was 224 generally several hundred centistokes (cSt) more viscous than MEOA 130.8. The ability of a substance to resist oxidative degradation is another important property for biolubricants. Therefore, LA and MEOA were screened to measure their OT which was observed at 189 and 168°C, respectively.

Salimon, Jumat; Salih, Nadia; Abdullah, Bashar Mudhaffar

2012-01-01

328

Dephenolization of industrial wastewaters catalyzed by polyphenol oxidase  

SciTech Connect

A new enzymatic method for the removal of phenols from industrial aqueous effluents has been developed. The method uses the enzyme polyphenol oxidase which oxidizes phenols to the corresponding o-quinones; the latter then undergo a nonenzymatic polymerization to form water-insoluble aggregates. Therefore, the enzyme in effect precipitates phenols from water. Polyphenol oxidase has been found to nearly completely dephenolize solutions of phenol in the concentration range from 0.01 to 1.0 g/L. The enzymatic treatment is effective over a wide range of pH and temperature; a crude preparation of polyphenol oxidase (mushroom extract) is as effective as a purified, commercially obtained version. In addition to phenol itself, polyphenol oxidase is capable of precipitating from water a number of substituted phenols (cresols, chlorophenols, naphthol, etc.). Also, even pollutants which are unreactive towards polyphenol oxidase can be enzymatically coprecipitated with phenol. The polyphenol oxidase treatment has been successfully used to dephenolize two different real industrial wastewater samples, from a plant producing triarylphosphates and from a coke plant. The advantage of the polyphenol oxidase dephenolization over the peroxidase-catalyzed one previously elaborated by the authors is that the former enzyme uses molecular oxygen instead of costly hydrogen peroxide (used by peroxidase) as an oxidant.

Atlow, S.C.; Bonadonna-Aparo, L.; Klibanov, A.M.

1984-01-01

329

Dynamin-Catalyzed Membrane Fission Requires Coordinated GTP Hydrolysis  

PubMed Central

Dynamin is the most-studied membrane fission machinery and has served as a paradigm for studies of other fission GTPases; however, several critical questions regarding its function remain unresolved. In particular, because most dynamin GTPase domain mutants studied to date equally impair both basal and assembly-stimulated GTPase activities, it has been difficult to distinguish their respective roles in clathrin-mediated endocytosis (CME) or in dynamin catalyzed membrane fission. Here we compared a new dynamin mutant, Q40E, which is selectively impaired in assembly-stimulated GTPase activity with S45N, a GTP-binding mutant equally defective in both basal and assembly-stimulated GTPase activities. Both mutants potently inhibit CME and effectively recruit other endocytic accessory proteins to stalled coated pits. However, the Q40E mutant blocks at a later step than S45N, providing additional evidence that GTP binding and/or basal GTPase activities of dynamin are required throughout clathrin coated pit maturation. Importantly, using in vitro assays for assembly-stimulated GTPase activity and membrane fission, we find that the latter is much more potently inhibited by both dominant-negative mutants than the former. These studies establish that efficient fission from supported bilayers with excess membrane reservoir (SUPER) templates requires coordinated GTP hydrolysis across two rungs of an assembled dynamin collar.

Liu, Ya-Wen; Mattila, Juha-Pekka; Schmid, Sandra L.

2013-01-01

330

Muon reactivation in muon-catalyzed D-T fusion  

NASA Astrophysics Data System (ADS)

We comprehensively reanalyze and search for the density dependence of the effective muon alpha sticking fraction ?sff observed experimentally in muon catalyzed deuterium-tritium fusion. In our work particular emphasis has been put on the density dependent dense hydrogen stopping power. The main technical details and improvements in this work are: The (??) + 2s and 2p states are treated independently and are assigned individual reaction rates. The essential muonic excitation rates have been recalculated taking into account finite nuclear mass effects. The stopping power for a charged projectile in liquid heavy hydrogen is modified to account for dynamic screening effects and a density dependent effective ionization potential. It is shown that the medium dependent stopping power for the (??) + ion is the crucial factor controlling the density dependence of the effective sticking fraction. It is also pointed out that the muonic helium K ? X-ray yield and the sticking fraction at high density can not be simultaneously brought into agreement with the experimental results without invoking novel mechanisms suppressing Stark mixing in the (He?) L-shell.

Rafelski, H. E.; Müller, B.; Rafelski, J.; Trautmann, D.; Viollier, R. D.

331

Study of muon catalyzed dd-fusion in HD gas  

NASA Astrophysics Data System (ADS)

The results of an experiment on muon catalyzed dd-fussion in HD gas are presented. The experiment was performed at the muon beam of PSI using a high-pressure ionization chamber filled with pure HD-gas of low D2 concentration on the level 1%, at temperatures 50, 150 and 300 K. The non-resonant character of dd?-molecule formation on HD molecules was confirmed by measuring the ratio of yields of the two dd?-fusion channels, R=Y(3He,n)/Y(3H,p), which proved to be close to unity. The dd? formation rate was found to vary from ?dd?-HD=0.05· 106 s-1 at T=50 K to ?dd?-HD=0.12· 106 s-1 at T=300 K, in agreement with the theoretical prediction. A prominent peak at t<60 ns was observed in the time spectrum of fusion neutrons indicating a resonant contribution of dd? formation from epithermal d? atoms.

Semenchuk, G. G.; Balin, D. V.; Case, T.; Crowe, K. M.; Ganzha, V. A.; Hartmann, F. J.; Kozlov, S. M.; Lauss, B.; Maev, E. M.; Mühlbauer, M.; Petitjean, C.; Petrov, G. E.; Sadetsky, S. M.; Schapkin, G. N.; Schott, W.; Smirenin, Yu. V.; Soroka, M. A.; Vasiliev, A. A.; Vorobyov, A. A.; Voropaev, N. I.; Zmeskal, J.

1999-06-01

332

Ceramide Glycosylation Catalyzed by Glucosylceramide Synthase and Cancer Drug Resistance  

PubMed Central

Glucosylceramide synthase (GCS), converting ceramide to glucosylceramide, catalyzes the first reaction of ceramide glycosylation in sphingolipid metabolism. This glycosylation by GCS is a critical step regulating the modulation of cellular activities by controlling ceramide and glycosphingolipids (GSLs). An increase of ceramide in response to stresses, such as chemotherapy, drives cells to proliferation arrest and apoptosis or autophagy; however, ceramide glycosylation promptly eliminates ceramide and consequently, these induced processes, thus protecting cancer cells. Furthermore, persistently enhanced ceramide glycosylation can increase GSLs, participating in selecting cancer cells to drug resistance. GCS is overexpressed in diverse drug-resistant cancer cells and in tumors of breast, colon, and leukemia that display poor response to chemotherapy. As ceramide glycosylation by GCS is a rate-limiting step in GSL synthesis, inhibition of GCS sensitizes cancer cells to anticancer drugs and eradicates cancer stem cells. Mechanistic studies indicate that uncoupling ceramide glycosylation can modulate gene expression, decreasing MDR1 through the cSrc/?-catenin pathway and restoring p53 expression via RNA splicing. These studies not only expand our knowledge in understanding how ceramide glycosylation affects cancer cells, but also provide novel therapeutic approaches for targeting refractory tumors.

Liu, Yong-Yu; Li, Yu-Teh

2014-01-01

333

Transamidation of Carboxamides Catalyzed by Fe(III) and Water.  

PubMed

The highly efficient transamidation of several primary, secondary, and tertiary amides with aliphatic and aromatic amines (primary and secondary) is described. The reaction is performed in the presence of a 5 mol % concentration of different hydrated salts of Fe(III), and the results show that the presence of water is crucial. The methodology was also applied to urea and phthalimide to demonstrate its versatility and wide substrate scope. An example of its use is an intramolecular application in the synthesis of 2,3-dihydro-5H-benzo[b]-1,4-thiazepin-4-one, which is the bicyclic core of diltiazem and structurally related drugs (Budriesi, R.; Cosimelli, B.; Ioan, P.; Carosati, E.; Ugenti, M. P.; Spisani, R. Curr. Med. Chem. 2007, 14, 279-287). A plausible mechanism that explains the role of water is proposed on the basis of experimental observations and previous mechanistic suggestions for transamidation reactions catalyzed by transition metals such as copper and aluminum. This methodology represents a significant improvement over other existing methods; it can be performed in air and with wet or technical grade solvents. PMID:24758779

Becerra-Figueroa, Liliana; Ojeda-Porras, Andrea; Gamba-Sánchez, Diego

2014-05-16

334

MEMS-based satellite micropropulsion via catalyzed hydrogen peroxide decomposition  

NASA Astrophysics Data System (ADS)

Microelectromechanical systems (MEMS) techniques offer great potential in satisfying the mission requirements for the next generation of miniaturized spacecraft being designed by NASA and Department of Defense agencies. More commonly referred to as `nanosats', these spacecraft feature masses in the range of 10-100 kg and therefore have unique propulsion requirements. The propulsion systems must be capable of providing extremely low levels of thrust and impulse while also satisfying stringent demands on size, mass, power consumption and cost. We begin with an overview of micropropulsion requirements and some current MEMS-based strategies being developed to meet these needs. The remainder of the paper focuses on the progress being made at NASA Goddard Space Flight Center toward the development of a prototype monopropellant MEMS thruster which uses the catalyzed chemical decomposition of high-concentration hydrogen peroxide as a propulsion mechanism. The products of decomposition are delivered to a microscale converging/diverging supersonic nozzle, which produces the thrust vector; the targeted thrust level is approximately 500 µN with a specific impulse of 140-180 s. Macroscale hydrogen peroxide thrusters have been used for satellite propulsion for decades; however, the implementation of traditional thruster designs on the MEMS scale has uncovered new challenges in fabrication, materials compatibility, and combustion and hydrodynamic modeling. A summary of the achievements of the project to date is given, as is a discussion of remaining challenges and future prospects.

Hitt, Darren L.; Zakrzwski, Charles M.; Thomas, Michael A.

2001-12-01

335

Some effects on the kinetics of muon-catalyzed fusion  

SciTech Connect

Two important stages in the kinetics of muon-catalyzed d-t fusion are discussed: (1) atomic thermalization and hyperfine-state relaxation preceding molecular formation and (2) muon stripping and x-ray production if sticking occurs after nuclear fusion. Thermalization is accurately treated by Monte Carlo simulation. It is shown that thermalization and triplet quenching of the ..cap alpha mu.. atom may not finish before dt..mu.. formation in low-tritium targets, but that epithermal transients are most important in high-tritium targets. A complete kinetic treatment of muon stripping from ..cap alpha mu.. is made using newly calculated stripping (ionization and charge transfer) and inelastic excitation cross sections and explicitly treating the 2s-2p Stark mixing. The calculated values of the sticking probability and K..cap alpha.. ..cap alpha mu.. x-rays per fusion are ..omega../sub s/ = 0.53% (0.59%) and I/sub K..cap alpha..//chi = 0.23% (0.28%) at density phi = 1.2 (0.1) times liquid-hydrogen density. Sensitivities to the various kinetic rates are evaluated, and error bars are estimated.

Cohen, J.S.

1986-01-01

336

Kinetics of Platinum-Catalyzed Decomposition of Hydrogen Peroxide  

NASA Astrophysics Data System (ADS)

CIBA Vision Corporation markets a contact lens cleaning system that consists of an AOSEPT disinfectant solution and an AOSEPT lens cup. The disinfectant is a buffered 3.0% m/v hydrogen peroxide solution and the cup includes a platinum-coated AOSEPT disc. The hydrogen peroxide disinfects by killing bacteria, fungi, and viruses found on the contact lenses. Because the concentration of hydrogen peroxide needed to disinfect is irritating to eyes, the hydrogen peroxide needs to be neutralized, or decomposed, before the contact lenses can be used again. A general chemistry experiment is described where the kinetics of the catalyzed decomposition of the hydrogen peroxide are studied by measuring the amount of oxygen generated as a function of time. The order of the reaction with respect to the hydrogen peroxide, the rate constant, and the energy of activation are determined. The integrated rate law is used to determine the time required to decompose the hydrogen peroxide to a concentration that is safe for eyes.

Vetter, Tiffany A.; Colombo, D. Philip, Jr.

2003-07-01

337

Helium Catalyzed D-D Fusion in a Levitated Dipole  

NASA Astrophysics Data System (ADS)

Fusion research has focused on the goal of deuterium and tritium (D-T) fusion power because the reaction rate is large compared with the other fusion fuels: D-D or D-He3. Furthermore, the D-D cycle is difficult in traditional confinement devices, such as tokamaks, because good energy confinement is accompanied by good particle confinement which leads to an accumulation of ash. Fusion reactors based on the D-D reaction would be advantageous to D-T based reactors since they do not require the breeding of tritium and can reduce the flux of energetic neutrons that cause material damage. We propose a fusion power source based on the levitated dipole fusion concept that uses a "helium catalyzed D-D" fuel cycle, where rapid circulation of plasma allows the removal of tritium and the re-injection of the He3 decay product, eliminating the need for a massive blanket and shield. Stable dipole confinement derives from plasma compressibility instead of the magnetic shear and average good curvature. As a result, a dipole magnetic field can stabilize plasma at high beta while allowing large-scale adiabatic particle circulation. These properties may make the levitated dipole uniquely capable of achieving good energy confinement with low particle confinement. We find that a dipole based D-D power source can provide better utilization of magnetic field energy with a comparable mass power density to a D-T based tokamak power source.

Kesner, J.; Bromberg, L.; Garnier, D. T.; Hansen, A.; Mauel, M. E.

2003-10-01

338

Cyclophilin A catalyzes proline isomerization by an electrostatic handle mechanism.  

PubMed

Proline isomerization is a ubiquitous process that plays a key role in the folding of proteins and in the regulation of their functions. Different families of enzymes, known as "peptidyl-prolyl isomerases" (PPIases), catalyze this reaction, which involves the interconversion between the cis and trans isomers of the N-terminal amide bond of the amino acid proline. However, complete descriptions of the mechanisms by which these enzymes function have remained elusive. We show here that cyclophilin A, one of the most common PPIases, provides a catalytic environment that acts on the substrate through an electrostatic handle mechanism. In this mechanism, the electrostatic field in the catalytic site turns the electric dipole associated with the carbonyl group of the amino acid preceding the proline in the substrate, thus causing the rotation of the peptide bond between the two residues. We identified this mechanism using a combination of NMR measurements, molecular dynamics simulations, and density functional theory calculations to simultaneously determine the cis-bound and trans-bound conformations of cyclophilin A and its substrate as the enzymatic reaction takes place. We anticipate that this approach will be helpful in elucidating whether the electrostatic handle mechanism that we describe here is common to other PPIases and, more generally, in characterizing other enzymatic processes. PMID:24982184

Camilloni, Carlo; Sahakyan, Aleksandr B; Holliday, Michael J; Isern, Nancy G; Zhang, Fengli; Eisenmesser, Elan Z; Vendruscolo, Michele

2014-07-15

339

Chloroperoxidase-catalyzed enantioselective oxidations in hydrophobic organic media.  

PubMed

Chloroperoxidase from Caldariomyces fumago, a peroxidase that performs P450-like chemistry, was immobilized via covalent attachment into polyurethane foam as well as conjugated with a surfactant or polymer via colyophilization. The resulting preparations catalyzed enantio- and regioselective oxidations in hydrophobic organic media with tert-butyl hydroperoxide as the oxidant. Dried PUR-foam immobilized CPO mediated the selective oxidation of indole to 2-oxindole (regioselectivity: 99%) in water-saturated isooctane or 1-octanol. Thioanisole was converted into the corresponding (R)-sulfoxide (ee > 99%) in isooctane medium. The complexes of CPO with sodium octadecylsulphate or ethyl cellulose mediated the oxidation of thioanisole in water-immiscible organic media with variable enantioselectivity due to radical side-reactions. In the presence of alpha-tocopherol, acting as radical scavenger, the (R)-sulfoxide was formed with ee > 90%. The effect of the water activity on the catalytic activity of the complexes was investigated. The CPO complexes likewise mediated the regioselective oxidation of indole into 2-oxindole in water-saturated isooctane or 1-octanol and its kinetics were investigated. The reaction suffered from substrate inhibition when carried out in isooctane. PMID:11460242

van de Velde, F; Bakker, M; van Rantwijk, F; Sheldon, R A

2001-03-01

340

ATP-dependent nucleosome unwrapping catalyzed by human RAD51  

PubMed Central

Double-strand breaks (DSB) occur in chromatin following replication fork collapse and chemical or physical damage [Symington and Gautier (Double-strand break end resection and repair pathway choice. Annu. Rev. Genet. 2011;45:247–271.)] and may be repaired by homologous recombination (HR) and non-homologous end-joining. Nucleosomes are the fundamental units of chromatin and must be remodeled during DSB repair by HR [Andrews and Luger (Nucleosome structure(s) and stability: variations on a theme. Annu. Rev. Biophys. 2011;40:99–117.)]. Physical initiation of HR requires RAD51, which forms a nucleoprotein filament (NPF) that catalyzes homologous pairing and strand exchange (recombinase) between DNAs that ultimately bridges the DSB gap [San Filippo, Sung and Klein. (Mechanism of eukaryotic HR. Annu. Rev. Biochem. 2008;77:229–257.)]. RAD51 forms an NPF on single-stranded DNA and double-stranded DNA (dsDNA). Although the single-stranded DNA NPF is essential for recombinase initiation, the role of the dsDNA NPF is less clear. Here, we demonstrate that the human RAD51 (HsRAD51) dsDNA NPF disassembles nucleosomes by unwrapping the DNA from the core histones. HsRAD51 that has been constitutively or biochemically activated for recombinase functions displays significantly reduced nucleosome disassembly activity. These results suggest that HsRAD51 can perform ATP hydrolysis-dependent nucleosome disassembly in addition to its recombinase functions.

North, Justin A.; Amunugama, Ravindra; Klajner, Marcelina; Bruns, Aaron N.; Poirier, Michael G.; Fishel, Richard

2013-01-01

341

A Single Amino Acid Change Is Responsible for Evolution of Acyltransferase Specificity in Bacterial Methionine Biosynthesis  

Microsoft Academic Search

Bacteria and yeast rely on either homoserine transsuccinylase (HTS, metA) or homoserine transacetylase (HTA; met2) for the biosynthesis of methionine. Although HTS and HTA catalyze similar chemical reactions, these proteins are typically unrelated in both sequence and three-dimensional structure. Here we present the 2.0 resolution x-ray crystal structure of the Bacillus cereus metA protein in complex with homoserine, which provides

C. Zubieta; K. A. J. Arkus; R. E. Cahoon; J. M. Jez

2009-01-01

342

Existence of efficient divalent metal ion-catalyzed and inefficient divalent metal ion-independent channels in reactions catalyzed by a hammerhead ribozyme  

PubMed Central

The hammerhead ribozyme is generally accepted as a well characterized metalloenzyme. However, the precise nature of the interactions of the RNA with metal ions remains to be fully defined. Examination of metal ion-catalyzed hammerhead reactions at limited concentrations of metal ions is useful for evaluation of the role of metal ions, as demonstrated in this study. At concentrations of Mn2+ ions from 0.3 to 3 mM, addition of the ribozyme to the reaction mixture under single-turnover conditions enhances the reaction with the product reaching a fixed maximum level. Further addition of the ribozyme inhibits the reaction, demonstrating that a certain number of divalent metal ions is required for proper folding and also for catalysis. At extremely high concentrations, monovalent ions, such as Na+ ions, can also serve as cofactors in hammerhead ribozyme-catalyzed reactions. However, the catalytic efficiency of monovalent ions is extremely low and, thus, high concentrations are required. Furthermore, addition of monovalent ions to divalent metal ion-catalyzed hammerhead reactions inhibits the divalent metal ion-catalyzed reactions, suggesting that the more desirable divalent metal ion–ribozyme complexes are converted to less desirable monovalent metal ion–ribozyme complexes via removal of divalent metal ions, which serve as a structural support in the ribozyme complex. Even though two channels appear to exist, namely an efficient divalent metal ion-catalyzed channel and an inefficient monovalent metal ion-catalyzed channel, it is clear that, under physiological conditions, hammerhead ribozymes are metalloenzymes that act via the significantly more efficient divalent metal ion-dependent channel. Moreover, the observed kinetic data are consistent with Lilley’s and DeRose’s two-phase folding model that was based on ground state structure analyses.

Zhou, Jing-Min; Zhou, De-Min; Takagi, Yasuomi; Kasai, Yasuhiro; Inoue, Atsushi; Baba, Tadashi; Taira, Kazunari

2002-01-01

343

Oxidative tailoring reactions catalyzed by nonheme iron-dependent enzymes: streptorubin B biosynthesis as an example.  

PubMed

Tailoring enzymes catalyze reactions that modify natural product backbone structures before, during, or after their biosynthesis to create a final product with specific biological activities. Such reactions can be catalyzed by a myriad of different enzyme families and are responsible for a wide variety of transformations including regio- and/or stereospecific acylation, alkylation, glycosylation, halogenation, and oxidation. Within a broad group of oxidative tailoring enzymes, there is a rapidly growing family of nonheme iron- and oxygen-dependent enzymes that catalyze a variety of remarkable hydroxylation, desaturation, halogenation, and oxidative cyclization reaction in the biosynthesis of several important metabolites, including carbapenems, penicillins, cephalosporins, clavams, prodiginines, fosfomycin, syringomycin, and coronatine. In this chapter, we report an expedient method for analyzing tailoring enzymes that catalyze oxidative cyclization reactions in prodiginine biosynthesis via expression of the corresponding genes in a heterologous host, feeding of putative biosynthetic intermediates to the resulting strains, and liquid chromatography-mass spectrometry analyses of the metabolites produced. PMID:23034230

Sydor, Paulina K; Challis, Gregory L

2012-01-01

344

Copper-catalyzed oxyazidation of unactivated alkenes: a facile synthesis of isoxazolines featuring an azido substituent.  

PubMed

A novel and efficient Cu(OAc)2-catalyzed oxyazidation of unactivated alkenes was developed. The reactions are easy to conduct, occur under mild conditions, and form azido-substituted isoxazolines in good yields. PMID:24597742

Zhu, Liping; Yu, Hongmei; Xu, Zhaoqing; Jiang, Xianxing; Lin, Li; Wang, Rui

2014-03-21

345

Gold-catalyzed reactions of 2-alkynyl-phenylamines with alpha,beta-enones.  

PubMed

[reaction: see text] The gold-catalyzed reaction of 2-alkynyl-phenylamines with alpha,beta-enones represents a new general one-pot entry into C-3-alkyl-indoles by sequential reactions. Gold-catalyzed sequential cyclization/alkylation, N-alkylation/cyclization, or N-alkylation/cyclization/alkylation reactions leading to different indoles can be directed by changing the 2-alkynyl-phenylamine 1/alpha,beta-enone 3 ratio and the reaction temperature. Unusual gold-catalyzed rearrangement reaction of indoles are observed at 140 degrees C. New gold-catalyzed formation of propargyl-alkyl ether under mild conditions and the hydration reaction of N-acetyl-2-ethynyl-phenylamine are reported. PMID:15760214

Alfonsi, Maria; Arcadi, Antonio; Aschi, Massimiliano; Bianchi, Gabriele; Marinelli, Fabio

2005-03-18

346

New chiral ligands from myrtenal and caryophyllene for asymmetric oxydation of sulfides catalyzed by metal complexes  

Microsoft Academic Search

From myrtenal and caryophyllene, widespread terpene compounds, three new chiral Schiff bases were prepared suitable for ligands\\u000a in vanadium ions catalyzed sulfides oxidation to chiral sulfoxides.

T. M. Khomenko; O. V. Salomatina; S. Yu. Kurbakova; I. V. Il’ina; K. P. Volcho; N. I. Komarova; D. V. Korchagina; N. F. Salakhutdinov; A. G. Tolstikov

2006-01-01

347

Enzymatically-Catalyzed Polymerization (ECP)- Derived Polymer Electrolyte for Rechargeable Li-Ion Batteries.  

National Technical Information Service (NTIS)

Report developed under SBIR contract covers the syntheses and electrochemical characterizations of novel polymer electrolytes derived from compounds synthesized via enzyme-catalyzed polymerization(ECP) techniques. A reproducible method was developed to fu...

D. L. Chua H. Lin G. Wnek K. McGrady

1998-01-01

348

N-heterocyclic carbene-catalyzed highly enantioselective synthesis of substituted dihydropyranopyrazolones.  

PubMed

Highly optically pure multisubstituted dihydropyrano[2,3-c]pyrazol-6-(1H)-ones were synthesized via the N-heterocyclic carbene-catalyzed enantioselective [4 + 2] annulation of ?-chloroaldehydes and pyrazolone-derived oxodienes. PMID:23959516

Zhang, Han-Ming; Lv, Hui; Ye, Song

2013-10-01

349

Recent Developments in Pd-Catalyzed Alkene Aminoarylation Reactions for the Synthesis of Nitrogen Heterocycles  

PubMed Central

This short review describes new developments in Pd-catalyzed aminoarylation reactions between aryl halides and alkenes bearing pendant nitrogen nucleophiles. These transformations provide a novel and powerful method for accessing numerous 3-, 5-, 6-, and 7-membered nitrogen heterocycles.

Schultz, Danielle M.; Wolfe, John P.

2012-01-01

350

Rhodium-catalyzed carbene transfer to alkynes via 2-furylcarbenes generated from enynones.  

PubMed

A rhodium-catalyzed carbene transfer to alkynes is reported. Easily available enynones served as the carbene source replacing diazocompounds. The overall process involved a cyclization-cyclopropenation-ring enlargement sequence. PMID:24175321

González, María J; López, Enol; Vicente, Rubén

2014-05-25

351

Access to the protoilludane core by gold-catalyzed allene-vinylcyclopropane cycloisomerization.  

PubMed

Gold(I)-catalyzed allene-vinylcyclopropane cycloisomerization leads to the tricyclic framework of the protoilludanes in a single step by a reaction that involves a cyclopropane ring expansion and a Prins cyclization. PMID:23962171

Pitaval, Anthony; Leboeuf, David; Ceccon, Julien; Echavarren, Antonio M

2013-09-01

352

Dendronized cyclocopolymers with a radial gradient of polarity and their use to catalyze a difficult esterification.  

PubMed

A cyclocopolymer containing pyrrolidinopyridine pendant groups was dendronized with polyester dendrons terminated with long alkyl chain ends and the microenvironment created by the dendrons was used to catalyze the difficult esterification of a tertiary alcohol with pivalic anhydride. PMID:14594262

Liang, Catherine O; Helms, Brett; Hawker, Craig J; Fréchet, Jean M J

2003-10-21

353

OXIDATION OF CYCLOHEXANE WITH AIR CATALYZED BY A STERICALLY HINDERED IRON (II) COMPLEX  

EPA Science Inventory

Oxidation of Cyclohexane with Air Catalyzed by a Sterically Hindered Iron(II) Complex. Thomas M. Becker, Michael A. Gonzalez* United States Environmental Protection Agency; National Risk Management Research Laboratory; Sustainable Technology Division; Clean Pr...

354

Chiral Brønsted acid-catalyzed enantioselective addition of indoles to ketimines.  

PubMed

A highly enantioselective addition of indoles to a readily available ketimine was found to be catalyzed by a chiral phosphoric acid. This organocatalytic process represents a rare example of an addition reaction to a non-aromatic ketimine. PMID:24323293

Kano, Taichi; Takechi, Ryosuke; Kobayashi, Ryohei; Maruoka, Keiji

2014-02-01

355

Identification and stereochemistry of the product of 4-HPPD catalyzed oxidation of the ketoacid of methionine  

Microsoft Academic Search

4-Hydroxyphenylpyruvate dioxygenase catalyzes the conversion of 2-oxo-5-thiahexanoic acid 1, the ketoacid from methionine (Scheme 1) to an unequal mixture of 4-thiapentanoic acid-4-oxide enantiomers 2a.

Robert M. Adlington; Jack E. Baldwin; Nicholas P. Crouch; Meng-Huee Lee; Colin H. MacKinnon

1996-01-01

356

Facile and selective copper–palladium catalyzed addition of terminal alkynes to activated alkynes in water  

Microsoft Academic Search

The combination of palladium and copper catalyzes the addition of terminal alkynes to electron-deficient alkynes selectively and effectively in water without the competition of terminal alkynes’ homo-coupling.

Liang Chen; Chao-Jun Li

2004-01-01

357

lipase-catalyzed regioselective esterification of rapamycin: synthesis of temsirolimus (CCI-779).  

PubMed

A lipase-catalyzed acylation of the immunosuppressant rapamycin with complete regioselectivity is described. The method was successfully applied to the synthesis of 42-hemiesters and temsirolimus (CCI-779), an investigational oncology drug.[reaction: see text] PMID:16119938

Gu, Jianxin; Ruppen, Mark E; Cai, Ping

2005-09-01

358

Efficient and enantioselective nitroaldol reaction catalyzed by copper Schiff-base complexes  

Microsoft Academic Search

Mild and efficient enantioselective nitroaldol reactions of nitromethane with various aldehydes were catalyzed by chiral copper Schiff-base complexes, which can be readily prepared from amino acid, yielding the corresponding adducts with high yields and good enantiometric excess (ee).

Changsheng Gan; Guoyin Lai; Zuhui Zhang; Zhiyong Wang; Ming-Ming Zhou

2006-01-01

359

N-heterocyclic carbene catalyzed nucleophilic substitution reaction for construction of benzopyrones and benzofuranones.  

PubMed

N-Heterocyclic carbene as an efficient organic catalyst was employed to catalyze an intramolecular nucleophilic substitution reaction. When R(2) was a phenyl group, the cyclization process underwent isomerization, leading to generation of benzofuranone. PMID:16986969

He, Jinmei; Zheng, Jiyue; Liu, Jian; She, Xuegong; Pan, Xinfu

2006-09-28

360

Synthesis of fluorinated allenes via palladium-catalyzed monofluoromethylation using FBSM.  

PubMed

Palladium-catalyzed monofluoromethylation of substituted 2-bromo-1,3-dienes using fluorobis(phenylsulfonyl)methane (FBSM) as a pronucleophile gave previously unknown monofluoromethylated allenes in high yields, which are the isosteres of biologically attractive allenic alcohols. PMID:20024230

Ogasawara, Masamichi; Murakami, Hidetoshi; Furukawa, Tatsuya; Takahashi, Tamotsu; Shibata, Norio

2009-12-21

361

Ytterbium(III) triflate-catalyzed selective methanolysis of methoxyacetates: A new deprotective method  

SciTech Connect

The authors describe a novel method for the deprotection of the methoxyacetyl functionality under the catalytic influence of ytterbium(III) triflates. The ytterbium complex catalyzes the alcoholysis of methoxyacetyl under nonbasic conditions. The results for nine esters are reported.

Hanamoto, Takeshi; Sugimoto, Yuichi; Yokoyama, Yasuo; Inanaga, Junji [Inst. for Molecular Science, Okazaki (Japan)] [Inst. for Molecular Science, Okazaki (Japan); [Kyushu Univ., Fukuoka (Japan)

1996-06-28

362

Addition reaction of dialkyl disulfides to terminal alkynes catalyzed by a rhodium complex and trifluoromethanesulfonic acid.  

PubMed

[reaction: see text]. Addition of dialkyl disulfides to terminal alkynes is catalyzed by a rhodium-phosphine complex and trifluoromethanesulfonic acid giving (Z)-bis(alkylthio)olefins stereoselectively. PMID:11259056

Arisawa, M; Yamaguchi, M

2001-03-01

363

Copper(I)-catalyzed cascade dearomatization of 2-substituted tryptophols with iodonium [corrected] salts.  

PubMed

Copper(I)-catalyzed dearomative arylation and vinylation of 2-substituted tryptophols were realized with a subsequent cyclization reaction. The cascade dearomatization sequence provided versatile furoindoline derivatives with two quaternary carbon centers in good to excellent yields. PMID:22891935

Liu, Chuan; Zhang, Wei; Dai, Li-Xin; You, Shu-Li

2012-09-01

364

Superconductive Contacts with Hydroxide-catalyzed Bonds that Retain Superconductivity and Provide Mechanical fastening Strength.  

National Technical Information Service (NTIS)

A superconductive contact or contact structure composed mainly of superconductors and a hydroxide-catalyzed bond that establishes electrical contacts, retains superconductivity, and provides the full mechanical fastening strength between the superconducto...

D. Gwo, J. Mester

2004-01-01

365

Enantioselective Palladium-Catalyzed [3+2] Cycloadditions of Trimethylenemethane with Nitroalkenes  

PubMed Central

Nitroalkenes readily undergo palladium-catalyzed [3+2] cycloaddition with trimethylenemethane to generate nitrocyclopentanes in excellent yield and enantioselectivity. Furthermore, the products thus formed are highly versatile synthetic intermediates and provide convenient access to both cyclopentylamines and cyclopentenones.

Trost, Barry M.; Bringley, Dustin A.; Seng, Pamela S.

2012-01-01

366

Nickel-Catalyzed Borylation of Halides and Pseudo-Halides with Tetrahydroxydiboron [B2(OH)4  

PubMed Central

Arylboronic acids are gaining increased importance as reagents and target structures in a variety of useful applications. Recently, the palladium-catalyzed synthesis of arylboronic acids employing the atom economical tetrahydroxydiboron (BBA) reagent has been reported. The high cost associated with palladium, combined with several limitations of both palladium and copper-catalyzed processes, prompted us to develop an alternative method. Thus, the nickel-catalyzed borylation of aryl and heteroaryl halides and pseudo-halides using tetrahydroxydiboron (BBA) has been formulated. The reaction proved to be widely functional group tolerant and applicable to a number of heterocyclic systems. To the best of our knowledge, the examples presented here represent the only effective Ni-catalyzed Miyaura borylations conducted at room temperature.

Molander, Gary A.; Cavalcanti, Livia N.; Garcia-Garcia, Carolina

2013-01-01

367

PALLADIUM-CATALYZED OXIDATION OF STYRENE AND ALKENES IN PRESENCE OF IONIC LIQUIDS (WACKER REACTION)  

EPA Science Inventory

The use of ionic liquids in various synthetic transformations is gaining significance due to the enhanced reaction rates, potential for recycling and compatibility with various organic compounds and organometallic catalysts. Palladium-catalyzed oxidation of styrene and other alk...

368

Palladium-Catalyzed Ortho-Alkoxylation of 2-Aryl-1,2,3-triazoles.  

PubMed

Palladium-catalyzed alkoxylation of 2-aryl-1,2,3-triazoles was described in the presence of various groups in the aromatic rings. In addition, some other directing groups of heterocycles containing nitrogen were explored. PMID:24915142

Shi, Suping; Kuang, Chunxiang

2014-07-01

369

Carbon Isotope Systematics in Mineral-Catalyzed Hydrothermal Organic Synthesis Processes at High Temperature and Pressures.  

National Technical Information Service (NTIS)

Observation of methane in the Martian atmosphere has been reported by different detection techniques. Reduction of CO2 and/or CO during serpentization by mineral surface catalyzed Fischer-Tropsch Type (FTT) synthesis may be one possible process responsibl...

P. B. Niles Q. Fu R. A. Socki

2011-01-01

370

Silver-catalyzed PuO sub 2 dissolution with persulfate  

SciTech Connect

This report consists of 14 slides and associated narrative for a presentation to be given at the 15th Annual Actinide Separations Conference on silver-catalyzed PuO{sub 2} dissolution with persulfate. (JL)

Fisher, F D; Barney, G S; Cooper, T D; Duchsherer, M J

1991-06-01

371

Bi(OTf)3-catalyzed three-component synthesis of ?-amino acid derivatives.  

PubMed

A highly efficient Bi(OTf)3-catalyzed multicomponent synthesis of arylglycines from readily available starting materials is described. The reaction proceeds under mild conditions and provides a general route to various N-protected arylglycines. PMID:24599384

Schneider, Angelika E; Beisel, Tamara; Shemet, Andrej; Manolikakes, Georg

2014-04-21

372

Iron-catalyzed tetrasubstituted alkene formation from alkynes and sodium sulfinates.  

PubMed

An iron-catalyzed sulfenylation and arylation of alkynes with aryl sulfinic acid sodium salts is described. Various aromatic sodium sulfinates acted both as aryl and sulfenylation reagents, affording tetrasubstituted alkenes in one pot with good yields. PMID:25001418

Liu, Saiwen; Tang, Lichang; Chen, Hui; Zhao, Feng; Deng, Guo-Jun

2014-08-28

373

Efficient and Stereoselective Synthesis of Yellow Scale Pheromone via Alkyne Haloboration, Zr-Catalyzed Asymmetric Carboalumination of Alkenes (ZACA Reaction), and Pd-Catalyzed Tandem Negishi Coupling  

PubMed Central

A Pd-catalyzed reaction of allylzincs with the 1-octyne bromoboration product gives the desired allyl-alkenyl coupling products in good yields except with H2C=CHCH2ZnBr. This reaction is suitable for converting an alkyne bromoboration product 3 into 4 with no isomerization or ?-elimination. The Pd-catalyzed isoalkyl-alkenyl coupling of 4 with the isoalkylzinc reagent derived from 2 provides yellow scale pheromone (1) of ?98% isomeric purity in 34% in six steps from TBDPS-protected homoallyl alcohol.

Xu, Zhaoqing; Negishi*, Ei-ichi

2008-01-01

374

Synthesis of terminal Si–H irregular tetra-branched star polysiloxanes. Pt-catalyzed hydrosilylation with unsaturated epoxides. Polysiloxane films by photo-acid catalyzed crosslinking  

Microsoft Academic Search

Acid catalyzed insertion of octamethylcyclotetrasiloxane (D4) into the Si–O bonds of tetrakis(dimethylsiloxy)silane leads to irregular tetra-branched star polymers—tetrakis(?-dimethylsiloxy)poly(dimethylsiloxy)silane (I). The terminal Si–H bonds of I have been modified by Pt-catalyzed hydrosilylation with 4-vinylcyclohexane-1,2-epoxide to yield a tetra-branched star polydimethylsiloxanes (PDMS) with terminal 2?-ethyl-4-cyclohexanyl-1,2-epoxide groups (II). Solutions of this material and a catalytic amounts of diaryl iodonium hexafluoroantimonate, a photo-acid catalyst,

Guoping Cai; William P Weber

2004-01-01

375

Optimization of Lipase-Catalyzed Transesterification of Lard for Biodiesel Production Using Response Surface Methodology  

Microsoft Academic Search

Biodiesel, an alternative diesel fuel made from renewable biological resources, has become more and more attractive recently.\\u000a Combined use of two immobilized lipases with complementary position specificity instead of one lipase is a potential way to\\u000a significantly reduce cost of lipase-catalyzed biodiesel production. In this study, the process of biodiesel production from\\u000a lard catalyzed by the combined use of Novozym435

Ying Huang; Hai Zheng; Yunjun Yan

2010-01-01

376

Nickel-Catalyzed Amination of Aryl Sulfamates and Carbamates Using an Air-Stable Precatalyst  

PubMed Central

A facile nickel-catalyzed method to achieve the amination of synthetically useful aryl sulfamates and carbamates is reported. Contrary to most Ni-catalyzed amination reactions, this user-friendly approach relies on an air-stable Ni(II) precatalyst, which, when employed with a mild reducing agent, efficiently delivers aminated products in good to excellent yields. The scope of the method is broad with respect to both coupling partners and includes heterocyclic substrates.

Hie, Liana; Ramgren, Stephen D.; Mesganaw, Tehetena; Garg, Neil K.

2012-01-01

377

Ruthenium-catalyzed oxidation of allyl alcohols with intermolecular hydrogen transfer: synthesis of ?,?-unsaturated carbonyl compounds.  

PubMed

Ruthenium-catalyzed oxidation of multisubstituted allyl alcohols in the presence of benzaldehyde gives enals or enones in good yields. Unlike the commonly reported ruthenium-catalyzed isomerization reaction of allyl alcohols to give saturated ketones, an intermolecular rather than intramolecular hydrogen transfer is involved in this transformation. This reaction offers an efficient, mild, and high-yielding method for the preparation of substituted ?,?-unsaturated compounds. PMID:24571413

Ren, Kai; Hu, Bei; Zhao, Mengmeng; Tu, Yahui; Xie, Xiaomin; Zhang, Zhaoguo

2014-03-01

378

Stereoselective synthesis of 2,5-disubstituted morpholines using a palladium-catalyzed hydroamination reaction.  

PubMed

A palladium-catalyzed hydroamination reaction is the key step in a stereoselective synthesis of 2,5-disubstituted and 2,3,5-trisubsituted morpholines from carbamate-protected aziridines. Aziridines are selectively attacked at the more substituted position by unsaturated alcohol nucleophiles using Lewis acid catalysts. Palladium-catalyzed hydroamination of the resulting aminoalkenes gives morpholines as a single diastereomer in excellent yield. PMID:23784260

McGhee, Alicia; Cochran, Brian M; Stenmark, Torrey A; Michael, Forrest E

2013-08-01

379

Palladium-catalyzed chemoselective decarboxylative ortho acylation of benzoic acids with ?-oxocarboxylic acids.  

PubMed

Palladium-catalyzed chemoselective decarboxylative cross coupling of benzoic acids with ?-oxocarboxylic acids was realized via an arene sp(2) C-H functionalization process. This work represents the first example of transition-metal-catalyzed cross-coupling reactions with two acids acting in different roles. The synthetic utility of this method was confirmed by the synthesis of pitofenone, an antispasmodic used in the combined drug Spasmalgon. PMID:23721458

Miao, Jinmin; Ge, Haibo

2013-06-21

380

Mineralization of paracetamol by ozonation catalyzed with Fe 2+, Cu 2+ and UVA light  

Microsoft Academic Search

Acid solutions containing up to 1gl?1 of the drug paracetamol have been treated with ozone alone and ozonation catalyzed with Fe2+, Cu2+ and\\/or UVA light at 25.0°C. Direct ozonation yields poor degradation due to the high stability of final carboxylic acids formed, whereas more than 83% of mineralization is attained with the catalyzed methods. Under UVA irradiation, organics can be

Marcel Skoumal; Pere-Lluís Cabot; Francesc Centellas; Conchita Arias; Rosa María Rodríguez; José Antonio Garrido; Enric Brillas

2006-01-01

381

Transition-Metal-Catalyzed Denitrogenative Transannulation: Converting Triazoles into Other Heterocyclic Systems  

PubMed Central

Transition metal catalyzed denitrogenative transannulation of a triazole ring has recently received considerable attention as a new concept for the construction of diverse nitrogen-containing heterocyclic cores. This method allows a single-step synthesis of complex nitrogen heterocycles from easily available and cheap triazole precursors. In this Minireview, recent progress of the transition metal catalyzed denitrogenative transannulation of a triazole ring, which was discovered in 2007, is discussed.

Chattopadhyay, Buddhadeb

2012-01-01

382

Chiral Phosphoric Acid-Catalyzed Asymmetric Transfer Hydrogenation of Quinolin-3-amines.  

PubMed

A chiral phosphoric acid catalyzed asymmetric transfer hydrogenation of aromatic amines, quinolin-3-amines, was successfully developed with up to 99% ee. To supplement our previous work on the Ir-catalyzed asymmetric hydrogenation of 2-alkyl substituted quinolin-3-amines, a number of 2-aryl substituted substrates were reduced to provide a series of valuable chiral exocyclic amines with high diastereo- and enantioselectivities. PMID:24766611

Cai, Xian-Feng; Guo, Ran-Ning; Feng, Guang-Shou; Wu, Bo; Zhou, Yong-Gui

2014-05-16

383

Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase  

PubMed Central

Waves and patterns in living systems are often driven by biochemical reactions with enzymes as catalysts and regulators. We present a reaction–diffusion system catalyzed by the enzyme glucose oxidase that exhibits traveling wave patterns in a spatially extended medium. Fronts and pulses propagate as a result of the coupling between the enzyme-catalyzed autocatalytic production and diffusion of hydrogen ions. A mathematical model qualitatively explains the experimental observations.

Miguez, David G.; Vanag, Vladimir K.; Epstein, Irving R.

2007-01-01

384

Silver-catalyzed decarboxylative trifluoromethylthiolation of aliphatic carboxylic acids in aqueous emulsion.  

PubMed

A silver-catalyzed decarboxylative trifluoromethylthiolation of secondary and tertiary carboxylic acids under mild conditions tolerates a wide range of functional groups. The reaction was dramatically accelerated by its performance in an aqueous emulsion, which was formed by the addition of sodium dodecyl sulfate to water. It was proposed that the radical, which was generated from the silver-catalyzed decarboxylation in the "oil-in-water" droplets, could easily react with the trifluoromethylthiolating reagent to form the product. PMID:24764209

Hu, Feng; Shao, Xinxin; Zhu, Dianhu; Lu, Long; Shen, Qilong

2014-06-10

385

Functional Effects of Casein Kinase I-Catalyzed Phosphorylation on Lens Cell-to-Cell Coupling  

Microsoft Academic Search

.   The functional consequence of the casein kinase I-catalyzed phosphorylation of the lens gap junctional protein connexin49\\u000a was investigated using a sheep primary lens cell culture system. To determine whether the phosphorylation of connexin49 catalyzed\\u000a by endogenous casein kinase I results in an altered junctional communication between lens cells, the effect of the casein\\u000a kinase I-specific inhibitor CKI-7 on Lucifer

Hsueh-Ling Cheng; Charles F. Louis

2001-01-01

386

Microwave-Assisted Base-Catalyzed Decomposition Process for the Degradation of Polychlorinated Biphenyl  

Microsoft Academic Search

Microwave irradiation was adopted to combine with the traditional base-catalyzed decomposition (BCD) process for the degradation of polychlorinated biphenyl, thus formed the so-called microwave-assisted base-catalyzed decomposition (MA-BCD) process. 2, 4, 5-trichlorobiphenyl (PCB29) dissolved in hexane or cetane was used to test the effectiveness of the MA-BCD process, where the solvent acted both as reaction medium and as hydrogen donor. The

Xitao Liu; Wei Zhao

2010-01-01

387

Mechanism of base-catalyzed Schiff base deprotonation in halorhodopsin  

SciTech Connect

It has been shown earlier that the deprotonation of the Schiff base of illuminated halorhodopsin proceeds with a much lower pK/sub a/ than that of the unilluminated pigment and the reversible protonation change is catalyzed by azide and cyanate. The authors have studied the kinetics of the proton-transfer events with flash spectroscopy and compared a variety of anionic bases with different pK/sub a/ with regard to the apparent binding constants and the catalytic activities. The results suggest a general base catalysis mechanism in which the anionic bases bind with apparently low affinity to halorhodopsin, although with some degree of size- and/or shape-dependent specificity. The locus of the catalysis is accessible from the cytoplasmic side of the membrane and is not at site I, where various anions bind and shift the pK/sub a/ of the deprotonation. Neither is it at site II, where a few specific anions (like chloride) bind to the all-trans pigment. It may be concluded that while the all-trans pigment loses its Schiff base proton very rapidly at its pK/sub a/, there is a kinetic barrier to this deprotonation in the 13-cis photointermediate that can be partially overcome by the reversible protonation of an extrinsic anionic base, which shuttles protons between the interior of the protein and the aqueous medium. The need for an extrinsic proton acceptor for efficient deprotonation of the Schiff base of halorhodopsin is one of the main differences between this pigment and the analogous retinal protein, bacteriorhodopsin.

Lanyi, J.K.

1986-10-21

388

The mechanism for iron-catalyzed alkene isomerization in solution  

SciTech Connect

Here we report nano- through microsecond time-resolved IR experiments of iron-catalyzed alkene isomerization in room-temperature solution. We have monitored the photochemistry of a model system, Fe(CO){sub 4}({eta}{sup 2}-1-hexene), in neat 1-hexene solution. UV-photolysis of the starting material leads to the dissociation of a single CO to form Fe(CO){sub 3}({eta}{sup 2}-1-hexene), in a singlet spin state. This CO loss complex shows a dramatic selectivity to form an allyl hydride, HFe(CO){sub 3}({eta}{sup 3}-C{sub 6}H{sub 11}), via an internal C-H bond-cleavage reaction in 5-25 ns. We find no evidence for the coordination of an alkene molecule from the bath to the CO loss complex, but do observe coordination to the allyl hydride, indicating that it is the key intermediate in the isomerization mechanism. Coordination of the alkene ligand to the allyl hydride leads to the formation of the bis-alkene isomers, Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) and Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2}. Because of the thermodynamic stability of Fe(CO){sub 3}({eta}{sup 2}-1-hexene)({eta}{sup 2}-2-hexene) over Fe(CO){sub 3}({eta}{sup 2}-1-hexene){sub 2} (ca. 12 kcal/mol), nearly 100% of the alkene population will be 2-alkene. The results presented herein provide the first direct evidence for this mechanism in solution and suggest modifications to the currently accepted mechanism.

Sawyer, Karma R.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Harris, Charles B.

2008-05-27

389

Comparative effectiveness research and personalized medicine: catalyzing or colliding?  

PubMed

Comparative effectiveness research (CER) is generating intense attention as interest grows in finding new and better drug technology assessment processes. The federal government is supporting the expansion of CER through funding made available in the American Recovery and Reinvestment Act of 2009 (ARRA) and by establishing the Patient-Centered Outcomes Research Institute through the Patient Protection and Affordable Care Act of 2010. At the same time, personalized medicine is generating debate about its place in clinical medicine, and so, naturally, how CER can or cannot play a role in personalized medicine is part of these debates. At the heart of the debate around the role of CER in personalized medicine is the nature of personalized medicine and how it fits within contemporary clinical research concepts. We maintain in this article that CER can serve to catalyze personalized medicine, but we recognize that, for this to happen, researchers will need to embrace new data sources and new analytic approaches. We also recognize that drug technology assessment processes will have to undergo necessary adaptations to accommodate CER as configured for personalized medicine, and that clinicians will need to be educated appropriately and provided access to decision-support systems through health information technology to use the information coming from this research. To illustrate our argument, we describe two ongoing CER studies funded and managed in the private sector evaluating personalized medicine interventions that have important clinical and financial implications. One of the studies investigates the clinical and financial effects of pharmacogenomic testing for warfarin as prescribed in conditions of typical practice settings. The other study is also set in community practice settings and compares cardiovascular outcomes of patients receiving clopidogrel who are extensive metabolizer phenotypes for the cytochrome P450 2C19 hepatic isoenzyme with all patients receiving prasugrel. PMID:20831298

Epstein, Robert S; Teagarden, J Russell

2010-01-01

390

Kinetics of catalyzed sodium borohydride hydrolysis and fuel cell applicability  

NASA Astrophysics Data System (ADS)

Metal boride catalysts have been developed through reduction of (Ni, Co, and Ru) metal salts with sodium borohydride solutions. The resulting metal borides were determined to be Ni3B, Co3B, and elemental Ru by use of XRD analysis. SEM images give the particle size of the catalyst to be in the range or 65-150nm. Optimum heat treatment for the samples was determined to be 150°C for Ni3B, 200°C for Co3B, and 400°C for Ru. Ruthenium catalysts were found to have the greatest catalytic activity followed by cobalt boride and nickel boride. Hydrolysis testing with nickel boride catalysts has shown that the maximum hydrolysis rate as a function of sodium borohydride occurs at 5-10 wt% NaBH 4 when considered in solution with 5 wt% NaOH. The hydrolysis rate increases for the nickel boride catalyst with increasing NaOH concentration. Tests were performed at elevated pressures and showed that reaction rate could be controlled and even stopped with sufficient hydrogen pressures on the order of 10 MPa. Decreases in system pressure cause the reaction rate to increase, which tends to maintain the system at the equilibrium pressure. Thus, a high pressure hydrogen generator is considered. 210mg of Co3B catalyst in a 30 wt% solution of sodium borohydride can produce 30kW of hydrogen electrical power equivalent if utilized within a fuel cell operating at 40% efficiency. A semi-empirical isotherm model has been developed to accurately calculate the reaction rate for a Co3B catalyzed reaction as a function of temperature (35-80°C) and pressure (0.1-10MPa).

Walter, Joshua C.

391

Mechanistic studies of copper(I)-catalyzed allylic amination.  

PubMed

The reactions of nitrosobenzene and N,N'-diethyl-4-nitrosoaniline with [Cu(CH3CN)4]PF6 provide novel Cu(I) complexes, [Cu(PhNO)3]PF6 (1) and [Cu(Et2NPhNO)3]PF6 (2); in 2 the copper atom is N-coordinated to the nitrosoarenes in a distorted trigonal planar geometry. Complex 1 is strongly implicated as a reactive intermediate in the Cu(I)-catalyzed allylic amination of olefins based on (i) its isolation from the catalytic reaction, (ii) its stoichiometric regioselective allylic amination of alpha-methyl styrene (AMS), (iii) the non-involvement of free PhNO in its amination of AMS, and (iv) its function as a catalyst for the amination of alkenes from phenylhydroxylamine. The reaction between AMS and 1 (80 degrees C, dioxane) is first order in both alkene and 1. Relative rate studies of the reaction of 1 with para substituted AMS derivatives gives a Hammett rho value of -0.035. Alkene adducts isolated from the reaction of 1 with styrene and alpha-methylstyrene are formulated as [(PhNO)3Cu(eta(2)-alkene)]PF6 (7,8) on the basis of spectroscopic characterization and thermolysis. PM3 and DFT MO calculations support the role of [(alkene)Cu(RNO)3]+ and (eta(1)- or eta(3)-allyl)Cu(RNO)2(RNHOH)+ complexes as probable catalytic intermediates and address the origin of the distinctive reaction regioselectivity. A mechanistic scheme is proposed which is consistent with the accumulated experimental and computational results. PMID:18004850

Srivastava, Radhey S; Tarver, Nathan R; Nicholas, Kenneth M

2007-12-12

392

Mechanistic insights into the rhodium-catalyzed intramolecular ketone hydroacylation.  

PubMed

[Rh((R)-DTBM-SEGPHOS)]BF(4) catalyzes the intramolecular hydroacylation of ketones to afford seven-membered lactones in large enantiomeric excess. Herein, we present a combined experimental and theoretical study to elucidate the mechanism and origin of selectivity in this C-H bond activation process. Evidence is presented for a mechanistic pathway involving three key steps: (1) rhodium(I) oxidative addition into the aldehyde C-H bond, (2) insertion of the ketone CO double bond into the rhodium hydride, and (3) C-O bond-forming reductive elimination. Kinetic isotope effects and Hammett plot studies support that ketone insertion is the turnover-limiting step. Detailed kinetic experiments were performed using both 1,3-bis(diphenylphosphino)propane (dppp) and (R)-DTBM-SEGPHOS as ligands. With dppp, the keto-aldehyde substrate assists in dissociating a dimeric precatalyst 8 and binds an active monomeric catalyst 9. With [Rh((R)-DTBM-SEGPHOS)]BF(4), there is no induction period and both substrate and product inhibition are observed. In addition, competitive decarbonylation produces a catalytically inactive rhodium carbonyl species that accumulates over the course of the reaction. Both mechanisms were modeled with a kinetics simulation program, and the models were consistent with the experimental data. Density functional theory calculations were performed to understand more elusive details of this transformation. These simulations support that the ketone insertion step has the highest energy transition state and reveal an unexpected interaction between the carbonyl-oxygen lone pair and a Rh d-orbital in this transition state structure. Finally, a model based on the calculated transition-state geometry is proposed to rationalize the absolute sense of enantioinduction observed using (R)-DTBM-SEGPHOS as the chiral ligand. PMID:19128061

Shen, Zengming; Dornan, Peter K; Khan, Hasan A; Woo, Tom K; Dong, Vy M

2009-01-28

393

The mechanism of the NHC catalyzed aza-Morita-Baylis-Hillman reaction: insights into a new substrate-catalyzed bimolecular pathway.  

PubMed

The first mechanistic study on the NHC-catalyzed aza-MBH reaction between cyclopentenone and N-mesylbenzaldimine using density functional theory reveals that a bimolecular mechanism, involving two molecules of benzaldimine in the proton transfer, is energetically more preferred over the conventional direct proton transfer. PMID:24569854

Verma, Pritha; Verma, Pragya; Sunoj, Raghavan B

2014-04-14

394

Growth and characterization of gold catalyzed SiGe nanowires and alternative metal-catalyzed Si nanowires  

NASA Astrophysics Data System (ADS)

The growth of semiconductor (SC) nanowires (NW) by CVD using Au-catalyzed VLS process has been widely studied over the past few years. Among others SC, it is possible to grow pure Si or SiGe NW thanks to these techniques. Nevertheless, Au could deteriorate the electric properties of SC and the use of other metal catalysts will be mandatory if NW are to be designed for innovating electronic. First, this article's focus will be on SiGe NW's growth using Au catalyst. The authors managed to grow SiGe NW between 350 and 400°C. Ge concentration ( x) in Si1- x Ge x NW has been successfully varied by modifying the gas flow ratio: R = GeH4/(SiH4 + GeH4). Characterization (by Raman spectroscopy and XRD) revealed concentrations varying from 0.2 to 0.46 on NW grown at 375°C, with R varying from 0.05 to 0.15. Second, the results of Si NW growths by CVD using alternatives catalysts such as platinum-, palladium- and nickel-silicides are presented. This study, carried out on a LPCVD furnace, aimed at defining Si NW growth conditions when using such catalysts. Since the growth temperatures investigated are lower than the eutectic temperatures of these Si-metal alloys, VSS growth is expected and observed. Different temperatures and HCl flow rates have been tested with the aim of minimizing 2D growth which induces an important tapering of the NW. Finally, mechanical characterization of single NW has been carried out using an AFM method developed at the LTM. It consists in measuring the deflection of an AFM tip while performing approach-retract curves at various positions along the length of a cantilevered NW. This approach allows the measurement of as-grown single NW's Young modulus and spring constant, and alleviates uncertainties inherent in single point measurement.

Potié, Alexis; Baron, Thierry; Dhalluin, Florian; Rosaz, Guillaume; Salem, Bassem; Latu-Romain, Laurence; Kogelschatz, Martin; Gentile, Pascal; Oehler, Fabrice; Montès, Laurent; Kreisel, Jens; Roussel, Hervé

2011-12-01

395

Growth and characterization of gold catalyzed SiGe nanowires and alternative metal-catalyzed Si nanowires.  

PubMed

The growth of semiconductor (SC) nanowires (NW) by CVD using Au-catalyzed VLS process has been widely studied over the past few years. Among others SC, it is possible to grow pure Si or SiGe NW thanks to these techniques. Nevertheless, Au could deteriorate the electric properties of SC and the use of other metal catalysts will be mandatory if NW are to be designed for innovating electronic. First, this article's focus will be on SiGe NW's growth using Au catalyst. The authors managed to grow SiGe NW between 350 and 400°C. Ge concentration (x) in Si1-xGex NW has been successfully varied by modifying the gas flow ratio: R = GeH4/(SiH4 + GeH4). Characterization (by Raman spectroscopy and XRD) revealed concentrations varying from 0.2 to 0.46 on NW grown at 375°C, with R varying from 0.05 to 0.15. Second, the results of Si NW growths by CVD using alternatives catalysts such as platinum-, palladium- and nickel-silicides are presented. This study, carried out on a LPCVD furnace, aimed at defining Si NW growth conditions when using such catalysts. Since the growth temperatures investigated are lower than the eutectic temperatures of these Si-metal alloys, VSS growth is expected and observed. Different temperatures and HCl flow rates have been tested with the aim of minimizing 2D growth which induces an important tapering of the NW. Finally, mechanical characterization of single NW has been carried out using an AFM method developed at the LTM. It consists in measuring the deflection of an AFM tip while performing approach-retract curves at various positions along the length of a cantilevered NW. This approach allows the measurement of as-grown single NW's Young modulus and spring constant, and alleviates uncertainties inherent in single point measurement. PMID:21711709

Potié, Alexis; Baron, Thierry; Dhalluin, Florian; Rosaz, Guillaume; Salem, Bassem; Latu-Romain, Laurence; Kogelschatz, Martin; Gentile, Pascal; Oehler, Fabrice; Montès, Laurent; Kreisel, Jens; Roussel, Hervé

2011-01-01

396

Theoretical study of water cluster catalyzed decomposition of formic Acid.  

PubMed

We have performed a number of quantum chemical simulations to examine water cluster catalyzed decomposition of formic acid. The decomposition of formic acid consists of two competing pathways, dehydration, and decarboxylation. We use the Gaussian 4 method of the Gaussian09 software to locate and optimize a transition state of the decomposition reaction and obtain the activation energy. The decomposition starts by transferring a proton of a formic acid to a water molecule. The de Broglie wavelength of a proton is similar to the width of the potential barrier of the decomposition reaction at low temperature. The tunneling, in which a proton penetrates the potential barrier, enhances the decomposition rate. Water molecules serve as the catalyst in the decomposition and reduce the activation energy. The relay of a proton from a water molecule to a neighboring water molecule is accomplished with little change of the geometry of a molecule, resulting in the reduction of the activation energy. Two water molecules are actively involved in the decomposition reaction to reduce the activation energy. We have also examined the effect of water clusters with three, four, and five water molecules on the decomposition reaction. The noncovalent distance between a hydrogen atom of a water molecule and an oxygen atom of a neighboring water molecule decreases in a water cluster due to the cooperative many-body interactions. A water molecule in a water cluster becomes a better proton donor as well as a better proton acceptor. The activation energy of the decomposition is further decreased by the catalytic effect of a water cluster. We calculate the reaction rate using the transition state theory corrected by the tunneling effect of a proton. The calculated reaction rate of the decarboxylation is smaller than that of the dehydration when less than three water molecules are included in the simulation. However, the major product of the decomposition of a formic acid becomes carbon dioxide and hydrogen molecule formed by the decarboxylation when a water cluster with more than four water molecules serves as catalyst in the decomposition of formic acid. PMID:24735438

Inaba, Satoshi

2014-04-24

397

Copper-catalyzed intermolecular amidation and imidation of unactivated alkanes.  

PubMed

We report a set of rare copper-catalyzed reactions of alkanes with simple amides, sulfonamides, and imides (i.e., benzamides, tosylamides, carbamates, and phthalimide) to form the corresponding N-alkyl products. The reactions lead to functionalization at secondary C-H bonds over tertiary C-H bonds and even occur at primary C-H bonds. [(phen)Cu(phth)] (1-phth) and [(phen)Cu(phth)2] (1-phth2), which are potential intermediates in the reaction, have been isolated and fully characterized. The stoichiometric reactions of 1-phth and 1-phth2 with alkanes, alkyl radicals, and radical probes were investigated to elucidate the mechanism of the amidation. The catalytic and stoichiometric reactions require both copper and tBuOOtBu for the generation of N-alkyl product. Neither 1-phth nor 1-phth2 reacted with excess cyclohexane at 100 °C without tBuOOtBu. However, the reactions of 1-phth and 1-phth2 with tBuOOtBu afforded N-cyclohexylphthalimide (Cy-phth), N-methylphthalimide, and tert-butoxycyclohexane (Cy-OtBu) in approximate ratios of 70:20:30, respectively. Reactions with radical traps support the intermediacy of a tert-butoxy radical, which forms an alkyl radical intermediate. The intermediacy of an alkyl radical was evidenced by the catalytic reaction of cyclohexane with benzamide in the presence of CBr4, which formed exclusively bromocyclohexane. Furthermore, stoichiometric reactions of [(phen)Cu(phth)2] with tBuOOtBu and (Ph(Me)2CO)2 at 100 °C without cyclohexane afforded N-methylphthalimide (Me-phth) from ?-Me scission of the alkoxy radicals to form a methyl radical. Separate reactions of cyclohexane and d12-cyclohexane with benzamide showed that the turnover-limiting step in the catalytic reaction is the C-H cleavage of cyclohexane by a tert-butoxy radical. These mechanistic data imply that the tert-butoxy radical reacts with the C-H bonds of alkanes, and the subsequent alkyl radical combines with 1-phth2 to form the corresponding N-alkyl imide product. PMID:24405209

Tran, Ba L; Li, Bijie; Driess, Matthias; Hartwig, John F

2014-02-12

398

Evidence of catalyzed oxidation of Li2O2 for rechargeable Li-air battery applications.  

PubMed

The oxidation kinetics of Li(2)O(2) was studied in a carbonate-free electrolyte using electrodes consisting of non-catalyzed and catalyzed Vulcan carbon (VC) and chemically synthesized Li(2)O(2) particles. VC and Au nanoparticles supported on VC (Au/C) were fairly inactive for catalyzing the oxidation of Li(2)O(2), where oxidation currents greater than 10 mA g(carbon)(-1) were found only at voltages equal to and greater than 4.0 V vs. Li (V(Li)). Pt and Ru nanoparticles supported on VC (Pt/C and Ru/C) could significantly increase the kinetics of Li(2)O(2) oxidation, where Li(2)O(2) could be removed largely at voltages below 4 V(Li). In addition, Pt/C and Ru/C showed quick initiation of Li(2)O(2) oxidation in contrast to VC and Au/C. PMID:22751524

Harding, Jonathon R; Lu, Yi-Chun; Tsukada, Yasuhiro; Shao-Horn, Yang

2012-08-14

399

Palladium catalyzed synthesis and physical properties of indolo[2,3-b]quinoxalines.  

PubMed

A series of indolo[2,3-b]quinoxaline derivatives were efficiently synthesized from 2,3-dibromoquinoxaline by two pathways. A one-pot approach using Pd-catalyzed two-fold C-N coupling and C-H activation reactions gave indolo[2,3-b]quinoxaline derivatives in good yields, but with limited substrate scope. In addition, a two-step approach to indolo[2,3-b]quinoxalines was developed which is based on Pd-catalyzed Suzuki coupling reactions and subsequent annulation by Pd-catalyzed two-fold C-N coupling with aromatic and aliphatic amines. The electrochemical and photochemical properties of indolo[2,3-b]quinoxaline derivatives were investigated. These studies show that 6-(4-methoxyphenyl)-6H-indolo[2,3-b]quinoxaline showed the highest HOMO energy level and lowest band gap. PMID:25001519

Hung, Tran Quang; Hoang, Do Huy; Thang, Ngo Ngoc; Dang, Tuan Thanh; Ayub, Khurshid; Villinger, Alexander; Friedrich, Aleksej; Lochbrunner, Stefan; Flechsig, Gerd-Uwe; Langer, Peter

2014-08-28

400

Rhodium-Catalyzed Acyloxy Migration of Propargylic Esters in Cycloadditions, Inspiration from Recent "Gold Rush"  

PubMed Central

Transition metal-catalyzed acyloxy migration of propargylic esters offers versatile entries to allene and vinyl carbene intermediates for various fascinating subsequent transformations. Most ?-acidic metals (e.g. gold and platinum) are capable of facilitating these acyloxy migration events. However, very few of these processes involve redox chemistry, which are well-known for most other transition metals such as rhodium. The coupling of acyloxy migration of propargylic esters with oxidative addition, migratory insertion, and reductive elimination may lead to ample new opportunities for the design of new reactions. This tutorial review summarizes recent developments in Rh-catalyzed 1,3- and 1,2-acyloxy migration of propargylic esters in a number of cycloaddition reactions. Related Au- and Pt-catalyzed cycloadditions involving acyloxy migration are also discussed.

Shu, Xing-Zhong; Shu, Dongxu; Schienebeck, Casi M.

2012-01-01

401

Bulk Gold-Catalyzed Reactions of Isocyanides, Amines, and Amine N-Oxides  

SciTech Connect

Bulk gold powder (5–50 ?m particles) catalyzes the reactions of isocyanides with amines and amine N-oxides to produce ureas. The reaction of n-butyl isocyanide (nBu–N?C) with di-n-propylamine and N-methylmorpholine N-oxide in acetonitrile, which was studied in the greatest detail, produced 3-butyl-1,1-dipropylurea (O?C(NHnBu)(NnPr2)) in 99% yield at 60 °C within 2 h. Sterically and electronically different isocyanides, amines, and amine N-oxides react successfully under these conditions. Detailed studies support a two-step mechanism that involves a gold-catalyzed reaction of adsorbed isocyanide with the amine N-oxide to form an isocyanate (RN?C?O), which rapidly reacts with the amine to give the urea product. These investigations show that bulk gold, despite its reputation for poor catalytic activity, is capable of catalyzing these reactions.

Klobukowski, Erik; Angelici, Robert; Woo, Keith L.

2012-01-26

402

Continuous In Vitro Evolution of a Ribozyme that Catalyzes Three Successive Nucleotidyl Addition Reactions  

NASA Technical Reports Server (NTRS)

Variants of the class I ligase ribozyme, which catalyzes joining of the 3' end of a template bound oligonucleotide to its own 5' end, have been made to evolve in a continuous manner by a simple serial transfer procedure that can be carried out indefinitely. This process was expanded to allow the evolution of ribozymes that catalyze three successive nucleotidyl addition reactions, two template-directed mononucleotide additions followed by RNA ligation. During the development of this behavior, a population of ribozymes was maintained against an overall dilution of more than 10(exp 406). The resulting ribozymes were capable of catalyzing the three-step reaction pathway, with nucleotide addition occurring in either a 5' yieldig 3' or a 3' yielding 5' direction. This purely chemical system provides a functional model of a multi-step reaction pathway that is undergoing Darwinian evolution.

McGinness, Kathleen E.; Wright, Martin C.; Joyce, Gerald F.

2002-01-01

403

Sequential Aldol Condensation - Transition Metal-Catalyzed Addition Reactions of Aldehydes, Methyl Ketones and Arylboronic Acids  

PubMed Central

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form ?-substituted ketones is described. By using the 1,1?-spirobiindane-7,7?-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access ?-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step.

Liao, Yuan-Xi; Xing, Chun-Hui; Israel, Matthew; Hu, Qiao-Sheng

2011-01-01

404

Rhodium-catalyzed direct oxidative carbonylation of aromatic C-H bond with CO and alcohols.  

PubMed

A general protocol for the rhodium-catalyzed oxidative carbonylation of arenes to form esters has been developed. A broad substrate scope has been demonstrated allowing carbonylation of electron-rich, electron-poor, and heterocyclic arenes, and the reaction shows wide functional group tolerance and excellent regioselectivities. Up to 96% yield of ortho-substituted aryl or heteroaryl carboxylic esters were obtained with this methodology. The possible mechanism for the rhodium-catalyzed oxidative carbonylation reaction was proposed in this article. Studies show that Oxone play an important role in the transformation. PMID:19099479

Guan, Zheng-Hui; Ren, Zhi-Hui; Spinella, Stephen M; Yu, Shichao; Liang, Yong-Min; Zhang, Xumu

2009-01-21

405

A modified approach to muon-catalyzed fusion, employing helium-3 as fuel  

NASA Astrophysics Data System (ADS)

Muon-catalyzed fusion (?CF) or cold fusion, employing hydrogen isotopes, is the only known form of fusion not requiring extremely high temperatures in order to catalyze a reaction. A modified approach utilizing existing and currently developing technology but employing helium-3 as the fuel source is proposed, offering a potential solution to some inherent problems including the need to deal with radioactive materials. A prediction based on Monte Carlo simulations also points to a potential method to partially negate alpha sticking, allowing a greater energy output than input.

Egan, Cooroo

2012-09-01

406

Probability of twin formation on self-catalyzed GaAs nanowires on Si substrate  

PubMed Central

We attempted to control the incorporation of twin boundaries in self-catalyzed GaAs nanowires (NWs). Self-catalyzed GaAs NWs were grown on a Si substrate under various arsenic pressures using molecular beam epitaxy and the vapor-liquid-solid method. When the arsenic flux is low, wurtzite structures are dominant in the GaAs NWs. On the other hand, zinc blende structures become dominant as the arsenic flux rises. We discussed this phenomenon on the basis of thermodynamics and examined the probability of twin-boundary formation in detail.

2012-01-01

407

Iron-catalyzed radical oxidative coupling reaction of aryl olefins with 1,3-dithiane.  

PubMed

An alternative method to an iron-catalyzed radical oxidative cross-coupling reaction followed by 2-chloro-1,3-dithiane and aryl olefins for the synthesis of ?-chloro substituent 1,3-dithiane products is presented. The described method has the advantage of mildness of the reaction conditions and tolerates a variety of functional groups. Preliminary mechanistic studies have confirmed the first example of a coupling of 1,3-dithiane with unactivated alkenes that proceeds via an iron-catalyzed oxidative radical intermediate along the reaction pathway. PMID:24749868

Du, Wenbin; Tian, Lixia; Lai, Junshan; Huo, Xing; Xie, Xingang; She, Xuegong; Tang, Shouchu

2014-05-01

408

Enzyme-Catalyzed Gel Proteolysis: An Anomalous Diffusion-Controlled Mechanism  

PubMed Central

Enzyme-catalyzed proteolysis of gelatin gels has been studied. We report a gel degradation rate varying as the square of the enzyme concentration. The diffusion motion of enzymes in the gel has been measured by two-photon fluorescence correlation spectroscopy and identified as being anomalously slow. These experimental results are discussed from a theoretical point of view and interpreted in terms of a diffusion-controlled mechanism for the gel degradation. These results make a step toward the understanding of enzyme-catalyzed gel degradation and give new insight on biological processes such as the action of metalloproteinases in the extracellular matrix involved in cellular invasion.

Fadda, G. C.; Lairez, D.; Arrio, B.; Carton, J.-P.; Larreta-Garde, V.

2003-01-01

409

Cu-catalyzed trifluoromethylation of aryl iodides with trifluoromethylzinc reagent prepared in situ from trifluoromethyl iodide  

PubMed Central

Summary The trifluoromethylation of aryl iodides catalyzed by copper(I) salt with trifluoromethylzinc reagent prepared in situ from trifluoromethyl iodide and Zn dust was accomplished. The catalytic reactions proceeded under mild reaction conditions, providing the corresponding aromatic trifluoromethylated products in moderate to high yields. The advantage of this method is that additives such as metal fluoride (MF), which are indispensable to activate silyl groups for transmetallation in the corresponding reactions catalyzed by copper salt by using the Ruppert–Prakash reagents (CF3SiR3), are not required.

Nakamura, Yuzo; Fujiu, Motohiro; Murase, Tatsuya; Itoh, Yoshimitsu; Serizawa, Hiroki; Aikawa, Kohsuke

2013-01-01

410

Enantioselective TADMAP-Catalyzed Carboxyl Migration Reactions for the Synthesis of Stereogenic Quaternary Carbon  

PubMed Central

The chiral, nucleophilic catalyst TADMAP (1) has been prepared from 3-lithio-4-dimethylamino-pyridine (5) and triphenylacetaldehyde (3), followed by acylation and resolution. TADMAP catalyzes the carboxyl migration of oxazolyl, furanyl, and benzofuranyl enol carbonates with good to excellent levels of enantioselection. The oxazole reactions are especially efficient, and are used to prepare chiral lactams (23) and lactones (30) containing a quaternary asymmetric carbon. TADMAP-catalyzed carboxyl migrations in the indole series are relatively slow and proceed with inconsistent enantioselectivity. Modeling studies (B3LYP/6-31G*) have been used in qualitative correlations of catalyst conformation, reactivity, and enantioselectivity.

Shaw, Scott A.; Aleman, Pedro; Christy, Justin; Kampf, Jeff W.; Va, Porino

2008-01-01

411

Concise, convergent syntheses of (±)-trichostatin A utilizing a Pd-catalyzed ketone enolate ?-alkenylation reaction.  

PubMed

Two concise, convergent syntheses of (±)-trichostatin A (1), a potent histone deacetylase inhibitor, have been accomplished. The key step in both is a Pd-catalyzed ?-alkenylation reaction between ketone 2 and either dienyl bromide 3 or alkenyl bromide 9 using a modification of cross-coupling conditions described by Negishi and Hartwig. A brief investigation has shown the potential utility of a Ni-catalyzed version of this reaction. The overall synthetic routes are short and amenable to scaleup, providing access to trichostatin A via trichostatic acid as a direct precursor. PMID:21688856

Cosner, Casey C; Helquist, Paul

2011-07-15

412

Iridium-catalyzed borylation of thiophenes: versatile, synthetic elaboration founded on selective C-H functionalization  

PubMed Central

Iridium-catalyzed borylation has been applied to various substituted thiophenes to synthesize poly-functionalized thiophenes in good to excellent yields. Apart from common functionalities compatible with iridium-catalyzed borylations, additional functional group tolerance to acyl (COMe), and trimethylsilyl (TMS) groups was also observed. High regioselectivities were observed in borylation of 3-and 2,5-di-substituted thiophenes. Electrophilic aromatic C–H/C-Si bromination on thiophene boronate esters is shown to take place without breaking the C–B bond, and one-pot C–H borylation/Suzuki-Miyaura cross-coupling has been accomplished on 2- and 3-borylated thiophenes.

Chotana, Ghayoor A.; Kallepalli, Venkata A.; Maleczka, Robert E.; Smith, Milton R.

2013-01-01

413

Assessing the regioselectivity of OleD-catalyzed glycosylation with a diverse set of acceptors.  

PubMed

To explore the acceptor regioselectivity of OleD-catalyzed glucosylation, the products of OleD-catalyzed reactions with six structurally diverse acceptors flavones- (daidzein), isoflavones (flavopiridol), stilbenes (resveratrol), indole alkaloids (10-hydroxycamptothecin), and steroids (2-methoxyestradiol)-were determined. This study highlights the first synthesis of flavopiridol and 2-methoxyestradiol glucosides and confirms the ability of OleD to glucosylate both aromatic and aliphatic nucleophiles. In all cases, molecular dynamics simulations were consistent with the determined product distribution and suggest the potential to develop a virtual screening model to identify additional OleD substrates. PMID:23360118

Zhou, Maoquan; Hamza, Adel; Zhan, Chang-Guo; Thorson, Jon S

2013-02-22

414

Iron-catalyzed cycloaddition reaction of diynes and cyanamides at room temperature.  

PubMed

An iron-catalyzed [2 + 2 + 2] cycloaddition reaction of diynes and cyanamides at room temperature is reported. Highly substituted 2-aminopyridines were obtained in good to excellent yields with high regioselectivity. Insights toward the reaction process were investigated through in situ IR spectra and control experiments. In this iron-catalyzed cycloaddition reaction, the active iron species was generated only in the presence of both alkynes and nitriles. The lower reaction temperature, broad substrates scope, and inversed regioselectivity make it a complementary method to the previously developed iron catalytic system. PMID:23373593

Wang, Chunxiang; Wang, Dongping; Xu, Fen; Pan, Bin; Wan, Boshun

2013-04-01

415

C1-symmetric aminosulfoximines in copper-catalyzed asymmetric vinylogous Mukaiyama aldol reactions.  

PubMed

Vinylogous Mukaiyama-type aldol reactions have been catalyzed by a combination of Cu(OTf)2 and readily available C1-symmetric aminosulfoximines. After a fine-tuning of the reaction conditions and an optimization of the modularly assembled ligand structure, high stereoselectivities and excellent yields have been achieved in catalyzed reactions involving various electrophile/nucleophile combinations. The relative and absolute configurations of two products were assigned by X-ray single crystal structure analysis and a comparison of calculated and experimental CD spectra. PMID:20229533

Frings, Marcus; Atodiresei, Iuliana; Wang, Yutian; Runsink, Jan; Raabe, Gerhard; Bolm, Carsten

2010-04-19

416

Mechanism of maltal hydration catalyzed by. beta. -amylase: Role of protein structure in controlling the steric outcome of reactions catalyzed by a glycosylase  

SciTech Connect

Crystalline (monomeric) soybean and (tetrameric) sweet potato {beta}-amylase were shown to catalyze the cis hydration of maltal ({alpha}-D-glucopyranosyl-2-deoxy-D-arabino-hex-1-enitol) to form {beta}-2-deoxymaltose. As reported earlier with the sweet potato enzyme, maltal hydration in D{sub 2}O by soybean {beta}-amylase was found to exhibit an unusually large solvent deuterium kinetic isotope effect (V{sub H}/V{sub D}=6.5), a reaction rate linearly dependent on the mole fraction of deuterium, and 2-deoxy-(2(a)-{sup 2}H)maltose as product. These results indicate (for each {beta}-amylase) that protonation is the rate-limiting step in a reaction involving a nearly symmetric one-proton transition state and that maltal is specifically protonated from above the double bond. That maltal undergoes cis hydration provides evidence in support of a general-acid-catalyzed, carbonium ion mediated reaction. Of fundamental significance is that {beta}-amylase protonates maltal from a direction opposite that assumed for protonating strach, yet creates products of the same anomeric configuration from both. Such stereochemical dichotomy argues for the overriding role of protein structures is dictating the steric outcome of reactions catalyzed by a glycosylase, by limiting the approach and orientation of water or other acceptors to the reaction center.

Kitahata, Sumio (Osaka Municipal Technical Research Inst. (Japan)); Chiba, S. (Hokkaido Univ. (Japan)); Brewer, C.F.; Hehre, E.J. (Albert Einstein Coll. of Medicine, Bronx, NY (United States))

1991-07-09

417

Micellar catalysis using a photochromic surfactant: application to the Pd-catalyzed Tsuji-Trost reaction in water.  

PubMed

The first example of a Pd-catalyzed Tsuji-Trost reaction, applied in a photochromic micellar media under conventional heating and microwave irradiation, is reported. The surfactant activity and recycling ability were investigated and compared with those of a few commercially available surfactants. The synthetic photochromic surfactant proved to be efficient, recyclable, and versatile for Pd-catalyzed coupling reactions. PMID:24295431

Billamboz, Muriel; Mangin, Floriane; Drillaud, Nicolas; Chevrin-Villette, Carole; Banaszak-Léonard, Estelle; Len, Christophe

2014-01-17

418

Theoretical study of chloroperoxidase catalyzed chlorination of beta-cyclopentanedione and role of water in the chlorination mechanism  

Microsoft Academic Search

Chloroperoxidase (CPO) is a potential biocatalyst for use in asymmetric synthesis. The mechanisms of CPO catalysis are therefore of interest. The halogenation reaction, one of several chemical reactions that CPO catalyzes, is not fully understood and is the subject of this dissertation. ^ The mechanism by which CPO catalyzes halogenation is disputed. It has been postulated that halogenation of substrates

Cassian DCunha

2011-01-01

419

Efficient synthesis of benzofuranones: N-heterocyclic carbene (NHC)/base-catalyzed hydroacylation-Stetter-rearrangement cascade.  

PubMed

A N-heterocyclic carbene/base-catalyzed cascade reaction leading to the formation of functionalized benzofuranones is reported. The reaction proceeds via an intramolecular hydroacylation of unactivated alkynes followed by an intermolecular Stetter reaction and a base-catalyzed chromanone to benzofuranone rearrangement. PMID:21919536

Padmanaban, Mohan; Biju, Akkattu T; Glorius, Frank

2011-10-21

420

Rhodium-catalyzed 1,3-acyloxy migration and subsequent intramolecular [4 + 2] cycloaddition of vinylallene and unactivated alkyne†  

PubMed Central

A Rh-catalyzed 1,3-acyloxy migration of propargyl ester followed by intramolecular [4 + 2] cycloaddition of vinylallene and unactivated alkyne was developed. This tandem reaction provides access to bicyclic compounds containing a highly functionalized isotoluene or cyclohexenone structural motif, while only aromatic compounds were observed in related transition metal-catalyzed cycloadditions.

Huang, Suyu; Li, Xiaoxun; Lin, Claire L.; Guzei, Ilia A.

2012-01-01

421

Direct conversion and NMR observation of cellulose to glucose and 5-hydroxymethylfurfural (HMF) catalyzed by the acidic ionic liquids  

Microsoft Academic Search

The hydrolysis of cellulose was catalyzed over a variety of acidic ionic liquids (ILs). It is found that the hydrolysis activity is directly associated with the acidity of catalysts, as evidenced by IR spectroscopy. 13C NMR characterization results confirm the majority product of cellulose hydrolysis is glucose, and the resulting carbohydrates undergo further degradation, possibly also catalyzed by the acidic

Feng Jiang; Qingjun Zhu; Ding Ma; Xiumei Liu; Xiuwen Han

2011-01-01

422

Epoxidation of Cyclooctene with Aqueous Hydrogen Peroxide Catalyzed by Molybdate Bound to Colloidal Polymers. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

Epoxidation of cyclooctene in aqueous hydrogen peroxide was catalyzed by ammonium molybdate in the absence of organic solvent. Typically 1.3 mol % of Mo(VI) bound to 60 nm colloidal anion exchange polymers catalyzed 90% conversion of cyclooctene to > 99% ...

S. Srinivasan W. T. Ford

1991-01-01

423

Modulation of cellular immunity by antibodies against calreticulin.  

PubMed

Although caltreticulin (CRT) is mainly a residential ER protein, it is also expressed on the membrane surface of various types of cells exhibiting multiple functions. We report here that intraperitoneal administration of a soluble recombinant CRT fragment (rCRT/39-272) led to a substantial decrease in delayed type hypersensitivity (DTH) responses in BALB/c mice and EAE in C57BL/6 mice. In the recall response against keyhole limpet hemocyanin (KLH) in vitro, draining lymph node cells from the rCRT/39-272-treated mice produced less IFN-? but more IL-4 as compared with the cells from the control group. The immunomodulating effect of intraperitoneally administered rCRT/39-272 was attributed to anti-CRT Abs thereby induced, because, in passive transfer experiments, the CRT-specific antiserum could suppress DTH in BALB/c mice. B-cell-deficient ?MT mice were not susceptible to rCRT/39-272-mediated DTH suppression. Furthermore, CRT appears on the surface of murine T cells soon after activation and remains detectable (at relatively low level) by flow cytometry for approximately 5 days in vitro. Anti-CRT Abs were able to inhibit AKT phosphorylation, proliferation, and cytokine production by activated murine T cells. We propose that cell surface CRT could play a role in the function of effector T cells and may be considered a target for immunological manipulation. PMID:22685035

Qiu, Xiang; Hong, Chao; Zhong, Zhaoyan; Li, Yue; Zhang, Tengteng; Bao, Wanrong; Xiong, Sidong; Gao, Xiao-Ming

2012-09-01

424

Metabolism of Monoterpenes  

PubMed Central

The essential oil from mature leaves of flowering peppermint (Mentha piperita L.) contains up to 15% (—)-menthyl acetate, and leaf discs converted exogenous (—)-[G-3H]menthol into this ester in approximately 15% yield of the incorporated precursor. Leaf extracts catalyzed the acetyl coenzyme A-dependent acetylation of (—)-[G-3H]menthol and the product of this transacetylase reaction was identified by radiochromatographic techniques. Transacetylase activity was located mainly in the 100,000g supernatant fraction, and the preparation was partially purified by combination of Sephadex G-100 gel filtration and chromatography on O-diethylaminoethyl-cellulose. The transacetylase had a molecular weight of about 37,000 as judged by Sephadex G-150 gel filtration, and a pH optimum near 9. The apparent Km and velocity for (—)-menthol were 0.3 mm and 16 nmol/hr· mg of protein, respectively. The saturation curve for acetyl coenzyme A was sigmoidal, showing apparent saturation near 0.1 mm. Dithioerythritol was required for maximum activity and stability of the enzyme, and the enzyme was inhibited by thiol directed reagents such as p-hydroxymercuribenzoate. Diisopropylfluorophosphate also inhibited transacylation suggesting the involvement of a serine residue in catalysis. The transacylase was highly specific for acetyl coenzyme A; propionyl coenzyme A and butyryl coenzyme A were not nearly as efficient as acyl donors (11% and 2%, respectively). However, the enzyme was much less selective with regard to the alcohol substrate, suggesting that the nature of the acetate ester synthesized in mint is more dependent on the type of alcohol available than on the specificity of the transacetylase. This is the first report on an enzyme involved in monoterpenol acetylation in plants. A very similar enzyme, catalyzing this key reaction in the metabolism of menthol, was also isolated from the flowers of peppermint.

Croteau, Rodney; Hooper, Caroline Lee

1978-01-01

425

Investigation of the complex reaction coordinate of acid catalyzed amide hydrolysis from molecular dynamics simulations  

Microsoft Academic Search

The rate-determining step of acid catalyzed peptide hydrolysis is the nucleophilic attack of a water molecule to the carbon atom of the amide group. Therein the addition of the hydroxyl group to the amide carbon atom involves the association of a water molecule transferring one of its protons to an adjacent water molecule. The protonation of the amide nitrogen atom

Dirk Zahn

2004-01-01

426

AgOTf-catalyzed one-pot reactions of 2-alkynylbenzaldoximes with ?,?-unsaturated carbonyl compounds  

PubMed Central

Summary AgOTf-catalyzed one-pot reactions of 2-alkynylbenzaldoximes with various ?,?-unsaturated carbonyl compounds under mild conditions are described, which provides a facile and efficient pathway for the synthesis of 1-alkylated isoquinoline derivatives. The method tolerates a wide range of substrates and allows for the preparation of the products of interest in moderate to excellent yields.

Ding, Qiuping; Wang, Dan; Liu, Meiling; Zhou, Liyun

2013-01-01

427

Chiral Brønsted acid catalyzed enantioselective addition of alpha-isocyanoacetamides to aldehydes.  

PubMed

A clean and highly efficient enantioselective addition of alpha-isocyanoacetamides to aliphatic aldehydes catalyzed by chiral phosphoric acid in the presence of MS 5 A in toluene at -40 degrees C was developed. Excellent yields (85-98%) and good to excellent enantioselectivities (up to >99% ee) were achieved. PMID:20429535

Zeng, Xiaofei; Ye, Kehan; Lu, Min; Chua, Pei Juan; Tan, Bin; Zhong, Guofu

2010-05-21

428

Iron-catalyzed radical aryldifluoromethylation of activated alkenes to difluoromethylated oxindoles.  

PubMed

An iron-catalyzed aryldifluoromethylation of activated alkenes under mild reaction conditions has been developed, which is a rare example where a cosolvent is used to improve the reaction yield along with Fenton's reagent and thus provides an economic and green method for the synthesis of a variety of difluoromethylated oxindoles. Preliminary mechanistic investigations indicate a radical addition path. PMID:24963706

Wang, Jian-Yong; Zhang, Xin; Bao, Yan; Xu, Yue-Ming; Cheng, Xiu-Fen; Wang, Xi-Sheng

2014-08-14

429

C3-Symmetric chiral trisimidazoline-catalyzed Friedel-Crafts (FC)-type reaction.  

PubMed

Imidazoline-catalyzed enantioselective Friedel-Crafts (FC)-type reactions were established using C3-symmetric chiral trisimidazolines. The imidazoline catalysts promoted the FC-type reaction of aldimines with 2-naphthols to produce the corresponding adducts in high yields with up to 99% ee. PMID:24971875

Takizawa, Shinobu; Hirata, Shuichi; Murai, Kenichi; Fujioka, Hiromichi; Sasai, Hiroaki

2014-07-16

430

La2O3 Catalyzed C-C Coupling of Aryl Iodides and Boronic Acids  

PubMed Central

An efficient La2O3-catalyzed new route for the carbon-carbon bond formation in particular, symmetrical and unsymmetrical biphenyls has been developed, which proceeds through carbon-carbon coupling reaction of aryl iodides with boronic acids. The reaction provided the desired products in moderate-to-good yields with a wide range of functional group tolerance.

Malik, Payal; Chakraborty, Debashis

2012-01-01

431

Tandem Nazarov cyclization-michael addition sequence catalyzed by an Ir(III) complex.  

PubMed

The first examples of a tandem Nazarov cyclization/Michael addition process are described. The sequence is efficiently catalyzed by Ir[Me(CO)(dppe)(DIB)]2+ and occurs with high diastereoselectivity, creating three contiguous stereocenters. The mechanistic factors controlling the reactivity and diastereoselectivity are discussed. PMID:16620081

Janka, Mesfin; He, Wei; Haedicke, Inga E; Fronczek, Frank R; Frontier, Alison J; Eisenberg, Richard

2006-04-26

432

Syntheses of calix[4]pyrroles by amberlyst-15 catalyzed cyclocondensations of pyrrole with selected ketones.  

PubMed

A facile and efficient protocol is reported for the synthesis of calix[4]pyrroles and N-confused calix[4]pyrroles in moderate to excellent yields by reaction of dialkyl or cycloalkyl ketones with pyrrole catalyzed by reusable Amberlyst(TM)-15 under eco-friendly conditions. PMID:18065950

Chauhan, Shive Murat Singh; Garg, Bhaskar; Bisht, Tanuja

2007-01-01

433

Phosphine-catalyzed annulation of ethyl (arylimino)acetates: synthesis of highly functionalized oxoimidazolidines.  

PubMed

This paper describes an unexpected and novel nucleophilic phosphine-catalyzed annulation of ethyl (arylimino)acetates to give polysubstituted oxoimidazolidine derivatives in moderate to good yields from simple and easily available starting materials under mild conditions. In this reaction, the addition of methyl vinyl ketone (MVK) is essential to induce the formation of oxoimidazolidines. PMID:18931765

Ma, Guang-Ning; Wang, Fei-Jun; Gao, Jun; Shi, Min

2008-10-28

434

Pd/C-Catalyzed Cross-Coupling of Arenediazonium Salts with Potassium Aryltrifluoroborates  

PubMed Central

A convenient protocol for the synthesis of biaryls from arenediazonium salts and potassium aryltrifluoroborates in refluxing methanol catalyzed by Pd/C is described. The protocol is simple to execute and gives moderate to high yields of cross-coupling products in most cases.

Varnedoe, Lee S.; Angel, Brad D.; McClellan, Joshua L.

2014-01-01

435

Synthesis of 3-substituted and 2,3-disubstituted quinazolinones via Cu-catalyzed aryl amidation.  

PubMed

CuI/4-hydroxy-L-proline catalyzed coupling of N-substituted o-bromobenzamides with formamide takes place at 80 °C, affording 3-substituted quinazolinones directly. Under these conditions other amides that were tested only provided simple coupling products, which can be converted into 2,3-disubstituted quinazolinones via HMDS/ZnCl(2) mediated condensative cyclization. PMID:22313025

Xu, Lanting; Jiang, Yongwen; Ma, Dawei

2012-02-17

436

Palladium/copper-catalyzed oxidative C-H alkenylation/N-dealkylative carbonylation of tertiary anilines.  

PubMed

C-H/C-N activation: The first palladium/copper-catalyzed aerobic oxidative C-H alkenylation/N-dealkylative carbonylation of tertiary anilines has been developed. Various functional groups were tolerated and acrylic ester could also be suitable substrates. This transformation provided efficient and straightforward synthesis of biologically active 3-methyleneindolin-2-one derivatives from cheap and simple substrates. PMID:23946242

Shi, Renyi; Lu, Lijun; Zhang, Hua; Chen, Borui; Sha, Yuchen; Liu, Chao; Lei, Aiwen

2013-09-27

437

Development of palladium catalyzed methodology to synthesize alpha-substituted alpha,beta-unsaturated carbonyl derivatives  

Microsoft Academic Search

A novel and highly selective methodology based on palladium catalyzed cross coupling of either ?-halo-?,?-unsaturated carbonyl compounds or the corresponding ?-metallo derivatives was developed. Simple alkyl, homoallyl, homopropargyl, benzyl, aryl, and alkenyl groups could be introduced into the ?-position of 2-iodocyclohexenone and 2-iodocylopentenone. The yields ranged from good to acceptable. In order to find the optimal conditions, a systematic screening

Baiqiao Liao

1999-01-01

438

AgOTf-catalyzed one-pot reactions of 2-alkynylbenzaldoximes with ?,?-unsaturated carbonyl compounds.  

PubMed

AgOTf-catalyzed one-pot reactions of 2-alkynylbenzaldoximes with various ?,?-unsaturated carbonyl compounds under mild conditions are described, which provides a facile and efficient pathway for the synthesis of 1-alkylated isoquinoline derivatives. The method tolerates a wide range of substrates and allows for the preparation of the products of interest in moderate to excellent yields. PMID:24204406

Ding, Qiuping; Wang, Dan; Luo, Puying; Liu, Meiling; Pu, Shouzhi; Zhou, Liyun

2013-01-01

439

Palladium-catalyzed Saegusa-Ito oxidation: synthesis of ?,?-unsaturated carbonyl compounds from trimethylsilyl enol ethers.  

PubMed

Palladium-catalyzed Saegusa-Ito oxidation of trimethylsilyl enol ethers is possible using Oxone as a stoichiometric oxidant and sodium hydrogen phosphate as a buffer. Cyclic and acyclic enones as well as ?,?-unsaturated aldehydes are obtained in good to excellent yields. PMID:23256839

Lu, Yingdong; Nguyen, Pierre Long; Lévaray, Nicolas; Lebel, Hélène

2013-01-18

440

Copper-catalyzed free-radical C-H arylation of pyrroles.  

PubMed

A room temperature copper-catalyzed radical arylation of pyrroles with anilines, through in situ generated aryl diazonium salts, has been developed under neutral conditions. Experimental and theoretical studies explain the crucial role of CaCO3 and the high regioselectivity observed. PMID:23970307

Honraedt, Aurélien; Raux, Marie-Audrey; Grognec, Erwan Le; Jacquemin, Denis; Felpin, François-Xavier

2014-05-25

441

Cobalt-catalyzed electrophilic amination of arylzincs with N-chloroamines.  

PubMed

Roles reversed: An efficient cobalt-catalyzed electrophilic amination of arylzinc reagents has been achieved. A variety of functionalized arylzincs and N-chloroamines were coupled under mild conditions (see scheme). Both secondary and tertiary arylamines were obtained in moderate to excellent yields. PMID:23526669

Qian