Sample records for calreticulin transacetylase catalyzed

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

    PubMed

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

    2000-07-25

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

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

    SciTech Connect

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

    2005-01-01

    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.

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

    PubMed

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

    2011-07-01

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

  4. Calreticulin inhibits commitment to adipocyte differentiation

    PubMed Central

    Szabo, Eva; Qiu, Yuanyuan; Baksh, Shairaz; Michalak, Marek; Opas, Michal

    2008-01-01

    Calreticulin, an endoplasmic reticulum (ER) resident protein, affects many critical cellular functions, including protein folding and calcium homeostasis. Using embryonic stem cells and 3T3-L1 preadipocytes, we show that calreticulin modulates adipogenesis. We find that calreticulin-deficient cells show increased potency for adipogenesis when compared with wild-type or calreticulin-overexpressing cells. In the highly adipogenic crt?/? cells, the ER lumenal calcium concentration was reduced. Increasing the ER lumenal calcium concentration led to a decrease in adipogenesis. In calreticulin-deficient cells, the calmodulin–Ca2+/calmodulin-dependent protein kinase II (CaMKII) pathway was up-regulated, and inhibition of CaMKII reduced adipogenesis. Calreticulin inhibits adipogenesis via a negative feedback mechanism whereby the expression of calreticulin is initially up-regulated by peroxisome proliferator–activated receptor ? (PPAR?). This abundance of calreticulin subsequently negatively regulates the expression of PPAR?, lipoprotein lipase, CCAAT enhancer–binding protein ?, and aP2. Thus, calreticulin appears to function as a Ca2+-dependent molecular switch that regulates commitment to adipocyte differentiation by preventing the expression and transcriptional activation of critical proadipogenic transcription factors. PMID:18606846

  5. Transcriptional control of the calreticulin gene in health and disease.

    PubMed

    Qiu, Yuanyuan; Michalak, Marek

    2009-03-01

    Calreticulin is a multifunctional Ca(2+) binding chaperone in the endoplasmic reticulum and expression of the protein is tightly regulated at the transcriptional level. There are two calreticulin genes, named calreticulin-1 and calreticulin-2 gene. The calreticulin-1 promoter contains a number of putative binding sites for transcription factors including tissue specific factors. Direct regulation of the calreticulin-1 promoter by several of these factors has been confirmed experimentally including Nkx2.5, MEF2C, GATA6, PPAR, COUP-TF1 and Evi-1 factors. Studies on calreticulin-deficient mice and transgenic animal models indicate that calreticulin is critical for cardiac development and that expression of the protein must be tightly regulated during cardiogenesis. Moreover, differential expression of calreticulin has been associated with several diseases, including neurodegenerative problems, cancers, autoimmune diseases and wound healing. Understanding the mechanisms responsible for the regulation of expression of calreticulin may contribute to the treatment of many diverse diseases. PMID:18765291

  6. Calreticulin inhibits vitamin D3 signal transduction.

    PubMed Central

    Wheeler, D G; Horsford, J; Michalak, M; White, J H; Hendy, G N

    1995-01-01

    Calreticulin is a calcium binding protein present primarily in the lumen of the endoplasmic reticulum. However, it can also localize to the cytoplasm adjacent to the cell membrane where it binds integrins, and to the nucleus. Recent studies showed that calreticulin inhibits DNA binding and transcriptional activity of glucocorticoid, androgen and retinoic acid receptors. The DNA binding domains of nuclear receptors share a common motif based upon the amino acid sequence KVFFKR which has been implicated in the binding of calreticulin. The vitamin D receptor (VDR) DNA binding domain contains the related motif KgFFrR. Here we show that calreticulin blocks specific DNA binding by the isolated VDR DNA binding domain in DNA mobility shift assays. Importantly, calreticulin blocks specific DNA binding by the full length VDR-RXR heterodimers. By contrast, calreticulin had no effect on specific DNA binding by the transcription factor ATF-a delta which lacks a KVFFKR-like motif in its DNA binding domain. We further showed that overexpression of calreticulin in the rat osteoblast-like cell line (ROS 17/2.8) inhibited the 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] responsive transcriptional activation of a vitamin D-sensitive reporter gene, whereas the response to forskolin stimulation of a control promoter-reporter construct containing a cAMP response element (CRE), but no vitamin D response element (VDRE), was not affected by overexpression of calreticulin. Thus, calreticulin inhibits transcriptional activation by the VDR in vivo. Given the ubiquitous expression of calreticulin and the widespread expression of the VDR the studies described here may point to an important new mechanism whereby VDR mediated gene transcription can be modulated. Images PMID:7667104

  7. Maize calreticulin localizes preferentially to plasmodesmata in root apex.

    PubMed

    Baluska, F; Samaj, J; Napier, R; Volkmann, D

    1999-08-01

    Using a polyclonal antibody raised against calreticulin purified and sequenced from maize, we performed an immunocytological study to characterize putative domain-specific subcellular distributions of endoplasmic reticulum (ER)-resident calreticulin in meristematic cells of maize root tip. At the light microscopy level, calreticulin was immunolocalized preferentially at cellular peripheries, in addition to nuclear envelopes and cytoplasmic structures. Punctate labelling at the longitudinal walls and continuous labelling at the transverse walls was characteristic. Immunogold electron microscopy revealed plasmodesmata as the most prominently labelled cell periphery structure. In order to further probe the ER-domain-specific distribution of maize calreticulin at plasmodesmata, root apices were exposed to mannitol-induced osmotic stress. Plasmolysis was associated with prominent accumulations of calreticulin at callose-enriched plasmodesmata and pit fields while the contracting protoplasts were depleted of calreticulin. In contrast, other ER-resident proteins recognized by HDEL peptide and BiP antibodies localized exclusively to contracted protoplasts. This finding reveals that, in plasmolysed cells, calreticulin enriched ER domains at plasmodesmata and pit fields are depleted of other ER-resident proteins containing the HDEL retention peptide. PMID:10504570

  8. Differential Modulation of SERCA2 Isoforms by Calreticulin

    PubMed Central

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

    1998-01-01

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

  9. Calreticulin Exon 9 Mutations in Myeloproliferative Neoplasms

    PubMed Central

    Kim, Yu-Kyung

    2015-01-01

    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

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

    PubMed Central

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

    2007-01-01

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

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

    Microsoft Academic Search

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

    2011-01-01

    The cloning and characterization of a cDNA encoding a calreticulin from the pinewood nematode Bursaphelenchus xylophilus is described herein. The full-length cDNA (Bx-crt-1) contained a 1200bp open reading frame that could be translated to a 399 amino acid polypeptide. The deduced protein contained highly conserved regions of a calreticulin gene and had 66.2–70.1% amino acid sequence identity to other calreticulin

  12. Calreticulin expression in infiltrating ductal breast carcinomas: relationships with disease progression and humoral immune responses.

    PubMed

    Kabbage, Maria; Trimeche, Mounir; Bergaoui, Sarra; Hammann, Philippe; Kuhn, Lauriane; Hamrita, Bechr; ben Nasr, Hela; Chaieb, Anouar; Chouchane, Lotfi; Chahed, Karim

    2013-04-01

    The aim of this study was to evaluate calreticulin expression in infiltrating ductal breast carcinomas (IDCAs), as well as its relationships with clinicopathological parameters of the disease. Using a two-dimensional gel electrophoresis/matrix-assisted laser desorption ionization time of flight mass spectrometry investigation coupled to an immunohistochemical approach, we have assessed the expression of calreticulin in IDCAs, as well as in other types of breast tumors. The humoral immune response against calreticulin was estimated using a serological proteomics-based strategy. Proteomic analyses revealed an increased expression of calreticulin in IDCA tumors. Using immunohistochemistry, overexpression of calreticulin was confirmed in 51 additional tumor specimens. Statistical analyses revealed, however, no significant correlations between calreticulin expression and clinicopathological parameters of the disease including tumor stage, patient age, SBR grade, and lymph node metastasis occurrence. A significant association was found, however, with estrogen receptor status. This study demonstrates the upregulation of calreticulin in IDCA tissues which may highlight its involvement in breast cancer development. Our findings also support a link between calreticulin expression and estrogen transduction pathways. Our results do not, however, support the involvement of calreticulin in the development of a humoral immune response in IDCAs. PMID:23334957

  13. Calreticulin gene mutations in myeloproliferative neoplasms without Janus kinase 2 mutations.

    PubMed

    Sun, Chao; Zhang, Sujiang; Li, Jianyong

    2015-06-01

    Calreticulin, an endoplasmic reticulum protein with multiple functions involving chaperone activity and calcium homeostasis, plays an important role in cellular proliferation and differentiation. Calreticulin dysfunction is known to be associated with different cancers. Very recently, calreticulin mutations have been identified in myeloproliferative neoplasms (MPNs), with a particularly high frequency in MPNs without Janus kinase 2 (JAK2) mutations, which exhibit clinical characteristics different from those with mutant JAK2. Here, we focus on the structure, function and carcinogenicity of calreticulin, as well as its relationship with MPNs not involving JAK2 mutations. PMID:25115511

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

    PubMed Central

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

    2015-01-01

    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

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

    PubMed Central

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

    2014-01-01

    Our laboratory is credited for the discovery of enzymatic acetylation of protein, a phenomenon unknown till we identified an enzyme termed acetoxy drug: protein transacetylase (TAase), catalyzing the transfer of acetyl group from polyphenolic acetates to receptor proteins (RP). Later, TAase was identified as calreticulin (CR), an endoplasmic reticulum luminal protein. CR was termed calreticulin transacetylase (CRTAase). Our persistent study revealed that CR like other families of histone acetyltransferases (HATs) such as p300, Rtt109, PCAF, and ESA1, undergoes autoacetylation. The autoacetylated CR was characterized as a stable intermediate in CRTAase catalyzed protein acetylation, and similar was the case with ESA1. The autoacetylation of CR like that of HATs was found to enhance protein-protein interaction. CR like HAT-1, CBP, and p300 mediated the acylation of RP utilizing acetyl CoA and propionyl CoA as the substrates. The similarities between CRTAase and HATs in mediating protein acylation are highlighted in this review. PMID:24688408

  16. The calreticulin-binding sequence of thrombospondin 1 regulates collagen expression and organization during tissue remodeling.

    PubMed

    Sweetwyne, Mariya T; Pallero, Manuel A; Lu, Ailing; Van Duyn Graham, Lauren; Murphy-Ullrich, Joanne E

    2010-10-01

    Amino acids 17-35 of the thrombospondin1 (TSP1) N-terminal domain (NTD) bind cell surface calreticulin to signal focal adhesion disassembly, cell migration, and anoikis resistance in vitro. However, the in vivo relevance of this signaling pathway has not been previously determined. We engineered local in vivo expression of the TSP1 calreticulin-binding sequence to determine the role of TSP1 in tissue remodeling. Surgical sponges impregnated with a plasmid encoding the secreted calreticulin-binding sequence [NTD (1-35)-EGFP] or a control sequence [mod NTD (1-35)-EGFP] tagged with enhanced green fluorescent protein were implanted subcutaneously in mice. Sponges expressing NTD (1-35)-EFGP formed a highly organized capsule despite no differences in cellular composition, suggesting stimulation of collagen deposition by the calreticulin-binding sequence of TSP1. TSP1, recombinant NTD, or a peptide of the TSP1 calreticulin-binding sequence (hep I) increased both collagen expression and matrix deposition by fibroblasts in vitro. TSP1 stimulation of collagen was inhibited by a peptide that blocks TSP1 binding to calreticulin, demonstrating the requirement for cell surface calreticulin. Collagen stimulation was independent of TGF-? activity and Smad phosphorylation but was blocked by an Akt inhibitor, suggesting that signaling through the Akt pathway is important for regulation of collagen through TSP1 binding to calreticulin. These studies identify a novel function for the NTD of TSP1 as a mediator of collagen expression and deposition during tissue remodeling. PMID:20724603

  17. Trypanosoma cruzi Calreticulin Is a Lectin That Binds Monoglucosylated Oligosaccharides but Not Protein Moieties of Glycoproteins

    PubMed Central

    Labriola, Carlos; Cazzulo, Juan J.; Parodi, Armando J.

    1999-01-01

    Trypanosoma cruzi is a protozoan parasite that belongs to an early branch in evolution. Although it lacks several features of the pathway of protein N-glycosylation and oligosaccharide processing present in the endoplasmic reticulum of higher eukaryotes, it displays UDP-Glc:glycoprotein glucosyltransferase and glucosidase II activities. It is herewith reported that this protozoan also expresses a calreticulin-like molecule, the third component of the quality control of glycoprotein folding. No calnexin-encoding gene was detected. Recombinant T. cruzi calreticulin specifically recognized free monoglucosylated high-mannose-type oligosaccharides. Addition of anti-calreticulin serum to extracts obtained from cells pulse–chased with [35S]Met plus [35S]Cys immunoprecipitated two proteins that were identified as calreticulin and the lysosomal proteinase cruzipain (a major soluble glycoprotein). The latter but not the former protein disappeared from immunoprecipitates upon chasing cells. Contrary to what happens in mammalian cells, addition of the glucosidase II inhibitor 1-deoxynojirimycin promoted calreticulin–cruzipain interaction. This result is consistent with the known pathway of protein N-glycosylation and oligosaccharide processing occurring in T. cruzi. A treatment of the calreticulin-cruzipain complexes with endo-?-N-acetylglucosaminidase H either before or after addition of anti-calreticulin serum completely disrupted calreticulin–cruzipain interaction. In addition, mature monoglucosylated but not unglucosylated cruzipain isolated from lysosomes was found to interact with recombinant calreticulin. It was concluded that the quality control of glycoprotein folding appeared early in evolution, and that T. cruzi calreticulin binds monoglucosylated oligosaccharides but not the protein moiety of cruzipain. Furthermore, evidence is presented indicating that glucosyltransferase glucosylated cruzipain at its last folding stages. PMID:10233151

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

    PubMed Central

    Lin, Qiao; Cao, Yunpeng; Gao, Jie

    2014-01-01

    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

  19. Modulation of gene expression by calreticulin binding to the glucocorticoid receptor

    Microsoft Academic Search

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

    1994-01-01

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

  20. Aminoglycoside induced nephrotoxicity: molecular modeling studies of calreticulin-gentamicin complex.

    PubMed

    Hariprasad, Gururao; Kumar, Manoj; Rani, Komal; Kaur, Punit; Srinivasan, Alagiri

    2012-06-01

    Gentamicin is a member of aminoglycoside group of broad spectrum antibiotics. It impairs protein synthesis by binding to A site of the 30S subunit of bacterial ribosomes. One of the main side effects of this drug is nephrotoxicity. The drug is known to bind to calreticulin, a chaperone essential for the folding of glycosylated proteins. We provide a detailed structural insight of the calreticulin-gentamicin complex by molecular modeling and the binding of the drug in the presence of explicit solvent was analyzed by molecular dynamics simulation. The gentamicin molecule binds to the lectin site of the calreticulin and lies in the concave channel formed by the long beta sheets. It makes interactions with residues Tyr109, Asp125, Asp135, Asp317 and Trp319 which are crucial for the chaperone function of the calreticulin. The superimposing of the modeled complex with the only available crystal structure complex of calreticulin with a tetrasaccharide (Glc(1)Man(3)) shows interesting features. First, the rings of the gentamicin occupy the positions of glucose and the first two mannose sugars of the tetrasaccharide molecule. Second, the oxygen atoms of the glycosidic linkage of these two ligands have a positional deviation of 1.3 ?. The predicted binding constant of 16.9 ?M is in accordance with the previous kinetic study experiments. The details therefore, strongly implicate gentamicin as a competitive inhibitor of sugar binding with calreticulin. PMID:22086461

  1. Enhanced calreticulin expression triggers apoptosis in the MCF-7 cell line.

    PubMed

    Prathyuman, Shibily; Sellappa, Sudha; Joseph, Shyn; Keyan, Kripa Subhadra

    2010-01-01

    Calreticulin, since its discovery as a ubiquitous protein of endoplasmic reticulum, has become recognized as a multifunctional luminal resident protein affecting many cellular functions ranging from development to death of a cell. However its role in cancer and significance for therapy remains to be clarified. Here to examine its effects, the calreticulin gene was over expressed in MCF-7 human breast cancer cell lines and influence on apoptosis was examined through an MTT assay. Upon culture in a suitable medium, cells transfected with the calreticulin gene were significantly more susceptible to apoptosis compared to controls. These findings therefore render a novel mechanism by which cancerous cells can be triggered to undergo death by upregulation of a protein resident in the lumen of the endoplasmic reticulum. PMID:21133637

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

    PubMed Central

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

    2010-01-01

    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

  3. Generation of amyloid-? is reduced by the interaction of calreticulin with amyloid precursor protein, presenilin and nicastrin.

    PubMed

    Stemmer, Nina; Strekalova, Elena; Djogo, Nevena; Plöger, Frank; Loers, Gabriele; Lutz, David; Buck, Friedrich; Michalak, Marek; Schachner, Melitta; Kleene, Ralf

    2013-01-01

    Dysregulation of the proteolytic processing of amyloid precursor protein by ?-secretase and the ensuing generation of amyloid-? is associated with the pathogenesis of Alzheimer's disease. Thus, the identification of amyloid precursor protein binding proteins involved in regulating processing of amyloid precursor protein by the ?-secretase complex is essential for understanding the mechanisms underlying the molecular pathology of the disease. We identified calreticulin as novel amyloid precursor protein interaction partner that binds to the ?-secretase cleavage site within amyloid precursor protein and showed that this Ca(2+)- and N-glycan-independent interaction is mediated by amino acids 330-344 in the C-terminal C-domain of calreticulin. Co-immunoprecipitation confirmed that calreticulin is not only associated with amyloid precursor protein but also with the ?-secretase complex members presenilin and nicastrin. Calreticulin was detected at the cell surface by surface biotinylation of cells overexpressing amyloid precursor protein and was co-localized by immunostaining with amyloid precursor protein and presenilin at the cell surface of hippocampal neurons. The P-domain of calreticulin located between the N-terminal N-domain and the C-domain interacts with presenilin, the catalytic subunit of the ?-secretase complex. The P- and C-domains also interact with nicastrin, another functionally important subunit of this complex. Transfection of amyloid precursor protein overexpressing cells with full-length calreticulin leads to a decrease in amyloid-?42 levels in culture supernatants, while transfection with the P-domain increases amyloid-?40 levels. Similarly, application of the recombinant P- or C-domains and of a synthetic calreticulin peptide comprising amino acid 330-344 to amyloid precursor protein overexpressing cells result in elevated amyloid-?40 and amyloid-?42 levels, respectively. These findings indicate that the interaction of calreticulin with amyloid precursor protein and the ?-secretase complex regulates the proteolytic processing of amyloid precursor protein by the ?-secretase complex, pointing to calreticulin as a potential target for therapy in Alzheimer's disease. PMID:23585889

  4. Fine specificity of autoantibodies to calreticulin: epitope mapping and characterization.

    PubMed

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

    2000-05-01

    Extracellular calreticulin (CRT) as well as anti-CRT antibodies have been reported in patients with various autoimmune disorders and CRT has been implicated in 'epitope spreading' to other autoantigens such as the Ro/SS-A complex. In addition, antibodies against parasite forms of the endoplasmic reticulum chaperone, CRT, have been found in patients suffering from onchocerciasis and schistosomiasis. In this study, we screened sera for anti-CRT antibodies from patients with active and inactive systemic lupus ertythematosus (SLE) and primary or secondary Sjögren's syndrome. Approximately 40% of all SLE patients were positive for anti-CRT antibodies. The antigenic regions of CRT were determined using full length CRT and fragments of CRT prepared in yeast and Escherichia coli, respectively. Synthetic 15mer peptides corresponding to the major autoantigenic region of CRT (amino acids 1-289), each one overlapping by 12 amino acids, were used to map the B cell epitopes on the CRT protein recognized by autoimmune sera. Major antigenic epitopes were found to be associated with the N-terminal half of the protein in 69% of the SLE sera from active disease patients, while the C-domain was not antigenic. Major epitopes were found to be reactive with antibodies in sera from SLE patients with both active and inactive disease, spanning different regions of the N and P-domains. Sera from both healthy and disease controls and primary Sjögren's syndrome patients were non-reactive to these sequences. Limited proteolysis of CRT with two major leucocyte serine proteases, elastase and cathepsin G, demonstrated that an N-terminal region of CRT is resistant to digestion. Interestingly, some of the epitopes with the highest reactivity belong to the fragments of the protein which bind to C1q and inhibit complement activation. Whether C1q association with CRT is a pathological or protective interaction between these two proteins is currently under investigation. PMID:10792392

  5. Fine specificity of autoantibodies to calreticulin: epitope mapping and characterization

    PubMed Central

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

    2000-01-01

    Extracellular calreticulin (CRT) as well as anti-CRT antibodies have been reported in patients with various autoimmune disorders and CRT has been implicated in ‘epitope spreading’ to other autoantigens such as the Ro/SS-A complex. In addition, antibodies against parasite forms of the endoplasmic reticulum chaperone, CRT, have been found in patients suffering from onchocerciasis and schistosomiasis. In this study, we screened sera for anti-CRT antibodies from patients with active and inactive systemic lupus ertythematosus (SLE) and primary or secondary Sjögren's syndrome. Approximately 40% of all SLE patients were positive for anti-CRT antibodies. The antigenic regions of CRT were determined using full length CRT and fragments of CRT prepared in yeast and Escherichia coli, respectively. Synthetic 15mer peptides corresponding to the major autoantigenic region of CRT (amino acids 1–289), each one overlapping by 12 amino acids, were used to map the B cell epitopes on the CRT protein recognized by autoimmune sera. Major antigenic epitopes were found to be associated with the N-terminal half of the protein in 69% of the SLE sera from active disease patients, while the C-domain was not antigenic. Major epitopes were found to be reactive with antibodies in sera from SLE patients with both active and inactive disease, spanning different regions of the N and P-domains. Sera from both healthy and disease controls and primary Sjögren's syndrome patients were non-reactive to these sequences. Limited proteolysis of CRT with two major leucocyte serine proteases, elastase and cathepsin G, demonstrated that an N-terminal region of CRT is resistant to digestion. Interestingly, some of the epitopes with the highest reactivity belong to the fragments of the protein which bind to C1q and inhibit complement activation. Whether C1q association with CRT is a pathological or protective interaction between these two proteins is currently under investigation. PMID:10792392

  6. Higher Plant Calreticulins Have Acquired Specialized Functions in Arabidopsis

    PubMed Central

    Zhang, Wenjing; Tintor, Nico; Prins, Daniel; Funke, Norma; Michalak, Marek; Schulze-Lefert, Paul; Saijo, Yusuke; Sommarin, Marianne; Widell, Susanne; Persson, Staffan

    2010-01-01

    Background Calreticulin (CRT) is a ubiquitous ER protein involved in multiple cellular processes in animals, such as protein folding and calcium homeostasis. Like in animals, plants have evolved divergent CRTs, but their physiological functions are less understood. Arabidopsis contains three CRT proteins, where the two CRTs AtCRT1a and CRT1b represent one subgroup, and AtCRT3 a divergent member. Methodology/Principal Findings Through expression of single Arabidopsis family members in CRT-deficient mouse fibroblasts we show that both subgroups have retained basic CRT functions, including ER Ca2+-holding potential and putative chaperone capabilities. However, other more general cellular defects due to the absence of CRT in the fibroblasts, such as cell adhesion deficiencies, were not fully restored. Furthermore, in planta expression, protein localization and mutant analyses revealed that the three Arabidopsis CRTs have acquired specialized functions. The AtCRT1a and CRT1b family members appear to be components of a general ER chaperone network. In contrast, and as recently shown, AtCRT3 is associated with immune responses, and is essential for responsiveness to the bacterial Pathogen-Associated Molecular Pattern (PAMP) elf18, derived from elongation factor (EF)-Tu. Whereas constitutively expressed AtCRT1a fully complemented Atcrt1b mutants, AtCRT3 did not. Conclusions/Significance We conclude that the physiological functions of the two CRT subgroups in Arabidopsis have diverged, resulting in a role for AtCRT3 in PAMP associated responses, and possibly more general chaperone functions for AtCRT1a and CRT1b. PMID:20596537

  7. Calreticulin as a potential diagnostic biomarker for lung cancer.

    PubMed

    Liu, Rongrong; Gong, Jiuyu; Chen, Jun; Li, Qi; Song, Chaojun; Zhang, Jian; Li, Yongming; Liu, Zhijia; Dong, Yun; Chen, Lihua; Jin, Boquan

    2012-06-01

    Calreticulin (CRT) is an endoplasmic reticulum luminal Ca(2+)-binding chaperone protein. By immunizing mice with recombinant fragment (rCRT/39-272), six clones of monoclonal antibodies (mAbs) were generated and characterized. Based on these mAbs, a microplate chemiluminescent enzyme immunoassay (CLEIA) system with a measured limit of detection of 0.09 ng/ml was developed. Using this CLEIA system, it was found that soluble CRT (sCRT) level in serum samples from 58 lung cancer patients was significantly higher than that from 40 healthy individuals (only 9 were detectable, P < 0.0001). Among them, serum sCRT in the small cell lung cancer was lower than that in adenocarcinoma (P = 0.0085), while both were lower than that in the squamous cell carcinoma (P = 0.013, P = 0.0012, respectively). Moreover, it was found that sCRT in sera from the patients after chemotherapy was higher than that from the patients without chemotherapy (P = 0.042). Further study by immunohistochemistry showed that CRT was also highly expressed in the cytoplasm and on the membrane of the lung cancer cells, while there was a trace amount of CRT expression in normal lung cells. Correspondingly, the expression level of CRT on lung cancer cell membrane was associated with the tumor pathological grade. This study demonstrates that sCRT concentration in sera of lung cancer patients is higher than that in sera of healthy individuals, and CRT expression level on lung cancer cell membrane is associated with tumor pathological classification and grade. These findings suggest that CRT may be used as a biomarker in lung cancer prediction and diagnosis. PMID:22083347

  8. The tobacco homolog of mammalian calreticulin is present in protein complexes in vivo.

    PubMed Central

    Denecke, J; Carlsson, L E; Vidal, S; Höglund, A S; Ek, B; van Zeijl, M J; Sinjorgo, K M; Palva, E T

    1995-01-01

    The analysis of protein sorting signals responsible for the retention of reticuloplasmins (RPLs), a group of soluble proteins that reside in the lumen of the endoplasmic reticulum (ER), has revealed a structural similarity between mammalian and plant ER retention signals. We present evidence that the corresponding epitope is conserved in a vast family of soluble ER resident proteins. Microsequences of RPL60 and RPL90, two abundant members of this family, show high sequence similarity with mammalian calreticulin and endoplasmin. RPL60/calreticulin cofractionates and costains with the lumenal binding protein (BiP). Both proteins were detected in the nuclear envelope and the ER, and in mitotic cells in association with the spindle apparatus and the phragmoplast. Immunoprecipitation of proteins from in vivo-labeled cells demonstrated that RPL60/calreticulin is associated with other polypeptides in a stress- and ATP-dependent fashion. RPL60/calreticulin transcript levels increased rapidly in abundance during the proliferation of the secretory apparatus and the onset of hydrolase secretion in gibberellic acid-treated barley aleurone cells. This induction profile is identical to that of the well-characterized ER chaperones BiP and endoplasmin. However, expression patterns in response to different stress conditions as well as tissue-specific expression patterns indicate that these genes are differentially regulated and may not act in concert. PMID:7773014

  9. Overview of the Role for Calreticulin in the Enhancement of Wound Healing through Multiple Biological Effects

    Microsoft Academic Search

    Leslie I Gold; Mohammad Rahman; Keith M Blechman; Matthew R Greives; Samara Churgin; Joseph Michaels; Matthew J Callaghan; Nancy L Cardwell; Alonda C Pollins; Marek Michalak; John W Siebert; Jamie P Levine; Geoffrey C Gurtner; Lillian B Nanney; Robert D Galiano; Caprice L Cadacio

    2006-01-01

    Calreticulin (CRT), an intracellular chaperone protein crucial for the proper folding and transport of proteins through the endoplasmic reticulum, has more recent acclaim as a critical regulator of extracellular functions, particularly in mediating cellular migration and as a requirement for phagocytosis of apoptotic cells. Consistent with these functions, we show that the topical application of CRT has profound effects on

  10. Calreticulin-dependent recycling in the early secretory pathway mediates optimal peptide loading of MHC class I molecules

    PubMed Central

    Howe, Christopher; Garstka, Malgorzata; Al-Balushi, Mohammed; Ghanem, Esther; Antoniou, Antony N; Fritzsche, Susanne; Jankevicius, Gytis; Kontouli, Nasia; Schneeweiss, Clemens; Williams, Anthony; Elliott, Tim; Springer, Sebastian

    2009-01-01

    Calreticulin is a lectin chaperone of the endoplasmic reticulum (ER). In calreticulin-deficient cells, major histocompatibility complex (MHC) class I molecules travel to the cell surface in association with a sub-optimal peptide load. Here, we show that calreticulin exits the ER to accumulate in the ER–Golgi intermediate compartment (ERGIC) and the cis-Golgi, together with sub-optimally loaded class I molecules. Calreticulin that lacks its C-terminal KDEL retrieval sequence assembles with the peptide-loading complex but neither retrieves sub-optimally loaded class I molecules from the cis-Golgi to the ER, nor supports optimal peptide loading. Our study, to the best of our knowledge, demonstrates for the first time a functional role of intracellular transport in the optimal loading of MHC class I molecules with antigenic peptide. PMID:19851281

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

    Microsoft Academic Search

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

    2002-01-01

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

  12. Agarose gel shift assay reveals that calreticulin favors substrates with a quaternary structure in solution.

    PubMed

    Boelt, Sanne Grundvad; Houen, Gunnar; Højrup, Peter

    2015-07-15

    Here we present an agarose gel shift assay that, in contrast to other electrophoresis approaches, is loaded in the center of the gel. This allows proteins to migrate in either direction according to their isoelectric points. Therefore, the presented assay enables a direct visualization, separation, and prefractionation of protein interactions in solution independent of isoelectric point. We demonstrate that this assay is compatible with immunochemical methods and mass spectrometry. The assay was used to investigate interactions with several potential substrates for calreticulin, a chaperone that is involved in different biological aspects through interaction with other proteins. The current analytical assays used to investigate these interactions are mainly spectroscopic aggregation assays or solid phase assays that do not provide a direct visualization of the stable protein complex but rather provide an indirect measure of interactions. Therefore, no interaction studies between calreticulin and substrates in solution have been investigated previously. The results presented here indicate that calreticulin has a preference for substrates with a quaternary structure and primarily ?-sheets in their secondary structure. It is also demonstrated that the agarose gel shift assay is useful in the study of other protein interactions and can be used as an alternative method to native polyacrylamide gel electrophoresis. PMID:25908558

  13. Enhancement of vaccinia vaccine potency by linkage of tumor antigen gene to gene encoding calreticulin.

    PubMed

    Hsieh, Chia-Jung; Kim, Tae Woo; Hung, Chien-Fu; Juang, Jeremy; Moniz, Michelle; Boyd, David A K; He, Liangmei; Chen, Pei-Jer; Chen, Chien-Hung; Wu, T-C

    2004-09-28

    Vaccinia vaccines have become important vectors for antigen-specific immunotherapy. Calreticulin has been shown to enhance MHC class I presentation of linked peptide/protein and may be useful for antigen-specific cancer treatment. An innovative vaccine administering antigen linked to calreticulin via a vaccinia vector may generate a potent antigen-specific antitumor response. We tested the efficacy of linking calreticulin (CRT) to model antigen human papilloma virus type 16 (HPV-16) E7 in the context of a vaccinia vaccine (Vac-CRT/E7). Intraperitoneal vaccination of C57BL/6 mice with Vac-CRT/E7 led to a dramatic increase in E7-specific IFN-gamma-secreting CD8+ T cells and a potent antitumor effect against E7-expressing tumors compared to immunization with Vac-E7 or Vac-CRT. When compared to other chimeric vaccinia vaccines employing various intracellular targeting strategies previously developed in our lab, Vac-CRT/E7 elicited the highest number of E7-specific CD8+ T cells. Thus, vaccination with vaccinia expressing CRT linked to a tumor antigen may represent an advantageous strategy for cancer immunotherapy. PMID:15364449

  14. Antitumor immunity triggered by melphalan is potentiated by melanoma cell surface-associated calreticulin.

    PubMed

    Dudek-Peri?, Aleksandra M; Ferreira, Gabriela B; Muchowicz, Angelika; Wouters, Jasper; Prada, Nicole; Martin, Shaun; Kiviluoto, Santeri; Winiarska, Magdalena; Boon, Louis; Mathieu, Chantal; van den Oord, Joost; Stas, Marguerite; Gougeon, Marie-Lise; Golab, Jakub; Garg, Abhishek D; Agostinis, Patrizia

    2015-04-15

    Systemic chemotherapy generally has been considered immunosuppressive, but it has become evident that certain chemotherapeutic drugs elicit immunogenic danger signals in dying cancer cells that can incite protective antitumor immunity. In this study, we investigated whether locoregionally applied therapies, such as melphalan, used in limb perfusion for melanoma (Mel-ILP) produce related immunogenic effects. In human melanoma biopsies, Mel-ILP treatment upregulated IL1B, IL8, and IL6 associated with their release in patients' locoregional sera. Although induction of apoptosis in melanoma cells by melphalan in vitro did not elicit threshold levels of endoplasmic reticulum and reactive oxygen species stress associated with danger signals, such as induction of cell-surface calreticulin, prophylactic immunization and T-cell depletion experiments showed that melphalan administration in vivo could stimulate a CD8(+) T cell-dependent protective antitumor response. Interestingly, the vaccination effect was potentiated in combination with exogenous calreticulin, but not tumor necrosis factor, a cytokine often combined with Mel-ILP. Our results illustrate how melphalan triggers inflammatory cell death that can be leveraged by immunomodulators such as the danger signal calreticulin. Cancer Res; 75(8); 1603-14. ©2015 AACR. PMID:25762540

  15. N-linked oligosaccharides are necessary and sufficient for association of glycosylated forms of bovine RNase with calnexin and calreticulin.

    PubMed Central

    Rodan, A R; Simons, J F; Trombetta, E S; Helenius, A

    1996-01-01

    Calnexin and calreticulin are lectin-like molecular chaperones that promote folding and assembly of newly synthesized glycoproteins in the endoplasmic reticulum. While it is well established that they interact with substrate monoglucosylated N-linked oligosaccharides, it has been proposed that they also interact with polypeptide moieties. To test this notion, glycosylated forms of bovine pancreatic ribonuclease (RNase) were translated in the presence of microsomes and their folding and association with calnexin and calreticulin were monitored. When expressed with two N-linked glycans in the presence of micromolar concentrations of deoxynojirimycin, this small soluble protein was found to bind firmly to both calnexin and calreticulin. The oligosaccharides were necessary for association, but it made no difference whether the RNase was folded or not. This indicated that unlike other chaperones, calnexin and calreticulin do not select their substrates on the basis of folding status. Moreover, enzymatic removal of the oligosaccharide chains using peptide N-glycosidase F or removal of the glucoses by ER glucosidase II resulted in dissociation of the complexes. This indicated that the lectin-like interaction, and not a protein-protein interaction, played the central role in stabilizing RNase-calnexin/calreticulin complexes. Images PMID:9003768

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

    Microsoft Academic Search

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

    2010-01-01

    Experiments performed in mice revealed that anthracyclines stimulate immunogenic cell death that is characterized by the pre-apoptotic exposure of calreticulin (CRT) on the surface of dying tumor cells. Here, we determined whether CRT exposure at the cell surface (ecto-CRT) occurs in human cancer in response to anthracyclines in vivo, focusing on acute myeloid leukemia (AML), which is currently treated with

  17. Thyroid Hormone Receptor ?1 Follows a Cooperative CRM1/Calreticulin-mediated Nuclear Export Pathway*

    PubMed Central

    Grespin, Matthew E.; Bonamy, Ghislain M. C.; Roggero, Vincent R.; Cameron, Nicole G.; Adam, Lindsay E.; Atchison, Andrew P.; Fratto, Victoria M.; Allison, Lizabeth A.

    2008-01-01

    The thyroid hormone receptor ?1 (TR?) exhibits a dual role as an activator or repressor of its target genes in response to thyroid hormone (T3). Previously, we have shown that TR?, formerly thought to reside solely in the nucleus bound to DNA, actually shuttles rapidly between the nucleus and cytoplasm. An important aspect of the shuttling activity of TR? is its ability to exit the nucleus through the nuclear pore complex. TR? export is not sensitive to treatment with the CRM1-specific inhibitor leptomycin B (LMB) in heterokaryon assays, suggesting a role for an export receptor other than CRM1. Here, we have used a combined approach of in vivo fluorescence recovery after photobleaching experiments, in vitro permeabilized cell nuclear export assays, and glutathione S-transferase pull-down assays to investigate the export pathway used by TR?. We show that, in addition to shuttling in heterokaryons, TR? shuttles rapidly in an unfused monokaryon system as well. Furthermore, our data show that TR? directly interacts with calreticulin, and point to the intriguing possibility that TR? follows a cooperative export pathway in which both calreticulin and CRM1 play a role in facilitating efficient translocation of TR? from the nucleus to cytoplasm. PMID:18641393

  18. Hijacking of host calreticulin is required for the white spot syndrome virus replication cycle.

    PubMed

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

    2014-07-01

    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

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

    PubMed Central

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

    2014-01-01

    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

  20. Molecular cloning and functional study of calreticulin from a lepidopteran pest, Pieris rapae.

    PubMed

    Wang, Lei; Fang, Qi; Zhu, Jiaying; Wang, Fei; Rean Akhtar, Zunnu; Ye, Gongyin

    2012-09-01

    Insects have an effective innate immune system to protect themselves from exogenous invaders. Calreticulin is a multifunctional protein mainly involved in directing proper conformation of proteins, controlling calcium level, and participating in immune responses. Previous suppression subtractive hybridization assay showed that the expression of Pieris rapae calreticulin (PrCRT) was suppressed after injection of Pteromalus puparum venom. In this study, we obtained a full length cDNA of PrCRT and expressed recombinant wild type and the N-domain deleted mutant PrCRT in bacteria. Real time quantitative PCR and western blot analyses showed that PrCRT mRNA and protein were expressed in hemocytes, Malpighian tubule, midgut, epidermis and fat body, with a higher level in hemocytes. PrCRT was probably located in endoplasmic reticulum distributing in the cytoplasm of hemocytes. Recombinant PrCRT was first able to attach and then enter the hemocytes by endocytosis. PrCRT mRNA in hemocytes was significantly induced after injection of yeast or beads, but did not change noticeably after injection of Escherichia coli or Micrococcus lysodeikticus. Recombinant PrCRT enhanced cellular encapsulation by P. rapae hemocytes in vitro, and the N-domain of PrCRT was required for encapsulation. RNAi of PrCRT by dsRNA injection impaired the ability of hemocytes to encapsulate beads. After parasitization by P. puparum, PrCRT mRNA and protein levels in P. rapae pupal hemocytes were significantly suppressed compared to non-parasitized control. Our results suggest that PrCRT is involved in cellular encapsulation and the pupal parasitoid P. puparum can decrease PrCRT expression to impair host cellular immune response. PMID:22516748

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    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.

  2. Calreticulin binding and other biological activities of survival peptide Y-P30 including effects of systemic treatment of rats.

    PubMed

    Cunningham, T J; Jing, H; Wang, Y; Hodge, L

    2000-06-01

    Neuron survival-promoting peptide Y-P30, purified from oxidatively stressed neural cell lines, inhibits the appearance of microglia and rescues neurons 1 week after direct application to lesions of the rat cerebral cortex (7). Y-P30 affinity matrices treated with solubilized membranes from a variety of cell lines including human neuroblastoma SY5Y, mouse hippocampal cells HN 33.1, and human promonocytes HL-60, as well as with cerebral cortex tissue from both humans and rats, showed highly specific binding to calreticulin, a ubiquitous calcium binding protein that may be critical for integrin function. Treatment of cultures with 0.1 nM Y-P30 stabilized all these cell types whether differentiated or not, while 1 microM peptide also inhibited the morphological differentiation of the HL-60 cells into macrophages. Western analysis of the medium of SY5Y cell cultures suggested Y-P30-stimulated release of calreticulin, a result consistent with its other biological activities. Likewise, single dose systemic application of Y-P30 in unoperated rats and in rats with cerebral cortex lesions produced significant reductions in cerebral cortex membrane-associated calreticulin. Both direct and intravenous treatment with peptide also reduced cortical neuron atrophy 4 days after these lesions but only direct application consistently inhibited the appearance of ED-1(+) monocyte derivatives. We suggest that in vitro and in vivo mechanisms of Y-P30 effects are similar and involve the targeting of calreticulin. The results also suggest that some of these activities are apparent in the cerebral cortex after systemic application of this peptide. PMID:10833321

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

    PubMed

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

    2014-08-01

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

  4. Recombinant adenovirus delivery of calreticulin-ESAT-6 produces an antigen-specific immune response but no protection against a Mycobacterium tuberculosis challenge.

    PubMed

    Esparza-González, S C; Troy, A; Troudt, J; Loera-Arias, M J; Villatoro-Hernández, J; Torres-López, E; Ancer-Rodríguez, J; Gutiérrez-Puente, Y; Muñoz-Maldonado, G; Saucedo-Cárdenas, O; Montes-de-Oca-Luna, R; Izzo, A

    2012-03-01

    Bacillus Calmette-Guerin (BCG) has failed to efficaciously control the worldwide spread of the disease. New vaccine development targets virulence antigens of Mycobacterium tuberculosis that are deleted in Mycobacterium bovis BCG. Immunization with ESAT-6 and CFP10 provides protection against M. tuberculosis in a murine infection model. Further, previous studies have shown that calreticulin increases the cell-mediated immune responses to antigens. Therefore, to test whether calreticulin enhances the immune response against M. tuberculosis antigens, we fused ESAT-6 to calreticulin and constructed a recombinant replication-deficient adenovirus to express the resulting fusion protein (AdCRT-ESAT-6). The adjuvant effect of calreticulin was assayed by measuring cytokine responses specific to ESAT-6. Recombinant adenovirus expressing the fusion protein produced higher levels of interferon-? and tumour necrosis factor-? in response to ESAT-6. This immune response was not improved by the addition of CFP-10 to the CRT-ESAT-6 fusion protein (AdCRT-ESAT-6-CFP10). Mice immunized with these recombinant adenoviruses did not decrease the mycobacterial burden after low-dose aerosol infection with M. tuberculosis. We conclude that calreticulin can be used as an adjuvant to enhance the immune response against mycobacterial antigens, but it is not enough to protect against tuberculosis. PMID:22010821

  5. Calreticulin expression in the clonal plasma cells of patients with systemic light-chain (AL-) amyloidosis is associated with response to high-dose melphalan

    PubMed Central

    Zhou, Ping; Teruya-Feldstein, Julie; Lu, Ping; Fleisher, Martin; Olshen, Adam

    2008-01-01

    In high doses with stem-cell transplantation, melphalan is an effective but toxic therapy for patients with systemic light-chain (AL-) amyloidosis, a protein deposition and monoclonal plasma cell disease. Melphalan can eliminate the indolent clonal plasma cells that cause the disease, an achievement called a complete response. Such a response is usually associated with extended survival, while no response (a less than 50% reduction) is not. Gene-expression studies and a stringently supervised analysis identified calreticulin as having significantly higher expression in the pretreatment plasma cells of patients with systemic AL-amyloidosis who then had a complete response to high-dose melphalan. Calreticulin is a pleiotropic calcium-binding protein found in the endoplasmic reticulum and the nucleus whose overexpression is associated with increased sensitivity to apoptotic stimuli. Real-time PCR and immunohistochemical staining also showed that expression of calreticulin was higher in the plasma cells of those with a complete response. Furthermore, wild-type murine embryonic fibroblasts were significantly more sensitive to melphalan than calreticulin knock-out murine embryonic fibroblasts. These data have important implications for understanding the activity of melphalan in plasma-cell diseases and support further investigation of calreticulin and its modulation in patients with systemic AL-amyloidosis receiving high-dose melphalan. PMID:17982021

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

    PubMed

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

    2014-01-01

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

  7. Plasmodesmata without callose and calreticulin in higher plants – open channels for fast symplastic transport?

    PubMed Central

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

    2014-01-01

    Plasmodesmata (PD) represent membrane-lined channels that link adjacent plant cells across the cell wall. PD of higher plants contain a central tube of endoplasmic reticulum (ER) called desmotubule. Membrane and lumen proteins seem to be able to move through the desmotubule, but most transport processes through PD occur through the cytoplasmic annulus (Brunkard etal., 2013). Calreticulin (CRT), a highly conserved Ca2+-binding protein found in all multicellular eukaryotes, predominantly located in the ER, was shown to localize to PD, though not all PD accumulate CRT. In nitrogen-fixing actinorhizal root nodules of the Australian tree Casuarina glauca, the primary walls of infected cells containing the microsymbiont become lignified upon infection. TEM analysis of these nodules showed that during the differentiation of infected cells, PD connecting infected cells, and connecting infected and adjacent uninfected cells, were reduced in number as well as diameter (Schubert etal., 2013). In contrast with PD connecting young infected cells, and most PD connecting mature infected and adjacent uninfected cells, PD connecting mature infected cells did not accumulate CRT. Furthermore, as shown here, these PD were not associated with callose, and based on their diameter, they probably had lost their desmotubules. We speculate that either this is a slow path to PD degradation, or that the loss of callose accumulation and presumably also desmotubules leads to the PD becoming open channels and improves metabolite exchange between cells. PMID:24634671

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

    PubMed

    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

    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

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

    PubMed

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

    2014-12-01

    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

  10. Endoplasmic Reticulum Calcium Regulates the Retrotranslocation of Trypanosoma Cruzi Calreticulin to the Cytosol

    PubMed Central

    Labriola, Carlos A.; Conte, Ianina L.; López Medus, Máximo; Parodi, Armando J.; Caramelo, Julio J.

    2010-01-01

    For most secretory pathway proteins, crossing the endoplasmic reticulum (ER) membrane is an irreversible process. However, in some cases this flow can be reversed. For instance, misfolded proteins retained in the ER are retrotranslocated to the cytosol to be degraded by the proteasome. This mechanism, known as ER associated degradation (ERAD), is exploited by several bacterial toxins to gain access to the cytosol. Interestingly, some ER resident proteins can also be detected in the cytosol or nucleus, calreticulin (CRT) being the most studied. Here we show that in Trypanosoma cruzi a minor fraction of CRT localized to the cytosol. ER calcium depletion, but not increasing cytosolic calcium, triggered the retrotranslocation of CRT in a relatively short period of time. Cytosolic CRT was subsequently degraded by the proteasome. Interestingly, the single disulfide bridge of CRT is reduced when the protein is located in the cytosol. The effect exerted by ER calcium was strictly dependent on the C-terminal domain (CRT-C), since a CRT lacking it was totally retained in the ER, whereas the localization of an unrelated protein fused to CRT-C mirrored that of endogenous CRT. This finding expands the regulatory mechanisms of protein sorting and may represent a new crossroad between diverse physiological processes. PMID:20957192

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

    PubMed

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

    2014-07-01

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

  12. A novel pathway combining calreticulin exposure and ATP secretion in immunogenic cancer cell death

    PubMed Central

    Garg, Abhishek D; Krysko, Dmitri V; Verfaillie, Tom; Kaczmarek, Agnieszka; Ferreira, Gabriela B; Marysael, Thierry; Rubio, Noemi; Firczuk, Malgorzata; Mathieu, Chantal; Roebroek, Anton J M; Annaert, Wim; Golab, Jakub; de Witte, Peter; Vandenabeele, Peter; Agostinis, Patrizia

    2012-01-01

    Surface-exposed calreticulin (ecto-CRT) and secreted ATP are crucial damage-associated molecular patterns (DAMPs) for immunogenic apoptosis. Inducers of immunogenic apoptosis rely on an endoplasmic reticulum (ER)-based (reactive oxygen species (ROS)-regulated) pathway for ecto-CRT induction, but the ATP secretion pathway is unknown. We found that after photodynamic therapy (PDT), which generates ROS-mediated ER stress, dying cancer cells undergo immunogenic apoptosis characterized by phenotypic maturation (CD80high, CD83high, CD86high, MHC-IIhigh) and functional stimulation (NOhigh, IL-10absent, IL-1?high) of dendritic cells as well as induction of a protective antitumour immune response. Intriguingly, early after PDT the cancer cells displayed ecto-CRT and secreted ATP before exhibiting biochemical signatures of apoptosis, through overlapping PERK-orchestrated pathways that require a functional secretory pathway and phosphoinositide 3-kinase (PI3K)-mediated plasma membrane/extracellular trafficking. Interestingly, eIF2? phosphorylation and caspase-8 signalling are dispensable for this ecto-CRT exposure. We also identified LRP1/CD91 as the surface docking site for ecto-CRT and found that depletion of PERK, PI3K p110? and LRP1 but not caspase-8 reduced the immunogenicity of the cancer cells. These results unravel a novel PERK-dependent subroutine for the early and simultaneous emission of two critical DAMPs following ROS-mediated ER stress. PMID:22252128

  13. A novel pathway combining calreticulin exposure and ATP secretion in immunogenic cancer cell death.

    PubMed

    Garg, Abhishek D; Krysko, Dmitri V; Verfaillie, Tom; Kaczmarek, Agnieszka; Ferreira, Gabriela B; Marysael, Thierry; Rubio, Noemi; Firczuk, Malgorzata; Mathieu, Chantal; Roebroek, Anton J M; Annaert, Wim; Golab, Jakub; de Witte, Peter; Vandenabeele, Peter; Agostinis, Patrizia

    2012-03-01

    Surface-exposed calreticulin (ecto-CRT) and secreted ATP are crucial damage-associated molecular patterns (DAMPs) for immunogenic apoptosis. Inducers of immunogenic apoptosis rely on an endoplasmic reticulum (ER)-based (reactive oxygen species (ROS)-regulated) pathway for ecto-CRT induction, but the ATP secretion pathway is unknown. We found that after photodynamic therapy (PDT), which generates ROS-mediated ER stress, dying cancer cells undergo immunogenic apoptosis characterized by phenotypic maturation (CD80(high), CD83(high), CD86(high), MHC-II(high)) and functional stimulation (NO(high), IL-10(absent), IL-1?(high)) of dendritic cells as well as induction of a protective antitumour immune response. Intriguingly, early after PDT the cancer cells displayed ecto-CRT and secreted ATP before exhibiting biochemical signatures of apoptosis, through overlapping PERK-orchestrated pathways that require a functional secretory pathway and phosphoinositide 3-kinase (PI3K)-mediated plasma membrane/extracellular trafficking. Interestingly, eIF2? phosphorylation and caspase-8 signalling are dispensable for this ecto-CRT exposure. We also identified LRP1/CD91 as the surface docking site for ecto-CRT and found that depletion of PERK, PI3K p110? and LRP1 but not caspase-8 reduced the immunogenicity of the cancer cells. These results unravel a novel PERK-dependent subroutine for the early and simultaneous emission of two critical DAMPs following ROS-mediated ER stress. PMID:22252128

  14. C/EBP? mediates the transcriptional suppression of human calreticulin gene expression by TNF?.

    PubMed

    Vig, Saurabh; Pandey, Amit K; Verma, Gaurav; Datta, Malabika

    2012-01-01

    Calreticulin (CRT), a 46 kDa endoplasmic reticulum chaperone, is critical in the folding and quality control of proteins. However, the mechanisms of its regulation are not fully understood. Our previous study had demonstrated that elevated TNF? levels that are hallmarks of diverse metabolic diseases negatively regulate cellular CRT levels. Here, we attempted to study the mode of this regulation of CRT by TNF?. Using luciferase reporter deletion constructs of the CRT promoter, we demonstrate that while the -2 kb and -1 kb promoter constructs depict comparable activities, the activity of the -0.5 kb region was greatly reduced suggesting the significance of the region between -1.0 kb and -0.5 kb during CRT promoter activity. Of the transcription factors that possess binding elements within this region, C/EBP? was prioritized since it was shown to be inhibited by TNF? in an earlier report from our laboratory. TNF? significantly inhibited the wild-type CRT promoter activity that was attenuated in a C/EBP?-deleted construct. C/EBP? mRNA levels and its nuclear content was also reduced in the presence of TNF?. This led to reduced C/EBP? occupancy on the CRT promoter and a decreased binding of the nuclear protein to the C/EBP?-consensus sequence. TNF? also reduced the nuclear content of C/EBP? but it did not bind to the CRT promoter suggesting that it does not contribute to the inhibitory effect of TNF?. To conclude, our results suggest that C/EBP? is critical in mediating the inhibitory effect of TNF? on CRT expression that might be crucial in determining the deleterious cellular effects of TNF?. PMID:22024156

  15. Immunogenic calreticulin exposure occurs through a phylogenetically conserved stress pathway involving the chemokine CXCL8.

    PubMed

    Sukkurwala, A Q; Martins, I; Wang, Y; Schlemmer, F; Ruckenstuhl, C; Durchschlag, M; Michaud, M; Senovilla, L; Sistigu, A; Ma, Y; Vacchelli, E; Sulpice, E; Gidrol, X; Zitvogel, L; Madeo, F; Galluzzi, L; Kepp, O; Kroemer, G

    2014-01-01

    The exposure of calreticulin (CRT) on the surface of stressed and dying cancer cells facilitates their uptake by dendritic cells and the subsequent presentation of tumor-associated antigens to T lymphocytes, hence stimulating an anticancer immune response. The chemotherapeutic agent mitoxantrone (MTX) can stimulate the peripheral relocation of CRT in both human and yeast cells, suggesting that the CRT exposure pathway is phylogenetically conserved. Here, we show that pheromones can act as physiological inducers of CRT exposure in yeast cells, thereby facilitating the formation of mating conjugates, and that a large-spectrum inhibitor of G protein-coupled receptors (which resemble the yeast pheromone receptor) prevents CRT exposure in human cancer cells exposed to MTX. An RNA interference screen as well as transcriptome analyses revealed that chemokines, in particular human CXCL8 (best known as interleukin-8) and its mouse ortholog Cxcl2, are involved in the immunogenic translocation of CRT to the outer leaflet of the plasma membrane. MTX stimulated the production of CXCL8 by human cancer cells in vitro and that of Cxcl2 by murine tumors in vivo. The knockdown of CXCL8/Cxcl2 receptors (CXCR1/Cxcr1 and Cxcr2) reduced MTX-induced CRT exposure in both human and murine cancer cells, as well as the capacity of the latter-on exposure to MTX-to elicit an anticancer immune response in vivo. Conversely, the addition of exogenous Cxcl2 increased the immunogenicity of dying cells in a CRT-dependent manner. Altogether, these results identify autocrine and paracrine chemokine signaling circuitries that modulate CRT exposure and the immunogenicity of cell death. PMID:23787997

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

    Microsoft Academic Search

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

    2011-01-01

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

  17. Collaboration between a soluble C-type lectin and calreticulin facilitates white spot syndrome virus infection in shrimp.

    PubMed

    Wang, Xian-Wei; Xu, Yi-Hui; Xu, Ji-Dong; Zhao, Xiao-Fan; Wang, Jin-Xing

    2014-09-01

    White spot syndrome virus (WSSV) mainly infects crustaceans through the digestive tract. Whether C-type lectins (CLs), which are important receptors for many viruses, participate in WSSV infection in the shrimp stomach remains unknown. In this study, we orally infected kuruma shrimp Marsupenaeus japonicus to model the natural transmission of WSSV and identified a CL (designated as M. japonicus stomach virus-associated CL [MjsvCL]) that was significantly induced by virus infection in the stomach. Knockdown of MjsvCL expression by RNA interference suppressed the virus replication, whereas exogenous MjsvCL enhanced it. Further analysis by GST pull-down and coimmunoprecipitation showed that MjsvCL could bind to viral protein 28, the most abundant and functionally relevant envelope protein of WSSV. Furthermore, cell-surface calreticulin was identified as a receptor of MjsvCL, and the interaction between these proteins was a determinant for the viral infection-promoting activity of MjsvCL. The MjsvCL-calreticulin pathway facilitated virus entry likely in a cholesterol-dependent manner. This study provides insights into a mechanism by which soluble CLs capture and present virions to the cell-surface receptor to facilitate viral infection. PMID:25070855

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

    PubMed

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

    2014-01-30

    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

  19. Hypericin-based photodynamic therapy induces surface exposure of damage-associated molecular patterns like HSP70 and calreticulin.

    PubMed

    Garg, Abhishek D; Krysko, Dmitri V; Vandenabeele, Peter; Agostinis, Patrizia

    2012-02-01

    Surface-exposed HSP70 and calreticulin are damage-associated molecular patterns (DAMPs) crucially involved in modulating the success of cancer therapy. Photodynamic therapy (PDT) involves the administration of a photosensitising (PTS) agent followed by visible light-irradiation. The reactive oxygen species that are thus generated directly kill tumours by damaging their microvasculature and inducing a local inflammatory reaction. PDT with the PTS photofrin is associated with DAMPs exposure, but the same is not true for other PTSs. Here, we show that when cancer cells are treated with hypericin-based PDT (Hyp-PDT), they surface-expose both HSP70 and calreticulin (CRT). Induction of CRT exposure was not accompanied by co-exposure of ERp57, but this did not compromise the ability of the exposed CRT to regulate the phagocytosis of Hyp-PDT-treated cancer cells by dendritic cells. Interestingly, we found that Hyp-PDT-induced CRT exposure (in contrast to anthracycline-induced CRT exposure) was independent of the presence of ERp57. Our results indicate that Hyp-PDT is a potential anti-cancer immunogenic modality. PMID:22193987

  20. Purification of an inositol 1,4,5-trisphosphate-binding calreticulin-containing intracellular compartment of HL-60 cells.

    PubMed Central

    Van Delden, C; Favre, C; Spät, A; Cerny, E; Krause, K H; Lew, D P

    1992-01-01

    To investigate the identity of Ins(1,4,5)P3-sensitive intracellular Ca2+ stores in myeloid cells, we have developed a method that yields subcellular fractions highly enriched in Ins(1,4,5)P3 binding. HL-60 cells were disrupted by nitrogen cavitation, and subcellular fractions were obtained by differential centrifugation, followed by Percoll- and sucrose-density-gradient separations. A subcellular fraction enriched 26-fold in Ins(1,4,5)P3-binding sites was obtained. This fraction showed no enrichment in plasma-membrane markers and only a comparatively moderate enrichment (7-fold) in endoplasmic-reticulum markers. The ratio between specific enrichment of Ins(1,4,5)P3 binding and endoplasmic-reticulum markers in the different fractions varied over 50-fold, from less than 0.1 to greater than 5. The purified Ins(1,4,5)P3-binding fraction was enriched to a similar extent (27-fold) in the putative intravesicular Ca(2+)-storage protein calreticulin. Our results favour the concept of a distinct Ins(1,4,5)P3-binding, calreticulin-containing compartment (i.e. the calciosome) in HL-60 cells. Images Fig. 1. Fig. 3. PMID:1536644

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

    PubMed Central

    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

    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

  2. Molecular insight into the effect of lipid bilayer environments on thrombospondin-1 and calreticulin interactions.

    PubMed

    Wang, Lingyun; Murphy-Ullrich, Joanne E; Song, Yuhua

    2014-10-14

    Thrombospondin-1 (TSP1) binding to cell surface calreticulin (CRT) stimulates the association of CRT with low-density lipoprotein (LDL) receptor-related protein (LRP1) to signal focal adhesion disassembly and engagement of cellular activities. A recent study demonstrated that membrane rafts are necessary for TSP1-mediated focal adhesion disassembly, but the molecular role of membrane rafts in mediating TSP1-CRT-LRP1 signaling is unknown. In this study, we investigated the effect of lipid bilayer environments on TSP1 and CRT interactions via atomically detailed molecular dynamics simulations. Results showed that the microscopic structural properties of lipid molecules and mesoscopic mechanical properties and electrostatic potential of the bilayer were significantly different between a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer and a raftlike lipid bilayer [a POPC/cholesterol (CHOL) raftlike lipid bilayer or a POPC/CHOL/sphingomyelin (SM) raftlike lipid bilayer], and the difference was enhanced by SM lipids in a raftlike lipid bilayer. These bilayer property differences affect the interactions of CRT with the bilayer, further influencing CRT conformation and TSP1-CRT interactions. A raftlike lipid bilayer stabilized CRT conformation as compared to a POPC bilayer environment. TSP1 binding to CRT resulted in a conformation for the CRT N-domain more "open" than that of the CRT P-domain in a raftlike lipid bilayer environment, which could facilitate binding of CRT to LRP1 to engage downstream signaling. The open conformational changes of CRT by binding to TSP1 in a raftlike lipid bilayer were enhanced by SM lipids in a lipid bilayer. The direct interactions of both the N- and P-domains of CRT with the bilayer contribute to the more open conformation of CRT in the TSP1-CRT complex on a raftlike lipid bilayer as compared to that on a POPC bilayer. The interactions of CRT or the TSP1-CRT complex with the lipid bilayer also caused CHOL molecules and/or lipids to be more coordinated and to aggregate into patchlike regions in the raftlike lipid bilayers. The lipid and CHOL molecule coordination and aggregation could in turn affect the interactions of CRT with the membrane raft, thereby altering TSP1-CRT interactions and CRT conformational changes that potentially regulate its interactions with LRP1. This study provides molecular insights into the role of lipid bilayer environments in TSP1-CRT interactions and in the CRT conformational changes that are predicted to facilitate binding of CRT to LRP1 to engage downstream signaling events. PMID:25260145

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

    PubMed Central

    2013-01-01

    Background Calreticulin (CRT) is a chaperone protein, which aids correct folding of glycosylated proteins in the endoplasmic reticulum (ER). Under conditions of ER stress, CRT is upregulated and may be displayed on the surface of cells or be secreted. This ‘ecto-CRT’ may activate the innate immune response or it may aid clearance of apoptotic cells. Our and other studies have demonstrated upregulation of ER stress markers CHOP, BiP, ATF4, XBP1 and phosphorylated e-IF2 alpha (p-eIF2 alpha) in biopsy and post-mortem human multiple sclerosis (MS) samples. We extend this work by analysing changes in expression of CRT, BiP, CHOP, XBP1 and p-eIF2 alpha in a rat model of inflammatory demyelination. Demyelination was induced in the spinal cord by intradermal injection of recombinant mouse MOG mixed with incomplete Freund’s adjuvant (IFA) at the base of the tail. Tissue samples were analysed by semi-quantitative scoring of immunohistochemically stained frozen tissue sections. Data generated following sampling of tissue from animals with spinal cord lesions, was compared to that obtained using tissue derived from IFA- or saline-injected controls. CRT present in rat serum and in a cohort of human serum derived from 14 multiple sclerosis patients and 11 healthy controls was measured by ELISA. Results Stained tissue scores revealed significantly (p<0.05) increased amounts of CRT, CHOP and p-eIF2 alpha in the lesion, lesion edge and normal-appearing white matter when compared to controls. CHOP and p-eIF2 alpha were also significantly raised in regions of grey matter and the central canal (p<0.05). Immunofluorescent dual-label staining confirmed expression of these markers in astrocytes, microglia or neurons. Dual staining of rat and human spinal cord lesions with Oil Red O and CRT antibody showed co-localisation of CRT with the rim of myelin fragments. ELISA testing of sera from control and EAE rats demonstrated significant down-regulation (p<0.05) of CRT in the serum of EAE animals, compared to saline and IFA controls. This contrasted with significantly increased amounts of CRT detected in the sera of MS patients (p<0.05), compared to controls. Conclusion This data highlights the potential importance of CRT and other ER stress proteins in inflammatory demyelination. PMID:24252779

  4. Catalyzed sodium chlorate candles

    NASA Technical Reports Server (NTRS)

    Malich, C. W.; Wydeven, T.

    1972-01-01

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

  5. Catalyzed gasification of biomass

    Microsoft Academic Search

    L. J. Jr. Sealock; R. J. Robertus; L. K. Mudge; D. H. Mitchell; J. L. Cox

    1978-01-01

    Catalyzed biomass gasification studies are being conducted by Battelle's Pacific Northwest Laboratories. Investigations are being carried out concurrently at the bench and process development unit scales. These studies are designed to test the technical and economic feasibility of producing specific gaseous products from biomass by enhancing its reactivity and product specificity through the use of specific catalysts. The program is

  6. Muon-catalyzed fusion

    Microsoft Academic Search

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

    1989-01-01

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

  7. Root to shoot communication and abscisic acid in calreticulin ( CR) gene expression and salt-stress tolerance in grafted diploid potato clones

    Microsoft Academic Search

    Javad Shaterian; Fawzy Georges; Atta Hussain; Doug Waterer; Hielke De Jong; Karen K. Tanino

    2005-01-01

    Potato is an important world crop but its cultivation is relatively limited by its sensitivity to salt-stress. Auto- and hetero-grafting was used to examine the effect of rootstock and abscisic acid (ABA) on expression of the Ca2+-storage protein calreticulin (CR) and salt-stress tolerance in potato. Sibling-selected diploid clones of potato (S. tuberosum) were utilized that are distinguished by differential root

  8. Tritium catalyzed deuterium tokamaks

    SciTech Connect

    Greenspan, E.; Miley, G.H.; Jung, J.; Gilligan, J.

    1984-04-01

    A preliminary assessment of the promise of the Tritium Catalyzed Deuterium (TCD) tokamak power reactors relative to that of deuterium-tritium (D-T) and catalyzed deuterium (Cat-D) tokamaks is undertaken. The TCD mode of operation is arrived at by converting the /sup 3/He from the D(D,n)/sup 3/He reaction into tritium, by neutron capture in the blanket; the tritium thus produced is fed into the plasma. There are three main parts to the assessment: blanket study, reactor design and economic analysis and an assessment of the prospects for improvements in the performance of TCD reactors (and in the promise of the TCD mode of operation, in general).

  9. CRT-1/calreticulin and the E3 ligase EEL-1/HUWE1 control hemidesmosome maturation in C. elegans development.

    PubMed

    Zahreddine, Hala; Zhang, Huimin; Diogon, Marie; Nagamatsu, Yasuko; Labouesse, Michel

    2010-02-23

    Hemidesmosomes connect the extracellular matrix (ECM) to intermediate filaments through ECM receptors and plakins (plectin and BPAG1e). They affect tissue integrity, wound healing, and carcinoma invasion. Although biochemical and time-lapse studies indicate that alpha6beta4-integrin (ECM receptor) and plectin play a central role in modulating hemidesmosome disassembly, the mechanisms controlling hemidesmosome biogenesis in vivo remain poorly understood. The nematode C. elegans provides a powerful genetic model to address this issue. We performed a genome-wide RNA interference screen in C. elegans, searching for genes that decrease the viability of a weak VAB-10A/plakin mutant. We identified 14 genes that have human homologs with predicted roles in different cellular processes. We further characterized two genes encoding the chaperone CRT-1/calreticulin and the HECT domain E3 ubiquitin ligase EEL-1/HUWE1. CRT-1 controls by as little as 2-fold the abundance of UNC-52/perlecan, an essential hemidesmosome ECM ligand. Likewise, EEL-1 fine tunes by 2-fold the abundance of myotactin, the putative hemidesmosome ECM receptor. CRT-1 and EEL-1 activities, and by extension other genes identified in our screen, are essential during embryonic development to enable hemidesmosomes exposed to mechanical tension to mature into a tension-resistant form. Our findings should help understand how hemidesmosome dynamics are regulated in vertebrate systems. PMID:20153198

  10. Calreticulin is required for responding to stress, foraging, and fertility in the white-tip nematode, Aphelenchoides besseyi.

    PubMed

    Feng, Hui; Wei, Lihui; Chen, Huaigu; Zhou, Yijun

    2015-08-01

    Calreticulin (CRT) regulates a wide array of cellular responses in physiological and pathological processes. A full-length cDNA-encoding CRT protein, namely AbCRT-1, was isolated from Aphelenchoides besseyi, an ectoparasitic plant nematode and the agent of white tip disease of rice. The deduced amino acid sequence of AbCRT-1 was highly homologous with other nematode CRTs, and showed the closest evolutionary relationship with BxCRT-1. In-situ hybridization showed that AbCRT-1 is specifically located in the oesophageal gland and gonads of A. besseyi, suggesting its potential role in parasitism and reproduction. Quantity real-time PCR analysis showed that AbCRT-1 is highly expressed in female nematodes but poorly expressed in eggs, juveniles, and male nematodes. Exposing the nematode to relatively low osmotic stress promotes the transcription of AbCRT-1 whereas extreme desiccation suppresses the transcription significantly. Nematodes in which AbCRT-1 mRNA level had been knocked down by soaking them in AbCRT-1 dsRNA solution distributed randomly and did not aggregate temporally, with a decreased capacity of food discernment. Thus the affected nematodes were markedly less fecund. These results demonstrate that AbCRT-1 is required in A. besseyi for responding to stress, foraging, and fertility. PMID:25999293

  11. Molecular cloning of calnexin and calreticulin in the Pacific oyster Crassostrea gigas and its expression in response to air exposure.

    PubMed

    Kawabe, Shinya; Yokoyama, Yoshihiro

    2010-03-01

    Calnexin (CNX) and calreticulin (CRT) are endoplasmic reticulum (ER) chaperones. CNX is a type I transmembrane protein and CRT is a soluble CNX homologue. In the ER, CNX and CRT are important for Ca(2+) homeostasis and protein maturation. Here, we describe the full-length cDNA of the first mollusk CNX (cgCNX) and a second mollusk CRT (cgCRT) from the oyster Crassostrea gigas. CgCNX, containing 3255bp, was composed of a 1764bp open reading frame (ORF) that encodes a 588-amino acid protein. CgCRT, containing 1727bp, was composed of a 1242bp ORF that encodes a 414-amino acid protein. CgCNX and cgCRT contains an N-terminal 21- and 16-amino acid sequence, respectively, which is characteristic of a signal sequence. At the C-terminus, cgCRT also contains the KDEL (-Lys-Asp-Glu-Leu) peptide motif suggesting that cgCRT localizes in the ER. Northern blot analysis showed that both cgCNX and cgCRT mRNAs are induced by air exposure. The expression patterns of cgCNX mRNA differed from those of cgCRT during air exposure. This suggests that these two molecular chaperones have different roles in the response to air exposure. PMID:21798193

  12. Pd-Catalyzed Wacker Cyclizations Palladium-Catalyzed Oxidative Wacker

    E-print Network

    Stoltz, Brian M.

    Pd-Catalyzed Wacker Cyclizations Palladium-Catalyzed Oxidative Wacker Cyclizations in Nonpolar. Trend, Yeeman K. Ramtohul, Eric M. Ferreira, and Brian M. Stoltz* Catalytic asymmetric oxidation-electron oxidations that do not involve heteroatom transfer. Some potentially valuable reactions of this type include

  13. Rhenium-Catalyzed Aromatic Propargylation

    E-print Network

    Toste, Dean

    Rhenium-Catalyzed Aromatic Propargylation Joshua J. Kennedy-Smith, Lauren A. Young, and F. Dean propargylation reaction, employing an air- and moisture-tolerant rhenium-oxo complex ((dppm)ReOCl3) as a catalyst. The potential of this rhenium(V)-catalyzed reaction is exemplified by application of the propargylation

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    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.

  15. A Nematode Calreticulin, Rs-CRT, Is a Key Effector in Reproduction and Pathogenicity of Radopholus similis.

    PubMed

    Li, Yu; Wang, Ke; Xie, Hui; Wang, Yan-Tao; Wang, Dong-Wei; Xu, Chun-Lin; Huang, Xin; Wang, De-Sen

    2015-01-01

    Radopholus similis is a migratory plant-parasitic nematode that causes severe damage to many agricultural and horticultural crops. Calreticulin (CRT) is a Ca2+-binding multifunctional protein that plays key roles in the parasitism, immune evasion, reproduction and pathogenesis of many animal parasites and plant nematodes. Therefore, CRT is a promising target for controlling R. similis. In this study, we obtained the full-length sequence of the CRT gene from R. similis (Rs-crt), which is 1,527-bp long and includes a 1,206-bp ORF that encodes 401 amino acids. Rs-CRT and Mi-CRT from Meloidogyne incognita showed the highest similarity and were grouped on the same branch of the phylogenetic tree. Rs-crt is a multi-copy gene that is expressed in the oesophageal glands and gonads of females, the gonads of males, the intestines of juveniles and the eggs of R. similis. The highest Rs-crt expression was detected in females, followed by juveniles, eggs and males. The reproductive capability and pathogenicity of R. similis were significantly reduced after treatment with Rs-crt dsRNA for 36 h. Using plant-mediated RNAi, we confirmed that Rs-crt expression was significantly inhibited in the nematodes, and resistance to R. similis was significantly improved in transgenic tomato plants. Plant-mediated RNAi-induced silencing of Rs-crt could be effectively transmitted to the F2 generation of R. similis; however, the silencing effect of Rs-crt induced by in vitro RNAi was no longer detectable in F1 and F2 nematodes. Thus, Rs-crt is essential for the reproduction and pathogenicity of R. similis. PMID:26061142

  16. A conserved basic residue cluster is essential for the protein quality control function of the Arabidopsis calreticulin 3

    PubMed Central

    Liu, Yidan; Li, Jianming

    2013-01-01

    Calreticulin (CRT) is a highly conserved chaperone-like lectin that regulates Ca2+ homeostasis and participates in protein quality control in the endoplasmic reticulum (ER). Most of our CRT knowledge came from mammalian studies, but our understanding of plant CRTs is limited. Many plants contain more than two CRTs that form two distinct groups: CRT1/CRT2 and CRT3. Previous studies on plant CRTs were focused on their Ca2+-binding function, but recent studies revealed a crucial role for the Arabidopsis CRT3 in ER retention of a mutant brassinosteroid receptor, brassinosteroid-insensitive 1-9 (bri1-9) and in complete folding of a plant immunity receptor EF-Tu Receptor (EFR). However, little is known about the molecular basis of the functional specification of the CRTs. We have recently shown that the C-terminal domain of CRT3, which is rich in basic residues, is essential for retaining bri1-9 in the ER; however, its role in assisting EFR folding has not been studied. Here, we used an insertional mutant of CRT3, ebs2-8 (EMS mutagenized bri1 suppressor 2-8), in the bri1-9 background as a genetic system to investigate the functional importance of two basic residue clusters in the CRT3?s C-terminal domain. Complementation experiments of ebs2-8 bri1-9 with mutant CRT3M transgenes showed that a highly conserved basic tetrapeptide Arg392Arg393Arg394Lys395 is essential but a less conserved basic tetrapeptide Arg401Arg402Arg403Arg404 is dispensable for the quality control function of CRT3 that retains bri1-9 in the ER and facilitates the complete folding of EFR. PMID:23425854

  17. Artificial feeding of Rhipicephalus microplus female ticks with anti calreticulin serum do not influence tick and Babesia bigemina acquisition.

    PubMed

    Antunes, Sandra; Merino, Octávio; Lérias, Joana; Domingues, Nuno; Mosqueda, Juan; de la Fuente, José; Domingos, Ana

    2015-02-01

    Ticks are obligate haematophagous ectoparasites considered the principal vectors of disease among animals. Rhipicephalus microplus and R. annulatus ticks are the most important vectors for Babesia bigemina and B. bovis, two of the most important intraerythrocytic protozoan parasites species in cattle, responsible for babesiosis which together with anaplasmosis account for substantial economic losses in the livestock industry worldwide. Anti-tick vaccines are a proved alternative to traditional tick and tick borne diseases control methods but are still limited primarily due to the lack of effective antigens. Subsequently to the identification of antigens the validation is a laborious work often expensive. Tick artificial feeding, is a low cost alternative to test antigens allowing achieving critical data. Herein, R. microplus females were successfully artificially fed using capillary tubes. Calreticulin (CRT) protein, which in a previous study has been identified as being involved in B. bigemina infection in R. annulatus ticks, was expressed as recombinant protein (rCRT) in an E. coli expression system and antibodies raised against rCRT. Anti-rCRT serum was supplemented to a blood meal, offered to partially engorged R. microplus females and their effect in feeding process as well as infection by B. bigemina was analyzed. No significant reductions in tick and egg weight were observed when ticks fed with anti-rCRT serum. Furthermore, B. bigemina infection levels did not show a statistically significant decrease when ticks fed with anti-rCRT antibodies. Results suggest that CRT is not a suitable candidate for cattle vaccination trials. PMID:25262467

  18. A Nematode Calreticulin, Rs-CRT, Is a Key Effector in Reproduction and Pathogenicity of Radopholus similis

    PubMed Central

    Li, Yu; Wang, Ke; Xie, Hui; Wang, Yan-Tao; Wang, Dong-Wei; Xu, Chun-Lin; Huang, Xin; Wang, De-Sen

    2015-01-01

    Radopholus similis is a migratory plant-parasitic nematode that causes severe damage to many agricultural and horticultural crops. Calreticulin (CRT) is a Ca2+-binding multifunctional protein that plays key roles in the parasitism, immune evasion, reproduction and pathogenesis of many animal parasites and plant nematodes. Therefore, CRT is a promising target for controlling R. similis. In this study, we obtained the full-length sequence of the CRT gene from R. similis (Rs-crt), which is 1,527-bp long and includes a 1,206-bp ORF that encodes 401 amino acids. Rs-CRT and Mi-CRT from Meloidogyne incognita showed the highest similarity and were grouped on the same branch of the phylogenetic tree. Rs-crt is a multi-copy gene that is expressed in the oesophageal glands and gonads of females, the gonads of males, the intestines of juveniles and the eggs of R. similis. The highest Rs-crt expression was detected in females, followed by juveniles, eggs and males. The reproductive capability and pathogenicity of R. similis were significantly reduced after treatment with Rs-crt dsRNA for 36 h. Using plant-mediated RNAi, we confirmed that Rs-crt expression was significantly inhibited in the nematodes, and resistance to R. similis was significantly improved in transgenic tomato plants. Plant-mediated RNAi-induced silencing of Rs-crt could be effectively transmitted to the F2 generation of R. similis; however, the silencing effect of Rs-crt induced by in vitro RNAi was no longer detectable in F1 and F2 nematodes. Thus, Rs-crt is essential for the reproduction and pathogenicity of R. similis. PMID:26061142

  19. Honokiol confers immunogenicity by dictating calreticulin exposure, activating ER stress and inhibiting epithelial-to-mesenchymal transition.

    PubMed

    Liu, Shing-Hwa; Lee, Wen-Jane; Lai, De-Wei; Wu, Sheng-Mao; Liu, Chia-Yu; Tien, Hsing-Ru; Chiu, Chien-Shan; Peng, Yen-Chun; Jan, Yee-Jee; Chao, Te-Hsin; Pan, Hung-Chuan; Sheu, Meei-Ling

    2015-04-01

    Peritoneal dissemination is a major clinical obstacle in gastrointestinal cancer therapy, and it accounts for the majority of cancer-related mortality. Calreticulin (CRT) is over-expressed in gastric tumors and has been linked to poor prognosis. In this study, immunohistochemistry studies revealed that the up-regulation of CRT was associated with lymph node and distant metastasis in patients with gastric cancer specimens. CRT was significantly down-regulated in highly metastatic gastric cancer cell lines and metastatic animal by Honokiol-treated. Small RNA interference blocking CRT by siRNA-CRT was translocated to the cells in the early immunogenic response to Honokiol. Honokiol activated endoplasmic reticulum (ER) stress and down-regulated peroxisome proliferator-activated receptor-? (PPAR?) activity resulting in PPAR? and CRT degradation through calpain-II activity, which could be reversed by siRNA-calpain-II. The Calpain-II/PPAR?/CRT axis and interaction evoked by Honokiol could be blocked by gene silencing or pharmacological agents. Both transforming growth factor (TGF)-?1 and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) induced cell migration, invasion and reciprocal down-regulation of epithelial marker E-cadherin, which could be abrogated by siRNA-CRT. Moreover, Honokiol significantly suppressed MNNG-induced gastrointestinal tumor growth and over-expression of CRT in mice. Knockdown CRT in gastric cancer cells was found to effectively reduce growth ability and metastasis in vivo. The present study provides insight into the specific biological behavior of CRT in epithelial-to-mesenchymal transition (EMT) and metastasis. Taken together, our results suggest that the therapeutic inhibition of CRT by Honokiol suppresses both gastric tumor growth and peritoneal dissemination by dictating early translocation of CRT in immunogenic cell death, activating ER stress, and blocking EMT. PMID:25619450

  20. C1q and Mannose Binding Lectin Engagement of Cell Surface Calreticulin and Cd91 Initiates Macropinocytosis and Uptake of Apoptotic Cells

    PubMed Central

    Ogden, Carol Anne; deCathelineau, Aimee; Hoffmann, Peter R.; Bratton, Donna; Ghebrehiwet, Berhane; Fadok, Valerie A.; Henson, Peter M.

    2001-01-01

    Removal of apoptotic cells is essential for maintenance of tissue homeostasis, organogenesis, remodeling, development, and maintenance of the immune system, protection against neoplasia, and resolution of inflammation. The mechanisms of this removal involve recognition of the apoptotic cell surface and initiation of phagocytic uptake into a variety of cell types. Here we provide evidence that C1q and mannose binding lectin (MBL), a member of the collectin family of proteins, bind to apoptotic cells and stimulate ingestion of these by ligation on the phagocyte surface of the multifunctional protein, calreticulin (also known as the cC1qR), which in turn is bound to the endocytic receptor protein CD91, also known as the ?-2-macroglobulin receptor. Use of these proteins provides another example of apoptotic cell clearance mediated by pattern recognition molecules of the innate immune system. Ingestion of the apoptotic cells through calreticulin/CD91 stimulation is further shown to involve the process of macropinocytosis, implicated as a primitive and relatively nonselective uptake mechanism for C1q- and MBL-enhanced engulfment of whole, intact apoptotic cells, as well as cell debris and foreign organisms to which these molecules may bind. PMID:11560994

  1. Enantioselective nucleophile-catalyzed cycloadditions

    E-print Network

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

    2007-01-01

    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. ...

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

    PubMed

    Wu, Qingyu; Shigaki, Toshiro; Han, Jeung-Sul; Kim, Chang Kil; Hirschi, Kendal D; Park, Sunghun

    2012-12-01

    Deregulated expression of an Arabidopsis H?/Ca²? antiporter (sCAX1) in agricultural crops increases total calcium (Ca²?) but may result in yield losses due to Ca²? deficiency-like symptoms. Here we demonstrate that co-expression of a maize calreticulin (CRT, a Ca²? binding protein located at endoplasmic reticulum) in sCAX1-expressing tobacco and tomato plants mitigated these adverse effects while maintaining enhanced Ca²? content. Co-expression of CRT and sCAX1 could alleviate the hypersensitivity to ion imbalance in tobacco plants. Furthermore, blossom-end rot (BER) in tomato may be linked to changes in CAX activity and enhanced CRT expression mitigated BER in sCAX1 expressing lines. These findings suggest that co-expressing Ca²? transporters and binding proteins at different intracellular compartments can alter the content and distribution of Ca²? within the plant matrix. PMID:23007728

  3. Iodine-Catalyzed Polysaccharide Esterification

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A review is provided of the recent reports to use iodine-catalyzed esterification reaction to produce esters from polysaccharides. The process entails reaction of the polysaccharide with an acid anhydride in the presence of a catalytic level of iodine, and in the absence of additional solvents. T...

  4. Copper Substrate Catalyzes Tetraazaperopyrene Polymerization

    E-print Network

    Schmidt, Wolf Gero

    Copper Substrate Catalyzes Tetraazaperopyrene Polymerization W.G. Schmidt, E. Rauls, U. Gerstmann-up approach, appears to be a very promising way to fabricate functional systems with nanometer dimensions [1 found that the copper substrate is crucial for the formation of the various aggregates they observed, i

  5. Thermodynamics of Enzyme-Catalyzed Reactions Database

    National Institute of Standards and Technology Data Gateway

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

  6. Compressibility of cold catalyzed matter

    NASA Astrophysics Data System (ADS)

    Haensel, P.

    1980-10-01

    The properties of cold catalyzed matter (CCM) of density near and above the density characteristic of the central region of heavy atomic nuclei are of fundamental importance for the physics of neutron stars. In this paper the compression modulus of CCM (an electrically neutral, spatially homogeneous mixture of electrons, neutrons, and protons at a temperature of 0 K) is studied for nucleon number density in the range 0.15-0.4 per cu fm. To a very good approximation the compression modulus is given by the nucleon contribution calculated at a fixed composition of the matter.

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

    PubMed Central

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

    2013-01-01

    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

  8. A calreticulin/gC1qR complex prevents cells from dying: a conserved mechanism from arthropods to humans.

    PubMed

    Watthanasurorot, Apiruck; Jiravanichpaisal, Pikul; Söderhäll, Kenneth; Söderhäll, Irene

    2013-04-01

    The crossroad between cell death and proliferation is a general target for viral infections because viruses need to obstruct apoptosis to use cells for their own replication. Inducing immunogenic cell death in proliferating cells is also an important aim of anticancer chemotherapy. The C1q-binding proteins calreticulin (CRT) and gC1qR are highly conserved ubiquitous proteins, which are putative targets for viral manipulation and are associated with cancer. Here we show that these proteins form a complex in the cytoplasm as a response to viral infection resulting in apoptosis prevention. The formation of a cytosolic CRT/gC1qR complex prevents cell death by reducing gC1qR translocation into the mitochondria, and we provide evidence that this mechanism is conserved from arthropods to human cancer cells. Furthermore, we show that it is possible to prevent this complex from being formed in cancer cells. When the peptides of the complex proteins are overexpressed in these cells, the cells undergo apoptosis. This finding shows a causal link between virus and cancer and may be used to develop new tools in anticancer or antiviral therapy. PMID:23378602

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

    PubMed

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

    2015-01-01

    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

  10. Iron Catalyzed Cycloaddition of Alkynenitriles and Alkynes

    PubMed Central

    D’Souza, Brendan R.; Lane, Timothy K.

    2011-01-01

    The combination of Fe(OAc)2 and an electron-donating, sterically-hindered pyridyl bisimine ligand catalyzes the cycloaddition of alkynenitriles and alkynes. A variety of substituted pyridines were obtained in good yields. PMID:21557582

  11. Manganese-catalyzed carbonylation of alkyl iodides

    E-print Network

    Westerhaus, Felix Alexander

    2009-01-01

    The palladium-catalyzed cross-coupling of aryl bromides with zirconocene-benzyne complexes has been investigated by S.L. Buchwald and coworkers. This method allows the formation of substituted biphenyls and terphenyls, ...

  12. Can laccases catalyze bond cleavage in lignin?

    PubMed

    Munk, Line; Sitarz, Anna K; Kalyani, Dayanand C; Mikkelsen, J Dalgaard; Meyer, Anne S

    2015-01-01

    Modification of lignin is recognized as an important aspect of the successful refining of lignocellulosic biomass, and enzyme-assisted processing and upcycling of lignin is receiving significant attention in the literature. Laccases (EC 1.10.3.2) are taking the centerstage of this attention, since these enzymes may help degrading lignin, using oxygen as the oxidant. Laccases can catalyze polymerization of lignin, but the question is whether and how laccases can directly catalyze modification of lignin via catalytic bond cleavage. Via a thorough review of the available literature and detailed illustrations of the putative laccase catalyzed reactions, including the possible reactions of the reactive radical intermediates taking place after the initial oxidation of the phenol-hydroxyl groups, we show that i) Laccase activity is able to catalyze bond cleavage in low molecular weight phenolic lignin model compounds; ii) For laccases to catalyze inter-unit bond cleavage in lignin substrates, the presence of a mediator system is required. Clearly, the higher the redox potential of the laccase enzyme, the broader the range of substrates, including o- and p-diphenols, aminophenols, methoxy-substituted phenols, benzenethiols, polyphenols, and polyamines, which may be oxidized. In addition, the currently available analytical methods that can be used to detect enzyme catalyzed changes in lignin are summarized, and an improved nomenclature for unequivocal interpretation of the action of laccases on lignin is proposed. PMID:25560931

  13. In Silico and In Vitro Studies on the Protein-Protein Interactions between Brugia malayi Immunomodulatory Protein Calreticulin and Human C1q

    PubMed Central

    Yadav, Sunita; Gupta, Smita; Selvaraj, Chandrabose; Doharey, Pawan Kumar; Verma, Anita; Singh, Sanjeev Kumar; Saxena, Jitendra Kumar

    2014-01-01

    Filarial parasites modulate effective immune response of their host by releasing a variety of immunomodulatory molecules, which help in the long persistence of the parasite within the host. The present study was aimed to characterize an immunomodulatory protein of Brugia malayi and its interaction with the host immune component at the structural and functional level. Our findings showed that Brugia malayi Calreticulin (BmCRT) is responsible for the prevention of classical complement pathway activation via its interaction with the first component C1q of the human host. This was confirmed by inhibition of C1q dependent lysis of immunoglobulin-sensitized Red Blood Cells (S-RBCs). This is possibly the first report which predicts CRT-C1q interaction on the structural content of proteins to explain how BmCRT inhibits this pathway. The molecular docking of BmCRT-C1q complex indicated that C1qB chain (IgG/M and CRP binding sites on C1q) played a major role in the interaction with conserved and non-conserved regions of N and P domain of BmCRT. Out of 37 amino acids of BmCRT involved in the interaction, nine amino acids (Pro126, Glu132, His147, Arg151, His153, Met154, Lys156, Ala196 and Lys212) are absent in human CRT. Both ELISA and in silico analysis showed the significant role of Ca+2 in BmCRT-HuC1q complex formation and deactivation of C1r2–C1s2. Molecular dynamics studies of BmCRT-HuC1q complex showed a deviation from ?0.4 nm to ?1.0 nm. CD analyses indicated that BmCRT is composed of 49.6% ? helix, 9.6% ? sheet and 43.6% random coil. These findings provided valuable information on the architecture and chemistry of BmCRT-C1q interaction and supported the hypothesis that BmCRT binds with huC1q at their targets (IgG/M, CRP) binding sites. This interaction enables the parasite to interfere with the initial stage of host complement activation, which might be helpful in parasites establishment. These results might be utilized for help in blocking the C1q/CRT interaction and preventing parasite infection. PMID:25184227

  14. s-cyclophilin is retained intracellularly via a unique COOH-terminal sequence and colocalizes with the calcium storage protein calreticulin

    PubMed Central

    1992-01-01

    Cyclophilins (cyclosporin A-binding proteins) are conserved, ubiquitous, and abundant proteins that accelerate the isomerization of XaaPro peptide bonds and the refolding of proteins in vitro. s- Cyclophilin is a member of the cyclophilin family with unique NH2- and COOH-terminal extensions, and with a signal sequence. We now report that s-cyclophilin is retained in the cell, and that the conserved s- cyclophilin-specific COOH-terminal extension VEKPFAIAKE is sufficient to direct a secretory protein to s-cyclophilin containing structures. Antibodies to s-cyclophilin-specific peptides were produced and the location of the protein was determined by an immunocytochemical study at the light microscopic level. s-Cyclophilin colocalized with the Ca(2+)-binding protein calreticulin and, to a lesser extent, with the microsomal Ca(2+)-ATPase in the myogenic cell line L6, and with the Ca(2+)-binding protein calsequestrin in skeletal muscle. In activated platelets, s-cyclophilin immunoreactivity was detected in a ring-like structure that might correspond to the Ca(2+)-storing and -releasing dense tubular network. In spreading cells, s-cyclophilin containing vesicular structures accumulated at actin-rich protrusion sites. While s-cyclophilin consistently codistributed with Ca2+ storage site markers, the distribution of s-cyclophilin immunoreactivity was not identical to that of ER markers. To determine whether the COOH-terminal extension of s-cyclophilin was involved in its intracellular transport we added this sequence to the COOH-terminus of the secretory protein glia-derived nexin. Appropriate constructs were expressed transiently in cultured cells and proteins were detected with specific antibodies. We found that glia-derived nexin with the COOH-terminal sequence VEKPFAIAKE (but not with the control sequence GLVVMNIT) colocalized with endogenous s-cyclophilin, indicating that the sequence contained retention information. These results indicate that s-cyclophilin is a retained component of an intracellular organelle and that it may accumulate in specialized portions of the ER, and possibly in calciosomes. Because of its conserved structure, widespread distribution, and abundance s-cyclophilin may be a useful marker to study the biogenesis and distribution of ER subcompartments. PMID:1530944

  15. Attractor Explosions and Catalyzed Vacuum Decay

    E-print Network

    Daniel Green; Eva Silverstein; David Starr

    2006-05-04

    We present a mechanism for catalyzed vacuum bubble production obtained by combining moduli stabilization with a generalized attractor phenomenon in which moduli are sourced by compact objects. This leads straightforwardly to a class of examples in which the Hawking decay process for black holes unveils a bubble of a different vacuum from the ambient one, generalizing the new endpoint for Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble production can occur for both charged and uncharged bodies, including Schwarzschild black holes for which massive particles produced in the Hawking process can trigger vacuum decay. We briefly discuss applications of this process to the population and stability of metastable vacua.

  16. Oligonucleotide formation catalyzed by mononucleotide matrices

    NASA Technical Reports Server (NTRS)

    Lohrmann, R.

    1982-01-01

    Pb(2+)-containing precipitates of mononucleotides form matrices which catalyze the self-condensation of nucleotide 5-prime-phosphorimidazolides and their condensation with nucleosides. The reactions exhibit base-pairing specificity between matrix nucleotide and substrate, and usually follow the Watson-Crick pairing rules. Although purine polynucleotides do not facilitate the oligomerization of pyrimidine nucleotide monomers in solution, it is interesting that purine-containing matrices do catalyze such a reaction. The significance of the results in the context of the prebiotic evolution of polynucleotides is discussed.

  17. Rh-catalyzed linear hydroformylation of styrene.

    PubMed

    Boymans, Evert; Janssen, Michèle; Müller, Christian; Lutz, Martin; Vogt, Dieter

    2013-01-01

    Usually the Rh-catalyzed hydroformylation of styrene predominantly yields the branched, chiral aldehyde. An inversion of regioselectivity can be achieved using strong ?-acceptor ligands. Binaphthol-based diphosphite and bis(dipyrrolyl-phosphorodiamidite) ligands were applied in the Rh-catalyzed hydroformylation of styrene. High selectivities up to 83% of 3-phenylpropanal were obtained with 1,1-bi-2-naphthol-based bis(dipyrrolyl-phosphorodiamidite) with virtually no hydrogenation to ethyl benzene. The coordination chemistry of those ligands towards Rh(I) was investigated spectroscopically and structurally. PMID:23104326

  18. Attractor Explosions and Catalyzed Vacuum Decay

    SciTech Connect

    Green, Daniel; Silverstein, Eva; Starr, David

    2006-05-05

    We present a mechanism for catalyzed vacuum bubble production obtained by combining moduli stabilization with a generalized attractor phenomenon in which moduli are sourced by compact objects. This leads straightforwardly to a class of examples in which the Hawking decay process for black holes unveils a bubble of a different vacuum from the ambient one, generalizing the new endpoint for Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble production can occur for both charged and uncharged bodies, including Schwarzschild black holes for which massive particles produced in the Hawking process can trigger vacuum decay. We briefly discuss applications of this process to the population and stability of metastable vacua.

  19. Palladium-Catalyzed Arylation of Cyanamides

    PubMed Central

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

    2014-01-01

    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

  20. Titanium-Catalyzed Enantioselective Additions of

    E-print Network

    Walsh, Patrick J.

    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

  1. Data, Leadership, and Catalyzing Culture Change

    ERIC Educational Resources Information Center

    Benson, R. Todd; Trower, Cathy A.

    2012-01-01

    It is crucial to understand today's tenure-track workers so that colleges and universities can continue to attract and retain a large subset of them by understanding and supporting their satisfaction and success at work. In this article, the authors talk about data, leadership, and catalyzing culture change. They discuss data use in the academy…

  2. Pd-Catalyzed Cyclizations Direct Oxidative Heck

    E-print Network

    Stoltz, Brian M.

    Pd-Catalyzed Cyclizations Direct Oxidative Heck Cyclizations: Intramolecular Fujiwara (Scheme 1a). A potentially more efficient process would involve oxidative coupling of an unfunction olefins (e.g., acrylate esters).[3] In fact, the direct intramolecular oxidative arene/ olefin coupling (i

  3. Microorganisms detected by enzyme-catalyzed reaction

    NASA Technical Reports Server (NTRS)

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

    1966-01-01

    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.

  4. Phosphine-catalyzed construction of sulfur heterocycles.

    PubMed

    Gabillet, Sandra; Lecerclé, Delphine; Loreau, Olivier; Carboni, Michael; Dézard, Sophie; Gomis, Jean-Marie; Taran, Frédéric

    2007-09-27

    A simple and efficient method for constructing sulfur heterocycles was developed using a phosphine-catalyzed tandem umpolung addition and intramolecular cyclization of bifunctional sulfur pronucleophiles on arylpropiolates. The reaction offers a promising route to synthetically useful as well as biologically active heterocycles under neutral conditions. PMID:17803312

  5. Lipase catalyzed formation of flavour esters

    Microsoft Academic Search

    G. Langrand; C. Triantaphylides; J. Baratti

    1988-01-01

    Summary Thirteen commercial lipase preparations were checked for their ability to catalyse the formation of flavour esters (isoamyl or geranyl acetate, propionate and butyrate) by either direct esterification or ester solvolysis in n-heptane. The formation of isoamyl or geranyl butyrates and propionates by direct esterification was catalyzed by the majority of the tested lipases. Acetic acid esters were more difficult

  6. Highly regioselective osmium-catalyzed hydroformylation.

    PubMed

    Wu, Lipeng; Liu, Qiang; Spannenberg, Anke; Jackstell, Ralf; Beller, Matthias

    2015-02-21

    The first highly regioselective and general osmium-catalyzed hydroformylation of olefins to aldehydes is reported. The combination of Os3(CO)12 and imidazoyl-substituted phosphine ligands allows n-selective (up to 99%) hydroformylation of bulk aliphatic as well as functional alkenes in good yields (64-87%). PMID:25620413

  7. Carboxylic Acid catalyzed hydration of acetaldehyde.

    PubMed

    Rypkema, Heather A; Sinha, Amitabha; Francisco, Joseph S

    2015-05-14

    Electronic structure calculations of the pertinent stationary points on the potential energy surface show that carboxylic acids can act effectively as catalysts in the hydration of acetaldehyde. Barriers to this catalyzed process correlate strongly with the pKa of the acid, providing the potential to provide the predictive capacity of the effectiveness of carboxylic acid catalysts. Transition states for the acid-catalyzed systems take the form of pseudo-six-membered rings through the linear nature of their hydrogen bonds, which accounts for their relative stability compared to the more strained direct and water-catalyzed systems. When considered as a stepwise reaction of a dimerization followed by reaction/complexation, it is likely that collisional stabilization of the prereactive complex is more likely than reaction in the free gas phase, although the catalyzed hydration does retain the potential to proceed on water surfaces or in droplets. Lastly, it is observed that postreactive diol-acid complexes are significantly stable (?12-17 kcal/mol) relative to isolated products, suggesting the possibility of long-lived hygroscopic species that could act as a seed molecule for condensation of secondary organic aerosols. PMID:25734508

  8. Stochastic Simulation of Enzyme-Catalyzed Reactions with Disparate Timescales

    E-print Network

    Paul, Mark

    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

  9. Enzyme-Catalyzed Processes in Organic Solvents

    Microsoft Academic Search

    Aleksey Zaks; Alexander M. Klibanov

    1985-01-01

    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,

  10. Gold-catalyzed carbene transfer reactions.

    PubMed

    Shin, Seunghoon

    2015-01-01

    In homogeneous gold catalysis, generations and reactions of metal carbenes have been one of the most rapidly developing areas because of their diverse reactivity under mild conditions. This review covers recent advances in the gold-catalyzed oxygen atom transfer and carbene transfer reactions to alkynes. Atom transfer to an alkyne enables alkynes to function as metal carbene synthons. Many such reactions fulfill redox neutrality starting from safe and easily handled precursors. PMID:25518973

  11. AMMONIA CATALYZED ORGANOSOLV DELIGNIFICATION OF POPLAR

    Microsoft Academic Search

    JUNG-KEUG PARK; JANICE A. PHILLIPS

    1988-01-01

    A parametric investigation of NH4OH catalyzed solvent delignification of poplar was conducted to define pretreatment conditions which would yield an optimal separation of the biomass components and an enzymatic susceptible solid carbohydrate phase. Delignification parameters of interest included concentration of NH4OH, time and temperature of the reaction, and type of solvent. The addition of 0.82 M NH4OH to the delignification

  12. Imidazole catalyzes chlorination by unreactive primary chloramines.

    PubMed

    Roemeling, Margo D; Williams, Jared; Beckman, Joseph S; Hurst, James K

    2015-05-01

    Hypochlorous acid and simple chloramines (RNHCl) are stable biologically derived chlorinating agents. In general, the chlorination potential of HOCl is much greater than that of RNHCl, allowing it to oxidize or chlorinate a much wider variety of reaction partners. However, in this study we demonstrate by kinetic analysis that the reactivity of RNHCl can be dramatically promoted by imidazole and histidyl model compounds via intermediary formation of the corresponding imidazole chloramines. Two biologically relevant reactions were investigated--loss of imidazole-catalyzed chlorinating capacity and phenolic ring chlorination using fluorescein and the tyrosine analog, 4-hydroxyphenylacetic acid (HPA). HOCl reacted stoichiometrically with imidazole, N-acetylhistidine (NAH), or imidazoleacetic acid to generate the corresponding imidazole chloramines which subsequently decomposed. Chloramine (NH2Cl) also underwent a markedly accelerated loss in chlorinating capacity when NAH was present, although in this case N-?-acetylhistidine chloramine (NAHCl) did not accumulate, indicating that the catalytic intermediate must be highly reactive. Mixing HOCl with 1-methylimidazole (MeIm) led to very rapid loss in chlorinating capacity via formation of a highly reactive chlorinium ion (MeImCl(+)) intermediate; this behavior suggests that the reactive forms of the analogous imidazole chloramines are their conjugate acids, e.g., the imidazolechlorinium ion (HImCl(+)). HOCl-generated imidazole chloramine (ImCl) reacted rapidly with fluorescein in a specific acid-catalyzed second-order reaction to give 3'-monochloro and 3',5'-dichloro products. Equilibrium constants for the transchlorination reactions HOCl + HIm = H2O + ImCl and NH2Cl + HIm = NH3 + ImCl were estimated from the dependence of the rate constants on [HIm]/[HOCl] and literature data. Acid catalysis again suggests that the actual chlorinating agent is HImCl(+); consistent with this interpretation, MeIm markedly catalyzed fluorescein chlorination by HOCl. Time-dependent imidazole-catalyzed HPA chlorination by NH2Cl was also demonstrated by product analyses. Quantitative assessment of the data suggests that physiological levels of histidyl groups will react with primary chloramines to generate a flux of imidazole chloramine sufficient to catalyze biological chlorination via HImCl(+), particularly in environments that generate high concentrations of HOCl such as the neutrophil phagosome. PMID:25660996

  13. Gold-catalyzed oxime-oxime rearrangement.

    PubMed

    Guven, Sinem; Ozer, Merve Sinem; Kaya, Serdal; Menges, Nurettin; Balci, Metin

    2015-06-01

    The gold-catalyzed reaction of pyrrole and indole oximes having a propargyl group attached to the nitrogen atom was studied. The selective 6-endo-dig mode of cyclization was observed for the terminal alkynes giving rise to the formation of pyrazine N-oxides in the presence of a gold catalyst. However, the reaction with substituted alkyne transferred the oxime functionality intramolecularly from one carbon atom to another via the 7-endo-dig cyclization process. This transformation is unprecedented in the literature and is named an oxime-oxime rearrangement. PMID:25992473

  14. Ligand Intermediates in Metal-Catalyzed Reactions

    SciTech Connect

    Gladysz, John A.

    1999-07-31

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

  15. Antibody-catalyzed anaerobic destruction of methamphetamine.

    PubMed

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

    2007-03-01

    Methamphetamine [(+)-2] abuse has emerged as a fast-rising global epidemic, with immunopharmacotherapeutic approaches being sought for its treatment. Herein, we report the generation and characterization of a monoclonal antibody, YX1-40H10, that catalyzes the photooxidation of (+)-2 into the nonpsychoactive compound benzaldehyde (14) under anaerobic conditions in the presence of riboflavin (6). Studies have revealed that the antibody facilitates the conversion of (+)-2 into 14 by binding the triplet photoexcited state of 6 in proximity to (+)-2. The antibody binds riboflavin (K(d) = 180 muM), although this was not programmed into hapten design, and the YX1-40H10-catalyzed reaction is inhibited by molecular oxygen via the presumed quenching of the photoexcited triplet state of 6. Given that this reaction is another highlight in the processing of reactive intermediates by antibodies, we speculate that this process may have future significance in vivo with programmed immunoglobulins that use flavins as cofactors to destroy selectable molecular targets under hypoxic or even anoxic conditions. PMID:17360412

  16. Biginelli Reaction Catalyzed by Copper Nanoparticles

    PubMed Central

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

    2012-01-01

    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

  17. Palladium-Catalyzed Arylation of Fluoroalkylamines.

    PubMed

    Brusoe, Andrew T; Hartwig, John F

    2015-07-01

    We report the synthesis of fluorinated anilines by palladium-catalyzed coupling of fluoroalkylamines with aryl bromides and aryl chlorides. The products of these reactions are valuable because anilines typically require the presence of an electron-withdrawing substituent on nitrogen to suppress aerobic or metabolic oxidation, and the fluoroalkyl groups have steric properties and polarity distinct from those of more common electron-withdrawing amide and sulfonamide units. The fluoroalkylaniline products are unstable under typical conditions for C-N coupling reactions (heat and strong base). However, the reactions conducted with the weaker base KOPh, which has rarely been used in cross-coupling to form C-N bonds, occurred in high yield in the presence of a catalyst derived from commercially available AdBippyPhos and [Pd(allyl)Cl]2. Under these conditions, the reactions occur with low catalyst loadings (<0.50 mol % for most substrates) and tolerate the presence of various functional groups that react with the strong bases that are typically used in Pd-catalyzed C-N cross-coupling reactions of aryl halides. The resting state of the catalyst is the phenoxide complex, (BippyPhosPd(Ar)OPh); due to the electron-withdrawing property of the fluoroalkyl substituent, the turnover-limiting step of the reaction is reductive elimination to form the C-N bond. PMID:26065341

  18. Manganese Catalyzed C-H Halogenation.

    PubMed

    Liu, Wei; Groves, John T

    2015-06-16

    The remarkable aliphatic C-H hydroxylations catalyzed by the heme-containing enzyme, cytochrome P450, have attracted sustained attention for more than four decades. The effectiveness of P450 enzymes as highly selective biocatalysts for a wide range of oxygenation reactions of complex substrates has driven chemists to develop synthetic metalloporphyrin model compounds that mimic P450 reactivity. Among various known metalloporphyrins, manganese derivatives have received considerable attention since they have been shown to be versatile and powerful mediators for alkane hydroxylation and olefin epoxidation. Mechanistic studies have shown that the key intermediates of the manganese porphyrin-catalyzed oxygenation reactions include oxo- and dioxomanganese(V) species that transfer an oxygen atom to the substrate through a hydrogen abstraction/oxygen recombination pathway known as the oxygen rebound mechanism. Application of manganese porphyrins has been largely restricted to catalysis of oxygenation reactions until recently, however, due to ultrafast oxygen transfer rates. In this Account, we discuss recently developed carbon-halogen bond formation, including fluorination reactions catalyzed by manganese porphyrins and related salen species. We found that biphasic sodium hypochlorite/manganese porphyrin systems can efficiently and selectively convert even unactivated aliphatic C-H bonds to C-Cl bonds. An understanding of this novel reactivity derived from results obtained for the oxidation of the mechanistically diagnostic substrate and radical clock, norcarane. Significantly, the oxygen rebound rate in Mn-mediated hydroxylation is highly correlated with the nature of the trans-axial ligands bound to the manganese center (L-Mn(V)?O). Based on the ability of fluoride ion to decelerate the oxygen rebound step, we envisaged that a relatively long-lived substrate radical could be trapped by a Mn-F fluorine source, effecting carbon-fluorine bond formation. Indeed, this idea led to the discovery of the first Mn-catalyzed direct aliphatic C-H fluorination reactions utilizing simple, nucleophilic fluoride salts. Mechanistic studies and DFT calculations have revealed a trans-difluoromanganese(IV) species as the key fluorine transfer intermediate. In addition to catalyzing normal (19)F-fluorination reactions, manganese salen complexes were found to enable the incorporation of radioactive (18)F fluorine via C-H activation. This advance represented the first direct Csp(3)-H bond (18)F labeling with no-carrier-added [(18)F]fluoride and facilitated the late-stage labeling of drug molecules for PET imaging. Given the high reactivity and enzymatic-like selectively of metalloporphyrins, we envision that this new Heteroatom-Rebound Catalysis (HRC) strategy will find widespread application in the C-H functionalization arena and serve as an effective tool for forming new carbon-heteroatom bonds at otherwise inaccessible sites in target molecules. PMID:26042637

  19. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    Ault, Addison

    2011-01-01

    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…

  20. 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...

  1. Acid-Catalyzed Isomerization of Carvone to Carvacrol

    ERIC Educational Resources Information Center

    Kjonaas, Richard A.; Mattingly, Shawn P.

    2005-01-01

    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.

  2. Iron-catalyzed amination of alcohols assisted by Lewis acid.

    PubMed

    Pan, Hui-Jie; Ng, Teng Wei; Zhao, Yu

    2015-07-01

    An efficient Lewis acid-assisted, iron-catalyzed amination of alcohols using borrowing hydrogen methodology was developed. In particular, silver fluoride was identified to be a highly effective additive to overcome the low efficiency in the amination of secondary alcohols catalyzed by Knölker's complex. PMID:26111504

  3. Nickel(0)-Catalyzed Asymmetric Hydrocyanation of 1,3-Dienes

    E-print Network

    RajanBabu, T. V. "Babu"

    Nickel(0)-Catalyzed Asymmetric Hydrocyanation of 1,3-Dienes Biswajit Saha and T. V. Rajan.; Druliner, J. D.; Stevens, W. R. Homogeneous Nickel-Catalyzed Olefin Hydrocyanation. AdV. Catal. 1985, 33, 1. (b) Tolman, C. A. Chem. ReV. 1977, 77, 313. (c) Tolman, C. A. J. Chem. Educ. 1986, 63, 199. ORGANIC

  4. Fabrication of catalyzed ion transport membrane systems

    DOEpatents

    Carolan, Michael Francis; Kibby, Charles Leonard

    2013-06-04

    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).

  5. Efficient antibody-catalyzed oxygenation reaction

    SciTech Connect

    Hsieh, L.C.; Stephans, J.C.; Schultz, P.G. (Univ. of California, Berkeley, CA (United States))

    1994-03-09

    Biological oxygen-transfer reactions are essential for the biosynthesis of steroids and neurotransmitters, the degradation of endogenous substances, and the detoxification of xenobiotics. The monooxygenase enzymes responsible for these transformations require biological cofactors such as flavin, heme and non-heme iron, copper, or pterin and typically utilize NADPH for cofactor regeneration. We now report an antibody-catalyzed sulfide oxygenation reaction mediated by the chemical cofactor sodium periodate, with turnover numbers similar to those of the corresponding enzymatic reactions. Sodium periodate NaIO[sub 4]O was chosen as the oxidant, since sulfoxide formation occurs under mild aqueous conditions with minimal overoxidation to the sulfone. Furthermore, compared to the flavin and heme cofactors required by the monooxygenase enzymes, NaIO[sub 4] is very inexpensive, obviating the need for cofactor recycling. Overall, these results raise the possibility of using antibodies as catalysts for regio- and stereoselective sulfide oxidations. 18 refs., 1 fig.

  6. Porphyrin-catalyzed oxidation of trichlorophenol

    SciTech Connect

    Hasan, S.; Sublette, K.L. [Univ. of Tulsa, OK (United States)

    1997-12-31

    Porphyrin-metal complexes are potentially useful to catalyze redox reactions, which convert toxic and biologically recalcitrant compounds to compounds that are less toxic and more amenable to biotreatment. Porphyrins, in the absence of proteins as in ligninases, peroxidases, and oxidases, are potentially more robust than enzymes and microbial cultures in the treatment of inhibitory substances. 2,4,6-Trichlorophenol was used as a model compound for chlorinated phenols and as a substrate for various porphyrin-metal complexes acting as oxidation catalysts. t-Butyl hydroperoxide was the oxidizing agent. TCP was shown to be at least partially dechlorinated and the aromatic ring broken in reaction products. All porphyrins exhibited saturation kinetics with regard to the initial TCP concentration in reaction mixtures. Electron-withdrawing substituents on the porphyrins were observed to increase stability of the catalysts to inactivating ring-centered oxidation. 16 refs., 3 figs., 2 tabs.

  7. Alternative metals for homogeneous catalyzed hydroformylation reactions.

    PubMed

    Pospech, Jola; Fleischer, Ivana; Franke, Robert; Buchholz, Stefan; Beller, Matthias

    2013-03-01

    Transition-metal-catalyzed hydroformylation reactions constitute one of the most powerful tools for C-C bond formation in organic synthesis and represent an outstanding example of the application of homogeneous catalysis on an industrial scale. This process allows for the straightforward conversion of inexpensive chemical feedstock into broadly applicable aldehydes, which serve as major building blocks for numerous chemical products. These products are highly valuable for the chemical industry and used as plasticizers, detergents, and surfactants on a million ton scale. Moreover, aldehydes serve as versatile chemical intermediates for the production of fine chemicals and pharmaceuticals. Currently, most of the bulk hydroformylation processes rely on rhodium-based catalysts. The increasing demand and resulting high cost of this precious metal has resulted in alternative transition-metal catalysts becoming highly desirable. The following Review summarizes the progress achieved utilizing Ru, Ir, Pd, Pt, and Fe catalysts in hydroformylation reactions. PMID:23436281

  8. Pd and Mo Catalyzed Asymmetric Allylic Alkylation

    PubMed Central

    Trost, Barry M.

    2012-01-01

    The ability to control the alkylation of organic substrates becomes ever more powerful by using metal catalysts. Among the major benefits of metal catalysis is the possibility to perform such processes asymmetrically using only catalytic amounts of the chiral inducing agent which is a ligand to the metal of the catalyst. A unique aspect of asymmetric metal catalyzed processes is the fact that many mechanisms exist for stereoinduction. Furthermore, using the same catalyst system, many types of bonds including but not limited to C-C, C-N, C-O, C-S, C-P, and C-H can be formed asymmetrically. An overview of this process using palladium and molybdenum based metals being developed in my laboratories and how they influence strategy in synthesizing bioactive molecular targets is presented. PMID:22736934

  9. NEW CORDIERITE DIESEL PARTICULATE FILTERS FOR CATALYZED AND NON-CATALYZED APPLICATIONS

    SciTech Connect

    Merkel, G; Cutler, W; Tao, T Chiffey, A; Phillips, P; Twigg, M; Walker, A

    2003-08-24

    Cordierite diesel particulate filters provide an economical approach to diesel emissions control. However, further reduction in the pressure drop of catalyzed and non-catalyzed cordierite filters is desirable. In order to derive a fundamental understanding of the relationship between clean and sootloaded pressure drop and the pore microstructure of the ceramic, and to optimize the microstructure for filter performance, cordierite filters have been fabricated spanning an extended range in porosity, pore size distribution, and pore connectivity. Analysis of the results has been applied to the development of several new cordierite diesel particulate filters that possess a unique combination of high filtration efficiency, high strength, and very low clean and soot-loaded pressure drop. Furthermore, catalyst systems have been developed that result in a minimal pressure drop increase of the catalyzed filter. Optimization of porosity and cell geometry has enabled fabrication o f filters with either high or low thermal mass appropriate to the regeneration strategy employed for a given engine management system.

  10. Tax Posttranslational Modifications and Interaction with Calreticulin in MT-2 Cells and Human Peripheral Blood Mononuclear Cells of Human T Cell Lymphotropic Virus Type-I-Associated Myelopathy/Tropical Spastic Paraparesis Patients

    PubMed Central

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

    2014-01-01

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

  11. Rhodium-Catalyzed Asymmetric Intramolecular Hydroamination of Unactivated Alkenes

    E-print Network

    Shen, Xiaoqiang

    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). ...

  12. Silver-catalyzed vinylogous fluorination of vinyl diazoacetates.

    PubMed

    Qin, Changming; Davies, Huw M L

    2013-12-20

    A silver-catalyzed vinylogous fluorination of vinyl diazoacetates to generate ?-fluoro-?,?-unsaturated carbonyls is presented. Application of this method to the fluorination of farnesol and steroid derivatives was achieved. PMID:24228754

  13. Nickel-Catalyzed Allylic Substitution of Simple Alkenes

    E-print Network

    Matsubara, Ryosuke

    This report describes a nickel-catalyzed allylic substitution process of simple alkenes whereby an important structural motif, a 1,4-diene, was prepared. The key to success is the use of an appropriate nickel–phosphine ...

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

    E-print Network

    Okiomah, Ogheneruno E. (Ogheneruno Elo)

    2011-01-01

    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 ...

  15. Pd-catalyzed arylation of chlorotrifluoroethylene using arylboronic acids.

    PubMed

    Yamamoto, Tetsuya; Yamakawa, Tetsu

    2012-07-01

    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

  16. A preliminary study of zinc-catalyzed polycarbonate production 

    E-print Network

    Griffith, Amy Elizabeth

    1992-01-01

    A PRELIMINARY STUDY OF ZINC-CATALYZED POLYCARBONATE PRODUCTION A Thesis by AMY ELIZABETH GRIFFITH Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER... OF SCIENCE May 1992 Major Subject: Chemistry A PREUMINARY STUDY OF ZINC-CATALYZED POLYCARBONATE PRODUCTION A Thesis by AMY ELIZABETH GRIFFITH Approved as to style and content by; . J. Darensbour Chair of Co i ee) J. Kelly (Member) T. Hug anks (Me...

  17. Nickel-Catalyzed Coupling of Alkenes, Aldehydes, and Silyl Triflates

    PubMed Central

    Ng, Sze-sze; Ho, Chun-Yu; Jamison, Timothy F.

    2011-01-01

    A full account of two recently developed nickel-catalyzed coupling reactions of alkenes, aldehydes and silyl triflates is presented. These reactions provide either allylic alcohol or homoallylic alcohol derivatives selectively, depending on the ligand employed. These processes are believed to be mechanistically distinct from Lewis acid-catalyzed carbonyl-ene reactions, and several lines of evidence supporting this hypothesis are discussed. PMID:16939275

  18. Optimization of lipase-catalyzed biodiesel by response surface methodology

    Microsoft Academic Search

    C.-J. Shieh; H.-F. Liao; C.-C. Lee

    2003-01-01

    Biodiesel prepared by catalyzed mild transesterification has become of much current interest for bioenergy. The ability of a commercial immobilized lipase (Novo Industries––Bagsvaerd, Denmark) from Rhizomucor miehei (Lipozyme IM-77) to catalyze the transesterification of soybean oil and methanol was investigated in this study. Response surface methodology and 5-level-5-factor central composite rotatable design were employed to evaluate the effects on reaction

  19. Toluene Monooxygenase-Catalyzed Epoxidation of Alkenes

    PubMed Central

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

    2000-01-01

    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

  20. Mechanisms of bacterially catalyzed reductive dehalogenation

    SciTech Connect

    Picardal, F.W.

    1992-12-31

    Nine bacteria were tested for the ability to dehalogenate tetrachloromethane (CT), tetrachloroethene (PCE), and 1, 1, 1-trichloroethane (TCA) under anaerobic conditions. Three bacteria were able to reductively dehalogenate CT. Dehalogenation ability was not readily linked to a common metabolism or changes in culture redox potential. None of the bacteria tested were able to dehalogenate PCE or TCA. One of the bacteria capable of dehalogenating CT, Shewanella putrefaciens, was chosen as a model organism to study mechanisms of bacterially catalyzed reductive dehalogenation. The effect of a variety of alternate electron acceptors on CT dehalogenation ability by S. putrefaciens was determined. oxygen and nitrogen oxides were inhibitory but Fe (III), trimethylamine oxide, and fumarate were not. A model of the electron transport chain of S. putrefaciens was developed to explain inhibition patterns. A period of microaerobic growth prior to CT exposure increased the ability of S. putrefaciens to dehalogenate CT. A microaerobic growth period also increased cytochrome concentrations. A relationship between cytochrome content and dehalogenation ability was developed from studies in which cytochrome concentrations in S. putrefaciens were manipulated by changing growth conditions. Stoichiometry studies using {sup 14}C-CT suggested that CT was first reduced to form a trichloromethyl radical. Reduction of the radical to produce chloroform and reaction of the radical with cellular biochemicals explained observed product distributions. Carbon dioxide or other fully dehalogenated products were not found.

  1. Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

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

    E-print Network

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

    2014-01-01

    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 ...

  3. Conservation Kickstart- Catalyzing Conservation Initiatives Worldwide

    NASA Astrophysics Data System (ADS)

    Treinish, G.

    2014-12-01

    Adventurers and Scientists for Conservation (ASC) is a nonprofit organization that collects environmental data to catalyze conservation initiatives worldwide. Adventure athletes have the skills and motivation to reach the most remote corners of the world. ASC utilizes those skills to provide the scientific community with data while providing the outdoor community with purpose beyond the personal high of reaching a summit or rowing across an ocean. We carefully select projects, choosing partnerships that will maximize the impact of ASC volunteers. Each project must have a clear path to a tangible conservation outcome and demonstrate a clear need for our brand of volunteers. We partner with government agencies, universities, and independant reseachers to kickstart data collection efforts around the world. Last year, through a partnership with the Olympic National Forest, 20 volunteers from the Seattle area set up and monitored camera traps in an effort to survey for costal Pacific marten. Our work led to the species' listing as "critically imperiled" with NatureServe. A partnership with the inaugural Great Pacific Race, engaging trans-Pacific rowing teams, searched for microplastics in the Pacific Ocean as part of our ongoing microplastics campaign. In a multi-year partnership with the American Prairie Reserve (APR), ASC volunteer crews live and work on the Reserve collecting wildlife data year round. The data we obtain directly informs the Reserve's wildlife management decisions. On this project, our crews have safely and effectively navigated temperature extremes from -30 degrees to 100+ degrees while traveling in a remote location. We are currently scouting projects in the Okavango Delta of Botswana and the rainforest of Suriname where we will be able to cover large amounts of area in a short periord of time. ASC is at the crossroads of the adventure and coservation science communities. Our approach of answering specific questions by using highly skilled and motivate volunteers ensures that we are able to collect quality data, cost effectively, and in a fraction of the traditional timeframe.

  4. DNA-Catalyzed Hydrolysis of Esters and Aromatic Amides

    PubMed Central

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

    2013-01-01

    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

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

    E-print Network

    Ng, Sze-Sze

    2008-01-01

    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 ...

  6. Coalification by clay-catalyzed oligomerization of plant monomers

    SciTech Connect

    Orchin, M.; Wilson, R.M.

    1990-01-01

    The main objective of this research program is to devise laboratory methods to mimic the processes by which plants synthesize lignans, lignins and the processes by which these materials are transformed further by geochemical reactions catalyzed by certain clays to coal-like materials. We believe that the radical cation Diels-Alder reaction is one of the principal routes which transforms simple plant materials to coal-like substances and that such reactions may be catalyzed by clays that occur in the environment of the decaying plant materials. Progress is described.

  7. Microbial-Catalyzed Biotransformation of Multifunctional Triterpenoids Derived from Phytonutrients

    PubMed Central

    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

    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

  8. N-Heterocyclic Carbene-Catalyzed Conjugate Additions of Alcohols

    PubMed Central

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

    2010-01-01

    An efficient intermolecular conjugate addition of alcohols to activated alkenes catalyzed by N-heterocyclic carbenes has been developed. With 5 mol % of the free carbene derived from IMes•HCl, unsaturated ketones and esters are competent substrates and a variety of primary and secondary alcohols can be employed as the nucleophile. No oligomerization is observed under these mild conditions for effective hydroalkoxylation. In addition to reactions with activated alkenes, IMes catalyzes the formation of vinyl ethers through the 1,4-addition of alcohols to ynones and promotes tandem conjugate addition/Michael cascade reactions. Preliminary data supports a Brønsted base mechanism with the free carbene. PMID:20809579

  9. Radiation catalyzed conversion of tritium gas to tritiated water

    SciTech Connect

    Easterly, C.E.; Bennett, M.R.

    1983-01-01

    A survey of water production dependence on tritium concentration and external radiation fields has been made for the tritium-in-air concentration range of 0.01 to 1 Ci/m/sup 3/. Results of reactions taking place under static conditions (in Pyrex flasks at 20/sup 0/C) indicate that: (1) self-catalyzed rates may be first-order-dependent on tritium concentration; and (2) external radiation fields may cause a virtual steady-state condition to occur (in terms of additional self-catalyzed water production).

  10. New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

    SciTech Connect

    Qinhua Huang

    2004-12-19

    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.

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

    PubMed

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

    2014-09-21

    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

  12. Nickel-Catalyzed Asymmetric Negishi Cross-Couplings of Racemic Secondary Allylic Chlorides with Alkylzincs

    E-print Network

    Fu, Gregory C.

    The transition metal-catalyzed enantioselective coupling of allylic electrophiles with carbon nucleophiles has been the focus of intense investigation.5 Salient examples include palladium-catalyzed couplings with enolates, ...

  13. Domino Pd-catalyzed Heck cyclization and bismuth-catalyzed hydroamination: formal synthesis of elacomine and isoelacomine.

    PubMed

    Kamisaki, Haruhi; Nanjo, Takeshi; Tsukano, Chihiro; Takemoto, Yoshiji

    2011-01-10

    The formal synthesis of hemiterpene spirooxindole alkaloids elacomine (1) and isoelacomine (2) is described. Heck reaction of protected iodoanilines with 5,6-dihydro-2H-pyran-2-one or six-membered unsaturated lactams was investigated. The coupling product was readily converted to a carbamoyl chloride with an incorporated diene unit. The spiro(pyrrolidine-3,3'-oxindole) skeleton, which corresponds to the carbon skeleton of 1 and 2, was efficiently constructed from this intermediate by using a domino palladium-catalyzed Heck reaction and bismuth-catalyzed hydroamination. An isolated byproduct of the reaction could also be converted to the spirooxindole skeleton. PMID:21207582

  14. Diversity in chemistry: catalyzing change Irving R Epstein

    E-print Network

    Epstein, Irving R.

    Diversity in chemistry: catalyzing change Irving R Epstein African Americans, Hispanics and Native Americans are significantly underrepresented in chemistry and related sciences. An innovative approach based,I consider some of the reasons for the dearth of URMs in science--particularly in chemistry--and some

  15. Iron-Catalyzed Heterocycle and Arene Deprotonative Alkylation

    PubMed Central

    Tran, Ly Dieu; Daugulis, Olafs

    2010-01-01

    A method for iron-catalyzed deprotonative alkylation of arene C-H bonds by alkyl iodides and bromides has been developed. In the presence of an amide base, both primary and secondary alkyl halides can be coupled with furans, thiophenes, pyridine derivatives, and some electron-withdrawing-group containing arenes. PMID:20825168

  16. Copper-Catalyzed Intermolecular Asymmetric Propargylic Dearomatization of Indoles.

    PubMed

    Shao, Wen; Li, He; Liu, Chuan; Liu, Chen-Jiang; You, Shu-Li

    2015-06-22

    The first copper-catalyzed intermolecular dearomatization of indoles by an asymmetric propargylic substitution reaction was developed. This method provides a highly efficient synthesis of versatile furoindoline and pyrroloindoline derivatives containing a quaternary carbon stereogenic center and a terminal alkyne moiety with up to 86?% yield and 98?% ee. PMID:25968474

  17. Aerobic oxidative amination of unactivated alkenes catalyzed by palladium.

    PubMed

    Brice, Jodie L; Harang, Jenna E; Timokhin, Vitaliy I; Anastasi, Natia R; Stahl, Shannon S

    2005-03-01

    The first examples of palladium-catalyzed oxidative amination of unactivated alkyl olefins have been identified. To be successful, these reactions must be conducted under cocatalyst-free conditions that involve direct dioxygen-coupled turnover of the palladium catalyst. The oxidative amination products of norbornene and other cyclic alkenes implicate a cis-aminopalladation mechanism. PMID:15740119

  18. Enantioselective N-heterocyclic carbene-catalyzed synthesis of trifluoromethyldihydropyridinones.

    PubMed

    Wang, Dong-Ling; Liang, Zhi-Qin; Chen, Kun-Quan; Sun, De-Qun; Ye, Song

    2015-06-01

    The enantioselective N-heterocyclic carbene-catalyzed [4 + 2] cyclocondensation of ?-chloroaldehydes and trifluoromethyl N-Boc azadienes was developed, giving the corresponding 3,4-disubstituted-6-trifluoromethyldihydropyridin-2(1H)-ones in good yields with exclusive cis-selectivities and excellent enantioselectivities. PMID:25933360

  19. Transition-Metal-Catalyzed Carbonylation of Methyl Acetate.

    ERIC Educational Resources Information Center

    Polichnowski, S. W.

    1986-01-01

    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)

  20. Strictosidine Synthase: Mechanism of a Pictet–Spengler Catalyzing Enzyme

    PubMed Central

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

    2010-01-01

    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

  1. Catalyzing Graduate Teaching Assistants' Laboratory Teaching through Design Research

    ERIC Educational Resources Information Center

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

    2006-01-01

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

  2. Ru-BICP-Catalyzed Asymmetric Hydrogenation of Aromatic Ketones

    E-print Network

    Zhang, Xumu

    for hydrogenation of simple ketones remains a challenging problem.1 Recently, Noyori2 disclosed a ter- nary catalyst in explor- ing the Ru-BICP-catalyzed hydrogenation of simple ketones using Noyori's protocol (Scheme 1). Our enantioselectivity, which is consistent with Noyori's observation.2 For example, combination of (S,S)-1

  3. Intramolecular Acid-Catalyzed Amide Isomerization in Aqueous Solution

    E-print Network

    Lectka, Thomas

    experimental verification that hydrogen bond donation to the amide nitrogen by charged proton donors may play. Scheme 1. Acid-Catalyzed Isomerization of Amides ORGANIC LETTERS 1999 Vol. 1, No. 5 749-752 10.1021/ol bond donation to the amide nitrogen by charged proton donors may play a significant role

  4. Mechanism of Rhodium-Catalyzed Carbene Formation from Diazo

    E-print Network

    Wang, Jianbo

    Mechanism of Rhodium-Catalyzed Carbene Formation from Diazo Compounds Freeman M. Wong, Jianbo WangVersity, Logan, Utah 84322, and Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking UniVersity, Beijing, China hengge@mail.usu.edu; wuw

  5. Novobiocin and Coumermycin Inhibit DNA Supercoiling Catalyzed by DNA Gyrase

    Microsoft Academic Search

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

    1976-01-01

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

  6. Hydrous zinc halide-catalyzed aminosulfonation of hydrocarbons.

    PubMed

    Kalita, Biswajit; Lamar, Angus A; Nicholas, Kenneth M

    2008-09-28

    Benzylic and allylic hydrocarbons are selectively converted to the corresponding sulfonamides by a ZnBr2-H2O-catalyzed reaction with PhI=NTs; saturated adamantane is aminosulfonated at the tertiary C-H bond. PMID:18802547

  7. Cobalt-catalyzed cyclization of carbon monoxide, imine, and epoxide.

    PubMed

    Zhang, Yubo; Ji, Jiamin; Zhang, Xiuliang; Lin, Shaohui; Pan, Qinmin; Jia, Li

    2014-04-18

    Cobalt-catalyzed cyclization of CO, imine, and epoxide has been developed. A convenient catalyst system composed of Co2(CO)8 and LiCl is identified, and the substrate scope has been explored. The reaction provides an efficient method for the synthesis of substituted 1,3-oxazinan-4-ones. PMID:24679164

  8. ACID CATALYZED SYNTHESIS OF HYPERBRANCHED POLY(GLYCEROL-DIACID) OLIGOMERS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Novel oligomeric prepolymers were synthesized by acid-catalyzed condensation of glycerol with iminodiacetic, azelaic, or succinic acid. The prepolymers were obtained, on average, in 62% yield and were characterized by 13C NMR, 1H NMR, MALDI-TOF mass spectrometry, and GPC. The synthesized oligome...

  9. ACID CATALYZED SYNTHESIS OF HYPERBRANCHED POLY(GLYCEROL-DIACID) OLIGOMERS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Novel oligomeric prepolymers were synthesized by acid-catalyzed condensation of glycerol with iminodiacetic, azelaic, or succinic acid. The prepolymers were obtained, on average, in 62% yield and were characterized by 13C NMR, 1H NMR, MALDI-TOF mass spectrometry, and GPC. The synthesized oligomer...

  10. ACID CATALYZED SYNTHESIS OF HYPERBRANCHED POLY(GLYCEROL-DIACID) OLIGOMERS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Novel oligomeric prepolymers were synthesized by acid-catalyzed condensation of glycerol with iminodiacetic, azelaic, or succinic acid. The prepolymers were obtained, on average in 62% yield and were characterized by 13C NMR, 1H NMR, MALDI-TOF mass spectrometry, and GPC. The synthesized oligomers ...

  11. Carbon-catalyzed gasification of organic feedstocks in supercritical water

    Microsoft Academic Search

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

    1996-01-01

    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

  12. Zinc—Proline Catalyzed Pathway for the Formation of Sugars

    Microsoft Academic Search

    Jacob Kofoed; Miguel Machuqueiro; Jean-Louis Reymond; Tamis Darbre

    2004-01-01

    Zn-proline catalyzes the aldolisation of unprotected glycolalde- hyde in water to give tetroses and hexoses; threose (33% of the product mixture) was formed with 10% enantiomeric excess of the D-isomer. The prebiotic formation of sugars has been a subject of several studies and speculations. One prevailing theory accepted today has sugars being formed by a sequence of aldol reactions, starting

  13. A phosphine-catalyzed preparation of 4-arylidene-5-imidazolones.

    PubMed

    Gabillet, Sandra; Loreau, Olivier; Specklin, Simon; Rasalofonjatovo, Evelia; Taran, Frédéric

    2014-10-17

    A simple and efficient method for constructing 4-arylidene-5-imidazolones was developed using a phosphine-catalyzed tandem umpolung addition and intramolecular cyclization of amidine pronucleophiles on arylpropiolates. The reaction offers a robust route to heterocycle analogues of the fluorescent protein chromophores. PMID:25238600

  14. Development of a Lewis Base Catalyzed Selenocyclization Reaction

    ERIC Educational Resources Information Center

    Collins, William

    2009-01-01

    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,…

  15. Methyltrioxorhenium-catalyzed epoxidation of homoallylic alcohols with hydrogen peroxide.

    PubMed

    Yamazaki, Shigekazu

    2012-11-01

    Homoallylic alcohols were efficiently converted to the corresponding 3,4-epoxy alcohols in excellent yields by methyltrioxorhenium (MTO)-catalyzed epoxidation with aqueous hydrogen peroxide as the terminal oxidant and 3-methylpyrazole (10 mol %) as an additive. The epoxidations of homoallylic alcohols proceeded under organic solvent-free conditions faster than those in dichloromethane. PMID:23035973

  16. CuI-catalyzed cycloisomerization of propargyl amides.

    PubMed

    Alhalib, Ali; Moran, Wesley J

    2014-02-01

    The synthesis of substituted dihydrooxazoles by the CuI-catalyzed cycloisomerization of terminal propargyl amides is reported. The reaction has been shown to have good substrate scope and experiments to delineate the mechanism have been performed. Substrates containing a benzylic methylene were oxidized to the ketone under the reaction conditions. PMID:24306143

  17. An iron catalyzed regioselective oxidation of terminal alkenes to aldehydes.

    PubMed

    Chowdhury, Abhishek Dutta; Ray, Ritwika; Lahiri, Goutam Kumar

    2012-06-01

    Fe(BF(4))(2)·6H(2)O with pyridine-2,6-dicarboxylic acid and PhIO can efficiently catalyze the regioselective oxidation of terminal alkene derivatives to aldehydes under mild and benign reaction conditions. PMID:22538415

  18. Zinc-catalyzed copolymerization of carbon dioxide and propylene oxide

    E-print Network

    Katsurao, Takumi

    1994-01-01

    dioxide has recently been paid attention in the field of extraction, separation, and reaction medium, its aptitude for both a reaction solvent and a reactant was examined in zinc glutarate-catalyzed reactions. As a result, it was proved that supercritical...

  19. Synthesis of Cyclic Guanidines via Pd-Catalyzed Alkene Carboamination

    PubMed Central

    Zavesky, Blane P.; Babij, Nicholas R.; Fritz, Jonathan A.

    2013-01-01

    A new approach to the synthesis of substituted 5-membered cyclic guanidines is described. Palladium-catalyzed alkene carboamination reactions between acyclic N-allyl guanidines and aryl or alkenyl halides provide these products in good yield. This method allows access to a number of different cyclic guanidine derivatives in only two steps from readily available allylic amines. PMID:24147839

  20. Catalyzed Cyclization of r,-Dienes: A Versatile Protocol for the Synthesis of Functionalized

    E-print Network

    RajanBabu, T. V. "Babu"

    Catalyzed Cyclization of r,-Dienes: A Versatile Protocol for the Synthesis of Functionalized. In contrast, very little attention7 has been paid to the corre- sponding Ni or Pd-catalyzed cyclization of R,-dienes 1, entry 2). Not surprisingly, the palladium-catalyzed reactions are slower and varying amounts

  1. Transition metal-catalyzed oxidation of atmospheric sulfur: Global implications for the sulfur budget

    E-print Network

    Alexander, Becky

    Transition metal-catalyzed oxidation of atmospheric sulfur: Global implications for the sulfur(IV)) oxidation by O2 catalyzed by transition metals. Due to the lack of photochemically produced OH and H2O2), Transition metal-catalyzed oxidation of atmospheric sulfur: Global implications for the sulfur budget, J

  2. 9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica

    E-print Network

    McFadden, Geoff

    9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica 9482 Identifying deteriorates with age CHEMISTRY Stratospheric ice catalyzes chlorine reactions To explain how ice crystals can catalyze chlorine reactions in the stratosphere, Faye McNeill et al. report that small amounts

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

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    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)

  4. Enzymatic alpha-glucosaminylation of maltooligosaccharides catalyzed by phosphorylase.

    PubMed

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

    2008-10-13

    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

  5. Ligand development in the Ni-catalyzed hydrocyanation of alkenes.

    PubMed

    Bini, Laura; Müller, Christian; Vogt, Dieter

    2010-11-28

    The addition of HCN to alkenes is a very useful reaction for the synthesis of functional organic substrates. Industrially the nickel-catalyzed hydrocyanation has gained considerable importance mainly because of the production of adiponitrile in the DuPont process. In this process the hydrocyanation of butadiene is carried out using aryl phosphite-modified nickel catalyst. Since the performance of organo-transition metal complexes is largely determined by the ligand environment of the metal, fundamental understanding and ligand development is of pivotal importance for any progress. This feature article gives an account of the development and application of different mono- and bidentate phosphorus-based ligands in the Ni-catalyzed hydrocyanation reaction of alkenes. Special attention will be paid to the development of insight and understanding of the ligand structural and electronic properties towards the improvement of the catalyst performance in terms of stability, activity, and selectivity. PMID:20972491

  6. Investigations into Transition Metal Catalyzed Arene Trifluoromethylation Reactions

    PubMed Central

    Ye, Yingda; Sanford, Melanie S.

    2015-01-01

    Trifluoromethyl-substituted arenes and heteroarenes are widely prevalent in pharmaceuticals and agrochemicals. As a result, the development of practical methods for the formation of aryl–CF3 bonds has become an active field of research. Over the past five years, transition metal catalyzed cross-coupling between aryl–X (X = halide, organometallic, or H) and various “CF3” reagents has emerged as a particularly exciting approach for generating aryl–CF3 bonds. Despite many recent advances in this area, current methods generally suffer from limitations such as poor generality, harsh reaction conditions, the requirement for stoichiometric quantities of metals, and/or the use of costly CF3 sources. This Account describes our recent efforts to address some of these challenges by: (1) developing aryl trifluoromethylation reactions involving high oxidation state Pd intermediates, (2) exploiting AgCF3 for C–H trifluoromethylation, and (3) achieving Cu-catalyzed trifluoromethylation with photogenerated CF3•. PMID:25838638

  7. Polymerization of phenols catalyzed by peroxidase in nonaqueous media

    SciTech Connect

    Dordick, J.S.; Marletta, M.A.; Klibanov, A.M.

    1987-01-01

    Polymers produced by horseradish-peroxidase-catalyzed coupling of phenols have been explored as potential substitutes for phenol-formaldehyde resins. To overcome low substrate solubilities and product molecular weights in water, enzymatic polymerizations in aqueous-organic mixtures have been examined. Peroxidase vigorously polymerizes a number of phenols in mixtures of water with water-miscible solvents such as dioxane, acetone, dimethylformamide, and methyl formate with the solvent content up to 95%. As a result, various phenolic polymers with average molecular weights from 400 to 2.6 x 10/sup 4/ D were obtained depending on the reaction medium composition and the nature of the phenol. Peroxidase-catalyzed copolymerization of different phenols in 85% dioxane was demonstrated. Poly(p-phenylphenol) and poly(p-cresol) were enzymatically prepared on a gram scale. They had much higher melting points, and in addition, poly(p-phenylphenol) was found to have a much higher electrical conductivity than phenol-formaldehyde resins.

  8. Cholera toxin can catalyze ADP-ribosylation of cytoskeletal proteins

    SciTech Connect

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

    1981-11-01

    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.

  9. Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.

    PubMed Central

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

    1993-01-01

    The negative strand of the satellite RNA of tobacco ringspot virus (sTobRV(-)) contains a hairpin catalytic domain that shows self-cleavage and self-ligation activities in the presence of magnesium ions. We describe here that the minimal catalytic domain can catalyze a cross-ligation reaction between two kinds of substrates in trans. The cross-ligated product increased when the reaction temperature was decreased during the reaction from 37 degrees C to 4 degrees C. A two-stranded hairpin ribozyme, divided into two fragments between G45 and U46 in a hairpin loop, showed higher ligation activity than the nondivided ribozyme. The two stranded ribozyme also catalyzed an exchange reaction of the 3'-portion of the cleavage site. Images PMID:8441626

  10. Cytochrome c catalyzes the in vitro synthesis of arachidonoyl glycine

    SciTech Connect

    McCue, Jeffrey M.; Driscoll, William J. [Department of Anatomy Physiology and Genetics, Uniformed Services University of the Health Sciences, F. Edward Herbert School of Medicine, 4301 Jones Bridge Road, Bethesda, MD 20814 (United States); Mueller, Gregory P. [Department of Anatomy Physiology and Genetics, Uniformed Services University of the Health Sciences, F. Edward Herbert School of Medicine, 4301 Jones Bridge Road, Bethesda, MD 20814 (United States)], E-mail: gmueller@usuhs.mil

    2008-01-11

    Long chain fatty acyl glycines are an emerging class of biologically active molecules that occur naturally and produce a wide array of physiological effects. Their biosynthetic pathway, however, remains unknown. Here we report that cytochrome c catalyzes the synthesis of N-arachidonoyl glycine (NAGly) from arachidonoyl coenzyme A and glycine in the presence of hydrogen peroxide. The identity of the NAGly product was verified by isotope labeling and mass analysis. Other heme-containing proteins, hemoglobin and myoglobin, were considerably less effective in generating arachidonoyl glycine as compared to cytochrome c. The reaction catalyzed by cytochrome c in vitro points to its potential role in the formation of NAGly and other long chain fatty acyl glycines in vivo.

  11. Copper-Catalyzed Oxidative Heck Reactions between Alkyltrifluoroborates and Vinylarenes

    PubMed Central

    Liwosz, Timothy W.; Chemler, Sherry R.

    2013-01-01

    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

  12. Pheromone Deactivation Catalyzed by Receptor Molecules: a Quantitative Kinetic Model

    Microsoft Academic Search

    Karl-Ernst Kaissling

    1998-01-01

    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

  13. Electrophilic phosphonium cations catalyze hydroarylation and hydrothiolation of olefins.

    PubMed

    Pérez, Manuel; Mahdi, Tayseer; Hounjet, Lindsay J; Stephan, Douglas W

    2015-06-30

    Electrophilic phosphonium cations (EPCs) are efficient main group catalysts for the hydroarylation of olefins under mild conditions, providing a facile route to substituted aniline, bis-arylamine, phenol, furan, thiophene, pyrrole, and indole derivatives. Similarly, EPCs catalyze the hydrothiolation of aryl olefins with thiophenol affording a series of alkyl aryl thioethers. Experimental data support a mechanism for these reactions that involves initial activation of the olefin. PMID:26083901

  14. Lipase-catalyzed kinetic resolution of aryltrimethylsilyl chiral alcohols.

    PubMed

    Palmeira, Dayvson J; Abreu, Juliana C; Andrade, Leandro H

    2011-01-01

    Lipase-catalyzed kinetic resolution of aryltrimethylsilyl chiral alcohols through a transesterification reaction was studied. The optimal conditions found for the kinetic resolution of m- and p-aryltrimethylsilyl chiral alcohols, led to excellent results, high conversions (c = 50%), high enantiomeric ratios (E > 200) and enantiomeric excesses for the remaining (S)-alcohol and (R)-acetylated product (>99%). However, kinetic resolution of o-aryltrimethylsilyl chiral alcohols did not occur under the same conditions applied to the other isomers. PMID:22113578

  15. Palladium-catalyzed regioselective domino cyclization of cyclohexadienones.

    PubMed

    Murthy, Akondi Srirama; Donikela, Sangeetha; Reddy, Cirandur Suresh; Chegondi, Rambabu

    2015-06-01

    A mild and efficient Pd-catalyzed arylative domino carbocyclization of cyclohexadienone-containing 1,6-enynes is described. The reaction tolerates a variety of functionalized boronic acids to afford a cis-fused bicyclic framework containing an ?,?-unsaturated ketone with excellent regio- and diastereoselectivity in good yields. The tandem process proceeds with ?-arylation of propargylic ether followed by conjugate addition of a vinyl palladium intermediate and subsequent protonolysis of a palladium enolate. PMID:25938739

  16. DBU catalyzed cyanoacylation of ketones with acyl cyanides.

    PubMed

    Zhang, Wen; Shi, Min

    2006-05-01

    The reaction of cyclohexanone with benzoyl cyanide catalyzed by amines provides the corresponding O-benzoyl cyanohydrin adducts in moderate to good yields under mild conditions. Among the catalysts, DBU was found to be the most effective promoter allowing the reaction to proceed smoothly at room temperature and to give the corresponding O-acyl cyanohydrin adducts in higher yields for a variety of substituted cyclohexanones, cyclopentanone, acetone or pentan-3-one and various acyl cyanides. PMID:16633559

  17. Asymmetric rearrangement of racemic epoxides catalyzed by chiral Brønsted acids.

    PubMed

    Zhuang, Minyang; Du, Haifeng

    2013-03-01

    This paper describes a chiral Brønsted acid catalyzed asymmetric 1,2-rearrangement of racemic epoxides via a hydrogen-shift process for the synthesis of chiral aldehydes, and, followed by a reduction, a variety of optically active alcohols can be furnished in moderate yields with up to 50% ee. Especially, a facile one-pot synthesis of chiral alcohols directly from simple alkenes by a sequential epoxidation, rearrangement, and reduction has also been realized. PMID:23361172

  18. Wildcat: A catalyzed D-D Tokamak reactor

    Microsoft Academic Search

    K. Evans Jr.; C. C. Baker; J. N. Brooks; R. G. Clemmer; D. A. Ehst; H. Herman; J. Jung; R. F. Mattas; B. Misra; D. L. Smith

    1981-01-01

    The WILDCAT is a conceptual design of a catalyzed D-D, Tokamak, commercial, fusion reactor. The 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

  19. Deglutathionylation of 2-Cys Peroxiredoxin Is Specifically Catalyzed by Sulfiredoxin*

    PubMed Central

    Park, Ji Won; Mieyal, John J.; Rhee, Sue Goo; Chock, P. Boon

    2009-01-01

    Reversible protein glutathionylation plays a key role in cellular regulation and cell signaling and protects protein thiols from hyperoxidation. Sulfiredoxin (Srx), an enzyme that catalyzes the reduction of Cys-sulfinic acid derivatives of 2-Cys peroxiredoxins (2-Cys Prxs), has been shown to catalyze the deglutathionylation of actin. We show that deglutathionylation of 2-Cys Prx, a family of peroxidases, is specifically catalyzed by Srx. Using the ubiquitously expressed member of 2-Cys Prx, Prx I, we revealed the following. (i) Among its four Cys residues, Cys52, Cys83, and Cys173 can be glutathionylated in vitro. Deglutathionylation with Cys mutants showed that Cys83 and Cys173 were preferentially catalyzed by Srx, with glutathionylated Srx as the reaction intermediate, whereas glutaredoxin I was more favorable for deglutathionylating Cys52. (ii) Studies using site-directed mutagenesis coupled with binding and deglutathionylation activities revealed that Pro174 and Pro179 of Prx I and Tyr92 of Srx are essential for both activities. Furthermore, relative to glutaredoxin I, Srx exhibited negligible deglutathionylation activity for glutathionylated cysteine and glutathionylated BSA. These results indicate that Srx is specific for deglutathionylating Prx I due to its favorable affinity for Prx I. To assess the biological relevance of these observations, we showed that Prx I is glutathionylated in A549 and HeLa cells under modest levels of H2O2. In addition, the level of glutathionylated Prx I was substantially elevated in small interfering RNA-mediated Srx-knocked down cells, whereas the reverse was observed in Srx-overexpressing cells. However, glutathionylation of Prx V, not known to bind to Srx, was not affected by the change in Srx expression levels. PMID:19561357

  20. Sterically controlled, palladium-catalyzed intermolecular amination of arenes.

    PubMed

    Shrestha, Ruja; Mukherjee, Paramita; Tan, Yichen; Litman, Zachary C; Hartwig, John F

    2013-06-12

    We report the Pd-catalyzed amination of arenes to form N-aryl phthalimides with regioselectivity controlled predominantly by steric effects. Mono-, di-, and trisubstituted arenes lacking a directing group undergo amination reactions with moderate to high yields and high regioselectivities from sequential addition of PhI(OAc)2 as an oxidant in the presence of Pd(OAc)2 as catalyst. This sterically derived selectivity contrasts that for analogous arene acetoxylation. PMID:23678959

  1. Enzymatic peptide synthesis. Carboxypeptidase Y catalyzed formation of peptide bonds

    Microsoft Academic Search

    Fred Widmer; Jack T. Johansen

    1979-01-01

    It is demonstrated that carboxypeptidase Y from Saccharomyces cerevisiae can catalyze the formation of peptide bonds using\\u000a N-acylamino acid esters as substrates and free amino acids or amino acid amides as nucleophiles. The coupling yields observed\\u000a with free amino acids were max. 60% for alanine and lysine and they depended strongly on the reaction parameters; viz. pH,\\u000a temperature and concentration

  2. Carboxypeptidase Y catalyzed transpeptidations and enzymatic peptide synthesis

    Microsoft Academic Search

    Klaus Breddam; Fred Widmer; Jack T. Johansen

    1980-01-01

    It is shown that carboxypeptidase Y, in addition to its known amidase and peptidase activities, also exhibits peptidyl-amino-acid-amide\\u000a hydrolase activity, i.e., amino acid amides are released from peptide amides. These three activities were investigated as\\u000a to their usefulness in catalyzing transpeptidation reactions in the presence of suitable nucleophiles. Using peptides and\\u000a peptide amides as substrates and amino acids or amino

  3. Gold(i)-catalyzed hydroindolylation of allenyl ethers.

    PubMed

    Kona, Chandrababu Naidu; Shinde, Mahesh H; Ramana, Chepuri V

    2015-05-01

    The gold(i)-catalyzed reaction/rearrangement of allenyl ethers has been investigated in the presence of indoles. Either hydroindolylation or alkylation of an indole with the pendant group of allenyl ether has been observed. The reaction outcome seems to be decided mainly by the nature of the pendant group of the allenyl ether. Control experiments are indicative of an inner sphere mechanism for the hydroindolylation reaction. PMID:25873185

  4. Pd-Catalyzed Enantioselective Allyl-Allyl Cross Coupling

    PubMed Central

    Zhang, Ping; Brozek, Laura A.; Morken, James P.

    2010-01-01

    The Pd-catalyzed cross coupling of terminal allylic carbonates and allylB(pin) is described. The regioselectivity of this reaction is sensitive to the bite angle of the ligand with small bite angle ligands favoring the branched substitution product. This mode of regioselection is consistent with a reaction that operates by a 3,3? reductive elimination reaction. In the presence of appropriate chiral ligands, this reaction is rendered enantioselective and applies to both aromatic and aliphatic allylic carbonates. PMID:20681700

  5. Palladium Catalyzed Intramolecular Acylcyanation of Alkenes Using ?-Iminonitriles

    PubMed Central

    Rondla, Naveen R.; Ogilvie, Jodi M.; Pan, Zhongda

    2014-01-01

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

  6. Synthesis of Graphite Encapsulated Metal Nanoparticles and Metal Catalyzed Nanotubes

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    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.

  7. Recent Progress towards Transition-Metal-Catalyzed Synthesis of Fluorenes.

    PubMed

    Zhou, Ai-Hua; Pan, Fei; Zhu, Chunyin; Ye, Long-Wu

    2015-07-13

    Fluorenes are a commonly encountered structural motif in materials science, pharmaceutical chemistry, and organic synthesis. Among various strategies towards the synthesis of this unique structure, transition metal-catalyzed functionalization has emerged as one of the most efficient methods. This Minireview presents an overview of the recent advances in this emerging area by highlighting the reactions' specificity and applicability and, where possible, provides a mechanistic rationale. PMID:25858775

  8. Computational kinetics of cobalt-catalyzed alkene hydroformylation.

    PubMed

    Rush, Laura E; Pringle, Paul G; Harvey, Jeremy N

    2014-08-11

    Density functional theory, coupled-cluster theory, and transition state theory are used to build a computational model of the kinetics of phosphine-free cobalt-catalyzed hydroformylation and hydrogenation of alkenes. The model provides very good agreement with experiment, and enables the factors that determine the selectivity and rate of catalysis to be determined. The turnover rate is mainly determined by the alkene coordination step. PMID:24700408

  9. Experimental investigation of muon-catalyzed d-t fusion

    Microsoft Academic Search

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

    1983-01-01

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

  10. Protection of Wood from Microorganisms by Laccase-Catalyzed Iodination

    PubMed Central

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

    2012-01-01

    In the present work, Norway spruce wood (Picea abies L.) was reacted with a commercial Trametes versicolor laccase in the presence of potassium iodide salt or the phenolic compounds thymol and isoeugenol to impart an antimicrobial property to the wood surface. In order to assess the efficacy of the wood treatment, a leaching of the iodinated and polymerized wood and two biotests including bacteria, a yeast, blue stain fungi, and wood decay fungi were performed. After laccase-catalyzed oxidation of the phenols, the antimicrobial effect was significantly reduced. In contrast, the enzymatic oxidation of iodide (I?) to iodine (I2) in the presence of wood led to an enhanced resistance of the wood surface against all microorganisms, even after exposure to leaching. The efficiency of the enzymatic wood iodination was comparable to that of a chemical wood preservative, VP 7/260a. The modification of the lignocellulose by the laccase-catalyzed iodination was assessed by the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. The intensities of the selected lignin-associated bands and carbohydrate reference bands were analyzed, and the results indicated a structural change in the lignin matrix. The results suggest that the laccase-catalyzed iodination of the wood surface presents an efficient and ecofriendly method for wood protection. PMID:22865075

  11. Stau-catalyzed big-bang nucleosynthesis reactions

    SciTech Connect

    Kamimura, Masayasu [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Kino, Yasushi [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Hiyama, Emiko [RIKEN Nishina Center, Wako 351-0198 (Japan)

    2010-06-01

    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{sup -}) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X{sup -} particle has a lifetime of tau{sub X} > or approx. 10{sup 3} 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{sup -} acts as a catalyst. Some of these X{sup -} 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.

  12. Phosphorylase-catalyzed N-formyl-alpha-glucosaminylation of maltooligosaccharides.

    PubMed

    Kawazoe, Satoshi; Izawa, Hironori; Nawaji, Mutsuki; Kaneko, Yoshiro; Kadokawa, Jun-ichi

    2010-03-30

    This paper describes the phosphorylase-catalyzed enzymatic N-formyl-alpha-glucosaminylation of maltooligosaccharides for direct incorporation of 2-deoxy-2-formamido-alpha-D-glucopyranose units into maltooligosaccharides. When the reaction of 2-deoxy-2-formamido-alpha-D-glucopyranose-1-phosphate (GlcNF-1-P) as the glycosyl donor and maltotetraose as a glycosyl acceptor was performed in the presence of phosphorylase, the N-formyl-alpha-D-glucosaminylated pentasaccharide was produced, as confirmed by MALDI-TOF MS. Furthermore, the glucoamylase-catalyzed reaction of the crude products supported that the 2-deoxy-2-formamido-alpha-D-glucopyranoside unit was positioned at the non-reducing end of the pentasaccharide. The pentasaccharide was isolated from the crude products and its structure was further determined by the (1)H NMR analysis. On the other hand, when the phosphorylase-catalyzed reactions of maltotriose and maltopentaose using GlcNF-1-P were conducted, no N-formyl-alpha-glucosaminylation took place in the former system, whereas the latter system gave N-formyl-alpha-D-glucosaminylated oligosaccharides with various degrees of polymerization. These results could be explained by the recognition behavior of phosphorylase toward maltooligosaccharides. PMID:20096828

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

    Microsoft Academic Search

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

    2011-01-01

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

  14. Assessment of lipase- and chemically catalyzed lipid modification strategies for the production of structured lipids

    Microsoft Academic Search

    Wendy M. Willis; Alejandro G. Marangoni

    1999-01-01

    The purpose of the present study was to devise a two-step reaction to produce partial glycerides, which would subsequently\\u000a be used as substrates in both lipase-catalyzed and chemically catalyzed esterification reactions with caprylic acid. The yields\\u000a and kinetics of these two-step reactions were compared to established lipase-catalyzed acidolysis and transesterification\\u000a as well as to chemical transesterification reactions. Acyl migration did

  15. Solid oxide fuel cell with internal reforming, catalyzed interconnect for use therewith, and methods

    SciTech Connect

    Liu, Di-Jia; Guan, Jie; Minh, Nguyen

    2010-06-08

    A catalyzed interconnect for an SOFC electrically connects an anode and an anodic current collector and comprises a metallic substrate, which provides space between the anode and anodic current collector for fuel gas flow over at least a portion of the anode, and a catalytic coating on the metallic substrate comprising a catalyst for catalyzing hydrocarbon fuel in the fuel gas to hydrogen rich reformate. An SOFC including the catalyzed anodic inter-connect, a method for operating an SOFC, and a method for making a catalyzed anodic interconnect are also disclosed.

  16. Processivity of Ribozyme-Catalyzed RNA Polymerization Michael S. Lawrence and David P. Bartel*

    E-print Network

    Bartel, David

    * Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of TechnologyProcessivity of Ribozyme-Catalyzed RNA Polymerization Michael S. Lawrence and David P. Bartel

  17. Recent Developments in Metal-Catalyzed Additions of Oxygen Nucleophiles to Alkenes and Alkynes

    NASA Astrophysics Data System (ADS)

    Hintermann, Lukas

    Progress in the field of metal-catalyzed redox-neutral additions of oxygen nucleophiles (water, alcohols, carboxylic acids, and others) to alkenes, alkynes, and allenes between 2001 and 2009 is critically reviewed. Major advances in reaction chemistry include development of chiral Lewis acid catalyzed asymmetric oxa-Michael additions and Lewis-acid catalyzed hydro-alkoxylations of nonactivated olefins, as well as further development of Markovnikov-selective cationic gold complex-catalyzed additions of alcohols or water to alkynes and allenes.

  18. Ruthenium(II)-catalyzed reactions of 1,4-epiperoxides

    SciTech Connect

    Suzuki, Masaaki; Ohtake, Hiroaki; Kameya, Yoshimi; Noyori, Ryoji (Nagoya Univ. (Japan)); Hamanaka, Nobuyuki (Ono Pharmaceutical Co., Osaka (Japan))

    1989-10-27

    The behavior of 1,4-epiperoxides in the presence of transition-metal complexes is highly dependent on the structures of the substrates and the nature of the metal catalysts. Reaction of saturated epiperoxides such as 1,3-epiperoxycyclopentane, 1,4-epiperoxycyclohexane, or dihydroascaridole catalyzed by RuCl{sub 2}(PPh{sub 3}){sub 3} in dichloromethane gives a mixture of products arising from fragmentation, rearrangement, reduction, disproportionation, etc. Prostaglandin H{sub 2} methyl ester undergoes clean and stereospecific fragmentation to afford methyl (5Z,8E,10E,12S)-12-hydroxy-5,8,10-heptadecatrienoate and malonaldehyde. Bicyclic 2,3-didehydro 1,4-epiperoxides give the syn-1,2:3,4-diepoxides by the same catalyst. The monocyclic analogues are transformed to a mixture of diepoxides and furan products. The stereochemical outcome of the epoxide formation reflects unique differences in the ground-state geometry of the starting epiperoxide substrates. FeCl{sub 2}(PPh{sub 3}){sub 2} serves as a useful catalyst for the skeletal change of sterically hindered bicyclic 2,3-didehydro 1,4-epiperoxides to the syn-diepoxides. In addition, the Fe complex best effects the conversion of 1,4-unsubstituted 2,3-didehydro epiperoxides to furans. The Ru-catalyzed reactions are interpreted in terms of the intermediacy of inner-sphere radicals formed by atom transfer of the Ru(II) species to peroxy substrates, in contrast to the Fe-catalyzed reactions proceeding via free, outer-sphere radicals generated by an electron-transfer mechanism.

  19. Antibody-catalyzed oxidation of delta(9)-tetrahydrocannabinol.

    PubMed

    Brogan, Andrew P; Eubanks, Lisa M; Koob, George F; Dickerson, Tobin J; Janda, Kim D

    2007-03-28

    Marijuana abuse continues to plague society and the lack of effective treatments warrants concern. Catalytic antibodies capable of oxidatively degrading the major psychoactive component of marijuana, Delta9-tetrahydrocannabinol (Delta9-THC), are presented. The antibodies generate reactive oxygen species from singlet oxygen (1O2*), using riboflavin (vitamin B2) and visible light as the 1O2* source. Cannabitriol was identified as the major degradation product of this reaction, demonstrating the ability of an antibody to catalyze a complex chemical transformation with therapeutic implications for treating marijuana abuse. PMID:17335216

  20. Facile Rh(III)-Catalyzed Synthesis of Fluorinated Pyridines.

    PubMed

    Chen, Shuming; Bergman, Robert G; Ellman, Jonathan A

    2015-06-01

    A Rh(III)-catalyzed C-H functionalization approach was developed for the preparation of multisubstituted 3-fluoropyridines from ?-fluoro-?,?-unsaturated oximes and alkynes. Oximes substituted with aryl, heteroaryl, and alkyl ?-substituents were effective coupling partners, as were symmetrical and unsymmetrical alkynes with aryl and alkyl substituents. The first examples of coupling ?,?-unsaturated oximes with terminal alkynes was also demonstrated and proceeded with uniformly high regioselectivity to provide single 3-fluoropyridine regioisomers. Reactions were also conveniently set up in air on the benchtop. PMID:25992591

  1. Copper-catalyzed decarboxylative trifluoromethylation of allylic bromodifluoroacetates.

    PubMed

    Ambler, Brett R; Altman, Ryan A

    2013-11-01

    The development of new synthetic fluorination reactions has important implications in medicinal, agricultural, and materials chemistries. Given the prevalence and accessibility of alcohols, methods to convert alcohols to trifluoromethanes are desirable. However, this transformation typically requires four-step processes, specialty chemicals, and/or stoichiometric metals to access the trifluoromethyl-containing product. A two-step copper-catalyzed decarboxylative protocol for converting allylic alcohols to trifluoromethanes is reported. Preliminary mechanistic studies distinguish this reaction from previously reported Cu-mediated reactions. PMID:24117395

  2. Enantioselective Copper-Catalyzed Carboetherification of Unactivated Alkenes**

    PubMed Central

    Bovino, Michael T.; Liwosz, Timothy W.; Kendel, Nicole E.; Miller, Yan; Tyminska, Nina

    2014-01-01

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

  3. Silver-Catalyzed Aldehyde Olefination Using Siloxy Alkynes.

    PubMed

    Sun, Jianwei; Keller, Valerie A; Meyer, S Todd; Kozmin, Sergey A

    2010-03-20

    We describe the development of a silver-catalyzed carbonyl olefination employing electron rich siloxy alkynes. This process constitutes an efficient synthesis of trisubstituted unsaturated esters, and represents an alternative to the widely utilized Horner-Wadsworth-Emmons reaction. Excellent diastereoselectivities are observed for a range of aldehydes using either 1-siloxy-1-propyne or 1-siloxy-1-hexyne. This mild catalytic process also enables chemoselective olefination of aldehydes in the presence of either ester or ketone functionality. Furthermore, since no by-products are generated, this catalytic process is perfectly suited for development of sequential reactions that can be carried out in a single flask. PMID:24273478

  4. Silver-Catalyzed Aldehyde Olefination Using Siloxy Alkynes

    PubMed Central

    Sun, Jianwei; Keller, Valerie A.; Meyer, S. Todd

    2013-01-01

    We describe the development of a silver-catalyzed carbonyl olefination employing electron rich siloxy alkynes. This process constitutes an efficient synthesis of trisubstituted unsaturated esters, and represents an alternative to the widely utilized Horner-Wadsworth-Emmons reaction. Excellent diastereoselectivities are observed for a range of aldehydes using either 1-siloxy-1-propyne or 1-siloxy-1-hexyne. This mild catalytic process also enables chemoselective olefination of aldehydes in the presence of either ester or ketone functionality. Furthermore, since no by-products are generated, this catalytic process is perfectly suited for development of sequential reactions that can be carried out in a single flask. PMID:24273478

  5. Complex Biotransformations Catalyzed by Radical S-Adenosylmethionine Enzymes*

    PubMed Central

    Zhang, Qi; Liu, Wen

    2011-01-01

    The radical S-adenosylmethionine (AdoMet) superfamily currently comprises thousands of proteins that participate in numerous biochemical processes across all kingdoms of life. These proteins share a common mechanism to generate a powerful 5?-deoxyadenosyl radical, which initiates a highly diverse array of biotransformations. Recent studies are beginning to reveal the role of radical AdoMet proteins in the catalysis of highly complex and chemically unusual transformations, e.g. the ThiC-catalyzed complex rearrangement reaction. The unique features and intriguing chemistries of these proteins thus demonstrate the remarkable versatility and sophistication of radical enzymology. PMID:21771780

  6. Gold-catalyzed intermolecular anti-markovnikov hydroamination of alkylidenecyclopropanes.

    PubMed

    Timmerman, Jacob C; Robertson, Bradley D; Widenhoefer, Ross A

    2015-02-01

    The cationic gold phosphine complex [{PCy2 (o-biphenyl)}Au(NCMe)](+) SbF6 (-) (Cy=cyclohexyl) catalyzes the intermolecular, anti-Markovnikov hydroamination reaction of monosubstituted and cis- and trans-disubstituted alkylidenecyclopropanes (ACPs) with imidazolidin-2-ones and other nucleophiles. This reaction forms 1-cyclopropyl alkylamine derivatives in high yield and with high regio- and diastereoselectivity. NMR spectroscopic analysis of gold ?-ACP complexes and control experiments point to the sp?hybridization of the ACP internal alkene carbon atom as controlling the regiochemistry of the ACP hydroamination reaction. PMID:25533892

  7. List-Barbas-Mannich reaction catalyzed by modularly designed organocatalysts.

    PubMed

    Perera, Sandun; Sinha, Debarshi; Rana, Nirmal K; Trieu-Do, Van; Zhao, John Cong-Gui

    2013-11-01

    The List-Barbas-Mannich reaction of ethyl (p-methoxyphenylimino)acetate (p-methoxyphenyl = PMP) with unmodified aldehydes or ketones catalyzed by modularly designed organocatalysts (MDOs) that are self-assembled from proline and cinchona alkaloid thioureas (such as a quinidine-derived thiourea) produces the corresponding ?-oxo-?-amino acid derivatives in high yields and excellent stereoselectivities. No solvent is necessary for this reaction. Aldehydes are especially good substrates for this reaction: The reaction takes only a few minutes to yield the corresponding List-Barbas-Mannich products in excellent dr (up to >99:1) and ee values (up to >99% ee). PMID:24106958

  8. Nickel-Catalyzed Allylic Substitution of Simple Alkenes

    PubMed Central

    Matsubara, Ryosuke; Jamison, Timothy F.

    2011-01-01

    This report describes a nickel-catalyzed allylic substitution process of simple alkenes whereby an important structural motif, a 1,4-diene, was prepared. A key for this success is the use of an appropriate Ni-phosphine complex and a stoichiometric amount of silyl triflate. Reactions of 1-alkyl-substituted alkenes consistently provided 1,1-disubstituted alkenes with high selectivity. Insight into the reaction mechanism as well as miscellaneous application of the developed catalytic process is also documented. PMID:21387565

  9. Copper-Catalyzed Azide–Alkyne Click Chemistry for Bioconjugation

    PubMed Central

    Presolski, Stanislav I.; Hong, Vu Phong; Finn, M.G.

    2012-01-01

    The copper-catalyzed azide-alkyne cycloaddition reaction is widely used for the connection of molecular entities of all sizes. A protocol is provided here for the process with biomolecules. Ascorbate is used as reducing agent to maintain the required cuprous oxidation state. Since these convenient conditions produce reactive oxygen species, five equivalents of a copper-binding ligand is used with respect to metal. The ligand both accelerates the reaction and serves as a sacrificial reductant, protecting the biomolecules from oxidation. A procedure is also described for testing the efficiency of the reaction under desired conditions for purposes of optimization, before expensive biological reagents are used. PMID:22844652

  10. Synthesis of Dihydrobenzofurans via Palladium-Catalyzed Heteroannulations

    SciTech Connect

    Roman Vladimirovich Rozhkov

    2004-12-19

    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.

  11. Flame synthesis of Fe catalyzed single-walled carbon nanotubes and Ni catalyzed nanofibers: growth mechanisms and consequences

    NASA Astrophysics Data System (ADS)

    Vander Wal, Randall L.; Hall, Lee J.

    2001-11-01

    Flame synthesis of single-walled carbon nanotubes and nanofibers is demonstrated using a pyrolysis flame configuration. Fe reacts preferentially with CO/H 2/He mixtures to produce single-walled nanotubes (SWNTs). In contrast, Ni reacts preferentially with C 2H 2/H 2/He mixtures to yield nanofibers. Both catalyst metals exhibit a marked size dependent reactivity towards these reactant gas mixtures. The yarmulke mechanism and a carbon solvation/diffusion/precipitation account for the different catalyzed products; SWNTs and nanofibers, respectively. Consequences of the size dependent reactivities of Fe and Ni nanoparticles and the respective growth mechanisms for the SWNTs and nanofibers are discussed.

  12. An antibody-catalyzed bimolecular Diels-Alder reaction

    SciTech Connect

    Braisted, A.C.; Schultz, P.G. (Lawrence Berkeley Laboratory, CA (USA))

    1990-09-26

    There exist over 1,500 known enzymes which carry out a vast array of chemical reactions with remarkable specificity and reaction rates. It is surprising then that there are no documented examples of enzyme-catalyzed pericyclic cycloaddition reactions, yet there are among the most powerful and commonly used reactions in synthetic organic chemistry. The most important of these is the Diels-Alder reaction of a diene with a dienophile, which provides a straightforward and highly stereospecific route to cyclohexene derivatives. Given the importance of this reaction in organic chemistry and its novel mechanism, it was of interest to ask whether a Diels-Alderase enzymatic catalyst could be evolved from an antibody combining site. Generation of antibodies to a structure that mimics the pericyclic transition state for a Diels-Alder reaction should result in an antibody combining site that lowers the entropy of activation {Delta}S{sup {double dagger}} by binding both the diene and the dienophile in a reactive conformation. The authors approach toward the design of a transition-state analogue involves incorporation of an ethano bridge, which locks the cyclohexene ring of hapten in a conformation that resembles the proposed pericyclic transition state for the Diels-Alder reaction of cisoid diene with dienophile. The authors now report that antibodies generated to the transition-state analogue catalyze the addition of the acyclic water-soluble diene to the maleimide derivative to give the cyclohexene product.

  13. Chloride-catalyzed corrosion of plutonium in glovebox atmospheres

    SciTech Connect

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

    1998-04-01

    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.

  14. Triethylenetetramine prevents insulin aggregation and fragmentation during copper catalyzed oxidation.

    PubMed

    Torosantucci, Riccardo; Weinbuch, Daniel; Klem, Robin; Jiskoot, Wim

    2013-08-01

    Metal catalyzed oxidation via the oxidative system Cu(2+)/ascorbate is known to induce aggregation of therapeutic proteins, resulting in enhanced immunogenicity. Hence, inclusion of antioxidants in protein formulations is of great interest. In this study, using recombinant human insulin (insulin) as a model, we investigated the ability of several excipients, in particular triethylenetetramine (TETA), reduced glutathione(GSH) and ethylenediamine tetraacetic acid (EDTA), for their ability to prevent protein oxidation, aggregation, and fragmentation. Insulin (1mg/ml) was oxidized with 40 ?M Cu(2+) and 4mM ascorbic acid in absence or presence of excipients. Among the excipients studied, 1mM of TETA, EDTA, or GSH prevented insulin aggregation upon metal catalyzed oxidation (MCO) for 3h at room temperature, based on size exclusion chromatography (SEC). At lower concentration (100 ?M), for 72 h at +4 °C, TETA was the only one to inhibit almost completely oxidation-induced insulin aggregation, fragmentation, and structural changes, as indicated by SEC, nanoparticle tracking analysis, light obscuration particle counting, intrinsic/extrinsic fluorescence, circular dichroism, and chemical derivatization. In contrast, GSH had a slight pro-oxidant effect, as demonstrated by the higher percentage of aggregates and a more severe structural damage, whereas EDTA offered substantially less protection. TETA also protected a monoclonal IgG1 against MCO-induced aggregation, suggesting its general applicability. In conclusion, TETA is a potential candidate excipient for inclusion in formulations of oxidation-sensitive proteins. PMID:23403016

  15. Antibody-catalyzed oxidative degradation of nicotine using riboflavin.

    PubMed

    Dickerson, Tobin J; Yamamoto, Noboru; Janda, Kim D

    2004-09-15

    Tobacco abuse remains a major cause of death worldwide despite ample evidence linking nicotine to various disease states. Consequently, immunopharmacotherapeutic approaches for the treatment of nicotine abuse have received increasing attention. Although a number of nicotine-binding antibodies have been disclosed, no antibody catalysts exist which efficiently degrade nicotine into pharmacologically inactive substances. Herein, we report the first catalytic antibodies which can oxidatively degrade nicotine. These biocatalysts use the micronutrient riboflavin and visible light as a source of singlet oxygen for the production of reactive oxygen species. Along with various known nicotine metabolites, antibody-catalyzed nicotine oxidations produce two novel nicotine oxidation products that were also detected in control ozonation reactions of nicotine. The reaction is efficient, with multiple turnovers of catalyst observed and total consumption of nicotine attained. These results demonstrate the potential of harnessing riboflavin as an endogenous sensitizer for antibody-catalyzed oxidations and demonstrate a new approach for the development of an active vaccine for the treatment of nicotine addiction using in vivo catalytically active antibodies. PMID:15336277

  16. Realistic modeling of ruthenium-catalyzed transfer hydrogenation.

    PubMed

    Handgraaf, Jan-Willem; Meijer, Evert Jan

    2007-03-21

    We report the first computational study of a fully atomistic model of the ruthenium-catalyzed transfer hydrogenation of formaldehyde and the reverse reaction in an explicit methanol solution. Using ab initio molecular dynamics techniques, we determined the thermodynamics, mechanism, and electronic structure along the reaction path. To assess the effect of the solvent quantitatively, we make a direct comparison with the gas-phase reaction. We find that the energy profile in solution bears little resemblance to the profile in the gas phase and a distinct solvation barrier is found: the activation barriers in both directions are lowered and the concerted hydride and proton transfer in the gas phase are converted into a sequential mechanism in solution with the substrate appearing as methoxide-like intermediate. Our results indicate that besides the metal-ligand bifunctional mechanism, as proposed by Noyori, also a concerted solvent-mediated mechanism is feasible. Our study gives a new perspective of the active role a solvent can have in transition-metal-catalyzed reactions. PMID:17319655

  17. Criteria for identifying homogeneous transition metal cluster-catalyzed reactions

    SciTech Connect

    Laine, R.M.

    1980-01-01

    Four criteria were developed for distinguishing homogeneous cluster from mononuclear catalysis. A criterion based on reaction kinetics, which distinguishes catalysis by clusters from catalysis by mononuclear complexes in equilibrium with the clusters, is illustrated with the hydroformylation of 1-pentene by Ru/sub 3/(CO)/sub 12/ clusters in equilibrium with 3Ru(CO)/sub 5/ complexes in the presence of CO. A criterion based on selectivity is illustrated by the water gas shift and deuterium-exchange reactions catalyzed by ruthenium and rhodium carbonyl clusters in methanol and triethylamine; the scope of this criterion is limited to deuterium exchange reactions. A criterion based on mixed-metal catalysis, in which a mixed-metal system has higher catalytic activity than each transition metal cluster alone, is illustrated with hydroformylation of 1-pentene and the water gas shift reaction catalyzed by Ru/sub 3/(CO)/sub 12//Fe/sub 3/(CO)/sub 2/ and Rh/sub 6/(CO)/sub 16//Fe/sub 3/(CO)/sub 12/. A criterion based on changes in asymmetric induction is a special case of the selectivity criterion, in which specific starting metal complexes may produce either of two enantiomers. Catalysis by metal clusters is an analytical tool for modeling heterogeneous catalytic mechanisms.

  18. AID from bony fish catalyzes class switch recombination

    PubMed Central

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

    2005-01-01

    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

  19. Muon-catalyzed fusion: a new direction in fusion research

    SciTech Connect

    Jones, S.E.

    1986-01-01

    In four years of intensive research, muon-catalyzed fusion has been raised from the level of a scientific curiosity to a potential means of achieving clean fusion energy. This novel approach to fusion is based on the fact that a sub-atomic particle known as a ''muon'' can induce numerous energy-releasing fusion reactions without the need for high temperatures or plasmas. Thus, the muon serves as a catalyst to facilitate production for fusion energy. The success of the research effort stems from the recent discovery of resonances in the reaction cycle which make the muon-induced fusion process extremely efficient. Prior estimates were pessimistic in that only one fusion per muon was expected. In that case energy balance would be impossible since energy must be invested to generate the muons. However, recent work has gone approximately half-way to energy balance and further improvements are being worked on. There has been little time to assess the full implications of these discoveries. However, various ways to use muon-catalyzed fusion for electrical power production are now being explored.

  20. Titanium-Catalyzed Silicon Nanostructures Grown by APCVD

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  1. Readily accessible chiral diene ligands for Rh-catalyzed enantioselective conjugate additions of boronic acids.

    PubMed

    Trost, Barry M; Burns, Aaron C; Tautz, Thomas

    2011-09-01

    Enabled by the broad scope of the Pd-catalyzed asymmetric alkylation of meso- and d,l-divinylethylene carbonate, several chiral diene ligands were prepared in two steps from commercial materials. Subsequently, these ligands were evaluated in the Rh-catalyzed asymmetric conjugate addition of boronic acids to enones. PMID:21834567

  2. Palladium-catalyzed reaction of allyl halides with a-diazocarbonyl Shufeng Chen and Jianbo Wang*

    E-print Network

    Wang, Jianbo

    Palladium-catalyzed reaction of allyl halides with a-diazocarbonyl compoundsw Shufeng Chen-diazocarbonyl compounds and allyl bromides or chlorides leads to the forma- tion of 1,3-diene derivatives. p-Allylic palladium complexes are important intermediates in palladium-catalyzed reactions.1 The p-allylic palladium

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

    E-print Network

    van Vliet, Lucas J.

    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

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

    E-print Network

    Magee, Joseph W.

    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

  5. Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase

    E-print Network

    Epstein, Irving R.

    Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase David G. Míguez* , Vladimir as catalysts and regulators. We present a reaction­diffusion system catalyzed by the enzyme glucose oxidase previously studied the temporal dynamics of the enzymatic autocatalytic reaction between glucose and ferricya

  6. Abstract: Several unsymmetrical heterobiaryls have been synthesized through palladium-catalyzed cross-coupling reactions

    E-print Network

    zincates using only one third equivalent of zinc chloride for the synthesis of 5-aryl-2-furaldehydes from 5 chloride to perform nickel- or palladium-catalyzed couplings of aryl Grignard reagents with aryl halides.10, respectively. Nickel-catalyzed cross-couplings of organozinc compounds have been described.14 However

  7. Amine-catalyzed direct Diels–Alder reactions of ?,?-unsaturated ketones with nitro olefins

    Microsoft Academic Search

    Rajeswari Thayumanavan; Buchiramachary Dhevalapally; Kandasamy Sakthivel; Fujie Tanaka; Carlos F Barbas

    2002-01-01

    Amine-catalyzed Diels–Alder reactions of ?,?-unsaturated ketones with dienophiles have been developed. Either (S)-1-(2-pyrrolidinylmethyl)pyrrolidine or l-proline catalyzed the in situ-generation and reaction of 2-amino-1,3-dienes to provide cyclohexanone derivatives in good yield (up to 87%) in one step with modest enantioselectivity.

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

    E-print Network

    Vallino, Joseph J.

    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

  9. Combined Experimental and Computational Investigation of the Mechanism of Nickel-Catalyzed

    E-print Network

    Schlegel, H. Bernhard

    Combined Experimental and Computational Investigation of the Mechanism of Nickel-Catalyzed Three University, Detroit, Michigan 48202-3489 Received July 14, 2004 The mechanism of nickel-catalyzed couplings of an enone, alkyne, and organozinc has been studied. Adducts of the substrates with nickel(0) have been

  10. Oxygenase-Catalyzed Desymmetrization of N,N-Dialkyl-piperidine-4-carboxylic Acids**

    PubMed Central

    Rydzik, Anna M; Leung, Ivanhoe K H; Kochan, Grazyna T; McDonough, Michael A; Claridge, Timothy D W; Schofield, Christopher J

    2014-01-01

    ?-Butyrobetaine hydroxylase (BBOX) is a 2-oxoglutarate dependent oxygenase that catalyzes the final hydroxylation step in the biosynthesis of carnitine. BBOX was shown to catalyze the oxidative desymmetrization of achiral N,N-dialkyl piperidine-4-carboxylates to give products with two or three stereogenic centers. PMID:25164544

  11. Hydrochloric Acid-Catalyzed Levulinic Acid Formation from Cellulose: Data and Kinetic

    E-print Network

    California at Riverside, University of

    Hydrochloric Acid-Catalyzed Levulinic Acid Formation from Cellulose: Data and Kinetic Model.com). In this study, the kinetics of the acid catalyzed hydrolysis of microcrystalline cellulose (Avicel PH101) to levulinic (LA) and formic (FA) acids was investigated in a batch reactor over the following range

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

    E-print Network

    Elrod, Matthew J.

    2006-01-01

    Atmospheric Environment 40 (2006) 6863­6878 Acid-catalyzed reactions of hexanal on sulfuric acid are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe

  13. Cu-Catalyzed Direct Amidation of Aromatic C–H Bonds: An Access to Arylamines

    PubMed Central

    2015-01-01

    A Cu-catalyzed aromatic C–H amidation with phthalimide under oxygen as a terminal oxidant without using additional additives has been achieved. This reaction has the broad substrate scope and shows moderate to good yields in most cases. This method is complementary to the previously reported metal-catalyzed C–H amination systems. PMID:24735227

  14. 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 ...

  15. Gold-Catalyzed Cycloisomerization of 1,5-Allenynes via Dual Activation of an Ene Reaction

    E-print Network

    Toste, Dean

    Gold-Catalyzed Cycloisomerization of 1,5-Allenynes via Dual Activation of an Ene Reaction Paul Ha an atom-economical entry into polyunsaturated carbo- and heterocycles.1-3 These reactions involving Rh, Pd an increase in the formal oxidation state of the metal.1,4 On the other hand, gold(I)- catalyzed enyne5

  16. Synthetic Methods Gold(i)-Catalyzed 5-endo-dig Carbocyclization of

    E-print Network

    Toste, Dean

    Synthetic Methods Gold(i)-Catalyzed 5-endo-dig Carbocyclization of Acetylenic Dicarbonyl Compounds] For example, the Conia­ene reaction provides an atom- economical synthesis of methylenecy- clopentanes have recently demonstrated that cationic gold(i) complexes catalyze the Conia­ene reaction

  17. Exploration Into Copper Catalyzed and Copper-less Click Reactions with Re(CO)3 Complexes

    E-print Network

    Collins, Gary S.

    Exploration Into Copper Catalyzed and Copper-less Click Reactions with Re(CO)3 Complexes Nicholas that combines a alkyne and an oxime to generate a isoxazole cycloaddtion product. Compared to the copper and then proceeding with the typical copper(I) catalyzed "click" reaction procedure, while the other approach involves

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

    E-print Network

    Zhang, Xumu

    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

  19. Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation

    E-print Network

    Amrhein, Valentin

    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

  20. ENZYME-CATALYZED GEL-FORMATION OF GELATIN AND CHITOSAN. POTENTIAL FOR IN SITU APPLICATIONS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We compared the ability of two enzymes to catalyze the formation of gels from solutions of gelatin and chitosan. A microbial transglutaminase, currently under investigation for food applications, was observed to catalyze the formation of strong and permanent gels from gelatin solutions. Chitosan w...

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

    PubMed Central

    Zhang, Min

    2012-01-01

    The cyclohexenone core of welwitindolinones was synthesized by a Rh(I)-catalyzed [5+1]-cycloaddition of an allenylcyclopropane with CO. A penta-substituted cyclopropane was prepared successfully by a Rh(II)-catalyzed intramolecular cyclopropanation of alkenes with chlorodiazoacetates. PMID:22783971

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

    E-print Network

    Moslin, Ryan Thomas McLeod

    2007-01-01

    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 ...

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

    PubMed

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

    2014-08-30

    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

  4. Montmorillonite Clay-Catalyzed Synthesis of RNA Oligomers

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  5. Experimental investigation of muon-catalyzed t + t fusion

    SciTech Connect

    Bogdanova, L. N. [Institute of Theoretical and Experimental Physics, State Scientific Center of Russian Federation (Russian Federation); Bom, V. R. [Delft University of Technology (Netherlands); Demin, A. M. [All-Russian Research Institute of Experimental Physics, Russian Federal Nuclear Center (Russian Federation); Demin, D. L. [Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems (Russian Federation); Eijk, C. W. E. van [Delft University of Technology (Netherlands); Filchagin, S. V. [All-Russian Research Institute of Experimental Physics, Russian Federal Nuclear Center (Russian Federation); Filchenkov, V. V.; Grafov, N. N. [Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems (Russian Federation)], E-mail: grafov@nusun.jinr.ru; Grishechkin, S. K. [All-Russian Research Institute of Experimental Physics, Russian Federal Nuclear Center (Russian Federation); Gritsaj, K. I.; Konin, A. D. [Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems (Russian Federation); Kuryakin, A. V. [All-Russian Research Institute of Experimental Physics, Russian Federal Nuclear Center (Russian Federation); Medved', S. V. [Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems (Russian Federation); Musyaev, R. K. [All-Russian Research Institute of Experimental Physics, Russian Federal Nuclear Center (Russian Federation); Rudenko, A. I. [Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems (Russian Federation); Tumkin, D. P.; Vinogradov, Yu. I.; Yukhimchuk, A. A. [All-Russian Research Institute of Experimental Physics, Russian Federal Nuclear Center (Russian Federation); Yukhimchuk, S. A.; Zinov, V. G. [Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems (Russian Federation)] (and others)

    2009-02-15

    The muon-catalyzed fusion ({mu}CF) process in tritium was studied by the {mu}CF collaboration on the muon beam of the JINR Phasotron. The measurements were carried out with a liquid tritium target at the temperature 22 K and density approximately 1.25 of the liquid hydrogen density (LHD). Parameters of the {mu}CF cycle were determined: the tt{mu} muonic molecule formation rate {lambda}{sub tt{mu}} = 2.84(0.32) {mu}s{sup -1}, the tt{mu} fusion reaction rate {lambda}{sub f} = 15.6(2.0) {mu}s{sup -1}, and the probability of muon sticking to helium {omega}{sub tt}= 13.9(1.5)%. The results agree with those obtained earlier by other groups, but better accuracy was achieved due to our unique experimental method.

  6. Calcium-catalyzed pyrolysis of lignocellulosic biomass components.

    PubMed

    Case, Paige A; Truong, Chi; Wheeler, M Clayton; DeSisto, William J

    2015-09-01

    The present study examines the effect of calcium pretreatment on pyrolysis of individual lignocellulosic compounds. Previous work has demonstrated that the incorporation of calcium compounds with the feedstock prior to pyrolysis has a significant effect on the oxygen content and stability of the resulting oil. The aim of this work was to further explore the chemistry of calcium-catalyzed pyrolysis. Bench-scale pyrolysis of biomass constituents, including lignin, cellulose and xylan is performed and compared to the oils produced from pyrolysis of the same components after calcium pretreatment. The resulting oils were analyzed by quantitative GC-MS and SEC. These analyses, together with data collected from previous work provide evidence which was used to develop proposed reaction pathways for pyrolysis of calcium-pretreatment biomass. PMID:26038329

  7. Wildcat: A catalyzed D-D Tokamak reactor

    NASA Astrophysics Data System (ADS)

    Evans, K., Jr.; Baker, C. C.; Brooks, J. N.; Clemmer, R. G.; Ehst, D. A.; Herman, H.; Jung, J.; Mattas, R. F.; Misra, B.; Smith, D. L.

    1981-11-01

    The WILDCAT is a conceptual design of a catalyzed D-D, Tokamak, commercial, fusion reactor. The 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 two versions, a steady state one with Alfven wave current drive and a pulsed version. Comparison with D-T devices were made, and cost and safety analyses are included. All of the major reactor systems are worked out to a level of detail appropriate to a complete, conceptual design.

  8. Ligand-controlled regiodivergent nickel-catalyzed annulation of pyridones.

    PubMed

    Donets, Pavel A; Cramer, Nicolai

    2015-01-01

    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

  9. Rhenium-catalyzed deoxydehydration of diols and polyols.

    PubMed

    Dethlefsen, Johannes R; Fristrup, Peter

    2015-03-01

    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

  10. Guide to Enantioselective Dirhodium(II)-Catalyzed Cyclopropanation with Aryldiazoacetates.

    PubMed

    Chepiga, Kathryn M; Qin, Changming; Alford, Joshua S; Chennamadhavuni, Spandan; Gregg, Timothy M; Olson, Jeremy P; Davies, Huw M L

    2013-07-01

    Catalytic enantioselective methods for the generation of cyclopropanes has been of longstanding pharmaceutical interest. Chiral dirhodium(II) catalysts prove to be an effective means for the generation of diverse cyclopropane libraries. Rh2(R-DOSP)4 is generaally the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh2(S-PTAD)4 provides high levels of enantioinduction with ortho-substituted aryldiazoacetates. The less-established Rh2(R-BNP)4 plays a complementary role to Rh2(R-DOSP)4 and Rh2(S-PTAD)4 in catalyzing highly enantioselective cyclopropanation of 3- methoxy-substituted aryldiazoacetates. Substitution on the styrene has only moderate influence on the asymmetric induction of the cyclopropanation. PMID:24273349

  11. Trypsin-catalyzed oxygen-18 labeling for quantitative proteomics

    SciTech Connect

    Qian, Weijun; Petritis, Brianne O.; Nicora, Carrie D.; Smith, Richard D.

    2011-07-01

    Stable isotope labeling based on relative peptide/protein abundance measurements is commonly applied for quantitative proteomics. Recently, trypsin-catalyzed oxygen-18 labeling has grown in popularity due to its simplicity, cost-effectiveness, and its ability to universally label peptides with high sample recovery. In (18)O labeling, both C-terminal carboxyl group atoms of tryptic peptides can be enzymatically exchanged with (18)O, thus providing the labeled peptide with a 4 Da mass shift from the (16)O-labeled sample. Peptide (18)O labeling is ideally suited for generating a labeled "universal" reference sample used for obtaining accurate and reproducible quantitative measurements across large number of samples in quantitative discovery proteomics.

  12. Synthesis of Rosin Acid Starch Catalyzed by Lipase

    PubMed Central

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

    2014-01-01

    Rosin, an abundant raw material from pine trees, was used as a starting material directly for the synthesis of rosin acid starch. The esterification reaction was catalyzed by lipase (Novozym 435) under mild conditions. Based on single factor experimentation, the optimal esterification conditions were obtained as follows: rosin acid/anhydrous glucose unit in the molar ratio 2?:?1, reaction time 4?h at 45°C, and 15% of lipase dosage. The degree of substitution (DS) reaches 0.098. Product from esterification of cassava starch with rosin acid was confirmed by FTIR spectroscopy and iodine coloration analysis. Scanning electron microscopy and X-ray diffraction analysis showed that the morphology and crystallinity of the cassava starch were largely destroyed. Thermogravimetric analysis indicated that thermal stability of rosin acid starch decreased compared with native starch. PMID:24977156

  13. WILDCAT: a catalyzed D-D tokamak reactor

    SciTech Connect

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

    1981-11-01

    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.

  14. Rhodium-catalyzed hydroformylation in fused azapolycycles synthesis.

    PubMed

    Settambolo, Roberta

    2013-01-01

    N-Heterocycles, including fused ones, have proven to be an important class of compounds since they possess biological and pharmacological activities themselves and serve as valuable intermediates for synthetic drug discovery. My interest in the synthesis of these compounds stems from studies dealing with the hydroformylation (oxo) of olefins. The dihydroindolizines and benzofused ones are easily generated via rhodium-catalyzed hydroformylation of N-allylpyrroles and indoles: the butanal intermediate undergoes an intramolecular cyclodehydration giving the final polycyclic compound. This chapter reports my results in the area of the conversions of oxo aldehydes with additional C,C-bond-forming reactions together with relevant work from other laboratories on additional C,N-bond-forming reactions, encountered in the field of Azapolycycles synthesis over the last 5 years or so. The intramolecular sequences for polycylization will be especially emphasized using rhodium complexes to effect these transformations, under both conventional and microwave heating. PMID:23609320

  15. Reactions of ethyl diazoacetate catalyzed by methylrhenium trioxide

    SciTech Connect

    Zhu, Z.; Espenson, H. [Iowa State Univ., Ames, IA (United States)

    1995-11-03

    Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) has found wise use in catalysis, including the epoxidation and metathesis of olefins, aldehyde olefination, and oxygen transfer. Extensive reports have now appeared in the area of MTO-catalyzed substrate oxidations with hydrogen peroxide. Certain catalytic applications of MTO for organic reactions that do not utilize peroxide have now been realized. In particular, a catalytic amount of MTO with ethyl diazoacetate (EDA) will convert aromatic imines to aziridines and convert aldehydes and ketones to epoxides. The aziridine preparation proceeds in high yields under anaerobic conditions more conveniently than with existing methods. Compounds with a three-membered heterocyclic ring can be obtained with the EDA/MTO catalytic system. Aromatic imines undergo cycloaddition reactions to give aziridines under mild conditions.

  16. Mechanism of Brønsted acid-catalyzed glucose dehydration.

    PubMed

    Yang, Liu; Tsilomelekis, George; Caratzoulas, Stavros; Vlachos, Dionisios G

    2015-04-24

    We present the first DFT-based microkinetic model for the Brønsted acid-catalyzed conversion of glucose to 5-hydroxylmethylfurfural (HMF), levulinic acid (LA), and formic acid (FA) and perform kinetic and isotopic tracing NMR spectroscopy mainly at low conversions. We reveal that glucose dehydrates through a cyclic path. Our modeling results are in excellent agreement with kinetic data and indicate that the rate-limiting step is the first dehydration of protonated glucose and that the majority of glucose is consumed through the HMF intermediate. We introduce a combination of 1)?automatic mechanism generation with isotopic tracing experiments and 2)?elementary reaction flux analysis of important paths with NMR spectroscopy and kinetic experiments to assess mechanisms. We find that the excess formic acid, which appears at high temperatures and glucose conversions, originates from retro-aldol chemistry that involves the C6 carbon atom of glucose. PMID:25572774

  17. [Ru/AC catalyzed ozonation of recalcitrant organic compounds].

    PubMed

    Wang, Jian-Bing; Hou, Shao-Pei; Zhou, Yun-Rui; Zhu, Wan-Peng; He, Xu-Wen

    2009-09-15

    Ozonation and Ru/AC catalyzed ozonation of dimethyl phthalate (DMP), phenols and disinfection by-products precursors were studied. It shows that Ru/AC catalyst can obviously enhance the mineralization of organic compounds. In the degradation of DMP, TOC removal was 28.84% by ozonation alone while it was 66.13% by catalytic ozonation. In the oxidation of 23 kinds of phenols, TOC removals were 9.57%-56.08% by ozonation alone while they were 41.81%-82.32% by catalytic ozonation. Compared to ozonation alone, Ru/AC catalyzed ozonation was more effective for the reduction of disinfection by-products formation potentials in source water. The reduction of haloacetic acids formation potentials was more obvious than thichlomethane formation potentials. After the treatment by catalytic ozonation, the haloacetic acids formation potentials decreased from 144.02 microg/L to 58.50 microg/L, which was below the standard value of EPA. However ozonation alone could not make it reach the standard. The treatments of source water by BAC, O3 + BAC, O3/AC + BAC and Ru/AC + O3 + BAC were also studied. In the four processes, TOC removal was 3.80%, 20.14%, 27.45% and 48.30% respectively, COD removal was 4.37%, 27.22%, 39.91% and 50.00% respectively, UV254 removal was 8.16%, 62.24%, 67.03% and 84.95% respectively. Ru/AC + O3 + BAC process is more effective than the other processes for the removal of TOC, COD and UV254 and no ruthenium leaching observed in the solution. It is a promising process for the treatment of micro polluted source water. PMID:19927805

  18. Activity of formylphosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Jahansouz, H.; Kofron, J.L.; Smithers, G.W.; Himes, R.H.; Reed, G.H.

    1986-05-01

    Formylphosphate (FP), a putative enzyme-bound intermediate in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase, was synthesized from formylfluoride and Pi. Measurement of hydrolysis rates by /sup 31/P NMR showed that FP is very unstable with a half-life of 48 min at 20/sup 0/C and pH 7. At pH 7 hydrolysis occurs with O-P bond cleavage as shown by /sup 18/O incorporation from /sup 18/O-H/sub 2/O into Pi. The substrate activity of FP was tested in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase isolated from Clostridium cylindrosporum. MgATP + H/sub 4/folate + HCOO/sup -/ in equilibrium MgADP + Pi +N/sup 10/-formylH/sub 4/folate FP supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formylH/sub 4/folate is produced from H/sub 4/-folate and FP but only if ADP is present, and ATP is produced from FP and ADP but only if H/sub 4/folate is present. The requirements for H/sub 4/folate in the synthesis of ATP from ADP and FP and for ADP in the synthesis of N/sup 10/-formylH/sub 4/folate from FP and H/sub 4/folate, are consistent with past kinetic and isotope exchange studies which showed that the reaction proceeds by a sequential mechanism and that all three substrates must be present for any reaction to occur.

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

    PubMed Central

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

    2014-01-01

    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

  20. Acid-catalyzed Heterogeneous Reactions in SOA Formation

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

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

  1. Flame Synthesis Used to Create Metal-Catalyzed Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    VanderWal, Randy L.

    2001-01-01

    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.

  2. Anti-Markovnikov hydroimination of terminal alkynes in gold-catalyzed pyridine construction from ammonia.

    PubMed

    Wang, Liliang; Kong, Lingbing; Li, Yongxin; Ganguly, Rakesh; Kinjo, Rei

    2015-07-21

    Gold-catalyzed hydroimination of terminal alkynes, giving rise to anti-Markovnikov adducts concomitant with unstable Markovnikov adducts is described. The elementary step can be applied for the construction of pyridine derivatives from ammonia and alkynes. PMID:26144528

  3. The two types of 3-dehydroquinase have distinct structures but catalyze the same overall reaction 

    E-print Network

    Gourley, David G; Shrive, Annette K; Polikarpov, Igor; Krell, Tino; Coggins, John R; Hawkins, Alastair R; Isaacs, Neil W; Sawyer, Lindsay

    The structures of enzymes catalyzing the reactions in central metabolic pathways are generally well conserved as are their catalytic mechanisms. The two types of 3-dehydroquinate dehydratase (DHQase) are therefore most ...

  4. Pd-catalyzed addition–carbocyclization of ?,?-diynes with H–P(O)R 2 compounds

    Microsoft Academic Search

    Jun Kanada; Koh-ichiro Yamashita; Satish Kumar Nune; Masato Tanaka

    2009-01-01

    Chelating phosphines are much higher performing than mono-dentate phosphines in palladium-catalyzed reaction of ?,?-diynes with HP(O)R1R2 (R1,R2=Ph, alkoxy) to afford (E)-3-(phosphorylmethylene)-2-methylcyclopentenes.

  5. 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

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

    E-print Network

    Sniady, Adam

    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, ...

  7. Cerium(III)-Catalyzed Synthesis of Schiff Bases: A Green Approach

    Microsoft Academic Search

    Lakshmy Ravishankar; Siddhartha A. Patwe; Nehal Gosarani; Aparajita Roy

    2010-01-01

    The reaction of primary aromatic amines with aryl aldehydes is found to be catalyzed by cerium chloride heptahydrate under solvent-free conditions to give the corresponding Schiff bases in good yields.

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

    E-print Network

    Matsubara, Ryosuke

    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 ...

  9. Combined Oxypalladation/C-H Functionalization: Palladium(II)-Catalyzed Intramolecular Oxidative Oxyarylation of Hydroxyalkenes

    E-print Network

    Zhu, Rong

    An efficient protocol has been developed for the intramolecular oxidative oxyarylation using a Pd[superscript II]-catalyzed tandem oxypalladation/C-H functionalization strategy. This methodology allows rapid access to ...

  10. Synthesis of (-)-?9-trans-Tetrahydrocannabinol - Stereocontrol via Mo-catalyzed Asymmetric Allylic Alkylation Reaction

    PubMed Central

    Trost, Barry M.; Dogra, Kalindi

    2008-01-01

    ?9-THC is synthesized in enantiomericaly pure form, where all of the stereochemistry is derived from the molybdenum catalyzed asymmetric alkylation reaction of the extremely sterically congested bis-ortho substituted cinnamyl carbonate in high regio- and enantioselectivity. PMID:17266321

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

    E-print Network

    Gomez Ruiz, Alejandro

    1998-01-01

    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...

  12. Iridium-Catalyzed Branch-Selective Hydroarylation of Vinyl Ethers via C-H Bond Activation.

    PubMed

    Ebe, Yusuke; Nishimura, Takahiro

    2015-05-13

    Iridium-catalyzed hydroarylation of vinyl ethers via a directed C-H bond activation of aromatic compounds gave high yields of the corresponding addition products with high branch selectivity. PMID:25928127

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

    E-print Network

    Burgess, Kevin

    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

  14. Silver-catalyzed PuO sub 2 dissolution with persulfate

    SciTech Connect

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

    1991-06-01

    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)

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

    E-print Network

    Salvi, Luca

    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 ...

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

    E-print Network

    Huang, Xiaohua, 1973-

    2003-01-01

    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 ...

  17. Gold-catalyzed efficient tandem assembly of terminal alkynes and arynes: synthesis of alkynylated biphenyl derivatives.

    PubMed

    Xie, Chunsong; Zhang, Yuhong; Yang, Yuzhu

    2008-10-21

    Gold catalysts have been found to catalyze the tandem assembly of arynes and terminal alkynes efficiently in the presence of CuI under mild reaction conditions to provide useful alkynylated biphenyl derivatives. PMID:18830501

  18. Enantioselective Functionalization of Radical Intermediates in Redox Catalysis: Copper-Catalyzed Asymmetric Oxytrifluoromethylation of Alkenes

    E-print Network

    Zhu, Rong

    Something radical: An 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 ...

  19. Development of novel transition metal-catalyzed cross-coupling reactions and applications thereof

    E-print Network

    Teverovskiy, Georgiy

    2013-01-01

    Chapter 1 The first example of Pd(0)/(II) catalyzed fluorination of aryl bromides is reported herein. Based on these data, an analogous method was developed for the fluorination of aryl triflates. The reaction proceeds ...

  20. Mechanistic studies on metal-catalyzed carbon-nitrogen bond forming reactions

    E-print Network

    Strieter, Eric R

    2005-01-01

    Mechanistic studies on copper and palladium-catalyzed C-N bond forming reactions are described. To understand the mechanistic details of these processes, several principles of physical organic chemistry have been employed. ...

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

    E-print Network

    Schleicher, Kristin D. (Kristin Diann)

    2010-01-01

    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 ...

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

    E-print Network

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

    2005-01-01

    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 ...

  3. Synthesis of diphenylhexatriene by the Pd-catalyzed dimerization of cinnamyl acetate.

    PubMed

    Mesganaw, Tehetena; Im, G-Yoon J; Garg, Neil K

    2013-04-01

    A mild and operationally simple method to synthesize diphenylhexatriene (DPH) is reported. The method relies on the Pd-catalyzed dimerization of cinnamyl acetate and provides efficient access to DPH in a single step. PMID:23414259

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

    E-print Network

    Breitler, Simon

    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 ...

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

    E-print Network

    Armbrust, Kurt W. (Kurt Willes)

    2014-01-01

    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 ...

  6. Alkene epoxidation catalyzed by cytochrome P450 BM-3 139-3 Edgardo T. Farinas,

    E-print Network

    Arnold, Frances H.

    Catalyzing a wide range of oxidative reactions under mild conditions in aqueous solutions, cytochrome P450, and methanol in potassium phosphate buffer. For propylene oxidation, the buffer was first saturated

  7. The Biginelli Reaction Is a Urea-Catalyzed Organocatalytic Multicomponent Reaction.

    PubMed

    Puripat, Maneeporn; Ramozzi, Romain; Hatanaka, Miho; Parasuk, Waraporn; Parasuk, Vudhichai; Morokuma, Keiji

    2015-07-17

    The recently developed artificial force induced reaction (AFIR) method was applied to search systematically all possible multicomponent pathways for the Biginelli reaction mechanism. The most favorable pathway starts with the condensation of the urea and benzaldehyde, followed by the addition of ethyl acetoacetate. Remarkably, a second urea molecule catalyzes nearly every step of the reaction. Thus, the Biginelli reaction is a urea-catalyzed multicomponent reaction. The reaction mechanism was found to be identical in both protic and aprotic solvents. PMID:26066623

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

    PubMed

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

    2015-02-01

    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

  9. Palladium-catalyzed chemoselective decarboxylative ortho acylation of benzoic acids with ?-oxocarboxylic acids.

    PubMed

    Miao, Jinmin; Ge, Haibo

    2013-06-21

    Palladium-catalyzed chemoselective decarboxylative cross coupling of benzoic acids with ?-oxocarboxylic acids was realized via an arene sp(2) C-H functionalization process. This work represents the first example of transition-metal-catalyzed cross-coupling reactions with two acids acting in different roles. The synthetic utility of this method was confirmed by the synthesis of pitofenone, an antispasmodic used in the combined drug Spasmalgon. PMID:23721458

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

    Microsoft Academic Search

    Christian. Brandt; Rudi. van Eldik

    1995-01-01

    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

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

    PubMed Central

    Bartlett, Mark J.

    2012-01-01

    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

  12. Silver-catalyzed bioleaching of low-grade copper ores. Part II: Stirred tank tests

    Microsoft Academic Search

    J. A. Muñoz; D. B. Dreisinger; W. C. Cooper; S. K. Young

    2007-01-01

    A study of the effect of different variables (inoculation, aeration, silver complexants, [Ag], [Fe3+], temperature and chemical activation stage) on the silver-catalyzed bioleaching of two different low-grade copper ores has been carried out in stirred tanks. The catalyzed bioleaching process was greatly affected by bacterial activity. Aeration and the use of different complexing agents (thiosulfate and thiosulfate plus cupric ions)

  13. Esterification and interesterification reactions catalyzed by acetone powder from germinating rapeseed

    Microsoft Academic Search

    I. Jachmanilin; K. D. Mukherjee

    1996-01-01

    Acetone powder from germinating rape (Brassica napus L.) seedlings exhibits essentially similar activity in lipolysis of triacylglycerols as the corresponding seedling homogenates.\\u000a Acetone powder from rape seedlings catalyzes the esterification of a fatty acid, such as oleic acid, withn-butanol or a long-chain alcohol, such as oleyl alcohol. Furthermore, the acetone powder catalyzes alcoholysis of a methyl\\u000a ester, such as methyl

  14. A concise synthetic approach to brazilin via Pd-catalyzed allylic arylation.

    PubMed

    Jung, Youngeun; Kim, Ikyon

    2015-04-14

    A short synthetic route to the trimethyl ether of brazilin was developed in 6 steps from 7-methoxychromene with 78% overall yield. Regioselective installation of a formyl group onto 7-methoxychromene followed by reduction and acetylation afforded allylic acetate. Palladium-catalyzed allylic coupling of allylic acetate with arylboronic acid provided direct access to 3-benzylchromene which was converted to the target molecule upon ensuing dihydroxylation and acid-catalyzed cyclization in a highly concise manner. PMID:25767080

  15. Use of a palladium(II)-catalyzed oxidative kinetic resolution in synthetic efforts toward bielschowskysin.

    PubMed

    Meyer, Michael E; Phillips, John H; Ferreira, Eric M; Stoltz, Brian M

    2013-09-01

    Progress toward the cyclobutane core of bielshowskysin is reported. The core was thought to arise from a cyclopropane intermediate via a furan-mediated cyclopropane fragmentation, followed by a 1,4-Michael addition. The synthesis of the cyclopropane intermediate utilizes a Suzuki coupling reaction, an esterification with 2-diazoacetoacetic acid, and a copper catalyzed cyclopropanation. An alcohol intermediate within the synthetic route was obtained in high enantiopurity via a highly selective palladium(II)-catalyzed oxidative kinetic resolution (OKR). PMID:23913988

  16. 2,3-Migration in Rh(II)-Catalyzed Reactions of -Trifluoroacetamido

    E-print Network

    Wang, Jianbo

    2,3-Migration in Rh(II)-Catalyzed Reactions of -Trifluoroacetamido r-Diazocarbonyl Compounds Feng(II)-catalyzed reactions of these diazo compounds gave 2,3-migration products in high yields. 1,2-Migration is one,2-migration reactions, the 1,2-hydride migration is generally predominant, but 1,2-alkyl, 1,2-aryl, 1,2-thio

  17. Multidirectional Synthesis of Substituted Indazoles via Iridium-Catalyzed C-H Borylation.

    PubMed

    Sadler, Scott A; Hones, Andrew C; Roberts, Bryan; Blakemore, David; Marder, Todd B; Steel, Patrick G

    2015-05-15

    In the absence of a steric directing group, iridium-catalyzed C-H borylation of N-protected indazoles occurs rapidly and selectively at C-3 and the resulting boronate esters can be utilized in a range of downstream conversions. The functional group tolerance of the iridium-catalyzed C-H borylation reaction enables simple and efficient multidirectional syntheses of substituted indazoles to be realized. PMID:25894824

  18. Lipase-catalyzed enantioselective esterification of (S)-naproxen hydroxyalkyl ester in organic media.

    PubMed

    Chang, Chun-Sheng; Hsu, Chin-Shuo; Shang, Chun-Sheng

    2003-03-01

    A lipase-catalyzed, enantioselective esterification process in organic solvents was developed for the synthesis of (S)-naproxen hydroxyalkyl ester. With the selection of lipase (Candida rugosa lipase) and reaction medium (isooctane and cyclohexane), a high enantiomeric ratio of > 100 for the enzyme was obtained. 1,4-Butanediol was the best acyl acceptor. The carbon chain length of the alcohol had a major effect on the enzyme activity and enantioselectivity of lipase-catalyzed esterification. PMID:12882564

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

    E-print Network

    Hilscher, Larry Wayne

    1985-01-01

    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...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...

  20. Purification and characterization of 2,6-dihydroxybenzoate decarboxylase reversibly catalyzing nonoxidative decarboxylation

    Microsoft Academic Search

    Toyokazu Yoshida; Yutaka Hayakawa; Tsuyoshi Matsui; Toru Nagasawa

    2004-01-01

    A nonoxidative decarboxylase, 2,6-dihydroxybenzoate decarboxylase, was found in Agrobacterium tumefaciens IAM12048. The enzyme activity was induced specifically by 2,6-dihydroxybenzoate. The purified enzyme was a homotetramer of identical 38 kDa subunits. The purified decarboxylase catalyzed the nonoxidative decarboxylation of 2,6-dihydroxybenzoate and 2,3-dihydroxybenzoate without requiring any cofactors. In the presence of KHCO 3, the enzyme also catalyzed the regioselective carboxylation of 1,3-dihydroxybenzene into

  1. Transition State Structure for ADP-Ribosylation of Eukaryotic Elongation Factor 2 Catalyzed by Diphtheria Toxin

    Microsoft Academic Search

    Sapan L. Parikh; Vern L. Schramm

    2004-01-01

    Bacterial protein toxins are the most powerful human poisons known, exhibiting an LD50 of 0.1- 1n g kg -1. A major subset of such toxins is the NAD+-dependent ADP-ribosylating exotoxins, which include pertussis, cholera, and diphtheria toxin. Diphtheria toxin catalyzes the ADP ribosylation of the diphthamide residue of eukaryotic elongation factor 2 (eEF-2). The transition state of ADP ribosylation catalyzed

  2. Kinetic modeling of Pt-catalyzed glycolaldehyde decomposition to syngas.

    PubMed

    Salciccioli, Michael; Vlachos, Dionisios G

    2012-05-10

    Fundamental knowledge of the elementary reaction mechanisms involved in oxygenate decomposition on transition metal catalysts can facilitate the optimization of future catalyst and reactor systems for biomass upgrade to fuels and chemicals. Pt-catalyzed decomposition of glycolaldehyde, as the smallest oxygenate with alcohol and aldehyde functionality, was studied via a DFT-based microkinetic model. It was found that two decomposition pathways exist. Under conditions of low hydrogen surface coverage, the initial C-H bond breaking reaction to HOCH(2)CO* is prevalent, while under conditions of high hydrogen coverage, the rather unexpected O-H bond forming reaction to HOCH(2)CHOH* is more active (subsequent decomposition is energetically favorable from HOCH(2)CHOH*). Our results indicate the possibility that (de)hydrogenation chemistry is rate-controlling in many small polyoxygenate biomass derivatives, and suitable catalysts are needed. Finally, DFT was used to understand the increased decomposition activity observed on the surface segregated Ni-Pt-Pt bimetallic catalyst. It was found that the initial O-H bond breaking of glycolaldehyde to OCH(2)CHO* has an activation barrier of just 0.21 eV. This barrier is lower than that of any glycolaldehyde consuming reaction on Pt. These computational predictions are in qualitative agreement with experimental results. PMID:22483365

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

    PubMed

    Kaissling, K E

    1998-08-01

    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

  4. MEMS-based satellite micropropulsion via catalyzed hydrogen peroxide decomposition

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  5. Kinetics of Platinum-Catalyzed Decomposition of Hydrogen Peroxide

    NASA Astrophysics Data System (ADS)

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

    2003-07-01

    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.

  6. Primordial lithium abundance in catalyzed big bang nucleosynthesis

    SciTech Connect

    Bird, Chris [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada); Koopmans, Kristen [Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2J 2W9 (Canada); Pospelov, Maxim [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada); Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2J 2W9 (Canada)

    2008-10-15

    There exists a well-known problem with the {sup 7}Li+{sup 7}Be 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}{sub X} > or approx. 10{sup 3} sec, charged particles X{sup -} is capable of suppressing the primordial {sup 7}Li+{sup 7}Be 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{sup -} at temperatures of 4x10{sup 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 {sup 7}Li+{sup 7}Be is triggered by the formation of ({sup 7}BeX{sup -}) compound nuclei, with fast depletion of their abundances by catalyzed proton reactions, and in some models by direct capture of X{sup -} on {sup 7}Be. The combination of {sup 7}Li+{sup 7}Be and {sup 6}Li constraints favors the window of lifetimes, 1000 s < or approx. {tau}{sub X}{<=}2000 s.

  7. Microperoxidase 8 catalyzed nitration of phenol by nitrogen dioxide radicals.

    PubMed

    Ricoux, R; Boucher, J L; Mansuy, D; Mahy, J P

    2001-07-01

    Microperoxidase 8 (MP8) is a heme octapeptide obtained by hydrolytic digestion of horse heart cytochrome c. At pH below 9, the heme iron is axially coordinated to the imidazole side chain of His18 and to a water molecule. Replacement of this weak ligand by H2O2 allows the formation of high-valent iron-oxo species which are responsible for both peroxidase-like and cytochrome P450-like activities of MP8. This paper shows that MP8 is able to catalyze the nitration of phenol by nitrite. The reaction requires H2O2 and is inhibited by ligands having a high affinity for the iron, catalase and radical scavengers. This suggests that the nitrating species could be NO2* radicals formed by the oxidation of nitrite by high-valent iron-oxo species. This new activity of MP8 opens a new access to nitro-aromatic compounds under mild conditions and validates the use of this minienzyme to mimick heme peroxidases, especially in the reactions of NO-derived species with biomolecules under oxidative stress conditions. PMID:11432746

  8. Carbon-catalyzed gasification of organic feedstocks in supercritical water

    SciTech Connect

    Xu, X.; Matsumura, Y.; Stenberg, J.; Antal, M.J. Jr. [Univ. of Hawaii, Honolulu, HI (United States). Hawaii Natural Energy Inst.] [Univ. of Hawaii, Honolulu, HI (United States). Hawaii Natural Energy Inst.

    1996-08-01

    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 effects of temperature, pressure, reactant concentration, weight hourly space velocity, and the type of catalyst on the gasification of glucose are reported. Complete conversion of glucose (22% by weight in water) to a hydrogen-rich synthesis gas was realized at a weight hourly space velocity (WHSV) of 22.2 h{sup {minus}1} in supercritical water at 600 C, 34.5 MPa. Complete conversions of the whole biomass feeds were also achieved at the same temperature and pressure. The destruction efficiencies for the representative DoD wastes were also high. Deactivation of the carbon catalyst was observed after 4 h of operation without swirl in the entrance region of the reactor, but the carbon gasification efficiency remained near 100% for more than 6 h when a swirl generator was employed in the entrance of the reactor.

  9. Iodide-Catalyzed Ozonation of ?-Pinene on Aqueous Surfaces

    NASA Astrophysics Data System (ADS)

    Hoffmann, M. R.; Enami, S.; Colussi, A. J.

    2011-12-01

    Biogenic terpenes are the dominant global source of volatile organic compounds (VOC) and secondary organic aerosols (SOA). Their atmospheric chemistry has therefore major direct and indirect impacts on global climate change. At the same time, it has become apparent that organic and inorganic iodine species of marine origin are ubiquitous in the troposphere. They are found over the open ocean (even in the absence of biogenic sources), the Antarctic coast, in rain, aerosols, ice, and snow, and participate in HOx/NOx cycles in the troposphere. Here we report that iodide catalyzes the ozonation of ?-pinene on aqueous surfaces. Nebulizer-assisted online electrospray mass spectrometry of ?-pinene solutions briefly exposed to gaseous ozone reveals that alpha-pinene, which is unreactive during 10 ?s contact times, is converted into acids (e.g., pinonic acid) and previously unreported iodine-containing species in the presence of millimolar iodide.. These newly found products were characterized by MS/MS in conjunction with isotope and kinetic studies, and may account for unidentified organoiodine species observed in recent field measurements.

  10. Iodide-catalyzed ozonation of terpenes on aqueous surfaces

    NASA Astrophysics Data System (ADS)

    Enami, S.; Hayase, S.; Kawasaki, M.; Hoffmann, M. R.; Colussi, A. J.

    2011-12-01

    Biogenic terpenes are the dominant global source of volatile organic compounds (VOC) and secondary organic aerosols (SOA). Their atmospheric chemistry has therefore major direct and indirect impacts on global climate change. At the same time, it has become apparent that organic and inorganic iodine species of marine origin are ubiquitous in the troposphere. They are found over the open ocean (even in the absence of biogenic sources), the Antarctic coast, in rain, aerosols, ice, and snow, and participate in HOx/NOx cycles in the troposphere. Here we report that iodide catalyzes the ozonation of alpha-pinene on aqueous surfaces. Nebulizer-assisted online electrospray mass spectrometry of alpha-pinene solutions briefly exposed to gaseous ozone reveals that alpha-pinene, which is unreactive during 10 microsecond contact times, is converted into acids (e.g., pinonic acid) and previously unreported iodine-containing species in the presence of millimolar iodide. These newly found products were characterized by MS/MS in conjunction with isotope and kinetic studies, and may account for unidentified organoiodine species observed in recent field measurements.

  11. Mechanistic studies of the catalyzed carbon gasification reactions

    SciTech Connect

    Goethel, P.J.

    1989-01-01

    The catalyzed graphite hydrogenation reaction was studied employing the Etch Decoration Transmission Electron Microscope technique to view the monolayer channeling action of nickel and ruthenium catalysts. The results indicate a carbidic catalyst surface carbon reacting with surface hydrogen to form methane as the rate limiting step of the mechanism. The mechanism is compared to the methanation reaction from CO + H{sub 2} feedstocks and also to the catalytic growth of carbon filaments. A new mode of catalytic action termed tunneling was shown to exist for Pt, Ni, and Ru in the graphite hydrogenation reaction. For monolayer channeling and tunneling the overall contribution to bulk gasification is shown to be significant. A TGA technique for measuring the solubility and diffusion coefficient of carbon in metals is presented. The technique is shown to be accurate and to give quick results in comparison to other techniques. The monolayer channeling action of Pt, Cu, V{sub 2}O{sub 5}, V and Mo{sub 2}C was examined in the graphite oxidation reaction. Pt and Cu show C-C bond breakage as the rate limiting step while V, V{sub 2}O{sub 5} and Mo{sub 2}C reveal a gas-catalyst interface reaction limiting the process. V{sub 2}O{sub 5}, V and Mo{sub 2}C were also found to participate in monolayer edge recession thus forming elongated hexagon pits.

  12. Predictive modeling of metal-catalyzed polyolefin processes

    NASA Astrophysics Data System (ADS)

    Khare, Neeraj Prasad

    2003-10-01

    This dissertation describes the essential modeling components and techniques for building comprehensive polymer process models for metal-catalyzed polyolefin processes. The significance of this work is that it presents a comprehensive approach to polymer process modeling applied to large-scale commercial processes. Most researchers focus only on polymerization mechanisms and reaction kinetics, and neglect physical properties and phase equilibrium. Both physical properties and phase equilibrium play key roles in the accuracy and robustness of a model. This work presents the fundamental principles and practical guidelines used to develop and validate both steady-state and dynamic simulation models for two large-scale commercial processes involving the Ziegler-Natta polymerization to produce high-density polyethylene (HDPE) and polypropylene (PP). It also provides a model for the solution polymerization of ethylene using a metallocene catalyst. Existing modeling efforts do not include physical properties or phase equilibrium in their calculations. These omissions undermine the accuracy and predictive power of the models. The forward chapters of the dissertation discuss the fundamental concepts we consider in polymer process modeling. These include physical and thermodynamic properties, phase equilibrium, and polymerization kinetics. The later chapters provide the modeling applications described above.

  13. Mild palladium-catalyzed selective monoarylation of nitriles.

    PubMed

    Wu, Lingyun; Hartwig, John F

    2005-11-16

    Two new palladium-catalyzed procedures for the arylation of nitriles under less basic conditions than previously reported have been developed. The selective monoarylation of acetonitrile and primary nitriles has been achieved using alpha-silyl nitriles in the presence of ZnF2. This procedure is compatible with a variety of functional groups, including cyano, keto, nitro, and ester groups, on the aryl bromide. The arylation of secondary nitriles occurred in high yield by conducting reactions with zinc cyanoalkyl reagents. These reaction conditions tolerated base-sensitive functional groups, such as ketones and esters. The combination of these two methods, one with alpha-silyl nitriles and one with zinc cyanoalkyl reagents, provides a catalytic route to a variety of benzylic nitriles, which have not only biological significance but utility as synthetic intermediates. The utility of these new coupling reactions has been demonstrated by a synthesis of verapamil, a clinically used drug for the treatment of heart disease, by a three-step route from commercial materials that allows convenient variation of the aryl group. PMID:16277525

  14. Ceramide Glycosylation Catalyzed by Glucosylceramide Synthase and Cancer Drug Resistance

    PubMed Central

    Liu, Yong-Yu; Li, Yu-Teh

    2014-01-01

    Glucosylceramide synthase (GCS), converting ceramide to glucosylceramide, catalyzes the first reaction of ceramide glycosylation in sphingolipid metabolism. This glycosylation by GCS is a critical step regulating the modulation of cellular activities by controlling ceramide and glycosphingolipids (GSLs). An increase of ceramide in response to stresses, such as chemotherapy, drives cells to proliferation arrest and apoptosis or autophagy; however, ceramide glycosylation promptly eliminates ceramide and consequently, these induced processes, thus protecting cancer cells. Furthermore, persistently enhanced ceramide glycosylation can increase GSLs, participating in selecting cancer cells to drug resistance. GCS is overexpressed in diverse drug-resistant cancer cells and in tumors of breast, colon, and leukemia that display poor response to chemotherapy. As ceramide glycosylation by GCS is a rate-limiting step in GSL synthesis, inhibition of GCS sensitizes cancer cells to anticancer drugs and eradicates cancer stem cells. Mechanistic studies indicate that uncoupling ceramide glycosylation can modulate gene expression, decreasing MDR1 through the cSrc/?-catenin pathway and restoring p53 expression via RNA splicing. These studies not only expand our knowledge in understanding how ceramide glycosylation affects cancer cells, but also provide novel therapeutic approaches for targeting refractory tumors. PMID:23290777

  15. Lipase catalyzed esterification of glycidol in organic solvents

    SciTech Connect

    Martins, J.F.; Nunes da Ponte, M.; Barreiros, S. (Univ. Nova de Lisboa, Oeiras (Portugal). Centro de Tecnologia Quimica e Biologica)

    1993-08-05

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

  16. Hydroformylation of 1-heptene catalyzed by ruthenium cluster

    SciTech Connect

    Li, Z.; Zhang, J.; Wang, C. [Taiyuan Univ. of Technology (China). Inst. of Coal Chemical Engineering

    1994-12-31

    Hydroformylation of 1-heptane catalyzed by homogeneous and heterogeneous Ru{sub 3}(CO){sub 12} catalyst has been investigated. Ru{sub 3}(CO){sub 12} has almost no activity when reaction temperature is below 60 C, and nearly stable activity when over 100 C. The maximum selectivity to aldehyde is obtained at 120 C and N/I values of aldehyde and alcohol decrease rapidly with temperature increase. Supported Ru{sub 3}(CO){sub 12} catalyst modified with NaBH{sub 4} or KOH has higher catalytic activity and selectivity to aldehyde in heterogeneous catalysis. Compared with supported Ru{sub 3}(CO){sub 12} catalyst modified with NaBH{sub 4} or KOH has higher catalytic activity and selectivity to aldehyde in heterogeneous catalysis. Compared with supported Ru{sub 3}(CO){sub 12} catalysts, Ru{sub 3}(CO){sub 12}/Co{sub 2}(CO){sub 8}/{gamma}-Al{sub 2}O{sub 3} has high activity and selectivity. When PPh{sub 3} or (NEt{sub 4}) Cl is added to the reaction system, the selectivity to aldehyde and N/I increase. The FTIR spectra of catalysts after reaction show that Ru{sub 3}(CO){sub 12} and Co{sub 2}(CO){sub 8} are changed to new carbonyl complexes which may have catalytic activity.

  17. A Personal Adventure in Muon-Catalyzed Fusion

    NASA Astrophysics Data System (ADS)

    Jackson, John David

    2010-03-01

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

  18. Mechanistic study of silver-catalyzed decarboxylative fluorination.

    PubMed

    Patel, Niki R; Flowers, Robert A

    2015-06-01

    The silver-catalyzed fluorination of aliphatic carboxylic acids by Selectfluor in acetone/water provides access to fluorinated compounds under mild and straightforward reaction conditions. Although this reaction provides efficient access to fluorinated alkanes from a pool of starting materials that are ubiquitous in nature, little is known about the details of the reaction mechanism. We report spectroscopic and kinetic studies on the role of the individual reaction components in decarboxylative fluorination. The studies presented herein provide evidence that Ag(II) is the intermediate oxidant in the reaction. In the rate-limiting step of the reaction, Ag(I)-carboxylate is oxidized to Ag(II) by Selectfluor. Substrate inhibition of the process occurs through the formation of a silver-carboxylate. Water is critical for solubilizing reaction components and ligates to Ag(I) under the reaction conditions. The use of donor ligands on Ag(I) provides evidence of oxidation to Ag(II) by Selectfluor. The use of sodium persulfate as an additive in the reaction as well as NFSI as a fluorine source further supports the generation of a Ag(II) intermediate; this data will enable the development of a more efficient set of reaction conditions for the fluorination. PMID:25927595

  19. Cyclophilin A catalyzes proline isomerization by an electrostatic handle mechanism

    PubMed Central

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

    2014-01-01

    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

  20. Production of Chemoenzymatic Catalyzed Monoepoxide Biolubricant: Optimization and Physicochemical Characteristics

    PubMed Central

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

    2012-01-01

    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

  1. Dynamin-Catalyzed Membrane Fission Requires Coordinated GTP Hydrolysis

    PubMed Central

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

    2013-01-01

    Dynamin is the most-studied membrane fission machinery and has served as a paradigm for studies of other fission GTPases; however, several critical questions regarding its function remain unresolved. In particular, because most dynamin GTPase domain mutants studied to date equally impair both basal and assembly-stimulated GTPase activities, it has been difficult to distinguish their respective roles in clathrin-mediated endocytosis (CME) or in dynamin catalyzed membrane fission. Here we compared a new dynamin mutant, Q40E, which is selectively impaired in assembly-stimulated GTPase activity with S45N, a GTP-binding mutant equally defective in both basal and assembly-stimulated GTPase activities. Both mutants potently inhibit CME and effectively recruit other endocytic accessory proteins to stalled coated pits. However, the Q40E mutant blocks at a later step than S45N, providing additional evidence that GTP binding and/or basal GTPase activities of dynamin are required throughout clathrin coated pit maturation. Importantly, using in vitro assays for assembly-stimulated GTPase activity and membrane fission, we find that the latter is much more potently inhibited by both dominant-negative mutants than the former. These studies establish that efficient fission from supported bilayers with excess membrane reservoir (SUPER) templates requires coordinated GTP hydrolysis across two rungs of an assembled dynamin collar. PMID:23383266

  2. Ab initio study of ice catalyzation of HOCl + HCl reaction

    SciTech Connect

    Zhou, Y.F.; Liu, C.B.

    2000-06-15

    The observations by Farman et al. revealed remarkable depletions in the total atmospheric ozone content in Antarctica. The observed total ozone decreased smoothing during the spring season from about 1975. Satellite observations have proved Antarctic ozone depletions over a very extended region, in general agreement with the local ground-based data of Farman et al. It was suggested that heterogeneous reactions occurring on particles in polar stratospheric clouds (PSCs) play a central role in the depletion of stratospheric ozone. Experiments proved that the reaction of HOCl + HCl was very slow in the gas phase, but on ice surface it was rapid. In this work the ice catalysis of HOCl + HCl reaction was investigated by using ab initio molecular orbital theory. The authors applied the Hartree-Fock self-consistent field and the second-order Moeller-Plesset perturbation theory with the basis sets of 6-31G* to the model system. The complexes and transition state were obtained along the reaction with and without the presence of ice surface. By comparing the results, a possible catalyzation mechanism of ice on the reaction is proposed.

  3. Investigating antibody-catalyzed ozone generation by human neutrophils

    PubMed Central

    Babior, Bernard M.; Takeuchi, Cindy; Ruedi, Julie; Gutierrez, Abel; Wentworth, Paul

    2003-01-01

    Recent studies have suggested that antibodies can catalyze the generation of previously unknown oxidants including dihydrogen trioxide (H2O3) and ozone (O3) from singlet oxygen (1O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\mathrm{_{2}^{*}}}\\end{equation*}\\end{document}) and water. Given that neutrophils have the potential both to produce 1O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\mathrm{_{2}^{*}}}\\end{equation*}\\end{document} and to bind antibodies, we considered that these cells could be a biological source of O3. We report here further analytical evidence that antibody-coated neutrophils, after activation, produce an oxidant with the chemical signature of O3. This process is independent of surface antibody concentration down to 50% of the resting concentration, suggesting that surface IgG is highly efficient at intercepting the neutrophil-generated 1O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\mathrm{_{2}^{*}}}\\end{equation*}\\end{document}. Vinylbenzoic acid, an orthogonal probe for ozone detection, is oxidized by activated neutrophils to 4-carboxybenzaldehyde in a manner analogous to that obtained for its oxidation by ozone in solution. This discovery of the production of such a powerful oxidant in a biological context raises questions about not only the capacity of O3 to kill invading microorganisms but also its role in amplification of the inflammatory response by signaling and gene activation. PMID:12601145

  4. Mechanistic studies of copper(I)-catalyzed allylic amination.

    PubMed

    Srivastava, Radhey S; Tarver, Nathan R; Nicholas, Kenneth M

    2007-12-12

    The reactions of nitrosobenzene and N,N'-diethyl-4-nitrosoaniline with [Cu(CH3CN)4]PF6 provide novel Cu(I) complexes, [Cu(PhNO)3]PF6 (1) and [Cu(Et2NPhNO)3]PF6 (2); in 2 the copper atom is N-coordinated to the nitrosoarenes in a distorted trigonal planar geometry. Complex 1 is strongly implicated as a reactive intermediate in the Cu(I)-catalyzed allylic amination of olefins based on (i) its isolation from the catalytic reaction, (ii) its stoichiometric regioselective allylic amination of alpha-methyl styrene (AMS), (iii) the non-involvement of free PhNO in its amination of AMS, and (iv) its function as a catalyst for the amination of alkenes from phenylhydroxylamine. The reaction between AMS and 1 (80 degrees C, dioxane) is first order in both alkene and 1. Relative rate studies of the reaction of 1 with para substituted AMS derivatives gives a Hammett rho value of -0.035. Alkene adducts isolated from the reaction of 1 with styrene and alpha-methylstyrene are formulated as [(PhNO)3Cu(eta(2)-alkene)]PF6 (7,8) on the basis of spectroscopic characterization and thermolysis. PM3 and DFT MO calculations support the role of [(alkene)Cu(RNO)3]+ and (eta(1)- or eta(3)-allyl)Cu(RNO)2(RNHOH)+ complexes as probable catalytic intermediates and address the origin of the distinctive reaction regioselectivity. A mechanistic scheme is proposed which is consistent with the accumulated experimental and computational results. PMID:18004850

  5. Comparative effectiveness research and personalized medicine: catalyzing or colliding?

    PubMed

    Epstein, Robert S; Teagarden, J Russell

    2010-01-01

    Comparative effectiveness research (CER) is generating intense attention as interest grows in finding new and better drug technology assessment processes. The federal government is supporting the expansion of CER through funding made available in the American Recovery and Reinvestment Act of 2009 (ARRA) and by establishing the Patient-Centered Outcomes Research Institute through the Patient Protection and Affordable Care Act of 2010. At the same time, personalized medicine is generating debate about its place in clinical medicine, and so, naturally, how CER can or cannot play a role in personalized medicine is part of these debates. At the heart of the debate around the role of CER in personalized medicine is the nature of personalized medicine and how it fits within contemporary clinical research concepts. We maintain in this article that CER can serve to catalyze personalized medicine, but we recognize that, for this to happen, researchers will need to embrace new data sources and new analytic approaches. We also recognize that drug technology assessment processes will have to undergo necessary adaptations to accommodate CER as configured for personalized medicine, and that clinicians will need to be educated appropriately and provided access to decision-support systems through health information technology to use the information coming from this research. To illustrate our argument, we describe two ongoing CER studies funded and managed in the private sector evaluating personalized medicine interventions that have important clinical and financial implications. One of the studies investigates the clinical and financial effects of pharmacogenomic testing for warfarin as prescribed in conditions of typical practice settings. The other study is also set in community practice settings and compares cardiovascular outcomes of patients receiving clopidogrel who are extensive metabolizer phenotypes for the cytochrome P450 2C19 hepatic isoenzyme with all patients receiving prasugrel. PMID:20831298

  6. Target catalyzed hairpin assembly for constructing a ratiometric electrochemical aptasensor.

    PubMed

    Gao, Fenglei; Qian, Yong; Zhang, Lei; Dai, Shizhen; Lan, Yanfei; Zhang, Yu; Du, Lili; Tang, Daoquan

    2015-09-15

    In this paper, we develop a novel dual-signaling amplified aptasensor for protein detection via target-catalyzed hairpin assembly. Thrombin was chosen as a model target. This aptasensor contains two DNA hairpins termed as H1 and H2. H1, which is modified at its 3' ends with a methylene blue (MB), consists of the aptamer sequence of human thrombin. Meanwhile, H2 which is modified at its 3' ends with a ferrocene (Fc), is partially complementary to H1. Upon the addition of target protein, it can facilitate the opening of the hairpin structure of H1 and thus accelerate the hybridization between H1 and H2, the target protein can be displaced from hairpin H1 by hairpin H2 through a process similar to DNA branch migration. The released target found another H1 to trigger the cycle, resulting in the multiplication of the Fc confined near the GE surface and MB away from the GE surface. When IFc/IMB is used as the response signal for quantitative determination of thrombin, the detection limit (41fM) is much lower than that by using either MB or Fc alone. This new dual-signaling aptasensor is readily regenerated and shows good response toward the target. Furthermore, this amplified aptasensor shows high selectivity toward its target protein. The clever combination of the functional DNA hairpin and the novel device achieved a ratiometric electrochemical aptasensor, which could be used as a simple, sensitive high repeatability and selective platform for target protein detection. PMID:25897885

  7. Oxidations of cyclic {beta}-diketones catalyzed by methylrhenium trioxide

    SciTech Connect

    Abu-Omar, M.M.; Espenson, J.H. [Ames Lab., IA (United States)] [Ames Lab., IA (United States); [Iowa State Univ., Ames, IA (United States)

    1996-08-06

    Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) catalyzes the oxidation of {beta}-diketones by hydrogen peroxide. The kinetics of the initial oxidation step have been investigated in CH{sub 3}CN/H{sub 2}O (1:1 v/v) at 25{degree}C for a group of cyclic {beta}-diketones. The initial oxidation step features the enol form, the majority species, as the reactant. Its rate responds to substituents in the `normal` manner: electron-donating groups accelerate the reaction. We suggest that the double bond of the enol attacks a peroxo oxygen of a peroxorhenium complex A = CH{sub 3}Re(O){sub 2}(O{sub 2}) or B = CH{sub 3}Re(O)(O{sub 2}){sub 2}(H{sub 2}O). This reaction affords a 2-hydroxy-1,3-dicarbonyl intermediate, which in some instances was detected by {sup 1}H NMR. This hydroxy intermediate is susceptible to cleavage via a Baeyer-Villiger oxidation to yield carboxylic acids as final products. In contrast to the first reaction, this step may feature the peroxorhenium complexes A and B as nucleophiles rather than their customary electrophilic behavior; perhaps the trend is reversed by substrate binding to rhenium. Time profiles for the different stages of the reaction were also determined. The mechanistic aspects of these multistep catalytic oxidations are discussed in terms of the electronic nature of the activated rhenium-bound peroxo ligands. 38 refs., 3 figs., 3 tabs.

  8. Copper-catalyzed azide alkyne cycloaddition polymer networks

    NASA Astrophysics Data System (ADS)

    Alzahrani, Abeer Ahmed

    The click reaction concept, introduced in 2001, has since spurred the rapid development and reexamination of efficient, high yield reactions which proceed rapidly under mild conditions. Prior to the discovery of facile copper catalysis in 2002, the thermally activated azide-alkyne or Huisgen cycloaddition reaction was largely ignored following its discovery in large part due to its slow kinetics, requirement for elevated temperature and limited selectivity. Now, arguably, the most prolific and capable of the click reactions, the copper-catalyzed azide alkyne cycloaddition (CuAAC) reaction is extremely efficient and affords exquisite control of the reaction. The orthogonally and chemoselectivity of this reaction enable its wide utility across varied scientific fields. Despite numerous inherent advantages and widespread use for small molecule synthesis and solution-based polymer chemistry, it has only recently and rarely been utilized to form polymer networks. This work focuses on the synthesis, mechanisms, and unique attributes of the CuAAC reaction for the fabrication of functional polymer networks. The photo-reduction of a series of copper(II)/amine complexes via ligand metal charge transfer was examined to determine their relative efficiency and selectivity in catalyzing the CuAAC reaction. The aliphatic amine ligands were used as an electron transfer species to reduce Cu(II) upon irradiation with 365 nm light while also functioning as an accelerating agent and as protecting ligands for the Cu(I) that was formed. Among the aliphatic amines studied, tertiary amines such as triethylamine (TEA), tetramethyldiamine (TMDA), N,N,N',N",N"-pentamethyldiethylenetriamine (PMDTA), and hexamethylenetetramine (HMTETA) were found to be the most effective. The reaction kinetics were accelerated by increasing the PMDETA : Cu(II) ratio with a ratio of ligand to Cu(II) of 4:1 yielding the maximum conversion in the shortest time. The sequential and orthogonal nature of the photo-CuAAC reaction and a chain-growth acrylate homopolymerization were demonstrated and used to form branched polymer structures. A bulk, organic soluble initiation system consisting of a Cu(II) salt and a primary amine was also examined in both model reactions and in bulk polymerizations. The system was shown to be highly efficient, leading to nearly complete CuAAC polymerization at ambient temperature. Increasing the ratio of amine to copper from 1 to 4 increases the CuAAC reaction rate significantly from 4 mM/min for 1:1 ratio of Cu(II):hexyalmine to 14mM/min for 1:4 ratio. The concentration dependence of the amine on the reaction rate enables the polymerization rate to be controlled simply by manipulating the hexylamine concentration. Sequential thiol--acrylate and photo-CuAAC click reactions were utilized to form two-stage reactive polymer networks capable of generating wrinkles in a facile manner. The click thiol-Michael addition reaction was utilized to form a cross-linked polymer with residual, reactive alkyne sites that remained tethered throughout the network. The latent, unreacted alkyne sites are subsequently reacted with diazide monomers via a photoinduced Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction to increase the cross-link density. Increased cross-linking raised the modulus and glass transition temperature from 1.6 MPa and 2 °C after the thiol-acrylate reaction to 4.4 MPa and 22 °C after the CuAAC reaction, respectively. The double click reaction approach led to micro-wrinkles with well-controlled wavelength and amplitude of 8.50 +/- 1.6 and 1.4 ?m, respectively, for a polymer with a 1280 ?m total film thickness. Additionally, this approach further enables spatial selectivity of wrinkle formation by photo-patterning. The CuAAC-based polymerization was also used to design smart, responsive porous materials from well-defined CuAAC networks, which possesses a high glass transition temperature (Tg= 115°C) due to the formation of the triazole linkages. The toughness, recovery, fixity, and shape memory attributes of this mater

  9. The RimL transacetylase provides resistance to translation inhibitor microcin C.

    PubMed

    Kazakov, Teymur; Kuznedelov, Konstantin; Semenova, Ekaterina; Mukhamedyarov, Damir; Datsenko, Kirill A; Metlitskaya, Anastasija; Vondenhoff, Gaston H; Tikhonov, Anton; Agarwal, Vinayak; Nair, Satish; Van Aerschot, Arthur; Severinov, Konstantin

    2014-10-01

    Peptide-nucleotide antibiotic microcin C (McC) is produced by some Escherichia coli strains. Inside a sensitive cell, McC is processed, releasing a nonhydrolyzable analog of aspartyl-adenylate, which inhibits aspartyl-tRNA synthetase. The product of mccE, a gene from the plasmid-borne McC biosynthetic cluster, acetylates processed McC, converting it into a nontoxic compound. MccE is homologous to chromosomally encoded acetyltransferases RimI, RimJ, and RimL, which acetylate, correspondingly, the N termini of ribosomal proteins S18, S5, and L12. Here, we show that E. coli RimL, but not other Rim acetyltransferases, provides a basal level of resistance to McC and various toxic nonhydrolyzable aminoacyl adenylates. RimL acts by acetylating processed McC, which along with ribosomal protein L12 should be considered a natural RimL substrate. When overproduced, RimL also makes cells resistant to albomycin, an antibiotic that upon intracellular processing gives rise to a seryl-thioribosyl pyrimidine that targets seryl-tRNA synthetase. We further show that E. coli YhhY, a protein related to Rim acetyltransferases but without a known function, is also able to detoxify several nonhydrolyzable aminoacyl adenylates but not processed McC. We propose that RimL and YhhY protect bacteria from various toxic aminoacyl nucleotides, either exogenous or those generated inside the cell during normal metabolism. PMID:25002546

  10. Zirconium(IV) chloride catalyzed one-pot synthesis of 3,4-dihydropyrimidin-2(1 H)-ones

    Microsoft Academic Search

    Ch. Venkateshwar Reddy; M Mahesh; P. V. K Raju; T. Ramesh Babu; V. V. Narayana Reddy

    2002-01-01

    Zirconium tetrachloride catalyzes efficiently the three component condensation reaction of an aromatic aldehyde, a ?-ketoester and urea in refluxing ethanol to afford the corresponding dihydropyrimidinone in high yield.

  11. Contaminated Groundwater Remediation by Catalyzed Hydrogen Peroxide and Persulfate Oxidants System

    NASA Astrophysics Data System (ADS)

    Yan, N.; Wang, Y.; Brusseau, M. L.

    2014-12-01

    A binary oxidant system, catalyzed hydrogen peroxide (H2O2) coupled with persulfate (S2O82-), was investigated for use in in-situ chemical oxidation (ISCO) applications. Trichloroethene (TCE) and 1,4-dioxane were used as target contaminants. Batch experiments were conducted to investigate the catalytic efficiency between ferrous ion (Fe2+) and base (NaOH), oxidant decomposition rates, and contaminant degradation efficiency. For the base-catalyzed H2O2-S2O82- system, oxidant release was moderate and sustained over the entire test period of 96 hours. Conversely, the oxidants were depleted within 24 hours for the Fe2+-catalyzed system. Solution pH decreased slightly for the Fe2+-catalyzed system, whereas the pH increased for the base-catalyzed system. The rates of degradation for TCE and 1,4-dioxane are compared as a function of system conditions. The results of this study indicate that the binary H2O2-S2O82- oxidant system is effective for oxidation of the tested contaminants.

  12. Continuous In Vitro Evolution of a Ribozyme that Catalyzes Three Successive Nucleotidyl Addition Reactions

    NASA Technical Reports Server (NTRS)

    McGinness, Kathleen E.; Wright, Martin C.; Joyce, Gerald F.

    2002-01-01

    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.

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

    PubMed

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

    1989-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  15. Ligand-Controlled Regioselective Copper-Catalyzed Trifluoromethylation To Generate (Trifluoromethyl)allenes.

    PubMed

    Ambler, Brett R; Peddi, Santosh; Altman, Ryan A

    2015-05-15

    "Cu-CF3" species have been used historically for a broad spectrum of nucleophilic trifluoromethylation reactions. Although recent advancements have employed ligands to stabilize and harness the reactivity of this key organometallic intermediate, the ability of a ligand to differentiate a regiochemical outcome of a Cu-CF3-mediated or -catalyzed reaction has not been previously reported. Herein, we report the first example of a Cu-catalyzed trifluoromethylation reaction in which a ligand controls the regiochemical outcome. More specifically, we demonstrate the ability of bipyridyl-derived ligands to control the regioselectivity of the Cu-catalyzed nucleophilic trifluoromethylation reactions of propargyl electrophiles to generate (trifluoromethyl)allenes. This method provides a variety of di-, tri-, and tetrasubstituted (trifluoromethyl)allenes, which can be further modified to generate complex fluorinated substructures. PMID:25910053

  16. Dechlorination of carbon tetrachloride by the catalyzed Fe-Cu process.

    PubMed

    Xu, Wen-Ying; Gao, Ting-Yao

    2007-01-01

    The electrochemical reduction characteristics of carbon tetrachloride (CT) were investigated using cyclic voltammetry in this study. In addition, the difference in reduction mechanisms of CT between Master Builders' iron and the catalyzed Fe-Cu process was discussed. The results showed that CT was reduced directly on the surface of copper rather than by atomic hydrogen produced at the cathode in the catalyzed Fe-Cu process. The reduction was realized largely by atomic hydrogen in Master Builders' iron. The entire CT in 350 ml aqueous solution with 320 mg/L was reduced to trichloromethane and dichloromethane in 2.25 h when 100 g of scrap iron with Fe/Cu ratio of 10:1 (w/w) were used. Moreover, the reduction rate slowed with time. CT could be reduced at acidic, neutral and alkaline pH from solution by Fe-Cu bimetallic media, but the mechanisms were different. The degradation rate was not significantly influenced by pH in the catalyzed Fe-Cu process; in Master Builders' iron it clearly increased with decreasing pH. The kinetics of the reductions followed pseudo-first order in both cases. Furthermore, the reductions under acidic conditions proceeded faster than that under the neutral and alkaline conditions. The catalyzed Fe-Cu process was superior to Master Builders' iron in treating CT-containing water and this advantage was particularly noticeable under alkaline conditions. The reduction was investigated in the cathode (Cu) and anode (Fe) compartments respectively, the results showed that the direct reduction pathway played an important role in the reduction by the catalyzed Fe-Cu process. The catalyzed Fe-Cu process is of practical value. PMID:17966865

  17. Production of conjugated linoleic acids through KOH-catalyzed dehydration of ricinoleic acid.

    PubMed

    Yang, Lin; Huang, Yu; Wang, Han Qing; Chen, Zhen-Yu

    2002-10-01

    Production of conjugated linoleic acids (CLA) using castor oil as starting material involves conversion of ricinoleic acid to methyl 12-mesyloxy-octadec-9-enoate (MMOE) followed by dehydration. This process usually uses 1,8-diazabicyclo-(5.4.0)-undec-7-ene (DBU) as an expensive dehydrating reagent. The present study reports that potassium hydroxide (KOH) can serve as a dehydrating reagent in replacement of DBU. The results showed that conversion of MMOE to CLA catalyzed by KOH was an efficient reaction, with a 77% conversion efficiency at 80 degrees C. The CLA isomeric profile produced in KOH-catalyzed dehydration reaction was similar to that catalyzed by DBU. The CLA mixture produced in KOH-catalyzed dehydration of MMOE at 80 degrees C contained 72% 9c,11t-18:2 and 26% 9c,11c-18:2 while in that catalyzed by DBU, 9c,11t-18:2 and 9c,11c-18:2 accounted for 78 and 16%, respectively. It was found that the temperature of dehydration was an important factor in the determination of CLA isomer composition and yield of conversion. Elevating the temperature from 78 to 180 degrees C decreased not only the conversion efficiency but also production of total c,t-18:2 and c,c-18:2 isomers regardless of dehydration catalyzed by either DBU or KOH. It is concluded that KOH may replace DBU as a dehydrating reagent in conversion of MMOE to CLA when the reaction conditions are optimized. PMID:12270670

  18. Reaction pathways and free energy profiles for cholinesterase-catalyzed hydrolysis of 6-monoacetylmorphine.

    PubMed

    Qiao, Yan; Han, Keli; Zhan, Chang-Guo

    2014-04-14

    As the most active metabolite of heroin, 6-monoacetylmorphine (6-MAM) can penetrate into the brain for the rapid onset of heroin effects. The primary enzymes responsible for the metabolism of 6-MAM to the less potent morphine in humans are acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The detailed reaction pathways for AChE- and BChE-catalyzed hydrolysis of 6-MAM to morphine have been explored, for the first time, in the present study by performing first-principles quantum mechanical/molecular mechanical free energy calculations. It has been demonstrated that the two enzymatic reaction processes follow similar catalytic reaction mechanisms, and the whole catalytic reaction pathway for each enzyme consists of four reaction steps. According to the calculated results, the second reaction step associated with the transition state TS2(a)/TS2(b) should be rate-determining for the AChE/BChE-catalyzed hydrolysis, and the free energy barrier calculated for the AChE-catalyzed hydrolysis (18.3 kcal mol(-1)) is 2.5 kcal mol(-1) lower than that for the BChE-catalyzed hydrolysis (20.8 kcal mol(-1)). The free energy barriers calculated for the AChE- and BChE-catalyzed reactions are in good agreement with the experimentally derived activation free energies (17.5 and 20.7 kcal mol(-1) for the AChE- and BChE-catalyzed reactions, respectively). Further structural analysis reveals that the aromatic residues Phe295 and Phe297 in the acyl pocket of AChE (corresponding to Leu286 and Val288 in BChE) contribute to the lower energy of TS2(a) relative to TS2(b). The obtained structural and mechanistic insights could be valuable for use in future rational design of a novel therapeutic treatment of heroin abuse. PMID:24595354

  19. The iron(III)-catalyzed oxidation of DTPA in an aqueous solution / longy Steven Harry Christiansen 

    E-print Network

    Christiansen, Steven Harry

    1988-01-01

    THE IRON(III) -CATALYZED OXIDATION OF DTPA IN AN AQUEOUS SOLUTION A Thesis by STEVEN HARRY CHRISTIANSEN Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... August 1988 Major Subject: Chemistry THE IRON(III) -CATALYZED OXIDATION OF DTPA IN AN AQUEOUS SOLUTION A Thesis by STEVEN HARRY CHRISTIANSEN Approved as to style and content by: A. E. Martell (Chair of Committee) M. B. Hall (Member) R. H...

  20. The Enterobactin Synthetase Catalyzed Formation of P1, P3-diadenosine-5?-tetraphosphate

    PubMed Central

    Sikora, Alison L.; Cahill, Sean M.; Blanchard, John S.

    2009-01-01

    The EntE enzyme involved in the synthesis of the iron siderophore enterobactin, catalyzes the adenylation of 2,3-dihydroxybenzoic acid, followed by its transfer to the phosphopantetheine arm of holo-EntB, an aryl carrier protein. In the absence of EntB, EntE catalyzes the formation of Ap4A, a molecule that is implicated in regulating cell division during oxidative stress. We propose that the expression of EntE during iron starvation produces Ap4A to slow growth until intracellular iron stores can be restored. PMID:19852513

  1. Design of New Ligands for the Palladium-Catalyzed Arylation of ?-Branched Secondary Amines.

    PubMed

    Park, Nathaniel H; Vinogradova, Ekaterina V; Surry, David S; Buchwald, Stephen L

    2015-07-01

    In Pd-catalyzed C?N cross-coupling reactions, ?-branched secondary amines are difficult coupling partners and the desired products are often produced in low yields. In order to provide a robust method for accessing N-aryl ?-branched tertiary amines, new catalysts have been designed to suppress undesired side reactions often encountered when these amine nucleophiles are used. These advances enabled the arylation of a wide array of sterically encumbered amines, highlighting the importance of rational ligand design in facilitating challenging Pd-catalyzed cross-coupling reactions. PMID:26032920

  2. Cu-catalyzed trifluoromethylation of aryl iodides with trifluoromethylzinc reagent prepared in situ from trifluoromethyl iodide

    PubMed Central

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

    2013-01-01

    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

  3. The pH dependence of dihydroorotic acid synthesis catalyzed by zinc and cobalt dihydroorotase 

    E-print Network

    Roy Choudhury, Rita

    1984-01-01

    (IU with Co(II), Cd(II) amnd )(n(II) (15). The classical pH rate profile for carboxypeptidase A catalyzed hydrolysis is bell shaped with apparent acidic and alkaline pK val- ues of 6. 5 and 7. 5 reapectively. The pK value of 6. 5 could be at- tributed... of Dihydroorotic Acid Synthesis Catalyzed by Zinc and Cobalt Dihydroorotase. (August 1984 ) Rita Roy Choudhury, N. Sc, University of Banbay Chairman af Advisory Ccmitee: Dr. E. G. Sander Dihydroorotase (1-5, 6 dihydroorotate mnidohydrolase E. C. 3. 5. 2. 3...

  4. Formation of C–C bonds via ruthenium-catalyzed transfer hydrogenation*

    PubMed Central

    Moran, Joseph; Krische, Michael J.

    2013-01-01

    Ruthenium-catalyzed transfer hydrogenation of diverse ?-unsaturated reactants in the presence of aldehydes provides products of carbonyl addition. Dehydrogenation of primary alcohols in the presence of the same ?-unsaturated reactants provides identical products of carbonyl addition. In this way, carbonyl addition is achieved from the alcohol or aldehyde oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. In this account, the discovery of ruthenium-catalyzed C–C bond-forming transfer hydrogenations and the recent development of diastereo- and enantioselective variants are discussed. PMID:23430602

  5. Asymmetric copper-catalyzed Diels-Alder reaction revisited: control of the structure of bis(oxazoline) ligands.

    E-print Network

    Paris-Sud XI, Université de

    1 Asymmetric copper-catalyzed Diels-Alder reaction revisited: control of the structure of bis,R)-dihydroethano trans-dicarboxylic acid, a complete series of ligands was evaluated in the copper-catalyzed Diels[2.2.2] backbone; Diels-Alder catalysis; Copper; Enantioselectivity. * Corresponding author. E

  6. Palladium-Catalyzed Enantioselective Cyclization of Silyloxy-1,6-Enynes Britton K. Corkey and F. Dean Toste*

    E-print Network

    Toste, Dean

    Palladium-Catalyzed Enantioselective Cyclization of Silyloxy-1,6-Enynes Britton K. Corkey and F employed in the preparation of enantioenriched 1,4-diene containing structures.2-4 Despite its potential silyloxy-substituted olefins. On the basis of our recent report on palladium-catalyzed enantio- selective 5

  7. Micellar catalysis using a photochromic surfactant: application to the Pd-catalyzed Tsuji-Trost reaction in water.

    PubMed

    Billamboz, Muriel; Mangin, Floriane; Drillaud, Nicolas; Chevrin-Villette, Carole; Banaszak-Léonard, Estelle; Len, Christophe

    2014-01-17

    The first example of a Pd-catalyzed Tsuji-Trost reaction, applied in a photochromic micellar media under conventional heating and microwave irradiation, is reported. The surfactant activity and recycling ability were investigated and compared with those of a few commercially available surfactants. The synthetic photochromic surfactant proved to be efficient, recyclable, and versatile for Pd-catalyzed coupling reactions. PMID:24295431

  8. Enantioselective direct Mannich reactions of cyclic ?-ketoesters catalyzed by chiral phosphine via a novel dual-reagent catalysis.

    PubMed

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

    2015-02-01

    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

  9. Gold-catalyzed cascade C-H/C-H cross-coupling/cyclization/alkynylation: an efficient access to 3-alkynylpyrroles.

    PubMed

    Zhang, Shuai; Ma, Yuanhong; Lan, Jingbo; Song, Feijie; You, Jingsong

    2015-06-01

    An efficient approach to 3-alkynylpyrroles has been developed through the gold-catalyzed reaction of ?-enamino derivatives with terminal alkynes, which features complete regiocontrol, relatively wide substrate scope, and high functional group tolerance. Mechanistic studies show that the reaction proceeds through the gold-catalyzed cascade oxidative C-H/C-H cross-coupling, cyclization and alkynylation. PMID:25917176

  10. Amino Alcohols as Ligands for Nickel-Catalyzed Suzuki Reactions of Unactivated Alkyl Halides, Including Secondary Alkyl Chlorides, with

    E-print Network

    Fu, Gregory C.

    Amino Alcohols as Ligands for Nickel-Catalyzed Suzuki Reactions of Unactivated Alkyl Halides February 27, 2006; E-mail: gcf@mit.edu Early work in the area of palladium- and nickel-catalyzed cross of unactivated secondary alkyl halides is based on nickel/bathophenanthroline.4 This method can be applied

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

    E-print Network

    Weber, Rodney

    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. S. Holloway, C. A. Brock, J. A. de Gouw, and E. L. Atlas (2007), No evidence for acid

  12. Journal of Molecular Catalysis A: Chemical 275 (2007) 5462 Mechanistic insights into iron porphyrin-catalyzed olefin epoxidation by

    E-print Network

    Bell, Alexis T.

    2007-01-01

    porphyrin-catalyzed olefin epoxidation by hydrogen peroxide: Factors controlling activity and selectivity; accepted 8 May 2007 Available online 22 May 2007 Abstract Iron porphyrins are well known for their ability peroxide catalyzed by iron porphyrins that is consistent with all experimental evidence. Rate parameters

  13. Mathematical Analysis of Activation Thresholds in Enzyme-Catalyzed Positive Feedbacks: Application to the Feedbacks of Blood Coagulation

    Microsoft Academic Search

    Edward Beltrami; Jolyon Jesty

    1995-01-01

    A hierarchy of enzyme-catalyzed positive feedback loops is examined by mathematical and numerical analysis. Four systems are described, from the simplest, in which an enzyme catalyzes its own formation from an inactive precursor, to the most complex, in which two sequential feedback loops act in a cascade. In the latter we also examine the function of a long-range feedback, in

  14. Mechanistic studies of the copper-catalyzed electrophilic amination of diorganozinc reagents and development of a zinc-free protocol.

    PubMed

    Campbell, Matthew J; Johnson, Jeffrey S

    2007-04-12

    [reaction: see text] An SN2 mechanism for the copper-catalyzed amination of diorganozinc reagents by O-benzoyl-N,N-dialkylhydroxylamines is supported by following stereochemically defined organometallics through the reaction and by employing the endocyclic restriction test. A copper-catalyzed electrophilic amination of organomagnesium compounds is also described in which the use of zinc halides has been eliminated. PMID:17362022

  15. Solid/gas biocatalysis: an appropriate tool to study the influence of organic components on kinetics of lipase catalyzed alcoholysis

    E-print Network

    Paris-Sud XI, Université de

    on kinetics of lipase catalyzed alcoholysis Fabien Létisse, Sylvain Lamare, Marie-Dominique Legoy and Marianne : Corresponding author : Dr. Marianne Graber, fax: 33 5 46 45 82 65, Email: mgraber@univ-lr.fr KEY WORDS Lipase B-propanol catalyzed by immobilized lipase B from Candida antarctica was studied in a continuous solid/gas reactor

  16. Alcoholysis catalyzed by Candida antarctica lipase B in a gas/solid system : effects of water on kinetic parameters

    E-print Network

    Paris-Sud XI, Université de

    1 Alcoholysis catalyzed by Candida antarctica lipase B in a gas/solid system : effects of water from Candida antarctica ­ kinetics ­ transesterification ­ water ­ solid/gas biocatalysis - hydration propionate and n-propanol catalyzed by immobilized lipase B from Candida antarctica was studied

  17. The phosphoenolpyruvate carboxykinase also catalyzes C 3 carboxylation at the interface of glycolysis and the TCA cycle of Bacillus subtilis

    Microsoft Academic Search

    Nicola Zamboni; Hannu Maaheimo; Thomas Szyperski; Hans-Peter Hohmann; Uwe Sauer

    2004-01-01

    Quantitative physiological characterization and isotopic tracer experiments revealed that pyruvate kinase mutants of Bacillus subtilis produced significantly more CO2 from glucose in the tricarboxylic acid cycle than is explained by the remaining conversion of phosphoenolpyruvate (PEP) to pyruvate catalyzed by the phosphotransferase system. We show here that this additional catabolic flux into the tricarboxylic acid cycle was catalyzed by the

  18. Rhenium-Catalyzed Coupling of Propargyl Alcohols and Allyl Silanes Michael R. Luzung and F. Dean Toste*

    E-print Network

    Toste, Dean

    Rhenium-Catalyzed Coupling of Propargyl Alcohols and Allyl Silanes Michael R. Luzung and F. Dean by stoichiometric transition metal complexes.5,6 We have recently reported that rhenium(V)-oxo complex 1 serves attempts at rhenium-catalyzed coupling of propargyl alcohols and allyl trimethylsilane were complicated

  19. Direct Detection and Kinetic Analysis of Covalent Intermediate Formation in the 4-Amino-4-deoxychorismate Synthase Catalyzed Reaction

    E-print Network

    Toney, Michael

    with isochorismate synthase (IS) and anthranilate synthase (AS), in which nucleophile addition at C2 initiates- aminobenzoate (PABA). ADCS catalyzes the first step of PABA biosynthesis, which starts from chorismate. It adds they catalyze. This group of enzymes includes anthranilate synthase (AS) (6), isochoris- mate synthase (IS) (7

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

    E-print Network

    Colby Davie, Elizabeth A. (Elizabeth Anne)

    2005-01-01

    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 ...

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

    PubMed Central

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

    2014-01-01

    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

  2. Efficient chromium(II)-catalyzed cross-coupling reactions between Csp2 centers.

    PubMed

    Steib, Andreas K; Kuzmina, Olesya M; Fernandez, Sarah; Flubacher, Dietmar; Knochel, Paul

    2013-10-16

    Low-toxicity chromium(II) chloride catalyzes at 25 °C within minutes the coupling reactions of various (hetero)arylmagnesium reagents with N-heterocyclic halides, aromatic halogenated ketones or imines, and alkenyl iodides. Remarkably, much lower amounts of homo-coupling side products are obtained compared to related iron, cobalt, or manganese cross-couplings. PMID:24053764

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

    SciTech Connect

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

    2012-05-09

    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.

  4. Synthesis of Polycyclic Nitrogen Heterocycles via Cascade Pd-Catalyzed Alkene Carboamination/Diels-Alder Reactions.

    PubMed

    White, Derick R; Wolfe, John P

    2015-05-15

    Cascade Pd-catalyzed alkene carboamination/Diels-Alder reactions between bromodienes and amines bearing two pendant alkenes are described. These transformations generate 4 bonds, 3 rings, and 3-5 stereocenters to afford polycyclic nitrogen heterocycles with high diastereoselectivity. PMID:25946563

  5. Iron-Catalyzed Formation of 2-Aminopyridines from Diynes and Cyanamides

    PubMed Central

    Lane, Timothy K.; D’Souza, Brendan R.; Louie, Janis

    2012-01-01

    Diynes and cyanamides undergo an iron-catalyzed [2+2+2] cycloaddition to form highly substituted 2-aminopyridines in an atom-efficient manner that is both high yielding and regioselective. This system was also used to cyclize two terminal alkynes and a cyanamide to afford a 2,4,6-trisubstituted pyridine product regioselectively. PMID:22845666

  6. Mechanistic study of palladium catalyzed S–S and Se–Se bonds addition to alkynes

    Microsoft Academic Search

    Valentine P Ananikov; Michael A Kabeshov; Irina P Beletskaya; Grigory G Aleksandrov; Igor L Eremenko

    2003-01-01

    The mechanistic study of palladium catalyzed S–S and Se–Se bonds addition to alkynes revealed the involvement of dinuclear transition metal complexes in the catalytic cycle. Coordination of alkyne to dinuclear transition metal complex was found to be the rate determining step of the reaction. An unusual phosphine ligand effect increasing the yield of addition reaction was found in the studied

  7. Structural Formation Studies of UV-Catalyzed Gels and Aerogels byLight Scattering

    SciTech Connect

    Hunt, Arlon J.; Ayers, Michael R.

    1998-04-01

    The skeletal structure of aerogel is determined before, during, and after the gel is formed. Supercritical drying of aerogel largely preserves the pore structure that is determined near the time of gelation. To better understand these gel formation mechanisms we carried out measurements of the time evolution of light scattering in a series of gels prepared without conventional acid or base catalysis. Instead, ultraviolet light was used to catalyze the formation of silica gels made from the hydrolysis of tetraethylorthosilicate and partly prehydrolyzed tetraethylorthosilicate in ethanol. Time evolution of light scattering provides information regarding the rate and geometrical nature of the assembly of the primary silica particles formed in the sol. UV-catalyzed gels show volumetric growth typical of acid-catalyzed gels, except when UV exposure is discontinued at the gel point, where gels then show linear chain formation typical of base-catalyzed gels. Long term UV exposure leads to coarsening of the pore network, a decrease in the clarity of the aerogel, and an increase in the surface area of the aerogel. Additionally, UV exposure up to the gel point leads to increased crystallinity in the final aerogel.

  8. ParA resolvase catalyzes site-specific excision of DNA from the Arabidopsis genome

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The small serine resolvase ParA from bacterial plasmids RK2 and RP4 catalyzes the recombination of two identical 133 bp recombination sites known as MRS. Previously, we reported that ParA is active in the fission yeast Schizosaccharomyces pombe. In this work, the parA recombinase gene was placed un...

  9. Synthesis of saturated 1,4-benzodiazepines via Pd-catalyzed carboamination reactions.

    PubMed

    Neukom, Joshua D; Aquino, Alvin S; Wolfe, John P

    2011-05-01

    A new synthesis of 1,4-benzodiazepines and 1,4-benzodiazepin-5-ones is reported. The Pd-catalyzed coupling of N-allyl-2-aminobenzylamine derivatives with aryl bromides affords the heterocyclic products in good yield, and substrates bearing allylic methyl groups are transformed to cis-2,3-disubstituted products with >20:1 dr. PMID:21446677

  10. Synthesis of Saturated 1,4-Benzodiazepines via Pd-Catalyzed Carboamination Reactions

    PubMed Central

    Neukom, Joshua D.; Aquino, Alvin S.; Wolfe, John P.

    2011-01-01

    A new synthesis of 1,4-benzodiazepines and 1,4-benzodiazepin-5-ones is reported. The Pd-catalyzed coupling ofN-allyl-2-aminobenzylamine derivatives with aryl bromides affords the heterocyclic products in good yield, and substrates bearing allylic methyl groups are transformed toc is-2,3-disubstituted products with >20:1 dr. PMID:21446677

  11. Synthesis of dihydrofuroflavonoids via palladium-catalyzed annulation of 1,3-dienes

    Microsoft Academic Search

    Roman V. Rozhkov; Richard C. Larock

    2004-01-01

    The palladium-catalyzed annulation of 1,3-dienes by o-iodoacetoxyflavonoids provides an efficient approach to biologically interesting dihydrofuroflavonoids. This reaction is very general, regioselective, and a wide variety of terminal, cyclic, and internal 1,3-dienes can be utilized.

  12. Palladium-catalyzed oxidative regio- and diastereoselective diarylating carbocyclization of dienynes.

    PubMed

    Jiang, Min; Bäckvall, Jan-E

    2013-05-17

    Transmetallation: A highly regio- and diastereoselective carbocyclization involving a palladium-catalyzed 1,2-addition of two carbon atoms across a conjugated diene has been developed (see scheme). The reaction is performed with dienynes and an oxygen tether containing a terminal or internal triple bond. PMID:23576471

  13. Pd-Catalyzed Cross-Coupling Reactions of Amides and Aryl Mesylates

    PubMed Central

    Dooleweerdt, Karin; Fors, Brett P.; Buchwald, Stephen L.

    2010-01-01

    A catalyst, based on a biarylphosphine ligand, for the Pd-catalyzed cross-coupling reactions of amides and aryl mesylates is described. This system allows an array of aryl and heteroaryl mesylates to be transformed into the corresponding N-arylamides in moderate to excellent yields. PMID:20420379

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

    ERIC Educational Resources Information Center

    Pearce, Joshua M.

    2006-01-01

    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…

  15. Pd(II)-catalyzed C-H Iodination Using Molecular I2 as the Sole Oxidant

    PubMed Central

    Wang, Xiao-Chen; Hu, Yi; Bonacorsi, Samuel; Hong, Yang; Burrell, Richard; Yu, Jin-Quan

    2013-01-01

    Pd-catalyzed ortho-C–H iodination directed by a weakly coordinating amide auxiliary using I2 as the sole oxidant was developed. This reaction is compatible with a wide range of heterocycles including pyridines, imidazoles, oxazoles, thiazoles, isoxazoles and pyrazoles. PMID:23837737

  16. Iridium-Catalyzed, Regio- and Enantioselective Allylic Substitution with Aromatic and Aliphatic Sulfinates

    PubMed Central

    Ueda, Mitsuhiro; Hartwig, John F.

    2009-01-01

    The iridium-catalyzed allylation of sodium sulfinate to form branched allylic sulfones is reported. The reactions between various sodium sulfinates and achiral allylic carbonates occur in good yields, with high selectivity for the branched isomer, and high enantioselectivities (up to 98% ee). PMID:19954200

  17. Functional Analysis of DNA Replication Fork Reversal Catalyzed by Mycobacterium tuberculosis RuvAB Proteins*

    PubMed Central

    Khanduja, Jasbeer Singh; Muniyappa, K.

    2012-01-01

    Initially discovered in Escherichia coli, RuvAB proteins are ubiquitous in bacteria and play a dual role as molecular motor proteins responsible for branch migration of the Holliday junction(s) and reversal of stalled replication forks. Despite mounting genetic evidence for a crucial role of RuvA and RuvB proteins in reversal of stalled replication forks, the mechanistic aspects of this process are still not fully understood. Here, we elucidate the ability of Mycobacterium tuberculosis RuvAB (MtRuvAB) complex to catalyze the reversal of replication forks using a range of DNA replication fork substrates. Our studies show that MtRuvAB, unlike E. coli RuvAB, is able to drive replication fork reversal via the formation of Holliday junction intermediates, suggesting that RuvAB-catalyzed fork reversal involves concerted unwinding and annealing of nascent leading and lagging strands. We also demonstrate the reversal of replication forks carrying hemi-replicated DNA, indicating that MtRuvAB complex-catalyzed fork reversal is independent of symmetry at the fork junction. The fork reversal reaction catalyzed by MtRuvAB is coupled to ATP hydrolysis, is processive, and culminates in the formation of an extended reverse DNA arm. Notably, we found that sequence heterology failed to impede the fork reversal activity of MtRuvAB. We discuss the implications of these results in the context of recognition and processing of varied types of replication fork structures by RuvAB proteins. PMID:22094465

  18. Tyrosinase-catalyzed grafting of sericin peptides onto chitosan and production of protein–polysaccharide bioconjugates

    Microsoft Academic Search

    Anna Anghileri; Raija Lantto; Kristiina Kruus; Cristina Arosio; Giuliano Freddi

    2007-01-01

    The capability of Agaricus bisporus tyrosinase to catalyze the oxidation of tyrosine residues of silk sericin was studied under homogeneous reaction conditions, by using sericin peptides purified from industrial wastewater as the substrate. Tyrosinase was able to oxidize about 57% of sericin-bound tyrosine residues. The reaction rate was higher than with silk fibroin, but lower than with other silk-derived model

  19. Cu-catalyzed cross-coupling reactions of epoxides with organoboron compounds.

    PubMed

    Lu, Xiao-Yu; Yang, Chu-Ting; Liu, Jing-Hui; Zhang, Zheng-Qi; Lu, Xi; Lou, Xin; Xiao, Bin; Fu, Yao

    2015-02-11

    A copper-catalyzed cross-coupling reaction of epoxides with arylboronates is described. This reaction is not limited to aromatic epoxides, because aliphatic epoxides are also suitable substrates. In addition, N-sulfonyl aziridines can be successfully converted into the products. This reaction provides convenient access to ?-phenethyl alcohols, which are valuable synthetic intermediates. PMID:25564373

  20. Copper-catalyzed oxidative ring closure and carboarylation of 2-ethynylanilides.

    PubMed

    Sinai, Ádám; Mészáros, Ádám; Gáti, Tamás; Kudar, Veronika; Palló, Anna; Novák, Zoltán

    2013-11-15

    A new copper-catalyzed oxidative ring closure of ethynyl anilides with diaryliodonium salts was developed for the highly modular construction of benzoxazines bearing a fully substituted exo double bond. The oxidative transformation includes an unusual 6-exo-dig cyclization step with the formation of C-O and C-C bonds. PMID:24188109

  1. Efficient copper-catalyzed trifluoromethylation of aromatic and heteroaromatic iodides: the beneficial anchoring effect of borates.

    PubMed

    Gonda, Zsombor; Kovács, Szabolcs; Wéber, Csaba; Gáti, Tamás; Mészáros, Attila; Kotschy, András; Novák, Zoltán

    2014-08-15

    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

  2. Acid-catalyzed transformation of ionophore veterinary antibiotics: reaction mechanism and product implications.

    PubMed

    Sun, Peizhe; Yao, Hong; Minakata, Daisuke; Crittenden, John C; Pavlostathis, Spyros G; Huang, Ching-Hua

    2013-07-01

    Ionophore antibiotics (IPAs) are polyether antimicrobials widely used in the livestock industry and may enter the environment via land application of animal waste and agricultural runoff. Information is scarce regarding potential transformation of IPAs under environmental conditions. This study is among the first to identify the propensity of IPAs to undergo acid-catalyzed transformation in mildly acidic aquatic systems and characterize the reactions in depth. The study focused on the most widely used monensin (MON) and salinomycin (SAL), and also included narasin (NAR) in the investigation. All three IPAs are susceptible to acid-catalyzed transformation. MON reacts much more slowly than SAL and NAR and exhibits a different kinetic behavior that is further evaluated by a reversible reaction kinetic model. Extensive product characterization identifies that the spiro-ketal group of IPAs is the reactive site for the acid-catalyzed hydrolytic transformation, yielding predominantly isomeric and other products. Toxicity evaluation of the transformation products shows that the products retain some antimicrobial properties. The occurrence of IPAs and isomeric transformation products is also observed in poultry litter and agricultural runoff samples. Considering the common presence of mildly acidic environments (pH 4-7) in soils and waters, the acid-catalyzed transformation identified in this study likely plays an important role in the environmental fate of IPAs. PMID:23373828

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

    PubMed

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

    2014-12-01

    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

  4. Synthesis of thin silicon nanowires using gold-catalyzed chemical vapor deposition

    Microsoft Academic Search

    S. Sharma; T. I. Kamins; R. Stanley Williams

    2005-01-01

    Silicon nanowires were synthesized using chemical vapor deposition catalyzed by gold nanoparticles deposited on silicon substrates. Silicon nanowires grew epitaxially in directions on (100)-oriented silicon substrates. For a particular set of process parameters, we observed a critical thickness of the nucleating gold film, below which nanowires could not be grown. We studied the dependence of the Au-Si alloy droplet size

  5. Self-assembly of bidentate ligands for combinatorial homogeneous catalysis: asymmetric rhodium-catalyzed hydrogenation.

    PubMed

    Weis, Martine; Waloch, Christoph; Seiche, Wolfgang; Breit, Bernhard

    2006-04-01

    The first chiral ligand library based on self-assembly through complementary hydrogen-bonding was realized. From a 10 x 4 ligand library, catalysts that show excellent activity and enantioselectivity for the asymmetric rhodium-catalyzed hydrogenation have been identified. PMID:16568968

  6. Formal total synthesis of okadaic acid via regiocontrolled gold(I)-catalyzed spiroketalizations.

    PubMed

    Fang, Chao; Pang, Yucheng; Forsyth, Craig J

    2010-10-15

    Both C19 and C34 spiroketal domains of okadaic acid were assembled using gold(I) chloride catalyzed spiroketalizations, and the two resulting fragments were coupled to give the C15-C38 fragment of okadaic acid, a known intermediate for the total synthesis of this important natural product. PMID:20849144

  7. Lipase-catalyzed production of biodiesel fuel from vegetable oils contained in waste activated bleaching earth

    Microsoft Academic Search

    Ana V Lara Pizarro; Enoch Y Park

    2003-01-01

    Waste bleaching earths from crude vegetable oil refining process contain approximately 40% of its weight as oil. Low valued oils are potential substrates for biodiesel fuel production. Vegetable oils from waste bleaching earth samples were organic-solvent extracted and identified as soybean, palm and rapeseed oil. Methanolysis was efficiently catalyzed by Rhizopus oryzae lipase in the presence of high water content,

  8. Palladium-catalyzed, pyrrolidine-mediated arylmethylation of ketones and aldehydes with coumarinyl(methyl) acetates†

    PubMed Central

    Cattopadhyay, Kalicharan; Recio, Antonio; Tunge, Jon A.

    2012-01-01

    We report the palladium-catalyzed, pyrrolidine-mediated ?-benzylation of enamines generated from aldehydes and ketones. The method allows for direct coupling of medicinally relevant coumarin moieties with aldehydes and ketones in good yield under mild conditions. The reaction is believed to proceed via a Pd-?-benzyl complex generated from (coumarinyl)methyl acetates. PMID:22832549

  9. Palladium-Catalyzed Hiyama Cross-Coupling of Aryltrifluorosilanes with Aryl and Heteroaryl Chlorides

    PubMed Central

    Molander, Gary A.; Iannazzo, Laura

    2011-01-01

    An efficient, palladium-catalyzed Hiyama cross-coupling reaction of aryltrifluorosilanes with aryl chlorides has been developed. A wide variety of functionalized biaryl derivatives were isolated in good to excellent yields. The scope of this reaction has also been extended to heteroaryl chlorides, affording the corresponding heterobiaryl compounds in high yields. PMID:21978184

  10. Acid-catalyzed heterogeneous reaction of 3-methyl-2-buten-1-ol with hydrogen peroxide.

    PubMed

    Liu, Qifan; Wang, Weigang; Ge, Maofa

    2015-05-01

    Acid-catalyzed heterogeneous oxidation with hydrogen peroxide (H2O2) has been suggested to be a potential pathway for secondary organic aerosol (SOA) formation from isoprene and its oxidation products. However, knowledge of the chemical mechanism and kinetics for this process is still incomplete. 3-Methyl-2-buten-1-ol (MBO321), an aliphatic alcohol structurally similar to isoprene, is emitted by pine forests and widely used in the manufacturing industries. Herein the uptake of MBO321 into H2SO4-H2O2 mixed solution was investigated using a flow-tube reactor coupled to a mass spectrometer. The reactive uptake coefficients (?) were acquired for the first time and were found to increase rapidly with increasing acid concentration. Corresponding aqueous-phase reactions were performed to further study the mechanism of this acid-catalyzed reaction. MBO321 could convert to 2-methyl-3-buten-2-ol (MBO232) and yield isoprene in acidic media. Organic hydroperoxides (ROOHs) were found to be generated through the acid-catalyzed route, which could undergo a rearrangement reaction and result in the formation of acetone and acetaldehyde. Organosulfates, which have been proposed to be SOA tracer compounds in the atmosphere, were also produced during the oxidation process. These results suggest that the heterogeneous acid-catalyzed reaction of MBO321 with H2O2 may contribute to SOA mass under certain atmospheric conditions. PMID:25968263

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

    PubMed Central

    Nguyen, Minh H.

    2013-01-01

    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

  12. Microcalorimetric study of the enzymatic hydrolysis of starch: An ?-amylase catalyzed reaction

    Microsoft Academic Search

    G. Salieri; G. Vinci; M. L. Antonelli

    1995-01-01

    Microcalorimetric studies of enzyme activities have been made on the hydrolysis of starch catalyzed by ?-amylase. The best conditions for the hydrolysis of starch in the presence of ?-amylase have been pointed out and the ?-amylase activity was determined by isothermal batch microcalorimetry. The heat changes involved during the hydrolytic reaction can be related to the starch concentrations in a

  13. Asymmetric reduction of ?-amino ketones with a KBH4 solution catalyzed by chiral Lewis acids.

    PubMed

    He, Peng; Zheng, Haifeng; Liu, Xiaohua; Lian, Xiangjin; Lin, Lili; Feng, Xiaoming

    2014-10-13

    An efficient enantioselective reduction of ?-amino ketones with potassium borohydride solution catalyzed by chiral N,N'-dioxide-metal complex catalysts was accomplished under mild reaction conditions for the first time. It provided a simple, convenient, and practical approaches for obtaining synthetically important chiral ?-amino alcohols in good to excellent yields (up to 98%) and enantioselectivities (up to 97% ee). PMID:25223259

  14. Enzyme-catalyzed oxidation facilitates the return of fluorescence for single-walled carbon nanotubes.

    PubMed

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

    2013-09-11

    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 defect sites on SWCNTs and suppressed their near-infrared (NIR) fluorescence, our results indicated that the fluorescence of SWCNTs was restored upon enzymatic oxidation, providing 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, when acid oxidation followed by HRP-catalyzed enzyme oxidation was employed, shortened (<300 nm in length) and NIR-fluorescent SWCNTs were produced. In contrast, upon treatment with myeloperoxidase, 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

  15. ?-Ketophosphonates as ester surrogates: isothiourea-catalyzed asymmetric diester and lactone synthesis.

    PubMed

    Smith, Siobhan R; Leckie, Stuart M; Holmes, Reuben; Douglas, James; Fallan, Charlene; Shapland, Peter; Pryde, David; Slawin, Alexandra M Z; Smith, Andrew D

    2014-05-01

    Isothiourea HBTM-2.1 catalyzes the asymmetric Michael addition/lactonization of aryl- and alkenylacetic acids using ?-keto-?,?-unsaturated phosphonates as ?,?-unsaturated ester surrogates, giving access to a diverse range of stereodefined lactones or enantioenriched functionalized diesters upon ring-opening. PMID:24734989

  16. THE TRIACYLGLYCEROL SYNTHESIS ENZYME DGAT1 ALSO CATALYZES THE SYNTHESIS OF DIACYLGLYCEROLS, WAXES, AND RETINYL ESTERS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The final step of triacylglycerol biosynthesis is catalyzed by acyl CoA:diacylglycerol acyltransferase (DGAT) enzymes. The two known DGATs, DGAT1 and DGAT2, are encoded by unrelated genes. Although both DGAT1 and DGAT2 knockout mice have reduced tissue triacylglycerol contents, they have disparate p...

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

    PubMed

    Domaille, Dylan W; Cha, Jennifer N

    2014-04-14

    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

  18. Trifluoromethyl-substituted sulfonium ylide: rh-catalyzed carbenoid addition to trifluoromethylthioether.

    PubMed

    Liu, Yafei; Shao, Xinxin; Zhang, Panpan; Lu, Long; Shen, Qilong

    2015-06-01

    A highly efficient Rh-catalyzed carbenoid addition to trifluoromethylthioether for the formation of trifluoromethyl-substituted sulfonium ylide is described. The trifluoromethyl-substituted sulfonium ylide can act as an electrophilic trifluoromethylation reagent, as demonstrated by trifluoromethylation of ?-ketoesters and aryl iodides. PMID:25974253

  19. Unusual specificity of polyethylene glycol-modified thermolysin in peptide synthesis catalyzed in organic solvents

    Microsoft Academic Search

    Anne Ferjancic; Antoine Puigserver; Hubert Gaertner

    1988-01-01

    Summary Polyethylene glycol-modified thermolysin was found to efficiently catalyze peptide synthesis in organic solvents. As in aqueous media, the reaction occurred through a rapid equilibrium random bireactant mechanism. However, the substrate specificity of modified thermolysin was actually changed since hydrophilic as well as acidic amino acids were better carboxyl group donors than hydrophobic residues, contrary to what is observed in

  20. Visible light promoted hydration of alkynes catalyzed by rhodium(iii) porphyrins.

    PubMed

    Liu, Xu; Liu, Lianghui; Wang, Zikuan; Fu, Xuefeng

    2015-07-01

    Visible light promoted hydration of a wide scope of alkynes to ketones catalyzed by rhodium(iii) porphyrin complexes was described. The key intermediate ?-carbonyl alkyl was observed and independently synthesized. The rate of photolysis is over two orders of magnitude faster than that of the thermal process. PMID:26111988

  1. Helium Catalyzed D-D Fusion in a Levitated Dipole J. Kesner, D.T. Garnier

    E-print Network

    Mauel, Michael E.

    Helium Catalyzed D-D Fusion in a Levitated Dipole J. Kesner, D.T. Garnier , A. Hansen , M. Mauel than the rate coefficient for Deuterium-3 Helium (D-3 He) reaction or for the deuterium-deuterium (D a different approach for a fusion power source, based on an alternative fuel cycle which we call "helium

  2. Ligand Control of E/Z Selectivity in Nickel-Catalyzed Transfer Hydrogenative Alkyne Semireduction.

    PubMed

    Richmond, Edward; Moran, Joseph

    2015-07-01

    A nickel-catalyzed transfer hydrogenative alkyne semireduction protocol that can be applied to both internal and terminal alkynes using formic acid and Zn as the terminal reductants has been developed. In the case of internal alkynes, the (E)- or (Z)-olefin isomer can be accessed selectively under the same reaction conditions by judicious inclusion of a triphos ligand. PMID:26030191

  3. Muon Catalyzed Fusion 2 (1988) 261-272 LOW ENERGY CROSS SECflON

    E-print Network

    Shlyakhter, Ilya

    1988-01-01

    Muon Catalyzed Fusion 2 (1988) 261-272 LOW ENERGY CROSS SECflON OF MESIC MOLECULES FORMA DON Yu.)F+ (D2).;K; -+ [(dtp.)iVdee].,K, is calculated at low energies (E contribute to the cross section. Comparing the MMC formation rates calculated at low energies with the data

  4. Synthesis of biaryls via AlCl3 catalyzed domino reaction involving cyclization, dehydration, and oxidation.

    PubMed

    Narender, Tadigoppula; Sarkar, Satinath; Rajendar, Kandikonda; Tiwari, Sriniwas

    2011-12-01

    A new chemical access has been developed to synthesize biaryls from substituted acetophenones, phenylacetones, dihydrochalcone, and 2-acetylnaphthalene in reasonably good yields at room temperature via a domino reaction sequence of AlCl(3) catalyzed cyclization, dehydration, and then oxidation. PMID:22040063

  5. Pd-Catalyzed stereospecific allyl-aryl coupling of allylic alcohols with arylboronic acids.

    PubMed

    Ye, Jiang; Zhao, Jingming; Xu, Jing; Mao, Yuxue; Zhang, Yong Jian

    2013-10-28

    An efficient method for Pd-catalyzed stereospecific allyl-aryl coupling of allylic alcohols with arylboronic acids has been described. The reactions proceeded smoothly in the presence of Pd2(dba)3·CHCl3 and racemic BINAP under mild and neutral conditions, affording allyl-aryl coupling products in moderate to high yields with excellent stereospecificities. PMID:24025990

  6. Copper-catalyzed ?-selective hydrostannylation of alkynes for the synthesis of branched alkenylstannanes.

    PubMed

    Yoshida, H; Shinke, A; Kawano, Y; Takaki, K

    2015-07-01

    A variety of branched alkenylstannanes can directly be synthesized with excellent ?-selectivity by the copper-catalyzed hydrostannylation using a distannane or a silylstannane, irrespective of the electronic and steric characteristics of terminal alkynes employed. Synthetic utility of the resulting branched alkenylstannane has been demonstrated by the total synthesis of bexarotene. PMID:25944075

  7. Flavins secreted by bacterial cells of Shewanella catalyze cathodic oxygen reduction.

    PubMed

    Liu, Huan; Matsuda, Shoichi; Hashimoto, Kazuhito; Nakanishi, Shuji

    2012-06-01

    On Her Majesty's Secrete Service: Oxygen reduction is an important process for microbial fuel cells (MFCs) and microbiologically-influenced corrosion (MIC). We demonstrate that flavins secreted by anode-respiring Shewanella cells can catalyze cathodic oxygen reduction via adsorption on the cathode. The findings will provide new insight for developing methods to improve MFC performance and to prevent MIC. PMID:22489008

  8. Monooxygenation of small hydrocarbons catalyzed by bacterial cytochrome p450s.

    PubMed

    Shoji, Osami; Watanabe, Yoshihito

    2015-01-01

    Cytochrome P450s (P450s) catalyze the NAD(P)H/O2-dependent monooxygenation of less reactive organic molecules under mild conditions. The catalytic activity of bacterial P450s is very high compared with P450s isolated from animals and plants, and the substrate specificity of bacterial P450s is also very high. Accordingly, their catalytic activities toward nonnative substrates are generally low especially toward small hydrocarbons. However, mutagenesis approaches have been very successful for engineering bacterial P450s for the hydroxylation of small hydrocarbons. On the other hand, "decoy" molecules, whose structures are very similar to natural substrates, can be used to trick the substrate recognition of bacterial P450s, allowing the P450s to catalyze oxidation reactions of nonnative substrates without any substitution of amino acid residues in the presence of decoy molecules. Thus, the hydroxylation of small hydrocarbons such as ethane, propane, butane and benzene can be catalyzed by P450BM3, a long-alkyl-chain hydroxylase, using substrate misrecognition of P450s induced by decoy molecules. Furthermore, a number of H2O2-dependent bacterial P450s can catalyze the peroxygenation of a variety of nonnative substrates through a simple substrate-misrecognition trick, in which catalytic activities and enantioselectivity are dependent on the structure of decoy molecules. PMID:26002736

  9. The gas phase reaction of singlet dioxygen with water: A water-catalyzed mechanism

    E-print Network

    Goddard III, William A.

    this remarkable and unexpected chemistry, we need to understand how 1 O2 can interact with H2O to produce H2O2­10935] that Abs efficiently catalyze the conversion of molecular singlet oxygen (1O2) plus water to hydrogen peroxide (HOOH), we used quantum chemical methods (B3LYP density functional theory) to delineate the most

  10. Nitrate reduction catalyzed by nanocomposite layer of Ag and Pb Seongpil Hwang, Joohan Lee, Juhyoun Kwak *

    E-print Network

    Kwak, Juhyoun

    Nitrate reduction catalyzed by nanocomposite layer of Ag and Pb on Au(111) Seongpil Hwang, Joohan) of silver and lead on Au(111) was performed sequentially to produce a thin composite layer. Ag was deposited of the Ag adlayer in the Pb2+ electrolyte. In the presence of sodium nitrate, this composite system exhibits

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

    E-print Network

    Goddard III, William A.

    by Nickel Jonathan E. Mueller, Adri C. T. van Duin, and William A. Goddard III*, Materials and Process reactions catalyzed by nickel surfaces and particles using reactive molecular dynamics on thousands of atoms adsorption, decomposition, reformation and desorption of hydrocarbons as they interact with the nickel

  12. Kinetic understanding of asymmetric amplification in amino-alcohol catalyzed organozinc additions

    Microsoft Academic Search

    Jean-Claude Micheau; Thomas Buhse; Dominique Lavabre; Jesús Rivera Islas

    2008-01-01

    The dynamic features of Noyori’s mechanism for the dimethylaminoisoborneol (DAIB) catalyzed alkylzinc addition to benzaldehyde have been investigated using the whole set of differential equations that describe the evolution of 19 species (starting products, intermediates, final compounds) involved in 36 coupled reversible or non-reversible processes. Using all the data available in the literature regarding the kinetic and thermodynamic parameters, the

  13. Ni-Catalyzed direct 1,4-difunctionalization of [60]fullerene with benzyl bromides.

    PubMed

    Si, Weili; Zhang, Xuan; Asao, Naoki; Yamamoto, Yoshinori; Jin, Tienan

    2015-04-14

    A new Ni-catalyzed direct 1,4-difunctionalization of [60]fullerene with various benzyl bromides has been developed. The use of a DMSO additive combined with a nickel catalyst is indispensable for the formation of 1,4-dibenzyl fullerenes with a variety of functional groups. The reaction proceeds through the formation of a fullerene monoradical species. PMID:25765232

  14. Rhodium-catalyzed C-H activation and conjugate addition under mild conditions.

    PubMed

    Yang, Luo; Correia, Camille A; Li, Chao-Jun

    2011-10-21

    An efficient rhodium(III)-catalyzed C-H activation and subsequent conjugate addition was achieved under mild conditions. The reaction utilized inert arenes to replace stoichiometric organometallic reagents and can tolerate various functional groups as well as air and water. PMID:21850341

  15. Enantioselective Rh(I)-catalyzed cyclization of arylboron compounds onto ketones.

    PubMed

    Low, Darryl W; Pattison, Graham; Wieczysty, Martin D; Churchill, Gwydion H; Lam, Hon Wai

    2012-05-18

    Rhodium complexes based upon chiral sulfinamide-alkene, TADDOL-derived phosphoramidite, or diene ligands catalyze cyclizations of arylboron compounds onto ketones, generating a variety of products containing five-, six-, or seven-membered rings with good yields and high enantioselectivities. PMID:22540631

  16. Copper-Catalyzed ?-Selective and Stereospecific Allylic Cross-Coupling with Secondary Alkylboranes.

    PubMed

    Yasuda, Yuto; Nagao, Kazunori; Shido, Yoshinori; Mori, Seiji; Ohmiya, Hirohisa; Sawamura, Masaya

    2015-06-26

    The scope of the copper-catalyzed coupling reactions between organoboron compounds and allylic phosphates is expanded significantly by employing triphenylphosphine as a ligand for copper, allowing the use of secondary alkylboron compounds. The reaction proceeds with complete ?-E-selectivity and preferential 1,3-syn stereoselectivity. The reaction of ?-silicon-substituted allylic phosphates affords enantioenriched ?-stereogenic allylsilanes. PMID:26013036

  17. Dextransucrase-catalyzed elongation of polysaccharide brushes with immobilized mono-/di-saccharides as acceptors.

    PubMed

    Fang, Yan; Wu, Jian; Xu, Zhi-Kang

    2015-01-01

    A quartz crystal microbalance (QCM) was used to monitor dextransucrase (DSase)-catalyzed polysaccharide elongation on the glucose-/maltose-ended self-assembly monolayer (SAM) surfaces. Kinetic parameters of the enzymatic elongation indicate that maltose is a promising substrate acceptor for DSase. PMID:25383964

  18. Fluorescence In Situ Hybridization and Catalyzed Reporter Deposition for the Identification of Marine Bacteria

    Microsoft Academic Search

    Annelie Pernthaler; Jakob Pernthaler; Rudolf Amann

    2002-01-01

    Fluorescence in situ hybridization (FISH) with horseradish peroxidase (HRP)-labeled oligonucleotide probes and tyramide signal amplification, also known as catalyzed reporter deposition (CARD), is currently not generally applicable to heterotrophic bacteria in marine samples. Penetration of the HRP molecule into bacterial cells requires permeabilization procedures that cause high and most probably species-selective cell loss. Here we present an improved protocol for

  19. Nickel-catalyzed carboannulation reaction of o-bromobenzyl zinc bromide with unsaturated compounds.

    PubMed

    Deng, Ruixue; Sun, Liangdong; Li, Zhi

    2007-12-01

    A number of indenes have been prepared in good yields by treating o-bromobenzyl zinc bromide 1 with various terminal and internal alkynes in the presence of a nickel catalyst. The nickel-catalyzed carboannulation reaction was successfully extended to the synthesis of indane derivatives by reaction of 1 with acrylates and styrene. PMID:17990889

  20. Palladium-catalyzed formylation of aryl halides with tert-butyl isocyanide.

    PubMed

    Jiang, Xiao; Wang, Jin-Mei; Zhang, Ying; Chen, Zhong; Zhu, Yong-Ming; Ji, Shun-Jun

    2014-07-01

    A novel palladium-catalyzed formylation of aryl halides with isocyanide in the presence of Et3SiH has been demonstrated, which provides a strategy toward important aldehydes with moderate to excellent yield. The advantage of this reaction includes milder conditions, convenient operation, lower toxicity, and wide functional group tolerance. PMID:24956352

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

    ERIC Educational Resources Information Center

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

    2014-01-01

    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…

  2. 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 ...

  3. Cationic dirhodium carboxylate-catalyzed synthesis of dihydropyrimidones from propargyl ureas.

    PubMed

    Yang, Miao; Odelberg, Shannon J; Tong, Zongzhong; Li, Dean Y; Looper, Ryan E

    2013-07-01

    Cationic Rh(II) complexes are able to catalyze the regioselective hydroamination of propargyl ureas in a 6-endo fashion. This transformation permits access to interesting substitution patterns of dihydropyrimidines which have found use as nucleotide exchange factor inhibitors. PMID:23807819

  4. Trans-Cyclization of Phosphatidylinositol Catalyzed by Phospholipase C from Streptomyces antibioticus

    E-print Network

    Tsai, Ming-Daw

    Because of its homology with PI-PLC1, we initially assumed the analogous mechanism for this enzyme.5 We now report that saPLC1 catalyzes the hydrolysis of PI via a different mechanism involving formation2+ - dependent PI-PLC have been thoroughly investigated.1-3 The results of the studies performed so

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    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.

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

    PubMed

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

    2014-01-28

    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

  7. Probing Nucleation Mechanism of Self-Catalyzed InN Nanostructures

    E-print Network

    Xu, Guowei; Li, Zhuangzhi; Baca, Francisco Javier A.; Wu, Judy

    2009-09-16

    The nucleation and evolution of InN nanowires in a self-catalyzed growth process have been investigated to probe the microscopic growth mechanism of the self-catalysis and a model is proposed for high pressure growth window at ~760 Torr...

  8. PtCl2-Catalyzed Cyclization of o-Diethynylbenzene Derivatives Triggered by Intramolecular Nucleophilic Attack

    Microsoft Academic Search

    Koji Miki; Hiroyuki Kuge; Rui Umeda; Motohiro Sonoda; Yoshito Tobe

    2011-01-01

    PtCl2-catalyzed cyclization of o-diethynylbenzene derivatives bearing a hydroxyethyl group yielded naphthofuran derivatives by initial intramolecular cyclization of the hydroxy group to an activated ethynyl group followed by attack of the second ethynyl group to a vinylplatinum intermediate. When the ethynyl terminal is substituted by a hydroxypropyl group, not only homologous naphthodihydropyran but also indenylidenetetrahydrofuran derivatives were formed.

  9. Lipase-catalyzed regioselective monoacetylation of unsymmetrical 1,5-primary diols Camille Oger

    E-print Network

    Paris-Sud XI, Université de

    1 Lipase-catalyzed regioselective monoacetylation of unsymmetrical 1,5-primary diols Camille Oger Monoacetylation 100% regioselective Lipase B from Candida antarctica (CALB) has been selected as the most suitable 1a (Scheme 1) using the Mucor miehei lipase (MML) and vinyl benzoate (VB) as an acyl transfer agent

  10. Regioselective acylation of nucleosides and their analogs catalyzed by Pseudomonas cepacia lipase: enzyme substrate recognition

    E-print Network

    Bao, Xinhe

    Regioselective acylation of nucleosides and their analogs catalyzed by Pseudomonas cepacia lipase: Floxuridine Lipase Nucleosides Regioselective acylation Substrate recognition a b s t r a c t The substrate recognition of Pseudomonas cepacia lipase in the acylation of nucleosides was investigated by means

  11. Textured catalysts, methods of making textured catalysts, and methods of catalyzing reactions conducted in hydrothermal conditions

    DOEpatents

    Werpy, Todd [West Richland, WA; Wang, Yong [Richland, WA

    2003-12-30

    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.

  12. Fe-Catalyzed Oxidation Reactions of Olefins, Alkanes, and Alcohols: Involvement of Oxo- and Peroxo Complexes

    NASA Astrophysics Data System (ADS)

    Schröder, Kristin; Junge, Kathrin; Bitterlich, Bianca; Beller, Matthias

    In this review, recent developments of iron-catalyzed oxidations of olefins (epoxidation), alkanes, arenes, and alcohols are summarized. Special focus is given on the ligand systems and the catalytic performance of the iron complexes. In addition, the mechanistic involvement of high-valent iron-oxo species is discussed.

  13. Ipso-Borylation of Aryl Ethers via Ni-Catalyzed C-OMe Cleavage.

    PubMed

    Zarate, Cayetana; Manzano, Rubén; Martin, Ruben

    2015-06-01

    A Ni-catalyzed ipso-borylation of aryl ethers via C(sp(2))-OMe and C(sp(3))-OMe cleavage is described. The transformation is characterized by its wide substrate scope under mild conditions and an exquisite divergence in site selectivity that can be easily switched by selecting the appropriate boron reagent. PMID:25978094

  14. Regioselective Ruthenium Catalyzed Hydrohydroxyalkylation of Dienes with 3-Hydroxy-2-oxindoles: Prenylation, Geranylation and Beyond

    PubMed Central

    Chen, Te-Yu; Krische, Michael J.

    2013-01-01

    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

  15. Towards the development of a selective ruthenium-catalyzed hydroformylation of olefins.

    PubMed

    Fleischer, Ivana; Wu, Lipeng; Profir, Irina; Jackstell, Ralf; Franke, Robert; Beller, Matthias

    2013-08-01

    The ruthenium-catalyzed hydroformylation of 1- and 2-octene to give preferentially the corresponding linear aldehyde is reported. The catalyst system comprising of Ru3 (CO)12 and an imidazole-substituted monophosphine ligand allows for high chemo- and regioselectivity. The hydroformylation proceeds with unprecedented rates for a ruthenium-based catalyst. PMID:23828402

  16. Selective metal-catalyzed transfer of H2 and CO from polyols to alkenes.

    PubMed

    Verendel, J Johan; Nordlund, Michael; Andersson, Pher G

    2013-03-01

    Transmission of alcohols achieved: A method for the direct transfer of the CHOH function from simple polyols to alkenes has been developed. In a dual-reactor system, successive iridium-catalyzed dehydrogenations and decarbonylations of polyols such as glycerol and sorbitol generates a low pressure of syngas, which is directly used in ex?situ alkene hydroformylation. PMID:23303703

  17. Copper(II) catalyzed selective oxidation of primary alcohols to aldehydes with atmospheric oxygen

    Microsoft Academic Search

    Subbarayan Velusamy; Arumugam Srinivasan; T. Punniyamurthy

    2006-01-01

    Copper(II) complex 1 selectively catalyzes the oxidation of primary alcohols to aldehydes in high yields by atmospheric oxygen in the presence of TEMPO. This procedure does not require an additive and the catalyst 1 is recyclable without loss of activity.

  18. Copper catalyzed oxidation of sulfides to sulfoxides with aqueous hydrogen peroxide

    Microsoft Academic Search

    Subbarayan Velusamy; Akkilagunta V. Kumar; Rakesh Saini; T. Punniyamurthy

    2005-01-01

    Copper(II) complex 1 catalyzes the oxidation of sulfides to sulfoxides with 30% H2O2 in high yields. Addition of a catalytic amount of TEMPO to the reaction mixture enhances the conversion and selectivity. Complex 1 can be recycled without loss of activity.

  19. Palladium-catalyzed regioselective decarboxylative alkylation of arenes and heteroarenes with aliphatic carboxylic acids.

    PubMed

    Premi, Chanchal; Dixit, Ankit; Jain, Nidhi

    2015-06-01

    An unprecedented Pd(OAc)2-catalyzed decarboxylative alkylation of unactivated arenes, with aliphatic carboxylic acids as inexpensive alkyl sources, is reported. The alkylation, controlled by the directing group, is regioselective, shows high functional group tolerance, and provides mild access to alkylated indolines, 2-phenylpyridines, and azobenzenes under solvent-free conditions in moderate to high yields. PMID:25997514

  20. Highly enantioselective kinetic resolution of axially chiral BINAM derivatives catalyzed by a Brønsted acid.

    PubMed

    Cheng, Dao-Juan; Yan, Liang; Tian, Shi-Kai; Wu, Ming-Yue; Wang, Lu-Xin; Fan, Zi-Li; Zheng, Sheng-Cai; Liu, Xin-Yuan; Tan, Bin

    2014-04-01

    A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid-catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities. PMID:24591330

  1. An efficient transformation of primary halides into nitriles through palladium-catalyzed hydrogen transfer reaction.

    PubMed

    Zou, Tao; Yu, Xiaoqiang; Feng, Xiujuan; Bao, Ming

    2015-07-01

    Two-step one-pot transformation of primary halides into corresponding nitriles is successfully achieved. Nucleophilic substitution of primary halides with sodium azide and subsequent palladium-catalyzed hydrogen transfer proceeds smoothly in the presence of sterically bulky ligand dicyclohexyl(2',4',6'-triisopropylbiphenyl-2-yl)phosphine (XPhos) in acetone to produce nitriles in satisfactory to good yields. PMID:26050994

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

    E-print Network

    Maiti, Debabrata

    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 ...

  3. Divergent syntheses of 2-aminonicotinonitriles and pyrazolines by copper-catalyzed cyclization of oxime ester.

    PubMed

    Wu, Qifan; Zhang, Yan; Cui, Sunliang

    2014-03-01

    Copper-catalyzed cyclization of an oxime ester toward divergent heterocycle synthesis is reported. Oxime ester serves as an enamine precursor to cyclize with malononitrile and aldehydes for access to 2-aminonicotinonitriles in a one-pot reaction, while cyclizing with N-sulfonylimines leads to synthesis of pyrazolines. PMID:24571784

  4. CuI/DMPAO-catalyzed N-arylation of acyclic secondary amines.

    PubMed

    Zhang, Yu; Yang, Xinye; Yao, Qizheng; Ma, Dawei

    2012-06-15

    DMPAO has been found to be a powerful ligand to enable copper-catalyzed coupling of aryl halides with aliphatic acyclic secondary amines take place under relatively mild conditions, and coupling of aryl halides with primary amines and cyclic secondary amines proceeds at low catalyst loading. PMID:22662962

  5. Convergent synthesis of geometrically disassembling dendrimers using Cu(I)-catalyzed C-O bond formation.

    PubMed

    Polaske, Nathan W; Szalai, Michael L; Shanahan, Charles S; McGrath, Dominic V

    2010-11-01

    The convergent synthesis of geometrically degradable dendrimers based on the 2,4-bis(hydroxymethyl)phenol subunit is presented. The key step of the synthetic scheme involves the CuI/3,4,7,8-tetramethyl-1,10-phenanthroline-catalyzed coupling of aryl iodides and alcohols. The synthesis and disassembly of these compounds is discussed. PMID:20925328

  6. Synthesis of 6,7,8-trisubstituted purines via a copper-catalyzed amidation reaction.

    PubMed

    Ibrahim, Nada; Legraverend, Michel

    2009-01-01

    We report herein an efficient method for the synthesis of 6,7,8-trisubstituted purines via a copper-catalyzed amidation reaction from easily accessible starting materials. Furthermore, the resulting 6-benzylsulfanyl-substituted purine derivatives may be readily oxidized for substitution by nucleophiles to give access to 6,7,8-trisubstituted purines for biological screening purposes. PMID:19012431

  7. Copper-catalyzed trifluoromethylation of alkenes with an electrophilic trifluoromethylating reagent

    PubMed Central

    Wang, Xiao-Ping; Lin, Jin-Hong; Zhang, Cheng-Pan; Zheng, Xing

    2013-01-01

    Summary An efficient method for the copper-catalyzed trifluoromethylation of terminal alkenes with an electrophilic trifluoromethylating reagent has been developed. The reactions proceeded smoothly to give trifluoromethylated alkenes in good to excellent yields. The results provided a versatile approach for the construction of Cvinyl–CF3 bonds without using prefunctionalized substrates. PMID:24367428

  8. Copper-catalyzed multicomponent reaction: synthesis of 4-arylsulfonylimino-4,5-dihydrofuran derivatives.

    PubMed

    Shang, Yongjia; Ju, Kai; He, Xinwei; Hu, Jinsong; Yu, Shuyan; Zhang, Min; Liao, Kaisheng; Wang, Lifen; Zhang, Ping

    2010-08-20

    A series of 4-arylsulfonylimino-4,5-dihydrofurans (14 examples) were efficiently synthesized in good to excellent yields by using the copper-catalyzed three-component reaction between sulfonyl azides, phenylacetylene, and beta-ketoesters in tetrahydrofuran (THF) at 40 degrees C for 8 h in the presence of triethylamine (TEA). A plausible mechanism for this process is proposed. PMID:20704448

  9. Iron-catalyzed homo-coupling of simple and functionalized arylmagnesium reagents.

    PubMed

    Cahiez, Gérard; Chaboche, Christophe; Mahuteau-Betzer, Florence; Ahr, Mathieu

    2005-05-12

    Iron-catalyzed homo-coupling of simple and functionalized arylmagnesium reagents is described. The reaction is highly chemoselective (CN, COOEt and NO(2) groups are tolerated). The procedure was used to perform intramolecular couplings. This cyclization reaction is the key step of the total synthesis of the N-methylcrinasiadine. PMID:15876025

  10. Stereochemistry of the microsomal glutathione S-transferase catalyzed addition of glutathione to chlorotrifluoroethene.

    PubMed

    Hargus, S J; Fitzsimmons, M E; Aniya, Y; Anders, M W

    1991-01-22

    The stereochemistry of S-(2-chloro-1,1,2-trifluoroethyl)glutathione formation was studied in rat liver cytosol, microsomes, N-ethylmaleimide-treated microsomes, 9000g supernatant fractions, purified rat liver microsomal glutathione S-transferase, and isolated rat hepatocytes. The absolute configuration of the chiral center generated by the addition of glutathione to chlorotrifluoroethene was determined by degradation of S-(2-chloro-1,1,2-trifluoroethyl)glutathione to chlorofluoroacetic acid, followed by derivatization to form the diastereomeric amides N-(S)-alpha-methylbenzyl-(S)-chlorofluoacetamide and N-(S)-alpha-methylbenzyl-(R)-chlorofluoroacetamide, which were separated by gas chromatography. Native and N-ethylmaleimide-treated rat liver microsomes, purified rat liver microsomal glutathione S-transferase, rat liver 9000g supernatant, and isolated rat hepatocytes catalyzed the formation of 75-81% (2S)-S-(2-chloro-1,1,2-trifluoroethyl)glutathione; rat liver cytosol catalyzed the formation of equal amounts of (2R)- and (2S)-S-(2-chloro-1,1,2-trifluoroethyl)glutathione. In rat hepatocytes, microsomal glutathione S-transferase catalyzed the formation of 83% of the total S-(2-chloro-1,1,2-trifluoroethyl)glutathione formed. These observations show that the microsomal glutathione S-transferase catalyzes the first step in the intracellular, glutathione-dependent bioactivation of the nephrotoxin chlorotrifluoroethene. PMID:1988059

  11. FeCl3-catalyzed self-cleaving deprotection of methoxyphenylmethyl-protected alcohols.

    PubMed

    Sawama, Yoshinari; Masuda, Masahiro; Asai, Shota; Goto, Ryota; Nagata, Saori; Nishimura, Shumma; Monguchi, Yasunari; Sajiki, Hironao

    2015-02-01

    4-Methoxyphenylmethyl ethers are widely utilized as alcohol protecting groups. FeCl3 effectively catalyzes the deprotection of methoxyphenylmethyl-type ethers in a self-cleaving manner to produce oligomeric derivatives and alcohols. Remarkably, the highly pure mother alcohols can be obtained without silica gel column chromatography by using the 2,4-dimethoxyphenylmethyl group as a protective group. PMID:25615562

  12. Pd-catalyzed direct C-H bond sulfonylation of azobenzenes with arylsulfonyl chlorides.

    PubMed

    Zhang, Duo; Cui, Xiuling; Zhang, Qianqian; Wu, Yangjie

    2015-02-01

    Pd(II)-catalyzed C-H sulfonylation of azobenzenes with arylsulfonyl chlorides has been developed. The sulfonylazobenzenes were obtained in moderate to excellent yields for 28 examples. This protocol features high efficiency, wide functional group tolerance, and atom economy. PMID:25558920

  13. Sequential Au(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates

    PubMed Central

    Zhou, Lei; Liu, Yizhou; Zhang, Yan

    2011-01-01

    Summary The gold(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates provides 1H-isochromene derivatives in good yields. The reaction follows a catalytic sequence of gold carbene formation/water O–H insertion/alcohol-alkyne cyclization. The gold(I) complex is the only catalyst in each of these steps. PMID:21647254

  14. Fischer chromium carbene complexes as nucleophiles in palladium-catalyzed allylic substitution reactions

    Microsoft Academic Search

    Dušan Draho?ovský; Vincent Borgo; Dalimil Dvo?ák

    2002-01-01

    The Pd-catalyzed reaction of carbanions derived from chromium aminocarbene complexes with allylic acetates and carbonates smoothly affords the corresponding allyl-substituted aminocarbenes. On the contrary, the same reaction of the anion derived from pentacarbonyl[(methoxy)methylcarbene]chromium(0) with cinnamyl acetate affords 5-methoxy-1-phenylhexa-1,5-diene, the product of 1-methoxyethen-1-yl group transfer.

  15. Palladium(II)/Brønsted Acid-Catalyzed Enantioselective Oxidative Carbocyclization–Borylation of Enallenes**

    PubMed Central

    Jiang, Tuo; Bartholomeyzik, Teresa; Mazuela, Javier; Willersinn, Jochen; Bäckvall, Jan-E

    2015-01-01

    An enantioselective oxidative carbocyclization–borylation of enallenes that is catalyzed by palladium(II) and a Brønsted acid was developed. Biphenol-type chiral phosphoric acids were superior co-catalysts for inducing the enantioselective cyclization. A number of chiral borylated carbocycles were synthesized in high enantiomeric excess. PMID:25808996

  16. Myeloperoxidase and Horseradish Peroxidase Catalyze Tyrosine Nitration in Proteins from Nitrite and Hydrogen Peroxide

    Microsoft Academic Search

    Jacinda B. Sampson; YaoZu Ye; Henry Rosen; Joseph S. Beckman

    1998-01-01

    Nitration of tyrosine residues in proteins occurs in a wide range of inflammatory diseases involving neutrophil and macrophage activation. We report that both myeloperoxidase (MPO) and horseradish peroxidase (HRP) utilize nitrite (NO2?) and hydrogen peroxide (H2O2) as substrates to catalyze tyrosine nitration in proteins. MPO was approximately 10 times more effective than HRP as a nitration catalyst of bovine serum

  17. 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...

  18. DOI: 10.1002/cbic.201402255 A Generalizable DNA-Catalyzed Approach to Peptide

    E-print Network

    Silverman, Scott K.

    DOI: 10.1002/cbic.201402255 A Generalizable DNA-Catalyzed Approach to Peptide­ Nucleic Acid of joining unprotected peptide to nucleic acid in one step by using DNA catalysts identified by in vitro selection. Peptide­nucleic acid conjugates play key roles in many biolog- ical processes, including

  19. A New Copper-Catalyzed [3 + 2] Cycloaddition: Enantioselective Coupling of Terminal Alkynes with Azomethine Imines To Generate Five-Membered

    E-print Network

    Fu, Gregory C.

    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

  20. One-pot synthesis of pyrimido[1,6-a]indol-1(2H)-one derivatives by a nucleophilic addition/Cu-catalyzed N-arylation/Pd-catalyzed C-H activation sequential process.

    PubMed

    Wang, Zhi-Jing; Yang, Jian-Guo; Yang, Fan; Bao, Weiliang

    2010-07-01

    A novel and convenient one-pot synthesis of pyrimido[1,6-a]indol-1(2H)-one derivatives through a nucleophilic addition/Cu-catalyzed N-arylation/Pd-catalyzed C-H activation sequential process is described. The reaction of easily prepared ortho-gem-dibromovinyl isocyanates with N-alkyl-anilines gave the desired indole derivatives in moderate to good yields. PMID:20527777

  1. Synthesis of naturally occurring pyridine alkaloids via palladium-catalyzed coupling/migration chemistry.

    PubMed

    Wang, Yao; Dong, Xiaoyang; Larock, Richard C

    2003-04-18

    The palladium-catalyzed cross-coupling of 3-iodopyridine, long-chain terminal dienes, and benzylic amines or tosylamides provides a novel route to key intermediates for the synthesis of the naturally occurring, biologically active pyridine alkaloids theonelladins C and D, niphatesine C, and xestamine D. This process involves (1) oxidative addition of the heterocyclic iodide to Pd(0), (2) carbopalladation of the least hindered carbon-carbon double bond of the diene, (3) palladium migration, and (4) pi-allylpalladium displacement by the nitrogen nucleophile with simultaneous regeneration of the Pd catalyst. Subsequent hydrogenation and deprotection affords good yields of the natural products. The Pd-catalyzed coupling of 3-iodopyridine and 2-methyl-11-dodecen-1-ol provides a convenient synthesis of a long-chain aldehyde by an analogous palladium migration process, which is easily converted to the pyridine alkaloid ikimine A. PMID:12688777

  2. Synergistic effect of two E2 ubiquitin conjugating enzymes in SCFhFBH1 catalyzed polyubiquitination

    PubMed Central

    Choi, Jin Sun; Kim, Sunhong; Kim, Kidae; Myung, Pyung Keun; Park, Sung Goo; Seo, Yeon-Soo; Park, Byoung Chul

    2015-01-01

    Ubiquitination is a post translational modification which mostly links with proteasome dependent protein degradation. This process has been known to play pivotal roles in the number of biological events including apoptosis, cell signaling, transcription and translation. Although the process of ubiquitination has been studied extensively, the mechanism of polyubiquitination by multi protein E3 ubiquitin ligase, SCF complex remains elusive. In the present study, we identified UbcH5a as a novel stimulating factor for poly-ubiquitination catalyzed by SCFhFBH1 using biochemical fractionations and MALDI-TOF. Moreover, we showed that recombinant UbcH5a and Cdc34 synergistically stimulate SCFhFBH1 catalyzed polyubiquitination in vitro. These data may provide an important cue to understand the mechanism how the SCF complex efficiently polyubiquitinates target substrates. [BMB Reports 2015; 48(1): 25-29] PMID:24667174

  3. Study on the synthesis of sucrose-6-acetate catalyzed by fructosyltransferase from Aspergillus oryzae.

    PubMed

    Han, Yawei; Liu, Guoming; Huang, Dongye; Qiao, Baojian; Chen, Liping; Guan, Lihong; Mao, Duobin

    2011-01-31

    The study had mainly investigated the synthesis of sucrose-6-acetate (s-6-a) in fructosyltransferase action. The synthesis reaction of s-6-a was performed between sucrose and glucose-6-acetate (g-6-a), and identified by high performance liquid chromatography (HPLC). According to the reaction of s-6-a catalyzed by fructosyltransferase from Aspergillus oryzae, the effect factors of reaction, such as the ratio of g-6-a to sucrose, temperature, time, pH, substrate and enzyme concentration in the reaction, were investigated. All results indicated that the fructosyltransferase could catalyze the s-6-a synthesis, and the optimal conditions of fructosyltransferase in reaction were 50°C, pH 6.2, 48h reaction time, 60% sucrose, 1:3 ratio of g-6-a to sucrose and 4.0mg/L concentration of enzyme. This study plays the important role in sucralose synthesis, because it is very cumbersome in the reported methods. PMID:20643232

  4. Ultrasound assisted lipase catalyzed synthesis of cinnamyl acetate via transesterification reaction in a solvent free medium.

    PubMed

    Tomke, Prerana D; Rathod, Virendra K

    2015-11-01

    Cinnamyl acetate is known for its use as flavor and fragrance material in different industries such as food, pharmaceutical, cosmetic etc. This work focuses on ultrasound assisted lipase (Novozym 435) catalyzed synthesis of cinnamyl acetate via transesterification of cinnamyl alcohol and vinyl acetate in non-aqueous, solvent free system. Optimization of various parameters shows that a higher yield of 99.99% can be obtained at cinnamyl alcohol to vinyl acetate ratio of 1:2 with 0.2% of catalyst, at 40°C and 150rpm, with lower ultrasound power input of 50W (Ultrasound intensity 0.81W/cm(2)), at 25kHz frequency, 50% duty cycle. Further, the time required for the maximum conversion is reduced to 20min as compared to 60min of conventional process. Similarly, the enzyme can be successfully reused seven times without loss of enzyme activity. Thus, ultrasound helps to enhance the enzyme catalyzed synthesis of flavors. PMID:26186841

  5. Biodiesel production from Jatropha oil catalyzed by immobilized Burkholderia cepacia lipase on modified attapulgite.

    PubMed

    You, Qinghong; Yin, Xiulian; Zhao, Yuping; Zhang, Yan

    2013-11-01

    Lipase from Burkholderia cepacia was immobilized on modified attapulgite by cross-linking reaction for biodiesel production with jatropha oil as feedstock. Effects of various factors on biodiesel production were studied by single-factor experiment. Results indicated that the best conditions for biodiesel preparation were: 10 g jatropha oil, 2.4 g methanol (molar ratio of oil to methanol is 1:6.6) being added at 3h intervals, 7 wt% water, 10 wt% immobilized lipase, temperature 35°C, and time 24h. Under these conditions, the maximum biodiesel yield reached 94%. The immobilized lipase retained 95% of its relative activity during the ten repeated batch reactions. The half-life time of the immobilized lipase is 731 h. Kinetics was studied and the Vmax of the immobilized lipases were 6.823 mmol L(-1). This immobilized lipase catalyzed process has potential industrial use for biodiesel production to replace chemical-catalyzed method. PMID:24055964

  6. Cytochrome P4502D isozymes catalyze the 4-hydroxylation of methamphetamine enantiomers.

    PubMed

    Lin, L Y; Kumagai, Y; Hiratsuka, A; Narimatsu, S; Suzuki, T; Funae, Y; Distefano, E W; Cho, A K

    1995-06-01

    The 4-hydroxylation of S(+)- and R(-)-methamphetamine by rat liver microsomes was examined in Sprague-Dawley and Dark Agouti strains to determine the role of cytochrome P4502D (CYP2D) subfamily isozymes in catalyzing the reaction. In the study, anti-P450-BTL IgG, bufuralol, and quinine, a substrate and inhibitors of CYP2D isozymes, respectively, were found to block approximately 90% of the reaction as catalyzed by microsomes from Sprague-Dawley rats. Reconstituted systems of CYP2D isozymes purified from rat liver microsomes also mediated the reaction. These observations and the minimal activity found in microsomes from Dark Agouti rats support the notion that methamphetamine, like other phenylisopropylamine compounds, is oxidized on the 4-position of the aromatic ring by CYP2D isozymes. PMID:7587941

  7. Reaction mechanism of epoxide cycloaddition to CO? catalyzed by salen-M (M = Co, Al, Zn).

    PubMed

    Wang, Ting-Ting; Xie, Yong; Deng, Wei-Qiao

    2014-10-01

    We propose a catalytic mechanism for the cycloaddition of epoxide to carbon dioxide catalyzed by salen-M (M = Co, Zn, Al) based on density functional theory calculations. The catalytic reaction follows a single-site mechanism rather than a bimetallic-site mechanism, which includes four steps: epoxide adsorption by salen-M, ring opening of epoxide, CO2 insertion, and intramolecular rearrangement. Our calculation results showed that the highest reaction barrier for salen-Co catalyst is only 9.94 kcal/mol, which is lower than that of salen-Al (14.38 kcal/mol) and salen-Zn (13.05 kcal/mol). The results indicate that the reaction catalyzed by salen-Al, salen-Co, or salen-Zn can occur at room temperature and atmospheric pressure, which is in agreement with experimental results. The mechanism can be used for the design of a novel catalyst for this reaction. PMID:25046346

  8. Recent advances in the gold-catalyzed additions to C–C multiple bonds

    PubMed Central

    Huang, He; Zhou, Yu

    2011-01-01

    Summary C–O, C–N and C–C bonds are the most widespread types of bonds in nature, and are the cornerstone of most organic compounds, ranging from pharmaceuticals and agrochemicals to advanced materials and polymers. Cationic gold acts as a soft and carbophilic Lewis acid and is considered one of the most powerful activators of C–C multiple bonds. Consequently, gold-catalysis plays an important role in the development of new strategies to form these bonds in more convenient ways. In this review, we highlight recent advances in the gold-catalyzed chemistry of addition of X–H (X = O, N, C) bonds to C–C multiple bonds, tandem reactions, and asymmetric additions. This review covers gold-catalyzed organic reactions published from 2008 to the present. PMID:21804887

  9. Recent advances in transition metal-catalyzed Csp2-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

    PubMed Central

    Landelle, Grégory; Panossian, Armen; Pazenok, Sergiy; Vors, Jean-Pierre

    2013-01-01

    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

  10. Regioselective Pd-Catalyzed Synthesis of 2,3,6-Trisubstituted Pyridines from Isoxazolinones.

    PubMed

    Rieckhoff, Stefan; Hellmuth, Tina; Peters, René

    2015-07-01

    Substituted pyridines are prevalent heterocycles of fundamental importance. Their efficient regioselective preparation is often still a challenge despite a large number of reported synthetic methodologies. In this letter we report an operationally simple approach that makes use of readily accessible isoxazolinones. The protocol involves a Pd(II)-catalyzed C-regioselective 1,4-addition to vinylketones, followed by a Pd(0)-catalyzed transformation, which is assumed to proceed via vinylnitrene-Pd intermediates. Both hydrogen and air are necessary for the pyridine formation step and could be employed at ratios above the upper explosive limit thus avoiding a safety issue. This new strategy allows an effective, scalable and practical access to various previously unknown 2,3,6-trisubstituted pyridines. PMID:26101943

  11. Silver-mediated palladium-catalyzed direct C-H arylation of 3-bromoisothiazole-4-carbonitrile.

    PubMed

    Ioannidou, Heraklidia A; Koutentis, Panayiotis A

    2011-03-18

    Silver(I) fluoride-mediated Pd-catalyzed C-H direct arylation/heteroarylation of 3-bromoisothiazole-4-carbonitrile (1a) gives twenty-four 5-aryl/heteroaryl-3-bromoisothiazole-4-carbonitriles. The reaction was partially optimized with respect to catalyst, ligand, and base. During this study 3,3'-dibromo-5,5'-biisothiazole-4,4'-dicarbonitrile (3a) was isolated as a byproduct and subsequently prepared via the silver-mediated Pd-catalyzed oxidative dimerization of 3-bromoisothiazole-4-carbonitrile in 67% yield. The analogous phenylation and oxidative dimerization of 3-chloroisothiazole-4-carbonitrile (1b) gave 3-chloro-5-phenylisothiazole-4-carbonitrile (4) and 3,3'-dichloro-5,5'-biisothiazole-4,4'-dicarbonitrile (3b) in 96% and 69% yields, respectively. PMID:21314108

  12. Stem cells catalyze cartilage formation by neonatal articular chondrocytes in 3D biomimetic hydrogels

    NASA Astrophysics Data System (ADS)

    Lai, Janice H.; Kajiyama, Glen; Smith, Robert Lane; Maloney, William; Yang, Fan

    2013-12-01

    Cartilage loss is a leading cause of disability among adults and effective therapy remains elusive. Neonatal chondrocytes (NChons) are an attractive allogeneic cell source for cartilage repair, but their clinical translation has been hindered by scarce donor availability. Here we examine the potential for catalyzing cartilage tissue formation using a minimal number of NChons by co-culturing them with adipose-derived stem cells (ADSCs) in 3D hydrogels. Using three different co-culture models, we demonstrated that the effects of co-culture on cartilage tissue formation are dependent on the intercellular distance and cell distribution in 3D. Unexpectedly, increasing ADSC ratio in mixed co-culture led to increased synergy between NChons and ADSCs, and resulted in the formation of large neocartilage nodules. This work raises the potential of utilizing stem cells to catalyze tissue formation by neonatal chondrocytes via paracrine signaling, and highlights the importance of controlling cell distribution in 3D matrices to achieve optimal synergy.

  13. Aza Cope Rearrangement of Propargyl Enammonium Cations Catalyzed By a Self-Assembled `Nanozyme

    SciTech Connect

    Hastings, Courntey J.; Fiedler, Dorothea; Bergman, Robert G.; Raymond, Kenneth N.

    2008-02-27

    The tetrahedral [Ga{sub 4}L{sub 6}]{sup 12-} assembly (L = N,N-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene) encapsulates a variety of cations, including propargyl enammonium cations capable of undergoing the aza Cope rearrangement. For propargyl enammonium substrates that are encapsulated in the [Ga{sub 4}L{sub 6}]{sup 12-} assembly, rate accelerations of up to 184 are observed when compared to the background reaction. After rearrangement, the product iminium ion is released into solution and hydrolyzed allowing for catalytic turnover. The activation parameters for the catalyzed and uncatalyzed reaction were determined, revealing that a lowered entropy of activation is responsible for the observed rate enhancements. The catalyzed reaction exhibits saturation kinetics; the rate data obey the Michaelis-Menten model of enzyme kinetics, and competitive inhibition using a non-reactive guest has been demonstrated.

  14. CF?I synthesis catalyzed by activated carbon: a density functional theory study.

    PubMed

    Hu, Yingjie; Wu, Taiping; Liu, Weizhou; Zhang, Liyang; Pan, Renming

    2014-03-13

    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

  15. Ni-Catalyzed Alkenylation of Ketone Enolates under Mild Conditions: Catalyst Identification and Optimization.

    PubMed

    Grigalunas, Michael; Ankner, Tobias; Norrby, Per-Ola; Wiest, Olaf; Helquist, Paul

    2015-06-10

    A procedure for Ni-catalyzed cross-coupling of ketone enolates with alkenyl halides has been developed. Intermolecular coupling of aromatic and aliphatic ketone lithium enolates with a variety of alkenyl halides is achieved in the presence of Ni(cod)2 catalyst (5 mol %), an N-heterocyclic carbene (NHC) ligand, and LiI (10 mol %) at 6-22 °C for 0.5-12 h with yields of up to 90%. During the initial development of this reaction, a misleading result with respect to the actual active catalyst was obtained using commercially available Q-Phos ligand, which was found to contain a trace of Pd metal contaminant sufficient to catalyze the reaction. However, under the final conditions optimized for Ni(cod)2 in the presence of an NHC ligand, Pd was incompetent as a catalyst. PMID:26024472

  16. Labeling Live Cells by Copper-Catalyzed Alkyne-Azide Click Chemistry

    PubMed Central

    Hong, Vu; Steinmetz, Nicole F.; Manchester, Marianne

    2010-01-01

    The copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, optimized for biological molecules in aqueous buffers, has been shown to rapidly label mammalian cells in culture with no loss in cell viability. Metabolic uptake and display of the azide derivative of N-acetylmannosamine developed by Bertozzi, followed by CuAAC ligation using sodium ascorbate and the ligand tris(hydroxypropyltriazolyl)methylamine (THPTA), gave rise to abundant covalent attachment of dye-alkyne reactants. THPTA serves both to accelerate the CuAAC reaction and to protect the cells from damage by oxidative agents produced by the Cu-catalyzed reduction of oxygen by ascorbate, which is required to maintain the metal in the active +1 oxidation state. This procedure extends the application of this fastest of azide-based bioorthogonal reactions to the exterior of living cells. PMID:20886827

  17. Organic reactions catalyzed by methylrhenium trioxide: Dehydration, amination, and disproportionation of alcohols

    SciTech Connect

    Zhu, Zuolin; Espenson, J.H. [Iowa State Univ., Ames, IA (United States)] [Iowa State Univ., Ames, IA (United States)

    1996-01-12

    Methylrhenium trioxide (MTO) is the first transition metal complex in trace quantity to catalyze the direct formation of ethers from alcohols. The reactions are independent of the solvents used: benzene, toluene, dichloromethane, chloroform, acetone, and in the alcohols themselves. Aromatic alcohols gave better yields than aliphatic. Reactions between two different alcohols could also be used to prepare unsymmetric ethers, the best yields being obtained when one of the alcohols is aromatic alcohols proceeding in better yield. When primary (secondary) amines were used as the limiting reagent, direct amination of alcohols catalyzed by MTO gave good yields of the expected secondary (tertiary) amines at room temperature. Disproportionation of alcohols to alkanes and carbonyl compounds was also observed for aromatic alcohols in the presence of MTO. On the basis of the results of this investigation and a comparison with the interaction between MTO and water, a concerted process and a mechanism involving carbocation intermediates have been suggested. 5 tabs.

  18. Direct Evidence of a Dinuclear Copper Intermediate in Cu(I)-Catalyzed Azide–Alkyne Cycloadditions

    PubMed Central

    Worrell, B. T.; Malik, J. A.; Fokin, V. V.

    2013-01-01

    The copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) has become a commonly employed method for the synthesis of complex molecular architectures under challenging conditions. Despite the widespread use of copper-catalyzed cycloaddition reactions, the mechanism of these processes has remained difficult to establish due to the involvement of multiple equilibria between several reactive intermediates. Real-time monitoring of a representative cycloaddition process via heat flow reaction calorimetry revealed that monomeric copper acetylide complexes are not reactive toward organic azides unless an exogenous copper catalyst is added. Furthermore, crossover experiments with an isotopically enriched exogenous copper source illustrated the stepwise nature of the C–N bond-forming events and the equivalence of the two copper atoms within the cycloaddition steps. PMID:23558174

  19. Palladium-catalyzed regio- and enantioselective allylic alkylation of bis allylic carbonates derived from Morita-Baylis-Hillman adducts.

    PubMed

    Trost, Barry M; Brennan, Megan K

    2007-09-27

    Morita-Baylis-Hillman diene adducts are used as substrates in the palladium-catalyzed asymmetric allylic alkylation reaction with oxygen and carbon nucleophiles in good regio- and enantioselectivity. PMID:17803313

  20. Synthesis of ethoxy dibenzooxaphosphorin oxides through palladium-catalyzed C(sp2)–H activation/C–O formation

    PubMed Central

    Jeon, Woo Hyung

    2014-01-01

    Summary We report an efficient Pd-catalyzed C(sp2)–H activation/C–O bond formation for the synthesis of ethoxy dibenzooxaphosphorin oxides from 2-(aryl)arylphosphonic acid monoethyl esters under aerobic conditions. PMID:24991271