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1

Crystal Structure of Homoserine Transacetylase from Haemophilus Influenzae Reveals a New Family of alpha/beta-Hydrolases  

SciTech Connect

Homoserine transacetylase catalyzes one of the required steps in the biosynthesis of methionine in fungi and several bacteria. We have determined the crystal structure of homoserine transacetylase from Haemophilus influenzae to a resolution of 1.65 A. The structure identifies this enzyme to be a member of the alpha/beta-hydrolase structural superfamily. The active site of the enzyme is located near the end of a deep tunnel formed by the juxtaposition of two domains and incorporates a catalytic triad involving Ser143, His337, and Asp304. A structural basis is given for the observed double displacement kinetic mechanism of homoserine transacetylase. Furthermore, the properties of the tunnel provide a rationale for how homoserine transacetylase catalyzes a transferase reaction vs. hydrolysis, despite extensive similarity in active site architecture to hydrolytic enzymes.

Mirza,I.; Nazi, I.; Korczynska, M.; Wright, G.; Berghuis, A.

2005-01-01

2

Platelet-activating factor acetylhydrolase and transacetylase activities in human aorta and mammary artery*  

PubMed Central

Platelet-activating factor (PAF), the potent phospholipid mediator of inflammation, is involved in atherosclerosis. Platelet-activating factor-acetylhydrolase (PAF-AH), the enzyme that inactivates PAF bioactivity, possesses both acetylhydrolase and transacetylase activities. In the present study, we measured acetylhydrolase and transacetylase activities in human atherogenic aorta and nonatherogenic mammary arteries. Immunohistochemistry analysis showed PAF-AH expression in the intima and the media of the aorta and in the media of mammary arteries. Acetylhydrolase and transacetylase activities were (mean ± SE, n = 38): acetylhydrolase of aorta, 2.8 ± 0.5 pmol/min/mg of tissue; transacetylase of aorta, 3.3 ± 0.7 pmol/min/mg of tissue; acetylhydrolase of mammary artery, 1.4 ± 0.3 pmol/min/mg of tissue (P < 0.004 as compared with acetylhydrolase of aorta); transacetylase of mammary artery, 0.8 ± 0.2 pmol/min/mg of tissue (P < 0.03 as compared with acetylhydrolase of mammary artery). Lyso-PAF accumulation and an increase in PAF bioactivity were observed in the aorta of some patients. Reverse-phase HPLC and electrospray ionization mass spectrometry analysis revealed that 1-O-hexadecyl-2 acetyl-sn glycero-3-phosphocholine accounted for 60% of the PAF bioactivity and 1-O-hexadecyl-2-butanoyl-sn-glycerol-3-phosphocholine for 40% of the PAF bioactivity. The nonatherogenic properties of mammary arteries may in part be due to low PAF formation regulated by PAF-AH activity. In atherogenic aortas, an imbalance between PAF-AH and transacetylase activity, as well as lyso-PAF accumulation, may lead to unregulated PAF formation and to progression of atherosclerosis. PMID:18587071

Tsoukatos, Demokritos C.; Brochériou, Isabelle; Moussis, Vassilios; Panopoulou, Christina P.; Christofidou, Elena D.; Koussissis, Stamatis; Sismanidis, Socratis; Ninio, Ewa; Siminelakis, Stavros

2008-01-01

3

Calreticulin Mutations in Myeloproliferative Neoplasms  

PubMed Central

With the discovery of the JAK2V617F mutation in patients with Philadelphia chromosome-negative (Ph?) myeloproliferative neoplasms (MPNs) in 2005, major advances have been made in the diagnosis of MPNs, in understanding of their pathogenesis involving the JAK/STAT pathway, and finally in the development of novel therapies targeting this pathway. Nevertheless, it remains unknown which mutations exist in approximately one-third of patients with non-mutated JAK2 or MPL essential thrombocythemia (ET) and primary myelofibrosis (PMF). At the end of 2013, two studies identified recurrent mutations in the gene encoding calreticulin (CALR) using whole-exome sequencing. These mutations were revealed in the majority of ET and PMF patients with non-mutated JAK2 or MPL but not in polycythemia vera patients. Somatic 52-bp deletions (type 1 mutations) and recurrent 5-bp insertions (type 2 mutations) in exon 9 of the CALR gene (the last exon encoding the C-terminal amino acids of the protein calreticulin) were detected and found always to generate frameshift mutations. All detected mutant calreticulin proteins shared a novel amino acid sequence at the C-terminal. Mutations in CALR are acquired early in the clonal history of the disease, and they cause activation of JAK/STAT signaling. The CALR mutations are the second most frequent mutations in Ph? MPN patients after the JAK2V617F mutation, and their detection has significantly improved the diagnostic approach for ET and PMF. The characteristics of the CALR mutations as well as their diagnostic, clinical, and pathogenesis implications are discussed in this review. PMID:25386351

Lavi, Noa

2014-01-01

4

Calreticulin mutations in myeloproliferative neoplasms.  

PubMed

With the discovery of the JAK2V617F mutation in patients with Philadelphia chromosome-negative (Ph(-)) myeloproliferative neoplasms (MPNs) in 2005, major advances have been made in the diagnosis of MPNs, in understanding of their pathogenesis involving the JAK/STAT pathway, and finally in the development of novel therapies targeting this pathway. Nevertheless, it remains unknown which mutations exist in approximately one-third of patients with non-mutated JAK2 or MPL essential thrombocythemia (ET) and primary myelofibrosis (PMF). At the end of 2013, two studies identified recurrent mutations in the gene encoding calreticulin (CALR) using whole-exome sequencing. These mutations were revealed in the majority of ET and PMF patients with non-mutated JAK2 or MPL but not in polycythemia vera patients. Somatic 52-bp deletions (type 1 mutations) and recurrent 5-bp insertions (type 2 mutations) in exon 9 of the CALR gene (the last exon encoding the C-terminal amino acids of the protein calreticulin) were detected and found always to generate frameshift mutations. All detected mutant calreticulin proteins shared a novel amino acid sequence at the C-terminal. Mutations in CALR are acquired early in the clonal history of the disease, and they cause activation of JAK/STAT signaling. The CALR mutations are the second most frequent mutations in Ph(-) MPN patients after the JAK2V617F mutation, and their detection has significantly improved the diagnostic approach for ET and PMF. The characteristics of the CALR mutations as well as their diagnostic, clinical, and pathogenesis implications are discussed in this review. PMID:25386351

Lavi, Noa

2014-10-01

5

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. PMID:10567207

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

1999-01-01

6

Calreticulin: Roles in Cell-Surface Protein Expression  

PubMed Central

In order to perform their designated functions, proteins require precise subcellular localizations. For cell-surface proteins, such as receptors and channels, they are able to transduce signals only when properly targeted to the cell membrane. Calreticulin is a multi-functional chaperone protein involved in protein folding, maturation, and trafficking. However, evidence has been accumulating that calreticulin can also negatively regulate the surface expression of certain receptors and channels. In these instances, depletion of calreticulin enhances cell-surface expression and function. In this review, we discuss the role of calreticulin with a focus on its negative effects on the expression of cell-surface proteins. PMID:25230046

Jiang, Yue; Dey, Sandeepa; Matsunami, Hiroaki

2014-01-01

7

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. 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

2014-01-01

8

Structural Basis of Carbohydrate Recognition by Calreticulin*  

PubMed Central

The calnexin cycle is a process by which glycosylated proteins are subjected to folding cycles in the endoplasmic reticulum lumen via binding to the membrane protein calnexin (CNX) or to its soluble homolog calreticulin (CRT). CNX and CRT specifically recognize monoglucosylated Glc1Man9GlcNAc2 glycans, but the structural determinants underlying this specificity are unknown. Here, we report a 1.95-? crystal structure of the CRT lectin domain in complex with the tetrasaccharide ?-Glc-(1?3)-?-Man-(1?2)-?-Man-(1?2)-Man. The tetrasaccharide binds to a long channel on CRT formed by a concave ?-sheet. All four sugar moieties are engaged in the protein binding via an extensive network of hydrogen bonds and hydrophobic contacts. The structure explains the requirement for glucose at the nonreducing end of the carbohydrate; the oxygen O2 of glucose perfectly fits to a pocket formed by CRT side chains while forming direct hydrogen bonds with the carbonyl of Gly124 and the side chain of Lys111. The structure also explains a requirement for the Cys105–Cys137 disulfide bond in CRT/CNX for efficient carbohydrate binding. The Cys105–Cys137 disulfide bond is involved in intimate contacts with the third and fourth sugar moieties of the Glc1Man3 tetrasaccharide. Finally, the structure rationalizes previous mutagenesis of CRT and lays a structural groundwork for future studies of the role of CNX/CRT in diverse biological pathways. PMID:20880849

Kozlov, Guennadi; Pocanschi, Cosmin L.; Rosenauer, Angelika; Bastos-Aristizabal, Sara; Gorelik, Alexei; Williams, David B.; Gehring, Kalle

2010-01-01

9

Calreticulin Exon 9 Mutations in Myeloproliferative Neoplasms  

PubMed Central

Background Calreticulin (CALR) mutations were recently discovered in patients with myeloproliferative neoplasms (MPNs). We studied the frequency and type of CALR mutations and their hematological characteristics. Methods A total of 168 MPN patients (36 polycythemia vera [PV], 114 essential thrombocythemia [ET], and 18 primary myelofibrosis [PMF] cases) were included in the study. CALR mutation was analyzed by the direct sequencing method. Results CALR mutations were detected in 21.9% of ET and 16.7% of PMF patients, which accounted for 58.5% and 33.3% of ET and PMF patients without Janus kinase 2 (JAK2) or myeloproliferative leukemia virus oncogenes (MPL) mutations, respectively. A total of five types of mutation were detected, among which, L367fs*46 (53.6%) and K385fs*47 (35.7%) were found to be the most common. ET patients with CALR mutation had lower leukocyte counts and ages compared with JAK2-mutated ET patients. Conclusion Genotyping for CALR could be a useful diagnostic tool for JAK2-or MPL-negative ET or PMF patients. CALR mutation may be a distinct disease group, with different hematological characteristics than that of JAK2-positive patients. PMID:25553276

Kim, Yu-Kyung

2015-01-01

10

Calreticulin as Cancer Treatment Adjuvant: Combination with Photodynamic Therapy and Photodynamic Therapy-Generated Vaccines  

PubMed Central

Calreticulin is recognized as one of the pivotal damage-associated molecular pattern molecules alerting the host of the presence of distressed cells. In this role, calreticulin becomes exposed on the surface of tumor cells treated by several types of cancer therapy including photodynamic therapy (PDT). The goal of the present study was to examine the potential of externally added calreticulin for augmenting antitumor effect mediated by PDT. Recombinant calreticulin was found to bind to mouse SCCVII tumor cells treated by PDT. Compared to the outcome with PDT alone, cure rates of SCCVII tumors grown in immunocompetent C3H/HeN mice were elevated when calreticulin (0.4?mg/mouse) was injected peritumorally immediately after PDT. Such therapeutic gain with PDT plus calreticulin combination was not obtained with SCCVII tumors growing in immunodeficient NOD-scid mice. In PDT-vaccine protocol, where PDT-treated SCCVII cells are used for vaccination of SCCVII tumor-bearing mice, adding recombinant calreticulin to cells before their injection produced improved therapeutic effect. The expression of calreticulin gene was reduced in PDT-treated cells, while no changes were observed with the expression of this gene in tumor, liver, and spleen tissues in PDT-vaccine-treated mice. These findings reveal that externally added recombinant calreticulin can boost antitumor response elicited by PDT or PDT-generated vaccines, and can thus serve as an effective adjuvant for cancer treatment with PDT and probably other cancer cell stress-inducing modalities. PMID:25692097

Korbelik, Mladen; Banáth, Judit; Saw, Kyi Min; Zhang, Wei; ?iplys, Evaldas

2015-01-01

11

BiP and calreticulin form an abundant complex that is independent of endoplasmic reticulum stress  

PubMed Central

BiP is found in association with calreticulin, both in the presence and absence of endoplasmic reticulum stress. Although the BiP-calreticulin complex can be disrupted by ATP, several properties suggest that the calreticulin associated with BiP is neither unfolded nor partially or improperly folded. (1) The complex is stable in vivo and does not dissociate during 8 hr of chase. (2) When present in the complex, calreticulin masks epitopes at the C terminus of BiP that are not masked when BiP is bound to an assembly-defective protein. And (3) overproduction of calreticulin does not lead to the recruitment of more BiP into complexes with calreticulin. The BiP-calreticulin complex can be disrupted by low pH but not by divalent cation chelators. When the endoplasmic reticulum retention signal of BiP is removed, complex formation with calreticulin still occurs, and this explains the poor secretion of the truncated molecule. Gel filtration experiments showed that BiP and calreticulin are present in distinct high molecular weight complexes in which both molecules interact with each other. The possible functions of this complex are discussed. PMID:9596639

Crofts, AJ; Leborgne-Castel, N; Pesca, M; Vitale, A; Denecke, J

1998-01-01

12

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 7: assay and characterization of 7,8-diacetoxy-4-methylcoumarin:protein transacetylase from rat liver microsomes based on the irreversible inhibition of cytosolic glutathione S-Transferase  

Microsoft Academic Search

The enzymatic transfer of acetyl groups from acetylated xenobiotics to specific proteins is a relatively grey area in the evergreen field of biotransformation of foreign compounds. In this paper, we have documented evidence for the existence of a transacetylase in liver microsomes that catalyses the transfer of acetyl groups from 7,8-diacetoxy-4-methylcoumarin (DAMC) to glutathione S-transferase (GST), either purified or present

Hanumantharao G Raj; Virinder S Parmar; Subhash C Jain; Ekta Kohli; Nizamuddin Ahmad; Sanjay Goel; Yogesh K Tyagi; Sunil K Sharma; Jesper Wengel; Carl E Olsen

2000-01-01

13

Serum Calreticulin Is a Negative Biomarker in Patients with Alzheimer’s Disease  

PubMed Central

Calreticulin is down-regulated in the cortical neurons of patients with Alzheimer’s disease (AD) and may be a potential biomarker for the diagnosis of AD. A total of 128 AD patients were randomly recruited from May 2012 to July 2013. The mRNA levels of calreticulin were measured from the serum of tested subjects using real-time quantitative reverse transcriptase-PCR (real-time qRT-PCR). Serum levels of calreticulin were determined by ELISA and Western Blot. Serum levels of calreticulin in AD patients were significantly lower than those from a healthy group (p < 0.01). The baseline characters indicated that sample size, gender, mean age, diabetes and BMI (body mass index) were not major sources of heterogeneity. The serum levels of mRNA and protein of calreticulin were lower in AD patients than those from a healthy group, and negatively associated with the progression of AD according to CDR scores (p < 0.01). Thus, there is a trend toward decreased serum levels of calreticulin in the patients with progression of AD. Serum levels of calreticulin can be a negative biomarker for the diagnosis of AD patients. PMID:25429433

Lin, Qiao; Cao, Yunpeng; Gao, Jie

2014-01-01

14

Calreticulin mutation-specific immunostaining in myeloproliferative neoplasms: pathogenetic insight and diagnostic value  

PubMed Central

Mutations in the gene calreticulin (CALR) occur in the majority of JAK2- and MPL-unmutated patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF); identifying CALR mutations contributes to the diagnostic pathway of ET and PMF. CALR mutations are heterogeneous spanning over the exon 9, but all result in a novel common protein C terminus. We developed a polyclonal antibody against a 17-amino-acid peptide derived from mutated calreticulin that was used for immunostaining of bone marrow biopsies. We show that this antibody specifically recognized patients harboring different types of CALR mutation with no staining in healthy controls and JAK2- or MPL-mutated ET and PMF. The labeling was mostly localized in megakaryocytes, whereas myeloid and erythroid cells showed faint staining, suggesting a preferential expression of calreticulin in megakaryocytes. Megakaryocytic-restricted expression of calreticulin was also demonstrated using an antibody against wild-type calreticulin and by measuring the levels of calreticulin RNA by gene expression analysis. Immunostaining using an antibody specific for mutated calreticulin may become a rapid, simple and cost-effective method for identifying CALR-mutated patients complementing molecular analysis; furthermore, the labeling pattern supports the preferential expansion of megakaryocytic cell lineage as a result of CALR mutation in an immature hematopoietic stem cell. PMID:24618731

Vannucchi, A M; Rotunno, G; Bartalucci, N; Raugei, G; Carrai, V; Balliu, M; Mannarelli, C; Pacilli, A; Calabresi, L; Fjerza, R; Pieri, L; Bosi, A; Manfredini, R; Guglielmelli, P

2014-01-01

15

Calreticulin affects cell adhesiveness through differential phosphorylation of insulin receptor substrate-1.  

PubMed

Cellular adhesion to the underlying substratum is regulated through numerous signaling pathways. It has been suggested that insulin receptor substrate 1 (IRS-1) is involved in some of these pathways, via association with and activation of transmembrane integrins. Calreticulin, as an important endoplasmic reticulum-resident, calcium-binding protein with a chaperone function, plays an obvious role in proteomic expression. Our previous work showed that calreticulin mediates cell adhesion not only by affecting protein expression but also by affecting the state of regulatory protein phosphorylation, such as that of c-src. Here, we demonstrate that calreticulin affects the abundance of IRS-1 such that the absence of calreticulin is paralleled by a decrease in IRS-1 levels and the unregulated overexpression of calreticulin is accompanied by an increase in IRS-1 levels. These changes in the abundance of calreticulin and IRS-1 are accompanied by changes in cell-substratum adhesiveness and phosphorylation, such that increases in the expression of calreticulin and IRS-1 are paralleled by an increase in focal contact-based cell-substratum adhesiveness, and a decrease in the expression of these proteins brings about a decrease in cell-substratum adhesiveness. Wild type and calreticulin-null mouse embryonic fibroblasts (MEFs) were cultured and the IRS-1 isoform profile was assessed. Differences in morphology and motility were also quantified. While no substantial differences in the speed of locomotion were found, the directionality of cell movement was greatly promoted by the presence of calreticulin. Calreticulin expression was also found to have a dramatic effect on the phosphorylation state of serine 636 of IRS-1, such that phosphorylation of IRS-1 on serine 636 increased radically in the absence of calreticulin. Most importantly, treatment of cells with the RhoA/ROCK inhibitor, Y-27632, which among its many effects also inhibited serine 636 phosphorylation of IRS-1, had profound effects on cell-substratum adhesion, in that it suppressed focal contacts, induced extensive close contacts, and increased the strength of adhesion. The latter effect, while counterintuitive, can be explained by the close contacts comprising labile bonds but in large numbers. In addition, the lability of bonds in close contacts would permit fast locomotion. An interesting and novel finding is that Y-27632 treatment of MEFs releases them from contact inhibition of locomotion, as evidenced by the invasion of a cell's underside by the thin lamellae and filopodia of a cell in close apposition. PMID:24470116

Czarnowski, Arthur; Papp, Sylvia; Szaraz, Peter; Opas, Michal

2014-03-01

16

Overexpression of calreticulin sensitizes SERCA2a to oxidative stress.  

PubMed

Calreticulin (CRT), a Ca(2+)-binding molecular chaperone in the endoplasmic reticulum, plays a vital role in cardiac physiology and pathology. Oxidative stress is a main cause of myocardiac disorder in the ischemic heart, but the function of CRT under oxidative stress is not fully understood. In this study, the effect of overexpression of CRT on sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) 2a under oxidative stress was examined using myocardiac H9c2 cells transfected with the CRT gene. The in vitro activity of SERCA2a and uptake of (45)Ca(2+) into isolated microsomes were suppressed by H(2)O(2) in CRT-overexpressing cells compared with controls. Moreover, SERCA2a protein was degraded via a proteasome-dependent pathway following the formation of a complex with CRT under the stress with H(2)O(2). Thus, we conclude that overexpression of CRT enhances the inactivation and degradation of SERCA2a in the cells under oxidative stress, suggesting some pathophysiological functions of CRT in Ca(2+) homeostasis of myocardiac disease. PMID:15766574

Ihara, Yoshito; Kageyama, Kan; Kondo, Takahito

2005-04-22

17

Calreticulin chaperones regulate functional expression of vomeronasal type 2 pheromone receptors.  

PubMed

A variety of social behaviors like intermale aggression, fear, and mating rituals are important for sustenance of a species. In mice, these behaviors have been implicated to be mediated by peptide pheromones that are sensed by a class of G protein-coupled receptors, vomeronasal receptor type 2 (V2Rs), expressed in the pheromone detecting vomeronasal organ. Matching V2Rs with their cognate ligands is required to learn what receptors the biologically relevant pheromones are acting on. However, this feat has been greatly limited by the unavailability of appropriate heterologous tools commonly used to study ligand receptor specificity, because this family of receptors fails to traffic to the surface of heterologous cells. Here we show that calreticulin, a housekeeping chaperone commonly expressed in most eukaryotic cells, is sparsely expressed in the vomeronasal sensory neurons (VSNs). Correspondingly, knockdown of calreticulin in commonly available cell lines enables V2Rs to efficiently target to the cell membrane. Using this knowledge, we have now been able to successfully surface express receptors and functionally identify cognate ligands. Additionally, calreticulin4, a homolog of calreticulin shows restricted and enriched expression in the VSNs. Interestingly, in heterologous cells, calreticulin4 does not inhibit surface expression of V2Rs and can in part carry out functions of calreticulin. On the basis of our data, we postulate that V2Rs may use a unique trafficking mechanism whereby an important and more commonly expressed chaperone is deleterious for membrane export and is replaced by a functionally equivalent homolog that does not inhibit export while carrying out its functions. PMID:21933956

Dey, Sandeepa; Matsunami, Hiroaki

2011-10-01

18

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. PMID:20337411

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

2010-01-01

19

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. PMID:23564462

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

2013-01-01

20

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

21

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

22

Mapping the complement C1q binding site in Haemonchus contortus calreticulin  

Microsoft Academic Search

Haemonchus contortus is an economically important gastrointestinal parasite of domestic animals. The parasite secretes calreticulin (CalR), a Ca++ binding protein which modulates the host immune response. One way by which this protein acts is by inhibiting the classical complement pathway by binding to complement C1q protein. Understanding CalR–C1q interaction is important to develop methods to enhance host immune response. In

S. Naresha; A. Suryawanshi; M. Agarwal; B. P. Singh; P. Joshi

2009-01-01

23

Comparative effect of human and Trypanosoma cruzi calreticulin in wound healing.  

PubMed

In orthopaedics, the use of factors that enhance granulation tissue formation and prevent or delay new bone regeneration is sometimes desirable. Calreticulin (CRT), a unique endoplasmic reticulum luminal Ca(2+) -binding chaperone widely distributed in eukaryotic cells, is involved in many cellular functions. Among them, CRT has an important influence in cutaneous wound healing and diverse processes associated with cutaneous repair, inhibition of angiogenesis, promotion of cell adhesion and antitumour effect. One of the molecules involved in several aspects of the host-parasite interplay is Trypanosoma cruzi calreticulin (TcCRT), which is highly homologous to human calreticulin (HuCRT). Here, recombinant (r)HuCRT and rTcCRT are compared on their abilities to affect fibroblast behaviour in a scratch plate assay, and wound healing in in vivo skin rat models. In molar terms, rTcCRT is three orders of magnitude more efficient than rHuCRT in increasing proliferation and migration of human fibroblasts in vitro. A similar effect was observed in vivo on rat skin wounds and inhibition of bone gap bridging in rabbit unicortical bone osteotomies. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23109509

Ignacio Arias, J; Sepulveda, Caroll; Bravo, Patricia; Hamilton-West, Christopher; Maldonado, Ismael; Ferreira, Arturo

2015-01-01

24

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

PubMed

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, 10rho and 17rho 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. PMID:12974767

Staikou, E V; Routsias, J G; Makri, A A; Terzoglou, A; Sakarellos-Daitsiotis, M; Sakarellos, C; Panayotou, G; Moutsopoulos, H M; Tzioufas, A G

2003-10-01

25

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. PMID:12974767

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

26

Proteomic identification of calcium-binding chaperone calreticulin as a potential mediator for the neuroprotective and neuritogenic activities of fruit-derived glycoside amygdalin.  

PubMed

Amygdalin is a fruit-derived glycoside with the potential for treating neurodegenerative diseases. This study was designed to identify the neuroprotective and neuritogenic activities of amygdalin. We initially demonstrated that amygdalin enhanced nerve growth factor (NGF)-induced neuritogenesis and attenuated 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in rat dopaminergic PC12 cells. To define protein targets for amygdalin, we selected a total of 11 mostly regulated protein spots from two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels for protein identification by matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry. We verified the effect of amygdalin on six representative proteins (i.e., calreticulin, Hsp90?, Grp94, 14-3-3?, 14-3-3?/? and Rab GDI-?) for biological relevance to neuronal survival and differentiation. Calcium-binding chaperone calreticulin is of special interest for its activities to promote folding, oligomeric assembly and quality control of proteins that modulate cell survival and differentiation. We transiently knocked down calreticulin expression by specific siRNA and studied its effect on the neuroprotective and neuritogenic activities of amygdalin. We found that amygdalin failed to enhance NGF-induced neuritogenesis in calreticulin-siRNA transfected cells. On the other hand, amygdalin rescued 6-OHDA-induced loss of calreticulin expression. We also found that amygdalin increased the intracellular calcium concentration possibly via inducing calreticulin. Collectively, our results demonstrated the role of calreticulin in mediating the neuroprotective and neuritogenic activities of amygdalin. PMID:25465157

Cheng, Yuanyuan; Yang, Chuanbin; Zhao, Jia; Tse, Hung Fat; Rong, Jianhui

2015-02-01

27

Hijacking of Host Calreticulin Is Required for the White Spot Syndrome Virus Replication Cycle  

PubMed Central

ABSTRACT We have previously shown that multifunctional calreticulin (CRT), which resides in the endoplasmic reticulum (ER) and is involved in ER-associated protein processing, responds to infection with white spot syndrome virus (WSSV) by increasing mRNA and protein expression and by forming a complex with gC1qR and thereby delaying apoptosis. Here, we show that CRT can directly interact with WSSV structural proteins, including VP15 and VP28, during an early stage of virus infection. The binding of VP28 with CRT does not promote WSSV entry, and CRT-VP15 interaction was detected in the viral genome in virally infected host cells and thus may have an effect on WSSV replication. Moreover, CRT was detected in the viral envelope of purified WSSV virions. CRT was also found to be of high importance for proper oligomerization of the viral structural proteins VP26 and VP28, and when CRT glycosylation was blocked with tunicamycin, a significant decrease in both viral replication and assembly was detected. Together, these findings suggest that CRT confers several advantages to WSSV, from the initial steps of WSSV infection to the assembly of virions. Therefore, CRT is required as a “vital factor” and is hijacked by WSSV for its replication cycle. IMPORTANCE White spot syndrome virus (WSSV) is a double-stranded DNA virus and the cause of a serious disease in a wide range of crustaceans that often leads to high mortality rates. We have previously shown that the protein calreticulin (CRT), which resides in the endoplasmic reticulum (ER) of the cell, is important in the host response to the virus. In this report, we show that the virus uses this host protein to enter the cell and to make the host produce new viral structural proteins. Through its interaction with two viral proteins, the virus “hijacks” host calreticulin and uses it for its own needs. These findings provide new insight into the interaction between a large DNA virus and the host protein CRT and may help in understanding the viral infection process in general. PMID:24807724

Watthanasurorot, Apiruck; Guo, Enen; Tharntada, Sirinit; Lo, Chu-Fang; Söderhäll, Kenneth

2014-01-01

28

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. PMID:24747831

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

2014-01-01

29

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

30

ANTIBODY TO A cDNA-DERIVED CALRETICULIN PROTEIN FROM AMBLYOMMA AMERICANUMAS A BIOMARKER OF TICK EXPOSURE IN HUMANS  

Microsoft Academic Search

The antibody responses of human and animal hosts were studied to determine the utility of antibody against recombinant tick calreticulin (rTC), a cDNA-derived protein isolated from salivary glands of Amblyomma americanum L., as a biologic marker of tick exposure. Rabbits fed upon by either A. americanum or Dermacentor variabilis Say developed significant anti-rTC antibody responses, as measured by both ELISA

MARTIN L. SANDERS; DEBORAH C. JAWORSKI; JOSE L. SANCHEZ; ROBERT F. D EFRAITES; GREGORY E. GLASS; ALAN L. SCOTT; SYAMAL RAHA; BRUCE C. RITCHIE; GLEN R. NEEDHAM; BRIAN S. SCHWARTZ

31

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

32

Calreticulin levels determine onset of early muscle denervation by fast motoneurons of ALS model mice.  

PubMed

Although the precise signaling mechanisms underlying the vulnerability of some sub-populations of motoneurons in ALS remain unclear, critical factors such as metallo-proteinase 9 expression, neuronal activity and endoplasmic reticulum stress have been shown to be involved. In the context of SOD1(G93A) ALS mouse model, we previously showed that a two-fold decrease in calreticulin (CRT) is occurring in the vulnerable fast motoneurons. Here, we asked to which extent the decrease in CRT levels was causative to muscle denervation and/or motoneuron degeneration. Toward this goal, a hemizygous deletion of the crt gene in SOD1(G93A) mice was generated since the complete ablation of crt is embryonic lethal. We observed that SOD1(G93A);crt(+/-) mice display increased and earlier muscle weakness and muscle denervation compared to SOD1(G93A) mice. While CRT reduction in motoneurons leads to a strong upregulation of two factors important in motoneuron dysfunction, ER stress and mTOR activation, it does not aggravate motoneuron death. Our results underline a prevalent role for CRT levels in the early phase of muscle denervation and support CRT regulation as a potential therapeutic approach. PMID:25277755

Bernard-Marissal, Nathalie; Sunyach, Claire; Marissal, Thomas; Raoul, Cédric; Pettmann, Brigitte

2015-01-01

33

Disruption of the PP1/GADD34 complex induces calreticulin exposure.  

PubMed

In response to some chemotherapeutic agents, tumor cells can translocate calreticulin (CRT), which is usually contained in the lumen of the endoplasmic reticulum, to the surface of the plasma membrane. This effect requires the phosphorylation of the eukaryotic initiation factor 2alpha(eIF2alpha) by the eIF2alpha kinase PERK, yet may also be triggered by inhibition of the eIF2alpha phosphatase, which is composed by a catalytic subunit (PP1) and a regulatory subunit (GADD34). Here, we addressed the question whether the dissociation of the PP1/GADD34 complex would be sufficient to trigger CRT exposure. Molecular modeling led to the design of a GADD34-derived peptide that competitively disrupts the PP1/GADD34 complex. When added to intact cells, the GADD34-derived peptide fused to a plasma membrane translocation domain abolished the interaction between PP1 and GADD34, stimulated the phosphorylation of eIF2alpha, and triggered CRT exposure. However, the resolution of the PP1/GADD34 complex did not evoke apoptosis, allowing for the dissociation of CRT exposure and cell death. Anthracyclins, which are highly efficient in inducing CRT translocation to the cell surface also stimulated the dissociation of the PP1/GADD34 complex. These results suggest that the PP1/GADD34 complex plays a major role in the regulation of CRT exposure. PMID:19901557

Kepp, Oliver; Galluzzi, Lorenzo; Giordanetto, Fabrizio; Tesniere, Antoine; Vitale, Ilio; Martins, Isabelle; Schlemmer, Frederic; Adjemian, Sandy; Zitvogel, Laurence; Kroemer, Guido

2009-12-01

34

Calreticulin is localized at mitochondria of rat cardiomyocytes and affected by furazolidone.  

PubMed

Calreticulin (CRT) is a calcium-buffering protein which is predominantly located in endoplasmic reticulum. In the previous mitochondria proteome analysis, we accidentally found that CRT may be also localized at myocardial mitochondria and was upregulated in a rat model of furazolidone-induced dilated cardiomyopathy. To our knowledge, there has not yet been any report of its presence in mitochondria of any cell types. The present study aimed to determine whether CRT was located at the mitochondria of rat cardiomyocytes and whether the mitochondrial CRT was affected by furazolidone. Mitochondrial preparations were isolated from primary cultured neonatal rat cardiomyocytes and purified by differential centrifugation. The purity of mitochondria was assessed by the reduction or elimination of the immunoreactivities of markers for cytosol, nucleus, sarcolemma, and endoplasmic reticulum. Western blot analysis demonstrated the presence of CRT in purified mitochondria of rat cardiomyocytes. The distribution of CRT to mitochondria was further confirmed by immuno-electron microscopy, flow cytometry, and laser scanning confocal microscopy (double staining with MitoTracker Red and CRT-Alexa Fluor 488). Western blot analysis also demonstrated that the mitochondrial content of CRT was significantly enhanced by furazolidone treatment by 2.73 ± 0.13 fold (P < 0.05) in rat cardiomyocytes, which was verified by immuno-electron microscopy. In summary, the present results suggest that CRT is localized at mitochondria of rat cardiomyocytes and such localization is affected by furazolidone. PMID:25087122

Shan, Hu; Wei, Jin; Zhang, Ming; Lin, Lin; Yan, Rui; Zhu, Yanhe; Zhang, Rong

2014-12-01

35

Identification of the Rheumatoid Arthritis Shared Epitope Binding Site on Calreticulin  

PubMed Central

Background The rheumatoid arthritis (RA) shared epitope (SE), a major risk factor for severe disease, is a five amino acid motif in the third allelic hypervariable region of the HLA-DR? chain. The molecular mechanisms by which the SE affects susceptibility to – and severity of - RA are unknown. We have recently demonstrated that the SE acts as a ligand that interacts with cell surface calreticulin (CRT) and activates innate immune signaling. In order to better understand the molecular basis of SE-RA association, here we have undertaken to map the SE binding site on CRT. Principal Findings Surface plasmon resonance (SPR) experiments with domain deletion mutants suggested that the SE binding site is located in the P-domain of CRT. The role of this domain as a SE-binding region was further confirmed by a sulfosuccinimidyl-2-[6-(biotinamido)-2-(p-azido-benzamido) hexanoamido] ethyl-1,3-dithiopropionate (sulfo-SBED) photoactive cross-linking method. In silico analysis of docking interactions between a conformationally intact SE ligand and the CRT P-domain predicted the region within amino acid residues 217–224 as a potential SE binding site. Site-directed mutagenesis demonstrated involvement of residues Glu217 and Glu223 - and to a lesser extent residue Asp220 - in cell-free SPR-based binding and signal transduction assays. Significance We have characterized here the molecular basis of a novel ligand-receptor interaction between the SE and CRT. The interaction represents a structurally and functionally well-defined example of cross talk between the adaptive and innate immune systems that could advance our understanding of the pathogenesis of autoimmunity. PMID:20661469

Ling, Song; Cheng, Andrew; Pumpens, Paul; Michalak, Marek; Holoshitz, Joseph

2010-01-01

36

Topical application of recombinant calreticulin peptide, vasostatin 48, alleviates laser-induced choroidal neovascularization in rats  

PubMed Central

Purpose Vasostatin 48 (VS48) is a peptide of 48 amino acids derived from calreticulin. This study aimed to investigate the effects of topical application of VS48 eyedrops on experimental choroidal neovascularization (CNV). Methods Recombinant VS48 was expressed and purified as a thioredoxin (TRX)-fused protein, TRX-VS48. The anti-angiogenic effects of TRX-VS48 were validated by migration and tube formation assays performed on cultured endothelial cells, and by rat aorta ring assays. CNV lesions were created in Brown Norway rats by laser-induced photocoagulation at day 1. After topical TRX-VS48 application for 21 days, the CNV lesions were monitored via either choroidal flat mounts on day 21 or by fluorescent angiography on days 21, 28, 35, and 42. CNV lesions were evaluated by histological analysis. The retinal function of animals was examined by electroretinogram (ERG) to evaluate the safety and therapeutic efficacy of TRX-VS48. Results Application of TRX-VS48 inhibited the migration and tube formation of endothelial cells. TRX-VS48 inhibited the growth of sprouting vessels in aorta rings. ERG analysis revealed that topical TRX-VS48 application for 21 days had no effect on rat retinal functions. After CNV induction, topical TRX-VS48 application for 21 days significantly reduced the size of CNV, as assayed by flat mounts. Fluorescent angiography revealed that the CNV areas in TRX-VS48-treated eyes were significantly reduced compared with TRX-treated eyes on days 21, 28, 35, and 42. Histological analysis also revealed attenuated CNV lesions in TRX-VS48-treated eyes. Topical TRX-VS48 treatment significantly reversed the CNV-induced alterations in ERG parameters on day 35. Conclusions Topical TRX-VS48 application suppressed laser-induced CNV in rats, thereby constituting a possible modality for ocular diseases due to excessive angiogenesis. PMID:20454694

Bee, Youn-Shen; Sheu, Shwu-Jiuan; Ma, Yi-Ling; Lin, Hsiu-Chen; Weng, Wen-Tsang; Kuo, Hsiao-Mei; Hsu, Huei-Chun; Tang, Chia-Hua; Liou, Jau-Cheng

2010-01-01

37

EPAC2-mediated calreticulin regulates LIF and COX2 expression in human endometrial glandular cells.  

PubMed

The proper production of the implantation-related factors, leukemia inhibitory factor (LIF), cyclooxygenase 2 (COX2, PTGS2), and prostaglandin E2 (PGE2) in the uterine glands is essential for embryo implantation and the establishment of endometrial receptivity. It has been shown that cAMP-mediated protein kinase A (PKA) signaling regulates the production of these factors. We have previously reported that exchange protein directly activated by cAMP 2 (EPAC2, RAPGEF4), another cAMP mediator, is involved in the differentiation of endometrial stromal cells through the regulation of the expression of calreticulin (CALR). To address whether EPAC2-CALR signaling is involved in the expression of implantation-related factors, we examined the effect of EPAC2 and CALR knockdown on their expression in cultured human endometrial glandular epithelial EM1 cells, treated with forskolin, an adenylyl cyclase activator, an EPAC-selective cAMP analog (8-(4-chlorophenylthio)-2'-O-methyl cAMP (CPT)), or a PKA-selective cAMP analog (N(6)-phenyl-cAMP (Phe)). In addition, the status of cell senescence was examined. EPAC2 knockdown suppressed the expression of CALR protein and mRNA in EM1 cells. Forskolin- or Phe-, but not CPT-, induced expression of LIF or PTGS2 and secretion of PGE2 was inhibited in EPAC2- or CALR-silenced EM1 cells. In addition, knockdown of EPAC2 or CALR increased senescence-associated beta galactosidase activity and expression of p21 but decreased expression of p53. These findings indicate that expression of CALR regulated by EPAC2 in endometrial glandular epithelial cells is critical for the expression of LIF and PTGS2-mediated production of PGE2 through cAMP signaling. Furthermore, EPAC2 and CALR could play a role in the maintenance of gland function. PMID:25378661

Kusama, Kazuya; Yoshie, Mikihiro; Tamura, Kazuhiro; Imakawa, Kazuhiko; Tachikawa, Eiichi

2015-02-01

38

Calreticulin promotes angiogenesis via activating nitric oxide signalling pathway in rheumatoid arthritis.  

PubMed

Calreticulin (CRT) is a multi-functional endoplasmic reticulum protein implicated in the pathogenesis of rheumatoid arthritis (RA). The present study was undertaken to determine whether CRT was involved in angiogenesis via the activating nitric oxide (NO) signalling pathway. We explored the profile of CRT expression in RA (including serum, synovial fluid and synovial tissue). In order to investigate the role of CRT on angiogenesis, human umbilical vein endothelial cells (HUVECs) were isolated and cultured in this study for in-vitro experiments. Our results showed a significantly higher concentration of CRT in serum (5·4?±?2·2?ng/ml) of RA patients compared to that of osteoarthritis (OA, 3·6?±?0·9?ng/ml, P?

Ding, H; Hong, C; Wang, Y; Liu, J; Zhang, N; Shen, C; Wei, W; Zheng, F

2014-11-01

39

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

PubMed Central

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.; Jammed, Momodou L.; Wattenberg, Max M.; Tsang, Kwong Y.; Ferrone, Soldano; Hodge, James W.

2014-01-01

40

Ectopic expression of a maize calreticulin mitigates calcium deficiency-like disorders in "sCAX1"-expressing tobacco and tomato  

Technology Transfer Automated Retrieval System (TEKTRAN)

Deregulated expression of an Arabidopsis H(+)/Ca(2+) antiporter (sCAX1) in agricultural crops increases total calcium (Ca(2+)) but may result in yield losses due to Ca(2+) deficiency-like symptoms. Here we demonstrate that co-expression of a maize calreticulin (CRT, a Ca(2+) binding protein located ...

41

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. 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

42

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 PMID:7520419

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

1994-01-01

43

Genotoxicity induced by Taenia solium and its reduction by immunization with calreticulin in a hamster model of taeniosis.  

PubMed

Genotoxicity induced by neurocysticercosis has been demonstrated in vitro and in vivo in humans. The adult stage of Taenia solium lodges in the small intestine and is the main risk factor to acquire neurocysticercosis, nevertheless its carcinogenic potential has not been evaluated. In this study, we determined the genotoxic effect of T. solium infection in the hamster model of taeniosis. In addition, we assessed the effect of oral immunization with recombinant T. solium calreticulin (rTsCRT) plus cholera toxin as adjuvant on micronuclei induction, as this protein has been shown to induce 33-44% protection in the hamster model of taeniosis. Blood samples were collected from the orbital venous plexus of noninfected and infected hamsters at different days postinfection, as well as from orally immunized animals, to evaluate the frequency of micronucleated reticulocytes as a measure of genotoxicity induced by parasite exposure and rTsCRT vaccination. Our results indicate that infection with T. solium caused time-dependent DNA damage in vivo and that rTsCRT immunization reduced the genotoxic damage induced by the presence of the tapeworms. PMID:23704053

Salazar, Ana María; Mendlovic, Fela; Cruz-Rivera, Mayra; Chávez-Talavera, Oscar; Sordo, Monserrat; Avila, Guillermina; Flisser, Ana; Ostrosky-Wegman, Patricia

2013-06-01

44

Occurrence of calreticulin during the exchange of nucleohistones into protamine-type proteins in Chara vulgaris spermiogenesis.  

PubMed

During spermiogenesis of an alga Chara vulgaris, which resembles that of animals, nucleohistones are replaced by protamine-type proteins. This exchange takes place in a spermatid nucleus during the key V spermiogenesis stage, in which rough endoplasmic reticulum is the site of protamine-type protein synthesis and is also the pathway guiding the proteins to their destination, nucleus. In the present work, it was shown that a chaperon protein, calreticulin (CRT), abundantly present at this significant V stage of spermiogenesis in a few cellular compartments, i.e., a nucleus, lumen of cisternae, and vesicles of significantly swollen ER as well as outside these structures, e.g., in Golgi apparatus, could have taken part in the process of exchange of nuclear proteins. Colocalization of two proteins, protamine-type proteins, crucial for reproduction, and CRT, was especially visible in a nucleus, mainly on its peripheries where condensed chromatin was present. Localization of protamine-type proteins and CRT in nucleus is in agreement with our previous results showing that protamine-type proteins were twofold more labelled in the peripheral area in comparison to the nucleus center occupied by noncondensed chromatin. The role of CRT in the reproduction of both plants and animals is also discussed. PMID:22198493

Pop?o?ska, Katarzyna

2013-02-01

45

Catalyzed Ceramic Burner Material  

SciTech Connect

Catalyzed combustion offers the advantages of increased fuel efficiency, decreased emissions (both NOx and CO), and an expanded operating range. These performance improvements are related to the ability of the catalyst to stabilize a flame at or within the burner media and to combust fuel at much lower temperatures. This technology has a diverse set of applications in industrial and commercial heating, including boilers for the paper, food and chemical industries. However, wide spread adoption of catalyzed combustion has been limited by the high cost of precious metals needed for the catalyst materials. The primary objective of this project was the development of an innovative catalyzed burner media for commercial and small industrial boiler applications that drastically reduce the unit cost of the catalyzed media without sacrificing the benefits associated with catalyzed combustion. The scope of this program was to identify both the optimum substrate material as well as the best performing catalyst construction to meet or exceed industry standards for durability, cost, energy efficiency, and emissions. It was anticipated that commercial implementation of this technology would result in significant energy savings and reduced emissions. Based on demonstrated achievements, there is a potential to reduce NOx emissions by 40,000 TPY and natural gas consumption by 8.9 TBtu in industries that heavily utilize natural gas for process heating. These industries include food manufacturing, polymer processing, and pulp and paper manufacturing. Initial evaluation of commercial solutions and upcoming EPA regulations suggests that small to midsized boilers in industrial and commercial markets could possibly see the greatest benefit from this technology. While out of scope for the current program, an extension of this technology could also be applied to catalytic oxidation for volatile organic compounds (VOCs). Considerable progress has been made over the course of the grant period in accomplishing these objectives. Our work in the area of Pd-based, methane oxidation catalysts has led to the development of highly active catalysts with relatively low loadings of Pd metal using proprietary coating methods. The thermal stability of these Pd-based catalysts were characterized using SEM and BET analyses, further demonstrating that certain catalyst supports offer enhanced stability toward both PdO decomposition and/or thermal sintering/growth of Pd particles. When applied to commercially available fiber mesh substrates (both metallic and ceramic) and tested in an open-air burner, these catalyst-support chemistries showed modest improvements in the NOx emissions and radiant output compared to uncatalyzed substrates. More significant, though, was the performance of the catalyst-support chemistries on novel media substrates. These substrates were developed to overcome the limitations that are present with commercially available substrate designs and increase the gas-catalyst contact time. When catalyzed, these substrates demonstrated a 65-75% reduction in NOx emissions across the firing range when tested in an open air burner. In testing in a residential boiler, this translated into NOx emissions of <15 ppm over the 15-150 kBtu/hr firing range.

Barnes, Amy S., Dr.

2012-06-29

46

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

47

Role of calreticulin in the sensitivity of myocardiac H9c2 cells to oxidative stress caused by hydrogen peroxide.  

PubMed

Calreticulin (CRT), a Ca2+-binding molecular chaperone in the endoplasmic reticulum, plays a vital role in cardiac physiology and pathology. Oxidative stress is a main cause of myocardiac apoptosis in the ischemic heart, but the function of CRT under oxidative stress is not fully understood. In the present study, the effect of overexpression of CRT on susceptibility to apoptosis under oxidative stress was examined using myocardiac H9c2 cells transfected with the CRT gene. Under oxidative stress due to H2O2, the CRT-overexpressing cells were highly susceptible to apoptosis compared with controls. In the overexpressing cells, the levels of cytoplasmic free Ca2+ ([Ca2+]i) were significantly increased by H2O2, whereas in controls, only a slight increase was observed. The H2O2-induced apoptosis was enhanced by the increase in [Ca2+]i caused by thapsigargin in control cells but was suppressed by BAPTA-AM, a cell-permeable Ca2+ chelator in the CRT-overexpressing cells, indicating the importance of the level of [Ca2+]i in the sensitivity to H2O2-induced apoptosis. Suppression of CRT by the introduction of the antisense cDNA of CRT enhanced cytoprotection against oxidative stress compared with controls. Furthermore, we found that the levels of activity of calpain and caspase-12 were elevated through the regulation of [Ca2+]i in the CRT-overexpressing cells treated with H2O2 compared with controls. Thus we conclude that the level of CRT regulates the sensitivity to apoptosis under oxidative stress due to H2O2 through a change in Ca2+ homeostasis and the regulation of the Ca2+-calpain-caspase-12 pathway in myocardiac cells. PMID:16135540

Ihara, Yoshito; Urata, Yoshishige; Goto, Shinji; Kondo, Takahito

2006-01-01

48

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

49

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. PMID:24860808

Ximénez, Cecilia; González, Enrique; Nieves, Miriam E.; Silva-Olivares, Angélica; Shibayama, Mineko; Galindo-Gómez, Silvia; Escobar-Herrera, Jaime; García de León, Ma del Carmen; Morán, Patricia; Valadez, Alicia; Rojas, Liliana; Hernández, Eric G.; Partida, Oswaldo; Cerritos, René

2014-01-01

50

Gold-Catalyzed Multi-Component Reactions  

NASA Astrophysics Data System (ADS)

The following sections are included: * Introduction * Gold-Catalyzed Three-Component Reactions * Gold-Catalyzed Three-Component Reactions/Tandem Cyclization * Concluding Remarks * Acknowledgments * References

Skouta, Rachid; Li, Chao-Jun

2014-04-01

51

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

52

Enantioselective nucleophile-catalyzed cycloadditions  

E-print Network

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

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

2007-01-01

53

Reductions of the components of the calreticulin/calnexin quality-control system by proteasome inhibitors and their relevance in a rodent model of Parkinson's disease.  

PubMed

Evidence indicates that the ubiquitin-proteasome system and the endoplasmic retculum (ER) quality-control system work in concert to ensure that proteins are correctly folded in the ER and that misfolded proteins are retrotransported to the cytosol for degradation by proteasomes. Dysfunction of either system results in developmental abnormalities and even death in animals. This study investigates whether and how proteasome inhibition impacts the components of the calreticulin (CRT)/calnexin (CNX) glycoprotein folding machinery, a typical ER protein quality-control system, in the context of early neuronal injury. Here we report that proteasome inhibitor treatments, at nonlethal levels, reduced protein levels of CRT and ERp57 but not of CNX. These treatments increased protein levels of CRT in culture media, an effect blocked by brefeldin A, an inhibitor of protein trafficking; by contrast, ERp57 was not detected in culture media. Knockdown of CRT levels alone increased the vulnerability of SH-SY5Y, a neuronal cell line, to 6-hydroxydopamine (6-OHDA) toxicity. In a rat model of Parkinson's disease, intrastriatal 6-OHDA lesions resulted in decreased levels of CRT and ERp57 in the midbrain. These findings suggest that reduction of the components of CRT/CNX glycoprotein quality-control system may play a role in neuronal injury in Parkinson's disease and other neurodegenerative disorders associated with dysfunction of the ubiquitin-proteasome system. PMID:24860980

Kuang, Xiu-Li; Liu, Fang; Chen, Huifang; Li, Yiping; Liu, Yimei; Xiao, Jian; Shan, Ge; Li, Mingjie; Snider, B Joy; Qu, Jia; Barger, Steven W; Wu, Shengzhou

2014-10-01

54

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. PMID:24566135

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

2014-01-01

55

Adjuvanticity of a Recombinant Calreticulin Fragment in Assisting Anti-?-Glucan IgG Responses in T Cell-Deficient Mice  

PubMed Central

Polysaccharide-encapsulated fungi are the chief source of diseases in immunocompromised hosts such as those infected with human immunodeficiency virus or neutropenia patients. Currently available polysaccharide-protein conjugate vaccines are mainly T cell dependent and are usually ineffective in weakened immune systems. In this study, laminarin, a well-characterized ?-1,3-glucan, was conjugated with a prokaryotically expressed recombinant fragment (amino acids [aa] 39 to 272) of calreticulin (rCRT/39–272), which exhibits extraordinarily potent immunogenicity and adjuvanticity in experimental animals. The resultant conjugate reserves the immunostimulatory effect of rCRT/39–272 on naïve murine B cells and is capable of eliciting anti-?-glucan IgG (mostly IgG1) responses in not only BALB/c mice but also athymic nude mice. Laminarin-CRT-induced mouse antibodies (Abs) are able to bind with Candida albicans and inhibit its growth in vitro. In addition, vaccination with laminarin-CRT partially protects mice from lethal C. albicans challenge. These results imply that rCRT/39–272 could be used as an ideal carrier or adjuvant for carbohydrate vaccines aimed at inducing or boosting IgG responses to fungal infections in immunodeficient hosts. PMID:23408527

Li, Wei-Ji; Long, Kai; Dong, Hong-Liang

2013-01-01

56

Is it all That Bad When Living with an Intracellular Protozoan? The Role of Trypanosoma cruzi Calreticulin in Angiogenesis and Tumor Growth  

PubMed Central

The immune system protects against disease, but may aberrantly silence immunity against “altered self,” with consequent development of malignancies. Among the components of the endoplasmic reticulum (ER), important in immunity, is calreticulin (CRT) that, in spite of its residence in the ER, can be translocated to the exterior. Trypanosoma cruzi is the agent of Chagas disease, one of the most important global neglected infections, affecting several hundred thousand people. The syndrome, mainly digestive and circulatory, affects only one-third of those infected. The anti-tumor effects of the infection are known for several decades, but advances in the identification of responsible T. cruzi molecules are scarce. We have shown that T. cruzi CRT (TcCRT) better executes the antiangiogenic and anti-tumor effects of mammal CRT and its N-terminus vasostatin. In this regard, recombinant TcCRT (rTcCRT) and/or its N-terminus inhibit angiogenesis in vitro, ex vivo, and in vivo. TcCRT also inhibits the growth of murine adenocarcinomas and melanomas. Finally, rTcCRT fully reproduces the anti-tumor effect of T. cruzi infection in mice. Thus, we hypothesize that, the long reported anti-tumor effect of T. cruzi infection is mediated at least in part by TcCRT.

Ramírez-Toloza, Galia; Aguilar-Guzmán, Lorena; Valck, Carolina; Abello, Paula; Ferreira, Arturo

2014-01-01

57

Calreticulin expression in relation to exchangeable Ca(2+) level that changes dynamically during anthesis, progamic phase, and double fertilization in Petunia.  

PubMed

Calcium (Ca(2+)) plays essential roles in plant sexual reproduction, but the sites and the mechanism of Ca(2+) mobile storage during pollen-pistil interactions have not been fully defined. Because the Ca(2+)-buffering protein calreticulin (CRT) is able to bind and sequester Ca(2+), it can serve as a mobile intracellular store of easily releasable Ca(2+) and control its local concentration within the cytoplasm. Our previous studies showed an enhanced expression of Petunia hybrida CRT gene (PhCRT) during pistil transmitting tract maturation, pollen germination and tube outgrowth on the stigma, gamete fusion, and early embryogenesis. Here, we demonstrate that elevated expression of CRT results in the accumulation of this protein in response to anthesis, pollination, sperm cells deposition within the receptive synergid and fertilization, when the level of exchangeable Ca(2+) changes dynamically. CRT localizes mainly to the endoplasmic reticulum and Golgi compartments in the pistil transmitting tract cells, germinated pollen/tubes, and sporophytic/gametophytic cells of the ovule and corresponds with loosely bound Ca(2+). Additionally, the immunogold research shows, for the first time, highly selective CRT distribution in specific nuclear sub-domains. On the basis of our results, we discuss the possible functions of CRT with respect to the critical role of Ca(2+) homeostasis during key events of the multi-step process of generative reproduction in angiosperms. PMID:25262422

Lenartowski, Robert; Suwi?ska, Anna; Lenartowska, Marta

2015-01-01

58

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

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. PMID:24566135

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

2014-01-01

59

Changes in the Glucocorticoid Receptor and Ca(2+)/Calreticulin-Dependent Signalling Pathway in the Medial Prefrontal Cortex of Rats with Post-traumatic Stress Disorder.  

PubMed

The glucocorticoid receptor (GR), calreticulin (CRT) and protein kinase C (PKC) have all been implicated in the Ca(2+)-dependent signalling pathway, which plays an important role in the plasticity of the central nervous system, learning and memory. The medial prefrontal cortex (mPFC) is known to be involved in mechanisms of learning and memory. In the present study, single prolonged stress (SPS) was used as an animal model of post-traumatic stress disorder (PTSD). The Morris water maze test was used to detect rats' ability for spatial memory and learning. A fluorescence spectrophotometer was used to measure the concentration of intracellular Ca(2+) in mPFC. Immunohistochemistry, immunofluorescence, western blot and reverse transcription polymerase chain reaction were used to explore changes in GR, CRT and PKC in mPFC of SPS rats. The concentration of Ca(2+) in mPFC was increased in the SPS rats. We found increased intensity of GR and CRT immunoreactivity and increased messenger RNA (mRNA) levels of GR, CRT and PKC in mPFC of the SPS groups, although the degree and time of increase was different among them. The protein levels of cytoplasmic GR, cytoplasmic CRT and cytoplasmic pPKC increased in mPFC of the SPS groups, whereas the protein level of nuclear GR decreased in comparison with the control group. As a conclusion, changed CRT and GR/PKC were involved in the mechanism of SPS-induced dysfunctional mPFC. PMID:25407822

Wen, Lili; Han, Fan; Shi, Yuxiu

2014-11-19

60

Iron Catalyzed Aminohydroxylation of Olefins  

PubMed Central

We have discovered that N-sulfonyl oxaziridines react with a broad range of olefins in the presence of iron salts to afford 1,3-oxazolidines. This process provides access to 1,2-aminoalcohols with the opposite sense of regioselectivity produced from the copper-catalyzed oxyamination previously reported from our labs. Thus, either regioisomeric form of 1,2-aminoalcohols can easily be obtained from the reaction of oxaziridines with olefins, and the sense of regioselectivity can be controlled by the appropriate choice of inexpensive, non-toxic first row transition metal catalyst. PMID:20232850

Williamson, Kevin S.; Yoon, Tehshik P.

2010-01-01

61

Stau-catalyzed Nuclear Fusion  

E-print Network

We point out that the stau may play a role of a catalyst for nuclear fusions if the stau is a long-lived particle as in the scenario of gravitino dark matter. In this letter, we consider d d fusion under the influence of stau where the fusion is enhanced because of a short distance between the two deuterons. We find that one chain of the d d fusion may release an energy of O(10) GeV per stau. We discuss problems of making the stau-catalyzed nuclear fusion of practical use with the present technology of producing stau.

K. Hamaguchi; T. Hatsuda; T. T. Yanagida

2006-07-24

62

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.

63

Enzyme-catalyzed polymerization to functional polymers  

Microsoft Academic Search

In this article, described are our recent advances in enzymatic polymerization, defined as chemical polymer syntheses in vitro (in test tubes) via non-biosynthetic pathways catalyzed by an isolated enzyme. The major target macromolecules formed via the enzymatic polymerizations in this article are polyesters and polyphenols. For synthesis of polyesters, hydrolases are used as catalyst; hydrolases, enzymes catalyzing a bond-cleavage reaction

Hiroshi Uyama; Shiro Kobayashi

2002-01-01

64

Copper-Catalyzed Trifluoromethylation of Unactivated Olefins  

E-print Network

Activating the inactive: A copper-catalyzed allylic trifluoromethylation of unactivated terminal olefins proceeds under mild conditions to produce linear allylic trifluoromethylated products with high E/Z selectivity (see ...

Parsons, Andrew T.

65

Trypsin-Catalyzed Deltamethrin Degradation  

PubMed Central

To explore if trypsin could catalyze the degradation of non-protein molecule deltamethrin, we compared in vitro hydrolytic reactions of deltamethrin in the presence and absence of trypsin with ultraviolet-visible (UV/Vis) spectrophotometry and gas chromatography-mass spectrometry (GC/MS). In addition, acute oral toxicity of the degradation products was determined in Wistar rats. The results show that the absorption peak of deltamethrin is around 264 nm, while the absorption peaks of deltamethrin degradation products are around 250 nm and 296 nm. In our GC setting, the retention time of undegraded deltamethrin was 37.968 min, while those of deltamethrin degradation products were 15.289 min and 18.730 min. The LD50 of deltamethrin in Wistar rats is 55 mg/kg, while that of deltamethrin degradation products is 3358 mg/kg in female rats and 1045 mg/kg in male rates (61-fold and 19-fold reductions in toxicity), suggesting that trypsin could directly degrade deltamethrin, which significantly reduces the toxicity of deltamethrin. These results expand people's understanding of the functions of proteases and point to potential applications of trypsin as an attractive agent to control residual pesticides in the environment and on agricultural products. PMID:24594869

Xiong, Chunrong; Fang, Fujin; Chen, Lin; Yang, Qinggui; He, Ji; Zhou, Dan; Shen, Bo; Ma, Lei; Sun, Yan; Zhang, Donghui; Zhu, Changliang

2014-01-01

66

Transition metal catalyzed borylation of functional ?-systems  

PubMed Central

Borylated functional ?-systems are useful building blocks to enable efficient synthesis of novel molecular architectures with beautiful structures, intriguing properties and unique functions. Introduction of boronic ester substituents to a variety of extended ?-systems can be achieved through either iridium-catalyzed direct C–H borylation or the two-step procedure via electrophilic halogenation followed by palladium-catalyzed borylation. This review article focuses on our recent progress on borylation of large ?-conjugated systems such as porphyrins, perylene bisimides, hexabenzocoronenes and dipyrrins. PMID:24492644

SHINOKUBO, Hiroshi

2014-01-01

67

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. (Richland, WA); Hu, Jianli (Kennewick, WA); Hart, Todd R. (Kennewick, WA); Neuenschwander, Gary G. (Burbank, WA)

2008-09-16

68

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. PMID:22142553

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

2014-01-01

69

Titanium-Catalyzed Enantioselective Additions of  

E-print Network

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

Walsh, Patrick J.

70

Ruthenium-catalyzed regioselective allylic trifluoromethylthiolation reaction.  

PubMed

An efficient Ru-catalyzed regioselective allylic trifluoromethylthiolation reaction of allylic carbonates was developed. The linear allylic trifluoromethyl thioethers were obtained in 52-91% yields. Mechanistic investigation revealed that this reaction proceeds via a double allylic trifluoromethylthiolation sequence. PMID:25203498

Ye, Ke-Yin; Zhang, Xiao; Dai, Li-Xin; You, Shu-Li

2014-12-19

71

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

72

Zeolite 5A Catalyzed Etherification of Diphenylmethanol  

ERIC Educational Resources Information Center

An experiment for the synthetic undergraduate laboratory is described in which zeolite 5A catalyzes the room temperature dehydration of diphenylmethanol, (C[subscript 6]H[subscript 5])[subscript 2]CHOH, producing 1,1,1',1'-tetraphenyldimethyl ether, (C[subscript 6]H[subscript 5])[subscript 2]CHOCH(C[subscript 6]H[subscript 5])[subscript 2]. The…

Cooke, Jason; Henderson, Eric J.; Lightbody, Owen C.

2009-01-01

73

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. PMID:22804336

Zhu, Rong; Buchwald, Stephen L.

2012-01-01

74

Stochastic Simulation of Enzyme-Catalyzed Reactions with Disparate Timescales  

E-print Network

Stochastic Simulation of Enzyme-Catalyzed Reactions with Disparate Timescales Debashis Barik-steady-state approximation'' for enzyme-catalyzed reactions provides a useful framework for efficient and accurate stochastic simulations. The method is applied to three examples: a simple enzyme-catalyzed reaction where enzyme

Paul, Mark

75

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

76

Nonmetal catalyzed hydrogenation of carbonyl compounds.  

PubMed

Solutions of the Lewis acid B(C6F5)3 in 1,4-dioxane are found to effectively catalyze the hydrogenation of a variety of ketones and aldehydes. These reactions, the first to allow entirely metal-free catalytic hydrogenation of carbonyl groups under relatively mild reaction conditions, are found to proceed via a "frustrated Lewis pair" mechanism in which the solvent, a weak Brønsted base yet moderately strong donor, plays a pivotal role. PMID:25333722

Scott, Daniel J; Fuchter, Matthew J; Ashley, Andrew E

2014-11-12

77

Lipase catalyzed alcoholysis of sunflower oil  

Microsoft Academic Search

Lipase-catalyzed alcoholysis of sunflower oil under anhydrous conditions was examined. Lipases fromPseudomonas fluorescens and 2 immobilized enzymes fromMucor miehei and aCandida sp. gave sufficient conversion with petroleum ether as the solvent, even when methanol and ethanol were used. The overall content\\u000a of tri-, di- and monoglycerides, as well as the corresponding alkyl esters, was measured. BecausePseudomonas lipase led to almost

Martin Mittelbach; Karl Franzens

1990-01-01

78

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

79

Indium-catalyzed intramolecular hydroarylation of aryl propargyl ethers.  

PubMed

Indium(iii) halides catalyze efficiently the intramolecular hydroarylation (IMHA) of aryl propargyl ethers. The reaction proceeds regioselectively with terminal and internal alkynes bearing electron-rich and electron-deficient substituents in the benzenes and alkynes affording only the 6-endo dig cyclization product. Additionally, a sequential indium-catalyzed IMHA and palladium-catalyzed Sonogashira coupling can be performed in one reaction vessel. Experiments with deuterium support a mechanism through electrophilic aromatic substitution. PMID:25376147

Alonso-Marañón, Lorena; Martínez, M Montserrat; Sarandeses, Luis A; Sestelo, José Pérez

2015-01-14

80

Ferric microperoxidase-11 catalyzes peroxynitrite isomerization.  

PubMed

Microperoxidase-11 (MP11) is an undecapeptide derived from horse heart cytochrome c offering the possibility to study the reactivity of the heme group relatively unshielded by the protein. Here, the peroxynitrite isomerization to NO3(-) catalyzed by ferric MP11 (MP11-Fe(III)) is reported. Data were obtained between pH3.6 and 8.1, at 20.0°C. The value of the second-order rate constant (kon) for peroxynitrite isomerization to NO3(-) by MP11-Fe(III) decreases from (1.1±0.1)×10(5)M(-1)s(-1), at pH3.6, to (6.1±0.6)×10(3)M(-1)s(-1), at pH8.1. The pH dependence of kon (pKa=6.9) suggests that peroxynitrous acid reacts preferentially with MP11-Fe(III). The MP11-Fe(III)-catalyzed isomerization of peroxynitrite to NO3(-) has been ascribed to the reactive penta-coordinated heme-Fe atom of MP11-Fe(III). In fact, cyanide binding to the sixth coordination position of the heme-Fe atom inhibits the MP11-Fe(III)-catalyzed isomerization of peroxynitrite to NO3(-). The values of the first-order rate constant (k0) for isomerization of peroxynitrite to NO3(-) in the presence of the MP11-Fe(III)-CN complex are superimposable to those obtained in the absence of MP-Fe(III). Values of kon for peroxynitrite isomerization to NO3(-) by MP11-Fe(III) overlap those obtained for penta-coordinated cardiolipin-cytochrome c complex and for carboxymethylated cytochrome c in absence and presence of cardiolipin. Present results highlight the role of the heme-Fe(III) co-ordination state in the modulation of cytochrome c reactivity. PMID:25578411

Ascenzi, Paolo; Leboffe, Loris; Santucci, Roberto; Coletta, Massimo

2015-03-01

81

N-Heterocyclic Carbene-Catalyzed Oxidations  

PubMed Central

N-Heterocyclic carbenes catalyze the oxidation of allylic and benzylic alcohols as well as saturated aldehydes to esters with manganese(IV) oxide in excellent yields. A variety of esters can be synthesized, including protected carboxylates. The oxidation proceeds under mild conditions, with low loadings of a simple triazolium salt pre-catalyst in the presence of base. Substrates containing potentially epimerizable centers are oxidized while preserving stereochemical integrity. The acyl triazolium intermediate generated under catalytic conditions can be employed as a chiral acylating agent in the desymmetrization of meso-diols. PMID:20161230

Maki, Brooks E.; Chan, Audrey; Phillips, Eric M.; Scheidt, Karl A.

2009-01-01

82

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. PMID:22912792

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

2012-01-01

83

Mechanism of combustion of catalyzed double base propellants  

Microsoft Academic Search

Existing combustion models, namely, photo chemical theory, chelate and ..pi..-complex theory, and free radical mechanism and carbon\\/carbonaceous matter formation theory, for catalyzed double base propellants have been evaluated in the light of the experimental findings of the present study. Results obtained suggest that carbon formation and its availability to catalyze the reactions in foam and fizz zones are the probable

H. Singh; K. R. K. Rao

1988-01-01

84

Synthetic applications of gold-catalyzed ring expansions  

PubMed Central

Summary The development of new methodologies catalyzed by late transition metals involving cycloisomerizations of strained rings can open new venues for the synthesis of structurally complex molecules with interesting biological activities. Herein we summarize, from both a synthetic as well as a mechanistic point of view, the most recent developments in gold-catalyzed ring expansions. PMID:21772928

Garayalde, David

2011-01-01

85

Au(I)-Catalyzed Ring Expanding Cycloisomerizations: Total Synthesis of  

E-print Network

Au(I)-Catalyzed Ring Expanding Cycloisomerizations: Total Synthesis of Ventricosene Steven G The gold(I)-catalyzed cycloisomerization of enynes containing an embedded cyclopropane unit leads assembly of polycyclic ring systems is illustrated by the total synthesis of the angular triquinane

Toste, Dean

86

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

87

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

88

ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT: ENVIROFUELS DIESEL FUEL CATALYZER FUEL ADDITIVE  

EPA Science Inventory

EPA's Environmental Technology Verification Program has tested EnviroFuels diesel fuel additive, called the Diesel Fuel Catalyzer. EnviroFuels has stated that heavy-duty on and off road diesel engines are the intended market for the catalyzer. Preliminary tests conducted indicate...

89

RNA-Catalyzed RNA Ligation on an External RNA Template  

NASA Technical Reports Server (NTRS)

Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside '5-triphosphates onto the '3 end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth.

McGinness, Kathleen E.; Joyce, Gerald F.

2002-01-01

90

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

91

Uroporphyrinogen oxidation catalyzed by human cytochromes P450.  

PubMed

Porphyria cutanea tarda is associated with excess hepatic production of uroporphyrin. Oxidation of uroporphyrinogen to uroporphyrin was previously demonstrated to be specifically catalyzed by cytochrome P450 (CYP) 1A2. Here, we investigated the ability of human CYP1A2 to catalyze uroporphyrinogen oxidation (UROX). UROX activity in human liver microsomes was maximally only 10% of the activity in microsomes from livers of untreated mice. There was a poor correlation of UROX activity with methoxyresorufin demethylation, an activity catalyzed predominantly by CYP1A2 and strongly correlated with immunodetectable CYP1A2. With CYP forms expressed in HepG2 cells, the methoxyresorufin demethylation and (ethoxyresorufin deethylation) activities of murine and human CYP1A2 forms were similar, but UROX activity catalyzed by human CYP1A2 was only 15-20% of the activity catalyzed by murine CYP1A2. Human CYP1A1, CYP1A2, and CYP3A4 expressed in lymphoblastoid cells all catalyzed UROX. In insect cells, CYP1A2 was more active in catalyzing UROX than was CYP1A1, CYP2E, CYP3A4, or CYP3A5. Human CYP1A2 expressed in Escherichia coli as a fusion protein with rat CYP oxidoreductase also catalyzed UROX. Reconstituted human CYP1A2 and CYP3A4 were active in catalyzing UROX, with reconstituted CYP1A2 having the highest specific activity obtained in this study. From inhibitor studies, it was concluded that some of the UROX activity in the insect cell microsomes was attributable to expressed CYP and some to an unidentified source. These results indicate that human CYP1A2 is active in catalyzing UROX but has lower activity than the murine orthologue. The results also indicate that most of the UROX activity found in human liver microsomes is not due to CYP1A2. PMID:9763408

Sinclair, P R; Gorman, N; Tsyrlov, I B; Fuhr, U; Walton, H S; Sinclair, J F

1998-10-01

92

Catalyzed modified clean fractionation of switchgrass.  

PubMed

Switchgrass was used as a lignocellulosic feedstock for second generation ethanol production, after pretreatment using sulfuric acid-catalyzed modified clean fractionation based on NREL's (National Renewable Energy Laboratory) original procedure. Optimization of temperature, catalyst concentration and solvent composition was performed using Response Surface Methodology, and 59.03 ± 7.01% lignin recovery, 84.85 ± 1.34% glucose, and 44.11 ± 3.44% aqueous fraction xylose yields were obtained at 140.00 °C, 0.46% w/w catalyst concentration, 36.71% w/w ethyl acetate concentration, and 25.00% w/w ethanol concentration. The cellulose fraction did not inhibit the fermentation performance of Saccharomyces cerevisiae and resulted in an ethanol yield of 89.60 ± 2.1%. PMID:23131627

Cybulska, Iwona; Brudecki, Grzegorz P; Hankerson, Brett R; Julson, James L; Lei, Hanwu

2013-01-01

93

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

94

SidL, an Aspergillus fumigatus Transacetylase Involved in Biosynthesis of the Siderophores Ferricrocin and Hydroxyferricrocin ? † ‡  

PubMed Central

The opportunistic fungal pathogen Aspergillus fumigatus produces four types of siderophores, low-molecular-mass iron chelators: it excretes fusarinine C (FsC) and triacetylfusarinine C (TAFC) for iron uptake and accumulates ferricrocin (FC) for hyphal and hydroxyferricrocin (HFC) for conidial iron distribution and storage. Siderophore biosynthesis has recently been shown to be crucial for fungal virulence. Here we identified a new component of the fungal siderophore biosynthetic machinery: AFUA_1G04450, termed SidL. SidL is conserved only in siderophore-producing ascomycetes and shows similarity to transacylases involved in bacterial siderophore biosynthesis and the N5-hydroxyornithine:anhydromevalonyl coenzyme A-N5-transacylase SidF, which is essential for TAFC biosynthesis. Inactivation of SidL in A. fumigatus decreased FC biosynthesis during iron starvation and completely blocked FC biosynthesis during iron-replete growth. In agreement with these findings, SidL deficiency blocked conidial accumulation of FC-derived HFC under iron-replete conditions, which delayed germination and decreased the size of conidia and their resistance to oxidative stress. Remarkably, the sidL gene is not clustered with other siderophore-biosynthetic genes, and its expression is not affected by iron availability. Tagging of SidL with enhanced green fluorescent protein suggested a cytosolic localization of the FC-biosynthetic machinery. Taken together, these data suggest that SidL is a constitutively active N5-hydroxyornithine-acetylase required for FC biosynthesis, in particular under iron-replete conditions. Moreover, this study revealed the unexpected complexity of siderophore biosynthesis, indicating the existence of an additional, iron-repressed N5-hydroxyornithine-acetylase. PMID:21622789

Blatzer, Michael; Schrettl, Markus; Sarg, Bettina; Lindner, Herbert H.; Pfaller, Kristian; Haas, Hubertus

2011-01-01

95

Enzyme-catalyzed degradation of carbon nanomaterials  

NASA Astrophysics Data System (ADS)

Carbon nanotubes and graphene, the nanoscale sp 2 allotropes of carbon, have garnered widespread attention as a result of their remarkable electrical, mechanical, and optical properties and the promise of new technologies that harness these properties. Consequently, these carbon nanomaterials (CNMs) have been employed for diverse applications such as electronics, sensors, composite materials, energy conversion devices, and nanomedicine. The manufacture and eventual disposal of these products may result in the release of CNMs into the environment and subsequent exposure to humans, animals, and vegetation. Given the possible pro-inflammatory and toxic effects of CNMs, much attention has been focused on the distribution, toxicity, and persistence of CNMs both in living systems and the environment. This dissertation will guide the reader though recent studies aimed at elucidating fundamental insight into the persistence of CNMs such as carbon nanotubes (CNTs) and graphene derivatives (i.e., graphene oxide and reduced graphene oxide). In particular, in-testtube oxidation/degradation of CNMs catalyzed by peroxidase enzymes will be examined, and the current understanding of the mechanisms underlying these processes will be discussed. Finally, an outlook of the current field including in vitro and in vivo biodegradation experiments, which have benefits in terms of human health and environmental safety, and future directions that could have implications for nanomedical applications such as imaging and drug delivery will be presented. Armed with an understanding of how and why CNMs undergo enzyme-catalyzed oxidation/biodegradation, researchers can tailor the structure of CNMs to either promote or inhibit these processes. For example, in nanomedical applications such as drug delivery, the incorporation of carboxylate functional groups could facilitate biodegradation of the nanomaterial after delivery of the cargo. Also, the incorporation of CNMs with defect sites in consumer goods could provide a mechanism that promotes the degradation of these materials once these products reach landfills.

Kotchey, Gregg P.

96

Rhodium-Catalyzed Asymmetric Intramolecular Hydroamination of Unactivated Alkenes  

E-print Network

One for the Rh(oad): The first rhodium-catalyzed asymmetric intramolecular hydroamination of unactivated olefins was developed by using dialkylbiaryl phosphine ligands (see scheme; cod=1,5-cyclooctadiene, Cy=cyclohexyl). ...

Shen, Xiaoqiang

97

Hydrolase-catalyzed biotransformations in deep eutectic solvents.  

PubMed

Hydrolases show good catalytic activity in deep eutectic solvents, despite the presence of urea, which can denature enzymes, or alcohols, which can interfere with hydrolase-catalyzed reactions. PMID:18309428

Gorke, Johnathan T; Srienc, Friedrich; Kazlauskas, Romas J

2008-03-14

98

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

99

Maa-Bara : catalyzing change in Nigeria's Niger delta  

E-print Network

Can architecture catalyze economic growth? This thesis serves as a design contribution to the war against poverty by proving that small-scale architectural interventions can propagate large-scale economic growth. It ...

Okiomah, Ogheneruno E. (Ogheneruno Elo)

2011-01-01

100

Palladium-catalyzed carboxylative coupling of allylstannanes and allyl halides  

SciTech Connect

A three-component carboxylative coupling between allyl halides, allylstannanes, and CO{sub 2} to produce allyl esters is catalyzed by Pd and Pt phosphine complexes. Tentative mechanistic pathways for the catalytic reaction are proposed.

Franks, R.J.; Nicholas, K.M.

2000-04-17

101

Electrooxidation of Alcohols Catalyzed by Amino Alcohol Ligated Ruthenium Complexes  

E-print Network

Electrooxidation of Alcohols Catalyzed by Amino Alcohol Ligated Ruthenium Complexes Kristen R Supporting Information ABSTRACT: Ruthenium transfer hydrogenation catalysts physisorbed onto edge that require high overpotentials to achieve reasonable rates.2-11 Polypyridyl ruthenium-oxo complexes are among

Zare, Richard N.

102

Palladium-Catalyzed N-Arylation of 2-Aminothiazoles  

E-print Network

A method for the Pd-catalyzed coupling of 2-aminothiazole derivatives with aryl bromides and triflates is described. Significantly, for this class of nucleophiles, the coupling exhibits a broad substrate scope and proceeds ...

McGowan, Meredeth A.

103

NHCs Catalyzed Hydrophosphonylation of ?-Ketoesters and ?-Trifluoromethyl Ketones  

PubMed Central

N-Heterocyclic carbenes catalyzed hydrophosphonylation reaction of ?-ketoesters and ?-trifluoromethyl ketones was developed. Under the catalysis of 10?mol% IPr, ?-ketoesters or ?-trifluoromethyl ketones reacted with dialkyl phosphites to provide quaternary ?-hydroxyphosphonates in good to excellent yield. PMID:24489517

He, Lin; Cai, Zhi-Hua; Pian, Ji-Xin; Du, Guang-Fen

2013-01-01

104

Iron catalyzed asymmetric hydrogenation of ketones.  

PubMed

Chiral molecules, such as alcohols, are vital for the manufacturing of fine chemicals, pharmaceuticals, agrochemicals, fragrances, and novel materials. These molecules need to be produced in high yield and high optical purity and preferentially catalytically. Among all the asymmetric catalytic reactions, asymmetric hydrogenation with H2 (AH) is the most widely used in the industry. With few exceptions, these AH processes use catalysts based on the three critical metals, rhodium, ruthenium, and iridium. Herein we describe a simple, industrially viable iron catalyst that allows for the AH of ketones, a process currently dominated by ruthenium and rhodium catalysts. By combining a chiral, 22-membered macrocyclic ligand with the cheap, readily available Fe3(CO)12, a wide variety of ketones have been hydrogenated under 50 bar H2 at 45-65 °C, affording highly valuable chiral alcohols with enantioselectivities approaching or surpassing those obtained with the noble metal catalysts. In contrast to AH by most noble metal catalysts, the iron-catalyzed hydrogenation appears to be heterogeneous. PMID:24524277

Li, Yanyun; Yu, Shenluan; Wu, Xiaofeng; Xiao, Jianliang; Shen, Weiyi; Dong, Zhenrong; Gao, Jingxing

2014-03-12

105

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. PMID:10788354

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

2000-01-01

106

Vanadium-Catalyzed C(sp3 )H Fluorination Reactions  

E-print Network

S1 Vanadium-Catalyzed C(sp3 )­H Fluorination Reactions Ji-Bao Xia, Yuyong Ma, and Chuo Chen. Vanadium(III) Oxide (95%) was purchased from Strem Chemicals Inc. Fluorobenzene (99.5%) was purchased from procedure for the V2O3-catalyzed C(sp3 )­H fluorination reaction. To a 4 mL clear vial charged with vanadium

Chen, Chuo

107

Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies  

NASA Technical Reports Server (NTRS)

The surface-catalyzed air oxidation reactions of fuel hydrazines were studied in a 6500-liter fluorocarbon-film chamber at 80 to 100 ppm concentrations. First-order rate constants for the reactions catalyzed by aluminum, water-damaged aluminum (Al/Al2O3), stainless steel 304L, galvanized steel and titanium plates with surface areas of 2 to 24 sq m were determined. With 23.8 sq m of Al/Al2O3 the surface-catalyzed air oxidation of hydrazine had a half-life of 2 hours, diimide (N2H2) was observed as an intermediate and traces of ammonia were present in the final product mixture. The Al/Al2O3 catalyzed oxidation of monomethylhydrazine yielded methyldiazine (HN = NCH3) as an intermediate and traces of methanol. Unsymmetrical dimethylhydrazine gave no detectable products. The relative reactivities of hydrazine, MMH and UDMH were 130 : 7.3 : 1.0, respectively. The rate constants for Al/Al2O3-catalyzed oxidation of hydrazine and MMH were proportional to the square of the surface area of the plates. Mechanisms for the surface-catalyzed oxidation of hydrazine and diimide and the formation of ammonia are proposed.

Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

1988-01-01

108

Nickel-catalyzed asymmetric cross-couplings of secondary alkyl electrophiles and photoinduced, copper-catalyzed C-N couplings  

E-print Network

Chapter 1 describes the development of three nickel-catalyzed asymmetric Negishi cross-couplings of secondary alkyl electrophiles via a stereoconvergent process. In Section 1.1, asymmetric Negishi arylations and alkenylations ...

Choi, Junwon, Ph. D. Massachusetts Institute of Technology

2014-01-01

109

DNA-Catalyzed Hydrolysis of Esters and Aromatic Amides  

PubMed Central

We previously reported that DNA catalysts (deoxyribozymes) can hydrolyze DNA phosphodiester linkages, but DNA-catalyzed amide bond hydrolysis has been elusive. Here we used in vitro selection to identify DNA catalysts that hydrolyze ester linkages as well as DNA catalysts that hydrolyze aromatic amides, for which the leaving group is an aniline moiety. The aromatic amide-hydrolyzing deoxyribozymes were examined using linear free energy relationship analysis. The hydrolysis reaction is unaffected by substituents on the aromatic ring (? ? 0), suggesting general acid-catalyzed elimination as the likely rate-determining step of the addition-elimination hydrolysis mechanism. These findings establish that DNA has the catalytic ability to achieve hydrolysis of esters and aromatic amides as carbonyl-based substrates, and they suggest a mechanism-based approach to achieve DNA-catalyzed aliphatic amide hydrolysis. PMID:24127695

Brandsen, Benjamin M.; Hesser, Anthony R.; Castner, Marissa A.; Chandra, Madhavaiah

2013-01-01

110

Stau-catalyzed big-bang nucleosynthesis reactions  

NASA Astrophysics Data System (ADS)

We study the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X-) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X- particle has a lifetime of ?X>~103 s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X- acts as a catalyst. Some of these X- catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high-accuracy three-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

Kamimura, Masayasu; Kino, Yasushi; Hiyama, Emiko

2010-06-01

111

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

112

Helical polymer as mimetic enzyme catalyzing asymmetric aldol reaction.  

PubMed

This Communication reports optically active helical substituted polyacetylenes which solely catalyzed asymmetric Aldol reaction between cyclohexanone and p-nitrobenzaldehyde; more importantly the helical structures are found to play crucial roles in the asymmetric catalysis, with a remarkable yield and ee (both up to 80%). A synergic effect is observed between the helical structures in the polymer main chains and the pendent prolinamide moieties for successfully catalyzing the asymmetric reaction. The role of the helical polymer backbones is further verified by tuning the relative helical structure content. PMID:22318956

Zhang, Dongyue; Ren, Chonglei; Yang, Wantai; Deng, Jianping

2012-04-23

113

Platinum-catalyzed hydrosilylation - colloid formation as the essential step  

SciTech Connect

In a reaction which has broad implications for many ostensibly homogeneous metal-catalyzed reduction processes, it is shown that platinum-catalyzed hydrosilylation proceeds with formation of platinum colloids. The reaction of COD PtCl/sub 2/ with (EtO/sub 2/)/sub 3/SiH demonstrated that colloid formation is the key step in hydrosilylation. Colloids are generated from the reaction of Pt(COD)/sub 2/ and CODPtCl/sub 2/ with hydrosilanes and analyzed by light scattering, TEM, and ESCA.

Lewis, L.N.; Lewis, N.

1986-11-12

114

Microbial-Catalyzed Biotransformation of Multifunctional Triterpenoids Derived from Phytonutrients  

PubMed Central

Microbial-catalyzed biotransformations have considerable potential for the generation of an enormous variety of structurally diversified organic compounds, especially natural products with complex structures like triterpenoids. They offer efficient and economical ways to produce semi-synthetic analogues and novel lead molecules. Microorganisms such as bacteria and fungi could catalyze chemo-, regio- and stereospecific hydroxylations of diverse triterpenoid substrates that are extremely difficult to produce by chemical routes. During recent years, considerable research has been performed on the microbial transformation of bioactive triterpenoids, in order to obtain biologically active molecules with diverse structures features. This article reviews the microbial modifications of tetranortriterpenoids, tetracyclic triterpenoids and pentacyclic triterpenoids. PMID:25003642

Shah, Syed Adnan Ali; Tan, Huey Ling; Sultan, Sadia; Mohd Faridz, Muhammad Afifi Bin; Mohd Shah, Mohamad Azlan Bin; Nurfazilah, Sharifah; Hussain, Munawar

2014-01-01

115

Nickel-catalyzed coupling reactions and synthetic studies toward ent-dioxepandehydrothyrsiferol via an epoxide-opening cascade  

E-print Network

Nickel-Catalyzed Coupling Reactions. Nickel-catalyzed allene--aldehyde coupling and alkene--aldehyde coupling represent two methods of preparing allylic alcohols. Most asymmetric transition metal-catalyzed methods of ...

Ng, Sze-Sze

2008-01-01

116

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. PMID:24175907

2013-01-01

117

The Development of the First Catalyzed Reaction of Ketenes and Imines: Catalytic, Asymmetric Synthesis of -Lactams  

E-print Network

The Development of the First Catalyzed Reaction of Ketenes and Imines: Catalytic, Asymmetric for the catalytic, asymmetric synthesis of -lactams resulting from the development of a catalyzed reaction resistance pressures,1 recently -lactams (especially nonnatural ones) have achieved many important

Lectka, Thomas

118

Copper-catalyzed hydrophosphinations of styrenes in water at room temperature.  

PubMed

Copper-catalyzed hydrophosphinations of styrenyl systems in water, at room temperature is herein reported, enabled by our 'designer' surfactant TPGS-750-M. This is an attractive alternative to the more common Pd and Pt catalyzed versions. PMID:25058397

Isley, Nicholas A; Linstadt, Roscoe T H; Slack, Eric D; Lipshutz, Bruce H

2014-09-21

119

Calreticulin mutations in Chinese with primary myelofibrosis  

PubMed Central

We tested 357 Chinese with primary myelofibrosis for mutations in CALR, JAK2 and MPL. CALR mutations were detected in 76 subjects (21%). There were 24 (32%) type-1 (L367fs*46) and 49 (64%) type-2 (K385fs*47) mutations. Seventy-two of 168 subjects (43%) without a JAK2 or MPL mutation had a CALR mutation. Subjects with a type-2 CALR mutation had lower hemoglobin concentrations (P=0.001), lower WBC counts (P<0.001), a higher percentage of blood blasts (P=0.009), and higher conventional (P<0.001) and Chinese-adjusted Dynamic International Prognostic Scoring System (P<0.001) scores compared with subjects with JAK2 mutations. Subjects with a type-2 CALR mutation were also likely to have abnormal platelet levels (<100 × 109/L, P=0.01 or >450 × 109/L, P=0.042) and no splenomegaly (P=0.004). Type-2 CALR mutation or no detectable mutation was an independent high-risk factor for survival in multivariate analyses. These data suggest the ratio between type-1 and type-2 mutations is reversed in Chinese with primary myelofibrosis compared with populations of subjects with primary myelofibrosis of predominately European descent. The unfavorable prognostic impact of CALR mutations in Chinese with primary myelofibrosis is only seen in those with type-2 mutations. These data underscore the need to evaluate the prognostic impact of genetic mutations in different populations. PMID:24997152

Li, Bing; Xu, Junqing; Wang, Jingya; Gale, Robert Peter; Xu, Zefeng; Cui, Yajuan; Yang, Lin; Xing, Ruixian; Ai, Xiaofei; Qin, Tiejun; Zhang, Yue; Zhang, Peihong; Xiao, Zhijian

2014-01-01

120

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. PMID:21915211

2011-01-01

121

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

122

Gold-catalyzed propargylic substitutions: Scope and synthetic developments  

PubMed Central

Summary 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

2011-01-01

123

Dynamic kinetic resolution of azlactones catalyzed by chiral Brønsted acids.  

PubMed

Chiral Brønsted acids have been shown for the first time to catalyze the dynamic kinetic resolution of azlactones. 3,3'-Bis-(9-anthryl)-BINOL phosphoric acid 3c is particularly effective in the case of 4-aryl-substituted substrates, producing 85-92% ee's. PMID:21175181

Lu, Guojian; Birman, Vladimir B

2011-02-01

124

Gold-catalyzed spiro-N,O-ketal synthesis.  

PubMed

An efficient method for the synthesis of spiro-N,O-ketals with 5- and 6-membered rings was developed via a gold-catalyzed spiroamidoketalization of alkynyl amidoalcohols under mild conditions. This methodology has been successfully applied to the synthesis of a spiro-N,O-ketal analogue of marineosin A. PMID:25427870

Grammatikopoulou, M; Thysiadis, S; Sarli, V

2015-01-28

125

Highly Enantioselective Hydrogenation of Cyclic Enamides Catalyzed by a  

E-print Network

of cyclic enamides catalyzed by a Rh-PennPhos compound. In our continuing work on catalytic asymmetric of the asymmetric hydrogenation of enamides to include this unique catalytic system. N-(3,4-Dihydro-1-naphthyl H2 pressure of 40 psi at room temperature with a ratio of substrate/Rh/Me-PennPhos of 100

Zhang, Xumu

126

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

127

Highly enantioselective hydrogenation of enamides catalyzed by chiral phosphoric acids.  

PubMed

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

Li, Guilong; Antilla, Jon C

2009-03-01

128

Development of a Lewis Base Catalyzed Selenocyclization Reaction  

ERIC Educational Resources Information Center

The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

Collins, William

2009-01-01

129

Endo-selective pd-catalyzed silyl methyl heck reaction.  

PubMed

A palladium (Pd)-catalyzed endo-selective Heck reaction of iodomethylsilyl ethers of phenols and aliphatic alkenols has been developed. Mechanistic studies reveal that this silyl methyl Heck reaction operates via a hybrid Pd-radical process and that the silicon atom is crucial for the observed endo selectivity. The obtained allylic silyloxycycles were further oxidized into (Z)-alkenyldiols. PMID:25494921

Parasram, Marvin; Iaroshenko, Viktor O; Gevorgyan, Vladimir

2014-12-31

130

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); Baker, Ralph Thomas (Los Alamos, NM)

2010-01-12

131

PtCl 2-catalyzed cycloisomerizations of allenynes.  

PubMed

The PtCl2-catalyzed cycloisomerization of allenyne systems has been examined. This process is a highly versatile tool for obtaining products that cannot be attainable with other metals. Simple adjustment of the allene or alkyne substitution can direct the reactivity in a selective manner and give birth to important carbocyclic frameworks (hydrindenes, cyclic vinylallenes, and trienes). PMID:15025452

Cadran, Nicolas; Cariou, Kevin; Hervé, Gwénaëlle; Aubert, Corinne; Fensterbank, Louis; Malacria, Max; Marco-Contelles, José

2004-03-24

132

Carbon-catalyzed gasification of organic feedstocks in supercritical water  

Microsoft Academic Search

Spruce wood charcoal, macadamia shell charcoal, coal activated carbon, and coconut shell activated carbon catalyze the gasification of organic compounds in supercritical water. Feedstocks studied in this paper include glycerol, glucose, cellobiose, whole biomass feedstocks (depithed bagasse liquid extract and sewage sludge), and representative Department of Defense (DoD) wastes (methanol, methyl ethyl ketone, ethylene glycol, acetic acid, and phenol). The

Xiaodong Xu; Yukihiko Matsumura; Jonny Stenberg; Michael Jerry Antal

1996-01-01

133

Ti-Catalyzed Reactions of Hindered Isocyanates with Alcohols  

E-print Network

Ti-Catalyzed Reactions of Hindered Isocyanates with Alcohols Claude Spino,* Marc-Andre´ Joly, Ce with an alcohol or an amine to produce a carbamate or a urea, respectively, with water to produce a primary amine. The reactions between many unhindered isocy- anates and primary alcohols proceed without catalysis

Spino, Claude

134

A common topology of proteins catalyzing ATP-triggered reactions  

Microsoft Academic Search

A protein fold, six parallel ? strands surrounding the central ? helix, is likely to be a common structure in protein families known to have a typical set of nucleotide binding consensus sequenced motifs A and B and to catalyze ATP-triggered reactions. According to this ATP-triggered protein fold, the conserved Glu (or Asp), which acts as a general base to

Masasuke Yoshida; Toyoki Amano

1995-01-01

135

Solid acid catalyzed biodiesel production from waste cooking oil  

Microsoft Academic Search

Various solid acid catalysts were evaluated for the production of biodiesel from low quality oil such as waste cooking oil (WCO) containing 15wt.% free fatty acids. The zinc stearate immobilized on silica gel (ZS\\/Si) was the most effective catalyst in simultaneously catalyzing the transesterification of triglycerides and esterification of free fatty acid (FFA) present in WCO to methyl esters. The

Kathlene Jacobson; Rajesh Gopinath; Lekha Charan Meher; Ajay Kumar Dalai

2008-01-01

136

Epoxidation of olefins with hydrogen peroxide catalyzed by polyoxometalates  

Microsoft Academic Search

Epoxides are an important class of industrial chemicals that have been used as chemical intermediates. Catalytic epoxidation of olefins affords an interesting technology for their production. This review summarizes recent developments for the epoxidation of olefins with hydrogen peroxide catalyzed by polyoxometalates. The versatility, accessibility, and tunability of polyoxometalates open up the development of effective epoxidation systems. Polyoxometalates for H2O2-based

Noritaka Mizuno; Kazuya Yamaguchi; Keigo Kamata

2005-01-01

137

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

138

Gold Catalyzed Cyclization of Alkyne-Tethered Dihydropyrimidones  

PubMed Central

Dihydropyrimidones are an important class of biologically active heterocycles accessible from the multicomponent Biginelli condensation. Further manipulation of the dihydropyrimidone skeleton gives access to unique heterocycles. Presented herein is a Au-catalyzed cyclization of alkyne-tethered dihydropyrimidinones to yield pyridopyrimidones. PMID:21749159

Brown, Lauren E.; Dai, Peng; Porco, John A.; Schaus, Scott E.

2011-01-01

139

Gold superacid-catalyzed preparation of benzo[c]thiophenes.  

PubMed

A three-step synthesis of benzo[c]thiophenes is presented in which the key transformation is the gold-catalyzed 5-exo-dig migratory cycloisomerization of a diallyl thioacetal. It was shown that a small amount of in situ generated HAuCl4 from AuCl3 is the active catalytic species. A mechanism was proposed. PMID:25418863

Debrouwer, Wouter; Seigneur, Ruben A J; Heugebaert, Thomas S A; Stevens, Christian V

2015-01-14

140

Au-catalyzed reaction of propargylic sulfides and dithioacetals.  

PubMed

Propargylic sulfides and dithioacetals are found to undergo similar transformations as propargylic carboxylates when catalyzed by AuCl or AuCl3, affording indene derivatives through pentannulation of aromatic rings. The reaction presumably involves Au carbene as the reactive intermediate. PMID:17288372

Peng, Lingling; Zhang, Xiu; Zhang, Shiwei; Wang, Jianbo

2007-02-16

141

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. PMID:18081287

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

2010-01-01

142

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

143

Calcium(II)-catalyzed aza-Piancatelli reaction.  

PubMed

The first examples of calcium-catalyzed aza-Piancatelli reactions between substituted 2-furylcarbinols and aniline derivatives are described. A variety of 4-aminocyclopentenones have been synthesized stereoselectively in high yields. The experimental procedure utilizes simple salts and does not require specific precautions. PMID:25485996

Lebœuf, David; Schulz, Emmanuelle; Gandon, Vincent

2014-12-19

144

Asymmetric Processes Catalyzed by Chiral (Salen)Metal Complexes  

Microsoft Academic Search

A wide variety of highly selective asymmetric reactions catalyzed by chiral (salen)metal complexes have been disclosed over the past decade. Salen ligands are among the most synthetically accessible frameworks for asymmetric catalysts, and their structures are readily tuned both sterically and electronically. However, one particular chiral salen ligand ( 1) has been demonstrated to be highly effective for a wide

Jay F. Larrow; Eric N. Jacobsen

145

Gold-Catalyzed Cross-Coupling DOI: 10.1002/anie.201402924  

E-print Network

Gold-Catalyzed Cross-Coupling DOI: 10.1002/anie.201402924 Gold-Catalyzed Allylation of Aryl Boronic Acids: Accessing Cross- Coupling Reactivity with Gold** Mark D. Levin and F. Dean Toste* Abstract: A sp3 ­sp2 C�C cross-coupling reaction catalyzed by gold in the absence of a sacrificial oxidant

Toste, Dean

146

Direct Functionalization of Arenes by Primary Alcohol Sulfonate Esters Catalyzed by Gold(III)  

E-print Network

Direct Functionalization of Arenes by Primary Alcohol Sulfonate Esters Catalyzed by Gold catalyzed by gold have been a focus of attention recently.1 Gold(I) and gold(III) show unique activity in mediating reactions involving alkynes. In contrast, gold-catalyzed arene functionalization has been less

He, Chuan

147

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

148

Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.  

ERIC Educational Resources Information Center

Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

Lombardo, Anthony

1982-01-01

149

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

150

Enzymatic alpha-glucosaminylation of maltooligosaccharides catalyzed by phosphorylase.  

PubMed

This paper describes phosphorylase-catalyzed enzymatic alpha-glucosaminylation for the direct incorporation of a 2-amino-2-deoxy-alpha-D-glucopyranose unit into maltooligosaccharides. When the reaction of 2-amino-2-deoxy-alpha-D-glucopyranosyl 1-phosphate as the glycosyl donor with maltotetraose as a glycosyl acceptor was performed in the presence of phosphorylase, glucosaminylated oligosaccharides were produced, which were characterized by MALDI-TOF MS measurement after N-acetylation of the crude products. The N-acetylated derivative of the main product in this system was isolated by using HPLC, and its structure was confirmed by MS and (1)H NMR spectra. Furthermore, glucoamylase-catalyzed reaction of the isolated compound provided support that the alpha-glucosamine unit is positioned at the non-reducing end of the oligosaccharide. PMID:18768171

Nawaji, Mutsuki; Izawa, Hironori; Kaneko, Yoshiro; Kadokawa, Jun-Ichi

2008-10-13

151

Imidazolidinone intermediates in prolinamide-catalyzed aldol reactions.  

PubMed

The reaction between acetone and 4-nitrobenzaldehyde catalyzed by aniline prolinamide 1 was studied in depth. Working in different solvents with equimolar amounts of reagents and monitoring the reaction by 1H NMR, we detected and identified several imidazolidinones, such as those of the acetone 4, the aldol products 5a and 5b, and aldehydes 10a and 10b. According to our results, these compounds could influence the reaction rate and diminish product enantioselectivity. Furthermore, acetone imidazolidinone 4 was seen to react with 4-nitrobenzaldehyde to furnish the aldol product 3. This reaction can be catalyzed by different nucleophiles and acids. In fact, strong acids such as camphorsulfonic or trifluoroacetic acid, convert imidazolidinones into iminium salts and afford more enantioselective aldol reactions when different aromatic prolinamides are used. Enantiomeric excesses of ca. 82% are reached. PMID:20461270

Fuentes de Arriba, Angel L; Simón, Luis; Raposo, César; Alcázar, Victoria; Sanz, Francisca; Muñiz, Francisco M; Morán, Joaquín R

2010-06-28

152

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

153

Mild and efficient cyanuric chloride catalyzed Pictet–Spengler reaction  

PubMed Central

Summary A practical, mild and efficient protocol for the Pictet–Spengler reaction catalyzed by cyanuric chloride (trichloro-1,3,5-triazine, TCT) is described. The 6-endo cyclization of tryptophan/tryptamine and modified Pictet–Spengler substrates with both electron-withdrawing and electron-donating aldehydes was carried out by using a catalytic amount of TCT (10 mol %) in DMSO under a nitrogen atmosphere. TCT catalyzed the Pictet–Spengler reaction involving electron-donating aldehydes in excellent yield. Thus, it has a distinct advantage over the existing methodologies where electron-donating aldehydes failed to undergo 6-endo cyclization. Our methodology provided broad substrate scope and diversity. This is indeed the first report of the use of TCT as a catalyst for the Pictet–Spengler reaction. PMID:23843919

Sharma, Ashish; Singh, Mrityunjay; Rai, Nitya Nand

2013-01-01

154

Ruthenium-Catalyzed Cascade C—H Functionalization of Phenylacetophenones**  

PubMed Central

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

2014-01-01

155

Copper-catalyzed rearrangement of oximes into primary amides  

Microsoft Academic Search

The atom-efficient and cost-effective rearrangement of oximes into primary amides is catalyzed by simple copper salts. The use of homogeneous Cu(OAc)2 (1–2mol%) was found to be effective for this transformation at 80°C. The reaction was successful with either conventional or microwave heating. CuO and CuO\\/ZnO on activated carbon provided a competent reuseable heterogeneous catalyst which could be used in a

Sumeet K. Sharma; Simon D. Bishopp; C. Liana Allen; Ruth Lawrence; Mark J. Bamford; Alexei A. Lapkin; Pawel Plucinski; Robert J. Watson; Jonathan M. J. Williams

2011-01-01

156

Perfluorooctanesulfonic Acid Catalyzed Friedel-Crafts Alkylation with Alkyl Halides  

Microsoft Academic Search

A New procedure to prepare superacid perfluorooctanesulfonic acid (POSA) is reported. POSA catalyzed Friedel-Crafts alkylation of aromatic compounds with alkyl halides in liquid-phase reactions. Alkylation gave higher total yields than the corresponding reactions with Nafion-H, without the need of any complex decomposition or work-up. The reactions do not need to be carried out under absolutely anhydrous condition. The catalyst POSA

Xiangkai Fu; Mingqian He; Qingying Lei; Bikuei Luo

1991-01-01

157

Electronic differentiations in palladium-catalyzed allylic substitutions  

Microsoft Academic Search

The “trans rule” in Pd-catalyzed allylic substitutions predicts trans to phosphorus additions of nucleophiles to Pd–allyl intermediates, e.g., with P,N-ligands. This computational study reveals that not only the intrinsic electronic differentiation between P- (i.e., PH3) and N-ligands (i.e., para-X-substituted pyridines), but also the “late” or “early” nature of the transition structures is crucial for strong cis vs. trans discriminations and

Bernd Goldfuss

2006-01-01

158

Copper-Catalyzed Oxidative Heck Reactions between Alkyltrifluoroborates and Vinylarenes  

PubMed Central

We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented. PMID:23734764

Liwosz, Timothy W.; Chemler, Sherry R.

2013-01-01

159

Transition metal-catalyzed enantioselective hydrogenation of enamides and enamines.  

PubMed

Transition metal-catalyzed enantioselective hydrogenation of enamides and enamines is one of the most important methods for the preparation of optically active amines. This review describes the recent developments of highly efficient catalytic asymmetric hydrogenation of enamides, and enamines. It specifically focuses on the substrates because hydrogenation of enamides and enamines is highly dependent on the substrates although the chiral metal catalysts play a significant role. PMID:24595741

Zhou, Qi-Lin; Xie, Jian-Hua

2014-01-01

160

Frustrated Lewis pair catalyzed hydroamination of terminal alkynes.  

PubMed

Catalytic amounts of the Lewis acid B(C6 F5 )3 enable the hydroamination of terminal alkynes by aryl amines to the corresponding enamines. In accord with the results of stoichiometric reactions, the mechanism of this reaction involves a frustrated Lewis pair (FLP). The hydroamination can be followed by an FLP-catalyzed hydrogenation, resulting in a one-pot stepwise synthesis of amine derivatives. PMID:24115279

Mahdi, Tayseer; Stephan, Douglas W

2013-11-18

161

Distinct Reactions Catalyzed by Bacterial and Yeast trans Aconitate Methyltransferases †  

Microsoft Academic Search

The trans-aconitate methyltransferase from the bacterium Escherichia coli catalyzes the monomethyl esterification of trans-aconitate and related compounds. Using two-dimensional 1H\\/13C nuclear magnetic resonance spectroscopy, we show that the methylation is specific to one of the three carboxyl groups and further demonstrate that the product is the 6-methyl ester of trans-aconitate (E-3-carboxy-2- pentenedioate 6-methyl ester). A similar enzymatic activity is present

Hui Cai; Jane Strouse; Darren Dumlao; Michael E. Jung; Steven Clarke

2001-01-01

162

Hydrosilylation of alkynes catalyzed by ruthenium carbene complexes  

Microsoft Academic Search

Hydrosilylation of terminal alkynes with a variety of silanes catalyzed by Cl2(PCy3)2RuCHPh (1) affords mainly the Z-isomer via trans addition in excellent yields. The presence of a hydroxyl group in close proximity to the triple bond was observed to exert a strong directing effect, resulting in the highly selective formation of the ?-isomer. Intramolecular hydrosilylation of a homopropargylic silyl ether

Sarah V. Maifeld; Michael N. Tran; Daesung Lee

2005-01-01

163

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. PMID:24062838

Vasu, Dhananjayan; Pawar, Samir Kundlik

2013-01-01

164

Proline catalyzes direct C-H arylations of unactivated arenes.  

PubMed

Several amino acids were tested to catalyze the transition-metal-free direct C-H arylation of unactivated benzene derivatives. Among them, proline was found to be an excellent catalyst for the cross-coupling between aryl halides and unactivated arenes. The reaction presumably involves an aryl radical anion as the intermediate based on several experiments. The reaction using this catalyst system offers an option toward establishing an environmentally benign and cost-effective route to biaryls. PMID:22920286

Tanimoro, Kouichi; Ueno, Minoru; Takeda, Kazutaka; Kirihata, Mitsunori; Tanimori, Shinji

2012-09-21

165

Chiral bicyclic guanidine-catalyzed enantioselective reactions of anthrones.  

PubMed

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

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

2006-10-25

166

Palladium-Catalyzed Aminocarbonylation of Alkynes to Succinimides.  

PubMed

Succinimide derivatives are useful building blocks for the synthesis of natural products and drugs. We describe an efficient route to succinimide derivatives comprising Pd(xantphos)Cl2-catalyzed aminocarbonylation of alkynes with aromatic or aliphatic amines in the presence of p-TsOH. The utility of this route is demonstrated with the synthesis of a large number of succinimide compounds including an important photochromic molecule. PMID:25418524

Liu, Huizhen; Lau, Genevieve P S; Dyson, Paul J

2014-12-01

167

Palladium catalyzed aryl(alkyl)thiolation of unactivated arenes.  

PubMed

A general palladium-catalyzed aryl(alkyl)thiolation of various substituted unactivated arenes is accomplished for the synthesis of diverse unsymmetrical diaryl(alkyl) sulfides in good yield employing electrophilic sulfur reagent 6 derived from succinimide. The developed strategy was coupled with intramolecular arylation of a C-H bond to afford dibenzothiphene derivatives, an important moiety in material science as organic semiconductors. PMID:24437617

Saravanan, Perumal; Anbarasan, Pazhamalai

2014-02-01

168

Strictosidine synthase: mechanism of a Pictet-Spengler catalyzing enzyme.  

PubMed

The Pictet-Spengler reaction, which yields either a beta-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 beta-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 beta-carboline product is proposed from these data. PMID:18081287

Maresh, Justin J; Giddings, Lesley-Ann; Friedrich, Anne; Loris, Elke A; Panjikar, Santosh; Trout, Bernhardt L; Stöckigt, Joachim; Peters, Baron; O'Connor, Sarah E

2008-01-16

169

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

170

Synthesis of Graphite Encapsulated Metal Nanoparticles and Metal Catalyzed Nanotubes  

NASA Technical Reports Server (NTRS)

This work focuses on the growth and inception of graphite encapsulated metal nanoparticles and metal catalyzed nanotubes using combustion chemistry. Deciphering the inception and growth mechanism(s) for these unique nanostructures is essential for purposeful synthesis. Detailed knowledge of these mechanism(s) may yield insights into alternative synthesis pathways or provide data on unfavorable conditions. Production of these materials is highly desirable given many promising technological applications.

vanderWal, R. L.; Dravid, V. P.

1999-01-01

171

Cu-catalyzed aerobic oxidative cyclization of guanidylpyridines and derivatives.  

PubMed

A new method for the straightforward synthesis of 2-amino-[1,2,4]triazolo[1,5-a]pyridines and derivatives is presented. The target products are synthesized in high yields from guanidylpyridines and analogues via copper-catalyzed N-N coupling. The present methodology shows a wide scope, tolerating not only different substituents on the pyridine ring but also different heterocylic rings such as pyrazines, pyrimidines, and pyridazines. PMID:25495477

Bartels, Björn; Bolas, Conor Gordon; Cueni, Philipp; Fantasia, Serena; Gaeng, Nicolas; Trita, Andrada Stefania

2015-01-16

172

Comparing Ru and Fe-catalyzed olefin metathesis.  

PubMed

Density functional theory calculations have been used to explore the potential of Fe-based complexes with an N-heterocyclic carbene ligand, as olefin metathesis catalysts. Apart from a less endothermic reaction energy profile, a small reduction in the predicted upper energy barriers (? 2 kcal mol(-1)) is calculated in the Fe catalyzed profile with respect to the Ru catalysed profile. Overall, this study indicates that Fe-based catalysts have the potential to be very effective olefin metathesis catalysts. PMID:24821502

Poater, Albert; Chaitanya Vummaleti, Sai Vikrama; Pump, Eva; Cavallo, Luigi

2014-08-01

173

Development of a Palladium-Catalyzed ?-Arylation of Cyclopropyl Nitriles.  

PubMed

1,1-Disubstituted aryl cyclopropyl nitriles are useful moieties in biologically active compounds and provide access to a range of cyclopropyl derivatives. Herein, we describe the development of a palladium-catalyzed ?-arylation of cyclopropyl, cyclobutyl, and cyclopentyl nitriles that affords these functional groups in one step from a variety of aryl bromides in good to excellent yields. Furthermore, we demonstrate the transformation of aryl cyclopropyl nitriles into aryl trifluoromethyl cyclopropanes. PMID:25474721

McCabe Dunn, Jamie M; Kuethe, Jeffrey T; Orr, Robert K; Tudge, Matthew; Campeau, Louis-Charles

2014-12-19

174

Asymmetric Stetter reactions catalyzed by thiamine diphosphate-dependent enzymes.  

PubMed

The intermolecular asymmetric Stetter reaction is an almost unexplored transformation for biocatalysts. Previously reported thiamine diphosphate (ThDP)-dependent PigD from Serratia marcescens is the first enzyme identified to catalyze the Stetter reaction of ?,?-unsaturated ketones (Michael acceptor substrates) and ?-keto acids. PigD is involved in the biosynthesis of the potent cytotoxic agent prodigiosin. Here, we describe the investigation of two new ThDP-dependent enzymes, SeAAS from Saccharopolyspora erythraea and HapD from Hahella chejuensis. Both show a high degree of homology to the amino acid sequence of PigD (39 and 51 %, respectively). The new enzymes were heterologously overproduced in Escherichia coli, and the yield of soluble protein was enhanced by co-expression of the chaperone genes groEL/ES. SeAAS and HapD catalyze intermolecular Stetter reactions in vitro with high enantioselectivity. The enzymes possess a characteristic substrate range with respect to Michael acceptor substrates. This provides support for a new type of ThDP-dependent enzymatic activity, which is abundant in various species and not restricted to prodigiosin biosynthesis in different strains. Moreover, PigD, SeAAS, and HapD are also able to catalyze asymmetric carbon-carbon bond formation reactions of aldehydes and ?-keto acids, resulting in 2-hydroxy ketones. PMID:24957249

Kasparyan, Elena; Richter, Michael; Dresen, Carola; Walter, Lydia S; Fuchs, Georg; Leeper, Finian J; Wacker, Tobias; Andrade, Susana L A; Kolter, Geraldine; Pohl, Martina; Müller, Michael

2014-12-01

175

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

176

Thiocyanate catalyzes myeloperoxidase-initiated lipid oxidation in LDL.  

PubMed

There is evidence that LDL oxidation may render the lipoprotein atherogenic. The myeloperoxidase-hydrogen peroxide (MPO/H2O2) system of activated phagocytes may be involved in this process. Chloride is supposed to be the major substrate for MPO, generating reactive hypochlorous acid (HOCl), modifying LDL. The pseudo-halide thiocyanate (SCN-) has been shown to be a suitable substrate for MPO, forming reactive HOSCN/SCN*. As relatively abundant levels of SCN- are found in plasma of smokers--a well-known risk group for cardiovascular disease--the ability of SCN- to act as a catalyst of LDL atherogenic modification by MPO/H2O2 was tested. Measurement of conjugated diene and lipid hydroperoxide formation in LDL preparations exposed to MPO/H2O2 revealed that SCN- catalyzed lipid oxidation in LDL. Chloride did not diminish the effect of SCN- on lipid oxidation. Surprisingly, SCN inhibited the HOCl-mediated apoprotein modification in LDL. Nitrite--recently found to be a substrate for MPO--showed some competing properties. MPO-mediated lipid oxidation was inhibited by heme poisons (azide, cyanide) and catalase. Ascorbic acid was the most effective compound in inhibiting the SCN- -catalyzed reaction. Bilirubin showed some action, whereas tocopherol was ineffective. When LDL oxidation was performed with activated human neutrophils, which employ the MPO pathway, SCN- catalyzed the cell-mediated LDL oxidation. The MPO/H2O2/SCN- system may have the potential to play a significant role in the oxidative modification of LDL--an observation further pointing to the link between the long-recognized risk factors of atherosclerosis: elevated levels of LDL and smoking. PMID:15203186

Exner, Markus; Hermann, Marcela; Hofbauer, Roland; Hartmann, Beda; Kapiotis, Stylianos; Gmeiner, Bernhard

2004-07-15

177

Palladium-Catalyzed anti-Markovnikov Oxidation of Terminal Alkenes.  

PubMed

The palladium-catalyzed oxidation of alkenes, the Wacker-Tsuji reaction, is undoubtedly a classic in organic synthesis and provides reliable access to methyl ketones from terminal alkenes under mild reaction conditions. Methods that switch the selectivity of the reaction to provide the aldehyde product are desirable because of the access they provide to a valuable functional group, however such methods are elusive. Herein we survey both the methods which have been developed recently in achieving such selectivity and discuss common features and mechanistic insight which offers promise in achieving the goal of a general method for anti-Markovnikov-selective olefin oxidations. PMID:25367376

Dong, Jia Jia; Browne, Wesley R; Feringa, Ben L

2015-01-12

178

Iridium-catalyzed reductive nitro-mannich cyclization.  

PubMed

A new chemoselective reductive nitro-Mannich cyclization reaction sequence of nitroalkyl-tethered lactams has been developed. Relying on the rapid and chemoselective iridium(I)-catalyzed reduction of lactams to the corresponding enamine, subsequent nitro-Mannich cyclization of tethered nitroalkyl functionality provides direct access to important alkaloid natural-product-like structures in yields up to 81?% and in diastereoselectivities that are typically good to excellent. An in-depth understanding of the reaction mechanism has been gained through NMR studies and characterization of reaction intermediates. The new methodology has been applied to the total synthesis of (±)-epi-epiquinamide in four steps. PMID:25399919

Gregory, Alex W; Chambers, Alan; Hawkins, Alison; Jakubec, Pavol; Dixon, Darren J

2015-01-01

179

Stereoselective hydrolysis catalyzed by a Bacillus endoglucanase in family D.  

PubMed

An endoglucanase in family D, purified from a strain of Bacillus, was found to catalyze the hydrolysis of p-nitrophenyl beta-D-cellotrioside to generate alpha-cellobiose, as determined by 1H-NMR spectroscopy. The hydrolysis of the beta-1,4 glucosidic bond by the enzyme proceeds, therefore, by an inversion mechanism. Furthermore, the interconversion of the alpha- and beta-anomeric protons in the products of hydrolysis, after equilibrium had been reached by mutarotation, was directly characterized by magnetization transfer NMR experiment that exploited the truncated driven nuclear Overhauser effect. PMID:7626068

Kawaminami, S; Ozaki, K; Ito, S

1995-07-17

180

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

181

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

182

Surface-catalyzed singlet oxygen production on iodine oxide films  

NASA Astrophysics Data System (ADS)

Enhanced production of singlet oxygen, O2(a1?g), was observed by reaction of O2/He discharge effluents on an iodine oxide film surface in a microwave discharge-flow reactor at 320 K. We observed a two-fold increase in the O2(a) yields over discharge-generated amounts for non-catalytic conditions. The iodine oxide surface appears to catalyze the heterogeneous reaction to form O2(a) with high collision efficiency. The observed catalytic effect could significantly benefit the development of electrically driven oxygen-iodine laser systems, and may also have implications for the chemistry of atmospheric iodine oxide aerosol.

Lee, Seonkyung; Terry Rawlins, W.; Davis, Steven J.

2009-02-01

183

Catalyzed growth of doped TGS single crystals for infrared applications  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with Pr3+ Sm3+, Pd2+, Co2+, Pt4+ and PO43- with L-alanin were grown from aqueous solutions by means of the slow cooling method. Surface morphology, domain structure and P-E hysteresis loops have been investigated. The model of catalyzed growth of {001}and{101}crystal pyramids on the basis of metal-glycine complexes has been suggested. We have found on the basis of experimental results that TGS single crystals doped with Pt4+ and L-alanin are excellent materials for construction of infrared detectors.

Novotny, Jan; Zelinka, J.; Podvalova, Z.

2002-03-01

184

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

185

Palladium-catalyzed coupling reactions of tetrafluoroethylene with arylzinc compounds.  

PubMed

Organofluorine compounds are widely used in all aspects of the chemical industry. Although tetrafluoroethylene (TFE) is an example of an economical bulk organofluorine feedstock, the use of TFE is mostly limited to the production of poly(tetrafluoroethylene) and copolymers with other alkenes. Furthermore, no catalytic transformation of TFE that involves carbon-fluorine bond activation has been reported to date. We herein report the first example of a palladium-catalyzed coupling reaction of TFE with arylzinc reagents in the presence of lithium iodide, giving ?,?,?-trifluorostyrene derivatives in excellent yields. PMID:21322557

Ohashi, Masato; Kambara, Tadashi; Hatanaka, Tsubasa; Saijo, Hiroki; Doi, Ryohei; Ogoshi, Sensuke

2011-03-16

186

Stereoretentive Copper (II) Catalyzed Ritter Reactions of Secondary Cycloalkanols.  

PubMed

A Ritter-like coupling reaction of cyclic alcohols and both aryl and alkyl nitriles to form amides catalyzed by copper (II) triflate is described. These reactions proceed in good yields under mild and often solvent-free conditions. With 2- and 3-substituted cycloalkanols, amide products are formed with near complete retention of configuration. This is likely due to fast nucleophilic capture of a non-planar carbocations (hyperconjomers) stabilized by ring hyperconjugation. A critical aspect of this novel catalytic cycle is the in situ activation of the alcohol substrates by thionyl chloride to form chlorosulfites. PMID:24376393

Al-Huniti, Mohammed H; Lepore, Salvatore D

2013-10-11

187

Stereoretentive Copper (II) Catalyzed Ritter Reactions of Secondary Cycloalkanols  

PubMed Central

A Ritter-like coupling reaction of cyclic alcohols and both aryl and alkyl nitriles to form amides catalyzed by copper (II) triflate is described. These reactions proceed in good yields under mild and often solvent-free conditions. With 2- and 3-substituted cycloalkanols, amide products are formed with near complete retention of configuration. This is likely due to fast nucleophilic capture of a non-planar carbocations (hyperconjomers) stabilized by ring hyperconjugation. A critical aspect of this novel catalytic cycle is the in situ activation of the alcohol substrates by thionyl chloride to form chlorosulfites. PMID:24376393

Al-huniti, Mohammed H.

2013-01-01

188

Stau-catalyzed d-t Nuclear Fusion  

E-print Network

The gravitino of mass 10-100 GeV is a well motivated scenario in supergravity. If the stau is the next lightest supersymmetry particle, its life-time becomes order of $10^{6-8}$ sec. If it is the case the stau makes a big impact on the nuclear fusion, since it is a charged particle. In this paper we perform a detailed calculation of a stau-catalyzed d-t fusion. We find that if certain technical conditions are satisfied, it is not hopeless to use the nuclear fusion as a source of energy.

Koichi Hamaguchi; Tetsuo Hatsuda; Masayasu Kamimura; Tsutomu T. Yanagida

2012-02-13

189

Rhodium-catalyzed enantioselective cyclopropanation of electron deficient alkenes  

PubMed Central

The rhodium-catalyzed reaction of electron-deficient alkenes with substituted aryldiazoacetates and vinyldiazoacetates results in highly stereoselective cyclopropanations. With adamantylglycine derived catalyst Rh2(S-TCPTAD)4, high asymmetric induction (up to 98% ee) can be obtained with a range of substrates. Computational studies suggest that the reaction is facilitated by weak interaction between the carbenoid and the substrate carbonyl but subsequently proceeds via different pathways depending on the nature of the carbonyl.. Acrylates and acrylamides result in the formation of cyclopropanation products while the use of unsaturated aldehydes and ketones results in the formation of epoxides. PMID:24049630

Wang, Hengbin; Guptill, David M.; Alvarez, Adrian Varela

2013-01-01

190

Porous silicon formation during Au-catalyzed etching  

SciTech Connect

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 [Walter Schottky Institut, Technische Universität München, 85748 Garching (Germany)

2014-04-28

191

Titanium-Catalyzed Silicon Nanostructures Grown by APCVD  

NASA Astrophysics Data System (ADS)

We report on growth of Ti-catalyzed silicon nanostructures (SNCs) through atmospheric-pressure chemical vapor deposition. An extensive growth study relating the growth condition parameters, including the partial pressure of SiCl4 gas, reaction temperature, and reaction time, was carried out to obtain insight into the growth regimes for the observed SNCs. Based on phase diagram analysis of Ti-Si alloy and growth rate analysis of the silicon nanowires (SNWs) and silicon nanoplatelets, we believe the growth mechanism to be strongly dependent on the thermodynamics of the system, exhibiting a delicate balance that can easily tip between the growth and etching regimes of the system. Three types of SNCs were observed frequently throughout the study: nanowires, nanoplatelets, and balls. Regimes for highly etched growth were also noted through growth conditions plots. Ti-catalyzed SNWs grown using SiCl4 gas strongly suggest growth occurring through a type of vapor-solid-solid (VSS) mechanism that is limited by diffusion through the solid-catalyst interface. On the other hand, the two-dimensional SNP morphologies suggest growth occurring through the twin-plane mechanism at the edges, at 10 nm to 100 nm scales, also through a similar, VSS mechanism.

Usman, Mohammad A. U.; Smith, Brady J.; Jackson, Justin B.; De Long, Matthew C.; Miller, Mark S.

2014-11-01

192

Retention of anomeric form in lysozyme-catalyzed reaction.  

PubMed

A lysozyme-catalyzed reaction is initiated by a cleavage of the beta-1, 4-glucosaminide linkage, followed by hydration and transglycosylation. Since all glycosides produced by transglycosylation have beta-glycosidic linkages between the sugar and the acceptor moieties, the lysozyme-catalyzed reaction has been classified as an anomer-retention reaction. However, there is no experimental evidence on the anomer retention of the new reducing residue produced by the hydrolysis of the substrate. In the present study, an attempt was made to determine the anomeric form of the GlcNAc residue at the reducing end in nascent hydrolytic products. The anomeric forms of the enzymatic products were separated and quantitatively analyzed by high-performance liquid chromatography. The amounts of alpha- and beta-anomers in the product were plotted against the reaction time. Computer analysis of the experimental data indicated that the nascent hydrolytic product takes only the beta-anomeric form and that the alpha-anomer is formed from beta-anomer by mutarotation. PMID:3813561

Yanase, Y; Fukamizo, T; Hayashi, K; Goto, S

1987-02-15

193

Firefly bioluminescence: a mechanistic approach of luciferase catalyzed reactions.  

PubMed

Luciferase is a general term for enzymes catalyzing visible light emission by living organisms (bioluminescence). The studies carried out with Photinus pyralis (firefly) luciferase allowed the discovery of the reaction leading to light production. It can be regarded as a two-step process: the first corresponds to the reaction of luciferase's substrate, luciferin (LH(2)), with ATP-Mg(2+) generating inorganic pyrophosphate and an intermediate luciferyl-adenylate (LH(2)-AMP); the second is the oxidation and decarboxylation of LH(2)-AMP to oxyluciferin, the light emitter, producing CO(2), AMP, and photons of yellow-green light (550- 570 nm). In a dark reaction LH(2)-AMP is oxidized to dehydroluciferyl-adenylate (L-AMP). Luciferase also shows acyl-coenzyme A synthetase activity, which leads to the formation of dehydroluciferyl-coenzyme A (L-CoA), luciferyl-coenzyme A (LH(2)-CoA), and fatty acyl-CoAs. Moreover luciferase catalyzes the synthesis of dinucleoside polyphosphates from nucleosides with at least a 3'-phosphate chain plus an intact terminal pyrophosphate moiety. The LH(2) stereospecificity is a particular feature of the bioluminescent reaction where each isomer, D-LH(2) or L-LH(2), has a specific function. Practical applications of the luciferase system, either in its native form or with engineered proteins, encloses the analytical assay of metabolites like ATP and molecular biology studies with luc as a reporter gene, including the most recent and increasing field of bioimaging. PMID:18949818

Marques, Simone M; Esteves da Silva, Joaquim C G

2009-01-01

194

Can proteins and crystals self-catalyze methyl rotations?  

SciTech Connect

The {chi} (C{sub {alpha}}-C{sub {beta}}) torsional barrier in the dipeptide alanine (N-methyl-l-alanyl-N-methylamide) crystal was investigated using ab initio calculations at various levels of theory, molecular mechanics, and molecular dynamics. For one of the two molecules in the asymmetric unit the calculations suggest that rotation around the ? dihedral angle is catalyzed by the crystal environment, reducing by up to 2kT the torsional barrier in the crystal with respect to that in the gas phase. This catalytic effect is present at both low and room temperature and originates from a van der Waals destabilization of the minima in the methyl dihedral potential coming from the nonbonded environment of the side chain. Screening of a subset of the Protein Data Bank with a pharmacophore model reproducing the crystal environment around this side chain methyl identified a protein containing an alanine residue with an environment similar to that in the crystal. Calculations indicate that this ? torsional barrier is also reduced in the protein at low temperature but not at room temperature. This suggests that environment-catalyzed rotation of methyl groups can occur both in the solid phase and in native biological structures, though this effect might be temperature-dependent. The relevance of this catalytic effect is discussed in terms of its natural occurrence and its possible contribution to the low-frequency vibrational modes of molecules.

Smith, Jeremy C [ORNL; Baudry, Jerome [University of Illinois

2005-10-01

195

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. PMID:16157688

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

2005-01-01

196

CO2 reduction catalyzed by mercaptopteridine on glassy carbon.  

PubMed

The catalytic reduction of CO2 is of great current interest because of its role in climate change and the energy cycle. We report a pterin electrocatalyst, 6,7-dimethyl-4-hydroxy-2-mercaptopteridine (PTE), that catalyzes the reduction of CO2 and formic acid on a glassy carbon electrode. Pterins are natural cofactors for a wide range of enzymes, functioning as redox mediators and C1 carriers, but they have not been exploited as electrocatalysts. Bulk electrolysis of a saturated CO2 solution in the presence of the PTE catalyst produces methanol, as confirmed by gas chromatography and (13)C NMR spectroscopy, with a Faradaic efficiency of 10-23%. FTIR spectroelectrochemistry detected a progression of two-electron reduction products during bulk electrolysis, including formate, aqueous formaldehyde, and methanol. A transient intermediate was also detected by FTIR and tentatively assigned as a PTE carbamate. The results demonstrate that PTE catalyzes the reduction of CO2 at low overpotential and without the involvement of any metal. PMID:25259884

Xiang, Dongmei; Magana, Donny; Dyer, R Brian

2014-10-01

197

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

198

Titanium-Catalyzed Silicon Nanostructures Grown by APCVD  

NASA Astrophysics Data System (ADS)

We report on growth of Ti-catalyzed silicon nanostructures (SNCs) through atmospheric-pressure chemical vapor deposition. An extensive growth study relating the growth condition parameters, including the partial pressure of SiCl4 gas, reaction temperature, and reaction time, was carried out to obtain insight into the growth regimes for the observed SNCs. Based on phase diagram analysis of Ti-Si alloy and growth rate analysis of the silicon nanowires (SNWs) and silicon nanoplatelets, we believe the growth mechanism to be strongly dependent on the thermodynamics of the system, exhibiting a delicate balance that can easily tip between the growth and etching regimes of the system. Three types of SNCs were observed frequently throughout the study: nanowires, nanoplatelets, and balls. Regimes for highly etched growth were also noted through growth conditions plots. Ti-catalyzed SNWs grown using SiCl4 gas strongly suggest growth occurring through a type of vapor-solid-solid (VSS) mechanism that is limited by diffusion through the solid-catalyst interface. On the other hand, the two-dimensional SNP morphologies suggest growth occurring through the twin-plane mechanism at the edges, at 10 nm to 100 nm scales, also through a similar, VSS mechanism.

Usman, Mohammad A. U.; Smith, Brady J.; Jackson, Justin B.; De Long, Matthew C.; Miller, Mark S.

2015-01-01

199

Chloride-catalyzed corrosion of plutonium in glovebox atmospheres  

SciTech Connect

Characterization of glovebox atmospheres and the black reaction product formed on plutonium surfaces shows that the abnormally rapid corrosion of components in the fabrication line is consistent with a complex salt-catalyzed reaction involving gaseous hydrogen chloride (HCl) and water. Analytical data verify that chlorocarbon and HCl vapors are presented in stagnant glovebox atmospheres. Hydrogen chloride concentrations approach 7 ppm at some locations in the glovebox line. The black corrosion product is identified as plutonium monoxide monohydride (PuOH), a product formed by hydrolysis of plutonium in liquid water and salt solutions at room temperature. Plutonium trichloride (PuCl{sub 3}) produced by reaction of HCl at the metal surface is deliquescent and apparently forms a highly concentrated salt solution by absorbing moisture from the glovebox atmosphere. Rapid corrosion is attributed to the ensuing salt-catalyzed reaction between plutonium and water. Experimental results are discussed, possible involvement of hydrogen fluoride (HF) is examined, and methods of corrective action are presented in this report.

Burgess, M. [ed.; Haschke, J.M.; Allen, T.H.; Morales, L.A.; Jarboe, D.M.; Puglisi, C.V.

1998-04-01

200

Enantioselective Carbonyl-Ene Reactions Catalyzed by Chiral Cationic Dirhodium(II,III) Carboxamidates.  

PubMed

An enantioselective carbonyl-ene reaction of glyoxylate esters with 1,1-disubstituted alkenes catalyzed by chiral cationic dirhodium(II,III) carboxamidates is described. The paddlewheel dirhodium(II,III) carboxamidates having one open coordination site at each rhodium smoothly catalyze the carbonyl-ene reaction to afford homoallylic alcohol products in good isolated yields with high enantioselectivities. PMID:25084486

Xu, Xichen; Wang, Xiaochen; Liu, Yuxiao; Doyle, Michael P

2014-12-19

201

Vanadium-Catalyzed Asymmetric Oxidation of r-Hydroxy Esters Using Molecular Oxygen as Stoichiometric Oxidant  

E-print Network

Vanadium-Catalyzed Asymmetric Oxidation of r-Hydroxy Esters Using Molecular Oxygen of coordination chemistry literature for vanadium, we became interested in exploring the possibility of employing a vanadium-catalyzed oxidative kinetic resolution of R-hydroxy esters using molecular oxygen as the terminal

Toste, Dean

202

Synthesis of acylphosphonates by a palladium-catalyzed phosphonocarbonylation reaction of aryl iodides with phosphites.  

PubMed

Acylphosphonates are conveniently synthesized from aryl iodides by a palladium-catalyzed reaction with dialkyl phosphites under an atmospheric pressure of carbon monoxide. The reaction demonstrates the first example of the use of phosphorus nucleophiles in related metal-catalyzed carbonylation reactions. PMID:25414042

Masuda, Yusuke; Ishida, Naoki; Murakami, Masahiro

2015-02-01

203

Contamination removal from EUV multilayer using atomic hydrogen generated by heated catalyzer  

Microsoft Academic Search

A rapid, damage-free method of removing carbon contamination from EUV multilayer has been developed that employs atomic hydrogen generated by a heated catalyzer consisting of a W wire. Test samples were prepared by contaminating Mo\\/Si multilayers with carbon using EB or synchrotron radiation (SR). The insertion of a thermal shield between the catalyzer and a sample prevented radiant heat from

H. Oizumi; H. Yamanashi; I. Nishiyama; K. Hashimoto; S. Ohsono; A. Masuda; A. Izumi; H. Matsumura

2005-01-01

204

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

PubMed Central

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

2015-01-01

205

ROLE OF COPPER,ZINC-SUPEROXIDE DISMUTASE IN CATALYZING NITROTYROSINE FORMATION IN MURINE LIVER  

Technology Transfer Automated Retrieval System (TEKTRAN)

The solely known function of Cu,Zn-superoxide dismutase (SOD1) is to catalyze the dismutation of superoxide anion into hydrogen peroxide. Our objective was to determine if SOD1 catalyzed murine liver protein nitration induced by acetaminophen (APAP) and lipopolysaccharide (LPS). Liver and plasma ...

206

Thermodynamics of Enzyme-Catalyzed Reactions: Part 7--2007 Update Robert N. Goldberg,a...  

E-print Network

Thermodynamics of Enzyme-Catalyzed Reactions: Part 7--2007 Update Robert N. Goldberg,a... Yadu B evaluations of equilibrium constants and enthalpy changes for enzyme-catalyzed reactions. For each reaction, the following information is given: the reference for the data, the reaction studied, the name of the enzyme

Magee, Joseph W.

207

Monitoring Enzyme-catalyzed Reactions in Micromachined Nanoliter Wells using a Conventional Microscope based  

E-print Network

Monitoring Enzyme-catalyzed Reactions in Micromachined Nanoliter Wells using a Conventional to ethanol and carbon dioxide. This pathway consists of 12 enzyme-catalyzed reactions. With the approach � 300µm2 . The depth varies from 20 to 50µm. Enzyme activity levels can be derived by monitoring

van Vliet, Lucas J.

208

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation  

E-print Network

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

Amrhein, Valentin

209

Rhodium(III)-catalyzed oxidative olefination of N-allyl sulfonamides.  

PubMed

Rhodium(III)-catalyzed oxidative couplings between N-sulfonyl allylamines and activated olefins have been achieved. Only olefination occurred for acrylates, and the butadiene product can be further cyclized under palladium-catalyzed aerobic conditions. The coupling with N,N-dimethylacrylamide followed a cyclization pathway. PMID:23532183

Hu, Shui; Wang, Dongqi; Liu, Jiexiang; Li, Xingwei

2013-05-01

210

Theoretical Study of Zeolite-Catalyzed Dimethoxymethane Carbonylation to Methyl Methoxyacetate  

E-print Network

Theoretical Study of Zeolite-Catalyzed Dimethoxymethane Carbonylation to Methyl Methoxyacetate be catalyzed by acid zeolites. This reaction is a critical step in the synthesis of monoethylene glycol (MEG-FAU zeolites has been investigated using density functional theory. We find that the reaction involves three

Bell, Alexis

211

From anilines to isatins: oxidative palladium-catalyzed double carbonylation of c?h bonds.  

PubMed

A novel palladium-catalyzed C?H double carbonylation introduces two adjacent carbonyl groups for the synthesis of isatins from readily available anilines. The reaction proceeds under atmospheric pressure of CO with high regioselectivity and without any additives. Density functional theory investigations indicate that the palladium-catalyzed double carbonylation catalytic cycle is plausible. PMID:25521770

Li, Wu; Duan, Zhengli; Zhang, Xueye; Zhang, Heng; Wang, Mengfan; Jiang, Ru; Zeng, Hongyao; Liu, Chao; Lei, Aiwen

2015-02-01

212

Addition of heterocycles to electron deficient olefins and alkynes catalyzed by gold(III)  

E-print Network

Addition of heterocycles to electron deficient olefins and alkynes catalyzed by gold(III) Zigang Li Abstract A gold(III)-catalyzed hydroarylation of different olefins is reported here. AuCl3 works and alkynes under mild conditions. This gold(III)-based method tolerates different functional groups

He, Chuan

213

Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to cyclic enones with spirocyclic phosphoramidite ligands  

E-print Network

Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to cyclic enones spirocyclic diol (R)-5. These monodentate ligands have been applied in copper-catalyzed conjugate addition ligands com- bined with copper salts have shown excellent enantio- selectivities in the conjugate addition

Zhang, Xumu

214

~ristalsof bovine chyrnotrypsin. Enzymes are proteins specialized to catalyze biological reac-  

E-print Network

Figure 8-1 ~ristalsof bovine chyrnotrypsin. 1 Enzymes are proteins specialized to catalyze of biochemistry is the history of en- zyme research. The name enzyme ("in yeast") was not used until 1877- furic acid. Although Louis Pasteur recognized that fermentation is catalyzed by enzymes, he postulated

Vallino, Joseph J.

215

Nickel-catalyzed reductive coupling reactions of 1,6-enynes and the total synthesis of (+)-acutiphycin  

E-print Network

Nickel-Catalyzed Reductive Coupling Reactions of Aldehydes and Chiral 1,6-Enynes. A study of nickel-catalyzed reductive coupling reactions of aldehydes and chiral 1,6-enynes has provided evidence for stereospecific ligand ...

Moslin, Ryan Thomas McLeod

2007-01-01

216

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

E-print Network

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

Son, Sunghee

2008-01-01

217

Degradation and transformation of atrazine under catalyzed ozonation process with TiO2 as catalyst.  

PubMed

Degradation of atrazine by heterogeneously catalyzed ozonation was carried out with TiO2 in the form of rutile as the catalyst. Some experimental factors such as catalyst dose, ozone dose and initial concentration of atrazine were investigated for their influence on catalyzed ozonation process. Although atrazine was effectively removed from aqueous solution by catalyzed ozonation process, the mineralization degree only reached 56% at the experimental conditions. Five transformation products were identified by GC/MS analysis. The degradation of atrazine involved de-alkylation, de-chlorination and de-amination. Diaminotriazine and 5-azauracil were the de-chlorinated and de-aminated products, respectively. The evolution of concentration of transformation products during catalyzed ozonation process was compared with uncatalyzed ozonation to show the degradation pathway. Toxicity tests based on the inhibition of the luminescence emitted by Vibrio fisheri indicated the detoxification of atrazine by catalyzed ozonation. PMID:25106044

Yang, Yixin; Cao, Hongbin; Peng, Pai; Bo, Hongmiao

2014-08-30

218

Gold(I)-Catalyzed Synthesis of Dihydrobenzofurans from Aryl Allyl Ethers Gold(I)-CatalyzedSynthesisofDihydrobenzofuransfromArylAllylEthersNicholas W. Reich, Cai-Guang Yang, Zhangjie Shi,1  

E-print Network

LETTER1278 Gold(I)-Catalyzed Synthesis of Dihydrobenzofurans from Aryl Allyl Ethers Gold in cationic gold species as effective Lewis acid catalysts, we sought to catalyze the synthesis 5 mol% catalyst 80 °C, 16 h, solvent 1 2 #12;LETTER Gold(I)-Catalyzed Synthesis of Dihydrobenz

He, Chuan

219

Gold-catalyzed tandem reactions of methylenecyclopropanes and vinylidenecyclopropanes.  

PubMed

Gold catalysis is often the key step in the synthesis of natural products, and is a powerful tool for tandem or domino reaction processes. Both gold salts and complexes are among the most powerful soft Lewis acids for electrophilic activation of carbon-carbon multiple bonds toward a variety of nucleophiles. The core of these reactions relies on the interaction between gold catalysts and ?-bonds of alkenes, alkynes, and allenes. Activation of functional groups by gold complexes provides a useful and important method for facilitating many different organic transformations with high atom efficiency. Although they are highly strained, methylenecyclopropanes (MCPs) and vinylidenecyclopropanes (VDCPs) are readily accessible molecules that have served as useful building blocks in organic synthesis. Because of their unique structural and electronic properties, significant developments have been made in the presence of transition metal catalysts such as nickel, rhodium, palladium, and ruthenium during the past decades. However, less attention has been paid to the gold-catalyzed chemistry of MCPs and VDCPs. In this Account, we describe gold-catalyzed chemical transformations of MCPs and VDCPs developed both in our laboratory and by other researchers. Chemists have demonstrated that MCPs and VDCPs have amphiphilic properties. When MCPs or VDCPs are activated by a gold catalyst, subsequent nucleophilic attack by other reagents or ring-opening (ring-expansion) of the cyclopropane moiety will occur. However, the C-C double bonds of MCPs and VDCPs can also serve as nucleophilic reagents while more electrophilic reagents are present and activated by gold catalyst, and then further cascade reactions take place as triggered by the release of ring strain of cyclopropane. Based on this strategy, both our group and others have found some interesting gold-catalyzed transformations in recent years. These transformations of MCPs and VDCPs can produce a variety of polycyclic and heterocyclic structures, containing different sized skeletons. Moreover, we have carried out some isotopic labeling experiments and computational studies for mechanistic investigation. These reactions always give the desired products with high level control of chemo-, regio-, and diastereoselectivities, making them highly valuable for the synthesis of natural products and to the pharmaceutical industry and medicine in general. PMID:24168021

Zhang, Di-Han; Tang, Xiang-Ying; Shi, Min

2014-03-18

220

Rhenium-Catalyzed Deoxydehydration of Diols and Polyols.  

PubMed

The substitution of platform chemicals of fossil origin by biomass-derived analogues requires the development of chemical transformations capable of reducing the very high oxygen content of biomass. One such reaction, which has received increasing attention within the past five years, is the rhenium-catalyzed deoxydehydration (DODH) of a vicinal diol into an alkene; this is a model system for abundant polyols like glycerol and sugar alcohols. The present contribution includes a review of early investigations of stoichiometric reactions involving rhenium, diols, and alkenes followed by a discussion of the various catalytic systems that have been developed with emphasis on the nature of the reductant, the substrate scope, and mechanistic investigations. PMID:25477245

Dethlefsen, Johannes R; Fristrup, Peter

2014-12-01

221

Photodecomposition of chloroform catalyzed by unmodified MCM-41 mesoporous silica.  

PubMed

Unactivated MCM-41 mesoporous silica catalyzes the photodecomposition of chloroform to phosgene and hydrogen chloride under near-UV (? > 360 nm) irradiation. The rate of photodecomposition increases toward an asymptotic limit as the O(2) partial pressure is increased. Deuterochloroform does not decompose under the same experimental conditions. Low concentrations of both cyclohexane and ethanol quench the photodecomposition, whereas water, up to its solubility limit, does not. Dissolved tetraalkylammonium salts suppress photodecomposition. The data are consistent with a mechanism in which light absorption by an SiO(2) defect yields an electron-deficient oxygen atom, which then abstracts hydrogen from chloroform. The resulting CCl(3) radicals react with oxygen to form a peroxy radical that decomposes, eventually yielding phosgene and hydrogen chloride. PMID:24460571

Peña, Laura A; Chan, Alissa M; Cohen, Larissa R; Hou, Karen; Harvey, Brent M; Hoggard, Patrick E

2014-01-01

222

Cobalt-catalyzed reductive coupling of activated alkenes with alkynes.  

PubMed

Cobalt complex/Zn systems effectively catalyze the reductive coupling of activated alkenes with alkynes in the presence of water to give substituted alkenes with very high regio- and stereoselectivity in excellent yields. While the intermolecular reaction of acrylates, acrylonitriles, and vinyl sulfones with alkynes takes place in the presence of CoI2(PPh3)2/Zn, the reaction of enones and enals with alkynes requires the use of the CoI2(dppe)/Zn/ZnI2 system. The intramolecular reductive coupling of activated alkenes (enones, enals, acrylates, and acrylonitriles) with alkynes also works efficiently. Further a variety of cyclic lactones and lactams were prepared using this methodology. Possible mechanistic pathways are proposed based on a deuterium-labeling experiment carried out in the presence of D2O. PMID:17845040

Chang, Hong-Tai; Jayanth, Thiruvellore Thatai; Wang, Chun-Chih; Cheng, Chien-Hong

2007-10-01

223

Oligonucleotide synthesis catalyzed by the Zn/2+/ ion  

NASA Technical Reports Server (NTRS)

Results of experiments are reported in which Zn(2+) ion catalyzed the formation of oligonucleotides from nucleoside phosphorimidazolides in aqueous solution, even in the absence of a template. Specifically, the imidazolides (ImpU or ImpA) polymerized to form ImpApA, and pApA, pApApA, and pApApApA, or the analogous uracil compounds. In addition, the expected hydrolysis products of the hydrolysis of ImpA were formed (pA, imidazole). Judging from the ratio of pA(n) over pA (with and without zinc ion), this ion increased the efficiency of phosphodiester-bond formation by up to 10 times. Possible mechanisms for the reaction are tentatively proposed.

Sawai, H.; Orgel, L. E.

1975-01-01

224

Acid-catalyzed reactions of epoxides for atmospheric nanoparticle growth.  

PubMed

Although new particle formation accounts for about 50% of the global aerosol production in the troposphere, the chemical species and mechanism responsible for the growth of freshly nucleated nanoparticles remain largely uncertain. Here we show large size growth when sulfuric acid nanoparticles of 4-20 nm are exposed to epoxide vapors, dependent on the particle size and relative humidity. Composition analysis of the nanoparticles after epoxide exposure reveals the presence of high molecular weight organosulfates and polymers, indicating the occurrence of acid-catalyzed reactions of epoxides. Our results suggest that epoxides play an important role in the growth of atmospheric newly nucleated nanoparticles, considering their large formation yields from photochemical oxidation of biogenic volatile organic compounds. PMID:25338124

Xu, Wen; Gomez-Hernandez, Mario; Guo, Song; Secrest, Jeremiah; Marrero-Ortiz, Wilmarie; Zhang, Annie L; Zhang, Renyi

2014-11-01

225

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

226

Water oxidation catalyzed by a dinuclear cobalt-polypyridine complex.  

PubMed

The dinuclear Co complex [(TPA)Co(?-OH)(?-O2 )Co(TPA)](ClO4 )3 (1, TPA=tris(2-pyridylmethyl)amine) catalyzes the oxidation of water. In the presence of [Ru(bpy)3 ](2+) and S2 O8 (2-) , photoinduced oxygen evolution can be observed with a turnover frequency (TOF) of 1.4±0.1?mol(O2 )?mol(1)(-1) ?s(-1) and a maximal turnover number (TON) of 58±5?mol(O2 )?mol(1)(-1) . The complex is shown to act as a molecular and homogeneous catalyst and a mechanism is proposed based on the combination of EPR data and light-driven O2 evolution kinetics. PMID:25348687

Wang, Hong-Yan; Mijangos, Edgar; Ott, Sascha; Thapper, Anders

2014-12-22

227

The role of fluoride in montmorillonite-catalyzed RNA synthesis.  

PubMed

The montmorillonite-catalyzed reactions of the 5'-phosphorimidazolide of adenosine in the presence of fluoride were investigated to complete our study on the effect of salts on this type of reaction. Both anions and cations have been found to influence the oligomerization reactions of the activated nucleotides, being used here as a model system for pre-biotic RNA synthesis. However, in total contrast to the behavior of the activated nucleotides in the presence of montmorillonite and other salts, alkali metal fluorides did not yield any detectable oligomerization products except in very dilute (<0.005 M) solutions of fluoride. Instead, 5'-phosphorofluoridates were formed. Their identity was confirmed by a combination of HPLC, mass spectrometry, synthesis, and NMR. PMID:24756181

Aldersley, Michael F; Joshi, Prakash C

2014-05-01

228

Enantioselective Cyclizations of Silyloxyenynes Catalyzed by Cationic Metal Phosphine Complexes  

PubMed Central

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

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

2012-01-01

229

Mechanistic origin of chemoselectivity in thiolate-catalyzed Tishchenko reactions.  

PubMed

The thiolate-catalyzed Tishchenko reaction has shown high chemoselectivity for the formation of double aromatic-substituted esters. In the present study, the detailed reaction mechanism and, in particular, the origin of the observed high chemoselectivity, have been studied with DFT calculations. The catalytic cycle mainly consisted of three steps: 1,2-addition, hydride transfer, and acyl transfer steps. The calculation results reproduce the experimental observations that 4-chlorobenzaldehyde acts as the hydrogen donor (carbonyl part in the ester product), while 2-methoxybenzaldehyde acts as the hydrogen acceptor (alcohol part in the product). The two main factors are responsible for such chemoselectivity: 1) in the rate-determining hydride transfer step, the para-chloride substituent facilitates the hydride-donating process by weakening the steric hindrance, and 2) the ortho-methoxy substituent facilitates the hydride-accepting process by stabilizing the magnesium center (by compensating for the electron deficiency). PMID:25213329

Yu, Hai-Zhu; Tian, Xue-Jiao; Lin, Xiang; Hu, Guo-Hua; Dang, Zhi-Min

2014-12-01

230

Ligand-controlled regiodivergent nickel-catalyzed annulation of pyridones.  

PubMed

The 1,6-annulated 2-pyridone motif is found in many biologically active compounds and its close relation to the indolizidine and quinolizidine alkaloid core makes it an attractive building block. A nickel-catalyzed C?H functionalization of 2-pyridones and subsequent cyclization affords 1,6-annulated 2-pyridones by selective intramolecular olefin hydroarylation. The switch between the exo- and endo-cyclization modes is controlled by two complementary sets of ligands. Irrespective of the ring size, the regioselectivity during the cyclization is under full catalyst control. Simple cyclooctadiene promotes an exo-selective cyclization, whereas a bulky N-heterocyclic carbene ligand results in an endo-selective mode. The method was further applied in the synthesis of the lupin alkaloid cytisine. PMID:25378295

Donets, Pavel A; Cramer, Nicolai

2015-01-01

231

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

232

Instructions for use A Palladium-Catalyzed Biaryl Coupling of Arylboronic Acids in Aqueous Media Using A  

E-print Network

Instructions for use #12;A Palladium-Catalyzed Biaryl Coupling of Arylboronic Acids in Aqueous), was newly synthesized to perform the palladium-catalyzed biaryl coupling of arylboronic acids in a single-catalyzed biaryl coupling of arylboronic acids.2 A fine metallic palladium generated in situ from Pd(OAc)2

Tachizawa, Kazuya

233

COPPER-CATALYZED CROSS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS  

E-print Network

COPPER-CATALYZED CROSS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS Chemistry #12;© Copyright by Craig G. Bates 2005 All Rights Reserved #12;COPPER-CATALYZED CROSS without her. Thank You January 24, 2005 #12;vi ABSTRACT COPPER-CATALYZED CROSS-COUPLING REACTIONS

Venkataraman, Dhandapani "DV"

234

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

235

Cyclic peptide formation catalyzed by an antibody ligase.  

PubMed

Cyclic hexapeptides represent a class of compounds with important, diverse biological activities. We report herein that the antibody 16G3 catalyzes the cyclization of d-Trp-Gly-Pal-Pro-Gly-Phe small middle dotp-nitrophenyl ester (8a) to give c-(d-Trp-Gly-Pal-Pro-Gly-l-Phe) (11a). The antibody does not, however, catalyze either epimerization or hydrolysis. The resulting rate enhancement of the cyclization by 16G3 (22-fold) was sufficient to form the desired product in greater than 90% yield. In absolute rate terms, the turnover of 16G3 is estimated to be 2 min(-1). The background rate of epimerization of 8a was reduced from 10 to 1% and hydrolysis from 50 to 4% in the presence of 16G3. As expected, the catalytic effects of 16G3 were blocked by the addition of an amount of the hapten equal to twice the antibody concentration. We also synthesized three diastereomers of 8a: the d-Trp(1)-d-Phe(6) (8b), l-Trp(1)-l-Phe(6) (8c), and l-Trp(1)-d-Phe(6) (8d) hexapeptides as well as d-Trp'-l-Trp(6) (12) and d-Phe'-l-Phe(6) (13). As expected, the rate enhancement by 16G3 was greatest for 8a, because the stereochemistry of Trp(1) and Phe(6) matches that of the corresponding residues on the hapten used to induce the biosynthesis of 16G3. A model of the variable domain of 16G3 was generated from the primary sequence using the antibody structural database to guide the model construction. The resulting model provided support for some previously proposed interpretations of the kinetic data, while providing valuable new insights for others. PMID:10688882

Smithrud, D B; Benkovic, P A; Benkovic, S J; Roberts, V; Liu, J; Neagu, I; Iwama, S; Phillips, B W; Smith, A B; Hirschmann, R

2000-02-29

236

Metal-catalyzed protein tyrosine nitration in biological systems.  

PubMed

Protein tyrosine nitration is an oxidative postranslational modification that can affect protein structure and function. It is mediated in vivo by the production of nitric oxide-derived reactive nitrogen species (RNS), including peroxynitrite (ONOO(-)) and nitrogen dioxide ((•)NO?). Redox-active transition metals such as iron (Fe), copper (Cu), and manganese (Mn) can actively participate in the processes of tyrosine nitration in biological systems, as they catalyze the production of both reactive oxygen species and RNS, enhance nitration yields and provide site-specificity to this process. Early after the discovery that protein tyrosine nitration can occur under biologically relevant conditions, it was shown that some low molecular weight transition-metal centers and metalloproteins could promote peroxynitrite-dependent nitration. Later studies showed that nitration could be achieved by peroxynitrite-independent routes as well, depending on the transition metal-catalyzed oxidation of nitrite (NO?(-)) to (•)NO? in the presence of hydrogen peroxide. Processes like these can be achieved either by hemeperoxidase-dependent reactions or by ferrous and cuprous ions through Fenton-type chemistry. Besides the in vitro evidence, there are now several in vivo studies that support the close relationship between transition metal levels and protein tyrosine nitration. So, the contribution of transition metals to the levels of tyrosine nitrated proteins observed under basal conditions and, specially, in disease states related with high levels of these metal ions, seems to be quite clear. Altogether, current evidence unambiguously supports a central role of transition metals in determining the extent and selectivity of protein tyrosine nitration mediated both by peroxynitrite-dependent and independent mechanisms. PMID:24977336

Campolo, Nicolás; Bartesaghi, Silvina; Radi, Rafael

2014-11-01

237

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

238

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

PubMed Central

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

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

2014-01-01

239

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

240

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

241

Flame Synthesis Used to Create Metal-Catalyzed Carbon Nanotubes  

NASA Technical Reports Server (NTRS)

Metal-catalyzed carbon nanotubes are highly ordered carbon structures of nanoscale dimensions. They may be thought of as hollow cylinders whose walls are formed by single atomic layers of graphite. Such cylinders may be composed of many nested, concentric atomic layers of carbon or only a single layer, the latter forming a single-walled carbon nanotube. This article reports unique results using a flame for their synthesis. Only recently were carbon nanotubes discovered within an arc discharge and recognized as fullerene derivatives. Today metal-catalyzed carbon nanotubes are of great interest for many reasons. They can be used as supports for the metal catalysts like those found in catalytic converters. Open-ended nanotubes are highly desirable because they can be filled by other elements, metals or gases, for battery and fuel cell applications. Because of their highly crystalline structure, they are significantly stronger than the commercial carbon fibers that are currently available (10 times as strong as steel but possessing one-sixth of the weight). This property makes them highly desirable for strengthening polymer and ceramic composite materials. Current methods of synthesizing carbon nanotubes include thermal pyrolysis of organometallics, laser ablation of metal targets within hydrocarbon atmospheres at high temperatures, and arc discharges. Each of these methods is costly, and it is unclear if they can be scaled for the commercial synthesis of carbon nanotubes. In contrast, flame synthesis is an economical means of bulk synthesis of a variety of aerosol materials such as carbon black. Flame synthesis of carbon nanotubes could potentially realize an economy of scale that would enable their use in common structural materials such as car-body panels. The top figure is a transmission electron micrograph of a multiwalled carbon nanotube. The image shows a cross section of the atomic structure of the nanotube. The dark lines are individual atomic layer planes of carbon, seen here in cross section. They form a nested series of concentric cylinders, much like the growth rings on a tree. This sample was obtained by the supported catalyst method, whereby the nanoscale catalysts are dispersed on a substrate providing their support. The substrate with catalyst particles was immersed within an acetylene diffusion flame to which nitrogen had been added to eliminate soot formation. Upon removal from the flame, the nanotubes were dispersed on a holder suitable for electron microscopy. Although not seen in the figure, the tube diameter reflects that of the catalyst particle.

VanderWal, Randy L.

2001-01-01

242

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

243

Palladium-catalyzed C-C, C-N and C-O bond formation  

E-print Network

New methods for Pd-catalyzed cross-coupling reactions of aryl halides or arenesulfonates are described. Key to the success of these transformations is the proper choice of ligand and reaction conditions. Palladium catalysts ...

Huang, Xiaohua, 1973-

2003-01-01

244

A New Biarylphosphine Ligand for the Pd-Catalyzed Synthesis of Diaryl Ethers under Mild Conditions  

E-print Network

A new bulky biarylphosphine ligand (L8) has been developed that allows the Pd-catalyzed C–O cross-coupling of a wide range of aryl halides and phenols under milder conditions than previously possible. A direct correlation ...

Salvi, Luca

245

Trisoxazoline\\/Cu(II)-catalyzed asymmetric intramolecular Friedel–Crafts alkylation reaction of indoles  

Microsoft Academic Search

Intramolecular Friedel–Crafts alkylation reaction of indoles catalyzed by trisoxazoline\\/copper(II) is described. This annulation provides an easy access to polycyclic indole derivatives with up to 90% ee in up to 99% yield.

Jiao-Long Zhou; Meng-Chun Ye; Xiu-Li Sun; Yong Tang

2009-01-01

246

Nickel-Catalyzed Heck-Type Reactions of Benzyl Chlorides and Simple Olefins  

E-print Network

Nickel-catalyzed intermolecular benzylation and heterobenzylation of unactivated alkenes to provide functionalized allylbenzene derivatives are described. A wide range of both the benzyl chloride and alkene coupling partners ...

Matsubara, Ryosuke

247

2-Halogenoimidazolium Salt Catalyzed Aza-Diels-Alder Reaction through Halogen-Bond Formation.  

PubMed

2-Halogenoimidazolium salts are found to catalyze aza-Diels-Alder reaction of aldimines with Danishefsky diene in an efficient manner. Comparative studies and titration experiments support the formation of halogen bonding between imines and catalysts. PMID:25551775

Takeda, Youhei; Hisakuni, Daichi; Lin, Chun-Hsuan; Minakata, Satoshi

2015-01-16

248

One-Flow, Multi-Step Synthesis of Nucleosides via Brønsted Acid- Catalyzed Glycosylation  

E-print Network

Nucleosides in flow: A general, scalable method of Brønsted acid-catalyzed nucleoside formation is described. Because of the high reaction temperatures readily available to the flow reaction format, mild Brønsted acids, ...

Sniady, Adam

249

Lipase catalyzed resolution of chiral acids or alcohols using mixed carboxylic-carbonic anhydrides  

Microsoft Academic Search

Mixed carboxylic-carbonic anhydrides are efficient irreversible acyl transfer reagents for lipase catalyzed esterification in organic media, and can be used for the resolution of chiral carboxylic acids or alcohols.

Eryka Guibé-Jampel; Zbigniew Chalecki; Mohamed Bassir; Mirjana Gelo-Pujic

1996-01-01

250

Rhodium-catalyzed epoxide-opening cascades toward brevisin and hemibrevetoxin B  

E-print Network

CHAPTER I. Rhodium-Catalyzed Epoxide-Opening Cascades: Formal Synthesis of (-)-Brevisin [chemical formula inserted] [Rh(CO)?Cl]? was found to be an effective catalyst for endo-selective cyclizations and cascades of ...

Armbrust, Kurt W. (Kurt Willes)

2014-01-01

251

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

252

Iron- and Cobalt-Catalyzed Arylation of Azetidines, Pyrrolidines, and Piperidines with Grignard Reagents.  

PubMed

Iron- and cobalt-catalyzed cross-couplings between iodo-azetidines, -pyrrolidines, -piperidines, and Grignard reagents are disclosed. The reaction is efficient, cheap, chemoselective and tolerates a large variety of (hetero)aryl Grignard reagents. PMID:25401684

Barré, Baptiste; Gonnard, Laurine; Campagne, Rémy; Reymond, Sébastien; Marin, Julien; Ciapetti, Paola; Brellier, Marie; Guérinot, Amandine; Cossy, Janine

2014-11-17

253

Regioselectivity in the oxidative deamination of 2-methyl-1,4-diaminobutane catalyzed by diamine oxidases  

Microsoft Academic Search

Summary Diamine oxidase from pea seedlings (PDAO) catalyzes the oxidation of 2-methyl-1,4-diaminobutane in a regioselective fashion, whereas diamine oxidase from pig kidney (KDAO) shows no regioselectivity for the same reaction.

E. Santaniello; Ada Manzocchi; P. A. Biondi; Tatjana Simonic

1982-01-01

254

The development and application of metal-catalyzed processes for organic synthesis  

E-print Network

Chapter 1. Copper-Catalyzed Arylation of Stabilized Carbanions A mild, general catalytic system for the synthesis of [alpha]-aryl malonates has been developed. Aryl iodides bearing a variety of functional groups can be ...

Hennessy, Edward J. (Edward John), 1977-

2005-01-01

255

Esterification kinetics of triglycerides in n-hexane catalyzed by an immobilized lipase  

E-print Network

The kinetics of enzyme-catalyzed esterification of triglycerides over immobilized lipase in n-hexane was investigated. The reaction kinetics were described in terms of a mechanism developed following the Langmuir-Hinshelwood-Hougen-Watson (LHHW...

Gomez Ruiz, Alejandro

1998-01-01

256

Synthesis of Unsymmetrical Diarylureas via Pd-Catalyzed C–N Cross-Coupling Reactions  

E-print Network

A facile synthesis of unsymmetrical N,N?-diarylureas is described. The utilization of the Pd-catalyzed arylation of ureas enables the synthesis of an array of diarylureas in good to excellent yields from benzylurea via a ...

Breitler, Simon

257

Palladium-catalyzed direct ?-arylation of methyl sulfones with aryl bromides.  

PubMed

A direct and efficient approach for palladium-catalyzed arylation of aryl and alkyl methyl sulfones with aryl bromides has been developed. The catalytic system affords arylated sulfones in good to excellent yields (73-90%). PMID:23517309

Zheng, Bing; Jia, Tiezheng; Walsh, Patrick J

2013-04-01

258

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...

259

GREEN CATALYZED OXIDATION OF HYDROCARBONS IN ALTERNATIVE SOLVENT SYSTEMS GENERATED BY PARIS II  

EPA Science Inventory

Green Catalyzed Oxidation of Hydrocarbons in Alternative Solvent Systems Generated by PARIS II Michael A. Gonzalez*, Thomas M. Becker, and Paul F. Harten; Sustainable Technology Division, Office of Research and Development; United States Environmental Protection Agency, 26...

260

Myoglobin-catalyzed intermolecular carbene N-H insertion with arylamine substrates.  

PubMed

Engineered variants of the heme-containing protein myoglobin can efficiently catalyze the insertion of ?-diazo esters into the N-H bond of arylamines, featuring a combination of high chemoselectivity, elevated turnover numbers, and broad substrate scope. PMID:25504318

Sreenilayam, Gopeekrishnan; Fasan, Rudi

2015-01-01

261

DOI: 10.1002/adsc.200700546 Iridium-Catalyzed Asymmetric Hydrogenation of Vinyl Ethers  

E-print Network

DOI: 10.1002/adsc.200700546 Iridium-Catalyzed Asymmetric Hydrogenation of Vinyl Ethers Ye Zhua,P-ligated iridium complexes in asymmetric hydrogenations of the silyl and methyl enol ethers D and E, but complex

Burgess, Kevin

262

Palladium-catalyzed allylic alkylation via decarboxylative and retro-Claisen C-C cleavage methods  

E-print Network

Presented herein is the development of new methods for Pd-catalyzed allylic alkylation with a central focus on reactions that generate molecular complexity rapidly with little waste byproduct. With this simply stated, yet ...

Grenning, Alexander James

2012-05-31

263

53. VIEW LOOKING S.E. AT THE CATALYZER BUILDINGS, COOLING SHEDS ...  

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

53. VIEW LOOKING S.E. AT THE CATALYZER BUILDINGS, COOLING SHEDS AND ABSORPTION BUILDINGS IN THE BACKGROUND. MAY 29, 1919. - United States Nitrate Plant No. 2, Reservation Road, Muscle Shoals, Muscle Shoals, Colbert County, AL

264

Formal Total Synthesis of (-)-Taxol through Pd-Catalyzed Eight-Membered Carbocyclic Ring Formation.  

PubMed

A formal total synthesis of (-)-taxol by a convergent approach utilizing Pd-catalyzed intramolecular alkenylation is described. Formation of the eight-membered carbocyclic ring has been a problem in the convergent total synthesis of taxol but it was solved by the Pd-catalyzed intramolecular alkenylation of a methyl ketone affording the cyclized product in excellent yield (97?%), indicating the high efficiency of the Pd-catalyzed intramolecular alkenylation. Rearrangement of the epoxy benzyl ether through a 1,5-hydride shift, generating the C3 stereogenic center and subsequently forming the C1-C2 benzylidene, was discovered and utilized in the preparation of a substrate for the Pd-catalyzed reaction. PMID:25346263

Hirai, Sho; Utsugi, Masayuki; Iwamoto, Mitsuhiro; Nakada, Masahisa

2015-01-01

265

Nickel-catalyzed preparation of acrylamides from alpha olefins and isocyanates ; Synthetic studies toward ripostatin A  

E-print Network

Chapter I. In the presence of the N-heterocyclic carbene ligand IPr, the nickel(0)-catalyzed coupling reaction of a-olefins and branched aliphatic isocyanates provides c,-unsaturated amides arising from preferential C-C ...

Schleicher, Kristin D. (Kristin Diann)

2010-01-01

266

Pd-Catalyzed Synthesis of Ar-SCF3 Compounds under Mild Conditions  

E-print Network

Good to excellent yields of aryl trifluoromethyl sulfides, which are an important class of compounds in both the pharmaceutical and agrochemical areas, can be achieved under mild conditions by the Pd-catalyzed reaction of ...

Teverovskiy, Georgiy

267

The development and synthetic applications of Ti- and Pd-catalyzed processes  

E-print Network

Chapter 1. Ti-Catalyzed Asymmetric Reduction of Aromatic Heterocycles A method for the highly selective asymmetric reduction of quinoxalines and quinazolines was developed. This complements technologies developed by others ...

Hyde, Alan M. (Alan Michael)

2009-01-01

268

Synthesis of indoles via palladium-catalyzed annulation of aryl chlorides and internal alkynes  

E-print Network

A palladium-catalyzed preparation of 2,3-disubstituted indoles from commercially available and relatively inexpensive reagents, o-chloroacetanilide and internal alkynes, is reported. The system is efficient in delivering ...

Dussault, Daemian David, 1973-

2005-01-01

269

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

270

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

271

Treatment Of Polychlorinated Biphenyls In Two Surface Soils Using Catalyzed H2O2 Propagations  

EPA Science Inventory

Two surface soils contaminated with polychlorinated biphenyls (PCBs) collected from Superfund sites in the New England region of the United States, Fletcher Paints and Merrimack Industrial Metals, were evaluated for field treatment at the bench level using catalyzed H2...

272

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...

273

Phosphine-catalyzed dearomatizing [3+2] annulations of isoquinolinium methylides with allenes.  

PubMed

A phosphine-catalyzed dearomatizing [3+2] annulation of isoquinolinium methylides with allenoates or allenones yields highly functionalized pyrroloisoquinolines with high regioselectivity and in viable yields. PMID:25434405

Jia, Zhi-Jun; Daniliuc, Constantin Gabriel; Antonchick, Andrey P; Waldmann, Herbert

2015-01-21

274

Synthesis of 3-indole derivatives by copper sulfonato Salen catalyzed three-component reactions in water.  

PubMed

An efficient three-component reaction of indole, aldehyde, and malononitrile in water catalyzed by a copper(II) sulfonato Salen complex afforded 3-indole derivatives in good to excellent yields up to 97%. PMID:21340052

Qu, Yanyang; Ke, Fang; Zhou, Li; Li, Zhengkai; Xiang, Haifeng; Wu, Di; Zhou, Xiangge

2011-04-01

275

Periodic Current Oscillation Catalyzed by ?-MnO2 Nanosheets.  

PubMed

The oxygen evolution reaction (OER) is of wide interest for both fuel and hydrometallurgy applications. Different types of nanoscale MnO2 , varying from nanosheets to nanoneedles, are synthesized and assembled on the anode to investigate their catalytic effect on the nonlinear kinetics of the MnO2 -catalyzed OER at high current. For ?-MnO2 nanosheets, periodic current oscillations (PCO) occurr and occupy up to 40?% of the total energy consumption. The PCO can help to reduce the energy consumption under constant current conditions. Its amplitude could be twice of that for the previously reported MnO2 grown by an in?situ electrochemical method. If the amount of ?-MnO2 nanoneedles increases, the oscillation disappears. For different Mn oxides, the rate constants of H2 O2 decomposition differ, resulting in changes in oscillation features. The results of this study may enable new ideas to improve the efficiency of industrial electrolysis and charging-discharging of supercapacitors. PMID:25382485

Fan, Xing; Yang, Dianpeng; Ding, Lifeng; Du, Jun; Tao, Changyuan

2014-11-01

276

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

277

Tin(IV) catalyzed D-galacturonic acid anomerization.  

PubMed

A comparative kinetic study of anomerization between the four main forms (alpha/beta-pyranosides and alpha/beta-furanosides) of D-galacturonic acid (GalAH(2), 1) and tin(IV) complexed D-galacturonate ([Sn(CH(3))(2)(GalA)(H(2)O)(2)], 2) in D(2)O, is reported. Important differences are shown by pD vs. mutarotation rate profiles of 1 and 2. Coordination, in fact, causes: i) a spectacular increase of the rate due to kinetic template assistance of the carboxylic tail holding the metal in close proximity to the reactive centre and ii) a change in the dependence of the rate on the pD. Entropic and enthalpic factors contribute to the huge activation energy decrease in 2. Anomerization rates of the complexed ligand are determined by 2D-EXSY cross-peak integration. Analysis of up to twelve direct and reverse rate constants in the pD range 7.0-2.5 evidences ring size memory, and at least one reaction path which bypasses the aldehydo open chain intermediate. Solvent oxygen atom incorporation into the ligand is, at pH 4.5, about ten fold faster when catalyzed by the metal, and proves that the metal-assisted nucleophilic attack of water on the anomeric carbon atom cannot significantly contribute to mutarotation rates that are thousands of times faster. PMID:18217114

Rotondo, Archimede; Rotondo, Enrico; Casella, Girolamo A; Grasso, Giulia

2008-02-01

278

Clay-catalyzed reactions of coagulant polymers during water chlorination.  

PubMed

The influence of suspended clay/solid particles on organic-coagulant reactions during water chlorination was investigated by analyses of total product formation potential (TPFP) and disinfection by-product (DBP) distribution as a function of exchanged clay cation, coagulant organic polymer, and reaction time. Montmorillonite clays appeared to act as a catalytic center where the reaction between adsorbed polymer and disinfectant (chlorine) was mediated closely by the exchanged clay cation. The transition-metal cations in clays catalyzed more effectively than other cations the reactions between a coagulant polymer and chlorine, forming a large number of volatile DBPs. The relative catalytic effects of clays/solids followed the order Ti-Mont > Fe-Mont > Cu-Mont > Mn-Mont > Ca-Mont > Na-Mont > quartz > talc. The effects of coagulant polymers on TPFP follow the order nonionic polymer > anionic polymer > cationic polymer. The catalytic role of the clay cation was further confirmed by the observed inhibition in DBP formation when strong chelating agents (o-phenanthroline and ethylenediamine) were added to the clay suspension. Moreover, in the presence of clays, total DBPs increased appreciably when either the reaction time or the amount of the added clay or coagulant polymer increased. For volatile DBPs, the formation of halogenated methanes was usually time-dependent, with chloroform and dichloromethane showing the greatest dependence. PMID:14697704

Lee, Jiunn-Fwu; Liao, Pao-Mei; Lee, Chung-Kung; Chao, Huan-Ping; Peng, Chin-Luen; Chiou, Cary T

2004-02-15

279

Primordial Lithium Abundance in Catalyzed Big Bang Nucleosynthesis  

E-print Network

There exists a well known problem with the Li7+Be7 abundance predicted by standard big bang nucleosynthesis being larger than the value observed in population II stars. The catalysis of big bang nucleosynthesis by metastable, \\tau_X \\ge 10^3 sec, charged particles X^- is capable of suppressing the primordial Li7+Be7, abundance and making it consistent with the observations. We show that to produce the correct abundance, this mechanism of suppression places a requirement on the initial abundance of X^- at temperatures of 4\\times 10^8 K to be on the order of or larger than 0.02 per baryon, which is within the natural range of abundances in models with metastable electroweak-scale particles. The suppression of Li7+Be7, is triggered by the formation of (Be7X^-), compound nuclei, with fast depletion of their abundances by catalyzed proton reactions, and in some models by direct capture of X^- on Be7. The combination of Li7+Be7 and Li6 constraints favours the window of lifetimes, 1000s \\la tau_X \\leq 2000 s.

Chris Bird; Kristen Koopmans; Maxim Pospelov

2007-03-08

280

Cyclophilin A catalyzes proline isomerization by an electrostatic handle mechanism  

PubMed Central

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

2014-01-01

281

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. PMID:23610417

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

2013-01-01

282

Broadening the scope of glycosyltransferase-catalyzed sugar nucleotide synthesis.  

PubMed

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 k(cat)/K(m) 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. PMID:23610417

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

2013-05-01

283

Copper catalyzed oxidation of ascorbate: chemical and ESR studies.  

PubMed

Cu-catalyzed oxidation of ascorbate has been studied in the absence and the presence of superoxide dismutase, catalase, mannitol, glycerol, ethanol, formate, and thiourea. None of these agents except thiourea inhibited the reaction. Therefore, the role of the Haber-Weiss reaction in the ascorbate oxidation could not be demonstrated. Electron spin resonance studies demonstrated that the preventive effect of the thiol is primarily due to the chelation of the reduced copper ions with the sulphur atom. The oxidation was also prevented by the chelation of copper with physiological levels of bovine serum albumin. These observations are consistent with the concept that a metal-oxygen complex is perhaps directly involved in the oxidative process. Measurements of the peroxide produced during oxidation indicated that significant amounts of this compound accumulates only at lower levels of ascorbate and in the absence of a protein or other chelating agents. At higher ascorbate levels no peroxide accumulation takes place. These results are, thus, useful in predicting the conditions under which the nutrient may act as a pro-oxidant or as an anti-oxidant. The observations suggest that under normal conditions low levels of ascorbate may act as a pro-oxidant through H2O2 production if the system has transition metal ions devoid of chelating agents. At higher concentrations ascorbate acts predominantly as an antioxidant. PMID:2177351

Varma, S D; Shen, X; Lohman, W

1990-01-01

284

Stereochemical course of enzyme-catalyzed aminopropyl transfer: spermidine synthase  

SciTech Connect

The R and S enantionmers of S-adenosyl-3-(/sup 2/H)3-(methylthio)-1-propylamine (decarboxylated S-adenosylmethionine), previously synthesized in this laboratory, were incubated with (1,4-/sup 2/H/sub 4/)-putrescine in the presence of spermidine synthase from E. coli. The resulting chiral (/sup 2/H/sub 5/)spermidines were isolated and converted to their N/sub 1/,N/sub 7/-dibocspermidine-N/sub 4/-(1S,4R)-camphanamides. The derivatives were analyzed by 500 MHz /sup 1/H-NMR and the configuration of the chiral center assigned by correlation with the spectra of synthetic chiral (/sup 2/H/sub 3/)dibocspermidine camphanamide standards. The enzyme-catalyzed aminopropyl transfer was shown to occur with net retention of configuration, indicative of a double-displacement mechanism. This result concurs with that of a previous steady-state kinetics study of spermidine synthase isolated from E. coli, but contradicts the single-displacement mechanism suggested by a stereochemical analysis of chiral spermidines biosynthesized in E. coli treated with chirally deuterated methionines. It also indicates that this aminopropyltransferase is mechanistically distinct from the methyltransferases, which have been shown to act via a single-displacement mechanism (net inversion at -CH/sub 3/) in all cases studied to date.

Kullberg, D.W.; Orr, G.R.; Coward, J.K.

1986-05-01

285

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. PMID:22346338

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

2012-01-01

286

Production of chemoenzymatic catalyzed monoepoxide biolubricant: optimization and physicochemical characteristics.  

PubMed

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 H(2)O(2), 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. PMID:22346338

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

2012-01-01

287

Kinetics of phenolic polymerization catalyzed by peroxidase in organic media.  

PubMed

Phenolic polymerization was carried out by enzymatic catalysis in organic media, and its kinetics was studied by using high-pressure liquid chromatography (HPLC). Phenols and aromatic amines with electron-withdrawing groups could hardly be polymerized by HRP catalysis, but phenols and aromatic amines with electron-donating groups could easily be polymerized. The reaction rate of either the para-substituted substrate or meta-substituted substrate was higher than that of ortho-substituted substrate. When ortho-position of hydroxy group of phenols was occupied by an electron-donating group and if another electron-donating group occupied para-position of hydroxy group, the reaction rate increased. Horseradish peroxidase and lactoperoxidase could easily catalyze the polymerization, but chloroperoxidase and laccase failed to yield polymers. Metallic ions such as Mn(2+), Fe(2+), or Fe(3+), and Cu(2+) could poison horseradish peroxidase to various extents, but ions such as Co(2+), Cd(2+), Zn(2+), and K(+) were not found to inhibit the reaction. (c) 1995 John Wiley & Sons, Inc. PMID:18623373

Xu, Y P; Huang, G L; Yu, Y T

1995-07-01

288

MEMS-Based Satellite Micropropulsion Via Catalyzed Hydrogen Peroxide Decomposition  

NASA Technical Reports Server (NTRS)

Micro-electromechanical systems (MEMS) techniques offer great potential in satisfying the mission requirements for the next generation of "micro-scale" satellites being designed by NASA and Department of Defense agencies. More commonly referred to as "nanosats", these miniature satellites 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 article focuses the progress being made at NASA Goddard Space Flight Center towards 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 micro-scale converging/diverging supersonic nozzle which produces the thrust vector; the targeted thrust level approximately 500 N with a specific impulse of 140-180 seconds. Macro-scale hydrogen peroxide thrusters have been used for satellite propulsion for decades; however, the implementation of traditional thruster designs on a 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.; Bauer, Frank H. (Technical Monitor)

2001-01-01

289

Pheromone deactivation catalyzed by receptor molecules: a quantitative kinetic model.  

PubMed

A quantitative model of pheromone-receptor interaction and pheromone deactivation, the supposed rate-limiting processes underlying the receptor potential kinetics, is worked out for the moth Antheraea polyphemus. In this model, the pheromone interacts with the receptor molecule while bound to the reduced form of the pheromone binding protein. The receptor molecules--besides their receptor function--catalyze the observed shift of the pheromone-binding protein from the reduced to the oxidized form (Ziegelberger, G., Eur. J. Biochem., 232, 706-711, 1995), which deactivates the pheromone bound to pheromone binding protein. With the following parameters, the model fits morphological, radiometric, electrophysiological and biochemical data: a maximum estimate of 1.7 x 10(7) receptor molecules/cell (with 40,000 units/micron 2 of receptor cell membrane), rate constants k1 = 0.2/(s.microM) for the association, k2 = 10/s for the dissociation of the ternary complex of binding protein, pheromone and receptor, and k3 = 10/s for the deactivation via the redox shift. With these parameters, the duration of elementary receptor potentials elicited by single pheromone molecules (approximately 50 ms) reflects the lifetime of the ternary complex, tau = 1/(k2 + k3). The receptor occupancy produced by the model for threshold stimuli fits the sensitivity of the receptor cell to single pheromone molecules. PMID:9759524

Kaissling, K E

1998-08-01

290

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

291

Reaction Dynamics of ATP Hydrolysis Catalyzed by P-Glycoprotein  

PubMed Central

P-glycoprotein (P-gp) is a member of the ABC transporter family that confers drug resistance to many tumors by catalyzing their efflux, and it is a major component of drug–drug interactions. P-gp couples drug efflux with ATP hydrolysis by coordinating conformational changes in the drug binding sites with the hydrolysis of ATP and release of ADP. To understand the relative rates of the chemical step for hydrolysis and the conformational changes that follow it, we exploited isotope exchange methods to determine the extent to which the ATP hydrolysis step is reversible. With ?18O4-labeled ATP, no positional isotope exchange is detectable at the bridging ?-phosphorus–O??-phosphorus bond. Furthermore, the phosphate derived from hydrolysis includes a constant ratio of three 18O/two 18O/one 18O that reflects the isotopic composition of the starting ATP in multiple experiments. Thus, H2O-exchange with HPO42– (Pi) was negligible, suggesting that a [P-gp·ADP·Pi] is not long-lived. This further demonstrates that the hydrolysis is essentially irreversible in the active site. These mechanistic details of ATP hydrolysis are consistent with a very fast conformational change immediately following, or concomitant with, hydrolysis of the ?-phosphate linkage that ensures a high commitment to catalysis in both drug-free and drug-bound states. PMID:24506763

2015-01-01

292

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

293

Polysilsesquioxanes through base-catalyzed redistribution of oligohydridosiloxanes  

SciTech Connect

Organopolysilsesquioxanes have recently gained much interest as materials for low-K dielectrics, ceramic precursors and photoresists. Typical sol-gel synthesis of polysilsesquioxanes involves the hydrolysis of organotricholorosilanes and/or organotrialkoxysilanes in the presence of acid or base catalysts and organic solvents. However, under sol-gel conditions most organotrialkoxysilanes do not afford silsesquioxane gels. This limits the range of organic functionalities that can be introduced into these hybrid organic-inorganic materials. An alternative route to polysilsesquioxanes is through oligohydridosiloxanes. Catalytic disproportionation, by titanium complexes, of linear or cyclic oligomers of methylhydridosiloxanes can lead to polymethylsilsesquioxanes. The authors have shown that disproportionation of oligomethylhydridosiloxanes can also be catalyzed by tetrabutylammonium hydroxide to yield polymethylsilsesquioxanes (scheme 1). This replaces the step-growth sol-gel polymerization process of organotrialkoxysilanes, which requires solvent, stoichiometric water and produces alcohol and water condensation by-products. Tetraalkylammonium hydroxides, as catalysts, are also attractive because they readily decompose by heating above 150 C; thus, they can be easily removed from the final materials. In this paper the authors report on both the catalytic and stoichiometric redistribution of organohydridosiloxanes to produce polysilsesquioxane foams and gels of the formula (RSiO{sub 1.5}){sub n} which otherwise cannot be obtained through traditional sol-gel means.

RAHIMIAN,KAMYAR; ASSINK,ROGER A.; LANG,DAVID P.; LOY,DOUGLAS A.

2000-05-01

294

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. PMID:23757189

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

2013-01-01

295

Clay-catalyzed reactions of coagulant polymers during water chlorination  

USGS Publications Warehouse

The influence of suspended clay/solid particles on organic-coagulant reactions during water chlorination was investigated by analyses of total product formation potential (TPFP) and disinfection by-product (DBP) distribution as a function of exchanged clay cation, coagulant organic polymer, and reaction time. Montmorillonite clays appeared to act as a catalytic center where the reaction between adsorbed polymer and disinfectant (chlorine) was mediated closely by the exchanged clay cation. The transition-metal cations in clays catalyzed more effectively than other cations the reactions between a coagulant polymer and chlorine, forming a large number of volatile DBPs. The relative catalytic effects of clays/solids followed the order Ti-Mont > Fe-Mont > Cu-Mont > Mn-Mont > Ca-Mont > Na-Mont > quartz > talc. The effects of coagulant polymers on TPFP follow the order nonionic polymer > anionic polymer > cationic polymer. The catalytic role of the clay cation was further confirmed by the observed inhibition in DBP formation when strong chelating agents (o-phenanthroline and ethylenediamine) were added to the clay suspension. Moreover, in the presence of clays, total DBPs increased appreciably when either the reaction time or the amount of the added clay or coagulant polymer increased. For volatile DBPs, the formation of halogenated methanes was usually time-dependent, with chloroform and dichloromethane showing the greatest dependence. ?? 2003 Elsevier Inc. All rights reserved.

Lee, J.-F.; Liao, P.-M.; Lee, C.-K.; Chao, H.-P.; Peng, C.-L.; Chiou, C.T.

2004-01-01

296

New cardiolipin analogs synthesized by phospholipase D-catalyzed transphosphatidylation.  

PubMed

Cardiolipin (CL) and related diphosphatidyl lipids are hardly accessible because of the complexity of their chemical synthesis. In the present paper, the transphosphatidylation reaction catalyzed by phospholipase D (PLD) from Streptomyces sp. has been proven as an alternative enzyme-assisted strategy for the synthesis of new CL analogs. The formation of this type of compounds from phosphatidylcholine was compared for a series of N- and C2-substituted ethanolamine derivatives as well as non-charged alcohols such as glycerol and ethylene glycol. The rapid exchange of the choline head group by ethanolamine derivatives having a low molecular volume (diethanolamine and serinol) gave rise to an efficient production of the corresponding CL analogs. In contrast, the yields were comparably low in the reaction with bulky nitrogenous acceptor alcohols (triethanolamine, tris(hydroxymethyl)aminomethane, tetrakis(hydroxyethyl)ammonium) or the non-charged alcohols. Therefore, a strong dependence of the conversion of the monophosphatidyl to the diphosphatidyl compound on steric parameters and the head group charge was concluded. The enzyme-assisted strategy was used for the preparation of purified diphosphatidyldiethanolamine and diphosphatidylserinol. PMID:23059117

Müller, Anna O; Mrestani-Klaus, Carmen; Schmidt, Jürgen; Ulbrich-Hofmann, Renate; Dippe, Martin

2012-10-01

297

Measurement of positional isotope exchange rates in enzyme catalyzed reactions by fast atom bombardment mass spectrometry  

E-print Network

MEASUREMENT OF POSITIONAL ISOTOPE EXCHANGE RATES IN ENZYME CATALYZED REACTIONS BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY A Thesis by LARRY NAYNE HILSCHER Submitted to the Gradu te College of Texas A&M University in partial fulfil" mert... of the requiremer ts for the degree of MASTEP. QF SCIENCE August 1985 Major Subject: Chemistry MEASUREMENT OF POSITIONAL ISOTOPE EXCHANGE RATES IN ENZYME CATALYZED REACTIONS BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY A Thesis LARRY NAYNE HILSCHER Approved...

Hilscher, Larry Wayne

1985-01-01

298

Transition-metal-catalyzed facile access to 3,11-dialkylfulminenes for transistor applications.  

PubMed

Novel [6]phenacenes (fulminenes) with two long alkyl chains at the axis positions were synthesized. This short synthesis comprises the following three steps: (1) ruthenium-catalyzed direct C-H bond arylation; (2) conversion of directing groups by Wittig reaction; and (3) bismuth- or gold-catalyzed cyclization of vinyl ether. Organic field-effect transistor devices fabricated with a thin film of 3,11-di(tetradecyl)fulminene exhibited typical p-channel normally-off properties. PMID:25633847

Murai, Masahito; Maekawa, Hiroyuki; Hamao, Shino; Kubozono, Yoshihiro; Roy, David; Takai, Kazuhiko

2015-02-01

299

Transition metal-catalyzed oxidation of sulfur(IV) oxides. Atmospheric-relevant processes and mechanisms  

Microsoft Academic Search

The transition metal-catalyzed oxidation of sulfur(IV) oxides has been known for more than 100 years. There is a significant lack of information on the actual role of the transition metal-catalyzed reactions, and much of the earlier work was performed without a detailed knowledge of the chemical system. For this reason attention is focused on the role of transition metal ions

Christian. Brandt; Rudi. van Eldik

1995-01-01

300

Transition-Metal Catalyzed Synthesis of Aspergillide B: An Alkyne Addition Strategy  

PubMed Central

A catalytic enantioselective formal total synthesis of aspergillide B is reported. This linchpin synthesis was enabled by the development of new conditions for Zn-ProPhenol catalyzed asymmetric alkyne addition. This reaction was used in conjunction with ruthenium-catalyzed trans-hydrosilylation to affect the rapid construction of a late-stage synthetic intermediate of aspergillide B to complete a formal synthesis of aspergillide B in a highly efficient manner. PMID:22356535

Bartlett, Mark J.

2012-01-01

301

Copper(II)-catalyzed lipid peroxidation in liposomes and erythrocyte membranes  

Microsoft Academic Search

Cu++ was uniquely capable of catalyzing the peroxidation of rat erythrocyte membrane lipid in the presence of 10 mM H2O2, whereas several other transition metal ions were without significant effect. In contrast, peroxidation of soybean phospholipid\\u000a liposomes could be catalyzed with decreasing efficiency by Co++, Cu++, Pb++, or Cr+++ also in the presence of H2O2. The effect of imidazole on

Phillip C. Chan; Owen G. Peller; Leo Kesner

1982-01-01

302

Copper-catalyzed C-H cyanation of terminal alkynes with cyanogen iodide.  

PubMed

A copper-catalyzed reaction of terminal alkynes with cyanogen iodide (ICN) that produces alkynyl cyanides has been developed. The use of tetramethylpiperidine as a sterically congested base was successful in this reaction. Some control experiments revealed that the reaction involves the noncatalyzed formation of alkynyl iodides followed by copper-catalyzed cyanation of the iodides without the formation of copper(I) acetylide. This observation contrasts with what is normally observed in various copper-mediated reactions using terminal alkynes. PMID:24191758

Okamoto, Kazuhiro; Watanabe, Masahito; Sakata, Naoki; Murai, Masahito; Ohe, Kouichi

2013-11-15

303

Pd- and Cu-catalyzed one-pot multicomponent synthesis of hetero ?,?'-dimers of heterocycles.  

PubMed

A novel palladium- and copper-catalyzed one-pot multicomponent synthesis of hetero ?,?'-dimers of heterocycles via Sonogashira coupling and double cyclization cascade involving imine formation has been developed. This reaction cascade proceeded under mild conditions, providing a powerful synthetic tool for the assembly of ?-conjugated systems with a combination of palladium-catalyzed post-direct C-H bond arylations. PMID:22533860

Murata, Takahiko; Murai, Masahito; Ikeda, Yuji; Miki, Koji; Ohe, Kouichi

2012-05-01

304

Synthesis of ortho-acylphenols through the palladium-catalyzed ketone-directed hydroxylation of arenes.  

PubMed

Ketone in charge: a formal ketone-directed palladium-catalyzed ortho-hydroxylation of arenes has been developed as an effective approach to access o-acylphenols from simple arylketones. A Pd-catalyzed oxidative ortho-carbonylation reaction using ketone directing groups to access a ketal-lactone motif is also demonstrated. The ubiquity and versatile nature of ketones make these methods attractive. BTI=PhI(TFA)(2); DCE=1,2-dichloroethane. PMID:23161515

Mo, Fanyang; Trzepkowski, Louis J; Dong, Guangbin

2012-12-21

305

Palladium-Catalyzed Decarboxylative Allylation and Benzylation of N-Alloc and N-Cbz Indoles  

PubMed Central

A set of general methods for the palladium-catalyzed decarboxylative C3-allylation and C3-benzylation of indoles, starting from the corresponding N-alloc and N-Cbz indoles, respectively, is reported. This chemistry provides ready access to a wide range of functionalized indolenines in good to excellent yields. A tandem process, wherein the palladium catalyzed allylation chemistry is coupled with a Mizoroki-Heck reaction, offers a simple route to diverse cinnamylated products. PMID:23427905

Montgomery, Thomas D.; Zhu, Ye; Kagawa, Natsuko; Rawal, Viresh H.

2014-01-01

306

Ag/ThioClickFerrophos-catalyzed enantioselective Mannich reaction and amination of glycine Schiff base.  

PubMed

The AgOAc/ThioClickFerrophos complex catalyzed the asymmetric Mannich reaction of glycine Schiff base with N-tosylimines effectively to give a mixture of syn and anti adducts (syn/anti = 60/40-70/30) at high yields with high enantioselectivities (up to 98% ee). The complex also catalyzed the asymmetric amination of glycine Schiff base with di-tert-butyl azodicarboxylate with high enantioselectivity. PMID:21410238

Imae, Kazumi; Shimizu, Kenta; Ogata, Kenichi; Fukuzawa, Shin-ichi

2011-05-01

307

Transesterification of oil mixtures catalyzed by microencapsulated cutinase in reversed micelles  

Microsoft Academic Search

Recombinant cutinase from Fusarium solani pisi was used to catalyze the transesterification reaction between a mixture of triglycerides (oils) and methanol in reversed\\u000a micelles of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in isooctane for the purposes of producing biodiesel. The use of\\u000a a bi-phase lipase-catalyzed system brings advantages in terms of catalyst re-use and the control of water activity in the\\u000a medium

Sara M. Badenes; Francisco Lemos; Joaquim M. S. Cabral

2010-01-01

308

Improvement of the enantioselectivity of lipase-catalyzed naproxen ester hydrolysis in organic solvent  

Microsoft Academic Search

A method is presented to improve the enantioselectivity of lipase-catalyzed hydrolysis of naproxen methyl ester in water-saturated isooctane. It is shown that coupling of the enantioselective hydrolysis of Naproxen methyl ester with the photo-dissociation methanol leads to the photocatalytic conversion of methanol into water, by which the equilibrium constant (K) of the lipase-catalyzed hydrolysis was changed. The equilibrium yield and

Jia-Ying Xin; Shu-Ben Li; Xi-Hui Chen; Lai-Lai Wang; Yi Xu

2000-01-01

309

Rhodium-Catalyzed Ketone Methylation Using Methanol Under Mild Conditions: Formation of ?-Branched Products**  

PubMed Central

The rhodium-catalyzed methylation of ketones has been accomplished using methanol as the methylating agent and the hydrogen-borrowing method. The sequence is notable for the relatively low temperatures that are required and for the ability of the reaction system to form ?-branched products with ease. Doubly alkylated ketones can be prepared from methyl ketones and two different alcohols by using a sequential one-pot iridium- and rhodium-catalyzed process. PMID:24288297

Chan, Louis K M; Poole, Darren L; Shen, Di; Healy, Mark P; Donohoe, Timothy J

2014-01-01

310

Rhodium-Catalyzed Oxidative Annulation of Hydrazines with Alkynes Using a Nitrobenzene Oxidant.  

PubMed

Rhodium-catalyzed oxidative annulation of hydrazines with alkynes has been accomplished using 1,3-dinitrobenzene as an oxidant. A variety of hydrazines with alkynes were converted to 1-aminoindole derivatives in good to high yields. Mechanistic investigations support the idea that 1,3-dinitrobenzene serves as the oxidant during C-H activation. This is, to our knowledge, the first report of a nitrobenzene compound used as the oxidant in transition-metal-catalyzed C-H activation. PMID:25396747

Li, Deng Yuan; Chen, Hao Jie; Liu, Pei Nian

2014-11-14

311

Microcalorimetric studies on the dismutation of superoxide anion catalyzed by superoxide dismutase  

Microsoft Academic Search

Thermokinetics of the dismutation of superoxide anion (O\\u000a 2\\u000a .-\\u000a ) catalyzed by superoxide dismutase (SOD), in which the decomposition of hydrogen peroxide catalyzed by catalase is utilized\\u000a as a source of oxygen and the autoxidation of pyrogallod as a source of the substrate (O\\u000a 2\\u000a .-\\u000a ), has been studied by microcalorimetry. The molar reaction enthalpies of the SOD

Yi Liang; Songsheng Qu; Cunxin Wang; Yuwen Liu; Zhiyong Wang; Zhaohua Song; Guolin Zou

1998-01-01

312

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. PMID:16660375

Croteau, Rodney; Hooper, Caroline Lee

1978-01-01

313

Synthesis of dinucleoside polyphosphates catalyzed by firefly luciferase.  

PubMed

In the presence of ATP, luciferin (LH2), Mg2+ and pyrophosphatase, the firefly (Photinus pyralis) luciferase synthesizes diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) through formation of the E-LH2-AMP complex and transfer of AMP to ATP. The maximum rate of the synthesis is observed at pH 5.7. The Km values for luciferin and ATP are 2-3 microM and 4 mM, respectively. The synthesis is strictly dependent upon luciferin and a divalent metal cation. Mg2+ can be substituted with Zn2+, Co2+ or Mn2+, which are about half as active as Mg2+, as well as with Ni2+, Cd2+ or Ca2+, which, at 5 mM concentration, are 12-20-fold less effective than Mg2+. ATP is the best substrate of the above reaction, but it can be substituted with adenosine 5'-tetraphosphate (p4A), dATP, and GTP, and thus the luciferase synthesizes the corresponding homo-dinucleoside polyphosphates:diadenosine 5',5"'-P1,P5-pentaphosphate (Ap5A), dideoxyadenosine 5',5"'-P1,P4-tetraphosphate (dAp4dA) and diguanosine 5',5"'-P1,P4-tetraphosphate (Gp4G). In standard reaction mixtures containing ATP and a different nucleotide (p4A, dATP, adenosine 5'-[alpha,beta-methylene]-triphosphate, (Ap[CH2]pp), (S')-adenosine-5'-[alpha-thio]triphosphate [Sp)ATP[alpha S]) and GTP], luciferase synthesizes, in addition to Ap4A, the corresponding hetero-dinucleoside polyphosphates, Ap5A, adenosine 5',5"'-P1,P4-tetraphosphodeoxyadenosine (Ap4dA), diadenosine 5',5"'-P1,P4-[alpha,beta-methylene] tetraphosphate (Ap[CH2]pppA), (Sp-diadenosine 5',5"'-P1,P4-[alpha-thio]tetraphosphate [Sp)Ap4A[alpha S]) and adenosine-5',5"'-P1,P4-tetraphosphoguanosine (Ap4G), respectively. Adenine nucleotides, with at least a 3-phosphate chain and with an intact alpha-phosphate, are the preferred substrates for the formation of the enzyme-nucleotidyl complex. Nucleotides best accepting AMP from the E-LH2-AMP complex are those which contain at least a 3-phosphate chain and an intact terminal pyrophosphate moiety. ADP or other NDP are poor adenylate acceptors as very little diadenosine 5',5"'-P1,P3-triphosphate (Ap3A) or adenosine-5',5"'-P1,P3-triphosphonucleosides (Ap3N) are formed. In the presence of NTP (excepting ATP), luciferase is able to split Ap4A, transferring the resulting adenylate to NTP, to form hetero-dinucleoside polyphosphates. In the presence of PPi, luciferase is also able to split Ap4A, yielding ATP. The cleavage of Ap4A in the presence of Pi or ADP takes place at a very low rate. The synthesis of dinucleoside polyphosphates, catalyzed by firefly luciferase, is compared with that catalyzed by aminoacyl-tRNA synthetases and Ap4A phosphorylase. PMID:1761051

Sillero, M A; Guranowski, A; Sillero, A

1991-12-01

314

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

Microsoft Academic Search

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+

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

2002-01-01

315

I. Studies on the Metal-Catalyzed Cycloadditions of Isocyanates and Unsaturated Systems and II. Chromium-Catalyzed Synthesis of 1,3-Butadienes via (Silylmethyl)allenes  

E-print Network

of disocyanates with 1,3-dienes or allenes are not known and the asymmetric cycloadditions of isocyanates are scarce. To expand the scope of these powerful reactions, we studied the semi-intramolecular metal-catalyzed cycloaddition of several unsaturated systems...

Duran Galvan, Maria

2011-10-21

316

Enantioselective Diels–Alder reactions catalyzed by hydrogen bonding  

PubMed Central

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

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

2004-01-01

317

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

318

Total synthesis of cis-solamin: exploiting the RuO4-catalyzed oxidative cyclization of dienes.  

PubMed

[structure: see text] An enantioselective total synthesis of cis-solamin has been accomplished using a highly diastereoselective ruthenium tetroxide catalyzed oxidative cyclization as a crucial transformation. Further key steps involved an enzymatic desymmetrization, a TPAP-catalyzed oxidative termini differentiation, and a ruthenium-catalyzed Alder-ene reaction. Thus, the total synthesis of cis-solamin was achieved in 11 steps with an overall yield of 7.5%. PMID:16869628

Göksel, Hülya; Stark, Christian B W

2006-08-01

319

Methanogen Homoaconitase Catalyzes Both Hydrolyase Reactions in Coenzyme B Biosynthesis*S?  

PubMed Central

Homoaconitase enzymes catalyze hydrolyase reactions in the ?-aminoadipate pathway for lysine biosynthesis or the 2-oxosuberate pathway for methanogenic coenzyme B biosynthesis. Despite the homology of this iron-sulfur protein to aconitase, previously studied homoaconitases catalyze only the hydration of cis-homoaconitate to form homoisocitrate rather than the complete isomerization of homocitrate to homoisocitrate. The MJ1003 and MJ1271 proteins from the methanogen Methanocaldococcus jannaschii formed the first homoaconitase shown to catalyze both the dehydration of (R)-homocitrate to form cis-homoaconitate, and its hydration is shown to produce homoisocitrate. This heterotetrameric enzyme also used the analogous longer chain substrates cis-(homo)2aconitate, cis-(homo)3aconitate, and cis-(homo)4aconitate, all with similar specificities. A combination of the homoaconitase with the M. jannaschii homoisocitrate dehydrogenase catalyzed all of the isomerization and oxidative decarboxylation reactions required to form 2-oxoadipate, 2-oxopimelate, and 2-oxosuberate, completing three iterations of the 2-oxoacid elongation pathway. Methanogenic archaeal homoaconitases and fungal homoaconitases evolved in parallel in the aconitase superfamily. The archaeal homoaconitases share a common ancestor with isopropylmalate isomerases, and both enzymes catalyzed the hydration of the minimal substrate maleate to form d-malate. The variation in substrate specificity among these enzymes correlated with the amino acid sequences of a flexible loop in the small subunits. PMID:18765671

Drevland, Randy M.; Jia, Yunhua; Palmer, David R. J.; Graham, David E.

2008-01-01

320

Metal-Catalyzed Cascade Reactions: Useful Synthetic Tools for the Preparation of Polycyclic Arenes.  

PubMed

This account summarizes our recent efforts to synthesize numerous important and interesting polycyclic arenes under mild conditions using metal-catalyzed protocols. The palladium-catalyzed annulations of 2-iodobiphenyls or 2,2'-diiodobiphenyls with alkynes efficiently generated phenanthrene derivatives. This synthetic method was utilized as the key step when preparing phenanthrene-based alkaloids, tetrabenzopyracylenes and persubstituted [8]circulenes. Depending on whether a palladium or nickel catalytic system was used, 1-ethynyl-8-iodonaphthalenes underwent either a cyclodimerization or a nitrile-incorporated cascade reaction to produce zethrenes or pyrroloarenes, respectively. Methylene-bridged polyarenes are generated easily from 2-halo-2'-methylbiaryls through benzylic C-H bond activation and subsequent carbon-carbon bond formation, and palladium complexes promote the arylation of methylene carbons. The palladium-catalyzed annulations of 1,8-bis(arylethynyl)naphthalene derivatives with o-diiodoarenes yielded benzo[k]fluoranthene-based linear acenes, which can be applied to synthesize highly curved fragments of fullerenes. The self-reactions of diarylethynes formed either dihydrocyclopenta[a]indenes or octaaryl-1,3,5,7-octatetraenes through palladium-catalyzed cycloisomerization or nickel-catalyzed tetramerization, respectively. In the presence of palladium catalysts, the hydroalkynylation of terminal arylalkynes directly generated angular trimerization adduct dienynes. PMID:25376430

Feng, Chieh-Ning; Hsieh, Ya-Chu; Wu, Yao-Ting

2014-11-01

321

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

322

Effect of metal catalyzed oxidation in recombinant viral protein assemblies  

PubMed Central

Background Protein assemblies, such as virus-like particles, have increasing importance as vaccines, delivery vehicles and nanomaterials. However, their use requires stable assemblies. An important cause of loss of stability in proteins is oxidation, which can occur during their production, purification and storage. Despite its importance, very few studies have investigated the effect of oxidation in protein assemblies and their structural units. In this work, we investigated the role of in vitro oxidation in the assembly and stability of rotavirus VP6, a polymorphic protein. Results The susceptibility to oxidation of VP6 assembled into nanotubes (VP6NT) and unassembled VP6 (VP6U) was determined and compared to bovine serum albumin (BSA) as control. VP6 was more resistant to oxidation than BSA, as determined by measuring protein degradation and carbonyl content. It was found that assembly protected VP6 from in vitro metal-catalyzed oxidation. Oxidation provoked protein aggregation and VP6NT fragmentation, as evidenced by dynamic light scattering and transmission electron microscopy. Oxidative damage of VP6 correlated with a decrease of its center of fluorescence spectral mass. The in vitro assembly efficiency of VP6U into VP6NT decreased as the oxidant concentration increased. Conclusions Oxidation caused carbonylation, quenching, and destruction of aromatic amino acids and aggregation of VP6 in its assembled and unassembled forms. Such modifications affected protein functionality, including its ability to assemble. That assembly protected VP6 from oxidation shows that exposure of susceptible amino acids to the solvent increases their damage, and therefore the protein surface area that is exposed to the solvent is determinant of its susceptibility to oxidation. The inability of oxidized VP6 to assemble into nanotubes highlights the importance of avoiding this modification during the production of proteins that self-assemble. This is the first time that the role of oxidation in protein assembly is studied, evidencing that oxidation should be minimized during the production process if VP6 nanotubes are required. PMID:24533452

2014-01-01

323

Copper-Catalyzed Intermolecular Amidation and Imidation of Unactivated Alkanes  

PubMed Central

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

2015-01-01

324

Revised role of selectfluor in homogeneous Au-catalyzed oxidative C-O bond formations.  

PubMed

The pairing of transition metal catalysis with the reagent Selectfluor (F-TEDA-BF4) has attracted considerable attention due to its utility in myriad C-C and C-heteroatom bond-forming reactions. However, little mechanistic information is available for Selectfluor-mediated transition metal-catalyzed reactions and controversy surrounds the precise role of Selectfluor in these processes. We present herein a systematic investigation of homogeneous Au-catalyzed oxidative C-O bond-forming reactions using density functional theory calculations. Currently, Selectfluor is thought to serve as an external oxidant in Au(I)/Au(III) catalysis. However, our investigations suggest that these reactions follow a newly proposed mechanism in which Selectfluor functions as an electrophilic fluorinating reagent involved in a fluorination/defluorination cycle. We have also explored Selectfluor-mediated gold-catalyzed homocoupling reactions, which, when cyclopropyl propargylbenzoate is used as a substrate, lead to an unexpected byproduct. PMID:25293670

Geng, Cuihuan; Zhu, Rongxiu; Li, Mingxia; Lu, Tongxiang; Wheeler, Steven E; Liu, Chengbu

2014-11-24

325

Using Simple Donors to Drive the Equilibria of Glycosyltransferase-Catalyzed Reactions  

PubMed Central

We report the ability of simple glycoside donors to drastically shift the equilibria of glycosyltransferase-catalyzed reactions, transforming NDP-sugar formation from an endo- to an exothermic process. To demonstrate the utility of this thermodynamic adaptability, we highlight the glycosyltransferase-catalyzed synthesis of 22 sugar nucleotides from simple aromatic sugar donors as well as the corresponding in situ formation of sugar nucleotides as a driving force in context of glycosyltransferase-catalyzed reactions for small molecule glycodiversification. These simple aromatic donors also enabled the first general colorimetric assay for glycosyltransfer, applicable to drug discovery, protein engineering, and other fundamental sugar nucleotide-dependent investigations. This study directly challenges the general notion that NDP-sugars are ‘high-energy’ sugar donors when taken out of their traditional biological context. PMID:21857660

Gantt, Richard W.; Peltier-Pain, Pauline; Cournoyer, William J.; Thorson, Jon S.

2011-01-01

326

Using simple donors to drive the equilibria of glycosyltransferase-catalyzed reactions.  

PubMed

We report that simple glycoside donors can drastically shift the equilibria of glycosyltransferase-catalyzed reactions, transforming NDP-sugar formation from an endothermic to an exothermic process. To demonstrate the utility of this thermodynamic adaptability, we highlight the glycosyltransferase-catalyzed synthesis of 22 sugar nucleotides from simple aromatic sugar donors, as well as the corresponding in situ formation of sugar nucleotides as a driving force in the context of glycosyltransferase-catalyzed reactions for small-molecule glycodiversification. These simple aromatic donors also enabled a general colorimetric assay for glycosyltransfer, applicable to drug discovery, protein engineering and other fundamental sugar nucleotide-dependent investigations. This study directly challenges the general notion that NDP-sugars are 'high-energy' sugar donors when taken out of their traditional biological context. PMID:21857660

Gantt, Richard W; Peltier-Pain, Pauline; Cournoyer, William J; Thorson, Jon S

2011-10-01

327

Primary product of the horseradish peroxidase-catalyzed oxidation of pentachlorophenol  

SciTech Connect

Peroxidases are a class of enzymes that catalyze the oxidation of various phenolic substrates by hydrogen peroxide. They are common enzymes in soil and are also available commercially, so that they have been proposed as agents of phenolic pollutant transformation both in the environment and in engineered systems. Previous research on the peroxidase-catalyzed oxidation of pentachlorophenol (PCP) has suggested that tetrachloro-p-benzoquinone (chloranil) is the principal product and that a considerable fraction of the PCP added to reaction mixtures appears to be resistant to oxidation. In experiments employing alternative methods of product separation and analysis, the authors found that both of these observations are artifacts of extraction and analytical methods used in previous studies. The major product of the horseradish peroxidase-catalyzed oxidation of pentachlorophenol from pH 4--7 was 2,3,4,5,6-pentachloro-4-pentachlorophenoxy-2,5-cyclohexadienone (PPCHD), which is formed by the coupling of two pentachlorophenoxyl radicals.

Kazunga, C.; Aitken, M.D.; Gold, A. [Univ. of North Carolina, Chapel Hill, NC (United States)] [Univ. of North Carolina, Chapel Hill, NC (United States)

1999-05-01

328

Comparative evaluation of autohydrolysis and acid-catalyzed hydrolysis of Eucalyptus globulus wood.  

PubMed

Three different acids (acetic, oxalic and sulfuric acid) were tested for their catalytic activity during the pretreatment of Eucalyptus globulus wood comparatively to autohydrolysis in order to extract valuable products prior to kraft pulping and to reduce lignin precipitation in the pretreatment step. The utilization of oxalic and sulfuric acid reduces treatment temperatures at a given wood yield as compared to autohydrolysis and acetic acid addition and thus decreases the insoluble lignin content in the hydrolyzates. Due to the high temperatures of autohydrolysis xylose dehydration to furfural occurs at high wood yield losses, while during acid catalyzed hydrolysis degradation of cellulose to glucose is more pronounced. The main difference between the acid catalyzed and non-catalyzed reaction constitutes the ratio of monomeric xylose and xylooligosaccharides in solution. PMID:22297049

Gütsch, Jenny Sabrina; Nousiainen, Tiia; Sixta, Herbert

2012-04-01

329

Contamination removal from EUV multilayer using atomic hydrogen generated by heated catalyzer  

NASA Astrophysics Data System (ADS)

A rapid, damage-free method of removing carbon contamination from EUV multilayer has been developed that employs atomic hydrogen generated by a heated catalyzer consisting of a W wire. Test samples were prepared by contaminating Mo/Si multilayers with carbon using EB or synchrotron radiation (SR). The insertion of a thermal shield between the catalyzer and a sample prevented radiant heat from the catalyzer from damaging the sample during cleaning. Ex situ XPS measurements and measurements of the thickness of the carbon layer with optical thickness measurement systems showed that the new treatment completely removes carbon from multilayers. The EUV reflectivity of multilayers was measured before and after cleaning to assess any resulting damage. It was found that cleaning changed the reflectivity and the centroid wavelength only marginally, within the measurement error.

Oizumi, H.; Yamanashi, H.; Nishiyama, I.; Hashimoto, K.; Ohsono, S.; Masuda, A.; Izumi, A.; Matsumura, H.

2005-05-01

330

Development of a novel cost effective methanol electrolyzer stack with Pt-catalyzed membrane  

NASA Astrophysics Data System (ADS)

This paper demonstrates a novel polymer electrolyte membrane (PEM) based methanol electrolyzer stack with a catalyzed membrane for hydrogen production. The physical and electrochemical properties of the catalyzed membrane, single cell and stack are examined using various characterization techniques, such as X-ray diffraction, scanning electron microscopy with EDX and polarization studies. The results demonstrate that the with Pt-catalyzed membrane electrode assembly (MEA) exhibits significantly better performance than a normal MEA. The developed electrolyzer stack produces 102 L h-1 of 99% pure hydrogen without CO and CO2. The excellent stability of the PEM methanol electrolyzer system is demonstrated by running the stack for 2500 h of intermittent operation with constant current density.

Sethu, Sundar Pethaiah; Gangadharan, Sasikumar; Chan, Siew Hwa; Stimming, Ulrich

2014-05-01

331

[Analogs of pyrophosphate in a pyrophosphorolysis reaction catalyzed by DNA polymerases].  

PubMed

The reaction of pyrophosphorolysis catalyzed by Escherichia coli DNA polymerase I Klenov fragment, calf thymus DNA polymerase alpha, rat liver DNA polymerase beta and AMV reverse transcriptase was studied. Some pyrophosphate (PPi) analogs were taken as low molecular weight substrates. It was shown that only imidodiphosphonic acid acted as the PPi substrate analog for the reactions catalyzed by DNA polymerases I and alpha, both imidodiphosphonic acid and methylenediphosphonic acid were active in the case of DNA polymerase beta and reverse transcriptase. Other analogs tested were neither nucleotide residue acceptors, nor inhibitors of the pyrophosphorolysis reaction with PPi. The abilities of some PPi analogs to inhibit the DNA elongation catalyzed by reverse transcriptase were investigated. The principles of specificity of low molecular substrates recognition by DNA polymerases and some problems concerning the mechanisms of DNA synthesis inhibition by PPi analogues are discussed. PMID:2549402

Rozovskaia, T A; Tarusova, N B; Minasian, Sh Kh; Atrazhev, A M; Kukhanova, M K

1989-01-01

332

Iridium and ruthenium catalyzed syntheses, hydroborations, and metathesis reactions of alkenyl-decaboranes.  

PubMed

The selective syntheses of new classes of 6,9-dialkenyl- and 6-alkenyl-decaboranes and 6-alkyl-9-alkenyl-decaboranes have been achieved via iridium and ruthenium catalyzed decaborane and 6-alkyl-decaborane alkyne-hydroborations. Reactions employing [Cp*IrCl2]2 and [RuCl2(p-cymene)]2 precatalysts gave ?-E-alkenyl-decaboranes, while the corresponding reactions with [RuI2(p-cymene)]2 gave the ?-alkenyl-decaborane isomers, with the differences in product selectivity suggesting quite different mechanistic steps for the catalysts. The alkenyl-decaboranes were easily converted to other useful derivatives, including coupled-cage and functionally substituted compounds, via iridium-catalyzed hydroborations and ruthenium-catalyzed homo and cross olefin-metathesis reactions. PMID:23859100

Chatterjee, Shahana; Carroll, Patrick J; Sneddon, Larry G

2013-08-01

333

Carbon dioxide reduction to methane and coupling with acetylene to form propylene catalyzed by remodeled nitrogenase  

PubMed Central

A doubly substituted form of the nitrogenase MoFe protein (?-70Val?Ala, ?-195His?Gln) has the capacity to catalyze the reduction of carbon dioxide (CO2) to yield methane (CH4). Under optimized conditions, 1 nmol of the substituted MoFe protein catalyzes the formation of 21 nmol of CH4 within 20 min. The catalytic rate depends on the partial pressure of CO2 (or concentration of HCO3?) and the electron flux through nitrogenase. The doubly substituted MoFe protein also has the capacity to catalyze the unprecedented formation of propylene (H2C = CH-CH3) through the reductive coupling of CO2 and acetylene (HC?CH). In light of these observations, we suggest that an emerging understanding of the mechanistic features of nitrogenase could be relevant to the design of synthetic catalysts for CO2 sequestration and formation of olefins. PMID:23150564

Yang, Zhi-Yong; Moure, Vivian R.; Dean, Dennis R.; Seefeldt, Lance C.

2012-01-01

334

Acid-catalyzed autohydrolysis of wheat straw to improve sugar recovery.  

PubMed

A comparison study of autohydrolysis and acid-catalyzed autohydrolysis of wheat straw was performed to understand the impact of acid addition on overall sugar recovery. Autohydrolysis combined with refining is capable of achieving sugar recoveries in the mid 70s. If the addition of a small amount of acid is capable of increasing the sugar recovery even higher it may be economically attractive. Acetic, sulfuric, hydrochloric and sulfurous acids were selected for acid-catalyzed autohydrolysis pretreatments. Autohydrolysis with no acid at 190 °C showed the highest total sugar in the prehydrolyzate. Enzymatic hydrolysis was performed for all the post-treated solids with and without refining at enzyme loadings of 4 and 10 FPU/g for 96 h. Acid-catalyzed autohydrolysis at 190 °C with sulfurous acid showed the highest total sugar recovery of 81.2% at 4 FPU/g enzyme charge compared with 64.3% at 190 °C autohydrolysis without acid. PMID:25014168

Ertas, Murat; Han, Qiang; Jameel, Hasan

2014-10-01

335

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. PMID:22895533

Shu, Xing-Zhong; Shu, Dongxu; Schienebeck, Casi M.

2012-01-01

336

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

337

Transesterification of oil mixtures catalyzed by microencapsulated cutinase in reversed micelles.  

PubMed

Recombinant cutinase from Fusarium solani pisi was used to catalyze the transesterification reaction between a mixture of triglycerides (oils) and methanol in reversed micelles of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in isooctane for the purposes of producing biodiesel. The use of a bi-phase lipase-catalyzed system brings advantages in terms of catalyst re-use and the control of water activity in the medium and around the enzyme micro-environment. Small-scale batch studies were performed to study the influence of the initial enzyme and alcohol concentrations, and the substrates molar ratio. Conversions in excess of 75 were obtained with reaction times under 24 h, which makes this enzymatic process highly competitive when compared to similar lipase catalyzed reactions for biodiesel production using methanol. PMID:19943181

Badenes, Sara M; Lemos, Francisco; Cabral, Joaquim M S

2010-03-01

338

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

339

Phosphine/Palladium-Catalyzed Syntheses of Alkylidene Phthalans, 3-Deoxyisoochracinic Acid, Isoochracinic Acid, and Isoochracinol  

PubMed Central

In this study we used sequential-catalysis—PPh3-catalyzed nucleophilic addition followed by Pd(0)-catalyzed Heck cyclization—to construct complex functionalized alkylidene phthalans rapidly, in high yields, and with good stereoselectivities (E:Z ratios of up to 1:22). The scope of this Michael–Heck reaction includes substrates bearing various substituents around the alkylidene phthalan backbone. Applying this efficient sequential-catalysis, we accomplished concise total syntheses of 3-deoxyisoochacinic acid, isoochracinic acid, and isoochracinol. PMID:22721256

Fan, Yi Chiao; Kwon, Ohyun

2012-01-01

340

Synthesis of oligonucleotides carrying 5'-5' linkages using copper-catalyzed cycloaddition reactions.  

PubMed

There is considerable interest in coupling oligonucleotides to molecules and surfaces. Although amino- and thiol-containing oligonucleotides are being successfully used for this purpose, cycloaddition reactions may offer greater advantages due to their higher chemoselectivity and speed. In this study, copper-catalyzed 1,3-dipolar cycloaddition reactions between oligonucleotides carrying azido and alkyne groups are examined. For this purpose, several protocols for the preparation of oligonucleotides carrying these two groups are described. The non-templated chemical ligation of two oligonucleotides via copper-catalyzed [3+2] cycloaddition is described. By solid-phase methodology, oligonucleotides carrying 5'-5' linkages can be obtained in good yields. PMID:18081090

Alvira, Margarita; Eritja, Ramon

2007-12-01

341

Assessing the Regioselectivity of OleD-Catalyzed Glycosylation with a Diverse Set of Acceptors  

PubMed Central

To explore the acceptor regioselectivity of OleD-catalyzed glucosylation, the products of OleD-catalyzed reactions with the 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.

2013-01-01

342

Frustrated Lewis pair catalyzed hydrosilylation and hydrosilane mediated hydrogenation of fulvenes.  

PubMed

The frustrated Lewis pair (FLP) mediated hydrosilylation of pentafulvenes is described yielding allyl silanes with high regioselectivity in excellent yields. While phenyl substituted allyl silanes undergo B(C6F5)3-mediated rearrangement to vinyl silanes, dimethyl derivatives experience FLP-catalyzed hydrogenation followed by an unprecedented protodesilylation. This observation allowed the metal-free hydrogenation of 6,6-dimethylfulvene to iso-propyl cyclopentene according to a FLP-catalyzed triple domino reaction consisting of hydrosilylation, hydrogenation and protodesilylation. The mechanisms were investigated by deuteration experiments. PMID:25293817

Tamke, Sergej; Daniliuc, Constantin-G; Paradies, Jan

2014-12-01

343

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. PMID:24367406

Nakamura, Yuzo; Fujiu, Motohiro; Murase, Tatsuya; Itoh, Yoshimitsu; Serizawa, Hiroki; Aikawa, Kohsuke

2013-01-01

344

Advanced strategies for efficient macrocyclic Cu(I)-catalyzed cycloaddition of azides.  

PubMed

An advanced strategy for efficient macrocyclic Cu(I)-catalyzed cycloaddition is described. The key features include employing azide-iodoalkyne cycloadditions (CuAiAC), low catalyst loadings, relatively high concentrations (30 mM ? 300 mM), and application to continuous flow. The remarkably efficient new tool affords a variety of macrocyclic skeletons having either different alkyl, aryl, or amino acid spacers in high yields (70-97%). The macrocyclic CuAiAC process affords macrocycles having an iodotriazole moiety that can be further functionalized using standard Pd-catalyzed cross-couplings. PMID:25265521

Bédard, Anne-Catherine; Collins, Shawn K

2014-10-17

345

Iridium catalyzed carbocyclizations: efficient (5+2) cycloadditions of vinylcyclopropanes and alkynes.  

PubMed

Third-row transition metal catalysts remain a largely untapped resource in cycloaddition reactions for the formation of medium-sized rings. Herein, we report the first examples of iridium-catalyzed inter- and intramolecular vinylcyclopropane (VCP)-alkyne (5+2) cycloadditions. DFT modeling suggests that catalysis by iridium(I) proceeds through a mechanism similar to that previously reported for rhodium(I)-catalyzed VCP-alkyne cycloadditions, but a smaller free energy span for iridium enables substantially faster catalysis under favorable conditions. The system is characterized by up to quantitative yields and is amenable to an array of disubstituted alkynes and vinylcyclopropanes. PMID:25413863

Melcher, Michaela-Christina; von Wachenfeldt, Henrik; Sundin, Anders; Strand, Daniel

2015-01-01

346

Metal-catalyzed decaborane-alkyne hydroboration reactions: efficient routes to alkenyldecaboranes.  

PubMed

Transition-metal-catalyzed decaborane-alkyne hydroboration reactions have been developed that provide high-yield routes to the previously unknown di- and monoalkenyldecaboranes. These alkenyl derivatives should be easily modified starting materials for many biomedical and/or materials applications. Unusual catalyst product selectivity was observed that suggests quite different mechanistic steps, with the reactions catalyzed by the [RuCl(2)(p-cymene)](2) and [Cp*IrCl(2)](2) complexes giving the beta-E alkenyldecaboranes and the corresponding reactions with the [RuI(2)(p-cymene)](2) complex giving the alpha-alkenyldecaborane isomers. PMID:20222715

Chatterjee, Shahana; Carroll, Patrick J; Sneddon, Larry G

2010-04-01

347

Rhodium(III)- and Iridium(III)-Catalyzed C7 Alkylation of Indolines with Diazo Compounds.  

PubMed

A Rh(III) -catalyzed procedure for the C7-selective C?H alkylation of various indolines with ?-diazo compounds at room temperature is reported. The advantages of this process are: 1)?simple, mild, and pH-neutral reaction conditions, 2)?broad substrate scope, 3)?complete regioselectivity, 4)?no need for an external oxidant, and 5)?N2 as the sole byproduct. Furthermore, alkylation and bis-alkylation of carbazoles at the C1 and C8 positions have also been developed. More significantly, for the first time, a successful Ir(III) -catalyzed intermolecular insertion of arene C?H bonds into ?-diazo compounds is reported. PMID:25359110

Ai, Wen; Yang, Xueyan; Wu, Yunxiang; Wang, Xuan; Li, Yuanchao; Yang, Yaxi; Zhou, Bing

2014-12-22

348

Mild Palladium-Catalyzed Cyanation of (Hetero)aryl Halides and Triflates in Aqueous Media.  

PubMed

A mild, efficient, and low-temperature palladium-catalyzed cyanation of (hetero)aryl halides and triflates is reported. Previous palladium-catalyzed cyanations of (hetero)aryl halides have required higher temperatures to achieve good catalytic activity. This current reaction allows the cyanation of a general scope of (hetero)aryl halides and triflates at 2-5 mol % catalyst loadings with temperatures ranging from rt to 40 °C. This mild method was applied to the synthesis of lersivirine, a reverse transcriptase inhibitor. PMID:25555140

Cohen, Daniel T; Buchwald, Stephen L

2015-01-16

349

Polymerization of humic substances by an enzyme-catalyzed oxidative coupling  

NASA Astrophysics Data System (ADS)

A novel understanding of the structural features of humic substances supports the self-assembly supramolecular association of relatively small molecules rather than their polymeric nature. An increase in the conformational stability of humus may thus be achieved through promotion of intermolecular covalent bondings between heterogeneous humic molecules by an enzyme-catalyzed oxidative reaction. We present evidence from high performance size exclusion chromatography (HPSEC) and diffuse reflectance infrared spectrometry (DRIFT) that oxidation of a humic material catalyzed by horseradish peroxidase stabilizes the humic structure by the formation of aryl and alkyl ethers and permanently enhances its molecular size.

Piccolo, A.; Cozzolino, A.; Conte, P.; Spaccini, R.

2000-10-01

350

Improvement of the enantioselectivity of lipase-catalyzed naproxen ester hydrolysis in organic solvent.  

PubMed

A method is presented to improve the enantioselectivity of lipase-catalyzed hydrolysis of naproxen methyl ester in water-saturated isooctane. It is shown that coupling of the enantioselective hydrolysis of Naproxen methyl ester with the photo-dissociation methanol leads to the photocatalytic conversion of methanol into water, by which the equilibrium constant (K) of the lipase-catalyzed hydrolysis was changed. The equilibrium yield and enantiomeric excess are increased. Because the lipase would not dissolve in the organic solvent, it was adsorbed on photocatalyst particles, which may facilitate the isolation of enzyme from reaction system. PMID:10689069

Xin; Li; Chen; Wang; Xu

2000-02-01

351

Silica, alumina and clay catalyzed peptide bond formation: enhanced efficiency of alumina catalyst.  

PubMed

Catalytic efficiencies of clay (hectorite), silica and alumina were tested in peptide bond formation reactions of glycine (Gly), alanine (Ala), proline (Pro), valine (Val) and leucine (Leu). The reactions were performed as drying/wetting (hectorite) and temperature fluctuation (silica and alumina) experiments at 85 degrees C. The reactivity of amino acids decreased in order Gly > Ala > Pro approximately Val approximately Leu. The highest catalytic efficiency was observed for alumina, the only catalyst producing oligopeptides in all investigated reaction systems. The peptide bond formation on alumina is probably catalyzed by the same sites and via similar reaction mechanisms as some alumina-catalyzed dehydration reactions used in industrial chemistry. PMID:10573687

Bujdák, J; Rode, B M

1999-10-01

352

Pd- and Ni-catalyzed cross-coupling reactions in the synthesis of organic electronic materials  

NASA Astrophysics Data System (ADS)

Organic molecules and polymers with extended ?-conjugation are appealing as advanced electronic materials, and have already found practical applications in thin-film transistors, light emitting diodes, and chemical sensors. Transition metal (TM)-catalyzed cross-coupling methodologies have evolved over the past four decades into one of the most powerful and versatile methods for C-C bond formation, enabling the construction of a diverse and sophisticated range of ?-conjugated oligomers and polymers. In this review, we focus our discussion on recent synthetic developments of several important classes of ?-conjugated systems using TM-catalyzed cross-coupling reactions, with a perspective on their utility for organic electronic materials.

Xu, Shiqing; Hoo Kim, Eun; Wei, Alexander; Negishi, Ei-ichi

2014-08-01

353

Primary-tertiary diamine-catalyzed Michael addition of ketones to isatylidenemalononitrile derivatives  

PubMed Central

Summary Simple primary-tertiary diamines easily derived from natural primary amino acids were used to catalyze the Michael addition of ketones with isatylidenemalononitrile derivatives. Diamine 1a in combination with D-CSA as an additive provided Michael adducts in high yield (up to 94%) and excellent enantioselectivity (up to 99%). The catalyst 1a was successfully used to catalyze the three-component version of the reaction by a domino Knoevenagel–Michael sequence. The Michael adduct 4a was transformed into spirooxindole 6 by a reduction with sodium borohydride in a highly enantioselective manner. PMID:24991242

Kumar, Akshay

2014-01-01

354

Gold(I)-Catalyzed Synthesis of Dihydropyrans Benjamin D. Sherry, Lisa Maus, Brian Ngo Laforteza, and F. Dean Toste*  

E-print Network

Gold(I)-Catalyzed Synthesis of Dihydropyrans Benjamin D. Sherry, Lisa Maus, Brian Ngo Laforteza of these results, we hypothesized that the gold(I)-catalyzed reaction might provide a stereoselective synthesis, and F. Dean Toste* Center for New Directions in Organic Synthesis, Department of Chemistry, Uni

Toste, Dean

355

Real-Time Observation of the Swelling and Hydrolysis of a Single Crystalline Cellulose Fiber Catalyzed by Cellulase 7B  

E-print Network

Catalyzed by Cellulase 7B from Trichoderma reesei Jingpeng Wang, Amanda Quirk, Jacek Lipkowski,*, John R Information ABSTRACT: The biodegradation of cellulose involves the enzymatic action of cellulases-hydrolysis in real time directly as catalyzed by a single cellulase, the industrially important cellulase 7B from

Dutcher, John

356

DNA-Catalyzed Hydrolysis of Esters and Aromatic Amides Benjamin M. Brandsen, Anthony R. Hesser, Marissa A. Castner, Madhavaiah Chandra,  

E-print Network

DNA-Catalyzed Hydrolysis of Esters and Aromatic Amides Benjamin M. Brandsen, Anthony R. Hesser phosphodiester linkages, but DNA-catalyzed amide bond hydrolysis has been elusive. Here we used in vitro-hydrolyzing deoxyribozymes were examined using linear free energy relationship analysis. The hydrolysis reaction

Silverman, Scott K.

357

Theoretical Study of Acid-Catalyzed Hydrolysis of Epoxides Raimundo Clecio Dantas Muniz Filho, Samuel Anderson Alves de Sousa,  

E-print Network

Theoretical Study of Acid-Catalyzed Hydrolysis of Epoxides Raimundo Clecio Dantas Muniz Filho A theoretical study of propylene oxide acid-catalyzed hydrolysis was performed by investigation of the SN1 in biological and industrial applications is its hydrolysis.5 From the biological point of view, the hydrolysis

Ferreira, Márcia M. C.

358

No evidence for acid-catalyzed secondary organic aerosol formation in power plant plumes over metropolitan Atlanta, Georgia  

E-print Network

No evidence for acid-catalyzed secondary organic aerosol formation in power plant plumes over that secondary organic aerosol formation via heterogeneous acid-catalyzed reactions within power plant plumes conducted in the summer of 2004. Five notable plumes of SO2, apparently from coal-fired power plants, were

Weber, Rodney

359

Gold(I)-Catalyzed Ring Expansion of Cyclopropanols and Cyclobutanols Jordan P. Markham, Steven T. Staben, and F. Dean Toste*  

E-print Network

Gold(I)-Catalyzed Ring Expansion of Cyclopropanols and Cyclobutanols Jordan P. Markham, Steven T of heteroatom4 nucleophiles or -bonds5 to gold(I)-activated alkynes have recently been described. We hy- pothesized that related cationic gold(I) complexes might be capable of catalyzing ring expansion6 reactions

Toste, Dean

360

Gold(I)-Catalyzed Intermolecular Addition of Phenols and Carboxylic Acids to Cai-Guang Yang and Chuan He*  

E-print Network

Gold(I)-Catalyzed Intermolecular Addition of Phenols and Carboxylic Acids to Olefins Cai-Guang Yang 60637 Received January 20, 2005; E-mail: chuanhe@uchicago.edu Gold-catalyzed reactions have emerged as important synthetic methods.1 Cationic gold(I) and gold(III) show exceptional activities to activate alkynes

He, Chuan

361

Gold(I)-Catalyzed [2 + 2]-Cycloaddition of Allenenes Michael R. Luzung, Pablo Mauleon, and F. Dean Toste*  

E-print Network

Gold(I)-Catalyzed [2 + 2]-Cycloaddition of Allenenes Michael R. Luzung, Pablo Mauleo´n, and F. Dean, 2007; E-mail: fdtoste@berkeley.edu Stabilization of cationic intermediates as gold(I)-carbenoids is proposed to be essential in a variety of gold(I)-catalyzed cycloi- somerization reactions.1,2 In an effort

Toste, Dean

362

Enantioselective Direct Mannich Reactions of Cyclic ?-Ketoesters Catalyzed by Chiral Phosphine via a Novel Dual-Reagent Catalysis.  

PubMed

A combination of an amino acid derived chiral phosphine catalyst and methyl acrylate efficiently catalyzed the direct Mannich reaction of cyclic ?-ketoesters and N-Boc-aldimines. The dual-reagent catalysis was presumed to function through the formation of a zwitterion, which catalyzed the reaction with excellent stereocontrol via a hydrogen-bonding assisted chiral ion-pair pathway. PMID:25621822

Lou, Yan-Peng; Zheng, Chang-Wu; Pan, Ren-Ming; Jin, Qiao-Wen; Zhao, Gang; Li, Zhong

2015-02-01

363

Influence of Solvent Composition on the Kinetics of Cyclooctene Epoxidation by Hydrogen Peroxide Catalyzed by Iron(III)  

E-print Network

Catalyzed by Iron(III) [tetrakis(pentafluorophenyl)] Porphyrin Chloride [(F20TPP)FeCl] Ned A. Stephenson The epoxidation of cyclooctene catalyzed by iron(III) [tetrakis(pentafluorophenyl)] porphyrin chloride [(F20TPP cleavage increases with alcohol acidity. Heterolytic cleavage is envisioned to form iron(IV) -radical

Bell, Alexis T.

364

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

E-print Network

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

Colby Davie, Elizabeth A. (Elizabeth Anne)

2005-01-01

365

Chemoselective Functionalization of Carboxylic Acid and Phenol Containing Natural Products and the Development and Use of a Nucleophile Catalyzed Michael Aldol Lactonization Process  

E-print Network

catalyzed aldol lactonization (NCAL) reaction for synthesizing highly substituted cyclopentane fused beta-lactones, we developed a nucleophile catalyzed, tandem Michael aldol lactonization (NCMAL) reaction. Herein, we show the synthetic utility...

McFarlin, Rae

2013-05-02

366

Cu-Catalyzed Arylation of Phenols: Synthesis of Sterically Hindered and Heteroaryl Diaryl Ethers  

E-print Network

Cu-catalyzed O-arylation of phenols with aryl iodides and bromides can be performed under mild condition in DMSO/K3PO4 with use of picolinic acid as the ligand for copper. This method tolerates a variety of functional ...

Maiti, Debabrata

367

An Improved Protocol for the Pd-catalyzed ?-Arylation of Aldehydes with Aryl Halides  

PubMed Central

An improved protocol for the Pd-catalyzed ?-arylation of aldehydes with aryl halides has been developed. The new catalytic system allows for the coupling of an array of substrates including challenging electron-rich aryl bromides and less reactive aryl chlorides. The utility of this method has been demonstrated in a new total synthesis of (±)-sporochnol. PMID:18808127

Martín, Rubén; Buchwald, Stephen L.

2009-01-01

368

Investigation of the regiospecificity and stereospecificity of proton transfer in the yeast inorganic pyrophosphatase catalyzed reaction  

SciTech Connect

The regiospecificity and stereospecificity of proton transfer in the yeast inorganic pyrophosphatase (PPase) catalyzed hydrolysis of P1,P2-bidentate Mg(H/sub 2/O)4(PPi)/sub 2/- were probed with exchange-inert metal complexes of imidodiphosphate (PNP) and thiopyrophosphate (PPS). PPase was unable to catalyze the hydrolysis of Mg(H/sub 2/O)4PNP and P1,P2-bidentate Co(NH/sub 3/)4PNP under conditions that resulted in rapid hydrolysis of the corresponding metal-PPi complexes. PPase was found to catalyze the hydrolysis of Mg(H/sub 2/O)4PPS at 17% the rate of Mg(H/sub 2/O)4PPi hydrolysis. The Km of Mg(H/sub 2/O)4PPS was determined to be 300 microM, which is a value 10-fold greater than that observed for Mg(H/sub 2/O)4PPi. P1,P2-Bidentate Cr(H/sub 2/O)4PPS and Co(NH/sub 3/)4PPS (prepared from PPS) were both found to be substrates for PPase. The enzyme specifically catalyzed the hydrolysis of the Rp enantiomers of these complexes and not the Sp enantiomers. These results are accommodated by a reaction mechanism involving enzyme-mediated proton transfer to the pro-R oxygen atom of the incipient phosphoryl leaving group of the bound P1,P2-bidentate Mg(H/sub 2/O)4PPi2- complex.

Lin, I.; Knight, W.B.; Hsueh, A.; Dunaway-Mariano, D.

1986-08-12

369

EFFECT OF A BASE-CATALYZED DECHLORINATION PROCESS ON THE GENOTOXICITY OF PCB-CONTAMINATED SOIL  

EPA Science Inventory

We evaluated the genotoxicity of dichloromethane (DCM) extracts of PCB-contaminated soil before and after the soil had been treated by a base-catalyzed dechlorination process, which involved heating a mixture of the soil, polyethylene glycol, and sodium hydroxide to 250-350 degre...

370

Friedel–Crafts alkylation of indoles with nitroalkenes catalyzed by Cu(II)–imine complex  

Microsoft Academic Search

A series of new ligands L1–L7 were readily prepared in one step. Friedel–Crafts alkylation of indoles with nitroalkenes catalyzed by a novel Cu(II)–L complex has been developed. The remarkable advantages of this reaction are mild reaction conditions, simple workup procedure, high yields of products and the use of ethanol as a green solvent.

Ning Ning Wan; Yong Lei Yang; Wen Ping Wang; Zheng Feng Xie; Ji De Wang

2011-01-01

371

Metal-catalyzed asymmetric sulfoxidation, epoxidation and hydroxylation by hydrogen peroxide  

E-print Network

1 Metal-catalyzed asymmetric sulfoxidation, epoxidation and hydroxylation by hydrogen peroxide transition-metal complexes are limited when the oxidant is hydrogen peroxide. The two main difficulties of using hydrogen peroxide in the presence of transition metal complexes are the homolytic cleavage

Paris-Sud XI, Université de

372

Optimizing the Acid Catalyzed Synthesis of Hyperbranched Poly(Glycerol-diacids) Oligomers  

Technology Transfer Automated Retrieval System (TEKTRAN)

Oligomeric pre-polymers were synthesized by the acid-catalyzed condensation of glycerol with succinic acid, glutaric acid and azelaic acid in dimethylsulfoxide (DMSO) or dimethylformamide (DMF). The prepolymers were obtained, on average in 84% yield, and were characterized by proton NMR, MALDI-TOF ...

373

Non-conventional hydrolase chemistry: amide and carbamate bond formation catalyzed by lipases  

Microsoft Academic Search

Biocatalysis in nonaqueous media is becoming increasingly important in organic synthesis. Lipases are the most used enzymes, especially in transesterification reactions. However, in the last years the amidation reaction catalyzed by lipases has also been shown to be a useful tool for the organic chemists. In this review, we discuss the possibilities of the enzymatic aminolysis and ammonolysis reactions for

Vicente Gotor

1999-01-01

374

Rh(III)-catalyzed directed C–H bond amidation of ferrocenes with isocyanates  

PubMed Central

Summary [RhCp*(OAc)2(H2O)] [Cp* = pentamethylcyclopentadienyl] catalyzed the C–H bond amidation of ferrocenes possessing directing groups with isocyanates in the presence of 2 equiv/Rh of HBF4·OEt2. A variety of disubstituted ferrocenes were prepared in high yields, or excellent diastereoselectivities. PMID:23209521

Takebayashi, Satoshi; Shizuno, Tsubasa; Otani, Takashi

2012-01-01

375

Beta-D-xylosidase from Selenomonas ruminantium: thermodynamics of enzyme-catalyzed and noncatalyzed reactions  

Technology Transfer Automated Retrieval System (TEKTRAN)

Beta-D-xylosidase/alpha-L-arabinofuranosidase from Selenomonas ruminantium (SXA) is the most active enzyme known for catalyzing hydrolysis of 1,4-beta-D-xylooligosaccharides to D-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-beta-D-xylopyranoside (4NPX), 4-nitrophenyl-alpha-L-arabi...

376

The iron-catalyzed construction of 2-aminopyrimidines from alkynenitriles and cyanamides†  

PubMed Central

Several cycloaddition catalysts and reagents were surveyed for their effectiveness toward cyclizing alkynenitriles with cyanamides. Catalytic amounts of FeI2, iPrPDAI and Zn were found to effectively catalyze the [2+2+2] cycloaddition of a variety of cyanamides and alkynenitriles to afford bicyclic 2-aminopyrimidines. PMID:23877441

Lane, Timothy K.; Nguyen, Minh H.; D'Souza, Brendan R.; Spahn, Nathan A.

2014-01-01

377

Ruthenium-Catalyzed ?-Carbolinium Ion Formation from Aryl Azides. Synthesis of Dimebolin  

PubMed Central

A range of ?-carbolines were produced stereoselectively from ruthenium(III)-catalyzed reactions of 3-pyridyl substituted aryl azides. Other catalysts and conditions were neither as selective nor as high yielding. This method was used to synthesize Dimebolin in a concise and efficient manner. PMID:21517088

Dong, Huijun; Latka, Regina T.; Driver, Tom G.

2011-01-01

378

Efficient Synthesis of Trimethylsilyl Pseudohalides Catalyzed by PEG400\\/ZnI2 under Ultrasound Irradiation  

Microsoft Academic Search

Trimethylsilyl pseudohalides Me3SiX, where X?=?NCS, NCO, or CN, were readily prepared conveniently in desirable yields by the reaction of Me3SiCl with NaX or KX catalyzed by PEG400 and zinc iodide under ultrasound irradiation.

Wang Sufang; Wang Shaobing; Xu Yongshen

2005-01-01

379

Bi(OTf)3-Catalyzed 5-Exo-Trig Cyclization via Halide Activation  

PubMed Central

Lewis acid activation of allyl halides utilizing Bi(OTf)3 resulted in cationic cyclization of alkenes with high efficiency. While other Lewis acids could catalyzed this process with highly substituted alkenes, bismuth salts demonstrated unique reactivity in come cases. This suggested that bismuth triflate possesses intersting halophilic properties. PMID:19122872

Hayashi, Ryuji; Cook, Gregory R.

2008-01-01

380

Toward the ideal synthesis. New transition metal-catalyzed reactions inspired by novel medicinal leads  

Microsoft Academic Search

Studies in our laboratory are directed at the advancement of synthesis, biology, and medicine. This lecture will focus on new transition metal-catalyzed reactions that have been inspired by biologically potent targets such as phorbol and Taxol ® and by the more general interest in producing syntheses that are concise, efficient, cost- and resource-effective, envi- ronmentally benign, quick, and simple to

Paul A. Wender; F. Christopher Bi; Gabriel G. Gamber; Francis Gosselin; Robert D. Hubbard; Marc J. C. Scanio; Robert Sun; Travis J. Williams; Lei Zhang

2002-01-01

381

Molybdenum nitrogenase catalyzes the reduction and coupling of CO to form hydrocarbons.  

PubMed

The molybdenum-dependent nitrogenase catalyzes the multi-electron reduction of protons and N(2) to yield H(2) and 2NH(3). It also catalyzes the reduction of a number of non-physiological doubly and triply bonded small molecules (e.g. C(2)H(2), N(2)O). Carbon monoxide (CO) is not reduced by the wild-type molybdenum nitrogenase but instead inhibits the reduction of all substrates catalyzed by nitrogenase except protons. Here, we report that when the nitrogenase MoFe protein ?-Val(70) residue is substituted by alanine or glycine, the resulting variant proteins will catalyze the reduction and coupling of CO to form methane (CH(4)), ethane (C(2)H(6)), ethylene (C(2)H(4)), propene (C(3)H(6)), and propane (C(3)H(8)). The rates and ratios of hydrocarbon production from CO can be adjusted by changing the flux of electrons through nitrogenase, by substitution of other amino acids located near the FeMo-cofactor, or by changing the partial pressure of CO. Increasing the partial pressure of CO shifted the product ratio in favor of the longer chain alkanes and alkenes. The implications of these findings in understanding the nitrogenase mechanism and the relationship to Fischer-Tropsch production of hydrocarbons from CO are discussed. PMID:21454640

Yang, Zhi-Yong; Dean, Dennis R; Seefeldt, Lance C

2011-06-01

382

Practical, Modular, and General Synthesis of 3-Coumaranones through Gold-Catalyzed Intermolecular Alkyne Oxidation Strategy.  

PubMed

A gold-catalyzed intermolecular alkyne oxidation for the preparation of 3-coumaranones has been developed. Using 8-isopropylquinoline N-oxides as oxidants, the reactions of o-ethynylanisoles afford versatile 3-coumaranones in moderate to good isolated yields. The synthetic utility of this chemistry is also indicated by the synthesis of the natural product sulfuretin. PMID:25287758

Shu, Chao; Liu, Rongfu; Liu, Shuang; Li, Jian-Qiao; Yu, Yong-Fei; He, Qiao; Lu, Xin; Ye, Long-Wu

2015-01-01

383

Stereoselective Synthesis of Vinylsilanes by a Gold(I)-Catalyzed Acetylenic Sila-Cope Rearrangement  

E-print Network

Stereoselective Synthesis of Vinylsilanes by a Gold(I)-Catalyzed Acetylenic Sila-Cope Rearrangement- coupling reactions.1 The application of these reactions to stereo- selective olefin synthesis is contingent reactions to the stereoselective synthesis of olefins substituted with the allyl group cis to silicon

Toste, Dean

384

Synthesis of Indenyl Ethers by Gold(I)-Catalyzed Intramolecular Carboalkoxylation of Alkynes  

E-print Network

Synthesis of Indenyl Ethers by Gold(I)-Catalyzed Intramolecular Carboalkoxylation of Alkynes Pascal gold(I) into a cationic intermediate may be essential to some of these transformations,1 a more conventional reaction pathway relies on the -acidity of cationic gold(I) complexes to induce a trans

Toste, Dean

385

Synthesis of 2-Cyclopentenones by Gold(I)-Catalyzed Rautenstrauch Rearrangement  

E-print Network

Synthesis of 2-Cyclopentenones by Gold(I)-Catalyzed Rautenstrauch Rearrangement Xiaodong Shi, David J. Gorin, and F. Dean Toste* Center for New Directions in Organic Synthesis, Department of Chemistry@uclink.berkeley.edu The importance of cyclopentenones as building blocks for organic synthesis continues to inspire the development

Toste, Dean

386

Enantioposition-selective copper-catalyzed azide-alkyne cycloaddition for construction of chiral biaryl derivatives.  

PubMed

A highly enantioposition-selective copper-catalyzed azide-alkyne cycloaddition (CuAAC) of dialkynes bearing prochiral biaryls has been developed for the construction of 1,2,3-triazoles bearing axially chiral biaryl groups in up to 76% yield and up to 99% ee. PMID:25360824

Osako, Takao; Uozumi, Yasuhiro

2014-11-21

387

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

388

4844 Biochemistry 1991, 30, 4844-4854 Ribozyme-Catalyzed and Nonenzymatic Reactions of Phosphate  

E-print Network

4844 Biochemistry 1991, 30, 4844-4854 Ribozyme-Catalyzed and Nonenzymatic Reactions of Phosphate Received March I , 1991 ABSTRACT: The L-21 ScaI ribozyme derived from the intervening sequence of cleavage, that test aspects of a kinetic model proposed for the ribozyme reaction (Herschlag, D., & Cech, T

Herschlag, Dan

389

3C-like Proteinase from SARS Coronavirus Catalyzes Substrate Hydrolysis by a General Base Mechanism  

E-print Network

3C-like Proteinase from SARS Coronavirus Catalyzes Substrate Hydrolysis by a General Base Mechanism ReceiVed January 26, 2004 ABSTRACT: SARS 3C-like proteinase has been proposed to be a key enzyme for drug design against SARS. Lack of a suitable assay has been a major hindrance for enzyme kinetic

Luhua, Lai

390

Asymmetric Dearomatization of ?-Naphthols through an Amination Reaction Catalyzed by a Chiral Phosphoric Acid.  

PubMed

A highly efficient catalytic asymmetric dearomatization of naphthols by means of an electrophilic amination reaction catalyzed by chiral phosphoric acid is presented. This protocol provides a facile access to functionalized ?-naphthalenone compounds with a chiral quaternary carbon center in excellent yields and enantioselectivity (up to 99?% yield, up to 96?%?ee). PMID:25414091

Wang, Shou-Guo; Yin, Qin; Zhuo, Chun-Xiang; You, Shu-Li

2015-01-01

391

Bound Lac repressor protein differentially inhibits the unwinding reactions catalyzed by DNA helicases.  

PubMed Central

A partial duplex DNA substrate containing the Lac repressor binding site, within the duplex region, was constructed to examine the effect of bound Lac repressor on the unwinding reaction catalyzed by several DNA helicases. The substrate contained 90 base pairs of double-stranded DNA and, in the absence of Lac repressor, was effectively unwound by each of the seven helicases tested. The unwinding reactions catalyzed by Escherichia coli Rep protein, bacteriophage T4 Dda protein and E. coli DNA helicase I were not inhibited by the presence of bound Lac repressor. Both SV40 T antigen and E. coli helicase II were partially inhibited by bound repressor at the highest repressor concentrations tested. The helicase reactions catalyzed by E. coli DnaB protein and helicase IV were substantially inhibited by the presence of bound protein. When the length of the duplex region was increased to 323 base pairs the inhibition spectrum caused by bound Lac repressor on the unwinding reactions catalyzed by DnaB protein, helicase I and helicase II was essentially the same as that observed using the shorter partial duplex molecule. Inhibition of the unwinding reaction was due to the presence of bound Lac repressor as evidenced by the substantially weaker inhibition of helicase IV by Lac repressor in the presence of IPTG. In addition, we have shown that Rep protein displaces the bound repressor protein during the course of an unwinding reaction. Images PMID:1336182

Yancey-Wrona, J E; Matson, S W

1992-01-01

392

The DNA unwinding reaction catalyzed by Rep protein is facilitated by an RHSP-DNA interaction.  

PubMed Central

The unwinding reaction catalyzed by the Escherichia coli Rep protein is stimulated by a small 15 kDa protein called Rep helicase stimulatory protein (RHSP)(1). The RHSP-stimulated unwinding reaction catalyzed by Rep protein proceeded at a rapid rate after a time lag of 1-2 min at 37 degrees C. This time lag was eliminated by preincubating RHSP with the DNA substrate, indicating that stimulation resulted from an interaction between RHSP and DNA. RHSP was shown to increase the rate as well as the extent of the unwinding reaction catalyzed by Rep protein. RHSP bound both single- and double-stranded DNA with apparent equal affinity, forming an unusually stable complex. Electron microscopy illustrated that the RHSP-DNA complex consisted of large protein aggregates bound to DNA forming a highly condensed, aggregated DNA-protein complex. The protein aggregates were not observed in the absence of DNA and appeared to form cooperatively in the presence of DNA. NH2-terminal amino acid sequence analysis suggested that RHSP was identical to E. coli ribosomal-protein L14. Binding assays showed that the interaction between RHSP and rRNA was similar to the RHSP-DNA interaction. Several models are put forth to explain the stimulation of the unwinding reaction catalyzed by Rep protein. In addition, the potential physiological significance of the RHSP-stimulated Rep protein unwinding reaction is discussed. Images PMID:1650456

Yancey, J E; Matson, S W

1991-01-01

393

Pd- and Cu-catalyzed stereo- and regiocontrolled decarboxylative/C-H fluoroalkenylation of heteroarenes.  

PubMed

Pd/Cu-catalyzed decarboxylative/direct C-H alkenylations of heteroarenes with ?-fluoroacrylic acid is reported. This method offers step-economical and stereocontrolled access to valuable heteroarylated monofluoroalkenes as both Z and E isomers, which are known to be useful in the synthesis of fluorinated biomolecules. PMID:25303004

Rousée, Kevin; Schneider, Cédric; Couve-Bonnaire, Samuel; Pannecoucke, Xavier; Levacher, Vincent; Hoarau, Christophe

2014-11-10

394

Palladium-catalyzed alkoxyamination of alkenes with use of N-fluorobenzenesulfonimide as oxidant.  

PubMed

A Pd-catalyzed alkoxyamination of protected aminoalkenes promoted by N-fluorobenzenesulfonimide is described. This mild transformation allows the direct formation of ethers from carbon-carbon double bonds. An unusual switch from exo to endo selectivity in polar solvents was discovered, allowing the selective formation of either regioisomer by careful choice of reaction conditions. PMID:20738146

Liskin, Dmitry V; Sibbald, Paul A; Rosewall, Carolyn F; Michael, Forrest E

2010-09-17

395

BASE-CATALYZED DESTRUCTION OF PCBS-NEW DONORS, NEW TRANSFER AGENTS/CATALYSTS  

EPA Science Inventory

The use of hydrogen transfer agents and catalysts to improve the base-catalyzed decomposition of polychlorinated biphenyls (PCBs) was investigated. The reaction proceeded only in the presence of base, but the rate of PCB disappearance increased with increasing amount of hydrogen ...

396

Intermolecular Dynamic Kinetic Resolution Cooperatively Catalyzed by an N-Heterocyclic Carbene and a Lewis Acid.  

PubMed

The ubiquitous structure of ?-lactones makes the development of new methods for their enantioselective and stereoselective synthesis an important ongoing challenge. The intermolecular dynamic kinetic resolution (DKR) of ?-halo-?-ketoesters cooperatively catalyzed by an N-heterocyclic carbene and a Lewis acid generates two contiguous stereocenters with remarkable diastereoselectivity through an oxidation/lactonization sequence. PMID:25447028

Wu, Zijun; Li, Fangyi; Wang, Jian

2014-11-28

397

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

398

Intramolecular arylation of benzimidazoles via Pd(II)/Cu(I) catalyzed cross-dehydrogenative coupling.  

PubMed

Electron poor benzimidazole substrates were arylated via an intramolecular cross-dehydrogenative coupling (CDC) reaction. These CDC reactions were catalyzed by a Pd(II)/Cu(I) catalyst system, capable of producing moderate yields on a large library of substrates. The substrate scope consisted of tethered arene-benzimidazoles that upon coupling, produced a fused polycyclic motif. PMID:24764603

Pereira, Kyle C; Porter, Ashley L; Deboef, Brenton

2014-03-01

399

The Isomerization of (-)-Menthone to (+)-Isomenthone Catalyzed by an Ion-Exchange Resin  

ERIC Educational Resources Information Center

A traditional organic chemistry laboratory experiment involves the acid-catalyzed isomerization of (-)-menthone to (+)-isomenthone. This experiment generates large quantities of organic and aqueous waste, and only allows the final ratio of isomers to be determined. A "green" modification has been developed that replaces the mineral acid…

Ginzburg, Aurora L.; Baca, Nicholas A.; Hampton, Philip D.

2014-01-01

400

NHC-Catalyzed/Titanium(IV);#8722;Mediated Highly Diastereo- and Enantioselective Dimerization of Enals  

SciTech Connect

An NHC-catalyzed, diastereo- and enantioselective dimerization of enals has been developed. The use of Ti(Oi-Pr){sub 4} is a key element for the reactivity and selectivity of this process. The cyclopentenes are obtained with high levels of diastereo- and enantioselectivity and their synthetic utility is demonstrated by functionalization of the product alkene.

Cohen, Daniel T.; Cardinal-David, Benoit; Roberts, John M.; Sarjeant, Amy A.; Scheidt, Karl A. (NWU)

2012-05-09

401

ON-LINE OPTIMIZATION, ENERGY ANALYSIS AND ENVIRONMENTAL IMPACT ASSESSMENT OF SULFURIC ACID CATALYZED ALKYLATION  

E-print Network

ON-LINE OPTIMIZATION, ENERGY ANALYSIS AND ENVIRONMENTAL IMPACT ASSESSMENT OF SULFURIC ACID in sulfuric acid consumption potentially could be obtained. 1. Introduction Alkylation process is one and procedures (Albright 1990, Cupit et al. 1961). In this study a commercial sulfuric acid catalyzed alkylation

Pike, Ralph W.

402

Atmospheric Environment 40 (2006) 68636878 Acid-catalyzed reactions of hexanal on sulfuric acid particles  

E-print Network

Atmospheric Environment 40 (2006) 6863­6878 Acid-catalyzed reactions of hexanal on sulfuric acid the uptake of gas- phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced condensation product was formed only at initial concentrations of 75­96 wt% sulfuric acid in water

Elrod, Matthew J.

403

Influence of an internal trifluoromethyl group on the rhodium(II)-catalyzed reactions of vinyldiazocarbonyl compounds.  

PubMed

Incorporation of a trifluoromethyl group into the structure of 4-(alkoxycarbonyl)vinyldiazocarbonyl compounds greatly decreases the tendency of the carbenoid intermediates formed during Rh(II)-catalyzed reactions to undergo intermolecular processes. Instead, they are prone to experience intramolecular [1,5]- and [1,3]-electrocyclizations to produce reactive cyclopropenes and furans, and these are capable of further transformations. PMID:23614681

Nikolaev, Valerij A; Supurgibekov, Murat B; Davies, Huw M L; Sieler, Joachim; Zakharova, Valerija M

2013-05-01

404

Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products  

Microsoft Academic Search

While it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne

Rebecca M. Garland; Matthew J. Elrod; Kristi Kincaid; Melinda R. Beaver; Jose L. Jimenez; Margaret A. Tolbert

2006-01-01

405

Examples of acid-catalyzed mineral dissolution reactions resulting in pH  

E-print Network

Examples of acid-catalyzed mineral dissolution reactions resulting in pH buffering: The goal and analyzed by the Alberta Geological Survey. Percent mineral composition for each sample is presented sample was assumed to have a porosity of 20% and a total rock mass of 12 kg. 4.61 Calcite(78), Quartz(18

Peters, Catherine A.

406

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

407

Lewis Acid Catalyzed Ring-opening Polymerization of Epoxidized Soybean Oil in Liquid Carbon Dioxide  

Technology Transfer Automated Retrieval System (TEKTRAN)

Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by boron trifluoride diethyl etherate (BF3•OEt2), in liquid carbon dioxide, was conducted in an effort to develop useful biobased biodegradable polymers. The resulting polymers (RPESO) were characterized by FTIR spectroscopy, diff...

408

Development and Validation of ReaxFF Reactive Force Field for Hydrocarbon Chemistry Catalyzed by Nickel  

E-print Network

Development and Validation of ReaxFF Reactive Force Field for Hydrocarbon Chemistry Catalyzed as a function of temperature and pressure, we have developed the ReaxFF reactive force field to describe surface. The ReaxFF parameters were determined by fitting to the geometries and energy surfaces from

Goddard III, William A.

409

Activator-free palladium-catalyzed silylation of aryl chlorides with silylsilatranes.  

PubMed

The palladium-catalyzed silylation of aryl chlorides with silylsilatranes proceeds under activator-free conditions; hence, wide functional group compatibility is displayed and boryl and siloxy groups are able to survive. Experimental and computational studies revealed that smooth transmetalation from the silylsilatrane to the arylpalladium chloride is facilitated by strong interaction between the Lewis acidic silicon and the chloride. PMID:25123398

Yamamoto, Yutaro; Matsubara, Hiroshi; Murakami, Kei; Yorimitsu, Hideki; Osuka, Atsuhiro

2015-01-01

410

Mobile-Learning for Boise State: A Proposal to Catalyze a Transformation in  

E-print Network

Mobile-Learning for Boise State: A Proposal to Catalyze a Transformation in Teaching and Learning Fall 2011 Task Force for Teaching, Learning and Technology #12;Mobile-Learning for Boise State University 2 proposal submitted August 2011 EXECUTIVE SUMMARY The integration of mobile technology

Barrash, Warren

411

Advances in palladium-catalyzed carbon-nitrogen bond forming processes  

E-print Network

Chapter 1. Microwave-assisted, palladium-catalyzed C-N bond-forming reactions with aryl/heteroaryl nonaflates/halides and amines using the soluble amine bases DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) or MTBD (7-methyl-1, ...

Tundel, Rachel E. (Rachel Elizabeth)

2006-01-01

412

The effect of Mg/2+/ and Ca/2+/ on urea-catalyzed phosphorylation reactions  

NASA Technical Reports Server (NTRS)

The effect of Mg(2+) and Ca(2+) on phosphorylation reactions catalyzed by urea is investigated, showing that Mg(2+) improves markedly the yield of products containing pyrophosphate bonds. Yields of up to 25% of uridine diphosphate can be obtained with struvite at temperatures as low as 65 C.

Handschuk, G. J.; Lohrmann, R.; Orgel, L. E.

1973-01-01

413

Oscillating photoluminescence in the cerium ion catalyzed Belousov-Zhabotinsky reaction  

Microsoft Academic Search

Oscillating photoluminescence in the Ce(III)\\/Ce(IV) catalyzed Belousov-Zhabotinsky reaction is described. No quantitative data can be obtained from luminescence intensity measurements, due to quenching and inner filter effects. From lifetime measurements, it is possible to evaluate the quenching effect, which is attributed to bromate ions that oxidize the excited Ce(III) species. Some consequences are discussed.

F. Bolletta; L. Prodi; N. Zaccheroni

1995-01-01

414

Lipase-catalyzed ?-butylglucoside lactate synthesis in organic solvent for dermo-cosmetic application  

Microsoft Academic Search

?-Butylglucoside can be used as a vector for lactic acid: ?-butylglucoside lactate synthesis can be achieved through transesterification catalyzed by immobilized Candida antarctica lipase. Synthesis was performed in an inert tertiary alcohol, 2-methyl-2-butanol. The reaction rapidly reached a thermodynamic equilibrium which could be shifted towards synthesis by alcohol product removal under reduced pressure: more than 95% of ?-butylglucoside could be

Marie-Pierre Bousquet; René-Marc Willemot; Pierre Monsan; Emmanuel Boures

1999-01-01

415

Gallium-catalyzed reductive chlorination of carboxylic acids with copper(II) chloride.  

PubMed

Described herein is the direct chlorination of carboxylic acids using copper(II) chloride via a gallium(III)-catalyzed reduction in the presence of a hydrosiloxane. During this reductive chlorination, the counteranions of CuCl2 functioned as a chloride source. PMID:25295703

Sakai, Norio; Nakajima, Takumi; Yoneda, Shinichiro; Konakahara, Takeo; Ogiwara, Yohei

2014-11-01

416

Copper-catalyzed aerobic oxidative coupling of aromatic alcohols and acetonitrile to ?-ketonitriles.  

PubMed

A practical, convenient, and cheap copper-catalyzed aerobic oxidative coupling of aromatic alcohols and acetonitrile to ?-ketonitriles has been developed. The green C-C bond formation involving the loss of two hydrogen atoms from the corresponding two carbons, respectively, unlocks opportunities for markedly different synthetic strategies. PMID:24392889

Shen, Jiaxuan; Yang, Dejun; Liu, Yuxiao; Qin, Shuangshuang; Zhang, Jingwu; Sun, Jiangkai; Liu, Chunhui; Liu, Chaoyang; Zhao, Xiaomei; Chu, Changhu; Liu, Renhua

2014-01-17

417

Copper-Catalyzed Electrophilic Amination of Organolithiums Mediated by Recoverable Siloxane Transfer Agents  

PubMed Central

The development and validation of copper-catalyzed, electrophilic amination of aryl and heteroaryl organolithiums with N,N-dialkyl -O-benzoylhydroxylamineshavebeenachievedexploitingrecoverablesiloxanetransferagents. Given the readily availability of organolithium compounds, the mild reaction conditions, the ease of product purification and the ready recovery of the siloxane transfer agents, this transformation comprises a useful tactic to access diverse aryl and heteroaryl amines. PMID:24000819

Nguyen, Minh H.

2013-01-01

418

Ligand-Controlled Regiodivergent Palladium-Catalyzed Decarboxylative Allylation Reaction to Access ?,?-Difluoroketones.  

PubMed

?,?-Difluoroketones possess unique physicochemical properties that are useful for developing therapeutics and probes for chemical biology. To access the ?-allyl-?,?-difluoroketone substructure, complementary palladium-catalyzed decarboxylative allylation reactions were developed to provide linear and branched ?-allyl-?,?-difluoroketones. For these orthogonal processes, the fluorination pattern of the substrate enabled the ligands to dictate the regioselectivity of the transformations. PMID:25581845

Yang, Ming-Hsiu; Orsi, Douglas L; Altman, Ryan A

2015-02-16

419

Kinetic Parameters for the Noncatalyzed and Enzyme-Catalyzed Mutarotation of Glucose Using a Blood Glucometer  

ERIC Educational Resources Information Center

The kinetic parameters for the conversion of alpha-D-glucose to beta-D-glucose were measured using a blood glucometer. The reaction order, rate constant, and Arrhenius activation energy are reported for the noncatalyzed reaction and turnover number and Michaelis constant are reported for the reaction catalyzed by porcine kidney mutarotase. The…

Hardee, John R.; Delgado, Bryan; Jones, Wray

2011-01-01

420

From vinyl pyranoses to carbasugars by an iron-catalyzed reaction complementary to classical Ferrier carbocyclization.  

PubMed

Starting from vinyl pyranoses an iron-catalyzed tandem isomerization-intramolecular aldolization reaction was developed to prepare cyclohexenone derivatives bearing substituents on the double bond, and it has been applied in a short synthesis of 4-epi-gabosines A and B, from d-glucose. PMID:19641820

Mac, Dinh Hung; Samineni, Ramesh; Petrignet, Julien; Srihari, Pabbaraja; Chandrasekhar, Srivari; Yadav, Jhillu Singh; Grée, René

2009-08-21

421

A Novel Methyltransferase Catalyzes the Methyl Esterification of trans-Aconitate in Escherichia coli*  

E-print Network

A Novel Methyltransferase Catalyzes the Methyl Esterification of trans-Aconitate in Escherichia of trans- aconitate at high affinity (Km 0.32 mM) and cis-aconi- tate, isocitrate, and citrate at lower, and we have now designated it tam for trans-aconitate methyltrans- ferase. We have generated a knock

Clarke, Steven

422

Catalyzing Mass Production of Solar Photovoltaic Cells Using University Driven Green Purchasing  

ERIC Educational Resources Information Center

Purpose: The purpose of this paper is to explore the use of the purchase power of the higher education system to catalyze the economy of scale necessary to ensure market competitiveness for solar photovoltaic electricity. Design/methodology/approach: The approach used here was to first determine the demand necessary to construct "Solar City…

Pearce, Joshua M.

2006-01-01

423

Distinct Reactions Catalyzed by Bacterial and Yeast trans-Aconitate Methyltransferases  

E-print Network

, suggesting that methylation occurs on a specific site in trans-aconitate (11). Tandem mass spectrometry didDistinct Reactions Catalyzed by Bacterial and Yeast trans-Aconitate Methyltransferases Hui Cai-1569 ReceiVed September 29, 2000; ReVised Manuscript ReceiVed December 14, 2000 ABSTRACT: The trans-aconitate

Clarke, Steven

424

Formal palladium-catalyzed asymmetric hydrogenolysis of racemic N-sulfonyloxaziridines.  

PubMed

Highly enantioselective palladium-catalyzed formal hydrogenolysis of racemic N-sulfonyloxaziridines has been realized, providing a novel access to sultams with up to 99% ee. Preliminary mechanistic insights revealed that the reaction proceeded through a N-O bond cleavage, dehydration, and the sequential asymmetric hydrogenation. PMID:25560229

Song, Bo; Yu, Chang-Bin; Huang, Wen-Xue; Chen, Mu-Wang; Zhou, Yong-Gui

2015-01-16

425

Palladium-Catalyzed Decarbonylative Dehydration of Fatty Acids for the Production of Linear Alpha Olefins  

PubMed Central

A highly efficient palladium-catalyzed decarbonylative dehydration reaction of carboxylic acids is reported. This method transforms abundant and renewable even-numbered natural fatty acids into valuable and expensive odd-numbered alpha olefins. Additionally, the chemistry displays a high functional group tolerance. The process employs low loading of palladium catalyst and proceeds under solvent-free and relatively mild conditions. PMID:24772061

Liu, Yiyang; Kim, Kelly E.; Herbert, Myles B.; Fedorov, Alexey; Grubbs, Robert H.; Stoltz, Brian M.

2014-01-01

426

Corona charge selective micelle degradation catalyzed by P. cepacia lipase isoforms.  

PubMed

Micelles derived from poly(?-caprolactone) (PCL) poly(ethylene glycol)(PEG) diblock copolymers (HO-PCLn-b-PEG32-RX, R = -O(CH2)3S(CH2)2-; X = -CO2(-), -SO3(-), -NH3(+)) show corona charge selective degradation catalyzed by P. cepacia lipase isoforms. PMID:24301683

Zhu, Xiaobo; Fryd, Michael; Valentine, Ann M; Wayland, Bradford B

2014-01-28

427

Menaquinone is an obligatory component of the chain catalyzing succinate respiration in Bacillus subtilis  

Microsoft Academic Search

The question was investigated as to whether the bacterial menaquinone (MK) is a component of the electron transport chain catalyzing succinate respiration in Bacillus subtilis. Three different methods were applied, and the following consistent results were obtained. (i) Solvent extraction of MK from the bacterial membrane caused total inhibition of the respiratory activities with succinate and NADH, while the activity

Elena Lemma; Gottfried Unden; Achim Kröger

1990-01-01

428

Direct enantiospecific substitution of primary ?-aminoalkylferrocenes via Lewis acid-catalyzed C-N bond cleavage.  

PubMed

Highly enantioenriched primary ?-aminoalkylferrocenes were found to undergo zinc chloride-catalyzed substitution with various carbon, nitrogen, and sulfur nucleophiles in an enantiospecific fashion through C-N bond cleavage. The reaction tolerates air and moisture and exhibits high atom-economy by releasing ammonia as the sole byproduct. PMID:25307165

Zhou, Meng-Guang; Zhang, Wen-Zhao; Tian, Shi-Kai

2014-12-01

429

Catalyzed deuterium-deuterium and deuterium-tritium fusion blankets for high temperature process heat production  

Microsoft Academic Search

Tritiumless blanket designs, associated with a catalyzed deuterium-deuterium (D-D) fusion cycle and using a single high temperature solid pebble or falling bed zone, for process heat production, are proposed. Neutronics and photonics calculations, using the Monte Carlo method, show that an about 90% heat deposition fraction is possible in the high temperature zone, compared to a 30 to 40% fraction

M. M. H. Ragheb; B. Salimi

1982-01-01

430

Mechanism of the Reaction Catalyzed by Isoaspartyl Dipeptidase from Escherichia coli,  

E-print Network

superfamily and catalyzes the hydrolytic cleavage of -aspartyl dipeptides. Structural studies of the wild-type enzyme have demonstrated that the active site consists of a binuclear metal center positioned at the C with the free R-amino group of the dipeptide substrate. Kinetic constants were obtained for the mutant enzymes

Holden, Hazel

431

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. PMID:25083143

Varnedoe, Lee S.; Angel, Brad D.; McClellan, Joshua L.

2014-01-01

432

H-ZSM-5 catalyzed formation of ethylene from methanol or higher olefins  

SciTech Connect

The distributions of olefins formed in the HZSM-5 catalyzed total conversions of methanol and heptene-1 were examined at low partial pressures as a function of contact time. The results clearly indicated that ethylene was only obtained at long contact times, and then via secondary reequilibration of the primary kinetic olefinic products, propylene and butenes.

Dessau, R.M.

1986-05-01

433

Ir-catalyzed reverse prenylation of 3-substituted indoles: total synthesis of (+)-aszonalenin and (-)-brevicompanine B.  

PubMed

The selective reverse prenylation of 3-substituted-1H-indoles at C3 is described. The iridium-catalyzed reaction proceeds with high branched to linear selectivity (>20:1) for a variety of indoles. In addition, a diastereoselective reverse prenylation of tryptophan methyl ester is disclosed, and its synthetic utility is demonstrated in the synthesis of (+)-aszonalenin and (-)-brevicompanine B. PMID:25365411

Ruchti, Jonathan; Carreira, Erick M

2014-12-01

434

Aniline-terminated DNA catalyzes rapid DNA-hydrazone formation at physiological pH.  

PubMed

We report the effect of DNA-templation on aniline-catalyzed N-acylhydrazone formation. The reaction occurs in both two-component and three-component systems. Through systematic catalyst modifications, we are able to increase the efficiency of the DNA-templated variant to 85-fold above that of the uncatalyzed reaction at physiological pH. PMID:24590233

Domaille, Dylan W; Cha, Jennifer N

2014-04-14

435

Cu(II)-Catalyzed Olefin Migration and Prins Cyclization: Highly Diastereoselective Synthesis of Substituted Tetrahydropyrans  

PubMed Central

The metal-ligand complexes of Cu(OTf)2 with an appropriate bisphosphine ligand have been shown to effectively catalyze the formation of substituted tetrahydropyrans via a sequential olefin migration and Prins-type cyclization. This methodology provides convenient access to a variety of functionalized tetrahydropyrans in excellent diastereoselectivities and good to excellent yields. PMID:21797234

Ghosh, Arun K.; Nicponski, Daniel R.

2011-01-01

436

Tyrosinase-Catalyzed Synthesis of a Universal Coil-Chitosan Bioconjugate for Protein Immobilization  

E-print Network

that Kcoil peptide was covalently grafted to amines of chitosan. The ability of Kcoil-chitosan conjugate, demonstrating that grafting to chitosan did not negatively impact binding characteristics of Kcoil peptideTyrosinase-Catalyzed Synthesis of a Universal Coil-Chitosan Bioconjugate for Protein Immobilization

Buschmann, Michael

437

Palladium-Catalyzed Synthesis of Six-Membered Benzofuzed Phosphacycles via Carbon-Phosphorus Bond Cleavage.  

PubMed

The palladium-catalyzed synthesis of dibenzofused six-membered phosphacycles via carbon-phosphorus bond cleavage is developed. This method is compatible with a range of functional groups, such as esters, amides, and carbamates, which is in sharp contrast to the limitations of the classical method using organolithium reagents. PMID:25521158

Baba, Katsuaki; Tobisu, Mamoru; Chatani, Naoto

2015-01-01

438

Acetylcholinesterase-Catalyzed Hydrolysis Allows Ultrasensitive Detection of Pathogens with the Naked Eye**  

PubMed Central

This paper describes a rapid diagnostic platform for pathogen detection based on the acetylcholinesterase-catalyzed hydrolysis reaction. Owing to the signal amplification strategies, the sensitivity of this assay is comparable to that of PCR. In addition, the readout of this assay is based on the color change of solutions, which can be easily observed by the naked eye alone. PMID:24155243

Liu, Dingbin; Wang, Zhantong; Jin, Albert; Huang, Xinglu; Sun, Xiaolian; Wang, Fu; Yan, Qiang; Ge, Shengxiang; Xia, Ningshao; Niu, Gang; Liu, Gang; HightWalker, A. R.

2013-01-01

439

Rhodium-complex-catalyzed addition reactions of chloroacetyl chlorides to alkynes.  

PubMed

The addition reaction of chloroacetyl chloride derivatives with terminal alkynes was found to be catalyzed by Rh(acac)(CO)(AsPh(3)) to afford (Z)-1,4-dichloro-3-buten-2-one derivatives, which displayed diverse reactivities in synthetic elaboration. PMID:18991444

Kashiwabara, Taigo; Fuse, Kouichiro; Hua, Ruimao; Tanaka, Masato

2008-12-01

440

Characterization of fatty amides produced by lipase-catalyzed amidation of multihydroxylated fatty acids  

Technology Transfer Automated Retrieval System (TEKTRAN)

Novel multi-hydroxylated primary fatty amides produced by direct amidation of 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) and 7,10,12-trihydroxy-8(E)-octadecenoic acid (TOD) were characterized by GC-MS and NMR. The amidation reactions were catalyzed by immobilized Pseudozyma (Candida) antarctica li...

441

Enzyme-catalyzed Oxidation Facilitates the Return of Fluorescence for Single-Walled Carbon Nanotubes  

PubMed Central

In this work, we studied enzyme-catalyzed oxidation of single-walled carbon nanotubes (SWCNTs) produced by the high-pressure carbon monoxide (HiPco) method. While oxidation via strong acids introduced defects sites on SWCNTs and suppressed their near-infrared (NIR) fluorescence, our results indicated that the fluorescence of SWCNTs was restored upon enzymatic oxidation, which provided new evidence that the reaction catalyzed by horseradish peroxidase (HRP) in the presence of H2O2 is mainly a defect-consuming step. These results were further supported by both UV-vis-NIR and Raman spectroscopy. Therefore, employing acid oxidation followed by HRP-catalyzed enzyme oxidation, shortened (< 300 nm in length) and NIR-fluorescent SWCNTs were produced. In contrast, when treated with myeloperoxidase (MPO), H2O2, and NaCl, the oxidized HiPco SWCNTs underwent complete oxidation (i.e. degradation). The shortened, NIR-fluorescent SWCNTs resulting from HRP-catalyzed oxidation of acid cut HiPco SWCNTs may find applications in cellular NIR imaging and drug delivery systems. PMID:23672715

Chiu, Cheuk Fai; Barth, Brian A.; Kotchey, Gregg P.; Zhao, Yong; Gogick, Kristy A.; Saidi, Wissam A.; Petoud, Stéphane; Star, Alexander

2013-01-01

442

Catalyzing mass production of solar photovoltaic cells using university driven green  

Microsoft Academic Search

Purpose - The purpose of this paper is to explore the use of the purchase power of the higher education system to catalyze the economy of scale necessary to ensure market competitiveness for solar photovoltaic electricity. Design\\/methodology\\/approach - The approach used here was to first determine the demand necessary to construct \\

Joshua M. Pearce

443

Catalyzing mass production of solar photovoltaic cells using university driven green purchasing  

Microsoft Academic Search

Purpose – The purpose of this paper is to explore the use of the purchase power of the higher education system to catalyze the economy of scale necessary to ensure market competitiveness for solar photovoltaic electricity. Design\\/methodology\\/approach – The approach used here was to first determine the demand necessary to construct “Solar City factories”, factories that possess equipment and processes

Joshua M. Pearce

2006-01-01

444

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones  

PubMed Central

Summary 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 has been carried out. PMID:23766795

Quirós, M Teresa; Fernández, Israel

2013-01-01

445

Highly efficient addition of activated methylene compounds to alkenes catalyzed by gold and silver.  

PubMed

A highly efficient intermolecular addition of 1,3-diketones to alkenes catalyzed by AuCl3/AgOTf was developed. A mechanistic rationale for the reaction has been proposed via a alpha-C-H activation. PMID:15174855

Yao, Xiaoquan; Li, Chao-Jun

2004-06-01

446

Aminofluorination of 2-alkynylanilines: a Au-catalyzed entry to fluorinated indoles  

PubMed Central

Summary The scope and limitations of gold-catalyzed tandem cycloisomerization/fluorination reactions of unprotected 2-alkynylanilines to have access to 3,3-difluoro-2-aryl-3H-indoles and 3-fluoro-2-arylindoles are described. An unprecedented aminoauration/oxidation/fluorination cascade reaction of 2-alkynylanilines bearing a linear alkyl group on the terminal triple bond is reported. PMID:24605165

Pietropaolo, Emanuela; Alvino, Antonello

2014-01-01

447

Chiral (Acyclic Diaminocarbene)Gold(I)-Catalyzed Dynamic Kinetic Asymmetric Transformation of Propargyl Esters  

PubMed Central

A highly enantioselective transformation catalyzed by chiral (acyclic diaminocarbene)gold(I) complexes is reported. The enantioselective synthesis of 2-substituted chromenyl pivalates from racemic phenol-substituted propargyl pivalates was developed. Rearrangement of the substrates in the presence of cationic gold gave allene intermediates, whose cyclization resulted in formation of enantioenriched product through a dynamic kinetic asymmetric transformation. PMID:21797265

Wang, Yi-Ming; Kuzniewski, Christian N.; Rauniyar, Vivek; Hoong, Christina; Toste, F. Dean

2013-01-01

448

?–Aryl-Substituted Allenamides in an Imino-Nazarov Cyclization Cascade Catalyzed by Au(I)  

PubMed Central

An imino-Nazarov cyclization using ?–aryl-substituted allenamides is described. This gold(I)-catalyzed cascade is efficient and regioselective in constructing a diverse array of synthetically useful aromatic-ring fused cyclopentenamides. The success in this transformation represents a solution to the challenge in establishing an imino-Nazarov cyclization process. PMID:23121692

Ma, Zhi-Xiong; He, Shuzhong; Song, Wangze

2012-01-01

449

Development of the Pictet-Spengler reaction catalyzed by AuCl3/AgOTf.  

PubMed

Mild and efficient AuCl3/AgOTf-catalyzed Pictet-Spengler reactions were developed to afford in good yields a variety of tetrahydroisoquinoline and tetrahydro-beta-carboline ring systems, which constitute important motifs in biologically active natural and synthetic organic compounds. PMID:16526809

Youn, So Won

2006-03-17

450

Stereoretentive Pd-catalyzed Kumada-Corriu couplings of alkenyl halides at room temperature.  

PubMed

Stereoselective palladium-catalyzed Kumada-Corriu reactions of functionalized alkenyl halides and a variety of Grignard reagents, including those bearing ?-hydrogen atoms and sensitive functional groups, can be carried out at room temperature using a new combination of reagents. PMID:25102436

Krasovskiy, Arkady L; Haley, Stephen; Voigtritter, Karl; Lipshutz, Bruce H

2014-08-15

451

Transition metal-catalyzed oxidation of atmospheric sulfur: Global implications for the sulfur budget  

E-print Network

the atmosphere by oxidation of SO2, which is itself directly emitted (fossil fuel combustion, industrial measurements of sulfate aerosol collected in Alert, Canada, are not consistent with O3 as the dominant oxidant importance of sulfate production by Fe(III)- and Mn(II)-catalyzed oxidation of S(IV) by O2. We scale

Alexander, Becky

452

Modification of vegetable oils. VII. Alkali catalyzed interesterification of peanut oil with ethanol  

Microsoft Academic Search

HE alkali-catalyzed displacement of the glycerol in a fat by methanol or ethanol is an important reaction in fat and oil technology. Besides producing monoesters for use as such, the reaction simplifies the manufacture of some soaps, especially anhydrous soaps (2, 3); and it is valuable in conjunction with processes for fraetionating fatty acids. Potentially the reaction is important in

R. O. Feuge; Audrey T. Gros

1949-01-01

453

Enantioselective Functionalization of Radical Intermediates in Redox Catalysis: Copper-Catalyzed Asymmetric Oxytrifluoromethylation of Alkenes**  

PubMed Central

A method for the efficient enantioselective oxytrifluoromethylation of alkenes has been developed using a copper catalyst system. Mechanistic studies are consistent with a metal-catalyzed redox radical addition mechanism, in which a C–O bond is formed via the copper-mediated enantioselective trapping of a prochiral alkyl radical intermediate derived from the initial trifluoromethyl radical addition. PMID:24133010

Zhu, Rong

2013-01-01

454

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

PubMed Central

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

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

2012-01-01

455

Textured catalysts, methods of making textured catalysts, and methods of catalyzing reactions conducted in hydrothermal conditions  

DOEpatents

A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

Werpy, Todd [West Richland, WA; Wang, Yong [Richland, WA

2003-12-30

456

The action of iron particles at catalyzed hydrogenation of {100} and {110} faces of synthetic diamond  

Microsoft Academic Search

Results of treatment of {100} and {110} faces of synthetic diamond with dispersed iron at catalyzed hydrogenation are presented. The experiments were held at a temperature of 900 °C in flow hydrogen medium. The regular behavior of iron particles on the surface of diamond crystals was established. It was found that breaking of –C–C- bonds in diamond during its dissolution

V. M. Sonin; A. I. Chepurov; I. I. Fedorov

2003-01-01

457

Ellagitannin biosynthesis: laccase-catalyzed dimerization of tellimagrandin II to cornusiin E in Tellima grandiflora  

Microsoft Academic Search

A new laccase (EC 1.10.3.2)-type phenol oxidase has been purified from leaves of Tellima grandiflora (fringe cups, Saxifragaceae) that catalyzed the O2-dependent coupling of two tellimagrandin II molecules to the dimeric ellagitannin, cornusiin E.

Ruth Niemetz; Georg G. Gross

2003-01-01

458

9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica  

E-print Network

9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica 9482 Identifying, and Mario J. Molina (see pages 9422­9427) CHEMISTRY Fusing silk and silica An engineered protein combining the flexibility and tensile strength of spider silk with the resilience of silica has been developed. The result

McFadden, Geoff

459

TfOH-catalyzed synthesis of 3-aryl isoindolinones via a tandem reaction.  

PubMed

A convenient metal-free method for the synthesis of 3-aryl isoindolinones via TfOH catalyzed aromatic C-H functionalization of electron-rich arenes with 2-formylbenzonitriles is developed. This process provided a new efficient strategy for the synthesis of isoindolinone derivatives in good to high yields and regioselectivities by forming two bonds. PMID:25370938

Hu, Jiaxing; Qin, Hua-Li; Xu, Wengang; Li, Junli; Zhang, Fanglin; Zheng, Hua

2014-12-25

460

Molecular dynamics simulations of gold-catalyzed growth of silicon bulk crystals and nanowires  

E-print Network

ARTICLES Molecular dynamics simulations of gold-catalyzed growth of silicon bulk crystals with Au­Si liquids is studied by molecular dynamics simulations using an empirical potential fitted of the NW nucleation and growth mechanisms at the atomistic level. Atomistic simulations, such as molecular

Cai, Wei

461

A proposed mechanism for Pt/SnO(x)-catalyzed CO oxidation  

NASA Technical Reports Server (NTRS)

A mechanism for Pt/SnO(x)-catalyzed CO oxidation is proposed, which is consistent with a broad range of experimental observations. CO oxidation catalysts with high activity at or near room temperature are used in closed-cycle CO2 lasers and air purification.

Schryer, David R.; Upchurch, Billy T.; Sidney, Barry D.; Brown, Kenneth G.; Hoflund, Gar B.; Herz, Richard K.

1991-01-01

462

Regioselective Ruthenium Catalyzed Hydrohydroxyalkylation of Dienes with 3-Hydroxy-2-oxindoles: Prenylation, Geranylation and Beyond  

PubMed Central

The direct conversion of secondary to tertiary alcohols via ruthenium(0) catalyzed C-C coupling of substituted 3-hydroxy-2-oxindoles with various dienes is described. Coupling occurs in a completely regioselective manner in the absence of stoichiometric byproducts. PMID:23721207

Chen, Te-Yu; Krische, Michael J.

2013-01-01

463

Effective dehydrogenation of 2-pyridylmethanol derivatives catalyzed by an iron complex.  

PubMed

An unprecedented iron complex-catalyzed dehydrogenation of alcohols was achieved using CpFe(CO)2Cl with a base or CpFe(CO)(Py)(Ph) as a catalyst without sacrificing the hydrogen acceptors. This reaction effectively (up to TON 67,000) converted 2-pyridylmethanol derivatives to the corresponding ketones or aldehydes. The mechanistic study is also discussed. PMID:24740678

Kamitani, Masahiro; Ito, Masaki; Itazaki, Masumi; Nakazawa, Hiroshi

2014-07-28

464

High performance catalyzed membranes of ultra-low Pt loadings for polymer electrolyte fuel cells  

Microsoft Academic Search

This paper reports on polymer electrolyte membranes that are catalyzed by the direct application of thin film catalyst layers cast from solutions of suspended Pt\\/C catalyst and solubilized Nafion ionomer. Both the ionomeric membrane and the solubilized ionmer are in the Na{sup +} form during casting to enable higher curing temperatures, which results in more robust catalyst layers. In addition

Mahlon S. Wilson; S. Gottesfeld

1992-01-01

465

Nickel/zinc-catalyzed decarbonylative addition of anhydrides to alkynes: a DFT study.  

PubMed

Density functional theory (DFT) was used to investigate the nickel- or nickel(0)/zinc- catalyzed decarbonylative addition of phthalic anhydrides to alkynes. All intermediates and transition states were optimized completely at the B3LYP/6-31+G(d,p) level. Calculated results indicated that the decarbonylative addition of phthalic anhydrides to alkynes was exergonic, and the total free energy released was -87.6 kJ mol(-1). In the five-coordinated complexes M4a and M4b, the insertion reaction of alkynes into the Ni-C bond occurred prior to that into the Ni-O bond. The nickel(0)/zinc-catalyzed decarbonylative addition was much more dominant than the nickel-catalyzed one in whole catalytic decarbonylative addition. The reaction channel CA?M1'?T1'?M2'?T2'?M3a'?M4a'?T3a1'?M5a1' ?T4a1'?M6a'?P was the most favorable among all reaction pathways of the nickel- or nickel(0)/zinc- catalyzed decarbonylative addition of phthalic anhydrides to alkynes. And the alkyne insertion reaction was the rate-determining step for this channel. The additive ZnCl2 had a significant effect, and it might change greatly the electron and geometry structures of those intermediates and transition states. On the whole, the solvent effect decreased the free energy barriers. PMID:23955705

Meng, Qingxi; Li, Ming

2013-10-01

466

Mechanism of alkane dehydrogenation catalyzed by acidic zeolites: Ab initio transition path sampling  

E-print Network

Mechanism of alkane dehydrogenation catalyzed by acidic zeolites: Ab initio transition path alkanes have been studied rather frequently. As these reactions yield rather small number of different elementary step. Dehydrogenation of short alkanes belongs to simple re- actions studied to learn more about C

Dellago, Christoph

467

Copper-catalyzed enantioselective Friedel-Crafts alkylation of pyrrole with isatins.  

PubMed

The highly enantioselective Friedel-Crafts alkylation of pyrrole with isatins catalyzed by the tridentate Schiff base/Cu catalyst was developed. Hexafluoroisopropanol (HFIP) was used as a crucial additive to improve the enantioselectivity. In the case of N-unprotected isatins, an innovative substrate slow-releasing strategy was applied by virtue of a Henry/retro-Henry reaction. PMID:24912009

Li, Chong; Guo, Fengfeng; Xu, Kun; Zhang, Sheng; Hu, Yanbin; Zha, Zhenggen; Wang, Zhiyong

2014-06-20

468

The Lewis acid catalyzed synthesis of hyperbranched Oligo(glycerol-diacid)s in aprotic polar media  

Technology Transfer Automated Retrieval System (TEKTRAN)

The Lewis-acid, titanium (IV) butoxide (15% (w/w; catalyst/reactants)), was used to catalyze the condensation of 0.05 mol glycerol with 0.10 mol of either succinic acid, glutaric acid, or azelaic acid to produce oligomers. The reactions were refluxed in dilute solutions of dimethylsulfoxide (DMSO) o...

469

DIPLOMA!WORK!(201412015)! Membrane! protein! transporters! catalyze! fundamental! cellular! processes! and! are!  

E-print Network

! ! DIPLOMA!WORK!(201412015)! ! Membrane! protein! transporters! catalyze! fundamental! cellular'Structural'&'Molecular'Biology,!2013)!and!Znta!(Wang!et!al.!Nature,!2014),!and! follow1up!work!is!already!in!progress.!As!part!of!our!research!team!the!diploma!is!long1term,!a!dedicated!diploma!worker!naturally!becomes!a!possible!candidate! for

Uppsala Universitet

470

Efficient copper-catalyzed trifluoromethylation of aromatic and heteroaromatic iodides: the beneficial anchoring effect of borates.  

PubMed

Efficient copper-catalyzed trifluoromethylation of aromatic iodides was achieved with TMSCF3 in the presence of trimethylborate. The Lewis acid was used to anchor the in situ generated trifluoromethyl anion and suppress its rapid decomposition. Broad applicability of the new trifluoromethylating reaction was demonstrated in the functionalization of different aromatic and heteroaromatic iodides. PMID:25068681

Gonda, Zsombor; Kovács, Szabolcs; Wéber, Csaba; Gáti, Tamás; Mészáros, Attila; Kotschy, András; Novák, Zoltán

2014-08-15

471

Palladium-catalyzed annulation of alkynes with ortho-halide-containing benzyl alcohols in aqueous medium.  

PubMed

The Pd-catalyzed annulations of ortho-halide-containing benzyl alcohols with alkynes for the synthesis of indenones were achieved in aqueous Triton X-100 micelles with good yields and wide substrate scopes. Moreover, the indenones obtained in this procedure can be further functionalized to form some more synthetic useful derivatives via an environmental-friendly way. PMID:25310371

Feng, Jie; Lu, Guoping; Lv, Meifang; Cai, Chun

2014-11-01

472

Copper-catalyzed aerobic aliphatic C–H oxygenation with hydroperoxides  

PubMed Central

Summary We report herein Cu-catalyzed aerobic oxygenation of aliphatic C–H bonds with hydroperoxides, which proceeds by 1,5-H radical shift of putative oxygen-centered radicals (O-radicals) derived from hydroperoxides followed by trapping of the resulting carbon-centered radicals with molecular oxygen. PMID:23843917

Too, Pei Chui; Tnay, Ya Lin

2013-01-01

473

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

PubMed

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

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

2013-12-01

474

Gold(III)-catalyzed three-component coupling reaction (TCC) selective toward furans.  

PubMed

An efficient three-component coupling reaction toward a variety of furan derivatives has been developed. This cascade transformation proceeds via the gold-catalyzed coupling reaction of phenylglyoxal derivatives, secondary amines, and terminal alkynes, under the reaction conditions, that undergoes cyclization into the furan core. PMID:23687935

Li, Jian; Liu, Li; Ding, Dong; Sun, Jiangtao; Ji, Yangxuan; Dong, Jialing

2013-06-01

475

Palladium(II)-catalyzed dehydrogenative alkenylation of cyclic enaminones via the Fujiwara-Moritani reaction.  

PubMed

A new Pd(II)-catalyzed dehydrogenative alkenylation reaction involving two alkenes was developed. A variety of nonaromatic, cyclic enaminones were successfully coupled to primary and secondary alkenes yielding a series of unique 1,3-dienes. The generality of this transformation presents a useful strategy for directly cross-coupling alkenes and offers an attractive new approach to functionalize enaminones. PMID:21995751

Yu, Yi-Yun; Niphakis, Micah J; Georg, Gunda I

2011-11-01

476

Lipase-catalyzed synthesis of acetylated EGCG and antioxidant properties of the acetylated derivatives  

Technology Transfer Automated Retrieval System (TEKTRAN)

(-)-Epigallocatechin-3-O-gallate (EGCG) acetylated derivatives were prepared by lipase catalyzed acylation of EGCG with vinyl acetate to improve its lipophilicity and expand its application in lipophilic media. The immobilized lipase, Lipozyme RM IM, was found to be the optimum catalyst. The optimiz...

477

A New Copper-Catalyzed [3 + 2] Cycloaddition: Enantioselective Coupling of Terminal Alkynes with Azomethine Imines To Generate Five-Membered  

E-print Network

A New Copper-Catalyzed [3 + 2] Cycloaddition: Enantioselective Coupling of Terminal Alkynes(I)-catalyzed 1,3-dipolar cycloadditions to terminal alkyness presumably proceeding via a copper acetylideshave, copper-catalyzed processes can overcome the poor regioselectivity observed in some of the corresponding

Fu, Gregory C.

478

Calreticulin enhances B2 bradykinin receptor maturation and heterodimerization  

Microsoft Academic Search

In different native tissues and cells the receptor for the vasodepressor bradykinin, B2, forms dimers with the receptor for the vasopressor angiotensin II, AT1. Because AT1\\/B2 heterodimers may contribute to enhanced angiotensin II-stimulated signaling under pathophysiological conditions, we analyzed mechanisms of AT1\\/B2 heterodimerization. We found that efficient B2 receptor maturation was a prerequisite for heterodimerization because only the fully mature

Joshua Abd Alla; Kristin Reeck; Andreas Langer; Thomas Streichert; Ursula Quitterer

2009-01-01

479

Construction of dispirocyclohexanes via amine-catalyzed [2 + 2 + 2] annulations of Morita-Baylis-Hillman acetates with exocyclic alkenes.  

PubMed

Amine-catalyzed [2 + 2 + 2] annulations of one molecule of Morita-Baylis-Hillman (MBH) acetates 1 with two molecules of 2-(arylmethylidene)indane-1,3-diones 2 or methyleneindolinones 4 have been developed under very mild conditions, which produce multistereogenic dispirocyclohexanes 3 and 5, respectively, in moderate to excellent yields and good diastereoselectivity. This amine-catalyzed annulation constitutes a novel and efficient method for the construction of dispirocyclohexane motifs, and also showcases the divergent catalysis between amines and phosphines with regard to the corresponding phosphine-catalyzed [3 + 2] annulations. PMID:25369534

Chen, Rongshun; Xu, Silong; Fan, Xia; Li, Hanyuan; Tang, Yuhai; He, Zhengjie

2015-01-14

480

Particle growth by acid-catalyzed heterogeneous reactions of organic carbonyls on preexisting aerosols.  

PubMed

Aerosol growth by the heterogeneous reactions of different aliphatic and alpha,beta-unsaturated carbonyls in the presence/absence of acidified seed aerosols was studied in a 2 m long flow reactor (2.5 cm i.d.) and a 0.5-m3 Teflon film bag under darkness. For the flow reactor experiments, 2,4-hexadienal, 5-methyl-3-hexen-2-one, 2-cyclohexenone, 3-methyl-2-cyclopentenone, 3-methyl-2-cyclohexenone, and octanal were studied. The carbonyls were selected based on their reactivity for acid-catalyzed reactions, their proton affinity, and their similarity to the ring-opening products from the atmospheric oxidation of aromatics. To facilitate acid-catalyzed heterogeneous hemiacetal/acetal formation, glycerol was injected along with inorganic seed aerosols into the flow reactor system. Carbonyl heterogeneous reactions were accelerated in the presence of acid catalysts (H2SO4), leading to higher aerosol yields than in their absence. Aldehydes were more reactive than ketones for acid-catalyzed reactions. The conjugated functionality also resulted in higher organic aerosol yieldsthan saturated aliphatic carbonyls because conjugation with the olefinic bond increases the basicity of the carbonyl leading to increased stability of the protonated carbonyl. Aerosol population was measured from a series of sampling ports along the length of the flow reactor using a scanning mobility particle sizer. Fourier transform infrared spectrometry of either an impacted liquid aerosol layer or direct reaction of carbonyls as a thin liquid layer on a zinc selenide FTIR disk was employed to demonstrate the direct transformation of chemical functional groups via the acid-catalyzed reactions. These results strongly indicate that atmospheric multifunctional organic carbonyls, which are created by atmospheric photooxidation reactions, can contribute significantly to secondary organic aerosol formation through acid-catalyzed heterogeneous reactions. Exploratory studies in 25- and 190-m3 outdoor chambers were also implemented to demonstrate the formation of high molecular weight organic structures. The reaction of ozone with alpha-pinene to generate secondary organic aerosols (SOAs) was performed in the presence of background aerosol consisting of a mixture of wood soot and diesel soot. Results strongly suggest that indigenous sulfuric acid associated with the combustion of fossil fuels (e.g., diesel soot) can initiate acid-catalyzed heterogeneous reactions of SOAs on the particle phase. PMID:12967102

Jang, Myoseon; Carroll, Brian; Chandramouli, Bharadwaj; Kamens, Richard M

2003-09-01

481

A recyclable and reusable supported Cu(I) catalyzed azide-alkyne click polymerization  

PubMed Central

The azide–alkyne click polymerization (AACP) has emerged as a powerful tool for the synthesis of functional polytriazoles. While, for the Cu(I)-catalyzed AACP, the removal of the catalytic Cu(I) species from the resulting polytriazoles is difficult, and the research on the recyclability and reusability of the catalyst remains intact. Herein, we reported the first example of using recyclable and reusable supported Cu(I) catalyst of CuI@A-21 for the AACP. CuI@A-21 could not only efficiently catalyze the AACP but also be reused for at least 4 cycles. Moreover, pronounced reduction of copper residues in the products was achieved. Apart from being a green and cost-effective polymer synthesis strategy, this method will also broaden the application of AACP in material and biological sciences and provide guidelines for other polymerizations with metal catalysts. PMID:24875854

Wu, Haiqiang; Li, Hongkun; Kwok, Ryan T. K.; Zhao, Engui; Sun, Jing Zhi; Qin, Anjun; Tang, Ben Zhong

2014-01-01

482

Synthesis of phenanthridines via palladium-catalyzed picolinamide-directed sequential C–H functionalization  

PubMed Central

Summary We report a new synthesis of phenanthridines based on palladium-catalyzed picolinamide-directed sequential C–H functionalization reactions starting from readily available benzylamine and aryl iodide precursors. Under the catalysis of Pd(OAc)2, the ortho-C–H bond of benzylpicolinamides is first arylated with an aryl iodide. The resulting biaryl compound is then subjected to palladium-catalyzed picolinamide-directed intramolecular dehydrogenative C–H amination with PhI(OAc)2 oxidant to form the corresponding cyclized dihydrophenanthridines. The benzylic position of these dihydrophenanthridines could be further oxidized with Cu(OAc)2, removing the picolinamide group and providing phenathridine products. The cyclization and oxidation could be carried out in a single step and afford phenathridines in moderate to good yields. PMID:23766804

Pearson, Ryan; Zhang, Shuyu; He, Gang; Edwards, Nicola

2013-01-01

483

Advances in transition metal-catalyzed asymmetric hydrogenation of heteroaromatic compounds.  

PubMed

Transition metal-catalyzed asymmetric hydrogenation of heteroaromatic compounds is undoubtedly a straightforward and environmentally friendly method for the synthesis of a wide range of optically active heterocyclic compounds, which are widespread and ubiquitous in naturally occurring and artificial bioactive molecules. Over the past decade, a number of transition metal (Ir, Rh, Ru, and Pd) catalysts bearing chiral phosphorus ligands, amine-tosylamine ligands, and N-heterocyclic carbene ligands have been developed for such challenging transformation. This review will describe the significant contributions concerning the transition metal-catalyzed asymmetric hydrogenation of N-, O-, and S-containing heteroaromatic compounds, with emphasis on the evolution of different chiral ligands, related catalyst immobilization, and mechanism investigations. PMID:24173671

He, Yan-Mei; Song, Feng-Tao; Fan, Qing-Hua

2014-01-01

484

Estimation of rate constants in lysozyme-catalyzed reaction of chitooligosaccharides.  

PubMed

The rate constants of the cleavage of glycoside linkage, hydration (hydrolysis) and transglycosylation in a lysozyme-catalyzed reaction of substrate chitooligosaccharides were evaluated by computer analysis of the experimentally obtained reaction time-courses. In the computer analysis, the rate equation was numerically solved by use of the known binding constants for each subsite. Because of the complexity of the lysozyme-catalyzed reaction, optimal values of rate constants were determined by checking the sensitivity of each rate constant to the computed time-courses. It was not possible to estimate uniquely the rate constants for transglycosylation and hydration, owing to the nature of the enzymatic reaction, but it was possible to estimate accurately their ratio. The estimated values were 0.94 s-1 for the rate constant for the cleavage of glycosidic linkage and 133 for the ratio of rate constants of transglycosylation and hydration. PMID:7309713

Masaki, A; Fukamizo, T; Otakara, A; Torikata, T; Hayashi, K; Imoto, T

1981-10-01

485

Entropy is Key to the Formation of Pentacyclic Terpenoids by Enzyme-Catalyzed Polycyclization.  

PubMed

Polycyclizations constitute a cornerstone of chemistry and biology. Multicyclic scaffolds are generated by terpene cyclase enzymes in nature through a carbocationic polycyclization cascade of a prefolded polyisoprene backbone, for which electrostatic stabilization of transient carbocationic species is believed to drive catalysis. Computational studies and site-directed mutagenesis were used to assess the contribution of entropy to the polycyclization cascade catalyzed by the triterpene cyclase from A. acidocaldarius. Our results show that entropy contributes significantly to the rate enhancement through the release of water molecules through specific channels. A single rational point mutation that results in the disruption of one of these water channels decreased the entropic contribution to catalysis by 60?kcal?mol(-1) . This work demonstrates that entropy is the key to enzyme-catalyzed polycyclizations, which are highly relevant in biology since 90?% of all natural products contain a cyclic subunit. PMID:24711227

Syrén, Per-Olof; Hammer, Stephan C; Claasen, Birgit; Hauer, Bernhard

2014-05-01

486

Tracking the catalyzed growth process of nanowires by in situ x-ray diffraction  

NASA Astrophysics Data System (ADS)

Quasi-one-dimensional nanostructures of silicon, oxides, and other materials show great promise for a variety of applications. These nanostructures are commonly grown using metal catalyst nanoparticles. This paper investigates the growth mechanism of Au-catalyzed Si nanowires through in situ x-ray diffraction, and the results are compared to previously studied Au-catalyzed ZnO nanorods. The Si nanowires were found to grow from molten catalyst particles, however, the ZnO nanorods were found to grow from solid catalyst particles through a surface diffusion process. From this comparison, the relative bonding types of the catalyst and source material are determined to have a significant effect on the growth mechanism.

Kirkham, Melanie; Wang, Zhong Lin; Snyder, Robert L.

2010-07-01

487

Kinetics of gas-phase hydrolysis of ethyl acetate catalyzed by immobilized lipase.  

PubMed

Reactions catalyzed by supported enzymes present important advantages when compared with those in aqueous media or organic solvents: separation of enzymes from substrate is easily accomplished, enzyme stability may be improved, and control of the reaction products is more accurate. We present the experimental results of the kinetic study of ethyl acetate hydrolysis in gaseous phase catalyzed by a commercial immobilized lipase (Lipozyme IM; Novo Nordisk). The hydrolysis reaction was studied as a function of ethyl ester and water partial pressure at a constant temperature of 318 K. The amount of biocatalyst used was varied between 100 and 300 mg, and the reaction was studied in a flow-through glass microreactor. Under the conditions used, water was an important parameter in the gas-phase reaction. Activation energy was 24.8 kJ/mol and the overall order of reaction was one. Finally, a Bi-Bi reaction mechanism is proposed. PMID:17416975

Perez, Victor H; Miranda, Everson A; Valença, Gustavo P

2007-01-01

488

Recent advances in transition metal-catalyzed Csp2-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation  

PubMed Central

Summary In the last few years, transition metal-mediated reactions have joined the toolbox of chemists working in the field of fluorination for Life-Science oriented research. The successful execution of transition metal-catalyzed carbon–fluorine bond formation has become a landmark achievement in fluorine chemistry. This rapidly growing research field has been the subject of some excellent reviews. Our approach focuses exclusively on transition metal-catalyzed reactions that allow the introduction of –CFH2, –CF2H, –CnF2 n +1 and –SCF3 groups onto sp² carbon atoms. Transformations are discussed according to the reaction-type and the metal employed. The review will not extend to conventional non-transition metal methods to these fluorinated groups. PMID:24367416

Landelle, Grégory; Panossian, Armen; Pazenok, Sergiy; Vors, Jean-Pierre

2013-01-01

489

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

PubMed

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

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

2012-06-01

490

Kinetic study of the oxidation of 4-hydroxyanisole catalyzed by tyrosinase.  

PubMed

Despite the importance of the substrate 4-hydroxyanisole in melanoma therapy, the kinetics of its oxidation catalyzed by tyrosinase has never been properly characterized. This approach is reported here for the first time. The applicability to 4-hydroxyanisole of the reaction mechanism of tyrosinase previously proposed for other monophenols has been corroborated. The Michaelis constant for the oxidation of 4-hydroxyanisole catalyzed by mushroom tyrosinase was (62 +/- 1.5) microM at pH 7 and increased when the pH decreased, reaching a value of (195 +/- 5) microM at pH 5.5. However the maximum steady-state rate, whose value was (0.54 +/- 0.01) microM/min, did not change with the pH. The apparent catalytic constant was (184 +/- 5) s-1, around twenty three times higher than that previously described for L-tyrosine (8 s-1). PMID:9161722

Espín, J C; Varón, R; Tudela, J; García-Cánovas, F

1997-05-01

491

Rubber muscle actuation with pressurized CO2 from enzyme-catalyzed urea hydrolysis  

NASA Astrophysics Data System (ADS)

A biologically inspired pneumatic pressure source was designed and sized to supply high pressure CO2(g) to power a rubber muscle actuator. The enzyme urease served to catalyze the hydrolysis of urea, producing CO2(g) that flowed into the actuator. The actuator’s power envelope was quantified by testing actuator response on a custom-built linear-motion rig. Reaction kinetics and available work density were determined by replacing the actuator with a double-action piston and measuring volumetric gas generation against a fixed pressure on the opposing piston. Under the conditions investigated, urease catalyzed the generation of up to 0.81 MPa (117 psi) of CO2(g) in the reactor headspace within 18 min, and the evolved gas produced a maximum work density of 0.65 J ml-1.

Sutter, Thomas M.; Dickerson, Matthew B.; Creasy, Terry S.; Justice, Ryan S.

2013-09-01

492

Surface-modified carbon nanotubes catalyze oxidative dehydrogenation of n-butane.  

PubMed

Butenes and butadiene, which are useful intermediates for the synthesis of polymers and other compounds, are synthesized traditionally by oxidative dehydrogenation (ODH) of n-butane over complex metal oxides. Such catalysts require high O2/butane ratios to maintain the activity, which leads to unwanted product oxidation. We show that carbon nanotubes with modified surface functionality efficiently catalyze the oxidative dehydrogenation of n-butane to butenes, especially butadiene. For low O2/butane ratios, a high selectivity to alkenes was achieved for periods as long as 100 hours. This process is mildly catalyzed by ketonic CO groups and occurs via a combination of parallel and sequential oxidation steps. A small amount of phosphorus greatly improved the selectivity by suppressing the combustion of hydrocarbons. PMID:18832641

Zhang, Jian; Liu, Xi; Blume, Raoul; Zhang, Aihua; Schlögl, Robert; Su, Dang Sheng

2008-10-01

493

Iridium Catalyzed Dehydrogenation of Substituted Amine Boranes: Kinetics, Thermodynamics and Implications for Hydrogen Storage.  

SciTech Connect

Dehydrogenation of ammonia borane (AB) and methylamine-borane (MeAB) is catalyzed efficiently by the iridium pincer complex (?3-1,3-(OPtBu2)2C6H3)Ir(H)2 (1). With MeAB and with MeAB/AB mixtures, rapid release of one equivalent of H2 is observed to yield soluble oligomeric products at rates similar to those previously reported for the dehydrogenation of AB catalyzed by 1. The rapid dehydrogenation reaction has allowed the experimental determination of the reaction enthalpy (?H) for the dehydrogenation of AB, MeAB, and AB/MeAB mixtures by calorimetry. The reactions are significantly more exothermic than suggested by some computational studies. This work was supported by the U.S. Department of Energy (DOE) as part of the Center of Excellence for Chemical Hydrogen Storage. PNNL is operated by Battelle for DOE.

Dietrich, Brandon L.; Goldberg, Karen I.; Heinekey, D. M.; Autrey, Thomas; Linehan, John C.

2008-10-06

494

CF?I synthesis catalyzed by activated carbon: a density functional theory study.  

PubMed

A revised reaction mechanism of CF3I synthesis catalyzed by activated carbon is investigated with quantum chemistry methods using density functional theory (DFT). The adsorption configurations of possible intermediates are carefully examined. The reaction pathway and related transition states are also analyzed. According to our calculations, first, the dehydrofluorination of CHF3 is catalyzed by -COOH groups, which possesses the highest barrier and is accordingly identified as the rate-determining step. Second, the difluorocarbene disproportionation over graphite (001) surface proceeds instead of dimerization. The next reaction steps involving the association of fluoromethine and trifluoromethyl, the fluorine abstractions between intermediates and the iodine abstractions by the desorbed CF3 and CF2CF3 from molecular iodine are also feasible over graphite (001) surfaces. It is also found that the coke deposition in experiments is due to the fluorine abstraction from fluoromethine. This revised mechanism is in agreement with available experimental data and our theoretical computations. PMID:24491216

Hu, Yingjie; Wu, Taiping; Liu, Weizhou; Zhang, Liyang; Pan, Renming

2014-03-13

495

Palladium(II)-Catalyzed Intramolecular Tandem Aminoalkylation via Divergent C(sp(3))-H Functionalization.  

PubMed

We have developed a Pd(II)-catalyzed oxidative tandem aminoalkylation via divergent C(sp(3))-H functionalization, affording three- and five-membered-ring fused indolines in good yields under two optimized conditions, respectively. The mechanism studies have indicated that the benzylic C-H cleavage involved in the former transformation is the rate-determining step, while the cleavage of amide ?-C-H in the latter is not. This is the first example of a Pd-catalyzed tandem reaction involving C(sp(3))-H activation without the employment of prefunctionalized reagents (e.g., halogenated and boron reagents) and directing groups, representing a green and economic protocol for the construction of N-containing heterocycles. PMID:25541675

Du, Wei; Gu, Qiangshuai; Li, Zhongliang; Yang, Dan

2015-01-28

496

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

PubMed Central

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

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

2012-01-01

497

Diastereoselective osmium-catalyzed vicinal oxyamination of acyclic allylic alcohol derivatives.  

PubMed

The osmium-catalyzed oxyamination of chiral acyclic allylic alcohol derivatives bearing mono- and 1,1-di-substituted double bonds with benzyl N-(4-tosyloxy)carbamate proceeds with high regioselectivity and moderate levels of diastereoselectivity favoring the anti product. The observed stereoselectivity shows a clear and systematic trend with anti:syn ratios increasing in line with the size of substituent at both the allylic stereocenter and double bond ?-carbon. The stereoinduction is in accord with the sense of diastereoselectivity predicted by Kishi's empirical rule and a previously reported transition state model for the osmium-catalyzed dihydroxylation of allylic alcohol derivatives. In contrast, allylic alcohol derivatives bearing trisubstituted double bonds show low or no reactivity in the oxyamination reaction affording the syn product in low yield in the cases examined. PMID:25513679

Masruri; Kanizaj, Nicholas; McLeod, Malcolm D

2014-11-01

498

Copper(I)-catalyzed amination of aryl halides in liquid ammonia.  

PubMed

The amination of aryl halides in liquid ammonia (LNH(3)) is catalyzed by a copper(I) salt/ascorbate system to yield primary aromatic amines in good to excellent yields. The low concentrations of catalyst required and the ease of product isolation suggest that this process has potential industrial applications. Commonly used ligands for analogous metal-catalyzed reactions are not effective. The rate of amination of iodobenzene in liquid ammonia is first order in copper(I) catalyst concentration. The small Hammett ? = 0.49 for the amination of 4-substituted iodobenzenes in liquid ammonia at 25 °C indicates that the C-I bond is not significantly broken in the transition state structure and that there is a small generation of negative charge in the aryl ring, which is compatible with the oxidative addition of the copper ion being rate limiting. PMID:22849292

Ji, Pengju; Atherton, John H; Page, Michael I

2012-09-01

499

Palladium-catalyzed aryl C-H olefination with unactivated, aliphatic alkenes.  

PubMed

Palladium-catalyzed coupling between aryl halides and alkenes (Mizoroki-Heck reaction) is one of the most popular reactions for synthesizing complex organic molecules. The limited availability, problematic synthesis, and higher cost of aryl halide precursors (or their equivalents) have encouraged exploration of direct olefination of aryl carbon-hydrogen (C-H) bonds (Fujiwara-Moritani reaction). Despite significant progress, the restricted substrate scope, in particular noncompliance of unactivated aliphatic olefins, has discouraged the use of this greener alternative. Overcoming this serious limitation, we report here a palladium-catalyzed chelation-assisted ortho C-H bond olefination of phenylacetic acid derivatives with unactivated, aliphatic alkenes in good to excellent yields with high regio- and stereoselectivities. The versatility of this operationally simple method has been demonstrated through drug diversification and sequential C-H olefination for synthesizing divinylbenzene derivatives. PMID:25188679

Deb, Arghya; Bag, Sukdev; Kancherla, Rajesh; Maiti, Debabrata

2014-10-01

500

Ellagitannin biosynthesis: laccase-catalyzed dimerization of tellimagrandin II to cornusiin E in Tellima grandiflora.  

PubMed

An enzyme has been purified from leaves of the weed Tellima grandiflora (fringe cups, Saxifragaceae) that catalyzed the O2-dependent oxidation of the monomeric ellagitannin, tellimagrandin II, to a dimeric derivative, cornusiin E. The apparently homogeneous enzyme preparation had a Mr of ca. 160,000 (with four subunits of Mr 40,000), a pH-optimum and an isoelectric point at pH 5.2, and was most stable at pH 4.3. Inhibition studies revealed that this new enzyme, for which the systematic name 'tellimagrandin II: O2 oxidoreductase' is proposed, is a member of the laccase (EC 1.10.3.2) family of phenol oxidases. The properties of this enzyme differed from that of a related laccase that catalyzed the transition of 1,2,3,4,6-pentagalloylglucopyranose to tellimagrandin II, the preceding step in the biosynthetic route to cornusin E. PMID:14599517

Niemetz, Ruth; Gross, Georg G

2003-12-01